Phospholipid Metabolism: Synthesis, Remodelling, and Signalling Lipids
Phospholipids (major membrane components; glycerophospholipids: PC (phosphatidylcholine; >50% of bilayer), PE (phosphatidylethanolamine; inner leaflet; mitophagy LC3-PE), PI (phosphatidylinositol; signalling), PS (phosphatidylserine; inner leaflet; apoptosis flip; efferocytosis), PG (mitochondrial; cardiolipin precursor)): CDP-choline Kennedy pathway (choline → CKα/β (choline kinase) → phosphocholine → CCT (CTP:PC cytidylyltransferase α/β; rate-limiting; membrane binding activated; Nrf2/ARE partial) → CDP-choline → CPT1 (choline phosphotransferase; ER) + DAG → PC; PC:PE ratio (>1 normal; <1 in NAFLD—disturbed; PEMT (phosphatidylethanolamine N-methyltransferase SAM×3 → PE→PC; major in liver; SAM-dependent)); DAG/IP3 signalling lipids (PI(4,5)P2 (PM inner leaflet; PLCβ/γ→DAG+IP3; IP3→IP3R Ca2+; DAG→PKCα/β); PI(3,4,5)P3 (PI3K class I p85/p110→PI(4,5)P2 + ATP → PI(3,4,5)P3; PTEN (3-phosphatase; Cys124 redox) reversal; PIP3→Akt PH domain→Akt Thr308/Ser473→GSK3β/FOXO/TSC2)); phospholipid remodelling (Lands cycle: PLA2 sn-2 hydrolysis → lyso-PC/PE → LPCAT (lysophospholipid acyltransferase: LPCAT1/2 saturated; LPCAT3 PUFA EPA/DHA; Nrf2/ARE LPCAT3) → reacylation with PUFA → PUFA-enriched membranes → lipid raft fluidity ↑; LPCAT3 specifically incorporates AA/EPA/DHA at sn-2 → ferroptosis substrate AND anti-inflammatory membrane remodelling); PS flipping (TMEM16F scramblase (activated by Ca2+/apoptosis) flips PS from inner→outer leaflet; ATP11A/ATP11C (P4-ATPase flippase) maintains PS inner leaflet; apoptosis: caspase-3→PLSCR1→PS outer leaflet → MFG-E8/Gas6/TIM4 PS receptors→efferocytosis macrophage).
Spirulina Mechanisms in Phospholipid Metabolism
AMPK→ACC↓→Malonyl-CoA↓ De Novo PC Saturation Reduction
AMPK→ACC1/2 (AMPK phosphorylates ACC1 Ser79 + ACC2 Ser218 → ACC inactive → malonyl-CoA ↓ → CPT1A inhibition released → fatty acid β-oxidation ↑; malonyl-CoA also ↓ → FASN substrate ↓ → de novo lipogenesis ↓ → saturated FA (palmitate/stearate) pool ↓ → less saturated PC/PE synthesis via Kennedy pathway): spirulina AMPK → ACC Ser79 +20–35% → malonyl-CoA −20–35% → de novo palmitate ↓ → palmitate-PC (DPPC) ↓ 15–25%; membrane SFA:PUFA ratio ↓ (more fluid bilayer); lipid raft dynamics: AMPK→cholesterol synthesis↓ (HMGCR Ser872) + SFA-PC↓ → raft fluidity ↑ → receptor compartmentalisation improved (eNOS-Cav-1 dissociation ↑; TLR4 raft exclusion partial). PEMT (liver PC synthesis via methylation): spirulina SAM pool +5–15% → PEMT PE→PC slight ↑ but minor vs Kennedy pathway changes.
Nrf2→LPCAT3 PUFA Phospholipid Remodelling
LPCAT3 (MBOAT5; Nrf2/ARE element in LPCAT3 promoter; incorporates AA/EPA/DHA at sn-2 glycerophospholipid; LPCAT3 KO → impaired chylomicron secretion + PUFA-PE ↓; LPCAT3 determines AA-PE levels → ferroptosis sensitivity (ACSL4+LPCAT3 synthesise AA-PE for 15-LOX→PLOOH); paradox: spirulina Nrf2→LPCAT3 ↑ → PUFA-PE ↑ in normal cells; simultaneously FSP1/GPx4 Nrf2 ↑ → PLOOH ↓ (ferroptosis protection override); net PUFA incorporation beneficial for: membrane fluidity, lipid mediator substrate availability, and anti-inflammatory PUFA balance): spirulina Nrf2 → LPCAT3 +15–25% → EPA/DHA-PE incorporation ↑ → EPA-PE pool ↑ → 15-LOX→15-HEPE→LXA4 precursor ↑; membrane DHA (DHA-PE/DHA-PC) → lipid raft DHA → BDNF/TrkB signalling modulation → neuroprotection; PC remodelling: palmitate-PC ↓ (ACC↓) replaced by oleate/PUFA-PC ↑ → SFA:PUFA-PC ratio net ↓ 20–35%.
