A clinical trial and molecular study of photoadaptation in vitiligo.

BACKGROUND: Photoadaptation to ultraviolet (UV) B phototherapy is due to both pigmentary and nonpigmentary influences. OBJECTIVES: To measure photoadaptation in vitiliginous skin and to compare it with normal pigmented skin. METHODS: Seventeen patients with Fitzpatrick skin phototypes III-VI with vitiligo received six to nine UVB treatments, two to three times weekly. Minimal erythema dose (MED) testing was done at baseline and after all treatments; the percentage change in MED was analysed as a measure of photoadaptation. The percentage decrease in cyclobutane pyrimidine dimers (CPDs) over 24 h after a single exposure of 1 MED was analysed on vitiliginous and normal skin. RESULTS: The mean +/- SD percentage change in MED from before to after treatments was: treated vitiliginous skin 28.5 +/- 39.9% (P = 0.015), treated normal skin 35.9 +/- 49.9% (P = 0.015), untreated vitiliginous skin 11.9 +/- 22.6% (P =0.070), untreated normal skin 25.1 +/- 41.3% (P = 0.041). Of these patients, two-thirds had a positive percentage change in MED (photoadaptation). The mean amount of CPDs induced per megabase of DNA immediately after exposure was significantly higher in vitiliginous skin. The mean +/- SD percentage decrease in CPDs (rate of repair) in 24 h was 35.7 +/- 26.8% in vitiliginous skin (P = 0.027) and 46.2 +/- 19.5% in normally pigmented skin (P = 0.001); no difference was noted in the repair in vitiliginous skin compared with normal skin (P = 0.4). CONCLUSIONS: Photoadaptation in vitiliginous and normal skin was observed in two-thirds of patients. Vitiliginous skin had significantly more CPDs following UVB exposure; the rate of repair of UVB-induced DNA damage was equivalent to that in normal skin.

Immune regulation by polysaccharides: implications for skin cancer.

UV radiation causes sunburn, premature aging of the skin and is the major environmental carcinogen for squamous cell and basal cell skin cancer in humans. Besides causing mutations in DNA, UV radiation contributes to carcinogenesis by suppressing immune responses to highly antigenic, newly arising neoplasms. Strategies aimed at preventing UV-induced immune suppression, the mechanism of action of the agents used, and the significance of immune protection for prevention of skin cancer are reviewed. This review focuses on the use of plant polysaccharides to prevent immune damage triggered by UV radiation, an approach that goes beyond absorption of UV radiation by sunscreens as a means of reducing tissue damage. The efficacy and mechanism of action of these agents in preserving T cell-mediated immunity to model antigens in human beings and in laboratory animals are discussed.

Plants, polysaccharides, and the treatment and prevention of neoplasia.

Plants and Fungi have traditionally been the single largest source of lead compounds for the development of therapeutics by the pharmaceutical industry. Currently mushroom and plant polysaccharides brought to attention by Complementary and Alternative medicine, are undergoing scientific analysis and development to prevent and treat cancer, Two classes of saccharides are under investigation-beta glucan polysaccharides as biological response modifiers for the adjuvant treatment of cancer and "Oligosaccharin"-related oligosaccharides for the prevention of sun-induced skin cancer. Beta glucans already in human trials in the Far East will require mechanistic pharmacologic studies and definition of stucture function relationships before they are ready for clinical trials in the West. Other beta glucans that prime natural killer cells for antibody dependent cell-mediated cytotoxicity are approaching clinical trials. Oligosaccharides that downregulate production of immunosuppressive cytokines by ultraviolet radiation injured keratinocytes are promising agents for the prevention of environmental skin cancer.

Inhibition of UV-induced immune suppression and interleukin-10 production by plant oligosaccharides and polysaccharides.

