Renoprotective Effects of the Dipeptidyl Peptidase-4 Inhibitor Sitagliptin: A Review in Type 2 Diabetes

Sitagliptin alleviates renal steatosis and endoplasmic reticulum stress in high fat diet-induced obese rats by targeting SREBP-1/CD36 signaling pathway

High fat diet (HFD) consumption can cause dysregulation of glucose and lipid metabolism, coupled with increased ectopic lipid deposition in renal tissue leading to steatosis and dysfunction. Sitagliptin is a dipeptidyl peptidase-4 (DPP-4) inhibitor clinically used for type II diabetes therapy; however its effect on renal steatosis in obese state is still uncertain. Herein, obesity was induced by feeding male Wistar rats HFD for 18 weeks, thereafter received either drug vehicle, or sitagliptin (10 mg/kg, PO) along with HFD for further 6 weeks and compared with age-matched rats receiving normal chow diet (NCD). After 24 weeks, serum and kidneys were collected for histological and biochemical assessments. Compared to NCD-fed group, HFD-fed rats displayed marked weight gain, increased fat mass, insulin resistance, dyslipidemia, impaired kidney functions and renal histological alterations. Sitagliptin effectively ameliorated obesity and related metabolic perturbations and improved kidney architecture and function. There were increased levels of triglycerides and cluster of differentiation 36 (CD36) in kidneys of obese rats, that were lowered by sitagliptin therapy. Sitagliptin significantly repressed the expression of lipogenesis genes, while up-regulated genes involved in mitochondrial biogenesis and fatty acid oxidation in kidneys of HFD-fed rats. Sitagliptin was found to induce down-regulation of endoplasmic reticulum (ER) stress and apoptotic markers in kidneys of obese rats. These findings together may emphasize a novel concept that sitagliptin can be an effective therapeutic approach for halting obesity-related renal steatosis and CKD.

A cross talk study on sitagliptin mediated reclamation on TGF β signalling, DPP 4, miR-29a and miR-24 expression in PCOS rats fed with high fat-high fructose diet

Polycystic Ovary Syndrome (PCOS) is a multifactorial reproductive, endocrine and metabolic disturbance which is very commonly observed in females of reproductive age group. The disease is still incurable however the use of synthetic drugs in combination with lifestyle is recommended. Accordingly, the present study was conducted to investigate the possible beneficial effects of sitagliptin on PCOS induced rats on control diet (CD)/high fat- high fructose diet (HFFD). PCOS was induced by giving testosterone propionate (TP) for 28 days to both the CD/HFFD rats and treated with STG i.p. for last 15 days. At the end of the experiment lipid profile, inflammatory markers, expression of NF-κB-p65, miR-24 and miR-29a, fibrotic and apoptotic proteins from ovary tissue were examined. Moreover, lipid accumulation and fibrosis of ovary tissue was further confirmed using Sudan III and Masson's trichrome stain. STG treated rats exerted a significant decrease in levels of cholesterol, TG, LDL-C, VLDL-C, IL-6 and TNF-α and increased HDL-C level, miR-24 and miR-29a expression. STG treated groups expressed significantly decreased expression of NF-κB-p65, TGF-β1, p-Smad 2 and p-Smad 3 followed by no significant changes in the expression of BAX, caspase-9, caspase-3 and Bcl-2 in all the PCOS induced groups. Among all the CD/ HFFD fed groups, rats on HFFD showed more devastating effect which suggests that diet plays a major role in genesis of PCOS. In conclusion, current results reflect the potential impact of STG against dyslipidaemia, inflammation and fibrosis in PCOS rats via regulating dyslipidaemia and fibrosis via DPP 4 mediated miR-29a expression.

Cyclosporine-induced kidney damage was halted by sitagliptin and hesperidin via increasing Nrf2 and suppressing TNF-α, NF-κB, and Bax

Cyclosporine A (CsA) is employed for organ transplantation and autoimmune disorders. Nephrotoxicity is a serious side effect that hampers the therapeutic use of CsA. Hesperidin and sitagliptin were investigated for their antioxidant, anti-inflammatory, and tissue-protective properties. We aimed to investigate and compare the possible nephroprotective effects of hesperidin and sitagliptin. Male Wistar rats were utilized for induction of CsA nephrotoxicity (20 mg/kg/day, intraperitoneally for 7 days). Animals were treated with sitagliptin (10 mg/kg/day, orally for 14 days) or hesperidin (200 mg/kg/day, orally for 14 days). Blood urea, serum creatinine, albumin, cystatin-C (CYS-C), myeloperoxidase (MPO), and glucose were measured. The renal malondialdehyde (MDA), glutathione (GSH), catalase, and SOD were estimated. Renal TNF-α protein expression was evaluated. Histopathological examination and immunostaining study of Bax, Nrf-2, and NF-κB were performed. Sitagliptin or hesperidin attenuated CsA-mediated elevations of blood urea, serum creatinine, CYS-C, glucose, renal MDA, and MPO, and preserved the serum albumin, renal catalase, SOD, and GSH. They reduced the expressions of TNF-α, Bax, NF-κB, and pathological kidney damage. Nrf2 expression in the kidney was raised. Hesperidin or sitagliptin could protect the kidney against CsA through the mitigation of oxidative stress, apoptosis, and inflammation. Sitagliptin proved to be more beneficial than hesperidin.

