PDH kinase inhibitors: a novel therapy for Type II diabetes?

The pyruvate dehydrogenase multienzyme complex catalyses the oxidative decarboxylation of pyruvate, which is an important regulatory step in oxidative metabolism. Phosphorylation of the E1 (pyruvate decarboxylase) subunit on one of three specific serine residues results in loss of enzyme activity. Four dedicated PDHK (pyruvate dehydrogenase kinase) isoenzymes have been identified, each of which display a distinct tissue-specific expression profile, and have differential regulatory properties. Thus PDHK play a key role in controlling the balance between glucose and lipid oxidation according to substrate supply. Increasing glucose oxidation by inhibiting PDHK may be an effective mechanism to increase glucose utilization; additionally, increasing pyruvate oxidation may further contribute to lowering of glucose level by decreasing the supply of gluconeogenic substrates. A number of PDHK inhibitors are now available to enable this mechanism to be evaluated as a therapy for diabetes. The isoenzyme selectivity profile of AZD7545 and related compounds will be described and evidence for their non-ATP-competitive mode of action presented. These compounds increase PDH activity in vivo, and when dosed chronically, improve glycaemic control in Zucker rats. Furthermore, glucose lowering has been demonstrated in the hyperglycaemic Zucker diabetic fatty rat. This result supports the hypothesis that inhibition of PDHK may be an effective therapy for Type II diabetes.