Life Extension Magazine®

Issue: Aug 2015

Glycation, Dry Eyes, and Aging Facial Skin

Glycation, Dry Eyes, and Aging Facial Skin

By Life Extension.

Glycation

Mutagenic potential of DNA glycation: miscoding by (R)- and (S)-N2-(1-carboxyethyl)-2’-deoxyguanosine.

Elevated circulating glucose resulting from complications of obesity and metabolic disease can result in the accumulation of advanced glycation end products (AGEs) of proteins, lipids, and DNA. The formation of DNA-AGEs assumes particular importance as these adducts may contribute to genetic instability and elevated cancer risk associated with metabolic disease. The principal DNA-AGE, N(2)-(1-carboxyethyl)-2’-deoxyguanosine (CEdG), is formed as a mixture of R and S isomers at both the polymer and monomer levels. In order to examine the miscoding potential of this adduct, oligonucleotides substituted with (R)- and (S)-CEdG and the corresponding triphosphates (R)- and (S)-CEdGTP were synthesized, and base-pairing preferences for each stereoisomer were examined using steady-state kinetic approaches. Purine dNTPs were preferentially incorporated opposite template CEdG when either the Klenow (Kf(-)) or Thermus aquaticus (Taq) polymerases were used. The Kf(-) polymerase preferentially incorporated dGTP, whereas Taq demonstrated a bias for dATP. Kf(-) incorporated purines opposite the R isomer with greater efficiency, but Taq favored the S isomer. Incorporation of (R)- and (S)-CEdGTP only occurred opposite dC and was catalyzed by Kf(-) with equal efficiencies. Primer extension from a 3’-terminal CEdG was observed only for the R isomer. These data suggest CEdG is the likely adduct responsible for the observed pattern of G transversions induced by exposure to elevated glucose or its alpha-oxoaldehyde decomposition product methylglyoxal. The results imply that CEdG within template DNA and the corresponding triphosphate possess different syn/anti conformations during replication which influence base-pairing preferences. The implications for CEdG-induced mutagenesis in vivo are discussed.

Biochemistry. 2010 Mar 9;49(9):1814-21

Mutagenesis and repair induced by the DNA advanced glycation end product N2-1-(carboxyethyl)-2’-deoxyguanosine in human cells.

Glycation of biopolymers by glucose-derived a-oxo-aldehydes such as methylglyoxal (MG) is believed to play a major role in the complex pathologies associated with diabetes and metabolic disease. In contrast to the extensive literature detailing the formation and physiological consequences of protein glycation, there is little information about the corresponding phenomenon for DNA. To assess the potential contribution of DNA glycation to genetic instability, we prepared shuttle vectors containing defined levels of the DNA glycation adduct N(2)-(1-carboxyethyl)-2’-deoxyguanosine (CEdG) and transfected them into isogenic human fibroblasts that differed solely in the capacity to conduct nucleotide excision repair (NER). In the NER-compromised fibroblasts, the induced mutation frequencies increased up to 18-fold relative to background over a range of ~10-1400 CEdG adducts/10(5) dG, whereas the same substrates transfected into NER-competent cells induced a response that was 5-fold over background at the highest adduct density. The positive linear correlation (R(2) = 0.998) of mutation frequency with increasing CEdG level in NER-defective cells suggested that NER was the primary if not exclusive mechanism for repair of this adduct in human fibroblasts. Consistent with predictions from biochemical studies using CEdG-substituted oligonucleotides, guanine transversions were the predominant mutation resulting from replication of MG-modified plasmids. At high CEdG levels, significant increases in the number of AT ® GC transitions were observed exclusively in NER-competent cells (P < 0.0001). This suggested the involvement of an NER-dependent mutagenic process in response to critical levels of DNA damage, possibly mediated by error-prone Y-family polymerases.

Biochemistry. 2011 Mar 29;50(12):2321-9

Inflammatory mediators are induced by dietary glycotoxins, a major risk factor for diabetic angiopathy.

Diet is a major environmental source of proinflammatory AGEs (heat-generated advanced glycation end products); its impact in humans remains unclear. We explored the effects of two equivalent diets, one regular (high AGE, H-AGE) and the other with 5-fold lower AGE (L-AGE) content on inflammatory mediators of 24 diabetic subjects: 11 in a 2-week crossover and 13 in a 6-week study. After 2 weeks on H-AGE, serum AGEs increased by 64.5% (P = 0.02) and on L-AGE decreased by 30% (P = 0.02). The mononuclear cell tumor necrosis factor-alphabeta-actin mRNA ratio was 1.4 +/- 0.5 on H-AGE and 0.9 +/- 0.5 on L-AGE (P = 0.05), whereas serum vascular adhesion molecule-1 was 1,108 +/- 429 and 698 +/- 347 ngml (P = 0.01) on L- and H-AGE, respectively. After 6 weeks, peripheral blood mononuclear cell tumor necrosis factor-alpha rose by 86.3% (P = 0.006) and declined by 20% (P, not significant) on H- or L-AGE diet, respectively; C-reactive protein increased by 35% on H-AGE and decreased by 20% on L-AGE (P = 0.014), and vascular adhesion molecule-1 declined by 20% on L-AGE (P < 0.01) and increased by 4% on H-AGE. Serum AGEs were increased by 28.2% on H-AGE (P = 0.06) and reduced by 40% on L-AGE (P = 0.02), whereas AGE low density lipoprotein was increased by 32% on H-AGE and reduced by 33% on L-AGE diet (P < 0.05). Thus in diabetes, environmental (dietary) AGEs promote inflammatory mediators, leading to tissue injury. Restriction of dietary AGEs suppresses these effects.

Proc Natl Acad Sci U S A. 2002 Nov 26;99(24):15596-601

N-Acetyltransferase-2 genetic polymorphism, well-done meat intake, and breast cancer risk among postmenopausal women.

Heterocyclic amines found in well-done meat require host-mediated metabolic activation before initiating DNA mutations and tumors in target organs. Polymorphic N-acetyltransferase-2 (NAT2) catalyzes the activation of heterocyclic amines via O-acetylation, suggesting that NAT2 genotypes with high O-acetyltransferase activity (rapid/intermediate acetylator phenotype) increase the risk of breast cancer in women who consume well-done meat. To test this hypothesis, DNA samples and information on diet and other breast cancer risk factors were obtained from a nested case-control study of postmenopausal women. Twenty-seven NAT2 genotypes were determined and assigned to rapid, intermediate, or slow acetylator groups based on published characterizations of recombinant NAT2 allozymes. NAT2 genotype alone was not associated with breast cancer risk. A significant dose-response relationship was observed between breast cancer risk and consumption of well-done meat among women with the rapid/intermediate NAT2 genotype (trend test, P = 0.003) that was not evident among women with the slow acetylator genotype (trend test, P = 0.22). These results suggest an interaction between NAT2 genotype and meat doneness, although a test for multiplicative interaction was not statistically significant (P = 0.06). Among women with the rapid/intermediate NAT2 genotype, consumption of well-done meat was associated with a nearly 8-fold (odds ratio, 7.6; 95% confidence interval, 1.1-50.4) elevated breast cancer risk compared with those consuming rare or medium-done meats. These results are consistent with a role for O-acetylation in the activation of heterocyclic amine carcinogens and support the hypothesis that the NAT2 acetylation polymorphism is a breast cancer risk factor among postmenopausal women with high levels of heterocyclic amine exposure.

Cancer Epidemiol Biomarkers Prev. 2000 Sep;9(9):905-10

Well-done meat intake and the risk of breast cancer.

BACKGROUND: Heterocyclic amines, mutagens formed in meats cooked at high temperatures, have been demonstrated as mammary carcinogens in animals. We conducted a nested, case-control study among 41,836 cohort members of the Iowa Women’s Health Study to evaluate the potential role of heterocyclic amines and intake of well-done meat in the risk for human breast cancer. METHODS: A questionnaire was mailed to individuals in the cohort who had breast cancer diagnosed during the period from 1992 through 1994 and a random sample of cancer-free cohort members to obtain information on usual intake of meats and on meat preparation practices. Color photographs showing various doneness levels of hamburger, beefsteak, and bacon were included. Multivariate analysis was performed on data from 273 case subjects and 657 control subjects who completed the survey. RESULTS: A dose-response relationship was found between doneness levels of meat consumed and breast cancer risk. The adjusted odds ratios (ORs) for very well-done meat versus rare or medium-done meat were 1.54 (95% confidence interval [CI]=0.96-2.47) for hamburger, 2.21 (95% CI=1.30-3.77) for beef steak, and 1.64 (95% CI=0.92-2.93) for bacon. Women who consumed these three meats consistently very well done had a 4.62 times higher risk (95% CI=1.36-15.70) than that of women who consumed the meats rare or medium done. Risk of breast cancer was also elevated with increasing intake of well-done to very well-done meat. CONCLUSIONS: Consumption of well-done meats and, thus, exposures to heterocyclic amines (or other compounds) formed during high-temperature cooking may play an important role in the risk of breast cancer.

