In vitro activation of protein kinase C by beta-N-oxalyl-L-alpha,beta-diaminopropionic acid, the Lathyrus sativus neurotoxin

Proteomic Changes in Chick Brain Proteome Post Treatment with Lathyrus Sativus Neurotoxin, β-N-Oxalyl-L-α,β-Diaminopropionic Acid (L-ODAP): A Better Insight to Transient Neurolathyrism

Neurolathyrism is a neurodegenerative disorder characterized by spastic paraplegia resulting from the excessive consumption of Lathyrus sativus (Grass pea). β-N-Oxalyl-L-α,β-diaminopropionic acid (L-ODAP) is the primary neurotoxic component in this pea. The present study attempted to evaluate the proteome-wide alterations in chick brain 2 hr and 4 hr post L-ODAP treatment. Proteomic analysis of chick brain homogenates revealed several proteins involved in cytoskeletal structure, signaling, cellular metabolism, free radical scavenging, oxidative stress and neurodegenerative disorders were initially up-regulated at 2 hr and later recovered to normal levels by 4 hr. Since L-ODAP mediated neurotoxicity is mainly by excitotoxicity and oxidative stress related dysfunctions, this study further evaluated the role of L-ODAP in apoptosis in vitro using human neuroblastoma cell line, IMR-32. The in vitro studies carried out at 200 μM L-ODAP for 4 hr indicate minimal intracellular ROS generation and alteration of mitochondrial membrane potential though not leading to apoptotic cell death. L-ODAP at low concentrations can be explored as a stimulator of various reactive oxygen species (ROS) mediated cell signaling pathways not detrimental to cells. Insights from our study may provide a platform to explore the beneficial side of L-ODAP at lower concentrations. This study is of significance especially in view of the Government of India lifting the ban on cultivation of low toxin Lathyrus varieties and consumption of this lentil.

Current scenario of consumption of Lathyrus sativus and lathyrism in three districts of Chhattisgarh State, India

Lathyrism is a disease caused by excessive consumption of grass pea, Lathyrus sativus especially under conditions of severe drought. Grass pea contains 3-N-oxalyl-L-2, 3-diaminopropanoic acid (β-ODAP) a putative neurotoxin which acts through excitatory mechanism causing Neurolathyrism. Due to awareness of the disease, availability of food and levels of consumption of L. sativus there is reduction in lathyrism cases where higher consumption of L. sativus is reported in India. The present study was undertaken with the objective to assess the current scenario of consumption of L. sativus, incidence of cases of lathyrism, β-ODAP, protein and amino acids content in L. sativus pulse collected from three districts (Bilaspur, Durg and Raipur) of Chattisgarh state. For this purpose, a total of 17,755 (13,129 rural and 4626 urban) individuals from 151 villages and 60 wards from urban area were covered for clinical examination. Out of total 5769 households (HHs) covered during the survey, 1602 HHs were cultivators, 1791 HHs non-cultivators and 2376 agricultural and other labourers. A one day 24-hour re-call diet survey was carried out in 5758 HHs (4549 rural and 1209 urban). A total of 360 split grass pea (SGP) samples were collected to estimate β-ODAP, protein and amino acids content. Results of the study revealed that an average consumption of SGP was 20.9 gm/CU/day in Bilaspur and no consumption was reported among urban population of Raipur. Only nine old cases of lathyrism were found during the study. The mean β-ODAP content in SGP was 0.63 ± 0.14, 0.65 ± 0.13 and 0.65 ± 0.14 gm/100 gm, whereas the protein content was 27.0 ± 2.39, 27.0 ± 1.99 and 26.7 ± 1.90 gm/100 gm in samples collected from Bilaspur, Durg and Raipur districts respectively. Arginine content was high in SGP and sulphur containing amino acids (cysteine and methionine) were less than other amino acids. In conclusion, the consumption of SGP was lower in these three districts with lower β-ODAP content than earlier reports, thus the lower prevalence of lathyrism in the districts surveyed.

β-N-oxalyl-L-α,β-diaminopropionic acid induces wound healing by stabilizing HIF-1α and modulating associated protein expression

BACKGROUND

β-N-oxalyl-L-α,β-diaminopropionic acid (L-ODAP) is a non-protein amino acid with haemostatic property present in Lathyrus sativus. It is considered to be the causative agent of neurolathyrism that occurs upon prolonged overconsumption of Lathyrus sativus seeds. L-ODAP is used as a haemostatic drug in surgical dressings. We previously reported that it can stabilize hypoxia inducible factor (HIF)-1α in normoxic conditions.

