[3H]T-401 binding to monoacylglycerol lipase (MAGL) in the brains of patients and mice with temporal lobe epilepsy

Monoacylglycerol lipase (MAGL) inhibitors are considered as drug candidates for epilepsy. In order to determine the level of MAGL and evaluate changes in the epileptic brain, we have validated and used autoradiography and the MAGL radiotracer [³H]T-401 on resected temporal neocortex specimens obtained from patients with temporal lobe epilepsy and in brains from mice with chronic reoccurring hippocampal seizures. Saturation experiments revealed a K_D around 4 nM for the human temporal cortex and 7 nM for the mouse brain. In the human brain, binding of [³H]T-401 was detected mostly in the grey matter, and in the subcortical white matter in lower amounts. The levels were strongly correlated in the two cortical compartments. The level of [³H]T-401 binding in the human temporal cortex varied about a 4-fold among the patients, but was not correlated to either epilepsy duration or the age of the patients. In the epileptic mouse brain, a significant reduction was observed bilaterally in the hippocampus, as well as in other cortical regions, including the temporal cortex. Interestingly, a highly significant negative correlation was seen between MAGL and binding of [³H]PBR28 to the translocator protein 18 kDa (TSPO) expressed in glia. These data support the presence of MAGL in neuronal and non-neuronal cells, and indicate that MAGL levels in the brains of either patients with epilepsy or mice after intra-hippocampal kainic acid injection are reduced not only in the epileptic zone in the hippocampus, but more widespread in the brain.