Liraglutide ameliorates palmitate-induced oxidative injury in islet microvascular endothelial cells through GLP-1 receptor/PKA and GTPCH1/eNOS signaling pathways

Research Progress on Peptide Drugs for Type 2 Diabetes and the Possibility of Oral Administration

Diabetes is a global disease that can lead to a range of complications. Currently, the treatment of type 2 diabetes focuses on oral hypoglycemic drugs and insulin analogues. Studies have shown that drugs such as oral metformin are useful in the treatment of diabetes but can limit the liver's ability to release sugar. The development of glucose-lowering peptides has provided new options for the treatment of type 2 diabetes. Peptide drugs have low oral utilization due to their easy degradation, short half-life, and difficulty passing through the intestinal mucosa. Therefore, improving the oral utilization of peptide drugs remains an urgent problem. This paper reviews the research progress of peptide drugs in the treatment of diabetes mellitus and proposes that different types of nano-formulation carriers, such as liposomes, self-emulsifying drug delivery systems, and polymer particles, should be combined with peptide drugs for oral administration to improve their absorption in the gastrointestinal tract.

Anti-atherosclerotic effect of incretin receptor agonists

Incretin receptor agonists (IRAs), primarily composed of glucagon-like peptide-1 receptor agonists (GLP-1RAs) and glucose-dependent insulinotropic polypeptide receptor agonists (GIPRAs), work by mimicking the actions of the endogenous incretin hormones in the body. GLP-1RAs have been approved for use as monotherapy and in combination with GIPRAs for the management of type 2 diabetes mellitus (T2DM). In addition to their role in glucose regulation, IRAs have demonstrated various benefits such as cardiovascular protection, obesity management, and regulation of bone turnover. Some studies have suggested that IRAs not only aid in glycemic control but also exhibit anti-atherosclerotic effects. These agents have been shown to modulate lipid abnormalities, reduce blood pressure, and preserve the structural and functional integrity of the endothelium. Furthermore, IRAs have the ability to mitigate inflammation by inhibiting macrophage activation and promoting M2 polarization. Research has also indicated that IRAs can decrease macrophage foam cell formation and prevent vascular smooth muscle cell (VSMC) phenotype switching, which are pivotal in atheromatous plaque formation and stability. This review offers a comprehensive overview of the protective effects of IRAs in atherosclerotic disease, with a focus on their impact on atherogenesis.

Liraglutide ameliorates high glucose-induced vascular endothelial injury through TRIB3/NF-κB signaling pathway

As one of the most commonly used antidiabetic medications clinically, liraglutide is involved in the protection of vascular endothelium, and whether it can relieve high glucose-induced vascular endothelial damage was unknown. This study aims to address the response of liraglutide (LIRA) on human umbilical vein endothelial cells, as well as to elucidate its possible underlying mechanism. We established a vascular endothelial cell injury model by exposing human umbilical vein endothelial cells (HUVECs) to high glucose, and used LIRA pretreatment before HG treatment to address the endothelial protective effect of LIRA. Our results suggest that LIRA prevented HG-induced HUVEC apoptosis, oxidative stress, inflammasome activation, and pyroptosis. Furthermore, silencing of tribbles homolog 3 (TRIB3) could markedly reduce HG-induced HUVEC apoptosis, ROS level, the expressions of TXNIP, cleaved caspase3, NLRP3, and caspase1, indicating TRIB3 inhibition protected HUVECs against HG-induced vascular endothelial injury. In addition, LIRA restrained NF-κB/IκB-α signaling pathway activation in HUVECs. Thus, LIRA appears to mitigate HG-induced apoptosis, oxidative stress, inflammasome activation, and pyroptosis in HUVECs via regulating the TRIB3/NF-κB/IκB-α signaling pathway. Our study provides new insight into the mechanisms underlying the protective activity of LIRA against the vascular endothelial injury in diabetic vascular complication.

