Diabetes and brain damage: more (or less) than meets the eye?

The clinical features and potential mechanisms of cognitive disorders in peripheral autoimmune and inflammatory diseases

According to a study from World Health Organization's Global Burden of Disease, mental and neurological disorders have accounted for 13% of global diseases in recent years and are on the rise. Neuropsychiatric conditions or neuroinflammatory disorders are linked by the presence of an exaggerated immune response both peripherally and in the central nervous system (CNS). Cognitive dysfunction (CD) encompasses a complex group of diseases and has frequently been described in the field of autoimmune diseases, especially in multiple non-CNS-related autoimmune diseases. Recent studies have provided various hypotheses regarding the occurrence of cognitive impairment in autoimmune diseases, including that abnormally activated immune cells can disrupt the integrity of the blood-brain barrier (BBB) to trigger a central neuroinflammatory response. When the BBB is intact, autoantibodies and pro-inflammatory molecules in peripheral circulation can enter the brain to activate microglia, inducing CNS inflammation and CD. However, the mechanisms explaining the association between the immune system and neural function and their contribution to diseases are uncertain. In this review, we used clinical statistics to illustrate the correlation between CD and autoimmune diseases that do not directly affect the CNS, summarized the clinical features and mechanisms by which autoimmune diseases trigger cognitive impairment, and explored existing knowledge regarding the link between CD and autoimmune diseases from the perspective of the field of neuroimmunology.

The Association between Cognitive Impairment and Diabetic Foot Care: Role of Neuropathy and Glycated Hemoglobin

Diabetes mellitus is associated with impairment in cognitive functions which can complicate adherence to self-care behaviors. We evaluated the incidence of cognitive impairment in patients with diabetes mellitus to determine the strength of the association between diabetic foot (a complication that occurs in about 10% of diabetic patients), adherence to the clinician’s recommendations, glycemic control, and cognitive function. A prospective study was carried out in a probabilistic sample of older patients with diabetic foot living in three nursing homes. Cognitive functions were evaluated by the MMSE (Mini-Mental State Examination), the Trail Making test (TMT), and the Michigan neuropathy screening instrument (MNSI). There were no significant associations between cognitive function and neuropathy or foot alterations, although glycated hemoglobin (HB1Ac > 7%) significantly (p < 0.05) associated with MMSE and adherence to treatment in the 1 month follow-up visit. Receiver operating characteristic curve analysis showed that both HB1Ac and the MNSI score significantly (p < 0.05) discriminate subsequent adherence to treatment for foot complication, with a sensitivity of 80.0–73.3% and specificity 70.6–64.7%, respectively. Proper control of foot complications in diabetic patients involves appropriate glycemic control and less severe neuropathy, and seems to be unrelated to cognitive dysfunction, and warrants further studies in order to tailor appropriate treatments to central and peripheral nervous system disorders. Poor glycemic control (Hb1Ac level > 7%) and a neuropathy score of 5.5 in the MNSI are the best-cut off points to discriminate poor adherence to the clinician’s recommendations for self-care behaviors in people with diabetic foot complication. In this study, we observed that foot disorders were associated with impaired global cognitive function in elderly patients (aged ≥ 65). Podiatrists and physicians should consider cognitive dysfunction as an important chronic complication in the management of diabetic foot.

Association of Depression With Functional Mobility in Schizophrenia

BACKGROUND

Functional immobility can cause functional disability in patients with schizophrenia and has been linked to prognosis and mortality. Although depression might be a barrier for physical activity engagement, scarce data are present on the relationship between depression and functional mobility (FM) in schizophrenia. Thus, we aimed to investigate the associations among FM, depression, and other clinical correlates in individuals with schizophrenia.

METHODS

FM was evaluated by the pedometer-assessed daily steps and Timed Up-and-Go (TUG) test in the daily-living and clinical settings, respectively. Psychiatric symptoms were assessed using the Beck Depression Inventory, Brief Psychiatric Rating Scale (BPRS), and State-Trait Anxiety Inventory. Cognitive function was evaluated using the Sternberg Working Memory (SWM) Task. Multiple regression analyses were performed to identify predictive factors associated with FM, with adjustment for relevant covariates.

RESULTS

Sixty patients were enrolled in this study. Depression was the most consistent explanatory variable for both pedometer (β = -0.34, p = 0.011) and TUG time (β = 0.32, p = 0.018). Additionally, SWM accuracy (β = -0.29, p = 0.018), BPRS-Withdrawal (β = 0.19, p = 0.139), and fasting blood sugar (β = 0.34, p = 0.008) were associated with TUG time. However, psychotic symptoms and anxiety were not associated with pedometer and TUG.

