Metformin improves endothelial function in aortic tissue and microvascular endothelial cells subjected to diabetic hyperglycaemic conditions

Metformin ameliorates valve interstitial cell calcification by promoting autophagic flux

Calcific aortic valve disease (CAVD) is the most common heart disease of the developed world. It has previously been established that metformin administration reduces arterial calcification via autophagy; however, whether metformin directly regulates CAVD has yet to be elucidated. In the present study we investigated whether metformin alleviates valvular calcification through the autophagy-mediated recycling of Runx2. Calcification was reduced in rat valve interstitial cells (RVICs) by metformin treatment (0.5-1.5 mM) (P < 0.01), with a marked decrease in Runx2 protein expression compared to control cells (P < 0.05). Additionally, upregulated expression of Atg3 and Atg7 (key proteins required for autophagosome formation), was observed following metformin treatment (1 mM). Blocking autophagic flux using Bafilomycin-A1 revealed colocalisation of Runx2 with LC3 puncta in metformin treated RVICs (P < 0.001). Comparable Runx2 accumulation was seen in LC3 positive autolysosomes present within cells that had been treated with both metformin and hydroxychloroquine in combination (P < 0.001). Mechanistic studies employing three-way co-immunoprecipitation with Runx2, p62 and LC3 suggested that Runx2 binds to LC3-II upon metformin treatment in VICs. Together these studies suggest that the utilisation of metformin may represent a novel strategy for the treatment of CAVD.

Pharmacological effects of statins in adult patients with type 2 diabetes mellitus: A protocol for systematic review and meta-analysis

BACKGROUND

Due to contradicting findings on impact of statins on endothelial function in type 2 diabetes mellitus especially across the randomized controlled trials (RCTs). With this systematic review, we aim to evaluate whether the use of statins improves endothelial function in adults with type 2 diabetes. We will further highlight if these biomarkers are ideal therapeutic targets for risk for atherosclerosis and cardiovascular disease.

METHODS

This protocol was carried out according to the preferred reporting items for systematic review and meta-analysis protocols-2015 guideline. The online databases, such as MEDLINE, Scopus, and Web of Sciences, will be targeted using the medical subject heading terms (MeSH) and text words. The review will include clinical studies on the effect of statins on markers of endothelial function in type 2 diabetes. The Cochrane risk of bias guideline will be used to assess the quality and risk of bias. We are planning to use the grading of recommendation assessment, development, and evaluation approach to evaluate the strength and quality of evidence.

RESULTS

This study will not involve human samples and patient data; hence ethics approval will not be required. The findings will be presented in journal clubs and conferences and published in peer-reviewed journals.

Metformin protects against vascular calcification through the selective degradation of Runx2 by the p62 autophagy receptor

Vascular calcification is associated with aging, type 2 diabetes, and atherosclerosis, and increases the risk of cardiovascular morbidity and mortality. It is an active, highly regulated process that resembles physiological bone formation. It has previously been established that pharmacological doses of metformin alleviate arterial calcification through adenosine monophosphate-activated protein kinase (AMPK)-activated autophagy, however the specific pathway remains elusive. In the present study we hypothesized that metformin protects against arterial calcification through the direct autophagic degradation of runt-related transcription factor 2 (Runx2). Calcification was blunted in vascular smooth muscle cells (VSMCs) by metformin in a dose-dependent manner (0.5-1.5 mM) compared to control cells (p < 0.01). VSMCs cultured under high-phosphate (Pi) conditions in the presence of metformin (1 mM) showed a significant increase in LC3 puncta following bafilomycin-A1 (Baf-A; 5 nM) treatment compared to control cells (p < 0.001). Furthermore, reduced expression of Runx2 was observed in the nuclei of metformin-treated calcifying VSMCs (p < 0.0001). Evaluation of the functional role of autophagy through Atg3 knockdown in VSMCs showed aggravated Pi-induced calcification (p < 0.0001), failure to induce autophagy (punctate LC3) (p < 0.001) and increased nuclear Runx2 expression (p < 0.0001) in VSMCs cultured under high Pi conditions in the presence of metformin (1 mM). Mechanistic studies employing three-way coimmunoprecipitation with Runx2, p62, and LC3 revealed that p62 binds to both LC3 and Runx2 upon metformin treatment in VSMCs. Furthermore, immunoblotting with LC3 revealed that Runx2 specifically binds with p62 and LC3-II in metformin-treated calcified VSMCs. Lastly, we investigated the importance of the autophagy pathway in vascular calcification in a clinical setting. Ex vivo clinical analyses of calcified diabetic lower limb artery tissues highlighted a negative association between Runx2 and LC3 in the vascular calcification process. These studies suggest that exploitation of metformin and its analogues may represent a novel therapeutic strategy for clinical intervention through the induction of AMPK/Autophagy Related 3 (Atg3)-dependent autophagy and the subsequent p62-mediated autophagic degradation of Runx2.

Protective effects of metformin in various cardiovascular diseases: Clinical evidence and AMPK-dependent mechanisms

Metformin, a well-known AMPK agonist, has been widely used as the first-line drug for treating type 2 diabetes. There had been a significant concern regarding the use of metformin in people with cardiovascular diseases (CVDs) due to its potential lactic acidosis side effect. Currently growing clinical and preclinical evidence indicates that metformin can lower the incidence of cardiovascular events in diabetic patients or even non-diabetic patients beyond its hypoglycaemic effects. The underlying mechanisms of cardiovascular benefits of metformin largely involve the cellular energy sensor, AMPK, of which activation corrects endothelial dysfunction, reduces oxidative stress and improves inflammatory response. In this minireview, we summarized the clinical evidence of metformin benefits in several widely studied cardiovascular diseases, such as atherosclerosis, ischaemic/reperfusion injury and arrhythmia, both in patients with or without diabetes. Meanwhile, we highlighted the potential AMPK-dependent mechanisms in in vitro and/or in vivo models.

