Hippocampal damage and memory impairments as possible early brain complications of type 2 diabetes

Brain imaging in type 2 diabetes

Type 2 diabetes mellitus (T2DM) is associated with cognitive dysfunction and dementia. Brain imaging may provide important clues about underlying processes. This review focuses on the relationship between T2DM and brain abnormalities assessed with different imaging techniques: both structural and functional magnetic resonance imaging (MRI), including diffusion tensor imaging and magnetic resonance spectroscopy, as well as positron emission tomography and single-photon emission computed tomography. Compared to people without diabetes, people with T2DM show slightly more global brain atrophy, which increases gradually over time compared with normal aging. Moreover, vascular lesions are seen more often, particularly lacunar infarcts. The association between T2DM and white matter hyperintensities and microbleeds is less clear. T2DM has been related to diminished cerebral blood flow and cerebrovascular reactivity, particularly in more advanced disease. Diffusion tensor imaging is a promising technique with respect to subtle white matter involvement. Thus, brain imaging studies show that T2DM is associated with both degenerative and vascular brain damage, which develops slowly over the course of many years. The challenge for future studies will be to further unravel the etiology of brain damage in T2DM, and to identify subgroups of patients that will develop distinct progressive brain damage and cognitive decline.

Neuropathology of type 2 diabetes: a short review on insulin-related mechanisms

Postmortem studies have shown that cerebrovascular disease (CVD) neuropathology occurs frequently in type 2 diabetes (T2D) through mechanisms associated with chronic hyperglycemia such as advanced glycation end-products (AGEs). The involvement of T2D in Alzheimer׳s disease (AD)-type neuropathology has been more controversial. While postmortem data from animal studies have supported the involvement of T2D in AD-type neuropathology through insulin mechanism that may affect the development of neuritic plaques and neurofibrillary tangles (NFTs), findings from postmortem studies in humans, of the association of T2D with AD, have been mainly negative. To complicate matters, medications to treat T2D have been implicated in reduced AD-type neuropathology. In this review we summarize the literature on animal and human postmortem studies of T2D neuropathology, mainly the mechanisms involved in hyperglycemia-related CVD neuropathology and hyperinsulinemia-related AD-type neuropathology.

Severity of Type 2 Diabetes, Cognitive Function, and Self-Care

Type 2 diabetes mellitus (T2DM) is associated with poorer performance on certain measures of cognitive function. However, little is known about the associations among working memory (WM), executive function (EF), and self-care in those with severe T2DM. This investigation explored these relationships among 67 middle-aged and older individuals with T2DM (mean age of 62.9 years). Severity of T2DM was measured with a health status composite (HSC) score from the Diabetes Care Profile, the number of prescribed medications, and the number of comorbid conditions. Cognitive assessments included the Working Memory Index and the Executive Interview 25 (EXIT 25). Self-care was measured using the Self-Care Inventory-Revised (SCI-R) and hemoglobin A1c (HgbA1c). WM was significantly correlated with all measures of severity of T2DM (HSC, r = .542, p < . 01; number of comorbidities, r = -.476, p < .01; and number of prescription medications, r = -.344, p < .01). EF was significantly correlated with all measures of severity of T2DM (HSC, r = -.504, p < .01; number of comorbidities, r = .492, p < .01; and number of prescription medications, r = .326, p < .01). The self-care measure HgbA1c was significantly correlated with WM (r = -.352, p < .01) and EF (r = .510, p < .01). The EXIT 25 score fully mediated the relationship between severity of T2DM and self-care as measured by HgbA1c (β = .431, p < .001). These findings provide preliminary evidence for the associations among severity of T2DM, WM, EF, and self-care.

Insulin resistance, diabetes mellitus, and brain structure in bipolar disorders

Type 2 diabetes mellitus (T2DM) damages the brain, especially the hippocampus, and frequently co-occurs with bipolar disorders (BD). Reduced hippocampal volumes are found only in some studies of BD subjects and may thus be secondary to the presence of certain clinical variables. Studying BD patients with abnormal glucose metabolism could help identify preventable risk factors for hippocampal atrophy in BD. We compared brain structure using optimized voxel-based morphometry of 1.5T MRI scans in 33 BD subjects with impaired glucose metabolism (19 with insulin resistance/glucose intolerance (IR/GI), 14 with T2DM), 15 euglycemic BD participants and 11 euglycemic, nonpsychiatric controls. The group of BD patients with IR, GI or T2DM had significantly smaller hippocampal volumes than the euglycemic BD participants (corrected p=0.02) or euglycemic, nonpsychiatric controls (corrected p=0.004). Already the BD subjects with IR/GI had smaller hippocampal volumes than euglycemic BD participants (t(32)=-3.15, p=0.004). Age was significantly more negatively associated with hippocampal volumes in BD subjects with IR/GI/T2DM than in the euglycemic BD participants (F(2, 44)=9.96, p=0.0003). The gray matter reductions in dysglycemic subjects extended to the cerebral cortex, including the insula. In conclusion, this is the first study demonstrating that T2DM or even prediabetes may be risk factors for smaller hippocampal and cortical volumes in BD. Abnormal glucose metabolism may accelerate the age-related decline in hippocampal volumes in BD. These findings raise the possibility that improving diabetes care among BD subjects and intervening already at the level of prediabetes could slow brain aging in BD.

Cortical thinning in type 2 diabetes mellitus and recovering effects of insulin therapy

The purpose of this study was to explore the brain structural changes in type 2 diabetes and the effect of insulin on the brain using a surface-based cortical thickness analysis. High-resolution three-dimensional T1-weighted fast spoiled gradient recalled echo MRI were obtained from 11 patients with type 2 diabetes before and after insulin therapy. The cortical thickness over the entire brain was calculated, and cross-sectional and longitudinal surface-based cortical thickness analyses were also performed. Regional cortical thinning was demonstrated in the middle temporal gyrus, posterior cingulate gyrus, precuneus, right lateral occipital gyrus and entorhinal cortex bilaterally for patients with type 2 diabetes mellitus compared with normal controls. Cortical thickening was seen in the middle temporal gyrus, entorhinal cortex and left inferior temporal gyrus bilaterally after patients underwent 1 year of insulin therapy. These findings suggest that insulin therapy may have recovering effects on the brain cortex in type 2 diabetes mellitus. The precise mechanism should be investigated further.

Brain structural changes and their correlation with vascular disease in type 2 diabetes mellitus patients: a voxel-based morphometric study

Voxel-based morphometry has been used in the study of alterations in brain structure in type 1 diabetes mellitus patients. These changes are associated with clinical indices. The age at onset, pathogenesis, and treatment of type 1 diabetes mellitus are different from those for type 2 diabetes mellitus. Thus, type 1 and type 2 diabetes mellitus may have different impacts on brain structure. Only a few studies of the alterations in brain structure in type 2 diabetes mellitus patients using voxel-based morphometry have been conducted, with inconsistent results. We detected subtle changes in the brain structure of 23 cases of type 2 diabetes mellitus, and demonstrated that there was no significant difference between the total volume of gray and white matter of the brain of type 2 diabetes mellitus patients and that in controls. Regional atrophy of gray matter mainly occurred in the right temporal and left occipital cortex, while regional atrophy of white matter involved the right temporal lobe and the right cerebellar hemisphere. The ankle-brachial index in patients with type 2 diabetes mellitus strongly correlated with the volume of brain regions in the default mode network. The ankle-brachial index, followed by the level of glycosylated hemoglobin, most strongly correlated with the volume of gray matter in the right temporal lobe. These data suggest that voxel-based morphometry could detect small structural changes in patients with type 2 diabetes mellitus. Early macrovascular atherosclerosis may play a crucial role in subtle brain atrophy in type 2 diabetes mellitus patients, with chronic hyperglycemia playing a lesser role.