Renoprotective Potency of Sitagliptin versus Pioglitazone in Type 2 Diabetic Patients: Impact on LncMIAT

Background: Diabetes mellitus (DM) represents one of the most important reasons for chronic kidney diseases due to the high level of blood glucose that destructs blood vessels. Objective: The present study focused on investigating the protective impact of sitagliptin on kidney complication in type 2 diabetes mellitus (T2DM) patients in comparison to pioglitazone to examine which has the superior effect against the nephritic complication of DM. Methods: Eighty adult subjects were classified into four groups: control group, pioglitazone-treated T2DM patients (P group), sitagliptin-treated T2DM patients for less than one year (SL group), and sitagliptin-treated T2DM patients for more than one year (SM group). Blood samples were withdrawn from all subjects for analysis of neutrophil gelatinase-associated lipocalin (NGAL), vanin-1, kidney injury molecule-1 (KIM-1), glyoxalase-1 (Glo-1), methylglyoxal (MG), cystatin-C, and interleukin-18 (IL-18) using competitive ELISA kits. Also, long noncoding myocardial infarction associated transcript (lncMIAT) was measured in whole blood using qRT-PCR. Results: The present study revealed that the lncMIAT expression level was significantly higher in the P group as compared to the SL group, SM group, or healthy control group. Additionally, serum NGAL, vanin-1, KIM-1, Glo-1, MG, and cystatin-C were significantly higher in the P group and SL group as compared to the SM group and healthy control group. Conclusion: Sitagliptin protected the kidney through downregulation of lncMIAT besides amelioration of kidney injury marker levels, which was more preferable than in pioglitazone therapy.

DLBS3233 enhances nephrin and podocin expression also reduces oxidative stress marker and insulin receptor serine diabetic rats' podocytes

Numerous oxidative stresses are detected in patients with diabetic kidney disease, resulting in insulin resistance that damages the pancreas and kidney. Renal podocytes insensitive to insulin lead to decreased nephrin and podocin and increased insulin receptor serine. The authors did an experiment on diabetic rats to examine the effect of DLBS3233 on repairing insulin resistance.

MATERIALS AND METHODS

Thirty adult male Wistar rats were randomly divided into six groups (n=5 per group): group of nondiabetic rats as a negative control (group 1); untreated diabetic rats (group 2); diabetic rats treated with DLBS3233 4.5 mg/kg BB (group 3); 9 mg/kg BB (group 4); 18 mg/kg BB (group 5); and diabetic rats treated with pioglitazone (group 6). The authors checked Homeostatic Model Assessment for Insulin Resistance to corroborate insulin resistance prior to DLBS3233 administration in diabetic rats. Immunohistochemistry was performed to examine the expression of renal antimalondialdehyde (MDA) antibodies, nephrin, podocin, and insulin receptor serine. The data were analyzed using analysis of variance and the t-test.

RESULT

In the DBLS3233 group, immunohistochemistry showed enhanced expression of renal nephrin and podocin, as well as diminished expression of anti-MDA antibody, along with decreased insulin receptor serine. From statistical analysis, anti-MDA antibodies and insulin receptor serine showed lower expression, whereas the expression of nephrin and podocin were enhanced compared to untreated groups (P<0.05).

CONCLUSION

DLBS3233 reduces oxidative stress by decreasing MDA and improves insulin resistance by increasing the expression of renal nephrin and podocin as well as decreasing insulin receptor serine.

Sitagliptin ameliorates diabetic nephropathy by upregulating renal nephrin and podocin expression through modulation of adipokines levels

Diabetic nephropathy is the leading cause of end-stage renal failure, but the effectiveness of currently available strategies for preventing diabetic nephropathy remains unsatisfactory. This study was designed to evaluate the changes in adipokines levels caused by dipeptidyl peptidase-4 inhibitor sitagliptin therapy as one of the possible mechanisms of sitagliptin's amelioration of diabetic nephropathy. Twenty-four male Wistar rats weighing 180-200 g were taken and divided into three groups, that is, control, diseased, and treatment group. High-fat diet and streptozotocin-induced Type 2 diabetic rats were divided into diseased and treatment groups. The treatment group was given sitagliptin orally, 10 mg/kg per day for 6 weeks. Serum glucose, serum insulin, serum blood urea nitrogen, serum creatinine, and 24-h urinary protein levels were measured in serum and urine samples. mRNA expression levels of podocin, nephrin, and adipokines in renal tissues were determined. Results showed that sitagliptin treatment effectively reduced serum glucose, serum creatinine, serum blood urea nitrogen, and 24-h proteinuria, along with partial prevention of insulinopenia, in the treatment group as compared to the diseased group. The renal mRNA expression levels of podocin, nephrin, and adiponectin were significantly upregulated, while those of leptin and resistin were significantly downregulated in the diabetic rats receiving sitagliptin therapy compared to the non-treated diabetic rats. Based on these findings, it is suggested that sitagliptin, via mediating the modulation of adipokines levels, upregulates renal nephrin and podocin expression, which leads to the amelioration of diabetic nephropathy.

