Brain functional alterations in Type 2 Diabetes - A systematic review of fMRI studies

Less Is Better: Single-Digit Brain Functional Connections Predict T2DM and T2DM-Induced Cognitive Impairment

Type 2 diabetes mellitus (T2DM) leads to a higher risk of brain damage and adversely affects cognition. The underlying neural mechanism of T2DM-induced cognitive impairment (T2DM-CI) remains unclear. This study proposes to identify a small number of dysfunctional brain connections as imaging biomarkers, distinguishing between T2DM-CI, T2DM with normal cognition (T2DM-NC), and healthy controls (HC). We have recruited 22 T2DM-CI patients, 31 T2DM-NC patients, and 39 HCs. The structural Magnetic Resonance Imaging (MRI) and resting state fMRI images are acquired, and neuropsychological tests are carried out. Amplitude of low frequency fluctuations (ALFF) is analyzed to identify impaired brain regions implicated with T2DM and T2DM-CI. The functional network is built and all connections connected to impaired brain regions are selected. Subsequently, L₁-norm regularized sparse canonical correlation analysis and sparse logistic regression are used to identify discriminative connections and Support Vector Machine is trained to realize three two-category classifications. It is found that single-digit dysfunctional connections predict T2DM and T2DM-CI. For T2DM-CI versus HC, T2DM-NC versus HC, and T2DM-CI versus T2DM-NC, the number of connections is 6, 7, and 5 and the area under curve (AUC) can reach 0.912, 0.901, and 0.861, respectively. The dysfunctional connection is mainly related to Default Model Network (DMN) and long-distance links. The strength of identified connections is significantly different among groups and correlated with cognitive assessment score (p < 0.05). Via ALFF analysis and further feature selection algorithms, a small number of dysfunctional brain connections can be identified to predict T2DM and T2DM-CI. These connections might be the imaging biomarkers of T2DM-CI and targets of intervention.

Aberrant Brain Functional Connectivity Strength and Effective Connectivity in Patients with Type 2 Diabetes Mellitus

Alterations of brain functional connectivity in patients with type 2 diabetes mellitus (T2DM) have been reported by resting-state functional magnetic resonance imaging studies, but the underlying precise neuropathological mechanism remains unclear. This study is aimed at investigating the implicit alterations of functional connections in T2DM by integrating functional connectivity strength (FCS) and Granger causality analysis (GCA) and further exploring their associations with clinical characteristics. Sixty T2DM patients and thirty-three sex-, age-, and education-matched healthy controls (HC) were recruited. Global FCS analysis of resting-state functional magnetic resonance imaging was performed to explore seed regions with significant differences between the two groups; then, GCA was applied to detect directional effective connectivity (EC) between the seeds and other brain regions. Correlations of EC with clinical variables were further explored in T2DM patients. Compared with HC, T2DM patients showed lower FCS in the bilateral fusiform gyrus, right superior frontal gyrus (SFG), and right postcentral gyrus, but higher FCS in the right supplementary motor area (SMA). Moreover, altered directional EC was found between the left fusiform gyrus and bilateral lingual gyrus and right medial frontal gyrus (MFG), as well as between the right SFG and bilateral frontal regions. In addition, triglyceride, insulin, and plasma glucose levels were correlated with the abnormal EC of the left fusiform, while disease duration and cognitive function were associated with the abnormal EC of the right SFG in T2DM patients. These results suggest that T2DM patients show aberrant brain function connectivity strength and effective connectivity which is associated with the diabetes-related metabolic characteristics, disease duration, and cognitive function, providing further insights into the complex neural basis of diabetes.

Neurovascular coupling alterations in type 2 diabetes: a 5-year longitudinal MRI study

INTRODUCTION

Respective alterations in resting-state brain neural activity and cerebral blood flow (CBF) in type 2 diabetes mellitus (T2DM) have been reported. However, their coupling alteration in T2DM remains largely unknown.

RESEARCH DESIGN AND METHODS

Twenty-seven patients with T2DM aged 40-67 years and 36 well-matched healthy controls (HCs) underwent resting-state functional MRI (rs-fMRI) and arterial spin labeling (ASL) scans at two time points with a 5-year interval. Regional homogeneity (ReHo) and CBF were calculated from rs-fMRI and ASL, respectively. The standardized ReHo:CBF ratio (mReHo:mCBF ratio), the spontaneous neuronal activity per unit CBF supply, was compared between the two time points. Relationships between the mReHo:mCBF ratio and memory performance were analyzed.

RESULTS

Over 5 years, decreased mReHo:mCBF ratios in patients with T2DM were mainly distributed in four regions, among which the left insula exhibited more severely decreased mReHo:mCBF ratio in patients with T2DM than in HCs, while the left postcentral gyrus, the right Rolandic operculum, and the right precentral gyrus showed no significant intergroup difference. Correlations between the mReHo:mCBF ratio and memory performance were also found in patients with T2DM.

