Spirulina and Adipokine Signalling: Adiponectin, Leptin, and Adipose-Brain Cross-talk

Adiponectin: Anti-Inflammatory Insulin Sensitiser

Adiponectin (AdipoQ/ADIPOQ) is the most abundant adipokine, secreted by adipocytes as trimers, hexamers, and high-molecular-weight multimers. It acts through AdipoR1 (skeletal muscle, high affinity for globular adiponectin) and AdipoR2 (liver, full- length adiponectin) via the adaptor APPL1. Downstream: AdipoR1/R2 activate AMPK (via PP2A-mediated dephosphorylation of AMPK Ser485 negative site), and activate PPAR-alpha (via ceramide hydrolysis by neutral ceramidase recruited by AdipoR2). Adiponectin is reduced in obesity and type 2 diabetes; spirulina supplementation increases adiponectin in several rodent and human studies, providing an AMPK- activating hormonal axis complementary to direct cellular AMPK activation by PCB.

Leptin and the ObRb-STAT3-NPY Circuit

Leptin (LEP) is produced by white adipose tissue proportional to fat mass, signalling satiety through the long-form receptor ObRb (LEPR) in hypothalamic arcuate nucleus neurons. ObRb activates JAK2 (Tyr1007/1008 trans-autophosphorylation), then STAT3 (Tyr705 phosphorylation), and IRS-1/PI3K (AMPK activation in hypothalamus). STAT3 drives POMC expression (anorexigenic) and suppresses AgRP/NPY (orexigenic). In diet-induced obesity, hypothalamic leptin resistance develops (suppressor SOCS3 upregulation, ER stress, and ceramide accumulation in hypothalamic neurons). Spirulina reduces hypothalamic ER stress (via Nrf2/UPR modulation) and ceramide (via nSMase2 suppression through PCB), potentially partially restoring leptin receptor sensitivity.

Adipose NF-kB: Inflammatory Adipokine Production

In obese adipose tissue, lipid-activated TLR4 signalling, hypoxia (from adipocyte hypertrophy), and ceramide collectively activate NF-kB in adipocytes and resident macrophages (crown-like structures), driving production of inflammatory adipokines: TNF-alpha (inhibits insulin receptor signalling via IRS-1 Ser307 phosphorylation), IL-6 (STAT3-driven SOCS3 induction causing leptin/insulin resistance), MCP-1/CCL2 (macrophage recruitment), PAI-1 (fibrinolysis suppression). PCB-driven NF-kB suppression in adipose tissue would attenuate this inflammatory adipokine profile, reducing systemic metabolic inflammation.

Resistin, Visfatin, and Chemerin

Resistin (RETN) is elevated in obese rodents and activates TLR4-NF-kB and SOCS3, impairs adiponectin signalling. Visfatin (NAMPT/PBEF), also the rate-limiting enzyme in NAD+ biosynthesis (discussed in sirtuins post), links adipose inflammation to NAD+ availability and SIRT1 activity. Chemerin (RARRES2) activates CMKLR1 on DCs, NK cells, and adipocytes, linking adipose to innate immunity. Spirulina's effects on NF-kB and AMPK/NAMPT axes would collectively suppress pro-inflammatory resistin and modulate visfatin/NAMPT activity.

Adiponectin-AMPK-PGC-1alpha in Skeletal Muscle

Adiponectin via AdipoR1 activates muscle AMPK, which: (1) phosphorylates ACC2 Ser221 to de-repress CPT1 and fatty acid beta-oxidation; (2) phosphorylates AS160 Thr642 to increase GLUT4 translocation and glucose uptake; (3) phosphorylates PGC-1alpha Thr177/Ser538 and induces SIRT1 (via NAMPT-NAD+ elevation) to deacetylate PGC-1alpha, driving mitochondrial biogenesis and oxidative fibre gene expression. The adiponectin- AMPK-PGC-1alpha cascade thus mediates much of the metabolic benefit of spirulina in peripheral tissues, providing a hormonal amplification of spirulina's direct cellular AMPK effects.

Brown Adipose Tissue and UCP1

Brown adipose tissue (BAT) uncouples mitochondrial proton gradient via UCP1 (thermogenin), dissipating energy as heat (thermogenesis). BAT activity is activated by cold/sympathetic nervous system (beta3-AR/cAMP/PKA), AMPK, and PPAR-gamma/PGC-1alpha co-regulation. White adipose browning (beiging) through PRDM16/PGC-1alpha increases UCP1-positive beige adipocytes. Spirulina's AMPK and PPARalpha activation has been associated with reduced adipocyte size and lipid accumulation in animal models, consistent with increased lipid oxidation, and preliminary evidence suggests UCP1 upregulation in adipose of spirulina-fed rodents.