In vitro lipolytic effect of leptin on mouse adipocytes: evidence for a possible autocrine/paracrine role of leptin

Metabolic Water As a Route for Water Acquisition in Vertebrates Inhabiting Dehydrating Environments

Vertebrates have expanded their habitats during evolution, which accompanies diversified routes for water acquisition. Water is acquired by oral intake and subsequent absorption by the intestine in terrestrial and marine animals which are subjected to constant dehydration, whereas most water is gained osmotically across body surfaces in freshwater animals. In addition, a significant amount of water, called metabolic water, is produced within the body by the oxidation of hydrogen in organic substrates. The importance of metabolic water production as a strategy for water acquisition has been well documented in desert animals, but its role has attracted little attention in marine animals which also live in a dehydrating environment. In this article, the author has attempted to reevaluate the role of metabolic water production in body fluid regulation in animals inhabiting desiccating environments. Because of the exceptional ability of their kidney, marine mammals are thought to typically gain water by drinking environmental seawater and excreting excess NaCl in the urine. On the other hand, it is established that marine teleosts drink seawater to enable intestinal water and ion absorption, and the excess NaCl is excreted by branchial ionocytes. In addition to the oral route, we suggest through experiments using eels that water production by lipid metabolism is an additional route for water acquisition when they encounter seawater. It seems that metabolic water production contributes to counteract dehydration before mechanisms for water regulation are reversed from excretion in freshwater to acquisition in seawater.

Minireview: Glucocorticoid-Leptin Crosstalk: Role of Glucocorticoid-Leptin Counterregulation in Metabolic Homeostasis and Normal Development

Glucocorticoids and leptin are two important hormones that regulate metabolic homeostasis by controlling appetite and energy expenditure in adult mammals. Also, glucocorticoids and leptin strongly counterregulate each other, such that chronic stress-induced glucocorticoids upregulate the production of leptin and leptin suppresses glucocorticoid production directly via action on endocrine organs and indirectly via action on food intake. Altered glucocorticoid or leptin levels during development can impair organ development and increase the risk of chronic diseases in adults, but there are limited studies depicting the significance of glucocorticoid-leptin interaction during development and its impact on developmental programming. In mammals, leptin-induced suppression of glucocorticoid production is critical during development, where leptin prevents stress-induced glucocorticoid production by inducing a period of short-hyporesponsiveness when the adrenal glands fail to respond to certain mild to moderate stressors. Conversely, reduced or absent leptin signaling increases glucocorticoid levels beyond what is appropriate for normal organogenesis. The counterregulatory interactions between leptin and glucocorticoids suggest the potential significant involvement of leptin in disorders that occur from stress during development.

Eccentric and concentric exercises induce different adaptions in adipose tissue biology

Alterations in adipose tissue (AT) metabolism related to inflammation and adipokine's production lead to perturbations in its capacity to store lipids and release fatty acids (FA) during feeding/fasting transition or during exercise. Exercise has a beneficial effect on AT metabolism, but conventional trainings are not always suitable for patients with functional limitations. Dynamic eccentric (ECC) exercise prevents the accumulation of AT and may then overcome those limitations. Consequently, this study aimed at investigating AT's adaptations after ECC training. Nine-week-old male rats were randomly assigned to a control sedentary or three-trained groups for which treadmill slopes modulated exercise oxygen consumption (VO₂) and mechanical work (n = 15 per group): (1) + 15% uphill-concentric group (CONC), (2) - 15% downhill group (ECC15, same mechanical work as CONC) and (3) - 30% downhill group (ECC30, same VO₂, or oxygen cost as CONC). Body composition and energy expenditure (EE) were measured before and after 8 weeks of training. Subcutaneous AT was collected to study total FA profile and gene expression. Higher total EE was driven by lean mass gain in trained animals. In AT, there was a decrease in arachidonic acid with CONC or ECC15 training. Increased adiponectin, leptin, lipases, Glut4 and Igf1 mRNA levels in ECC15 group suggested major metabolic adaption in AT. In conclusion, ECC could induce beneficial modifications in AT fatty acid profile and the expression of key genes related to metabolism and insulin sensitivity.

A novel anti-obesity mechanism for liraglutide by improving adipose tissue leptin resistance in high-fat diet-fed obese mice

Liraglutide has been approved for the treatment of obesity in the past few years. Both oxidative stress and leptin resistance are the critical drivers of obesity. The present study investigated the mechanism of liraglutide protection against obesity by ameliorating leptin resistance and oxidative stress. Male C57BL/6J mice were fed a high-fat diet (HFD) and subcutaneously injected with 200 μg/kg/d liraglutide for 20 weeks. Body weight, fat mass, serum levels of leptin, insulin, and superoxide dismutase (SOD) activities were measured. In addition, glucose and insulin tolerance tests were performed. The expressions of leptin, its signaling genes, and antioxidant enzymes were detected using RT-qPCR and western blot methods in liver and white adipose tissue (WAT) of mice. The results depicted that liraglutide treatment significantly slowed weight gain of body, reduced the fat mass, ameliorated glucose and lipid metabolism, and hepatic steatosis in HFD-fed obese mice. Further study demonstrated that liraglutide treatment resulted in decreased serum levels and the transcript levels of leptin as well as leptin signaling inhibitory regulators. However, it increased leptin receptor expression and the phosphorylation of signal transducer and activator of transcription 3 (p-STAT3) in WAT (p < 0.05). In addition, the antioxidant enzyme expression was elevated in both liver and WAT of liraglutide-treated mice (p < 0.05). In conclusion, liraglutide conspicuously prevented obesity and ameliorated glucose and lipid metabolism in obese mice through a novel mechanism that improves peripheral leptin resistance in WAT and enhance the antioxidant enzyme expression in both liver and WAT.

Adipocyte Phenotype Flexibility and Lipid Dysregulation

The prevalence of obesity and associated cardiometabolic diseases continues to rise, despite efforts to improve global health. The adipose tissue is now regarded as an endocrine organ since its multitude of secretions, lipids chief among them, regulate systemic functions. The loss of normal adipose tissue phenotypic flexibility, especially related to lipid homeostasis, appears to trigger cardiometabolic pathogenesis. The goal of this manuscript is to review lipid balance maintenance by the lean adipose tissue’s propensity for phenotype switching, obese adipose tissue’s narrower range of phenotype flexibility, and what initial factors account for the waning lipid regulatory capacity. Metabolic, hypoxic, and inflammatory factors contribute to the adipose tissue phenotype being made rigid. A better grasp of normal adipose tissue function provides the necessary context for recognizing the extent of obese adipose tissue dysfunction and gaining insight into how pathogenesis evolves.

Leptin as a key regulator of the adipose organ

Leptin is a hormone primarily produced by the adipose tissue in proportion to the size of fat stores, with a primary function in the control of lipid reserves. Besides adipose tissue, leptin is also produced by other tissues, such as the stomach, placenta, and mammary gland. Altogether, leptin exerts a broad spectrum of short, medium, and long-term regulatory actions at the central and peripheral levels, including metabolic programming effects that condition the proper development and function of the adipose organ, which are relevant for its main role in energy homeostasis. Comprehending how leptin regulates adipose tissue may provide important clues to understand the pathophysiology of obesity and related diseases, such as type 2 diabetes, as well as its prevention and treatment. This review focuses on the physiological and long-lasting regulatory effects of leptin on adipose tissue, the mechanisms and pathways involved, its main outcomes on whole-body physiological homeostasis, and its consequences on chronic diseases.

The Action of Vitamin D in Adipose Tissue: Is There the Link between Vitamin D Deficiency and Adipose Tissue-Related Metabolic Disorders?

