Ghrelin reductions following bariatric surgery were associated with decreased resting state activity in the hippocampus

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.

Habenula Volume and Functional Connectivity Changes Following Laparoscopic Sleeve Gastrectomy for Obesity Treatment

BACKGROUND

Neuroimaging studies have revealed alterations in habenular (Hb) structure and functional connectivity (FC) in psychiatric conditions. The Hb plays a particularly critical role in regulating negative emotions, which trigger excessive food intake and obesity. However, obesity and weight loss intervention (i.e., laparoscopic sleeve gastrectomy [LSG])-associated changes in Hb structure and FC have not been studied.

METHODS

We used voxel-based morphometry analysis to measure changes in gray matter volume (GMV) in the Hb in 56 patients with obesity at pre-LSG and 12 months post-LSG and in 78 normal-weight (NW) control participants. Then, we conducted Hb seed-based resting-state FC (RSFC) to examine obesity-related and LSG-induced alterations in RSFC. Finally, we used mediation analysis to characterize the interrelationships among Hb GMV, RSFC, and behaviors.

RESULTS

Compared with NW participants, Hb GMV was smaller in patients at pre-LSG and increased at 12 months post-LSG to levels equivalent to that of NW; in addition, increases in Hb GMV were correlated with reduced body mass index (BMI). Compared with NW participants, pre-LSG patients showed greater RSFCs of the Hb-insula, Hb-precentral gyrus, and Hb-rolandic operculum and weaker RSFCs of the Hb-thalamus, Hb-hypothalamus, and Hb-caudate; LSG normalized these RSFCs. Decreased RSFC of the Hb-insula was correlated with reduced BMI, Yale Food Addiction Scale rating, and emotional eating; reduced hunger levels were correlated with increased RSFCs of the Hb-thalamus and Hb-hypothalamus; and reduced BMI and Yale Food Addiction Scale ratings were correlated with increased RSFCs of the Hb-thalamus and Hb-hypothalamus, respectively. The bidirectional relationships between Hb GMV and RSFC of the Hb-insula contributed to reduced BMI.

CONCLUSIONS

These findings indicate that LSG increased Hb GMV and that its related improvement in RSFC of the Hb-insula may mediate long-term benefits of LSG for eating behaviors and weight loss.

Obesity is associated with alterations in anatomical connectivity of frontal-corpus callosum

Obesity has been linked to abnormal frontal function, including the white matter fibers of anterior portion of the corpus callosum, which is crucial for information exchange within frontal cortex. However, alterations in white matter anatomical connectivity between corpus callosum and cortical regions in patients with obesity have not yet been investigated. Thus, we enrolled 72 obese and 60 age-/gender-matched normal weight participants who underwent clinical measurements and diffusion tensor imaging. Probabilistic tractography with connectivity-based classification was performed to segment the corpus callosum and quantify white matter anatomical connectivity between subregions of corpus callosum and cortical regions, and associations between corpus callosum-cortex white matter anatomical connectivity and clinical behaviors were also assessed. Relative to normal weight individuals, individuals with obesity exhibited significantly greater white matter anatomical connectivity of corpus callosum-orbitofrontal cortex, which was positively correlated with body mass index and self-reported disinhibition of eating behavior, and lower white matter anatomical connectivity of corpus callosum-prefrontal cortex, which was significantly negatively correlated with craving for high-calorie food cues. The findings show that alterations in white matter anatomical connectivity between corpus callosum and frontal regions involved in reward and executive control are associated with abnormal eating behaviors.

Obesity surgery and neural correlates of human eating behaviour: A systematic review of functional MRI studies

Changes in eating behaviour including reductions in appetite and food intake, and healthier food cue reactivity, reward, hedonics and potentially also preference, contribute to weight loss and its health benefits after obesity surgery. Functional magnetic resonance imaging (fMRI) has been increasingly used to interrogate the neural correlates of eating behaviour in obesity, including brain reward-cognitive systems, changes after obesity surgery, and links with alterations in the gut-hormone-brain axis. Neural responses to food cues can be measured by changes in blood oxygen level dependent (BOLD) signal in brain regions involved in reward processing, including caudate, putamen, nucleus accumbens, insula, amygdala, orbitofrontal cortex, and top-down inhibitory control, including dorsolateral prefrontal cortex (dlPFC). This systematic review aimed to examine: (i) results of human fMRI studies involving obesity surgery, (ii) important methodological differences in study design across studies, and (iii) correlations and associations of fMRI findings with clinical outcomes, other eating behaviour measures and mechanistic measures. Of 741 articles identified, 23 were eligible for inclusion: 16 (69.6%) longitudinal, two (8.7%) predictive, and five (21.7%) cross-sectional studies. Seventeen studies (77.3%) included patients having Roux-en-Y gastric bypass (RYGB) surgery, six (26.1%) vertical sleeve gastrectomy (VSG), and five (21.7%) laparoscopic adjustable gastric banding (LAGB). The majority of studies (86.0%) were identified as having a very low risk of bias, though only six (27.3%) were controlled interventional studies, with none including randomisation to surgical and control interventions. The remaining studies (14.0%) had a low risk of bias driven by their control groups not having an active treatment. After RYGB surgery, food cue reactivity often decreased or was unchanged in brain reward systems, and there were inconsistent findings as to whether reductions in food cue reactivity was greater for high-energy than low-energy foods. There was minimal evidence from studies of VSG and LAGB surgeries for changes in food cue reactivity in brain reward systems, though effects of VSG surgery on food cue reactivity in the dlPFC were more consistently found. There was consistent evidence for post-operative increases in satiety gut hormones glucagon-like-peptide 1 (GLP-1) and peptide YY (PYY) mediating reduced food cue reactivity after RYGB surgery, including two interventional studies. Methodological heterogeneity across studies, including nutritional state, nature of food cues, post-operative timing, lack of control groups for order effects and weight loss or dietary/psychological advice, and often small sample sizes, limited the conclusions that could be drawn, especially for correlational analyses with clinical outcomes, other eating behaviour measures and potential mediators. This systematic review provides a detailed data resource for those performing or analysing fMRI studies of obesity surgery and makes suggestions to help improve reporting and design of such studies, as well as future directions.

Effects of bariatric surgery and dietary interventions for obesity on brain neurotransmitter systems and metabolism: A systematic review of positron emission tomography (PET) and single-photon emission computed tomography (SPECT) studies

This systematic review collates studies of dietary or bariatric surgery interventions for obesity using positron emission tomography and single-photon emission computed tomography. Of 604 publications identified, 22 met inclusion criteria. Twelve studies assessed bariatric surgery (seven gastric bypass, five gastric bypass/sleeve gastrectomy), and ten dietary interventions (six low-calorie diet, three very low-calorie diet, one prolonged fasting). Thirteen studies examined neurotransmitter systems (six used tracers for dopamine DRD2/3 receptors: two each for 11 C-raclopride, 18 F-fallypride, 123 I-IBZM; one for dopamine transporter, 123 I-FP-CIT; one used tracer for serotonin 5-HT2A receptor, 18 F-altanserin; two used tracers for serotonin transporter, 11 C-DASB or 123 I-FP-CIT; two used tracer for μ-opioid receptor, 11 C-carfentanil; one used tracer for noradrenaline transporter, 11 C-MRB); seven studies assessed glucose uptake using 18 F-fluorodeoxyglucose; four studies assessed regional cerebral blood flow using 15 O-H2 O (one study also used arterial spin labeling); and two studies measured fatty acid uptake using 18 F-FTHA and one using 11 C-palmitate. The review summarizes findings and correlations with clinical outcomes, eating behavior, and mechanistic mediators. The small number of studies using each tracer and intervention, lack of dietary intervention control groups in any surgical studies, heterogeneity in time since intervention and degree of weight loss, and small sample sizes hindered the drawing of robust conclusions across studies.

