Roux-en-Y gastric bypass contributes to weight loss-independent improvement in hypothalamic inflammation and leptin sensitivity through gut-microglia-neuron-crosstalk

Metabolic Surgery and Chronic Traumatic Encephalopathy: Perceptions of Former NFL Players

PURPOSE

Chronic traumatic encephalopathy (CTE) has been diagnosed in 91.7% of retired United States National Football League (NFL) players at postmortem. There is no treatment or cure for CTE. Most living former NFL athletes with probable CTE suffer from obesity and its comorbidities. Our previous reviews document the improvement in cognition following metabolic/bariatric surgery (MBS) (e.g., gastric bypass, sleeve gastrectomy). These operations might reduce microglial maladaptive states, thereby attenuating neurodegeneration and CTE-like neurocognitive impairment. The study evaluated former NFL players' views on metabolic surgery in relation to reduction of obesity and CTE risk.

MATERIALS AND METHODS

An online multiple-choice questionnaire (30 items, 125 response options, 10-min completion) developed in the Research Electronic Data Capture (REDCap) system was sent to 1,014 athletes screened in 2017-2022 by the Living Heart Foundation.

RESULTS

From 2/2022 to 7/2023, of 700 surveys opened, 72 (10.3%) of the retired players responded. Mean age was 61.6 ± 12.6 years; 45.0% had the disease of obesity with a mean BMI 35.5 ± 4.6 kg/m2. Thirty-three percent reported ≥ 2 obesity-related comorbidities; 40.3% memory-related TBI symptoms; 66.7% ≥ 1 cognitive symptom; 85.0% believed MBS was safe and effective but were unlikely to elect MBS for weight management. Yet, 57.0% of the entire cohort, and 68.8% of players with obesity were more likely to elect MBS if it could also reduce CTE risk.

CONCLUSIONS

Results of the study bode well for future research recruitment. Most surveyed retired NFL players with obesity believed MBS to be effective and would be more likely to undergo MBS if it also reduced CTE risk.

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

OBJECTIVE

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

RESEARCH DESIGN AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Gut peptides before and following Roux-En-Y gastric bypass: A systematic review and meta-analysis

A systematic search was conducted in Medline Ovid, Embase, Scopus, and Cochrane Central Register of Controlled Trials up until March 2021 following PRISMA guidelines. Studies included evaluated ghrelin, GLP-1, PYY or appetite sensation via visual analogue scales (VASs) before and after Roux-en-Y gastric bypass (RYGB) in adults. A multilevel model with random effects for study and follow-up time points nested in study was fit to the data. The model included kcal consumption as a covariate and time points as moderators. Among the 2559 articles identified, k = 47 were included, among which k = 19 evaluated ghrelin, k = 40 GLP-1, k = 22 PYY, and k = 8 appetite sensation. Our results indicate that fasting ghrelin levels are decreased 2 weeks post-RYGB (p = 0.005) but do not differ from baseline from 6 weeks to 1-year post-RYGB. Postprandial ghrelin and fasting GLP-1 levels were not different from pre-surgical values. Postprandial levels of GLP-1 increased significantly from 1 week (p < 0.001) to 2 years post-RYGB (p < 0.01) compared with pre-RYGB. Fasting PYY increased at 6 months (p = 0.034) and 1 year (p = 0.029) post-surgery; also, postprandial levels increased up to 1 year (p < 0.01). Insufficient data on appetite sensation were available to be meta-analyzed.

Influence of Bariatric Surgery on Gut Microbiota Composition and Its Implication on Brain and Peripheral Targets

