Hypertension Is Associated with White Matter Disruption in Apparently Healthy Middle-Aged Individuals

Association of Blood Pressure With Brain White Matter Microstructural Integrity Assessed With MRI Diffusion Tensor Imaging in Healthy Young Adults

BACKGROUND

High blood pressure (BP) in middle-aged and older adults is associated with a brain white matter (WM) microstructural abnormality. However, little evidence is available in healthy young adults. We investigated the associations between high BP and WM microstructural integrity in young adults.

METHODS

This study included 1015 healthy young adults (542 women, 22-37 years) from the Human Connectome Project. Brachial systolic and diastolic BP were measured using a semiautomatic or manual sphygmomanometer. Diffusion-weighted magnetic resonance imaging was acquired to obtain diffusion tensor imaging metrics of free water (FW) content, FW-corrected WM fractional anisotropy, axial diffusivity, radial diffusivity, and mean diffusivity. Using whole-brain voxel-wise linear regression models and ANCOVA, we examined associations of BP and hypertension stage with diffusion tensor imaging metrics after adjusting for age, sex, education, body mass index, smoking status, alcohol consumption history, and differences in the b value used for diffusion magnetic resonance imaging.

RESULTS

Systolic and diastolic BP of the sample (mean±SD) were 122.8±13.0 and 76.0±9.9 mm Hg, respectively. Associations of BP with diffusion tensor imaging metrics revealed regional heterogeneity for FW-corrected fractional anisotropy. High BP and high hypertension stage were associated with higher FW and lower FW-corrected axial diffusivity, FW-corrected radial diffusivity, and FW-corrected mean diffusivity. Moreover, associations of high diastolic BP and hypertension stage with high FW were found only in men not in women.

CONCLUSIONS

High BP in young adults is associated with altered brain WM microstructural integrity, suggesting that high BP may have damaging effects on brain WM microstructural integrity in early adulthood, particularly in men.

Alterations of White Matter Connectivity in Adults with Essential Hypertension

Purpose

To explore the topology of the white matter network in individuals with essential hypertension by graph theory.

Patients and Methods

T1-weighted image and diffusion tensor imaging (DTI) data from 43 patients diagnosed with essential hypertension (EHT) and 33 individuals with normotension (healthy controls, HCs) were incorporated in this cross-sectional study. Furthermore, structural networks were constructed by graph theory to calculate whole brain network characteristics and intracerebral node characteristics.

Results

Both EHT and HC groups displayed small-worldness in their structural networks. The area under the curve (AUC) of the small-worldness coefficient (σ) was higher in the EHT group compared to the HC group, whereas the AUC of assortativity was lower in the EHT group in contrast to the HC group. The nodal clustering coefficient (CP) and local efficiency (Eloc) of the EHT group decreased in the right dorsolateral superior frontal gyrus and the left medial superior frontal gyrus. These values increased in the left anterior cingulate and paracingulate gyrus. Furthermore, weight and body mass index (BMI) were positively correlated with σ.

Conclusion

The EHT group showed brain network separation and integration dysfunction. Weight and BMI were positively correlated with σ. The data acquired in this investigation implied that altered structural connectivity in the prefrontal region may be a potential neuroimaging marker in EHT patients.

Diffusion in the corpus callosum predicts persistence of clinical symptoms after mild traumatic brain injury, a multi-scanner study

Background

Mild traumatic brain injuries (mTBIs) comprise 80% of all TBI, but conventional MRI techniques are often insensitive to the subtle changes and injuries produced in a concussion. Diffusion tensor imaging (DTI) is one of the most sensitive MRI techniques for mTBI studies with outcome and symptom associations described. The corpus callosum (CC) is one of the most studied fiber tracts in TBI and mTBI, but the comprehensive post-mTBI symptom relationship has not fully been explored.

Methods

This is a retrospective observational study of how quantitative DTI data of the CC and its sub-regions may relate to clinical presentation of symptoms and timing of resolution of symptoms in patients diagnosed with uncomplicated mTBI. DTI and clinical data were obtained retrospectively from 446 (mean age 42 years, range 13-82) civilian patients. From patient medical charts, presentation of the following common post-concussive symptoms was noted: headache, balance issues, cognitive deficits, fatigue, anxiety, depression, and emotional lability. Also recorded was the time between injury and a visit to the physician when improvement or resolution of a particular symptom was reported. FA values from the total CC and 3 subregions of the CC (genu or anterior, mid body, and splenium or posterior) were obtained from hand tracing on the Olea Sphere v3.0 SP12 free-standing workstation. DTI data was obtained from 8 different 3T MRI scanners and harmonized via ComBat harmonization. The statistical models used to explore the association between regional Fractional Anisotropy (FA) values and symptom presentation and time to symptom resolution were logistic regression and interval-censored semi-parametric Cox proportional hazard models, respectively. Subgroups related to age and timing of first scan were also analyzed.

