Endocrine Abstracts

Macrophages play essential roles in the immune defence and their hyperactivation has been implicated in epithelial damage in acute respiratory distress syndrome (ARDS), commonly observed in severe COVID-19 patients. In these cells, SARS-CoV-2 spike (S) protein triggers aberrant production of pro-inflammatory cytokines like interleukin-1 beta (IL-1β), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α), as well as reactive oxygen species (ROS) and matrix metalloproteinases (MMPs), which contribute to viral pathogenesis. Thus, one of the therapeutic strategies to reduce acute lung injury and multi-organ dysfunction in COVID-19 would be to blunt macrophage-mediated inflammatory response. Interestingly, it has been recently shown that the interaction between S protein and lipopolysaccharide (LPS) leads to aggravated inflammation in monocytes and peripheral blood mononuclear cells (PBMCs). The hypothalamic hormone growth hormone-releasing hormone (GHRH), in addition to promoting pituitary GH release, exerts many peripheral functions, including the regulation of inflammatory responses. GHRH antagonists, in turn, display potent anticancer and antinflammatory activities, also on in vitro and in vivo models of LPS-induced inflammation and lung diseases. However, the role of GHRH antagonists in models of COVID-19 remains to be explored. Thus, we aimed to assess the potential antinflammatory role of GHRH antagonist MIA-602 in human THP-1 macrophages and PBMCs stimulated with LPS, either alone or in combination with S protein. Human monocytic THP-1 cells were differentiated into macrophages with phytohemagglutinin (PMA); PBMCs were obtained from buffy coats of healthy donors by density-gradient separation. Both THP-1 cells and PBMCs were pretreated for 2 h with LPS, then incubated for 24 h with MIA-602, alone or in combination with S protein. The mRNA and protein levels of cytokines were analyzed by real-time PCR and ELISA, respectively. We found that the combination of S protein and LPS potently enhanced the levels of inflammatory cytokines, when compared with each compound alone. Importantly, MIA-602 completely blocked the inflammatory response to LPS+S protein and reduced by over 50% the increase in both gene expression and secretion of TNF-α, IL-1β and IL-6. Moreover, in support of its antinflammatory role, MIA-602 reduced ROS and MMP-9 levels, by 10% and over 30% respectively, as assessed by Muse cell analyzer and gelatin zymography. Overall, these results suggest that GHRH antagonists may be potential therapeutic candidates for attenuating the inflammatory cascade in patients with COVID19.