Impaired glucose regulation is associated with poorer performance on the Stroop Task

A Stress Syndrome Prototype Reflects Type 3 Diabetes and Ischemic Stroke Risk: The SABPA Study

Type 3 diabetes (T3D) accurately reflects that dementia, e.g., Alzheimer's disease, represents insulin resistance and neurodegeneration in the brain. Similar retinal microvascular changes were observed in Alzheimer's and chronic stressed individuals. Hence, we aimed to show that chronic stress relates to T3D dementia signs and retinopathy, ultimately comprising a Stress syndrome prototype reflecting risk for T3D and stroke. A chronic stress and stroke risk phenotype (Stressed) score, independent of age, race or gender, was applied to stratify participants (N = 264; aged 44 ± 9 years) into high stress risk (Stressed, N = 159) and low stress risk (non-Stressed, N = 105) groups. We determined insulin resistance using the homeostatic model assessment (HOMA-IR), which is interchangeable with T3D, and dementia risk markers (cognitive executive functioning (cognitiveexe-func); telomere length; waist circumference (WC), neuronal glia injury; neuron-specific enolase/NSE, S100B). Retinopathy was determined in the mydriatic eye. The Stressed group had greater incidence of HOMA-IR in the upper quartile (≥5), larger WC, poorer cognitiveexe-func control, shorter telomeres, consistently raised neuronal glia injury, fewer retinal arteries, narrower arteries, wider veins and a larger optic cup/disc ratio (C/D) compared to the non-Stressed group. Furthermore, of the stroke risk markers, arterial narrowing was related to glaucoma risk with a greater C/D, whilst retinal vein widening was related to HOMA-IR, poor cognitiveexe-func control and neuronal glia injury (Adjusted R2 0.30; p ≤ 0.05). These associations were not evident in the non-Stressed group. Logistic regression associations between the Stressed phenotype and four dementia risk markers (cognitiveexe-func, telomere length, NSE and WC) comprised a Stress syndrome prototype (area under the curve 0.80; sensitivity/specificity 85%/58%; p ≤ 0.001). The Stress syndrome prototype reflected risk for HOMA-IR (odds ratio (OR) 7.72) and retinal glia ischemia (OR 1.27) and vein widening (OR 1.03). The Stressed phenotype was associated with neuronal glia injury and retinal ischemia, potentiating glaucoma risk. The detrimental effect of chronic stress exemplified a Stress syndrome prototype reflecting risk for type 3 diabetes, neurodegeneration and ischemic stroke.

Exploring brain insulin resistance in adults with bipolar depression using extracellular vesicles of neuronal origin

Accumulating evidence suggests that disrupted insulin signaling is involved in bipolar disorder (BD) pathogenesis. Herein, we aimed to directly explore the potential role of neuronal insulin signaling using an innovative technique based on biomarkers derived from plasma extracellular vesicles enriched for neuronal origin (NEVs). We leveraged plasma samples from a randomized, double-blind, placebo-controlled, 12-week clinical trial evaluating infliximab as a treatment of bipolar depression. We isolated NEVs using immunoprecipitation against neuronal marker L1CAM from samples collected at baseline and weeks 2, 6 and 12 (endpoint) and measured NEV biomarkers using immunoassays. We assessed neuronal insulin signaling at its first node (IRS-1) and along the canonical (Akt, GSK-3β, p70S6K) and alternative (ERK1/2, JNK and p38-MAPK) pathways. A subset of participants (n = 27) also underwent whole-brain magnetic resonance imaging (MRI) at baseline and endpoint. Pre-treatment, NEV biomarkers of insulin signaling were independently associated with cognitive function and MRI measures (i.e. hippocampal and ventromedial prefrontal cortex [vmPFC] volumes). In fact, the association between IRS-1 phosphorylation at serine site 312 (pS312-IRS-1), an indicator of insulin resistance, and cognitive dysfunction was mediated by vmPFC volume. In the longitudinal analysis, patients treated with infliximab, a tumor necrosis factor-alpha antagonist with known insulin sensitizing properties, compared to those treated with placebo, had augmented phosphorylation of proteins from the alternative pathway. Infliximab responders had significant increases in phosphorylated JNK levels, relative to infliximab non-responders and placebo responders. In addition, treatment with infliximab resulted in increase in MRI measures of brain volume; treatment-related changes in the dorsolateral prefrontal cortex volume were mediated by changes in biomarkers from the insulin alternative pathway. In conclusion, our findings support the idea that brain insulin signaling is a target for further mechanistic and therapeutic investigations.