CONCLUSIONS

This study suggests that T2DM may accelerate neurovascular coupling impairment in specific brain regions (the left insula), contributing to memory decline. This study implies that the mReHo:mCBF ratio is a potential imaging marker for detecting neurovascular changes.

Using multimodal MRI to investigate alterations in brain structure and function in the BBZDR/Wor rat model of type 2 diabetes

BACKGROUND

This is an exploratory study using multimodal magnetic resonance imaging (MRI) to interrogate the brain of rats with type 2 diabetes (T2DM) as compared to controls. It was hypothesized there would be changes in brain structure and function that reflected the human disorder, thus providing a model system by which to follow disease progression with noninvasive MRI.

METHODS

The transgenic BBZDR/Wor rat, an animal model of T2MD, and age-matched controls were studied for changes in brain structure using voxel-based morphometry, alteration in white and gray matter microarchitecture using diffusion weighted imaging with indices of anisotropy, and functional coupling using resting-state BOLD functional connectivity. Images from each modality were registered to, and analyzed, using a 3D MRI rat atlas providing site-specific data on over 168 different brain areas.

RESULTS

There was an overall reduction in brain volume focused primarily on the somatosensory cortex, cerebellum, and white matter tracts. The putative changes in white and gray matter microarchitecture were pervasive affecting much of the brain and not localized to any region. There was a general increase in connectivity in T2DM rats as compared to controls. The cerebellum presented with strong functional coupling to pons and brainstem in T2DM rats but negative connectivity to hippocampus.

CONCLUSION

The neuroradiological measures collected in BBBKZ/Wor rats using multimodal imaging methods did not reflect those reported for T2DB patients in the clinic. The data would suggest the BBBKZ/Wor rat is not an appropriate imaging model for T2DM.

Altered Cerebellar-Cerebral Circuits in Patients With Type 2 Diabetes Mellitus

The role of the cerebellum in type 2 diabetes mellitus (T2DM) has been receiving increased attention. However, the functional connectivity (FC) between the cerebellar subregions and the cerebral cortex has not been investigated in T2DM. Therefore, the purpose of this study was to investigate cerebellar-cerebral FC and the relationship between FC and clinical/cognitive variables in patients with T2DM. A total of 34 patients with T2DM and 30 healthy controls were recruited for this study to receive a neuropsychological assessment and undergo resting-state FC. We selected four subregions of the cerebellum (bilateral lobules IX, right and left Crus I/II, and left lobule VI) as regions of interest (ROIs) to examine the differences in cerebellar-cerebral circuits in patients with T2DM compared to healthy controls. Correlation analysis was performed to examine the relationship between FC and clinical/cognitive variables in the patients. Compared to healthy controls, patients with T2DM showed significantly decreased cerebellar-cerebral FC in the default-mode network (DMN), executive control network (ECN), and visuospatial network (VSN). In the T2DM group, the FC between the left cerebellar lobule VI and the right precuneus was negatively correlated with the Trail Making Test A (TMT-A) score (r = −0.430, P = 0.013), after a Bonferroni correction. In conclusion, patients with T2DM have altered FC between the cerebellar subregions and the cerebral networks involved in cognitive and emotional processing. This suggests that a range of cerebellar-cerebral circuits may be involved in the neuropathology of T2DM cognitive dysfunction.

Reduced regional homogeneity and neurocognitive impairment in patients with moderate-to-severe obstructive sleep apnea

BACKGROUND

Neurocognitive dysfunction and abnormal regional homogeneity (ReHo) have been reported in patients with obstructive sleep apnea (OSA). However, little is known about whether brain functional alteration could be used to differentiate from healthy controls (HCs) and its correlation with neurocognitive impairment.

METHODS

Thirty-three treatment-naive patients with moderate-to-severe OSA and 22 HCs with matched age, sex and education underwent the evaluation of Epworth sleepiness scale, neurocognitive function, full night polysomnography and resting-state functional magnetic resonance imaging scan. ReHo, support vector machine, and correlation with neurocognitive function were administrated to analyze the data.

RESULTS

Compared with HCs, patients with OSA showed decreased ReHo in the bilateral superior frontal gyrus (FG), bilateral superior medial prefrontal cortex (PFC)/right supplementary motor area (SMA), left middle FG, and right precentral/postcentral gyrus. Negative correlations were observed between the ReHo values in the left superior FG/middle FG and apnea hypopnea index, oxygen desaturation index in the OSA group. The scores of Stroop word test, Stroop color-word test, symbol coding test were all negatively correlated with the ReHo values in the right precentral gyrus/postcentral gyrus in patients. Scores of the animal naming fluency test were positively correlated with the ReHo values in the left superior FG/middle FG in patients. Moreover, support vector machine analysis showed the ReHo values in the left superior FG/middle FG or bilateral superior medial PFC/right SMA both could discriminate patients from HCs with good accuracies, sensitivities, and specificities (85.45%, 87.88%, 81.82% and 81.82%, 84.85%, 77.27%, respectively).

