Protective effect of thioredoxin upon NO-mediated cell injury in THP1 monocytic human cells

Although NO has been postulated to play important roles in host defences, i t is potentially damaging for exposed cells, including for the macrophages producing the NO. Thus a network of radical accepters and enzymes is though t to play an important redox-buffering role to protect cells against NO-med iated injury. We examined the properties of the redox systems superoxide di smutase (SOD)/catalase, glutathione (GSH) and thioredoxin (Trx), in regulat ing the viability of two human monocytic cell lines (THP1 and U937) exposed to the NO-generating compound diethylene triamine-nitric oxide (DETA-NO). We observed that NO-induced cytotoxic effects were time- and dose-dependent towards the two cell lines. After vitamin-induced differentiation in vitro with retinoic acid (RA) and 1,25-dihydroxy vitamin D-3 (VD), termed RA/VD, we observed that THP1 RA/VD cells became more resistant to NO-mediated cyt otoxicity whereas the susceptibility of U937 cells was not modified. Using Western blotting and reverse-transcriptase PCR methods, we observed that ge ne transcription and protein expression of Trx and thioredoxin reductase we re significantly increased upon RA/VD treatment and differentiation in THP1 cells. By contrast, SOD/catalase and GSH redox state remained unmodified. Finally, a stable transfectant THP1 line overexpressing Trx was found to be more resistant than THP 1 control cells that were untransfected or transfe cted with an empty plasmid, when exposed to DETA-NO in vitro. In conclusion , we observed an inverse correlation between cell susceptibility to NO dama ging effects and Trx expression, suggesting that the Trx system may have im portant preventative capacities towards NO-mediated cellular injury in mono cytic macrophage cells.