Type 2 Diabetes Mellitus Is Associated with the Risk of Cognitive Impairment: a Meta-Analysis

The Effects of Type 2 Diabetes on Cognitive Performance: A Review of Reviews

BACKGROUND

Multiple systematic reviews have found that type 2 diabetes is associated with cognitive decrements. However, these reviews are heterogeneous in terms of methodology, quality and results, making it difficult for researchers and clinicians to build an informed overall picture. We therefore conducted a review of systematic reviews on the association between type 2 diabetes and cognitive decrements in relation to healthy controls.

METHODS

Following a pre-registered research protocol, we searched four major databases. Nine systematic reviews met our inclusion criteria: seven were meta-analyses and two were narrative syntheses. We assessed the risk of bias in each review and reported all effect sizes and confidence intervals obtained.

RESULTS

Type 2 diabetes was associated with cognitive decrements in all reviews, with small or negligible effect sizes obtained in the largest meta-analyses. The most studied cognitive domains were attention, executive functions, memory, processing speed and working memory. All reviews had methodological issues and were rated as having a high or an unclear risk of bias.

CONCLUSIONS

Type 2 diabetes appears to be associated with lower cognitive performance in several cognitive domains and in different age groups. However, high-quality meta-analyses on the subject are still needed. Future reviews must follow the PRISMA guidelines and take into account the risk of bias of the original studies through sensitivity analyses and the heterogeneity of the studies by conducting subgroup analyses for example according to age group and disease duration. The meta-analyses that aim to study the entire type 2 diabetes population without excluding severe comorbidities, should assess concept formation and reasoning, construction and motor performance, perception, and verbal functions and language skills in addition to the cognitive domains that have been most frequently analysed in the reviews conducted so far.

Characterizing cognitive phenotypes and clinical correlates in type 2 diabetes using fuzzy clustering and decision tree analysis

Cognitive impairment is frequently seen in patients with type 2 diabetes (T2DM), ranging from mild impairment to dementia. However, our knowledge of the specific profiles and risk factors for these different levels of impairment is limited. In this study involving 152 patients with T2DM, cognitive function was assessed using the Montreal Cognitive Assessment test. The Fuzzy C-means clustering algorithm was utilized to group individuals with similar cognitive characteristics. The study evaluated how well clinical parameters could classify characteristics of clusters using the Classification and Regression Trees algorithm. ROC analysis was then used to assess the classification success. Three distinct cognitive clusters were identified. Cluster 1 had the poorest cognitive performance and was characterized by more women, lower education levels, and lower levels of iron, hemoglobin, and creatine. Cluster 3, the amnestic cluster, was distinguished by low TSH levels. The decision tree model highlighted several parameters, including education level, hemoglobin, duration of diabetes mellitus (DM), iron, TSH, gender, family history of diabetes, and microalbumin/creatinine ratio, as significantly affecting the distinction of cognitive clusters. Diabetes-associated cognitive impairment stems from multifaceted pathophysiological mechanisms influenced by complex risk factors, resulting in diverse types of cognitive deficits.

Untargeted Metabolomic Profiling Reveals Differentially Expressed Serum Metabolites and Pathways in Type 2 Diabetes Patients with and without Cognitive Decline: A Cross-Sectional Study

