Structural and Functional Brain Changes in Middle-Aged Type 2 Diabetic Patients: A Cross-Sectional Study

Alterations of spontaneous brain activity in type 2 diabetes mellitus without mild cognitive impairment: a resting-state functional magnetic resonance study

Background

Type 2 diabetes mellitus (T2DM) has been demonstrated an increased risk factor of cognitive impairment or even dementia. Kinds of resting-state functional magnetic resonance imaging indices have been proposed and used to investigate the brain mechanism underlying diabetic cognitive impairment. This study aimed to explore the early changes in spontaneous neural activity among T2DM patients without cognitive impairment by means of multiple rs-fMRI indices.

Methods

T2DM patients without cognitive impairment and age-, sex-, and education matched control subjects were included in this study. Three rs-fMRI indices, namely amplitude of low-frequency fluctuation (ALFF), regional homogeneity (ReHo) and voxel-mirrored homotopic connectivity (VMHC) were computed after image pre-processing. The Montreal Cognitive Assessment (MoCA) was performed to distinguish normal cognition. Brain volume was also evaluated. Correlation analyses were conducted to explore any relationship among rs-fMRI indices and clinical characteristics.

Results

The T2DM patients were detected significantly decreased neural activity in right angular and left prefrontal gyrus including middle and superior frontal gyrus. Increased activities were also observed in left caudate and the supplementary motor area. No correlation between rs-fMRI indices and clinical characteristics was survived after multiple comparison correction. But we observed a significant, but decreased correlation between ALFF and ReHo values in the reported brain areas.

Conclusion

The combination of ALFF, ReHo and VMHC analyses demonstrated abnormal spontaneous neural activity in brain regions which were reported in T2DM patients without cognitive impairment. These results may enhance our understanding of the diabetic brain changes at the early stage.

The hemodynamic response function as a type 2 diabetes biomarker: a data-driven approach

Introduction

There is a need to better understand the neurophysiological changes associated with early brain dysfunction in Type 2 diabetes mellitus (T2DM) before vascular or structural lesions. Our aim was to use a novel unbiased data-driven approach to detect and characterize hemodynamic response function (HRF) alterations in T2DM patients, focusing on their potential as biomarkers.

Methods

We meshed task-based event-related (visual speed discrimination) functional magnetic resonance imaging with DL to show, from an unbiased perspective, that T2DM patients' blood-oxygen-level dependent response is altered. Relevance analysis determined which brain regions were more important for discrimination. We combined explainability with deconvolution generalized linear model to provide a more accurate picture of the nature of the neural changes.

Results

The proposed approach to discriminate T2DM patients achieved up to 95% accuracy. Higher performance was achieved at higher stimulus (speed) contrast, showing a direct relationship with stimulus properties, and in the hemispherically dominant left visual hemifield, demonstrating biological interpretability. Differences are explained by physiological asymmetries in cortical spatial processing (right hemisphere dominance) and larger neural signal-to-noise ratios related to stimulus contrast. Relevance analysis revealed the most important regions for discrimination, such as extrastriate visual cortex, parietal cortex, and insula. These are disease/task related, providing additional evidence for pathophysiological significance. Our data-driven design allowed us to compute the unbiased HRF without assumptions.

Conclusion

We can accurately differentiate T2DM patients using a data-driven classification of the HRF. HRF differences hold promise as biomarkers and could contribute to a deeper understanding of neurophysiological changes associated with T2DM.

Voxel-based morphometry reveals the correlation between gray matter volume and serum P-tau-181 in type 2 diabetes mellitus patients with different HbA1c levels

Introduction

Emerging evidence suggested widespread decreased gray matter volume (GMV) and tau hyperphosphorylation were associated with type 2 diabetes mellitus (T2DM). Insulin resistance is one of the mechanisms of neuron degeneration in T2DM; it can decrease the activity of protein kinase B and increase the activity of glycogen synthesis kinase-3β, thus promoting the hyperphosphorylation of tau protein and finally leading to neuronal degeneration. However, the association between GMV and serum tau protein phosphorylated at threonine 181 (P-tau-181) in T2DM patients lacks neuroimaging evidence. We aimed to investigate the difference in brain GMV between T2DM patients with different glycated hemoglobin A1c (HbA1c) levels and healthy control (HC) subjects and the correlation between serum P-tau-181 and GMV in T2DM patients.

Methods

Clinical parameters, biochemical indicators, and MRI data were collected for 41 T2DM patients with high glycosylated hemoglobin level (HGL), 17 T2DM patients with normal glycosylated hemoglobin level (NGL), and 42 HC subjects. Voxel-based morphometry (VBM) method was applied to investigate GMV differences among groups, and multiple regression analysis was used to examine the correlation between serum P-tau-181 and GMV.

Results

Compared with HC subjects, the T2DM patients with HGL or NGL all showed significantly decreased GMV. Briefly, the GMV decreased in T2DM patients with HGL was mainly in the bilateral parahippocampal gyrus (PHG), right middle temporal gyrus (MTG), temporal pole (TPOmid), hippocampus (HIP), and left lingual gyrus. The GMV reduction in T2DM patients with NGL was in the right superior temporal gyrus (STG), and there was no significant difference in GMV between the two diabetic groups. The GMV values of bilateral PHG, right MTG, TPOmid, HIP, and STG can significantly (p < 0.0001) distinguish T2DM patients from HC subjects in ROC curve analysis. In addition, we found that serum P-tau-181 levels were positively correlated with GMV in the right superior and middle occipital gyrus and cuneus, and negatively correlated with GMV in the right inferior temporal gyrus in T2DM patients.

Conclusion

Our study shows that GMV atrophy can be used as a potential biological indicator of T2DM and also emphasizes the important role of P-tau-181 in diabetic brain injury, providing new insights into the neuropathological mechanism of diabetic encephalopathy.

Changes of brain function in patients with type 2 diabetes mellitus measured by different analysis methods: A new coordinate-based meta-analysis of neuroimaging

Objective

Neuroimaging meta-analysis identified abnormal neural activity alterations in patients with type 2 diabetes mellitus (T2DM), but there was no consistency or heterogeneity analysis between different brain imaging processing strategies. The aim of this meta-analysis was to determine consistent changes of regional brain functions in T2DM via the indicators obtained by using different post-processing methods.

Methods

Since the indicators obtained using varied post-processing methods reflect different neurophysiological and pathological characteristics, we further conducted a coordinate-based meta-analysis (CBMA) of the two categories of neuroimaging literature, which were grouped according to similar data processing methods: one group included regional homogeneity (ReHo), independent component analysis (ICA), and degree centrality (DC) studies, while the other group summarized the literature on amplitude of low-frequency fluctuation (ALFF) and cerebral blood flow (CBF).

Results

The final meta-analysis included 23 eligible trials with 27 data sets. Compared with the healthy control group, when neuroimaging studies were combined with ReHo, ICA, and DC measurements, the brain activity of the right Rolandic operculum, right supramarginal gyrus, and right superior temporal gyrus in T2DM patients decreased significantly. When neuroimaging studies were combined with ALFF and CBF measurements, there was no clear evidence of differences in the brain function between T2DM and HCs.

Conclusion

T2DM patients have a series of spontaneous abnormal brain activities, mainly involving brain regions related to learning, memory, and emotion, which provide early biomarkers for clarifying the mechanism of cognitive impairment and neuropsychiatric disorders in diabetes.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=247071, PROSPERO [CRD42021247071].

Causal Structural Covariance Network Suggesting Structural Alterations Progression in Type 2 Diabetes Patients

Background and Purpose

According to reports, type 2 diabetes (T2D) is a progressive disease. However, no known research has examined the progressive brain structural changes associated with T2D. The purpose of this study was to determine whether T2D patients exhibit progressive brain structural alterations and, if so, how the alterations progress.

Materials and Methods

Structural magnetic resonance imaging scans were collected for 81 T2D patients and 48 sex-and age-matched healthy controls (HCs). Voxel-based morphometry (VBM) and causal structural covariance network (CaSCN) analyses were applied to investigate gray matter volume (GMV) alterations and the likely chronological processes underlying them in T2D. Two sample t-tests were performed to compare group differences, and the differences were corrected using Gaussian random field (GRF) correction (voxel-level p < 0.001, cluster-level p < 0.01).