Adipose tissue plays an important role in systemic metabolism via the secretion of adipocytokines and storing and releasing energy. In obesity, adipose tissue becomes dysfunctional and characterized by hypertrophied adipocytes, increased inflammation, hypoxia, and decreased angiogenesis. Although adipose tissue is one of the major stores of vitamin D, its deficiency is detective in obese subjects. In the presented review, we show how vitamin D regulates numerous processes in adipose tissue and how their dysregulation leads to metabolic disorders. The molecular response to vitamin D in adipose tissue affects not only energy metabolism and adipokine and anti-inflammatory cytokine production via the regulation of gene expression but also genes participating in antioxidant defense, adipocytes differentiation, and apoptosis. Thus, its deficiency disturbs adipocytokines secretion, metabolism, lipid storage, adipogenesis, thermogenesis, the regulation of inflammation, and oxidative stress balance. Restoring the proper functionality of adipose tissue in overweight or obese subjects is of particular importance in order to reduce the risk of developing obesity-related complications, such as cardiovascular diseases and diabetes. Taking into account the results of experimental studies, it seemed that vitamin D may be a remedy for adipose tissue dysfunction, but the results of the clinical trials are not consistent, as some of them show improvement and others no effect of this vitamin on metabolic and insulin resistance parameters. Therefore, further studies are required to evaluate the beneficial effects of vitamin D, especially in overweight and obese subjects, due to the presence of a volumetric dilution of this vitamin among them.

The Roles and Associated Mechanisms of Adipokines in Development of Metabolic Syndrome

Metabolic syndrome is a cluster of metabolic indicators that increase the risk of diabetes and cardiovascular diseases. Visceral obesity and factors derived from altered adipose tissue, adipokines, play critical roles in the development of metabolic syndrome. Although the adipokines leptin and adiponectin improve insulin sensitivity, others contribute to the development of glucose intolerance, including visfatin, fetuin-A, resistin, and plasminogen activator inhibitor-1 (PAI-1). Leptin and adiponectin increase fatty acid oxidation, prevent foam cell formation, and improve lipid metabolism, while visfatin, fetuin-A, PAI-1, and resistin have pro-atherogenic properties. In this review, we briefly summarize the role of various adipokines in the development of metabolic syndrome, focusing on glucose homeostasis and lipid metabolism.

Peripheral versus central insulin and leptin resistance: Role in metabolic disorders, cognition, and neuropsychiatric diseases

Insulin and leptin are classically regarded as peptide hormones that play key roles in metabolism. In actuality, they serve several functions in both the periphery and central nervous system (CNS). Likewise, insulin and leptin resistance can occur both peripherally and centrally. Metabolic disorders such as diabetes and obesity share several key features including insulin and leptin resistance. While the peripheral effects of these disorders are well-known (i.e. cardiovascular disease, hypertension, stroke, dyslipidemia, etc.), the CNS complications of leptin and insulin resistance have come into sharper focus. Both preclinical and clinical findings have indicated that insulin and leptin resistance are associated with cognitive deficits and neuropsychiatric diseases such as depression. Importantly, these studies also suggest that these deficits in neuroplasticity can be reversed by restoration of insulin and leptin sensitivity. In view of these observations, this review will describe, in detail, the peripheral and central functions of insulin and leptin and explain the role of insulin and leptin resistance in various metabolic disorders, cognition, and neuropsychiatric diseases.

Fluoxetine ameliorates high-fat diet-induced metabolic abnormalities partially via reduced adipose triglyceride lipase-mediated adipocyte lipolysis

Patients with type 2 diabetes mellitus have more risk to develop depression. Fluoxetine (FLX), a selective serotonin reuptake inhibitor (SSRI), is drug for mood and anxiety disorders. Previous studies showed that FLX could induce weight loss in non-depressed clinically overweight individuals. Although the anti-appetite effect of FLX is well-documented, its potential effects on metabolic abnormalities have not been investigated. In this study, we want to investigate whether FLX could be a therapeutic drug against high fat diet (HFD)-induced metabolic disorder. We generated metabolic disorders and depressed mouse model by feeding HFD for 12 weeks at the age of 8 weeks. Then, mice were intraperitoneally injected once daily with FLX (10 mg/kg or 20 mg/kg) for four weeks. Our results showed that FLX alleviated the HFD-induced metabolic dysfunctions and depressive phenotypes in mice. FLX improved systemic glucose homeostasis, at least in part, by improving visceral white adipose tissue (vWAT) insulin signaling. Moreover, FLX reduced circulating plasma leptin level, and decreased the expression of adipose triglyceride lipase (ATGL) and peroxisome proliferator-activated receptor gamma (PPARγ) in vWAT. Our data revealed that FLX also reduced the triglyceride (TG) accumulation in vWAT. Therefore, these findings suggest that FLX exhibits significant potential on comorbidity of metabolic disorder and depression in mice.

Tissue-Specific Effects of Leptin on Glucose and Lipid Metabolism

The discovery of leptin was intrinsically associated with its ability to regulate body weight. However, the effects of leptin are more far-reaching and include profound glucose-lowering and anti-lipogenic effects, independent of leptin's regulation of body weight. Regulation of glucose metabolism by leptin is mediated both centrally and via peripheral tissues and is influenced by the activation status of insulin signaling pathways. Ectopic fat accumulation is diminished by both central and peripheral leptin, an effect that is beneficial in obesity-associated disorders. The magnitude of leptin action depends upon the tissue, sex, and context being examined. Peripheral tissues that are of particular relevance include the endocrine pancreas, liver, skeletal muscle, adipose tissues, immune cells, and the cardiovascular system. As a result of its potent metabolic activity, leptin is used to control hyperglycemia in patients with lipodystrophy and is being explored as an adjunct to insulin in patients with type 1 diabetes. To fully understand the role of leptin in physiology and to maximize its therapeutic potential, the mechanisms of leptin action in these tissues needs to be further explored.

Adipokine signatures of subcutaneous and visceral abdominal fat in normal-weight and obese women with different metabolic profiles

INTRODUCTION

Metabolic syndrome arises from abnormal adipose function accompanied by insulin resistance. As early factors reflecting/impacting lipid storage dysfunction of adipose tissues, we sought to determine adipokine levels in subcutaneous and visceral adipose tissues (SAT and VAT).

MATERIAL AND METHODS

Gene and protein expression levels of leptin, adiponectin, and resistin were analysed in SAT and VAT of normal-weight and overweight/obese women, subclassified according to insulin resistance index, triglyceride, total, low-density lipoprotein (LDL) and high-density lipoprotein (HDL) cholesterol levels into metabolically healthy and "at risk" groups.

RESULTS

Compared with normal-weight women, obese women had higher serum leptin levels (p < 0.05), as well as increased leptin gene and protein expression in VAT. Conversely, expression levels of leptin were lower in SAT of obese women, and minor in the SAT of "at risk" groups of women, compared with weight-matched healthy groups. In addition, lower adiponectin levels were detected in SAT of metabolically healthy obese women (p < 0.01), and lower in SAT and VAT (p < 0.05) of "at risk" obese women compared to healthy, obese women. Significant differences in resistin levels were only observed in obese women; resistin gene expression was higher in VAT and SAT of obese, compared to normal-weight women. However, higher gene expression was not consistent with protein expression of resistin.

CONCLUSIONS

Low adiponectin in both examined adipose tissues and inappropriate leptin expression levels in SAT appear to be important characteristics of obesity-related metabolic syndrome. Intriguingly, this adipokine dysregulation is primary seen in SAT, suggesting that endocrine dysfunction in this abdominal depot may be an early risk sign of metabolic syndrome.

