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

Therapeutic Advances in Diabetic Nephropathy

Diabetic kidney disease (DKD) is the most common cause of end-stage kidney disease (ESKD) in the United States. Risk factor modification, such as tight control of blood glucose, management of hypertension and hyperlipidemia, and the use of renin–angiotensin–aldosterone system (RAAS) blockade have been proven to help delay the progression of DKD. In recent years, new therapeutics including sodium-glucose transport protein 2 (SGLT2) inhibitors, endothelin antagonists, glucagon like peptide-1 (GLP-1) agonists, and mineralocorticoid receptor antagonists (MRA), have provided additional treatment options for patients with DKD. This review discusses the various treatment options available to treat patients with diabetic kidney disease.

Hypoxia-inducible factor-prolyl hydroxylase inhibitors for renal anemia in chronic kidney disease: Advantages and disadvantages

Anemia is a common feature and complication of chronic kidney disease (CKD). Erythropoiesis-stimulating agents (ESAs) and recombinant human erythropoietin have been used widely in renal anemia treatment. Recently, hypoxia-inducible factor-prolyl hydroxylase domain inhibitors (HIF-PHIs) that may improve the treatment of renal anemia patients were launched. Previous studies indicated that HIF-PHIs may decrease hepcidin levels and modulate iron metabolism, thereby increasing total iron-binding capacity and reducing the need for iron supplementation. Furthermore, HIF-PHIs can reduce inflammation and oxidative stress in CKD. Recombinant erythropoietin has become a routine treatment for patients with CKD and end-stage renal disease with relatively few adverse effects. However, higher doses of recombinant erythropoietin have been demonstrated to be an independent predictor of mortality in patients under hemodialysis. Phase III clinical trials of HIF-PHIs in patients with anemia and dialysis-dependent CKD have shown their efficacy and safety in both non-dialysis and dialysis CKD patients. However, HIFα binds to specific hypoxia-response elements in the vascular endothelial growth factor or retinoic acid-related orphan receptor gamma t (RORγt) promoter, which may be involved in the progression of cancer, psoriasis, and rheumatoid arthritis. In this paper, we have summarized the mechanism, clinical application, and clinical trials of HIF-PHIs in the treatment of renal anemia and aimed to provide an overview of the new drugs in clinical practice, as well as reconsider the advantages and disadvantages of HIF-PHIs and ESAs. Presently, there are not enough clinical studies examining the effects of long-term administration of HIF-PHIs. Therefore, further studies will be needed.

Mitochondria in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the leading cause of end stage renal disease (ESRD) in the USA. The pathogenesis of DKD is multifactorial and involves activation of multiple signaling pathways with merging outcomes including thickening of the basement membrane, podocyte loss, mesangial expansion, tubular atrophy, and interstitial inflammation and fibrosis. The glomerulo-tubular balance and tubule-glomerular feedback support an increased glomerular filtration and tubular reabsorption, with the latter relying heavily on ATP and increasing the energy demand. There is evidence that alterations in mitochondrial bioenergetics in kidney cells lead to these pathologic changes and contribute to the progression of DKD towards ESRD. This review will focus on the dialogue between alterations in bioenergetics in glomerular and tubular cells and its role in the development of DKD. Alterations in energy substrate selection, electron transport chain, ATP generation, oxidative stress, redox status, protein posttranslational modifications, mitochondrial dynamics, and quality control will be discussed. Understanding the role of bioenergetics in the progression of diabetic DKD may provide novel therapeutic approaches to delay its progression to ESRD.

CARDIOVASCULAR EFFECTS OF NON-INSULIN GLUCOSE-LOWERING AGENTS: A COMPREHENSIVE REVIEW OF TRIAL EVIDENCE AND POTENTIAL CARDIOPROTECTIVE MECHANISMS

Type 2 diabetes mellitus (T2DM) is highly prevalent and associated with a 2-fold increased mortality, mostly explained by cardiovascular diseases. Trial evidence on older glucose-lowering agents such as metformin and sulfonylureas is limited in terms of cardiovascular efficacy. Since 2008, after rosiglitazone was observed to increase the risk of myocardial infarction and heart failure (HF), cardiovascular outcome trials (CVOT) have been required by regulators for licensing new glucose-lowering agents. In the following CVOTs, dipeptidyl peptidase 4 inhibitors (DPP4i) have been shown to be safe but not to improve morbidity/mortality, except for saxagliptin which increased the risk of HF. Several glucagon-like peptide-1 receptor agonists (GLP1-Ra) and sodium-glucose cotransporter-2 inhibitors (SGLT2i) have been demonstrated to reduce the risk of cardiovascular morbidity and mortality. SGLT2i have shown a class effect for the reduction in risk of HF events in patients with T2DM, leading to trials testing their efficacy/safety in HF regardless of T2DM. In the DAPA-HF and the EMPEROR-Reduced trials dapagliflozin and empagliflozin, respectively, improved cardiovascular mortality/morbidity in patients with HF and reduced ejection fraction (HFrEF), with and without T2DM. Therefore, these drugs are now key part of HFrEF pharmacotherapy. In the SOLOIST-WHF, sotagliflozin reduced cardiovascular mortality/morbidity in patients with T2DM and a recent acute episode of HF regardless of EF. The DELIVER and the EMPEROR-Preserved are testing dapagliflozin and empagliflozin, respectively, in patients with HF with mildly reduced and preserved EF. A strong renal protective role of SGLT2i has also emerged in trials enrolling patients with and without T2DM.

Comparative effects of incretin-based therapy on early-onset diabetic nephropathy in rats: Role of TNF-α, TGF-β and c-caspase-3

AIMS

Diabetic nephropathy, a major threat to diabetic patients, is considered as the main reason for end-stage renal disease. Fortunately, incretin-based therapy has been aroused as considerable source to attenuate diabetic renal damage. This study aimed to investigate whether superior protective effects on the progression of diabetic kidney are exerted by glucagon-like peptide-1 analog, exenatide, or dipeptidyl peptidase-4 inhibitor, sitagliptin.

MATERIALS AND METHODS

Male Wistar rats were fed high-fat diet for 2 weeks followed by injection of low dose streptozotocin to induce type 2 diabetes mellitus. Four weeks after induction of diabetes, diabetic rats were administered vehicle, exenatide (5 μg/kg/day, SC) or sitagliptin (10 mg/kg/day, orally) for 4 weeks.

KEY FINDINGS

Different incretin mimetic agents improved renal function as evident by significant decreases in serum creatinine and urea levels with decline in urinary microalbuminuria and marked improvement in histological alterations. Both treated diabetic rats also exhibited a significant improvement in metabolic intolerance with more pronounced effect of exenatide on glucose regulation. Ameliorated renal oxidative stress alongside significant downregulation in transforming growth factor-beta, tumor necrosis factor-alpha and cleaved-caspase-3 protein expressions in renal tissues were recorded in treated diabetic rats.

SIGNIFICANCE

Administration of either exenatide or sitagliptin showed ameliorative effects on early diabetic nephropathy without notable differences between their renal protective effects. However, further clinical studies are still required to ensure their comparative promising effects on the management of renal complication of diabetes.

Sodium-Glucose Cotransporter 2 Inhibitors in Patients with Non-Diabetic Chronic Kidney Disease

BACKGROUND

Sodium-glucose cotransporter 2 (SGLT2) inhibitors can reduce cardiovascular morbidity and mortality in patients with type 2 diabetes. Furthermore, recent clinical studies have revealed that SGLT2 inhibitors decrease the risk of renal function impairment in patients with type 2 diabetes. However, the effects of SGLT2 inhibitors on non-diabetic chronic kidney disease (CKD) remains unclear. Regarding long-term clinical outcomes, the Dapagliflozin and Prevention of Adverse Outcomes in Heart Failure (DAPA-HF) trial explicitly showed improvements in cardiovascular outcomes in patients presenting with heart failure, even in the absence of diabetes. The reduction in heart failure in patients without diabetes was confirmed following empagliflozin administration in the EMPagliflozin outcomE tRial in patients with chrOnic heart failure with Reduced ejection fraction (EMPEROR-Reduced) trial. A recent systematic review and meta-analysis of DAPA-HF and EMPEROR-Reduced showed improvements in the composite renal endpoint regardless of the presence of diabetes or baseline estimated glomerular filtration rate. The Dapagliflozin and Prevention of Adverse outcomes in Chronic Kidney Disease (DAPA-CKD) trial evaluated patients with CKD with or without type 2 diabetes, irrespective of whether SGLT2 inhibitor dapagliflozin was added for renin-angiotensin system blockade as background renoprotective therapy. In this trial, dapagliflozin reduced the hazard ratio for a composite renal and cardiovascular death endpoint in patients with CKD attributed to various causes, with or without type 2 diabetes.

Renoprotective effect of GLP-1 receptor agonist, liraglutide, in early-phase diabetic kidney disease in spontaneously diabetic Torii fatty rats

BACKGROUND

The aim of this study is to investigate the renoprotective effect of the GLP-1 receptor agonist, liraglutide, in early-phase diabetic kidney disease (DKD) using an animal model of type 2 diabetes with several metabolic disorders.