Spontaneous brain activity in type 2 diabetics revealed by amplitude of low-frequency fluctuations and its association with diabetic vascular disease: a resting-state FMRI study

Purpose

To investigate correlations between altered spontaneous brain activity, diabetic vascular disease, and cognitive function for patients with type 2 diabetes mellitus (T2DM) using resting-state functional magnetic resonance imaging (rs-fMRI).

Methods

Rs-fMRI was performed for T2DM patients (n = 26) and age-, gender-, and education-matched non-diabetic control subjects (n = 26). Amplitude of low frequency fluctuations (ALFF) were computed from fMRI signals to measure spontaneous neuronal activity. Differences in the ALFF patterns between patients and controls, as well as their correlations with clinical variables, were evaluated.

Results

Compared with healthy controls, T2DM patients exhibited significantly decreased ALFF values mainly in the frontal and parietal lobes, the bilateral thalumi, the posterior lobe of the cerebellum, and increased ALFF values mainly in the visual cortices. Furthermore, lower ALFF values in the left subcallosal gyrus correlated with lower ankle-brachial index values (r = 0.481, p = 0.020), while lower ALFF values in the bilateral medial prefrontal gyri correlated with higher urinary albumin-creatinine ratio (r = −0.418, p = 0.047). In addition, most of the regions with increased ALFF values in the visual cortices were found to negatively correlate with MoCA scores.

Conclusions

These results confirm that ALFF are altered in many brain regions in T2DM patients, and this is associated with the presence of diabetic vascular disease and poor cognitive performance. These findings may provide additional insight into the neurophysiological mechanisms that mediate T2DM-related cognitive dysfunction, and may also serve as a reference for future research.

Genetic, psychosocial and clinical factors associated with hippocampal volume in the general population

The hippocampus--crucial for memory formation, recall and mood regulation--is involved in the pathophysiology of dementia and depressive disorders. Recent genome-wide association studies (GWAS) have identified five genetic loci associated with hippocampal volume (HV). Previous studies have described psychosocial and clinical factors (for example, smoking, type 2 diabetes and hypertension) to have an impact on HV. However, the interplay between genetic, psychosocial and clinical factors on the HV remains unclear. Still, it is likely that genetic variants and clinical or psychosocial factors jointly act in modifying HV; it might be possible they even interact. Knowledge of these factors might help to quantify ones individual risk of or rather resilience against HV loss. We investigated subjects (N=2463; 55.7% women; mean age 53 years) from the Study of Health in Pomerania (SHIP-2; SHIP-TREND-0) who underwent whole-body magnetic resonance imaging (MRI) and genotyping. HVs were estimated with FreeSurfer. For optimal nonlinear model fitting, we used regression analyses with restricted cubic splines. Genetic variants and associated psychosocial or clinical factors were jointly assessed for potential two-way interactions. We observed associations between HV and gender (P<0.0001), age (P<0.0001), body height (P<0.0001), education (P=0.0053), smoking (P=0.0058), diastolic blood pressure (P=0.0211), rs7294919 (P=0.0065), rs17178006 (P=0.0002), rs6581612 (P=0.0036), rs6741949 (P=0.0112) and rs7852872 (P=0.0451). In addition, we found three significant interactions: between rs7294919 and smoking (P=0.0473), rs7294919 and diastolic blood pressure (P=0.0447) and between rs7852872 and rs6581612 (P=0.0114). We suggest that these factors might have a role in the individual susceptibility to hippocampus-associated disorders.

Coupling physical exercise with dietary glucose supplement for treating cognitive impairment in schizophrenia: a theoretical model and future directions

AIMS

Metabolic dysregulation may disrupt the complex neuroprotective mechanisms essential for brain health. Recent studies have pointed out the possible aetiological role of metabolic dysregulation in the onset of schizophrenia and the associated cognitive impairment. In this paper, we aimed to generate a theoretical model of how a combination of physical exercise and dietary glucose supplement may help to alleviate cognitive impairment in schizophrenia.

METHODS

Literature on metabolic dysregulation, especially insulin resistance, in relation to the onset of schizophrenia and the associated cognitive impairment is reviewed. The cognitive enhancement effects of physical exercise and dietary glucose supplement are then summarised. Finally, we propose a theoretical model based on the concerted effects of physical exercise and glucose supplement.

RESULTS

In general, the joint action of physical exercise and dietary glucose supplement could up-regulate glucose and insulin transport into the brain, as well as augmenting the release of insulin growth factor-1 and brain-derived neurotrophic factor. Physical exercise and glucose supplement could enhance energy supply and neuroplasticity in brain, subsequently leading to potential cognitive enhancement in schizophrenia. However, glucose supplement is not suitable for patients with abnormal metabolic profile.

CONCLUSIONS

The combination of physical exercise and glucose supplement has potential therapeutic values in treating cognitive impairment in schizophrenia. Further research is necessary to investigate the optimal patterns of exercise and doses of glucose for treating cognitive impairment in schizophrenia.

A systematic review of type 2 diabetes mellitus and hypertension in imaging studies of cognitive aging: time to establish new norms

The rising prevalence of type 2 diabetes (T2DM) and hypertension in older adults, and the deleterious effect of these conditions on cerebrovascular and brain health, is creating a growing discrepancy between the "typical" cognitive aging trajectory and a "healthy" cognitive aging trajectory. These changing health demographics make T2DM and hypertension important topics of study in their own right, and warrant attention from the perspective of cognitive aging neuroimaging research. Specifically, interpretation of individual or group differences in blood oxygenation level dependent magnetic resonance imaging (BOLD MRI) or positron emission tomography (PET H2O(15)) signals as reflective of differences in neural activation underlying a cognitive operation of interest requires assumptions of intact vascular health amongst the study participants. Without adequate screening, inclusion of individuals with T2DM or hypertension in "healthy" samples may introduce unwanted variability and bias to brain and/or cognitive measures, and increase potential for error. We conducted a systematic review of the cognitive aging neuroimaging literature to document the extent to which researchers account for these conditions. Of the 232 studies selected for review, few explicitly excluded individuals with T2DM (9%) or hypertension (13%). A large portion had exclusion criteria that made it difficult to determine whether T2DM or hypertension were excluded (44 and 37%), and many did not mention any selection criteria related to T2DM or hypertension (34 and 22%). Of all the surveyed studies, only 29% acknowledged or addressed the potential influence of intersubject vascular variability on the measured BOLD or PET signals. To reinforce the notion that individuals with T2DM and hypertension should not be overlooked as a potential source of bias, we also provide an overview of metabolic and vascular changes associated with T2DM and hypertension, as they relate to cerebrovascular and brain health.