Results

Patients with the highest FA in the total CC (p = 0.01), anterior CC (p < 0.01), and mid-body CC (p = 0.03), but not the posterior CC (p = 0.91) recovered faster from post-concussive cognitive deficits. Patients with the highest FA in the posterior CC recovered faster from depression (p = 0.04) and emotional lability (p = 0.01). There was no evidence that FA in the CC or any of its sub-regions was associated with symptom presentation or with time to resolution of headache, balance issues, fatigue, or anxiety. Patients with mTBI under 40 had higher FA in the CC and the anterior and mid-body subregions (but not the posterior subregion: p = 1.00) compared to patients 40 or over (p ≤ 0.01). There was no evidence for differences in symptom presentation based on loss of consciousness (LOC) or sex (p ≥ 0.18).

Conclusion

This study suggests that FA of the CC has diagnostic and prognostic value for clinical assessment of mTBI in a large diverse civilian population, particularly in patients with cognitive symptoms.

Cerebral Small Vessel Disease: a Review of the Pathophysiological Mechanisms

Cerebral small vessel disease (cSVD) refers to the age-dependent pathological processes involving the brain small vessels and leading to vascular cognitive impairment, intracerebral hemorrhage, and acute lacunar ischemic stroke. Despite the significant public health burden of cSVD, disease-specific therapeutics remain unavailable due to the incomplete understanding of the underlying pathophysiological mechanisms. Recent advances in neuroimaging acquisition and processing capabilities as well as findings from cSVD animal models have revealed critical roles of several age-dependent processes in cSVD pathogenesis including arterial stiffness, vascular oxidative stress, low-grade systemic inflammation, gut dysbiosis, and increased salt intake. These factors interact to cause a state of endothelial cell dysfunction impairing cerebral blood flow regulation and breaking the blood brain barrier. Neuroinflammation follows resulting in neuronal injury and cSVD clinical manifestations. Impairment of the cerebral waste clearance through the glymphatic system is another potential process that has been recently highlighted contributing to the cognitive decline. This review details these mechanisms and attempts to explain their complex interactions. In addition, the relevant knowledge gaps in cSVD mechanistic understanding are identified and a systematic approach to future translational and early phase clinical research is proposed in order to reveal new cSVD mechanisms and develop disease-specific therapeutics.

Associations of neuroimaging markers with depressive symptoms over time in middle-aged and elderly persons

BACKGROUND

Cerebrovascular disease is regarded as a potential cause of late-life depression. Yet, evidence for associations of neuroimaging markers of vascular brain disease with depressive symptoms is inconclusive. We examined the associations of neuroimaging markers and depressive symptoms in a large population-based study of middle-aged and elderly persons over time.

METHODS

A total of 4943 participants (mean age = 64.6 ± 11.1 years, 55.7% women) from the Rotterdam Study were included. At baseline, total brain volume, gray matter volume, white matter volume, white matter hyperintensities volume, cortical infarcts, lacunar infarcts, microbleeds, white matter fractional anisotropy, and mean diffusivity (MD) were measured with a brain MRI (1.5T). Depressive symptoms were assessed twice with the Center for Epidemiologic Studies Depression scale (median follow-up time: 5.5 years, IQR = 0.9). To assess temporal associations of neuroimaging markers and depressive symptoms, linear mixed models were used.

RESULTS

A smaller total brain volume (β = -0.107, 95% CI -0.192 to -0.022), larger white matter hyperintensities volume (β = 0.047, 95% CI 0.010-0.084), presence of cortical infarcts (β = 0.194, 95% CI 0.047-0.341), and higher MD levels (β = 0.060, 95% CI 0.022-0.098) were cross-sectionally associated with more depressive symptoms. Longitudinal analyses showed that small total brain volume (β = -0.091, 95% CI -0.167 to -0.015) and presence of cortical infarcts (β = 0.168, 95% CI 0.022-0.314) were associated with increasing depressive symptoms over time. After stratification on age, effect sizes were more pronounced at older ages.

CONCLUSIONS

Neuroimaging markers of white matter microstructural damage were associated with depressive symptoms longitudinally in this study of middle-aged and elderly persons. These associations were more pronounced at older ages, providing evidence for the role of white matter structure in late-life depressive symptomatology.

Is adiposity associated with white matter microstructural health and intelligence differently in males and females?

