Life Extension Magazine®

Issue: Sep 2000

Copper, Acids, more


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Copper

Copper bioavailability and requirements

Knowledge of factors affecting the bioavailability of dietary copper is limited. Intestinal absorption of copper appears to be facilitated by L-amino acids. Picolinic acid has a favorable binding affinity for copper and may facilitate its absorption. Measurements of the dietary requirements for copper in adult men have shown the requirement to range from about 1.5 to 2.0 mg daily, levels similar to the 2.0 mg estimate suggested in the past. Comparison of the copper requirements with the levels of copper present in some contemporary diets suggests that marginal copper nutriture may not be rare. Persons who consume diets high in zinc and low in protein are at risk of copper deficiency. High intakes of sources of dietary fiber apparently increase the dietary requirement for copper. Studies in one man have shown that signs of mild copper deficiency can be produced experimentally when a conventional diet containing about 0.8 mg of copper is fed. At this time, the 2 to 3 mg daily intake of dietary copper suggested by the National Research Council (63) seems appropriate.

JAm J Clin Nutr 1982 Apr;35(4):809-14

Adverse effects of high dietary iron and ascorbic acid on copper status in copper-deficient and copper-adequate rats

The effects of elevated dietary ascorbic acid and iron on copper utilization were examined. Male Sprague-Dawley rats were fed one of two levels of Cu (deficient, 0.42 microgram Cu/g, or adequate, 5.74 micrograms Cu/g), Fe (moderate, 38 micrograms Fe/g or high, 191 micrograms Fe/g), and ascorbic acid (low, 0% or high, 1% of the diet) for 20 d. High Fe decreased (p less than 0.05) Cu absorption only in Cu-deficient rats. High ascorbic acid significantly decreased tissue Cu levels in Cu-adequate rats. High Fe with ascorbic acid caused severe anemia in Cu-deficient rats and decreased plasma ceruloplasmin by 44% in Cu-adequate rats. Cu,Zn-superoxide dismutase activity in erythrocytes was decreased (p less than 0.05) by 14% during Cu deficiency but was not affected by Fe or ascorbic acid. These results may be important to individuals with high intakes of Fe and ascorbic acid.

Am J Clin Nutr 1988 Jan;47(1):96-101

Copper and immunity

The immune system requires copper to perform several functions, of which little is known about the direct mechanism of action. Animal models and cells in culture have been used to assess copper's role in the immune response. Some of the recent research showed that interleukin 2 is reduced in copper deficiency and is likely the mechanism by which T cell proliferation is reduced. These results were extended to show that even in marginal deficiency, when common indexes of copper are not affected by the diet, the proliferative response and interleukin concentrations are reduced. The number of neutrophils in human peripheral blood is reduced in cases of severe copper deficiency. Not only are they reduced in number, but their ability to generate superoxide anion and kill ingested microorganisms is also reduced in both overt and marginal copper deficiency. This mechanism is not yet understood. Neutrophil-like HL-60 cells accumulate copper as they differentiate into a more mature cell population and this accumulation is not reflected by increases in Cu/Zn superoxide dismutase or cytochrome-c oxidase activities. The identity of copper-binding proteins in this cell type may be useful in learning new functions of copper or assessing copper status. Neutrophils, because they are short-lived and homogeneous cell populations, are predicted to be an effective and valuable tool for assessing nutrient status in human populations.

Am J Clin Nutr 1998 May;67(5 Suppl):1064S-1068S

Essentiality of copper in humans

The biochemical basis for the essentiality of copper, the adequacy of the dietary copper supply, factors that condition deficiency, and the special conditions of copper nutriture in early infancy are reviewed. New biochemical and crystallographic evidence define copper as being necessary for structural and catalytic properties of cuproenzymes. Mechanisms responsible for the control of cuproprotein gene expression are not known in mammals; however, studies using yeast as a eukaryote model support the existence of a copper-dependent gene regulatory element. Diets in Western countries provide copper below or in the low range of the estimated safe and adequate daily dietary intake. Copper deficiency is usually the consequence of decreased copper stores at birth, inadequate dietary copper intake, poor absorption, elevated requirements induced by rapid growth, or increased copper losses. The most frequent clinical manifestations of copper deficiency are anemia, neutropenia, and bone abnormalities. Recommendations for dietary copper intake and total copper exposure, including that from potable water, should consider that copper is an essential nutrient with potential toxicity if the load exceeds tolerance. A range of safe intakes should be defined for the general population, including a lower safe intake and an upper safe intake, to prevent deficiency as well as toxicity for most of the population.

