Targeting Sympathetic Overactivity in CKD patients: Mechanisms & Novel Therapies

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 DESCRIPTION (provided by applicant): More patients with chronic kidney disease (CKD) die of cardiovascular complications than progress to end stage renal disease. An overactive sympathetic nervous system and hypertension are known cardiovascular risk factors present in CKD. The increase in sympathetic nerve activity (SNA) may not only contribute to hypertension, but also accelerate the progression of end organ damage (kidney, heart, and vasculature) that is independent of any rise in blood pressure (BP). Thus, the sympathetic nervous system constitutes a primary drug target for improving cardiovascular outcomes in CKD patients. However, limited effort has been directed at identifying the mechanisms driving elevated SNA in CKD. We propose a comprehensive plan to test the novel hypothesis that accumulation of the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) constitutes a major mechanism for sympathetic overactivity in CKD. Our emphasis is on pre-dialysis CKD patients (hypertensive CKD stage 3 and 4) in order to intervene and offset the substantial cardiovascular risk present in this group. We also consider a potential role for oxidative stress i increasing ADMA and contributing to high SNA in CKD, because oxidative stress is elevated in these patients and this may increase ADMA by inhibiting its breakdown as well as having direct sympatho-excitatory effects. Given the increased prevalence of Type 2 Diabetes Mellitus (T2D) in the CKD population, and the ability of T2D to also increase ADMA as well as oxidative stress, we will study CKD patients with and without T2D to better understand these pathways and their potential to increase ADMA and SNA in the CKD population (Aim 1). Aim 1 will determine whether acute L-arginine infusion to overcome the accumulation of endogenous ADMA reduces SNA in CKD patients. Next, to provide immediate clinical application and further examine the role of ADMA in elevating SNA, we will perform a double-blinded, randomized, placebo controlled crossover design study including 4 weeks of placebo and pioglitazone in T2D CKD patients (Aim 2). Recent work indicates that pioglitazone reduces ADMA. We will use microneurography for direct measures of SNA, plasma and intracellular ADMA measures, electron paramagnetic resonance spectroscopy for measures of reactive oxygen species, along with BP and leg blood flow (duplex Doppler ultrasound). Healthy sex-age-weight matched controls will be studied for baseline comparisons. Overall, we propose a blend of complementary strategies to comprehensively probe the role of ADMA in mediating sympathetic overactivity in CKD patients. Our approach will provide a definitive role for a potential major mechanisms driving SNA in CKD, which has been suggested by previous studies as a strong candidate, but not rigorously tested. At the same time we will provide direct therapeutic information by determining whether pioglitazone, a readily available drug, may provide a novel treatment for reducing ADMA and sympathetic overactivity in CKD patients and if this is accompanied by an improvement in renal function.