Obesity-Induced Neuroinflammation: Beyond the Hypothalamus

Visceral adipose tissue-derived extracellular vesicles promote stress susceptibility in obese mice via miR-140-5p

Obesity increases the risk of depression. Evidence shows that peripheral inflammation, glycemic dysregulation, and hyperactivity within the hypothalamic-pituitary-adrenal axis are implicated in both obesity and depression. In this study we investigated the impact of visceral adipose tissue (VAT), a crucial characteristic of obesity, on stress susceptibility in obese mice. Age-matched mice were fed with chow diet (CD) or high-fat diet (HFD), respectively, for 12 weeks. CD mice were deprived of VAT and received transplantation of VAT from HFD mice (TransHFD) or CD mice (TransCD). Extracellular vesicles (EVs) were prepared from VAT of CD or HFD mice, and intravenously injected (100 μg, 4 times in 2 weeks) in naïve mice or injected into hippocampus (5 μg, 4 times in 2 weeks) through implanted bilateral cannula. Depression-like behaviors were assessed 14 days after transplantation. We showed that HFD mice exhibited significantly higher body weight gain and impaired insulin and glucose tolerance, accompanied by increased stress susceptibility. Transplantation of VAT or VAT-derived EVs from HFD mice caused synaptic damage and promoted stress susceptibility in recipient mice. Through inhibiting miRNA biogenesis in the VAT and miRNA sequencing analysis, we demonstrated that miR-140-5p was significantly upregulated in both VAT-EVs and hippocampus of HFD mice. Overexpression of hippocampal miR-140-5p in naïve mice not only facilitated acute stress-induced depression-like behaviors, but also decreased hippocampal CREB-BDNF signaling cascade and synaptic plasticity. Conversely, knockdown of miR-140-5p in the VAT, VAT-EVs or hippocampus of HFD mice protected against acute stress, reducing stress susceptibility that were mediated via CREB-BDNF pathway. In summary, VAT-EVs or the cargo miRNAs in obese mice promote synaptic damage and stress susceptibility, providing potential therapeutic targets for metabolism-related affective disorders.

Novel Thyroid Hormone Receptor-β Agonist TG68 Exerts Anti-Inflammatory, Lipid-Lowering and Anxiolytic Effects in a High-Fat Diet (HFD) Mouse Model of Obesity

Recent advances in drug development allowed for the identification of THRβ-selective thyromimetic TG68 as a very promising lipid lowering and anti-amyloid agent. In the current study, we first investigated the neuroprotective effects of TG68 on in vitro human models of neuroinflammation and β-amyloid neurotoxicity in order to expand our knowledge of the therapeutic potential of this novel thyromimetic. Subsequently, we examined metabolic and inflammatory profiles, along with cognitive changes, using a high-fat diet (HFD) mouse model of obesity. Our data demonstrated that TG68 was able to prevent either LPS/TNFα-induced inflammatory response or β-amyloid-induced cytotoxicity in human microglial (HMC3) cells. Next, we demonstrated that in HFD-fed mice, treatment with TG68 (10 mg/kg/day; 2 weeks) significantly reduced anxiety-like behavior in stretch-attend posture (SAP) tests while producing a 12% BW loss and a significant decrease in blood glucose and lipid levels. Notably, these data highlight a close relationship between improved serum metabolic parameters and a reduction of anxious behavior. Moreover, TG68 administration was observed to efficiently counteract HFD-altered central and peripheral expressions in mice with selected biomarkers of metabolic dysfunction, inflammation, and neurotoxicity, revealing promising neuroprotective effects. In conclusion, our work provides preliminary evidence that TG68 may represent a novel therapeutic opportunity for the treatment of interlinked diseases such as obesity and neurodegenerative diseases.

Computational detection, characterization, and clustering of microglial cells in a mouse model of fat-induced postprandial hypothalamic inflammation

Obesity is associated with brain inflammation, glial reactivity, and immune cells infiltration. Studies in rodents have shown that glial reactivity occurs within 24 h of high-fat diet (HFD) consumption, long before obesity development, and takes place mainly in the hypothalamus (HT), a crucial brain structure for controlling body weight. Understanding more precisely the kinetics of glial activation of two major brain cells (astrocytes and microglia) and their impact on eating behavior could prevent obesity and offer new prospects for therapeutic treatments. To understand the mechanisms pertaining to obesity-related neuroinflammation, we developed a fully automated algorithm, NutriMorph. Although some algorithms were developed in the past decade to detect and segment cells, they are highly specific, not fully automatic, and do not provide the desired morphological analysis. Our algorithm copes with these issues and performs the analysis of cells images (here, microglia of the hypothalamic arcuate nucleus), and the morphological clustering of these cells through statistical analysis and machine learning. Using the k-Means algorithm, it clusters the microglia of the control condition (healthy mice) and the different states of neuroinflammation induced by high-fat diets (obese mice) into subpopulations. This paper is an extension and re-analysis of a first published paper showing that microglial reactivity can already be seen after few hours of high-fat diet (Cansell et al., 2021 [5]). Thanks to NutriMorph algorithm, we unravel the presence of different hypothalamic microglial subpopulations (based on morphology) subject to proportion changes in response to already few hours of high-fat diet in mice.

Mast cell promotes obesity by activating microglia in hypothalamus

Background

Obesity has become a significant public health issue, yet its underlying mechanisms remain complex. The hypothalamus, a crucial part of the central nervous system, plays a vital role in maintaining energy balance. Disruptions in hypothalamic homeostasis can lead to obesity and related metabolic disorders. Recent studies have increasingly focused on the role of intercellular interactions within the hypothalamus in obesity development, though the exact mechanisms are still under investigation. Mast cells, as innate immune cells, have been linked to obesity, but their specific roles and mechanisms require further exploration. This study aims to investigate whether hypothalamic mast cells influence microglia and subsequently affect metabolic homeostasis.

Methods

We conducted experiments to examine the effects of high-fat diets on mast cells in the arcuate nucleus of the hypothalamus. We analyzed the activation of microglia and the activity of POMC neurons in response to mast cell activation. The study involved feeding mice a high-fat diet and then assessing changes in mast cell populations, microglial activation, and neuronal activity in the hypothalamus.

Results

Our findings indicate that high-fat feeding increases the number of mast cells in the arcuate nucleus of the hypothalamus. These mast cells activate microglia, which in turn suppress the activity of POMC neurons. This suppression promotes appetite and reduces energy expenditure, leading to obesity. The results suggest a direct role of hypothalamic mast cells in the regulation of energy balance and obesity development.

Discussion

This study highlights the regulatory role of mast cells in the hypothalamus in the formation of obesity. By activating microglia and influencing POMC neuron activity, mast cells contribute to metabolic dysregulation. These findings provide a new target for the treatment of obesity and related metabolic diseases, emphasizing the importance of hypothalamic immune interactions in metabolic health. Further research is needed to explore the potential therapeutic applications of targeting mast cells in obesity management.

Exploring nutraceutical approaches linking metabolic syndrome and cognitive impairment

Metabolic syndrome (MetS) and mild cognitive impairment (MCI) are interconnected conditions sharing common pathological pathways, such as inflammation and oxidative stress, leading to the concept of "metabolic-cognitive syndrome." This highlights their mutual influence and potential overlapping therapeutic strategies. Although lifestyle modifications remain essential, nutraceutical supplementation has emerged as a promising adjunct for the prevention and management of these preclinical conditions. This review examines clinical and translational evidence on commonly used nutraceuticals targeting shared pathophysiological mechanisms of MetS and MCI. By addressing inflammation, oxidative stress, and metabolic dysfunction, these supplements may offer a valuable approach to mitigating the progression and consequences of both conditions. Understanding their efficacy could provide practical tools to complement lifestyle changes, offering a more comprehensive strategy for managing metabolic-cognitive syndrome.

High-fat diet and neuroinflammation: The role of mitochondria

In recent years, increasing evidence has supported that high-fat diet (HFD) can induce the chronic, low-grade neuroinflammation in the brain, which is closely associated with the impairment of cognitive function. As the key organelles responsible for energy metabolism in the cell, mitochondria are believed to involved in the pathogenesis of a variety of neurological disorders. This review summarizes the current progress in the field of the relationship between HFD exposure and neurodegenerative diseases, and outline the major routines of HFD induced neuroinflammation and its pathological significance in the pathogenesis of neurodegenerative diseases. Furthermore, the article highlights the pivotal role of mitochondrial dysfunction in driving the neuroinflammation in the setting of HFD. Danger-associated molecular patterns (DAMPs) from damaged mitochondria can activate innate immune signaling pathways, while mitochondrial dysfunction itself can lead to metabolic remodeling of inflammatory cells, thus inducing neuroinflammation. More importantly, mitochondrial damage, neuroinflammation, and insulin resistance caused by HFD form a mutually reinforcing vicious cycle, ultimately leading to the death of neurons and promoting the progression of neurodegenerative diseases. Thus, in-depth elucidation of the role and underlying mechanisms of mitochondrial dysfunction in HFD-induced metabolic disorders may not only expand our understanding of the mechanistic linkages between HFD and etiology of neurodegenerative diseases, but also help develop the specific strategies for the prevention and treatment of neurodegenerative diseases.

Red blood cell distribution width to albumin ratio is associated with increased depression: the mediating role of atherogenic index of plasma

Background

Recent studies have identified a correlation between inflammation and depression. This study aims to explore the correlation between the red blood cell distribution width (RDW) to albumin ratio (RAR), a practical measure for assessing inflammation, and depression in the general population.

