Peroxynitrite production, DNA breakage, and poly(ADP-ribose) polymerase activation in a mouse model of oxazolone-induced contact hypersensitivity

Peroxynitrite-induced poly(ADP-ribose) polymerase activation has been impli cated in the pathogenesis of various inflammatory conditions, Here we have investigated whether peroxynitrite and poly(ADP-ribose) polymerase may play a role in the pathophysiology of the elicitation phase of contact hypersen sitivity. We have detected nitrotyrosine, DNA breakage, and poly(ADP-ribose ) polymerase activation in the epidermis of mice in an oxazolone-induced co ntact hypersensitivity model. As tyrosine nitration is mostly mediated by p eroxynitrite, a nitric-oxide-derived cytotoxic oxidant capable of causing D NA breakage, we have applied peroxynitrite directly on mouse skin and showe d poly(ADP-ribose) polymerase activation in keratinocytes and in some scatt ered dermal cells. We have also investigated the cellular effects of peroxy nitrite in HaCaT cells, a human keratinocyte cell line. We found that perox ynitrite inhibited cell proliferation and at higher concentrations also cau sed cytotoxicity, Peroxynitrite activates poly(ADP-ribose) cells and poly(A DP-ribose) polymerase activation contributes to peroxynitrite-induced cytot oxicity, as indicated by the cytoprotective effect of the poly(ADP-ribose) polymerase inhibitor 3-aminobenzamide, The cytoprotective effect of 3-amino benzamide cannot be attributed to inhibition of apoptosis, as apoptotic par ameters (caspase activation and DNA fragmentation) were not reduced in the presence of 3-aminobenzamide in peroxynitrite-treated cells. Moreover, poly (ADP-ribose) polymerase inhibition by 3-aminobenzamide dose-dependently red uced interferon-induced intercellular adhesion molecule 1 expression as wel l as interleukin-1 beta -induced interleukin-8 expression. Our results indi cate that peroxynitrite and poly(ADP-ribose) polymerase regulate keratinocy te function and death in contact hypersensitivity.