Objective: To investigate the antiviral effect of Salvia plebeia R. Br. polysaccharides (SPP) against RSV and underlying mechanisms.
Methods: SPP was extracted via alcohol-precipitation method and extract was separated into various fractions using ultrafiltration method. The polysaccharide content was determined using UV-Vis. Antiviral effect of SPP and fractions was measured using MTT method and Reed-Muench method. Sixty Balb/c mice were randomly divided into 6 groups, and received either Ribavirin or SPP. Their body weight and food intake were recorded every day throughout the experiment period. The lung index inhibition ratio and pulmonary virus titer were determined followed by the histological analysis of lungs. Furthermore, time-of-addition and effective stage analysis were carried out to determine the mechanism of action. The TLR-3 and TLR-4 levels in the lungs were determined using qRT-PCR. The levels of IFN-γ, IL-2 and TNF-α in serum were determined using ELISA.
Results: The SPP content is 4.396%. SPP has shown a good anti-RSV effect both in vitro (TI = 123.041) and in vivo models. The antiviral activity of fractions with molecular weight ≥ 10,000 is found to possess more potent antiviral activity than other fractions. SPP inhibits the RSV proliferation and reduces the lung lesions induced by RSV. The mechanism of action involves the inhibition of TLR-3 and TLR-4 in lungs, up-regulation of IFN-γ and IL-2, and down-regulation of TNF-α in serum. It is also shown to improve the body's immune function.
Conclusion: SPP has a potential to treat diseases caused by RSV.
Keywords: Cytokines; Polysaccharides; RSV; Salvia plebeia R. Br. (SP); TI (therapeutic index); Toll-like receptors.
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