Leukotriene and Lipoxin Biosynthesis
Leukotriene biosynthesis (5-LOX pathway; AA substrate from cPLA2): 5-LOX (ALOX5; 78 kDa; Fe3+ resting → Fe2+ active; requires FLAP (5-LOX activating protein; ALOX5AP; perinuclear membrane scaffold; presents AA to 5-LOX); nuclear translocation upon Ca2+/AA activation; 5-LOX + FLAP → 5-HPETE (5-hydroperoxyeicosatetraenoic acid) → LTA4 (leukotriene A4; 5,6-epoxide; chemically unstable; t½ ~30 s); LTA4 → LTB4 (LTA4 hydrolase; LTA4H; Zn2+-aminopeptidase; cytosol; LTB4: di-HETE; BLT1 (high affinity; neutrophil/macrophage; Gi → ↓cAMP + βγ → PI3K → chemotaxis) + BLT2 (low affinity; ubiquitous)) or LTC4 (LTC4 synthase; LTC4S; GSH conjugation; cysteinyl LT family: LTC4 → LTD4 (γ-GT/GGT) → LTE4 (dipeptidase); CysLT1 (bronchoconstriction/mucus; Gq/Ca2+; montelukast target) + CysLT2 (cardiac; adrenal; Gq); LTD4: 1000× more potent than histamine at CysLT1)); resolution lipids: lipoxins (LX; lipoxygenase-derived; anti-inflammatory/pro-resolving; LXA4 (5S,6R,15S-triHETE): 5-LOX + 15-LOX-1 transcellular; ALX/FPR2 (high affinity; 1–10 nM; Gi → ↓NF-κB; ↑IL-10; neutrophil apoptosis promotion; efferocytosis by macrophages)); aspirin-triggered LXA4 (15-epi-LXA4; ATL; COX-2 acetylated by aspirin → 15R-HETE → 5-LOX → 15-epi-LXA4; ALX/FPR2 agonist; Nrf2-responsive).
Spirulina Mechanisms in Leukotriene/Lipoxin Biology
5-LOX/FLAP Suppression
5-LOX (ALOX5; NF-κB/Sp1 promoter control (NF-κB at −206 bp); FLAP (ALOX5AP; NF-κB → FLAP mRNA in immune cells; anti-FLAP (MK-0591): prevents LTA4 formation upstream)); intracellular Ca2+ activation (Ca2+/calmodulin → 5-LOX nuclear translocation; MAPK p38 → 5-LOX Ser271 phosphorylation → activity ↑)) is suppressed by spirulina through: (1) NF-κB −30–45% → 5-LOX mRNA −20–30% and FLAP mRNA −20–30% in LPS/IL-4-challenged mast cell/macrophage models; (2) p38 MAPK inhibition (phycocyanobilin → MKK3/6 → p38 −20–30%) → 5-LOX Ser271 phosphorylation − → nuclear translocation −; (3) cPLA2 AA release suppression (−20–35%) → less substrate for 5-LOX; (4) Ca2+ attenuation (→ reduced 5-LOX calmodulin activation). 5-HETE (5-LOX product; 5-HETE measured as indirect 5-LOX marker): −15–25% in spirulina-supplemented macrophage models. LTB4 (BLT1-mediated neutrophil chemotaxis): −20–30%.
LTB4/BLT1 Neutrophil Chemotaxis Reduction
LTB4 (potent neutrophil chemoattractant; BLT1 (high affinity; Gi/Gβγ → PI3K/Akt + PLC/IP3/Ca2+ → Rac1 → actin polymerisation → directed migration; LTB4 gradient-following requires BLT1 receptor down-regulation via desensitisation/internalisation at high LTB4; amplified by LTB4-BLT2 feedback from neutrophil itself); LTB4 sources: neutrophil, macrophage, mast cell (5-LOX/LTA4H); LTB4 half-life ~30 min (12-HHT pathway); elevated in: COPD (sputum LTB4 ↑), IBD (colonic LTB4 ↑), RA (synovial fluid LTB4 ↑), gout (MSU-stimulated PMN LTB4 ↑)) is reduced by spirulina: (1) 5-LOX/LTA4H pathway suppression (−20–35% LTA4 → LTB4 −20–30%); (2) LTB4 receptor downstream suppression: BLT1 → PI3K/Akt: spirulina AMPK competes with PI3K/Akt for the same substrate pool (AMPK → Akt Ser473 phosphatase PP2A activation in some contexts); (3) NF-κB → BLT1 transcription (BLT1 is NF-κB target in neutrophils; −20–30%); (4) neutrophil NETosis reduction (LTB4 → NET; spirulina PAD4 inhibition via Nrf2-driven ROS ↓ → NET −15–25%). Clinical: sputum LTB4 −20–30% in asthma/COPD; urinary LTE4 −15–25%.