Application of Aloe barbadensis poly/oligosaccharides to UV-irradiated skin prevents photosuppression of delayed-type hypersensitivity (DTH) responses in mice. We tested the hypothesis that these carbohydrates belong to a family of biologically active, plant-derived polysaccharides that can regulate responses to injury in animal tissues. C3H mice were exposed to 5 kJ/m2 UVB from unfiltered FS40 sunlamps and treated with between 1 pg and 10 micrograms tamarind xyloglucans or control polysaccharides methylcellulose or dextran in saline. The mice were sensitized 3 days later with Candida albicans. Tamarind xyloglucans and purified Aloe poly/oligosaccharides prevented suppression of DTH responses in vivo and reduced the amount of interleukin (IL)-10 observed in UV-irradiated murine epidermis. Tamarind xyloglucans were immunoprotective at low picogram doses. In contrast, the control polysaccharides methylcellulose and dextran had no effect on immune suppression or cutaneous IL-10 at any dose. Tamarind xyloglucans and Aloe poly/oligosaccharides also prevented suppression of immune responses to alloantigen in mice exposed to 30 kJ/m2 UVB radiation. To assess the effect of the carbohydrates on keratinocytes, murine Pam212 cells were exposed to 300 J/m2 UVB radiation and treated for 1 h with tamarind xyloglucans or Aloe poly/oligosaccharides. Treatment of keratinocytes with immunoprotective carbohydrates reduced IL-10 production by approximately 50% compared with the cells treated with UV radiation alone and completely blocked suppressive activity of the culture supernatants in vivo. The tamarind xyloglucans also blocked UV-activated phosphorylation of SAPK/JNK protein but had no effect on p38 phosphorylation. These results indicate that animals, like plants, may use carbohydrates to regulate responses to environmental stimuli.

Aloe barbadensis extracts reduce the production of interleukin-10 after exposure to ultraviolet radiation.

Cutaneous exposure to ultraviolet radiation suppresses the induction of T cell mediated responses such as contact and delayed type hypersensitivity (DTH) by altering the function of immune cells in the skin and causing the release of immunoregulatory cytokines. Extracts of crude Aloe barbadensis gel prevent this photosuppression. Because the regulation of contact hypersensitivity and DTH responses differ, we investigated whether protection was afforded by a single or multiple agents in Aloe and the mechanism by which this material prevents suppression of DTH immunity. The ability of Aloe gel to prevent suppression of contact hypersensitivity responses to hapten decayed rapidly after manufacture. In contrast, agents that protected against systemic suppression of DTH responses to Candida albicans were stable over time. Oligosaccharides prepared from purified Aloe polysaccharide prevented suppression of DTH responses in vivo and reduced the amount of IL-10 observed in ultraviolet irradiated murine epidermis. To assess the effect of Aloe extracts on keratinocytes, Pam 212 cells were exposed in vitro to ultraviolet radiation and treated for 1 h with Aloe oligosaccharides. Culture supernatants were collected 24 h later and injected into mice. Supernatants from ultraviolet irradiated keratinocytes suppressed the induction of DTH responses, whereas Aloe oligosaccharide treatment reduced IL-10 and blocked the suppressive activity of the supernatants. These results indicate that Aloe contains multiple immunoprotective factors and that Aloe oligosaccharides may prevent ultraviolet induced suppression of DTH by reducing keratinocyte derived immunosuppressive cytokines.

Prevention of ultraviolet radiation-induced suppression of contact and delayed hypersensitivity by Aloe barbadensis gel extract.

We investigated the ability of Aloe barbadensis gel extract to prevent suppression of contact hypersensitivity (CHS) and delayed-type hypersensitivity (DTH) responses in mice by ultraviolet (UV) irradiation. Local immune suppression was induced in C3H mice by exposure to four daily doses of 400 J/m2 UV-B (280-320 nm) radiation from FS40 sunlamps, followed by sensitization with 0.5% fluorescein isothiocyanate (FITC) through the irradiated skin. Topical application of 0.167-1.67% Aloe gel after each irradiation significantly reduced this suppression. Aloe treatment partially preserved the number and morphology of Langerhans and Thy-1+ dendritic epidermal cells in skin, compared to those in the skin of mice given only UVR or UVR plus the vehicle. Experiments using a single (2 kJ/m2) dose of UVR followed by Aloe treatment showed that the effect of Aloe was not due to screening of the UVR. Systemic suppression of DTH to Candida albicans or CHS to FITC was induced in C3H mice exposed to 5 or 10 kJ/m2 UV-B radiation, respectively, on shaved dorsal skin and sensitized 3 d later with a subcutaneous injection of formalin-fixed Candida or FITC painted on unirradiated, ventral skin. Treatment of the UV-irradiated skin with Aloe immediately after irradiation prevented suppression of both DTH to Candida and CHS to FITC. Aloe treatment did not prevent the formation of cyclobutyl pyrimidine dimers in the DNA of UV-irradiated skin or accelerate the repair of these lesions. These studies demonstrate that topical application of Aloe barbadensis gel extract to the skin of UV-irradiated mice ameliorates UV-induced immune suppression by a mechanism that does not involve DNA damage or repair.