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

Leptin in anorexia and cachexia syndrome

Leptin is a product of the obese (OB) gene secreted by adipocytes in proportion to fat mass. It decreases food intake and increases energy expenditure by affecting the balance between orexigenic and anorexigenic hypothalamic pathways. Low leptin levels are responsible for the compensatory increase in appetite and body weight and decreased energy expenditure (EE) following caloric deprivation. The anorexia-cachexia syndrome is a complication of many chronic conditions including cancer, chronic obstructive pulmonary disease, congestive heart failure, chronic kidney disease, and aging, where the decrease in body weight and food intake is not followed by a compensatory increase in appetite or decreased EE. Crosstalk between leptin and inflammatory signaling known to be activated in these conditions may be responsible for this paradox. This manuscript will review the evidence and potential mechanisms mediating changes in the leptin pathway in the setting of anorexia and cachexia associated with chronic diseases.

TTF-1 action on the transcriptional regulation of cyclooxygenase-2 gene in the rat brain

We have recently found that thyroid transcription factor-1 (TTF-1), a homeodomain-containing transcription factor, is postnatally expressed in discrete areas of the hypothalamus and closely involved in neuroendocrine functions. We now report that transcription of cyclooxygenase-2 (COX-2), the rate limiting enzyme in prostaglandin biosynthesis, was inhibited by TTF-1. Double immunohistochemistry demonstrated that TTF-1 was expressed in the astrocytes and endothelial cells of blood vessel in the hypothalamus. Promoter assays and electrophoretic mobility shift assays showed that TTF-1 inhibited COX-2 transcription by binding to specific binding domains in the COX-2 promoter. Furthermore, blocking TTF-1 synthesis by intracerebroventricular injection of an antisense oligomer induced an increase of COX-2 synthesis in non-neuronal cells of the rat hypothalamus, and resulted in animals' hyperthermia. These results suggest that TTF-1 is physiologically involved in the control of thermogenesis by regulating COX-2 transcription in the brain.

Deletion of interleukin-6 improves pyruvate tolerance without altering hepatic insulin signaling in the leptin receptor-deficient mouse

Obesity is associated with increased circulating interleukin-6 (IL-6), which may contribute to hepatic insulin resistance by impairing insulin receptor signaling. This study was designed to assess the impact of the systemic absence of IL-6 on the development of insulin resistance and glucose intolerance in an obese mouse model. Systemic insulin, glucose, and pyruvate tolerance tests were performed in IL-6 knockout (IL6KO) mice that had been crossed with a genetically obese (leptin receptor-deficient mouse model [Lep(db)]) mouse model. Real-time reverse transcriptase polymerase chain reaction and Western blot analysis assessed cellular and molecular markers of insulin signaling, inflammation, and metabolism. Absence of IL-6 did not improve systemic glucose or insulin tolerance, but Lep(db) × IL6KO mice displayed a smaller blood glucose increase following a pyruvate challenge. These results suggest that loss of IL-6 in the context of obesity may locally reduce hepatic glucose production from a gluconeogenic precursor. Hepatic insulin-dependent insulin receptor autophosphorylation, Akt activation, and FoxO1 phosphorylation were similar between Lep(db) × IL6KO mice and Lep(db) controls. Basal gene expression of the gluconeogenic enzyme phosphoenolpyruvate carboxykinase was reduced in male Lep(db) × IL6KO mice relative to Lep(db) controls; but gene expression of another regulatory enzyme, glucose-6-phosphatase, remained unaltered. Absence of IL-6 reduced gene expression of serum amyloid A and RelA in female Lep(db) mice, but did not alter hepatic triglyceride accumulation or lipogenic gene expression. Overall, our results suggest that IL-6 may be detrimental in obesity by contributing to elevated hepatic glucose output.

A multifaceted analysis of immune-endocrine-metabolic alterations in patients with pulmonary tuberculosis

Our study investigated the circulating levels of factors involved in immune-inflammatory-endocrine-metabolic responses in patients with tuberculosis with the aim of uncovering a relation between certain immune and hormonal patterns, their clinical status and in vitro immune response. The concentration of leptin, adiponectin, IL-6, IL-1β, ghrelin, C-reactive protein (CRP), cortisol and dehydroepiandrosterone (DHEA), and the in vitro immune response (lymphoproliferation and IFN-γ production) was evaluated in 53 patients with active untreated tuberculosis, 27 household contacts and 25 healthy controls, without significant age- or sex-related differences. Patients had a lower body mass index (BMI), reduced levels of leptin and DHEA, and increased concentrations of CRP, IL-6, cortisol, IL-1β and nearly significant adiponectin values than household contacts and controls. Within tuberculosis patients the BMI and leptin levels were positively correlated and decreased with increasing disease severity, whereas higher concentrations of IL-6, CRP, IL-1β, cortisol, and ghrelin were seen in cases with moderate to severe tuberculosis. Household contacts had lower DHEA and higher IL-6 levels than controls. Group classification by means of discriminant analysis and the k-nearest neighbor method showed that tuberculosis patients were clearly different from the other groups, having higher levels of CRP and lower DHEA concentration and BMI. Furthermore, plasma leptin levels were positively associated with the basal in vitro IFN-γ production and the ConA-driven proliferation of cells from tuberculosis patients. Present alterations in the communication between the neuro-endocrine and immune systems in tuberculosis may contribute to disease worsening.

PI3Kγ within a nonhematopoietic cell type negatively regulates diet-induced thermogenesis and promotes obesity and insulin resistance

Obesity is associated with a chronic low-grade inflammation, and specific antiinflammatory interventions may be beneficial for the treatment of type 2 diabetes and other obesity-related diseases. The lipid kinase PI3Kγ is a central proinflammatory signal transducer that plays a major role in leukocyte chemotaxis, mast cell degranulation, and endothelial cell activation. It was also reported that PI3Kγ activity within hematopoietic cells plays an important role in obesity-induced inflammation and insulin resistance. Here, we show that protection from insulin resistance, metabolic inflammation, and fatty liver in mice lacking functional PI3Kγ is largely consequent to their leaner phenotype. We also show that this phenotype is largely based on decreased fat gain, despite normal caloric intake, consequent to increased energy expenditure. Furthermore, our data show that PI3Kγ action on diet-induced obesity depends on PI3Kγ activity within a nonhematopoietic compartment, where it promotes energetic efficiency for fat mass gain. We also show that metabolic modulation by PI3Kγ depends on its lipid kinase activity and might involve kinase-independent signaling. Thus, PI3Kγ is an unexpected but promising drug target for the treatment of obesity and its complications.

