Altered hypothalamic function in response to glucose ingestion in obese humans

Prolonged latency of the gustatory evoked potentials for sucrose solution in subjects living with obesity compared with normal-weight subjects

OBJECTIVES

A difference in cortical treatment of taste information could alter food intake promoting the development of obesity. The main purpose was to compare, in subjects living with obesity (OB) and normal-weight subjects (NW), the characteristics of gustatory evoked potentials (GEP) for sucrose solution (10 g.100 mL-1) before and after a standard lunch. The secondary objective was to evaluate the correlations between GEP and the plasmatic levels of acylated ghrelin, leptin, insulin and serotonin.

METHODS

Each subject had 2 randomized sessions spaced by an interval of 2 days. During one session, subjects were fasting and during the other, subjects took a lunch low in sugar. In each session, subjects had a blood test before a first GEP recording followed by a second GEP recording either after a lunch (feeding session) or no lunch (fasting session).

RESULTS

Twenty-eight OB (BMI: 38.6 ± 9.0 kg.m-2) were matched to 22 NW (BMI: 22.3 ± 2.2 kg.m-2). GEP latencies were prolonged in OB regardless the sessions and the time before and after lunch, compared with NW (in Cz at the morning: 170 ± 33 ms vs 138 ± 25 ms respectively; p < 0.001). The increase in latency observed in NW after lunch was not observed in OB. Negative or positive correlations were noted in all participants between GEP latencies and ghrelin, leptin, insulin plasmatic levels (P1Cz, r = -0.38, r = 0.33, r = 0.37 respectively, p < 0.0001).

CONCLUSIONS

This study highlights a slower activation in the taste cortex in OB compared with NW.

Low-calorie diet-induced weight loss is associated with altered brain connectivity and food desire in obesity

OBJECTIVE

The main objective of this study is to better understand the effects of diet-induced weight loss on brain connectivity in response to changes in glucose levels in individuals with obesity.

METHODS

A total of 25 individuals with obesity, among whom 9 had a diagnosis of type 2 diabetes, underwent functional magnetic resonance imaging (fMRI) scans before and after an 8-week low-calorie diet. We used a two-step hypereuglycemia clamp approach to mimic the changes in glucose levels observed in the postprandial period in combination with task-mediated fMRI intrinsic connectivity distribution (ICD) analysis.

RESULTS

After the diet, participants lost an average of 3.3% body weight. Diet-induced weight loss led to a decrease in leptin levels, an increase in hunger and food intake, and greater brain connectivity in the parahippocampus, right hippocampus, and temporal cortex (limbic-temporal network). Group differences (with vs. without type 2 diabetes) were noted in several brain networks. Connectivity in the limbic-temporal and frontal-parietal brain clusters inversely correlated with hunger.

CONCLUSIONS

A short-term low-calorie diet led to a multifaceted body response in patients with obesity, with an increase in connectivity in the limbic-temporal network (emotion and memory) and hormone and eating behavior changes that may be important for recovering the weight lost.

Environmental enrichment accentuates glucose-induced feeding suppression and glial cell line-derived neurotrophic factor gene expression in the hypothalamus of mice

The hypothalamus controls food intake by integrating nutrient signals, of which one of the most important is glucose. Consequently, impairments in hypothalamic glucose-sensing mechanisms are associated with hyperphagia and obesity. Environmental enrichment (EE) is an animal housing protocol that provides complex sensory, motor, and social stimulations and has been proven to reduce adiposity in laboratory mice. However, the mechanism by which EE promotes adiposity-suppressing effect remains incompletely understood. Neurotrophic factors play an important role in the development and maintenance of the nervous system, but they are also involved in the hypothalamic regulation of feeding. Brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) are expressed in the hypothalamus and their expression is stimulated by glucose. EE is associated with increased expression of Bdnf mRNA in the hypothalamus. Therefore, we hypothesized that EE potentiates the anorectic action of glucose by altering the expression of neurotrophic factor genes in the hypothalamus. Male C57BL/6 mice were maintained under standard or EE conditions to investigate the feeding response to glucose and the associated expression of feeding-related neurotrophic factor genes in the hypothalamus. Intraperitoneal glucose injection reduced food intake in both control and EE mice with a significantly greater reduction in the EE group compared to the control group. EE caused a significantly enhanced response of Gdnf mRNA expression to glucose without altering basal Gdnf mRNA expression and Bdnf mRNA response to glucose. These findings suggest that EE enhances glucose-induced feeding suppression, at least partly, by enhancing hypothalamic glucose-sensing ability that involves GDNF.

Glucose-sensitive hypothalamic nuclei traced through functional magnetic resonance imaging

Introduction

Hypothalamic glucose-sensitive neural circuits, which regulate energy metabolism and can contribute to diseases such as obesity and type 2 diabetes, have been difficult to study in humans. We developed an approach to assess hypothalamic functional connectivity changes during glucose loading using functional magnetic resonance imaging (fMRI).

Methods

To do so, we conducted oral glucose tolerance tests while acquiring functional images before, and 10 and 45 min after glucose ingestion in a healthy male and cross-sectionally in 20 healthy participants on two different diets.

Results

At group level, 39 fMRI sessions were not sufficient to detect glucose-mediated connectivity changes. However, 10 repeated sessions in a single subject revealed significant intrinsic functional connectivity increases 45 min after glucose intake in the arcuate, paraventricular, and dorsomedial nuclei, as well as in the posterior hypothalamic area, median eminence, and mammillary bodies.

Discussion

Our methodology allowed to outline glucose-sensitive hypothalamic pathways in a single human being and holds promise in delineating individual pathophysiology mechanisms in patients with dysglycemia.

Sweet taste preference is associated with greater hypothalamic response to glucose and longitudinal weight gain

The hypothalamus has an abundant expression of sweet taste receptors that play a role in glucose sensing and energy homeostasis. Evidence suggests that liking "sweets" can be associated with weight gain, but the relationship between sweet taste preference and hypothalamic regulation of appetite is unknown. This study tested the hypothesis that sweet taste preference is associated with increased hypothalamic activation in response to glucose (a purported neural marker for weight gain risk) and greater longitudinal increases in body mass index (BMI). Fifty-four adults aged 18-35 years with a mean (± SD) BMI of 27.99 ± 5.32 kg/m2 completed the study. Height and weight were measured at baseline and 6-12 months later in a subset of 36 participants. Sweet taste preference was assessed via the Monell 2-series, forced-choice tracking procedure. Arterial spin labeling magnetic resonance imaging was performed before and after oral glucose ingestion to determine hypothalamic blood flow response to glucose. Linear models were used to examine relationships between sweet taste preference and the hypothalamic response to glucose and longitudinal changes in BMI, adjusting for age, sex, and baseline BMI. Sweet taste preference was positively associated with glucose-linked hypothalamic blood flow (beta = 0.017, p = 0.043), adjusted for age, sex and BMI. We also observed a positive association between sweet taste preference and longitudinal change in BMI (beta = 0.088, p = 0.015), adjusted for age, sex and baseline BMI. These findings suggest that heightened sweet taste preference is associated with glucose-linked hypothalamic activation and may be linked to increased susceptibility for weight gain.

Control of energy homeostasis by the lateral hypothalamic area

The lateral hypothalamic area (LHA) is a subcortical brain region that exerts control over motivated behavior, feeding, and energy balance across species. Recent single-cell sequencing studies have defined at least 30 distinct LHA neuron types. Some of these influence specific aspects of energy homeostasis; however, the functions of many LHA cell types remain unclear. This review addresses the rapidly emerging evidence from cell-type-specific investigations that the LHA leverages distinct neuron populations to regulate energy balance through complex connections with other brain regions. It will highlight recent findings demonstrating that LHA control of energy balance extends beyond mere food intake and propose outstanding questions to be addressed by future research.

