Leptin actions on food intake and body temperature are mediated by IL-1

Induction of proinflammatory cytokines and caspase-1 by leptin in monocyte/macrophages from holstein cows

The proliferation of peripheral blood mononuclear cells (PBMC) containing both monocyte/macrophages and T lymphocytes increased after treatment with T-cell mitogen (concanavalin A: Con A). PBMC treated with either leptin alone or combination of leptin and ConA showed enhanced proliferative activity by 10-40%, compared with those treated with ConA alone. In contrast, isolated T lymphocytes treated with leptin and ConA showed lowered proliferative activity than the ConA-treated alone, indicating that leptin induced production of some cytokines from monocyte/macrophages, that subsequently resulted in enhancement of T lymphocytes proliferation in PBMC. Among the cytokines examined, monocyte/monocytes constitutively expressed interleukin (IL)-1beta, IL-12p35, IL-18 mRNA, and faintly expressed tumor necrosis factor (TNF)-alpha and IL-12p40 mRNA. Leptin treatment augmented the monocyte/macrophages mRNA expression of only TNF-alpha and IL-12p40 to comparable levels of cells treated with lipopolysaccharide (LPS). However, leptin treatment increased monocyte/macrophages production of IL-1beta as well as TNF-alpha, and induced the mRNA expression of caspase-1, which is shown to mediate the conversion of latent pro-IL-1beta and pro-IL-18 to active forms. These results suggest that leptin directly acts on monocyte/macrophages to produce factors that induce T lymphocytes proliferation such as IL-12p35/p40 complex through IL-12p40 induction and IL-1beta/IL-18 production through caspase-1 induction.

Stress-induced cytokine responses and central adiposity in young women

BACKGROUND

Evidence suggests that people who are more responsive to psychological stress are at an increased risk of developing obesity. However, the biological mechanisms underlying this phenomenon are poorly understood. The cytokines leptin, interleukin-1 receptor antagonist (IL-1Ra) and interleukin-6 (IL-6) play a key role in fat metabolism and abnormal circulating levels of these proteins have been reported in obese people and in individuals subject to stress.

OBJECTIVE

This study investigated whether cytokine responses to acute mental stress are associated with adiposity in healthy young women.

DESIGN AND SUBJECTS

A laboratory study of 67 women, aged 18-25 years, recruited from University College London.

MEASUREMENTS

Height, weight and waist circumference were measured and body fat mass was estimated by bioelectrical impedance body composition analysis. Laboratory mental stress testing was carried out and blood pressure and heart rate were recorded at baseline, during two moderately challenging tasks (Stroop and speech) and during recovery 40-45 min post-stress. Blood samples taken at baseline, immediately post-stress and 45 min post-stress, were used for assessment of circulating cytokines. Saliva samples taken throughout the session were assessed for cortisol.

RESULTS

Women who had larger cytokine responses to stress were more abdominally obese than women with smaller cytokine stress responses. Specifically, there was a positive correlation between waist circumference and stress-induced increases in plasma levels of leptin (r=0.35, P<0.05) and IL-1Ra responses (r=0.29, P<0.05). There was also a significant positive correlation between prolonged diastolic blood pressure responses to stress and measures of total and abdominal obesity (r=0.28-0.33, P<0.05).

CONCLUSION

Increased cytokine production could be a mechanism linking stress and abdominal obesity.

Acute Hypoxia, Diabetes, and Neuroimmune Dysregulation: Converging Mechanisms in the Brain

Acute hypoxia is experienced by a variety of individuals (neonates to the elderly) and in an assortment of conditions and diseases (terrorist bomb attack to decompensated heart failure). Increasingly, elaboration of inflammatory cytokines appears key to the brain-based response to hypoxia, as evidenced by the biobehaviors of malaise, fatigue, lethargy, and loss of interest in the physical and social environment. These sickness symptoms implicate hypoxia-dependent activation of the neuroimmune system as a key component of acute hypoxia. Type 2 diabetes (T2D) is associated with increased incidence, severity, and delayed recovery from hypoxic events. Why T2D negatively affects acute hypoxia is not well understood. Recent work, however, reveals that anti-inflammatory pathways tied to the interleukin (IL)-1β arm of the neuroimmune system may be critical. In this review, the authors examine the link between acute hypoxia, T2D, and neuroimmunity. NEUROSCIENTIST 14(3):235–239, 2008. DOI: 10.1177/1073858407309544

Signals generating anorexia during acute illness

Anorexia is part of the body's acute-phase response to illness. Microbial products such as lipopolysaccharides (LPS), which are also commonly used to model acute illness, trigger the acute-phase response and cause anorexia mainly through pro-inflammatory cytokines. LPS stimulate cytokine production through the cell-surface structural molecule CD14 and toll-like receptor-4. Cytokines ultimately change neural activity in brain areas controlling food intake and energy balance. The blood-brain barrier endothelial cells (BBB EC) are an important site of cytokine action in this context. BBB EC and perivascular cells (microglia and macrophages) form a complex regulatory interface that modulates neuronal activity by the release of messengers (e.g. PG, NO) in response to peripheral challenges. Serotonergic neurons originating in the raphe nuclei and glucagon-like peptide-1-expressing neurons in the hindbrain may be among the targets of these messengers, because serotonin (5-HT), acting through the 5-HT2C receptor, and glucagon-like peptide-1 have recently emerged as neurochemical mediators of LPS anorexia. The central melanocortin system, which is a downstream target of serotonergic neurons, also appears to be involved in mediation of LPS anorexia. Interestingly, LPS also reduce orexin expression and the activity of orexin neurons in the lateral hypothalamic area of fasted mice. As the eating-stimulatory properties of orexin are apparently related to arousal, the inhibitory effect of LPS on orexin neurons might be involved in LPS-induced inactivity and anorexia. In summary, the immune signalling pathways of LPS-induced, and presumably acute illness-induced, anorexia converge on central neural signalling systems that control food intake and energy balance in healthy individuals.

Effects of chronic exercise on cytokine production in white adipose tissue and skeletal muscle of rats

White adipose tissue (WAT) is a major source of production of cytokines involved in chronic diseases such as obesity, type 2 diabetes, and atherosclerosis. Long-term exercise has been proposed as a therapy to reduce chronic inflammation. We investigated here the influence of an intense exercise training (over 7 weeks) on several cytokine concentrations including interleukin 1 receptor antagonist (IL-1ra), IL-1beta, and IL-12 in serum, WAT, and skeletal muscle (SM) from non-obese rats. Two groups of 10 rats were investigated: one group was progressively trained (the two last weeks: 120min per day, 25m/min, 7% grade, 5 days per week) and the other age-matched group was used as a sedentary control. Compared to sedentary rats, weight gain was lower in the trained rats (P<0.01). In WAT, concentrations of IL-1ra, IL-1beta, and IL-12 were lower (P<0.001 for IL-1ra and IL-12, P<0.05 for IL-1beta) while they were higher in SM (P<0.01 for IL-1ra, P<0.001 for IL-1beta, P<0.05 for IL-12), and similar in serum. Significant correlations were noted between (i) body weight and WAT concentrations of IL-1ra, IL-1beta, and IL-12 (0.595, 0.450, and 0.481, respectively), (ii) body weight and IL-1beta concentration in SM (-0.526). We also observed significant negative correlations between WAT and SM concentrations of the three cytokines. We show here for the first time that intense exercise training with weight loss reduced concentrations of IL-1ra, IL-1beta, and IL-12 in WAT, while it increased them in SM. These results suggest that exercise could help reduce inflammation in WAT through mobilization of immune cells producing pro- and anti-inflammatory cytokines in SM.

