Brain effect of bariatric surgery in people with obesity

Regional brain glucose uptake following gastric bypass surgery during normo- and hypoglycemic clamp: a pilot FDG-PET study

PURPOSE

We aimed to characterize the RYGB-induced changes in the dynamics of brain glucose uptake. We addressed heterogeneity between brain regions during experimental normo- and hypoglycemia and explored associations with anthropometric and metabolic outcomes of RYGB.

METHODS

Analyses of regional brain glucose uptake were performed on 9 individuals with obesity and no diabetes, investigated with combined brain 18F-FDG-PET and fMRI during hyperinsulinemic normo- and hypoglycemic clamp, one month before and four months after RYGB. FDG clearance, reflecting glucose uptake rate, was assessed in 38 brain regions, covering all cortical areas and subcortical nuclei, during hyperinsulinemic normo- and hypoglycemia. Correlation analyses were performed to identify associations with other outcomes of RYGB.

RESULTS

FDG uptake rate during hypoglycemia was higher than during normoglycemia in all brain regions, both before and after RYGB. Moreover, in most regions and especially in cortical areas involved in inhibitory behavioral control, FDG uptake rate tended to be reduced after surgery during normoglycemia but elevated during hypoglycemia. However, these post-surgical changes in FDG uptake rate were opposite in the hypothalamus. Thus, the hypo-to-normoglycemia FDG clearance ratio tended to increase in all brain regions following RYGB, but not in the amygdala and the hypothalamus. Changes in regional FDG uptake rate after RYGB during normoglycemia were associated with weight loss and improved systemic insulin sensitivity.

CONCLUSION

Using dynamic FDG-PET, we show region-specific patterns of changes in glucose utilization following RYGB. In the hypothalamus, glucose uptake during normoglycemia tended to rise after RYGB while it was reduced in cortical regions involved in behavioral control. Following RYGB, the hypothalamus and amygdala, in contrast to other regions, displayed trends of reduced glucose uptake during hypoglycemia. These pilot results highlight the brain effects of RYGB and suggest behavioral and neuroendocrine adaptations which contribute to its antidiabetic effects.

State of the Science on Brain Insulin Resistance and Cognitive Decline Due to Alzheimer's Disease

Type 2 diabetes mellitus (T2DM) is common and increasing in prevalence worldwide, with devastating public health consequences. While peripheral insulin resistance is a key feature of most forms of T2DM and has been investigated for over a century, research on brain insulin resistance (BIR) has more recently been developed, including in the context of T2DM and non-diabetes states. Recent data support the presence of BIR in the aging brain, even in non-diabetes states, and found that BIR may be a feature in Alzheimer's disease (AD) and contributes to cognitive impairment. Further, therapies used to treat T2DM are now being investigated in the context of AD treatment and prevention, including insulin. In this review, we offer a definition of BIR, and present evidence for BIR in AD; we discuss the expression, function, and activation of the insulin receptor (INSR) in the brain; how BIR could develop; tools to study BIR; how BIR correlates with current AD hallmarks; and regional/cellular involvement of BIR. We close with a discussion on resilience to both BIR and AD, how current tools can be improved to better understand BIR, and future avenues for research. Overall, this review and position paper highlights BIR as a plausible therapeutic target for the prevention of cognitive decline and dementia due to AD.

Applying Dynamical Systems Theory to Improve Personalized Medicine Following Mild Traumatic Brain Injury