Obesity remains a significant global health challenge, with bariatric surgery remaining as one of the most effective treatments for severe obesity and its related comorbidities. This review highlights the multifaceted impact of bariatric surgery beyond mere physical restriction or nutrient malabsorption, underscoring the importance of the gut microbiome and neurohormonal signals in mediating the profound effects on weight loss and behavior modification. The various bariatric surgery procedures, such as Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG), act through distinct mechanisms to alter the gut microbiome, subsequently impacting metabolic health, energy balance, and food reward behaviors. Emerging evidence has shown that bariatric surgery induces profound changes in the composition of the gut microbiome, notably altering the Firmicutes/Bacteroidetes ratio and enhancing populations of beneficial bacteria such as Akkermansia. These microbiota shifts have far-reaching effects beyond gut health, influencing dopamine-mediated reward pathways in the brain and modulating the secretion and action of key gut hormones including ghrelin, leptin, GLP-1, PYY, and CCK. The resultant changes in dopamine signaling and hormone levels contribute to reduced hedonic eating, enhanced satiety, and improved metabolic outcomes. Further, post-bariatric surgical effects on satiation targets are in part mediated by metabolic byproducts of gut microbiota like short-chain fatty acids (SCFAs) and bile acids, which play a pivotal role in modulating metabolism and energy expenditure and reducing obesity-associated inflammation, as well as influencing food reward pathways, potentially contributing to the regulation of body weight and reduction in hedonic eating behaviors. Overall, a better understanding of these mechanisms opens the door to developing non-surgical interventions that replicate the beneficial effects of bariatric surgery on the gut microbiome, dopamine signaling, and gut hormone regulation, offering new avenues for obesity treatment.

The Mechanism of Leptin Resistance in Obesity and Therapeutic Perspective

Leptin resistance is induced via leptin signaling blockade by chronic overstimulation of the leptin receptor and intracellular signaling defect or increased hypothalamic inflammation and suppressor of cytokine signaling (SOCS)-3 expression. High-fat diet triggers leptin resistance induced by at least two independent causes: first, the limited ability of peripheral leptin to activate hypothalamic signaling transducers and activators of transcription (STAT) signaling and secondly a signaling defect in leptin-responsive hypothalamic neurons. Central leptin resistance is dependent on decreased leptin transport efficiency across the blood brain barrier (BBB) rather than hypothalamic leptin insensitivity. Since the hypothalamic phosphorylated STAT3 (pSTAT3) represents a sensitive and specific readout of leptin receptor-B signaling, the assessment of pSTAT3 levels is the gold standard. Hypertriglyceridemia is one of important factors to inhibit the transport of leptin across BBB in obesity. Mismatch between high leptin and the amount of leptin receptor expression in obesity triggers brain leptin resistance via increasing hypothalamic inflammation and SOCS-3 expression. Therapeutic strategies that regulate the passage of leptin to the brain include the development of modifications in the structure of leptin analogues as well as the synthesis of new leptin receptor agonists with increased BBB permeability. In the hyperleptinemic state, polyethylene glycol (PEG)-modified leptin is unable to pass through the BBB. Peripheral histone deacetylase (HDAC) 6 inhibitor, tubastatin, and metformin increase central leptin sensitization. While add-on therapy with anagliptin, metformin and miglitol reduce leptin concentrations, the use of long-acting leptin analogs, and exendin-4 lead to the recovery of leptin sensitivity. Contouring surgery with fat removal, and bariatric surgery independently of the type of surgery performed provide significant improvement in leptin concentrations. Although approaches to correcting leptin resistance have shown some success, no clinically effective application has been developed to date. Due to the impairment of central and peripheral leptin signaling, as well as the extensive integration of leptin-sensitive metabolic pathways with other neurons, the effectiveness of methods used to eliminate leptin resistance is extremely limited.

Bariatric Surgery in Obesity: Metabolic Quality Analysis and Comparison of Surgical Options

Obesity is a constantly growing health problem which reduces quality of life and life expectancy. Bariatric surgery (BS) for obesity is considered when all other conservative treatment modalities have failed. Comparison of the multidisciplinary programs with BS regarding to the weight loss showed that substantial and durable weight reduction have been achieved only with bariatric surgical treatments. Although laparoscopic sleeve gastrectomy is the most popular BS, it has high long-term failure rates, and it is claimed that one of every three patients will undergo another bariatric procedure within a 10-year period. Although BS provides weight loss and improvement of metabolic comorbidities, in long-term follow-up, weight gain is observed in half of the patients, while decrease in bone mass and nutritional deficiencies occur in up to 90%. Moreover, despite significant weight loss, several psychological aspects of patients are worsened in comparison to preoperative levels. Nearly one-fifth of postoperative patients with "Loss-of-eating control" meet food addiction criteria. Therefore, the benefits of weight loss following bariatric procedures alone are still debated in terms of the proinflammatory and metabolic profile of obesity.

