Binding of the monoacylglycerol lipase (MAGL) radiotracer [3H]T-401 in the rat brain after status epilepticus.

OBJECTIVES: Monoacylglycerol lipase (MAGL) is a cytosolic serine hydrolase considered a potential novel drug target for the treatment of CNS disorders including epilepsy. Here we examined MAGL levels in a rat model of epilepsy. METHODS: Autoradiography has been used to validate the binding properties of the MAGL radiotracer, [3H]T-401, in the rat brain, and to explore spatial and temporal changes in binding levels in a model of temporal lobe epilepsy model using unilateral intra-hippocampal injections of kainic acid (KA) in rats. RESULTS: Specific and saturable binding of [3H]T-401 was detected in both cortical grey and subcortical white matter. Saturation experiments revealed a KD in the range between 15 nM and 17 nM, and full saturation was achieved at concentrations around 30 nM. The binding could be completely blocked with the cold ligand (Ki 44.2 nM) and at higher affinity (Ki 1.27 nM) with another structurally different MAGL inhibitor, ABD 1970. Bilateral reduction in [3H]T-401 binding was observed in the cerebral cortex and the hippocampus few days after status epilepticus that further declined to a level of around 30% compared to the control. No change in binding was observed in either the hypothalamus nor the white matter at any time point. Direct comparison to [3H]UCB-J binding to synaptic vesicle glycoprotein 2 A (SV2A), another protein localized in the pre-synapse, revealed that while binding to MAGL remained low in the chronic phase, SV2A was increased significantly in some cortical areas. SIGNIFICANCE: These data show that MAGL is reduced in the cerebral cortex and hippocampus in a chronic epilepsy model and indicate that MAGL inhibitors may further reduce MAGL activity in the treatment resistant epilepsy patient.

Temporal and spatial changes in synaptic vesicle glycoprotein 2A (SV2A) under kainic acid induced epileptogenesis: An autoradiographic study.

Synaptic Vesicle Glycoprotein 2A (SV2A) has been proposed as a presynaptic marker in several neurological disorders. Not only is SV2A the target for the antiepileptic drug levetiracetam, but also considered a marker of mature pre-synapses. In this study, we aimed to assess the binding of [3H]UCB-J as a selective radioligand for SV2A to visualize and determine changes during different stages of epileptogenesis by in-vitro autoradiography in rat models of temporal lobe epilepsy. Two different kainic acid (KA) injection routes were used to model temporal lobe epilepsy in the rat; a systemic (10 mg/kg KA injected intraperitoneally) and a local model (1.875 mM KA injected intrahippocampally). Brain tissue was sampled at different time points after the initial status epilepticus and semi-quantitative [3H]UCB-J autoradiography was performed to determine temporal and spatial changes under the progression of epileptogenesis. A decrease in [3H]UCB-J binding was observed in many brain areas in the acute phases after both types of kainic acid administration. Peak reductions occurred slightly before in systemic-treated animals (within 3-10 days) than after local-treated animals (within 5-15 days). Interestingly in the systemic model, we observed a full restoration in the binding level 30 days after the treatment in most areas probably reflecting neuronal reorganization. However, after the local injection in the hippocampus, the binding in the hippocampus, and in temporal and piriform cortices did not return to basal levels. The time-course profile displayed lateralization in the local model. These results demonstrate changes in the amount of a presynaptic SV2A binding site after seizures and suggest that SV2A may have importance in eliciting spontaneous seizures and/or be a biomarker for epileptogenesis. The present study shows that SV2A is a biomarker of acute phase epileptogenesis in specific brain regions.