Diabetes is recognized as a risk factor for cognitive decline, but the underlying mechanisms remain elusive. We aimed to identify the metabolic pathways altered in diabetes-associated cognitive decline (DACD) using untargeted metabolomics. We conducted liquid chromatography-mass spectrometry-based untargeted metabolomics to profile serum metabolite levels in 100 patients with type 2 diabetes (T2D) (54 without and 46 with DACD). Multivariate statistical tools were used to identify the differentially expressed metabolites (DEMs), and enrichment and pathways analyses were used to identify the signaling pathways associated with the DEMs. The receiver operating characteristic (ROC) analysis was employed to assess the diagnostic accuracy of a set of metabolites. We identified twenty DEMs, seven up- and thirteen downregulated in the DACD vs. DM group. Chemometric analysis revealed distinct clustering between the two groups. Metabolite set enrichment analysis found significant enrichment in various metabolite sets, including galactose metabolism, arginine and unsaturated fatty acid biosynthesis, citrate cycle, fructose and mannose, alanine, aspartate, and glutamate metabolism. Pathway analysis identified six significantly altered pathways, including arginine and unsaturated fatty acid biosynthesis, and the metabolism of the citrate cycle, alanine, aspartate, glutamate, a-linolenic acid, and glycerophospholipids. Classifier models with AUC-ROC > 90% were developed using individual metabolites or a combination of individual metabolites and metabolite ratios. Our study provides evidence of perturbations in multiple metabolic pathways in patients with DACD. The distinct DEMs identified in this study hold promise as diagnostic biomarkers for DACD patients.

Diabetes, antidiabetic medications and risk of dementia: A systematic umbrella review and meta-analysis

AIMS

The objective of this umbrella review and meta-analysis was to evaluate the effect of diabetes on risk of dementia, as well as the mitigating effect of antidiabetic treatments.

MATERIALS AND METHODS

We conducted a systematic umbrella review on diabetes and its treatment, and a meta-analysis focusing on treatment. We searched MEDLINE/PubMed, Embase, PsycINFO, CINAHL and the Cochrane Library for systematic reviews and meta-analyses assessing the risk of cognitive decline/dementia in individuals with diabetes until 2 July 2023. We conducted random-effects meta-analyses to obtain risk ratios and 95% confidence intervals estimating the association of metformin, thiazolidinediones, pioglitazone, dipeptidyl peptidase-4 inhibitors, α-glucosidase inhibitors, meglitinides, insulin, sulphonylureas, glucagon-like peptide-1 receptor agonists (GLP1RAs) and sodium-glucose cotransporter-2 inhibitors (SGLT2is) with risk of dementia from cohort/case-control studies. The subgroups analysed included country and world region. Risk of bias was assessed with the AMSTAR tool and Newcastle-Ottawa Scale.

RESULTS

We included 100 reviews and 27 cohort/case-control studies (N = 3 046 661). Metformin, thiazolidinediones, pioglitazone, GLP1RAs and SGLT2is were associated with significant reduction in risk of dementia. When studies examining metformin were divided by country, the only significant effect was for the United States. Moreover, the effect of metformin was significant in Western but not Eastern populations. No significant effect was observed for dipeptidyl peptidase-4 inhibitors, α-glucosidase inhibitors, or insulin, while meglitinides and sulphonylureas were associated with increased risk.

CONCLUSIONS

Metformin, thiazolidinediones, pioglitazone, GLP1RAs and SGLT2is were associated with reduced risk of dementia. More longitudinal studies aimed at determining their relative benefit in different populations should be conducted.

Cognitive Benefits of Sodium-Glucose Co-Transporters-2 Inhibitors in the Diabetic Milieu

Patients with diabetes are at higher risk of cognitive impairment and memory loss than the normal population. Thus, using hypoglycemic agents to improve brain function is important for diabetic patients. Sodium-glucose cotransporters-2 inhibitors (SGLT2i) are a class of therapeutic agents used in the management of diabetes that has some pharmacologic effects enabling them to fight against the onset and progress of memory deficits. Although the exact mediating pathways are not well understood, emerging evidence suggests that SGLT2 inhibition is associated with improved brain function. This study reviewed the possible mechanisms and provided evidence suggesting SGLT2 inhibitors could ameliorate cognitive deficits.

Distinct Roles for Brain and Pancreas in Basal and Postprandial Glucose Homeostasis

The glucose homeostasis system ensures that the circulating glucose level is maintained within narrow physiological limits both in the fasting (or basal) state and following a nutrient challenge. Although glucose homeostasis is traditionally conceptualized as a single overarching system, evidence reviewed here suggests that basal glycemia and glucose tolerance are governed by distinct control systems. Specifically, whereas glucose tolerance appears to be determined largely by interactions between insulin secretion and insulin sensitivity, basal-state glucose homeostasis is predominated by insulin-independent mechanisms governed largely by the brain. In addition to a new perspective on how glucose homeostasis is achieved, this "dual control system" hypothesis offers a feasible and testable explanation for observations that are otherwise difficult to reconcile and sheds new light on the integration of central and peripheral metabolic control mechanisms. The implications of this model for the pathogenesis and treatment of impaired fasting glucose, impaired glucose tolerance, and type 2 diabetes are also discussed.