Electrical signalling and plant response to herbivory: A short review

For a long time, electrical signaling was neglected at the expense of signaling studies in plants being concentrated with chemical and hydraulic signals. Studies conducted in recent years have revealed that plants are capable of emitting, processing, and transmitting bioelectrical signals to regulate a wide variety of physiological functions. Many important biological and physiological phenomena are accompanied by these cellular electrical manifestations, which supports the hypothesis about the importance of bioelectricity as a fundamental 'model' for response the stresses environmental and for activities regeneration of these organisms. Electrical signals have also been characterized and discriminated against in genetically modified plants under stress mediated by sucking insects and/or by the application of systemic insecticides. Such results can guide future studies that aim to elucidate the factors involved in the processes of resistance to stress and plant defense, thus aiding in the development of successful strategies in integrated pest management. Therefore, this mini review includes the results of studies aimed at electrical signaling in response to biotic stress. We also demonstrated how the generation and propagation of electrical signals takes place and included a description of how these electrical potentials are measured.

Cellular mechanism of diabetes remission by bariatric surgery

Bariatric surgery is a powerful therapy for type 2 diabetes in patients with obesity. The mechanism of insulin sensitization by surgery has been extensively investigated in weight loss-dependent and weight loss-independent conditions. However, a consensus remains to be established regarding the underlying mechanisms. Energy deficit induced by calorie restriction (CR), that occurs both before and after surgery, represents a unique physiological basis for insulin sensitization regardless of weight loss. In support, we integrate evidence in the literature to provide an energy-based view of insulin sensitization as follows: surgery improves insulin sensitivity through the energy deficit induced by CR, leading to correction of mitochondrial overload in multiple cell types; this then triggers functional reprogramming of relevant tissues leading to diabetes remission.

Peripheral and central macrophages in obesity

Obesity is associated with chronic, low-grade inflammation. Excessive nutrient intake causes adipose tissue expansion, which may in turn cause cellular stress that triggers infiltration of pro-inflammatory immune cells from the circulation as well as activation of cells that are residing in the adipose tissue. In particular, the adipose tissue macrophages (ATMs) are important in the pathogenesis of obesity. A pro-inflammatory activation is also found in other organs which are important for energy metabolism, such as the liver, muscle and the pancreas, which may stimulate the development of obesity-related co-morbidities, including insulin resistance, type 2 diabetes (T2D), cardiovascular disease (CVD) and non-alcoholic fatty liver disease (NAFLD). Interestingly, it is now clear that obesity-induced pro-inflammatory signaling also occurs in the central nervous system (CNS), and that pro-inflammatory activation of immune cells in the brain may be involved in appetite dysregulation and metabolic disturbances in obesity. More recently, it has become evident that microglia, the resident macrophages of the CNS that drive neuroinflammation, may also be activated in obesity and can be relevant for regulation of hypothalamic feeding circuits. In this review, we focus on the action of peripheral and central macrophages and their potential roles in metabolic disease, and how macrophages interact with other immune cells to promote inflammation during obesity.

Dietary Fat Modulation of Gut Microbiota and Impact on Regulatory Pathways Controlling Food Intake

Obesity is a multifactorial disease that continues to increase in prevalence worldwide. Emerging evidence has shown that the development of obesity may be influenced by taxonomic shifts in gut microbiota in response to the consumption of dietary fats. Further, these alterations in gut microbiota have been shown to promote important changes in satiation signals including gut hormones (leptin, ghrelin, GLP-1, peptide YY and CCK) and orexigenic and anorexigenic neuropeptides (AgRP, NPY, POMC, CART) that influence hyperphagia and therefore obesity. In this review, we highlight mechanisms by which gut microbiota can influence these satiation signals both locally in the gastrointestinal tract and via microbiota-gut-brain communication. Then, we describe the effects of dietary interventions and associated changes in gut microbiota on satiety signals through microbiota-dependent mechanisms. Lastly, we present microbiota optimizing therapies including prebiotics, probiotics, synbiotics and weight loss surgery that can help restore beneficial gut microbiota by enhancing satiety signals to reduce hyperphagia and subsequent obesity. Overall, a better understanding of the mechanisms by which dietary fats induce taxonomical shifts in gut microbiota and their impact on satiation signaling pathways will help develop more targeted therapeutic interventions in delaying the onset of obesity and in furthering its treatment.

