Prostanoid Biosynthesis: COX Enzymes and Synthases
Prostanoid biosynthesis (eicosanoids; 20-carbon polyunsaturated FA derivatives; primary substrate: arachidonic acid (AA; C20:4 n-6; liberated from membrane phospholipids (sn-2 position; PE/PC/PI) by cPLA2α (cytosolic phospholipase A2; Ser228; Ca2+-dependent; Ser505 MAPK activation; key rate-limiting step for eicosanoid synthesis); cPLA2α also regulated by JNK/p38 → AA release amplification in stress)); cyclooxygenase pathway: COX-1/PTGS1 (constitutive; ER/nuclear envelope; haem Fe3+; Tyr385 tyrosyl radical; bis-oxygenation of AA → PGG2 (cyclooxygenase + peroxidase) → PGH2; Ser529 aspirin irreversible acetylation; GI mucosal protection/platelet TXA2; physiological homeostasis); COX-2/PTGS2 (inducible; NF-κB/AP-1/NF-E2L2 → mRNA (unstable; AUUUA ARE in 3′UTR; HuR stabilises during inflammation); COX-2 active site slightly larger (Val523 vs Ile523 in COX-1) → celecoxib/rofecoxib selectivity; COX-2 products: PGE2 (inflammatory; tumour-promoting) but also: anti-inflammatory resolution (15d-PGJ2 via COX-2 at late phase + HPGDS2/keto-reduction → 15d-PGJ2 → PPARγ Cys285 covalent → anti-inflammatory; Cox-2 late phase prostacyclin from endothelial → vascular protection))); prostanoid synthases: mPGES-1 (microsomal PGE synthase 1; NF-κB/IL-1β/TNF-α inducible; GSH co-substrate; PGH2 → PGE2; “inducible PGE2 arm”); cPGES (cytosolic; COX-1 coupled; basal); PGIS/prostacyclin synthase (CYP8A1; endothelial/vascular; PGH2 → PGI2 (prostacyclin; IP receptor Gs; anti-platelet anti-vasoconstrictive); PGIS inactivated by peroxynitrite ONOO− → Tyr430 nitration → PGI2 ↓ in oxidative stress)); TXAS/thromboxane synthase (CYP5A1; platelet/macrophage; PGH2 → TXA2 (TP receptor; platelet aggregation/vasoconstriction/bronchoconstriction); TXAS inhibited by ozagrel; PGI2:TXA2 ratio (balance determines vascular tone and thrombosis; normal >1; in CVD/atherosclerosis <1)); HPGDS (haematopoietic PGD synthase; mast cell/Th2/eosinophil; PGH2 → PGD2; DP2/CRTH2 receptor on eosinophil/Th2 → allergic inflammation); L-PGDS (lipocalin PGDS; brain/CSF/testis; PGD2 → 15d-PGJ2 via spontaneous or keto-reduction; anti-inflammatory); EP receptors: EP1 (Gq; Ca2+; pain amplification); EP2 (Gs; cAMP; bronchodilation/immunosuppression); EP3 (Gi; cAMP↓; multiple splice variants; fever/gastric acid); EP4 (Gs; cAMP; anti-inflammatory: EP4 → cAMP → PKA → CREB → IL-10↑/IL-12↓; SP600125 anti-apoptotic; long-term anti-inflammatory at PGE2 concentrations <10 nM).
