Inhibition of human aldehyde reductase by drugs for testing the function of liver and kidney

Drugs for testing the function of liver and kidney (sulfobromophthalein, ph enolsulfonphthalein, indigo carmine and indocyanine green) and other organi c anions (rose bengal and haematin) were found to potently inhibit human li ver aldehyde reductase that is involved in the detoxification of 3-deoxyglu cosone and methylglyoxal, reactive intermediates, during the formation of a dvanced glycation end products. The inhibition patterns by the compounds we re non-competitive with respect to both coenzyme (NADPH) and substrate (D-g lucuronate). The kinetics of the inhibition by a mixture of the 2 inhibitor s suggests that all the inhibitory compounds bind to overlapping sites on t he enzyme. The binding of rose bengal, sulfobromophthalein and phenylsulfon phthalein to the free enzyme was detected by ultrafiltration assay. However , in the reverse reaction, the enzyme was inhibited competitively with resp ect to the alcohol substrate by rose bengal, haematin, phenolsulfonphthalei n, sulfobromophthalein, indigo carmine and indocyanine green, which showed K-i values of 0.1, 1, 3, 4, 4 and 10 mu M, respectively. The results sugges t that these potent inhibitors bind weakly to the free enzyme and tightly t o the enzyme-NADP binary complex.