CONCLUSIONS

We identified an association between depression and FM after adjusting for other disorder-related correlates in schizophrenia. Since the intervention goal is functional recovery, improving FM by treating depression may have considerable therapeutic value.

Neurovascular Organotypic Culture Models Using Induced Pluripotent Stem Cells to Assess Adverse Chemical Exposure Outcomes

Introduction: Human-induced pluripotent stem cells (iPSCs) represent a promising cell source for the construction of organotypic culture models for chemical toxicity screening and characterization. Materials and Methods: To characterize the effects of chemical exposure on the human neurovasculature, we constructed neurovascular unit (NVU) models consisting of endothelial cells (ECs) and astrocytes (ACs) derived from human-iPSCs, as well as human brain-derived pericytes (PCs). The cells were cocultured on synthetic poly(ethylene glycol) (PEG) hydrogels that guided the self-assembly of capillary-like vascular networks. High-content epifluorescence microscopy evaluated dose-dependent changes to multiple aspects of NVU morphology. Results: Cultured vascular networks underwent quantifiable morphological changes when incubated with vascular disrupting chemicals. The activity of predicted vascular disrupting chemicals from a panel of 38 compounds (U.S. Environmental Protection Agency) was ranked based on morphological features detected in the NVU model. In addition, unique morphological neurovascular disruption signatures were detected per chemical. A comparison of PEG-based NVU and Matrigel^™-based NVU models found greater sensitivity and consistency in chemical detection by the PEG-based NVU models. Discussion: We suspect that specific morphological changes may be used for discerning adverse outcome pathways initiated by chemical exposure and rapid mechanistic characterization of chemical exposure to neurovascular function. Conclusion: The use of human stem cell-derived vascular tissue and PEG hydrogels in the construction of NVU models leads to rapid detection of adverse chemical effects on neurovascular stability. The use of multiple cell types in coculture elucidates potential mechanisms of action by chemicals applied to the model.

Pre-clinical investigation of Diabetes Mellitus as a risk factor for schizophrenia

This study investigated the behavioral and biochemical parameters of DM1 as a risk factor in an animal model of schizophrenia (SZ). All groups: 1 Control (saline+saline); 2 Alloxan (alloxan+saline); 3 Ketamine (saline+ketamine); 4 (Alloxan+Ketamine) were fasted for a period of 18h before the subsequent induction of DM via a single intraperitoneal (i.p) injection of alloxan (150mg/kg). From the 4th to the 10th days, the animals were injected i.p with ketamine (25mg/kg) or saline, once a day, to induce a model of SZ and 30min after the last administration were subjected to behavioral testing. After, the animals were decapitated and the brain structures were removed. Ketamine induced hyperactivity and in the social interaction, ketamine, alloxan and the association of alloxan+ketamine increased the latency and decreased the number of contacts between animals. The animals from the ketamine, alloxan and alloxan+ketamine groups showed a prepulse startle reflex (PPI) deficit at the three intensities (65, 70 and 75dB). Ketamine was shown to be capable of increasing the activity of acetylcholinesterase (AChE) in the brain structures. Combination of alloxan+ketamine seems to have an exacerbated effect within the cholinergic system. For lipid peroxidation and protein carbonyls, alloxan+ketamine appear to have intensified lipid and protein damage in the three structures. Ketamine and the combination of ketamine+alloxan induced DNA damage in both frequency and damage index. This research found a relationship between DM1 and SZ.

Neurological outcomes of antidiabetic therapy: What the neurologist should know

Considering the causative or contributory effects of diabetes mellitus on common neurological diseases such as polyneuropathy, stroke and dementia, modern antidiabetic drugs may be expected to reduce incidence or progression of these conditions. Nevertheless, most observed benefits have been small, except in the context of therapy for diabetes mellitus type I and new-onset polyneuropathy. Recently, semaglutide, a GLP-1 analog, has been shown to significantly reduce stroke incidence in a randomized controlled trial. Beneficial effects of antidiabetic drugs on stroke severity or outcome have been controversial, though. The level of risk conferred by diabetes mellitus, the complex pathophysiology of neurological diseases, issues of trial design, side-effects of antidiabetic drugs as well as co-medication might be interacting factors that determine the performance of antidiabetic therapy with respect to neurological outcomes. It might be speculated that early treatment of prediabetes might prevent cerebral arteriosclerosis, cognitive decline or polyneuropathy more effectively, but this remains to be demonstrated.