Cognitive and emotional alterations are related to hippocampal inflammation in a mouse model of metabolic syndrome

Converging clinical data suggest that peripheral inflammation is likely involved in the pathogenesis of the neuropsychiatric symptoms associated with metabolic syndrome (MetS). However, the question arises as to whether the increased prevalence of behavioral alterations in MetS is also associated with central inflammation, i.e. cytokine activation, in brain areas particularly involved in controlling behavior. To answer this question, we measured in a mouse model of MetS, namely the diabetic and obese db/db mice, and in their healthy db/+ littermates emotional behaviors and memory performances, as well as plasma levels and brain expression (hippocampus; hypothalamus) of inflammatory cytokines. Our results shows that db/db mice displayed increased anxiety-like behaviors in the open-field and the elevated plus-maze (i.e. reduced percent of time spent in anxiogenic areas of each device), but not depressive-like behaviors as assessed by immobility time in the forced swim and tail suspension tests. Moreover, db/db mice displayed impaired spatial recognition memory (hippocampus-dependent task), but unaltered object recognition memory (hippocampus-independent task). In agreement with the well-established role of the hippocampus in anxiety-like behavior and spatial memory, behavioral alterations of db/db mice were associated with increased inflammatory cytokines (interleukin-1β, tumor necrosis factor-α and interleukin-6) and reduced expression of brain-derived neurotrophic factor (BDNF) in the hippocampus but not the hypothalamus. These results strongly point to interactions between cytokines and central processes involving the hippocampus as important contributing factor to the behavioral alterations of db/db mice. These findings may prove valuable for introducing novel approaches to treat neuropsychiatric complications associated with MetS.

Alterations in cognitive function and behavioral response to amphetamine induced by prenatal inflammation are dependent on the stage of pregnancy

Maternal infection during human pregnancy has been associated with the development of schizophrenia in the adult offspring. The stage of development and the maternal inflammatory response to infection, which undergoes quantitative and qualitative changes throughout gestation, are thought to determine critical windows of vulnerability for the developing brain. In order to investigate how these two factors may contribute to the outcome in the offspring, we studied the inflammatory response to turpentine (TURP) injection (100 μl/dam) and its consequences in the adult offspring, in pregnant rats at gestational day (GD) 15 or 18, which correspond to late first and early second trimester of human pregnancy, respectively. Maternal inflammatory response to TURP was different between the two GDs, with fever and circulating levels of the pro-inflammatory interleukin (IL)-6 significantly attenuated at GD 18, compared to GD 15. In the adult offspring, TURP challenge at GD 15 induced a significant decrease in pre-pulse inhibition (PPI) of acoustic startle, increased latency in the cued task of the Morris-water maze, prolonged conditioned fear response and enhanced locomotor effect of amphetamine. In contrast, the same immune challenge at GD 18 induced only a prolonged conditioned fear response. These results suggest a window of vulnerability at GD 15, at which TURP seems to affect several behaviors that are strongly modulated by dopamine. This was supported by increased tyrosine hydroxylase expression in the nucleus accumbens of the adult offspring of mothers treated at GD 15.

Calorie restriction attenuates LPS-induced sickness behavior and shifts hypothalamic signaling pathways to an anti-inflammatory bias

Calorie restriction (CR) has been demonstrated to alter cytokine levels; however, its potential to modify sickness behavior (fever, anorexia, cachexia) has not. The effect of CR on sickness behavior was examined in male C57BL/6J mice fed ad libitum or restricted 25% (CR25%) or restricted 50% (CR50%) in food intake for 28 days and injected with 50 μg/kg of LPS on day 29. Changes in body temperature, locomotor activity, body weight, and food intake were determined. A separate cohort of mice were fed ad libitum or CR50% for 28 days, and hypothalamic mRNA expression of inhibitory factor κB-α (IκB-α), cyclooxygenase-2 (COX-2), prostaglandin E(2) (PGE(2)), suppressor of cytokine signaling 3 (SOCS3), IL-10, neuropeptide Y (NPY), leptin, proopiomelanocortin (POMC), and corticotrophin-releasing hormone (CRH) were determined at 0, 2, and 4 h post-LPS. CR50% mice did not develop fevers, whereas the CR25% mice displayed a fever shorter in duration but with the same peak as the controls. Both CR25% and CR50% mice showed no sign of anorexia and reduced cachexia after LPS administration. Hypothalamic mRNA expression of NPY and CRH were both increased by severalfold in CR50% animals preinjection compared with controls. The CR50% mice did not demonstrate the expected rise in hypothalamic mRNA expression of COX-2, microsomal prostaglandin E synthase-1, POMC, or CRH 2 h post-LPS, and leptin expression was decreased at this time point. Increases in SOCS3, IL-10, and IκB-α expression in CR50% animals were enhanced compared with ad libitum-fed controls at 4 h post-LPS. CR results in a suppression of sickness behavior in a dose-dependent manner, which may be due to CR attenuating proinflammatory pathways and enhancing anti-inflammatory pathways.

Osteoarthritis: another component of metabolic syndrome?

Osteoarthritis (OA) has become a major public health problem not only because of its increasing prevalence worldwide but also because of its frequent association with cardiovascular disease, the leading cause of death in industrialized countries. There is growing evidence that OA is not simply a disease related to aging or mechanical stress of joints but rather a "metabolic disorder" in which various interrelated lipid, metabolic, and humoral mediators contribute to the initiation and progression of the disease process. Indeed, OA has been linked not only to obesity but also to other cardiovascular risk factors, namely, diabetes, dyslipidemia, hypertension, and insulin resistance.

