Abstract 14913: Renal Function Underpins Cox-2: Methylarginine Axis in Mouse and Man

Abstract

Introduction and Hypothesis: Through the production of prostacyclin (PGI2), cyclooxygenase (COX)-2 protects the cardio-renal system. Restraining methylarginines (ADMA, SDMA), which are biomarkers of renal and cardiovascular disease and inhibitors (ADMA) of cardioprotective endothelial nitric oxide synthase (eNOS), has been suggested as a contributory pathway. However, the relationship between renal function, COX-2 and methylarginines remains unclear. Methods: Using plasma from genetically modified mice with germline global deletion of COX-2 or PGI 2 synthase (PGIS) and human plasma from a unique individual lacking COX-derived prostaglandins due to a loss of cPLA 2 , before and after receiving a cPLA 2 -replete transplanted donor kidney, we measured methylarginines, arginine and citrulline using UHPLC-MS/MS. Renal function was assessed by measuring cystatin C by ELISA. To eliminate the impact of renal function in vivo , methylarginine and PGI 2 release from organotypic kidney slices in culture were quantified by ELISA. Results: Plasma ADMA, SDMA, citrulline and cystatin C, were similarly elevated in samples from the patient lacking COX/PGI 2 capacity compared to levels in healthy volunteers. Renal function, ADMA, SDMA and citrulline returned towards normal range when the patient received a genetically normal kidney, capable of COX/PGI 2 activity. Cystatin C correlated with ADMA, SDMA and citrulline. Loss of COX-2 or PGIS in mice increased plasma levels of ADMA, SDMA and cystatin C. As in human, SDMA, ADMA and citrulline but not arginine positively correlated with cystatin C. Levels of analytes in conditioned media of kidney slices (24h) were not altered in tissue from COX-2 KO (6-keto=14.0±1.8, ADMA=1.0±0.06, SDMA=0.30±0.05; n=8) compared to wildtype mice (66-keto=15.0±1.7, ADMA=0.98±0.06, SDMA=0.24±0.01; n=12). Conclusions: COX-2 and PGI2 are critical regulators of renal function. Plasma methylarginines are integrally linked to renal homeostasis.