Hypothalamic inflammation and obesity

Association between systemic immune-inflammatory index and diabetes mellitus: mediation analysis involving obesity indicators in the NHANES

Background

Inflammation and obesity have been widely recognized to play a key role in Diabetes mellitus (DM), and there exists a complex interplay between them. We aimed to clarify the relationship between inflammation and DM, as well as the mediating role of obesity in the relationship.

Methods

Based on the National Health and Nutrition Examination Survey (NHANES) 2005-2018. Univariate analyses of continuous and categorical variables were performed using t-test, linear regression, and χ2 test, respectively. Logistic regression was used to analyze the relationship between Systemic Immune-Inflammatory Index (SII) or natural logarithm (Ln)-SII and DM in three different models. Mediation analysis was used to determine whether four obesity indicators, including body mass index (BMI), waist circumference (WC), visceral adiposity index (VAI) and lipid accumulation product index (LAP), mediated the relationship between SII and DM.

Results

A total of 9,301 participants were included, and the levels of SII and obesity indicators (BMI, WC, LAP, and VAI) were higher in individuals with DM (p < 0.001). In all three models, SII and Ln-SII demonstrated a positive correlation with the risk of DM and a significant dose-response relationship was found (p-trend <0.05). Furthermore, BMI and WC were associated with SII and the risk of DM in all three models (p < 0.001). Mediation analysis showed that BMI and WC mediated the relationship between SII with DM, as well as Ln-SII and DM, with respective mediation proportions of 9.34% and 12.14% for SII and 10.23% and 13.67% for Ln-SII (p < 0.001).

Conclusion

Our findings suggest that increased SII levels were associated with a higher risk of DM, and BMI and WC played a critical mediating role in the relationship between SII and DM.

Physiopathological mechanisms related to inflammation in obesity and type 2 diabetes mellitus

Overweight, obesity, and type 2 diabetes mellitus pose global health problems that are ever-increasing. A chronic low-grade inflammatory status and the presence of various pro-inflammatory markers either in circulation or within dysfunctional metabolic tissues are well established. The presence of these factors can, to some extent, predict disease development and progression. A central role is played by the presence of dysfunctional adipose tissue, liver dysfunction, and skeletal muscle dysfunction, which collectively contribute to the increased circulatory levels of proinflammatory factors. Weight loss and classical metabolic interventions achieve a decrease in many of these factors’ circulating levels, implying that a better understanding of the processes or even the modulation of inflammation may alleviate these diseases. This review suggests that inflammation plays a significant role in the development and progression of these conditions and that measuring inflammatory markers may be useful for assessing disease risk and development of future treatment methods.

Potential relationship between dietary long-chain saturated fatty acids and hypothalamic dysfunction in obesity

Diet-induced hypothalamic inflammation, which leads to hypothalamic dysfunction and a loss of regulation of energy balance, is emerging as a potential driver of obesity. Excessive intake of long-chain saturated fatty acids is held to be the causative dietary component in hypothalamic inflammation. This review summarizes current evidence on the role of long-chain saturated fatty acids in promoting hypothalamic inflammation and the related induction of central insulin and leptin insensitivity. Particularly, the present review focuses on the molecular mechanisms linking long-chain saturated fatty acids and hypothalamic inflammation, emphasizing the metabolic fate of fatty acids and the resulting lipotoxicity, which is a key driver of hypothalamic dysfunction. In conclusion, long-chain saturated fatty acids are key nutrients that promote hypothalamic inflammation and dysfunction by fostering the build-up of lipotoxic lipid species, such as ceramide. Furthermore, when long-chain saturated fatty acids are consumed in combination with high levels of refined carbohydrates, the proinflammatory effects are exacerbated via a mechanism that relies on the formation of advanced glycation end products.

Memory impairments and increased GFAP expression in hippocampal astrocytes following hypercaloric diet in rats

ABSTRACT Objective: Hypothalamic inflammation and glial fibrillary acidic protein (GFAP) overexpression in astrocytes are well described in obese animals, as are some cognitive and memory deficits. As the hippocampus plays important roles in the consolidation of information, this investigation aimed to observe the memory function and the astrocyte expression of GFAP in the hippocampus of rats that received either a hypercaloric or a normocaloric diet. Methods: Adult male Wistar rats received a high-fat (cafeteria) or a standard diet for 60 days. On the 61st day, the rats were submitted to the novel object recognition (NOR) test at three and 24 hours after the first contact with objects, to assess short-term and long-term memory, respectively. Thereafter, the rats were euthanized and their brains were collected for GFAP immunohistochemical investigation in the hippocampus (CA1, CA2, CA3 areas) and hypothalamus (periventricular and arcuate nuclei). Astrocytic reactivity was assessed by morphometry. Different white adipose tissue depots and brown adipose tissue were weighed to calculate the adiposity index. Results: The hypercaloric diet increased body weight gain, adiposity index, white adipose tissue weight (epididymal, subcutaneous and retroperitoneal) and brown adipose tissue weight. Rats fed with the hypercaloric diet showed short-term and long-term memory impairments in the NOR test, as well as increased GFAP expression in astrocytes from all analyzed hypothalamic and hippocampal areas. Conclusion: This astrogliosis suggests that the neuroinflammatory response also occurs in the hippocampus and may be involved in the memory losses observed in obese/overweight animals.

