KINETIC CHARACTERISTICS OF ZENECA ZD5522, A POTENT INHIBITOR OF HUMANAND BOVINE LENS ALDOSE REDUCTASE

Aldose reductase (aldehyde reductase 2) catalyses the conversion of gl ucose to sorbitol, and methylglyoxal to acetol. Treatment with aldose reductase inhibitors (ARIs) is a potential approach to decrease the de velopment of diabetic complications. The sulphonylnitromethanes are a recently discovered class of aldose reductase inhibitors, first exempl ified by ICI215918. We now describe enzyme kinetic characterization of a second sulphonylnitromethane, 3',5'-dimethyl-4'-nitromethylsulphony l-2- (2-tolyl)acetanilide (ZD5522), which is at least 10-fold more pot ent against bovine lens aldose reductase in vitro and which also has a greater efficacy for reduction of rat nerve sorbitol levels in vivo ( ED(95) = 2.8 mg kg(-1) for ZD5522 and 20 mg kg(-1) for ICI 215918). ZD 5522 follows pure noncompetitive kinetics against bovine lens aldose r eductase when either glucose or methylglyoxal is varied (K-is = K-ii = 7.2 and 4.3 nM, respectively). This contrasts with ICI215918 which is an uncompetitive inhibitor (K-ii = 100 nM) of bovine lens aldose redu ctase when glucose is varied. Against human recombinant aldose reducta se, ZD5522 displays mixed noncompetitive kinetics with respect to both substrates (K-is = 41 nM, K-ii= 8 nM with glucose and K-is = 52 nM, K -ii = 3.8 nM with methylglyoxal). This is the first report of the effe cts of a sulphonylnitromethane on either human aldose reductase or uti lization of methylglyoxal. These results are discussed with reference to a Di Iso Ordered Bi Bi mechanism for aldose reductase, where the in hibitors compete with binding of both the aldehyde substrate and alcoh ol product. This model may explain why aldose reductase inhibitors fol low noncompetitive or uncompetitive kinetics with respect to aldehyde substrates, and X-ray crystallography paradoxically locates an ARI wit hin the substrate binding site. Aldehyde reductase (aldehyde reductase 1) is closely related to aldose reductase. Inhibition of bovine kidne y aldehyde reductase by ZD5522 follows uncompetitive kinetics with res pect to glucuronate (K-ii = 39 nM), indicating a selectivity greater t han 5-fold for bovine aldose reductase relative to aldehyde reductase.