Astragaloside IV attenuates inflammatory reaction via activating immune function of regulatory T-cells inhibited by HMGB1 in mice

Context: High-mobility group box 1 (HMGB1) protein is a highly abundant protein that can promote the pathogenesis of inflammatory. Some experiments have demonstrated a vital role for HMGB1 to modulate the immune function of regulatory T-cells (Tregs). Astragaloside IV (AST IV), an extract from Astragalus membranaceus Moench (Leguminosae), has been shown to exert potent cardioprotective and anti-inflammatory effects. It is still unclear whether AST IV has a latent effect on the proinflammatory ability of HMGB1 with subsequent activation of Tregs in vivo. Objective: This research explores the antagonism of different doses of AST IV on the immunologic function of Tregs mediated by HMGB1. Materials and methods: Mouse models (BALB/c) were constructed by which normal saline or AST IV was administered i.p. at 2, 4 and 6 days after the administration i.p. of 20 mu g recombinate HMGB1. Spleen was used to procure Treg and CD4(+)CD25(-) T-cells which were co-cultured with Treg. Cell phenotypes of Tregs(Foxp3) were examined, and the cytokine levels in supernatants and the proliferation of T-cells were assayed. Gene expression was measured by RT-PCR. Results: (1) The expression levels of Foxp3 in Treg on post-stimulus days (PSD) 1-7 were significantly decreased in the HMGB1 group in comparison to those in the control group mice (p < 0.01). The Foxp3 expression was markedly increased in a dose-dependent manner in the AST group as compared with those in the HMGB1 group (p < 0.01-0.05). The same results were found in the contents of cytokines (IL-10 and TGF-beta) released into supernatants by Treg. (2) When CD4(+)CD25(-) T-cells were co-cultured with Treg stimulated by HMGB1, the cell proliferation and the levels of cytokines (IL-2 and IFN-gamma) in supernatant were markedly increased as compared with those in the HMGB1 group. The level of IL-4 was markedly decreased as compared with that in the HMGB1 group. The same results were found when CD4(+)CD25(-) T-cells were co-cultured with Treg in the NS group. Compared with those in the NS group, the contrary results were shown in a dose-dependent manner in the AST group. Discussion and conclusion: These results showed that AST IV has a therapeutic effect on inflammation promoted by HMGB1, and it should be studied as a new drug for the treatment of sepsis.