Abstracts

Rationale: Epilepsy occurs in over 80% of patients with tuberous sclerosis complex (TSC). Previously, we have demonstrated that epileptogenic tubers frequently show high tryptophan metabolism in vivo and increased in vitro expression of indoleamine 2,3-dioxygenase, the rate-limiting enzyme of tryptophan metabolism by the kynurenine pathway. Several downstream metabolites of the kynurenine pathway have either pro-convulsant or anti-convulsant properties. Here, we investigated the expression of key enzymes along this pathway in surgical brain specimens from patients with TSC, to determine whether there is preferential expression of the pathway branch producing pro-convulsant metabolites in epileptogenic tubers. We also assessed the expression of those enzymes in specimens from patients undergoing epilepsy surgery who did not have TSC.Methods: Eight children with TSC (9m 16y) underwent surgery to remove epileptogenic tubers. Both epileptogenic tubers and a relatively normal cortical area (control region) were resected. Additional surgical specimens (N=4) were collected from patients with epilepsy associated with the following conditions: Sturge-Weber syndrome (1y6m), porencephalic cyst (9y), migrational abnormalities (17y), and dysembryoplastic neuroepithelial tumor (DNET) (6y). Western blotting was performed with antibodies against IDO (isoforms 1 and 2), 3-hydroxyanthranilate-3,4-dioxygenase (HAO), and kynurenine aminotransferase (KAT). Protein expression was normalized to actin levels.Results: Expression of IDO1 and HAO (HAO leads to the production of the pro-convulsant metabolite quinolinate) in tubers was higher than in control regions (0.93 vs. 0.87 a.u., p = 0.01 and 0.61 vs. 0.49 a.u., p = 0.04, respectively) (Fig.1A). On the other hand, analysis of IDO2 and KAT (KAT leads to the production of the anti-convulsant metabolite kynureninate) showed no significant difference between epileptogenic tubers and control tissue (Fig.1B). Compared to the other diseases, epileptogenic tubers showed increased expression (at least a 10% difference) of IDO1 and HAO (Fig.2), while expression of KAT was decreased. Expression of IDO2 did not show significant differences between TSC and the other conditions (<10%).Conclusions: Our data show activation of the kynurenine pathway enzymes leading to production of pro-convulsant metabolites in epileptogenic tubers. In this study, activation of the pro-convulsant branch was more remarkable in TSC compared to other types of disease. This feature could be a consequence of the particular signaling pathway which is altered in this disease, and additional experiments are warranted to confirm this preliminary finding. Further validation may provide targets for alternative therapeutic approaches, ameliorating the symptoms of this disease.