Insulin resistance accounts for metabolic syndrome-related alterations in brain structure

Metabolic syndrome (MetS) is a major public health burden worldwide and associated with brain abnormalities. Although insulin resistance is considered a pivotal feature of MetS, its role in the pathogenesis of MetS‐related brain alterations in the general population is unclear. Therefore, in 973 participants (mean age 52.5 years) of the population‐based Rhineland Study, we assessed brain morphology in relation to MetS and insulin resistance, and evaluated to what extent the pattern of structural brain changes seen in MetS overlap with those associated with insulin resistance. Cortical reconstruction and volumetric segmentation were obtained from high‐resolution brain images at 3 Tesla using FreeSurfer. The relations between metabolic measures and brain structure were assessed through (generalized) linear models. Both MetS and insulin resistance were associated with smaller cortical gray matter volume and thickness, but not with white matter or subcortical gray matter volume. Age‐ and sex‐adjusted vertex‐based brain morphometry demonstrated that MetS and insulin resistance were related to cortical thinning in a similar spatial pattern. Importantly, no independent effect of MetS on cortical gray matter was observed beyond the effect of insulin resistance. Our findings suggest that addressing insulin resistance is critical in the prevention of MetS‐related brain changes in later life.

Spectral Diffusion Analysis of Intravoxel Incoherent Motion MRI in Cerebral Small Vessel Disease

Background

Cerebral intravoxel incoherent motion (IVIM) imaging assumes two components. However, more compartments are likely present in pathologic tissue. We hypothesized that spectral analysis using a nonnegative least‐squares (NNLS) approach can detect an additional, intermediate diffusion component, distinct from the parenchymal and microvascular components, in lesion‐prone regions.

Purpose

To investigate the presence of this intermediate diffusion component and its relation with cerebral small vessel disease (cSVD)‐related lesions.

Study Type

Prospective cross‐sectional study.

Population

Patients with cSVD (n = 69, median age 69.8) and controls (n = 39, median age 68.9).

Field Strength/Sequence

Whole‐brain inversion recovery IVIM acquisition at 3.0T.

Assessment

Enlarged perivascular spaces (PVS) were rated by three raters. White matter hyperintensities (WMH) were identified on a fluid attenuated inversion recovery (FLAIR) image using a semiautomated algorithm.

Statistical Tests

Relations between IVIM measures and cSVD‐related lesions were studied using the Spearman's rank order correlation.

Results

NNLS yielded diffusion spectra from which the intermediate volume fraction f_int was apparent between parenchymal diffusion and microvasular pseudodiffusion. WMH volume and the extent of MRI‐visible enlarged PVS in the basal ganglia (BG) and centrum semiovale (CSO) were correlated with f_int in the WMHs, BG, and CSO, respectively. f_int was 4.2 ± 1.7%, 7.0 ± 4.1% and 13.6 ± 7.7% in BG and 3.9 ± 1.3%, 4.4 ± 1.4% and 4.5 ± 1.2% in CSO for the groups with low, moderate, and high number of enlarged PVS, respectively, and increased with the extent of enlarged PVS (BG: r = 0.49, P < 0.01; CSO: r = 0.23, P = 0.02). f_int in the WMHs was 27.1 ± 13.1%, and increased with the WMH volume (r = 0.57, P < 0.01).

Data Conclusion

We revealed the presence of an intermediate diffusion component in lesion‐prone regions of cSVD and demonstrated its relation with enlarged PVS and WMHs. In tissue with these lesions, tissue degeneration or perivascular edema can lead to more freely diffusing interstitial fluid contributing to f_int.

Level of Evidence: 2

Technical Efficacy: Stage 2

J. Magn. Reson. Imaging 2020;51:1170–1180.

Functional magnetic resonance imaging response as an early biomarker of cognitive decline in elderly patients with metabolic syndrome

OBJECTIVES

We assessed whether potential changes in brain activation patterns of elderly individuals with metabolic syndrome (MetS) who were cognitively healthy (without mild cognitive impairment or dementia) were associated with cognitive decline in executive function in the short-term.