Association between Blood Glucose Control and Subjective Cognitive Decline in Korean Patients with Diabetes Aged over 50 Years

This study aimed to investigate the association between blood glucose control and subjective cognitive decline in adult patients with diabetes. Using the 2018 data from the community health survey, we included 18,789 patients with diabetes aged ≥50 years who had complete responses recorded. Blood glucose control was the independent variable, and subjective cognitive decline was the dependent variable. Multivariable logistic regression analysis was used to analyze the association between blood glucose control and subjective cognitive decline. Multivariable logistic regression analysis showed that blood glucose control was inversely associated with subjective cognitive decline in patients with diabetes. Patients with uncontrolled blood glucose levels had higher odds of subjective cognitive decline than those with controlled blood glucose levels (odds ratio = 1.22; 95% confidence interval: 1.10, 1.34). Our findings suggest that patients with diabetes may demonstrate subjective cognitive decline if their blood glucose levels are not well-controlled.

Urban Neighbourhood Environments, Cardiometabolic Health and Cognitive Function: A National Cross-Sectional Study of Middle-Aged and Older Adults in Australia

Population ageing and urbanisation are global phenomena that call for an understanding of the impacts of features of the urban environment on older adults' cognitive function. Because neighbourhood characteristics that can potentially have opposite effects on cognitive function are interdependent, they need to be considered in conjunction. Using data from an Australian national sample of 4141 adult urban dwellers, we examined the extent to which the associations of interrelated built and natural environment features and ambient air pollution with cognitive function are explained by cardiometabolic risk factors relevant to cognitive health. All examined environmental features were directly and/or indirectly related to cognitive function via other environmental features and/or cardiometabolic risk factors. Findings suggest that dense, interconnected urban environments with access to parks, blue spaces and low levels of air pollution may benefit cognitive health through cardiometabolic risk factors and other mechanisms not captured in this study. This study also highlights the need for a particularly fine-grained characterisation of the built environment in research on cognitive function, which would enable the differentiation of the positive effects of destination-rich neighbourhoods on cognition via participation in cognition-enhancing activities from the negative effects of air pollutants typically present in dense, destination-rich urban areas.

Altered Regional Homogeneity in Patients With Diabetic Erectile Dysfunction: A Resting-State fMRI Study

INTRODUCTION

Erectile dysfunction (ED) is a common complication of Type-2 Diabetes Mellitus (T2DM) for male patients and it is considered to be associated with different causes including hyperglicemia-induced vascular endothelial cell damages. However, the possible central neural mechanisms shared by these two diseases remain unclear. This study aimed to explore the changes of brain activity and their relationships with the clinical characteristics in patients with diabetic ED.

METHODS

The data of resting-state functional magnetic resonance imaging were acquired in 31 T2DM patients with ED (DM-ED) and 31 matched healthy controls (HCs). The whole-brain regional homogeneity (ReHo) values were calculated and compared between groups. In addition, Pearson correlation analysis was performed to evaluate the relationships between brain regions with altered ReHo values and clinical characteristics in the patient group.

RESULTS

The DM-ED group exhibited increased ReHo values in the right middle frontal gyrus (orbital part) and decreased ReHo values in the left superior frontal gyrus (dorsolateral), paracentral lobule, precuneus and bilateral supplementary motor area when compared with the HCs group. Moreover, significantly negative correlations were found between ReHo values of the left superior frontal gyrus (dorsolateral) and IIEF-5 scores, as well as the level of HbA1c in the DM-ED group.

