Brown Adipose Tissue: A New Potential Target for Glucagon-like Peptide 1 Receptor Agonists in the Treatment of Obesity

Energy balance and obesity: the emerging role of glucagon like peptide-1 receptor agonists

PURPOSE OF REVIEW

With obesity affecting over one billion people globally, understanding and managing this complex condition is more crucial than ever. This review explores the emerging role of GLP-1 receptor agonists (GLP-1RA) in weight management, focusing on their impact on energy balance. It highlights the necessity of this investigation due to the limited knowledge on both the short-term and long-term implications of GLP-1RA on energy expenditure (EE) and energy intake (EI).

RECENT FINDINGS

GLP-1RA, such as liraglutide and semaglutide, have shown significant efficacy in promoting weight loss by reducing appetite, cravings and consequently, EI. Newer medications such as tirzepatide have demonstrated even greater weight loss success. Emerging evidence also suggests potential effects on EE, which could explain the greater weight loss success achieved with GLP-1 RA rather than typical lifestyle changes. However, comprehensive data on the total impact of these drugs on energy balance remain limited.

SUMMARY

The findings underscore the promising role of GLP-1RA in obesity management, particularly through mechanisms influencing both EI and EE. Future research should focus on systematically measuring all components of energy balance to fully elucidate the mechanisms of GLP-1RA and optimize their therapeutic use for personalized medicine.

Adipose Tissue: A Novel Target of the Incretin Axis? A Paradigm Shift in Obesity-Linked Insulin Resistance

Adipose tissue (AT) represents a plastic organ that can undergo significant remodeling in response to metabolic demands. With its numerous checkpoints, the incretin system seems to play a significant role in controlling glucose homeostasis and energy balance. The importance of the incretin hormones, namely the glucagon-like peptide-1 (GLP-1) and the glucose-dependent insulinotropic peptide (GIP), in controlling the function of adipose cells has been brought to light by recent studies. Notably, a "paradigm shift" in reevaluating the role of the incretin system in AT as a potential target to treat obesity-linked metabolic disorders resulted from the demonstration that a disruption of the GIP and GLP-1 signaling axis in fat is associated with adiposity-induced insulin-resistance (IR) and/or type 2 diabetes mellitus (T2D). We will briefly discuss the (patho)physiological functions of GLP-1 and GIP signaling in AT in this review, emphasizing their potential impacts on lipid storage, adipogenesis, glucose metabolism and inflammation. We will also address the conundrum with the perturbation of the incretin axis in white or brown fat tissue and the emergence of metabolic disorders. In order to reduce or avoid adiposity-related metabolic complications, we will finally go over a potential scientific rationale for suggesting AT as a novel target for GLP-1 and GIP receptor agonists and co-agonists.

Do anti-obesity medical treatments have a direct effect on adipose tissue?

During the past years, several drugs have been developed for the treatment of obesity. Some are already used in clinical practice: orlistat, GLP-1 receptor agonists (RA), GLP-1/GIP biagonists and the melanocortin 4 receptor (MC4R) agonist, setmelanotide. Some should be available in the future: GLP-1/glucagon biagonists, GLP-1/GIP/glucagon triagonists. These drugs act mainly by reducing food intake or fat absorption. However, many of them show specific effects on the adipose tissue. All these drugs show significant reduction of fat mass and, more particularly of visceral fat. If most of the drugs, except orlistat, have been shown to increase energy expenditure in rodents with enhanced thermogenesis, this has not yet been clearly demonstrated in humans. However, biagonists or triagonist stimulating glucagon seem to a have a more potent effect to increase thermogenesis in the adipose tissue and, thus, energy expenditure. Most of these drugs have been shown to increase the production of adiponectin and to reduce the production of pro-inflammatory cytokines by the adipose tissue. GLP-1RAs reduce the size of adipocytes and promote their differentiation. GLP-1RAS and GLP-1/GIP biagonists reduce, in the adipose tissue, the expression of several genes involved in lipogenesis. Further studies are still needed to clarify the precise roles, on the adipose tissue, of these drugs dedicated for the treatment of obesity.

Preventing maternal morbidity and mortality from preeclampsia and eclampsia particularly in low- and middle-income countries

Preeclampsia (PE) is a complex heterogeneous disorder with overlapping clinical phenotypes that complicate diagnosis and management. Although several pathophysiological mechanisms have been proposed, placental dysfunction due to inadequate remodelling of uterine spiral arteries leading to mal-perfusion and syncytiotrophoblast stress is recognized as the unifying characteristic of early-onset PE. Placental overgrowth and or premature senescence are probably the causes of late-onset PE. The frequency of PE has increased over the last few decades due to population-wide increases in risk factors viz. obesity, diabetes, multifetal pregnancies and pregnancies at an advanced maternal age. Whilst multimodal tools with components comprising risk factors, biomarkers and sonography are used for predicting PE, aspirin is most effective in preventing early-onset PE. The incidence and clinical consequences of PE and eclampsia are influenced by socioeconomic and cultural factors, therefore management strategies should involve multi-sector partnerships to mitigate the adverse outcomes.

New Mediators in the Crosstalk between Different Adipose Tissues

Adipose tissue is a multifunctional organ that regulates many physiological processes such as energy homeostasis, nutrition, the regulation of insulin sensitivity, body temperature, and immune response. In this review, we highlight the relevance of the different mediators that control adipose tissue activity through a systematic review of the main players present in white and brown adipose tissues. Among them, inflammatory mediators secreted by the adipose tissue, such as classical adipokines and more recent ones, elements of the immune system infiltrated into the adipose tissue (certain cell types and interleukins), as well as the role of intestinal microbiota and derived metabolites, have been reviewed. Furthermore, anti-obesity mediators that promote the activation of beige adipose tissue, e.g., myokines, thyroid hormones, amino acids, and both long and micro RNAs, are exhaustively examined. Finally, we also analyze therapeutic strategies based on those mediators that have been described to date. In conclusion, novel regulators of obesity, such as microRNAs or microbiota, are being characterized and are promising tools to treat obesity in the future.

MRI Methods to Visualize and Quantify Adipose Tissue in Health and Disease

MRI is the modality of choice for a vast range of pathologies but also a sensitive probe into human physiology and tissue function. For this reason, several methodologies have been developed and continuously evolve in order to non-invasively monitor underlying phenomena in human adipose tissue that were difficult to assess in the past through visual inspection of standard imaging modalities. To this end, this work describes the imaging methodologies used in medical practice and lists the most important quantitative markers related to adipose tissue physiology and pathology that are currently supporting diagnosis, longitudinal evaluation and patient management decisions. The underlying physical principles and the resulting markers are presented and associated with frequently encountered pathologies in radiology in order to set the frame of the ability of MRI to reveal the complex role of adipose tissue, not as an inert tissue but as an active endocrine organ.