Methods

In this population-based cross-sectional study, data from 28932 adults aged≥18 years old in the NHANES during the period of 1999-2018 were analyzed. To examine the correlation between RAR and depression, multivariate logistic regression analyses, subgroup analyses, restricted cubic spline analyses, and interaction tests were conducted. Furthermore, a mediation analysis was performed to elucidate the role of atherogenic index of plasma (AIP) in mediating the effect of RAR on depression.

Results

Multivariate logistic regression analyses and restricted cubic splines analysis indicated that RAR can exhibit a linearly correlation with depression (OR = 1.335; 95% CI: 1.222, 1.458). Subjects in RAR Q2, Q3, Q4 groups had an increased risk on depression as 22.8%, 22.9% and 51.9% than those in the Q1 group. This positive correlation was more pronounced in those with history of cancers. The ROC analysis indicated that the area under the curve (AUC) for RAR (AUC=0.593) was significantly greater than that for RDW and albumin individually. Mediation analysis indicated that AIP mediated 7.8% of the correlation of RAR with depression.

Conclusions

The findings of this study indicated a significant linear positive correlation between RAR and the prevalence of depression, with AIP serving as a mediator.

Nut Consumption Is Associated with Cognitive Status in Southern Italian Adults

BACKGROUND

Nut consumption has been considered a potential protective factor against cognitive decline. The aim of this study was to test whether higher total and specific nut intake was associated with better cognitive status in a sample of older Italian adults.

METHODS

A cross-sectional analysis on 883 older adults (>50 y) was conducted. A 110-item food frequency questionnaire was used to collect information on the consumption of various types of nuts. The Short Portable Mental Status Questionnaire was used to assess cognitive status. Multivariate logistic regression analyses were performed to calculate odds ratios (ORs) and 95% confidence intervals (CIs) for the association between nut intake and cognitive status after adjusting for potential confounding factors.

RESULTS

The median intake of total nuts was 11.7 g/day and served as a cut-off to categorize low and high consumers (mean intake 4.3 g/day vs. 39.7 g/day, respectively). Higher total nut intake was significantly associated with a lower prevalence of impaired cognitive status among older individuals (OR = 0.35, CI 95%: 0.15, 0.84) after adjusting for potential confounding factors. Notably, this association remained significant after additional adjustment for adherence to the Mediterranean dietary pattern as an indicator of diet quality, (OR = 0.32, CI 95%: 0.13, 0.77). No significant associations were found between cognitive status and specific types of nuts.

CONCLUSIONS

Habitual nut intake is associated with better cognitive status in older adults.

Exploring the reduction in aquaporin-4 and increased expression of ciliary neurotrophic factor with the frontal-striatal gliosis induced by chronic high-fat dietary stress

High-fat diet (HFD)-induced obesity induces peripheral inflammation and hypothalamic pathogenesis linking the activation of astrocytes and microglia. Clinical evidence indicates a positive correlation between obesity and psychiatric disorders, such as depression. The connectivity of the frontal-striatal (FS) circuit, involving the caudate putamen (CPu) and anterior cingulate cortex (ACC) within the prefrontal cortex (PFC), is known for its role in stress-induced depression. Thus, there is a need for a thorough investigation into whether chronic obesity-induced gliosis, characterized by the activation of astrocytes and microglia, in these brain regions of individuals with chronic obesity. The results revealed increased S100β+ astrocytes and Iba1+ microglia in the CPu and ACC of male obese mice, along with immune cell accumulation in meningeal lymphatic drainage. Activated GFAP+ astrocytes and Iba1+ microglia were observed in the corpus callosum of obese mice. Gliosis in the CPu and ACC was linked to elevated cleaved caspase-3 levels, indicating potential neural cell death by chronic HFD feeding. There was a loss of myelin and adenomatous polyposis coli (APC)+ oligodendrocytes (OLs) in the corpus callosum, an area known to be linked with injury to the CPu. Additionally, reduced levels of aquaporin-4 (AQP4), a protein associated within the glymphatic systems, were noted in the CPu and ACC, while ciliary neurotrophic factor (CNTF) gene expression was upregulated in these brain regions of obese mice. The in vitro study revealed that high-dose CNTF causing a trend of reduced astrocytic AQP4 expression, but it significantly impaired OL maturation. This pathological evidence highlights that prolonged HFD consumption induces persistent FS gliosis and demyelination in the corpus callosum. An elevated level of CNTF appears to act as a potential regulator, leading to AQP4 downregulation in the FS areas and demyelination in the corpus callosum. This cascade of events might contribute to neural cell damage within these regions and disrupt the glymphatic flow.

Cerebrospinal fluid Visinin-like protein-1 was associated with the relationship of body mass index with Alzheimer's disease pathology and cognition in non-demented elderly

Background

The relationship and mechanisms between body mass index (BMI) and cognition are complex and inconclusive. Additionally, the role of neuronal calcium dysfunction, reflected by cerebrospinal fluid (CSF) Visinin-like protein 1 (VILIP-1), in the mechanisms linked with BMI and Alzheimer's disease (AD) has not been investigated.

Objective

To investigate the relationship between CSF VILIP-1, BMI, and AD pathologies in non-demented elderly at early stages of AD.

Methods

Baseline CSF AD core biomarkers (amyloid-β42 [Aβ42], phosphorylated tau [P-tau], and total tau [T-tau]) were measured for 1201 non-demented participants, selected from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database, among whom 128 had measurements of CSF VILIP-1. Multivariate linear regression, causal mediation analyses, and linear mixed effects models were conducted to detect these associations.

Results

The average age of participants was 72.6. CSF VILIP-1 was decreased in A+/TN- (A-positive/T- and N- negative) group and elevated in A-/TN + (A-negative/T- or N-positive) and A+/TN + groups, as compared with A-/TN- group. In total participants, BMI was negatively related to CSF P-tau, T-tau, P-tau/Aβ42 and T-tau/Aβ42. Noticeable associations were also presented between CSF VILIP-1 and AD core biomarkers, but not with Aβ42 after stratification by A/T/N scheme. Furthermore, the influences of BMI on CSF tau pathology were mediated by CSF VILIP-1. Higher baseline CSF VILIP-1 correspond to faster longitudinal cognitive decline.

Conclusions

Our findings indicated that CSF VILIP-1 changed dynamically and might be a key mediator in the associations between BMI and tau pathology, providing new insights into understanding the mechanisms underlying BMI-related cognitive deficits in non-demented elderly.

Oxytocin alleviates high-fat diet-induced anxiety by decreasing glutamatergic synaptic transmission in the ventral dentate gyrus in adolescent mice

A high-fat diet (HFD)-induced obesity is associated with mental disorders in adolescence. However, the mechanisms underlying these associations remain unclear. In this study, we hypothesized that synaptic remodeling occurs in the ventral hippocampus (vHP) of obese mice. To investigate this, we established a postnatal model of HFD-induced obesity in mice and observed increased body weight, elevated plasma luteinizing hormone and testosterone levels, premature puberty, and enhanced anxiety-like behavior in male subjects. We also examined the effect of HFD on the c-Fos protein expression in the ventral dentate gyrus (vDG) and explored the influence of intracerebroventricular (i.c.v) oxytocin injections on HFD-induced anxiety. Our results indicated an increase in c-Fos-positive cells in the vDG following HFD consumption. Additionally, we recorded the spontaneous synaptic activity of miniature excitatory postsynaptic currents (mEPSCs) in the vDG. Notably, HFD resulted in an elevated mEPSC frequency without affecting mEPSC amplitude. Subsequently, investigations demonstrated that i.c.v oxytocin injections reversed anxiety-like behavior induced by HFD. Moreover, the application of oxytocin in a bath solution reduced the mEPSC frequency in the vDG. These findings suggest that postnatal HFD intake induces synaptic dysfunction in the vDG, associated with the hyperactivity of vDG neurons, potentially contributing to the anxiety-like behavior in juvenile obesity.

Human gut microbiome, diet, and mental disorders

Diet is one of the most important external factor shaping the composition and metabolic activities of the gut microbiome. The gut microbiome plays a crucial role in host health, including immune system development, nutrients metabolism, and the synthesis of bioactive molecules. In addition, the gut microbiome has been described as critical for the development of several mental disorders. Nutritional psychiatry is an emerging field of research that may provide a link between diet, microbial function, and brain health. In this study, we have reviewed the influence of different diet types, such as Western, Mediterranean, vegetarian, and ketogenic, on the gut microbiota composition and function, and their implication in various neuropsychiatric and psychological disorders.

Reversion of metabolic dysfunction-associated steatohepatitis by skeletal muscle-directed FGF21 gene therapy

The highly prevalent metabolic dysfunction-associated steatohepatitis (MASH) is associated with liver steatosis, inflammation, and hepatocyte injury, which can lead to fibrosis and may progress to hepatocellular carcinoma and death. New treatment modalities such as gene therapy may be transformative for MASH patients. Here, we describe that one-time intramuscular administration of adeno-associated viral vectors of serotype 1 (AAV1) encoding native fibroblast growth factor 21 (FGF21), a key metabolic regulator, resulted in sustained increased circulating levels of the factor, which mediated long-term (>1 year) MASH and hepatic fibrosis reversion and halted development of liver tumors in obese male and female mouse models. AAV1-FGF21 treatment also counteracted obesity, adiposity, and insulin resistance, which are significant drivers of MASH. Scale-up to large animals successfully resulted in safe skeletal muscle biodistribution and biological activity in key metabolic tissues. Moreover, as a step toward the clinic, circulating FGF21 levels were characterized in obese, insulin-resistant and MASH patients. Overall, these results underscore the potential of the muscle-directed AAV1-FGF21 gene therapy to treat MASH and support its clinical translation.

