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

Glucagon-like peptide-1 receptor agonists favorably address all components of metabolic syndrome

Cardiovascular death is the leading cause of mortality for patients with type 2 diabetes mellitus. The etiology of cardiovascular disease in diabetes may be divided into hyperglycemia per se and factors operating through components of metabolic syndrome (MetS). Hyperglycemia causes direct injury to vascular endothelium and possibly on cardiac myocytes. MetS is a cluster of risk factors like obesity, hyperglycemia, hypertension and dyslipidemia. The incidence of this syndrome is rising globally. Glucagon-like peptide-1 receptor agonists (GLP-1RA) are a group of drugs, which address all components of this syndrome favorably. Experimental evidence suggests that they have favorable actions on myocardium as well. Several compounds belonging to GLP-1RA class are in market now and a large number awaiting their entry. Although, originally this class of drugs emerged as a treatment for type 2 diabetes mellitus, more recent data generated revealed beneficial effects on multiple metabolic parameters. We have studied literature published between 2000 and 2016 to look into effects of GLP-1RA on components of MetS. Results from recently concluded clinical trials suggest that some of the molecules in this class may have favorable effects on cardiovascular outcome.

Glucagon-Like Peptide-1 and Its Class B G Protein-Coupled Receptors: A Long March to Therapeutic Successes

The glucagon-like peptide (GLP)-1 receptor (GLP-1R) is a class B G protein-coupled receptor (GPCR) that mediates the action of GLP-1, a peptide hormone secreted from three major tissues in humans, enteroendocrine L cells in the distal intestine, α cells in the pancreas, and the central nervous system, which exerts important actions useful in the management of type 2 diabetes mellitus and obesity, including glucose homeostasis and regulation of gastric motility and food intake. Peptidic analogs of GLP-1 have been successfully developed with enhanced bioavailability and pharmacological activity. Physiologic and biochemical studies with truncated, chimeric, and mutated peptides and GLP-1R variants, together with ligand-bound crystal structures of the extracellular domain and the first three-dimensional structures of the 7-helical transmembrane domain of class B GPCRs, have provided the basis for a two-domain-binding mechanism of GLP-1 with its cognate receptor. Although efforts in discovering therapeutically viable nonpeptidic GLP-1R agonists have been hampered, small-molecule modulators offer complementary chemical tools to peptide analogs to investigate ligand-directed biased cellular signaling of GLP-1R. The integrated pharmacological and structural information of different GLP-1 analogs and homologous receptors give new insights into the molecular determinants of GLP-1R ligand selectivity and functional activity, thereby providing novel opportunities in the design and development of more efficacious agents to treat metabolic disorders.

Renoprotective effects of berberine and its potential effect on the expression of β-arrestins and intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 in streptozocin-diabetic nephropathy rats

BACKGROUND

Berberine has been shown to exert protective effects against diabetic nephropathy (DN), but the mechanisms involved have not been fully characterized. The aim of the present study was to explore the effects of berberine on the expression of β-arrestins, intercellular cell adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) in DN rat kidneys and investigate the underlying molecular mechanisms.

METHODS

To create the DN model, rats fed a high-fat and high-glucose diet were injected with a single dose of streptozotocin (35 mg/kg, i.p.). Then, DN rats were either treated or not with berberine (50, 100, 200 mg/kg per day, i.g., 8 weeks). Periodic acid-Schiff staining was used to evaluate renal histopathological changes. Renal tissue levels of β-arrestin 1 and β-arrestin 2 were determined by Western blot analysis, whereas immunohistochemistry was used to determine renal ICAM-1 and VCAM-1 levels.

RESULTS

Berberine (100, 200 mg/kg) ameliorated the histopathological changes in the diabetic kidney. Western blot analysis revealed significant increases in ICAM-1 and VCAM-1 levels in the kidneys of DN rats, which were reversed by treatment with 100 and 200 mg/kg berberine. In addition, berberine treatment (50, 100, 200 mg/kg) increased diabetic-induced decreases in β-arrestin 1 and β-arrestin 2.

CONCLUSIONS

Berberine exhibited renoprotective effects in DN rats. The underlying molecular mechanisms may be associated with changes in the levels and regulation of β-arrestin expression, as well as ICAM-1 and VCAM-1 levels in the rat kidney.

Linagliptin Ameliorates Methylglyoxal-Induced Peritoneal Fibrosis in Mice

Recent studies have reported increases of methylglyoxal (MGO) in peritoneal dialysis patients, and that MGO-mediated inflammation plays an important role in the development of peritoneal fibrosis through production of transforming growth factor-β1 (TGF-β1). Linagliptin, a dipeptidyl peptidase-4 inhibitor, exerts anti-inflammatory effects independent of blood glucose levels. In this study, we examined whether linagliptin suppresses MGO-induced peritoneal fibrosis in mice. Male C57/BL6 mice were divided into three groups: control, MGO injection plus saline, and MGO injection plus linagliptin (n = 6 per group). Peritoneal fibrosis was induced by daily intraperitoneal injection of saline containing 40 mmol/L MGO for 21 days. Saline was administered intraperitoneally to the control group. Linagliptin (10 mg/kg) or saline were administrated by once-daily oral gavage from 3 weeks before starting MGO injections. Immunohistochemical staining revealed that linagliptin suppressed expression of α-smooth muscle actin and fibroblast-specific protein-1, deposition of type I and III collagen, and macrophage (F4/80) infiltration. Peritoneal equilibration testing showed improved peritoneal functions in mice treated with linagliptin. Peritoneal injection of MGO increased plasma levels of glucagon-like peptide-1 (GLP-1) in mice, and a further increase was observed in linagliptin-treated mice. Although MGO increased plasma glucose levels, linagliptin did not decrease plasma glucose levels. Moreover, linagliptin reduced the TGF-β1 concentration in the peritoneal fluid of MGO-treated mice. GLP-1 receptor (GLP-1R) was expressed in monocytes/macrophages and linagliptin suppressed GLP-1R expression in MGO-injected mice. These results suggest that oral administration of linagliptin ameliorates MGO-induced peritoneal fibrosis.

Incretin-Based Therapies for Diabetic Complications: Basic Mechanisms and Clinical Evidence

An increase in the rates of morbidity and mortality associated with diabetic complications is a global concern. Glycemic control is important to prevent the development and progression of diabetic complications. Various classes of anti-diabetic agents are currently available, and their pleiotropic effects on diabetic complications have been investigated. Incretin-based therapies such as dipeptidyl peptidase (DPP)-4 inhibitors and glucagon-like peptide-1 receptor agonists (GLP-1RA) are now widely used in the treatment of patients with type 2 diabetes. A series of experimental studies showed that incretin-based therapies have beneficial effects on diabetic complications, independent of their glucose-lowering abilities, which are mediated by anti-inflammatory and anti-oxidative stress properties. Based on these findings, clinical studies to assess the effects of DPP-4 inhibitors and GLP-1RA on diabetic microvascular and macrovascular complications have been performed. Several but not all studies have provided evidence to support the beneficial effects of incretin-based therapies on diabetic complications in patients with type 2 diabetes. We herein discuss the experimental and clinical evidence of incretin-based therapy for diabetic complications.

Exenatide and metformin express their anti-inflammatory effects on human monocytes/macrophages by the attenuation of MAPKs and NFκB signaling

Metformin and exenatide are effective antidiabetic drugs, and they seem to have pleiotropic properties improving cardiovascular outcomes. Macrophages' phenotype is essential in the development of atherosclerosis, and it can be modified during antidiabetic therapy, resulting in attenuated atherogenesis. The mechanism orchestrating this phenomenon is not fully clear. We examined the impact of exenatide and metformin on the level of TNF alpha, MCP-1, reactive oxygen species (ROS), and the activation of mitogen-activated protein kinases (MAPK), nuclear factor kappa B (NFκB), and CCAAT/enhancer-binding protein beta (C/EBP beta) in human monocytes/macrophages. We found that both drugs reduced levels of TNF alpha, ROS, and NFκB binding activity to a similar extent. Compared to metformin, exenatide was more effective in reducing MCP-1 levels. We noted that Compound C (AMPK inhibitor) reduced the impact of exenatide on cytokines, ROS, and NFκB in cultures. Both drugs elevated the C/EBP beta phosphorylation level. Experiments on MAPKs showed effective inhibitory potential of exenatide toward p38, JNK, and ERK, whereas metformin inhibited JNK and ERK only. Exenatide was more effective in the inhibition of JNK than metformin. Interestingly, an in vitro setting additive effect of drugs was absent. In conclusion, here, we report that metformin and exenatide inhibit the proinflammatory phenotype of human monocytes/macrophages via influence on MAPK, C/EBP beta, and NFκB. Exenatide was more effective than metformin in reducing MCP-1 expression and JNK activity. We also showed that some effects of exenatide relied on AMPK activation. This shed light on the possible mechanisms responsible for pleiotropic effects of metformin and exenatide.

