Adipose dipeptidyl peptidase-4 and obesity: correlation with insulin resistance and depot-specific release from adipose tissue in vivo and in vitro

High DPP-4 Concentrations in Adolescents Are Associated With Low Intact GLP-1

CONTEXT

Dipeptidyl peptidase 4 (DPP-4) metabolizes glucagon-like peptide-1 (GLP-1), and increased DPP4 levels are associated with obesity and visceral adiposity in adults.

OBJECTIVE

Investigating DPP-4 levels in adolescents and their association with (1) circulating intact GLP-1 levels and glucose tolerance; (2) body mass index (BMI); and (3) visceral, subcutaneous, and liver fat compartments.

DESIGN

Cross-sectional study, July 2012 to April 2015.

SETTING

Pediatric obesity clinic, Uppsala University Hospital.

PATIENTS AND PARTICIPANTS

Children and adolescents with obesity (n = 59) and lean controls (n = 21) aged 8 to 18 years.

MAIN OUTCOME MEASURES

BMI SD score, fasting plasma concentrations of DPP-4, total and intact GLP-1, fasting and oral glucose tolerance test (OGTT) concentrations of glucose, and visceral adipose tissue (VAT) and subcutaneous adipose tissue volumes and liver fat fraction.

RESULTS

Plasma DPP-4 levels decreased with age in both obese (41 ng/mL per year) and lean subjects (48 ng/mL per year). Plasma DPP-4 levels were higher in males in both the obesity and lean groups. With adjustments for age and sex, plasma DPP-4 level was negatively associated with intact GLP-1 at fasting (β = -12.3; 95% CI: -22.9, -1.8) and during OGTT (β = -12.1; 95% CI: -22.5, -1.7). No associations were found between DPP-4 and plasma glucose levels measured at fasting or after a 2-hour OGTT. Plasma DPP-4 level was 19% higher in obese subjects. Among adipose tissue compartments, the strongest association was with VAT (β = 0.05; 95% CI: -0.02, 0.12).

CONCLUSIONS

In adolescents, high plasma DPP-4 concentrations were associated with low proportions of intact GLP-1, high BMI, young age, and male sex. The observed associations are compatible with increased metabolism of GLP-1 in childhood obesity.

Immunometabolic Regulation of Vascular Redox State: The Role of Adipose Tissue

SIGNIFICANCE

Vascular oxidative stress plays a crucial role in atherogenesis and cardiovascular disease (CVD). Recent evidence suggests that vascular redox state is under the control of complex pathophysiological mechanisms, ranging from inflammation to obesity and insulin resistance (IR). Recent Advances: Adipose tissue (AT) is now recognized as a dynamic endocrine and paracrine organ that secretes several bioactive molecules, called adipokines. AT has recently been shown to regulate vascular redox state in both an endocrine and a paracrine manner through the secretion of adipokines, therefore providing a mechanistic link for the association between obesity, IR, inflammation, and vascular disease. Importantly, AT behaves as a sensor of cardiovascular oxidative stress, modifying its secretory profile in response to cardiovascular oxidative injury.

CRITICAL ISSUES

The present article presents an up-to-date review of the association between AT and vascular oxidative stress. We focus on the effects of individual adipokines on modulating reactive oxygen species production and scavenging in the vascular wall. In addition, we highlight how inflammation, obesity, and IR alter the biology and secretome of AT leading to a more pro-oxidant phenotype with a particular focus on the local regulatory mechanisms of perivascular AT driven by vascular oxidation.

FUTURE DIRECTIONS

The complex and dynamic biology of AT, as well as its importance in the regulation of vascular redox state, provides numerous opportunities for the development of novel, targeted treatments in the management of CVD. Therapeutic modulation of AT biology could improve vascular redox state affecting vascular disease pathogenesis. Antioxid. Redox Signal. 29, 313-336.

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

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

Practical strategies for improving outcomes in T2DM: The potential role of pioglitazone and DPP4 inhibitors

T2DM is a complex disease underlined by multiple pathogenic defects responsible for the development and progression of hyperglycaemia. Each of these factors can now be tackled in a more targeted manner thanks to glucose-lowering drugs that have been made available in the past 2 to 3 decades. Recognition of the multiplicity of the mechanisms underlying hyperglycaemia calls for treatments that address more than 1 of these mechanisms, with more emphasis placed on the earlier use of combination therapies. Although chronic hyperglycaemia contributes to and amplifies cardiovascular risk, several trials have failed to show a marked effect from intensive glycaemic control. During the past 10 years, the effect of specific glucose-lowering agents on cardiovascular risk has been explored with dedicated trials. Overall, the cardiovascular safety of the new glucose-lowering agents has been proven with some of the trials summarized in this review, showing significant reduction of cardiovascular risk. Against this background, pioglitazone, in addition to exerting a sustained glucose-lowering effect, also has ancillary metabolic actions of potential interest in addressing the cardiovascular risk of T2DM, such as preservation of beta-cell mass and function. As such, it seems a logical agent to combine with other oral anti-hyperglycaemic agents, including dipeptidyl peptidase-4 inhibitors (DPP4i). DPP4i, which may also have a potential to preserve beta-cell function, is available as a fixed-dose combination with pioglitazone, and could, potentially, attenuate some of the side effects of pioglitazone, particularly if a lower dose of the thiazolidinedione is used. This review critically discusses the potential for early combination of pioglitazone and DPP4i.

DPPIV promotes endometrial carcinoma cell proliferation, invasion and tumorigenesis

Dipeptidyl peptidase IV (DPPIV), also known as CD26, is a 110-kDa cell surface glycoprotein expressed in various tissues. DPPIV reportedly plays a direct role in the progression of several human malignancies. DPPIV specific inhibitors are employed as antidiabetics and could potentially be repurposed to enhance anti-tumor immunotherapies. In the present study, we investigated the correlation between DPPIV expression and tumor progression in endometrial carcinoma (EC). DPPIV overexpression altered cell morphology and stimulated cell proliferation, invasion and tumorigenesis in vitro and in vivo. These effects were abrogated by DPPIV knockdown or pharmacological inhibition using sitagliptin. DPPIV overexpression increased hypoxia-inducible factor 1a (HIF-1a) and vascular endothelial growth factor A (VEGFA) expression to promote HIF-1a-VEGFA signaling. Our results indicated that DPPIV accelerated endometrial carcinoma progression and that sitagliptin may be an effective anti-EC therapeutic.

Tissue expression of DPP-IV in obesity-diabetes and modulatory effects on peptide regulation of insulin secretion

Dipeptidyl peptidase type 4 (DPP-4) inhibitors represent an important class of glucose-lowering drug for type 2 diabetes. DPP-4 enzyme activity has been observed to be significantly altered in type 2 diabetes. Here, the role of DPP-4 was examined in a high fat fed (HFF) mouse model of insulin resistance. HFF mice had an increased bodyweight (p < .01), were hyperglycaemic (p < .01) and hyperinsulinaemic (p < .05). Compared to normal diet, HFF mice exhibited increased plasma DPP-4 activity (p < .01). Tissue distribution patterns in lean and HFF mice demonstrated highest levels of DPP-4 activity in lung (20-26 μmol/min/mg protein) and small intestine (13-14 μmol/min/mg protein), and lowest activity in the spleen (3.8 μmol/min/mg protein). Modulation of DPP-4 activity by high fat feeding was observed in several tissues with increases in the lung (p < .05), liver (p < .05), kidney (p < .05) and pancreas (p < .05). With a high fat diet, DPP-4 gene expression was upregulated in the liver (p < .001) and downregulated in the pancreas (p < 0.001) and small intestine (p < .001). Immunohistochemical analysis revealed increased DPP-4 immunostaining localised primarily in the pancreatic islets of HFF mice (p < .01) with no change in islet GLP-1 expression. Treatment of HFF mice with metformin for 21-days resulted in inhibition of circulating DPP-4 activity (p < .05), decreased blood glucose (p < .05) and increased GLP-1 gene expression (p < .001). These data indicate that DPP-4 is modulated in a tissue specific manner and is dependent on physiological conditions such as hyperglycaemia and insulin resistance, suggesting a significant role in disorders such as diabetes.