CONCLUSION

Dysfunction in the frontal lobe is a potentially pivotal neuro-pathophysiological mechanism of neurocognitive impairment in patients with moderate-to-severe OSA. And significantly lower ReHo values in the left superior FG/middle FG and/or superior medial PFC/SMA are promising imaging biomarkers to discriminate moderate-to-severe patients with OSA from HCs.

Altered functional connectivity of brain regions based on a meta-analysis in patients with T2DM: A resting-state fMRI study

OBJECTIVE

To explore the neural mechanisms of brain impairment in type 2 diabetes mellitus (T2DM), abnormal changes to the functional connections between brain regions in the resting state were investigated based on a meta-analysis.

METHODS

Resting-state functional magnetic resonance imaging (fMRI) and neuropsychological assessment were performed on 38 patients with T2DM and 33 healthy controls (HCs). Functional connectivity between regions based on a meta-analysis and other voxels in the brain was calculated and compared between the two groups using a two-sample t test. A correlation analysis was conducted between clinical/cognitive variables and functional connection values from the regions with significant differences in the above comparison.

RESULTS

Patients in the T2DM group showed a significantly decreased functional connection between the right posterior cerebellum and the right middle/inferior occipital gyrus, left middle temporal gyrus, left superior frontal gyrus, left middle frontal gyrus, left insula, left precuneus, and right paracentral lobule/left precuneus when compared with HC group. The functional connection values between the right insula and left medial frontal gyrus, left supplementary motor area, and between the left lingual gyrus and right middle/inferior occipital gyrus in patients with T2DM were significantly decreased. Moreover, the functional connection values between the right posterior cerebellum and left middle frontal gyrus, and between the right posterior cerebellum and left precuneus were negatively correlated with HbA1c in the T2DM group (r = -.356, p = .03; r = -.334, p = .043).

CONCLUSIONS

Our study showed a wide range of cerebellar-cerebral circuit abnormalities in patients with T2DM, which provides a new direction to investigate the neuropathological mechanisms of T2DM from the perspective of the cerebellum.

Potential Biochemical Mechanisms of Brain Injury in Diabetes Mellitus

The goal of this review was to summarize current biochemical mechanisms of and risk factors for diabetic brain injury. We mainly summarized mechanisms published in the past three years and focused on diabetes induced cognitive impairment, diabetes-linked Alzheimer's disease, and diabetic stroke. We think there is a need to conduct further studies with increased sample sizes and prolonged period of follow-ups to clarify the effect of DM on brain dysfunction. Additionally, we also think that enhancing experimental reproducibility using animal models in conjunction with application of advanced devices should be considered when new experiments are designed. It is expected that further investigation of the underlying mechanisms of diabetic cognitive impairment will provide novel insights into therapeutic approaches for ameliorating diabetes-associated injury in the brain.

Association of Educational Attainment With Adiposity, Type 2 Diabetes, and Coronary Artery Diseases: A Mendelian Randomization Study

Background: Observational studies showed that educational attainment (EA) is associated with cardiometabolic diseases, but the long interval between exposure and outcome makes it difficult to infer causality. We herein used Mendelian randomization (MR) to examine the causal effects of EA on adiposity, type 2 diabetes (T2D), and coronary artery disease (CAD).

Methods: A two-sample MR analysis was conducted using genome-wide association study (GWAS) summary statistics. Seventy-four instrumental variables (IVs) were used to determine the causal effect of EA on cardiometabolic diseases. Sensitivity analyses were also performed to detect the pleiotropy of the IVs.

Results: Using the MR approach, we found that each additional year in EA is associated with a reduction in the body mass index (BMI) (β −0.17 [95% CI −0.23, −0.10], P = 8.85 × 10⁻⁷), a 39% reduction in the odds of having T2D (OR 0.61 [95% CI 0.50, 0.75], P = 1.16 × 10⁻⁶), and a 36% reduction in the odds of having CAD (OR 0.64 [95% CI 0.55, 0.75], P = 2.38 × 10⁻⁸) at the Bonferroni-adjusted level of significance.

Conclusion: Our findings suggest a causal role of EA on the cardiometabolic diseases including adiposity, T2D, and CAD.

Association between diabetes and cognitive function at baseline in the Brazilian Longitudinal Study of Adult Health (ELSA- Brasil)

Diabetes has been associated with cognitive changes and an increased risk of vascular dementia and Alzheimer’s disease, but it is unclear whether there are associations between diabetes and early alterations in cognitive performance. The present study consisted of a cross-section analysis of 14,444 participants aged 35–74 years and from a developing country at baseline in the Brazilian Longitudinal Study of Adult Health (ELSA–Brasil); these participants were recruited between 2008 and 2010. We investigated whether there was an association between diabetes and early changes in the cognitive performance of this Brazilian population. To assess cognitive domains, we used the word-list learning, word-list delayed recall and word recognition tests along. Phonemic verbal fluency tests included semantic phonemic test (animals) and a phonemic test (words beginning with the letter F). Executive functions associated with attention, concentration and psychomotor speed were evaluated using the Trail Making Test B. The exposure variable in the study was defined as diabetes. Multiple linear regression was used to estimate the association between diabetes and cognitive performance. The results were adjusted for age, sex, education, hypertension, coronary disease, depression, physical activity, smoking, alcohol consumption, and the cholesterol/HDL-C ratio. We found a significant association between diabetes and decreased memory, language and executive function (attention, concentration and psychomotor speed) performance in this population from a country with a distinct epidemiological profile, even after adjusting for the main intervening variables.

