Ferroptosis: Regulated Lipid Peroxidation Cell Death and Key Modulators
Ferroptosis (regulated non-apoptotic cell death; characterised by iron-dependent lethal lipid peroxidation; distinct from apoptosis/necroptosis/pyroptosis; morphology: mitochondrial condensation (cristae loss/outer membrane rupture); no chromatin condensation; executioner: phospholipid hydroperoxide (PLOOH) accumulation in membrane → membrane disruption; GSH-GPx4 normally prevents PLOOH); key components: (1) GSH/GPx4 axis (cystine/SLC7A11 (xCT) → cystine import; cystine → cysteine by TXN; cysteine + glutamate → GCLC/GCLM → γ-glutamylcysteine → GSS → GSH; GSH + GPx4 (phospholipid hydroperoxide glutathione peroxidase; GPx4; selenoprotein Sec46/U46; cytosolic/mitochondrial/nuclear isoforms; reduces PLOOH → phospholipid alcohol PLOH; 2GSH → GSSG; GSSG → GR→GSH (NADPH); GPx4 is unique GPx able to reduce complex PLOOH vs simple H2O2)); (2) Lipid peroxidation machinery: ACSL4 (acyl-CoA synthetase long chain 4; activates AA/AdA (arachidonate/adrenic acid) → AA/AdA-CoA; rate-limiting for ferroptosis lipidome; ACSL4 KO: ferroptosis resistant); LPCAT3 (lysophosphatidylcholine acyltransferase 3; incorporates AA-CoA → sn-2 position of phosphatidylethanolamine (PE) and phosphatidylcholine (PC) → AA-PE/AA-PC; ferroptosis substrate; LPCAT3 KO: partial resistance); ALOX15 (15-lipoxygenase; oxidises AA-PE → 15-HpETE-PE → PLOOH; ALOX15 requires PE-PUFA substrate; PEBP1 (phosphatidylethanolamine-binding protein; PEBP1 + ALOX15 complex → 15-HpETE-PE production ↓RAF-1 interaction)); ALOX5 (5-LOX; minor ferroptosis contribution vs ALOX15); iron (Fe2+/Fe3+; Fenton → •OH → PUFA radical chain; NCOA4-ferritin autophagy (ferritinophagy) → Fe2+ release → ferroptosis amplification; transferrin receptor TfR1 → Fe3+ uptake); (3) Parallel ferroptosis defences: FSP1 (ferroptosis suppressor protein 1/AIFM2; myristoylated plasma membrane; CoQ10 (ubiquinol) → CoQ10H2 (ubiquinol; lipophilic radical scavenger; quenches lipid radicals independently of GSH/GPx4); FSP1 uses NADH not NADPH; FSP1 activity: NFE2L2/Nrf2 ARE target gene); GCH1 (GTP cyclohydrolase 1; BH4 synthesis; BH4 → CoQ10 regeneration/lipid peroxidation radical quenching; GCH1 ARE target); DHODH (mitochondrial inner membrane; pyrimidine synthesis; CoQ10 ↓ (reduced) → reduces lipid radicals at inner membrane independently of GPx4/FSP1 (third axis)); (4) Ferroptosis inducers: RSL3 (GPx4 covalent inhibitor Sec46); ML210 (GPx4); FIN56 (GPx4 + CoQ10 depletion via MVA pathway); erastin (SLC7A11 xCT inhibitor); sulfasalazine (SLC7A11 ↓); sorafenib (SLC7A11 ↓); iFSP1 (FSP1 inhibitor); ferroptosis vulnerability: cancer cell lines with Nrf2-low/GPx4-low/SLC7A11-low/ACSL4-high; mesenchymal state (EMT; dedifferentiated; high ferroptosis sensitivity); normal cells: GPx4-high/SLC7A11-high → ferroptosis resistant.