Neuroimaging and neuroendocrine insights into food cravings and appetite interventions in obesity

This article reviews the previous studies on the distinction between food cravings and appetite, and how they are regulated by hormones and reflected in brain activity. Based on existing research, food cravings are defined as individual preferences influenced by hormones and psychological factors, which differ from appetite, as they are not necessarily related to hunger or nutritional needs. The article also evaluates the neuroimaging findings about food cravings, and interventions to reduce food cravings, such as mindfulness training, alternative sweeteners, non-invasive brain stimulation techniques, cognitive-behavioral therapy, and imaginal retraining, and points out their advantages, disadvantages, and limitations. Furthermore, the article delves into the potential future directions in the field, emphasizing the need for a neuroendocrine perspective, considerations for associated psychiatric disorders, innovative clinical interventions, and emerging therapeutic frontiers in obesity management. The article outlines the neuro-endocrine basis of food cravings, including ghrelin, leptin, melanocortin, oxytocin, glucagon-like peptide-1, baclofen, and other hormones and their brain regions of action. The article argues that food cravings are an important target for obesity, and more research is needed to explore their complex characteristics and mechanisms, and how to effectively interact with their neuro-endocrine pathways. The article provides a new perspective and approach to the prevention and treatment of obesity.

Effect of laparoscopic sleeve gastrectomy on platelet count and mean platelet volume

Objective

Several studies have reported an increase in platelet (PLT) count with chronic inflammation in the presence of obesity. Mean platelet volume (MPV) is an important marker for PLT activity. Our study aims to demonstrate if laparoscopic sleeve gastrectomy (LSG) has any effect on PLT, MPV and white blood cells (WBCs).

Methods

A total of 202 patients undergoing LSG for morbid obesity between January 2019 and March 2020 who completed at least 1 year of follow-up were included in the study. Patients' characteristics and laboratory parameters were recorded preoperatively and were compared in the 6th and 12th months.

Results

Two hundred and two patients (50% - female) with a mean age of 37.5 ± 12.2 years and mean pre-operative body mass index (BMI) of 43 (34.1-62.5) kg/m2 underwent LSG. BMI regressed to 28.2 ± 4.5 kg/m2 at 1 year after LSG (P < 0.001). The mean PLT count, MPV and WBC during the pre-operative period were 293.2 ± 70.3 103 cells/μL, 10.22 ± 0.9 fL and 7.8 ± 1.9 103 cells/μL, respectively. A significant decrease was seen in mean PLT count, with 257.3 ± 54.2 103cell/μL (P < 0.001) at 1 year post-LSG. The mean MPV was increased at 6 months 10.5 ± 1.2 fL (P < 0.001) and remained unchanged at 1 year 10.3 ± 1.3 fL (P = 0.9). The mean WBC levels were significantly decreased with 6.5 ± 1.7 103 cells/μL (P < 0.001) at 1 year. At the end of the follow-up, weight loss showed no correlation with PLT and MPV (P = 0.42, P = 0.32).

Conclusion

Our study has shown a significant decrease in circulating PLT and WBC levels while MPV remained unchanged after LSG.

Systematic Review and Meta-Analysis of the Impact of Bariatric Surgery on Future Cancer Risk

The study aimed to perform a systematic review and meta-analysis of the evidence for the prevention of future cancers following bariatric surgery. A systematic literature search of the Cochrane Library, Embase, Scopus, Web of Science and PubMed databases (2007–2023), Google Scholar and grey literature was conducted. A meta-analysis was performed using the inverse variance method and random effects model. Thirty-two studies involving patients with obesity who received bariatric surgery and control patients who were managed with conventional treatment were included. The meta-analysis suggested bariatric surgery was associated with a reduced overall incidence of cancer (RR 0.62, 95% CI 0.46–0.84, p < 0.002), obesity-related cancer (RR 0.59, 95% CI 0.39–0.90, p = 0.01) and cancer-associated mortality (RR 0.51, 95% CI 0.42–0.62, p < 0.00001). In specific cancers, bariatric surgery was associated with reduction in the future incidence of hepatocellular carcinoma (RR 0.35, 95% CI 0.22–0.55, p < 0.00001), colorectal cancer (RR 0.63, CI 0.50–0.81, p = 0.0002), pancreatic cancer (RR 0.52, 95% CI 0.29–0.93, p = 0.03) and gallbladder cancer (RR 0.41, 95% CI 0.18–0.96, p = 0.04), as well as female specific cancers, including breast cancer (RR 0.56, 95% CI 0.44–0.71, p < 0.00001), endometrial cancer (RR 0.38, 95% CI 0.26–0.55, p < 0.00001) and ovarian cancer (RR 0.45, 95% CI 0.31–0.64, p < 0.0001). There was no significant reduction in the incidence of oesophageal, gastric, thyroid, kidney, prostate cancer or multiple myeloma after bariatric surgery as compared to patients with morbid obesity who did not have bariatric surgery. Obesity-associated carcinogenesis is closely related to metabolic syndrome; visceral adipose dysfunction; aromatase activity and detrimental cytokine, adipokine and exosomal miRNA release. Bariatric surgery results in long-term weight loss in morbidly obese patients and improves metabolic syndrome. Bariatric surgery may decrease future overall cancer incidence and mortality, including the incidence of seven obesity-related cancers.

Brain functional and structural magnetic resonance imaging of obesity and weight loss interventions

Obesity has tripled over the past 40 years to become a major public health issue, as it is linked with increased mortality and elevated risk for various physical and neuropsychiatric illnesses. Accumulating evidence from neuroimaging studies suggests that obesity negatively affects brain function and structure, especially within fronto-mesolimbic circuitry. Obese individuals show abnormal neural responses to food cues, taste and smell, resting-state activity and functional connectivity, and cognitive tasks including decision-making, inhibitory-control, learning/memory, and attention. In addition, obesity is associated with altered cortical morphometry, a lowered gray/white matter volume, and impaired white matter integrity. Various interventions and treatments including bariatric surgery, the most effective treatment for obesity in clinical practice, as well as dietary, exercise, pharmacological, and neuromodulation interventions such as transcranial direct current stimulation, transcranial magnetic stimulation and neurofeedback have been employed and achieved promising outcomes. These interventions and treatments appear to normalize hyper- and hypoactivations of brain regions involved with reward processing, food-intake control, and cognitive function, and also promote recovery of brain structural abnormalities. This paper provides a comprehensive literature review of the recent neuroimaging advances on the underlying neural mechanisms of both obesity and interventions, in the hope of guiding development of novel and effective treatments.

Habenular connectivity predict weight loss and negative emotional-related eating behavior after laparoscopic sleeve gastrectomy

Habenular (Hb) processes negative emotions that may drive compulsive food-intake. Its functional changes were reported following laparoscopic-sleeve-gastrectomy (LSG). However, structural connectivity (SC) of Hb-homeostatic/hedonic circuits after LSG remains unclear. We selected regions implicated in homeostatic/hedonic regulation that have anatomical connections with Hb as regions-of-interest (ROIs), and used diffusion-tensor-imaging with probabilistic tractography to calculate SC between Hb and these ROIs in 30 obese participants before LSG (PreLSG) and at 12-month post-LSG (PostLSG12) and 30 normal-weight controls. Three-factor-eating-questionnaire (TFEQ) and Dutch-eating-behavior-questionnaire (DEBQ) were used to assess eating behaviors. LSG significantly decreased weight, negative emotion, and improved self-reported eating behavior. LSG increased SC between the Hb and homeostatic/hedonic regions including hypothalamus (Hy), bilateral superior frontal gyri (SFG), left amygdala (AMY), and orbitofrontal cortex (OFC). TFEQ-hunger negatively correlated with SC of Hb-Hy at PostLSG12; and increased SC of Hb-Hy correlated with reduced depression and DEBQ-external eating. TFEQ-disinhibition negatively correlated with SC of Hb-bilateral SFG at PreLSG. Increased SC of Hb-left AMY correlated with reduced DEBQ-emotional eating. Higher percentage of total weight-loss negatively correlated with SC of Hb-left OFC at PreLSG. Enhanced SC of Hb-homeostatic/hedonic regulatory regions post-LSG may contribute to its beneficial effects in improving eating behaviors including negative emotional eating, and long-term weight-loss.

