IDENTIFICATION OF 4-(N,N-DIPROPYLAMINO)BENZALDEHYDE AS A POTENT, REVERSIBLE INHIBITOR OF MOUSE AND HUMAN CLASS-I ALDEHYDE DEHYDROGENASE

As the physiologic roles for the different classes of aldehyde dehydro genase (ALDH) enzymes are elucidated, the identification of specific, reversible inhibitors becomes of great pharmacologic interest. Previou s structure-function studies identified dialkylamino substituted benza ldehyde compounds as a novel class of reversible inhibitors of class I ALDH. To examine further structural requirements for inhibition, we t ested a series of 4-(N,N-dialkylamino)benzaldehyde analogs as inhibito rs of propanal oxidation by mouse liver and human erythrocyte class I ALDH. 4-(N,N-dipropylamino)benzaldehyde (DPAB) was identified as the m ost potent, reversible inhibitor of propanal oxidation by class I ALDH in spectrophotometric enzyme assays. In kinetic studies, DPAB showed mixed-type inhibition with respect to the aldehyde substrates propanal , phenylacetaldehyde, benzaldehyde, and aldophosphamide. DPAB exhibite d uncompetitive inhibition with respect to the cofactor NAD. Inhibitio n constants (K-i) for DPAB, estimated from Dixon plots, were 10 nM (pr opanal) and 77 nM (phenylacetaldehyde) for mouse ALDH and 3 nM (propan al) and 70 nM (phenylacetaldehyde) for human ALDH. These K-i values ar e 100-fold lower than those reported for class I specific inhibitors. At low (<1 mu M) DPAB concentrations, inhibition of propanal and aldop hosphamide oxidation was > 75%, whereas inhibition of benzaldehyde (32 %) and phenylacetaldehyde (19%) oxidation was reduced markedly. These results indicate that DPAB exhibits potent, reversible inhibition of m ouse and human class I ALDH. The degree of inhibition was highly depen dent on the structure of the aldehyde substrate.