A sizable proportion of patients with mild traumatic brain injury (mTBI) have persistent symptoms and functional impairments months to years following injury. This phenomenon is continually observed despite an explosion of research and interest in improving mTBI clinical outcomes over the last two decades. All pharmacological clinical trials to date have failed to demonstrate improved outcomes for mTBI. One possible explanation for these continued failures is an overly myopic approach to treating mTBI (i.e., testing the effect of a single drug with a specific mechanism on a group of people with highly heterogenous injuries). Clinical presentation and prognosis of mTBI vary considerably between patients, and yet we continue to assess group-level effects of a homogenized treatment. We need to utilize an equally complex treatment approach to match the extraordinary complexity of the human brain. Dynamical systems theory has been used to describe systems composed of multiple subsystems who function somewhat independently but are ultimately interconnected. This theory was popularized in the motor control literature as an overarching framework for how the mind and body connect to interact and move through the environment. However, the human body can be viewed as a dynamical system composed of multiple subsystems (i.e., organ systems) who have isolated functions, which are also codependent on the health and performance of other interconnected organ systems. In this perspective piece, we will use the example of mTBI in the obese patient to demonstrate how broadening our approach to treatment of the individual (and not necessarily the injury) may ultimately yield improved outcomes. Furthermore, we will explore clinical and pre-clinical evidence demonstrating multiple system interactions in the context of obesity and TBI and discuss how expanding our understanding of the mechanistic interplay between multiple organ systems may ultimately provide a more personalized treatment approach for this mTBI patient subpopulation.

Impact of Bariatric Surgery on Circulating Metabolites and Cognitive Performance

INTRODUCTION

Bariatric surgery is an effective intervention to reduce obesity and improve associated comorbidities. However, its effects on cognitive function are still the subject of debate. Given that the bioavailability of circulating metabolites can influence brain metabolism and cognitive performance, we aimed to assess the effects of bariatric surgery on plasma metabolic profiles and cognitive performance.

METHODS

We recruited 26 women undergoing gastric bypass surgery. We conducted anthropometric assessments and collected plasma samples for metabolomic analysis. A set of 4 cognitive tests were used to evaluate cognitive performance. Participants were reevaluated 1 year post-surgery.

RESULTS

After surgery, attention capacity and executive function were improved, while immediate memory had deteriorated. Regarding metabolic profile, reduction of beta-tocopherol and increase of serine, glutamic acid, butanoic acid, and glycolic acid were observed. To better understand the relationship between cognitive function and metabolites, a cluster analysis was conducted to identify more homogeneous subgroups based on the cognitive performance. We identified cluster 1, which did not show changes in cognitive performance after surgery, and cluster 2, which showed improved attention and executive function, but reduced performance in the immediate memory test. Thus, cluster 2 was more homogeneous group that replicated the results of non-clustered subjects. Analysis of the metabolic profile of cluster 2 confirmed serine, glutamic acid, and glycolic acid as potential metabolites associated with cognitive performance.

CONCLUSIONS

Metabolites identified in this study have potential for biomarkers and alternative therapeutic target to prevent obesity-related cognitive decline.

KEY POINTS

• Attention capacity and executive function were improved 12 months post bariatric surgery. • Immediate memory was worsened 12 months post bariatric surgery. • Serine, glutamic acid, and glycolic acid are potential metabolites linked to the alteration of cognitive performance.

Cognitive functioning in adolescents with severe obesity undergoing bariatric surgery or intensive non-surgical treatment in Sweden (AMOS2): a multicentre, open-label, randomised controlled trial

Background

Severe obesity during childhood is associated with cognitive deficits. Studies in adults have suggested improvements in executive functioning and memory after bariatric surgery. Our aim was to explore changes in cognitive function in adolescents over two years after bariatric surgery or intensive non-surgical treatment.

Methods

The Adolescent Morbid Obesity Surgery 2 (AMOS2) is a multicentre, open-label, randomised controlled trial in which adolescents (aged 13-16 years) with severe obesity (defined as body mass index (BMI) ≥35 kg/m2) at three specialised obesity centres in Sweden, were randomly assigned to receive bariatric surgery or intensive non-surgical treatment. Herein we report the results of the prespecified exploratory endpoint of change in cognitive functioning. Inclusion in AMOS2 required Tanner pubertal stage ≥3, previous participation in lifestyle obesity treatment for at least one year, and passed assessment form a paediatrician and a paediatric psychologist. Adolescents with severe intellectual disability or other severe, pervasive developmental disorder were excluded. Participants underwent baseline assessment of general intellectual ability, executive functioning, and memory before randomisation. Tests were administrated by clinical psychologists and repeated at one- and two-year follow-up timepoints. Differences in means between groups during follow-up are provided with confidence intervals. The trial is registered at ClinicalTrials.gov, NCT02378259.

