Receptor interactions of beta-N-oxalyl-L-alpha,beta-diaminopropionic acid, the Lathyrus sativus putative excitotoxin, with synaptic membranes

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.

L-beta-ODAP alters mitochondrial Ca2+ handling as an early event in excitotoxicity

The neurotoxin beta-N-oxalyl-L-alpha,beta-diaminopropionic acid (L-beta-ODAP) is an L-glutamate analogue at alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)/kainate receptors in neurons and therefore acts as an excitotoxic substance. Chronic exposure to L-beta-ODAP present in Lathyrus sativus L. (L. sativus) seeds is proposed as the cause of the neurodegenerative disease neurolathyrism, but the mechanism of its action has not been conclusively identified. A key factor in excitotoxic neuronal cell death is a disturbance of the intracellular Ca2+ homeostasis, including changes in the capacity of intracellular Ca2+ stores like the endoplasmic reticulum (ER) or mitochondria. In this study, aequorin and other Ca2+ indicators were used in N2a neuroblastoma cells to investigate alterations of cellular Ca2+ handling after 24 h exposure to L-beta-ODAP. Our data demonstrate increased mitochondrial Ca2+ loading and hyperpolarization of the mitochondrial membrane potential (Psi(m)), which was specific for L-beta-ODAP and not observed with L-glutamate. We conclude that L-beta-ODAP disturbs the ER-mitochondrial Ca2+ signaling axis and thereby renders the cells more vulnerable to its excitotoxic effects that ultimately will lead to cell death.

Lathyrus sativus (grass pea) and its neurotoxin ODAP

Lathyrus sativus (grass pea) is a high-yielding, drought-resistant legume consumed as a food in Northern India and neighboring countries as well as in Ethiopia. Its development into an important food legume, however, has been hindered by the presence of the neurotoxin - beta-N-oxalyl-L-alpha,beta-diaminopropionic acid (beta-ODAP) in seeds which, if consumed in large quantities for prolonged periods, can cause irreversible paralysis. Recently, some low-toxin lines have been developed that may prove safe for both animal and human foods. Cultivation of L. sativus should thus be considered in suitable regions because the demand for legume animal feed protein products is expected to increase. This paper addresses advances in understanding L. sativus from the perspective of its taxonomy, genetics, ecology, chemistry, nutrition, medicine, biology and for animal nutrition.

ABO blood groups, grass pea preparation, and neurolathyrism in Ethiopia

An exploratory study was conducted in the rural Estie district of Ethiopia in 1997 to identify the role of ABO blood group, rhesus factor, and type of grass pea (Lathyrus sativus) diet in the susceptibility to neurolathyrism. Five-hundred study subjects (250 cases and 250 controls) were examined and interviewed, and had their ABO and rhesus blood groups determined. The majority (86%) of the cases were males. Blood group O was the most common in the patients and controls followed by groups A, B, and AB. The vast majority of the study subjects were rhesus-positive. The gravy (Shiro) grass pea preparation was consumed by 91.6% of the study population, boiled (Nifiro) by 86%, and roasted (Kollo) by 56.4%. Almost half (48%) of the cases had consumed grass pea for > 4 months compared to 8% of controls (P < 0.001). There was a significant association between the risk for neurolathyrism and the consumption of boiled (adjusted odds ratio [AOR] = 98.4) and roasted (AOR = 55.62) forms of grass pea. There was no risk of paralysis associated with consumption of the gravy form of grass pea (AOR = 0.40, 95% confidence interval 0.1-2.0). Blood group O remained significantly associated with the disease after adjusting for age, type of grass pea preparation consumed, and duration of consumption (AOR = 2.90).

Pattern and associated factors of the neurolathyrism epidemic in Ethiopia

OBJECTIVES

To describe the neurolathyrism epidemic in Ethiopia and to identify associated household factors.

METHODS

We interviewed 589 randomly selected heads of household in Debre Sina district of Ethiopia, the area afflicted by the recent neurolathyrism epidemic. Disease information was obtained for 2987 family members.

RESULTS

Neurolathyrism patients were detected in 56 (9.5%) households (prevalence rate 2.38%). The mean number of affected family members per household was 1.27 (SD 0.65, range 1-3). Most (77.5%) patients developed the disability during the epidemic (1995-1999). The median age at onset of paralysis was 11 years with a range of 41 (range 3-44). Younger people were more affected during the epidemic than during the non-epidemic period (P=0.01). The presence of a neurolathyrism patient in the family was associated with illiteracy [adjusted OR (95% CI)=2.23 (1.07-5.10)] of the head of household, with owning a grass pea farm [adjusted OR (95% CI)=2.01 (1.04-3.88)] and with the exclusive cooking of grass pea foods using handmade traditional clay pots [adjusted OR (95% CI=2.06 (1.08-3.90)].

CONCLUSION

Males aged 10-14 years were most affected by neurolathyrism. Increased household risk was associated with illiteracy of the head of the household and exclusive cooking of grass pea foods with handmade traditional clay pots.

Neurotoxic potential of three structural analogs of beta-N-oxalyl-alpha,beta-diaminopropanoic acid (beta-ODAP)

Lathyrism is a non-progressive motor neuron disease produced by consumption of the excitatory amino acid, 3-N-oxalyl-L-2,3-diaminopropanoic acid (beta-ODAP). To learn more about the mechanisms underlying Lathyrism three structural analogs of beta-ODAP were synthesized. Carboxymethyl-alpha,beta-diaminopropanoic acid (CMDAP) evoked inward currents which were antagonized by APV (30 microM), but not by CNQX (10 microM). N-acetyl-alpha,beta-diaminopropanoic acid (ADAP) evoked no detectable ionic currents but potentiated N-methyl-D-aspartate (NMDA)-activated currents. The potentiation of NMDA currents by ADAP was blocked by 7-chlorokynurenic acid. Carboxymethylcysteine (CMC) did not activate any detectable ionic currents. None of the three beta-ODAP analogs produced visible symptoms of toxicity in day old chicks when administered for 2-3 consecutive days. Ligand binding studies demonstrated that all the three compounds were effective to in displacing [3H]glutamate. The maximum inhibition was 92% for CMDAP, 61% for ADAP, 65% for CMC and 99% for beta-ODAP. These data indicate that analogs of beta-ODAP may interact with glutamate receptors without producing neurotoxicity.