Food for thought: The role of appetitive peptides in age-related cognitive decline

Through their well described actions in the hypothalamus, appetitive peptides such as insulin, orexin and leptin are recognized as important regulators of food intake, body weight and body composition. Beyond these metabolic activities, these peptides also are critically involved in a wide variety of activities ranging from modulation of immune and neuroendocrine function to addictive behaviors and reproduction. The neurological activities of insulin, orexin and leptin also include facilitation of hippocampal synaptic plasticity and enhancement of cognitive performance. While patients with metabolic disorders such as obesity and diabetes have greater risk of developing cognitive deficits, dementia and Alzheimer's disease (AD), the underlying mechanisms that are responsible for, or contribute to, age-related cognitive decline are poorly understood. In view of the importance of these peptides in metabolic disorders, it is not surprising that there is a greater focus on their potential role in cognitive deficits associated with aging. The goal of this review is to describe the evidence from clinical and pre-clinical studies implicating insulin, orexin and leptin in the etiology and progression of age-related cognitive decline. Collectively, these studies support the hypothesis that leptin and insulin resistance, concepts normally associated with the hypothalamus, are also applicable to the hippocampus.     

瘦素、抵抗素、2型糖尿病间的相关性研究

目的：研究血浆瘦素与抵抗素、体重指数、腰围、腰臀比、血脂、胰岛素敏感性指数等的关系。方法：对43例新诊断2型糖尿病患者及37例糖耐量正常者，测定空腹血浆瘦素、胰岛素、血糖、血脂及抵抗素浓度。结果：相关分析显示性别、体重指数（BMI）、腰围、腰臀比、胰岛素与瘦素呈显著正相关（r分别为0.623,0.534，0.516，0.302，0.354，均P<0.01），IAI与瘦素呈显著负相关(r=-0.373,P<0.01),甘油三酯、胆固醇空腹血糖与瘦素无明显相关。瘦素与抵抗素无相关性（r=0.101,P>0.05）结论：空腹血浆瘦素水平与肥胖程度、胰岛素抵抗呈显著正相关，与抵抗素无关。瘦素可能与2型糖尿病的发病有关。     

Adipocytokines as mediators of metabolic role of adipose tissue

The discovery of adipocytokines, products of adipose tissue, has been a turning point in the understanding of metabolic disorders. Historically considered as a passive depot of energy, adipose tissue has become an important active participant and adipocytokines crucial mediators of its metabolic role. Among a number of adipose tissue products, leptin and adiponectin are exclusively secreted by adipocytes. Leptin regulates energy homeostasis and interferes with several neuroendocrine and immune functions. Adiponectin is an intriguing adipocytokine with its serum level inversely correlated with fatness. It has been related to enhanced insulin sensitivity, anti-inflammatory and anti-atherogenic actions. Recent investigations have also emphasized the important role of resistin, visfatin, retinol binding protein 4, and of a whole list of cytokines like interleukin-6, tumor necrosis factor a, plasminogen activator inhibitor-1, or a chemokine, monocyte chemoattractant protein-1. The fact that secretory balance of adipose tissue in obesity is shifted towards the proinflammatory spectrum has supported the hypothesis on the development of dysfunctional adipose tissue in these circumstances. It contributes to the state of chronic inflammation and insulin resistance, and it seems to be a fundamental link between obesity and atherosclerosis.     

Interaction of Metabolic Syndrome with Asthma in Postmenopausal Women: Role of Adipokines

The increasing prevalence of both asthma and obesity are major health problems. Recent studies established a possible link between obesity and asthma; however, the underlying mechanism is not clear. The aim of the study was to analyze the prevalence of metabolic syndrome in postmenopausal subjects with asthma and search the interactions between adipokines, metabolic syndrome, and asthma. A total of 45 female patients (57.5?±?13.9 years) with asthma and 30 healthy subjects (59.6?±?12.8 years) in postmenopausal status were enrolled in this study. For the diagnosis of metabolic syndrome, modified World Health Organization diagnostic criteria were used. Blood levels of glucose, lipid profile, HbA1c, insulin, CRP, leptin, adiponectin, tumor necrosis factor-alpha, interleukin (IL)-6, IL-8 and plasminogen activator inhibitor-1 (PAI-1) were measured. The mean body mass index was 29.6?±?5.4 for asthma patients and 28.2?±?5.3 for the control group. The incidence of metabolic syndrome was found as 26 % for both groups. Insulin resistance as calculated by homeostasis model assessment (HOMA-IR) and fasting insulin levels were significantly higher in asthma patients (p?<?0.001 for both parameters). Leptin levels were significantly higher (p?=?0.001) and adiponectin levels were lower (p?=?0.029) in asthma patients compared to controls. We concluded that although incidence of obesity and metabolic syndrome was not higher in postmenopausal asthma patients than controls, there was an impairment of glucose metabolism and altered adipokine levels in asthma patients.     

