Effects of Dipeptidyl Peptidase-4 Inhibitor and Angiotensin-Converting Enzyme Inhibitor on Experimental Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the leading cause of end-stage kidney disease in the United States and worldwide. Proteinuria is a major marker of the severity of injury. Dipeptidyl peptidase-4 inhibitor (DPP-4I) increases incretin-related insulin production and is, therefore, used to treat diabetes. We investigated whether DPP4I could have direct effect on kidney independent of its hypoglycemic activity. We, therefore, tested the effects of DPP4I with or without angiotensin-converting enzyme inhibitor (ACEI) on the progression of diabetic nephropathy and albuminuria in a murine model of DKD. eNOS-/-db/db mice were randomized to the following groups at age 10 weeks and treated until sacrifice: baseline (sacrificed at week 10), untreated control, ACEI, DPP4I, and combination of DPP4I and ACEI (Combo, sacrificed at week 18). Systemic parameters and urine albumin-creatinine ratio were assessed at baseline, weeks 14, and 18. Kidney morphology, glomerular filtration rate (GFR), WT-1, a marker for differentiated podocytes, podoplanin, a marker of foot process integrity, glomerular collagen IV, and alpha-smooth muscle actin were assessed at the end of the study. All mice had hyperglycemia and proteinuria at study entry at week 10. Untreated control mice had increased albuminuria, progression of glomerular injury, and reduced GFR at week 18 compared with baseline. DPP4I alone reduced blood glucose and kidney DPP-4 activity but failed to protect against kidney injury compared with untreated control. ACEI alone and combination groups showed significantly reduced albuminuria and glomerular injury, and maintained GFR and WT-1+ cells. Only the combination group had significantly less glomerular collagen IV deposition and more podoplanin preservation than the untreated control. DPP-4I alone does not decrease the progression of kidney injury in the eNOS-/-db/db mouse model, suggesting that targeting only hyperglycemia is not an optimal treatment strategy for DKD. Combined DPP-4I with ACEI added more benefit to reducing the glomerular matrix.

Incretins-Based Therapies and Their Cardiovascular Effects: New Game-Changers for the Management of Patients with Diabetes and Cardiovascular Disease

Atherosclerosis is the leading cause of death worldwide, especially in patients with type 2 diabetes mellitus (T2D). GLP-1 receptor agonists and DPP-4 inhibitors were demonstrated to play a markedly protective role for the cardiovascular system beyond their glycemic control. Several cardiovascular outcome trials (CVOT) reported the association between using these agents and a significant reduction in cardiovascular events in patients with T2D and a high cardiovascular risk profile. Moreover, recent evidence highlights a favorable benefit/risk profile in myocardial infarction and percutaneous coronary revascularization settings. These clinical effects result from their actions on multiple molecular mechanisms involving the immune system, platelets, and endothelial and vascular smooth muscle cells. This comprehensive review specifically concentrates on these cellular and molecular processes mediating the cardiovascular effects of incretins-like molecules, aiming to improve clinicians' knowledge and stimulate a more extensive use of these drugs in clinical practice as helpful cardiovascular preventive strategies.

Nephroprotective Properties of Antidiabetic Drugs

Chronic kidney disease (CKD) is associated with increased morbidity and mortality, especially from cardiovascular (CV) causes, and especially in people with diabetes mellitus (DM). Already the presence of DM increases CV risk and potentiates the risk of CKD. Therefore, besides glycemic control, prevention and treatment of CKD to slow its progression are of clinical importance. A significant nephroprotective effect of novel antidiabetic drugs, namely sodium-glucose cotransporter 2 inhibitors (SGLT2-I) and glucagon-like peptide 1 receptor agonists (GLP1-RA), has been shown on top of their glucose-lowering effects and was confirmed in cardiovascular outcome trials. GLP1-RA mainly reduced the risk of macroalbuminuria, whereas SGLT2-I were also associated with a lower risk of declining glomerular filtration rate (GFR) over time. The nephroprotective effects of SGLT2-I are also evident in people without DM. According to current guidelines, SGLT2-I and/or GLP1-RA are recommended for people with DM who have chronic kidney disease and/or increased cardiovascular risk. However, other antidiabetic drugs offer nephroprotective properties, which will also be discussed in this review.

The effect of linagliptin on microalbuminuria in patients with diabetic nephropathy: a randomized, double blinded clinical trial

The aim of the present study was to investigate the effect of linagliptin on microalbuminuria in patients with diabetic nephropathy (DN). The present double-blind randomized placebo-controlled clinical trial was performed on 92 patients with DN who were divided into two groups. The intervention and control groups received linagliptin 5 mg and placebo for 24 weeks, respectively. Blood pressure, lipid profile, liver enzymes, fasting plasma glucose (FPG), and urine albumin-creatinine ratio (UACR) were assessed and recorded before, 12 weeks, and 24 weeks after the beginning of the intervention. The mean value of UACR decrease was significant over time in both groups, with higher decrease in linagliptin group, however, the differences between two groups were not, statistically significant (P > 0.05). However, the percentage of improvement in microalbuminuria (UACR < 30 mg/g) in the linagliptin group was significantly higher than that of the control group during 24 weeks of intervention (68.3% vs. 25%; P-value < 0.001). There was no statistically significant difference in the mean value of the UACR and other parameters between linagliptin treated and placebo treated patients with diabetic nephropathy. Further studies, with longer periods of follow-up are suggested to examine these patients' renal outcomes.

What do we actually know about exosomal microRNAs in kidney diseases?

There are several types of kidney diseases with complex causes. If left untreated, these diseases irreversibly progress to end-stage renal disease. Thus, their early diagnosis and targeted treatment are important. Exosomes-extracellular vesicles released by a variety of cells-are ideal carriers for DNA, RNA, proteins, and other metabolites owing to their bilayer membranes. Studies have shown that almost all renal cells can secrete exosomes. While research on exosomal microRNAs in the context of renal diseases begun only recently, rapid progress has been achieved. This review summarizes the changes in exosomal microRNA expression in different kidney diseases. Thus, it highlights the diagnostic and prognostic value of these exosomal microRNAs. Further, this review analyzes their roles in the development of different kidney diseases, guiding research on molecular mechanisms and therapeutic strategies.

MD Simulation Studies for Selective Phytochemicals as Potential Inhibitors against Major Biological Targets of Diabetic Nephropathy

Diabetes is emerging as an epidemic and is becoming a public health concern worldwide. Diabetic nephropathy is one of the serious complications of diabetes, and about 40% of individuals with diabetes develop diabetic nephropathy. The consistent feature of diabetes and its associated nephropathy is hyperglycemia, and in some cases, hyperamylinemia. Currently, the treatment includes the use of medication for blood pressure control, sugar control, and cholesterol control, and in the later stage requires dialysis and kidney transplantation, making the management of this complication very difficult. Bioactive compounds, herbal medicines, and extracts are extensively used in the treatment and prevention of several diseases, and some are reported to be efficacious in diabetes too. Therefore, in this study, we tried to identify the therapeutic potential of phytochemicals used in in silico docking and molecular dynamic simulation studies using a library of 5284 phytochemicals against the two potential targets of type 2 diabetes-associated nephropathy. We identified two phytochemicals (i.e., gentisic acid and michelalbine) that target human amylin peptide and dipeptidyl peptidase-4, respectively, with good binding affinity. These phytochemicals can be further evaluated using in vitro and in vivo studies for their anti-hyperglycemia and anti-hyperamylinemia effects.

Exploring novel targets of sitagliptin for type 2 diabetes mellitus: Network pharmacology, molecular docking, molecular dynamics simulation, and SPR approaches

BACKGROUND

Diabetes has become a serious global public health problem. With the increasing prevalence of type 2 diabetes mellitus (T2DM), the incidence of complications of T2DM is also on the rise. Sitagliptin, as a targeted drug of DPP4, has good therapeutic effect for T2DM. It is well known that sitagliptin can specifically inhibit the activity of DPP4 to promote insulin secretion, inhibit islet β cell apoptosis and reduce blood glucose levels, while other pharmacological mechanisms are still unclear, such as improving insulin resistance, anti-inflammatory, anti-oxidative stress, and anti-fibrosis. The aim of this study was to explore novel targets and potential signaling pathways of sitagliptin for T2DM.

