Role of zinc in pulmonary endothelial cell response to oxidative stress

Although zinc is a well-known inhibitor of apoptosis, it may contribute to oxidative stress-induced necrosis. We noted that N,N,N',N'-tetrakis(2-pyrid ylmethyl)ethylenediamine (TPEN; > 10 muM), a zinc chelator, quenched fluore scence of the zinc-specific fluorophore Zinquin and resulted in an increase in spontaneous apoptosis in cultured sheep pulmonary artery endothelial ce lls (SPAECs). Addition of exogenous zinc (in the presence of pyrithione, a zinc ionophore) to the medium of SPAECs caused an increase in Zinquin fluor escence and was associated with a concentration-dependent increase in necro tic cell death. Exposure of SPAECs to TPEN (10 muM) resulted in enhanced ap optosis after lipopolysaccharide or complete inhibition of t-butyl hydroper oxide (tBH)-induced necrosis. We further investigated the role of two zinc- dependent enzymes, poly(ADP-ribose) polymerase (PARP) and protein kinase (P K) C, in tBH toxicity, tBH toxicity was only affected by the PARP inhibitor s 4-amino-1,8-naphthalimide or 3-aminobenzamide over a narrow range, wherea s the PKC inhibitors bisindolylmaleimide and staurosporine significantly re duced tBH toxicity. tBH caused translocation of PKC to the plasma membrane of SPAECs that was partially inhibited by TPEN. Thus pulmonary endothelial cell zinc inhibits spontaneous and lipopolysaccharide-dependent apoptosis b ut contributes to tBH-induced necrosis, in part, via a PKC-dependent pathwa y.