J Natl Cancer Inst. 1998 Nov 18;90(22):1724-9

A prospective study of meat and meat mutagens and prostate cancer risk.

High-temperature cooked meat contains heterocyclic amines, including 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), and polycyclic aromatic hydrocarbons, such as benzo(a)pyrene (BaP). In rodents, a high intake of PhIP induces prostate tumors. We prospectively investigated the association between meat and meat mutagens, specifically PhIP, and prostate cancer risk in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. Diet was assessed using a 137-item food frequency questionnaire and a detailed meat-cooking questionnaire linked to a database for BaP and the heterocyclic amines 2-amino-3,8-dimethylimidazo[4,5-b]quinoxaline (MeIQx), 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx), and PhIP. During follow-up, we ascertained a total of 1,338 prostate cancer cases among 29,361 men; of these, 868 were incident cases (diagnosed after the first year of follow-up) and 520 were advanced cases (stage III or IV or a Gleason score of > or =7). Total, red, or white meat intake was not associated with prostate cancer risk. More than 10 g/d of very well done meat, compared with no consumption, was associated with a 1.4-fold increased risk of prostate cancer [95% confidence interval (95% CI), 1.05-1.92] and a 1.7-fold increased risk (95% CI, 1.19-2.40) of incident disease. Although there was no association with MeIQx and DiMeIQx, the highest quintile of PhIP was associated with a 1.2-fold increased risk of prostate cancer (95% CI, 1.01-1.48) and a 1.3-fold increased risk of incident disease (95% CI, 1.01-1.61). In conclusion, very well done meat was positively associated with prostate cancer risk. In addition, this study lends epidemiologic support to the animal studies, which have implicated PhIP as a prostate carcinogen.

Cancer Res. 2005 Dec 15;65(24):11779-84

Meat and meat-related compounds and risk of prostate cancer in a large prospective cohort study in the United States.

The authors examined associations between meat consumption (type, cooking method, and related mutagens), heme iron, nitrite/nitrate, and prostate cancer in a cohort of 175,343 US men aged 50-71 years. During 9 years of follow-up (1995-2003), they ascertained 10,313 prostate cancer cases (1,102 advanced) and 419 fatal cases. Hazard ratios comparing the fifth intake quintile with the first revealed elevated risks associated with red and processed meat for total (red meat: hazard ratio (HR) = 1.12, 95% confidence interval (CI): 1.04, 1.21; processed meat: HR = 1.07, 95% CI: 1.00, 1.14) and advanced (red meat: HR = 1.31, 95% CI: 1.05, 1.65; processed meat: HR = 1.32, 95% CI: 1.08, 1.61) prostate cancer. Heme iron, barbecued/grilled meat, and benzo[a]pyrene were all positively associated with total (HR = 1.09 (95% CI: 1.02, 1.17), HR = 1.11 (95% CI: 1.03, 1.19), and HR = 1.09 (95% CI: 1.00, 1.18), respectively) and advanced (HR = 1.28 (95% CI: 1.03, 1.58), HR = 1.36 (95% CI: 1.10, 1.69), and HR = 1.28 (95% CI: 1.00, 1.65), respectively) disease. Nitrite (HR = 1.24, 95% CI: 1.02, 1.51) and nitrate (HR = 1.31, 95% CI: 1.07, 1.61) intakes were associated with advanced prostate cancer. There were no clear associations for fatal prostate cancer. Red and processed meat may be positively associated with prostate cancer via mechanisms involving heme iron, nitrite/nitrate, grilling/barbecuing, and benzo[a]pyrene.

Am J Epidemiol. 2009 Nov 1;170(9):1165-77

Meat consumption, cooking practices, meat mutagens, and risk of prostate cancer.

Consumption of red meat, particularly well-done meat, has been associated with increased prostate cancer risk. High-temperature cooking methods such as grilling and barbecuing may produce heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs), which are known carcinogens. We assessed the association with meat consumption and estimated HCA and PAH exposure in a population-based case-control study of prostate cancer. Newly diagnosed cases aged 40-79 years (531 advanced cases, 195 localized cases) and 527 controls were asked about dietary intake, including usual meat cooking methods and doneness levels. Odds ratios (OR) and 95% confidence intervals (CI) were calculated using multivariate logistic regression. For advanced prostate cancer, but not localized disease, increased risks were associated with higher consumption of hamburgers (OR = 1.79, CI = 1.10-2.92), processed meat (OR = 1.57, CI = 1.04-2.36), grilled red meat (OR = 1.63, CI = 0.99-2.68), and well-done red meat (OR = 1.52, CI = 0.93-2.46), and intermediate intake of 2-amino-1-methyl1-6-phenylimidazo[4,5-b]pyridine (PhIP) (Quartile 2 vs. 1: OR = 1.41, CI = 0.98-2.01; Quartile 3 vs. 1: OR = 1.42, CI = 0.98-2.04), but not for higher intake. White meat consumption was not associated with prostate cancer. These findings provide further evidence that consumption of processed meat and red meat cooked at high temperature is associated with increased risk of advanced, but not localized, prostate cancer.

Nutr Cancer. 2011;63(4):525-37

Oral advanced glycation endproducts (AGEs) promote insulin resistance and diabetes by depleting the antioxidant defenses AGE receptor-1 and sirtuin 1.

The epidemics of insulin resistance (IR) and type 2 diabetes (T2D) affect the first world as well as less-developed countries, and now affect children as well. Persistently elevated oxidative stress and inflammation (OS/Infl) precede these polygenic conditions. A hallmark of contemporary lifestyle is a preference for thermally processed nutrients, replete with pro-OS/Infl advanced glycation endproducts (AGEs), which enhance appetite and cause overnutrition. We propose that chronic ingestion of oral AGEs promotes IR and T2D. The mechanism(s) involved in these findings were assessed in four generations of C57BL6 mice fed isocaloric diets with or without AGEs [synthetic methyl-glyoxal-derivatives (MG(+))]. F3/MG(+) mice manifested increased adiposity and premature IR, marked by severe deficiency of anti-AGE advanced glycation receptor 1 (AGER1) and of survival factor sirtuin 1 (SIRT1) in white adipose tissue (WAT), skeletal muscle, and liver. Impaired 2-deoxy-glucose uptake was associated with marked changes in insulin receptor (InsR), IRS-1, IRS-2, Akt activation, and a macrophage and adipocyte shift to a pro-OS/inflammatory (M1) phenotype. These features were absent in F3/MG(-) mice. MG stimulation of 3T3-L1 adipocytes led to suppressed AGER1 and SIRT1, and altered InsR, IRS-1, IRS-2 phosphorylation, and nuclear factor kappa-light chain enhancer of activated B cells (Nf-κB) p65 acetylation. Gene modulation revealed these effects to be coregulated by AGER1 and SIRT1. Thus, prolonged oral exposure to MG-AGEs can deplete host-defenses AGER1 and SIRT1, raise basal OS/Infl, and increase susceptibility to dysmetabolic IR. Because exposure to AGEs can be decreased, these insights provide an important framework for alleviating a major lifestyle-linked disease epidemic.

Proc Natl Acad Sci U S A. 2012 Sep 25;109(39):15888-93

Genotoxicity of heat-processed foods.