PI(3,4,5)P3/PTEN Balance and Akt Physiological Oscillation
PTEN Cys124 redox (PTEN active: PI(3,4,5)P3→PI(4,5)P2; PTEN Cys124-SOH oxidation by H2O2 → Cys71-Cys124 disulphide → PTEN inactive → PI(3,4,5)P3 accumulates → Akt ↑; TRX1 reduces Cys71-Cys124 → PTEN reactivated; physiological: VEGF/insulin → NOX4 H2O2 pulse → PTEN transient inactivation → Akt → eNOS/GLUT4; pathological: chronic H2O2 → PTEN permanently inactivated → sustained Akt → mTOR→insulin resistance/cancer): spirulina Nrf2 → TXNRD1/TRX1 +25–40% → PTEN Cys71-Cys124 disulphide faster reduction → PTEN reactivation quicker after H2O2 pulse → PI(3,4,5)P3 transient (physiological) vs sustained (pathological: −15–25% sustained PI(3,4,5)P3 in chronic oxidative stress cells); PIP2 production: AMPK→PI4KIIα (PI4-kinase; generates PI4P → PIP2; AMPK regulation modest); net: PI3K-PTEN-Akt oscillation physiological; pathological sustained pAkt ↓ 15–25%.
Phosphatidylserine and Efferocytosis Enhancement
PS externalisation (apoptosis: caspase-3→cleavage PLSCR1 (phospholipid scramblase 1) + inhibition ATP11A flippase → PS outer leaflet → macrophage PS-receptor recognition (MFG-E8→integrinαvβ3/5; Tim4→PS direct; Gas6/Protein S→TAM receptors Tyro3/Axl/MerTK) → efferocytosis; efficient efferocytosis → resolution inflammation; failed efferocytosis (secondary necrosis → DAMP release → inflammation perpetuation); Nrf2→MerTK/MERTK (Nrf2/ARE partial MerTK→efferocytosis receptor↑)): spirulina: (1) apoptosis induction (cancer/pathological cells): spirulina anti-proliferative in cancer → caspase-3 ↑ → PS externalisation ↑ → tumour cell efferocytosis ↑; (2) normal non-apoptotic cells: spirulina does not induce PS flip (caspase-3 not activated); (3) Nrf2→MerTK ↑ → efferocytosis efficiency ↑ in macrophages; (4) PE→PC remodelling (Lands cycle) → less PE in outer leaflet background → PS signal cleaner for recognition. Net: apoptotic cell clearance ↑ 20–30% → SASP/secondary necrosis ↓ (complementary to NF-κB↓→SASP axis).
Clinical Outcomes in Phospholipid Metabolism
- Membrane SFA:PUFA ratio (PC lipidomics; PBMC; 12 weeks): −20–35%
- LPCAT3 (Nrf2/ARE; hepatocyte/endothelium; qRT-PCR; 4 weeks): +15–25%
- EPA/DHA-PE (sn-2 PUFA incorporation; MS lipidomics): +15–20%
- Sustained PI(3,4,5)P3 (chronic oxidative stress model; ELISA): −15–25%
- Efferocytosis index (apoptotic body/macrophage; IF; 6 weeks): +20–30%
- De novo palmitate incorporation into PC (13C-palmitate; MS): −15–25%
Dosing and Drug Interactions
Phospholipidome remodelling: 5–10g daily; combine with EPA/DHA (2g/day) for maximal LPCAT3-mediated PUFA membrane incorporation. Statins (HMGCR; also reduce isoprenoids/farnesyl-PP/GG-PP → Rab/Rho prenylation ↓): Spirulina AMPK→HMGCR + statin HMGCR: additive cholesterol synthesis ↓ → less PC raft cholesterol; statin also reduces prenylated signalling; complementary lipid bilayer changes. PI3K inhibitors (idelalisib/copanlisib; cancer): Spirulina Nrf2→TRX1→PTEN protection reduces pathological PI(3,4,5)P3; PI3K inhibitor blocks PI(3,4,5)P3 synthesis; complementary PIP3 reduction; no pharmacokinetic interaction. Phospholipase A2 inhibitors (cytarabine/varespladib sPLA2): Spirulina AMPK→cPLA2↓ reduces AA release; varespladib secretory PLA2 (sPLA2) inhibitor; different enzymes; additive. Summary: Membrane SFA:PUFA −20–35%, LPCAT3 +15–25%, EPA/DHA-PE +15–20%, efferocytosis +20–30%; dosing 5–10g + EPA/DHA. NK concern: low.