Obesity and IL-6 interact in modulating the response to endotoxemia in mice

Galectin-1 in Obesity and Type 2 Diabetes

Galectin-1 is a carbohydrate-binding protein expressed in many tissues. In recent years, increasing evidence has emerged for the role of galectin-1 in obesity, insulin resistance and type 2 diabetes. Galectin-1 has been highly conserved through evolution and is involved in key cellular functions such as tissue maturation and homeostasis. It has been shown that galectin-1 increases in obesity, both in the circulation and in the adipose tissue of human and animal models. Several proteomic studies have independently identified an increased galectin-1 expression in the adipose tissue in obesity and in insulin resistance. Large population-based cohorts have demonstrated associations for circulating galectin-1 and markers of insulin resistance and incident type 2 diabetes. Furthermore, galectin-1 is associated with key metabolic pathways including glucose and lipid metabolism, as well as insulin signalling and inflammation. Intervention studies in animal models alter animal weight and metabolic profile. Several studies have also linked galectin-1 to the progression of complications in diabetes, including kidney disease and retinopathy. Here, we review the current knowledge on the clinical potential of galectin-1 in obesity and type 2 diabetes.

Short-term Obesity Worsens Heart Inflammation and Disrupts Mitochondrial Biogenesis and Function in an Experimental Model of Endotoxemia

Cardiomyopathy is a well-known complication of sepsis that may deteriorate when accompanied by obesity. To test this hypothesis we fed C57black/6 male mice for 6 week with a high fat diet (60% energy) and submitted them to endotoxemic shock using E. coli LPS (10 mg/kg). Inflammatory markers (cytokines and adhesion molecules) were determined in plasma and heart tissue, as well as heart mitochondrial biogenesis and function. Obesity markedly shortened the survival rate of mouse after LPS injection and induced a persistent systemic inflammation since TNFα, IL-1β, IL-6 and resistin plasma levels were higher 24 h after LPS injection. Heart tissue inflammation was significantly higher in obese mice, as detected by elevated mRNA expression of pro-inflammatory cytokines (IL-1β, IL-6 and TNFα). Obese animals presented reduced maximum respiratory rate after LPS injection, however fatty acid oxidation increased in both groups. LPS decreased mitochondrial DNA content and mitochondria biogenesis factors, such as PGC1α and PGC1β, in both groups, while NRF1 expression was significantly stimulated in obese mice hearts. Mitochondrial fusion/fission balance was only altered by obesity, with no influence of endotoxemia. Obesity accelerated endotoxemia death rate due to higher systemic inflammation and decreased heart mitochondrial respiratory capacity.

Let-7i-5p Mediates the Therapeutic Effects of Exosomes from Human Placenta Choriodecidual Membrane-Derived Mesenchymal Stem Cells on Mitigating Endotoxin-Induced Mortality and Liver Injury in High-Fat Diet-Induced Obese Mice

Obesity complicates sepsis and increases the mortality of sepsis. We examined the effects of exosomes (from human placenta choriodecidual membrane-derived mesenchymal stem cells, pcMSCs) on preventing sepsis in obesity and the mitigating role of hsa-let-7i-5p microRNA. Obese mice (adult male C57BL/6J mice fed a high-fat diet for 12 weeks) received normal saline (HFD), endotoxin (10 mg/kg, intraperitoneal (ip); HFDLPS), endotoxin with exosomes (1 × 10⁸ particles/mouse, ip; HLE), or endotoxin with let-7i-5p microRNA inhibitor-pretreated exosomes (1 × 10⁸ particles/mouse, ip; HLEi). Our data demonstrated that the 48-h survival rate in the HLE (100%) group was significantly higher than in the HFDLPS (50%) and HLEi (58.3%) groups (both p < 0.05). In the surviving mice, by contrast, levels of liver injury (injury score, plasma aspartate transaminase and alanine transaminase concentrations, tissue water content, and leukocyte infiltration in liver tissues; all p < 0.05), inflammation (nuclear factor-κB activation, hypoxia-inducible factor-1α activation, macrophage activation, and concentrations of tumor necrosis factor-α, interleukin-6, and leptin in liver tissues; all p < 0.05), and oxidation (malondialdehyde in liver tissues, with p < 0.001) in the HLE group were significantly lower than in the HFDLPS group. Levels of mitochondrial injury/dysfunction and apoptosis in liver tissues in the HLE group were also significantly lower than in the HFDLPS group (all p < 0.05). Inhibition of let-7i-5p microRNA offset the effects of the exosomes, with most of the aforementioned measurements in the HLEi group being significantly higher than in the HLE group (all p < 0.05). In conclusion, exosomes mitigated endotoxin-induced mortality and liver injury in obese mice, and these effects were mediated by let-7i-5p microRNA.