Gene-environment interactions include exposure to genotoxic compounds from our diet and it is no doubt, that humans are regularly exposed to e.g. food toxicants, not least from cooked foods. This paper reviews briefly four classes of cooked food toxicants, e.g. acrylamide, heterocyclic amines, nitrosamines and polyaromatic hydrocarbons. Many of these compounds have been recognised for decades also as environmental pollutants. In addition cigarette smokers and some occupational workers are exposed to them. Their occurrence, formation, metabolic activation, genotoxicity and human cancer risk are briefly presented along with figures on estimated exposure. Several lines of evidence indicate that cooking conditions and dietary habits can contribute to human cancer risk through the ingestion of genotoxic compounds from heat-processed foods. Such compounds cause different types of DNA damage: nucleotide alterations and gross chromosomal aberrations. Most genotoxic compounds begin their action at the DNA level by forming carcinogen-DNA adducts, which result from the covalent binding of a carcinogen or part of a carcinogen to a nucleotide. The genotoxic and carcinogenic potential of these cooked food toxicants have been evaluated regularly by the International Agency for Research on Cancer (IARC), which has come to the conclusion that several of these food-borne toxicants present in cooked foods are possibly (2A) or probably (2B) carcinogenic to humans, based on both high-dose, long-term animal studies and in vitro and in vivo genotoxicity tests. Yet, there is insufficient scientific evidence that these genotoxic compounds really cause human cancer, and no limits have been set for their presence in cooked foods. However, the competent authorities in most Western countries recommend minimising their occurrence, therefore this aspect is also included in this review.

Mutat Res. 2005 Jul 1;574(1-2):156-72. Epub 2005 Apr 1

Diet-derived advanced glycation end products are major contributors to the body’s AGE pool and induce inflammation in healthy subjects.

Advanced glycation end products (AGEs) are a heterogeneous group of compounds that form continuously in the body. Their rate of endogenous formation is markedly increased in diabetes mellitus, a condition in which AGEs play a major pathological role. It is also known, however, that AGEs form during the cooking of foods, primarily as the result of the application of heat. This review focuses on the generation of AGEs during the cooking of food, the gastrointestinal absorption of these compounds, and their biological effects in vitro and in vivo. We also present preliminary evidence of a direct association between dietary AGE intake and markers of systemic inflammation such as C-reactive protein in a large group of healthy subjects. Together with previous evidence from diabetics and renal failure patients, these data suggest that dietary AGEs may play an important role in the causation of chronic diseases associated with underlying inflammation.

Ann N Y Acad Sci. 2005 Jun;1043:461-6

Obesity and low-grade systemic inflammation.

The aim of this review is to deal with the significance of obesity as a promotor of a chronic low-grade inflammatory reaction favouring the development of atherosclerosis and cardiovascular diseases. Adipose tissue synthetizes and releases inflammatory cytokines involved in various atherothrombotic mechanisms and in glucose and lipid metabolism. A local renin-angiotensin system may partially support the obesity related hypertension. Most obese subjects had elevated plasma levels of inflammatory markers which correlate with the degree of obesity and insulin resistance and decrease after weight reduction and exercise. Some evidences suggest that long-chain polyunsaturated fatty acids and thiazolidinediones may be useful in preventing atherosclerosis. Obesity, by itself, has been considered an independent risk factor for cardiovascular diseases. The hypothesis that it is linked to the associated low-grade chronic inflammation is supported by the existence of altered indexes of chronic inflammation also in obese children who are free of other pathological conditions. Further research will be required to determine the pathophysiological meaning of the chronic inflammation associated to obesity.

Minerva Endocrinol. 2002 Sep;27(3):209-14

Inflammation-sensitive plasma proteins are associated with future weight gain.

Cross-sectional studies have associated obesity and other components of the so-called metabolic syndrome with low-grade inflammation. The temporal and causal relations of this association have not been fully explored. This study explored whether elevated levels of inflammation-sensitive plasma proteins (ISPs) (fibrinogen, orosomucoid, alpha1-antitrypsin, haptoglobin, and ceruloplasmin) are associated with future weight gain. Five ISPs were measured in 2,821 nondiabetic healthy men (38-50 years of age) who were reexamined after a mean follow-up of 6.1 years. Future weight gain was studied in relation to the number of elevated ISPs (i.e., in the top quartile). The proportion with a large weight gain (75th percentile >/= 3.8 kg) was 21.0, 25.9, 26.8, and 28.3%, respectively, among men with none, one, two, and three or more ISPs in the top quartile (P for trend 0.0005). This relation remained significant after adjustments for weight at baseline, follow-up time, height (at baseline and follow-up), physical inactivity (at baseline and follow-up), smoking (at baseline and follow-up), high alcohol consumption, and insulin resistance. The relations were largely similar for all individual ISPs. Elevated ISP levels predict a large weight gain in middle-aged men. This relation could contribute to the relation between inflammation, the metabolic syndrome, and cardiovascular disease.

Diabetes. 2003 Aug;52(8):2097-101

Chronic inflammation in fat plays a crucial role in the development of obesity-related insulin resistance.

Insulin resistance arises from the inability of insulin to act normally in regulating nutrient metabolism in peripheral tissues. Increasing evidence from human population studies and animal research has established correlative as well as causative links between chronic inflammation and insulin resistance. However, the underlying molecular pathways are largely unknown. In this report, we show that many inflammation and macrophage-specific genes are dramatically upregulated in white adipose tissue (WAT) in mouse models of genetic and high-fat diet-induced obesity (DIO). The upregulation is progressively increased in WAT of mice with DIO and precedes a dramatic increase in circulating-insulin level. Upon treatment with rosiglitazone, an insulin-sensitizing drug, these macrophage-originated genes are downregulated. Histologically, there is evidence of significant infiltration of macrophages, but not neutrophils and lymphocytes, into WAT of obese mice, with signs of adipocyte lipolysis and formation of multinucleate giant cells. These data suggest that macrophages in WAT play an active role in morbid obesity and that macrophage-related inflammatory activities may contribute to the pathogenesis of obesity-induced insulin resistance. We propose that obesity-related insulin resistance is, at least in part, a chronic inflammatory disease initiated in adipose tissue.

J Clin Invest. 2003 Dec;112(12):1821-30

A prospective study of weight change and systemic inflammation over 9 y.

BACKGROUND: An increase in weight is a risk factor for cardiovascular disease and cancer. This increased risk may be mediated by inflammation, but no long-term data are available on the effect of weight gain on systemic inflammation. OBJECTIVE: We tested the hypothesis that weight gain is associated with an increase in systemic inflammation during a 9-y period. DESIGN: In 1991 data on body weight and a blood sample were collected from a random sample of 2,425 randomly selected adults from a community-based cohort in Nottingham, United Kingdom. In 2000, these measures were repeated in 1,301 of these participants. The main outcome measure was change in systemic inflammation as measured by serum C-reactive protein (CRP) from the 1,222 participants who provided paired samples. RESULTS: The mean change in weight from 1991 to 2000 was 2.9 kg (95% CI: 2.6, 3.2 kg). The geometric mean of CRP in 1991 was 1.22 mg/L (95% CI: 0.03, 125.0 mg/L), and it increased to 1.76 mg/L (95% CI: 0.09, 62.0 mg/L) in 2000 (P<0.001). A linear association was observed between increase in weight and serum CRP, with a 1-kg increment in weight being associated with an additional increase in CRP of 0.09 mg/L (95% CI: 0.02, 0.16 mg/L) during this time period. CONCLUSION: During a 9-y period, an increase in weight is associated with an increase in systemic inflammation. This provides a mechanism that may explain some of the previously reported association of weight gain with an increased risk of both cancer and cardiovascular disease.

Am J Clin Nutr. 2008 Jan;87(1):30-5

Non-enzymatic glycation of proteins: a cause for complications in diabetes.

Diabetes mellitus is one of the most common non-communicable diseases, and is the fifth leading cause of death in most of the developed countries. It can affect nearly every organ and system in the body and may result in blindness, end stage renal disease, lower extremity amputation and increase risk of stroke, ischaemic heart diseases and peripheral vascular disease. Hyperglycemia in diabetes causes non-enzymatic glycation of free amino groups of proteins (of lysine residues) and leads to their structural and functional changes, resulting in complications of the diabetes. Glycation of proteins starts with formation of Shiff’s base, followed by intermolecular rearrangement and conversion into Amadori products. When large amounts of Amadori products are formed, they undergo cross linkage to form a heterogeneous group of protein-bound moieties, termed as advanced glycated end products (AGEs). Rate of these reactions are quite slow and only proteins with large amounts of lysine residues undergo glycation with significant amounts of AGEs. The formation of AGEs is a irreversible process, causing structural and functional changes in protein leading to various complications in diabetes like nephropathy, retinopathy, neuropathy and angiopathy. The present review discusses about role of glycation in various complications of diabetes.