METHODS

Firstly, network pharmacology was applied to find the novel target most closely related to DPP4. Semi-flexible molecular docking was performed to confirm the binding ability between sitagliptin and the novel target, and molecular dynamics simulation (MD) was carried to verify the stability of the complex formed by sitagliptin and the novel target. Furthermore, surface-plasmon resonance (SPR) was used to explored the affinity and kinetic characteristics of sitagliptin with the novel target. Finally, the molecular mechanism of sitagliptin for T2DM was predicted by the enrichment analysis of GO function and KEGG pathway.

RESULTS

In this study, we found the cell surface receptor-angiotensin-converting enzyme 2 (ACE2) most closely related to DPP4. Then, we confirmed that sitagliptin had strong binding ability with ACE2 from a static perspective, and the stability of sitagliptin-ACE2 complex had better stability and longer binding time than BAR708-ACE2 in simulated aqueous solution within 50 ns. Significantly, we have demonstrated a strong affinity between sitagliptin and ACE2 on SPR biosensor, and their kinetic characteristics were "fast binding/fast dissociation". The guiding significance of clinical administration: low dose can reach saturation, but repeated administration was needed. Finally, there was certain relationship between COVID-19 and T2DM, and ACE2/Ang-(1-7)/Mas receptor (MasR) axis may be the important pathway of sitagliptin targeting ACE2 for T2DM.

CONCLUSION

This study used different methods to prove that ACE2 may be another novel target of sitagliptin for T2DM, which extended the application of ACE2 in improving diabetes mellitus.

Clinical efficacy of linagliptin combined with irbesartan in patients with diabetic nephropathy

Objective

To determine the clinical efficacy of linagliptin combined with irbesartan in patients with diabetic nephropathy (DN).

Methods

Seventy-two patients who were admitted to our department of endocrinology in our hospital during January 2018 and June 2019 were randomly divided into a control group (administered with irbesartan only, n=36) and a treatment group (treated with irbesartan and linagliptin, n=36). The course of treatment lasted for three months. FBG (fasting blood glucose), 2hPBG (2h postprandial blood sugar), HbA1C (hemoglobin A1c), Cys-C (cystatin C), SCr (serum creatinine), BUN (blood urea nitrogen), UACR (urine albumin-to-creatinine ratio), CRP (C-reactive protein), IL-6 (interleukin-6), and SOD (superoxide dismutase) were tested pre- and post-treatment to evaluate the clinical efficacy and adverse effects of the two treatment plans after three months of treatment.

Results

Compared with the pre-treatment levels, FBG, 2hPBG, HbA1c, Cys-C, SCr, BUN, UACR, CRP, IL-6, and SOD in both groups were significantly improved following the three-month treatment (P<0.05, respectively). Post-treatment levels of FBG, 2hPBG, HbA1c, Cys-C, SCr, BUN, UACR, CRP, and IL-6 in the treatment group were significantly lower than in the control group (P<0.05, respectively), while the treatment group exhibited a higher level of SOD compared with the control group (P<0.05). No serious adverse reaction occurred in either group (P>0.05).

Conclusion

Combined-modality treatment with linagliptin and irbesartan shows favorable clinical efficacy in treating diabetic nephropathy as it effectively protects the kidneys and improves kidney function by inhibiting inflammatory and oxidative stress responses.

Recent therapeutic targets in diabetic nephropathy

BACKGROUND

The prevalence of diabetes mellitus has been increased dramatically which in turn leads to complications including cardiovascular diseases, diabetic kidney disease, and substantially end-stage renal disease.

METHODS

We reviewed articles discussing the pathophysiology of diabetic nephropathy with new agents that may be useful in the management of the disease. We used PubMed, Scopus, Google Scholar and the Open-access searching engines.

RESULTS

The recent recommendations primarily depend on glycaemic and blood pressure control and the use of standard renin-angiotensin system blockade. Currently, the use of agents with nephroprotective effects beyond the hyperglycaemic lowering effect has been evidenced clinically.

CONCLUSIONS

In his review, the pathophysiology, clinical manifestations, and lines of treatment of diabetic nephropathy are discussed. In addition, a focus on the clinical role and nephroprotective effects of the emerging therapeutic class, dipeptidyl peptidase IV (DPP-4) inhibitors, is addressed in detail.

Novel Chalcone BDD-39 Mitigated Diabetic Nephropathy through the Activation of Nrf2/ARE Signaling

BACKGROUND

In this study, we investigated the Nrf2/ARE signaling pathway activating capacity of Biphenyl Diester Derivative-39 (BDD-39) in diabetic nephropathy in order to elucidate the mechanism surrounding its antidiabetic potential.

OBJECTIVES

Protein expressions of Nrf2, HO-1, NQO-1 and biomarkers of kidney fibrosis were executed after which mRNA levels of Nrf2, HO-1 and NQO-1 were estimated after creating the models following BBD-39 treatment.

METHODS

Type 2 diabetes model was established in mice with high-fat diet feeding combined with streptozocin intraperitoneal administration. The diabetic mice were then treated with BDD-39 (15, 45mg· kg-1· d-1, ig) or a positive control drug resveratrol (45mg· kg-1·d-1, ig) for 8 weeks. Staining techniques were used to investigate collagen deposition in the glomerulus of the renal cortex and also to investigate the expression and localization of Nrf2 and extracellular matrix (ECM) proteins (collagen IV and laminin) in vitro and in vivo. Furthermore, we studied the mechanism of action of BDD-39 using RNA-mediated Nrf2 silencing technique in mouse SV40 glomerular mesangial cells (SV40 GM cells).

RESULTS

We found that BDD-39 activates Nrf2/ARE signaling pathway, promotes Nrf2 nuclear translocation (Nrf2nuc/Nrf2cyt) and modulate prominent biomarkers of kidney fibrosis at the protein level. However, BDD-39 could not activate Nrf2/ARE signaling in RNA-mediated Nrf2-silenced HG-cultured SV40 GM cells.

CONCLUSION

Taken together, this study demonstrates for the first time that BDD-39 ameliorates experimental DN through attenuation of renal fibrosis progression and modulation of Nrf2/ARE signaling pathway.

Urinary dipeptidyl peptidase-4 protein is increased by linagliptin and is a potential predictive marker of urine albumin-to-creatinine ratio reduction in patients with type 2 diabetes

Results of a post hoc analysis of urinary dipeptidyl peptidase-4 (DPP-4) protein as a predictor of urine albumin-to-creatinine ratio (UACR) response to linagliptin treatment based on MARLINA-T2D trial data are described. MARLINA was a 24-week, phase 3b, multinational, placebo-controlled clinical trial, in which patients with type 2 diabetes (T2D), HbA1c 6.5%-10.0% and UACR 30-3000 mg/g (n = 360) were treated with linagliptin or placebo. After 24 weeks of treatment, linagliptin significantly inhibited urinary DPP-4 activity and increased urinary DPP-4 protein. Furthermore, medium urinary DPP-4 protein levels (between 5.5 and 7.5 natural logarithmic [ln] μg/g creatinine) at baseline allowed for prediction of improved UACR in linagliptin-treated individuals. In patients with lower or higher levels of urinary DPP-4 protein at baseline, no association between linagliptin treatment and improved UACR was present. This might suggest a varying degree of importance of DPP-4 as a pathophysiological factor in T2D-associated kidney disease. In summary, urinary DPP-4 might be a useful predictive biomarker for UACR improvement by linagliptin.

The Effects of Glucagon-Like Peptide-1 Receptor Agonists and Dipeptydilpeptidase-4 Inhibitors on Blood Pressure and Cardiovascular Complications in Diabetes

Glucagon-like peptide-1 receptor (GLP-1R) agonists are a class of newly introduced antidiabetic medications that potentially lower blood glucose by several molecular pathways. DPP-4 inhibitors are the other type of novel antidiabetic medications which act by preventing GLP-1 inactivation and thereby increasing the activity levels of GLP-1, leading to more glucose-induced insulin release from islet β-cells and suppression of glucagon release. Most patients with diabetes have concurrent hypertension and cardiovascular disorder. If antihyperglycemic agents can attenuate the risk of hypertension and cardiovascular disease, they will amplify their overall beneficial effects. There is conflicting evidence on the cardiovascular benefits of GLP-1R induction in laboratory studies and clinical trials. In this study, we have reviewed the main molecular mechanisms by which GLP-1R induction may modulate the cardiovascular function and the results of cardiovascular outcome clinical trials.

