Low molecular weight antioxidants and their role in skin ageing.
There is increasing evidence that reactive oxygen species play a pivotal role in the process of ageing. The skin, as the outermost barrier of the body, is exposed to various exogenous sources of oxidative stress, in particular UV-irradiation. These are believed to be responsible for the extrinsic type of skin ageing, termed photo-ageing. It therefore seems reasonable to try to increase levels of protective low molecular weight antioxidants through a diet rich in fruits and vegetables or by direct topical application. Indeed, various in vitro and animal studies have proved that low molecular weight antioxidants, especially vitamins C and E, ascorbate and tocopherol, as well as lipoic acid, exert protective effects against oxidative stress. However, controlled long-term studies on the efficacy of low molecular weight antioxidants in the prevention or treatment of skin ageing in humans are still lacking.
Clin Exp Dermatol. 2001 Oct;26(7):578-82
Photoaging is associated with protein oxidation in human skin in vivo.
There is increasing evidence for the generation of reactive oxygen species in skin upon ultraviolet exposure, but little is known about their pathophysiologic relevance in human skin in vivo. We hypothesized that chronic and acute photodamage is mediated by depleted antioxidant enzyme expression and increased oxidative protein modifications. Biopsies from patients with histologically confirmed solar elastosis, from non-ultraviolet-exposed sites of age-matched controls, and from young subjects were analyzed. To evaluate the influence of acute ultraviolet exposures, buttock skin of 12 healthy subjects was irradiated repetitively on 10 d with a solar simulator and compared intraindividually to non-ultraviolet-treated contralateral sites. The antioxidant enzymes catalase, copper-zinc superoxide dismutase, and manganese superoxide dismutase were investigated by immunohistochemistry. Protein carbonyls were analyzed by immunohistochemical and immunoblotting techniques in human skin and in cell models. Whereas overall expression of antioxidant enzymes was very high in the epidermis, low baseline levels were found in the dermis. In photoaged skin, a significant depletion of antioxidant enzyme expression was observed within the stratum corneum and in the epidermis. Importantly, an accumulation of oxidatively modified proteins was found specifically within the upper dermis of photoaged skin. Upon acute ultraviolet exposure of healthy subjects, depleted catalase expression and increased protein oxidation were detected. Exposures of keratinocytes and fibroblasts to ultraviolet B, ultraviolet A, and H2O2 led to dose-dependent protein oxidation and thus confirmed in vivo results. In conclusion, the correlation between photodamage and protein oxidation was demonstrated for the first time, which hence may be a relevant pathophysiologic factor in photoaging.
J Invest Dermatol. 2002 Apr;118(4):618-25
Skin photodamage and lifetime photoprotection.
Ultraviolet (UV) radiation is a very small part of the electromagnetic radiation spectrum, released and transported from the source in the form of photons. Disposal of these photons within the skin causes cutaneous photodamage, which leads to clinical, histologic, and biochemical changes. Aging is a complex process characterized by cellular attrition, decreased cellular reserve capacity, and compromised ability to perform normal cellular function. Intrinsic aging, which steadily develops with time, is linked to chronologic age; it is the result of a genetic program. Photoaging, on the other hand, develops as a consequence of UV radiation-induced degenerative changes in the skin. Intrinsic aging is a universal, inevitable process, whereas photoaging is neither universal nor inevitable and can be prevented. UV radiation can also suppress the immune system in both local and systemic way and lead to simultaneous and sequential biochemical events that ultimately cause photocarcinogenesis. Therefore, everyday use of products that protect against UV radiation is necessary to prevent acute and long-term photodamage (clinical and cellular changes) leading to photoaging, photoimmunosuppression, and photocarcinogenesis.
Acta Dermatovenerol Croat. 2003;11(1):32-40
Topical applications of caffeine or (-)-epigallocatechin gallate (EGCG) inhibit carcinogenesis and selectively increase apoptosis in UVB-induced skin tumors in mice.
