Drug-enhanced carbon monoxide production from heme by cytochrome P450 reductase

Abstract

Carbon monoxide (CO) formed endogenously is considered to be cytoprotective, and the vast majority of CO formation is attributed to the degradation of heme by heme oxygenases-1 and -2 (HO-1, HO-2). Previously, we observed that brain microsomes containing HO-2 produced many-fold more CO in the presence of menadione and its congeners; herein we explored these observations further. We determined the effects of various drugs on CO production of rat brain microsomes and recombinant human cytochrome P450 reductase (CPR); CO was measured by gas chromatography with reductive detection. Brain microsomes of Sprague-Dawley rats or recombinant human cytochrome P450 reductase (CPR) were incubated with NADPH and various drugs in closed vials in phosphate buffer at pH 7.4 and 37°C. After 15 minutes, the reaction was stopped by cooling in dry ice, and the headspace gas was analyzed for CO production using gas chromatography with reductive (mercuric oxide) detection. We observed drug-enhanced CO production in the presence of both microsomes and recombinant CPR alone; the presence of HO was not required. A range of structurally diverse drugs were capable of amplifying this CO formation; these molecules had structures consistent with redox cycling capability. The addition of catalase to a reaction mixture, that contained activating drugs, inhibited the production of CO. Drug-enhanced CO formation can be catalyzed by CPR. The mechanism of CPR activation was not through classical drug-receptor mediation. Redox cycling may be involved in the drug-induced amplification of CO production by CPR through the production of reactive oxygen species.

Heme Oxygenase-1 as a Pharmacological Target for Host-Directed Therapy to Limit Tuberculosis Associated Immunopathology

“…Regulating their infiltration into the lung by modulating HO-1 expression, decreasing their oxidative capacity, and increasing their reductive capacity is an appealing, reversible approach to limit immunopathology in TB without deleterious effects of major immunosuppression (Figure 2). Lastly, heme degradation by HO-1 may be the predominant heme degrading mechanism but novel approaches such as targeting cytochrome P450 reductase to generate CO could be tested in heme-related tissue pathologies [120].…”