Heme oxygenase-1 mediates cytoprotection against nitric oxide-induced cytotoxicity via the cGMP pathway in human pulp cells.

OBJECTIVE

This study examined the effects of exogenous nitric oxide (NO) on human pulp cells and the involvement of cyclic 3',5'-monophosphate (cGMP) in pulpal protection induced by heme oxygenase-1 (HO-1) against NO-induced cytotoxicity.

STUDY DESIGN

This study investigated cytotoxicity and HO-1 induction in pulp cells induced by the NO donor S-nitroso-N-acetyl-D,L-penicillamine (SNAP), by using Western blotting and a cell viability assay. It also investigated whether HO-1 contributes to the cytoprotective effect against the cytotoxicity caused by NO and the relationship between HO-1 and cGMP in the signaling pathway.

RESULTS

S-nitroso-N-acetyl-D,L-penicillamine decreased cell viability, but increased HO-1 expression in a concentration- and time-dependent manner in human pulp cells. NO-induced cytotoxicity was inhibited in the presence of hemin (inducer of HO-1), whereas it was enhanced in the presence of zinc protoporphyrin IX (ZnPP IX, HO-1 inhibitor); therefore, the NO-induced cytotoxicity was correlated with HO-1 expression. Pretreatment with a membrane-permeable cGMP analog, 8-bromo-cGMP, restored cell death and enhanced the HO-1 protein expression induced by SNAP. By contrast, 1 mM SNAP inhibited guanylate cyclase in pulp cells pretreated with 1H-[1,2,4]oxadiazole[4,3-alpha]quinoxalin-1-one (ODQ), resulting in marked cytotoxicity.

CONCLUSION

These findings of a link between HO-1, regulated via the cGMP system and NO-induced cytotoxicity in human pulp cells, suggest a protective role for HO-1 in pulpal inflammation.