Cardiovascular Effectiveness and Safety of Antidiabetic Drugs in Patients with Type 2 Diabetes and Peripheral Artery Disease: Systematic Review

Peripheral artery disease (PAD) is an atherosclerotic condition commonly complicating type 2 diabetes (T2D), leading to poor quality of life and increased risk of major adverse lower-limb (MALE) and cardiovascular (CV) events (MACE). Therapeutic management of PAD in T2D patients is much more arduous, often due to bilateral, multi-vessel, and distal vascular involvement, in addition to increased systemic polyvascular atherosclerotic burden. On the other hand, the pathophysiological link between PAD and T2D is very complex, involving mechanisms such as endothelial dysfunction and increased subclinical inflammation in addition to chronic hyperglycemia. Therefore, the clinical approach should not ignore vascular protection with the aim of reducing limb and overall CV events besides a mere glucose-lowering effect. However, the choice of the best medications in this setting is challenging due to low-grade evidence or lacking targeted studies in PAD patients. The present review highlighted the strong relationship between T2D and PAD, focusing on the best treatment strategy to reduce CV risk and prevent PAD occurrence and worsening in patients with T2D. The Medline databases were searched for studies including T2D and PAD up to June 2024 and reporting the CV effectiveness and safety of the most used glucose-lowering agents, with no restriction on PAD definition, study design, or country. The main outcomes considered were MACE-including nonfatal acute myocardial infarction, nonfatal stroke, and CV death-and MALE-defined as lower-limb complications, amputations, or need for revascularization. To the best of our current knowledge, GLP-1 receptor agonists and SGLT2 inhibitors represent the best choice to reduce CV risk in T2D and PAD settings, but a personalized approach should be considered. GLP-1 receptor agonists should be preferred in subjects with prevalent atherosclerotic burden and a history of previous MALE, while SGLT2 inhibitors should be used in those with heart failure if overall CV benefits outweigh the risk of lower-limb complications.

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.

Citronellal improves endothelial dysfunction by affecting the stability of the GCH1 protein

Endothelial dysfunction (ED) serves as the pathological basis for various cardiovascular diseases. Guanosine triphosphate cyclopyrrolone 1 (GCH1) emerges as a pivotal protein in sustaining nitric oxide (NO) production within endothelial cells, yet it undergoes degradation under oxidative stress, contributing to endothelial cell dysfunction. Citronellal (CT), a monoterpenoid, has been shown to ameliorate endothelial dysfunction induced by in atherosclerosis rats. However, whether CT can inhibit the degradation of GCH1 protein is not clear. It has been reported that ubiquitination may play a crucial role in regulating GCH1 protein levels and activities. However, the specific E3 ligase for GCH1 and the molecular mechanism of GCH1 ubiquitination remain unclear. Using data-base exploration analysis, we find that the levels of the E3 ligase Smad-ubiquitination regulatory factor 2 (Smurf2) negatively correlate with those of GCH1 in vascular tissues and HUVECs. We observe that Smurf2 interacts with GCH1 and promotes its degradation via the proteasome pathway. Interestingly, ectopic Smurf2 expression not only decreases GCH1 levels but also reduces cell proliferation and reactive oxygen species (ROS) levels, mostly because of increased GCH1 accumulation. Furthermore, we identify BH 4/eNOS as downstream of GCH1. Taken together, our results indicate that CT can obviously improve vascular endothelial injury in Type 1 diabetes mellitus (T1DM) rats and reverse the expressions of GCH1 and Smurf2 proteins in aorta of T1DM rats. Smurf2 promotes ubiquitination and degradation of GCH1 through proteasome pathway in HUVECs. We conclude that the Smurf2-GCH1 interaction might represent a potential target for improving endothelial injury.

