Threshold of peroxynitrite cytotoxicity in bovine pulmonary artery endothelial and smooth muscle cells.

Peroxynitrite is widely reported as highly cytotoxic; yet recent evidence indicates that at certain concentrations, it can induce pulmonary cell hyper-proliferation and tissue remodelling. This study aimed to establish the threshold concentration of peroxynitrite to induce functional impairment of bovine pulmonary artery endothelial (PAEC) and smooth muscle cells (PASMC). PAEC or PASMC were exposed to solution of peroxynitrite or 3-morpholinosydnonimine (SIN-1). Twenty-four hour cell viability, DNA synthesis, and protein biochemistry were assessed by trypan blue dye exclusion, [3H] thymidine incorporation and western blot analysis, respectively. Threshold concentration of peroxynitrite to significantly impair viability of PAEC and PASMC was 2 μM peroxynitrite. In PASMC and PAEC, low concentrations of peroxynitrite (2 nM-0.2 μM) increased cell proliferation and did not activate p38 MAP kinase. The decrease in DNA synthesis and cell viability caused by 2 μM peroxynitrite was associated with caspase-3 cleavage but not p38 activation. Also, 2-20 μM peroxynitrite significantly activated poly ADP ribose polymerase and stress activated kinase JNK in PAEC. However, the higher concentration of 20 μM peroxynitrite did cause a threefold increase in p38 activation. In conclusion, the threshold for the cytotoxic effects of peroxynitrite was 2 μM; which caused apoptotic cell death independent of p38 MAP kinase activation in pulmonary artery cells.