In vivo γ‐aminobutyric acid increase as a biomarker of the epileptogenic zone: An unbiased metabolomics approach

Abstract

ObjectiveFollowing surgery, focal seizures relapse in 20% to 50% of cases due to the difficulty of delimiting the epileptogenic zone (EZ) by current imaging or electrophysiological techniques. Here, we evaluate an unbiased metabolomics approach based on ex vivo and in vivo nuclear magnetic resonance spectroscopy (MRS) methods to discriminate the EZ in a mouse model of mesiotemporal lobe epilepsy (MTLE).MethodsFour weeks after unilateral injection of kainic acid (KA) into the dorsal hippocampus of mice (KA‐MTLE model), we analyzed hippocampal and cortical samples with high‐resolution magic angle spinning (HRMAS) magnetic resonance spectroscopy (MRS). Using advanced multivariate statistics, we identified the metabolites that best discriminate the injected dorsal hippocampus (EZ) and developed an in vivo MEGAPRESS MRS method to focus on the detection of these metabolites in the same mouse model.ResultsMultivariate analysis of HRMAS data provided evidence that γ‐aminobutyric acid (GABA) is largely increased in the EZ of KA‐MTLE mice and is the metabolite that best discriminates the EZ when compared to sham and, more importantly, when compared to adjacent brain regions. These results were confirmed by capillary electrophoresis analysis and were not reversed by a chronic exposition to an antiepileptic drug (carbamazepine). Then, using in vivo noninvasive GABA‐edited MRS, we confirmed that a high GABA increase is specific to the injected hippocampus of KA‐MTLE mice.SignificanceOur strategy using ex vivo MRS‐based untargeted metabolomics to select the most discriminant metabolite(s), followed by in vivo MRS‐based targeted metabolomics, is an unbiased approach to accurately define the EZ in a mouse model of focal epilepsy. Results suggest that GABA is a specific biomarker of the EZ in MTLE.

Neurovascular multiparametric MRI defines epileptogenic and seizure propagation regions in experimental mesiotemporal lobe epilepsy

“…Although it may lead to partial volume effects in the slice thickness direction, this choice impacted both KA-MTLE and sham animals similarly. Our investigation did not include functional MRI 47,48 or MR spectroscopy (eg, glutamate, γ-aminobutyric acid [GABA] 49 ), two important approaches generating potentially complementary information. Furthermore, the diffusion acquisition protocol used could be refined to analyze fractional anisotropy of diffusion kurtosis.…”

Aberrant hippocampal mossy fibers in temporal lobe epilepsy target excitatory and inhibitory neurons

“…38 In magnetic resonance spectroscopy, an increase of GABA was seen in the epileptic hippocampus of an animal model. 39 Our findings add to the field that sprouted MFs impinge on inhibitory interneurons and that the inhibitory axonal endings outnumber the newly created MF boutons, which might possibly result in hippocampal hyperinhibition. This hyperinhibition might be worsened by the loss of hilar mossy cells, 40 which deprive granule cells of their excitation.…”

“…Searching for excitatory or inhibitory neurotransmitters, it was shown in patients analyzed with stereoencephalographic electrodes in addition to microdialysis probes that glutamate levels were elevated in both the epileptic neocortex and the hippocampus, whereas GABA and glutamine levels remained equal 38 . In magnetic resonance spectroscopy, an increase of GABA was seen in the epileptic hippocampus of an animal model 39 …”

A roadmap to high‐resolution standard microcoil MAS NMR spectroscopy for metabolomics

“…95 Another advantage is the possibility of analyzing tiny spatial tissue regions, allowing a direct characterization of the metabolite in question that can be concealed in large sampling tissue mass. For example, a recent ex vivo HR-MAS study 96 of epilepsy with a kainate-injected epileptic mouse model reported an increased -aminobutyric acid (GABA) level in the entire ipsilateral anterior region of the hippocampus, eliciting the relevancy of GABA as a biomarker of the epileptogenic zone. However, the extensive sampling tissue mass (5 mg) made it impossible to delineate further the epileptic zone within the region.…”