Eating-induced seizures: A semiological sign of the right temporal pole

OBJECTIVE

Eating-induced seizures (EIS) are a rare form of reflex seizures. The objective of this study was to report a series of cases of EIS involving patients admitted to our epilepsy unit, and to analyze the clinical characteristics, etiology, and treatment response of this type of infrequent seizure.

METHODS

We performed a single-center retrospective analysis of all consecutive patients diagnosed with epilepsy with eating-induced seizures between 2008 and 2020.

RESULTS

We included eight patients (six women) with mean age 54.75 years (range: 40-79), and mean age at epilepsy onset 30.75 years (range: 9-58 years). EIS were triggered during a meal in 5/8 (at dinner 1/8, at breakfast in 1/8, and without time preference in 3/8), by a certain flavor in 1/8, by eating different textures or drinking soft drinks in 1/8, and by slicing food in 1/8. All patients suffered nonreflex seizures and 3/8 other types of reflex seizures. In 6/8 of patients, EIS originated in the right hemisphere. In 5/8, the EIS progressed to impaired awareness with oromandibular automatisms. In 6/8, the epilepsy was drug-resistant. Temporopolar encephalocele was the most frequent etiology, in 4/8. Three of the eight underwent surgical treatment, with Engel IA 1 year in 3/3. Three of the eight were treated with vagal stimulation therapy, with McHugh A 1 year in 2/3.

SIGNIFICANCE

In our series, eating-induced seizures were observed in patients with focal epilepsy. It was frequently drug-resistant and started predominantly in the right hemisphere, due to temporal pole involvement in half of the patients.

Hypothalamic volume is associated with body mass index

The hypothalamus is an important neuroendocrine hub for the control of appetite and satiety. In animal studies it has been established that hypothalamic lesioning or stimulation causes alteration to feeding behaviour and consequently body mass, and exposure to high calorie diets induces hypothalamic inflammation. These findings suggest that alterations in hypothalamic structure and function are both a cause and a consequence of changes to food intake. However, there is limited in vivo human data relating the hypothalamus to obesity or eating disorders, in part due to technical problems relating to its small size. Here, we used a novel automated segmentation algorithm to exploratorily investigate the relationship between hypothalamic volume, normalised to intracranial volume, and body mass index (BMI). The analysis was applied across four independent datasets comprising of young adults (total n = 1,351 participants) spanning a range of BMIs (13.3 - 47.8 kg/m2). We compared underweight (including individuals with anorexia nervosa), healthy weight, overweight and obese individuals in a series of complementary analyses. We report that overall hypothalamic volume is significantly larger in overweight and obese groups of young adults. This was also observed for a number of hypothalamic sub-regions. In the largest dataset (the HCP-Young Adult dataset (n = 1111)) there was a significant relationship between hypothalamic volume and BMI. We suggest that our findings of a positive relationship between hypothalamic volume and BMI is potentially consistent with hypothalamic inflammation as seen in animal models in response to high fat diet, although more research is needed to establish a causal relationship. Overall, we present novel, in vivo findings that link elevated BMI to altered hypothalamic structure. This has important implications for study of the neural mechanisms of obesity in humans.

Hypothalamic Reactivity and Connectivity following Intravenous Glucose Administration

Dysfunctional glucose sensing in homeostatic brain regions such as the hypothalamus is interlinked with the pathogenesis of obesity and type 2 diabetes mellitus. However, the physiology and pathophysiology of glucose sensing and neuronal homeostatic regulation remain insufficiently understood. To provide a better understanding of glucose signaling to the brain, we assessed the responsivity of the hypothalamus (i.e., the core region of homeostatic control) and its interaction with mesocorticolimbic brain regions in 31 normal-weight, healthy participants. We employed a single-blind, randomized, crossover design of the intravenous infusion of glucose and saline during fMRI. This approach allows to investigate glucose signaling independent of digestive processes. Hypothalamic reactivity and connectivity were assessed using a pseudo-pharmacological design and a glycemia-dependent functional connectivity analysis, respectively. In line with previous studies, we observed a hypothalamic response to glucose infusion which was negatively related to fasting insulin levels. The observed effect size was smaller than in previous studies employing oral or intragastric administration of glucose, demonstrating the important role of the digestive process in homeostatic signaling. Finally, we were able to observe hypothalamic connectivity with reward-related brain regions. Given the small amount of glucose employed, this points toward a high responsiveness of these regions to even a small energy stimulus in healthy individuals. Our study highlights the intricate relationship between homeostatic and reward-related systems and their pronounced sensitivity to subtle changes in glycemia.

Acute inorganic nitrate intake increases regional insulin action in the brain: Results of a double-blind, randomized, controlled cross-over trial with abdominally obese men

AIMS

Improving brain insulin sensitivity may be a promising approach in the prevention and treatment of metabolic and cognitive diseases. Our aim was to investigate acute effects of inorganic nitrate on regional cerebral blood flow (CBF) responses to intranasal insulin in abdominally obese men.

METHODS

Eighteen apparently healthy men, aged 18-60 years and with a waist circumference ≥ 102 cm, participated in a randomized, double-blind, placebo-controlled cross-over trial. The study consisted of two test days separated by at least one week. Men received in random order a drink providing 10 mmol (i.e., 625 mg nitrate) potassium nitrate or an isomolar placebo drink with potassium chloride. Brain insulin action was assessed 120-150 min after the drinks by quantifying acute effects of nasal insulin on regional CBF using arterial spin labeling Magnetic Resonance Imaging. Glucose and insulin concentrations were measured at regular intervals, while blood pressure was determined fasted and at 240 min.

RESULTS

Inorganic nitrate intake increased regional insulin action in five brain clusters. The two largest clusters were located in the right temporal lobe (ΔCBF: 7.0 ± 3.8 mL/100 g/min, volume: 5296 mm³, P < 0.001; and ΔCBF: 6.5 ± 4.3 mL/100 g/min, volume: 3592 mm³, P < 0.001), while two other cortical clusters were part of the right frontal (ΔCBF: 9.0 ± 6.0 mL/100 g/min, volume: 1096 mm³, P = 0.007) and the left parietal lobe (ΔCBF: 6.1 ± 4.3 mL/100 g/min, volume: 1024 mm³, P = 0.012). One subcortical cluster was located in the striatum (ΔCBF: 5.9 ± 3.2 mL/100 g/min, volume: 1792 mm³, P < 0.001). No effects of nitrate were observed on CBF before administration. Following nitrate intake, circulating nitrate plus nitrite concentrations increased over time (P = 0.003), but insulin and glucose concentrations and blood pressure did not change.

CONCLUSION

Acute inorganic nitrate intake may improve regional brain insulin action in abdominally obese men. These regions are involved in the regulation of different metabolic and cognitive processes. The trial was registered on January 6th, 2021 at ClinicalTrials.gov as NCT04700241.

Brain effect of bariatric surgery in people with obesity

BACKGROUND/OBJECTIVES

The link between obesity and brain function is a fascinating but still an enigmatic topic. We evaluated the effect of Roux-en-Y gastric bypass (RYGB) on peripheral glucose metabolism, insulin sensitivity, brain glucose utilization and cognitive abilities in people with obesity.

SUBJECTS/METHODS

Thirteen subjects with obesity (F/M 11/2; age 44.4 ± 9.8 years; BMI 46.1 ± 4.9 kg/m²) underwent 75-g OGTT during a [18F]FDG dynamic brain PET/CT study at baseline and 6 months after RYGB. At the same timepoints, cognitive performance was tested with Mini Mental State Examination (MMSE), Montreal Cognitive Assessment (MoCA), Trail making test (TMT) and Token test (TT). Glucose, insulin, C-peptide, GLP-1, GIP, and VIP levels were measured during OGTT. Leptin and BDNF levels were measured before glucose ingestion.