Obesity, inflammatory markers, and endometrial cancer risk: a prospective case-control study

Obesity, a major risk factor for endometrial cancer, is a low-grade inflammatory state characterized by elevated concentrations of cytokines and acute phase reactants. The current study had two aims: first to investigate the associations of C-reactive protein (CRP), interleukin 6 (IL6), and IL1 receptor antagonist (IL1Ra) with endometrial cancer risk and second to examine to which extent these markers can influence the association between obesity and endometrial cancer. We conducted a case-control study, nested within the European Prospective Investigation into Cancer and Nutrition, which comprised 305 incident cases of endometrial cancer and 574 matched controls. CRP, IL6, and IL1Ra were measured in prospectively collected blood specimens by immunoassays. Data were analyzed using conditional logistic regression. All statistical tests were two-sided, and P values <0.05 were considered statistically significant. We observed a significant increase in risk of endometrial cancer with elevated levels of CRP (odds ratio (OR) for top versus bottom quartile: 1.58, 95% confidence interval (CI): 1.03-2.41, P(trend)=0.02), IL6 (OR for top versus bottom quartile: 1.66, 95% CI: 1.08-2.54, P(trend)=0.008), and IL1Ra (OR for top versus bottom quartile: 1.82, 95% CI: 1.22-2.73, P(trend)=0.004). After adjustment for body mass index (BMI), the estimates were strongly reduced and became non-significant. The association between BMI and endometrial cancer was also substantially attenuated (∼10-20%) after adjustment for inflammatory markers, even when the effects of C-peptide or estrone had already been taken into account. We provided epidemiological evidence that chronic inflammation might mediate the association between obesity and endometrial cancer and that endometrial carcinogenesis could be promoted by an inflammatory milieu.

Galanin-like peptide: a key player in the homeostatic regulation of feeding and energy metabolism?

The hypothalamus has a critical role in the regulation of feeding behavior, energy metabolism and reproduction. Galanin-like peptide (GALP), a novel 60 amino-acid peptide with a nonamidated C-terminus, was first discovered in porcine hypothalamus. GALP is mainly produced in the hypothalamic arcuate nucleus and is involved in the regulation of feeding behavior and energy metabolism, with GALP-containing neurons forming networks with several feeding-regulating peptide-containing neurons. The effects of GALP on food intake and body weight are complex. In rats, the central effect of GALP is to first stimulate and then reduce food intake, whereas in mice, GALP has an anorectic function. Furthermore, GALP regulates plasma luteinizing hormone levels through activation of gonadotropin-releasing hormone-producing neurons, suggesting that it is also involved in the reproductive system. This review summarizes the research on these topics and discusses current evidence regarding the function of GALP, particularly in relation to feeding and energy metabolism. We also discuss the effects of GALP activity on food intake, body weight and locomotor activity after intranasal infusion, a clinically viable mode of delivery.

Serum leptin levels, hormone levels, and hot flashes in midlife women

OBJECTIVE

To examine the associations between serum leptin levels, sex steroid hormone levels, and hot flashes in normal weight and obese midlife women.

DESIGN

Cross-sectional study.

SETTING

University clinic.

PATIENT(S)

201 Caucasian, nonsmoking women aged 45 to 54 years with a body mass index of <25 kg/m2 or >or=30 kg/m2.

INTERVENTION(S)

Questionnaire, fasting blood samples.

MAIN OUTCOME MEASURE(S)

Serum leptin and sex steroid hormone levels.

RESULT(S)

Correlation and regression models were performed to examine associations between leptin levels, hormone levels, and hot flashes. Leptin levels were associated with BMI, with "ever experiencing hot flashes" (questionnaire), with hot flashes within the last 30 days, and with duration of hot flashes (>1 year, P=.03). Leptin was positively correlated with testosterone, free testosterone index, and free estrogen index and inversely associated with levels of sex hormone-binding globulin. In women with a body mass index>or=30 kg/m2, leptin levels no longer correlated with testosterone levels.

CONCLUSION(S)

Serum leptin levels are associated with the occurrence and duration of hot flashes in midlife women; however, no correlation was found between leptin and serum estradiol.

Leptin regulates leukocyte recruitment into the brain following systemic LPS-induced inflammation

The appetite suppressing hormone leptin has emerged as an important modulator of immune function and is now considered to be a critical link between energy balance and host defense responses to pathogens. These 'adaptive' responses can, in situations of severe and sustained systemic inflammation, lead to adverse effects including brain damage that is partly mediated by neutrophil recruitment into the brain. We examined the contribution of leptin to this process in leptin-deficient (ob/ob), -resistant (db/db) and wild-type (WT) mice injected intraperitoneally with a septic dose of lipopolysaccharide (LPS). This treatment induced a dramatic increase in the number of neutrophils entering the brain of WT mice, an effect that was almost totally abolished in the mutant mice and correlated with a significant reduction in the mRNA levels of interleukin-1beta, intracellular adhesion molecule-1 and neutrophil-specific chemokines. These effects were reversed with leptin replenishment in ob/ob mice leading to recovery of neutrophil recruitment into the brain. Moreover, 48 h food deprivation in WT mice, which decreased circulating leptin levels, attenuated the LPS-induced neutrophil recruitment as did a single injection of an anti-leptin antiserum 4 h before LPS treatment in WT mice. These results provide the first demonstration that leptin has a critical role in leukocyte recruitment to the brain following severe systemic inflammation with possible implications for individuals with altered leptin levels such as during obesity or starvation.