Liraglutide attenuates palmitate-induced apoptosis via PKA/β-catenin/Bcl-2/Bax pathway in MC3T3-E1 cells

Liraglutide (LRG), one agonist of glucagon-like peptide-1 receptor (GLP1R), has multiple lipid-lowering effects in type 2 diabetes mellitus, however, studies on the role of LRG in saturated fatty acid-induced bone loss are limited. Therefore, our aim was to investigate whether LRG reduces palmitate (PA)-induced apoptosis and whether the mechanism involves PKA/β-catenin/Bcl-2/Bax in osteoblastic MC3T3-E1 cells. MC3T3-E1 cells were treated with different concentrations of PA, LRG, or pretreated with Exendin 9-39 and H89, cell viability, intracellular reactive oxygen species (ROS), cAMP levels, apoptosis and the expression of protein kinase A (PKA) and phosphorylation of PKA (p-PKA), β-catenin and phosphorylation of β-catenin (Ser675)(p-β-catenin), GLP1R, cleaved-capase 3, Bcl2-Associated X Protein (Bax) and B-cell lymphoma-2 (Bcl-2) along with expression of Osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL) were evaluated. PA treatment inhibited cell proliferation and cAMP levels, elevated intracellular ROS levels and promoted apoptosis, increased protein expressions of RANKL, Bax and cleaved-caspase3, meanwhile decreased protein expression of OPG and Bcl-2 in a dose-dependent manner. LRG inverted PA-induced apoptosis, increased cAMP levels, promoted expression of p-PKA, p-β-catenin (Ser675) and reversed these gene expressions via increasing GLP1R expression. Pretreatment of the cells with Exendin 9-39 and H89 partially eradicated the protective effect of LRG on PA-induced apoptosis and gene expressions. Therefore, these findings indicated that LRG attenuates PA-induced apoptosis possibly by GLP1R-mediated PKA/β-catenin/Bcl-2/Bax pathway in MC3T3-E1 cells. Our results point to LRG as a new strategy to attenuate bone loss associated with high fat diet beyond its lipid-lowering actions. LRG inhibits PA-mediated apoptosis via GLP1R-mediated PKA/β-catenin/Bcl-2/ Bax pathway, while possibly enhances PA-inhibited differentiation by regulating the expression of OPG and RANKL.

Liraglutide Suppresses Myocardial Fibrosis Progression by Inhibiting the Smad Signaling Pathway

OBJECTIVE

Liraglutide is a commonly used hypoglycemic agent in clinical practice, and has been demonstrated to have protective effects against the development of cardiovascular disease. However, its potential role in myocardial fibrosis remains unexplored. The present study aims to assess the impact of liraglutide on the activation of cardiac fibroblasts.

METHODS

Primary rat adult fibroblasts were isolated, cultured, and randomly allocated into 4 groups: control group, transforming growth factor beta1 (TGFβ1) stimulation group, liraglutide group, and TGFβ1+liraglutide group. Fibroblast activation was induced by TGFβ1. Cell proliferation activity was assessed using the CKK-8 kit, and cellular activity was determined using the MTT kit. Reverse transcrition-quantitative polymerase chain reaction (RT-qPCR) was utilized to quantify the level of collagen transcription, immunofluorescence staining was performed to detect the expression level of type III collagen and α-smooth muscle protein (α-SMA), and immunoblotting was conducted to monitor alterations in signal pathways.

RESULTS

The addition of 10, 25, 50 and 100 nmol/L of liraglutide did not induce any significant impact on the viability of fibroblasts (P>0.05). The rate of cellular proliferation was significantly higher in the TGFβl stimulation group than in the control group. However, the treatment with 50 and 100 nmol/L of liraglutide resulted in the reduction of TGFβl-induced cell proliferation (P<0.05). The RT-qPCR results revealed that the transcription levels of type I collagen, type III collagen, and α-SMA were significantly upregulated in the TGFβl stimulation group, when compared to the control group (P<0.05). However, the expression levels of these aforementioned factors significantly decreased in the TGFβl+liraglutide group (P<0.05). The immunofluorescence staining results revealed a significant increase in the expression levels of type III collagen and α-SMA in the TGFβl stimulation group, when compared to the control group (P<0.05). However, these expression levels significantly decreased in the TGFβl+liraglutide group, when compared to the TGFβl stimulation group (P<0.05). The Western blotting results revealed that the expression levels of phosphorylated smad2 and smad3 significantly increased in the TGFβl stimulation group, when compared to the control group (P<0.05), while these decreased in the TGFβl+liraglutide group (P<0.05).

