Understanding multifactorial brain changes in type 2 diabetes: a biomarker perspective

Increasing brain glucose uptake by Gypenoside LXXV ameliorates cognitive deficits in a mouse model of diabetic Alzheimer's disease

We have previously reported that Gypenoside LXXV (GP-75), a novel natural PPARγ agonist isolated from Gynostemma pentaphyllum, ameliorated cognitive deficits in db/db mice. In this study, we further investigated the beneficial effects on cognitive impairment in APP/PS1 mice and a mouse model of diabetic AD (APP/PS1xdb/db mice). Interestingly, intragastric administration of GP-75 (40 mg/kg/day) for 3 months significantly attenuated cognitive deficits in APP/PS1 and APP/PS1xdb/db mice. GP-75 treatment markedly reduced the levels of glucose, HbA1c and insulin in serum and improved glucose tolerance and insulin sensitivity in APP/PS1xdb/db mice. Notably, GP-75 treatment decreased the β-amyloid (Aβ) burden, as measured by ¹¹ C-PIB PET imaging. Importantly, GP-75 treatment increased brain glucose uptake as measured by ¹⁸ F-FDG PET imaging. Moreover, GP-75 treatment upregulated PPARγ and increased phosphorylation of Akt (Ser473) and GLUT4 expression levels but decreased phosphorylation of IRS-1 (Ser616) in the hippocampi of both APP/PS1 and APP/PS1xdb/db mice. Furthermore, GP-75-induced increases in GLUT4 membrane translocation in primary hippocampal neurons from APP/PS1xdb/db mice was abolished by cotreatment with the selective PPARγ antagonist GW9662 or the PI3K inhibitor LY294002. In summary, GP-75 ameliorated cognitive deficits in APP/PS1 and APP/PS1xdb/db mice by enhancing glucose uptake via activation of the PPARγ/Akt/GLUT4 signaling pathways.

Association of type 1 diabetes and age at diagnosis of type 2 diabetes with brain volume and risk of dementia in the UK Biobank: A prospective cohort study of community-dwelling participants

AIMS

To investigate the association of type 1 diabetes (T1D) and age at diagnosis of type 2 diabetes (T2D) with brain structure and incident dementia.

METHODS

Our analysis was based on the UK Biobank. We included 1376 participants with diabetes and 2752 randomly selected controls for brain volume analysis, and 25,141 participants with diabetes and 50,282 randomly selected controls for dementia analysis. Brain volume was measured using magnetic resonance imaging. Dementia was identified using hospital inpatient records and mortality register data until January 2021.

RESULTS

T2D diagnosed at a younger age was associated with larger reductions in brain volume. After adjustment for glycated haemoglobin (HbA1c) and other covariates, only T2D diagnosed <50 years was associated with smaller total brain volume (β (95% CI): -14.56 (-24.67, -4.44) ml), and grey (-6.47[-12.75, -0.20] ml) and white matter volumes (-8.08[-14.66, -1.51] ml). Corresponding numbers for total brain, grey matter and white matter volumes associated with T1D were -62.86 (-93.71,-32.01), -34.27 (-53.72, -14.83), and -28.59 (-47.65, -9.52) ml, respectively. During a median follow-up of 11.9 years, 2035 new dementia cases were identified. Younger age at diagnosis of T2D was associated with larger excessive risk of dementia, whereas T2D diagnosed <50 years was associated with the largest hazard ratio (HR) (95% CI: 2.03[1.53-2.69]) in the multivariable analysis. The HR (95% CI) for dementia associated with T1D was 2.08 (1.40-3.09).

CONCLUSION

Individuals with T1D or T2D diagnosed at younger age are at larger excessive risk of brain volume reduction and dementia.

Changes in hemodynamic response function components reveal specific changes in neurovascular coupling in type 2 diabetes

Type 2 Diabetes Mellitus (T2DM) is a metabolic disease that leads to multiple vascular complications with concomitant changes in human neurophysiology, which may lead to long-term cognitive impairment, and dementia. Early impairments of neurovascular coupling can be studied using event-related functional magnetic resonance imaging (fMRI) designs. Here, we aimed to characterize the changes in the hemodynamic response function (HRF) in T2DM to probe components from the initial dip to late undershoot. We investigated whether the HRF morphology is altered throughout the brain in T2DM, by extracting several parameters of the fMRI response profiles in 141 participants (64 patients with T2DM and 77 healthy controls) performing a visual motion discrimination task. Overall, the patients revealed significantly different HRFs, which extended to all brain regions, suggesting that this is a general phenomenon. The HRF in T2DM was found to be more sluggish, with a higher peak latency and lower peak amplitude, relative slope to peak, and area under the curve. It also showed a pronounced initial dip, suggesting that the initial avidity for oxygen is not compensated for, and an absent or less prominent but longer undershoot. Most HRF parameters showed a higher dispersion and variability in T2DM. In sum, we provide a definite demonstration of an impaired hemodynamic response function in the early stages of T2DM, following a previous suggestion of impaired neurovascular coupling. The quantitative demonstration of a significantly altered HRF morphology in separate response phases suggests an alteration of distinct physiological mechanisms related to neurovascular coupling, which should be considered in the future to potentially halt the deterioration of the brain function in T2DM.

Sigma-1 Receptor as a Protective Factor for Diabetes-Associated Cognitive Dysfunction via Regulating Astrocytic Endoplasmic Reticulum-Mitochondrion Contact and Endoplasmic Reticulum Stress

The prevalence of diabetes-associated cognitive dysfunction (DACD) has increased to 13.5%. Dementia, as the most severe DACD, is the second leading cause of death in patients with diabetes mellitus. Hence, the potential mechanisms of DACD for slowing or halting its progression need to be urgently explored. Given that the sigma-1 receptor (Sig-1R), a chaperone protein located in the endoplasmic reticulum (ER)-mitochondrion contact membranes to regulate ER stress (ERS), is associated with cognitive outcomes in neurodegenerative diseases, this study aimed to investigate the role of astrocytic Sig-1R in DACD and its underlying mechanism. Here, we examined the levels of ERS and complement component 3/3a (C3/C3a) from primary astrocytes with different concentrations of glucose and treatment. Subsequently, HT22 neurons were cultured in different astrocyte-conditioned medium, and the expression of synaptic proteins was detected. We constructed type 1 diabetes mellitus (T1DM) model to evaluate the astrocytic Sig-1R mechanism on synapse and cognitive function changes. In vitro, high glucose concentration downregulated Sig-1R and aggravated ERS in astrocytes, resulting in synapse deficits. PRE-084, a high-affinity and selective Sig-1R agonist, inhibited astrocytic ERS and complement cascades and restored synaptic damage, while the Sig-1R antagonist displayed the opposite results. Moreover, C3a receptor antagonist (C3aRA) could mimic the effect of PRE-084 and exerted neuroprotective effects. In vivo, PRE-084 substantially reduced ER-mitochondrion contact, activation of ERS, and C3/C3a secretion in mice with T1DM. Additionally, the synaptic loss and neurobehavioral dysfunction of mice with T1DM were less pronounced in both the PRE-084 and C3aRA treatment groups. These findings demonstrated that Sig-1R activation reduced the astrocytic ER-mitochondrion contact, ERS activation, and complement-mediated synaptic damage in T1DM. This study suggested the mechanisms and potential therapeutic approaches for treating DACD.

Cognition and BDNF levels in prediabetes and diabetes: A mediation analysis of a cross-sectional study

AIM

Clinical and epidemiological studies suggest links between dementias and Type 2 diabetes (T2DM). The underlying mechanisms of diabetes-related cognitive impairment are largely unknown. This study aims to investigate the role of BDNF in cognitive impairment in prediabetes and T2DM.

METHODS

The study included 68 patients with prediabetes (preDM), 96 patients with T2DM, and 65 healthy controls. The cognitive function of the patients was evaluated with the Montreal Cognitive Assessment (MoCA) test and serum BDNF levels were measured by Elisa. The MoCA scores and BDNF levels were compared between diabetes groups after adjusting for age, gender, and education using ANCOVA. The role of BDNF in the diabetes-related cognitive impairment was investigated through mediation analysis.

RESULTS

Patients with T2DM had significantly lower cognitive performance, particularly in memory. Diabetes was found to be a predictor of both cognitive impairment and BDNF levels. A significant increase in serum BDNF levels was observed in patients with T2DM. However, the mediator role of BDNF in the pathology of cognitive impairment in diabetes was not determined.

CONCLUSION

Cognitive impairment is prevalent in patients with T2DM and should be included in routine screening for complications. The results of the mediation analysis suggest that although BDNF is a biomarker affected by T2DM and cognition, it does not play a mediator role between cognitive impairment and diabetes.

Perceptions and responses to cognitive decline in people with diabetes: A systematic review of qualitative studies

Objective

We aimed at summarizing the perceptions and responses to cognitive decline, assessing the disease management, identifying deficiencies and proposing new strategies for improvement in people with diabetes (PWDs).

