An In-Depth Discussion
Last time we briefly reviewed NAD, how it’s made, and the novel compound nicotinamide riboside (NR). As discussed, NAD plays a huge role in energy production and the health of cells, especially the mitochondria. What you need to know, which is very important, is that all seven of the sirtuin enzymes need NAD in order for them to do the many good things they do in the body. The sirtuin enzymes consume and destroy NAD in the process of deacetylating various proteins.
So, in order to fully grasp the benefit of supplementing with NR (NiaCel), we really must review the sirtuins and gain exposure to other NAD+ dependent processes. If I were to ask you to tell me about sirtuins, you’d likely answer that they extend the lifespan of simpler organisms or improve some profiles for fat mice. And yes, that would be true, but how? How does that relate to us as humans? What is out there for current data? Lastly, how does NR turn the promise of resveratrol into resveratrol on steroids?
Resveratrol is a plant compound that is produced under times of stress; it’s a self-protective mechanism. Humans and other higher organisms ingest these compounds, and through a xenohormetic relationship, they essentially serve as an early warning device; for example, of impending famine. This is nutrigenomics. Of the natural Sirt1-activating compounds, resveratrol is still the most potent, enhancing Sirt1-mediated deacetylation by 8-fold. Resveratrol works by affecting the Km (substrate affinity) and Vmax (maximum velocity at which the reaction occurs) of a wide variety of key deacetylase enzymes for both histone and non-histone proteins, which results in resveratrol being the true “master switch of metabolism.” Seven mammalian sirtuin enzymes have been identified.
- Sirt 1 primarily in the nucleus, also in the cytosol affects metabolism, lipids, inflammation, stress response, cell cycling, neurogenesis, hormones, DNA repair, telomere maintenance, circadian
- Sirt 2 primarily in cytosol, also in nucleus cell cycling
- Sirt 3 primarily in mitochondria, also nucleus thermogenesis, ATP production
- Sirt 4 mitochondria, ATP production, insulin
- Sirt 5 mitochondria, urea cycle
- Sirt 6 nucleus, DNA stability and repair, metabolism
- Sirt 7 nucleolus, rDNA transcription
Sirt 1 is the most researched, but we’ll briefly touch on some of the others, as well as other NAD+ degrading enzymes.
The following are the key targets of the sirtuins:
- Sirt 1
- Histones 1, 3, and 4 – both work in a capacity to protect DNA in response to damage.
- Ku70 and 80 – this non-histone protein helps to maintain telomere length. During periods of oxidative stress Ku70 is a pro-apoptotic factor down-regulated by sirt1.
- PGC-1alpha – Upon deacetylation, it induces expression of genes in various tissues for gluconeogenesis, fatty acid oxidation, UCP1 and 2, catalase and MnSOD, repression of glycolysis, and mitochondrial biogenesis, whose end results are improved insulin sensitivity, lowered body weight, reduction in fat deposits, oxygen detoxification, and increased endurance. In fact, there have been 13 different sites on this all-important metabolic regulator identified that are sensitive to Sirt1 deacetylation. As a part of PGC-1apha’s role in glucose metabolism, up-regulation of PGC-1alpha has been shown to be beneficial in dementia models, and additionally, glucose metabolism (which is impacted substantially by PGC-1alpha) if the brain is impaired in cognitive impairment and early stage Alzheimer’s.
- PPAR gamma – Repression of PPAR gamma, through deacetylation, which is up-regulated by resveratrol results in repression of fat storage, and increased lipolysis and free fatty acid mobilization.
- UCP2 – This member of a family of inner mitochondrial proteins is capable of modulating and driving the ATP synthase pathway; however, its exact role in mitochondrial function is not fully understood. It is thought that the Sirt1-mediated decrease in UCP2 expression impedes H+ leakage and allows a more efficient coupling of electron transport with the ATP production. UCP2 has been implicated in thermogenesis, lipid metabolism, ROS regulation, diabetes, aging, and diseases of the immunological, circulatory, and neurological systems. For example, in a diabetes model, deacetylation of UCP2 resulted in suppression of its expression, the result being an improvement in insulin secretion from the beta cells, and improved survivability. Data shows NR administration decreases UCP2 mRNA, and knocking down (chemically preventing) Sirt1 prevented the action of NR on UCP2 showing that NR affects UCP2 through Sirt1. UCP2 is down-regulated via the Sirt1 pathway, which allows beta cells to better secrete insulin in response to glucose, yet blunt chronic high levels in insulin in caloric restriction. This makes sense as insulin is anabolic, and starvation is catabolic.
- eNOS – Sirt 1 deacetylates endothelial nitric oxide synthase, resulting in improved NO activity. The increased expression might help to overcome the inactivation of NO by the oxidative stress induced by age and obesity. Sirt1 activation seems to inhibit macrophage TNF release in the vasculature likely through NFKB modulation.
