Effect of white matter lesions on brain perfusion in Alzheimer's disease

Association of Cerebral Blood Flow With Longitudinal Changes in Cerebral Microstructural Integrity in the Coronary Artery Risk Development in Young Adults (CARDIA) Study

IMPORTANCE

Decreased cerebral tissue integrity and cerebral blood flow (CBF) are features of neurodegenerative diseases. Brain tissue maintenance is an energy-demanding process, making it particularly sensitive to hypoperfusion. However, little is known about the association between blood flow and brain microstructural integrity, including in normative aging.

OBJECTIVE

To assess associations between CBF and changes in cerebral tissue integrity in white matter and gray matter brain regions.

DESIGN, SETTING, AND PARTICIPANTS

In this longitudinal cohort study, magnetic resonance imaging was performed on 732 healthy adults from the Coronary Artery Risk Development in Young Adults (CARDIA) study, a prospective longitudinal study (baseline age of 18-30 years) that examined participants up to 8 times during 30 years (1985-1986 to 2015-2016). Cerebral blood flow was measured at baseline (year 25 of the CARDIA study), and changes in diffusion tensor indices of fractional anisotropy (FA) and mean diffusivity (MD), measures of microstructural tissue integrity, were measured at both baseline and after approximately 5 years of follow-up (year 30). Analyses were conducted from November 5, 2020, to January 29, 2022.

MAIN OUTCOMES AND MEASURES

Automated algorithms and linear mixed-effects statistical models were used to evaluate the associations between CBF at baseline and changes in FA or MD.

RESULTS

After exclusion of participants with missing or low-quality data, 654 at baseline (342 women; mean [SD] age, 50.3 [3.5] years) and 433 at follow-up (230 women; mean [SD] age, 55.1 [3.5] years) were scanned for CBF or FA and MD imaging. In the baseline cohort, 247 participants were Black (37.8%) and 394 were White (60.2%); in the follow-up cohort, 156 were Black (36.0%) and 277 were White (64.0%). Cross-sectionally, FA and MD were associated with CBF in most regions evaluated, with lower CBF values associated with lower FA or higher MD values, including the frontal white matter lobes (for CBF and MD: mean [SE] β = -1.4 [0.5] × 10-6; for CBF and FA: mean [SE] β = 2.9 [1.0] × 10-4) and the parietal white matter lobes (for CBF and MD: mean [SE] β = -2.4 [0.6] × 10-6; for CBF and FA: mean [SE] β = 4.4 [1.1] × 10-4). Lower CBF values at baseline were also significantly associated with steeper regional decreases in FA or increases in MD in most brain regions investigated, including the frontal (for CBF and MD: mean [SE] β = -1.1 [0.6] × 10-6; for CBF and FA: mean [SE] β = 2.9 [1.0] × 10-4) and parietal lobes (for CBF and MD: mean [SE] β = -1.5 [0.7] × 10-6; for CBF and FA: mean [SE] β = 4.4 [1.1] × 10-4).

CONCLUSIONS AND RELEVANCE

Results of this longitudinal cohort study of the association between CBF and diffusion tensor imaging metrics suggest that blood flow may be significantly associated with brain tissue microstructure. This work may lay the foundation for investigations to clarify the nature of early brain damage in neurodegeneration. Such studies may lead to new neuroimaging biomarkers of brain microstructure and function for disease progression.

Relationship between Cerebrospinal Fluid Matrix Metalloproteinases Levels and Brain Amyloid Deposition in Mild Cognitive Impairment