Change in medial frontal cerebral metabolite concentrations following bariatric surgery

Obesity is associated with adverse effects on brain health, including an increased risk of neurodegenerative diseases. Changes in cerebral metabolism may underlie or precede structural and functional brain changes. While bariatric surgery is known to be effective in inducing weight loss and improving obesity-related medical comorbidities, few studies have examined whether it may be able to improve brain metabolism. In the present study, we examined changes in cerebral metabolite concentrations in participants with obesity who underwent bariatric surgery. Thirty-five patients with obesity (body mass index ≥ 35 kg/m2 ) were recruited from a bariatric surgery candidate nutrition class. They completed single voxel proton magnetic resonance spectroscopy at baseline (presurgery) and within 1 year postsurgery. Spectra were obtained from a large medial frontal brain region using a PRESS sequence on a 3-T Siemens Verio scanner. The acquisition parameters were TR = 3000 ms and TE = 37 ms. Tissue-corrected metabolite concentrations were determined using Osprey. Paired t-tests were used to examine within-subject change in metabolite concentrations, and correlations were used to relate these changes to other health-related outcomes, including weight loss and glycated hemoglobin (HbA1c ), a measure of blood sugar levels. Bariatric surgery was associated with a reduction in cerebral choline-containing compounds (Cho; t [34] = - 3.79, p < 0.001, d = -0.64) and myo-inositol (mI; t [34] = - 2.81, p < 0.01, d = -0.47) concentrations. There were no significant changes in N-acetyl-aspartate, creatine, or glutamate and glutamine concentrations. Reductions in Cho were associated with greater weight loss (r = 0.40, p < 0.05), and reductions in mI were associated with greater reductions in HbA1c (r = 0.44, p < 0.05). In conclusion, participants who underwent bariatric surgery exhibited reductions in cerebral Cho and mI concentrations, which were associated with improvements in weight loss and glycemic control. Given that elevated levels of Cho and mI have been implicated in neuroinflammation, reduction in these metabolites after bariatric surgery may reflect amelioration of obesity-related neuroinflammatory processes. As such, our results provide evidence that bariatric surgery may improve brain health and metabolism in individuals with obesity.

Distinct adaptations of endocrine and cognitive functions may contribute to high variability in long-term weight loss outcome after bariatric surgery

BACKGROUND

Bariatric surgery has been widely recognized as the most efficient long-term treatment method in severe obesity, yet therapy success shows considerable interindividual variability. Postoperative metabolic adaptations, including improved gut hormone secretion (GLP-1, PYY and ghrelin), and restored executive function may play an explanatory role in weight loss, yet causes for poor success in individual patients remain unknown. This study investigates gut-hormonal and cognitive characteristics in extreme weight loss responders to bariatric surgery.

METHODS

Patients (n=47) with high or low excessive weight loss (EWL) at least 2 years after Roux-en-Y-gastric bypass or sleeve gastrectomy were allocated into good responders (GR, EWL 82.4 ± 11.6%) and poor responders (PR, EWL 24.0 ± SD 12.8%) to study differences in postprandial secretion of GLP-1, PYY, ghrelin and in working memory (WM).

RESULTS

Mean BMI was 47.1 ± 6.2 kg/m² in PR (n=21) and 28.9 ± 3.1 kg/m² in GR (n=26, p < 0.001). Fasted GLP-1 and PYY were comparable for GR and PR (p > 0.2) and increased strongly after a standardized test meal (300 kcal liquid meal) with a peak at 15 to 30 minutes. The increase was stronger in GR compared to PR (GLP-1, PYY: Time x Group p < 0.05). Plasma ghrelin levels already differed between groups at fasted state, showing significantly higher levels for GR (p < 0.05). Postprandially, ghrelin secretion was suppressed in both groups, but suppression was higher in GR (Time x Group p < 0.05). GR showed significantly higher WM scores than PR (p < 0.05). Postprandial ghrelin (iAUC), but not GLP-1 or PYY plasma levels, significantly mediated the relationship between EWL and a WM subscore (IS score, CI = 0.07 - 1.68), but not WM main score (MIS score, CI = -0.07 - 1.54), in mediation analyses.

CONCLUSION

Excess weight loss success after bariatric surgical procedures is associated with distinct profiles of gut-hormones at fasted and postprandial state, and differences in working memory. Better working memory performance in GR might be mediated by higher postprandial reduction in ghrelin plasma levels. Future studies need to integrate longitudinal data, larger samples and more sensitive cognitive tests.

