Glucagon-like peptide-1 and vitamin D: anti-inflammatory response in diabetic kidney disease in db/db mice and in cultured endothelial cells

Liraglutide ameliorates diabetic kidney disease by modulating gut microbiota and L-5-Oxoproline

The gut microbiome-metabolites-kidney axis is a potential target for treating diabetic kidney disease (DKD). Our previous study found that Liraglutide attenuated DKD in rats by decreasing renal tubular ectopic lipid deposition (ELD) and serum metabolites levels, including L-5-Oxoproline (5-OP). However, the response of gut microbiome-metabolites-kidney axis to Liraglutide in DKD rats and the effect of 5-OP on ELD remain unknown. In this study, Sprague-Dawley rats were used as an animal model of DKD. They were subjected to a high fat diet, streptozotocin and uninephrectomy, followed by Liraglutide treatment (0.4 mg/kg d). Additionally, HK-2 cells were incubated with 30 mM glucose and 200 μM palmitate for 24h, and exposed to different concentrations of 5-OP. In DKD rats, Liraglutide dramatically improved the renal tubule structure. It increased the Simpson index (F = 4.487, p = 0.035) and reduced the Actinobacteria-to-Bacteroidetes ratio (F = 6.189, p = 0.014). At the genus level, Liraglutide increased the relative abundance of Clostridium, Oscillospira, Sarcina, SMB53, and 02d06 while decreasing that of Allobaculum. Meanwhile, 13 metabolites were significantly altered after Liraglutide treatment. Multi-omics analysis found that 5-OP levels were positively correlated with Clostridium abundance but negatively correlated with renal injury related indicators. In HK-2 cells, 5-OP significantly reduced the ELD in a dose-dependent manner through inhibiting the expression of SREBP1 and FAS. Overall, the renoprotective effect of Liraglutide in DKD rats is linked to the improvement of the gut microbiota composition and increased serum 5-OP levels, which may reduce ELD in renal tubular cells by lowering lipid synthesis.

The role of glucagon-like peptide-1/GLP-1R and autophagy in diabetic cardiovascular disease

Diabetes leads to a significantly accelerated incidence of various related macrovascular complications, including peripheral vascular disease and cardiovascular disease (the most common cause of mortality in diabetes), as well as microvascular complications such as kidney disease and retinopathy. Endothelial dysfunction is the main pathogenic event of diabetes-related vascular disease at the earliest stage of vascular injury. Understanding the molecular processes involved in the development of diabetes and its debilitating vascular complications might bring up more effective and specific clinical therapies. Long-acting glucagon-like peptide (GLP)-1 analogs are currently available in treating diabetes with widely established safety and extensively evaluated efficacy. In recent years, autophagy, as a critical lysosome-dependent self-degradative process to maintain homeostasis, has been shown to be involved in the vascular endothelium damage in diabetes. In this review, the GLP-1/GLP-1R system implicated in diabetic endothelial dysfunction and related autophagy mechanism underlying the pathogenesis of diabetic vascular complications are briefly presented. This review also highlights a possible crosstalk between autophagy and the GLP-1/GLP-1R axis in the treatment of diabetic angiopathy.

PGC1-α in diabetic kidney disease: unraveling renoprotection and molecular mechanisms

Mitochondrial dysfunction represents a pivotal aspect of the pathogenesis and progression of diabetic kidney disease (DKD). Central to the orchestration of mitochondrial biogenesis is the peroxisome proliferator-activated receptor γ coactivator 1-α (PGC1-α), a master regulator with a profound impact on mitochondrial function. In the context of DKD, PGC1-α exhibits significant downregulation within intrinsic renal cells, precipitating a cascade of deleterious events. This includes a reduction in mitochondrial biogenesis, heightened levels of mitochondrial oxidative stress, perturbed mitochondrial dynamics, and dysregulated mitophagy. Concurrently, structural and functional abnormalities within the mitochondrial network ensue. In stark contrast, the sustained expression of PGC1-α emerges as a beacon of hope in maintaining mitochondrial homeostasis within intrinsic renal cells, ultimately demonstrating an impressive renoprotective potential in animal models afflicted with DKD. This comprehensive review aims to delve into the recent advancements in our understanding of the renoprotective properties wielded by PGC1-α. Specifically, it elucidates the potential molecular mechanisms underlying PGC1-α's protective effects within renal tubular epithelial cells, podocytes, glomerular endothelial cells, and mesangial cells in the context of DKD. By shedding light on these intricate mechanisms, we aspire to provide valuable insights that may pave the way for innovative therapeutic interventions in the management of DKD.