This study aimed to explore whether cerebrospinal fluid (CSF) levels of matrix metalloproteinases (MMPs), and their inhibitors (TIMPs) were associated with brain amyloid deposition, cortical glucose metabolism, and white matter lesions (WMLs) in individuals with amnestic mild cognitive impairment (MCI). A total of 33 individuals with amnestic MCI (mean age, 75.6 years) underwent ¹¹C-Pittsburgh compound B positron emission tomography (PiB-PET), ¹⁸F-fluorodeoxyglucose positron emission tomography, magnetic resonance imaging or computed tomography, and CSF analysis. PET uptake of the frontal and temporoparietal lobes and posterior cingulate gyrus was assessed using the cerebellar cortex as the reference region. WMLs were assessed by the Fazekas scale. CSF levels of MMPs and TIMPs were measured with bead-based multiplex assays. After adjusting for covariates, multiple linear regression analysis showed that CSF levels of MMP-2 were negatively correlated with global PiB uptake (p = 0.035), especially in the parietotemporal lobe and posterior cingulate gyrus (p = 0.016 and p = 0.041, respectively). Moreover, CSF levels of MMP-7 were positively correlated with the severity of WMLs (p = 0.033). CSF levels of MMP-2 and MMP-7 are associated with brain amyloid deposition and severity of WMLs, respectively. These findings provide valuable insights into the role of MMPs in amyloid β catabolism and blood-brain barrier integration at the MCI stage.

Association between Matrix Metalloproteinases, Their Tissue Inhibitor and White Matter Lesions in Mild Cognitive Impairment

BACKGROUND

White matter lesions are frequently found in mild cognitive impairments and Alzheimer's disease. Matrix metalloproteinases and the tissue inhibitor of metalloproteinases are implicated in amyloid-β catabolism and blood brain barrier permeability. However, it remains unclear whether they are associated with white matter lesions in Alzheimer's disease.

OBJECTIVE

The aim of this study was to examine the association of matrix metalloproteinases and tissue inhibitor of metalloproteinases with white matter degeneration in subjects with amyloid-positive mild cognitive impairment.

METHODS

Thirty subjects with amnestic mild cognitive impairment (14 men and 16 women; mean age, 75.6 ± 5.8 years) underwent magnetic resonance imaging, ¹¹C-Pittsburgh Compound B positron emission tomography, and ¹⁸F-fluorodeoxyglucose positron emission tomography. Levels of plasma matrix metalloproteinases and tissue inhibitor of metalloproteinases were measured using multiplex assays. All subjects had an abnormal brain amyloid burden. Subjects were divided into two groups according to the presence of white matter lesions using the Fazekas scale. Cognitive function testing results i.e., mean ¹¹C-Pittsburgh Compound B and ¹⁸F-fluorodeoxyglucose uptake, concentrations of matrix metalloproteinases and tissue inhibitor of metalloproteinases, and matrix metalloproteinases/tissue inhibitor of metalloproteinases ratios were compared between the groups. Correlation analysis was conducted to investigate the association between Fazekas scale score and clinical and neuroimaging variables as well as concentrations of matrix metalloproteinases and tissue inhibitor of metalloproteinases.

RESULTS

Matrix metalloproteinases-2, -8, and -9 levels, matrix metalloproteinases-2/ tissue inhibitor of metalloproteinases-2, matrix metalloproteinases-8/ tissue inhibitor of metalloproteinases-1, and matrix metalloproteinases-9/tissue inhibitor of metalloproteinases-1 significantly increased and tissue inhibitor of metalloproteinases-1 and-2 levels significantly decreased in the group with white matter lesions compared with the group without white matter lesions. Matrix metalloproteinases-2, -8, and -9 levels correlated positively and tissue inhibitor of metalloproteinases-1 and -2 levels correlated negatively with Fazekas scale score.

CONCLUSION

Plasma matrix metalloproteinases-2, -8, -9 and tissue inhibitor of metalloproteinases-1 and -2 levels are associated with white matter lesions in the mild cognitive impairment stage of Alzheimer's disease.

Association of cerebral blood flow with myelin content in cognitively unimpaired adults

Background

Myelin loss and cerebral blood flow (CBF) decline are central features of several neurodegenerative diseases. Myelin maintenance through oligodendrocyte metabolism is an energy-demanding process, so that myelin homeostasis is particularly sensitive to hypoxia, hypoperfusion or ischaemia. However, in spite of its central importance, little is known about the association between blood supply and myelin integrity.