Brain changes underlying cognitive dysfunction in diabetes: what can we learn from MRI?

Diabetes is associated with cognitive dysfunction and an increased risk of dementia. This article addresses findings with brain MRI that may underlie cognitive dysfunction in diabetes. Studies in adults with type 1 diabetes show regional reductions in brain volume. In those with a diabetes onset in childhood, these volume reductions are likely to reflect the sum of changes that occur during brain development and changes that occur later in life due to exposure to diabetes-related factors. Type 2 diabetes is associated with global brain atrophy and an increased burden of small-vessel disease. These brain changes occur in the context of aging and often also in relation to an adverse vascular risk factor profile. Advanced imaging techniques detect microstructural lesions in the cerebral gray and white matter of patients with diabetes that affect structural and functional connectivity. Challenges are to further unravel the etiology of these cerebral complications by integrating findings from different imaging modalities and detailed clinical phenotyping and by linking structural MRI abnormalities to histology. A better understanding of the underlying mechanisms is necessary to establish interventions that will improve long-term cognitive outcomes for patients with type 1 and type 2 diabetes.

Diabetes mellitus and disturbances in brain connectivity: a bidirectional relationship?

Diabetes mellitus (DM) is associated with deficits across multiple cognitive domains. The observed impairments in cognitive function are hypothesized to be subserved by alterations in brain structure and function. Several lines of evidence indicate that alterations in glial integrity and function, as well as abnormal synchrony within brain circuits and associated networks, are observed in adults with DM. Microangiopathy and alterations in insulin homeostasis appear to be principal effector systems, although a unitary explanation subsuming the complex etiopathology of white matter in DM is unavailable. A contemporary model of disease pathophysiology for several mental disorders, including but not limited to mood disorders, posits abnormalities in the synchronization of cellular systems in circuits. The observation that similar abnormalities occur in diabetic populations provides the basis for hypothesizing the convergence of pathoetiological factors. Herein, we propose that abnormal structure, function and chemical composition as well as synchrony within and between circuits is an accompaniment of DM and is shared in common with several mental disorders.

Type 2 diabetes as a risk factor for cognitive impairment: current insights

Type 2 diabetes mellitus (T2DM) is a risk factor for cognitive dysfunction and dementia in the elderly. T2DM has been thought to be associated with vascular diseases, eventually leading to vascular dementia, but recent studies have established that T2DM is also associated with Alzheimer's disease (AD). With the increase in the number of elderly individuals with T2DM, the number of diabetic patients with cognitive dysfunction has been increasing. T2DM may accelerate AD-associated pathologies through insulin resistance. Vascular pathologies may also be associated with cognitive dysfunction and dementia in T2DM subjects. Several other mechanisms also seem to be involved in T2DM-related cognitive dysfunction. More investigations to clarify the association of T2DM with cognitive impairment are warranted. These investigations may help to increase our understanding of AD and open a new door to the development of therapeutics. Recent pharmaceutical advancement in T2DM treatment has resulted in the availability of a wide range of antidiabetics. Some evidence has suggested that antidiabetic therapies help to prevent cognitive dysfunction. At present, however, the optimal level of blood glucose control and the best combination of medications to achieve it in terms of cognitive preservation have not been established. More investigation is warranted. Cognitive dysfunction is an emerging new complication of T2DM that requires further study.

Duration of type 2 diabetes and very low density lipoprotein levels are associated with cognitive dysfunction in metabolic syndrome

Type 2 diabetes (T2D) is now recognized as an independent risk factor for accelerated cognitive decline and neurological conditions like Alzheimer's disease. Less is known about the neurocognitive function of T2D patients with comorbid metabolic syndrome, despite their elevated risk for impairment. Computerized testing in 47 adults with T2D that met criteria for NCEP metabolic syndrome revealed that cognitive impairment was prevalent, including 13% in tests of memory, 50% in attention, and 35% in executive function. Partial correlations showed that longer duration of diabetes was associated with poorer performance on tests of basic attention (r = -0.43), working memory (r = 0.43), and executive function (r = 0.42). Strong associations between very low density lipoprotein and poor cognitive function also emerged, including tests of set shifting (r = 0.47) and cognitive inhibition (r = -0.51). Findings suggest that patients with T2D that meet criteria for metabolic syndrome are at high risk for cognitive impairment. Prospective studies should look to replicate these findings and examine the possible neuroprotective effects of lipid-lowering medication in this population.

Global brain atrophy but not hippocampal atrophy is related to type 2 diabetes

AIMS

It has been suggested that in patients with type 2 diabetes mellitus (T2DM), brain atrophy is most pronounced in the hippocampus, but this has not been investigated systematically. The present pooled analysis of three studies examined if hippocampal atrophy is more prominent than global brain atrophy in patients with T2DM relative to controls.

METHODS

Data were derived from a cohort study of patients with vascular disease (SMART-Medea (T2DM=120; no T2DM=502)), and from two case-control studies (UDES1 (T2DM=61; controls=30) and UDES2 (T2DM=54; controls=53)). In SMART-Medea and UDES1, hippocampal volume was obtained by manual tracing on 1.5 Tesla (T) MRI scans. Total brain and intracranial volume (ICV) were determined by an automated segmentation method. In UDES2, hippocampal and total brain volume were determined by FreeSurfer and ICV by manual segmentation on 3 T MRI scans.

RESULTS

The pooled analyses, adjusted for age and sex, showed a significant negative relation between T2DM and total brain-to-ICV ratio (standardized mean difference=-1.24%, 95% CI: -1.63; -0.86), but not between T2DM and hippocampal-to-ICV ratio (0.00%, 95% CI: -0.01; 0.00) or between T2DM and hippocampal-to-total brain volume ratio (0.01%, 95% CI: -0.01; 0.02). In patients with T2DM no associations were found between brain volume measures and HbA1c or memory.

CONCLUSION

Patients with T2DM had greater brain atrophy but not hippocampal atrophy, compared to controls. These findings do not support specific vulnerability of the hippocampus in patients with T2DM.

Short-term high-fat-and-fructose feeding produces insulin signaling alterations accompanied by neurite and synaptic reduction and astroglial activation in the rat hippocampus

Chronic consumption of high-fat-and-fructose diets (HFFD) is associated with the development of insulin resistance (InsRes) and obesity. Systemic insulin resistance resulting from long-term HFFD feeding has detrimental consequences on cognitive performance, neurogenesis, and long-term potentiation establishment, accompanied by neuronal alterations in the hippocampus. However, diet-induced hippocampal InsRes has not been reported. Therefore, we investigated whether short-term HFFD feeding produced hippocampal insulin signaling alterations associated with neuronal changes in the hippocampus. Rats were fed with a control diet or an HFFD consisting of 10% lard supplemented chow and 20% high-fructose syrup in the drinking water. Our results show that 7 days of HFFD feeding induce obesity and InsRes, associated with the following alterations in the hippocampus: (1) a decreased insulin signaling; (2) a decreased hippocampal weight; (3) a reduction in dendritic arborization in CA1 and microtubule-associated protein 2 (MAP-2) levels; (4) a decreased dendritic spine number in CA1 and synaptophysin content, along with an increase in tau phosphorylation; and finally, (5) an increase in reactive astrocyte associated with microglial changes. To our knowledge, this is the first report addressing hippocampal insulin signaling, as well as morphologic, structural, and functional modifications due to short-term HFFD feeding in the rat.