Adipocyte inflammation and pathogenesis of viral pneumonias: an overlooked contribution

Epidemiological evidence establishes obesity as an independent risk factor for increased susceptibility and severity to viral respiratory pneumonias associated with H1N1 influenza and SARS-CoV-2 pandemics. Given the global obesity prevalence, a better understanding of the mechanisms behind obese susceptibility to infection is imperative. Altered immune cell metabolism and function are often perceived as a key causative factor of dysregulated inflammation. However, the contribution of adipocytes, the dominantly altered cell type in obesity with broad inflammatory properties, to infectious disease pathogenesis remains largely ignored. Thus, skewing of adipocyte-intrinsic cellular metabolism may lead to the development of pathogenic inflammatory adipocytes, which shape the overall immune responses by contributing to either premature immunosenescence, delayed hyperinflammation, or cytokine storm in infections. In this review, we discuss the underappreciated contribution of adipocyte cellular metabolism and adipocyte-produced mediators on immune system modulation and how such interplay may modify disease susceptibility and pathogenesis of influenza and SARS-CoV-2 infections in obese individuals.

Chlorogenic Acid-Induced Gut Microbiota Improves Metabolic Endotoxemia

BACKGROUND

Coffee can regulate glucose homeostasis but the underlying mechanism is unclear. This study investigated the preventive and therapeutic effects of chlorogenic acid (CGA), a polyphenol that is found in coffee, on obesity and obesity-related metabolic endotoxemia.

METHOD

Male 4-week-old C57BL/6 mice were fed either normal chow or a high-fat diet or 20 weeks and half the mice in each group were gavaged with CGA. Oral glucose tolerance tests (OGTTs) and insulin tolerance tests (ITTs) were performed. Markers of inflammation and intestinal barrier function were assayed. The composition of the gut microbiota was analyzed by 16S rRNA high-throughput pyrosequencing. The role of CGA-altered microbiota in metabolic endotoxemia was verified by fecal microbiota transplantation.

RESULTS

CGA protected against HFD-induced weight gain, decreased the relative weight of subcutaneous and visceral adipose, improved intestinal barrier integrity, and prevented glucose metabolic disorders and endotoxemia (P <0.05). CGA significantly changed the composition of the gut microbiota and increased the abundance of short chain fatty acid (SCFA)-producers (e.g., Dubosiella, Romboutsia, Mucispirillum, and Faecalibaculum) and Akkermansia, which can protect the intestinal barrier. In addition, mice with the CGA-altered microbiota had decreased body weight and fat content and inhibited metabolic endotoxemia.

CONCLUSION

CGA-induced changes in the gut microbiota played an important role in the inhibition of metabolic endotoxemia in HFD-fed mice.