CONCLUSION

Liraglutide inhibits myocardial fibrosis development by suppressing the smad signaling pathway, reducing the activation and secretion of cardiac fibroblasts.

The role of oxidative stress in diabetes mellitus-induced vascular endothelial dysfunction

Diabetes mellitus is a metabolic disease characterized by long-term hyperglycaemia, which leads to microangiopathy and macroangiopathy and ultimately increases the mortality of diabetic patients. Endothelial dysfunction, which has been recognized as a key factor in the pathogenesis of diabetic microangiopathy and macroangiopathy, is characterized by a reduction in NO bioavailability. Oxidative stress, which is the main pathogenic factor in diabetes, is one of the major triggers of endothelial dysfunction through the reduction in NO. In this review, we summarize the four sources of ROS in the diabetic vasculature and the underlying molecular mechanisms by which the pathogenic factors hyperglycaemia, hyperlipidaemia, adipokines and insulin resistance induce oxidative stress in endothelial cells in the context of diabetes. In addition, we discuss oxidative stress-targeted interventions, including hypoglycaemic drugs, antioxidants and lifestyle interventions, and their effects on diabetes-induced endothelial dysfunction. In summary, our review provides comprehensive insight into the roles of oxidative stress in diabetes-induced endothelial dysfunction.

New Insights into the Use of Liraglutide-Impact on Cardiovascular Risk and Microvascular Outcomes

Despite the availability of many glucose-lowering drugs, patients with type 2 diabetes mellitus (T2DM) often do not achieve the desired effect, and cardiovascular complications remain the leading cause of death in this group of patients. Recently, more and more attention has been paid to the properties of drugs, with particular emphasis on the possibility of reducing cardiovascular risk. One of them is liraglutide, which belongs to long-acting analogs of glucagon-like peptides-1 (GLP-1); it imitates incretins and causes an increase in insulin secretion. The current study focused on analyzing the efficacy and safety of liraglutide, as well as its impact on microvascular and cardiovascular outcomes in the treatment of patients with T2DM. Hyperglycemia-induced endothelial dysfunction, which is known to play a key role in maintaining cardiovascular homeostasis, is common in diabetes. Liraglutide reduces endothelial dysfunction by reversing damage to endothelial cells. By reducing the generation of reactive oxygen species (ROS), thereby affecting Bax, Bcl-2 protein levels, and restoring signaling pathways, Liraglutide reduces oxidative stress, inflammation, and prevents endothelial cell apoptosis. Liraglutide has beneficial effects on the cardiovascular system; patients with high cardiovascular risk particularly benefit from treatment, as it reduces their major adverse cardiovascular event (MACE) rate, which takes into account cardiovascular death, stroke, and non-fatal myocardial infarction. Liraglutide reduces the occurrence and progression of nephropathy, which is one of the most common microvascular complications of diabetes.

Extracellular cyclophilins A and C induce dysfunction of pancreatic microendothelial cells