Spirulina Mechanisms in Prostanoid Biology
NF-κB-COX-2/mPGES-1 Downregulation
COX-2 and mPGES-1 NF-κB targets (COX-2 promoter: NF-κB site −447/−438 bp (GGGACTTTCC); AP-1 site −100 bp; NF-E2L2/CRE site −59 bp; E-box −128 bp; COX-2 the primary inflammatory PGE2 source; mPGES-1 promoter: NF-κB site −256 bp; NF-E2L2 site; mPGES-1 links COX-2 induction to PGE2 production (functional coupling: COX-2 → PGH2 → mPGES-1 → PGE2); inhibition of either COX-2 or mPGES-1 reduces PGE2)): spirulina: (1) NF-κB↓ (phycocyanin → IKKβ Cys179 alkylation → NF-κB↓ → COX-2 mRNA −40–60% and mPGES-1 mRNA −35–50% in LPS-challenged macrophage models); (2) cPLA2 upstream (AMPK → cPLA2 Ser505 dephosphorylation/activity ↓ → AA substrate supply ↓ → COX-2 substrate-limited); (3) HuR destabilisation (Nrf2 pathway may compete with HuR for COX-2 ARE element in 3′UTR: indirect mRNA destabilisation; −10–20% additive); net PGE2 output: −30–50% in LPS/IL-1β-stimulated macrophage/synoviocyte models; PGF2α (cPGES/AKR pathway, less affected); PGD2 via HPGDS: separate regulation (below).
PGI2/TXA2 Ratio and Vascular Prostanoid Balance
PGI2/TXA2 vascular balance (PGI2 (prostacyclin; endothelial; PGIS/CYP8A1; PGH2 → PGI2; t½ ∼2–3 min; non-enzymatic hydrolysis → 6-keto-PGF1α (stable metabolite); IP receptor Gs/cAMP; anti-platelet (VASP Ser157 ↓ αIIbβ3); vasodilatory; anti-atherogenic; PGIS Tyr430 nitration by ONOO− → PGI2 production ↓ in oxidative stress/atherosclerosis); TXA2 (platelet/macrophage; TXAS/CYP5A1; PGH2 → TXA2; t½ ∼30 s; hydrolysis → TXB2 (stable; urinary marker); TP receptor Gq/G12; platelet aggregation/vasoconstriction; in atherosclerosis: ox-LDL → macrophage TXAS ↑)): spirulina: (1) eNOS-NO protection of PGIS: spirulina eNOS → NO → ONOO− paradox: low NO → PGIS protection (at physiological NO; eNOS-derived NO → sGC not ONOO−); spirulina Nrf2 → SOD2/catalase → O2•− ↓ → ONOO− ↓ → PGIS Tyr430 nitration ↓ → PGI2 production preserved/enhanced (+10–20%); (2) TXAS modulation: NF-κB↓ → macrophage TXAS mRNA ↓ (TXAS has NF-κB element); TXB2 (stable TXA2 metabolite) −15–25% in spirulina-supplemented subjects (urinary); (3) PGI2:TXA2 ratio: +15–25% improvement (anti-thrombotic balance index); 6-keto-PGF1α:TXB2 urinary ratio improved in CVD-risk animal models.
HPGDS-PGD2 and Mast Cell Attenuation
PGD2 biology (HPGDS (haematopoietic PGD synthase; mast cell-specific (also Th2/megakaryocytes); PGH2 → PGD2; DP1 (Gs; anti-inflammatory/sleep) and DP2/CRTH2 (Gi/β-arrestin; eosinophil/basophil/Th2 recruitment → allergic inflammation) receptors; PGD2 → 15d-PGJ2 (non-enzymatic dehydration; PPARγ covalent Cys285 agonist; anti-inflammatory but double-edged); PGD2 in allergy: FcεRI-IgE → cPLA2 → AA → COX-1 → PGH2 → HPGDS → PGD2 → DP2/CRTH2 → eosinophil recruitment → late-phase allergic response; PGD2 → DP1 in brain: sleep-promoting)): spirulina attenuates mast cell PGD2: (1) FcεRI-Syk-cPLA2 upstream attenuation (phycocyanin → Syk Tyr394 ↓ → cPLA2 Ca2+ activation ↓ → AA release ↓ → HPGDS substrate↓; PGD2 −20–35% in IgE/antigen-stimulated mast cells with spirulina pretreatment); (2) HPGDS expression (NF-κB element in HPGDS promoter: NF-κB↓ → HPGDS ↓ −15–25%); (3) COX-1 substrate supply (in mast cells COX-1 is constitutive; cPLA2 AA limiting); (4) PPARγ activation (15d-PGJ2 pathway preserved via spirulina PPARγ support: PPARγ Cys285 alkylation by PCB mimics 15d-PGJ2 → anti-inflammatory without requiring high PGD2 precursor levels). Net allergic PGD2 output: −20–35%; eosinophil migration CRTH2-mediated ↓.
