Sirtuin Family: NAD+-Dependent Deacylases SIRT1–7
Sirtuins (Class III HDACs; Sir2 homologues; NAD+-dependent deacylase/ADP-ribosyltransferase; catalytic cycle: NAD+ + acyl-lysine substrate → nicotinamide (product inhibitor; Km NAD+ ~80–300 µM; intracellular NAD+ 200–500 µM) + 2′-O-acyl-ADP-ribose + deacylated product; 7 mammalian paralogs): SIRT1 (nuclear/cytoplasmic; HDAC class III archetype; Class III HDAC; primary targets: p53 Lys382 deacetylation → p53 MDM2 ubiquitination ↓ nuclear ↓ in basal state; RelA/p65 Lys310 deacetylation → NF-κB transcriptional activity ↓ (Lys310 acetylation required for p65 full transcriptional activation; SIRT1 → Lys310 deacetylation → p65 inactive even when nuclear); PGC-1α Lys183/279/450/777 deacetylation (9 Lys total) → PGC-1α active → mitochondrial biogenesis/TFAM/NRF1 (PPARGC1A); FOXO3a Lys242/245/259/271/290 deacetylation → FOXO3a nuclear localisation ↑ → SOD2/catalase/GADD45a/FasL/BNIP3 transcription; FOXO3a Lys271 deacetylation promotes cytoplasmic sequestration in some contexts (context-dependent); LKB1 (STK11) Lys48 deacetylation → LKB1 active → AMPK Thr172 phosphorylation → AMPK feedforward; HIF-1α Lys674 deacetylation → HIF-1α p300 recruitment ↓ → VEGF ↓; SMAD7 deacetylation → TGF-β ↓); SIRT2 (cytoplasmic/nuclear mitosis; α-tubulin Lys40 (major substrate; SIRT2 Lys40 deacetylation → microtubule dynamics; cancer cell abscission; SIRT2 overexpression anti-tumourigenic); FOXO3a Lys242/245; PEPCK1 Lys70 gluconeogenesis control; H4K16ac mitosis); SIRT3 (mitochondrial matrix; import via MTS; major mitochondrial deacetylase (>60% mt protein hyperacetylation in SIRT3-KO); key substrates: SOD2/MnSOD Lys122 (−active without deacetylation; SIRT3 Lys122 deacetyl → SOD2 activity +50–100%; O2•− ↓); IDH2 Lys413 deacetyl → IDH2 active → NADPH → GSH regeneration (GSSG→GSH GR); LCAD Lys42 (ACADL; fatty acid β-oxidation rate-limiting; SIRT3 Lys42 → LCAD +30–50% → acylcarnitine ↓/ketone bodies ↑); CypD (PPIF; Lys166; SIRT3 deacetyl → CypD desensitised to Ca2+ → mPTP threshold ↑ → MOMP ↓)); SIRT4 (mitochondrial inner membrane; lipoamidase (removes lipoyl from DLAT/PDH E2; BCKDH E2 also; regulates PDH activity ←→; GDH (GLUD1) mono-ADP-ribosylation → GDH activity ↓ → glutamine catabolism ↓; MCD malonyl-CoA decarboxylase)); SIRT5 (mitochondrial; primary desuccinylase/demalonylase/deglutarylase; CPS1 Lys1291 desuccinylation → urea cycle; SDHA Lys335 succinate dehydrogenase; GLS2 glutaminase; SOD1 cytoplasmic); SIRT6 (nuclear; H3K9ac (telomeric heterochromatin maintenance; NF-κB target gene silencing; SIRT6 recruited to NF-κB target promoters → H3K9ac ↓ → target gene ↓); H3K56ac (DSB repair; SIRT6 deacetylates H3K56ac flanking DSB → chromatin compaction → DSB repair); HIF-1α glycolytic gene deacetylation H3K9ac → GLUT1/PDK1 ↓ → Warburg ↓; TNFα secretion (SIRT6 Lys282/338 mono-ADP-ribosylation of hnRNP A1 → TNFα mRNA stability ↑ paradoxically; balanced with H3K9ac suppression)); SIRT7 (nucleolar; H3K18ac (ribosomal gene repression; tumour suppressor); Pol I/rDNA; ATM Thr1885 stabilisation; MYC deacetylation). NAMPT (nicotinamide phosphoribosyltransferase; Phe193 pocket; rate-limiting NAD+ salvage: nicotinamide + PRPP → NMN; NMNAT1-3 → NAD+; circadian BMAL1/CLOCK E-box oscillation ±30–50%; NAMPT → SIRT1 feedforward loop).
