Gut hormones and obesity: physiology and therapies

Tea Plant (Camellia sinensis): A Current Update on Use in Diabetes, Obesity, and Cardiovascular Disease

The tea plant (C. sinensis) has traditionally been consumed worldwide as "tea" for its many health benefits, with the potential for the prevention and therapy of various conditions. Regardless of its long history, the use of tea plants in modern times seems not to have changed much, as the beverage remains the most popular form. This review aimed to compile scientific information about the role and action of tea plants, as well as their status concerning clinical applications, based on the currently available evidence, with a focus on metabolic syndrome, mainly covering obesity, diabetes, and cardiovascular disease. It has been recognized that these diseases pose a significant threat to public health, and the development of effective treatment and prevention strategies is necessary but still challenging. In this article, the potential benefits of tea plants and their derived bioactive components (such as epigallocatechin-3-gallate) as anti-obesity, anti-diabetic, and anti-cardiovascular agents are clearly shown and emphasized, along with their mechanisms of action. However, according to the status of the clinical translation of tea plants, particularly in drug development, more substantial efforts in well-designed, randomized, controlled trials are required to expand their applications in treating the three major metabolic disorders and avoiding the toxicity caused by overconsumption.

Cognitive reappraisal of low-calorie food predicts real-world craving and consumption of high- and low-calorie foods in daily life

In an increasingly obesogenic environment, an individual's regulatory capacity to pursue nutrient-rich, low-calorie foods over palatable, energy-dense items is essential to maintaining a healthy weight and preventing the detrimental health risks of obesity. Cognitive reappraisal, the process by which one changes the meaning of a stimulus by altering its emotional impact (or in this case, its appetitive value) demonstrates promise as a regulatory strategy to decrease obesogenic food consumption, but little research has directly addressed the relationship between cognitive reappraisal of food cravings and real-world eating behaviors. Additionally, research examining self-regulation of eating has typically focused exclusively on diminishing cravings and consumption of unhealthy, high-calorie foods, rather than examining, in tandem, ways to strengthen (or, up-regulate) cravings for healthier, low-calorie alternatives. In the present study, fifty-seven college aged participants first completed a cognitive reappraisal task in the laboratory in which they practiced regulating their craving responses to high- and low-calorie food items by focusing on the long-term health consequences of repeatedly consuming the pictured foods. Next, for a week following the laboratory session, participants reported daily eating behaviors via ecological momentary assessment. Participants who reported greater up-regulatory success during the reappraisal task also reported increased craving strength for low-calorie foods as well as decreased consumption of high-calorie foods in their daily lives. Greater overall regulation success also predicted more frequent consumption of craved low-calorie foods. These findings substantiate the association between cognitive reappraisal ability and real-world appetitive behaviors, and suggest that future interventions may benefit from specifically targeting individuals' evaluations of low-calorie foods.

Brown and Beige Adipose Tissues in Health and Disease

Brown and beige adipocytes arise from distinct developmental origins. Brown adipose tissue (BAT) develops embryonically from precursors that also give to skeletal muscle. Beige fat develops postnatally and is highly inducible. Beige fat recruitment is mediated by multiple mechanisms, including de novo beige adipogenesis and white-to-brown adipocyte transdifferentiaiton. Beige precursors reside around vasculatures, and proliferate and differentiate into beige adipocytes. PDGFRα+Ebf2+ precursors are restricted to beige lineage cells, while another PDGFRα+ subset gives rise to beige adipocytes, white adipocytes, or fibrogenic cells. White adipocytes can be reprogramed and transdifferentiated into beige adipocytes. Brown and beige adipocytes display many similar properties, including multilocular lipid droplets, dense mitochondria, and expression of UCP1. UCP1-mediated thermogenesis is a hallmark of brown/beige adipocytes, albeit UCP1-independent thermogenesis also occurs. Development, maintenance, and activation of BAT/beige fat are guided by genetic and epigenetic programs. Numerous transcriptional factors and coactivators act coordinately to promote BAT/beige fat thermogenesis. Epigenetic reprograming influences expression of brown/beige adipocyte-selective genes. BAT/beige fat is regulated by neuronal, hormonal, and immune mechanisms. Hypothalamic thermal circuits define the temperature setpoint that guides BAT/beige fat activity. Metabolic hormones, paracrine/autocrine factors, and various immune cells also play a critical role in regulating BAT/beige fat functions. BAT and beige fat defend temperature homeostasis, and regulate body weight and glucose and lipid metabolism. Obesity is associated with brown/beige fat deficiency, and reactivation of brown/beige fat provides metabolic health benefits in some patients. Pharmacological activation of BAT/beige fat may hold promise for combating metabolic diseases. © 2017 American Physiological Society. Compr Physiol 7:1281-1306, 2017.

