Modulation of Prostanoids Profile and Counter-Regulation of SDF-1α/CXCR4 and VIP/VPAC2 Expression by Sitagliptin in Non-Diabetic Rat Model of Hepatic Ischemia-Reperfusion Injury

Abstract

Molecular mechanisms underlying the beneficial effect of sitagliptin repurposed for hepatic ischemia-reperfusion injury (IRI) are poorly understood. We aimed to evaluate the impact of IRI and sitagliptin on the hepatic profile of eicosanoids (LC-MS/MS) and expression/concentration (RTqPCR/ELISA) of GLP-1/GLP-1R, SDF-1α/CXCR4 and VIP/VPAC1, VPAC2, and PAC1 in 36 rats. Animals were divided into four groups and subjected to ischemia (60 min) and reperfusion (24 h) with or without pretreatment with sitagliptin (5 mg/kg) (IR and SIR) or sham-operated with or without sitagliptin pretreatment (controls and sitagliptin). PGI₂, PGE₂, and 13,14-dihydro-PGE₁ were significantly upregulated in IR but not SIR, while sitagliptin upregulated PGD₂ and 15-deoxy-12,14-PGJ₂. IR and sitagliptin non-significantly upregulated GLP-1 while Glp1r expression was borderline detectable. VIP concentration and Vpac2 expression were downregulated in IR but not SIR, while Vpac1 was significantly downregulated solely in SIR. IRI upregulated both CXCR4 expression and concentration, and sitagliptin pretreatment abrogated receptor overexpression and downregulated Sdf1. In conclusion, hepatic IRI is accompanied by an elevation in proinflammatory prostanoids and overexpression of CXCR4, combined with downregulation of VIP/VPAC2. Beneficial effects of sitagliptin during hepatic IRI might be mediated by drug-induced normalization of proinflammatory prostanoids and upregulation of PGD₂ and by concomitant downregulation of SDF-1α/CXCR4 and reinstating VIP/VCAP2 signaling.

Keywords: dipeptidyl peptidase IV (DPP4); drug repurposing; gliptins; glucagon-like peptide 1 (GLP-1); hepatoprotection; incretins; liver transplantation; prostaglandins; stromal-derived factor 1α (SDF-1α); vasoactive intestinal peptide (VIP).

Figure 1

Validation of hepatic ischemia-reperfusion model—the effect of injury on the dynamics of liver enzymes: (a) alanine aminotransferase (ALT); (b) aspartate aminotransferase. Data are presented as mean ± SEM and were analyzed using repeated-measures ANOVA. F, the effect of factor (time of blood sampling after IR); G, the effect of group (C, IR, S, SIR); I, the effect of factor × group interaction; C, control sham-operated animals; IR, animals subjected to ischemia-reperfusion; S, sham-operated animals pretreated with sitagliptin; SIR, animals subjected to ischemia-reperfusion pretreated with sitagliptin.

Figure 2

Effect of IR injury and sitagliptin on CXCR4/SDF1 axis in the liver: (a) Cxcr4 expression; (b) CXCR4 concentration; (c) Sdf1 expression; (d) SDF1α concentration. Data were analyzed using the Kruskal–Wallis H test and are presented as medians with IQR (red squares with whiskers and numbers below dot-plots). Significant (p < 0.05) differences between groups, identified in post-hoc analysis (Conover test), are indicated by connectors with * symbol. NRQ, normalized relative quantity; IR, ischemia-reperfusion; SIR, sitagliptin pretreatment and ischemia-reperfusion; IQR, interquartile range.

Figure 2

Effect of IR injury and sitagliptin on CXCR4/SDF1 axis in the liver: (a) Cxcr4 expression; (b) CXCR4 concentration; (c) Sdf1 expression; (d) SDF1α concentration. Data were analyzed using the Kruskal–Wallis H test and are presented as medians with IQR (red squares with whiskers and numbers below dot-plots). Significant (p < 0.05) differences between groups, identified in post-hoc analysis (Conover test), are indicated by connectors with * symbol. NRQ, normalized relative quantity; IR, ischemia-reperfusion; SIR, sitagliptin pretreatment and ischemia-reperfusion; IQR, interquartile range.

Figure 3

Effect of IR injury and sitagliptin on PAC1, VPAC1, VPAC2/VIP axis in the liver: (a) Pac1 expression; (b) Vpac1 expression; (c) Vpac2 expression; (d) VIP concentration. Data were analyzed using the Kruskal–Wallis H test and are presented as medians with IQR (red squares with whiskers and numbers below dot-plots). Significant (p < 0.05) differences between groups, identified in post-hoc analysis (Conover test), are indicated by connectors with * symbol. NRQ, normalized relative quantity; IR, ischemia-reperfusion; SIR, sitagliptin pretreatment and ischemia-reperfusion; IQR, interquartile range.

Figure 4

Effect of IR injury and sitagliptin on GLP1R/GLP1 axis in the liver: (a) Glp1r expression; (b) GLP1 concentration. Data were analyzed using the Kruskal–Wallis H test and are presented as medians with IQR (red squares with whiskers and numbers below dot-plots). NRQ, normalized relative quantity; IR, ischemia-reperfusion; SIR, sitagliptin pretreatment and ischemia-reperfusion; IQR, interquartile range.