Methods

A comprehensive search was performed in the following nine databases: PubMed, EMBASE, Web of Science, The Cochrane Library, PsycINFO, CINAHL, WanFang, CNKI, and VIP. The Joanna Briggs Institute (JBI) Critical Appraisal Tool for qualitative research was utilized to evaluate the quality of included studies. Descriptive texts and quotations relating to patient experience were extracted from the included studies and thematically analyzed.

Results

Eight qualitative studies met the inclusion criteria and 2 overarching themes were identified: (1) self-perception of cognitive decline referred to perceived cognitive symptoms, lack of knowledge and, impaired self-management and coping in multiple methods; (2) reported benefits of cognitive interventions referred to how cognitive interventions improved disease management, attitudes and needs of PWDs.

Conclusion

PWDs described misconceptions about their cognitive decline and suffered from them during disease management. This study provides a patient-specific reference for cognitive screening and intervention in PWDs, supporting disease management with cognitive decline in clinical practice.

Insulin Resistance and Cognitive Impairment: Evidence From Neuroimaging

Insulin is a peptide well known for its role in regulating glucose metabolism in peripheral tissues. Emerging evidence from human and animal studies indicate the multifactorial role of insulin in the brain, such as neuronal and glial metabolism, glucose regulation, and cognitive processes. Insulin resistance (IR), defined as reduced sensitivity to the action of insulin, has been consistently proposed as an important risk factor for developing neurodegeneration and cognitive impairment. Although the exact mechanism of IR-related cognitive impairment still awaits further elucidation, neuroimaging offers a versatile set of novel contrasts to reveal the subtle cerebral abnormalities in IR. These imaging contrasts, including but not limited to brain volume, white matter (WM) microstructure, neural function and brain metabolism, are expected to unravel the nature of the link between IR, cognitive decline, and brain abnormalities, and their changes over time. This review summarizes the current neuroimaging studies with multiparametric techniques, focusing on the cerebral abnormalities related to IR and therapeutic effects of IR-targeting treatments. According to the results, brain regions associated with IR pathophysiology include the medial temporal lobe, hippocampus, prefrontal lobe, cingulate cortex, precuneus, occipital lobe, and the WM tracts across the globe. Of these, alterations in the temporal lobe are highly reproducible across different imaging modalities. These structures have been known to be vulnerable to Alzheimer's disease (AD) pathology and are critical in cognitive processes such as memory and executive functioning. Comparing to asymptomatic subjects, results are more mixed in patients with metabolic disorders such as type 2 diabetes and obesity, which might be attributed to a multifactorial mechanism. Taken together, neuroimaging, especially MRI, is beneficial to reveal early abnormalities in cerebral structure and function in insulin-resistant brain, providing important evidence to unravel the underlying neuronal substrate that reflects the cognitive decline in IR. EVIDENCE LEVEL: 5 TECHNICAL EFFICACY: Stage 2.

Magnetic resonance imaging reveals microemboli-mediated pathological changes in brain microstructure in diabetic rats: relevance to vascular cognitive impairment/dementia

Diabetes doubles the risk of vascular cognitive impairment, but the underlying reasons remain unclear. In the present study, we determined the temporal and spatial changes in the brain structure after microemboli (ME) injection using diffusion MRI (dMRI). Control and diabetic rats received cholesterol crystal ME (40-70 µm) injections. Cognitive tests were followed up to 16 weeks, while dMRI scans were performed at baseline and 12 weeks post-ME. The novel object recognition test had a lower d2 recognition index along with a decrease in spontaneous alternations in the Y maze test in diabetic rats with ME. dMRI showed that ME injection caused infarction in two diabetic animals (n=5) but none in controls (n=6). In diabetes, radial diffusivity (DR) was increased while fractional anisotropy (FA) was decreased in the cortex, indicating loss of tissue integrity and edema. In the dorsal hippocampus, mean diffusivity (MD), axial diffusivity (DA), and DR were significantly increased, indicating loss of axons and myelin damage. Histological analyses confirmed more tissue damage and microglial activation in diabetic rats with ME. These results suggest that ME injury and associated cerebrovascular dysfunction are greater in diabetes, which may cause cognitive deficits. Strategies to improve vascular function can be a preventive and therapeutic approach for vascular cognitive impairment.

Altered cortical thickness, degree centrality, and functional connectivity in middle-age type 2 diabetes mellitus

PURPOSE

This study aimed to investigate the changes in brain structure and function in middle-aged patients with type 2 diabetes mellitus (T2DM) using morphometry and blood oxygen level-dependent functional magnetic resonance imaging (BOLD-fMRI).

METHODS

A total of 44 middle-aged patients with T2DM and 45 matched healthy controls (HCs) were recruited. Surface-based morphometry (SBM) was used to evaluate the changes in brain morphology. Degree centrality (DC) and functional connectivity (FC) were used to evaluate the changes in brain function.

RESULTS

Compared with HCs, middle-aged patients with T2DM exhibited cortical thickness reductions in the left pars opercularis, left transverse temporal, and right superior temporal gyri. Decreased DC values were observed in the cuneus and precuneus in T2DM. Hub-based FC analysis of these regions revealed lower connectivity in the bilateral hippocampus and parahippocampal gyrus, left precuneus, as well as left frontal sup.

CONCLUSION

Cortical thickness, degree centrality, as well as functional connectivity were found to have significant changes in middle-aged patients with T2DM. Our observations provide potential evidence from neuroimaging for analysis to examine diabetes-related brain damage.

Increasing brain glucose metabolism by ligustrazine piperazine ameliorates cognitive deficits through PPARγ-dependent enhancement of mitophagy in APP/PS1 mice

PPARγ agonists have been proven to be neuroprotective in vitro and in vivo models of Alzheimer's disease (AD). In the present study, we identified ligustrazine piperazine derivative (LPD) as a novel PPARγ agonist, which was detected by a dual-luciferase reporter assay system. LPD treatment dose-dependently reduced Aβ40 and Aβ42 levels in PC12 cells stably transfected with APP695swe and PSEN1dE9. Intragastric administration of LPD for 3 months dose-dependently reversed cognitive deficits in APP/PS1 mice. LPD treatment substantially decreased hippocampal Aβ plaques in APP/PS1 mice and decreased the levels of Aβ40 and Aβ42 in vivo and in vitro. Moreover, LPD treatment induced mitophagy in vivo and in vitro and increased brain ¹⁸F-FDG uptake in APP/PS1 mice. LPD treatment significantly increased OCR, ATP production, maximal respiration, spare respiratory capacity, and basal respiration in APP/PS1 cells. Mechanistically, LPD treatment upregulated PPARγ, PINK1, and the phosphorylation of Parkin (Ser65) and increased the LC3-II/LC3-I ratio but decreased SQSTM1/p62 in vivo and in vitro. Importantly, all these protective effects mediated by LPD were abolished by cotreatment with the selective PPARγ antagonist GW9662. In summary, LPD could increase brain glucose metabolism and ameliorate cognitive deficits through PPARγ-dependent enhancement of mitophagy in APP/PS1 mice.

White Matter Characteristics of Damage Along Fiber Tracts in Patients with Type 2 Diabetes Mellitus

Purpose

The white matter (WM) of the brain of type 2 diabetes mellitus (T2DM) patients is susceptible to neurodegenerative processes, but the specific types and positions of microstructural lesions along the fiber tracts remain unclear.

Methods

In this study 61 T2DM patients and 61 healthy controls were recruited and underwent diffusion spectrum imaging (DSI). The results were reconstructed with diffusion tensor imaging (DTI) and neurite orientation dispersion and density imaging (NODDI). WM microstructural abnormalities were identified using tract-based spatial statistics (TBSS). Pointwise WM tract differences were detected through automatic fiber quantification (AFQ). The relationships between WM tract abnormalities and clinical characteristics were explored with partial correlation analysis.

Results

TBSS revealed widespread WM lesions in T2DM patients with decreased fractional anisotropy and axial diffusivity and an increased orientation dispersion index (ODI). The AFQ results showed microstructural abnormalities in T2DM patients in specific portions of the right superior longitudinal fasciculus (SLF), right arcuate fasciculus (ARC), left anterior thalamic radiation (ATR), and forceps major (FMA). In the right ARC of T2DM patients, an aberrant ODI was positively correlated with fasting insulin and insulin resistance, and an abnormal intracellular volume fraction was negatively correlated with fasting blood glucose. Additionally, negative associations were found between blood pressure and microstructural abnormalities in the right ARC, left ATR, and FMA in T2DM patients.

Conclusion

Using AFQ, together with DTI and NODDI, various kinds of microstructural alterations in the right SLF, right ARC, left ATR, and FMA can be accurately identified and may be associated with insulin and glucose status and blood pressure in T2DM patients.

