Vildagliptin inhibits oxidative stress and vascular damage in streptozotocin-induced diabetic rats

SARS-CoV-2 and diabetes: A potential therapeutic effect of dipeptidyl peptidase 4 inhibitors in diabetic patients diagnosed with COVID-19

COVID-19 is caused by severe acute respiratory syndrome coronavirus 2 and has become an urgent economic and health challenge. Dipeptidyl peptidase 4 (DPP4), also mentioned as a cluster of differentiation 26 (CD26) is a serine exopeptidase found in two arrangements: a soluble form (sDPP-4) and a plasma membrane-bound form. Because other coronaviruses enter the cells by binding to DPP-4, it has been speculated that DPP-4 inhibitors may exert activity against COVID-19. Therefore, this review aimed to summarize the potential therapeutic effect of dipeptidyl peptidase 4 inhibitors in diabetic patients diagnosed with COVID-19. To include different studies, publications related to Dipeptidyl peptidase-4 inhibitor use and clinical outcomes from COVID-19 were searched from the databases such as Web of Science, PubMed, Medline, Elsevier, Google Scholar, and SCOPUS, via English key terms. A direct engrossment of DPP4 in COVID-19 needs to be elucidated, there is also evidence confirming that DPP4 inhibitors exert anti-fibrotic and modulate inflammation activity. Thus, the use of DPP-4 inhibitors could reduce mortality due to COVID-19 or improve the progression of COVID-19; this evidence may support the management of diabetic patients diagnosed with COVID-19; however more well-designed investigation is urgently required.

Platelet Effects of Anti-diabetic Therapies: New Perspectives in the Management of Patients with Diabetes and Cardiovascular Disease

In type 2 diabetes, anti-thrombotic management is challenging, and current anti-platelet agents have demonstrated reduced efficacy. Old and new anti-diabetic drugs exhibited—besides lowering blood glucose levels—direct and indirect effects on platelet function and on thrombotic milieu, eventually conditioning cardiovascular outcomes. The present review summarizes existing evidence on the effects of glucose-lowering agents on platelet properties, addressing pre-clinical and clinical research, as well as drug–drug interactions with anti-platelet agents. We aimed at expanding clinicians’ understanding by highlighting new opportunities for an optimal management of patients with diabetes and cardiovascular disease. We suggest how an improvement of the thrombotic risk in this large population of patients may be achieved by a careful and tailored combination of anti-diabetic and anti-platelet therapies.

DPP4 and ACE2 in Diabetes and COVID-19: Therapeutic Targets for Cardiovascular Complications?

COVID-19 outbreak, caused by severe acute respiratory syndrome (SARS)-CoV-2 coronavirus has become an urgent health and economic challenge. Diabetes is a risk factor for severity and mortality of COVID-19. Recent studies support that COVID-19 has effects beyond the respiratory tract, with vascular complications arising as relevant factors worsening its prognosis, then making patients with previous vascular disease more prone to severity or fatal outcome. Angiotensin-II converting enzime-2 (ACE2) has been proposed as preferred receptor for SARS-CoV-2 host infection, yet specific proteins participating in the virus entry are not fully known. SARS-CoV-2 might use other co-receptor or auxiliary proteins allowing virus infection. In silico experiments proposed that SARS-CoV-2 might bind dipeptidyl peptidase 4 (DPP4/CD26), which was established previously as receptor for MERS-CoV. The renin-angiotensin-aldosterone system (RAAS) component ACE2 and DPP4 are proteins dysregulated in diabetes. Imbalance of the RAAS and direct effect of soluble DPP4 exert deleterious vascular effects. We hypothesize that diabetic patients might be more affected by COVID-19 due to increased presence ACE2 and DPP4 mediating infection and contributing to a compromised vasculature. Here, we discuss the role of ACE2 and DPP4 as relevant factors linking the risk of SARS-CoV-2 infection and severity of COVID-19 in diabetic patients and present an outlook on therapeutic potential of current drugs targeted against RAAS and DPP4 to treat or prevent COVID-19-derived vascular complications. Diabetes affects more than 400 million people worldwide, thus better understanding of how they are affected by COVID-19 holds an important benefit to fight against this disease with pandemic proportions.