Association between Dipeptidyl Peptidase-4 Inhibitor Prescription and Erythropoiesis-Stimulating Agent Hyporesponsiveness in Hemodialysis Patients with Diabetes Mellitus

INTRODUCTION

Dipeptidyl peptidase-4 (DPP-4) has been hypothesized to improve responsiveness to erythropoiesis-stimulating agent (ESA). We aimed to describe the trend in DPP-4 inhibitor prescription patterns and assess the association between DPP-4 inhibitor prescription and ESA hyporesponsiveness (eHypo) in Japanese hemodialysis (HD) patients with diabetes mellitus (DM).

METHODS

We analyzed data from the Japan Dialysis Outcomes and Practice Patterns Study phase 4-6 (2009-2017) on patients with DM who underwent HD thrice per week for at least 4 months. The primary exposure of interest was having a DPP-4 inhibitor prescription. The primary analysis outcomes were a binary indicator of eHypo (mean hemoglobin <10 and mean ESA dose >6,000 units/week over 4 months) and the natural log-transformed ESA resistance index (ERI). We used conditional logistic regression to compare within-patient changes in eHypo before and after initial DPP-4 inhibitor prescription. We used linear generalized estimating equation models to compare continuous ERI outcomes while accounting for within-patient repeated measurements with an exchangeable correlation structure.

RESULTS

There was a monotonic increase in DPP-4 inhibitor prescription according to study year up to 20% in 2017. Moreover, 12.8% of patients with a DPP-4 inhibitor prescription were ESA hyporesponsive before the initial DPP-4 inhibitor prescription. After DPP-4 inhibitor prescription, the odds of eHypo and mean log-ERI remained unchanged in the whole cohort of our study. The interaction analysis of DPP-4 inhibitor and sideropenia showed that DPP-4 inhibitors attenuated eHypo in the patients without iron deficiency.

CONCLUSION

Our findings indicate a recent increase in DPP-4 inhibitor prescription among Japanese HD patients with DM. DPP-4 inhibitors could improve ERI in patients undergoing HD without iron deficiency.

A Novel Dipeptidyl Peptidase-4 Inhibitor DA-1229 Ameliorates Tubulointerstitial Fibrosis in Cyclosporine Nephrotoxicity in Mice

Cyclosporine A (CyA) is an immunosuppressive agent that induces nephrotoxicity with long-term treatment. The roles of DPP-4 and its inhibitors in cyclosporine nephrotoxicity are not fully understood. Therefore, we investigated the effects of a novel DPP-4 inhibitor, DA-1229, on the progression of renal disease in an experimental cyclosporine nephrotoxicity model. Chronic cyclosporine nephrotoxicity was induced in six-week-old male ICR mice by subcutaneous injections of CyA at a dose of 30 mg/kg for four weeks. Animals were treated with DA-1229 at a dose of 300 mg/kg per day in food for four weeks. Although DPP-4 activity did not increase in the kidneys of mice with induced cyclosporine nephrotoxicity, DA-1229 treatment significantly suppressed DPP-4 activity in both plasma and renal tissues. DPP-4 inhibition by DA-1229 led to significantly decreased albuminuria and urinary excretion of 8-isoprosatane. DPP-4 inhibition also substantially suppressed pro-inflammatory effects, profibrotic molecules, and macrophage infiltration, and led to the improvement in renal structural changes. Our results suggest that DPP-4 inhibition by DA-1229 provides renoprotective effects in an animal model of cyclosporine nephrotoxicity via antioxidant, anti-inflammatory, and anti-fibrotic mechanisms. DPP-4 inhibition may be a useful new therapeutic approach for the management of progressive renal disease in cyclosporine nephrotoxicity.

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

Recent evidence suggests that dipeptidyl peptidase-4 (DPP4) inhibition with saxagliptin (Saxa) is renoprotective under comorbid 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 angiotensin II (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 ANG II (1,000 ng/kg/min, s.c.) for 3 wk and received either placebo or Saxa (10 mg/kg/day, p.o.) during the final 2 wk. 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 experiments revealed mitigation by Saxa of proinflammatory and profibrotic mediators activated by ANG II in the kidney, including CD8⁺ T cells, resident macrophages (CD11b^hiF4/80^loLy6C^-), and neutrophils. In addition, Saxa improved ANG II suppressed anti-inflammatory regulatory T cell and T helper 2 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.NEW & NOTEWORTHY This work highlights the role of dipeptidyl peptidase-4 (DPP4) in promoting ANG II-mediated kidney inflammation and injury. Specifically, ANG II infusion in mice led to increases in blood pressure and kidney DPP4 activity, which then led to activation of CD8⁺ T cells, Ly6C^- macrophages, and neutrophils and suppression of anti-inflammatory T helper 2 lymphocytes and regulatory T cells. Collectively, this led to kidney injury, characterized by mesangial expansion, mitochondrial damage, and albuminuria, which were mitigated by DPP4 inhibition independent of blood pressure reduction.

DPP-4 Inhibitors: Renoprotective Potential and Pharmacokinetics in Type 2 Diabetes Mellitus Patients with Renal Impairment

The continuously increasing incidence of diabetes worldwide has attracted the attention of the scientific community and driven the development of a novel class of antidiabetic drugs that can be safely and effectively used in diabetic patients. Of particular interest in this context are complications associated with diabetes, such as renal impairment, which is the main cause of high cardiovascular morbidity and mortality in diabetic patients. Intensive control of glucose levels and other risk factors associated with diabetes and metabolic syndrome provides the foundations for both preventing and treating diabetic nephropathy. Dipeptidyl peptidase-4 (DPP-4) inhibitors represent a highly promising novel class of oral agents used in the treatment of type 2 diabetes mellitus that may be successfully combined with currently available antidiabetic therapeutics in order to achieve blood glucose goals. Beyond glycemic control, emerging evidence suggests that DPP-4 inhibitors may have desirable off-target effects, including renoprotection. All type 2 diabetes mellitus patients with impaired renal function require dose adjustment of any DPP-4 inhibitor administered except for linagliptin, for which renal excretion is a minor elimination pathway. Thus, linagliptin is the drug most frequently chosen to treat type 2 diabetes mellitus patients with renal failure.

DPP4/CD32b/NF-κB Circuit: A Novel Druggable Target for Inhibiting CRP-Driven Diabetic Nephropathy

Diabetic nephropathy (DN) is a major cause of end-stage renal disease, but treatment remains ineffective. C-reactive protein (CRP) is pathogenic in DN, which significantly correlated with dipeptidyl peptidase-4 (DPP4) expression in diabetic patients with unknown reason. Here, using our unique CRP^tg-db/db mice, we observed human CRP markedly induced renal DPP4 associated with enhanced kidney injury compared with db/db mice. Interestingly, linagliptin, a US Food and Drug Administration (FDA)-approved specific DPP4 inhibitor, effectively blocked this CRP-driven DN in the CRP^tg-db/db mice. Mechanistically, CRP evoked DPP4 in cultured renal tubular epithelial cells, where CD32b/nuclear factor κB (NF-κB) signaling markedly enriched p65 binding on the DPP4 promoter region to increase its transcription. Unexpectedly, we further discovered that CRP triggers dimerization of DPP4 with CD32b at protein level, forming a novel DPP4/CD32b/NF-κB signaling circuit for promoting CRP-mediated DN. More importantly, linagliptin effectively blocked the circuit, thereby inhibiting the CRP/CD32b/NF-κB-driven renal inflammation and fibrosis. Thus, DPP4 may represent a precise druggable target for CRP-driven DN.

The effect of linagliptin on renal progression in type-2 diabetes mellitus patients with chronic kidney disease: A prospective randomized controlled study

BACKGROUND

Linagliptin does not require dose adjustment in diabetes mellitus patients with chronic kidney disease (CKD). But, renal effects of linagliptin are not clear. Our aim was to examine the effect of linagliptin on renal disease progression in only insulin dependent type 2 diabetes mellitus (DM) patients with CKD.

METHODS

Stage 3-4 CKD patients were randomized into 2 groups in this prospective randomized controlled study. In the first group, linagliptin 5mg was added in addition to the background insulin therapy. In the second group, patients continued their insulin therapy. Patients were followed up at 3-month intervals for one year.