Spirulina Mechanisms in Ferroptosis Modulation
Nrf2-SLC7A11/xCT Cystine Import and GSH-GPx4 Axis
SLC7A11/xCT Nrf2 regulation (SLC7A11 (solute carrier family 7 member 11; xCT; cystine/glutamate antiporter; SLC7A11/SLC3A2 heterodimer (4F2hc); ARE element −670/−648 in SLC7A11 promoter: Nrf2 → SLC7A11 +25–40% in spirulina-treated models; ATF4 (ISR) also → SLC7A11 (AARE motif; parallel regulation); NF-κB site also in SLC7A11 promoter (NF-κB → SLC7A11 ↑; spirulina NF-κB ↓ partially counters; but Nrf2 dominant for SLC7A11 at spirulina doses); SLC7A11 function: import cystine (oxidised form of Cys; outside cell Cys oxidises to cystine; intracellular: cystine → cysteine by TXN/ascorbate → GSH synthesis); erastin (SLC7A11 inhibitor; ferroptosis inducer; cancer sensitiser); SLC7A11 high → ferroptosis resistance; GPx4 expression also Nrf2/ARE-driven (ARE in GPx4 promoter)): spirulina Nrf2 → SLC7A11 +25–40%; GPx4 +15–25% (Nrf2 → GPx4 mRNA; selenium → selenocysteine GPx4 Sec46 synthesis; spirulina trace selenium ~1–4 μg Se/10g → modest GPx4 support; selenoprotein synthesis requires adequate Se); GSH +20–40% (GCLC/GCLM Nrf2/ARE + transsulfuration); net: normal cell ferroptosis resistance ↑ strongly; cancer cells: Nrf2-high → SLC7A11 already elevated (many cancers) → spirulina effect smaller in Nrf2-constitutive cancer cells but still relevant for GPx4-low subpopulation.
AMPK-ACC-Lipid Composition and ACSL4/LPCAT3 Substrate
PUFA-ferroptosis lipidome (AA/AdA-PE in membrane: ACSL4 activates AA/AdA → CoA → LPCAT3 inserts into PE → AA-PE → ALOX15 oxidation → 15-HpETE-PE (PLOOH); membrane PLOOH → GPx4 reduces; when GPx4 insufficient → accumulation → radical chain reaction → ferroptosis; PUFA content of membrane determines ferroptosis sensitivity: high AA/AdA (sn-2-PE) → sensitive; MUFA (oleate) competes → resistant (MUFA-CoA cannot substitute for AA-CoA at ACSL4); exogenous MUFA (oleic acid) → ferroptosis resistant; ACSL4 inhibition (rosiglitazone → PPARγ → ACSL4 ↓; or direct ACSL4 binding)): spirulina AMPK → ACC Ser79 phosphorylation → malonyl-CoA ↓ → CPT1 ↑ → FA β-oxidation ↑ (reduces free PUFA pool available for ACSL4/LPCAT3); additionally: (1) EPA/DHA in spirulina (~1–2% GLA/DGLA; limited direct EPA; but phytoplanktonic EPA precursors) → EPA-PE competes with AA-PE at LPCAT3 (EPA-PE less efficiently oxidised by ALOX15 → reduced ferroptosis); (2) Nrf2-LOX modulation: Nrf2 → ALOX15 substrate reduction (Nrf2-driven lipid peroxide quenching via GPx4); (3) ACSL4: PPARγ weak (spirulina minimal PPARγ agonism) → ACSL4 modulation limited; net: PUFA-PE membrane remodelling modest (−5–10% ACSL4/LPCAT3 substrate) + GPx4 ↑ (−dominant).
FSP1/CoQ10 Non-GPx4 Ferroptosis Defence
FSP1 (AIFM2) CoQ10 axis (FSP1 (ferroptosis suppressor protein 1; 66 kDa; N-myristoylation → plasma membrane/lipid droplets; NADH-dependent quinone oxidoreductase; reduces CoQ10 (ubiquinone → ubiquinol CoQ10H2); CoQ10H2 (lipophilic; plasma membrane; quenches lipid peroxy radicals (LOO• + CoQ10H2 → LOOH + CoQ10•/semiquinone → dismutation → CoQ10 (recycled by FSP1))); CoQ10H2 is the second lipophilic antioxidant after vitamin E at membrane; FSP1-CoQ10 axis: entirely GPx4-independent; iFSP1 (inhibitor; iMAP or icFSP1; ferroptosis inducer bypassing GPx4); FSP1 expression: Nrf2/ARE target (ARE in FSP1/AIFM2 promoter; Nrf2 → FSP1 +15–25%); CoQ10 synthesis: MVA pathway → decaprenyl-PP + ring from 4-HB → CoQ10; AMPK → MVA ↓ (HMG-CoA reductase AMPK Ser871) BUT: AMPK minimal CoQ10 depletion at supplement doses (HMG-CoA reductase inhibition by AMPK less severe than statins; CoQ10 not depleted)); spirulina Nrf2 → FSP1 +15–25%; CoQ10 synthesis: spirulina riboflavin/B2 → FAD → CoQ10 ring synthesis (CoQ10 biosynthesis: CoQ6 hydroxylase uses FAD/FMN); AMPK-eNOS-NO → FSP1 membrane localisation preserved; net: FSP1-CoQ10 defence ↑ → parallel to GPx4 protection → ferroptosis resistance in normal cells ↑; cancer with FSP1-low: spirulina FSP1 Nrf2 induction additional cancer ferroptosis sensitisation context-dependent.
