Glucagon-like peptide-1 receptor agonist ameliorates renal injury through its anti-inflammatory action without lowering blood glucose level in a rat model of type 1 diabetes

Long-term treatment with the sodium glucose cotransporter 2 inhibitor, dapagliflozin, ameliorates glucose homeostasis and diabetic nephropathy in db/db mice

Inhibition of sodium glucose cotransporter 2 (SGLT2) has been reported as a new therapeutic strategy for treating diabetes. However, the effect of SGLT2 inhibitors on the kidney is unknown. In addition, whether SGLT2 inhibitors have an anti-inflammatory or antioxidative stress effect is still unclear. In this study, to resolve these issues, we evaluated the effects of the SGLT2 inhibitor, dapagliflozin, using a mouse model of type 2 diabetes and cultured proximal tubular epithelial (mProx24) cells. Male db/db mice were administered 0.1 or 1.0 mg/kg of dapagliflozin for 12 weeks. Body weight, blood pressure, blood glucose, hemoglobin A1c, albuminuria and creatinine clearance were measured. Mesangial matrix accumulation and interstitial fibrosis in the kidney and pancreatic β-cell mass were evaluated by histological analysis. Furthermore, gene expression of inflammatory mediators, such as osteopontin, monocyte chemoattractant protein-1 and transforming growth factor-β, was evaluated by quantitative reverse transcriptase-PCR. In addition, oxidative stress was evaluated by dihydroethidium and NADPH oxidase 4 staining. Administration of 0.1 or 1.0 mg/kg of dapagliflozin ameliorated hyperglycemia, β-cell damage and albuminuria in db/db mice. Serum creatinine, creatinine clearance and blood pressure were not affected by administration of dapagliflozin, but glomerular mesangial expansion and interstitial fibrosis were suppressed in a dose-dependent manner. Dapagliflozin treatment markedly decreased macrophage infiltration and the gene expression of inflammation and oxidative stress in the kidney of db/db mice. Moreover, dapagliflozin suppressed the high-glucose-induced gene expression of inflammatory cytokines and oxidative stress in cultured mProx24 cells. These data suggest that dapagliflozin ameliorates diabetic nephropathy by improving hyperglycemia along with inhibiting inflammation and oxidative stress.

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.

Clinical therapeutic strategies for early stage of diabetic kidney disease

Diabetic kidney disease (DKD) is the most common cause of chronic kidney disease, leading to end-stage renal disease and cardiovascular disease. The overall number of patients with DKD will continue to increase in parallel with the increasing global pandemic of type 2 diabetes. Based on landmark clinical trials, DKD has become preventable by controlling conventional factors, including hyperglycemia and hypertension, with multifactorial therapy; however, the remaining risk of DKD progression is still high. In this review, we show the importance of targeting remission/regression of microalbuminuria in type 2 diabetic patients, which may protect against the progression of DKD and cardiovascular events. To achieve remission/regression of microalbuminuria, several steps are important, including the early detection of microalbuminuria with continuous screening, targeting HbA1c < 7.0% for glucose control, the use of renin angiotensin system inhibitors to control blood pressure, the use of statins or fibrates to control dyslipidemia, and multifactorial treatment. Reducing microalbuminuria is therefore an important therapeutic goal, and the absence of microalbuminuria could be a pivotal biomarker of therapeutic success in diabetic patients. Other therapies, including vitamin D receptor activation, uric acid-lowering drugs, and incretin-related drugs, may also be promising for the prevention of DKD progression.

Prevention of obesity-induced renal injury in male mice by DPP4 inhibition

Therapies to prevent renal injury in obese hypertensive individuals are being actively sought due to the obesity epidemic arising from the Western diet (WD), which is high in fructose and fat. Recently, activation of the immune system and hyperuricemia, observed with high fructose intake, have been linked to the pathophysiology of hypertension and renal injury. Because dipeptidyl peptidase 4 (DPP4) is a driver of maladaptive T-cell/macrophage responses, renal-protective benefits of DPP4 inhibition in the WD-fed mice were examined. Mice fed a WD for 16 weeks were given the DPP4 inhibitor MK0626 in their diet beginning at 4 weeks of age. WD-fed mice were obese, hypertensive, and insulin-resistant and manifested proteinuria and increased plasma DPP4 activity and uric acid levels. WD-fed mice also had elevated kidney DPP4 activity and monocyte chemoattractant protein-1 and IL-12 levels and suppressed IL-10 levels in the kidney, suggesting macrophage-driven inflammation, glomerular and tubulointerstitial injury. WD-induced increases in DPP4 activation in the plasma and kidney and proteinuria in WD mice were abrogated by MK0626, although blood pressure and systemic insulin sensitivity were not improved. Contemporaneously, MK0626 reduced serum uric acid levels, renal oxidative stress, and IL-12 levels and increased IL-10 levels, suggesting that suppression of DPP4 activity leads to suppression of renal immune/inflammatory injury responses to a WD. Taken together, these results demonstrate that DPP4 inhibition prevents high-fructose/high-fat diet-induced glomerular and tubular injury independent of blood pressure/insulin sensitivity and offers a potentially novel therapy for diabetic and obesity-related kidney disease.

Adenosine kinase inhibition protects the kidney against streptozotocin-induced diabetes through anti-inflammatory and anti-oxidant mechanisms

Adenosine provides anti-inflammatory effects in cardiovascular disease via the activation of adenosine A2A receptors; however, the physiological effect of adenosine could be limited due to its phosphorylation by adenosine kinase. We hypothesized that inhibition of adenosine kinase exacerbates extracellular adenosine levels to reduce renal inflammation and injury in streptozotocin-induced diabetes. Diabetes was induced in male C57BL/6 mice by daily injection of streptozotocin (50mg/kg/day, i.p. for 5 days). Control and diabetic mice were then treated with the adenosine kinase inhibitor ABT702 (1.5mg/kg, i.p. two times a week for 8 weeks, n=7-8/group) or the vehicle (5% DMSO). ABT702 treatment reduced blood glucose level in diabetic mice (∼20%; P<0.05). ABT702 also reduced albuminuria and markers of glomerular injury, nephrinuria and podocalyxin excretion levels, in diabetic mice. Renal NADPH oxidase activity and urinary thiobarbituric acid reactive substances (TBARS) excretion, indices of oxidative stress, were also elevated in diabetic mice and ABT702 significantly reduced these changes. ABT702 increased renal endothelial nitric oxide synthase expression (eNOS) and nitrate/nitrite excretion levels in diabetic mice. In addition, the diabetic mice displayed an increase in renal macrophage infiltration, in association with increased renal NFκB activation. Importantly, treatment with ABT702 significantly reduced all these inflammatory parameters (P<0.05). Furthermore, ABT702 decreased glomerular permeability and inflammation and restored the decrease in glomerular occludin expression in vitro in high glucose treated human glomerular endothelial cells. Collectively, the results suggest that the reno-protective effects of ABT702 could be attributed to the reduction in renal inflammation and oxidative stress in diabetic mice.

Sitagliptin improves albuminuria in patients with type 2 diabetes mellitus

INTRODUCTION

The aim of the present study was to determine the effect of sitagliptin on microalbuminuria in patients with type 2 diabetes mellitus.

MATERIALS AND METHODS

A total of 85 patients with type 2 diabetes mellitus (age >20 years, <80 years, hemoglobin A1c [HbA1c] <8.4%) were randomized to patients taking sitagliptin 50 mg or other oral glucose-lowering agents. The following parameters were evaluated at 0, 3 and 6 months after the treatment: bodyweight, blood pressure, HbA1c, fasting plasma glucose, fasting plasma insulin, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, triglycerides, estimated glomerular filtration rate and urinary albumin excretion. The primary outcome was changes in urinary albumin excretion at 6 months.

RESULTS

Significant and comparable falls in HbA1c and fasting plasma glucose were found in both groups. However, sitagliptin significantly reduced urinary albumin excretion within 6 months, especially in patients with high urinary albumin at baseline. A total of 27 patients with normoalbuminuria showed a reduction in urinary albumin excretion, suggesting that sitagliptin prevents the development of albuminuria. A total of 15 patients with albuminuria showed a reduction in urinary albumin excretion, suggesting the beneficial effect of sitagliptin in the early stage of diabetic nephropathy. There was a significant correlation between improvement of proteinuria and that of diastolic blood pressure.