Computational approaches to predicting treatment response to obesity using neuroimaging

Obesity is a worldwide disease associated with multiple severe adverse consequences and comorbid conditions. While an increased body weight is the defining feature in obesity, etiologies, clinical phenotypes and treatment responses vary between patients. These variations can be observed within individual treatment options which comprise lifestyle interventions, pharmacological treatment, and bariatric surgery. Bariatric surgery can be regarded as the most effective treatment method. However, long-term weight regain is comparably frequent even for this treatment and its application is not without risk. A prognostic tool that would help predict the effectivity of the individual treatment methods in the long term would be essential in a personalized medicine approach. In line with this objective, an increasing number of studies have combined neuroimaging and computational modeling to predict treatment outcome in obesity. In our review, we begin by outlining the central nervous mechanisms measured with neuroimaging in these studies. The mechanisms are primarily related to reward-processing and include "incentive salience" and psychobehavioral control. We then present the diverse neuroimaging methods and computational prediction techniques applied. The studies included in this review provide consistent support for the importance of incentive salience and psychobehavioral control for treatment outcome in obesity. Nevertheless, further studies comprising larger sample sizes and rigorous validation processes are necessary to answer the question of whether or not the approach is sufficiently accurate for clinical real-world application.

Alterations in Functional and Structural Connectivity of Basal Ganglia Network in Patients with Obesity

Obesity is related to overconsumption of high-calorie (HiCal) food, which is modulated by brain reward and inhibitory control circuitries. The basal ganglia (BG) are a key set of nuclei within the reward circuitry, but obesity-associated functional and structural abnormalities of BG have not been well studied. Resting-state functional MRI with independent component analysis (ICA) and probabilistic tractography were employed to investigate differences in BG-related functional-(FC) and structural connectivity (SC) between 32 patients with obesity (OB) and 35 normal-weight (NW) participants. Compared to NW, OB showed significantly lower FC strength in the caudate nucleus within the BG network, and seed-based FC analysis showed lower FC between caudate and dorsolateral prefrontal cortex (DLPFC), which was negatively correlated with craving for HiCal food cues. Further SC analysis revealed that OB showed lower SC than NW between left caudate and left DLPFC as measured with fractional anisotropy (FA). Alterations in FC and SC between caudate and DLPFC in obese patients, which highlights the role of BG network in modulating the balance between reward and inhibitory-control.

Altered Intrinsic Regional Spontaneous Brain Activity in Patients With Severe Obesity and Meibomian Gland Dysfunction: A Resting-State Functional Magnetic Resonance Imaging Study

Purpose

To evaluate potential regional homogeneity (ReHo) cerebrum function lesions in people with severe obesity and meibomian gland dysfunction (SM) and probe the connection between aberrant cerebrum activity and clinical manifestations.

Patients and Methods

An aggregation of 12 patients with SM, and 12 healthy controls (HCs) closely matched in age and gender were enrolled. We applied corneal confocal microscopy and fundus angiography to compare imaging distinctions between the two groups. SMs were required to carefully fill out the Hospital Anxiety Depression Scale (HADS) forms, and a correlation analysis was performed. ReHo was also utilized to appraise partial differences in spontaneous cerebrum function. Receiver operating characteristic (ROC) curves were created to partition ReHo values between patients with SM and the HCs.

Results

ReHo values for the left cerebellum (LC), right fusiform gyrus (RFG), left inferior temporal gyrus (LITG), left rectus gyrus (LRG), right thalamus (RT), right caudate (RC), left insula (LI), and left thalamus (LT) of subjects with SM were notably higher than those of the HCs (P < 0.05). ReHo values of the right middle frontal gyrus (RMFG) in subjects with SM were decreased notably compared to the HCs (P < 0.05). ReHo values for the RMFG showed a negative correlation with the anxiety scores (ASs; r = −0.961, P < 0.001) and ReHo values for the RFG showed a positive correlation with the depression scores (DSs; r = 0.676, P = 0.016). The areas under the ROC curve were 1.000 (P < 0.001) for the RMFG, LC, LITG, LRG, RC, LI, and LT and 0.993 (P < 0.001) for the RFG and RT. The results from the ROC curve analysis indicated that changes in the ReHo values of some brain regions may help diagnose SM.

Conclusion

Our research emphasized that patients with SM had lesions in synchronized neural activity in many encephalic areas. Our discoveries may provide beneficial information for exploring the neuromechanics of SM.

Emerging Roles of FTO in Neuropsychiatric Disorders

FTO (fat mass and obesity associated) is a recently discovered gene related to obesity and expressed in various tissues of the human body, especially with high expression in the brain. Earlier studies have found that FTO is involved in several biological processes, including brain development and function. In particular, recent studies have found that FTO is a demethylase of N6-methyladenosine (m6A) and it can affect neurological function through the m6A modification of mRNA. At present, a number of studies have shown that FTO is associated with many neuropsychiatric disorders. This paper reviews the discovery, structure, function, and tissue expression of FTO followed by discussing the relationship between FTO and neuropsychiatric diseases. In addition, the potential roles of FTO gene in drug addiction, major depression (MDD), and schizophrenia (SCZ) through regulating m6A modification of dopamine related genes were also highlighted.

Fetal programming of human energy homeostasis brain networks: Issues and considerations

In this paper, we present a transdisciplinary framework and testable hypotheses regarding the process of fetal programming of energy homeostasis brain circuitry. Our model proposes that key aspects of energy homeostasis brain circuitry already are functional by the time of birth (with substantial interindividual variation); that this phenotypic variation at birth is an important determinant of subsequent susceptibility for energy imbalance and childhood obesity risk; and that this brain circuitry exhibits developmental plasticity, in that it is influenced by conditions during intrauterine life, particularly maternal-placental-fetal endocrine, immune/inflammatory, and metabolic processes and their upstream determinants. We review evidence that supports the scientific premise for each element of this formulation, identify future research directions, particularly recent advances that may facilitate a better quantification of the ontogeny of energy homeostasis brain networks, highlight animal and in vitro-based approaches that may better address the determinants of interindividual variation in energy homeostasis brain networks, and discuss the implications of this formulation for the development of strategies targeted towards the primary prevention of childhood obesity.

Habenular and mediodorsal thalamic connectivity predict persistent weight loss after laparoscopic sleeve gastrectomy

OBJECTIVE

The aim of this study was to investigate laparoscopic sleeve gastrectomy (LSG)-induced changes in connectivity between regions involved with reward/antireward and cognitive control and the extent to which these changes persist after surgery and predict sustainable weight loss.

METHODS

Whole-brain local functional connectivity density (lFCD) was studied in 25 participants with obesity who underwent resting-state functional MRI before (PreLSG), 1 month after (PostLSG₁ ), and 12 months after (PostLSG₁₂ ) LSG and compared with 25 normal-weight controls. Regions with significant time effects of LSG on functional connectivity density were identified for subsequent seed-based connectivity analyses and to examine associations with behavior.

RESULTS

LSG significantly increased lFCD in the mediodorsal thalamic nucleus (MD) and in the habenula (Hb) at PostLSG₁₂ compared with PreLSG/PostLSG₁ , whereas it decreased lFCD in the posterior cingulate cortex/precuneus (PCC/PreCun) at PostLSG₁ /PostLSG₁₂ , and these changes were associated with reduction in BMI. In contrast, controls had no significant lFCD differences between baseline and repeated measures. MD had stronger connectivity with PreCun and Hb at PostLSG₁₂ compared with PreLSG/PostLSG₁ , and the increased MD-left PreCun and Hb-MD connectivity correlated with decreases in hunger and BMI, respectively. PCC/PreCun had stronger connectivity with the insula at PostLSG_1-12 .