Indian J Biochem Biophys. 2006 Dec;43(6):337-44

Dry Eyes

Dry eye disease is associated with deterioration of mental health in male Japanese university staff.

Dry eye disease (DED) is defined as a multifactorial disease of the tears and ocular surface that results in symptoms of discomfort, visual disturbance, and tear-film instability, with potential damage to the ocular surface. It is thought to be associated with reduced quality of life (QOL). The aim of the present study was to investigate the effects of DED on health-related QOL in Japanese university sedentary office workers who are daily users of visual display terminal. In this study, 163 university staff (99 male and 64 female), aged 23-69 years, served as study subjects. Subjects were asked to answer the following three questions. (1) How often do your eyes feel dry? (2) How often do your eyes feel irritated? (3) Have you ever been diagnosed by a clinician as having dry eye syndrome? Sixty-eight subjects who answered “constantly,” “often”, or “sometimes” to both questions 1 and 2 were classified as the DED Group, and the remaining 95 were defined as the Non-DED Group. QOL was assessed by the SF-36 questionnaire, which consisted of 36 items to produce three summary scores, namely, mental, physical, and role/social component summary scores. For males, the DED Group had significantly lower scores than the Non-DED Group for mental component summary (MCS) (P = 0.005). In multiple regression analysis, MCS scores were adversely related to DED in males (P = 0.015). DED was associated with worsened QOL. DED should be regarded as a factor that can lead to deterioration of mental health.

Tohoku J Exp Med. 2014;233(3):215-20

Change in tear film characteristics in visual display terminal users.

PURPOSE: To evaluate changes in symptoms and tear film characteristics in young computer users. METHODS: Fifty-one computer users and 26 controls were evaluated at the beginning and the end of the working day. Subjects with ocular or systemic disease, history of ocular surgery, use of contact lenses or glasses with antireflective surfaces, and use of topical or systemic medications were excluded from the study. Computer use duration, Ocular Surface Disease Index (OSDI) questionnaire, tear osmolarity, Schirmer test, tear break-up time (TBUT), and ocular surface vital dye staining were performed prevocationally and postvocationally. RESULTS: The mean age was 31.2 ± 6.3 years in computer users and 33.7 ± 5.8 in controls. The mean reported computer use was 6.9 ± 2.7 hours/day in computer users and 0.4 ± 0.5 hours/day in controls. The mean prevocational and postvocational values in computer users for OSDI, osmolarity, TBUT, and Schirmer test were 23.2 ± 16.6 and 27.0 ± 17.6, 306.6 ± 14.9 and 311.0 ± 12.5 mOsm/L, 13.9 ± 4.0 and 13.2 ± 3.8 seconds, 22.7 ± 11.8 and 20.6 ± 12.5 mm, respectively. The vocational change was significant for all parameters in the computer user group but not in the control group. The osmolarity-based dry eye diagnosis was 27.4% in the computer users while it was 15.4% in the control group. Oxford score was only grade 1 in 5.9% of visual display terminal users and did not change at the end of the day. CONCLUSIONS: Both symptoms and signs of dry eye increased significantly with computer use. Approximately 1 of every 3-4 computer users was found to have dry eye with higher tear osmolarity values.

Eur J Ophthalmol. 2015 Mar-Apr;25(2):85-9

Prevalence of dry eye syndrome among US women.

PURPOSE: Dry eye syndrome (DES) is believed to be one of the most common ocular problems in the United States (US), particularly among older women. However, there are few studies describing the magnitude of the problem in women and how this may vary with demographic characteristics. DESIGN: Cross-sectional prevalence survey. METHODS: STUDY POPULATION: we surveyed 39,876 US women participating in the Women’s Health Study about a history of diagnosed DES and dry eye symptoms. MAIN OUTCOME MEASURE: we defined DES as the presence of clinically diagnosed DES or severe symptoms (both dryness and irritation constantly or often). We calculated the age-specific prevalence of DES and adjusted the overall prevalence to the age distribution of women in the US population. We used logistic regression to examine associations between DES and other demographic factors. RESULTS: The prevalence of DES increased with age, from 5.7% among women < 50 years old to 9.8% among women aged > or = 75 years old. The age-adjusted prevalence of DES was 7.8%, or 3.23 million women aged > or = 50 in the US. Compared with Whites, Hispanic (odds ratio [OR] = 1.81, confidence interval [CI] = 1.18-2.80) and Asian (OR = 1.77, CI = 1.17-2.69) women were more likely to report severe symptoms, but not clinically diagnosed DES. There were no significant differences by income (P([trend]) =.78), but more educated women were less likely to have DES (P([trend]) =.03). Women from the South had the highest prevalence of DES, though the magnitude of geographic differences was modest. CONCLUSIONS: Dry eye syndrome leading to a clinical diagnosis or severe symptoms is prevalent, affecting over 3.2 million American women middle-aged and older. Although the condition is more prevalent among older women, it also affects many women in their 40s and 50s. Further research is needed to better understand DES and its impact on public health and quality of life.

Am J phthalmol. 2003 Aug;136(2):318-26

Increasing importance of dry eye syndrome and the ideal artificial tear: consensus views from a roundtable discussion.

BACKGROUND: Dry eye syndrome is a highly prevalent, yet largely under diagnosed, condition that can substantially affect quality of life. Left untreated, dry eye is associated with chronic eye pain and increased risk of ocular surface disease. Current demographic changes and lifestyle factors indicate that the dry eye syndrome patient population will increase significantly, ensuring that general practitioners and ophthalmic clinicians alike will experience more patients presenting with dry eye symptoms. Greater public and practitioner awareness of emerging research, technologies, and therapies is crucial to ensuring appropriate interventions to meet specific patient needs and result in clinically favorable outcomes. ROUNDTABLE ASSEMBLY: In August 2005, a team of ocular surface experts convened for a 1-day roundtable session to discuss the latest information on diagnosing and treating dry eye syndrome and real-world issues in artificial tear therapy, including preservative use. ROUNDTABLE DISCUSSION: The discussion centered on the mild to moderate dry eye patient and critical features of the ideal artificial tear, which are preservative-free formulation, protection from microbial contamination, cost-effective, non-blurring, and easy to use. Products that match this profile have the advantage of being able to benefit the myriad of patients who comprise the dry eye syndrome population. Ocular surface health should always remain a top priority. Preferred Practice Pattern Dry Eye Syndrome Medical Treatment guidelines should be modified to recommend the use of preservative-free formula artificial tear products for all levels of dry eye conditions in consideration of the medical benefit they offer to dry eye syndrome sufferers. CONCLUSION: The growing prevalence of dry eye syndrome demands increased attention. Further research, enhanced diagnostic tests, increased use of preservative-free artificial tear formulations as first-line therapy, greater patient-practitioner interaction, and patient education are warranted.

Curr Med Res Opin. 2006 Nov;22(11):2149-57

Dry eye in LASIK patients.

BACKGROUND: Increasing age is a known risk factor for developing dry eye. The specific aims of the present study were to determine the prevalence of dry eye syndrome (DES) and use of post-operative dry eye medications in a relatively young population presenting for LASIK surgery at an academic ophthalmology clinic. FINDINGS: A retrospective, analysis of 948 de-identified patient charts (median age 39 years, not age stratified) was performed to extract pre-LASIK diagnoses and post-LASIK medication lists. Clinical evaluation for DES and the results of Schirmer’s reflex tear flow test were used to assign LASIK patients into Normal, Pre-dry eye (Pre-DES), and Dry Eye Syndrome (DES) groups; which were then compared for use of dry eye medications.Based on pre-operative diagnoses, only 2% (CI: 1.3 - 3.1) of LASIK patients presented with overt DES. Unexpectantly, 25% (CI: 22.2 - 27.6) of LASIK patients labeled Pre-DES were not classified by the clinician as having overt DES, yet they showed poor reflex tear flow rates ≤ 5 mm before surgery, and frequently used post-operative lubricant dry eye medications. CONCLUSIONS: Although the number of patients with pre-existing eye conditions was unknown, a sizable portion of relatively young LASIK patients displays poor reflex tear flow without overt DES. Such patients could go on to develop more serious consequences of poor tear flow, such as corneal abrasion and erosion. More specific, dry eye medications may be needed for ideal treatment.

