Effects of hypoglycaemia on working memory and regional cerebral blood flow in type 1 diabetes: a randomised, crossover trial

The Glucagon Receptor Is Expressed in the Frontal Cortex and Impaired Signaling Associates With Cognitive Decline

Individuals with type 2 diabetes (T2D) have an elevated risk of cognitive decline, yet the mechanisms connecting these pathologies remain unclear. Altered glucagon and insulin signaling contribute to T2D, and insulin resistance may also be associated with cognitive decline. The role of glucagon in this context is unknown. Here we aimed to characterize glucagon receptor (GCGR) expression in brain tissue and investigate the potential impact of altered GCGR signaling on dementia prevalence and cognitive function. We investigated GCGR protein expression in various human brain regions and cell types in postmortem brain samples. To explore the potential link between GCGR signaling and cognitive function, individuals with specific GCGR mutations with known or predicted impaired GCGR signaling were examined in connection to the prevalence of dementia defined by International Classification of Diseases, Tenth Revision coding and by cognitive function using population-scale cognitive tests in the UK Biobank. GCGR mRNA and protein were expressed specifically in neurons of the frontal cortex. Varying degrees of expression were observed across brain regions and with higher expression in the parietal cortex and thalamus by antibody-dependent analyses. GCGR variant carriers did not have a significantly higher prevalence of dementia, but 1 cognitive test was significantly impaired in individuals with a GCGR cAMP loss-of-function variant compared to sex- and age-matched nonvariant carrier controls. Our findings indicate GCGR expression in the human brain, particularly in neurons of the frontal cortex, and altered glucagon signaling may be associated with lower cognitive function. Further research is needed to elucidate mechanisms underlying the potential link between altered GCGR signaling and cognitive decline.

The effects of acute hyperglycaemia on sports and exercise performance in type 1 diabetes: A systematic review and meta-analysis

OBJECTIVES

People with type 1 diabetes (T1D) are advised by health care professionals to target mild hyperglycaemia before and during exercise, to reduce the risk of hypoglycaemia. This review aimed to summarise the available evidence on the effects of acute hyperglycaemia on sports and exercise performance in T1D.

DESIGN

Systematic review and meta-analysis.

METHODS

Medline, EMBASE, CENTRAL, and Web of Science were searched until 29th May 2023 for studies investigating the effects of acute hyperglycaemia on any sports or exercise performance outcome in T1D. Random-effects meta-analysis was performed using standardised mean differences (SMD) when more than one study reported data for similar outcomes. Certainty of evidence for each outcome was assessed using GRADE.

RESULTS

Seven studies were included in the review, comprising data from 119 people with T1D. Meta-analysis provided moderate-certainty evidence that acute hyperglycaemia does not significantly affect aerobic exercise performance (SMD -0.17; 95 % CI -0.59, 0.26; p = 0.44). There is low- or very-low certainty evidence that acute hyperglycaemia has no effect on anaerobic (two outcomes), neuromuscular (seven outcomes) or neurocognitive performance (three outcomes), except impaired isometric knee extension strength. One study provided low-certainty evidence that the performance effects of hyperglycaemia may depend on circulating insulin levels.

CONCLUSIONS

Acute hyperglycaemia before or during exercise appears unlikely to affect aerobic performance to an extent that is relevant to most people with T1D, based on limited evidence. Future research in this field should focus on anaerobic, neuromuscular and neurocognitive performance, and examine the relevance of circulating insulin levels.

Effect of hypoglycemia on cognitive performance in older patients with diabetes: A meta-analysis

GOALS

The goal of this study was to use meta-analysis to compile information from various studies to investigate the existence and severity of cognitive impairment in elderly diabetes patients who have hypoglycemic episodes.

MATERIALS AND TECHNIQUES

For research studies on the relationship between hypoglycemia and cognitive decline or dementia in persons older than 45 years, we searched the PubMed, EMBASE, Cochrane Library, CNKI, WanFang, CBM and VIP databases for the period 1989 to 2022. We conducted random effects inverse variance on the meta-analysis and used the I2 statistic to assess heterogeneity.

RESULT

We selected 44 of the 518 studies we retrieved, 7 being appropriate for meta-analysis. Six thousand and forty-five individuals were involved in total. Both types of older diabetic patients with hypoglycemia performed considerably worse on tests of general intelligence than control participants (standardized mean difference, 0.58; 95% CI, 0.88-0.28). Also, elderly type-2 diabetes patients with hypoglycemic episodes had significantly worse memory performance (standardized mean difference, 0.19; 95% CI, 0.29-0.09). Additionally, we found that older type-2 diabetes patients with hypoglycemia had significantly poorer psychomotor function than those without hypoglycemia (standardized mean difference, 0.51; 95% CI, 0.38-0.63).