The Molecular Mechanisms by Which Vitamin D Prevents Insulin Resistance and Associated Disorders

Numerous studies have shown that vitamin D deficiency is very common in modern societies and is perceived as an important risk factor in the development of insulin resistance and related diseases such as obesity and type 2 diabetes (T2DM). While it is generally accepted that vitamin D is a regulator of bone homeostasis, its ability to counteract insulin resistance is subject to debate. The goal of this communication is to review the molecular mechanism by which vitamin D reduces insulin resistance and related complications. The university library, PUBMED, and Google Scholar were searched to find relevant studies to be summarized in this review article. Insulin resistance is accompanied by chronic hyperglycaemia and inflammation. Recent studies have shown that vitamin D exhibits indirect antioxidative properties and participates in the maintenance of normal resting ROS level. Appealingly, vitamin D reduces inflammation and regulates Ca²⁺ level in many cell types. Therefore, the beneficial actions of vitamin D include diminished insulin resistance which is observed as an improvement of glucose and lipid metabolism in insulin-sensitive tissues.

There and Back Again: Leptin Actions in White Adipose Tissue

Leptin is a hormone discovered almost 30 years ago with important implications in metabolism. It is primarily produced by white adipose tissue (WAT) in proportion to the amount of fat. The discovery of leptin was a turning point for two principle reasons: on one hand, it generated promising expectations for the treatment of the obesity, and on the other, it changed the classical concept that white adipose tissue was simply an inert storage organ. Thus, adipocytes in WAT produce the majority of leptin and, although its primary role is the regulation of fat stores by controlling lipolysis and lipogenesis, this hormone also has implications in other physiological processes within WAT, such as apoptosis, browning and inflammation. Although a massive number of questions related to leptin actions have been answered, the necessity for further clarification facilitates constantly renewing interest in this hormone and its pathways. In this review, leptin actions in white adipose tissue will be summarized in the context of obesity.

Anti-inflammatory effects of troxerutin are mediated through elastase inhibition

CONTEXT

Obesity is a chronic low-grade inflammatory state associated with immune cell infiltration into the adipose tissue (AT). We hypothesize that the anti-obesity and anti-inflammatory effects of troxerutin (TX) are mediated through inhibition of elastase.

OBJECTIVE

To determine the inhibitory effect of TX on elastase in vitro and in tumor necrosis factor alpha (TNFα) induced 3T3-L1 adipocytes and the molecular interaction of TX with human neutrophil elastase (HNE).

MATERIALS AND METHODS

Differentiated 3T3-L1 adipocytes were pretreated with TX, elastatinal (ELAS) or sodium salicylate (SAL) before exposure to TNFα. Lipid accumulation, reactive oxygen species (ROS) generation and oxidant-antioxidant balance were examined. The mRNA and protein expression of TNFα, interleukin-6, monocyte chemoattractant protein-1, adiponectin, leptin, resistin, chemerin, and elastase were analyzed. Elastase inhibition by TX and ELAS in a cell free system and docking studies for HNE with TX and ELAS were performed.

RESULTS

TX, ELAS or SAL pretreatment had lowered lipid droplets formation and TG content. TX suppressed ROS generation, oxidative stress and improved antioxidant status. The expression of inflammatory cytokines and elastase was downregulated while that of adiponectin was upregulated by TX. The concentration required to produce 50% inhibition in vitro (IC₅₀) was 11.5 μM for TX and 16.9 μM for ELAS. TX showed hydrogen bonding and hydrophobic interactions with elastase.

DISCUSSION

TNFα induces inflammation of 3T3-L1 cells through elastase activation. TX inhibits elastase activity, downregulates expression and binds with elastase.

CONCLUSION

The antioxidant and anti-inflammatory activities of TX in AT could be of relevance in the management of obesity.

Leptin: Is It Thermogenic?

Animals that lack the hormone leptin become grossly obese, purportedly for 2 reasons: increased food intake and decreased energy expenditure (thermogenesis). This review examines the experimental evidence for the thermogenesis component. Analysis of the data available led us to conclude that the reports indicating hypometabolism in the leptin-deficient ob/ob mice (as well as in the leptin-receptor-deficient db/db mice and fa/fa rats) derive from a misleading calculation artefact resulting from expression of energy expenditure per gram of body weight and not per intact organism. Correspondingly, the body weight-reducing effects of leptin are not augmented by enhanced thermogenesis. Congruent with this, there is no evidence that the ob/ob mouse demonstrates atrophied brown adipose tissue or diminished levels of total UCP1 mRNA or protein when the ob mutation is studied on the inbred C57BL/6 mouse background, but a reduced sympathetic nerve activity is observed. On the outbred "Aston" mouse background, brown adipose tissue atrophy is seen, but whether this is of quantitative significance for the development of obesity has not been demonstrated. We conclude that leptin is not a thermogenic hormone. Rather, leptin has effects on body temperature regulation, by opposing torpor bouts and by shifting thermoregulatory thresholds. The central pathways behind these effects are largely unexplored.

Differential Roles of Two Leptin Gene Paralogues on Food Intake and Hepatic Metabolism Regulation in Mandarin Fish

Leptin affects food intake regulation and energy homeostasis in mammals, as opposed to mammals who have a single leptin gene, fish have duplicated leptin gene paralogues. Until now, most functional studies on fish focused on the first reported paralogue without much explanation on specific gene paralogue. This study successfully expressed two homologous recombinant mandarin fish leptin genes (LepA and LepB) for the first time. To explore the differential roles of these two gene paralogues involved in food intake and energy homeostasis, mandarin fish were treated with homologous recombinant LepA and LepB proteins by acute IP administration. The results showed that LepB inhibited the food intake of mandarin fish after acute IP administration through modifying the expressions of hypothalamic orexigenic genes, while LepA had no significant effect on its food intake. In addition, LepB administration decreased the hepatic glycogen level through regulating the gene expressions of glycogen synthase and glycogen phosphorylase in mandarin fish until 4 d, while LepA did not change the hepatic glycogen level as it failed to change the expressions of these regulatory genes. Moreover, LepA and LepB downregulated the expressions of key gluconeogenic genes (phosphofructokinase, phosphoenolpyruvate carboxykinase, and glucose-6-phosphatase), indicating both mandarin fish leptins could regulate the rate of glucose production. However, these two gene paralogues presented secondary effects on lipid metabolism as they only enhanced the triglyceride level by modifying the gene expressions of adipose triglyceride lipase or acetyl CoA carboxylase just for 1 d after IP. Therefore, LepB played an important role in food intake and glucose homeostasis regulation, while LepA showed a limited role in gluconeogenesis and lipid metabolism.

Mechanistic Links Between Obesity, Diabetes, and Blood Pressure: Role of Perivascular Adipose Tissue

Obesity is increasingly prevalent and is associated with substantial cardiovascular risk. Adipose tissue distribution and morphology play a key role in determining the degree of adverse effects, and a key factor in the disease process appears to be the inflammatory cell population in adipose tissue. Healthy adipose tissue secretes a number of vasoactive adipokines and anti-inflammatory cytokines, and changes to this secretory profile will contribute to pathogenesis in obesity. In this review, we discuss the links between adipokine dysregulation and the development of hypertension and diabetes and explore the potential for manipulating adipose tissue morphology and its immune cell population to improve cardiovascular health in obesity.

Functional Relationship between Leptin and Nitric Oxide in Metabolism

Leptin, the product of the ob gene, was originally described as a satiety factor, playing a crucial role in the control of body weight. Nevertheless, the wide distribution of leptin receptors in peripheral tissues supports that leptin exerts pleiotropic biological effects, consisting of the modulation of numerous processes including thermogenesis, reproduction, angiogenesis, hematopoiesis, osteogenesis, neuroendocrine, and immune functions as well as arterial pressure control. Nitric oxide (NO) is a free radical synthesized from L-arginine by the action of the NO synthase (NOS) enzyme. Three NOS isoforms have been identified: the neuronal NOS (nNOS) and endothelial NOS (eNOS) constitutive isoforms, and the inducible NOS (iNOS). NO mediates multiple biological effects in a variety of physiological systems such as energy balance, blood pressure, reproduction, immune response, or reproduction. Leptin and NO on their own participate in multiple common physiological processes, with a functional relationship between both factors having been identified. The present review describes the functional relationship between leptin and NO in different physiological processes.

