Effect of hypoglycemia on brain structure in people with type 2 diabetes: epidemiological analysis of the ACCORD-MIND MRI trial

Hypoglycaemia and the risk of dementia: a population-based cohort study using exposure density sampling

BACKGROUND

Previous studies have shown hypoglycaemia to be associated with an increased risk of dementia; however, there are several design challenges to consider. The objective of this study is to assess the association between hypoglycaemia and dementia while addressing these challenges using a lag period, exposure density sampling (EDS) and inverse probability of treatment weighting (IPTW).

METHODS

This was a population-based cohort using data (1996-2018) from British Columbia, Canada. From a cohort of incident type 2 diabetes patients aged 40-70 years, we created a dynamic sub-cohort of hypoglycaemia-exposed (≥1 episode requiring hospitalization or a physician visit) and unexposed individuals using EDS, in which four unexposed individuals per one exposed were randomly selected into risk sets based on diabetes duration and age. Follow-up was until dementia diagnosis, death, emigration or 31 December 2018. Those diagnosed with dementia within 2 years of follow-up were censored. We adjusted for confounding using IPTW and estimated the hazard ratio (HR, 95% CI) of dementia using weighted conditional cause-specific hazards risk models with death as a competing risk.

RESULTS

Among 13 970 patients with incident type 2 diabetes, 2794 experienced hypoglycaemia. There were 329 dementia events over a median (interquartile range: IQR) follow-up of 5.03 (5.7) years. IPTW resulted in well-balanced groups with weighted incidence rates (95% CI) of 4.59 (3.52, 5.98)/1000 person-years among exposed and 3.33 (2.58, 3.88)/1000 person-years among unexposed participants. The risk of dementia was higher among those with hypoglycaemia (HR, 1.83; 95% CI 1.31, 2.57).

CONCLUSIONS

After addressing several methodological challenges, we showed that hypoglycaemia contributes to an increased risk of all-cause dementia among patients with type 2 diabetes.

Pathophysiological Mechanisms Linking Type 2 Diabetes and Dementia: Review of Evidence from Clinical, Translational and Epidemiological Research

BACKGROUND

Type 2 diabetes represents an increasing health burden world-wide and its prevalence in particularly higher in elderly population. Consistent epidemiological evidence suggests an increased risk of dementia associated to type 2 diabetes; the mechanisms underlying these associations, however, remain unclear.

OBJECTIVE

The study aims to review epidemiological, clinical and pre-clinical data that weigh on pathophysiological links, mechanisms of disease and associations between type 2 diabetes and dementia to identify areas of opportunity for future research.

METHODS

We searched the following electronic bibliographic databases: PUBMED, EMBASE, SCIELO, MEDLINE and OVID for clinical, translational and epidemiological research literature that summarize diabetes-related risk factors for dementia, metabolic and neurological changes associated to T2D, evidence of therapeutic approaches in type 2 diabetes and its pathophysiological implications for dementia.

RESULTS

Type 2 diabetes mellitus increases risk for all-cause dementia, vascular dementia and Alzheimer's disease. The most evaluated mechanisms linking both disorders in pre-clinical studies include an increase in neuronal insulin resistance, impaired insulin signaling, pro-inflammatory state, mitochondrial dysfunction and vascular damage which increase deposition of β-amyloid, tau proteins and GSK3β, leading to an earlier onset of dementia in individuals with impairment in the glucose metabolism. Neuroimaging and neuropathology evidence linking cerebrovascular lesions, neurodegeneration and particularly small-vessel disease in the onset of dementia is consistent with the increased risk of incident dementia in type 2 diabetes, but consistent evidence of AD-related pathology is scarce. Epidemiological data shows increased risk of dementia related to hypoglycemic episodes, glycemic control, metabolic syndrome, insulin resistance and genetic predisposition, but the evidence is not consistent and statistical analysis might be affected by inconsistent covariate controlling. Therapeutic approaches for T2D have shown inconsistent result in relation to dementia prevention and delay of cognitive decline; lifestyle intervention, particularly physical activity, is a promising alternative to ameliorate the impact of disability and frailty on T2D-related dementia.

CONCLUSION

Vascular disease, inflammation and impaired brain insulin signaling might occur in T2D and contribute to dementia risk. Evidence from epidemiological studies has not consistently reported associations that could integrate a unified mechanism of disease in humans. Evaluation of the effect of antidiabetic medications and non-pharmacological interventions in dementia prevention in type 2 diabetes is promising but has thus far offered inconsistent results.