Bis(ethylmaltolato)oxidovanadium(iv) inhibited the pathogenesis of Alzheimer's disease in triple transgenic model mice

Vanadium compounds have been reported to mimic the anti-diabetes effects of insulin on rodent models, but their effects on Alzheimer's disease (AD) have rarely been explored. In this paper, 9-month-old triple transgenic AD model mice (3×Tg-AD) received bis(ethylmaltolato)oxidovanadium(iv) (BEOV) at doses of 0.2 mmol L^-1 (68.4 μg mL^-1) and 1.0 mmol L^-1 (342 μg mL^-1) for 3 months. BEOV at both doses was found to improve contextual memory and spatial learning in AD mice. It also improved glucose metabolism and protected neuronal synapses in the AD brain, as evidenced respectively by ¹⁸F-labeled fluoro-deoxyglucose positron emission tomography (¹⁸F-FDG-PET) scanning and by transmission electron microscopy. Inhibitory effects of BEOV on β-amyloid (Aβ) plaques and neuronal impairment in the cortex and hippocampus of fluorescent AD mice were visualized three-dimensionally by applying optical clearing technology to brain slices before confocal laser scanning microscopy. Western blot analysis semi-quantitatively revealed the altered levels of Aβ₄₂ in the brains of wildtype, AD, and AD treated with 0.2 and 1.0 mmol L^-1 BEOV mice (70.3%, 100%, 83.2% and 56.8% in the hippocampus; 82.4%, 100%, 66.9% and 42% in the cortex, respectively). The mechanism study showed that BEOV increased the expression of peroxisome proliferator-activated receptor γ (PPARγ) (140%, 100%, 142% and 160% in the hippocampus; 167%, 100%, 124% and 133% in the cortex) to inactivate the JAK2/STAT3/SOCS-1 pathway and to block the amyloidogenesis cascade, thus attenuating Aβ-induced insulin resistance in AD models. BEOV also reduced protein tyrosine phosphatase 1B (PTP1B) expression (74.8%, 100%, 76.5% and 53.8% in the hippocampus; 71.8%, 100%, 94.2% and 81.8% in cortex) to promote insulin sensitivity and to stimulate the PI3K/Akt/GSK3β pathway, subsequently reducing tau hyperphosphorylation (phosphorylated tau396 levels were 51.1%, 100%, 56.1% and 50.2% in the hippocampus; 22.2%, 100%, 36.1%, and 24% in the cortex). Our results suggested that BEOV reduced the pathological hallmarks of AD by targeting the pathways of PPARγ and PTP1B in 3×Tg AD mice.

Chikusetsu saponin IVa protects pancreatic β cell against intermittent high glucose-induced injury by activating Wnt/β-catenin/TCF7L2 pathway

Islet β cell mass reduction induced by glucose fluctuation is crucial for the development and progression of T2DM. Chikusetsu saponin IVa (CHS) had protective effects against DM and related injuries. Here we aimed to investigate the role of CHS in β cell injuries and its possible mechanism involved. Isolated rat islets, βTC3 cells and T2DM mice were used in this study. The results showed that CHS restored the secretion activity, promoted β cell survival by increasing β cell proliferation and decreasing apoptosis which induced by intermittent high glucose (IHG). In vivo, CHS protected β cell apoptosis to normalize blood glucose and improve insulin sensitivity in DM mice. Further studies showed that CHS activated Wnt3a signaling, inhibited HBP1, promoted β-catenin nuclear translocation, enhanced expressions of TCF7L2, GIPR and GLP-1R, inhibited p53, p27 and p21. The protective effect of CHS was remarkably suppressed by siRNAs against TCF7L2 or XAV-939 (a Wnt/β-catenin antagonist) in vitro and in β-catenin^-/- mice. In conclusion, we identified a novel role of CHS in protecting β cell survival and regeneration by mechanisms involving the activation of Wnt3a/β-catenin/TCF7L2 signaling. Our results indicated the potential value of CHS as a possible intervention drug for T2DM.

Glucose Fluctuations Are Linked to Disrupted Brain Functional Architecture and Cognitive Impairment

BACKGROUND

Type 2 diabetes mellitus (T2DM) accelerates cognitive decline, which is believed to be triggered by aberrant neural activity.

OBJECTIVE

To explore how glucose fluctuations impact brain functional architecture and cognition in T2DM patients.