Am J Clin Nutr 1998 May;67(5 Suppl):952S-959S

Primary structure of rat ceruloplasmin and analysis of tissue-specific gene expression during development

cDNA clones corresponding to rat ceruloplasmin were isolated from newborn rat lung and liver cDNA libraries and the nucleotide sequence was obtained. The derived amino acid sequence of rat ceruloplasmin is 93% homologous to the corresponding human sequence and contains a 19-amino acid leader peptide plus 1040 amino acids of mature protein. Southern blot analysis indicates that the ceruloplasmin gene exists as a single copy in the rat haploid genome. Using these cDNA clones in RNA blot analysis, a single 3.7-kilobase ceruloplasmin-specific transcript is detected in fetal rat liver and lung by day 15 of gestation. During fetal development the abundance of this transcript increases selectively in these two tissues and at birth is 60% of that found in the adult liver. Postnatally the temporal pattern of ceruloplasmin gene expression in lung and liver differs. Within the first 3 weeks postpartum ceruloplasmin mRNA content decreases in lung to undetectable levels, while that in the liver reaches adult levels. Primer extension reveals a single identical start site of ceruloplasmin gene transcription in lung and liver and biosynthetic studies indicate that each tissue synthesizes a ceruloplasmin protein which is qualitatively similar to that synthesized by adult liver. Ceruloplasmin mRNA is also detected in human fetal lung explant and a human lung adenocarcinoma cell line suggesting that a similar pattern of expression occurs in the developing human lung. These data indicate that lung is the predominant extrahepatic site of ceruloplasmin gene expression during fetal development and suggest that this protein may play a previously unappreciated role in lung development or pulmonary antioxidant defense.

J Biol Chem 1990 May 5;265(13):7701-7

Human whole-body copper metabolism

Whole-body copper metabolism is difficult to study in human subjects. However, the use of isotopic tracers and kinetics modeling has added a dimension beyond what can be learned in humans by direct measurement. Mechanisms regulating total body copper seem to be strong, given the relatively small and constant body pool, but they are not yet well understood. The efficiency of copper absorption varies greatly, depending on dietary intake. Changes in efficiency of absorption help to regulate the amount of copper retained by the body. In addition, endogenous excretion of copper into the gastrointestinal tract depends heavily on the amount of copper absorbed. When dietary copper is high and more is absorbed, endogenous excretion increases, protecting against excess accumulation of copper in the body. When intake is low, little endogenous copper is excreted, protecting against copper depletion. Regulation is not sufficient with very low amounts of ietary copper (0.38 mg/d) and appears to be delayed when copper intake is high. The use of isotopic tracers and kinetic modeling should aid in elucidating the regulatory mechanisms.

Am J Clin Nutr 1998 May;67(5 Suppl):960S-964S

A role for ascorbic acid in copper transport

Scurvy-like symptoms have been seen in experimental copper deficiency. This forecasts a role for the vitamin in copper metabolism. Ascorbate has been known to antagonize the intestinal absorption of copper. More recent studies have characterized a postabsorption role for ascorbate in the transfer of copper ions into cells. The vitamin reacts directly or indirectly with ceruloplasmin, a serum copper protein, specifically labilizing the bound copper atoms and facilitating their cross-membrane transport. Ascorbate at physiological levels and above impedes the intracellular binding of copper to Cu,Zn superoxide dismutase. The mechanism is unclear but nonetheless suggests both positive and negative regulatory functions for ascorbate in copper metabolism.

Am J Clin Nutr 1991 Dec;54(6 Suppl):1193S-1197S

The effect of dietary zinc on intestinal copper absorption

Everted duodenal segments, tied into sacs, taken from animals fed different amounts of zinc were used to investigate the antagonistic effect of dietary zinc on copper absorption. The intestinal segments taken from animals fed low amounts of zinc transferred more copper from a nutrient medium across the mucosal cells than did intestines from rats fed high levels of zinc. The mucosal cells from animals fed low amounts of zinc retained less copper than the cells from animals fed high amounts of the element. This retained copper was bound to a protein fraction having a molecular weight similar to that of metallothionein. The data suggest that zinc exerts its antagonistic effect by inducing the synthesis of a copper-binding ligand, probably a thionein, in the mucosal cells which sequesters copper from the nutrient medium, making it unavailable for serosal transfer. This may be a possible mechanism by which dietary zinc decreases copper absorption and leads to a decreased copper status.

