Cognitive assessment in diabetes: the need for consensus

The attenuation effect of potassium 2-(1-hydroxypentyl)-benzoate in a mouse model of diabetes-associated cognitive decline: The protein expression in the brain

Aims

dl‐PHPB (potassium 2‐(1‐hydroxypentyl)‐benzoate) has been shown to have neuroprotective effects against acute cerebral ischemia, vascular dementia, and Alzheimer's disease. The aim of this study was to investigate the effects of dl‐PHPB on memory deficits and preliminarily explore the underlying molecular mechanism.

Methods

Blood glucose and behavioral performance were evaluated in the KK‐A^y diabetic mouse model before and after dl‐PHPB administration. Two‐dimensional difference gel electrophoresis (2D‐DIGE)‐based proteomics was used to identify differentially expressed proteins in brain tissue. Western blotting was used to study the molecular mechanism of the related signaling pathways.

Results

Three‐month‐old KK‐A^y mice were given 150 mg/kg dl‐PHPB by oral gavage for 2 months, which produced no effect on the level of serum glucose. In the Morris water maze test, KK‐A^y mice treated with dl‐PHPB showed significant improvements in spatial learning and memory deficits compared with vehicle‐treated KK‐A^y mice. Additionally, we performed 2D‐DIGE to compare brain proteomes of 5‐month KK‐A^y mice treated with and without dl‐PHPB. We found 14 altered proteins in the cortex and 11 in the hippocampus; two of the 25 altered proteins and another four proteins that were identified in a previous study on KK‐A^y mice were then validated by western blot to further confirm whether dl‐PHPB can reverse the expression levels of these proteins. The phosphoinositide 3‐kinase/protein kinase B/glycogen synthase kinase‐3β (PI3K/Akt/GSK‐3β) signaling pathway was also changed in KK‐A^y mice and dl‐PHPB treatment could reverse it.

Conclusions

These results indicate that dl‐PHPB may play a potential role in diabetes‐associated cognitive impairment through PI3K/Akt/GSK‐3β signaling pathway and the differentially expressed proteins may become putative therapeutic targets.

Is there an association between non-alcoholic fatty liver disease and cognitive function? A systematic review

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is represented as the most common liver disease worldwide. NAFLD is associated with metabolic risk factors underpinned by insulin resistance, inflammation and endothelial dysfunction, leading to extrahepatic changes in central nervous diseases such as cognitive impairment, Alzheimer's disease and dementia. The aim of the review is to explore the association between NAFLD and cognitive function.

METHODS

Using the PRISMA guidelines, a systematic electronic literature search was conducted in four databases: MEDLINE, PsychINFO, Embase and CINAHL from inception until March 2021. Neuropsychological tests utilised within each study were grouped into relevant cognitive domains including 'general cognition', 'reasoning', 'mental speed, attention and psychomotor speed', 'memory and learning', 'language', 'visuospatial perception' and 'ideas, abstraction, figural creations and mental flexibility'.

RESULTS

Eleven observational studies that involved 7978 participants with a mean age of 51 years were included. Those with NAFLD had poor cognitive performance in three cognitive domains, including 'general cognition', 'mental speed, attention and psychomotor speed', and 'ideas, abstraction, figural creations and mental flexibility'.

CONCLUSION

The observed results from the 11 included studies showed that NAFLD was associated with lower cognitive performance across several domains. However, studies conducted to date are limited to observational designs and are heterogeneous with varying diagnostic tools used to assess cognitive function.

TRIAL REGISTRATION

PROSPERO Registration: CRD42020161640 .

Effects of exercise, cognitive, and dual-task interventions on cognition in type 2 diabetes mellitus: A systematic review and meta-analysis

Introduction

Previous evidence has shown significant effects of exercise, cognitive and dual-task training for improving cognition in healthy cohorts. The effects of these types of interventions in type 2 diabetes mellitus is unclear. The aim of this research was to systematically review evidence, and estimate the effect, of exercise, cognitive, and dual-task interventions on cognition in type 2 diabetes mellitus.

Method

Electronic databases including PubMed, EMBASE, CINAHL, PsycINFO, SPORTDiscus, and MEDLINE were searched for ongoing and completed interventional trials investigating the effect of either an exercise, cognitive or dual-task intervention on cognition in type 2 diabetes mellitus.