Estradiol effects on hypothalamic AMPK and BAT thermogenesis: A gateway for obesity treatment?

In addition to their prominent roles in the control of reproduction, estrogens are important modulators of energy balance, as evident in conditions of deficiency of estrogens, which are characterized by increased feeding and decreased energy expenditure, leading to obesity. AMP-activated protein kinase (AMPK) is a ubiquitous cellular energy gauge that is activated under conditions of low energy, increasing energy production and reducing energy wasting. Centrally, the AMPK pathway is a canonical route regulating energy homeostasis, by integrating peripheral signals, such as hormones and metabolites, with neuronal networks. As a result of those actions, hypothalamic AMPK modulates feeding, as well as brown adipose tissue (BAT) thermogenesis and browning of white adipose tissue (WAT). Here, we will review the central actions of estrogens on energy balance, with particular focus on hypothalamic AMPK. The relevance of this interaction is noteworthy, because some agents with known actions on metabolic homeostasis, such as nicotine, metformin, liraglutide, olanzapine and also natural molecules, such as resveratrol and flavonoids, exert their actions by modulating AMPK. This evidence highlights the possibility that hypothalamic AMPK might be a potential target for the treatment of obesity.

Estradiol Regulation of Brown Adipose Tissue Thermogenesis

Physiologically, estrogens carry out a myriad of functions, the most essential being the regulation of the reproductive axis. Currently, it is also dogmatic that estrogens play an important role modulating energy balance and metabolism. In this sense, it is well known that low estrogens levels, occurring due to ovarian insufficiency, in conditions such as menopause or ovariectomy (OVX), are associated with increased food intake and decreased energy expenditure, leading to weight gain and obesity at long term. Concerning energy expenditure, the main effect of estradiol (E2) is on brown adipose tissue (BAT) thermogenesis. Thus, acting through a peripheral or a central action, E2 activates brown fat activity and increases body temperature, which is negatively associated with body weight. Centrally, the hypothalamic AMP-activated protein kinase (AMPK) mediates the E2 action on BAT thermogenesis. In this chapter, we will summarize E2 regulation of BAT thermogenesis and how this can influence energy balance and metabolism in general.

Analysis of energy metabolism in humans: A review of methodologies

Background

Obesity is a consequence of chronic energy imbalance. We need accurate and precise measurements of energy intake and expenditure, as well as the related behaviors, to fully understand how energy homeostasis is regulated in order to develop interventions and evaluate their effectiveness to combat the global obesity epidemic.

Scope of review

We provide an in-depth review of the methodologies currently used to measure energy intake and expenditure in humans, including their principles, advantages, and limitations in the clinical research setting. The aim is to provide researchers with a comprehensive guide to conduct obesity research of the highest possible quality.

Major conclusions

An array of methodologies is available to measure various aspects of energy metabolism and none is perfect under all circumstances. The choice of methods should be specific to particular research questions with practicality and quality of data the priorities for consideration. A combination of complementary measurements may be preferable. There is an imperative need to develop new methodologies to improve the accuracy and precision of energy intake assessments.

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Image-based technology is a significant step to improve energy intake measurement.

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Physical activity informs patterns but not absolute energy expenditure.

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Combining complementary measurements overcomes shortfalls of individual methods.

Estradiol and brown fat

Ovarian steroids, such as estradiol (E2), control a vastness of physiological processes, such as puberty, reproduction, growth, development and metabolic rate. In fact, physiological, pathological, pharmacological or genetically-induced estrogen deficiency causes increased appetite and reduced energy expenditure, promoting weight gain and ultimately leading to obesity. Remarkably, estrogen replacement reverts those effects. Interestingly, although a wealth of evidence has shown that E2 can directly modulate peripheral tissues to exert their metabolic actions, novel data gathered in recent years have shown that those effects are mainly central and occur in the hypothalamus. Here, we will review what is known about the actions of E2 on energy homeostasis, with particular focus on brown adipose tissue (BAT) thermogenesis.