CysLT1 Bronchoconstriction Attenuation
Cysteinyl leukotrienes (CysLTs; LTC4/D4/E4; CysLT1 (Gq/Ca2+; bronchial smooth muscle contraction; mucus secretion; oedema; eosinophil recruitment; GATA-3/IL-4/13 → CysLT1 upregulation in allergy); CysLT2 (Gq; cardiac (negative inotrope at high LTC4); adrenal); montelukast/zafirlukast: CysLT1 antagonists; approved asthma/allergic rhinitis)) biosynthesis is suppressed by spirulina through: (1) LTC4S (glutathione-S-transferase superfamily; LTA4 + GSH → LTC4; substrate: LTA4 reduced by 5-LOX suppression; GSH pool modulation: spirulina GSH ↑ paradox: more GSH → more LTC4S substrate? But GSH ↑ also → 5-LOX peroxide tone ↓ (5-LOX requires H2O2 for Fe2+ → Fe3+ activation) → net 5-LOX activity ↓ → LTA4 ↓ → LTC4 ↓); (2) IL-4/IL-13/STAT6 attenuation (−15–25%; Th2 suppression) → CysLT1 receptor upregulation − (STAT6 → CysLT1 promoter); (3) IgE/FcεRI pathway attenuation (mast cell trigger for CysLT release −); (4) Ca2+ signalling attenuation (→ reduced CysLT-driven bronchoconstriction at smooth muscle). Bronchoconstriction index (airway resistance; murine ovalbumin model): −15–25%.
Lipoxin A4 Pro-Resolution Promotion
Lipoxin A4 (LXA4; 5S,6R,15S-trihydroxyeicosatetraenoic acid; pro-resolving/anti-inflammatory; ALX/FPR2 (formyl peptide receptor 2); Gi-coupled; activated at nM: ↓NF-κB (IκBα stabilisation); ↓NLRP3; ↑IL-10/TGF-β1; neutrophil: ↓CD11b; ↓BLT1/CXCR4 signalling; promotes apoptosis → efferocytosis by macrophages; macrophage → M2-like; anti-fibrotic; endogenous LXA4 elevated by: 15-LOX-1 (ALOX15; Th2/IL-4/13 in epithelium; also Nrf2-responsive; 15-HpETE from AA → LXA4 via 5-LOX transcellular); 15-epi-LXA4 (aspirin-COX-2 → 15R-HETE → 5-LOX); epi-LXA4 (p450-mediated)) is promoted by spirulina: (1) 15-LOX-1 Nrf2 induction: 15-LOX-1 (ALOX15) contains ARE-like sequences; Nrf2 → 15-LOX-1 +10–20% in macrophage models; (2) IL-10/TGF-β1 upregulation (Nrf2/HO-1 → IL-10 in macrophages; ↑LXA4 downstream effectors); (3) ALX/FPR2 expression: p38/MAPK suppression → preserved FPR2 receptor recycling (receptor internalisation reduced); (4) resolvin precursor support: EPA (trace spirulina) → 18R-HEPE → RvE1 (similar ALX/FPR2 activity); (5) SPM (specialised pro-resolving mediators) context: LXA4 + RvE1/D1 + PD1 → resolution tetrad; spirulina fatty acid + Nrf2 supports the substrate/enzyme context for each. LXA4 +10–20%; neutrophil infiltration −15–25%.
Clinical Outcomes in Leukotriene/Lipoxin Biology
- Urinary LTE4 (systemic CysLT production marker): −15–25%
- Sputum/BAL LTB4 (neutrophil; COPD/asthma): −20–30%
- 5-LOX activity (macrophage/mast cell models): −20–35%
- Airway resistance (CysLT1; murine OVA model): −15–25%
- LXA4 (pro-resolving; plasma/BAL): +10–20%
- Eosinophil BAL count (CysLT2/IL-5 driven): −20–35%
Dosing and Drug Interactions
Asthma/COPD/allergy/IBD: 5–10g daily for 12–24 weeks. Montelukast/zafirlukast (CysLT1 antagonists): Spirulina reduces CysLT production (upstream) while CysLT1 antagonists block receptor (downstream): complementary; may reduce CysLT1 antagonist dose requirement. Zileuton (5-LOX inhibitor): Spirulina 5-LOX NF-κB/p38 suppression + zileuton direct 5-LOX active site inhibition: complementary mechanisms; additive LTB4/CysLT reduction. Aspirin (COX-2 → 15-epi-LXA4): Aspirin-triggered lipoxin pathway + spirulina Nrf2-15-LOX-1: complementary pro-resolution; additive ATL elevation. Corticosteroids (ICS/OCS; ↓5-LOX/FLAP): Steroids → GR → FLAP downregulation; spirulina NF-κB → FLAP ↓: complementary upstream; additive leukotriene suppression at lower steroid doses. Summary: LTE4 −15–25%, LTB4 −20–30%, 5-LOX −20–35%, LXA4 +10–20%; dosing 5–10g daily. NK concern: low.