Relationship between hemoglobin A1c level and flow-mediated vasodilation in patients with type 2 diabetes mellitus receiving antidiabetic drugs

Aims/Introduction

Diabetes mellitus is associated with endothelial dysfunction. However, it is still controversial as to whether antidiabetic drug treatment affects endothelial function. The purpose of this study was to evaluate the relationships of the hemoglobin A1c (HbA1c) level with flow‐mediated vasodilation (FMD) and nitroglycerine‐induced vasodilation (NID) in patients with type 2 diabetes mellitus who are receiving antidiabetic drugs.

Materials and Methods

The FMD was measured in 866 patients with type 2 diabetes mellitus who were receiving antidiabetic drugs (625 men and 241 women; mean age: 62 ± 10 years). The patients were divided into four groups according to HbA1c levels: <6.5, 6.5–6.9, 7.0–7.9, and ≥8.0%.

Results

There was an inverted U‐shaped pattern of association of the HbA1c level with the FMD at an HbA1c level of about 7% of the peak of FMD in patients with type 2 diabetes mellitus who were receiving antidiabetic drugs. The FMD was significantly smaller in the HbA1c <6.5% group than in the HbA1c 6.5–6.9% group and the HbA1c 7.0–7.9% group (P < 0.001 and P < 0.001, respectively). The FMD values were similar in the HbA1c <6.5% group and HbA1c ≥8.0% group (P = 0.10). There were no significant differences in NID among the four groups (P = 0.98).

Conclusions

These findings suggest that a low HbA1c <6.5% as well as a high HbA1c ≥8.0% is associated with endothelial dysfunction in patients with type 2 diabetes mellitus who are receiving antidiabetic drugs and that vascular smooth muscle function is similar in such patients regardless of the HbA1c level.

The Protective Effect of Tetrahydroxystilbene Glucoside on High Glucose-Induced Injury in Human Umbilical Vein Endothelial Cells through the PI3K/Akt/eNOS Pathway and Regulation of Bcl-2/Bax

Endothelial dysfunction plays a central role in the patho-genesis of diabetic vascular complications. 2,3,5,4'-tetra-hydroxystilbene-2-O-β-D-glucoside (TSG), an active component extracted from the roots of Polygonum multiflorum Thunb, has been shown to have strong antioxidant and antiapoptotic activities. In the present study, we investigated the protective effect of TSG on apoptosis induced by high glucose in human umbilical vein endothelial cells (HUVECs) and the possible mechanisms. Our data demonstrated that TSG significantly reversed the high glucose-induced decrease in cell viability, suppressed high glucose-induced generation of intracellular reactive oxygen species (ROS), the activity of caspase-3, and decreased the percentage of apoptotic cells in a dose-dependent manner. In addition, we found that TSG not only increased the expression of Bcl-2, while decreasing Bax expression, but also activated phosphorylation of Akt and endothelial nitric oxide synthase (eNOS) with subsequent nitric oxide production and ultimately reduced high glucose-induced apoptosis. However, the antiapoptotic effects of TSG were abrogated by pretreatment of the cells with PI3K inhibitor (LY294002) or eNOS inhibitor NG-L-nitro-arginine methyl ester, respectively. These results suggest that TSG inhibits high glucose-induced apoptosis in HUVECs through inhibition of ROS production, activation of the PI3K/Akt/eNOS pathway, and upregulation of the Bcl-2/Bax ratio, and thus may demonstrate significant potential for preventing diabetic cardiovascular complications.

Metformin Protects against Radiation-Induced Acute Effects by Limiting Senescence of Bronchial-Epithelial Cells

Radiation-induced damage to normal lung parenchyma remains a dose-limiting factor in thorax-associated radiotherapy (RT). Severe early and late complications with lungs can increase the risk of morbidity in cancer patients after RT. Herein, senescence of lung epithelial cells following RT-induced cellular stress, or more precisely the respective altered secretory profile, the senescence-associated secretory phenotype (SASP), was suggested as a central process for the initiation and progression of pneumonitis and pulmonary fibrosis. We previously reported that abrogation of certain aspects of the secretome of senescent lung cells, in particular, signaling inhibition of the SASP-factor Ccl2/Mcp1 mediated radioprotection especially by limiting endothelial dysfunction. Here, we investigated the therapeutic potential of a combined metformin treatment to protect normal lung tissue from RT-induced senescence and associated lung injury using a preclinical mouse model of radiation-induced pneumopathy. Metformin treatment efficiently limited RT-induced senescence and SASP expression levels, thereby limiting vascular dysfunctions, namely increased vascular permeability associated with increased extravasation of circulating immune and tumor cells early after irradiation (acute effects). Complementary in vitro studies using normal lung epithelial cell lines confirmed the senescence-limiting effect of metformin following RT finally resulting in radioprotection, while fostering RT-induced cellular stress of cultured malignant epithelial cells accounting for radiosensitization. The radioprotective action of metformin for normal lung tissue without simultaneous protection or preferable radiosensitization of tumor tissue might increase tumor control probabilities and survival because higher radiation doses could be used.

Cellular and Functional Effects of Insulin Based Therapies and Exercise on Endothelium

Endothelial dysfunction is a hallmark of type 2 diabetes that can have severe consequences on vascular function, including hypertension and changes in blood flow, as well as exercise performance. Because endothelium is also the barrier for insulin movement into tissues, it acts as a gatekeeper for transport and glucose uptake. For this reason, endothelial dysfunction is a tempting area for pharmacological and/or exercise intervention with insulin-based therapies. In this review, we describe the current state of drugs that can be used to treat endothelial dysfunction in type 2 diabetes and diabetes-related diseases (e.g., obesity) at the molecular levels, and also discuss their role in exercise.

