Linagliptin improves insulin sensitivity and hepatic steatosis in diet-induced obesity

Vildagliptin inhibits high fat and fetuin-A mediated DPP-4 expression, intracellular lipid accumulation and improves insulin secretory defects in pancreatic beta cells

Dipeptidyl peptidase-4 (DPP-4), a ubiquitous proteolytic enzyme, inhibits insulin secretion from pancreatic beta cells by inactivating circulating incretin hormones GLP-1 and GIP. High circulating levels of DPP-4 is presumed to compromise insulin secretion in people with type 2 diabetes (T2D). Our group recently reported lipid induced DPP-4 expression in pancreatic beta cells, mediated by the TLR4-NFkB pathway. In the present study, we looked at the role of Vildagliptin on pancreatic DPP-4 inhibition, preservation of islet mass and restoration of insulin secretion. MIN6 mouse insulinoma cells incubated with palmitate and fetuin-A, a proinflammatory organokine associated with insulin resistance, showed activation of TLR4-NFkB pathway, which was rescued on Vildagliptin treatment. In addition, Vildagliptin, by suppressing palmitate-fetuin-A mediated DPP-4 expression in MIN6, prevented the secretion of IL-1beta and fetuin-A in the culture media. DPP-4 siRNA abrogated TLR4-NFkB pathway mediated islet cell inflammation. Vildagliptin also reduced palmitate-fetuin-A mediated intracellular lipid accumulation in MIN6 and isolated islets from high fat fed (HFD) mice as observed by Oil O Red staining with downregulation of CD36 and PPARgamma. Vildagliptin also preserved islet mass and rescued insulin secretory defect in HFD mice. Our results suggest that inhibition of DPP-4 by Vildagliptin protects pancreatic beta cells from the deleterious effects of lipid and fetuin-A, preserves insulin secretory functions and improves hyperglycemia.

Pylorus ligation-induced hyperacidity: synergistic prophylactic effects of linagliptin and L-arginine via up-regulation of EP4 receptor subtype and improvement of vascular endothelial damage

Gastric hyperacidity and ulceration are chronic diseases characterized by repeated healing followed by re-exacerbation. The study aims to protect against gastric hyperacidity without interfering with gastric acid secretion. Pylorus ligation-induced hyperacidity is commonly utilized in the induction of gastric ulcers.Forty-two rats were distributed into seven groups (n = 6). Group I comprised sham-operated group. Group II served as pylorus-ligation group. Groups III-VII were given oral Linagliptin (LN; 3 and 6 mg/kg), L-arginine (LA; 150 and 300 mg/kg) and their combination (LN 3 + LA 150 mg/kg), respectively for 7 days. On the 8th day, groups II-VII were subjected to pylorus-ligation.Treatment of pylorus-ligated rats with LN, LA and their combination improved the gastric hyperacidity as exhibited by a marked reduction in the gastric juice volume, total and free acidities and pepsin contents with a noticeable increase in pH. Pre-treatment with LN, LA and their combination showed a marked alleviation in the gastric inflammatory indicators evidenced by reduction in the gastric levels of MCP-1and Il-1β as well as elevation of eNOS levels versus the sham-operated group. A marked up-regulation in the gastric gene expression of PGE, EP4 and VEGF accompanied by an improvement of the histopathologic pictures/scores, and TNF-α and caspase-3 immuno-staining were also recorded.By estimating the combination-index, it can be concluded that combining LN with LA exhibited prophylactic synergistic effects in ameliorating pylorus ligated-induced hyperacidity, mainly via up-regulation of EP4 receptor and improvement of vascular endothelial damage through VEGF expression in gastric mucosa.

Gemigliptin, a DPP4 inhibitor, ameliorates nonalcoholic steatohepatitis through AMP-activated protein kinase-independent and ULK1-mediated autophagy

OBJECTIVE

Abnormal autophagic function and activated inflammasomes are typical features in the liver of patients with non-alcoholic steatohepatitis (NASH). Here, we explored whether gemigliptin, a dipeptidyl peptidase 4 (DPP4) inhibitor for treatment of type 2 diabetes, can induce autophagy and regulate inflammasome activation as a potential NASH treatment independent of its anti-diabetic effect.

METHODS

Expression analysis was performed using human liver samples obtained from 18 subjects who underwent hepatectomy. We explored the function and mechanism of gemigliptin using a methionine- and choline-deficient diet (MCD)-induced NASH mouse model and HepG2 cells cultured in MCD-mimicking medium.

RESULTS

Autophagy was suppressed by marked decreases in the expression of ULK1 and LC3II/LC3I ratio in human NAFLD/NASH patients, a NASH mouse model, and HepG2 cells cultured with MCD-mimicking media. Surprisingly, we found that the expression of p-AMPK decreased in liver tissues from patients with steatosis but was restored in NASH patients. The expression of p-AMPK in the NASH mouse model was similar to that of the control group. Hence, these results indicate that autophagy was reduced in NASH via an AMPK-independent pathway. However, gemigliptin treatment attenuated lipid accumulation, inflammation, and fibrosis in the liver of MCD diet-fed mice with restoration of ULK1 expression and autophagy induction. In vitro, gemigliptin alleviated inflammasome activation through induction of ULK1-dependent autophagy. Furthermore, gemigliptin treatment upregulated ULK1 expression and activated AMPK even after siRNA-mediated knockdown of AMPKα1/2 and ULK1, respectively.

CONCLUSIONS

Collectively, these results suggest that gemigliptin ameliorated NASH via AMPK-independent, ULK1-mediated effects on autophagy.

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.

Combined saline and vildagliptin induced M2 macrophage polarization in hepatic injury induced by acute kidney injury

Acute kidney injury (AKI) is a prevalent medical condition accompanied by mutual affection of other organs, including the liver resulting in complicated multiorgan malfunction. Macrophages play a vital role during tissue injury and healing; they are categorized into "classically activated macrophages" (M1) and "alternatively activated macrophages" (M2). The present study investigated and compared the conventional fluid therapy vs Dipeptidyl peptidase 4 inhibitor (DPP-4i) vildagliptin on the liver injury induced by AKI and evaluated the possible molecular mechanisms. Thirty rats comprised five groups (n = 6 rats/group): control, AKI, AKI+saline (received 1.5 mL of normal saline subcutaneous injection), AKI+vildagliptin (treated with oral vildagliptin 10 mg/kg), AKI+saline+vildagliptin. AKI was induced by intramuscular (i.m) injection of 50% glycerol (5 ml/kg). At the end of the work, we collected serum and liver samples for measurements of serum creatinine, blood urea nitrogen (BUN), alanine aminotransferase (ALT), aspartate aminotransferase (AST), tumor necrotic factor-α (TNF-α), and interleukin-10 (IL-10). Liver samples were processed for assessment of inducible nitric oxide synthase (iNOS) as a marker for M1, arginase 1 (Arg-1) as an M2 marker, c-fos, c-Jun, mitogen-activated protein kinase (MAPK), activator protein 1 (AP-1), and high-mobility-group-box1 (HMGB1) protein. The difference was insignificant regarding the relative expression of AP-1, c-Jun, c-fos, MAPK, and HMGB between the AKI+saline group and the AKI+Vildagliptin group. The difference between the same two groups concerning the hepatic content of the M1 marker (iNOS) and the M2 marker Arg-1 was insignificant. However, combined therapy produced more pronounced changes in these markers, as the difference in their relative expression between the AKI+saline+Vildagliptin group and both the AKI+saline group and the AKI+Vildagliptin group was significant. Accordingly, we suggest that the combined saline and vildagliptin hepatoprotective effect involves the downregulation of the MAPK/AP-1 signaling pathway.

A nexus of lipid and O-Glcnac metabolism in physiology and disease

Although traditionally considered a glucose metabolism-associated modification, the O-linked β-N-Acetylglucosamine (O-GlcNAc) regulatory system interacts extensively with lipids and is required to maintain lipid homeostasis. The enzymes of O-GlcNAc cycling have molecular properties consistent with those expected of broad-spectrum environmental sensors. By direct protein-protein interactions and catalytic modification, O-GlcNAc cycling enzymes may provide both acute and long-term adaptation to stress and other environmental stimuli such as nutrient availability. Depending on the cell type, hyperlipidemia potentiates or depresses O-GlcNAc levels, sometimes biphasically, through a diversity of unique mechanisms that target UDP-GlcNAc synthesis and the availability, activity and substrate selectivity of the glycosylation enzymes, O-GlcNAc Transferase (OGT) and O-GlcNAcase (OGA). At the same time, OGT activity in multiple tissues has been implicated in the homeostatic regulation of systemic lipid uptake, storage and release. Hyperlipidemic patterns of O-GlcNAcylation in these cells are consistent with both transient physiological adaptation and feedback uninhibited obesogenic and metabolic dysregulation. In this review, we summarize the numerous interconnections between lipid and O-GlcNAc metabolism. These links provide insights into how the O-GlcNAc regulatory system may contribute to lipid-associated diseases including obesity and metabolic syndrome.

