Spirulina and Endocannabinoid System: CB1/CB2 Receptors, 2-AG, and AEA Metabolism

Endocannabinoid Biosynthesis: 2-AG and AEA

The two principal endocannabinoids are: (1) 2-arachidonoylglycerol (2-AG), synthesised from diacylglycerol by DAGL-alpha (DAGLA) and DAGL-beta (DAGLB), acting as a retrograde synaptic messenger and CB1/CB2 full agonist; (2) anandamide (AEA/ arachidonoyl ethanolamine), synthesised by NAPE-PLD (from N-arachidonoyl phosphatidylethanolamine) as a CB1 partial agonist and TRPV1 agonist. Both are synthesised on demand from membrane phospholipid precursors (arachidonate-containing PE/DAG) by Ca2+-activated and Gq/PLC-dependent mechanisms, released as retrograde messengers in neuronal synapses.

CB1 and CB2 Receptors: Downstream Signalling

CB1 (CNR1): abundant in brain (cerebellum, basal ganglia, hippocampus, cortex), primarily Gi-coupled (inhibiting adenylyl cyclase, reducing cAMP/PKA; activating K+ channels GIRK; inhibiting Ca2+ channels VGCC N/P/Q-type), reducing presynaptic neurotransmitter release (DSI: depolarisation-induced suppression of inhibition; DSE: suppression of excitation). CB2 (CNR2): predominantly immune cells (macrophages, DCs, B cells, NK cells, microglia), Gi/Gs-coupled, modulating cytokine production and immune cell migration. CB2 activation suppresses NF-kB and MAPK in macrophages, reducing TNF-alpha and IL-1beta.

FAAH and MAGL: Endocannabinoid Degradation

AEA is degraded by fatty acid amide hydrolase (FAAH, intracellular membrane enzyme, Ser241 nucleophile, also hydrolysing oleamide, PEA) to arachidonic acid and ethanolamine. 2-AG is degraded primarily by monoacylglycerol lipase (MAGL/MGLL, Ser122 nucleophile) to arachidonic acid and glycerol. Both FAAH and MAGL release arachidonic acid that can enter the COX/LOX eicosanoid pathway, linking endocannabinoid tone to eicosanoid metabolism. FAAH inhibitors (URB597) and MAGL inhibitors (JZL184) elevate tissue endocannabinoid levels with anti-inflammatory effects. Spirulina's GLA/DGLA substrate shift also affects the AA precursor pool for endocannabinoid synthesis.

TRPV1: Vanilloid Receptor and Capsaicin/AEA Overlap

TRPV1 (transient receptor potential vanilloid 1) is activated by capsaicin, heat (above 43 celsius), acidic pH, and anandamide (all acting as ligands of different affinity). TRPV1 mediates heat nociception and inflammatory hyperalgesia. Inflammatory mediators (PGE2, bradykinin, NGF) sensitise TRPV1 through PKA/PKC phosphorylation, lowering the activation threshold. TRPV1 desensitisation by sustained activation (calcium entry → calcineurin-mediated dephosphorylation) is exploited in capsaicin patches for pain. Spirulina's PGE2/inflammatory mediator reduction (via GLA/NF-kB) reduces TRPV1 sensitisation, attenuating inflammatory heat hyperalgesia.

CB2 and Neuroinflammation

Microglial CB2 is markedly upregulated in neuroinflammation (ALS, Alzheimer, MS, brain injury), where CB2 activation reduces NF-kB-driven TNF-alpha, IL-6, and NO production via Gi-cAMP inhibition and beta-arrestin-mediated pathway switching. 2-AG (the primary microglial CB2 ligand) is synthesised by DAGLB in microglia. Spirulina's GLA/AA substrate effects alter DAGLB substrate availability: GLA- derived DGLA could generate 2-dihomo-linoleoyl-glycerol (2-DLHG, a DGLA-derived DAG) that acts as a partial CB2 agonist, providing an alternative endocannabinoid- like anti-inflammatory signal with lower psychoactive potential than 2-AG.

Energy Homeostasis: CB1 and Appetite

Hypothalamic CB1 activation increases food intake (the "munchies" effect of THC/cannabis), reducing POMC and increasing NPY/AgRP expression via Gi-mediated suppression of cAMP and AMPK modulation. Obese patients show elevated endocannabinoid tone and CB1 supersensitivity in peripheral metabolic tissues (liver, adipose). CB1 blockade (rimonabant, withdrawn due to psychiatric effects) reduced obesity and metabolic syndrome markers. Spirulina's AMPK activation (opposing CB1-Gi-cAMP suppression of AMPK) and hypothalamic NF-kB/ER stress attenuation may counter hypothalamic CB1 hypersensitivity in the obese state, contributing to reported appetite/BMI effects in spirulina clinical studies.