Interleukin-6 Expression by Hypothalamic Microglia in Multiple Inflammatory Contexts: A Systematic Review

Interleukin-6 (IL-6) is a unique cytokine that can play both pro- and anti-inflammatory roles depending on the anatomical site and conditions under which it has been induced. Specific neurons of the hypothalamus provide important signals to control food intake and energy expenditure. In individuals with obesity, a microglia-dependent inflammatory response damages the neural circuits responsible for maintaining whole-body energy homeostasis, resulting in a positive energy balance. However, little is known about the role of IL-6 in the regulation of hypothalamic microglia. In this systematic review, we asked what types of conditions and stimuli could modulate microglial IL-6 expression in murine model. We searched the PubMed and Web of Science databases and analyzed 13 articles that evaluated diverse contexts and study models focused on IL-6 expression and microglia activation, including the effects of stress, hypoxia, infection, neonatal overfeeding and nicotine exposure, lipopolysaccharide stimulus, hormones, exercise protocols, and aging. The results presented in this review emphasized the role of "injury-like" stimuli, under which IL-6 acts as a proinflammatory cytokine, concomitant with marked microglial activation, which drive hypothalamic neuroinflammation. Emerging evidence indicates an important correlation of basal IL-6 levels and microglial function with the maintenance of hypothalamic homeostasis. Advances in our understanding of these different contexts will lead to the development of more specific pharmacological approaches for the management of acute and chronic conditions, like obesity and metabolic diseases, without disturbing the homeostatic functions of IL-6 and microglia in the hypothalamus.

Hypothalamic inflammation and obesity: a mechanistic review

Obesity is one of the worldwide prevalent disease caused by the imbalance between food intake and energy expenditure. Over a 100 years of research demonstrate that hypothalamus is the critical brain region regulating energy homeostasis, and evidences suggest the participation of non-neuronal populations such as astrocytes and microglia in the regulation of energy homeostasis. Recently, fat-rich diet induced hypothalamic inflammation has been found to deregulate the energy homeostasis, leading to the insulin resistance, glucose intolerance, and obesity. Several underlying mechanisms have been proposed, yet compelling evidences require further elucidations. This review discusses the up to date proposed mechanisms by which fat-rich diet induces hypothalamic inflammation and obesity.

Reduced astrocytic expression of GFAP in the offspring of female rats that received hypercaloric diet

Introduction: Obesity promotes hypothalamic inflammation and local morphological changes in astrocytes, including the increased expression of the astrocytic biomarker glial fibrillary acidic protein (GFAP), which is seen as a sign of neuroinflammation.Objective: This study aimed to observe the astrocytic expression of GFAP in different brain areas from female rats that received a hypercaloric (HD) or a normocaloric (ND) diet during puberty (F0 generation) as well as in their male pups (F1 generation).Methods: Female rats received highly palatable HD (Ensure®) or ND from postnatal day (PND) 23-65. On PND90-95, some were euthanized for the immunohistochemical study and some were mated to obtain the F1 generation. Male pups were immunochallenged on PND50 with lipopolysaccharide (LPS, 100 μg/kg) or 0.9% saline solution (1 mL/kg) intraperitoneal injection. Body weight (BW) and retroperitoneal fat weight (RFW) were recorded on PND95 for F0 generation and on PND50 for F1 generation. GFAP expression for both generations was assessed by morphometry in the parietal/frontal cortex, corpus callosum, nucleus accumbens, arcuate/periventricular nuclei of hypothalamus, pons, molecular/granular layers of cerebellum.Results: Female rats fed with HD presented a significant increase in the GFAP expression in all evaluated areas as well as in the RFW. Male rats born from mothers that received HD showed decreased GFAP expression, BW and RFW when treated with LPS in relation to those from mothers fed with ND.Discussion: HD induced astrogliosis in several brain areas in females from F0 generation and an adaptive phenotypic change of decreased GFAP expression in males from F1 generation after LPS challenge.

