Curbs the main NAD⁺ consumer
Almost everything sold for NAD+ works on the supply side. This pathway is the demand side, and it may be the larger half of the problem. CD38 is a NAD glycohydrolase found on inflammatory cells; as senescent cells accumulate they recruit CD38-positive macrophages, and tissue NAD+ falls in step. That reframes two separate hallmarks of aging — the senescence burden and the NAD+ deficit — as one process seen at two points. The reversal experiments are what make it convincing: a specific CD38 inhibitor restores NAD+ in old animals and improves glucose tolerance, muscle function, exercise capacity and cardiac function, and it extends both lifespan and healthspan in naturally aged mice. Several common dietary flavonoids inhibit the same enzyme. Now the boundary, and it is a hard one: all of this is preclinical. Cells, mice, and one small molecule that has never been given to a person. There is no human trial of CD38 inhibition, so what this pathway offers is a mechanism worth understanding, not a proven human intervention.
In depth
An enzyme that sits on immune cells and eats NAD+. Its expression climbs steadily with age, and it is now the leading explanation for why NAD+ falls at all — not because the body makes less, but because something is consuming more.
What drives it
Clears worn-out cells increases it.
10.1038/s42255-020-00305-3 — Senescent cells promote tissue NAD+ decline during aging via the activation of CD38+ macrophages — which makes CD38 the mechanistic link between the senescence burden and the NAD+ deficit, rather than two separate hallmarks of aging. murine. Covarrubias 2020 (Verdin lab) — senescent cells promote tissue NAD+ decline during aging via the activation of CD38+ macrophages. doi 10.1038/s42255-020-00305-3
Calms body-wide inflammation increases it.
The accumulation of CD38+ inflammatory cells is what lowers NAD levels in aging tissue, so the inflammatory burden and the NAD+ deficit are the same process observed at two points. murine and cell-based. Camacho-Pereira 2016, Cell Metab 23(6):1127-1139, PMID 27304511 / PMC4911708 — CD38 dictates age-related NAD decline and mitochondrial dysfunction through an SIRT3-dependent mechanism ; Covarrubias 2020 (Verdin lab) — senescent cells promote tissue NAD+ decline during aging via the activation of CD38+ macrophages. PMID 27304511 · PMC4911708
Calms inflammation increases it.
Promoter-level and mutation-confirmed — the strongest form of evidence a transcriptional edge can carry. The human cd38 promoter contains an NF-kB binding site (GGGATTCCTC, -1728 to -1719) alongside AP-1 and glucocorticoid response elements. TNF-alpha increases binding to that site, and mutations in the binding sites abolish promoter activation — so the site is not merely present, it is required. TNF-alpha augmented CD38 expression and ADP-ribosyl cyclase activity in human airway smooth muscle, and an NF-kB inhibitor blocked it; dexamethasone reversed the induction. CD38 expression is under the transcriptional control of type I and II interferon as well as TNF-alpha/NF-kB stimulation. This edge closes a self-reinforcing loop: NF-κB raises the CD38 NADase, the NADase drains NAD+, SIRT1 needs NAD+, and SIRT1 holds NF-κB down. Inflammation induces the NADase; the NADase drains NAD+; less NAD+ means less SIRT1; and SIRT1 is what deacetylates and restrains NF-kB. Each arm is independently cited. That circle is a mechanistic account of inflammaging, and it is why an NAD+ product that ignores inflammation is working against a loop rather than a line. promoter and cell work (human airway smooth muscle, K562, macrophages) plus knockout mice — no human trial measures this axis. Tirumurugaan 2008, PMC2278140 ; PMID 16571778 ; Front Immunol 2020, doi 10.3389/fimmu.2020.597959 ; Qian 2018, Mediators Inflamm. doi 10.3389/fimmu.2020.597959 · PMID 16571778 · PMC2278140
What it drives
It reduces Cellular fuel.
The enzyme that explains why NAD+ falls with AGE. CD38 is a NAD glycohydrolase (EC 3.2.2.5) and one of the primary enzymes that degrade NAD in mammals; increased CD38 expression is responsible for NAD decline and mitochondrial dysfunction in older mice, acting through an SIRT3-dependent mechanism. The direction is destructive, so the edge is inhibitory: more CD38 activity, less NAD+. Corroborated by inhibition in both directions: the specific inhibitor 78c reverses tissue NAD+ decline and improves glucose tolerance, muscle function, exercise capacity and cardiac function in aged mice, and increases lifespan and healthspan in naturally aged male mice (Peclat 2022, doi 10.1111/acel.13589). Limit, and it binds the whole node: every CD38 finding here is preclinical — cells, mice and one small molecule that has never been given to a human. No CD38 inhibitor has a human trial. Camacho-Pereira 2016, Cell Metab 23(6):1127-1139, PMID 27304511 / PMC4911708 — CD38 dictates age-related NAD decline and mitochondrial dysfunction through an SIRT3-dependent mechanism. doi 10.1111/acel.13589 · PMID 27304511 · PMC4911708
It increases Sleep pressure.
The second output of CD38, and it is not a loss but a product. Extracellular NAD+ is converted to AMP by CD38 and CD203a, and AMP is then hydrolyzed by CD73 to adenosine. So the same enzyme that drains the NAD+ pool also manufactures an immunosuppressive signaling molecule from the wreckage — CD38 is a source, not only a sink. This is why CD38 sits in tumor immunology as well as in aging: adenosine acting at its receptors suppresses inflammatory and anti-tumor immune responses. this is the extracellular arm of CD38 activity and the chain is enzymatic and mechanistic — no human trial measures it, and this edge makes no claim that a botanical moves it. Found in the Chinese-language immuno-oncology literature, which foregrounds this route where the NAD+ aging reviews do not. PMC9346148 — Blocking Adenosine/A2AR Pathway for Cancer Therapy. PMC9346148
It increases Adenosine A2B receptor.
Supplies the ligand to the receptor, by the established route: extracellular NAD+ is converted to AMP by CD38 and CD203a, and AMP is hydrolyzed by CD73 to adenosine — which is the agonist at the A2B receptor. Drawn so the A2B node is not an orphan and so the CD38 route to adenosine signaling is traceable end to end. enzymatic chain, extracellular arm; no human trial measures it and NO botanical claim attaches. PMC9346148 ; Iino 2007 J Invest Dermatol 127(7):1825. PMID 17301835 · PMC9346148
It reduces Heart calcium handling.
CD38 is the ADP-ribosyl cyclase generating cyclic ADP-ribose, the ryanodine-receptor calcium messenger. PMID 28539361
It reduces Longevity gene.
CD38 is the dominant NAD+ consumer limiting sirtuin cosubstrate availability with age. PMID 16935261
Blends that modulate it
Each blend page names this pathway and carries the study behind its claim.
See it on the map
Open the causal map to follow this pathway upstream and downstream, arrow by arrow, each with its study.