Early-life obesogenic environment integrates immunometabolic and epigenetic signatures governing neuroinflammation

Childhood overweight/obesity is associated with stress-related psychopathology, yet the pathways connecting childhood obesity to stress susceptibility are poorly understood. We employed a systems biology approach with 62 adolescent Lewis rats fed a Western-like high-saturated fat diet (WD, 41% kcal from fat) or a control diet (CD, 13% kcal from fat). A subset of rats underwent a 31-day model of predator exposures and social instability (PSS). Effects were assessed using behavioral tests, DTI (diffusion tensor imaging), NODDI (neurite orientation dispersion and density imaging), 16S rRNA gene sequencing for gut microbiome profiling, hippocampal microglia analysis, and targeted gene methylation. Parallel experiments on human microglia cells (HMC3) examined how palmitic acid influences cortisol-related inflammatory responses. Rats exposed to WD and PSS exhibited deficits in sociability, increased fear/anxiety-like behaviors, food consumption, and body weight. WD/PSS altered hippocampal microstructure (subiculum, CA1, dentate gyrus), and microbiome analysis showed a reduced abundance of members of the phylum Firmicutes. WD/PSS synergistically promoted neuroinflammatory changes in hippocampal microglia, linked with microbiome shifts and altered Fkbp5 expression/methylation. In HMC3, palmitate disrupted cortisol responses, affecting morphology, phagocytic markers, and cytokine release, partially mediated by FKBP5. This study identifies gene-environment interactions that influence microglia biology and may contribute to the connection between childhood obesity and stress-related psychopathology later in life.

Exercise-produced irisin effects on brain-related pathological conditions

Exercise increases peroxisome proliferator-activated receptor-gamma coactivator 1-alpha (PGC-1α) expression, which in turn causes the fibronectin type III domain containing 5 (FNDC5) protein to be produced. This protein is then cleaved, primarily in skeletal muscle fibers, to produce irisin. When the mature FNDC5 is cleaved by proteases, Irisin - which is the fibronectin III domain without the signal sequence - is released. Resistance, aerobic, and high-intensity interval training (HIIT) are recognized as forms of physical exercise that raise irisin levels, and insulin receptor phosphorylation in tyrosine residues, favoring an increase in the activity of the insulin-dependent pathway (PI3K pathway) and assisting in the fight against insulin resistance, inflammation, and cognitive decline. Irisin may represent a promising option for the therapeutic targeting in several brain-related pathological conditions, like Alzheimer's disease (AD), Parkinson's disease (PD), epilepsy, type 2 diabetes, and obesity. Exercise protocols are healthy and inexpensive interventions that can help find cellular and molecular changes in several brain-related pathological conditions. Here, it was reviewed what is known about exercise-produced irisin studies involving AD, PD, epilepsy, type 2 diabetes, and obesity.

TLR4-dependent neuroinflammation mediates LPS-driven food-reward alterations during high-fat exposure

BACKGROUND

Obesity has become a global pandemic, marked by significant shifts in both the homeostatic and hedonic/reward aspects of food consumption. While the precise causes are still under investigation, recent studies have identified the role of gut microbes in dysregulating the reward system within the context of obesity. Unravelling these gut-brain connections is crucial for developing effective interventions against eating and metabolic disorders, particularly in the context of obesity. This study explores the causal role of LPS, as a key relay of microbiota component-induced neuroinflammation in the dysregulation of the reward system following exposure to high-fat diet (HFD).

METHODS

Through a series of behavioural paradigms related to food-reward events and the use of pharmacological agents targeting the dopamine circuit, we investigated the mechanisms associated with the development of reward dysregulation during HFD-feeding in male mice. A Toll-like receptor 4 (TLR4) full knockout model and intraventricular lipopolysaccharide (LPS) diffusion at low doses, which mimics the obesity-associated neuroinflammatory phenotype, were used to investigate the causal roles of gut microbiota-derived components in neuroinflammation and reward dysregulation.

RESULTS

Our study revealed that short term exposure to HFD (24 h) tended to affect food-seeking behaviour, and this effect became significant after 1 week of HFD. Moreover, we found that deletion of TLR4 induced a partial protection against HFD-induced neuroinflammation and reward dysregulation. Finally, chronic brain diffusion of LPS recapitulated, at least in part, HFD-induced molecular and behavioural dysfunctions within the reward system.

CONCLUSIONS

These findings highlight a link between the neuroinflammatory processes triggered by the gut microbiota components LPS and the dysregulation of the reward system during HFD-induced obesity through the TLR4 pathway, thus paving the way for future therapeutic approaches.

Neurometabolic Profile in Obese Patients: A Cerebral Multi-Voxel Magnetic Resonance Spectroscopy Study

Background and Objectives: Obesity-related chronic inflammation may lead to neuroinflammation and neurodegeneration. This study aimed to evaluate the neurometabolic profile of obese patients using cerebral multivoxel magnetic resonance spectroscopy (mvMRS) and assess correlations between brain metabolites and obesity markers, including body mass index (BMI), waist circumference, waist-hip ratio, body fat percentage, and indicators of metabolic syndrome (e.g., triglycerides, HDL cholesterol, fasting blood glucose, insulin, and insulin resistance index (HOMA-IR)). Materials and Methods: This prospective study involved 100 participants, stratified into two groups: 50 obese individuals (BMI ≥ 30 kg/m2) and 50 controls (18.5 ≤ BMI < 25 kg/m2). Anthropometric measurements, body fat percentage, and biochemical markers were evaluated. All subjects underwent long- and short-echo mvMRS analysis of the frontal and parietal supracallosal subcortical and deep white matter, as well as the cingulate gyrus, analyzing NAA/Cr, Cho/Cr, and mI/Cr ratios, along with absolute concentrations of NAA and Cho. Results: Obese participants exhibited significantly decreased NAA/Cr and Cho/Cr ratios in the deep white matter of the right cerebral hemisphere (p < 0.001), while absolute concentrations of NAA and Cho did not differ significantly between groups (p > 0.05). NAA levels showed negative correlations with more reliable obesity parameters (waist circumference and waist-to-hip ratio) but not with BMI, particularly in the deep frontal white matter and dorsal anterior cingulate gyrus of the left cerebral hemisphere. Notably, insulin demonstrated a significant negative impact on NAA (ρ = -0.409 and ρ = -0.410; p < 0.01) and Cho levels (ρ = -0.403 and ρ = -0.392; p < 0.01) at these locations in obese individuals. Conclusions: Central obesity and hyperinsulinemia negatively affect specific brain regions associated with cognitive and emotional processing, while BMI is not a reliable parameter for assessing brain metabolism.

Estimated glucose disposal rate is correlated with increased depression: a population-based study

BACKGROUND

Recent studies have identified a correlation between insulin resistance (IR) and depression. This study aims to explore the correlation between estimated glucose disposal rate (eGDR), a practical and noninvasive measure for assessing IR, and depression in the general population.

METHODS

In this population-based cross-sectional study, data from 28,444 adults aged 18 years old or older in the NHANES during the period from 1999 to 2018 were analyzed. The correlation between eGDR and depression was examined through multivariate logistic regression analyses, subgroup analyses, restricted cubic spline, and interaction tests. Furthermore, a mediation analysis was conducted to elucidate the role of the atherogenic index of plasma (AIP) in mediating the effect of eGDR on depression.

RESULTS

Multivariate logistic regression analysis and restricted cubic splines analysis indicated that eGDR can exhibit a linearly correlation with depression (OR = 0.913; 95% CI: 0.875, 0.953). Subjects in eGDR6-8 and eGDR > 8 groups had a decrease risk of depression as 25.4% and 41.5% than those in the eGDR < 4 group. This negative correlation was more pronounced in those with obesity. Mediation analysis indicated that AIP mediated 9.6% of the correlation between eGDR and depression.

CONCLUSIONS

eGDR was linear negatively correlated with depression, with AIP playing a mediating role. This study provides a novel perspective on the mechanism connecting IR to depression. Managing IR and monitoring AIP may contribute to alleviating depression.

High-Fat Diet-Induced Blood-Brain Barrier Dysfunction: Impact on Allodynia and Motor Coordination in Rats

The associations among increased pain sensitivity, obesity, and systemic inflammation have not been described as related to BBB dysfunctions. To analyze the metabolic, behavioral, and inflammatory effects of a high-fat diet (HFD) and ultrastructural modifications in brain regions, we used an in vivo experimental model. Adult male Wistar rats were randomly assigned to one of two conditions, an ad libitum control group or an HFD (60%)-fed group, for eight weeks. At the end of the protocol, glucose and insulin tolerance tests were performed. Additionally, we analyzed the response to a normally innocuous mechanical stimulus and changes in motor coordination. At the end of the protocol, HFD-fed rats presented increased HOMA-IR and metabolic syndrome (MetS) prevalence. HFD-fed rats also developed an increased nociceptive response to mechanical stimuli and neurological injury, resulting in impaired motor function. Hypothalamus and cerebellum neurons from HFD-fed rats presented with nuclear swelling, an absence of nucleoli, and karyolysis. These results reveal that HFD consumption affects vital brain structures such as the cerebellum, hippocampus, and hypothalamus. This, in turn, could be producing neuronal damage, impairing cellular communication, and consequently altering motricity and pain sensitivity. Although direct evidence of a causal link between BBB dysfunction and sensory-motor changes was not observed, understanding the association uncovered in this study could lead to targeted therapeutic strategies.