Diabetes mellitus and cognitive impairments

There is strong evidence that diabetes mellitus increases the risk of cognitive impairment and dementia. Insulin signaling dysregulation and small vessel disease in the base of diabetes may be important contributing factors in Alzheimer’s disease and vascular dementia pathogenesis, respectively. Optimal glycemic control in type 1 diabetes and identification of diabetic risk factors and prophylactic approach in type 2 diabetes are very important in the prevention of cognitive complications. In addition, hypoglycemic attacks in children and elderly should be avoided. Anti-diabetic medications especially Insulin may have a role in the management of cognitive dysfunction and dementia but further investigation is needed to validate these findings.

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

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

Glycemic extremes in youth with T1DM: the structural and functional integrity of the developing brain

The adult brain accounts for a disproportionally large percentage of the body’s total energy consumption (1). However, during brain development,energy demand is even higher, reaching the adult rate by age 2 and increasing to nearly twice the adult rate by age 10, followed by gradual reduction toward adult levels in the next decade (1,2). The dramatic changes in brain metabolism occurring over the first two decades of life coincide with the initial proliferation and then pruning of synapses to adult levels.The brain derives its energy almost exclusively from glucose and is largely driven by neuronal signaling, biosynthesis, and neuroprotection (3–6).Glucose homeostasis in the body is tightly regulated by a series of hormones and physiologic responses. As a result, hypoglycemia and hyperglycemia are rare occurrences in normal individuals, but they occur commonly inpatients with type 1 diabetes mellitus (T1DM) due to a dysfunction of peripheral glucose-insulin-glucagon responses and non-physiologic doses of exogenous insulin, which imperfectly mimic normal physiology. These extremes can occur more frequently in children and adolescents with T1DM due to the inadequacies of insulin replacement therapy, events leading to the diagnosis [prolonged untreated hyperglycemia and diabetic ketoacidosis (DKA)], and to behavioral factors interfering with optimal treatment. When faced with fluctuations in glucose supply the metabolism of the body and brain change dramatically, largely to conserve resources and, at a cost to other organs, to preserve brain function (7). However,if the normal physiological mechanisms that prevent these severe glucose fluctuations and maintain homeostasis are impaired, neuronal function and potentially viability can be affected (8–11).

[Astrogliopathy as a loss of astroglial protective function against glycoxidative stress under hyperglycemia]

Reactive oxygen species (ROS) derived from mitochondria play an essential role in stroke as well as in neurodegenerative disorders. Although hyperglycemia associated with diabetes mellitus is well known to enhance ROS production in vascular endothelial cells, the effects of either acute or chronic high glucose environments on neurons and glial cells remain unclear. Astroglia play a pivotal role in glucose metabolism. Thus, the astroglial metabolic response to high glucose environments is an interesting subject. In particular, the glutathione/pentose phosphate pathway (PPP) system, which is a major defense mechanism against ROS in the brain, contributes to glucose metabolism and is more active in astroglia. We propose that high glucose environments activate PPP through an increased flux to the hexosamine biosynthetic pathway (HBP). HBP is known to induce endoplasmic reticulum (ER) stress under hyperglycemia, resulting in the nuclear translocation of nuclear factor-erythroid-2-related factor 2 (Nrf2), a master regulator of phase 2 detoxifying enzymes including glucose-6-phosphate dehydrogenase that regulates PPP activity, as Nrf2 is reported to be a direct substrate of protein kinase RNA (PKR)-like ER kinase (PERK), a transducer of ER stress. Therefore, the phosphorylation of Nrf2 by hyperglycemia-induced ER stress facilitates Nrf2 translocation through PERK, thus activating the PPP. If acute or chronic hyperglycemia induces PPP activation in astroglia to reduce ROS, reducing the glucose concentration may be accompanied by a risk, which may explain the lack of evidence that strict glycemic control during the acute phase of stroke conveys no beneficial effect.

Diabetes and cognitive dysfunction

Cognitive dysfunction in type 1 and type 2 diabetes share many similarities, but important differences do exist. A primary distinguishing feature of type 2 diabetes is that people with this disorder often (but not invariably) do poorly on measures of learning and memory, whereas deficits in these domains are rarely seen in people with type 1 diabetes. Chronic hyperglycaemia and microvascular disease contribute to cognitive dysfunction in both type 1 and type 2 diabetes, and both disorders are associated with mental and motor slowing and decrements of similar magnitude on measures of attention and executive functioning. Additionally, both types are characterised by neural slowing, increased cortical atrophy, microstructural abnormalities in white matter tracts, and similar, but not identical, changes in concentrations of brain neurometabolites. Disconcertingly, the rapid rise in obesity and type 2 diabetes in all age groups might result in a substantial increase in prevalence of diabetes-related cognitive dysfunction.