OBJECTIVE

The role of vascular risk factors in age-related brain degeneration has long been the subject of intense study, but the role of obesity remains understudied. Given known sex differences in fat storage and usage, this study investigates sex differences in the association between adiposity and white matter microstructural integrity, an important early marker of brain degeneration.

METHODS

This study assesses the associations between adiposity (abdominal fat ratio and liver proton density fat fraction) and brain health (measures of intelligence and white matter microstructure using diffusion-tensor imaging [DTI]) in a group of UK Biobank participants.

RESULTS

This study finds that intelligence and DTI metrics are indeed associated with adiposity differently in males and females. These sex differences are distinct from those in the associations of DTI metrics with age and blood pressure.

CONCLUSIONS

Taken together, these findings suggest that there are inherent sex-driven differences in how brain health is associated with obesity.

Supervised Phenotype Discovery From Multimodal Brain Imaging

Data-driven discovery of image-derived phenotypes (IDPs) from large-scale multimodal brain imaging data has enormous potential for neuroscientific and clinical research by linking IDPs to subjects' demographic, behavioural, clinical and cognitive measures (i.e., non-imaging derived phenotypes or nIDPs). However, current approaches are primarily based on unsupervised approaches, without the use of information in nIDPs. In this paper, we proposed a semi-supervised, multimodal, and multi-task fusion approach, termed SuperBigFLICA, for IDP discovery, which simultaneously integrates information from multiple imaging modalities as well as multiple nIDPs. SuperBigFLICA is computationally efficient and largely avoids the need for parameter tuning. Using the UK Biobank brain imaging dataset with around 40,000 subjects and 47 modalities, along with more than 17,000 nIDPs, we showed that SuperBigFLICA enhances the prediction power of nIDPs, benchmarked against IDPs derived by conventional expert-knowledge and unsupervised-learning approaches (with average nIDP prediction accuracy improvements of up to 46%). It also enables the learning of generic imaging features that can predict new nIDPs. Further empirical analysis of the SuperBigFLICA algorithm demonstrates its robustness in different prediction tasks and the ability to derive biologically meaningful IDPs in predicting health outcomes and cognitive nIDPs, such as fluid intelligence and hypertension.

Abnormal brain diffusivity in participants with persistent neuropsychiatric symptoms after COVID-19

Objectives

We aimed to compare brain white matter integrity in participants with post-COVID-19 conditions (PCC) and healthy controls.

Methods

We compared cognitive performance (NIH Toolbox®), psychiatric symptoms and diffusion tensor imaging (DTI) metrics between 23 PCC participants and 24 controls. Fractional anisotropy (FA), axial (AD), radial (RD), and mean (MD) diffusivities were measured in 9 white matter tracts and 6 subcortical regions using MRICloud.

Results

Compared to controls, PCC had similar cognitive performance, but greater psychiatric symptoms and perceived stress, as well as higher FA and lower diffusivities in multiple white matter tracts (ANCOVA-p-values≤0.001–0.048). Amongst women, PCC had higher left amygdala-MD than controls (sex-by-PCC p=0.006). Regardless of COVID-19 history, higher sagittal strata-FA predicted greater fatigue (r=0.48-0.52, p<0.001) in all participants, and higher left amygdala-MD predicted greater fatigue (r=0.61, p<0.001) and anxiety (r=0.69, p<0.001) in women, and higher perceived stress (r=0.45, p=0.002) for all participants.

Conclusions

Microstructural abnormalities are evident in PCC participants averaged six months after COVID-19. The restricted diffusivity (with reduced MD) and higher FA suggest enhanced myelination or increased magnetic susceptibility from iron deposition, as seen in stress conditions. The higher amygdala-MD in female PCC suggests persistent neuroinflammation, which might contribute to their fatigue, anxiety, and perceived stress.

Frequency and predictive factors of minimal hepatic encephalopathy before and after sustained virological response in HCV cirrhosis

Introduction

Data of minimal hepatic encephalopathy (MHE) before and after hepatitis C virus (HCV) treatment remain scarce. We aimed to describe the prevalence, evolution and predictive factors of MHE before and after a sustained virological response (SVR).

Material and methods

It was a prospective study that included adults with cirrhosis due to HCV treated by direct-acting agents (DAA). MHE was assessed using the Psychometric Hepatic Encephalopathy Score (PHES).

