Glycyrrhizic Acid Showed Therapeutic Effects on Severe Pulmonary Damages in Mice Induced by Pneumonia Virus of Mice Infection

Abstract

Objective In this study, inbred BALB/c mice infected with the pneumonia virus of mice (PVM) were used to establish an animal model of viral pneumonia, and the changes in the pro-inflammatory alarmin molecule, high mobility group box 1 protein (HMGB1), during PVM infection were observed, as well as the in vivo intervention effects of the HMGB1 inhibitor, glycyrrhizic acid (GA), on PVM-induced lung injury.Methods Three-week-old female BALB/c mice were randomly divided into three groups, each consisting of 6 mice. One group, uninfected by PVM, served as the control group (Control). The other two groups were inoculated intranasally with PVM at a dose of 1×104 50% tissue culture infective dose (TCID50)/25 μL, and subsequently treated with GA saline solution (GA group) or plain saline solution (normal saline, NS group) via gavage for 15 consecutive days. During this period, changes in body weight and appearance were monitored in each group. At the end of the experiment, lung tissue samples were collected from all groups. The distribution of PVM and HMGB1 proteins in the lung tissues was analyzed using hematoxylin-eosin staining and immunohistochemistry. The expression levels of HMGB1 and its Toll-like receptor 4 (TLR-4), advanced glycosylation end-product-specific receptor (AGER), and inflammatory cytokines such as interleukin (IL)-1β, IL-2, and tumor necrosis factor-α (TNF-α) in lung tissues of mice were measured using real time fluorescence quantitative PCR.Results Compared with the Control group, the NS group showed a significant weight loss after 6 days (P<0.05). Histopathological tests revealed pronounced inflammatory lesions in their lungs. Immunohistochemistry results showed that HMGB1 was released from the nucleus to the cytoplasm, and real time fluorescence quantitative PCR results indicated that the expression levels of HMGB1, IL-1β, and IL-2 were significantly upregulated (P<0.05). In the GA group, there was no significant change in the clinical symptoms or body weight. However, compared with the NS group, the pathological damages of lung tissues in the GA group were significantly reduced, and the expression levels of HMGB1, IL-1β, IL-2, and interferon-γ (IFN-γ) in lung tissues were also significantly decreased (P<0.05), although the expression level of AGER was significantly increased (P<0.05). ConclusionPVM infection can cause significant inflammatory pathological lung damages in mice, and GA can effectively alleviate the damages. Its therapeutic effect may be related to the activation of HMGB1 signaling pathway.

Keywords

• glycyrrhizic acid
• high mobility group box 1
• pneumonia virus of mice
• lung damage
• balb/c mice