Vasodilatory Actions of Glucagon-Like Peptide 1 Are Preserved in Skeletal and Cardiac Muscle Microvasculature but Not in Conduit Artery in Obese Humans With Vascular Insulin Resistance

The impact of GLP-1 signalling on the energy metabolism of pancreatic islet β-cells and extrapancreatic tissues

Glucagon-like peptide-1 signalling impacts glucose homeostasis and appetite thereby indirectly affecting substrate availability at the whole-body level. The incretin canonically produces an insulinotropic effect, thereby lowering blood glucose levels by promoting the uptake and inhibiting the production of the sugar by peripheral tissues. Likewise, GLP-1 signalling within the central nervous system reduces the appetite and food intake, whereas its gastric effect delays the absorption of nutrients, thus improving glycaemic control and reducing the risk of postprandial hyperglycaemia. We review the molecular aspects of the GLP-1 signalling, focusing on its impact on intracellular energy metabolism. Whilst the incretin exerts its effects predominantly via a Gs receptor, which decodes the incretin signal into the elevation of intracellular cAMP levels, the downstream signalling cascades within the cell, acting on fast and slow timescales, resulting in an enhancement or an attenuation of glucose catabolism, respectively.

Obesity and MASLD: Is weight loss the (only) key to treat metabolic liver disease?

Metabolic dysfunction-associated steatotic liver disease (MASLD) closely associates with obesity and type 2 diabetes. Lifestyle intervention and bariatric surgery aiming at substantial weight loss are cornerstones of MASLD treatment by improving histological outcomes and reducing risks of comorbidities. Originally developed as antihyperglycemic drugs, incretin (co-)agonists and SGLT2 inhibitors also reduce steatosis and cardiorenovascular events. Certain incretin agonists effectively improve histological features of MASLD, but not fibrosis. Of note, beneficial effects on MASLD may not necessarily require weight loss. Despite moderate weight gain, one PPARγ agonist improved adipose tissue and MASLD with certain benefit on fibrosis in post-hoc analyses. Likewise, the first THRβ-agonist was recently provisionally approved because of significant improvements of MASLD and fibrosis. We here discuss liver-related and metabolic effects induced by different MASLD treatments and their association with weight loss. Therefore, we compare results from clinical trials on drugs acting via weight loss (incretin (co)agonists, SGLT2 inhibitors) with those exerting no weight loss (pioglitazone; resmetirom). Furthermore, other drugs in development directly targeting hepatic lipid metabolism (lipogenesis inhibitors, FGF21 analogs) are addressed. Although THRβ-agonism may effectively improve hepatic outcomes, MASLD treatment concepts should consider all cardiometabolic risk factors for effective reduction of morbidity and mortality in the affected people.

Identification of HDAC9 and ARRDC4 as potential biomarkers and targets for treatment of type 2 diabetes

We aimed to identify the key potential insulin resistance (IR)-related genes and investigate their correlation with immune cell infiltration in type 2 diabetes (T2D). The GSE78721 dataset (68 diabetic patients and 62 controls) was downloaded from the Gene Expression Omnibus database and utilized for single-sample gene set enrichment analysis. IR-related genes were obtained from the Comparative Toxicology Genetics Database, and the final IR-differentially expressed genes (DEGs) were screened by intersecting with the DEGs obtained from the GSE78721 datasets. Functional enrichment analysis was performed, and the networks of the target gene with microRNA, transcription factor, and drug were constructed. Hub genes were identified based on a protein-protein interaction network. Least absolute shrinkage and selection operator regression and Random Forest and Boruta analysis were combined to screen diagnostic biomarkers in T2D, which were validated using the GSE76894 (19 diabetic patients and 84 controls) and GSE9006 (12 diabetic patients and 24 controls) datasets. Quantitative real-time polymerase chain reaction was performed to validate the biomarker expression in IR mice and control mice. In addition, infiltration of immune cells in T2D and their correlation with the identified markers were computed using CIBERSORT. We identified differential immune gene set regulatory T-cells in the GSE78721 dataset, and T2D samples were assigned into three clusters based on immune infiltration. A total of 2094 IR-DEGs were primarily enriched in response to endoplasmic reticulum stress. Importantly, HDAC9 and ARRDC4 were identified as markers of T2D and associated with different levels of immune cell infiltration. HDAC9 mRNA level were higher in the IR mice than in control mice, while ARRDC4 showed the opposite trend. In summary, we discovered potential vital biomarkers that contribute to immune cell infiltration associated with IR, which offers a new sight of immunotherapy for T2D.

Impact of Free Fatty Acids on Vascular Insulin Responses Across the Arterial Tree: A Randomized Crossover Study

CONTEXT

Vascular insulin resistance is commonly observed in obesity and diabetes; yet, insulin action across the vascular tree and the relationship between insulin responses at different vascular locations remains incompletely defined.

OBJECTIVE

To elucidate the impact of elevated free fatty acids (FFAs) on insulin action across the arterial tree and define the relationship among insulin actions in the different arterial segments.

METHODS

This randomized crossover study assigned healthy lean adults to 2 separate admissions with euglycemic insulin clamp superimposed for the final 120 minutes of 5-hour lipid or matched-volume saline infusion. Vascular measures including peripheral and central arterial blood pressure, brachial artery flow-mediated dilation (FMD), carotid femoral pulse wave velocity (cfPWV), augmentation index (AIx), pulse wave separation analysis, subendocardial viability ratio (SEVR), and skeletal and cardiac muscle microvascular perfusion were determined before and after insulin clamp. Insulin-mediated whole body glucose disposal was calculated.