Leptin modulates cell morphology and cytokine release in microglia

The appetite suppressing hormone, leptin is now established as an important component of the immune response to pathogens partly via the induction of brain IL-1beta. We have previously demonstrated that this hormone acts on microglia to induce the release of IL-1beta through actions on its functional receptors. In the present study, we extended these findings by demonstrating that leptin's action on microglia is that of a modulator rather than a direct trigger of inflammation. Using primary microglia cultures prepared from rat brain we show that pre-incubation of these cells with leptin for 24h prior to treatment with LPS increased the IL-1beta output 2-fold. This effect was not limited to IL-1beta but was also true for another cytokine, TNF-alpha and chemokines such as CINC-1 and MIP-2. The role of leptin in potentiating the microglial response to LPS appeared to be linked to morphological changes rendering the microglia more reactive. These results suggest that leptin has an important role in microglial function in inflammation and given that its circulating levels fluctuate across a number of conditions, these findings can have important implications for an individual's ability to mount an efficient and complete response to invading pathogens.

Arcuate nucleus proopiomelanocortin neurons mediate the acute anorectic actions of leukemia inhibitory factor via gp130

The proinflammatory cytokine leukemia inhibitory factor (LIF) is induced in disease states and is known to inhibit food intake when administered centrally. However, the neural pathways underlying this effect are not well understood. We demonstrate that LIF acutely inhibits food intake by directly activating pro-opiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus. We show that arcuate POMC neurons express the LIF-R, and that LIF stimulates the release of the anorexigenic peptide, alpha-MSH from ex vivo hypothalami. Transgenic mice lacking gp130, the signal transducing subunit of the LIF-R complex, specifically in POMC neurons fail to respond to LIF. Furthermore, LIF does not stimulate the release of alpha-MSH from the transgenic hypothalamic explants. These findings indicate that POMC neurons mediate the acute anorectic actions of central LIF administration and provide a mechanistic link between inflammation and food intake.

Gene expression of the liver in response to chronic hypoxia

Hypoxia is an important ecological, evolutionary, and biomedical stressor. While physiological acclimatization of mammals to hypoxia is well studied, the variation in gene expression that underlies acclimatization is not well studied. We acclimatized inbred mice for 32 days to hypoxic conditions that simulated altitudes of 1400, 3000, and 4500 m. We used oligonucleotide microarrays to measure changes in steady-state abundance of mRNA in the livers of these mice. Mice exposed to more severe hypoxia (simulated altitude of 4500 m) were smaller in mass and had higher hematocrit than mice exposed to less severe hypoxia. ANOVA and false discovery rate tests indicated that 580 genes were significantly differentially expressed in response to chronic hypoxia. Few of these 580 genes have previously been reported to respond to hypoxia. In contrast, many of these 580 genes belonged to same functional groups typically respond to acute hypoxia. That is, both chronic and acute hypoxia elicit changes in transcript abundance for genes involved in angiogenesis, glycolysis, lipid metabolism, carbohydrate metabolism, and protein amino acid phosphorylation, but the particular genes affected by the two types of hypoxia were mostly different. Numerous genes affecting the immune system were differentially expressed in response to chronic hypoxia, which supports recently proposed hypotheses that link immune function and hypoxia. Furthermore, our results discovered novel elevated mRNA abundance of genes involved in hematopoiesis and oxygen transport not reported previously, but consistent with extreme hematocrits found in hypoxic mice.

Association between interleukin-1 beta polymorphism (+3953) and obesity

It now appears that obesity is associated with a low-grade inflammation of white adipose tissue resulting from chronic activation of the innate immune system as interleukin-1 beta (IL-1). Previous investigations have described a positive association between IL-1 beta +3953 (C>T) gene polymorphism (rs 1143634) and obesity, suggesting functional effects on fat mass, fat metabolism and body mass. However, it is necessary to determine if these results occur in other populations and if they are influenced by sex and age. Therefore, we performed a case-control study using 880 Caucasian subjects (59.7+/-11.9 years old) from the Brazilian Aging Research Program (non-overweight=283, overweight=334, obese=263) previously investigated in genetic studies, in whom we analyzed the IL-1 beta +3953C/T polymorphism. We observed higher T allele (CT/TT) frequency in non-overweight than overweight and obese groups. The odds ratio showed 1.340 (95% CI: 1.119-1.605) times more chance of the obese group being CC carriers compared to non-overweight group independent of sex and age. This study corroborates the idea that the IL-1 system is linked to the development of obesity.

Kitasato symposium 2009: new prospects for cytokine inhibition

The Kitasato Symposium 2009: New Prospects for Cytokine Inhibition was held in Berlin, Germany from 7 to 9 May 2009. The key aims of this meeting were to bring together a group of front-line researchers and rheumatologists to evaluate the use of cytokine blockade and to examine the role of certain cytokines in the pathogenesis of rheumatoid arthritis and other autoimmune diseases. A keynote lecture delivered by Professor Jean-Michel Dayer provided an up-to-date overview of the interactions occurring between the immune system and acute phase proteins. Other speakers discussed the role of cytokines in rheumatoid arthritis, including their role in joint destruction, as well as their regulatory role upon T cells and B cells. The involvement of cytokines in other autoimmune diseases was also addressed.

Homeostatic alterations after IL-1beta microinjection into the nucleus accumbens of the rat

The present study investigates the effects of direct administration of interleukin-1beta (IL-1beta) into the nucleus accumbens (NAcc) on homeostatic regulation. Short- and long-term food intakes (FI), water intakes (WI) and body temperature (BT) were measured before and after bilateral microinjection of IL-1beta (with or without paracetamol pretreatment) into the NAcc of Wistar rats, and the effects were compared with those found in vehicle treated control animals. In addition, blood glucose levels, along with a glucose tolerance test (GTT), and plasma concentrations of metabolic parameters, such as total cholesterol, triglycerides, HDL, LDL and uric acid were determined in cytokine treated and control rats. Short-term FI and WI were suppressed after intraaccumbens application of IL-1beta. A significant increase of BT was also observed after the cytokine microinjection. Pretreatment with paracetamol failed to influence the anorexigenic, adipsogenic, and pyrogenic effects of IL-1beta. A definite glucose intolerance of the cytokine treated animals and their pathologically elevated blood glucose levels became obvious in the acute GTT. Following IL-1beta microinjection, plasma levels of triglycerides, total cholesterol and LDL were found increased. Our present findings show that the NAcc is an important site of action of IL-1beta mediated processes in central homeostatic regulation.