Interleukin-1 system in CNS stress: seizures, fever, and neurotrauma

Proteins of the interleukin-1 (IL-1) system include the secreted agonist IL-1beta, and the receptor antagonist IL-1ra, both competing for binding to the IL-1 receptor (IL-1R). IL-1beta and IL-1ra are highly inducible under different forms of stress, such as excitatory neurotransmitter excess occurring during seizures, in infection and inflammation, and during neurotrauma. In each of these conditions induction of IL-1beta precedes that of IL-1ra, resulting in up to 10-20-fold elevation of IL-1beta concentrations. Consequently, IL-1beta induces the elevation of other proinflammatory molecules, including IL-6, IL-1R1, COX2, and iNOS, as well as of IL-1ra. Elevation of IL-1ra is of key importance for quenching the inflammatory response at the IL-1R1 as part of an autoregulatory loop. In seizures, IL-1ra is a strong anticonvulsant and in IL-1beta-dependent fever, a powerful antipyretic. In traumatic brain injury (TBI), the ability of patients to mount an IL-1ra response, as measured in the CSF, strongly correlated with the neurological outcome. Selective induction or pharmacological application of IL-1ra may be sparing neurons in seizures and neurotrauma.

Prevalence of hot flushes and night sweats around the world: a systematic review

OBJECTIVE

Many studies have evaluated the relationships between ethnicity and culture, prevalence of menopausal symptoms, and attitudes toward them, but few have assessed menopausal symptoms across cultures world-wide. This paper aims to systematically review the prevalence of hot flushes and night sweats, two prevalent symptoms of menopause, across the menopausal stages in different cultures and considers potential explanations for differences in prevalence rates.

DESIGN

Sixty-six papers formed the basis for this review. Studies were organized by geographic region, and results are presented for North America, Europe, East Asia, Southeast Asia, Australia, Latin America, South Asia, Middle East, and Africa. Studies were included if they provided quantitative information on the occurrence of hot flushes. This report focuses on hot flushes and night sweats, the most common menopausal symptoms reported in epidemiologic studies.

RESULTS

Studies reviewed indicate that vasomotor symptoms are highly prevalent in most societies. The prevalence of these symptoms varies widely and may be influenced by a range of factors, including climate, diet, lifestyle, women's roles, and attitudes regarding the end of reproductive life and aging. Patterns in hot flush prevalence were apparent for menopausal stages and, to a lesser degree, for regional variation.

CONCLUSIONS

Caregivers should recognize that variations exist and ask patients specific questions about symptoms and their impact on usual functioning.

Leptin induces interleukin-1beta release from rat microglial cells through a caspase 1 independent mechanism

Leptin regulates energy balance by suppressing appetite and increasing energy expenditure through actions in the hypothalamus. Recently we demonstrated that the effects of leptin are, at least in part, mediated by the release of interleukin (IL)-1beta in the brain. Microglia constitute the major source of IL-1beta in the brain but it is not known whether these cells express leptin receptors, or respond to leptin to produce IL-1beta. Using RT-PCR and immunocytochemistry, we demonstrate that primary rat microglial cells express the short (non-signalling) and long (signalling) isoforms of the leptin receptors (Ob-R)s. Immunoassays performed on cell medium collected 24 h after leptin treatment (0.01-10 microg/mL) demonstrated a dose-dependent production and release of IL-1beta and its endogenously occurring receptor antagonist IL-1RA. In addition leptin-induced IL-1beta release occurs via a signal transducer and activator of transcription 3 (STAT3)-dependent mechanism. Western blot analysis demonstrated that leptin induced the synthesis of pro-IL-1beta in microglial cells and the release of mature 17 kDa isoform into the culture medium. Leptin-induced IL-1beta release was neither inhibited by the pan-caspase inhibitor BOC-D-FMK, nor by the caspase 1 inhibitor Ac-YVAD-CHO indicating that IL-1 cleavage is independent of caspase activity. These results confirm our earlier observations in vivo and demonstrate that microglia are an important source of IL-1beta in the brain in response to leptin.

Cold-seeking behavior as a thermoregulatory strategy in systemic inflammation

Systemic inflammation (SI) is a leading cause of hospital death. Although fever and hypothermia are listed as symptoms in every definition of SI, how SI affects thermoregulatory behavior is unclear. SI is often modeled by systemic administration of bacterial lipopolysaccharide (LPS) to rats. When rats are not allowed to regulate their body temperature (Tb) behaviorally, LPS causes either fever or hypothermia, and the direction of the response is determined by LPS dose and ambient temperature (Ta). However, in many studies in which rats were allowed to regulate Tb behaviorally (by selecting their preferred Ta in a thermogradient apparatus), they consistently expressed warmth-seeking behavior and developed fever. We hypothesized that SI can cause not only warmth-seeking behavior but also cold-seeking behavior; we then tested this hypothesis by studying LPS-induced thermoregulatory behavior in adult Wistar rats. A multichannel thermogradient apparatus, implantable data loggers and infrared thermography were used; multiple control experiments were conducted; and the ability of the apparatus to reliably register the changes in rats' preferred Ta induced by thermal (external cooling or heating) or chemical (TRPV1 or TRPM8 agonist) stimuli was confirmed. The rats responded to a low dose of LPS (10 microg/kg i.v.) with warmth-seeking behavior and a polyphasic fever, but to a high dose (5 mg/kg i.v.) with marked cold-seeking behavior and hypothermia followed by warmth-seeking behavior and fever. This is the first well-controlled study to report SI-associated cold-seeking behavior in rats. Cold-seeking behavior is likely to be an important defense response in severe SI.

The role of the vagus nerve in mediating the long-term anorectic effects of leptin

Leptin, the product of the obese (ob) gene, is mainly known for its regulatory role of energy balance by direct activation of hypothalamic receptors. Recently, its function in the acute control of food intake was additionally attributed to activation of the vagus nerve to regulate meal termination. Whether vagal afferent neurones are involved in longer term effects of leptin on food intake, however, remains undetermined. Using vagotomised (VGX) rats, we sought to clarify the contributions of vagal afferents in mediating the long-lasting effect of leptin on appetite suppression. Intraperitoneal (i.p.) injection of leptin (3.5 mg/kg) attenuated food intake at 4, 6, 8 and 24 h and body weight at 24 h postinjection in SHAM-operated rats; however, this response was not abrogated by vagotomy. In a separate study using immunohistochemistry, we observed leptin-induced Fos expression in the nucleus tractus solitarii, a brain structure where vagal afferent fibres terminate. This signal was not attenuated in VGX animals compared to the SHAM group. Moreover, leptin treatment led to a similar level of nuclear STAT3 translocation, a marker of leptin signalling, in the hypothalami of SHAM and VGX animals. In addition to the effects of leptin, vagotomy surgery itself resulted in a decrease of 24 h food intake. Analyses of brains from saline-treated VGX animals revealed a significant induction of Fos in the nucleus tractus solitarii and changes in agouti-related peptide and pro-opiomelanocortin mRNA expression in the hypothalamus compared to their SHAM counterparts, indicating that the vagotomy surgery itself induced a modification of brain activity in areas involved in regulating appetite. Collectively, our data suggest that vagal afferents do not constitute a major route of mediating the regulatory effect of leptin on food intake over a period of several hours.

Relationship between adipocyte size and adipokine expression and secretion

CONTEXT

Adipocytes are known to release a variety of factors that may contribute to the proinflammatory state characteristic for obesity. This secretory function is considered to provide the basis for obesity-related complications such as type 2 diabetes and atherosclerosis.

OBJECTIVE

To get a better insight into possible underlying mechanisms, we investigated the effect of adipocyte size on adipokine production and secretion.

DESIGN, PATIENTS, AND MAIN OUTCOME MEASURES

Protein secretion and mRNA expression in cultured adipocytes separated according to cell size from 30 individuals undergoing elective plastic surgery were investigated.

RESULTS

The mean adipocyte volume of the four fractions ranged from 205 +/- 146 to 1.077 +/- 471 pl. There were strong linear correlations for the secretion of adipokines over time. Secretion of leptin, IL-6, IL-8, TNF-alpha, monocyte chemoattractant protein-1, interferon-gamma-inducible protein 10, macrophage inflammatory protein-1beta, granulocyte colony stimulating factor, IL-1ra, and adiponectin was positively correlated with cell size. After correction for cell surface, there was still a significant difference between fraction IV (very large) and fraction I (small cells), for leptin, IL-6, IL-8, monocyte chemoattractant protein-1, and granulocyte colony-stimulating factor. In contrast, antiinflammatory factors such as IL-1ra and adiponectin lost their association after correction for cell surface area comparing fraction I and IV. In addition, there was a decrease of IL-10 secretion with increasing cell size.