Neurocognitive changes and their neural correlates in patients with type 2 diabetes mellitus

As the prevalence and life expectancy of type 2 diabetes mellitus (T2DM) continue to increase, the importance of effective detection and intervention for the complications of T2DM, especially neurocognitive complications including cognitive dysfunction and dementia, is receiving greater attention. T2DM is thought to influence cognitive function through an as yet unclear mechanism that involves multiple factors such as hyperglycemia, hypoglycemia, and vascular disease. Recent developments in neuroimaging methods have led to the identification of potential neural correlates of T2DM-related neurocognitive changes, which extend from structural to functional and metabolite alterations in the brain. The evidence indicates various changes in the T2DM brain, including global and regional atrophy, white matter hyperintensity, altered functional connectivity, and changes in neurometabolite levels. Continued neuroimaging research is expected to further elucidate the underpinnings of cognitive decline in T2DM and allow better diagnosis and treatment of the condition.

Adherence and weight loss outcomes in bariatric surgery: does cognitive function play a role?

Although bariatric surgery is the most effective intervention for severe obesity, a significant minority of participants fail to achieve or maintain optimal weight loss at extended follow-up. Accumulating evidence suggests that adherence to prescribed postoperative recommendations, including attendance at follow-up appointments and dietary and physical activity, is related to improved weight loss outcomes. However, adherence to these guidelines presents a significant challenge for many patients, potentially due in part to deficits in cognitive function. In this paper, we briefly examine current literature of adherence on postoperative weight loss outcomes, and review emerging evidence that the cognitive dysfunction present in a subset of obese individuals is related to weight loss outcomes following bariatric procedures. We then extend these findings, positing a role for cognitive function in moderating the relationship between adherence and postoperative outcomes.

Depression, deficits in functional capacity, and impaired glycemic control in urban African Americans with type 2 diabetes

BACKGROUND

Effective depression treatment does not reliably reduce glycosylated hemoglobin (HbA1c) in depressed patients with type 2 diabetes, possibly in part due to deficits in functional capacity, i.e. performance of certain everyday living skills, essential for effective diabetes self-management. We sought to determine: a) the magnitude of deficits in functional capacity among urban, African American (AA) patients with type 2 diabetes, and b) whether these deficits were associated with poorer glycemic control.

METHODS

At their initial visit to an inner-city diabetes clinic, 172 AA patients with type 2 diabetes were assessed with a variety of instruments, including the Mini International Neuropsychiatric Interview (MINI) and the UCSD Performance Skills Assessment-Brief (UPSA-B). They then entered a comprehensive diabetes management intervention, whose success was indexed by HbA1c levels at up to four reassessments over a one-year period. A mixed-effects model repeated-measures method was used to predict HbA1c.

RESULTS

The prevalence of depression was 19%; the mean UPSA-B score was 81 ± 17. After multivariate adjustment, increased HbA1c levels over time were predicted by the presence of major depression (B = .911, p = .002) and decreasing (worse) scores on the UPSA-B (B = -.016, p = .027), respectively. Further adjustment for increasing the dosage of oral or insulin during the treatment eliminated the association between the UPSA score and HbA1c level (B = -.010, p = .115).

CONCLUSIONS

Depression, as well as deficits in functional capacity, predicted reduced effectiveness of a diabetes self-management intervention. Future studies will determine whether interventions targeted at both improve glycemic control.

Association of type 2 diabetes with brain atrophy and cognitive impairment

OBJECTIVE

We investigated the associations of diabetes and hypertension with imaging biomarkers (markers of neuronal injury and ischemic damage) and with cognition in a population-based cohort without dementia.

METHODS

Participants (n = 1,437, median age 80 years) were evaluated by a nurse and physician and underwent neuropsychological testing. A diagnosis of cognitively normal, mild cognitive impairment (MCI), or dementia was made by an expert panel. Participants underwent MRI to determine cortical and subcortical infarctions, white matter hyperintensity (WMH) volume, hippocampal volume (HV), and whole brain volume (WBV). The medical records were reviewed for diabetes and hypertension in midlife or later.

RESULTS

Midlife diabetes was associated with subcortical infarctions (odds ratio, 1.85 [95% confidence interval, 1.09-3.15]; p = 0.02), reduced HV (-4% [-7 to -1.0]; p = 0.01), reduced WBV (-2.9% [-4.1 to -1.6]), and prevalent MCI (odds ratio, 2.08; p = 0.01). The association between diabetes and MCI persisted with adjustment for infarctions and WMH volume but was attenuated after adjustment for WBV (1.60 [0.87-2.95]; p = 0.13) and HV (1.82 [1.00-3.32]; p = 0.05). Midlife hypertension was associated with infarctions and WMH volume and was marginally associated with reduced performance in executive function. Effects of late-life onset of diabetes and hypertension were few.

CONCLUSIONS

Midlife onset of diabetes may affect late-life cognition through loss of brain volume. Midlife hypertension may affect executive function through ischemic pathology. Late-life onset of these conditions had fewer effects on brain pathology and cognition.

Gray matter volume abnormalities in type 2 diabetes mellitus with and without mild cognitive impairment

This study sought to evaluate the potential brain gray matter (GM) volume changes that occur with the transition from normal cognition to mild cognitive impairment (MCI) in patients with type 2 diabetes mellitus (T2DM) using voxel-based morphometry (VBM). VBM analyses of brain GM based on magnetic resonance imaging (MRI) data were performed on 28 T2DM patients with MCI, 25 T2DM patients without MCI, 28 MCI patients and 29 healthy controls (HC). Compared with the HC, the T2DM patients both with and without MCI showed significantly decreased total GM volume. Furthermore, the VBM results indicated that the T2DM patients without MCI exhibited extensively decreased GM volume compared with the HC in certain brain regions, including the superior and middle temporal gyrus (MTG), the superior and medial frontal gyrus and the middle occipital gyrus. In addition to more extensive GM atrophy in the aforementioned brain regions, the medial temporal lobe also exhibited GM loss in the T2DM patients with MCI. Furthermore, relative to the patients without MCI, only the left MTG exhibited a lower GM volume in the T2DM patients with MCI, which was positively correlated with the total MoCA score (r=0.699, P<0.01). Finally, relative to MCI, the left MTG atrophy was also found in the T2DM patients with MCI. Our findings suggest that MTG atrophy was associated with an increased risk for MCI in T2DM patients. The brain structural changes in many brain regions may underlie the transition from normal cognition to MCI in T2DM patients.