METHODS

Male 8-week-old spontaneously diabetic Torii (SDT) fatty rats (n = 19) were randomly assigned to three groups. The liraglutide group (n = 6) was injected subcutaneously with liraglutide. Another treatment group (n = 6) received subcutaneous insulin against hyperglycemia and hydralazine against hypertension for matching blood glucose levels and blood pressure with the liraglutide group. The control groups of SDT fatty (n = 7) and non-diabetic Sprague-Dawley rats (n = 7) were injected only with a vehicle.

RESULTS

The control group of SDT fatty rats exhibited hyperglycemia, obesity, hypertension, hyperlipidemia, glomerular sclerosis, and tubulointerstitial injury with high urinary albumin and L-FABP levels. Liraglutide treatment reduced body weight, food intake, blood glucose and blood pressure levels, as well as ameliorated renal pathologic findings with lower urinary albumin and L-FABP levels. Liraglutide increased expressions of phosphorylated (p)-eNOS and p-AMPK in glomeruli, downregulated renal expression of p-mTOR, and increased renal expressions of LC3B-II, suggesting activation of autophagy. However, these effects were not caused by the treatments with insulin and hydralazine, despite comparable levels of hyperglycemia and hypertension to those achieved with liraglutide treatment.

CONCLUSIONS

Liraglutide may exert a renoprotective effect via prevention of glomerular endothelial abnormality and preservation of autophagy in early-phase DKD, independent of blood glucose, and blood pressure levels.

Protective Effects of Eicosapentaenoic Acid on the Glomerular Endothelium via Inhibition of EndMT in Diabetes

Diabetes-induced endothelial pathologies are hypothesized to lead to the progression of diabetic kidney disease (DKD). The endothelial to mesenchymal transition (EndMT) possibly induces fibrosis, leading to glomerulosclerosis in the kidney. Furthermore, this could lead to albuminuria in diabetic nephropathy due to glomerular endothelial dysfunction. Eicosapentaenoic acid (EPA), purified from fish oil, decreases inflammatory cytokine levels in glomerulonephritis. Here, we aimed at finding whether ethyl eicosapentaenoate (EPA-E) exerts renal protective effects via EndMT inhibition. To find out whether EPA inhibits EndMT in vitro, the changes in CD31 expression were studied in cultured mouse endothelial cells. The addition of the conditioned medium from the adipocyte culture significantly decreased the protein levels of CD31, while the addition of EPA-E partially reversed this inhibition. Further, EndMT inhibition by EPA-E treatment might occur via the inhibition of the protein kinase Cβ (PKCβ)/transforming growth factor-β (TGF-β)/plasminogen activator inhibitor-1 (PAI-1) signaling and not via microRNAs. Streptozotocin-induced diabetic mice fed a high-fat diet (60% from fat) exhibited mesangial expansion and albuminuria. Induction of EPA-E ameliorated the mesangial expansion and decreased albuminuria without affecting blood pressure, triglyceride and free fatty acid levels, and intraperitoneal glucose. These findings suggest that EPA-E exerts renal protective effects on endothelial cells, by normalizing EndMT followed by the PKCβ/TGF-β/PAI-1 signaling. Thus, EPA-E has the potential for imparting renal protection by regulating EndMT in DKD.

Effects of SGLT2 Inhibitors and GLP-1 Receptor Agonists on Renin-Angiotensin-Aldosterone System

Sodium-glucose cotransporters inhibitors (SGLT2-i) and GLP-1 receptor agonists (GLP1-RA) are glucose-lowering drugs that are proved to reduce the cardiovascular (CV) risk in type 2 diabetes mellitus (T2DM). In this process, the renin-angiotensin-aldosterone system (RAAS) is assumed to play a role. The inhibition of SGLT2 improves hyperglycemia hampering urinary reabsorption of glucose and inducing glycosuria. This "hybrid" diuretic effect, which couples natriuresis with osmotic diuresis, potentially leads to systemic RAAS activation. However, the association between SGLT2-i and systemic RAAS activation is not straightforward. Available data indicate that SGLT2-i cause plasma renin activity (PRA) increase in the early phase of treatment, while PRA and aldosterone levels remain unchanged in chronic treated patients. Furthermore, emerging studies provide evidence that SGLT2-i might have an interfering effect on aldosterone/renin ratio (ARR) in patients with T2DM, due to their diuretic and sympathoinhibition effects. The cardio- and reno-protective effects of GLP-1-RA are at least in part related to the interaction with RAAS. In particular, GLP1-RA counteract the action of angiotensin II (ANG II) inhibiting its synthesis, increasing the inactivation of its circulating form and contrasting its action on target tissue like glomerular endothelial cells and cardiomyocytes. Furthermore, GLP1-RA stimulate natriuresis inhibiting Na+/H+ exchanger NHE-3, which is conversely activated by ANG II. Moreover, GLP1 infusion acutely reduces circulating aldosterone, but this effect does not seem to be chronically maintained in patients treated with GLP1-RA. In conclusion, both SGLT2-i and GLP1-RA seem to have several effects on RAAS, though additional studies are needed to clarify this relationship.

Cardiovascular and renal outcomes by baseline albuminuria status and renal function: Results from the LEADER randomized trial

AIM

To assess cardiorenal outcomes by baseline urinary albumin-to-creatinine ratio (UACR) and estimated glomerular filtration rate (eGFR) in the contemporary LEADER cohort.

MATERIALS AND METHODS

LEADER was a multinational, double-blind trial. Patients with type 2 diabetes and high cardiovascular (CV) risk were randomized 1:1 to the glucagon-like peptide-1 analogue liraglutide (≤1.8 mg daily; n = 4668) or placebo (n = 4672) plus standard care and followed for 3.5 to 5 years. Primary composite outcomes were time to first non-fatal myocardial infarction, non-fatal stroke or CV death. Post hoc Cox regression analyses of outcomes by baseline UACR and eGFR subgroups were conducted with adjustment for baseline variables.

RESULTS

In the LEADER population, 1598 (17.5%), 2917 (31.9%), 1200 (13.1%), 1611 (17.6%), 845 (9.2%) and 966 (10.6%) had UACR = 0, >0 to <15, 15 to <30, 30 to <100, 100 to <300 and ≥300 mg/g, respectively. Increasing UACR and decreasing eGFR were linked with higher risks of the primary outcome, heart failure hospitalization, a composite renal outcome and death (P-values for the Cochran-Armitage test for trends were all <.0001). Across UACR and eGFR subgroups, risks of cardiorenal events and death were generally lower or similar with liraglutide versus placebo.

CONCLUSIONS

In a contemporary type 2 diabetes population, increasing baseline UACR and declining eGFR were linked with higher risks of cardiorenal events and death.

Rat pancreatectomy combined with isoprenaline or uninephrectomy as models of diabetic cardiomyopathy or nephropathy

Cardiovascular and renal complications are the predominant causes of morbidity and mortality amongst patients with diabetes. Development of novel treatments have been hampered by the lack of available animal models recapitulating the human disease. We hypothesized that experimental diabetes in rats combined with a cardiac or renal stressor, would mimic diabetic cardiomyopathy and nephropathy, respectively. Diabetes was surgically induced in male Sprague Dawley rats by 90% pancreatectomy (Px). Isoprenaline (Iso, 1 mg/kg, sc., 10 days) was administered 5 weeks after Px with the aim of inducing cardiomyopathy, and cardiac function and remodeling was assessed by echocardiography 10 weeks after surgery. Left ventricular (LV) fibrosis was quantified by Picro Sirius Red and gene expression analysis. Nephropathy was induced by Px combined with uninephrectomy (Px-UNx). Kidney function was assessed by measurement of glomerular filtration rate (GFR) and urine albumin excretion, and kidney injury was evaluated by histopathology and gene expression analysis. Px resulted in stable hyperglycemia, hypoinsulinemia, decreased C-peptide, and increased glycated hemoglobin (HbA1c) compared with sham-operated controls. Moreover, Px increased heart and LV weights and dimensions and caused a shift from α-myosin heavy chain (MHC) to β-MHC gene expression. Isoprenaline treatment, but not Px, decreased ejection fraction and induced LV fibrosis. There was no apparent interaction between Px and Iso treatment. The superimposition of Px and UNx increased GFR, indicating hyperfiltration. Compared with sham-operated controls, Px-UNx induced albuminuria and increased urine markers of kidney injury, including neutrophil gelatinase-associated lipocalin (NGAL) and podocalyxin, concomitant with upregulated renal gene expression of NGAL and kidney injury molecule 1 (KIM-1). Whereas Px and isoprenaline separately produced clinical endpoints related to diabetic cardiomyopathy, the combination of the two did not accentuate disease development. Conversely, Px in combination with UNx resulted in several clinical hallmarks of diabetic nephropathy indicative of early disease development.