JAK/STAT signaling in diabetic kidney disease

Diabetic kidney disease (DKD) is the most important microvascular complication of diabetes and the leading cause of end-stage renal disease (ESRD) worldwide. The Janus kinase/signal transducer and activator of the transcription (JAK/STAT) signaling pathway, which is out of balance in the context of DKD, acts through a range of metabolism-related cytokines and hormones. JAK/STAT is the primary signaling node in the progression of DKD. The latest research on JAK/STAT signaling helps determine the role of this pathway in the factors associated with DKD progression. These factors include the renin-angiotensin system (RAS), fibrosis, immunity, inflammation, aging, autophagy, and EMT. This review epitomizes the progress in understanding the complicated explanation of the etiologies of DKD and the role of the JAK/STAT pathway in the progression of DKD and discusses whether it can be a potential target for treating DKD. It further summarizes the JAK/STAT inhibitors, natural products, and other drugs that are promising for treating DKD and discusses how these inhibitors can alleviate DKD to explore possible potential drugs that will contribute to formulating effective treatment strategies for DKD in the near future.

Hemodialysis Serum Stimulates the TXNIP-eNOS-STAT3 Inflammatory Pathway In Vitro

BACKGROUND

Endothelial dysfunction, vascular inflammation and accelerated atherosclerosis have been investigated extensively in patients with chronic kidney disease (CKD). These conditions, as well as protein-energy malnutrition and oxidative stress, impair kidney function and contribute to increased morbidity and mortality among patients with end-stage kidney disease undergoing hemodialysis (HD). TXNIP, a key regulator of oxidative stress, has been linked to inflammation and suppresses eNOS activity. STAT3 activation adds to endothelial cell dysfunction, macrophage polarization, immunity and inflammation. Therefore, it is critically involved in atherosclerosis. This study evaluated the effect of sera from HD patients on the TXNIP-eNOS-STAT3 pathway using an in vitro model of human umbilical vein endothelial cells (HUVECs).

METHODS

Thirty HD patients with end-stage kidney disease and ten healthy volunteers were recruited. Serum samples were taken at dialysis initiation. HUVECs were treated with HD or healthy serum (10% v/v) for 24 h. Then, cells were collected for mRNA and protein analysis.

RESULTS

TXNIP mRNA and protein expression were significantly increased in HUVECs treated with HD serum compared to healthy controls (fold changes: 2.41 ± 1.84 vs. 1.41 ± 0.5 and 2.04 ± 1.16 vs. 0.92 ± 0.29, respectively), as were IL-8 mRNA (fold changes: 2.22 ± 1.09 vs. 0.98 ± 0.64) and STAT3 protein expression (fold changes: 1.31 ± 0.75 vs. 0.57 ± 0.43). The expression of eNOS mRNA and protein (fold changes: 0.64 ± 0.11 vs. 0.95 ± 0.24; 0.56 ± 0.28 vs. 4.35 ± 1.77, respectively) and that of SOCS3 and SIRT1 proteins were decreased. Patients' nutritional status, reflected by their malnutrition-inflammation scores, did not affect these inflammatory markers.

CONCLUSIONS

This study showed that sera from HD patients stimulated a novel inflammatory pathway, regardless of their nutritional status.