THE EFFECT OF BLOOD GLUCOSE ON QUIET STANDING BALANCE IN YOUNG HEALTHY INDIVIDUALS

Falling is one of the leading causes of accidental injury and death among elderly adults and construction workers, with costs exceeding US$31 billion each year. Having good balance reduces the likelihood of falling - therefore it is important to determine which possible factors might influence balance. The purpose of this study was to determine if consuming three different types of breakfast altered blood glucose levels in such a way that young healthy individual's balance control was compromised. Balance was then measured while the subjects completed single- and dual-task standing trials with eyes open and closed. Although changing blood glucose did alter quiet standing balance - as measured by the separation distance between the COG and COP, the velocity of the COM, and the total distance traveled by the COG and COP along the anterior-posterior (AP) and medial-lateral (ML) axes - the results were contradictory to what was hypothesized. Subjects with lower blood glucose swayed less than those with higher blood glucose. This could potentially be due to the habitual skipping of breakfast in young adults. Though the changing of blood glucose did influence quiet standing balance of young healthy adults, it was not in a way which increased the risk of falling.

Prospective associations between cardiac stress, glucose dysregulation and executive cognitive function in Black men: The Sympathetic activity and Ambulatory Blood Pressure in Africans study

OBJECTIVE

Glucose dysregulation is an independent risk factor for cardiovascular and neurodegenerative disease development through synaptic dysfunction resulting in cognitive decline. The aim of this study was to study the interplay between impaired glycaemic metabolism (hyperglycaemia and insulin resistance), cardiac stress (cardiac troponin T and N-terminal brain natriuretic peptide) and executive cognitive function prospectively, in a bi-ethnic sex cohort.

METHODS

Black and White teachers (N = 338, aged 20-63 years) from the Sympathetic activity and Ambulatory Blood Pressure in Africans study were monitored over a 3-year period. Fasting blood samples were obtained for cardiac troponin T, N-terminal brain natriuretic peptide, glycated haemoglobin and the homeostatic model assessment-insulin resistance for insulin resistance. The Stroop colour-word conflict test was applied to assess executive cognitive function at baseline.

RESULTS

Over the 3-year period, Black men revealed constant high levels of cardiac troponin T (⩾4.2 ng/L), pre-diabetes (glycated haemoglobin > 5.7%) and insulin resistance (homeostatic model assessment-insulin resistance >3). %Δ Glycated haemoglobin was associated with %Δ insulin resistance (p < 0.001) and increases in %ΔN-terminal brain natriuretic peptide (p = 0.02) in Black men only. In the latter, baseline Stroop colour-word conflict test was inversely associated with %Δ cardiac troponin T (p = 0.001) and %Δ insulin resistance levels (p = 0.01).

CONCLUSION

Progressive myocyte stretch and chronic myocyte injury, coupled with glucose dysregulation, may interfere with processes related to interference control in Black men.

Oral Glucose Tolerance is Associated with Neuroelectric Indices of Attention Among Adults with Overweight and Obesity

OBJECTIVE

This study aimed to elucidate the relationship between glucose levels and insulin resistance and sensitivity obtained from oral glucose tolerance tests and neurophysiological indices of attention among adults with overweight and obesity.

METHODS

Forty adults with overweight or obesity (BMI ≥ 25 kg/m² ) underwent dual-energy x-ray absorptiometry to assess visceral adipose tissue. Repeated venous blood samples were collected during an oral glucose tolerance test to measure insulin resistance (homeostatic model assessment of insulin resistance) and indices of insulin sensitivity (Matsuda index and Stumvoll metabolic clearance rate). Attention was assessed using event-related brain potentials recorded during a visual oddball task. Amplitude and latency of the P3 wave form in a central-parietal region of interest were used to index attentional resource allocation and information processing speed.

RESULTS

Following adjustment for visceral adipose tissue, reduced values of Matsuda index and Stumvoll metabolic clearance rate (indicating poor insulin sensitivity) were correlated with longer peak latency, whereas insulin area under the curve was positively related to peak latency, indicating slower information processing. Individuals with decreased insulin sensitivity (Matsuda index < 4.3) had significantly longer P3 latencies compared with individuals with normal insulin sensitivity.

CONCLUSIONS

Higher fasting glucose, but not homeostatic model assessment of insulin resistance, and reduced indices of glucose sensivity are associated with decrements in attention characterized by slower reaction time and slower information processing speed among adults with overweight and obesity.

Cognitive dysfunction and metabolic comorbidities in mood disorders: A repurposing opportunity for glucagon-like peptide 1 receptor agonists?