Acute renal effects of the GLP-1 receptor agonist exenatide in overweight type 2 diabetes patients: a randomised, double-blind, placebo-controlled trial

AIMS/HYPOTHESIS

This study aimed to investigate the acute renal effects of the glucagon-like peptide-1 receptor agonist (GLP-1RA) exenatide in type 2 diabetes patients.

METHODS

We included overweight (BMI 25-40 kg/m(2)) men and postmenopausal women, aged 35-75 years with type 2 diabetes (HbA1c 48-75 mmol/mol; 6.5-9.0%) and estimated GFR ≥ 60 ml min(-1) 1.73 m(-2). Exenatide or placebo (NaCl solution, 154 mmol/l) was administrated intravenously in an acute, randomised, double-blind, placebo-controlled trial conducted at the Diabetes Center VU University Medical Center (VUMC). GFR (primary endpoint) and effective renal plasma flow (ERPF) were determined by inulin and para-aminohippurate clearance, respectively, based on timed urine sampling. Filtration fraction (FF) and effective renal vascular resistance (ERVR) were calculated, and glomerular hydrostatic pressure (PGLO) and vascular resistance of the afferent (RA) and efferent (RE) renal arteriole were estimated. Tubular function was assessed by absolute and fractional excretion of sodium (FENa), potassium (FEK) and urea (FEU), in addition to urine osmolality, pH and free water clearance. Renal damage markers, BP and plasma glucose were also determined.

RESULTS

Of the 57 patients randomised by computer, 52 were included in the final analyses. Exenatide (n = 24) did not affect GFR (mean difference +2 ± 3 ml min(-1) 1.73 m(-2), p = 0.489), ERPF, FF, ERVR or PGLO, compared with placebo (n = 28). Exenatide increased RA (p < 0.05), but did not change RE. Exenatide increased FENa, FEK, urine osmolality and pH, while FEU, urinary flow and free water clearance were decreased (all p < 0.05). Osmolar clearance and renal damage makers were not affected. Diastolic BP and mean arterial pressure increased by 3 ± 1 and 6 ± 2 mmHg, respectively, whereas plasma glucose decreased by 1.4 ± 0.1 mmol/l (all p < 0.05).

CONCLUSIONS/INTERPRETATION

Exenatide infusion does not acutely affect renal haemodynamics in overweight type 2 diabetes patients at normal filtration levels. Furthermore, acute GLP-1RA administration increases proximal sodium excretion in these patients.

TRIAL REGISTRATION

ClincialTrials.gov NCT01744236 FUNDING : The research leading to these results has been funded from: (1) the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement number 282521 - the SAFEGUARD project; and (2) the Dutch Kidney Foundation, under grant agreement IP12.87.

Glucagon-Like Peptide 1 Receptor Activation Attenuates Platelet Aggregation and Thrombosis

Short-term studies in subjects with diabetes receiving glucagon-like peptide 1 (GLP-1)-targeted therapies have suggested a reduced number of cardiovascular events. The mechanisms underlying this unexpectedly rapid effect are not known. We cloned full-length GLP-1 receptor (GLP-1R) mRNA from a human megakaryocyte cell line (MEG-01), and found expression levels of GLP-1Rs in MEG-01 cells to be higher than those in the human lung but lower than in the human pancreas. Incubation with GLP-1 and the GLP-1R agonist exenatide elicited a cAMP response in MEG-01 cells, and exenatide significantly inhibited thrombin-, ADP-, and collagen-induced platelet aggregation. Incubation with exenatide also inhibited thrombus formation under flow conditions in ex vivo perfusion chambers using human and mouse whole blood. In a mouse cremaster artery laser injury model, a single intravenous injection of exenatide inhibited thrombus formation in normoglycemic and hyperglycemic mice in vivo. Thrombus formation was greater in mice transplanted with bone marrow lacking a functional GLP-1R (Glp1r(-/-)), compared with those receiving wild-type bone marrow. Although antithrombotic effects of exenatide were partly lost in mice transplanted with bone marrow from Glp1r(-/-) mice, they were undetectable in mice with a genetic deficiency of endothelial nitric oxide synthase. The inhibition of platelet function and the prevention of thrombus formation by GLP-1R agonists represent potential mechanisms for reduced atherothrombotic events.

Renoprotective Effect of Gemigliptin, a Dipeptidyl Peptidase-4 Inhibitor, in Streptozotocin-Induced Type 1 Diabetic Mice

BACKGROUND

Dipeptidyl peptidase-4 (DPP-4) inhibitors are widely used in the treatment of patients with type 2 diabetes and have proven protective effects on diabetic kidney disease (DKD). Whether DPP-4 inhibitors have renoprotective effects on insulin-deficient type 1 diabetes has not been comprehensively examined. The aim of this study was to determine whether gemigliptin, a new DPP-4 inhibitor, has renoprotective effects in streptozotocin (STZ)-induced type 1 diabetic mice.

METHODS

Diabetes was induced by intraperitoneal administration of a single dose of STZ. Mice with diabetes were treated without or with gemigliptin (300 mg/kg) for 8 weeks. Morphological changes of the glomerular basement membrane (GBM) were observed by electron microscopy and periodic-acid Schiff staining. In addition, we measured blood glucose and urinary albumin excretion and evaluated fibrotic markers using immunohistochemical staining, quantitative reverse transcription polymerase chain reaction analysis, and Western blot analysis.

RESULTS

Gemigliptin did not reduce the blood glucose levels of STZ-treated mice. In gemigliptin-treated mice with STZ, a significant reduction in urinary albumin excretion and GBM thickness was observed. Immunohistological examination revealed that gemigliptin attenuated renal fibrosis induced by STZ and decreased extracellular matrix protein levels, including those of type I collagen and fibronectin, and Smad3 phosphorylation. In cultured rat renal cells, gemigliptin inhibited transforming growth factor β-stimulated type I collagen and fibronectin mRNA and protein levels via down-regulation of Smad3 phosphorylation.

CONCLUSION

Our data demonstrate that gemigliptin has renoprotective effects on DKD, regardless of its glucose-lowering effect, suggesting that it could be used to prevent DKD, including in patients with type 1 diabetes.

The glucagon like peptide 1 analogue, exendin-4, attenuates oxidative stress-induced retinal cell death in early diabetic rats through promoting Sirt1 and Sirt3 expression

This study was aimed to further investigate the possible mechanisms by which the glucagon like peptide 1 analogue, exendin-4 (EX4), protects rat retinal cells at the early stage of diabetes. EX4 was injected intravitreally into normal and early-stage streptozotocin-diabetic rats. Cell death, reactive oxygen species (ROS), and electroretinogram (ERG) were measured. Sirtuin (Sirt) mRNA and protein were analyzed. In retinas of diabetic rats 1 month after diabetes onset, cell death and ROS level increased significantly, and the b-wave amplitudes and OPs were significantly reduced. Four days after intravitreal EX4 treatment, retinal cell death and ROS level in retinas reduced significantly, and visual function was recovered. In the retinas of early-stage diabetic rats, the expressions of Sirt1 and Sirt3 were also found to be significantly decreased, and both were back to normal levels after intravitreal injection of EX4. In R28 cells, hydrogen peroxide (H2O2) treatment increased ROS and cell death and decreased Sirt1 and Sirt3. With the addition of EX4 into the culture system, the expressions of Sirt1 and Sirt3 were increased, and the H2O2-induced ROS and cell death were significantly reduced. These results confirm a mechanism for EX4 to protect retinal cells from diabetic damage and oxidative injury. EX4 reduces retinal cell death and ROS generation by upregulating Sirt1 and Sirt3 expressions in the retina of early-stage diabetic rats as well as in H2O2-treated R28 cells.

Combination therapy of SGLT2 inhibitors with incretin-based therapies for the treatment of type 2 diabetes mellitus: Effects and mechanisms of action

Type 2 diabetes mellitus (T2DM) is a growing health problem worldwide; its pathogenesis is multifactorial and its progressive nature often necessitates a combination therapy with multiple antihyperglycemic agents. Sodium glucose cotransporter 2 (SGLT2) inhibitors and the incretin-based therapies - dipeptidyl peptidase 4(DPP-4) inhibitors and glucagon-like peptide 1 (GLP-1) receptor agonists - were introduced for the treatment of T2DM within the last decade. Evidence of the beneficial effects of these antihyperglycemic agents on micro- and macrovascular complications have started to emerge, which will become important in individualizing different combinations of antihyperglycemic agents to different patient populations. We review here the mechanisms of action, glycemic and cardiovascular effects of SGLT2 inhibitors and incretin-based therapies and their combination in the treatment of T2DM.

