Mechanistic Studies of NAD+/NADH in Human Heart Failure

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Project Summary/Abstract Mitochondrial dysfunction and energy deficiency have been strongly implicated in the development of heart failure (HF). Yet, the exact mechanisms remain poorly understood and mitochondria-targeted therapy is lacking. Recently, a causal relationship between the loss of cardiac NAD(H) homeostasis and mitochondrial dysfunction has been proposed in HF. The NAD(H) redox balance, i.e. NAD+/NADH ratio, is a critical regulator of multiple enzymatic reactions in cell metabolism. NAD+ also functions as a co-substrate for sirtuin deacylase, ADP-ribose transferases, and cyclic ADP-ribose synthases that post-translationally modify proteins; including enzymes important for energy transduction and cell signaling. In prior studies, we and others have observed lower NAD+/NADH ratio and elevated protein acetylation (LysAc) in cardiac tissue from mice and human patients of advanced HF. Importantly, increasing NAD+ levels by pharmacological or genetic approach normalized the loss of NAD(H) redox imbalance and reversed mitochondrial protein hyperacetylation leading to improved cardiac function in multiple animal models of HF. In the preliminary studies, we have demonstrated that oral NR supplementation significantly increases whole blood NAD+ levels and improves peripheral blood mononuclear cell (PMBC) oxidative metabolism in humans. While these studies provide us the unique advantage of moving the translational research forward, two major gaps in our knowledge remain to be addressed. One is that no study has addressed the critical questions of whether oral NR increases NAD+ levels in the myocardium of HF patients. The other is that the mechanisms by which increasing NAD+ level benefit HF is unclear. Therefore, here we propose to determine whether oral NR supplementation for eight days prior to surgery can increase NAD+ levels and improve mitochondrial function in human failing myocardium obtained at the time of left ventricular assist device (LVAD) implantation. We hypothesize that participants randomized to NR will have higher myocardial NAD+ levels, improved mitochondrial function and reduced inflammatory response as compared to participants randomized to placebo. Preliminary data from a non- randomized Pilot Study of NR pretreatment prior to LVAD implantation suggest that NR does, in fact, increase myocardial NAD+ levels, improve mitochondrial function in PBMCs and myocardium, and decreases inflammatory response gene expression in PBMCs. The randomized study proposed in this application also will examine the effects of increasing intracellular NAD+ level on mitochondrial and non-mitochondrial compartments, including epigenetic modifications and regulation of inflammation, as well as correlate these changes in myocardium with corresponding changes in blood. Confirmation by this study of the anticipated effects of NR on human myocardium would represent an important advance in investigating the potential of NR as the first, mitochondria-targeted metabolic therapy in heart failure.