Results

Our findings demonstrated that GMV alterations progressed in T2D patients as disease duration increased. In the early stages of the disease, the right temporal pole of T2D patients had GMV atrophy. As the diseases duration prolonged, the limbic system, cerebellum, subcortical structures, parietal cortex, frontal cortex, and occipital cortex progressively exhibited GMV alterations. The patients also exhibited a GMV alterations sequence exerting from the right temporal pole to the limbic-cerebellum-striatal-cortical network areas.

Conclusion

Our results indicate that the progressive GMV alterations of T2D patients manifested a limbic-cerebellum-striatal-cortical sequence. These findings may contribute to a better understanding of the progression and an improvement of current diagnosis and intervention strategies for T2D.

Poor Sleep Quality Linked to Decreased Brain Gray Matter Density in Adults with Type 2 Diabetes

BACKGROUND

Poor sleep is common in adults with Type 2 Diabetes Mellitus (T2DM), which may contribute to brain tissue changes. However, the impact of sleep quality on brain tissue in T2DM individuals is unclear. We aimed to evaluate differential sleep quality with brain changes, and brain tissue integrity in T2DM patients.

METHODS

Data were collected from 34 patients with T2DM and included sleep quality (assessed by the Pittsburgh Sleep Quality Index [PSQI], and high-resolution T1-weighted brain images using a 3.0-Tesla MRI scanner. Gray matter density (GMD) maps were compared between subjects with good vs poor sleep quality as assessed by PSQI (covariates: age, sex, BMI).

RESULTS

Of 34 T2DM patients, 17 showed poor sleep quality. Multiple brain sites, including the hippocampus, cerebellum, prefrontal, amygdala, thalamus, hypothalamus, insula, cingulate, and temporal areas, showed reduced gray matter in T2DM patients with poor sleep quality over patients with good sleep quality. Negative associations emerged between PSQI scores and gray matter density in multiple areas.

CONCLUSIONS

T2DM patients with poor sleep quality show brain tissue changes in sites involved in sleep regulation. Findings indicate that improving sleep may help mitigate brain tissue damage, and thus, improve brain function in T2DM patients.

Identifying Type 2 Diabetic Brains by Investigating Disease-Related Structural Changes in Magnetic Resonance Imaging

Diabetes with high blood glucose levels may damage the brain nerves and thus increase the risk of dementia. Previous studies have shown that dementia can be reflected in altered brain structure, facilitating computer-aided diagnosis of brain diseases based on structural magnetic resonance imaging (MRI). However, type 2 diabetes mellitus (T2DM)-mediated changes in the brain structures have not yet been studied, and only a few studies have focused on the use of brain MRI for automated diagnosis of T2DM. Hence, identifying MRI biomarkers is essential to evaluate the association between changes in brain structure and T2DM as well as cognitive impairment (CI). The present study aims to investigate four methods to extract features from MRI, characterize imaging biomarkers, as well as identify subjects with T2DM and CI.

Sex Differences in the Effect of Diabetes on Cerebral Glucose Metabolism

The neuroimaging literature indicates that brain structure and function both deteriorate with diabetes, but information on sexual dimorphism in diabetes-related brain alterations is limited. This study aimed to ascertain whether brain metabolism is influenced by sex in an animal model of diabetes. Eleven rats (male, n = 5; female, n = 6) received a single intraperitoneal injection of 70 mg/kg streptozotocin (STZ) to develop diabetes. Another 11 rats (male, n = 5; female, n = 6) received the same amount of solvent through a single intraperitoneal injection. Longitudinal positron emission tomography scans were used to assess cerebral glucose metabolism before and 4 weeks after STZ or solvent administration. Before STZ or solvent injections, there was no evidence of sexual dimorphism in cerebral metabolism (p > 0.05). Compared with healthy control animals, rats with diabetes had significantly decreased brain metabolism in all brain regions (all p < 0.05). In addition, female diabetic rats exhibited further reduction in cerebral metabolism, relative to male diabetic rats (p < 0.05). The results of this study may provide some biological evidence, supporting the existence of a sexual dimorphism in diabetes-related complications.

Altered Gray Matter Volume, Functional Connectivity, and Degree Centrality in Early-Onset Type 2 Diabetes Mellitus

Background: Structural and functional brain alterations that underlie cognitive decline have been observed in elderly adults with type 2 diabetes mellitus (T2DM); however, whether these alterations can be observed in patients with early-onset T2DM remains unclear. Therefore, we aimed to describe the abnormalities in brain volume and functional patterns in patients with early-onset T2DM in the present study.

Methods: We enrolled 20 patients with early-onset T2DM and 20 healthy controls (HCs). Changes in brain volume were assessed using voxel-based morphology (VBM), while changes in brain function were assessed using degree centrality (DC) and functional connectivity (FC).

Results: Compared to HCs, patients with early-onset T2DM exhibited gray matter reductions in the left orbital superior, middle, and inferior frontal gyri as well as the right superior frontal gyrus. The gray matter reductions in the right superior frontal gyrus were negatively associated with the urine albumin to creatinine ratio. Furthermore, increased DC values were observed in the left superior temporal gyrus, left Heschl gyrus, and left hippocampus in patients with early-onset T2DM. An FC analysis of these regions revealed elevated connectivity in the right precuneus, left inferior parietal gyrus, left Heschl gyrus, bilateral post-central gyrus, bilateral insula, bilateral superior temporal gyrus, and bilateral medial and paracingulate gyrus. Furthermore, the FC of the hubs to the superior temporal gyrus, insula, and Heschl gyrus was increased and positively correlated with trail making test-B.

Conclusion: Decreased local gray matter volume and increased DC and FC may represent the neurobiological mechanism underlying cognitive dysfunction in patients with early-onset T2DM.

Obesity and Gray Matter Volume Assessed by Neuroimaging: A Systematic Review

Obesity has become a major public and individual health problem due to its high worldwide prevalence and its relation with comorbid conditions. According to previous studies, obesity is related to an increased risk of cognitive impairment and dementia. This systematic review aims to further examine the present state of the art about the association between obesity and gray matter volume (GMV) as assessed by magnetic resonance imaging (MRI). A search was conducted in Pubmed, SCOPUS and Cochrane of those studies released before 1 February 2021 including MRIs to assess the GMVs in obese participants. From this search, 1420 results were obtained, and 34 publications were finally included. Obesity was mainly measured by the body mass index, although other common types of evaluations were used (e.g., waist circumference, waist-to-hip ratio and plasma leptin levels). The selected neuroimaging analysis methods were voxel-based morphometry (VBM) and cortical thickness (CT), finding 21 and 13 publications, respectively. There were 30 cross-sectional and 2 prospective longitudinal studies, and 2 articles had both cross-sectional and longitudinal designs. Most studies showed a negative association between obesity and GMV. This would have important public health implications, as obesity prevention could avoid a potential risk of GMV reductions, cognitive impairment and dementia.

Cognitive Functioning and Cortical Brain Thickness in Acromegaly Patients: A Pilot study

OBJECTIVE

Cognitive effects in acromegaly patients are poorly understood and the mechanisms involved are still unclear. The aim of this study was to evaluate the cognitive function, depression, and quality of life of acromegaly patients treated with pegvisomant versus somatostatin analogues (SRLs) and to analyze the effect of the different treatments on cognition and possible structural brain changes.

METHODS

This cross-sectional study involved 23 acromegaly patients divided into two groups according to treatment modality: One group of 9 patients treated with pegvisomant and another group of 14 patients treated with SRLs. All participants underwent blood analysis, neuropsychological tests, depression tests, quality of life assessment, and 3-Tesla magnetic resonance imaging.

RESULTS

We found no significant differences between groups in the neuropsychological tests, depression or quality of life; nor in the whole-brain cortical thickness. In the SRL group, the volume of the thalamus correlated positively with executive function, a correlation not found in the pegvisomant group. In addition, the pegvisomant group had significantly higher levels of insulin than the SRL group.

CONCLUSIONS

In conclusion, in this pilot study, the type of pharmacological treatment in patients with acromegaly and good glycemic control did not influence the cognitive function and cortical brain thickness. However, pegvisomant could play a neuroprotective role on the thalamus that will have to be demonstrated with larger samples in future studies.

