BIOCHEMICAL-STUDIES OF A NEW CLASS OF ALCOHOL-DEHYDROGENASE INHIBITORS FROM RADIX PUERARIAE

Two potent, reversible inhibitors of human alcohol dehydrogenase (ADH) isozymes were isolated from Radix puerariae (RP, commonly known as kudzu root) and identified as the isoflavones daidzein and genistein. The 4'-methoxy derivatives of daidzein (trivial name, formononetin) and genistein (biochanin A), minor constituents of RP, were also shown to be ADH inhibitors. All of these isoflavones inhibit the human gamma(2) gamma(2)-ADH isozyme competitively with respect to ethanol and uncompetitively with respect to NAD(+). A survey of more than 40 structurally related compounds revealed one more isoflavone (prunetin) and four flavones (7-hydroxyflavone, apigenin, galangin, and kaempferol) that inhibit ADH. The isoflavone inhibitors, however, are far more potent than the flavone inhibitors. Among the isoflavones studied, genistein is the most potent with K-i = 0.1 mu M toward gamma(2) gamma(2)-ADH. Human ADH isozymes differ in their sensitivity to these inhibitors in the order gamma(2) gamma(2)-, gamma(1) gamma(1)- > alpha alpha-, pi pi- > chi chi-ADH. These inhibitors do not affect the beta(1) beta(1)- and beta(2) beta(2)-ADH isozymes at concentrations as high as 20 mu M. Rat and rabbit class I ADHs are also inhibited by these isoflavone inhibitors. The 7-O-glucosyl derivatives of daidzein, genistein, formononetin, and biochanin A do not inhibit ADH, but are potent aldehyde dehydrogenase inhibitors.