Epicardial Fat Inflammation and GLP-1/GIP Receptor Analogs: Are we Shifting our Perspective?

Human epicardial adipose tissue (EAT) plays a crucial role in the development and progression of coronary artery disease, atrial fibrillation, and heart failure. Microscopically, EAT is composed of adipocytes, nerve tissues, inflammatory, stromovascular, and immune cells. Epicardial adipose tissue is a white adipose tissue, albeit it also has brown fat-like or beige fat-like features. No muscle fascia divides EAT and myocardium; this allows a direct interaction and crosstalk between the epicardial fat and the myocardium. Thus, it might be a therapeutic target for pharmaceutical compounds acting on G-protein-coupled receptors, such as those for glucose-dependent insulinotropic polypeptide (GIP), glucagon (GCG), and glucagon-like peptide-1 (GLP-1), whose selective stimulation with innovative drugs has demonstrated beneficial cardiovascular effects. The precise mechanism of these novel drugs and their tissue and cellular target(s) need to be better understood. We evaluate whether human EAT expresses GIP, GCG, and GLP-1 receptors and whether their presence is related to EAT transcriptome. We also investigated protein expression and cell-type localization specifically for GIP receptor (GIPR) and glucagon receptor (GCGR). Epicardial adipose tissue samples were collected from 33 patients affected by cardiovascular diseases undergoing open heart surgery (90.9% males, age 67.2 ± 10.5 years mean ± SD). Microarray and immunohistochemistry analyses were performed. Microarray analysis showed that GIPR and GCGR messenger ribonucleic acids (mRNAs) are expressed in EAT, beyond confirming the previously found GLP-1 [3776 ± 1377 arbitrary unit (A.U.), 17.77 ± 14.91 A.U., and 3.41 ± 2.27 A.U., respectively]. The immunohistochemical analysis consistently indicates that GIPR and GCGR are expressed in EAT, mainly in macrophages, isolated, and in crown-like structures. In contrast, only some mature adipocytes of different sizes showed cytoplasmic immunostaining, similar to endothelial cells and pericytes in the capillaries and pre-capillary vascular structures. Notably, EAT GIPR is statistically associated with the low expression of genes involved in free fatty acid (FFA) oxidation and transport and those promoting FFA biosynthesis and adipogenesis (P < 0.01). Epicardial adipose tissue GCGR, in turn, is related to genes involved in FFA transport, mitochondrial fatty acid oxidation, and white-to-brown adipocyte differentiation, in addition to genes involved in the reduction of fatty acid biosynthesis and adipogenesis (P < 0.01). Having reported the expression of the GLP-1 receptor previously, here, we showed that GIPR and GCGR similarly present at mRNA and protein levels in human EAT, particularly in macrophages and partially adipocytes, suggesting these G-protein-coupled receptors as pharmacological targets on the ongoing innovative drugs, which seem cardiometabolically healthy well beyond their effects on glucose and body weight.

BackgroundAlthough an increased epicardial adipose tissue (EAT) volume around the left atrium (LA) is related to the atrial fibrillation (AF) burden, the role of EAT inflammation in AF is unclear. We investigated the association between AF and inflammation of the EAT around the LA. MethodsWe retrospectively identified regions of EAT around the LA and measured the density of these areas using computed tomography (CT). ResultsA total of 32 patients who underwent their first catheter ablation for paroxysmal AF (PAF) were enrolled (mean age 62.5±11.1 years). Patients without a history of AF (n=32), but who underwent cardiac CT and were matched by age, sex, and metabolic risk factors, were enrolled in the control group (62.2±12.1 years). The mean EAT density around the LA was significantly higher in the PAF group than in the control group (−108.1±6.7 vs. −111.6±5.5 Hounsfield units; p=0.02), while the densities of subcutaneous adipose tissue (SAT) in the abdomen and thorax did not differ between the two groups. In a multiple logistic regression analysis, a higher EAT density was significantly associated with the presence of PAF after adjusting for other risk factors (odds ratio: 1.25; 95% confidence interval: 1.08–1.45, p=0.003). ConclusionsThis study supports the hypothesis that inflammation of EAT around the LA, but not SAT, is related to the presence of PAF.