Prolonged effects of DPP-4 inhibitors on steato-hepatitic changes in Sprague-Dawley rats fed a high-cholesterol diet

OBJECTIVE

Sitagliptin and other dipeptidyl peptidase (DPP)-4 inhibitors/gliptins are antidiabetic drugs known to improve lipid profile, and confer anti-inflammatory and anti-fibrotic effects, which are independent of their hypoglycemic effects. However, in our previous short-term (35 days) studies, we showed that sitagliptin accentuates the hepato-inflammatory effects of high dietary cholesterol (Cho) in male Sprague-Dawley rats. Since most type 2 diabetics also present with lipid abnormalities and use DPP-4 inhibitors for glucose management, the present study was conducted to assess the impact of sitagliptin during long-term (98 days) feeding of a high Cho diet. An additional component of the present investigation was the inclusion of other gliptins to determine if hepatic steatosis, necro-inflammation, and fibrosis were specific to sitagliptin or are class effects.

METHODS

Adult male Sprague-Dawley rats were fed control or high Cho (2.0%) diets, and gavaged daily (from day 30 through 98) with vehicle or DPP-4 inhibitors (sitagliptin or alogliptin or saxagliptin). On day 99 after a 4 h fast, rats were euthanized. Blood and liver samples were collected to measure lipids and cytokines, and for histopathological evaluation, determination of hepatic lesions (steatosis, necrosis, inflammation, and fibrosis) using specific staining and immunohistochemical methods.

RESULTS

Compared to controls, the high Cho diet produced a robust increase in NASH like phenotype that included increased expression of hepatic (Tnfa, Il1b, and Mcp1) and circulatory (TNFα and IL-1β) markers of inflammation, steatosis, necrosis, fibrosis, and mononuclear cell infiltration. These mononuclear cells were identified as macrophages and T cells, and their recruitment in the liver was facilitated by marked increases in endothelium-expressed cell adhesion molecules. Importantly, treatment with DPP-4 inhibitors (3 tested) neither alleviated the pathologic responses induced by high Cho diet nor improved lipid profile.

CONCLUSIONS

The potential lipid lowering effects of DPP-4 inhibitors were diminished by high Cho (a significant risk factor for inducing liver damage). The robust inflammatory responses induced by high Cho feeding in long-term experiment were not exacerbated by DPP-4 inhibitors and a consistent hepatic inflammatory environment persisted, implying a prospective physiological adaptation.

Effects of sitagliptin on intrahepatic lipid content in patients with non-alcoholic fatty liver disease

PURPOSE

Dipeptidyl peptidase-4 inhibitors (DPP-4I), key regulators of the actions of incretin hormones, exert anti-hyperglycemic effects in type 2 diabetes mellitus (T2DM) patients. A major unanswered question concerns the potential ability of DPP-4I to improve intrahepatic lipid (IHL) content in nonalcoholic fatty liver disease (NAFLD) patients. The aim of this study was to evaluate the effects of sitagliptin on IHL in NAFLD patients.

METHODS

A prospective, 24-week, single-center, open-label, comparative study enrolled 68 Chinese NAFLD patients with T2DM. Subjects were randomly divided into 4 groups: control group who did not take medicine (14 patients); sitagliptin group who received sitagliptin treatment (100mg per day) (17 patients); metformin group who received metformin (500mg three times per day) (17 patients); and sitagliptin plus metformin group who received sitagliptin (100mg per day) and metformin (500 mg three times per day) (20 patients). IHL, physical examination (waist circumstances, WC; body mass index, BMI), glucose-lipid metabolism (fasting plasma glucose, FPG; hemoglobin A1c, Hb1A1c; triglycerides; cholesterol; alanine aminotransferase, ALT; aspartate aminotransferase, AST) were measured at baseline and at 24 weeks.

RESULTS

1) WC and BMI were decreased significantly in all groups except control group (all P<0.05). 2) There was no statistically significant difference in IHL among the sitagliptin, metformin, and sitagliptin plus metformin groups before and after treatment(all P>0.05). Only the metformin group showed a statistically significant difference in IHL before and after treatment(P<0.05). 3) Sitagliptin treatment led to a significant decrease in FBG and HbA1c when compared with the control group (all P<0.01). Additionally, HhA1c was significant decreased in the sitagliptin group when compared with the metformin group (P< 0.05). 4) HbA1c and FBG were decreased by 0.8% and 0.7 mmol/l respectively and the percentage of patients with HbA1c less than 7% was 65% with sitagliptin treatment.

CONCLUSION

Sitagliptin improves abnormalities in glucose metabolism, but not reduces the IHL in T2DM with NAFLD, indicating that sitagliptin might be a therapeutic option for treatment of NAFLD indirectly while not directly on IHL. Clinical Trial Registration: https://clinicaltrials.gov/, identifier CTR# NCT05480007.

Targeting the GPR119/incretin axis: a promising new therapy for metabolic-associated fatty liver disease

In the past decade, G protein-coupled receptors have emerged as drug targets, and their physiological and pathological effects have been extensively studied. Among these receptors, GPR119 is expressed in multiple organs, including the liver. It can be activated by a variety of endogenous and exogenous ligands. After GPR119 is activated, the cell secretes a variety of incretins, including glucagon-like peptide-1 and glucagon-like peptide-2, which may attenuate the metabolic dysfunction associated with fatty liver disease, including improving glucose and lipid metabolism, inhibiting inflammation, reducing appetite, and regulating the intestinal microbial system. GPR119 has been a potential therapeutic target for diabetes mellitus type 2 for many years, but its role in metabolic dysfunction associated fatty liver disease deserves further attention. In this review, we discuss relevant research and current progress in the physiology and pharmacology of the GPR119/incretin axis and speculate on the potential therapeutic role of this axis in metabolic dysfunction associated with fatty liver disease, which provides guidance for transforming experimental research into clinical applications.

Effects of Whole-Body Adenylyl Cyclase 5 (Adcy5) Deficiency on Systemic Insulin Sensitivity and Adipose Tissue

Genome-wide association studies have identified adenylyl cyclase type 5 (ADCY5) as candidate gene for diabetes-related quantitative traits and an increased risk of type 2 diabetes. Mice with a whole-body deletion of Adcy5 (Adcy5-/-) do not develop obesity, glucose intolerance and insulin resistance, have improved cardiac function and increased longevity. Here, we investigated Adcy5 knockout mice (Adcy5-/-) to test the hypothesis that changes in adipose tissue (AT) may contribute to the reported healthier phenotype. In contrast to previous reports, we found that deletion of Adcy5 did not confer any physiological or biochemical benefits. However, this unexpected finding allowed us to investigate the effects of Adcy5 depletion on AT independently of lower body weight and a metabolically healthier phenotype. Adcy5-/- mice exhibited an increased number of smaller adipocytes, lower mean adipocyte size and a distinct AT gene expression pattern with midline 1 (Mid1) as the most significantly downregulated gene compared to control mice. Our Adcy5-/- model challenges previously described beneficial effects of Adcy5 deficiency and suggests that targeting Adcy5 does not improve insulin sensitivity and may therefore limit the relevance of ADCY5 as potential drug target.

Characterization of combined linagliptin and Y2R agonist treatment in diet-induced obese mice

Dipeptidyl peptidase IV (DPP-IV) inhibitors improve glycemic control by prolonging the action of glucagon-like peptide-1 (GLP-1). In contrast to GLP-1 analogues, DPP-IV inhibitors are weight-neutral. DPP-IV cleavage of PYY and NPY gives rise to PYY3-36 and NPY3-36 which exert potent anorectic action by stimulating Y2 receptor (Y2R) function. This invites the possibility that DPP-IV inhibitors could be weight-neutral by preventing conversion of PYY/NPY to Y2R-selective peptide agonists. We therefore investigated whether co-administration of an Y2R-selective agonist could unmask potential weight lowering effects of the DDP-IV inhibitor linagliptin. Male diet-induced obese (DIO) mice received once daily subcutaneous treatment with linagliptin (3 mg/kg), a Y2R-selective PYY3-36 analogue (3 or 30 nmol/kg) or combination therapy for 14 days. While linagliptin promoted marginal weight loss without influencing food intake, the PYY3-36 analogue induced significant weight loss and transient suppression of food intake. Both compounds significantly improved oral glucose tolerance. Because combination treatment did not further improve weight loss and glucose tolerance in DIO mice, this suggests that potential negative modulatory effects of DPP-IV inhibitors on endogenous Y2R peptide agonist activity is likely insufficient to influence weight homeostasis. Weight-neutrality of DPP-IV inhibitors may therefore not be explained by counter-regulatory effects on PYY/NPY responses.