Age-Dependent Changes of Adipokine and Cytokine Secretion From Rat Adipose Tissue by Endogenous and Exogenous Toll-Like Receptor Agonists

White adipose tissue but recently also brown adipose tissue have emerged as endocrine organs. Age-associated obesity is accompanied by prolonged and elevated lipopolysaccharide (LPS)-induced sickness symptoms and increased cytokine and adipokine levels in the circulation partially originating from adipose tissue. In the present study, ex vivo fat explants were used to investigate how the exogenous pathogen-associated molecular pattern (PAMP) LPS or the endogenous danger-associated molecular patterns (DAMPs) high mobility group box-1 protein (HMGB1) and biglycan modulate the release of cytokines and adipokines/batokines and, thus, could influence systemic and/or local inflammation. The response of adipose tissue (epididymal, retroperitoneal, subcutaneous, and brown) was compared between young lean and old obese rats (2 vs. 24 months old). LPS induced a strong interleukin (IL)-6 and tumor necrosis factor (TNF) alpha release into the supernatant of all adipose tissue types investigated. HMGB1 (subcutaneous) and biglycan (retroperitoneal) led to an increased release of IL-6 and TNFalpha (HMGB1) and decreased visfatin and adiponectin (biglycan) secretion from epididymal adipose tissue (young rats). Visfatin was also decreased by HMGB1 in retroperitoneal adipose tissue of old rats. We found significantly higher leptin (all fat pads) and adiponectin (subcutaneous) levels in supernatants of adipose tissue from old compared to young rats, whereas visfatin secretion showed the opposite. The expression of the biglycan receptor Toll-like receptor (TLR) 2 as well as the LPS and HMGB1 receptors TLR4 and receptor for advanced glycation end products (RAGE) were reduced with age (TLR4/RAGE) and by stimulation with their ligands (subcutaneous). Overall, we revealed that adipokines/adipose-tissue released cytokines show some modulation of their release caused by mediators of septic (batokines) and sterile inflammation with potential implication for acute and chronic disease. Moreover, aging may increase or decrease the release of fat-derived mediators. These data show that DAMPS and LPS locally modulate cytokine secretion while only DAMPS but not LPS can locally alter adipokine secretion during inflammation.

The Effects of Obesity on Outcome in Preclinical Animal Models of Infection and Sepsis: A Systematic Review and Meta-Analysis

BACKGROUND

Clinical studies suggest obesity paradoxically increases survival during bacterial infection and sepsis but decreases it with influenza, but these studies are observational. By contrast, animal studies of obesity in infection can prospectively compare obese versus nonobese controls. We performed a systematic review and meta-analysis of animal investigations to further examine obesity's survival effect in infection and sepsis.

METHODS

Databases were searched for studies comparing survival in obese versus nonobese controls. We performed a systematic review and meta-analysis of animal investigations to further examine obesity's survival effect in infection and sepsis. Methods. Databases were searched for studies comparing survival in obese versus nonobese animals following bacteria, lipopolysaccharide, or influenza virus challenges.

RESULTS

Twenty-one studies (761 obese and 603 control animals) met the inclusion criteria. Obesity reduced survival in 19 studies (11 significantly) and the odds ratio (95% CI) of survival (0.21(0.13, 0.35); I ² = 64%, p < 0.01p < 0.01p < 0.01) but with high heterogeneity. Obesity reduced survival (1) consistently in both single-strain bacteria- and lipopolysaccharide-challenged studies (n = 6 studies, 0.21(0.13, 0.34); I ² = 64%, p < 0.01p < 0.01) but with high heterogeneity. Obesity reduced survival (1) consistently in both single-strain bacteria- and lipopolysaccharide-challenged studies (n = 6 studies, 0.21(0.13, 0.34); I ² = 64%, p < 0.01p < 0.01) but with high heterogeneity. Obesity reduced survival (1) consistently in both single-strain bacteria- and lipopolysaccharide-challenged studies (n = 6 studies, 0.21(0.13, 0.34); I ² = 64%, p < 0.01p < 0.01) but with high heterogeneity. Obesity reduced survival (1) consistently in both single-strain bacteria- and lipopolysaccharide-challenged studies (n = 6 studies, 0.21(0.13, 0.34); I ² = 64%, p < 0.01p < 0.01p < 0.01) but with high heterogeneity. Obesity reduced survival (1) consistently in both single-strain bacteria- and lipopolysaccharide-challenged studies (n = 6 studies, 0.21(0.13, 0.34); I ² = 31%, p=0.20 and n = 5, 0.22(0.13, 0.36); I ² = 0%, p=0.59, respectively), (2) not significantly with cecal ligation and puncture (n = 4, 0.72(0.08, 6.23); I ² = 75%, p < 0.01), and (3) significantly with influenza but with high heterogeneity (n = 6, 0.12(0.04, 0.34); I ² = 73%, p < 0.01). Obesity's survival effects did not differ significantly comparing the four challenge types (p=0.49). Animal models did not include antimicrobials or glycemic control and study quality was low.