Astroglial pentose phosphate pathway rates in response to high-glucose environments

ROS (reactive oxygen species) play an essential role in the pathophysiology of diabetes, stroke and neurodegenerative disorders. Hyperglycaemia associated with diabetes enhances ROS production and causes oxidative stress in vascular endothelial cells, but adverse effects of either acute or chronic high-glucose environments on brain parenchymal cells remain unclear. The PPP (pentose phosphate pathway) and GSH participate in a major defence mechanism against ROS in brain, and we explored the role and regulation of the astroglial PPP in response to acute and chronic high-glucose environments. PPP activity was measured in cultured neurons and astroglia by determining the difference in rate of ¹⁴CO₂ production from [1-¹⁴C]glucose and [6-¹⁴C]glucose. ROS production, mainly H₂O₂, and GSH were also assessed. Acutely elevated glucose concentrations in the culture media increased PPP activity and GSH level in astroglia, decreasing ROS production. Chronically elevated glucose environments also induced PPP activation. Immunohistochemical analyses revealed that chronic high-glucose environments induced ER (endoplasmic reticulum) stress (presumably through increased hexosamine biosynthetic pathway flux). Nuclear translocation of Nrf2 (nuclear factor-erythroid 2 p45 subunit-related factor 2), which regulates G6PDH (glyceraldehyde-6-phosphate dehydrogenase) by enhancing transcription, was also observed in association with BiP (immunoglobulin heavy-chain-binding protein) expression. Acute and chronic high-glucose environments activated the PPP in astroglia, preventing ROS elevation. Therefore a rapid decrease in glucose level seems to enhance ROS toxicity, perhaps contributing to neural damage when insulin levels given to diabetic patients are not properly calibrated and plasma glucose levels are not adequately maintained. These findings may also explain the lack of evidence for clinical benefits from strict glycaemic control during the acute phase of stroke.

Cognitive functioning in type 1 diabetes: the Diabetes Control and Complications Trial (DCCT) revisited

The Diabetes Control and Complications Trial (DCCT)/Epidemiology of Diabetes Interventions and Complications (EDIC) study has allowed an examination of the long-term effects of type 1 diabetes and intensity of treatment on cognitive function. The association observed between chronic hyperglycaemia and mild cognitive dysfunction, affecting motor speed and psychomotor efficiency, has been re-evaluated by Jacobson et al. (Diabetologia doi: 10.1007/s00125-010-1883-9) to determine the possible contribution of macrovascular risk factors, subclinical macrovascular disease and microvascular complications (retinopathy and nephropathy). This has revealed associations between mild impairment of psychomotor efficiency and hypertension, glycaemic control and the presence of retinopathy and nephropathy, while smoking history was associated with modest abnormalities in several cognitive domains. Neither macrovascular risk factors nor a history of severe hypoglycaemia was associated with the cognitive decrements; cerebral microangiopathy has been proposed as a possible underlying cause. Although the degree of cognitive impairment was mild and limited to a few domains, these decrements may influence the performance of everyday activities, such as driving.

The associations of apolipoprotein E and angiotensin-converting enzyme polymorphisms and cognitive function in Type 1 diabetes based on an 18-year follow-up of the DCCT cohort

AIMS

Specific polymorphisms of the apolipoprotein E (APOE) and angiotensin-converting enzyme (ACE) genes appear to increase risk for Alzheimer's disease and cognitive dysfunction in the general population, yet little research has examined whether genetic factors influence risk of cognitive dysfunction in patients with Type 1 diabetes. The long-term follow-up of the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC) population provides an opportunity to examine if specific genetic variations in APOE and ACE alter risk for cognitive decline.

METHODS

Neurocognitive function in Type 1 diabetic subjects from the DCCT/EDIC study was assessed at DCCT entry and re-assessed approximately 18 years later, using a comprehensive cognitive test battery. Glycated haemoglobin (HbA(1c)) and the frequency of severe hypoglycaemic events leading to coma or seizures were measured over the 18-year follow-up. We determined whether the APO epsilon4 and ACE intron 16 indel genotypes were associated with baseline cognitive function and with change over time, and whether they conferred added risk in those subjects experiencing severe hypoglycaemic events or greater glycaemic exposure.

