Glucose-induced hyperproliferation of cultured rat aortic smooth muscle cells through polyol pathway hyperactivity

The protein kinase C (PKC), platelet-derived growth factor (PDGF) and polyol pathway play important parts in the hyperproliferation of smooth muscle cells, a characteristic feature of diabetic macroangiopathy. The precise mechanism, however, remains unclear. This study investigated the relation between polyol pathway, protein kinase C and platelet-derived growth factor in the development of diabetic macroangiopathy.

Smooth muscle cells were cultured with 5.5 or 20 mmol/l glucose with or without an aldose reductase inhibitor, epalrestat, or a PKC-beta specific inhibitor, LY333531. Protein kinase C activities, the expression of PKC-beta II isoform and PDGF-beta receptor protein, free cytosolic NAD+:NADH ratio, the contents of reduced glutathione, and proliferation activities were measured.

Smooth muscle cells cultured with 20 mmol/l glucose showed statistically significant increases in protein kinase C activities, the expression of PKC-beta II isoform and PDGF-beta receptor protein, and proliferation activities, compared with smooth muscle cells cultured with 5.5 mmol/l glucose. Although epalrestat and LY333531 inhibited protein kinase C activation induced by glucose to the same degree, the effects of epalrestat on proliferation activities and expression of the PDGF-beta receptor were more prominent than those of LY333531. Epalrestat improved the glucose-induced decrease in free cytosolic NAD+:NADH ratio and reduced glutathione content, but LY333531 did not. The increased expression of membranous PKC-beta II isoform was normalized by epalrestat.

These observations suggest that polyol pathway hyperactivity contributes to the development of diabetic macroangiopathy through protein kinase C, PDGF-beta receptor, and oxidative stress, and that an aldose reductase inhibitor has a therapeutic value for this complication.