RESULTS

RYGB resulted in significant weight loss (from 46.1 ± 4.9 to 35.3 ± 5.0 kg/m²; p < 0.01 vs baseline). Insulin sensitivity improved (disposition index: from 1.1 ± 0.2 to 2.9 ± 1.1; p = 0.02) and cerebral glucose metabolic rate (CMRg) declined in various brain areas (all p ≤ 0.01). MMSE and MoCA score significantly improved (p = 0.001 and p = 0.002, respectively). TMT and TT scores showed a slight improvement. A positive correlation was found between CMRg change and HOMA-IR change in the caudate nucleus (ρ = 0.65, p = 0.01). Fasting leptin decreased (from 80.4 ± 13.0 to 16.1 ± 2.4 ng/dl; p = 0.001) and correlated with CMRg change in the hippocampus (ρ = 0.50; p = 0.008). CMRg change was correlated with cognitive scores changes on the TMT and TT (all p = 0.04 or less).

CONCLUSIONS

Bariatric surgery improves CMRg directly related to a better cognitive testing result. This study highlights the potential pleiotropic effects of bariatric surgery.

TRIAL REGISTRY NUMBER

NCT03414333.

FGF21 response to sucrose is associated with BMI and dorsal striatal signaling in humans

OBJECTIVE

This study examined associations between BMI and dietary sugar intake with sucrose-induced fibroblast growth factor 21 (FGF21) and whether circulating FGF21 is associated with brain signaling following sucrose ingestion in humans.

METHODS

A total of 68 adults (29 male; mean [SD), age 23.2 [3.8] years; BMI 27.1 [4.9] kg/m² ) attended visits after a 12-hour fast. Plasma FGF21 was measured at baseline and at 15, 30, and 120 minutes after sucrose ingestion (75 g in 300 mL of water). Brain cerebral blood flow responses to sucrose were measured using arterial spin labeling magnetic resonance imaging.

RESULTS

Higher circulating FGF21 levels were associated with reduced blood flow in the striatum in response to sucrose (β = -7.63, p = 0.03). This association was greatest among persons with healthy weight (β = -15.70, p = 0.007) and was attenuated in people with overweight (β = -4.00, p = 0.63) and obesity (β = -12.45, p = 0.13). BMI was positively associated with FGF21 levels in response to sucrose (β = 0.53, p = 0.02). High versus low dietary sugar intake was associated with greater FGF21 responses to acute sucrose ingestion in individuals with healthy weight (β = 8.51, p = 0.04) but not in individuals with overweight or obesity (p > 0.05).

CONCLUSIONS

These correlative findings support evidence in animals showing that FGF21 acts on the brain to regulate sugar consumption through a negative feedback loop.

Integrative Hedonic and Homeostatic Food Intake Regulation by the Central Nervous System: Insights from Neuroimaging

Food intake regulation in humans is a complex process controlled by the dynamic interaction of homeostatic and hedonic systems. Homeostatic regulation is controlled by appetitive signals from the gut, adipose tissue, and the vagus nerve, while conscious and unconscious reward processes orchestrate hedonic regulation. On the one hand, sight, smell, taste, and texture perception deliver potent food-related feedback to the central nervous system (CNS) and influence brain areas related to food reward. On the other hand, macronutrient composition stimulates the release of appetite signals from the gut, which are translated in the CNS into unconscious reward processes. This multi-level regulation process of food intake shapes and regulates human ingestive behavior. Identifying the interface between hormones, neurotransmitters, and brain areas is critical to advance our understanding of conditions like obesity and develop better therapeutical interventions. Neuroimaging studies allow us to take a glance into the central nervous system (CNS) while these processes take place. This review focuses on the available neuroimaging evidence to describe this interaction between the homeostatic and hedonic components in human food intake regulation.

The timeline of neuronal and glial alterations in experimental obesity

In experimental models, hypothalamic dysfunction is a key component of the pathophysiology of diet-induced obesity. Early after the introduction of a high-fat diet, neurons, microglia, astrocytes and tanycytes of the mediobasal hypothalamus undergo structural and functional changes that impact caloric intake, energy expenditure and systemic glucose tolerance. Inflammation has emerged as a central component of this response, and as in other inflammatory conditions, there is a time course of events that determine the fate of distinct cells involved in the central regulation of whole-body energy homeostasis. Here, we review the work that identified key mechanisms, cellular players and temporal features of diet-induced hypothalamic abnormalities.

The Role of the Human Hypothalamus in Food Intake Networks: An MRI Perspective

Hypothalamus (HT), this small structure often perceived through the prism of neuroimaging as morphologically and functionally homogeneous, plays a key role in the primitive act of feeding. The current paper aims at reviewing the contribution of magnetic resonance imaging (MRI) in the study of the role of the HT in food intake regulation. It focuses on the different MRI techniques that have been used to describe structurally and functionally the Human HT. The latest advances in HT parcellation as well as perspectives in this field are presented. The value of MRI in the study of eating disorders such as anorexia nervosa (AN) and obesity are also highlighted.

Brain responses to glucose ingestion are greater in children than adults and are associated with overweight and obesity

OBJECTIVE

This study investigated whether brain regions involved in the regulation of food intake respond differently to glucose ingestion in children and adults and the relationship between brain responses and weight status.

METHODS

Data included 87 children (ages 7-11 years) and 94 adults (ages 18-35 years) from two cohorts. Healthy weight, overweight, and obesity were defined by Centers for Disease Control and Prevention criteria. Brain responses to glucose were determined by measuring cerebral blood flow using arterial spin labeling magnetic resonance imaging in brain regions involved in the regulation of eating behavior.

RESULTS

Children showed significantly larger increases in brain responses to glucose than adults in the dorsal striatum (p < 0.01), insula (p < 0.01), hippocampus (p < 0.01), and dorsal-lateral prefrontal cortex (p < 0.01). Responses to glucose in the dorsal striatum (odds ratio [OR] = 1.52, 95% CI 1.05-2.20; p = 0.03), hippocampus (OR = 1.51, 95% CI: 1.02-2.22; p = 0.04), insula (OR = 1.64, 95% CI: 1.11-2.42; p = 0.01), and orbitofrontal cortex (OR = 1.63 95% CI: 1.12-2.39; p = 0.01) were positively associated with overweight or obesity, independent of age group.

CONCLUSIONS

Children have greater brain responses to glucose ingestion than adults in regions involved in eating behavior, and these responses are associated with weight status.

Behavioral outputs of negative symptom domains of schizophrenia

The present study aimed to validate the hypothesis that negative symptoms of schizophrenia encompass two domains, namely avolition-apathy (AA) and diminished expression (DE), and to investigate the relationship of these domains with behavioral outputs which imply hedonic activities: Cigarette use and weight gain. A total of 106 consecutive schizophrenia outpatients with primary negative symptoms were evaluated using the Positive and Negative Syndrome Scale (PANSS), the Negative Symptoms Assessment Scale (NSA-16), the Calgary Depression Scale for Schizophrenia (CDSS), and the Simpson-Angus Scale (SAS). A semi-structured interview was used to assess demographic features, the number of cigarettes smoked per day, and body mass index. Data were analyzed using descriptive statistics, principal component analysis, analysis of variance, and covariance. A two-factor solution was revealed for the negative symptoms of schizophrenia represented by AA and DE. Analyses of variance and covariance suggested that higher AA scores were associated with normal weight and non-smoking status. No significant differences were revealed regarding DE scores in relationship with the same behavioral hedonic outputs. The present results indicated the AA and DE domains exhibit meaningful differences concerning the outcome, which may imply the need for different approaches regarding rating and treatment.