Changes in brain regions associated with food-intake regulation, body mass and metabolic profiles during acute antipsychotic treatment in first-episode schizophrenia

We investigated whether morphological brain changes occurred in brain regions associated with body-weight homeostasis during acute antipsychotic treatment, and if so, whether they were related to changes in body mass and metabolic profile. Twenty-two antipsychotic-naive patients with first-episode schizophrenia received either risperidone long acting injection or flupenthixol decanoate over 13 weeks and were compared by structural MRI with 23 matched healthy volunteers at weeks 0, 4 and 13. Images were reconstructed using freesurfer fully-automated whole brain segmentation. The ventral diencephalon and prefrontal cortex were selected to represent the homeostatic and hedonic food intake regulatory systems respectively. Body mass was measured at weeks 0, 7 and 13 and fasting glucose and lipid profiles at weeks 0 and 13. Linear mixed effect models indicated significant group(⁎)time interactions for the ventral diencephalon volumes bilaterally. Ventral diencephalon volume reduction was strongly correlated bilaterally with body mass increase and HDL-cholesterol reductions, and unilaterally with blood glucose elevation. There were no significant changes in prefrontal cortical thickness. These findings implicate the ventral diencephalon, of which the hypothalamus is the main component, in the acute adipogenic and dyslipidaemic effects of antipsychotic medication.

Maternal high-fat diet consumption modulates hepatic lipid metabolism and microRNA-122 (miR-122) and microRNA-370 (miR-370) expression in offspring

Maternal consumption of a high-fat diet (HFD) during pregnancy and lactation is closely related to hepatic lipid accumulation, insulin resistance and increased serum cytokine levels in offspring and into their adulthood. MicroRNA (miRNA) have been implicated in cholesterol biosynthesis and fatty acid metabolism. We evaluated the modulation of hepatic fatty acid synthesis (de novo), β-oxidation pathways, and miRNA-122 (miR-122) and miRNA-370 (miR-370) expression in recently weaned offspring (day 28) of mouse dams fed a HFD (HFD-O) or a standard chow (SC-O) during pregnancy and lactation. Compared with SC-O mice, HFD-O mice weighed more, had a larger adipose tissue mass and were more intolerant to glucose and insulin (P< 0·05). HFD-O mice also presented more levels of serum cholesterol, TAG, NEFA and hepatic IκB kinase and c-Jun N-terminal kinase phosphorylation compared with SC-O mice (P< 0·05). Protein levels of fatty acid synthase, acetyl-CoA carboxylase and 3-hydroxy-3-methylglutaryl-CoA reductase were similar in HFD-O and SC-O mice, whereas expression levels of SCD1 mRNA and protein were more abundant in HFD-O mice than in SC-O mice (P< 0·05). Interestingly, mRNA expression levels of the β-oxidation-related genes ACADVL and CPT1 were decreased in HFD-O mice (P< 0·05). Furthermore, the expression of miR-122 was reduced but that of miR-370 was increased in HFD-O mice compared with that in SC-O mice (P< 0·05). Changes in hepatic lipid metabolism were accompanied by increased mRNA content of AGPAT1 and TAG deposition in HFD-O mice (P< 0·05). Taken together, the present results strongly suggest that maternal consumption of a HFD affects the early lipid metabolism of offspring by modulating the expression of hepatic β-oxidation-related genes and miRNA that can contribute to metabolic disturbances in adult life.

MAP2K3 is associated with body mass index in American Indians and Caucasians and may mediate hypothalamic inflammation

To identify genes that affect body mass index (BMI) in American Indians who are predominately of Pima Indian heritage, we previously completed a genome-wide association study in 1120 American Indians. That study also included follow-up genotyping for 9 SNPs in 2133 additional subjects. A comprehensive follow-up study has subsequently been completed where 292 SNPs were genotyped in 3562 subjects, of which 128 SNPs were assessed for replication in 3238 additional subjects. In the combined subjects (n = 6800), BMI associations for two SNPs, rs12882548 and rs11652094, approached genome-wide significance (P = 6.7 × 10⁻⁷ and 8.1 × 10⁻⁷, respectively). Rs12882548 is located in a gene desert on chromosome 14 and rs11652094 maps near MAP2K3. Several SNPs in the MAP2K3 region including rs11652094 were also associated with BMI in Caucasians from the GIANT consortium (P = 10⁻²–10⁻⁵), and the combined P-values across both American Indians and Caucasian were P = 10⁻⁴–10⁻⁹. Follow-up sequencing across MAP2K3 identified several paralogous sequence variants indicating that the region may have been duplicated. MAP2K3 expression levels in adipose tissue biopsies were positively correlated with BMI, although it is unclear if this correlation is a cause or effect. In vitro studies with cloned MAP2K3 promoters suggest that MAP2K3 expression may be up-regulated during adipogenesis. Microarray analyses of mouse hypothalamus cells expressing constitutively active MAP2K3 identified several up-regulated genes involved in immune/inflammatory pathways and a gene, Hap1, thought to play a role in appetite regulation. We conclude that MAP2K3 is a reproducible obesity locus that may affect body weight via complex mechanisms involving appetite regulation and hypothalamic inflammation.

