Minalrestat

Diabetes mellitus occurrence has been associated to the modification of the physiological levels of glucose and is often accompanied by several long-term complications, namely neuropathy, nephropathy, retinopathy, cataract, and cardiovascular. Aldose reductase (AR) is an enzyme of aldoketo reductase super-family that catalyzes the conversion of glucose to sorbitol in the polyol pathway of glucose metabolism. In this context, aldose reductase inhibitors (ARIs) have received much attention worldwide. Decreased sorbitol flux through polyol pathway by ARIs could be an emerging target for the management of major complications of diabetes. The present review article describes a brief overview of the role of aldose reductase in the diabetic complications, advances achieved on ARIs and their potential use in the treatment and management of the major diabetic complications such as cataract, retinopathy, neuropathy, nephropathy and cardiovascular. The ARIs developed vary structurally, and representative structural classes of ARIs include i) carboxylic acid derivatives (such as Epalrestat, Alrestatin, Zopalrestat, Zenarestat, Ponalrestat, Lidorestat, and Tolrestat), ii) spirohydantoins and related cyclic amides (such as Sorbinil, Minalrestat, and Fidarestat), and iii) phenolic derivatives (related to Benzopyran-4-one and Chalcone). Among these inhibitors, Epalrestat is the only commercially available inhibitor till date. In addition, some other ARIs such as Sorbinil and Ranirestat had been advanced into late stage of clinical trials and found to be safe for human use. The role of various natural ARIs in management of diabetic complications will be discussed. Adapting ARIs could prevent sepsis complications, prevent angiogenesis, ameliorate mild or asymptomatic diabetic cardiovascular autonomic neuropathy and appear to be a promising strategy for the treatment of endotoxemia and other ROS-induced inflammatory diseases. The role of ARIs in non-diabetic diseases will also be discussed.

Aldose reductase (ALR2) belongs to the aldo-keto reductase (AKR) superfamily of enzymes, is the first enzyme involved in the polyol pathway of glucose metabolism and has been linked to the pathologies associated with diabetes. Molecular modelling studies together with binding constant measurements for the four inhibitors Tolrestat, Minalrestat, quercetin and 3,5-dichlorosalicylic acid (DCL) were used to determine the type of inhibition, and correlate inhibitor potency and binding energies of the complexes with ALR2 and the homologous aldehyde reductase (ALR1), another member of the AKR superfamily. Our results show that the four inhibitors follow either uncompetitive or non-competitive inhibition pattern of substrate reduction for ALR1 and ALR2. Overall, there is correlation between the IC(50) (concentration giving 50% inhibition) values of the inhibitors for the two enzymes and the binding energies (DeltaH) of the enzyme-inhibitor complexes. Additionally, the results agree with the detailed structural information obtained by X-ray crystallography suggesting that the difference in inhibitor binding for the two enzymes is predominantly mediated by non-conserved residues. In particular, Arg312 in ALR1 (missing in ALR2) contributes favourably to the binding of DCL through an electrostatic interaction with the inhibitor's electronegative halide atom and undergoes a conformational change upon Tolrestat binding. In ALR2, Thr113 (Tyr116 in ALR1) forms electrostatic interactions with the fluorobenzyl moiety of Minalrestat and the 3- and 4-hydroxy groups on the phenyl ring of quercetin. Our modelling studies suggest that Minalrestat's binding to ALR1 is accompanied by a conformational change including the side chain of Tyr116 to achieve the selectivity for ALR1 over ALR2.