Evaluation of glucagon-like peptide-1 receptor expression in nondiabetic and diabetic atherosclerotic mice using PET tracer 68Ga-NODAGA-exendin-4

Uncovering atherosclerotic cardiovascular disease by PET imaging

Assessing atherosclerosis severity is essential for precise patient stratification. Specifically, there is a need to identify patients with residual inflammation because these patients remain at high risk of cardiovascular events despite optimal management of cardiovascular risk factors. Molecular imaging techniques, such as PET, can have an essential role in this context. PET imaging can indicate tissue-based disease status, detect early molecular changes and provide whole-body information. Advances in molecular biology and bioinformatics continue to help to decipher the complex pathogenesis of atherosclerosis and inform the development of imaging tracers. Concomitant advances in tracer synthesis methods and PET imaging technology provide future possibilities for atherosclerosis imaging. In this Review, we summarize the latest developments in PET imaging techniques and technologies for assessment of atherosclerotic cardiovascular disease and discuss the relationship between imaging readouts and transcriptomics-based plaque phenotyping.

GLP-1 increases preingestive satiation via hypothalamic circuits in mice and humans

Glucagon-like peptide-1 (GLP-1) receptor agonists (GLP-1RAs) are effective antiobesity drugs. However, the precise central mechanisms of GLP-1RAs remain elusive. We administered GLP-1RAs to patients with obesity and observed a heightened sense of preingestive satiation. Analysis of human and mouse brain samples pinpointed GLP-1 receptor (GLP-1R) neurons in the dorsomedial hypothalamus (DMH) as candidates for encoding preingestive satiation. Optogenetic manipulation of DMHGLP-1R neurons caused satiation. Calcium imaging demonstrated that these neurons are actively involved in encoding preingestive satiation. GLP-1RA administration increased the activity of DMHGLP-1R neurons selectively during eating behavior. We further identified that an intricate interplay between DMHGLP-1R neurons and neuropeptide Y/agouti-related peptide neurons of the arcuate nucleus (ARCNPY/AgRP neurons) occurs to regulate food intake. Our findings reveal a hypothalamic mechanism through which GLP-1RAs control preingestive satiation, offering previously unexplored neural targets for obesity and metabolic diseases.

Comparative Analysis of the Anti-Inflammatory Effects of Liraglutide and Dulaglutide

Inflammation plays a pathophysiological role in atherosclerosis and its clinical consequences. In addition to glycemic control, glucagon-like peptide-1 receptor agonists (GLP-1RAs) are of wide concern for cardioprotective effects. The structure, half-life, homology, and clinical efficacy of GLP-1RAs exhibit remarkable disparity. Several studies have compared the disparities in anti-inflammatory effects between daily and weekly GLP-1RAs. This study aimed to compare the similarities and differences between liraglutide and dulaglutide in terms of inhibiting atherosclerotic inflammation and improving co-cultured endothelial cell function. The expression of inflammation markers was examined by immunofluorescence, Western blotting, and real-time PCR. The tube-forming ability of endothelial cells was tested on Matrigel. The results verify that 10/50/100 nmol/L liraglutide and 100 nmol/L dulaglutide markedly suppressed the expression of inflammatory factors in LPS-induced atherosclerosis after 24 and 72 hours, respectively. Moreover, they promoted the polarization of M1 macrophages toward the M2 phenotype and improved the function of co-cultured endothelial cells. Both liraglutide and dulaglutide ameliorate atherosclerosis development. The difference between the two resided in the extended intervention duration required to observe the effect of dulaglutide, and liraglutide demonstrated a superior dose-dependent manner. We provide a potential strategy to understand the dynamics of drug action and possible timing administration.

Exenatide regulates Th17/Treg balance via PI3K/Akt/FoxO1 pathway in db/db mice

BACKGROUND

The T helper 17 (Th17)/T regulatory (Treg) cell imbalance is involved in the course of obesity and type 2 diabetes mellitus (T2DM). In the current study, the exact role of glucagon-like peptide-1 receptor agonist (GLP-1RA) exenatide on regulating the Th17/Treg balance and the underlying molecular mechanisms are investigated in obese diabetic mice model.

METHODS

Metabolic parameters were monitored in db/db mice treated with/without exenatide during 8-week study period. The frequencies of Th17 and Treg cells from peripheral blood and pancreas in db/db mice were assessed. The phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/Forkhead box O1 (FoxO1) pathway in Th17 and Treg cells from the spleens of male C57BL/6J mice was detected by western blotting. In addition, the expression of glucagon-like peptide-1 receptor (GLP-1R) in peripheral blood mononuclear cells (PBMCs) of male C57BL/6J mice was analyzed.