Extracellular cyclophilins (eCyps) A and B are chemotactic mediators in several illnesses in which inflammation plays an important role such as diabetes and cardiovascular diseases. Recently, eCypC has been reported as a potential biomarker for coronary artery disease but its effect in endothelium has not been determined. Moreover, there is a lack of studies with all these proteins in the same model, which makes difficult a direct comparison of their effects. In this work, MS1 pancreatic microendothelial cells were treated with eCyps A, B and C and their impact on endothelial function was analysed. eCyps A and C stimulated the release of IL-6 and MCP-1 and increased the expression of the receptor CD147, but eCypB did not affect these pro-inflammatory markers. Moreover, eCypC activated the translocation of NFkB-p65 to the nucleus. All these effects were reversed by pre-treatment with cyclosporine A. eCyps also produced endothelial dysfunction, as evidenced by the decrease in eNOS activation. Finally, the crosstalk among eCyps addition and their protein and gene expression was evaluated. eCypA generated a depletion in its protein and gene levels, whilst eCyps B and C upregulated their own protein expression. Moreover, each eCyp altered the intracellular expression of other Cyps, including cyclophilin D. This work is the first report of eCyps influence on iCyps expression, as well as the first description of eCypC as an activator of CD147 receptor and a mediator of endothelial dysfunction, which points to a potential role of this protein in vascular complications associated to diabetes.

Dapagliflozin, Liraglutide, and Their Combination Attenuate Diabetes Mellitus-Associated Hepato-Renal Injury—Insight into Oxidative Injury/Inflammation/Apoptosis Modulation

In this study, we aim to explore the beneficial therapeutic impacts of dapagliflozin (Dapa), a highly potent, reversible, and selective sodium–glucose cotransporter-2 inhibitor, and liraglutide (Lira), a glucagon-like peptide-1 (GLP-1) receptor agonist, as hypoglycaemic agents for the management of diabetes mellitus (DM), as well as their combination against DM-induced complications, including hepato-renal injury. Indeed, the progression of DM was found to be associated with significant hepatic and renal injury, as confirmed by the elevated biochemical indices of hepatic and renal functions, as well as histopathological examination. Dapa, Lira, and their combination effectively attenuated DM-induced hepatic and renal injury, as confirmed by the recovery of hepatic and renal functional biomarkers. The administration of both drugs significantly reduced the tissue contents of MDA and restored the contents of GSH and catalase activity. Moreover, NF-κB and TNF-α expression at the protein and gene levels was significantly reduced in the liver and the kidney. This was in parallel with the significant reduction in the caspase-3 content in the liver and the kidney, as well as suppressed cleaved caspase-3 expression in the hepatic and renal specimens, as confirmed by immune–histochemical analysis. Notably, the combined Dapa/Lira treatment demonstrated an additive superior hepato-renal protective impact compared with the use of either drug alone. Thus, it appears that Dapa and Lira, through the coordinated modulation of oxidative, inflammatory, and apoptotic signalling, confer a significant hepato-renal protective impact against DM-induced complications and tissue injury.

Metformin attenuates high glucose-induced injury in islet microvascular endothelial cells

As one of the most frequently prescribed antidiabetic drugs, metformin can lower glucose levels, improve insulin resistance manage body weight. However, the effect of metformin on islet microcirculation remains unclear. In the present study, to explore the effect of metformin on islet endothelial cells and investigated the underlying mechanism, we assessed the effects of metformin on islet endothelial cell survival, proliferation, oxidative stress and apoptosis. Our results suggest that metformin stimulates the proliferation of pancreatic islet endothelial cells and inhibits the apoptosis and oxidative stress caused by high glucose levels. By activating farnesoid X receptor (FXR), metformin increases the expression of vascular endothelial growth factor-A (VEGF-A) and endothelial nitric oxide synthase (eNOS), improves the production of nitric oxide (NO) and decreases the production of ROS. After the inhibition of FXR or VEGF-A, all of the effects disappeared. Thus, metformin appears to regulate islet microvascular endothelial cell (IMEC) proliferation, apoptosis and oxidative stress by activating the FXR/VEGF-A/eNOS pathway. These findings provide a new mechanism underlying the islet-protective effect of metformin.