RESULTS

None of the APOE or ACE polymorphisms were associated with either baseline cognitive performance or change in cognition over the 18-year follow-up. Moreover, none of the genotype variations altered the risk of cognitive dysfunction in those subjects with severe hypoglycaemic episodes or high HbA(1c).

CONCLUSIONS

In this sample of young and middle-aged adults with Type 1 diabetes, APO epsilon4 and ACE D alleles do not appear to increase risk of cognitive dysfunction.

The role of metabolic derangements and glucocorticoid excess in the aetiology of cognitive impairment in type 2 diabetes. Implications for future therapeutic strategies

Dementia is becoming increasingly common in western societies and carries with it a substantial clinical, social and economic burden. It is now well established that type 2 diabetes is a risk factor for dementia and it is likely that this association has a multifactorial aetiology. There is a relative paucity of data on interventions to improve cognitive function in people with type 2 diabetes. Two small randomized controlled trials have suggested that better glycaemic control, over a relatively short time period, can improve or prevent decline in cognitive function. There is also increasing interest in the link between intracerebral insulin and cognitive impairment. Several studies have suggested that relative and/or absolute deficiency of insulin may occur in Alzheimer's dementia and, although one small randomized trial was essentially negative, randomized trials are currently underway to investigate the impact of thiazolidinediones on cognitive function in dementia. The hypothalamic-pituitary-adrenal axis is also activated in people with type 2 diabetes and there are data linking increased cortisol concentrations with cognitive impairment. Inhibition of the 11 beta-hydroxysteroid dehydrogenase type 1 enzyme, which generates cortisol from inactive cortisone in many tissues including the brain, is an attractive therapeutic target to enhance cognition. Large-scale epidemiological and intervention studies are now underway, which should enhance our understanding and management of cognitive impairment in type 2 diabetes.

Association of type 2 diabetes with depression, brain atrophy, and reduced fine motor speed in a 60- to 64-year-old community sample

OBJECTIVE

To examine the relationship of diabetes mellitus to depression, cognition, and structural brain anatomical variables in a 60-64-year-old community-dwelling sample. The authors hypothesized that subjects with Type 2 diabetes are more likely to be depressed, have more brain atrophy, and poorer cognitive function compared with nondiabetic comparison subjects.

METHODS

A random sample of 478 subjects aged 60-64 years from a larger community sample were interviewed and underwent physical examinations, assessment of depression, standard cognitive assessments, brain magnetic resonance imaging (MRI) scans, and fasting blood tests. Subjects were considered diabetic if they were on treatment for diabetes or recorded a fasting blood glucose level of greater than 10 mmol/L. The MRI scans were analyzed for brain atrophy, gray matter (GM), white matter (WM), cerebrospinal fluid (CSF), hippocampal, and white matter hyperintensity (WMH) volumes.

RESULTS

MRI data were available for 39 subjects with diabetes and 428 subjects without diabetes. Descriptive analyses showed that subjects with diabetes were more likely to have poor physical health, a higher body mass index, and higher scores of depression and anxiety compared with comparison subjects without diabetes. In multiple regression analyses, diabetes was associated with greater total brain atrophy and larger CSF volume, but did not differ in the WM, GM, and WMH volumes. Diabetes patients performed less well on a task of fine motor dexterity.

CONCLUSIONS

Diabetes is related to increased brain atrophy and poor motor function in 60-64 year olds, independent of depression, vascular risk factors, and small vessel disease of the brain.

Cognition and diabetes: a lifespan perspective

Diabetes mellitus is associated with cognitive dysfunction and abnormalities that can be seen with brain imaging. Recent studies provide important new insights into the nature and severity of these cerebral complications that help to explain why some patients with diabetes have clinically relevant neurocognitive morbidity, whereas most are apparently unaffected. This Personal View investigates the hypothesis that clinically relevant diabetes-related cognitive decrements mainly occur at two crucial periods in life: when the brain is developing in childhood, and when the brain undergoes neurodegenerative changes associated with ageing. Outside of these periods cognitive decrements mainly occur in patients with notable diabetes-related comorbidities, in particular microvascular or macrovascular complications. The identification of crucial periods and conditions for the development of diabetes-related cognitive decrements helps to draw the attention of physicians to individuals at risk and can direct future studies into the mechanisms that underlie these conditions.