Oral formulation of DPP-4 inhibitor plus Quercetin improves metabolic homeostasis in type 1 diabetic rats

This study aimed to investigate the potential of an oral formulation (QV formulation) containing Quercetin and a Dipeptidyl Peptidase-4 Inhibitor (DPP-4 inhibitor), Vildagliptin, in improving metabolic homeostasis in type 1 diabetes model. Female albino Fischer rats were divided into four groups: untreated control animals (C), untreated diabetic animals (D), diabetic animals treated with QV formulation (DQV), and diabetic animals treated with insulin (DI). Diabetes was induced by injection of alloxan (135 mg kg body mass)^-1 and confirmed by glycemic test. After the 30-day treatment period, biochemical parameters were analyzed in the pancreas, liver, and serum. Histopathological changes in pancreatic tissue were examined by Hematoxyline & Eosin staining and the insulin content in the islet measured by immunohistochemistry with anti-insulin antibody. The glycogen content in the hepatocytes was quantified by Periodic Schiff Acid staining. The QV formulation reduced the glycemia, preserved the pancreatic architecture, increased insulin levels, furthermore ameliorated lipid profile and to promote higher survival rate of animals. Together, our data suggest that the QV formulation treatment was able to normalize metabolic homeostasis in type 1 diabetic rats.

Vildagliptin/pioglitazone combination improved the overall glycemic control in type I diabetic rats

Type I diabetes (TID) is generally assumed to be caused by an immune associated, if not directly immune-mediated, destruction of pancreatic β-cells. In patients with long-term diabetes, the pancreas lacks insulin-producing cells and the residual β-cells are unable to regenerate. Patients with TID are subjected to a lifelong insulin therapy which shows risks of hypoglycemia, suboptimal control and ketosis. In this study, we investigated the potential role of vildagliptin (Vilda) alone or in combination with pioglitazone (Pio), as treatment regimens for TID using streptozotocin (STZ)-induced TID model in rats. Daily oral administration of Vilda (5 mg/kg) alone or in combination with Pio (20 mg/kg) for 7 weeks significantly reduced blood glucose levels and HbA1c. It increased serum insulin levels and decreased serum glucagon. It also showed a strong antioxidant activity. Immunohistochemical analysis showed a marked improvement in β-cells in treated groups when compared with the diabetic group, which appeared in the normal cellular and architecture restoration of β-cells in the islets of Langerhans. Vilda alone or in combination with Pio has the ability to improve the overall glycemic control in type I diabetic rats and may be considered a hopeful and effective remedy for TID.

Vildagliptin and caloric restriction for cardioprotection in pre-diabetic rats

Long-term high-fat diet (HFD) consumption causes cardiac dysfunction. Although calorie restriction (CR) has been shown to be useful in obesity, we hypothesized that combined CR with dipeptidyl peptidase-4 (DPP-4) inhibitor provides greater efficacy than monotherapy in attenuating cardiac dysfunction and metabolic impairment in HFD-induced obese-insulin resistant rats. Thirty male Wistar rats were divided into 2 groups to be fed on either a normal diet (ND, n = 6) or a HFD (n = 24) for 12 weeks. Then, HFD rats were divided into 4 subgroups (n = 6/subgroup) to receive just the vehicle, CR diet (60% of mean energy intake and changed to ND), vildagliptin (3 mg/kg/day) or combined CR and vildagliptin for 4 weeks. Metabolic parameters, heart rate variability (HRV), cardiac mitochondrial function, left ventricular (LV) and fibroblast growth factor (FGF) 21 signaling pathway were determined. Rats on a HFD developed insulin and FGF21 resistance, oxidative stress, cardiac mitochondrial dysfunction and impaired LV function. Rats on CR alone showed both decreased body weight and visceral fat accumulation, whereas vildagliptin did not alter these parameters. Rats in CR, vildagliptin and CR plus vildagliptin subgroups had improved insulin sensitivity and oxidative stress. However, vildagliptin improved heart rate variability (HRV), cardiac mitochondrial function and LV function better than the CR. Chronic HFD consumption leads to obese-insulin resistance and FGF21 resistance. Although CR is effective in improving metabolic regulation, vildagliptin provides greater efficacy in preventing cardiac dysfunction by improving anti-apoptosis and FGF21 signaling pathways and attenuating cardiac mitochondrial dysfunction in obese-insulin-resistant rats.