CONCLUSIONS

The results suggested that sitagliptin improved albuminuria, in addition to improving glucose. The mechanism of the reduction of albuminuria by sitagliptin could be a direct effect, as well as an increase in active glucagon-like peptide-1, independently affecting blood pressure, bodyweight and glucose metabolism. This trial was registered with the University Hospital Medical Information Network (UMIN no. #000010871).

The stem cell adjuvant with Exendin-4 repairs the heart after myocardial infarction via STAT3 activation

The poor survival of cells in ischaemic myocardium is a major obstacle for stem cell therapy. Exendin-4 holds the potential of cardioprotective effect based on its pleiotropic activity. This study investigated whether Exendin-4 in conjunction with adipose-derived stem cells (ADSCs) could improve the stem cell survival and contribute to myocardial repairs after infarction. Myocardial infarction (MI) was induced by the left anterior descending artery ligation in adult male Sprague-Dawley rats. ADSCs carrying double-fusion reporter gene [firefly luciferase and monomeric red fluorescent protein (fluc-mRFP)] were quickly injected into border zone of MI in rats treated with or without Exendin-4. Exendin-4 enhanced the survival of transplanted ADSCs, as demonstrated by the longitudinal in vivo bioluminescence imaging. Moreover, ADSCs adjuvant with Exendin-4 decreased oxidative stress, apoptosis and fibrosis. They also improved myocardial viability and cardiac function and increased the differentiation rates of ADSCs into cardiomyocytes and vascular smooth muscle cells in vivo. Then, ADSCs were exposed to hydrogen peroxide/serum deprivation (H₂O₂/SD) to mimic the ischaemic environment in vitro. Results showed that Exendin-4 decreased the apoptosis and enhanced the paracrine effect of ADSCs. In addition, Exendin-4 activated signal transducers and activators of transcription 3 (STAT3) through the phosphorylation of Akt and ERK1/2. Furthermore, Exendin-4 increased the anti-apoptotic protein Bcl-2, but decreased the pro-apoptotic protein Bax of ADSCs. In conclusion, Exendin-4 could improve the survival and therapeutic efficacy of transplanted ADSCs through STAT3 activation via the phosphorylation of Akt and ERK1/2. This study suggests the potential application of Exendin-4 for stem cell–based heart regeneration.

Sitagliptin prevents inflammation and apoptotic cell death in the kidney of type 2 diabetic animals

This study aimed to evaluate the efficacy of sitagliptin, a dipeptidyl peptidase IV (DPP-IV) inhibitor, in preventing the deleterious effects of diabetes on the kidney in an animal model of type 2 diabetes mellitus; the Zucker diabetic fatty (ZDF) rat: 20-week-old rats were treated with sitagliptin (10 mg/kg bw/day) during 6 weeks. Glycaemia and blood HbA1c levels were monitored, as well as kidney function and lesions. Kidney mRNA and/or protein content/distribution of DPP-IV, GLP-1, GLP-1R, TNF-α, IL-1β, BAX, Bcl-2, and Bid were evaluated by RT-PCR and/or western blotting/immunohistochemistry. Sitagliptin treatment improved glycaemic control, as reflected by the significantly reduced levels of glycaemia and HbA1c (by about 22.5% and 1.2%, resp.) and ameliorated tubulointerstitial and glomerular lesions. Sitagliptin prevented the diabetes-induced increase in DPP-IV levels and the decrease in GLP-1 levels in kidney. Sitagliptin increased colocalization of GLP-1 and GLP-1R in the diabetic kidney. Sitagliptin also decreased IL-1β and TNF-α levels, as well as, prevented the increase of BAX/Bcl-2 ratio, Bid protein levels, and TUNEL-positive cells which indicates protective effects against inflammation and proapoptotic state in the kidney of diabetic rats, respectively. In conclusion, sitagliptin might have a major role in preventing diabetic nephropathy evolution due to anti-inflammatory and antiapoptotic properties.

Effect of exenatide on the cardiac expression of adiponectin receptor 1 and NADPH oxidase subunits and heart function in streptozotocin-induced diabetic rats

BACKGROUND

This study investigated the effect of exenatide on the cardiac expression of adiponectin receptor 1 and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunits and heart function in streptozotocin-induced diabetic rats.

METHODS

Male Sprague-Dawley rats were randomly divided into four groups, i.e. control group, diabetic group, diabetic treated with low doses of exenatide (2 μg · kg-1.d-1) and diabetic treated with high doses of exenatide (10 μg · kg-1.d-1). Diabetes was induced by intraperitoneal injection of streptozotocin (65 mg/kg body weight). At the termination after exenatide treatment for eight weeks, following anesthesia of the rats, a catheter was inserted into the left ventricle through the right common carotid artery for measurement of left ventricular pressure, which included left ventricular systolic pressure (LVSP), left ventricular end-diastolic pressure (LVEDP) and the maximal rate of rise and decline of ventricular pressure (±dp/dt[max]). Plasma and myocardial adiponectin levels, and the expressions of myocardial adiponectin receptor 1, p22phox, NADPH oxidase 4 (NOX4), glucose transporter type 4 (Glut4), AMPK-α, phosphorylated-AMPK-α, connective tissue growth factor (CTGF) and copper zinc superoxide dismutase (Cu-Zn-SOD) were assayed.

RESULTS

Heart function, plasma adiponectin levels, the protein expression of myocardial phosphorylated-AMPK-α, the mRNA expression of myocardial Glut4, and the positive expression of myocardial Cu-Zn-SOD were significantly decreased in diabetic. The protein expression of myocardial adiponectin receptor 1, the mRNA expression of myocardial p22phox and NOX4, and the positive expression of myocardial CTGF were significantly increased in diabetic. Low and high doses of exenatide treatment significantly attenuated these changes in diabetic rats.

CONCLUSIONS

These results suggest that exenatide may contribute to the improvement of the heart function in diabetic rats by down-regulating the expression of myocardial adiponectin receptor 1, p22phox and NOX4, and up-regulating plasma adiponectin level and the expression of myocardial AMPK-α, Glut4 and Cu-Zn-SOD.

Metabolic surgery: shifting the focus from glycaemia and weight to end-organ health

Bariatric surgery is the most effective treatment for weight loss and glycaemic control. The focus of clinical studies and clinical experience has predominantly been on the numerical reductions of bodyweight and glucose after surgery. In this Series paper, we examine evidence on the efficacy of bariatric surgery for pancreatic, renal, retinal, peripheral nervous, cardiovascular, hepatic, and reproductive end-organ damage or disease. The overall conclusions are that, in most cases, patients' end-organ damage is expected to either stabilise or improve postoperatively. However, some of these clinical outcomes have not been assessed with robust methods and, in many cases, do not have support from randomised controlled clinical trials comparing bariatric surgery with non-surgical interventions. Such trials are urgently needed to inform patients and clinicians on whether the risks of surgery outweigh the significant benefits for end-organ health.

Improvement in psoriasis after treatment with the glucagon-like peptide-1 receptor agonist liraglutide

A 59-year old man with moderate and stable psoriasis through 15 years was admitted to our Department with inadequately controlled type 2 diabetes. Treatment was initiated with the glucagon-like peptide-1 receptor (GLP-1R) agonist liraglutide. The patient experienced marked improvement in his psoriasis immediately after the start of liraglutide treatment. Itching stopped within days, scaling was reduced and spots of normal skin emerged. After 3 months, psoriasis was still improving. Excellent glycaemic control and a weight loss of approximately 8 kg over 3 months were moreover obtained. The patient had previously been well controlled in his diabetes without improvement in psoriasis, and the effect of liraglutide on psoriasis started before weight loss occurred. We discuss the possibility of a direct anti-inflammatory effect of liraglutide in psoriasis as well as indirect effects through improvement in comorbidities such as overweight. Randomized clinical trials are needed to reveal whether GLP-1R agonists represent a new therapeutic option for psoriasis.