A multimodal meta-analysis of regional structural and functional brain alterations in type 2 diabetes

Neuroimaging studies have identified brain structural and functional alterations of type 2 diabetes mellitus (T2DM) patients; however, there is no systematic information on the relations between abnormalities in these two domains. We conducted a multimodal meta-analysis of voxel-based morphometry and regional resting-state functional MRI studies in T2DM, including fifteen structural datasets (693 patients and 684 controls) and sixteen functional datasets (378 patients and 358 controls). We found, in patients with T2DM compared to controls, conjoint decreased regional gray matter volume (GMV) and altered intrinsic activity mainly in the default mode network including bilateral superior temporal gyrus/Rolandic operculum, left middle and inferior temporal gyrus, and left supramarginal gyrus; decreased GMV alone in the limbic system; and functional abnormalities alone in the cerebellum, insula, and visual cortex. This meta-analysis identified complicated patterns of conjoint and dissociated brain alterations in T2DM patients, which may help provide new insight into the neuropathology of T2DM.

Regional Spontaneous Neural Activity Alterations in Type 2 Diabetes Mellitus: A Meta-Analysis of Resting-State Functional MRI Studies

Objective: Resting-state functional magnetic resonance imaging (rs-fMRI) studies have revealed inconsistent regional spontaneous neural activity alterations in patients with type 2 diabetes mellitus (T2DM). The aim of our meta-analysis was to identify concordant regional spontaneous neural activity abnormalities in patients with T2DM. Methods: A systematic search was conducted to identify voxel-based rs-fMRI studies comparing T2DM patients with healthy controls. The permutation of subject images seed-based d mapping (SDM) was used to quantitatively estimate the regional spontaneous neural activity abnormalities in patients with T2DM. Metaregression was conducted to examine the associations between clinical characteristics and functional alterations. Results: A total of 16 studies with 19 datasets including 434 patients with T2DM and 391 healthy controls were included. Patients with T2DM showed hypoactivity in the right medial superior frontal gyrus, right superior temporal gyrus, and left lingual gyrus, whereas hyperactivity in the right cerebellum. Metaregression analysis identified negative correlation between regional activity in the medial superior frontal and anterior cingulate gyri and illness duration of patients with T2DM. Conclusion: The patterns of regional spontaneous neural activity alterations, characterized by hypoactivity in the medial pre-frontal cortex, visual cortex, and superior temporal gyrus, whereas hyperactivity in the cerebellum, might represent the underlying neuropathological mechanisms of T2DM.

Gray Matter Abnormalities in Type 1 and Type 2 Diabetes: A Dual Disorder ALE Quantification

Aims/hypothesis: Diabetes mellitus (DM) is associated with comorbid brain disorders. Neuroimaging studies in DM revealed neuronal degeneration in several cortical and subcortical brain regions. Previous studies indicate more pronounced brain alterations in type 2 diabetes mellitus (T2DM) than in type 1 diabetes mellitus (T1DM). However, a comparison of both types of DM in a single analysis has not been done so far. The aim of this meta-analysis was to conduct an unbiased objective investigation of neuroanatomical differences in DM by combining voxel-based morphometry (VBM) studies of T1DM and T2DM using dual disorder anatomical likelihood estimation (ALE) quantification.

Methods: PubMed, Web of Science and Medline were systematically searched for publications until June 15, 2020. VBM studies comparing gray matter volume (GMV) differences between DM patients and controls at the whole-brain level were included. Study coordinates were entered into the ALE meta-analysis to investigate the extent to which T1DM, T2DM, or both conditions contribute to gray matter volume differences compared to controls.

Results: Twenty studies (comprising of 1,175 patients matched with 1,013 controls) were included, with seven studies on GMV alterations in T1DM and 13 studies on GMV alterations in T2DM. ALE analysis revealed seven clusters of significantly lower GMV in T1DM and T2DM patients relative to controls across studies. Both DM subtypes showed GMV reductions in the left caudate, right superior temporal lobe, and left cuneus. Conversely, GMV reductions associated exclusively with T2DM (>99% contribution) were found in the left cingulate, right posterior lobe, right caudate and left occipital lobe. Meta-regression revealed no significant influence of study size, disease duration, and HbA1c values.

Conclusions/interpretation: Our findings suggest a more pronounced gray matter atrophy in T2DM compared to T1DM. The increased risk of microvascular or macrovascular complications, as well as the disease-specific pathology of T2DM may contribute to observed GMV reductions.

Systematic Review Registration: [PROSPERO], identifier [CRD42020142525].

Upregulated expression of a subset of genes in APP;ob/ob mice: Evidence of an interaction between diabetes-linked obesity and Alzheimer's disease

Clinical studies have indicated that obesity and diabetes are associated with Alzheimer's disease (AD) and neurodegeneration. However, the mechanism by which obesity/diabetes and AD interact with each other and contribute to dementia remains elusive. To obtain insights into their interaction at molecular levels, we performed gene expression analysis of APP;ob/ob mice, which were generated by crossing transgenic AD model mice (APP23 mice) with ob/ob mice, which are obese and mildly diabetic. The Aβ level in these mice was reduced compared with that in pure APP mice. However, we identified a cluster of genes (cluster 10) upregulated in APP;ob/ob mice but not in either APP or ob/ob mice. Interestingly, genes upregulated in the human AD brain were enriched in cluster 10. Moreover, genes in cluster 10 formed a network and shared upregulated genes with a cell model of neurodegeneration and other models of neurological disorders such as ischemia and epilepsy. In silico analyses showed that serum response factor (SRF), recently identified in a single-cell analysis of human brains as a transcription factor that can control the conversion from healthy cells to AD cells, might be a common transcriptional regulator for a subset of cluster 10 genes. These data suggest that upregulation of genes uniquely associated with APP;ob/ob mice is an evidence of the interaction between obesity/diabetes and AD.

Glucose-level dependent brain hypometabolism in type 2 diabetes mellitus and obesity

BACKGROUND

Metabolic syndrome and its individual components lead to wide-ranging consequences, many of which affect the central nervous system. In this study, we compared the [18F]FDG regional brain metabolic pattern of participants with type 2 diabetes mellitus (T2DM) and non-DM obese individuals.

METHODS

In our prospective study, 51 patients with controlled T2DM (ages 50.6 ± 8.0 years) and 45 non-DM obese participants (ages 52.0 ± 9.6 years) were enrolled. Glucose levels measured before PET/CT examination (pre-PET glucose) as well as laboratory parameters assessing glucose and lipid status were determined. NeuroQ application (NeuroQTM 3.6, Syntermed, Philips) was used to evaluate regional brain metabolic differences. [18F]FDG PET/CT (AnyScan PC, Mediso) scans, estimating brain metabolism, were transformed to MNI152 brain map after T1 registration and used for SPM-based group comparison of brain metabolism corrected for pre-PET glucose, and correlation analysis with laboratory parameters.

RESULTS

NeuroQ analysis did not reveal significant regional metabolic defects in either group. Voxel-based group comparison revealed significantly (PFWE<0.05) decreased metabolism in the region of the precuneus and in the right superior frontal gyrus (rSFG) in the diabetic group as compared to the obese patients. Data analysis corrected for pre-PET glucose level showed a hypometabolic difference only in the rSFG in T2DM. Voxel-based correlation analysis showed significant negative correlation of the metabolism in the following brain regions with pre-PET glucose in diabetes: precuneus, left posterior orbital gyrus, right calcarine cortex and right orbital part of inferior frontal gyrus; whilst in the obese group only the right rolandic (pericentral) operculum proved to be sensitive to pre-PET glucose level.

CONCLUSIONS

To our knowledge, this is the first study to perform pre-PET glucose level corrected comparative analysis of brain metabolism in T2DM and obesity. We also examined the pre-PET glucose level dependency of regional cerebral metabolism in the two groups separately. Large-scale future studies are warranted to perform further correlation analysis with the aim of determining the effects of metabolic disturbances on brain metabolism.

Altered Brain Network Centrality in Patients with Diabetic Optic Neuropathy: A Resting-State FMRI Study

OBJECTIVE

Recent studies have suggested that diabetic optic neuropathy (DON) independently increases the incidence of brain diseases like cerebral infarction and hemorrhage. In this study, voxel-level degree centrality (DC) was used to study potential changes in functional network brain activity in DON patients.