DPP-4 Inhibitors: Renoprotective Potential and Pharmacokinetics in Type 2 Diabetes Mellitus Patients with Renal Impairment

The continuously increasing incidence of diabetes worldwide has attracted the attention of the scientific community and driven the development of a novel class of antidiabetic drugs that can be safely and effectively used in diabetic patients. Of particular interest in this context are complications associated with diabetes, such as renal impairment, which is the main cause of high cardiovascular morbidity and mortality in diabetic patients. Intensive control of glucose levels and other risk factors associated with diabetes and metabolic syndrome provides the foundations for both preventing and treating diabetic nephropathy. Dipeptidyl peptidase-4 (DPP-4) inhibitors represent a highly promising novel class of oral agents used in the treatment of type 2 diabetes mellitus that may be successfully combined with currently available antidiabetic therapeutics in order to achieve blood glucose goals. Beyond glycemic control, emerging evidence suggests that DPP-4 inhibitors may have desirable off-target effects, including renoprotection. All type 2 diabetes mellitus patients with impaired renal function require dose adjustment of any DPP-4 inhibitor administered except for linagliptin, for which renal excretion is a minor elimination pathway. Thus, linagliptin is the drug most frequently chosen to treat type 2 diabetes mellitus patients with renal failure.

Incretin-based therapies and renin-angiotensin system: Looking for new therapeutic potentials in the diabetic milieu

Incretin-based therapies include pharmacologic agents such as glucagon like peptide-1 receptor agonists and dipeptidyl peptidase-4 inhibitors which exert potent anti-hyperglycemic effects in the diabetic milieu. They are also shown to have extra-pancreatic effects. Renin-angiotensin system is part of the endocrine system which is widely distributed in the body and is closely involved in water and electrolyte homeostasis as well as renal and cardiovascular functions. Hence the renin-angiotensin system is the main target for treating patients with various renal and cardiovascular disorders. There is growing evidence that incretins have modulatory effects on renin-angiotensin system activity; thereby, can be promising therapeutic agents for the management of renal and cardiovascular disorders. But the exact molecular interactions between incretins and renin-angiotensin system are not clearly understood. In this current study, we have reviewed the possible molecular mechanisms by which incretins modulate renin-angiotensin system activity.

Renin-Angiotensin System overactivation in polycystic ovary syndrome, a risk for SARS-CoV-2 infection?

Background

The SARS-CoV-2 coronavirus gains entry to target cells via the angiotensin-converting enzyme 2 (ACE2) receptor present on cells in blood vessels, lungs, heart, intestines, and kidneys. Renin-Angiotensin System (RAS) overactivity has also been described in metabolic syndrome, type 2 diabetes (T2D) and obesity, conditions shared by women with polycystic ovary syndrome (PCOS) We hypothesized that RAS overactivity may be present in PCOS.

Methods

We determined plasma levels of RAS-related proteins in a cohort of age matched control women (n = 97) and women with PCOS (n = 146). Plasma levels of RAS-related proteins (ACE2, Renin and Angiotensinogen (AGT)) were determined by Slow Off-rate Modified Aptamer (SOMA)-scan plasma protein measurement.

Results

PCOS women had a higher BMI (p < 0.001), systolic (p < 0.0001) and diastolic (p < 0.05) blood pressure, waist circumference (p < 0.0001), testosterone (p < 0.0001), free androgen index (p < 0.0001) and CRP (p < 0.0001). Renin was elevated in PCOS (p < 0.05) and angiotensinogen was lower in PCOS (p < 0.05), indicating overactivity of the RAS system in PCOS. ACE2 levels were lower in PCOS (p < 0.05), suggesting that PCOS women are at risk for development of hypertension.

Conclusion

RAS proteins levels differed between PCOS and control women, suggesting that the insulin resistance inherent in PCOS may predispose these women to more severe COVID-19 infection.

Anti-hyperglycemic activity of myricetin, through inhibition of DPP-4 and enhanced GLP-1 levels, is attenuated by co-ingestion with lectin-rich protein

Dipeptidyl peptidase-4 (DPP-4) is a proteolytic enzyme responsible for the rapid degradation of Glucagon-like peptide 1 (GLP-1) that is required for the secretion of insulin. DPP-4 also influences activation of node like receptor family, pyrin domain containing 3 (NLRP3) inflammasome under diabetic conditions. Although several polyphenols are reported for various bioactivities, they are consumed as part of the food matrix and not in isolation. Horsegram (Macrotyloma uniflorum) is a rich source of myricetin (Myr) (35 μg/g flour), reported for its anti-hyperglycemic effect. In this investigation, we aimed to study the effect of Myr, singly, and in the presence of co-nutrient horsegram protein (HP) on DPP-4 activity and its consequential impact on GLP-1, insulin, and NLRP3 inflammasome in high-fat diet and single low dose streptozotocin (STZ)-induced diabetic male Wistar rats. In diabetic control (DC), the activity of DPP-4 and its expression were higher compared to treated groups. The consequential decrease in the circulating GLP-1 levels in the DC group, but not treated groups, further indicated the effectiveness of our test molecules under diabetic conditions. Specifically, Myr decreased DPP-4 activity and its expression levels with enhanced circulating GLP-1 and insulin levels. Myr administration also resulted in a lessening of diabetes-induced NLRP3 inflammasome activation and enhanced antioxidant enzyme activities. HP also proved to be efficient in reducing elevated blood glucose levels and enhancing antioxidant enzyme activities. However, Myr, in the presence of HP as a co-nutrient, had diminished capacity to inhibit DPP-4 and, consequently, reduced potential in ameliorating diabetic conditions. Myr proved to be a potent inhibitor of DPP-4 in vitro and in vivo, resulting in enhanced circulating GLP-1 and insulin levels, thereby improving diabetic conditions. Though Myr and HP, individually ameliorate diabetic conditions, their dietary combination had reduced efficiency.

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

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

Exendin-4 Improves Diabetic Kidney Disease in C57BL/6 Mice Independent of Brown Adipose Tissue Activation

BACKGROUND

The role of exendin-4 in brown adipose tissue (BAT) activation was not very clear. This study is to verify the role of BAT involved in renal benefits of exendin-4 in diabetes mellitus (DM).

METHODS

In vivo, C57BL/6 mice were randomly divided into nondiabetic (control) and diabetic groups (DM). The diabetic mice were randomized into a control group (DM-Con), BAT-excision group (DM+Exc), exendin-4-treated group (DM+E4), and BAT-excision plus exendin-4-treated group (DM+Exc+E4). The weight, blood glucose and lipids, 24 h urine albumin and 8-OH-dG, and renal fibrosis were analyzed. In vitro, we investigated the role of exendin-4 in the differentiation process of 3T3-L1 and brown preadipocytes and its effect on the rat mesangial cells induced by oleate.

RESULTS

The expressions of UCP-1, PGC-1α, ATGL, and CD36 in BAT of DM mice were all downregulated, which could be upregulated by exendin-4 treatment with significant effects on ATGL and CD36. BAT-excision exacerbated high blood glucose (BG) with no significant effect on the serum lipid level. Exendin-4 significantly lowered the level of serum triglycerides (TG) and low-density lipoprotein- (LDL-) c, 24 h urine albumin, and 8-OH-dG; improved renal fibrosis and lipid accumulation; and activated renal AMP-activated protein kinase (AMPK) in diabetic mice regardless of BAT excision. In vitro, there was no significant effect of exendin-4 on brown or white adipogenesis. However, exendin-4 could improve lipid accumulation and myofibroblast-like phenotype transition of mesangial cells induced by oleate via activating the AMPK pathway.

CONCLUSIONS

Exendin-4 could decrease the renal lipid deposit and improve diabetic nephropathy via activating the renal AMPK pathway independent of BAT activation.

Odds of Acute Kidney Injury in Patients Receiving Dipeptidyl Peptidase 4 Inhibitors: A National Cohort Study Within the Department of Veterans Affairs

Preclinical and clinical data of dipeptidyl peptidase 4 (DPP-4) inhibitors have demonstrated discordant data regarding acute kidney injury (AKI). Therefore, we aimed to evaluate the association between DPP-4 use and AKI. This cohort study utilized data from the Department of Veterans Affairs evaluating patients diagnosed with type 2 (T2) diabetes with a DPP-4 inhibitor and compared with nondiabetic and diabetic patients. The primary end point is the development of AKI, and statistical analyses were performed to examine the association. DPP-4 use is associated with a lower odds of AKI compared with diabetics (adjusted odds ratio (OR) = 0.39; 95% confidence interval (CI) = 0.32-0.48) and nondiabetics (OR = 0.64; 95% CI = 0.52-0.79). DPP-4 use in patients with T2 diabetes mellitus is associated with lower odds of AKI within 120 days compared with nondiabetic and diabetic controls when adjusting for study covariates.