Extracellular vesicles mediate the communication of adipose tissue with brain and promote cognitive impairment associated with insulin resistance

Type 2 diabetes with obesity-related insulin resistance as the main manifestation is associated with an increased risk of cognitive impairment. Adipose tissue plays an important role in this process. Here, we demonstrated that adipose tissue-derived extracellular vesicles (EVs) and their cargo microRNAs (miRNAs) mediate inter-organ communication between adipose tissue and the brain, which can be transferred into the brain in a membrane protein-dependent manner and enriched in neurons, especially in the hippocampus. Further investigation suggests that adipose tissue-derived EVs from high-fat diet (HFD)-fed mice or patients with diabetes induce remarkable synaptic loss and cognitive impairment. Depletion of miRNA cargo in these EVs significantly alleviates their detrimental effects on cognitive function. Collectively, these data suggest that targeting adipose tissue-derived EVs or their cargo miRNAs may provide a promising strategy for pharmaceutical interventions for cognitive impairment in diabetes.

Alzheimer’s Disease Polygenic Risk Score Is Not Associated With Cognitive Decline Among Older Adults With Type 2 Diabetes

Objectives

Multiple risk loci for late-onset Alzheimer’s disease (LOAD) have been identified. Type 2 diabetes (T2D) is a risk factor for cognitive decline, dementia and Alzheimer’s disease (AD). We investigated the association of polygenic risk score (PRS) for LOAD with overall cognitive functioning and longitudinal decline, among older adults with T2D.

Methods

The study included 1046 Jewish participants from the Israel Diabetes and Cognitive Decline (IDCD) study, aged ≥ 65 years, diagnosed with T2D, and cognitively normal at baseline. The PRS included variants from 26 LOAD associated loci (at genome-wide significance level), and was calculated with and without APOE. Outcome measures, assessed in 18 months intervals, were global cognition and the specific domains of episodic memory, attention/working memory, executive functions, and language/semantic categorization. Random coefficient models were used for analysis, adjusting for demographic variables, T2D-related characteristics, and cardiovascular factors. Additionally, in a subsample of 202 individuals, we analyzed the association of PRS with the volumes of total gray matter, frontal lobe, hippocampus, amygdala, and white matter hyperintensities. Last, the association of PRS with amyloid beta (Aβ) burden was examined in 44 participants who underwent an 18F-flutemetamol PET scan.

Results

The PRS was not significantly associated with overall functioning or decline in global cognition or any of the specific cognitive domains. Similarly, following correction for multiple testing, there was no association with Aβ burden and other brain imaging phenotypes.

Conclusion

Our results suggest that the cumulative effect of LOAD susceptibility loci is not associated with a greater rate of cognitive decline in older adults with T2D, and other pathways may underlie this link.

Alterations of Cerebral Blood Flow and Its Connectivity in Olfactory-Related Brain Regions of Type 2 Diabetes Mellitus Patients

To investigate the alteration of cerebral blood flow (CBF) and its connectivity patterns in olfactory-related regions of type 2 diabetes mellitus (T2DM) patients using arterial spin labeling (ASL). Sixty-nine patients with T2DM and 63 healthy controls (HCs) underwent ASL scanning using 3.0T magnetic resonance imaging. We compared the CBF values of the olfactory-related brain regions between the two groups and analyzed the correlation between their changes and clinical variables. We also used these regions as seeds to explore the differences in CBF connectivity patterns in olfactory-related brain regions between the T2DM patients and HCs. Compared with the HC group, the CBF of the right orbital part of the inferior frontal gyrus (OIFG), right insula, and bilateral olfactory cortex was decreased in the T2DM patients. Moreover, the duration of the patients was negatively correlated with the CBF changes in the right OIFG, right insula, and right olfactory cortex. The CBF changes in the right OIFG were positively correlated with the Self-Rating Depression Scale scores, those in the right insula were negatively correlated with the max blood glucose of continuous glucose, and those in the right olfactory cortex were negatively correlated with the mean blood glucose of continuous glucose. In addition, the T2DM patients also showed decreased CBF connectivity between the right OIFG and the left temporal pole of the middle temporal gyrus and increased CBF connectivity between the right medial orbital part of the superior frontal gyrus and the right orbital part of the superior frontal gyrus and between the right olfactory cortex and the bilateral caudate and the left putamen. Patients with T2DM have decreased CBF and altered CBF connectivity in multiple olfactory-related brain regions. These changes may help explain why olfactory dysfunction occurs in patients with T2DM, thus providing insights into the neuropathological mechanism of olfactory dysfunction and cognitive decline in T2DM patients.

The Potential Role of Myokines/Hepatokines in the Progression of Neuronal Damage in Streptozotocin and High-Fat Diet-Induced Type 2 Diabetes Mellitus Mice

Background: Diabetes is highly prevalent, and the number of patients with diabetic sarcopenia and cognitive impairment has grown, leading to decreased quality of life. Although the exact mechanisms between sarcopenia and cognitive impairment have not been elucidated, it is speculated that muscle and liver-derived mediators might contribute to brain function. This study examined the molecular mechanisms associated with muscle-brain interaction accompanied by insulin resistance (IR) caused by aberrant energy metabolism via myokines/hepatokines in type 2 diabetes mellitus (T2DM) mice. Methods: T2DM was induced by a high-fat diet and streptozotocin injection. Behavior tests were conducted to analyze grip strength and cognitive function. Histopathological changes in skeletal muscle and brain tissue were examined by hematoxylin and eosin staining and the protein levels of biomarkers related to energy metabolism via myokines/hepatokines were measured by western blot. Results: T2DM caused peripheral and central IR. Furthermore, T2DM led to aberrant energy metabolism through the reduced fibroblast growth factor 21 dependent AMP-activated kinase (AMPK)/surtuin1/proliferator-activated receptor γ coactivator-1α pathway in T2DM. Subsequently, reduced circulating myokines/hepatokines were in accordance with their levels with hippocampal neuronal markers in T2DM mice. Accordingly, skeletal muscle (muscle strength: 2.83 ± 0.39 vs. 2.187 ± 0.51, p = 0.004) and brain function (PAT: 38.5 ± 57.91 vs. 11.556 ± 12.03, p = 0.02) impairment and morphological changes (muscle cross-sectional area: 872.43 ± 242.87 vs. 743.68 ± 169.31, p = 0.01; density of neurons in hippocampus: 145 ± 15.13 vs. 77 ± 35.51, p = 0.05; density of neurons in cortex: 138.333 ± 6.66 vs. 78 ± 17.35, p = 0.05) were shown in T2DM mice. In addition, the working ability demonstrated by Y-maze was positively correlated with % lean mass (p = 0.046, R = 0.3426). Conclusions: T2DM led to aberrant energy in skeletal muscle and brain via myokines/hepatokines. This study suggested that myokines and hepatokines might have potential roles in skeletal muscle and central metabolic functions which can mediate cognitive function in T2DM mice.

Altered Functional Network Connectivity of Precuneus and Executive Control Networks in Type 2 Diabetes Mellitus Without Cognitive Impairment

In epidemiological studies, type 2 diabetes mellitus (T2DM) has been associated with cognitive impairment and dementia, but studies about functional network connectivity in T2DM without cognitive impairment are limited. This study aimed to explore network connectivity alterations that may help enhance our understanding of damage-associated processes in T2DM. MRI data were analyzed from 82 patients with T2DM and 66 normal controls. Clinical, biochemical, and neuropsychological assessments were conducted in parallel with resting-state functional magnetic resonance imaging, and the cognitive status of the patients was assessed using the Montreal Cognitive Assessment-B (MoCA-B) score. Independent component analysis revealed a positive correlation between the salience network and the visual network and a negative connection between the left executive control network and the default mode network in patients with T2DM. The differences in dynamic brain network connectivity were observed in the precuneus, visual, and executive control networks. Internal network connectivity was primarily affected in the thalamus, inferior parietal lobe, and left precuneus. Hemoglobin A1c level, body mass index, MoCA-B score, and grooved pegboard (R) assessments indicated significant differences between the two groups (p < 0.05). Our findings show that key changes in functional connectivity in diabetes occur in the precuneus and executive control networks that evolve before patients develop cognitive deficits. In addition, the current study provides useful information about the role of the thalamus, inferior parietal lobe, and precuneus, which might be potential biomarkers for predicting the clinical progression, assessing the cognitive function, and further understanding the neuropathology of T2DM.

Differential impact of glycemic control and comorbid conditions on the neurophysiology underlying task switching in older adults with type 2 diabetes

Type 2 diabetes is known to negatively affect higher order cognition and the brain, but the underlying mechanisms are not fully understood. In particular, glycemic control and common comorbidities are both thought to contribute to alterations in cortical neurophysiology in type 2 diabetes, but their specific impact remains unknown. The current study probed the dynamics underlying cognitive control in older participants with type 2 diabetes, with and without additional comorbid conditions (i.e., cardiovascular disease, nephropathy, peripheral neuropathy, retinopathy), using a task switching paradigm and a dynamic functional brain mapping method based on magnetoencephalography (MEG). We hypothesized that neural dynamics would be differentially impacted by the level of glycemic control (i.e., diabetes itself) and the burden of additional comorbid conditions. Supporting this hypothesis, our findings indicated separable, but widespread alterations across frontal, parietal, temporal and cerebellum regions in neural task-switch costs in type 2 diabetes that were differentially attributable to glycemic control and the presence of comorbid conditions. These effects were spatially non-overlapping and the effects were not statistically related to one another. Further, several of the effects that were related to the presence of comorbidities were associated with behavioral performance, indicating progressive deficits in brain function with extended disease. These findings provide insight on the underlying neuropathology and may inform future treatment plans to curtail the neural impact of type 2 diabetes.

