Astragalus polysaccharides have been widely used as immunopotentiators in aquaculture, however, the best way of their administration remains to be explored. In the present study, Astragalus polysaccharide 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-1β, 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.

黄芪多糖已被广泛用作水产养殖中的免疫增强剂，但是，其最佳给药方式仍有待探索。本研究采用膜分散-超声波法制备黄芪多糖脂质体（APSL）。通过响应面法确定APSL的最佳制备条件，大豆卵磷脂与APS的比例为10：1（w / w），大豆卵磷脂与胆固醇的比例为8：1（w / w），超声时间为15分钟，其封装效率为APSL的73.88±0.88％。体内大黄鱼的饲养实验表明，APS和APSL均可提高血清总蛋白（TP）和白蛋白（ALB）的含量，提高血清非特异性免疫酶的活性，如酸性磷酸酶（ACP），碱性磷酸酶（AKP） ，溶菌酶（LZM）和头部肾脏巨噬细胞的吞噬活性。同时，它们都增加了血清抗氧化酶超氧化物歧化酶（SOD）和过氧化氢酶（CAT）的活性，并降低了血清中最终脂质过氧化产物丙二醛（MDA）的含量，从而发挥了抗氧化作用。体外原发性肾脏巨噬细胞（PKM）的实验表明，APS和APSL均抑制ROS的产生，但明显增强PKM的NO产生和吞噬活性。此外，APS和APSL处理后，PKM中促炎细胞因子（IL-1β，IL-6，IL-8和TNF-α），IFN-γ和iNOS的表达水平显着上调，但无表达观察到IFN-h的变化。综上所述，我们的结果表明，APS和APSL均可在体内或体外改善大黄鱼的一些免疫参数和抗氧化能力，并且APSL的疗效明显优于APS。因此，这些发现表明，用脂质体包封后，APS的免疫调节和抗氧化活性可以增强，并且APSL可能代表了APS潜在的药物递送系统，用于开发水产养殖中的免疫增强剂。