Real-world comparison of mono and dual combination therapies of metformin, sulfonylurea, and dipeptidyl peptidase-4 inhibitors using a common data model: A retrospective observational study

The comparative effectiveness of oral hypoglycemic agents on glycemic control and chronic complications in clinical practice is unknown in Korea. This study aimed to compare glycemic control and the incidence of hypoglycemia and chronic complications among adult patients with type 2 diabetes prescribed metformin, dipeptidyl peptidase-4 inhibitors (DPP4I), and sulfonylurea (SU) as monotherapy or dual combination therapy.We retrospectively analyzed propensity-matched cohort data from 3 national university hospitals in Korea. All electronic health records were transformed into a unified Observational Medical Outcomes Partnership Common Data Model and analyzed using ATLAS, an open-source analytical tool, and R software. Glycemic control was assessed as the first observation of a reduction in glycosylated hemoglobin (HbA1c) level below 7% after prescription of the drug. Differences in the incidence of chronic complications were compared based on the first observation of each complication. Glycemic control and chronic complications were evaluated in patients who maintained the same prescription for at least 3 and 12 months, respectively.Patients who received metformin had lower hazard of reaching HbA1c levels below 7% as compared with those who received SU, and had higher hazard compared with those who received DPP4I (hazard ratio [HR], 0.86; 95% confidence interval [CI], 0.75-0.98; and HR, 1.68; 95% CI, 1.42-1.99, respectively). The incidence of hypoglycemia was significantly higher in the SU group than in the metformin and DPP4I groups (metformin vs SU; HR, 0.30; 95% CI, 0.21-0.43; SU vs DPP4I; HR, 4.42; 95% CI, 2.35-8.31). Metformin + DPP4I had similar hazard of reaching HbA1c levels below 7% compared with metformin + SU (HR, 1.19; 95% CI, 0.99-1.43) and the incidence of hypoglycemia was significantly lower in the metformin + DPP4I group (HR 0.13; 95% CI 0.05-0.30). There was no significant difference in the analysis of the occurrence of chronic complications.SU followed by metformin was effective, and both drugs showed an increased hazard of reaching HbA1c levels below 7% compared with DPP4I. Metformin + DPP4I is comparatively effective for HbA1c level reduction below 7% compared with metformin + SU. Hypoglycemia was high in the SU-containing therapy.

Sitagliptin protects renal glomerular endothelial cells against high glucose-induced dysfunction and injury

Sitagliptin is a well-established anti-diabetic drug that also exerts protective effects on diabetic complications. Previous work reveals that sitagliptin has a protective effect on diabetic nephropathy (DN). Vascular impairment frequently occurs in diabetic renal complications. Here, we evaluated the protective function of sitagliptin in human renal glomerular endothelial cells (HrGECs) under high glucose (HG) conditions. Expressions of the pro-inflammatory cytokines interleukin-1β (IL-1β) and interleukin-8 (IL-8) were assessed using real-time PCR and ELISA. Endothelial cells permeability was assayed using the fluorescein isothiocyanate dextran (FITC-dextran) and trans-endothelial electrical resistance (TEER) assay. The results show that sitagliptin mitigated HG-induced oxidative stress in HrGECs with decreased levels of mitochondrial reactive oxygen species (ROS), Malondialdehyde (MDA), and 8-hydroxydeoxyguanosine (8-OHdG). Sitagliptin inhibited HG-induced production of pro-inflammatory cytokines interleukin-1β (IL-1β) and interleukin-8 (IL-8) in HrGECs. It also ameliorated HG-induced aggravation of HrGECs permeability and reduction of the tight junction component claudin-5. Moreover, kruppel Like Factor 6 (KLF6) mediated the protective effects of sitagliptin on endothelial monolayer permeability against HG. Collectively, sitagliptin reversed the HG-induced oxidative stress, inflammation, and increased permeability in HrGECs via regulating KLF6. This study suggests that sitagliptin might be implicated as an effective strategy for preventing diabetic renal injuries in the future.

Simultaneous determination of rivaroxaban and sitagliptin in rat plasma by LC–MS/MS and its application to pharmacokinetic drug-drug interaction study

A sensitive and accurate LC-MS/MS method was developed and validated for the simultaneous quantification of rivaroxaban (RIV) and sitagliptin (SIT) in rat plasma using apixaban as internal standard (IS). An Agilent Eclipse plus C18 column (2.1 × 100 mm, 3.5 µm, Agilent) was used for chromatographic separation with isocratic elution. Multiple reaction monitoring (MRM) using positive-ion ESI mode to monitor ion transitions of m/z 436.8→144.9 for RIV, m/z 407.7→173.8 for SIT, m/z 459.8→442.8 for IS. The procedure of method validation included selectivity, linearity, precision, accuracy, matrix effect, extraction recovery and stability were conducted according to the guidelines of EMA and FDA. The results indicated that no obvious drug-drug interactions occurred might be owing to their differences in metabolic pathways.

Sitagliptin's renoprotective effect in a diabetic nephropathy model in rats: The potential role of PI3K/AKT pathway

Management of diabetic nephropathy (DN) is far from satisfactory. There is a rising role of the involvement of phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) pathway in the pathogenesis of DN. This study aimed at investigating the renoprotective effects of PI3K/AKT pathway via sitagliptin in a rat model of DN. Thirty-two male Wistar rats were divided into four groups (eight rats each): (I) control, (II) sitagliptin, (III) DN, and (IV) DN + sitagliptin. Fasting blood glucose (FBG), kidney index, and kidney function tests in both blood and urine were measured. The levels of superoxide dismutase (SOD), tumor necrosis factor-alpha (TNF-α), and transforming growth factor-beta (TGF-β) and gene expressions of PI3K, pPI3K, AKT, and pAKT in renal tissue were detected. Renal histopathological and immunohistochemical studies were evaluated. DN + sitagliptin group showed significant decrease in FBG and kidney index, improvement in kidney function tests, and a decrease in levels of TNF-α and TGF-β in renal tissues compared with DN group. This was associated with significant increase in SOD and gene expressions of PI3K and AKT and their phosphorylated active forms in renal tissue in DN + sitagliptin group compared with DN group. Moreover, DN + sitagliptin group showed apparent decrease in amount of collagen fibers and expression of alpha-smooth muscle actin (α-SMA) compared with DN group. This work shows that sitagliptin improved renal functions and histopathological changes, impeded inflammation, and oxidative stress and upregulated PI3K/AKT pathway which highlights its renoprotective effects in a rat model of DN.

