Sitagliptin phosphate ameliorates chronic inflammation in diabetes mellitus via modulating macrophage polarization

Aim: To investigate the effect and mechanism of Sitagliptin phosphate on inflammation and macrophage polarization in a mouse model of type 2 diabetes. Methods: In vitro, Raw264.7 cells were cultured with a high concentration of glucose (HG) and sitagliptin phosphate (SIG). The levels of inflammatory factors and the regulation of macrophage polarization were investigated, and the differentially expressed genes between HG and HG+SIG intervention were analyzed and enriched through transcriptomics. In vivo, C57BL/6J male mice were treated with HFD+STZ to establish a type 2 diabetes mouse model were investigated the effects of regulation of macrophage polarization in the pancreas and visceral adipose tissue. Results:In vitro cell experiments and transcriptomics showed that Sitagliptin phosphate decreased the secretion of inflammatory factors IL-6 and TNF-α induced by high-glucose, and increased secretion of anti-inflammatory factor IL-10 by enhancing macrophage polarization. In vivo, the body weight and abdominal visceral fat weight, the ratio of visceral fat weight to body weight and fasting blood glucose were significantly increased in the DM group compared with the Control (P<0.05), Sitagliptin phosphate treatments reversed the changes in the DM group. Moreover, histological analysis showed that compared with the Control group, the size of visceral adipocytes, hepatocyte lipid deposition and the ratio of M1/M2 macrophage were higher in the DM group, which were reversed by Sitagliptin phosphate treatments (P<0.05), insulin treatments did not have a significant effect(P＞0.05).Mechanistically, Western blot showed that compared with the normal group, HG upregulated the expression of mTORc1 protein, P-65 phosphorylation and P-65 protein expression in Raw264.7 cells (P<0.05), downregulated the expression of IKKβ (P<0.05) and PPAR-γ proteins (P<0.05), Sitagliptin phosphate and insulin treatments rescued these changes. Conclusion: These results indicated that Sitagliptin phosphate reduced high glucose-induced inflammation by improving the imbalance of macrophage polarization via modulating the mTORc1/ PPAR-γ/NF-κB in vitro and in vivo. The Raw264.7 cells were incubated with 35 mmol/l hyperglycemia (HG) and 35mmol/l hyperglycemia Sitagliptin phosphate (HG＋SIG) for 6 hours (with three replicates per group) and subjected to full transcriptional sequencing. Differentially expressed genes between the two groups were identified based on the (|log2 (fold change)|>1) criterion. All bulk RNA-seq data were transformed into TPM and log2, and differential gene analysis was performed using the limma R package v3.54.0 (cite: https://www.ncbi.nlm.nih.gov/ pmc/articles/PMC4402510/). Pathway gene set signature was derived from the Molecular Signatures Database (MSigDB) (https://www.gseamsigdb.org/gsea/msigdb) and the ssgsea function from the GSVA R package v1.46.0 as described previously (https://bmcbioinformatics.biomedcentral.com/articles/10.1186/1471-2105-14-7) were utilized to determine the pathway score. The results were visualized using ggplot2 v3.5.0 (https://doi.org/10.32614/CRAN.package.ggplot2).