Metallothionein deficiency exacerbates diabetic nephropathy in streptozotocin-induced diabetic mice

Oxidative stress and inflammation play important roles in diabetic complications, including diabetic nephropathy. Metallothionein (MT) is induced in proximal tubular epithelial cells as an antioxidant in the diabetic kidney; however, the role of MT in renal function remains unclear. We therefore investigated whether MT deficiency accelerates diabetic nephropathy through oxidative stress and inflammation. Diabetes was induced by streptozotocin injection in MT-deficient (MT−/−) and MT+/+ mice. Urinary albumin excretion, histological changes, markers for reactive oxygen species (ROS), and kidney inflammation were measured. Murine proximal tubular epithelial (mProx24) cells were used to further elucidate the role of MT under high-glucose conditions. Parameters of diabetic nephropathy and markers of ROS and inflammation were accelerated in diabetic MT−/− mice compared with diabetic MT+/+ mice, despite equivalent levels of hyperglycemia. MT deficiency accelerated interstitial fibrosis and macrophage infiltration into the interstitium in the diabetic kidney. Electron microscopy revealed abnormal mitochondrial morphology in proximal tubular epithelial cells in diabetic MT−/− mice. In vitro studies demonstrated that knockdown of MT by small interfering RNA enhanced mitochondrial ROS generation and inflammation-related gene expression in mProx24 cells cultured under high-glucose conditions. The results of this study suggest that MT may play a key role in protecting the kidney against high glucose-induced ROS and subsequent inflammation in diabetic nephropathy.

Effects of alogliptin in chronic kidney disease patients with type 2 diabetes

OBJECTIVE

Diabetes is a major risk factor for chronic kidney disease (CKD). In this study, we examined the effects of alogliptin on blood glucose control and the renal function in type 2 diabetes CKD patients.

METHODS

We recruited 36 CKD patients with type 2 diabetes. The patients were followed up for six months after adding alogliptin. Blood biochemical, urine test and office BP values were obtained six months before and after the start of treatment.

RESULTS

The mean HbA1c value was not decreased; however, the 1,5-AG values tended to improve (p=0.1023). The mean eGFR was unchanged. There were no significant changes in the patients with an eGFR of 60 mL/min/1.73 m2 or more (25 patients) or in the patients with an eGFR less than 60 mL/min/1.73 m2 (11 patients). A total of 15 patients were identified to have rapidly declining diabetic nephropathy, with an annual reduction in eGFR of 5 mL/min/1.73 m2 or more. The slope of the regression line for eGFR (-1.296 before starting treatment with alogliptin) was positive, increasing up to 0.08786. The eGFR values appeared to stop decreasing and positively reversed. The urinary albumin-to-creatinine ratio exhibited a downward trend. The effect on the renal function was independent of the levels of blood sugar, blood pressure and lipids.

CONCLUSION

We examined the ability of alogliptin to maintain the renal function in patients with CKD complicated by type 2 diabetes. Our study suggests that alogliptin can be safely administered in patients with CKD. However, although we expected alogliptin to demonstrate renal protective effects, were unable to detect statistically significant differences. One reason for this finding is that there are few registered cases.

The gut-renal axis: do incretin-based agents confer renoprotection in diabetes?

Diabetic nephropathy is the leading cause of end-stage renal disease worldwide, and is associated with a high risk of cardiovascular morbidity and mortality. Intensive control of glucose levels and blood pressure is currently the mainstay of both prevention and treatment of diabetic nephropathy. However, this strategy cannot fully prevent the development and progression of diabetic nephropathy, and an unmet need remains for additional novel therapies. The incretin-based agents--agonists of glucagon-like peptide 1 receptor (GLP-1R) and inhibitors of dipeptidyl peptidase 4 (DPP-4), an enzyme that degrades glucagon-like peptide 1--are novel blood-glucose-lowering drugs used in the treatment of type 2 diabetes mellitus (T2DM). Therapeutic agents from these two drug classes improve pancreatic islet function and induce extrapancreatic effects that ameliorate various phenotypic defects of T2DM that are beyond glucose control. Agonists of GLP-1R and inhibitors of DPP-4 reduce blood pressure, dyslipidaemia and inflammation, although only GLP-1R agonists decrease body weight. Both types of incretin-based agents inhibit renal tubular sodium reabsorption and decrease glomerular pressure as well as albuminuria in rodents and humans. In rodents, incretin-based therapies also prevent onset of the morphological abnormalities of diabetic nephropathy.

Dipeptidyl peptidase-4 inhibitor ameliorates early renal injury through its anti-inflammatory action in a rat model of type 1 diabetes

INTRODUCTION

Dipeptidyl peptidase-4 (DPP-4) inhibitors are incretin-based drugs in patients with type 2 diabetes. In our previous study, we showed that glucagon-like peptide-1 (GLP-1) receptor agonist has reno-protective effects through anti-inflammatory action. The mechanism of action of DPP-4 inhibitor is different from that of GLP-1 receptor agonists. It is not obvious whether DPP-4 inhibitor prevents the exacerbation of diabetic nephropathy through anti-inflammatory effects besides lowering blood glucose or not. The purpose of this study is to clarify the reno-protective effects of DPP-4 inhibitor through anti-inflammatory actions in the early diabetic nephropathy.

MATERIALS AND METHODS

Five-week-old male Sprague-Dawley (SD) rats were divided into three groups; non-diabetes, diabetes and diabetes treated with DPP-4 inhibitor (PKF275-055; 3 mg/kg/day). PKF275-055 was administered orally for 8 weeks.

RESULTS

PKF275-055 increased the serum active GLP-1 concentration and the production of urinary cyclic AMP. PKF275-055 decreased urinary albumin excretion and ameliorated histological change of diabetic nephropathy. Macrophage infiltration was inhibited, and inflammatory molecules were down-regulated by PKF275-055 in the glomeruli. In addition, nuclear factor-κB (NF-κB) activity was suppressed in the kidney.

CONCLUSIONS

These results indicate that DPP-4 inhibitor, PKF275-055, have reno-protective effects through anti-inflammatory action in the early stage of diabetic nephropathy. The endogenous biological active GLP-1 might be beneficial on diabetic nephropathy besides lowering blood glucose.

Alleviation of hyperglycemia induced vascular endothelial injury by exenatide might be related to the reduction of nitrooxidative stress

We will investigate the effects of exenatide on vascular endothelial injury and nitrooxidative stress in hyperglycemia both in vivo and in vitro and explore the role of nitrooxidative stress in endothelium-protective action of exenatide. Healthy male Wistar rats were randomly divided into 4 groups: control, diabetes mellitus (DM) model, low dose of exenatide treatment, and high dose of exenatide treatment. In vitro study showed that, compared with control group, the DM rats exhibited a lowered endothelium-dependent relaxation and damaged structural integrity of thoracic aortas, and there was a significant increase in plasma nitrotyrosine concentration. These parameters were improved after treatment with either low dose or high dose of exenatide for 45 days. In vitro study showed that exendin-4 (the active ingredient of exenatide) attenuated HUVECs injury induced by high glucose, with improving cell viability and attenuating cell apoptosis. Exendin-4 also significantly alleviated the increased malondialdehyde (MDA), nitrotyrosine content, and inducible nitric oxide synthase (iNOS) expression induced by high glucose in HUVECs. In conclusion, this study demonstrates that exenatide treatment can alleviate the vascular endothelial injury, as well as attenuating the nitrooxidative stress in hyperglycemia, implying that the endothelium-protective effect of exenatide might be related to the reduction of nitrooxidative stress.

The protective roles of GLP-1R signaling in diabetic nephropathy: possible mechanism and therapeutic potential

Glucagon-like peptide-1 (GLP-1) is a gut incretin hormone that has an antioxidative protective effect on various tissues. Here, we determined whether GLP-1 has a role in the pathogenesis of diabetic nephropathy using nephropathy-resistant C57BL/6-Akita and nephropathy-prone KK/Ta-Akita mice. By in situ hybridization, we found the GLP-1 receptor (GLP-1R) expressed in glomerular capillary and vascular walls, but not in tubuli, in the mouse kidney. Next, we generated C57BL/6-Akita Glp1r knockout mice. These mice exhibited higher urinary albumin levels and more advanced mesangial expansion than wild-type C57BL/6-Akita mice, despite comparable levels of hyperglycemia. Increased glomerular superoxide, upregulated renal NAD(P)H oxidase, and reduced renal cAMP and protein kinase A (PKA) activity were noted in the Glp1r knockout C57BL/6-Akita mice. Treatment with the GLP-1R agonist liraglutide suppressed the progression of nephropathy in KK/Ta-Akita mice, as demonstrated by reduced albuminuria and mesangial expansion, decreased levels of glomerular superoxide and renal NAD(P)H oxidase, and elevated renal cAMP and PKA activity. These effects were abolished by an adenylate cyclase inhibitor SQ22536 and a selective PKA inhibitor H-89. Thus, GLP-1 has a crucial role in protection against increased renal oxidative stress under chronic hyperglycemia, by inhibition of NAD(P)H oxidase, a major source of superoxide, and by cAMP-PKA pathway activation.