More than just an enzyme: Dipeptidyl peptidase-4 (DPP-4) and its association with diabetic kidney remodelling

PURPOSE OF THE REVIEW

This review article discusses recent advances in the mechanism of dipeptidyl peptidase-4 (DPP-4) actions in renal diseases, especially diabetic kidney fibrosis, and summarizes anti-fibrotic functions of various DPP-4 inhibitors in diabetic nephropathy (DN).

RECENT FINDINGS

DN is a common complication of diabetes and is a leading cause of the end-stage renal disease (ESRD). DPP-4 is a member of serine proteases, and more than 30 substrates have been identified that act via several biochemical messengers in a variety of tissues including kidney. Intriguingly, DPP-4 actions on the diabetic kidney is a complex mechanism, and a variety of pathways are involved including increasing GLP-1/SDF-1, disrupting AGE-RAGE pathways, and integrin-β- and TGF-β-Smad-mediated signalling pathways that finally lead to endothelial to mesenchymal transition. Interestingly, an array of DPP-4 inhibitors is well recognized as oral drugs to treat type 2 diabetic (T2D) patients, which promote better glycemic control. Furthermore, recent experimental and preclinical data reveal that DPP-4 inhibitors may also exhibit protective effects in renal disease progression including anti-fibrotic effects in the diabetic kidney by attenuating above signalling cascade(s), either singly or as a combinatorial effect. In this review, we discussed the anti-fibrotic effects of DPP-4 inhibitors based on recent reports along with the possible mechanism of actions and future perspectives to underscore the beneficial effects of DPP-4 inhibitors in DN.

SUMMARY

With recent experimental, preclinical, and clinical evidence, we summarized DPP-4 activities and its mechanism of actions in diabetic kidney diseases. A knowledge gap of DPP-4 inhibition in controlling renal fibrosis in DN has also been postulated in this review for future research perspectives.

Hyperglycemia induces NF-κB activation and MCP-1 expression via downregulating GLP-1R expression in rat mesangial cells: inhibition by metformin

Hyperglycemia impairs glucagon-like peptide-1 receptor (GLP-1R) signaling in multiple cell types and thereby potentially attenuates the therapeutic effects of GLP-1R agonists. We hypothesized that the downregulation of GLP-1R by hyperglycemia might reduce the renal-protective effects of GLP-1R agonists in diabetic nephropathy (DN). In this study, we examined the effects of high glucose on the expression of GLP-1R and its signaling pathways in the HBZY-1 rat mesangial cell line. We found that high glucose reduced GLP-1R messenger RNA (mRNA) levels in HBZY-1 cells and in the renal cortex in db/db mice comparing with control groups. In consistence, GLP-1R agonist exendin-4 induced CREB phosphorylation was attenuated by high glucose but not low glucose treatment, which is paralleled with abrogated anti-inflammatory functions in HBZY-1 cells linked with nuclear factor-κB (NF-κB) activation. In consistence, GLP-1R inhibition aggravated the high glucose-induced activation of NF-κB and MCP-1 protein levels in cultured HBZY-1 cells while overexpression of GLP-1R opposite effects. We further proved that metformin restored high glucose-inhibited GLP-1R mRNA expression and decreased high glucose evoked inflammation in HBZY-1 cells. On the basis of these findings, we conclude that high glucose lowers GLP-1R expression and leads to inflammatory responses in mesangial cells, which can be reversed by metformin. These data support the rationale of combinative therapy of metformin with GLP-1R agonists in DN.

Renal effects of glucagon-like peptide receptor agonists in patients with type 1 diabetes mellitus

AIM

The purpose of our study is to assess the effects of glucagon-like peptide-1 receptor agonists (GLP-1R agonists) on early markers of kidney damage in patients with type 1 diabetes mellitus (DM).

MATERIALS AND METHODS

The study included 27 patients with type 1 diabetes with normo- (n=16) and microalbuminuria (n=11) on intensive insulin injection regimen with insulin analogs. Patients were divided into two groups: 15 patients continued insulin therapy throughout the follow-up period, 12 patients were given 1.2 mg GLP-1R agonist (Liraglutide) once a day in addition to the insulin therapy for 6 months. HbA1c, lipid profile, classic markers of kidney damage (albuminuria, creatinine, glomerular filtration rate); plazma (neutrophilic gelatinase-associated lipoxalin - NGAL, molecule renal damage of type 1 - KIM-1, cystatin C, osteopontin) and urinary kidney biomarkers (nephrin, podocyne, uromodulin, NGAL, KIM-1, collagen type IV, cystatin C) were evaluated prior and in dynamics at 6 months. Kidney biomarkers levels were assessed by the enzyme-linked immunosorbent assay (ELISA).

RESULTS

We observed a significant decrease in the urinary excretion of type IV collagen, cystatin C, increased uromodulin excretion and decrease in the plasma levels of osteopontin, NGAL and cystatin C in the group of combined insulin and GLP-1R agonist therapy.

CONCLUSION

Changes in the level of sensitive kidney biomarkers indicate a possible renoprotective effect of GLP-1R agonist therapy in patients with type 1 diabetes at an early stages of kidney damage.

Liraglutide Inhibits Endothelial-to-Mesenchymal Transition and Attenuates Neointima Formation after Endovascular Injury in Streptozotocin-Induced Diabetic Mice

Hyperglycaemia causes endothelial dysfunction, which is the initial process in the development of diabetic vascular complications. Upon injury, endothelial cells undergo an endothelial-to-mesenchymal transition (EndMT), lose their specific marker, and gain mesenchymal phenotypes. This study investigated the effect of liraglutide, a glucagon-like peptide 1 (GLP-1) receptor agonist, on EndMT inhibition and neointima formation in diabetic mice induced by streptozotocin. The diabetic mice with a wire-induced vascular injury in the right carotid artery were treated with or without liraglutide for four weeks. The degree of neointima formation and re-endothelialisation was evaluated by histological assessments. Endothelial fate tracing revealed that endothelium-derived cells contribute to neointima formation through EndMT in vivo. In the diabetic mouse model, liraglutide attenuated wire injury-induced neointima formation and accelerated re-endothelialisation. In vitro, a high glucose condition (30 mmol/L) triggered morphological changes and mesenchymal marker expression in human umbilical vein endothelial cells (HUVECs), which were attenuated by liraglutide or Activin receptor-like 5 (ALK5) inhibitor SB431542. The inhibition of AMP-activated protein kinase (AMPK) signaling by Compound C diminished the liraglutide-mediated inhibitory effect on EndMT. Collectively, liraglutide was found to attenuate neointima formation in diabetic mice partially through EndMT inhibition, extending the potential therapeutic role of liraglutide.

Liraglutide Improves Renal Endothelial Function in Obese Zucker Rats on a High-Salt Diet

Metabolic syndrome is a common risk factor in chronic kidney disease. We investigated whether liraglutide [(LIRA), a glucagon-like peptide-1 receptor (GLP-1R) agonist] treatment improved renal vascular function and renal remodeling in male Zucker rats on a high-salt diet (6% NaCl). Zucker lean (+/+) and obese (fa/fa) rats (8 weeks old) were treated with vehicle or LIRA (0.1 mg/kg per day) for 8 weeks on a high-salt diet. The glomerular filtration rate (GFR) was measured at 0 and 8 weeks using the fluorescein isothiocyanate/sinistrin method in conscious rats. We used X-ray microangiography to measure renal arterial vessel diameter (70-350 µm) and vessel number in vivo in anesthetized rats. Renal protein expression levels of nitrotyrosine, CD-68, endothelial nitric oxide synthase (eNOS), vascular endothelial growth factor (VEGF), transforming growth factor-β1, cyclooxygenase-2, and GLP-1R were assessed by western blotting. Renal gene expressions were determined by real-time polymerase chain reaction. In contrast to vehicle-treated rats, fa/fa-LIRA rats improved GFR, nitric oxide (NO)-mediated vasodilation in response to acetylcholine and sodium nitroprusside in small arterial vessels (<200 µm diameter). LIRA treatment increased vessel responsivity to NO donors in comparison with vehicle treatment. Increases in the expressions of proinflammatory, profibrotic, and oxidative stress related genes in fa/fa rats relative to +/+ were unaltered by LIRA, other than a trend toward attenuation of VCAM-1 gene expression. However, LIRA treatment increased protein expressions of eNOS (P = 0.014) and VEGF (P = 0.063), while reducing glomerular macrophage infiltration in comparison with vehicle-treated fa/fa rats. Low-dose LIRA treatment improved renal vascular function through amelioration of vascular dysfunction and improved NO-mediated dilation of small intrarenal arteries and arterioles and a reduction in renal inflammation.

Incidence of acute kidney disease after receiving hematopoietic stem cell transplantation: a single-center retrospective study

Background

Previous reports have shown that acute kidney injury (AKI) is common after hematopoietic stem cell transplantation (HSCT), which is a crucial treatment for patients with hematological disorders. AKI could increase mortality and induce adverse effects including the development of chronic kidney disease. The incidence of AKI in association with HSCT reportedly varies significantly because several definitions of AKI have been adopted. Acute kidney disease (AKD) is a new concept that can clinically define both AKI and persistent decreases in glomerular filtration rate (GFR) state. We conducted a retrospective cohort study to determine the incidence of AKD after HSCT.