The epicardial adipose tissue (EAT) serves in physiological conditions as a mechanical and thermal myocardial protective layer, as well as a readily available lipid-storage unit. In pathological conditions, EAT expansion becomes deleterious and is currently recognized as an independent risk factor for the progression of cardiovascular diseases. The EAT phenotypic shift from protective to pro-inflammatory/pro-oxidant is facilitated by the presence of metabolic diseases (obesity, metabolic syndrome, and diabetes), which further increase its expansion and dysregulation, favor the occurrence of complications (mainly atrial fibrillation), and promote progression towards heart failure. Glucagon-like peptide-1 (GLP-1) receptor agonists are novel antidiabetic medications belonging to the incretin class that have demonstrated efficacy beyond glycemic control, in terms of weight reduction and cardiorenal protection in patients with type 2 diabetes mellitus. The GLP-1 receptors and glucose-dependent insulinotropic polypeptide (GIP) receptors are expressed in the human EAT and are targeted by an increasing number of pharmacological agonists, with pleiotropic protective effects on EAT structure and function. Herein we review the literature characterizing the benefits of GLP-1 and GIP receptors activation by single and dual agonists with particular emphasis on their effects on EAT and highlight the role of incretin-based therapy for the management of cardiometabolic pathologies.

The role of vitamin D deficiency in coronary artery disease (CAD) progression is uncertain. Chronic inflammation in epicardial adipose tissue (EAT) has been implicated in the pathogenesis of CAD. However, the molecular mechanism underlying vitamin D deficiency-enhanced inflammation in the EAT of diseased coronary arteries remains unknown. We examined a mechanistic link between 1,25-dihydroxyvitamin D-mediated suppression of nuclear factor-κB (NF-κB) transporter, karyopherin α4 (KPNA4) expression and NF-κB activation in preadipocytes. Furthermore, we determined whether vitamin D deficiency accelerates CAD progression by increasing KPNA4 and nuclear NF-κB levels in EAT. Nuclear protein levels were detected by immunofluorescence and Western blot. Exogenous KPNA4 was transported into cells by a transfection approach and constituted lentiviral vector. Swine were administered vitamin D-deficient or vitamin D-sufficient hypercholesterolemic diet. After 1 year, the histopathology of coronary arteries and nuclear protein expression of EAT were assessed. 1,25-dihydroxyvitamin D inhibited NF-κB activation and reduced KPNA4 levels through increased vitamin D receptor expression. Exogenous KPNA4 rescued 1,25-dihydroxyvitamin D-dependent suppression of NF-κB nuclear translocation and activation. Vitamin D deficiency caused extensive CAD progression and advanced atherosclerotic plaques, which are linked to increased KPNA4 and nuclear NF-κB levels in the EAT. 1,25-dihydroxyvitamin D attenuates NF-κB activation by targeting KPNA4. Vitamin D deficiency accelerates CAD progression at least, in part, through enhanced chronic inflammation of EAT by upregulation of KPNA4, which enhances NF-κB activation. These novel findings provide mechanistic evidence that vitamin D supplementation could be beneficial for the prevention and treatment of CAD.

The regional distribution of adipose tissue (AT) is a major determinant of metabolic and cardiovascular diseases. The mass of fat in the visceral area associates independently of obesity with the development and progression of cardiovascular diseases in a series of clinical and epidemiological studies.1 This led to the concept of a pathophysiological link between abdominal obesity and metabolic syndrome. More recently, fat depots localized around the heart, highly variable among individuals, were proposed to contribute to the pathogenesis of coronaropathy independently of other visceral depots (ie, in the omental and mesenteric area).2,3 The study by Greif et al3a in this issue of Arteriosclerosis, Thrombosis, and Vascular Biology highlights the association between pericardial adipose tissue (PAT) and the number of atherosclerotic plaques evaluated concomitantly by Dual source CT scan. This measurement was qualitatively interpretable in 264 consecutive patients with a large range of age, a normal or moderately increased body mass index (BMI), and no a priori coronary disease. An estimated volume of pericardial fat more than 300 cm3 provided an incremental value for the presence of coronary atherosclerosis (odds ratio 4.1) independently of well known risk factors (hyperglycemia or diabetes, hypercholesterolemia, hypertension, and smoking). Ninety-five percent of patients with PAT volume >300 cm3 had one or more atherosclerotic plaques by ROC estimation. In univariate statistical analysis, PAT …

