The Plasma NAD+ Metabolome is Dysregulated in ‘Normal’ Ageing
Rejuvenation Res. 2018 Aug 19. doi: 10.1089/rej.2018.2077. [Epub ahead of print]
Mr. James Clement, Mr. Matthew Wong, Dr. Anne Poljak, Prof. Perminder Sachdev, Dr. Nady Braidy
We quantified changes in the NAD+ metabolome in plasma samples collected from consenting healthy human subjects across a wide age range (20-85 years [9-10 subjects in age groups 20-40, 41-60, and 60+]) using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS).
Our data shows a significant decline in the plasma levels of NAD+, NADP+, and other important metabolites including nicotinamide mononucleotide (NMN) and nicotinic acid adenine dinucleotide (NAAD) with age. ... NAD had the steepest age decrease, averaging 4% SD units decline per year, ...
However, an age-related increase in ... NADH and NADPH - and nicotinamide (NAM), N-methyl-nicotinamide (MeNAM), and the products of adenosine diphosphoribosylation, including ADP-ribose (ADPR) was also reported. ... MeNAM and NADPH had the average increases of 2.8 and 2.7% SD units per year, respectively. Individual models explained up to 86% of the variance in metabolite levels with age. ...
Figure 1. Scatterplots of NAD+ metabolites normalised abundance across age groups
Figure 2. Boxplots of NAD+ metabolite abundances across age groups.
In mammalian cells, NAM is methylated by the enzyme, nicotinamide N-methyltransferase (NNMT) to form N-methyl-nicotinamide (MeNAM), which is further metabolised to Nmethyl- 2-pyridone-5-carboxamide (2PY) [66]. ... One study showed that knockdown to NNMT protected against high fat-diet induced obesity. ... Our data also shows that the level of MeNAM was correlated with BMI (Supplementary table 2), and MeNAM has been strongly associated with obesity and diabetes [70]. Therefore, a higher level of MeNAM is likely to predispose individuals to a greater risk of obesity or insulin resistance in adulthood. Increased NNMT activity and elevations in MeNAM and 2-PY levels have also been reported in type-2 diabetes [71]. [MeNAM has also been implicated in Parkinson's disease,(1,2) and coronary artery disease.(3). -MR]. Increased NNMT activity in tumor cells has been shown to impair polyamine flux [72]. Therefore, increased NNMT activity and upregulated levels of MeNAM can alter individual methylation capacity, with epigenetic consequences.
Recently, it has been shown that metabolites of NAM may serve as uremic toxins at high amounts [73]. These findings originated from findings of interventional trials using NAM to manage end-stage renal disease [74]. In the context of uremia, increased plasma levels of MeNAM, as we have reported, may inhibit NAD-dependent processes. Our current findings can there provide additional mechanisms to explain poor outcomes in the elderly, and the potential effects of impaired NAD+ anabolism on the epigenome due to potentially reduced methylation capacity in the aged individuals. ...
No significant differences were reported across age for nicotinic acid (NA) and nicotinic acid mononucleotide (NAMN).
Taken together, our data cumulatively suggests that age-related impairments may also be associated with alterations in the extracellular plasma NAD+ metabolome.
PMID: 30124109 DOI:10.1089/rej.2018.2077
It's notable that both NAM and MeNAM rise with age: NAM presumably as a result of increased consumption (contributing to the decline in NAD+ and NAD:NADH), and MeNAM due to some combination of the sheer rise in NAM requiring greater engagement of its disposal metabolism, and a decline in methylation capacity. Both of these are also elevated at high levels and longer durations of NAD+ precursor supplementation, with NAM ≥ NR > NA for MeNAM and NR > NAM > NA for NAM (eg. Figure 4, Trammel & Brenner PMID 27721479). In this respect, then, higher dose and/or uninterrupted use of NAD+ precursors actually exacerbates rather than opposes age-related changes in the NAD+ metabolome.
References
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