Now, here's a surprising twist ....
Recall from the opening post that NAMPT, the rate-limiting enzyme for NAD+ synthesis via the dominant salvage pathway, "has been implicated in a variety of inflammatory disorders such as sepsis, rheumatoid arthritis and diabetes.18–20 Furthermore, NAMPT overexpression has been associated with tumorigenesis.21 We have reported elevated NAMPT concentrations in colonic tissue and serum of patients with IBD [inflammatory bowel disease] and recently, NAMPT has been identified as a marker for severity in paediatric IBD." The study in the opening post found that FK866, an inhibitor of NAMPT, inhibited inflammation in animal models of IBD and in vulnerable tissues from human IBD patients, with evidence that it worked via inhibiting levels and activity of the NAD+-dependent enzymes PARP1 AND CD38 (both previously implicated in inflammation) as well as and multiple sirtuins (most profoundly SIRT6, but also a rather striking effect on SIRT1), surprisingly.
Because the canonical function of NAMPT is NAD+ biosynthesis, and because PARP1 and CD38 are NAD+-dependent enzymes, I speculated that NAD+ precursors might similarly exacerbate inflammatory disease by providing additional substrate for these enzymes
This group of Chinese researchers claims (a bit prematurely, based on very preliminary evidence) that contrary to what you might expect, NMN actually "alleviates diabetic nephropathy inflammatory‑fibrosis by inhibiting endogenous Nampt."
Hi Michael, interesting study indeed. Wrt SIRT1 I understood the study to suggest that increased NAMPT leads to sgnalling causing SIRT1 down regulation:
-Increased Nampt and NF‐κB p65 expression and decreased Sirt1 expression in response to HG conditions over time.
And that NMN not only activates SIRT1 via more NAD+ as is usually shown but also:
-The results indicated that NMN was able to activate Sirt1 by inhibiting the Nampt pathway.
You're misreading either my post, or the first study, or both: when I say, above, "The study in the opening post found that FK866, an inhibitor of NAMPT, inhibited inflammation [...] with evidence that it worked via inhibiting levels and activity of the NAD+-dependent enzymes PARP1 AND CD38 (both previously implicated in inflammation) as well as and multiple sirtuins (most profoundly SIRT6, but also a rather striking effect on SIRT1), surprisingly," note that I am referring to "the study in the opening post," which indeed did find:
FK866 impairs mucosal NAD recycling resulting in a dampened PARP/SIRT-mediated inflammatory response ... FK866 reduced mucosal abundance of various SIRT (online supplementary figure 3A) during intestinal inflammation with the most pronounced effect on Sirt6 (figure 4B,D). Again this was paralleled by a markedly decreased enzymatic function as measured by deacetylase activity (figure 4C).
Their supplementary figure 3A shows that SIRT1 protein levels are more than doubled in DSS-IBS mice vs. water-treated non-IBD controls, and FK866 reduced it down even below that control baseline. (Quantitation of immunoblots is a soft science, but that's a very large and obvious effect).
When you say:
And that NMN not only activates SIRT1 via more NAD+ as is usually shown but also:
-The results indicated that NMN was able to activate Sirt1 by inhibiting the Nampt pathway.
... those are results from the second, Chinese study, which does report to the contrary that NMN was able to increase gene expression of Sirt1 in association with decresed expression of NAMPT. (Despite their sloppy use of language, they provide no data on "activation" (increased activity) of SIRT1 — just increased gene expression). So that's another oddity in all of this. I would certainly trust protein levels more than gene expression readouts, which can always be nullified posttranslationally.
stefan_001 wrote: Or?
I have read couple studies indicating that during aging the salvage effectives goes down and there is compensation via increased NAMPT. So perhaps we are seeing here a NMN specific anti aging effect via direct signalling pathway leading to more sirt1 apart fom the nad+ boosting.
All the studies I've seen show either no effect of aging on NAMPT (Chini & Sinclair) or downregulation (Imai, Radak, and importantly Miao, which as you spotted the other day gives the first human data on this question in addition to more mouse data, finding a "decrease of NAD+ content in livers from elderly patients compared with those from middle-aged patients and found that the NAMPT-mediated NAD+ salvage pathway, but not indolamine 2,3-dioxygenase (IDO)-mediated NAD+ de novo pathway, was impaired in livers from elderly humans compared with those from middle-aged patients." One caution is that these are all "patients" with either hepatolithiasis or hepatocellular carcinoma, rather than otherwise-healthy aging people. Still, even among patients, the levels were down with age.
I am aware of no proposed mechanism or data to support a role for NMN in controlling SIRT1 expression, and the only role of which I'm aware for NMN in SIRT1 activity is via NAD+. Are you aware of any such?
stefan_001 wrote: then again that only makes sense if the NMN adds more NAD+ than is reduced by the NAMPT inhibition. Unless the path of action is still different and that NMN blocks the NAMPT pathway that inhibits SIRT1 without actually inhibiting NAMPT. Mmmm...