GLP-1 RA Improves Diabetic Retinopathy by Protecting the Blood-Retinal Barrier through GLP-1R-ROCK-p-MLC Signaling Pathway

BACKGROUND

GLP-1 receptor agonists (GLP-1RA) are common clinical agents that are clinically protective against diabetic complications, such as diabetic retinopathy (DR). Previous studies have shown that the RhoA/ROCK pathway plays an important role in the development of DR. However, the specific mechanism of action between GLP-1RA and DR remains unclear. The aim of this study was thus to investigate the main mechanism involved in the protective effect of GLP-1RA on DR.

METHODS

Type 2 diabetic mice were fed a high-sugar, high-fat diet. Changes in the retinal structure were observed via HE staining and transmission electron microscopy. The expression of retinal GLP-1R, blood-retinal barrier- (BRB-) related proteins, inflammatory factors, and related pathway proteins were studied via Western blot or immunohistochemistry/immunofluorescence analysis.

RESULTS

GLP-1RA treatment reduced the blood glucose and lipid levels as well as the body weight of the diabetic mice while also improving retinal thickness, morphology, and vascular ultrastructure. Moreover, restored GLP-1R expression, increased Occludin and ZO-1 levels, and decreased albumin expression led to reduced retinal leakage and improved the BRB by inhibiting the RhoA/ROCK pathway.

CONCLUSIONS

We found that the protective effect of GLP-1RA on the retina may be realized through the GLP-1R-ROCK-p-MLC signaling pathway.

Vascular endothelial growth factor ameliorated palmitate-induced cardiomyocyte injury via JNK pathway

Enhanced apoptosis of cardiomyocytes in suffering overloaded saturated fatty acids (SFAs) can result in myocardial infarction and cardiac dysfunction. The function of vascular endothelial growth factor (VEGF) in cardiomyocyte protection was not clearly described. To investigate the preservative effects of VEGF sensitization on ceramide-mediated programmed cell death of cardiomyocytes, palmitate-induced injury in H9c2 cells was established as an in vitro model. Results revealed that 0.5 mM palmitate application effectively led to debased viability and activated apoptotic factors. A significant time-dependent relation between PAL and cardiomyocyte injury was observed. The apoptosis rate was increased greatly after 16 h of treatment with 0.5 mM PAL. In addition, cell viability was restored by VEGF overexpression during treatment with 0.5 mM PAL. Reduced apoptosis rate and expression of caspase 3, Bax, and NF-κB p65 were observed in this process, while boosted Bcl-2, p-JNK/JNK expression and activity of caspase 3 were checked. However, p-ERK/ERK levels did not exhibit a significant change. These findings indicated the protective effects of VEGF in confronting the ceramide-induced cardiomyocyte apoptosis, and would devote therapeutic targets for cardiovascular safeguard in dealing with fatty acid stress.

Identification of key genes and pathways in mild and severe nonalcoholic fatty liver disease by integrative analysis

Background

The global prevalence of nonalcoholic fatty liver disease (NAFLD) is increasing. The pathogenesis of NAFLD is multifaceted, and the underlying mechanisms are elusive. We conducted data mining analysis to gain a better insight into the disease and to identify the hub genes associated with the progression of NAFLD.

Methods

The dataset GSE49541, containing the profile of 40 samples representing mild stages of NAFLD and 32 samples representing advanced stages of NAFLD, was acquired from the Gene Expression Omnibus database. Differentially expressed genes (DEGs) were identified using the R programming language. The Database for Annotation, Visualization and Integrated Discovery (DAVID) online tool and Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) database were used to perform the enrichment analysis and construct protein–protein interaction (PPI) networks, respectively. Subsequently, transcription factor networks and key modules were identified. The hub genes were validated in a mice model of high fat diet (HFD)-induced NAFLD and in cultured HepG2 cells by real-time quantitative PCR.

Results

Based on the GSE49541 dataset, 57 DEGs were selected and enriched in chemokine activity and cellular component, including the extracellular region. Twelve transcription factors associated with DEGs were indicated from PPI analysis. Upregulated expression of five hub genes (SOX9, CCL20, CXCL1, CD24, and CHST4), which were identified from the dataset, was also observed in the livers of HFD-induced NAFLD mice and in HepG2 cells exposed to palmitic acid or advanced glycation end products.

