Andrographolide attenuates RSV-induced inflammation by suppressing apoptosis and promoting pyroptosis after respiratory syncytial virus infection in vitro

Abstract

Respiratory syncytial virus (RSV), the most common viral pathogen causing acute lower respiratory tract infection among children under five years old worldwide, still lacks specific therapeutic drugs. Andrographolide has been found efficacious in various virus infections, however, its effects on RSV infection remains unknown. Herein, in this study we quantified RSV virus load, IL-6 and IL-8 in A549 cell supernatant, and found andrographolide decreased the viral load and attenuated RSV-induced inflammation. Then, using online databases, we discovered 25 potential targets of andrographolide in the treatment of RSV-infected airway epithelial cells. Subsequently, GO and KEGG enrichment analysis led to the identification of CASP1, CCL5, JAK2, STAT1 as significant players. We verified the mRNA expression change of the potential target genes, which showed that andrographolide noticeably suppressed the increase of CASP1, CCL5, JAK2 and STAT1 post RSV infection. IL-1β, which is downstream of CASP1, was also up-regulated after RSV infection and down-regulated by andrographolide. Furthermore, we conducted Annexin V-FITC/PI apoptosis assay and Western blotting to determine whether andrographolide has an impact on the death pattern of RSV-infected cells. Interestingly, RSV infection decreased the protein levels of caspase-1, cleaved caspase-1, cleaved IL-1β, N terminal of GSDMD and Bcl-2, while andrographolide elevated them. These results suggested that andrographolide might attenuate RSV-induced inflammation by suppressing apoptosis and promoting pyroptosis of infected epithelial cells and thus inducing effective viral clearance.