METHODS

The study included 14 DON patients and 14 healthy controls (HCs) matched by age, sex, and weight. All subjects underwent resting functional magnetic resonance imaging. Receiver operating characteristic curves and Pearson correlation analysis were performed.

RESULTS

The DC values of the left frontal mid-orb and right middle frontal gyrus/right frontal sup were significantly lower in DON patients compared to HCs. The DC value of the left temporal lobe was also significantly higher than in HCs.

CONCLUSION

Three different brain regions show DC changes in DON patients, suggesting common optic neuropathy in the context of diabetes and providing new ideas for treating optic nerve disease in patients with long-term diabetes.

ABBREVIATIONS

AUC = area under the curve; BCVA = best corrected visual acuity; DC = degree centrality; DON = diabetic optic neuropathy; fMRI = functional magnetic resonance imaging; HC = healthy control; LFMO = left frontal mid orb; LTL = left temporal lobe; RFS = right frontal sup; RMFG = right middle frontal gyrus; ROC = receiver operating characteristic.

Type 2 Diabetes Mellitus May Exacerbate Gray Matter Atrophy in Patients With Early-Onset Mild Cognitive Impairment

Background

The precise physiopathological association between the courses of neurodegeneration and cognitive decline in type 2 diabetes mellitus (T2DM) remains unclear. This study sought to comprehensively investigate the distribution characteristics of gray matter atrophy in middle-aged T2DM patients with newly diagnosed mild cognitive impairment (MCI).

Methods

Four groups, including 28 patients with early-onset MCI, 28 patients with T2DM, 28 T2DM patients with early-onset MCI (T2DM-MCI), and 28 age-, sex-, and education-matched healthy controls underwent three-dimensional high-resolution structural magnetic resonance imaging. Cortical and subcortical gray matter volumes were calculated, and a structural covariance method was used to evaluate the morphological relationships within the default mode network (DMN).

Results

Overlapped and unique cortical/subcortical gray matter atrophy was found in patients with MCI, T2DM and T2DM-MCI in our study, and patients with T2DM-MCI showed lower volumes in several areas than patients with MCI or T2DM. Volume loss in subcortical areas (including the thalamus, putamen, and hippocampus), but not in cortical areas, was related to cognitive impairment in patients with MCI and T2DM-MCI. No associations between biochemical measurements and volumetric reductions were found. Furthermore, patients with MCI and those with T2DM-MCI showed disrupted structural connectivity within the DMN.

Conclusion

These findings provide further evidence that T2DM may exacerbate atrophy of specific gray matter regions, which may be primarily associated with MCI. Impairments in gray matter volume related to T2DM or MCI are independent of cardiovascular risk factors, and subcortical atrophy may play a more pivotal role in cognitive impairment than cortical alterations in patients with MCI and T2DM-MCI. The enhanced structural connectivity within the DMN in patients with T2DM-MCI may suggest a compensatory mechanism for the chronic neurodegeneration.

Elevating Insulin Signaling Using a Constitutively Active Insulin Receptor Increases Glucose Metabolism and Expression of GLUT3 in Hippocampal Neurons

Insulin signaling is an integral component of healthy brain function, with evidence of positive insulin-mediated alterations in synaptic integrity, cerebral blood flow, inflammation, and memory. However, the specific pathways targeted by this peptide remain unclear. Previously, our lab used a molecular approach to characterize the impact of insulin signaling on voltage-gated calcium channels and has also shown that acute insulin administration reduces calcium-induced calcium release in hippocampal neurons. Here, we explore the relationship between insulin receptor signaling and glucose metabolism using similar methods. Mixed, primary hippocampal cultures were infected with either a control lentivirus or one containing a constitutively active human insulin receptor (IRβ). 2-NBDG imaging was used to obtain indirect measures of glucose uptake and utilization. Other outcome measures include Western immunoblots of GLUT3 and GLUT4 on total membrane and cytosolic subcellular fractions. Glucose imaging data indicate that neurons expressing IRβ show significant elevations in uptake and rates of utilization compared to controls. As expected, astrocytes did not respond to the IRβ treatment. Quantification of Western immunoblots show that IRβ is associated with significant elevations in GLUT3 expression, particularly in the total membrane subcellular fraction, but did not alter GLUT4 expression in either fraction. Our work suggests that insulin plays a significant role in mediating neuronal glucose metabolism, potentially through an upregulation in the expression of GLUT3. This provides further evidence for a potential therapeutic mechanism underlying the beneficial impact of intranasal insulin in the clinic.

Tau, Diabetes and Insulin

Tau protein which was discovered in 1975 [310] became of great interest when it was identified as the main component of neurofibrillary tangles (NFT), a pathological feature in the brain of patients with Alzheimer's disease (AD) [39, 110, 232]. Tau protein is expressed mainly in the brain as six isoforms generated by alternative splicing [46, 97]. Tau is a microtubule associated proteins (MAPs) and plays a role in microtubules assembly and stability, as well as diverse cellular processes such as cell morphogenesis, cell division, and intracellular trafficking [49]. Additionally, Tau is involved in much larger neuronal functions particularly at the level of synapses and nuclei [11, 133, 280]. Tau is also physiologically released by neurons [233] even if the natural function of extracellular Tau remains to be uncovered (see other chapters of the present book).

"Need to Know" or the Strong Urge to Find Names of Unique Entities in Acquired Obsessive-Compulsive Disorder

The two forms of obsessive-compulsive disorder (OCD), idiopathic and acquired, have been linked to abnormalities in the fronto-striato-thalamo-cortical circuitry, involving the orbitofrontal cortex, anterior cingulate cortex, thalamus, and striatum. Accumulating evidence indicates that damage to other brain regions (ie, temporal lobes) is also implicated in the pathogenesis of both types of OCD. In addition, some discrete OCD symptoms have received less attention because of their presumed low occurrence and difficultly of categorization. Among these, one intriguing and potentially severe type of obsessive thinking is the so-called "need to know" (NtK), which is a strong urge to access certain information, particularly proper names. In some patients, this monosymptomatic presentation may constitute the major feature of OCD. Here we report the cases of two patients who developed NtK obsessions with tenacious time-consuming, answer-seeking compulsions as the only or more disabling symptomatology in association with malignant tumors involving the right temporal lobe and connected fronto-subcortical circuits.

Neuroimaging endophenotypes of type 2 diabetes mellitus: a discordant sibling pair study

Background

Type 2 diabetes mellitus (T2DM) is characterized by notable familial aggregation involving common variants of many genes, and its heritability leads to a high prevalence in the siblings of affected individuals compared with the general population. Endophenotypes are objective, heritable, quantitative traits that appear to reflect the genetic risk for polygenic disorders at more biologically tractable levels. Based on a sibling pair design, we aimed to find the neuroimaging endophenotypes of T2DM and investigate the role of inherent neurological disorders in the pathogenesis and deterioration of T2DM.

Methods

Twenty-six pairs of diagnosed T2DM patients with unaffected siblings and 26 unrelated controls were included in this study. Both high-resolution structural MRI and three-dimensional pseudo-continuous arterial spin labelling (3D-pCASL) MRI data were acquired with a 3.0 T MRI system. Voxel-based morphometry (VBM) analysis was performed on the structural T1W images, and cerebral blood flow (CBF) maps were obtained. All data were processed with the SPM8 package under the MATLAB 7.6 operation environment.

Results

The T2DM patients and their unaffected siblings shared significant atrophy in the right inferior/middle temporal gyrus, and left insula, in addition to elevated CBF in the right prefrontal lobe. Several regions with abnormal CBF in siblings, including the right inferior/middle temporal gyrus, left insula, left operculum, right supramarginal gyrus, right prefrontal lobe, and bilateral anterior cingulate cortex, also presented significant atrophy in T2DM patients.

Conclusions

The shared brain regions with grey matter (GM) loss and CBF increases may serve as neuroimaging endophenotypes of T2DM, and the regions with abnormal CBF in siblings indicate an increased risk for T2DM.

