Compartment-specific activation of kinin B1 and B2 receptors drives the production of vasoactive and inflammatory mediators during SARS-CoV-2 infection

Abstract

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) disrupts multiple host regulatory systems, including the kallikrein–kinin system (KKS), which plays a central role in vascular homeostasis and inflammation. Following viral entry, angiotensin-converting enzyme 2 (ACE2) is internalized and inactivated, impairing the degradation of des-Arg⁹-bradykinin (DABK), a selective agonist of the inducible kinin B1 receptor (B1R), while inflammatory feedback mechanisms may further elevate bradykinin (BK), the kinin B2 receptor (B2R) agonist. It has been postulated that the kinin storm observed in COVID-19 patients may lead to pulmonary angioedema, promote the exacerbated production of pro-inflammatory cytokines, and be related to disease progression, permanent sequelae, and death. However, it remains unknown whether in vitro SARS-CoV-2 infection triggers alterations in the KKS and its downstream inflammatory and vasoactive mediators. Here, we investigated how SARS-CoV-2 infection modulates kinin signaling and its downstream inflammatory and vasoactive mediators in Vero E6 and human endothelial (HUVEC) cells. SARS-CoV-2 infection increased BK levels and markedly upregulated B1R gene expression in Vero E6 cells (up to 20-fold), while B2R expression remained unchanged. Both BK and DABK reduced ACE2 expression in Vero E6 cells, an effect most likely mediated by DABK–B1R signaling due to the minimal expression of B2R in this cell line. Viral infection induced robust production of nitric oxide (NO) and interleukin-6 (IL-6) in Vero E6 cells, and supernatants from infected cells triggered similar responses in HUVECs. Pharmacological blockade of B1R with R-715 selectively prevented SARS-CoV-2–induced NO production in Vero E6 cells, whereas IL-6 induction occurred through B1R-independent mechanisms. In contrast, in endothelial HUVEC cells exposed to serum from patients with severe COVID-19, B2R antagonism with HOE-140 prevented both NO and IL-6 production, suggesting a key role for B2R in both vascular cytokine amplification and vasoactive mediator production. Our findings reveal a compartment-specific and complementary activation of B1R and B2R during SARS-CoV-2 infection, establishing the KKS as a key mediator of endothelial alterations and inflammatory amplification in COVID-19 and positioning B1R and B2R as therapeutic targets.