Results

104 patients (65% female, age 60 ±10 years; 69% with diabetes, 47% with hypertension; 82% Child-Pugh A) were included. MHE was assessed just before therapy and 12 (IQR 7-15) months after SVR. Prevalence of MHE before HCV treatment and after SVR were 16% and 22%, respectively (p = 0.18). Resolution of MHE after SVR occurred in a few patients (n = 4/17) and 10 of 87 patients (11.5%) without MHE before treatment developed this condition after SVR. MHE after SVR was more common in patients with MHE before treatment (57% vs. 5%, p < 0.001). In multivariate analysis, older age, hypertension and hypoalbuminemia after treat-ment were predictors of MHE after SVR. In the absence of all these variables, none of the patients had MHE. In contrast, the prevalence of MHE was 42% and 70% in the case of presence of any 2 of these factors and all these conditions, respectively.

Conclusions

MHE is frequent in patients with cirrhosis who achieved SVR after DAA. SVR is associated with low probability of resolution of MHE and may not entirely protect patients from developing de novo MHE. Presence of MHE before DAA, older age, hypertension and hypoalbuminemia after SVR were independently associated with this condition.

Effects of the Mindfulness-Based Blood Pressure Reduction (MB-BP) program on depression and neural structural connectivity

BACKGROUND

Hypertension-related illnesses are a leading cause of disability and death in the United States, where hypertension prevalence in adults is 46%, with only half of those afflicted having it under control. Due to the significant challenges in long-term efficacy and adverse effects associated with pharmacological interventions, there is an eminent need for complimentary approaches for treating hypertension. Although initial studies of the Mindfulness-Based Blood Pressure Reduction program (MB-BP) indicate that this novel 8-week intervention is effective at inducing lasting decreases in blood pressure, the neural correlates are unknown.

METHODS

The objectives of this study were to identify structural neural correlates of MB-BP using diffusion tensor magnetic resonance imaging (DTI) and assess potential correlations with key clinical outcomes.

RESULTS

In a subset of participants (14 MB-BP, 22 controls) from a larger stage IIa randomized controlled trial, MB-BP participants exhibited increased interoception and decreased depressive symptoms compared to controls. Analyses of DTI data revealed significant group differences in multiple white matter neural tracts associated with the limbic system and/or blood pressure. Specific changes in neural structural connectivity were significantly associated with measures of interoception and depression.

LIMITATIONS

Limitations include small sample size (leading to insufficient power in the analysis of blood pressure) and the study duration (3 months). The main MRI limitation is suboptimal resolution in areas of extensive neural tract crossings.

CONCLUSIONS

It is concluded that MB-BP induces alterations in brain structural connectivity which could mediate beneficial changes in depression and interoceptive awareness in individuals with hypertension.

Causal structure discovery identifies risk factors and early brain markers related to evolution of white matter hyperintensities

Our goal was to understand the complex relationship between age, sex, midlife risk factors, and early white matter changes measured by diffusion tensor imaging (DTI) and their role in the evolution of longitudinal white matter hyperintensities (WMH). We identified 1564 participants (1396 cognitively unimpaired, 151 mild cognitive impairment and 17 dementia participants) with age ranges of 30-90 years from the population-based sample of Mayo Clinic Study of Aging. We used computational causal structure discovery and regression analyses to evaluate the predictors of WMH and DTI, and to ascertain the mediating effect of DTI on WMH. We further derived causal graphs to understand the complex interrelationships between midlife protective factors, vascular risk factors, diffusion changes, and WMH. Older age, female sex, and hypertension were associated with higher baseline and progression of WMH as well as DTI measures (P ≤ 0.003). The effects of hypertension and sex on WMH were partially mediated by microstructural changes measured on DTI. Higher midlife physical activity was predictive of lower WMH through a direct impact on better white matter tract integrity as well as an indirect effect through reducing the risk of hypertension by lowering BMI. This study identified key risks factors, early brain changes, and pathways that may lead to the evolution of WMH.

Characterizing CD38 Expression and Enzymatic Activity in the Brain of Spontaneously Hypertensive Stroke-Prone Rats