CONCLUSIONS

The findings highlight the importance of reward and interoceptive regions as well as that of regions mediating negative emotions in the long-term therapeutic benefits of LSG.

Nonobese Male Patients with Alzheimer's Disease Are Vulnerable to Decrease in Plasma Leptin

BACKGROUND

Metabolic dysfunction links to cognitive deficits in Alzheimer's disease (AD). Leptin is an anti-obesity hormone that modulates energy homeostasis and memory function. Although leptin deregulation is implicated in mouse models of AD-like brain pathology, clinical studies have shown inconsistent results regarding an association of leptin with the development of this neurodegenerative disorder.

OBJECTIVE

We investigated the changes of plasma leptin and the correlation of sex-stratified circulating leptin with cognitive performance, AD-related biological markers, and metabolic status in patients with AD and cognitively unimpaired (CU) counterparts.

METHODS

We used nonobese AD patients and CU controls in a University of Kansas Medical Center (KUMC) cohort. Plasma leptin levels, circulating AD-related molecules and metabolic profiles were examined and analyzed.

RESULTS

In contrast to unchanged circulating leptin in females, male patients exhibited decreased plasma leptin levels compared with male CU counterparts. Moreover, plasma leptin showed no correlation with cognitive performance and AD blood biomarkers in patients with either sex. Of note, females but not males demonstrated an association of plasma leptin with body mass index, high density lipoprotein-cholesterol and its ratio with total cholesterol and triglycerides.

CONCLUSION

Our findings suggest that leptin deficiency is associated with nonobese male AD patients, supporting systemic dysmetabolism in the development of this neurodegenerative disorder in certain populations. Although plasma leptin may have limited capacity to reflect disease severity or progression, future mechanistic studies on the regulation of leptin in nonobese patients with AD would deepen our understanding of the sex-related disparity of AD etiopathogenesis.

How Impulsiveness Influences Obesity: The Mediating Effect of Resting-State Brain Activity in the dlPFC

Impulsiveness is a stable personal characteristic that contributes to obesity and may interact with it. Specifically, obesity is caused by unrestrained impulse eating that is not consciously controlled and leads to a hormonal imbalance that also can impair impulse control. However, the mechanism of this relationship is unclear. In our study, 35 obese individuals (body mass index, BMI > 28) were recruited and matched with 31 healthy controls (BMI < 24) in age and education level. All the participants underwent a resting-state fMRI and completed the Barratt Impulsiveness Scale-11. The results showed that patients with obesity had a significantly lower fractional amplitude of low-frequency fluctuations (fALFF) in the bilateral dorsolateral prefrontal cortex (dlPFC) and higher fALFF in the left fusiform cortex. In addition, non-planning impulsiveness was positively correlated with BMI. Importantly, we found that the right dlPFC completely mediated the relationship between non-planning impulsiveness and BMI. Our findings suggest that impulsivity is statistically more likely to precede obesity than to precede impulsivity and contributes to obesity by downregulating spontaneous activity in the dlPFC. This suggests that the dlPFC, which is associated with executive control, may be able a potential target for treating obesity.

Functional Abnormality of the Executive Control Network in Individuals With Obesity During Delay Discounting

Individuals with obesity (OB) prefer immediate rewards of food intake over the delayed reward of healthy well-being achieved through diet management and physical activity, compared with normal-weight controls (NW). This may reflect heightened impulsivity, an important factor contributing to the development and maintenance of obesity. However, the neural mechanisms underlying the greater impulsivity in OB remain unclear. Therefore, the current study employed functional magnetic resonance imaging with a delay discounting (DD) task to examine the association between impulsive choice and altered neural mechanisms in OB. During decision-making in the DD task, OB compared with NW had greater activation in the dorsolateral prefrontal cortex (DLPFC) and posterior parietal cortex, which was associated with greater discounting rate and weaker cognitive control as measured with the Three-Factor Eating Questionnaire (TFEQ). In addition, the association between DLPFC activation and cognitive control (TFEQ) was mediated by discounting rate. Psychophysiological interaction analysis showed decreased connectivity of DLPFC-inferior parietal cortex (within executive control network [ECN]) and angular gyrus-caudate (ECN-reward) in OB relative to NW. These findings reveal that the aberrant function and connectivity in core regions of ECN and striatal brain reward regions underpin the greater impulsivity in OB and contribute to abnormal eating behaviors.

Alteration of regional heterogeneity and functional connectivity for obese undergraduates: evidence from resting-state fMRI

Obesity was found to be related with the changes of brain functions in human beings. There were several brain areas that were verified to be correlated with the obesity, including the parietal cortex, frontal cortex and so on. However, the cortical regions found from different studies were discrepant due to the different ages, gender distribution and satiation degree of participants. We found that the regional homogeneity of right angular gyrus were smaller in obese undergraduates than that in normal-weight undergraduates. Moreover, functional connectivity of the left middle temporal cortex and the right angular gyrus were found to be smaller in obese group than that in normal-weight group by setting the right angular gyrus as seed region. In addition, multiple regression analysis suggested that the right superior frontal gyrus and left middle temporal gyrus were significantly correlated with their body mass index for normal-weight undergraduates, but no significant correlation was found for obese group. In summary, these findings indicated the functional changes of the cortex in obese undergraduates, which might be significant for providing imaging-based biomarkers for intervention and therapy of obesity.

Electroacupuncture enhances resting-state functional connectivity between dorsal caudate and precuneus and decreases associated leptin levels in overweight/obese subjects

Electroacupuncture (EA) is a safe and effective method for treating obesity. However, how it modulates reward-related brain activity/functional connectivity and gut hormones remains unclear. We employed resting-state functional magnetic resonance imaging (RS-fMRI) and resting-state functional connectivity (RSFC) to investigate EA induced changes in resting-state activity and RSFC in reward-related regions and its association with gut hormones in overweight/obese subjects who received real (n = 20) and Sham (n = 15) stimulation. Results showed reduced leptin levels was positively correlated with reduced body mass index (BMI) and negatively correlated with increased cognitive-control as measured with Three-Factor-Eating-Questionnaire (TFEQ). Significant time effects on RSFC between dorsal caudate (DC) and precuneus were due to significant increased RSFC strength in both EA and Sham groups. In addition, increased RSFC of DC-precuneus was negatively correlated with reduced BMI and leptin levels in the EA group. Mediation analysis showed that the relationship between increased DC-precuneus RSFC strength and reduced BMI was mediated by reduced leptin levels. These findings reflect the association between EA-induced brain reward-related RSFC and leptin levels, and decreased leptin levels mediated altered DC-precuneus RSFC strength and consequent weight-loss, suggesting the potential role of EA in reducing weight and appetite.

Spontaneous neural activity changes after bariatric surgery: A resting-state fMRI study

BACKGROUND

Metabolic disorders associated with obesity could lead to alterations in brain structure and function. Whether these changes can be reversed after weight loss is unclear. Bariatric surgery provides a unique opportunity to address these questions because it induces marked weight loss and metabolic improvements which in turn may impact the brain in a longitudinal fashion. Previous studies found widespread changes in grey matter (GM) and white matter (WM) after bariatric surgery. However, findings regarding changes in spontaneous neural activity following surgery, as assessed with the fractional amplitude of low frequency fluctuations (fALFF) and regional homogeneity of neural activity (ReHo), are scarce and heterogenous. In this study, we used a longitudinal design to examine the changes in spontaneous neural activity after bariatric surgery (comparing pre- to post-surgery), and to determine whether these changes are related to cardiometabolic variables.