In Covid-19, variations in fasting blood glucose are considered a distinct risk element for a bad prognosis and outcome in Covid-19 patients. Tirazepatide (TZT), a dual glucagon-like peptide-1 (GLP-1)and glucose-dependent insulinotropic polypeptide (GIP) receptor agonist may be effective in managing Covid-19-induced hyperglycemia in diabetic and non-diabetic patients. The beneficial effect of TZT in T2DM and obesity is related to direct activation of GIP and GLP-1 receptors with subsequent improvement of insulin sensitivity and reduction of body weight. TZT improves endothelial dysfunction (ED) and associated inflammatory changes through modulation of glucose homeostasis, insulin sensitivity, and pro-inflammatory biomarkers release. TZT, through activation of the GLP-1 receptor, may produce beneficial effects against Covid-19 severity since GLP-1 receptor agonists (GLP-1RAs) have anti-inflammatory and pulmoprotective implications in Covid-19. Therefore, GLP-1RAs could effectively treat severely affected Covid-19 diabetic and non-diabetic patients. Notably, using GLP-1RAs in T2DM patients prevents glucose variability, a common finding in Covid-19 patients. Therefore, GLP-1RAs like TZT could be a therapeutic strategy in T2DM patients with Covid-19 to prevent glucose variability-induced complications. In Covid-19, the inflammatory signaling pathways are highly activated, resulting in hyperinflammation. GLP-1RAs reduce inflammatory biomarkers like IL-6, CRP, and ferritin in Covid-19 patients. Therefore, GLP-1RAs like TZ may be effective in Covid-19 patients by reducing the inflammatory burden. The anti-obesogenic effect of TZT may reduce Covid-19 severity by ameliorating body weight and adiposity. Furthermore, Covid-19 may induce substantial alterations in gut microbiota. GLP-1RA preserves gut microbiota and prevents intestinal dysbiosis. Herein, TZT, like other GLP-1RA, may attenuate Covid-19-induced gut microbiota alterations and, by this mechanism, may mitigate intestinal inflammation and systemic complications in Covid-19 patients with either T2DM or obesity. As opposed to that, glucose-dependent insulinotropic polypeptide (GIP) was reduced in obese and T2DM patients. However, activation of GIP-1R by TZT in T2DM patients improves glucose homeostasis. Thus, TZT, through activation of both GIP and GLP-1, may reduce obesity-mediated inflammation. In Covid-19, GIP response to the meal is impaired, leading to postprandial hyperglycemia and abnormal glucose homeostasis. Therefore, using TZT in severely affected Covid-19 patients may prevent the development of glucose variability and hyperglycemia-induced oxidative stress. Moreover, exaggerated inflammatory disorders in Covid-19 due to the release of pro-inflammatory cytokines like IL-1β, IL-6, and TNF-α may lead to systemic inflammation and cytokine storm development. Besides, GIP-1 inhibits expression of IL-1β, IL-6, MCP-1, chemokines and TNF-α. Therefore, using GIP-1RA like TZT may inhibit the onset of inflammatory disorders in severely affected Covid-19 patients. In conclusion, TZT, through activation of GLP-1 and GIP receptors, may prevent SARS-CoV-2-induced hyperinflammation and glucose variability in diabetic and non-diabetic patients.

Effects of vitamin K2 and D3 supplementation on epicardial adipose tissue and systemic inflammation: A substudy of the AVADEC trial.

Dietary patterns influence epicardial adipose tissue fatty acid composition and inflammatory gene expression in the Ossabaw pig

the physiological roles of human epicardial adipose tissue (EAT) are not well defined because this strategically located white adipose tissue (WAT) depot is difficult to access and study, and most of the information about it comes from humans with severe cardiac diseases undergoing open heart