METHODS

T2DM patients were divided according to glycemic variability, forming two categories: patients with fluctuating glucose levels and patients with stable glucose levels. Degree centrality (DC) was calculated within the cerebral gray matter of each participant and was compared among the two patient groups and a healthy control group. The relationships between glucose fluctuations and aberrant DC and cognitive performance, as well as the relationship between aberrant DC and cognitive performance, were further explored.

RESULTS

Compared with T2DM patients with stable glucose levels, T2DM patients with fluctuating glucose levels exhibited significantly worse performance on the Montreal Cognitive Assessment, Trail Making Test-B (TMT-B), and verbal fluency test (VFT), as well as significant decreases in DC in certain regions, most of which were within the default mode network. In the combined T2DM group, the mean amplitude of glycemic excursions (MAGE) was positively correlated with TMT-B scores and negatively correlated with VFT scores. Moreover, the MAGE was negatively correlated with DC in the left medial prefrontal cortex (mPFC). In addition, TMT-B scores were negatively correlated with reduced DC in the left mPFC.

CONCLUSION

These findings further contribute to the mounting evidence of the effects of glycemic variability on the diabetic brain. Tightened control of glucose fluctuations might prevent cognitive decline and changes in brain functional architecture in T2DM individuals.

Brain microstructural abnormalities in type 2 diabetes mellitus: A systematic review of diffusion tensor imaging studies

Type 2 diabetes mellitus (T2DM) is associated with deficits in the structure and function of the brain. Diffusion tensor imaging (DTI) is a highly sensitive method for characterizing cerebral tissue microstructure. Using PRISMA guidelines, we identified 29 studies which have demonstrated widespread brain microstructural impairment and topological network disorganization in patients with T2DM. Most consistently reported structures with microstructural abnormalities were frontal, temporal, and parietal lobes in the lobar cluster; corpus callosum, cingulum, uncinate fasciculus, corona radiata, and internal and external capsules in the white matter cluster; thalamus in the subcortical cluster; and cerebellum. Microstructural abnormalities were correlated with pathological derangements in the endocrine profile as well as deficits in cognitive performance in the domains of memory, information-processing speed, executive function, and attention. Altogether, the findings suggest that the detrimental effects of T2DM on cognitive functions might be due to microstructural disruptions in the central neural structures.

Theaflavin 3,3'-digallate reverses the downregulation of connexin 43 and autophagy induced by high glucose via AMPK activation in cardiomyocytes

Theaflavin 3,3'-digallate (TF3), is reported to protect cardiomyocytes from lipotoxicity and reperfusion injury. However, the role of TF3 in the protection of high-glucose injury is still poorly understood. This study investigated the protective effects of TF3 on gap junctions and autophagy in neonatal cardiomyocytes (NRCMs). NRCMs preincubated with high glucose were coincubated with TF3. The expression of connexins and autophagy-related proteins was determined. The functioning of gap-junctional intercellular communication (GJIC) was measured by a dye transfer assay. Adenosine monophosphate-activated protein kinase (AMPK) activity was determined by western blot. Moreover, AMPK was activated with aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) or inhibited by AMPKα small interfering RNA (siRNA) to explore the role of AMPK in the modulation of connexin 43 (Cx43) and autophagy. Meanwhile, autophagy was activated or blocked to observe the change in Cx43 expression. It was found that the protein expression of Cx43 and autophagy-related proteins was increased in a TF3 dose- and time-dependent manner under high glucose. TF3 also recovered the reduced GJIC function induced by high glucose concentrations. TF3 activated phosphorylated AMPK in a time-dependent way. AMPKα siRNA abrogated the protection of TF3, while AICAR showed similar results compared to the TF3 treatment. Meanwhile, autophagy activation caused decreased Cx43, while cotreatment with baf A1 enhanced Cx43 expression further compared with the TF3 treatment alone under high glucose. We concluded that TF3 partly reversed the inhibition of Cx43 expression and autophagy induced by high glucose in NRCMs, partly by restoring AMPK activity. Inhibition of autophagy might be protective by preserving Cx43 expression in NRCMs stimulated by high glucose.

Compensatory Hippocampal Connectivity in Young Adults With Early-Stage Type 2 Diabetes

CONTEXT

Middle-aged to elderly patients with type 2 diabetes mellitus (T2DM) exhibit reduced functional connectivity and brain atrophy underlying cognitive decrements; however, little is known about brain abnormalities in young patients.

OBJECTIVE

To detect brain anatomical and functional changes in young patients with T2DM during the early disease stage.

DESIGN

Case-control study.

SETTING

Tertiary referral hospital.

PARTICIPANTS

Thirty-five young patients with T2DM (<40 years of age) with no detectable microangiopathy and 32 nondiabetic control subjects.

INTERVENTION

None.

MAIN OUTCOME MEASURES

Subjects underwent neuropsychological assessments and structural and resting-state functional MRI. Both voxel-based morphometry and resting-state functional connectivity analyses were performed.

