Functional Roles for CD26/DPP4 in Mediating Inflammatory Responses of Pulmonary Vascular Endothelial Cells

Excessive inflammation in the lung is a primary cause of acute respiratory distress syndrome (ARDS). CD26/dipeptidyl peptidase-4 (DPP4) is a transmembrane protein that is expressed in various cell types and exerts multiple pleiotropic effects. We recently reported that pharmacological CD26/DPP4 inhibition ameliorated lipopolysaccharide (LPS)-induced lung injury in mice and exerted anti-inflammatory effects on human lung microvascular endothelial cells (HLMVECs), in vitro. However, the mechanistic roles of CD26/DPP4 in lung injury and its effects on HLMVECs remain unclear. In this study, transcriptome analysis, followed by various confirmation experiments using siRNA in cultured HLMVECs, are performed to evaluate the role of CD26/DPP4 in response to the pro-inflammatory involved in inflammation, barrier function, and regenerative processes in HLMVECs after pro-inflammatory stimulation. These are all functions that are closely related to the pathophysiology and repair process of lung injury. Confirmatory experiments using flow cytometry; enzyme-linked immunosorbent assay; quantitative polymerase chain reaction; dextran permeability assay; WST-8 assay; wound healing assay; and tube formation assay, reveal that the reduction of CD26/DPP4 via siRNA is associated with altered parameters of inflammation, barrier function, and the regenerative processes in HLMVECs. Thus, CD26/DPP4 can play a pathological role in mediating injury in pulmonary endothelial cells. CD26/DPP4 inhibition can be a new therapeutic strategy for inflammatory lung diseases, involving pulmonary vascular damage.

Ammonium Formate-Pd/C as a New Reducing System for 1,2,4-Oxadiazoles. Synthesis of Guanidine Derivatives and Reductive Rearrangement to Quinazolin-4-Ones with Potential Anti-Diabetic Activity

1,2,4-Oxadiazole is a heterocycle with wide reactivity and many useful applications. The reactive O-N bond is usually reduced using molecular hydrogen to obtain amidine derivatives. NH4CO2H-Pd/C is here demonstrated as a new system for the O-N reduction, allowing us to obtain differently substituted acylamidine, acylguanidine and diacylguanidine derivatives. The proposed system is also effective for the achievement of a reductive rearrangement of 5-(2′-aminophenyl)-1,2,4-oxadiazoles into 1-alkylquinazolin-4(1H)-ones. The alkaloid glycosine was also obtained with this method. The obtained compounds were preliminarily tested for their biological activity in terms of their cytotoxicity, induced oxidative stress, α-glucosidase and DPP4 inhibition, showing potential application as anti-diabetics.

DPP4 inhibition mitigates Ang II-mediated kidney immune activation and injury in male mice

Recent evidence suggests that DPP4 inhibition with saxagliptin (Saxa) is renoprotective in co-morbid conditions associated with activation of the renin-angiotensin-aldosterone system (RAAS), such as diabetes, obesity and hypertension, which confer a high cardiovascular risk. Immune system activation is now recognized as a contributor to RAAS-mediated tissue injury and, importantly, immunomodulatory effects of DPP4 have been reported. Accordingly, we examined the hypothesis that DPP4 inhibition with Saxa attenuates Ang II-induced kidney injury and albuminuria via attenuation of immune activation in the kidney. To this end, male mice were infused with either vehicle or angiotensin II (Ang II, 1000ng/kg/min, sc) for 3 weeks receiving either placebo or Saxa (10mg/kg/d, po) during the final 2 weeks. Ang II infusion increased kidney, but not plasma, DPP4 activity in vivo as well as DPP4 activity in cultured proximal tubule cells. The latter was prevented by angiotensin receptor blockade with Olmesartan. Further, Ang II induced hypertension and kidney injury characterized by mesangial expansion, mitochondrial damage, reduced brush border megalin expression, and albuminuria. Saxa inhibited DPP4 activity ~50% in vivo and attenuated Ang II-mediated kidney injury, independent of blood pressure. Further mechanistic studies revealed mitigation by Saxa of pro-inflammatory and pro-fibrotic mediators activated by Ang II in the kidney, including CD8+ T cells, resident macrophages (CD11bhiF4/80loLy6C-), and neutrophils. In addition, Saxa improved Ang II suppressed anti-inflammatory Treg and Th2 lymphocyte activity. Taken together, these results demonstrate, for the first time, blood pressure-independent involvement of renal DPP4 activation contributing to RAAS-dependent kidney injury and immune activation.

Urinary DPP4 correlates with renal dysfunction, and DPP4 inhibition protects against the reduction in megalin and podocin expression in experimental CKD

This study investigated the molecular mechanisms underlying the antiproteinuric effect of DPP4 inhibition in 5/6 renal ablation rats and tested the hypothesis that the urinary activity of DPP4 correlates with chronic kidney disease (CKD) progression. Experiments were conducted in male Wistar rats who underwent 5/6 nephrectomy (Nx) or sham operation, followed by 8 weeks of treatment with the DPP4 inhibitor (DPP4i) sitagliptin or vehicle. Proteinuria increased progressively in Nx rats throughout the observation period. This increase was remarkably mitigated by sitagliptin. Higher levels of proteinuria in Nx rats compared to control rats were accompanied by higher urinary excretion of retinol-binding protein 4 (RBP4), a marker of tubular proteinuria, as well as higher urinary levels of podocin, a marker of glomerular proteinuria. RBP4 and podocin were not detected in the urine of Nx+DPP4i rats. Tubular and glomerular proteinuria was associated with the reduced expression of megalin and podocin in the renal cortex of Nx rats. Sitagliptin treatment partially prevented this decrease. Besides, the angiotensin II renal content was significantly reduced in the Nx rats that received sitagliptin compared to vehicle-treated Nx rats. Interestingly, both urinary DPP4 activity and abundance increased progressively in Nx rats. Additionally, urinary DPP4 activity correlated positively with serum creatinine levels, proteinuria, and blood pressure. Collectively, these results suggest that DPP4 inhibition ameliorated both tubular and glomerular proteinuria and prevented the reduction of megalin and podocin expression in CKD rats. Furthermore, these findings suggest that urinary DPP4 activity may serve as a biomarker of renal disease and progression.