Aging, lifestyle and dementia

Aging is the greatest risk factor for most diseases including cancer, cardiovascular disorders, and neurodegenerative disease. There is emerging evidence that interventions that improve metabolic health with aging may also be effective for brain health. The most robust interventions are non-pharmacological and include limiting calorie or protein intake, increasing aerobic exercise, or environmental enrichment. In humans, dietary patterns including the Mediterranean, Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability (FINGER) and Okinawan diets are associated with improved age-related health and may reduce neurodegenerative disease including dementia. Rapamycin, metformin and resveratrol act on nutrient sensing pathways that improve cardiometabolic health and decrease the risk for age-associated disease. There is some evidence that they may reduce the risk for dementia in rodents. There is a growing recognition that improving metabolic function may be an effective way to optimize brain health during aging.

Brain Functional Networks in Type 2 Diabetes Mellitus Patients: A Resting-State Functional MRI Study

Background

Previous diabetes mellitus studies of cognitive impairments in the early stages have focused on changes in brain structure and function, and more recently the focus has shifted to the relationships between encephalic regions and diversification of network topology. However, studies examining network topology in diabetic brain function are still limited.

Methods

The study included 102 subjects; 55 type 2 diabetes mellitus (T2DM) patients plus 47 healthy controls. All subjects were examined by resting-state functional magnetic resonance imaging (rs-fMRI) scan. According to Automated Anatomical Labeling, the brain was divided into 90 anatomical regions, and every region corresponds to a brain network analysis node. The whole brain functional network was constructed by thresholding the correlation matrices of the 90 brain regions, and the topological properties of the network were computed based on graph theory. Then, the topological properties of the network were compared between different groups by using a non-parametric test. Finally, the associations between differences in topological properties and the clinical indicators were analyzed.

Results

The brain functional networks of both T2DM patients and healthy controls were found to possess small-world characteristics, i.e., normalized clustering coefficient (γ) > 1, and normalized characteristic path length (λ) close to 1. No significant differences were found in the small-world characteristics (σ). Second, the T2DM patient group displayed significant differences in node properties in certain brain regions. Correlative analytic results showed that the node degree of the right inferior temporal gyrus (ITG) and the node efficiencies of the right ITG and superior temporal gyrus of T2DM patients were positively correlated with body mass index.

Conclusion

The brain network of T2DM patients has the same small-world characteristics as normal people, but the normalized clustering coefficient is higher and the normalized characteristic path length is lower than that of the normal control group, indicating that the brain function network of the T2DM patients has changed. The changes of node properties were mostly concentrated in frontal lobe, temporal lobe and posterior cingulate gyrus. The abnormal changes in these indices in T2DM patients might be explained as a compensatory behavior to reduce cognitive impairments, which is achieved by mobilizing additional neural resources, such as the excessive activation of the network and the efficient networking of multiple brain regions.

Local Diffusion Homogeneity Provides Supplementary Information in T2DM-Related WM Microstructural Abnormality Detection

Objectives: We aimed to investigate whether an inter-voxel diffusivity metric (local diffusion homogeneity, LDH), can provide supplementary information to traditional intra-voxel metrics (i.e., fractional anisotropy, FA) in white matter (WM) abnormality detection for type 2 diabetes mellitus (T2DM).

Methods: Diffusion tensor imaging was acquired from 34 T2DM patients and 32 healthy controls. Voxel-based group-difference comparisons based on LDH and FA, as well as the association between the diffusion metrics and T2DM risk factors [i.e., body mass index (BMI) and systolic blood pressure (SBP)], were conducted, with age, gender and education level controlled.

Results: Compared to the controls, T2DM patients had higher LDH in the pons and left temporal pole, as well as lower FA in the left superior corona radiation (p < 0.05, corrected). In T2DM, there were several overlapping WM areas associated with BMI as revealed by both LDH and FA, including right temporal lobe and left inferior parietal lobe; but the unique areas revealed only by using LDH included left inferior temporal lobe, right supramarginal gyrus, left pre- and post-central gyrus (at the semiovale center), and right superior radiation. Overlapping WM areas that associated with SBP were found with both LDH and FA, including right temporal pole, bilateral orbitofrontal area (rectus gyrus), the media cingulum bundle, and the right cerebellum crus I. However, the unique areas revealed only by LDH included right inferior temporal lobe, right inferior occipital lobe, and splenium of corpus callosum.

Conclusion: Inter- and intra-voxel diffusivity metrics may have different sensitivity in the detection of T2DM-related WM abnormality. We suggested that LDH could provide supplementary information and reveal additional underlying brain changes due to diabetes.

Evidence of altered brain network centrality in patients with diabetic nephropathy and retinopathy: an fMRI study using a voxel-wise degree centrality approach

BACKGROUND

Over recent years, some researchers believe that diabetic nephropathy (DN) and diabetic retinopathy (DR) both independently increase the incidence of brain diseases, such as stroke, cerebral infarction, and cerebral hemorrhage. In the present study, we used the voxel-wise degree centrality (DC) method to investigate potential changes of functional network brain activity in patients with DN and retinopathy (DNR).

METHODS

Twenty DNR patients (9 men, 11 women) and 20 healthy controls (HCs; 9 men, 11 women) were recruited; the controls were matched for age, sex, and educational background. All subjects underwent resting-state functional magnetic resonance imaging. Ophthalmoscopy, renal biopsy and single-photon emission computed tomography were used to evaluate microvascular lesions in the eye and kidney. Data were categorized using receiver operating characteristic curves, and correlation analysis was performed using Pearson's correlation analysis.

RESULTS

Compared with HCs, DNR patients showed reduced mean DC values in the right inferior temporal gyrus (RITG) and left subcallosal gyrus regions (LSG) and increased mean DC values in the bilateral precuneus (BP). Moreover, mean DC in the BP was correlated with renal estimated glomerular filtration rate (eGFR; r = 0.762). The area under the curve (AUC) value was 0.829 for BP and 0.839 for RITG and LSG.

CONCLUSION

DNR patients showed dysfunction in three different brain regions. The linear correlation between eGFR and mean brain DC values indicates the presence of common diabetic microangiopathy in the brain and kidney, which may provide new ideas for multiorgan microvascular lesions of diabetics.

What magnetic resonance imaging reveals - A systematic review of the relationship between type II diabetes and associated brain distortions of structure and cognitive functioning

Due to its increasing prevalence, Type 2 diabetes mellitus (T2DM) represents a major health challenge for modern society. Despite it being of fundamental interest, only a few MRI studies have conducted statistical analyses to draw scientifically valid conclusions about the complex interplay of T2DM and its associated clinical, structural, functional, metabolite, as well as cognitive distortions. Therefore, a systematic review of 68 manuscripts, following the PRISMA guidelines, was conducted. Notably, although the associations between imaging, clinical, and cognitive variables are not fully homogeneous, findings show a clear trend towards a link between altered brain structure and a decline in cognitive processing ability. The results of the review highlight the heterogeneity of the methods used across manuscripts in terms of assessed clinical variables, imaging, and data analysis methods. This is particularly significant as, if the subjects' criteria are not carefully considered, results are easily prone to confounding factors.

Brain GLP-1/IGF-1 Signaling and Autophagy Mediate Exendin-4 Protection Against Apoptosis in Type 2 Diabetic Rats

Type 2 diabetes (T2D) is a modern socioeconomic burden, mostly due to its long-term complications affecting nearly all tissues. One of them is the brain, whose dysfunctional intracellular quality control mechanisms (namely autophagy) may upregulate apoptosis, leading to cognitive dysfunction and Alzheimer disease (AD). Since impaired brain insulin signaling may constitute the crosslink between T2D and AD, its restoration may be potentially therapeutic herein. Accordingly, the insulinotropic anti-T2D drugs from glucagon-like peptide-1 (GLP-1) mimetics, namely, exendin-4 (Ex-4), could be a promising therapy. In line with this, we hypothesized that peripherally administered Ex-4 rescues brain intracellular signaling pathways, promoting autophagy and ultimately protecting against chronic T2D-induced apoptosis. Thus, we aimed to explore the effects of chronic, continuous, subcutaneous (s.c.) exposure to Ex-4 in brain cortical GLP-1/insulin/insulin-like growth factor-1 (IGF-1) signaling, and in autophagic and cell death mechanisms in middle-aged (8 months old), male T2D Goto-Kakizaki (GK) rats. We used brain cortical homogenates obtained from middle-aged (8 months old) male Wistar (control) and T2D GK rats. Ex-4 was continuously administered for 28 days, via s.c. implanted micro-osmotic pumps (5 μg/kg/day; infusion rate 2.5 μL/h). Peripheral characterization of the animal models was given by the standard biochemical analyses of blood or plasma, the intraperitoneal glucose tolerance test, and the heart rate. GLP-1, insulin, and IGF-1, their downstream signaling and autophagic markers were evaluated by specific ELISA kits and Western blotting. Caspase-like activities and other apoptotic markers were given by colorimetric methods and Western blotting. Chronic Ex-4 treatment attenuated peripheral features of T2D in GK rats, including hyperglycemia and insulin resistance. Furthermore, s.c. Ex-4 enhanced their brain cortical GLP-1 and IGF-1 levels, and subsequent signaling pathways. Specifically, Ex-4 stimulated protein kinase A (PKA) and phosphoinositide 3-kinase (PI3K)/Akt signaling, increasing cGMP and AMPK levels, and decreasing GSK3β and JNK activation in T2D rat brains. Moreover, Ex-4 regulated several markers for autophagy in GK rat brains (as mTOR, PI3K class III, LC3 II, Atg7, p62, LAMP-1, and Parkin), ultimately protecting against apoptosis (by decreasing several caspase-like activities and mitochondrial cytochrome c, and increasing Bcl2 levels upon T2D). Altogether, this study demonstrates that peripheral Ex-4 administration may constitute a promising therapy against the chronic complications of T2D affecting the brain.