Conjugated linoleic acid and betaine affect lipolysis in pig adipose tissue explants

Consumers' demand of leaner meat products is a challenge. Although betaine and conjugated linoleic acid (CLA) have the potential to decrease porcine adipose tissue, their mode of action is poorly understood. The aim of the study was to determine the lipolytic effect of betaine and CLA in the adipose tissue of Iberian pigs. Adipose tissue explants from five pigs (38 kg BW) were prepared from dorsal subcutaneous adipose tissue samples and cultivated for 2 h (acute experiments) or 72 h (chronic experiments). Treatments included 100 µM linoleic acid (control), 100 µM trans-10, cis-12 CLA, 100 µM linoleic acid + 1 mM betaine and 100 µM trans-10, cis-12 CLA + 1 mM betaine (CLABET). To examine the ability of betaine or CLA to inhibit insulin's suppression of isoproterenol-stimulated lipolysis, test medium was amended with 1 µM isoproterenol ±10 nM insulin. Media glycerol was measured at the end of the incubations. Acute lipolysis (2 h) was increased by CLA and CLABET (85% to 121%; P < 0.05) under basal conditions. When lipolysis was stimulated with isoproterenol (1090%), acute exposure to betaine tended to increase (13%; P = 0.071), while CLA and CLABET increased (14% to 18%; P < 0.05) isoproterenol-stimulated lipolysis compared with control. When insulin was added to isoproterenol-stimulated explants, lipolytic rate was decreased by 50% (P < 0.001). However, supplementation of betaine to the insulin + isoproterenol-containing medium tended to increase (P = 0.07), while CLABET increased (45%; P < 0.05) lipolysis, partly counteracting insulin inhibition. When culture was extended for 72 h, CLA decreased lipolysis under basal conditions (18%; P < 0.05) with no effect of betaine and CLABET (P > 0.10). When lipolysis was stimulated by isoproterenol (125% increase in rate compared with basal), CLA and CLABET decreased glycerol release (27%; P < 0.001) compared with control (isoproterenol alone). When insulin was added to isoproterenol-stimulated explants, isoproterenol stimulation of lipolysis was completely blunted and neither betaine nor CLA altered the inhibitory effect of insulin on lipolysis. Isoproterenol, and especially isoproterenol + insulin, stimulated leptin secretion compared with basal conditions (68% and 464%, respectively; P < 0.001), with no effect of CLA or betaine (P > 0.10). CLA decreased leptin release (25%; P < 0.001) when insulin was present in the media, partially inhibiting insulin stimulation of leptin release. In conclusion, betaine and CLA produced a biphasic response regarding lipolysis so that glycerol release was increased in acute conditions, while CLA decreased glycerol release and betaine had no effect in chronic conditions. Furthermore, CLA and CLABET indirectly increased lipolysis by reducing insulin-mediated inhibition of lipolysis during acute conditions.

Analysis of Association between Vitamin D Deficiency and Insulin Resistance

Recent evidence revealed extra skeleton activity of vitamin D, including prevention from cardiometabolic diseases and cancer development as well as anti-inflammatory properties. It is worth noting that vitamin D deficiency is very common and may be associated with the pathogenesis of insulin-resistance-related diseases, including obesity and diabetes. This review aims to provide molecular mechanisms showing how vitamin D deficiency may be involved in the insulin resistance formation. The PUBMED database and published reference lists were searched to find studies published between 1980 and 2019. It was identified that molecular action of vitamin D is involved in maintaining the normal resting levels of ROS and Ca²⁺, not only in pancreatic β-cells, but also in insulin responsive tissues. Both genomic and non-genomic action of vitamin D is directed towards insulin signaling. Thereby, vitamin D reduces the extent of pathologies associated with insulin resistance such as oxidative stress and inflammation. More recently, it was also shown that vitamin D prevents epigenetic alterations associated with insulin resistance and diabetes. In conclusion, vitamin D deficiency is one of the factors accelerating insulin resistance formation. The results of basic and clinical research support beneficial action of vitamin D in the reduction of insulin resistance and related pathologies.

n-3 polyunsaturated fatty acids provoke a specific transcriptional profile in rabbit adipose-derived stem cells in vitro

Adipose-derived stem cells (ADSCs) possess multipotent properties, and their proper functionality is essential for further development of metabolic disorders. In the current study, we explored the impact of two n-3 LC-PUFAs (long-chain polyunsaturated fatty acids, DHA-docosahexaenoic; C22:6, and EPA-eicosapentaenoic; C20:5) on a specific profile of lipolytic-related gene expressions in the in vitro-differentiated subcutaneous and visceral ADSCs from rabbits. The subcutaneous and visceral ADSCs were obtained from 28-day-old New Zealand rabbits. The primary cells were cultured up to passage 4 and were induced for adipogenic differentiation. Thereafter, the differentiated cells were treated with 100 µg EPA or DHA for 48 hr. The total mRNA was isolated and target genes expression evaluated by real-time RCR. The results demonstrated that treatment of rabbit ADSCs with n-3 PUFAs significantly enhanced mRNA expression of Perilipin A, while the upregulation of leptin and Rab18 genes was seen mainly in ADSCs from visceral adipose tissue. Moreover, the EPA significantly enhanced PEDF (Pigment Derived Epithelium Factor) mRNA expression only in visceral cells. Collectively, the results suggest activation of an additional lipolysis pathway most evident in visceral cells. The data obtained in our study indicate that in vitro EPA up-regulates the mRNA expression of the studied lipolysis-associated genes stronger than DHA mainly in visceral rabbit ADSCs.

Epithelial expression of the hormone leptin by bovine skin

Leptin (Lep) stimulates keratinocytes to proliferate, intervenes in the wound healing and participates to hair follicle morphogenesis and cycle. While it is secreted by skin structures including epidermis and hair follicles, intradermal adipose tissue also seems to have a role in Lep secretion and accordingly in the control of hair follicle growth in mice and humans. Lep was investigated in the skin of humans and laboratory animals but there are not data regarding bovine species. The aim of this work was to study the expression of Lep and its receptor (LepR) in the skin of bovine and, at the same time, to investigate the presence and extension of intradermal adipose tissue. A morphological evaluation of the skin was performed while the presence and localization of Lep and LepR were analyzed by RT-PCR and immunohistochemistry. A high and thick dermis without adipocytes was observed. Hair follicles and sebaceous and sweat glands were located in the proximal part of the skin while a thick layer of connective tissue, lacking adipose cells, separated these structures by subcutis. RT-PCR evidenced the transcripts for both molecules. By immunohistochemistry, Lep and LepR were observed in the epidermis and hair follicles. Based on the absence of intradermal adipose tissue and the presence of both Lep and LepR in the epidermis and in the hair follicle epithelium, it can be posited that in bovine skin Lep participates to the control of epidermis growth and hair follicle cycle through a paracrine and autocrine mechanisms.

The Role of Oxidative Stress and Hormones in Controlling Obesity

The accumulation of adipose tissue in the body occurs because the energy introduced with food and drink exceeds that expense, but to understand why this imbalance is established and why it is maintained over time, it is important to consider the main causes and risk factors of excess weight. In this review, we will refer to the main factors linked to obesity, starting from oxidative stress to hormonal factors including the role of obesity in breast cancer. Among the many hypotheses formulated on the etiopathology of obesity, a key role can be attributed to the relationship between stress oxidative and intestinal microbiota. Multiple evidences tend to show that genetic, epigenetic, and lifestyle factors contribute to determine in the obese an imbalance of the redox balance correlated with the alteration of the intestinal microbial flora. Obesity acts negatively on the wound healing, in fact several studies indicate morbid obesity significantly increased the risk of a post-operative wound complication and infection. Currently, in the treatment of obesity, medical interventions are aimed not only at modifying caloric intake, but also to modulate and improve the composition of diet with the aim of rebalancing the microbiota-redox state axis.