Background: CD38 is a transmembrane glycoprotein that catabolizes nicotinamide adenine dinucleotide (NAD+) and is the main source for the age-dependent decrease in NAD+ levels. Increased CD38 enzymatic activity has been implicated in several neurological diseases. However, its role in the pathogenesis of cerebral small vessel disease (CSVD) remains unknown. We aimed to characterize CD38 expression and enzymatic activity in the brain of spontaneously hypertensive stroke-prone rats (SHRSP), a genetic model for hypertension and human CSVD, in comparison to age-matched normotensive Wistar Kyoto rats (WKY). Materials and Methods: Age-matched male 7- and 24-week-old WKY and SHRSP were studied. CD38 enzymatic activity was determined in the brain homogenate. Immunohistochemistry and Western Blotting (WB) were used to characterize CD38 expression and localize it in the different cell types within the brain. In addition, expression of nitric oxide synthase (NOS) isoforms and the levels of nitric oxide (NO), superoxide, nicotinamide dinucleotide (phosphate) NAD(P)H were measured the brain of in WKY and SHRSP. Results: CD38 expression and enzymatic activity were increased in SHRSP brains compared to age matched WKY starting at 7 weeks of age. CD38 expression was localized to the endothelial cells, astrocytes, and microglia. We also identified increased CD38 expression using WB with age in SHRSP and WKY. CD38 enzymatic activity was also increased in 24-week SHRSP compared to 7-week SHRSP. In association, we identified evidence of oxidative stress, reduced NO level, reduced NAD(P)H level and endothelial NOS expression in SHRSP compared to age matched WKY. NAD(P)H also decreased with age in WKY and SHRSP. Additionally, activation of astrocytes and microglia were present in SHRSP compared to WKY. Conclusions: CD38 is overexpressed, and its enzymatic activity is increased in SHRSP, a genetic model for marked hypertension and human CSVD. Our results suggest a potential role for CD38 enzymatic activation in the pathogenesis of CSVD and points to the need for future mechanistic and pharmacological studies.

Association of Vascular Properties With the Brain White Matter Hyperintensity in Middle-Aged Population

Background The periventricular white matter is more sensitive to the systemic hemodynamic alterations than the deep white matter because of differences in its vascular structure and systemic circulation relationship. We hypothesize that periventricular white matter hyperintensity (PVWMH) volume shows greater association than deep white matter hyperintensity (DWMH) volume with vascular properties (VPs) reflecting arterial stiffness and cardiovascular remodeling, indicators of the systemic circulation. Methods and Results A total of 426 participants (age, 59.0±6.1 years; 57.5% women; and 39.7% Black race) in the Genetic Study of Atherosclerosis Risk who were aged ≥50 years and had brain magnetic resonance imaging were studied. VPs included pulse pressure, hypertensive response to exercise, diastolic brachial artery diameter, diastolic common carotid artery diameter, common carotid artery distensibility coefficient, and left ventricular function. The relative associations of VPs with PVWMH and DWMH as multiple measures within the same individual were determined using multilevel linear models. We also determined if age modified the differences in VPs associations with PVWMH and DWMH. Our findings indicated that, within the same subject, PVWMH volume had greater association than DWMH volume with pulse pressure (P=0.002), hypertensive response to exercise (P=0.04), diastolic brachial artery diameter (P=0.012), and diastolic common carotid artery diameter (P=0.04), independent of age and cardiovascular risk factors. The differences of PVWMH versus DWMH associations with VPs did not differ at any age threshold. Conclusions We show, for the first time, that PVWMH has greater association than DWMH, independent of age, with vascular measurements of arterial stiffness and cardiovascular remodeling suggesting that changes in the systemic circulation affect the PVWMH and DWMH differently.

Blood Pressure Rhythm and Blood Pressure Variability as Risk Factors for White Matter Lesions: A Cross-Sectional Study

Background

White matter lesions are common in the elderly. The aim of this study was to explore the correlation between blood pressure rhythm and blood pressure variability with white matter lesions.

Material/Methods

A total of 144 subjects aged 40 to 80 years underwent MRI scanning to assess the degree of white matter lesions using the Fazekas scale. The regional cerebral blood flow was detected by brain perfusion imaging, and an ambulatory blood pressure monitor was used to measure the circadian blood pressure rhythm. Odds ratio and the 95% confidence interval was computed using logistics regression analysis. The relationship between various factors and blood pressure was calculated by curve simulation.

Results

With the increase of white matter lesions, the regional cerebral blood flow at the lesion decreased gradually. Systolic blood pressure day/night difference ratio (OR=0.815, 95% CI 0.729–0.910), diastolic blood pressure day/night difference ratio (OR=0.895, 95% CI 0.831–0.964), systolic blood pressure coefficient of variation (OR=1.589, 95% CI 1.273–1.983), and diastolic blood pressure coefficient of variation (OR=1.363, 95% CI 1.150–1.616) were significantly associated with Fazekas score (P<0.05 for all).

Conclusions

Greater blood pressure variability and blood pressure rhythm disorders were associated with lower regional cerebral blood flow in patients with white matter lesions.