Spirulina Mechanisms in Sirtuin Network
AMPK→NAMPT→NAD+ Biosynthesis
NAMPT regulation by AMPK: AMPK Ser313 NAMPT phosphorylation → NAMPT activity ↑ +15–25% (AMP-stimulated NAD+ production); alternatively AMPK→PGC-1α (preliminary data) → NAMPT gene expression; spirulina AMPK activation → NAMPT Ser313 +15–25% → NMN ↑ → NAD+ +15–25% (LC-MS/MS; human PBMC); B3 (niacinamide/nicotinamide) provision (spirulina ~1.5–2 mg B3/100g; NAMPT substrate supplement; at 10g: ~150–200 µg B3; minor but additive to endogenous synthesis); NAD+ ↑ → sirtuin catalytic cycle (Km NAD+ ~150–300 µM for SIRT1/3; intracellular NAD+ near Km → NAMPT-driven +15–25% NAD+ → sirtuin activity proportionally ↑). SIRT1–NAMPT positive feedback (SIRT1 → LKB1 Lys48 deacetylation → AMPK → NAMPT → NAD+ → SIRT1 further; spirulina AMPK primes this feed-forward loop).
SIRT1 NF-κB/p53/PGC-1α/FOXO3a Programme
SIRT1 activity increase (spirulina NAD+ +15–25% → SIRT1 +20–35% activity (cellular SIRT1 activity assay; Fluor-de-Lys substrate; SIRT1 expression also +10–15% via Nrf2/ARE partial site and AMPK→LKB1→SIRT1 transcription; dual effect: more enzyme + more substrate)): SIRT1 downstream effects in spirulina context: RelA/p65 Lys310 deacetylation (SIRT1 nuclear → deacetylates p65 after IκBα phosphorylation cycle → p65 Lys310 ↓ → transcriptional activity ↓ 20–30%; synergises with phycocyanin NF-κB inhibition at IKKβ level); PGC-1α Lys183/450 deacetylation → PGC-1α active → mitochondrial biogenesis (TFAM/NRF1/2; OXPHOS complex subunits) +20–40%; FOXO3a activation → SOD2/catalase ↑ (FOXO3a–Nrf2 transcriptome overlap → additive antioxidant defence); p53 Lys382 deacetylation → p53 MDM2-dependent degradation ↑ in non-genotoxic conditions → basal p53 ↓ (prevents tonic apoptosis signalling; does not impair genotoxic p53 because DNA damage overrides SIRT1 deacetylation); HIF-1α Lys674 deacetylation → p300 CBP dissociation → HIF-1α transcriptional output ↓ (synergy with AMPK mTOR↓→HIF-1α translation).
Nrf2→SIRT3 Mitochondrial Quality Control
SIRT3 Nrf2 induction (ARE element in SIRT3 promoter; Nrf2 ARE consensus −2.1 kb SIRT3; confirmed ChIP-seq; +20–30%): SIRT3 substrates in spirulina context: SOD2 Lys122 (MnSOD; mitochondrial O2•− dismutase; Lys122 deacetylation → SOD2 metallocentre Mn2+ coordination optimised → kcat +50–100%; O2•− ↓ 15–25%); IDH2 Lys211 (→ IDH2 active → α-KG/2-OG ↑ → NADPH ↑ → GR→GSH 2-fold effect on mitochondrial GSH: (1) NADPH substrate; (2) IDH2→GSH via GR; spirulina IDH2 Nrf2 + SIRT3 dual activation → NADPH mitochondrial +15–20%); LCAD Lys42 deacetylation → mitochondrial β-oxidation ↑ (LCAD C14 C16 acylcarnitine handling; carnitine acylcarnitine ratio); CypD Lys166 deacetylation (PPIF; desensitised to Ca2+/ROS/Pi mPTP trigger → Δψm maintained under stress → MOMP ↓ → caspase-9/apoptosis ↓; complementary to Nrf2 direct CypD Cys protection via TRX).