Results

Nine trials met the inclusion criteria–one dual-task, two cognitive, and six exercise. Meta-analyses of exercise trials showed no significant effects of exercise on measures of executive function (Stroop task, SMD = -0.31, 95% CI -0.71–0.09, P = 0.13, trail making test part A SMD = 0.28, 95% CI -0.20–0.77 P = 0.25, trail making test part B SMD = -0.15, 95% CI -0.64–0.34 P = 0.54, digit symbol SMD = 0.09, 95% CI -0.39–0.57 P = 0.72), and memory (immediate memory SMD = 0.20, 95% CI -0.28–0.69, P = 0.41 and delayed memory SMD = -0.06, 95% CI -0.55–0.42, P = 0.80). A meta-analysis could not be conducted using cognitive or dual-task data, but individual trials did report a favourable effect of interventions on cognition. Risk of bias was considered moderate to high for the majority of included trials.

Conclusions

Meta-analyses of exercise trials identified a small effect size (0.31), which whilst not significant warrants further investigation. Larger and more robust trials are needed that report evidence using appropriate reporting guidelines (e.g. CONSORT) to increase confidence in the validity of results.

Trial registration

Protocol was registered (CRD42017058526) on the International Prospective Register of Systematic Reviews (http://www.crd.york.ac.uk/PROSPERO).

Evaluation of Relation between HbA1c Level with Cognitive Disorders and Depression in Type 2 Diabetes Mellitus Patients

BACKGROUND:

The role of HbA1c level in cognition decline and depression in type 2 diabetic patients is reported in some studies.

AIM:

We evaluated the possible significant relationship between HbA1c level and cognition decline and depression in type 2 diabetic patients.

MATERIAL AND METHODS:

This descriptive-analytic study was performed on 512 patients with a different HbA1c level and ages range. All subjects were administered a structured clinical interview. Cognitive functions and depressive disorders were assessed through the Mini-Mental Status Exam (MMSE) and Patient Health Questionnaire-9 (PHQ-9) respectively. Chi-square test was used for relationships between variables.

RESULTS:

HbA1c mean in all patients was 7.58%. MMSE score mean in total was 27.28. 83.3% of patients had a depressive disorder, and 8.59% of patients had an MMSE score < 24. There was no significant relationship between HbA1c level and cognitive problems, but there was a significant relationship between recent memory declines with the level of HbA1c (P = 0.03). Also, there was no significant relationship between attention-deficit with HbA1c level.

CONCLUSION:

Our finding provides that even though there is no significant difference between HbA1c level and cognitive problems and depression, recent memory state in these patients are more affected than the normal population and these patients have a worse state of depressive disorders.

Effects of Regular Physical Activity on the Cognitive Performance of Type 2 Diabetic Patients: A Systematic Review

BACKGROUND

Cognitive decline has been shown to be associated with long-term type 2 diabetes mellitus (T2DM). This review analyzes the present literature to ascertain the role of regular physical activity (PA) for the functioning of the diabetic brain.

METHODS

PubMed was systematically searched for relevant publications up to July 2017.

RESULTS

Four cross-sectional, one longitudinal observational, and nine interventional studies with a total of ∼7000 T2DM subjects are included in this review. Some significant positive relationships between the PA level of T2DM patients and their performance in several cognitive tests are reported in the cross-sectional studies. The longitudinal observational study implies a higher risk for developing dementia/mild cognitive impairment in T2DM patients with low PA behavior. Some significantly improved cognitive test results are reported for T2DM patients following physical training (PT) in six interventional studies. The quality of most of the training studies is low due to small sample sizes and/or missing control groups.

DISCUSSION

PT may potentially contribute to improving the cognitive performance in T2DM patients. Additional high-quality studies with standardized cognitive assessments are needed to further determine the dose-effect relationships between PA and cognitive performance in T2DM patients.

Magnitude of cognitive dysfunction in adults with type 2 diabetes: a meta-analysis of six cognitive domains and the most frequently reported neuropsychological tests within domains