METHODS

The study included 57 participants with severe obesity (mean BMI=43.1 ± 4.3 kg/m²) who underwent sleeve gastrectomy (SG), biliopancreatic diversion with duodenal switch (BPD), or Roux-en-Y gastric bypass (RYGB), scanned prior to bariatric surgery and at follow-up visits of 4 months (N = 36), 12 months (N = 29), and 24 months (N = 14) after surgery. We examined fALFF and ReHo measures across 1022 cortical and subcortical regions (based on combined Schaeffer-Xiao parcellations) using a linear mixed effect model. Voxel-based morphometry (VBM) based on T1-weighted images was also used to measure GM density in the same regions. We also used an independent sample from the Human Connectome Project (HCP) to assess regional differences between individuals who had normal-weight (N = 46) or severe obesity (N = 46).

RESULTS

We found a global increase in the fALFF signal with greater increase within dorsolateral prefrontal cortex, precuneus, inferior temporal gyrus, and visual cortex. This effect was more significant 4 months after surgery. The increase within dorsolateral prefrontal cortex, temporal gyrus, and visual cortex was more limited after 12 months and only present in the visual cortex after 24 months. These increases in neural activity measured by fALFF were also significantly associated with the increase in GM density following surgery. Furthermore, the increase in neural activity was significantly related to post-surgery weight loss and improvement in cardiometabolic variables, such as blood pressure. In the independent HCP sample, normal-weight participants had higher global and regional fALFF signals, mainly in dorsolateral/medial frontal cortex, precuneus and middle/inferior temporal gyrus compared to the obese participants. These BMI-related differences in fALFF were associated with the increase in fALFF 4 months post-surgery especially in regions involved in control, default mode and dorsal attention networks.

CONCLUSIONS

Bariatric surgery-induced weight loss and improvement in metabolic factors are associated with widespread global and regional increases in neural activity, as measured by fALFF signal. These findings alongside the higher fALFF signal in normal-weight participants compared to participants with severe obesity in an independent dataset suggest an early recovery in the neural activity signal level after the surgery.

Obese Individuals Show Disrupted Dynamic Functional Connectivity between Basal Ganglia and Salience Networks

Previous functional magnetic resonance imaging (fMRI) studies have showed obesity (OB)-related alterations in intrinsic functional connectivity (FC) within and between different resting-state networks (RSNs). However, few studies have examined dynamic functional connectivity (DFC). Thus, we employed resting-state fMRI with independent component analysis (ICA) and DFC analysis to investigate the alterations in FC within and between RSNs in 56 individuals with OB and 46 normal-weight (NW) controls. ICA identified six RSNs, including basal ganglia (BG), salience network (SN), right executive control network/left executive control network, and anterior default-mode network (aDMN)/posterior default-mode network. The DFC analysis identified four FC states. OB compared with NW had more occurrences and a longer mean dwell time (MDT) in state 2 (positive connectivity of BG with other RSN) and also had higher FC of BG-SN in other states. Body mass index was positively correlated with MDT and FCs of BG-aDMN (state 2) and BG-SN (state 4). DFC analysis within more refined nodes of RSNs showed that OB had more occurrences and a longer MDT in state 1 in which caudate had positive connections with the other network nodes. The findings suggest an association between caudate-related and BG-related positive FC in OB, which was not revealed by traditional FC analysis, highlighting the utility of adding DFC to the more conventional methods.

Resting activity of the hippocampus and amygdala in obese individuals predicts their response to food cues

Obese individuals exhibit brain functional abnormalities in multiple regions implicated in reward/motivation, emotion/memory, homeostatic regulation, and executive control when exposed to food cues and during rest. However, it remains unclear whether abnormal brain responses to food cues might account for or relate to their abnormal activity in resting state. This information would be useful for understanding the neural mechanisms behind hyperactive responses to food cues, a critical marker of obesity. Resting-state functional magnetic resonance imaging (RS-fMRI) and a cue-reactivity fMRI task with high- (HiCal) and low-caloric (LoCal) food cues were employed to investigate brain baseline activity and food cue-induced activation differences in 44 obese participants (OB), in 37 overweight participants (OW), and in 37 normal weight (NW) controls. One-way analyses of variance showed there was a group difference in the left hippocampus/amygdala activity during resting state and during food-cue stimulation (p_FWE < 0.05); post-hoc tests showed the OB group had both greater basal activity and greater food cue-induced activation than the OW and NW groups; OW had higher activity in the hippocampus/amygdala than the NW group, which was only significant during resting state. In the OB group, resting-state activity in the left hippocampus/amygdala was positively correlated with activation induced by HiCal food cues, and both of these measures correlated with body mass index (BMI). Mediation analysis showed that the relationship between BMI and hippocampus/amygdala response to HiCal food cues was mediated by their resting-state activity. These findings suggest a close association between obesity and brain functional abnormality in the hippocampus/amygdala. They also indicate that resting-state activity in the hippocampus/amygdala may impact these regions' responses to food cues.

Abnormalities in the thalamo-cortical network in patients with functional constipation

Functional constipation (FCon) is a common functional gastrointestinal disorder (FGID); neuroimaging studies have shown brain functional abnormalities in thalamo-cortical regions in patients with FGID. However, association between FCon and topological characteristics of brain networks remains largely unknown. We employed resting-state functional magnetic resonance imaging (RS-fMRI) and graph theory approach to investigate functional brain topological organization in 42 patients with FCon and 41 healthy controls (HC) from perspectives of global, regional and modular levels. Results showed patients with FCon had a significantly lower normalized clustering coefficient and small-worldness, implying decreased brain functional connectivity. Regions showed altered nodal degree and efficiency mainly located in the thalamus, rostral anterior cingulate cortex (rACC), and supplementary motor area (SMA), which are involved in somatic/sensory, emotional processing and motor-control. For the modular analysis, thalamus, rACC and SMA had an aberrant within-module nodal degree and nodal efficiency, and thalamus-related network exhibited abnormal interaction with the limbic network (amygdala and hippocampal gyrus). Nodal degree in the thalamus was negatively correlated with difficulty of defecation, and nodal degree in the rACC was negatively correlated with sensation of incomplete evacuation. These findings indicated that FCon was associated with abnormalities in the thalamo-cortical network.

Physiologic Mechanisms of Weight Loss Following Metabolic/Bariatric Surgery

Bariatric and metabolic surgery has evolved from simple experimental procedures for a chronic problem associated with significant morbidity into a sophisticated multidisciplinary treatment modality rooted in biology and physiology. Although the complete mechanistic narrative of bariatric surgery cannot yet be written, significant advance in knowledge has been made in the past 2 decades. This article provides a brief overview of the most studied hypotheses and their supporting evidence. Ongoing research, especially in frontier areas, such as the microbiome, will continue to refine, and perhaps even revise, current mechanistic understanding.

Ghrelin and Glucagon-Like Peptide-1: A Gut-Brain Axis Battle for Food Reward

Eating behaviors are influenced by the reinforcing properties of foods that can favor decisions driven by reward incentives over metabolic needs. These food reward-motivated behaviors are modulated by gut-derived peptides such as ghrelin and glucagon-like peptide-1 (GLP-1) that are well-established to promote or reduce energy intake, respectively. In this review we highlight the antagonizing actions of ghrelin and GLP-1 on various behavioral constructs related to food reward/reinforcement, including reactivity to food cues, conditioned meal anticipation, effort-based food-motivated behaviors, and flavor-nutrient preference and aversion learning. We integrate physiological and behavioral neuroscience studies conducted in both rodents and human to illustrate translational findings of interest for the treatment of obesity or metabolic impairments. Collectively, the literature discussed herein highlights a model where ghrelin and GLP-1 regulate food reward-motivated behaviors via both competing and independent neurobiological and behavioral mechanisms.

