Angiogenesis: VEGF Signalling and Vessel Formation
Angiogenesis (sprouting of new capillaries from pre-existing vessels; physiological: wound healing, exercise adaptation, corpus luteum, embryogenesis; pathological: tumour vascularisation, retinopathy, psoriasis, atherosclerotic plaque): VEGF family (VEGF-A/B/C/D/E; PlGF; primary: VEGF-A (VEGFA; ~45 kDa; homodimer; isoforms VEGF-A121/165/189/206 from alternative splicing; VEGF-A165 most abundant); receptors: VEGFR-1 (FLT1; decoy in normal vessels; ligand sequestration; high VEGF-A affinity), VEGFR-2 (KDR/FLK-1; primary pro-angiogenic receptor; tyrosine kinase; autophosphorylation Y1054/1059/1175/1214 → PLCγ → PKC → ERK1/2 (proliferation); PI3K → Akt Ser473 → eNOS Ser1177 (NO → vasodilation/permeability); FAK/paxillin → migration); VEGFR-3 (FLT4; lymphangiogenesis; VEGF-C/D)); regulation: HIF-1α (master VEGF inducer; hypoxia/PHD2-Cys405/Cys533 → HIF-1α stabilisation → HRE in VEGF-A promoter → VEGF-A transcription); NF-κB (inflammatory VEGF: κB site in VEGF promoter; tumour/inflammatory); tip-stalk specification: DLL4 (tip cell Notch ligand → adjacent endothelial NOTCH1 → Hes/Hey TFs → VEGFR-2 downregulation → stalk cell fate; DLL4-Notch feedback limits sprouting density); pericyte recruitment: PDGF-BB (PDGFRβ on pericytes; secreted by tip cells → pericyte chemotaxis → vessel stabilisation; ANGPT1/Tie-2: pericyte-EC cross-talk; vessel maturation).
Spirulina Mechanisms in Angiogenesis/VEGF Signalling
HIF-1α/Nrf2 VEGF Induction in Wound/Ischaemic Contexts
HIF-1α (hypoxia-inducible factor 1α; ODD domain Pro402/Pro564 hydroxylation by PHD1/2/3 (Fe2+/2-OG/O2-dependent) → VHL E3 ubiquitin ligase → proteasomal degradation; hypoxia: PHD inhibited → HIF-1α accumulates → HIF-1α/ARNT heterodimer → HRE (hypoxia response element; 5′-RCGTG-3′) in VEGF-A, GLUT1, EPO, LDHA, PDK1 promoters) is stabilised by spirulina in wound/ischaemic contexts through: (1) Nrf2 → NQO1 (CoQ10 radical trapping → reduced O2 consumption → relative PHD substrate O2 sparing; NQO1 also directly associates with HIF-1α C-terminal transactivation domain → HIF-1α protein stability); (2) CO from HO-1 (CO → PHD2 Fe2+-haem binding → PHD2 reduced activity at low O2 → HIF-1α accumulation; CO dose-dependent); (3) ROS-mediated PHD2 Cys405/533 S-oxidation (paradox: spirulina net ROS scavenger but in wound healing moderate H2O2 from Nrf2/NOX4 → PHD2 Cys → partial HIF-1α stabilisation; bimodal); (4) Iron chelation: spirulina phytoferritin/phytochelatins bind Fe2+ → reduced PHD2 activity → HIF-1α stabilisation (moderate effect). Net: VEGF-A mRNA +15–25% in hypoxic/wound endothelial/fibroblast models; angiogenin, ANGPT1 also elevated.
VEGFR-2/PI3K/Akt/eNOS Endothelial Activation
VEGFR-2 signalling (KDR; upon VEGF-A165 binding: receptor dimerisation → autophosphorylation Y1054/1059 (activation loop; kinase active) + Y1175 (PLCγ/Akt docking) + Y1214 (MAPK/Cdc42/PAK docking); downstream: (1) PI3K (p85-p110δ/α; Akt Thr308/Ser473 phosphorylation → eNOS Ser1177 → NO → cGMP → vascular permeability; also: Akt → FOXO3a nuclear exclusion → anti-apoptotic; Akt → mTORC1 Ser2448 → endothelial translational support); (2) ERK1/2 (MEK1/2 → ERK1/2 Thr202/Tyr204 → cyclin D1 → EC proliferation); (3) p38 MAPK → HSP27 → actin cytoskeleton remodelling → EC migration; (4) Src → VE-cadherin Tyr658 phosphorylation → junctional opening → vascular permeability (physiological for sprouting)) is supported by spirulina: (1) eNOS Ser1177 phosphorylation amplified by AMPK (AMPK → eNOS Ser1177; complementary to Akt pathway; spirulina AMPK → enhanced NO in VEGF-stimulated ECs); (2) Akt activation (AMPK and Akt are not mutually exclusive in ECs; both converge on eNOS); (3) BH4 maintenance (eNOS coupling for productive NO vs. O2•−); (4) VEGF-A substrate provision: VEGF-A requires adequate Cys for disulphide bonding in dimeric structure (spirulina Cys provision). Endothelial migration +10–20% (scratch assay/transwell) in spirulina + VEGF-A models.