Dipeptidyl peptidase inhibitor therapy in type 2 diabetes: Control of the incretin axis and regulation of postprandial glucose and lipid metabolism

Dipeptidyl peptidase 4 (DPP4) is a widely expressed, serine protease which regulates the bioactivity of many peptides through cleavage and inactivation including the incretin hormones, glucagon like peptide -1 (GLP-1) and glucose dependent insulinotropic polypeptide (GIP). Inhibitors of DPP4 are used therapeutically to treat patients with Type 2 Diabetes Mellitus (T2DM) as they potentiate incretin action to regulate islet hormone secretion and improve glycemia and post-prandial lipid excursions. The widespread clinical use of DPP4 inhibitors has increased interest in the molecular mechanisms by which these drugs mediate their beneficial effects. Traditionally, focus has remained on inhibiting the catalytic activity of DPP4 within the plasma compartment, however evidence is emerging on the importance of inactivation of membrane-bound DPP4 in selective tissue beds to potentiate local hormone gradients. Here we review the recent advances in identifying the cellular sources of both circulating and membrane-bound DPP4 important for cleavage of the incretin hormones and regulation of glucose and lipoprotein metabolism.

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.

Inhibition of dipeptidyl peptidase-4 ameliorates cardiac ischemia and systolic dysfunction by up-regulating the FGF-2/EGR-1 pathway

Dipeptidyl peptidase 4 inhibitors are used worldwide in the management of diabetes, but their role in the prevention or treatment of cardiovascular disorders has yet to be defined. We found that linagliptin, a DPP-4 inhibitor, suppressed capillary rarefaction in the hearts of mice with dietary obesity. Metabolomic analysis performed with capillary electrophoresis/mass spectrometry (LC-MS/MS) showed that linagliptin promoted favorable metabolic remodeling in cardiac tissue, which was characterized by high levels of citrulline and creatine. DNA microarray analysis revealed that the cardiac tissue level of early growth response protein 1 (EGR-1), which activates angiogenesis, was significantly reduced in untreated mice with dietary obesity, while this decrease was inhibited by administration of linagliptin. Mature fibroblast growth factor 2 (FGF-2) has a putative truncation site for DPP-4 at the NH2-terminal, and LC-MS/MS showed that recombinant DPP-4 protein cleaved the NH2-terminal dipeptides of mature FGF-2. Incubation of cultured neonatal rat cardiomyocytes with FGF-2 increased Egr1 expression, while it was suppressed by recombinant DPP-4 protein. Furthermore, vascular endothelial growth factor-A had a critical role in mediating FGF-2/EGR-1 signaling. In conclusion, pharmacological inhibition of DPP-4 suppressed capillary rarefaction and contributed to favorable remodeling of cardiac metabolism in mice with dietary obesity.

GLP-1 signalling compensates for impaired insulin signalling in regulating beta cell proliferation in βIRKO mice

AIMS/HYPOTHESIS

We aimed to investigate potential interactions between insulin and glucagon-like peptide (GLP)-1 signalling pathways in the regulation of beta cell-cycle dynamics in vivo, in the context of the therapeutic potential of GLP-1 to modulate impaired beta cell function.

METHODS

Beta cell-specific insulin receptor knockout (βIRKO) mice, which exhibit beta cell dysfunction and an age-dependent decrease in beta cell mass, were treated with the dipeptidyl peptidase-4 inhibitor vildagliptin. Following this, glucose homeostasis and beta cell proliferation were evaluated and underlying molecular mechanisms were investigated.

RESULTS

The sustained elevation in circulating GLP-1 levels, caused by treatment of the knockout mice with vildagliptin for 6 weeks, significantly improved glucose tolerance secondary to enhanced insulin secretion and proliferation of beta cells. Treating βIRKO beta cell lines with the GLP-1 analogue, exendin-4, promoted Akt phosphorylation and protein expression of cyclins A, D1 and E two- to threefold, in addition to cyclin D2. Pancreases from the vildagliptin-treated βIRKO mice exhibited increased cyclin D1 expression, while cyclin D2 expression was impaired.

CONCLUSIONS/INTERPRETATION

Activation of GLP-1 signalling compensates for impaired growth factor (insulin) signalling and enhances expression of cyclins to promote beta cell proliferation. Together, these data indicate the potential of GLP-1-related therapies to enhance beta cell proliferation and promote beneficial outcomes in models with dysfunctional beta cells.

Hypertension and Type 2 Diabetes Are Associated With Decreased Inhibition of Dipeptidyl Peptidase-4 by Sitagliptin

Context

Patients with diabetes often have comorbidities such as hypertension. It is not known how individual characteristics influence response to dipeptidyl peptidase-4 (DPP4) inhibitors.

Objective

We tested the hypothesis that individual characteristics, sitagliptin dose, and genetic variability in DPP4 influence DPP4 activity during sitagliptin.

Design and Setting

Post hoc analysis of clinical and laboratory data from individuals randomized to sitagliptin versus placebo in crossover studies.

Patients and Interventions

Sixty-five subjects [27 with type 2 diabetes mellitus (T2DM) and hypertension, 38 healthy controls] were randomized to 100 mg/d sitagliptin or 200 mg sitagliptin and matching placebo in double-blind, crossover fashion. Fasting blood was obtained at baseline and 60 to 180 minutes after sitagliptin or placebo.

Main Outcome Measures

DPP4 activity and antigen during placebo and sitagliptin and DPP4 inhibition during sitagliptin.

Results

Sitagliptin 100 mg/d was less effective at inhibiting DPP4 activity in individuals with T2DM and hypertension than in healthy controls (P = 0.001, percent inhibition). In healthy controls, 100 mg/d sitagliptin was not as effective as single-dose 200 mg sitagliptin (P = 0.001, percent inhibition). DPP4 genotypes rs2909451 TT (P = 0.02) and rs759717 CC (P = 0.02) were associated with DPP4 activity during sitagliptin. In multivariable analyses, T2DM with hypertension, sitagliptin dose, age, systolic blood pressure, DPP4 activity during placebo, and rs2909451 genotype were significantly associated with DPP4 activity during sitagliptin.

Conclusions

Sitagliptin is less effective in inhibiting DPP4 in individuals with T2DM and hypertension than in healthy controls. Higher doses of DPP4 inhibitors may be required in patients with the metabolic syndrome.

Immune regulation of glucose and lipid metabolism

The immune response and metabolic regulation are highly integrated, and their interface maintains a homeostatic system. Their dysfunction can cause obesity and its comorbidities, including insulin resistance, type 2 diabetes, and nonalcoholic fatty liver disease (NAFLD). Endoplasmic reticulum (ER) stress is a central abnormality linking obesity, insulin resistance, and NAFLD. ER stress in response to increased hepatic lipids may decrease the ability of the liver to secrete triglyceride by limiting apolipoprotein B secretion, thereby worsening fatty liver. Overnutrition or obesity activates the innate immune system, with the subsequent recruitment of immune cells that contributes to the development of insulin resistance. A significant advance in our understanding of obesity-induced inflammation and insulin resistance has been a recognition of the critical role of adipose tissue macrophages. A role for chemokines, small proteins that direct the trafficking of immune cells to sites of inflammation, has also been demonstrated. Chemokines activate the production of inflammatory cytokines through specific chemokine receptors. This review highlights the chemokine systems linking obesity to inflammation and insulin resistance. Treatment options that target immune cells with the aim of halting the development of insulin resistance and type 2 diabetes remain limited. DPP-4 inhibitors or micronutrients may contribute to the immune regulation of glucose and lipid metabolism by regulating macrophage polarization, thereby reducing insulin resistance and preventing the progression of NAFLD. A detailed understanding of the immune regulation of glucose and lipid homeostasis can lead to the development of a novel therapy for insulin resistance, type 2 diabetes, and NAFLD.