Altered Brain Functional Hubs and Connectivity in Type 2 Diabetes Mellitus Patients: A Resting-State fMRI Study

Type 2 diabetes mellitus (T2DM) affects a vast population and is closely associated with cognitive impairment. However, the mechanisms of cognitive impairment in T2DM patients have not been unraveled. Research on the basic units (nodes or hubs and edges) of the brain functional network on the basis of neuroimaging may advance our understanding of the network change pattern in T2DM patients. This study investigated the change patterns of brain functional hubs using degree centrality (DC) analysis and the connectivity among these hubs using functional connectivity and Granger causality analysis. Compared to healthy controls, the DC values were higher in the left anterior cingulate gyrus (ACG) and lower in the bilateral lateral occipital cortices (LOC) and right precentral gyrus (PreCG) in T2DM patients. The functional connectivity between the left ACG and the right PreCG was stronger in T2DM patients, whereas the functional connectivity among the right PreCG and bilateral LOC was weaker. A negative causal effect from the left ACG to left LOC and a positive effect from the left ACG to right LOC were observed in T2DM patients, while in healthy controls, the opposite occurred. Additionally, the reserve of normal brain function in T2DM patients was negatively associated with the elevated glycemic parameters. This study demonstrates that there are brain functional hubs and connectivity alterations that may reflect the aberrant information communication in the brain of T2DM patients. The findings may advance our understanding of the mechanisms of T2DM-related cognitive impairment.

Psychiatric polygenic risk associates with cortical morphology and functional organization in aging

Common brain abnormalities in cortical morphology and functional organization are observed in psychiatric disorders and aging, reflecting shared genetic influences. This preliminary study aimed to examine the contribution of a polygenetic risk for psychiatric disorders (PRS_cross) to aging brain and to identify molecular mechanisms through the use of multimodal brain images, genotypes, and transcriptome data. We showed age-related cortical thinning in bilateral inferior frontal cortex (IFC) and superior temporal gyrus and alterations in the functional connectivity between bilateral IFC and between right IFC and right inferior parietal lobe as a function of PRS_cross. Interestingly, the genes in PRS_cross, that contributed most to aging neurodegeneration, were expressed in the functioanlly connected cortical regions. Especially, genes identified through the genotype-functional connectivity association analysis were commonly expressed in both cortical regions and formed strong gene networks with biological processes related to neural plasticity and synaptogenesis, regulated by glutamatergic and GABAergic transmission, neurotrophin signaling, and metabolism. This study suggested integrating genotype and transcriptome with neuroimage data sheds new light on the mechanisms of aging brain.

Brain gray matter changes in type 2 diabetes mellitus: A meta-analysis of whole-brain voxel-based morphometry study

AIMS

We aimed to identify alterations in global gray matter volumes (GMV) and consistent regional abnormalities in T2DM patients via meta-analysis.

METHODS

A systematic search for relevant studies indexed in the PubMed and Embase databases was conducted. A quantitative meta-analysis of volumetric and whole-brain VBM data was conducted using STATA v.12.0 and AES-SDM software packages, respectively.

RESULTS

A total of 15 volumetric studies and five VBM studies of GM in T2DM patients vs. healthy controls (HCs) were identified. The volumetric meta-analysis showed that the GMV of patients with T2DM is lower than in HCs (SMD = -0.56, 95% CI = -0.81 to -0.31, P 0.01). The whole-brain VBM meta-analysis revealed GM reductions in the left superior temporal gyrus, the right middle temporal gyrus, the right rolandic operculum, and the left fusiform gyrus in T2DM patients compared with HCs. Meta-regression analysis showed that Mini-Mental State Examination (MMSE) scores have a positive relationship with GMV in the right insula.

CONCLUSIONS

The results showed a reduced volume of whole and regional GM in T2DM patients, which may indicate a risk for dementia. Further longitudinal research is needed to confirm GM changes, cognitive dysfunction, and their relationship in T2DM.

Repeated transcranial direct current stimulation improves cognitive dysfunction and synaptic plasticity deficit in the prefrontal cortex of streptozotocin-induced diabetic rats

BACKGROUND

Cognitive dysfunction is commonly observed in diabetic patients. We have previously reported that anodal transcranial direct current stimulation (tDCS) over the dorsolateral prefrontal cortex can facilitate visuospatial working memory in diabetic patients with concomitant diabetic peripheral neuropathy and mild cognitive impairment, but the underlying mechanisms remain unclear.

OBJECTIVE

We investigated the cellular mechanisms underlying the effect of tDCS on cognitive decline in streptozotocin (STZ)-induced diabetic rats.

METHODS

STZ-induced diabetic rats were subjected to either repeated anodal tDCS or sham stimulation over the medial prefrontal cortex (mPFC). Spatial working memory performance in delayed nonmatch-to-place T maze task (DNMT), the induction of long-term potentiation (LTP) in the mPFC, and dendritic morphology of Golgi-stained pyramidal neurons in the mPFC were assessed.

RESULTS

Repeated applications of prefrontal anodal tDCS improved spatial working memory performance in DNMT and restored the impaired mPFC LTP of diabetic rats. The mPFC of tDCS-treated diabetic rats exhibited higher levels of brain-derived neurotrophic factor (BDNF) protein and N-Methyl-d-aspartate receptor (NMDAR) subunit mRNA and protein compared to sham stimulation group. Furthermore, anodal tDCS significantly increased dendritic spine density on the apical dendrites of mPFC layer V pyramidal cells in diabetic rats, whereas the complexity of basal and apical dendritic trees was unaltered.

CONCLUSIONS

Our findings suggest that repeated anodal tDCS may improve spatial working memory performance in streptozotocin-induced diabetic rats through augmentation of synaptic plasticity that requires BDNF secretion and transcription/translation of NMDARs in the mPFC, and support the therapeutic potential of tDCS for cognitive decline in diabetes mellitus patients.

Extending Inferential Group Analysis in Type 2 Diabetic Patients with Multivariate GLM Implemented in SPM8

Background:

Although voxel based morphometry studies are still the standard for analyzing brain structure, their dependence on massive univariate inferential methods is a limiting factor. A better understanding of brain pathologies can be achieved by applying inferential multivariate methods, which allow the study of multiple dependent variables, e.g. different imaging modalities of the same subject.

Objective:

Given the widespread use of SPM software in the brain imaging community, the main aim of this work is the implementation of massive multivariate inferential analysis as a toolbox in this software package. applied to the use of T1 and T2 structural data from diabetic patients and controls. This implementation was compared with the traditional ANCOVA in SPM and a similar multivariate GLM toolbox (MRM).

Method:

We implemented the new toolbox and tested it by investigating brain alterations on a cohort of twenty-eight type 2 diabetes patients and twenty-six matched healthy controls, using information from both T1 and T2 weighted structural MRI scans, both separately – using standard univariate VBM - and simultaneously, with multivariate analyses.

