Abstract
The effects of the oral administration of Rehmannia glutinosa polysaccharide (RGP-1) on the immunoregulatory properties, antioxidant activity, and resistance against Aeromonas hydrophila in Cyprinus carpio L. were investigated. The purified RGP-1 (250, 500, and 1,000 μg/mL) was co-cultured with the head kidney cells of the common carp. The proliferation and phagocytosis activities of the head kidney cells, and the concentration of nitric oxide (NO) and cytokines in the culture medium were determined. Next, 300 common carps (47.66 ± 0.43 g) were randomly divided into five groups; the two control groups (negative and positive) were administered sterile PBS and the three treatment groups were administered different concentrations of RGP-1 (250, 500, and 1,000 μg/mL) for seven days. Subsequently, the positive and treatment groups were infected with A. hydrophila, and the negative group was administered sterile PBS for 24 h. The concentration of NO, cytokines, lysozyme (LZM), and alkaline phosphatase (AKP) in serum, the total antioxidant capacity (T-AOC), the levels of malonaldehyde (MDA) and glutathione (GSH), and the total activities of superoxide dismutase (T-SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) in the hepatopancreas of the common carp were tested. We observed that RGP-1 could significantly enhance the proliferation and phagocytosis activities (P < 0.05), besides inducing the production of NO, pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, IL-12) and anti-inflammatory cytokines (IL-10, TGF-β) (P < 0.05) in vitro. The in vivo experimental results revealed that RGP-1 significantly enhanced NO production, protein levels of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, IL-12), LZM and AKP activities, and the antioxidant content (T-AOC, SOD, CAT, GSH, GSH-Px, and MDA) compared to that observed in the negative group prior to A. hydrophila infection (P < 0.05). NO, pro-inflammatory cytokines, LZM and AKP activities were significantly lower than that in the positive group after infection (P < 0.05). However, whether infected or not, the expression of anti-inflammatory cytokines (IL-10, TGF-β) increased significantly in the RGP-1-treated groups (P < 0.05). Therefore, the results suggested that RGP-1 could enhance the non-specific immunity, antioxidant activity and anti-A. hydrophila activity of the common carp, and could be used as a safe and effective feed additive in aquaculture.
Highlights
Cyprinus carpio is the major commercial fish species in China
The effects exerted by R. glutinosa polysaccharide (RGP)-1 on the proliferation and phagocytosis of the head kidney cells are presented in Figures 1, 2
RGP treatment induced the maturation of natural killer (NK) cells and exerted an anticancer effect [35]; RGP could be used as a mucosal adjuvant for inducing the activation of immune responses in the lungs of mice [34]
Summary
Cyprinus carpio is the major commercial fish species in China. In recent years, the increased frequency of diseases in the breeding process of the common carp have severely hindered industrial development. In recent years, increasing attention has been paid to the effect of TCM on immune regulation [2,3,4,5,6], and several studies have demonstrated that polysaccharides are one of the important active ingredients. The addition of Ganoderma lucidum polysaccharide to the basic diet significantly improved the survival and growth rates and the digestive enzyme activities of Macrobrachium rosenbergii [12]. Both Ficus carica polysaccharide and Hericium caput-medusae polysaccharide stimulated the immune response in grass carp, and upregulated the immune-related genes, thereby enhancing the host’s disease resistance ability [3, 13]. Polysaccharides from algae and other species are widely used in aquaculture [16, 17]
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