Chronic hypoperfusion is not associated with cerebral amyloidosis

Insufficient cerebral perfusion is suggested to play a role in the development of AD. We investigated the effect of chronic cerebral hypoperfusion on AD-related pathology, 26 including β - amyloid (Aβ) deposition and brain atrophy in humans. We enrolled 10 cognitively normal patients (median age: 64 years old) with unilateral 29 chronic cerebral hypoperfusion. Volumes of interest (VOIs) and regions of interest 30 (ROIs) with the most pronounced hypoperfusion changes were created in the 31 hypoperfused region, and were then mirrored into the contralateral hemisphere to 32 create a control region with normal perfusion respectively.11C-Pittsburgh 33 compound-PET (PiB-PET) imaging standard uptake ratios (SUVRs) and several brain atrophy indices from the CT images of each patient were calculated. findings


Abstract 23
Background 24 Insufficient cerebral perfusion is suggested to play a role in the development of AD. 25 We investigated the effect of chronic cerebral hypoperfusion on AD-related pathology, 26 including β-amyloid (Aβ) deposition and brain atrophy in humans. 27

Methods 28
We enrolled 10 cognitively normal patients (median age: 64 years old) with unilateral 29 chronic cerebral hypoperfusion. Volumes of interest (VOIs) and regions of interest 30 (ROIs) with the most pronounced hypoperfusion changes were created in the 31 hypoperfused region, and were then mirrored into the contralateral hemisphere to 32 create a control region with normal perfusion respectively.11C-Pittsburgh 33 compound-PET (PiB-PET) imaging standard uptake ratios (SUVRs) and several brain 34 atrophy indices from the CT images of each patient were calculated. 35 7 model. PiB-PET was performed according to standardized research protocols (17). A 118 dynamic 90 minutes emission scan was administered with an intravenous injection of 119 11 C-PiB after 10 minutes of transmission scan. Standardized images were extracted 120 within the regulated interval time after injection. All scans were performed in a dimly 121 lit and quiet room with subjects in a resting state. 122

Image analysis
123 β-amyloid burden. CapAIBL (Australian eHealth Research Centre, CSIRO, 124 Australian) was used to calculate the cortical SUVRs (18) and determine the negative 125 or positive of PiB-PET amyloid burden using the cut-off value of 1.42 (19). Pmod 126 software (version 3.5, Pmod technologies, Zurich, Switzerland) was used to analyze 127 the amyloid burden in the volume of interest (VOI) and region of interest (ROI). 128 PiB-PET series and standard MRI-T1 templates were spatially merged by the fusion 129 module. VOI and ROI were created in the MRI images according to the MTT and 130 CBF of CTP by a researcher blinded to the PET images. A sphere (VOI) with a 131 diameter of 15 mm was created in the region with the most pronounced hypoperfusion 132 changes of each subject, and an irregular ROI was manually drawn to cover the 133 hypoperfused region as much as possible. The hypoperfused VOI and ROI were then 134 mirrored into the contralateral hemisphere to create a control region with normal 135 perfusion. For 3 cases with minor infarcts, the infarction regions were completely 136 avoided in VOI and ROI. 137 All regions were then intersected using the gray/white matter segmentation mask into 138 VOI (or ROI) and control. The SUVR of cortex and white matter in each region was 139 8 subsequently measured using the cerebellar composite gray matter as the reference 140 region. 141 Brain atrophy. In all the patients, the brain atrophy indices were measured on the CT 142 scans, based on the commonly-used method described by Meese (20). These indices, 143 including Bicaudate index, Bifrontal index, Evans index, Cella index, Celda media 144 index, Ventricular index, were calculated unilaterally by the distance from the midline 145 of the brain (shown in detail in Fig. 2) (21, 22). Every index was measured twice and 146 the mean value was calculated to increase accuracy and limit the "partial volume" 147 effect by RadiAnt DICOM Viewer 5.0.1 (Medixant, Poznan, Poland). 148