Relationships between cerebral structure and cognitive function in African Americans with type 2 diabetes

BACKGROUND

Relationships between cognitive function and brain structure remain poorly defined in African Americans with type 2 diabetes.

METHODS

Cognitive testing and cerebral magnetic resonance imaging in African Americans from the Diabetes Heart Study Memory IN Diabetes (n = 480) and Action to Control Cardiovascular Risk in Diabetes MIND (n = 104) studies were examined for associations. Cerebral gray matter volume (GMV), white matter volume (WMV) and white matter lesion volume (WMLV) and cognitive performance (Mini-mental State Exam [MMSE and 3MSE], Digit Symbol Coding (DSC), Stroop test, and Rey Auditory Verbal Learning Test) were recorded. Multivariable models adjusted for age, sex, BMI, scanner, intracranial volume, education, diabetes duration, HbA1c, LDL-cholesterol, smoking, hypertension and cardiovascular disease assessed associations between cognitive tests and brain volumes by study and meta-analysis.

RESULTS

Mean(SD) participant age was 60.1(7.9) years, diabetes duration 12.1(7.7) years, and HbA1c 8.3(1.7)%. In the fully-adjusted meta-analysis, lower GMV associated with poorer global performance on MMSE/3MSE (β̂ = 7.1 × 10-3, SE 2.4 × 10-3, p = 3.6 × 10-3), higher WMLV associated with poorer performance on DSC (β̂ = -3 × 10-2, SE 6.4 × 10-3, p = 5.2 × 10-5) and higher WMV associated with poorer MMSE/3MSE performance (β̂ = -7.1 × 10-3, SE = 2.4 × 10-3, p = 3.6 × 10-3).

CONCLUSIONS

In African Americans with diabetes, smaller GMV and increased WMLV associated with poorer performance on tests of global cognitive and executive function. These data suggest that WML burden and gray matter atrophy associate with cognitive performance independent of diabetes-related factors in this population.

Postprandial Hyperglycemia Is Associated With White Matter Hyperintensity and Brain Atrophy in Older Patients With Type 2 Diabetes Mellitus

Type 2 diabetes mellitus is associated with neurodegeneration and cerebrovascular disease. However, the precise mechanism underlying the effects of glucose management on brain abnormalities is not fully understood. The differential impacts of glucose alteration on brain changes in patients with and without cognitive impairment are also unclear. This cross-sectional study included 57 older type 2 diabetes patients with a diagnosis of Alzheimer's disease (AD) or normal cognition (NC). We examined the effects of hypoglycemia, postprandial hyperglycemia and glucose fluctuations on regional white matter hyperintensity (WMH) and brain atrophy among these patients. In a multiple regression analysis, postprandial hyperglycemia was independently associated with frontal WMH in the AD patients. In addition, postprandial hyperglycemia was significantly associated with brain atrophy, regardless of the presence of cognitive decline. Altogether, our findings indicate that postprandial hyperglycemia is associated with WMH in AD patients but not NC patients, which suggests that AD patients are more susceptible to postprandial hyperglycemia associated with WMH.

Severe hypoglycaemia, mild cognitive impairment, dementia and brain volumes in older adults with type 2 diabetes: the Atherosclerosis Risk in Communities (ARIC) cohort study

AIMS/HYPOTHESIS

We aimed to evaluate the link between severe hypoglycaemia and domain-specific cognitive decline, smaller brain volumes and dementia in adults with type 2 diabetes, which so far has been relatively poorly characterised.

METHODS

We included participants with diagnosed diabetes from the community-based Atherosclerosis Risk in Communities (ARIC) study. At the participants' fifth study visit (2011-2013), we examined the cross-sectional associations of severe hypoglycaemia with cognitive status, brain volumes and prior 15 year cognitive decline. We also conducted a prospective survival analysis of incident dementia from baseline, visit 4 (1996-1998), to 31 December 2013. Severe hypoglycaemia was identified, using ICD-9 codes, from hospitalisations, emergency department visits and ambulance records. Prior cognitive decline was defined as change in neuropsychological test scores from visit 4 (1996-1998) to visit 5 (2011-2013). At visit 5, a subset of participants underwent brain MRIs. Analyses were adjusted for demographics, APOE genotype, use of diabetes medication, duration of diabetes and glycaemic control.