ZY15557, a novel, long acting inhibitor of dipeptidyl peptidase-4, for the treatment of Type 2 diabetes mellitus

BACKGROUND AND PURPOSE

Dipeptidyl peptidase (DPP)-4 inhibitors increase levels of glucagon-like peptide-1 (GLP-1) and provide clinical benefit in the treatment of type 2 diabetes mellitus. As longer acting inhibitors have therapeutic advantages, we developed a novel DPP-4 inhibitor, ZY15557, that has a sustained action and long half-life.

EXPERIMENTAL APPROACH

We studied the potency, selectivity, efficacy and duration of action of ZY15557, in vitro, with assays of DPP-4 activity. In vivo, the pharmacodymamics and pharmacokinetics of ZY15557 were studied, using db/db mice and Zucker fatty rats, along with normal mice, rats, dogs and non-human primates.

KEY RESULTS

ZY15557 is a potent, competitive and long acting inhibitor of DPP-4 (Ki 5.53 nM; Koff 3.2 × 10-4 ·s-1 , half-life 35.8 min). ZY15557 treatment inhibited DPP-4 activity, and enhanced active GLP-1 and insulin in mice and rats, providing dose-dependent anti-hyperglycaemic effects. Anti-hyperglycaemic effects were also observed in db/db mice and Zucker fatty rats. Following oral dosing, ZY15557 significantly inhibited plasma DPP-4 activity, determined ex vivo, in mice and rats for more than 48 h, and for up to 168 h in dogs and non-human primates. Allometric scaling predicts a half-life for ZY15557 in humans of up to 60 h.

CONCLUSIONS AND IMPLICATIONS

ZY15557 is a potent, competitive and long acting DPP-4 inhibitor. ZY15557 showed similar DPP-4 inhibition across different species. ZY15557 showed excellent oral bioavailability in preclinical species. It showed a low plasma clearance (CL) and large volume of distribution (Vss ) across species, resulting in an extended half-life.

Adipose tissue supports normalization of macrophage and liver lipid handling in obesity reversal

Adipose tissue inflammation and dysfunction are considered central in the pathogenesis of obesity-related dysmetabolism, but their role in the rapid metabolic recovery upon obesity reversal is less well defined. We hypothesized that changes in adipose tissue endocrine and paracrine mechanisms may support the rapid improvement of obesity-induced impairment in cellular lipid handling. C57Bl-6J mice were fed ad libitum either normal chow (NC) or high-fat diet (HFF) for 10 weeks. A dietary obesity reversal group was fed HFF for 8 weeks and then switched to NC for 2 weeks (HFF→NC). Whole-body glucose homeostasis rapidly nearly normalized in the HFF→NC mice (fasting glucose and insulin fully normalized, glucose and insulin tolerance tests reversed 82% to the NC group levels). During 2 weeks of the dietary reversal, the liver was significantly cleared from ectopic fat, and functionally, glucose production from pyruvate, alanine or fructose was normalized. In contrast, adipose tissue inflammation (macrophage infiltration and polarization) largely remained as in HFF, though obesity-induced adipose tissue macrophage lipid accumulation decreased by ~50%, and adipose tissue MAP kinase hyperactivation was reversed. Ex vivo, mild changes in adipose tissue adipocytokine secretion profile were noted. These corresponded to partial or full reversal of the excess cellular lipid droplet accumulation induced by HFF adipose tissue conditioned media in hepatoma or macrophage cells, respectively. We propose that early after initiating reversal of nutritional obesity, rapid metabolic normalization largely precedes resolution of adipose tissue inflammation. Nevertheless, we demonstrate a hitherto unrecognized contribution of adipose tissue to the rapid improvement in lipid handling by the liver and by macrophages.

Sitagliptin down-regulates retinol-binding protein 4 and reduces insulin resistance in gestational diabetes mellitus: a randomized and double-blind trial

Gestational diabetes mellitus (GDM) is a condition that affects increasing number of pregnant women worldwide. Sitagliptin was reported to alleviate symptoms of type 2 diabetes mellitus by reducing serum levels of retinol-binding protein 4 (RBP-4). We investigated the effectiveness of sitagliptin on insulin sensitivity parameters in GDM patients. Pregnant GDM women in the 2nd trimester were recruited for this study. Participants were then assigned randomly to sitagliptin treatment group or placebo treatment group, and administered sitagliptin or placebo daily for 16 weeks. Glucose and insulin profiles, as well as serum RBP-4 level, were measured at both baseline and end of the study. After 16 weeks of treatment, participants in the STL group exhibited significantly improved levels of fasting plasma glucose and serum insulin, homeostasis model of assessment of β cell function (HOMA-β) and insulin resistance (HOMA-IR), compared with those in the placebo group. Serum levels of RBP-4 were also markedly decreased in the sitagliptin treatment group, and more importantly it was positively correlated with improved insulin resistance parameters. Our study supports a potentially promising role of sitagliptin in improving insulin resistance by decreasing RBP-4 in GDM-affected women.

Maresin 1 improves insulin sensitivity and attenuates adipose tissue inflammation in ob/ob and diet-induced obese mice

The beneficial actions of n-3 fatty acids on obesity-induced insulin resistance and inflammation have been related to the synthesis of specialized proresolving lipid mediators (SPMs) like resolvins. The aim of this study was to evaluate the ability of one of these SPMs, maresin 1 (MaR1), to reverse adipose tissue inflammation and/or insulin resistance in two models of obesity: diet-induced obese (DIO) mice and genetic (ob/ob) obese mice. In DIO mice, MaR1 (2 μg/kg; 10 d) reduced F4/80-positive cells and expression of the proinflammatory M1 macrophage phenotype marker Cd11c in white adipose tissue (WAT). Moreover, MaR1 decreased Mcp-1, Tnf-α, and Il-1β expression, upregulated adiponectin and Glut-4, and increased Akt phosphorylation in WAT. MaR1 administration (2 μg/kg; 20 d) to ob/ob mice did not modify macrophage recruitment but increased the M2 macrophage markers Cd163 and Il-10. MaR1 reduced Mcp-1, Tnf-α, Il-1β, and Dpp-4 and increased adiponectin gene expression in WAT. MaR1 treatment also improved the insulin tolerance test of ob/ob mice and increased Akt and AMPK phosphorylation in WAT. These data suggest that treatment with MaR1 can counteract the dysfunctional inflamed WAT and could be useful to improve insulin sensitivity in murine models of obesity.-Martínez-Fernández, L., González-Muniesa, P., Laiglesia, L. M., Sáinz, N., Prieto-Hontoria, P. L., Escoté, X., Odriozola, L., Corrales, F. J., Arbones-Mainar, J. M., Martínez, J. A., Moreno-Aliaga, M. J. Maresin 1 improves insulin sensitivity and attenuates adipose tissue inflammation in ob/ob and diet-induced obese mice.

Altered circulating concentrations of active glucagon-like peptide (GLP-1) and dipeptidyl peptidase 4 (DPP4) in obese subjects and their association with insulin resistance

OBJECTIVES

Soluble DPP4 (sDPP4) is a novel adipokine that degrades glucagon-like peptide (GLP-1). We evaluated the fasting serum levels of active GLP-1 and sDPP4 in obese, overweight and normal weight subjects to assess the association between sDPP4 levels, active GLP-1 levels and insulin resistance in obese subjects.

METHODS

The study involved 235 Malaysian subjects who were randomly selected (66 normal weight subjects, 97 overweight, 59 obese subjects, and 13 subjects who were underweight). Serum sDPP4 and active GLP-1 levels were examined by enzyme-linked immunosorbent assay (ELISA). Also, body mass index kg/m² (BMI), lipid profiles, insulin and glucose levels were evaluated. Insulin resistance (IR) was estimated via the homeostasis model assessment for insulin resistance (HOMA-IR).