Hypothalamic functional MRI activity in the initiation phase of spontaneous and glyceryl trinitrate-induced migraine attacks

The hypothalamus has been suggested to be important in the initiation cascade of migraine attacks based on clinical and biochemical observations. Previous imaging studies could not disentangle the changes due to the attack and those due to the trigger compound. With a novel approach, we assessed hypothalamic neuronal activity in early premonitory phases of glyceryl‐trinitrate (GTN)‐induced and spontaneous migraine attacks. We measured the hypothalamic blood oxygen level‐dependent (BOLD) response to oral glucose ingestion with 3T‐functional magnetic resonance imaging (MRI) in 27 women, 16 with migraine without aura and 11 controls group matched for age and body mass index (BMI), on 1 day without prior GTN administration and on a second day after GTN administration (to coincide with the premonitory phase of an induced attack). Interestingly, subgroups of patients with and without GTN‐triggered attacks could be compared. Additionally, five migraineurs were investigated in a spontaneous premonitory phase. Linear mixed models were used to study between‐ and within‐group effects. Without prior GTN infusion, the BOLD response to glucose was similar in migraine participants and controls (P = .41). After prior GTN infusion, recovery occurred steeper and faster in migraineurs (versus Day 1; P < .0001) and in those who developed an attack versus those who did not (P < .0001). Prior GTN infusion did not alter the glucose‐induced response in controls (versus baseline; P = .71). Just before spontaneous attacks, the BOLD‐response recovery was also faster (P < .0001). In this study, we found new and direct evidence of altered hypothalamic neuronal function in the immediate preclinical phase of both GTN‐provoked and spontaneous migraine attacks.

Bariatric surgery restores visual cortical plasticity in nondiabetic subjects with obesity

BACKGROUND/OBJECTIVES

Obesity leads to changes in synaptic plasticity. We aimed at investigating the impact of bariatric surgery (RYGB) on visual neural plasticity (NP) and its relationship with the main gut peptides, leptin, and brain-derived neurotrophic factor (BDNF).

SUBJECTS/METHODS

NP was assessed testing binocular rivalry before and after 2 h of monocular deprivation (index of visual brain plasticity) in 15 subjects with obesity (age 42.3 ± 9.8 years; BMI 46.1 ± 4.9 kg/m²) before and after RYGB. Gut peptides, leptin, and BDNF were obtained at baseline and 6 months after surgery in 13 subjects.

RESULTS

A significant reduction in BMI (p < 0.001 vs. baseline) and a significant increase of disposition index (DI, p = 0.02 vs baseline) were observed after RYGB. Total and active GLP-1 release in response to glucose ingestion significantly increased after RYGB, while no changes occurred in VIP, GIP, and BDNF levels. Fasting leptin concentration was lower after RYGB (p = 0.001 vs. baseline). Following RYGB, NP was progressively restored (p < 0.002). NP was correlated with DI and fasting glucose at baseline (r = 0.75, p = 0.01; r = -0.7, p = 0.02; respectively), but not with BMI. A positive correlation between post-pre-RYGB changes in AUC_{active GLP-1} and NP was observed (r = 0.70, p < 0.01). Leptin was inversely correlated with NP 6 months after surgery (r = -0.63, p = 0.02). No correlation was observed between GIP, VIP, BDNF, and NP.

CONCLUSIONS

Visual plasticity is altered in subjects with obesity, and it can be restored after RYGB. The improvement may be mediated by amelioration of insulin sensitivity, increased GLP-1 levels, and reduced leptin levels.

Associations Between Exposure to Gestational Diabetes Mellitus In Utero and Daily Energy Intake, Brain Responses to Food Cues, and Adiposity in Children

OBJECTIVE

Children exposed to gestational diabetes mellitus (GDM) or maternal obesity in utero have an increased propensity to develop obesity. Little is known about the mechanisms underlying this phenomenon. We aimed to examine relationships between exposure to GDM or maternal obesity and daily energy intake (EI), brain responses to food cues within reward regions, and adiposity in children.

RESEARCH DESIGN AND METHODS

Participants were 159 children ages 7-11 years. Repeated 24-h recalls were conducted to assess mean daily EI. A subset of children (n = 102) completed a food cue task in the MRI scanner. A priori regions of interest included the orbital frontal cortex (OFC), insula, amygdala, ventral striatum, and dorsal striatum. Adiposity measurements, BMI z-scores, percent body fat, waist-to-height ratio (WtHR), and waist-to-hip ratio (WHR) were assessed.

RESULTS

Exposure to GDM was associated with greater daily EI, and children exposed to GDM diagnosed before 26 weeks gestation had greater OFC food cue reactivity. Children exposed to GDM also had larger WHR. Results remained significant after adjusting for child's age and sex, maternal education and race/ethnicity, maternal prepregnancy BMI, and child's physical activity levels. Furthermore, children who consumed more daily calories had greater WHR, and the relationship between GDM exposure and WHR was attenuated after adjustment for daily EI. Prepregnancy BMI was not significantly related to daily EI or food cue reactivity in reward regions. However, prepregnancy BMI was significantly related to all adiposity measurements; results remained significant for BMI z-scores, WtHR, and WHR after controlling for child's age and sex, maternal education and race/ethnicity, maternal GDM exposure, and child's physical activity levels.

CONCLUSIONS

Exposure to GDM in utero, in particular before 26 weeks gestation, is associated with increased EI, enhanced OFC food cue reactivity, and increased WHR. Future study with longitudinal follow-up is merited to assess potential pathways of daily EI and food cue reactivity in reward regions on the associations between GDM exposure and childhood adiposity.

Neuroimaging of hypothalamic mechanisms related to glucose metabolism in anorexia nervosa and obesity

BACKGROUNDGiven the heightened tolerance to self-starvation in anorexia nervosa (AN), a hypothalamic dysregulation of energy and glucose homeostasis has been hypothesized. Therefore, we investigated whether hypothalamic reactivity to glucose metabolism is impaired in AN.METHODSTwenty-four participants with AN, 28 normal-weight participants, and 24 healthy participants with obesity underwent 2 MRI sessions in a single-blind, randomized, case-controlled crossover study. We used an intragastric infusion of glucose and water to bypass the cephalic phase of food intake. The responsivity of the hypothalamus and the crosstalk of the hypothalamus with reward-related brain regions were investigated using high-resolution MRI.RESULTSNormal-weight control participants displayed the expected glucose-induced deactivation of hypothalamic activation, whereas patients with AN and participants with obesity showed blunted hypothalamic reactivity. Furthermore, patients with AN displayed blunted reactivity in the nucleus accumbens and amygdala. Compared with the normal-weight participants and control participants with obesity, the patients with AN failed to show functional connectivity between the hypothalamus and the reward-related brain regions during water infusion relative to glucose infusion. Finally, the patients with AN displayed typical baseline levels of peripheral appetite hormones during a negative energy balance.CONCLUSIONThese results indicate that blunted hypothalamic glucose reactivity might be related to the pathophysiology of AN. This study provides insights for future research, as it is an extended perspective of the traditional primary nonhomeostatic understanding of the disease.FUNDINGThis study was supported by a grant from the DFG (SI 2087/2-1).

Resting-state functional connectivity of the human hypothalamus

Communication pathways of the hypothalamus with other brain regions and the periphery are critical to successfully control key physiological and psychological processes. With advanced functional magnetic resonance imaging (fMRI) techniques, it is possible to target hypothalamic function and infer discrete hypothalamus networks. Resting-state functional connectivity (RSFC) is a promising tool to study the functional organization of the brain and may act as a marker of individual differences and dysfunctions. Based on recent fMRI findings, the hypothalamus is mostly connected to parts of the striatum, midbrain, thalamus, insula, frontal, cingulate, and temporal cortices and the cerebellum. There is a strong interplay of the hypothalamus with these regions in response to different metabolic, hormonal, and nutritional states. In a state of hunger, hypothalamus RSFC increases with a strong shift to reward-related brain regions, especially in person with excessive weight. Nutrient signals and hormones, as insulin, act on these same connections conveying reward and internal signals to regulate homeostatic control. Moreover, dysfunctional hypothalamus communication has been documented in persons with neurological and psychiatric diseases. The results implicate that patients with depression, epilepsy, and neurodegenerative diseases show mostly a reduction in hypothalamus RSFC, whereas patients with migraine and headache display predominantly increased hypothalamus RSFC. The extent of these changes and regions affected depend on the disorder and symptom severity. Whether hypothalamus RSFC can serve as a marker for disease states or is a prodromal neurobiological feature still needs to be investigated.

