Impaired Arginine Metabolism Coupled to a Defective Redox Conduit Contributes to Low Plasma Nitric Oxide in Polycystic Ovary Syndrome

Abstract

Background: Though oxidative stress is associated with Polycystic Ovary Syndrome (PCOS), the status of nitric oxide is still unclear. Nitric Oxide (NO) plays pivotal roles in many physiological functions which are compromised in PCOS. Our recent study reveals lowered T-regulatory cells (Tregs) in PCOS, and Treg generation is known to be regulated by NO levels. However concrete evidences are lacking on mechanisms modulating NO levels under PCOS. Methods: This is a retrospective case-control cohort study, comprised of PCOS women (N=29) and normal menstruating women as controls (N=20). We analysed NOx (nitrite+nitrate) and hydrogen peroxide (H 2 O 2 ) concentrations, transcript levels of endothelial nitric oxide synthase (eNOS)/inducible nitric oxide synthase (iNOS) and arginine modulators, hydrogen peroxide regulators in the cohort. Results: PCOS women showed reduced plasma NOx(nitrate+nitrite) and H 2 O 2 compared to controls. We report reduction in transcript levels of iNOS/NOS2 and eNOS/NOS3 in PCOS peripheral blood. The transcripts involved in arginine bioavailability: Argininosuccinate lyase (ASL), Solute Carrier Family1, member 7 (SLC7A1) and Arginase 1 (ARG1) and Asymmetric Dimethyl Arginine (ADMA) metabolism: Protein arginine methyltransferase 1 (PRMT1) and Dimethylarginine dimethylaminohydrolase 2 (DDAH2) also showed differential expression. H 2 O 2 concentration in PCOS women was also found to be reduced. The reduction can be attributed to increase in catalase levels as a consequence of the body's effort to alleviate the oxidative burden in the system. Conclusion: Our study advocates that PCOS women have lowered NO due to reduced iNOS/eNOS expression, low H 2 O 2 , high ADMA synthesis and reduced arginine bioavailability. An in-depth analysis of redox biology of PCOS to open up potential therapeutic strategies is highly recommended.