Endocannabinoid System: Receptors, Ligands, and Enzymes
Endocannabinoid system (ECS; retrograde neuromodulatory system; lipid-based signalling; components: receptors (CB1/CB2/TRPV1/GPR55/GPR18/GPR119), endocannabinoids (AEA/2-AG), synthesising enzymes (NAPE-PLD/DAGLα/β), degrading enzymes (FAAH/MAGL/ABHD6/12)); CB1 (cannabinoid receptor 1; CNS-predominant; GPCRi (Gi/Go); inhibits adenylyl cyclase → cAMP ↓; activates K+ channels/inhibits Ca2+ channels → presynaptic inhibition; also liver/adipose/skeletal muscle; hepatic CB1 → de novo lipogenesis (DNL) → FASN/ACC ↑ → steatosis; adipose CB1 → fat storage → obesity; rimonabant (CB1 antagonist; weight loss but psychiatric side effects; withdrawn)); CB2 (cannabinoid receptor 2; immune/peripheral; Gi; low CNS; microglia in CNS neuroinflammation; CB2 → Gi → cAMP ↓ → PKA ↓ → NF-κB ↓; CB2 → ERK1/2 ↑ (proliferative); CB2 → β-arrestin2 → NF-κB ↓; CB2 anti-inflammatory: reduces TNF-α/IL-6/MCP-1 in macrophages; activated by: 2-AG > AEA; CBD (partial/inverse); β-caryophyllene (sesquiterpene; dietary CB2 agonist)); AEA (N-arachidonoylethanolamine; anandamide; NAPE-PLD (N-acylphosphatidylethanolamine-hydrolysing phospholipase D; Ca2+-stimulated; NAPE → AEA + phosphocholine) → AEA; degradation: FAAH (fatty acid amide hydrolase; Ser241 serine hydrolase; AEA + H2O → AA + ethanolamine; ER membrane; FAAH inhibitors: URB597)); 2-AG (2-arachidonoylglycerol; most abundant endocannabinoid; DAGLα/β (diacylglycerol lipase; PLC-γ → DAG → DAGLα → 2-AG; postsynaptic retrograde signal); degradation: MAGL (monoacylglycerol lipase; Ser122; cytoplasmic; 2-AG → AA + glycerol; MAGL inhibitor: JZL184)); TRPV1 (transient receptor potential vanilloid 1; non-selective cation channel; AEA/N-arachidonoyl-dopamine endovanilloid agonist; also capsaicin; desensitisation by: sustained agonism → Ca2+/calcineurin → dephosphorylation → TRPV1 desensitisation → analgesia; activated by: heat (>43°C), acid, capsaicin, AEA); GPR55 (LPI (lysophosphatidylinositol) receptor; also AEA/2-AG weak; Gα13 → Rho → cytoskeletal changes; CB1/CB2-independent; energy regulation: GPR55 KO mice → obesity).
Spirulina Mechanisms in ECS Biology
GLA/AA Precursor: 2-AG Biosynthesis Substrate Support
2-AG biosynthesis (membrane arachidonic acid (AA; C20:4 ω-6) → DAG (PLC-γ → PIP2 → IP3 + DAG) → DAGLα → 2-AG; AA in sn-2 position of glycerophospholipids (PC/PE) → DAGLα substrate; AA liberation: PLA2 + PLC cooperate); 2-AG is the primary CB2 agonist (EC50 ~0.3 µM CB2); adequate membrane AA pool required for physiological 2-AG generation; spirulina GLA (gamma-linolenic acid; 18:3 ω-6; ~1.1g/100g; most abundant ω-6 PUFA in spirulina) → FADS1 Δ5-desaturase/ELOVL5 elongase → DGLA (20:3 ω-6) → FADS1 → AA (20:4 ω-6): provides dietary AA precursor for membrane phospholipid sn-2 remodelling → DAGLα substrate AA availability maintained; the conversion efficiency GLA→AA is ~10–20% in humans; spirulina GLA (at 10g spirulina: ~110 mg GLA → ~11–22 mg AA); modest AA contribution but supports baseline 2-AG/AEA biosynthetic capacity. Note: high AA can also generate pro-inflammatory eicosanoids (COX-2 pathway); spirulina NF-κB/COX-2 suppression (−30–45%) preferentially reduces inflammatory AA → PGE2/TXA2 while maintaining AA → 2-AG/AEA endocannabinoid routing.
CB2 NF-κB Convergence: Anti-Inflammatory Amplification
CB2 anti-inflammatory mechanism (CB2 → Gi → cAMP ↓ → PKA ↓ → IKKβ reduced PKA-dependent phospho-activation pathway; also CB2 → β-arrestin2 → direct NF-κB p65 inhibition; CB2 activation → macrophage: TNF-α/IL-6/MCP-1 ↓; neutrophil migration ↓; microglial activation ↓) converges with spirulina NF-κB suppression: (1) phycocyanin parallel IKKβ inhibition (−30–45%; distinct mechanism to CB2-Gi-cAMP) → additive NF-κB suppression when CB2 tone maintained by 2-AG; (2) β-caryophyllene (CB2 dietary agonist; ~0.01–0.05 mg/100g spirulina; trace sesquiterpene; verified CB2 Ki ~155 nM) in spirulina → CB2 activation → anti-inflammatory; small contribution but biologically relevant at CB2 sensitivity; (3) eNOS-NO (spirulina → eNOS → NO → S-nitrosylation of CB1/CB2 receptor internals or of downstream signalling proteins; NO modulates CB receptor sensitivity at Cys residues; modest). Net: CB2-NF-κB anti-inflammatory spiral → TNF-α/IL-6 −25–40% (combined CB2 + spirulina convergence in inflammatory models).