A Critical Review of the Evidence That Metformin Is a Putative Anti-Aging Drug That Enhances Healthspan and Extends Lifespan

The numerous beneficial health outcomes associated with the use of metformin to treat patients with type 2 diabetes (T2DM), together with data from pre-clinical studies in animals including the nematode, C. elegans, and mice have prompted investigations into whether metformin has therapeutic utility as an anti-aging drug that may also extend lifespan. Indeed, clinical trials, including the MILES (Metformin In Longevity Study) and TAME (Targeting Aging with Metformin), have been designed to assess the potential benefits of metformin as an anti-aging drug. Preliminary analysis of results from MILES indicate that metformin may induce anti-aging transcriptional changes; however it remains controversial as to whether metformin is protective in those subjects free of disease. Furthermore, despite clinical use for over 60 years as an anti-diabetic drug, the cellular mechanisms by which metformin exerts either its actions remain unclear. In this review, we have critically evaluated the literature that has investigated the effects of metformin on aging, healthspan and lifespan in humans as well as other species. In preparing this review, particular attention has been placed on the strength and reproducibility of data and quality of the study protocols with respect to the pharmacokinetic and pharmacodynamic properties of metformin. We conclude that despite data in support of anti-aging benefits, the evidence that metformin increases lifespan remains controversial. However, via its ability to reduce early mortality associated with various diseases, including diabetes, cardiovascular disease, cognitive decline and cancer, metformin can improve healthspan thereby extending the period of life spent in good health. Based on the available evidence we conclude that the beneficial effects of metformin on aging and healthspan are primarily indirect via its effects on cellular metabolism and result from its anti-hyperglycemic action, enhancing insulin sensitivity, reduction of oxidative stress and protective effects on the endothelium and vascular function.

Can Metformin Exert as an Active Drug on Endothelial Dysfunction in Diabetic Subjects?

Cardiovascular mortality is a major cause of death among in type 2 diabetes (T2DM). Endothelial dysfunction (ED) is a well-known important risk factor for the development of diabetes cardiovascular complications. Therefore, the prevention of diabetic macroangiopathies by preserving endothelial function represents a major therapeutic concern for all National Health Systems. Several complex mechanisms support ED in diabetic patients, frequently cross-talking each other: uncoupling of eNOS with impaired endothelium-dependent vascular response, increased ROS production, mitochondrial dysfunction, activation of polyol pathway, generation of advanced glycation end-products (AGEs), activation of protein kinase C (PKC), endothelial inflammation, endothelial apoptosis and senescence, and dysregulation of microRNAs (miRNAs). Metformin is a milestone in T2DM treatment. To date, according to most recent EASD/ADA guidelines, it still represents the first-choice drug in these patients. Intriguingly, several extraglycemic effects of metformin have been recently observed, among which large preclinical and clinical evidence support metformin’s efficacy against ED in T2DM. Metformin seems effective thanks to its favorable action on all the aforementioned pathophysiological ED mechanisms. AMPK pharmacological activation plays a key role, with metformin inhibiting inflammation and improving ED. Therefore, aim of this review is to assess metformin’s beneficial effects on endothelial dysfunction in T2DM, which could preempt development of atherosclerosis.

Mechanisms of action of metformin in type 2 diabetes: Effects on mitochondria and leukocyte-endothelium interactions

Type 2 diabetes (T2D) is a very prevalent, multisystemic, chronic metabolic disorder closely related to atherosclerosis and cardiovascular diseases. It is characterised by mitochondrial dysfunction and the presence of oxidative stress. Metformin is one of the safest and most effective anti-hyperglycaemic agents currently employed as first-line oral therapy for T2D. It has demonstrated additional beneficial effects, unrelated to its hypoglycaemic action, on weight loss and several diseases, such as cancer, cardiovascular disorders and metabolic diseases, including thyroid diseases. Despite the vast clinical experience gained over several decades of use, the mechanism of action of metformin is still not fully understood. This review provides an overview of the existing literature concerning the beneficial mitochondrial and vascular effects of metformin, which it exerts by diminishing oxidative stress and reducing leukocyte-endothelium interactions. Specifically, we describe the molecular mechanisms involved in metformin's effect on gluconeogenesis, its capacity to interfere with major metabolic pathways (AMPK and mTORC1), its action on mitochondria and its antioxidant effects. We also discuss potential targets for therapeutic intervention based on these molecular actions.

Why the endothelium? The endothelium as a target to reduce diabetes-associated vascular disease

Over the past 66 years, our knowledge of the role of the endothelium in the regulation of cardiovascular function and dysfunction has advanced from the assumption that it is a single layer of cells that serves as a barrier between the blood stream and vascular smooth muscle to an understanding of its role as an essential endocrine-like organ. In terms of historical contributions, we pay particular credit to (1) the Canadian scientist Dr. Rudolf Altschul who, based on pathological changes in the appearance of the endothelium, advanced the argument in 1954 that "one is only as old as one's endothelium" and (2) the American scientist Dr. Robert Furchgott, a 1998 Nobel Prize winner in Physiology or Medicine, who identified the importance of the endothelium in the regulation of blood flow. This review provides a brief history of how our knowledge of endothelial function has advanced and now recognize that the endothelium produces a plethora of signaling molecules possessing paracrine, autocrine, and, arguably, systemic hormone functions. In addition, the endothelium is a therapeutic target for the anti-diabetic drugs metformin, glucagon-like peptide I (GLP-1) receptor agonists, and inhibitors of the sodium-glucose cotransporter 2 (SGLT2) that offset the vascular disease associated with diabetes.

The Vascular Consequences of Metabolic Syndrome: Rodent Models, Endothelial Dysfunction, and Current Therapies

Metabolic syndrome is characterized by visceral obesity, dyslipidemia, hyperglycemia and hypertension, and affects over one billion people. Independently, the components of metabolic syndrome each have the potential to affect the endothelium to cause vascular dysfunction and disrupt vascular homeostasis. Rodent models of metabolic syndrome have significantly advanced our understanding of this multifactorial condition. In this mini-review we compare the currently available rodent models of metabolic syndrome and consider their limitations. We also discuss the numerous mechanisms by which metabolic abnormalities cause endothelial dysfunction and highlight some common pathophysiologies including reduced nitric oxide production, increased reactive oxygen species and increased production of vasoconstrictors. Additionally, we explore some of the current therapeutics for the comorbidities of metabolic syndrome and consider how these benefit the vasculature.