Type 2 diabetes and cognitive impairment: contributions from neuroimaging

Type 2 diabetes mellitus (T2D) and Alzheimer disease (AD) are major public health burdens associated with aging. As the age of the population rapidly increases, a sheer increase in the incidence of these diseases is expected. Research has identified T2D as a risk factor for cognitive impairment and potentially AD, but the neurobiological pathways that are affected are only beginning to be understood. The rapid advances in neuroimaging in the past decade have added significant understanding to how T2D affects brain structure and function and possibly lead to AD. This article provides a review of studies that have utilized structural and functional neuroimaging to identify neural pathways that link T2D to impaired cognitive performance and potentially AD. A primary focus of this article is the potential for neuroimaging to assist in understanding the mechanistic pathways that may provide translational opportunities for clinical intervention.

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.

Ginsenoside Rb1 protects hippocampal neurons from high glucose-induced neurotoxicity by inhibiting GSK3β-mediated CHOP induction

Ginsenoside Rb1 is generally recognized as one of the principal bioactive ingredients in ginseng and shows neuroprotective effects in various neurons. Endoplasmic reticulum (ER) stress is considered to play an important role in numerous neurodegenerative disorders. Recently, glucogen synthase kinase 3β (GSK3β) was reported to regulate ER stress-induced C/EBP homologous protein (CHOP) in neuronal cells. Therefore, in this study, we investigated the effects of ginsenoside Rb1 on GSK3β-mediated ER stress in high glucose-treated hippocampal neurons. Results from the MTT assay showed that treatment with 1 µM Rb1 for 72 h protected neurons from high glucose-induced cell injury. Using western blot analysis, we found that treatment with Rb1 effectively inhibited the phosphorylation of the high glucose-induced protein kinase RNA-like ER kinase (PERK) and of GSK3β, and reduced the level of the CHOP protein. The levels of these proteins were also decreased by treatment with the GSK3β inhibitor Licl. Rb1 also significantly decreased the mRNA expression of the gene CHOP, as shown by quantitative RT-PCR analysis. Taken together, the present results suggested that Rb1 may protect neurons from high glucose-induced cell damage by inhibiting GSK3β‑mediated CHOP induction, providing a potentially new strategy for preventing and treating cognitive impairment caused by diabetes.

Landmarking the brain for geometric morphometric analysis: an error study

Neuroanatomic phenotypes are often assessed using volumetric analysis. Although powerful and versatile, this approach is limited in that it is unable to quantify changes in shape, to describe how regions are interrelated, or to determine whether changes in size are global or local. Statistical shape analysis using coordinate data from biologically relevant landmarks is the preferred method for testing these aspects of phenotype. To date, approximately fifty landmarks have been used to study brain shape. Of the studies that have used landmark-based statistical shape analysis of the brain, most have not published protocols for landmark identification or the results of reliability studies on these landmarks. The primary aims of this study were two-fold: (1) to collaboratively develop detailed data collection protocols for a set of brain landmarks, and (2) to complete an intra- and inter-observer validation study of the set of landmarks. Detailed protocols were developed for 29 cortical and subcortical landmarks using a sample of 10 boys aged 12 years old. Average intra-observer error for the final set of landmarks was 1.9 mm with a range of 0.72 mm-5.6 mm. Average inter-observer error was 1.1 mm with a range of 0.40 mm-3.4 mm. This study successfully establishes landmark protocols with a minimal level of error that can be used by other researchers in the assessment of neuroanatomic phenotypes.

Neural substrates of verbal memory impairments in adults with type 2 diabetes mellitus

BACKGROUND

Verbal memory impairment is well documented in type 2 diabetes mellitus (T2DM) but, to date, the neural substrates remain unclear. The present study evaluated verbal memory and ascertained the degree of frontal and temporal lobe involvement in the anticipated verbal memory impairment among adults with T2DM.

METHOD

Forty-six late-middle-aged and elderly adults with T2DM and 50 age-, sex-, and education-matched adults without T2DM underwent medical evaluation, verbal memory assessment, and brain magnetic resonance imaging (MRI) evaluations.

RESULTS

As anticipated, participants with T2DM had clear verbal memory impairments. Consistent with prior reports, we found volume reductions restricted to the hippocampus. Our diffusion tensor imaging analysis revealed that participants with T2DM had extensive cerebral gray and white matter microstructural abnormalities predominantly in the left hemisphere, with a larger concentration present in the temporal lobe. In contrast, we uncovered mostly nonspecific microstructural abnormalities in the absence of tissue loss in the frontal lobe. Of great importance, we present the first evidence among participants with T2DM linking verbal memory impairment and compromised microstructural integrity of the left parahippocampal gyrus, a key memory-relevant structure.

CONCLUSIONS

Our results suggest that the hippocampus and parahippocampal gyrus may be particularly vulnerable to the deleterious effects of T2DM. The parahippocampal gyrus in particular may play a crucial role in the verbal memory impairments frequently reported in T2DM. Future studies should employ methods such as resting state functional magnetic resonance imaging and diffusion tensor imaging tractography to better characterize network connectivity, which may help further characterize the verbal memory impairment frequently reported in T2DM.

Issues in the timing of integrated early interventions: contributions from nutrition, neuroscience, and psychological research

A central issue when designing multidimensional biological and psychosocial interventions for children who are exposed to multiple developmental risks is identification of the age period(s) in which such interventions will have the strongest and longest lasting effects (sensitive periods). In this paper, we review nutritional, neuroscientific, and psychological evidence on this issue. Nutritional evidence is used to identify nutrient-sensitive periods of age-linked dimensions of brain development, with specific reference to iron deficiency. Neuroscience evidence is used to assess the importance of timing of exposures to environmental stressors for maintaining neural, neuroendocrine, and immune systems integrity. Psychological evidence illustrates the sensitivity of cognitive and social-emotional development to contextual risk and protective influences encountered at different ages. Evidence reviewed documents that the early years of life are a sensitive period when biological or psychosocial interventions or exposure to risk or protective contextual influences can produce unique long-term influences upon human brain, neuroendocrine, and cognitive or psychosocial development. However, the evidence does not identify the early years as the sole sensitive time period within which to have a significant influence upon development. Choice of age(s) to initiate interventions should be based on what outcomes are targeted and what interventions are used.

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.

Retinal vessel abnormalities as a possible biomarker of brain volume loss in obese adolescents

OBJECTIVE

Endothelial dysfunction in childhood obesity may precede cerebrovascular damage and cognitive impairment in adulthood. A noninvasive proxy of microvascular health is required to identify the risk for microvascular damage in obese children.

DESIGN AND METHODS

The associations of hippocampal volumes and global cerebral atrophy were assessed with retinal vessel caliber in 40 normal BMI controls and 62 obese age-matched nondiabetic adolescents and the contribution of inflammation, obesity, and insulin resistance to retinal vessel caliber was evaluated.

RESULTS

Compared to controls, obese adolescents had smaller retinal arterioles (8.3% decrease, P < 0.05) and wider venules (5.4% increase, P < 0.01). Larger retinal arteriole diameters were associated with less global cerebral atrophy (B = -0.24 [95% confidence interval, CI: -0.48, -0.002]) and larger hippocampal volumes (B = 0.01 [95% CI: 0, 0.02]). Venule diameters (B = 84.2 [95% CI: 30.3, 138.1]) were predicted by inflammation (fibrinogen). Arteriolar diameters were predicted by insulin resistance, indicated by logHOMA (homeostatic model assessment, HOMA) values (B = -17.03 [95% CI: -28.25, -5.81)] and body mass index (BMI) (B = -.67 [95% CI: -1.09, -0.24)]. All analyses were adjusted for mean arterial pressure, sleep apnea, and vessel diameter.

