Description

Chronic Kidney Disease (CKD) is a major health problem affecting more than 26 million Americans. Notably, more patients with CKD die of cardiovascular complications than progress to dialysis. An overactive sympathetic nervous system is a well known cardiovascular risk factor present in CKD. The increase in sympathetic nerve activity (SNA) may not only contribute to hypertension, but also accelerates the progression of end organ damage that is independent of any rise in blood pressure. Indeed, elevated SNA is associated with poor prognosis and increased risk of cardiovascular morbidity and mortality. Thus, the sympathetic nervous system constitutes a primary novel drug target needed for improving cardiovascular outcomes in CKD patients. However, limited effort has been directed at identifying the mechanisms driving sympathetic overactivity in CKD and importantly, SNA remains high in these patients despite standard drug therapy including angiotensin converting enzyme inhibitors and angiotensin II receptor blockers. Thus, a better understanding of the mechanism(s) of the elevated SNA would enable us to devise more effective countermeasures and help reduce the subsequent morbidity and mortality among CKD patients. A potential signal driving SNA involves accumulation of the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA). ADMA is elevated in CKD and is a strong, independent predictor of future cardiovascular events in these patients. Much of the work with ADMA has been correlational in nature with a focus on the well-known vascular endothelial properties of nitric oxide. However, increasing functional evidence indicates that nitric oxide is also a key signaling molecule involved in the tonic restraint of sympathetic outflow from the brainstem. Indeed, the investigators have recently demonstrated that systemic experimental inhibition of nitric oxide synthase causes sympathetic activation in healthy humans. In the current study, the investigators will target the pathophysiological nitric oxide synthase inhibition caused by elevated ADMA concentrations in CKD and its role in mediating sympathetic overactivity. Recent work has reported that thiazolidinediones, such as pioglitazone, reduce ADMA likely by upregulating dimethylarginine dimethylamino-hydrolase (DDAH), the enzyme responsible for the breakdown of ADMA. Indeed, analysis of the DDAH gene revealed the presence of a thiazolidinedione binding site, implying that thiazolidinediones can directly regulate DDAH expression and subsequently ADMA levels. Thus, thiazolidinediones may provide a promising therapy in CKD. Indeed, in a recent study, CKD patients treated with pioglitazone were less likely to reach the composite end points of cardiovascular morbidity and mortality. Importantly, this effect was independent of the level of renal impairment suggesting protective effects even in moderate CKD. However, the mechanisms for these improvements remain unclear. In this study, the investigators hypothesize that these favorable cardiovascular effects are through a lowering of ADMA and SNA. Thus, the ability of pioglitazone to reduce ADMA and SNA in CKD patients will be tested.