Spirulina and Ferroptosis: GPx4, Lipid Peroxidation, and Iron-Dependent Cell Death

Ferroptosis: Mechanistic Definition

Ferroptosis is a regulated, non-apoptotic cell death triggered by the lethal accumulation of iron-dependent phospholipid hydroperoxides (PLOOH). It requires: (1) a labile iron pool (LIP) to drive Fenton chemistry, (2) polyunsaturated fatty acid (PUFA)-containing phospholipids—especially arachidonate- or adrenate-phosphatidylethanolamine (AA/AdA-PE) esterified by ACSL4 and LPCAT3, and (3) failure of the two major PLOOH-reducing systems: GPx4 and the FSP1 (AIFM2)-CoQ10 axis.

GPx4 as the Central Ferroptosis Suppressor

GPx4 uses GSH to reduce PLOOH to the corresponding hydroxylipid (PLOH) and water, preventing radical-chain amplification. The active-site selenocysteine (Sec46) reacts with PLOOH forming selenenyl-glutathione, regenerated by a second GSH. System Xc⁻ (SLC7A11/SLC3A2) imports cystine for GSH synthesis; its transcription is driven by Nrf2 and ATF4. Pharmacological GPx4 inhibition (RSL3) or System Xc⁻ blockade (erastin) are canonical ferroptosis triggers. Spirulina's PCB activates Nrf2 → SLC7A11 + GCLC/GCLM, elevating both cystine import and GSH synthesis, thereby sustaining GPx4 activity.

ACSL4 and LPCAT3: Building the Ferroptotic Substrate

Long-chain acyl-CoA synthetase 4 (ACSL4) preferentially activates AA and AdA to AA-CoA/AdA-CoA, which are incorporated into PE by LPCAT3, forming the PLOOH precursors oxidised by 15-LOX (ALOX15/ALOX15B) in complex with PEBP1. Spirulina's GLA content shifts eicosanoid substrate availability: DGLA (derived from GLA) competes with AA at ACSL4 and LOX active sites, reducing AA-PE esterification and PLOOH generation. NF-κB inhibition by PCB further reduces ACSL4 transcription (an NF-κB target gene).

Labile Iron Pool and Ferritin

The LIP—chelatable, redox-active iron—fuels Fenton reactions: Fe²⁺ + H₂O₂ → Fe³⁺ + •OH + OH⁻. Ferritin (FTH1/FTL) sequesters iron; its synthesis is controlled by IRP1/2 sensing cytosolic iron via IRE stem-loops, and by NRF2 (FTH1 has an ARE). Heme oxygenase-1 (HMOX1), also NRF2-driven, releases iron from heme—a potential pro-ferroptotic effect if iron accumulates. Spirulina's spirulan polysaccharides chelate Fe³⁺ extracellularly, while NRF2 activation simultaneously raises FTH1 to buffer intracellular LIP, managing the HMOX1 iron paradox.

FSP1-CoQ10: The Parallel Defence

Ferroptosis suppressor protein 1 (FSP1, formerly AIFM2) reduces CoQ10 (ubiquinone) to CoQ10H₂ (ubiquinol) using NADPH at the plasma membrane, trapping lipid peroxyl radicals independently of GPx4. FSP1 expression is induced by NRF2 and by the NRF2-independent transcription factor NF-E2. Spirulina provides: (a) NRF2 activation for FSP1 transcription, (b) NADPH preservation (via G6PD/pentose phosphate pathway support), and (c) CoQ10 biosynthetic precursors (4-hydroxybenzoate, decaprenyl-PP via MVA pathway).

DHODH in Mitochondria

Dihydroorotate dehydrogenase (DHODH) reduces CoQ to CoQH₂ in the mitochondrial inner membrane as a byproduct of pyrimidine synthesis, providing a third GPx4-independent anti-ferroptotic route. Cells with high mitochondrial activity (e.g., oxidative muscle fibres, neurons) rely more on DHODH-CoQH₂. Spirulina's AMPK-PGC-1α axis upregulates mitochondrial biogenesis, potentially elevating DHODH-CoQH₂ flux in these cells.

Lipid Peroxidation Markers and Spirulina Evidence

4-Hydroxynonenal (4-HNE) and malondialdehyde (MDA) are electrophilic aldehydes formed from PLOOH decomposition, used as ferroptosis/oxidative stress biomarkers. Multiple animal studies report significant reductions in plasma/tissue MDA following spirulina supplementation, consistent with GPx4/GSH support and LIP chelation. 4-HNE adducts on proteins (e.g., KEAP1 Cys273) can paradoxically activate NRF2, representing a feed-forward protective loop triggered by early lipid peroxidation.