CONCLUSIONS

The results clearly suggest that adipocyte size is an important determinant of adipokine secretion. There seems to be a differential expression of pro- and antiinflammatory factors with increasing adipocyte size resulting in a shift toward dominance of proinflammatory adipokines largely as a result of a dysregulation of hypertrophic, very large cells.

Clinical outcome following acute ischaemic stroke relates to both activation and autoregulatory inhibition of cytokine production

BACKGROUND

As critical mediators of local and systemic inflammatory responses, cytokines are produced in the brain following ischaemic stroke. Some have been detected in the circulation of stroke patients, but their role and source is unclear. Focusing primarily on interleukin(IL)-1-related mechanisms, we serially measured plasma inflammatory markers, and the production of cytokines by whole blood, from 36 patients recruited within 12 h and followed up to 1 year after acute ischaemic stroke (AIS).

RESULTS

Admission plasma IL-1 receptor antagonist (IL-1ra) concentration was elevated, relative to age-, sex-, and atherosclerosis-matched controls. IL-1beta, soluble IL-1 receptor type II, tumour necrosis factor (TNF)-alpha, TNF-RII, IL-10 and leptin concentrations did not significantly differ from controls, but peak soluble TNF receptor type I (sTNF-RI) in the first week correlated strongly with computed tomography infarct volume at 5-7 days, mRS and BI at 3 and 12 months. Neopterin was raised in patients at 5-7 d, relative to controls, and in subjects with significant atherosclerosis. Spontaneous IL-1beta, TNF-alpha and IL-6 gene and protein expression by blood cells was minimal, and induction of these cytokines by lipopolysaccharide (LPS) was significantly lower in patients than in controls during the first week. Minimum LPS-induced cytokine production correlated strongly with mRS and BI, and also with plasma cortisol.

CONCLUSION

Absence of spontaneous whole blood gene activation or cytokine production suggests that peripheral blood cells are not the source of cytokines measured in plasma after AIS. Increased plasma IL-1ra within 12 h of AIS onset, the relationship between sTNF-RI and stroke severity, and suppressed cytokine induction suggests early activation of endogenous immunosuppressive mechanisms after AIS.

Central interleukin-1 (IL1) signaling is required for pharmacological, but not physiological, effects of leptin on energy balance

Hypothalamic IL1 is suggested to be a critical mediator of the central effects of the adipocyte hormone leptin on energy balance. We hypothesized that IL1 receptor signaling is required for exogenously administered leptin to cause anorexia and weight loss, but not for physiological effects of endogenous leptin signaling on energy balance. To test this hypothesis, we investigated whether chronic hypothalamic over-expression of an IL1 receptor antagonist (AdV-IL1ra) alters food intake and weight gain in normal rats. Our findings demonstrate that impaired IL1 signaling in the CNS did not cause excess weight gain over a period of 11 days (AdV-IL1ra +38.1+/-4.1 g vs. VEH +42.2+/-5.6g; p=0.6) and caused a slightly reduced daily food intake (AdV-IL1ra 29.0+/-1.1 g/day vs. VEH 33.0+/-1.6 g/day; p<0.05). Blocking central IL1 signaling also did not alter the re-feeding response to a prolonged fast, yet was entirely effective in preventing the anorexic effect of exogenously administered leptin (2 mg/kg ip, cumulative food intake at 18 h AdV-IL1ra 30.5+/-1.1 g vs. VEH 26.4+/-1.7 g, p<0.05) and prevented leptin-induced weight loss (AdV-IL1ra -0.1+/-1.3 g vs. VEH -2.7+/-1.9 g, p<0.05). Together these findings suggest that hypothalamic IL1 signaling is required for the pharmacological effects of leptin administration, but that impaired hypothalamic IL1 signaling does not alter the physiological regulation of energy balance.

Regulation of food intake by inflammatory cytokines in the brain

A number of inflammatory cytokines are synthesized and released after activation of the immune system. In addition to other biological effects, these cytokines can potently inhibit food intake. Cytokine-mediated inhibition of food intake is of particular importance because excessive production of peripheral inflammatory cytokines is often associated with the cachexia-anorexia syndrome seen in some chronic diseases. The weight loss in cachexia is associated with an increase in morbidity and mortality. Understanding how cytokines regulate food intake may be crucial in enhancing quality of life and facilitating recovery in patients exhibiting cachexia. This review describes the main inflammatory cytokines that influence food intake and explores how peripheral cytokines communicate with hypothalamic nuclei to influence feeding.

Bridges between nervous and immune systems: their disconnection and clinical consequences

Nervous and immune systems are connected by several mutual links, thus constituting a diffuse functional network in the body. In particular, neurohormones, neuropeptides, and cytokines represent the major mediators of the so-called psychoneuroendocrinoimmune axis. In this review, special emphasis is placed on certain pathologies characterized by a disconnection of the existing bridges between nervous and immune systems. For instance, spinal cord injury (SCI) is a clinical condition in which loss of neurons and very poor axon growth represent the main features. The role played by infiltrating and resident immunocompetent cells is still debated in SCI. However, to enhance axon growth in SCI, current therapeutic attempts are based on the stimulation of the immune response within the central nervous system, thus triggering either cell-mediated or humoral immune responsiveness.

Leptin induces cyclooxygenase-2 via an interaction with interleukin-1beta in the rat brain

In addition to its central effects on appetite regulation, leptin has been implicated in immune function and inflammation. Previous data suggested that leptin acts as an inflammatory signal within the brain, as exogenously administered leptin induced fever, a typical brain-regulated inflammatory response. The present study aimed to delineate the inflammatory actions and cellular targets of leptin in the brain by examining its effects on the expression of interleukin (IL)-1beta and cyclooxygenase (COX)-2, two important inflammatory components of the fever response. Intracerebroventricular injection of leptin (5 microg/rat) induced IL-1beta and COX-2 mRNA and protein in the hypothalamus between 1 and 3 h after treatment as determined by reverse transcription-polymerase chain reaction and immunohistochemistry. Coinjection of IL-1 receptor antagonist (100 microg/rat, intracerebroventricular) attenuated leptin-induced COX-2, whereas IL-1 receptor antagonist had no effect on endogenous IL-1beta levels, suggesting that leptin induces COX-2 via, at least partly, IL-1beta action. IL-1beta protein expression was induced in macrophages in the meningis and perivascular space after leptin treatment, whereas COX-2 induction was observed in endothelial cells, indicating the roles for these non-neuronal cells in mediating inflammatory actions of leptin. In addition, neutralization of endogenous circulating leptin with anti-leptin antiserum attenuated intraperitoneal lipopolysaccharide (100 microg/kg)-induced brain IL-1beta and COX-2 upregulation, suggesting that leptin indeed acts as an inflammatory signal to the brain during systemic inflammation. These findings are in contrast to the effects of leptin on appetite regulation where it is believed to act primarily on neurons, thus presenting a distinct anatomical basis for the inflammatory and appetite regulatory actions of leptin in the brain.

Leptin: at the crossroads of energy balance and systemic inflammation

In addition to playing a central role in energy homeostasis, leptin is also an important player in the inflammatory response. Systemic inflammation is accompanied by fever (less severe cases) or hypothermia (more severe cases). In leptin-irresponsive mutants, the hypothermia of systemic inflammation is exaggerated, presumably due to the enhanced production and cryogenic action of tumor necrosis factor (TNF)-alpha. Mechanisms that exaggerate hypothermia can also attenuate fever, particularly in a cool environment. Another common manifestation of systemic inflammation is behavioral depression. Along with the production of interleukin (IL)-1beta, this manifestation is exaggerated in leptin-irresponsive mutants. The enhanced production of TNF-alpha and IL-1beta may be due, at least in part, to insufficient activation of the anti-inflammatory hypothalamo-pituitary-adrenal axis by immune stimuli in the absence of leptin signaling. In experimental animals and humans that are responsive to leptin, suppression of leptin production under conditions of negative energy balance (e.g., fasting) can exaggerate both hypothermia and behavioral depression. Since these manifestations aid energy conservation, exaggeration of these manifestations under conditions of negative energy balance is likely to be beneficial.