RESULTS

Among 2001 participants with diabetes at visit 5 (mean age 76 years), a history of severe hypoglycaemia (3.1% of participants) was associated with dementia (vs normal cognitive status): OR 2.34 (95% CI 1.04, 5.27). In the subset of participants who had undergone brain MRI (n = 580), hypoglycaemia was associated with smaller total brain volume (-0.308 SD, 95% CI -0.612, -0.004). Hypoglycaemia was nominally associated with a 15 year cognitive change (-0.14 SD, 95% CI -0.34, 0.06). In prospective analysis (n = 1263), hypoglycaemia was strongly associated with incident dementia (HR 2.54, 95% CI 1.78, 3.63).

CONCLUSIONS/INTERPRETATION

Our results demonstrate a strong link between severe hypoglycaemia and poor cognitive outcomes, suggesting a need for discussion of appropriate diabetes treatments for high-risk older adults.

Long-term Impact of Weight Loss Intervention on Changes in Cognitive Function: Exploratory Analyses from the Action for Health in Diabetes Randomized Controlled Clinical Trial

Background

Diabetes adversely impacts cognition. Lifestyle change can improve diabetes control and potentially improve cognition. We examined whether weight loss through reduced caloric intake and increased physical activity was associated with slower cognitive aging in older adults with type 2 diabetes mellitus.

Methods

The Look AHEAD randomized controlled clinical trial delivered 10 years of intensive lifestyle intervention (ILI) that yielded long-term weight losses. During 5 years spanning the end of intervention and postintervention follow-up, repeated cognitive assessments were obtained in 1,091 individuals who had been assigned to ILI or a control condition of diabetes support and education (DSE). We compared the means and slopes of scores on cognitive testing over these repeated assessments.

Results

Compared with DSE, assignment to ILI was associated with a -0.082 SD deficit in mean global cognitive function across repeated assessments (p = .010). However, overweight (body mass index [BMI] < 30 kg/m2) ILI participants had 0.099 (95% confidence interval [CI]: -0.006, 0.259) better mean global cognitive function compared with overweight DSE participants, while obese (BMI ≥ 30 kg/m2) ILI participants had -0.117 (-0.185, -0.049) SD worse mean composite cognitive function scores (interaction p = .014) compared to obese DSE participants. For both overweight and obese participants, cognitive decline was marginally (-0.014 SD/y overall) steeper for ILI participants (p = .068), with 95% CI for differences in slopes excluding 0 for measures of attention and memory.

Conclusions

The behavioral weight loss intervention was associated with small relative deficits in cognitive function among individuals who were obese and marginally greater cognitive decline overall compared to control. ClinicalTrials.gov Identifier: NCT00017953.

Piracetam Facilitates the Anti-Amnesic but not Anti-Diabetic Activity of Metformin in Experimentally Induced Type-2 Diabetic Encephalopathic Rats

Piracetam exhibits anti-amnesic activity in several animal models of dementia. However, its anti-amnesic potential has yet to be evaluated in type-2 diabetes mellitus (T2DM)-induced encephalopathy. Therefore, in the present study, piracetam (25, 50 and 100 mg/kg) was screened for anti-amnesic and anti-diabetic activity in T2DM-induced encephalopathic male rats. Subsequently, anti-amnesic and anti-diabetic activities were evaluated for piracetam, metformin and their combination in T2DM-induced encephalopathic animals. Rats received streptozotocin (45 mg/kg) and nicotinamide (110 mg/kg) injections on day-1 (D-1) of the experimental schedule and were kept undisturbed for 35 days to exhibit T2DM-induced encephalopathy. All drug treatments were continued from D-7 to D-35 in both experiments. Piracetam (100 mg/kg) attenuated loss in learning and memory in terms of increase in escape latency on D-4 (D-34) and decrease in time spent in the target quadrant on D-5 (D-35) of Morris water maze test protocol, and spatial memory in terms of reduced spontaneous alternation behavior in Y-maze test of encephalopathic rats. Additionally, piracetam attenuated altered levels of fasting plasma glucose and insulin, HOMA-IR and HOMA-B in encephalopathic animals, comparatively lesser than metformin. In the next experiment, combination of piracetam and metformin exhibited better anti-amnesic but not anti-diabetic activity than respective monotherapies in encephalopathic rats. Further, the combination attenuated reduced acetylcholine level and increased acetylcholinesterase activity, increased glycogen synthase kinase-3β level and decreased brain-derived neurotropic factor level in hippocampus and pre-frontal cortex of encephalopathic animals. Thus, piracetam could be used as an adjuvant to metformin in the management of dementia in T2DM-induced encephalopathy.

