Role of antioxidants in the survival of normal and vitiliginous avian melanocytes

Mutant feather melanocytes from Barred Plymouth Rock (BPR) and White Leghor n (WL) chickens are currently being used as avian models of vitiligo. Feath er melanocytes in BPR and WL chickens die prematurely in vivo due to low (5 0-66%) antioxidant,glutathione and superoxide dismutase levels when compare d to the wild type Jungle Fowl (JF) melanocytes. Excess superoxide anions, generated by xanthine:xanthine oxidase (X:XO), caused a 15-20% increase in mortality after 1 and 2 hrs. in all three genotypes of in vitro melanocytes as compared to control values that received no X:XO. Overall, the JF wild type melanocytes had the lowest mortality rate, WL melanocytes had the high est mortality rate and the BPR melanocytes had an intermediate mortality ra te. Superoxide anion and hydroxyl radical production in the WL feather were double the production in the JF wild type feather. The production of react ive oxygen species in BPR was intermediate to the other two genotypes. In a n effort to mimic the low antioxidant levels of the BPR and WL feathers in the JF feather, JF in vitro feather melanocytes were treated with buthionin e sulfoximine (BSO), a glutathione synthesis inhibitor. With BSO added to t he medium, the JF mortality rates increased by 20-25%, reaching the mortali ty levels of the mutant BPR melanocytes. The addition of iron to the JF mel anocyte X:XO medium increased their mortality rate by 20%, probably via the Fenton reaction. Thus, antioxidants play an extremely important role in bo th the viability of normal avian melanocytes and the premature death of the vitiliginous avian melanocytes. A working hypothesis, supported in part by the current results, is that the premature death of the mutant melanocytes could be precipitated in the poorly vascularized feather by low antioxidan t protection due to both low turnover of tissue fluids which contain SOD an d to genetically determined low levels of internal antioxidant protection i n these melanocytes. This same mechanistic hypothesis could apply as "a" ca use of premature melanocyte cell death in human vitiligo wherein the vitili ginous melanocytes may have a genetic defect in their antioxidant protectio n system and blood flow to an area may be restricted.