Spirulina and Sirtuins / NAD&sup+; Metabolism.

Sirtuin Catalysis: NAD&sup+;-Dependent Deacylation

The seven human sirtuins (SIRT1–7) are class III lysine deacylases that consume one NAD&sup+; per catalytic cycle, generating nicotinamide (NAM), O-acetyl-ADP-ribose (OAADPR), and the deacylated substrate. The catalytic mechanism proceeds: substrate acetyl-lysine + NAD&sup+; → alkylamidate intermediate (C1′ of the nicotinamide ribose attacks the carbonyl of the acyl-lysine) → OAADPR + NAM + deacylated product. NAM is a product-inhibitor (Ki ~50–100 μM), creating a self-limiting feedback. SIRT1 (nuclear/cytoplasmic) deacetylates: p53 Lys382 (p53 activity ↓); FOXO1/3a (nuclear translocation ↓ for FOXO1; ↑ for FOXO3a stress resistance); NF-κB p65 Lys310 (transcriptional activity ↓); PGC-1α Lys13/14 (deacetylation → PGC-1α activation → OXPHOS/FAO gene programme); and histone H3K9Ac/H4K16Ac. SIRT3 (mitochondrial matrix) deacetylates and activates SOD2 Lys68/122, LCAD Lys42, IDH2 Lys413, PDHA1 Lys321, complex I/II/III subunits, and HMGCS2 Lys310, positioning it as the primary mitochondrial redox and metabolic sirtuin. SIRT5 provides mitochondrial desuccinylation and demalonylation (broad substrate specificity); SIRT6 ADP-ribosylates and deacetylates histones and maintains telomere integrity; SIRT7 is nucleolar and regulates rDNA transcription via RNA Pol I and H3K18Ac.

NAD&sup+; Salvage: NAMPT, NMNAT, and CD38/PARP Competition

The NAD&sup+; salvage pathway is the dominant intracellular NAD&sup+; biosynthetic route in mammals: nicotinamide (NAM) + phosphoribosyl pyrophosphate (PRPP) → nicotinamide mononucleotide (NMN) catalysed by NAMPT (nicotinamide phosphoribosyltransferase; EC 2.4.2.12; rate-limiting; Km for NAM ~0.5–1 mM); NMN + ATP → NAD&sup+; catalysed by NMNAT1/2/3 (EC 2.7.7.1; nuclear/Golgi/mitochondrial isoforms). NAMPT is the intracellular rate-limiting enzyme; its expression is induced by AMPK (AMPK→NAMPT promoter via CREB/PGC-1α), fasting, exercise, and resveratrol. NAMPT is also secreted as eNAMPT, functioning as a cytokine (PBEF). NAD&sup+; is consumed by: (i) SIRT1–7 (deacylation); (ii) PARP1 (poly-ADP-ribosylation; major consumer under genotoxic stress; PARP1 activity depletes NAD&sup+; by >80% in stressed cells); (iii) CD38 (ADP-ribose cyclase; ecto- and intracellular; major age-associated NAD&sup+; consumer; generates cADPR and ADPR; induced by NF-κB); (iv) SARM1 (neuronal; NADase; axon degeneration). Thus NF-κB → CD38 ↑ → NAD&sup+; ↓ → SIRT1 ↓ → NF-κB p65 Lys310 acetylated ↑ forms a pro-inflammatory, pro-ageing positive feedback loop.

AMPK–SIRT1–PGC-1α Axis

AMPK and SIRT1 form a mutually reinforcing metabolic axis: AMPK→NAMPT→NAD&sup+;↑→SIRT1 activity ↑→LKB1 deacetylation→LKB1-STRAD nuclear export→cytoplasmic LKB1 AMPK activation (LKB1-AMPK positive loop). SIRT1→PGC-1α deacetylation→PGC-1α active→PPARα/RRE-driven OXPHOS (NDUFA9, SDHA, UQCRB, ATP5A1, CYC1) and FAO (CPT1A, ACADM, HADHB) gene expression ↑; SIRT1→FOXO3a deacetylation Lys271/2/4→FOXO3a nuclear→SOD2/CAT/GADD45/Bnip3 ↑; SIRT1→p65 Lys310 deacetylation→NF-κB transcriptional activity ↓ (without affecting nuclear translocation).

Spirulina’s Mechanistic Actions

• AMPK → NAMPT → NAD&sup+; ↑: Spirulina AMPK Thr172 ↑ → NAMPT mRNA ↑ 20–35% via CREB/PGC-1α → NMN ↑ → NAD&sup+; ↑ 20–35%; SIRT1 activity ↑ 25–40% (measured by p53 Lys382 deacetylation and NF-κB p65 Lys310 deacetylation in liver/adipose models).
• NF-κB ↓ → CD38 ↓ → NAD&sup+; spared: PCB→IKKβ↓→NF-κB↓→CD38 ↓ 25–40% in macrophage/adipose models → NAD&sup+; salvaged from CD38-mediated hydrolysis → SIRT1 substrate available ↑.
• Nrf2 → NQO1 → NADH re-oxidation: NQO1 (NAD(P)H:quinone oxidoreductase) re-oxidises NADH→NAD&sup+; using quinone substrates; Nrf2→NQO1 +25–40% → cytoplasmic NAD&sup+; pool supplemented.
• SIRT3 → SOD2/LCAD: Elevated NAD&sup+; → SIRT3 activity ↑ → SOD2 Lys68/122 deacetylation → SOD2 activity ↑ 20–35% → mitochondrial O&sub2;•− ↓; LCAD Lys42 deacetylation → FAO flux ↑ 15–25%.
• SIRT1 → NF-κB p65 Lys310 ↓: Reinforces PCB-driven NF-κB suppression at the transcriptional level (SIRT1 deacetylation of p65 ↓ NF-κB-driven gene transcription without reducing nuclear content).
• PARP1 suppression (indirect): Nrf2→BER/NER DNA repair enzyme expression ↑ (OGG1, APEX1) reduces genotoxic DNA strand breaks, lowering PARP1 activation and NAD&sup+; depletion under oxidative stress.

Clinical Correlates and Dosing

Animal models: spirulina (50–200 mg/kg) raises hepatic NAD&sup+; 20–35% and SIRT1 activity 25–40%; FOXO3a nuclear translocation ↑ 20–30%; SOD2 ↑ 20–30%; NF-κB p65 Lys310 acetylation ↓ 25–40%. Human indirect data: ageing markers (SIRT1 protein expression declines with age and metabolic disease); 4–8 g/day spirulina lowers fasting glucose, CRP, and oxidative stress markers consistent with SIRT1/SIRT3 activation. Interactions: NMN/NR supplements + spirulina — additive NAD&sup+; elevation possible; theoretically beneficial; no adverse interactions reported. Nicotinamide (high-dose) inhibits SIRT1 via product inhibition — avoid combining with very high-dose niacinamide at spirulina initiation.