RESULTS

Insulin enhanced FMD, AIx, reflection magnitude, and cardiac and skeletal muscle microvascular perfusion. Elevation of plasma FFA concentrations to the levels seen in the postabsorptive state in people with insulin resistance suppressed SEVR, blunted insulin-induced increases in FMD and cardiac and skeletal muscle microvascular blood volume, and lowered insulin's ability to reduce AIx and reflection magnitude. In multivariate regression, insulin-mediated muscle microvascular perfusion was independently associated with insulin-mediated FMD and cfPWV.

CONCLUSION

Clinically relevant elevation of plasma FFA concentrations induces pan-arterial insulin resistance, the vascular insulin resistance outcomes are interconnected, and insulin-mediated muscle microvascular perfusion associates with cardiovascular disease predictors. Our data provide biologic plausibility whereby a causative relationship between FFAs and cardiovascular disease could exist, and suggest that further attention to interventions that block FFA-mediated vascular insulin resistance may be warranted.

GLP1 Receptor Agonists-Effects beyond Obesity and Diabetes

Glucagon-like peptide-1 receptor agonists (GLP1RA) have been transformative for patients and clinicians in treating type-2 diabetes and obesity. Drugs of this class, the bioavailability of which is continuously improving, enable weight loss and control blood glucose with minimal unwanted side effects. Since adopting GLP1RA for treating metabolic diseases, animal and clinical studies have revealed their beneficial effects on several other pathologies, including cardiovascular diseases, neurodegeneration, kidney disease, and cancer. A notable commonality between these diseases is their association with older age. Clinical trials and preclinical data suggest that GLP1RA may improve outcomes in these aging-related diseases. Some of the benefits of GLP1RA may be indirect due to their effects on obesity and glucose metabolism. However, there is building evidence that GLP1RA may also act directly on multiple organs implicated in aging-related pathology. This review aims to compile the studies reporting the effects of GLP1RA on aging-related diseases and discuss potential underlying mechanisms.

Glucagon-Like Peptide-1 Receptor Agonists in the Treatment of Idiopathic Inflammatory Myopathy: From Mechanisms of Action to Clinical Applications

Idiopathic inflammatory myopathies (IIMs) result in proximal muscle weakness and other intramuscular and extramuscular manifestations. Pharmacologic treatments in use for IIMs are limited to corticosteroids and immunosuppressants in addition to supportive physical and occupational therapy. Glucagon-like peptide-1 receptor (GLP-1R) agonists are currently utilized in the treatment of type II diabetes and obesity but may play a role in the treatment of IIMs. The current scoping review of extant literature aims to synthesize findings from studies assessing the therapeutic effects of GLP-1R agonists in the management of inflammatory myopathy and muscle atrophy. A literature search was conducted through PubMed, resulting in a total of 19 research-based articles included in this review. Mice and human studies showed, with varying levels of significance, that GLP-1R agonists led to decreases in muscle atrophy, inflammation, adiposity, and weakness; improvement in muscle microvasculature and endurance; and promotion of muscle mitochondria biogenesis. The potential for GLP-1R agonists to improve muscle function and architecture underscores the need for large randomized controlled, clinically comparative trials of GLP-1R agonists in patients with IIM.

Microvascular Dysfunction in Obesity-Hypertension

PURPOSE OF REVIEW

This review aims to explore the role of microvascular dysfunction in obesity-hypertension, discuss the effects obesity has on renal microvasculature, review the current methods for assessing microvascular dysfunction and available therapeutic options, and identify critical areas for further research.

RECENT FINDINGS

There is a strong association between obesity and hypertension. However, the pathophysiology of obesity-hypertension is not clear. Microvascular dysfunction has been linked to hypertension and obesity and could be an important mediator of obesity-related hypertension. Newer therapies for hypertension and obesity could have ameliorating effects on microvascular dysfunction, including GLP-1 agonists and SGLT-2 inhibitors. There is still much progress to be made in our understanding of the complex interplay between obesity, hypertension, and microvascular dysfunction. Continued efforts to understand microvascular dysfunction and its role in obesity-hypertension are crucial to develop precision therapy to target obesity-hypertension.

A narrative review of exercise participation among adults with prediabetes or type 2 diabetes: barriers and solutions

Type 2 diabetes (T2D) has been rising in prevalence over the past few decades in the US and worldwide. T2D contributes to significant morbidity and premature mortality, primarily due to cardiovascular disease (CVD). Exercise is a major cornerstone of therapy for T2D as a result of its positive effects on glycemic control, blood pressure, weight loss and cardiovascular risk as well as other measures of health. However, studies show that a majority of people with T2D do not exercise regularly. The reasons given as to why exercise goals are not met are varied and include physiological, psychological, social, cultural and environmental barriers to exercise. One potential cause of inactivity in people with T2D is impaired cardiorespiratory fitness, even in the absence of clinically evident complications. The exercise impairment, although present in both sexes, is greater in women than men with T2D. Women with T2D also experience greater perceived exertion with exercise than their counterparts without diabetes. These physiological barriers are in addition to constructed societal barriers including cultural expectations of bearing the burden of childrearing for women and in some cultures, having limited access to exercise because of additional cultural expectations. People at risk for and with diabetes more commonly experience unfavorable social determinants of health (SDOH) than people without diabetes, represented by neighborhood deprivation. Neighborhood deprivation measures lack of resources in an area influencing socioeconomic status including many SDOH such as income, housing conditions, living environment, education and employment. Higher indices of neighborhood deprivation have been associated with increased risk of all-cause, cardiovascular and cancer related mortality. Unfavorable SDOH is also associated with obesity and lower levels of physical activity. Ideally regular physical activity should be incorporated into all communities as part of a productive and healthy lifestyle. One potential solution to improve access to physical activity is designing and building environments with increased walkability, greenspace and safe recreational areas. Other potential solutions include the use of continuous glucose monitors as real-time feedback tools aimed to increase motivation for physical activity, counseling aimed at improving self-efficacy towards exercise and even acquiring a dog to increase walking time. In this narrative review, we aim to examine some traditional and novel barriers to exercise, as well as present evidence on novel interventions or solutions to overcome barriers to increase exercise and physical activity in all people with prediabetes and T2D.