Synergy Between Gαz Deficiency and GLP-1 Analog Treatment in Preserving Functional β-Cell Mass in Experimental Diabetes

A defining characteristic of type 1 diabetes mellitus (T1DM) pathophysiology is pancreatic β-cell death and dysfunction, resulting in insufficient insulin secretion to properly control blood glucose levels. Treatments that promote β-cell replication and survival, thus reversing the loss of β-cell mass, while also preserving β-cell function, could lead to a real cure for T1DM. The α-subunit of the heterotrimeric Gz protein, Gαz, is a tonic negative regulator of adenylate cyclase and downstream cAMP production. cAMP is one of a few identified signaling molecules that can simultaneously have a positive impact on pancreatic islet β-cell proliferation, survival, and function. The purpose of our study was to determine whether mice lacking Gαz might be protected, at least partially, from β-cell loss and dysfunction after streptozotocin treatment. We also aimed to determine whether Gαz might act in concert with an activator of the cAMP-stimulatory glucagon-like peptide 1 receptor, exendin-4 (Ex4). Without Ex4 treatment, Gαz-null mice still developed hyperglycemia, albeit delayed. The same finding held true for wild-type mice treated with Ex4. With Ex4 treatment, Gαz-null mice were protected from developing severe hyperglycemia. Immunohistological studies performed on pancreas sections and in vitro apoptosis, cytotoxicity, and survival assays demonstrated a clear effect of Gαz signaling on pancreatic β-cell replication and death; β-cell function was also improved in Gαz-null islets. These data support our hypothesis that a combination of therapies targeting both stimulatory and inhibitory pathways will be more effective than either alone at protecting, preserving, and possibly regenerating β-cell mass and function in T1DM.

GLP-1 and weight loss: unraveling the diverse neural circuitry

Glucagon-like peptide-1 (GLP-1) is currently one of the most promising biological systems for the development of effective obesity pharmacotherapies. Long-acting GLP-1 analogs potently reduce food intake and body weight, and recent discoveries reveal that peripheral administration of these drugs reduces food intake largely through humoral pathways involving direct action on brain GLP-1 receptors (GLP-1R). Thus, it is of critical importance to understand the neural systems through which GLP-1 and long-acting GLP-1 analogs reduce food intake and body weight. In this review, we discuss several neural, physiological, cellular and molecular, as well as behavioral mechanisms through which peripheral and central GLP-1R signaling reduces feeding. Particular attention is devoted to discussion regarding the numerous neural substrates through which GLP-1 and GLP-1 analogs act to reduce food intake and body weight, including various hypothalamic nuclei (arcuate nucleus of the hypothalamus, periventricular hypothalamus, lateral hypothalamic area), hindbrain nuclei (parabrachial nucleus, medial nucleus tractus solitarius), hippocampus (ventral subregion; vHP), and nuclei embedded within the mesolimbic reward circuitry [ventral tegmental area (VTA) and nucleus accumbens (NAc)]. In some of these nuclei [VTA, NAc, and vHP], GLP-1R activation reduces food intake and body weight without concomitant nausea responses, suggesting that targeting these specific pathways may be of particular interest for future obesity pharmacotherapy. The widely distributed neural systems through which GLP-1 and GLP-1 analogs act to reduce body weight highlight the complexity of the neural systems regulating energy balance, as well as the challenges for developing effective obesity pharmacotherapies that reduce feeding without producing parallel negative side effects.

Anti-Inflammatory Effects of GLP-1-Based Therapies beyond Glucose Control

Glucagon-like peptide-1 (GLP-1) is an incretin hormone mainly secreted from intestinal L cells in response to nutrient ingestion. GLP-1 has beneficial effects for glucose homeostasis by stimulating insulin secretion from pancreatic beta-cells, delaying gastric emptying, decreasing plasma glucagon, reducing food intake, and stimulating glucose disposal. Therefore, GLP-1-based therapies such as GLP-1 receptor agonists and inhibitors of dipeptidyl peptidase-4, which is a GLP-1 inactivating enzyme, have been developed for treatment of type 2 diabetes. In addition to glucose-lowering effects, emerging data suggests that GLP-1-based therapies also show anti-inflammatory effects in chronic inflammatory diseases including type 1 and 2 diabetes, atherosclerosis, neurodegenerative disorders, nonalcoholic steatohepatitis, diabetic nephropathy, asthma, and psoriasis. This review outlines the anti-inflammatory actions of GLP-1-based therapies on diseases associated with chronic inflammation in vivo and in vitro, and their molecular mechanisms of anti-inflammatory action.

Blood pressure and glucose independent renoprotective effects of dipeptidyl peptidase-4 inhibition in a mouse model of type-2 diabetic nephropathy

BACKGROUND

Despite the beneficial effects of type 4 dipeptidyl peptidase (DPP-4) inhibitors on glucose levels, its effects on diabetic nephropathy remain unclear.

METHOD

This study examined the long-term renoprotective effects of DPP-4 inhibitor linagliptin in db/db mice, a model of type 2 diabetes. Results were compared with the known beneficial effects of renin-angiotensin system blockade by enalapril. Ten-week-old male diabetic db/db mice were treated for 3 months with either vehicle (n = 10), 3 mg linagliptin/kg per day (n = 8), or 20 mg enalapril/kg per day (n = 10). Heterozygous db/m mice treated with vehicle served as healthy controls (n = 8).

RESULTS

Neither linagliptin nor enalapril had significant effects on the parameters of glucose metabolism or blood pressure in diabetic db/db mice. However, linagliptin treatment reduced albuminuria and attenuated kidney injury. In addition, expression of podocyte marker podocalyxin was normalized. We also analysed DPP-4 expression by immunofluorescence in human kidney biopsies and detected upregulation of DPP-4 in the glomeruli of patients with diabetic nephropathy, suggesting that our findings might be of relevance for human kidney disease as well.

CONCLUSION

Treatment with DPP-4 inhibitor linagliptin delays the progression of diabetic nephropathy damage in a glucose-independent and blood-pressure-independent manner. The observed effects may be because of the attenuation of podocyte injury and inhibition of myofibroblast transformation.

Incretin-based therapy: renal effects

Glucagon like peptide-1 (GLP-1) analogues and dipeptidyl peptidase-4 (DPP-4) inhibitors are new classes of hypoglycemic agents with numerous pleiotropic effects. The review summarises data about the influence of GLP-1 analogues and DPP-4 inhibitors on structural and functional changes in diabetic kidneys. Growing evidence indicates that the kidney is one of the loci of the effects and degradation of GLP-1. The potency of the effects of GLP-1 in diabetic kidneys can be reduced by decrease in GLP-1 receptor expression or enhancement of GLP-1 degradation. In experimental models of diabetic nephropathy and non-diabetic renal injury, GLP-1 analogues and DPP-4 inhibitors slow the development of kidney fibrosis and prevent the decline of kidney function. The mechanisms of protective effect include hyperglycaemia reduction, enhancement of sodium excretion, suppression of inflammatory and fibrogenic signalling pathways, reduction of oxidative stress and apoptosis in the kidneys. In clinical studies, the urinary albumin excretion reduction rate while using the GLP-1 analogue and DPP-4 inhibitor treatment was demonstrated in patients with type 2 diabetes. Long-term impact of these agents on renal function in diabetes needs further investigations.

Incretin-Based Therapy for Prevention of Diabetic Vascular Complications

Diabetic vascular complications are the most common cause of mortality and morbidity worldwide, with numbers of affected individuals steadily increasing. Diabetic vascular complications can be divided into two categories: macrovascular andmicrovascular complications. Macrovascular complications include coronary artery diseaseand cerebrovascular disease, while microvascular complications include retinopathy and chronic kidney disease. These complications result from metabolic abnormalities, including hyperglycemia, elevated levels of free fatty acids, and insulin resistance. Multiple mechanisms have been proposed to mediate the adverse effects of these metabolic disorders on vascular tissues, including stimulation of protein kinase C signaling and activation of the polyol pathway by oxidative stress and inflammation. Additionally, the loss of tissue-specific insulin signaling induced by hyperglycemia and toxic metabolites can induce cellular dysfunction and both macro- and microvascular complications characteristic of diabetes. Despite these insights, few therapeutic methods are available for the management of diabetic complications. Recently, incretin-based therapeutic agents, such as glucagon-like peptide-1 and dipeptidyl peptidase-4 inhibitors, have been reported to elicit vasotropic actions, suggesting a potential for effecting an actual reduction in diabetic vascular complications. The present review will summarize the relationship between multiple adverse biological mechanisms in diabetes and putative incretin-based therapeutic interventions intended to prevent diabetic vascular complications.