Inhibition of notch signalling and mesangial expansion by combined glucagon like peptide-1 agonist and crocin therapy in animal model of diabetic nephropathy

Diabetic nephropathy (DN) is one of the devastating complications in diabetes mellitus (DM). Glucagon-like peptide-1 (GLP-1) is one of the incretins secreted from L cells in the intestine. Crocin (a carotenoid component of saffron) has antioxidants properties. We investigated the renal effects of Exendin-4 as a GLP-1 agonist and Crocin in DN.Thirty male rats were divided into five groups: control, type II DM, type II DM + Exendin-4, type II DM + Crocin ‏ and type II DM + Exendine-4 + Crocin. At the end of the experimental period, systolic and diastolic blood pressures were measured, and GFR was calculated. Blood and urine samples were collected for biochemical analysis. Tissue samples were collected from the kidney for histological examination and biochemical measurements of protein expression.Treatment with GLP-1 agonist or Crocin caused a significant improvement in renal function. Better results were achieved with simultaneous administration of both drugs with inhibition of notch signalling pathway and the related proteins.

Disturbed Lipid Metabolism in Diabetic Patients with Manifest Coronary Artery Disease Is Associated with Enhanced Inflammation

Background: Diabetic vasculopathy plays an important role in the pathophysiology of coronary artery disease (CAD) with oxidative stress as a strong mediator. This study aims to elucidate the underlying pathomechanisms of diabetic cardiac vasculopathy leading to coronary disease with an emphasis on the role of oxidative stress. Therefore, novel insights into antioxidant pathways might contribute to new strategies in the treatment and prevention of diabetic CAD. Methods: In 20 patients with insulin-dependent or non-insulin dependent diabetes mellitus (IDDM/NIDDM) and 39 non-diabetic (CTR) patients, myocardial markers of oxidative stress, vasoactive proteins, endothelial nitric oxide synthase (eNOS), activated phosphorylated eNOS (p-eNOS), and antioxidant enzymes, e.g., tetrahydrobiopterin generating dihydrofolate reductase (DHFR), heme oxygenase (HO-1), as well as serum markers of inflammation, e.g., E-selectin, interleukin-6 (IL-6), and lipid metabolism, e.g., high- and low-density lipoptrotein (HDL- and LDL-cholesterol) were determined in specimens of right atrial tissue and in blood samples from type 2 diabetic and non-diabetic patients undergoing coronary artery bypass graft (CABG) surgery. Results: IDDM/NIDDM increased markers of inflammation (e.g., E-selectin, p = 0.005 and IL-6, p = 0.051), decreased the phosphorylated myocardial p-eNOS (p = 0.032), upregulated the myocardial stress response protein HO-1 (p = 0.018), and enhanced the serum LDL-/HDL-cholesterol ratio (p = 0.019). However, the oxidative stress markers in the myocardium and the expression of vasoactive proteins (eNOS, DHFR) showed only marginal adverse changes in patients with IDDM/NIDDM. Conclusion: Dyslipidemia and myocardial inflammation seem to be the major determinants of diabetic CAD complications. Dysregulation in pro-oxidative enzymes might be attributable to the severity of CAD and oxidative stress levels in all included patients undergoing CABG.

Vitamin D3 decreases TNF-α-induced inflammation in lung epithelial cells through a reduction in mitochondrial fission and mitophagy

Previous work has shown an association between vitamin D₃ deficiency and an increased risk for acquiring various inflammatory diseases. Vitamin D₃ can reduce morbidity and mortality in these patients via different mechanisms. Lung inflammation is an important event in the initiation and development of respiratory disorders. However, the anti-inflammatory effects of vitamin D₃ and the underlying mechanisms remained to be determined. The purpose of this study was to examine the effects and mechanisms of action of vitamin D₃ (Vit. D) on the expression of intercellular adhesion molecule-1 (ICAM-1) in vitro and in vivo with or without tumor necrosis factor α (TNF-α) treatment. Pretreatment with Vit. D reduced the expression of ICAM-1 and leukocyte adhesion in TNF-α-treated A549 cells. TNF-α increased the accumulation of mitochondrial reactive oxygen species (mtROS), while Vit. D reduced this effect. Pretreatment with Vit. D attenuated TNF-α-induced mitochondrial fission, as shown by the increased expression of mitochondrial fission factor (Mff), phosphorylated dynamin-related protein 1 (p-DRP1), and mitophagy-related proteins (BCL2/adenovirus E1B 19 kDa protein-interacting protein 3, Bnip3) in A549 cells. Inhibition of DRP1 or Mff significantly decreased ICAM-1 expression. In addition, we found that Vit. D decreased TNF-α-induced ICAM-1 expression, mitochondrial fission, and mitophagy via the AKT and NF-κB pathways. Moreover, ICAM-1 expression, mitochondrial fission, and mitophagy were increased in the lung tissues of TNF-α-treated mice, while Vit. D supplementation reduced these effects. In this study, we elucidated the mechanisms by which Vit. D reduces the expression of adhesion molecules in models of airway inflammation. Vit. D might be served as a novel therapeutic agent for the targeting of epithelial activation in lung inflammation.