Repurposing Drugs for Diabetes Mellitus as Potential Pharmacological Treatments for Sarcopenia - A Narrative Review

Sarcopenia, the age-related loss of muscle strength and mass or quality, is a common condition with major adverse consequences. Although the pathophysiology is incompletely understood, there are common mechanisms between sarcopenia and the phenomenon of accelerated ageing seen in diabetes mellitus. Drugs currently used to treat type 2 diabetes mellitus may have mechanisms of action that are relevant to the prevention and treatment of sarcopenia, for those with type 2 diabetes and those without diabetes. This review summarises shared pathophysiology between sarcopenia and diabetes mellitus, including the effects of advanced glycation end products, mitochondrial dysfunction, chronic inflammation and changes to the insulin signalling pathway. Cellular and animal models have generated intriguing, albeit mixed, evidence that supports possible beneficial effects on skeletal muscle function for some classes of drugs used to treat diabetes, including metformin and SGLT2 inhibitors. Most human observational and intervention evidence for the effects of these drugs has been derived from populations with type 2 diabetes mellitus, and there is a need for intervention studies for older people with, and at risk of, sarcopenia to further investigate the balance of benefit and risk in these target populations. Not all diabetes treatments will be safe to use in those without diabetes because of variable side effects across classes. However, some agents [including glucagon-like peptide (GLP)-1 receptor agonists and SGLT2 inhibitors] have already demonstrated benefits in populations without diabetes, and it is these agents, along with metformin, that hold out the most promise for further investigation in sarcopenia.

Liraglutide and Exercise Synergistically Attenuate Vascular Inflammation and Enhance Metabolic Insulin Action in Early Diet-Induced Obesity

Inflammation-induced vascular insulin resistance is an early event in diet-induced obesity and contributes to metabolic insulin resistance. To examine whether exercise and glucagon-like peptide 1 (GLP-1) receptor agonism, alone or in combination, modulate vascular and metabolic insulin actions during obesity development, we performed a euglycemic insulin clamp in adult male rats after 2 weeks of high-fat diet feeding with either access to a running wheel (exercise), liraglutide, or both. Rats exhibited increased visceral adiposity and blunted microvascular and metabolic insulin responses. Exercise and liraglutide alone each improved muscle insulin sensitivity, but their combination fully restored insulin-mediated glucose disposal rates. The combined exercise and liraglutide intervention enhanced insulin-mediated muscle microvascular perfusion, reduced perivascular macrophage accumulation and superoxide production in the muscle, attenuated blood vessel inflammation, and improved endothelial function, along with increasing endothelial nucleus translocation of NRF2 and increasing endothelial AMPK phosphorylation. We conclude that exercise and liraglutide synergistically enhance the metabolic actions of insulin and reduce vascular oxidative stress and inflammation in the early stage of obesity development. Our data suggest that early combination use of exercise and GLP-1 receptor agonism might be an effective strategy in preventing vascular and metabolic insulin resistance and associated complications during the development of obesity.

ARTICLE HIGHLIGHTS

Inflammation-induced vascular insulin resistance occurs early in diet-induced obesity and contributes to metabolic insulin resistance. We examined whether exercise and GLP-1 receptor agonism, alone or in combination, modulate vascular and metabolic insulin actions during obesity development. We found that exercise and liraglutide synergistically enhanced the metabolic actions of insulin and reduced perimicrovascular macrophage accumulation, vascular oxidative stress, and inflammation in the early stage of obesity development. Our data suggest that early combination use of exercise and a GLP-1 receptor agonist might be an effective strategy in preventing vascular and metabolic insulin resistance and associated complications during the development of obesity.

Oral Semaglutide Induces Loss of Body Fat Mass Without Affecting Muscle Mass in Patients With Type 2 Diabetes

Background

Excessive body fat may be a major cause of insulin resistance and diabetes. But body weight reduction by energy restriction may simultaneously reduce both fat and muscle. Skeletal muscle is an important organ for glucose metabolism regulation, and loss of muscle may deteriorate glucose metabolism. Therefore, it is preferable to predominantly reduce fat without significant loss of muscle with weight loss in patients with type 2 diabetes. Previously, the anti-diabetic agent glucagon-like peptide-1 receptor agonists (GLP-1RAs) liraglutide and semaglutide given by injection were reported to decrease fat with less effect on muscle in diabetic patients. Recently oral semaglutide was developed and was reported to decrease body weight, but the effect on muscle has not been fully evaluated.

Methods

This was a non-interventional retrospective longitudinal study. We evaluated the effect of 24-week treatment with oral semaglutide on body fat and muscle mass in 25 Japanese patients with type 2 diabetes. Laboratory examination and body composition test by bioelectrical impedance analysis (BIA) were performed at baseline, 12 weeks, and 24 weeks, and the effects on glycemic control and body composition were assessed.

Results

Hemoglobin A1c significantly decreased at 12 weeks and further ameliorated at 24 weeks (8.7±0.87% at baseline; 7.6±1.00% at 12 weeks; 7.0±0.80% at 24 weeks; mean ± standard error (SE)). While body fat significantly decreased (28.3 ± 1.52 kg at baseline; 26.8 ± 1.59 kg at 12 weeks; 25.5 ± 1.57 kg at 24 weeks; mean ± SE), whole-body lean mass was not significantly changed (48.1 ± 1.92 kg at baseline; 47.7 ± 1.93 kg at 12 weeks; 47.6 ± 1.89 kg at 24 weeks; mean ± SE). Furthermore, the appendicular skeletal muscle index (SMI) defined as appendicular skeletal muscle mass (ASM)/height squared (units; kg/m2) was also unchanged.

Conclusion

The 24-week treatment with oral semaglutide ameliorated glycemic control with reduction of body fat but not muscle mass in Japanese patients with type 2 diabetes.