Urinary exosomal microRNA profiling in type 2 diabetes patients taking dipeptidyl peptidase-4 inhibitor compared with sulfonylurea

Background

Dipeptidyl peptidase-4 (DPP-4) inhibitor has been reported to have kidney-protective benefits. To elucidate how antidiabetic agents prevent diabetic kidney disease progression, it is important to investigate their effect on the kidney environment in type 2 diabetes mellitus (DM) patients. Herein, we investigated the expression pattern of urinary exosome-derived microRNA (miRNA) in patients taking a combination of DPP-4 inhibitor and metformin (DPP-4 inhibitor group) and compared them with patients taking a combination of sulfonylurea and metformin (sulfonylurea group).

Methods

This was a prospective study involving 57 patients with type 2 DM (DPP-4 inhibitor group, n = 34; sulfonylurea group, n = 23) and healthy volunteers (n = 7). We measured urinary exosomal miRNA using the NanoString nCounter miRNA array (NanoString Technologies) across the three groups (n = 4 per each group) and validated findings using real-time polymerase chain reaction.

Results

Twenty-one differentially expressed candidate miRNAs were identified, and six (let-7c-5p, miR-23a-3p, miR-26a-3p, miR-30d, miR-205, and miR-200a) were selected for validation. Validation showed no significant difference in miRNA expression between the DPP-4 inhibitor and sulfonylurea groups. Only miR-23a-3p was significantly overexpressed in the diabetes group compared with the control group (DPP-4 inhibitor vs. control, p = 0.01; sulfonylurea vs. control, p = 0.007). This trend was consistent even after adjusting for age, sex, and body mass index.

Conclusion

There was no significant difference in urine exosome miRNA expression between diabetic participants taking DPP-4 inhibitor and those taking sulfonylurea. The miR-23a levels were higher in diabetic participants than in nondiabetic controls.

Novel stability-indicating RP-UPLC method for simultaneous estimation of sitagliptin and ertugliflozin in bulk and pharmaceutical formulations

Background

The present investigation was proposed to develop a simple, sensitive, rapid, accurate, precise stability-indicating RP-UPLC method for simultaneous estimation of sitagliptin and ertugliflozin. Chromatographic separation was performed with Waters Hibar C8 [100×2.1mm, 2μ] column and mobile phase acetonitrile: water (pH 3.5) [50:50%, v/v], pumped at a flow rate 0.2ml/min. The separated analytes were detected with a UV detector at a wavelength of 218nm.

Results

The separation of sitagliptin and ertugliflozin was done at a retention time of 0.859min and 1.570min, respectively. The present method was validated according to the ICH guidelines Q2 R1, and stability-indicating studies were carried out as per ICH guidelines Q1A R2. Intra-day and inter-day precision were found to be within acceptable limits. The linearity of the proposed method was in the concentration range of 25–125μg/ml and 3.75–22.5μg/ml for sitagliptin and ertugliflozin, respectively. Limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.5μg/ml and 1.53μg/ml for sitagliptin and 0.13μg/ml and 0.38μg/ml for ertugliflozin, respectively. The recovery of the method was found in between 99.7% and 100.7%.

Conclusion

The proposed method was able to distinguish the analytes from by-products. Hence, the method was successfully implied for stability-indicating studies and for routine examination of sitagliptin and ertugliflozin in pharmaceutical formulation.

Towards Better Drug Repositioning: Targeted Immunoinflammatory Therapy for Diabetic Nephropathy

Diabetic nephropathy (DN) is one of the most common and important microvascular complications of diabetes mellitus (DM). The main clinical features of DN are proteinuria and a progressive decline in renal function, which are associated with structural and functional changes in the kidney. The pathogenesis of DN is multifactorial, including genetic, metabolic, and haemodynamic factors, which can trigger a sequence of events. Controlling metabolic risks such as hyperglycaemia, hypertension, and dyslipidaemia is not enough to slow the progression of DN. Recent studies emphasized immunoinflammation as a critical pathogenic factor in the progression of DN. Therefore, targeting inflammation is considered a potential and novel treatment strategy for DN. In this review, we will briefly introduce the inflammatory process of DN and discuss the anti-inflammatory effects of antidiabetic drugs when treating DN.

Cost-Effectiveness of Dipeptidylpeptidase-4 Inhibitors Added to Metformin in Patients With Type 2 Diabetes in China

PURPOSE

Dipeptidylpeptidase-4 (DPP-4) inhibitors, including linagliptin, alogliptin, saxagliptin, sitagliptin, and vildagliptin, are used for the treatment of type 2 diabetes mellitus (T2DM) patients in China. This study assessed the economic outcomes of different DPP-4 inhibitors in patients with T2DM inadequately controlled with metformin in the Chinese context.

MATERIALS AND METHODS

In this study, the validated Chinese Outcomes Model for T2DM (COMT) was conducted to project economic outcomes from the perspective of Chinese healthcare service providers. Efficacy and safety, medical expenditure, and utility data were derived from the literature, which were assigned to model variables. The primary outputs of the model included the lifetime costs, quality-adjusted life years (QALYs), and incremental cost-effectiveness ratio (ICER). One-way and probability sensitivity analysis was conducted to assess the potential uncertainties of parameters.