Leptin in early life: a key factor for the development of the adult metabolic profile

Leptin levels during the perinatal period are important for the development of metabolic systems involved in energy homeostasis. In rodents, there is a postnatal leptin surge, with circulating leptin levels increasing around postnatal day (PND) 5 and peaking between PND 9 and PND 10. At this time circulating leptin acts as an important trophic factor for the development of hypothalamic circuits that control energy homeostasis and food seeking and reward behaviors. Blunting the postnatal leptin surge results in long-term leptin insensitivity and increased susceptibility to diet-induced obesity during adulthood. Pharmacologically increased leptin levels in the postnatal period also have long-term effects on metabolism. Nevertheless, this effect is controversial as postnatal hyperleptinemia is reported to both increase and decrease the predisposition to obesity in adulthood. The different effects reported in the literature could be explained by the different moments at which this hormone was administered, suggesting that modifications of the neonatal leptin surge at specific time points could selectively affect the development of central and peripheral systems that are undergoing modifications at this moment resulting in different metabolic and behavioral outcomes. In addition, maternal nutrition and the hormonal environment during pregnancy and lactation may also modulate the offspring's response to postnatal modifications in leptin levels. This review highlights the importance of leptin levels during the perinatal period in the development of metabolic systems that control energy homeostasis and how modifications of these levels may induce long-lasting and potentially irreversible effects on metabolism.     

Obesity, inflammation and diabetes

Integration of metabolism and immunity in normal physiology is beneficial to maintain homeostasis. It can also become deleterious under conditions such as the immunosuppression observed among the malnourished. With the increase of excess weight and obesity, a new set of problems and complications has emerged at the intersection of metabolic activity and immunity. As examples of the latter we find obesity associated with inflammatory diseases, diabetes, fatty liver disease and atherosclerosis. Obesity is characterized by inflammation; there are common factors at the crossroads of inflammation and metabolic disease. Obesity is characterized by an inflammatory response and many inflammatory mediators exhibit expression patterns that interfere with insulin action. The high level of coordination of inflammatory and metabolic pathways is highlighted by the overlapping biology of macrophage and adipocite function observed in obesity. The intracellular signaling pathways activated by inflammatory and stress responses inhibit insulin signaling and the loss of inflammatory mediators prevents insulin resistance. In the absence of obesity, an infusion of inflammatory cytokines or lipids causes insulin resistance. Understanding the mechanisms leading from obesity to inflammation will have important implications to help reduce the morbidity and mortality associated with obesity by preventing its association with inflammatory disorders.     

Obesity and susceptibility to autoimmune diseases

For decades, obesity has been considered to be the result of the complex interaction between genes and the environment and its pathogenesis is still unresolved. The discovery of hormones and neural mediators responsible for the control of food intake and metabolism at the hypothalamic level has provided fundamental insights into the complicated pathways that control food intake. However, the molecular basis for the association between obesity and low-degree chronic inflammation is still unknown. More recently, the discovery of leptin, one of the most abundant adipocyte-derived hormones, has suggested that nutritional status, through leptin secretion, can control immune self-tolerance modulating Treg suppressive function and responsiveness. Furthermore, recent experimental evidence has shown the presence of an abundant adipose tissue-resident Treg population responsible for the control of metabolic parameters and glucose homeostasis. Better knowledge of the intricate network of interactions among leptin-related energy regulation, Treg activities and obesity could lead to valuable strategies for therapeutic intervention in obesity and obesity-associated insulin resistance.     