High-fat fish oil diet prevents hypothalamic inflammatory profile in rats

Whether PUFA diets affect inflammatory mediators in central and peripheral sites is not clear. We investigated the effect of high-fat PUFA diets on the expression of proteins involved in inflammatory pathways in hypothalamus, muscle, and liver. Male rats were fed for 2 months with either chow or high-fat diets enriched with either soy (n-6 PUFAs) or fish oil (n-3 PUFAs). The fish group had normal body weight, low serum NEFA, reduced hypothalamic levels of TNF-α, IL-6, and TRAF6, and increased levels of IL-10 receptor. In contrast, the soy group had increased body weight and hypothalamic levels of TRAF6 and NFκBp65. In muscle, the fish diet reduced TNF-α and IL-6 levels. Both PUFA diets increased muscle IL-10 levels and reduced liver TNF-α and IL-6 levels. The data showed that the high-fat soy diet induced activation of the hypothalamic NFκB inflammatory pathway, a feature predisposing to feeding and energy expenditure disturbances associated with the development of obesity. On the other hand, the high-fat fish diet improved the central and the peripheral inflammatory profile via reduction of intracellular inflammatory mediators, suggesting a protection against obesity.

Association of obesity-mediated insulin resistance and hypothalamic volumes: possible sex differences

The hypothalamus is important in hunger and metabolism. Although a lot is known about the basic role of the human hypothalamus, less is known about how the in vivo volume is affected in obesity, particularly among adolescents. Based on pediatric body mass index percentiles, 95 participants were assigned to lean or obese groups. All subjects had medical evaluations, including fasting blood tests, to assess insulin sensitivity and circulating CRP and neurotrophins (NGF and BDNF) and an MRI of the brain. Hypothalamic volumes were measured by a segmentation method combining manual and automated steps. Overall, obese participants had descriptively smaller hypothalamic volumes, although this difference did not reach statistical significance; however, among obese participants, females had significantly smaller hypothalamic volumes than their male counterparts. There was a significant interaction between insulin resistance and sex on hypothalamus volume; obese females with significant insulin resistance have smaller hypothalamic volumes than obese males. Obese adolescents had higher circulating CRP and neurotrophin levels. Furthermore, among obese females, BDNF concentrations were inversely associated with hypothalamus volumes (r = −0.48). Given this negative association between BDNF and hypothalamus volumes among obese insulin-resistant females, elevated neurotrophin levels may suggest an attempt at protective compensation.

High-fat diets rich in soy or fish oil distinctly alter hypothalamic insulin signaling in rats

Hypothalamic insulin inhibits food intake, preventing obesity. High-fat feeding with polyunsaturated fats may be obesogenic, but their effect on insulin action has not been elucidated. The present study evaluated insulin hypophagia and hypothalamic signaling after central injection in rats fed either control diet (15% energy from fat) or high-fat diets (50% energy from fat) enriched with either soy or fish oil. Soy rats had increased fat pad weight and serum leptin with normal body weight, serum lipid profile and peripheral insulin sensitivity. Fish rats had decreased body and fat pad weight, low leptin and corticosterone levels, and improved serum lipid profile. A 20-mU dose of intracerebroventricular (ICV) insulin inhibited food intake in control and fish groups, but failed to do so in the soy group. Hypothalamic protein levels of IR, IRS-1, IRS-2, Akt, mTOR, p70S6K and AMPK were similar among groups. ICV insulin stimulated IR tyrosine phosphorylation in control (68%), soy (36%) and fish (34%) groups. Tyrosine phosphorylation of the pp185 band was significantly stimulated in control (78%) and soy (53%) rats, but not in fish rats. IRS-1 phosphorylation was stimulated only in control rats (94%). Akt serine phosphorylation was significantly stimulated only in control (90%) and fish (78%) rats. The results showed that, rather than the energy density, the fat type was a relevant aspect of high-fat feeding, since blockade of hypothalamic insulin signal transmission and insulin hypophagia was promoted only by the high-fat soy diet, while they were preserved in the rats fed with the high-fat fish diet.

