Integrative analysis of physiological responses to high fat feeding with diffusion tensor images and neurochemical profiles of the mouse brain

Hypothalamic Inflammation Improves Through Bariatric Surgery, and Hypothalamic Volume Predicts Short-Term Weight Loss Response in Adults With or Without Type 2 Diabetes

OBJECTIVE

Preclinical research implicates hypothalamic inflammation (HI) in obesity and type 2 diabetes pathophysiology. However, their pathophysiological relevance and potential reversibility need to be better defined. We sought to evaluate the effect of bariatric surgery (BS) on radiological biomarkers of HI and the association between the severity of such radiological alterations and post-BS weight loss (WL) trajectories. The utility of cerebrospinal fluid large extracellular vesicles (CSF-lEVs) enriched for microglial and astrocyte markers in studying HI was also explored.

RESEARCH DESIGN AND METHODS

We included 72 individuals with obesity (20 with and 52 without type 2 diabetes) and 24 control individuals. Participants underwent lumbar puncture and 3-T MRI at baseline and 1-year post-BS. We assessed hypothalamic mean diffusivity (MD) (higher values indicate lesser microstructural integrity) and the volume of the whole and main hypothalamic subregions. CSF-lEVs enriched for glial and astrocyte markers were determined by flow cytometry.

RESULTS

Compared with control group, the obesity and type 2 diabetes groups showed a larger volume and higher MD in the hypothalamic tubular inferior region, the area encompassing the arcuate nucleus. These radiological alterations were positively associated with baseline anthropometric and metabolic measures and improved post-BS. A larger baseline tubular inferior hypothalamic volume was independently related to lesser WL 1 and 2 years after BS. CSF-lEVs did not differ among groups and were unrelated to WL trajectories.

CONCLUSIONS

These findings suggest HI improvement after BS and may support a role for HI in modulating the WL response to these interventions.

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.

High-fat diet feeding triggers a regenerative response in the adult zebrafish brain

Non-alcoholic fatty liver disease (NAFLD) includes a range of liver conditions ranging from excess fat accumulation to liver failure. NAFLD is strongly associated with high-fat diet (HFD) consumption that constitutes a metabolic risk factor. While HFD has been elucidated concerning its several systemic effects, there is little information about its influence on the brain at the molecular level. Here, by using a high-fat diet (HFD)-feeding of adult zebrafish, we first reveal that excess fat uptake results in weight gain and fatty liver. Prolonged exposure to HFD induces a significant increase in the expression of pro-inflammation, apoptosis, and proliferation markers in the liver and brain tissues. Immunofluorescence analyses of the brain tissues disclose stimulation of apoptosis and widespread activation of glial cell response. Moreover, glial activation is accompanied by an initial decrease in the number of neurons and their subsequent replacement in the olfactory bulb and the telencephalon. Long-term consumption of HFD causes activation of Wnt/β-catenin signaling in the brain tissues. Finally, fish fed an HFD induces anxiety, and aggressiveness and increases locomotor activity. Thus, HFD feeding leads to a non-traumatic brain injury and stimulates a regenerative response. The activation mechanisms of a regeneration response in the brain can be exploited to fight obesity and recover from non-traumatic injuries.

Magnetic resonance imaging to assess the brain response to fasting in glioblastoma-bearing rats as a model of cancer anorexia

BACKGROUND

Global energy balance is a vital process tightly regulated by the brain that frequently becomes dysregulated during the development of cancer. Glioblastoma (GBM) is one of the most investigated malignancies, but its appetite-related disorders, like anorexia/cachexia symptoms, remain poorly understood.

METHODS

We performed manganese enhanced magnetic resonance imaging (MEMRI) and subsequent diffusion tensor imaging (DTI), in adult male GBM-bearing (n = 13) or control Wistar rats (n = 12). A generalized linear model approach was used to assess the effects of fasting in different brain regions involved in the regulation of the global energy metabolism: cortex, hippocampus, hypothalamus and thalamus. The regions were selected on the contralateral side in tumor-bearing animals, and on the left hemisphere in control rats. An additional DTI-only experiment was completed in two additional GBM (n = 5) or healthy cohorts (n = 6) to assess the effects of manganese infusion on diffusion measurements.

RESULTS

MEMRI results showed lower T₁ values in the cortex (p-value < 0.001) and thalamus (p-value < 0.05) of the fed ad libitum GBM animals, as compared to the control cohort, consistent with increased Mn²⁺ accumulation. No MEMRI-detectable differences were reported between fed or fasting rats, either in control or in the GBM group. In the MnCl₂-infused cohorts, DTI studies showed no mean diffusivity (MD) variations from the fed to the fasted state in any animal cohort. However, the DTI-only set of acquisitions yielded remarkably decreased MD values after fasting only in the healthy control rats (p-value < 0.001), and in all regions, but thalamus, of GBM compared to control animals in the fed state (p-value < 0.01). Fractional anisotropy (FA) decreased in tumor-bearing rats due to the infiltrate nature of the tumor, which was detected in both diffusion sets, with (p-value < 0.01) and without Mn²⁺ administration (p-value < 0.001).

CONCLUSIONS

Our results revealed that an altered physiological brain response to fasting occurred in hunger related regions in GBM animals, detectable with DTI, but not with MEMRI acquisitions. Furthermore, the present results showed that Mn²⁺ induces neurotoxic inflammation, which interferes with diffusion MRI to detect appetite-induced responses through MD changes.