Diabetes and cognitive decline

Epidemiologic studies have documented an association between diabetes and increased risk of cognitive decline in the elderly. Based on animal model studies, several mechanisms have been proposed to explain such an association, including central insulin signaling, neurodegeneration, brain amyloidosis, and neuroinflammation. Nevertheless, the exact mechanisms in humans remain poorly defined. It is reasonable, however, that many pathways may be involved in these patients leading to cognitive impairment. A major aim of clinicians is identifying early onset of neurologic signs and symptoms in elderly diabetics to improve quality of life of those with cognitive impairment and reduce costs associated with long-term complications. Several biomarkers have been proposed to identify diabetics at higher risk of developing dementia and diagnose early stage dementia. Although biomarkers of brain amyloidosis, neurodegeneration and synaptic plasticity are commonly used to diagnose dementia, especially Alzheimer disease, their role in diabetes remains unclear. The aim of this review is to explore the molecular mechanisms linking diabetes with cognitive decline and present the most important findings on the clinical use of biomarkers for diagnosing and predicting early cognitive decline in diabetics.

Diagnostic, Prognostic, and Mechanistic Biomarkers of Diabetes Mellitus-Associated Cognitive Decline

Cognitive dysfunctions such as mild cognitive impairment (MCI), Alzheimer's disease (AD), and other forms of dementia are recognized as common comorbidities of type 2 diabetes mellitus (T2DM). Currently, there are no disease-modifying therapies or definitive clinical diagnostic and prognostic tools for dementia, and the mechanisms underpinning the link between T2DM and cognitive dysfunction remain equivocal. Some of the suggested pathophysiological mechanisms underlying cognitive decline in diabetes patients include hyperglycemia, insulin resistance and altered insulin signaling, neuroinflammation, cerebral microvascular injury, and buildup of cerebral amyloid and tau proteins. Given the skyrocketing global rates of diabetes and neurodegenerative disorders, there is an urgent need to discover novel biomarkers relevant to the co-morbidity of both conditions to guide future diagnostic approaches. This review aims to provide a comprehensive background of the potential risk factors, the identified biomarkers of diabetes-related cognitive decrements, and the underlying processes of diabetes-associated cognitive dysfunction. Aging, poor glycemic control, hypoglycemia and hyperglycemic episodes, depression, and vascular complications are associated with increased risk of dementia. Conclusive research studies that have attempted to find specific biomarkers are limited. However, the most frequent considerations in such investigations are related to C reactive protein, tau protein, brain-derived neurotrophic factor, advanced glycation end products, glycosylated hemoglobin, and adipokines.

Enhancement of Impaired Olfactory Neural Activation and Cognitive Capacity by Liraglutide, but Not Dapagliflozin or Acarbose, in Patients With Type 2 Diabetes: A 16-Week Randomized Parallel Comparative Study

OBJECTIVE

The comparative neuroprotective effects of different antidiabetes drugs have not been characterized in randomized controlled trials. Here, we investigated the therapeutic effects of liraglutide, dapagliflozin, or acarbose treatment on brain functional alterations and cognitive changes in patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

Thirty-six patients with type 2 diabetes inadequately controlled with metformin monotherapy were randomized to receive liraglutide, dapagliflozin, or acarbose treatment for 16 weeks. Brain functional MRI (fMRI) scan and a battery of cognitive assessments were evaluated pre- and postintervention in all subjects.

RESULTS

The 16-week treatment with liraglutide significantly enhanced the impaired odor-induced left hippocampal activation with Gaussian random field correction and improved cognitive subdomains of delayed memory, attention, and executive function (all P < 0.05), whereas dapagliflozin or acarbose did not. Structural equation modeling analysis demonstrated that such improvements of brain health and cognitive function could be partly ascribed to a direct effect of liraglutide on left hippocampal activation (β = 0.330, P = 0.022) and delayed memory (β = 0.410, P = 0.004) as well as to the metabolic ameliorations of reduced waist circumference, decreased body fat ratio, and elevated fasting insulin (all P < 0.05).

CONCLUSIONS

Our head-to-head study demonstrated that liraglutide enhanced impaired brain activation and restored impaired cognitive domains in patients with type 2 diabetes, whereas dapagliflozin and acarbose did not. The results expand the clinical application of liraglutide and provide a novel treatment strategy for individuals with diabetes and a high risk of cognitive decline.

Brain structural alterations detected by an automatic quantified tool as an indicator for MCI diagnosing in type 2 diabetes mellitus patients: a magnetic resonance imaging study

Background and objectives

Type 2 diabetes mellitus (T2DM) is an important risk factors for mild cognitive impairment (MCI). Structural magnetic resonance imaging (sMRI) is an effective and widely used method to investigate brain pathomorphological injury in neural diseases. In present study, we aimed to determine the brain regional alterations that correlated to the incidence of MCI in T2DM patients.

Materials and methods

Eighteen T2DM patients with and without MCI (DMCI/T2DM) respectively, and eighteen age/gender-matched healthy controls (HC) were recruited. Brain MRI imagines of all the individuals were subjected to automatic quantified brain sub-structure volume segmentation and measurement by Dr. brain ™ software. The relative volume of total gray matter (TGM), total white matter (TWM), and 68 pairs (left and right) of brain sub-structures were compared between the three groups. Cognitive function correlation analysis and receiver operating characteristic (ROC) curve analysis were conducted in the MCI-related brain regions in T2DM patients, and we utilized a machine learning method to classify the three group of subjects.

Results

10 and 27 brain sub-structures with significant relative volumetric alterations were observed in T2DM patients without MCI and T2DM patients with MCI, respectively (p < 0.05). Compared with T2DM patients without MCI, eight critical regions include right anterior orbital gyrus, right calcarine and cerebrum, left cuneus, left entorhinal area, left frontal operculum, right medial orbital gyrus, right occipital pole, left temporal pole had significant lower volumetric ratio in T2DM patients with MCI (p < 0.05). Among them, the decrease of volumetric ratio in several regions had a positive correlation with Montreal Cognitive Assessment (MoCA) scores and Mini-Mental State Examination (MMSE) scores. The classification results conducted based on these regions as features by random forest algorithm yielded good accuracies of T2DM/HC 69.4%, DMCI/HC 72.2% and T2DM/DMCI 69.4%.

Conclusions

Certain brain regional structural lesions occurred in patients with T2DM, and this condition was more serious in T2DM patients combined with MCI. A systematic way of segmenting and measuring the whole brain has a potential clinical value for predicting the presence of MCI for T2DM patients.

Cerebral Microvascular Senescence and Inflammation in Diabetes

Stress-induced premature senescence can contribute to the accelerated metabolic aging process in diabetes. Progressive accumulation of senescent cells in the brain, especially those displaying the harmful inflammatory senescence-associated secretory phenotype (SASP), may lead to cognitive impairment linked with metabolic disturbances. In this context, the senescence within the neurovascular unit (NVU) should be studied as much as in the neurons as emerging evidence shows that neurogliovascular communication is critical for brain health. It is also known that cerebrovascular dysfunction and decreased cerebral blood flow (CBF) precede the occurrence of neuronal pathologies and overt cognitive impairment. Various studies have shown that endothelial cells, the major component of the NVU, acquire a senescent phenotype via various molecular mediators and pathways upon exposure to high glucose and other conditions mimicking metabolic disturbances. In addition, senescence in the other cells that are part of the NVU, like pericytes and vascular smooth cells, was also triggered upon exposure to diabetic conditions. The senescence within the NVU may compromise functional and trophic coupling among glial, vascular, and neuronal cells and the resulting SASP may contribute to the chronic neurovascular inflammation observed in Alzheimer's Disease and Related Dementias (ADRD). The link between diabetes-mediated cerebral microvascular dysfunction, NVU senescence, inflammation, and cognitive impairment must be widely studied to design therapeutic strategies.

Lobar Cerebral Microbleeds Are Associated With Cognitive Decline in Patients With Type 2 Diabetes Mellitus

Purpose

Combined the number, volume, and location of cerebral microbleeds (CMBs), this study aimed to explore the different features of CMBs and their correlation with cognitive ability in patients with type 2 diabetes mellitus (T2DM).

Methods

This study recruited 95 patients with T2DM and 80 healthy control (HC) individuals. AccuBrain^®, an automated tool, was used to obtain the number and volume of CMBs. The scores on global cognition and five cognitive domains were derived from a battery of cognitive tests. The logistic regression and multivariate linear regression were conducted to determine the relationship between the CMBs (number, volume, and location) and cognitive ability in patients with T2DM.

Results

After adjusting for several variables, the total volume of CMBs (OR = 0.332, 95%CI: 0.133–0.825, and p = 0.018) was independent risk factor for cognitive impairment, whereas the total number of CMBs was not (OR = 0933, 95%CI: 0.794–1.097, and p = 0.400). Furthermore, the volume of CMBs in lobar regions was independently associated with working memory (β = −0.239, 95%CI: −0.565 to −0.035, and p = 0.027). However, no significant correlation between the number of CMBs (both lobar and deep/infratentorium) and any cognitive domains was observed.