Impact of body mass index on CT attenuation of adrenal adenoma

OBJECTIVE

To investigate whether lipid metabolism-related factors regulate unenhanced CT attenuation in adrenal adenoma (AA).

MATERIALS AND METHODS

Thirty-six patients with surgically proven AAs were enrolled in this study. The patients' underlying diseases were the following: primary aldosteronism (n = 24), Cushing's syndrome (n = 8), subclinical Cushing's syndrome (n = 3) and non-functioning AA (n = 1). Unenhanced CT attenuation of AAs and liver was measured. Pathologically, clear cell ratio (CCR) constituting each AA was qualitatively assessed. Clinical data including tumor diameter, body mass index (BMI), hemoglobin A1c, triglyceride, total cholesterol, blood cortisol and plasma aldosterone levels were also obtained. Simple and multiple linear regression analyses were performed to evaluate the radiological and clinicopathological factors associated with CT attenuation of AAs for all patients and separately for 25 patients with primary aldosteronism or non-functioning AA.

RESULTS

For all patients, there was a significant correlation between CT attenuation and each of CCR, BMI and blood cortisol levels (p < 0.05). For patients with primary aldosteronism or non-functioning AA, there was also a significant correlation between CT attenuation and CCR or BMI (p < 0.05).

CONCLUSION

In addition to pathological factors, lipid-metabolism-related factors including BMI and blood cortisol levels can affect unenhanced CT attenuation of AA.

Short-term time-restricted feeding during the resting phase is sufficient to induce leptin resistance that contributes to development of obesity and metabolic disorders in mice

Feeding at unusual times of the day is thought to be associated with obesity and metabolic disorders in both experimental animals and humans. We previously reported that time-imposed feeding during the sleep phase (daytime feeding, DF) induces obesity and metabolic disorders compared with mice fed only during the active phase (nighttime feeding, NF). The present study aimed to determine whether leptin resistance is caused by DF, and whether it is involved in the underlying mechanisms of DF-induced obesity in mice, since leptin plays an essential role in regulating energy expenditure and adiposity in addition to food intake. We compared leptin sensitivity by evaluating the effects of exogenous injected leptin on food intake and body weight in wild-type C57BL/6J mice under NF and DF. The mice were fed with a high-fat high-sucrose diet throughout the study. To determine whether leptin resistance is a cause or a result of DF-induced obesity with metabolic disorders, we restricted the feeding times of leptin resistant db/db mice. We also examined leptin sensitivity in leptin deficient ob/ob mice under NF and DF to elucidate the underlying mechanisms of DF-induced leptin resistance. C57BL/6J mice under DF gained more weight and adiposity compared with mice under NF, and developed hyperleptinemia and hypothermia. We found that six days of DF abolished exogenous leptin-induced hypophagia and reduction in body weight in mice. We also found that the leptin injection significantly suppressed the mRNA expression of lipogenic genes in the liver of NF, but not in DF mice, suggesting that short-term DF was sufficient to induce metabolic leptin resistance. The DF-induced increases in body weight gain, food efficiency, adipose tissue mass, lipogenic gene expression in metabolic tissues, and hepatic lipid accumulation were abolished in db/db mice, suggesting that the leptin resistance is a cause of DF-induced metabolic disorders. DF resulted in deep hypothermia in db/db, as well as in wild-type mice, suggesting that a decrease in energy expenditure was not the main cause of DF-induced obesity. Exogenous leptin reduced the body weight of ob/ob mice under both NF and DF, and the effect was significantly higher in DF- than in NF-ob/ob mice. Therefore, the development of DF-induced leptin resistance requires endogenous leptin, and central leptin sensitivity fluctuates in a circadian manner. The present findings suggest that leptin resistance is responsible for DF-induced obesity and metabolic disorders, and that the circadian fluctuation of central leptin sensitivity might be involved in leptin resistance induced by DF, although further studies are needed to elucidate the mechanisms of metabolic disorders that depend on the time of feeding. Abbreviations: AMPK, adenosine monophosphate-activated protein kinase; ANOVA, analysis of variance; DF, daytime feeding; FFA, free fatty acid; HOMA-IR, homeostasis model assessment of insulin resistance; NEAT, non-exercise activity thermogenesis; NF, nighttime feeding; PI3, phosphatidylinositol 3; RF, restricted feeding; RW, running-wheel; SCN, suprachiasmatic nucleus; SEM, standard error of the mean; STAT3, signal transducer and activator of transcription 3; T-Cho, total cholesterol; TG, triglyceride; WAT, white adipose tissues.

Feed-efficient pigs exhibit molecular patterns allowing a timely circulation of hormones and nutrients

Feed efficiency (FE) is a measure of the rate between feed intake and body weight gain and is subject to constant progress in pigs, based on extensive performance tests and analyses of physiological parameters. However, endocrine regulatory circuits that comprise the sensation and perception of intrinsic requirements and appropriate systemic responses have not yet been fully elucidated. It is hypothesized that the gut-brain axis, which is a network of hierarchical anterior regulatory tissues, contributes largely to variations in FE. Therefore, full-sib pigs with extreme residual feed intake values were assigned to experimental groups of high and low FE. Relevant hormones, minerals, and metabolites including fatty acid profiles were analyzed in serum to assess postprandial conditions. Transcriptome profiles were deduced from intestinal (duodenum, jejunum, ileum) and neuroendocrine tissues (hypothalamus). Serum analyses of feed-efficient animals showed an increased content of the incretin GIP, calcium, magnesium, β-hydroxybutyric acid, and fat compared with low-FE pigs. Complementary expression profiles in intestinal tissues indicate a modulated permeability and host-microbe interaction in FE-divergent pigs. Transcriptomic analyses of the hypothalamus showed that differences between the FE groups in appetite and satiety regulation are less pronounced. However, hypothalamic abundance of transcripts like ADCY7, LHCGR, and SLC2A7 and molecular signatures in local and systemic tissue sites indicate that increased allocation and circulation of energy equivalents, minerals, and hormones are promoted in feed-efficient animals. Overall, patterns of gastrointestinal hormones and gene expression profiles identified host-microbiota interaction, intestinal permeability, feed intake regulation, and energy expenditure as potential mechanisms affecting FE in pigs.

DEHP deregulates adipokine levels and impairs fatty acid storage in human SGBS-adipocytes

DEHP is a plasticizer which has been used in plastic products of everyday use for decades. Studies in mice and murine cell culture models identified DEHP as an endocrine disruptor that may also act as an obesogen. As this is of high concern in respect of the worldwide obesity epidemic, our aim is the translation of these findings into a human model system. On the basis of DOHaD, we investigated the influence of an environmentally relevant dose of DEHP [50 µg/ml] on adipogenesis in the human cell culture model SGBS. Pre-adipocytes were exposed to DEHP and differentiated into mature adipocytes. At different stages of differentiation, markers of adipogenesis like GLUT4, FABP4, LPL and PPARs, and of signaling pathways like AMPK/ACC2, JAK/STAT and MAPK were analyzed. Functional markers like adipokine secretion and triglyceride content as well as ROS production were measured in mature adipocytes. We found significantly lower expression levels of adipogenic markers, a reduction in lipid accumulation, higher leptin- and reduced adiponectin levels in the supernatant of treated adipocytes. Moreover, ROS production was significantly elevated after DEHP-exposure. In conclusion, DEHP led to lower grade of adipogenic differentiation in human SGBS-adipocytes under the chosen conditions.