BMC Res Notes. 2014 Jul 3;7:420

Rethinking dry eye disease: a perspective on clinical implications.

Publication of the DEWS report in 2007 established the state of the science of dry eye disease (DED). Since that time, new evidence suggests that a rethinking of traditional concepts of dry eye disease is in order. Specifically, new evidence on the epidemiology of the disease, as well as strategies for diagnosis, have changed the understanding of DED, which is a heterogeneous disease associated with considerable variability in presentation. These advances, along with implications for clinical care, are summarized herein. The most widely used signs of DED are poorly correlated with each other and with symptoms. While symptoms are thought to be characteristic of DED, recent studies have shown that less than 60% of subjects with other objective evidence of DED are symptomatic. Thus the use of symptoms alone in diagnosis will likely result in missing a significant percentage of DED patients, particularly with early/mild disease. This could have considerable impact in patients undergoing cataract or refractive surgery as patients with DED have less than optimal visual results. The most widely used objective signs for diagnosing DED all show greater variability between eyes and in the same eye over time compared with normal subjects. This variability is thought to be a manifestation of tear film instability which results in rapid breakup of the tearfilm between blinks and is an identifier of patients with DED. This feature emphasizes the bilateral nature of the disease in most subjects not suffering from unilateral lid or other unilateral destabilizing surface disorders. Instability of the composition of the tears also occurs in dry eye disease and shows the same variance between eyes. Finally, elevated tear osmolarity has been reported to be a global marker (present in both subtypes of the disease- aqueous-deficient dry eye and evaporative dry eye). Clinically, osmolarity has been shown to be the best single metric for diagnosis of DED and is directly related to increasing severity of disease. Clinical examination and other assessments differentiate which subtype of disease is present. With effective treatment, the tear osmolarity returns to normal, and its variability between eyes and with time disappears. Other promising markers include objective measures of visual deficits, proinflammatory molecular markers and other molecular markers, specific to each disease subtype, and panels of tear proteins. As yet, however, no single protein or panel of markers has been shown to discriminate between the major forms of DED. With the advent of new tests and technology, improved endpoints for clinical trials may be established, which in turn may allow new therapeutic agents to emerge in the foreseeable future. Accurate recognition of disease is now possible and successful management of DED appears to be within our grasp, for a majority of our patients.

Ocul Surf. 2014 Apr;12(2 Suppl):S1-31

Pharmacological management of dry eye in the elderly patient.

Dry eye disease is a common and increasingly prevalent condition particularly associated with advancing age and postmenopausal women. Epidemiological studies identify prevalence rates ranging from 7% in the US to 33% in the Asian population. Research increasingly identifies risk factors of increasing age, female sex, smoking, use of video display terminals and use of certain medications as well as environmental stresses as aggravating factors for the disease. Basic and clinical investigations provide cumulative evidence of hyperosmolarity of the tear film and ocular surface/lacrimal gland inflammation as pathogenic features of dry eye disease. A decline in systemic and local levels of sex hormones is associated with advancing age and advancing disease. Pharmacological therapeutic interventions include enhanced lubricants and anti-inflammatory drugs such as topical corticosteroids and ciclosporin (cyclosporine A). Secretagogues and hormonal supplementation are potential future therapies. The increased understanding of the contributing and pathogenetic factors responsible for dry eye provides a rationale for multiple therapeutic options for this multi-factorial disease. In the elderly patient it is important to recognize the physical and cognitive limitations that will influence the selection of appropriate topical medication.

Drugs Aging. 2008;25(2):105-18

Dry eye medication use and expenditures: data from the medical expenditure panel survey 2001 to 2006.

PURPOSE: To study dry eye medication use and expenditures from 2001 to 2006 using a nationally representative sample of US adults. METHODS: This study retrospectively analyzed dry eye medication use and expenditures of participants of the 2001 to 2006 Medical Expenditure Panel Survey, a nationally representative subsample of the National Health Interview Survey. After adjusting for survey design and for inflation using the 2009 inflation index, data from 147 unique participants aged 18 years or older using the prescription medications Restasis and Blephamide were analyzed. The main outcome measures were dry eye medication use and expenditures from 2001 to 2006. RESULTS: Dry eye medication use and expenditures increased between the years 2001 and 2006, with the mean expenditure per patient per year being $55 in 2001 to 2002 (n=29), $137 in 2003 to 2004 (n=32), and $299 in 2005 to 2006 (n=86). This finding was strongly driven by the introduction of topical cyclosporine emulsion 0.05% (Restasis; Allergan, Irvine, CA). In analysis pooled over all survey years, demographic factors associated with dry eye medication expenditures included gender (female: $244 vs. male: $122, P<0.0001), ethnicity (non-Hispanic: $228 vs. Hispanic: $106, P<0.0001), and education (greater than high school: $250 vs. less than high school: $100, P<0.0001). CONCLUSIONS: We found a pattern of increasing dry eye medication use and expenditures from 2001 to 2006. Predictors of higher dry eye medication expenditures included female gender, non-Hispanic ethnicity, and greater than a high school education.

Cornea. 2012 Dec;31(12):1403-7

Dry eye predisposes to corneal neovascularization and lymphangiogenesis after corneal injury in a murine model.

PURPOSE: Dry eye disease is becoming recognized as an immune-inflammation mediated disorder. Surgical insults such as corneal incision or suture can aggravate dry eye. We sought to determine whether underlying dry eye aggravates corneal inflammatory infiltration, hemangiogenesis, and lymphangiogenesis (LY) induced by surgical injury in a murine model. METHODS: We used treatment arms; one, normal eye (non-dry eye) and the other, a scopolamine-induced dry eye model. We first compared the corneas of both groups on which no surgery was performed with confocal and fluorescent microscopy. In subgroups of each treatment arm, we made a corneal incision followed by 2 corneal sutures to approximate the wound. After harvesting the cornea on postoperative day 9 and immunohistochemical staining, we compared corneal neovascularization (NV), LY, and CD11b inflammatory cell infiltration between non-dry eye and dry eye groups. RESULTS: In corneas in which no surgery was performed, the dry eye group showed more CD11b cell infiltration than did the non-dry eye group (P < 0.05). With respect to corneas after injury, there was significantly more hemangiogenesis, LY, and inflammatory infiltration in the dry eye group than in the non-dry eye group (all P < 0.05). CONCLUSIONS: The underlying status of the cornea, whether it is dry or not, plays a significant role in the development of NV, LY, and inflammation after corneal injury. Dry eye can aggravate post-injury NV, LY, and inflammation.

Cornea. 2014 Jun;33(6):621-7

The role and treatment of inflammation in dry eye disease.

Dry eye syndrome is a common ocular surface problem, affects 10-30 % of the population, especially in those who are older than 40 years. As a consequence of the demographic pressure created by the aging population, its prevalence is expected to increase as well as its burden on ophthalmologic practices. Thus, understanding the complex underlying mechanisms and development of thoughtful, effective strategies that involve these mechanisms are critical. Many factors causing ocular surface damage and inflammation have been shown to contribute to the etiopathogenesis. Increased osmolarity induces ocular surface inflammation leading to disruption of both the quality and quantity of tears. Pathologic tear function and the ocular surface inflammation affects the neural arcade and increases apoptosis in the ocular surface cells thus creating a viscous cycle for dry eye by causing unstable and hyperosmolar tears. Thus, the treatment objective is to prevent severe dry eye complications via preventing inflammation and apoptosis of the ocular surface cells. The ultimate target is a normalized ocular surface, increased tear stability, and decreased osmolarity of the tear film. In the light of current literature, this review aims to elucidate the role of inflammation as the main etiological factor in dry eye disease and discuss current therapeutic approaches to overcome it.

Int Ophthalmol. 2014 Dec;34(6):1291-301

Age-dependent changes in rat lacrimal gland anti-oxidant and vesicular related protein expression profiles.

