An EPR method for estimating activity of antioxidants in mouse skin using an anthralin-derived radical model.

Inhibitory effects of intravenously or orally administered antioxidants on the anthralin-derived radical generated in skin (mainly in the epidermis) of living mice by ultraviolet-A (UVA) irradiation were estimated. Anthralin was applied to the dorsal skin of living mice and the mice were then exposed to UVA. The EPR signal intensity in skin tissue strips obtained from mice after anthralin-UVA treatment was measured by an X-band EPR spectrometer. Several common antioxidants such as ascorbate, glutathione and Trolox (a vitamin E analogue) intravenously administered to mice reduced anthralin-derived radical generation. Trolox showed the most prolonged and powerful effect. Intravenous injection of a clinically used cerebral neuroprotective drug, Edarabone (Radicut), also showed depletion for the anthralin-derived radical. Oral administration of a commercialized nutritional supplement (a cocktail of 17 herbals and vitamins) also attenuated the anthralin-derived radical. The anthralin-UVA treatment model for antioxidant activity in the epidermis is a potentially feasible method to estimate activity of antioxidants in the body.

Low-dose dithranol treatment and tape stripping induce tolerance to dithranol in a mouse ear oedema model.

BACKGROUND: It is well known from clinical practice that repeated treatment with dithranol leads to the development of tolerance. OBJECTIVES: To investigate the characteristics and mechanism of such dithranol tolerance. METHODS: The mouse ear was pretreated with a low dose of dithranol or croton oil or, in previously sensitized animals, with dinitrofluorobenzene (DNFB). Twenty-four hours later irritant dermatitis was elicited by painting the mouse ear with a high dose of dithranol, croton oil or DNFB, and the dermatitis was characterized by measurement of ear thickness. RESULTS: Low-dose dithranol significantly suppressed dithranol-induced oedema, whereas it had no effect on croton oil- or DNFB-induced dermatitis, suggesting that dithranol-induced tolerance is specific. Tolerance to dithranol could not be induced by pretreatment of the mouse ear with a low dose of croton oil or DNFB. Mild tape stripping of the mouse ear also inhibited the inflammatory effect of dithranol applied 24 h later. Superoxide dismutase treatment abolished the tolerance-inducing effect of low-dose dithranol or stripping. CONCLUSIONS: These results suggest that superoxide anion radicals are involved not only in the inflammatory effect of dithranol, but also in the induction of tolerance.

A 6-month dermal toxicity test with dithranol and butantrone in miniature swine.

Continuous topical administration of dithranol and butantrone for 6 months caused different irritation profiles in miniature swine. In paraffin wax sticks in white petrolatum, butantrone gave rise to much less initial irritation than dithranol, but after 2-3 weeks the situation had equalized. In gel formulations, butantrone was initially more irritant than dithranol. The vehicles themselves induced significant irritation. Signs of skin hyperplasia (parakeratosis and acanthosis) and inflammation were frequent histopathological findings at the end of the study, but no malignant changes were found. Dithranol and butantrone did not produce any chemical, hematological or serious histological abnormalities during the treatment, suggesting a lack of systemic toxicity. No evidence of systemic absorption was found. This long-term study did not predict delayed irritation of butantrone observed in about 1/3 of the psoriatic patients after treatment for 1-2 months.

Irritant potential of dithranol.

The minimal irritation dose (MID) for dithranol in 5% salicylic acid vaseline was determined by open patch testing. From the MID, the irritation dose 50 (ID50) was evaluated. It was 0.057% in 100 controls and 0.046% in 100 psoriatic patients, which is not statistically different due to the great differences between individuals. 20 other patients claimed a dithranol hyperreactivity in their history. Only 13 of them, however, showed a decrease in the MID, which was between 0.01 and 0.02% (means = 0.014%), i.e. outside the confidence interval found in the 100 psoriatic patients. 8 of these 13 reacted with blister formation after exposure to 0.1-0.16% dithranol. An allergic contact dermatitis was excluded as the cause of the hyperreactivity. The tolerance to increasing dithranol concentrations after beginning with the MID up to clearance of the lesions, as well as the predominance of granulocytes as compared to lymphocytes in blisters due to dithranol testing, suggest an irritant inflammatory mechanism. In such hyperreactive cases therapy should be started with the MID established in the open patch test.