The Significance of Hypothalamic Inflammation and Gliosis for the Pathogenesis of Obesity in Humans

Accumulated preclinical literature demonstrates that hypothalamic inflammation and gliosis are underlying causal components of diet-induced obesity in rodent models. This review summarizes and synthesizes available translational data to better understand the applicability of preclinical findings to human obesity and its comorbidities. The published literature in humans includes histopathologic analyses performed postmortem and in vivo neuroimaging studies measuring indirect markers of hypothalamic tissue microstructure. Both support the presence of hypothalamic inflammation and gliosis in children and adults with obesity. Findings predominantly point to tissue changes in the region of the arcuate nucleus of the hypothalamus, although findings of altered tissue characteristics in whole hypothalamus or other hypothalamic regions also emerged. Moreover, the severity of hypothalamic inflammation and gliosis has been related to comorbid conditions, including glucose intolerance, insulin resistance, type 2 diabetes, and low testosterone levels in men, independent of elevated body adiposity. Cross-sectional findings are augmented by a small number of prospective studies suggesting that a greater degree of hypothalamic inflammation and gliosis may predict adiposity gain and worsening insulin sensitivity in susceptible individuals. In conclusion, existing human studies corroborate a large preclinical literature demonstrating that hypothalamic neuroinflammatory responses play a role in obesity pathogenesis. Extensive or permanent hypothalamic tissue remodeling may negatively affect the function of neuroendocrine regulatory circuits and promote the development and maintenance of elevated body weight in obesity and/or comorbid endocrine disorders.

Calorie restriction, but not Roux-en-Y gastric bypass surgery, increases [3 H] PK11195 binding in a rat model of obesity

Roux-en-Y gastric bypass surgery (RYGB) remains an effective weight-loss method used to treat obesity. While it is successful in combating obesity, there are many lingering questions related to the changes in the brain following RYGB surgery, one of them being its effects on neuroinflammation. While it is known that chronic high-fat diet (HFD) contributes to obesity and neuroinflammation, it remains to be understood whether bariatric surgery can ameliorate diet-induced inflammatory responses. To examine this, rats were assigned to either a normal diet (ND) or a HFD for 8 weeks. Rats fed a HFD were split into the following groups: sham surgery with ad libitum access to HFD (sham-HF); sham surgery with calorie-restricted HFD (sham-FR); RYGB surgery with ad libitum access to HFD (RYGB). Following sham or RYGB surgeries, rats were maintained on their diets for 9 weeks before being euthanized. [³ H] PK11195 autoradiography was then performed on fresh-frozen brain tissue in order to measure activated microglia. Sham-FR rats showed increased [³ H] PK11195 binding in the amygdala (63%), perirhinal (60%), and ectorhinal cortex (53%) compared with the ND rats. Obese rats who had the RYGB surgery did not show this increased inflammatory effect. Since the sham-FR and RYGB rats were fed the same amount of HFD, the surgery itself seems responsible for this attenuation in [³ H] PK11195 binding. We speculate that calorie restriction following obese conditions may be seen as a stressor and contribute to inflammation in the brain. Further research is needed to verify this mechanism.

Leptin Increases: Physiological Roles in the Control of Sympathetic Nerve Activity, Energy Balance, and the Hypothalamic-Pituitary-Thyroid Axis

It is well established that decreases in plasma leptin levels, as with fasting, signal starvation and elicit appropriate physiological responses, such as increasing the drive to eat and decreasing energy expenditure. These responses are mediated largely by suppression of the actions of leptin in the hypothalamus, most notably on arcuate nucleus (ArcN) orexigenic neuropeptide Y neurons and anorexic pro-opiomelanocortin neurons. However, the question addressed in this review is whether the effects of increased leptin levels are also significant on the long-term control of energy balance, despite conventional wisdom to the contrary. We focus on leptin's actions (in both lean and obese individuals) to decrease food intake, increase sympathetic nerve activity, and support the hypothalamic-pituitary-thyroid axis, with particular attention to sex differences. We also elaborate on obesity-induced inflammation and its role in the altered actions of leptin during obesity.