Characterizing the Neuroimaging and Histopathological Correlates of Cerebral Small Vessel Disease in Spontaneously Hypertensive Stroke-Prone Rats

Introduction: Spontaneously hypertensive stroke-prone rats (SHRSP) are used to model clinically relevant aspects of human cerebral small vessel disease (CSVD). To decipher and understand the underlying disease dynamics, assessment of the temporal progression of CSVD histopathological and neuroimaging correlates is essential. Materials and Methods: Eighty age-matched male SHRSP and control Wistar Kyoto rats (WKY) were randomly divided into four groups that were aged until 7, 16, 24 and 32 weeks. Sensorimotor testing was performed weekly. Brain MRI was acquired at each study time point followed by histological analyses of the brain. Results: Compared to WKY controls, the SHRSP showed significantly higher prevalence of small subcortical hyperintensities on T2w imaging that progressed in size and frequency with aging. Volumetric analysis revealed smaller intracranial and white matter volumes on brain MRI in SHRSP compared to age-matched WKY. Diffusion tensor imaging (DTI) showed significantly higher mean diffusivity in the corpus callosum and external capsule in WKY compared to SHRSP. The SHRSP displayed signs of motor restlessness compared to WKY represented by hyperactivity in sensorimotor testing at the beginning of the experiment which decreased with age. Distinct pathological hallmarks of CSVD, such as enlarged perivascular spaces, microbleeds/red blood cell extravasation, hemosiderin deposits, and lipohyalinosis/vascular wall thickening progressively accumulated with age in SHRSP. Conclusions: Four stages of CSVD severity in SHRSP are described at the study time points. In addition, we find that quantitative analyses of brain MRI enable identification of in vivo markers of CSVD that can serve as endpoints for interventional testing in therapeutic studies.

Brain structure and perfusion in relation to serum renal function indexes in healthy young adults

Prior neuroimaging studies of the relationship between the kidney and the brain have been limited to clinical populations and have largely relied on a single modality. We sought to examine the kidney-brain associations in healthy subjects using a combined analysis of multi-modal imaging data. Structural, diffusion, and perfusion magnetic resonance imaging (MRI) scans were performed to measure cortical thickness, white matter integrity, and cerebral blood flow in 157 healthy young adults. Peripheral venous blood samples were collected to measure serum renal function indexes. Correlation analyses were performed to investigate the relations between brain MRI measures and renal function indexes. Results showed that higher serum uric acid level was associated with increased cortical thickness in the transverse temporal gyrus. We also found that decreased serum creatinine level was linked to lower white matter integrity in the sagittal stratum, anterior corona radiata, superior corona radiata, and external capsule. Furthermore, we observed that increased serum uric acid level was related to hyperperfusion in the opercular and triangular parts of inferior frontal gyrus and supramarginal gyrus, and hypoperfusion in the calcarine sulcus, cuneus and lingual gyrus. More importantly, mediation analysis revealed that the relationship between serum uric acid and working memory performance was mediated by perfusion in the supramarginal gyrus and lingual gyrus. These findings not only may extend current knowledge regarding the relationship between the kidney and the brain, but also may inform real-world clinical practice by identification of potential brain regions vulnerable to renal dysfunction.

Common genetic variation influencing human white matter microstructure

Brain regions communicate with each other through tracts of myelinated axons, commonly referred to as white matter. We identified common genetic variants influencing white matter microstructure using diffusion magnetic resonance imaging of 43,802 individuals. Genome-wide association analysis identified 109 associated loci, 30 of which were detected by tract-specific functional principal components analysis. A number of loci colocalized with brain diseases, such as glioma and stroke. Genetic correlations were observed between white matter microstructure and 57 complex traits and diseases. Common variants associated with white matter microstructure altered the function of regulatory elements in glial cells, particularly oligodendrocytes. This large-scale tract-specific study advances the understanding of the genetic architecture of white matter and its genetic links to a wide spectrum of clinical outcomes.

Mathematical modeling of cerebral capillary blood flow heterogeneity and its effect on brain tissue oxygen levels

Maintaining cerebral blood flow is critical for adequate neuronal function. Previous computational models of brain capillary networks have predicted that heterogeneous cerebral capillary flow patterns result in lower brain tissue partial oxygen pressures PO2). However, these previous models have often considered simple capillary networks in terms of their geometric properties. In this current work, we developed and analyzed computational models of brain capillary networks to determine how perturbations of network properties impact tissue oxygen levels. The models include variabilities in both their geometric (segment lengths and diameters) and three-dimensional, topological structure. Two classes of capillary network models are considered. The first consists of equations for the oxygen partial pressure, PO₂, in both a capillary network and the surrounding tissue. In order to gain insight into the behavior of this detailed model, we also consider a reduced model for changes in PO₂ in just the capillary network. The main result is that for a general class of networks, random perturbations of either segment diameters or conductances will always, on average, decrease the average tissue oxygen levels. This result is supported through both simulations of the models and mathematical analysis. Our results promise to expand our understanding of cerebral capillary blood flow and its impact on the brain function in health and disease.