Treatment with a Combination of Metformin and 2-Deoxyglucose Upregulates Thrombospondin-1 in Microvascular Endothelial Cells: Implications in Anti-Angiogenic Cancer Therapy

Metformin, the most widely used anti-diabetic drug, also exhibits anti-cancer properties; however, the true potential of metformin as an anticancer drug remains largely unknown. In this study using mouse microvascular endothelial cells (MMECs), we investigated the effects of metformin alone or in combination with the glycolytic inhibitor, 2-deoxyglucose (2DG), on angiogenesis-a process known to be an integral part of tumor growth, cancer cell survival and metastasis. MMECs were exposed to 2DG (1–10 mM) for 48 h in the absence or presence of metformin (2 mM). The status of angiogenic and anti-angiogenic marker proteins, proteins of the mTOR pathway and cell-cycle-related proteins were quantified by Western blot analysis. Assays for cell proliferation, migration and tubulogenesis were also performed. We observed robust up-regulation of anti-angiogenic thrombospondin-1 (TSP1) and increased TSP1-CD36 co-localization with a marked decrease in the levels of phosphorylated vascular endothelial growth factor receptor-2 (pVEGFR2; Y1175) in 2DG (5 mM) exposed cells treated with metformin (2 mM). Additionally, treatment with metformin and 2DG (5 mM) inhibited the Akt/mTOR pathway and down-regulated the cell-cycle-related proteins such as p-cyclin B1 (S147) and cyclins D1 and D2 when compared to cells that were treated with either 2DG or metformin alone. Treatment with a combination of 2DG (5 mM) and metformin (2 mM) also significantly decreased cell proliferation, migration and tubulogenic capacity when compared to cells that were treated with either 2DG or metformin alone. The up-regulation of TSP1, inhibition of cell proliferation, migration and tubulogenesis provides support to the argument that the combination of metformin and 2DG may prove to be an appropriate anti-proliferative and anti-angiogenic therapeutic strategy for the treatment of some cancers.

Metformin alleviates hyperglycemia-induced endothelial impairment by downregulating autophagy via the Hedgehog pathway

Studies regarding macroautophagic/autophagic regulation in endothelial cells (ECs) under diabetic conditions are very limited. Clinical evidence establishes an endothelial protective effect of metformin, but the underlying mechanisms remain unclear. We aimed to investigate whether metformin exerts its protective role against hyperglycemia-induced endothelial impairment through the autophagy machinery. db/db mice were treated with intravitreal metformin injections. Human umbilical vein endothelial cells (HUVECs) were cultured either in normal glucose (NG, 5.5 mM) or high glucose (HG, 33 mM) medium in the presence or absence of metformin for 72 h. We observed an obvious inhibition of hyperglycemia-triggered autophagosome synthesis in both the diabetic retinal vasculature and cultured HUVECs by metformin, along with restoration of hyperglycemia-impaired Hedgehog (Hh) pathway activity. Specifically, deletion of ATG7 in retinal vascular ECs of db/db mice and cultured HUVECs indicated a detrimental role of autophagy in hyperglycemia-induced endothelial dysfunction. Pretreatment with GANT61, a Hh pathway inhibitor, abolished the metformin-mediated downregulation of autophagy and endothelial protective action. Furthermore, GLI-family (transcription factors of the Hh pathway) knockdown in HUVECs and retinal vasculature revealed that downregulation of hyperglycemia-activated autophagy by the metformin-mediated Hh pathway activation was GLI1 dependent. Mechanistically, GLI1 knockdown-triggered autophagy was related to upregulation of BNIP3, which subsequently disrupted the association of BECN1/Beclin 1 and BCL2. The role of BNIP3 in BECN1 dissociation from BCL2 was further confirmed by BNIP3 overexpression or BNIP3 RNAi. Taken together, the endothelial protective effect of metformin under hyperglycemia conditions could be partly attributed to its role in downregulating autophagy via Hh pathway activation. Abbreviations: 3-MA = 3-methyladenine; 8×GLI BS-FL = 8×GLI-binding site firefly luciferase; AAV = adeno-associated virus; AAV-Cdh5-sh-Atg7 = AAV vectors carrying shRNA against murine Atg7 under control of murine Cdh5 promoter; AAV-Cdh5-sh-Gli1 = AAV vectors carrying shRNA against murine Gli1 under control of murine Cdh5 promoter; AAV-Cdh5-Gli1 = AAV vectors carrying murine Gli1 cDNA under the control of murine Cdh5 core promoter; ACAC = acetyl-CoA carboxylase; Ad-BNIP3 = adenoviruses harboring human BNIP3`; Ad-GLI1 = adenoviruses harboring human GLI1; Ad-sh-ATG7 = adenoviruses harboring shRNA against human ATG7; Ad-sh-BNIP3 = adenoviruses harboring shRNA against human BNIP3; Ad-sh-GLI = adenoviruses harboring shRNA against human GLI; AGEs = advanced glycation end products; ATG = autophagy-related; atg7^flox/flox mice = mice bearing an Atg7^flox allele, in which exon 14 of the Atg7 gene is flanked by 2 loxP sites; BafA1 = bafilomycin A₁; BECN1 = beclin 1; CDH5/VE-cadherin = cadherin 5; CASP3 = caspase 3; CASP8 = caspase 8; CASP9 = caspase 9; ECs = endothelial cells; GAPDH = glyceraldehyde-3-phosphate dehydrogenase; GCL = ganglion cell layer; GFP-LC3B = green fluorescent protein labelled LC3B; HG = high glucose; Hh = Hedgehog; HHIP = hedgehog interacting protein; HUVECs = human umbilical vein endothelial cells; IB4 = isolectin B4; INL = inner nuclear layer; i.p. = intraperitoneal; MAP1LC3/LC3 = microtubule-associated protein 1 light chain 3; MAN = mannitol; MET = metformin; NG = normal glucose; ONL = outer nuclear layer; p-ACAC = phosphorylated acetyl-CoA carboxylase; PECAM1/CD31= platelet/endothelial cell adhesion molecule 1; PRKAA1/2 = protein kinase AMP-activated catalytic subunits alpha 1/2; p-PRKAA1/2 = phosphorylated PRKAA1/2; PTCH1 = patched 1; RAPA = rapamycin; RL = Renilla luciferase; SHH = sonic hedgehog; shRNA = short hairpin RNA; sh-PRKAA1/2 = short hairpin RNA against human PRKAA1/2; scrambled shRNA = the scrambled short hairpin RNA serves as a negative control for the target-specific short hairpin RNA, which has the same nucleotide composition as the input sequence and has no match with any mRNA of the selected organism database; SMO = smoothened, frizzled class receptor; sqRT-PCR = semi-quantitative RT-PCR; TEK/Tie2 = TEK receptor tyrosine kinase; Tek-Cre (+) mice = a mouse strain expressing Cre recombinase under the control of the promoter/enhancer of Tek, in a pan-endothelial fashion; TUNEL = terminal deoxynucleotidyl transferase dUTP-mediated nick-end labeling.

