Glucose metabolism and the risk of Alzheimer's disease and dementia: a population-based 12 year follow-up study in 71-year-old men

Diabetes, Prediabetes, and Brain Aging: The Role of Healthy Lifestyle

OBJECTIVE

Diabetes is a well-known risk factor for dementia. We investigated the association between (pre)diabetes and older brain age and whether this can be attenuated by modifiable lifestyle behaviors.

RESEARCH DESIGN AND METHODS

The study included 31,229 dementia-free adults from the UK Biobank between the ages of 40 and 70 years. Glycemic status (normoglycemia, prediabetes, or diabetes) was ascertained based on medical history, medication use, and HbA1c measured at baseline. Information on cardiometabolic risk factors (obesity, hypertension, low HDL, and high triglycerides) and lifestyle behaviors (smoking, drinking, and physical activity) was also collected at baseline. Participants underwent up to two brain MRI scans over 11 years of follow-up. Brain age was estimated using a machine learning model based on 1,079 brain MRI phenotypes and used to calculate brain age gap (BAG; i.e., brain age minus chronological age).

RESULTS

At baseline, 13,518 participants (43.3%) had prediabetes and 1,149 (3.7%) had diabetes. Prediabetes (β = 0.22 [95% CI 0.10, 0.34]) and diabetes (2.01 [1.70, 2.32]) were both associated with significantly higher BAG, and diabetes was further associated with significant increase in BAG over time (0.27 [0.01, 0.53]). The association between (pre)diabetes and higher BAG was more pronounced in men and in people with two or more cardiometabolic risk factors. In joint exposure analysis, having a healthy lifestyle (i.e., no smoking, no heavy drinking, and high physical activity) significantly attenuated the diabetes-BAG association.

CONCLUSIONS

Diabetes and even prediabetes are associated with accelerated brain aging, especially among men and people with poor cardiometabolic health. However, a healthy lifestyle may counteract this.

Effects of maternal mild hyperglycemia associated with snack intake on offspring metabolism and behavior across the lifespan

The increasing prevalence of diabetes is of particular concern in women of childbearing age because of the short and long-term consequences of maternal diabetes for the health of the offspring, such as a greater risk of developing metabolic impairments and cognitive deficits. In addition, maternal diet during pregnancy and lactation might contribute to preventing or ameliorating adverse offspring outcomes. Recently, we described that access to snacks exacerbates glucose intolerance in mildly hyperglycemic pregnant dams. Therefore, we hypothesized that these offspring would show greater impairment in metabolic and behavioral outcomes across the lifespan. Neonatal STZ treatment was employed to induce maternal mild hyperglycemia in females. After mating, normo- and hyperglycemic dams were given access either to standard chow or standard show plus snacks. Male and female offspring were evaluated on postnatal days (PND) 30, 90, and 360. Offspring behavior was assessed in the marble burying task, the open-field test, the elevated-plus maze, and sucrose preference. Glucose tolerance and morphometric analyses were also carried out. Maternal hyperglycemia increased body weight and fat deposition only on PND 30, while retroperitoneal fat deposition was reduced in the offspring of snack-fed dams. However, maternal snack intake reduced offspring body weight and length on PND 90. Fasting glucose was increased in females born to hyperglycemic, snack-fed dams on PND 90. Glucose clearance was altered by both maternal conditions in male offspring on PND 30, however, this sex difference was reversed on PND 90, with maternal hyperglycemia impairing glucose clearance only in females. In addition, maternal hyperglycemia reduced anxiety-like behavior in female offspring on PND 30, especially in the offspring of snack-fed dams, while maternal snack intake reduced sucrose preference in both males and females in adulthood. These results suggest that the effects of maternal hyperglycemia during pregnancy and lactation on offspring outcomes were not exacerbated by snack intake. Although additive effects of the two maternal conditions were hypothesized, the absence of such effects could be related to the mild maternal hyperglycemia induced by STZ treatment even when combined with snack intake. While maternal hyperglycemia alone impaired some offspring outcomes, its association with snack intake did not aggravate those impairments but rather resulted in outcomes more similar to those of offspring born to normoglycemic dams. Finally, females were found to be more susceptible to both the effects of maternal hyperglycemia and snack intake on metabolism and behavior.

Relationship Between Fasting Blood Glucose Levels in Middle Age and Cognitive Function in Later Life: The Aichi Workers' Cohort Study

BACKGROUND

There is limited evidence regarding the relationship between Diabetes mellitus (DM) in middle age and mild cognitive impairment after a follow-up. Therefore, we investigated the relationship between fasting blood glucose (FBG) levels in middle age and cognitive function assessed using the Japanese version of the Montreal Cognitive Assessment (MoCA-J) in later life, following over 15 years of follow-up in the Aichi Workers' Cohort Study in Japan.

METHODS

Participants were 253 former local government employees aged 60-79 years in 2018 who participated in a baseline survey conducted in 2002. Using baseline FBG levels and self-reported history, participants were classified into the normal, impaired fasting glucose (IFG) and, and DM groups. Total MoCA-J score ranges from 0 to 30, and cognitive impairment was defined as MoCA-J score ≤25 in this study. A general linear model was used to estimate the mean MoCA-J scores in the FBG groups, adjusted for age, sex, educational year, smoking status, alcohol consumption, physical activity, body mass index, systolic blood pressure, total cholesterol, and estimated glomerular filtration rate.

RESULTS

The mean MoCA-J score in the total population was 25.0, and the prevalence of MoCA-J score ≤25 was 49.0%. Multivariable-adjusted total MoCA-J scores were 25.2, 24.8, and 23.4 in the normal, IFG, and DM groups, respectively. The odds ratio of MoCA-J score ≤25 in the DM group was 3.29.

CONCLUSION

FBG level in middle age was negatively associated with total MoCA-J scores assessed later in life, independent of confounding variables.

Impaired Early Insulin Response to Glucose Load Predicts Episodic Memory Decline: A 10-Year Population-Based Cohort Follow-Up of 45-74-Year-Old Men and Women

BACKGROUND

Diabetes increases the risk for cognitive decline, but the mechanisms behind this association remain unknown. Impaired early insulin secretion in elderly men and insulin resistance, both of which are pathophysiological features of type 2 diabetes, have previously been linked to Alzheimer's disease.

OBJECTIVE

To examine if the early insulin response to oral glucose load predicts cognitive performance after 10 years in men and women aged 45-74 years.

METHODS

This study was based on a subpopulation of the Health 2000 Survey, a Finnish nationwide, population-based health examination study, and its follow-up, the Health 2011 Study. In total, 961 45-74-year-old individuals (mean age at baseline 55.6 years, 55.8% women) were examined. An oral glucose tolerance test was performed in 2001-2002, and early insulin response was defined as the ratio of the 30-min increment in insulin concentration to that of glucose concentration. Cognitive function was evaluated at baseline and follow-up with categorical verbal fluency, word-list learning, and word-list delayed recall. Statistical analyses were performed using multivariable linear models adjusted for age, sex, education, APOE&z.epsi;4 genotype, vascular risk factors including diabetes, and depressive symptoms.

RESULTS

A lower early insulin response to glucose load predicted lower performance (β: 0.21, p = 0.03) and greater decline (β: 0.19, p = 0.03) in the word-list delayed recall test. Baseline early insulin response did not predict verbal fluency or word-list learning (all p-values≥0.13).