Release of interleukins and other inflammatory cytokines by human adipose tissue is enhanced in obesity and primarily due to the nonfat cells

The white adipose tissue, especially of humans, is now recognized as the central player in the mild inflammatory state that is characteristic of obesity. The question is how the increased accumulation of lipid seen in obesity causes an inflammatory state and how this is linked to the hypertension and type 2 diabetes that accompanies obesity. Once it was thought that adipose tissue was primarily a reservoir for excess calories that were stored in the adipocytes as triacylglycerols. In times of caloric deprivation these stored lipids were mobilized as free fatty acids and the insulin resistance of obesity was attributed to free fatty acids. It is now clear that in humans the expansion of adipose tissue seen in obesity results in more blood vessels, more connective tissue fibroblasts, and especially more macrophages. There is an enhanced secretion of some interleukins and inflammatory cytokines in adipose tissue of the obese as well as increased circulating levels of many cytokines. The central theme of this chapter is that human adipose tissue is a potent source of inflammatory interleukins plus other cytokines and that the majority of this release is due to the nonfat cells in the adipose tissue except for leptin and adiponectin that are primarily secreted by adipocytes. Human adipocytes secrete at least as much plasminogen activator inhibitor-1 (PAI-1), MCP-1, interleukin-8 (IL-8), and IL-6 in vitro as they do leptin but the nonfat cells of adipose tissue secrete even more of these proteins. The secretion of leptin, on the other hand, by the nonfat cells is negligible. The amount of serum amyloid A proteins 1 & 2 (SAA 1 & 2), haptoglobin, nerve growth factor (NGF), macrophage migration inhibitory factor (MIF), and PAI-1 secreted by the adipocytes derived from a gram of adipose tissue is 144%, 75%, 72%, 37%, and 23%, respectively, of that by the nonfat cells derived from the same amount of human adipose tissue. However, the release of IL-8, MCP-1, vascular endothelial growth factor (VEGF), TGF-beta1, IL-6, PGE(2), TNF-alpha, cathepsin S, hepatocyte growth factor (HGF), IL-1beta, IL-10, resistin, C-reactive protein (CRP), and interleukin-1 receptor antagonist (IL-1Ra) by adipocytes is less than 12% of that by the nonfat cells present in human adipose tissue. Obesity markedly elevates the total release of TNF-alpha, IL-6, and IL-8 by adipose tissue but only that of TNF-alpha is enhanced in adipocytes. However, on a quantitative basis the vast majority of the TNF-alpha comes from the nonfat cells. Visceral adipose tissue also releases more VEGF, resistin, IL-6, PAI-1, TGF-beta1, IL-8, and IL-10 per gram of tissue than does abdominal subcutaneous adipose tissue. In conclusion, there is an increasing recognition that adipose tissue is an endocrine organ that secretes leptin and adiponectin along with a host of other paracrine and endocrine factors in addition to free fatty acids.

Alterations in peripheral blood lymphocyte cytokine expression in obesity

Obesity is characterized by alterations in immune and inflammatory function. In order to evaluate the potential role of cytokine expression by peripheral blood mononuclear cells (PBMC) in obesity-associated inflammation, we studied serum protein levels and mRNA levels in PBMC of interleukin (IL)-6, IL-1beta, tumour necrosis factor (TNF)-alpha and IL-1Ra in nine lean and 10 obese subjects. Serum IL-1beta was undetectable, IL-1Ra serum levels were elevated, serum levels of TNF-alpha were decreased and serum levels of IL-6 were similar in obese subjects compared to lean subjects, while transcript levels of IL-6, IL-1beta and TNF-alpha, but not IL-1Ra, were decreased in PBMC from obese subjects. PBMC from obese subjects did, however, up-regulate cytokine expression in response to leptin. Thus, obesity-associated changes in IL-1Ra serum levels and IL-6 mRNA levels were not correlated with changes in cognate mRNA and serum levels, respectively, while TNF-alpha serum levels and PBMC mRNA levels were both decreased in obese patients. While immune alterations in obesity are manifest in peripheral blood lymphocytes, the general lack of correlation between altered serum levels and altered PBMC gene expression suggests that PBMC may not be the source of aberrant serum cytokine levels in obesity.

IL-1 receptor antagonist in metabolic diseases: Dr Jekyll or Mr Hyde?

Interleukin-1 receptor antagonist (IL-1ra) has been shown to play a crucial role in the prevention of various inflammatory diseases. There is also convincing evidence that IL-1ra is able to counteract inflammatory effects of IL-1 members implicated in insulin resistance and diabetes. However, the use of knock-out animal models provides evidence to the contrary and the role of IL-1ra in obesity-linked anomalies remains controversial. This minireview gets an insight into recent findings on the implication of IL-1ra and its gene polymorphism in diabetes and obesity, discusses the potential dual effects of IL-1ra observed in different models, and comments on future directions.

Interleukin-6 and leptin mediate lipopolysaccharide-induced fever and sickness behavior

Pro-inflammatory cytokines, interleukin (IL)-1beta, IL-6 and tumor necrosis factor-alpha (TNF-alpha) synthesized by activated macrophages and monocytes in response to administration of lipopolysaccharide (LPS), are considered important mediators of fever and sickness behavior. We administered rat-specific antisera for TNF-alpha, IL-1beta, IL-6 and leptin, to determine the involvement of peripherally released cytokines in LPS-induced fever and sickness behavior, measured as suppression of voluntary wheel-running and food intake. Male Sprague-Dawley rats (approximately 200 g) selected for their predisposition to spontaneously run on running wheels were anaesthetized with a combination of ketamine hydrochloride (80 mg/kg i.m.) and xylazine (4 mg/kg i.m.) and implanted intra-abdominally with temperature-sensitive radiotelemeters. Rats were injected intraperitoneally with anti-rat sera to one of the following, TNF-alpha, IL-1beta, IL-6 or leptin or with pre-immune sheep serum, followed by a subcutaneous injection of either LPS (250 microg/kg) or sterile saline. Lipopolysaccharide administration induced a approximately 1.3 (0.2) degrees C fever lasting approximately 10 h and reduced voluntary running by 93 (8.6)% and food intake by 51 (21.3)% compared to the saline response (ANOVA, P<0.05). Injection of anti-IL-6 serum or anti-leptin serum abolished the LPS-induced fever, anti-TNF-alpha serum affected only the early phase of fever and anti-IL-1beta serum had no effect on fever (ANOVA, P<0.05). LPS-induced suppression of voluntary running and food intake were attenuated in rats receiving anti-IL-6 serum, while the decrease in food intake was totally abolished in rats receiving anti-leptin serum (ANOVA, P<0.05). Injection of anti-TNF-alpha or anti-IL-1beta serum had no effect on LPS-induced sickness behavior. Peripherally released IL-6 and leptin therefore appear to be important in regulating LPS-induced fever and sickness behavior.

Leptin selectively augments thymopoiesis in leptin deficiency and lipopolysaccharide-induced thymic atrophy

The thymus is a lymphoid organ that selects T cells for release to the peripheral immune system. Unfortunately, thymopoiesis is highly susceptible to damage by physiologic stressors and can contribute to immune deficiencies that occur in a variety of clinical settings. No treatment is currently available to protect the thymus from stress-induced involution. Leptin-deficient (ob/ob) mice have severe thymic atrophy and this finding suggests that this hormone is required for normal thymopoiesis. In this study, the ability of leptin to promote thymopoiesis in wild-type C57BL/6 and BALB/c mice, as well as in leptin-deficient (ob/ob) and endotoxin-stressed (Escherichia coli LPS) mice, was determined. Leptin administration induced weight loss and stimulated thymopoiesis in ob/ob mice, but did not stimulate thymopoiesis in wild-type C57BL/6 nor BALB/c mice. In endotoxin-stressed mice, however, leptin prevented LPS-induced thymus weight loss and stimulated TCRalpha gene rearrangement. Coadministration of leptin with LPS blunted endotoxin-induced systemic corticosterone response and production of proinflammatory cytokines. Thus, leptin has a selective thymostimulatory role in settings of leptin deficiency and endotoxin administration, and may be useful for protecting the thymus from damage and augmenting T cell reconstitution in these clinical states.