Altered Functional Connectivity Within and Between Salience and Sensorimotor Networks in Patients With Functional Constipation

Functional constipation (FCon) is a common functional gastrointestinal disorder. A considerable portion of patients with FCon is associated with anxiety/depressive status (FCAD). Previous neuroimaging studies mainly focused on patients with FCon without distinguishing FCAD from FCon patients without anxiety/depressive status (FCNAD). Differences in brain functions between these two subtypes remain unclear. Thus, we employed resting-state functional magnetic resonance imaging (RS-fMRI) and graph theory method to investigate differences in brain network connectivity and topology in 41 FCAD, 42 FCNAD, and 43 age- and gender-matched healthy controls (HCs). FCAD/FCNAD showed significantly lower normalized clustering coefficient and small-world-ness. Both groups showed altered nodal degree/efficiency mainly in the rostral anterior cingulate cortex (rACC), precentral gyrus (PreCen), supplementary motor area (SMA), and thalamus. In the FCAD group, nodal degree in the SMA was negatively correlated with difficulty of defecation, and abdominal pain was positively correlated with nodal degree/efficiency in the rACC, which had a lower within-module nodal degree. The salience network (SN) exhibited higher functional connectivity (FC) with the sensorimotor network (SMN) in FCAD/FCNAD, and FC between these two networks was negatively correlated with anxiety ratings in FCAD group. Additionally, FC of anterior insula (aINS)-rACC was only correlated with constipation symptom (i.e., abdominal pain) in the FCNAD group. In the FCAD group, FCs of dorsomedial prefrontal cortex-rACC, PreCen-aINS showed correlations with both constipation symptom (i.e., difficulty of defecation) and depressive status. These findings indicate the differences in FC of the SN-SMN between FCAD and FCNAD and provide neuroimaging evidence based on brain function, which portrays important clues for improving new treatment strategies.

Gut hormones in microbiota-gut-brain cross-talk

The homeostasis of the gut-brain axis has been shown to exert several effects on physiological and psychological health. The gut hormones released by enteroendocrine cells scattered throughout the gastrointestinal tract are important signaling molecules within the gut-brain axis. The interaction between gut microbiota and gut hormones has been greatly appreciated in gut-brain cross-talk. The microbiota plays an essential role in modulating many gut-brain axis-related diseases, ranging from gastrointestinal disorders to psychiatric diseases. Similarly, gut hormones also play pleiotropic and important roles in maintaining health, and are key signals involved in gut-brain axis. More importantly, gut microbiota can affect the release and functions of gut hormones. This review highlights the role of gut microbiota in the gut-brain axis and focuses on how microbiota-related gut hormones modulate various physiological functions. Future studies could target the microbiota-hormones-gut brain axis to develop novel therapeutics for different psychiatric and gastrointestinal disorders, such as obesity, anxiety, and depression.

From Entero-Endocrine Cell Biology to Surgical Interventional Therapies for Type 2 Diabetes

The physiological roles of the enteroendocrine system in relation to energy and glucose homeostasis regulation have been extensively studied in the past few decades. Considerable advances were made that enabled to disclose the potential use of gastro-intestinal (GI) hormones to target obesity and type 2 diabetes (T2D). The recognition of the clinical relevance of these discoveries has led the pharmaceutical industry to design several hormone analogues to either to mitigate physiological defects or target pharmacologically T2D.Amongst several advances, a major breakthrough in the field was the unexpected observation that enteroendocrine system modulation to T2D target could be achieved by surgically induced anatomical rearrangement of the GI tract. These findings resulted from the widespread use of bariatric surgery procedures for obesity treatment, which despite initially devised to induce weight loss by limiting the systemic availably of nutrients, are now well recognized to influence GI hormone dynamics in a manner that is highly dependent on the type of anatomical rearrangement produced.This chapter will focus on enteroendocrine system related mechanisms leading to improved glycemic control in T2D after bariatric surgery interventions.

Connectome-Based Prediction of Optimal Weight Loss Six Months After Bariatric Surgery

Despite bariatric surgery being the most effective treatment for obesity, a proportion of subjects have suboptimal weight loss post-surgery. Therefore, it is necessary to understand the mechanisms behind the variance in weight loss and identify specific baseline biomarkers to predict optimal weight loss. Here, we employed functional magnetic resonance imaging (fMRI) with baseline whole-brain resting-state functional connectivity (RSFC) and a multivariate prediction framework integrating feature selection, feature transformation, and classification to prospectively identify obese patients that exhibited optimal weight loss at 6 months post-surgery. Siamese network, which is a multivariate machine learning method suitable for small sample analysis, and K-nearest neighbor (KNN) were cascaded as the classifier (Siamese-KNN). In the leave-one-out cross-validation, the Siamese-KNN achieved an accuracy of 83.78%, which was substantially higher than results from traditional classifiers. RSFC patterns contributing to the prediction consisted of brain networks related to salience, reward, self-referential, and cognitive processing. Further RSFC feature analysis indicated that the connection strength between frontal and parietal cortices was stronger in the optimal versus the suboptimal weight loss group. These findings show that specific RSFC patterns could be used as neuroimaging biomarkers to predict individual weight loss post-surgery and assist in personalized diagnosis for treatment of obesity.

Comparing the Impact of Laparoscopic Sleeve Gastrectomy and Gastric Cancer Surgery on Resting-State Brain Activity and Functional Connectivity

Laparoscopic sleeve gastrectomy (LSG) is one of the most performed bariatric surgeries in clinical practice. Growing neuroimaging evidence shows that LSG induces brain functional and structural alterations accompany with sustained weight-loss. Meanwhile, for clinical treatment of gastric cancer, stomach removal surgery is a similar procedure to LSG. It is unclear if the gastric cancer surgery (GCS) would induce the similar alterations in brain functions and structures as LSG, and it would help to clarify the specificity of the LSG. We recruited 24 obese patients who received LSG in the LSG group and 16 normal weight patients with gastric cancer who received GCS as the control group. Functional magnetic resonance imaging was employed to investigate the differences and similarity of surgery’s impact on resting-state brain activity and functional connectivity (RSFC) between LSG and GCS groups. Both LSG and GCS groups showed increased activities in the posterior cingulate cortex (PCC) and supplementary motor area (SMA) as well as the decreased RSFC of PCC- dorsomedial prefrontal cortex and SMA- dorsolateral prefrontal cortex. There were decreased resting-state activity of hippocampus and putamen in LSG group and increases in GCS group. In LSG group, resting-state activities of hippocampus and putamen were correlated with craving for high-caloric food and body mass index after surgery, respectively. These findings suggest LSG induced alterations in resting-state activity and RSFC of hippocampus and putamen specifically regulate the obese state and overeating behaviors in obese patients.

Brain Connectivity, and Hormonal and Behavioral Correlates of Sustained Weight Loss in Obese Patients after Laparoscopic Sleeve Gastrectomy

The biological mediators that support cognitive-control and long-term weight-loss after laparoscopic sleeve gastrectomy (LSG) remain unclear. We measured peripheral appetitive hormones and brain functional-connectivity (FC) using magnetic-resonance-imaging with food cue-reactivity task in 25 obese participants at pre, 1 month, and 6 month after LSG, and compared with 30 normal weight controls. We also used diffusion-tensor-imaging to explore whether LSG increases brain structural-connectivity (SC) of regions involved in food cue-reactivity. LSG significantly decreased BMI, craving for high-calorie food cues, ghrelin, insulin, and leptin levels, and increased self-reported cognitive-control of eating behavior. LSG increased FC between the right dorsolateral prefrontal cortex (DLPFC) and the pregenual anterior cingulate cortex (pgACC) and increased SC between DLPFC and ACC at 1 month and 6 month after LSG. Reduction in BMI correlated negatively with increased FC of right DLPFC-pgACC at 1 month and with increased SC of DLPFC-ACC at 1 month and 6 month after LSG. Reduction in craving for high-calorie food cues correlated negatively with increased FC of DLPFC-pgACC at 6 month after LSG. Additionally, SC of DLPFC-ACC mediated the relationship between lower ghrelin levels and greater cognitive control. These findings provide evidence that LSG improved functional and structural connectivity in prefrontal regions, which contribute to enhanced cognitive-control and sustained weight-loss following surgery.

