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Abstract
The immunomodulation of chemically selenylated polysaccharides has been attracting more attention recently, but the corresponding performance of the yam polysaccharides (YPS) with lower selenylation extent remains, thus far, unsolved. In this study, the YPS was selenylated with Na2SeO3 under acidic conditions generated by HNO3 to reach two lower selenylation extents, yielding two selenylated YPSs, namely SeYPS-1 and SeYPS-2 with selenium contents of 715 and 1545 mg/kg, respectively. The results indicated that YPS, SeYPS-1, and SeYPS-2 all had in vitro immuno-modulation when using RAW 264.7 macrophages and murine splenocytes as cell models. In detail, the three polysaccharide samples at dose levels of 5–160 μg/mL showed insignificant cytotoxicity to the macrophages and splenocytes with cell exposure times of 12–24 h, because of the measured values of cell viability larger than 100%. However, Na2SeO3 at dose levels of 1.3–3.25 μg/mL mostly caused obvious cytotoxic effects on the cells, resulting in reduced cell viability values or cell death, efficiently. The results demonstrated that, compared with YPS, both SeYPS-1 and SeYPS-2 at a lower dose level (5 μg/mL) were more active at promoting phagocytosis activity, increasing the CD4+/CD8+ ratio of the T-lymphocyte sub-population in the murine splenocyte, improving cytokine secretion, including interleukin-6 (IL-6), IL-1β, and tumor necrosis factor-α in the macrophages, or increasing interferon-γ secretion, but suppressing IL-4 production in the splenocytes. Consistently, SeYPS-2 has more potential than SeYPS-1 at exerting these assessed bioactivities in the cells. Thus, we conclude that a chemical modification of YPS using trace element Se at a lower selenylation extent could bring about higher immunomodulatory activity towards macrophages and splenocytes, while selenylation extent of YPS is a critical factor used to govern the assessed activity changes of YPS.
Highlights
The three samples did not show any cytotoxicity on the cells, because the measured values of cell viability were all larger than 100%
The results indicated that yam polysaccharides (YPS), SeYPS-1, and SeYPS-2 could improve the immune status of macrophages efficiently, because they showed the ability to promote the secretion of three immune cytokines dose-dependently (Figure 2b–d)
The present study highlighted that a chemical selenylation of yam polysaccharides by Na2 SeO3 -HNO3, to lower selenylation extent, might cause a covalent connection of a trance nutrient Se into the polysaccharide molecules, and yield effectively higher immune
Summary
The main biological activities of Se include its ability to prevent diabetes, eliminate free radicals, enhance immunity, and exert anti-cancer and anti-oxidant effects [2]. Non-digestible polysaccharides have attracted more interest in recent years, due to their unique physicochemical structure, biological functioning, and food uses, especially their roles as dietary fibers and the potential to lower the risk of cardiovascular disease, obesity, diabetes, and some cancers [6]. These non-digestible polysaccharides have recently been widely assessed for their biological activities (e.g., immune–modulatory, anti-oxidant, and anti-cancer effects) [7]
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