allopurinol and Vitiligo

Xanthine dehydrogenase/xanthine oxidase (XDH/XO) catalyses the hydroxylation of hypoxanthine to xanthine and finally to uric acid in purine degradation. These reactions generate H(2)O(2) yielding allantoin from uric acid when reactive oxygen species accumulates. The presence of XO in the human epidermis has not been shown so far. As patients with vitiligo accumulate H(2)O(2) up to mm levels in their epidermis, it was tempting to examine whether this enzyme and consequently allantoin contribute to the oxidative stress theory in this disease. To address this question, reverse transcription-polymerase chain reaction, immunoreactivity, western blot, enzyme kinetics, computer modelling and high performance liquid chromatography/mass spectrometry analysis were carried out. Our results identified the presence of XDH/XO in epidermal keratinocytes and melanocytes. The enzyme is regulated by H(2)O(2) in a concentration-dependent manner, where concentrations of 10(-6 )m upregulates the activity. Moreover, we demonstrate the presence of epidermal allantoin in acute vitiligo, while this metabolite is absent in healthy controls. H(2)O(2)-mediated oxidation of Trp and Met in XO yields only subtle alterations in the enzyme active site, which is in agreement with the enzyme kinetics in the presence of 10(-3 )m H(2)O(2). Systemic XO activities are not affected. Taken together, our results provide evidence that epidermal XO contributes to H(2)O(2)-mediated oxidative stress in vitiligo via H(2)O(2)-production and allantoin formation in the epidermal compartment.

Topics: Allantoin; Blotting, Western; Case-Control Studies; Catalytic Domain; Cells, Cultured; Computer Simulation; Epidermis; Flavin-Adenine Dinucleotide; Humans; Hydrogen Peroxide; Immunohistochemistry; Keratinocytes; Melanocytes; Models, Chemical; Molecular Structure; Oxidation-Reduction; Oxidative Stress; RNA, Messenger; Uric Acid; Vitiligo; Xanthine Dehydrogenase; Xanthine Oxidase

Vitiligo is a common pigmentary disorder of the skin with selective destruction of melanocytes. The pathogenetic mechanisms in vitiligo have not been completely clarified. The aim of our investigation was to evaluate the oxidative stress in the pathogenesis of generalized vitiligo. Twenty-seven patients with generalized vitiligo and 24 phototype-, age-, and sex-matched healthy controls were included in this study. We analysed serum levels of malondialdehyde (MDA), nitric oxide (NO), and serum activities of superoxide dismutase (SOD) and xanthine oxidase (XO) in the patients with vitiligo and in the controls. We found significantly higher levels of MDA and XO activity (P < 0.001 and P < 0.05, respectively), and a significantly lower level of serum SOD activity (P < 0.05) in patients with vitiligo compared with the controls. However, the increase in the level of serum NO was insignificant (P > 0.05). These results suggest that lipid peroxidation of cellular membrane of melanocytes by free radicals may have a significant role in the pathogenesis of generalized vitiligo.

Topics: Adolescent; Adult; Female; Humans; Lipid Peroxidation; Male; Malondialdehyde; Middle Aged; Nitric Oxide; Oxidative Stress; Superoxide Dismutase; Vitiligo; Xanthine Oxidase