Inactivated Wild-Type Yellow Fever Virus (French Neurotropic)

Several studies have implicated viral infection-induced oxidative stress as one of its pathogenesis. Here, researchers evaluated whether yellow fever virus (YFV) infection of human hepatocytes induces an imbalance in redox homeostasis, ultimately leading to oxidative stress. YFV infection resulted in a significant increase in reactive oxygen species (ROS) levels from 2 to 4 days post infection (dpi). When oxidative parameters were measured at 4 dpi, YFV infection caused oxidative damage to lipids, proteins, and DNA, as evidenced by increases in lipid peroxidation/8-isoprostanes, carbonyl proteins, and 8-hydroxy-2′-deoxyguanosine. In addition, the activities of the antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPx) were significantly reduced, and the ratio of reduced glutathione to oxidized glutathione (GSH/GSSG) was also reduced, indicating a pro-oxidative environment. However, no changes were observed in the enzymatic activity of catalase (CAT) and the gene expression of SOD isoforms (1/2/3), CAT, or GPx. Thus, these results suggest that yellow fever virus (YFV) infection causes an imbalance in redox homeostasis, leading to overproduction of reactive oxygen species (ROS) and depletion of antioxidant enzymes, thus inducing oxidative damage to cellular components.

ROS quantification was performed from 1 dpi to 5 dpi of infection (Figure 1). At 1 dpi of infection, ROS levels in YFV-infected cells were at baseline, while no difference was observed in inactivated YFV-infected cells (control) (Figure 1a). From 2 dpi to 4 dpi of infection, ROS production in YFV-infected cells gradually increased, with significant differences compared to the cell control, while no difference was observed compared to the positive control (H2O2) at 3 dpi and 4 dpi of infection (Figure 1b-d). At 5 dpi of infection, ROS levels in YFV-infected cells were very close to those of control cells (Figure 1e). This was expected, as it has been observed that at 5 dpi of infection, cells begin to be damaged by the lack of nutrients in the culture medium and the acidic pH. Since the cell death process itself naturally increases ROS, and the results were normalized by the fluorescence level of control cells, no statistical difference was observed between control and yellow fever virus-infected cells at 5 dpi. At all dpi, infection of cells with UV-inactivated YFV did not stimulate ROS production, indicating that the exacerbated production of ROS is related to the viral activity and multiplication of YFV in hepatocytes, and not just the presence of viral particles themselves.

Figure 1. Yellow fever virus (YFV) infection of human hepatocytes increases levels of reactive oxygen species (ROS). (Ferraz A C, et al., 2024)