A novel DPP-4 inhibitor teneligliptin scavenges hydroxyl radicals: In vitro study evaluated by electron spin resonance spectroscopy and in vivo study using DPP-4 deficient rats

AIMS

Recently various dipeptidyl peptidase-4 (DPP-4) inhibitors have emerged because of their high effectiveness and safety. In spite of their common effect of DPP-4 inhibition, the chemical structures are diverse. Here we show that the structure of teneligliptin, a novel DPP-4 inhibitor, has a scavenging activity on hydroxyl radical (·OH).

METHODS

·OH and superoxide (O2(-)) were detected by electron spin resonance (ESR) spectroscopy. ·OH and O2(-) were generated in vitro by the Fenton reaction and a hypoxanthine-xanthine oxidase system, respectively. The level of free radicals was estimated from the ESR signal intensity. The product via teneligliptin and ·OH reaction was identified by thin layer chromatography and mass spectrometry analysis. In vivo effect was also evaluated using DPP-4 deficient rats with streptozotocin-induced diabetes.

RESULTS

ESR spectroscopy analysis showed that teneligliptin did not scavenge O2(-), but scavenged ·OH in a dose dependent manner. Its activity was greater than that of glutathione. The reaction product appeared to have an oxygen-atom added structure to that of teneligliptin, which was identical to the most abundant metabolite of teneligliptin in human plasma. Furthermore, using DPP-4 deficient rat, teneligliptin did not affect plasma glucose levels or body weight, but normalized increased levels of 8-hydroxy-2'-deoxyguanosine in urine, kidney and aorta of diabetic rats, supporting that teneligliptin may have a ·OH scavenging activity in vivo independently of DPP-4 inhibition.

CONCLUSIONS

Teneligliptin is not only effective as DPP-4 inhibitor, but may also be beneficial as ·OH scavenger, which may be useful in the prevention of diabetic complications.

Favorable effects of vildagliptin on metabolic and cognitive dysfunctions in streptozotocin-induced diabetic rats

Progression of diabetes mellitus is accompanied by metabolic disorders together with psychological deficits including cognitive dysfunctions. Herein, we used a murine streptozotocin (STZ)-induced diabetes to investigate the beneficial effects of vildagliptin not only on metabolic abnormalities, but also on diabetes-induced cognitive decline. Sixty rats were divided randomly and equally into 2 groups; one remains normal and the other serves as STZ- induced diabetic. Both groups were further divided equally into 2 groups; one received vehicle and the other received oral vildagliptin for 8 weeks. Cognitive behavior was assessed using novel object recognition test. Blood samples were collected to measure metabolic parameters and dipeptidyl peptidase (DPP)-IV activity. Brains were removed and investigated for the levels of inflammatory and oxidative stress markers malondialdehyde (MDA), superoxide dismutase (SOD) and tumor necrosis factor-α (TNF-α), in addition to brain-derived neurotrophic factor (BDNF) and relative expression of nuclear factor kappa B (NF-κB)/p65. Treatment of STZ-induced diabetic rats with vildagliptin increased their body weight and corrected diabetes-induced memory and learning impairment. Moreover, vildagliptin significantly decreased serum levels of glucose and lipids (except high density lipoprotein) together with brain MDA, TNF-α, serum DPP-IV activities and NF-κB/p65 gene expression. On the other hand, vildagliptin significantly increased brain BDNF, SOD as well as serum insulin. Results suggested that vildagliptin has a protective role in counteracting both metabolic abnormalities and memory deficits in diabetic rats, possibly via its anti-hyperglycemic, anti-inflammatory, antioxidant effects, together with reduction of brain NF-κB/p65 over expression.

DPP-4 inhibitors: pharmacological differences and their clinical implications

INTRODUCTION

Recently, incretin-based therapy was introduced for the treatment of type 2 diabetes (T2D). In particular, dipeptidyl peptidase-4 inhibitors (DPP-4i) (sitagliptin, vildagliptin, saxagliptin, linagliptin and alogliptin) play an increasing role in the management of T2D.

AREAS COVERED

An extensive literature search was performed to analyze the pharmacological characteristics of DPP-4i and their clinical implications.

EXPERT OPINION

DPP-4i present significant pharmacokinetic differences. They also differ in chemical structure, in the interaction with distinct subsites of the enzyme and in different levels of selectivity and potency of enzyme inhibition. Moreover, disparities in the effects on glycated hemoglobin, glucagon-like peptide-1 and glucagon levels and on glucose variability have been observed. However, indirect comparisons indicate that all DPP-4i have a similar safety and efficacy profiles. DPP-4i are preferred in overweight/obese and elderly patients because of the advantages of minimal or no influence on weight gain and low risk of hypoglycemia. For the same reasons, DPP-4i can be safely combined with insulin. However, currently cardiovascular outcomes related to DPP-4i are widely debated and the available evidence is controversial. Today, long-term studies are still in progress and upcoming results will allow us to better define the strengths and limits of this therapeutic class.

