Reactive oxygen species (ROS) are the key factors that cause many diseases in the human body. Polysaccharides from seaweed have been shown to have significant antioxidant activity both in vivo and in vitro. The ameliorative effect of Ulva lactuca polysaccharide extract (UPE) on renal injury induced by oxidative stress was analyzed. As shown by hematoxylin–eosin staining results, UPE can significantly improve the kidney injury induced by D-galactose (D-gal). Additionally, the protective mechanism of UPE on the kidney was explored. The results showed that UPE could decrease the levels of serum creatinine (Scr), blood urea nitrogen (BUN), serum cystatin C (Cys-C), lipid peroxidation, protein carbonylation, and DNA oxidative damage (8-OHdG) and improve kidney glutathione content. Moreover, UPE significantly increased the activities of superoxide dismutase and glutathione peroxidase and total antioxidant activity in mice. UPE also decreased the levels of inflammatory cytokines TNF-α and IL-6. Further investigation into the expression of apoptotic protein caspase-3 showed that UPE decreased the expression of apoptotic protein caspase-3. These results indicate that UPE has a potential therapeutic effect on renal injury caused by oxidative stress, providing a new theoretical basis for the treatment of oxidative damage diseases in the future.

The immunomodulatory effects of R-phycoerythrin (R-PE) from Porphyra haitanensis were investigated by a hydrocortisone (HC)-induced immunosuppressive model in the present research. The results showed that R-PE had immunomodulatory potential, such as increasing spleen and thymus indexes, ameliorating spleen morphology, enhancing the phagocytic capability of macrophages, promoting spleen T lymphocyte proliferation, and strengthening serum hemolysin formation. Furthermore, R-PE elevated the CD4⁺/CD8⁺ ratio and up-regulated the levels of cytokines for Th1, Th2, and Th17 and the mRNA expression of transcription factors T-bet, GATA3, and RORγt. Besides, the levels of cytokines for Treg and transcription factor Foxp3 were down-regulated. The levels of T-bet/GATA3 and RORγt/Foxp3 were increased. R-PE activated the phosphorylation of NF-κB through the TLR4-mediated differentiation pathway. These findings suggested that R-PE exerted immunomodulatory activities in the innate and adaptive immune systems through TLR4/NF-κB mediated CD4⁺ T cell activation and differentiation, which facilitated the further application of R-PE as an immunomodulator.