- LXR – The liver X receptor is a nuclear transcription factor that controls lipid homeostasis. Upon deacetylation LXR transcribes a number of proteins that positively impact serum lipids. Of note, flushing niacin does not impact serum lipids due to the flush response. The Gpr109A protein responsible for the flush is not present in the liver as it is in the skin. Niacin seems to impact serum lipids by deacetylating the liver X receptor (LXR), in a Sirt1 dependent manner via its conversion to NAD+.
- SREBP1 – This protein regulates triglyceride synthesis. Upon deacetylation its expression is down-regulated in the liver, resulting in lower serum triglycerides, and lower hepatic fat, impacting NAFLD.
- NFKB – We are familiar with NFKB. It’s atop the inflammatory cascade. Residing in the cytoplasm, this protein, this master regulator of inflammation, is active on cellular insult, the end result being the up-regulation of inflammatory genes. Deacetylation of NFKB results in a blunting of its inflammatory potential. If this sounds familiar, this is essentially how curcumin works, and curcumin alone has thousands of papers and several synthetic derivatives in clinical trials. In addition, Sirt1 activation significantly decreases neuronal cell death induced by beta amyloid peptides through inhibition of NFKB signaling; in other words, reduced inflammation associated with the plaque formation, likely from in part glucose hypometabolism.
- FOXO – The forkhead box proteins are a family of transcription factors that play important roles in regulating the expression of genes involved in cell growth, proliferation, oxidation, differentiation, and longevity, and inflammation/immune and neurological function. Data shows NR positively effects the FOXO1 target SOD2, and this benefit was prevented by knockdown of either FOXO1 or Sirt1 (canto), again showing NR works through Sirt1.
- AMPK – is an enzyme that plays a role in cellular energy homeostasis. It is expressed in a number of tissues, including the liver, brain, and skeletal muscle. The net effect of AMPK activation is stimulation of hepatic fatty acid oxidation and ketogenesis, inhibition of cholesterol synthesis, lipogenesis, and triglyceride synthesis, stimulation of skeletal muscle fatty acid oxidation and muscle glucose uptake, and modulation of insulin secretion by pancreatic beta-cells. The energy-sensing capability of AMPK can be attributed to its ability to detect and react to fluctuations in the AMP:ATP ratio that take place during rest and exercise.
Sounds a bit like PGC-1alpha. In fact, resveratrol may also stimulate PGC-1alpha indirectly through AMPK. AMPK activation by resveratrol is both independent and mediated by Sirt1 deacetylation. Contrarily, AMPK can also stimulate Sirt1 activity by increasing cellular NAD+ levels, resulting in the consequent deacetylation of PGC-1alpha and FOXOs. In fact, the conventional standards of care for metabolic disorders – metformin, exercise, and thiazolidinediones – impact AMPK
- Sirt3 – We’ll just touch on Sirt3 briefly. Data shows NR positively affects Sirt3 targets, and that this affect was abolished in Sirt3 knockout mice, and in Sirt3 null mice no effect was seen. These results show that NR triggers Sirt3 activity, likely through increased NAD+ concentrations, the result being all the mitochondrial benefits associated with calorie restriction or exercise. Interestingly, in a human study looking at longevity in males, those with the G477T genotype on Sirt3 were found to have decreased survival; whereas, those having the T447T had increased.
- Sirt6 – It is interesting to note that Sirt6 null mice die prematurely of many of the same pathologies found in elderly humans. Its impact on DNA integrity is thought to play an essential role in aging organs.
- Sirt7 – This is the only sirtuin located in the nucleolus, where transcription occurs for ribosomal biogenesis as the likely primary task. It has been suggested that Sirt7 regulates ribosomal DNA transcription by sensing cellular NAD+ levels and that diet-induced changes in NAD+/NADH ratio might modulate Sirt7 to link the energy status with ribosomal RNA synthesis and ribosome production.
We have skipped many other effects resveratrol has on the body. They range from other deacetylase activities to direct effects on numerous health parameters such as inflammatory response and glucose metabolism, to name just a few. But the purpose of this posting is not to fully review resveratrol; it’s to show the link between the many benefits of resveratrol, its limitations of which are controlled by NAD/NAM metabolism.
Depending on whom you reference, resveratrol, amazing as it is, which is essentially a caloric-restriction mimic, only impacts 3-4 of the sirtuins, although granted sirtuin 1 has numerous benefits alone. On the other hand, increases in NAD, through NR, feeds all seven sirtuins. Resveratrol and nicotinamide riboside – when used together – can be an amazing one-two punch.
I don’t expect everyone to understand all of the biochemistry described thus far, nor that which will be described in the next two postings, but even a cursory look at the foregoing highlights a number of benefits most individuals can understand. Improvements in glucose metabolism (blood sugar), fat burning (weight management), serum lipids (cholesterol and triglyceride metabolism), energy, DNA repair, normal inflammatory response, oxidation, and many more, have been covered. Welcome to the cutting edge of functional medicine.
Guy Daniels MS MH
Functional Medicine Consultant – Thorne Research