Methods

This study included 108 patients aged between 16 and 70 years undergoing HSCT. In this study, AKD included clinical condition of AKI or subacute decreases in GFR. AKI was defined according to the Kidney Disease: Improving Global Outcomes guidelines based on serum creatinine. However, urine output data were not included to define AKI because the database lacked some of these data. Comparisons were made between groups using the Mann–Whitney U test.

Results

Acute kidney disease occurred in 17 patients (15.7%). There were significant differences between the AKD and non-AKD with respect to ABO-incompatible HSCT (p = 0.001) and incidence of acute graft versus host disease (GVHD) after HSCT (p < 0.001). The 100-day overall survival of patients with AKD and without AKD after HSCT was 70.6% and 79.8%, respectively (p = 0.409).

Discussion

ABO-incompatible HSCT and acute GVHD after HSCT were risk factors for the incidence of AKD. However, we could not find a significant association between AKD after HSCT and mortality.

Mechanisms of GLP-1 receptor-independent renoprotective effects of the dipeptidyl peptidase type 4 inhibitor linagliptin in GLP-1 receptor knockout mice with 5/6 nephrectomy

Dipeptidyl peptidase type 4 (DPP-4) inhibitors were reported to have beneficial effects in experimental models of chronic kidney disease. The underlying mechanisms are not completely understood. However, these effects could be mediated via the glucagon-like peptide-1 (GLP-1)/GLP-1 receptor (GLP1R) pathway. Here we investigated the renal effects of the DPP-4 inhibitor linagliptin in Glp1r-/- knock out and wild-type mice with 5/6 nephrectomy (5/6Nx). Mice were allocated to groups: sham+wild type+placebo; 5/6Nx+ wild type+placebo; 5/6Nx+wild type+linagliptin; sham+knock out+placebo; 5/6Nx+knock out+ placebo; 5/6Nx+knock out+linagliptin. 5/6Nx caused the development of renal interstitial fibrosis, significantly increased plasma cystatin C and creatinine levels and suppressed renal gelatinase/collagenase, matrix metalloproteinase-1 and -13 activities; effects counteracted by linagliptin treatment in wildtype and Glp1r-/- mice. Two hundred ninety-eight proteomics signals were differentially regulated in kidneys among the groups, with 150 signals specific to linagliptin treatment as shown by mass spectrometry. Treatment significantly upregulated three peptides derived from collagen alpha-1(I), thymosin β4 and heterogeneous nuclear ribonucleoprotein A1 (HNRNPA1) and significantly downregulated one peptide derived from Y box binding protein-1 (YB-1). The proteomics results were further confirmed using western blot and immunofluorescence microscopy. Also, 5/6Nx led to significant up-regulation of renal transforming growth factor-β1 and pSMAD3 expression in wild type mice and linagliptin significantly counteracted this up-regulation in wild type and Glp1r-/- mice. Thus, the renoprotective effects of linagliptin cannot solely be attributed to the GLP-1/GLP1R pathway, highlighting the importance of other signaling pathways (collagen I homeostasis, HNRNPA1, YB-1, thymosin β4 and TGF-β1) influenced by DPP-4 inhibition.

Essential Role Of High Glucose-Induced Overexpression Of PKCβ And PKCδ In GLP-1 Resistance In Rodent Cardiomyocytes

PURPOSE

Myocardia in diabetic patients exhibit increased vulnerability after ischemia/reperfusion injury (IRI). It has been demonstrated that glucagon-like peptide-1 (GLP-1) has a protective effect on cardiomyocytes. Protein kinase C (PKC) acts as a key regulator of many signaling pathways including oxidative stress and apoptosis. Our hypothesis is that increased vulnerability of myocardia in diabetic patients is partly due to GLP-1 resistance. The aim of this study was to explore the role of PKC in GLP-1 resistance in diabetic cardiomyocytes.

METHODS

Cardiac function of diabetic or non-diabetic mice after myocardial IRI was detected with or without administration of GLP-1 analog exendin-4. Impacts of diabetes mellitus on GLP-1R expression in myocardia after IRI were accessed by Western blot. By transfecting PKC isoforms siRNA, in vitro study helped to identify the exact PKC isoforms which contributed to the downregulatio n of GLP-1R or impaired post-receptor signaling pathways in rodent cardiomyocytes (H9C2 cells) cultured by high glucose.

RESULTS

The cardioprotective effects of endogenous GLP-1 were impaired in diabetic mice after myocardial IRI and administration of exendin-4 had no significant effects in restoring cardiac function. GLP-1 receptor (GLP-1R) expression decreased in H9C2 cells cultured by high glucose and knockdown of PKCβ partly restored GLP-1R expression. Overexpression of PKCδ induced by high glucose in H9C2 cells impaired GLP-1 post-receptor anti-apoptotic signaling pathways by inhibition of Akt phosphorylation. Knockdown of both PKCβ and PKCδ significantly restored cardioprotective effects of GLP-1 in H9C2 cells cultured by high glucose.

CONCLUSION

Our study found out a new mechanism of GLP-1 resistance that high glucose-induced overexpression of PKCβ and PKCδ impaired cardioprotective effects of GLP-1 by downregulation of GLP-1R and inhibition of GLP-1 post-receptor anti-apoptotic signaling pathways, thus provided a new perspective in treating myocardial IRI in diabetic patients.

Glucagon-Like Peptide-1 Infusion Suppresses Aldosterone Levels in Healthy Normal-Weight Individuals: Double-Blind, Placebo-Controlled Crossover Study

INTRODUCTION

Glucagon-like peptide-1 (GLP-1) has many effects on the human body, but its glucose-lowering effect through its stimulation of insulin secretion is the most significant. GLP-1 also acts on renal function and hemodynamics. The antihypertensive and renoprotective effects of GLP-1 receptor agonists are partly explained by their vasoactive effect and increased natriuresis, but their positive influences on blood pressure and the development and progression of kidney disease are attributed to many effects beyond glycemic control. The aim of this study was to determine how the native gut hormone GLP-1 influences the renin-angiotensin-aldosterone system (RAAS).

METHODS

Fourteen healthy participants (6 males and 8 females) were included in a double-blind, placebo-controlled crossover study. After overnight fasting and oral sodium loading, participants were randomly assigned to receive either placebo (500 ml of 0.9% saline) or GLP-1 infusion (1.5 pmol/kg/min dissolved in 500 ml of 0.9% saline) over a 3-h period. After 3 and 6 h, the following parameters were measured: glucose, insulin, plasma renin activity, aldosterone, GLP-1, and antidiuretic hormone. After 7 days, the protocol was repeated, except that those who had previously received placebo now received GLP-1 infusion, and those who had previously received GLP-1 now received placebo.

RESULTS

Three hours after GLP-1 infusion, aldosterone had decreased by a statistically significant amount (p < 0.008) compared to the baseline level.

CONCLUSION

The present study showed that native GLP-1 can decrease aldosterone secretion in a group of healthy individuals, supporting the idea of beneficial outcomes of GLP-1-activating agents on blood pressure and the RAAS.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02130778.

Cardiovascular safety of GLP-1 receptor agonists for diabetes patients with high cardiovascular risk: A meta-analysis of cardiovascular outcomes trials

AIM

To show long-term cardiovascular safety of the GLP-1 receptor agonists for diabetes patients with cardiovascular risk.

METHODS

For cardiovascular outcomes, the association between treatment and outcomes was estimated using the odds ratio and 95% confidence interval. I² test was adopted to assess the magnitude of heterogeneity between studies, with values more than 25%, 50%, and 75% defined as low, moderate, or high heterogeneity.

RESULTS

We combined data from four cardiovascular outcomes trials and prospectively blinded endpoint adjudication. 4105 cardiovascular events including cardiovascular death, acute MI or stroke experienced during the trials. And the odds ratios of the cardiovascular outcomes were 0.90 (95% CI 0.81, 1.00) for the cardiovascular outcome, 0.93 (95% CI 0.85, 1.02) for nonfatal myocardial infarction, 0.88 (95% CI 0.76, 1.03) for nonfatal stroke, 0.94 (95% CI 0.84, 1.05) for heart failure hospitalization, 0.89 (95% CI 0.63, 1.27) for pancreatitis, 0.98 (95% CI 0.92, 1.05) for any hypoglycemic events, 0.92 (95% CI 0.83, 1.01) for the severe hypoglycemic events, 0.96 (95% CI 0.83, 1.01) for serious adverse events. Significant differences showed in mortality parameters: 0.88 (95% CI 0.81, 0.95) for all-cause mortality, 0.87 (95% CI 0.79, 0.97) for cardiovascular mortality. CV benefits were obtained in the male, black, Asian patients and patients with BMI ≥ 30 kg/m².