Objective

To assess associations between cortical and subcortical CBF, and subcortical myelin content, in critical brain white matter regions.

Materials and methods

MRI was performed on a cohort of 67 cognitively unimpaired adults. Using advanced MRI methodology, we measured whole-brain longitudinal and transverse relaxation rates (R₁ and R₂), sensitive but non-specific markers of myelin content, and myelin water fraction (MWF), a direct surrogate of myelin content, as well as regional CBF, from each of these participants.

Results

All quantitative relaxometry metrics were positively associated with CBF in all brain regions evaluated. These associations between MWF or R₁ and CBF, and, to a lesser extent, between R₂ and CBF, were statistically significant in most brain regions examined, indicating that lower regional cortical or subcortical CBF corresponds to a decrease in local subcortical myelin content. Finally, all relaxometry metrics exhibited a quadratic, inverted U-shaped, association with age; this is attributed to the development of myelination from young to middle age, followed by progressive loss of myelin in later years.

Conclusions

In this first study examining the association between local blood supply and myelin integrity, we found that myelin content declines with CBF across a wide age range of cognitively normal subjects.

Associations between cerebral blood flow and structural and functional brain imaging measures in individuals with neuropsychologically defined mild cognitive impairment

Reduced cerebral blood flow (CBF), an indicator of neurovascular processes and metabolic demands, is a common finding in Alzheimer's disease. However, little is known about what contributes to CBF deficits in individuals with mild cognitive impairment (MCI). We examine regional CBF differences in 17 MCI compared with 21 age-matched cognitively healthy older adults. Next, we examined associations between CBF, white matter lesion (WML) volume, amplitude of low-frequency fluctuations, and cortical thickness to better understand whether altered CBF was detectable before other markers and the potential mechanistic underpinnings of CBF deficits in MCI. MCI had significantly reduced CBF, whereas cortical thickness and amplitude of low-frequency fluctuation were not affected. Reduced CBF was associated with the WML volume but not associated with other measures. Given the presumed vascular etiology of WML and relative worsening of vascular health in MCI, it may suggest CBF deficits result from early vascular as opposed to metabolic deficits in MCI. These findings may support vascular mechanisms as an underlying component of cognitive impairment.

Endothelins in inflammatory neurological diseases

Endothelins were discovered more than thirty years ago as potent vasoactive compounds. Beyond their well-documented cardiovascular properties, however, the contributions of the endothelin pathway have been demonstrated in several neuroinflammatory processes and the peptides have been reported as clinically relevant biomarkers in neurodegenerative diseases. Several studies report that endothelin-1 significantly contributes to the progression of neuroinflammatory processes, particularly during infections in the central nervous system (CNS), and is associated with a loss of endothelial integrity at the blood brain barrier level. Because of the paucity of clinical trials with endothelin-1 antagonists in several infectious and non-infectious neuroinflammatory diseases, it remains an open question whether the 21 amino acid peptide is a mediator/modulator rather than a biomarker of the progression of neurodegeneration. This review focuses on the potential roles of endothelins in the pathology of neuroinflammatory processes, including infectious diseases of viral, bacterial or parasitic origin in which the synthesis of endothelins or its pharmacology have been investigated from the cell to the bedside in several cases, as well as in non-infectious inflammatory processes such as neurodegenerative disorders like Alzheimers Disease or central nervous system vasculitis.

Effects of white matter lesions on brain perfusion in patients with mild cognitive impairment

OBJECTIVE

To evaluate the effects of white matter lesions on regional cerebral blood flow in subjects with amnestic mild cognitive impairment.

PATIENTS AND METHODS

Seventy-five subjects with mild cognitive impairment (36 men and 39 women; mean age, 78.1 years) were included in the study. We used the Mini-Mental State Examination to assess cognitive function. All subjects underwent brain magnetic resonance imaging and ^99mTc ethylcysteinate dimer single photon emission computed tomography. Subjects were stratified based on the presence or absence of white matter lesions on magnetic resonance imaging. Statistical parametric mapping of differences in regional cerebral blood flow between the two groups were assessed by voxel-by-voxel group analysis using SPM8.