SKH-1 hairless mice were irradiated with ultraviolet B (UVB) twice weekly for 20 weeks. These tumor-free mice, which had a high risk of developing skin tumors during the next several months, were then treated topically with caffeine (6.2 micromol) or (-)-epigallocatechin gallate (EGCG; 6.5 micromol) once a day 5 days a week for 18 weeks in the absence of further treatment with UVB. Topical applications of caffeine to these mice decreased the number of nonmalignant and malignant skin tumors per mouse by 44% and 72%, respectively. Topical applications of EGCG decreased the number of nonmalignant and malignant tumors per mouse by 55% and 66%, respectively. Immunohistochemical analysis showed that topical applications of caffeine or EGCG increased apoptosis as measured by the number of caspase 3-positive cells in nonmalignant skin tumors by 87% or 72%, respectively, and in squamous cell carcinomas by 92% or 56%, respectively, but there was no effect on apoptosis in nontumor areas of the epidermis. Topical applications of caffeine or EGCG had a small inhibitory effect on proliferation in nonmalignant tumors as measured by BrdUrd labeling (16-22%), and there was also a similar, but nonsignificant, inhibitory effect on proliferation in malignant tumors. The results suggest a need for further studies to determine whether topical applications of caffeine or EGCG can inhibit sunlight-induced skin cancer in humans.
Proc Natl Acad Sci U S A. 2002 Sep 17;99(19):12455-60. Epub 2002 Aug 30
Green tea polyphenols: DNA photodamage and photoimmunology.
Green tea is a popular beverage consumed worldwide. The epicatechin derivatives, which are commonly called 'polyphenols', are the active ingredients in green tea and possess antioxidant, anti-inflammatory and anti-carcinogenic properties. Studies conducted by our group on human skin have demonstrated that green tea polyphenols (GTP) prevent ultraviolet (UV)-B-induced cyclobutane pyrimidine dimers (CPD), which are considered to be mediators of UVB-induced immune suppression and skin cancer induction. GTP treated human skin prevented penetration of UV radiation, which was demonstrated by the absence of immunostaining for CPD in the reticular dermis. The topical application of GTP or its most potent chemopreventive constituent (-)-epigallocatechin-3-gallate (EGCG) prior to exposure to UVB protects against UVB-induced local as well as systemic immune suppression in laboratory animals. Additionally, studies have shown that EGCG treatment of mouse skin inhibits UVB-induced infiltration of CD11b+ cells. CD11b is a cell surface marker for activated macrophages and neutrophils, which are associated with induction of UVB-induced suppression of contact hypersensitivity responses. EGCG treatment also results in reduction of the UVB-induced immunoregulatory cytokine interleukin (IL)-10 in skin as well as in draining lymph nodes, and an elevated amount of IL-12 in draining lymph nodes. These in vivo observations suggest that GTPs are photoprotective, and can be used as pharmacological agents for the prevention of solar UVB light-induced skin disorders associated with immune suppression and DNA damage.
J Photochem Photobiol B. 2001 Dec 31;65(2-3):109-14
Preformulation study of epigallocatechin gallate, a promising antioxidant for topical skin cancer prevention.
Epigallocatechin gallate (EGCG) is a potent polyphenolic antioxidant extracted from green tea. Due to its antimutagenic and antitumor activities, it is a promising candidate for use in topical formulations for skin cancer prevention. The overall goal of this study was therefore to determine the influence of several factors on the stability of EGCG in solution to obtain information that would facilitate the subsequent development of topical formulations. Our first objective was to determine the influence of pH, temperature, and ionic strength on the aqueous stability of EGCG. A second objective was to determine the stability of EGCG in various solvents in the presence and absence of different antioxidants. A simple and rapid stability indicating high-performance liquid chromatography assay for EGCG was developed. Stability studies were performed in 0.05 M aqueous buffers at pH 3, 5, 7, and 9 at 4, 25, and 50 degrees C. The effect of ionic strength on EGCG stability was evaluated in 0.05 M acetate buffer, pH 5, adjusted to the desired ionic strength with sodium chloride. An accelerated stability study of EGCG was performed at 50 degrees C in the organic solvents glycerin and Transcutol P in the presence of antioxidants. The degradation of EGCG increased rapidly as temperature and solution pH were increased. Ionic strength increases also caused an accelerated degradation. The solution stability of EGCG was prolonged in glycerin and Transcutol P compared with an aqueous environment. The addition of 0.1% concentrations of several antioxidants in combination with 0.025% EDTA caused variable effects on EGCG stability. Butylated hydroxytoluene in glycerin produced the greatest stability improvement for EGCG. The t(90) (time for 10% degradation to occur) was 76.1 days at 50 degrees C. It can be concluded that glycerin-based vehicles are suitable for stabilizing EGCG.
J Pharm Sci. 2002 Jan;91(1):111-6