CONCLUSION

Our results suggest that decreased early insulin secretion predicts episodic memory decline in middle-aged to elderly men and women.

The Triglyceride-Glucose Index Is Associated with Longitudinal Cognitive Decline in a Middle-Aged to Elderly Population: A Cohort Study

BACKGROUND

To examine the effect of the triglyceride-glucose (TyG) index on longitudinal cognitive decline in a healthy middle-aged-to-elderly population.

METHODS

We conducted a population-based longitudinal study. A total of 1774 participants without cognitive impairment were enrolled in the 4-year follow-up. They were divided into four groups according to the quartile of the TyG index. Multivariable-adjusted Cox proportional hazard models were performed to examine the association between the TyG index and cognitive decline. Discrimination tests were used to evaluate the incremental predictive value of the TyG index beyond conventional risk factors.

RESULTS

During the follow-up, compared with those in the bottom quartile group, participants in the top TyG quartile group presented a 51% increase in the risk of cognitive decline (OR 1.51 (95% CI: 1.06-2.14)). As shown by discrimination tests, adding the TyG index into the conventional model resulted in a slight improvement in predicting the risk of cognitive decline (NRI 16.00% (p = 0.004)).

CONCLUSION

This study demonstrated that increasing values of the TyG index were positively associated with the risk of cognitive decline. Monitoring the TyG index may help in the early identification of individuals at high risk of cognitive deterioration.

Oral Glucose Tolerance Test Predicts Episodic Memory Decline: A 10-Year Population-Based Follow-up Study

OBJECTIVE

To examine if the 2-h value of an oral glucose tolerance test (OGTT) can predict cognitive decline.

RESEARCH DESIGN AND METHODS

This study is based on a subpopulation of the Finnish population-based Health 2000 Survey and its follow-up, the Health 2011 study. Altogether, 961 individuals aged 45-74 (mean 55.6 years; 55.8% women) underwent OGTT in 2001-2002. Categorical verbal fluency, word-list learning, and word-list delayed recall were tested at baseline and at follow-up in 2011. Statistical analyses were performed with multivariable linear models adjusted for previously reported risk factors for cognitive decline.

RESULTS

A higher 2-h glucose value in the OGTT at baseline predicted worse performance (slope: -0.08; P = 0.01) and greater decline (slope: -0.07; P = 0.007) in the word-list delayed recall test after 10 years.

CONCLUSIONS

Our results indicate that higher 2-h glucose values in the OGTT predict a decline in episodic memory after 10 years.

The relationship of glucose-stimulated insulin secretion to cerebral glucose metabolism and cognition in healthy middle-aged and older adults

Insulin resistance (IR) has been related to reduced cerebral glucose metabolism in regions identified as hypometabolic in Alzheimer's clinical syndrome. Insulin secretion (IS) has been less studied than IR despite findings that decreased IS is an early indicator of future type 2 diabetes and a potential predictor of Alzheimer's clinical syndrome. We investigated whether higher IR and lower IS would be associated with greater age-related reductions in regional cerebral glucose metabolism and worse cognitive performance. Two-hour oral glucose tolerance testing and 18F-fluorodeoxyglucose positron emission tomography were performed on 1-2 occasions on a sample of healthy middle-aged and older adults from the Wisconsin Alzheimer's Disease Research Center. Neuropsychological tests were completed during Alzheimer's Disease Research Center Clinical Core visits. Pattern of findings suggested that lower (not higher) IS was related to higher regional cerebral glucose metabolism in middle aged but not older adults, and lower (not higher) IS was also related to better immediate recall. In the context of healthy insulin sensitivity, lower IS may be beneficial to brain health.

Glucose-Dementia Association Is Consistent Over Blood Pressure/Antihypertensive Groups

BACKGROUND

Higher glucose levels are associated with dementia risk in people with and without diabetes. However, little is known about how this association might vary by hypertension status and antihypertensive treatment. Most studies on modifiable dementia risk factors consider each factor in isolation.

OBJECTIVE

To test the hypothesis that hypertension and antihypertensive treatments may modify associations between glucose levels and dementia.

METHODS

Analyses of data generated from a research study and clinical care of participants from a prospective cohort of dementia-free older adults, including glucose measures, diabetes and antihypertensive treatments, and blood pressure data. We defined groups based on blood pressure (hypertensive versus not, ≥140/90 mmHg versus <140/90 mmHg) and antihypertensive treatment intensity (0, 1, or ≥2 classes of antihypertensives). We used Bayesian joint models to jointly model longitudinal exposure and time to event data.

RESULTS

A total of 3,056 participants without diabetes treatment and 480 with diabetes treatment were included (mean age at baseline, 75.1 years; mean 7.5 years of follow-up). Higher glucose levels were associated with greater dementia risk among people without and with treated diabetes. Hazard ratios for dementia were similar across all blood pressure/antihypertensive treatment groups (omnibus p = 0.82 for people without and p = 0.59 for people with treated diabetes).

CONCLUSION

Hypertension and antihypertensive treatments do not appear to affect the association between glucose and dementia risk in this population-based longitudinal cohort study of community-dwelling older adults. Future studies are needed to examine this question in midlife and by specific antihypertensive treatments.

The insulin resistance by triglyceride glucose index and risk for dementia: population-based study

Background

Insulin resistance is suggested to have negative effects on cognition; however, results from large population studies are lacking. In this study, the potential relationships between the triglyceride glucose (TyG) index, a simple surrogate marker of insulin resistance, and dementia were evaluated using a large-scale population dataset.

Methods

This was a retrospective, observational, cohort study using data from the National Health Information Database from 2009 to 2015 and included 5,586,048 participants 40 years age or older. The TyG index was used as a measure of insulin resistance, and participants were divided into quartiles based on TyG index. The incidence of dementia was assessed using hazard ratios (HRs) estimated with Cox proportional hazard modeling.

Results

During a median follow-up of 7.21 years, dementia was diagnosed in 142,714 (2.55%) participants. Alzheimer’s disease (AD) and vascular dementia (VD) were diagnosed in 74.3% and 12.5% of the participants. Multivariate-adjusted HRs for patients in the TyG index 4th quartile were higher for dementia (HRs = 1.14; 95% confidence interval [CI] 1.12–1.16), AD (HRs = 1.12; 95% CI 1.09–1.14), and VD (HRs = 1.18; 95% CI 1.12–1.23) compared with the 1st quartile of TyG index; however, this had a small effect size (Cohen’s d = 0.10, 0.08, and 0.13, respectively). These effects were independent of age, sex, smoking status, physical activity, body mass index, systolic blood pressure, and total cholesterol.

Conclusion

In this large population study, TyG index was associated with an increased risk of dementia, including AD and VD, that was independent of traditional cardiovascular risk factors, although the effect size of the TyG index was small.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-020-00758-4.

The Association between HbA1c Levels, Olfactory Memory and Cognition in Normal, Pre-Diabetic and Diabetic Persons

BACKGROUND AND AIM

Recent data have shown that olfactory dysfunction is strongly related to Alzheimer's Disease (AD) that is often preceded by olfactory deficits suggesting that olfactory dysfunction might represent an early indicator of future cognitive in prediabetes.

METHODS

We have applied to a group of normal (n=15), prediabetic (n=16) and type 2 diabetic outpatients (n=15) olfactory testing, 1.5-T MRI scanner and detailed cognitive evaluation including the standard Mini-Mental State Examination (MMSE) form, Short Blessed Test (SBT), Letter Fluency Test (LFT) and the category fluency test with animal, Fruit and Vegetable Naming (CFT).