The objectives were to conduct a meta-analysis in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) standards to determine effect sizes (Cohen's d) for cognitive dysfunction in adults with type 2 diabetes, relative to nondiabetic controls, and to obtain effect sizes for the most commonly reported neuropsychological tests within domains. Twenty-four studies, totaling 26,137 patients (n = 3351 with diabetes), met study inclusion criteria. Small to moderate effect sizes were obtained for five of six domains: motor function (3 studies, n = 2374; d = -0.36), executive function (12 studies, n = 1784; d = -0.33), processing speed (16 studies, n = 3076; d = -0.33), verbal memory (15 studies, n = 4,608; d = -0.28), and visual memory (6 studies, n = 1754; d = -0.26). Effect size was smallest for attention/concentration (14 studies, n = 23,143; d = -0.19). The following tests demonstrated the most notable performance decrements in diabetes samples: Grooved Pegboard (dominant hand) (d = -0.60), Rey Auditory Verbal Learning Test (immediate) (d = -0.40), Trails B (d = -0.39), Rey-Osterreith Complex Figure (delayed) (d = -0.38), Trails A (d = -0.34), and Stroop Part I (d = -0.28). This study provides effect sizes to power future epidemiological and clinical diabetes research studies examining cognitive function and to help inform the selection of neuropsychological tests.

Testing covariates of Type 2 diabetes-cognition associations in older adults: moderating or mediating effects?

OBJECTIVE

The general goal of this study was to advance our understanding of Type 2 diabetes (T2D)-cognition relationships in older adults by linking and testing comprehensive sets of potential moderators, potential mediators, and multiple cognitive outcomes.

METHOD

We identified in the literature 13 health-related (but T2D-distal) potential covariates, representing four informal domains (i.e., biological vitality, personal affect, subjective health, lifestyle activities). Cross-sectional data from the Victoria Longitudinal Study (age range = 53-90 years; n = 41 T2D and n = 458 control participants) were used. We first examined whether any of the 13 potential covariates influenced T2D-cognition associations, as measured by a comprehensive neuropsychological battery (15 measures). Next, using standard regression-based moderator and mediator analyses, we systematically tested whether the identified covariates would significantly alter observed T2D-cognition relationships.

RESULTS

Six potential covariates were found to be sensitive to T2D associations with performance on seven cognitive measures. Three factors (systolic blood pressure, gait-balance composite, subjective health) were significant mediators. Each mediated multiple cognitive outcomes, especially measures of neurocognitive speed, executive functioning, and episodic memory.

CONCLUSIONS

Our findings offer a relatively comprehensive perspective of T2D-related cognitive deficits, comorbidities, and modulating influences. The implications for future research reach across several fields of study and application. These include (1) neuropsychological research on neural and biological bases of T2D-related cognitive decline, (2) clinical research on intervention and treatment strategies, and (3) larger-scale longitudinal studies examining the potential multilateral and dynamic relationships among T2D status, related comorbidities, and cognitive outcomes.

Cranial volume, mild cognitive deficits, and functional limitations associated with diabetes in a community sample

Diabetes is associated with dementia in older adults, but it remains unclear whether nondemented adults with type 2 diabetes show subtle abnormalities across cognition, neuroanatomy, and everyday functioning. Using the Aging, Brain Imaging, and Cognition study sample of 301 community-dwelling, middle-aged and older adults, we conducted a secondary analysis on 28 participants with and 150 participants without diabetes. We analyzed brain magnetic resonance imaging data, cognitive test performance, and informant ratings of personal and instrumental activities of daily living (PADL/IADL). Relative to controls, participants with diabetes had lower brain-to-intracranial volume ratios (69.3 +/- 4.5% vs. 71.7 +/- 4.6%; p < .02), and performed more poorly on measures of working memory, processing speed, fluency, and crystallized intelligence (all p <.05). Decrements in working memory and processing speed were associated with IADL limitations (p < .01). Nondemented adults with diabetes exhibit neuroanatomic and cognitive abnormalities. Their cognitive deficits correlate with everyday functional limitations.

Cognitive decline and dementia in diabetes--systematic overview of prospective observational studies

AIMS/HYPOTHESIS

We systematically reviewed and summarised prospective data relating diabetes status to changes in cognitive function over time.

METHODS

Published reports of longitudinal studies that described assessment of cognitive function in people with diabetes were sought. Studies were included if they assessed cognitive function in participants with diabetes at the beginning and at follow-up. Studies were excluded if they had (1) a follow-up period of less than 1 year, (2) a rate of loss to follow-up in excess of 30%, or (3) described selected subgroups. Change in cognitive function was recorded as either the mean change in score and/or the proportion of individuals developing various degrees of change in cognitive function. A pooled estimate was calculated for the latter.

