There has been much interest in NAD+ precursors following the 2013 paper by Dr David Sinclair et al. entitled "Declining NAD+ Induces a Pseudohypoxic State Disrupting Nuclear-Mitochondrial Communication during Aging". For those that missed it the highlights in this article were that:
- Aging leads to a specific decline in mitochondrially encoded genes
- Nuclear NAD+ levels regulate mitochondirally encoded genes
- SIRT1 can regulate mitochodria via a PGC-1 alpha/beta independent pathway: HIF-1 alpha stabilization via VHL and consequent activation of TFAM via c-Myc
- AMPK acts as a switch between the PGC-1 aplha dependent and independent pathways
- Increasing NAD+ levels restores mitochondrial homeostasis through the SIRT1-HIF-1alpha-c-Myc pathway
- Old mice receiving the NAD+ precursor nicotinamide mononucleotide ('NMN') showed a reversal of impaired insulin signalling and insulin stimulated glucose uptake, muscle atrophy, and inflammation after 1 week. Muscle strength was not improved, but they hypothesized that a longer treatment could potentially reverse whole-organism aging.
The Conversion of Precursors into NAD+
As a result of the previous article and many others, NAD+ precursors have become a focus of attention. There are many different NAD+ precursors, these include:
- Nicotinamide ('Nam'): the most commonly found form of vitamin B3, while it is normally converted to NAD+ in vivo, the enzyme responsible for this (NAMPT) is easily saturated and its functionality declines with age. It has also been reported to act as a SIRT1 inhibitor. Nam > NMN (via NAMPT) > NAD+ (via NMNAT1-3) > Nam (via NAD+ consuming enzymes)
- Nicotinic Acid ('NA') - is also known as niacin, this NAD+ precursor is not subject to NAMPT and instead utilizes the Preiss-Handler pathway. NA > NaMN (via NaPRT1) > NaAD+ (via NMNAT1-3) > NAD+ (via glutamine dependent NaDSYN1) > Nam (via NAD+ consuming enzymes)
- Nicotinamide Riboside ('NR') - this more recently discovered NAD+ precursor is currently available to consumers as 'Niagen' and at the time of writing this is seems like a feasible, yet comparably expensive, NAD+ precursor. NR > NMN (via NRK1.2) > NAD+ (via NMNAT1-3) > Nam (via NAD+ consuming enzymes)
- Nicotinamide Mononucleotide ('NMN') - this is the precursor which was used by Dr Sinclair et al. in 2013, it is at the time of posting extremely expensive and not available to consumers. NMN > NAD+ (via NMNAT1-3) > Nam (via NAD+ consuming enzymes) [although, apparently it must be converted to Nr before entering the cell?]
See the Following Diagram:
[...]
Intracellular NAD+ metabolism in humans. Tryptophan (Trp), nicotinic acid (Na), nicotinamide (Nam), nicotinamide riboside (NR),and nicotinic acid riboside (NaR) are utilized through distinct metabolic pathways to form NAD+.Tryptophan (Trp) is converted to NAD+ in the eight-step de novo pathway through quinolinate (Quin), which is converted to nicotinic acid mononucleotide (NaMN) by quinolinate phosphoribosyltransferase (QPRT). NaMN is then adenylylated by the products of the NMNAT1-3 genes toform nicotinic acid adenine dinucleotide (NaAD+), which is converted to NAD+ by glutamine-dependent NAD+ synthetase (NADSYN1).Nicotinic acid (Na) is utilized in the three-step Preiss-Handler pathway. Nicotinic acid phosphoribosyltransferase (NAPRT1) forms NaMN by addition of the 5-phosphoribose group from 5-phosphoribosyl-1-pyrophosphate to Na. In two steps shared with the de novo pathway, NaMN is then converted to NaAD+ and NAD+ via activity of NMNAT1-3 and NADSYN1.Nicotinamide (Nam) is utilized via nicotinamide phosphoribosyltransferase (Nampt), encoded by the PBEF1 (NAMPT) gene. Nampt catalyzes the addition of a phosphoribose moiety onto Nam to form nicotinamide mononucleotide (NMN). NMN is subsequently converted to NAD+ by the products of NMNAT1-3. Nam is produced by NAD+-consuming enzymes.Nicotinamide riboside (NR) is phosphorylated by the products of nicotinamide riboside kinase genes (NRK1 and NRK2) to form NMN, which is converted to NAD+ by NMNAT1-3. NR may also be utilized by the product of the NP gene, purine nucleoside phosphorylase, for subsequent Nam salvage.From Bogan, K. L., & Brenner, C. (2008). Nicotinic acid, nicotinamide, and nicotinamide riboside: a molecular evaluation of NAD+ precursor vitamins in human nutrition. Annu. Rev. Nutr., 28, 115-130.
