Xanthine Oxidase-Induced Inflammatory Responses in Respiratory Epithelial Cells: A Review in Immunopathology of COVID-19

Abstract

Xanthine oxidase (XO) is an enzyme that catalyzes the production of uric acid and superoxide radicals from purine bases: hypoxanthine and xanthine and is also expressed in respiratory epithelial cells. Uric acid, which is also considered a danger associated molecule pattern (DAMP), could trigger a series of inflammatory responses by activating the inflammasome complex path and NF-κB within the endothelial cells and by inducing proinflammatory cytokine release. Concurrently, XO also converts the superoxide radicals into hydroxyl radicals that further induce inflammatory responses. These conditions will ultimately sum up a hyperinflammation condition commonly dubbed as cytokine storm syndrome (CSS). The expression of proinflammatory cytokines and neutrophil chemokines may be reduced by XO inhibitor, as observed in human respiratory syncytial virus (HRSV)-infected A549 cells. Our review emphasizes that XO may have an essential role as an anti-inflammation therapy for respiratory viral infection, including coronavirus disease 2019 (COVID-19).

Figure 1

Neutrophils recruitment during RCoV infection. RCoV infects AT1 cells, induces secretion of IL-1, induces CXC in uninfected cells, and triggers neutrophils recruitment (adaptation from Miura et al. [30]).

Figure 2

Association between XO activity and uric acid level and kidney tubulus proximal.

Figure 3

mechanism that explained SARS-CoV-2 infections NETosis and relations to hypoxic cell damage. The mechanism was adapted from Zhou et al. and Khafarijiy et al. [65, 66].

Figure 4

Allopurinol suppressed NETosis formations in vitro. XO activity triggered NETosis in vitro while administration of allopurinol inhibits NETosis. The figure was adapted from Khafarijiy et al. [66].