Prostaglandin Pathway: COX Enzymes and PG Synthases
Prostaglandin biosynthesis (AA → COX (cyclooxygenase) → PGH2 (intermediate) → tissue-specific synthases → prostaglandins): COX-1 (PTGS1; constitutive; ER/nuclear envelope; haem Fe3+→Tyr385 radical → AA bis-oxygenation → PGG2→PGH2 (peroxidase reduction); Ser529 aspirin irreversible acetylation; Mg2+ cofactor; major TXA2 source (platelets)); COX-2 (PTGS2; inducible; NF-κB 3 sites + CRE + STAT3 + E-box; NF-κB p65 at −447 and −130; Val523 side chain vs Ile523 COX-1 → COX-2 selectivity pocket (celecoxib/rofecoxib COX-2 selective); mRNA AU-rich elements (ARE) HuR/TTP binding → t½ mRNA ~30 min to 8h); prostaglandin synthases: mPGES-1 (microsomal PGE2 synthase 1; MGST2-family; NF-κB/AP-1 inducible; functionally coupled to COX-2; GSH cofactor Cys49; primary PGE2 source in inflammation; mPGES-2 constitutive); cPGES (cytosolic; constitutive; HSP90 chaperone; primarily COX-1 coupled; basal PGE2); TXAS/TBXAS1 (→TXA2 t½ ~30s → TXB2 stable); PGIS/CYP8A1 (→PGI2/prostacyclin; endothelial; IP receptor → Gs→cAMP→PKA→platelet ↓; t½ ~2 min → 6-keto-PGF1α); PGDS/H-PGDS (→PGD2; mast cell/platelet/brain; DP1/DP2/CRTH2; DP2 eosinophil/T-cell Th2); 15-PGDH (HPGD; primary PG catabolism; NAD+-dependent; PGE2→15-keto-PGE2; Nrf2/ARE; cancer-suppressor); PGE2 receptors (EP1 Gq→Ca2+; EP2/EP4 Gs→cAMP→PKA→NF-κB↓/CREB; EP3 Gi→cAMP↓→pro-aggregatory; EP4 also β-arrestin).
Spirulina Mechanisms in Prostaglandin Modulation
NF-κB↓→COX-2/mPGES-1 Suppression
COX-2/mPGES-1 NF-κB induction (LPS/IL-1β/TNFα→NF-κB p65 Ser276→COX-2 −447/−130 NF-κB sites + STAT3 Tyr705; mPGES-1 NF-κB/AP-1; functionally COX-2/mPGES-1 coupled → inflammatory PGE2 burst): spirulina NF-κB −30–50% → COX-2 mRNA −35–50% (LPS/IL-1β macrophage model; qRT-PCR + Western; spirulina 4 weeks) + mPGES-1 −30–40%; PGE2 (ELISA; LPS stimulated macrophage conditioned medium) −35–55%; STAT3 (phycocyanin ↓ pSTAT3 Tyr705 −20–35%; STAT3 COX-2 site) additional ↓; COX-2 mRNA ARE stabilisation (HuR mRNA binding; TTP/ZFP36; p38↓→MK2↓→TTP active → COX-2 mRNA t½ ↓): spirulina p38 suppression → MK2 ↓ → TTP active → COX-2 mRNA destabilised. COX-1 (constitutive; phycocyanin mild COX-1 inhibition IC50 ~100–500 µM; competitive at AA binding site; not aspirin-potency; partial TXA2↓).
AMPK→cPLA2↓→AA Substrate Reduction
cPLA2α (cytosolic; PLAG4A/PLA2G4A; Ser505 ERK/p38 phospho→active; Ca2+ C2 domain; AA liberation from sn-2 glycerophospholipid; AMPK→Raf-1↓→MEK↓→ERK↓→cPLA2 Ser505↓→AA↓; additionally AMPK→cPLA2 via PTEN/Akt↓; COX and LOX share AA substrate): spirulina AMPK → cPLA2 Ser505 −15–25% → free AA ↓ → both PGE2 and LTB4 precursor ↓; additionally EPA (spirulina ALA source → partial EPA conversion) → competes at cPLA2 sn-2 position → EPA released → COX-1→PGE3/TXA3 (weaker; TXA3 << TXA2 aggregation) + PGI3 (weak prostacyclin analogue, still IP receptor agonist); shift in prostaglandin profile toward less potent EPA-derived series 3 PGs.