High-resolution magic angle spinning NMR for intact biological specimen analysis: Initial discovery, recent developments, and future directions

High-resolution magic angle spinning (HRMAS) NMR, an approach for intact biological material analysis discovered more than 25 years ago, has been advanced by many technical developments and applied to many biomedical uses. This article provides a history of its discovery, first by explaining the key scientific advances that paved the way for HRMAS NMR's invention, and then by turning to recent developments that have profited from applying and advancing the technique during the last 5 years. Developments aimed at directly impacting healthcare include HRMAS NMR metabolomics applications within studies of human disease states such as cancers, brain diseases, metabolic diseases, transplantation medicine, and adiposity. Here, the discussion describes recent HRMAS NMR metabolomics studies of breast cancer and prostate cancer, as well as of matching tissues with biofluids, multimodality studies, and mechanistic investigations, all conducted to better understand disease metabolic characteristics for diagnosis, opportune windows for treatment, and prognostication. In addition, HRMAS NMR metabolomics studies of plants, foods, and cell structures, along with longitudinal cell studies, are reviewed and discussed. Finally, inspired by the technique's history of discoveries and recent successes, future biomedical arenas that stand to benefit from HRMAS NMR-initiated scientific investigations are presented.

Short-term high-fat diet alters the mouse brain magnetic resonance imaging parameters consistently with neuroinflammation on males and metabolic rearrangements on females. A pre-clinical study with an optimized selection of linear mixed-effects models

Introduction

High-fat diet (HFD) consumption is known to trigger an inflammatory response in the brain that prompts the dysregulation of energy balance, leads to insulin and leptin resistance, and ultimately obesity. Obesity, at the same, has been related to cerebral magnetic resonance imaging (MRI) alterations, but the onset of HFD-induced neuroinflammation, however, has been principally reported on male rodents and by ex vivo methods, with the effects on females and the origin of MRI changes remaining unassessed.

Methods

We characterized the onset and evolution of obesity on male and female mice during standard or HFD administration by physiological markers and multiparametric MRI on four cerebral regions involved in appetite regulation and energy homeostasis. We investigated the effects of diet, time under diet, brain region and sex by identifying their significant contributions to sequential linear mixed-effects models, and obtained their regional neurochemical profiles by high-resolution magic angle spinning spectroscopy.

Results

Male mice developed an obese phenotype paralleled by fast increases in magnetization transfer ratio values, while females delayed the obesity progress and showed no MRI-signs of cerebral inflammation, but larger metabolic rearrangements on the neurochemical profile.

Discussion

Our study reveals early MRI-detectable changes compatible with the development of HFD-induced cerebral cytotoxic inflammation on males but suggest the existence of compensatory metabolic adaptations on females that preclude the corresponding detection of MRI alterations.

Obesity-Related Neuroinflammation: Magnetic Resonance and Microscopy Imaging of the Brain

Obesity is a major risk factor of Alzheimer's disease and related dementias. The principal feature of dementia is a loss of neurons and brain atrophy. The mechanistic links between obesity and the neurodegenerative processes of dementias are not fully understood, but recent research suggests that obesity-related systemic inflammation and subsequent neuroinflammation may be involved. Adipose tissues release multiple proinflammatory molecules (fatty acids and cytokines) that impact blood and vessel cells, inducing low-grade systemic inflammation that can transition to tissues, including the brain. Inflammation in the brain-neuroinflammation-is one of key elements of the pathobiology of neurodegenerative disorders; it is characterized by the activation of microglia, the resident immune cells in the brain, and by the structural and functional changes of other cells forming the brain parenchyma, including neurons. Such cellular changes have been shown in animal models with direct methods, such as confocal microscopy. In humans, cellular changes are less tangible, as only indirect methods such as magnetic resonance (MR) imaging are usually used. In these studies, obesity and low-grade systemic inflammation have been associated with lower volumes of the cerebral gray matter, cortex, and hippocampus, as well as altered tissue MR properties (suggesting microstructural variations in cellular and molecular composition). How these structural variations in the human brain observed using MR imaging relate to the cellular variations in the animal brain seen with microscopy is not well understood. This review describes the current understanding of neuroinflammation in the context of obesity-induced systemic inflammation, and it highlights need for the bridge between animal microscopy and human MR imaging studies.

Dual-model wearable photoacoustic microscopy and electroencephalograph: study of neurovascular coupling in anesthetized and freely moving rats

Observing microscale neurovascular dynamics under different physiological conditions is of great importance to understanding brain functions and disorders. Here, we report a dual-model wearable device and an auxiliary data processing algorithm to derive neurovascular dynamics. The device integrates high-resolution photoacoustic microscopy and electroencephalography (EEG), which allows observing capillary-level hemodynamics and neural activities in anesthesia and freely moving rats. By using the developed algorithm, multiple photoacoustic/EEG parameters extracted and correlated enables investigation of the interplay between neural and vascular activities. We employed this platform to study the neurovascular coupling during different types of seizures in rats under various physiological conditions. We observed cerebral vascular vasodilation/constriction corresponding well to the seizure on/off in rats under regular anesthesia conditions, showing a strong neurovascular coupling coefficient. In rats under weak anesthesia and freely moving conditions, more intense cerebral hemodynamics and neural activities occurred with a weaker neurovascular coupling coefficient. The comprehensively quantitative analyses suggest that anesthesia has a dominant impact on the seizure onset and affect the neurovascular coupling correlation in the current drug-induced localized seizure model. Our study reveals that the designed platform has the potential to support studies on brain functions and disorders in diseased rodent models in various physiological states.