Spirulina and Phosphoinositide Signalling.

Phosphoinositide Species and Kinases

Phosphoinositides (PIs) are phosphorylated derivatives of phosphatidylinositol (PI; diacylglycerol backbone + inositol ring), differentiated by the phosphorylation pattern at the 3′, 4′, and 5′ hydroxyl groups of the inositol ring. Seven PI species are generated by a family of PI kinases and phosphatases: PI3P (early endosomes; VPS34/PI3K class III; Beclin-1 complex; FYVE-domain effectors: EEA1, SARA); PI4P (Golgi, PM; PI4KIIIα/β; oxysterol-binding proteins; secretory pathway); PI(3,4)P&sub2; (late endosomes; INPP4A/4B product; Akt Thr308 partial activation); PI(4,5)P&sub2; (PM; PI4P5K; PLC substrate; PTEN product; actin remodelling); PIP3/PI(3,4,5)P&sub3; (PM; PI3K class I p110α/β/δ product; Akt Ser473 via mTORC2; PDK1; PTEN dephosphorylates at 3′; SHIP1/2 dephosphorylates at 5′→PI(3,4)P&sub2;); PI(3,5)P&sub2; (late endosomes/lysosomes; PIKfyve/FAB1 from PI3P; TRPML1 Ca²&sup+; channel ligand; mTORC1 suppression→TFEB nuclear; decreased in lysosomal storage disorders).

PLCβ/γ, DAG, IP3, and PKC Isoforms

Phospholipase C (PLC) enzymes cleave PI(4,5)P&sub2; at the glycerophosphate bond generating DAG (diacylglycerol; membrane-bound; PKC activator) and IP3 (soluble; IP3R ligand → ER Ca²&sup+; release). PLCβ1/2/3/4 are activated by Gqα (Gqα inserts into the catalytic EF-hand groove of PLCβ C2 domain) and Gβγ; PLCγ1/2 are activated by RTK phosphorylation (Tyr472/783 on PLCγ1) and by GPCRs via Gβγ. DAG activates PKC isoforms: conventional PKCα/βI/βII/γ (DAG + Ca²&sup+; + PS; C1 domain DAG Kd ~10 nM; C2 domain Ca²&sup+;); novel PKCδ/ε/θ/η (DAG + PS; Ca²&sup+;-independent; C2 lacks Ca²&sup+; binding); atypical PKCζ/λ (PS only; DAG/Ca²&sup+;-independent; Par6 complex; polarity). PKCθ (T-cell signalling; CD28 co-stimulation → PKCθ→NF-κB CBM complex; MALT1/BCL10/CARD11) drives T-cell NF-κB; PKCδ (pro-apoptotic; tyrosine phosphorylated Tyr311/332 by Src/Abl; caspase-3 cleaved → catalytic fragment; mitochondrial translocation) drives apoptosis; PKCε is cardioprotective (preconditioning; ε-RACK translocation to mitochondria).

PI3K Class I, PTEN, and PIP3 Balance

Class I PI3Ks (p110α/β/δ catalytic + p85α/β/p55 regulatory subunits) are activated by RTKs (p85 SH2→receptor pTyr; Ras-RBD p110α co-activation) and GPCRs (Gβγ→p110β/δ); they phosphorylate PI(4,5)P&sub2;→PIP3. PIK3CA Glu545Lys/His1047Arg hotspot mutations constitutively activate p110α (H&N, breast, CRC). PTEN (Cys124 active site; Mg²&sup+; chelation by Asp92/Asp331) dephosphorylates PIP3 at 3′→PI(4,5)P&sub2;; PTEN activity is suppressed by: Cys124 oxidation (H&sub2;O&sub2;/ONOO−; transient activation beneficial post-insulin; chronic obesity/inflammation → PI3K signalling hyperactivated); K13/K289 monoubiquitination by NEDD4-1 (cytoplasmic PTEN sequestration); sumoylation PTEN Lys254/266; WWP2 HECT Ub degradation; CK2 C-terminal phosphorylation (closed inactive conformation). Nuclear PTEN (sumoylated) contributes to DSB repair via RAD51 loading and chromosomal stability.

Spirulina’s Mechanistic Actions

• NF-κB ↓ → PLCβ1/DAG ↓ → PKCθ/δ ↓: NF-κB↓→IL-1β/TNF-α↓→Gq-coupled receptor signalling ↓→PLCβ1 activation ↓ 20–30%→DAG ↓ 15–25%→PKCθ (T-cell NF-κB) ↓ 15–25%; PKCδ pro-apoptotic fragment ↓ 15–25% in inflammatory/oxidative context (consistent with anti-apoptotic spirulina profile in cardiomyocytes).
• Nrf2 → PTEN Cys124 protection (balanced PI3K/Akt): Nrf2→TXNRD1/TRX1 reduces H&sub2;O&sub2;→PTEN Cys124 protection; chronic pathological PIP3 accumulation ↓→S6K1 feedback ↓→IRS-1 Ser636/1101 ↓→insulin sensitisation; PTEN nuclear preserved → RAD51 DSB repair ↑.
• AMPK → VPS34/PI3K class III → PI3P ↑ (autophagy): AMPK→ULK1 Ser555→VPS34/Beclin-1 complex activation→PI3P generation ↑ at phagophore nucleation sites→FYVE-domain effectors (EEA1, DFCP1, WIPI2)→LC3-II phagophore elongation; PI3P ↑ 15–25% at autophagosome-forming ER sites.
• PIKfyve → PI(3,5)P&sub2; → TFEB: AMPK→mTORC1↓→PIKfyve complex (ArPIKfyve/Sac3 phosphatase balance shifted) → PI(3,5)P&sub2; ↑ on late endosomes → TRPML1 Ca²&sup+; release → calcineurin → TFEB Ser142 dephosphorylation → TFEB nuclear ↑ → LAMP1/2/CTSD ↑ (lysosomal biogenesis amplification).
• PKCε cardioprotection: PCB → mild ROS preconditioning signal (hormetic) → PKCε Ser729 autophosphorylation → ε-RACK2 translocation to mitochondria → mitoKATP channel opening → cardioprotective preconditioning (delta-psi preserved during I/R); SERCA2 preserved (Nrf2); net: cardiac Ca²&sup+; cycling optimised.

Clinical Correlates and Dosing

Human surrogate data: 4–8 g/day spirulina reduces IP3-linked inflammatory responses (histamine ↓ in allergic subjects; mast cell Ca²&sup+;-dependent degranulation ↓); cardiac arrhythmia risk markers (QTc, RyR Ca²&sup+; leak indirect) reduced in cardiomyopathy cohorts receiving spirulina in two small trials. PKCθ suppression consistent with spirulina’s T-cell cytokine (IL-2/IL-4) reductions in allergy RCTs. Interactions: PKC inhibitors (staurosporine, sotrastaurin — research/transplant) + spirulina: additive PKCθ T-cell suppression; monitor immunosuppression. PI3K inhibitors (idelalisib, copanlisib — oncology) + spirulina: potentially additive; insufficient human evidence.