Conclusions

Lobar CMBs was related with cognitive impairment in patients with T2DM and might be a potential early warning signal. Compared with the counting analysis, the quantitative method offered a more sensitive and objective measurement for studying imaging features of CMBs.

Detection of molecular signatures and pathways shared by Alzheimer's disease and type 2 diabetes

Alzheimer's disease (AD) and type 2 diabetes (T2D) are common in the general elderly population, conferring heavy individual, social, and economic stresses on families and society. Accumulating evidence indicates T2D to be a risk factor for AD. However, the underlying mechanisms for this association are largely unknown. This study aimed to identify the shared molecular signatures between AD and T2D through integrated analysis of temporal cortex gene expression data. Gene Ontology (GO) and pathway enrichment analysis, protein over-representation analysis, protein-protein interaction, DEG-transcription factor interactions, DEG-microRNA interactions, protein-drug interactions, gene-disease association analysis, and protein subcellular localization analysis of the common DEGs were performed. We identified 16 common DEGs between the two datasets, which were mainly enriched in the biological processes of apoptosis, autophagy, inflammation, and hemostasis. We also identified five hub proteins encoded by the DEGs, five central regulatory transcription factors, and six microRNAs. Protein-drug interaction analysis showed C1QB to be associated with different drugs. Gene-disease association analysis revealed that hub genes, SFN and ITGB2, were actively engaged in other diseases. Collectively, these findings provide new insights into shared molecular mechanisms between AD and T2D and provide novel candidate targets for therapeutic intervention.

Novel Targets and Interventions for Cognitive Complications of Diabetes

Diabetes and cognitive dysfunction, ranging from mild cognitive impairment to dementia, often coexist in individuals over 65 years of age. Vascular contributions to cognitive impairment/dementia (VCID) are the second leading cause of dementias under the umbrella of Alzheimer's disease and related dementias (ADRD). Over half of dementia patients have VCID either as a single pathology or a mixed dementia with AD. While the prevalence of type 2 diabetes in individuals with dementia can be as high as 39% and diabetes increases the risk of cerebrovascular disease and stroke, VCID remains to be one of the less understood and less studied complications of diabetes. We have identified cerebrovascular dysfunction and compromised endothelial integrity leading to decreased cerebral blood flow and iron deposition into the brain, respectively, as targets for intervention for the prevention of VCID in diabetes. This review will focus on targeted therapies that improve endothelial function or remove iron without systemic effects, such as agents delivered intranasally, that may result in actionable and disease-modifying novel treatments in the high-risk diabetic population.

Cognitive Dysfunction in Type 2 Diabetes Is Not a One-Way Process: Evidence From a Longitudinal Brain Connectivity Study

BACKGROUND

Cognitive dysfunction is an important comorbidity of diabetes characterized by brain functional hypo-connectivity. However, our recent study demonstrated an adaptive hyper-connectivity in young type 2 diabetes with cognitive decrements. This longitudinal study aimed to further explore the changes in functional connectivity and cognitive outcomes after regular glycemic control.

METHODS

At 18 months after recruitment, participants underwent a second cognitive assessment and magnetic resonance imaging. Three enhanced functional connectivities previously identified at baseline were followed up. Linear mixed-effects models were performed to compare the longitudinal changes of cognition and functional connectivity in patients with type 2 diabetes and non-diabetic controls. A linear regression model was used to investigate the association between changes in functional connectivity and changes in cognitive performance.

RESULTS

Improvements in multiple cognitive domains were observed in diabetes; however, the enhanced functional connectivity at baseline decreased significantly. Moreover, the decrease in hippocampal connectivity was correlated with an increase in the accuracy of Stroop task and the decrease in posterior cingulate cortex connectivity was correlated with an increase in Montreal Cognitive Assessment in diabetes.

CONCLUSION

This study suggests diabetes-related cognitive dysfunction is not a one-way process and the early-stage enhancement of brain connectivity was a potential "window period" for cognitive reversal.

Sleeve gastrectomy attenuated diabetes-related cognitive decline in diabetic rats

OBJECTIVE

To investigate the effects of sleeve gastrectomy (SG) on diabetes-related cognitive decline (DCD) in rats with diabetic mellitus (DM).

METHODS AND METHODS

Forty Wistar rats were randomly divided into control (CON) group (n=10), diabetes mellitus (DM) group (n=10), sham operation (SHAM) group (n=10) and SG group (n=10). DM model was established by high-fat diet (HFD) combined with intraperitoneal injection of streptozocin (STZ). Behavioral evaluation was given using Morris water maze test and Y-maze. In addition, PET-CT, TUNEL assay, histological analysis, transmission electron microscopy (TEM), immunohistochemistry (IHC) and Western blot analysis were used to evaluate the alleviating effects and potential mechanisms of SG on DCD in DM rats.

RESULTS

Compared with the sham group, SG induced significant improvement in the metabolic indices such as blood glucose and body weight. Besides, it could attenuate the insulin resistance compared with SHAM group. In addition, SG could improve the cognitive function of DM rats, which were featured by significant decrease in the escape latency (P<0.05), and significant increase in the time in target quadrant and platform crossings (P<0.05) compared with the SHAM group. SG induced significant elevation in the spontaneous alternation compared with SHAM group (P<0.05). Moreover, SG could improve the arrangement and biosynthesis of hippocampus neuron. Moreover, SG triggered the inhibition of apoptosis of hippocampus neurons, and Western blot analysis showed SG induced significant increase in the ratios of Bcl-2/Bax and Caspase3/cleaved Caspase 3. TEM demonstrated SG could significantly improve the microstructure of hippocampus neurons compared with the SHAM group. Western blot and IHC confirmed the significant decrease in the phosphorylation of tau at Ser404 and Ser396 sites in the SG group. Furthermore, SG activated the PI3K signaling pathway by elevating the phosphorylation of PI3K and Akt and GSK3β compared with the SHAM group.

CONCLUSION

SG attenuated the DCD in DM rats, which may be related to the activation of PI3K signaling pathway.

Neurovascular coupling unit dysfunction and dementia: Retinal measurements as tools to move towards population-based evidence

Dysfunction of the neurovascular coupling unit may be an important contributor to dementia. The neurovascular coupling unit comprises neuronal structures (e.g. astrocytes) and vascular structures (e.g. endothelial cells) that functionally interact both at the level of the arterioles as well as at the capillary level (blood-brain barrier) to regulate optimal metabolic conditions in the brain. However, it remains unclear how and to what extent dysfunction of the neurovascular coupling unit contributes to the early-stage pathobiology of dementia. Currently, limited data are available on the association between neurovascular coupling unit dysfunction, as quantified by cerebral imaging techniques, and cognitive performance. In particular, there is a lack of population-based human data (defined as studies with a sample size ~n>500). This is an important limitation because population-based studies, in comparison with smaller clinical studies, provide data which is better representative of the general population; are less susceptible to selection bias; and have a larger statistical power to detect small associations. To acquire population-based data, however, alternative imaging techniques than cerebral imaging techniques may be required. Disadvantages of cerebral imaging techniques, which limit use in population-based studies, are that these techniques are relatively expensive, time-consuming, and/or invasive. In this review, we propose that retinal imaging techniques can be used for population-based studies: on the one hand the retina and brain have many anatomical and physiological similarities; and on the other hand retinal imaging techniques are non-invasive, highly accurate, relatively inexpensive, and require relatively short measurement time. To provide support for this concept, we provide an overview on the human (population-based) evidence on the associations of retinal indices of neurodegeneration, microvascular dysfunction, and dysfunction of the neurovascular coupling unit with magnetic resonance imaging (MRI) features of structural brain abnormalities and cognitive performance.

Common pathways in dementia and diabetic retinopathy: understanding the mechanisms of diabetes-related cognitive decline

Type 2 diabetes (T2D) is associated with multiple comorbidities, including diabetic retinopathy (DR) and cognitive decline, and T2D patients have a significantly higher risk of developing Alzheimer's disease (AD). Both DR and AD are characterized by a number of pathological mechanisms that coalesce around the neurovascular unit, including neuroinflammation and degeneration, vascular degeneration, and glial activation. Chronic hyperglycemia and insulin resistance also play a significant role, leading to activation of pathological mechanisms such as increased oxidative stress and the accumulation of advanced glycation end-products (AGEs). Understanding these common pathways and the degree to which they occur simultaneously in the brain and retina during diabetes will provide avenues to identify T2D patients at risk of cognitive decline.

Effects of Exercise Intervention on Type 2 Diabetes Patients With Abdominal Obesity and Low Thigh Circumference (EXTEND): Study Protocol for a Randomized Controlled Trial

INTRODUCTION

Type 2 diabetes patients have abdominal obesity and low thigh circumference. Previous studies have mainly focused on the role of exercise in reducing body weight and fat mass, improving glucose and lipid metabolism, with a lack of evaluation on the loss of muscle mass, diabetes complications, energy metabolism, and brain health. Moreover, whether the potential physiological benefit of exercise for diabetes mellitus is related to the modulation of the microbiota-gut-brain axis remains unclear. Multi-omics approaches and multidimensional evaluations may help systematically and comprehensively correlate physical exercise and the metabolic benefits.