Effects of the Combination of Evogliptin and Leucine on Insulin Resistance and Hepatic Steatosis in High-Fat Diet-Fed Mice

In this study, we aimed to investigate the effects of 8 weeks of treatment with a combination of evogliptin and leucine, a branched-chain amino acid, in mice with high-fat diet (HFD)-induced diabetes. Treatment with evogliptin alone or in combination with leucine reduced the body weight of the mice, compared to the case for those from the HFD control group. Long-term treatment with evogliptin alone or in combination with leucine resulted in a significant reduction in glucose intolerance; however, leucine alone did not affect postprandial glucose control, compared to the case for the mice from the HFD control group. Furthermore, the combination of evogliptin and leucine prevented HFD-induced insulin resistance, which was associated with improved homeostasis model assessment for insulin resistance, accompanied by markedly reduced liver fat deposition, hepatic triglyceride content, and plasma alanine aminotransferase levels. The combination of evogliptin and leucine increased the gene expression levels of hepatic peroxisome proliferator-activated receptor alpha, whereas those of the sterol regulatory element-binding protein 1 and stearoyl-CoA desaturase 1 were not altered, compared to the case in the HFD-fed mice (p<0.05). Thus, our results suggest that the combination of evogliptin and leucine may be beneficial for treating patients with type 2 diabetes and hepatic steatosis; however, further studies are needed to delineate the molecular mechanisms underlying the action of this combination.

The protective effects of trelagliptin on high-fat diet-induced nonalcoholic fatty liver disease in mice

Nonalcoholic fatty liver disease (NAFLD) occurs in patients with type 2 diabetes mellitus (T2DM). Trelagliptin is an important member of the Gliptins family, which has been recently licensed for the treatment of T2DM. However, the pharmacological function of trelagliptin in NAFLD has not been previously reported. In this study, we aimed to investigate the roles of trelagliptin in the development of NAFLD in a mouse model. To induce NAFLD disease, C57BL/6 mice were fed a high-fat diet for 10 weeks. Our results indicate that trelagliptin reduced plasma lipid levels in NAFLD mice by reducing triglycerides, total cholesterol, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol. Treatment with trelagliptin exhibited an improvement in insulin resistance. More important, trelagliptin improved liver function by reducing alanine transaminase, aspartate transaminase, lactate dehydrogenase, and total bile acid. In addition, trelagliptin ameliorated oxidative stress in the liver of NAFLD mice by reducing malondialdehyde and increasing the levels of reduced glutathione and superoxide dismutase activity. Also, the enzyme-linked immunosorbent assay results indicate that trelagliptin-treated mice displayed anti-inflammatory properties by reducing the levels of interleukin 1β (IL-1β), IL-6, and tumor necrosis factor-α. Hematoxylin and eosin and Oil red O staining show that trelagliptin treatment ameliorates liver tissue damage and hepatic lipid deposition. Mechanistically, we found that the administration of trelagliptin reduced the activity of hepatic nuclear factor-κB but increased the activity of AMP-activated protein kinase. These findings suggest that trelagliptin might become a promising therapeutic agent for the treatment of NAFLD.

Effects of the linagliptin, dipeptidyl peptidase-4 inhibitor, on bone fragility induced by type 2 diabetes mellitus in obese mice

Recently, it has been suggested that glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1), which play important roles in the homeostasis of glucose metabolism, could be involved in the regulation of bone metabolism. Inhibitors of dipeptidyl peptidase 4 (DPP-4), an enzyme that degrades GIP and GLP-1, are widely used clinically as a therapeutic agent for diabetes. However, the effects of DPP-4 inhibitors on bone metabolism remain unclear. In this study, we investigated the effects of linagliptin, a DPP-4 inhibitor, on bone fragility induced by type 2 diabetes mellitus (T2DM). Non-diabetic mice were used as controls, and T2DM mice were administered linagliptin orally on a daily basis for 12 weeks. In T2DM mice, decreased bone mineral density was observed in the lower limb bones along with low serum osteocalcin levels and high serum tartrate-resistant acid phosphatase-5b (TRAP) levels. In contrast, the decreased serum osteocalcin levels and increased serum TRAP levels observed in T2DM mice were significantly suppressed after the administration of linagliptin 30 mg/kg. Bone histomorphometric analysis revealed a reduced osteoid volume and osteoblast surface with an increase in the eroded surface and number of osteoclasts in T2DM mice. This decreased bone formation and increased bone resorption observed in the T2DM mice were suppressed and trabecular bone volume increased following the administration of 30 mg/kg linagliptin. Collectively, these findings suggest that linagliptin may improve the microstructure of trabecular bone by inhibiting both a decrease in bone formation and an increase in bone resorption induced by T2DM.

Linagliptin Ameliorates Hepatic Steatosis via Non-Canonical Mechanisms in Mice Treated with a Dual Inhibitor of Insulin Receptor and IGF-1 Receptor

Abnormal hepatic insulin signaling is a cause or consequence of hepatic steatosis. DPP-4 inhibitors might be protective against fatty liver. We previously reported that the systemic inhibition of insulin receptor (IR) and IGF-1 receptor (IGF1R) by the administration of OSI-906 (linsitinib), a dual IR/IGF1R inhibitor, induced glucose intolerance, hepatic steatosis, and lipoatrophy in mice. In the present study, we investigated the effects of a DPP-4 inhibitor, linagliptin, on hepatic steatosis in OSI-906-treated mice. Unlike high-fat diet-induced hepatic steatosis, OSI-906-induced hepatic steatosis is not characterized by elevations in inflammatory responses or oxidative stress levels. Linagliptin improved OSI-906-induced hepatic steatosis via an insulin-signaling-independent pathway, without altering glucose levels, free fatty acid levels, gluconeogenic gene expressions in the liver, or visceral fat atrophy. Hepatic quantitative proteomic and phosphoproteomic analyses revealed that perilipin-2 (PLIN2), major urinary protein 20 (MUP20), cytochrome P450 2b10 (CYP2B10), and nicotinamide N-methyltransferase (NNMT) are possibly involved in the process of the amelioration of hepatic steatosis by linagliptin. Thus, linagliptin improved hepatic steatosis induced by IR and IGF1R inhibition via a previously unknown mechanism that did not involve gluconeogenesis, lipogenesis, or inflammation, suggesting the non-canonical actions of DPP-4 inhibitors in the treatment of hepatic steatosis under insulin-resistant conditions.

Protective Effects of Evogliptin on Steatohepatitis in High-Fat-Fed Mice

There are few studies on the effects of dipeptidyl peptidase-4 inhibitors on steatohepatitis. We explored whether evogliptin (Evo), a dipeptidyl peptidase-4 inhibitor, protects against steatohepatitis in a high-fat diet (HFD)-fed mice and whether these effects involve modulation of mitophagy. Adult male C57BL/J mice were divided into the normal diet (ND), HFD (45% of energy from fat) with Evo (250 mg/kg) (HFD + Evo), and HFD groups at 4 weeks of age and were sacrificed at 20 weeks of age. The HFD group showed hepatic lipid accumulation; this was decreased in the Evo + HFD group. There was an increased 8-hydroxydeoxyguanosine (8-OHDG) expression in the HFD group compared to ND mice. However, 8-OHDG expression levels were significantly decreased in the HFD + Evo group. Expressions of the mitophagy markers PTEN-induced kinase 1 (PINK1), Parkin, and BNIP-3 (BCL2 Interacting Protein 3) were significantly increased in the HFD group. However, the expressions of these markers were lower in the HFD + Evo group than that in the HFD group. Phospho-Akt was upregulated and p53 was downregulated in the HFD + Evo group compared to the HFD group. Evogliptin may alleviate steatohepatitis in HFD-fed mice by ameliorating steatosis and oxidative stress and by modulating mitophagy in the liver.