HYPOTHESIS

We hypothesised that L-ODAP might affect wound healing by modulating cellular proliferation, migration and angiogenesis via HIF-1α stabilization.

STUDY DESIGN

We performed in vitro assays to evaluate wound healing activity of L-ODAP. Further, we prepared pharmaceutical gel containing L-ODAP and checked its effect on healing of full thickness excision wounds using Wistar albino rats.

METHODS

Effect of L-ODAP on HT1080 cell line proliferation, migration and invasion was investigated. Further, gel containing L-ODAP was applied on full thickness excision wounds of Wistar rats. Western blot and zymography were performed with wound tissue extracts obtained 2 days post-wounding and histological and immunohistochemical analysis with regenerated tissue obtained 10 days post-wounding. Evaluation was made based on wound contraction percentage, histological analysis and protein expression levels.

RESULTS

L-ODAP significantly (P < 0.05) affected wound healing both in vitro and in vivo. At non-toxic concentrations, it induced cell proliferation, migration, invasion and MMP-2 & -9 expressions. L-ODAP treated wounds healed faster than vehicle treated ones. Significantly higher expression level of HIF-1α, VEGF-A, PDGF-A and matrix metalloproteases were observed in L-ODAP treated wounds.

CONCLUSION

The present investigation explores potential of L-ODAP as a wound healing agent. L-ODAP positively affected wound healing both in vitro and in vivo and thus could be considered a natural wound healing agent.

Unlocking the potential of orphan legumes

Orphan, or underutilized, legumes are domesticated legumes with useful properties, but with less importance than major world crops due to use and supply constraints. However, they play a significant role in many developing countries, providing food security and nutrition to consumers, as well as income to resource-poor farmers. They have been largely neglected by both researchers and industry due to their limited economic importance in the global market. Orphan legumes are better adapted than the major legume crops to extreme soil and climatic conditions, with high tolerance to abiotic environmental stresses such as drought. As a stress response they can also produce compounds with pharmaceutical value. Orphan legumes are therefore a likely source of important traits for introduction into major crops to aid in combating the stresses associated with global climate change. Modern large-scale genomics techniques are now being applied to many of these previously understudied crops, with the first successes reported in the genomics area. However, greater investment of resources and manpower are necessary if the potential of orphan legumes is to be unlocked and applied in the future.

Plant toxin β-ODAP activates integrin β1 and focal adhesion: A critical pathway to cause neurolathyrism

Neurolathyrism is a unique neurodegeneration disease caused by β-N-oxalyl-L-α, β- diaminopropionic (β-ODAP) present in grass pea seed (Lathyrus stativus L.) and its pathogenetic mechanism is unclear. This issue has become a critical restriction to take full advantage of drought-tolerant grass pea as an elite germplasm resource under climate change. We found that, in a human glioma cell line, β-ODAP treatment decreased mitochondrial membrane potential, leading to outside release and overfall of Ca²⁺ from mitochondria to cellular matrix. Increased Ca²⁺ in cellular matrix activated the pathway of ECM, and brought about the overexpression of β1 integrin on cytomembrane surface and the phosphorylation of focal adhesion kinase (FAK). The formation of high concentration of FA units on the cell microfilaments further induced overexpression of paxillin, and then inhibited cytoskeleton polymerization. This phenomenon turned to cause serious cell microfilaments distortion and ultimately cytoskeleton collapse. We also conducted qRT-PCR verification on RNA-sequence data using 8 randomly chosen genes of pathway enrichment, and confirmed that the data was statistically reliable. For the first time, we proposed a relatively complete signal pathway to neurolathyrism. This work would help open a new window to cure neurolathyrism, and fully utilize grass pea germplasm resource under climate change.