Am J Clin Nutr 1981 Sep;34(9):1670-5

Mechanisms of copper conservation in organs

Organ copper is conserved in response to dietary copper restriction. In organs such as brain and heart, conservation is highly efficient, resulting in the loss of little organ copper. In contrast, conservation of copper in liver is induced only after a significant amount of organ copper is lost. Thus, the conservation of copper during dietary restriction is highly organ specific. Although the long-term pattern of organ copper conservation in rats has now been described through use of the continuous feeding of a single stable isotope, the mechanisms responsible for this conservation have not been identified or studied. These mechanisms may include copper-regulated changes in gene expression as well as other mechanisms. We now have the molecular tools that will permit the isolation of copper-regulated genes that may play a role in the conservation of organ copper. Identification of these mechanisms will allow the exploration of the effects of mild short-term and long-term copper deficiency and the role of copper in other physiologic and biochemical systems.

Am J Clin Nutr 1998 May;67(5 Suppl):978S-981S

Cellular expression of ceruloplasmin in baboon and mouse lung during development and inflammation

Ceruloplasmin (CP) is an important extracellular antioxidant and free radical scavenger. Although CP is expressed mainly in the liver, recent studies have identified the lung as another major site of CP synthesis. The sites and cell types that are responsible for CP expression in baboon and mouse lung are described. CP mRNA is detected in primordial bronchial epithelium in baboon fetuses by 60 days of gestation. At 140 days of gestation and thereafter, CP mRNA is found in airway epithelium and in the ductal cells of the submucosal glands. In developing and mature mice, CP mRNA is present in epithelial cells throughout the airway. In endotoxin-treated mice, the amount of CP mRNA increases several-fold in large airways but increases only moderately in small airways. This suggests that the high concentration of CP in the mucus lining of the upper airway, which serves to filter harmful substances, is particularly important during stressful conditions. Endotoxin treatment in mice also results in the induction of high levels of CP mRNA in a subset of alveolar wall cells. The data suggest that the airway epithelial cells are the major source of CP in the lung fluid and support ceruloplasmin's critical role in host defense against oxidative damage and infection in the lung.

Am J Respir Cell Mol Biol 1996 Feb;14(2):161-9

 


Acids

Methylation of the estrogen receptor gene is associated with aging and atherosclerosis in the cardiovascular system

OBJECTIVE: Methylation of the promoter region of the estrogen receptor gene alpha (ER alpha) occurs as a function of age in human colon, and results in inactivation of gene transcription. In this study, we sought to determine whether such age-related methylation occurs in the cardiovascular system, and whether it is associated with atherosclerotic disease. METHODS: We used Southern blot analysis to determine the methylation state of the ER alpha gene in human right atrium, aorta, internal mammary artery, saphenous vein, coronary atherectomy samples, as well as cultured aortic endothelial cells and smooth muscle cells. RESULTS: An age related increase in ER alpha gene methylation occurs in the right atrium (range 6 to 19%, R = 0.36, P < 0.05). Significant levels of ER alpha methylation were detected in both veins and arteries. In addition, ER alpha gene methylation appears to be increased in coronary atherosclerotic plaques when compared to normal proximal aorta (10 +/- 2% versus 4 +/- 1%, P < 0.01). In endothelial cells explanted from human aorta and grown in vitro, ER alpha gene methylation remains low. In contrast, cultured aortic smooth muscle cells contain a high level of ER alpha gene methylation (19-99%). CONCLUSIONS: Methylation associated inactivation of the ER alpha gene in vascular tissue may play a role in atherogenesis and aging of the vascular system. This potentially reversible defect may provide a new target for intervention in heart disease.