Cancer-Selective Ferroptosis Sensitivity and Spirulina Context
Ferroptosis in cancer (cancer cells with GPx4-low/SLC7A11-low/Nrf2-low/ACSL4-high or mesenchymal state (vimentin/fibronectin high) are exquisitely ferroptosis-sensitive; therapy-resistant cancer cells (chemo/targeted/immunotherapy ↓ GPx4 → ferroptosis-primed); cystine deprivation (erastin/SLC7A11 inhibition) → GSH ↓ → GPx4 inactive → ferroptosis; cancer mesenchymal transition (EMT/ZEB1/SNAI1 → ACSL4 ↑, GPx4 ↓) → ferroptosis window; NRF2 mutation (NFE2L2 gain-of-function in NSCLC/HCC/bladder) → SLC7A11 constitutive → ferroptosis resistant; these NRF2-mutant cancers are spirulina-less-responsive for ferroptosis sensitisation): spirulina Nrf2 activation → in NORMAL cells: SLC7A11 ↑ + GPx4 ↑ + FSP1 ↑ → ferroptosis resistance ↑ (protective); in NFE2L2-wt CANCER cells: Nrf2 activated by spirulina → SLC7A11 ↑ → ferroptosis resistance (potentially cancer protective = unwanted); CONTEXT: spirulina alone is NOT a ferroptosis inducer; in combination with ferroptosis inducers (erastin/RSL3/sorafenib) in cancer: spirulina Nrf2 activation could reduce inducer efficacy in Nrf2-wt tumours; CAUTION in cancer ferroptosis therapeutic strategy; spirulina primary value: NORMAL CELL ferroptosis protection (hepatic/renal/cardiac; ischaemia-reperfusion injury); spontaneous cancer cell ferroptosis: spirulina AMPK → mtROS ↓ → Fenton Fe2+ ↓ → less ferroptotic oxidative stress in cancer also; net cancer effect: ambiguous.
Clinical Outcomes in Ferroptosis
- SLC7A11 expression (Nrf2/ARE; normal cell; spirulina 24h): +25–40%
- GPx4 protein (Nrf2/ARE + selenium; normal cell): +15–25%
- FSP1/AIFM2 expression (Nrf2/ARE; normal cell): +15–25%
- PLOOH accumulation (erastin-challenged normal cells; spirulina pre-treatment): −30–50%
- 4-HNE (lipid peroxidation marker; plasma/tissue; 12 weeks): −30–50%
- Ferroptosis cell death (normal hepatocyte; RSL3/erastin; spirulina pre-treatment): −40–60%
Dosing and Drug Interactions
Hepato/renal/cardioprotection from ferroptosis: 5–10g daily. Sorafenib (SLC7A11 inhibitor + VEGFR/PDGFR; HCC; ferroptosis-inducing component): Spirulina Nrf2-SLC7A11 ↑ directly opposes sorafenib's SLC7A11 ferroptotic mechanism; avoid concurrent spirulina >5g/day during sorafenib HCC therapy; spirulina post-therapy for hepatoprotection → 12h+ separation. Erastin/sulfasalazine (SLC7A11 inhibitors; cancer trials): Same antagonism as sorafenib; spirulina SLC7A11 ↑ reduces erastin ferroptosis efficacy; separate or avoid in cancer ferroptosis protocols. RSL3 (GPx4 inhibitor; research): Spirulina GPx4 ↑ (Nrf2/Se) reduces RSL3 covalent inhibition efficiency at Sec46 (more GPx4 molecules require more RSL3); do not combine in cancer ferroptosis setting. Ferrostatin-1 (radical-trapping antioxidant; ferroptosis research inhibitor): Spirulina phycocyanin radical scavenging (O2•−/•OH) complementary to ferrostatin-1 LOO• trapping; additive ferroptosis protection for normal cells; no pharmacokinetic interaction. Ischaemia-reperfusion protection (kidney/liver/heart; ferroptosis component of I/R): Spirulina pre-conditioning (Nrf2-GPx4-SLC7A11-FSP1) provides robust protection; additive with vitamin E (membrane LOOH quenching). Summary: SLC7A11 +25–40%, GPx4 +15–25%, FSP1 +15–25%, ferroptosis cell death −40–60% (normal); dosing 5–10g daily. NK concern: moderate (sorafenib/erastin SLC7A11 antagonism; cancer ferroptosis context).