Nicotinamide Riboside Enhances In Vitro Betaadrenergic Brown Adipose Tissue Activity in Humans

Context: Elevating nicotinamide adenine dinucleotide ([NAD.sup.+]) levels systemically improves metabolic health, which can be accomplished via nicotinamide riboside (NR). Previously, it was demonstrated that NR supplementation in high-fat-diet (HFD)-fed mice decreased weight gain, normalized glucose metabolism, and enhanced cold tolerance. Objective: Because brown adipose tissue (BAT) is a major source of thermogenesis, we hypothesize that NR stimulates BAT in mice and humans. Design and intervention. HFD-fed C56BL/6J mice were supplemented with 400 mg/kg/day NR for 4 weeks and subsequently exposed to cold. In vitro primary adipocytes derived from human BAT biopsies were pretreated with 50 [micro]M or 500 [micro]M NR before measuring mitochondrial uncoupling. Human volunteers (45-65 years; body mass index, 27-35 kg/[m.sup.2]) were supplemented with 1000 mg/day NR for 6 weeks to determine whether BAT activity increased, as measured by [18F]FDG uptake via positron emission tomography-computed tomography (randomized, double blinded, placebo-controlled, crossover study with NR supplementation). Results: NR supplementation in HFD-fed mice decreased adipocyte cell size in BAT. Cold exposure further decreased adipocyte cell size on top of that achieved by NR alone independent of ex vivo lipolysis. In adipocytes derived from human BAT, NR enhanced in vitro norepinephrine-stimulated mitochondrial uncoupling. However, NR supplementation in human volunteers did not alter BAT activity or cold-induced thermogenesis. Conclusions: NR stimulates in vitro human BAT but not in vivo BAT in humans. Our research demonstrates the need for further translational research to better understand the differences in [NAD.sup.+] metabolism in mouse and human. Key Words: NR; brown adipose tissue; mitochondria