Hypothalamic inflammation and energy homeostasis: resolving the paradox

Determining the effect of hypothalamic inflammatory signals on energy balance presents a paradox. On the one hand, a large body of work has identified inflammatory signaling in the hypothalamus as an essential mediator of the sickness response--the anorexia, cachexia, fever, inactivity, lethargy, anhedonia and adipsia that are triggered by systemic inflammatory stimuli and promote negative energy balance. On the other hand, numerous recent studies implicate inflammatory activation within the hypothalamus as a key factor whereby high-fat diets--and saturated fats in particular--cause central leptin and insulin resistance and thereby promote the defense of elevated body weight. This paradox will likely remain unresolved until several issues have been addressed. Firstly, the hypothalamus--unlike many peripheral inflamed tissues--is an extremely heterogeneous tissue comprised of astrocytes, oligodendrocytes, microglia, endothelial cells, ependymal cells as well as numerous neuronal subgroups. Determining exactly which cells activate defined inflammatory signals in response to a particular stimulus--i.e. sepsis vs. nutrient excess--may yield critical clues. Secondly, for the sake of simplicity many studies evaluate inflammation as an on/off phenomenon. More realistically, inflammatory signaling occurs as a cascade or cycle that changes and progresses over time. Accordingly, even within the same cell type, the low-grade, chronic signal induced by nutrient excess may invoke a different cascade of signals than a strong, acute signal such as sepsis. In addition, because tolerance can develop to certain inflammatory mediators, physiological outcomes may not correlate with early biochemical markers. Lastly, the neuroanatomical location, magnitude, and duration of the inflammatory stimulus can undoubtedly influence the net CNS response. Rigorously evaluating the progression of the inflammatory signaling cascade within specific hypothalamic cell types is a key next step towards resolving the paradox surrounding the effect of inflammatory signaling on energy homeostasis.

Metabolic characterization of a mouse deficient in all known leptin receptor isoforms

We have characterized a newly generated mouse model of obesity, a mouse strain deficient in all five previously described leptin receptor isoforms. These transgenic mice, named the db (333)/db (333) mice, were identified from an ENU mutagenesis screen and carry a point mutation in the seventh exon of the db gene encoding the leptin receptor, resulting in a premature stop codon (Y(333)Stop) and gene product that lacks STAT signaling domains. db (333)/db (333) mice have a morbidly obese phenotype, with body weights diverging from wild type as early as 4 weeks of age (P < 0.05). To determine the contribution of the short isoforms of the leptin receptor in this metabolic phenotype, we performed an extensive metabolic characterization of the db (333)/db (333) mouse in relation to the well-characterized db/db mouse lacking only the long form of the leptin receptor. db (333)/db (333) mice have similar endocrine and metabolic parameters as previously described in other leptin receptor transgenic mice including db/db mice that lack only the long isoform of the leptin receptor. However, db (333)/db (333) mice show a subtle trend toward higher body weight and insulin levels, lower oxygen, carbon dioxide production, respiratory exchange ratio (RER), and temperature than db/db mice suggesting the short isoforms may play an additional role in energy homeostasis.

Shifts in diet from high fat to high carbohydrate improved levels of adipokines and pro-inflammatory cytokines in mice fed a high-fat diet

High-fat diets induce an expansion of the adipose tissue (AT) that can be characterized by chronic low-grade inflammation. AT is an important source of adipokines and pro-inflammatory cytokines. The purpose of this study was to evaluate the effects of a shift from a high-fat diet to high-carbohydrate (CHO) diet on the blood levels of adipokines and pro-inflammation cytokines in mice fed a high-fat diet. Six-week-old male C57BL/6 mice were fed a high-fat diet (40% of the total calories) for 9 weeks to induce obesity, and then the diet was shifted to a high CHO diet (70% of the total calories) for 3 weeks. Body weight and organ weight as well as blood lipid levels were measured. The serum levels of adipokines and pro-inflammatory cytokines were analyzed. Shifting the diet from high fat to high CHO decreased significantly body weight, adipose tissues, and liver weight (p < 0.05). The lipid blood levels (TG, Total-chol, and LDL-chol) decreased. The leptin and resistin blood levels significantly decreased after the diet was shifted to a high-CHO diet (p < 0.05); however, the adiponectin concentrations did not change. The IL-6 levels were also significantly decreased by the high-CHO diet (p < 0.05). The IL-13 serum levels were significantly increased by the high-CHO diet (p < 0.05). Further, the serum levels of the TNF-alpha and supernatant IL-1 beta concentrations in mice fed a high-carbohydrate diet were significantly increased after the mice were shifted to a high-fat diet. On the other hand, the serum IL-4 and supernatant levels did not change. Conclusively, reduction of body weight and adipose tissues through shifts from a high-fat diet to a high-carbohydrate diet effectively improved low-grade inflammation states in mice fed a high-fat diet. Particularly, the reduction of body weight was associated with the levels of leptin, resistin, and IL-6.

Uncoupling of inflammation and insulin resistance by NF-kappaB in transgenic mice through elevated energy expenditure

To study the metabolic activity of NF-kappaB, we investigated phenotypes of two different mouse models with elevated NF-kappaB activities. The transcriptional activity of NF-kappaB is enhanced either by overexpression of NF-kappaB p65 (RelA) in aP2-p65 mice or inactivation of NF-kappaB p50 (NF-kappaB1) through gene knock-out. In these models, energy expenditure was elevated in day and night time without a change in locomotion. The mice were resistant to adulthood obesity and diet-induced obesity without reduction in food intake. The adipose tissue growth and adipogenesis were inhibited by the elevated NF-kappaB activity. Peroxisome proliferator-activator receptor gamma expression was reduced by NF-kappaB at the transcriptional level. The two models exhibited elevated inflammatory cytokines (tumor necrosis factor-alpha and interleukin-6) in adipose tissue and serum. However, insulin sensitivity was not reduced by the inflammation in the mice on a chow diet. On a high fat diet, the mice were protected from insulin resistance. The glucose infusion rate was increased more than 30% in the hyperinsulinemic-euglycemic clamp test. Our data suggest that the transcription factor NF-kappaB promotes energy expenditure and inhibits adipose tissue growth. The two effects lead to prevention of adulthood obesity and dietary obesity. The energy expenditure may lead to disassociation of inflammation with insulin resistance. The study indicates that inflammation may prevent insulin resistance by eliminating lipid accumulation.