RESULTS

Of 1,165 abstracts and titles initially identified, 25 articles met the inclusion and exclusion criteria. Individuals with diabetes had a 1.2- to 1.5-fold greater change over time in measures of cognitive function than those without diabetes. When assessed by the Mini-Mental State Exam and the Digit Symbol Span tests, a diagnosis of diabetes increased the odds of cognitive decline 1.2-fold (95% CI 1.05-1.4) and 1.7-fold (95% CI 1.3-2.3), respectively . The odds of future dementia increased 1.6-fold (95% CI 1.4-1.8).

CONCLUSIONS/INTERPRETATION

Compared to people without diabetes, people with diabetes have a greater rate of decline in cognitive function and a greater risk of cognitive decline. Cognitive dysfunction should therefore be added to the list of chronic complications of diabetes.

The relationship between type 2 diabetes and cognitive dysfunction: longitudinal studies and their methodological limitations

Type 2 diabetes and dementia in the elderly are major public health problems. Cross-sectional studies have suggested that these two conditions may be inter-related, but the nature of this association is uncertain. Causation can only be established through studies with a longitudinal design, taking into account the many potential confounding factors in any study of cognition. A literature search has identified 10 studies (nine population-based and one of case-controlled design) that included a definable diabetic population and assessments of cognitive function at baseline and at follow-up. These 10 studies utilised a combination of domain-specific cognitive assessments and a clinical diagnosis of dementia in the assessment of cognitive function. Diabetes was associated with either an accelerated cognitive decline or an increased incidence of dementia in eight of nine of the population-based studies. One study demonstrated a relationship between diabetes and vascular cognitive impairment, but not with other types of dementia. No association between type 2 diabetes and cognitive decline was demonstrated in the case-controlled study. These studies provide compelling evidence to support the view that people with type 2 diabetes are at increased risk of developing cognitive impairment in comparison with the general population.

Effects of improved glycaemic control maintained for 3 months on cognitive function in patients with Type 2 diabetes

BACKGROUND AND AIM

In a previous study we failed to find beneficial short-term effects of improved glycaemic control on cognitive functioning in patients with Type 2 diabetes mellitus. A subgroup of the entire sample was tested again to examine the effect of longer-lasting improvement of metabolic control on cognitive functioning.

METHODS

The cognitive performance of 26 patients with Type 2 diabetes was assessed at baseline and 3 months after discharge. Thirteen controls were tested at the similar time-points. Attention/concentration, psychomotor speed, verbal fluency, verbal memory and depressive symptoms were assessed. Improved glycaemic control was generally achieved with insulin therapy (20/26).

RESULTS

At baseline, there was a trend for diabetic patients to perform worse than controls. Both groups improved significantly over 3 months in several measures. However, diabetic patients did not improve more than controls.

CONCLUSIONS

In individuals with long-standing Type 2 diabetes, previous reports of improved cognitive capacity following restoration and maintenance of near-normoglycaemia were not confirmed. This might relate to the type of anti-diabetic therapy.

Short-term effects of improved glycemic control on cognitive function in patients with type 2 diabetes

BACKGROUND

According to numerous studies, type 2 diabetes is associated with mild cognitive dysfunction, and there is some evidence suggesting favorable effects of improved metabolic control on the mental capability of elderly diabetic patients.

OBJECTIVE

To compare patients with type 2 diabetes to normal controls with respect to cognitive performance and to investigate the consequences of glycemic adjustment.

METHODS

53 patients with type 2 diabetes, most of them in secondary failure on oral antidiabetic drugs, but free from conditions which may cause brain dysfunction, were included (mean age 58.8 +/- 6.1 years, duration of disease 12.0 +/- 6.4 years). They were examined prior to (t1), and following (t2) glycemic adjustment with a time interval of approximately 2 weeks. 29 non-diabetic controls, comparable with regard to age, gender, education and verbal intelligence were examined twice with a corresponding time interval. Cognitive performance was assessed by well-standardized tests with a focus on attention/concentration, psychomotor speed, verbal fluency and verbal memory; mood status by two self-rating scales. Restoration of glycemic control included insulin treatment in the majority of patients (46/53).

RESULTS

Diabetic subjects scored significantly lower in all cognitive tests used, while they did not differ from controls in mood status. From t1 to t2 they improved in those tests measuring attention/concentration, and psychomotor speed. With regard to similar changes in controls, we interpret these improvements as practice effects rather than the consequence of altered metabolic control.

CONCLUSION

In a sample of patients with long-standing type 2 diabetes we could not confirm previous reports of improved cognitive capacity with restoration of glycemic control. Further studies on the effects of changes in control of blood glucose on cognitive performance in type 2 diabetes should be conducted with special regard to drugs used to lower blood glucose.

