The role of astrogliosis in the pathology of brain aging and neurodegenerative diseases has recently drawn great attention. Imidazoline-2 binding sites (I2BS) represent a possible target to map the distribution of reactive astrocytes. In this study, we use 11C-BU99008, an I2BS-specific PET radioligand, to image reactive astrocytes in vivo in healthy controls (HCs) and
patients with established Parkinson’s disease dementia (PDD).

Eighteen HCs (age: 45−78 years) and six patients with PDD (age: 64−77 years) had one 11C-BU99008 PET-CT scan with arterial input function. All subjects underwent one 3T MRI brain scan to facilitate the analysis of the PET-CT data and to capture individual cerebral atrophy. Regional 11C-BU99008 volumes of distribution (VT) were calculated for each subject by two-tissue compartmental modelling.

Positive correlations between 11C-BU99008 VT values and age were found for all tested regions across the brain within HCs (p<0.05); furthermore, multiple regression indicated that aging affects 11C-BU99008 VT values in a region-specific manner. Independent samples t-test indicated that there was no significant group difference in 11C-BU99008 VT values between
PDD (n=6; mean age = 71.97±4.66 years) and older HCs (n=9; mean age = 71.90±5.51 years).

Our dataset shows that astrogliosis is common with aging in a region-specific manner. However, in this set-up, 11C-BU99008 PET cannot differentiate patients with PDD from healthy controls of similar age.