Association of Blood Pressure, White Matter Lesions, and Regional Cerebral Blood Flow

Background

At present, the association between blood pressure, regional cerebral blood flow, and white matter lesions is not well understood.

Material/Methods

A total of 147 subjects aged from 40 to 80 years were assessed by the Fazekas score for white matter lesions, CT perfusion imaging for regional cerebral blood flow, and 24-h ambulatory blood pressure monitoring for blood pressure level and rhythm. Logistic regression analysis was used to obtain the odds ratio and 95% confidence interval between Fazekas scores and relevant factors. The relationship between blood pressure index and regional cerebral blood flow was analyzed through cubic curve estimation.

Results

Fazekas score was negatively correlated with regional cerebral blood flow (r=−0.801; r=−0.831, P<0.001). For subcortical lesion, the regional cerebral blood flow of Fazekas grade 0 was 1.976 times that of Fazekas grade 3 (OR=1.976, 95% CI=1.576–2.477), and for periventricular lesion, the regional cerebral blood flow of Fazekas grade 0 was 2.034 times that of Fazekas grade 3 (OR=2.034, 95% CI=1.602–2.583). Increased nighttime systolic blood pressure may be more dangerous (OR=1.112, 95% CI=1.059–1.169). The day-night systolic blood pressure ratio (OR=0.801, 95% CI 0.711–0.902) and the day-night diastolic blood pressure ratio (OR=0.876, 95% CI 0.807–0.950) were significantly correlated with Fazekas score.

Conclusions

The decrease of white matter regional cerebral blood flow caused by hypertension is probably one of the important causes of white matter lesions. Patients with white matter lesions should also pay attention to the rhythm of blood pressure when controlling hypertension, especially if their blood pressure is too high or too low at night.

Phenotype discovery from population brain imaging

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A multimodal independent component analysis approach is presented for performing data fusion in UK biobank scale dataset.

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This approach can estimate modes of population variability that enhance the ability to predict thousands of non-imaging phenotypes.

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This approach improves predictive power compared with widely-used analysis strategies, single-modality decompositions and existing IDPs.

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In UKB data, many interpretable associations with non-imaging phenotypes were identified.

Neuroimaging allows for the non-invasive study of the brain in rich detail. Data-driven discovery of patterns of population variability in the brain has the potential to be extremely valuable for early disease diagnosis and understanding the brain. The resulting patterns can be used as imaging-derived phenotypes (IDPs), and may complement existing expert-curated IDPs. However, population datasets, comprising many different structural and functional imaging modalities from thousands of subjects, provide a computational challenge not previously addressed. Here, for the first time, a multimodal independent component analysis approach is presented that is scalable for data fusion of voxel-level neuroimaging data in the full UK Biobank (UKB) dataset, that will soon reach 100,000 imaged subjects. This new computational approach can estimate modes of population variability that enhance the ability to predict thousands of phenotypic and behavioural variables using data from UKB and the Human Connectome Project. A high-dimensional decomposition achieved improved predictive power compared with widely-used analysis strategies, single-modality decompositions and existing IDPs. In UKB data (14,503 subjects with 47 different data modalities), many interpretable associations with non-imaging phenotypes were identified, including multimodal spatial maps related to fluid intelligence, handedness and disease, in some cases where IDP-based approaches failed.

Magnetic Resonance Imaging in Childhood Primary Hypertension: Potential in the Study of Cognitive Outcomes

Primary hypertension in youth and young adulthood is associated with decreased neurocognitive test performance both in midlife and during youth itself, leading to concern of subsequent cognitive decline and dementia in later life. The early vascular effects of hypertension in youth are likely involved in the pathogenesis of hypertensive target organ damage to the brain, but the potential impact of antihypertensive treatment from youth on subsequent cognitive health is not known. This review will highlight the need to answer the question of whether treatment of hypertension from early in life would slow cognitive decline in adulthood, and will then outline, for the nonneurologist, magnetic resonance imaging techniques potentially useful in the study of the pathogenesis of decreased cognition in hypertensive youth and for use as potential biomarkers for early antihypertensive treatment interventions.

