BJRP 011209

DEVELOPMENT OF BIOSENSORS TO INVESTIGATE THE MECHANISMS OF EPILEPTOGENESIS: ADDRESSING NEGLECTED ISSUES IN EPILEPSY

Abstract

Epilepsy is a common neurological disorder, affecting around 50.000.000 people worldwide. The unpredictability of seizure occurrence continuously exposes patients to physical and psychological harm, thus having a major negative impact upon social development, integration and overall quality of life [1]. Although epilepsy generates a lot of interest in the scientific community, most research lacks a direct link with pressing patient needs to practically improve quality of life. In other words, there are several neglected issues in the understanding and treatment of the disease and particularly a paucity of research focusing specifically in strategies, which might have a major impact on seizure control and prevention of physical harm [2].
For example, most pharmacological studies in patients with refractory seizures do not target the identification of specific ‘niches’ of patients, to whom specific medications or combinations of antiepileptic drugs (AEDs) could really be a breakthrough in seizure control [3,4]. Instead, the vast majority of studies with AEDs include patients with heterogeneous types of epilepsy and target heterogeneous seizure types originating from heterogeneous cortical areas [2]. Not unexpectedly, such studies consistently show ‘redundant’ results in that only around 50% of patients achieve an overall reduction of only 50% of seizure frequency. In brief, new AEDs developed in basic science laboratories are shown effective in animal models, but do not have a major impact in the quality of life of a sizable proportion of patients – i.e., do not reduce the practical risk of physical and psychological harm – beyond what was already obtainable with medications developed more than 30 or 40 years ago. A change of paradigm is thus clearly needed. However, such need has been consistently neglected by medical sciences, contributing to the continuous suffering of a large proportion of patients with epilepsy.
Unsolved questions of utmost importance for the success of new therapeutic paradigms based on AED or new strategies based on direct brain electrical stimulation [5,6] include the understanding of mechanisms of seizure generation (epileptogenesis), the location in the brain where stimuli should be delivered (localization and recording from epileptic networks), the determination of what type of stimulation would be most effective (to modulate/inhibit neuronal function), and the identification of specific patient niches.
Also, any advance that improves the ability to predict seizures can enhance the ability to optimally intervene, e.g. via local drug infusion and electrical stimulation, to prevent seizure occurrence.
We propose a distinct novel approach to seizure prediction based upon the application of biosensors to detect electrochemical changes heralding the interictal-to-ictal transition. The pivotal technological step proposed here and that should allow us to develop this novel approach is a multidisciplinary partnership with specialists from Brazil and Switzerland to develop biosensors customized to epilepsy research. In particular, the proposed approach involves the use of multi-electrode arrays (MEAs) for the creation of multiple interaction sites with human epileptic tissue.
As site-specific differences and patterns of neuronal activity across brain slices are important to understand mechanisms of epileptogenesis, customized MEAs can highlight differences and interconnections within epileptic networks, in ways most extracellular recordings cannot attain. In a first stage, we plan to optimize state-of the-art planar arrays (similar to those already tested in the recordings from rat hippocampus slices [7-10], by controlling electrode shape and size and, most importantly, spatial distribution. In addition, we plan to enhance the amplitude of evoked responses, which are typically one order of magnitude smaller than responses obtained with conventional patch clamp, and to improve the ability to evaluate neural interconnections relevant to epileptogenesis within extended areas of the brain. In a second stage, we plan to implement different sensor arrangements such as protruding 3D electrodes [11] or the fusion of the 3D electrodes to the cell membranes by means of inorganic structures [12] (a process still under development at EPFL). These architectures can, in principle, increase signal-to-noise ratio, improve the bio-electronic integration and augment penetration in the ‘dead’ superficial tissue layers of in vitro slices. 
    We understand that most of the first 2 years will be dedicated to the development of the sensor itself, but still some important issues may be already tackled during the testing of the arrays. Those are described in detail in the objectives section below. Here we would like to stress that, if successful, our approach will allow, in the long run, the investigation of neglected/unsolved issues in epilepsy, such as:
(i) the identification of electrochemical changes heralding seizure occurrence. Should this be possible, a major vulnerability of patients with epilepsy would be addressed and prophylactic measures could be implemented to prevent physical and psychological harm. Attempts are on the way to ‘predict’ seizure occurrence, mostly through the non-linear analysis of EEG signals, which have been shown to progressively change as seizures approach [13].
However, we propose a distinct novel approach to seizure prediction based upon the application of biosensors to detect electrochemical changes heralding the interictal-to-ictal transition in different epileptic scenarios. Specifically, we propose to apply MEAs to examine two key aspects of epileptogenesis in the two most common pathologies associated with partial refractory human epilepsies, ie, focal cortical dysplasia and hippocampal sclerosis [14-16]: (i) focal and regional mechanisms of epileptogenesis within epileptic networks in the interictal period and (ii) the “intimacy” of the interictal-to-ictal transition in terms of electrical changes (shifts). The findings will be compared with those in non-epileptic, non-sclerotic control hippocampal tissue and from non-dysplasic neocortex adjacent to areas of cortical dysplasia.
ii) the investigation of the effect of delivery of antiepileptic medication to the epileptogenic tissue, at the time of electrochemical changes heralding seizure occurrence; i.e., at the earliest time in which the interictal-to-ictal transition could be sensed.
Strategies (i) and (ii) would follow a stepwise approach, in which proof of concept would be obtained by in-vitro studies with epileptic tissue acutely obtained from epilepsy surgery.

Prof. Philippe RENAUD
Prof. Ricardo PAPALEO