Vasomotor symptoms are associated with a lower bone mineral density

OBJECTIVE

The severity of vasomotor symptoms has been hypothesized to be linked to a lower bone mineral density (BMD). We examined whether women with vasomotor symptoms are different from women without symptoms with regard to BMD.

METHODS

We used data from a population-based sample of 5,600 women, aged 46 to 57 years and free from bone diseases, who participated in the first cross-sectional part of the Eindhoven Perimenopausal Osteoporosis Study between 1994 and 1995. Questionnaires at baseline were used to collect data on vasomotor symptoms and potential confounders. At baseline, BMD of the lumbar spine was measured using dual energy x-ray absorptiometry. Linear regression analysis was used to analyze the data.

RESULTS

Flushing was reported by 39% of all women, and night sweats, by 38% of all women. The average BMD was 1.01 +/- 0.14 g/cm and decreased with increasing frequency of flushing (P for trend < 0.0001) and night sweats (P for trend = 0.03). After multivariate adjustments for age, body mass index, menopause status, smoking, education, exercise, and hormone use, women with the highest frequency of symptoms had a 0.022 g/cm (95% CI, -0.03 to -0.01) lower BMD compared with asymptomatic women. Women who reported having the highest frequency of night sweats had a 0.011 g/cm (95% CI, -0.02 to -0.001) lower BMD compared with women with no symptoms of night sweats.

CONCLUSIONS

Our findings show that vasomotor symptoms are associated with reduced bone density. It could be hypothesized that women with vasomotor symptoms might be more susceptible to the beneficial effects of estrogens, possibly by neutralizing the effect of estrogen fluctuations. Further research is needed to extend these findings to other estrogen-sensitive end organs.

MyD88 signaling in the CNS is required for development of fatty acid-induced leptin resistance and diet-induced obesity

Obesity-associated activation of inflammatory pathways represents a key step in the development of insulin resistance in peripheral organs, partially via activation of TLR4 signaling by fatty acids. Here, we demonstrate that palmitate acting in the central nervous system (CNS) inhibits leptin-induced anorexia and Stat3 activation. To determine the functional significance of TLR signaling in the CNS in the development of leptin resistance and diet-induced obesity in vivo, we have characterized mice deficient for the TLR adaptor molecule MyD88 in the CNS (MyD88(DeltaCNS)). Compared to control mice, MyD88(DeltaCNS) mice are protected from high-fat diet (HFD)-induced weight gain, from the development of HFD-induced leptin resistance, and from the induction of leptin resistance by acute central application of palmitate. Moreover, CNS-restricted MyD88 deletion protects from HFD- and icv palmitate-induced impairment of peripheral glucose metabolism. Thus, we define neuronal MyD88-dependent signaling as a key regulator of diet-induced leptin and insulin resistance in vivo.

Infection, immunity and the neuroendocrine response

The Central Nervous (CNS) and Immune Systems (IS) are the two major adaptive systems which respond rapidly to numerous challenges that are able to compromise health. The defensive response strictly linking innate to acquired immunity, works continuously to limit pathogen invasion and damage. The efficiency of the innate response is crucial for survival and for an optimum priming of acquired immunity. During infection, the immune response is modulated by an integrated neuro-immune network which potentiates innate immunity, controls potential harmful effects and also addresses metabolic and nutritional modifications supporting immune function. In the last decade much knowledge has been gained on the molecular signals that orchestrate this integrated adaptive response, with focus on the systemic mediators which have a crucial role in driving and controlling an efficient protective response. These mediators are also able to signal alterations and control pathway dysfunctions which may be involved in the persistence and/or overexpression of inflammation that may lead to tissue damage and to a negative metabolic impact, causing retarded growth. This review aims to describe some important signalling pathways which drive bidirectional communication between the Immune and Nervous Systems during infection. Particular emphasis is placed on pro-inflammatory cytokines, immunomodulator hormones such as Glucocorticoids (GCs), Growth hormone (GH), Insulin-like Growth Factor-1 (IGF-1), and Leptin, as well as nutritional factors such as Zinc (Zn). Finally, the review includes up-to-date information on this neuroimmune cross-talk in domestic animals. Data in domestic animal species are still limited, but there are several exciting areas of research, like the potential interaction pathways between mediators (i.e. cytokine-HPA regulation, IL-6-GCS-Zn, cytokines-GH/IGF-1, IL-6-GH-Leptin and thymus activity) that are or could be promising topics of future research in veterinary medicine.

Galanin-like peptide modulates energy balance by affecting inflammatory mediators?

Galanin-like peptide (GALP) is a neuropeptide that is thought to play a role in the regulation of energy balance. However, the effects of GALP on food intake and body weight appear to be complex. In rats, central administration of GALP initially stimulates food intake, an effect that is followed by a reduction in food intake and body weight, whereas in mice, GALP has an anorectic action only. In rats and mice, GALP also causes a prostaglandin-dependent increase in core body temperature. These anorectic effects of GALP are similar to those observed after central administration of the pro-inflammatory cytokine interleukin-1 (IL-1). This review will discuss the evidence for the dichotomous actions of GALP on energy balance, and the potential mechanisms involved. I also describe a role for IL-1 in mediating the anorectic and febrile actions of GALP, and consider the possibility that GALP may act like an inflammatory mediator.