PURPOSE: Anti-oxidation and exocytosis are important for maintaining exocrine tissue homeostasis. During aging, functional and structural alterations occur in the lacrimal gland (LG), including oxidative damage to proteins, lipids, and DNA. The aims of the present study were to determine in the aging LG: a) the effects of aging on LG structure and secretory activity and b) changes in the expression of oxidative stress markers. METHODS: To address these goals, tear secretion composition and corneal impression cytology were compared between male Wistar rats of 2 (control) and 24 (aged) months. LG morphology and the expression levels of vitamin E and malonaldehyde (MDA) were evaluated to determine the anti-oxidant activity and lipid peroxidation, respectively. RT-PCR and western blot analysis were used for the analysis of Ras related in brain GTPase protein (Rab) and soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins of the secretory machinery (i.e.; Rab 3d, Rab 27, vesicle-associated membrane protein-2 (Vamp-2), and syntaxin). RESULTS: Histological analysis of aged rats revealed a higher frequency of corneal epithelia metaplasia. In the acinar cells, organelles underwent degeneration, and lipofucsin-like material accumulated in the cytoplasm along with declines in the anti-oxidant marker vitamin E. Rab3d and Rab27b mRNA levels fell along with Rab3d protein expression, whereas syntaxin levels increased. CONCLUSIONS: These findings indicate that exocytotic and anti-oxidant mechanisms become impaired with age in the rat LG. In parallel with these structural alterations, functional declines may contribute to the pathophysiology caused by tear film modification in dry eye disease.

Mol Vis. 2012;18:194-202

Aging and dry eye disease.

Dry eye disease is a prevalent eye disorder that in particular affects the elderly population. One of the major causes of dry eye, meibomian gland dysfunction (MGD), shows increased prevalence with aging. MGD is caused by hyperkeratinization of the ductal epithelium of meibomian gland and reduced quantity and/or quality of meibum, the holocrine product that stabilizes and prevents the evaporation of the tear film. Of note, retinoids which are used in current anti-aging cosmetics may promote the development of MGD and dry eye disease. In this review, we will discuss the possible mechanisms of age-related MGD.

Exp Gerontol. 2012 Jul;47(7):483-90

The impact of artificial tears containing hydroxypropyl guar on mucous layer.

PURPOSE: The aim of this study was to investigate the effect of lubricant eyedrops containing propylene glycol 400 (PEG) and polyethylene glycol (PG) with hydroxypropyl guar (HP-guar) as a gelling agent on the precorneal mucous layer in vivo. METHODS: Sixteen New Zealand white rabbits were randomly assigned to 1 of 4 groups. All rabbits received PEG/PG/HP-guar tear products in the right eye. PEG/PG/HP-guar with Polyquad, 0.1% hyaluronate sodium, 0.5% carboxymethylcellulose, or phosphate-buffered saline was placed in the left eyes of animals in each group. All eyedrops were used 4 times a day for 7 days. An additional 8 rabbits were randomly assigned to 1 of 2 groups. One group received PEG/PG/HP-guar products 4 times a day for 7 days (long-term exposure group), and the other group received PEG/PG/HP-guar products 3 times at 5-minute intervals (short-term exposure group). Fifteen minutes after the last drop was administered, each cornea was immediately excised and mucous layer thickness measured by transmission electron microscopy. RESULTS: Mucous layer thickness was significantly greater in eyes treated with PEG/PG/HP-guar products compared with those treated with 0.1% hyaluronate sodium, 0.5% carboxymethylcellulose, or phosphate-buffered saline (all P values < 0.001). There were no significant differences in mucous layer thickness between PEG/PG/HP-guar products and PEG/PG/HP-guar with Polyquad or in the long- and short-term exposure animals. CONCLUSIONS: This study demonstrates that even a short exposure to PEG/PG/HP-guar tear product increased precorneal mucous layer thickness.

Cornea. 2010 Dec;29(12):1430-5

Systane lubricant eye drops in the management of ocular dryness.

The understanding of dry eye disease has advanced recently through increasing recognition that the etiology of the condition involves both tear evaporation and insufficient tear production, and that tear film instability and inflammation play roles in the various stages of the disease. Of significance, it has been recognized that lipid layer thickness correlates with tear film stability. The management of dry eye involves various strategies and therapeutic approaches that address one or more etiopathological components of the disease. The purpose of this review is to outline the characteristics and clinical utility of the Systane(®) ocular lubricants that contain hydroxypropyl-guar and one or both of the demulcents, ie, polyethylene glycol 400 and propylene glycol. Clinically, these products are safe and are indicated for the temporary relief of burning and irritation due to dryness of the eye. In particular, this review describes the formulations, mechanisms of action, and clinical utility of the newest additions to this topical ocular lubricant family, Systane Ultra(®) and Systane Balance(®). Both of these ocular products are formulated with an intelligent delivery system and both provide symptomatic relief to patients with dry eye. However, Systane Balance is a novel formulation that contains both polymer and lipid components designed to protect the ocular surface and replenish tear film lipids simultaneously, a factor that is of particular relevance to patients who have dry eye associated with meibomian gland dysfunction.

Clin Ophthalmol. 2011;5:783-90

Morphologic and physiologic effects of artificial tear formulations on corneal epithelial derived cells.

The biological effects of four commercially available artificial tear formulations were evaluated using sensitive in vitro techniques. Two of the formulations contained ingredients implicated in cell damage; the other two products were not chemically preserved, and their components have not been reported to damage corneal tissue. We assayed the effects of these formulations on viability, morphology, and physiology in corneal cell (SIRC) cultures. Their effect on the hydration of excised rabbit corneas was also determined. In all formulations, cell viability declined with time relative to control cells, but the time course varied significantly. Viability remained at 100% for 6 h in an unpreserved carboxymethylcellulose-based product (CMC-U), and decreased to 50% after greater than 16 hours. Viability decreased to 50% in 3 h for the other unpreserved, polyvinyl alcohol-based product (PVA-U), and in 1 h for a hydroxypropylmethylcellulose formulation (HPMC-P) that contains edetate disodium (EDTA). Cells in a preserved formulation (PVA-P), using polyvinyl alcohol as the polymer and containing EDTA and benzalkonium chloride (BAK), failed to survive even 15 min of treatment. Overall, cells treated with the unpreserved products were nearly indistinguishable from those in the control solution with respect to morphology, electrophysiology, and corneal hydration. Also, the relative ranking from least to most deleterious (control less than CMC-U less than PVA-U less than HPMC-P less than PVA-P) was consistent across several measures. Of the preserved formulations, HPMC-P, which contains the chelating agent EDTA as an additive, was less damaging than was PVA-P, which contains two chemicals, EDTA and BAK, that reportedly damage cells.

Cornea. 1992 May;11(3):234-41

Aging Facial Skin

Structure and function of the epidermis related to barrier properties.

The most important function of the skin is the formation of a barrier between the “inside” and the “outside” of the organism, which prevents invasion of pathogens and fends off chemical assaults as well as the unregulated loss of water and solutes. The physical barrier is mainly localized in the stratum corneum, which consists of protein-enriched cells and lipid-enriched intercellular domains. Any modifications in epidermal differentiation and lipid composition results in altered barrier function, a central event in various skin alterations and diseases. This contribution presents a brief description of the structure of the skin, paying attention to the most important components responsible for skin barrier function.

Clin Dermatol. 2012 May-Jun;30(3):257-62

Barrier function of the skin: “la raison d’être” of the epidermis.

The primary function of the epidermis is to produce the protective, semi-permeable stratum corneum that permits terrestrial life. The barrier function of the stratum corneum is provided by patterned lipid lamellae localized to the extracellular spaces between corneocytes. Anucleate corneocytes contain keratin filaments bound to a peripheral cornified envelope composed of cross-linked proteins. The many layers of these specialized cells in the stratum corneum provide a tough and resilient framework for the intercellular lipid lamellae. The lamellae are derived from disk-like lipid membranes extruded from lamellar granules into the intercellular spaces of the upper granular layer. Lysosomal and other enzymes present in the extracellular compartment are responsible for the lipid remodeling required to generate the barrier lamellae as well as for the reactions that result in desquamation. Lamellar granules likely originate from the Golgi apparatus and are currently thought to be elements of the tubulo-vesicular trans-Golgi network. The regulation of barrier lipid synthesis has been studied in a variety of models, with induction of several enzymes demonstrated during fetal development and keratinocyte differentiation, but an understanding of this process at the molecular genetic level awaits further study. Certain genetic defects in lipid metabolism or in the protein components of the stratum corneum produce scaly or ichthyotic skin with abnormal barrier lipid structure and function. The inflammatory skin diseases psoriasis and atopic dermatitis also show decreased barrier function, but the underlying mechanisms remain under investigation. Topically applied “moisturizers” work by acting as humectants or by providing an artificial barrier to trans-epidermal water loss; current work has focused on developing a more physiologic mix of lipids for topical application to skin. Recent studies in genetically engineered mice have suggested an unexpected role for tight junctions in epidermal barrier function and further developments in this area are expected. Ultimately, more sophisticated understanding of epidermal barrier function will lead to more rational therapy of a host of skin conditions in which the barrier is impaired.