Diabetic aggravation of stroke and animal models

Cerebral ischemia in diabetics results in severe brain damage. Different animal models of cerebral ischemia have been used to study the aggravation of ischemic brain damage in the diabetic condition. Since different disease conditions such as diabetes differently affect outcome following cerebral ischemia, the Stroke Therapy Academic Industry Roundtable (STAIR) guidelines recommends use of diseased animals for evaluating neuroprotective therapies targeted to reduce cerebral ischemic damage. The goal of this review is to discuss the technicalities and pros/cons of various animal models of cerebral ischemia currently being employed to study diabetes-related ischemic brain damage. The rational use of such animal systems in studying the disease condition may better help evaluate novel therapeutic approaches for diabetes related exacerbation of ischemic brain damage.

Cognitive impairment and dementia: a new emerging complication of type 2 diabetes-The diabetologist's perspective

Type 2 diabetes mellitus (T2D) and Alzheimer's disease (AD) are two of the most common diseases of aging around the world. Given the frequency with which T2D and AD occur, the notion that people with T2D may be at increased risk for AD has large societal consequences, and understanding the mechanistic links between these diseases is imperative for the development of effective AD prevention and treatment strategies. Apart from being an accelerator of AD, T2D is associated with a progressive cognitive decline. Impaired insulin signaling, inflammation, the accumulation of advanced glycation end-products and oxidative stress all play an essential role in the pathogenesis of both AD and diabetic complications. Therefore, it is reasonable to postulate that these pathways are involved in the increased risk of dementia that occurs in the T2D population. The early diagnosis of cognitive impairment and the identification of the subset of patients at a higher risk of developing AD is a challenge for healthcare providers, and meeting it will permit us to implement a personalized medicine, which is an essential issue in diabetes care with significant therapeutic implications. The main gaps that should be filled to achieve this objective are examined.

Diabetes mellitus and white matter hyperintensity

White matter hyperintensity (WMH) is a brain lesion detected as a high-intensity area in magnetic resonance imaging T2 and fluid-attenuated inversion recovery images, and it has been suggested that WMH reflects damage to small vessels in periventricular and subcortical areas. Although WMH has been linked to the incidence of stroke, more recently it has been clarified that WMH is also associated with progression of cognitive decline and functional disability, which are components of so-called geriatric syndrome. In addition to hypertension, which is the classical risk factor for WMH, evidence has been accumulating to suggest that diabetes mellitus could also be associated with WMH progression, and some studies have shown that WMH severity is correlated with cognitive decline in patients with diabetes. The factors that accelerate WMH formation in elderly patients with diabetes remain poorly defined. It is considered that insulin resistance is an exacerbating factor, but the effects of hypertension, dyslipidemia or other vascular risk factors have yet be clarified, and further studies are required.

Metabolic pathways in the periphery and brain: Contribution to mental disorders?

The association between mental disorders and diabetes has a long history. Recent large-scale, well-controlled epidemiological studies confirmed a link between diabetes and psychiatric illnesses. The scope of this review is to summarize our current understanding of this relationship from a molecular perspective. We first discuss the potential contribution of diabetes-associated metabolic impairments to the etiology of mental conditions. Then, we focus on possible shared molecular risk factors and mechanisms. Simple comorbidity, shared susceptibility loci, and common pathophysiological processes in diabetes and mental illnesses have changed our traditional way of thinking about mental illness. We conclude that schizophrenia and affective disorders are not limited to an imbalance in dopaminergic and serotoninergic neurotransmission in the brain. They are also systemic disorders that can be considered, to some extent, as metabolic disorders.

Glucose Control and Vascular Outcomes in Type 2 Diabetes: Is the Picture Clear?