Conclusion

The hub genes SOX9, CCL20, CXCL1, CD24, and CHST4 are involved in the aggravation of NAFLD. Our results offer new insights into the underlying mechanism of NAFLD progression.

Role of moesin in the effect of glucagon-like peptide-1 on advanced glycation end products-induced endothelial barrier dysfunction

Glucagon-like peptide-1 (GLP-1) analogues have been found to exert protective effect on endothelial barrier dysfunction in vascular diseases. Moesin phosphorylation participates in the process of advanced glycation end products (AGEs) induced disruption of endothelial barrier integrity. Whether and how GLP-1 modulating moesin phosphorylation in endothelium under diabetic condition needs further clarification. Consistent with previous studies, our data showed that hyperglycemia and AGEs promoted moesin phosphorylation in ECs in vivo and vitro experiments. With or without AGEs incubation, overexpression of moesin and activated mutant moesin T558D increased ECs permeability, whereas knockdown of moesin decreased ECs permeability. Inhibition of Rho/ROCK, p38/MAPK and PKC β signal pathways also decreased moesin phosphorylation in ECs incubated with AGEs. Importantly, GLP-1 inhibited moesin phosphorylation in AGE-induced ECs in a dose-dependent manner. Intriguingly, the effects of GLP-1 elicited on moesin phosphorylation in ECs under diabetic condition were blunted by inhibition of cAMP/PKA and stimulation of Rho/ROCK, p38 and PKC β signaling pathways. Therefore, this study verified that the stabilizing effect of GLP-1 on the moesin phosphorylation mediated endothelial barrier function is mediated by GLP-1R/cAMP/PKA activation and subsequent down-regulation of Rho/ROCK, p38 and PKC β signaling pathways.

Vitamin B12 Inhibits Streptozotocin-Induced Islet β-Cell Oxidative Stress and Apoptosis by Activating Peroxisome Proliferator-Activated Receptor-γ Signaling Pathway

The present study aimed to investigate the effects of vitamin B12 on islet β-cell (INS-1) induced by streptozotocin (STZ) and the potential mechanisms. In this study, CCK8 was used to detect cell viability and TUNEL assay was used to detect apoptosis levels of treated INS-1 cells. The expression level of oxidative stress factors was measured by ELISA. Furthermore, western blot assay was used to detect the expression of PPAR-γ and apoptotic factors in treated INS-1 cells. Vitamin B12 improves STZ-induced insulin secretion in INS-1 cells, oxidative stress injury and apoptosis. Moreover, Vitamin B12 can activate the PPAR-γ signaling pathway and inhibit STZ-induced INS-1 cell damage. Taken together, our study demonstrated that vitamin B12 inhibits streptozotocin-induced islet β-cell oxidative stress and apoptosis by activating PPAR-γ signaling pathway.

Berberine is an insulin secretagogue targeting the KCNH6 potassium channel

Coptis chinensis is an ancient Chinese herb treating diabetes in China for thousands of years. However, its underlying mechanism remains poorly understood. Here, we report the effects of its main active component, berberine (BBR), on stimulating insulin secretion. In mice with hyperglycemia induced by a high-fat diet, BBR significantly increases insulin secretion and reduced blood glucose levels. However, in mice with hyperglycemia induced by global or pancreatic islet β-cell-specific Kcnh6 knockout, BBR does not exert beneficial effects. BBR directly binds KCNH6 potassium channels, significantly accelerates channel closure, and subsequently reduces KCNH6 currents. Consequently, blocking KCNH6 currents prolongs high glucose-dependent cell membrane depolarization and increases insulin secretion. Finally, to assess the effect of BBR on insulin secretion in humans, a randomized, double-blind, placebo-controlled, two-period crossover, single-dose, phase 1 clinical trial (NCT03972215) including 15 healthy men receiving a 160-min hyperglycemic clamp experiment is performed. The pre-specified primary outcomes are assessment of the differences of serum insulin and C-peptide levels between BBR and placebo treatment groups during the hyperglycemic clamp study. BBR significantly promotes insulin secretion under hyperglycemic state comparing with placebo treatment, while does not affect basal insulin secretion in humans. All subjects tolerate BBR well, and we observe no side effects in the 14-day follow up period. In this study, we identify BBR as a glucose-dependent insulin secretagogue for treating diabetes without causing hypoglycemia that targets KCNH6 channels.