Which Precursors are Interesting?
NMN is not currently commercially available and does not seem to be very competitive with NR and NA in this study. Nam may be unsuitable for older people because of declining NAMPT levels with age and has also bee shown to inhibit SIRT1. That leaves NA and NR.
Darryl wrote this concise post, which to some extent sheds more light on this question:
Nicotinamide (Nam) and nicotinamide riboside (NR) differ only through a ribosylation on NR.
Its difficult to raise NAD+ levels with Nam as the enzyme Nampt is saturated at low concentration. Moreover, Nam itself functions as a feedback inhibitor of sirtuins and PARPs, but this suppression of NAD+ consumption has benefits in ischemia-reperfusion injury, like stroke.
Nicotinic acid utilizes the Preiss-Handler pathway, which isn't subject to the Nampt bottleneck. High doses cause flushing which many dislike, but the same mechanism has antiinflammatory benefits.
NMN is the subject of Sinclair's study. While an intermediate for Nam and NR, it only can enter cells as NR.
NR isn't rate-limited by NAMPT, and doesn't cause flushing, but only some tissues (in animals) express NR kinases to utilize it.
[...]From Bogan, K. L., & Brenner, C. (2008). Nicotinic acid, nicotinamide, and nicotinamide riboside: a molecular evaluation of NAD+ precursor vitamins in human nutrition. Annu. Rev. Nutr., 28, 115-130.
Is NA Converted to Nam in vivo?
Posts in this forum stating that NA is inferior to NR because it is "converted to Nam" in vivo are misleading. It must be said that all NAD+ precursors are converted into Nam in vivo because this is the work of NAD+ consuming enzymes. Take a look at the above diagram; the three step Preiss-Handler pathway converts NA into NAD+ and only then, once that NAD+ is used up, is Nam formed as a product. Even NMN ends up as Nam after it is converted to NAD+ and utilized by NAD+ consuming enzymes.
NR on the other hand can indeed be converted into Nam before even making it to NAD+. The exact mechanism by which this occurs and how much is converted into Nam instead of NMN needs further research.
NA vs NR
In terms of NAD+ yield, this study found that in rats (see Figure 1) NA surpasses NR in liver tissues and the two produce roughly the same amount in the muscle tissues. NA is currently much cheaper than NR: Na costs about $5.00 for 100 x 250mg capsules, whereas NR costs about $47.00 for 30 x 250mg. The most widely perceived disadvantage of NA is that it causes a vasodilatory GPR109A receptor 'flush response'. Once again I feel obliged to refer to Darryl, who made these informative posts covering this 'side effect', which comes with benefits too:
Among the NAD+ precursors, nicotinic acid additionally has anti-inflammatory effects through GPR109A activation, independent of its lipid modifying effects. As the other precursors lack this activity, they may not be as effective as anti-inflammatories.
Plaisance, Eric P., et al. "Niacin stimulates adiponectin secretion through the GPR109A receptor." American Journal of Physiology-Endocrinology and Metabolism 296.3 (2009): E549-E558.
Digby, Janet E., et al. "Anti-inflammatory effects of nicotinic acid in adipocytes demonstrated by suppression of fractalkine, RANTES, and MCP-1 and upregulation of adiponectin." Atherosclerosis 209.1 (2010): 89-95.