RESULTS

Of the five competing strategies, alogliptin 25 mg strategy yielded the most significant health outcome, which associated with improvements in discounted QALY of 0.007, 0.014, 0.011, and 0.022 versus linagliptin 5 mg, saxagliptin 5 mg, sitagliptin 100 mg and vildagliptin50 mg, respectively. The sitagliptin 100 mg strategy was the cheapest option. The ICER of alogliptin 25 mg against sitagliptin 100 mg strategy was $6,952 per additional QALY gained, and the rest of the strategies were dominated or extended dominated. The most influential parameters were the cost of DPP-4 inhibitors and their treatment efficacy.

CONCLUSIONS

These results suggested that alogliptin was a preferred treatment option compared with other DPP-4 inhibitors for Chinese patients whose T2DM are inadequately controlled on metformin monotherapy.

Alogliptin attenuates cyclophosphamide-induced nephrotoxicity: a novel therapeutic approach through modulating MAP3K/JNK/SMAD3 signaling cascade

Cyclophosphamide (CP) is widely used as a chemotherapy against various types of cancers. However, CP is accompanied with multiple organ toxicity due to production of reactive oxygen species (ROS), induction of inflammation and consequently apoptosis. Alogliptin (Alo) is a dipeptidyl peptidase 4 (DPP-IV) inhibitor, which is booming as an antidiabetic agent. Interestingly, gliptins are currently studied for their counter-regulatory effects against oxidative stress and inflammation via multiple pathways, among which is the mitogen-activated protein kinase (MAPK)/c-Jun N-terminal kinase (JNK) pathway. This cascade can reduce inflammation via mitigating the activity of mothers against decapentaplegic homolog 3 (SMAD3) and c-Jun. However, Alo effect against CP-induced kidney injury has not been previously elucidated. This tempted us to investigate the possible beneficial effect of Alo against CP-induced kidney injury via modulating the MAP3K/JNK/SMAD3 signaling cascade. Thirty-two male Wistar rats were randomly allocated into four groups. CP-treated group received a single dose of CP (200 mg/kg; i.p.). Alo-treated group received Alo (20 mg/kg/day; p.o.) for 7 days with single CP injection on day 2. Marked decrease in renal injury was observed upon Alo treatment, as evidenced through declined serum kidney function markers, oxidative stress and apoptosis markers, MAP3K expression, phospho (p)-SMAD3, p-JNK, and p-c-Jun levels. These cellular effects were reflected in reduced transforming growth factor beta (TGF-β) and tumor necrosis factor alpha (TNF-α) fibrotic and inflammatory mediators, coinciding with improved histopathological portrait. In conclusion, the current study provides novel application of Alo as a therapeutic modality against CP-induced nephrotoxicity.

Association of Glycemic Indices (Hyperglycemia, Glucose Variability, and Hypoglycemia) with Oxidative Stress and Diabetic Complications

Oxidative stress (OS) is defined as a disturbance in the prooxidant-antioxidant balance of the cell, in favor of the former, which results in the antioxidant capacity of the cell to be overpowered. Excess reactive oxygen species (ROS) production is very harmful to cell constituents, especially proteins, lipids, and DNA, thus causing damage to the cell. Oxidative stress has been associated with a variety of pathologic conditions, including diabetes mellitus (DM), cancer, atherosclerosis, neurodegenerative diseases, rheumatoid arthritis, ischemia/reperfusion injury, obstructive sleep apnea, and accelerated aging. Regarding DM specifically, previous experimental and clinical studies have pointed to the fact that oxidative stress probably plays a major role in the pathogenesis and development of diabetic complications. It is postulated that hyperglycemia induces free radicals and impairs endogenous antioxidant defense systems through several different mechanisms. In particular, hyperglycemia promotes the creation of advanced glycation end-products (AGEs), the activation of protein kinase C (PKC), and the hyperactivity of hexosamine and sorbitol pathways, leading to the development of insulin resistance, impaired insulin secretion, and endothelial dysfunction, by inducing excessive ROS production and OS. Furthermore, glucose variability has been associated with OS as well, and recent evidence suggests that also hypoglycemia may be playing an important role in favoring diabetic vascular complications through OS, inflammation, prothrombotic events, and endothelial dysfunction. The association of these diabetic parameters (i.e., hyperglycemia, glucose variability, and hypoglycemia) with oxidative stress will be reviewed here.

The Biological Impacts of Sitagliptin on the Pancreas of a Rat Model of Type 2 Diabetes Mellitus: Drug Interactions with Metformin

Sitagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor, is a beneficial class of antidiabetic drugs. However, a major debate about the risk of developing pancreatitis is still existing. The aim of the work was to study the histological and immunohistochemical effects of sitagliptin on both endocrine and exocrine pancreases in a rat model of type 2 diabetes mellitus and to correlate these effects with the biochemical findings. Moreover, a possible synergistic effect of sitagliptin, in combination with metformin, was also evaluated. Fifty adult male rats were used and assigned into five equal groups. Group 1 served as control. Group 2 comprised of untreated diabetic rats. Group 3 diabetic rats received sitagliptin. Group 4 diabetic rats received metformin. Group 5 diabetic rats received both combined. Treatments were given for 4 weeks after the induction of diabetes. Blood samples were collected for biochemical assay before the sacrification of rats. Pancreases were removed, weighed, and were processed for histological and immunohistochemical examination. In the untreated diabetic group, the islets appeared shrunken with disturbed architecture and abnormal immunohistochemical reactions for insulin, caspase-3, and inducible nitric oxide synthase (iNOS). The biochemical findings were also disturbed. Morphometrically, there was a significant decrease in the islet size and islet number. Treatment with sitagliptin, metformin, and their combination showed an improvement, with the best response in the combined approach. No evidence of pancreatic injury was identified in the sitagliptin-treated groups. In conclusion, sitagliptin had a cytoprotective effect on beta-cell damage. Furthermore, the data didn't indicate any detrimental effects of sitagliptin on the exocrine pancreas.