METHOD

We analyzed 43 individuals (23 MetS, 20 controls) using a global geriatric evaluation, a neuropsychological battery, and task-related (attention) fMRI exam. Correlation analysis between the fMRI signal at baseline and cognitive impairment after 1year was based on the voxel-based Pearson coefficient, corrected for multiple comparisons.

RESULTS

At baseline, MetS patients showed reduced brain response in frontal and parietal regions compared to controls. After one year, the MetS group also showed a decline in verbal fluency performance. fMRI response in the right dorsolateral prefrontal cortex and bilateral parietal lobes was negatively correlated with verbal fluency decline in the MetS group.

DISCUSSION

Our results provide an early biomarker of the possible development of cognitive impairment, particularly in the executive function, of elderly individuals suffering from MetS. These findings also point to an up or down regulation which could be interpreted as compensatory mechanism for possible brain tissue burden caused by MetS.

Measuring subtle leakage of the blood-brain barrier in cerebrovascular disease with DCE-MRI: Test-retest reproducibility and its influencing factors

PURPOSE

Increased blood-brain barrier (BBB) permeability has been shown to play a significant role in the pathophysiology of cerebrovascular disease and it may provide an early functional marker of progression or treatment effects. The aim of the study was to investigate the test-retest reproducibility and influencing factors of dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) in measuring subtle leakage in patients with cerebrovascular disease.

MATERIAL AND METHODS

DCE-MRI (3T) was performed on two separate days in 16 patients (age 66 ± 9 years) with cerebrovascular disease, prospectively. The leakage rate was quantified for white matter (WM) and gray matter (GM) using the Patlak graphical approach with individual vascular input functions (VIFs). Furthermore, the influence of session-averaged VIFs, the average of the VIFs obtained on two days, and shorter scan times (range 5-25 minutes) on the reproducibility were evaluated in WM and GM.

RESULTS

Coefficients of variation (CV) ≤14.4% (WM and GM), intraclass correlation coefficients (ICCs) of 0.77 (WM) and 0.49 (GM), were observed for the leakage rate. Session-averaged VIFs hardly affected these results (CV ≤13.4%). The repeatability coefficients (RCs) of the leakage rate decreased from 2.7·10^-3 to 0.4·10^-3 min^-1 in WM (P < 0.01) and 4.4·10^-3 to 0.9·10^-3 min^-1 in GM (P < 0.01) with increasing scan time (range 5-25 minutes).

CONCLUSION

Based on the moderate CVs and moderate-to-excellent ICCs, we demonstrate that measuring subtle BBB leakage using DCE-MRI is moderate-to-excellent reproducible. Longer scan times improve the reproducibility. The provided RCs at various scan times may assist future clinical studies investigating BBB leakage using DCE-MRI.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;46:159-166.

Blood-brain barrier leakage is more widespread in patients with cerebral small vessel disease

OBJECTIVE

As blood-brain barrier (BBB) dysfunction may occur in normal aging but may also play a pivotal role in the pathophysiology of cerebral small vessel disease (cSVD), we used dynamic contrast-enhanced (DCE)-MRI to quantify the rate and the spatial extent of BBB leakage in patients with cSVD and age- and sex-matched controls to discern cSVD-related BBB leakage from aging-related leakage.

METHODS

We performed structural brain MRI and DCE-MRI in 80 patients with clinically overt cSVD and 40 age- and sex-matched controls. Using the Patlak pharmacokinetic model, we calculated the leakage rate. The mean leakage rate and relative leakage volume were calculated using noise-corrected histogram analysis. Leakage rate and leakage volume were compared between patients with cSVD and controls for the normal-appearing white matter (NAWM), white matter hyperintensities (WMH), cortical gray matter (CGM), and deep gray matter.

RESULTS

Multivariable linear regression analyses adjusting for age, sex, and cardiovascular risk factors showed that the leakage volume of the NAWM, WMH, and CGM was significantly larger in patients with cSVD compared with controls. No significant difference was found for leakage rate in any of the tissue regions.

CONCLUSION

We demonstrated a larger tissue volume with subtle BBB leakage in patients with cSVD than in controls. This was shown in the NAWM, WMH, and CGM, supporting the generalized nature of cSVD.

