In Vivo Effects of Disulfiram and Cyanamide on Canine Liver Aldehyde Dehydrogenase Isoenzymes as Detected by High‐Performance (Pressure) Liquid Chromatography

Methods for analysis of aldehyde dehydrogenase isoenzymes using high‐performance (pressure) liquid chromatography (HPLC) were used to determine in vivo effects of disulfiram and cyanamide on canine liver aldehyde dehydrogenase (ALDH) isoenzymes. Liver ALDH isoenzymes from control and disulfiram‐ or cyanamide‐treated dogs were separated by ion‐exchange HPLC, and enzyme activity was detected using a postcolumn reactor. Two major peaks of ALDH activity (peaks I and II) were detected. Varying the composition of the reaction column reagents resulted in alterations in the elution profiles consistent with the kinetic properties of individual isoenzymes (i.e., ALDH IB in peak I and ALDH IIB in peak II), including estimates of the K_m for acetaldehyde and the effects of magnesium ions on ALDH activity. Disulfiram treatment decreased both peaks depending on disulfiram dose and length of treatment, with peak I being more sensitive to inactivation than peak II. Reagents containing MgCI: (1 mM) decreased peak I and increased peak II compared with EDTA (1 mM) for samples from both control and disulfiramtreated animals. These data are consistent with the assignment of the disulfiram‐sensitive isoenzyme (ALDH IB) to peak I and the isoenzyme stimulated by magnesium ions (ALDH IIB) to peak II. In vivo cyanamide treatment produced similar decreases in both peaks to a maximum decrease of ‐30% of control depending on cyanamide dose. Peak I, however, was more sensitive than peak II to in vitro inactivation by cyanamide, which suggests that cytosolic ALDH in the dog (in contrast to other mammals) is more sensitive to inactivation than mitochondrial ALDH.