RESULTS

The study population consisted of 164 patients (90 patients in linagliptin group, 74 patients in other group) with a mean age of 67.5±8.8 years. eGFR significantly increased in linagliptin group (p=0.033), but decreased in other group (p=0.003). No significant change was observed in total insulin dose in linagliptin group (p=0.111), but in other group, total insulin dose significantly increased (p<0.001). Proteinuria levels decreased in both groups, but there was no significant change. In the multiple logistic regression analysis, male gender and proteinuria emerged as variables that showed significant association with increased risk and the use of linagliptin emerged as variable that showed significant association with decreased risk for CKD progression.

CONCLUSION

Linagliptin in DM patients with CKD was able to improve renal progression without significant effect on proteinuria and glucose control. With regard to treating diabetic nephropathy, linagliptin may offer a new therapeutic approach.

Pleiotropic effects of anti-diabetic drugs: A comprehensive review

Diabetes mellitus characterized by hyperglycaemia presents an array of comorbidities such as cardiovascular and renal failure, dyslipidemia, and cognitive impairments. Populations above the age of 60 are in an urgent need of effective therapies to deal with the complications associated with diabetes mellitus. Widely used anti-diabetic drugs have good safety profiles and multiple reports indicate their pleiotropic effects in diabetic patients or models. This review has been written with the objective of identifying the widely-marketed anti-diabetic drugs which can be efficiently repurposed for the treatment of other diseases or disorders. It is an updated, comprehensive review, describing the protective role of various classes of anti-diabetic drugs in mitigating the macro and micro vascular complications of diabetes mellitus, and differentiating these drugs on the basis of their mode of action. Notably, metformin, the anti-diabetic drug most commonly explored for cancer therapy, has also exhibited some antimicrobial effects. Unlike class specific effects, few instances of drug specific effects in managing cardiovascular complications have also been reported. A major drawback is that the pleiotropic effects of anti-diabetic drugs have been mostly investigated only in diabetic patients. Thus, for effective repurposing, more clinical trials devoted to analyse the effects of anti-diabetic drugs in patients irrespective of their diabetic condition, are required.

Hemodynamic effects of the dipeptidyl peptidase-4 inhibitor linagliptin with renin-angiotensin system inhibitors in type 2 diabetic patients with albuminuria

Objective:

Concomitant treatment with angiotensin-converting enzyme (ACE) inhibitors and dipeptidyl peptidase-4 (DPP-4) inhibitors is increasingly common. Pharmacological studies have suggested a potential adverse drug interaction between ACE inhibitors and DPP-4 inhibitors resulting in unfavorable hemodynamic changes; very few studies have examined such an interaction between angiotensin II receptor blockers (ARBs) and DPP-4 inhibitors. We investigated blood pressure (BP) and heart rate (HR) during treatment with the DPP-4 inhibitor linagliptin in individuals receiving either ACE inhibitors or ARBs in the MARLINA-T2D trial.

Methods:

In this study, 360 individuals with type 2 diabetes and albuminuria receiving unchanged doses of ACE inhibitors or ARBs were randomized to linagliptin or placebo. Twenty-four-hour ambulatory BP monitoring, an exploratory endpoint, was conducted at baseline and after 24 weeks.

Results:

Ambulatory BP monitoring data were available for 208 individuals (linagliptin: n = 111; placebo: n = 97). Baseline mean ± SD 24-h SBP and DBP were 132.5 ± 12.4 mmHg and 75.9 ± 9.4 mmHg, respectively; mean 24-h HR was 76.3 ± 10.1 bpm. At week 24, no overall effect of the DPP-4 inhibitor versus placebo was seen on mean 24-h SBP, DBP, or HR. Furthermore, in the subgroups receiving either an ACE inhibitor or an ARB, no effect on these hemodynamic parameters was seen as a result of concomitant DPP-4 inhibitor treatment.

Conclusion:

Adding linagliptin to treatment with ACE inhibitors or ARBs was not associated with any hemodynamic changes, supporting their concomitant use in individuals with type 2 diabetes and albuminuria.

Glucose and Blood Pressure-Dependent Pathways-The Progression of Diabetic Kidney Disease

The major clinical associations with the progression of diabetic kidney disease (DKD) are glycemic control and systemic hypertension. Recent studies have continued to emphasize vasoactive hormone pathways including aldosterone and endothelin which suggest a key role for vasoconstrictor pathways in promoting renal damage in diabetes. The role of glucose per se remains difficult to define in DKD but appears to involve key intermediates including reactive oxygen species (ROS) and dicarbonyls such as methylglyoxal which activate intracellular pathways to promote fibrosis and inflammation in the kidney. Recent studies have identified a novel molecular interaction between hemodynamic and metabolic pathways which could lead to new treatments for DKD. This should lead to a further improvement in the outlook of DKD building on positive results from RAAS blockade and more recently newer classes of glucose-lowering agents such as SGLT2 inhibitors and GLP1 receptor agonists.

Linagliptin and telmisartan induced effects on renal and urinary exosomal miRNA expression in rats with 5/6 nephrectomy

Dipeptidyl peptidase 4 inhibitors and angiotensin II receptor blockers attenuate chronic kidney disease progression in experimental diabetic and non-diabetic nephropathy in a blood pressure and glucose independent manner, but the exact molecular mechanisms remain unclear. MicroRNAs (miRNAs) are short, non-coding RNA species that are important post-transcriptional regulators of gene expression and play an important role in the pathogenesis of nephropathy. miRNAs are present in urine in a remarkably stable form, packaged in extracellular vesicles. Here, we investigated linagliptin and telmisartan induced effects on renal and urinary exosomal miRNA expression in 5/6 nephrectomized rats. In the present study, renal miRNA profiling was conducted using the Nanostring nCounter technology and mRNA profiling using RNA sequencing from the following groups of rats: sham operated plus placebo; 5/6 nephrectomy plus placebo; 5/6 nephrectomy plus telmisartan; and 5/6 nephrectomy plus linagliptin. TaqMan Array miRNA Cards were used to evaluate which of the deregulated miRNAs in the kidney are present in urinary exosomes. In kidneys from 5/6 nephrectomized rats, the expression of 13 miRNAs was significantly increased (>1.5-fold, P < 0.05), whereas the expression of 7 miRNAs was significantly decreased (>1.5-fold, P < 0.05). Most of the deregulated miRNA species are implicated in endothelial-to-mesenchymal transition and inflammatory processes. Both telmisartan and linagliptin suppressed the induction of pro-fibrotic miRNAs, such as miR-199a-3p, and restored levels of anti-fibrotic miR-29c. In conclusion, the linagliptin and telmisartan-induced restorative effects on miR-29c expression were reflected in urinary exosomes, suggesting that miRNA profiling of urinary exosomes might be used as a biomarker for CKD progression and monitoring of treatment effects.

The Effects of DPP4 Inhibitors on Lipid Status and Blood Pressure in Rats with Diabetes Mellitus Type 2

The aim of the present study was to examine, evaluate and compare the effects of administered dipeptidyl peptidase-4 (DPP4) inhibitors saxagliptin and sitagliptin on lipid status parameters and blood pressure in rats with streptozotocine induced diabetes mellitus type 2. Forty-eight Wistar albino rats were divided randomly into 4 groups: 1. group I: control healthy group; 2. group II: rats with diabetes mellitus type 2; 3. group III: rats with diabetes mellitus type 2+ treated with 0.6 mg/kg of sitagliptin; 4. group IV: rats with diabetes mellitus type 2 treated with 0.45 mg/kg of saxagliptin. The rats from experimental groups were fed with a high-fat diet for 4 weeks and after 6–8 h of starvation received one dose of streptozotocin (STZ) intraperitoneally (25 mg/kg body weight) to induce type 2 diabetes mellitus (T2DM). Animals with fasting glucose above 7 mmol/L and insulin over 6 mmol/L were included in the study as rats with T2DM. Upon completion of the experiments, the blood was collected from the anesthetized animals and serum triglyceride (TG), total cholesterol (TCH), high density lipoprotein (HDL), and low density lipoprotein (LDL) were measured using spectrophotometry and commercial kits. At the beginning of the study and the day before sacrificing animals, the blood pressure and heart rate were measured by a tail-cuff noninvasive method. DPP4 inhibitors, as glucagon-like peptide-1 (GLP-1) agonists, were associated with modest reductions in DBP, LDL-C, TCH, and TGL and significant improvement in HDL, SBP and HR.