CONCLUSION

The altered spontaneous brain activity in cognitive-related regions revealed by ReHo values might provide new insights into the neurological pathophysiology underlying DM-ED and serve as potential neuroimaging biomarkers for detecting and evaluating ED in diabetes patients.

Glycemic Dysregulations Are Associated With Worsening Cognitive Function in Older Participants at High Risk of Cardiovascular Disease: Two-Year Follow-up in the PREDIMED-Plus Study

INTRODUCTION

Type 2 diabetes has been linked to greater cognitive decline, but other glycemic parameters such as prediabetes, diabetes control and treatment, and HOMA-IR and HbA1c diabetes-related biomarkers have shown inconsistent results. Furthermore, there is limited research assessing these relationships in short-term studies. Thus, we aimed to examine 2-year associations between baseline diabetes/glycemic status and changes in cognitive function in older participants at high risk of cardiovascular disease.

METHODS

We conducted a 2-year prospective cohort study (n=6,874) within the framework of the PREDIMED-Plus study. The participants (with overweight/obesity and metabolic syndrome; mean age 64.9 years; 48.5% women) completed a battery of 8 cognitive tests, and a global cognitive function Z-score (GCF) was estimated. At baseline, participants were categorized by diabetes status (no-diabetes, prediabetes, and <5 or ≥5-year diabetes duration), and also by diabetes control. Furthermore, insulin resistance (HOMA-IR) and glycated hemoglobin (HbA1c) levels were measured, and antidiabetic medications were recorded. Linear and logistic regression models, adjusted by potential confounders, were fitted to assess associations between glycemic status and changes in cognitive function.

RESULTS

Prediabetes status was unrelated to cognitive decline. However, compared to participants without diabetes, those with ≥5-year diabetes duration had greater reductions in GCF (β=-0.11 (95%CI -0.16;-0.06)], as well as in processing speed and executive function measurements. Inverse associations were observed between baseline HOMA-IR and changes in GCF [β=-0.0094 (95%CI -0.0164;-0.0023)], but also between HbA1c levels and changes in GCF [β=-0.0085 (95%CI -0.0115, -0.0055)], the Mini-Mental State Examination, and other executive function tests. Poor diabetes control was inversely associated with phonologic fluency. The use of insulin treatment was inversely related to cognitive function as measured by the GCF [β=-0.31 (95%CI -0.44, -0.18)], and other cognitive tests.

CONCLUSIONS

Insulin resistance, diabetes status, longer diabetes duration, poor glycemic control, and insulin treatment were associated with worsening cognitive function changes in the short term in a population at high cardiovascular risk.

CLINICAL TRIAL REGISTRATION

http://www.isrctn.com/ISRCTN89898870, identifier ISRCTN: 89898870.

Recent Developments in Medicinal Chemistry of Allosteric Activators of Human Glucokinase for Type 2 Diabetes Mellitus Therapeutics

BACKGROUND

Glucokinase (GK), a cytoplasmic enzyme catalyzes the metabolism of glucose to glucose- 6-phosphate with the help of ATP and aids in the controlling of blood glucose levels within the normal range in humans. In pancreatic β-cells, it plays a chief role by controlling the glucose-stimulated secretion of insulin and in liver hepatocyte cells, it controls the metabolism of carbohydrates. GK acts as a promising drug target for the pharmacological treatment of patients with type 2 diabetes mellitus (T2DM) as it plays an important role in the control of carbohydrate metabolism.

METHODS

Data used for this review was based on the search from several science databases as well as various patent databases. The main data search terms used were allosteric GK activators, diabetes mellitus, type 2 diabetes, glucokinase, glucokinase activators and human glucokinase.

RESULTS

This article discusses an overview of T2DM, the biology of GK, the role of GK in T2DM, recent updates in the development of small molecule GK activators reported in recent literature, mechanism of action of GK activators and their clinical status.