Does Glucagon-like Peptide-1 Ameliorate Oxidative Stress in Diabetes? Evidence Based on Experimental and Clinical Studies

Glucagon-like peptide-1 (GLP-1) has shown to influence the oxidative stress status in a number of in vitro, in vivo and clinical studies. Well-known effects of GLP-1 including better glycemic control, decreased food intake, increased insulin release and increased insulin sensitivity may indirectly contribute to this phenomenon, but glucose-independent effects on ROS level, production and antioxidant capacity have been suggested to also play a role. The potential 'antioxidant' activity of GLP-1 along with other proposed glucose-independent modes of action related to ameliorating redox imbalance remains a controversial topic but could hold a therapeutic potential against micro- and macrovascular diabetic complications. This review discusses the presently available knowledge from experimental and clinical studies on the effects of GLP-1 on oxidative stress in diabetes and diabetes-related complications.

Dipeptidyl peptidase-4 inhibition by Saxagliptin prevents inflammation and renal injury by targeting the Nlrp3/ASC inflammasome

BACKGROUND

Glucagon-like peptide-1 (GLP-1) receptor activation delays the progression of diabetic nephropathy (DN) in rodents. The NOD-like receptor 3 (Nlrp3) inflammasome plays an important role in DN. Dipeptidyl peptidase-4 inhibitors (DPP4I) inhibit the degradation of endogenous GLP-1 and various other active substances. We assessed whether DPP4I attenuates diabetes-induced activation of the inflammasome and progression of DN in mice with type 2 diabetes mellitus (T2DM) and type 1 diabetes mellitus (T1DM).

METHODS

BTBR (T2DM), Akita (T1DM) and their matched non-diabetic control (wild-type (WT)) mice received 8-week treatment with Saxagliptin (Saxa) or vehicle.

RESULTS

Kidney weight and kidney/body weight ratio increased in the BTBR and Akita mice compared to their WT mice. Saxa attenuated these changes in the BTBR, but not in the Akita mice and had no effect in the WT mice. Serum blood urea nitrogen and creatinine significantly increased in the BTBR and Akita mice. Saxa attenuated the increase in the BTBR and Akita mice. Saxa improved glycemic control in the BTBR mice, but had no effect on glucose levels in the Akita and WT mice. Serum C reactive protein, tumor necrosis factor α (TNFα), interleukin (IL)-1β, IL-6 and IL-18 were significantly higher in the BTBR and Akita mice than in the WT mice. Saxa attenuated the increase in the BTBR and Akita mice. Kidney and adipose protein levels of apoptosis-associated speck-like protein 1, NLRP3, TNFα and Caspase-1 were higher in the BTBR and Akita mice than in the WT mice. Saxa reduced the levels in both types of diabetic mice.

CONCLUSIONS

Saxa attenuated diabetes-induced activation of the inflammasome and progression of DN. As Saxa did not affect glucose levels in the Akita mice, these effects are independent of glucose lowering.

Acarbose Decreases the Rheumatoid Arthritis Risk of Diabetic Patients and Attenuates the Incidence and Severity of Collagen-induced Arthritis in Mice

Acarbose has been found to decrease some inflammatory parameters in diabetic patients. This study aimed to examine the influence of acarbose on rheumatoid arthritis (RA) risk in diabetes mellitus (DM) patients and on the incidence and severity of collagen-induced arthritis (CIA) in mice. In a nationwide, matched case–control study, we identified 723 incident RA cases and selected 7,230 age-, sex- and RA diagnosis date–matched controls from all newly treated DM patients. We found that use of acarbose at > 16,950 mg per year was associated with a lower RA risk (odds ratio 0.60; 95% CI, 0.41–0.89). In the CIA mouse study, acarbose was orally administered from days -7 to 38 relative to type II collagen (CII) immunization. The results revealed that acarbose at the dose of 500 mg/kg/day attenuated the incidence and severity of arthritis and the expression of proinflammatory cytokines, including TNF-α, IL-6 and IL-17 in the paw tissues. Acarbose further decreased the productions of anti-CII-IgG, IL-17 and IFN-γ by collagen-reactive lymph node cells. This work suggests that the use of acarbose decreased RA risk in DM patients and the incidence of CIA in mice. Acarbose also attenuated the severity of CIA via anti-inflammatory and immunomodulatory effects.

G protein-coupled receptors: potential therapeutic targets for diabetic nephropathy

Diabetic nephropathy, a lethal microvascular complication of diabetes mellitus, is characterized by progressive albuminuria, excessive deposition of extracellular matrix, thickened glomerular basement membrane, podocyte abnormalities, and podocyte loss. The G protein-coupled receptors (GPCRs) have attracted considerable attention in diabetic nephropathy, but the specific effects have not been elucidated yet. Likewise, abnormal signaling pathways are closely interrelated to the pathologic process of diabetic nephropathy, despite the fact that the mechanisms have not been explored clearly. Therefore, GPCRs and its mediated signaling pathways are essential for priority research, so that preventative strategies and potential targets might be developed for diabetic nephropathy. This article will give us comprehensive overview of predominant GPCR types, roles, and correlative signaling pathways in diabetic nephropathy.

Advances in understanding relationship between GLP-1 based drugs and the kidney

The drugs based on glucagon-like peptide-1 (GLP-1) not only lower urinary protein, but also increase urine sodium excretion and improve the pathological changes of kidney disease. However, the mechanism is not very clear and may be associated with atrial natriuretic peptide, renin angiotensin axis, and oxidative stress. This review focuses on the progress in understanding the relationship between GLP-1 and the kidney.

Exenatide (a GLP-1 agonist) expresses anti-inflammatory properties in cultured human monocytes/macrophages in a protein kinase A and B/Akt manner

BACKGROUND

Incretin-based therapies in the treatment of type 2 diabetes mellitus are associated with significant improvements in glycemic control, which are accompanied by a beneficial impact on atherosclerosis. Macrophages are essential in the development of atherosclerotic plaques and may develop features that accelerate atherosclerosis (classically activated macrophages) or protect arterial walls against it (alternatively activated macrophages). Therefore, we explored whether beneficial actions of exenatide are connected with the influence on the macrophages' phenotype and synthesis of inflammatory and anti-inflammatory cytokines.

METHODS

Monocytes/macrophages were harvested from 10 healthy subjects. Cells were cultured in the presence of exenatide, exendin 9-39 (GLP-1 antagonist), LPS, IL-4, PKI (PKA inhibitor) and triciribine (PKB/Akt inhibitor). We measured the effects of the above-mentioned compounds on markers of macrophages' phenotype (inducible nitrous oxide (iNOS), arginase 1 (arg1) and mannose receptors) and concentration of nitrite, IL-1β, TNF-α and IL-10.

RESULTS

Exenatide significantly increased the level of IL-10 and decreased both TNF-α and IL-1β in LPS-treated monocytes/macrophages. Furthermore exenatide increased the expression of arg1-a marker of classical activation and reduced the LPS-induced expression of iNOS-a marker of classical activation. According to experiments with protein kinases inhibitors we found that proinflammatory markers were protein kinase A dependent, whereas the activation of alternative activation was similarly reliant on protein kinase A and B/Akt.

CONCLUSIONS

We showed that exenatide skewed the macrophages phenotype toward anti-inflammatory phenotype and this effect is predominantly attributable to protein kinase A and to a less extent to B/Akt activation.

Nephroprotection by Hypoglycemic Agents: Do We Have Supporting Data?

Current therapy directed at delaying the progression of diabetic nephropathy includes intensive glycemic and optimal blood pressure control, renin angiotensin-aldosterone system blockade and multifactorial intervention. However, the renal protection provided by these therapeutic modalities is incomplete. There is a scarcity of studies analysing the nephroprotective effect of antihyperglycaemic drugs beyond their glucose lowering effect and improved glycaemic control on the prevention and progression of diabetic nephropathy. This article analyzes the exisiting data about older and newer drugs as well as the mechanisms associated with hypoglycemic drugs, apart from their well known blood glucose lowering effect, in the prevention and progression of diabetic nephropathy. Most of them have been tested in humans, but with varying degrees of success. Although experimental data about most of antihyperglycemic drugs has shown a beneficial effect in kidney parameters, there is a lack of clinical trials that clearly prove these beneficial effects. The key question, however, is whether antihyperglycemic drugs are able to improve renal end-points beyond their antihyperglycemic effect. Existing experimental data are post hoc studies from clinical trials, and supportive of the potential renal-protective role of some of them, especially in the cases of dipeptidyl peptidase-4 inhibitors, glucagon-like peptide-1 receptor agonists and sodium-glucose cotransporter 2 inhibitors. Dedicated and adequately powered renal trials with renal outcomes are neccessary to assess the nephrotection of antihyperglycaemic drugs beyond the control of hyperglycaemia.