Metabolic Profile and Metabolite Analyses in Extreme Weight Responders to Gastric Bypass Surgery

Background: Roux-en-Y gastric bypass (RYGB) surgery belongs to the most frequently performed surgical therapeutic strategies against adiposity and its comorbidities. However, outcome is limited in a substantial cohort of patients with inadequate primary weight loss or considerable weight regain. In this study, gut microbiota composition and systemically released metabolites were analyzed in a cohort of extreme weight responders after RYGB. Methods: Patients (n = 23) were categorized based on excess weight loss (EWL) at a minimum of two years after RYGB in a good responder (EWL 93 ± 4.3%) or a bad responder group (EWL 19.5 ± 13.3%) for evaluation of differences in metabolic outcome, eating behavior and gut microbiota taxonomy and metabolic activity. Results: Mean BMI was 47.2 ± 6.4 kg/m² in the bad vs. 26.6 ± 1.2 kg/m² in the good responder group (p = 0.0001). We found no difference in hunger and satiety sensation, in fasting or postprandial gut hormone release, or in gut microbiota composition between both groups. Differences in weight loss did not reflect in metabolic outcome after RYGB. While fecal and circulating metabolite analyses showed higher levels of propionate (p = 0.0001) in good and valerate (p = 0.04) in bad responders, respectively, conjugated primary and secondary bile acids were higher in good responders in the fasted (p = 0.03) and postprandial state (GCA, p = 0.02; GCDCA, p = 0.02; TCA, p = 0.01; TCDCA, p = 0.02; GDCA, p = 0.05; GUDCA, p = 0.04; TLCA, p = 0.04). Conclusions: Heterogenous weight loss response to RYGB surgery separates from patients’ metabolic outcome, and is linked to unique serum metabolite signatures post intervention. These findings suggest that the level of adiposity reduction alone is insufficient to assess the metabolic success of RYGB surgery, and that longitudinal metabolite profiling may eventually help us to identify markers that could predict individual adiposity response to surgery and guide patient selection and counseling.

Renal Function Following Bariatric Surgery: a Literature Review of Potential Mechanisms

Obesity is a major and independent risk factor for onset and progression of many renal diseases. Bariatric surgery (BS) improves renal function by improving obesity-related metabolic disorders. However, the procedure is also accompanied by renal risks, including acute kidney injury (AKI) and oxalate nephropathy. Here, we briefly review the history and principle of frequently applied technique for BS and summarize the comprehensive BS effect on kidney function. Importantly, we highlight the possible molecular mechanisms associated with the recovery of renal function to provide novel ideas for future studies and clinical applications.

Roux-en-Y Gastric Bypass and Caloric Restriction but Not Gut Hormone-Based Treatments Profoundly Impact the Hypothalamic Transcriptome in Obese Rats

BACKGROUND

The hypothalamus is an important brain region for the regulation of energy balance. Roux-en-Y gastric bypass (RYGB) surgery and gut hormone-based treatments are known to reduce body weight, but their effects on hypothalamic gene expression and signaling pathways are poorly studied.

METHODS

Diet-induced obese male Wistar rats were randomized into the following groups: RYGB, sham operation, sham + body weight-matched (BWM) to the RYGB group, osmotic minipump delivering PYY3-36 (0.1 mg/kg/day), liraglutide s.c. (0.4 mg/kg/day), PYY3-36 + liraglutide, and saline. All groups (except BWM) were kept on a free choice of high- and low-fat diets. Four weeks after interventions, hypothalami were collected for RNA sequencing.

RESULTS

While rats in the RYGB, BWM, and PYY3-36 + liraglutide groups had comparable reductions in body weight, only RYGB and BWM treatment had a major impact on hypothalamic gene expression. In these groups, hypothalamic leptin receptor expression as well as the JAK-STAT, PI3K-Akt, and AMPK signaling pathways were upregulated. No significant changes could be detected in PYY3-36 + liraglutide-, liraglutide-, and PYY-treated groups.

CONCLUSIONS

Despite causing similar body weight changes compared to RYGB and BWM, PYY3-36 + liraglutide treatment does not impact hypothalamic gene expression. Whether this striking difference is favorable or unfavorable to metabolic health in the long term requires further investigation.

