Early glycation products of endothelial plasma membrane proteins in experimental diabetes.

The participation of glucose and two intermediates of glucose metabolism: glucose-6-phosphate (G6P) and glyceraldehyde-3-phosphate (Gald3P) to the formation of early glycation products was comparatively evaluated in the endothelial plasma membrane of streptozotocin-induced diabetic rats. Antibodies risen to a carrier protein reductively glycated by each of the sugars mentioned above were used to probe by immunoblotting the proteins of the lung microvascular endothelium plasmalemma purified from normal and diabetic rats. The amount of glycated endothelial plasma membrane proteins was below the limit of detection in normoglycemic animals but increased dramatically in diabetic animals for glucose and G6P. In contrast, no signal was found in diabetic rats for Gald3P, indicating that either the contribution of this phosphotriose to the glycation of intracellular proteins is negligible in vivo, or the Schiff base generated by this sugar transforms very rapidly into products of advanced glycation. Globally, the endothelial plasma membrane proteins bound on average 300 times more glucose than G6P proving that, in spite of its low in vitro potency as glycating agent, glucose represents the main contributor to the intracellular formation of early glycation products. The most abundant glycated proteins of the lung endothelial plasma membrane were separated by two dimensional electrophoresis and identified by mass spectrometry.