Potential risk factors for mild cognitive impairment among patients with type 2 diabetes experiencing hypoglycemia

AIMS

This study examined the association between hypoglycemia and mild cognitive impairment (MCI) among patients with type 2 diabetes mellitus (T2DM) and identified risk factors for MCI in patients with hypoglycemia.

METHODS

In this retrospective study, 328 patients with T2DM were screened in 2019 and followed up in 2022. Cognitive performance was assessed using the Montreal Cognitive Assessment (MoCA). The diagnosis of MCI was based on established criteria. Risk ratio (RR) with 95 % confidence intervals (CI) was calculated to estimate the risk of MCI. Univariate and multivariate logistic regression analyses were conducted to identify risk factors for MCI in those with hypoglycemia.

RESULTS

Patients with hypoglycemia had lower cognitive performance 3 years later. The RR of MCI was 2.221 (95 % CI 1.269-3.885). Multivariate logistic analysis showed that low grip strength, existing diabetic retinopathy (DR), and multiple hypoglycemia episodes were associated with higher odds of MCI in patients with hypoglycemia (adjusted odds ratio [OR] 0.909 [95 % CI 0.859-0.963]), 3.078 [95 % CI 1.158-12.358], and 4.642 [95 % CI 1.284-16.776], respectively, all P < 0.05).

CONCLUSIONS

Hypoglycemia increased MCI risk among patients with T2DM. Low grip strength, DR, and multiple hypoglycemia episodes may be potential risk factors for hypoglycemia-associated MCI.

Central nervous system microstructural alterations in Type 1 diabetes mellitus: A systematic review of diffusion Tensor imaging studies

AIMS

Type 1 diabetes mellitus (T1DM) is a chronic childhood disease with potentially persistent CNS disruptions. In this study, we aimed to systematically review diffusion tensor imaging studies in patients with T1DM to understand the microstructural effects of this entity on individuals' brains METHODS: We performed a systematic search and reviewed the studies to include the DTI studies in individuals with T1DM. The data for the relevant studies were extracted and a qualitative synthesis was performed.

RESULTS

A total of 19 studies were included, most of which showed reduced FA widespread in optic radiation, corona radiate, and corpus callosum, as well as other frontal, parietal, and temporal regions in the adult population, while most of the studies in the juvenile patients showed non-significant differences or a non-persistent pattern of changes. Also, reduced AD and MD in individuals with T1DM compared to controls and non-significant differences in RD were noted in the majority of studies. Microstructural alterations were associated with clinical profile, including age, hyperglycemia, diabetic ketoacidosis and cognitive performance.

CONCLUSION

T1DM is associated with microstructural brain alterations including reduced FA, MD, and AD in widespread brain regions, especially in association with glycemic fluctuations and in adult age.

Potential Biochemical Mechanisms of Brain Injury in Diabetes Mellitus

The goal of this review was to summarize current biochemical mechanisms of and risk factors for diabetic brain injury. We mainly summarized mechanisms published in the past three years and focused on diabetes induced cognitive impairment, diabetes-linked Alzheimer's disease, and diabetic stroke. We think there is a need to conduct further studies with increased sample sizes and prolonged period of follow-ups to clarify the effect of DM on brain dysfunction. Additionally, we also think that enhancing experimental reproducibility using animal models in conjunction with application of advanced devices should be considered when new experiments are designed. It is expected that further investigation of the underlying mechanisms of diabetic cognitive impairment will provide novel insights into therapeutic approaches for ameliorating diabetes-associated injury in the brain.

Characteristics influencing expected cognitive performance during hypoglycaemia in type 2 diabetes

BACKGROUND

Acute hypoglycaemia is associated with cognitive impairment in patients with type 2 diabetes. However, there is limited understanding of the relationship between patients' expected cognitive difficulties and their objectively-measured deficits during non-severe hypoglycaemia.

OBJECTIVE

This report investigates demographic and clinical factors associated with the discrepancy between expected (i.e., self-evaluated) and measurable (i.e., neuropsychological) cognitive functions in patients with type 2 diabetes during acute non-severe hypoglycaemia.

METHODS

We performed an analysis of factors associated with the relationship between expected and measurable cognitive performance for data collected from a cohort of patients with type 2 diabetes (N = 25). Patients attended two experimental visits during which we performed hyper-insulinaemic glucose clamping; (i) non-severe hypoglycaemic clamp (plasma glucose (PG): 3.1 ± 0.3 mmol/L) and (ii) normoglycaemic clamp (PG: 5.8 ± 0.3 mmol/L), as part of a double-blinded cross-over study. During hypoglycaemia, patients' expected cognitive performance was assessed with a visual analogue scale after which objective cognitive functions were assessed with a neuropsychological test battery. We computed a global 'cognitive discrepancy' composite variable with score values on a scale between -10 and +10 using a novel statistical formula that creates a discrepancy score between subjective and objective cognition. Positive values reflect more expected than objectively-measured difficulties, while negative values reflect disproportionately more objectively-measured than expected cognitive difficulties. We used paired samples t-tests to compare degree of cognitive discrepancy between conditions of hypo- and normoglycaemia, while multiple regression analysis was performed to identify factors associated with the degree and direction of the cognitive discrepancy. The significance level for the analyses was p ≤ 0.05 (two-tailed).