Results:

Univariate VBM replicated predominantly bilateral changes in basal ganglia and insular regions in type 2 diabetes patients. On the other hand, multivariate analyses replicated key findings of univariate results, while also revealing the thalami as additional foci of pathology.

Conclusion:

While the presented algorithm must be further optimized, the proposed toolbox is the first implementation of multivariate statistics in SPM8 as a user-friendly toolbox, which shows great potential and is ready to be validated in other clinical cohorts and modalities.

Reduced Gray Matter Volume in Patients with Type 2 Diabetes Mellitus

Background and Purpose: Previous studies of voxel-based morphometry (VBM) have found that patients with type 2 diabetes mellitus (T2DM) exhibit gray matter alterations, but these findings are inconsistent and have not been quantitatively reviewed. Therefore, the aim of this study was to conduct a quantitative meta-analysis of VBM studies of patients with T2DM.

Materials and Methods: The seed-based d mapping method was applied to quantitatively estimate the regional gray matter abnormalities in T2DM patients. We also used meta-regression to explore the effects of some demographics and clinical characteristics.

Results: Seven studies, with 8 datasets comprising 530 participants with T2DM and 549 non-T2DM controls, were included. The pooled and subgroup meta-analyses found that T2DM patients showed robustly reduced gray matter in the bilateral superior temporal gyrus, middle temporal gyrus, medial superior frontal gyrus, insula, median cingulate cortex, precuneus cortex and the left lentiform nucleus extending into the parahippocampus. The meta-regression also found that the percentage of female patients with T2DM was negatively associated with gray matter in the right superior temporal gyrus and illness duration was negatively associated with gray matter in the right middle temporal gyrus.

Conclusion: This meta-analysis indicates that T2DM patients have significantly and robustly reduced gray matter mainly in the cortical-striatal-limbic networks, which are associated with human cognition. Thereby implicating this finding in the pathophysiology of cognitive impairment in T2DM patients.

Bipolar disorder and diabetes mellitus: evidence for disease-modifying effects and treatment implications

BACKGROUND

Bipolar disorder refers to a group of chronic psychiatric disorders of mood and energy levels. While dramatic psychiatric symptoms dominate the acute phase of the diseases, the chronic course is often determined by an increasing burden of co-occurring medical conditions. High rates of diabetes mellitus in patients with bipolar disorder are particularly striking, yet unexplained. Treatment and lifestyle factors could play a significant role, and some studies also suggest shared pathophysiology and risk factors.

OBJECTIVE

In this systematic literature review, we explored data around the relationship between bipolar disorder and diabetes mellitus in recently published population-based cohort studies with special focus on the elderly.

METHODS

A systematic search in the PubMed database for the combined terms "bipolar disorder" AND "elderly" AND "diabetes" in papers published between January 2009 and December 2015 revealed 117 publications; 7 studies were large cohort studies, and therefore, were included in our review.

RESULTS

We found that age- and gender- adjusted risk for diabetes mellitus was increased in patients with bipolar disorder and vice versa (odds ratio range between 1.7 and 3.2).

DISCUSSION

Our results in large population-based cohort studies are consistent with the results of smaller studies and chart reviews. Even though it is likely that heterogeneous risk factors may play a role in diabetes mellitus and in bipolar disorder, growing evidence from cell culture experiments and animal studies suggests shared disease mechanisms. Furthermore, disease-modifying effects of bipolar disorder and diabetes mellitus on each other appear to be substantial, impacting both treatment response and outcomes.

CONCLUSIONS

The risk of diabetes mellitus in patients with bipolar disorder is increased. Our findings add to the growing literature on this topic. Increasing evidence for shared disease mechanisms suggests new disease models that could explain the results of our study. A better understanding of the complex relationship between bipolar disorder and diabetes mellitus could lead to novel therapeutic approaches and improved outcomes.

Telmisartan-mediated metabolic profile conferred brain protection in diabetic hypertensive rats as evidenced by magnetic resonance imaging, behavioral studies and histology

Type 2 diabetes and hypertension are associated with cognitive dysfunction that includes pathological changes in brain tissue. It was speculated that the beneficial hypotensive effect of telmisartan, an angiotensin receptor 1 blocker, and its unique hypoglycemic effect due to its PPARγ-activation, could ameliorate the ​ pathological changes in the brain​ that accompany​ these diseases. We examined the effect of telmisartan on brain changes in magnetic resonance imaging (MRI) T2-weighted scans, and behavioral and histological findings in the Cohen-Rosenthal Diabetic Hypertensive (CRDH) rat. Baseline and post-treatment values with telmisartan/vehicle (3 months) of blood pressure, blood glucose levels, behavioral tests, brain MRI scanning and immunohistological staining were obtained. Telmisartan significantly lowered blood pressure and blood glucose levels; induced consistent T2 reduction in specific gray and white regions including hippocampus, corpus callosum, amygdala and cortical regions; and significantly improved performance on behavioral tasks. Immunohistological analysis of the brain revealed significant amelioration of diabetes/hypertension-induced changes in white matter regions and microglia, evidenced by preserved myelin (LBF marker), and improved microglial neuronal markers GFAP, GAP43 and Iba1 expression. In conclusion, the behavioral performance, longitudinal MRI study and histology staining revealed the protective effects of telmisartan on brain microstructure and cognitive function.

Altered Intranetwork and Internetwork Functional Connectivity in Type 2 Diabetes Mellitus With and Without Cognitive Impairment

Type 2 diabetes mellitus (T2DM) is associated with cognitive impairment. We investigated whether alterations of intranetwork and internetwork functional connectivity with T2DM progression exist, by using resting-state functional MRI. MRI data were analysed from 19 T2DM patients with normal cognition (DMCN) and 19 T2DM patients with cognitive impairment (DMCI), 19 healthy controls (HC). Functional connectivity among 36 previously well-defined brain regions which consisted of 5 resting-state network (RSN) systems [default mode network (DMN), dorsal attention network (DAN), control network (CON), salience network (SAL) and sensorimotor network (SMN)] was investigated at 3 levels (integrity, network and connectivity). Impaired intranetwork and internetwork connectivity were found in T2DM, especially in DMCI, on the basis of the three levels of analysis. The bilateral posterior cerebellum, the right insula, the DMN and the CON were mainly involved in these changes. The functional connectivity strength of specific brain architectures in T2DM was found to be associated with haemoglobin A1c (HbA1c), cognitive score and illness duration. These network alterations in intergroup differences, which were associated with brain functional impairment due to T2DM, indicate that network organizations might be potential biomarkers for predicting the clinical progression, evaluating the cognitive impairment, and further understanding the pathophysiology of T2DM.

Type 2 diabetes mellitus is associated with brain atrophy and hypometabolism in the ADNI cohort

OBJECTIVE

We investigated type 2 diabetes mellitus (T2DM) as a risk factor for brain atrophy and glucose hypometabolism in older adults with or at risk of cognitive impairment.

METHODS

Participants with the T2DM were identified from the Alzheimer's Disease Neuroimaging Initiative (ADNI-1/GO/2 cohorts). Analysis of covariance models were used to compare participants with and without T2DM, controlling for potential confounding factors.

RESULTS

Whole brain volume and whole brain [(18)F]-fluorodeoxyglucose (FDG) uptake were significantly different as a function of T2DM status, independent of baseline clinical diagnosis. On post hoc analysis, a lower whole brain volume was seen in participants with both mild cognitive impairment (MCI) and T2DM (n = 76) compared with participants who had MCI but not T2DM (n = 747; p = 0.009). Similarly, mean FDG uptake in gray matter and white matter was lower in participants with both MCI and T2DM (n = 72) than in participants with MCI without T2DM (n = 719; p = 0.04). Subsequent regional analysis revealed that the decreased FDG uptake in participants with both MCI and T2DM was mainly manifested in 3 brain regions: frontal lobe, sensory motor cortex, and striatum.

CONCLUSIONS

T2DM may accelerate cognition deterioration in patients with MCI by affecting glucose metabolism and brain volume.