急性冠状动脉综合征血清瘦素与血脂、胰岛素的关联研究

目的:探讨瘦素、胰岛素抵抗与血脂的相互关系,评价瘦素在急性冠状动脉综合征(ACS)中的作用。方法:38例ACS、34例稳定型心绞痛患者和36例正常人,采用放射免疫分析和生化法测定空腹血清瘦素、血脂、胰岛素水平,并进行相关分析。结果:ACS患者瘦素水平明显高于对照组;血脂与胰岛素水平类似瘦素变化。相关实验显示,瘦素水平与CH、TG呈正相关(r=0.41,P<0.05;r=0.36,P<0.05),与INS呈显著正相关(r=0.58;P<0.01),与HDL-c呈显著负相关(r=-0.40,P<0.05)。结论:ACS患者的瘦素水平与血脂代谢、高胰岛素血症/胰岛素抵抗以及代谢综合征的其他成分密切相关,并通过氧化应激、血栓形成等加速动脉粥样硬化的发展。     

代谢性核受体及其与代谢综合征的关系

代谢性核受体是一组与代谢调节相关的配体激活核受体转录因子,主要包括脂质过氧化物体增殖物激活受体(PPARs)、肝X受体(LXRs)和法尼酯衍生物X受体(FXRs)3种。它们在胰岛素敏感性、脂肪生成、脂质代谢、能量代谢、血压调节、炎症、细胞生长和分化等过程中起着关键的调节作用,因而近年来倍受关注。越来越多的研究表明这3种核受体不仅与代谢综合征,包括胰岛素抵抗、糖耐量受损2、型糖尿病、肥胖、高脂血症、高血压和微白蛋白尿之间存在密切的关系,也在动脉粥样硬化的发生及发展中有重要的作用。本文就代谢性核受体的生物学活性和生理功能作一简述,并对其在代谢综合征发病机制中的作用进行重点讨论。     

Oxygenation of adipose tissue: A human perspective

Obesity is a complex disorder of excessive adiposity, and is associated with adverse health effects such as cardiometabolic complications, which are to a large extent attributable to dysfunctional white adipose tissue. Adipose tissue dysfunction is characterized by adipocyte hypertrophy, impaired adipokine secretion, a chronic low‐grade inflammatory status, hormonal resistance and altered metabolic responses, together contributing to insulin resistance and related chronic diseases. Adipose tissue hypoxia, defined as a relative oxygen deficit, in obesity has been proposed as a potential contributor to adipose tissue dysfunction, but studies in humans have yielded conflicting results. Here, we will review the role of adipose tissue oxygenation in the pathophysiology of obesity‐related complications, with a specific focus on human studies. We will provide an overview of the determinants of adipose tissue oxygenation, as well as the role of adipose tissue oxygenation in glucose homeostasis, lipid metabolism and inflammation. Finally, we will discuss the putative effects of physiological and experimental hypoxia on adipose tissue biology and whole‐body metabolism in humans. We conclude that several lines of evidence suggest that alteration of adipose tissue oxygenation may impact metabolic homeostasis, thereby providing a novel strategy to combat chronic metabolic diseases in obese humans.     

Role of orexin in the regulation of glucose homeostasis

Orexin-A (hypocretin-1) and orexin-B (hypocretin-2) are hypothalamic neuropeptides that play key roles in the regulation of wakefulness, feeding, reward, autonomic functions and energy homeostasis. To control these functions indispensable for survival, orexin-expressing neurones integrate peripheral metabolic signals, interact with many types of neurones in the brain and modulate their activities via the activation of orexin-1 receptor or orexin-2 receptor. In addition, a new functional role of orexin is emerging in the regulation of insulin and leptin sensitivities responsible for whole-body glucose metabolism. Recent evidence indicates that orexin efficiently protects against the development of peripheral insulin resistance induced by ageing or high-fat feeding in mice. In particular, the orexin receptor-2 signalling appears to confer resistance to diet-induced obesity and insulin insensitivity by improving leptin sensitivity. In fact, the expression of orexin gene is known to be down-regulated by hyperglycaemia in the rodent model of diabetes, such as ob/ob and db/db mice. Moreover, the levels of orexin receptor-2 mRNA have been shown to decline in the brain of mice along with ageing. These suggest that hyperglycaemia due to insulin insensitivity during ageing or by habitual consumption of a high-fat diet leads to the reduction in orexin expression in the hypothalamus, thereby further exacerbating peripheral insulin resistance. Therefore, orexin receptor controlling hypothalamic insulin/leptin actions may be a new target for possible future treatment of hyperglycaemia in patients with type 2 diabetes.     

