Research

Introduction

            Glutamate (Glu), the  major excitatory amino acid neurotransmitter in the central nervous system, mediates a number of physiological processes and is involved in the pathological process of excitotoxicity  by which nerve cells are damaged and killed by the excess Glu present in brain fluids after various acute and chronic neurodegenerative disorders. The latter brain insults include, among others, stroke, traumatic brain injury amyotrophic lateral sclerosis, brain tumors, HIV dementia and others.

            The research in our laboratory centers on the role played in brain pathology by the presence in brain fluids of excess Glu and aims to contribute in a practical way to the rational development of novel means to treat Glu-linked neurodegenerative conditions. We are presently focusing our research on a novel neuroprotective brain strategy based on the accelerated removal of excess Glu from brain into blood using blood Glu scavengers, and we study the modalities of its application on animal models of head trauma, brain stroke, glioblastoma, amyotrophic lateral sclerosis and nerve gas exposure.  Our research is carried out using both in vitro and in vivo experimental systems. An important experimental system in our laboratory is an in vitro model of the blood brain barrier.

The blood-brain barrier in brain physiology and its therapeutic exploitation.

            Our investigations of  the blood brain barrier wish to unravel the mechanisms by which the brain eliminates excess Glu and GABA (the CNS major inhibitory neurotransmitter) into blood. We study also  the processes used by prion proteins to possibly access the brain from blood.  For answering these questions, we make use of three in vitro models of the BBB.

Boosting brain autoprotective mechanisms in neurodegenerative diseases

            Abnormally high Glutamate (Glu)  levels are found in brain fluids of victims of acute brain insults such as stroke,  traumatic brain injury and bacterial meningitis, or suffering from chronic diseases such as amyotrophic lateral sclerosis or HIV dementia. Glu is also released by glial tumor cells to create space in brain for their expansion. Because Glu has well established neurotoxic properties, a great deal of efforts have been made in recent years to reach a better understanding of how the brain protects itself from excess Glu and on ways that novel drugs could provide neuroprotection.

            Until now, brain inherent protection from the neurotoxic (excitotoxic) effects of excess Glu has been credited mainly to the presence, both on nerve terminals and on astrocytes, of members of a large family of Na+-dependent  Glu transporters which  bind and take up Glu and guarantee that the very high concentrations of Glu (~100 mM) transiently present after synaptic or astrocytic release  are soon decreased to concentrations  at which Glu exerts neither overt excitatory nor excitotoxic activities. In the clearance of Glu, little attention has been given to the blood-brain barrier in general and to the Glu transporters present on brain vasculature that include the astrocytic endfeet and the capillary endothelial cells. These Glu transporters are involved in the brain-to-blood Glu efflux that contributes  to the control of brain extracellular Glu.

            We have shown that the Glu transporters present on the brain vasculature are indeed involved in a brain to blood Glu efflux since the injection of radioactive Glu either in the brain parenchyma, lateral ventricles or by ventriculo-cisternal perfusion causes a rapid appearance of radioactivity in blood. We have then defined the conditions that could boost the process of brain Glu detoxification via an increased brain-to-blood Glu efflux with the prospect that such studies could lead to a novel approach to the treatment of brain neurodegenerative diseases. We have demonstrated that the creation of a larger Glu concentration gradient between the cerebrospinal fluid/capillary endothelial cell and blood plasma, increases the driving force for such efflux. The increased driving force for the efflux of excess Glu from brain fluids into blood is achieved by the intravenous administration of pyruvate or of oxaloacetate which respectively activate the blood liver enzymes glutamate-pyruvate transaminase and glutamate-oxaloacetate transaminase and cause a transamination of Glu into 2-ketoglutarate, and thereby a reduction of the blood Glu levels. Since the blood Glu scavengers pyruvate and oxaloacetate lead to an accelerated efflux of excess Glu from brain fluids into blood, we used this strategy with animal models of closed head injury, stroke, brain glioma and amyotrophic lateral sclerosis and demonstrated highly significant neuroprotective effects. We are now planning to test this technology in clinical trials.