Dipeptidyl Peptidase-IV Inhibitory Activity and Related Molecular Mechanism of Bovine α-Lactalbumin-Derived Peptides

Identifying DPP-IV inhibitory peptides from dietary protein has attracted increased attention. In the present study, bovine α-lactalbumin hydrolysates were generated by alcalase for various hydrolysis times, and DPP-IV inhibitory activity of these hydrolysates was determined. The 4 h hydrolysates displayed the most potent DPP-IV inhibitory activity, with DPP-IV inhibition rate of 82.30 ± 1.39% at concentration of 1.0 mg/mL. DPP-IV inhibitory peptides were isolated from the 4 h-hydrolysates with gel filtration chromatography and reversed-phase high-performance liquid chromatography (RP-HPLC). Using liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI MS/MS), two DPP-IV inhibitory peptides were identified, and their amino acid sequences were Glu-Leu-Lys-Asp-Leu-Lys-Gly-Tyr (ELKDLKGY) and Ile-Leu-Asp-Lys-Val-Gly-Ile-Asn-Tyr (ILDKVGINY), respectively. Furthermore, molecular docking analysis showed that peptides ELKDLKGY and ILDKVGINY could form hydrogen bonds, pi-cation interactions, and salt bridges with DPP-IV. These findings indicated that bovine α-lactalbumin may be a potential source of natural DPP-IV inhibitor.

Anti-steatotic linagliptin pleiotropic effects encompasses suppression of de novo lipogenesis and ER stress in high-fat-fed mice

AIM

To investigate the effects of linagliptin treatment on hepatic energy metabolism and ER stress in high-fat-fed C57BL/6 mice.

METHODS

Forty male C57BL/6 mice, three months of age, received a control diet (C, 10% of lipids as energy, n = 20) or high-fat diet (HF, 50% of lipids as energy, n = 20) for 10 weeks. The groups were randomly subdivided into four groups to receive linagliptin, for five weeks, at a dose of 30 mg/kg/day added to the diets: C, C-L, HF, and HF-L groups.

RESULTS

The HF group showed higher body mass, total and hepatic cholesterol levels and total and hepatic triacylglycerol levels than the C group, all of which were significantly diminished by linagliptin in the HF-L group. The HF group had higher hepatic steatosis than the C group, whereas linagliptin markedly reduced the hepatic steatosis (less 52%, P < 0.001). The expression of Sirt1 and Pgc1a was more significant in the HF-L group than in the HF group. Linagliptin also elicited enhanced GLP-1 concentrations and a reduction in the expression of the lipogenic genes Fas and Srebp1c. Besides, HF-L showed a reduction in the genes related to endoplasmic reticulum stress Chop, Atf4, and Gadd45 coupled with reduced apoptotic nuclei immunostaining.

CONCLUSION

Linagliptin caused a marked reduction in hepatic steatosis as a secondary effect of its glucose-lowering property. NAFLD countering involved reduced lipogenesis, increased beta-oxidation, and relief in endoplasmic reticulum stress, leading to reduced apoptosis and better preservation of the hepatic structure. Therefore, linagliptin may be used, preferably in diabetic patients, to avoid the progression of hepatic steatosis.

Effects of dipeptidyl peptidase 4 inhibition on inflammation in atherosclerosis: A 18F-fluorodeoxyglucose study of a mouse model of atherosclerosis and type 2 diabetes

BACKGROUND AND AIMS

Dipeptidyl peptidase 4 (DPP-4) inhibitors have anti-inflammatory and atheroprotective effects. We evaluated the effects of the DPP-4 inhibitor linagliptin on atherosclerotic plaque and hepatic inflammation using histology and 2-deoxy-2-[¹⁸F]-fluoro-d-glucose (¹⁸F-FDG), a positron emission tomography tracer of inflammation, in a mouse model of hypercholesterolemia and type 2 diabetes.

METHODS

Igf2/Ldlr^-/-Apob^100/100 mice were fed a high-fat diet (HFD) for 8 weeks and then randomly allocated to receive HFD (n = 14), or HFD with added linagliptin (n = 15) for additional 12 weeks. Five mice fed a chow diet were studied as an additional control. At the end of the study, glucose tolerance, aortic and liver uptake of ¹⁸F-FDG, and histology were studied.

RESULTS

Mice in linagliptin and HFD groups had similar fasting glucose concentrations, but linagliptin improved glucose tolerance. Aortas of linagliptin and HFD groups showed advanced atherosclerotic plaques with no difference in the mean intima-to-media ratio or number of macrophages in the plaques. Autoradiography showed similar ¹⁸F-FDG uptake by atherosclerotic plaques in linagliptin and HFD groups (plaque-to-wall ratio: 1.7 ± 0.25 vs. 1.6 ± 0.21; p = 0.24). In the liver, linagliptin reduced the histologic inflammation score but had no effect on ¹⁸F-FDG uptake. Compared with chow diet, uptake of ¹⁸F-FDG was similar in the aorta, but higher in the liver after HFD.

CONCLUSIONS

Linagliptin therapy improved glucose tolerance and reduced hepatic inflammation but had no effect on plaque burden or atherosclerotic inflammation, as determined by histology and ¹⁸F-FDG uptake, in atherosclerotic mice with type 2 diabetes.

Linagliptin affects IRS1/Akt signaling and prevents high glucose-induced apoptosis in podocytes

Diabetes-induced podocyte apoptosis is considered to play a critical role in the pathogenesis of diabetic kidney disease (DKD). We proposed that hyperglycaemia can induce podocyte apoptosis by inhibiting the action of podocyte survival factors, thus inactivating the cellular effects of insulin signalling. In this study, we aimed to determine the effects of linagliptin on high glucose-induced podocyte apoptosis. Linagliptin reduced the increase in DNA fragmentation as well as the increase in TUNEL-positive cells in podocytes induced by high-glucose condition. Furthermore, linagliptin improved insulin-induced phosphorylation of insulin receptor substrate 1 (IRS1) and Akt, which was inhibited in high-glucose conditions. Adenoviral vector-mediated IRS1 overexpression in podocytes partially normalised DNA fragmentation in high-glucose conditions, while downregulation of IRS1 expression using small interfering RNA increased DNA fragmentation even in low-glucose conditions. Because reactive oxygen species inhibit glomerular insulin signalling in diabetes and Kelch-like ECH-associated protein 1 (Keap1)/nuclear factor erythroid 2-related factor 2 (Nrf2) pathway is one of the most important intrinsic antioxidative systems, we evaluated whether linagliptin increased Nrf2 in podocytes. High-glucose condition and linagliptin addition increased Nrf2 levels compared to low-glucose conditions. In summary, linagliptin offers protection against DKD by enhancing IRS1/Akt insulin signalling in podocytes and partially via the Keap1/Nrf2 pathway. Our findings suggest that linagliptin may induce protective effects in patients with DKD, and increasing IRS1 levels could be a potential therapeutic target in DKD.

A siRNA mediated hepatic dpp4 knockdown affects lipid, but not glucose metabolism in diabetic mice

Systemic inhibition of dipeptidyl peptidase 4 (dpp4) represents an effective and established treatment option for type 2 diabetes (T2D). The current study investigated in mice if a liver selective knock-down of dpp4 by therapeutic siRNAs could be a novel, similarly effective treatment option for T2D. Furthermore, the potential effects on hepatic steatosis, inflammation and lipid metabolism were investigated after hepato-selective knock-down of dpp4. The knock-down efficiency and IC50 values of siRNAs targeting dpp4 were analyzed in PC3 cells. In two independent studies, either db/db mice or C57BL/6J mice were injected intravenously with a liposomal formulation of siRNAs targeting either dpp4 or a non-targeting control, followed by metabolically characterization. In comparator groups, additional cohorts of mice were treated with an oral dpp4 inhibitor. In both animal studies, we observed a robust knock-down (~75%) of hepatic dpp4 with a potent siRNA. Hepatic dpp4 knockdown did not significantly affect glucose metabolism or circulating incretin concentrations in both animal studies. However, in obese and diabetic db/db mice hepatic steatosis was reduced and hepatic mRNA expression of acaca, scd1, fasn and pparg was significantly lower after siRNA treatment. Systemic inhibition of the enzymatic dpp4 activity by an oral dpp4 inhibitor significantly improved glucose handling in db/db mice but did not affect hepatic endpoints. These data demonstrate that a targeted reduction of dpp4 expression in the liver may not be sufficient to improve whole-body glucose metabolism in obese and diabetic mice but may improve hepatic lipid metabolism.

From NASH to diabetes and from diabetes to NASH: Mechanisms and treatment options

The worldwide prevalence of non-alcoholic fatty liver disease (NAFLD) is estimated to have reached 25% or more in adults. NAFLD is prevalent in obese individuals, but may also affect non-obese insulin-resistant individuals. NAFLD is associated with a 2- to 3-fold increased risk of developing type 2 diabetes (T2D), which may be higher in patients with more severe liver disease - fibrosis increases this risk. In NAFLD, not only the close association with obesity, but also the impairment of many metabolic pathways, including decreased hepatic insulin sensitivity and insulin secretion, increase the risk of developing T2D and related comorbidities. Conversely, patients with diabetes have a higher prevalence of steatohepatitis, liver fibrosis and end-stage liver disease. Genetics and mechanisms involving dysfunctional adipose tissue, lipotoxicity and glucotoxicity appear to play a role. In this review, we discuss the altered pathophysiological mechanisms that underlie the development of T2D in NAFLD and vice versa. Although there is no approved therapy for the treatment of NASH, we discuss pharmacological agents currently available to treat T2D that could potentially be useful for the management of NASH.