RESULTS

Of all 75 subjects with mild cognitive impairment, 46 (61.3%) had mild to moderate white matter lesions. The prevalence of hypertension tended to be higher in subjects with white matter lesions than in those without white matter lesions. Mini-Mental State Examination scores were significantly lower in subjects with white matter lesions than in those without white matter lesions. Subjects with white matter lesions had decreased regional cerebral blood flow mainly in the frontal, parietal, and medial temporal lobes, as well as the putamen, compared to those without white matter lesions.

CONCLUSION

In subjects with mild cognitive impairment, white matter lesions were associated with cognitive impairment and mainly frontal lobe brain function.

Cerebral blood flow in small vessel disease: A systematic review and meta-analysis

White matter hyperintensities are frequent on neuroimaging of older people and are a key feature of cerebral small vessel disease. They are commonly attributed to chronic hypoperfusion, although whether low cerebral blood flow is cause or effect is unclear. We systematically reviewed studies that assessed cerebral blood flow in small vessel disease patients, performed meta-analysis and sensitivity analysis of potential confounders. Thirty-eight studies (n = 4006) met the inclusion criteria, including four longitudinal and 34 cross-sectional studies. Most cerebral blood flow data were from grey matter. Twenty-four cross-sectional studies (n = 1161) were meta-analysed, showing that cerebral blood flow was lower in subjects with more white matter hyperintensity, globally and in most grey and white matter regions (e.g. mean global cerebral blood flow: standardised mean difference-0.71, 95% CI -1.12, -0.30). These cerebral blood flow differences were attenuated by excluding studies in dementia or that lacked age-matching. Four longitudinal studies (n = 1079) gave differing results, e.g., more baseline white matter hyperintensity predated falling cerebral blood flow (3.9 years, n = 575); cerebral blood flow was low in regions that developed white matter hyperintensity (1.5 years, n = 40). Cerebral blood flow is lower in subjects with more white matter hyperintensity cross-sectionally, but evidence for falling cerebral blood flow predating increasing white matter hyperintensity is conflicting. Future studies should be longitudinal, obtain more white matter data, use better age-correction and stratify by clinical diagnosis.

Influence of cerebral white matter hyperintensities on cognitive impairment in elderly medical patients

AIM

We investigated the characteristics of elderly medical patients with white matter hyperintensities on magnetic resonance imaging.

METHODS

A total of 213 patients (123 men and 90 women; mean age 74.8 years) reported their history of hypertension, diabetes, dyslipidemia, previous stroke, coronary heart disease and chronic kidney disease (CKD). All patients completed the Mini-Mental State Examination and Geriatric Depression Scale. White matter hyperintensities were evaluated for the periventricular region, basal ganglia (BGH), deep white matter and infratentorial region, and brain atrophy was calculated as bicaudate ratios.

RESULTS

Patients with cognitive impairment (Mini-Mental State Examination score < 24) were significantly older (P = 0.001), had periventricular region hyperintensities (P = 0.029) and BGH (P = 0.0015), and showed atrophy (P < 0.0001). Logistic regression showed that cognitive impairment was predicted by stroke (OR 2.5, 95% CI 0.033-0.894, P = 0.036) and atrophy (OR 8.43, 95% CI 5.71-37.0, P = 0.0109). Multiple regressions showed that BGH was associated with CKD (β = 0.213; P = 0.003), and infratentorial region was associated with stroke (β = 0.157; P =0.035) and CKD (β = 0.172; P = 0.016). Periventricular region was associated with age (β = 0.2; P = 0.011) and Geriatric Depression Scale (β = 0.151; P = 0.037), and deep white matter hyperintensities with age (β = 0.189; P = 0.016).