CONCLUSION

GK activators are the novel class of pharmacological agents that enhance the catalytic activity of GK enzyme and display their antihyperglycemic effects. Broad diversity of chemical entities including benzamide analogues, carboxamides, acrylamides, benzimidazoles, quinazolines, thiazoles, pyrimidines, pyridines, orotic acid amides, amino acid derivatives, amino phosphates and urea derivatives have been synthesized in past two decades as potent allosteric activators of GK. Presently, the pharmaceutical companies and researchers are focusing on the design and development of liver-selective GK activators for preventing the possible adverse effects associated with GK activators for the long-term treatment of T2DM.

Informal Caregiving, Poor Mental Health, and Subjective Cognitive Decline: Results From a Population-Based Sample

The current study examined potential gender differences in the associations between informal caregiving, poor mental health, and subjective cognitive decline (SCD). Data were obtained from the U.S. Behavioral Risk Factor Surveillance System (N = 16,042; 9,410 women, 6,632 men). Multivariate linear and logistic regression models were used to obtain adjusted βs and odds ratios (ORs), and 95% confidence intervals (CIs) depicting the association between informal caregiving, poor mental health, and SCD overall and by gender. Caregiving was positively associated with poor mental health among men (adjusted β = 2.60; 95% CI [2.59, 2.62]) and women (adjusted β = 0.40; 95% CI [0.23, 0.57]). Poor mental health was positively associated with SCD among men (adjusted OR = 1.05; 95% CI [1.02, 1.08]) and women (adjusted OR = 1.07; 95% CI [1.04, 1.10]). Poor mental health may be associated with SCD, irrespective of gender, and additional studies are needed that will identify key variables influencing SCD among male and female informal caregivers. [Journal of Gerontological Nursing, 46(12), 31-41.].

Mild Cognitive Impairment Subtypes and Type 2 Diabetes in Elderly Subjects

Background: Type 2 diabetes (T2D) is correlated to amnestic mild cognitive impairment (aMCI) and to non-amnestic mild cognitive impairment (naMCI). This study evaluated whether the T2D variable characterizes a peculiar cognitive profile in elderly patients. Moreover, it explores the association between glycated hemoglobin levels (HbA1c), T2D duration, insulin and oral hypoglycemic agent treatment, and cognition in elderly diabetic patients. Methods: Detailed neuropsychological battery was used to diagnose MCI subtypes. A total of 39 MCI subjects with T2D (T2D-MCI) and 37 MCI subjects without T2D (ND-MCI), matched for age, educational level, and Mini-Mental State Examination score, were included. Results: ND-MCI performed worse in memory and language domains than T2D-MCI. The amnestic subtype is more frequent among ND-MCI and non-amnestic subtype in T2D-MCI. In T2D-MCI, high HbA1c levels correlate with episodic memory (immediate recall) and T2D duration. Some indexes of episodic memory (immediate recall), attention, and visual-spatial ability correlate with insulin treatment. Conclusions: An association between T2D and non-amnestic MCI is suggested. In the T2D-MCI group, significant associations between insulin treatment and memory (immediate recall), complex figure copy, and attention were found.

A compound reflects the level of homocysteine based on Rhodamine B and its ability to respond to homocysteine in the plasma of diabetic patients

BACKGROUND

The level of homocysteine (Hcy) is significantly elevated in the plasma of patients with diabetes. The increased plasma Hcy level is positively correlated with the severity of the disease and is one of the important causes of diabetic complications.

METHODS

We designed and synthesized a compound could reflect the level of Hcy based on rhodamine B, and the structure was verified by 1H-NMR and EI-HRMS. Then, the linearity, repeatability, selectivity, and cellar toxicity, the effects of the fluid viscosity and pH of compound on Hcy were measured; meanwhile, the response of Hcy level in the plasma of diabetic patients was detected.

RESULTS

This is a novel compound that has never been reported. The compound showed a satisfactory linear range and repeatability at the viscosity and pH of physiological fluid. In addition, the compound was capable of evading the interference from other amino acids and metal ions, and it exhibited high selectivity toward Hcy.

CONCLUSION

The compound showed increased responsiveness to plasma Hcy in patients with diabetes in comparison with healthy individuals and effectively reflected plasma Hcy levels in healthy individuals and diabetic patients. Therefore, the compound is expected to be used in the diagnosis of diabetes mellitus.