Dipeptidyl peptidase-4 inhibitors in progressive kidney disease

PURPOSE OF REVIEW

Dipeptidyl peptidase-4 (DPP-4) inhibitors are incretin-based drugs approved for the treatment of type 2 diabetes. The main action of DPP-4 inhibitors is to increase the level of incretin hormones such as glucagon-like peptide-1 (GLP-1), thereby stimulating insulin secretion from pancreatic β cells. Recently emerging evidence suggests the pleiotropic extrapancreatic function of GLP-1 or DPP-4 inhibitors, including kidney and cardiovascular protection. Here, we review the effects of DPP-4 inhibitors on progressive kidney disease such as diabetic nephropathy from a therapeutic point of view.

RECENT FINDINGS

A growing number of studies in animal models and human diseases have shown that DPP-4 inhibition ameliorates kidney disease by a process independent of glucose lowering. Possible mechanisms underlying such protective properties include the facilitation of natriuresis and reduction of blood pressure, and also local effects of the reduction of oxidative stress, inflammation and improvement of endothelial function in the kidney. DPP-4 inhibitors may also restore other DPP-4 substrates which have proven renal effects.

SUMMARY

Treatment of diabetes with DPP-4 inhibitors is likely to involve a variety of extrapancreatic effects including renal protection. Such pleiotropic action of DPP-4 inhibitors might occur by both incretin-dependent and incretin-independent mechanisms. Conclusive evidence is needed to translate the favorable results from animal models to humans.

Effects of exendin-4, a glucagon like peptide-1 receptor agonist, on neutrophil count and inflammatory cytokines in a rat model of endotoxemia

Background

Sepsis remains a major cause of morbidity and mortality. A variety of strategies targeting modulation of the pro-inflammatory response associated with early sepsis have been reported without clinical success. GLP-1 enhances glucose-stimulated insulin secretion. In addition, it was shown to have anti-inflammatory effects. We hypothesized that treatment with exendin-4, a GLP-1 receptor agonist, would attenuate inflammation and improve glucose control in a lipopolysaccharide (LPS) rat model of inflammation.

Methods

Two-month-old male Wistar rats were randomly assigned to one of the following four groups: 1) treatment: intraperitoneal (IP) injection of LPS 10 mg/kg followed by exendin-4, 30 μg/kg, 10 minutes later; 2) control-1: IP injection of LPS 10 mg/kg, followed by normal saline (NS); 3) control-2: IP NS injection followed by exendin-4; 4) sham: IP injection of NS followed by another NS injection. Glucose concentration, total white blood count with absolute neutrophil count, and pro- and anti-inflammatory cytokine concentrations were measured at 0, 3, 6, and 10 hours following LPS injection.

Results

At 3 hours, rats injected with LPS developed neutropenia, elevated pro- and anti-inflammatory cytokines, and mild hypoglycemia. Treatment with exendin-4 significantly modulated neutropenia, and decreased pro-inflammatory cytokine concentrations (IL-1α, IL-1β, IL-6, TNFα, and IFNγ). However, exendin-4 had no effect on IL-10 concentrations. LPS injection led to mild hypoglycemia, that was not observed in rats treated with exendin-4. Sham animals exhibited no significant change from baseline in all parameters.

Conclusion

In this LPS model of acute early phase inflammation, treatment with exendin-4 decreased pro-inflammatory cytokine concentrations without changing IL-10 blood levels and improved neutropenia. Following LPS injection, rats developed a tendency toward hypoglycemia that improved with exendin-4. Overall our data suggest that exogenous exendin-4 mediates anti-inflammatory effects early in this rat model of endotoxin-induced inflammation.

Pleiotropic effects of the dipeptidylpeptidase-4 inhibitors on the cardiovascular system

Dipeptidylpeptidase-4 (DPP-4) is a ubiquitously expressed transmembrane protein that removes NH2-terminal dipeptides from various substrate hormones, chemokines, neuropeptides, and growth factors. Two known substrates of DPP-4 include the incretin hormones glucagon-like peptide-1 (GLP-1) and gastric inhibitory peptide, which are secreted by enteroendocrine cells in response to postprandial hyperglycemia and account for 60–70% of postprandial insulin secretion. DPP-4 inhibitors (DPP-4i) block degradation of GLP-1 and gastric inhibitory peptide, extend their insulinotropic effect, and improve glycemia. Since 2006, several DPP-4i have become available for treatment of type 2 diabetes mellitus. Clinical trials confirm that DPP-4i raises GLP-1 levels in plasma and improves glycemia with very low risk for hypoglycemia and other side effects. Recent studies also suggest that DPP-4i confers cardiovascular and kidney protection, beyond glycemic control, which may reduce the risk for further development of the multiple comorbidities associated with obesity/type 2 diabetes mellitus, including hypertension and cardiovascular disease (CVD) and kidney disease. The notion that DPP-4i may improve CVD outcomes by mechanisms beyond glycemic control is due to both GLP-1-dependent and GLP-1-independent effects. The CVD protective effects by DPP-4i result from multiple factors including insulin resistance, oxidative stress, dyslipidemia, adipose tissue dysfunction, dysfunctional immunity, and antiapoptotic properties of these agents in the heart and vasculature. This review focuses on cellular and molecular mechanisms mediating the CVD protective effects of DPP-4i beyond favorable effects on glycemic control.

Glucagon-like peptide 1 receptor agonist (GLP-1 RA): long-term effect on kidney function in patients with type 2 diabetes

AIMS

In a short-term study including 31 patients with type 2 diabetes, glucagon-like peptide 1 receptor agonist (GLP-1 RA) treatment was associated with a significant reversible decline in GFR. Twenty-three patients re-initiated GLP-1 RA treatment after the primary study, and the aim was to investigate the long-term effect on kidney function.

METHODS

We included 30 patients in a one-year extension study, all initially treated with liraglutide for seven weeks. During follow-up 23 were treated with liraglutide and seven untreated. Primary outcome was change in GFR ((51)Cr-EDTA plasma clearance).

RESULTS

Patients were 61.5 (10.0) years and HbA(1c) 60.1 (13.8) mmol/mol. Baseline GFR was 100.6 (24.9) mL/min/1.73 m(2) and was reduced by 11 (95% CI: 6.6-15.7, p < 0.001) mL/min/1.73 m(2), independent of change in 24-h systolic blood pressure (SBP), weight, UAER or HbA(1c) (p≥0.33). Geometric mean (IQR) of UAER was 25.5 (9.9-50.9) mg/d and was reduced by 27 (95% CI: 5-44; p = 0.020)%, and 24-h SBP was reduced by 8.2 (p = 0.048) mmHg. No changes occurred in untreated patients.

CONCLUSIONS

Long-term treatment with liraglutide was associated with a reduction in measured GFR similar to the effect during short-term treatment, suggesting a metabolic or haemodynamic reversible effect and not structural changes. Moreover, UAER and 24-h SBP were reduced.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT01499108.

Anti-inflammatory effects of gastric bypass surgery and their association with improvement in metabolic profile

Obesity is associated with chronic inflammation and metabolic disease. Bariatric surgery offers a treatment that can effectively reduce weight and improve the metabolic function. However, the effect of bariatric surgery on chronic inflammation in obesity is under-investigated. In this expert review, the authors outline the effect of Roux-en-Y gastric bypass, the most commonly performed bariatric surgery in current practice, on the markers of inflammation. They include a discussion of the relationship between inflammation and weight loss after surgery, the interaction between these markers and metabolic disease, and the effect on adipose tissue inflammation. They also briefly explore the role of glucagon-like-peptide 1 in remediating inflammation and the changes in gut microbiota after Roux-en-Y gastric bypass, and how they may be important in inflammation.

GLP-1 receptor agonists: Nonglycemic clinical effects in weight loss and beyond

OBJECTIVE

Glucagon-like peptide-1 (GLP-1) receptor agonists are indicated for treatment of type 2 diabetes since they mimic the actions of native GLP-1 on pancreatic islet cells, stimulating insulin release, while inhibiting glucagon release, in a glucose-dependent manner. The observation of weight loss has led to exploration of their potential as antiobesity agents, with liraglutide 3.0 mg day(-1) approved for weight management in the US on December 23, 2014, and in the EU on March 23, 2015. This review examines the potential nonglycemic effects of GLP-1 receptor agonists.

METHODS

A literature search was conducted to identify preclinical and clinical evidence on nonglycemic effects of GLP-1 receptor agonists.

RESULTS

GLP-1 receptors are distributed widely in a number of tissues in humans, and their effects are not limited to the well-recognized effects on glycemia. Nonglycemic effects include weight loss, which is perhaps the most widely recognized nonglycemic effect. In addition, effects on the cardiovascular, neurologic, and renal systems and on taste perception may occur independently of weight loss.