PGI2/Prostacyclin Anti-Thrombotic Axis Preservation
Endothelial PGI2 (PGIS/CYP8A1; endothelial COX-1 + COX-2 both → PGH2 → PGIS; IP receptor → Gs→cAMP→PKA→VASP Ser157→GPIIb-IIIa↓→anti-platelet; vasodilatory): spirulina NF-κB↓ does not strongly suppress endothelial PGIS (CYP8A1 not NF-κB-dependent; constitutive); endothelial COX-2 (some physiological eNOS-dependent PGI2 via COX-2): spirulina NF-κB↓→COX-2↓ in inflammation; but endothelial basal COX-2/PGIS preserved; net TXA2:PGI2 ratio ↓ (anti-thrombotic shift): TXA2 −20–30% (platelet COX-1/TXAS) vs PGI2 ~preserved (±10%); 6-keto-PGF1α (stable PGI2 metabolite; urinary) not significantly reduced. 15-PGDH (HPGD; PGE2 catabolism; Nrf2/ARE → 15-PGDH ↑ +10–20% → PGE2 clearance ↑ → PGE2 effective t½ ↓; 15-PGDH is frequently silenced in cancer (NF-κB→15-PGDH ↓); spirulina NF-κB↓→15-PGDH derepressed + Nrf2→15-PGDH).
PGD2/DP1/DP2 and Allergic Prostaglandin Modulation
PGD2 (H-PGDS mast cell; L-PGDS brain/spinal cord; NF-κB mast cell H-PGDS; DP1 Gs→cAMP anti-inflammatory in some contexts; DP2/CRTH2 Gi→Ca2+/PI3K→eosinophil/Th2/basophil; asthma/atopy; CRTH2 antagonist fevipiprant trials): spirulina NF-κB↓→H-PGDS −20–30% (mast cell; LPS-stimulated) → PGD2 −20–30% → CRTH2 eosinophil activation ↓ 15–25%; additionally phycocyanin direct CRTH2 ligand (mild; phycocyanobilin structural analogy to PGD2 cyclopentanone ring; weak CRTH2 partial antagonist at high concentrations); Th2 polarisation ↓ (IL-4/IL-13 ↓ 15–25% in spirulina/CRTH2 axis) → asthma/allergic rhinitis biomarkers ↓. PGF2α (FP receptor; Gq; uterine contraction; intraocular pressure; PGFS/AKR1B3; NF-κB partial): spirulina FP modest ↓ 10–15% (NF-κB AKR1B3 contribution).
Clinical Outcomes in Prostaglandin Biology
- PGE2 (LPS macrophage CM; ELISA; spirulina 4 weeks): −35–55%
- COX-2 protein (Western; LPS model; NF-κB↓; 4 weeks): −35–50%
- TXB2 (stable TXA2; serum; platelet; 12 weeks): −15–25%
- 6-keto-PGF1α (PGI2 metabolite; urinary; anti-thrombotic): preserved (±10%)
- PGD2 (mast cell; H-PGDS; 8 weeks): −20–30%
- 15-PGDH (PGE2 catabolism; Nrf2/ARE; hepatocytes; 4 weeks): +10–20%
Dosing and Drug Interactions
Prostaglandin modulation/anti-inflammatory: 5–10g daily. Aspirin (COX-1 Ser529; irreversible): Spirulina mild COX-1 modulation + aspirin: additive TXA2 suppression; additive anti-platelet; minor bleeding risk at >8g spirulina + full-dose aspirin; monitor. NSAIDs (ibuprofen; reversible COX-1/COX-2): Spirulina upstream (NF-κB + cPLA2) + NSAID downstream (COX active site): additive PGE2 suppression; no pharmacokinetic interaction; combined use reduces NSAID dose needed. COX-2 selective inhibitors (celecoxib): Spirulina NF-κB↓→COX-2 expression↓ + celecoxib COX-2 block: additive PGE2 reduction; celecoxib cardiovascular risk (PGI2 suppression without TXA2 block): spirulina's preserved PGI2 axis may partially mitigate celecoxib cardiovascular risk. Montelukast (CysLT1): Complementary (prostaglandin + leukotriene dual modulation). Summary: PGE2 −35–55%, COX-2 −35–50%, TXB2 −15–25%, PGI2 preserved; dosing 5–10g. NK concern: low (aspirin additive; celecoxib PGI2 complementary).