149
The Shapiro-Wilk test was used to test for normal distribution. The differences in 150 SUVRs and atrophy indices of bilateral cerebral hemispheres between the 151 hypoperfused regions (Hypo) and the normally-perfused contralateral regions (Ctrl) 152 were analyzed using Wilcoxon's-signed test. All hypothesis-testing was two-sided, 153 and statistical significance was defined as P＜0.05. All statistical computations were 154 performed using SPSS version 19.0 (SPSS, Inc., Chicago, IL). 155

156
The data that support the findings of this study are available on request from the 157 corresponding author. The data are not publicly available as they include information 158 that could compromise the privacy of the research participants 159 160

9
Characteristics of the study subjects 162 Subjects' characteristics were shown in Table 1 functions, which may be caused by their effects on Aβ metabolism and 204 neurodegeneration in the brain. A recent large prospective cohort study further 205 11 focused on the relationship between VRFs and AD and found that midlife but not 206 late-life VRFs were significantly associated with elevated amyloid deposition in 207 cognitively normal participants (23). This effect is probably due to insufficient 208 cerebral blood supply, which may impair the function of the neurovascular unit, cause 209 the cerebral hypoperfusion and imbalance between the production and clearance of 210 Aβ, and finally lead to the deterioration of AD pathological changes and cognitive 211 dysfunction(7, 10). Some studies found that there there is cerebral hypoperfusion in 212 the temporal and parietal lobes in AD patients (4). 213 However, whether hypoperfusion can directly lead to the AD-related pathological 214 changes remains uncertain. Previous animal studies have found that cerebral 215 hypoperfusion triggered Aβ deposition in vessel walls parenchyma in the brain. It was 216 found that in a mild chronic cerebral hypoperfusion animal model using C57BL/6J 217 mice subjected to the right common carotid artery permanent ligation, the cerebral 218 hypoperfusion triggered both early vascular deposition of peripherally applied human 219 Aβ1-42 peptides and small stable Aβ deposits in the hypoperfused brain parenchyma 220 6 weeks later (12). On the contrary, hypoperfusion was shown to have little or no 221 effect on an altered brain Aβ burden in human studies (13-15), which was consistent 222 with the results of our study. As to the acute hypoperfusion, several studies found that 223 acute stroke was not associated with sustained or increased Aβ deposition (24, 25). 224 Therefore, it is probable that both chronic and acute hypoperfusion does not generate 225 a direct impact on cerebral Aβ deposition. 12 Some studies found hypoperfusion is associated with progress from MCI to dementia 227 and subsequent cognitive decline in humans (26,27). However, it remains uncertain 228 whether cerebral hypoperfusion aggravates Aβ deposition and neurodegeneration in 229 AD. In AD transgenic mice, ligation of carotid arteries increased Aβ deposition and 230 neuron loss in the brain (11,28). But in our study, chronic cerebral hypoperfusion is 231 not associated with increased Aβ deposition and aggravated brain atrophy in a 232 The limitation of our study is that the number of participants is relatively small, yet 246 patients with chronic unilateral cerebral hypoperfusion were difficult to enroll in 247 clinical practice. In addition, previous studies suggested that brain microvascular 248 13 changes have an impact on the pathology of AD (29), but our study only included the 249 hypoperfusion caused by large blood vessel stenosis, which may not be generalized to 250 hypoperfusion due to small vessel diseases. Third, the duration of hypoperfusion of 251 our participants is unknown. We could not completely exclude the possibility that the 252 duration of hypoperfusion is not long enough to induce cerebral amyloidosis and 253 neurodegeneration in our cohort. 254 In conclusion, we found that chronic cerebral hypoperfusion due to large vessel 255 lesions is not associated with increased β-amyloid deposition or aggravated brain 256 atrophy, implying that chronic hypoperfusion does not directly induce Aβ deposition 257 and neurodegeneration in the brain.