CONCLUSIONS

Preclinical and clinical studies together emphasize the need for prospective studies in patients accurately assessing obesity's impact on survival during severe infection.

Site-Specific Reprogramming of Macrophage Responsiveness to Bacterial Lipopolysaccharide in Obesity

The mechanisms by which obesity may alter immune responses to pathogens are poorly understood. The present study assessed whether the intrinsic responsiveness of resident macrophages to bacterial lipopolysaccharide (LPS) is reprogrammed in high-fat diet (HFD)-induced obesity. Macrophages from adipose tissue, lung alveoli, and the peritoneal cavity were extracted from obese rats on a HFD or from their lean counterparts, and subsequently studied in culture under identical conditions. CD45⁺/CD68⁺ cells (macrophages) were abundant in all cultures, and became the main producers of TNF-α upon LPS stimulation. But although all macrophage subpopulations responded to LPS with an M1-like profile of cytokine secretion, the TNF-α/IL-10 ratio was the lowest in adipose tissue macrophages, the highest in alveolar macrophages, and intermediary in peritoneal macrophages. What is more, diet exerted qualitatively distinct effects on the cytokine responses to LPS, with obesity switching adipose tissue macrophages to a more pro-inflammatory program and peritoneal macrophages to a less pro-inflammatory program, while not affecting alveolar macrophages. Such reprogramming was not associated with changes in the inflammasome-dependent secretion of IL-1β. The study further shows that the effects of diet on TNF-α/IL-10 ratios were linked to distinct patterns of NF-κB accumulation in the nucleus: while RelA was the NF-κB subunit most impacted by obesity in adipose tissue macrophages, cRel was the subunit affected in peritoneal macrophages. It is concluded that obesity causes dissimilar, site-specific changes in the responsiveness of resident macrophages to bacterial LPS. Such plasticity opens new avenues of investigation into the mechanisms linking obesity to pathogen-induced immune responses.

Lipopolysaccharide and inflammatory cytokines levels decreased after sleeve gastrectomy in Chinese adults with obesity

Obesity is linked to a low-grade systemic inflammation and lipopolysaccharide (LPS) is a key factor. Sleeve gastrectomy (SG) can significantly cause weight loss, but few reports have looked into the changes of LPS and inflammatory cytokines after surgery. To explore the potential short-term impact of SG on LPS and inflammatory cytokines and their relationship to early metabolic changes in obesity. 30 Chinese adults with obesity (BMI 39.37 ± 8.22 kg/m², 25 female) receiving SG were included in this study. Fasting blood samples were collected at baseline and 30 days after SG. Serum LPS markedly reduced from 336.50 (73.54, 500) pg/mL to 5.00 (5.00, 5.24) pg/mL at 1 month after SG (p < 0.05). There was a significant decrease in plasma IL-6, IL-8, and serum CRP after SG (all p < 0.05). Insulin resistance improved remarkably after surgery as displayed by reductions in fasting insulin level (FINS, p < 0.001), and HOMA-IR (p < 0.001). In addition, visceral fat area (VFA) decreased from 209.70 ± 39.96 cm² to 193.28 ± 43.68 cm² after SG (p < 0.001). LPS was positively correlated with FINS (r = 0.391, p = 0.033) and HOMA-IR (r = 0.38, p = 0.038) before SG. Meanwhile, VFA was positively associated with CRP (r = 0.388, p = 0.034) before surgery. When assessing 30-days postoperative changes, a positive correlation was found between the variations of LPS, IL-8 and the reduction of VFA. After multivariate analyses, only the reduced IL-8 level was independently associated with the reduction of VFA (p = 0.015). In conclusion, SG can significantly relieve the inflammation in obesity in the short term and LPS might be an earlier predictor of inflammatory changes after surgery.