Modulation of neural fMRI responses to visual food cues by overeating and fasting interventions: A preliminary study

Neural processing of visual food stimuli is perturbated at extremes of weight. Human fMRI studies investigating diet effects on neural processing of food cues could aid in understanding altered brain activation in conditions of under- and overnutrition. In this preliminary study, we examined brain activity changes in response to 10 days of high-calorie-diet (HCD), followed by 10 days of fasting, hypothesizing that HCD would decrease activation in homeostatic and reward regions, while fasting would increase activation in homeostatic/reward regions and decrease activation of self-control regions. Seven adults completed fMRI scanning during a food-cue paradigm (high- and low-calorie food images and nonfood objects), pre- and post-10-day HCD. Six adults completed fMRI scanning pre- and post-10-day fasting. BOLD response changes for contrasts of interest pre- versus post-intervention in regions of interest were examined (peak-level significance set at p(FWE)<0.05). BMI increased by 6.8% and decreased by 8.1% following HCD and fasting, respectively. Following HCD, BOLD response in the hypothalamus (homeostatic control), was attenuated at trend level in response to high- versus low-calorie foods. Following fasting, BOLD response to food versus objects in inhibitory-control areas (dorsolateral prefrontal cortex) was reduced, whereas the activation of homeostatic (hypothalamus), gustatory, and reward brain areas (anterior insula and orbitofrontal cortex) increased. Overfeeding and fasting for 10 days modulate brain activity in response to food stimuli, suggesting that in healthy adults, changes in energy balance affect saliency and reward value of food cues. Future studies are required to understand this interaction in states of unhealthy weight.

Glucose and fat sensing in the human hypothalamus

Energy balance is centrally regulated by the brain through several interacting neuronal systems involving external, peripheral, and central factors within the brain. The hypothalamus integrates these factors and is the key brain area in the regulation of energy balance. In this review, we will explain the structure of the hypothalamus and its role in the regulation of energy balance. An important part of energy balance regulation is the sensing of nutrient status and availability. This review will focus on the sensing of the two main sources of energy by the hypothalamus: glucose and fat. As many common health problems and chronic diseases can be traced back to a disrupted hypothalamic function, we will also discuss hypothalamic sensing of glucose and fats in these pathologies. Finally, we will summarize the current knowledge and discuss how this may be applied clinically and for future research perspectives.

S1P Signaling Pathways in Pathogenesis of Type 2 Diabetes

The pathogenesis of type 2 diabetes mellitus (T2DM) is very complicated. The currently well-accepted etiology is the "Ominous Octet" theory proposed by Professor Defronzo. Since presently used drugs for T2DM have limitations and harmful side effects, studies regarding alternative treatments are being conducted. Analyzing the pharmacological mechanism of biomolecules in view of pathogenesis is an effective way to assess new drugs. Sphingosine 1 phosphate (S1P), an endogenous lipid substance in the human body, has attracted increasing attention in the T2DM research field. This article reviews recent study updates of S1P, summarizing its effects on T2DM with respect to pathogenesis, promoting β cell proliferation and inhibiting apoptosis, reducing insulin resistance, protecting the liver and pancreas from lipotoxic damage, improving intestinal incretin effects, lowering basal glucagon levels, etc. With increasing research, S1P may help treat and prevent T2DM in the future.

A Perspective on Candidate Neural Underpinnings of Binge Eating Disorder: Reward and Homeostatic Systems

People with Binge Eating Disorder (BED) exhibit heightened sensitivity to rewarding stimuli and elevated activity in reward-related brain regions, including the orbitofrontal cortex (OFC), ventral striatum (VS) and insula, during food-cue exposure. BED has also been associated with altered patterns of functional connectivity during resting-state. Investigating neural connectivity in the absence of task stimuli provides knowledge about baseline communication patterns that may influence the behavioural and cognitive manifestation of BED. Elevated resting-state functional connectivity (rsFC) between reward-related brain regions may contribute to uncontrolled eating bouts observed in BED, through heightened food-cue sensitivity and food-craving. The impact of homeostatic state on rsFC of the reward system has not yet been investigated in people with BED. Homeostatic dysfunction is a key driver of excessive food consumption in obesity, whereby rsFC between rewardrelated brain regions does not attenuate during satiety. Future studies should investigate BED related differences in rsFC within the reward system during hunger and satiety, in order to determine whether individuals with BED display an abnormal neural response to changes in homeostatic state. This knowledge would further enhance current understandings of the mechanisms contributing to BED, potentially implicating both reward and homeostatic dysfunctions as drivers of BED.

Connectivity-based localization of human hypothalamic nuclei in functional images of standard voxel size

Despite their critical roles in autonomic functions, individual hypothalamic nuclei have not been extensively investigated in humans using functional magnetic resonance imaging, partly due to the difficulty in resolving individual nuclei contained in the small structure of the hypothalamus. Areal parcellation analyses enable discrimination of individual hypothalamic nuclei but require a higher spatial resolution, which necessitates long scanning time or large amounts of data to compensate for the low signal-to-noise ratio in 3T or 1.5T scanners. In this study, we present analytic procedures to estimate likely locations of individual nuclei in the standard 2-mm resolution based on our higher resolution dataset. The spatial profiles of functional connectivity with the cerebral cortex for each nucleus in the medial hypothalamus were calculated using our higher resolution dataset. Voxels in the hypothalamus in standard resolution images from the Human Connectome Project (HCP) database that predominantly shared connectivity profiles with the same nucleus were subsequently identified. Voxels representing individual nuclei, as identified with the analytic procedures, were reproducible across 20 HCP datasets of 20 subjects each. Furthermore, the identified voxels were spatially separate. These results suggest that these analytic procedures are capable of refining voxels that represent individual hypothalamic nuclei in standard resolution. Our results highlight the potential utility of these procedures in various settings such as patient studies, where lengthy scans are infeasible.

Magnetic resonance assessment of the cerebral alterations associated with obesity development

Obesity is a current threat to health care systems, affecting approximately 13% of the world's adult population, and over 18% children and adolescents. The rise of obesity is fuelled by inadequate life style habits, as consumption of diets rich in fats and sugars which promote, additionally, the development of associated comorbidities. Obesity results from a neuroendocrine imbalance in the cerebral mechanisms controlling food intake and energy expenditure, including the hypothalamus and the reward and motivational centres. Specifically, high-fat diets are known to trigger an early inflammatory response in the hypothalamus that precedes weight gain, is time-dependent, and eventually extends to the remaining appetite regulating regions in the brain. Multiple magnetic resonance imaging (MRI) and spectroscopy (MRS) methods are currently available to characterize different features of cerebral obesity, including diffusion weighted, T2 and volumetric imaging and 1H and 13C spectroscopic evaluations. In particular, consistent evidences have revealed increased water diffusivity and T2 values, decreased grey matter volumes, and altered metabolic profiles and fluxes, in the brain of animal models and in obese humans. This review provides an integrative interpretation of the physio-pathological processes associated with obesity development in the brain, and the MRI and MRS methods implemented to characterize them.

Effects of Non-nutritive Sweeteners on Sweet Taste Processing and Neuroendocrine Regulation of Eating Behavior

PURPOSE OF REVIEW

Non-nutritive sweeteners (NNS) are increasingly used as a replacement for nutritive sugars as means to quench the desire for "sweets" while contributing few or no dietary calories. However, there is concern that NNS may uncouple the evolved relationship between sweet taste and post-ingestive neuroendocrine signaling. In this review, we examine the effects of NNS exposure on neural and peripheral systems in humans.