Beyond the pancreas: contrasting cardiometabolic actions of GIP and GLP1

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP1) exhibit incretin activity, meaning that they potentiate glucose-dependent insulin secretion. The emergence of GIP receptor (GIPR)-GLP1 receptor (GLP1R) co-agonists has fostered growing interest in the actions of GIP and GLP1 in metabolically relevant tissues. Here, we update concepts of how these hormones act beyond the pancreas. The actions of GIP and GLP1 on liver, muscle and adipose tissue, in the control of glucose and lipid homeostasis, are discussed in the context of plausible mechanisms of action. Both the GIPR and GLP1R are expressed in the central nervous system, wherein receptor activation produces anorectic effects enabling weight loss. In preclinical studies, GIP and GLP1 reduce atherosclerosis. Furthermore, GIPR and GLP1R are expressed within the heart and immune system, and GLP1R within the kidney, revealing putative mechanisms linking GIP and GLP1R agonism to cardiorenal protection. We interpret the clinical and mechanistic data obtained for different agents that enable weight loss and glucose control for the treatment of obesity and type 2 diabetes mellitus, respectively, by activating or blocking GIPR signalling, including the GIPR-GLP1R co-agonist tirzepatide, as well as the GIPR antagonist-GLP1R agonist AMG-133. Collectively, we update translational concepts of GIP and GLP1 action, while highlighting gaps, areas of uncertainty and controversies meriting ongoing investigation.

Liraglutide Accelerates Ischemia-Induced Angiogenesis in a Murine Diabetic Model

Background Severe hindlimb ischemia is a chronic disease with poor prognosis that can lead to amputation or even death. This study aimed to assess the therapeutic effect of liraglutide on hind-limb ischemia in type 2 diabetic mice and to elucidate the underlying mechanism. Methods and Results Blood flow reperfusion and capillary densities after treatment with liraglutide or vehicle were evaluated in a mouse model of lower-limb ischemia in a normal background or a background of streptozotocin-induced diabetes. The proliferation, migration, and tube formation of human umbilical vein endothelial cells were analyzed in vitro upon treatment with liraglutide under normal-glucose and high-glucose conditions. Levels of phospho-Akt, phospho-endothelial nitric oxide synthase, and phospho-extracellular signal-related kinases 1 and 2 under different conditions in human umbilical vein endothelial cells and in ischemic muscle were determined by western blotting. Liraglutide significantly improved perfusion recovery and capillary density in both nondiabetic and diabetic mice. Liraglutide also promoted, in a concentration-dependent manner, the proliferation, migration, and tube formation of normal glucose- and high glucose-treated human umbilical vein endothelial cells, as well as the phosphorylation of Akt, endothelial nitric oxide synthase, and extracellular signal-related kinases 1 and 2 both in vitro and in vivo. The liraglutide antagonist exendin (9-39) reversed the promoting effects of liraglutide on human umbilical vein endothelial cell functions. Furthermore, exendin (9-39), LY294002, and PD98059 blocked the liraglutide-induced activation of Akt/endothelial nitric oxide synthase and extracellular signal-related kinases 1 and 2 signaling pathways. Conclusions These studies identified a novel role of liraglutide in modulating ischemia-induced angiogenesis, possibly through effects on endothelial cell function and activation of Akt/endothelial nitric oxide synthase and extracellular signal-related kinases 1 and 2 signaling, and suggested the glucagon-like peptide-1 receptor may be an important therapeutic target in diabetic hind-limb ischemia.

Metformin's Impact on the Microvascular Response to Insulin

Metformin improves insulin's action on whole-body glucose metabolism in various insulin-resistant populations. The detailed cellular mechanism(s) for its metabolic actions are multiple and still incompletely understood. Beyond metabolic actions, metformin also impacts microvascular function. However, the effects of metformin on microvascular function and microvascular insulin action specifically are poorly defined. In this mini-review, we summarize what is currently known about metformin's beneficial impact on both microvascular function and the microvascular response to insulin while highlighting methodologic issues in the literature that limit straightforward mechanistic understanding of these effects. We examine potential mechanisms for these effects based on pharmacologically dosed studies and propose that metformin may improve human microvascular insulin resistance by attenuating oxidative stress, inflammation, and endothelial dysfunction. Finally, we explore several important evidence gaps and discuss avenues for future investigation that may clarify whether metformin's ability to improve microvascular insulin sensitivity is linked to its positive impact on vascular outcomes.

Coronary Microvascular Dysfunction in Diabetes Mellitus: Pathogenetic Mechanisms and Potential Therapeutic Options

Diabetic patients are frequently affected by coronary microvascular dysfunction (CMD), a condition consisting of a combination of altered vasomotion and long-term structural change to coronary arterioles leading to impaired regulation of blood flow in response to changing cardiomyocyte oxygen requirements. The pathogenesis of this microvascular complication is complex and not completely known, involving several alterations among which hyperglycemia and insulin resistance play particularly central roles leading to oxidative stress, inflammatory activation and altered barrier function of endothelium. CMD significantly contributes to cardiac events such as angina or infarction without obstructive coronary artery disease, as well as heart failure, especially the phenotype associated with preserved ejection fraction, which greatly impact cardiovascular (CV) prognosis. To date, no treatments specifically target this vascular damage, but recent experimental studies and some clinical investigations have produced data in favor of potential beneficial effects on coronary micro vessels caused by two classes of glucose-lowering drugs: glucagon-like peptide 1 (GLP-1)-based therapy and inhibitors of sodium-glucose cotransporter-2 (SGLT2). The purpose of this review is to describe pathophysiological mechanisms, clinical manifestations of CMD with particular reference to diabetes, and to summarize the protective effects of antidiabetic drugs on the myocardial microvascular compartment.