INTERLEUKIN-1 RECEPTOR ANTAGONIST GENE POLYMORPHISM AND TRADITIONAL CLASSIFICATION IN OBESE WOMEN

Cytokines appear to be the major regulators of adipose tissue metabolism. Interleukin- 1 receptor antagonist (IL-1ra) serum levels are increased in human obesity, and are under strong genetic control. The hypothesis was tested that the IL-1ra gene might be a candidate for obesity. Furthermore, the relationship was investigated between Sasang constitution and IL-1ra polymorphism. The frequency of a penta-allelic 86-bp tandem repeat (VNTR) in the intron 2 of IL-1ra gene in 67 lean (BMI<25 kg/m2), 133 overweight (BMI 25-29.9 kg/m2) and 61 obese (BMI>or=30 kg/m2) otherwise healthy Korean subjects was investigated. Total fat mass and percentage body fat were determined by dual-energy X-ray absorptiometry. Subjects were discriminated into four types by QSCC II program as well as clinical data (weight, height, blood pressure, etc.); Teaeumin, Taeyangin, Soyangin, and Soeumin. Genomic DNA was extracted and used for polymerase chain reaction-based genotyping of IL-1ra. The genotypic, or allelic distribution did not differ markedly between the three groups. The relative risk of being obese in comparison with lean was twofold increased in allele 2 carriers, although it was not statistically significant. Carriers of the allele 2 did not show a significant difference in physical and clinical characteristics. However, the relative risk of being obese in comparison with lean was increased in Taeumin subjects (p=.050), and so was in IL-1ra A2- carriers (p=.047). No relationship was found between the IL-1ra polymorphism and BMI in Korean women, but the authors first attempted to find an association among IL-1ra polymorphism, obesity, and Sasang constitution.

The role of interleukins in insulin resistance and type 2 diabetes mellitus

In the past few years, several interleukins (ILs) attracted considerable attention as potential effectors in the pathology and physiology of insulin resistance associated with type 2 diabetes mellitus (T2DM) and obesity. IL-1, a major proinflammatory cytokine, is present at increased levels in patients with diabetes mellitus, and could promote beta-cell destruction and alter insulin sensitivity. The effects of IL-1 are likely to be counteracted by IL-1 receptor antagonist protein (IL-1ra), as suggested by interventional studies in patients with T2DM who were treated with a recombinant form of this protein. However, studies in IL-1ra-deficient mice provided controversial results on the exact effect of the IL-1 signaling pathway on insulin secretion, insulin sensitivity and accumulation of adipose tissue. Likewise, IL-6 has been suggested to be involved in the development of obesity-related and T2DM-related insulin resistance. The action of IL-6 on glucose homeostasis is also complex and integrates central and peripheral mechanisms. Both experimental and clinical studies now converge to show that several ILs contribute to the pathology and physiology of T2DM through their interaction with insulin signaling pathways and beta-cell function.

Association between Interleukin-1B C-31T polymorphism and obesity in Japanese

Background

Recent studies have revealed a close relationship between obesity and polymorphism in the inflammation gene. However, the association between interleukin-1beta (IL-1β) and obesity remains controversial. We therefore investigated the association between IL-1B C-31T polymorphism and obesity in Japanese.

Methods

The participants were 802 inhabitants (281 men and 521 women) of Japan, aged 39 to 88 years, who attended a health examination in 2003. Body height, weight, waist and hip circumferences, and body fat percentage were measured. The IL-1B C-31T polymorphism was genotyped by polymerase chain reaction with confronting 2-pair primers. The association between IL-1B C-31T genotypes and various indices of obesity was then investigated. The confounding factor-adjusted odds ratios (OR) and 95% confidence intervals (CI) for obesity were calculated for each IL-1B C-31T genotype by using unconditional logistic regression analysis.

Results

Among male carriers of the CT and TT genotypes, the ORs for high body fat percentage were 2.58 (95% CI, 1.17–6.34) and 2.81 (1.17–7.33), respectively, as compared to carriers of the CC genotype (P for trend = 0.037). Among women, carriers of the TT genotype had significantly higher ORs for high BMI (OR, 2.13; 95% CI, 1.25–3.67) and large waist circumference (2.49; 1.37–4.66), as compared to women with the CC genotype (P for trend = 0.005 and 0.004, respectively).

Conclusions

The IL-1B C-31T polymorphism is associated with obesity in Japanese. Men and women with the TT genotype of IL-1B C-31T had a higher risk for obesity than those with the CC genotype.

Variants of the interleukin-1 receptor antagonist gene are associated with fat mass in men

CONTEXT

Immune functions seem to have connections to variations in body fat mass. Studies of knockout mice indicate that endogenous interleukin (IL)-1 can suppress mature-onset obesity.

OBJECTIVE

To systematically investigate our hypotheses that single-nucleotide polymorphisms (SNPs) and/or haplotypes variants in the IL-1 gene system are associated with fat mass.

SUBJECTS

The Gothenburg osteoporosis and obesity determinants (GOOD) study is a population-based cross-sectional study of 18-20 year-old men (n=1068), from Gothenburg, Sweden. Major findings were confirmed in elderly men (n=3014) from the Swedish part of the osteoporotic fractures in men (MrOS) multicenter population-based study.

MAIN OUTCOME MEASURE

The genotype distributions and their association with body fat mass in different compartments, measured with dual-energy X-ray absorptiometry (DXA).

RESULTS

Out of 15 investigated SNPs in the IL-1 receptor antagonist (IL1RN) gene, a recently identified 3' untranslated region C>T (rs4252041, minor allele frequency=4%) SNP was associated with the primary outcome total fat mass (P=0.003) and regional fat masses, but not with lean body mass or serum IL-1 receptor 1 (IL1RN) levels. This SNP was also associated with body fat when correcting the earlier reported IL1RN+2018 T>C (rs419598) SNP (in linkage disequilibrium with a well-studied variable number tandem repeat of 86 bp). The association between rs4252041 SNP and body fat was confirmed in the older MrOS population (P=0.03). The rs4252041 SNP was part of three haplotypes consisting of five adjacent SNPs that were identified by a sliding window approach. These haplotypes had a highly significant global association with total body fat (P<0.001). None of the other investigated members of the IL-1 gene family displayed any SNPs that have not been described previously to be significantly associated with body fat.