Effects of glucagon-like peptide-1 receptor agonists on renal function

Glucagon-like peptide-1 (GLP-1) receptor agonists result in greater improvements in glycemic control than placebo and promote weight loss with minimal hypoglycemia in patients with type 2 diabetes mellitus. A number of case reports show an association of GLP-1 receptor agonists, mainly exenatide, with the development of acute kidney injury. The present review aims to present the available data regarding the effects of GLP-1 receptor agonists on renal function, their use in subjects with chronic renal failure and their possible association with acute kidney injury. Based on the current evidence, exenatide is eliminated by renal mechanisms and should not be given in patients with severe renal impairment or end stage renal disease. Liraglutide is not eliminated by renal or hepatic mechanisms, but it should be used with caution since there are only limited data in patients with renal or hepatic impairment. There is evidence from animal studies that GLP-1 receptor agonists exert protective role in diabetic nephropathy with mechanisms that seem to be independent of their glucose-lowering effect. Additionally, there is evidence that GLP-1 receptor agonists influence water and electrolyte balance. These effects may represent new ways to improve or even prevent diabetic nephropathy.

The effect of bariatric surgery on renal function and disease: a focus on outcomes and inflammation

Renal dysfunction and disease, including hyperfiltration, proteinuria and hypofiltration, are commonly associated with obesity. Diabetic kidney disease is also common in obese cohorts. Weight loss interventions, including bariatric surgery, can effectively reduce weight and improve renal outcomes. Some of this effect may be due to the remission of Type 2 diabetes and hypertension. However, other mechanisms, including the resolution of inflammatory processes, may also contribute. The effect of bariatric surgery on renal function has only recently become a focus of particular investigation. In this study, we will review the effects of bariatric surgery on obesity-associated kidney disease. We will discuss the pitfalls in assessing renal function in obese cohorts and will examine the effect of bariatric surgery on renal function and urinary protein excretion using different mechanisms. We will give particular attention to the evidence for bariatric surgery in cohorts with established renal disease and suggest future directions. In particular, we will outline the evidence for inflammation as an important therapeutic target, and the emerging medical therapies being considered to exploit this target in obesity- and diabetes-related kidney disease.

Exendin-4 inhibits iNOS expression at the protein level in LPS-stimulated Raw264.7 macrophage by the activation of cAMP/PKA pathway

Glucagon-like peptide-1 (GLP-1) and its potent agonists have been widely studied in pancreatic islet β-cells. However, GLP-1 receptors are present in many extrapancreatic tissues including macrophages, and thus GLP-1 may have diverse actions in these tissues and cells. Therefore, we examined the mechanism by which exendin-4 (EX-4), a potent GLP-1 receptor agonist, inhibits lipopolysaccharide (LPS)-induced iNOS expression in Raw264.7 macrophage cells. EX-4 significantly inhibited LPS-induced iNOS protein expression and nitrite production. However, Northern blot and promoter analyses demonstrated that EX-4 did not inhibit LPS-induced iNOS mRNA expression and iNOS promoter activity. Electrophoretic mobility shift assay (EMSA) showed that EX-4 did not alter the binding activity of NF-κB to the iNOS promoter. Consistent with the result of EMSA, LPS-induced IκBα phosphorylation and nuclear translocation of p65 were not inhibited by EX-4. Also, actinomycin D chase study and the promoter assay using the construct containing 3'-untranslated region of iNOS showed that EX-4 did not affect iNOS mRNA stability. Meanwhile, cycloheximide chase study demonstrated that EX-4 significantly accelerated iNOS protein degradation. The EX-4 inhibition of LPS-induced iNOS protein was significantly reversed by adenylate cyclase inhibitors (MDL-12330A and SQ 22536), a PKA inhibitor (H-89) and PKAα gene silencing. These findings suggest that EX-4 inhibited LPS-induced iNOS expression at protein level, but not at transcriptional mechanism of iNOS gene and this inhibitory effect of EX-4 was mainly dependent on cAMP/PKA system.

Renal Effects of DPP-4 Inhibitors: A Focus on Microalbuminuria

Incretin-based therapies represent one of the most promising options in type 2 diabetes treatment owing to their good effectiveness with low risk of hypoglycemia and no weight gain. Other numerous potential beneficial effects of incretin-based therapies have been suggested based mostly on experimental and small clinical studies including its beta-cell- and vasculo-protective actions. One of the recently emerged interesting features of dipeptidyl peptidase-4 (DPP-4) inhibitors is its possible protective effect on the diabetic kidney disease. Here, we review the renal effects of DPP-4 inhibitors with special focus on its influence on the onset and progression of microalbuminuria, as presence of microalbuminuria represents an important early sign of kidney damage and is also associated with increased risk of hypoglycemia and cardiovascular complications. Mechanisms underlying possible nephroprotective properties of DPP-4 inhibitors include reduction of oxidative stress and inflammation and improvement of endothelial dysfunction. Effects of DPP-4 inhibitors may be both glucagon-like peptide-1 (GLP-1) dependent and independent. Ongoing prospective studies focused on the nephroprotective effects of DPP-4 inhibitors will further clarify its possible role in the prevention/attenuation of diabetic kidney disease beyond its glucose lowering properties.

Diabetic nephropathy: protective factors and a new therapeutic paradigm

Diabetic nephropathy (DN) is the most common cause of chronic kidney disease (CKD) and its number has been increasing. CKD is a worldwide threat to health but the precise mechanism of this problem is not fully appreciated. It is believed that hyperglycemia is one of the most important metabolic factors in the development of DN. Multiple molecular mechanisms have been proposed to mediate hyperglycemia's adverse effects on kidney. To identify targets for therapeutic intervention, most studies have focused on understanding how abnormal levels of such metabolities cause DN. However, there have been few reports regarding endogenous renal protective factors. Thus, recognition of the importance of this could be providing a new perspective for understanding the development of DN and a new therapeutic paradigm to combat DN.

Pharmacology, physiology, and mechanisms of incretin hormone action

Incretin peptides, principally GLP-1 and GIP, regulate islet hormone secretion, glucose concentrations, lipid metabolism, gut motility, appetite and body weight, and immune function, providing a scientific basis for utilizing incretin-based therapies in the treatment of type 2 diabetes. Activation of GLP-1 and GIP receptors also leads to nonglycemic effects in multiple tissues, through direct actions on tissues expressing incretin receptors and indirect mechanisms mediated through neuronal and endocrine pathways. Here we contrast the pharmacology and physiology of incretin hormones and review recent advances in mechanisms coupling incretin receptor signaling to pleiotropic metabolic actions in preclinical studies. We discuss whether mechanisms identified in preclinical studies have potential translational relevance for the treatment of human disease and highlight controversies and uncertainties in incretin biology that require resolution in future studies.

Dipeptidyl peptidase IV inhibitor attenuates kidney injury in rat remnant kidney

BACKGROUND

The inhibition of dipeptidyl peptidase (DPP) IV shows protective effects on tissue injury of the heart, lung, and kidney. Forkhead box O (FoxO) transcriptional factors regulate cellular differentiation, growth, survival, the cell cycle, metabolism, and oxidative stress. The aims of this study were to investigate whether the DPP IV inhibitor sitagliptin could attenuate kidney injury and to evaluate the status of FoxO3a signaling in the rat remnant kidney model.

METHODS

Rats were received two-step surgery of 5/6 renal mass reduction and fed on an oral dose of 200 mg/kg/day sitagliptin for 8 weeks. Before and after the administration of sitagliptin, physiologic parameters were measured. After 8 weeks of treatment, the kidneys were harvested.