I agree with your first sentence; I'm not clear on what you're suggesting with the second, but their entire thesis is that NMN is providing product inhibition of the NAMPT enzyme, and support that with expression data.
Great study!
Diabetes causes inflammation which lowers NAD+. This up regulates NAMPT and other bad genes and down regulate Sirt1.
Supplementing NMN or NR increase NAD+ and suppress NAMPT and other bad genes through the negative feed back loop
And up regulate Sirt1.
So keeping NAD+ high with external NMN and NR will suppress NAMPT and bad genes and increase Sirt1
Expression.
It's a bit silly to describe any gene as a "bad gene" (unless maybe you mean a disease-associated mutation), and certainly calling the most important gene in NAD+ biosynthesis a "bad gene" is a bit rich. FK866 inhibits NAMPT and thereby PARP1, SIRT1, SIRT3, and SIRT6; "Sirt6 regulated TNFα production in dendritic cells in a NAD and NAMPT-dependent manner39 and Sirt1 represents an important regulator of monocyte/macrophage polarisation towards M1.4" Are those 'bad genes' for their role in inflammation?
MikeDC wrote:
They also did in vivo study on NMN supplementation.
"To explore the effect of these results in the whole animal, severely diabetic rats were treated with NMN in the present study, and mRNA was isolated and measured from kidney tissues of the rats. The results indicated that the mRNA expression levels of Nampt, NF‐κB p65 and vimentin were significantly decreased in the NMN‐treated tissue, whereas Sirt1 expression was significantly increased compared with the untreated groups, respectively. The results further indicated that the Nampt‐NF‐κB p65 signaling pathway is likely inhibited via NMN‐induced inhibition of Nampt in a negative feedback loop. This suggests that endogenous Nampt overexpression may be closely involved in the pathogenesis of glomeruli fibrosis of DN"
Yes — as I noted in my post, they show "that expression of NAMPT and inflammation- and fibrosis-associated genes are suppressed upon NMN treatment in cells in high glucose and diabetic mice, without either showing effects on protein levels or activity, or actually showing any effect in vivo on actual inflammation and renal disease."
MikeDC wrote:to reconcile the papers, NAMPT up regulation is pro inflammatory and down regulation is anti inflammatory.
Low NAD+ up regulate NAMPT.
External NMN and NR increase NAD+ and down regulate NAMPT
Any process that decreases NAD+ create a vicious cycle of inflammation.
NAD+ precursors can put a stop to it by creating a positive feed back loop.
That just restates the paradox — it doesn't resolve it, unless (contrary to the implications of the presented evidence) there is some hitherto-unknown NAD+-independent pro-inflammatory effect of NAMPT. (Again, there are claims of a non-NAD+-synthesizing function for extracellular NAMPT ("visfatin"/PBEF), but those are now largely-discounted, and IAC they wouldn't explain the cell culture data). And most studies find NAMPT activity or expression is downregulated in aging, and CR protects against that decline, so certainly it would be prima facie unwise for otherwise-healthy aging people to be doing anything to downregulate NAMPT.
able wrote:
NAMPT IS critical for NAD+ synthesis.
I don't see that this study tells us if it is inhibition of NAMPT, or, the resulting decrease in NAD+ that results in decreased PARP and inflammation.
Would be good if they supplemented NR, NMN, and/or NAD+ to the same mouse model to see what effect it has on the inflammation, both before, and after fk866 NAMPT inhibition. IF inflammation was less after fk866, then returned (or not) after NAD+ replenishment, then we'd know if it was the NAMPT, or NAD+ itself.
Correct — that would be ideal. Again, however, from the known biology I can't think of a non-NAD+-based mechanism, and they provide evidence of effects via NAD+-consuming enzymes (albeit not conclusively).
MikeDC wrote: The paper did what you said in a different way. They showed increasing NAD+ from NMN that doesn't need NAMPT reduced inflammation and increased Sirt1 expression. So NAD+ is not the cause of inflammation.
That doesn't follow, absent a mechanism for an NAD+-independent effect of NAMPT in ignoring the dependence of PARP1 and the rest on NAD+.
MikeDC wrote:
NMN increases NAD+ which causes down regulation of NAMPT through the negative feed back loop between NAD+ and NAMPT.
That's not what they're suggesting: they're suggesting product inhibition by NMN itself. Did you misspeak, or do you have evidence for what you wrote? Their mechanism certainly is more prima facie plausible.
MikeDC wrote: Also note that even though NAMPT is increased greatly during inflammation, the NAD+ and NAD/NADH ratio still are below controls.
Yes, but that's because of reductive stress created by hyperglycemia leading to an excess of glycolytic and TCA cycle intermediates and activation of the polyol pathway, as well as increased consumption of NAD+ by PARP1, all of which alters the ratio of the NAD+:NADH couple, not a reduction in NAD+ biosynthesis (via salvage or otherwise).