Leptin gene transfer in the hypothalamus enhances longevity in adult monogenic mutant mice in the absence of circulating leptin

Leptin, a product of the ob gene, is a pleiotropic signal implicated in regulation of multiple physiological functions in the periphery and centrally, including hypothalamic integration of energy homeostasis. Recessive mutations of ob gene result in early onset of hyperphagia, morbid obesity, metabolic disorders, early mortality and shortened life-span. Intracerebroventricular injection of recombinant adeno-associated virus vector (rAAV) encoding the leptin gene in adult obese ob/ob mice enhanced leptin transgene expression only in the hypothalamus, normalized food intake, body weight and more than doubled the life-span as compared to control cohorts and extended it to near that of normal wild type mice. These life-extending benefits were associated with drastic reductions in visceral fat, and blood glucose and insulin levels, but elevated ghrelin levels, the anti-aging biomarkers. Thus, bioavailability of leptin transduced by ectopic gene in the hypothalamus alone is both necessary and sufficient to normalize life-span. Evidently, site-specific ectopic gene expression with rAAV is durable and safe for alleviating neural disorders that stem from missing or functional disruption of a single gene.     

果糖与代谢性疾病

随着社会经济的发展,肥胖、糖尿病、脂肪肝、高血脂和痛风等代谢性疾病的患病率在全球呈现快速上升趋势。这些代谢性疾病可进一步发展为动脉粥样硬化、高血压和冠心病等心血管疾病或肾脏疾病,严重危害人们的身心健康和社会发展。因此,代谢性疾病及其相关心血管疾病已经成为我国公共卫生领域的重大挑战。     

Role of leptin in immunity

Leptin, a protein hormone produced by the adipocytes, has long been recognized to regulate metabolism, neuroendorine and other physiological functions. Early findings of increased leptin production during infection and inflammation and dysregulated immune response in leptin signaling-deficient mice provide strong evidence for the involvement of leptin in the immune responses. Recent data have established the regulatory function for leptin in immunity similar to the function of a pro-inflammatory cytokine, while gene-targeting studies also demonstrated an essential role of leptin in regulating hematopoiesis and lymphopoiesis. Moreover, there has been increasing evidence that leptin is involved in the pathogenesis of various autoimmune diseases. This review discusses recent advances in understanding the role of leptin in immunity and leptin-signaling pathways involved in modulating immune homeostasis and autoimmune pathogenesis. Cellular ＆ Molecular Immunology. 2007;4（1）：1-13.     

Gut microbiota: A player in aging and a target for anti-aging intervention

Aging-associated alterations in composition, diversity and functional features of intestinal microbiota are well-described in the modern literature. They are suggested to be caused by an age-related decline in immune system functioning (immunosenescence) and a low-grade chronic inflammation (inflammaging), which accompany many aging-associated pathologies. The microbiota-targeted dietary and probiotic interventions have been shown to favorably affect the host health and aging by an enhancement of antioxidant activity, improving immune homeostasis, suppression of chronic inflammation, regulation of fat deposition and metabolism and prevention of insulin resistance. Recently, a high effectiveness and safety of novel therapeutic application such as fecal microbiota transplantation in the prevention and treatment of age-related pathological conditions including atherosclerosis, type 2 diabetes and Parkinson’s disease has been demonstrated. In this review, recent research findings are summarized on the role of gut micribiota in aging processes with emphasis on therapeutic potential of microbiome-targeted interventions in anti-aging medicine,     