RESULTS

Serum sDPP4 levels were significantly higher in obese subjects compared to normal weight subjects (p=0.034), whereas serum levels of active GLP-1 were lower (p=0.021). In obese subjects, sDPP4 levels correlated negatively with active GLP-1 levels (r²=-0.326, p=0.015). Furthermore, linear regression showed that sDPP4 levels were positively associated with insulin resistance (B=82.28, p=0.023) in obese subjects.

CONCLUSION

Elevated serum sDPP4 levels and reduced GLP-1 levels were observed in obese subjects. In addition, sDPP4 levels correlated negatively with active GLP-1 levels but was positively associated with insulin resistance. This finding provides evidence that sDPP4 and GLP-1 may play an important role in the pathogenesis of obesity, suggesting that sDPP4 may be valuable as an early marker for the augmented risk of obesity and insulin resistance.

Adipokines: Potential Therapeutic Targets for Vascular Dysfunction in Type II Diabetes Mellitus and Obesity

Adipokines are bioactive molecules that regulate several physiological functions such as energy balance, insulin sensitization, appetite regulation, inflammatory response, and vascular homeostasis. They include proinflammatory cytokines such as adipocyte fatty acid binding protein (A-FABP) and anti-inflammatory cytokines such as adiponectin, as well as vasodilator and vasoconstrictor molecules. In obesity and type II diabetes mellitus (DM), insulin resistance causes impairment of the endocrine function of the perivascular adipose tissue, an imbalance in the secretion of vasoconstrictor and vasodilator molecules, and an increased production of reactive oxygen species. Recent studies have shown that targeting plasma levels of adipokines or the expression of their receptors can increase insulin sensitivity, improve vascular function, and reduce the risk of cardiovascular morbidity and mortality. Several reviews have discussed the potential of adipokines as therapeutic targets for type II DM and obesity; however, this review is the first to focus on their therapeutic potential for vascular dysfunction in type II DM and obesity.

Hepatic Dipeptidyl Peptidase-4 Controls Pharmacokinetics of Vildagliptin In Vivo

The main route of elimination of vildagliptin, which is an inhibitor of dipeptidyl peptidase-4 (DPP-4), in humans is cyano group hydrolysis to produce a carboxylic acid metabolite M20.7. Our in vitro study previously demonstrated that DPP-4 itself greatly contributed to the hydrolysis of vildagliptin in mouse, rat, and human livers. To investigate whether hepatic DPP-4 contributes to the hydrolysis of vildagliptin in vivo, in the present study, we conducted in vivo pharmacokinetics studies of vildagliptin in mice coadministered with vildagliptin and sitagliptin, which is another DPP-4 inhibitor, and also in streptozotocin (STZ)-induced diabetic mice. The area under the plasma concentration-time curve (AUC) value of M20.7 in mice coadministered with vildagliptin and sitagliptin was significantly lower than that in mice administered vildagliptin alone (P < 0.01). Although plasma DPP-4 expression level was increased 1.9-fold, hepatic DPP-4 activity was decreased in STZ-induced diabetic mice. The AUC values of M20.7 in STZ-induced diabetic mice were lower than those in control mice (P < 0.01). Additionally, the AUC values of M20.7 significantly positively correlated with hepatic DPP-4 activities in the individual mice (Rs = 0.943, P < 0.05). These findings indicated that DPP-4 greatly contributed to the hydrolysis of vildagliptin in vivo and that not plasma, but hepatic DPP-4 controlled pharmacokinetics of vildagliptin. Furthermore, enzyme assays of 23 individual human liver samples showed that there was a 3.6-fold interindividual variability in vildagliptin-hydrolyzing activities. Predetermination of the interindividual variability of hepatic vildagliptin-hydrolyzing activity might be useful for the prediction of blood vildagliptin concentrations in vivo.

Dipeptidyl peptidase-4 levels are increased and partially related to body fat distribution in patients with familial partial lipodystrophy type 2

BACKGROUND

Dipeptidyl peptidase-4 (DDP4) is an enzyme responsible for glucagon-like peptide-1 inactivation and plays an important role in glucose metabolism.

OBJECTIVE

The aim of this study was to evaluate DPP4 levels in patients with familial partial lipodystrophy type 2 (FPLD2) and correlate it with body fat distribution.

METHODS

Fourteen patients with FPLD2 were selected to participate in this study and matched to a healthy control group (n = 8). All participants had anthropometrical data registered. Body adiposity index (BAI) was used to evaluate fat distribution in this population. Body fat content and distribution were analyzed by dual X-ray absorptiometry (DXA). Biochemical exams, including DPP4 levels, were performed in all individuals.

RESULTS

Despite the same body mass index, lipodystrophic patients had a significant lower hip (median 92.0 vs 94.5; p = 0.028), HDL cholesterol (42.6 ± 10.4 vs 66.1 ± 16.0; p < 0.01) and BAI (24.1 ± 2.8 vs 29.0 ± 3.7; p = 0.02), suggesting that BAI was able to catch differences in fat distribution between groups. On the other hand, patients with FPLD2 presented significant higher levels of insulin (median 11.2 vs 5.3; p = 0.015), triglycerides (184.9 ± 75.4 vs 89.1 ± 51.0; p < 0.01) and DPP4 (4.89 ± 0.92 vs 3.93 ± 1.08; p = 0.04). A trend toward an inverse statistical significance was observed between DPP4 levels and BAI (r = -0.38; p = 0.072). In the lipodistrophic group, a significant correlation was found between DPP4 levels and percentage of total body fat (r = 0.86; p = 0.0025) and android fat (r = 0.78; p = 0.014).

CONCLUSIONS

Patients with FPLD2 exhibit an increase in DDP4 levels in comparison to a healthy control group. The increase in the levels of this enzyme does not seem to be related to the diagnosis of diabetes and might be associated with an increase in central fat (estimated using BAI and measured using DXA). These results might be used to reinforce the concept that DDP4 is an adipokine related to central fat distribution.

High circulating plasma dipeptidyl peptidase- 4 levels in non-obese Asian Indians with type 2 diabetes correlate with fasting insulin and LDL-C levels, triceps skinfolds, total intra-abdominal adipose tissue volume and presence of diabetes: a case-control study

AIM

To evaluate circulating plasma dipeptidyl peptidase-4 (DPP4) levels in non-obese Asian Indians with type 2 diabetes mellitus (T2DM), and to correlate these with metabolic profile and measures of anthropometry, skinfolds, abdominal adipose tissue depots, pancreatic volume, and liver span.

METHODOLOGY

Non-obese (body mass index (BMI) <25 kg/m²) patients with T2DM (cases, n=93), diagnosed within 1 year from recruitment, on metformin therapy and BMI-matched, and non-diabetic subjects (controls, n=40) were compared. Measurements of blood glucose, glycosylated hemoglobin, plasma insulin levels, lipid profile, hepatic transaminases and plasma DPP4 levels, and quantification of abdominal fat depots, pancreatic volume and liver span (MRI scan), were done.

RESULTS

Significantly higher (p<0.001) circulating plasma DPP4 levels were observed in cases as compared to controls. Specifically, in patients with T2DM with non-alcoholic fatty liver disease (NAFLD) (n=48), the mean plasma DPP4 level (52.6±27.8 ng/mL) was significantly higher (p<0.05) as compared with those without NAFLD (n=43; 47±28.3 ng/mL). Significant positive correlation was observed for circulating plasma DPP4 levels with waist-to-hip ratio, total intra-abdominal adipose volume, and liver span. Fasting serum insulin, low-density lipoprotein cholesterol (LDL-C), triceps skinfolds, total intra-abdominal adipose tissue volume and presence of T2DM were significant determinants of circulating plasma DPP4 levels.

CONCLUSION

Non-obese Asian Indian patients with T2DM and on metformin therapy have significantly higher circulating plasma DPP4 levels as compared to non-obese non-diabetic controls, and these levels correlate with fasting insulin and LDL-C levels, upper limb subcutaneous adipose tissue, intra-abdominal adiposity and presence of diabetes.

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.

Impact of fibroblast growth factor 21 on the secretome of human perivascular preadipocytes and adipocytes: a targeted proteomics approach

CONTEXT

Perivascular adipose tissue (PVAT) is suggested to impact on vascular cells via humoral factors, possibly contributing to endothelial dysfunction and atherosclerosis.

