White matter penetrating arteriole dysfunction correlates with MRI-defined white matter integrity in patients with Alzheimer's disease

Abstract

Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): National Institute of Health Objectives Patients with Alzheimer’s Disease (AD) display cerebral white matter (WM) hyperintensities in association with microvascular brain injury (mVBI) and cerebral microinfarcts. We determined the extent to which vasomotor dysfunction of WM penetrating arterioles is associated with mVBI in autopsy brains from patients with low or high AD neuropathology, and determined if these changes correlate with quantitative indices of MRI-defined WM integrity. Methods We analyzed 28 consecutive cases of prefrontal rapid autopsies in a population-based cohort with low or high AD neuropathological changes, and with or without cerebral microinfarcts (mVBI). WM penetrating and pial surface arteriolar responses to the endothelium-dependent agonist, bradykinin were assessed ex vivo with videomicroscopy. Expression of vascular endothelial nitric oxide synthase (eNOS) and NAD(P)H-oxidase (Nox1,2 and 4 isoforms) was measured with quantitative PCR. Diffusion tensor imaging was used to measure mean apparent diffusion coefficient (ADC) and fractional anisotropy (FA) in post-mortem prefrontal WM. Results Patients with high AD neuropathology and mVBI exhibited a significantly reduced dilation in response to bradykinin selectively in WM arterioles, when compared to low or high AD cases without mVBI or to pial surface arterioles. Expression of eNOS was reduced, whereas Nox-1 expression was increased in WM arterioles in AD and mVBI cases. Moreover, we found that in cases with low AD pathology the magnitude of bradykinin-induced WM arteriole dilation was correlated with higher FA and lower ADC. In contrast, dilation to bradykinin was associated with lower FA and higher ADC in cases with high AD neuropathology. Interpretation: Selectively impaired vasodilation to the endothelium-dependent agonist, bradykinin occurs in WM penetrating arterioles in AD patients with WM microinfarcts, which is likely due to reduced nitric oxide and an increase in Nox1-derived reactive oxygen species production. Notably, the bradykinin response of WM arterioles strongly correlated with MRI-defined WM integrity suggesting that impaired bradykinin-mediated vasodilation in WM penetrating arterioles contributes to disrupted white matter microstructural integrity as defined by MRI.