Exposures to Heat‐Inactivated SARS‐CoV‐2 Causes Reactive Oxygen Species Generation And Inflammatory Response in RAW 264.7 Cells

Adla, Akhil; Traore, Kassim

INTRODUCTION AND OBJECTIVES: Novel SARS‐CoV‐2 virus has been implicated in prompting a bold immune response that leads to severe Coronavirus disease 2019 (COVID‐19). Recent studies have shown that SARS‐CoV‐2‐infected monocytes and macrophages are stimulated to produce an overabundance of pro‐inflammatory cytokines and chemokines to generate a cytokine storm. Cytokines in excess can contribute to local tissue inflammation and the pathogenesis of COVID‐19. However, the mechanism by which SARS‐CoV‐2 signal macrophage‐derived inflammatory response remains unclear. In the present study, we used RAW 264.7 cells, a well‐characterized macrophage model, to study the in vitro effects of SARS‐CoV‐2 on reactive oxygen species (ROS) production and its potential role in the signal transduction of cytokine production. METHODS: The effect of SARS‐CoV‐2 on ROS and cytokine generation in macrophages was assessed by treating RAW 264.7 cells with SARS‐CoV‐2 heat inactivated virus (0‐20 million viral particles) or recombinant proteins for 24 hours. 2′,7′‐Dichlorodihydrofluorescein (2′,7′‐DCF) fluorescence analysis was utilized to quantify ROS generation within the RAW 264.7 macrophage cell line. Cell culture medium was sampled to quantify the levels of tumor necrosis factor (TNF) using enzyme‐linked immunosorbent assay (ELISA). To assess the effects of SARS‐CoV‐2 on mitochondrial function, cells were treated with SARS‐CoV‐2 heat inactivated virus (0‐20 million viral particles) for 24 hrs. Mitochondria‐derived superoxide was measured using the MitoSOX™ red mitochondrial superoxide indicator. RESULTS: Treatment of RAW 264.7 cells with inactivated SARS‐CoV‐2 viral particles or recombinant proteins stimulated ROS production. Mitochondria‐derived superoxide and hydrogen peroxide production were increased in response to inactivated SARS‐CoV‐2 viral particles and recombinant protein exposure. The increased ROS generation is linked to macrophage activation induced by SARS‐CoV‐2 exposures. Along with the ROS generation, increased TNF production was observed. CONCLUSIONS: The results of this study suggest that both SARS‐CoV‐2 viral proteins and heat‐inactivated viral particle exposures cause significant generation of ROS and cytokines by RAW 264.7 cells. ROS generation and the subsequent cytokine release apparently play a significant role in the pathogenesis associated with the SARS‐CoV‐2 viral infection. The imbalanced cellular defense system against oxidative stress commonly associated with aging could explain the increased occurrence of more severe SARS‐CoV‐2 illness in seniors and in patients with underlying health conditions. Based on the results from this study, we propose that antioxidants such as N‐acetyl‐L‐cysteine, resveratrol, or Vitamin E in combination with anti‐inflammatory drug could be used to control excess ROS and cytokines in patients with severe COVID‐19.