CONCLUSION

Additional GLP-1 receptor agonists treatment did not increase cardiovascular outcomes in diabetes patients with high cardiovascular risk or established cardiovascular disease.

Renal protection by sodium-glucose cotransporter 2 inhibitors and its underlying mechanisms in diabetic kidney disease

AIM

Diabetic kidney disease (DKD) is the most frequent cause of mortality and morbidity, leading a global health burden. This review will focus on the potential therapeutic interventions using Sodium-glucose cotransporter-2 (SGLT2) inhibitors that could prevent the development and progression of DKD.

RESULTS

SGLT2 inhibitors have been widely used as anti-diabetic drugs. Recent clinical studies have demonstrated that these drugs, which improve glycemic control and hypertension and decrease body weight, decrease the risk of renal function impairment and heart failure in patients with type 2 diabetes. With regard to long-term clinical outcomes, the Empagliflozin, Cardiovascular Outcomes, and Mortality in Type 2 Diabetes (EMPA-REG OUTCOME), the EMPA-REG Renal OUTCOME, and the CANagliflozin cardioVascular Assessment Study (CANVAS) program which have been integrated from CANVAS and CANVAS-Renal (CANVAS-R) trials reported significant risk reductions in primary combined major adverse cardiovascular events. Furthermore, regarding renal outcomes, the EMPA-REG Renal OUTCOME and CANVAS program clearly showed improvements in renal outcomes, including decreases in albuminuria and progression of nephropathy, doubling of serum creatinine levels, and initiation of renal replacement therapy.

CONCLUSIONS

Potential mechanisms of SGLT2 inhibitors related to renoprotection can be divided into two categories: hemodynamic actions and metabolic actions.

The potential and pitfalls of GLP-1 receptor agonists for renal protection in type 2 diabetes

Glucagon-Like Peptide-1 Receptor agonists (GLP-1 RA) offer substantial benefits for the management of glucose levels in type 2 diabetes. In addition, recent data from clinical trials have demonstrated that treatment with Glucagon-Like Peptide-1 Receptor agonists (GLP-1 RA) are also able to reduce new onset macroalbuminuria. These benefits may be consistent with the known effects of GLP-1 RA on traditional risk factors for progressive kidney disease including glucose lowering, blood pressure lowering, reduced insulin levels and weight reduction. However, emerging evidence suggests that GLP-1 RA can also have direct effects in the kidney, including inhibiting NHE3-dependent sodium reabsorption in the proximal tubule. Additional effects on the intrarenal renin angiotensin system, ischaemia/hypoxia, inflammation, apoptosis and neural signalling may also contribute to renal benefits. The extent to which these effects are mediated by the GLP-1R remains to be established. Recent studies confirm that the metabolic products of GLP-1 retain important antioxidant and anti-apoptotic activities that are GLP-1 R independent. Moreover the divergent peptide sequences of the currently available GLP-1 RA may mean that divergent reno-protective efficacy could be anticipated from different GLP-1 RA on this basis. Kidney disease is an important and deadly clinical outcome, and one worth preventing. Although both experimental and clinical data now support the possibility of renoprotective effects arising from treatment with GLP-1 RA, further work is needed to optimise these effects. A logical synergism with SGLT2 inhibition also exists, and at least in the short term, this combination approach may become the most useful way to protect the kidney in type 2 diabetes.

The glucagon-like peptide-1 receptor agonist Exendin-4, ameliorates contrast-induced nephropathy through suppression of oxidative stress, vascular dysfunction and apoptosis independent of glycaemia

Contrast-induced nephropathy (CIN) is a leading cause of hospital-acquired acute kidney injury, particularly in diabetic patients. Previous studies have shown renoprotective effects of glucagon-like peptide-1 (GLP-1) signalling; however, its role in CIN remains unexplored. This study investigates the prophylactic effect of exendin-4, a GLP-1R agonist, against CIN in a rat model mimicking both healthy and diabetic conditions. Animals were randomly divided into 7 groups: a control sham group (n = 8), and 2 identical sets of 3 disease groups, one received exendin-4 before exposure to contrast medium (CM), while the other served as untreated control. The 3 disease groups represented diabetes (n = 8), CIN (n = 8), or diabetes and CIN combined (n = 8). Untreated groups showed deteriorating renal function as indicated by significantly higher levels of serum creatinine and blood urea nitrogen, malondialdehyde, and endothelin-1 and caspase-3 expression compared to the sham control group. This was accompanied by a significant decrease in tissue reserves of reduced glutathione, superoxide dismutase, nitrate and endothelin nitric oxide synthase as well as deteriorating renal histology. The CM-induced changes in diabetic rats indicate impaired renal function, oxidative stress, vascular dysfunction, and apoptosis, and were significance higher in intensity compared to non-diabetic rats. Pretreatment with exendin-4 ameliorated all the aforementioned CM-induced nephropathic effects independent of the glycemic state. To our knowledge, this is the first study describing the prophylactic renoprotective effects of exendin-4 against CIN. With the current pharmaceutical use of exendin-4 as a hypoglycaemic agent, the GLP-1R agonist becomes an interesting candidate for human clinical trials on CIN prevention.

Exogenous SERP1 attenuates restenosis by restoring GLP-1 receptor activity in diabetic rats following vascular injury

The activity of glucagon-like peptide 1 (GLP-1R) is essential for preventing restenosis following vascular injury; however, the mechanism of dysfunctional GLP-1R glycosylation and ways to enhance the activity of GLP-1R on vascular surfaces in diabetic patients are poorly understood. In the present study, we investigated the N-glycosylation level and role of stress-associated endoplasmic reticulum protein 1 (SERP1) in preventing restenosis following carotid injury in diabetic rats. Our results showed that N-glycosylation levels in both rat aortic endothelial cells (RAOECs) and rat vascular smooth muscle cells (VSMCs) decreased gradually following glucose treatment in a concentration dependant manner. Furthermore, co-immunoprecipitation (Co-IP) analyses indicated that SERP1 could interact with GLP-1R in RAOECs and VSMCs. Moreover, SERP1 enhanced GLP-1R N-glycosylation and increased the production of phosphorylated endothelial nitric oxide synthase (eNOS) as well as proliferation of RAOECs. SERP1 also increased phosphorylated adenosine monophosphate activated protein kinase (AMPK) and decreased the migration of VSMCs. Importantly, intima media thickness (IMT) and neointimal hyperplasia were alleviated in the carotid artery of diabetic rats injected with SERP1 following balloon injury. We also found an increase in re-endothelialization and a decrease in VSMC proliferation in the carotid artery of diabetic rats injected with SERP1. In summary, the remarkable effects of SERP1 on reducing restenosis following vascular injury may contribute to future advancements in the treatment of diabetic vascular complications.

Exenatide Delays the Progression of Nonalcoholic Fatty Liver Disease in C57BL/6 Mice, Which May Involve Inhibition of the NLRP3 Inflammasome through the Mitophagy Pathway

Objective

This study is aimed at investigating whether exenatide (Exe) delays the progression of nonalcoholic fatty liver disease (NAFLD) in C57BL/6 mice by targeting the NLRP3 inflammasome through the autophagy/mitophagy pathway.

Methods

Thirty male C57BL/6 mice were randomly divided into three groups: control group (n = 10), model group (n = 10), and Exe (exenatide) group (n = 10). Mouse models of NAFLD and diabetes were established using a high-fat diet and streptozocin.

Results

The levels of fasting blood glucose (FBG), total cholesterol (TC), and triglyceride (TG) in the serum were significantly reduced after Exe treatment. The body weight, liver weight/body weight, and number of lipid droplets in the liver significantly decreased in Exe-treated mice. Treatment with Exe markedly reduced the levels of liver lipids, malondialdehyde (MDA), and alanine aminotransferase (ALT) in serum and livers. The number of autophagosomes increased significantly in the Exe group. The expression of LC3A/B-II/I, Beclin-1, Parkin, and BNIP3L increased significantly, whereas NLRP3 and IL-1β proteins were suppressed after Exe treatment.

Conclusion

We successfully established a mouse model of NAFLD and diabetes. Exe may reduce oxidative stress injury and inhibit the NLRP3 inflammasome by enhancing the autophagy/mitophagy pathway in liver, which has a protective effect on the liver in NAFLD and diabetes in C57BL/6 mice.