High dose of linagliptin induces thermogenic beige adipocytes in the subcutaneous white adipose tissue in diet-induced obese C57BL/6 mice

PURPOSE

To verify whether the treatment with linagliptin induces the browning of the subcutaneous WAT (sWAT) and thermogenesis in murine diet-induced obesity (DIO) model.

METHODS

Forty animals were randomly assigned to receive a control diet (C, 10% lipids as energy) or a high-fat diet (HF, 50% lipids as energy) for 10 weeks. Each group was re-divided to begin the 5-week treatment, totalizing four experimental groups: C, C-L (C plus linagliptin, 30 mg/kg body mass; BM), HF, and HF-L (HF plus linagliptin, 30 mg/kg BM). The drug was mixed with diet.

RESULTS

HF animals showed overweight, glucose intolerance, and a greater cross-sectional area of adipocytes. The treatment with linagliptin was able to normalize the BM, restore the glucose tolerance and the cross-sectional area of adipocytes. These observations comply with the observation of UCP1-positive multilocular adipocytes in the sWAT of treated animals. Both treated groups (C-L and HF-L) showed high expression of thermogenic and type 2 cytokines genes, which agree with the enhanced body temperature and the lower respiratory exchange ratio, implying enhanced thermogenesis with the use of lipids as fuel.

CONCLUSIONS

The reduced BM, the enhanced body temperature, and the presence of positive UCP1 beige cells in the sWAT point to the activation of the browning cascade on the sWAT of linagliptin-treated mice, and hence, linagliptin could induce the thermogenic pathway as a pleiotropic effect that can have translational potential.

Rationale, Design for the ASSET Study: A Prospective Randomized Study Comparing Empagliflozin's Effect to Sitagliptin on Cardiac Fat Accumulation/Function in Patients with Type 2 Diabetes

INTRODUCTION

Ectopic fat accumulation has been found to play a pathophysiological role in insulin resistance, type 2 diabetes (T2DM), and coronary artery diseases. Findings from a number of previous studies suggest that sodium glucose cotransporter 2 (SGLT2) inhibitors reduce lipid accumulation, including myocardial and pericardial fat, while dipeptidyl peptidase 4 (DPP4) inhibitors suppress ectopic lipid accumulation and improve cardiac function. However, a clinical study that precisely explains and compares the efficacy of SGLT2 inhibitors and DPP4 inhibitors on cardiac fat accumulation has not been performed. Moreover, the association between cardiac fat accumulation and cardiac function or metabolic changes, such as tissue-specific insulin resistance, remains unclear. It is our intention to conduct the first study to assess the effects of empagliflozin compared to sitagliptin in reducing ectopic fat accumulation, specifically pericardial fat, and its association with improvement in cardiac function and tissue-specific insulin sensitivity.

METHODS

We have designed a prospective, randomized open-label, and blinded-endpoint study with the intention to enroll 44 Japanese patients with T2DM. The patients are to be divided them into two groups, an empagliflozin group and an sitagliptin group, with the former to be supplemented with empagliflozin 10 mg and the latter to be supplemented with sitagliptin 100 mg, both groups for 12 weeks. The primary endpoint of the study is the change in the amount of pericardial fat. The secondary endpoints are the changes in the amount of intracellular fat in the myocardium, cardiac function, tissue-specific insulin sensitivity, fatty acid metabolism in myocardial tissue, assessed by parameters of iodine-123-β-methyl-iodophenyl pentadecanoic acid myocardial scintigraphy, blood and urine biomarkers, and lifestyle evaluation.

PLANNED OUTCOMES

The results of this study will be available in 2020. The aim of this study is to provide an effective treatment strategy for patients with T2DM by considering cardiac fat accumulation, cardiac function, and insulin resistance.

FUNDING

Boehringer Ingelheim & Eli Lilly and Company Diabetes Alliance.

TRIAL REGISTRATION

University Hospital Medical Information Network Clinical Trial Registry: UMIN000026340.

Effect of Linagliptin on the Ratio of Apoptosis Regulators in the Model of Non-Alcoholic Fatty Liver Disease in db/db Mice

We studied the effects of dipeptidyl peptidase 4 (DPP4) inhibitor linagliptin on the expression of apoptosis regulator proteins Bcl-2 and Bad in the liver of db/db mice with genetically determined obesity and type 2 diabetes mellitus. The mice received daily linagliptin or saline (placebo) by gavage from week 10 to week 18 of life. In the liver of non-treated mice, the area positively stained for Bad was greater than the area of Bcl-2 expression, which created the conditions for apoptosis activation in liver at this age. Administration of linagliptin decreased Bad stained area and increased Bcl-2 stained area in the liver cells. At the same time, Bad stained area remained larger in treated mice than the area of Bcl-2 expression area, which attested to partial normalization of pro- and antiapoptotic protein balance.

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).

Circulating Levels of Soluble Dipeptidyl Peptidase-4 Are Dissociated from Inflammation and Induced by Enzymatic DPP4 Inhibition

Dipeptidyl peptidase-4 (DPP-4) controls glucose homeostasis through enzymatic termination of incretin action. We report that plasma DPP-4 activity correlates with body weight and fat mass, but not glucose control, in mice. Genetic disruption of adipocyte Dpp4 expression reduced plasma DPP-4 activity in older mice but did not perturb incretin levels or glucose homeostasis. Knockdown of hepatocyte Dpp4 completely abrogated the obesity-associated increase in plasma DPP-4 activity, reduced liver cytokine expression, and partially attenuated inflammation in adipose tissue without changes in incretin levels or glucose homeostasis. In contrast, circulating levels of soluble DPP4 (sDPP4) were dissociated from inflammation in mice with endothelial-selective or global genetic inactivation of Dpp4. Remarkably, inhibition of DPP-4 enzymatic activity upregulated circulating levels of sDPP4 originating from endothelial or hematopoietic cells without inducing systemic or localized inflammation. Collectively, these findings reveal unexpected complexity in regulation of soluble versus enzymatic DPP-4 and control of inflammation and glucose homeostasis.

Influence of type-4 dipeptidyl peptidase inhibition on endothelium-dependent relaxation of aortae from a db/db mouse model of type 2 diabetes: a comparison with the effect of glimepiride

PURPOSE

The aim of this study was to investigate the effects of the type-4 dipeptidyl peptidase (DPP-4) inhibitors linagliptin and vildagliptin as well as the sulfonylurea glimepiride on endothelium-dependent relaxation of aortae from female db/db mice with established hyperglycemia to determine whether these treatments were able to attenuate diabetes-induced endothelial dysfunction.

MATERIALS AND METHODS

The mice were treated with glimepiride (2 mg/kg po per day, weeks 1-6, n=12), glimepiride plus vildagliptin (glimepiride 2 mg/kg po per day, weeks 1-6; vildagliptin 3 mg/kg po per day, weeks 4-6, n=11), glimepiride plus linagliptin (glimepiride 2 mg/kg po per day, weeks 1-6; linagliptin 3 mg/kg po per day, weeks 4-6, n=11) or linagliptin (3 mg/kg po per day, weeks 1-6, n=12). Endothelium-dependent relaxation using acetylcholine was assessed in the absence and presence of pharmacological tools (TRAM-34 1 μM; apamin 1 μM; N-nitro-L-arginine [L-NNA] 100 μM; 1H-[1,2,4]oxadiazolo [4,3-a]quinoxalin-1-one [ODQ] 10 μM) to distinguish relaxation mediated by nitric oxide (NO).

RESULTS

Linagliptin was associated with a significant improvement in endothelium-dependent relaxation (ACh Rmax; db/db 41±1%, linagliptin 73±6%, p<0.05). The enhanced response was maintained in the presence of TRAM-34+ apamin (ACh Rmax; db/db 23±6%, linagliptin 60±6%, p<0.01), ie, when the endothelium-dependent relaxation was mediated by NO. There was no evidence for a contribution from K_Ca channel opening to responses under any conditions. Glimepiride had no effect on endothelium-dependent relaxation when given alone (ACh Rmax 38±3%). The addition of linagliptin or vildagliptin to glimepiride did not significantly improve endothelium-dependent relaxation. All treatments caused some decrease in aortic superoxide production but the effect of linagliptin was significantly greater than glimepiride (linagliptin 534±60 relative luminescence unit [RLU], glimepiride 1471±265 RLU, p<0.05).