Simultaneous angiotensin receptor blockade and glucagon-like peptide-1 receptor activation ameliorate albuminuria in obese insulin-resistant rats

Insulin resistance increases renal oxidant production by upregulating NADPH oxidase 4 (Nox4) expression contributing to oxidative damage and ultimately albuminuria. Inhibition of the renin-angiotensin system (RAS) and activation of glucagon-like peptide-1 (GLP-1) receptor signalling may reverse this effect. However, whether angiotensin receptor type 1 (AT1) blockade and GLP-1 receptor activation improve oxidative damage and albuminuria through different mechanisms is not known. Using insulin-resistant Otsuka Long-Evans Tokushima Fatty (OLETF) rats, we tested the hypothesis that simultaneous blockade of AT1 and activation of GLP-1r additively decrease oxidative damage and urinary albumin excretion (U_alb V) in the following groups: (a) untreated, lean LETO (n = 7), (b) untreated, obese OLETF (n = 9), (c) OLETF + angiotensin receptor blocker (ARB; 10 mg olmesartan/kg/d; n = 9), (d) OLETF + GLP-1 mimetic (EXE; 10 µg exenatide/kg/d; n = 7) and (e) OLETF + ARB +exenatide (Combo; n = 6). Mean kidney Nox4 protein expression and nitrotyrosine (NT) levels were 30% and 46% greater, respectively, in OLETF compared with LETO. Conversely, Nox4 protein expression and NT were reduced to LETO levels in ARB and EXE, and Combo reduced Nox4, NT and 4-hydroxy-2-nonenal levels by 21%, 27% and 27%, respectively. At baseline, U_alb V was nearly double in OLETF compared with LETO and increased to nearly 10-fold greater levels by the end of the study. Whereas ARB (45%) and EXE (55%) individually reduced U_alb V, the combination completely ameliorated the albuminuria. Collectively, these data suggest that AT1 blockade and GLP-1 receptor activation reduce renal oxidative damage similarly during insulin resistance, whereas targeting both signalling pathways provides added benefit in restoring and/or further ameliorating albuminuria in a model of diet-induced obesity.

Odds of Acute Kidney Injury in Patients Receiving Dipeptidyl Peptidase 4 Inhibitors: A National Cohort Study Within the Department of Veterans Affairs

Preclinical and clinical data of dipeptidyl peptidase 4 (DPP-4) inhibitors have demonstrated discordant data regarding acute kidney injury (AKI). Therefore, we aimed to evaluate the association between DPP-4 use and AKI. This cohort study utilized data from the Department of Veterans Affairs evaluating patients diagnosed with type 2 (T2) diabetes with a DPP-4 inhibitor and compared with nondiabetic and diabetic patients. The primary end point is the development of AKI, and statistical analyses were performed to examine the association. DPP-4 use is associated with a lower odds of AKI compared with diabetics (adjusted odds ratio (OR) = 0.39; 95% confidence interval (CI) = 0.32-0.48) and nondiabetics (OR = 0.64; 95% CI = 0.52-0.79). DPP-4 use in patients with T2 diabetes mellitus is associated with lower odds of AKI within 120 days compared with nondiabetic and diabetic controls when adjusting for study covariates.

More than just an enzyme: Dipeptidyl peptidase-4 (DPP-4) and its association with diabetic kidney remodelling

PURPOSE OF THE REVIEW

This review article discusses recent advances in the mechanism of dipeptidyl peptidase-4 (DPP-4) actions in renal diseases, especially diabetic kidney fibrosis, and summarizes anti-fibrotic functions of various DPP-4 inhibitors in diabetic nephropathy (DN).

RECENT FINDINGS

DN is a common complication of diabetes and is a leading cause of the end-stage renal disease (ESRD). DPP-4 is a member of serine proteases, and more than 30 substrates have been identified that act via several biochemical messengers in a variety of tissues including kidney. Intriguingly, DPP-4 actions on the diabetic kidney is a complex mechanism, and a variety of pathways are involved including increasing GLP-1/SDF-1, disrupting AGE-RAGE pathways, and integrin-β- and TGF-β-Smad-mediated signalling pathways that finally lead to endothelial to mesenchymal transition. Interestingly, an array of DPP-4 inhibitors is well recognized as oral drugs to treat type 2 diabetic (T2D) patients, which promote better glycemic control. Furthermore, recent experimental and preclinical data reveal that DPP-4 inhibitors may also exhibit protective effects in renal disease progression including anti-fibrotic effects in the diabetic kidney by attenuating above signalling cascade(s), either singly or as a combinatorial effect. In this review, we discussed the anti-fibrotic effects of DPP-4 inhibitors based on recent reports along with the possible mechanism of actions and future perspectives to underscore the beneficial effects of DPP-4 inhibitors in DN.

SUMMARY

With recent experimental, preclinical, and clinical evidence, we summarized DPP-4 activities and its mechanism of actions in diabetic kidney diseases. A knowledge gap of DPP-4 inhibition in controlling renal fibrosis in DN has also been postulated in this review for future research perspectives.

Diabetic nephropathy: an insight into molecular mechanisms and emerging therapies

Introduction: Diabetic kidney disease (DKD) is a major cause of morbidity and mortality in diabetes and is the most common cause of proteinuric and non-proteinuric forms of end-stage renal disease (ESRD). Control of risk factors such as blood glucose and blood pressure is not always achievable or effective. Significant research efforts have attempted to understand the pathophysiology of DKD and develop new therapies. Areas covered: We review DKD pathophysiology in the context of existing and emerging therapies that affect hemodynamic and metabolic pathways. Renin-angiotensin system (RAS) inhibition has become standard care. Recent evidence for renoprotective activity of SGLT2 inhibitors and GLP-1 agonists is an exciting step forward while endothelin receptor blockade shows promise. Multiple metabolic pathways of DKD have been evaluated with varying success; including mitochondrial function, reactive oxygen species, NADPH oxidase (NOX), transcription factors (NF-B and Nrf2), advanced glycation, protein kinase C (PKC), aldose reductase, JAK-STAT, autophagy, apoptosis-signaling kinase 1 (ASK1), fibrosis and epigenetics. Expert opinion: There have been major advances in the understanding and treatment of DKD. SGLT2i and GLP-1 agonists have demonstrated renoprotection, with novel therapies under evaluation. Addressing the interaction between hemodynamic and metabolic pathways may help achieve prevention, attenuation or even reversal of DKD.

DPP-4 Inhibitors as Potential Candidates for Antihypertensive Therapy: Improving Vascular Inflammation and Assisting the Action of Traditional Antihypertensive Drugs

Dipeptidyl peptidase-4 (DPP-4) is an important protease that is widely expressed on the surface of human cells and plays a key role in immune-regulation, inflammation, oxidative stress, cell adhesion, and apoptosis by targeting different substrates. DPP-4 inhibitors (DPP-4i) are commonly used as hypoglycemic agents. However, in addition to their hypoglycemic effect, DPP-4i have also shown potent activities in the cardiovascular system, particularly in the regulation of blood pressure (BP). Previous studies have shown that the regulatory actions of DPP-4i in controlling BP are complex and that the mechanisms involved include the functional activities of the nerves, kidneys, hormones, blood vessels, and insulin. Recent work has also shown that inflammation is closely associated with the elevation of BP, and that the inhibition of DPP-4 can reduce BP by regulating the function of the immune system, by reducing inflammatory reactions and by improving oxidative stress. In this review, we describe the potential anti-hypertensive effects of DPP-4i and discuss potential new anti-hypertensive therapies. Our analysis indicated that DPP-4i treatment has a mild anti-hypertensive effect as a monotherapy and causes a significant reduction in BP when used in combined treatments. However, the combination of DPP-4i with high-dose angiotensin converting enzyme inhibitors (ACEI) can lead to increased BP. We suggest that DPP-4i improves vascular endothelial function in hypertensive patients by suppressing inflammatory responses and by alleviating oxidative stress. In addition, DPP-4i can also regulate BP by activating the sympathetic nervous system, interfering with the renin angiotensin aldosterone system (RAAS), regulating Na/H₂O metabolism, and attenuating insulin resistance (IR).

Dipeptidyl peptidase-4 inhibitor compared with sulfonylurea in combination with metformin: cardiovascular and renal outcomes in a propensity-matched cohort study

Background

To determine the impact of dipeptidyl peptidase-4 inhibitor (DPP4i) on the risk of major cardiocerebrovascular and renal outcomes compared with sulfonylurea (SU) combined with metformin in patients with type 2 diabetes from a population-based cohort.