A new perspective on managing the onset of puberty and early reproductive performance in ewe lambs: a review

Global changes in industry and society have led us to reassess the numerous factors that combine to influence the time of onset of puberty and the efficiency of reproduction in young sheep. Age and weight have long been considered the dominant factors that influence the onset of puberty and, for many years, it has been accepted that these relationships are mediated by the hormone, leptin, produced by body fat. However, recent studies showing that muscle mass also plays a role have challenged this dogma and also presented new options for our understanding of metabolic inputs into the brain control of reproduction. Moreover, the possibility that an improvement in meat production will simultaneously advance puberty is exciting from an industry perspective. An industry goal of strong reproductive performance in the first year of life is becoming possible and, with it, a major step upwards in the lifetime reproductive performance of ewes. The concept of early puberty is not well accepted by producers for a variety of reasons, but the new data show clear industry benefits, so the next challenge is to change that perception and encourage producers to manage young ewes so they produce their first lamb at 1 year of age.

Metabolomics reveals an entanglement of fasting leptin concentrations with fatty acid oxidation and gluconeogenesis in healthy children

Background

Leptin and adiponectin communicate with organ systems in order to regulate energetic and metabolic homeostasis. Their different points of action have been well characterized; however, no study has investigated their interrelationship with the metabolism at the molecular level in vivo.

Objective

To examine the associations of leptin and adiponectin with the metabolic profile reflecting the intercellular and interorgan communication as well as activated metabolic pathways.

Patients/Methods

We measured plasma concentrations of leptin, adiponectin, and insulin along with concentrations of 196 metabolites in 400 healthy, fasting 8-years old German children who participated in the German Ulm Birth Cohort Study (UBCS). Using multiple linear mixed models, we evaluated the associations between hormones and metabolites.

Results

Leptin levels increased exponentially with increasing BMI. Leptin was furthermore strongly associated with alanine and aspartate (Bonferroni corrected P[P_BF] = 5.7×10⁻⁸ and 1.7×10⁻⁶, respectively), and negatively associated to the sum of the non-esterified fatty acids (NEFA) and the sum of the long-chain acylcarnitines C12–C18 (P_BF = 0.009 and 0.0001, respectively). Insulin showed a similar association pattern, although the associations were less strong than for leptin. Adiponectin was neither related to BMI nor to any metabolite.

Conclusion

Although children were presumably metabolically similar, we found strong associations of insulin and leptin with the metabolite profile. High alanine concentrations and the lower concentrations of NEFA in children with high fasting leptin concentrations might arise from an increased gluconeogenesis and from the disinhibiting effect of leptin on the carnitine-palmitoyltransferase-1, respectively. As insulin had the same trend towards these associations, both hormones seem to be related to processes that provide the body with energy in fasting state.

Normalization of adiponectin concentrations by leptin replacement in ob/ob mice is accompanied by reductions in systemic oxidative stress and inflammation

The circulating concentrations of adiponectin, an antidiabetic adipokine, have been shown to be reduced in obesity, in relation to an increase in inflammation. The aim of the present work was to assess the effect of leptin replacement on adiponectin levels and expression as well as on markers of oxidative stress and inflammation in leptin-deficient ob/ob mice. Twelve-week-old male mice (n = 7–10 per group) were treated with either saline (wild type and ob/ob mice) or leptin (ob/ob mice) for 18 days. A third group of ob/ob mice was treated with saline and pair-fed to the amount of food consumed by the leptin-treated group. Leptin replacement restored values of adiponectin (P < 0.001), reduced circulating 8-isoprostane and serum amyloid A (SAA) levels (P < 0.05 for both), and significantly downregulated the increased gene expression of osteopontin (Spp1, P < 0.05), Saa3 (P < 0.05), Cd68 (P < 0.01), Il6 (P < 0.01) and NADPH oxidase (Nox1 and Nox2, P < 0.01) in the perirenal WAT and Spp1 (P < 0.05) in the liver of ob/ob mice. In cultured adipocytes from ob/ob mice, leptin increased (P < 0.05) the mRNA expression and secretion of adiponectin. We concluded that circulating concentrations of adiponectin are positively regulated by leptin and ameliorate obesity-associated oxidative stress and inflammation in mice.

The glucoregulatory actions of leptin

Background

The hormone leptin is an important regulator of metabolic homeostasis, able to inhibit food intake and increase energy expenditure. Leptin can also independently lower blood glucose levels, particularly in hyperglycemic models of leptin or insulin deficiency. Despite significant efforts and relevance to diabetes, the mechanisms by which leptin acts to regulate blood glucose levels are not fully understood.

Scope of review

Here we assess literature relevant to the glucose lowering effects of leptin. Leptin receptors are widely expressed in multiple cell types, and we describe both peripheral and central effects of leptin that may be involved in lowering blood glucose. In addition, we summarize the potential clinical application of leptin in regulating glucose homeostasis.

Major conclusions

Leptin exerts a plethora of metabolic effects on various tissues including suppressing production of glucagon and corticosterone, increasing glucose uptake, and inhibiting hepatic glucose output. A more in-depth understanding of the mechanisms of the glucose-lowering actions of leptin may reveal new strategies to treat metabolic disorders.

Fetal Hyperglycemia Changes Human Preadipocyte Function in Adult Life

CONTEXT

Offspring of women with gestational diabetes (O-GDM) or type 1 diabetes mellitus (O-T1DM) have been exposed to hyperglycemia in utero and have an increased risk of developing metabolic disease in adulthood.

DESIGN

In total, we recruited 206 adult offspring comprising the two fetal hyperglycemic groups, O-GDM and O-T1DM, and, as a control group, offspring from the background population (O-BP). Subcutaneous fat biopsies were obtained and preadipocyte cell cultures were established from adult male O-GDM (n = 18, age 30.1 ± 2.5 years), O-T1DM (n = 18, age 31.6 ± 2.2 years), and O-BP (n = 16; age, 31.5 ± 2.7 years) and cultured in vitro.

MAIN OUTCOME MEASURES

First, we studied in vivo adipocyte histology. Second, we studied in vitro preadipocyte leptin secretion, gene expression, and LEP DNA methylation. This was studied in combination with in vitro preadipocyte lipogenesis, lipolysis, and mitochondrial respiration.

RESULTS

We show that subcutaneous adipocytes from O-GDM are enlarged compared with O-BP adipocytes. Preadipocytes isolated from male O-GDM and O-T1DM and cultured in vitro displayed decreased LEP promoter methylation, increased leptin gene expression, and elevated leptin secretion throughout differentiation, compared with adipocytes established from male O-BP. In addition, the preadipocytes demonstrated functional defects including decreased maximal mitochondrial capacity with increased lipolysis and decreased ability to store fatty acids when challenged with 3 days of extra fatty acid supply.

CONCLUSIONS

Taken together, these findings show that intrinsic epigenetic and functional changes exist in preadipocyte cultures from individuals exposed to fetal hyperglycemia who are at increased risk of developing metabolic disease.

Vitamin D deficiency and diabetes

Vitamin D deficiency has been linked to the onset of diabetes. This review summarizes the role of Vitamin D in maintaining the normal release of insulin by the pancreatic beta cells (β-cells). Diabetes is initiated by the onset of insulin resistance. The β-cells can overcome this resistance by releasing more insulin, thus preventing hyperglycaemia. However, as this hyperactivity increases, the β-cells experience excessive Ca2+ and reactive oxygen species (ROS) signalling that results in cell death and the onset of diabetes. Vitamin D deficiency contributes to both the initial insulin resistance and the subsequent onset of diabetes caused by β-cell death. Vitamin D acts to reduce inflammation, which is a major process in inducing insulin resistance. Vitamin D maintains the normal resting levels of both Ca2+ and ROS that are elevated in the β-cells during diabetes. Vitamin D also has a very significant role in maintaining the epigenome. Epigenetic alterations are a feature of diabetes by which many diabetes-related genes are inactivated by hypermethylation. Vitamin D acts to prevent such hypermethylation by increasing the expression of the DNA demethylases that prevent hypermethylation of multiple gene promoter regions of many diabetes-related genes. What is remarkable is just how many cellular processes are maintained by Vitamin D. When Vitamin D is deficient, many of these processes begin to decline and this sets the stage for the onset of diseases such as diabetes.