Liraglutide targets the gut microbiota and the intestinal immune system to regulate insulin secretion

AIMS

Liraglutide controls type 2 diabetes (T2D) and inflammation. Gut microbiota regulates the immune system and causes at least in part type 2 diabetes. We here evaluated whether liraglutide regulates T2D through both gut microbiota and immunity in dysmetabolic mice.

METHODS

Diet-induced dysmetabolic mice were treated for 14 days with intraperitoneal injection of liraglutide (100 µg/kg) or with vehicle or Exendin 4 (10 µg/kg) as controls. Various metabolic parameters, the intestinal immune cells were characterized and the 16SrDNA gene sequenced from the gut. The causal role of gut microbiota was shown using large spectrum antibiotics and by colonization of germ-free mice with the gut microbiota from treated mice.

RESULTS

Besides, the expected metabolic impacts liraglutide treatment induced a specific gut microbiota specific signature when compared to vehicle or Ex4-treated mice. However, liraglutide only increased glucose-induced insulin secretion, reduced the frequency of Th1 lymphocytes, and increased that of TReg in the intestine. These effects were abolished by a concomitant antibiotic treatment. Colonization of germ-free mice with gut microbiota from liraglutide-treated diabetic mice improved glucose-induced insulin secretion and regulated the intestinal immune system differently from what observed in germ-free mice colonized with microbiota from non-treated diabetic mice.

CONCLUSIONS

Altogether, our result demonstrated first the influence of liraglutide on gut microbiota and the intestinal immune system which could at least in part control glucose-induced insulin secretion.

Towards Better Drug Repositioning: Targeted Immunoinflammatory Therapy for Diabetic Nephropathy

Diabetic nephropathy (DN) is one of the most common and important microvascular complications of diabetes mellitus (DM). The main clinical features of DN are proteinuria and a progressive decline in renal function, which are associated with structural and functional changes in the kidney. The pathogenesis of DN is multifactorial, including genetic, metabolic, and haemodynamic factors, which can trigger a sequence of events. Controlling metabolic risks such as hyperglycaemia, hypertension, and dyslipidaemia is not enough to slow the progression of DN. Recent studies emphasized immunoinflammation as a critical pathogenic factor in the progression of DN. Therefore, targeting inflammation is considered a potential and novel treatment strategy for DN. In this review, we will briefly introduce the inflammatory process of DN and discuss the anti-inflammatory effects of antidiabetic drugs when treating DN.

Vitamin D Attenuates Ischemia/Reperfusion-Induced Cardiac Injury by Reducing Mitochondrial Fission and Mitophagy