CONCLUSIONS

GLP-1 receptor agonists may provide other nonglycemic clinical effects besides weight loss. Understanding these effects is important for prescribers in using GLP-1 receptor agonists for diabetic patients, but also if approved for chronic weight management.

Glucagon-like peptide-1 protects against cardiac microvascular endothelial cells injured by high glucose

OBJECTIVE

To investigate the protective effect of glucagon-like peptid-1 (GLP-1) against cardiac microvascular endothelial cell (CMECs) injured by high glucose.

METHODS

CMECs were isolated and cultured. Superoxide assay kit and dihydroethidine (DHE) staining were used to assess oxidative stress. TUNEL staining and caspase 3 expression were used to assess the apoptosis of CMECs. H89 was used to inhibit cAMP/PKA pathway; fasudil was used to inhibit Rho/ROCK pathway. The protein expressions of Rho, ROCK were examined by Western blot analysis.

RESULTS

High glucose increased the production of ROS, the activity of NADPH, the apoptosis rate and the expression level of Rho/ROCK in CMECs, while GLP-1 decreased high glucose-induced ROS production, the NADPH activity and the apoptosis rate and the expression level of Rho/ROCK in CMECs, the difference were statistically significant (P<0.05).

CONCLUSIONS

GLP-1 could protect the cardiac microvessels against oxidative stress and apoptosis. The protective effects of GLP-1 are dependent on downstream inhibition of Rho through a cAMP/PKA-dependent manner, resulting in a subsequent decrease in the expression of NADPH oxidase.

Beat it early: putative renoprotective haemodynamic effects of oral hypoglycaemic agents

Diabetic kidney disease represents a considerable burden; around one-third of patients with type 2 diabetes develop chronic kidney disease. In health, the kidneys play an important role in the regulation of glucose homeostasis via glucose utilization, gluconeogenesis and glucose reabsorption. In patients with diabetes, renal glucose homeostasis is significantly altered with an increase in both gluconeogenesis and renal tubular reabsorption of glucose. Environmental factors, both metabolic (hyperglycaemia, obesity and dyslipidaemia) and haemodynamic, together with a genetic susceptibility, lead to the activation of pro-oxidative, pro-inflammatory and pro-fibrotic pathways resulting in kidney damage. Hyperfiltration and its haemodynamic-driven insult to the kidney glomeruli is an important player in proteinuria and progression of kidney disease towards end-stage renal failure. Control of glycaemia and blood pressure are the mainstays to prevent kidney damage and slow its progression. There is emerging evidence that some hypoglycaemic agents may have renoprotective effects which are independent of their glucose-lowering effects. Sodium-glucose co-transporter-2 (SGLT-2) inhibitors may exert a renoprotective effect by a number of mechanisms including restoring the tubuloglomerular feedback mechanism and lowering glomerular hyperfiltration, reducing inflammatory and fibrotic markers induced by hyperglycaemia thus limiting renal damage. Simultaneous use of an SGLT-2 inhibitor and blockade of the renin-angiotensin-aldosterone system may be a strategy to slow progression of diabetic nephropathy more than either drug alone. The use of dipeptidyl peptidase-4 inhibitors and glucagon-like peptide 1 receptor agonists may exert a renoprotective effect by reducing inflammation, fibrosis and blood pressure. Given the burden of diabetic kidney disease, any additional renoprotective benefit with hypoglycaemic therapy is to be welcomed. Large randomized controlled trials are currently underway investigating if these new anti-diabetic agents can provide renoprotection in diabetes.

Anti-inflammatory role of DPP-4 inhibitors in a nondiabetic model of glomerular injury

Dipeptidyl peptidase (DPP)-4 is an enzyme that cleaves and inactivates incretin hormones capable of stimulating insulin secretion from pancreatic β-cells. DPP-4 inhibitors are now widely used for the treatment of type 2 diabetes. Experimental studies have suggested a renoprotective role of DPP-4 inhibitors in various models of diabetic kidney disease, which may be independent of lowering blood glucose levels. In the present study, we examined the effect of DPP-4 inhibitors in the rat Thy-1 glomerulonephritis model, a nondiabetic glomerular injury model. Rats were injected with OX-7 (1.2 mg/kg iv) and treated with the DPP-4 inhibitor alogliptin (20 mg·kg(-1)·day(-1)) or vehicle for 7 days orally by gavage. Alogliptin significantly reduced the number of CD68-positive inflammatory macrophages in the kidney, which was associated with a nonsignificant tendency to ameliorate glomerular injury and reduce proteinuria. Another DPP-4 inhibitor, anagliptin (300 mg·kg(-1)·day(-1) mixed with food) and a glucagon-like peptide-1 receptor agonist, exendin-4 (10 mg/kg sc), similarly reduced CD68-positive macrophage infiltration to the kidney. Furthermore, ex vivo transmigration assays using peritoneal macrophages revealed that exendin-4, but not alogliptin, dose dependently reduced monocyte chemotactic protein-1-stimulated macrophage infiltration. These data suggest that DPP-4 inhibitors reduced macrophage infiltration directly via glucagon-like peptide-1-dependent signaling in the rat Thy-1 nephritis model and indicate that the control of inflammation by DPP-4 inhibitors is useful for the treatment of nondiabetic kidney disease models.

Exendin-4 attenuates renal tubular injury by decreasing oxidative stress and inflammation in streptozotocin-induced diabetic mice

In this study, we aimed to research the restorative effects of exendin-4, a GLP-1 analog, on renal tubular injury in streptozotocin-induced diabetes model. BALB/c male mice were divided into four groups: non-diabetic, non-diabetic + exendin-4 (3 μg/kg), diabetic and diabetic + exendin-4. In our diabetic model, we observed renal injury mainly in tubular area rather than glomeruli and exendin-4 decreased tubular injury with its glucose lowering effect. Besides, PCNA positive tubular cells, activities of LDH and Na(+)-K(+)-ATPase were also significantly declined by the administration of exendin-4. Furthermore, exendin-4 attenuated the levels of ROS, MDA, 8-OHdG, proinflammatory cytokines (TNF-α, IL-1β), chemokine MCP-1, ICAM-1, and fibrosis-related molecules (transforming growth factor β1 and fibronectin). In consistent with reducing tubular injury, macrophage infiltration and both MCP-1 and ICAM-1 production in tubular cells were decreased. These results indicate that exendin-4 may decrease renal tubular injury seen in the beginning of diabetic nephropathy by decreasing ROS production and inflammation.

[Nonglycemic effects of incretins in patients with long-term type 1 diabetes mellitus and chronic kidney disease]

AIM

To investigate the nonglycemic effects of incretins in patients with type 1 diabetes mellitus (DM1) of long duration (for more than 20 years) and chronic kidney disease.

MATERIAL AND METHODS

Seventy-five patients with varying degrees of diabetic nephropathy (DN) and without this condition, including patients receiving renal replacement therapy with programmed hemodialysis and those who had undergone kidney transplantation were examined. The levels of phosphorus-calcium metabolic indicators (calcium, phosphorus, parathyroid hormone, vitamin D, and fibroblast growth factor 23 (FGF-23)), the cardiac damage marker atrial natriuretic peptide, the proinflammatory markers monocyte chemoattractant protein 1 (MCP-1) and C-reactive protein (CRP) and the fibrotic marker transforming growth factor-β, as well as those of glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP) were estimated in addition to conventional examination methods. All the patients underwent cardiac multislice spiral computed tomography, by calculating the Agatston index (calcium index (CI)) reflecting the degree of coronary artery calcification.

RESULTS

The investigation revealed no relationship of GLP-1 and GIP levels to the presence and degree of DN in the patients of the study groups. GLP-1 was noted to be inversely related to patient age, indicating the diminished secretion of this peptide in older people. There was evidence that GLP-1 positively affected blood lipid composition (total cholesterol: r=-0,320; p<0.05) and the magnitude of coronary artery calcification (CI: r=-0.308; p<0.05). GIP showed a differently directed effect on the proinflammatory factors: fibrinogen (r=-0.264; p<0.05), CRP (r=-0.626; p<0.05), and FGF-23 (r=-0.341; p<0.05).

CONCLUSION

The investigation has demonstrated the nonglycemic effects of incretins that favorably affect the pathogenetic processes underlying the late complications of DM1. The findings point to the potential efficacy of incretin-based drugs in preventing and treating the late complications of DM, which necessitates the conduction of larger investigations.

Urinary Angiotensinogen Could Be a Prognostic Marker of Renoprotective Effects of Alogliptin in Patients with Type 2 Diabetes

BACKGROUND

The aims of this study were (1) to examine the renoprotective effects of alogliptin and (2) to establish urinary angiotensinogen (AGT) as a prognostic marker of renoprotective effects of alogliptin in patients with type 2 diabetes (T2D).