RESULTS

No significant differences in brain volume were observed between the patients with T2DM and the controls after controlling for age, sex, education, and body mass index. Compared with the controls, the patients showed greater connectivity of the left hippocampus with the left inferior frontal gyrus and the left inferior parietal lobule. Moreover, the enhanced functional connectivity of left hippocampus with the left inferior frontal gyrus significantly correlated with disease severity (urinary albumin-to-creatinine ratio) (r = 0.613, P < 0.001) and executive function (completion time of Stroop Color and Word Test) (r = -0.461, P = 0.005) after false discovery rate correction.

CONCLUSIONS

Our findings suggest an adaptive compensation of brain function to counteract the insidious cognitive decrements during the early stage of T2DM. Additionally, the functional alterations occurring before changes in brain structure and peripheral microangiopathy might serve as early biomarkers related to cognitive decrements.

Altered Brain Regional Homogeneity in First-Degree Relatives of Type 2 Diabetics: A functional MRI Study

OBJECTIVE

This study aimed to investigate regional homogeneity in the first-: degree relatives of type 2 diabetes patients.

METHODS

Seventy-eight subjects, including 26 type 2 diabetes patients, 26 first-: degree relatives, and 26 healthy controls, were assessed. All participants underwent resting-state functional magnetic resonance imaging scanning. The estimated regional homogeneity value was used to evaluate differences in brain activities.

RESULTS

In first-: degree relatives, we observed significantly decreased regional homogeneity in the left anterior cingulate cortex, left insula, and bilateral temporal lobes, and increased regional homogeneity in the left superior frontal gyrus, right anterior cingulate cortex, and bilateral posterior cingulate cortex compared to healthy controls. In type 2 diabetes patients, we detected altered regional homogeneity in the left anterior cingulate cortex, left insula, bilateral posterior cingulate cortex, and several other brain regions compared to healthy controls. Both first-: degree relatives and type 2 diabetes patients showed decreased regional homogeneity in the left superior temporal gyrus, right middle temporal gyrus, left anterior cingulate cortex, left insula, and increased regional homogeneity in the left superior frontal gyrus and bilateral posterior cingulate cortex.

CONCLUSION

These findings suggest that altered regional homogeneity in the left anterior cingulate cortex, left insula, left superior frontal gyrus, bilateral posterior cingulate cortex, and bilateral temporal lobes might be a neuroimaging biomarker of type 2 diabetes -: related brain dysfunction.

Sweet Mitochondria: A Shortcut to Alzheimer's Disease

A growing body of evidence supports a clear association between Alzheimer's disease and diabetes and several mechanistic links have been revealed. This paper is mainly devoted to the discussion of the role of diabetes-associated mitochondrial defects in the pathogenesis of Alzheimer's disease. The research experience and views of the author on this subject will be highlighted.

Disturbed neurovascular coupling in type 2 diabetes mellitus patients: Evidence from a comprehensive fMRI analysis

Background

Previous studies presumed that the disturbed neurovascular coupling to be a critical risk factor of cognitive impairments in type 2 diabetes mellitus (T2DM), but distinct clinical manifestations were lacked. Consequently, we decided to investigate the neurovascular coupling in T2DM patients by exploring the MRI relationship between neuronal activity and the corresponding cerebral blood perfusion.

Methods

Degree centrality (DC) map and amplitude of low-frequency fluctuation (ALFF) map were used to represent neuronal activity. Cerebral blood flow (CBF) map was used to represent cerebral blood perfusion. Correlation coefficients were calculated to reflect the relationship between neuronal activity and cerebral blood perfusion.

Results

At the whole gray matter level, the manifestation of neurovascular coupling was investigated by using 4 neurovascular biomarkers. We compared these biomarkers and found no significant changes. However, at the brain region level, neurovascular biomarkers in T2DM patients were significantly decreased in 10 brain regions. ALFF-CBF in left hippocampus and fractional ALFF-CBF in left amygdala were positively associated with the executive function, while ALFF-CBF in right fusiform gyrus was negatively related to the executive function. The disease severity was negatively related to the memory and executive function. The longer duration of T2DM was related to the milder depression, which suggests T2DM-related depression may not be a physiological condition but be a psychological condition.

Conclusion

Correlations between neuronal activity and cerebral perfusion maps may be a method for detecting neurovascular coupling abnormalities, which could be used for diagnosis in the future.

Trial registry number: This study has been registered in ClinicalTrials.gov (NCT02420470) on April 2, 2015 and published on July 29, 2015.

•

Multi-modal MRI is a method to reflect neurovascular coupling condition.

•

Neurovascular coupling dysfunction was found in diabetics.

•

The memory, executive function and emotion were disrupted in diabetics.

•

The limbic system, basal ganglia, and prefrontal lobe was damaged in diabetics.

Youth-Onset Type 2 Diabetes and the Developing Brain

PURPOSE OF REVIEW

This review describes the literature evaluating the potential adverse effects of youth-onset type 2 diabetes on the developing brain. A summary of recently published articles and the current state of knowledge are covered succinctly in this manuscript.