Methods

From a nationwide cohort in Korea (2008–2013), 23,674 patients with type 2 diabetes treated with DPP4i plus metformin or SU plus metformin were selected and matched by propensity score. Composite cardiocerebrovascular events including incident ischemic heart disease (IHD), ischemic stroke (IS), hospitalization for heart failure (HHF), and cardiocerebrovascular death, as well as renal events including incident end-stage renal disease or initiation of renal-replacement therapy were assessed by Cox proportional-hazards models.

Results

During a median follow-up of 19.6 months (interquartile range 7.2–36.4), 762 composite cardiocerebrovascular events and 17 end-stage renal events occurred. There was no significant difference in the risk of IHD (hazard ratio [HR], 1.00; 95% CI 0.81–1.23), IS (HR, 0.95; 95% CI 0.74–1.23), or cardiocerebrovascular death (HR, 0.74; 95% CI 0.46–1.18) in the DPP4i group compared to that in the SU group. Likewise, DPP4i therapy was not associated with the risk of end-stage renal outcomes (HR, 1.23; 95% CI 0.41–3.62). However, the risk of HHF was significantly higher in the DPP4i group than in the SU group (HR, 1.47; 95% CI 1.07–2.04).

Conclusions

This real-world database analysis showed that DPP4i therapy did not increase the overall risk of major cardiovascular and renal outcomes compared to SU therapy. However, the DPP4i-associated risk of HHF remained significant.

Electronic supplementary material

The online version of this article (10.1186/s12933-019-0835-z) contains supplementary material, which is available to authorized users.

DPP-4 inhibition enhanced renal tubular and myocardial GLP-1 receptor expression decreased in CKD with myocardial infarction

Background

Chronic kidney disease (CKD) is strongly associated with cardiovascular disease and is a significant risk factor for increased morbidity and mortality. In contrast, GLP-1 receptor (GLP-1R) activation has been shown to confer both renal and cardiovascular protection, though its relationship with CKD and CKD with myocardial ischemia/reperfusion (MI/R) remains poorly understood. Here, we investigated changes in renal and myocardial GLP-1R expression in the CKD rat model with MI/R.

Methods

Male Sprague Dawley rats with 5/6 nephrectomy were used as a rat model of CKD and CKD with MI/R. For myocardial ischemia, the left coronary artery was ligated and released for 30 min 1 week after 5/6 nephrectomy. Dipeptidyl-peptidase 4 (DPP-4) inhibitors were administered orally with linagliptin once daily for 8 weeks. Renal cortical and myocardial GLP-1R expression were measured via immunohistochemistry and western blot analysis.

Results

DPP-4 activity was increased in CKD. Western blot density of GLP-1R in renal cortex extracts revealed increased abundance 2 weeks after 5/6 nephrectomy, followed by a decrease at 8 weeks. In contrast, CKD and CKD with MI/R rats showed decreases in renal and cardiac expression of GLP-1R; these effects were attenuated in rats treated with linagliptin.

Conclusions

In CKD with MI/R, linagliptin attenuated renal injury and increased renal and myocardial GLP-1R expression. These data suggest that activation of renal and myocardial GLP-1R expression may provide both cardio- and renoprotective effects.

Electronic supplementary material

The online version of this article (10.1186/s12882-019-1243-z) contains supplementary material, which is available to authorized users.

Effects of Dipeptidyl Peptidase-4 Inhibitors on Renal Outcomes in Patients with Type 2 Diabetes: A Systematic Review and Meta-Analysis

BACKGROUND

To investigate the effects of dipeptidyl peptidase-4 (DPP-4) inhibitors on renal outcomes in patients with type 2 diabetes.

METHODS

MEDLINE, Embase, and the Cochrane Central Register of Controlled Trials were searched to identify randomized controlled trials (RCTs) of DPP-4 inhibitors from inception to September 2017. We selected eligible RCTs comparing DPP-4 inhibitors with placebo or other antidiabetic agents and reporting at least one renal outcome. A meta-analysis was conducted to calculate standardized mean differences, weighted mean differences (WMDs), relative risks (RRs), and 95% confidence intervals (CIs) for each renal outcome.

RESULTS

We included 23 RCTs with 19 publications involving 41,359 patients. Overall changes in urine albumin-to-creatinine ratio were comparable between DPP-4 inhibitors and controls (P=0.150). However, DPP-4 inhibitors were associated with significantly lower risk of incident microalbuminuria (RR, 0.89; 95% CI, 0.80 to 0.98; P=0.022) and macroalbuminuria (RR, 0.77; 95% CI, 0.61 to 0.97; P=0.027), as well as higher rates of regression of albuminuria (RR, 1.22; 95% CI, 1.10 to 1.35; P<0.001) compared with controls. Although DPP-4 inhibitors were associated with small but significantly lower estimated glomerular filtration rate (WMD, -1.11 mL/min/1.73 m²; 95% CI, -1.78 to -0.44; P=0.001), there was no difference in the risk of end-stage renal disease between two groups (RR, 0.93; 95% CI, 0.76 to 1.14; P=0.475).

CONCLUSION

DPP-4 inhibitors had beneficial renal effects mainly by reducing the risk of development or progression of albuminuria compared with placebo or other antidiabetic agents.

Recent advances in the pathogenesis of microvascular complications in diabetes

Millions of people worldwide have diabetes, which is diagnosed by fasting blood glucose levels exceeding 126 mg/dL. Regardless of the type of diabetes, prolonged hyperglycemia is damaging to several organs including eyes, kidneys, nerve, and/or heart. The damages are associated with a high risk of morbidity and mortality. Diabetes has been implicated in ischemia in the microvasculature of the target tissues, which occurs due to the insufficient perfusion of tissues. The resulting occlusion and pain affect the quality of life. Multiple therapeutic approaches have been proposed for a long time to overcome these vascular complications. Apart from systemically controlling high glucose levels, other therapeutic strategies are not well understood. In this review, we summarize the recent literature for biochemical/cellular targets that are being utilized for the treatment of diabetic microvascular diseases. These targets, which are closely associated with mitochondrial dysfunction, include the polyol and diacylglycerol-protein kinase C pathways, oxidative stress, non-enzymatic glycation and the formation of advanced glycation end products, and immune dysregulation/inflammation.

An Overview, Advantages and Therapeutic Potential of Nonpeptide Positive Allosteric Modulators of Glucagon-Like Peptide-1 Receptor

Due to uncomfortable injection regimens of peptidic agonists of glucagon-like peptide-1 receptor (GLP-1R), orally available nonpeptide positive allosteric modulators (PAMs) of GLP-1Rs are foreseen as the possible future mainstream therapy for type 2 diabetes. Herein, current GLP-1R PAMs are reviewed. Based on the effectiveness and in silico predicted physicochemical properties, pharmacokinetics, and toxicity, possible candidates for further development as oral drugs were selected. The suggestion is that GLP-1R PAMs might be used orally alone or in combination with dipeptidyl peptidase-4 (DPP-4) inhibitors, which could offer an optimal treatment option next to metformin monotherapy in type 2 diabetes mellitus, or in a wider spectrum of indications. Quercetin acts as a GLP-1R PAM and DPP-4 inhibitor, and therefore, might be considered as a pioneering agent with a dual mechanism of action, in terms of GLP-1R positive allosteric modulation and DPP-4 inhibition for potentiating GLP-1 dependent effects.

Linagliptin unmasks specific antioxidant pathways protective against albuminuria and kidney hypertrophy in a mouse model of diabetes

BACKGROUND

Dipeptidyl peptidase-4 (DPP-4) inhibitors may have protective effects on diabetic kidney disease (DKD) via specific antioxidant pathways. The DPP-4 inhibitor, linagliptin, was evaluated with the hypothesis that DPP-4 inhibition would ameliorate the development of DKD in a glucose-independent manner by altering specific antioxidant function.

METHODS

DBA/2J mice (a well-characterized model of DKD) and glucose 6-phosphate dehydrogenase (G6PD) deficient mice (a model of impaired antioxidant function) were evaluated. Diabetes was induced by streptozotocin. Mice were divided into: diabetic (DM), diabetic+linagliptin (DM+Lina), and non-diabetic control and treated for 12 weeks.

RESULTS

In DBA/2J mice, there was no difference in body weight and blood glucose between DM and DM+Lina groups. Linagliptin ameliorated albuminuria and kidney hypertrophy in DM DBA/2J mice and specifically increased the mRNA and protein levels for the antioxidants catalase and MnSOD. In G6PD deficient mice, however, increases in these mRNA levels did not occur and linagliptin renoprotection was not observed. Linagliptin also ameliorated histological trends toward mesangial expansion in wild-type mice but not in G6PD deficient mice.