Interleukin-1 system gene polymorphisms are associated with fat mass in young men

CONTEXT

There is growing evidence for interactions between the regulation of body fat and the immune system. Studies of knockout mice indicate that IL-1 has an antiobesity effect.

OBJECTIVE

The objective of the study was to investigate our hypothesis that common polymorphisms of the IL-1 system, which are associated with IL-1 activity, also are associated with fat mass. DESIGN, SETTING, AND STUDY SUBJECTS: The Gothenburg Osteoporosis and Obesity Determinants (GOOD) study is a population-based cross-sectional study of 18- to 20-yr-old men (n = 1068), mostly Caucasian, from the Gothenburg area (Sweden). Three different polymorphisms, IL-1beta +3953 C/T, IL-1beta-31 T/C, and IL-1 receptor antagonist (IL-1RN) variable number tandem repeat of 86 bp, were investigated in relation to body fat mass.

MAIN OUTCOME MEASURE

The main outcome measures were genotype distributions and their association with body fat mass in different compartments, measured with dual-energy x-ray absorptiometry.

RESULTS

Carriers of the T variant (CT and TT) of the +3953 C to T (F(T) = 0.25) IL-1beta gene polymorphism had significantly lower total fat mass (P = 0.013) and also significantly reduced arm, leg, and trunk fat, compared with CC individuals. IL-1RN*2 carriers with two repeats of the IL-1RN variable number tandem repeat polymorphism had increased total fat (P = 0.036), serum leptin, and fat of trunk and arm as well as serum levels of IL-1RN and IL-1RN production ex vivo. The IL-1beta-31 polymorphism did not correlate with the fat measurements.

CONCLUSIONS

The IL-1 system, recently shown to affect fat mass in experimental animals, contains gene polymorphisms that are associated with fat mass in young men.

Adipose Tissue Has Anti-Inflammatory Properties: Focus on IL-1 Receptor Antagonist (IL-1Ra)

The formation of adipose tissue could result from abnormal metabolic processes and, at the local level, from chronic inflammatory processes such as those occurring in the synovial cavity in rheumatoid arthritis or osteoarthritis, or the peritoneal cavity in various inflammatory processes of the digestive system. Adipocytes are said to produce many hormones and proinflammatory mediators. So far, however, little attention has been paid to cytokine inhibitory molecules. Based on our observation of high levels of serum interleukin receptor antagonist (IL-1Ra) in obese patients contrasting with decreased levels after gastric bypass surgery, we found white adipose tissue (WAT) in the human system to be the main source of IL-1Ra. IL-10 was also present in WAT. Furthermore, we found that interferon-beta (IFN)-beta was the principal cytokine inducing IL-1Ra in various WAT, such as that present in the synovium. We suggest that in addition to other functions adipose tissue may give rise to a host-defense mechanism against local inflammation and that fibrotic tissue in the vicinity may further induce IL-1Ra in adipocytes via the production of IFN-beta.

Mature-onset obesity in interleukin-1 receptor I knockout mice

Interleukin-1 (IL-1) is a major mediator of inflammation that exerts its biological activities through the IL-1 type I receptor (IL-1RI). The body weights of IL-1RI(-/-) mice of both sexes started to deviate from those of wild-type mice at 5-6 months of age and were 20% higher at 9 months of age. Visceral and subcutaneous fat mass, measured by dual-energy X-ray absorptiometry and magnetic resonance imaging, was markedly (1.5- to 2.5-fold) increased. Lean body mass and crown-rump length were also slightly (11 and 5%, respectively) increased, as was serum IGF-I. Obese IL-1RI(-/-) mice were insulin resistant, as evidenced by hyperinsulinemia, decreased glucose tolerance, and insulin sensitivity. To elucidate the mechanisms for the development of obesity, young pre-obese IL-1RI(-/-) mice were investigated. They showed decreased suppression of body weight and food intake in response to systemic leptin treatment. The decreased leptin responsiveness was even more pronounced in older obese animals. Moreover, spontaneous locomotor activity and fat utilization, as measured by respiratory quotient, were decreased in pre-obese IL-1RI(-/-) mice. In conclusion, lack of IL-1RI-mediated biological activity causes mature-onset obesity. This obese phenotype is preceded by decreased leptin sensitivity, fat utilization, and locomotor activity.

Combined interleukin-6 and interleukin-1 deficiency causes obesity in young mice

Proinflammatory cytokines including interleukin (IL)-1 and IL-6 exert pleiotropic effects on the neuro-immuno-endocrine system. Previously, we showed that IL-1 receptor antagonist-deficient (IL-1Ra(-/-)) mice show a lean phenotype due to an abnormal lipid metabolism. On the contrary, it was reported that IL-6(-/-) mice exhibit obesity after 6 months of age. This study sought to assess the roles of IL-1 and IL-6 in body weight homeostasis. We generated mice deficient in IL-6 and IL-1Ra (IL-6(-/-) IL-1Ra(-/-)) and IL-6, IL-1alpha, and IL-1beta (IL-6(-/-) IL-1(-/-)). IL-6(-/-) IL-1Ra(-/-) mice exhibited a lean phenotype, similar to IL-1Ra(-/-) mice. On the other hand, IL-6(-/-) IL-1(-/-) mice became obese as early as 10 weeks of age, while IL-1(-/-) mice and IL-6(-/-) mice were normal at this age. The daily food intake was significantly higher in IL-6(-/-) IL-1(-/-) mice than in IL-6(-/-) IL-1(+/-) mice, while energy expenditure was comparable in these two strains. Acute anorexia induced by peripheral administration of IL-1 was significantly suppressed in IL-6(-/-) IL-1(-/-) mice, but not in IL-1(-/-) mice or IL-6(-/-) mice compared with wild-type mice. These results indicate that IL-1 and IL-6 are both involved in the regulation of body fat in a redundant manner in young mice.

Interleukin-1 mediates endothelin-1-induced fever and prostaglandin production in the preoptic area of rats

The intracerebroventricular injection of endothelin-1 (ET-1) induces fever and increases PG levels in the cerebrospinal fluid of rats. Likewise, the injection of IL-1 into the preoptic area (POA) of the rat hypothalamus causes both fever and increased PG production. In this study, we conducted in vivo and in vitro experiments in the rat to investigate 1) the hypothalamic region involved in ET-1-induced fever and PG biosynthesis and 2) whether hypothalamic IL-1 plays a role as a mediator of the above ET-1 activities. One hundred femtomoles of ET-1 increased body temperature when injected in the POA of conscious Wistar rats; this effect was significantly counteracted by the coinjection of 600 pmol IL-1 receptor antagonist (IL-1ra). In experiments on rat hypothalamic explants, 100 nM ET-1 caused a significant increase in PGE2 production and release from the whole hypothalamus and from the isolated POA, but not from the retrochiasmatic region, in 1-h incubations. Six nanomoles of IL-1ra or 10 nM of a cell-permeable interleukin-1 converting enzyme inhibitor completely counteracted the effect of ET-1 on PGE2 release from the POA. One hundred nanomoles ET-1 also caused a significant increase in IL-1beta immunoreactivity released into the bath solution of hypothalamic explants after 1 h of incubation, although during such time ET-1 failed to modify the gene expression of IL-1beta and other pyrogenic cytokines within the hypothalamus. In conclusion, our results show that ET-1 increases IL-1 production in the POA, and this effect appears to be correlated to ET-1-induced fever in vivo, as well as to PG production in vitro.

Role of hypothalamic interleukin-1beta (IL-1beta) in regulation of energy homeostasis by melanocortins

In the current study we sought to determine whether hypothalamic IL-1beta is regulated by melanocortin signaling and if melanocortin-induced changes in energy balance are dependent on IL-1beta. A melanocortin agonist, MTII, increased hypothalamic IL-1beta mRNA levels by two-fold, whereas a melanocortin antagonist, SHU9119, blunted lipopolysaccharide (LPS)-mediated increase of hypothalamic IL-1beta content. Pharmacological or genetic disruption of IL-1 receptor signaling prevented MTII-mediated reductions in locomotor activity, but did not reduce MTII-induced anorexia. These data suggest a potential role for central melanocortins in mediating the decrease of ambulation characteristic of the 'sickness' response.