Regular exercise ameliorates high-fat diet-induced depressive-like behaviors by activating hippocampal neuronal autophagy and enhancing synaptic plasticity

Exercise enhances synaptic plasticity and alleviates depression symptoms, but the mechanism through which exercise improves high-fat diet-induced depression remains unclear. In this study, 6-week-old male C57BL/6J mice were administered a high-fat diet (HFD, 60% kcal from fat) to a HFD model for 8 weeks. The RUN group also received 1 h of daily treadmill exercise in combination with the HFD. Depressive-like behaviors were evaluated by behavioral assessments for all groups. The key mediator of the effect of exercise on high-fat diet-induced depressive-like behaviors was detected by RNA-seq. The morphology and function of the neurons were evaluated via Nissl staining, Golgi staining, electron microscopy and electrophysiological experiments. The results showed that exercise attenuated high-fat diet-induced depressive-like behavior and reversed hippocampal gene expression changes. RNA-seq revealed Wnt5a, which was a key mediator of the effect of exercise on high-fat diet-induced depressive-like behaviors. Further work revealed that exercise significantly activated neuronal autophagy in the hippocampal CA1 region via the Wnt5a/CamkII signaling pathway, which enhanced synaptic plasticity to alleviate HFD-induced depressive-like behavior. However, the Wnt5a inhibitor Box5 suppressed the ameliorative effects of exercise. Therefore, this work highlights the critical role of Wnt5a, which is necessary for exercise to improve high-fat diet-induced depression.

The Downregulation of the Liver Lipid Metabolism Induced by Hypothyroidism in Male Mice: Metabolic Flexibility Favors Compensatory Mechanisms in White Adipose Tissue

In mammals, the maintenance of energy homeostasis relies on complex mechanisms requiring tight synchronization between peripheral organs and the brain. Thyroid hormones (THs), through their pleiotropic actions, play a central role in these regulations. Hypothyroidism, which is characterized by low circulating TH levels, slows down the metabolism, which leads to a reduction in energy expenditure as well as in lipid and glucose metabolism. The objective of this study was to evaluate whether the metabolic deregulations induced by hypothyroidism could be avoided through regulatory mechanisms involved in metabolic flexibility. To this end, the response to induced hypothyroidism was compared in males from two mouse strains, the wild-derived WSB/EiJ mouse strain characterized by a diet-induced obesity (DIO) resistance due to its high metabolic flexibility phenotype and C57BL/6J mice, which are prone to DIO. The results show that propylthiouracil (PTU)-induced hypothyroidism led to metabolic deregulations, particularly a reduction in hepatic lipid synthesis in both strains. Furthermore, in contrast to the C57BL/6J mice, the WSB/EiJ mice were resistant to the metabolic dysregulations induced by hypothyroidism, mainly through enhanced lipid metabolism in their adipose tissue. Indeed, WSB/EiJ mice compensated for the decrease in hepatic lipid synthesis by mobilizing lipid reserves from white adipose tissue. Gene expression analysis revealed that hypothyroidism stimulated the hypothalamic orexigenic circuit in both strains, but there was unchanged melanocortin 4 receptor (Mc4r) and leptin receptor (LepR) expression in the hypothyroid WSB/EiJ mice strain, which reflects their adaptability to maintain their body weight, in contrast to C57BL/6J mice. Thus, this study showed that WSB/EiJ male mice displayed a resistance to the metabolic dysregulations induced by hypothyroidism through compensatory mechanisms. This highlights the importance of metabolic flexibility in the ability to adapt to disturbed circulating TH levels.

The Hidden Dangers of Sedentary Living: Insights into Molecular, Cellular, and Systemic Mechanisms

With the aging of the global population, neurodegenerative diseases are emerging as a major public health issue. The adoption of a less sedentary lifestyle has been shown to have a beneficial effect on cognitive decline, but the molecular mechanisms responsible are less clear. Here we provide a detailed analysis of the complex molecular, cellular, and systemic mechanisms underlying age-related cognitive decline and how lifestyle choices influence these processes. A review of the evidence from animal models, human studies, and postmortem analyses emphasizes the importance of integrating physical exercise with cognitive, multisensory, and motor stimulation as part of a multifaceted approach to mitigating cognitive decline. We highlight the potential of these non-pharmacological interventions to address key aging hallmarks, such as genomic instability, telomere attrition, and neuroinflammation, and underscore the need for comprehensive and personalized strategies to promote cognitive resilience and healthy aging.

Brain energetics and glucose transport in metabolic diseases: role in neurodegeneration

OBJECTIVES

Neurons and glial cells are the main functional and structural elements of the brain, and the former depends on the latter for their nutritional, functional and structural organization, as well as for their energy maintenance.

METHODS

Glucose is the main metabolic source that fulfills energetic demands, either by direct anaplerosis or through its conversion to metabolic intermediates. Development of some neurodegenerative diseases have been related with modifications in the expression and/or function of glial glucose transporters, which might cause physiological and/or pathological disturbances of brain metabolism. In the present contribution, we summarized the experimental findings that describe the exquisite adjustment in expression and function of glial glucose transporters from physiologic to pathologic metabolism, and its relevance to neurodegenerative diseases.

RESULTS

A exhaustive literature review was done in order to gain insight into the role of brain energetics in neurodegenerative disease. This study made evident a critical involvement of glucose transporters and thus brain energetics in the development of neurodegenerative diseases.

DISCUSSION

An exquisite adjustment in the expression and function of glial glucose transporters from physiologic to pathologic metabolism is a biochemical signature of neurodegenerative diseases.

The effects of resistance training on cardiovascular factors and anti-inflammation in diabetic rats

Diabetes induces a range of macrovascular and microvascular changes, which lead to significant clinical complications. Although many studies have tried to solve the diabetic problem using drugs, it remains unclear. In this study, we investigated whether resistance exercise affects cardiovascular factors and inflammatory markers in diabetes. The study subjected Otsuka Long-Evans Tokushima Fatty (OLETF) rats, which have genetically induced diabetes mellitus, to a resistance exercise program for 12 weeks and assessed the levels of cardiovascular factors and inflammatory markers using western blotting analysis, ELISA, and immunohistochemistry. During the training period, OLETF + exercise (EX) group exhibited lower body weight and reduced glucose levels when compared with OLETF group. Western blotting analysis, ELISA, and immunohistochemistry revealed that the levels of PAI-1, VACM-1, ICAM-1, E-selectin, TGF-β, CRP, IL-6, and TNF-α were decreased in OLETF + EX group when compared with the OLETF group. Moreover, the anti-inflammatory markers, IL-4 and IL-10, were highly expressed after exercise. Therefore, these results indicate that exercise may influence the regulation of cardiovascular factors and inflammatory markers, as well as help patients with metabolic syndromes regulate inflammation and cardiovascular function.

Principal components analysis on genes related to inflammasome complex and microglial activation in the hypothalamus of obese mice treated with semaglutide (GLP-1 analog)

We studied the effect of semaglutide (glucagon-like peptide type 1 agonist) on hypothalamic pro-inflammatory genes in diet-induced obese mice. Male C57BL/6J mice were fed a control (C) or high-fat (HF) diet for 16 weeks, then divided into six groups and maintained for an additional four-week study: C, C+semaglutide (CS), C pair-feeding (CP), HF, HF+semaglutide (HFS), and HF pair-feeding (HFP).Weight gain (WG), food efficiency (FE), and plasmatic biochemistry were determined. The hypothalamus was removed and prepared for molecular analysis. Semaglutide reduced WG and FE in the HF group. High cytokines levels (tumor necrosis factor alpha, TNF alpha, monocyte chemoattractant protein 1, MCP1, and Resistin) in HF mice were reduced in HFS mice. High pro-inflammatory gene expressions were seen in HF (toll-like receptor 4, Tlr4; Mcp1; interleukin 6, Il6; Tnfa), inflammasome complex (Pirina domain-containing receptor 3, Nlrp3; Caspase 1, Il1b, Il18), and microglial activation (ionized calcium-binding adapter molecule 1, Iba1; cluster differentiation 68, Cd68; argirase 1, Arg1) but mitigated in HFS. The principal components analysis (PCA) based on these markers in a PC1 x PC2 scatterplot put HF and HFP together but far away from a cluster formed by C and HFS, indicating little significance of weight loss (HFP) but decisive action of semaglutide (HFS) in the results. In conclusion, semaglutide benefits hypothalamic pro-inflammatory genes, inflammasome complex, and microglial activation independent of the weight loss effect. Since GLP-1 receptor agonists such as semaglutide are already indicated to treat obesity and diabetes, the potential translational effects on neuroinflammation should be considered.