The overall impact of glucose lowering on vascular complications and major clinical outcomes, including mortality, in type 2 diabetes is still an open issue. While intensive glucose control has undoubted benefit for microvascular end points, the relationship between glucose-lowering approaches and reduced incidence and/or progression of macrovascular complications is less clear. This review article will discuss the effect of glucose lowering per se as well as the effects of specific glucose-lowering therapies on vascular outcomes in type 2 diabetes. The role of lifestyle changes on cardiovascular outcomes will be also addressed. Recent analyses from large cardiovascular outcome studies (ACCORD, ADVANCE, and VADT) provide new information on factors that modulate the impact of intensive glucose lowering on outcomes, helping to identify the specific clinical characteristics of the patients receiving the intervention that would show a better response. While several studies on cardiovascular outcomes with diabetes drugs are available, they do not clearly highlight a benefit from using a specific medication or will require additional evidence, as for the sodium-glucose cotransporter 2 blockers.

Diabetes, Dementia and Hypoglycemia

We are experiencing an epidemic of both diabetes and dementia among older adults in this country. The risk for dementia appears to be increased in patients with diabetes, and patients with dementia and diabetes appear to be at greater risk for severe hypoglycemia. In addition, there may be an increased risk for developing dementia by older patients with diabetes who have had episodes of severe hypoglycemia, although this issue is controversial. In this article, we review the factors that contribute to the increased risk for dementia in older adults with diabetes and outline the complex relationships between hypoglycemia and dementia.

[Diabetes mellitus and the central nervous system]

The review considers the current views on the central nervous system (CNS) in diabetes mellitus (DM). It discusses an attitude towards the term 'diabetic encephalopathy'. The data of investigations of cognitive functions in types 1 and 2 DM and the brain structural imaging results obtained using up-to-date technologies are considered. The results of studies of the factors that induce cerebral changes in DM and their associated cognitive impairments are given. There is evidence that hyperglycemia has a more considerable impact on the above processes than hypoglycemia; other possible factors, apart from blood glucose control, are set out. The current views on the function of insulin in the CNS and the relationship of central insulin resistance to Alzheimer's disease are outlined. There are current data on intranasal insulin application that is still exploratory, but, as might be judged from the findings, may by a promising method for the treatment and prevention of cognitive decline in both patients with DM and those without this condition.

Neurofunctional topography of the human hippocampus

Much of what was assumed about the functional topography of the hippocampus was derived from a single case study over half a century ago. Given advances in the imaging sciences, a new era of discovery is underway, with potential to transform the understanding of healthy processing as well as the ability to treat disorders. Coactivation-based parcellation, a meta-analytic approach, and ultra-high field, high-resolution functional and structural neuroimaging to characterize the neurofunctional topography of the hippocampus was employed. Data revealed strong support for an evolutionarily preserved topography along the long-axis. Specifically, the left hippocampus was segmented into three distinct clusters: an emotional processing cluster supported by structural and functional connectivity to the amygdala and parahippocampal gyrus, a cognitive operations cluster, with functional connectivity to the anterior cingulate and inferior frontal gyrus, and a posterior perceptual cluster with distinct structural connectivity patterns to the occipital lobe coupled with functional connectivity to the precuneus and angular gyrus. The right hippocampal segmentation was more ambiguous, with plausible 2- and 5-cluster solutions. Segmentations shared connectivity with brain regions known to support the correlated processes. This represented the first neurofunctional topographic model of the hippocampus using a robust, bias-free, multimodal approach.

Avoiding or coping with severe hypoglycemia in patients with type 2 diabetes

Hypoglycemia is a major barrier to achieving the glycemic goal in patients with type 2 diabetes. In particular, severe hypoglycemia, which is defined as an event that requires the assistance of another person to actively administer carbohydrates, glucagon, or take other corrective actions, is a serious clinical concern in patients with diabetes. If severe hypoglycemia is not managed promptly, it can be life threatening. Hypoglycemia-associated autonomic failure (HAAF) is the main pathogenic mechanism behind severe hypoglycemia. Defective glucose counter-regulation (altered insulin secretion, glucagon secretion, and an attenuated increase in epinephrine during hypoglycemia) and a lack of awareness regarding hypoglycemia (attenuated sympathoadrenal activity) are common components of HAAF in patients with diabetes. There is considerable evidence that hypoglycemia is an independent risk factor for cardiovascular disease. In addition, hypoglycemia has a significant influence on the quality of life of patients with diabetes. To prevent hypoglycemic events, the setting of glycemic goals should be individualized, particularly in elderly individuals or patients with complicated or advanced type 2 diabetes. Patients at high-risk for the future development of severe hypoglycemia should be selected carefully, and intensive education with reinforcement should be implemented.