Nitroxyl analogs as inhibitors of aldehyde dehydrogenase. C-nitroso compounds.

We previously postulated that the catalase-mediated oxidation of cyanamide leads to the formation of the unstable intermediate, N-hydroxycyanamide, which spontaneously decomposes to nitroxyl, the putative inhibitor of aldehyde dehydrogenase (EC 1.2.1.3; AlDH). Since it was not possible to provide direct evidence for the inhibition of AlDH by nitroxyl, we examined the activity of three representative substituted nitroxyls (C-nitroso compounds), viz. nitrosobenzene (NB), 1-nitrosoadamantane (NA), and 2-methyl-2-nitrosopropane (MNP), as direct inhibitors of yeast AlDH in vitro. While NB and NA were highly effective inhibitors in this system exhibiting IC50 values of 2.5 and 8.6 microM, respectively, MNP was considerably less effective with an IC50 of 0.15 mM. When tested in vivo, NA did not show any inhibitory activity on the hepatic AlDH, possibly due to the lack of site-specific delivery of the active monomeric form of this compound. However, NB at a low dose did inhibit hepatic AlDH as reflected by an increase in blood acetaldehyde levels. These results attest to the abilities of NB and NA to act as direct inhibitors of AlDH analogous to nitroxyl itself.