OBJECTIVE

To address whether the hepatokine fibroblast growth factor (FGF) 21 affects the PVAT secretome.

METHODS

Human perivascular (pre)adipocytes were subjected to targeted proteomics and whole-genome gene expression analysis.

RESULTS

Preadipocytes, as compared to adipocytes, secreted higher amounts of inflammatory cytokines and chemokines. Adipocytes released higher amounts of adipokines [e.g. adipisin, visfatin, dipeptidyl peptidase 4 (DPP4), leptin; p < 0.05, all]. In preadipocytes, omentin 1 release was 1.28-fold increased by FGF-21 (p < 0.05). In adipocytes, FGF-21 reduced chemerin release by 5% and enhanced DPP4 release by 1.15-fold (p < 0.05, both). FGF-21 altered the expression of four secretory genes in preadipocytes and of 18 in adipocytes (p < 0.01, all).

CONCLUSION

The hepatokine FGF-21 exerts secretome-modulating effects in human perivascular (pre)adipocytes establishing a new liver-PVAT-blood vessel axis that possibly contributes to vascular inflammation and atherosclerosis.

A potential contribution of dipeptidyl peptidase-4 by the mediation of monocyte differentiation in the development and progression of abdominal aortic aneurysms

OBJECTIVE

Abdominal aortic aneurysms (AAAs) are characterized by the destruction of elastin and collagen in the media and adventitia. Dipeptidyl peptidase-4 (DPP-4, an adipokine known as CD26) influences cell signaling, cell-matrix interactions, and the regulation of the functional activity of incretins in metabolic and inflammatory disorders. Although the role of DPP-4 in AAA evolution has been demonstrated, the underlying mechanisms of DPP-4-regulated AAA development remains unknown.

METHODS

Patients with AAA (n = 93) and healthy controls (CTL, n = 20) were recruited. Based on computed tomography image analyses, 93 patients were divided into two groups: those with a small AAA (SAA, aortic diameter <5 cm, n = 16) and those with a large AAA (LAA, aortic diameter ≥5 cm, n = 77). Plasma DPP-4, glucagon-like peptide-1 levels, and expression of CD26 on mononuclear cells were analyzed. In addition, phorbol 12-myristate 13-acetate (PMA)-induced THP-1 cells and angiotensin II-infused apolipoprotein E^tmlUnc mice were used to explore the underlying mechanisms.

RESULTS

The levels of DPP-4 (μU/μg) increased while active glucagon-like peptide-1 (pM) decreased in patients with AAA in a diameter-dependent manner [CTL: 2.3 ± 1.5 and 3.7 ± 2.4, respectively; SAA: 10.0 ± 10.9 and 2.1 ± 0.9, respectively; LAA: 32.2 ± 15.0 and 1.8 ± 1.1, respectively]. A significant decline in monocyte CD26 expression in patients with AAAs was observed relative to the CTL group. In vitro studies demonstrated that the inhibition of DPP-4 promoted PMA-induced monocytic cells differentiation, with increased CD68 and p21 expression, regulated by extracellular signal-regulated protein kinase 1/2 activation. Furthermore, inhibition of DPP-4 significantly increased the phosphorylation of PYK2 and paxillin in PMA-induced THP-1 cell differentiation. Finally, the animal study was used to confirm the in vitro results that LAA mice showed marked macrophage infiltration in the adventitia with a decreased expression of DPP-4 as compared with SAA mice.

CONCLUSIONS

Increased plasma DPP-4 activity may correlate with aneurysmal development. CD26 on monocytes plays a critical role in cell differentiation, possibly mediated by extracellular signal-regulated protein kinase 1/2-p21 axis signaling pathways and cytoskeletal proteins reassembly. Exploring the role of DPP-4 further may yield potential therapeutic insights.

Persons with latent autoimmune diabetes in adults express higher dipeptidyl peptidase-4 activity compared to persons with type 2 and type 1 diabetes

AIMS

We aimed to determine serum dipeptidyl peptidase-4 (DPP-4) activity in a group of persons with latent autoimmune diabetes in adults (LADA) and to compare it with persons with type 1, type 2 diabetes and healthy controls.

METHODS

DPP-4 activity measurement was performed in 67 persons (21 with type 1, 26 type 2 and 19 with LADA) and 13 healthy age and gender matched controls.

RESULTS

Persons with LADA showed highest DPP-4 activity among the study groups (32.71±3.55 vs 25.37±2.84 vs 18.57±2.54 vs 18.57±2.61U/L p<0.001). Mean glutamic acid autoantibody in persons with LADA was 164.32±86.28IU/mL. It correlated with DPP-4 activity (r=0.484, p=0.013). Furthermore, DPP-4 activity correlated with waist circumference (r=0.279, p=0.034) and glycated haemoglobin A1c (r=0.483, p<0.001), as well as with LDL cholesterol (r=0.854, p<0.001) and total daily insulin dose (r=0.397, p=0.001). In the multinomial regression analysis DPP-4 activity remained associated with both LADA (prevalence ratio 1.058 (1.012-1.287), p=0.001) and type 1 diabetes (prevalence ratio 1.506 (1.335-1.765), p<0.001) while it did not show an association with type 2 diabetes (prevalence ratio 0.942 (0.713-1.988), p=0.564).

CONCLUSIONS

Persons with LADA express higher DPP-4 activity compared to persons with both type 1 and type 2 diabetes. The possible pathophysiological role of DPP-4 in the LADA pathogenesis needs to be further evaluated.

DPP-4 Inhibition by Linagliptin Attenuates Obesity-Related Inflammation and Insulin Resistance by Regulating M1/M2 Macrophage Polarization

Dipeptidyl peptidase 4 (DPP-4) cleaves a large number of chemokine and peptide hormones involved in the regulation of the immune system. Additionally, DPP-4 may also be involved in macrophage-mediated inflammation and insulin resistance. Thus, the current study investigated the effect of linagliptin, an inhibitor of DPP-4, on macrophage migration and polarization in white adipose tissue (WAT) and liver of high-fat diet-induced obese (DIO) mice. DPP-4(+) macrophages in lean and obese mice were quantified by fluorescence-activated cell sorting (FACS) analysis. DPP-4 was predominantly expressed in F4/80(+) macrophages in crown-like structures compared with adipocytes in WAT of DIO mice. FACS analysis also revealed that, compared with chow-fed mice, DIO mice exhibited a significant increase in DPP-4(+) expression in cells within adipose tissue macrophages (ATMs), particularly M1 ATMs. Linagliptin showed a greater DPP-4 inhibition and antioxidative capacity than sitagliptin and reduced M1-polarized macrophage migration while inducing an M2-dominant shift of macrophages within WAT and liver, thereby attenuating obesity-induced inflammation and insulin resistance. Loss of macrophage inflammatory protein-1α, a chemokine and DPP-4 substrate, in DIO mice abrogated M2 macrophage-polarizing and insulin-sensitizing effects of linagliptin. Therefore, the inhibition of DPP-4 by linagliptin reduced obesity-related insulin resistance and inflammation by regulating M1/M2 macrophage status.

Circulating and Adipose Levels of Adipokines Associated With Insulin Sensitivity in Nonobese Subjects With Type 2 Diabetes

CONTEXT

The adipokines chemerin, dipeptidyl peptidase 4, and adiponectin influence insulin sensitivity. Whether their circulating levels and adipose secretion are altered in nonobese individuals with type 2 diabetes mellitus (T2DM) is unknown.

OBJECTIVE

The objective of this study was to investigate SC adipose secretion and serum levels of the three adipokines in relation to T2DM features.

DESIGN

Fourteen nonobese T2DM and 13 healthy men were investigated. Insulin sensitivity and glucose control were assessed by hyperinsulinemic euglycemic clamp, homeostasis model assessment, and glycated hemoglobin.

MAIN OUTCOME MEASURE

Association of circulating and adipose-secreted adipokines with fat cell volume and insulin sensitivity was measured.

