RESUMO
Astragalus polysaccharides (APS) have been widely used as immunopotentiators in aquaculture, however, the best way of their administration remains to be explored. In the present study, APS liposome (APSL) was prepared by film dispersion-ultrasonic method. The optimal conditions of APSL preparation were determined by response surface methodology, with a ratio of 10:1 (w/w) for soybean lecithin to APS and 8:1 (w/w) for soybean lecithin to cholesterol, and an ultrasound time of 15 min, which produced an encapsulation efficiency of 73.88 ± 0.88% of APSL. In vivo feeding experiments in large yellow croaker showed that both APS and APSL could enhance the contents of serum total protein (TP) and albumin (ALB), activities of serum non-specific immune enzymes such as acid phosphatase (ACP), alkaline phosphatase (AKP), and lysozyme (LZM), and phagocytic activity of head kidney macrophages. Meanwhile, they both increased the activities of serum antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) and reduced the content of final lipid peroxidation product malondialdehyde (MDA) in serum, thus exhibiting the antioxidant effects. In vitro experiments on primary head kidney macrophages (PKM) showed that both APS and APSL inhibited ROS production, but obviously enhanced NO production and phagocytic activity of PKM. Furthermore, expression levels of pro-inflammatory cytokines (IL-1ß, IL-6, IL-8, and TNF-α), IFN-γ, and iNOS in PKM were significantly up-regulated after APS and APSL treatments, but no expression change of IFN-h was observed. Taken together, our results showed that both APS and APSL could improve several immune parameters and antioxidant ability of large yellow croaker either in vivo or in vitro, and the efficacy of APSL was markedly better than APS. These findings therefore indicated that the immunomodulatory and antioxidant activities of APS could be enhanced after encapsulated with liposome, and APSL may represent a potential drug delivery system of APS for development of immunoenhancers in aquaculture.