Spirulina, Telomeres, and Genomic Stability.

Telomere Structure: Shelterin and G-Quadruplex

Mammalian telomeres consist of 5–15 kb of (TTAGGG)&sub∞ double-stranded repeats terminating in a 3′ single-stranded G-overhang (~200 nt) that invades the duplex to form a T-loop; the G-overhang can also form G-quadruplex (G4) secondary structures. The six-protein shelterin complex maintains telomere integrity: TRF1 (TERF1) and TRF2 (TERF2) bind double-stranded TTAGGG via their Myb/SANT domains; POT1 (Protection of Telomeres 1) binds single-stranded G-overhang (OB-fold; Kd ~1 nM); RAP1 (TERF2IP) interacts with TRF2 and suppresses NHEJ; TPP1 (ACD) bridges POT1 to TIN2; TIN2 (TINF2) crosslinks TRF1/TRF2/TPP1. Shelterin suppresses the DDR (DNA damage response) at telomeres: TRF2 inhibits ATM Ser1981 autophosphorylation (via TRFH domain blocking ATM recruitment to telomeres); POT1 inhibits ATR-ATRIP activation at the G-overhang. Loss of TRF2 → ATM-dependent telomere fusions; loss of POT1 → ATR-dependent elongated overhangs and replication stress.

Telomerase: hTERT, hTR, and Regulation

Telomerase is a ribonucleoprotein complex: hTERT (TERT; catalytic reverse transcriptase; 1,132 aa; TERT motifs 1, 2, A, B, C, D, E) and hTR (TERC; 451-nt RNA template; CR4/CR5 pseudoknot; box H/ACA domain for Cajal body targeting). hTERT adds TTAGGG repeats to the 3′ G-overhang. hTERT transcription is regulated by NF-κB (two κB sites at −1,340 and −1,130 bp — paradoxically NF-κB activates hTERT in cancer but suppresses it in normal cells via c-Myc competition/E-box sites); c-Myc (E-box at −88 bp); Sp1 (GC-boxes); and by repressors WT1, p53, and TGF-β/SMAD3. hTERT protein is also regulated post-translationally: Akt Ser473 phosphorylation → nuclear retention; SIRT1 deacetylation (Lys531) → stabilisation; CHIP (Hsp70-associated Ub E3) → K48-Ub degradation; Pin1 prolyl isomerisation → nuclear export.

Oxidative Telomere Attrition and SIRT6

Telomeric GGG triplets are the most oxidatively vulnerable DNA sequence (ΔG oxidation ~20-fold lower than bulk DNA). 8-oxoguanine (8-OHdG) at telomeres is repaired by OGG1 (8-oxoguanine DNA glycosylase; BER), but repeated rounds create single-strand nicks that stall replication forks → incomplete lagging-strand replication → 3′-overhang erosion → telomere shortening (~50–200 bp/cell division under oxidative stress vs. ~50 bp/division normally). SIRT6 (H3K9Ac/H3K56Ac deacetylase; ADP-ribosylase; base excision repair stimulator) is recruited to telomeres in S-phase; SIRT6 deacetylates H3K9Ac at telomere-flanking chromatin, stabilises WRN (Werner syndrome helicase) at telomeres, and stimulates PARP1-independent BER. SIRT6 knockout accelerates telomere dysfunction and premature ageing phenotype; NF-κB is also upregulated in SIRT6 KO, forming an amplifying loop.

Spirulina’s Mechanistic Actions

• Nrf2 → OGG1/BER → 8-OHdG ↓ at telomeres: Nrf2→OGG1 +15–25% (ARE at −1.8 kb of OGG1 promoter); APEX1 (APE1; Nrf2-induced) ↑ 15–25%; POLB ↑ 10–20%; net 8-OHdG at telomeres ↓ 20–35% in oxidative stress models → oxidative telomere attrition ↓.
• Nrf2/AMPK → NAD&sup+; → SIRT6 activity ↑: SIRT6 is NAD&sup+;-dependent; spirulina-driven NAD&sup+; ↑ 20–35% → SIRT6 activity ↑ → H3K9Ac at telomere-flanking chromatin ↓ → WRN stabilisation → replication fork stalling ↓; telomere length preservation in high-oxidative-stress cells.
• SIRT1 → hTERT Lys531 ↑: SIRT1 deacetylates hTERT Lys531 → CHIP-mediated K48-Ub degradation ↓ → hTERT half-life ↑ → telomerase processivity maintained; TERT ↑ 10–20% in non-cancer cell models under oxidative stress.
• NF-κB ↓ → TRF2 stability ↑: NF-κB drives TERF2 degradation via IKKβ→TRF2 Thr188 phosphorylation→SCF-βTrCP CRL1 K48-Ub in some contexts; PCB-driven NF-κB↓ reduces TRF2 phospho-degradation → shelterin integrity ↑ → ATM/ATR suppression at telomeres maintained.
• Replication stress ↓: AMPK→mTORC1↓→origin firing coordination improved (mTORC1 excess → over-firing → replication stress); nucleotide pool maintenance via Nrf2→PPP (R5P for purine synthesis) → replication fork stalling at GGG telomere sequences ↓.
• 8-OHdG (biomarker): Serum 8-OHdG ↓ 20–35% in human RCTs (4–8 g/day, 8–12 weeks), consistent with telomere BER induction.

Clinical Correlates and Dosing

Direct telomere length measurement in human spirulina trials is lacking. Indirect evidence: leukocyte telomere length (LTL) is inversely associated with CRP and oxidative stress, both of which spirulina reduces in RCTs. In rodent ageing models (D-galactose-induced accelerated ageing), spirulina preserved LTL 15–25% relative to control, correlated with OGG1 upregulation. Suggested mechanism-informed dosing: 4–8 g/day providing PCB (Nrf2), GLA (PPAR), selenium (GPx/OGG1 cofactor), and B12/iron for replication support. Interactions: antioxidant supplementation (vitamin C/E) + spirulina — potentially additive BER support; no known adverse interactions.