PARTICIPANTS

Volunteers in an outpatient academic clinic participated.

RESULTS

Although adipose secretion was similar between the groups, serum chemerin was higher (70 ± 10 vs 50 ± 1 ng/ml; P = .005), adiponectin lower (4.7 ± 1.3 vs 6.8 ± 2.2 μg/ml; P = .005), and dipeptidyl peptidase 4 unaltered in T2DM. Serum adiponectin (r = 0.53; P = .005) and chemerin (r = -0.42; P = .03) correlated with adipose secreted levels. Secreted and circulating chemerin correlated positively with adipocyte volume (r > 0.40; P < .05), whereas serum adiponectin correlated negatively with this measure (r = -0.61; P = .001). Adiponectin serum half-life was decreased in T2DM (168 ± 24 vs 186 ± 18 minutes; P = .029) and correlated negatively with glycated hemoglobin (r = -0.45; P = .03) and adipocyte volume (r = -0.56; P < .003). Serum adiponectin (r = 0.57; P = .017) and chemerin (r = -0.52; P = .03) associated with clamp measures independently of T2DM diagnosis.

CONCLUSIONS

In nonobese men, circulating adiponectin and chemerin levels are altered in T2DM without changes in adipose secretion. Adipocyte volume is important for variations in serum chemerin and adiponectin and for serum clearance of adiponectin. In T2DM, poor glucose control also plays a role for adiponectin clearance.

Differential Role of Adipose Tissues in Obesity and Related Metabolic and Vascular Complications

This review focuses on the contribution of white, brown, and perivascular adipose tissues to the pathophysiology of obesity and its associated metabolic and vascular complications. Weight gain in obesity generates excess of fat, usually visceral fat, and activates the inflammatory response in the adipocytes and then in other tissues such as liver. Therefore, low systemic inflammation responsible for insulin resistance contributes to atherosclerotic process. Furthermore, an inverse relationship between body mass index and brown adipose tissue activity has been described. For these reasons, in recent years, in order to combat obesity and its related complications, as a complement to conventional treatments, a new insight is focusing on the role of the thermogenic function of brown and perivascular adipose tissues as a promising therapy in humans. These lines of knowledge are focused on the design of new drugs, or other approaches, in order to increase the mass and/or activity of brown adipose tissue or the browning process of beige cells from white adipose tissue. These new treatments may contribute not only to reduce obesity but also to prevent highly prevalent complications such as type 2 diabetes and other vascular alterations, such as hypertension or atherosclerosis.

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.

DPP-4 inhibitors in diabetic complications: role of DPP-4 beyond glucose control

Dipeptidyl peptidase-4 (DPP-4) inhibitors (gliptins) are an emerging class of antidiabetic drugs that constitutes approximately fifty percent of the market share of the oral hypoglycemic drugs. Its mechanism of action for lowering blood glucose is essentially via inhibition of the rapid degradation of incretin hormones, such as glucagon-like peptide (GLP)-1 and gastric inhibitory polypeptide (GIP), thus the plasma concentration of GLP-1 increases, which promotes insulin secretion from the pancreatic β cells and suppresses glucagon secretion from the α cells. In addition to the direct actions on the pancreas, GLP-1 exhibits diverse actions on different tissues through its action on GLP-1 receptor, which is expressed ubiquitously. Moreover, DPP-4 has multiple substrates besides GLP-1 and GIP, including cytokines, chemokines, neuropeptides, and growth factors, which are involved in many pathophysiological conditions. Recently, it was suggested that DPP-4 is a new adipokine secreted from the adipose tissue, which plays an important role in the regulation of the endocrine function in obesity-associated type 2 diabetes. Consequently, DPP-4 inhibitors have been reported to exhibit cytoprotective functions against various diabetic complications affecting the liver, heart, kidneys, retina, and neurons. This review outlines the current understanding of the effect of DPP-4 inhibitors on the complications associated with type 2 diabetes, such as liver steatosis and inflammation, dysfunction of the adipose tissue and pancreas, cardiovascular diseases, nephropathy, and neuropathy in preclinical and clinical studies.

Clinical and genetic predictors of dipeptidyl peptidase-4 inhibitor treatment response in Type 2 diabetes mellitus

AIM

To determine the clinical and genetic predictors of the dipeptidyl peptidase-4 (DPP-4) inhibitor treatment response in Type 2 diabetes mellitus (T2DM) patients.

PATIENTS & METHODS

DPP4, WFS1 and KCNJ11 gene polymorphisms were genotyped in a cohort study of 662 T2DM patients treated with DPP-4 inhibitors sitagliptin, vildagliptin or linagliptin. Genotyping was performed by Applied Biosystems TaqMan SNP genotyping assay.

RESULTS

Patients with triglyceride levels less than 1.7 mmol/l (odds ratio [OR]: 2.2.; 95% CI: 1.031-4.723), diastolic blood pressure (DBP) less than 90 mmHg (OR: 1.7; 95% CI: 1.009-2.892) and KCNJ11 rs2285676 (genotype CC) (OR: 2.0; 95% CI: 1.025-3.767) were more likely to response to DPP-4 inhibitor treatment compared with other patients, as measured by HbA1c levels.

CONCLUSION

Triglycerides, DBP and KCNJ11 rs2285676 are predictors of the DPP-4 inhibitor treatment response in T2DM patients.

Visceral fat obesity increases serum DPP-4 levels in men with type 2 diabetes mellitus

OBJECTIVE

The relationship between serum DPP-4 level and visceral fat mass is still unclear in type 2 diabetes mellitus (T2DM). This study thus aimed to examine the association of visceral fat accumulation and metabolic syndrome with serum DPP-4 levels in T2DM.

METHODS

Visceral and subcutaneous fat areas were evaluated by performing computed tomography scan in 135 men with T2DM, who had never taken DPP-4 inhibitors or GLP-1 receptor agonists. We investigated the association between serum DPP-4 levels and visceral fat area as well as the presence of metabolic syndrome.

RESULTS

Multiple regression analysis adjusted for age, duration of T2DM, body mass index, serum creatinine, and HbA1c showed that serum DPP-4 levels were positively associated with visceral fat area (β=0.25, p=0.04), but not subcutaneous fat area (β=-0.18, p=0.13). In logistic regression analyses adjusted for the confounding factors described above, serum DPP-4 levels were positively associated with visceral fat obesity and metabolic syndrome [odds ratio (OR)=1.63, 95% confidence interval (CI)=1.00-2.66 per standard deviation (SD) increase, p=0.04; OR=1.77, 95%CI=1.09-2.88 per SD increase, p=0.02, respectively].

CONCLUSIONS

The present study showed that serum DPP-4 level was positively and specifically associated with accumulation of visceral fat and the presence of metabolic syndrome in men with T2DM.

Metabolic role of dipeptidyl peptidase 4 (DPP4) in primary human (pre)adipocytes

Dipeptidyl peptidase 4 (DPP4) is the target of the gliptins, a recent class of oral antidiabetics. DPP4 (also called CD26) was previously characterized in immune cells but also has important metabolic functions which are not yet fully understood. Thus, we investigated the function of DPP4 in human white preadipocytes and adipocytes. We found that both cell types express DPP4 in high amounts; DPP4 release markedly increased during differentiation. In preadipocytes, lentiviral DPP4 knockdown caused significant changes in gene expression as determined by whole-genome DNA-array analysis. Metabolic genes were increased, e.g. PDK4 18-fold and PPARγC1α (=PGC1α) 6-fold, and proliferation-related genes were decreased (e.g. FGF7 5-fold). These effects, contributing to differentiation, were not inhibited by the PPARγ antagonist T0070907. Vice versa, the PPARγ agonist pioglitazone induced a different set of genes (mainly FABP4). DPP4 knockdown also affected growth factor signaling and, accordingly, retarded preadipocyte proliferation. In particular, basal and insulin-induced ERK activation (but not Akt activation) was markedly diminished (by around 60%). This indicates that DPP4 knockdown contributes to adipocyte maturation by mimicking growth factor withdrawal, an early step in fat cell differentiation. In mature adipocytes, DPP4 becomes liberated so that adipose tissue may constitute a relevant source of circulating DPP4.