Role of glutamate and nitric oxide in onset of motor neuron degeneration in neurolathyrism

Neurolathyrism is associated with a complex pattern of alterations in the glutamatergic system of the cortical motor region of brain. It is a neurological disorder consorted with excessive consumption of Lathyrus sativus (Grass pea), comprising large amounts of the neurotoxin, β-N-oxalyl-L-α,β-diaminopropionic acid (ODAP). ODAP being a potent agonist of ionotropic glutamate receptors enhances their activity and also blocks the astrocytic glutamate/cystine transporters, abutting the neurons. This leads to the sustained increase in the concentration of Glutamate in the synapse which triggers excitotoxicity. L. sativus also contains high levels of arginine and homoarginine which are natural substrates of nitric oxide production, when NO levels increases, it forms peroxynitrite radicals which cause irreparable damage to mitochondria and cellular macromolecules leading to motor neuron degeneration. This review brings together all the molecular events reported so far, emphasizing on the possible role of glutamate and nitric oxide mediated cell death.

β-N-oxalyl-L-α,β-diaminopropionic acid regulates mitogen-activated protein kinase signaling by down-regulation of phosphatidylethanolamine-binding protein 1

β-N-Oxalyl-L-α,β-diaminopropionic acid (l-ODAP) an α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor agonist activates protein kinase C in white leghorn chick brain. The current study focuses on the protein kinase C downstream signaling targets associated with L-ODAP excitotoxicity in SK-N-MC human neuroblastoma cells and white leghorn male chick (Gallus domesticus) brain extracts. L-ODAP treatment in SK-N-MC cells (1.5 mM) and chicks (0.5 mg/g body weight) results in a decreased expression and increased phosphorylation of phosphatidylehthanolamine-binding protein 1 (PEBP1) up to 4 h which however, returns to normal by 8 h. D-ODAP, the non-toxic enantiomer however, did not affect PEBP1 levels in either chick brain or SK-N-MC cells. Decreased PEBP1 expression correlated with subsequent activation of Raf-1, MEK and ERK signaling components of the mitogen-activated protein kinase cascade and nuclear translocation of hypoxia inducible factor-1α (HIF-1α) in chick brain nuclear extracts and SK-N-MC cells. SK-N-MC cells over-expressing PEBP1 inhibited nuclear translocation of HIF-1α when treated with l-ODAP, indicating that down-regulation of PEBP1 is responsible for HIF-1α stabilization and nuclear localization. Excitotoxicity of L-ODAP may thus be the result of phosphorylation and down-regulation of PEBP1, a crucial signaling protein regulating diverse signaling cascades. L-ODAP induced convulsions and seizures in chicks could be the result of a hypoxic insult to brain.

A look at the brighter facets of β-N-oxalyl-l-α,β-diaminopropionic acid, homoarginine and the grass pea

The low incidence of neurolathyrism, its absence in several communities traditionally consuming Lathyrus sativus and the likely benefits of its inclusion as part of a normal diet are reviewed. The metabolism/detoxification of ODAP which is unique to humans may be a crucial factor in this regard. The presence of homoarginine in the pulse which has received scant attention in the past could make this an invaluable pulse since it could contribute to a sustained generation of NO. NO is well recognized for its role in cardiovascular physiology and general well-being and thus a daily dietary intake of homoarginine through small quantities of L. sativus may be of advantage and deserves to be exploited. The detoxification of ODAP in humans could spotlight the pulse further for its non-neurotoxic attributes. Activation of PKC by ODAP adds a new dimension to explore its possible therapeutic potentials in areas such as Alzheimer's disease, hypoxia, and long term potentiation. These novel approaches to both ODAP and homoarginine might entirely change our perception of this poor man's pulse.

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.

Comparison of urinary amino acids and trace elements (copper, zinc and manganese) of recent neurolathyrism patients and healthy controls from Ethiopia

OBJECTIVE

The irreversibly crippling disease neurolathyrism is caused by prolonged over-consumption of Lathyrus sativus seed. The molecular mechanism of toxicity is unclear and more biochemical information is needed.

METHODS

The urinary amino acids from 5 recent patients and 9 healthy subjects in Ethiopia were analysed by HPLC after PITC (phenyl isothiocyanate) derivatisation. The trace elements Cu, Zn and Mn of urine and seeds were determined by atomic absorption spectroscopy.

RESULTS

The free amino acids aspartic acid, glycine, beta-aminoisobutyric acid, arginine, alpha-aminoadipic acid and phenylalanine were statistically higher (p<0.05) in urine from patients than in urine from control subjects. The trace element Cu was also statistically higher (p<0.05) in patient urine.

CONCLUSION

The amino acid metabolism of the neurolathyrism patients is disturbed by over-consumption of grass pea seeds. The high concentrations of Cu found in the patient urine might indicate the involvement of trace elements in the aetiology of neurolathyrism.