Preventive Leptin Administration Protects Against Sepsis Through Improving Hypotension, Tachycardia, Oxidative Stress Burst, Multiple Organ Dysfunction, and Increasing Survival

Sepsis syndrome is the most important cause of mortality in critically ill patients admitted to intensive care units (ICUs). However, current therapies for its prevention and treatment are still unsatisfactory, and the mortality rate is still high. Non-septic ICU patients are vulnerable to acquire sepsis syndrome. Thus, a preventive treatment for this population is needed. During sepsis syndrome and endotoxemia, severe hypotension, tachycardia, oxidative and immune response increase, multiple organ dysfunction syndrome (MODS) and decreased survival are observed. Leptin administration protects against negative effects of sepsis syndrome and endotoxemia. Furthermore, it is has been reported that leptin elevates blood pressure mediated by sympathetic nervous system activation. However, whether leptin administration before sepsis induction mediates its protective effects during sepsis through blood pressure regulation is not known. Therefore, we investigated whether pre-treatment of leptin improves blood pressure and MODS, resulting in survival increase during endotoxemia. The results showed that leptin administration before endotoxemia induction reduced both the hypotension and tachycardia characteristically observed during endotoxemia. Notably, this protective effect was observed early and late in the course of endotoxemia. Endotoxemia-induced MODS decreased in leptin-treated rats, which was reflected in normal values for liver and kidney function, inhibition of muscle mass wasting and maintenance of glycemia. Furthermore, leptin pre-treatment decreased the oxidative stress burst in blood and blunted the increased pro-inflammatory cytokines TNF-α, IL-1β, and IL-6 observed during endotoxemia. Remarkably, according to the leptin-induced increase in survival, leptin pre-administration decreased the risk for death associated with sepsis syndrome at early and late times after endotoxemia induction. These results show a potential preventive therapy against sepsis syndrome and endotoxemia in vulnerable patients, based in the beneficial actions of leptin.

Comparison of a microsphere-based platform with a multiplex flow cytometric assay for determination of circulating cytokines in the mouse

Background

Measuring expression profiles of inflammatory biomarkers is important in monitoring the polarization of immune responses; therefore, results should be independent of quantitation methods if they are to be accepted as validated clinical pathology biomarkers. To evaluate effects of differing quantitation methods, the seven major circulating Th1/Th2/Th17 cytokines interleukin 2 (IL-2), interferon γ (IFN-γ), tumor necrosis factor α (TNF-α), IL-4, IL-6, IL-10 and IL-17A were quantified in plasma of lipopolysaccharide (LPS)-treated mice with two different multiplex platforms.

Methods

Female C57BL6 mice were treated orally with vehicle or dexamethasone, followed by LPS intravenously. Plasma samples were analyzed 0.5, 1, 2, 4, and 6 h post-LPS challenge with assays at Myriad-RBM and compared to assays performed on a BD Accuri C6 flow cytometer.

Results

IL-17A response to LPS was limited but sustained, and the response for the remaining cytokines were early and transient; dexamethasone reduced expression of all 7 cytokines. TNF-α and IL-6 levels were similar across both assays, and IL-4 levels were generally very low. Plasma levels of remaining cytokines were variably lower with BD assays than Myriad-RBM assays.

Conclusions

The present findings demonstrate that quantitation of circulating biomarkers of inflammation can be achieved using multiplexed flow cytometry, but careful consideration must be taken for assay validation when cross-referencing with another multiplexed assay.

