The lathyrus toxin, β-N-oxalyl-l-α,β-diaminopropionic acid (ODAP), and homocysteic acid sensitize CA1 pyramidal neurons to cystine and l-2-amino-6-phosphonohexanoic acid

[Research in Motor Neuron Diseases Caused by Natural Substances: Focus on Pathological Mechanisms of Neurolathyrism]

Diseases of the motor-conducting system that cause moving disability affect socio-economic activity as well as human dignity. Neurolathyrism, konzo, and amyotrophic lateral sclerosis-parkinsonism-dementia complex (ALS-PDC) have attracted researchers to study the pathology of motor neuron (MN) diseases such as ALS. I have been studying neurolathyrism, which is caused by overconsumption of a legume grass pea (Lathyrys sativus L.). Among people who consume the legume as a food staple, many developed life-long paraparesis in their legs. β-N-oxalyl-l-α,β- diaminopropionic (l-β-ODAP; BOAA), contained in this plant, is a neurotoxic analog of l-glutamic acid. We have clarified that in addition to the causal involvement of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) type glutamatergic receptor in MN death, a toxic role of group I metabotropic glutamate receptors as well as transient receptor potential channels were involved in the MN insult by l-β-ODAP using primary MN culture. We have also established a neurolathyrism rat model by repeated, peripheral l-β-ODAP treatment to newborn rats under mild stress. Rats showing hind-leg paraparesis with an incidence rate of around 25% were useful to study the in vivo pathology of MN disease. MNs of these rats were greatly decreased at their lumbo/sacral segments at various ages. Intra-parenchymal hemorrhage was consistently observed in paraparetic rats but not in cripple-free, treated rats. MN were depleted even at an acute period around bleeding spots, suggesting catastrophic neuro-vascular-glial interaction in this MN disease. Summaries of konzo and ALS-PDCs studies are also introduced.

Memory of chirality (MOC) concept in imino-aldol reaction: enantioselective synthesis of α,β-diamino esters and aziridines

A simple strategy for the synthesis of chiral α,β-diamino- and α-amino,β-hydroxy ester derivatives in high yields with moderate to high ee has been developed via asymmetric imino-aldol and aldol reactions, respectively, starting from protected aminoesters employing memory of chirality concept for chiral induction. This strategy has been extended for the enantioselective synthesis of aziridines (ee up to 92%). The absolute configuration of the imino-aldol adducts has been determined. The stereochemical outcome of the products has been explained by a suitable mechanism and supported by computational studies.

Possible therapy for ALS based on the cyanobacteria/BMAA hypothesis

Although the cyanobacteria/BMAA hypothesis of the cause of ALS and other age-related neurodegenerative diseases remains to be proven, it is not too early to ask whether treatment would be possible if the hypothesis were correct. This paper reviews the possible ways that chronic BMAA neurotoxicity could be prevented or treated.

Toxicity of Non-protein Amino Acids to Humans and Domestic Animals

Non-protein amino acids are common in plants and are present in widely consumed animal feeds and human foods such as alfalfa ( Medicago sativa), which contains canavanine, and lentil ( Lens culinaris), which contains homoarginine. Some occur in wild species that are inadvertently harvested with crop species. Some nonprotein amino acids and metabolites can be toxic to humans, e.g. Lathyrus species contain a neurotoxic oxalyl-amino acid. Some potential toxins may be passed along a food chain via animal intermediates. The increased interest in herbal medicines in the Western countries will increase exposure to such compounds.

beta-N-methylamino-l-alanine induces oxidative stress and glutamate release through action on system Xc(-)

beta-N-methylamino-l-alanine (BMAA) is a non-protein amino acid implicated in the neurodegenerative disease amyotrophic lateral sclerosis/Parkinson-dementia complex (ALS/PDC) on Guam. BMAA has recently been discovered in the brains of Alzheimer's patients in Canada and is produced by various species of cyanobacteria around the world. These findings suggest the possibility that BMAA may be of concern not only for specific groups of Pacific Islanders, but for a much larger population. Previous studies have indicated that BMAA can act as an excitotoxin by acting on the NMDA receptor. We have shown that the mechanism of neurotoxicity is actually three-fold; it involves not only direct action on the NMDA receptor, but also activation of metabotropic glutamate receptor 5 (mGluR5) and induction of oxidative stress. We now explore the mechanism by which BMAA activates the mGluR5 receptor and induces oxidative stress. We found that BMAA inhibits the cystine/glutamate antiporter (system Xc(-)) mediated cystine uptake, which in turn leads to glutathione depletion and increased oxidative stress. BMAA also appears to drive glutamate release via system Xc(-) and this glutamate induces toxicity through activation of the mGluR5 receptor. Therefore, the oxidative stress and mGluR5 activation induced by BMAA are both mediated through action at system Xc(-). The multiple mechanisms of BMAA toxicity, particularly the depletion of glutathione and enhanced oxidative stress, may account for its ability to induce complex neurodegenerative diseases.

Novel associations between rhizobial populations and legume species within the genera Lathyrus and O xytropis grown in the temperate region of China

Fifty rhizobial isolates of Lathyrus and Oxytropis collected from northern regions of China were studied in their genotypic characterization based upon analyses of ARDRA, 16S-23S IGS PCR-RFLP, TP-RAPD, MLEE, sequences of 16S rDNA gene and housekeeping genes of atpD, recA and glnII. The results demonstrated that most of the Lathyrus rhizobia belonged to Rhizobium and most of the Oxytropis rhizobia belonged to Sinorhizobium. A novel group of Rhizobium sp. I and S. meliloti were identified as the main microsymbionts respectively associated with Lathyrus and Oxytropis species in the collection area, which were new associations between rhizobia and the mentioned hosts. This study also provides new evidence for biogeography of rhizobia.

Blunted cystine-glutamate antiporter function in the nucleus accumbens promotes cocaine-induced drug seeking

Repeated cocaine alters glutamate neurotransmission, in part, by reducing cystine-glutamate exchange via system xc-, which maintains glutamate levels and receptor stimulation in the extrasynaptic compartment. In the present study, we undertook two approaches to determine the significance of plasticity involving system xc-. First, we examined whether the cysteine prodrug N-acetylcysteine attenuates cocaine-primed reinstatement by targeting system xc-. Rats were trained to self-administer cocaine (1 mg/kg/200 microl, i.v.) under extended access conditions (6 h/day). After extinction training, cocaine (10 mg/kg, i.p.) primed reinstatement was assessed in rats pretreated with N-acetylcysteine (0-60 mg/kg, i.p.) in the presence or absence of the system xc- inhibitor (S)-4-carboxyphenylglycine (CPG; 0.5 microM; infused into the nucleus accumbens). N-acetylcysteine attenuated cocaine-primed reinstatement, and this effect was reversed by co-administration of CPG. Secondly, we examined whether reduced system xc- activity is necessary for cocaine-primed reinstatement. To do this, we administered N-acetylcysteine (0 or 90 mg/kg, i.p.) prior to 12 daily self-administration sessions (1 mg/kg/200 microl, i.v.; 6 h/day) since this procedure has previously been shown to prevent reduced activity of system xc-. On the reinstatement test day, we then acutely impaired system xc- in some of the rats by infusing CPG (0.5 microM) into the nucleus accumbens. Rats that had received N-acetylcysteine prior to daily self-administration sessions exhibited diminished cocaine-primed reinstatement; this effect was reversed by infusing the cystine-glutamate exchange inhibitor CPG into the nucleus accumbens. Collectively these data establish system xc- in the nucleus accumbens as a key mechanism contributing to cocaine-primed reinstatement.