Incretin-based therapies are highly successful in combatting obesity and type 2 diabetes1. Yet both activation and inhibition of the glucose-dependent insulinotropic polypeptide (GIP) receptor (GIPR) in combination with glucagon-like peptide-1 (GLP-1) receptor (GLP-1R) activation have resulted in similar clinical outcomes, as demonstrated by the GIPR–GLP-1R co-agonist tirzepatide2 and AMG-133 (ref. 3) combining GIPR antagonism with GLP-1R agonism. This underlines the importance of a better understanding of the GIP system. Here we show the necessity of β-arrestin recruitment for GIPR function, by combining in vitro pharmacological characterization of 47 GIPR variants with burden testing of clinical phenotypes and in vivo studies. Burden testing of variants with distinct ligand-binding capacity, Gs activation (cyclic adenosine monophosphate production) and β-arrestin 2 recruitment and internalization shows that unlike variants solely impaired in Gs signalling, variants impaired in both Gs and β-arrestin 2 recruitment contribute to lower adiposity-related traits. Endosomal Gs-mediated signalling of the variants shows a β-arrestin dependency and genetic ablation of β-arrestin 2 impairs cyclic adenosine monophosphate production and decreases GIP efficacy on glucose control in male mice. This study highlights a crucial impact of β-arrestins in regulating GIPR signalling and overall preservation of biological activity that may facilitate new developments in therapeutic targeting of the GIPR system.

Glucose-dependent insulinotropic polypeptide (GIP) is a gastrointestinal hormone that exerts insulinotropic and growth and survival effects on pancreatic β-cells. Additionally, there is increasing evidence supporting an important role for GIP in the regulation of adipocyte metabolism. In the current study we examined the molecular mechanisms involved in the regulation of GIP receptor (GIPR) expression in 3T3-L1 cells. GIP acted synergistically with insulin to increase neutral lipid accumulation during progression of 3T3-L1 preadipocytes to the adipocyte phenotype. Both GIPR protein and mRNA expression increased during 3T3-L1 cell differentiation, and this increase was associated with upregulation of nuclear levels of sterol response element binding protein 1c (SREBP-1c) and peroxisome proliferator-activated receptor γ (PPARγ), as well as acetylation of histones H3/H4. The PPARγ receptor agonists LY171883 and rosiglitazone increased GIPR expression in differentiated 3T3-L1 adipocytes, whereas the antagonist GW9662 ablated expression. Additionally, both PPARγ and acetylated histones H3/H4 were shown to bind to a region of the GIPR promoter containing the peroxisome proliferator response element (PPRE). Knockdown of PPARγ in differentiated 3T3-L1 adipocytes, using RNA interference, reduced GIPR expression, supporting a functional regulatory role. Taken together, these studies show that GIP and insulin act in a synergistic manner on 3T3-L1 cell development and that adipocyte GIPR expression is upregulated through a mechanism involving interactions between PPARγ and a GIPR promoter region containing an acetylated histone region.

Effect of Type 2 Diabetes Mellitus on Epicardial Adipose Tissue Volume and Coronary Vasomotor Function

Inflammatory accumulation in epicardial adipose tissue (EAT) may influence the formation and development of coronary artery disease (CAD). EAT macrophages exhibit M1 polarization and the secretion of a large number of inflammatory factors in CAD patients. Emerging data demonstrate that Krüppel-like factor-7 (KLF7), contributes to the regulation of adipocyte differentiation and the secretion of adipose tissue inflammation. However, the function of KLF7 in EAT inflammation still remains to be uncovered. This study aims to investigate the role of KLF7 in macrophage activation in EAT. The levels of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in cell supernatant were measured by enzyme-linked immunosorbent assay (ELISA). The mRNA expression levels were measured by Real Time-PCR. The protein expression level was detected by Western blot. The expression of inflammatory factors and KLF7 were markedly increased in CAD EAT than non-CAD EAT. KLF7 is highly expressed in human THP-1-derived macrophages induced by inflammatory stimuli, such as LPS. The knockdown of KLF7 inhibited the release of inflammatory factors and significantly decreased the expression of KLF7 in human THP-1-derived macrophages stimulated by LPS. Moreover, transfection with KLF7-siRNA caused the marked inhibition of LPS-induced phosphorylation of JNK-MAPKs and also suppressed the levels of p-p65 and inhibited the activation of p-IκBα. Taken together, these results indicate that KLF7 enhances macrophage activation, mediated by JNK-NF-κB signaling pathways in EAT. This suggests that KLF7 may be a potential therapeutic target for cardiovascular diseases such as CAD.