METHODS

In 43 patients with T2D (18 women, 66.1 ± 1.71 years), 25 mg/day of alogliptin was added to the traditional hypoglycemic agents and/or nondrug treatments. Urinary concentrations of albumin (Alb) and AGT, normalized by urinary concentrations of creatinine (Cr) (UAlbCR and UAGTCR, respectively), were measured before and after the 12-week alogliptin treatment.

RESULTS

Alogliptin treatment tended to decrease UAlbCR (99.6 ± 26.8 versus 114.6 ± 36.0 mg/g Cr, P = 0.198). Based on % change in UAlbCR, patients were divided into two groups, responders (< -25%) and nonresponders (≥ -25%), and a logistic analysis of UAGTCR before treatment showed cutoff value of 20.8 µg/g Cr. When all patients were redivided into two groups, those with higher values of UAGTCR before the treatment (Group H, n = 20) and those with lower values (Group L), Group H showed significantly decreased UAlbCR in response to alogliptin (-14.6 ± 8.6 versus +22.8 ± 16.8%, P = 0.033).

CONCLUSION

Urinary AGT could be a prognostic marker of renoprotective effects of alogliptin in patients with T2D.

Effects of glucagon-like peptide-1 receptor agonists on non-alcoholic fatty liver disease and inflammation

Glucagon-like peptide1 (GLP-1) is secreted from Langerhans cells in response to oral nutrient intake. Glucagon-like peptide-1 receptor agonists (GLP-1RAs) are a new class of incretin-based anti-diabetic drugs. They function to stimulate insulin secretion while suppressing glucagon secretion. GLP-1-based therapies are now well established in the management of type 2 diabetes mellitus (T2DM), and recent literature has suggested potential applications of these drugs in the treatment of obesity and for protection against cardiovascular and neurological diseases. As we know, along with change in lifestyles, the prevalence of non-alcoholic fatty liver disease (NAFLD) in China is rising more than that of viral hepatitis and alcoholic fatty liver disease, and NAFLD has become the most common chronic liver disease in recent years. Recent studies further suggest that GLP-1RAs can reduce transaminase levels to improve NAFLD by improving blood lipid levels, cutting down the fat content to promote fat redistribution, directly decreasing fatty degeneration of the liver, reducing the degree of liver fibrosis and improving inflammation. This review shows the NAFLD-associated effects of GLP-1RAs in animal models and in patients with T2DM or obesity who are participants in clinical trials.

Targeting inflammation in diabetes: Newer therapeutic options

Inflammation has been recognised to both decrease beta cell insulin secretion and increase insulin resistance. Circulating cytokines can affect beta cell function directly leading to secretory dysfunction and increased apoptosis. These cytokines can also indirectly affect beta cell function by increasing adipocyte inflammation.The resulting glucotoxicity and lipotoxicity further enhance the inflammatory process resulting in a vicious cycle. Weight reduction and drugs such as metformin have been shown to decrease the levels of C-Reactive Protein by 31% and 13%, respectively. Pioglitazone, insulin and statins have anti-inflammatory effects. Interleukin 1 and tumor necrosis factor-α antagonists are in trials and NSAIDs such as salsalate have shown an improvement in insulin sensitivity. Inhibition of 12-lipo-oxygenase, histone de-acetylases, and activation of sirtuin-1 are upcoming molecular targets to reduce inflammation. These therapies have also been shown to decrease the conversion of pre-diabetes state to diabetes. Drugs like glicazide, troglitazone, N-acetylcysteine and selective COX-2 inhibitors have shown benefit in diabetic neuropathy by decreasing inflammatory markers. Retinopathy drugs are used to target vascular endothelial growth factor, angiopoietin-2, various proteinases and chemokines. Drugs targeting the proteinases and various chemokines are pentoxifylline, inhibitors of nuclear factor-kappa B and mammalian target of rapamycin and are in clinical trials for diabetic nephropathy. Commonly used drugs such as insulin, metformin, peroxisome proliferator-activated receptors, glucagon like peptide-1 agonists and dipeptidyl peptidase-4 inhibitors also decrease inflammation. Anti-inflammatory therapies represent a potential approach for the therapy of diabetes and its complications.

DPP4 inhibition attenuates filtration barrier injury and oxidant stress in the zucker obese rat

OBJECTIVE

Obesity-related glomerulopathy is characterized initially by glomerular hyperfiltration with hypertrophy and then development of proteinuria. Putative mechanisms include endothelial dysfunction and filtration barrier injury due to oxidant stress and immune activation. There has been recent interest in targeting dipeptidyl peptidase 4 (DPP4) enzyme due to increasing role in non-enzymatic cellular processes.

METHODS

The Zucker obese (ZO) rat (aged 8 weeks) fed a normal chow or diet containing the DPP4 inhibitor linagliptin for 8 weeks (83 mg/kg rat chow) was utilized.

RESULTS

Compared to lean controls, there were increases in plasma DPP4 activity along with proteinuria in ZO rats. ZO rats further displayed increases in glomerular size and podocyte foot process effacement. These findings occurred in parallel with decreased endothelial stromal-derived factor-1α (SDF-1α), increased oxidant markers, and tyrosine phosphorylation of nephrin and serine phosphorylation of the mammalian target of rapamycin (mTOR). DPP4 inhibition improved proteinuria along with filtration barrier remodeling, circulating and kidney tissue DPP4 activity, increased active glucagon like peptide-1 (GLP-1) as well as SDF-1α, and improved oxidant markers and the podocyte-specific protein nephrin.

CONCLUSIONS

These data support a role for DPP4 in glomerular filtration function and targeting DPP4 with inhibition improves oxidant stress-related glomerulopathy and associated proteinuria.

Endogenous Glucagon-Like Peptide-1 as a Potential Mediator of the Resolution of Diabetic Kidney Disease following Roux en Y Gastric Bypass: Evidence and Perspectives

Diabetic kidney disease in patients with type 2 diabetes strongly correlates with the incidence of major cardiovascular events and all-cause mortality. Pharmacological and lifestyle based management focusing on glycaemic, lipid, and blood pressure control is the mainstay of treatment but efficacy remains limited. Roux en Y gastric bypass is an efficacious intervention in diabetes. Emerging evidence also supports a role for bypass as an intervention for early diabetic kidney disease. This paper firstly presents level 1 evidence of the effects of bypass on hyperglycaemia and hypertension and then summarises emerging data on its effects on diabetic kidney disease. Glucagon-like peptide-1 is implicated as a central mediator of diabetes resolution following bypass through the incretin effect. It has been ascribed vasodilatory, pronatriuretic, and antioxidant properties and its exogenous administration or optimisation of its endogenous levels via dipeptidyl peptidase IV inhibition results in antioxidant and antiproteinuric effects in preclinical models of DKD. Some evidence is emerging of translation of coherent effects in the clinical setting. These findings raise the question of whether pharmacotherapy targeted at optimising circulating hormone levels may be capable of recapitulating some of the effects of bypass surgery on renal injury.

Effects of GLP-1 in the kidney

The incretin hormone, glucagon-like peptide-1 (GLP-1), stimulates insulin secretion and forms the basis of a new drug class for diabetes treatment. GLP-1 has several extra-pancreatic properties which include effects on kidney function. Although renal GLP-1 receptors have been identified, their exact localization and physiological role are incompletely understood. GLP-1 increases natriuresis through inhibition of the sodium-hydrogen ion exchanger isoform 3 in the proximal tubule. This may in part explain why GLP-1 receptor agonists have antihypertensive effects. Glomerular filtration rate is regulated by GLP-1, but the mechanisms are complex and may depend on e.g. glycaemic conditions. Atrial natriuretic peptide or the renin-angiotensin system may be involved in the signalling of GLP-1-mediated renal actions. Several studies in rodents have shown that GLP-1 therapy is renoprotective beyond metabolic improvements in models of diabetic nephropathy and acute kidney injury. Inhibition of renal inflammation and oxidative stress probably mediate this protection. Clinical studies supporting GLP-1-mediated renal protection exist, but they are few and with limitations. However, acute and chronic kidney diseases are major global health concerns and measures improving renal outcome are highly needed. Therefore, the renoprotective potential of GLP-1 therapy need to be thoroughly investigated in humans.

Lack of effect of the glucagon-like peptide-1 receptor agonist liraglutide on psoriasis in glucose-tolerant patients--a randomized placebo-controlled trial

BACKGROUND

It has been proposed that glucagon-like peptide-1 receptor (GLP-1R) agonists used for the treatment of patients with type 2 diabetes might also improve their psoriasis.

OBJECTIVE

To assess the efficacy and safety of the GLP-1R agonist liraglutide in glucose-tolerant patients with plaque psoriasis.