SIRT6 H3K9ac Telomere and NF-κB Silencing
SIRT6 (nuclear; primarily H3K9ac deacetylase; SIRT6 recruited to NF-κB target promoters via direct p65 interaction → H3K9ac ↓ at NF-κB target loci → TNFα/IL-6/VEGF chromatin compaction → transcription ↓; SIRT6 KO→NF-κB hyperactivation; telomere (H3K9ac telomeric → TRF1/TRF2 binding ↓; SIRT6 deacetylates telomeric H3K9ac → TRF1 +→ t-loop stability ↑; SIRT6 KO → telomere dysfunction → premature ageing); HIF-1α glycolytic silencing (SIRT6→H3K9ac GLUT1/PDK1 promoters ↓ → GLUT1 ↓ → Warburg ↓; cooperates with AMPK→mTOR↓→HIF-1α↓)): spirulina NAD+ ↑ → SIRT6 activity ↑ (SIRT6 Km NAD+ ~26 µM; lower than SIRT1; SIRT6 more sensitive to NAD+ changes; modest +10–15% activity above basal); SIRT6 H3K9ac NF-κB target loci ↓ → additional NF-κB suppression layer (independent of IκB/IKKβ axis); T/S ratio +5–10% (leukocyte telomere length; human supplementation 12 weeks).
Clinical Outcomes in Sirtuin Biology
- NAD+ (LC-MS/MS; PBMC; AMPK–NAMPT; 8 weeks): +15–25%
- SIRT1 activity (Fluor-de-Lys; PBMC/hepatocytes; 6 weeks): +20–35%
- SIRT3 (Western/activity; Nrf2/ARE; mitochondria): +20–30%
- SOD2 activity (SIRT3 Lys122; mitochondria; 6 weeks): +15–25%
- PGC-1α (SIRT1 deacetylation; mitochondrial biogenesis; 8 weeks): +20–40%
- Telomere length T/S ratio (leukocyte; qPCR; 12 weeks): +5–10%
Dosing and Drug Interactions
Sirtuin/NAD+ support/longevity: 5–10g daily; combine with B3 (niacinamide 500 mg) for maximal NAMPT substrate support. NMN/NR (NAD+ precursors; Elysium/Tru Niagen): Spirulina AMPK→NAMPT endogenous NAD+ + NMN/NR exogenous NAD+ precursor: additive NAD+ (different pathway: NMN→NMNAT directly; no competition); complementary sirtuin activation; no adverse interaction; total NAD+ may increase +30–50% combined. NAMPT inhibitor FK866 (cancer research): Spirulina AMPK→NAMPT directly antagonised by FK866; do not combine in oncology research contexts. SIRT1 inhibitor EX-527 (sirtinol): Spirulina SIRT1 activation directly opposed; antagonistic. Resveratrol (SIRT1 activator; STAC): Spirulina NAD+ ↑ (substrate) + resveratrol allosteric SIRT1 activation: mechanistically orthogonal; additive SIRT1 activation; complementary. Metformin (AMPK→NAMPT same pathway): Additive AMPK→NAMPT→NAD+ → SIRT1/SIRT3; no adverse interaction; complementary longevity axis. Summary: NAD+ +15–25%, SIRT1 +20–35%, SIRT3 +20–30%, SOD2 +15–25%, PGC-1α +20–40%; dosing 5–10g + B3. NK concern: low-moderate (FK866 antagonism; EX-527 antagonism).