RESULTS

We have shown that Odour Threshold (OT), Discrimination (OD), and Identification (OI) scores and most cognitive test results were significantly different in the prediabetes and diabetes group compared to those in the control group. OD and OT were significantly different between the prediabetes and diabetes group, although the cognitive test results were only significantly different in the prediabetes and diabetes group compared to those in the control group. In evaluating the association between OI, OT, OD scores and specific cognitive tests, we have found, that impaired olfactory identification was the only parameter that correlated significantly with the SBT both in the pre-diabetes and diabetes group. Although spot glucose values were only correlated with OT, HbA1c levels were correlated with OT, OD, and OI, as well as results of the letter fluency test suggesting that HbA1c levels rather than the spot glucose values play a critical role in specific cognitive dysfunction.

CONCLUSION

To the best of our knowledge, this is the first prospective study to demonstrate a strong association between olfactory dysfunction and specific memory impairment in a population with prediabetes and diabetes suggesting that impaired olfactory identification might play an important role as a specific predictor of memory decline.

Insulin sensitivity predicts cognitive decline in individuals with prediabetes

INTRODUCTION

Epidemiological studies indicate an association between type 2 diabetes and cognitive dysfunction that appear to start already in the prediabetic state. Although cross-sectional studies have linked insulin resistance to impaired cognition, the potential predictive value of insulin resistance has not yet been sufficiently studied longitudinally without confounding by overt diabetes (and its pharmacological treatment).

RESEARCH DESIGN AND METHODS

We investigated longitudinal data from participants of the 'Tübinger Evaluation of Risk Factors for Early Detection of Neurodegeneration' Study. Subjects underwent a neurocognitive assessment battery (CERAD Plus battery; Consortium to Establish a Registry for Alzheimer's Disease) at baseline and followed every 2 years (median follow-up 4.0 Q1-3: 2.2-4.3 years). Subjects within a pre-diabetic glycated hemoglobin range of 5.6%-6.5% underwent 5-point 75 g oral glucose tolerance tests (OGTTs) with assessment of insulin sensitivity and insulin secretion (n=175). Subjects with newly diagnosed diabetes mellitus or with major depressivity (Beck Depression Inventory >20) were excluded (n=15). Data were analyzed by mixed models using sex, age and glycemic trait as fixed effects. Subject and time since first measurement were used as random effects.

RESULTS

Insulin sensitivity was positively associated with the CERAD sum score (higher is better) in a time-dependent manner (p=0.0057). This result is mainly driven by a steeper decrease in the memory domain associated with lower insulin sensitivity (p=0.029). The interaction between age and insulin sensitivity was independent of glycemia (p=0.02). There was also no association between insulin secretion and cognition.

CONCLUSIONS

Insulin resistance rather than sole elevation of blood glucose predicts cognitive decline, specifically in the memory domain, in persons with prediabetes. Treatments of diabetes that improve insulin sensitivity might therefore have the potential to postpone or even prevent cognitive decline in patients with diabetes.

Insulin deficiency, but not resistance, exaggerates cognitive deficits in transgenic mice expressing human amyloid and tau proteins. Reversal by Exendin-4 treatment

Epidemiological studies have pointed at diabetes as a risk factor for Alzheimer's disease (AD) and this has been supported by several studies in animal models of both type 1 and type 2 diabetes. However, side-by-side comparison of the two types of diabetes is limited. We investigated the role of insulin deficiency and insulin resistance in the development of memory impairments and the effect of Exendin-4 (Ex4) treatment in a mouse model of AD. Three-4-month-old female wild type (WT) mice and mice overexpressing human tau and amyloid precursor protein (TAPP) were injected with streptozotocin (STZ) or fed a high-fat diet (HFD). A second study was performed in TAPP-STZ mice treated with Ex4, a long-lasting analog of GLP-1. Plasma and brain were collected at study termination for ELISA, Western blot, and immunohistochemistry analysis. Learning and memory deficits were impaired in TAPP transgenic mice compared with WT mice at the end of the study. Deficits were exaggerated by insulin deficiency in TAPP mice but 12 weeks of insulin resistance did not affect memory performances in either WT or TAPP mice. Levels of phosphorylated tau were increased in the brain of WT-STZ and TAPP-STZ mice but not in the brain of WT or TAPP mice on HFD. In the TAPP-STZ mice, treatment with Ex4 initiated after established cognitive deficits ameliorated learning, but not memory, impairments. This was accompanied by the reduction of amyloid β and phosphorylated tau expression. Theses studies support the role of Ex4 in AD, independently from its actions on diabetes.

Glycogen synthase kinase-3 as a key regulator of cognitive function

Glycogen synthase kinase-3 (GSK-3) is a highly conserved and multifunctional serine/threonine protein kinase widely distributed in eukaryotic cells. GSK-3 is originally thought to be an enzyme that regulates glycogen synthesis. It was subsequently found that GSK-3 influences many critical cellular functions, such as cell structure, neural plasticity, gene expression, and neuronal survival. Recently, GSK-3 has been found to be associated with cognition, and its dysregulation leads to cognitive impairments in many diseases, including Alzheimer's disease, diabetes, depression, Parkinson's disease, and others. In this review, we summarized the current knowledge about the structure of GSK-3, the regulation of GSK-3 activity, and its role in cognitive function and cognitive-related disease.

Crucial players in Alzheimer's disease and diabetes mellitus: Friends or foes?

Alzheimer's disease (AD) and diabetes mellitus, especially type 2 (T2DM), are very common and widespread diseases in contemporary societies, and their incidence is steadily on the increase. T2DM is a multiple metabolic disorder, with several mechanisms including hyperglycaemia, insulin resistance, insulin receptor and insulin growth factor disturbances, glucose toxicity, formation of advanced glycation end products (AGEs) and the activity of their receptors. AD is the most common form of dementia, characterized by the accumulation of extracellular beta amyloid peptide aggregates and intracellular hyper-phosphorylated tau proteins, which are thought to drive and/or accelerate inflammatory and oxidative stress processes leading to neurodegeneration. The aim of this paper is to provide a comprehensive review of the evidence linking T2DM to the onset and development of AD and highlight the unknown or poorly studied "nooks and crannies" of this interesting relationship, hence providing an opportunity to stimulate new ideas for the analysis of comorbidities between AD and DM. Despite, indication of possible biomarkers of early diagnosis of T2DM and AD, this review is also an attempt to answer the question as to whether the crucial factors in the development of both conditions support the link between DM and AD.

Serum Insulin and Cognitive Performance in Older Adults: A Longitudinal Study

PURPOSE

The aim of this study was to examine the association of serum glucose, insulin, and insulin resistance with cognitive functioning 7 years later in a longitudinal population-based study of Finnish older adults.

METHODS

Serum glucose and insulin were measured at baseline in 269 dementia-free individuals aged 65-79 years, from the Cardiovascular Risk Factors, Aging, and Dementia (CAIDE) study. Insulin resistance was estimated with the homeostasis model assessment (HOMA-IR). Participants were reexamined 7 years later, and global cognition, episodic memory, executive functioning, verbal expression, and psychomotor speed were assessed, both at baseline and at follow-up. Multiple linear regression was used to investigate the associations with cognitive performance at follow-up, after adjusting for several potential confounders, including common vascular risk factors.