RESULTS

The sitagliptin treatment attenuated renal dysfunction. A histological evaluation revealed that glomerulosclerosis and tubulointerstitial injury were significantly decreased by sitagliptin. Sitagliptin decreased DPP IV activity and increased the renal expression of glucagon-like peptide-1 receptor (GLP-1R). The subtotal nephrectomy led to the activation of phosphatidylinositol 3-kinase (PI3K)-Akt and FoxO3a phosphorylation, whereas sitagliptin treatment reversed these changes, resulting in PI3K-Akt pathway inactivation and FoxO3a dephosphorylation. The renal expression of catalase was increased and the phosphorylation of c-Jun N-terminal kinase (JNK) was decreased by sitagliptin. Sitagliptin treatment reduced apoptosis by decreasing cleaved caspase-3 and -9 and Bax levels and decreased macrophage infiltration.

CONCLUSIONS

In rat remnant kidneys, DPP IV inhibitor attenuated renal dysfunction and structural damage. A reduction of apoptosis, inflammation and an increase of antioxidant could be suggested as a renoprotective mechanism together with the activation of FoxO3a signaling. Therefore, DPP IV inhibitors might provide a promising approach for treating CKD, but their application in clinical practice remains to be investigated.

Anti-inflammatory effects of exendin-4, a glucagon-like peptide-1 analog, on human peripheral lymphocytes in patients with type 2 diabetes

Aims/Introduction

Type 2 diabetes is characterized by dysregulation of immunity, oxidative stress and reduced incretin effects. Experimental studies suggest that glucagon‐like peptide (GLP‐1) might have immunomodulating effects. We hypothesize that GLP‐1 receptor agonist, exendin‐4, might reduce inflammatory response in type 2 diabetes.

Materials and Methods

Using peripheral blood mononuclear cells (PBMC) sampled from 10 type 2 diabetes and 10 sex‐ and age‐matched control subjects and supernatants from PBMC culture, the expression of phospho‐mitogen activated protein kinase (MAPK) signaling pathways in CD4+ T helper lymphocytes and monocytes was analyzed using flow cytometry. Cytokines/chemokines and superoxide anion before and after treatment with exendin‐4 were measured by cytometric bead array and chemiluminesence assay, respectively.

Results

Compared with control subjects, PBMC from type 2 diabetes patients showed activated MAPK (P38, c‐Jun NH2‐terminal protein kinase and extracellular signal‐regulated kinase) signaling pathway, elevated superoxide anion, increased pro‐inflammatory cytokines (tumor necrosis factor‐α, interleukin‐1β, interleukin‐6) and chemokines (CCL5/regulated on activation normal T‐cell expressed and secreted and CXCL10/interferon‐γ‐induced protein 10). These changes were attenuated by exendin‐4, possibly through the suppression of p38 MAPK.

Conclusions

These results suggest that exendin‐4 might downregulate pro‐inflammatory responses and reduce oxidative stress by suppressing MAPK signaling pathways in type 2 diabetes.

Implications of treatment that target protective mechanisms against diabetic nephropathy

Diabetes results in vascular changes and dysfunction, and vascular complications are the leading cause of morbidity and mortality in diabetic patients. There has been a continual increase in the number of diabetic nephropathy patients and epidemic increases in the number of patients progressing to end-stage renal diseases. To identify targets for therapeutic intervention, most studies have focused on understanding how abnormal levels of glucose metabolites cause diabetic nephropathy, which is of paramount importance in devising strategies to combat the development and progression of diabetic nephropathy. However, less studied than the systemic toxic mechanisms, hyperglycemia and dyslipidemia might inhibit the endogenous vascular protective factors such as insulin, vascular endothelial growth factor, and platelet-derived growth factor. In this review, we highlight the importance of enhancing endogenous protective factors to prevent or delay diabetic nephropathy.

Incretin-based therapies in the treatment of type 2 diabetes--more than meets the eye?

A lot of contradictory data regarding the serious side effects of incretin-based therapies are currently available, with more being prepared or published every month. Considering the widespread use of these drugs it should be considered a priority to establish both short- and long-term risks connected with incretin treatment. We performed an extensive literature search of the PubMed database looking for articles dealing with connections between incretin-based therapies and pancreatitis, pancreatic cancer, thyroid cancer and other neoplasms. Data obtained indicate that GLP-1 agonists and DPPIV inhibitors could increase the risk of pancreatitis and pancreatic cancer, possibly due to their capacity to increase ductal cell turnover, which has previously been found to be up-regulated in patients with obesity and T2DM. GLP-1 analogues exenatide and liraglutide seem to be connected with medullary thyroid carcinoma in rat models and, surprisingly, GLP-1 receptors have been found in papillary thyroid carcinoma, currently the most common neoplasm of the thyroid gland in humans. Changes in expression of DPPIV have been described in ovarian carcinoma, melanoma, endometrial adenocarcinoma, prostate cancer, non-small cell lung cancer and in certain haematological malignancies. In most cases loss of DPPIV activity is connected with a higher grading scale, more aggressive tumour behaviour and higher metastatic potential. In conclusion animal and human studies indicate that there could be a connection between incretin-based therapies and pancreatitis, pancreatic cancer, thyroid cancer and other neoplasms. Therefore whenever such therapy is started it would be wise to proceed with caution, especially if personal history of neoplasms is present.

Extraglycemic effects of glp-1-based therapeutics: addressing metabolic and cardiovascular risks associated with type 2 diabetes

CONTEXT

To examine whether widespread tissue expression of the glucagon-like peptide (GLP)-1 receptor supports the possibility of differential effects of GLP-1-based therapeutics on cardiac function, blood pressure, food intake, gastric emptying, and other regulatory activities. GLP-1 receptor agonists (RAs) have demonstrated pleiotropic effects on overweight/obesity, hypertension, dyslipidemia, and cardiovascular (CV) disease. Food-regulatory effects have been demonstrated in preclinical and clinical trials, including reduced gastric motility and food intake leading to body weight reductions. Native GLP-1 and GLP-1 RAs have demonstrated cardioprotective effects in preclinical models.

EVIDENCE ACQUISITION

Using PubMed, we performed a search of the recent literature on GLP-1 and GLP-1 RAs.

EVIDENCE SYNTHESIS

Preliminary clinical data indicate native GLP-1 has beneficial effects on endothelial cell function and vascular inflammation. Native GLP-1 and GLP-1 RAs have demonstrated renoprotective and antihypertensive effects, and reductions in lipid parameters. The GLP-1 RA liraglutide has also demonstrated positive effects on such markers of endothelial dysfunction as tumor necrosis factor-α and plasminogen activator inhibitor-1.

CONCLUSION

Preliminary data suggest GLP-1 RAs could benefit type 2 diabetes patients at risk for CV comorbidities. Additional studies are needed to confirm the extraglycemic and extrapancreatic effects and determine whether outcomes will translate into beneficial effects for patient care.

Glucagon-like peptide-1 (GLP-1): effect on kidney hemodynamics and renin-angiotensin-aldosterone system in healthy men

INTRODUCTION

Glucagon-like peptide-1 (GLP-1) is an incretin hormone with multiple actions in addition to control of glucose homeostasis. GLP-1 is known to cause natriuresis in humans, but the effects on basic renal physiology are still partly unknown.

SUBJECTS AND METHODS

Twelve healthy young males were examined in a randomized, controlled, double-blinded, single-day, crossover trial to evaluate the effects of 2 hours GLP-1 infusion on kidney functions. Glomerular filtration rate (GFR) and renal plasma flow (RPF) were assessed with (51)Cr-EDTA and (123)I-hippuran, respectively, using a constant infusion renal clearance technique based on timed urine sampling.

RESULTS

GLP-1 had no significant effect on either GFR [+1.9%, 95% confidence interval (-0.8; 4.6%)] or RPF [+2.4%, 95% confidence interval (-3.6; 8.8%)]. Fractional urine excretion of lithium increased 9% (P = .013) and renal sodium clearance increased 40% (P = .007). Angiotensin II decreased 19% (P = .003), whereas renin, aldosterone, and the urinary excretion of angiotensinogen showed no significant changes. glp-1 did not affect blood pressure but induced a small transient increase in heart rate.

CONCLUSION

The results indicate that although GLP-1 markedly reduces proximal tubule sodium reabsorption, the acute effects on GFR and RPF are very limited in healthy humans. The finding of GLP-1's ability to reduce angiotensin II concentration is novel and should be further elucidated.