RECENT FINDINGS

Current literature suggests both cognitive and brain structural differences are found in youth with type 2 diabetes. Studies have shown poorer scores in a number of neurocognitive domains, particularly in areas of executive functioning and memory. Additionally, imaging studies have found differences in brain gray matter volume, white matter volume, and microstructural integrity. These findings are largely consistent with the adult literature. Youth with type 2 diabetes demonstrate lower cognitive scores and structural brain differences. Although causality has not yet been established, these findings are important because these individuals are still undergoing neurodevelopmental maturation.

Changes in default mode network connectivity in different glucose metabolism status and diabetes duration

Aims/hypotheses

It is now generally accepted that diabetes increases the risk for cognitive impairment, but the precise mechanisms are poorly understood. In recent years, resting-state functional magnetic resonance imaging (rs-fMRI) is increasingly used to investigate the neural basis of cognitive dysfunction in type 2 diabetes (T2D) patients. Alterations in brain functional connectivity may underlie diabetes-related cognitive dysfunction and brain damage. The aim of this study was to investigate the changes in default mode network (DMN) connectivity in different glucose metabolism status and diabetes duration.

Methods

We used a seed-based fMRI analysis to investigate positive and negative DMN connectivity in four groups (39 subjects with normal glucose metabolism [NGM], 23 subjects with impaired glucose metabolism [IGM; i.e., prediabetes], 59 T2D patients with a diabetes duration of <10 years, and 24 T2D patients with a diabetes duration of ≥10 years).

Results

Negative DMN connectivity increased and then regressed with deteriorating glucose metabolism status and extending diabetes duration. DMN connectivity showed a significant correlation with diabetes duration.

Conclusion/interpretation

This study suggests that DMN connectivity may exhibit distinct patterns in different glucose metabolism status and diabetes duration, providing some potential neuroimaging evidence for early diagnosis and further understanding of the pathophysiological mechanisms of diabetic brain damage.

•

Subjects include NGM, IGM, and T2D with different glucose metabolism status.

•

DMN connectivity exhibited distinct patterns in different glucose metabolism status.

•

Compensatory enhancement was observed in the negative DMN FC.

•

DMN FC showed a significant correlation with diabetes duration.

Neuroprotection of quercetin on central neurons against chronic high glucose through enhancement of Nrf2/ARE/glyoxalase-1 pathway mediated by phosphorylation regulation

Although dietary flavonoid quercetin alleviates diabetes-associated cognitive decline in rodents, the mechanisms are not clearly clarified. This study was designed to investigate whether quercetin showed neuroprotection on central neurons against chronic high glucose through the enhancement of Nrf2/ARE/glyoxalase 1 (Glo-1) pathway. SH-SY5Y cells were divided into 8 groups: normal glucose, high glucose (HG), osmotic pressure control, solvent control, HG plus low, middle, high concentrations of quercetin, or Nrf2 activator (sulforaphane). After treatment for 72 h, the associated parameters were measured. We found quercetin and sulforaphane increased cell viability, and enhanced Glo-1 functions (Glo-1 activity, the reduced glutathione and advanced glycation end-products levels) as well as Glo-1 protein and mRNA levels in SH-SY5Y cells cultured with HG. Meanwhile, quercetin and sulforaphane activated Nrf2/ARE pathway, reflected by the raised Nrf2 and p-Nrf2 levels, and the elevated protein and mRNA levels of γ-glutamycysteine synthase (γ-GCS), a known target gene of Nrf2/ARE signaling. Moreover, Nrf2/ARE pathway was activated after pretreatment with a PKC activator, p38 MAPK inhibitor, or GSK-3β inhibitor under the condition of HG, and quercetin addition further strengthened this pathway; however, PKC inhibition or GSK-3β activation pretreatment reversed the effects of quercetin on the protein expression of γ-GCS in the HG condition. In summary, quercetin exerts the neuroprotection by enhancing Glo-1 functions in central neurons under chronic HG condition, which may be mediated by activation of Nrf2/ARE pathway; furthermore, the increased Nrf2 phosphorylation mediated by PKC activation and/or GSK-3β inhibition may involve in the activation of Nrf2/ARE pathway.

WONOEP APPRAISAL: The many facets of epilepsy networks

The brain is a complex system composed of networks of interacting elements, from genes to circuits, whose function (and dysfunction) is not derivable from the superposition of individual components. Epilepsy is frequently described as a network disease, but to date, there is no standardized framework within which network concepts applicable to all levels from genes to whole brain can be used to generate deeper insights into the pathogenesis of seizures or the associated morbidities. To address this shortcoming, the Neurobiology Commission of the International League Against Epilepsy dedicated a Workshop on Neurobiology of Epilepsy (XIV WONOEP 2017) with the aim of formalizing network concepts as they apply to epilepsy and to critically discuss whether and how such concepts could augment current research endeavors. Here, we review concepts and strategies derived by considering epilepsy as a disease of different network hierarchies that range from genes to clinical phenotypes. We propose that the concept of networks is important for understanding epilepsy and is critical for developing new study designs. These approaches could ultimately facilitate the development of novel diagnostic and therapeutic strategies.