Type 2 diabetic patients with ischemic stroke: decreased insulin sensitivity and decreases in antioxidant enzyme activity are related to different stroke subtypes

We analyzed (a) insulin sensitivity (IS) and (b) glutathione peroxidase (GSH-Px), glutathione reductase (GR), and superoxide dismutase (SOD) antioxidant enzyme activity in type 2 diabetic (T2D) patients with atherothrombotic infarction (ATI) (group A), lacunar infarction (LI) (B), or without stroke (C) and in nondiabetics with ATI (D), LI (E), or without stroke (F). ATI and LI were confirmed by brain imaging IS levels were determined by minimal model (Si index), and the enzyme activity by spectrophotometry. In T2D patients, Si was lower in A and B versus C (1.14 ± 0.58, 1.00 ± 0.26 versus 3.14 ± 0.62 min(-1)/mU/l × 10(4), P < 0.001) and in nondiabetics in D and E versus F (3.38 ± 0.77, 3.03 ± 0.72 versus 6.03 ± 1.69 min(-1)/mU/l × 10(4), P < 0.001). Also, GSH-Px and GR activities were lower in A and B versus C (GSH-Px: 21.96 ± 3.56, 22.51 ± 1.23 versus 25.12 ± 1.67; GR: 44.37 ± 3.58, 43.50 ± 2.39 versus 48.58 ± 3.67 U/gHb; P < 0.001) and in D and E versus F (GSH-Px: 24.75 ± 3.02, 25.57 ± 1.92 versus 28.56 ± 3.91; GR: 48.27 ± 6.81, 49.17 ± 6.24 versus 53.67 ± 3.96 U/gHb; P < 0.001). Decreases in Si and GR were significantly related to both ATI and LI in T2D. Our results showed that decreased IS and impaired antioxidant enzymes activity influence ischemic stroke subtypes in T2D. The influence of insulin resistance might be exerted on the level of glutathione-dependent antioxidant enzymes.

How does metabolic syndrome affect the functional ambulation in stroke patients?

BACKGROUND/AIMS

Metabolic syndrome (MetS) is a risk factor for stroke. However, the role of MetS in stroke rehabilitation has not been assessed. The aim of this study was to evaluate the impact of MetS on rehabilitation from stroke.

MATERIALS AND METHODS

A total of 337 consecutive patients with subacute stroke and 220 age-matched healthy controls were studied. The diagnosis of MetS was based on the criteria of the National Cholesterol Education Program Adult Treatment Panel III. Ambulation levels were evaluated using the Functional Ambulation Classification (FAC) measure. The correlation between MetS and FAC was investigated. The regression analysis included presence of hypertriglyceridemia, high fasting glucose, low high-density lipoprotein cholesterol, hypertension, abdominal obesity, MetS, and age ≯65 years.

RESULTS

The prevalence of MetS in the control group and the ischemic and hemorrhagic stroke groups was 33.2% (n = 73), 59.8% (n = 156), and 68.4% (n = 52), respectively. MetS prevalence was significantly higher in stroke groups compared with the control group (P < .001). FAC and MetS were significantly and negatively correlated in the stroke groups (P < .001, rho = -0.387, for hemorrhagic stroke;P < .001, rho = -0.379, for ischemic stroke). Multivariable logistic regression analysis demonstrated that diastolic tension, MetS presence, and age were found to be independent risk factors for FAC in ischemic stroke groups.

CONCLUSIONS

MetS is associated with worse functional ambulation for both ischemic and hemorrhagic stroke patients. Aggressive rehabilitation can be advocated in the presence of MetS in ischemic stroke patients.

Biology of metabolic syndrome in a vascular patient

Metabolic syndrome is highly prevalent in vascular patients and has a significant impact on the outcomes of vascular interventions. It comprises of a set of metabolically driven risk factors, including truncal obesity, dyslipidemia, elevated blood pressure and elevated fasting blood glucose. Increased insulin resistance within the context of obesity and hypertension contributes to atherogenic dyslipidemia, hyperglycemia, and prothrombotic and proinflammatory states which lead to the adverse impact of metabolic syndrome on the response to injury and on atherosclerotic disease progression. This review focuses on the complex biology of metabolic syndrome and its relevance to management of vascular patients, including outcomes and implications for the coronary, cerebrovascular and lower-extremity vascular beds.