GLP-1 receptor agonist ameliorates obesity-induced chronic kidney injury via restoring renal metabolism homeostasis

Increasing evidence indicates that obesity is highly associated with chronic kidney disease (CKD). GLP-1 receptor (GLP-1R) agonist has shown benefits on kidney diseases, but its direct role on kidney metabolism in obesity is still not clear. This study aims to investigate the protection and metabolic modulation role of liraglutide (Lira) on kidney of obesity. Rats were induced obese by high-fat diet (HFD), and renal function and metabolism changes were evaluated by metabolomic, biological and histological methods. HFD rats exhibited systemic metabolic disorders such as obesity, hyperlipidemia and impaired glucose tolerance, as well as renal histological and function damages, while Lira significantly ameliorated these adverse effects in HFD rats. Metabolomic data showed that Lira directly reduced renal lipids including fatty acid residues, cholesterol, phospholipids and triglycerides, and improved mitochondria metabolites such as succinate, citrate, taurine, fumarate and nicotinamide adenine dinucleotide (NAD+) in the kidney of HFD rats. Furthermore, we revealed that Lira inhibited renal lipid accumulation by coordinating lipogenic and lipolytic signals, and partly rescued renal mitochondria function via Sirt1/AMPK/PGC1α pathways in HFD rats. This study suggested that Lira alleviated HFD-induced kidney injury at least partly via directly restoring renal metabolism, thus GLP-1R agonist is a promising therapy for obesity-associated CKD.

Sitagliptin improved glucose assimilation in detriment of fatty-acid utilization in experimental type-II diabetes: role of GLP-1 isoforms in Glut4 receptor trafficking

BACKGROUND

The distribution of glucose and fatty-acid transporters in the heart is crucial for energy consecution and myocardial function. In this sense, the glucagon-like peptide-1 (GLP-1) enhancer, sitagliptin, improves glucose homeostasis but it could also trigger direct cardioprotective actions, including regulation of energy substrate utilization.

METHODS

Type-II diabetic GK (Goto-Kakizaki), sitagliptin-treated GK (10 mg/kg/day) and wistar rats (n = 10, each) underwent echocardiographic evaluation, and positron emission tomography scanning for [¹⁸F]-2-fluoro-2-deoxy-D-glucose (¹⁸FDG). Hearts and plasma were isolated for biochemical approaches. Cultured cardiomyocytes were examined for receptor distribution after incretin stimulation in high fatty acid or high glucose media.

RESULTS

Untreated GK rats exhibited hyperglycemia, hyperlipidemia, insulin resistance, and plasma GLP-1 reduction. Moreover, GK myocardium decreased ¹⁸FDG assimilation and diastolic dysfunction. However, sitagliptin improved hyperglycemia, insulin resistance, and GLP-1 levels, and additionally, enhanced ¹⁸FDG uptake and diastolic function. Sitagliptin also stimulated the sarcolemmal translocation of the glucose transporter-4 (Glut4), in detriment of the fatty acyl translocase (FAT)/CD36. In fact, Glut4 mRNA expression and sarcolemmal translocation were also increased after GLP-1 stimulation in high-fatty acid incubated cardiomyocytes. PI3K/Akt and AMPKα were involved in this response. Intriguingly, the GLP-1 degradation metabolite, GLP-1(9-36), showed similar effects.

CONCLUSIONS

Besides of its anti-hyperglycemic effect, sitagliptin-enhanced GLP-1 may ameliorate diastolic dysfunction in type-II diabetes by shifting fatty acid to glucose utilization in the cardiomyocyte, and thus, improving cardiac efficiency and reducing lipolysis.

Oxidative Stress, Apoptosis, and Mitochondrial Function in Diabetic Nephropathy

Diabetic nephropathy (DN) is the second most frequent and prevalent complication of diabetes mellitus (DM). The increase in the production of oxidative stress (OS) is induced by the persistent hyperglycemic state capable of producing oxidative damage to the macromolecules (lipids, carbohydrates, proteins, and nucleic acids). OS favors the production of oxidative damage to the histones of the double-chain DNA and affects expression of the DNA repairer enzyme which leads to cell death from apoptosis. The chronic hyperglycemic state unchains an increase in advanced glycation end-products (AGE) that interact through the cellular receptors to favor activation of the transcription factor NF-κB and the protein kinase C (PKC) system, leading to the appearance of inflammation, growth, and augmentation of synthesis of the extracellular matrix (ECM) in DN. The reactive oxygen species (ROS) play an important role in the pathogenesis of diabetic complications because the production of ROS increases during the persistent hyperglycemia. The primary source of the excessive production of ROS is the mitochondria with the capacity to exceed production of endogenous antioxidants. Due to the fact that the mechanisms involved in the development of DN have not been fully clarified, there are different approaches to specific therapeutic targets or adjuvant management alternatives in the control of glycemia in DN.

The renoprotective effect and safety of a DPP-4 inhibitor, sitagliptin, at a small dose in type 2 diabetic patients with a renal dysfunction when changed from other DPP-4 inhibitors: REAL trial

BACKGROUND

We conducted the multicenter, prospective, open-label study in type 2 diabetic (T2DM) patients with renal dysfunction, to clarify the efficacy and the safety in relation to renal function and glycemic control, and the economic effect when other dipeptidyl peptidase-4 (DPP-4) inhibitors were switched to a small dose of sitagliptin depending on their renal function.

METHODS

Vildagliptin, alogliptin, or linagliptin received for more than 2 months were changed to sitagliptin at 25 or 12.5 mg/day depending on their renal function in 49 T2DMs. Renal function and glycemic control, and the drug cost were assessed during 6 months.

RESULTS

Estimated glomerular filtration rate was not changed in patients not on hemodialysis (n = 29). The HbA1c levels were not altered in all of the patients including those on hemodialysis (n = 20). The active glucagon-like peptide-1 levels or other renal parameters were not altered significantly. There were no adverse events to be related to the drugs. The daily drug expense was reduced by 88.1 yen per patient.

CONCLUSION

Switching to a small dose of sitagliptin according to the renal function in T2DM patients with renal dysfunction demonstrated the same efficacy and safety as those with other full-dose DPP-4 inhibitors, indicating a therapeutic option with a high cost performance.

Impact of diabetes on gingival wound healing via oxidative stress

The aim of this study is to investigate the mechanisms linking high glucose to gingival wound healing. Bilateral wounds were created in the palatal gingiva adjacent to maxillary molars of control rats and rats with streptozotocin-induced diabetes. After evaluating postsurgical wound closure by digital imaging, the maxillae including wounds were resected for histological examinations. mRNA expressions of angiogenesis, inflammation, and oxidative stress markers in the surgical sites were quantified by real-time polymerase chain reaction. Primary fibroblast culture from the gingiva of both rats was performed in high glucose and normal medium. In vitro wound healing and cell proliferation assays were performed. Oxidative stress marker mRNA expressions and reactive oxygen species production were measured. Insulin resistance was evaluated via PI3K/Akt and MAPK/Erk signaling following insulin stimulation using Western blotting. To clarify oxidative stress involvement in high glucose culture and cells of diabetic rats, cells underwent N-acetyl-L-cysteine treatment; subsequent Akt activity was measured. Wound healing in diabetic rats was significantly delayed compared with that in control rats. Nox1, Nox2, Nox4, p-47, and tumor necrosis factor-α mRNA levels were significantly higher at baseline in diabetic rats than in control rats. In vitro study showed that cell proliferation and migration significantly decreased in diabetic and high glucose culture groups compared with control groups. Nox1, Nox2, Nox4, and p47 expressions and reactive oxygen species production were significantly higher in diabetic and high glucose culture groups than in control groups. Akt phosphorylation decreased in the high glucose groups compared with the control groups. Erk1/2 phosphorylation increased in the high glucose groups, with or without insulin treatment, compared with the control groups. Impaired Akt phosphorylation partially normalized after antioxidant N-acetyl-L-cysteine treatment. Thus, delayed gingival wound healing in diabetic rats occurred because of impaired fibroblast proliferation and migration. Fibroblast dysfunction may occur owing to high glucose-induced insulin resistance via oxidative stress.

Renoprotective Effect of Dipeptidyl Peptidase-4 Inhibitors in Patients with Type 2 Diabetes Mellitus

Diabetic nephropathy is one of three major complications of diabetes mellitus, often leading to chronic renal failure requiring dialysis. Recently developed dipeptidyl peptidase-4 (DPP-4) inhibitors may exhibit renoprotective effects in addition to antihyperglycemic effects. In this study, we retrospectively investigated temporal changes in the renal function index of patients with type 2 diabetes mellitus (DM) and examined the influence of DPP-4 inhibitors on renal function. Patients with type 2 DM (>18 years old) prescribed hypoglycemic agents at Gifu Municipal Hospital for ≥3 months between March 2010 and April 2014 were included in the study. Renal function was evaluated as estimated the decline in 12-month glomerular filtration rate from the baseline in patients receiving and not receiving DPP-4 inhibitors. Patient data from the DPP-4 inhibitor-treated (501 patients, 58.6%) and untreated (354, 41.4%) groups were analyzed using multiple logistic regression analysis, as well as Cox proportional-hazards regression analysis (616, 55.6% and 491, 44.4%, for DPP-4 inhibitors-treated and untreated groups). Multiple logistic regression analysis indicated that DPP-4 inhibitors significantly lowered the estimated glomerular filtration rate (eGFR) decline [20% over 12 months; odds ratio (OR), 0.626; 95% confidence interval [CI], 0.409–0.958; P = 0.031]. Similar results were obtained using Cox proportional-hazards regression analysis (hazard ratio [HR], 0.707; 95% CI, 0.572–0.874; P = 0.001). These findings suggest that DPP-4 inhibitors suppress the decrease of estimated glomerular filtration rate in patients with type 2 DM and show a renoprotective effect.