Dipeptidyl peptidase 4 inhibitor improves insulin resistance in Japanese patients with type 2 diabetes: a single-arm study, a brief report

BACKGROUND

Dipeptidyl peptidase 4 inhibitor (DPP4i) is an effective medicine for type 2 diabetes mellitus (T2DM). Some articles reported DPP4i improves insulin secretion and insulin resistance. However, these effects are not well established by glucose clamp test and test meal in Japanese. We investigated the effect of DPP4i on insulin resistance and insulin secretion by using the glucose clamp test and meal tolerance test (MTT).

METHODS

We performed a MTT, and the hyperinsulinemic-euglycemic clamp in 8 Japanese patients with T2DM. This study was a single-arm study. We measured fasting and postprandial glucose, insulin, incretins, and glucagon levels. We also measured serum adiponectin levels.

RESULTS

HbA1c was significantly decreased after 3 months. The fasting and postprandial glucose levels were significantly decreased. Fasting and postprandial insulin levels were not changed. The insulin resistance derived from the glucose clamp test was significantly improved. HOMA-IR was not significantly changed. GLP-1 and GIP were significantly increased but glucagon did not change. Adiponectin was not significantly changed.

CONCLUSIONS

Although the number of patients was very small, these results suggested that DPP4i treatment might improve insulin resistance without changing insulin secretion.

GLP-1 Receptor Agonists and Coronary Arteries: From Mechanisms to Events

Objective: Glucagon-like peptide 1 receptor agonists (GLP-1 RAs) lower plasma glucose through effects on insulin and glucagon secretion and by decelerating gastric emptying. GLP-1 RAs have many beneficial effects beyond glycemic control, including a protective role on the cardiovascular system. However, underlying mechanisms linking GLP-1 RAs with coronary artery disease are complex and not fully elucidated. In this mini-review, we discuss these mechanisms and subsequent clinical events.

Data Sources: We searched PubMed and Google Scholar for evidence on GLP-1 RAs and coronary events. We did not apply restrictions on article type. We reviewed publications for clinical relevance.

Synopsis of Content: In the first part, we review the current evidence concerning the role of GLP-1 RAs on potential mechanisms underlying the development of coronary events. Specifically, we discuss the role of GLP-1 RAs on atherosclerosis and vasospasms of epicardial coronary arteries, as well as structural/functional changes of coronary microvasculature. In the second part, we summarize the clinical evidence on the impact of GLP-1 RAs in the prevention of acute and chronic coronary syndromes and coronary revascularization. We conclude by discussing existing gaps in the literature and proposing directions for future research.

Arterial responses to infusion of glucagon-like peptide-1 in humans: A randomized trial study

Glucagon-like-peptide-1 (GLP-1) is an incretin hormone implicated in several metabolic and neurological disorders. GLP-1 induces vasodilation and increases blood flow in the peripheral circulation. Whether GLP-1 alters cerebral hemodynamics in humans is yet to be elucidated. In a crossover, double-blind, placebo-controlled, and randomized design, 21 healthy volunteers were assigned to receive intravenous GLP-1 infusion (2.5 pmol/kg/min) or placebo over 20 min on two different days separated by at least one week. We used a noninvasive, well-validated transcranial doppler (TCD) and ultrasound dermascan to reveal the effect of GLP-1 on intra- and extracerebral arteries. The mean blood flow velocity in the middle cerebral artery (V_MCA), the diameter of the superficial temporal artery (STA) and radial artery (RA), and facial skin blood flow were measured. In addition, we documented headache and its associated symptoms during and after infusion. Twenty participants were included in the final analysis. We found no difference in the V_MCA (P = 0.227), diameter of the STA (P = 0.096) and the RA (P = 0.221) and facial blood flow (P = 0.814) after GLP-1 compared to placebo. There were no differences in HR, SAT, EtCO₂, or RF (P > 0.05) on the GLP-1 day compared to the placebo day. We found no differences in the incidence of headache after GLP-1 (n = 10) compared to placebo (n = 7) (P = 0.250). GLP-1 infusion did not affect cerebral hemodynamics and induce headache in humans. Further preclinical studies with validated methods are required to determine if intra - and extracerebral vasculature express GLP-1Rs in humans.

Oral and intravenous glucose administration elicit opposing microvascular blood flow responses in skeletal muscle of healthy people: role of incretins

Abstract

Insulin infusion increases skeletal muscle microvascular blood flow (MBF) in healthy people but is impaired during insulin resistance. However, we have shown that eliciting insulin secretion via oral glucose loading in healthy people impairs muscle MBF, whilst others have demonstrated intravenous glucose infusion stimulates MBF. We aimed to show that the route of glucose administration (oral versus intravenous) influences muscle MBF, and explore potential gut‐derived hormones that may explain these divergent responses. Ten healthy individuals underwent a 120 min oral glucose tolerance test (OGTT; 75 g glucose) and on a subsequent occasion an intravenous glucose tolerance test (IVGTT, bypassing the gut) matched for similar blood glucose excursions. Femoral artery and thigh muscle microvascular (contrast‐enhanced ultrasound) haemodynamics were measured at baseline and during the OGTT/IVGTT. Plasma insulin, C‐peptide, glucagon, non‐esterified fatty acids and a range of gut‐derived hormones and incretins (gastric inhibitory polypeptide (GIP) and glucagon‐like peptide‐1(GLP‐1)) were measured at baseline and throughout the OGTT/IVGTT. The IVGTT increased whereas the OGTT impaired MBF (1.3‐fold versus 0.5‐fold from baseline, respectively, P = 0.0006). The impairment in MBF during the OGTT occurred despite producing 2.8‐fold higher plasma insulin concentrations (P = 0.0001). The change in MBF from baseline (ΔMBF) negatively correlated with ΔGIP concentrations (r = −0.665, P < 0.0001). The natural log ratio of incretins GLP‐1:GIP was positively associated with ΔMBF (r = 0.658, P < 0.0001), suggesting they have opposing actions on the microvasculature. Postprandial hyperglycaemia per se does not acutely determine opposing microvascular responses between OGTT and IVGTT. Incretins may play a role in modulating skeletal muscle MBF in humans.