Factors Associated with the Development of Depression and the Influence of Obesity on Depressive Disorders: A Narrative Review

Depression affects several aspects of life, including socioeconomic status, relationships, behavior, emotions, and overall health. The etiology of depression is complex and influenced by various factors, with obesity emerging as a significant contributor. This narrative review aims to investigate the factors associated with the development of depression, with a particular focus on the role of obesity. The literature search was conducted on PubMed, Embase, and PsycINFO from May to July 2024. The review highlights the impact of environmental and socioeconomic conditions; lifestyle choices, including physical activity and dietary habits; stress; traumatic experiences; neurotransmitter imbalances; medical and psychological conditions; hormone fluctuations; and epigenetic factors on depression. A key emphasis is placed on the inflammatory processes linked to obesity, which may drive the bidirectional relationship between obesity and depression. The findings suggest that obesity is associated with an increased risk of depression, potentially due to chronic inflammation, neurochemical dysregulation, and the emotional and social challenges related to weight stigma and obesity management. Understanding these interconnected factors is important for developing targeted interventions to address both obesity and depression, leading to improved quality of life for those affected.

Combination of Gold Nanoparticles with Carnitine Attenuates Brain Damage in an Obesity Animal Model

Obesity causes inflammation in the adipose tissue and can affect the central nervous system, leading to oxidative stress and mitochondrial dysfunction. Therefore, it becomes necessary to seek new therapeutic alternatives. Gold nanoparticles (GNPs) could take carnitine to the adipose tissue, thus increasing fatty acid oxidation, reducing inflammation, and, consequently, restoring brain homeostasis. The objective of this study was to investigate the effects of GNPs associated with carnitine on the neurochemical parameters of obesity-induced mice. Eighty male Swiss mice that received a normal lipid diet (control group) or a high-fat diet (obese group) for 10 weeks were used. At the end of the sixth week, the groups were divided for daily treatment with saline, GNPs (70 µg/kg), carnitine (500 mg/kg), or GNPs associated with carnitine, respectively. Body weight was monitored weekly. At the end of the tenth week, the animals were euthanized and the mesenteric fat removed and weighed; the brain structures were separated for biochemical analysis. It was found that obesity caused oxidative damage and mitochondrial dysfunction in brain structures. Treatment with GNPs isolated reduced oxidative stress in the hippocampus. Carnitine isolated decreased the accumulation of mesenteric fat and oxidative stress in the hippocampus. The combination of treatments reduced the accumulation of mesenteric fat and mitochondrial dysfunction in the striatum. Therefore, these treatments in isolation, become a promising option for the treatment of obesity.

Diet-Induced Obesity Induces Transcriptomic Changes in Neuroimmunometabolic-Related Genes in the Striatum and Olfactory Bulb

The incidence of obesity has markedly increased globally over the last several decades and is believed to be associated with the easier availability of energy-dense foods, including high-fat foods. The reinforcing hedonic properties of high-fat foods, including olfactory cues, activate reward centers in the brain, motivating eating behavior. Thus, there is a growing interest in the understanding of the genetic changes that occur in the brain that are associated with obesity and eating behavior. This growing interest has paralleled advances in genomic methods that enable transcriptomic-wide analyses. Here, we examined the transcriptomic-level differences in the olfactory bulb and striatum, regions of the brain associated with olfaction and hedonic food-seeking, respectively, in high-fat-diet (HFD)-fed obese mice. To isolate the dietary effects from obesity, we also examined transcriptomic changes in normal-chow-fed and limited-HFD-fed groups, with the latter being pair-fed with an HFD isocaloric to the consumption of the normal-chow-fed mice. Using RNA sequencing, we identified 274 differentially expressed genes (DEGs) in the striatum and 11 in the olfactory bulb of ad libitum HFD-fed mice compared to the chow-fed group, and thirty-eight DEGs in the striatum between the ad libitum HFD and limited-HFD-fed groups. The DEGs in both tissues were associated with inflammation and immune-related pathways, including oxidative stress and immune function, and with mitochondrial dysfunction and reward pathways in the striatum. These results shed light on potential obesity-associated genes in these regions of the brain.

Limosilactobacillus fermentum HNU312 alleviates lipid accumulation and inflammation induced by a high-fat diet: improves lipid metabolism pathways and increases short-chain fatty acids in the gut microbiome

A high-fat diet can cause health problems, such as hyperlipidemia, obesity, cardiovascular disease, and metabolic disorders. Dietary supplementation with beneficial microbes might reduce the detrimental effects of a high-fat diet by modulating the gut microbiome, metabolic pathways and metabolites. This study assessed the effects of Limosilactobacillus fermentum HNU312 (L. fermentum HNU312) on blood lipid levels, fat accumulation, inflammation and the gut microbiome in mice on a high-fat diet. The results indicate that L. fermentum HNU312 supplementation to high-fat diet-fed mice led to decreases of 7.52% in the final body weight, 22.30% in total triglyceride, 24.87% in total cholesterol, and 27.3% in low-density lipoprotein cholesterol. Furthermore, the addition of L. fermentum HNU312 significantly reduced the fat accumulation in the liver and adipose tissue by 18.99% and 32.55%, respectively, and decreased chronic inflammation induced by a high-fat diet. Further analysis of the gut microbiome revealed that on the one hand, L. fermentum HNU312 changed the structure of the intestinal microbiota, increased the abundance of beneficial intestinal bacteria related to lipid metabolism, and reversed the enrichment of lipid-related metabolic pathways. On the other hand, L. fermentum HNU312 increased the production of short-chain fatty acids, which can reduce liver inflammation and chronic inflammation induced by a high-fat diet. In summary, by regulating gut microbiota, L. fermentum HNU312 improved lipid metabolism pathways and increased short-chain fatty acids, which reduced body weight, blood lipids, fat accumulation and chronic inflammation caused by high-fat diets. Therefore, L. fermentum HNU312 could be a good candidate probiotic for ameliorating metabolic syndrome.

Obesity as Inducer of Cognitive Function Decline via Dysbiosis of Gut Microbiota in Rats

Diet-induced obesity is a global phenomenon that affects the population worldwide with manifestations at both the phenotypic and genotypic levels. Cognitive function decline is a major global health challenge. The relation between obesity and cognitive function is a debatable issue. The main goal of the current research was to study the implications of obesity on cognitive function and gut microbiota diversity and its impact on plasma and brain metabolic parameters in rats. Obesity was induced in rats by feeding on a high-fat (HF) or a high-fat/high-sucrose (HFHS) diet. The results reveal that both the HF (0.683) and HFHS (0.688) diets were effective as obesity inducers, which was confirmed by a significant increase in the body mass index (BMI). Both diet groups showed dyslipidemia and elevation of oxidative stress, insulin resistance (IR), and inflammatory markers with alterations in liver and kidney functions. Obesity led to a reduction in cognitive function through a reduction in short-term memory by 23.8% and 30.7% in the rats fed HF and HFHS diets, respectively, and learning capacity and visuo-spatial memory reduced by 8.9 and 9.7 s in the rats fed an HF or HFHS diet, respectively. Bacteroidetes, Firmicutes, Proteobacteria, Fusobacteria, and Spirochaetes phyla were detected. The Firmicutes/Bacteroidetes ratio (F/B) significantly decreased in the HF group, while it increased in the HFHS group compared to the normal control. The two species, Bacteroides acidifaciens and Bacteroides ovatus, which are associated with IR, were drastically compromised by the high-fat/high-sucrose diet. Some species that have been linked to reduced inflammation showed a sharp decrease in the HFHS group, while Prevotella copri, which is linked to carbohydrate metabolism, was highly enriched. In conclusion: Obesity led to cognitive impairment through changes in short-term and visuo-spatial memory. A metagenomic analysis revealed alterations in the abundance of some microbial taxa associated with obesity, inflammation, and insulin resistance in the HF and HFHS groups.

Obesity-induced tissue alterations resist weight loss: A mechanistic review

Interventions aimed at weight control often have limited effectiveness in combating obesity. This review explores how obesity-induced dysfunction in white (WAT) and brown adipose tissue (BAT), skeletal muscle, and the brain blunt weight loss, leading to retention of stored fat. In obesity, increased adrenergic stimulation and inflammation downregulate β-adrenoreceptors and impair catecholaminergic signalling in adipocytes. This disrupts adrenergic-mediated lipolysis, diminishing lipid oxidation in both white and brown adipocytes, lowering thermogenesis and blunting fat loss. Emerging evidence suggests that WAT fibrosis is associated with worse weight loss outcomes; indeed, limiting collagen and laminin-α4 deposition mitigates WAT accumulation, enhances browning, and protects against high-fat-diet-induced obesity. Obesity compromises mitochondrial oxidative capacity and lipid oxidation in skeletal muscle, impairing its ability to switch between glucose and lipid metabolism in response to varying nutrient levels and exercise. This dysfunctional phenotype in muscle is exacerbated in the presence of obesity-associated sarcopenia. Additionally, obesity suppresses sarcolipin-induced sarcoplasmic reticulum calcium ATPase (SERCA) activation, resulting in reduced oxidative capacity, diminished energy expenditure, and increased adiposity. In the hypothalamus, obesity and overnutrition impair insulin and leptin signalling. This blunts central satiety signals, favouring a shift in energy balance toward energy conservation and body fat retention. Moreover, both obese animals and humans demonstrate impaired dopaminergic signalling and diminished responses to nutrient intake in the striatum, which tend to persist after weight loss. This may result in enduring inclinations toward overeating and a sedentary lifestyle. Collectively, the tissue adaptations described pose significant challenges to effectively achieving and sustaining weight loss in obesity.

