Youxian Zhou,Yue Gong,Zhengqi Liu,Lilong Wang,Chunqing Ai,Chengrong Wen,Taihai Zhu,Shuang Song
Although numerous polysaccharides have demonstrated potential immunostimulatory activities in in vitro models, only a few of them successfully stimulate the immune system in vivo. In order to explore the possible reasons for the activity loss of polysaccharides in in vivo models, the immunostimulatory activities in vitro and in vivo and the digestion behavior of a polysaccharide from Cyclina sinensis (CSP) were investigated in the present study. CSP showed obvious immunostimulatory activity in a RAW 264.7 cell model. In in vitro experiment, CSP did not exhibit cytotoxicity at concentrations of ≤10 µg/ml, and significantly increased NO production at concentrations of 0.4–10 µg/ml, suggesting CSP processes immunostimulatory activity in vitro. Further investigation using simulated digestion model indicated that CSP could bind with the protein in the digestive fluids to form precipitate in both the stomach and small intestine, and it could be seriously degraded by amylase during the digestion in the small intestine. Furthermore, the in vivo immunostimulatory activity evaluation demonstrated CSP had no effect on immunosuppressed mice as indicated by the body weight, thymus and spleen indexes, and TNF-α, IL-1β, IL-6, and IL-10 mRNA expression. Thus, the present study indicates that the degradation and precipitation of CSP in the digestive tract are the possible reasons for the activity loss of CSP after digestion. Practical Application Cyclina sinensis is the common aquatic shellfish in China and plays an important role in the marine aquaculture industry. Cyclina sinensis polysaccharide (CSP) is the main active component of C. sinensis . The structure characterization and immunostimulatory activity of a purified fraction of CSP (CSP-1) and the effect of digestion on CSP and its immunostimulatory activity were studied. The result of this study promotes the understanding of the nutritional function effects and provides a scientific reference for the rational development and high-value utilization of C. sinensis .
Cottonseed meal has been one of the predominant protein feedstuffs used in aqua feed, which contains gossypol . It is well known that gossypol, a natural polyphenolic compound found in seeds, can be toxic to fish. The toxicity of gossypol persists even after a recovery period; however, the underlying mechanism remains largely unknown. To investigate the toxic mechanism of gossypol after the recovery period, Cyprinus carpio were administered a continuous oral dose of 20 mg/kg·d gossypol (gossypol acetate dose/fish weight·d) for one week, followed by a two-week recovery period. The spleen index, spleen morphology, lysozyme (LZM) activity, acid phosphatase (ACP) activity and nitric oxide (NO) concentration were obviously changed in the spleens of C. carpio after two weeks of recovery. Then, miRNA sequencing identified 22 differentially expressed miRNAs in the spleens of C. carpio two weeks after the gossypol treatment. The mRNA expression levels of immune-associated genes were significantly increased in the spleens after recovery. MiR-194 was chosen for future study through a search of existing literature and an analysis of miRNA and mRNA expression levels. To further characterize the potential target of miR-194, we identified putative miR-194 binding sites in the 3′UTR of myeloid differentiation factor 88a (MyD88a). Dual-luciferase reporter assays revealed that miR-194 downregulated the expression level of MyD88a through binding to seed-matching sequence in the 3′ UTR of MyD88a. Moreover, C. carpio were intraperitoneally administered with miR-194 antagomir. Furthermore, down-regulation of miR-194 increased the expression levels of MyD88a and some pro-inflammatory cytokines and anti-inflammatory cytokines. Altogether, the results demonstrate miR-194 can target MyD88a to regulate the immune response of C. carpio after a two-week recovery period following gossypol administration.
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