OBESITY AND CRITICAL ILLNESS: INSIGHTS FROM ANIMAL MODELS

Critical illness is a major cause of morbidity and mortality around the world. While obesity is often detrimental in the context of trauma, it is paradoxically associated with improved outcomes in some septic patients. The reasons for these disparate outcomes are not well understood. A number of animal models have been used to study the obese response to various forms of critical illness. Just as there have been many animal models that have attempted to mimic clinical conditions, there are many clinical scenarios that can occur in the highly heterogeneous critically ill patient population that occupies hospitals and intensive care units. This poses a formidable challenge for clinicians and researchers attempting to understand the mechanisms of disease and develop appropriate therapies and treatment algorithms for specific subsets of patients, including the obese. The development of new, and the modification of existing animal models, is important in order to bring effective treatments to a wide range of patients. Not only do experimental variables need to be matched as closely as possible to clinical scenarios, but animal models with pre-existing comorbid conditions need to be studied. This review briefly summarizes animal models of hemorrhage, blunt trauma, traumatic brain injury, and sepsis. It also discusses what has been learned through the use of obese models to study the pathophysiology of critical illness in light of what has been demonstrated in the clinical literature.

Obesity Impacts Fever and Sickness Behavior During Acute Systemic Inflammation

Obesity is reaching dramatic proportions in humans and is associated with a higher risk for cardiovascular disease, diabetes, and cognitive alterations, and a higher mortality during infection and inflammation. The focus of the present review is on the influence of obesity on the presentation of fever, sickness behavior, and inflammatory responses during acute systemic inflammation.

Association between IL-6 and related risk factors of metabolic syndrome and cardiovascular disease in young rats

OBJECTIVE

Metabolic syndrome (MS) is conceived as the pathogenic basis of an increased cardiovascular burden. We investigate the correlation between interleukin-6 (IL-6) and the risk factors of MS and cardiovascular disease (CVD) in diet-induced model of MS and determined whether IL-6 was associated with the prevalence of MS and cardiovascular disease.

METHODS

A total of 40 Spague-Dawley (SD) rats were randomly divided into high-fat and high salt (FSC) group, high-fat (FC) group and normal control (NC) group. After feeding for 7 weeks, fasting blood glucose (FBG) and fasting insulin (FIN) were measured at the 60 min, 120 min and 180 min after the glucose administration. Blood pressure, body weight, height, waist circumference (WC), liver weight, visceral fat weight as well as blood lipid profile were determined at the end of 7-week. Furthermore, IL-6 levels from adipose tissues were analyzed using ELISA, and the correlation between IL-6 and the risk factors of MS and cardiovascular disease was investigated.

RESULTS

After treatment with different diets, significant difference was noted in the WC, body mass index (BMI), visceral fat weight and liver weight of FSC group compared with those of NC group (P<0.05). The levels of systolic blood pressure (SBP), diastolic blood pressure (DBP), total cholesterol (TC), triacylglycerol (TG) and low density lipoprotein (LDL) were markedly elevated in FSC group compared with those in NC group, while the level of high density lipoprotein (HDL) was remarkable lower in FSC group (P<0.05). After glucose administration, the concentrations of blood glucose and insulin were significant higher in FSC group than those in NC group at different time points (P<0.05). Moreover, high-fat and high salt diet brought about significant elevation of IL-6 compared with that with normal or high-fat diet in SD rats. Furthermore, IL-6 was significantly associated with FIN, HOMA-IR, LDL, TC, TG, HDL, visceral fat mass and body weight in FSC group, while IL-6 was markedly correlated with TC, LDL, TG, visceral fat mass and body weight (P<0.05).

CONCLUSION

A characteristic rat model of MS may be induced by the high-fat and high-salt diet. IL-6 may be considered as an early and representative marker in the pathogenesis of MS and related cardiovascular burden.

Circulating anti-inflammatory adipokines High Molecular Weight Adiponectin and Zinc-α2-glycoprotein (ZAG) are inhibited in early sepsis, but increase with clinical recovery: a pilot study

Background

Adipose tissue has been identified as an endocrine organ secreting adipokines involved in metabolic and inflammatory pathways. Adiponectin, an anti-inflammatory adipokine, is reduced in sepsis. High Molecular Weight (HMW) adiponectin, the biologically most relevant molecule, has been investigated very little in human sepsis. Zinc-alpha2-glycoprotein (ZAG) is a novel adipokine and its expression in adipose tissue is positively correlated with adiponectin expression. It is not yet known whether ZAG has a role in sepsis. In this study we assessed levels of HMW adiponectin and ZAG during different stages of sepsis.