The emerging role of the endocannabinoid system in cardiovascular disease

Endocannabinoids are endogenous bioactive lipid mediators present both in the brain and various peripheral tissues, which exert their biological effects via interaction with specific G-protein-coupled cannabinoid receptors, the CB₁ and CB₂. Pathological overactivation of the endocannabinoid system (ECS) in various forms of shock and heart failure may contribute to the underlying pathology and cardiodepressive state by the activation of the cardiovascular CB₁ receptors. Furthermore, tonic activation of CB₁ receptors by endocannabinoids has also been implicated in the development of various cardiovascular risk factors in obesity/metabolic syndrome and diabetes, such as plasma lipid alterations, abdominal obesity, hepatic steatosis, inflammation, and insulin and leptin resistance. In contrast, activation of CB₂ receptors in immune cells exerts various immunomodulatory effects, and the CB₂ receptors in endothelial and inflammatory cells appear to limit the endothelial inflammatory response, chemotaxis, and inflammatory cell adhesion and activation in atherosclerosis and reperfusion injury. Here, we will overview the cardiovascular actions of endocannabinoids and the growing body of evidence implicating the dysregulation of the ECS in a variety of cardiovascular diseases. We will also discuss the therapeutic potential of the modulation of the ECS by selective agonists/antagonists in various cardiovascular disorders associated with inflammation and tissue injury, ranging from myocardial infarction and heart failure to atherosclerosis and cardiometabolic disorders.     

Regulation of longevity by FGF21: Interaction between energy metabolism and stress responses

Fibroblast growth factor 21 (FGF21) is a hormone-like member of FGF family which controls metabolic multiorgan crosstalk enhancing energy expenditure through glucose and lipid metabolism. In addition, FGF21 acts as a stress hormone induced by endoplasmic reticulum stress and dysfunctions of mitochondria and autophagy in several tissues. FGF21 also controls stress responses and metabolism by modulating the functions of somatotropic axis and hypothalamic-pituitary-adrenal (HPA) pathway. FGF21 is a potent longevity factor coordinating interactions between energy metabolism and stress responses. Recent studies have revealed that FGF21 treatment can alleviate many age-related metabolic disorders, e.g. atherosclerosis, obesity, type 2 diabetes, and some cardiovascular diseases. In addition, transgenic mice overexpressing FGF21 have an extended lifespan. However, chronic metabolic and stress-related disorders involving inflammatory responses can provoke FGF21 resistance and thus disturb healthy aging process. First, we will describe the role of FGF21 in interorgan energy metabolism and explain how its functions as a stress hormone can improve healthspan. Next, we will examine both the induction of FGF21 expression via the integrated stress response and the molecular mechanism through which FGF21 enhances healthy aging. Finally, we postulate that FGF21 resistance, similarly to insulin resistance, jeopardizes human healthspan and accelerates the aging process.     

Melatonin and the metabolic syndrome: a tool for effective therapy in obesity‐associated abnormalities?

The metabolic syndrome (MetS) is a cluster of metabolic abnormalities associated with increased risk for cardiovascular diseases. Apart from its powerful antioxidant properties, the pineal gland hormone melatonin has recently attracted the interest of various investigators as a multifunctional molecule. Melatonin has been shown to have beneficial effects in cardiovascular disorders including ischaemic heart disease and hypertension. However, its role in cardiovascular risk factors including obesity and other related metabolic abnormalities is not yet established, particularly in humans. New emerging data show that melatonin may play an important role in body weight regulation and energy metabolism. This review will address the role of melatonin in the MetS focusing on its effects in obesity, insulin resistance and leptin resistance. The overall findings suggest that melatonin should be exploited as a therapeutic tool to prevent or reverse the harmful effects of obesity and its related metabolic disorders.     

Leptin in immuno-rheumatological diseases

Leptin is one of the most important hormones secreted by adipocytes, with a variety of physiological roles related to the control of metabolism and energy homeostasis. Since its discovery in 1994, leptin has attracted increasing interest in the scientific community for its pleiotropic actions. One of these functions is the relationship between nutritional status and immune competence. It structurally resembles proinflammatory cytokines, such as IL-6 and IL-12. The cytokine-like structural characteristic of leptin is implicative of its function in regulating immune responses. The role of leptin in regulating immune responses has been assessed in vitro as well as in clinical studies. It has been shown that disease conditions of reduced leptin production are associated with increased infection susceptibility. Conversely, immune-mediated disorders, such as autoimmune diseases, are associated with the increased secretion of leptin and the production of proinflammatory pathogenic cytokines. In this paper, we review the most recent advances of the role of leptin in immune-rheumatological diseases, and we discuss whether strategies aimed at modifying leptin levels could represent innovative and therapeutic tools for autoimmune disorders.