J Invest Dermatol. 2003 Aug;121(2):231-41

Epidermal surface lipids.

A layer of lipids, which are of both sebaceous and keratinocyte origin, covers the surface of the skin. The apparent composition of surface lipids varies depending on the selected method of sampling. Lipids produced by the epidermal cells are an insignificant fraction of the total extractable surface lipid on areas rich in sebaceous glands. Due to the holocrine activity of the sebaceous gland, its product of secretion (sebum) is eventually released to the surface of the skin and coats the fur as well. Lipids of epidermal origin fill the spaces between the cells, like mortar or cement. The sebaceous lipids are primarily non polar lipids as triglycerides, wax esters and squalene, while epidermal lipids are a mixture of ceramides, free fatty acids and cholesterol. The composition of the sebaceous lipids is unique and intriguing and elevated sebum excretion is a major factor involved in the pathophysiology of acne. Recent studies have elucidated the roles that epidermal surface lipids have on normal skin functions and acne.

Dermatoendocrinol. 2009 Mar;1(2):72-6

Role of fatty acid transporters in epidermis: Implications for health and disease.

Skin epidermis is an active site of lipid synthesis. The intercellular lipids of human stratum corneum (SC) are unique in composition and quite different from the lipids found in most biological membranes. The three major lipids in the SC are free fatty acids, cholesterol and ceramides. Fatty acids can be synthesized by keratinocytes de novo and, in addition, need to be taken up from the circulation. The latter process has been shown to be protein mediated, and several fatty acid transporters are expressed in skin. Recent studies of transgenic and knockout animal models for fatty acid transporters and the identification of fatty acid transport protein 4 (FATP4 or SLC27A4) mutations as causative for Ichthyosis Prematurity Syndrome highlight the vital roles of fatty acid transport and metabolism in skin homeostasis. This review provides an overview of our current understanding of the role of fatty acids and their transporters in cutaneous biology, including their involvement in epidermal barrier generation and skin inflammation

Dermatoendocrinol. 2011 Apr;3(2):53-61

The omega-3 fatty acid nutritional landscape: health benefits and sources.

Dietary fatty acids (FA) are increasingly recognized as major biologic regulators and have properties that relate to health outcomes and disease. The longer chain, more bioactive (n-6) (or omega-6) FA and (n-3) (or omega-3) FA share similar elongation and desaturation enzymes in their conversion from the essential (n-6) FA, linoleic acid, and (n-3) FA, a-linolenic acid (ALA). Conversion from these essential FA is very inefficient. However, now for the (n-3) FA series, soy oil can be enriched with (n-3) stearidonic acid (SDA) to allow for much more efficient conversion to longer chain EPA. EPA and the longer chain DHA possess distinct physical and biological properties that generally impart properties to cells and tissue, which underlie their ability to promote health and prevent disease. Although active in a number of areas of human biology, mechanisms of action of EPA and DHA are perhaps best defined in cardiovascular disease. There is concern that to reach the intake recommendations of EPA and DHA, their supply from cold water fish will be insufficient. Gaps in understanding mechanisms of action of (n-3) FA in a number of health and disease areas as well as optimal sources and intake levels for each need to be defined by further research. Because of the inefficient conversion of ALA, the appearance of SDA in enriched soy oil offers a biologically effective and cost effective approach to providing a sustainable plant source for (n-3) FA in the future.

J Nutr. 2012 Mar;142(3):587S-591S

Dietary intakes and food sources of omega-6 and omega-3 polyunsaturated fatty acids.

Both n-6 and n-3 polyunsaturated fatty acids (PUFA) are recognized as essential nutrients in the human diet, yet reliable data on population intakes are limited. The aim of the present study was to ascertain the dietary intakes and food sources of individual n-6 and n-3 PUFA in the Australian population. An existing database with fatty acid composition data on 1690 foods was updated with newly validated data on 150 foods to estimate the fatty acid content of foods recorded as eaten by 10,851 adults in the 1995 Australian National Nutrition Survey. Average daily intakes of linoleic (LA), arachidonic (AA), alpha-linolenic (LNA), eicosapentaenoic (EPA), docosapentaenoic (DPA), and docosahexaenoic (DHA) acids were 10.8, 0.052, 1.17, 0.056, 0.026, and 0.106 g, respectively, with long-chain (LC) n-3 PUFA (addition of EPA, DPA, and DHA) totaling 0.189 g; median intakes were considerably lower (9.0 g LA, 0.024 g AA, 0.95 g LNA, 0.008 g EPA, 0.006 g DPA, 0.015 g DHA, and 0.029 g LC n-3 PUFA). Fats and oils, meat and poultry, cereal-based products and cereals, vegetables, and nuts and seeds were important sources of n-6 PUFA, while cereal-based products, fats and oils, meat and poultry, cereals, milk products, and vegetable products were sources of LNA. As expected, seafood was the main source of LC n-3 PUFA, contributing 71%, while meat and eggs contributed 20 and 6%, respectively. The results indicate that the majority of Australians are failing to meet intake recommendations for LC n-3 PUFA (> 0.2 g per day) and emphasize the need for strategies to increase the availability and consumption of n-3-containing foods.

Lipids. 2003 Apr;38(4):391-8

Incorporation of linoleic acid by cultured human keratinocytes.

Linoleic acid is required for the formation and maintenance of the epidermal barrier, but most of the current in vitro keratinocyte culture systems are linoleic acid-deficient. The aim of the present study was to examine the efficiency of linoleic acid uptake in human keratinocyte cultures grown under submerged and air-exposed conditions in serum-free medium. The water-insoluble linoleic acid was bound to carrier molecules (cyclodextrin or bovine serum albumin). Comparable results were obtained with home-made and commercially available linoleic acid complexes. In the submerged cultures, the increase of the linoleic acid medium concentration (ranging from 0 to 20 microg/ml) resulted in a gradual increase in the linoleic acid cellular content, which exceeded 1.4 times the value found in native epidermis when the highest concentration of linoleic acid was used. The addition of linoleic acid did not alter the profile of the other epidermal fatty acids, with the exception of oleic acid, which decreased in parallel with the increasing linoleic acid content. While the content of linoleic acid found in phospholipids was similar to that in native epidermis, a large excess of linoleic acid was detected in triglycerides, the synthesis of which was markedly increased in cultures grown submerged in medium containing higher concentrations of linoleic acid. Under air-exposed conditions, the dermal substrate used seemed to be the most limiting factor for efficient linoleic acid supplementation. A low linoleic acid cellular content was detected when an inert filter was used. De-epidermized dermis was found to be the most permeable substrate for linoleic acid complexes. The cellular linoleic acid content increased in a parallel with the increasing linoleic acid concentration (ranging from 4 to 30 microg/ml), but the overall amount incorporated was lower than that in submerged cultures. The content of linoleic acid in the phospholipid and ceramide fractions isolated from reconstructed epidermis grown under air-exposed conditions was close to that of native epidermis, but the triglycerides remained abnormally enriched in linoleic acid, indicating persistence of some anomalies in epidermal lipogenesis in vitro.

Arch Dermatol Res. 1999 Jul-Aug;291(7-8):405-12

Optimization of submerged keratinocyte cultures for the synthesis of barrier ceramides.

