Endothelial protection by pentaerithrityl trinitrate: bilirubin and carbon monoxide as possible mediators

Pentaerithrityl tetranitrate (PETN) is a long-acting donor of nitric oxide (NO) and has recently been characterized as an antianginal agent that, in contrast with other nitric acid esters, does not induce oxidative stress and is therefore free of tolerance. Moreover, animal experiments have revealed that PETN actively reduces oxygen radical formation in vivoand specifically prevents atherogenesis and endothelial dysfunction. Because heme oxygenase-1 (HO-1) has been described as an antiatherogenic and cytoprotective gene in the endothelium, our aim was to investigate the effect of the active PETN metabolite pentaerithrityl trinitrate (PETriN) on HO-1 expression and catalytic activity in endothelial cells. Endothelial cells derived from human umbilical vein were incubated with PETriN (0.01-1 mM) for 8 hr. PETriN increased HO-1 mRNA and protein levels in a concentration-dependent fashion up to 3-fold over basal levels. Elevation of HO-1 protein was accompanied by a marked increase in catalytic activity of the enzyme as reflected by enhanced formation of both carbon monoxide and the endogenous antioxidant, bilirubin. Pretreatment of endothelial cells with PETriN or bilirubin at low micromolar concentrations protected endothelial cells from hydrogen peroxide-mediated toxicity. HO-1 induction and endothelial protection by PETriN were not mimicked by isosorbide dinitrate, another long-acting nitrate. The present study demonstrates that the active PETN metabolite, PETriN, stimulates mRNA and protein expression as well as enzymatic activity of the antioxidant defense protein, HO-1, in endothelial cells. Increased HO-1 expression and ensuing formation of bilirubin and carbon monoxide may contribute to and explain the specific antioxidant and antiatherogenic actions of PETN.