RESULTS

In the multivariable-adjusted linear regression models, no associations of insulin resistance with cognitive functioning were observed. After excluding 19 incident dementia cases, higher baseline HOMA-IR values were related to worse performance in global cognition (β [standard error (SE)] -.050 [0.02]; P = .043) and psychomotor speed (β [SE] -.064 [.03]; P = [.043]) 7 years later. Raised serum insulin levels were associated with lower scores on global cognition (β [SE] -.054 [.03]; P = .045) and tended to relate to poorer performance in psychomotor speed (β [SE] -.061 [.03]; P = .070).

CONCLUSIONS

Serum insulin and insulin resistance may be independent predictors of cognitive performance 7 years later in elderly individuals without dementia. Randomized controlled trials are needed to determine this issue.

Participating in Mental, Social, and Physical Leisure Activities and Having a Rich Social Network Reduce the Incidence of Diabetes-Related Dementia in a Cohort of Swedish Older Adults

OBJECTIVE

The effect of a healthy lifestyle on diabetes-related dementia remains unknown. We examined whether an active lifestyle and rich social network may counteract the increased risk of dementia in people with diabetes.

RESEARCH DESIGN AND METHODS

Dementia-free older adults from the Swedish National Study on Aging and Care in Kungsholmen (SNAC-K) (n = 2,650) were followed up for 10 years. Diabetes was ascertained on the basis of medical history, medication use, medical records, or glycated hemoglobin (HbA_1c) ≥6.5% and prediabetes as HbA_1c between 5.7 and 6.5%. Dementia was diagnosed by specialists following standard criteria. An active lifestyle was defined as a moderate to high (vs. low) level of engagement in leisure activities or a rich social network (having moderate to rich [vs. poor] social connections and support). Hazard ratios (HRs) of dementia risk were derived from Cox regression models.

RESULTS

There were 246 incident dementia cases during follow-up. Those with diabetes (n = 243), but not those with prediabetes (n = 921), had greater risk of dementia (adjusted HR 2.0 [95% CI 1.4-2.9]) than diabetes-free participants. Participants with diabetes but low level of engagement in leisure activities (HR 4.2 [95% CI 2.2-8.2]) or a poor social network (HR 3.4 [95% CI 1.9-6.1]) had greater dementia risk than diabetes-free participants with moderate to high levels of leisure activity engagement or a moderate to rich social network. In participants with diabetes, an active lifestyle (high level of engagement in leisure activities or a rich social network) was associated with less of a raised risk (HR 1.9 [95% CI 1.1-3.4]).

CONCLUSIONS

An active and socially integrated lifestyle may significantly counteract the detrimental effect of diabetes on dementia risk.

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.

Cortisol: Mediator of association between Alzheimer's disease and diabetes mellitus?

Numerous epidemiologic studies have identified an independent association between Alzheimer's disease (AD) and diabetes mellitus (DM), which remains unexplained. This review contends that the association is mediated by mild hypercortisolemia that is manifested in AD by early stages, as empirical evidence indicates that hypercortisolemia is diabetogenic even at subclinical levels. Subclinical Cushing's syndrome is discussed as the paradigm. It is proposed that hypercortisolemia increases the risk of pre-diabetes and DM during early AD and the preceding decades. That hypercortisolemia is exhibited during the AD prodromal stage has yet to be determined, but may be inferred from concurrent metabolic parameters as documented in the literature. Studies refuting association between AD and DM also are evaluated, and the relationship between AD and DM is deduced to be more complex than directly causal, with DM of longstanding duration having a protective role. Association between DM and AD may require reappraisal by APOE ε4 carrier status, in view of newly identified roles of APOE ε4 in pre-diabetes. That association of APOE ε4 with DM in AD may have been underestimated in epidemiologic studies also is highlighted. At the core of arguments and mechanisms presented in this review is the circadian rhythm of cortisol secretion, which is the main determinant of glycemic control in humans. Alterations to that rhythm and to the hypothalamic-pituitary-adrenal axis occurring in AD are examined. Consequently the cause of hypercortisolemia in AD, and therefore of association between AD and DM, is proposed to be adrenal hyper-responsiveness to adrenocorticotropic hormone.

What is Your Risk of Contracting Alzheimer's Disease? A Telematics Tool Helps you to Predict it

Alzheimer's disease (AD) is the most common dementia in developed countries. Between the identified risk factors, one of the most important is the age. Its prevalence reaches 24 % in men and 33 % in women over 85 years. Increase in life expectancy, making it a serious public health problem. Prevention of Alzheimer's disease represents a major challenge to health. Given that Alzheimer's disease is largely dependent on the genetics of each person and uninterrupted progress of the age, which is try to make people aware that there are other factors that can alter your chance of developing the Alzheimer disease and although currently not reduce, help is not increased in the near or distant future.The aim of this paper is to develop and evaluate a Web-Mobile application (Alzhe Alert) used to calculate the risk of Alzheimer's from a short questionnaire using a computer or mobile device, so that any user, without requiring computer skills, can access the website to estimate their risk of developing the disease in the coming years depending on their habits and daily basis activities. The users who have realized the questionnaire can to observe in a graph the result, and they will know which is at risk for Alzheimer's at present and over the next 50 years if they continue with the same habits and lifestyle. The objective is that the users can be aware of the risk they have different habits of life about their health. Currently, 243 users (84 women and 159 men) of white race have completed the questionnaire. 76 % of the users have got a risk below the average.

Diabetes care among elderly medicare beneficiaries with Parkinson's disease and diabetes

Background

Elderly individuals with type 2 diabetes mellitus (T2DM) suffer from several comorbidities, which affect their health outcomes, as well as process of care. This study assessed process and intermediate clinical outcomes of diabetes care among elderly individuals with T2DM and co-occurring Parkinson’s disease(PD).

Methods

This study used a retrospective cohort design with propensity score matching using Humana Medicare Advantage Part D claims database (2007-2011) and included elderly (age ≥ 65 years) Medicare beneficiaries with T2DM (identified by ICD-9-CM code of 250.x0 or 250.x2). PD was identified using ICD-9-CM code of 332.xx. After propensity score matching there were 2,703 individuals with T2DM and PD and 8,109 with T2DM and no PD. The three processes of care measures used in this study included: (i) HbA1c test; (ii) Lipid test; (iii) and Nephropathy screening. Intermediate clinical outcomes consisted of glycemic and lipid control.

Results

Multivariable conditional logistic regressions revealed that elderly individuals with T2DM and PD were 12 % (AOR: 0.88, 95 %CI: 0.79-0.97) and 18 % (AOR: 0.82, 95 %CI: 0.72-0.94) less likely to meet the annual American Diabetes Association (ADA) recommended HbA1c and lipid testing goals respectively compared to individuals with T2DM and no PD. Multinomial conditional logistic regressions showed that elderly individuals with T2DM and PD were more likely to have HbA1c and lipid (HbA1c < 8 %; LDL-C <100 mg/dl; HDL-C ≥ 50 mg/dl; triglyceride <150 mg/dl; and total cholesterol <200 mg/dl) control.

Conclusions

Among elderly individuals with T2DM, those with PD were less likely to achieve ADA recommended annual HbA1c and lipid testing compared to those without PD. However, PD individuals were more likely to achieve intermediate glycemic and lipid control.