The endothelium in diabetes: its role in insulin access and diabetic complications

The vascular endothelium has been identified as an important component in diabetes-associated complications, which include many cardiovascular disorders such as atherosclerosis, hypertension and peripheral neuropathy. Additionally, insulin's actions on the endothelium are now seen as a major factor in the metabolic effects of the hormone by increasing access to insulin sensitive tissues. Endothelial function is impaired in diabetes, obesity, and the metabolic syndrome, which could reduce insulin access to the tissue, and thus reduce insulin sensitivity independently of direct effects at the muscle cell. As such, the endothelium is a valid target for treatment of both the impaired glucose metabolism in diabetes, as well as the vascular based complications of diabetes. Here we review the basics of the endothelium in insulin action, with a focus on the skeletal muscle as insulin's major metabolic organ, and how this is affected by diabetes. We will focus on the most recent developments in the field, including current treatment possibilities.

Pleiotropic effects of incretins and antidiabetics with incretine mechanism

Discovery of physiological and pharmacological characteristics of incretins (glucagon-like peptide-1 and glucose-dependent insulinotrop polypeptide), and the introduction of various products of those into the clinical practice has fundamentally changed blood glucose lowering therapy in type 2 diabetes. In addition to the antidiabetic properties more attention is paid to their favourable pleiotropic effects independent from the blood glucose lowering such as cardio-, vaso- and renoprotectiv, blood pressure lowering effects, as well as beneficial changes on blood lipid values and hepatic steatosis. These preferential changes prevail in slightly different way when incretin mimetics applied and dipeptidyl peptidase-4 inhibitors, furthermore, prolonged action of peptides metabolised by this enzyme may serve additional benefits in this latter mentioned group. The article overviews the currently known most important pleiotropic effects of incretins from the point of view of cardiorenal risk accompanying type 2 diabetes. Orv. Hetil., 2013, 154, 248–255.

Coming full circle in diabetes mellitus: from complications to initiation

Glycaemic control, reduction of blood pressure using agents that block the renin-angiotensin system and control of dyslipidaemia are the major strategies used in the clinical management of patients with diabetes mellitus. Each of these approaches interrupts a number of pathological pathways, which directly contributes to the vascular complications of diabetes mellitus, including renal disease, blindness, neuropathy and cardiovascular disease. However, research published over the past few years has indicated that many of the pathological pathways important in the development of the vascular complications of diabetes mellitus are equally relevant to the initiation of diabetes mellitus itself. These pathways include insulin signalling, generation of cellular energy, post-translational modifications and redox imbalances. This Review will examine how the development of diabetes mellitus has come full circle from initiation to complications and suggests that the development of diabetes mellitus and the progression to chronic complications both require the same mechanistic triggers.

Telmisartan attenuates diabetic nephropathy by suppressing oxidative stress in db/db mice

BACKGROUND/AIMS

Telmisartan, an angiotensin II type 1 receptor blocker, is widely used to treat hypertension and kidney diseases, including diabetic nephropathy, because of its renoprotective effects. However, the mechanism by which telmisartan prevents proteinuria and renal dysfunction in diabetic nephropathy is still unclear. In this study, we examined the effects of telmisartan against diabetic nephropathy in db/db mice.

METHODS

Telmisartan was administered at a dose of 5 mg/kg/day for 3 weeks to db/db (diabetic) and db/m (control) mice. Urinary albumin excretion, renal histology, and the gene expression of oxidative stress and inflammatory markers in renal tissue were determined. To evaluate the effects of telmisartan on reactive oxygen species (ROS) production, superoxide was detected by dihydroethidium (DHE) staining in vivo and in vitro.

RESULTS

Telmisartan reduced albuminuria, mesangial matrix expansion, macrophage infiltration, and the expression of ROS markers (NADPH oxidase 4- and 8-hydroxydeoxyguanosine) and inflammatory cytokines (monocyte chemoattractant protein-1, osteopontin, and transforming growth factor-β) in the kidney. DHE staining showed that telmisartan decreased ROS generation in the kidney and in cultured mesangial and proximal tubular epithelial cells.

CONCLUSIONS

Taken together, these findings indicate that telmisartan protects against diabetic nephropathy by reducing diabetes-induced oxidative stress.

GLP-1 receptor activation indirectly reduces hepatic lipid accumulation but does not attenuate development of atherosclerosis in diabetic male ApoE(-/-) mice

Glucagon-like peptide-1 receptor (GLP-1R) agonists reduce lipid accumulation in peripheral tissues, attenuating atherosclerosis and hepatic steatosis in preclinical studies. We examined whether GLP-1R activation decreases atherosclerosis progression in high-fat diet-fed male ApoE(-/-) mice after administration of streptozotocin and treatment with the long-acting GLP-1R agonist taspoglutide administered once monthly vs. metformin in the drinking water for 12 wk. Taspoglutide did not reduce plaque area or lipid content in the aortic arch or abdominal aorta, and no significant change in aortic macrophage accumulation was detected after taspoglutide or metformin. In contrast, hepatic triglyceride levels were significantly reduced in livers from taspoglutide-treated mice. Both peripheral and intracerebroventricular administration of exendin-4 rapidly decreased plasma triglyceride levels in fasted mice, and taspoglutide therapy in ApoE(-/-) mice modulated the expression of hepatic genes controlling fatty acid uptake and oxidation. We were unable to detect expression of the entire Glp1r coding sequence in macrophages isolated from ApoE(-/-), C57BL/6, and IL10(-/-) mice. Similarly, Glp1r mRNA transcripts were not detected in RNA from isolated murine hepatocytes. Using Western blotting and tissue extracts from Glp1r(+/+) and Glp1r(-/-) mice, and cells transfected with a tagged murine GLP-1R cDNA, we could not validate the sensitivity and specificity of three different GLP-1R antisera commonly used for the detection of GLP-1R protein. Taken together, these findings illustrate divergent actions of GLP-1R agonists on atherosclerosis progression and accumulation of ectopic lipid in ApoE(-/-) mice and highlight the importance of indirect GLP-1R actions for the control of hepatic lipid accumulation.

Liraglutide, a long-acting GLP-1 mimetic, and its metabolite attenuate inflammation after intracerebral hemorrhage

The inflammatory response plays a pivotal role in propagating injury of intracerebral hemorrhage (ICH). Glucagon-like-peptide-1 (GLP-1) is a hormone with antidiabetic effect and may also have antiinflammatory properties. Despite consensus that the glucoregulatory action is mediated by the GLP-1 receptor (GLP-1R), mechanisms in the brain remain unclear. We investigated the effect of a long-acting GLP-1 analog, liraglutide, and its truncated metabolite, GLP-1(9-36)a from dipeptidyl peptidase-4 (DPP-4) cleavage in ICH-induced brain injury. Primary outcomes were cerebral edema formation, neurobehavior, and inflammatory parameters. GLP-1(9-36)a, GLP-1R inhibitor, adenosine monophosphate-activated protein kinase (AMPK) phosphorylation inhibitor and DPP-4 inhibitor were administered to examine the mechanisms of action. Liraglutide suppressed neuroinflammation, prevented brain edema and neurologic deficit following ICH, which were partially reversed by GLP-1R inhibitor and AMPK phosphorylation inhibitor. Liraglutide-mediated AMPK phosphorylation was unaffected by GLP-1R inhibitor, and was found to be induced by GLP-1(9-36)a. GLP-1(9-36)a showed salutary effects on primary outcomes that were reversed by AMPK phosphorylation inhibitor but not by GLP-1R inhibitor. Liraglutide and DPP-4 inhibitor co-administration reversed liraglutide-mediated AMPK phosphorylation and antiinflammatory effects. Liraglutide exerted duals actions and the antiinflammatory effects are partially mediated by its metabolite in a phosphorylated AMPK-dependent manner. Therapies that inhibit GLP-1 degradation may weaken the metabolite-mediated effects.

Role of GLP-1 and DPP-4 in diabetic nephropathy and cardiovascular disease

Although there have been major advances in the understanding of the molecular mechanisms that contribute to the development of diabetic nephropathy, current best practice still leaves a significant treatment gap. The incidence of diabetes and associated nephropathy is increasing, with the main cause of mortality being related to cardiovascular causes. Novel therapies which are both 'cardio-renal'-protective seem the logical way forward. In the present review, we discuss the GLP-1 (glucagon-like peptide-1) receptor agonists and DPP-4 (dipeptidyl peptidase-4) inhibitors (incretin-based therapies), which are novel antidiabetic agents used in clinical practice and their role in diabetic nephropathy with specific focus on renoprotection and surrogate markers of cardiovascular disease. We discuss the pleiotropic effects of the incretin-based therapies apart from glucose-lowering and highlight the non-GLP-1 effects of DPP (dipeptidyl peptidase) inhibition. Large-scale clinical studies with cardiovascular end points are underway; however, studies with renal end points are lacking but much needed.