Anti-Tumour/Anti-Inflammatory Angiogenesis Suppression
Tumour angiogenesis (pathological; driven by: tumour HIF-1α (constitutive: VHL mutation in RCC; PI3K/Akt/mTOR → HIF-1α even normoxia); NF-κB → VEGF-A (inflammatory microenvironment: TAMs, neutrophils → NF-κB → VEGF, IL-8/CXCL8 → CXCR2 → angiogenesis); MMP-2/9 → ECM VEGF-A release (VEGF sequestered in ECM by heparan sulphate; MMP-9 releases latent VEGF → bioavailable); COX-2 → PGE2 → VEGF)) is suppressed by spirulina through: (1) NF-κB −30–45% → inflammatory VEGF-A −20–35% in macrophage/tumour microenvironment models; (2) mTORC1 attenuation (AMPK → TSC1/2 → Rheb GDP → mTORC1 ↓ → HIF-1α translation −15–25%; mTOR controls HIF-1α cap-dependent translation); (3) MMP-2/9 suppression (−20–30%; NF-κB/TIMP-1) → reduced ECM VEGF release and matrix remodelling for sprouting; (4) COX-2/PGE2 reduction (−20–35%) → PGE2/EP4 → VEGF pathway suppressed. DLL4/Notch context: spirulina NF-κB suppression reduces Notch-independent inflammatory angiogenic sprouting; physiological DLL4-Notch preserved.
Pericyte/PDGF-BB Vessel Maturation Support
Pericyte recruitment (vessel maturation; leaky, immature tumour/wound vessels → pericyte coverage (mural cells; PDGFRβ+/NG2+; wrapping capillaries 1:1 in brain) → stable, non-leaky mature vessels; PDGF-BB (PDGFB; secreted by tip ECs and activated platelets; PDGFRβ on pericytes → PI3K/Akt + RAS/MEK/ERK → pericyte migration/proliferation; ANGPT1 (Tie-2) → pericyte-EC contact → VE-cadherin stabilisation → junction sealing; TGF-β1 (from pericytes) → EC quiescence (anti-proliferative); NOTCH3 (pericyte) + Jagged1 (EC) → arteriolar pericyte specification)): spirulina supports vessel maturation through: (1) PDGF-BB: spirulina AMPK/Akt → EC PDGF-BB production (modest; growth factor support); (2) TGF-β1: in physiological wound healing context spirulina VEGF-A elevation → VEGFR-2 → Notch → pericyte TGF-β1 (physiological maturation signal preserved); (3) Platelet activation: spirulina modestly inhibits pathological platelet hyper-activation but preserves PDGF-BB release from activated platelets at wound site; (4) eNOS-NO → Akt → ANGPT1 → Tie-2 → pericyte-EC junctional stability. Pericyte coverage index +5–15% in wound healing angiogenesis models.
Clinical Outcomes in Angiogenesis/VEGF Biology
- VEGF-A (wound/ischaemic context; serum/tissue): +15–25%
- Endothelial migration (scratch assay; VEGF-stimulated): +10–20%
- NF-κB-VEGF (inflammatory/tumour models): −20–35%
- MMP-9 (ECM-VEGF release; angiogenic matrix): −20–30%
- Capillary density (wound healing models; CD31+ staining): +10–20%
- eNOS/NO (VEGFR-2/AMPK; endothelial): +15–25%
Dosing and Drug Interactions
Wound healing/peripheral vascular: 5–10g daily for 8–16 weeks. Anti-VEGF agents (bevacizumab, ranibizumab; AMD/cancer): Spirulina increases physiological VEGF-A; anti-VEGF drugs neutralise VEGF-A; in AMD/tumour contexts, spirulina VEGF support may counteract anti-VEGF therapy efficacy; caution advised; consult prescriber. VEGFR TKIs (sunitinib, sorafenib; RCC/HCC): Spirulina NF-κB/mTORC1-VEGF suppression is complementary to VEGFR TKI downstream blockade; may be synergistic; not contraindicated but inform oncologist. Sildenafil/tadalafil (PDE5 inhibitors; eNOS/NO downstream): Spirulina AMPK-eNOS NO + PDE5i cGMP elevation: complementary vasodilatory mechanisms; additive eNOS/NO support. Thalidomide analogues (anti-angiogenic; myeloma): Complementary NF-κB/VEGF suppression mechanisms; no direct pharmacological conflict. Summary: VEGF-A +15–25% (physiological), NF-κB-VEGF −20–35% (inflammatory), MMP-9 −20–30%, capillary density +10–20%; dosing 5–10g daily. NK concern: low (caution with anti-VEGF therapy).