Major depressive disorder and bipolar disorder are highly prevalent and disabling conditions. Cognition is considered a core domain of their psychopathology and a principle mediator of psychosocial impairment, disproportionately accounting for overall illness-associated costs. There are few interventions with replicated evidence of efficacy in treating cognitive deficits in mood disorders. Evidence also indicates that cognitive deficits are associated with obesity and involve significant impairment across multiple domains. Conversely, weight-loss interventions, such as physical exercise and bariatric surgery, have been shown to beneficially affect cognitive function. This convergent phenomenology suggests that currently available agents that target metabolic systems may also be capable of mitigating deficits in cognitive functions, and are, therefore, candidates for repurposing. The incretin glucagon-like peptide-1 (GLP-1) is a hormone secreted by intestinal epithelial cells. GLP-1 receptors (GLP-1R) are widely expressed in the central nervous system. Activation of GLP-1R leads to facilitation of glucose utilization and antiapoptotic effects in various organs. Pre-clinical trials have demonstrated significant neuroprotective effects of GLP-1, including protection from cell death, promotion of neuronal differentiation and proliferation; and facilitation of long-term potentiation. Liraglutide is a GLP-1R agonist that has been approved for the treatment of type 2 diabetes mellitus and obesity. Convergent preclinical and clinical evidence, including a proof-of-concept pilot study from group, has suggested that liraglutide may improve objective measures of cognitive function in adults with mood disorders. The safety and availability of GLP-1R agonists indicate that they are promising candidates for repurposing, and that they may be viable therapeutic options for mood disorders. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'

Depressive symptoms and poorer performance on the Stroop Task are associated with weight gain

OBJECTIVE

Executive function impairments and depression are associated with obesity but whether they predict weight gain is unclear.

METHODS

Forty-six individuals (35m, 37±10y) completed the Stroop Task, Iowa Gambling Task (IGT), Wisconsin Card Sorting Task (WCST), Inventory for Depressive Symptomatology (IDS-SR), Physical Anhedonia Scale (PAS), and Perceived Stress Scale (PSS). Body composition (DXA) and fasting glucose were also measured. Data from return visits were used to assess changes in weight.

RESULTS

Poorer Stroop and WCST performance associated with higher BMI whereas poorer IGT and WCST performance associated with higher body fat (%; all p's≤0.05). Stroop interference (p=0.04; p=0.05) and IDS-SR (p=0.06; p=0.02) associated with increased BMI and weight gain (%/yr). In a multivariate linear model Stroop interference (β=0.40, p<0.01; β=0.35, p<0.01) and IDS-SR (β=0.38, p<0.01; β=0.37, p<0.01) independently predicted increased BMI and weight gain (%/yr) even after controlling for baseline weight and glucose levels.

CONCLUSIONS

Poorer response inhibition and depressive symptoms, but not glucose levels, predicted weight gain. Evaluating neurocognitive and mood deficits could improve current treatment strategies for weight loss. Clinical Trial Registration Numbers NCT00523627, NCT00342732, NCT01224704. clinicaltrials.gov.

Obesity, Appetite, and the Prefrontal Cortex

PURPOSE OF REVIEW

Obesity is a chronic illness and its prevalence is growing worldwide and numerous factors play a role in the regulation of food intake. The prefrontal cortex (PFC) is involved in high-order executive function, regulation of limbic reward regions, and the inhibition of impulsive behaviors. Understanding the role of the PFC in the control of appetite regulation may contribute to a greater understanding of the etiology of obesity and could improve weight loss outcomes.

RECENT FINDINGS

Neuroimaging studies have identified lower activation in the left dorsolateral PFC (DLPFC) in obese compared to lean individuals and others have focused on efforts to improve cognitive control in this area of the brain. The DLPFC is a critical brain area associated with appetitive control, food craving, and executive functioning, indicating a candidate target area for treatment. Further studies are needed to advance our understanding of the relationship between obesity, appetite, and the DLPFC and provide validation for the effectiveness of novel treatments in clinical populations.

Treatment with a GLP-1R agonist over four weeks promotes weight loss-moderated changes in frontal-striatal brain structures in individuals with mood disorders

Cognitive deficits are a core feature across psychiatric disorders. Emerging evidence indicates that metabolic pathways are highly relevant for the substrates and phenomenology of the cognitive domain. Herein, we aimed to determine the effects of liraglutide, a GLP-1R agonist, on brain structural/volumetric parameters in adults with a mood disorder. This is the secondary analysis of a 4-week, pilot, proof-of-concept, open-label study. Participants (N=19) exhibiting impairments in executive function with either major depressive disorder (MDD) or bipolar disorder (BD) were recruited. Liraglutide 1.8mg/day was added as an adjunct to existing pharmacotherapy. Structural magnetic resonance imaging (MRI) scanning was obtained at baseline and endpoint. Results showed that at endpoint there was significant weight loss (mean: 3.15%; p<0.001). Changes in frontal and striatal volumes were significantly correlated with changes in body mass index (BMI), indicating the weight loss was associated with volume increase in most regions (e.g. r=-0.561, p=0.042 in the left superior frontal area). After adjusting for intracranial volume, age, gender, and BMI, we observed significant changes from baseline to endpoint in multiple regions (e.g. RR: 1.011, p=0.049 in the left rostral middle frontal area). Changes in regional volumes were associated with improvement in executive function (e.g. r=0.698, p=0.003 for the right superior frontal area). Adjunctive liraglutide results in clinically significant weight loss, with corresponding improvement in cognitive function; changes in cognitive function were partially moderated by changes in brain morphometry, underscoring the interrelationship between weight and brain structure/function.

