Alleviative effects of astragaloside IV on cyclophosphamide-induced oxidative damage and immunosuppression in tilapia (Oreochromis niloticus)

Astragaloside IV (ASIV) has effects of antioxidation and immunologic enhancement. However, there are few reports on the application and potential mechanism of ASIV in aquaculture. In this study, we investigated the effect of ASIV on growth, antioxidation, and immune function of tilapia. Tilapia were fed a diet containing 0.1, 0.2, and 0.5 g·kg^-1 ASIV for 60 days, followed by an intrapleural injection of 50 mg·kg^-1 cyclophosphamide (CTX) to induce oxidative damage and immunosuppression. Then tilapia were weighed and blood, liver, spleen, kidney, and intestinal were collected. The results showed ASIV increased the final weight, relative weight rate, and specific growth rate of tilapia, reduce conversion ratio, and reduced the morphological lesions of tissues. Meanwhile, ASIV alleviated CTX-induced oxidative damage by improving antioxidant activity in serum and tissues and inhibiting lipid peroxidation. Additionally, ASIV attenuated the immunosuppression of tilapia caused by CTX, regulated immunochemical indexes in serum, increased the viability of peripheral blood leukocytes and head kidney macrophages, and restored respiratory burst activity (O₂^-) in head kidney macrophages and splenocytes. Furthermore, qPCR data showed ASIV up-regulated antioxidant-related gene expression of nrf2, ho-1, gpx3, and cat and immune-related gene expression including C3 and igm. In conclusion, ASIV as a feed additive can not only improve the growth performance but also enhance the antioxidant capacity and immune function of tilapia, which may be associated with the ability of ASIV to scavenge free radicals, reduce lipid peroxidation levels, and stabilize numbers of immune cells.

Effects of cyclophosphamide on antioxidative and immune functions of Nile tilapia (Oreochromis Niloticus) via the TLR-NF-κB signaling pathway

Intensive aquaculture often results in immunosuppression in fish, which may cause a series of diseases. In this study, to investigate the immunosuppressive mechanisms in fish, tilapia were intrapleural injected cyclophosphamide (CTX) at the doses of 10, 25, 50, 75 and 100 mg·kg^-1 to induce immunosuppression. We determined the viability of immune cells, the content of lysozyme (LZM) and immunoglobulin M (IgM), the levels of nitric oxide (NO) and antioxidant parameters. Meanwhile, the mRNA levels of complement C3 (c3), igm and the genes associated with the TLR-NF-κB signaling pathway in the head kidney (HK) and spleen were also determined. The results showed that CTX had a significant cytotoxic effect on peripheral blood leukocytes, HK macrophages and spleen cells in a dose-dependent manner. The protein and mRNA levels of C3 and IgM were down-regulated with the increase of CTX concentrations in serum, HK and/or spleen. The NO and LZM contents decreased significantly in HK and spleen after CTX treatments with 75 and 100 mg·kg^-1. CTX treatments with 50, 75 and/or 100 mg·kg^-1 markedly decreased the antioxidant ability and enhanced lipid peroxidation in HK and spleen. Furthermore, qPCR data showed that CTX treatments with 50-100 mg·kg^-1 clearly down-regulated the mRNA levels of tlr2, myd88, irak1, traf6, nfκb1, nfκb2, il-6, il-10 and tnf-α in the HK and/or spleen. Overall results suggested that CTX treatment had a cytotoxic effect on immune cells, induced lipid peroxidation, decreased the antioxidant capacity and inhibited immune function. The immunosuppressive mechanisms of CTX may be associated with the TLR-NF-κB signaling pathway.