BackgroundInflammation in epicardial adipose tissue (EAT) may contribute to coronary atherosclerosis. Myocardial bridge is a congenital anomaly in which the left anterior descending coronary artery takes a “tunneled” course under a bridge of myocardium: while atherosclerosis develops in the proximal left anterior descending coronary artery, the bridged portion is spared, highlighting the possibility that geographic separation from inflamed EAT is protective. We tested the hypothesis that inflammation in EAT was related to atherosclerosis by comparing EAT from proximal and bridge depots in individuals with myocardial bridge and varying degrees of atherosclerotic plaque.Methods and ResultsMaximal plaque burden was quantified by intravascular ultrasound, and inflammation was quantified by pericoronary EAT signal attenuation (pericoronary adipose tissue attenuation) from cardiac computed tomography scans. EAT overlying the proximal left anterior descending coronary artery and myocardial bridge was harvested for measurement of mRNA and microRNA (miRNA) using custom chips by Nanostring; inflammatory cytokines were measured in tissue culture supernatants. Pericoronary adipose tissue attenuation was increased, indicating inflammation, in proximal versus bridge EAT, in proportion to atherosclerotic plaque. Individuals with moderate‐high versus low plaque burden exhibited greater expression of inflammation and hypoxia genes, and lower expression of adipogenesis genes. Comparison of gene expression in proximal versus bridge depots revealed differences only in participants with moderate‐high plaque: inflammation was higher in proximal and adipogenesis lower in bridge EAT. Secreted inflammatory cytokines tended to be higher in proximal EAT. Hypoxia‐inducible factor 1a was highly associated with inflammatory gene expression. Seven miRNAs were differentially expressed by depot: 3192‐5P, 518D‐3P, and 532‐5P were upregulated in proximal EAT, whereas miR 630, 575, 16‐5P, and 320E were upregulated in bridge EAT. miR 630 correlated directly with plaque burden and inversely with adipogenesis genes. miR 3192‐5P, 518D‐3P, and 532‐5P correlated inversely with hypoxia/oxidative stress, peroxisome proliferator‐activated receptor gamma coactivator 1‐alpha (PCG1a), adipogenesis, and angiogenesis genes.ConclusionsInflammation is specifically elevated in EAT overlying atherosclerotic plaque, suggesting that EAT inflammation is caused by atherogenic molecular signals, including hypoxia‐inducible factor 1a and/or miRNAs in an “inside‐to‐out” relationship. Adipogenesis was suppressed in the bridge EAT, but only in the presence of atherosclerotic plaque, supporting cross talk between the vasculature and EAT. miR 630 in EAT, expressed differentially according to burden of atherosclerotic plaque, and 3 other miRNAs appear to inhibit key genes related to adipogenesis, angiogenesis, hypoxia/oxidative stress, and thermogenesis in EAT, highlighting a role for miRNA in mediating cross talk between the coronary vasculature and EAT.

Epicardial adipose tissue (EAT) is the visceral fat depot of the heart. Inflammation of EAT is thought to contribute to coronary artery disease (CAD). Therefore, we hypothesized that the EAT of patients with CAD would have increased inflammatory gene expression compared with controls without CAD. Cardiac surgery patients with (n = 13) or without CAD (n = 13) were consented, and samples of EAT and subcutaneous adipose tissue (SAT) were obtained. Transcriptomic analysis was performed using Affymetrix Human Gene 1.0 ST arrays. Differential expression was defined as a 1.5-fold change (ANOVA P < 0.05). Six hundred ninety-three genes were differentially expressed between SAT and EAT in controls and 805 in cases. Expression of 326 genes was different between EAT of cases and controls; expression of 14 genes was increased in cases, while 312 were increased in controls. Quantitative reverse transcription PCR confirmed that there was no difference in expression of CCL2, CCR2, TNF-α, IL-6, IL-8, and PAI1 between groups. Immunohistochemistry showed more macrophages in EAT than SAT, but there was no difference in their number or activation state between groups. In contrast to prior studies, we did not find increased inflammatory gene expression in the EAT of patients with CAD. We conclude that the specific adipose tissue depot, rather than CAD status, is responsible for the majority of differential gene expression.