Hypertensive adults exhibit lower myelin content: A multicomponent relaxometry and diffusion MRI study

It is unknown whether hypertension plays any role in cerebral myelination. To fill this knowledge gap, we studied ninety cognitively unimpaired adults, age range 40 to 94 years, that are participants in the Baltimore Longitudinal Study of Aging (BLSA) and the Genetic and Epigenetic Signatures of Translational Aging Laboratory Testing (GESTALT) to look for potential associations between hypertension and cerebral myelin content across fourteen white matter brain regions. Myelin content was probed using our advanced multicomponent magnetic resonance (MR) relaxometry method of myelin water fraction (MWF), a direct and specific MR imaging (MRI) measure of myelin content, and longitudinal and transverse relaxation rates (R1 and R2), two highly sensitive MRI metrics of myelin content. We also applied diffusion tensor imaging (DTI) MRI to measure fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD) and axial diffusivity (AxD) values, which are metrics of cerebral microstructural tissue integrity, to provide contact with previous MRI findings. After adjustment of age, sex, systolic blood pressure, smoking status, diabetes status and cholesterol level, our results indicated that participants with hypertension exhibited lower MWF, FA, R1 and R2 values and higher MD, RD and AxD values, indicating lower myelin content and higher impairment to the brain microstructure. These associations were significant across several white matter regions, particularly in the corpus callosum, fronto-occipital fasciculus, temporal lobes, internal capsules, and corona radiata. These original findings suggest a direct association between myelin content and hypertension, and form the basis for further investigations including longitudinal assessments of this relationship.