Mechanism of Action
NAD+ Biosynthesis (Intracellular NAMPT)
Intracellular NAMPT (iNAMPT) catalyzes the conversion of nicotinamide (NAM) to nicotinamide mononucleotide (NMN), the rate-limiting step in the NAD+ salvage pathway. As NAD+ is the essential cofactor for sirtuins (SIRT1-7), PARPs, and CD38, NAMPT activity directly regulates cellular energy metabolism, DNA repair, and stress resilience. NAD+ decline with aging is partly attributed to decreased NAMPT expression, making NAMPT a longevity target.
Extracellular Signaling (eNAMPT)
Secreted eNAMPT retains enzymatic activity and can synthesize NMN extracellularly, which cells then import to produce NAD+. Separately, eNAMPT acts as a DAMP (damage-associated molecular pattern), binding TLR4 on macrophages and endothelial cells to activate NFkB and stimulate IL-6, IL-1beta, and TNF-alpha production. This cytokine-like activity mediates inflammatory effects in metabolic disease, sepsis, and autoimmune conditions.
Angiogenesis and Tumor Promotion
eNAMPT promotes endothelial cell proliferation, tube formation, and VEGF production via MAPK/ERK and Akt activation. In cancer cells, NAMPT supports elevated NAD+ demand driven by high PARP activity and rapid proliferation. Tumor cells upregulate NAMPT, and high intratumoral NAMPT correlates with aggressive behavior and poor prognosis in breast, colorectal, and lung cancers. NAMPT inhibitors (FK866, GMX1778) are in oncology trials exploiting this dependency.
Research Summary
NAD+ Aging and Longevity
TranslationalNAMPT is the primary regulator of NAD+ levels in most mammalian tissues. Age-related NAD+ decline correlates with reduced NAMPT expression. Strategies to restore NAMPT (gene therapy, NAMPT activators, NMN/NR supplementation that bypass the rate-limiting step) are active longevity research areas. Exercise upregulates NAMPT in skeletal muscle, contributing to exercise-induced NAD+ elevation.
Metabolic Disease
Clinical AssociationSerum visfatin correlates with visceral adiposity, insulin resistance, and metabolic syndrome. Its predictive value for metabolic outcomes is debated due to overlap with BMI. In NAFLD, visfatin is elevated and promotes hepatic inflammation and steatosis via TLR4/NFkB. Paradoxically, some studies suggest visfatin may have beneficial effects in specific contexts by supporting NAD+-dependent SIRT1 activity.
Oncology (NAMPT Inhibitors)
Clinical TrialsFK866 (APO866) and GMX1778 are first-generation NAMPT inhibitors that deplete NAD+ in rapidly dividing cells, inducing apoptosis. Phase I/II trials in hematological malignancies and solid tumors showed manageable toxicity (thrombocytopenia) but modest single-agent activity. Combinations with chemotherapy, PARP inhibitors, or checkpoint immunotherapy are active areas of investigation.
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Research Protocols
| Goal | Dose | Frequency | Route |
|---|---|---|---|
| NAD+ depletion model | 10-100 nM FK866 (inhibitor) | 24-72 hours incubation | Cell culture |
| Inflammatory signaling study | 100-500 ng/mL eNAMPT | Acute exposure (4-24h) | Cell culture medium |
| Biomarker (clinical) | Blood draw (ELISA) | Fasting sample | Serum or plasma |
Visfatin/eNAMPT is primarily a biomarker and research target. NMN/NR supplementation targets the downstream product of NAMPT activity rather than the enzyme itself.
Interactions
Safety Profile
Elevated endogenous visfatin drives inflammation and potentially tumor growth. Exogenous recombinant visfatin/eNAMPT promotes inflammatory signaling. NAMPT inhibitors (therapeutic use) cause dose-limiting thrombocytopenia and, at higher doses, retinal toxicity (due to high NAD+ demand in photoreceptors). NMN/NR supplementation (downstream of NAMPT) has a clean safety profile in human trials. The dual roles of NAMPT as both pro-inflammatory (extracellular) and metabolically beneficial (intracellular NAD+) make therapeutic targeting complex.
References
- [1]Fukuhara A, et al. Visfatin: a protein secreted by visceral fat that mimics insulin. Science. 2005;307:426-430.
- [2]Revollo JR, et al. NAMPT/PBEF/visfatin regulates cardiac and liver metabolic function via NAD. Cell Metab. 2007.
- [3]Garten A, et al. Physiological and pathophysiological roles of NAMPT and NAD metabolism. Nature Rev Endocrinol. 2015.