Panax ginseng has been known to have a number of immuno-modulatory effects. In this study, we investigated whether Panax Korean red ginseng extract (KRGE) has in vitro and in vivo antiviral effects on respiratory syncytial virus (RSV) infection. KRGE improved the survival of human lung epithelial cells against RSV infection and inhibited RSV replication. In addition, KRGE treatment suppressed the expression of RSV-induced inflammatory cytokine genes (IL-6 and IL-8) and the formation of reactive oxygen species in epithelial cell cultures. Oral administration of mice with KRGE resulted in lowering lung viral loads after RSV infection. Additionally, the in vivo effects of KRGE showed an enhanced level of interferon-γ (IFN-γ) producing dendritic cells subsequent to RSV infection. Taken together, these results suggested that KRGE has antiviral activity against RSV infection.
Respiratory syncytial virus (RSV) is a non-segmented, negative-stranded RNA virus and a member of the Paramyxoviridae family. RSV is the leading cause of serious respiratory infections in children as well as in elderly and immune-suppressed individuals (1,2). The role of reactive oxygen species (ROS) as mediators of the virus-induced epithelial damage in RSV infected mice has been previously reported (3,4). Oxidative stress is one of the components of the pathophysiology of chronic obstructive pulmonary disease (5). RSV infection led to a ROS induction, which increases the expression of pro-inflammatory molecules such as interleukin-8 (IL-8), IL-6, CCL5 or CXCL10 (6). This production of pro-inflammatory cytokines induced by RSV infection resulted in type 1 and 2 cytokine imbalance. It was strongly suggested that excess type 2 and/or deficient type 1 immune responses were involved in the pathogenesis of RSV bronchiolitis (7).
Herbal medicines have been previously used in humans to treat medical illness or to improve physical performance. Panax ginseng is one of the most well-known herbal medicines that have been consumed for thousands of years. Experimental evidence suggests that ginseng modulates the host immune system and improves outcomes of inflammatory human diseases (8,9). Ginseng or its component ginsenoside protopanaxatriol was also reported to protect endothelial cells by scavenging hydroxyl radicals and modulating the antioxidant defense systems such as superoxide dismutase and glutathione peroxidase enzymes (10–12). Ginsenosides of ginseng were shown to protect human endothelial cells against influenza H9N2-induced inflammation and apoptosis (13). However, the potential antiviral effects of ginseng on RSV infection remain unknown.
In this study, we investigated the effect of Korean red ginseng extract (KRGE) on RSV replication, on RSV-induced cytokine expression, and RSV-induced cellular oxidative stress in a human epithelial cell line. In addition, we evaluated the possible in vivo antiviral effects of KRGE on clearing lung viral loads and host immune responses following RSV infection in a mouse model.
Ginseng has been known to have various immunomodulatory functions. However, the potential anti-viral activity, oxidative stress, inflammatory cytokine production, and immunomodulatory effects of Panax ginseng on RSV infection remain unknown. In the present study, we showed that KRGE inhibited the replication of RSV, RSV-induced cell death, expression of pro-inflammatory cytokines, and suppressed RSV-induced ROS formation in human epithelial cells. Oral intake of ginseng products is the most common means of consumption as a nutrient supplement in healthy individuals. Therefore, we assessed the potential antiviral effects and immunomodulatory functions of KRGE following RSV viral infection in a mouse model. Oral administration of KRGE to mice conferred moderate but significant resistance to RSV infection. Therefore, the present study provides evidence that KRGE has antiviral activity against RSV in vitro and in vivo. Anti-RSV activity of KRGE has a high significance considering the fact that RSV is the most frequent viral cause of respiratory diseases, asthma, and chronic obstructive pulmonary disease exacerbations early and later in life (27).
The results showed that RSV caused significant cell death following RSV infection in a dose-dependent manner, presumably due to RSV-induced oxidative damage to the cells (3). Cellular oxidative damage due to RSV infection was reported as a result of inducing an imbalance between ROS production and antioxidant cell defenses (3). Various cytokines and chemokines are known to be expressed during RSV infection, playing a central role in pathogenesis (28). These effects have been associated with activation of the transcription factor nuclear factor-κB and mitogen-activated protein kinase through oxidant-dependent mechanisms (25). KRGE treatment partially protected the cell death from RSV infection. The underlying mechanisms by which KRGE treatment improves cell survival during RSV infection remain to be defined. KRGE treatment significantly inhibited the in vitro growth of RSV by 3–5-fold as well as the production of RSV-induced pro-inflammatory cytokines and ROS formation. A possible mechanism is that the KRGE-mediated inhibition of RSV replication in alveolar epithelial cells may have resulted in a reduction of ROS and pro-inflammatory cytokine production, which subsequently resulted in improving cell survival. Alternatively, an anti-oxidant effect by KRGE may have independently contributed to improving cell survival protection. Thus, it is hypothesized that KRGE may exhibit antiviral activity against RSV in various ways during RSV infection.
Findings of a previous study demonstrated that oral administration of KRGE prior to infection significantly increased survival rates of mice following infection with 2009 pandemic H1N1 virus (20). Results of the present study have shown that oral administration of KRGE to mice prior to infection resulted in lowering lung viral loads subsequent to RSV infection. This reduction is highly significant as oral intake of KRGE protects the local infection of RSV in lungs. The anti-inflammatory effects of KRGE on inflammatory cytokines in BALF samples were minimal, likely because RSV is not highly pathogenic to mice although RSV replicates to a certain level (29).
The ginsenosides, the constituents of KRGE were shown to reduce IL-4 production but increase IFN-γ production, resulting in Th1-type immune responses in an ovalbumin-induced murine model of asthma (30). Dendritic cells are crucial in determining the fate of naïve T cells, whether Th1 or Th2 cells (26). However, the effects of ginseng on dendritic cells and resulting T-cell responses remain to be determined. A significant finding in this study on RSV is that KRGE oral treatment increased IFN-γ production in BALF following RSV infection. A detailed analysis of BALF cells provided evidence that KRGE may stimulate the production of IFN-γ-producing CD4 T lymphocytes as well as granulocytes such as CD11b+ and CD11c+ cells. Particularly, the increase in CD11b−/lowCD11c+CD8α+ cell populations was prominent as a result of KRGE treatment, which may contribute to the production of IFN-γ and the increased induction of CD4 T cells producing IFN-γ. The cellular phenotypes of IFN-γ production and RSV pathogenesis as a result of ginseng treatment may be different from those by RSV-infected epithelial cells that were associated with severe pneumonia due to RSV infection (31). Taken together, this study suggests a mechanism that ginseng may have antiviral activity against respiratory virus by modulating host cellular phenotypes producing cytokines.
In conclusion, the modulation of oxidative stress is a potential novel pharmacologic approach that may be used to ameliorate RSV-induced acute lung inflammation. Ginseng inhibited RSV-induced cellular oxidative damage and blocked the induction of RSV-induced pro-inflammatory gene expression in the human alveolar epithelial cell line. Furthermore, ginseng suppressed lung viral titer and contributed to protective immunity by enhancing IFN-γ production following RSV viral infection in an experimental RSV infection murine model. Based on the results, although the exact underlying anti-virus mechanism of ginseng remains to be determined, consumption of ginseng in healthy individuals would have beneficial effects in the prevention of unexpected RSV infections and/or reduction of the severity of RSV disease.