RESULTS

Exenatide treatment improved β-cell function and insulitis in addition to glucose, insulin sensitivity and weight. Increased Th17 and decreased Treg cells in peripheral blood were present as diabetes progressed while exenatide corrected this imbalance. Progressive IL-17 + T cell infiltration of pancreatic islets was alleviated by exenatide intervention. In vitro study showed no significant difference in the level of GLP-1R expression in PBMCs between control and palmitate (PA) groups. In addition, PA could promote Th17 but suppress Treg differentiation along with down-regulating the phosphorylation of PI3K/Akt/FoxO1, which was reversed by exenatide intervention. FoxO1 inhibitor AS1842856 could abrogate all these effects of exenatide against lipid stress.

CONCLUSIONS

Exenatide could restore systemic Th17/Treg balance via regulating FoxO1 pathway with the progression of diabetes in db/db mice. The protection of pancreatic β-cell function may be partially mediated by inhibiting Th17 cell infiltration into pancreatic islets, and the resultant alleviation of islet inflammation.

Exploiting Glutamine Consumption in Atherosclerotic Lesions by Positron Emission Tomography Tracer (2S,4R)-4-18F-Fluoroglutamine

Increased glutamine metabolism by macrophages is associated with development of atherosclerotic lesions. Positron emission tomography/computed tomography (PET/CT) with a glutamine analog (2S,4R)-4-¹⁸F-fluoroglutamine (¹⁸F-FGln) allows quantification of glutamine consumption in vivo. Here, we investigated uptake of ¹⁸F-FGln by atherosclerotic lesions in mice and compared the results with those obtained using the glucose analog 2-deoxy-2-¹⁸F-fluoro-D-glucose (¹⁸F-FDG). Uptake of ¹⁸F-FGln and ¹⁸F-FDG by healthy control mice (C57BL/6JRj) and atherosclerotic low-density lipoprotein receptor-deficient mice expressing only apolipoprotein B100 (LDLR^−/−ApoB^100/100) was investigated. The mice were injected intravenously with ¹⁸F-FGln or ¹⁸F-FDG for in vivo PET/CT imaging. After sacrifice at 70 minutes post-injection, tracer uptake was analyzed by gamma counting of excised tissues and by autoradiography of aorta cryosections, together with histological and immunohistochemical analyses. We found that myocardial uptake of ¹⁸F-FGln was low. PET/CT detected lesions in the aortic arch, with a target-to-background ratio (SUV_max, aortic arch/SUV_mean, blood) of 1.95 ± 0.42 (mean ± standard deviation). Gamma counting revealed that aortic uptake of ¹⁸F-FGln by LDLR^−/−ApoB^100/100 mice (standardized uptake value [SUV], 0.35 ± 0.06) was significantly higher than that by healthy controls (0.20 ± 0.08, P = 0.03). More detailed analysis by autoradiography revealed that the plaque-to-healthy vessel wall ratio of ¹⁸F-FGln (2.90 ± 0.42) was significantly higher than that of ¹⁸F-FDG (1.93 ± 0.22, P = 0.004). Immunohistochemical staining confirmed that ¹⁸F-FGln uptake in plaques co-localized with glutamine transporter SLC7A7-positive macrophages. Collectively these data show that the ¹⁸F-FGln PET tracer detects inflamed atherosclerotic lesions. Thus, exploiting glutamine consumption using ¹⁸F-FGln PET may have translational relevance for studying atherosclerotic inflammation.

GLP-1 receptor agonists (GLP-1RAs): cardiovascular actions and therapeutic potential

Type 2 diabetes mellitus (T2DM) is closely associated with cardiovascular diseases (CVD), including atherosclerosis, hypertension and heart failure. Some anti-diabetic medications are linked with an increased risk of weight gain or hypoglycemia which may reduce the efficacy of the intended anti-hyperglycemic effects of these therapies. The recently developed receptor agonists for glucagon-like peptide-1 (GLP-1RAs), stimulate insulin secretion and reduce glycated hemoglobin levels without having side effects such as weight gain and hypoglycemia. In addition, GLP1-RAs demonstrate numerous cardiovascular protective effects in subjects with or without diabetes. There have been several cardiovascular outcomes trials (CVOTs) involving GLP-1RAs, which have supported the overall cardiovascular benefits of these drugs. GLP1-RAs lower plasma lipid levels and lower blood pressure (BP), both of which contribute to a reduction of atherosclerosis and reduced CVD. GLP-1R is expressed in multiple cardiovascular cell types such as monocyte/macrophages, smooth muscle cells, endothelial cells, and cardiomyocytes. Recent studies have indicated that the protective properties against endothelial dysfunction, anti-inflammatory effects on macrophages and the anti-proliferative action on smooth muscle cells may contribute to atheroprotection through GLP-1R signaling. In the present review, we describe the cardiovascular effects and underlying molecular mechanisms of action of GLP-1RAs in CVOTs, animal models and cultured cells, and address how these findings have transformed our understanding of the pharmacotherapy of T2DM and the prevention of CVD.