Severe diabetic retinal disease and dementia risk in type 2 diabetes

BACKGROUND

Persons with type 2 diabetes are at an increased risk of dementia compared to those without, but the etiology of this increased risk is unclear.

OBJECTIVE

Cerebral microvascular disease may mediate the link between diabetes and dementia. Given the anatomical and physiological similarities between cerebral and retinal microvessels, we examined the longitudinal association between diabetic retinal disease and dementia in patients with type 2 diabetes.

METHODS

Longitudinal cohort study of 29,961 patients with type 2 diabetes aged ≥60 years. Electronic medical records were used to collect diagnoses and treatment of severe diabetic retinal disease (i.e., diabetic proliferative retinopathy and macular edema) between 1996-1998 and dementia diagnoses for the next ten years (1998-2008). The association between diabetic retinal disease and dementia was evaluated by Cox proportional hazard models adjusted for sociodemographics, as well as diabetes-specific (e.g., diabetes duration, pharmacotherapy, HbA1c, hypoglycemia, hyperglycemia) and vascular (e.g., vascular disease, smoking, body mass index) factors.

RESULTS

2,008 (6.8%) patients had severe diabetic retinal disease at baseline and 5,173 (17.3%) participants were diagnosed with dementia during follow-up. Those with diabetic retinal disease had a 42% increased risk of incident dementia (demographics adjusted Hazards Ratio (HR) = 1.42, 95% Confidence Interval (CI) 1.27, 1.58); further adjustment for diabetes-specific (HR 1.29; 95% CI 1.14, 1.45) and vascular-related disease conditions (HR 1.35; 95% CI 1.21, 1.52) attenuated the relation slightly.

CONCLUSION

Diabetic patients with severe diabetic retinal disease have an increased risk of dementia. This may reflect a causal link between microvascular disease and dementia.

Role of insulin signaling impairment, adiponectin and dyslipidemia in peripheral and central neuropathy in mice

One of the tissues or organs affected by diabetes is the nervous system, predominantly the peripheral system (peripheral polyneuropathy and/or painful peripheral neuropathy) but also the central system with impaired learning, memory and mental flexibility. The aim of this study was to test the hypothesis that the pre-diabetic or diabetic condition caused by a high-fat diet (HFD) can damage both the peripheral and central nervous systems. Groups of C57BL6 and Swiss Webster mice were fed a diet containing 60% fat for 8 months and compared to control and streptozotocin (STZ)-induced diabetic groups that were fed a standard diet containing 10% fat. Aspects of peripheral nerve function (conduction velocity, thermal sensitivity) and central nervous system function (learning ability, memory) were measured at assorted times during the study. Both strains of mice on HFD developed impaired glucose tolerance, indicative of insulin resistance, but only the C57BL6 mice showed statistically significant hyperglycemia. STZ-diabetic C57BL6 mice developed learning deficits in the Barnes maze after 8 weeks of diabetes, whereas neither C57BL6 nor Swiss Webster mice fed a HFD showed signs of defects at that time point. By 6 months on HFD, Swiss Webster mice developed learning and memory deficits in the Barnes maze test, whereas their peripheral nervous system remained normal. In contrast, C57BL6 mice fed the HFD developed peripheral nerve dysfunction, as indicated by nerve conduction slowing and thermal hyperalgesia, but showed normal learning and memory functions. Our data indicate that STZ-induced diabetes or a HFD can damage both peripheral and central nervous systems, but learning deficits develop more rapidly in insulin-deficient than in insulin-resistant conditions and only in Swiss Webster mice. In addition to insulin impairment, dyslipidemia or adiponectinemia might determine the neuropathy phenotype.

Diabetes mellitus and dementia

Growing epidemiologic evidence has suggested that people with diabetes mellitus are at an increased risk for the development of dementia. However, the results for the subtypes of dementia are inconsistent. This review examines the risk of dementia in people with diabetes mellitus, and discusses the possible mechanism underpinning this association. Diabetes mellitus is associated with a 1.5- to 2.5-fold greater risk of dementia among community-dwelling elderly people. Notably, diabetes mellitus is a significant risk factor for not only vascular dementia, but also Alzheimer's disease. The mechanisms underpinning the association are unclear, but it may be multifactorial in nature, involving factors such as cardiovascular risk factors, glucose toxicity, changes in insulin metabolism and inflammation. The optimal management of these risk factors in early life may be important to prevent late-life dementia. Furthermore, novel therapeutic strategies will be needed to prevent or reduce the development of dementia in people with diabetes mellitus.

Dysglycemia, brain volume and vascular lesions on MRI in a memory clinic population

OBJECTIVE

It is unclear, if the association between abnormalities in glucose metabolism (dysglycemia) and impaired cognitive functioning is primarily driven by degenerative or vascular brain damage. We therefore examined the relation between dysglycemia and brain volume and vascular lesions on MRI in a memory clinic population.

METHODS

The relations between markers of glycemia (HbA1c and fasting glucose levels) and normalized brain volume, medial temporal lobe atrophy and vascular lesions (white matter hyperintensities, lacunes) were assessed in 274 consecutive patients attending a memory clinic, using linear regression analyses.

RESULTS

Clinical diagnoses were subjective complaints (n=117), mild cognitive impairment (n=62), Alzheimer's disease (n=61) and other type of dementia (n=34). Twenty patients had a history of diabetes. Across the whole study population there was no relation between HbA1c or fasting glucose and the brain MRI measurements, after adjustments for age, sex and diagnostic group. Secondary analyses after stratification by diabetes status, diagnosis and median age (67 years) did not change the results.

CONCLUSION

In this memory clinic population, dysglycemia was not associated with either brain volume or vascular lesions. Apparently, dysglycemia is not associated with a specific class of brain pathology in patients with cognitive complaints.

Glucose levels and risk of dementia

BACKGROUND

Diabetes is a risk factor for dementia. It is unknown whether higher glucose levels increase the risk of dementia in people without diabetes.

METHODS

We used 35,264 clinical measurements of glucose levels and 10,208 measurements of glycated hemoglobin levels from 2067 participants without dementia to examine the relationship between glucose levels and the risk of dementia. Participants were from the Adult Changes in Thought study and included 839 men and 1228 women whose mean age at baseline was 76 years; 232 participants had diabetes, and 1835 did not. We fit Cox regression models, stratified according to diabetes status and adjusted for age, sex, study cohort, educational level, level of exercise, blood pressure, and status with respect to coronary and cerebrovascular diseases, atrial fibrillation, smoking, and treatment for hypertension.

RESULTS

During a median follow-up of 6.8 years, dementia developed in 524 participants (74 with diabetes and 450 without). Among participants without diabetes, higher average glucose levels within the preceding 5 years were related to an increased risk of dementia (P=0.01); with a glucose level of 115 mg per deciliter (6.4 mmol per liter) as compared with 100 mg per deciliter (5.5 mmol per liter), the adjusted hazard ratio for dementia was 1.18 (95% confidence interval [CI], 1.04 to 1.33). Among participants with diabetes, higher average glucose levels were also related to an increased risk of dementia (P=0.002); with a glucose level of 190 mg per deciliter (10.5 mmol per liter) as compared with 160 mg per deciliter (8.9 mmol per liter), the adjusted hazard ratio was 1.40 (95% CI, 1.12 to 1.76).