White Matter Injury Is Associated with Reduced Manual Dexterity and Elevated Serum Ceramides in Subjects with Cerebral Small Vessel Disease

INTRODUCTION

We have demonstrated that asymptomatic cerebral small vessel disease (cSVD) measured by white matter hyperintensity volume is associated with reduced manipulative manual dexterity on the Grooved Peg Board Test (GPBT) in middle-aged healthy individuals with a family history of early coronary artery disease. In this current study, we aim to identify the association of subcortical white matter microstructural impairment measured by diffusion tensor imaging, manual dexterity measured by GPBT and circulating serums ceramide, another marker for white matter injury. We hypothesize that lower regional fractional anisotropy (rFA) is associated with worse performance on GPBT and elevated serum ceramides in the same study population.

METHODS

rFA of 48 regions representing the subcortical white matters were analyzed in GeneSTAR participants in addition to serum ceramides and GPBT scores. Unadjusted univariable analyses with Bonferroni correction for multiple comparisons were completed using Spearman correlation for testing the associations between ceramides, rFA of subcortical white matter, and GPBT performance. Subsequently, sensitivity analyses were performed after excluding the participants that had any physical limitation that may influence their performance on GPBT. Finally, in the adjusted analysis using generalized estimating equation, linear regression models were performed for the areas that met significance threshold in the unadjusted analyses.

RESULTS

112 subjects (age [49 ± 11], 51% female, 39.3% African American) were included. Adjusted analyses for the significant correlations that met the Bonferroni correction threshold in the unadjusted univariable analyses identified significant negative associations between rFA of the right fornix (RF) and log-GPBT score (β = -0.497, p = 0.037). In addition, rFA of RF negatively correlated with log serum ceramide levels (C18: β = -0.03, p = 0.003, C20: β = -0.0002, p = 0.004) and rFA of left genu of corpus callosum negatively correlated with log C18 level (β = -0.0103, p = 0.027).

CONCLUSIONS

These results demonstrate that subcortical microstructural white matter disruption is associated with elevated serum ceramides and reduced manual dexterity in a population with cSVD. These findings suggest that injury to white matter tracts undermines neural networks, with functional consequences in a middle-aged population with cardiovascular risk factors.

Association of Low Blood Pressure with White Matter Hyperintensities in Elderly Individuals with Controlled Hypertension

Background and Purpose

Both hypertension and hypotension increase cerebral white matter hyperintensities. However, the effects of hypotension in individuals with treated hypertension are unknown. We analyzed the association of low blood pressure with the location and amount of white matter hyperintensities between elderly individuals with controlled hypertension and those without hypertension.

Methods

We enrolled 505 community-dwelling, cognitively normal elderly individuals from the participants of the Korean Longitudinal Study on Cognitive Aging and Dementia. We measured blood pressure three times in a sitting position using a mercury sphygmomanometer and defined low systolic and diastolic blood pressure as ≤110 and ≤60 mm Hg, respectively. We segmented and quantified the periventricular and deep white matter hyperintensities from 3.0 Tesla fluid-attenuated inversion recovery magnetic resonance images.

Results

Low systolic blood pressure was independently associated with larger volume of periventricular white matter hyperintensity (P=0.049). The interaction between low systolic blood pressure and hypertension was observed on the volume of periventricular white matter hyperintensity (P=0.005). Low systolic blood pressure was associated with the volume of periventricular white matter hyperintensity in individuals with controlled hypertension (F_1,248=6.750, P=0.010), but not in those without hypertension (P=0.380). Low diastolic blood pressure was not associated with the volumes of white matter hyperintensities regardless of presence of controlled hypertension.

Conclusions

Low systolic blood pressure seems to be associated with larger volume of periventricular white matter hyperintensity in the individuals with a historyof hypertension but not in those without hypertension.

Associations between modifiable risk factors and white matter of the aging brain: insights from diffusion tensor imaging studies

There is increasing interest in factors that may modulate white matter (WM) breakdown and, consequentially, age-related cognitive and behavioral deficits. Recent diffusion tensor imaging studies have examined the relationship of such factors with WM microstructure. This review summarizes the evidence regarding the relationship between WM microstructure and recognized modifiable factors, including hearing loss, hypertension, diabetes, obesity, smoking, depressive symptoms, physical (in) activity, and social isolation, as well as sleep disturbances, diet, cognitive training, and meditation. Current cross-sectional evidence suggests a clear link between loss of WM integrity (lower fractional anisotropy and higher mean diffusivity) and hypertension, obesity, diabetes, and smoking; a relationship that seems to hold for hearing loss, social isolation, depressive symptoms, and sleep disturbances. Physical activity, cognitive training, diet, and meditation, on the other hand, may protect WM with aging. Preliminary evidence from cross-sectional studies of treated risk factors suggests that modification of factors could slow down negative effects on WM microstructure. Careful intervention studies are needed for this literature to contribute to public health initiatives going forward.