Crosstalk between adipokines and myokines in fat browning

Skeletal muscle is the largest organ determining whole-body insulin sensitivity and metabolic homoeostasis. Adaptive changes of skeletal muscle in response to physical activity include adjustments in the production and secretion of muscle-derived bioactive factors, known as myokines, such as myostatin, IL-4, IL-6, IL-7 and IL-15, myonectin, follistatin-like 1 or leukaemia inhibitory factor. These myokines not only act locally in the muscle in an autocrine/paracrine manner, but also are released to the bloodstream as endocrine factors to regulate physiological processes in other tissues. Irisin, derived from the cleavage of FNDC5 protein, constitutes a myokine that induces myogenesis and fat browning (switch of white adipocytes to brown fat-like cells) together with a concomitant increase in energy expenditure. Besides being a target for irisin actions, the adipose tissue also constitutes a production site of FNDC5. Interestingly, irisin secretion from subcutaneous and visceral fat depots is decreased by long-term exercise training and fasting, suggesting a discordant regulation of FNDC5/irisin in skeletal muscle and adipose tissue. Accordingly, our group has recently reported that the adipokine leptin differentially regulates FNDC5/irisin expression in skeletal muscle and fat, confirming the crosstalk between both tissues. Moreover, irisin secretion and function are regulated by other myokines, such as follistatin or myostatin, as well as by other adipokines, including fibroblast growth factor 21 and leptin. Taken together, myokines have emerged as novel molecular mediators of fat browning and their activity can be modulated by adipokines, confirming the crosstalk between skeletal muscle and adipose tissue to regulate thermogenesis and energy expenditure.

Physiological functions of Vitamin D in adipose tissue

Adipose tissue has long been identified as the major site of vitamin D storage. Recent studies have demonstrated that VDR and vitamin D metabolizing enzymes are expressed in adipocytes. Furthermore, it has been shown that vitamin D regulates adipogenic gene expression as well as adipocyte apoptosis. Vitamin D is active in adipocytes at all levels. It interacts with membrane receptors, adaptor molecules, and nuclear coregulator proteins. Several functions of unliganded nVDR were discovered by studying human samples from patients having hereditary vitamin D resistant rickets, transgenic mice overexpressing the VDR and VDR knockout mice. Through its genomic action, vitamin D participates in the regulation of energy metabolism by controlling the expression of uncoupling proteins. In vitro, vitamin D stimulates lipogenesis and inhibits lipolysis by interacting with mVDR. mVDR is present in caveolae of the plasma membrane and is the same as the classic nVDR. In addition, vitamin D affects directly the expression of the appetite regulating hormone, leptin. Some researchers reported also that vitamin D regulates the expression of the insulin sensitizing hormone, adiponectin. Vitamin D reduced cytokine release and adipose tissue inflammation through the inhibition of NF-κB signaling. Scientific research investigating the role of adipose tissue resident immune cells in the pathogenesis of obesity-associated inflammation is scarce. Obesity is associated with vitamin D deficiency. However there is no scientific evidence to prove that vitamin D deficiency predispose to obesity. Vitamin D supplementation may prevent obesity but it does not lead to weight loss in obese subjects.

Beyond thermoregulation: metabolic function of cetacean blubber in migrating bowhead and beluga whales

The processes of lipid deposition and utilization, via the gene leptin (Lep), are poorly understood in taxa with varying degrees of adipose storage. This study examines how these systems may have adapted in marine aquatic environments inhabited by cetaceans. Bowhead (Balaena mysticetus) and beluga whales (Delphinapterus leucas) are ideal study animals-they possess large subcutaneous adipose stores (blubber) and undergo bi-annual migrations concurrent with variations in food availability. To answer long-standing questions regarding how (or if) energy and lipid utilization adapted to aquatic stressors, we quantified variations in gene transcripts critical to lipid metabolism related to season, age, and blubber depth. We predicted leptin tertiary structure conservation and assessed inter-specific variations in Lep transcript numbers between bowheads and other mammals. Our study is the first to identify seasonal and age-related variations in Lep and lipolysis in these cetaceans. While Lep transcripts and protein oscillate with season in adult bowheads reminiscent of hibernating mammals, transcript levels reach up to 10 times higher in bowheads than any other mammal. Data from immature bowheads are consistent with the hypothesis that short baleen inhibits efficient feeding. Lipolysis transcripts also indicate young Fall bowheads and those sampled during Spring months limit energy utilization. These novel data from rarely examined species expand the existing knowledge and offer unique insight into how the regulation of Lep and lipolysis has adapted to permit seasonal deposition and maintain vital blubber stores.

The changes in body weight and plasma metabolite levels during leptin injection are caused by the reduction of food intake in sheep

Leptin is thought to act on the central nervous system as an important regulator of food intake and body weight in mice. To examine the actions of leptin in sheep, we injected recombinant mouse leptin into the lateral cerebral ventricle of ewes. Six ewes were intracerebroventricularly cannulated and given free access to forage and water. The ewes were injected with phosphate-buffered saline (PBS) as a vehicle for 5 days through the cannula and then with PBS + leptin for 7 days consecutively. Although food intake and body weight did not change during PBS injection, the administration of leptin decreased food intake and body weight. Plasma glucose levels decreased and plasma non-esterified fatty acid levels increased on the last few days of leptin administration. Approximately 2 weeks after normal food intake was recovered, the amount of diet was individually reduced in accordance with the recorded food intake during the leptin administration in each sheep. During food restriction, body weight and plasma metabolite concentrations were similarly changed as during the leptin-administration period. These results indicate that leptin decreases food intake in sheep. Moreover, it is likely that the changes in body weight and plasma metabolites were mainly induced by the suppression of food intake during leptin injection.

The role of α1-adrenergic receptors in regulating metabolism: increased glucose tolerance, leptin secretion and lipid oxidation

The role of α₁-adrenergic receptors (α₁-ARs) and their subtypes in metabolism is not well known. Most previous studies were performed before the advent of transgenic mouse models and utilized transformed cell lines and poorly selective antagonists. We have now studied the metabolic regulation of the α_1A- and α_1B-AR subtypes in vivo using knock-out (KO) and transgenic mice that express a constitutively active mutant (CAM) form of the receptor, assessing subtype-selective functions. CAM mice increased glucose tolerance while KO mice display impaired glucose tolerance. CAM mice increased while KO decreased glucose uptake into white fat tissue and skeletal muscle with the CAM α_1A-AR showing selective glucose uptake into the heart. Using indirect calorimetry, both CAM mice demonstrated increased whole body fatty acid oxidation, while KO mice preferentially oxidized carbohydrate. CAM α_1A-AR mice displayed significantly decreased fasting plasma triglycerides and glucose levels while α_1A-AR KO displayed increased levels of triglycerides and glucose. Both CAM mice displayed increased plasma levels of leptin while KO mice decreased leptin levels. Most metabolic effects were more efficacious with the α_1A-AR subtype. Our results suggest that stimulation of α₁-ARs results in a favorable metabolic profile of increased glucose tolerance, cardiac glucose uptake, leptin secretion and increased whole body lipid metabolism that may contribute to its previously recognized cardioprotective and neuroprotective benefits.

