Metabotropic Glutamate Receptor Subtypes as Targets for Neuroprotective Drugs

Abstract

Summary: Metabotropic glutamate (mGlu) receptors have been considered as potential targets for neuroprotective drugs, but the lack of specific drugs has limited the development of neuroprotective strategies in experimental models of acute or chronic central nervous system (CNS) disorders. The advent of potent and centrally available subtype-selective ligands has overcome this limitation, leading to an extensive investigation of the role of mGlu receptor subtypes in neurodegeneration during the last 2 years. Examples of these drugs are the noncompetitive mGlu1 receptor antagonists, CPCCOEt and BAY-36-7620; the noncompetitive mGlu5 receptor antagonists, 2-methyl-6-(phenylethynyl)pyridine, SIB-1893, and SIB-1757; and the potent mGlu2/3 receptor agonists, LY354740 and LY379268. Pharmacologic blockade of mGlu1 or mGlu5 receptors or pharmacologic activation of mGlu2/3 or mGlu4/7/8 receptors produces neuroprotection in a variety of in vitro or in vivo models. MGlu1 receptor antagonists are promising drugs for the treatment of brain ischemia or for the prophylaxis of neuronal damage induced by synaptic hyperactivity. MGlu5 receptor antagonists may limit neuronal damage induced by a hyperactivity of N-methyl-d-aspartate (NMDA) receptors, because mGlu5 and NMDA receptors are physically and functionally connected in neuronal membranes. A series of observations suggest a potential application of mGlu5 receptor antagonists in chronic neurodegenerative disorders, such as amyotrophic lateral sclerosis and Alzheimer disease. MGlu2/3 receptor agonists inhibit glutamate release, but also promote the synthesis and release of neurotrophic factors in astrocytes. These drugs may therefore have a broad application as neuroprotective agents in a variety of CNS disorders. Finally, mGlu4/7/8 receptor agonists potently inhibit glutamate release and have a potential application in seizure disorders. The advantage of all these drugs with respect to NMDA or AMPA receptor agonists derives from the evidence that mGlu receptors do not "mediate," but rather "modulate" excitatory synaptic transmission. Therefore, it can be expected that mGlu receptor ligands are devoid of the undesirable effects resulting from the inhibition of excitatory synaptic transmission, such as sedation or an impairment of learning and memory.

Glutamate as a therapeutic target in psychiatric disorders

“…These include Group I metabotropic antagonists, which would be predicted to reduce NMDAR activation, 152 and group II/III agonists, which are reported to prevent neurodegeneration in a variety of clinical models. 138 To date, however, clinical data are lacking.…”

Metabotropic Glutamate Receptor Subtype 5 Antagonists MPEP and MTEP

“…2) reduction of the Mg 2+ block of NMDA receptors (102,103,215); 3) enhancement of glutamate release by decreasing endogenous inhibition (19,35); 4) the release of Ca 2+ from intracellular stores via IP3 dependent mechanisms (208); and 5) induction of the production of arachidonic acid (61), as well as other mechanisms.…”

εPKC Is Required for the Induction of Tolerance by Ischemic and NMDA-Mediated Preconditioning in the Organotypic Hippocampal Slice

“…For example, it has been established that overstimulation of glutamate receptors promotes neuronal cell death (Rothman and Olney, 1986;Albers et al, 1992;Choi, 1995;Pellegrini-Giampietro et al, 1999), whereas blocking NMDA receptors during ischemia appears to be neuroprotective (Simon et al, 1984;Goldberg et al, 1987;Ozyurt et al, 1988;Steinberg et al, 1988;Swan and Meldrum, 1990;Rao et al, 2000;Bruno et al, 2001;Liniger et al, 2001;Nishizawa, 2001). However, d] cyclohepten-5,10-imine maleate], an NMDA antagonist, administered during sublethal ischemia blocked the development of ischemic tolerance in gerbils (Kato et al, 1992a).…”