Myocardial infarction is the leading cause of morbidity and mortality worldwide. Although myocardial reperfusion after ischemia (I/R) is an effective method to save ischemic myocardium, it can cause adverse reactions, including increased oxidative stress and cardiomyocyte apoptosis. Mitochondrial fission and mitophagy are essential factors for mitochondrial quality control, but whether they play key roles in cardiac I/R injury remains unknown. New pharmacological or molecular interventions to alleviate reperfusion injury are currently considered desirable therapies. Vitamin D₃ (Vit D₃) regulates cardiovascular function, but its physiological role in I/R-exposed hearts, especially its effects on mitochondrial homeostasis, remains unclear. An in vitro hypoxia/reoxygenation (H/R) model was established in H9c2 cells to simulate myocardial I/R injury. H/R treatment significantly reduced H9c2 cell viability, increased apoptosis, and activated caspase 3. In addition, H/R treatment increased mitochondrial fission, as manifested by increased expression of phosphorylated dynein-related protein 1 (p-Drp1) and mitochondrial fission factor (Mff) as well as increased mitochondrial translocation of Drp1. Treatment with the mitochondrial reactive oxygen species scavenger MitoTEMPO increased cell viability and decreased mitochondrial fission. H/R conditions elicited excessive mitophagy, as indicated by increased expression of BCL2-interacting protein 3 (BNIP3) and light chain (LC3BII/I) and increased formation of autolysosomes. In contrast, Vit D₃ reversed these effects. In a mouse model of I/R, apoptosis, mitochondrial fission, and mitophagy were induced. Vit D₃ treatment mitigated apoptosis, mitochondrial fission, mitophagy, and myocardial ultrastructural abnormalities. The results indicate that Vit D₃ exerts cardioprotective effects against I/R cardiac injury by protecting mitochondrial structural and functional integrity and reducing mitophagy.

Renal protection with glucagon-like peptide-1 receptor agonists

There is an unmet need for renoprotective drugs for more pronounced reduction of albuminuria beyond that provided by renin-angiotensin system (RAS) blockers and for effective slowdown of eGFR decline independent of albuminuria. Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) have proven effective in reducing prespecified secondary composite kidney outcomes in cardiovascular outcome trials. However, GLP-1 RAs showed a prevailing anti-albuminuric effect, additional to that of RAS blockers, and a non-significant risk reduction in worsening of kidney function, at variance with sodium-glucose cotransporter 2 inhibitors. Mechanisms underlying renal protection with GLP-1 RAs are porly understood. Though treatment with GLP-1 RAs resulted in better glycaemic, blood pressure and body weight control versus placebo, correction for on-trial changes in these parameters did not significantly affect results. Anti-inflammatory/anti-oxidant effects via intracellular signalling through protein kinase A, natriuretic effect via inhibition of sodium-hydrogen exchanger 3 and reduction of hyperfiltration have been proposed as direct renoprotective effects.

Liraglutide Improves the Kidney Function in a Murine Model of Chronic Kidney Disease

BACKGROUND

Chronic kidney disease (CKD) is a global health burden, and the current treatment options only slow down the disease progression. GLP-1 receptor agonists (GLP-1 RA) have shown a renal protective effect in models of CKD; however, the mechanism behind the beneficial effect is not understood. In this study, we investigate the effect of the GLP-1 RA liraglutide in the nephrotoxic serum nephritis (NTN) CKD model. Moreover, we compare the gene expression pattern of liraglutide-treated mice to the gene expression pattern of mice treated with the angiotensin converting enzyme inhibitor, enalapril.

METHODS

The effect of liraglutide was tested in the NTN model by evaluating the glomerular filtration rate (GFR), albuminuria, mesangial expansion, renal fibrosis, and renal inflammation. Furthermore, the regulation of selected genes involved in CKD and in glomerular, cortical tubulointerstitial, and whole kidney structures was analyzed using a gene expression array on samples following laser capture microdissection.

RESULTS

Treatment with liraglutide improved CKD hallmarks including GFR, albuminuria, mesangial expansion, renal inflammation, and renal fibrosis. The gene expression revealed that both liraglutide and enalapril reversed the regulation of several fibrosis and inflammation associated genes, which are also regulated in human CKD patients. Furthermore, liraglutide and enalapril both regulated genes in the kidney involved in blood pressure control.

CONCLUSIONS

Treatment with liraglutide improved the kidney function and diminished renal lesions in NTN-induced mice. Both liraglutide and enalapril reversed the regulation of genes involved in CKD and regulated genes involved in blood pressure control.