RECENT FINDINGS

NNS exposure during early development may influence sweet taste preferences, and NNS consumption might increase motivation for sweet foods. Neuroimaging studies provide evidence that NNS elicit differential neuronal responsivity in areas related to reward and satiation, compared with caloric sweeteners. Findings are heterogenous regarding whether NNS affect physiological responses. Additional studies are warranted regarding the consequences of NNS on metabolic outcomes and neuroendocrine pathways. Given the widespread popularity of NNS, future studies are essential to establish their role in long-term health.

Brain insulin sensitivity is linked to adiposity and body fat distribution

Brain insulin action regulates eating behavior and energy fluxes throughout the body. However, numerous people are brain insulin resistant. How brain insulin responsiveness affects long-term weight and body fat composition in humans is still unknown. Here we show that high brain insulin sensitivity before lifestyle intervention associates with a more pronounced reduction in total and visceral fat during the program. High brain insulin sensitivity is also associated with less regain of fat mass during a nine year follow-up. Cross-sectionally, strong insulin responsiveness of the hypothalamus associates with less visceral fat, while subcutaneous fat is unrelated. Our results demonstrate that high brain insulin sensitivity is linked to weight loss during lifestyle intervention and associates with a favorable body fat distribution. Since visceral fat is strongly linked to diabetes, cardiovascular risk and cancer, these findings have implications beyond metabolic diseases and indicate the necessity of strategies to resolve brain insulin resistance.

Brain insulin action regulates eating behavior and whole-body energy fluxes, however the impact of brain insulin resistance on long-term weight and body fat composition is unknown. Here, the authors show that high brain insulin sensitivity is linked to weight loss during lifestyle intervention and associates with a favorable body fat distribution.

The interrelationship of body mass index with gray matter volume and resting-state functional connectivity of the hypothalamus

Background

The hypothalamus plays an important role in regulating body weight through its interactions with multiple brain circuits involved in distinct aspects of feeding behavior. Yet, how hypothalamic gray matter volume (GMV) and connectivity may be related to individual differences in body weight remains unclear. We tested the hypothesis that the hypothalamus shows enhanced resting-state functional connectivity (rsFC) with regions of the reward, motivation, and motor circuits in positive correlation with body mass index (BMI) and the opposite with those associated with inhibitory control. We further examined the interdependent relationships between hypothalamic GMV, connectivity, and body weight.

Methods

Using seed-based rsFC and voxel-based morphometry analyses, we examined the relationship between the rsFC and GMV of the hypothalamus and BMI in 105 healthy humans. Additionally, we employed mediation analyses to characterize the inter-relationships between hypothalamic connectivity, GMV, and BMI.

Results

A whole-brain multiple regression showed that BMI was positively correlated with hypothalamic rsFC with the insula, thalamus, globus pallidus, and cerebellum, and negatively correlated with hypothalamic rsFC with the superior parietal lobule. Thus, higher BMI was associated with enhanced hypothalamic connectivity with regions involved in motivated feeding and reduced connectivity with those in support of cognitive control of food intake. A second whole-brain multiple regression revealed a positive correlation between hypothalamic GMV and the hypothalamus-posterior insula connectivity. Finally, the relationship between hypothalamic GMV and BMI was significantly and bidirectionally mediated by the hypothalamus-posterior insula connectivity.

Conclusions

The current findings suggest that the hypothalamus differentially interacts with the motivation, motor, and control circuits to regulate BMI. We further found evidence for the interdependence of hypothalamic structure, function, and body weight, which provides potential insights into the brain mechanisms of obesity.

Imaging of brain glucose uptake by PET in obesity and cognitive dysfunction: life-course perspective

The prevalence of obesity has reached epidemic proportions and keeps growing. Obesity seems implicated in the pathogenesis of cognitive dysfunction, Alzheimer's disease and dementia, and vice versa. Growing scientific efforts are being devoted to the identification of central mechanisms underlying the frequent association between obesity and cognitive dysfunction. Glucose brain handling undergoes dynamic changes during the life-course, suggesting that its alterations might precede and contribute to degenerative changes or signaling abnormalities. Imaging of the glucose analog 18F-labeled fluorodeoxyglucose (18FDG) by positron emission tomography (PET) is the gold-standard for the assessment of cerebral glucose metabolism in vivo. This review summarizes the current literature addressing brain glucose uptake measured by PET imaging, and the effect of insulin on brain metabolism, trying to embrace a life-course vision in the identification of patterns that may explain (and contribute to) the frequent association between obesity and cognitive dysfunction. The current evidence supports that brain hypermetabolism and brain insulin resistance occur in selected high-risk conditions as a transient phenomenon, eventually evolving toward normal or low values during life or disease progression. Associative studies suggest that brain hypermetabolism predicts low BDNF levels, hepatic and whole body insulin resistance, food desire and an unfavorable balance between anticipated reward from food and cognitive inhibitory control. Emerging mechanistic links involve the microbiota and the metabolome, which correlate with brain metabolism and cognition, deserving attention as potential future prevention targets.

Effect of flavor on neuronal responses of the hypothalamus and ventral tegmental area

Although it is well known that food intake is affected by the palatability of food, the actual effect of flavoring on regulation of energy-homeostasis and reward perception by the brain, remains unclear. We investigated the effect of ethyl-butyrate (EB), a common non-caloric food flavoring, on the blood oxygen level dependent (BOLD) response in the hypothalamus (important in regulating energy homeostasis) and ventral tegmental area (VTA; important in reward processes). The 16 study participants (18-25 years, BMI 20-23 kg/m²) drank four study stimuli on separate visits using a crossover design during an fMRI setup in a randomized order. The stimuli were; plain water, water with EB, glucose solution (50gram/300 ml) and glucose solution with EB. BOLD responses to ingestion of the stimuli were determined in the hypothalamus and VTA as a measure of changes in neuronal activity after ingestion. In the hypothalamus and VTA, glucose had a significant effect on the BOLD response but EB flavoring did not. Glucose with and without EB led to similar decrease in hypothalamic BOLD response and glucose with EB resulted in a decrease in VTA BOLD response. Our results suggest that the changes in neuronal activity in the hypothalamus are mainly driven by energy ingestion and EB does not influence the hypothalamic response. Significant changes in VTA neuronal activity are elicited by energy combined with flavor.

Children Exposed to Maternal Obesity or Gestational Diabetes Mellitus During Early Fetal Development Have Hypothalamic Alterations That Predict Future Weight Gain

OBJECTIVE

Exposure in utero to maternal obesity or gestational diabetes mellitus (GDM) is linked to a high risk for obesity in offspring. Animal studies suggest that these exposures disrupt the development of the hypothalamus, a brain region that regulates body weight, predisposing offspring to develop obesity. This study tested the hypothesis in humans that in utero exposure to maternal obesity and/or GDM is associated with alterations in the hypothalamic response to glucose and the altered hypothalamic response would predict greater increases in child adiposity 1 year later.

RESEARCH DESIGN AND METHODS

Participants were 91 children aged 7-11 years with and without in utero exposure to GDM. Maternal prepregnancy BMI and GDM exposures were determined from electronic medical records. Arterial spin labeling MRI was used to determine the child's hypothalamic blood flow response to oral glucose. Anthropometric measures were acquired in all children at their initial visit and again 1 year later in a subset of 44 children.

RESULTS

Children exposed to GDM diagnosed at ≤26 weeks' gestation had increased hypothalamic blood flow (a marker of hypothalamic activation) in response to glucose when compared with unexposed children, and results remained after adjustments for child age, sex, BMI, and maternal prepregnancy BMI. Maternal prepregnancy BMI was positively associated with the child's hypothalamic response to glucose. Greater hypothalamic response to glucose predicted greater increases in child's BMI 1 year later.

CONCLUSIONS

Increased glucose-linked hypothalamic activation during childhood represents a possible mechanism by which exposure to maternal metabolic disorders during fetal development increases future risk for obesity.