Sleeve gastrectomy-induced endocrine changes in the remnant stomachs of premenopausal and postmenopausal rats: role of the estrogen receptors

BACKGROUND

Although alterations in the plasma levels of leptin, glucagon-like peptide-1, and gastrin were linked with bariatric surgery outcomes, gastric production of these peptides was not elucidated before.

OBJECTIVE

The aim was to evaluate the impact of estrogen depletion and estrogen receptors (ERs) on sleeve gastrectomy (SG)-induced alterations in gastric hormone production, gastric mucosal integrity, and bone mass.

SETTING

Physiology Research Lab at the University.

METHODS

Female Sprague-Dawley rats underwent ovariectomy or sham operation (control), and 2 months later SG or sham SG was performed. Rats received either nonselective agonist 17 β, ER-α agonist, ER-β agonist, or vehicle for 3 weeks. Trunk blood and gastric tissues were collected for biochemical measurements, while histopathologic examination was performed in gastric and femur samples.

RESULTS

In the presence of intact ovaries, SG-induced weight loss was accompanied by reductions in the gastric synthesis of leptin and gastrin, while gastric glucagon-like peptide-1 was additionally decreased when SG was performed at the postmenopausal state. SG elevated the depleted serum estradiol levels of menopause, implicating a beneficial effect, but the occurrence of severe gastric mucosal injury was triggered. On the other hand, using ER agonists upregulated gastrin-expressing cells, ameliorated gastric injury, and improved bone loss.

CONCLUSIONS

SG, either at premenopausal or postmenopausal state, resulted in considerable loss in bone mass, along with reductions in the gastric levels of gastrin and leptin. Functional status of the ovaries needs to be taken into consideration when monitoring the outcomes of SG, and ER agonists could be of value in controlling SG-induced complications.

Appetite control: hormones or diet strategies?

PURPOSE OF REVIEW

Appetite control results from metabolic, behavioral, and environmental factors that influence hunger and the desire to eat. We summarize the latest advances in the hormonal and nutritional strategies to control appetite and reduce hunger.

RECENT FINDINGS

The fed-hunger-state is regulated by central and peripheric hormones, which modulate energy balance. Leptin, insulin, ghrelin, peptide YY (PYY), and other gut-derived peptides represent the main appetite controllers. The role of orexins, obestatin, and liver-expressed antimicrobial peptide 2 has been uncovered recently. New insights have demonstrated the role of hippocampal activity as a possible mechanism of action. Glucagon-like peptide 1 (GLP1) receptor agonists are well known agents controlling appetite. Association of GLP1 receptor agonist, PYY, or glucose-dependent insulinotropic polypeptide agonists have been tested as new approaches. Appetite-control hormones have also risen as factors involved in the efficacy of bariatric procedures. High-protein, ketogenic diet, and intermittent fasting have been described as nutritional strategies to reduce appetite, although the physiological mechanism and long-term safety remains unclear.

SUMMARY

Appetite control has been an important target for the treatment of obesity and associated disorders. New studies have demonstrated promising adoption of dietary approaches, hormone-based drugs, and bariatric surgery to control energy intake. Further research will establish a significant association, benefits, and safety of these new therapies.

Acute and long-term effects of electroacupuncture alter frontal and insular cortex activity and functional connectivity during resting state

Electroacupuncture (EA) is a safe method for treating obesity; however, its underlying neural mechanisms remain unclear. We employed resting-state-functional-magnetic-resonance-imaging (RS-fMRI) and amplitude-of-low-frequency-fluctuation (ALFF) to investigate acute/long-term effects of EA on brain activity and resting-state-functional-connectivity (RSFC) in overweight/obesity subjects who received real/Sham stimulation. For acute effects, 26 and 19 overweight/obesity subjects were included in EA and Sham groups respectively. There were significant time effects on ALFF in the right insula (INS) and left dorsolateral-prefrontal-cortex (DLPFC) due to decreases/increases in INS/DLPFC in both groups. There were weaker positive RSFC between INS and supplementary-motor-area (SMA)/right DLPFC and weaker negative RSFC between INS and precuneus (PCUN); stronger negative RSFC between DLPFC and dorsomedial-prefrontal-cortex (DMPFC) in both groups. For long-term study, body-mass-index (BMI) had significant reduction in EA (n = 17) and Sham (15) groups; EA had higher BMI reduction than in Sham. There were significant time effects on ALFF in right ventrolateral-prefrontal-cortex (VLPFC) due to significant increases in EA group, and stronger positive RSFC between VLPFC and orbitofrontal-cortex and negative RSFC between VLPFC and left thalamus (THA) in both groups after long-term treatment. These findings suggest that changes in resting-activity and RSFC implicated in inhibitory-control, gastric-motility and satiety-control are associated with EA-induced weight-loss.

Altered Interactions Among Resting-State Networks in Individuals with Obesity

OBJECTIVE

The aim of this study was to investigate alterations in functional connectivity (FC) within and interactions between resting-state networks involved in salience, executive control, and interoception in participants with obesity (OB).

METHODS

Using resting-state functional magnetic resonance imaging with independent component analysis and FC, alterations within and interactions between resting-state networks in 35 OB and 35 normal-weight controls (NW) were investigated.

RESULTS

Compared with NW, OB showed reduced FC strength in the ventromedial prefrontal cortex and posterior cingulate cortex/precuneus within the default-mode network, dorsal anterior cingulate cortex within the salience network (SN), bilateral dorsolateral prefrontal cortex-angular gyrus within the frontoparietal network (FPN), and increased FC strength in the insula (INS) (P_{familywise error}  < 0.0125). The dorsal anterior cingulate cortex FC strength was negatively correlated with craving for food cues, left dorsolateral prefrontal cortex FC strength was negatively correlated with Yale Food Addiction Scale scores, and right INS FC strength was positively correlated with craving for high-calorie food cues. Compared with NW, OB also showed increased FC between the SN and FPN driven by altered FC of bilateral INS and anterior cingulate cortex-angular gyrus.

CONCLUSIONS

Alterations in FC within and interactions between the SN, default-mode network, and FPN might contribute to the high incentive value of food (craving), lack of control of overeating (compulsive overeating), and increased awareness of hunger (impaired interoception) in OB.

Resting-State Brain Connectivity Predicts Weight Loss and Cognitive Control of Eating Behavior After Vertical Sleeve Gastrectomy

OBJECTIVE

The effects of sleeve gastrectomy (SG) on functional connectivity (FC) and associations with weight loss and eating-related cognitive control were investigated.

METHODS

In a longitudinal study, 14 SG patients (13 female; 42.1 presurgery BMI) completed study visits 1 month pre surgery and 12 months post surgery. Patients completed the Dutch Eating Behavior Questionnaire and resting-state functional magnetic resonance imaging scanning to measure FC. Data were analyzed using a seed-to-voxel approach in the CONN Toolbox to investigate pre-/postsurgery changes (n = 12) and to conduct predictive analysis (n = 14).

RESULTS

Seed-to-voxel analysis revealed changes in magnitude (decreases) and directionality (positively correlated to anticorrelated) of FC pre to post surgery within and between default mode network, salience network, and frontoparietal network nodes [Family-Wise Error (FWE) corrected at P < 0.05]. Baseline FC of the nucleus accumbens (with insula) and hypothalamus (with precentral gyrus) predicted 12-month post-SG % total weight loss (FWE-P < 0.05). Baseline FC of the hippocampus, frontoparietal network, and default mode network nodes predicted improvement in cognitive control of eating behavior 12 months after SG (FWE-P < 0.05).

CONCLUSIONS

Our findings demonstrate changes in FC magnitude and directionality post versus pre surgery within and between resting-state networks and frontal, paralimbic, and visual areas in SG patients. Baseline FC predicted weight loss and changes in cognitive control of food intake behavior at 12 months. These could serve as predictive biomarkers for bariatric surgery.

