Spirulina and Peroxisome Biology: Catalase, β-Oxidation, and ROS Compartmentalisation

Peroxisome Function: Oxidative Metabolism Compartmentalised

Peroxisomes are single-membrane organelles that concentrate oxidases generating H₂O₂ and catalase (CAT) to dismutate it locally. Primary functions include: (1) β-oxidation of very-long-chain fatty acids (VLCFA, C≥22) and branched-chain fatty acids before mitochondrial hand-off; (2) plasmalogen (1-alkenyl ether phospholipid) synthesis— critical for brain myelin and erythrocyte membranes; (3) bile acid synthesis (AMACR, SCPx); (4) glyoxylate detoxification (AGXT alanine:glyoxylate aminotransferase); and (5) purine catabolism (urate oxidase in non-primates).

Catalase: H₂O₂ Dismutation and AMPK Regulation

Catalase (CAT) is a tetrameric haemoprotein that dismutates 2 H₂O₂ → 2 H₂O + O₂ with a kcat ~10⁷ s⁻¹. CAT also degrades short-chain alcohols via its peroxidatic activity. CAT expression is induced by NRF2 (ARE in promoter), FOXO3a (caloric restriction/SIRT1 axis), and PPAR-α (fatty acid loading). Spirulina activates all three: PCB→Nrf2 for direct ARE transactivation; AMPK→FOXO3a nuclear retention; and GLA→PPARα activation. Multiple rodent and human studies show elevated erythrocyte CAT activity with spirulina supplementation.

ACOX1 and Peroxisomal H₂O₂ Production

Acyl-CoA oxidase 1 (ACOX1) catalyses the first step of peroxisomal β-oxidation, transferring electrons directly to O₂ (producing H₂O₂, unlike mitochondrial FAO which uses FAD→ETF). If H₂O₂ production outpaces CAT, peroxisomal H₂O₂ leaks to the cytosol. ACOX1 is transcriptionally induced by PPARα; so is CAT—coupling substrate and dismutation. Spirulina's GLA-derived DGLA is a PPARα ligand, potentially co-inducing ACOX1 and CAT proportionally. ACOX1 also generates acetyl-CoA fed to the Krebs cycle, linking peroxisomal fat catabolism to mitochondrial energy metabolism.

Plasmalogen Synthesis and the Peroxisome-Membrane Connection

Plasmalogens (1-alkenyl-2-acyl-glycerophospholipids) are assembled exclusively in peroxisomes (GNPAT + AGPS steps) before transfer to the ER for fatty acid remodelling. They constitute ~20% of total phospholipids in brain and heart, and their vinyl ether bond acts as a sacrificial radical scavenger protecting polyunsaturated sn-2 chains from oxidation. Plasmalogen deficiency (Zellweger spectrum, RCDP) leads to severe neurological and skeletal disease. Spirulina's antioxidant protection of peroxisomal membrane integrity (through CAT induction and lipid peroxidation suppression) indirectly preserves GNPAT/AGPS enzyme activity and plasmalogen output.

PEX Genes and Peroxisome Biogenesis

Peroxins (PEX1–PEX26) mediate peroxisome biogenesis and protein import via PTS1/PTS2 targeting signals. Peroxisome number and size respond to fatty acid load (PPARα), to oxidative stress (AMPK), and to fission/fusion dynamics (DRP1, FIS1 at peroxisome membranes). AMPK activation promotes peroxisome proliferation in concert with mitochondrial biogenesis. Spirulina's AMPK activation thus may coordinately expand both mitochondrial and peroxisomal capacity—a synergistic effect in cells with high fat oxidation demand.

Uric Acid and the Xanthine Oxidase Connection

Xanthine oxidase (XO), while primarily cytosolic, shares substrate (hypoxanthine, xanthine) with peroxisomal urate oxidase (in animals expressing it). XO generates O₂•⁻ and H₂O₂. PCB inhibits XO directly (IC₅₀ ~50 μM in vitro), reducing uric acid production and O₂•⁻ generation—an effect complementary to CAT upregulation in clearing H₂O₂. This dual action (XO substrate reduction + CAT-mediated H₂O₂ dismutation) may explain part of spirulina's consistent anti-hyperuricaemia effects in clinical trials.