Impact of currently used anti-diabetic drugs on myoendothelial communication

Diabetes is associated with a high risk of cardiovascular complications and ideally anti-diabetic drugs should not only reduce metabolic abnormalities but also reduce the negative impact of diabetes on vascular function; however, lowering blood glucose levels does not necessarily reduce cardiovascular events. Endothelial dysfunction, defined as a reduction in endothelium-dependent vasodilation, is the earliest indicator of vascular disease and this raises the question: Do the currently used anti-diabetic drugs protect endothelial function? Metformin, in use for 60 years, is the first choice drug for type 2 diabetes and based on pre-clinical and clinical data metformin has proven cardiovascular protective actions; in contrast SGLT2 inhibitors were only introduced in 2013 but show great promise. This review compares metformin with SGLT2 inhibitors and the data supporting their protective effects on the endothelium.

Vildagliptin improves high glucose-induced endothelial mitochondrial dysfunction via inhibiting mitochondrial fission

The dipeptidyl peptidase 4 inhibitor vildagliptin (VLD), a widely used anti-diabetic drug, exerts favourable effects on vascular endothelium in diabetes. We determined for the first time the improving effects of VLD on mitochondrial dysfunction in diabetic mice and human umbilical vein endothelial cells (HUVECs) cultured under hyperglycaemic conditions, and further explored the mechanism behind the anti-diabetic activity. Mitochondrial ROS (mtROS) production was detected by fluorescent microscope and flow cytometry. Mitochondrial DNA damage and ATP synthesis were analysed by real time PCR and ATPlite assay, respectively. Mitochondrial network stained with MitoTracker Red to identify mitochondrial fragmentation was visualized under confocal microscopy. The expression levels of dynamin-related proteins (Drp1 and Fis1) were determined by immunoblotting. We found that VLD significantly reduced mtROS production and mitochondrial DNA damage, but enhanced ATP synthesis in endothelium under diabetic conditions. Moreover, VLD reduced the expression of Drp1 and Fis1, blocked Drp1 translocation into mitochondria, and blunted mitochondrial fragmentation induced by hyperglycaemia. As a result, mitochondrial dysfunction was alleviated and mitochondrial morphology was restored by VLD. Additionally, VLD promoted the phosphorylation of AMPK and its target acetyl-CoA carboxylase in the setting of high glucose, and AMPK activation led to a decreased expression and activation of Drp1. In conclusion, VLD improves endothelial mitochondrial dysfunction in diabetes, possibly through inhibiting Drp1-mediated mitochondrial fission in an AMPK-dependent manner.

Forskolin attenuates doxorubicin-induced accumulation of asymmetric dimethylarginine and s-adenosylhomocysteine via methyltransferase activity in leukemic monocytes

Doxorubicin (DOX) is an antitumor drug, associated with cardiomyopathy. Strategies to address DOX-cardiomyopathy are scarce. Here, we identify the effect of forskolin (FSK) on DOX-induced-asymmetric-dimethylarginine (ADMA) accumulation in monocytoid cells. DOX-challenge led to i) augmented cytotoxicity, reactive-oxygen-species (ROS) production and methyltransferase-enzyme-activity identified as ADMA and s-adenosylhomocysteine (SAH) accumulation (SAH-A). However, except cytotoxicity, other DOX effects were decreased by metformin and FSK. FSK, did not alter the DOX-induced cytotoxic effect, but, decreased SAH-A by >50% and a combination of three drugs restored physiological methyltransferase-enzyme-activity. Together, protective effect of FSK against DOX-induced SAH-A is associated with mitigated methyltransferase-activity, a one-of-a-kind report.

The Effects of Exenatide and Metformin on Endothelial Function in Newly Diagnosed Type 2 Diabetes Mellitus Patients: A Case-Control Study

INTRODUCTION

Exenatide is a new antidiabetic glucagon-like peptide-1 receptor agonist. In addition to its hypoglycemic effect, exenatide may have a potential protective benefit on vascular endothelial function. This study attempted to compare the effects of exenatide and traditional antidiabetic drug metformin treatment on endothelial function in overweight patients with type 2 diabetes.