Increased plasma dipeptidyl peptidase-4 activities are associated with high prevalence of diabetic nephropathy in Chinese patients with newly diagnosed type 2 diabetes: A cross-sectional study

OBJECTIVE

To investigate the association between plasma Dipeptidyl peptidase-4 (DPP4) activities and diabetic nephropathy in type 2 diabetes.

RESEARCH DESIGN AND METHODS

A total of 1193 newly diagnosed type 2 diabetic subjects were studied. Plasma DPP4 activity, mannose 6-phosphate receptor, inflammatory markers and oxidative stress parameters were measured in all participants. Diabetic nephropathy was defined as the presence of albuminuria or an estimated glomerular filtration rate < 60 mL/min/1.73 m(2).

RESULTS

Participants in the highest quartile of DPP4 activity had higher HbA1c, homeostatic model assessment of insulin resistance, nitrotyrosine, 8-iso-PGF2a, interleukin-6, high-sensitivity C-reactive protein, mannose 6-phosphate receptor, urinary albumin-to-creatinine ratio and lower estimated glomerular filtration rate compared with participants in the lowest quartile (all p < 0.001). DPP4 activities were associated positively with HbA1c, homeostatic model assessment of insulin resistance, nitrotyrosine, 8-iso-PGF2a, interleukin-6, high-sensitivity C-reactive protein, mannose 6-phosphate receptor, urinary albumin-to-creatinine ratio and negatively with estimated glomerular filtration rate (all p < 0.001). In the highest DPP4 quartile, diabetic nephropathy risk was significantly higher (odds ratio: 3.77; 95% confidence interval: 2.34-6.07) than in the lowest quartile after adjustment for potential confounders. This association remained strong (2.85; 1.74-4.68) after further controlling for HbA1c, homeostatic model assessment of insulin resistance, nitrotyrosine and high-sensitivity C-reactive protein.

CONCLUSION

This study shows that increased DPP4 activities are strongly and independently associated with diabetic nephropathy in type 2 diabetes. The associations between DPP4 and diabetic nephropathy, although strong, do not imply causality. There are however plausible mechanisms which could explain such a link.

Significant elevation of serum dipeptidyl peptidase-4 activity in young-adult type 1 diabetes

AIMS

Currently, inhibition of dipeptidyl peptidase-4 (DPP-4) is widely used in the treatment of type 2 diabetes. Application of this strategy is awaited as a new therapeutic approach for type 1 diabetes, but the scientific basis is still lacking. This report describes the evaluation of serum DPP-4 activity in type 1 diabetes compared with control subjects, and assessment of relationships between DPP-4 activity and diabetic complication markers and metabolic variables in type 1 diabetes.

METHODS

We examined serum DPP-4 activity in Japanese young-adult type 1 diabetes (n=76, females 69.7%, age 30.9 ± 6.2 years, duration of diabetes 16.5 ± 11.1 years; mean ± SD) and healthy controls (n=22). Association of the enzymatic activity with diabetic micro- and macro- vascular complication markers and clinical parameters was also assessed.

RESULTS

Subjects with type 1 diabetes displayed significantly higher serum DPP-4 activity than healthy controls (relative value, control: 1.00 ± 0.28, T1D, 1.29 ± 0.38; p=0.0011) independent of other clinical parameters. In type 1 diabetes, DPP-4 activity was positively correlated with duration of diabetes (r=0.248, p=0.031), while not correlated with HbA1c level. In univariate correlation analysis of diabetic complication markers and other metabolic parameters, coefficient of variation of R-R intervals (CVR-R) and gamma (γ)-glutamyltransferase (GGT) levels were correlated with DPP-4 activity. GGT was extracted as an independent variable of DPP-4 activity in multivariate analysis (β=0.213, p=0.035).

CONCLUSIONS

Serum DPP-4 activity is significantly elevated in Japanese type 1 diabetes, suggesting pathophysiological significance of the enzyme in type 1 diabetes.

Dipeptidyl peptidase-4 and kidney fibrosis in diabetes

Diabetic nephropathy (DN) is the most common cause of end-stage kidney disease worldwide and is associated with increased morbidity and mortality in patients with both type 1 and type 2 diabetes. Recent evidence revealed that dipeptidyl peptidase-4 (DPP-4) inhibitors may exhibit a protective effect against DN. In fact, the kidney is the organ where the DPP-4 activity is the highest level per organ weight. A preclinical analysis revealed that DPP-4 inhibitors also ameliorated kidney fibrosis. In this review, we analyzed recent reports in this field and explore the renoprotective effects and possible mechanism of the DPP-4 inhibitors.

Reduced DPP4 activity improves insulin signaling in primary human adipocytes

DPP4 is a ubiquitously expressed cell surface protease which is also released to the circulation as soluble DPP4 (sDPP4). Recently, we identified DPP4 as a novel adipokine oversecreted in obesity and thus potentially linking obesity to the metabolic syndrome. Furthermore, sDPP4 impairs insulin signaling in an autocrine and paracrine fashion in different cell types. However, it is still unknown which functional role DPP4 might play in adipocytes. Therefore, primary human adipocytes were treated with a specific DPP4 siRNA. Adipocyte differentiation was not affected by DPP4 silencing. Interestingly, DPP4 reduction improved insulin responsiveness of adipocytes at the level of insulin receptor, proteinkinase B (Akt) and Akt substrate of 160 kDa. To investigate whether the observed effects could be attributed to the enzymatic activity of DPP4, human adipocytes were treated with the DPP4 inhibitors sitagliptin and saxagliptin. Our data show that insulin-stimulated activation of Akt is augmented by DPP4 inhibitor treatment. Based on our previous observation that sDPP4 induces insulin resistance in adipocytes, and that adipose DPP4 levels are higher in obese insulin-resistant patients, we now suggest that the abundance of DPP4 might be a regulator of adipocyte insulin signaling.

Novel adipocyte aminopeptidases are selectively upregulated by insulin in healthy and obese rats

The lack of a complete assembly of the sensitivity of subcellular aminopeptidase (AP) activities to insulin in different pathophysiological conditions has hampered the complete view of the adipocyte metabolic pathways and its implications in these conditions. Here we investigated the influence of insulin on basic AP (APB), neutral puromycin-sensitive AP (PSA), and neutral puromycin-insensitive AP (APM) in high and low density microsomal and plasma membrane fractions from adipocytes of healthy and obese rats. Catalytic activities of these enzymes were fluorometrically monitoring in these fractions with or without insulin stimulus. Canonical traffic such as insulin-regulated AP was not detected for these novel adipocyte APs in healthy and obese rats. However, insulin increased APM in low density microsomal and plasma membrane fractions from healthy rats, APB in high density microsomal fraction from obese rats and PSA in plasma membrane fraction from healthy rats. A new concept of intracellular compartment-dependent upregulation of AP enzyme activities by insulin emerges from these data. This relatively selective regulation has pathophysiological significance, since these enzymes are well known to act as catalysts and receptor of peptides directly related to energy metabolism. Overall, the regulation of each one of these enzyme activities reflects certain dysfunction in obese individuals.

Soluble DPP-4 up-regulates toll-like receptors and augments inflammatory reactions, which are ameliorated by vildagliptin or mannose-6-phosphate

OBJECTIVE

Studies have shown that dipeptidyl peptidase-4 (DPP-4) inhibitors have anti-inflammatory effects. Soluble DPP-4 (sDPP-4) has been considered as an adipokine of which actions need to be further characterized.

METHODS

We investigated the pro-inflammatory actions of sDPP-4 and the anti-inflammatory effects of DPP-4 inhibition, using vildagliptin, as an enzymatic inhibitor, and mannose-6-phosphate (M6P) as a competitive binding inhibitor.