New strategy for the treatment of type 2 diabetes mellitus with incretin-based therapy

Incretin-based therapy was first made available for the treatment of type 2 diabetes mellitus (T2DM) in the US in 2006 and in Japan in 2009. Four DPP-4 inhibitors and two GLP-1 analog/receptor agonists are currently available. The effects of incretin-based therapy are assumed to be exerted mainly through the hormonal and neuronal actions of one of the incretins, GLP-1, which is secreted from L cells localized in the small intestine. The benefits of this therapy over conventional sulfonylureas or insulin injections, such as fewer hypoglycemic events and reduced body weight gain, derive from the glucose-dependent insulinotropic effect. The protective effects of this therapy on vulnerable pancreatic β-cells and against micro/macroangiopathy in T2DM are also most welcome. Indications and/or contraindications for incretin-based therapy should be clarified by prospectively studying the experiences of Japanese T2DM patients undergoing this therapy in the clinical setting.

Protective effects of GLP-1 on glomerular endothelium and its inhibition by PKCβ activation in diabetes

To characterize glucagon-like peptide (GLP)-1 signaling and its effect on renal endothelial dysfunction and glomerulopathy. We studied the expression and signaling of GLP-1 receptor (GLP-1R) on glomerular endothelial cells and the novel finding of protein kinase A-dependent phosphorylation of c-Raf at Ser259 and its inhibition of angiotensin II (Ang II) phospho-c-Raf(Ser338) and Erk1/2 phosphorylation. Mice overexpressing protein kinase C (PKC)β2 in endothelial cells (EC-PKCβ2Tg) were established. Ang II and GLP-1 actions in glomerular endothelial cells were analyzed with small interfering RNA of GLP-1R. PKCβ isoform activation induced by diabetes decreased GLP-1R expression and protective action on the renal endothelium by increasing its degradation via ubiquitination and enhancing phospho-c-Raf(Ser338) and Ang II activation of phospho-Erk1/2. EC-PKCβ2Tg mice exhibited decreased GLP-1R expression and increased phospho-c-Raf(Ser338), leading to enhanced effects of Ang II. Diabetic EC-PKCβ2Tg mice exhibited greater loss of endothelial GLP-1R expression and exendin-4-protective actions and exhibited more albuminuria and mesangial expansion than diabetic controls. These results showed that the renal protective effects of GLP-1 were mediated via the inhibition of Ang II actions on cRaf(Ser259) and diminished by diabetes because of PKCβ activation and the increased degradation of GLP-1R in the glomerular endothelial cells.

Physical exercise, fasting glucose, and renal hyperfiltration in the general population: the Renal Iohexol Clearance Survey in Tromsø 6 (RENIS-T6)

BACKGROUND AND OBJECTIVES

Abnormally elevated GFR, or hyperfiltration, is a proposed mechanism for kidney injury in diabetes, prediabetes, and obesity. This study investigated whether lack of physical exercise is associated with hyperfiltration and whether exercise modifies the positive association between fasting glucose and measured GFR.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The Renal Iohexol Clearance Survey in Tromsø 6 measured GFR as single-sample plasma iohexol clearance in 1506 members of the general population (age 50-62 years) without diabetes, cardiovascular disease, or kidney disease. Leisure-time physical exercise was assessed by a self-administered questionnaire. Hyperfiltration was defined as GFR above the 90th percentile after adjustment for sex, age, weight, height, and use of renin-angiotensin system inhibitors.

RESULTS

High-intensity exercise was associated with lower adjusted odds of hyperfiltration in men (odds ratio [OR], 0.47; 95% confidence interval [CI], 0.28-0.80) but not in women (OR, 1.02; 95% CI, 0.60-1.72). In both sexes, high-intensity exercise modified the association between fasting glucose and GFR. A fasting glucose level 1 mmol/L higher was associated with a GFR that was 7.3 (95% CI, 4.0-10.6) and 6.2 (95% CI, 3.4-9.0) ml/min per 1.73 m(2) higher in men and women who never exercised or exercised with low intensity. There was no association between fasting glucose and GFR in men and women who exercised with high intensity (interaction, P<0.001).

CONCLUSIONS

High-intensity exercise was associated with lower odds of hyperfiltration in men and modified the association between glucose and GFR of both sexes in a population without diabetes.

Glucagon-like peptide-1 receptor agonist protects against hyperglycemia-induced cardiocytes injury by inhibiting high mobility group box 1 expression

Glucagon-like peptide-1 (GLP-1), a gut incretin hormone secreted from L cells, and a GLP-1 receptor agonist, exendin-4 (Ex-4) has been shown to be cardioprotective and could exert beneficial effects through its anti-inflammatory property. However, the mechanism remains unclear. The purpose of this study was to investigate whether Ex-4 could ameliorate myocardial cell injury by inhibiting high mobility group box 1 (HMGB1) expression under high glucose condition. Neonatal rat ventricular myocytes were prepared and then cultured with high glucose and different concentration of Ex-4. Lactate dehydrogenase (LDH), creatine kinase (CK), tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), malondialdehyde (MDA) and superoxide dismutase (SOD) were measured. HMGB1 expression was assessed by western blotting. Ex-4 significantly inhibited the increase in LDH, CK, TNF-α, IL-1β and MDA levels induced by high glucose, especially at the 1 and 10 nM concentrations as well as suppressed the decrease in SOD level. Meanwhile, HMGB1 expression was markedly increased after 12 h of hyperglycaemia (P < 0.05), which was significantly inhibited by Ex-4, especially at the 1 and 10 nM concentrations (P < 0.05). The present study suggested that Ex-4 could reduce high glucose-induced cardiocytes injury, which may be associated with the inhibition of HMGB1 expression.

GLP1 and cancer: friend or foe?

The new incretin-based therapies, dipeptidyl peptidase-4 (DPP4) inhibitors and glucagon like peptide 1 (GLP1) receptor agonists are widely used for the treatment of type 2 diabetes because of their glucose-lowering capacity with low risk of hypoglycemia. As they are weight neutral or induce weight loss in this mostly overweight population, they are popular among clinicians and patients alike. Nonetheless, concerns have been raised about GLP1's trophic effects. While increased β cell mass observed in rodents sounds appealing for treatment of diabetes, there was also an increased incidence of medullary thyroid cancer (MTC) in some species. We reviewed literature available in the Medline database until March 2012. Safety signals have emerged for MTC and pancreatic carcinoma from adverse event databases in the United States and Europe. Considering the relatively short duration of these studies, it is more likely that premalignant lesions are stimulated in presence of GLP1, rather than new neoplasms induced. Moreover, interpreting results of animal studies is difficult because of species-specific differences in presence and density of GLP1 receptors. Furthermore, data are emerging suggesting beneficial effects of GLP1 on colon and breast cancer. In conclusion, presently, the benefits of using DPP4 inhibitors or GLP1 receptor agonists for treatment of type 2 diabetes outweigh the risks. Nonetheless, their safety profile should be monitored and their indications should be widened cautiously. At present they remain contra-indicated in patients with a personal or family history of MTC or multiple endocrine neoplasia type 2.

