New insights into the mechanism of neurolathyrism: L-ß-ODAP triggers [Ca2+]i accumulation and cell death in primary motor neurons through transient receptor potential channels and metabotropic glutamate receptors.

Neurolathyrism is a motor neuron (MN) disease caused by ß-N-oxalyl-L-α,ß-diaminopropionic acid (L-ß-ODAP), an AMPA receptor agonist. L-ß-ODAP caused a prolonged rise of intracellular Ca(2+) ([Ca(2+)]i) in rat spinal cord MNs, and the [Ca(2+)]i accumulation was inversely proportional to the MN's life span. The [Ca(2+)]i rise induced by L-ß-ODAP or (S)-AMPA was antagonized completely by NBQX, an AMPA-receptor blocker. However, blocking the L-type Ca(2+) channel with nifedipine significantly lowered [Ca(2+)]i induced by (S)-AMPA, but not that by L-ß-ODAP. Tetrodotoxin completely extinguished the [Ca(2+)]i rise induced by (S)-AMPA or kainic acid, whereas that induced by L-ß-ODAP was only attenuated by 65.6±6% indicating the prominent involvement of voltage-independent Ca(2+) entry. The tetrodotoxin-resistant [Ca(2+)]i induced by L-ß-ODAP was blocked by 2-APB, Gd(3+), La(3+), 1-(ß-[3-(4-methoxy-phenyl)propoxy]-4-methoxyphenethyl)-1H-imidazole hydrochloride (SKF-96365) and flufenamic acid, which all are blockers of the transient receptor potential (TRP) channels. Blockers of group I metabotropic glutamate receptors (mGluR I), 7-(hydroxyiminocyclopropan[b]chromen-1α-carboxylate ethyl ester (CPCCPEt) and 2-methyl-6-(phenylethynyl)-pyridine (MPEP) also lowered the [Ca(2+)]i rise by L-ß-ODAP. MN cell death induced by L-ß-ODAP was prolonged significantly with SKF-96365 as well as NBQX. The results show the involvement of TRPs and mGluR I in L-ß-ODAP-induced MN toxicity through prolonged [Ca(2+)]i mobilization, a unique characteristic of this neurotoxin.

Hind-limb paraparesis in a rat model for neurolathyrism associated with apoptosis and an impaired vascular endothelial growth factor system in the spinal cord.

Neurolathyrism is a motor neuron disease characterized by lower limb paraparesis. It is associated with ingestion of a plant excitotoxin, beta-N-oxalyl-L-alphabeta-diaminopropionic acid (L-beta-ODAP), an agonist of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate-type glutamatergic receptors. Previously, a limited model of neurolathyrism was reported for the rat. To improve upon the model, we stressed rat pups by separation from their mothers, followed by the subcutaneous L-beta-ODAP treatment, resulting in a 4.6-fold higher incidence (14.0-15.6%) of the paraparesis compared with the prior study. The number and size of motor neurons in these rats were decreased only in the lumbar and sacral cord segments, at approximately 13-36 weeks after treatment. Only lumbar and sacral spinal cord tissue revealed pathological insults typical of physical and ischemic spinal cord injury in the surviving motor neurons. In addition, extensive but transient hemorrhage occurred in the ventral spinal cord parenchyma of the rat, and numerous TdT-mediated dUTP-biotin nick end-labeling (TUNEL)-positive cells were also observed. In parallel, vascular endothelial growth factor receptor (VEGFR)-2 (Flk-1) levels were significantly lowered in the lumbosacral spinal cord of the paraparetic rats compared with their controls, suggesting a failure of the VEGF system to protect neurons against L-beta-ODAP toxicity. We propose, based on these data, a novel pathological process of motor neuron death induced by peripheral L-beta-ODAP. For the first time, we present a model of the early molecular events that occur during chemically induced spinal cord injury, which can potentially be applied to other neurodegenerative disorders.

Partial involvement of group I metabotropic glutamate receptors in the neurotoxicity of 3-N-oxalyl-L-2,3-diaminopropanoic acid (L-beta-ODAP).

Neurolathyrism is a human motoneuron disease caused by the overconsumption of grass pea (Lathyrus sativus) that contains a toxic non-protein amino acid, 3-N-oxalyl-L-2,3-diaminopropanoic acid (L-beta-ODAP). The preventive activities of various glutamatergic agents from acute neuronal death caused by L-beta-ODAP were studied using rat primary cortical neuron/glia culture. Nearly 80% of the rat primary cortical neurons were killed by 300 microM L-beta-ODAP within 24 h. Though antagonists acting on the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor prevented most of the toxicity, antagonists acting on group I metabotropic glutamatergic receptors (mGluRs), including (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA), (S)-alpha-methyl-4-carboxyphenylglycine (MCPG), and 2-methyl-6-(2-phenylethenyl)pyridine (SIB1893) partially and significantly prevented neuronal death due to L-beta-ODAP. These antagonists, within limited concentrations, did not have any inhibitory effects on the currents through AMPA receptors expressed in Xenopus oocytes. L-beta-ODAP itself did not induce the currents through group I mGluRs expressed in Xenopus oocytes. These results suggest that the neurotoxicity induced by L-beta-ODAP is partially mediated by the activation of group I mGluRs by an indirect mechanisms.