CONCLUSION

Linagliptin is superior to glimepiride in regard to the preservation of endothelium-dependent relaxation in the presence of hyperglycemia and the improvement in endothelial function in response to linagliptin treatment is associated with greater antioxidant activity compared to glimepiride.

Dipeptidyl peptidase-4 inhibition protects the liver of insulin-resistant female rats against triglyceride accumulation by suppressing uric acid

Dipeptidyl peptidase-4 (DPP-4) inhibition has been shown to exert beneficial effects against insulin resistance (IR) and type 2 diabetes. Combined oral contraceptive (COC) treatment is associated with impaired glucose and lipid metabolism but the mechanisms are elusive. We therefore, hypothesized that DPP-4 inhibition ameliorates COC-induced glucose dysregulation and hepatic triglyceride (TG) accumulation through adenosine deaminase (ADA) /xanthine oxidase (XO) /uric acid-dependent pathway. Female Wistar rats received (po) vehicle and COC (1.0 μg ethinylestradiol plus 5.0 μg levonorgestrel; po) with or without DPP-4 inhibitor (sitagliptin; 100 mg/kg; po) for 8 weeks (n = 6/group). Glucose dysmetabolism was assessed by elevated fasting blood glucose, impaired oral glucose tolerance test and homeostatic model assessment of IR. Treatment with COC led to increased plasma fasting glucose, triglyceride-glucose index, 1-h postload glucose response, insulin, free fatty acid, IR and impaired glucose tolerance. COC treatment also resulted in increased plasma and hepatic TG, TG/HDL-cholesterol ratio, malondialdehyde, uric acid (plasma; 25.2 ± 0.6 mg/dl; hepatic 128.9 ± 8.0 mg/100 mg tissue), lactate dehydrogenase, DPP-4, ADA and XO (plasma;10.5 ± 1.1 U/L; hepatic 21.2 ± 1.4 U/g protein) activities. Likewise, COC led to reduction in nitric oxide level. However, DPP-4 inhibition significantly ameliorated these alterations induced by COC treatment through suppression of uric acid (plasma; 15.1 ± 1.0 mg/dl, hepatic; 75.6 ± 5.0 mg/100 mg tissue), XO (plasma; 4.1 ± 0.9 U/L, hepatic; 8.7 ± 0.4 U/g protein), ADA and DPP-4 activities suggesting their involvement in glucose dysregulation and hepatic TG accumulation induced by COC treatment. Therefore, DPP-4 inhibition would impact positively on cardiometabolic disorders, at least in part, through XO, ADA and uric acid suppression.

Efficacy of anagliptin as compared to linagliptin on metabolic parameters over 2 years of drug consumption: A retrospective cohort study

AIM

To evaluate the comparative effectiveness of anagliptin and linagliptin on the clinical parameters in patients with type 2 diabetes mellitus (T2DM).

METHODS

A 2-year retrospective cohort study was conducted in patients with T2DM who received anagliptin and linagliptin. We enrolled 234 patients (anagliptin group, 117 patients; linagliptin group, 117 patients).

RESULTS

The glycemic control considerably improved 3, 6, 12, and 24 mo after the administration of both dipeptidyl peptidase-4 (DPP-4) inhibitors. Following the administration of anagliptin, the diastolic blood pressure and serum total cholesterol levels decreased. However, serum high-density lipoprotein cholesterol levels increased and urinary albumin-creatinine ratio decreased following linagliptin administration. Furthermore, the liver function improved after the administration of linagliptin.

CONCLUSION

These findings suggest that that the efficacy of DPP-4 inhibitors on the blood pressure, lipid profile, and liver function differs between anagliptin and linagliptin.

p8 deficiency leads to elevated pancreatic beta cell mass but does not contribute to insulin resistance in mice fed with high-fat diet

BACKGROUND

p8 was initially described as being overexpressed in acute pancreatitis and encoding a ubiquitous stress protein. Analysis of insulin sensitivity and glucose tolerance in p8-knockout and haplodeficient mice revealed counterintuitive results. Thus, we determined glycemic control of p8 in mice fed with standard (SD) and high-fat diet (HFD).

METHODS

p8-/- and wild type (p8+/+) mice were used for analysis of glucagon (immunohistochemistry), insulin levels (ELISA) and beta cell mass. Hyperinsulinemic- euglycemic glucose clamp technique, i.p. glucose tolerance test (ipGTT), i.p. insulin tolerance test (ipITT) and metabolic chamber analysis were performed in SD (4% fat) and HFD (55% fat) groups.

RESULTS

p8-/- mice showed no differences in glucagon or insulin content but higher insulin secretion from pancreatic islets upon glucose stimulation. p8 deficiency resulted in elevated beta cell mass but was not associated with increased insulin resistance in ipGTT or ipITT. Glucose clamp tests also revealed no evidence of association of p8 deficiency with insulin resistance. Metabolic chamber analysis showed equal energy expenditure in p8-/- mice and wild type animals.

CONCLUSION

p8 depletion may contribute to glucose metabolism via stress-induced insulin production and elevated beta cell mass. Nevertheless, p8 knockout showed no impact on insulin resistance in SD and HFD-fed mice.

NAFLD and cardiovascular disease

Nonalcoholic fatty liver disease (NAFLD) is an important cause of chronic hepatic disease and liver transplant in Western societies. The increasing prevalence is related to dietary changes and sedentarism and follows the increasing frequency of obesity and type 2 diabetes mellitus.

Growing evidence of association of NAFLD with cardiovascular diseases (CVD), independent of cardiovascular risk factors, has prompted the clarification of whether the liver is mainly a key-effector or a target-organ of the metabolic disarrangements in the metabolic syndrome. The therapeutic strategies able to alter liver disease progression and, through this, reduce the cardiovascular risk have also been tested in the last 2 decades.

This review focus on the possible interactions between hepatic disease, metabolic syndrome, and CVD, and on their implications for clinical practice.

Effect of Linagliptin and Voglibose on metabolic profile in patients with Type 2 Diabetes: a randomized, double-blind, placebo-controlled trial

Background

Dipeptidyl peptidase 4 (DPP4) inhibitors improve glycemic control by promoting GLP1-mediated glucose-dependent insulin secretion and suppression of glucagon. Sitagliptin and vildagliptin have been shown to improve insulin sensitivity in patients with type 2 diabetes mellitus (T2DM). However, these patients had uncontrolled blood glucose at inclusion; therefore, the improvement in insulin sensitivity observed in these studies could be attributed to the drug per se and/or reduction in glucotoxicity. This study examines the effect of linagliptin on insulin sensitivity and β-cell function in patients with well-controlled T2DM.

Methods

Thirty patients with T2DM of duration ≤5 years, and having HbA1c < 7.5% were randomized to receive linagliptin, voglibose or placebo (n = 10 each), and were followed up for 6 months. Insulin sensitivity was assessed by hyperinsulinemic-euglycemic clamp, and insulin secretory response was measured by basal (M₀) and postprandial (M₁) β-cell function, and area under curve (AUC) for C-peptide during mixed meal tolerance test.

Results

The median HbA1c of the study subjects at inclusion was 6.9% and there was no significant difference among the groups in terms of age, duration of diabetes, body mass index (BMI), HbA1c, insulin sensitivity, AUC of C-peptide and M₀ and M₁ at baseline. At the end of the study, there was a modest reduction in HbA1c (− 0.2%) in the linagliptin group, and a significant decrease (− 0.8%) in the voglibose group, as compared to placebo (p = 0.038). However, there were no significant differences in insulin sensitivity, M₀ and M₁ and AUC of C-peptide, within, or among the groups.

Conclusion

Linagliptin modestly improves glycemic profile in patients with well controlled T2DM; however, it may not have an effect on insulin sensitivity in these patients.

Trial registration

Retrospectively Registered in Clinicaltrials.gov (ID number, NCT02097342). Registered: March 27, 2014.