Cardiovasc Res 1999 Sep;43(4):985-91

Effects of 3-week oral treatment with the antioxidant thioctic acid (alpha-lipoic acid) in symptomatic diabetic polyneuropathy

AIMS: To evaluate the efficacy and safety of short-term oral treatment with the antioxidant thioctic acid (TA) on neuropathic symptoms and deficits in patients with Type 2 diabetes mellitus with symptomatic polyneuropathy. METHODS: Patients were randomly assigned to oral treatment with 600 mg of TA t.i.d. (n = 12) or placebo (n = 12) for 3 weeks. Neuropathic symptoms (pain, burning, paraesthesiae, and numbness) in the feet were scored at weekly intervals and summarized as a Total Symptom Score (TSS). The Hamburg Pain Adjective List (HPAL) and the Neuropathy Disability Score (NDS) were assessed at baseline and day 19. RESULTS: At baseline the TSS, HPAL, and NDS were not significantly different between the groups. The TSS in the foot decreased from baseline to day 19 by -3.75 +/- 1.88 points (-47%) in the TA group and by -1.94 +/- 1.50 points (-24%) in the placebo group (P= 0.021 for TA vs. placebo). The total HPAL score decreased from baseline to day 19 by -2.20 +/- 1.65 points (-60%) in the TA group and by -0.96 +/- 1.32 points (-29%) in the placebo group (P = 0.072 for TA vs. placebo). The NDS decreased by -0.27 +/- 0.47 points in the TA group, whereas it slightly increased by +0.18 +/- 0.4 points in the placebo group (P = 0.025 for TA vs. placebo). No differences between the groups were noted regarding the rates of adverse events. CONCLUSIONS: These preliminary findings indicate that oral treatment with 600 mg of TA t.i.d. for 3 weeks may improve symptoms and deficits resulting from polyneuropathy in Type 2 diabetic patients, without causing significant adverse reactions.

Diabet Med 1999 Dec;16(12):1040-3





 



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Long-term ascorbic acid administration reverses endothelial vasomotor dysfunction in patients with coronary artery disease

BACKGROUND: Loss of endothelium-derived nitric oxide (EDNO) contributes to the clinical expression of coronary artery disease (CAD). Increased oxidative stress has been linked to impaired endothelial vasomotor function in atherosclerosis, and recent studies demonstrated that short-term ascorbic acid treatment improves endothelial function. METHODS AND RESULTS: In a randomized, double-blind, placebo-controlled study, we examined the effects of single-dose (2 g PO) and long-term (500 mg/d) ascorbic acid treatment on EDNO-dependent flow-mediated dilation of the brachial artery in patients with angiographically established CAD. Flow-mediated dilation was examined by high-resolution vascular ultrasound at baseline, 2 hours after the single dose, and 30 days after long-term treatment in 46 patients with CAD. Flow-mediated dilation improved from 6.6+/-3.5% to 10.1+/-5.2% after single-dose treatment, and the effect was sustained after long-term treatment (9. 0+/-3.7%), whereas flow-mediated dilation was 8.6+/-4.7% at baseline and remained unchanged after single-dose (7.8+/-4.4%) and long-term (7.9+/-4.5%) treatment with placebo (P=0.005 by repeated-measures ANOVA). Plasma ascorbic acid concentrations increased from 41.4+/-12. 9 to 115.9+/-34.2 micromol/L after single-dose treatment and to 95. 0+/-36.1 micromol/L after long-term treatment (P<0.001). CONCLUSIONS: In patients with CAD, long-term ascorbic acid treatment has a sustained beneficial effect on EDNO action. Because endothelial dysfunction may contribute to the pathogenesis of cardiovascular events, this study indicates that ascorbic acid treatment may benefit patients with CAD.