Lukasova, Martina, et al. "Nicotinic acid inhibits progression of atherosclerosis in mice through its receptor GPR109A expressed by immune cells." The Journal of clinical investigation 121.3 (2011): 1163-1173.
Digby, Janet E., et al. "Anti-inflammatory effects of nicotinic acid in human monocytes are mediated by GPR109A dependent mechanisms."Arteriosclerosis, thrombosis, and vascular biology 32.3 (2012): 669-676.
Sia, Yanhong, et al. "Niacin inhibits vascular inflammation via down-regulating nuclear transcription factor-κB signaling pathway." (2014)
[...]
Maybe its not GPR109A activation, after all.
Ma, L., Lee, B. H., Mao, R., Cai, A., Jia, Y., Clifton, H., ... & Zheng, J. (2014). Nicotinic Acid Activates the Capsaicin Receptor TRPV1 Potential Mechanism for Cutaneous Flushing. Arteriosclerosis, thrombosis, and vascular biology,34(6), 1272-1280.
We observed that the nicotinic acid–induced increase in blood flow was substantially reduced in Trpv1–/– knockout mice, indicating involvement of the channel in flushing response. Using exogenously expressed TRPV1, we confirmed that nicotinic acid at submillimolar to millimolar concentrations directly and potently activates TRPV1 from the intracellular side. Binding of nicotinic acid to TRPV1 lowers its activation threshold for heat, causing channel opening at physiological temperatures. The activation of TRPV1 by voltage or ligands (capsaicin and 2-aminoethoxydiphenyl borate) is also potentiated by nicotinic acid. We further demonstrated that nicotinic acid does not compete directly with capsaicin but may activate TRPV1 through the 2-aminoethoxydiphenyl borate activation pathway. Using live-cell fluorescence imaging, we observed that nicotinic acid can quickly enter the cell through a transportermediated pathway to activate TRPV1.
Safety of Nicotinic Acid
I must stress that I am not qualified to give medical advice, this is for personal study purposes only and does not constitute medical advice. Everyone considering to take any of these substances does so at their own risk and should get independent medical advice before administering; especially when supplementing over longer periods and at high doses.
It seems clear that the extended release formulations of NA have been responsible for most cases of liver toxicity. Some physician like Dr. Abram Hoffer, who pioneered Niacin treatments for schizophrenia and TB, routinely prescribed divided (immediate release) doses of 3g / day (Anyone interested in reading more about this should see: Niacin: the Real Story by Dr. Abram Hoffer et al.). Even the immediate release formulation can affect each individual differently and it seems that with some people doses of above 1500mg can lead to health issues. These include, but are not limited to: reversible liver test abnormalities, blurry vision issues and mild glucose increases.
These articles address some of the the safety issues with Niacin and may be interesting to read:
- Liver Toxicity: Niacin
- Guyton, J. R., & Bays, H. E. (2007). Safety considerations with niacin therapy.The American journal of cardiology, 99(6), S22-S31.
- McKenney, J. M., Proctor, J. D., Harris, S., & Chinchili, V. M. (1994). A comparison of the efficacy and toxic effects of sustained-vs immediate-release niacin in hypercholesterolemic patients. Jama, 271(9), 672-677.
Remember, only a doctor can advise you on the side effects and safety!
My Own Experiences
Personally, I have been taking 1.5g IR NA / day for the past 2 months. I take 1g upon rising and another 500mg in the evening. I actually like the flush sensation and compare the feeling to being in the sauna. I think I have seen some improvement in energy, cognitive functions and endurance; but have not tested these.
I also like to take it with NAC since my research seems to indicate that this may attenuate the increase in homocysteine levels brought on by niacin. I have considered adding glutamine (NA > NAD+ involves glutamine-dependent NAD+ synthetase (NADSYN1)) and arginine, the author of this paper believes that this will increase efficacy. (note: I do not suffer for schizophrenia, I merely found the paper during research).
I am also interested in using this for neuro-protection from adderal induced DA decline (possibly via dopamine oxidation). I may start adderall soon if it's prescribed and will update with results in this thread and here.
Edited by Phoenicis, 21 July 2014 - 06:43 AM.