Patients with chronic kidney disease (CKD) often develop a ?uremic? cardiomyopathy characterized by diastolic dysfunction, left ventricular hypertrophy, and cardiac remodeling, despite contemporary therapies of neurohormonal blockade. We have described a central mechanistic role of cardiotonic steroids (CTS) in activating pro-inflammatory and pro-fibrotic pathways following renal insult that potentiate this uremic cardiomyopathy. CTS are a family of steroid hormones including bufadienolides such as marinobufagenin and telocinobufagin which are significantly elevated in volume expanded conditions such as CKD and can directly lead to inflammation and cardiac fibrosis upon binding and signaling through the Na+/K+-ATPase. Paraoxonases (PON) are hydrolytic lactonase enzymes that, depending on isoform, are either generated in the liver and circulate bound to high-density lipoprotein or are expressed intracellularly at the tissue level. Our preliminary experimental and clinical data demonstrate an association between diminished lactonase activities of PON and cardiac disease severity and progression in CKD. Yet the underlying cardioprotective mechanism(s) are largely unknown. Now, for the first time, we have identified novel mechanistic interactions between paraoxonases and endogenous CTS. Interestingly, the lactonase activities of PON hydrolyze CTS to their open-ring forms which, unlike native CTS, are incapable of stimulating collagen formation. Hence, the overall goal of this proposal is to test the hypotheses that cardioprotection by PON can deter progressive cardiac fibrosis and diastolic dysfunction in CKD, and that the mechanism occurs via modulation of pathogenetic pathways induced by endogenous CTS. Our studies will define a novel endogenous substrate for PON and establish for the first time a counter-regulatory mechanism of CTS activities in attenuating cardiac remodeling following renal insult.
Patients with chronic kidney disease suffer disproportionately for high cardiac morbidity and mortality. The present studies will help to establish the role of paraoxonases in the regulation of pro-fibrotic cardiotonic steroids and the development and progression of cardiac disease in patients with chronic kidney disease. Patients with chronic kidney disease are disproportionally affected by cardiac disease and cardiac death. The objective of our studies is to understand the mechanisms of how paraoxonases regulate and control levels of pro-fibrotic cardiotonic steroids so that we can develop better treatment strategies to fight against the cardiac disease that affects so many patients with chronic kidney disease.
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