Circulation 1999 Jun 29;99(25):3234-40

Risk factors for Ki-ras protooncogene mutation in sporadic colorectal adenomas

The Ki-ras protooncogene frequently is mutated in colorectal adenocarcinomas, but the etiology of this molecular event is uncertain. We investigated the association between variables known or suspected to be related to risk for colorectal cancer and the occurrence of Ki-ras mutations in colorectal adenomas. This study was conducted among 678 male and female participants, 40-80 years of age, enrolled in a phase III trial testing the effects of a wheat bran fiber supplement on adenoma recurrence. Exposure information on the risk factors of interest was assessed through self-administered questionnaires. Mutations in codons 12 and 13 of the Ki-ras protooncogene were analyzed in baseline adenomas 0.5 cm or larger by PCR amplification followed by direct sequencing. Eighteen percent (120 of 678) of the participants had one or more adenoma(s) with Ki-ras mutations. A higher risk of Ki-ras mutations was associated with increasing age and a lower intake of total folate. The odds ratio (OR) for Ki-ras mutations for individuals >72 years of age was 1.98 [95% confidence interval (CI) = 1.19-3.27; P for trend = 0.008] compared with those less than 65 years of age. Compared with individuals in the lower tertile of total folate, those in the upper tertile had an approximately 50% lower risk of having Ki-ras mutation-positive adenomas (OR = 0.52; 95% CI = 0.30-0.88; P for trend = 0.02). There was a suggestion of a stronger inverse association of total folate with G-->T transversions (OR = 0.41; 95% CI = 0.20-0.87) than G-->A transitions (OR = 0.61; 95% CI = 0.31-1.21), although the CIs for the associations overlap. The results of these analyses suggest that the protective effect of folate in colon cancer observed in published studies may be mediated through folate's effect on Ki-ras mutations.

Cancer Res 1999 Oct 15;59(20):5181-5

Double-blind intervention trial on modulation of ozone effects on pulmonary function by antioxidant supplements

The aim of this study was to investigate whether the acute effects of ozone on lung function could be modulated by antioxidant vitamin supplementation in a placebo-controlled study. Lung function was measured in Dutch bicyclists (n = 38) before and after each training session on a number of occasions (n = 380) during the summer of 1996. The vitamin group (n = 20) received 100 mg of vitamin E and 500 mg of vitamin C daily for 15 weeks. The average ozone concentration during exercise was 77 microg/m3 (range, 14-186 microg/m3). After exclusion of subjects with insufficient compliance from the analysis, a difference in ozone exposure of 100 microg/m3 decreased forced expiratory volume in 1 second (FEV1) 95 ml (95% confidence interval (CI) -265 to -53) in the placebo group and 1 ml (95% CI -94 to 132) in the vitamin group; for forced vital capacity, the change was -125 ml (95% CI -384 to -36) in the placebo group and -42 ml (95% CI -130 to 35) in the vitamin group. The differences in ozone effect on lung function between the groups were statistically significant. The results suggest that supplementation with the antioxidant vitamins C and E confers partial protection against the acute effects of ozone on FEV1 and forced vital capacity in cyclists.

Am J Epidemiol 1999 Feb 15;149(4):306-14

Use of topical ascorbic acid and its effects on photodamaged skin topography

OBJECTIVE: To determine the efficacy of topical ascorbic acid application in treating mild to moderate photodamage of facial skin using an objective, computer-assisted image analysis of skin surface topography and subjective clinical, photographic, and patient self-appraisal questionnaires. DESIGN: A 3-month, randomized, double-blind, vehicle-controlled study. SETTING: Facial plastic surgery private practice. PATIENTS: Nineteen evaluable volunteer sample patients aged between 36 and 72 years with Fitzpatrick skin types I, II, and III who were in good physical and mental health with mild to moderately photodamaged facial skin were considered for analysis. INTERVENTION: Coded, unmarked medications were randomly assigned to the left and right sides of each subject's face, one containing the active agent, topical ascorbic acid (Cellex-C high-potency serum; Cellex-C International, Toronto, Ontario), the other, the vehicle serum (Cellex-C International). Three drops (0.5 mL) of each formulation were applied daily to the randomly assigned hemifaces over the 3-month study period. Treatment assignments were not disclosed to subjects, clinicians, or personnel involved in analyzing skin replicas. MAIN OUTCOME MEASURES: Specific clinical parameters were evaluated and graded on a 0- to 9-point scale (0, none; 1-3, mild; 4-6, moderate; and 7-9, severe). Reference photographs were used to standardize grading criteria. Overall investigator scores were compared with baseline and graded as excellent (much improved), good (improved), fair (slightly improved), no change, or worse. Patient self-appraisal questionnaires rated the degree of improvement (much improved, improved, slightly improved, no change, or worse) and reported adverse effects (burning, stinging, redness, peeling, dryness, discoloration, itching, and rash). Standard photographs were taken at baseline, including anteroposterior and left and right oblique views to facilitate subsequent clinical evaluations, and at the end of therapy for comparison. Optical profilometry analysis was performed on the skin surface replicas of the lateral canthal (crow's feet) region, comparing baseline to end-of-study specimens. Using this computer-based system, the resulting image was digitally analyzed, and numeric values were assigned to reflect surface features. The parameters obtained included Rz, Ra, and shadows. These values provided objective data that document pretreatment and posttreatment texture changes proportional to the degree of wrinkling, roughness, and other surface irregularities. RESULTS: Optical profilometry image analysis demonstrated a statistically significant 73.7% improvement in the Ra and shadows north-south facial axis values with active treatment greater than vehicle control, as well as a trend for improvement in the Rz north-south facial axis parameter, showing a 68.4% greater improvement of active treatment vs vehicle control. Clinical assessment demonstrated significant improvement with active treatment greater than control for fine wrinkling, tactile roughness, coarse rhytids, skin laxity/tone, sallowness/yellowing, and overall features. Patient questionnaire results demonstrated statistically significant improvement overall, active treatment 84.2% greater than control. Photographic assessment demonstrated significant improvement, active treatment 57.9% greater than control. CONCLUSIONS: A 3-month daily regimen of topical ascorbic acid provided objective and subjective improvement in photodamaged facial skin. Skin replica optical profilometry is an objective method for quantification of the skin surface texture changes.