METHODS

A total of 20 obese (body mass index > 25 kg/m(2)), glucose-tolerant patients with plaque psoriasis (psoriasis area and severity index (PASI) of at least 8) were randomized 1:1 to once-daily subcutaneous injections with liraglutide or placebo for an 8-week period. The primary end points were improvement in PASI and dermatology life quality index (DLQI). Secondary end points included changes in weight and high sensitive C-reactive protein (hsCRP) levels, as well as adverse events.

RESULTS

After 8 weeks of treatment, no significant change in PASI was found in the liraglutide group (mean±standard deviation: -2.6 ± 2.1) compared with the placebo group (-1.3 ± 2.4) (P = 0.228). No difference in DLQI was observed between the groups [-2.5 ± 4.4 (liraglutide) vs. -3.7 ± 4.8 (placebo); P = 0.564]. HsCRP did not change in any of the groups (0.26 ± 1 (placebo) vs. 0.25 ± 2.2 (liraglutide); P = 0.992). Liraglutide treatment resulted in a bodyweight loss of 4.7 ± 2.5 kg compared with 1.6 ± 2.7 kg in the placebo group (P = 0.014) accompanied by decreased cholesterol levels. No serious adverse events occurred during the 8-week observation period. The most common complaint was transient nausea, which occurred in 45% of the liraglutide-treated patients but in none from the placebo group.

CONCLUSION

Liraglutide treatment for 8 weeks did not significantly change PASI, DLQI, or hsCRP in a small group of glucose-tolerant obese patients with plaque psoriasis compared with placebo. A significant weight loss and decrease in cholesterol levels was observed in liraglutide-treated patients.

Intestinal regulation of urinary sodium excretion and the pathophysiology of diabetic kidney disease: a focus on glucagon-like peptide 1 and dipeptidyl peptidase 4

The tubular hypothesis of glomerular filtration and nephropathy in diabetes is a pathophysiological concept that assigns a critical role to the tubular system, including proximal tubular hyper-reabsorption and growth, which is relevant for early glomerular hyperfiltration and later chronic kidney disease. Here we focus on how harnessing the bioactivity of hormones released from the gut may ameliorate the early effects of diabetes on the kidney in part by attenuating proximal tubular hyper-reabsorption and growth. The endogenous tone of the glucagon-like peptide 1 (GLP-1)/GLP-1 receptor (GLP-1R) system and its pharmacological activation are nephroprotective in diabetes independent of changes in blood glucose. This is associated with suppression of increases in kidney weight and glomerular hyperfiltration, which may reflect, at least in part, its inhibitory effects on tubular hyper-reabsorption and growth. Inhibition of dipeptidyl peptidase 4 (DPP-4) is also nephroprotective independent of changes in blood glucose and involves GLP-1/GLP-1R-dependent and -independent mechanisms. The GLP-1R agonist exendin-4 induces natriuresis via activation of the GLP-1R. In contrast, DPP4 inhibition increases circulating GLP-1, but drives a GLP-1R-independent natriuretic response, implying a role for other DPP-4 substrates. The extent to which the intrarenal DPP-4/GLP-1 receptor system contributes to all these changes remains to be established, as does the direct impact of the system on renal inflammation.

Physiology and pathophysiology of incretins in the kidney

PURPOSE OF REVIEW

Incretin-based therapy with glucagon-like peptide-1 receptor (GLP-1R) agonists and dipeptidyl peptidase-4 (DPP-4) inhibitors is considered a promising therapeutic option for type 2 diabetes mellitus. Cumulative evidence, mainly from preclinical animal studies, reveals that incretin-based therapies also may elicit beneficial effects on kidney function. This review gives an overview of the physiology, pathophysiology, and pharmacology of the renal incretin system.

RECENT FINDINGS

Activation of GLP-1R in the kidney leads to diuretic and natriuretic effects, possibly through direct actions on renal tubular cells and sodium transporters. Moreover, there is evidence that incretin-based therapy reduces albuminuria, glomerulosclerosis, oxidative stress, and fibrosis in the kidney, partially through GLP-1R-independent pathways. Molecular mechanisms by which incretins exert their renal effects are understood incompletely, thus further studies are needed.

SUMMARY

The GLP-1R and DPP-4 are expressed in the kidney in various species. The kidney plays an important role in the excretion of incretin metabolites and most GLP-1R agonists and DPP-4 inhibitors, thus special attention is required when applying incretin-based therapy in renal impairment. Preclinical observations suggest direct renoprotective effects of incretin-based therapies in the setting of hypertension and other disorders of sodium retention, as well as in diabetic and nondiabetic nephropathy. Clinical studies are needed in order to confirm translational relevance from preclinical findings for treatment options of renal diseases.

The glucagon-like peptide-1 receptor agonist, liraglutide, attenuates the progression of overt diabetic nephropathy in type 2 diabetic patients

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease. Glucagon-like peptide-1 (GLP-1) is one of the incretins, gut hormones released from the intestine in response to food intake. GLP-1 receptor (GLP-1R) agonists have been used to treat type 2 diabetes. Here, we studied the effect of the administration of a GLP-1R agonist, liraglutide, on proteinuria and the progression of overt DN in type 2 diabetic patients. Twenty-three type 2 diabetic patients with overt DN, who had already been treated with blockade of renin-angiotensin system under dietary sodium restriction, were given liraglutide for a period of 12 months. Treatment with liraglutide caused a significant decrease in HbA1c from 7.4 ± 0.2% to 6.9 ± 0.3% (p = 0.04), and in body mass index (BMI) from 27.6 ± 0.9 kg/m² to 26.5 ± 0.8 kg/m² after 12 months (p < 0.001), while systolic blood pressure did not change. The progression of DN was determined as the rate of decline in estimated glomerular filtration rate (eGFR). The 12-month administration of liraglutide caused a significant decrease in proteinuria from 2.53 ± 0.48 g/g creatinine to 1.47 ± 0.28 g/g creatinine (p = 0.002). The administration of liraglutide also substantially diminished the rate of decline in eGFR from 6.6 ± 1.5 mL/min/1.73 m²/year to 0.3 ± 1.9 mL/min/1.73 m²/year (p = 0.003). Liraglutide can be used not only for reducing HbA1c and BMI, but also for attenuating the progression of nephropathy in type 2 diabetic patients.

The potential for renoprotection with incretin-based drugs

Incretin-based drugs, i.e., glucagon-like peptide-1 (GLP-1) receptor agonists and dipeptidyl peptidase-4 (DPP-4) inhibitors, are widely used for the treatment of type 2 diabetes. In addition to the primary role of incretins in stimulating insulin secretion from pancreatic β-cells, they have extra pancreatic functions beyond glycemic control. Indeed, recent studies highlight the potential beneficial effects of incretin-based therapy in diabetic kidney disease (DKD). Experimental studies using various diabetic models suggest that incretins protect the vascular endothelium from injury by binding to GLP-1 receptors, thereby ameliorating oxidative stress and the local inflammatory response, which reduces albuminuria and inhibits glomerular sclerosis. In addition, there is some evidence that GLP-1 receptor agonists and DPP-4 inhibitors mediate sodium excretion and diuresis to lower blood pressure. The pleiotropic actions of DPP-4 inhibitors are ascribed primarily to their effects on GLP-1 signaling, but other substrates of DPP-4, such as brain natriuretic peptide and stromal-derived factor-1α, may have roles. In this review, we summarize recent studies of the roles of incretin-based therapy in ameliorating DKD and its complications.

Microinflammation in the pathogenesis of diabetic nephropathy

Diabetic nephropathy is the leading cause of end‐stage renal failure in developed countries. Furthermore, diabetic nephropathy is related to the risk of cardiovascular diseases and an increase in mortality of diabetic patients. Several factors are involved in the development of nephropathy, including glomerular hyperfiltration, oxidative stress, accumulation of advanced glycation end‐products, activation of protein kinase C, acceleration of the polyol pathway and over‐expression of transforming growth factor‐β. Recently, accumulated data have emphasized the critical roles of chronic low‐grade inflammation, ‘microinflammation’, in the pathogenesis of diabetic nephropathy, suggesting that microinflammation is a common mechanism in the development of diabetic vascular complications. Expression of cell adhesion molecules, chemokines and pro‐inflammatory cytokines are increased in the renal tissues of diabetic patients and animals. Deficiency of pro‐inflammatory molecules results in amelioration of renal injuries after induction of diabetes in mice. Plasma and urinary levels of cytokines, chemokines and cell adhesion molecules, are elevated and correlated with albuminuria. Several kinds of drugs that have anti‐inflammatory actions as their pleiotropic effects showed renoprotective effects on diabetic animals. Modulation of the inflammatory process prevents renal insufficiency in diabetic animal models, suggesting that microinflammation is one of the promising therapeutic targets for diabetic nephropathy, as well as for cardiovascular diseases.