The Anti-Inflammatory Effects of Glucagon-Like Peptide Receptor Agonist Lixisenatide on the Retinal Nuclear and Nerve Fiber Layers in an Animal Model of Early Type 2 Diabetes

This study explored the anti-inflammatory effects of a glucagon-like peptide-1 receptor agonist (GLP-1RA), known as lixisenatide, on the eyes of early type 2 diabetic mice. Diabetic (db/db) mice were divided into three groups: GLP-1RA [lixisenatide (LIX)], insulin (INS) with controlled hyperglycemia based on the glucose concentration of lixisenatide, and diabetic control (D-CON). Nondiabetic control mice (db/dm) were also characterized for comparison. After 8 weeks of treatment, mRNA levels of inflammatory markers, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling, immunohistochemical staining; Western blot of glial fibrillary acidic protein (GFAP) and thioredoxin-interacting protein; and retinal thickness were assessed in the central and peripheral neurosensory retina. LIX showed decreased immunohistochemical staining for both thioredoxin-interacting protein and GFAP in the central and peripheral neurosensory retina compared with D-CON and INS, and decreased expression of these proteins in the neurosensory retina and immunohistochemical staining in the optic nerve head for GFAP compared with D-CON. The inner nuclear layer in the peripheral retina in LIX was only thinner than those of D-CON and INS. In an early type 2 diabetic mouse model, lixisenatide treatment showed superior anti-inflammatory effects on the retina and optic nerve head independent of hyperglycemia. Thus, the neuroprotective effects of lixisenatide treatment in the peripheral inner nuclear layer should be evaluated in early type 2 diabetic retinopathy.

Renoprotective Effect of Formononetin by Suppressing Smad3 Expression in Db/Db Mice

PURPOSE

Glomerular sclerosis and renal interstitial fibrosis are the most important pathologies in the development of kidney damage under diabetic conditions. Smad3 plays antagonistic roles in high glucose-induced renal tubular fibrosis, which is an important treatment target for diabetic nephropathy (DN). Formononetin (FMN) has multiple effects on diabetic vascular complications including DN. However, whether it plays an anti-fibrosis role by regulating smad3 is unclear. The purpose of this study was to evaluate the renoprotective effect of FMN by suppressing smad3 expression in db/db mice.

METHODS

FMN was orally administered to db/db mice with a dose of 25 or 50 mg/kg/day for 8 weeks. At the end of the study, serum, urine, and kidney samples were collected for biochemical and pathological examinations. The expressions of proteins and mRNA associated with renal fibrosis were determined by biochemical, histological, immunofluorescence, and real-time PCR analysis.

RESULTS

The results showed that FMN substantially improved the glucolipid metabolism, reduced the oxidative stress, and protected renal function in db/db mice. Meanwhile, protein and mRNA expression of smad3 and related regulatory factor of extracellular matrix deposition were significantly suppressed.

CONCLUSION

The present study suggested that FMN has a good renoprotective effect in DN, which plays an anti-fibrosis role in db/db mice by suppressing the expression of smad3.

Glucagon-like peptide-1 receptor pathway inhibits extracellular matrix production by mesangial cells through store-operated Ca2+ channel

Glomerular mesangial cell is the major source of mesangial matrix. Our previous study demonstrated that store-operated Ca2+ channel signaling suppressed extracellular matrix protein production by mesangial cells. Recent studies demonstrated that glucagon-like peptide-1 receptor (GLP-1R) pathway had renoprotective effects. However, the underlying mechanism(s) remains unclear. The present study was aimed to determine if activation of GLP-1R decreased extracellular matrix protein production by mesangial cells through upregulation of store-operated Ca2+ function. Experiments were conducted in cultured human mesangial cells. Liraglutide and exendin 9–39 were used to activate and inhibit GLP-1R, respectively. Store-operated Ca2+ function was estimated by evaluating the SOC-mediated Ca2+ entry (SOCE). We found that liraglutide treatment reduced high glucose-stimulated production of fibronectin and collagen IV. The inhibitory effects of liraglutide were not observed in the presence of exendin 9–39. Exendin-4, another GLP-1R agonist also blunted high glucose-stimulated fibronectin and collagen IV production. Treatment of human mesangial cells with liraglutide for 24 h significantly attenuated the high glucose-induced reduction of Orai1 protein. Consistently, Ca2+ imaging experiments showed that the inhibition of high glucose on SOCE was significantly attenuated by liraglutide. However, in the presence of exendin 9–39, liraglutide failed to reverse the high glucose effect. Furthermore, liraglutide effects on fibronectin and collagen IV protein abundance were significantly attenuated by GSK-7975A, a selective blocker of store-operated Ca2+. Taken together, our findings suggest that GLP-1R signaling inhibited high glucose-induced extracellular matrix protein production in mesangial cells by restoring store-operated Ca2+ function.

