Eicosanoids in the pathogenesis of the functional and structural alterations of the kidney in diabetes

Diabetes mellitus alters the cellular production of eicosanoids in a number of tissues, including the kidney, and these agents have in turn been implicated in the pathogenesis of diabetic nephropathy. As delineated in the streptozotocin diabetic rat (SDR) model, a preferential enhancement of glomerular synthesis of the vasodilatory prostaglandins (PGs) PGE2 and PGI2 with concurrent smaller increases in thromboxane (TX)A2 occurs within 1 week after induction of diabetes. This early alteration in glomerular synthesis of eicosanoids in the SDR has been linked to glucose-induced activation of the glomerular protein kinase C signalling system that enhances phospholipase A2 activity and, therefore, release of membrane-bound arachidonic acid for oxygenation. The preferential increase in glomerular production of vasodilatory PGs may contribute to the glomerular hyperfiltration that is characteristic of early diabetes. After more prolonged (months) diabetes in the SDR, glomerular generation and urinary excretion of thromboxane (TX) are preferentially enhanced. Studies with selective inhibitors of TX synthesis in the SDR have implicated this eicosanoid in the pathogenesis of both albuminuria and glomerular structural changes (basement membrane thickening and mesangial matrix expansion). Direct stimulation of matrix protein production has been demonstrated in cultured mesangial cells in response to both TX and high ambient concentrations of glucose. The actions of TX and glucose on mesangial cell matrix production appear to be interactive, with each signalled through distinct pathways of protein kinase C activation.