Astaxanthin alleviates DSS-induced ulcerative colitis in mice associated with Nrf2-mediated ferroptosis independently of gut microbiota modulation.

Astaxanthin, a natural carotenoid predominantly synthesized by marine microorganisms, has shown promise in attenuating inflammatory diseases, yet its role in colitis remains unclear. Here, we evaluated the therapeutic effects of astaxanthin in dextran sulfate sodium (DSS)-induced ulcerative colitis in mice. Our findings revealed that astaxanthin significantly ameliorated colitis symptoms, notably at the dose of 100 mg/kg, demonstrated by reduced Disease Activity Index (DAI), increased colon length, diminished colon histopathological damage, and enhanced goblet cell population. Mechanistically, astaxanthin decreased proinflammatory cytokines and malondialdehyde (MDA) levels, suppressed Keap1 expression, activated phosphorylated Nuclear factor erythroid 2-related factor two (Nrf2), and increased downstream protein expression of HO-1 and GPX4, ultimately inhibiting ferroptosis. Although astaxanthin altered gut microbiota composition, antibiotic treatment and fecal microbiota transplantation confirmed that its anti-colitis effects were independent of microbiota changes. These findings suggest that astaxanthin alleviates colitis associated with Nrf2 pathway mediated ferroptosis, rather than through gut microbiota modulation.