Laparoscopic sleeve gastrectomy induces sustained changes in gray and white matter brain volumes and resting functional connectivity in obese patients

BACKGROUND

Obesity is associated with decreased brain gray- (GM) and white-matter (WM) volumes in regions. Laparoscopic sleeve gastrectomy (LSG) is an effective bariatric surgery associated with neuroplastic changes in patients with obesity at 1 month postLSG.

OBJECTIVE

To investigate whether LSG can induce sustained neuroplastic recovery of brain structural abnormalities, and whether structural changes are accompanied by functional alterations.

SETTING

University hospital, longitudinal study.

METHODS

Structural magnetic resonance imaging and voxel-based morphometry analysis were employed to assess GM/WM volumes in 30 obese participants at preLSG and 1 and 3 months postLSG. One-way analysis of variance modeled time effects on GM/WM volumes, and then alterations in resting-state functional connectivity (RSFC) were assessed.

RESULTS

Significant time effects on GM volumes were in caudate (F = 11.20), insula (INS; F = 10.11), posterior cingulate cortex (PCC; F = 13.32), and inferior frontal gyrus (F = 12.18), and on WM volumes in anterior cingulate cortex (F = 15.70), PCC (F = 15.56), and parahippocampus (F = 17.96, P_FDR < .05). Post hoc tests showed significantly increased GM volumes in caudate (mean change ± SEM .018 ± .005 and P = .001, .031 ± .007 and P < .001), INS (.027 ± .008 and P = .003, .043 ± .009 and P < .001), and PCC (.008 ± .004 and P = .042, .026 ± .006 and P < .001), and increased WM volumes in anterior cingulate cortex (.029 ± .006 and P < .001, .041 ± .008 and P < .001), PCC (.017 ± .004 and P < .001, .032 ± .006 and P < .001), and parahippocampus (.031 ± .008 and P =.001, .075 ± .013 and P < .001) at 1 and 3 months postLSG compared with preLSG. Significant increases in GM volumes were in caudate (.013 ± .006 and P = .036), PCC (.019 ± .006 and P = .006), and inferior frontal gyrus (.019 ± .005 and P = .001), and in WM volumes in anterior cingulate cortex (.012 ± .005 and P = .028), PCC (.014 ± .006 and P = .017), and parahippocampus (.044 ± .014 and P = .003) at 3 relative to 1 month postLSG. GM volumes in INS and PCC showed a positive correlation at 1 (r = .57, P = .001) and 3 months postLSG (r = .55, P = .001). GM volume in INS and PCC were positively correlated with RSFC of INS-PCC (r = .40 and P = .03, r = .55 and P = .001) and PCC-INS (r = .37 and P = .046, r = .57 and P < .001) at 1 month postLSG. GM volume in INS was also positively correlated with RSFC of INS-PCC (r = .44, P = .014) and PCC-INS (r = .38, P = .037) at 3 months postLSG.

CONCLUSION

LSG induces sustained structural brain changes, which might mediate long-term benefits of bariatric surgery in weight reduction. Associations between regional GM volume and RSFC suggest that LSG-induced structural changes contribute to RSFC changes.

Neuroendocrinological mechanisms underlying impulsive and compulsive behaviors in obesity: a narrative review of fMRI studies

Impulsivity and compulsivity are multidimensional constructs that are increasingly considered determinants of obesity. Studies using functional magnetic resonance imaging (fMRI) have provided insight on how differences in brain response during tasks exploring facets of impulsivity and compulsivity relate to the ingestive behaviors that support the etiology and maintenance of obesity. In this narrative review, we provide an overview of neuroimaging studies exploring impulsivity and compulsivity factors as they relate to weight status. Special focus will be placed on studies examining the impulsivity-related dimensions of attentional bias, delayed gratification and emotion regulation. Discussions of compulsivity within the context of obesity will be restricted to fMRI studies investigating habit formation and response flexibility under shifting contingencies. Further, we will highlight neuroimaging research demonstrating how alterations in neuroendocrine functioning are linked to excessive food intake and may serve as a driver of the impulsive and compulsive behaviors observed in obesity. Research on the associations between brain response with neuroendocrine factors, such as insulin, peptide YY (PYY), leptin, ghrelin and glucagon-like peptide 1 (GLP-1), will be reviewed.

Fto Deficiency Reduces Anxiety- and Depression-Like Behaviors in Mice via Alterations in Gut Microbiota

Depression and obesity have high concurrence within individuals, which may be explained by sharing the same risk factors, including disruption of the intestinal microbiota. However, evidence that delineated the causal connections is extremely scarce. Methods: Mice lacking fat mass- and obesity-associated gene (Fto) were generated. Fto-deficient and wild-type control mice were subjected to novel conditions with or without chronic unpredictable mild stress (CUMS) for 6 weeks. Some mice were treated with antibiotics via their drinking water for 6 weeks in order to deplete their microbiota. Behavioral tests were performed to evaluate anxiety- and depression-like behaviors. 16S rRNA amplicon and metagenomic sequencing were employed to analyse fecal microbiota. Plasma levels of inflammatory cytokines and lipopolysaccharides (LPS) were also compared. Results: Deletion of Fto led to lower body weight and decreased anxiety- and depression-like behaviors, Fto+/- mice were also less susceptible to stress stimulation, highlighting the essential role of Fto in pathogenesis of depression. With regard to gut microbiota, Fto deficiency mice harbored specific bacterial signature of suppressing inflammation, characterized with higher abundance of Lactobacillus, lower Porphyromonadaceae and Helicobacter. Critically, behavioral alterations of Fto+/- mice are mediated by shift in gut microbiota, as such changes can be partially attenuated using antibiotics. Exposure to CUMS increased serum IL-6 level while Fto deficiency reduced its level, which may be explained by a lower LPS concentration. Conclusion: Together, our findings uncover the roles of Fto on depression and provide insights into microbiota-related biological mechanisms underlying the association between obesity and depression.

Bariatric surgery in obese patients reduced resting connectivity of brain regions involved with self-referential processing

Obese individuals exhibit brain alterations of resting-state functional connectivity (RSFC) integrity of resting-state networks (RSNs) related to food intake. Bariatric surgery is currently the most effective treatment for combating morbid obesity. How bariatric surgery influences neurocircuitry is mostly unknown. Functional connectivity density (FCD) mapping was employed to calculate local (lFCD)/global (gFCD) voxelwise connectivity metrics in 22 obese participants who underwent functional magnetic resonance imaging before and 1 month after sleeve gastrectomy (SG), and in 19 obese controls (Ctr) without surgery but tested twice (baseline and 1-month later). Two factor (group, time) repeated measures ANOVA was used to assess main and interaction effects in lFCD/gFCD; regions of interest were identified for subsequent seed to voxel connectivity analyses to assess resting-state functional connectivity and to examine association with weight loss. Bariatric surgery significantly decreased lFCD in VMPFC, posterior cingulate cortex (PCC)/precuneus, and dorsal anterior cingulate cortex (dACC)/dorsomedial prefrontal cortex (DMPFC) and decreased gFCD in VMPFC, right dorsolateral prefrontal cortex (DLPFC) and right insula (p_FWE  < .05). lFCD decreased in VMPFC and PCC/precuneus correlated with reduction in BMI after surgery. Seed to voxel connectivity analyses showed the VMPFC had stronger connectivity with left DLPFC and weaker connectivity with hippocampus/parahippocampus, and PCC/precuneus had stronger connectivity with right caudate and left DLPFC after surgery. Bariatric surgery significantly decreased FCD in regions involved in self-referential processing (VMPFC, DMPFC, dACC, and precuneus), and interoception (insula), and changes in VMPFC/precuneus were associated with reduction in BMI suggesting a role in improving control of eating behaviors following surgery.