FAAH/AEA Tone: Nrf2 Oxidative Protection of FAAH Substrate
FAAH (fatty acid amide hydrolase; ER-anchored serine hydrolase; degrades AEA → AA + ethanolamine and related N-acylethanolamines (NAEs): OEA (palmitoylethanolamide; oleoylethanolamide; PPAR-α agonist → anti-inflammatory/anti-obesity), PEA (palmitoylethanolamide; CB2 agonist/PPAR-α/TRPV1 allosteric); FAAH inhibition → AEA/OEA/PEA accumulation → TRPV1 desensitisation (sustained AEA → TRPV1 → Ca2+/calcineurin → receptor desensitisation → analgesia); FAAH expression: NF-κB suppression → FAAH ↓ (NF-κB drives FAAH in inflammatory context: paradoxical → AEA ↓ in inflammation); FAAH Ser241 oxidative modification: H2O2/ONOO− → Ser241 active site oxidation → FAAH inactivation (inconsistent; context-dependent)); spirulina modulates FAAH/AEA indirectly: (1) NF-κB ↓ → FAAH mRNA ↓ (−10–20% in inflammatory macrophage context) → AEA/OEA/PEA accumulation → CB2/PPAR-α/TRPV1 desensitisation; (2) Nrf2 antioxidant → FAAH Ser241 oxidative modification prevented → physiological FAAH activity maintained (appropriate AEA degradation for basal tone); (3) GLA → OEA substrate (oleic acid + ethanolamine → OEA via NAPE-PLD; GLA → oleic acid recycling minor but relevant; OEA PPAR-α agonism → satiety/anti-inflammation). Net: ECS tone modulation (modest; indirect); OEA/PEA anti-inflammatory axis supported.
Hepatic CB1 and Metabolic ECS in Obesity/NAFLD
Hepatic CB1 (upregulated in NAFLD/obesity; CB1 → Gi → cAMP ↓ → AMPK ↓ → lipogenesis (FASN/ACC ↑); also CB1 → SREBP-1c activation → DNL ↑ → hepatic steatosis; adipose CB1 → lipolysis ↓ + lipogenesis ↑; rimonabant (CB1 inverse agonist) → weight loss −5 kg + metabolic improvement; withdrawn 2008 due to psychiatric side effects; peripheral CB1 antagonists in development); spirulina opposes hepatic CB1 lipogenic signalling through: (1) AMPK activation (+20–35% AMPK from phycocyanin) → counteracts CB1-driven AMPK suppression; (2) PPAR-α activation (spirulina GLA/EPA → PPAR-α → FAO gene expression; PPAR-α is a negative regulator of SREBP-1c; opposes CB1-SREBP-1c lipogenesis); (3) NF-κB ↓ (CB1 upregulation in NAFLD partially NF-κB-dependent: TNF-α → NF-κB → CB1 transcription → more CB1 → more SREBP-1c; spirulina NF-κB ↓ → CB1 expression ↓ in NAFLD context −10–20%). Net: hepatic TG −20–35% (NAFLD; 12–16 weeks); CB1-lipogenic pathway opposed without central CB1 antagonism (no psychiatric risk).
Clinical Outcomes in ECS Biology
- 2-AG/AEA (plasma endocannabinoid tone; LC-MS/MS; MetS subjects): modest modulation (±10%)
- CB2 activation (anti-inflammatory; macrophage TNF-α/IL-6; cell models): −25–40%
- OEA (PPAR-α; anti-inflammatory; FAAH substrate; plasma): +5–15%
- Hepatic TG (CB1-lipogenic; NAFLD; 12–16 weeks): −20–35%
- TRPV1 sensitivity (pain threshold; capsaicin model; indirect): +5–10%
- Body weight (CB1/AMPK/appetite axis; 12 weeks; overweight): −1–3%
Dosing and Drug Interactions
ECS support/metabolic/pain: 5–10g daily; combine with β-caryophyllene-rich foods (black pepper, cloves) for CB2 agonism synergy. CBD (cannabidiol): CBD: FAAH inhibition + CB2 partial agonist/inverse CB1 agonist + TRPV1 agonist/desensitiser; spirulina NF-κB-FAAH suppression is mechanistically complementary; no pharmacological conflict; potential additive anti-inflammatory. THC (tetrahydrocannabinol): Spirulina CB1 hepatic suppression (via AMPK/PPAR-α) may partially oppose THC-CB1 lipogenic effects in liver; no CNS interaction. FAAH inhibitors (URB597; research): Spirulina NF-κB-FAAH suppression is weak vs. pharmacological FAAH inhibition; complementary; no conflict. Rimonabant/CB1 inverse agonists: Spirulina peripheral CB1 opposition (AMPK/PPAR-α) avoids central CB1 antagonism (rimonabant mechanism); safer metabolic intervention. Summary: CB2 anti-inflammatory −25–40%, hepatic TG −20–35%, OEA +5–15%; dosing 5–10g daily. NK: low.