CONCLUSIONS

The IL1RN gene, shown to enhance obesity by suppressing IL-1 effects in experimental animals, have not [corrected] previously described gene polymorphisms and haplotypes that are associated with fat, but not lean mass in two populations of men.

Increased plasma interleukin-1 receptor antagonist levels in men with visceral obesity

BACKGROUND

Adipose tissue (AT) is an important source of interleukin-1 receptor antagonist (IL-1Ra). Its expression is markedly increased in obesity.

AIMS AND METHODS

To quantify the associations of IL-1Ra with body fat distribution as well as to examine the respective contributions of IL-1Ra and visceral adiposity to the variation in some cardiometabolic risk (CMR) markers. Plasma IL-1Ra levels were measured in a sample of 117 healthy non-diabetic men (age: 44.9+/-10.1 years; body mass index (BMI): 28.8+/-4.5 kg/m(2)).

RESULTS

Plasma IL-1Ra levels correlated positively with BMI, waist girth, and visceral and subcutaneous AT (0.39 < or = r<0.48; P < 0.0001). Multiple regression analyses revealed that visceral AT was the best independent predictor of IL-1Ra levels, explaining 22% (P < 0.0001) of its variance. IL-1Ra (P < 0.05) was an independent predictor of several CMR markers including triglyceride and high-density lipoprotein (HDL) cholesterol levels, cholesterol/HDL cholesterol ratio, glucose and insulin concentrations in response to a 75 g oral glucose load, and fasting insulin levels, in addition to the expected contribution of visceral AT (P < 0.05).

CONCLUSIONS

These results suggest that elevated IL-1Ra concentrations are influenced to a greater extent by visceral than subcutaneous adiposity and that IL-1Ra is independently related to some features of CMR beyond the known contribution of visceral adiposity.

Glucocorticoid-regulated crosstalk between arachidonic acid and endocannabinoid biochemical pathways coordinates cognitive-, neuroimmune-, and energy homeostasis-related adaptations to stress

Arachidonic acid and its derivatives constitute the major group of signaling molecules involved in the innate immune response and its communication with all cellular and systemic aspects involved on homeostasis maintenance. Glucocorticoids spread throughout the organism their influences over key enzymatic steps of the arachidonic acid biochemical pathways, leading, in the central nervous system, to a shift favoring the synthesis of anti-inflammatory endocannabinoids over proinflammatory metabolites, such as prostaglandins. This shift modifies local immune-inflammatory response and neuronal activity to ultimately coordinate cognitive, behavioral, neuroendocrine, neuroimmune, physiological, and metabolic adjustments to basal and stress conditions. In the hypothalamus, a reciprocal feedback between glucocorticoids and arachidonate-containing molecules provides a mechanism for homeostatic control. This neurochemical switch is susceptible to fine-tuning by neuropeptides, cytokines, and hormones, such as leptin and interleukin-1beta, assuring functional integration between energy homeostasis control and the immune/stress response.

Increased fat:carbohydrate oxidation ratio in Il1ra (-/-) mice on a high-fat diet is associated with increased sympathetic tone

AIMS/HYPOTHESIS

Proinflammatory cytokines, including IL-1, exert pleiotropic effects on the neuro-immuno-endocrine system. Previously, we showed that mice with knockout of the gene encoding IL-1 receptor antagonist (Il1ra (-/-), also known as Il1rn (-/-)) have a lean phenotype. The present study was designed to analyse the mechanisms leading to this lean phenotype.

METHODS

Il1ra (-/-) mice were fed a high-fat diet following weaning. Energy expenditure, body temperature, heart rate, blood parameters, urinary catecholamines and adipose tissue were analysed.

RESULTS

Il1ra (-/-) mice exhibited resistance to obesity induced by a high-fat diet; this resistance was associated with increased energy expenditure and a decreased respiratory quotient, indicating that the ratio of fat:carbohydrate metabolism in Il1ra (-/-) mice is greater than in controls. Activity level in Il1ra (-/-) mice was significantly decreased and body temperature was significantly increased, compared with wild-type (WT) mice. Inguinal white adipose tissues in Il1ra (-/-) mice express increased levels of Ucp1 and mitochondrial respiratory chain genes compared with WT mice. Histological analysis of adipose tissue in Il1ra (-/-) mice revealed that brown adipose tissue is hyperactive and inguinal white adipose tissue contains smaller cells, which exhibit the distinctive multilocular appearance of brown adipocytes. Urinary epinephrine and norepinephrine excretion in Il1ra (-/-) mice was significantly increased compared with WT mice, suggesting that Il1ra (-/-) mice have increased sympathetic tone. Consistent with this, heart rate in Il1ra (-/-) mice was also significantly increased.

CONCLUSIONS/INTERPRETATION

Our results show that Il1ra (-/-) mice have increased energy expenditure, fat:carbohydrate oxidation ratio, body temperature, heart rate and catecholamine production. All of these observations are consistent with an enhanced sympathetic tone.

A warmer ambient temperature increases the passage of interleukin-1beta into the brains of old rats

We have demonstrated that after intraperitoneal lipopolysaccharide (LPS) injection, old rats mount fevers similar to those of young rats at an ambient temperature (Ta) of 31 degrees C, but not at 21 degrees C. The same is true for intraperitoneal or intravenous IL-1beta administration. The underlying mechanism responsible for blunted fever in old rats may be a deficiency in communication between the periphery and the brain. Possibly, peripheral cytokine actions are altered in old rats, such that the signal that reaches the brain is diminished. Here, we hypothesized that at standard laboratory temperatures, not enough IL-1beta is reaching the brain for fever to occur and that a warmer Ta would increase the influx of IL-1beta into the brain, enabling old rats to generate fever. Young (3-5 mo) and old (23-29 mo) Long-Evans rats were maintained for 3 days at either Ta 21 or 31 degrees C prior to intravenous injection with radiolabeled IL-1beta to measure passage across the blood-brain barrier. Young rats showed similar influx of IL-1beta into the brain at the two Tas, but old rats showed significant influx only at the warmer Ta. These data suggest that the lack of fever at a cool Ta may be due to a reduced influx of IL-1beta into the brain.