Combination of APD668, a G protein-coupled receptor 119 agonist with linagliptin, a DPPIV inhibitor, prevents progression of steatohepatitis in a murine model of non-alcoholic steatohepatitis with diabetes

Non-alcoholic steatohepatitis (NASH) is characterized by the presence of hepatic steatosis, oxidative stress, inflammation, and hepatocyte injury with or without fibrosis. In this study, we explored the effect of APD668, a GPR119 agonist alone or in combination with linagliptin, a DPPIV inhibitor, on the progression of steatohepatitis in a murine model of NASH with diabetes. A novel NASH model with diabetes was generated by administration of streptozotocin injection to neonatal C57BL/6 mice (2-3 days old) combined with a high-fat diet feeding from the age of 4 weeks. The plasma biochemical parameters, oxidative stress, inflammation and histopathological changes were assessed. APD668 alone showed reduction in plasma glucose (- 39%, P < 0.05) and triglyceride level (- 26%) whereas a combined treatment of APD668 with linagliptin resulted in a more pronounced reduction in plasma glucose (- 52%, P < 0.001) and triglyceride (- 50%, P < 0.05) in NASH mice. In addition, co-administration of APD668 with linagliptin demonstrated a significant decrease in hepatic triglyceride, NAS score, hepatic TBARS and hepatic TNF-α in NASH mice with diabetes. These findings suggest that GPR119 receptor agonists in combination with DPPIV inhibitors may represent a promising therapeutic strategy for the treatment of NASH.

Vildagliptin Can Alleviate Endoplasmic Reticulum Stress in the Liver Induced by a High Fat Diet

Purpose. We investigated whether a DDP-4 inhibitor, vildagliptin, alleviated ER stress induced by a high fat diet and improved hepatic lipid deposition. Methods. C57BL/6 mice received standard chow diet (CD), high fat diet (HFD), and HFD administered with vildagliptin (50 mg/Kg) (V-HFD). After administration for 12 weeks, serum alanine aminotransferase, glucose, cholesterol, triglyceride, and insulin levels were analyzed. Samples of liver underwent histological examination and transmission electron microscopy, real-time PCR for gene expression levels, and western blots for protein expression levels. ER stress was induced in HepG2 cells with palmitic acid and the effects of vildagliptin were investigated. Results. HFD mice showed increased liver weight/body weight (20.27%) and liver triglycerides (314.75%) compared to CD mice, but these decreased by 9.27% and 21.83%, respectively, in V-HFD mice. In the liver, HFD induced the expression of ER stress indicators significantly, which were obviously decreased by vildagliptin. In vitro, the expressions of molecular indicators of ER stress were reduced in HepG2 when vildagliptin was administered. Conclusions. Vildagliptin alleviates hepatic ER stress in a mouse high fat diet model. In HepG2 cells, vildagliptin directly reduced ER stress. Therefore, vildagliptin may be a potential agent for nonalcoholic fatty liver disease.

Alogliptin alleviates hepatic steatosis in a mouse model of nonalcoholic fatty liver disease by promoting CPT1a expression via Thr172 phosphorylation of AMPKα in the liver

Pioglitazone (PIO) has been reported to be effective for nonalcoholic fatty liver disease (NAFLD) and alogliptin (ALO) may have efficacy against NAFLD progression in patients with type 2 diabetes mellitus (T2DM). The present study examined the effectiveness of ALO in a rodent model of NAFLD and diabetes mellitus. KK‑Ay mice were used to produce an NAFLD model via administration of a choline‑deficient (CD) diet. To examine the effects of alogliptin, KK‑Ay mice were provided with a CD diet with 0.03% ALO and/or 0.02% PIO orally for 8 weeks. Biochemical parameters, pathological alterations and hepatic mRNA levels associated with fatty acid metabolism were assessed. Severe hepatic steatosis was observed in KK‑Ay mice fed with a CD diet, which was alleviated by the administration of ALO and/or PIO. ALO administration increased the hepatic carnitine palmitoyltransferase 1a (CPT1a) mRNA expression level and enhanced the Thr172 phosphorylation of AMP‑activated protein kinase α (AMPKα) in the liver. PIO administration tended to decrease the hepatic fatty acid synthase mRNA expression level and increase the serum adiponectin level. Homeostasis model of assessment‑insulin resistance values tended to improve with ALO and PIO administration. ALO and PIO alleviated hepatic steatosis in KK‑Ay mice fed with a CD diet. ALO increased hepatic mRNA expression levels associated with fatty acid oxidation. In addition, the results of the present study suggested that ALO promotes CPT1a expression via Thr172 phosphorylation of AMPKα.

European contribution to the study of ROS: A summary of the findings and prospects for the future from the COST action BM1203 (EU-ROS)

The European Cooperation in Science and Technology (COST) provides an ideal framework to establish multi-disciplinary research networks. COST Action BM1203 (EU-ROS) represents a consortium of researchers from different disciplines who are dedicated to providing new insights and tools for better understanding redox biology and medicine and, in the long run, to finding new therapeutic strategies to target dysregulated redox processes in various diseases. This report highlights the major achievements of EU-ROS as well as research updates and new perspectives arising from its members. The EU-ROS consortium comprised more than 140 active members who worked together for four years on the topics briefly described below. The formation of reactive oxygen and nitrogen species (RONS) is an established hallmark of our aerobic environment and metabolism but RONS also act as messengers via redox regulation of essential cellular processes. The fact that many diseases have been found to be associated with oxidative stress established the theory of oxidative stress as a trigger of diseases that can be corrected by antioxidant therapy. However, while experimental studies support this thesis, clinical studies still generate controversial results, due to complex pathophysiology of oxidative stress in humans. For future improvement of antioxidant therapy and better understanding of redox-associated disease progression detailed knowledge on the sources and targets of RONS formation and discrimination of their detrimental or beneficial roles is required. In order to advance this important area of biology and medicine, highly synergistic approaches combining a variety of diverse and contrasting disciplines are needed.

Elevated hepatic DPP4 activity promotes insulin resistance and non-alcoholic fatty liver disease

OBJECTIVE

Increased hepatic expression of dipeptidyl peptidase 4 (DPP4) is associated with non-alcoholic fatty liver disease (NAFLD). Whether this is causative for the development of NAFLD is not yet clarified. Here we investigate the effect of hepatic DPP4 overexpression on the development of liver steatosis in a mouse model of diet-induced obesity.

METHODS

Plasma DPP4 activity of subjects with or without NAFLD was analyzed. Wild-type (WT) and liver-specific Dpp4 transgenic mice (Dpp4-Liv-Tg) were fed a high-fat diet and characterized for body weight, body composition, hepatic fat content and insulin sensitivity. In vitro experiments on HepG2 cells and primary mouse hepatocytes were conducted to validate cell autonomous effects of DPP4 on lipid storage and insulin sensitivity.

RESULTS

Subjects suffering from insulin resistance and NAFLD show an increased plasma DPP4 activity when compared to healthy controls. Analysis of Dpp4-Liv-Tg mice revealed elevated systemic DPP4 activity and diminished active GLP-1 levels. They furthermore show increased body weight, fat mass, adipose tissue inflammation, hepatic steatosis, liver damage and hypercholesterolemia. These effects were accompanied by increased expression of PPARγ and CD36 as well as severe insulin resistance in the liver. In agreement, treatment of HepG2 cells and primary hepatocytes with physiological concentrations of DPP4 resulted in impaired insulin sensitivity independent of lipid content.

CONCLUSIONS

Our results give evidence that elevated expression of DPP4 in the liver promotes NAFLD and insulin resistance. This is linked to reduced levels of active GLP-1, but also to auto- and paracrine effects of DPP4 on hepatic insulin signaling.

Dipeptidyl peptidase-4 (DPP-4) inhibition with linagliptin reduces western diet-induced myocardial TRAF3IP2 expression, inflammation and fibrosis in female mice

Background

Diastolic dysfunction (DD), a hallmark of obesity and primary defect in heart failure with preserved ejection fraction, is a predictor of future cardiovascular events. We previously reported that linagliptin, a dipeptidyl peptidase-4 inhibitor, improved DD in Zucker Obese rats, a genetic model of obesity and hypertension. Here we investigated the cardioprotective effects of linagliptin on development of DD in western diet (WD)-fed mice, a clinically relevant model of overnutrition and activation of the renin-angiotensin-aldosterone system.

Methods

Female C56Bl/6 J mice were fed an obesogenic WD high in fat and simple sugars, and supplemented or not with linagliptin for 16 weeks.

Results

WD induced oxidative stress, inflammation, upregulation of Angiotensin II type 1 receptor and mineralocorticoid receptor (MR) expression, interstitial fibrosis, ultrastructural abnormalities and DD. Linagliptin inhibited cardiac DPP-4 activity and prevented molecular impairments and associated functional and structural abnormalities. Further, WD upregulated the expression of TRAF3IP2, a cytoplasmic adapter molecule and a regulator of multiple inflammatory mediators. Linagliptin inhibited its expression, activation of its downstream signaling intermediates NF-κB, AP-1 and p38-MAPK, and induction of multiple inflammatory mediators and growth factors that are known to contribute to development and progression of hypertrophy, fibrosis and contractile dysfunction. Linagliptin also inhibited WD-induced collagens I and III expression. Supporting these in vivo observations, linagliptin inhibited aldosterone-mediated MR-dependent oxidative stress, upregulation of TRAF3IP2, proinflammatory cytokine, and growth factor expression, and collagen induction in cultured primary cardiac fibroblasts. More importantly, linagliptin inhibited aldosterone-induced fibroblast activation and migration.