Interleukin-1 beta: a potential link between stress and the development of visceral obesity

Background

A disproportionate amount of body fat within the abdominal cavity, otherwise known as visceral obesity, best predicts the negative health outcomes associated with high levels body fat. Growing evidence suggests that repeated activation of the stress response can favor visceral fat deposition and that visceral obesity may induce low-grade, systemic inflammation which is etiologically linked to the pathogenesis of obesity related diseases such as cardiovascular disease and type 2 diabetes. While the obesity epidemic has fueled considerable interest in these obesity-related inflammatory diseases, surprisingly little research is currently focused on understanding the functions of inflammatory proteins in healthy, non-obese white adipose tissue (WAT) and their possible role in modulating stress-induced shifts in body fat distribution.

Hypothesis

The current review presents evidence in support the novel hypothesis that stress-evoked interleukin-1 beta (IL-1β) signaling within subcutaneous adipose tissue, when repeatedly induced, contributes toward the development of visceral obesity. It is suggested that because acute stressor exposure differentially increases IL-1β levels within subcutaneous adipose relative to visceral adipose tissue in otherwise healthy, non-obese rats, repeated induction of this response may impair the ability of subcutaneous adipose tissue to uptake energy substrates, synthesize and retain triglycerides, and/or adapt to positive energy balance via hyperplasia. Consequently, circulating energy substrates may be disproportionately shunted to visceral adipose tissue for storage, thus driving the development of visceral obesity.

Conclusions

This review establishes the following key points: 1) body fat distribution outweighs the importance of total body fat when predicting obesity-related disease risk; 2) repeated exposure to stress can drive the development of visceral obesity independent of changes in body weight; 3) because of the heterogeneity of WAT composition and function, an accurate understanding of WAT responses requires sampling multiple WAT depots; 4) acute, non-pathogenic stressor exposure increases WAT IL-1β concentrations in a depot specific manner suggesting an adaptive, metabolic role for this cytokine; however, when repeated, stress-induced IL-1β in non-visceral WAT may result in functional impairments that drive the development of stress-induced visceral obesity.

Gut microbiota, epithelial function and derangements in obesity

The gut epithelium is a barrier between the 'outside' and 'inside' world. The major function of the epithelium is to absorb nutrients, ions and water, yet it must balance these functions with that of protecting the 'inside' world from potentially harmful toxins, irritants, bacteria and other pathogens that also exist in the gut lumen. The health of an individual depends upon the efficient digestion and absorption of all required nutrients from the diet. This requires sensing of meal components by gut enteroendocrine cells, activation of neural and humoral pathways to regulate gastrointestinal motor, secretory and absorptive functions, and also to regulate food intake and plasma levels of glucose. In this way, there is a balance between the delivery of food and the digestive and absorptive capacity of the intestine. Maintenance of the mucosal barrier likewise requires sensory detection of pathogens, toxins and irritants; breakdown of the epithelial barrier is associated with gut inflammation and may ultimately lead to inflammatory bowel disease. However, disruption of the barrier alone is not sufficient to cause frank inflammatory bowel disease. Several recent studies have provided compelling new evidence to suggest that changes in epithelial barrier function and inflammation are associated with and may even lead to altered regulation of body weight and glucose homeostasis. This article provides a brief review of some recent evidence to support the hypothesis that changes in the gut microbiota and alteration of gut epithelial function will perturb the homeostatic humoral and neural pathways controlling food intake and body weight.

Obesity and susceptibility to autoimmune diseases

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

Taurine enhances the anorexigenic effects of insulin in the hypothalamus of rats

Taurine is known to modulate a number of metabolic parameters such as insulin secretion and action and blood cholesterol levels. Recent data have suggested that taurine can also reduce body adiposity in C. elegans and in rodents. Since body adiposity is mostly regulated by insulin-responsive hypothalamic neurons involved in the control of feeding and thermogenesis, we hypothesized that some of the activity of taurine in the control of body fat would be exerted through a direct action in the hypothalamus. Here, we show that the intracerebroventricular injection of an acute dose of taurine reduces food intake and locomotor activity, and activates signal transduction through the Akt/FOXO1, JAK2/STAT3 and mTOR/AMPK/ACC signaling pathways. These effects are accompanied by the modulation of expression of NPY. In addition, taurine can enhance the anorexigenic action of insulin. Thus, the aminoacid, taurine, exerts a potent anorexigenic action in the hypothalamus and enhances the effect of insulin on the control of food intake.