Findings

Between October 28 2015 and June 7 2017, 46 adolescents (74% girls), with a mean age of 15.8 (±0.92) years and a mean BMI of 42.8 (±5.4) kg/m2, were included and randomised (23 to bariatric surgery and 23 to intensive non-surgical treatment). At baseline 23/46 (50%) of the adolescents had general intellectual functioning classified as borderline or below. For 15/18 (83%) aspects of cognitive functioning, no significant differences in change over two years were identified between groups; Immediate (average difference during follow-up 1.0 [95% CI: -2.6 to 4.6]) and Delayed (0.5 [95% CI: -0.6 to 1.6]) Verbal Recall, Category Fluency (1.1 [95% CI: -1.6 to 3.8]) and Switching (1.5 [95% CI: -0.0 to 2.9]), Number (-6.0 [95% CI: -12.3 to 0.3]) and Letter (0.1 [95% CI: -5.2 to 5.3]) Sequencing, Number-Letter Switching (-10.3 [95% CI: -26.4 to 5.8]), Motor Speed (-8.3 [95% CI: -17.5 to 0.9]), Colour Naming (-1.9 [95% CI: -4.2 to 0.3]), Inhibition (-3.6 [95% CI: -9.6 to 2.5]), Inhibition Switching (-6.7 [95% CI: -15.3 to 1.9]), Mazes (-0.5 [95% CI: -4.9 to 3.9]), Digit Span Forward (0.1 [95% CI: -0.6 to 0.9 ]) and Backward (0.6 [95% CI: -0.4 to 1.6 ]), and Estimated IQ (0.4 [95% CI: -3.9 to 4.8]; all p > 0.05). Three sub-tests assessing fundamental cognitive skills improved more over two years in operated adolescents than in intensive non-surgical treatment; Letter Fluency (average difference during follow-up 3.8 [95% CI: 0.1-7.5]; p = 0.046), Visual Scanning (-6.5 [95% CI: -11.6 to -1.5]; p = 0.011), and Word Reading (-1.9 [95% CI: -3.3 to -0.4]; p = 0.011).

Interpretation

In contrast to non-randomised studies in adults, we could not demonstrate an association of bariatric surgery and its accompanying significant weight loss with overall greater improvement in executive functions and memory in adolescents over two years compared with a non-surgical group without weight loss. However, lack of statistical power is a potential limitation. The clinical relevance of greater improvements in basic cognitive skills needs to be explored.

Funding

Sweden's innovation agency (VINNOVA), Swedish Research Council, Joanna Cocozza foundation for paediatric research, The Skane University Hospital Psychology Research and Development Grant, Tore Nilsson's Foundation, SUS Foundations and Donations, and Mary von Sydow's Foundation.

Kinetic Modeling of Brain [18-F]FDG Positron Emission Tomography Time Activity Curves with Input Function Recovery (IR) Method

