A double-blind placebo-controlled trial of minocycline on translocator protein distribution volume in treatment-resistant major depressive disorder

Gliosis is implicated in the pathophysiology of many neuropsychiatric diseases, including treatment-resistant major depressive disorder (TRD). Translocator protein total distribution volume (TSPO V(T)), a brain marker mainly reflective of gliosis in disease, can be measured using positron emission tomography (PET). Minocycline reduces gliosis and translocator protein binding in rodents, but this is not established in humans. Here, the ability of oral minocycline to reduce TSPO V(T) was assessed in TRD. To determine whether oral minocycline, as compared to placebo, can reduce prefrontal cortex (PFC), anterior cingulate cortex (ACC), and insula TSPO V(T) in TRD, twenty-one TRD participants underwent two [(18)F]FEPPA PET scans to measure TSPO V(T). These were completed before and after either oral minocycline 100 mg bid or placebo which was administered in a randomized double-blinded fashion for 8 weeks. There was no significant difference between the minocycline and placebo groups on change in TSPO V(T) within the PFC, ACC, and insula (repeated measures ANOVA, effect of group interaction, PFC: F(1,19) = 0.28, P = 0.60; ACC: F(1,19) = 0.54, P = 0.47; insula F(1,19) = 1.6, P = 0.22). Oral minocycline had no significant effect on TSPO V(T) which suggests that this dosage is insufficient to reduce gliosis in TRD. To target gliosis in TRD either alternative therapeutics or intravenous formulations of minocycline should be investigated. These results also suggest that across neuropsychiatric diseases in humans, it should be assumed that oral minocycline will not reduce TSPO V(T) or gliosis unless empirically demonstrated.