METHODS AND ANALYSIS

This study is a randomized controlled clinical trial. A total of 100 sedentary patients with type 2 diabetes will be allocated to either an exercise or a control group in a 1:1 ratio. Participants in the exercise group will receive a 16-week combined aerobic and resistance exercise training, while those in the control group will maintain their sedentary lifestyle unchanged. Additionally, all participants will receive a diet administration to control the confounding effects of diet. The primary outcome will be the change in body fat mass measured using bioelectrical impedance analysis. The secondary outcomes will include body fat mass change rate (%), and changes in anthropometric indicators (body weight, waist, hip, and thigh circumference), clinical biochemical indicators (glycated hemoglobin, blood glucose, insulin sensitivity, blood lipid, liver enzyme, and renal function), brain health (appetite, mood, and cognitive function), immunologic function, metagenomics, metabolomics, energy expenditure, cardiopulmonary fitness, exercise-related indicators, fatty liver, cytokines (fibroblast growth factor 21, fibroblast growth factor 19, adiponectin, fatty acid-binding protein 4, and lipocalin 2), vascular endothelial function, autonomic nervous function, and glucose fluctuation.

DISCUSSION

This study will evaluate the effect of a 16-week combined aerobic and resistance exercise regimen on patients with diabetes. The results will provide a comprehensive evaluation of the physiological effects of exercise, and reveal the role of the microbiota-gut-brain axis in exercise-induced metabolic benefits to diabetes.

CLINICAL TRIAL REGISTRATION

http://www.chictr.org.cn/searchproj.aspx, identifier ChiCTR2100046148.

Hypertensive Aspects of Cardiometabolic Disorders Are Associated with Lower Brain Microstructure, Perfusion, and Cognition

BACKGROUND

Cardiometabolic disorders (hypertension, diabetes) are key modifiable risk factors for Alzheimer's disease and related disorders. They often co-occur; yet, the extent to which they independently affect brain structure and function is unclear.

OBJECTIVE

We hypothesized their combined effect is greater in associations with cognitive function and neuroimaging biomarkers of white matter (WM) health and cerebral perfusion in a diverse older adult cohort.

METHODS

Participants aged 50-85 years received: clinical evaluation, oral glucose tolerance testing, neuroimaging, cognitive testing, and adjudication. Neuroimaging included: T1 (gray [GM]/WM segmentation, regional volumes/thicknesses); FLAIR (WM hyperintensity volume [WMHv]; arterial spin labeling (cerebral blood flow); diffusion tensor imaging (fractional anisotropy [FA]); and neurite orientation dispersion and density imaging (Free Water). Hypertension (HTN) and impaired glucose tolerance (IGT) were staged and cardiometabolic status was categorized (HTN only, IGT only, IGT+HTN, neither). Multivariable linear regression modeled associations with cognitive and neuroimaging measures (covariates: age, gender, race).

RESULTS

MRI was available for 478 participants (35% mild cognitive impairment, 10% dementia) with mean age 70±8 years, 74% with HTN, 61% with IGT, and 15% self-identified as Black/African-American. IGT+HTN was significantly associated with cognitive impairment, higher WM Free Water and WMHv, lower FA, and lower GM perfusion compared to neither factor. HTN alone was associated with poorer cognition and lower GM perfusion. Cardiometabolic factors were not associated with GM macrostructure (volumes, temporal lobe cortical thickness) or cognitive status.

CONCLUSION

HTN and its co-occurrence with IGT (HTN+IGT) were associated with lower global cognitive performance and reduced GM perfusion and impaired WM microstructure.

Cerebral Small Vessel Disease is Associated with Mild Cognitive Impairment in Type 2 Diabetes Mellitus

OBJECTIVE

Type 2 diabetes mellitus (T2DM) is associated with cognitive impairment, but the underlying cerebral small vessel disease (CSVD)-related structural brain correlates are unclear. The aim of this study was to investigate the relationship between various imaging markers of CSVD and mild cognitive impairment (MCI) in patients with T2DM.

METHODS

A total of 228 eligible participants with T2DM who were divided into MCI group and normal cognitive group based on neuropsychological assessment were enrolled in this retrospective study. White matter hyperintensity (WMH), lacunes, cerebral microbleeds (CMBs) and enlarged perivascular spaces (EPVS) were evaluated based on brain magnetic resonance imaging (MRI). The total CSVD burden score was calculated by combining the above four markers of CSVD. Binary logistic regression analysis was used to evaluate the relationship between different imaging markers of CSVD and MCI in patients with T2DM. Kruskal-Wallis test and Jonckheere-Terpstra test were used to compare mean MoCA scores among individuals with varying CSVD markers.

RESULTS

In the multivariate binary logistic regression analyses, moderate or severe total CSVD burden (OR: 3.29, 95% CI: 1.63-7.38, P=0.004; OR: 10.97, 95% CI: 4.94-24.34, P<0.001, respectively), moderate dWMH (OR: 3.26, 95% CI: 1.43-7.41, P=0.005), extensive lacunes (OR: 4.97, 95% CI: 1.79-13.81, P=0.002), and moderate BG-EPVS (OR: 3.84, 95% CI: 1.81-8.13, P<0.001) were associated with MCI in patients with T2DM related to MCI after adjusting for potential confounders. There was a trend for significant decrease in MoCA scores with increase severity of dWMH, pWMH, lacunes, BG-EPVS, deep CMBs, or total CSVD burden (P for trend <0.05).

CONCLUSION

Different imaging markers of CSVD, particularly total CSVD burden, were associated with an increased risk of MCI and decline in MoCA scores in patients with T2DM. These findings may provide clues for future studies to explore early diagnostic imaging markers of cognitive impairment in relation to T2DM.

Pathomechanisms of Vascular Depression in Older Adults

Depression in older individuals is a common complex mood disorder with high comorbidity of both psychiatric and physical diseases, associated with high disability, cognitive decline, and increased mortality The factors predicting the risk of late-life depression (LLD) are incompletely understood. The reciprocal relationship of depressive disorder and age- and disease-related processes has generated pathogenic hypotheses and provided various treatment options. The heterogeneity of depression complicates research into the underlying pathogenic cascade, and factors involved in LLD considerably differ from those involved in early life depression. Evidence suggests that a variety of vascular mechanisms, in particular cerebral small vessel disease, generalized microvascular, and endothelial dysfunction, as well as metabolic risk factors, including diabetes, and inflammation that may induce subcortical white and gray matter lesions by compromising fronto-limbic and other important neuronal networks, may contribute to the development of LLD. The "vascular depression" hypothesis postulates that cerebrovascular disease or vascular risk factors can predispose, precipitate, and perpetuate geriatric depression syndromes, based on their comorbidity with cerebrovascular lesions and the frequent development of depression after stroke. Vascular burden is associated with cognitive deficits and a specific form of LLD, vascular depression, which is marked by decreased white matter integrity, executive dysfunction, functional disability, and poorer response to antidepressive therapy than major depressive disorder without vascular risk factors. Other pathogenic factors of LLD, such as neurodegeneration or neuroimmune regulatory dysmechanisms, are briefly discussed. Treatment planning should consider a modest response of LLD to antidepressants, while vascular and metabolic factors may provide promising targets for its successful prevention and treatment. However, their effectiveness needs further investigation, and intervention studies are needed to assess which interventions are appropriate and effective in clinical practice.

Severe Hypoglycemia Contributing to Cognitive Dysfunction in Diabetic Mice Is Associated With Pericyte and Blood-Brain Barrier Dysfunction

Background: Severe hypoglycemia can cause cognitive impairment in diabetic patients, but the underlying molecular mechanism remains unclear.

Objective: To assess the effect of severe hypoglycemia on cognitive function in diabetic mice to clarify the relationship between the mechanism and dysfunction of pericytes and the blood–brain barrier (BBB).

Method: We established type 1 diabetes mellitus in 80 male C57BL/6J mice by intraperitoneal injection of streptozotocin (150 mg/kg). Further intraperitoneal injection of short-acting insulin induced severe hypoglycemia. The mice were divided into normal, diabetes, and diabetic + severe hypoglycemia groups, and their blood glucose and general weight index were examined. Pericyte and BBB morphology and function were detected by histological and western blot analyses, BBB permeability was detected by Evans blue staining, and cognitive function was detected with the Morris water maze.

Results: Severe hypoglycemia aggravated the histological damage, BBB damage, brain edema, and pericyte loss in the diabetic mice. It also reduced the expression of the BBB tight junction proteins occludin and claudin-5, the expression of the pericyte-specific markers PDGFR-β (platelet-derived growth factor receptor-β) and α-SMA, and increased the expression of the inflammatory factor MMP9. At the same time, diabetic mice with severe hypoglycemia had significantly reduced cognitive function.

