N-ACETYLCYSTEINE PROTECTS LYMPHOCYTES FROM NITROGEN MUSTARD-INDUCED APOPTOSIS

The ability of the antioxidant N-acetylcysteine to prevent apoptosis i nduced in lymphocytes by nitrogen mustard (HN2) was investigated. HN2 caused a concentration-dependent induction of apoptosis on C3H murine spleen cells, as identified by two criteria: morphological features re vealed by microscopical observations and DNA fragmentation visualized by the characteristic ''ladder'' pattern observed upon agarose gel ele ctrophoresis, as well as by hypodiploid DNA-containing cells revealed by the flow cytometric analysis of propidium iodide labelled cells. Th e antioxidant N-acetylcysteine (NAG) was found to markedly reduce the occurrence of HN2-induced apoptosis in these cells. This protective ef fect was still obtained when NAC was added 30 min after HN2. In contra st, the pretreatment of spleen cells with this antioxidant did not pro vide any significant protection. We also showed that lymphocytes prote cted by NAC are still able to respond to a mitogenic stimulation. To g ain some insight into the mechanisms underlying the cytoprotective act ion of NAC against HN2, we tested whether or not poly(ADP-ribose) poly merase (PARP, EC 2.4.2.30), a nuclear enzyme that participates in the triggering of apoptosis induced by alkylating agents, is involved. We report that 6(5H)-phenanthridinone, a potent PARP inhibitor, did not a ffect the ability of NAC to prevent HN2-induced apoptosis under our ex perimental conditions. Thus, the exact mechanism by which NAC protects lymphocytes from HN2 cytotoxicity has yet to be determined.