Pomelo polysaccharide extract inhibits oxidative stress, inflammation, and mitochondrial apoptosis of Epinephelus coioides

Although the production of pomelo, a citrus fruit, has recently increased considerably in China, the therapeutic potential of the fruitlets on aquatic animals has not been widely studied. Thus, in this study, we aimed to evaluate the protective effects of the crude polysaccharide extracted and purified from pomelo fruitlet (YZW-A), on oxidative stress, inflammation, and mitochondrial dysfunction-mediated apoptosis. For this, we added YZW-A (0, 100, 200 and 400 μg/mL) to Epinephelus coioides spleen (GS) cells before incubation with 0.8 mM of H₂O₂. Morphological indices showed significant deterioration when exposed to H₂O₂ (P < 0.05), whereas this was did not observed in the cells exposed to YZW-A. Administration of YZW-A (100 and 200 μg/mL) substantially mitigated the H₂O₂-induced oxidative stress, as shown by the elevated activities of the mitochondrial respiratory complexes and antioxidative enzymes, including superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR) and glutathione peroxidase (GSH-Px) (P < 0.05). NF-κB derived inflammation was also significantly attenuated by the diminished gene expression of the NF-κB regulated proinflammatory cytokines (TNF-α, IL-β and IL-6) (P < 0.05). In addition, apoptosis-related indicators (Bax, Bcl-2, and caspase-3, −8, and − 9) and the cell apoptosis rate showed that mitochondrial dysfunction-mediated apoptosis was alleviated due to the decreased oxidative stress. Pretreatment with the NF-κB inhibitor, BAY11–7082 (20 μM), dramatically reduced the expression of the downstream genes of NF-κB, including the proinflammatory genes, IL-β and IL-6 (P < 0.05), and the proapoptotic genes, Bax, caspase 3, and caspase 9 (P < 0.05), which confirmed that the NF-κB signaling pathway is involved in the mechanisms of inflammation and apoptosis. In support of the results in vitro study, we further added YZW-A at the doses of 0, 200, 400, 800 and 1600 mg/kg in the diet for 56 days prior to the treatment of H₂O₂ or saline. The results demonstrated that administration of YZW-A significantly ameliorated H₂O₂-induced liver injury as evident by the decline of Serum albumin (ALB), alkaline phosphatase (ALP), alanine transaminase (ALT), aspartate transaminase (AST), and cholinesterase (CHE) content in the groupers. Furthermore, the changes on the activities of the antioxidative enzymes and the mRNA expression of the apoptosis-related indicators and the proinflammatory cytokines corresponded well with that of in GS cells. In addition, YZW-A treatment repressed the enhancement of enzymic activities of the proinflammatory cytokines induced by H₂O₂. In summary, these findings showed the therapeutic potential of YZW-A on H₂O₂-induced oxidative stress, and further mitigated the NF-κB regulated inflammation and apoptosis.