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Sun protection

June 2006

Detection of reactive oxygen species in the skin of live mice and rats exposed to UVA light: a research review on chemiluminescence and trials for UVA protection.

The harmful effects of ultraviolet (UV) exposure on the skin are associated with the generation of reactive oxygen species (ROS) such as superoxide anion radical ( O(2)(-)), hydrogen peroxide (H(2)O(2)), hydroxyl radical ( OH), and singlet oxygen ((1)O(2)) as well as with lipid peroxides and their radicals (LOOH and LOO ). To give direct proof that such ROS are generated in UV-exposed skin, we proposed the in vivo detection and imaging method in which both a sensitive and specific chemiluminescence (CL) probe, such as CLA, and an ultralow-light imaging apparatus with a CCD camera were used. With this method we found that O(2)(-) is formed intrinsically and that (1)O(2) and O(2)(-) are generated in the UVA-exposed skin of mice. In addition, we indicated that antioxidative ability against ROS in the skin of hairless rats decreased as age increased. Using these findings, we demonstrated the protective abilities of sodium ascorbate, caffeic acid, essential aroma oils, and zinc(ii) ion and its complexes, which we administered to mice both topically and orally. We present a review for the current state of our research proposing the sensitive CL method as a useful in vivo tool in photobiological research for the detection of oxidative stress as well as for the evaluation of antioxidative agents to the skin.

Photochem Photobiol Sci. 2005 Sep;4(9):715-20

Ultraviolet radiation exposure and risk of malignant lymphomas.

BACKGROUND: The incidence of malignant lymphomas has been increasing rapidly, but the causes of these malignancies remain poorly understood. One hypothesis holds that exposure to ultraviolet (UV) radiation increases lymphoma risk. We tested this hypothesis in a population-based case-control study in Denmark and Sweden. METHODS: A total of 3,740 patients diagnosed between October 1, 1999, and August 30, 2002, with incident malignant lymphomas, including non-Hodgkin lymphoma, chronic lymphocytic leukemia, and Hodgkin lymphoma, and 3,187 population controls provided detailed information on history of UV exposure and skin cancer and information on other possible risk factors for lymphomas. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated by logistic regression. Statistical tests were two-sided. RESULTS: Multivariable-adjusted analyses revealed consistent, statistically significant negative associations between various measures of UV light exposure and risk of non-Hodgkin lymphoma. A high frequency of sun bathing and sunburns at age 20 years and 5-10 years before the interview and sun vacations abroad were associated with 30%-40% reduced risks of non-Hodgkin lymphoma (e.g., for sunbathing four times a week or more at age 20 versus never sunbathing, OR = 0.7, 95% CI = 0.6 to 0.9; for two or more sunburns a year at age 20 versus no sunburns, OR = 0.6, 95% CI = 0.5 to 0.8). These inverse associations increased in strength with increasing levels of exposure (all P(trend)< or =.01). Similar, albeit weaker, associations were observed for Hodgkin lymphoma. There were no clear differences among non-Hodgkin lymphoma subtypes, although associations were stronger for B-cell than for T-cell lymphomas. A history of skin cancer was associated with a doubling in risks of both non-Hodgkin and Hodgkin lymphoma. CONCLUSIONS: A history of high UV exposure was associated with reduced risk of non-Hodgkin lymphoma. The positive association between skin cancer and malignant lymphomas is, therefore, unlikely to be mediated by UV exposure.

J Natl Cancer Inst. 2005 Feb 2;97(3):199-209

Sun exposure and mortality from melanoma.

BACKGROUND: Melanoma incidence and survival are positively associated, both geographically and temporally. Solar elastosis, a histologic indicator of cutaneous sun damage, has also been positively associated with melanoma survival. Although these observations raise the possibility that sun exposure increases melanoma survival, they could be explained by an association between incidence and early detection of melanoma. We therefore evaluated the association between measures of skin screening and death from cutaneous melanoma. METHODS: Case subjects (n = 528) from a population-based study of cutaneous melanoma were followed for an average of more than 5 years. Data, including measures of intermittent sun exposure, perceived awareness of the skin, skin self-screening, and physician screening, were collected during in-person interviews and review of histopathology and histologic parameters (i.e., solar elastosis, Breslow thickness, and mitoses) for all of the lesions. Competing risk models were used to compute risk of death (hazard ratios [HRs], with 95% confidence intervals [CIs]) from melanoma. All statistical tests were two-sided. RESULTS: Sunburn, high intermittent sun exposure, skin awareness histories, and solar elastosis were statistically significantly inversely associated with death from melanoma. Melanoma thickness, mitoses, ulceration, and anatomic location on the head and neck were statistically significantly positively associated with melanoma death. In a multivariable competing risk analysis, skin awareness (with versus without, HR = 0.5, 95% CI = 0.3 to 0.9, P = .022) and solar elastosis (present versus absent, HR = 0.4, 95% CI = 0.2 to 0.8, P = .009) were strongly and independently associated with melanoma death after adjusting for Breslow thickness, mitotic index, and head and neck location, which were also independently associated with death. CONCLUSIONS: Sun exposure is associated with increased survival from melanoma.