METHODS

Ninety overweight patients with newly diagnosed type 2 diabetes were recruited; 45 patients received exenatide (Exe) treatment and 45 patients received metformin (Met) treatment for 12 weeks. The control groups included 37 overweight and 24 non-overweight individuals. The parameters of glucose and lipid metabolism and endothelial function were measured before and after treatment. Vascular endothelial dysfunction was measured by reactive hyperemia index.

RESULTS

Newly diagnosed patients with type 2 diabetes had more serious vascular endothelial dysfunction than both overweight and normal-weight control groups. The levels of body mass index, glucose, HbA1c, homeostasis model assessment insulin resistance, and homeostasis model assessment β-cell function were improved significantly by both exenatide and metformin treatment. Both exenatide and metformin treatment can improve vascular endothelial function (Exe group: 1.67 ± 0.52 vs 1.98 ± 0.67, P < 0.05; Met group: 1.68 ± 0.29 vs 1.82 ± 0.24, P < 0.05). Exenatide treatment was no less effective than metformin in improving endothelial function (0.31 ± 0.70 vs 0.13 ± 0.24, P > 0.05).

CONCLUSIONS

Newly diagnosed patients with type 2 diabetes may have vascular endothelial dysfunction. Both exenatide and metformin treatment can improve vascular endothelial dysfunction, and exenatide was no less effective than metformin treatment.

Hyperglycaemia disrupts conducted vasodilation in the resistance vasculature of db/db mice

Vascular dysfunction in small resistance arteries is observed during chronic elevations in blood glucose. Hyperglycaemia-associated effects on endothelium-dependent vasodilation have been well characterized, but effects on conducted vasodilation in the resistance vasculature are not known. Small mesenteric arteries were isolated from healthy and diabetic db/db mice, which were used as a model of chronic hyperglycaemia. Endothelium-dependent vasodilation via the G_q/11-coupled proteinase activated receptor 2 (PAR2) was stimulated with the selective agonist SLIGRL. The Ca²⁺-sensitive fluorescent indicator fluo-8 reported changes in endothelial cell (EC) [Ca²⁺]_i, and triple cannulated bifurcating mesenteric arteries were used to study conducted vasodilation. Chronic hyperglycaemia did not affect either EC Ca²⁺ or local vasodilation to SLIGRL. However, both acute and chronic exposure to high glucose or the mannitol osmotic control attenuated conducted vasodilation to 10μM SLIGRL. This investigation demonstrates for the first time that a hypertonic solution containing glucose or mannitol can interfere with the spread of a hyperpolarizing current along the endothelium in a physiological setting. Our findings reiterate the importance of studying the effects of hyperglycaemia in the vasculature, and provide the basis for further studies regarding the modulation of junctional proteins involved in cell to cell communication by diseases such as diabetes.

Downregulation of circulating MOTS-c levels in patients with coronary endothelial dysfunction

BACKGROUND

MOTS-c is one of the newly identified mitochondrial-derived peptides which play a role in regulating metabolic homeostasis. The current study aimed to investigate whether circulating MOTS-c levels are also associated with endothelial dysfunction(ED) in patients without significant structural coronary lesions.

METHODS

Forty patients undergoing coronary angiography and endothelial function testing for clinical indications of recurrent angina with no structural coronary lesions were included in the study. They were divided into two groups based on coronary blood flow response to intracoronary acetylcholine (ACh) as normal endothelial function (≥ 50% increase from baseline) or ED, (n=20 each). Aortic plasma samples were collected at the time of catheterization for analysis of circulating MOTS-c levels by ELISA. The effect of MOTS-c on vascular reactivity was assessed in organ chambers using aortic rings collected from rats and renal artery stenosis (RAS) mice.

RESULTS

Baseline characteristics were similar between the two groups. MOTS-c plasma levels were lower in patients with ED compared with patients with normal endothelial function (p=0.007). Furthermore, plasma MOTS-c levels were positively correlated with microvascular (p=0.01) and epicardial (p=0.02) coronary endothelial function. Although MOTS-c did not have direct vasoactive effects, pretreating aortic rings from rats or RAS mice with MOTS-c (2μg/ml) improved vessel responsiveness to ACh compared with vessels without MOTS-c treatment.

CONCLUSION

Lower circulating endogenous MOTS-c levels in human subjects are associated with impaired coronary endothelial function. In rodents, MOTS-c improves endothelial function in vitro. Thus, MOTS-c represents a novel potential therapeutic target in patients with ED.

Metformin regulates oxLDL-facilitated endothelial dysfunction by modulation of SIRT1 through repressing LOX-1-modulated oxidative signaling

It is suggested that oxLDL is decisive in the initiation and development of atherosclerotic injuries. The up-regulation of oxidative stress and the generation of ROS act as key modulators in developing pro-atherosclerotic and anti-atherosclerotic processes in the human endothelial wall. In this present study, we confirmed that metformin enhanced SIRT1 and AMPK expression in human umbilical vein endothelial cells (HUVECs). Metformin also inhibited oxLDL-increased LOX-1 expression and oxLDL-collapsed AKT/eNOS levels. However, silencing SIRT1 and AMPK diminished the protective function of metformin against oxidative injuries. These results provide a new insight regarding the possible molecular mechanisms of metformin.