Arch Otolaryngol Head Neck Surg 1999 Oct;125(10):1091-8

Plasma antioxidant defense in actinic keratosis and basal cell carcinoma

BACKGROUND: Reactive oxygen species and lipid peroxides have been implicated in the pathogenesis of a variety of diseases, particularly cancer. There may be an inverse correlation between lipid peroxidation and antioxidant defense mechanisms. The aim of this study was to investigate whether certain plasma antioxidants (ascorbic acid, alpha-tocopherol, total thiol groups, ceruloplasmin, urate, albumin and erythrocyte glutathione) are altered in actinic keratosis (AK) and basal cell carcinoma (BCC). METHODS: Plasma samples and red blood cells (RBC) of 13 patients with AK, 12 with BCC and 16 healthy controls were investigated. RESULTS: Data analysis indicates significant decrease of ascorbic acid (P < 0.001), alpha-tocopherol (P < 0.05 and P < 0.001), total thiol groups (P < 0.001), ceruloplasmin (P < 0.001 and P < 0.05), and RBC glutathione (P < 0.05) values in both AK and BCC groups compared to controls. Comparison of AK and BCC groups evidenced a significant decrease of alpha-tocopherol and RBC glutathione (P < 0.05) in BCC patient. CONCLUSION: Plasma antioxidants are decreased in the AK and BCC, probably due to the long exposure to UV irradiation which is one of the most important factors in the etiology of AK and BCC and alpha-tocopherol and RBC glutathione (P < 0.05) are most altered in BCC. J Eur Acad Dermatol Venereol 1999 Sep;13(2):96-101 Serum ascorbic acid and other correlates of self-reported cataract among older Americans The purpose of this study was to examine the correlates of self-reported cataract among older Americans, and specifically, to determine whether serum ascorbic acid levels are associated with a decreased prevalence of cataract. A national probability survey of Americans, the Second National Health and Nutrition Examination Survey (NHANES II), was conducted between 1976 and 1980. A total of 4001 participants were included between the ages of 60 and 74 years with data on serum ascorbic acid level and other variables of interest. A total of 252 women (12%) and 164 men (9%) reported a history of cataract. Serum ascorbic acid level was inversely associated with prevalence of cataract in multiple logistic regression analyses; each 1 mg/dl increase was independently associated with a 26% decrease in cataract (P = 0.03). Other independent correlates of cataract included increasing age, female sex, smoking, and diabetes mellitus (all P<0.01). We identified four correlates of cataract among older Americans: serum ascorbic acid level, increasing age, smoking, and diabetes mellitus. Ascorbic acid, a water-soluble antioxidant found in high concentrations in the lens, may be of importance for the prevention of cataract among older Americans.