CONCLUSIONS

Although cognitive impairment in elderly medical patients is associated with stroke and brain atrophy, white matter hyperintensities, especially BGH and infratentorial region, are associated with cognitive decline in relation to CKD. Geriatr Gerontol Int 2017; 17: 1488-1493.

Microstructure and Cerebral Blood Flow within White Matter of the Human Brain: A TBSS Analysis

BACKGROUND

White matter (WM) fibers connect different brain regions and are critical for proper brain function. However, little is known about the cerebral blood flow in WM and its relation to WM microstructure. Recent improvements in measuring cerebral blood flow (CBF) by means of arterial spin labeling (ASL) suggest that the signal in white matter may be detected. Its implications for physiology needs to be extensively explored. For this purpose, CBF and its relation to anisotropic diffusion was analyzed across subjects on a voxel-wise basis with tract-based spatial statistics (TBSS) and also across white matter tracts within subjects.

METHODS

Diffusion tensor imaging and ASL were acquired in 43 healthy subjects (mean age = 26.3 years).

RESULTS

CBF in WM was observed to correlate positively with fractional anisotropy across subjects in parts of the splenium of corpus callosum, the right posterior thalamic radiation (including the optic radiation), the forceps major, the right inferior fronto-occipital fasciculus, the right inferior longitudinal fasciculus and the right superior longitudinal fasciculus. Furthermore, radial diffusivity correlated negatively with CBF across subjects in similar regions. Moreover, CBF and FA correlated positively across white matter tracts within subjects.

CONCLUSION

The currently observed findings on a macroscopic level might reflect the metabolic demand of white matter on a microscopic level involving myelination processes or axonal function. However, the exact underlying physiological mechanism of this relationship needs further evaluation.

Evaluation of regional cerebral blood flow in Alzheimer's disease patients with subclinical hypothyroidism

BACKGROUND

This study examined regional cerebral blood flow (rCBF) in Alzheimer's disease (AD) patients with and without subclinical hypothyroidism (SCH).

METHODS

Eleven AD patients with SCH and 141 AD patients without SCH underwent brain perfusion single photon emission computed tomography (SPECT). The SPECT data were analyzed by statistical parametric mapping (SPM8) and FineSRT.

RESULTS

AD patients with SCH showed a significantly decreased rCBF mainly in the temporal lobe and thalamus, whereas those without SCH showed a significantly decreased rCBF in the parietotemporal lobe and cingulate gyrus as well as the frontal lobe.

CONCLUSION

Our findings suggest that SCH may affect cerebral perfusion in regions associated with the memory function.

Relationship between white matter lesions and regional cerebral blood flow changes during longitudinal follow up in Alzheimer's disease

AIM

The aim of the present study was to evaluate the relationship between baseline white matter lesions (WML) and changes in regional cerebral blood flow during longitudinal follow up of patients with Alzheimer's disease (AD).

METHODS

A total of 38 patients with AD were included in the study (16 men, 22 women; mean age 77.8 years). All patients were evaluated using the Mini-Mental State Examination and brain perfusion single-photon emission computed tomography at baseline with an approximately 2-year follow up. The patients were divided into two subgroups according to the presence of WML on magnetic resonance imaging. Single-photon emission computed tomography data were analyzed using a voxel-by-voxel group analysis with Statistical Parametric Mapping 8 and region of interest analysis using FineSRT. Changes in Mini-Mental State Examination scores and regional cerebral blood flow were analyzed using the Wilcoxon signed-rank test.

RESULTS

Mean Mini-Mental State Examination scores in AD patients with WML significantly decreased from 19.4 ± 4.8 to 15.5 ± 6.5 (P = 0.003). Statistical Parametric Mapping 8 and FineSRT analysis showed more severe and widespread regional cerebral blood flow reduction, mainly in the frontal and mesial temporal regions in AD patients with WML compared with those without WML.

CONCLUSION

Baseline WML could predict a rapid progression of cognitive and brain functional impairment during longitudinal follow up in AD. Geriatr Gerontol Int 2016; 16: 836-842.