Conclusions

Together, these in vivo and in vitro results suggest that inhibition of DPP-4 activity by linagliptin reverses WD-induced DD, possibly by targeting TRAF3IP2 expression and its downstream inflammatory signaling.

Hepatic DPP4 DNA Methylation Associates With Fatty Liver

Hepatic DPP4 expression is elevated in subjects with ectopic fat accumulation in the liver. However, whether increased dipeptidyl peptidase 4 (DPP4) is involved in the pathogenesis or is rather a consequence of metabolic disease is not known. We therefore studied the transcriptional regulation of hepatic Dpp4 in young mice prone to diet-induced obesity. Already at 6 weeks of age, expression of hepatic Dpp4 was increased in mice with high weight gain, independent of liver fat content. In the same animals, methylation of four intronic CpG sites was decreased, amplifying glucose-induced transcription of hepatic Dpp4 In older mice, hepatic triglyceride content was increased only in animals with elevated Dpp4 expression. Expression and release of DPP4 were markedly higher in the liver compared with adipose depots. Analysis of human liver biopsy specimens revealed a correlation of DPP4 expression and DNA methylation to stages of hepatosteatosis and nonalcoholic steatohepatitis. In summary, our results indicate a crucial role of the liver in participation to systemic DPP4 levels. Furthermore, the data show that glucose-induced expression of Dpp4 in the liver is facilitated by demethylation of the Dpp4 gene early in life. This might contribute to early deteriorations in hepatic function, which in turn result in metabolic disease such as hepatosteatosis later in life.

Prevention and treatment effect of evogliptin on hepatic steatosis in high-fat-fed animal models

Dipeptidyl peptidase 4 (DPP4) is an adipokine that interrupts insulin signaling. The resulting insulin resistance exacerbates hepatic steatosis. We previously reported that the novel DPP4 inhibitor evogliptin improves insulin resistance. This study aimed to verify the therapeutic potential of evogliptin for fatty liver. Evogliptin treatment was initiated simultaneously with a high-fat diet (HFD) feeding in normal mice and in a post-24 week HFD-fed rats. In a prevention study, insulin sensitivity was preserved in evogliptin-treated mice after a 16-week treatment. Overall plasma lipid levels stayed lower and hepatic lipid accumulation was drastically suppressed by evogliptin treatment. Evogliptin reduced hepatic expression of Srebf1, a key transcriptional factor for lipogenesis. Additionally, DPP4 inhibitor-treated mice showed less weight gain. In a treatment study, after evogliptin treatment for 14 weeks in pre-established HFD-fed obese rats, weight loss was marginal, while hepatic lipid accumulation and liver damage assessed by measuring plasma aminotransferase levels were completely resolved, suggesting weight loss-independent beneficial effects on fatty liver. Moreover, reduction in plasma non-esterified fatty acids supported the improvement of insulin resistance by evogliptin treatment. Conclusively, our findings suggest that evogliptin treatment ameliorates fatty liver by increasing insulin sensitivity and suppressing lipogenesis.

Linagliptin alleviates fatty liver disease in diabetic db/db mice

AIM

To study the effects of linagliptin on the structural signs of non-alcoholic fatty liver disease (NAFLD) in db/db mice.

METHODS

Male diabetic db/db mice (BKS.Cg-Dock7^m+/⁺Lepr^db/J) aged 10 wk received the dipeptidyl peptidase 4 (DPP4) inhibitor linagliptin (10 mg/kg) or saline as a placebo once per day by gavage for 8 wk. Intact db/db mice served as controls. Structural changes in the liver were analyzed from light and electron microscopic images of sections from intact, placebo-treated and linagliptin-treated animals. We estimated the changes in hepatocytes, sinusoidal cells, liver microvasculature and lymphatic roots. Hepatic staining for lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1) was assessed by immunohistochemistry.

RESULTS

In 18-wk-old diabetic mice, liver steatosis (predominantly microvesicular and mediovesicular steatosis) was accompanied by dilation of the roots of the lymphatic system, interlobular blood vessels and bile canaliculi. Compared to saline-treated mice, linagliptin-treated mice exhibited a reduction in the mean numeral densities of hepatocytes with lipid droplets (92.4% ± 1.7% vs 64.9% ± 5.8% per field of view, P = 0.0002) and a lower proportion of hepatocytes with a high density of lipid droplets (20.7% ± 3.6% vs 50.4% ± 3.1%, P = 0.0007). We observed heterogeneous hepatocytes and relatively preserved cell structures in the linagliptin group. Dilation of blood and lymphatic vessels, as well as ultrastructural changes in the hepatocyte endoplasmic reticulum and mitochondria, were alleviated by linagliptin treatment. In intact and placebo-treated mice, immunohistochemical staining for LYVE-1 was observed in the endothelial cells of interlobular lymphatic vessels and on the membranes of some endothelial sinusoidal cells. We observed an enlarged LYVE-1 reaction area in linagliptin-treated mice compared to intact and placebo-treated mice. The improvement in the structural parameters of the liver in linagliptin-treated mice was independent to changes in the plasma glucose levels.

CONCLUSION

The DPP4 inhibitor linagliptin alleviates liver steatosis and structural changes in the hepatic microvasculature and lymphatic roots in a model of NAFLD in diabetic db/db mice.

Effects of linagliptin monotherapy compared with voglibose on postprandial blood glucose responses in Japanese patients with type 2 diabetes: Linagliptin Study of Effects on Postprandial blood glucose (L-STEP)

AIMS

To compare the efficacy on glycemic parameters between a 12-week administration of once-daily linagliptin and thrice-daily voglibose in Japanese patients with type 2 diabetes.

METHODS

In a multi-center, randomized, parallel-group study, 382 patients with diabetes were randomized to the linagliptin group (n=192) or the voglibose group (n=190). A meal tolerance test was performed at weeks 0 and 12. Primary outcomes were the change from baseline to week 12 in serum glucose levels at 2h during the meal tolerance test, HbA1c levels, and serum fasting glucose levels, which were compared between the 2 groups.

RESULTS

Whereas changes in serum glucose levels at 2h during the meal tolerance test did not differ between the groups, the mean change in HbA1c levels from baseline to week 12 in the linagliptin group (-0.5±0.5% [-5.1±5.4mmol/mol]) was significantly larger than in the voglibose group (-0.2±0.5% [-2.7±5.4mmol/mol]). In addition, there was significant difference in changes in serum fasting glucose levels (-0.51±0.95mmol/L in the linagliptin group vs. -0.18±0.92mmol/L in the voglibose group, P<0.001). The incidences of hypoglycemia, serious adverse events (AEs), and discontinuations due to AEs were low and similar in both groups. However, gastrointestinal AEs were significantly lower in the linagliptin group (1.05% vs. 5.85%; P=0.01).

CONCLUSIONS

These data suggested that linagliptin monotherapy had a stronger glucose-lowering effect than voglibose monotherapy with respect to HbA1c and serum fasting glucose levels, but not serum glucose levels 2h after the start of the meal tolerance test.

Gemigliptin ameliorates Western-diet-induced metabolic syndrome in mice

Dipeptidyl peptidase 4 (DPP-4) inhibitors are widely used antihyperglycemic agents for type 2 diabetes mellitus. Recently, increasing attention has been focused on the pleiotropic actions of DPP-4 inhibitors. The aim of the present study was to examine whether gemigliptin, a recently developed DPP-4 inhibitor, could ameliorate features of metabolic syndrome. Mice were fed a Western diet (WD) for 12 weeks and were subsequently divided into 2 groups: mice fed a WD diet alone or mice fed a WD diet supplemented with gemigliptin for an additional 4 weeks. Gemigliptin treatment attenuated WD-induced body mass gain, hypercholesterolemia, adipocyte hypertrophy, and macrophage infiltration into adipose tissue, which were accompanied by an increased expression of uncoupling protein 1 in subcutaneous fat. These events contributed to improved insulin sensitivity, as assessed by the homeostasis model assessment of insulin resistance and intraperitoneal insulin tolerance test. Furthermore, gemigliptin reduced WD-induced hepatic triglyceride accumulation via inhibition of de novo lipogenesis and activation of fatty acid oxidation, which was accompanied by AMP-dependent protein kinase activation. Gemigliptin ameliorated WD-induced hepatic inflammation and fibrosis through suppression of oxidative stress. These results suggest that DPP-4 inhibitors may represent promising therapeutic agents for metabolic syndrome beyond their current role as antihyperglycemic agents.