State-associated changes in longitudinal [F]-PBR111 TSPO PET imaging of psychosis patients: Evidence for the accelerated ageing hypothesis?

Objective: To determine whether state-associated changes in microglial activity, measured with translocator-protein positron emission tomography (TSPO PET), can be identified in psychosis patients through longitudinal evaluation of their regional tracer uptake over the clinical course from acute psychosis to post-treatment follow-up, and comparison to healthy controls. We also evaluated the relation between tracer uptake, clinical symptoms and peripheral immunological markers.

Method: Second-generation radioligand [F]-PBR111 TSPO PET-CT was used for longitudinal dynamic imaging in 14 male psychosis patients and 17 male age-matched healthy control subjects. Patients were first scanned during an acute psychotic episode followed by a second scan after treatment. Prior genotyping of subjects for the rs6917 polymorphism distinguished high- and mixed-affinity binders. The main outcome was regional volume of distribution (V), representing TSPO binding. Plasma concentrations of CRP, cytokines and kynurenines were measured at each timepoint.

Results: We found a significant three-way interaction between time of scan, age and cohort (cortical grey matter F6.50, p.020). Age-dependent differences in V existed between cohorts during the psychotic state, but not at follow-up. Patients' relative change in V over time correlated with age (cortical grey matter Pearson's r.574). PANSS positive subscale scores correlated with regional V during psychosis (cortical grey matter r.767). Plasma CRP and quinolinic acid were independently associated with lower V.

Conclusions: We identified a differential age-dependent pattern of TSPO binding from psychosis to follow-up in our cohort of male psychosis patients. We recommend future TSPO PET studies in psychosis patients to differentiate between clinical states and consider potential age-related effects.