Abstract 15: The Role Of Opioid Receptors In Podocytes In The Development Of Hypertension In Dahl Salt-sensitive Rats

Abstract

The rise in opioid use underscores the importance to better understand the direct and indirect effects of opioids on renal function and blood pressure. Although opioid use is associated with predictors of cardiovascular diseases, these drugs are common analgesics for hypertensive patients. We hypothesize that stimulation of opioid receptors (ORs) leads to elevated intracellular calcium level in podocytes ultimately leading to cell apoptosis, development of albuminuria and consequent progression of hypertension. Live calcium imaging experiments on freshly isolated glomeruli from rat and human kidneys, as well as human immortalized podocyte cell line, was performed to test the effect of specific ORs agonists. Following experiments assessed the effect of opioid signaling on the development of hypertension and kidney function in Dahl salt-sensitive (SS) rats, which were fed a 0.4% (LS) or 8% (HS) NaCl diets for 14 days with or without a daily i.v. bolus infusion of BRL52537, a potent and selective kappa-OR agonist. Stimulation of kappa-ORs, but not mu-ORs or delta-ORs, mediated calcium influx in podocytes through activation of TRPC6 channels. The effect of BRL52537 was completely abolished when we used the 0 mM calcium media or when a TRPC6 channel inhibitor (SAR7334) was applied. Triggering the kappa-OR/TRPC6 pathway induced podocyte cell shape changes via actin cytoskeleton remodeling. In vivo studies revealed that rats chronically treated with BRL52537 exhibited augmented blood pressure (MAP was 179 ± 15 vs. 151 ± 11 mmHg), albuminuria, and elevation in podocyte calcium. Western blot analysis revealed elevated levels of nephrin in urine samples and pro-caspase-3 in renal cortex. Moreover, TRPC6 expression was elevated under hypertensive conditions and further promoted pathological increase in calcium influx in response to kappa-OR stimulation. Summarizing the data, the opioid-induced increase in the calcium flux in podocytes is expected to contribute to kidney injury leading to progression of salt-induced hypertension. These data demonstrate that the kappa-OR/TRPC6 signaling pathway directly influences podocyte calcium handling, provoking the development of kidney injury in the opioid treated hypertensive cohort.