Chronic hyperglycemia induces tau hyperphosphorylation by downregulating OGT-involved O-GlcNAcylation in vivo and in vitro

OBJECTIVE

Diabetes mellitus (DM) can increase the risk of cognitive dysfunction, but its exact mechanisms remain unclear. The involvement of aberrant O-GlcNAcylation has been identified in hyperglycemia and DM, as well as the pathogenesis of Alzheimer's disease via competition with tau phosphorylation. This study was designed to investigate the role of O-GlcNAcylation in diabetes-associated cognitive dysfunction (DACD).

METHODS

Fifteen-week old male KK-Ay mice were used as DACD models, and advanced glycation end product (AGE)-treated HT22 cells were used as a model of high glucose toxicity. Morris water maze tests, histological staining, real-time quantitative PCR, and Western blot were also applied.

RESULTS

Mice with DACD exhibited evident obesity, hyperinsulinemia, hyperglycemia, and impaired learning and memory function. O-GlcNAcylation levels decreased and tau phosphorylation levels at Ser396, Ser404, Thr212, and Thr231 increased in the hippocampus of mice with DACD, as well as in AGE-treated HT22 cells. Hypoglycemic therapy improved these anomalies and elevated O-GlcNAc transferase (OGT) levels in mice with DACD. OGT plasmid transfection in HT22 cells partially reversed AGE-induced decreases in O-GlcNAcylation levels and increased tau phosphorylation levels.

CONCLUSIONS

Chronic hyperglycemia can induce tau hyperphosphorylation by downregulating OGT-involved O-GlcNAcylation in vivo and in vitro, which mediates DACD.

Assessment of Appetite-Regulating Hormones Provides Further Evidence of Altered Adipoinsular Axis in Early Psychosis

It has been found that antipsychotic-naïve patients with first-episode psychosis (FEP) present with impaired hormonal regulation of appetite in terms of low leptin and high insulin levels (the adipoinsular axis). These findings imply that certain intrinsic mechanisms might play a role in the development of metabolic dysregulation in early psychosis. However, clinical correlates of this phenomenon remain unknown. Moreover, these alterations have not been tested in individuals at familial high risk of psychosis (FHR-P). In this study we aimed to assess the levels of adiponectin, insulin, leptin, glucose, total cholesterol, lipoproteins and triglycerides in FEP patients, unaffected offspring of schizophrenia patients (FHR-P individuals) and healthy controls (HCs) with respect to cognitive performance and psychopathological manifestation. Participants were 35 FEP patients, 33 FHR-P individuals, and 32 HCs. Cognitive performance was assessed using the Repeatable Battery for Assessment of Neuropsychological Status (RBANS). The levels of leptin and high-density lipoproteins (HDL) were significantly lower (leptin: 10.7 ± 15.7 vs. 12.6 ± 10.1, p = 0.046, and HDL: 48.0 ± 16.9 vs. 59.8 ± 17.5 mg/dl, p = 0.007), while the levels of triglycerides and insulin were significantly higher (triglycerides: 137.4 ± 58.8 vs. 77.5 ± 33.2 mg/dl, p < 0.001, and insulin: 15.2 ± 13.1 vs. 9.6 ± 5.0 µIU/ml, p = 0.023) in FEP patients compared to HCs. These differences were significant after controlling for the effects of potential confounding factors. No significant differences in the levels of serum markers between FHR-P individuals and HCs were found. There was a significant negative correlation between the level of leptin and the RBANS language score after covarying for potential confounding factors in FEP patients (B = -0.226, p = 0.006) but not in other subgroups of participants. Our findings confirm impairment of adipoinsular axis in early psychosis. However, results of our study do not support the hypothesis that familial liability to psychosis might be associated with metabolic dysregulation. Leptin levels might be associated with cognitive deficits in FEP patients. Longitudinal studies of individuals at risk of psychosis are needed to provide insights into causal mechanisms underlying our results.