Interleukin-1 receptor antagonist is upregulated during diet-induced obesity and regulates insulin sensitivity in rodents

AIMS/HYPOTHESIS

The IL-1 receptor antagonist (IL-1Ra) is an anti-inflammatory cytokine known to antagonise the actions of IL-1. We have previously shown that IL-1Ra is markedly upregulated in the serum of obese patients, is correlated with BMI and insulin resistance, and is overexpressed in the white adipose tissue (WAT) of obese humans. The aim of this study was to examine the role of IL-1Ra in the regulation of glucose homeostasis in rodents.

METHODS

We assessed the expression of genes related to IL-1 signalling in the WAT of mice fed a high-fat diet, as well as the effect of Il1rn (the gene for IL-1Ra) deletion and treatment with IL-1Ra on glucose homeostasis in rodents.

RESULTS

We show that the expression of Il1rn and the gene encoding the inhibitory type II IL-1 receptor was upregulated in diet-induced obesity. The blood insulin:glucose ratio was significantly lower in Il1rn ( -/- )animals, which is compatible with an increased sensitivity to insulin, reinforced by the fact that the insulin content and pancreatic islet morphology of Il1rn ( -/- ) animals were normal. In contrast, the administration of IL-1Ra to normal rats for 5 days led to a decrease in the whole-body glucose disposal due to a selective decrease in muscle-specific glucose uptake.

CONCLUSIONS/INTERPRETATION

The expression of genes encoding inhibitors of IL-1 signalling is upregulated in the WAT of mice with diet-induced obesity, and IL-1Ra reduces insulin sensitivity in rats through a muscle-specific decrease in glucose uptake. These results suggest that the markedly increased levels of IL-1Ra in human obesity might contribute to the development of insulin resistance.

Attenuation of fever at near term: is interleukin-6-STAT3 signalling altered?

Pregnant rats in late gestation show a reduced fever response after stimulation with lipopolysaccharide (LPS). This can result from either an increased action of endogenous antipyretics or a reduction in the production or action of endogenous pyrogens. Nonpregnant rats given LPS release interleukin (IL)-6, which causes nuclear translocation of the signal transducer and activator of transcription 3 (STAT3) in the vascular organ of the lamina terminalis (OVLT), followed by a significant increase in core body temperature. The present study investigated whether the reduced fever response in near-term pregnant rats is associated with a reduced nuclear STAT3 response. Rats at gestation day 15 (G15), gestation day 21 (G21, near term) and at lactation day 5 (L5) were injected with LPS (50 microg/kg, i.p.) or vehicle. Only near-term pregnant rats responded with an attenuated body temperature during the fever response. Immunohistological analysis indicated no significant difference in nuclear STAT3 in the OVLT of the different animal groups 2 h after LPS. Measurement of total and phosphorylated STAT3 protein in the OVLT with semiquantitative western blot revealed no significant differences of this protein among these immune challenged animal groups. IL-6 concentrations were also similar at G15, G21 and L5 2 h after injection of LPS. These results lead to the conclusion that the attenuation of the fever response at near-term pregnancy is not associated with a reduced amount of nuclear STAT3 in the OVLT, indicating a maintained IL-6-STAT3 signalling pathway in the OVLT.

Decreased fat mass in interleukin-1 receptor antagonist-deficient mice: impact on adipogenesis, food intake, and energy expenditure

Interleukin (IL)-1 is a regulator of inflammation but is also implicated in the control of energy homeostasis. Because the soluble IL-1 receptor antagonist (IL-1Ra) is markedly increased in the serum of obese patients and is overexpressed in white adipose tissue in obesity, we studied the metabolic consequences of genetic IL-1Ra ablation in mice. We have shown that IL-1Ra-/- mice have a lean phenotype due to decreased fat mass, related to a defect in adipogenesis and increased energy expenditure. The adipocytes were smaller in these animals, and the expression of genes involved in adipogenesis was reduced. Energy expenditure as measured by indirect calorimetry was elevated, and weight loss in response to a 24-h fast was increased in IL-1Ra-/- animals compared with wild-type mice. Lipid oxidation of IL-1Ra-/- mice was higher during the light period, reflecting their reduction in diurnal food intake. Interestingly, IL-1Ra-/- and IL-1Ra+/- mice presented an attenuation in high-fat diet-induced caloric hyperphagia, indicating a better adaptation to hypercaloric alimentation, which is in line with the role of IL-1Ra as a mediator of leptin resistance. Taken together, we show that IL-1Ra is an important regulator of adipogenesis, food intake, and energy expenditure.

Adipose tissue: a regulator of inflammation

Adipose tissue is a highly active organ. In addition to storing calories as triglycerides, it also secretes a large variety of proteins, including cytokines, chemokines and hormone-like factors, such as leptin, adiponectin and resistin. Intriguingly, many, if not most, of these adipose-derived proteins have dual actions; cytokines have both immunomodulatory functions and act as systemic or auto-/paracrine regulators of metabolism, while proteins such as leptin and adiponectin are regulators of both metabolism and inflammation. The production of pro-atherogenic chemokines by adipose tissue is of particular interest since their local secretion, e.g. by perivascular adipose depots, may provide a novel mechanistic link between obesity and the associated vascular complications.

Homeostatic alterations induced by interleukin-1β microinjection into the orbitofrontal cortex in the rat

The present experiments were designed to elucidate the effect of direct orbitofrontal cortical administration of interleukin-1beta (IL-1beta) on the homeostatic regulation. Short- and long-term food intakes (FI), water intakes and body temperature (BT) were measured before and after a bilateral microinjection of IL-1beta (with or without paracetamol /P/ pretreatment) into the orbitofrontal cortex (OBF) of Wistar rats, and the effects were compared with those found in vehicle-treated and i.p. injected IL-1beta, IL-1beta+P or control animals. In addition, blood glucose levels (BGLs), along a glucose tolerance test, and plasma concentrations of insulin, leptin, cholesterol, triglycerides and urate were determined in cytokine treated and control rats. Short-term FI was suppressed after orbitofrontal cortical or peripheral application of IL-1beta. In the long-term FI, however, there was no significant difference among the groups. Cytokine microinjection into the OBF, similar to the i.p. administration, was also followed by a significant increase in BT. Pretreatment with P failed to influence the anorexigenic and hyperthermic effects of the centrally administered IL-1beta. The sugar load led to a diabetes-like prolonged elevation of BGL in the IL-1beta treated animals. Following cytokine administration, plasma levels of insulin and that of triglycerides were found decreased, whereas that of uric acid increased. The present findings confirm that the OBF is one of the neural routes through which IL-1beta exerts modulatory effect on the central homeostatic regulation.

The menopausal transition was associated in a prospective study with decreased health functioning in women who report menopausal symptoms

OBJECTIVE

To examine change in health functioning as women progress through the menopausal transition.

STUDY DESIGN AND SETTING

Prospective study of 2,489 women followed through four phases of the Whitehall II study. Health functioning was assessed with the eight subscales of the SF-36.

RESULTS

Compared with peri- and postmenopausal women who did not experience menopausal symptoms, women who reported vasomotor symptoms or menopausal depression experienced large and significant declines on most scales of the SF-36. Women who reported the greatest symptom severity experienced the largest declines in functioning. For example, decline in physical functioning for perimenopausal women experiencing severe vasomotor symptoms was 3.3 (standard error SE=1.1) greater than those who experienced no vasomotor symptoms. Decline in role limitation-emotional for perimenopausal women experiencing severe menopause-associated depression was 18.4 (SE=2.3), compared with those who did not experience these symptoms. Vasomotor symptom reporting was predicted by low socioeconomic position, high body mass index, and limiting long-term illness at baseline. Menopause-associated depression was additionally predicted by smoking and depression.