Radiologic evidence that hypothalamic gliosis is improved after bariatric surgery in obese women with type 2 diabetes

BACKGROUND/OBJECTIVES

Hypothalamic neurons play a major role in the control of body mass. Obese subjects present radiologic signs of gliosis in the hypothalamus, which may reflect the damage or loss of neurons involved in whole-body energy homeostasis. It is currently unknown if hypothalamic gliosis (1) differs between obese nondiabetic (ND) and obese diabetic subjects (T2D) or (2) is modified by extensive body mass reduction via Roux-n-Y gastric bypass (RYGB).

SUBJECTS/METHODS

Fifty-five subjects (all female) including lean controls (CT; n = 13), ND (n = 28), and T2D (n = 14) completed at least one study visit. Subjects underwent anthropometrics and a multi-echo MRI sequence to measure mean bilateral T2 relaxation time in the mediobasal hypothalamus (MBH) and two reference regions (amygdala and putamen). The obese groups underwent RYGB and were re-evaluated 9 months later. Analyses were by linear mixed models.

RESULTS

Analyses of T2 relaxation time at baseline showed a group by region interaction only in the MBH (P < 0.0001). T2D had longer T2 relaxation times compared to either CT or ND groups. To examine the effects of RYGB on hypothalamic gliosis a three-way (group by region by time) mixed effects model adjusted for age was executed. Group by region (P < 0.0001) and region by time (P = 0.0005) interactions were significant. There was a reduction in MBH relaxation time by RYGB, and, although the T2D group still had higher T2 relaxation time overall compared to the ND group, the T2D group had significantly lower T2 relaxation time after surgery and the ND group showed a trend. The degree of reduction in MBH T2 relaxation time by RYGB was unrelated to clinical outcomes.

CONCLUSION

T2 relaxation times, a marker of hypothalamic gliosis, are higher in obese women with T2D and are reduced by RYGB-induced weight loss.

Is the Brain a Key Player in Glucose Regulation and Development of Type 2 Diabetes?

Ever since Claude Bernards discovery in the mid 19th-century that a lesion in the floor of the third ventricle in dogs led to altered systemic glucose levels, a role of the CNS in whole-body glucose regulation has been acknowledged. However, this finding was later overshadowed by the isolation of pancreatic hormones in the 20th century. Since then, the understanding of glucose homeostasis and pathology has primarily evolved around peripheral mechanism. Due to scientific advances over these last few decades, however, increasing attention has been given to the possibility of the brain as a key player in glucose regulation and the pathogenesis of metabolic disorders such as type 2 diabetes. Studies of animals have enabled detailed neuroanatomical mapping of CNS structures involved in glucose regulation and key neuronal circuits and intracellular pathways have been identified. Furthermore, the development of neuroimaging techniques has provided methods to measure changes of activity in specific CNS regions upon diverse metabolic challenges in humans. In this narrative review, we discuss the available evidence on the topic. We conclude that there is much evidence in favor of active CNS involvement in glucose homeostasis but the relative importance of central vs. peripheral mechanisms remains to be elucidated. An increased understanding of this field may lead to new CNS-focusing pharmacologic strategies in the treatment of type 2 diabetes.

Physiology of energy homeostasis: Models, actors, challenges and the glucoadipostatic loop

The aim of this review is to discuss the physiology of energy homeostasis (EH), which is a debated concept. Thus, we will see that the set-point theory is highly challenged and that other models integrating an anticipative component, such as energy allostasis, seem more relevant to experimental reports and life preservation. Moreover, the current obesity epidemic suggests that EH is poorly efficient in the modern human dietary environment. Non-homeostatic phenomena linked to hedonism and reward seem to profoundly impair EH. In this review, the apparent failed homeostatic responses to energy challenges such as exercise, cafeteria diet, overfeeding and diet-induced weight loss, as well as their putative determinants, are analyzed to highlight the mechanisms of EH. Then, the hormonal, neuronal, and metabolic factors of energy intake or energy expenditure are briefly presented. Last, this review focuses on the contributions of two of the most pivotal and often overlooked determinants of EH: the availability of endogenous energy and the pattern of energy intake. A glucoadipostatic loop model is finally proposed to link energy stored in adipose tissue to EH through changes in eating behavior via leptin and sympathetic nervous system activity.

Initial evidence for hypothalamic gliosis in children with obesity by quantitative T2 MRI and implications for blood oxygen-level dependent response to glucose ingestion

OBJECTIVE

In adults, hypothalamic gliosis has been documented using quantitative T2 neuroimaging, whereas functional magnetic resonance imaging (fMRI) has shown a defective hypothalamic response to nutrients. No studies have yet evaluated these hypothalamic abnormalities in children with obesity.

METHODS

Children with obesity and lean controls underwent quantitative MRI measuring T2 relaxation time, along with continuous hypothalamic fMRI acquisition to evaluate early response to glucose ingestion.

RESULTS

Children with obesity (N = 11) had longer T2 relaxation times, consistent with gliosis, in the mediobasal hypothalamus (MBH) compared to controls (N = 9; P = 0.004). Moreover, there was a highly significant group*region interaction (P = 0.002), demonstrating that signs of gliosis were specific to MBH and not to reference regions. Longer T2 relaxation times correlated with measures of higher adiposity, including visceral fat percentage (P = 0.01). Mean glucose-induced hypothalamic blood oxygen-level dependent signal change did not differ between groups (P = 0.11). However, mean left MBH T2 relaxation time negatively correlated with glucose-induced hypothalamic signal change (P < 0.05).

CONCLUSION

Imaging signs of hypothalamic gliosis were present in children with obesity and positively associated with more severe adiposity. Children with the strongest evidence for gliosis showed the least activation after glucose ingestion. These initial findings suggest that the hypothalamus is both structurally and functionally affected in childhood obesity.

Brain functional imaging in obese and diabetic patients

Obesity and type 2 diabetes are associated with greater risk of brain damage. Over the last decade, functional imaging techniques (functional magnetic resonance imaging, fMRI, positron emission tomography, PET, electroencephalography, magnetoencephalography, near infrared spectroscopy) have been exploited to better characterize behavioral and cognitive processes, by addressing cerebral reactions to a variety of stimuli or tasks, including hormones and substrates (e.g., glucose, insulin, gut peptides), environmental cues (e.g., presentation of sensory stimuli), and cognitive tasks. Among these techniques, fMRI and PET are most commonly used, and this review focuses on results obtained with these techniques in relation to brain substrate metabolism, appetite control and food intake, and cognitive decline in obesity and type 2 diabetes. The available knowledge indicates that there are a series of cerebral abnormalities associating with, or preceding obesity and type 2 diabetes, including impaired substrate handling, insulin resistance, disruption of inter-organ cross-talk and of resting state networking. Some of these abnormalities are reversed by metabolic interventions, suggesting that they are partly a consequence rather than cause of disease. Therefore, causal implications and mechanisms remain to be determined.

Molecular imaging of diabetes and diabetic complications: Beyond pancreatic β-cell targeting

Diabetes is a chronic non-communicable disease affecting over 400 million people worldwide. Diabetic patients are at a high risk of various complications, such as cardiovascular, renal, and other diseases. The pathogenesis of diabetes (both type 1 and type 2 diabetes) is associated with a functional impairment of pancreatic β-cells. Consequently, most efforts to manage and prevent diabetes have focused on preserving β-cells and their function. Advances in imaging techniques, such as magnetic resonance imaging, magnetic resonance spectroscopy, positron emission tomography, and single-photon-emission computed tomography, have enabled noninvasive and quantitative detection and characterization of the population and function of β-cells in vivo. These advantages aid in defining and monitoring the progress of diabetes and determining the efficacy of anti-diabetic therapies. Beyond β-cell targeting, molecular imaging of biomarkers associated with the development of diabetes, e.g., lymphocyte infiltration, insulitis, and metabolic changes, may also be a promising strategy for early detection of diabetes, monitoring its progression, and occurrence of complications, as well as facilitating exploration of new therapeutic interventions. Moreover, molecular imaging of glucose uptake, production and excretion in specified tissues is critical for understanding the pathogenesis of diabetes. In the current review, we summarize and discuss recent advances in noninvasive imaging technologies for imaging of biomarkers beyond β-cells for early diagnosis of diabetes, investigation of glucose metabolism, and precise diagnosis and monitoring of diabetic complications for better management of diabetic patients.