Accurate positron emission tomography (PET) data quantification relies on high-quality input plasma curves, but venous blood sampling may yield poor-quality data, jeopardizing modeling outcomes. In this study, we aimed to recover sub-optimal input functions by using information from the tail (5th-100th min) of curves obtained through the frequent sampling protocol and an input recovery (IR) model trained with reference curves of optimal shape. Initially, we included 170 plasma input curves from eight published studies with clamp [18F]-fluorodeoxyglucose PET exams. Model validation involved 78 brain PET studies for which compartmental model (CM) analysis was feasible (reference (ref) + training sets). Recovered curves were compared with original curves using area under curve (AUC), max peak standardized uptake value (maxSUV). CM parameters (ref + training sets) and fractional uptake rate (FUR) (all sets) were computed. Original and recovered curves from the ref set had comparable AUC (d = 0.02, not significant (NS)), maxSUV (d = 0.05, NS) and comparable brain CM results (NS). Recovered curves from the training set were different from the original according to maxSUV (d = 3) and biologically plausible according to the max theoretical K1 (53//56). Brain CM results were different in the training set (p < 0.05 for all CM parameters and brain regions) but not in the ref set. FUR showed reductions similarly in the recovered curves of the training and test sets compared to the original curves (p < 0.05 for all regions for both sets). The IR method successfully recovered the plasma inputs of poor quality, rescuing cases otherwise excluded from the kinetic modeling results. The validation approach proved useful and can be applied to different tracers and metabolic conditions.

Effects of bariatric surgery on cognitive function in older adults: a prospective longitudinal study

BACKGROUND

Obesity is now well-recognized as an independent risk factor for cognitive decline. Although extensive research has been conducted on cognitive outcomes following bariatric surgery in young adults, very little is known about the impact of advanced age on the cognitive benefits of weight-loss procedures.

OBJECTIVES

This study aimed to assess cognitive function in older Iranian patients before and after bariatric surgery.

SETTING

University Hospital METHODS: In this prospective longitudinal study, 24 older adults were examined before and 4 months after bariatric surgery using the Digit Span Test (DGS), the computerized version of the Wisconsin Card Sorting Test-64 (WCST-64), and the paper-and-pencil versions of the Trail Making Test (TMT), parts A and B, spanning the 4 cognitive domains of attention, working memory, processing speed, and executive functioning. The bariatric surgery group was simultaneously compared to a waiting list control group.

RESULTS

At 4 months of follow-up, comparisons between the groups revealed that the surgical group performed significantly better than the control group on the forward DGS, WCST, and TMT parts A and B. In contrast, there was no significant difference between groups on the backward DGS. Further within-group comparisons demonstrated significant improvements from baseline in forward DGS, WCST, and TMT components A and B. Nevertheless, the same variables did not alter significantly over time in the control group.

CONCLUSIONS

The study suggests measurable cognitive benefits following bariatric surgery in older adults.

Near-Infrared Spectroscopy: A Free-Living Neuroscience Tool to Better Understand Diabetes and Obesity

The human brain is the least accessible of all organs and attempts to study it in vivo rely predominantly on neuroimaging. Functional near-infrared spectroscopy (fNIRS) allows for the study of cortical neural activity in a non-invasive manner that may resemble free-living conditions. Moreover, compared to other neuroimaging tools, fNIRS is less expensive, it does not require the use of ionizing radiation, and can be applied to all study populations (patients suffering from claustrophobia, or neonates). In this narrative review, we provide an overview of the available research performed using fNIRS in patients with diabetes and obesity. The few studies conducted to date have presented controversial results regarding patients with diabetes, some reporting a greater hemodynamic response and others reporting a reduced hemodynamic response compared to the controls, with an unclear distinction between types 1 and 2. Subjects with obesity or a binge eating disorder have reduced prefrontal activation in response to inhibitory food or non-food stimuli; however, following an intervention, such as cognitive treatment, prefrontal activation is restored. Moreover, we discuss the potential of future applications of fNIRS for a better understanding of cortical neural activity in the context of metabolic disorders.