Impact statement

Diabetic kidney disease continues to be a major challenge to health care system in the world. There are no known therapies currently available that can cure the disease. The present study provided compelling evidence that activation of GLP-1R inhibited extracellular matrix protein production by glomerular mesangial cells. We further showed that the beneficial effect of GLP-1R was attributed to upregulation of store-operated Ca2+ channel function. Therefore, we identified a novel mechanism contributing to the renal protective effects of GLP-1R pathway. Activation of GLP-1R pathway and/or store-operated Ca2+ channel signaling in MCs could be an option for patients with diabetic kidney disease.

Effect of liraglutide on the Janus kinase/signal transducer and transcription activator (JAK/STAT) pathway in diabetic kidney disease in db/db mice and in cultured endothelial cells

BACKGROUND

Emerging evidence demonstrates the involvement of Janus tyrosine kinase/signal transducer and transcription activator (JAK/STAT) proteins in the pathophysiology of diabetic kidney disease (DKD). The JAK/STAT pathway is involved in the inflammatory response and endothelial cell dysfunction observed in DKD. The glucagon-like peptide-1 (GLP-1) analog liraglutide is an effective treatment for type 2 diabetes because it improves the inflammatory changes observed in experimental models of DKD. This study used db/db mice and endothelial cells (ECs) to determine the effect of diabetic environment on the JAK/STAT pathway and to assess the potential effect of liraglutide (200 μg/kg) in both models.

METHODS

Diabetic db/db mice (12 weeks old) were treated with liraglutide for 14 weeks. The kidneys were then perfused with saline and removed for mRNA, protein, and immunohistochemical analyses. Endothelial cells were stimulated advanced glycation end products (AGEs) (200 μg/μL) glucose (200 mg/dL) and liraglutide (100 nM) for 24 hours. Total RNA and protein were extracted and analyzed for expression of JAK/STAT signaling.

RESULTS

Phosphorylated (p-) STAT3 was significantly upregulated in db/db mice compared with non-diabetic mice. Liraglutide significantly downregulated p-STAT3 protein expression in db/db mice. In db/db mice, p-STAT3 was primarily expressed in the glomeruli, whereas p-JAK2 was also expressed in kidney tubules. In ECs, liraglutide treatment prevented increased expression of p-STAT3 and p-JAK2. Liraglutide inhibited the target gene suppressor of cytokine signaling 3 (SOCS3) and sirtuin 1 (SIRT1) in db/db mice and in cultured EC.

CONCLUSIONS

This study suggests that the GLP-1 analog liraglutide inhibits the JAK/STAT pathway, which participates in intracellular processes in experimental models of diabetes.

Protein kinase C and protein kinase A are involved in the protection of recombinant human glucagon-like peptide-1 on glomeruli and tubules in diabetic rats

AIMS/INTRODUCTION

Blockade or reversal the progression of diabetic nephropathy is a clinical challenge. The aim of the present study was to examine whether recombinant human glucagon-like peptide-1 (rhGLP-1) has an effect on alleviating urinary protein and urinary albumin levels in diabetic rats.

MATERIALS AND METHODS

Streptozotocin-induced diabetes rats were treated with rhGLP-1 insulin and saline. Using immunostaining, hematoxylin-eosin, electron microscopy and periodic acid-Schiff staining to study the pathology of diabetic nephropathy, and we carried out quantitative reverse transcription polymerase chain reaction, western blot and immunohistochemistry to identify the differentially expressed proteins. The mechanism was studied through advanced glycation end-products-induced tubular epithelial cells.