Weight loss from caloric restriction vs Roux-en-Y gastric bypass surgery differentially regulates systemic and portal vein GDF15 levels in obese Zucker fatty rats

Weight loss from caloric restriction (i.e. dieting) tends to be modest and short-lived, whereas from bariatric surgeries such as Roux-en-Y gastric bypass (RYGB) is pronounced and generally sustained. The reasons behind these opposing outcomes between interventions remain unclear, but likely involve differential effects on gut-brain communication. Growth differentiation factor 15 (GDF15) is a ubiquitously-induced, centrally-acting, anorexigenic cytokine whose systemic levels are elevated under a variety of conditions associated with a negative energy balance, including in patients following RYGB. We therefore asked whether systemic and portal vein GDF15 levels differ between obese Zucker fatty rats that experienced similar weight loss from RYGB or from forced caloric restriction (CR). Compared with ad libitum fed (ALF) controls, body weight, visceral adiposity and food intake of RYGB and CR rats were markedly lower during the postoperative observation period. Both systemic and portal vein GDF15 levels in RYGB rats at postoperative day 28 were higher compared with ALF rats and particularly compared with CR rats. Further, systemic and portal vein GDF15 levels negatively correlated with body weight and food intake specifically in RYGB rats. These findings provide evidence that, unlike dieting, RYGB might achieve sustained weight loss and appetite suppression partly through increased GDF15 release from epithelial cells of the gastrointestinal tract.

The Impact of Obesity on Microglial Function: Immune, Metabolic and Endocrine Perspectives

Increased life expectancy in combination with modern life style and high prevalence of obesity are important risk factors for development of neurodegenerative diseases. Neuroinflammation is a feature of neurodegenerative diseases, and microglia, the innate immune cells of the brain, are central players in it. The present review discusses the effects of obesity, chronic peripheral inflammation and obesity-associated metabolic and endocrine perturbations, including insulin resistance, dyslipidemia and increased glucocorticoid levels, on microglial function.

Bariatric Surgery Affects Plasma Levels of Alanine Aminotransferase Independent of Weight Loss: A Registry-Based Study

Patients that undergo bariatric surgery experience weight loss and a reduction in the plasma levels of the hepatic enzymes alanine aminotransferase (ALT) and aspartate aminotransferase (AST). We used the Israeli national bariatric registry, which includes demographic, clinical, and biochemical data on 19,403 patients, of which 1335 patients had two-year follow-up data on ALT, AST, A1C, and BMI, to test the dependence of the reduction in the levels of ALT and AST on weight loss. The data were analyzed using regression models, retrospective matching, and time course analyses. Changes in liver enzymes did not correlate with change in BMI, and linear regression models did not demonstrate that the change in ALT and AST values were dependent on pre-operative levels of BMI or the extent of weight loss. ALT and AST levels were reduced two years after surgery compared with a cohort of retrospectively matched patients for ethnicity, sex, age, BMI, and A1C. Finally, patients who regained weight displayed a reduction in levels of liver enzymes. Our results suggest that bariatric surgery affects AST and ALT levels via weight loss dependent and independent mechanisms. Mechanistic studies that will identify the nature of this effect and the clinical relevance of ALT and AST levels to the post-bariatric liver function are warranted.

Leptin Receptors Are Not Required for Roux-en-Y Gastric Bypass Surgery to Normalize Energy and Glucose Homeostasis in Rats

Sensitization to the adipokine leptin is a promising therapeutic strategy against obesity and its comorbidities and has been proposed to contribute to the lasting metabolic benefits of Roux-en-Y gastric bypass (RYGB) surgery. We formally tested this idea using Zucker fatty fa/fa rats as an established genetic model of obesity, glucose intolerance, and fatty liver due to leptin receptor deficiency. We show that the changes in body weight in these rats following RYGB largely overlaps with that of diet-induced obese Wistar rats with intact leptin receptors. Further, food intake and oral glucose tolerance were normalized in RYGB-treated Zucker fatty fa/fa rats to the levels of lean Zucker fatty fa/+ controls, in association with increased glucagon-like peptide 1 (GLP-1) and insulin release. In contrast, while fatty liver was also normalized in RYGB-treated Zucker fatty fa/fa rats, their circulating levels of the liver enzyme alanine aminotransferase (ALT) remained elevated at the level of obese Zucker fatty fa/fa controls. These findings suggest that the leptin system is not required for the normalization of energy and glucose homeostasis associated with RYGB, but that its potential contribution to the improvements in liver health postoperatively merits further investigation.