CONCLUSIONS

Measures of brain health, BMI, and insulin resistance are associated with retinal vessel caliber. If confirmed in larger studies, retinal arteriolar caliber may serve as a possible noninvasive proxy for brain atrophy in obese adolescents, and the identification of elevated risk for cerebral microvascular disease in adulthood.

Brain expansion in patients with type II diabetes following insulin therapy: a preliminary study with longitudinal voxel-based morphometry

OBJECTIVE

We performed a longitudinal analysis based on magnetic resonance (MR) imaging to investigate the brain structural and perfusion changes caused by insulin therapy in patients with type II diabetes.

METHODS

High resolution three-dimensional T1-weighted fast spoiled gradient recalled echo images and flow-sensitive alternating inversion recovery (FAIR) images were obtained from 11 patients with type II diabetes before and 1 year after initiation of insulin therapy and 11 normal controls. Brain volume changes were investigated by a longitudinal voxel-based morphometry (VBM), and perfusion changes were evaluated by FAIR imaging between baseline and follow-up data.

RESULTS

Significant regional gray matter (GM) expansion located in bilateral frontal, parietal, and left occipital lobes, and regional white matter (WM) expansion was shown in left precentral subcortical WM and right angular subcortical WM after insulin therapy (P < .05 with FDR correction). Brain hyperperfusion was detected in bilateral frontal cortex, left occipital cortex, and right temporal cortex after insulin therapy (P < .05).

CONCLUSIONS

In patients with type II diabetes, brain expansion and hyperperfusion were demonstrated 1 year after initiation of insulin therapy, and insulin therapy could contribute to the brain volume gainment in the patients with type II diabetes.

Neuroprotective effects of ginsenoside Rb1 on high glucose-induced neurotoxicity in primary cultured rat hippocampal neurons

Ginsenoside Rb1 is one of the main active principles in traditional herb ginseng and has been reported to have a wide variety of neuroprotective effects. Endoplasmic reticulum (ER) stress has been implicated in neurodegenerative diseases, so the present study aimed to observe the effects of ginsenoside Rb1 on ER stress signaling pathways in high glucose-treated hippocampal neurons. The results from MTT, TUNEL labeling and Annexin V-FITC/PI/Hoechst assays showed that incubating neurons with 50 mM high glucose for 72h decreased cell viability and increased the number of apoptotic cells whereas treating neurons with 1 μM Rb1 for 72h protected the neurons against high glucose-induced cell damage. Further molecular mechanism study demonstrated that Rb1 suppressed the activation of ER stress-associated proteins including protein kinase RNA (PKR)-like ER kinase (PERK) and C/EBP homology protein (CHOP) and downregulation of Bcl-2 induced by high glucose. Moreover, Rb1 inhibited both the elevation of intracellular reactive oxygen species (ROS) and the disruption of mitochondrial membrane potential induced by high glucose. In addition, the high glucose-induced cell apoptosis, activation of ER stress, ROS accumulation and mitochondrial dysfunction can also be attenuated by the inhibitor of ER stress 4-phenylbutyric acid (4-PBA) and anti-oxidant N-acetylcysteine(NAC). In conclusion, these results suggest that Rb1 may protect neurons against high glucose-induced cell injury through inhibiting CHOP signaling pathway as well as oxidative stress and mitochondrial dysfunction.

Altered baseline brain activity in type 2 diabetes: a resting-state fMRI study

PURPOSE

This study aims to investigate whether altered baseline brain activity exists in type 2 diabetes mellitus (T2DM) patients using resting-state functional magnetic resonance imaging (rs-fMRI) and whether abnormal neural activity in the middle temporal gyrus (MTG) is correlated with cognitive function.

METHODS

T2DM patients (n=28) were compared with nondiabetic age-, sex-, and education-matched control subjects (n=29) using rs-fMRI. We computed the amplitude of low-frequency fluctuations (ALFF) of fMRI signals to measure spontaneous neuronal activity and detect the relationship between rs-fMRI information and clinical data.

RESULTS

Compared with healthy controls, T2DM patients had significantly decreased ALFF values in the bilateral middle temporal gyrus, left fusiform gyrus, left middle occipital gyrus, right inferior occipital gyrus; and increased ALFF values in both the bilateral cerebellum posterior lobe and right cerebellum culmen. Moreover, we found an inverse correlation between the ALFF values in the MTG and both the HbA1c (r=-0.451, p=0.016) and the score of Trail Making Test-B (r=-0.420, p=0.026) in the patient group. On the other hand, C-peptide level and pancreatic β-cell function had a positive correlation (r=0.429, p=0.023; r=0.453, p=0.016, respectively) with the ALFF value in the middle temporal gyrus.

CONCLUSION

The present study confirms that T2DM patients have altered ALFF in many brain regions, which is associated with poor neurocognitive performances, severity of consistent hyperglycemic state and impaired β-cell function. ALFF disturbance in MTG may play a central role in cognitive decline associated with T2DM and serve as reference for future clinical diagnosis.

Hippocampal dysfunction in cured Cushing's syndrome patients, detected by (1) H-MR-spectroscopy

BACKGROUND

Proton magnetic resonance spectroscopy ((1) H-MRS) is a sensitive, noninvasive imaging technique capable of measuring brain metabolites in vivo. Chronic exposure to endogenous hypercortisolism in Cushing's syndrome (CS) is associated with negative effects on memory and hippocampal volumes, even after biochemical cure.

OBJECTIVE

To investigate metabolites in the hippocampi of CS patients and controls, using (1) H-MRS.

PATIENTS AND METHODS

Eighteen right-handed cured CS patients (age 44·8 ± 12·5 years, 12·6 ± 3·8 years of education) and 18 right-handed healthy controls, matched for age (40·0 ± 11·9) and years of education (14·4 ± 3·8), underwent 3-Tesla magnetic resonance imaging (3T MRI) and (1) H-MRS including the head of each hippocampus. Concentrations of Glu (Glutamate), Glx (Glutamate + Glutamine), NAA (N-Acetyl-aspartate), total NAA (N-Acetyl-aspartate + N-Acetyl-aspartyl-Glutamate), Cho (Glycerophosphocholine and Phosphocholine compounds), Cr (Creatine) and MI (mionositol) were measured (mmol/l). Hippocampal volumes (mm(3) ) were additionally calculated using an automated procedure (FreeSurfer).

RESULTS

CS patients had lower NAA than controls in the left and right hippocampus (5·2 ± 1·0 vs 6·1 ± 0·7, P < 0·05; 4·9 ± 0·8 vs 6·1 ± 0·6, P < 0·001, respectively), and lower total NAA on the right side (5·7 ± 0·9 vs 6·3 ± 0·9, P < 0·05), suggesting neuronal dysfunction/loss. CS patients had higher Glx than controls in both hippocampi (10·4 ± 1·9 vs 8·6 ± 1·4, P < 0·01; 9·9 ± 1·6 vs 8·9 ± 1·3, P < 0·05, respectively), suggesting glial proliferation, as a repair mechanism after neuronal dysfunction. No differences were found in the other brain metabolites, and there were no differences in left (3815·78 ± 502·96) and right (3980·75 ± 369·44) total hippocampal volumes between CS patients and controls (3945·08 ± 408·90 and 4108·39 ± 365·11, respectively).