Methods

A prospective observational pilot study was carried out on 21 septic patients. Serum samples were taken on day 1 and 2 post ICU admission and on day of discharge. Samples were analysed for total and HMW adiponectin, HMW/total adiponectin ratio, and ZAG. Results were correlated with clinical and metabolic data.

Results

There were no differences in total adiponectin, HMW adiponectin and ZAG plasma concentrations between day 1 (admission) and day 2 of the sepsis episode. Compared to admission, a significant increase in total and HMW adiponectin and ZAG was observed on the day of discharge when clinical improvement had been achieved. There was also an increase in the HMW/total adiponectin ratio at that time.

Conclusions

Our data demonstrate an increase in both HMW adiponectin and total adiponectin in patients who had clinically recovered from sepsis. The increase in HMW/total adiponectin ratio with improvement of the clinical condition suggests that HMW adiponectin may have a greater role in the inflammatory process and insulin resistance seen in sepsis. In this pilot study, we have also demonstrated a significant increase in ZAG in critically ill patients temporally related to recovery from sepsis.

Diet-induced obesity progressively alters cognition, anxiety-like behavior and lipopolysaccharide-induced depressive-like behavior: focus on brain indoleamine 2,3-dioxygenase activation

Obesity is associated with a high prevalence of mood symptoms and cognitive dysfunctions that emerges as significant risk factors for important health complications such as cardiovascular diseases and type 2 diabetes. It is therefore important to identify the dynamic of development and the pathophysiological mechanisms underlying these neuropsychiatric symptoms. Obesity is also associated with peripheral low-grade inflammation and increased susceptibility to immune-mediated diseases. Excessive production of proinflammatory cytokines and the resulting activation of the brain tryptophan catabolizing enzyme indoleamine 2,3-dioxygenase (IDO) have been shown to promote neurobehavioral complications, particularly depression. In that context, questions arise about the impact of diet-induced obesity on the onset of neuropsychiatric alterations and the increased susceptibility to immune-mediated diseases displayed by obese patients, particularly through brain IDO activation. To answer these questions, we used C57Bl/6 mice exposed to standard diet or western diet (WD; consisting of palatable energy-dense food) since weaning and for 20 weeks. We then measured inflammatory and behavioral responses to a systemic immune challenge with lipopolysaccharide (LPS) in experimental conditions known to alter cognitive and emotional behaviors independently of any motor impairment. We first showed that in absence of LPS, 9 weeks of WD is sufficient to impair spatial recognition memory (in the Y-maze). On the other hand, 18 weeks of WD increased anxiety-like behavior (in the elevated plus-maze), but did not affect depressive-like behavior (in the tail-suspension and forced-swim tests). However, 20 weeks of WD altered LPS-induced depressive-like behavior compared to LPS-treated lean mice and exacerbated hippocampal and hypothalamic proinflammatory cytokine expression and brain IDO activation. Taken together, these results show that WD exposure alters cognition and anxiety in unstimulated conditions and enhances activation of neurobiological mechanisms underlying depression after immune stimulation. They suggest therefore that obesity, and possibly obesity-associated inflammatory priming, may represent a vulnerability state to immune-mediated depressive symptoms.

Lipopolysaccharide binding protein, obesity status and incidence of metabolic syndrome: a prospective study among middle-aged and older Chinese

AIMS/HYPOTHESIS

Although microbiota-derived endotoxaemia has previously been shown to induce metabolic disorders, data from population-based longitudinal studies are scarce. This study therefore investigated the associations between lipopolysaccharide binding protein (LBP) levels and 6 year incident metabolic syndrome (MetS), as well as the potentially modifying effects of obesity status in middle-aged and older Chinese men and women.