Roles of leptin and ghrelin in adipogenesis and lipid metabolism of rainbow trout adipocytes in vitro

Leptin and ghrelin are important regulators of energy homeostasis in mammals, whereas their physiological roles in fish have not been fully elucidated. In the present study, the effects of leptin and ghrelin on adipogenesis, lipolysis and on expression of lipid metabolism-related genes were examined in rainbow trout adipocytes in vitro. Leptin expression and release increased from preadipocytes to mature adipocytes in culture, but did not affect the process of adipogenesis. While ghrelin and its receptor were identified in cultured differentiated adipocytes, ghrelin did not influence either preadipocyte proliferation or differentiation, indicating that it may have other adipose-related roles. Leptin and ghrelin increased lipolysis in mature freshly isolated adipocytes, but mRNA expression of lipolysis markers was not significantly modified. Leptin significantly suppressed the fatty acid transporter-1 expression, suggesting a decrease in fatty acid uptake and storage, but did not affect expression of any of the lipogenesis or β-oxidation genes studied. Ghrelin significantly increased the mRNA levels of lipoprotein lipase, fatty acid synthase and peroxisome proliferator-activated receptor-β, and thus appears to stimulate synthesis of triglycerides as well as their mobilization. Overall, the study indicates that ghrelin, but not leptin seems to be an enhancer of lipid turn-over in adipose tissue of rainbow trout, and this regulation may at least partly be mediated through autocrine/paracrine mechanisms. The mode of action of both hormones needs to be further explored to better understand their roles in regulating adiposity in fish.

De novo lipogenesis in metabolic homeostasis: More friend than foe?

Background

An acute surplus of carbohydrates, and other substrates, can be converted and safely stored as lipids in adipocytes via de novo lipogenesis (DNL). However, in obesity, a condition characterized by chronic positive energy balance, DNL in non-adipose tissues may lead to ectopic lipid accumulation leading to lipotoxicity and metabolic stress. Indeed, DNL is dynamically recruited in liver during the development of fatty liver disease, where DNL is an important source of lipids. Nonetheless, a number of evidences indicates that DNL is an inefficient road for calorie to lipid conversion and that DNL may play an important role in sustaining metabolic homeostasis.

Scope of review

In this manuscript, we discuss the role of DNL as source of lipids during obesity, the energetic efficiency of this pathway in converting extra calories to lipids, and the function of DNL as a pathway supporting metabolic homeostasis.

Major conclusion

We conclude that inhibition of DNL in obese subjects, unless coupled with a correction of the chronic positive energy balance, may further promote lipotoxicity and metabolic stress. On the contrary, strategies aimed at specifically activating DNL in adipose tissue could support metabolic homeostasis in obese subjects by a number of mechanisms, which are discussed in this manuscript.

Leptin signaling as a therapeutic target of obesity

INTRODUCTION

Leptin is a hormone with a key role in food intake and body weight homeostasis. Congenital leptin deficiency (CLD) is a rare disease that causes hyperphagia and early severe obesity. However, common obesity conditions are associated with hyperleptinemia and leptin resistance.

AREAS COVERED

The main signaling pathways activated by leptin as well as the mechanisms underlying the regulatory actions of leptin on food intake and on lipid and glucose metabolism are reviewed. The potential mechanisms involving leptin resistance and the main regulatory hormonal and nutritional factors controlling leptin production/functions are also analyzed. The pathophysiology of leptin in human obesity, and especially the trials analyzing effects of leptin replacement therapy in patients with CLD or in subjects with common obesity and in post-obese weight-reduced subjects are also summarized.

EXPERT OPINION

The use of drugs or specific bioactive food components with anti-inflammatory properties to reduce the inflammatory state associated with obesity, especially at the hypothalamus, may help to overcome leptin resistance. Research should also be focused on investigating dietary strategies, food supplements or drugs capable of avoiding or reversing the leptin fall during weight management, in order to promote sustained body weight lowering and weight loss maintenance.

Leptin resistance and diet-induced obesity: central and peripheral actions of leptin

Obesity is a chronic disease that represents one of the most serious global health burdens associated to an excess of body fat resulting from an imbalance between energy intake and expenditure, which is regulated by environmental and genetic interactions. The adipose-derived hormone leptin acts via a specific receptor in the brain to regulate energy balance and body weight, although this protein can also elicit a myriad of actions in peripheral tissues. Obese individuals, rather than be leptin deficient, have in most cases, high levels of circulating leptin. The failure of these high levels to control body weight suggests the presence of a resistance process to the hormone that could be partly responsible of disturbances on body weight regulation. Furthermore, leptin resistance can impair physiological peripheral functions of leptin such as lipid and carbohydrate metabolism and nutrient intestinal utilization. The present document summarizes those findings regarding leptin resistance development and the role of this hormone in the development and maintenance of an obese state. Thus, we focused on the effect of the impaired leptin action on adipose tissue, liver, skeletal muscle and intestinal function and the accompanying relationships with diet-induced obesity. The involvement of some inflammatory mediators implicated in the development of obesity and their roles in leptin resistance development are also discussed.

Neural innervation of white adipose tissue and the control of lipolysis

White adipose tissue (WAT) is innervated by the sympathetic nervous system (SNS) and its activation is necessary for lipolysis. WAT parasympathetic innervation is not supported. Fully-executed SNS-norepinephrine (NE)-mediated WAT lipolysis is dependent on β-adrenoceptor stimulation ultimately hinging on hormone sensitive lipase and perilipin A phosphorylation. WAT sympathetic drive is appropriately measured electrophysiologically and neurochemically (NE turnover) in non-human animals and this drive is fat pad-specific preventing generalizations among WAT depots and non-WAT organs. Leptin-triggered SNS-mediated lipolysis is weakly supported, whereas insulin or adenosine inhibition of SNS/NE-mediated lipolysis is strongly supported. In addition to lipolysis control, increases or decreases in WAT SNS drive/NE inhibit and stimulate white adipocyte proliferation, respectively. WAT sensory nerves are of spinal-origin and sensitive to local leptin and increases in sympathetic drive, the latter implicating lipolysis. Transsynaptic viral tract tracers revealed WAT central sympathetic and sensory circuits including SNS-sensory feedback loops that may control lipolysis.

Regulation of adipocytes lipolysis by n-3 HUFA in grass carp (Ctenopharyngodon idellus) in vitro and in vivo

N-3 highly unsaturated fatty acids (n-3 HUFA) have been shown to inhibit body fat accumulation in animals. To clarify the mechanism of this fat-lowering effect of n-3 HUFA in grass carp (Ctenopharyngodon idellus), two experiments were conducted. In experiment 1, isolated grass carp mature adipocytes were incubated with docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) at different concentrations for 6 h. The release of glycerol to the medium was detected, and the expression of the lipolysis-related genes was analyzed. In experiment 2, a 95-day feeding trial was conducted with two diets formulated with either lard oil (as control) or fish oil (supplying n-3 HUFA as treatment) as the main lipid source. The glycerol and free fatty acid (FFA) released from the isolated adipocytes of both groups were detected after the feeding period. The expression of select lipolysis-related genes in adipose tissue was also analyzed. The results from experiment 1 showed that the release of glycerol was significantly increased by DHA and EPA (P < 0.05). Moreover, the expression of lipolysis-related genes, such as adipose triglyceride lipase (ATGL), hormone-sensitive lipase (HSL), tumor necrosis factor α (TNFα) and leptin, was also significantly elevated in the treatment group (P < 0.05). Experiment 2 demonstrated that glycerol and FFA release from the isolated adipocytes were significantly higher in the treatment group compared to the control group (P < 0.05). The expression level of ATGL, HSL, TNFα and leptin in the treatment group was significantly higher than in the control group (P < 0.05). The present results provide novel evidence that n-3 HUFAs could regulate grass carp adipocyte lipolysis in vitro or in vivo, and the effect might be in part associated with their influence on the expression of lipolysis-related genes and lipolysis-related adipokines genes.