Endothelin receptor A-specific stimulation of glomerular inflammation and injury in a streptozotocin-induced rat model of diabetes

Aims/hypothesis: Activation of endothelin receptor-A (ET_A) increases glomerular permeability to albumin (P_alb) and elevates pro-inflammatory markers in hyperglycaemic rats. Methods: Male Sprague-Dawley rats were given streptozotocin (n=32) or saline (sham; n=32). Half of the animals in each group received the ET_A-selective antagonist, ABT-627 (atrasentan; orally), beginning immediately after hyperglycaemia was confirmed. Glomeruli were isolated by sieving techniques and P_alb determined from the change in glomerular volume induced by oncotic gradients of albumin. Glomerular nephrin levels were assessed by immunofluorescence, whereas urinary nephrin was measured by immunoassay. Results: At 3 and 6 weeks after streptozotocin injection, proteinuria was significantly increased compared with sham controls and significantly reduced by ABT-627 treatment. P_alb was also increased at 3 and 6 weeks post-streptozotocin. ABT-627 had no effect on P_alb or protein excretion in sham control rats. In glomeruli isolated from hyperglycaemic rats, incubation with BQ-123, a selective ET _A antagonist, reduced P_alb, whereas BQ-788, a selective endothelin receptor-B antagonist had no effect (n=6 rats per group, 5-8 glomeruli per rat). Glomerular and plasma content of soluble intercellular adhesion molecule-1 and monocyte chemoattractant protein-1 were significantly increased 6 weeks after streptozotocin (ELISA). ABT-627 attenuated these increases. After 6 weeks of hyperglycaemia, glomerular nephrin content was decreased with a concurrent increase in urinary nephrin excretion. ABT-627 prevented glomerular nephrin loss in hyperglycaemic rats (n=5-8 rats per group; eight groups). Conclusions/interpretation: These observations support the hypothesis that endothelin-1, via the ET_A receptor, directly increases P_alb, possibly via nephrin loss, as well as early inflammation in the hyperglycaemic rat.