Using neuroimaging to investigate the impact of Mandolean® training in young people with obesity: a pilot randomised controlled trial

BACKGROUND

Slowing eating rate using the Mandolean® previously helped obese adolescents to self-select smaller portion sizes, with no reduction in satiety, and enhanced ghrelin suppression. The objective of this pilot, randomised trial was to investigate the neural response to food cues following Mandolean® training using functional Magnetic Resonance Imaging (fMRI), and measures of ghrelin, PYY, glucose and self-reported appetite.

METHOD

Twenty-four obese adolescents (11-18 years; BMI ≥ 95th centile) were randomised (but stratified by age and gender) to receive six-months of standard care in an obesity clinic, or standard care plus short-term Mandolean® training. Two fMRI sessions were conducted: at baseline and post-intervention. These sessions were structured as an oral glucose tolerance test, with food cue-reactivity fMRI, cannulation for blood samples, and appetite ratings taken at baseline, 30 (no fMRI), 60 and 90 min post-glucose. As this was a pilot trial, a conservative approach to the statistical analysis of the behavioural data used Cliff's delta as a non-parametric measure of effect size between groups. fMRI data was analysed using non-parametric permutation analysis (RANDOMISE, FSL).

RESULTS

Following Mandolean® training: (i) relatively less activation was seen in brain regions associated with food cue reactivity after glucose consumption compared to standard care group; (ii) 22% reduction in self-selected portion size was found with no reduction in post-meal satiety. However, usage of the Mandolean® by the young people involved was variable and considerably less than planned at the outset (on average, 28 meals with the Mandolean® over six-months).

CONCLUSION

This pilot trial provides preliminary evidence that Mandolean® training may be associated with changes in how food cues in the environment are processed, supporting previous studies showing a reduction in portion size with no reduction in satiety. In this regard, the study supports targeting eating behaviour in weight-management interventions in young people. However, given the variable usage of the Mandolean® during the trial, further work is required to design more engaging interventions reducing eating speed.

TRIAL REGISTRATION

ISRCTN, ISRCTN84202126 , retrospectively registered 22/02/2018.

Humans with obesity have disordered brain responses to food images during physiological hyperglycemia

Blood glucose levels influence brain regulation of food intake. This study assessed the effect of mild physiological hyperglycemia on brain response to food cues in individuals with obesity (OB) versus normal weight individuals (NW). Brain responses in 10 OB and 10 NW nondiabetic healthy adults [body mass index: 34 (3) vs. 23 (2) kg/m², means (SD), P < 0.0001] were measured with functional MRI (blood oxygen level-dependent contrast) in combination with a two-step normoglycemic-hyperglycemic clamp. Participants were shown food and nonfood images during normoglycemia (~95 mg/dl) and hyperglycemia (~130 mg/dl). Plasma glucose levels were comparable in both groups during the two-step clamp ( P = not significant). Insulin and leptin levels were higher in the OB group compared with NW, whereas ghrelin levels were lower (all P < 0.05). During hyperglycemia, insula activity showed a group-by-glucose level effect. When compared with normoglycemia, hyperglycemia resulted in decreased activity in the hypothalamus and putamen in response to food images ( P < 0.001) in the NW group, whereas the OB group exhibited increased activity in insula, putamen, and anterior and dorsolateral prefrontal cortex (aPFC/dlPFC; P < 0.001). These data suggest that OB, compared with NW, appears to have disruption of brain responses to food cues during hyperglycemia, with reduced insula response in NW but increased insula response in OB, an area involved in food perception and interoception. In a post hoc analysis, brain activity in obesity appears to be associated with dysregulated motivation (striatum) and inappropriate self-control (aPFC/dlPFC) to food cues during hyperglycemia. Hyperstimulation for food and insensitivity to internal homeostatic signals may favor food consumption to possibly play a role in the pathogenesis of obesity.

Leptin Replacement Reestablishes Brain Insulin Action in the Hypothalamus in Congenital Leptin Deficiency

OBJECTIVE

Human obesity is associated with impaired central insulin signaling, and in very rare cases, severe obesity can be caused by congenital leptin deficiency. In such patients, leptin replacement results in substantial weight loss and improvement in peripheral metabolism.

RESEARCH DESIGN AND METHODS

In a leptin-deficient patient, we investigated the impact of leptin substitution on central insulin action, as quantified by changes in neuronal activity after intranasal insulin application. This was assessed before and during the first year of metreleptin substitution.

RESULTS

After only 1 year, treatment with metreleptin reestablishes brain insulin sensitivity, particularly in the hypothalamus and, to a lesser degree, in the prefrontal cortex. Results are depicted in comparison with a control group. In our patient, brain activation changes were accompanied by substantial weight loss, reduced visceral adipose tissue, reduced intrahepatic lipid content, and improved whole-body insulin sensitivity.

CONCLUSIONS

Leptin replacement and weight loss improved homeostatic insulin action in the patient in question.

Elevated glycemia and brain glucose utilization predict BDNF lowering since early life

Obesity and diabetes associate with neurodegeneration. Brain glucose and BDNF are fundamental in perinatal development. BDNF is related to brain health, food intake and glucose metabolism. We characterized the relationship between glycemia and/or brain glucose utilization (by 18FDG-PET during fasting and glucose loading), obesity and BDNF in 4-weeks old (pre-obese) and 12-weeks old (obese) Zucker fa/fa rats, and their age-matched fa/+ controls. In 75 human infants, we assessed cord blood BDNF and glucose levels, appetite regulating hormones, body weight and maternal factors. Young and adult fa/fa rats showed glucose intolerance and brain hyper-utilization compared to controls. Glycemia and age were positively related to brain glucose utilization, and were negative predictors of BDNF levels. In humans, fetal glycemia was dependent on maternal glycemia at term, and negatively predicted BDNF levels. Leptin levels were associated with higher body weight and lower BDNF levels. Glucose intolerance and elevated brain glucose utilization already occur in young, pre-obese rats, suggesting that they precede obesity onset in Zucker fatty rats. Glycemic elevation and brain glucose overexposure predict circulating BDNF deficiency since perinatal and early life. Future studies should evaluate whether the control of maternal and fetal glycemia during late intrauterine development can prevent these unfavorable interactions.

The Effect of Feeding Behavior on Hypothalamus in Obese Type 2 Diabetic Rats with Glucagon-like Peptide-1 Receptor Agonist Intervention

OBJECTIVE

To investigate the utility of intravoxel incoherent motion-diffusion weighted imaging (IVIM-DWI) derived parameters in hypothalamus for monitoring the effect of Exendin-4 (Ex-4) intervention on the feeding behavior in obese diabetic rats within early feeding.

METHODS

21 obese and 19 non-obese rats which were treated with streptozotocin injections were initially divided into an obese diabetes group (OD, n = 10), a non-obese diabetes group (D, n = 8), an obese group (O, n = 9) and a non-obese group (N, n = 9). Then, the rats in the 4 groups received subcutaneous injections of Ex-4, and feeding behavior was examined at 5, 35, 65, 95, and 125 min. The hypothalamic function was evaluated by IVIM-DWI. Finally, the relationship between the hypothalamic function and the amount of food intake was analyzed.

RESULTS

In comparison with the N group, the food intake significantly decreased in the O , OD, and D groups in response to Ex-4. Furthermore, a significant positive correlation was found between food intake and D values at different times from 5 to 125 min after Ex-4 intervention in all 4 groups.

CONCLUSION

A direct correlation between the change of hypothalamic function and feeding behavior was detected in OD rats with Ex-4 intervention in the early feeding period. The hypothalamic D value derived from IVIM-DWI is promising to reflect the dynamic change of hypothalamic function due to intervention.