GLP-1 and the kidney: from physiology to pharmacology and outcomes in diabetes

The gastrointestinal tract - the largest endocrine network in human physiology - orchestrates signals from the external environment to maintain neural and hormonal control of homeostasis. Advances in understanding entero-endocrine cell biology in health and disease have important translational relevance. The gut-derived incretin hormone glucagon-like peptide 1 (GLP-1) is secreted upon meal ingestion and controls glucose metabolism by modulating pancreatic islet cell function, food intake and gastrointestinal motility, amongst other effects. The observation that the insulinotropic actions of GLP-1 are reduced in type 2 diabetes mellitus (T2DM) led to the development of incretin-based therapies - GLP-1 receptor agonists and dipeptidyl peptidase 4 (DPP-4) inhibitors - for the treatment of hyperglycaemia in these patients. Considerable interest exists in identifying effects of these drugs beyond glucose-lowering, possibly resulting in improved macrovascular and microvascular outcomes, including in diabetic kidney disease. As GLP-1 has been implicated as a mediator in the putative gut-renal axis (a rapid-acting feed-forward loop that regulates postprandial fluid and electrolyte homeostasis), direct actions on the kidney have been proposed. Here, we review the role of GLP-1 and the actions of associated therapies on glucose metabolism, the gut-renal axis, classical renal risk factors, and renal end points in randomized controlled trials of GLP-1 receptor agonists and DPP-4 inhibitors in patients with T2DM.

Effects of Incretin-Based Therapies on Diabetic Microvascular Complications

The morbidity and mortality associated with diabetic complications impose a huge socioeconomic burden worldwide. Therefore, the ultimate goal of managing diabetes mellitus (DM) is to lower the risk of macrovascular complications and highly morbid microvascular complications such as diabetic nephropathy (DN) and diabetic retinopathy (DR). Potential benefits of incretin-based therapies such as glucagon-like peptide 1 receptor agonists (GLP-1 RAs) and dipeptidyl peptidase-4 (DPP-4) inhibitors on the diabetic macrovascular complications have been recently suggested, owing to their pleiotropic effects on multiple organ systems. However, studies primarily investigating the role of these therapies in diabetic microvascular complications are rare. Nevertheless, preclinical and limited clinical data suggest the potential protective effect of incretin-based agents against DN and DR via their anti-inflammatory, antioxidative, and antiapoptotic properties. Evidence also suggests that these incretin-dependent and independent beneficial effects are not necessarily associated with the glucose-lowering properties of GLP-1 RAs and DPP-4 inhibitors. Hence, in this review, we revisit the preclinical and clinical evidence of incretin-based therapy for DR and DN, the two most common, morbid complications in individuals with DM. In addition, the review discusses a few recent studies raising concerns of aggravating DR with the use of incretin-based therapies.

Dipeptidyl peptidase 4 inhibitor use is associated with a lower risk of incident acute kidney injury in patients with diabetes

OBJECTIVES

Dipeptidyl peptidase 4 inhibitor (DPP4i) use potentially slows the progression of diabetic kidney disease, but its effects on the risk of acute kidney injury (AKI) are unclear. We aimed to assess the association between DPP4i use and incident AKI episodes from a nationally representative cohort in Taiwan.

MATERIALS AND METHODS

All patients newly diagnosed with diabetes mellitus (DM) between 2008, when DPP4i use was first approved in Taiwan, and mid-2013 were enrolled. Propensity score-matched diabetic DPP4i users, who received DPP4i for at least 90 days, and nonusers were selected. The primary and secondary outcomes were incident AKI and dialysis-requiring AKI during follow-up. Cox proportional hazard analyses were performed to examine the effect of DPP4i on the risk of AKI.

RESULTS

We enrolled 923,936 diabetic patients; of these, 83,638 DPP4i users (75.7% sitagliptin, 14.6% vildagliptin, and 9.7% saxagliptin) were propensity score-matched to 83,638 non-users. After an average 3.6-year follow-up, 1.56% and 0.35% of DPP4i users and 2.53% and 0.56% of non-users developed incident AKI and dialysis-requiring AKI, respectively. DPP4i use was significantly associated with lower risk of incident AKI (hazard ratio [HR] 0.57, 95% confidence interval [CI] 0.53-0.61) and risk of dialysis-requiring AKI (HR 0.57, 95% CI 0.49-0.66). The risk reduction was consistent regardless of DPP4i type, the presence of chronic kidney disease, the previous acute kidney injury, and age.

CONCLUSIONS

DPP4i use is associated with reduced risk of mild and severe forms of AKI among patients with incident DM. DPP4i may be an important class of anti-glycaemic agent with reno-protective effects.

Role of soluble and membrane-bound dipeptidyl peptidase-4 in diabetic nephropathy

Diabetic nephropathy is one of the most frequent, devastating and costly complications of diabetes. The available therapeutic approaches are limited. Dipeptidyl peptidase type 4 (DPP-4) inhibitors represent a new class of glucose-lowering drugs that might also have reno-protective properties. DPP-4 exists in two forms: a plasma membrane-bound form and a soluble form, and can exert many biological actions mainly through its peptidase activity and interaction with extracellular matrix components. The kidneys have the highest DPP-4 expression level in mammalians. DPP-4 expression and urinary activity are up-regulated in diabetic nephropathy, highlighting its role as a potential target to manage diabetic nephropathy. Preclinical animal studies and some clinical data suggest that DPP-4 inhibitors decrease the progression of diabetic nephropathy in a blood pressure- and glucose-independent manner. Many studies reported that these reno-protective effects could be due to increased half-life of DPP-4 substrates such as glucagon-like peptide-1 (GLP-1) and stromal derived factor-1 alpha (SDF-1a). However, the underlying mechanisms are far from being completely understood and clearly need further investigations.

G-CSF and cognitive dysfunction in elderly diabetic mice with cerebral small vessel disease: Preventive intervention effects and underlying mechanisms

AIMS

Although cognitive dysfunction is a common neurological complication in elderly patients with diabetes, the mechanisms underlying this relationship remain unclear, and effective preventive interventions have yet to be developed. Thus, this study investigated the preventive effects and mechanisms of action associated with granulocyte colony-stimulating factor (G-CSF) on cognitive dysfunction in elderly diabetic mice with cerebral small vessel disease.

METHODS

This study included 40 male db/db diabetic and wild-type (WT) mice that were categorized into the following four groups at the age of 3 weeks: db/db group (DG), db/db+G-CSF group (DGG), WT group (WG), and WT+G-CSF group (WGG). The mice were fed normal diets for 4 months and then given G-CSF (75 μg/kg) via intraperitoneal injections for 1 month. At 7.5 months of age, the cognitive abilities of the mice were assessed with the Y-maze test and the Social Choice Test; body weight, blood pressure (BP), and blood glucose measurements were obtained throughout the study. Brain imaging and blood oxygen level-dependent (BOLD) contrast imaging analyses were performed with a small animal magnetic resonance imaging (MRI) system, autophagosome levels were detected with a transmission electron microscope (TEM), hippocampal neurons were assessed with hematoxylin and eosin (HE) staining, and protein expressions and distributions were evaluated using immunohistochemistry and Western blot analyses.

RESULTS

(i) The body weight and blood glucose levels of the DG and DGG mice were significantly higher than those of the WG and WGG mice; (ii) social choice and spatial memory capabilities were significantly reduced in DG mice but were recovered by G-CSF in DGG mice; (iii) the MRI scans revealed multiple lacunar lesions and apparent hippocampal atrophy in the brains of DG mice, but G-CSF reduced the number of lacunar lesions and ameliorated hippocampal atrophy; (iv) the MRI-BOLD scans showed a downward trend in whole-brain activity and reductions in the connectivities of the hippocampus and amygdala with subcortical structures in DG mice, but G-CSF clearly improved the altered brain activity as well as the connectivity of the hippocampus in DGG mice; (v) HE staining revealed fewer neurons in the hippocampus in DG mice; (vi) TEM analyses revealed significantly fewer autophagosomes in the hippocampi of DG mice, but G-CSF did not increase these numbers; (vii) there were significant reductions in mechanistic target of rapamycin (mTOR) and LC3-phosphatidylethanolamine conjugate (LC3)-II/I levels in the hippocampi of DG mice, whereas p62 was upregulated, and G-CSF significantly enhanced the levels of Beclin1, mTOR, and LC-II/I in DGG mice; and (viii) G-CSF significantly reversed increases in nuclear factor κB (NF-κB) protein levels in DG but not in WG mice.

CONCLUSIONS

In this study, aged diabetic mice were prone to cognitive dysfunction and cerebral small vessel disease. However, administration of G-CSF significantly improved cognitive function in elderly db/db diabetic mice, and this change was likely related to the regulation of autophagy and NF-κB signaling pathways.