A redox-based mechanism for nitric oxide-induced inhibition of DNA synthesis in human vascular smooth muscle cells

1 The current study explored potential redox mechanisms of nitric oxide (NO )-induced inhibition of DNA synthesis in cultured human and rat aortic smoo th muscle cells. 2 Exposure to S-nitrosothiols, DETA-NONOate and NO itself inhibited ongoing DNA synthesis and S phase progression in a concentration-dependent manner, as measured by thymidine incorporation and flow cytometry. Inhibition by N O donors occurred by release of NO, as detected by chemiluminescence and ju dged by the effects of NO scavengers, haemoglobin and cPTIO. 3 Go-incubation with redox compounds, N-acetyl-L-cysteine, glutathione and L-ascorbic acid prevented NO inhibition of DNA synthesis. These observation s suggest that redox agents may alternatively attenuate NO bioactivity extr acellularly, interfere with intracellular actions of NO on the DNA synthesi s machinery or restore DNA synthesis after established inhibition by NO. 4 Recovery of DNA synthesis after inhibition by NO was similar with and wit hout redox agents suggesting that augmented restoration of DNA synthesis is an unlikely mechanism to explain redox regulation. 5 Study of extracellular interactions revealed that all redox agents potent iated S-nitrosothiol decomposition and NO release. 6 Examination of intracellular NO bioactivity showed that as opposed to att enuation of NO inhibition of DNA synthesis by redox agents, there was no in hibition (potentiation in the presence of ascorbic acid) of soluble guanyla te cyclase (sGC) activation judged by cyclic GMP accumulation in rat cells. 7 These data provide evidence that NO-induced inhibition of ongoing DNA syn thesis is sensitive to redox environment. Redox processes might protect the DNA synthesis machinery from inhibition by NO, in the setting of augmented liberation of biologically active NO from NO donors.