Long-Term Administration of Nicotinamide Mononucleotide Mitigates Age-Associated Physiological Decline in Mice.

NAD+ availability decreases with age and in certain disease conditions. Nicotinamide mononucleotide (NMN), a key NAD+ intermediate, has been shown to enhance NAD+ biosynthesis and ameliorate various pathologies in mouse disease models. In this study, we conducted a 12-month-long NMN administration to regular chow-fed wild-type C57BL/6N mice during their normal aging. Orally administered NMN was quickly utilized to synthesize NAD+ in tissues. Remarkably, NMN effectively mitigates age-associated physiological decline in mice. Without any obvious toxicity or deleterious effects, NMN suppressed age-associated body weight gain, enhanced energy metabolism, promoted physical activity, improved insulin sensitivity and plasma lipid profile, and ameliorated eye function and other pathophysiologies. Consistent with these phenotypes, NMN prevented age-associated gene expression changes in key metabolic organs and enhanced mitochondrial oxidative metabolism and mitonuclear protein imbalance in skeletal muscle. These effects of NMN highlight the preventive and therapeutic potential of NAD+ intermediates as effective anti-aging interventions in humans.

Age-associated loss of Sirt1-mediated enhancement of glucose-stimulated insulin secretion in beta cell-specific Sirt1-overexpressing (BESTO) mice.

The Sir2 (silent information regulator 2) family of NAD-dependent deacetylases regulates aging and longevity across a wide variety of organisms, including yeast, worms, and flies. In mammals, the Sir2 ortholog Sirt1 promotes fat mobilization, fatty acid oxidation, glucose production, and insulin secretion in response to nutrient availability. We previously reported that an increased dosage of Sirt1 in pancreatic beta cells enhances glucose-stimulated insulin secretion (GSIS) and improves glucose tolerance in beta cell-specific Sirt1-overexpressing (BESTO) transgenic mice at 3 and 8 months of age. Here, we report that as this same cohort of BESTO mice reaches 18-24 months of age, the GSIS regulated by Sirt1 through repression of Ucp2 is blunted. Increased body weight and hyperlipidemia alone, which are observed in aged males and also induced by a Western-style high-fat diet, are not enough to abolish the positive effects of Sirt1 on beta cell function. Interestingly, plasma levels of nicotinamide mononucleotide (NMN), an important metabolite for the maintenance of normal NAD biosynthesis and GSIS in beta cells, are significantly reduced in aged BESTO mice. Furthermore, NMN administration restores enhanced GSIS and improved glucose tolerance in the aged BESTO females, suggesting that Sirt1 activity decreases with advanced age due to a decline in systemic NAD biosynthesis. These findings provide insight into the age-dependent regulation of Sirt1 activity and suggest that enhancement of systemic NAD biosynthesis and Sirt1 activity in tissues such as beta cells may be an effective therapeutic intervention for age-associated metabolic disorders such as type 2 diabetes.

Nampt/PBEF/Visfatin regulates insulin secretion in beta cells as a systemic NAD biosynthetic enzyme.

Intracellular nicotinamide phosphoribosyltransferase (iNampt) is an essential enzyme in the NAD biosynthetic pathway. An extracellular form of this protein (eNampt) has been reported to act as a cytokine named PBEF or an insulin-mimetic hormone named visfatin, but its physiological relevance remains controversial. Here we show that eNampt does not exert insulin-mimetic effects in vitro or in vivo but rather exhibits robust NAD biosynthetic activity. Haplodeficiency and chemical inhibition of Nampt cause defects in NAD biosynthesis and glucose-stimulated insulin secretion in pancreatic islets in vivo and in vitro. These defects are corrected by administration of nicotinamide mononucleotide (NMN), a product of the Nampt reaction. A high concentration of NMN is present in mouse plasma, and plasma eNampt and NMN levels are reduced in Nampt heterozygous females. Our results demonstrate that Nampt-mediated systemic NAD biosynthesis is critical for beta cell function, suggesting a vital framework for the regulation of glucose homeostasis.

Effects of chronic manganese toxicity on tissue levels and urinary excretion of nicotinamide nucleotides in rats.

Male rats were exposed to manganese sulphate i.p. daily for a period of four weeks to see its effects on tissue levels and urinary excretion of total nicotinamide nucleotides (TNN). Increased levels of TNN were observed in blood and brain while the levels were found to be decreased in liver. There was a progressive increase in the excretion of TNN during the experimental period. TNN levels in blood and urine might serve as useful biological indicators of Mn toxicity.

Nucleotide synthesis in human erythrocyte: correlations between purines and pyridines.

The regulation of erythrocyte synthesis of nicotinate and adenine nucleotides has been investigated. Some effectors of the two committed enzymes, nicotinate- and adenine phosphoribosyltransferases, have been identified on crude lysates and on partially purified preparations of the former. Enzyme characteristics have been correlated with the nucleotide synthesis achieved in intact cells incubated in suitable mediums containing (14-C)-nicotinate or adenine. Inorganic phosphate, Mg ions and adenine nucleotides proved to be important effectors of pyridine synthesis, whose products, in turn, do not influence adenine nucleotide production. The production of pyridine nucleotides is little lower than that of adenine nucleotides in intact cells, even if adenine phosphoribosyl-transferase activity appears to be much more limited, inside the cell, than nicotinate phosphoribosyltransferase.

Pyridine nucleotide synthesis in human blood--effect of leucine, alpha-ketoisocaproic acid and ketone bodies.

The effects of L-leucine and its metabolites on pyridine nucleotide synthesis were investigated in human blood. After 30 min-incubation 40% of the added (carboxyl-14C)-nicotinic acid was incorporated into pyridine nucleotides, most of which was nicotinic acid mononucleotide. Leucine and alpha-ketoisocaproic acid reduced pyridine nucleotide synthesis by 40% and 15%, respectively at 1 mM level. Ketone bodies were without effect. The results were different from those observed in rat hepatocytes [O. Yamada et al.: Internat. J. Vitam. Nutr. Res. 53, 184 (1983)], in which ketone bodies and the compounds metabolized to ketone bodies were inhibitory to the NAD biosynthesis.

Pyridine nucleotide metabolism in the erythrocyte of South African blacks with primary hepatoma.

Erthrocytes from African blacks with primary hepatoma were incubated with physiological amounts (1.64 microM) of nicotinamide-14C (NM-14C) and it was found that these erythrocytes could synthesize NAD from NM. After 3-hr incubation with NM-14C, a large percentage of the 14C was found in NMN, nicotinamide riboside (NR) and NAD, but was undetectable in nicotinic acid nucleotides (NAMN and NAAD). This suggested that the NAD synthesized from NM was not through the Preiss-Handler pathway. After 6-plus hr incubation, the 14C found in NAMN and NAAD suggested the NAD synthesized was being broken down and reutilized through Preiss-Handler pathway for synthesis of NAD. This reutilization pathway was confirmed by incubating nicotinic acid-14C (NA-14C) with erythrocytes. Apparently the metabolites from the breakdown of NAD were deaminated. The metabolism of NM-14C was slower than NA-14C. However, after 24 hr incubation with NM-14C, 72.26% of 14C was found in NAD. A high percentage of 14C in NR at the initial incubation and a later drop suggested that NR was another intermediate in the pathway.