Effects of polysaccharides on turbot Scophthalmus maximus: evaluation with a head kidney macrophage cellular model

ABSTRACT: Polysaccharides exhibit a multitude of biological activities, including antioxidant, antitumor, immunoregulatory, hepatoprotective, and anti-inflammatory effects, but it is not known whether such effects occur in fish. Head kidney macrophages from turbot Scophthalmus maximus L. were isolated and cultured to examine the responsiveness to natural polysaccharides as potential immune stimulators. Polysaccharides used in the research included Echinacea purpurea polysaccharide (EPP), Astragalus polysaccharide (APS), lentinan (LNT), seaweed polysaccharide (SPS), and laminarin (LAM). The test compounds were added to the cultures and assessed for their effects on the growth and immunomodulatory functions of the cells. Based on the results of cell activity, reactive oxygen species, and nitic oxide assays, APS was selected as an immune stimulator. After addition of APS to the culture medium, a comprehensive proteomic analysis was conducted to identify signaling pathways responsible for the immune effects on macrophages. Specific immune pathway proteins were upregulated in cells in response to the addition of APS, including macrophage migration inhibitory factor, myosin-α, metalloproteinase inhibitor, and collagenase type III. In particular, compared with non-stimulated cells, the expression level of the TLR22 receptor was significantly increased in stimulated macrophages (p < 0.01). A KEGG pathway analysis indicated that relevant pathways were activated, including TNF, PI3K-Akt, and NF-κB signaling pathways. ELISA and qRT-PCR analysis also indicated that APS reduced IL-1β and TNF-α levels in the cells following lipopolysaccharide (LPS) stimulation. These data suggest that APS produced an immunoprotective effect on the head kidney macrophages of turbot at 800 µg ml^-1, and enhanced cell proliferation. Our results provide evidence for anti-inflammatory properties of APS. As such, APS could be a candidate immunopotentiating agent for fish.