The Effect of Nicotinamide Riboside on Skeletal Muscle Function in Heart Failure Subjects

As life expectancy increases and acute cardiac mortality decreases, the incidence of chronic heart failure (HF) continues to rise, and despite this, conceptual advances in the treatment of chronic heart failure have not increased substantially over last few decades. One intracellular component of heart failure progression is mitochondrial bioenergetic dysfunction. Although the mechanism underpinning this is not completely understood, recent metabolomics data demonstrated an incomplete flux of metabolites through oxidative phosphorylation (OX PHOS) in HF. In parallel, data has shown that hyperacetylation of mitochondrial bioenergetic enzymes, with the concomitant blunting of enzymatic activity is evident in HF. Putting these together, an emerging hypothesis implicates excessive acetylation of mitochondrial proteins with the subsequent blunting of bioenergetic enzyme function, as a mechanism underpinning incomplete flux through OX PHOS resulting in HF progression.

In parallel with cardiac bioenergetic deficiency chronic HF subjects display disrupted skeletal muscle OX PHOS, which is thought to contribute towards overall fatigue and reduced exercise tolerance. Interestingly exercise training in HF subjects improves skeletal muscle mitochondrial OX PHOS capacity and subject activity levels. Exercise training additionally increases activity of the mitochondrial regulatory deacetylase sirtuin enzymes SIRT1 and SIRT3, in parallel with improved skeletal muscle OX PHOS capacity. At the same time HF-associated disruption in skeletal muscle metabolic function activates skeletal muscle cytokine production. These inflammatory programs, in turn, are proposed to contribute towards impaired functional capacity in HF. Interestingly, and mirroring improved OX PHOS following exercise programs in HF studies, exercise training similarly reduces skeletal muscle inflammatory effects.

Biochemical and bioenergetic consequences of impaired mitochondrial OX PHOS leads to decreased NAD+ levels, which exacerbate mitochondrial dysfunction by inactivating the NAD+ dependent sirtuin enzymes. Experimental studies using NAD+ precursors to increase NAD+ production have been shown to normalize NADH/NAD+ ratios and activate Sirtuin enzymes, resulting in enhanced OX PHOS with beneficial effects in numerous systems including skeletal muscle and in the blunting of inflammation.

In this pilot study we will directly assess the effect of the NAD+ precursor, nicotinamide riboside (NR) on skeletal muscle mitochondrial OX PHOS in HF subjects using: skeletal muscle Nuclear magnetic resonance (NMR) spectroscopy assessment of the rate of high energy phosphate recovery in response to submaximal exercise; assessment of the effect of NR on functional capacity using cardiopulmonary exercise testing (CPET) to determine VO(2max) and anaerobic threshold; evaluation of the NR effect on serum metabolomics at rest and in response to CPET; and by measuring circulating cytokine levels pre- and post- NR administration. These studies would enable a more comprehensive assessment of the role for NR supplementation on skeletal muscle mitochondrial function in subjects with systolic HF