CONCLUSIONS

Our results suggest that higher glucose levels may be a risk factor for dementia, even among persons without diabetes. (Funded by the National Institutes of Health.)

Insulin and sex interactions in older adults with mild cognitive impairment

Alzheimer's disease (AD) and other dementias are likely preceded by a protracted preclinical state. Thus, identification of biomarkers that signal potential points of intervention during this prodromal phase (during which patients are largely able to compensate for their cognitive deficits) is of paramount importance. Insulin is a pancreatic hormone with potent central nervous system effects, and insulin dysregulation has been implicated in the pathogenesis of both AD and vascular dementia. The aim of the current study was to determine whether circulating insulin differs as a function of mild cognitive impairment (MCI) diagnosis, and whether this relationship is mediated by sex and apolipoprotein E (APOE) genotype. A sample of 549 nondemented participants aged 65 and over from the Adult Changes in Thought community-based cohort underwent cognitive testing and blood draw to determine fasting levels of plasma insulin. Subjects were categorized as having normal cognitive functioning, amnestic MCI, or nonamnestic MCI. Results showed that the relationship between insulin and diagnostic category is moderated by sex, such that men with nonamnestic or amnestic MCI have higher fasting plasma insulin than cognitively normal men, while women with amnestic MCI have lower fasting plasma insulin than cognitively normal women. Exploratory analyses suggest that APOE ε4 genotype may further influence the relationship between sex and insulin. Future research will help determine whether insulin dysregulation results in differential effects on vascular function and AD pathology as a function of sex and/or APOE genotype.

Food for thought: the role of appetitive peptides in age-related cognitive decline

Through their well described actions in the hypothalamus, appetitive peptides such as insulin, orexin and leptin are recognized as important regulators of food intake, body weight and body composition. Beyond these metabolic activities, these peptides also are critically involved in a wide variety of activities ranging from modulation of immune and neuroendocrine function to addictive behaviors and reproduction. The neurological activities of insulin, orexin and leptin also include facilitation of hippocampal synaptic plasticity and enhancement of cognitive performance. While patients with metabolic disorders such as obesity and diabetes have greater risk of developing cognitive deficits, dementia and Alzheimer's disease (AD), the underlying mechanisms that are responsible for, or contribute to, age-related cognitive decline are poorly understood. In view of the importance of these peptides in metabolic disorders, it is not surprising that there is a greater focus on their potential role in cognitive deficits associated with aging. The goal of this review is to describe the evidence from clinical and pre-clinical studies implicating insulin, orexin and leptin in the etiology and progression of age-related cognitive decline. Collectively, these studies support the hypothesis that leptin and insulin resistance, concepts normally associated with the hypothalamus, are also applicable to the hippocampus.

Ambulant 24-h glucose rhythms mark calendar and biological age in apparently healthy individuals

Glucose metabolism marks health and disease and is causally inferred in the aging process. Ambulant continuous glucose monitoring provides 24-h glucose rhythms under daily life conditions. We aimed to describe ambulant 24-h glucose rhythms measured under daily life condition in relation to calendar and biological age in apparently healthy individuals. In the general population and families with propensity for longevity, we studied parameters from 24-h glucose rhythms; glucose levels; and its variability, obtained by continuous glucose monitoring. Participants were 21 young (aged 22-37 years), 37 middle-aged (aged 44-72 years) individuals from the general population, and 26 middle-aged (aged 52-74 years) individuals with propensity for longevity. All were free of diabetes. Compared with young individuals, middle-aged individuals from the general population had higher mean glucose levels (5.3 vs. 4.7 mmol L(-1) , P < 0.001), both diurnally (P < 0.001) and nocturnally (P = 0.002). Glucose variability was higher in the middle-aged compared with the young (standard deviation 0.70 vs. 0.57 mmol L(-1) , P = 0.025). Compared with middle-aged individuals from the general population, middle-aged individuals with propensity for longevity had lower overall mean glucose levels (5.2 vs. 5.4 mmol L(-1) , P = 0.047), which were more different nocturnally (4.8 vs. 5.2 mmol L(-1) , P = 0.003) than diurnally (5.3 vs. 5.5 mmol L(-1) , P = 0.14). There were no differences in glucose variability between these groups. Results were independent of body mass index. Among individuals without diabetes, we observed significantly different 24-h glucose rhythms depending on calendar and biological age.

Glycogen synthase kinase-3 inhibition prevents learning deficits in diabetic mice

There is an increasing awareness that diabetes has an impact on the central nervous system, with reports of impaired learning, memory, and mental flexibility being more common in diabetic subjects than in the general population. Insulin-deficient diabetic mice also display learning deficits associated with defective insulin-signaling in the brain and increased activity of GSK3. In the present study, AR-A014418, a GSK3β inhibitor, and TX14(A), a neurotrophic factor with GSK3 inhibitory properties, were tested against the development of learning deficits in mice with insulin-deficient diabetes. Treatments were started at onset of diabetes and continued for 10 weeks. Treatment with AR-A014418 or TX14(A) prevented the development of learning deficits, assessed by the Barnes maze, but only AR-A014418 prevented memory deficits, as assessed by the object recognition test. Diabetes-induced increased levels of amyloid β protein and phosphorylated tau were not significantly affected by the treatments. However, the diabetes-induced decrease in synaptophysin, a presynaptic protein marker of hippocampal plasticity, was partially prevented by both treatments. These results suggest a role for GSK3 and/or reduced neurotrophic support in the development of cognitive deficits in diabetic mice that are associated with synaptic damage.

The role of glucose transporters in brain disease: diabetes and Alzheimer’s Disease

The occurrence of altered brain glucose metabolism has long been suggested in both diabetes and Alzheimer’s diseases. However, the preceding mechanism to altered glucose metabolism has not been well understood. Glucose enters the brain via glucose transporters primarily present at the blood-brain barrier. Any changes in glucose transporter function and expression dramatically affects brain glucose homeostasis and function. In the brains of both diabetic and Alzheimer’s disease patients, changes in glucose transporter function and expression have been observed, but a possible link between the altered glucose transporter function and disease progress is missing. Future recognition of the role of new glucose transporter isoforms in the brain may provide a better understanding of brain glucose metabolism in normal and disease states. Elucidation of clinical pathological mechanisms related to glucose transport and metabolism may provide common links to the etiology of these two diseases. Considering these facts, in this review we provide a current understanding of the vital roles of a variety of glucose transporters in the normal, diabetic and Alzheimer’s disease brain.

The diabetes drug liraglutide ameliorates aberrant insulin receptor localisation and signalling in parallel with decreasing both amyloid-β plaque and glial pathology in a mouse model of Alzheimer's disease

Alzheimer's disease (AD) has been shown to involve desensitised insulin receptor (IR) signalling. Liraglutide, a novel glucagon-like peptide 1 (GLP-1) analogue that facilitates insulin signalling, is currently approved for use in type 2 diabetes mellitus. In the present study, we show that distinctive alterations in the localisation and distribution of the IR and increased levels of insulin receptor substrate (IRS)-1 phosphorylated at serine 616 (IRS-1 pS(616)), a key marker of insulin resistance, are associated with amyloid-β plaque pathology in the frontal cortex of a mouse model of AD, APPSWE/PS1dE9. Altered IR status in APPSWE/PS1dE9 is most evident in extracellular deposits with the appearance of dystrophic neurites, with significantly increased IRS-1 pS(616) levels detected within neurons and neurites. The IR and IRS-1 pS(616) changes occur in the vicinity of all plaques in the APPSWE/PS1dE9 brain, and a significant upregulation of astrocytes and microglia surround this pathology. We show that liraglutide treatment for 8 weeks at 25 nmol/kg body weight i.p. once daily in 7-month-old mice significantly decreases IR aberrations in conjunction with a concomitant decrease in amyloid plaque load and levels of IRS-1 pS(616). Liraglutide also induces a highly significant reduction in astrocytosis and microglial number associated with both plaques and IR pathology. The amelioration of IR aberrations and attenuation of IRS-1 pS(616) upregulation, plaque and glial activation in APPSWE/PS1dE9 mice treated with liraglutide support the investigation of the therapeutic potential of liraglutide and long-lasting GLP-1 agonists in patients with AD.

