Abstracts

Rationale: Even though the epileptogenesis in glioma is multifactorial, it is conceivable that a down-regulation of glutamine synthetase (GS) in astrocytes may have an important pro-epileptogenic role, through the slowing of glutamate-glutamine cycling. We hypothesized that a GS deficiency in astrocytes is a possible molecular basis for extracellular glutamate accumulation and seizure generation in GBM.Methods: A quantitative Western blot analysis of GS was performed in 20 individuals (10 male and 10 females) operated for GBL between 1th Nov 2003 and 1th Nov 2005 at the Neurosurgical Department of Bolzano, Italy, and prospectically followed until 1th Apr 2007. Patients were subdivided in two groups: 1) Group A, with epilepsy (10 pts); 2) Group B, without epilepsy (10 pts). In the histological slides was considered the presence of gliosis, necrosis, hemosiderine, gigant cells, struma and inflammatory cells. Western-blot analysis was performed to quantify the expression of GS and Actin in surgical specimens. Protein concentration was estimated according to the Bradford assay method, reading absorbance at 595nm. Specific protein bands were visualized by ECL Advanced Detection kit: GS gave a single band at 45kDa, whereas the band related to Actin was detectable at 42kDa. Relative expression of protein was determined by densitometric analysis using Image Scanner and the concentration of GS for each patient’s sample was obtained by comparison with the Actin’s amount. Results: Age at the GBL diagnosis ranged from 33 to 69 years (mean 56 +/- 11 yrs). Histological diagnosis was: GBL (14 pts), GBL with giant cells (2 pts) and GBL with oligodendroglial component (4 pts). None relationship has been found between epilepsy and GBL lateralization (Group A: 7/10 right hemisphere; Group B: 8/10 right hemisphere) and GBL localization (Group A: frontal (2), fronto-temporal (2), temporal (3), temporo-occipital (1), fronto-parietal (1), parietal (1); Group B: frontal (4), temporal (4), temporo-occipital (1), parieto-occipital (1)). In Western blot analysis, the expression of GS in the Group A (range: 0.04-1.15; media 0.35 +/- 0.36; median 0.25) was five times lower than in the Group B (range: 0.78-3.97; media 1.64 +/- 0.99; median 1.25; p=0.002). GS deficiency was independent from gliosis evidence. No correlations were found between gliosis, necrosis, struma, inflammatory cells, giant cells and haemosiderine and epilepsy. Conclusions: This study suggests that glutamate accumulation and epileptic seizures could be coupled to a highly localised enzyme defect. Manipulation of GS activity might constitute a novel principle for inhibiting seizures in patients with glioma epilepsy.