Metformin accelerates wound healing in type 2 diabetic db/db mice

Wound healing impairment is increasingly recognized to be a consequence of hyperglycemia-induced dysfunction of endothelial precursor cells (EPCs) in type 2 diabetes mellitus (T2DM). Metformin exhibits potential for the improvement of endothelial function and the wound healing process. However, the underlying mechanisms for the observed beneficial effects of metformin application remain to be completely understood. The present study assessed whether metformin, a widely used therapeutic drug for T2DM, may accelerate wound closure in T2DM db/db mice. Genetically hyperglycemic db/db mice were used as the T2DM model. Metformin (250 mg/kg/day; intragastric) was administered for two weeks prior to EPC collection and wound model creation in db/db mice. Wound healing was evaluated by alterations in the wound area and the number of platelet endothelial cell adhesion molecule-positive cells. The function of the isolated bone marrow-derived EPCs (BM-EPCs) was assessed by a tube formation assay. The number of circulating EPCs, and the levels of intracellular nitric oxide (NO) and superoxide (O₂⁻) were detected by flow cytometry. Thrombospondin-1 (TSP-1) expression was determined by western blot analysis. It was observed that treatment with metformin accelerated wound healing, improved angiogenesis and increased the circulating EPC number in db/db mice. In vitro, treatment with metformin reversed the impaired BM-EPC function reflected by tube formation, and significantly increased NO production while decreasing O₂⁻ levels in BM-EPCs from db/db mice. In addition, TSP-1 expression was markedly attenuated by treatment with metformin in cultured BM-EPCs. Metformin contributed to wound healing and improved angiogenesis in T2DM mice, which was, in part, associated with stimulation of NO, and inhibition of O₂⁻ and TSP-1 in EPCs from db/db mice.

Novel rhynchophylline analogues as microvascular relaxation agents for the treatment of microvascular dysfunction caused by diabetes

Dysfunction in vascular reactivity in the micro- and macrocirculation is well established in cardiovascular disease. However, little is known about methods that may improve vascular reactivity in patients likely to develop microvascular dysfunction. One of the racemic analogues of rhynchophylline (G2) and its stereoisomers (G2-a and G2-b) were synthesized to address this knowledge gap. The preliminary pharmaceutical studies on the relaxation of the rat thoracic aorta showed that G2 and its stereoisomers are more potent (at least 30-fold) than the natural product rhynchophylline, which encouraged us to further investigate their functions and mechanisms as treatments for microvascular dysfunction caused by diabetes. G2-a displayed the best microvascular relaxation activity on rat mesenteric arteries among the three compounds, and G2 or G2-a caused relaxation in an endothelium-dependent manner. In ex vivo tests, G2 and G2-a exhibited a weaker potency in inducing microvascular relaxation in mesenteric arteries from diabetic rats than from normal rats, most likely, due to microvascular endothelium damage caused by diabetes. However, based on the animal studies, G2 ameliorated diabetes-induced endothelial dysfunction in rat mesenteric arteries in vivo. Further investigations of the mechanism showed that G2 mainly induced the recovery of endothelial function by upregulating endothelial nitric oxide synthase (eNOS) expression and further increasing the concentration of nitric oxide (NO), which is required for vascular relaxation.

C1q/TNF-Related Protein-9 Ameliorates Ox-LDL-Induced Endothelial Dysfunction via PGC-1α/AMPK-Mediated Antioxidant Enzyme Induction

Oxidized low-density lipoprotein (ox-LDL) accumulation is one of the critical determinants in endothelial dysfunction in many cardiovascular diseases such as atherosclerosis. C1q/TNF-related protein 9 (CTRP9) is identified to be an adipocytokine with cardioprotective properties. However, the potential roles of CTRP9 in endothelial function remain largely elusive. In the present study, the effects of CTRP9 on the proliferation, apoptosis, migration, angiogenesis, nitric oxide (NO) production and oxidative stress in human umbilical vein endothelial cells (HUVECs) exposed to ox-LDL were investigated. We observed that treatment with ox-LDL inhibited the proliferation, migration, angiogenesis and the generation of NO, while stimulated the apoptosis and reactive oxygen species (ROS) production in HUVECs. Incubation of HUVECs with CTRP9 rescued ox-LDL-induced endothelial injury. CTRP9 treatment reversed ox-LDL-evoked decreases in antioxidant enzymes including heme oxygenase-1 (HO-1), nicotinamide adenine dinucleotide phosphate (NAD(P)H) dehydrogenase quinone 1, and glutamate-cysteine ligase (GCL), as well as endothelial nitric oxide synthase (eNOS). Furthermore, CTRP9 induced activation of peroxisome proliferator-activated receptor γ co-activator 1α (PGC1-α) and phosphorylation of adenosine monophosphate-activated protein kinase (AMPK). Of interest, AMPK inhibition or PGC1-α silencing abolished CTRP9-mediated antioxidant enzymes levels, eNOS expressions, and endothelial protective effects. Collectively, we provided the first evidence that CTRP9 attenuated ox-LDL-induced endothelial injury by antioxidant enzyme inductions dependent on PGC-1α/AMPK activation.

Pharmacological Strategies to Retard Cardiovascular Aging

Aging is the major risk factor for cardiovascular diseases, which are the leading cause of death in the United States. Traditionally, the effort to prevent cardiovascular disease has been focused on addressing the conventional risk factors, including hypertension, hyperglycemia, hypercholesterolemia, and high circulating levels of triglycerides. However, recent preclinical studies have identified new approaches to combat cardiovascular disease. Calorie restriction has been reproducibly shown to prolong lifespan in various experimental model animals. This has led to the development of calorie restriction mimetics and other pharmacological interventions capable to delay age-related diseases. In this review, we will address the mechanistic effects of aging per se on the cardiovascular system and focus on the prolongevity benefits of various therapeutic strategies that support cardiovascular health.