Cognitive impairment in diabetic patients: Can diabetic control prevent cognitive decline?

It is well recognized that the prevalence of dementia is higher in diabetic patients than non‐diabetic subjects. The incidence of diabetes has been increasing because of dramatic changes in lifestyles, and combined with longer lifespans as a result of advances in medical technology, this has brought about an increase in the number of elderly diabetic patients. Together, aging and diabetes have contributed to dementia becoming a serious problem. Progression to dementia reduces quality of life, and imposes a burden on both patients themselves and the families supporting them. Therefore, preventing the complication of dementia will become more and more important in the future. Although many mechanisms have been considered for an association between diabetes and cognitive dysfunction, glucose metabolism abnormalities such as hyperglycemia and hypoglycemia, and insulin action abnormalities such as insulin deficiency and insulin resistance can be causes of cognitive impairment. Recent large‐scale longitudinal studies have found an association between glycemic control and cognitive decline, although it is still unclear how cognitive decline might be prevented by good glycemic control. However, at an early stage, it is necessary to detect moderate cognitive dysfunction and try to reduce the risk factors for it, which should result in prevention of dementia, as well as vascular events. In the present review, in addition to outlining an association between diabetes and cognitive function, we discuss how glycemic control and cognitive decline are related.

Prediction of fracture risk in men: a cohort study

FRAX is a tool that identifies individuals with high fracture risk who will benefit from pharmacological treatment of osteoporosis. However, a majority of fractures among elderly occur in people without osteoporosis and most occur after a fall. Our aim was to accurately identify men with a high future risk of fracture, independent of cause. In the population-based Uppsala Longitudinal Study of Adult Men (ULSAM) and using survival analysis we studied different models' prognostic values (R(2)) for any fracture and hip fracture within 10 years from age 50 (n = 2322), 60 (n = 1852), 71 (n = 1221), and 82 (n = 526) years. During the total follow-up period from age 50 years, 897 fractures occurred in 585 individuals. Of these, 281 were hip fractures occurring in 189 individuals. The rates of any fracture were 5.7/1000 person-years at risk from age 50 years and 25.9/1000 person-years at risk from age 82 years. Corresponding hip fractures rates were 2.9 and 11.7/1000 person-years at risk. The FRAX model included all variables in FRAX except bone mineral density. The full model combining FRAX variables, comorbidity, medications, and behavioral factors explained 25% to 45% of all fractures and 80% to 92% of hip fractures, depending on age. The corresponding prognostic values of the FRAX model were 7% to 17% for all fractures and 41% to 60% for hip fractures. Net reclassification improvement (NRI) comparing the full model with the FRAX model ranged between 40% and 53% for any fracture and between 40% and 87% for hip fracture. Within the highest quintile of predicted fracture risk with the full model, one-third of the men will have a fracture within 10 years after age 71 years and two-thirds after age 82 years. We conclude that the addition of comorbidity, medication, and behavioral factors to the clinical components of FRAX can substantially improve the ability to identify men at high risk of fracture, especially hip fracture.

Similar pattern of peripheral neuropathy in mouse models of type 1 diabetes and Alzheimer's disease

There is an increasing awareness that diabetes has an impact on the CNS and that diabetes is a risk factor for Alzheimer's disease (AD). Links between AD and diabetes point to impaired insulin signaling as a common mechanism leading to defects in the brain. However, diabetes is predominantly characterized by peripheral, rather than central, neuropathy, and despite the common central mechanisms linking AD and diabetes, little is known about the effect of AD on the peripheral nervous system (PNS). In this study, we compared indexes of peripheral neuropathy and investigated insulin signaling in the sciatic nerve of insulin-deficient mice and amyloid precursor protein (APP) overexpressing transgenic mice. Insulin-deficient and APP transgenic mice displayed similar patterns of peripheral neuropathy with decreased motor nerve conduction velocity, thermal hypoalgesia, and loss of tactile sensitivity. Phosphorylation of the insulin receptor and glycogen synthase kinase 3β (GSK3β) was similarly affected in insulin-deficient and APP transgenic mice despite significantly different blood glucose and plasma insulin levels, and nerve of both models showed accumulation of Aβ-immunoreactive protein. Although diabetes and AD have different primary etiologies, both diseases share many abnormalities in both the brain and the PNS. Our data point to common deficits in the insulin-signaling pathway in both neurodegenerative diseases and support the idea that AD may cause disorders outside the higher CNS.

Diabetes and risk of Parkinson's disease: a systematic review and meta-analysis

OBJECTIVE

Diabetes has been associated with chronic neurodegeneration. We performed a systematic review and meta-analysis to assess the relationship between pre-existing diabetes and Parkinson's disease (PD).

RESEARCH DESIGN AND METHODS

Original articles in English published up to 10 May 2011 were searched for in electronic databases (PubMed, Embase, and Scopus) and by reviewing references of eligible articles. Prospective cohort and case-control studies providing risk and precision estimates relating to pre-existing diabetes and PD were considered eligible.

RESULTS

Nine studies/1,947 citations (cohort, N = 4; case-control, N = 5) fulfilled inclusion criteria for meta-analysis. In prospective studies, the onset of diabetes before onset of PD was found to be a risk factor for future PD (relative risk [RR] = 1.37 [95%CI 1.21-1.55]; P < 0.0001). This association was confirmed by secondary analyses based on estimates derived after the exclusion of participants who had vascular disease at baseline and/or who developed vascular disease during follow-up (RR = 1.34 [1.14-1.58]; P < 0.001) and by sensitivity analyses addressing the association with diabetes at baseline or during follow-up. However, the association found for case-control studies was not significant (odds ratio [OR] 0.75 [95%CI 0.50-1.11]; P = 0.835). Sensitivity analysis based on estimates adjusted for BMI confirmed the lack of a relationship between PD and diabetes (OR 0.56 [0.28-1.15]; P = 0.089).

CONCLUSIONS

Although data from cohort studies suggest that diabetes is a risk factor for PD, there is no conclusive evidence on this association. Further prospective studies focused on putative pathogenic pathways and taking a broad range of confounders into account is required to clarify this relationship.

Diabetes, hyperglycemia and the management of cerebrovascular disease

PURPOSE OF REVIEW

Hyperglycemia is frequent in patients with cerebrovascular disease. This review article aims to summarize the recent evidence from observational studies that examined the adverse cerebrovascular effects of dysglycemic states as well as interventional studies assessing intensive management strategies for hyperglycemia.