Correlation between improved leptin signaling and cognitive function post bariatric surgery

Determining whether changes in leptin signaling plays a role in the improvement of cognitive function post-bariatric surgery may aid in the understanding and development of novel therapeutic approaches targeting cognitive dysfunction through the greater understanding of processes connecting obesity and brain health. Several studies have explored the effects of cognition post bariatric surgery, and others have studied leptin and its changes post surgery. However the amalgamation of the effects of leptin signaling in relation to cognition post bariatric surgery have yet to be considered as key tools in the understanding of cognitive dysfunction in obese subjects with leptin resistance or insensitivity. This review serves to highlight the potential correlations, to further elucidate the effect of improved leptin signaling on cognition post bariatric surgery, and to propose a direct cause for the improvement of cognitive function via the amelioration of the leptin Janus kinase/Signal transducer and activator of transcription (JAK/STAT) signaling pathway as a result of the reversal of inflammatory processes involved in diseased individuals.

The effect of gastric bypass surgery on cognitive function of Alzheimer's disease and the role of GLP1-SGLT1 pathway

OBJECTIVE

Gastric bypass surgery has been shown to improve metabolic profiles via GLP1, which may also have cognitive benefits for Alzheimer's disease (AD) patients. However, the exact mechanism requires further investigation.

METHODS

Roux-en-Y gastric bypass or sham surgery was performed on APP/PS1/Tau triple transgenic mice (an AD mice model) or wild type C57BL/6 mice. Morris Water Maze (MWM) test was used to evaluate the cognitive function of mice and animal tissue samples were obtained for measurements two months after the surgery. Additionally, STC-1 intestine cells were treated with siTAS1R2 and siSGLT1, and HT22 nerve cells were treated with Aβ, siGLP1R, GLP1 and siSGLT1 in vitro to explore the role of GLP1-SGLT1 related signaling pathway in cognitive function.

RESULTS

The MWM test showed that bypass surgery significantly improved cognitive function in AD mice as measured by navigation and spatial probe tests. Moreover, bypass surgery reversed neurodegeneration, down-regulated hyperphosphorylation of Tau protein and Aβ deposition, improved glucose metabolism, and up-regulated the expression of GLP1, SGLT1, and TAS1R2/3 in the hippocampus. Furthermore, GLP1R silencing down-regulated SGLT1 expression, whereas SGLT1 silencing increased Tau protein deposition and exacerbated dysregulated of glucose metabolism in HT22 cells. However, RYGB did not alter the level of GLP1 secretion in the brainstem (where central GLP1 is mainly produced). Additionally, GLP1 expression was upregulated by RYGB via TAS1R2/3-SGLT1 activation sequentially in the small intestine.

CONCLUSION

RYGB surgery could improve cognition function in AD mice through facilitating glucose metabolism and reducing Tau phosphorylation and Aβ deposition in the hippocampus, mediated by peripheral serum GLP1 activation of SGLT1 in the brain. Furthermore, RYGB increased GLP1 expression through sequential activation of TAS1R2/TAS1R3 and SGLT1 in the small intestine.

Obesity-Induced Brain Neuroinflammatory and Mitochondrial Changes

Obesity is defined as abnormal and excessive fat accumulation, and it is a risk factor for developing metabolic and neurodegenerative diseases and cognitive deficits. Obesity is caused by an imbalance in energy homeostasis resulting from increased caloric intake associated with a sedentary lifestyle. However, the entire physiopathology linking obesity with neurodegeneration and cognitive decline has not yet been elucidated. During the progression of obesity, adipose tissue undergoes immune, metabolic, and functional changes that induce chronic low-grade inflammation. It has been proposed that inflammatory processes may participate in both the peripheral disorders and brain disorders associated with obesity, including the development of cognitive deficits. In addition, mitochondrial dysfunction is related to inflammation and oxidative stress, causing cellular oxidative damage. Preclinical and clinical studies of obesity and metabolic disorders have demonstrated mitochondrial brain dysfunction. Since neuronal cells have a high energy demand and mitochondria play an important role in maintaining a constant energy supply, impairments in mitochondrial activity lead to neuronal damage and dysfunction and, consequently, to neurotoxicity. In this review, we highlight the effect of obesity and high-fat diet consumption on brain neuroinflammation and mitochondrial changes as a link between metabolic dysfunction and cognitive decline.