Investigating white matter perfusion using optimal sampling strategy arterial spin labeling at 7 Tesla

PURPOSE

Cerebral blood flow (CBF) is an informative physiological marker for tissue health. Arterial spin labeling (ASL) is a noninvasive MRI method of measuring this parameter, but it has proven difficult to measure white matter (WM) CBF due to low intrinsic contrast-to-noise ratio compared with gray matter (GM). Here we combine ultra-high field and optimal sampling strategy (OSS) ASL to investigate WM CBF in reasonable scan times.

METHODS

A FAIR-based ASL sequence at 7T was combined with a real-time-feedback OSS technique, to iteratively improve post-label image acquisition times (TIs) on a tissue- and subject-specific basis to obtain WM CBF quantification.

RESULTS

It was found 77% of WM voxels gave a reasonable CBF fit. Averaged WM CBF for these voxels was found to be 16.3 ± 1.5 mL/100 g/min (discarding partial-volumed voxels). The generated TI schedule was also significantly different when altering the OSS weighted-tissue-mask, favoring longer TIs in WM.

CONCLUSION

WM CBF could be reasonably quantified in over 75% of identified voxels, from a total preparation and scan time of 15 min. OSS results suggest longer TIs should be used versus general GM ASL settings; this may become more important in WM disease studies.

Brain volume and white matter hyperintensities as determinants of cerebral blood flow in Alzheimer's disease

To better understand whether decreased cerebral blood flow (CBF) in patients with Alzheimer's disease (AD) reflects neurodegeneration or cerebral small vessel disease, we investigated the associations of normalized brain volume (NBV) and white matter hyperintensity (WMH) volume with CBF. We included 129 patients with AD (66 ± 7 years, 53% female) and 61 age-matched controls (64 ± 5 years, 43% female). CBF was measured with pseudocontinuous arterial spin labeling at 3T in the whole brain and in partial volume corrected cortical maps. When NBV and WMH were simultaneously entered in age and sex adjusted models, smaller NBV was associated with lower whole brain (Stβ: 0.29; p < 0.01) and cortical CBF (Stβ: 0.28; p < 0.01) in patients with AD. Larger WMH volume was also associated with lower whole brain (Stβ: -0.22; p < 0.05) and cortical CBF (Stβ: -0.24; p < 0.05) in AD. Additional adjustments did not change these results. In controls, neither NBV nor WMH was associated with CBF. Our results indicate that in AD, lower CBF as measured using pseudocontinuous arterial spin labeling, reflects the combined disease burden of both neurodegeneration and small vessel disease.

Relationship between White Matter Lesions and Progression of Cognitive Decline in Alzheimer's Disease

BACKGROUND

This study examined the relationship between baseline white matter lesions (WMLs) and the progression of cognitive decline in patients with late-onset Alzheimer's disease (AD).

METHODS

Fifty-six patients with AD were included in the study (23 men, 33 women; mean age, 77.8 years). All subjects were treated with acetylcholinesterase inhibitors and followed up for approximately 1 year. The Mini-Mental State Examination (MMSE) score was assessed at least twice to evaluate the progressive cognitive impairment. All subjects underwent brain MRI at baseline and were divided into WMLs(-), mild WMLs(+), and moderate WMLs(+) groups based on WML severity. Changes in MMSE scores between baseline and follow-up were analyzed using the Wilcoxon signed-rank test.

RESULTS

MMSE scores at baseline did not differ significantly among the three groups (p = 0.1658), whereas MMSE scores at the follow-up evaluation were significantly lower in the moderate WMLs(+) group than in the WMLs(-) group (p = 0.0257). The mean MMSE scores remained above baseline values during the approximately 1-year follow-up in the WMLs(-) group, whereas they were decreased in the mild and moderate WMLs(+) groups. Moreover, the frequency of improvement in patients from the WMLs(-) group tended to be higher than that in patients from the WMLs(+) groups.

CONCLUSION

Baseline WMLs may be associated with the heterogeneous progression of cognitive decline in patients with AD.