Daidzin inhibits mitochondrial aldehyde dehydrogenase and suppresses ethanol intake of Syrian golden hamsters

Abstract

Daidzin is the major active principle in extracts of radix puerariae, a traditional Chinese medication that suppresses the ethanol intake of Syrian golden hamsters. It is the first isoflavone recognized to have this effect. Daidzin is also a potent and selective inhibitor of human mitochondrial aldehyde dehydrogenase (ALDH-2). To establish a link between these two activities, we have tested a series of synthetic structural analogs of daidzin. The results demonstrate a direct correlation between ALDH-2 inhibition and ethanol intake suppression and raise the possibility that daidzin may, in fact, suppress ethanol intake of golden hamsters by inhibiting ALDH-2. Hamster liver contains not only mitochondrial ALDH-2 but also high concentrations of a cytosolic form, ALDH-1, which is a very efficient catalyst of acetaldehyde oxidation. Further, the cytosolic isozyme is completely resistant to daidzin inhibition. This unusual property of the hamster ALDH-1 isozyme accounts for the fact we previously observed that daidzin can suppress ethanol intake of this species without blocking acetaldehyde metabolism. Thus, the mechanism by which daidzin suppresses ethanol intake in golden hamsters clearly differs from that proposed for the classic ALDH inhibitor disulfiram. We postulate that a physiological pathway catalyzed by ALDH-2, so far undefined, controls ethanol intake of golden hamsters and mediates the antidipsotropic effect of daidzin.

Figure 1

Daidzin is a mixed inhibitor of hamster liver ALDH-2 oxidation of acetaldehyde. Conditions: pH 9.5, 3 mM NAD⁺. (A) Replot of kinetic constants obtained from progress kinetic curves based on Eq. 3. The y-intercept is equal to 0 and hence β (Eq. 3) is equal to 0; the slope of the straight line is equal to αK_i (0.65 μM), the noncompetitive inhibition constant. (B) Replot of kinetic constants based on Eq. 4; the slope of the straight line is equal to K_i⁻¹ (23.8 μM).

Figure 2

Competitive inhibition of human liver ALDH-1-catalyzed acetaldehyde oxidation by daidzin. Conditions: pH 7.5, 3 mM NAD⁺.