Formation of βTC3 and MIN6 Pseudoislets Changes the Expression Pattern of Gpr40, Gpr55, and Gpr119 Receptors and Improves Lysophosphatidylcholines-Potentiated Glucose-Stimulated Insulin Secretion

The impaired spatial arrangement and connections between cells creating islets of Langerhans as well as altered expression of G protein-coupled receptors (GPCRs) often lead to dysfunction of insulin-secreting pancreatic β cells and can significantly contribute to the development of diabetes. Differences in glucose-stimulated insulin secretion (GSIS) are noticeable not only in diabetic individuals but also in model pancreatic β cells, e.g., βTC3 and MIN6 β cell lines with impaired and normal insulin secretion, respectively. Now, we compare the ability of GPCR agonists (lysophosphatidylcholines bearing fatty acid chains of different lengths) to potentiate GSIS in βTC3 and MIN6 β cell models, cultured as adherent monolayers and in a form of pseudoislets (PIs) with pancreatic MS1 endothelial cells. Our aim was also to investigate differences in expression of the GPCRs responsive to LPCs in these experimental systems. Aggregation of β cells into islet-like structures greatly enhanced the expression of Gpr40, Gpr55, and Gpr119 receptors. In contrast, the co-culture of βTC3 cells with endothelial cells converted the GPCR expression pattern closer to the pattern observed in MIN6 cells. Additionally, the efficiencies of various LPC species in βTC3-MS1 PIs also shifted toward the MIN6 cell model.

Identification of New Targets and the Virtual Screening of Lignans against Alzheimer's Disease

Alzheimer's disease (AD) is characterized by the progressive disturbance in cognition and affects approximately 36 million people, worldwide. However, the drugs used to treat this disease are only moderately effective and do not alter the course of the neurodegenerative process. This is because the pathogenesis of AD is mainly associated with oxidative stress, and current drugs only target two enzymes involved in neurotransmission. Therefore, the present study sought to identify potential multitarget compounds for enzymes that are directly or indirectly involved in the oxidative pathway, with minimal side effects, for AD treatment. A set of 159 lignans were submitted to studies of QSAR and molecular docking. A combined analysis was performed, based on ligand and structure, followed by the prediction of absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties. The results showed that the combined analysis was able to select 139 potentially active and multitarget lignans targeting two or more enzymes, among them are c-Jun N-terminal kinase 3 (JNK-3), protein tyrosine phosphatase 1B (PTP1B), nicotinamide adenine dinucleotide phosphate oxidase 1 (NOX1), NADPH quinone oxidoreductase 1 (NQO1), phosphodiesterase 5 (PDE5), nuclear factor erythroid 2-related factor 2 (Nrf2), cycloxygenase 2 (COX-2), and inducible nitric oxide synthase (iNOS). The authors conclude that compounds (06) austrobailignan 6, (11) anolignan c, (19) 7-epi-virolin, (64) 6-[(2R,3R,4R,5R)-3,4-dimethyl-5-(3,4,5-trimethoxyphenyl)oxolan-2-yl]-4-methoxy-1,3-benzodioxole, (116) ococymosin, and (135) mappiodoinin b have probabilities that confer neuroprotection and antioxidant activity and represent potential alternative AD treatment drugs or prototypes for the development of new drugs with anti-AD properties.