Higher insulin and higher body fat via leptin are associated with disadvantageous decisions in the Iowa gambling task

Elevated body mass index and post-prandial state are associated with disadvantageous choices on the Iowa Gambling Task (IGT). Whether physiological factors including percent body fat, and peripheral glucose, insulin, and leptin concentrations, are associated with IGT performance is unknown. In196 healthy adults without diabetes, we measured body fat by DXA scan, glucose, insulin and leptin (n=138) concentrations during an oral glucose tolerance test and IGT performance after a standardized meal. Glucose was not associated with IGT performance. Disadvantageous IGT performance was associated with higher percent body fat (r=-0.16, p=0.03), 30-min insulin concentrations (insulin₃₀, r=-0.27, p<0.001), and 30-min leptin concentrations (leptin₃₀, r=-0.23, p=0.008). Mediation analysis demonstrated that leptin₃₀ was almost completely responsible for the percent body fat effect on IGT performance. Even adjusted for age, sex, race, and education, insulin₃₀ (b=-46.5, p=0.03) and leptin₃₀ (b=-50.9, p=0.03) concentrations remained independently associated with IGT performance and interacted together such that higher leptin₃₀ blunted effects of higher insulin₃₀ (b=23.8, p=0.048). These findings may indicate an internal metabolic signature of energy availability (higher body fat, insulin, and leptin levels) associated with disadvantageous IGT performance.

Modulation of Irisin and Physical Activity on Executive Functions in Obesity and Morbid obesity

Whether the executive profile is different between obesity (OB) and morbid obesity (MO) remains unclear. Recent evidence suggests that physical activity (PA) can act as a cognitive enhancer. Irisin is a recently discovered hormone associated with some of the positive effects of PA. The objective of the study was to investigate the executive profile in OB and MO, and to explore the role of PA and irisin. 114 participants were included (21 OB, 44 MO and 49 healthy controls-HC) in the study and assessed with the Wisconsin Card Sorting Test, Stroop Color and Word Test, and Iowa Gambling Task. All participants were female, aged between 18 and 60 years. Results showed a similar dysfunctional profile on decision making in OB and MO compared with HC. Thus, no specific neuropsychological profiles between OB and MO can be clearly observed in our sample. However, a negative correlation was found between irisin and executive functioning. These results demonstrate a specific executive profile in OB and a relevant and negative modulation of irisin on executive functioning. Although irisin might be a promising target for the treatment of obesity, its effects on cognition might be considered when thinking about its therapeutic use.

Associations between Markers of Glucose and Insulin Function and Cognitive Function in Healthy African American Elders

BACKGROUND

Glucose and insulin are important moderators of cognitive function. African Americans have poorer glycemic control across the glycemic spectrum and are at increased risk for type 2 diabetes and poor cognitive health. It is unclear which glucoregulatory markers predict cognitive function in this at-risk population. The purpose of this study was to examine the association between cognitive function and common markers of glucoregulation in non-diabetic African Americans elders.

METHODS

Thirty-four, community-dwelling African Americans, aged 50-75 years completed cognitive testing and blood collection as part of a health screening assessment. Cognitive outcomes were composite scores derived from neuropsychological tests of executive function and verbal memory. Linear regression was used to examine relationships between cognitive composite scores and fasting blood levels of glucose, insulin, and hemoglobin A1C, with adjustments for age, education, body mass index, and antihypertensive medication use.

RESULTS

Fasting plasma glucose was negatively associated with executive function (β=-0.41, p=0.03). There was a trend of an association between fasting plasma glucose and verbal memory (β=-0.34, p=0.06). Fasting insulin and hemoglobin A1c were not associated with cognitive function.

CONCLUSION

High non-diabetic fasting glucose levels were associated with poorer executive function and verbal memory. These results provide preliminary support for proactive glucose control in older African Americans even before glycemic criteria for type 2 diabetes are met. Our findings suggests that high-normal FPG levels may represent an early red-flag to signify increased risk of cognitive impairment or decline.