Selective activation of organic nitrates by, and inactivation of, ALDH isoforms

Abstract

The activation of nitroglycerin (NTG), isosorbide dinitrate (ISDN) and isosorbide‐5‐mononitrate (ISMN) by aldehyde dehydrogenases (ALDH1 and ALDH2), and their subsequent inactivation, were examined. Purified ALDH1 or ALHD2 were incubated with these organic nitrates (ORN), and NO production was monitored by a NO electrode. ALDH2 catalyzed NO production from NTG and ISDN, but not ISMN. In contrast, ALDH1 liberated NO from NTG, ISDN and ISMN similarly (ORN all 1 mM, AUC of NO production in µM*sec: NTG: 35.1± 4.7, ISDN: 30.5±3.1; ISMN: 35.6±1.9). The inactivation of the two ALDH isozymes was examined by incubating each ORN for 15 min, and the ability of these pretreated enzymes to produce NO from 0.1mM NTG was monitored. NTG (0.1 mM) and ISDN (1 mM) completely inactivated ALDH1, while 1 mM ISMN inactivated this enzyme partially (to 34.1±3.7% of control). In contrast, ALDH2 was completely inactivated by 0.1 mM NTG, partially by 1 mM ISDN (to 27.0±23.0% of control), and not by 1 mM ISMN (to 95.0±35.8% of control, p>0.05). The inhibition of ALDH esterase and dehydrogenase activities by ORN showed a similar pattern. These data suggest that activation of ORN to NO by ALDH isoforms, and subsequent enzyme inactivation by ORN, are selective. While NTG and ISDN are both activated by, and in turn inactivated, ALDH1 and ALDH2, ISMN is not a substrate or inactivator of ALDH2, but rather of ALDH1. (Supported in part by NIH grant HL81580).