Edge Density Imaging Identifies White Matter Biomarkers of Late-Life Obesity and Cognition

Alzheimer disease (AD) and obesity are related to disruptions in the white matter (WM) connectome. We examined the link between the WM connectome and obesity and AD through edge-density imaging/index (EDI), a tractography-based method that characterizes the anatomical embedding of tractography connections. A total of 60 participants, 30 known to convert from normal cognition or mild-cognitive impairment to AD within a minimum of 24 months of follow up, were selected from the Alzheimer disease Neuroimaging Initiative (ADNI). Diffusion-weighted MR images from the baseline scans were used to extract fractional anisotropy (FA) and EDI maps that were subsequently averaged using deterministic WM tractography based on the Desikan-Killiany atlas. Multiple linear and logistic regression analysis were used to identify the weighted sum of tract-specific FA or EDI indices that maximized correlation to body-mass-index (BMI) or conversion to AD. Participants from the Open Access Series of Imaging Studies (OASIS) were used as an independent validation for the BMI findings. The edge-density rich, periventricular, commissural and projection fibers were among the most important WM tracts linking BMI to FA as well as to EDI. WM fibers that contributed significantly to the regression model related to BMI overlapped with those that predicted conversion; specifically in the frontopontine, corticostriatal, and optic radiation pathways. These results were replicated by testing the tract-specific coefficients found using ADNI in the OASIS-4 dataset. WM mapping with EDI enables identification of an abnormal connectome implicated in both obesity and conversion to AD.

Stress and the domestic cat: have humans accidentally created an animal mimic of neurodegeneration?

Many neurodegenerative diseases (NDD) appear to share commonality of origin, chronic ER stress. The endoplasmic reticulum (ER) is a dynamic organelle, functioning as a major site of protein synthesis and protein posttranslational modifications, required for proper folding. ER stress can occur because of external stimuli, such as oxidative stress or neuroinflammatory cytokines, creating the ER luminal environment permissive for the accumulation of aggregated and misfolded proteins. Unresolvable ER stress upregulates a highly conserved pathway, the unfolded protein response (UPR). Maladaptive chronic activation of UPR components leads to apoptotic neuronal death. In addition to other factors, physiological responses to stressors are emerging as a significant risk factor in the etiology and pathogenesis of NDD. Owned cats share a common environment with people, being exposed to many of the same stressors as people and additional pressures due to their "quasi" domesticated status. Feline Cognitive Dysfunction Syndrome (fCDS) presents many of the same disease hallmarks as human NDD. The prevalence of fCDS is rapidly increasing as more people welcome cats as companions. Barely recognized 20 years ago, veterinarians and scientists are in infancy stages in understanding what is a very complex disease. This review will describe how cats may represent an unexplored animal mimetic phenotype for human NDD with stressors as potential triggering mechanisms. We will consider how multiple variations of stressful events over the short-life span of a cat could affect neuronal loss or glial dysfunction and ultimately tip the balance towards dementia.

Obesity-induced inflammation: connecting the periphery to the brain

Obesity is often associated with a chronic, low-grade inflammatory state affecting the entire body. This sustained inflammatory state disrupts the coordinated communication between the periphery and the brain, which has a crucial role in maintaining homeostasis through humoural, nutrient-mediated, immune and nervous signalling pathways. The inflammatory changes induced by obesity specifically affect communication interfaces, including the blood-brain barrier, glymphatic system and meninges. Consequently, brain areas near the third ventricle, including the hypothalamus and other cognition-relevant regions, become susceptible to impairments, resulting in energy homeostasis dysregulation and an elevated risk of cognitive impairments such as Alzheimer's disease and dementia. This Review explores the intricate communication between the brain and the periphery, highlighting the effect of obesity-induced inflammation on brain function.

The Impact of Obesity as a Peripheral Disruptor of Brain Inhibitory Mechanisms in Fibromyalgia: A Cross-Sectional Study

Background/Objective: Obesity, characterized by chronic inflammation, may serve as a surrogate marker for more dysfunctional peripheral inflammation, potentially exacerbating FM symptomatology. Given this premise, this study aimed to investigate the effects of obesity as an effect modifier on neural and clinical variables, specifically those indexing pain-compensatory mechanisms in FM symptoms. Methods: A cross-sectional study was conducted with 108 participants who underwent a standardized TMS protocol assessment to measure resting motor threshold (MT), intracortical facilitation (ICF), and intracortical inhibition (ICI). Clinical data were collected using Beck's Depression Index (BDI), PROMIS, the Brief Pain Inventory (BPI), and conditioned pain modulation (CPM). Linear regression models were used to explore the relationship between these variables while examining Body Mass Index (BMI) as a potential effect modifier. If it was found to be a modifier, we stratified the sample into two groups with a BMI cutoff of 30 and performed another regression model within the subgroups. Results: BMI was identified as an effect modifier in the relationships between ICI and BDI, PROMIS fatigue, and CPM and in MT versus CPM. After stratification, non-obese fibromyalgia subjects demonstrated significant correlations between clinical symptoms and CPM and ICI activity. However, these correlations were absent in the obese group, suggesting obesity disrupts pain mechanisms and their compensatory effects. Higher MT values were associated with weaker endogenous pain control, particularly evident in the obese group. Conclusions: Obesity appears to be a significant effect modifier and delineates two patient groups across multiple clinical and neural assessments of fibromyalgia. Additionally, it suggests a role for obesity in exacerbating fibromyalgia symptoms and disrupting physiological pain-inhibitory mechanisms.

Cannabidiol improves maternal obesity-induced behavioral, neuroinflammatory and neurochemical dysfunctions in the juvenile offspring

Maternal obesity is associated with an increased risk of psychiatric disorders such as anxiety, depression, schizophrenia and autism spectrum disorder in the offspring. While numerous studies focus on preventive measures targeting the mothers, only a limited number provide practical approaches for addressing the damages once they are already established. We have recently demonstrated the interplay between maternal obesity and treatment with cannabidiol (CBD) on hypothalamic inflammation and metabolic disturbances, however, little is known about this relationship on behavioral manifestations and neurochemical imbalances in other brain regions. Therefore, here we tested whether CBD treatment could mitigate anxiety-like and social behavioral alterations, as well as neurochemical disruptions in both male and female offspring of obese dams. Female Wistar rats were fed a cafeteria diet for 12 weeks prior to mating, and during gestation and lactation. Offspring received CBD (50 mg/kg) from weaning for 3 weeks. Behavioral tests assessed anxiety-like manifestations and social behavior, while neuroinflammatory and neurochemical markers were evaluated in the prefrontal cortex (PFC) and hippocampus. CBD treatment attenuated maternal obesity-induced anxiety-like and social behavioral alterations, followed by rescuing effects on imbalanced neurotransmitter and endocannabinoid concentrations and altered expression of glial markers, CB1, oxytocin and dopamine receptors, with important differences between sexes. Overall, the findings of this study provide insight into the signaling pathways for the therapeutic benefits of CBD on neuroinflammation and neurochemical imbalances caused by perinatal maternal obesity in the PFC and the hippocampus, which translates into the behavioral manifestations, highlighting the sexual dimorphism encompassing both the transgenerational effect of obesity and the endocannabinoid system.

High-fat diet consumption promotes adolescent neurobehavioral abnormalities and hippocampal structural alterations via microglial overactivation accompanied by an elevated serum free fatty acid concentration

Mounting evidence suggests that high-fat diet (HFD) consumption increases the risk for depression, but the neurophysiological mechanisms involved remain to be elucidated. Here, we demonstrated that HFD feeding of C57BL/6J mice during the adolescent period (from 4 to 8 weeks of age) resulted in increased depression- and anxiety-like behaviors concurrent with changes in neuronal and myelin structure in the hippocampus. Additionally, we showed that hippocampal microglia in HFD-fed mice assumed a hyperactive state concomitant with increased PSD95-positive and myelin basic protein (MBP)-positive inclusions, implicating microglia in hippocampal structural alterations induced by HFD consumption. Along with increased levels of serum free fatty acids (FFAs), abnormal deposition of lipid droplets and increased levels of HIF-1α protein (a transcription factor that has been reported to facilitate cellular lipid accumulation) within hippocampal microglia were observed in HFD-fed mice. The use of minocycline, a pharmacological suppressor of microglial overactivation, effectively attenuated neurobehavioral abnormalities and hippocampal structural alterations but barely altered lipid droplet accumulation in the hippocampal microglia of HFD-fed mice. Coadministration of triacsin C abolished the increases in lipid droplet formation, phagocytic activity, and ROS levels in primary microglia treated with serum from HFD-fed mice. In conclusion, our studies demonstrate that the adverse influence of early-life HFD consumption on behavior and hippocampal structure is attributed at least in part to microglial overactivation that is accompanied by an elevated serum FFA concentration and microglial aberrations represent a potential preventive and therapeutic target for HFD-related emotional disorders.

Smaller subcortical volume relates to greater weight gain in girls with initially healthy weight

OBJECTIVE

Among 3614 youth who were 9 to 12 years old and initially did not have overweight or obesity (12% [n = 385] developed overweight or obesity), we examined the natural progression of weight gain and brain structure development during a 2-year period with a high risk for obesity (e.g., pre- and early adolescence) to determine the following: 1) whether variation in maturational trajectories of the brain regions contributes to weight gain; and/or 2) whether weight gain contributes to altered brain development.

METHODS

Data were gathered from the Adolescent Brain Cognitive Development (ABCD) Study. Linear mixed-effects regression models controlled for puberty, caregiver education, handedness, and intracranial volume (random effects: magnetic resonance scanner [MRI] scanner and participant). Because pubertal development occurs earlier in girls, analyses were stratified by sex.

