Effects of GLP-1 Infusion Upon Whole-body Glucose Uptake and Skeletal Muscle Perfusion During Fed-state in Older Men

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.

Skeletal Muscle Injury in Chronic Kidney Disease-From Histologic Changes to Molecular Mechanisms and to Novel Therapies

Chronic kidney disease (CKD) is associated with significant reductions in lean body mass and in the mass of various tissues, including skeletal muscle, which causes fatigue and contributes to high mortality rates. In CKD, the cellular protein turnover is imbalanced, with protein degradation outweighing protein synthesis, leading to a loss of protein and cell mass, which impairs tissue function. As CKD itself, skeletal muscle wasting, or sarcopenia, can have various origins and causes, and both CKD and sarcopenia share common risk factors, such as diabetes, obesity, and age. While these pathologies together with reduced physical performance and malnutrition contribute to muscle loss, they cannot explain all features of CKD-associated sarcopenia. Metabolic acidosis, systemic inflammation, insulin resistance and the accumulation of uremic toxins have been identified as additional factors that occur in CKD and that can contribute to sarcopenia. Here, we discuss the elevation of systemic phosphate levels, also called hyperphosphatemia, and the imbalance in the endocrine regulators of phosphate metabolism as another CKD-associated pathology that can directly and indirectly harm skeletal muscle tissue. To identify causes, affected cell types, and the mechanisms of sarcopenia and thereby novel targets for therapeutic interventions, it is important to first characterize the precise pathologic changes on molecular, cellular, and histologic levels, and to do so in CKD patients as well as in animal models of CKD, which we describe here in detail. We also discuss the currently known pathomechanisms and therapeutic approaches of CKD-associated sarcopenia, as well as the effects of hyperphosphatemia and the novel drug targets it could provide to protect skeletal muscle in CKD.

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.

Oral semaglutide improves body composition and preserves lean mass in patients with type 2 diabetes: a 26-week prospective real-life study

Background

Oral semaglutide is the first glucagon-like peptide-1 receptor agonist (GLP-1RA) designed for oral administration; it offers a promising opportunity to facilitate an early approach to Type 2 Diabetes (T2D). The study aimed to evaluate, in a real-life setting, the effects of oral semaglutide on the body composition of patients with T2D after 26 weeks of therapy.

Methods

Thirty-two patients with T2D were evaluated at baseline (T0) and after three (T3) and six (T6) months of therapy with oral semaglutide. At each time point, body composition was assessed using a phase sensitive bioimpedance analyzer. Clinical, anthropometric and laboratory parameters, and the main biometric surrogates of liver steatosis and fibrosis, were also analyzed and compared.

Results

A significant and early reduction in anthropometric and glucometabolic parameters, alanine aminotransferase, Fatty Liver Index, and Fat Mass was observed. Visceral Adipose Tissue (VAT) decreased, while Fat Free Mass and Skeletal Muscle Mass (SMM) were preserved during therapy, resulting in a beneficial increase in the SMM/VAT ratio. Finally, an overall improvement in body fluid distribution was observed.

Conclusion

Our real-world data confirm the clinical efficacy of oral semaglutide and highlight its ability to improve the nutritional status of patients with T2D.

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.

Contrast-enhanced ultrasound repeatability for the measurement of skeletal muscle microvascular blood flow

NEW FINDINGS

What is the central question of this study? Contrast-enhanced ultrasound (CEUS) can be used to directly assess skeletal muscle perfusion but its day-to-day repeatability over time has not yet been validated: is CEUS a repeatable method for the measurement of skeletal muscle microvascular blood flow (MBF) at rest and in response to exercise, across independent assessment sessions? What is the main finding and its importance? A strong agreement between CEUS MBF measures across sessions suggests it is a repeatable method for assessing skeletal muscle perfusion over time. This validation provides confidence for incorporating these measures into longitudinal studies such as a chronic intervention or disease progression to gain further knowledge of skeletal muscle microvascular function.

ABSTRACT

Contrast-enhanced ultrasound (CEUS) can be used to directly assess skeletal muscle perfusion. However, its repeatability over time has not yet been validated and therefore its use in longitudinal measures (i.e., exploring the impact of a chronic intervention or disease progression) is limited. This study aimed to determine the repeatability of CEUS for the measurement of skeletal muscle microvascular blood flow (MBF) at baseline and in response to exercise, across independent assessment sessions. Ten healthy volunteers (five female; 30 ± 6 years) had CEUS of the right vastus lateralis recorded in two separate sessions, 14 days apart. Measurements were taken at baseline, during an isometric leg extension and during recovery. Acoustic intensity data from a region of interest were plotted as a replenishment curve to obtain blood volume (A) and flow velocity (β) values from a one-phase association non-linear regression of mean tissue echogenicity. Linear regression and Bland-Altman analyses of A and β values were performed, with significance assumed as P < 0.05. Strong positive correlations were observed across sessions for all A and β values (both P < 0.0001). Bland-Altman analysis showed a bias (SD) of -0.013 ± 1.24 for A and -0.014 ± 0.31 for β. A bias of 0.201 ± 0.770 at baseline, 0.527 ± 1.29 during contraction and -0.203 ± 1.29 at recovery was observed for A, and -0.0328 ± 0.0853 (baseline), -0.0446 ± 0.206 (contraction) and 0.0382 ± 0.233 (recovery) for β. A strong agreement between CEUS MBF measures across independent sessions suggests it to be a repeatable method for assessing skeletal muscle perfusion over time, and therefore facilitates wider use in longitudinal studies.