Crosstalk between advanced glycation end products (AGEs)-receptor RAGE axis and dipeptidyl peptidase-4-incretin system in diabetic vascular complications

Advanced glycation end products (AGEs) consist of heterogenous group of macroprotein derivatives, which are formed by non-enzymatic reaction between reducing sugars and amino groups of proteins, lipids and nucleic acids, and whose process has progressed at an accelerated rate under diabetes. Non-enzymatic glycation and cross-linking of protein alter its structural integrity and function, contributing to the aging of macromolecules. Furthermore, engagement of receptor for AGEs (RAGE) with AGEs elicits oxidative stress generation and subsequently evokes proliferative, inflammatory, and fibrotic reactions in a variety of cells. Indeed, accumulating evidence has suggested the active involvement of accumulation of AGEs in diabetes-associated disorders such as diabetic microangiopathy, atherosclerotic cardiovascular diseases, Alzheimer's disease and osteoporosis. Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are incretins, gut hormones secreted from the intestine in response to food intake, both of which augment glucose-induced insulin release, suppress glucagon secretion, and slow gastric emptying. Since GLP-1 and GIP are rapidly degraded and inactivated by dipeptidyl peptidase-4 (DPP-4), inhibition of DPP-4 and/or DPP-4-resistant GLP-1 analogues have been proposed as a potential target for the treatment of diabetes. Recently, DPP-4 has been shown to cleave multiple peptides, and blockade of DPP-4 could exert diverse biological actions in GLP-1- or GIP-independent manner. This article summarizes the crosstalk between AGEs-RAGE axis and DPP-4-incretin system in the development and progression of diabetes-associated disorders and its therapeutic intervention, especially focusing on diabetic vascular complications.

A 16-week study to compare the effect of vildagliptin versus gliclazide on postprandial lipoprotein concentrations and oxidative stress in patients with type 2 diabetes inadequately controlled with metformin monotherapy

BACKGROUND

Diabetes is closely linked with coronary artery disease, either by means of direct effects of hyperglycemia, or indirectly by its frequent association with dyslipidemia. Any treatment for diabetes that has beyond the capacity of reduce glycated hemoglobin, the propensity to improve lipid profile and reduce weight will bring many benefits to patients.

METHOD

We compare the effects of vildagliptin with the gliclazide on lipid profile before and after a standardized meal test, on glycemic control and oxidative stress in diabetic patients using metformin without adequate glycemic control. This is a prospective study of 16 weeks with diabetic patients using metformin without adequate glycemic control. Patients were randomized to receive gliclazide 30-120 mg/day or vildagliptin 100 mg/day.

RESULTS

36 patients were randomized, with no loss of follow up. Regarding the lipid profile the difference observed at the end of the study was a higher HDL level in the vildagliptin group compared with gliclazide fasting (62.3 vs. 51.3 mg/dL, p = 0.021) and postprandial (62.9 vs. 51.1 mg/dL, p = 0.015). We also observed a variation of negative weight (decrease the end compared to the beginning) of the vildagliptin and a positive (increase) in the gliclazide (-0.3 vs. +1.4 Kg, p = 0.048). The decrease in A1c was lower in the vildagliptin group compared to gliclazide (-1.7 vs.-2.3 %, P = 0.031), however there was no difference in the number of patients reaching target glycated hemoglobin <7 % (50 vs. 61.1 %, p = 0.738). Only the group of vildagliptin presented at the end of the study compared to the beginning, decreased insulin values (599.6 vs.705, 59 pg/ml, p = 0.021), glucagon (46.6 vs.65, 2 pg/ml, p = 0.004) and the marker of oxidative stress TBARS (8.0 vs. 9.0 nmol MDA/ml, p = 0.035).

CONCLUSION

Vildagliptin showed some advantages in addition to metformin in relation to addition of gliclazide. Patients treated with vildagliptin had a higher HDL at the end of the study, less variance in weight, reduced insulin and glucagon as well as reduction of oxidative stress.

