(24) Drug-resistant temporal lobe epilepsy alters the expression and functional coupling to G proteins of CB1 and CB2 receptors in the human blood-brain barrier

Rationale: The breakdown of the blood-brain barrier (BBB) is a common feature of several neurodegenerative disorders. Studies indicate that the activation of CB1 and CB2 receptors may protect BBB from damage. However, other studies support that the activation of these receptors induces neurotoxic effects. The aim of this study was to characterize the protein expression as well as the Gαi/o protein-induced activation by CB1 and CB2 receptors in the BBB isolated from hippocampus and temporal neocortex of patients with drug-resistant mesial temporal lobe epilepsy (DR-MTLE). The changes obtained were associated with the expression of the tight junction (TJ) proteins (claudin-5, occludin and ZO-1) in the BBB.

Methods: The hippocampus and temporal neocortex of 12 patients with DR-MTLE were obtained immediately after the surgical resection and stored at -70°C. The BBB was isolated from the frozen tissue and then used for the evaluation of the protein expression of CB1 and CB2 receptors (western blot experiments), their colocalization with TJ proteins (immunofluorescence experiments) and the Gαi/o protein activation induced by specific agonists (binding assay with [³⁵S]-GTPγS). The results were compared with those obtained from 12 autopsies.

Results: The immunofluorescence experiments indicated that CB1 and CB2 receptors were expressed in the BBB of patients with DR-MTLE and colocalized with claudin-5, occluding and ZO-1. In hippocampus of patients with DR-MTLE, the BBB showed lower protein expression of CB1 and CB2 receptors (66%, p< 0.001, and 43%, p< 0.001, respectively). However, [³⁵S]-GTPγS binding assay revealed a high Emax (251%, p< 0.0008; 255%, p< 0.0001, respectively). In temporal neocortex, BBB showed protein overexpression of CB1 and CB2 receptors (35%, p< 0.01 and 41%, p< 0.01, respectively). Their activation induced an Emax higher for CB1 receptors (103%, p< 0.006), and similar to autopsies for CB2 receptors (13%, p >0.05).

Conclusions: The results obtained revealed that the BBB of patients with DR-MTLE presents a high signal transduction efficiency when exposed to specific agonists to CB1 (hippocampus and temporal neocortex) and CB2 receptors (hippocampus). Some of these changes do not correlate with the protein expression of these receptors. The high function of CB1 and CB2 receptors can be associated with alterations in the integrity of BBB of patients with DR-MTLE.

Funding: Please list any funding that was received in support of this abstract.: MANL received support from Consejo Nacional de Ciencia y Tecnología (CONACyT) (scholarship 347414). LR received support from CONACyT (grant A3-S-26782).