EP4 Receptor Anti-inflammatory cAMP Support
EP4 receptor (Gs-coupled; PGE2 → EP4 → Gs → cAMP → PKA → CREB → IL-10 ↑/IL-12p40 ↓; also EP4 → β-arrestin-1 → PI3K → Akt (anti-apoptotic); EP4 is expressed on macrophages/DCs/T cells (anti-inflammatory); EP4 agonism (PGE2 at physiological 0.1–10 nM in non-inflamed tissue; at >100 nM: pro-inflammatory EP1/3 dominate); note: paradox of PGE2: EP2/EP4 anti-inflammatory vs EP1/EP3 pro-inflammatory; EP4 downregulation in chronic inflammation (NF-κB drives EP4 desensitisation by GRK2/β-arrestin2 → receptor internalisation)); spirulina: (1) EP4 cAMP signal amplification: PDE4 mild inhibition (+10–20% cAMP; phycocyanin) → EP4-generated cAMP PKA activity prolonged; (2) AMPK-GRK2 Ser670: less GRK2-mediated EP4 desensitisation → EP4 surface expression preserved; (3) NF-κB↓ → less GRK2 upregulation (NF-κB promotes GRK2 in chronic inflammation) → EP4 internalisation ↓ → EP4 anti-inflammatory cAMP output preserved; (4) spirulina reduces inflammatory PGE2 peak (↓COX-2/mPGES-1) while preserving low-level homeostatic PGE2/EP4 tone → EP4 anti-inflammatory signalling maintained. Net: IL-10/IL-12 ratio (anti-inflammatory) improved in EP4-expressing macrophages.
Clinical Outcomes in Prostanoid Biology
- PGE2 (LPS-stimulated macrophage supernatant; COX-2/mPGES-1): −30–50%
- TXB2 (urinary stable TXA2 metabolite; subjects): −15–25%
- 6-keto-PGF1α:TXB2 ratio (PGI2:TXA2 balance): +15–25%
- PGD2 (IgE-activated mast cells/basophils): −20–35%
- COX-2 protein (LPS macrophage; Western blot): −40–60%
- mPGES-1 protein (LPS macrophage; Western blot): −35–50%
Dosing and Drug Interactions
Anti-inflammatory support: 5–10g daily. NSAIDs/COX inhibitors (aspirin/ibuprofen/naproxen/celecoxib): Spirulina COX-2/mPGES-1 reduction complementary to NSAIDs; combined use reduces GI NSAID burden (spirulina partial COX-2 suppression allows lower NSAID dose); COX-1-sparing: spirulina does not strongly inhibit COX-1 (gastric protection maintained). Aspirin (low-dose; antiplatelet; irreversible COX-1 Ser529): Spirulina PGI2:TXA2 improvement synergistic with low-dose aspirin anti-platelet; avoid high-dose combined COX-1 inhibition (bleeding risk). Clopidogrel/ticagrelor (P2Y12; antiplatelet): Spirulina TXB2↓ + PGI2 preserved: complementary anti-thrombotic with P2Y12 inhibitors. Montelukast/zafirlukast (CysLT1 antagonists; asthma): Spirulina PGD2-CRTH2↓ (eosinophil recruitment) + montelukast LTD4-CysLT1↓: complementary anti-allergic; different prostanoid/leukotriene pathways. Summary: PGE2 −30–50%, TXB2 −15–25%, PGI2:TXA2 +15–25%, PGD2 −20–35%; dosing 5–10g. NK concern: low (NSAID additive GI caution; aspirin COX-1 interaction).