J Natl Cancer Inst. 2005 Feb 2;97(3):195-9

The green tea polyphenol (-)-epigallocatechin gallate and green tea can protect human cellular DNA from ultraviolet and visible radiation-induced damage.

BACKGROUND: Antioxidant compounds in green tea may be able to protect against skin carcinogenesis and it is of interest to investigate the mechanisms involved. A study was therefore conducted to determine whether the isolated green tea polyphenol (-)-epigallocatechin gallate (EGCG) could prevent ultraviolet radiation (UVR)-induced DNA damage in cultured human cells. This work was then extended to investigate whether drinking green tea could afford any UVR protection to human peripheral blood cells collected after tea ingestion. METHODS: The alkaline comet assay was used to compare the DNA damage induced by UVR in cultured human cells with and without the presence of EGCG. The same assay technique was then employed to assess UVR-induced DNA damage in peripheral leucocytes isolated from 10 adult human volunteers before and after drinking 540 ml of green tea. RESULTS: Initial trials found that EGCG afforded concentration-dependent photoprotection to cultured human cells with a maximal activity at a culture concentration of 250 microM. The cells types tested (lung fibroblasts, skin fibroblasts and epidermal keratinocytes) demonstrated varying susceptibility to the UVR insult provided. The in vivo trials of green tea also demonstrated a photoprotective effect, with samples of peripheral blood cells taken after green tea consumption showing lower levels of DNA damage than those taken prior to ingestion when exposed to 12 min ultraviolet A (UVA) radiation. CONCLUSION: The studies showed that green tea and/or some constituents can offer some protection against UV-induced DNA damage in human cell cultures and also in human peripheral blood samples taken post-tea ingestion.

Photodermatol Photoimmunol Photomed. 2005 Feb;21(1):15-22

Green tea polyphenols prevent ultraviolet light-induced oxidative damage and matrix metalloproteinases expression in mouse skin.

Chronic exposure of solar ultraviolet (UV) light to human skin results in photoaging. UV-induced oxidative damage and induction of matrix metalloproteinases (MMP) have been implicated in this process. Because polyphenols from green tea (GTP) prevent other cutaneous adverse effects of UV radiation we hypothesized that UV irradiation-induced oxidative damage and induction of MMP might be prevented in vivo in mouse skin by oral administration of GTP. GTP was administered in drinking water (0.2%, wt/vol) to SKH-1 hairless mice, which were then exposed to multiple doses of UVB (90 mJ per cm2, for 2 mo on alternate days) following in vivo photoaging animal protocol. Treatment of GTP resulted in inhibition of UVB-induced protein oxidation in vivo in mouse skin, a hallmark of photoaging, when analyzed biochemically, by immunoblotting, and immunohistochemistry. GTP treatment also inhibited UVB-induced protein oxidation in vitro in human skin fibroblast HS68 cells, which supports in vivo observations. Moreover, oral administration of GTP also resulted in inhibition of UVB-induced expression of matrix degrading MMP, such as MMP-2 (67%), MMP-3 (63%), MMP-7 (62%), and MMP-9 (60%) in hairless mouse skin. These data suggest that GTP as a dietary supplement could be useful to attenuate solar UVB light-induced premature skin aging.

J Invest Dermatol. 2004 Jun;122(6):1480-7

Ursolic acid induces apoptosis through mitochondrial intrinsic pathway and caspase-3 activation in M4Beu melanoma cells.

Over the coming years, skin cancer could become a significant public health problem. Previous results indicate that ursolic acid (UA), a pentacyclic triterpene acid, has pleiotropic biologic activities such as antiinflammatory and antiproliferative activities on cancer cells. As UA represents a promising chemical entity for the protection of human skin, in agreement with tests done by the cosmetic industry, we investigated its effects on the M4Beu human melanoma cell line. In this report, we demonstrated for the first time that UA had a significant antiproliferative effect on M4Beu, associated with the induction of an apoptotic process, characterized by caspase-3 activation, the downstream central effector of apoptosis. We demonstrated that UA-induced apoptosis was dependent on the mitochondrial intrinsic pathway, as shown by transmembrane potential collapse (DeltaPsim) and by alteration of the Bax-Bcl-2 balance, with a concomitant increase in Bax expression and decrease in Bcl-2 expression. We also showed that UA-induced DeltaPsim was associated with apoptosis-inducing factor leakage from mitochondria. Taken together, our results suggest that UA-induced apoptosis on M4Beu cells is accomplished via triggering of mitochondrial pathway. In conclusion, UA could be an encouraging compound in the treatment or prevention of skin cancer and may represent a new promising anticancer agent in the treatment of melanoma.

Int J Cancer. 2005 Mar 10;114(1):1-11

Mechanisms and preclinical efficacy of silibinin in preventing skin cancer.

