Hypothalamic lipotoxicity and the metabolic syndrome

Ectopic accumulation of lipids in peripheral tissues, such as pancreatic β cells, liver, heart and skeletal muscle, leads to lipotoxicity, a process that contributes substantially to the pathophysiology of insulin resistance, type 2 diabetes, steatotic liver disease and heart failure. Current evidence has demonstrated that hypothalamic sensing of circulating lipids and modulation of hypothalamic endogenous fatty acid and lipid metabolism are two bona fide mechanisms modulating energy homeostasis at the whole body level. Key enzymes, such as AMP-activated protein kinase (AMPK) and fatty acid synthase (FAS), as well as intermediate metabolites, such as malonyl-CoA and long-chain fatty acids-CoA (LCFAs-CoA), play a major role in this neuronal network, integrating peripheral signals with classical neuropeptide-based mechanisms. However, one key question to be addressed is whether impairment of lipid metabolism and accumulation of specific lipid species in the hypothalamus, leading to lipotoxicity, have deleterious effects on hypothalamic neurons. In this review, we summarize what is known about hypothalamic lipid metabolism with focus on the events associated to lipotoxicity, such as endoplasmic reticulum (ER) stress in the hypothalamus. A better understanding of these molecular mechanisms will help to identify new drug targets for the treatment of obesity and metabolic syndrome.     

代谢综合征与下丘脑功能改变

下丘脑对瘦素/胰岛素敏感性降低导致的能量平衡调节异常和下丘脑-垂体-肾上腺轴功能紊乱参与了代谢综合征的发生发展,下丘脑功能改变是代谢综合征重要的中枢病理生理学机制。代谢综合征下丘脑功能改变与局部炎性细胞因子表达增加有关,IKK/NF-κB激活可能是下丘脑功能改变的关键分子机制。     

Hypothalamic peptides: central nervous system control of visceral functions

Thyrotropin-releasing factor (TRF), somatostatin, and bombesin-like peptide are present in the brain and may be involved in central nervous system (CNS) control of visceral functions. All three peptides exert potent actions to modify animal thermoregulation. TRF and somatostatin or somatostatin analogs act within the brain to influence parasympathetic and sympathetic outflow resulting in changes of adrenal epinephrine secretion, gastric acid secretion, heart rate, and blood pressure. Bombesin acts within the brain to increase adrenal epinephrine secretion and to inhibit gastric acid secretion without influencing other sympathetic or parasympathetic activities. These peptides and others may be important physiological regulators of CNS information processing related to a variety of visceral systems.     

Hypothalamic self-stimulation during the abstinence syndrome in morphine-dependent rats

Rats with lateral hypothalamic self-stimulation were treated chronically with morphine (30 injections in the course of 15 days) in doses increasing stepwise from 20 to 120 mg/kg per injection. Morphine facilitated self-stimulation from the 9th injection. Both short-term abstinence (16-18 hours) and cessation of the narcotic resulted in inhibition of the response. Full suppression of self-stimulation occurred under the administration of nalorphine, morphine antagonist, in a dose of 5 mg/kg.     

Genome-wide association for abdominal subcutaneous and visceral adipose reveals a novel locus for visceral fat in women

Body fat distribution, particularly centralized obesity, is associated with metabolic risk above and beyond total adiposity. We performed genome-wide association of abdominal adipose depots quantified using computed tomography (CT) to uncover novel loci for body fat distribution among participants of European ancestry. Subcutaneous and visceral fat were quantified in 5,560 women and 4,997 men from 4 population-based studies. Genome-wide genotyping was performed using standard arrays and imputed to ~2.5 million Hapmap SNPs. Each study performed a genome-wide association analysis of subcutaneous adipose tissue (SAT), visceral adipose tissue (VAT), VAT adjusted for body mass index, and VAT/SAT ratio (a metric of the propensity to store fat viscerally as compared to subcutaneously) in the overall sample and in women and men separately. A weighted z-score meta-analysis was conducted. For the VAT/SAT ratio, our most significant p-value was rs11118316 at LYPLAL1 gene (p = 3.1 × 10E-09), previously identified in association with waist-hip ratio. For SAT, the most significant SNP was in the FTO gene (p = 5.9 × 10E-08). Given the known gender differences in body fat distribution, we performed sex-specific analyses. Our most significant finding was for VAT in women, rs1659258 near THNSL2 (p = 1.6 × 10-08), but not men (p = 0.75). Validation of this SNP in the GIANT consortium data demonstrated a similar sex-specific pattern, with observed significance in women (p = 0.006) but not men (p = 0.24) for BMI and waist circumference (p = 0.04 [women], p = 0.49 [men]). Finally, we interrogated our data for the 14 recently published loci for body fat distribution (measured by waist-hip ratio adjusted for BMI); associations were observed at 7 of these loci. In contrast, we observed associations at only 7/32 loci previously identified in association with BMI; the majority of overlap was observed with SAT. Genome-wide association for visceral and subcutaneous fat revealed a SNP for VAT in women. More refined phenotypes for body composition and fat distribution can detect new loci not previously uncovered in large-scale GWAS of anthropometric traits.     