Epidermal differentiation results in the formation of the extracellular lipid barrier in the stratum corneum, which mainly consists of ceramides, free fatty acids, and cholesterol. Differentiating keratinocytes of the stratum granulosum synthesize a series of complex long-chain ceramides and glucosylceramides with different chain lengths and hydroxylation patterns at intracellular membranes of the secretory pathway. Formation of complex extracellular ceramides parallels the transition of keratinocytes from the stratum granulosum to the stratum corneum, where their precursors, complex glucosylceramides and sphingomyelin, are secreted and exposed to extracellular lysosomal lipid hydrolases. Submerged cultures used so far showed a reduced ceramide content compared to the native epidermis or the air-exposed, organotypic culture system. In order to investigate the sphingolipid metabolism during keratinocyte differentiation, we optimized a simple cell culture system to generate the major barrier sphingolipids. This optimized model is based on the chemically well-defined serum-free MCDB medium. At low calcium ion concentrations (0.1mM), keratinocytes proliferate and synthesize mainly Cer(NS) and a small amount of Cer(NP). Supplementation of the MCDB cell culture medium with calcium ions (1.1mM) and 10 microM linoleic acid triggered differentiation of keratinocytes and synthesis of a complex pattern of free and covalently bound ceramides as found in native epidermis or air-exposed organotypic cultures, though at a reduced level. The mRNA levels of the differentiation markers keratin 10 and profilaggrin increased, as well as those of ceramide glucosyltransferase and glucosylceramide-beta-glucosidase. The described culture system was thus suitable for biochemical studies of the sphingolipid metabolism during keratinocyte differentiation. The addition of serum or vitamin A to the medium resulted in a decrease in ceramide and glucosylceramide content. Lowering the medium pH to 6, while maintained cell viability, led to an increase in the processing of probarrier lipids glucosylceramide and sphingomyelin to free ceramides and protein-bound ceramide Cer(OS).

Eur J Cell Biol. 2007 Dec;86(11-12):657-73

Gamma-linolenic acid levels correlate with clinical efficacy of evening primrose oil in patients with atopic dermatitis.

INTRODUCTION: Atopic dermatitis (AD) has been related to a deficiency of delta-6-desaturase, an enzyme responsible for the conversion of linoleic acid to gamma-linolenic acid (GLA). Evening primrose oil (EPO) contains high amounts of GLA. Therefore, this study investigated whether EPO supplementation results in an increase in plasma GLA and its metabolite dihomo-gamma-linolenic acid (DGLA) correlating with clinical improvement of AD, assessed by the SCORing Atopic Dermatitis (SCORAD) index. METHODS: The open study included 21 patients with AD. EPO (4-6 g) was administered daily for 12 weeks. Before treatment, and 4 and 12 weeks after initiation of EPO supplementation, objective SCORAD was assessed and plasma concentrations of GLA and DGLA were determined by gas chromatography. RESULTS: A significant increase in plasma GLA and DGLA levels and a decrease in the objective SCORAD were observed 4 and 12 weeks after initiation of EPO treatment. In the per-protocol population (n = 14), a significant inverse correlation between the changes in plasma GLA levels and SCORAD was found (P = 0.008). CONCLUSION: The clinical disease activity under EPO treatment correlates with the individual increase in plasma GLA levels. Thus, the results of this pilot study indicate that an increase in plasma GLA might be used as predictive parameter for responsiveness of AD to EPO therapy.

Adv Ther. 2014 Feb;31(2):180-8

Arachidonic acid metabolites and the skin.

The relevance of arachidonic acid metabolites in inflammatory skin diseases has been expanded by recent developments in analytical chemistry. The metabolites include prostaglandins, leukotrienes and monohydroxy fatty acids. In ultraviolet light-induced inflammation the concentrations of arachidonic acid, prostaglandin E2, prostaglandin F2 alpha and 6-oxo-prostaglandin F1 alpha are elevated. Indomethacin totally suppresses the evoked prostaglandin increase, but erythema is only partially suppressed. This indicates that prostaglandins are partially involved in erythema production. In psoriasis the first histological change is an infiltration into the epidermis by neutrophilic leucocytes. It has been suggested that chemotactic factors, such as complement derived factors or leukotriene B4 play a role in the pathogenesis of psoriasis.

Ann Acad Med Singapore. 1983 Jan;12(1):87-91

In vivo conversion of linoleic acid to arachidonic acid in human adults.

Human adults are shown to be capable of conversion of linoleic acid (LA, 18:2 n-6) to arachidonic acid (AA, 20:4 n-6) in vivo. It is confirmed that they can also convert alpha-linolenic acid (LNA, 18:3 n-3) to eicosapentaenoic acid (EPA, 20:5 n-3) and to docosahexaenoic acid (DHA, 22:6 n-3) in vivo. The time course and the maximal response for these processes during the first week after a single dose of the 18-carbon precursor is described. A stable-isotope method in which the protons of the C17 and C18 carbons are substituted with deuterium atoms is used in order to provide for a safe method for the study of human metabolism. High sensitivity and selectivity of detection is assured with negative ion, gas chromatography/mass spectrometry analysis. It is clear that human adults on an ad lib diet carry out EFA metabolism in vivo.

Prostaglandins Leukot Essent Fatty Acids. 1999 May-Jun;60(5-6):407-10

Metabolism of polyunsaturated fatty acids by skin epidermal enzymes: generation of antiinflammatory and antiproliferative metabolites.

In the skin epidermis, the metabolism of polyunsaturated fatty acids (PUFAs) is highly active. Dietary deficiency of linoleic acid (LA), the major 18-carbon n-6 PUFA in normal epidermis, results in a characteristic scaly skin disorder and excessive epidermal water loss. Because of the inability of normal skin epidermis to desaturate LA to gamma-linolenic acid, it is transformed by epidermal 15-lipoxygenase to mainly 13-hydroxyoctadecadienoic acid, which functionally exerts antiproliferative properties in the tissue. In contrast, compared with LA, arachidonic acid (AA) is a relatively minor 20-carbon n-6 PUFA in the skin and is metabolized via the cyclooxygenase pathway, predominantly to the prostaglandins E(2), F(2)(alpha), and D(2). AA is also metabolized via the 15-lipoxygenase pathway, predominantly to 15-hydroxyeicosatetraenoic acid. At low concentrations, the prostaglandins function to modulate normal skin physiologic processes, whereas at high concentrations they induce inflammatory processes. PUFAs derived from other dietary oils are also transformed mainly into monohydroxy fatty acids. For instance, epidermal 15-lipoxygenase transforms dihomo-gamma-linolenic acid (20:3n-6) to 15-hydroxyeicosatrienoic acid, eicosapentaenoic acid (20:5n-3) to 15-hydroxyeicosapentaenoic acid, and docosahexaenoic acid (22:6n-3) to 17-hydroxydocosahexaenoic acid, respectively. These monohydroxy acids exhibit antiinflammatory properties in vitro. Thus, supplementation of diets with appropriate purified vegetable oils, fish oil, or both may generate local cutaneous antiinflammatory and antiproliferative metabolites which could serve as less toxic in vivo monotherapies or as adjuncts to standard therapeutic regimens for the management of inflammatory skin disorders.

Am J Clin Nutr. 2000 Jan;71(1 Suppl):361S-6S

Differential effects of prostaglandin derived from omega-6 and omega-3 polyunsaturated fatty acids on COX-2 expression and IL-6 secretion.

Omega-6 (omega-6) polyunsaturated fatty acids (PUFA), abundant in the Western diet, are precursors for a number of key mediators of inflammation including the 2-series of prostaglandins (PG). PGE(2), a cyclooxygenase (COX) metabolite of arachidonic acid, a omega-6 PUFA, is a potent mediator of inflammation and cell proliferation. Dietary supplements rich in omega-3 PUFA reduce the concentrations of 2-series PG and increase the synthesis of 3-series PG (e.g., PGE(3)), which are believed to be less inflammatory. However, studies on cellular consequences of increases in 3-series PG in comparison to 2-series PG have not been reported. In this study, we compared the effects of PGE(2) and PGE(3) on (i) cell proliferation in NIH 3T3 fibroblasts, (ii) expression and transcriptional regulation of the COX-2 gene in NIH 3T3 fibroblasts, and (iii) the production of an inflammatory cytokine, IL-6, in RAW 264.7 macrophages. PGE(3), unlike PGE(2), is not mitogenic to NIH 3T3 fibroblasts. PGE(2) and PGE(3) both induce COX-2 mRNA via similar signaling mechanisms; however, compared with PGE(2), PGE(3) is significantly less efficient in inducing COX-2 gene expression. Furthermore, although both PGE(2) and PGE(3) induce IL-6 synthesis in RAW 264.7 macrophages, PGE(3) is substantially less efficient compared with PGE(2). We further show that increasing the omega-3 content of membrane phospholipid results in a decrease in mitogen-induced PGE(2) synthesis. Taken together, our data suggest that successful replacement of omega-6 PUFA with omega-3 PUFA in cell membranes can result in a decreased cellular response to mitogenic and inflammatory stimuli.

Proc Natl Acad Sci U S A. 2003 Feb 18;100(4):1751-6