CONCLUSION

The menopausal transition is associated with decreased health functioning in women who report menopausal symptoms. Menopausal symptoms are strongly related to all aspects of health functioning assessed by the SF-36. Socioeconomic and behavioral risk factors for menopausal symptoms and associated declines in health functioning have been identified.

Acute, subacute and chronic effects of central neuropeptide Y on energy balance in rats

Central neuropeptide Y (NPY) injection has been reported to cause hyperphagia and in some cases also hypometabolism or hypothermia. Chronic central administration induced a moderate rise of short duration in body weight, without consistent metabolic/thermal changes. In the present studies the acute and subsequent subacute ingestive and metabolic/thermal changes were studied following intracerebroventricular (i.c.v.) injections of NPY in cold-adapted and non-adapted rats, or the corresponding chronic changes following i.c.v. NPY infusion. Besides confirming basic earlier data, we demonstrated novel findings: a temporal relationship for the orexigenic and metabolic/thermal effects, and differences of coordination in acute/subacute/chronic phases or states. The acute phase (30-60 min after injection) was anabolic: coordinated hyperphagia and hypometabolism/hypothermia. NPY evoked a hypothermia by suppressing any (hyper)metabolism in excess of basal metabolic rate, without enhancing heat loss. Thus, acute hypothermia was observed in sub-thermoneutral but not thermoneutral environments. The subsequent subacute catabolic phase exhibited opposite effects: slight increase in metabolic rate, rise in body temperature, reaching a plateau within 3-4 h after injection -- this was maintained for at least 24 h; meanwhile the food intake decreased and the normal daily weight gain stopped. This rebound is only indirectly related to NPY. Chronic (7-day long) i.c.v. NPY infusion induced an anabolic phase for 2-3 days, followed by a catabolic phase and fever, despite continued infusion. In cold-adaptation environment the primary metabolic effect of the infusion induced a moderate hypothermia with lower daytime nadirs and nocturnal peaks of the circadian temperature rhythm, while at near-thermoneutral environments in non-adapted rats the infusion attenuated only the nocturnal temperature rise by suppressing night-time hypermetabolism. Further finding is that in cold-adapted animals, the early feeding effect of NPY-infusion was enhanced, whereas the early hypothermic effect in cold was limited by interference with competing thermoregulatory mechanisms.

Physiological regulation of hypothalamic IL-1beta gene expression by leptin and glucocorticoids: implications for energy homeostasis

Interleukin-1beta (IL-1beta) is synthesized in a variety of tissues, including the hypothalamus, where it is implicated in the control of food intake. The current studies were undertaken to investigate whether hypothalamic IL-1beta gene expression is subject to physiological regulation by leptin and glucocorticoids (GCs), key hormones involved in energy homeostasis. Adrenalectomy (ADX) increased hypothalamic IL-1beta mRNA levels twofold, measured by real-time PCR (P < 0.05 vs. sham-operated controls), and this effect was blocked by subcutaneous infusion of a physiological dose of corticosterone. Conversely, hypothalamic IL-1beta mRNA levels were reduced by 30% in fa/fa (Zucker) rats, a model of genetic obesity caused by leptin receptor mutation (P = 0.01 vs. lean littermates), and the effect of ADX to increase hypothalamic IL-1beta mRNA levels in fa/fa rats (P = 0.02) is similar to that seen in normal animals. Moreover, fasting for 48 h (which lowers leptin and raises corticosterone levels) reduced hypothalamic IL-1beta mRNA levels by 30% (P = 0.02), and this decrease was fully reversed by refeeding for 12 h. Thus leptin and GCs exert opposing effects on hypothalamic IL-1beta gene expression, and corticosterone plays a physiological role to limit expression of this cytokine in both the presence and absence of intact leptin signaling. Consistent with this hypothesis, systemic leptin administration to normal rats (2 mg/kg ip) increased hypothalamic IL-1beta mRNA levels twofold (P < 0.05 vs. vehicle), an effect similar to that of ADX. These data support a model in which expression of hypothalamic IL-1beta is subject to opposing physiological regulation by corticosterone and leptin.

Intercellular signaling between adipose tissue and muscle tissue

Adipose and muscle tissues undergo regulated growth and differentiation processes that are modulated by a wide range of factors. The interactions between myogenic cells and adipocytes play a significant role in growth and development, including the rate and extent of myogenesis, muscle growth, adipogenesis, lipogenesis/lipolysis, and in the utilization of energy substrates. Important hormones and growth factors involved in the regulation of these processes include glucocorticoids, insulin-like growth factors, various cytokines, insulin, and leptin. Interactions among these axes have important implications in their influence on relative fat and lean deposition and the efficiency of energy utilization in growth and development. As research progresses to better clarify the interactions among adipose tissue depots and muscle of different fiber types, pathways will become better understood, ultimately leading to the optimized management of fat and lean growth in domestic livestock species. This review will focus on elements of intercellular signaling, using data from cell culture studies to illustrate specific examples of signaling pathways between cells.

A review of the mechanisms involved in the acute MDMA (ecstasy)-induced hyperthermic response

The predominant severe acute adverse effect following ingestion of 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) by recreational users is hyperthermia which can induce other associated clinical problems and occasionally death. There is no pharmacologically specific treatment. MDMA also induces dose-dependent hyperthermia in experimental animals. This review examines the consequences of MDMA administration on body temperature in humans and rodents. In rats hyperthermia results primarily from dopamine release and is influenced by dose, ambient temperature and other housing conditions. The response is increased in rats with a prior MDMA-induced neurotoxic lesion of 5-hydroxytryptamine (5-HT) nerve endings. Increased MDMA-induced locomotor activity appears to play no role in the hyperthermic response. However, the size of the acute hyperthermic response plays a major role in determining the severity of the subsequent neurotoxicity. These results suggest that any MDMA-induced hyperthermic response will be enhanced in hot, crowded dance club conditions and that ingesting the drug in such conditions increases the possibility of subsequent cerebral neurotoxic effect.

A new function of the leptin receptor: mediation of the recovery from lipopolysaccharide-induced hypothermia

Obese (f/f) Koletsky rats lack the leptin receptor (LR), whereas their lean (F/?) counterparts bear a fully functional LR. By using f/f and F/? rats, we studied whether the LR is involved in lipopolysaccharide (LPS)-induced fever and hypothermia. The body temperature responses to LPS (10 or 100 microg/kg iv) were measured in Koletsky rats exposed to a thermoneutral (28 degrees C) or cool (22 degrees C) environment. Rats of both genotypes responded to LPS with fever at 28 degrees C and with dose-dependent hypothermia at 22 degrees C. The fever responses of the f/f and F/? rats were identical. The hypothermic response of the f/f rats was markedly prolonged compared with that of the F/? rats. The prolonged hypothermic response to LPS in the f/f rats was accompanied by enhanced NF-kappaB signaling in the hypothalamus and an exaggerated rise in the plasma concentration of tumor necrosis factor (TNF)-alpha. The f/f rats did not respond to LPS with an increase in the plasma concentration of corticosterone or adrenocorticotropic hormone, whereas their F/? counterparts did. The hypothermic response to TNF-alpha (80 microg/kg iv) was markedly prolonged in the f/f rats. These data show that the LR is essential for the recovery from LPS hypothermia. LR-dependent mechanisms of the recovery from LPS hypothermia include activation of the anti-inflammatory hypothalamo-pituitary-adrenal axis, inhibition of both the production and hypothermic action of TNF-alpha, and suppression of inflammatory (via NF-kappaB) signaling in the hypothalamus.