GLP-1 analog liraglutide protects against oxidative stress and albuminuria in streptozotocin-induced diabetic rats via protein kinase A-mediated inhibition of renal NAD(P)H oxidases

Accumulating evidence has implicated that GLP-1 may have a beneficial effect on cardiovascular and renal diseases but the mechanism is not fully understood. Here we show that GLP-1 analog, liraglutide, inhibits oxidative stress and albuminuria in streptozotocin (STZ)-induced type 1 diabetes mellitus rats, via a protein kinase A (PKA)-mediated inhibition of renal NAD(P)H oxidases. Diabetic rats were randomly treated with subcutaneous injections of liraglutide (0.3 mg/kg/12 h) for 4 weeks. Oxidative stress markers (urinary 8-hydroxy-2'-deoxyguanosine and renal dihydroethidium staining), expression of renal NAD(P)H oxidase components, transforming growth factor-β (TGF-β), fibronectin and urinary albumin excretion were measured. In vitro effect of liraglutide was evaluated using cultured renal mesangial cells. Administration of liraglutide did not affect plasma glucose levels or body weights in STZ diabetic rats, but normalized oxidative stress markers, expression of NAD(P)H oxidase components, TGF-β, fibronectin in renal tissues and urinary albumin excretion, all of which were significantly increased in diabetic rats. In addition, in cultured renal mesangial cells, incubation with liraglutide for 48 h inhibited NAD(P)H-dependent superoxide production evaluated by lucigenin chemiluminescence in a dose-dependent manner. This effect was reversed by both PKA inhibitor H89 and adenylate cyclase inhibitor SQ22536, but not by Epac2 inhibition via its small interfering RNA. Liraglutide may have a direct beneficial effect on oxidative stress and diabetic nephropathy via a PKA-mediated inhibition of renal NAD(P)H oxidase, independently of a glucose-lowering effect.

Glucagon-like peptide-1 inhibits adipose tissue macrophage infiltration and inflammation in an obese mouse model of diabetes

AIMS/HYPOTHESIS

Obesity and insulin resistance are associated with low-grade chronic inflammation. Glucagon-like peptide-1 (GLP-1) is known to reduce insulin resistance. We investigated whether GLP-1 has anti-inflammatory effects on adipose tissue, including adipocytes and adipose tissue macrophages (ATM).

METHODS

We administered a recombinant adenovirus (rAd) producing GLP-1 (rAd-GLP-1) to an ob/ob mouse model of diabetes. We examined insulin sensitivity, body fat mass, the infiltration of ATM and metabolic profiles. We analysed the mRNA expression of inflammatory cytokines, lipogenic genes, and M1 and M2 macrophage-specific genes in adipose tissue by real-time quantitative PCR. We also examined the activation of nuclear factor κB (NF-κB), extracellular signal-regulated kinase 1/2 and Jun N-terminal kinase (JNK) in vivo and in vitro.

RESULTS

Fat mass, adipocyte size and mRNA expression of lipogenic genes were significantly reduced in adipose tissue of rAd-GLP-1-treated ob/ob mice. Macrophage populations (F4/80(+) and F4/80(+)CD11b(+)CD11c(+) cells), as well as the expression and production of IL-6, TNF-α and monocyte chemoattractant protein-1, were significantly reduced in adipose tissue of rAd-GLP-1-treated ob/ob mice. Expression of M1-specific mRNAs was significantly reduced, but that of M2-specific mRNAs was unchanged in rAd-GLP-1-treated ob/ob mice. NF-κB and JNK activation was significantly reduced in adipose tissue of rAd-GLP-1-treated ob/ob mice. Lipopolysaccharide-induced inflammation was reduced by the GLP-1 receptor agonist, exendin-4, in 3T3-L1 adipocytes and ATM.

CONCLUSIONS/INTERPRETATION

We suggest that GLP-1 reduces macrophage infiltration and directly inhibits inflammatory pathways in adipocytes and ATM, possibly contributing to the improvement of insulin sensitivity.

Renal and cardiac effects of DPP4 inhibitors--from preclinical development to clinical research

Inhibitors of type 4 dipeptidyl peptidase (DDP-4) were developed and approved for the oral treatment of type 2 diabetes. Its mode of action is to inhibit the degradation of incretins, such as type 1 glucagon like peptide (GLP-1), and GIP. GLP-1 stimulates glucose-dependent insulin secretion from pancreatic beta-cells and suppresses glucagon release from alpha-cells, thereby improving glucose control. Besides its action on the pancreas type 1 glucagon like peptide has direct effects on the heart, vessels and kidney mainly via the type 1 glucagon like peptide receptor (GLP-1R). Moreover, there are substrates of DPP-4 beyond incretins that have proven renal and cardiovascular effects such as BNP/ANP, NPY, PYY or SDF-1 alpha. Preclinical evidence suggests that DPP-4 inhibitors may be effective in acute and chronic renal failure as well as in cardiac diseases like myocardial infarction and heart failure. Interestingly, large cardiovascular meta-analyses of combined phase II/III clinical trials with DPP-4 inhibitors point all in the same direction: a potential reduction of cardiovascular events in patients treated with these agents. A pooled analysis of pivotal phase III, placebo-controlled, registration studies of linagliptin further showed a significant reduction of urinary albumin excretion after 24 weeks of treatment. The observation suggests direct renoprotective effects of DPP-4 inhibition that may go beyond its glucose-lowering potential. Type 4 dipeptidyl peptidase inhibitors have been shown to be very well tolerated in general, but for those excreted via the kidney dose adjustments according to renal function are needed to avoid side effects. In conclusion, the direct cardiac and renal effects seen in preclinical studies as well as meta-analysis of clinical trials may offer additional potentials - beyond improvement of glycemic control - for this newer class of drugs, such as acute kidney failure, chronic kidney failure as well as acute myocardial infarction and heart failure.

Inhibition of the expression of TGF-β1 and CTGF in human mesangial cells by exendin-4, a glucagon-like peptide-1 receptor agonist

BACKGROUND

Despite the presence of glucagon-like peptide-1 receptor (GLP-1R) in kidney tissues, its direct effect on diabetic nephropathy remains unclear. The transforming growth factor-β(1) (TGF-β(1)) and the connective tissue growth factor (CTGF) both induce extracellular matrix accumulation and persistent fibrosis in the glomerular mesangium of patients with diabetic nephropathy.

OBJECTIVE

Herein, we demonstrate that a GLP-1R agonist, exendin-4, exerts renoprotective effects through its influence on TGF-β(1) and CTGF in human mesangial cells (HMCs), cultured in a high glucose medium.

METHOD

HMCs, cultured in a high glucose medium, were used for the current study. The direct effect of exendin-4 on TGF-β(1) and CTGF expression was confirmed in HMCs. MDL-12330A (a specific adenylate cyclase inhibitor) and PKI14-22 (a protein kinase A inhibitor) were used to examine the role of the cAMP signaling pathway in exendin's anti-fibrosis action.

RESULTS

The findings showed that exendin-4 inhibited the proliferation of HMCs, and upregulated the expression of TGF-β(1) and CTGF, induced by high glucose. The effect of exendin-4 is largely dependent on the activation of adenylate cyclase.

CONCLUSION

This study provides new evidence that GLP-1 acts as an antifibrotic agent in HMCs.

Effects of long-term treatment with the dipeptidyl peptidase-4 inhibitor vildagliptin on islet endocrine cells in non-obese type 2 diabetic Goto-Kakizaki rats

Reduced β cell mass is a characteristic feature of type 2 diabetes and incretin therapy is expected to prevent this condition. However, it is unknown whether dipeptidyl peptidase-4 inhibitors influence β and α cell mass in animal models of diabetes that can be translated to humans. Therefore, we examined the long-term effects of treatment with the dipeptidyl peptidase-4 inhibitor vildagliptin on islet morphology in Goto-Kakizaki (GK) rats, a spontaneous, non-obese model of type 2 diabetes, and explored the underlying mechanisms. Four-week-old GK rats were orally administered with vildagliptin (15 mg/kg) twice daily for 18 weeks. Glucose tolerance was monitored during the study. After 18 weeks, β and α cell morphology and the expression of molecules involved in cell proliferation and cell death were examined by immunohistochemistry and morphometric analysis. We found that vildagliptin improved glucose tolerance and insulin secretion, and suppressed hyperglucagonemia by increasing plasma active glucagon-like peptide-1 concentrations. β cell mass was reduced in GK rats to 40% of that in Wistar rats, but was restored to 80% by vildagliptin. Vildagliptin enhanced β and α cell proliferation, and increased the number of small neogenetic islets. Vildagliptin also reduced the number of 8-hydroxy-2'-deoxyguanosine-positive cells and forkhead box protein O1 expression, inhibited macrophage infiltration, and enhanced S6 ribosomal protein, molecule of target of rapamycin, and pancreatic duodenal homeobox 1 expression. These results indicate that starting vildagliptin treatment from an early age improved glucose tolerance and preserved islet β cell mass in GK rats by facilitating the proliferation of islet endocrine cells.