Key points

Insulin or mixed nutrient meals stimulate skeletal muscle microvascular blood flow (MBF) to aid in the delivery of nutrients; however, this vascular effect is lost during insulin resistance.

Food/drinks containing large glucose loads impair MBF in healthy people; however, this impairment is not observed when glucose is infused intravenously (bypassing the gut).

We investigated skeletal muscle MBF responses to a 75 g oral glucose tolerance test and intravenous glucose infusion and aimed to identify potential gut hormones responsible for glucose‐mediated changes in MBF.

Despite similar blood glucose concentrations, orally ingested glucose impaired, whereas intravenously infused glucose augmented, skeletal muscle MBF. The incretin gastric inhibitory polypeptide was negatively associated with MBF, suggestive of an incretin‐mediated MBF response to oral glucose ingestion.

This work provides new insight into why diets high in glucose may be detrimental to vascular health and provides new avenues for novel treatment strategies targeting microvascular dysfunction.

Vasodilator Dysfunction in Human Obesity: Established and Emerging Mechanisms

ABSTRACT

Human obesity is associated with insulin resistance and often results in a number of metabolic abnormalities and cardiovascular complications. Over the past decades, substantial advances in the understanding of the cellular and molecular pathophysiological pathways underlying the obesity-related vascular dysfunction have facilitated better identification of several players participating in this abnormality. However, the complex interplay between the disparate mechanisms involved has not yet been fully elucidated. Moreover, in medical practice, the clinical syndromes stemming from obesity-related vascular dysfunction still carry a substantial burden of morbidity and mortality; thus, early identification and personalized clinical management seem of the essence. Here, we will initially describe the alterations of intravascular homeostatic mechanisms occurring in arteries of obese patients. Then, we will briefly enumerate those recognized causative factors of obesity-related vasodilator dysfunction, such as vascular insulin resistance, lipotoxicity, visceral adipose tissue expansion, and perivascular adipose tissue abnormalities; next, we will discuss in greater detail some emerging pathophysiological mechanisms, including skeletal muscle inflammation, signals from gut microbiome, and the role of extracellular vesicles and microRNAs. Finally, it will touch on some gaps in knowledge, as well as some current acquisitions for specific treatment regimens, such as glucagon-like peptide-1 enhancers and sodium-glucose transporter2 inhibitors, that could arrest or slow the progression of this abnormality full of unwanted consequences.

Diabetes pathogenesis and management: the endothelium comes of age

Endothelium, acting as a barrier, protects tissues against factors that provoke insulin resistance and type 2 diabetes and itself responds to the insult of insulin resistance inducers with altered function. Endothelial insulin resistance and vascular dysfunction occur early in the evolution of insulin resistance-related disease, can co-exist with and even contribute to the development of metabolic insulin resistance, and promote vascular complications in those affected. The impact of endothelial insulin resistance and vascular dysfunction varies depending on the blood vessel size and location, resulting in decreased arterial plasticity, increased atherosclerosis and vascular resistance, and decreased tissue perfusion. Women with insulin resistance and diabetes are disproportionately impacted by cardiovascular disease, likely related to differential sex-hormone endothelium effects. Thus, reducing endothelial insulin resistance and improving endothelial function in the conduit arteries may reduce atherosclerotic complications, in the resistance arteries lead to better blood pressure control, and in the microvasculature lead to less microvascular complications and more effective tissue perfusion. Multiple diabetes therapeutic modalities, including medications and exercise training, improve endothelial insulin action and vascular function. This action may delay the onset of type 2 diabetes and/or its complications, making the vascular endothelium an attractive therapeutic target for type 2 diabetes and potentially type 1 diabetes.

Effects of GLP-1 receptor agonists and SGLT-2 inhibitors on cardiac structure and function: a narrative review of clinical evidence

The impressive results of recent clinical trials with glucagon-like peptide-1 receptor agonists (GLP-1Ra) and sodium glucose transporter 2 inhibitors (SGLT-2i) in terms of cardiovascular protection prompted a huge interest in these agents for heart failure (HF) prevention and treatment. While both classes show positive effects on composite cardiovascular endpoints (i.e. 3P MACE), their actions on the cardiac function and structure, as well as on volume regulation, and their impact on HF-related events have not been systematically evaluated and compared. In this narrative review, we summarize and critically interpret the available evidence emerging from clinical studies. While chronic exposure to GLP-1Ra appears to be essentially neutral on both systolic and diastolic function, irrespective of left ventricular ejection fraction (LVEF), a beneficial impact of SGLT-2i is consistently detectable for both systolic and diastolic function parameters in subjects with diabetes with and without HF, with a gradient proportional to the severity of baseline dysfunction. SGLT-2i have a clinically significant impact in terms of HF hospitalization prevention in subjects at high and very high cardiovascular risk both with and without type 2 diabetes (T2D) or HF, while GLP-1Ra have been proven to be safe (and marginally beneficial) in subjects with T2D without HF. We suggest that the role of the kidney is crucial for the effect of SGLT-2i on the clinical outcomes not only because these drugs slow-down the time-dependent decline of kidney function and enhance the response to diuretics, but also because they attenuate the meal-related anti-natriuretic pressure (lowering postprandial hyperglycemia and hyperinsulinemia and preventing proximal sodium reabsorption), which would reduce the individual sensitivity to day-to-day variations in dietary sodium intake.