Sitagliptin-Dependent Differences in the Intensity of Oxidative Stress in Rat Livers Subjected to Ischemia and Reperfusion

Purpose

Ischemia/reperfusion (IR) is the main cause of liver damage after transplantation. We evaluated the effect of sitagliptin (STG) on oxidative stress parameters in the rat liver under IR.

Methods

Rats were treated with STG (5 mg/kg) (S and SIR) or saline solution (C and CIR). Livers from CIR and SIR were subjected to ischemia (60 min) and reperfusion (24 h). During reperfusion, aminotransferases (ALT and AST) were determined in blood samples. Thiobarbituric acid reactive substances (TBARS), superoxide dismutase (SOD), catalase (CAT), paraoxonase-1 (PON1), glutathione peroxidase (GPx), and the mRNA expression of SOD1 were determined in liver homogenates after reperfusion. Different regions of livers were also histologically evaluated.

Results

The PON1 activity was higher, and the TBARS level was lower in SIR than in CIR. There was an inverse relationship between TBARS and PON1 levels in the whole cohort. The GPx activity was lower in ischemic than in nonischemic groups regardless of the STG treatment. In SIR, the SOD1 activity was higher compared to that in CIR. In S, the expression of SOD1 mRNA was the highest of all examined groups and positively correlated with the SOD1 activity in the whole animal cohort. During IR aminotransferases, the activity in the drug-treated group was lower in all examined points of time. In drug-treated groups, the percentage of steatosis was higher than that in nontreated groups regardless of IR.

Conclusions

The protective effect of STG on the rat liver, especially its antioxidant properties, was revealed under IR conditions.

Dipeptidyl peptidase-4 inhibitor sitagliptin induces vasorelaxation via the activation of Kv channels and PKA

The present study investigated the vasorelaxant effects of sitagliptin, which is a dipeptidyl peptidase-4 (DPP-4) inhibitor in aortic rings pre-contracted with phenylephrine (Phe). Sitagliptin induced vasorelaxation in a concentration-dependent manner but the inhibition of voltage-dependent K⁺ (Kv) channels by pretreatment with 4-aminopyridine (4-AP) effectively reduced this effect. By contrast, the inhibition of inward rectifier K⁺ (Kir) channels by pretreatment with barium (Ba²⁺), large-conductance calcium (Ca²⁺)-activated K⁺ (BK_Ca) channels with paxilline, and adenosine triphosphate (ATP)-sensitive K⁺ (K_ATP) channels with glibenclamide did not change this effect. Although the application of SQ 22536, which is an adenylyl cyclase inhibitor, also did not change this effect, treatment with KT 5720, a protein kinase A (PKA) inhibitor, effectively reduced the vasorelaxant effects of sitagliptin. ODQ, which is a guanylyl cyclase inhibitor, and KT 5823, a protein kinase G (PKG) inhibitor, did not impact the effect. Furthermore, neither the inhibition of Ca²⁺ channels by pretreatment with nifedipine nor the inhibition of sarcoplasmic/endoplasmic reticulum Ca²⁺-ATPase (SERCA) pumps by pretreatment with thapsigargin changed the effect. Similarly, the effects of sitagliptin were not altered by eliminating the endothelium, by pretreatment with a nitric oxide (NO) synthase inhibitor (L-NAME), or by inhibition of small- and intermediate-conductance Ca²⁺-activated K⁺ channels (SK_Ca and IK_Ca) using apamin and TRAM-34. Taken together, these results suggest that sitagliptin induces vasorelaxation by inhibiting both membrane potential (Em)-dependent and -independent vasoconstriction and activating PKA and Kv channels independently of PKG signaling pathways, other K⁺ channels, SERCA pumps, and the endothelium.

Dipeptidyl Peptidase-4 Inhibitors versus Other Antidiabetic Drugs Added to Metformin Monotherapy in Diabetic Retinopathy Progression: A Real World-Based Cohort Study

BACKGROUND

To investigate the effects of dipeptidyl peptidase-4 inhibitor (DPP4i) as add-on medications to metformin on progression of diabetic retinopathy (DR) in patients with type 2 diabetes mellitus, compared with sulfonylurea (SU) or thiazolidinedione (TZD).

METHODS

We identified 4,447 patients with DPP4i, 6,136 with SU, and 617 with TZD in addition to metformin therapy from the database of Korean National Health Insurance Service between January 2013 and December 2015. Cox proportional hazards regression models were used to calculate hazard ratios (HRs) for DR progression. The progression of DR was defined by the procedure code of panretinal photocoagulation, intravitreal injection or vitrectomy; or the addition of diagnostic code of vitreous hemorrhage, retinal detachment, or neovascular glaucoma.