Regulation of the inositol 1,4,5-trisphosphate receptor type I by O-GlcNAc glycosylation

The inositol 1,4,5-trisphosphate (InsP3) receptor type I (InsP3R-I) is the principle channel for intracellular calcium (Ca2+) release in many cell types, including central neurons. It is regulated by endogenous compounds like Ca2+ and ATP, by protein partners, and by posttranslational modification. We report that the InsP3R-I is modified by O-linked glycosylation of serine or threonine residues with beta-N-acetylglucosamine (O-GlcNAc). The level of O-GlcNAcylation can be altered in vitro by the addition of the enzymes which add [OGT (O-GlcNActransferase)] or remove (O-GlcNAcase) this sugar or by loading cells with UDP-GlcNAc. We monitored the effects of this modification on InsP3R function at the single-channel level and on intracellular Ca2+ transients. Single-channel activity was monitored with InsP3R incorporated into bilayers; Ca2+ signaling was monitored using cells loaded with a Ca2+-sensitive fluorophore. We found that channel activity was decreased by the addition of O-GlcNAc and that this decrease was reversed by removal of the sugar. Similarly, cells loaded with UDP-GlcNAc had an attenuated response to uncaging of InsP3. These results show that O-GlcNAcylation is an important regulator of the InsP3R-I and suggest a mechanism for neuronal dysfunction under conditions in which O-GlcNAc is high, such as diabetes or physiological stress.

Diabetes, cognitive impairment, and dementia

Are strongly linked, but the precise mechanisms are unclear

The relationship between type 2 diabetes and dementia

INTRODUCTION

The prevalence of type 2 diabetes and dementia are set to rise inexorably over the next 30-40 years. There are now substantial data to suggest that type 2 diabetes is associated with an increased risk of dementia.

SOURCES OF DATA

This is a narrative review using data from individual studies and review articles known to the authors. A Medline search was also undertaken and reference lists were reviewed to identify additional relevant studies.

AREAS OF AGREEMENT

Type 2 diabetes is associated with an increased risk of both Alzheimer's and Vascular dementia, although the reality is that many affected individuals have mixed forms of dementia.

AREAS OF CONTROVERSY

The mechanisms underpinning this association remain to be clearly delineated. Type 2 diabetes is a complex disorder and so it is likely that multiple different, synergistic processes may interact to promote cognitive decrements.

GROWING POINTS

Recent data suggest that glucocorticoids excess and elevated inflammatory markers may also have a role in the aetiology of diabetes-related cognitive impairment.

AREAS TIMELY FOR DEVELOPING RESEARCH

Large-scale, prospective epidemiological studies are now required to accurately delineate the pathogenesis of cognitive impairment in people with type 2 diabetes. These are underway and randomized trials of diabetes-specific interventions are also starting to include cognitive function as an outcome measure.

Long-term effect of diabetes and its treatment on cognitive function

BACKGROUND

Long-standing concern about the effects of type 1 diabetes on cognitive ability has increased with the use of therapies designed to bring glucose levels close to the nondiabetic range and the attendant increased risk of severe hypoglycemia.

METHODS

A total of 1144 patients with type 1 diabetes enrolled in the Diabetes Control and Complications Trial (DCCT) and its follow-up Epidemiology of Diabetes Interventions and Complications (EDIC) study were examined on entry to the DCCT (at mean age 27 years) and a mean of 18 years later with the same comprehensive battery of cognitive tests. Glycated hemoglobin levels were measured and the frequency of severe hypoglycemic events leading to coma or seizures was recorded during the follow-up period. We assessed the effects of original DCCT treatment-group assignment, mean glycated hemoglobin values, and frequency of hypoglycemic events on measures of cognitive ability, with adjustment for age at baseline, sex, years of education, length of follow-up, visual acuity, self-reported sensory loss due to peripheral neuropathy, and (to control for the effects of practice) the number of cognitive tests taken in the interval since the start of the DCCT.

RESULTS

Forty percent of the cohort reported having had at least one hypoglycemic coma or seizure. Neither frequency of severe hypoglycemia nor previous treatment-group assignment was associated with decline in any cognitive domain. Higher glycated hemoglobin values were associated with moderate declines in motor speed (P=0.001) and psychomotor efficiency (P<0.001), but no other cognitive domain was affected.

CONCLUSIONS

No evidence of substantial long-term declines in cognitive function was found in a large group of patients with type 1 diabetes who were carefully followed for an average of 18 years, despite relatively high rates of recurrent severe hypoglycemia. (ClinicalTrials.gov number, NCT00360893.)