Impact of para-phenylenediamine on cyclooxygenases expression and prostaglandin formation in human immortalized keratinocytes (HaCaT).

para-Phenylenediamine, a monocyclic arylamine, is a frequently used chemical and ingredient of oxidative hair coloring products. Thus exposure occurs predominantly via skin. Cyclooxygenases, the key enzymes in prostaglandin synthesis, exhibit manifold physiological and pathophysiologial functions in skin and skin cells such as keratinocytes. We studied if para-phenylenediamine impacts on the expression of enzymes in the cyclooxygenase pathway in human immortalized keratinocytes (HaCaT) as a model for keratinocytes. We analyzed COX-1, COX-2 and cPLA(2) steady state mRNA levels for 100-400 microM PPD after 2-24 h and found clear COX-2 induction for 400 microM PPD after 24 h, while cPLA(2) and COX-1 levels were increased dose-dependently between 8 and 24 h. Increased expression was accompanied by enhanced prostaglandin E(2) and F(2alpha) formation. Specific involvement of COX enzymes was confirmed by prostaglandin analysis in the presence of exogenous arachidonic acid and inhibition experiments using COX inhibitor NS-398. In addition, para-phenylenediamine-induced prostaglandin formation was completely inhibited in cells pre-stimulated with the anti-oxidant N-acetylcysteine. N-acetylation of PPD was observed in HaCaT yielding mono-acetyl-PPD (MAPPD) and di-acetyl-PPD (DAPPD). Further investigations of MAPPD and DAPPD and the generated auto-oxidation product Bandrowski's base (BB) found that these compounds were not able to impact on COX enzyme expression and activity. In sum, these results demonstrate that para-phenylenediamine, but not its generated acetylated derivatives or BB, induces COX expression and activity in human keratinocytes likely via oxidative processes.