METHODS

A total of 2,529 men and women aged 50-70 years from Beijing and Shanghai, China, were followed for 6 years. Those free of MetS at baseline (1,312) were included in the analyses for the risk of developing MetS. Baseline plasma LBP was measured using an ELISA kit.

RESULTS

During the 6 year follow-up, 449 (34.2%) participants developed MetS. Baseline LBP was significantly associated with BMI, waist circumference, blood lipid profile and C-reactive protein (CRP) both at baseline and during follow-up (all p < 0.05). The RR for incident MetS comparing extreme quartiles of LBP was 1.28 (95% CI 1.04, 1.58), after multivariate adjustment including BMI and CRP. In stratified analysis, LBP was positively associated with incident MetS only in normal-weight participants (RR, comparing extreme tertiles, 1.59; 95% CI 1.18, 2.15; p(trend)= 0.002), but not in their overweight/obese counterparts (RR, comparing extreme tertiles, 0.99; 95% CI 0.80, 1.22; p(trend) = 0.880). A significant interaction was observed between LBP and obesity status (p(interaction) = 0.013).

CONCLUSIONS/INTERPRETATION

Our study suggested that elevated plasma LBP was associated with an increased risk of developing MetS among middle-aged and older Chinese, especially in normal-weight individuals.

Site-specific changes in cytokine response to septic dose of lipopolysaccharide in ovariectomized female rats

PURPOSE

The immune response is altered according to hormonal and metabolic status. Obesity increases the inflammatory and fever response, whereas loss of gonadal steroid decreases behavioral response to immune stress. However, the immune systems of ovariectomized animals exhibiting obesity and gonadal steroid deficiency, particularly under septic conditions, have not been fully examined. In the present study, we evaluated the ovariectomy-induced changes of central and peripheral immune responses to life-threatening septic stimulus.

METHODS AND RESULTS

Ovariectomized rats showed heavier body weight and lighter uterine weight when compared with gonadally intact rats. Fever response to septic dose of lipopolysaccharide (LPS) in ovariectomized rats was less evident when compared with that in gonadally intact rats. In addition, under LPS-injected septic conditions, hypothalamic gene levels of Interleukin-1β (IL-1β), Interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) and serum protein levels of IL-1β and TNF-α in ovariectomized rats were lower than those in gonadally intact rats. On the other hand, IL-6 levels in visceral fat under septic conditions were higher in ovariectomized rats than in gonadally intact rats.

CONCLUSIONS

These findings indicate that ovariectomy-induced site-specific changes in cytokine response under septic conditions. As hypothalamic, but not peripheral, pro-inflammatory cytokines are directly involved in the fever response, the attenuation of fever response observed in ovariectomized rats may be caused by a reduction in central cytokine responses.

Development of a murine model of early sepsis in diet-induced obesity

Sepsis, a global health issue, is the most common cause of mortality in the intensive care unit. The aim of this study was to develop a new model of sepsis that investigates the impact of prolonged western diet (WD) induced obesity on the response to early sepsis. Male C57BL/6 mice were fed either a high fat WD or normal chow diet (NCD) for 6, 15, or 27 weeks. Septic obese mice at 15 and 27 weeks had significantly lower levels of lung myeloperoxidase (26.3 ± 3.80 U/mg tissue) compared to age matched ad lib (44.1 ± 2.86 U/mg tissue) and diet restricted (63.2 ± 5.60 U/mg tissue) controls. Low levels of lung inflammation were not associated with changes in hepatic cytokines and oxidative stress levels. Obese mice had significantly (P < 0.0001) larger livers compared to controls. Histological examination of the livers demonstrated that WD fed mice had increased inflammation with pronounced fat infiltration, steatosis, and hepatocyte ballooning. Using this model of prolonged exposure to high fat diet we have data that agree with recent clinical observations suggesting obese individuals are protected from sepsis-induced lung injury. This model will allow us to investigate the links between damage to the hepatic microcirculation, immune response, and lung injury.