Targeting endothelial metaflammation to counteract diabesity cardiovascular risk: Current and perspective therapeutic options

The association of obesity and diabetes, termed "diabesity", defines a combination of primarily metabolic disorders with insulin resistance as the underlying common pathophysiology. Cardiovascular disorders associated with diabesity represent the leading cause of morbidity and mortality in the Western world. This makes diabesity, with its rising impacts on both health and economics, one of the most challenging biomedical and social threats of present century. The emerging comprehension of the genes whose alteration confers inter-individual differences on risk factors for diabetes or obesity, together with the potential role of genetically determined variants on mechanisms controlling responsiveness, effectiveness and safety of anti-diabetic therapy underlines the need of additional knowledge on molecular mechanisms involved in the pathophysiology of diabesity. Endothelial cell dysfunction, resulting from the unbalanced production of endothelial-derived vascular mediators, is known to be present at the earliest stages of insulin resistance and obesity, and may precede the clinical diagnosis of diabetes by several years. Once considered as a mere consequence of metabolic abnormalities, it is now clear that endothelial dysfunctional activity may play a pivotal role in the progression of diabesity. In the vicious circle where vascular defects and metabolic disturbances worsen and reinforce each other, a low-grade, chronic, and 'cold' inflammation (metaflammation) has been suggested to serve as the pathophysiological link that binds endothelial and metabolic dysfunctions. In this paradigm, it is important to consider how traditional antidiabetic treatments (specifically addressing metabolic dysregulation) may directly impact on inflammatory processes or cardiovascular function. Indeed, not all drugs currently available to treat diabetes possess the same anti-inflammatory potential, or target endothelial cell function equally. Perspective strategies pointing at reducing metaflammation or directly addressing endothelial dysfunction may disclose beneficial consequences on metabolic regulation. This review focuses on existing and potential new approaches ameliorating endothelial dysfunction and vascular inflammation in the context of diabesity.

Metformin improves in vivo and in vitro B cell function in individuals with obesity and Type-2 Diabetes

Metformin (MET), the first-line medication for Type-2 Diabetes (T2D), has been shown to reduce chronic inflammation indirectly through reduction of hyperglycemia, or directly acting as anti-inflammatory drug. The effects of MET on B lymphocytes is uncharacterized. In the present study, we measured in vivo and in vitro influenza vaccine responses in 2 groups of T2D patients: recently diagnosed but not taking anti-diabetic drugs, and patients taking MET. Results show that B cell function and vaccine responses, hampered by obesity and T2D, are recovered by MET. Moreover, MET used in vitro to stimulate B cells from recently diagnosed T2D patients is also able to reduce B cell-intrinsic inflammation and increase antibody responses, similar to what we have seen in B cells from patients taking MET, who show increased responses to the influenza vaccine in vivo. These results are the first to show an effect of MET on B cells.

Metformin is not just an antihyperglycaemic drug but also has protective effects on the vascular endothelium

Metformin, a synthetic dimethyl biguanide, has been in clinical use for over 55 years, and today is considered the first-choice drug for the treatment of type 2 diabetes used by an estimated 125 million people worldwide. Metformin is orally effective, not metabolized, excreted unchanged by the kidney, relatively free of side effects and well tolerated by the majority of patients. Of importance is that the United Kingdom Prospective Diabetes Study 20-year study of type 2 diabetics, completed in 1998, compared patients treated with insulin, sulfonylureas and metformin and concluded that metformin provided vascular protective actions. Cardiovascular disease is the primary basis for the high morbidity and mortality that is associated with diabetes and that metformin proved to be protective resulted in a dramatic increase in its use. The vascular protective actions of metformin are thought to be secondary to the antihyperglycaemic effects of metformin that are mediated via activation of AMP kinase and subsequent inhibition of hepatic gluconeogenesis, fatty acid oxidation as well as an insulin sensitizing action in striated muscle and adipose tissue. As reflected by a number of clinical studies, patients treated with metformin also have improvement in endothelial function as measured by the use of plethysmography and measurement of flow-mediated vasodilatation. These data as well as data from animal studies are supportive that metformin has a direct protective action on the vascular endothelium. In this review article, we discuss the pharmacology of metformin and critique the literature as to its cellular sites and mechanism(s) of action.

Targeting Nitric Oxide with Natural Derived Compounds as a Therapeutic Strategy in Vascular Diseases

Within the family of endogenous gasotransmitters, nitric oxide (NO) is the smallest gaseous intercellular messenger involved in the modulation of several processes, such as blood flow and platelet aggregation control, essential to maintain vascular homeostasis. NO is produced by nitric oxide synthases (NOS) and its effects are mediated by cGMP-dependent or cGMP-independent mechanisms. Growing evidence suggests a crosstalk between the NO signaling and the occurrence of oxidative stress in the onset and progression of vascular diseases, such as hypertension, heart failure, ischemia, and stroke. For these reasons, NO is considered as an emerging molecular target for developing therapeutic strategies for cardio- and cerebrovascular pathologies. Several natural derived compounds, such as polyphenols, are now proposed as modulators of NO-mediated pathways. The aim of this review is to highlight the experimental evidence on the involvement of nitric oxide in vascular homeostasis focusing on the therapeutic potential of targeting NO with some natural compounds in patients with vascular diseases.

Jiang Tang Xiao Ke Granule, a Classic Chinese Herbal Formula, Improves the Effect of Metformin on Lipid and Glucose Metabolism in Diabetic Mice

In the present study, the hypoglycemic, hypolipidemic, and antioxidative effects of metformin (MET) combined with Jiang Tang Xiao Ke (JTXK) granule derived from the “Di Huang Tang” were evaluated in mice with type 2 diabetes mellitus (DM) induced by high-fat diet/streptozotocin. DM mice were orally treated with MET (0.19 g/kg) either alone or combined with different doses (1.75, 3.5, or 7 g/kg) of JTXK for 4 weeks. Results showed that the serum and hepatic glucose, lipids, and oxidative stress levels were elevated in DM mice, when compared with the normal mice. MET treatment decreased FBG and serum glucagon levels of DM mice. Combination treatment with MET and JTXK 3.5 g/kg increased the hypoglycemia and insulin sensitivity at 4 weeks when compared with the DM mice treated with MET alone. However, neither MET nor MET/JTXK treatment could completely reverse the hyperglycemia in DM mice. JTXK enhanced the serum triglyceride (TG) and hepatic lipid-lowering effect of MET in a dose-dependent manner in DM mice. JTXK 1.75 and 3.5 g/kg improved the hepatoprotective effect of MET in DM mice. Synergistic effect of combination treatment with MET and JTXK on antioxidant stress was also found in DM mice compared with MET alone.