RESULTS

For girls, but not boys, independent of puberty, greater increases in BMI were driven by smaller volumes over time in the bilateral accumbens, amygdala, hippocampus, and thalamus, right caudate and ventral diencephalon, and left pallidum (all p < 0.05).

CONCLUSIONS

The results suggest a potential phenotype for identifying obesity risk because underlying differences among regions involved in food intake were related to greater weight gain in girls, but not in boys. Importantly, 2 years of weight gain may not be sufficient to alter brain development, highlighting early puberty as a critical time to prevent negative neurological outcomes.

Quantitative MRI Biomarkers Measure Changes in Targeted Brain Areas in Patients With Obesity

CONTEXT

Obesity is accompanied by damages to several tissues, including the brain. Pathological data and animal models have demonstrated an increased inflammatory reaction in hypothalamus and hippocampus.

OBJECTIVE

We tested whether we could observe such pathological modifications in vivo through quantitative magnetic resonance imaging (MRI) metrics.

METHODS

This prospective study was conducted between May 2019 and November 2022. The study was conducted in the Specialized Center for the Care of Obesity in a French University Hospital. Twenty-seven patients with obesity and 23 age and gender-paired normal-weight controls were prospectively recruited. All participants were examined using brain MRI. Anthropometric and biological data, eating behavior, anxiety, depression, and memory performance were assessed in both groups. The main outcome measure was brain MRI with the following parametric maps: quantitative susceptibility mapping (QSM), mean diffusivity (MD), fractional anisotropy (FA), magnetization transfer ratio map, and T2 relaxivity map.

RESULTS

In the hypothalamus, patients with obesity had higher FA and lower QSM than normal-weight controls. In the hippocampus, patients with obesity had higher FA and lower MD. There was no correlation between imaging biomarkers and eating behavior or anxiety.

CONCLUSION

Our findings are consistent with the presence of neuroinflammation in brain regions involved in food intake. In vivo brain biomarkers from quantitative MRI appear to provide an incremental information for the assessment of brain damages in patients with obesity.

Atherogenic Index of Plasma as a Mediator in the association between Body Roundness Index and Depression: insights from NHANES 2005-2018

BACKGROUND

Previous studies have shown a correlation between depression and obesity, as well as between depression and the Atherogenic Index of Plasma (AIP). However, there is limited research on the association between visceral obesity and depression, as well as the potential mediating role of AIP in this relationship.

METHODS

This study included 13,123 participants from the 2005-2018 National Health and Nutrition Examination Survey. Visceral obesity was measured with the Body Roundness Index (BRI), while depression was evaluated with the Patient Health Questionnaire-9. The AIP served as a marker for lipid disorders. To investigate the association between the BRI and depression, multivariate logistic regressions, restricted cubic spline models, subgroup analyses, and interaction tests were used. Additionally, a mediation analysis was conducted to explore the role of AIP in mediating the effect of BRI on depression.

RESULTS

There was a positive linear correlation between the BRI and depression. After controlling for all covariates, individuals in the highest BRI (Q4) group had an OR of 1.42 for depression (95% CI: 1.12-1.82) in comparison with individuals in the lowest BRI (Q1) group. Moreover, the AIP partially mediated the association between the BRI and depression, accounting for approximately 8.64% (95% CI: 2.04-16.00%) of the total effect.

CONCLUSION

The BRI was positively associated with depression, with the AIP playing a mediating role. This study provides a novel perspective on the mechanism that connects visceral obesity to depression. Managing visceral fat and monitoring AIP levels may contribute to alleviating depression.

The effect of weight loss on hypothalamus structure and function in obese individuals: a systematic review and meta-analysis

INTRODUCTION

Obesity presents with structural and functional hypothalamic dysfunction. However, it is unclear whether weight loss can lead to hypothalamic changes. We therefore aimed to conduct a systematic review and meta-analysis to determine the effect of body mass reduction in obese individuals on hypothalamic structure and function.

METHODS

PubMed, Embase and Cochrane databases were searched for studies that reported the change in hypothalamic structure and function after weight loss. Qualitative and quantitative analyses were performed on magnetic resonance imaging techniques, medio-basal hypothalamus T2-relaxation time, blood oxygen level dependent (BOLD) contrast, voxel-based morphometry (VBM) and biomarkers including glucose, insulin, leptin, ghrelin and inflammatory markers of interleukins. Mean differences between pre- and post-weight loss and 95% confidence intervals (CIs) were pooled using random-effects models.

RESULTS

Thirteen pre-post studies were included, of which six accounted for the meta-analysis. Studies showed a favorable decrease in T2-relaxation time (n = 1), favorable change in hypothalamic activity after weight loss on BOLD contrast (n = 4), with higher peak activities after surgical weight loss (n = 2). No differences were found in the gray matter density of the hypothalamus on VBM (n = 1). Pooled mean differences between pre- and post-surgical weight loss revealed a decrease of 8.53 mg/dl (95% CI: 5.17, 11.9) in glucose, 7.73 pmol/l (95% CI: 5.07, 10.4) in insulin, 15.5 ng/ml (95% CI: 9.40, 21.6) in leptin, 142.9 pg/ml (95% CI: 79.0, 206.8) in ghrelin and 9.43 pg/ml (95% CI: -6.89, 25.7) in IL-6 level.

CONCLUSIONS

Our study showed weight reduction in obesity led to limited structural change and significant functional changes in the hypothalamus.

Childhood Obesity, Hypothalamic Inflammation, and the Onset of Puberty: A Narrative Review

The onset of puberty, which is under the control of the hypothalamic-pituitary-gonadal (HPG) axis, is influenced by various factors, including obesity, which has been associated with the earlier onset of puberty. Obesity-induced hypothalamic inflammation may cause premature activation of gonadotropin-releasing hormone (GnRH) neurons, resulting in the development of precocious or early puberty. Mechanisms involving phoenixin action and hypothalamic microglial cells are implicated. Furthermore, obesity induces structural and cellular brain alterations, disrupting metabolic regulation. Imaging studies reveal neuroinflammatory changes in obese individuals, impacting pubertal timing. Magnetic resonance spectroscopy enables the assessment of the brain's neurochemical composition by measuring key metabolites, highlighting potential pathways involved in neurological changes associated with obesity. In this article, we present evidence indicating a potential association among obesity, hypothalamic inflammation, and precocious puberty.

Neuroinflammation: From Molecular Basis to Therapy

Neuroinflammatory conditions in the central nervous system (CNS) are implicated in the pathogenesis of several neuroimmune disorders such as acquired demyelinating syndromes, autoimmune encephalopathies, acute or chronic bacterial and viral CNS infections as well as multiple sclerosis (MS) [...].

Western diet increases brain metabolism and adaptive immune responses in a mouse model of amyloidosis

Diet-induced increase in body weight is a growing health concern worldwide. Often accompanied by a low-grade metabolic inflammation that changes systemic functions, diet-induced alterations may contribute to neurodegenerative disorder progression as well. This study aims to non-invasively investigate diet-induced metabolic and inflammatory effects in the brain of an APPPS1 mouse model of Alzheimer's disease. [18F]FDG, [18F]FTHA, and [18F]GE-180 were used for in vivo PET imaging in wild-type and APPPS1 mice. Ex vivo flow cytometry and histology in brains complemented the in vivo findings. 1H- magnetic resonance spectroscopy in the liver, plasma metabolomics and flow cytometry of the white adipose tissue were used to confirm metaflammatory condition in the periphery. We found disrupted glucose and fatty acid metabolism after Western diet consumption, with only small regional changes in glial-dependent neuroinflammation in the brains of APPPS1 mice. Further ex vivo investigations revealed cytotoxic T cell involvement in the brains of Western diet-fed mice and a disrupted plasma metabolome. 1H-magentic resonance spectroscopy and immunological results revealed diet-dependent inflammatory-like misbalance in livers and fatty tissue. Our multimodal imaging study highlights the role of the brain-liver-fat axis and the adaptive immune system in the disruption of brain homeostasis in amyloid models of Alzheimer's disease.

Astrocytes at the intersection of ageing, obesity, and neurodegeneration

Once considered passive cells of the central nervous system (CNS), glia are now known to actively maintain the CNS parenchyma; in recent years, the evidence for glial functions in CNS physiology and pathophysiology has only grown. Astrocytes, a heterogeneous group of glial cells, play key roles in regulating the metabolic and inflammatory landscape of the CNS and have emerged as potential therapeutic targets for a variety of disorders. This review will outline astrocyte functions in the CNS in healthy ageing, obesity, and neurodegeneration, with a focus on the inflammatory responses and mitochondrial function, and will address therapeutic outlooks.

A biobehavioural and social-structural model of inflammation and executive function in pediatric chronic health conditions

Evidence indicates that pediatric chronic health conditions (CHCs) often impair executive functioning (EF) and impaired EF undermines pediatric CHC management. This bidirectional relationship likely occurs due to biobehavioural and social-structural factors that serve to maintain this feedback loop. Specifically, biobehavioural research suggests that inflammation may sustain a feedback loop that links together increased CHC severity, challenges with EF, and lower engagement in health promoting behaviours. Experiencing social and environmental inequity also maintains pressure on this feedback loop as experiencing inequities is associated with greater inflammation, increased CHC severity, as well as challenges with EF and engagement in health promoting behaviours. Amidst this growing body of research, a model of biobehavioural and social-structural factors that centres inflammation and EF is warranted to better identify individual and structural targets to ameliorate the effects of CHCs on children, families, and society at large. This paper proposes this model, reviews relevant literature, and delineates actionable research and clinical implications.