Dietary Capsaicin Protects Cardiometabolic Organs from Dysfunction

Chili peppers have a long history of use for flavoring, coloring, and preserving food, as well as for medical purposes. The increased use of chili peppers in food is very popular worldwide. Capsaicin is the major pungent bioactivator in chili peppers. The beneficial effects of capsaicin on cardiovascular function and metabolic regulation have been validated in experimental and population studies. The receptor for capsaicin is called the transient receptor potential vanilloid subtype 1 (TRPV1). TRPV1 is ubiquitously distributed in the brain, sensory nerves, dorsal root ganglia, bladder, gut, and blood vessels. Activation of TRPV1 leads to increased intracellular calcium signaling and, subsequently, various physiological effects. TRPV1 is well known for its prominent roles in inflammation, oxidation stress, and pain sensation. Recently, TRPV1 was found to play critical roles in cardiovascular function and metabolic homeostasis. Experimental studies demonstrated that activation of TRPV1 by capsaicin could ameliorate obesity, diabetes, and hypertension. Additionally, TRPV1 activation preserved the function of cardiometabolic organs. Furthermore, population studies also confirmed the beneficial effects of capsaicin on human health. The habitual consumption of spicy foods was inversely associated with both total and certain causes of specific mortality after adjustment for other known or potential risk factors. The enjoyment of spicy flavors in food was associated with a lower prevalence of obesity, type 2 diabetes, and cardiovascular diseases. These results suggest that capsaicin and TRPV1 may be potential targets for the management of cardiometabolic vascular diseases and their related target organs dysfunction.

Estrogens and the control of energy homeostasis: a brain perspective

Despite their prominent roles in the control of reproduction, estrogens pervade many other bodily functions. Key metabolic pathways display marked sexual differences, and estrogens are potent modulators of energy balance, as evidenced in extreme conditions of estrogen deficiency characterized by hyperphagia and decreased energy expenditure, and leading to obesity. Compelling evidence has recently demonstrated that, in addition to their peripheral effects, the actions of estrogens on energy homeostasis are exerted at central levels, to regulate almost every key aspect of metabolic homeostasis, from feeding to energy expenditure, to glucose and lipid metabolism. We review herein the state-of-the-art of the role of estrogens in the regulation of energy balance, with a focus on their central effects and modes of action.

Hormonal and neural mechanisms of food reward, eating behaviour and obesity

With rising rates of obesity, research continues to explore the contributions of homeostatic and hedonic mechanisms related to eating behaviour. In this Review, we synthesize the existing information on select biological mechanisms associated with reward-related food intake, dealing primarily with consumption of highly palatable foods. In addition to their established functions in normal feeding, three primary peripheral hormones (leptin, ghrelin and insulin) play important parts in food reward. Studies in laboratory animals and humans also show relationships between hyperphagia or obesity and neural pathways involved in reward. These findings have prompted questions regarding the possibility of addictive-like aspects in food consumption. Further exploration of this topic may help to explain aberrant eating patterns, such as binge eating, and provide insight into the current rates of overweight and obesity.

Insulin-like peptide 5 is an orexigenic gastrointestinal hormone

The gut endocrine system is emerging as a central player in the control of appetite and glucose homeostasis, and as a rich source of peptides with therapeutic potential in the field of diabetes and obesity. In this study we have explored the physiology of insulin-like peptide 5 (Insl5), which we identified as a product of colonic enteroendocrine L-cells, better known for their secretion of glucagon-like peptide-1 and peptideYY. i.p. Insl5 increased food intake in wild-type mice but not mice lacking the cognate receptor Rxfp4. Plasma Insl5 levels were elevated by fasting or prolonged calorie restriction, and declined with feeding. We conclude that Insl5 is an orexigenic hormone released from colonic L-cells, which promotes appetite during conditions of energy deprivation.

Brain regulation of energy balance and body weight

Body weight is determined by a balance between food intake and energy expenditure. Multiple neural circuits in the brain have evolved to process information about food, food-related cues and food consumption to control feeding behavior. Numerous gastrointestinal endocrine cells produce and secrete satiety hormones in response to food consumption and digestion. These hormones suppress hunger and promote satiation and satiety mainly through hindbrain circuits, thus governing meal-by-meal eating behavior. In contrast, the hypothalamus integrates adiposity signals to regulate long-term energy balance and body weight. Distinct hypothalamic areas and various orexigenic and anorexigenic neurons have been identified to homeostatically regulate food intake. The hypothalamic circuits regulate food intake in part by modulating the sensitivity of the hindbrain to short-term satiety hormones. The hedonic and incentive properties of foods and food-related cues are processed by the corticolimbic reward circuits. The mesolimbic dopamine system encodes subjective "liking" and "wanting" of palatable foods, which is subjected to modulation by the hindbrain and the hypothalamic homeostatic circuits and by satiety and adiposity hormones. Satiety and adiposity hormones also promote energy expenditure by stimulating brown adipose tissue (BAT) activity. They stimulate BAT thermogenesis mainly by increasing the sympathetic outflow to BAT. Many defects in satiety and/or adiposity hormone signaling and in the hindbrain and the hypothalamic circuits have been described and are believed to contribute to the pathogenesis of energy imbalance and obesity.