The effects of dipeptidyl peptidase-4 inhibition on microvascular diabetes complications

We performed a review of the literature to determine whether the dipeptidyl peptidase-4 inhibitors (DPP4-I) may have the capability to directly and positively influence diabetic microvascular complications. The literature was scanned to identify experimental and clinical evidence that DPP4-I can ameliorate diabetic microangiopathy. We retrieved articles published between 1 January 1980 and 1 March 2014 in English-language peer-reviewed journals using the following terms: ("diabetes" OR "diabetic") AND ("retinopathy" OR "retinal" OR "nephropathy" OR "renal" OR "albuminuria" OR "microalbuminuria" OR "neuropathy" OR "ulcer" OR "wound" OR "bone marrow"); ("dipeptidyl peptidase-4" OR "dipeptidyl peptidase-IV" OR "DPP-4" OR "DPP-IV"); and ("inhibition" OR "inhibitor"). Experimentally, DPP4-I appears to improve inflammation, endothelial function, blood pressure, lipid metabolism, and bone marrow function. Several experimental studies report direct potential beneficial effects of DPP4-I on all microvascular diabetes-related complications. These drugs have the ability to act either directly or indirectly via improved glucose control, GLP-1 bioavailability, and modifying nonincretin substrates. Although preliminary clinical data support that DPP4-I therapy can protect from microangiopathy, insufficient evidence is available to conclude that this class of drugs directly prevents or decreases microangiopathy in humans independently from improved glucose control. Experimental findings and preliminary clinical data suggest that DPP4-I, in addition to improving metabolic control, have the potential to interfere with the onset and progression of diabetic microangiopathy. Further evidence is needed to confirm these effects in patients with diabetes.

Glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1: Incretin actions beyond the pancreas

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are the two primary incretin hormones secreted from the intestine on ingestion of various nutrients to stimulate insulin secretion from pancreatic β-cells glucose-dependently. GIP and GLP-1 undergo degradation by dipeptidyl peptidase-4 (DPP-4), and rapidly lose their biological activities. The actions of GIP and GLP-1 are mediated by their specific receptors, the GIP receptor (GIPR) and the GLP-1 receptor (GLP-1R), which are expressed in pancreatic β-cells, as well as in various tissues and organs. A series of investigations using mice lacking GIPR and/or GLP-1R, as well as mice lacking DPP-4, showed involvement of GIP and GLP-1 in divergent biological activities, some of which could have implications for preventing diabetes-related microvascular complications (e.g., retinopathy, nephropathy and neuropathy) and macrovascular complications (e.g., coronary artery disease, peripheral artery disease and cerebrovascular disease), as well as diabetes-related comorbidity (e.g., obesity, non-alcoholic fatty liver disease, bone fracture and cognitive dysfunction). Furthermore, recent studies using incretin-based drugs, such as GLP-1 receptor agonists, which stably activate GLP-1R signaling, and DPP-4 inhibitors, which enhance both GLP-1R and GIPR signaling, showed that GLP-1 and GIP exert effects possibly linked to prevention or treatment of diabetes-related complications and comorbidities independently of hyperglycemia. We review recent findings on the extrapancreatic effects of GIP and GLP-1 on the heart, brain, kidney, eye and nerves, as well as in the liver, fat and several organs from the perspective of diabetes-related complications and comorbidities.

Dipeptidyl-peptidase 4 inhibition: linking metabolic control to cardiovascular protection

Dipeptidyl peptidases 4 (DPP4) inhibitors are a new class of oral anti-hyperglycemic drugs for the treatment of type 2 diabetes (T2DM). They are also called "incretins" because they act by inhibiting the degradation of endogenous incretin hormones, in particular GLP-1, that mediates their main metabolic effects. DPP4 is an ubiquitous protease that regulates not only glucose and lipid metabolism, but also exhibits several systemic effects at different site levels. DPP4 inhibition improves endothelial function, reduces the pro-oxidative and the pro-inflammatory state, and exerts renal effects. These actions are mediated by different DPP4 ligands, such as cytokines, growth factors, neuotransmitters etc. Clinical and experimental studies have demonstrated that DPP4 inhibitors are efficient in protecting cardiac, renal and vascular systems, through antiatherosclerotic and vasculoprotective mechanisms. For these reasons DDP4 inhibitors are thought to be "cardiovascular protective" as well as anti-diabetic drugs. Clinical trials aimed to demonstrate the efficacy of DPP4 inhibitors in reducing cardiovascular events, independent of their anti-hyperglycemic action, are ongoing. These trials will also give necessary information on their safety.