Intestinal permeability is associated with visceral adiposity in healthy women

Increased visceral fat, as opposed to subcutaneous/gluteal, most strongly relates to key metabolic dysfunctions including insulin resistance, hepatic steatosis, and inflammation. Mesenteric fat hypertrophy in patients with Crohn's disease and in experimental rodent models of gut inflammation suggest that impaired gut barrier function with increased leakage of gut-derived antigens may drive visceral lipid deposition. The aim of this study was to determine whether increased intestinal permeability is associated with visceral adiposity in healthy humans. Normal to overweight female subjects were recruited from a population-based cohort. Intestinal permeability was assessed using the ratio of urinary excretion of orally ingested sucralose to mannitol (S/M). In study 1 (n = 67), we found a positive correlation between waist circumference and S/M excretion within a time frame of urine collection consistent with permeability of the lower gastrointestinal tract (6-9 hours post-ingestion; P = 0.022). These results were followed up in study 2 (n = 55) in which we used computed tomography and dual energy X-ray absorptiometry to measure visceral and subcutaneous fat areas of the abdomen, liver fat content, and total body fat of the same women. The S/M ratio from the 6-12 h urine sample correlated with visceral fat area (P = 0.0003) and liver fat content (P = 0.004), but not with subcutaneous or total body fat. This novel finding of an association between intestinal permeability and visceral adiposity and liver fat content in healthy humans suggests that impaired gut barrier function should be further explored as a possible mediator of excess visceral fat accumulation and metabolic dysfunction.     

Impaired insulin action in subcutaneous adipocytes from women with visceral obesity

Visceral obesity is associated with resistance to the antilipolytic effect of insulin in vivo. We investigated whether subcutaneous abdominal and gluteal adipocytes from viscerally obese women exhibit insulin resistance in vitro. Subjects were obese black and white premenopausal nondiabetic women matched for visceral adipose tissue (VAT), total adiposity, and age. Independently of race and adipocyte size, increased VAT was associated with decreased sensitivity to insulin's antilipolytic effect in subcutaneous abdominal and gluteal adipocytes. Absolute lipolytic rates at physiologically relevant concentrations of insulin or the adenosine receptor agonist N(6)-(phenylisopropyl)adenosine were higher in subjects with the highest vs. lowest VAT area. Independently of cell size, abdominal adipocytes were less sensitive to the antilipolytic effect of insulin than gluteal adipocytes, which may partly explain increased nonesterified fatty acid fluxes in upper vs. lower body obese women. Moreover, increased VAT was associated with decreased responsiveness, but not decreased sensitivity, to insulin's stimulatory effect on glucose transport in abdominal adipocytes. These data suggest that insulin resistance of subcutaneous abdominal and, to a lesser extent, gluteal adipocytes may contribute to increased systemic lipolysis in both black and white viscerally obese women.     

Study results and prospects in the pathogenesis of neuroses]

An attempt is made to highlight the modern state of investigations concerning the experimental neuroses, to show new branches in studying pathogenesis of neuroses. A new concept is substantiated on a participation of the cerebral circulatory hypoxia at neuroses. Is demonstrated a high efficiency of prophylaxis and therapy of neuroses using the anti-oxidants of anti-hypoxic action.     

Function and reactivity of the microvascular bed in human neuroses

By contact microscopy the state and reactivity of the capillary bed (capillaries of the cheek mucosa) were studied in neurotic patients with different levels of arterial pressure (AP). It has been shown that at constant AP capillariscopic parameters (diameter, length and number of capillaries in the visual field) are relatively stable. Neuroses with hypertension are characterized by uneven (more expressed in arterioles) contraction of the capillaries, accelerated development and greater duration of reactions to the mental stress and applications of adrenaline and noradrenaline solutions in comparison with healthy persons. In hypotension, uniform capillaries contraction and slower development of the above reactions are observed.     

The contribution of visceral adiposity and mid-thigh fat-rich muscle to the metabolic profile in postmenopausal women

This study explored the relationship between muscle fat infiltration derived from mid-thigh computed tomography (CT) scan, central fat distribution and insulin sensitivity in postmenopausal women. Mid-thigh CT scans were used to measure low attenuation muscle surface (LAMS) (0-34 Hounsfield units (HU)), which represented a specific component of fat-rich muscle. Whole-body insulin sensitivity (M/I) was evaluated by an euglycemic-hyperinsulinemic clamp. A group of 103 women aged 57.0 ± 4.4 years was studied. Women with higher levels of LAMS presented higher metabolic risk features, particularly elevated fasting, 2-h plasma glucose (2hPG) concentrations and diminished M/I (P < 0.05). To further study the contribution of muscle fat infiltration and central adiposity on metabolic parameters, we divided the whole group based on the median of LAMS and visceral adipose tissue (VAT). As expected, the best metabolic profile was found in the Low-LAMS/Low-VAT group and the worst in the High-LAMS/High-VAT group. Women with Low-LAMS/High-VAT presented similar metabolic risks to those with High-LAMS/High-VAT. There was no difference between High-LAMS/Low-VAT and Low-LAMS/Low-VAT, which presents the most healthy metabolic and glycemic profiles as reflected by the lowest levels of cardiovascular disease risk variables. This suggests that High-LAMS/Low-VAT is also at low risk of metabolic deteriorations and that High-LAMS, only in the presence of High-VAT seems associated with deteriorated risks. Although increased mid-thigh fat-rich muscle was related to a deteriorated metabolic profile, VAT appears as a more important contributor to alterations in the metabolic profile in postmenopausal women.