Positron Emission Tomography Reveals Abnormal Topological Organization in Functional Brain Network in Diabetic Patients

Recent studies have demonstrated alterations in the topological organization of structural brain networks in diabetes mellitus (DM). However, the DM-related changes in the topological properties in functional brain networks are unexplored so far. We therefore used fluoro-D-glucose positron emission tomography (FDG-PET) data to construct functional brain networks of 73 DM patients and 91 sex- and age-matched normal controls (NCs), followed by a graph theoretical analysis. We found that both DM patients and NCs had a small-world topology in functional brain network. In comparison to the NC group, the DM group was found to have significantly lower small-world index, lower normalized clustering coefficients and higher normalized characteristic path length. Moreover, for diabetic patients, the nodal centrality was significantly reduced in the right rectus, the right cuneus, the left middle occipital gyrus, and the left postcentral gyrus, and it was significantly increased in the orbitofrontal region of the left middle frontal gyrus, the left olfactory region, and the right paracentral lobule. Our results demonstrated that the diabetic brain was associated with disrupted topological organization in the functional PET network, thus providing functional evidence for the abnormalities of brain networks in DM.

Alzheimer's like brain changes correlate with low adiponectin plasma levels in type 2 diabetic patients

AIM

To study the association between adiponectin plasma levels, and gray matter brain volume and cerebral glucose metabolism in a group of type 2 diabetes patients.

METHODS

We studied 25 type 2 diabetes patients and 25 age- and gender-matched healthy control participants. Biochemical analysis and structural cerebral magnetic resonance imaging, including voxel-based morphometry and (18)-fluorodeoxyglucose positron emission tomography, were performed. The gray matter volumes and metabolism changes were analyzed using statistical parametric mapping (SPM8).

RESULTS

Lower levels of adiponectin correlated with a lower gray matter volume in temporal regions and with reduced cerebral glucose metabolism in temporal regions (p<0.001), adjusted for age, gender, education, and the presence of at least one epsilon 4 allele for the apolipoprotein E (APOEε4 genotype).

CONCLUSIONS

Positive correlations between adiponectin plasma levels and both gray matter volume and cerebral glucose metabolism were found, predominantly in temporal regions, as in Alzheimer's disease. Adiponectin might be a biomarker for the cognitive decline associated with type 2 diabetic patients.

Regional Brain Glucose Hypometabolism in Young Women with Polycystic Ovary Syndrome: Possible Link to Mild Insulin Resistance

Objective

To investigate whether cerebral metabolic rate of glucose (CMR_glu) is altered in normal weight young women with polycystic ovary syndrome (PCOS) who exhibit mild insulin resistance.

Materials and methods

Seven women with PCOS were compared to eleven healthy female controls of similar age, education and body mass index. Regional brain glucose uptake was quantified using FDG with dynamic positron emission tomography and magnetic resonance imaging, and its potential relationship with insulin resistance assessed using the updated homeostasis model assessment (HOMA2-IR). A battery of cognitive tests was administered to evaluate working memory, attention and executive function.

Results

The PCOS group had 10% higher fasting glucose and 40% higher HOMA2-IR (p ≤ 0.035) compared to the Controls. The PCOS group had 9–14% lower CMR_glu in specific regions of the frontal, parietal and temporal cortices (p ≤ 0.018). A significant negative relation was found between the CMR_glu and HOMA2-IR mainly in the frontal, parietal and temporal cortices as well as in the hippocampus and the amygdala (p ≤ 0.05). Globally, cognitive performance was normal in both groups but scores on the PASAT test of working memory tended to be low in the PCOS group.

Conclusions

The PCOS group exhibited a pattern of low regional CMR_glu that correlated inversely with HOMA2-IR in several brain regions and which resembled the pattern seen in aging and early Alzheimer’s disease. These results suggest that a direct association between mild insulin resistance and brain glucose hypometabolism independent of overweight or obesity can exist in young adults in their 20s. Further investigation of the influence of insulin resistance on brain glucose metabolism and cognition in younger and middle-aged adults is warranted.

The roles of lipid and glucose metabolism in modulation of β-amyloid, tau, and neurodegeneration in the pathogenesis of Alzheimer disease

Diabetes is a risk factor for Alzheimer disease (AD). Apolipoprotein E (ApoE) and several genes related to AD have recently been identified by genome-wide association studies (GWAS) as being closely linked to lipid metabolism. Lipid metabolism and glucose-energy metabolism are closely related. Here, we review the emerging evidence regarding the roles of lipid and glucose metabolism in the modulation of β-amyloid, tau, and neurodegeneration during the pathogenesis of AD. Disruption of homeostasis of lipid and glucose metabolism affects production and clearance of β-amyloid and tau phosphorylation, and induces neurodegeneration. A more integrated understanding of the interactions among lipid, glucose, and protein metabolism is required to elucidate the pathogenesis of AD and to develop next-generation therapeutic options.

Cerebral alterations of type 2 diabetes mellitus on MRI: A pilot study

This study is to investigate gray matter volume, cortical thickness, and surface area of the brain in patients with type 2 diabetes mellitus (T2DM). High resolution T1-weighted MR images were obtained from eighteen T2DM and seventeen normal controls. All images were processed using our newly developed BrainLab toolbox. Declines of gray matter volume, cortical thickness, and surface area were found in T2DM patients. Significantly reduced ROIs of gray matter volume happened in subcortical gray nuclei (left caudate and right caudate), and significantly reduced ROIs of cortical thickness occurred in temporal lobe (left superior temporal gyrus), parietal lobe (left angular gyrus), and occipital lobe (right superior occipital gyrus, left middle occipital gyrus and right cuneus). Apparently reduced ROIs of surface area were mainly distributed in frontal lobe (right superior frontal gyrus (dorsal) and left paracentral lobule). The findings indicated that T2DM caused brain changes in specific regions. This work revealed neural alterations of T2DM, which had a great significance in early diagnosis of the disease.

Insulin resistance predicts medial temporal hypermetabolism in mild cognitive impairment conversion to Alzheimer disease

Alzheimer disease (AD) is characterized by progressive hypometabolism on [(18)F]-fluorodeoxyglucose positron emission tomography (FDG-PET) scans. Peripheral insulin resistance (IR) increases AD risk. No studies have examined associations between FDG metabolism and IR in mild cognitive impairment (MCI) and AD, as well as MCI conversion to AD. We studied 26 cognitively normal (CN), 194 MCI (39 MCI-progressors, 148 MCI-stable, 2 years after baseline), and 60 AD subjects with baseline FDG-PET from the Alzheimer's Disease Neuroimaging Initiative. Mean FDG metabolism was derived for AD-vulnerable regions of interest (ROIs), including lateral parietal and posteromedial cortices, medial temporal lobe (MTL), hippocampus, and ventral prefrontal cortices (vPFC), as well as postcentral gyrus and global cerebrum control regions. The homeostasis model assessment of IR (HOMA-IR) was used to measure IR. For AD, higher HOMA-IR predicted lower FDG in all ROIs. For MCI-progressors, higher HOMA-IR predicted higher FDG in the MTL and hippocampus. Control regions showed no associations. Higher HOMA-IR predicted hypermetabolism in MCI-progressors and hypometabolism in AD in medial temporal regions. Future longitudinal studies should examine the pathophysiologic significance of the shift from MTL hyper- to hypometabolism associated with IR.

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.

Brain alterations and clinical symptoms of dementia in diabetes: aβ/tau-dependent and independent mechanisms

Emerging evidence suggests that diabetes affects cognitive function and increases the incidence of dementia. However, the mechanisms by which diabetes modifies cognitive function still remains unclear. Morphologically, diabetes is associated with neuronal loss in the frontal and temporal lobes including the hippocampus, and aberrant functional connectivity of the posterior cingulate cortex and medial frontal/temporal gyrus. Clinically, diabetic patients show decreased executive function, information processing, planning, visuospatial construction, and visual memory. Therefore, in comparison with the characteristics of AD brain structure and cognition, diabetes seems to affect cognitive function through not only simple AD pathological feature-dependent mechanisms but also independent mechanisms. As an Aβ/tau-independent mechanism, diabetes compromises cerebrovascular function, increases subcortical infarction, and might alter the blood-brain barrier. Diabetes also affects glucose metabolism, insulin signaling, and mitochondrial function in the brain. Diabetes also modifies metabolism of Aβ and tau and causes Aβ/tau-dependent pathological changes. Moreover, there is evidence that suggests an interaction between Aβ/tau-dependent and independent mechanisms. Therefore, diabetes modifies cognitive function through Aβ/tau-dependent and independent mechanisms. Interaction between these two mechanisms forms a vicious cycle.