RESULTS

rhGLP-1 inhibits protein kinase C (PKC)-β, but increases protein kinase A (PKA), which reduces oxidative stress in glomeruli and in cultured glomerular microvascular endothelial cells. In tubules, rhGLP-1 increased the expression of two key proteins related to re-absorption - megalin and cubilin - which was accompanied by downregulation of PKC-β and upregulation of PKA. On human proximal tubular epithelial cells, rhGLP-1 enhanced the absorption of albumin, and this was blocked by a PKC activator or PKA inhibitor.

CONCLUSIONS

These findings suggest that rhGLP-1 can reverse diabetic nephropathy by protecting both glomeruli and tubules by inhibiting PKC and activating PKA.

High-density lipoproteins (HDL) composition and function in preeclampsia

PURPOSE

To evaluate (a) the properties of high-density lipoproteins (HDL)/cholesterol, which include apolipoprotein A-1 (ApoA1) and paraoxonase1 (PON1), both are negative predictors of cardiovascular risk and (b) HDL function, among women with preeclampsia (PE). PE is a multi-system disorder, characterized by onset of hypertension and proteinuria or other end-organ dysfunction in the second half of pregnancy. Preeclampsia is associated with increased risk for later cardiovascular disease. The inverse association between HDL, cholesterol levels and the risk of developing atherosclerotic cardiovascular disease is well-established.

METHODS

Twenty-five pregnant women [19 with PE and 6 with normal pregnancy (NP)] were recruited during admission for delivery. HDL was isolated from blood samples. PON1 activity and HDL were analyzed. An in vitro model of endothelial cells was used to evaluate the effect of HDL on the transcription response of vascular cell adhesion molecule-1 (VCAM-1) and endothelial nitric oxide synthase (eNOS) mRNA expression.

RESULTS

PON1 activity (units/ml serum) was lower in the PE group compared to normal pregnancy (NP) (6.51 ± 0.73 vs. 9.98 ± 0.54; P = 0.015). Increased ApoA1 was released from PE-HDL as compared to NP-HDL (3.54 ± 0.72 vs. 0.89 ± 0.35; P = 0.01). PE-HDL exhibited increased VCAM-1 mRNA expression and decreased eNOS mRNA expression on TNF-α stimulated endothelial cells as compared to NP-HDL.

CONCLUSIONS

HDL from women with PE reduced PON1 activity and increased ApoA1 release from HDL particles. This process was associated with increased HDL diameter, suggesting impaired HDL anti-oxidant activity. These changes might contribute to higher long-term cardiovascular risks among women with PE.

TXNIP in Metabolic Regulation: Physiological Role and Therapeutic Outlook

Background & Objective:

Thioredoxin-interacting protein (TXNIP) also known as thioredoxin binding protein-2 is a ubiquitously expressed protein that interacts and negatively regulates expression and function of Thioredoxin (TXN). Over the last few years, TXNIP has attracted considerable attention due to its wide-ranging functions impacting several aspects of energy metabolism. TXNIP acts as an important regulator of glucose and lipid metabolism through pleiotropic actions including regulation of β-cell function, hepatic glucose production, peripheral glucose uptake, adipogenesis, and substrate utilization. Overexpression of TXNIP in animal models has been shown to induce apoptosis of pancreatic β-cells, reduce insulin sensitivity in peripheral tissues like skeletal muscle and adipose, and decrease energy expenditure. On the contrary, TXNIP deficient animals are protected from diet induced insulin resistance and type 2 diabetes.

Summary:

Consequently, targeting TXNIP is thought to offer novel therapeutic opportunity and TXNIP inhibitors have the potential to become a powerful therapeutic tool for the treatment of diabetes mellitus. Here we summarize the current state of our understanding of TXNIP biology, highlight its role in metabolic regulation and raise critical questions that could help future research to exploit TXNIP as a therapeutic target.

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.