A biethnic community survey of cognition in participants with type 2 diabetes, impaired glucose tolerance, and normal glucose tolerance: the New Mexico Elder Health Survey

OBJECTIVE

To determine whether elderly individuals with type 2 diabetes or impaired glucose tolerance are at increased risk for cognitive impairment compared with individuals with normal glucose tolerance.

RESEARCH DESIGN AND METHODS

Elderly Hispanic individuals (n = 414) and non-Hispanic white individuals (n = 469) aged > or =65 years, randomly selected from the Medicare rolls of Bernalillo County (Albuquerque), NM, were recruited for an interview/examination that included an evaluation of glucose tolerance. Information on nine tests of cognitive function and two measures of depression allowed comparisons between diabetic status and these functions. Comparisons also were made between glycosolated hemoglobin concentrations and these cognitive tests in the 188 participants with diabetes.

RESULTS

None of the mean scores on the tests of cognitive function was significantly lower in the participants with diabetes compared with those participants with normal glucose tolerance after adjustments for ethnicity, sex, age, level of education, and presence of depression, with or without elimination of those with dementia (Mini-Mental State Exam <18). Interestingly, participants with impaired glucose tolerance tended to score higher than those with normal glucose tolerance. No significant associations were found between glycosolated hemoglobin concentrations and cognitive test scores in participants with diabetes.

CONCLUSIONS

We could not show any increased risk for cognitive impairment in participants with diabetes compared with those with normal glucose tolerance after adjustments for ethnicity, sex, age, education, and presence of depression, before or after elimination of dementia in this random sample from a biethnic population of predominantly community-dwelling elders.

Changes in cognitive abilities over a 4-year period are unfavorably affected in elderly diabetic subjects: results of the Epidemiology of Vascular Aging Study

OBJECTIVE

To compare 4-year changes in cognitive performance among elderly subjects according to category of fasting blood glucose (FBG) using American Diabetes Association criteria.

RESEARCH DESIGN AND METHODS

Subjects without any detectable cognitive dysfunction were selected from the Epidemiology of Vascular Aging (EVA) Study, a cohort of community-dlwelling people aged 59-71 years at baseline. They were classified into glucose categories (normal, impaired fasting glucose [IFG], or diabetic) based on FBG values or known diabetes. Their cognitive abilities were assessed by a global test (Mini Mental Status Examination [MMSE]) and eight domain-specific tests, and they were reassessed 4 years later. Serious cognitive worsening was defined as a score evolution into the worst 15% of the sample's distribution of score differences (4-year score minus baseline score) for each test.

RESULTS

At baseline, age-, sex-, and education-adjusted scores for all cognitive tests except one were similar across glucose categories. After 4 years, diabetic subjects had a lower performance on all tests except the MMSE, with differences reaching statistical significance on four tests. Adjusted odds ratios for serious worsening over 4 years in diabetic subjects, with reference to normal subjects, were >2 for four tests (P < 0.05) and bordering this value for two others (P < 0.09). Further adjustment for blood pressure or potential cognition-affecting substances (alcohol, tobacco, and medications) did not modify these results.

CONCLUSIONS

Despite similar high initial cognitive function, diabetic subjects tended to have an unfavorable evolution of cognitive performance over 4 years compared with subjects who had normal glucose or IFG.

Type 2 diabetes mellitus, cognitive impairment and dementia

AIMS

We set out to examine the evidence for an association between cognitive impairment or dementia and the presence of Type 2 diabetes mellitus (DM). We also sought evidence of potential mechanisms for such an association.

METHODS

A literature search of three databases was performed and the reference lists of the papers so identified were examined, using English language papers only.

RESULTS

We found evidence of cross-sectional and prospective associations between Type 2 DM and cognitive impairment, probably both for memory and executive function. There is also evidence for an elevated risk of both vascular dementia and Alzheimer's disease in Type 2 DM albeit with strong interaction of other factors such as hypertension, dyslipidaemia and apolipoprotein E phenotype. Both vascular and non-vascular factors are likely to play a role in dementia in diabetes.

CONCLUSIONS

Current classification structures for dementia may not be adequate in diabetes, where mixed pathogenesis is likely. Further research into the mechanisms of cognitive impairment in Type 2 DM may allow us to challenge the concept of dementia, at least in these patients, as an irremediable disease.