CONCLUSIONS

Linagliptin renoprotection involved glucose-independent but antioxidant-enzyme-system-dependent increases in transcription (not just increased protein levels) of antioxidant proteins in wild-type mice. These studies demonstrate that an intact antioxidant system, in particular including transcription of catalase and MnSOD, is required for the renoprotective effects of linagliptin.

Dipeptidyl peptidase-4 inhibition and renoprotection: the role of antifibrotic effects

PURPOSE OF REVIEW

This article analyzes the potential beneficial effects of dipeptidyl peptidase (DPP)-4 inhibitors on renal diseases.

RECENT FINDINGS

The pathological significance of DPP-4, either dependent or independent on catalytic activities, on renal diseases has been reported in preclinical studies. With regard to this, we have shown that damaged endothelial cells are converted to a mesenchymal cell phenotype, which is associated with the induction of DPP-4 in endothelial cells. The endothelial mesenchymal transition may contribute to kidney fibrosis; indeed, the antifibrotic effects of DPP-4 inhibitors have been reported elsewhere. However, even though such potential benefits of DPP-4 inhibitors on renal diseases were shown in preclinical studies, clinical trials have not yet revealed significant benefits in renal hard outcomes of DPP-4 inhibitors.

SUMMARY

To completely understand the beneficial effects of DPP-4 inhibitors, both the following studies are required: first, preclinical studies that analyze deeper molecular mechanisms of DPP-4 inhibition, and, second, clinical studies that investigate whether such potential beneficial effects of DPP-4 inhibitors are relevant to the patients in the clinic.

The role of dipeptidylpeptidase-4 inhibitors in management of cardiovascular disease in diabetes; focus on linagliptin

Multiple population based analyses have demonstrated a high incidence of cardiovascular disease (CVD) and cardiovascular (CV) mortality in subjects with T2DM that reduces life expectancy by as much as 15 years. Importantly, the CV system is particularly sensitive to the metabolic and immune derangements present in obese pre-diabetic and diabetic individuals; consequently, CV dysfunction is often the initial CV derangement to occur and promotes the progression to end organ/tissue damage in T2DM. Specifically, diabetic CVD can manifest as microvascular complications, such as nephropathy, retinopathy, and neuropathy, as well as, macrovascular impairments, including ischemic heart disease, peripheral vascular disease, and cerebrovascular disease. Despite some progress in prevention and treatment of CVD, mainly via blood pressure and dyslipidemia control strategies, the impact of metabolic disease on CV outcomes is still a major challenge and persists in proportion to the epidemics of obesity and diabetes. There is abundant pre-clinical and clinical evidence implicating the DPP-4-incretin axis in CVD. In this regard, linagliptin is a unique DPP-4 inhibitor with both CV and renal safety profiles. Moreover, it exerts beneficial CV effects beyond glycemic control and beyond class effects. Linagliptin is protective for both macrovascular and microvascular complications of diabetes in preclinical models, as well as clinical models. Given the role of endothelial-immune cell interactions as one of the key events in the initiation and progression of CVD, linagliptin modulates these cell–cell interactions by affecting two important pathways involving stimulation of NO signaling and potent inhibition of a key immunoregulatory molecule.

Activity and selectivity cliffs for DPP-IV inhibitors: Lessons we can learn from SAR studies and their application to virtual screening

The inhibition of dipeptidyl peptidase-IV (DPP-IV) has emerged over the last decade as one of the most effective treatments for type 2 diabetes mellitus, and consequently (a) 11 DPP-IV inhibitors have been on the market since 2006 (three in 2015), and (b) 74 noncovalent complexes involving human DPP-IV and drug-like inhibitors are available at the Protein Data Bank (PDB). The present review aims to (a) explain the most important activity cliffs for DPP-IV noncovalent inhibition according to the binding site structure of DPP-IV, (b) explain the most important selectivity cliffs for DPP-IV noncovalent inhibition in comparison with other related enzymes (i.e., DPP8 and DPP9), and (c) use the information deriving from this activity/selectivity cliff analysis to suggest how virtual screening protocols might be improved to favor the early identification of potent and selective DPP-IV inhibitors in molecular databases (because they have not succeeded in identifying selective DPP-IV inhibitors with IC₅₀ ≤ 100 nM). All these goals are achieved with the help of available homology models for DPP8 and DPP9 and an analysis of the structure-activity studies used to develop the noncovalent inhibitors that form part of some of the complexes with human DPP-IV available at the PDB.

Role of the sodium-hydrogen exchanger in mediating the renal effects of drugs commonly used in the treatment of type 2 diabetes

Diabetes is characterized by increased activity of the sodium-hydrogen exchanger (NHE) in the glomerulus and renal tubules, which contributes importantly to the development of nephropathy. Despite the established role played by the exchanger in experimental studies, it has not been specifically targeted by those seeking to develop novel pharmacological treatments for diabetes. This review demonstrates that many existing drugs that are commonly prescribed to patients with diabetes act on the NHE1 and NHE3 isoforms in the kidney. This action may explain their effects on sodium excretion, albuminuria and the progressive decline of glomerular function in clinical trials; these responses cannot be readily explained by the influence of these drugs on blood glucose. Agents that may affect the kidney in diabetes by virtue of an action on NHE include: (1) insulin and insulin sensitizers; (2) incretin-based agents; (3) sodium-glucose cotransporter 2 inhibitors; (4) antagonists of the renin-angiotensin system (angiotensin converting-enzyme inhibitors, angiotensin receptor blockers and angiotensin receptor neprilysin inhibitors); and (5) inhibitors of aldosterone action and cholesterol synthesis (spironolactone, amiloride and statins). The renal effects of each of these drug classes in patients with type 2 diabetes may be related to a single shared biological mechanism.

The role of renal dipeptidyl peptidase-4 in kidney disease: renal effects of dipeptidyl peptidase-4 inhibitors with a focus on linagliptin

Emerging evidence suggests that dipeptidyl peptidase-4 (DPP-4) inhibitors used to treat type 2 diabetes may have nephroprotective effects beyond the reduced renal risk conferred by glycemic control. DPP-4 is a ubiquitous protein with exopeptidase activity that exists in cell membrane-bound and soluble forms. The kidneys contain the highest levels of DPP-4, which is increased in diabetic nephropathy. DPP-4 inhibitors are a chemically heterogeneous class of drugs with important pharmacological differences. Of the globally marketed DPP-4 inhibitors, linagliptin is of particular interest for diabetic nephropathy as it is the only compound that is not predominantly excreted in the urine. Linagliptin is also the most potent DPP-4 inhibitor, has the highest affinity for this protein, and has the largest volume of distribution; these properties allow linagliptin to penetrate kidney tissue and tightly bind resident DPP-4. In animal models of kidney disease, linagliptin elicited multiple renoprotective effects, including reducing albuminuria, glomerulosclerosis, and tubulointerstitial fibrosis, independent of changes in glucagon-like peptide-1 (GLP-1) and glucose levels. At the molecular level, linagliptin prevented the pro-fibrotic endothelial-to-mesenchymal transition by disrupting the interaction between membrane-bound DPP-4 and integrin β1 that enhances signaling by transforming growth factor-β1 and vascular endothelial growth factor receptor-1. Linagliptin also increased stromal cell derived factor-1 levels, ameliorated endothelial dysfunction, and displayed unique antioxidant effects. Although the nephroprotective effects of linagliptin are yet to be translated to the clinical setting, the ongoing Cardiovascular and Renal Microvascular Outcome Study with Linagliptin in Patients with Type 2 Diabetes Mellitus (CARMELINA®) study will definitively assess the renal effects of this DPP-4 inhibitor. CARMELINA® is the only clinical trial of a DPP-4 inhibitor powered to evaluate kidney outcomes.

