Abstract: : Objective To evaluate the antioxidant, anti-tumor and immunomodulatory activities of exopolysaccharides with different molecular masses isolated from Rhizopus nigricans. Methods Three polysaccharides with different molecular masses, namely RPS-1, RPS-2 and RPS-3, were separated from the fermentation broth of Rhizopus nigricans by fractional ethanol precipitation, and their capacity for scavenging DPPH, ABTS, and hydroxyl radicals was assessed. Cell counting kit-8 was used to analyze the changes in the viability of MFC, A549 and RAW 264.7 cells following treatments with the 3 polysaccharides; The level of nitric oxide in the supernatant of RAW 264.7 cells was detected using a nitric oxide detection kit, and the apoptosis rate of A549 cells was analyzed with flow cytometry. Results All the 3 polysaccharides had good antioxidant activities, and among them RPS-1 with a medium molecular mass exhibited the strongest scavenging capacity for DPPH and ABTS radicals (P<0.05) while RPS-3 with the lowest molecular mass had the best scavenging activity for hydroxyl radicals (P<0.01). All the 3 polysaccharides were capable of inhibiting the proliferation of MFC cells and A549 cells, activating the macrophages RAW 264.7 cells, and inducing apoptosis of A549 cells. RPS-2 with the highest molecular mass showed the strongest inhibitory effects against MFC and A549 cells (P>0.05), and RPS-2 had the strongest activity for inducing apoptosis in A549 cells (P<0.05). Compared with the other two polysaccharides, RPS-2 more strongly promoted the proliferation of RAW 264.7 cells and enhanced NO release from the cells (P<0.05). Conclusion The 3 polysaccharides all have antioxidant, anti-tumor and immunomodulatory activities, and among them RPS-1 and RPS-3 have better antioxidant activities, and RPS-2 has stronger anti-tumor and immunomodulatory activities.

Key words: exopolysaccharide from Rhizopus nigricans; antioxidant; anti-tumor; macrophages cells