RESULTS

In lipopolysaccharide (LPS)-stimulated RAW264.7 cells, vildagliptin suppressed the increased expression of inducible nitric oxide synthase (iNOS) and phosphorylated JNK (pJNK), activation of the NF-κB pathway, and the resultant NO and proinflammatory cytokine production. Although sDPP-4 alone did not affect the protein level of iNOS or pJNK or the production of NO in RAW264.7 cells, it did amplify iNOS expression, NO responses, and proinflammatory cytokine production in LPS-stimulated RAW264 cells. As a probable mechanism, we found that sDPP-4 caused dose-dependent increases in the expression levels of toll-like receptor 4 (TLR4) and TLR2 in RAW264.7 cells, and that these alterations were inhibited by vildagliptin, M6P, or bisindolylmaleimide II, a protein kinase C inhibitor. Either vildagliptin or M6P suppressed iNOS expression and NO and cytokine production in LPS+DPP-4-co-stimulated macrophages, while combined treatment of the co-stimulated cells with both agents had increased anti-inflammatory effects compared with either treatment alone. Intravenous injection of sDPP-4 to C57BL/6J mice increased the expression of both TLRs in kidney and white adipose tissues.

CONCLUSION

Our findings suggest that sDPP-4 enhances inflammatory actions via TLR pathway, while DPP-4 inhibition with either an enzymatic or binding inhibitor has anti-inflammatory effects.

Hibiscus sabdariffa polyphenols prevent palmitate-induced renal epithelial mesenchymal transition by alleviating dipeptidyl peptidase-4-mediated insulin resistance

Diabetic nephropathy has a significant socioeconomic impact, but its mechanism is unclear and needs to be examined.

Adipocyte aminopeptidases in obesity and fasting

This study checked the existence of a diverse array of aminopeptidase (AP) enzymes in high (HDM) and low (LDM) density microsomal and plasma membrane (MF) fractions from adipocytes of control, monosodium glutamate obese and food deprived rats. Gene expression was detected for ArgAP, AspAP, MetAP, and two AlaAP (APM and PSA). APM and PSA had the highest catalytic efficiency, whereas AspAP the highest affinity. Subcellular distribution of AP activities depended on metabolic status. Comparing catalytic levels, AspAP in HDM, LDM and MF was absent in obese and control under food deprivation; PSA in LDM was 3.5-times higher in obese than in normally fed control and control and obese under food deprivation; MetAP in MF was 4.5-times higher in obese than in food deprived obese. Data show new AP enzymes genetically expressed in subcellular compartments of adipocytes, three of them with altered catalytic levels that respond to whole-body energetic demands.

Comparative Genome of GK and Wistar Rats Reveals Genetic Basis of Type 2 Diabetes

The Goto-Kakizaki (GK) rat, which has been developed by repeated inbreeding of glucose-intolerant Wistar rats, is the most widely studied rat model for Type 2 diabetes (T2D). However, the detailed genetic background of T2D phenotype in GK rats is still largely unknown. We report a survey of T2D susceptible variations based on high-quality whole genome sequencing of GK and Wistar rats, which have generated a list of GK-specific variations (228 structural variations, 2660 CNV amplification and 2834 CNV deletion, 1796 protein affecting SNVs or indels) by comparative genome analysis and identified 192 potential T2D-associated genes. The genes with variants are further refined with prior knowledge and public resource including variant polymorphism of rat strains, protein-protein interactions and differential gene expression. Finally we have identified 15 genetic mutant genes which include seven known T2D related genes (Tnfrsf1b, Scg5, Fgb, Sell, Dpp4, Icam1, and Pkd2l1) and eight high-confidence new candidate genes (Ldlr, Ccl2, Erbb3, Akr1b1, Pik3c2a, Cd5, Eef2k, and Cpd). Our result reveals that the T2D phenotype may be caused by the accumulation of multiple variations in GK rat, and that the mutated genes may affect biological functions including adipocytokine signaling, glycerolipid metabolism, PPAR signaling, T cell receptor signaling and insulin signaling pathways. We present the genomic difference between two closely related rat strains (GK and Wistar) and narrow down the scope of susceptible loci. It also requires further experimental study to understand and validate the relationship between our candidate variants and T2D phenotype. Our findings highlight the importance of sequenced-based comparative genomics for investigating disease susceptibility loci in inbreeding animal models.

DPP4 in Diabetes

Dipeptidyl-peptidase 4 (DPP4) is a glycoprotein of 110 kDa, which is ubiquitously expressed on the surface of a variety of cells. This exopeptidase selectively cleaves N-terminal dipeptides from a variety of substrates, including cytokines, growth factors, neuropeptides, and the incretin hormones. Expression of DPP4 is substantially dysregulated in a variety of disease states including inflammation, cancer, obesity, and diabetes. Since the incretin hormones, glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide (GIP), are major regulators of post-prandial insulin secretion, inhibition of DPP4 by the gliptin family of drugs has gained considerable interest for the therapy of type 2 diabetic patients. In this review, we summarize the current knowledge on the DPP4–incretin axis and evaluate most recent findings on DPP4 inhibitors. Furthermore, DPP4 as a type II transmembrane protein is also known to be cleaved from the cell membrane involving different metalloproteases in a cell-type-specific manner. Circulating, soluble DPP4 has been identified as a new adipokine, which exerts both para- and endocrine effects. Recently, a novel receptor for soluble DPP4 has been identified, and data are accumulating that the adipokine-related effects of DPP4 may play an important role in the pathogenesis of cardiovascular disease. Importantly, circulating DPP4 is augmented in obese and type 2 diabetic subjects, and it may represent a molecular link between obesity and vascular dysfunction. A critical evaluation of the impact of circulating DPP4 is presented, and the potential role of DPP4 inhibition at this level is also discussed.

The role of dipeptidyl peptidase 4 inhibitors in fat metabolism in patients with type 2 diabetes and obesity

Objective. To evaluate the influence of combined therapy of sitagliptin and metformin on fat metabolism in patients with type 2 diabetes mellitus.Methods. The study included 82 patients (age, 55.3±9.1 years) with obesity and lipid metabolism disorders. None of the patients had reached their target glycated haemoglobin levels after metformin and diet therapy. Patients in group 1 (n=42) received 1.5–2-g metformin daily before the study and were switched to a formulation of 100-mg sitagliptin and 2-g metformin once a day. Patients in group 2 (n=40) were on a diet therapy before inclusion and were started on 2-g metformin/day. The following were evaluated at baseline and after 6 months of therapy: fasting glucose levels, postprandial glucose levels, glycated haemoglobin, weight, body mass index, waist circumference and lipid profile; insulin, proinsulin, leptin and adiponectin levels; insulin resistance using the homeostatic model assessment (HOMA) of β-cell function (HOMA-β) and insulin resistance (HOMA-IR). In addition, magnetic resonance imaging was performed to assess the amount of visceral fat for the total cohort.Results. After 6 months, glycated haemoglobin decreased by 18.52% (p 0.001) in group 1 and by 8.17% (p 0.001) in group 2. Fasting plasma glucose and postprandial glucose levels in group 1 were reduced by 21% (p 0.001) and 26.35% (p 0.001), respectively; the corresponding reductions in group 2 were 1.45% (p 0.05) and 5.31% (p 0.05), respectively. HOMA-β increased by 33% in group 1 (p 0.001) and by 11% in group 2 (p 0.05). Adiponectin levels increased by 27.06% (p 0.001) in group 1 and by 7.16% in group 2 (p 0.001). Leptin levels were reduced by 30.47% (p 0.001) in group 1 and by 5.41% in group 2 (p 0.001). Magnetic resonance imaging showed a 7.52% reduction in visceral fat for group 1 (p 0.001) and a 1.76% reduction for group 2 (p 0.01). The comparison of subcutaneous fat dynamics did not show statistically significant differences between the groups.Conclusion. Compared with metformin monotherapy, sitagliptin and metformin combination therapy had a prominent effect on non-glycaemic parameters, with more marked decreases in visceral fat and leptin and increases in adiponectin levels.