CO-releasing molecules and increased heme oxygenase-1 induce protein S-glutathionylation to modulate NF-κB activity in endothelial cells.

Protein glutathionylation is a protective mechanism that functions in response to mild oxidative stress. Carbon monoxide (CO) can increase the reactive oxygen species concentration from a low level via the inhibition of cytochrome c oxidase. We therefore hypothesized that CO would induce NF-κB-p65 glutathionylation and then show anti-inflammatory effects. In this study, we found that CO-releasing molecules suppress TNFα-induced monocyte adhesion to endothelial cells (ECs) and reduce ICAM-1 expression. Moreover, CO donors were further found to exert their inhibitory effects by blocking NF-κB-p65 nuclear translocation, but do so independent of IκBα degradation, in TNFα-treated ECs. In addition, p65 protein glutathionylation represents the response signal to CO donors and is reversed by the reducing agent dithiothreitol. Thiol modification of the cysteine residue in the p65 RHD region was required for the CO-modulated NF-κB activation. The suppression of p65 glutathionylation by a GSH synthesis inhibitor, BSO, and by catalase could also attenuate TNFα-induced p65 nuclear translocation and ICAM-1 expression. CO donors induce Nrf2 activation and Nrf2 siRNA suppresses CO-induced p65 glutathionylation and inhibition. Furthermore, we found that the CO donors induce heme oxygenase-1 (HO-1) expression, which increases p65 glutathionylation. In contrast, HO-1 siRNA attenuates CO donor- and hemin-induced p65 glutathionylation. Our results thus indicate that the glutathionylation of p65 is likely to be responsible for CO-mediated NF-κB inactivation and that the HO-1-dependent pathway may prolong the inhibitory effects of CO donors upon TNFα treatment of ECs.