RESULTS

The age and sex-adjusted HR of DR progression was 0.74 for DPP4i add-on group compared with SU add-on group (95% confidence interval [CI], 0.62 to 0.89). This lower risk of DR progression remained significant after additional adjustments for comorbidities, duration of metformin therapy, intravitreal injections and calendar index year (HR, 0.80; 95% CI, 0.66 to 0.97).

CONCLUSION

This population-based cohort study showed that the use of DPP4i as add-on therapy to metformin did not increase the risk of DR progression compared to SU.

Sitagliptin protects against hypoxia/reoxygenation (H/R)-induced cardiac microvascular endothelial cell injury

Inhibition of hypoxia/reoxygenation (H/R)-induced insult in cardiac microvascular endothelial cells (CMECs) has been considered as a promising therapeutic strategy for the treatment of ischemic cardiovascular disease. In the present study, we found that H/R significantly increased the expression of dipeptidyl peptidase (DPP)-4 in CMECs. Treatment with the DPP-4 inhibitor sitagliptin, a licensed drug used for the treatment of type 2 diabetes mellitus (T2DM), ameliorated H/R-induced oxidative stress by decreasing the expression of NOX-4 and restoring the intracellular level of GSH in CMECs. Sitagliptin could also improve H/R-induced mitochondrial dysfunction by increasing intracellular MMP and ATP. Additionally, we found that the presence of sitagliptin prevented H/R-induced reduced cell viability and LDH release. Notably, our findings indicate that sitagliptin possesses an anti-inflammatory effect against H/R-induced expression of IL-6, IL-8, and TNF-α as well as secretion of HMGB1. Mechanistically, we found that sitagliptin suppresses activation of p38/NF-κB signaling. These findings suggest that sitagliptin may have potential as a therapeutic agent for the treatment of cardiovascular diseases.

A review of the molecular mechanisms of hyperglycemia-induced free radical generation leading to oxidative stress

The prevalence of diabetes is growing worldwide with an increasing morbidity and mortality associated with the development of diabetes complications. Free radical production is a normal biological process that is strictly controlled and has been shown to be important in normal cellular homeostasis, and in the bodies response to pathogens. However, there are several mechanisms leading to excessive free radical production that overcome the normal protective quenching mechanisms. Studies have shown that many of the diabetes complications result from excessive free radical generation and oxidative stress, and it has been shown that chronic hyperglycemia is a potent inducer for free radical production, generated through several pathways and triggering multiple molecular mechanisms. An understanding of these processes may help us to improving our preventive or therapeutic strategies. In this review, the major molecular pathways involved in free radical generation induced by hyperglycemia are described.

Therapeutic Options Targeting Oxidative Stress, Mitochondrial Dysfunction and Inflammation to Hinder the Progression of Vascular Complications of Diabetes

Type 2 diabetes mellitus is a leading cause of morbidity and mortality worldwide, given its serious associated complications. Despite constant efforts and intensive research, an effective, ubiquitous treatment still eludes the scientific community. As such, the identification of novel avenues of research is key to the potential discovery of this evasive "silver bullet." We focus on this review on the matter of diabetic injury to endothelial tissue and some of the pivotal underlying mechanisms, including hyperglycemia and hyperlipidemia evoked oxidative stress and inflammation. In this sense, we revisited the most promising therapeutic interventions (both non-pharmacological and antidiabetic drugs) targeting oxidative stress and inflammation to hinder progression of vascular complications of diabetes. This review article gives particular attention to the relevance of mitochondrial function, an often ignored and understudied organelle in the vascular endothelium. We highlight the importance of mitochondrial function and number homeostasis in diabetic conditions and discuss the work conducted to address the aforementioned issue by the use of various therapeutic strategies. We explore here the functional, biochemical and bioenergetic alterations provoked by hyperglycemia in the endothelium, from elevated oxidative stress to inflammation and cell death, as well as loss of tissue function. Furthermore, we synthetize the literature regarding the current and promising approaches into dealing with these alterations. We discuss how known agents and therapeutic behaviors (as, for example, metformin, dietary restriction or antioxidants) can restore normality to mitochondrial and endothelial function, preserving the tissue's function and averting the aforementioned complications.

Cyclin G2 Suppresses Glomerulosclerosis by Regulating Canonical Wnt Signalling

Recent data has shown that cyclin G2 (CCNG2) is an atypical cyclin that inhibits cell cycle progression and is often dysregulated in human cancers. The involvement of cyclin G2 in the occurrence and development of diabetic nephropathy (DN) has not been determined. In the present study, we conducted cyclin G2 knockout studies to determine whether this protein regulates glomerulosclerosis in DN mice. We found that cyclin G2 regulated the expression of renal glomerulosclerosis-related proteins via the canonical Wnt signalling pathway in glomerular mesangial cells. A cyclin G2 deficiency resulted in more severe renal injury in DN mice. These findings provided new insight into the pathogenesis of DN, revealing that cyclin G2 has a protective role in glomerulosclerosis and is a potential new target for the prevention and treatment of DN.