Dietary fatty acid composition drives neuroinflammation and impaired behavior in obesity

Nutrient composition in obesogenic diets may influence the severity of disorders associated with obesity such as insulin-resistance and chronic inflammation. Here we hypothesized that obesogenic diets rich in fat and varying in fatty acid composition, particularly in omega 6 (ω6) to omega 3 (ω3) ratio, have various effects on energy metabolism, neuroinflammation and behavior. Mice were fed either a control diet or a high fat diet (HFD) containing either low (LO), medium (ME) or high (HI) ω6/ω3 ratio. Mice from the HFD-LO group consumed less calories and exhibited less body weight gain compared to other HFD groups. Both HFD-ME and HFD-HI impaired glucose metabolism while HFD-LO partly prevented insulin intolerance and was associated with normal leptin levels despite higher subcutaneous and perigonadal adiposity. Only HFD-HI increased anxiety and impaired spatial memory, together with increased inflammation in the hypothalamus and hippocampus. Our results show that impaired glucose metabolism and neuroinflammation are uncoupled, and support that diets with a high ω6/ω3 ratio are associated with neuroinflammation and the behavioral deterioration coupled with the consumption of diets rich in fat.

Neural Correlates of Obesity and Inflammation in Children and Adolescents with Congenital Adrenal Hyperplasia

INTRODUCTION

Patients with classical congenital adrenal hyperplasia (CAH) exhibit an increased prevalence of obesity from childhood including central adiposity and inflammation. There is also an emerging affected brain phenotype in CAH, with decreased cortico-limbic gray matter volumes and white matter abnormalities. We aimed to study the relationship between brain structure, obesity, and inflammation in children and adolescents with CAH compared to controls.

METHODS

27 CAH (12.6 ± 3.4 y, 16 females) and 35 control (13.0 ± 2.8 y, 20 females) participants had MRI of gray matter regions of interest (prefrontal cortex [PFC], amygdala, hippocampus) and white matter microstructure (fornix, stria terminalis [ST]). Anthropometric measures and lab analytes were obtained. Relaimpo analyses (relative importance for linear regression; percent variance) identified which brain structures were most different between groups. Subsequent regressions further quantified the magnitude and direction of these relationships. Correlations analyzed relationships between brain structure, obesity, and inflammation in the context of CAH status.

RESULTS

PFC (13.3% variance) and its superior frontal (SF) subregion (14%) were most different between CAH and controls for gray matter; ST (16%) for white matter. Patients with CAH had lower caudal middle frontal (β = -0.56 [-0.96, -0.15]) and superior frontal (β = -0.58 [-0.92, -0.25]) subregion volumes, increased orientation dispersion index in the fornix (β = 0.56 [0.01, 1.10]) and ST (β = 0.85 [0.34, 1.36]), and decreased fractional anisotropy in the fornix (β = -0.91 [-1.42, -0.42]) and ST (β = -0.83 [-1.34, -0.33]) (all p's < 0.05) indicating axonal disorganization, reduced myelin content, and/or higher microglial density within the affected white matter tracts. For the full cohort, SF was correlated with MCP-1 (r = -0.41), visceral adipose tissue (r = -0.25), and waist-to-height ratio (r = -0.27, all p's < 0.05); ST was correlated with MCP-1 (r = 0.31) and TNF-α (r = 0.29, all p's < 0.05); however, after adjusting for CAH status, almost all correlations were attenuated for significance.

CONCLUSIONS

Relationships among key brain structures, body composition, and inflammatory markers in pediatric patients with CAH could be largely driven by having CAH, with implications for obesity and neuroinflammation in this high-risk population.

INTRODUCTION

Patients with classical congenital adrenal hyperplasia (CAH) exhibit an increased prevalence of obesity from childhood including central adiposity and inflammation. There is also an emerging affected brain phenotype in CAH, with decreased cortico-limbic gray matter volumes and white matter abnormalities. We aimed to study the relationship between brain structure, obesity, and inflammation in children and adolescents with CAH compared to controls.

METHODS

27 CAH (12.6 ± 3.4 y, 16 females) and 35 control (13.0 ± 2.8 y, 20 females) participants had MRI of gray matter regions of interest (prefrontal cortex [PFC], amygdala, hippocampus) and white matter microstructure (fornix, stria terminalis [ST]). Anthropometric measures and lab analytes were obtained. Relaimpo analyses (relative importance for linear regression; percent variance) identified which brain structures were most different between groups. Subsequent regressions further quantified the magnitude and direction of these relationships. Correlations analyzed relationships between brain structure, obesity, and inflammation in the context of CAH status.

RESULTS

PFC (13.3% variance) and its superior frontal (SF) subregion (14%) were most different between CAH and controls for gray matter; ST (16%) for white matter. Patients with CAH had lower caudal middle frontal (β = -0.56 [-0.96, -0.15]) and superior frontal (β = -0.58 [-0.92, -0.25]) subregion volumes, increased orientation dispersion index in the fornix (β = 0.56 [0.01, 1.10]) and ST (β = 0.85 [0.34, 1.36]), and decreased fractional anisotropy in the fornix (β = -0.91 [-1.42, -0.42]) and ST (β = -0.83 [-1.34, -0.33]) (all p's < 0.05) indicating axonal disorganization, reduced myelin content, and/or higher microglial density within the affected white matter tracts. For the full cohort, SF was correlated with MCP-1 (r = -0.41), visceral adipose tissue (r = -0.25), and waist-to-height ratio (r = -0.27, all p's < 0.05); ST was correlated with MCP-1 (r = 0.31) and TNF-α (r = 0.29, all p's < 0.05); however, after adjusting for CAH status, almost all correlations were attenuated for significance.

CONCLUSIONS

Relationships among key brain structures, body composition, and inflammatory markers in pediatric patients with CAH could be largely driven by having CAH, with implications for obesity and neuroinflammation in this high-risk population.

Electroacupuncture stimulation ameliorates cognitive impairment induced by long-term high-fat diet by regulating microglial BDNF

Long-term high-fat diet (HFD) in adolescents leads to impaired hippocampal function and increases the risk of cognitive impairment. Studies have shown that HFD activates hippocampal microglia and induces hippocampal inflammation, which is an important factor for cognitive impairment. Electroacupuncture stimulation (ES), a nerve stimulation therapy, is anti-inflammatory. This study explored its therapeutic potential and mechanism of action in obesity-related cognitive impairment. 4-week-old C57 mice were given either normal or HFD for 22 weeks. At 19 weeks, some of the HFD mice were treated with ES and nigericin sodium salt. The cognitive behavior was assessed through Morris water maze test at 23 weeks. Western blotting was used to detect the expression levels of pro-inflammatory molecules IL-1β and IL-1R, synaptic plasticity related proteins synaptophysin and Postsynaptic Density-95 (PSD-95), and apoptotic molecules (Caspase-3 and Bcl-2), in the hippocampus. The number, morphology, and status of microglia, along with the brain-derived neurotrophic factor（BDNF） content, were analyzed using immunofluorescence. ES treatment improved cognitive deficits in HFD model mice, and decreased the expressions of microglial activation marker, CD68, and microglial BDNF. Inhibition of proinflammatory cytokine, IL-1β, and IL-1R promoted PSD-95 and synaptophysin expressions. Peripheral NLRP3 inflammasome agonist injections exacerbated the cognitive deficits in HFD mice and promoted the expressions of IL-1β and IL-1R in the hippocampus. The microglia showed obvious morphological damage and apoptosis. Collectively, our findings suggest that ES inhibits inflammation, regulates microglial BDNF, and causes remodeling of hippocampal function in mice to counteract obesity-like induced cognitive impairment. Overexcitation of peripheral inflammasome complexes induces hippocampal microglia apoptosis, which hinders the effects of ES.

Microglia/macrophage-specific deletion of TLR-4 protects against neural effects of diet-induced obesity

Obesity is associated with numerous adverse neural effects, including reduced neurogenesis, cognitive impairment, and increased risks for developing Alzheimer's disease (AD) and vascular dementia. Obesity is also characterized by chronic, low-grade inflammation that is implicated in mediating negative consequences body-wide. Toll-like receptor 4 (TLR4) signaling from peripheral macrophages is implicated as an essential regulator of the systemic inflammatory effects of obesity. In the brain, obesity drives chronic neuroinflammation that involves microglial activation, however the contributions of microglia-derived TLR4 signaling to the consequences of obesity are poorly understood. To investigate this issue, we first generated mice that carry an inducible, microglia/macrophage-specific deletion of TLR4 that yields long-term TLR4 knockout only in brain indicating microglial specificity. Next, we analyzed the effects of microglial TLR4 deletion on systemic and neural effects of a 16-week of exposure to control versus obesogenic high-fat diets. In male mice, TLR4 deletion generally yielded limited effects on diet-induced systemic metabolic dysfunction but significantly reduced neuroinflammation and impairments in neurogenesis and cognitive performance. In female mice maintained on obesogenic diet, TLR4 deletion partially protected against weight gain, adiposity, and metabolic impairments. Compared to males, females showed milder diet-induced neural consequences, against which TLR4 deletion was protective. Collectively, these findings demonstrate a central role of microglial TLR4 signaling in mediating the neural effects of obesogenic diet and highlight sexual dimorphic responses to both diet and TLR4.