Circulating leptin mediates lipopolysaccharide-induced anorexia and fever in rats

Anorexia and fever are important features of the host's response to inflammation that can be triggered by the bacterial endotoxin lipopolysaccharide (LPS) and the appetite suppressant leptin. Previous studies have demonstrated that LPS induces leptin synthesis and secretion in the periphery, and that the action of leptin on appetite suppression and fever are dependent on brain interleukin (IL)-1beta. However, the role of leptin as a neuroimmune mediator of LPS-induced inflammation has not been fully elucidated. To address this issue, we neutralized circulating leptin using a leptin antiserum (LAS) and determined how this neutralization affected LPS-induced anorexia, fever and hypothalamic IL-1beta. Adult male rats were separated into four treatment groups, namely LPS + normal sheep serum (NSS), LPS + LAS, saline + LAS and saline + NSS. Intraperitoneal injection of LPS (100 microg kg(-1)) induced a significant reduction in food intake and body weight, which were significantly reversed in the presence of LAS (1 ml kg(-1)), 8 and 24 h after treatment. In addition, LPS-induced fever was significantly attenuated by LAS over the duration of the fever response (8 h). Lipopolysaccharide induced an increase of circulating IL-6, another potential circulating pyrogen, which was not affected by neutralization of leptin at 2 h. Interleukin-1beta mRNA at 1 and 8 h, and IL-1 receptor antagonist (ra) at 2 h were significantly upregulated in the hypothalamus of LPS-treated animals. The induction of these cytokines was attenuated in the presence of LAS. These results are the first to demonstrate that leptin is a circulating mediator of LPS-induced anorexia and fever, probably through a hypothalamic IL-1beta-dependent mechanism.

Ghrelin inhibits leptin- and activation-induced proinflammatory cytokine expression by human monocytes and T cells

Ghrelin, a recently described endogenous ligand for the growth hormone secretagogue receptor (GHS-R), is produced by stomach cells and is a potent circulating orexigen, controlling energy expenditure, adiposity, and growth hormone secretion. However, the functional role of ghrelin in regulation of immune responses remains undefined. Here we report that GHS-R and ghrelin are expressed in human T lymphocytes and monocytes, where ghrelin acts via GHS-R to specifically inhibit the expression of proinflammatory anorectic cytokines such as IL-1beta, IL-6, and TNF-alpha. Ghrelin led to a dose-dependent inhibition of leptin-induced cytokine expression, while leptin upregulated GHS-R expression on human T lymphocytes. These data suggest the existence of a reciprocal regulatory network by which ghrelin and leptin control immune cell activation and inflammation. Moreover, ghrelin also exerts potent anti-inflammatory effects and attenuates endotoxin-induced anorexia in a murine endotoxemia model. We believe this to be the first report demonstrating that ghrelin functions as a key signal, coupling the metabolic axis to the immune system, and supporting the potential use of ghrelin and GHS-R agonists in the management of disease-associated cachexia.

The viral mimic, polyinosinic:polycytidylic acid, induces fever in rats via an interleukin-1-dependent mechanism

Polyinosinic:polycytidylic acid (poly I:C) is a synthetic double-stranded RNA that is used experimentally to model viral infections in vivo. Previous studies investigating the inflammatory properties of this agent in rodents demonstrated that it is a potent pyrogen. However, the mechanisms underlying this response have not been fully elucidated. In the current study, we examined the effects of peripheral administration of poly I:C on body temperature and cytokine production. Male rats were implanted with biotelemetry devices and randomly assigned to one of the following three groups: poly I:C + saline, poly I:C + interleukin-1 receptor antagonist (IL-1ra), or saline + saline. Maximal fever of 1.6 degrees C above baseline was observed 3 h after an intraperitoneal injection of poly I:C (750 microg/kg). Pretreatment with IL-1ra diminished this response by >50% (maximum body temperature = 0.6 degrees C above baseline). Plasma IL-6 concentration increased fivefold 2 h post-poly I:C compared with saline-injected rats; levels returned to baseline 4 h postinjection. Pretreatment with IL-1ra prevented this rise in IL-6. Plasma tumor necrosis factor (TNF)-alpha was also increased more than fourfold 2 h postinjection but remained unaffected by IL-1ra treatment. IL-1beta and cyclooxygenase-2 mRNA were significantly upregulated in the hypothalamus of poly I:C-treated animals. Finally, poly I:C decreased food intake by 30%, but this response was not altered by pretreatment with IL-1ra. These results suggest that poly I:C induces fever, but not anorexia, through an IL-1 and prostaglandin-dependent mechanism.

Regulatory effects of interleukin (IL)-1, interferon-beta, and IL-4 on the production of IL-1 receptor antagonist by human adipose tissue

Adipose tissue is the source of production and site of action of several pro- and antiinflammatory cytokines. We have recently shown that white adipose tissue (WAT) is a major producer of the antiinflammatory IL-1 receptor antagonist (IL-1Ra). Because IL-1Ra serum levels are elevated 7-fold in human obesity and an excess of this protein has been implicated in the acquired resistance to leptin and insulin, we investigated the regulation of IL-1Ra in human WAT. We demonstrate that IL-1Ra is mainly produced by adipocytes, rather than the stromal fraction of WAT, and that IL-1alpha and beta, as well as interferon-beta (IFN-beta), strongly up-regulate the expression and secretion of IL-1Ra in WAT. Moreover, human WAT expresses the receptors and proteins known to be required for the action of IL-1 (IL-1 receptor type I, IL-1 receptor accessory protein) and IFN-beta (IFN-alpha/beta receptor subunits 1 and 2). Finally, human WAT actively secretes these regulatory cytokines, suggesting that they up-regulate IL-1Ra through a local autocrine/paracrine action, which is hypothesized to play a regulatory role in adipogenesis and metabolism.

3,4‐Methylenedioxymethamphetamine increases interleukin‐1β levels and activates microglia in rat brain: studies on the relationship with acute hyperthermia and 5‐HT depletion

3,4-Methylenedioxymethamphetamine (MDMA) administration to rats produces acute hyperthermia and 5-HT release. Interleukin-1beta (IL-1beta) is a pro-inflammatory pyrogen produced by activated microglia in the brain. We examined the effect of a neurotoxic dose of MDMA on IL-1beta concentration and glial activation and their relationship with acute hyperthermia and 5-HT depletion. MDMA, given to rats housed at 22 degrees C, increased IL-1beta levels in hypothalamus and cortex from 1 to 6 h and [(3)H]-(1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)3-isoquinolinecarboxamide) binding between 3 and 48 h. Increased immunoreactivity to OX-42 was also detected. Rats became hyperthermic immediately after MDMA and up to at least 12 h later. The IL-1 receptor antagonist did not modify MDMA-induced hyperthermia indicating that IL-1beta release is a consequence, not the cause, of the rise in body temperature. When MDMA was given to rats housed at 4 degrees C, hyperthermia was abolished and the IL-1beta increase significantly reduced. The MDMA-induced acute 5-HT depletion was prevented by fluoxetine coadministration but the IL-1beta increase and hyperthermia were unaffected. Therefore, the rise in IL-1beta is not related to the acute 5-HT release but is linked to the hyperthermia. Contrary to IL-1beta levels, microglial activation is not significantly modified when hyperthermia is prevented, suggesting that it might be a process not dependent on the hyperthermic response induced by MDMA.

Feeding and temperature responses to intravenous leptin infusion are differential predictors of obesity in rats

Obesity is frequently associated with leptin resistance. The present study investigated whether leptin resistance in rats is present before obesity develops, and thus could underlie obesity induced by 16 wk exposure to a liquid, palatable, high-energy diet (HED). Before HED exposure, male Wistar rats (weighing between 330 and 360 g) received intravenous infusions of 20 μg leptin 2 h before dark (∼57 μg/kg rat). Relative to saline infusion, this caused a highly variable effect on food intake (ranging between -94 and +129%), with food intake suppression that appeared negatively correlated with HED-induced increases in body weight gain, caloric intake, adiposity, and plasma leptin levels. In contrast, leptin's thermogenic response was positively correlated to body weight gain linked to weights of viscera, but not to adiposity. Before HED exposure, leptin unexpectedly increased food intake in some rats (fi+, n = 8), whereas others displayed the normal reduction in food intake (fi-, n = 7). HED-exposed fi+ rats had higher plasma leptin levels, retroperitoneal fat pad weight, HED intake, and body weight gain than fi- and chow-fed rats. These parameters were also higher in HED-exposed fi- rats relative to chow rats, except for plasma leptin concentrations. It is concluded that leptin's reduced efficacy to suppress food intake could predict obesity on an HED. An unexpected orexigenic effect of leptin might potentially contribute to this as well.