Insulin-mediated muscle microvascular perfusion and its phenotypic predictors in humans

Insulin increases muscle microvascular perfusion and enhances tissue insulin and nutrient delivery. Our aim was to determine phenotypic traits that foretell human muscle microvascular insulin responses. Hyperinsulinemic euglycemic clamps were performed in 97 adult humans who were lean and healthy, had class 1 obesity without comorbidities, or controlled type 1 diabetes without complications. Insulin-mediated whole-body glucose disposal rates (M-value) and insulin-induced changes in muscle microvascular blood volume (ΔMBV) were determined. Univariate and multivariate analyses were conducted to examine bivariate and multivariate relationships between outcomes, ΔMBV and M-value, and predictor variables, body mass index (BMI), total body weight (WT), percent body fat (BF), lean body mass, blood pressure, maximum consumption of oxygen (VO2max), plasma LDL (LDL-C) and HDL cholesterol, triglycerides (TG), and fasting insulin (INS) levels. Among all factors, only M-value (r = 0.23, p = 0.02) and VO2max (r = 0.20, p = 0.047) correlated with ΔMBV. Conversely, INS (r = - 0.48, p ≤ 0.0001), BF (r = - 0.54, p ≤ 0.001), VO2max (r = 0.5, p ≤ 0.001), BMI (r = - 0.40, p < 0.001), WT (r = - 0.33, p = 0.001), LDL-C (r = - 0.26, p = 0.009), TG (r = - 0.25, p = 0.012) correlated with M-value. While both ΔMBV (p = 0.045) and TG (p = 0.03) provided significant predictive information about M-value in the multivariate regression model, only M-value was uniquely predictive of ΔMBV (p = 0.045). Thus, both M-value and VO2max correlated with ΔMBV but only M-value provided unique predictive information about ΔMBV. This suggests that metabolic and microvascular insulin responses are important predictors of one another, but most metabolic insulin resistance predictors do not predict microvascular insulin responses.

Acute hyperglycaemia enhances both vascular endothelial function and cardiac and skeletal muscle microvascular function in healthy humans

KEY POINTS

Multiple clinical studies report that acute hyperglycaemia (induced by mixed meal or oral glucose) decreases arterial vascular function in healthy humans. Feeding, however, impacts autonomic output, blood pressure, and insulin and incretin secretion, which may themselves alter vascular function. No prior studies have examined the effect of acute hyperglycaemia on both macro- and microvascular function while controlling plasma insulin concentrations. Macrovascular and microvascular functional responses to euglycaemia and hyperglycaemia were compared. Octreotide was infused throughout both protocols to prevent endogenous insulin release. Acute hyperglycaemia (induced by intravenous glucose) enhanced brachial artery flow-mediated dilatation, increased skeletal muscle microvascular blood volume and flow, and expanded cardiac muscle microvascular blood volume. Compared to other published findings, the results suggest that vascular responses to acute hyperglycaemia differ based on the study population (i.e. normal weight vs. overweight/obese) and/or glucose delivery method (i.e. intravenous vs. oral glucose).

ABSTRACT

High glucose concentrations acutely provoke endothelial cell oxidative stress and are suggested to trigger diabetes-related macro- and microvascular injury in humans. Multiple clinical studies report that acute hyperglycaemia (induced by mixed meal or oral glucose) decreases arterial vascular function in healthy humans. Feeding, however, impacts autonomic output, blood pressure, and insulin and incretin secretion, which may each independently alter vascular function and obscure the effect of acute hyperglycaemia per se. Surprisingly, no studies have examined the acute effects of intravenous glucose-induced hyperglycaemia on both macro- and microvascular function while controlling plasma insulin concentrations. In this randomized study of healthy young adults, we compared macrovascular (i.e. brachial artery flow-mediated dilatation, carotid-femoral pulse wave velocity and post-ischaemic brachial artery flow velocity) and microvascular (heart and skeletal muscle perfusion by contrast-enhanced ultrasound) functional responses to euglycaemia and hyperglycaemia. Octreotide was infused throughout both protocols to prevent endogenous insulin release. Acute intravenous glucose-induced hyperglycaemia enhanced brachial artery flow-mediated dilatation (P = 0.004), increased skeletal muscle microvascular blood volume and flow (P = 0.001), and expanded cardiac muscle microvascular blood volume (P = 0.014). No measure of vascular function changed during octreotide-maintained euglycaemia. Our findings suggest that unlike meal-provoked acute hyperglycaemia, 4 h of intravenous glucose-induced hyperglycaemia enhances brachial artery flow-mediated dilatation, provokes cardiac and skeletal muscle microvascular function, and does not impair aortic stiffness. Previous findings of acute large artery vascular dysfunction during oral glucose or mixed meal ingestion may be due to differences in study populations and meal-induced humoral or neural factors beyond hyperglycaemia per se. (ClinicalTrials.gov number NCT03520569.).

Diastolic Cardiac Function Improvement by Liraglutide Is Mainly Body Weight Reduction Dependent but Independently Contributes to B-Type Natriuretic Peptide Reduction in Patients with Type 2 Diabetes with Preserved Ejection Fraction

OBJECTIVES

A single-arm prospective study was conducted among Japanese patients with type 2 diabetes having preserved ejection fraction. The aim was to investigate (1) whether liraglutide therapy could improve B-type natriuretic peptide (BNP) levels and diastolic cardiac function assessed by the E-wave to E' ratio (E/E') using transthoracic echocardiography (TTE), and (2) whether E/E' contributed to BNP improvement independent of bodyweight reduction (UMIN000005565).

METHODS

Patients with type 2 diabetes and left ventricular ejection fraction (LVEF) ≥ 40% without heart failure symptoms were enrolled, and daily injection with liraglutide (0.9 mg) was introduced. Cardiac functions were assessed by TTE before and after 26 weeks of liraglutide treatment. Diastolic cardiac function was defined as septal E/E' ≥ 13.0.

