Translational Research: Human Tissue & Pathology

Abstract

Abstract 1 Andreas V. Alexopoulos, 1 Cristiane Q. Tilelli, 1 Roger O. Oghlakian, 2 Jorge Gonzalez-Martinez, 2 William E. Bingaman, and 1 Imad M. Najm ( 1 Neurology, Epilepsy Center, Cleveland Clinic Foundation, Cleveland, OH ; and 2 Neurosurgegy, Epilepsy Center, Cleveland Clinic Foundation, Cleveland, OH ) Rationale: The synaptic vesicle protein 2A (SV2A) has been recently identified as the specific binding site for levetiracetam (LEV) in the brain and as a potential target for future antiepileptic drug (AED) therapy. LEV belongs to a new generation of AEDs with a novel mechanism of action seemingly unrelated to traditional AED targets. The objective of our study is to investigate the expression of the SV2A protein in the neocortex of patients with pharmacoresistant epilepsy. We hypothesize that surgically resected epileptic tissue shows a differential expression of the SV2A protein. Methods: Human neocortical tissue specimens from seven patients with histopathologically proven focal cortical dysplasia (FCD) were used for this set of experiments. All patients underwent chronic extraoperative electrocorticographic (ECoG) recordings using subdural grids. “Epileptic areas” exhibiting ictal activity on ECoG (with or without interictal spiking) were identified and separated during surgery from resected “non-epileptic” cortical regions (n = 7). Additional controls consisted of “non-epileptic” tissue acquired from lateral temporal neocortex of patients with hippocampal sclerosis and normal neocortical MRI (n = 3), and human neocortical tissue obtained from autopsy patients without a known history of neurological disease (n = 5). Immunocytochemical staining was performed using polyclonal antibodies against SV2A to study SV2A protein expression in the human tissue specimens. The extent, density and distribution of SV2A protein immunoreactivity were visually analyzed by three independent and blinded observers. Results: Immunocytochemical analysis revealed two main staining patterns: Autopsy controls were characterized by clusters of punctate, “terminal-like” SV2A labeling in the presence of a lightly stained background seen throughout all layers of cortex. In contrast, tissue identified by ECoG as “epileptic” showed intense and diffuse staining of the neuropil with disruption or absence of punctate labeling in all cortical layers. Finally, an intermediate mixed pattern was seen in tissue obtained from “non-epileptic” and lateral temporal neocortex. Conclusions: These distinct SV2A immunoreactivity patterns provide evidence for redistribution of the SV2A protein in the neocortex of patients with FCD and pharmacoresistant epilepsy. Further studies to elucidate the mechanism and functional significance of SV2A redistribution in these patients are currently underway in our laboratory. These findings may have implications for the pathogenesis and treatment of pharmacoresistant epilepsy in patients with focal cortical dysplasia. (Supported by Investigator-initiated study grant to A.V.A. sponsored by UCB-Pharma.)