RESULTS

Patients generally underestimated their cognitive abilities (M = 1.6, SD = 3.3) during hypoglycaemia compared to normoglycaemia (M = -1.0, SD = 3.5) (p = 0.2), t(23) = 2.9, p < 0.01. Underestimation of cognitive capacity during hypoglycaemia was more pronounced for patients with younger age (β = 0.5, p = 0.02), higher verbal IQ (β = 0.5, p = 0.03), and more hypoglycaemia-related shakiness (β = 0.4, p = 0.03).

LIMITATIONS

The modest sample size limits the generalizability of the findings.

CONCLUSIONS

Patients with type 2 diabetes underestimated their cognitive abilities during non-severe hypoglycaemic states, especially those with younger age, higher IQ, and more hypoglycaemia-related shakiness. These patients may thus have excessive preoccupations with their cognitive difficulties in relation to cognitively challenging daily life situations.

Type-1 diabetes shapes working memory processing strategies

BACKGROUND

Type 1 diabetes (T1D) is a metabolic disorder characterized by recurrent hypo- and hyperglycemic episodes, whose clinical development has been associated with cognitive and working memory (WM) deficits.

OBJECTIVE

To contrast quantitative electroencephalography (qEEG) measures between young patients with T1D and healthy controls while performing a visuospatial WM task with two memory load levels and facial emotional stimuli.

METHODS

Four or five neutral or happy faces were sequentially and pseudo-randomly presented in different spatial locations, followed by subsequent sequences displaying the reversed spatial order or any other. Participants were instructed to discriminate between these two alternatives during EEG recording.

RESULTS

A significant increase in the absolute power of the delta and theta bands, distributed mainly over the frontal region was found during task execution, with a slight decrease of alpha band power in both groups but mainly in control individuals. However, these changes were more pronounced in the T1D patients, and reached their maximum level during the WM encoding phase, even on trials with the lower memory load. In contrast, changes seemed to occur more gradually in controls and results differed significantly only on the trials with the higher WM load.

CONCLUSIONS

These results reflect adaptive WM-processing mechanisms in which cognitive strategies have evolved in T1D patients in order to meet task demands.

Impaired Awareness of Hypoglycemia Disrupts Blood Flow to Brain Regions Involved in Arousal and Decision Making in Type 1 Diabetes

OBJECTIVE

Impaired awareness of hypoglycemia (IAH) affects one-quarter of adults with type 1 diabetes and significantly increases the risk of severe hypoglycemia. Differences in regional brain responses to hypoglycemia may contribute to the susceptibility of this group to problematic hypoglycemia. This study investigated brain responses to hypoglycemia in hypoglycemia aware (HA) and IAH adults with type 1 diabetes, using three-dimensional pseudo-continuous arterial spin labeling (3D pCASL) functional MRI to measure changes in regional cerebral blood flow (CBF).

RESEARCH DESIGN AND METHODS

Fifteen HA and 19 IAH individuals underwent 3D pCASL functional MRI during a two-step hyperinsulinemic glucose clamp. Symptom, hormone, global, and regional CBF responses to hypoglycemia (47 mg/dL [2.6 mmol/L]) were measured.

RESULTS

In response to hypoglycemia, total symptom score did not change in those with IAH (P = 0.25) but rose in HA participants (P < 0.001). Epinephrine, cortisol, and growth hormone responses to hypoglycemia were lower in the IAH group (P < 0.05). Hypoglycemia induced a rise in global CBF (HA P = 0.01, IAH P = 0.04) but was not different between groups (P = 0.99). IAH participants showed reduced regional CBF responses within the thalamus (P = 0.002), right lateral orbitofrontal cortex (OFC) (P = 0.002), and right dorsolateral prefrontal cortex (P = 0.036) and a lesser decrease of CBF in the left hippocampus (P = 0.023) compared with the HA group. Thalamic and right lateral OFC differences survived Bonferroni correction.

CONCLUSIONS

Responses to hypoglycemia of brain regions involved in arousal, decision making, and reward are altered in IAH. Changes in these pathways may disrupt IAH individuals' ability to recognize hypoglycemia, impairing their capacity to manage hypoglycemia effectively and benefit fully from conventional therapeutic pathways to restore awareness.