Comparative Safety of Dipeptidyl Peptidase-4 Inhibitors Versus Sulfonylureas and Other Glucose-lowering Therapies for Three Acute Outcomes

Although the glucose lowering effect of dipeptidyl peptidase-4 (DPP4) inhibitors is well established, several potential serious acute safety concerns have been raised including acute kidney injury, respiratory tract infections, and acute pancreatitis. Using the UK-based Clinical Practice Research Datalink (CPRD), we identified initiators (365-day washout period) of DPP4 inhibitors and relevant comparators including initiators of sulfonylureas, metformin, thiazolidinediones, and insulin between January 2007 and January 2016 to quantify the association between DPP4 inhibitors and three acute health events – acute kidney injury, respiratory tract infections, and acute pancreatitis. The associations between drug and study outcomes were estimated using Cox proportional hazard models adjusted for deciles of high-dimensional propensity scores and number of additional glucose lowering agents. After controlling for potential confounders, the risk was not significantly increased or decreased for initiators of DPP4 inhibitors compared to sulfonylureas (hazard ratio (HR) [95% confidence interval (CI)] for acute kidney injury: 0.81 [0.56–1.18]; HR for respiratory tract infections: 0.93 [0.84–1.04]; HR for acute pancreatitis 1.03 [0.42–2.52], metformin (HR for respiratory tract infection 0.91 [0.65–1.27]), thiazolidinediones (HR for acute kidney injury: 1.12 [0.60–2.10]; HR for respiratory tract infections: 1.02 [0.86–1.21]; HR for acute pancreatitis: 1.21 [0.25–5.72]), or insulin (HR for acute kidney injury: 1.40 [0.77–2.55]; HR for respiratory tract infections: 0.74 [0.60–0.92]; HR for acute pancreatitis: 1.01 [0.24–4.19]). Initiators of DPP4 inhibitors were associated with an increased risk of acute kidney injury when compared to metformin initiators (HR [95% CI] for acute kidney injury: 1.85 [1.10–3.12], although this association was attenuated when DPP4 inhibitor monotherapy was compared to metformin monotherapy exposure as a time-dependent variable (HR 1.39 [0.91–2.11]). Initiation of a DPP4 inhibitor was not associated with an increased risk of acute kidney injury, respiratory tract infections, or acute pancreatitis compared to sulfonylureas or other glucose-lowering therapies.

Effect of sitagliptin, a DPP-4 inhibitor, against DENA-induced liver cancer in rats mediated via NF-κB activation and inflammatory cytokines

The target of the current research was to investigate the anticancer activity of sitagliptin on diethylnitrosamine (DENA)-induced cancer in the liver. Wistar rats were treated with or without sitagliptin before DENA treatment. We detected liver weight, blood glucose, and histopathology of the liver. Serum biochemical markers like serum glutamate pyruvate transaminase (SGPT), serum glutamate oxaloacetate transaminase (SGOT), serum alkaline phosphatase (SALP), gamma-glutamyl transpeptidase (GGTP), total bilirubin (TBR), total protein (TPR), and albumin (ALB) were also evaluated. In addition, lipid profile parameters comprising total cholesterol (TC), triglycerides, and high-density lipoprotein were also measured. Inflammatory mediators like interleukin-6 (IL-6), interleukin-1beta (IL-1β), and tumor necrosis factor-alpha (TNF-α) were determined in liver homogenate. Furthermore, the activity of nuclear factor (NF-κB) was also measured. Our results showed that sitagliptin (10 and 20 mg/kg) in a dose-dependent manner expressively decreased the DENA-induced elevation of SGPT, SGOT, SALP, and GGTP. Whereas sitagliptin (10 and 20 mg/kg) in a dose-dependent mode reduced the level of TBR and increased the TPR and ALB as well as improved the liver histopathology alterations in DENA-exposed rats. Lipid profile was also restored by the sitagliptin (10 and 20 mg/kg) in a DENA-treated rats. The level of IL-1β, IL-6, and TNF-α were suggestively suppressed. Moreover, pretreatment with sitagliptin (10 and 20 mg/kg) prevented the activation of NF-κB. In conclusion, sitagliptin (10 and 20 mg/kg) has a potential protective effect against DENA-induced liver cancer by inhibition of inflammation and NF-κB activation.

Differences in kidney-specific DPP-4 inhibition by linagliptin and sitagliptin

The two dipeptidyl peptidase (DPP)-4 inhibitors, linagliptin and sitagliptin, were shown to exert different binding kinetics in vitro. Twenty-four hours after oral dosing particularly in vivo inhibition of renal-specific DPP-4 activity was more sustained in Sprague Dawley rats after exposure to linagliptin than it was after sitagliptin.

Renal Outcomes of Antidiabetic Treatment Options for Type 2 Diabetes-A Proposed MARE Definition

One of the most critical long-term complications of type 2 diabetes is nephropathy, currently termed diabetic kidney disease. Although the prevalence is increasing, renal outcomes are heterogeneously defined. Intensive glucose control is effective for the prevention of microvascular complications, including kidney disease. However, the impact of specific drugs on renal outcome measures such as the incidence of kidney disease, albuminuria, progression to end-stage kidney disease, or death of renal cause remains unclear. Comparison of agents or drug classes is impossible, as renal outcomes are inconsistently defined in trials. Recent publications include more stringent criteria, but use only composite endpoints, which can reveal significant results driven by a single surrogate marker but not clinical events of true relevance to patients. This review discusses renal outcomes related to antidiabetic agents for type 2 diabetes, in an attempt to determine the influence of specific drugs on the incidence of diabetic kidney disease and various renal outcomes. There are marked differences among the various agents, but direct comparisons are difficult due to heterogeneous measures. Statements from Kidney Disease Improving Global Outcomes (KDIGO) or European Renal Best Practice (ERBP) highlight that “standardized outcome reporting is key to achieving evidence-based guidance and improving clinical care for patients.” Renal outcome studies including a well-defined, standardized core set of patient-relevant outcomes are needed. Here, we propose to define and establish major adverse renal events (MARE) as the outcome measure for future studies.