Eukaryotic cellular machineries including the genome face continuous challenge from environmental deleterious agents, as well as from the by products of their own metabolism. Our skin is the most important barrier. It protects us from xenobiotic and genotoxic agents including ultraviolet (UV) solar radiation and potential carcinogens, which are notorious for causing skin cancer. There is a rise in non-melanoma skin cancer (NMSC), which is diagnosed in more than a million people every year in the United States alone, and is also prevalent in the other Western countries. In addition to sunscreens, chemoprevention of skin cancer by natural non-toxic compounds is suggested as an effective strategy to prevent the incidence of skin cancer. Our extensive animal studies on silibinin, a non-toxic bioactive component in milk thistle, suggest that it has a strong potential to prevent skin cancer incidence, promotion and progression in response to chemical carcinogens and tumour promoters as well as UV radiation. Our data suggest that silibinin has multiple targets in the cell, and can be protective against the harmful effects of cytotoxic agents such as reactive oxygen species and inflammation. Further, silibinin modulates mitogenic and survival signalling, p53, Cip1/p21 and other cell cycle regulatory molecules to prevent UVB-induced skin carcinogenesis. Our ongoing studies also suggest the positive effect of silibinin on the repair of UVB-induced DNA damage in mouse skin. Overall, the protective efficacy of silibinin against skin cancer is supported by sound mechanistic rationale in animal and cell culture studies, and suggests its potential use for humans.

Eur J Cancer. 2005 Sep;41(13):1969-79

A history of the therapeutic use of liquorice in Europe.

Liquorice root has been used in Europe since prehistoric times, and is well documented in written form starting with the ancient Greeks. In this review we compare the independent development of medical uses of this botanical drug in several ancient cultures, attempting to show the rationality of specific indications across different ethnic groups with different cultural backgrounds. Identical specific indications in different cultures highlight universally reproducible therapeutic effects that are beyond those of a mere placebo. In the first part of the review, historical sources dealing with liquorice (Scythian, Greek, Roman, and from the Middle Ages in Germany, Italy, Spain, England) have been considered. In the second part, the historical records of diseases treated with liquorice have been presented. Finally, a comparison between traditional use in and outside Europe, with the most important recent scientific studies concerning its use, is presented.

J Ethnopharmacol. 2005 Jul 14;99(3):317-24

Effects of glycyrrhizin on UVB-irradiated melanoma cells.

It is known that liquorice root is rich in compounds which exert several pharmacological actions. In the present study, we evaluated the effect of glycyrrhizin (the main constituent of liquorice root) and of its metabolite aglycone, 18beta-glycyrrhetinic acid, on UVB-irradiated human melanoma cells: SKMEL-2 from metastatic tissue and SKMEL-28 from primary malignant melanoma. Tests performed (Trypan blue exclusion test, MTT and Western blot) showed that glycyrrhizin is not toxic for both types of cells. In SKMEL-28 cells, Bcl-2 expression was low after UVB irradiation, but it was increased when treated with glycyrrhizin. On the contrary, in the SKMEL-2 cell culture, Bcl-2 expression was not modified by the substances under study. The results show that glycyrrhizin treatment might offer protection from the damage induced in humans by UVB radiation, while it seems to be ineffective on metastatic cells. Further studies must be performed to understand the mechanism of the protective effect.

In Vivo. 2005 Jan-Feb;19(1):319-22

Comparison of antioxidant activity of extract from roots of licorice (Glycyrrhiza glabra L.) to commercial antioxidants in 2% hydroquinone cream.

Powdered dry roots of licorice (Glycyrrhiza glabra L.) were extracted with methanol. Licorice extract was tested for antioxidative activity in comparison with antioxidants (sodium metabisulfite and BHT) at 0.1%, 0.5%, 1.0%, and 2.0% w/w in 2% w/w hydroquinone cream. The systems were incubated in a dark room at 25 degrees +/- 0.5 degrees C and 45 degrees +/- 0.5 degrees C for three months. The physical stability and the percentages of hydroquinone remaining after two weeks and one, two, and three months were determined by UV spectrophotometer at 294 nm according to official standard procedures. The experiment revealed that oxidation degradation of hydroquinone was accelerated by heat even with the existence of antioxidants. The higher percentages of remaining hydroquinone were observed for higher antioxidant concentration but showed lower physical stability in the formulation in the presence of commercial antioxidants, especially in the cases of 1.0% and 2.0% BHT. In the third month, at 25 degrees +/- 0.5 degrees C and 45 degrees +/- 0.5 degrees C, the extract demonstrated more antioxidant activity from two other commercial antioxidants at all concentrations, with about 43-53% and 34-46%, respectively, more hydroquinone remaining than in the control system (p<0.001). In the third month, the preparation containing 0.1%, 0.5%, 1.0%, and 2.0% extract gave good physical formulation stability with about 72%, 76%, 78%, and 81 % hydroquinone remaining at 25 degrees +/- 0.5 degrees C and 51%, 55%, 60%, and 63% hydroquinone remaining at 45 degrees +/- 0.5 degrees C, respectively. This suggested the possibility of using a licorice extract at 0.5% and 1.0% as an effective natural antioxidant for substances that are oxidation-susceptible.

J Cosmet Sci. 2003 Nov-Dec;54(6):551-8