J Clin Epidemiol 1999 Dec;52(12):1207-11

Role of oxidant stress in endothelial dysfunction produced by experimental hyperhomocyst(e)inemia in humans

BACKGROUND: Moderate elevations in plasma homocyst(e)ine concentrations are associated with atherosclerosis and hypertension. We tested the hypothesis that experimental perturbation of homocysteine levels produces resistance and conduit vessel endothelial dysfunction and that this occurs through increased oxidant stress. METHODS AND RESULTS: Oral administration of L-methionine (100 mg/kg) was used to induce moderate hyperhomocyst(e)inemia ( approximately 25 micromol/L) in healthy human subjects. Endothelial function of forearm resistance vessels was assessed by use of forearm vasodilatation to brachial artery administration of the endothelium-dependent dilator acetylcholine. Conduit vessel endothelial function was assessed with flow-mediated dilatation of the brachial artery. Forearm resistance vessel dilatation to acetylcholine was significantly impaired 7 hours after methionine (methionine, 477+/-82%; placebo, 673+/-110%; P=0.016). Methionine did not alter vasodilatation to nitroprusside and verapamil. Flow-mediated dilatation was significantly impaired 8 hours after methionine loading (0.3+/-2.7%) compared with placebo (8. 2+/-1.6%, P=0.01). Oral administration of the antioxidant ascorbic acid (2 g) prevented methionine-induced endothelial dysfunction in both conduit and resistance vessels (P=0.03). CONCLUSIONS: Experimentally increasing plasma homocyst(e)ine concentrations by methionine loading rapidly impairs both conduit and resistance vessel endothelial function in healthy humans. Endothelial dysfunction in conduit and resistance vessels may underlie the reported associations between homocysteine and atherosclerosis and hypertension. Increased oxidant stress appears to play a pathophysiological role in the deleterious endothelial effects of homocysteine.

Circulation 1999 Sep 14;100(11):1161-8

Folic acid inhibits homocysteine-induced proliferation of human arterial smooth muscle cells

PURPOSE: An elevated plasma homocysteine level has been identified as an independent risk factor for atherosclerosis. Whether this represents a marker for vascular disease or a direct effect on the vasculature remains unclear. Because vascular smooth muscle cells (VSMCs) play an integral role in the atherosclerotic process, we studied the effect of homocysteine on human infragenicular VSMC proliferation and the role of folic acid in reversing the homocysteine effect. METHODS: Human infragenicular VSMCs harvested from amputation specimens were studied. Various cell groups were exposed to physiologic (6.25 micromol/L and 12.5 micromol/L) and pathologic (25 micromol/L to 500 micromol/L) concentrations of homocysteine. Similar groups were simultaneously exposed to 20 nmol/L of folic acid. Cell counts and DNA synthesis, as reflected by [methyl-(3)H]-thymidine incorporation, were performed at 6 days and 24 hours, respectively. Additional groups were exposed to various combinations of folic acid (20 nmol/L), vitamin B(6) (145 nmol/L), and vitamin B(12) (0.45 nmol/L) in the presence of homocysteine (25, 50, and 250 micromol/L). RESULTS: Homocysteine resulted in a dose-dependent increase in DNA synthesis and cell proliferation. Cell counts increased significantly at homocysteine concentrations ranging from 25 micromol/L to 500 micromol/L (P <.05), with a maximal increase of 98% at 500 micromol/L of homocysteine. The addition of 20 nmol/L folic acid resulted in significant inhibition of cell proliferation at all homocysteine concentrations studied (P <.001). Maximal inhibition of 70% occurred in the cells exposed to 50 micromol/L of homocysteine. The increases in [methyl-(3)H]-thymidine incorporation ranged from 36% at 6 micromol/L homocysteine to a maximum of 247% at 500 micromol/L homocysteine. All increases were statistically significant (P <.05). The addition of 20 nmol/L folic acid resulted in significant inhibition of DNA synthesis (P <.002). Vitamins B(6) and B(12) did not demonstrate significant antiproliferative properties. CONCLUSION: A possible role of homocysteine in the formation of atherosclerotic lesions is through a direct proliferative effect on VSMCs in a dose-dependent fashion. Folic acid intake at levels available in dietary supplements may prove protective in hyperhomocysteinemia-induced atherosclerosis. Vitamins B(6) and B(12) alone do not appear to exhibit a substantial inhibitory effect in the setting of elevated homocysteine levels.