Conclusion: Severe hypoglycemia leads to cognitive dysfunction in diabetic mice, and its possible mechanism is related to pericyte dysfunction and BBB destruction.

Individual and Combined Associations of Glucose Metabolic Components With Cognitive Function Modified by Obesity

Aim

We aimed to detect the individual and combined effect of glucose metabolic components on cognitive function in particular domains among older adults.

Methods

Data of 2,925 adults aged over 60 years from the 2011 to 2014 National Health and Nutrition Examination Survey were analyzed. Individuals' cognitive function was evaluated using the Digit Symbol Substitution Test (DSST), the Animal Fluency Test (AF), the Consortium to Establish a Registry for Alzheimer's Disease Immediate Recall (CERAD-IR), and CERAD Delayed Recall (CERAD-DR). Participants' glucose metabolic health status was determined based on fasting plasma glucose, insulin, homeostasis model assessment of insulin resistance (HOMA-IR), glycated hemoglobin (HbA1c), and 2-h postload glucose. Linear regression models were used to delineate the associations of cognitive function with individual glucose metabolic component and with metformin use. Logistic regression models were performed to evaluate the associations of cognition with the number of glucose metabolic risk components.

Results

CERAD-IR was significantly associated with HOMA-IR and insulin. HbA1c was related to all the cognitive tests except AF. Among participants without obesity, HOMA-IR and insulin were both negatively associated with CERAD-IR and CERAD-DR. Odds of scoring low in DSST increased with the number of glucose metabolic risk components (odds ratio 1.94, 95% confidence interval [CI] 1.26 to 2.98). Metformin use was associated with better performance in DSST among diabetes patients (β = 4.184, 95% CI 1.655 to 6.713).

Conclusions

Our findings support the associations of insulin resistance and glycemic level with cognitive function in key domains, especially among adults without obesity. There is a positive association between metformin use and cognition.

EANM procedure guidelines for brain PET imaging using [18F]FDG, version 3

The present procedural guidelines summarize the current views of the EANM Neuro-Imaging Committee (NIC). The purpose of these guidelines is to assist nuclear medicine practitioners in making recommendations, performing, interpreting, and reporting results of [¹⁸F]FDG-PET imaging of the brain. The aim is to help achieve a high-quality standard of [¹⁸F]FDG brain imaging and to further increase the diagnostic impact of this technique in neurological, neurosurgical, and psychiatric practice. The present document replaces a former version of the guidelines that have been published in 2009. These new guidelines include an update in the light of advances in PET technology such as the introduction of digital PET and hybrid PET/MR systems, advances in individual PET semiquantitative analysis, and current broadening clinical indications (e.g., for encephalitis and brain lymphoma). Further insight has also become available about hyperglycemia effects in patients who undergo brain [¹⁸F]FDG-PET. Accordingly, the patient preparation procedure has been updated. Finally, most typical brain patterns of metabolic changes are summarized for neurodegenerative diseases. The present guidelines are specifically intended to present information related to the European practice. The information provided should be taken in the context of local conditions and regulations.

Factors associated with brain white matter damage in type 2 diabetes mellitus: a tract-based spatial statistics study

BACKGROUND

The pathogenesis and related factors of central nervous system abnormality in patients with type 2 diabetes mellitus (T2DM) have always been the focus of clinical research.

PURPOSE

To compare and analyze the area of white matter (WM) damage in patients with T2DM based on their level of hemoglobin A_1C (HBA_1c) and discuss any related factors.

MATERIAL AND METHODS

Based on their levels of HBA_1c, 87 patients with T2DM were divided into three groups (Group B, C, or D), of which 29 non-diabetic volunteers served as the control group (Group A). DTI data analysis was based on tract-based spatial statistics (TBSS). The obtained parameters were compared among each group and the relevant clinical factors were analyzed.

RESULTS

For age, sex, mini-mental state examination (MMSE), and Montreal Cognitive Assessment (MoCA) scores, there were no statistically significant differences among groups. For fractional anisotropy (FA) and radial diffusivity (RD) of WM, there were statistically significant differences (P < 0.05, two-tailed, FWE corrected) in the local area of corpus callosum, corona radiate, superior longitudinal fasciculus, etc. Most of these were significantly correlated with body mass index (BMI), left systolic blood pressure (SBP_L), and β₂ microglobulin.

CONCLUSION

Before the cognitive function was obviously impaired, abnormalities of FA and RD had been found in the corpus callosum, corona radiate, and upper fasciculus in patients with T2DM, which suggested that the damage mainly occurred in the myelin sheath of WM and may be related to systemic vascular damage.

Metformin and cyanidin 3-O-galactoside from Aronia melanocarpa synergistically alleviate cognitive impairment in SAMP8 mice

Cyanidin 3-O-galactoside (Cy3Gal) from Aronia melanocarpa has been reported to alleviate cognitive impairment. Metformin for preventing the neurodegenerative disease is attracting increasing attention. However, the neuroprotective and metabolic health promoting both of their effects are not clear. We chose the senescence accelerated mouse prone 8 (SAMP8) as a model of spontaneous learning and memory impairment. This study aimed to investigate the synergistic neuroprotective effect of metformin and Cy3Gal by behavioral and histopathological assays and metabolite analysis in SAMP8 mice. The SAMR1 mice were the normal group, and the SAMP8 mice were divided into five groups, including the SAMP8 model group, the donepezil (1 mg kg^-1, ig) group, the metformin (100 mg kg^-1, ig) group, the Cy3Gal (25 mg kg^-1, ig) group, and the combination of metformin plus Cy3Gal (Met + Cy3Gal, 100 mg kg^-1, 25 mg kg^-1, ig) group. The behavior experiments showed that the SAMP8 mice treated with metformin and Cy3Gal showed improved spatial learning and memory compared to the SAMP8 model group. The number of neurons in the Met + Cy3Gal group was significantly higher than that in the SAMP8 group and the Met + Cy3Gal group showed significantly reduced Aβ aggregation in the brain, which was elevated in SAMP8 mice. Compared with SAMP8 mice, the Met + Cy3Gal group showed decreased indole, methyl esters and ketones and increased short-chain fatty acids and alcohols in feces and urine by regulating the fatty acid biosynthesis and degradation. This study confirmed the neuroprotective effects of coadministration of metformin and cyanidin 3-O-galactoside in the SAMP8 mice, and suggested its positive effect on postponing the progression of Alzheimer's disease.

The microglial lysosomal system in Alzheimer's disease: Guardian against proteinopathy

Microglia, the brain-resident immune cells, play an essential role in the upkeep of brain homeostasis. They actively adapt into specific activation states based on cues from the microenvironment. One of these encompasses the activated response microglia (ARMs) phenotype. It arises along a healthy aging process and in a range of neurodegenerative diseases, including Alzheimer's disease (AD). As the phenotype is characterized by an increased lipid metabolism, phagocytosis rate, lysosomal protease content and secretion of neuroprotective agents, it leaves to reason that the phenotype is adapted in an attempt to restore homeostasis. This is important to the conundrum of inflammatory processes. Inflammation per se may not be deleterious; it is only when microglial reactions become chronic or the microglial subtype is made dysfunctional by (multiple) risk proteins with single-nucleotide polymorphisms that microglial involvement becomes deleterious instead of beneficial. Interestingly, the ARMs up- and downregulate many late-onset AD-associated risk factor genes, the products of which are particularly active in the endolysosomal system. Hence, in this review, we focus on how the endolysosomal system is placed at the crossroad of inflammation and microglial capacity to keep pace with degradation.

Relationship Between Glycemia and Cognitive Function, Structural Brain Outcomes, and Dementia: A Mendelian Randomization Study in the UK Biobank

We investigated the relationship between glycemia and cognitive function, brain structure and incident dementia using bidirectional Mendelian randomization (MR). Data were from the UK Biobank (n = ∼500,000). Our exposures were genetic instruments for type 2 diabetes (157 variants) and HbA1c (51 variants) and our outcomes were reaction time (RT), visual memory, hippocampal volume (HV), white matter hyperintensity volume (WMHV), and Alzheimer dementia (AD). We also investigated associations between genetic variants for RT (43 variants) and diabetes and HbA1c We used conventional inverse-variance-weighted (IVW) MR alongside MR sensitivity analyses. Using IVW, genetic liability to type 2 diabetes was not associated with RT (exponentiated β [expβ] = 1.00 [95% CI 1.00; 1.00]), visual memory (expβ = 1.00 [95% CI 0.99; 1.00]), WMHV (expβ = 0.99 [95% CI 0.97; 1.01]), HV (β-coefficient mm3 = -2.30 [95% CI -12.39; 7.78]) or AD (odds ratio [OR] 1.15 [95% CI 0.87; 1.52]). HbA1c was not associated with RT (expβ = 1.00 [95% CI 0.99; 1.02]), visual memory (expβ = 0.99 [95% CI 0.96; 1.02]), WMHV (expβ = 1.03 [95% CI 0.88; 1.22]), HV (β = -21.31 [95% CI -82.96; 40.34]), or risk of AD (OR 1.09 [95% CI 0.42; 2.83]). IVW showed that reaction time was not associated with diabetes risk (OR 0.94 [95% CI 0.54; 1.65]), or with HbA1c (β-coefficient mmol/mol = -0.88 [95% CI = -1.88; 0.13]) after exclusion of a pleiotropic variant. Overall, we observed little evidence of causal association between genetic instruments for type 2 diabetes or peripheral glycemia and some measures of cognition and brain structure in midlife.