Hallmarks of Brain Aging: Adaptive and Pathological Modification by Metabolic States

During aging, the cellular milieu of the brain exhibits tell-tale signs of compromised bioenergetics, impaired adaptive neuroplasticity and resilience, aberrant neuronal network activity, dysregulation of neuronal Ca2+ homeostasis, the accrual of oxidatively modified molecules and organelles, and inflammation. These alterations render the aging brain vulnerable to Alzheimer's and Parkinson's diseases and stroke. Emerging findings are revealing mechanisms by which sedentary overindulgent lifestyles accelerate brain aging, whereas lifestyles that include intermittent bioenergetic challenges (exercise, fasting, and intellectual challenges) foster healthy brain aging. Here we provide an overview of the cellular and molecular biology of brain aging, how those processes interface with disease-specific neurodegenerative pathways, and how metabolic states influence brain health.

Altered Odor-Induced Brain Activity as an Early Manifestation of Cognitive Decline in Patients With Type 2 Diabetes

Type 2 diabetes is reported to be associated with olfactory dysfunction and cognitive decline. However, whether and how olfactory neural circuit abnormalities involve cognitive impairment in diabetes remains uncovered. This study thus aimed to investigate olfactory network alterations and the associations of odor-induced brain activity with cognitive and metabolic parameters in type 2 diabetes. Participants with normal cognition, including 51 patients with type 2 diabetes and 41 control subjects without diabetes, underwent detailed cognitive assessment, olfactory behavior tests, and odor-induced functional MRI measurements. Olfactory brain regions showing significantly different activation between the two groups were selected for functional connectivity analysis. Compared with the control subjects, patients with diabetes demonstrated significantly lower olfactory threshold score, decreased brain activation, and disrupted functional connectivity in the olfactory network. Positive associations of the disrupted functional connectivity with decreased neuropsychology test scores and reduced pancreatic function were observed in patients with diabetes. Notably, the association between pancreatic function and executive function was mediated by olfactory behavior and olfactory functional connectivity. Our results suggested the alteration of olfactory network is present before clinically measurable cognitive decrements in type 2 diabetes, bridging the gap between the central olfactory system and cognitive decline in diabetes.

Disrupted functional connectivity of the amygdala is associated with depressive mood in type 2 diabetes patients

BACKGROUND

Type 2 diabetes mellitus (T2DM) and mood disorders share pathophysiological commonalities in the central nervous system. The purpose of this study was to investigate the alterations in amygdala-based emotional processing circuits in T2DM patients with depressive mood using resting-state functional magnetic resonance imaging (rs-fMRI).

METHODS

T2DM patients with depressive mood (n = 25), T2DM patients without depressive mood (n = 28) and matched healthy controls (n = 25) underwent neuropsychological testing and rs-fMRI scanning. A seed-based correlation analysis was conducted to reveal the altered functional connectivity (FC) of the amygdala. The bilateral amygdala FC was compared among the three groups. Pearson correlation analyses were performed in a voxel-wise manner to investigate the relationship between amygdala FC and the clinical characteristics.

RESULTS

The depressed T2DM patients exhibited the worst performance on the neuropsychological tests among the three groups. Compared to the non-depressed T2DM patients, the depressed T2DM patients showed decreased amygdala FC in the cingulate cortex, inferior frontal gyrus, fusiform gyrus, and precentral gyrus. Moreover, the amygdala FC in the cingulate cortex was associated with the Self-Rating Depression Scale (SDS) score in the T2DM patients.

LIMITATIONS

Cross-sectional design.

CONCLUSIONS

The current study revealed the cognitive changes and alterations in the amygdala-cingulate functional disconnections in T2DM patients with depressive mood, which will advance the understanding of the neural mechanisms underlying depression in T2DM patients.

Dietary influences on cognition

Obesity is a world-wide crisis with profound healthcare and socio-economic implications and it is now clear that the central nervous system (CNS) is a target for the complications of metabolic disorders like obesity. In addition to decreases in physical activity and sedentary lifestyles, diet is proposed to be an important contributor to the etiology and progression of obesity. Unfortunately, there are gaps in our knowledge base related to how dietary choices impact the structural and functional integrity of the CNS. For example, while chronic consumption of hypercaloric diets (increased sugars and fat) contribute to increases in body weight and adiposity characteristic of metabolic disorders, the mechanistic basis for neurocognitive deficits in obesity remains to be determined. In addition, studies indicate that acute consumption of hypercaloric diets impairs performance in a wide variety of cognitive domains, even in normal non-obese control subjects. These results from the clinical and basic science literature indicate that diet can have rapid, as well as long lasting effects on cognitive function. This review summarizes our symposium at the 2017 Society for the Study of Ingestive Behavior (SSIB) meeting that discussed these effects of diet on cognition. Collectively, this review highlights the need for integrated and comprehensive approaches to more fully determine how diet impacts behavior and cognition under physiological conditions and in metabolic disorders like type 2 diabetes mellitus (T2DM) and obesity.