C-peptide reduces pro-inflammatory cytokine secretion in LPS-stimulated U937 monocytes in condition of hyperglycemia

Abstract

We investigated C-peptide effects on inflammatory cytokine release and adhesion of monocytes exposed to high glucose and lipopolysaccharide (LPS) in vitro. Monocytic cells (U-937) were cultured in the presence of 30mmol/L glucose and stimulated with 0.5ng/μL LPS in the presence or absence of C-peptide (1μmol/L) for 24h to induce inflammatory cytokine secretion. Adhesion of U-937 monocytes to human aortic endothelial cells (HAEC) was also studied in the presence or absence of C-peptide. Concentrations of IL-6, IL-8, macrophage inflammatory protein(MIP)-1α, and MIP-1β in supernatants from LPS-stimulated U-937 monocytes were assessed by Luminex. To gain insights into potential intracellular signaling pathways affected by C-peptide, we investigated nuclear translocation of nuclear factor(NF)-κB p65/p50 subunits by western blot in LPS-treated U-937 cells. The effect of C-peptide on LPS-induced phosphorylation of the cytoplasmic protein IκB-α was also investigated by immunoblotting. Addition of C-peptide significantly reduced cytokine secretion from LPS-stimulated U-937 monocytes. Adhesion of U-937 cells to HAEC was also significantly reduced by C-peptide. These effects were accompanied by reduced NF-κB p65/p50 nuclear translocation and decreased phosphorylation of IκB-α. We conclude that, in conditions of hyperglycemia, C-peptide reduces monocytes activation via inhibition of the NF-κB pathway.