Experimental non-severe hypoglycaemia substantially impairs cognitive function in type 2 diabetes: a randomised crossover trial

AIMS/HYPOTHESIS

Previous studies have demonstrated a relationship between cognitive impairment and hypoglycaemia (<3 mmol/l). This study hypothesised that non-severe insulin-induced hypoglycaemia reduces cognitive function in individuals with type 2 diabetes.

METHODS

In this randomised crossover study, 25 participants with type 2 diabetes attended two experimental visits with hyperinsulinaemic glucose clamping: one hypoglycaemic clamp (plasma glucose 3.0 ± 0.2 mmol/l) and one euglycaemic clamp (plasma glucose 6.0 ± 0.2 mmol/l). Participants were eligible if their diabetes was treated with diet or glucose-lowering medications (except sulfonylureas or insulin), age was 35-70 years, BMI was 23-35 kg/m² and HbA_1c was below 75 mmol/mol (9%). Cognitive function was assessed with a neurocognitive test battery measuring verbal memory, executive function, sustained attention and psychomotor speed. From the examined cognitive domains, a global cognition score was constructed estimating global cognition. A measurement for psychomotor speed was selected as the primary outcome. Participants and people assessing the outcomes were blinded to group assignment.

RESULTS

Cognitive performance was impaired during hypoglycaemia with a mean score in the primary outcome test, Symbol Digit Modalities Test measuring psychomotor speed, of 48.7 ± 9.8 (hypoglycaemia) vs 56.6 ± 12.0 (euglycaemia); i.e. a change of -7.9 points (95% CI -10.9, -4.9; p < 0.0001). In addition, hypoglycaemia reduced global cognitive score by -0.7 (95% CI -0.9, -0.6; p < 0.0001). A stable glucose plateau was achieved during both experimental visits. For the hypoglycaemic clamp, mean plasma glucose concentration (± SD) during neurocognitive testing was 3.1 (± 0.3) mmol/l. Age, sex, fasting C-peptide, counter-regulatory hormones and the severity of hypoglycaemic symptoms did not influence cognitive function.

CONCLUSIONS/INTERPRETATION

Acute non-severe hypoglycaemia (mean plasma glucose 3.1 mmol/l) has a substantial negative impact on cognitive function in individuals with type 2 diabetes.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03014011.

FUNDING

The study was supported in part by a research grant from the Investigator Initiated Studies Program of Merck Sharp & Dohme Corp (MSD-MA-NORD-007-01). The opinions expressed in this paper are those of the authors and do not necessarily represent those of Merck Sharp & Dohme Corp. Funding was also received from Skibsreder Per Henriksen, R. og hustrus Foundation, The Danish Alzheimer Foundation and Savværksejer Jeppe Juhl og hustrus Foundation.

Association of Type 1 Diabetes With Standardized Test Scores of Danish Schoolchildren

IMPORTANCE

Type 1 diabetes has been associated with cardiovascular disease and late complications such as retinopathy and nephropathy. However, it is unclear whether there is an association between type 1 diabetes and school performance in children.

OBJECTIVE

To compare standardized reading and mathematics test scores of schoolchildren with type 1 diabetes vs those without diabetes.

DESIGN, SETTING, AND PARTICIPANTS

Population-based retrospective cohort study from January 1, 2011, to December 31, 2015 (end date of follow-up), including Danish public schoolchildren attending grades 2, 3, 4, 6, and 8. Test scores were obtained in math (n = 524 764) and reading (n = 1 037 006). Linear regression models compared outcomes with and without adjustment for socioeconomic characteristics.

EXPOSURES

Type 1 diabetes.

MAIN OUTCOMES AND MEASURES

Primary outcomes were pooled test scores in math and reading (range, 1-100).

RESULTS

Among 631 620 included public schoolchildren, the mean (SD) age was 10.31 (SD, 2.42) years, and 51% were male; 2031 had a confirmed diagnosis of type 1 diabetes. Overall, the mean combined score in math and reading was 56.11 (SD, 24.93). There were no significant differences in test scores found between children with type 1 diabetes (mean, 56.56) and children without diabetes (mean, 56.11; difference, 0.45 [95% CI, -0.31 to 1.22]). The estimated difference in test scores between children with and without type 1 diabetes from a linear regression model with adjustment for grade, test topic, and year was 0.24 (95% CI, -0.90 to 1.39) and 0.45 (95% CI, -0.58 to 1.49) with additional adjustment for socioeconomic status.

CONCLUSIONS AND RELEVANCE

Among Danish public schoolchildren, there was no significant difference in standardized reading and mathematics test scores of children with type 1 diabetes compared with test scores of children without diabetes.