RECENT FINDINGS

In recent years, diabetes, prediabetic states and insulin resistance and their association with cerebrovascular disease were an important focus of research. The cerebrovascular consequences of these metabolic abnormalities were found to extend beyond ischemic stroke to covert brain infarcts, other structural brain changes and to cognitive impairment with and without dementia. Interventional studies did not reveal that more intensive management of chronic hyperglycemia and of hyperglycemia in the setting of acute stroke improves outcome. There is clear evidence, however, that the overall management of multiple risk factors and behavior modification in patients with dysglycemia may reduce the burden of cerebrovascular disease.

SUMMARY

Observational studies reveal the growing burden and adverse cerebrovascular effects of dysglycemic states. Currently available interventional studies assessing more intensive strategies for the management of hyperglycemia did not prove, however, to be effective. We discuss the current evidence, pathophysiological considerations and management implications.

Molecular basis for vulnerability to mitochondrial and oxidative stress in a neuroendocrine CRI-G1 cell line

Background

Many age-associated disorders (including diabetes, cancer, and neurodegenerative diseases) are linked to mitochondrial dysfunction, which leads to impaired cellular bioenergetics and increased oxidative stress. However, it is not known what genetic and molecular pathways underlie differential vulnerability to mitochondrial dysfunction observed among different cell types.

Methodology/Principal Findings

Starting with an insulinoma cell line as a model for a neuronal/endocrine cell type, we isolated a novel subclonal line (named CRI-G1-RS) that was more susceptible to cell death induced by mitochondrial respiratory chain inhibitors than the parental CRI-G1 line (renamed CRI-G1-RR for clarity). Compared to parental RR cells, RS cells were also more vulnerable to direct oxidative stress, but equally vulnerable to mitochondrial uncoupling and less vulnerable to protein kinase inhibition-induced apoptosis. Thus, differential vulnerability to mitochondrial toxins between these two cell types likely reflects differences in their ability to handle metabolically generated reactive oxygen species rather than differences in ATP production/utilization or in downstream apoptotic machinery. Genome-wide gene expression analysis and follow-up biochemical studies revealed that, in this experimental system, increased vulnerability to mitochondrial and oxidative stress was associated with (1) inhibition of ARE/Nrf2/Keap1 antioxidant pathway; (2) decreased expression of antioxidant and phase I/II conjugation enzymes, most of which are Nrf2 transcriptional targets; (3) increased expression of molecular chaperones, many of which are also considered Nrf2 transcriptional targets; (4) increased expression of β cell-specific genes and transcription factors that specify/maintain β cell fate; and (5) reconstitution of glucose-stimulated insulin secretion.

Conclusions/Significance

The molecular profile presented here will enable identification of individual genes or gene clusters that shape vulnerability to mitochondrial dysfunction and thus represent potential therapeutic targets for diabetes and neurodegenerative diseases. In addition, the newly identified CRI-G1-RS cell line represents a new experimental model for investigating how endogenous antioxidants affect glucose sensing and insulin release by pancreatic β cells.

Insulin metabolism and the risk of Alzheimer disease: the Rotterdam Study

OBJECTIVE

Diabetes mellitus has been associated with an increased risk of Alzheimer disease (AD), but how it exerts its effect remains controversial. Possible pathophysiologic mechanisms are glucose toxicity and a direct effect of insulin on amyloid metabolism. Most studies had short follow-up, and longer-term effects of diabetes on AD risk are unknown. We investigated whether fasting glucose and insulin levels and insulin resistance are associated with the risk of AD and whether this risk is constant over time.

METHODS

The study was based on 3,139 participants of the Rotterdam Study, a population-based cohort study. All subjects were free from dementia, did not have a history of diabetes, and had fasting levels of glucose and insulin measured at baseline. Insulin resistance was estimated with the homeostasis model assessment. We investigated how fasting glucose, insulin, and insulin resistance are related to the risk of AD in 3 different strata according to time-to-event, using Cox proportional hazards models.

RESULTS

During follow-up, 211 participants developed AD, 71 of them within 3 years of baseline. Levels of insulin and insulin resistance were associated with a higher risk of AD within 3 years of baseline. After 3 years, the risk was no longer increased. Glucose was not associated with a higher risk of AD. There was no interaction of APOE ε4 carriership and insulin metabolism on the risk of AD.

CONCLUSIONS

Our findings suggest that insulin metabolism influences the clinical manifestation of AD only within 3 years.

The link between iron, metabolic syndrome, and Alzheimer's disease

Both Alzheimer's disease (AD), the most common form of dementia, and type-2 diabetes mellitus (T2DM), a disease associated with metabolic syndrome (MetS), affect a great number of the world population and both have increased prevalence with age. Recently, many studies demonstrated that pre-diabetes, MetS, and T2DM are risk factors in the development of AD and have many common mechanisms. The main focus of studies is the insulin resistance outcome found both in MetS as well as in brains of AD subjects. However, oxidative stress (OS)-related mechanisms, which are well known to be involved in AD, including mitochondrial dysfunction, elevated iron concentration, reactive oxygen species (ROS), and stress-related enzyme or proteins (e.g. heme oxygenase-1, transferrin, etc.), have not been elucidated in MetS or T2DM brains although OS and iron are involved in the degeneration of the pancreatic islet β cells. Therefore, this review sets to cover the current literature regarding OS and iron in MetS and T2DM and the similarities to mechanisms in AD both in human subjects as well as in animal models.

Cognitive function and risks of cardiovascular disease and hypoglycaemia in patients with type 2 diabetes: the Action in Diabetes and Vascular Disease: Preterax and Diamicron Modified Release Controlled Evaluation (ADVANCE) trial

AIMS/HYPOTHESIS

The relationship between cognitive function, cardiovascular disease and premature death is not well established in patients with type 2 diabetes. We assessed the effects of cognitive function in 11,140 patients with type 2 diabetes who participated in the Action in Diabetes and Vascular Disease: Preterax and Diamicron Modified Release Controlled Evaluation (ADVANCE) trial. Furthermore, we tested whether level of cognitive function altered the beneficial effects of the BP-lowering and glycaemic-control regimens in the trial.

METHODS

Cognitive function was assessed using the Mini Mental State Examination at baseline, and defined by scores 28-30 ('normal', n = 8,689), 24-27 ('mild dysfunction', n = 2,231) and <24 ('severe dysfunction', n = 212). Risks of major cardiovascular events, death and hypoglycaemia and interactions with treatment were assessed using Cox proportional hazards analysis.

RESULTS

Relative to normal function, both mild and severe cognitive dysfunction significantly increased the multiple-adjusted risks of major cardiovascular events (HR 1.27, 95% CI 1.11-1.46 and 1.42, 95% CI 1.01-1.99; both p < 0.05), cardiovascular death (1.41, 95% CI 1.16-1.71 and 1.56, 95% CI 0.99-2.46; both p <or= 0.05) and all-cause death (1.33, 95% CI 1.16-1.54 and 1.50, 95% CI 1.06-2.12; both p < 0.03). Severe, but not mild, cognitive dysfunction increased the risk of severe hypoglycaemia (HR 2.10, 95% CI 1.14-3.87; p = 0.018). There was no evidence of heterogeneity of treatment effects on cardiovascular outcomes in subgroups defined by cognitive function at baseline.

CONCLUSIONS/INTERPRETATION

Cognitive dysfunction is an independent predictor of clinical outcomes in patients with type 2 diabetes, but does not modify the effects of BP lowering or glucose control on the risks of major cardiovascular events.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00145925.