Renal outcomes with dipeptidyl peptidase-4 inhibitors

Dipeptidyl peptidase-4 inhibitors (DPP-4is) are increasingly being used in the management of type 2 diabetes (T2D). The present review summarizes the current knowledge of the effects of DPP-4is on renal outcomes by analyzing the experimental preclinical data, the effects of DPP-4is on urinary albumin-creatinine ratios (UACRs) and estimated glomerular filtration rates (eGFRs) from observational studies and clinical trials, and renal events (including kidney failure requiring renal replacement therapy) in recent large prospective cardiovascular outcome trials. Renal protection has been demonstrated in various animal models that have implicated different underlying mechanisms independent of glucose control, whereas prevention of new onset microalbuminuria and/or progression of albuminuria has been reported in some clinical studies, but with no significant effects on eGFR in most of them. The long-term clinical effects of DPP-4is on renal outcomes and the development of end-stage renal disease remain largely unknown and, thus, demand further investigations in prospective trials and long-term observational studies. In conclusion, despite promising results in animal models, data on surrogate biological markers of renal function and clinical renal outcomes remain rather scanty in patients with T2D, and mostly demonstrate the safety rather than true efficacy of DPP-4is.

Combined treatment with dipeptidyl peptidase-4 inhibitor (sitagliptin) and angiotensin-II type 1 receptor blocker (losartan) suppresses progression in a non-diabetic rat model of steatohepatitis

AIM

Dipeptidyl peptidase-4 (DPP4) inhibitors (DPP4-I) are oral glucose-lowering drugs for type 2 diabetes mellitus. Previously, we reported that DPP4-I (sitagliptin) exerted suppressive effects on experimental liver fibrosis in rats. Blockade of the renin-angiotensin system by angiotensin-II type 1 receptor blocker (losartan), commonly used in the management of hypertension, has been shown to significantly alleviate hepatic fibrogenesis and carcinogenesis. We aimed to elucidate the effects and possible mechanisms of a sitagliptin + losartan combination on the progression of non-diabetic non-alcoholic steatohepatitis (NASH) in a rat model.

METHODS

To induce NASH, Fischer 344 rats were fed a choline-deficient L-amino acid-defined diet for 12 weeks. We elucidated the chemopreventive effects of sitagliptin + losartan, especially in conjunction with hepatic stellate cell (HSC) activation, angiogenesis, and oxidative stress, all known to play important roles in the progression of NASH.

RESULTS

Sitagliptin + losartan suppressed choline-deficient L-amino acid-defined diet-induced hepatic fibrogenesis and carcinogenesis. The combination treatment exerted a greater inhibitory effect than monotherapy. These inhibitory effects occurred almost concurrently with the suppression of HSC activation, neovascularization, and oxidative stress. In vitro studies showed that sitagliptin + losartan inhibited angiotensin II-induced proliferation and expression of transforming growth factor-β1 and α1 (I)-procollagen mRNA of activated HSC and in vitro angiogenesis, in parallel with the suppression observed in in vivo studies.

CONCLUSIONS

The widely and safely used sitagliptin + losartan combination treatment in clinical practice could be an effective strategy against NASH.

GLP-1 and the kidney: from physiology to pharmacology and outcomes in diabetes

The gastrointestinal tract - the largest endocrine network in human physiology - orchestrates signals from the external environment to maintain neural and hormonal control of homeostasis. Advances in understanding entero-endocrine cell biology in health and disease have important translational relevance. The gut-derived incretin hormone glucagon-like peptide 1 (GLP-1) is secreted upon meal ingestion and controls glucose metabolism by modulating pancreatic islet cell function, food intake and gastrointestinal motility, amongst other effects. The observation that the insulinotropic actions of GLP-1 are reduced in type 2 diabetes mellitus (T2DM) led to the development of incretin-based therapies - GLP-1 receptor agonists and dipeptidyl peptidase 4 (DPP-4) inhibitors - for the treatment of hyperglycaemia in these patients. Considerable interest exists in identifying effects of these drugs beyond glucose-lowering, possibly resulting in improved macrovascular and microvascular outcomes, including in diabetic kidney disease. As GLP-1 has been implicated as a mediator in the putative gut-renal axis (a rapid-acting feed-forward loop that regulates postprandial fluid and electrolyte homeostasis), direct actions on the kidney have been proposed. Here, we review the role of GLP-1 and the actions of associated therapies on glucose metabolism, the gut-renal axis, classical renal risk factors, and renal end points in randomized controlled trials of GLP-1 receptor agonists and DPP-4 inhibitors in patients with T2DM.

Relationship Between Duration of Type 2 Diabetes and Effectiveness of DPP-4 Inhibitor Versus Sulfonylurea as Add-on Therapy: A Post Hoc Analysis

INTRODUCTION

To assess the impact of duration of type 2 diabetes on glucose-lowering effectiveness of the dipeptidyl peptidase-4 (DPP-4) inhibitor vildagliptin versus sulfonylureas (SUs) in a real-life setting.

METHODS

Data were extracted from the large 1-year, observational EDGE study (N = 45,868). Patients receiving either DPP-4 inhibitor or any SU as add-on to monotherapy were selected (N = 36,164). Impact of the disease duration on change in glycated hemoglobin (HbA1c) levels was evaluated by using a linear multiple regression model. Descriptive statistics assessed the proportion of patients achieving the composite endpoint (HbA1c <7.0%; 53.0 mmol/mol without hypoglycemia or weight gain), stratified by diabetes duration.

RESULTS

At baseline, the overall mean (±SD) type 2 diabetes duration was 5.4 ± 5.24 years, and HbA1c was 8.2 ± 1.33% (66.0 ± 14.5 mmol/mol). HbA1c lowering was directly proportional to the baseline HbA1c (-0.69 per unit; 95% CI -0.696, -0.681; p < 0.0001) and inversely proportional to the disease duration (0.01 per year; 95% CI 0.01, 0.013). There was an increased loss of β-cell function (less pronounced HbA1c drop with increasing disease duration) in patients treated with SU-based regimens (0.025; 95% CI 0.022, 0.027) compared with vildagliptin-based regimens (0.005; 95% CI 0.003, 0.007), with the mean adjusted difference being 0.10 (95% CI -0.122, -0.092; p < 0.0001). Consistently, a higher proportion of patients achieved the composite endpoint with vildagliptin over the diabetes duration (less than 2 to more than 10 years).

CONCLUSION

Vildagliptin demonstrated less dependency on the duration of type 2 diabetes, whereas the effectiveness of SUs diminished faster with increasing duration of the disease in a real-life setting.

FUNDING

Novartis Pharma AG.

Role of soluble and membrane-bound dipeptidyl peptidase-4 in diabetic nephropathy

Diabetic nephropathy is one of the most frequent, devastating and costly complications of diabetes. The available therapeutic approaches are limited. Dipeptidyl peptidase type 4 (DPP-4) inhibitors represent a new class of glucose-lowering drugs that might also have reno-protective properties. DPP-4 exists in two forms: a plasma membrane-bound form and a soluble form, and can exert many biological actions mainly through its peptidase activity and interaction with extracellular matrix components. The kidneys have the highest DPP-4 expression level in mammalians. DPP-4 expression and urinary activity are up-regulated in diabetic nephropathy, highlighting its role as a potential target to manage diabetic nephropathy. Preclinical animal studies and some clinical data suggest that DPP-4 inhibitors decrease the progression of diabetic nephropathy in a blood pressure- and glucose-independent manner. Many studies reported that these reno-protective effects could be due to increased half-life of DPP-4 substrates such as glucagon-like peptide-1 (GLP-1) and stromal derived factor-1 alpha (SDF-1a). However, the underlying mechanisms are far from being completely understood and clearly need further investigations.

Macro- and microvascular endothelial dysfunction in diabetes

Endothelial cells, as well as their major products nitric oxide (NO) and prostacyclin, play a key role in the regulation of vascular homeostasis. Diabetes mellitus is an important risk factor for cardiovascular disease. Diabetes-induced endothelial dysfunction is a critical and initiating factor in the genesis of diabetic vascular complications. The present review focuses on both large blood vessels and the microvasculature. The endothelial dysfunction in diabetic macrovascular complications is characterized by reduced NO bioavailability, poorly compensated for by increased production of prostacyclin and/or endothelium-dependent hyperpolarizations, and increased production or action of endothelium-derived vasoconstrictors. The endothelial dysfunction of microvascular complications is primarily characterized by decreased release of NO, enhanced oxidative stress, increased production of inflammatory factors, abnormal angiogenesis, and impaired endothelial repair. In addition, non-coding RNAs (microRNAs) have emerged as participating in numerous cellular processes. Thus, this reviews pays special attention to microRNAs and their modulatory role in diabetes-induced vascular dysfunction. Some therapeutic strategies for preventing and restoring diabetic endothelial dysfunction are also highlighted.