Dihydronicotinamide riboside is a potent NAD + concentration enhancer in vitro and in vivo

Abstract

NAD+, traditionally known as a redox cofactor, is now considered a key modulator in many health conditions. NAD+ levels steadily decline with age, triggering age-associated pathophysiologies such as obesity, Type II diabetes mellitus, metabolic syndrome, and neurodegenerative diseases. On the other hand, increasing NAD+ levels provides resistant to obesity-induced metabolic syndrome, glucose intolerance and fatty liver disease, as well as neurodegenerative disorders such as Alzheimer's, Parkinson's and Huntington's diseases, making it a desirable target for therapy developments. Interests in pharmacological agents capable of increasing cellular NAD+ concentrations have stimulated investigations of nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN). Both NR and NMN require high doses for in vivo effect, with maximal increase of NAD+ by 2 fold. The limitations on existing NAD+ enhancers encouraged the exploration of new generation of NAD+ enhancing compounds with stronger effects. Here we synthesized dihydronicotinamide riboside (NRH) and discovered that NRH is a very potent NAD+ concentration enhancing agent, which increases NAD+ levels by 2.5-10 fold over control values in different mammalian cell lines and acts within as little as 1 hr after administration. At equivalent concentrations, NRH provides far greater NAD+ increases when compared to NR and NMN. NRH also provides substantial NAD+ increases in tissues when administered by intraperitoneal injection to C57/BL6 mice. NRH increases NAD+/NADH ratio in cultured cells and in liver, but without apparent toxicity as measured by cell counts, lactate levels and expressions of apoptotic markers. In addition, cells treated with NRH are resistant to cell death caused by NAD+-depleting agents such as hydrogen peroxide and methyl methanesulfonate. Studies to identify its biochemical mechanism of action showed that it does not inhibit NAD+ consumption suggesting it acts as a biochemical precursor to NAD+, also without utilizing the nicotinamide salvage pathway. Protein lysates extracted from mammalian cells possess an ATP-dependent kinase activity which efficiently converts NRH to the compound NMNH, but independent of NR kinases, suggesting NR is not an intermediate in the NRH-induced NAD+ synthesis pathway. These findings identify a putative new metabolic pathway to NAD+, and an extremely potent pharmacologic agent for NAD+ concentration enhancement in cells and tissues.