CONCLUSION

Persistently abnormal metabolites are evidenced in the hippocampi of CS patients despite endocrine cure. These functional alterations could be early markers of glucocorticoid neurotoxicity, preceding hippocampal volume reduction.

The influence of subclinical cardiovascular disease and related risk factors on cognition in type 2 diabetes mellitus: The DHS-Mind study

We hypothesized that measures of coronary artery calcified plaque (CAC) collected at baseline from the Diabetes Heart Study (DHS) would explain associations between cognition and diabetes collected at follow-up approximately 7 years later. The DHS is a sibling study of cardiovascular disease (CVD) in a cohort with a high prevalence of type 2 diabetes (~80%). Associations between baseline CAC and cognitive performance were tested using generalized estimating equations and mixed effects models to adjust for familial relationships. Diabetes status was associated (p<0.05) with poorer performance on tests of verbal memory, processing speed, and semantic fluency adjusting for age, sex, education, and hypertension status. As hypothesized, including CAC in the statistical model attenuated this association. Additionally, CAC and fasting glucose predicted performance in tasks not associated with diabetes status in this study (Stroop Task, Phonemic Fluency). These results confirm work attributing the heterogeneity of cognitive outcomes in type 2 diabetes to subclinical risk factors that combine to affect different aspects of brain function. Importantly, these results imply that risk factor intervention should begin before comorbidities, particularly CVD, become clinically apparent.

The emerging role of dietary fructose in obesity and cognitive decline

The incidence of obesity has increased dramatically over the past several years, and in parallel, so has the prevalence of type 2 diabetes (T2D). Numerous studies have demonstrated that both obesity and T2D are associated with lower cognitive performance, cognitive decline, and dementia. Intake of dietary fructose has also increased. In fact, high-fructose corn syrup (HFCS) accounts for as much as 40% of caloric sweeteners used in the United States. Given the increase in the incidence of Alzheimer’s disease (AD), characterized by an age-related decline in memory and cognitive functioning, in this report we review the effects of obesity on cognitive performance and the impact of high fructose intake in promoting cognitive decline. The paper then considers the effects of omega-3 fatty acids (FAs), which have been linked to promising results in cognitive function including ameliorating the impact of a high-fructose diet.

Spatial memory impairments in a prediabetic rat model

Diabetes is associated with an increased risk for brain disorders, namely cognitive impairments associated with hippocampal dysfunction underlying diabetic encephalopathy. However, the impact of a prediabetic state on cognitive function is unknown. Therefore, we now investigated whether spatial learning and memory deficits and the underlying hippocampal dysfunction were already present in a prediabetic animal model. Adult Wistar rats drinking high-sucrose (HSu) diet (35% sucrose solution during 9 weeks) were compared to controls' drinking water. HSu rats exhibited fasting normoglycemia accompanied by hyperinsulinemia and hypertriglyceridemia in the fed state, and insulin resistance with impaired glucose tolerance confirming them as a prediabetic rodent model. HSu rats displayed a poorer performance in hippocampal-dependent short- and long-term spatial memory performance, assessed with the modified Y-maze and Morris water maze tasks, respectively; this was accompanied by a reduction of insulin receptor-β density with normal levels of insulin receptor substrate-1 pSer636/639, and decreased hippocampal glucocorticoid receptor levels without changes of the plasma corticosterone levels. Importantly, HSu animals exhibited increased hippocampal levels of AMPA and NMDA receptor subunits GluA1 and GLUN1, respectively, whereas the levels of protein markers related to nerve terminals (synaptophysin) and oxidative stress/inflammation (HNE, RAGE, TNF-α) remained unaltered. These findings indicate that 9 weeks of sucrose consumption resulted in a metabolic condition suggestive of a prediabetic state, which translated into short- and long-term spatial memory deficits accompanied by alterations in hippocampal glutamatergic neurotransmission and abnormal glucocorticoid signaling.

Cerebral white matter and retinal arterial health in hypertension and type 2 diabetes mellitus

We examined 33 hypertensive (22 with comorbid type 2 diabetes mellitus (T2DM)) and 29 normotensive (8 with T2DM) middle-aged and elderly adults, comparable in age and education. Relative to normotensive participants, those with hypertension, in addition to a higher prevalence of periventricular white matter (WM) lesions, had significantly lower WM microstructural integrity of major fiber tracts as seen with MRI-based diffusion tensor imaging. Among participants with hypertension, those with co-morbid T2DM (n = 22) had more widespread WM pathology than those without T2DM (n = 11). Furthermore and consistent with previous research, both hypertension and T2DM were related to decreased retinal arterial diameter. Further exploratory analysis demonstrated that the observed retinal arteriolar narrowing among individual with hypertension was associated with widespread subclinical losses in WM microstructural integrity and these associations were present predominantly in the frontal lobe. We found that T2DM adds to the damaging effects of hypertension on cerebral WM, and notably these effects were independent of age and body mass index. Given that the decrease in retinal arteriolar diameter may be a biomarker for parallel pathology in cerebral arterioles, our data suggest that the frontal lobe may be particularly vulnerable to microvascular damage in the presence of hypertension and T2DM.

Views and opinion on BDNF as a target for diabetic cognitive dysfunction

Type 2 diabetes mellitus (T2DM) is a known cause of cognitive dysfunction and involves increased risk of dementia. Brain-derived neurotrophic factor (BDNF) is a member of neurotrophic family of nerve growth factors, a key protein in promoting memory, growth and survival of neurons. BDNF is recognized as a metabotrophic factor, a molecule that is involved in Alzheimer's disease (AD) as well as in other neurological disorders. It provides cellular and local regulatory mechanisms for mediating synaptic plasticity. Impaired BDNF signaling can compromise many aspects of brain functions. Studies investigating the relationship between diabetes and BDNF in adults demonstrate that BDNF levels are decreased in T2DM and are regulated in response to plasma levels of glucose. BDNF could serve as biomarker in predicting the development of obesity and T2DM. Thirty-two cavities were predicted to locate the active sites of BDNF for the ligands to bind. The shape of the site was identified by extracting the cavity volume surfaces enclosing regions with highest probability. Different ligands can be chosen for interaction of active sites of BDNF and can be targeted for drug discovery. This review focuses on computational exploitation selectively to deliver BDNF as a drug to appropriate hypothalamic neurons, which can serve as a novel approach in diabetic encephalopathy treatment.

