Abstract
Nicotinamide adenine dinucleotide (NAD+) is an essential pyridine nucleotide that serves as an electron carrier in cellular metabolism and plays a crucial role in the maintenance of balanced redox homeostasis. Quantification of NAD+:NADH and NADP+:NADPH ratios are pivotal to a wide variety of cellular processes, including intracellular secondary messenger signaling by CD38 glycohydrolases, DNA repair by poly(adenosine diphosphate ribose) polymerase (PARP), epigenetic regulation of gene expression by NAD-dependent histone deacetylase enzymes known as sirtuins, and regulation of the oxidative pentose phosphate pathway. We quantified changes in the NAD+ metabolome in plasma samples collected from consenting healthy human subjects across a wide age range (20–87 years) using liquid chromatography coupled to tandem mass spectrometry. Our data show a significant decline in the plasma levels of NAD+, NADP+, and other important metabolites such as nicotinic acid adenine dinucleotide (NAAD) with age. However, an age-related increase in the reduced form of NAD+ and NADP+—NADH and NADPH—and nicotinamide (NAM), N-methyl-nicotinamide (MeNAM), and the products of adenosine diphosphoribosylation, including adenosine diphosphate ribose (ADPR) was also reported. Whereas, plasma levels of nicotinic acid (NA), nicotinamide mononucleotide (NMN), and nicotinic acid mononucleotide (NAMN) showed no statistically significant changes across age groups. Taken together, our data cumulatively suggest that age-related impairments are associated with corresponding alterations in the extracellular plasma NAD+ metabolome. Our future research will seek to elucidate the role of modulating NAD+ metabolites in the treatment and prevention of age-related diseases.
Highlights
In the last decade, there has been growing interest in the role of redox active nucleotides in the metabolism.[1]
Quantification of NAD+:NADH and NADP+:NADPH ratios are pivotal to a wide variety of cellular processes, including intracellular secondary messenger signaling by CD38 glycohydrolases, DNA repair by poly(adenosine diphosphate ribose) polymerase (PARP), epigenetic regulation of gene expression by NAD-dependent histone deacetylase enzymes known as sirtuins, and regulation of the oxidative pentose phosphate pathway
nicotinic acid adenine dinucleotide (NAAD) trended a negative association with age ( p = 0.054), while NADH, nicotinamide mononucleotide (NMN), nicotinic acid mononucleotide (NAMN), and nicotinic acid (NA) levels did not show significant changes with age ( p > 0.05)
Summary
There has been growing interest in the role of redox active nucleotides in the metabolism.[1]. NAD+ represents one of the most important coenzymes in the hydride transfer reactions.[6] NAD+ is the precursor of the pyridine nucleotide family, including NADH, NADP+, and NADPH, and is the end product of tryptophan metabolism via the kynurenine pathway.[7] It has been well established that NAD+ is a substrate for major dehydrogenase enzymes involved in nutrient catabolism, including alcohol and lactate dehydrogenase reactions.[8] As well, NADH, which is the reduced form of NAD+, preferentially provides electrons to power mitochondrial oxidative phosphorylation.
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