RESULTS

Thirty-one patients were analyzed. BNP and E/E' improved, with BNP levels declining from 36.8 ± 30.5 pg/mL to 26.3 ± 25.9 pg/mL (p = 0.0014) and E/E' dropping from 12.7 ± 4.7 to 11.0 ± 3.3 (p = 0.0376). The LVEF showed no significant changes. E/E' improved only in patients with E/E' ≥ 13.0. Favorable changes in E/E' were canceled when adjusted for body mass index (BMI). Multivariate linear regression analysis revealed that the left ventricular diastolic diameter and ∆E/E'/∆BMI contributed to ∆BNP/baseline BNP (p = 0.0075, R ² = 0.49264).

CONCLUSIONS

Liraglutide had favorable effects on BNP and E/E' but not on LVEF. E/E' improvement was only seen in patients with diastolic cardiac function. Body weight reduction affected the change of E/E'. The BMI-adjusted E/E' significantly contributed to the relative change of BNP. GLP-1 analog treatment could be considered a therapeutic option against diabetic diastolic cardiac dysfunction regardless of body weight. This trial is registered with the University Hospital Medical Information Network in Japan, with clinical trial registration number: UMIN000005565.

Hyperglycemia does not Inhibit Insulin's Effects on Microvascular Perfusion in Healthy Humans: A Randomized Crossover Study

Diabetes mellitus accelerates vascular disease through multiple biochemical pathways driven by hyperglycemia, with insulin resistance and/or hyperinsulinemia also contributing. Persons with diabetes mellitus experience premature large vessel and microvascular disease when compared to normoglycemic controls. Currently there is a paucity of clinical data identifying how acutely the vasculature responds to hyperglycemia and whether other physiologic factors (e.g., vasoactive hormones) contribute. To our knowledge, no prior studies have examined the dynamic effects of acute hyperglycemia on insulin-mediated actions on both micro- and macrovascular function in the same subjects. In this randomized crossover trial, healthy young adults underwent two infusion protocols designed to compare the effects of insulin infusion during euglycemia and hyperglycemia on micro- and macrovascular function. Both euglycemic- and hyperglycemic-hyperinsulinemia increased skeletal (but not cardiac) muscle microvascular blood volume (each p<0.02) and blood flow significantly (each p<0.04), and these increases did not differ between protocols. Hyperglycemic-hyperinsulinemia trended towards increased carotid-femoral pulse wave velocity (indicating increased aortic stiffness; p= 0.065 after Bonferroni adjustment), while euglycemic-hyperinsulinemia did not. There were no changes in post-ischemic flow velocity or brachial artery flow-mediated dilation during either protocol. Plasma endothelin-1 levels significantly decreased during both protocols (each p<0.02). In this study, acute hyperglycemia for 4 hours did not inhibit insulin's ability to increase skeletal muscle microvascular perfusion but did provoke a slight increase in aortic stiffness. Hyperglycemia also did not adversely affect myocardial microvascular perfusion or endothelial function or prevent the decline of endothelin-1 during insulin infusion.

GLP-1 and insulin regulation of skeletal and cardiac muscle microvascular perfusion in type 2 diabetes

Muscle microvasculature critically regulates skeletal and cardiac muscle health and function. It provides endothelial surface area for substrate exchange between the plasma compartment and the muscle interstitium. Insulin fine-tunes muscle microvascular perfusion to regulate its own action in muscle and oxygen and nutrient supplies to muscle. Specifically, insulin increases muscle microvascular perfusion, which results in increased delivery of insulin to the capillaries that bathe the muscle cells and then facilitate its own transendothelial transport to reach the muscle interstitium. In type 2 diabetes, muscle microvascular responses to insulin are blunted and there is capillary rarefaction. Both loss of capillary density and decreased insulin-mediated capillary recruitment contribute to a decreased endothelial surface area available for substrate exchange. Vasculature expresses abundant glucagon-like peptide 1 (GLP-1) receptors. GLP-1, in addition to its well-characterized glycemic actions, improves endothelial function, increases muscle microvascular perfusion, and stimulates angiogenesis. Importantly, these actions are preserved in the insulin resistant states. Thus, treatment of insulin resistant patients with GLP-1 receptor agonists may improve skeletal and cardiac muscle microvascular perfusion and increase muscle capillarization, leading to improved delivery of oxygen, nutrients, and hormones such as insulin to the myocytes. These actions of GLP-1 impact skeletal and cardiac muscle function and systems biology such as functional exercise capacity. Preclinical studies and clinical trials involving the use of GLP-1 receptor agonists have shown salutary cardiovascular effects and improved cardiovascular outcomes in type 2 diabetes mellitus. Future studies should further examine the different roles of GLP-1 in cardiac as well as skeletal muscle function.

Mechanistic Causes of Reduced Cardiorespiratory Fitness in Type 2 Diabetes

Type 2 diabetes (T2D) has been rising in prevalence in the United States and worldwide over the past few decades and contributes to significant morbidity and premature mortality, primarily due to cardiovascular disease (CVD). Cardiorespiratory fitness (CRF) is a modifiable cardiovascular (CV) risk factor in the general population and in people with T2D. Young people and adults with T2D have reduced CRF when compared with their peers without T2D who are similarly active and of similar body mass index. Furthermore, the impairment in CRF conferred by T2D is greater in women than in men. Various factors may contribute to this abnormality in people with T2D, including insulin resistance and mitochondrial, vascular, and cardiac dysfunction. As proof of concept that understanding the mediators of impaired CRF in T2D can inform intervention, we previously demonstrated that an insulin sensitizer improved CRF in adults with T2D. This review focuses on how contributing factors influence CRF and why they may be compromised in T2D. Functional exercise capacity is a measure of interrelated systems biology; as such, the contribution of derangement in each of these factors to T2D-mediated impairment in CRF is complex and varied. Therefore, successful approaches to improve CRF in T2D should be multifaceted and individually designed. The current status of this research and future directions are outlined.