Effects of diabetes on hippocampal neurogenesis: links to cognition and depression

Diabetes often leads to a number of complications involving brain function, including cognitive decline and depression. In addition, depression is a risk factor for developing diabetes. A loss of hippocampal neuroplasticity, which impairs the ability of the brain to adapt and reorganize key behavioral and emotional functions, provides a framework for understanding this reciprocal relationship. The effects of diabetes on brain and behavioral functions in experimental models of type 1 and type 2 diabetes are reviewed, with a focus on the negative impact of impaired hippocampal neurogenesis, dendritic remodeling and increased apoptosis. Mechanisms shown to regulate neuroplasticity and behavior in diabetes models, including stress hormones, neurotransmitters, neurotrophins, inflammation and aging, are integrated within this framework. Pathological changes in hippocampal function can contribute to the brain symptoms of diabetes-associated complications by failing to regulate the hypothalamic-pituitary-axis, maintain learning and memory and govern emotional expression. Further characterization of alterations in neuroplasticity along with glycemic control will facilitate the development and evaluation of pharmacological interventions that could successfully prevent and/or reverse the detrimental effects of diabetes on brain and behavior.

Low BDNF is associated with cognitive deficits in patients with type 2 diabetes

OBJECTIVE

Studies suggest that brain-derived neurotrophic factor (BDNF) plays an essential role in regulating memory-related neuroplasticity in the hippocampus. Type 2 diabetes (T2DM) is associated with impairment in many domains of cognitive function which may result from reduced BDNF; however, the correlation of BDNF with cognitive impairment in T2DM has not been investigated.

MATERIALS AND METHODS

We compared 208 patients with T2DM to 212 normal controls on serum BDNF and the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS).

RESULTS

Serum BDNF levels were significantly decreased in T2DM patients compared to normal controls (p < 0.001). The total score and nearly all indexes (all p < 0.01) except for attention and visuospatial/constructional indexes (all p > 0.05) of RBANS were markedly lower in T2DM than controls. There was a positive relationship between serum BDNF and delayed memory in patients with T2DM.

CONCLUSION

Our results suggest that BDNF may play a role in the pathophysiology of cognitive deficits, especially delayed memory in T2DM.

Cognitive functions in type 1 and type 2 diabetes. Metaanalysis

Introduction: Diabetes has been repeatedly associated with a wide variety of cognitive impairments. Aim: To clarify the differences in cognitive dysfunctions between the two types of diabetes. Method: Metaanalysis was performed using databases of Medline, PubMed and ScienceDirect (3 studies with type 1 and 6 with type 2 diabetes). Results: Adults with type 1 diabetes showed lower performance than control subjects in all fields. The effect size had the highest value in psychomotor activity (D = –0.69). The effect size was small for delayed verbal memory (D = –0.48), attention (D = –0.47), language (D = –0.44), visual processing (D = –0.35), immediate verbal memory (D = –0.30), working memory (D = –0.27) and executive functions (D = –0.26). Adults with type 2 diabetes showed lower performance than control subjects in all cognitive domains, except for working memory (D = +0.03). The effect size had the highest value in immediate verbal memory (D = –1.12), psychomotor activity (D = –0.82) and delayed verbal memory (D = –0.81). The effect size was moderate for general intellectual abilities (D = –0.68) and small for general memory (D = –0.37), attention (D = –0.35), language (D = –0.35), visual processing (D = –0.33) and executive functions (D = –0.33). Conclusion: Both types of diabetes are associated with reduced performance in numerous cognitive domains. Orv. Hetil., 2013, 154, 694–699.

Morphometric changes in lateral ventricles of patients with recent-onset type 2 diabetes mellitus

It is becoming increasingly evident that type 2 diabetes mellitus can have effects on global and regional brain morphology. Ventricular enlargement reflecting cerebral atrophy has been reported particularly in elderly type 2 diabetes patients. However, little is known about its timing through the disease course and morphological variability. Using the combined volumetric and advanced three-dimensional morphological approach, we identified differences in size and shape of the lateral ventricles between recent-onset type 2 diabetes patients and healthy individuals. High-resolution T1-weighted images were obtained from 23 type 2 diabetes patients whose illness duration was less than 1 year and 23 carefully matched healthy individuals. By volume measurement, we found enlarged lateral and third ventricles in type 2 diabetes patients, relative to healthy individuals (F_1,41 = 7.96, P = 0.007; F_1,41 = 11.16, P = 0.002, respectively). Morphological analysis revealed that the expansion of lateral ventricles in the diabetic brain was prominent in the bilateral frontal horns. The current findings suggest that atrophic changes particularly of the anterior frontal lobe can occur as early as the first year after the clinical diagnosis of type 2 diabetes mellitus.

Brain insulin and leptin signaling in metabolic control: from animal research to clinical application

Besides the well-characterized effects of brain insulin and leptin in regulating food intake, insulin and leptin signaling to the central nervous system modulates a variety of metabolic processes, such as glucose and lipid homeostasis, as well as energy expenditure. This review summarizes the current literature on the contribution of central nervous insulin and leptin action to metabolic control in animals and humans. Potential therapeutic options based on the direct delivery of these peptides to the brain by, for example, intranasal administration, are discussed.

White matter microstructural integrity in youth with type 1 diabetes

Decreased white and gray matter volumes have been reported in youth with type 1 diabetes mellitus (T1DM), but the effects of hyperglycemia on white matter integrity have not been quantitatively assessed during brain development. We performed diffusion tensor imaging, using two complimentary approaches--region-of-interest and voxelwise tract-based spatial statistics--to quantify white matter integrity in a large retrospective study of T1DM youth and control participants. Exposure to chronic hyperglycemia, severe hyperglycemic episodes, and severe hypoglycemia, as defined in the Diabetes Control and Complications Trial (DCCT), were estimated through medical records review, HbA(1c) levels, and interview of parents and youth. We found lower fractional anisotropy in the superior parietal lobule and reduced mean diffusivity in the thalamus in the T1DM group. A history of three or more severe hyperglycemic episodes was associated with reduced anisotropy and increased diffusivity in the superior parietal lobule and increased diffusivity in the hippocampus. These results add microstructural integrity of white matter to the range of structural brain alterations seen in T1DM youth and suggest vulnerability of the superior parietal lobule, hippocampus, and thalamus to glycemic extremes during brain development. Longitudinal analyses will be necessary to determine how these alterations change with age or additional glycemic exposure.

Association of obesity-mediated insulin resistance and hypothalamic volumes: possible sex differences

The hypothalamus is important in hunger and metabolism. Although a lot is known about the basic role of the human hypothalamus, less is known about how the in vivo volume is affected in obesity, particularly among adolescents. Based on pediatric body mass index percentiles, 95 participants were assigned to lean or obese groups. All subjects had medical evaluations, including fasting blood tests, to assess insulin sensitivity and circulating CRP and neurotrophins (NGF and BDNF) and an MRI of the brain. Hypothalamic volumes were measured by a segmentation method combining manual and automated steps. Overall, obese participants had descriptively smaller hypothalamic volumes, although this difference did not reach statistical significance; however, among obese participants, females had significantly smaller hypothalamic volumes than their male counterparts. There was a significant interaction between insulin resistance and sex on hypothalamus volume; obese females with significant insulin resistance have smaller hypothalamic volumes than obese males. Obese adolescents had higher circulating CRP and neurotrophin levels. Furthermore, among obese females, BDNF concentrations were inversely associated with hypothalamus volumes (r = −0.48). Given this negative association between BDNF and hypothalamus volumes among obese insulin-resistant females, elevated neurotrophin levels may suggest an attempt at protective compensation.