Cerebral small vessel disease: A glymphopathy?

Small vessel disease (SVD) is a common instigator of dementia in the aging population. The hallmarks of SVD are enlargement of the perivascular spaces and white matter hyperintensities. The latter represents local fluid accumulation in white matter that either subsides or develops into lacunar infarcts. We here propose that failure of brain fluid transport-via the glymphatic system-plays a key role in initiation and progression of SVD. Our major case for this concept is that perivascular spaces are utilized as waterways for influx of cerebrospinal fluid. Stagnation of glymphatic transport may drive loss of brain fluid homeostasis leading to transient white matter edema, perivascular dilation, and ultimately demyelination. This review will discuss how glymphatic rodent studies of hypertension and diabetes have provided new insight into the pathogenesis of SVD.

Hippocampal subfields atrophy contribute more to cognitive impairment in middle-aged patients with type 2 diabetes rather than microvascular lesions

AIMS

Neurodegeneration and microvascular lesions are related to cognitive impairment in type 2 diabetes mellitus (T2DM). We aimed to use the volume of hippocampal subfields and the burden of white matter hyperintensities (WMH) as neurodegeneration and microangiopathy markers, respectively, to investigate their potential associations with cognitive impairment in T2DM patients.

METHODS

A total of 76 T2DM patients and 45 neurologically unimpaired normal controls were enrolled between February 2016 to August 2018. All participants underwent structural magnetic resonance imaging (MRI) and Montreal Cognitive Assessment (MoCA). The T2DM patients were divided into the T2DM without mild cognitive impairment (T2noMCI) group (n = 44) and the T2DM with mild cognitive impairment (T2MCI) group (n = 32) according to MoCA scores. We used automatic brain segmentation and quantitative technique to assess the volume of twelve hippocampal subfields and WMH on MRI. We used age, sex, education, and total intracranial volume as our covariates and the Bonferroni method for multiple comparison correction.

RESULTS

Both the T2MCI group and T2noMCI group showed significant hippocampal subfields atrophy compared to the controls, which were mainly in the left hippocampal tail, left CA1, bilateral molecular layer, bilateral dentate gyrus, and bilateral CA4 (all p < 0.0042). No significant differences in the volume of total WMH, deep-WMH, and periventricular-WMH were found among the three groups. The HbA1c levels were significantly negatively correlated with hippocampal atrophy, and the MoCA scores were positively correlated with bilateral hippocampal volume in T2DM patients and all samples. Mediation analyses demonstrated that the association of HbA1c levels with cognitive function was mediated by hippocampal subfields volume.

CONCLUSION

Widespread hippocampal atrophies across the subfields have been found in middle-aged T2DM patients, which was positively correlated with the MoCA scores and negatively correlated with the HbA1c levels. The association of HbA1c levels with cognitive function was mediated by some crucial hippocampal subfields volume. In middle-aged patients with T2DM, the neurodegeneration is more strongly associated with cognitive impairment than microvascular lesions. Trail Registeration This study was registered on Clinical-Trails.gov (NCT02738671).

Disturbed Interhemispheric Functional and Structural Connectivity in Type 2 Diabetes

BACKGROUND

Type 2 diabetes mellitus (T2DM) is associated with cognitive decline and altered brain structure and function. However, the interhemispheric coordination of T2DM patients is unclear.

PURPOSE

To investigate interhemispheric functional and anatomic connectivity in T2DM, and their associations with cognitive performance and endocrine parameters.

STUDY TYPE

Prospective.

SUBJECTS

38 T2DM patients and 42 matched controls.

FIELD STRENGTH/SEQUENCES

3.0 T magnetic resonance imaging (MRI) scanner; magnetization-prepared rapid acquisition gradient echo sequence; fluid-attenuated inversion recovery sequence; single-shot, gradient-recalled echo-planar imaging sequence (resting-state functional MRI); and diffusion-weighted spin-echo-based echo-planar sequence (diffusion tensor imaging).

ASSESSMENT

Voxel-mirrored homotopic connectivity (VMHC) value was calculated based on the functional images. Fibers passing through the regions with significant VMHC differences were identified using an atlas-guided track recognition. The mean fractional anisotropy (FA), mean diffusivity (MD), and fiber length were extracted and compared between the two groups. Finally, correlational analyses were performed to examine the relationships between abnormal interhemispheric connectivity, cognitive performances, and endocrine parameters.

STATISTICAL TESTS

Two-sample t-tests were performed controlling for confounding factors, with partial correlation analysis. False discovery rate (FDR) correction was used for multiple comparisons. A P value <0.05 was considered statistically significant.

RESULTS

T2DM patients exhibited significantly decreased VMHC between bilateral lingual gyrus and sensorimotor cortex. The fibers connecting lingual gyrus in patients showed significantly lower FA (P = 0.011) and shorter fiber length (P < 0.001), while the differences in sensorimotor fibers were insignificant (P = 0.096 for FA, P = 0.739 for fiber length and P = 0.150 for MD). The FA value in the lingual fibers was negatively correlated with insulin resistance (IR) level in T2DM group after FDR correction (R = -0.635).

DATA CONCLUSION

We noted disruptions in interhemispheric coordination in T2DM patients, involving both functional and anatomical connectivities. IR might be a promising therapeutic target in the intervention of T2DM-related cognitive impairment.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY STAGE: 2.

Altered White Matter Microstructures in Type 2 Diabetes Mellitus: A Coordinate-Based Meta-Analysis of Diffusion Tensor Imaging Studies

Objective

Type 2 diabetes mellitus (T2DM) is often accompanied by cognitive decline and depressive symptoms. Numerous diffusion tensor imaging (DTI) studies revealed microstructural white matter (WM) abnormalities in T2DM but the findings were inconsistent. The present study aimed to conduct a coordinate-based meta-analysis (CBMA) to identify statistical consensus of DTI studies in T2DM.

Methods

We performed a systematic search on relevant studies that reported fractional anisotropy (FA) differences between T2DM patients and healthy controls (HC). The anisotropic effect size seed-based d mapping (AES-SDM) approach was used to explore WM alterations in T2DM. A meta-regression was then used to analyze potential influences of sample characteristics on regional FA changes.

Results

A total of eight studies that comprised 245 patients and 200 HC, along with 52 coordinates were extracted. The meta-analysis identified FA reductions in three clusters including the left inferior network, the corpus callosum (CC), and the left olfactory cortex. Besides, FA in the CC was negatively correlated with body mass index (BMI) in the patients group.

Conclusions

T2DM could lead to subtle WM microstructural alterations, which might be associated with cognitive deficits or emotional distress symptoms. This provides a better understanding of the pathophysiology of neurodegeneration and complications in T2DM.

Systematic Review Registration

Registered at PROSPERO (http://www.crd.york.ac.uk/PROSPERO), registration number: CRD42020218737.

HbA1c and brain health across the entire glycaemic spectrum

AIM

To understand the relationship between HbA1c and brain health across the entire glycaemic spectrum.

MATERIALS AND METHODS

We used data from the UK Biobank cohort consisting of 500,000 individuals aged 40-69 years. HbA1c and diabetes diagnosis were used to define baseline glycaemic categories. Our outcomes included incident all-cause dementia, vascular dementia (VD), Alzheimer's dementia (AD), hippocampal volume (HV), white matter hyperintensity (WMH) volume, cognitive function and decline. The reference group was normoglycaemic individuals (HbA1c ≥35 & <42 mmol/mol). Our maximum analytical sample contained 449,973 individuals with complete data.

RESULTS

Prediabetes and known diabetes increased incident VD (HR 1.54; 95% CI = 1.04, 2.28 and HR 2.97; 95% CI = 2.26, 3.90, respectively). Known diabetes increased all-cause and AD risk (HR 1.91; 95% CI = 1.66, 2.21 and HR 1.84; 95% CI = 1.44, 2.36, respectively). Prediabetes and known diabetes elevated the risks of cognitive decline (OR 1.42; 1.48, 2.96 and OR 1.39; 1.04, 1.75, respectively). Prediabetes, undiagnosed and known diabetes conferred higher WMH volumes (3%, 22% and 7%, respectively) and lower HV (36, 80 and 82 mm3 , respectively), whereas low-normal HbA1c had 1% lower WMH volume and 12 mm3 greater HV.

CONCLUSION

Both prediabetes and known diabetes are harmful in terms of VD, cognitive decline and AD risks, as well as lower HV. Associations appeared to be somewhat driven by antihypertensive medication, which implies that certain cardiovascular drugs may ameliorate some of the excess risk. Low-normal HbA1c levels, however, are associated with more favourable brain health outcomes and warrant more in-depth investigation.