Cardiovascular actions of GLP-1 and incretin-based pharmacotherapy

Incretin-based therapy became recently available as antihyperglycemic treatment for patients with type 2 diabetes (T2DM). Incretin therapy comprises glucagon-like peptide receptor agonists (GLP-1RA) and dipeptidyl-peptidase 4 inhibitors (DPP4-I): these classes of drugs not only have the ability to reduce blood glucose, but also can exert several cardioprotective effects. They have been shown to positively influence some risk factors for cardiovascular disease (CVD), to improve endothelial function, and to directly affect cardiac function. For these reasons incretins are considered not only antidiabetic drugs, but also cardiovascular effective. The first clinical trials aimed to demonstrate the safety of DPP4 inhibitors have been recently published: their clinical significance will be discussed in light of the prior experimental findings.

Beneficial Effects of Vildagliptin on Retinal Injury in Obese Type 2 Diabetic Rats

<b><i>Background/Aims:</i></b> Vildagliptin is an oral inhibitor of dipeptidyl peptidase-4, an enzyme mainly responsible for inactivating incretins, and one of the widely used drugs for the treatment of type 2 diabetes. However, effects of vildagliptin on retinal injury in diabetes remain unclear. We examined here whether oral administration of vildagliptin inhibited gene expression of inflammatory and thrombogenic parameters in Otsuka Long-Evans Tokushima Fatty rats (OLETF rats), an animal model of obese type 2 diabetes. <b><i>Methods:</i></b> OLETF rats at 22 weeks of age were given vehicle or 3 mg/kg of vildagliptin for another 10 weeks. Gene expression was analyzed in quantitative real-time reverse transcription-polymerase chain reaction. <b><i>Results:</i></b> Vildagliptin significantly inhibited the increase in body weight and decreased average fasting blood glucose in the OLETF rats. Compared with 22-week-old OLETF rats, gene expression levels of vascular endothelial growth factor, intercellular adhesion molecule-1, plasminogen activator inhibitor-1 and pigment epithelium-derived factor were significantly increased in the retinas of OLETF rats at 32 weeks of age, all of which were inhibited by treatment with vildagliptin. <b><i>Conclusions:</i></b> The present study demonstrated for the first time that vildagliptin inhibited inflammatory and thrombogenic reactions in the retinas of obese type 2 diabetic rats. Vildagliptin may play a protective role against diabetic retinopathy.

Serum levels of advanced glycation end products (AGEs) are independently correlated with circulating levels of dipeptidyl peptidase-4 (DPP-4) in humans

OBJECTIVES

Inhibition of dipeptidyl peptidase-4 (DPP-4) has been proposed as a potential therapeutic target for type 2 diabetes. Although soluble DPP-4 has been identified in human serum and could be associated with DPP-4 activity, the kinetics and regulation of circulating DPP-4 levels remain unknown. In this study, we examined which anthropometric and metabolic variables, including serum levels of advanced glycation end products (AGEs), were independently associated with serum DPP-4 levels. Further, we investigated the effects of AGEs on DPP-4 expression in, and soluble DPP-4 release from human cultured proximal tubular epithelial cells.

DESIGN AND METHODS

The study involved 432 consecutive outpatients (301 males and 131 females; mean ages 61.8 ± 8.8) who underwent complete history and physical examinations, and determinations of blood chemistry and anthropometric variables. Serum DPP-4 and AGE levels were examined by enzyme-linked immunosorbent assay. Protein expression levels of DPP-4 and its release from the cells were analyzed with western blot analysis.

RESULTS

Mean serum levels of DPP-4 and AGEs were 520.2 ± 39.9 ng/mL and 8.96 ± 2.57 U/mL, respectively. In multiple regression analysis, female (p<0.001), HDL-cholesterol (p<0.001), glycated hemoglobin (p<0.001), AGEs (p<0.03), and the absence of hypertension medication (p<0.05) are independently associated with DPP-4 levels (R(2)=0.167). Western blot analysis revealed that AGEs significantly increased DPP-4 expression in, and soluble DPP-4 release from tubular cells.

CONCLUSIONS

The present study reveals that serum levels of DPP-4 are independently associated with various metabolic parameters in a general population. AGEs may up-regulate cellular DPP-4 expression and subsequently increase circulating levels of DPP-4 in humans.