In vitro toxicological investigations of isoxazolinone amino acids of Lathyrus sativus

The Potential of CRISPR/Cas9 to Circumvent the Risk Factor Neurotoxin β-N-oxalyl-L-α, β-diaminopropionic acid Limiting Wide Acceptance of the Underutilized Grass Pea (Lathyrus sativus L.)

Grass pea (Lathyrus sativus L.) is a protein-rich crop that is resilient to various abiotic stresses, including drought. However, it is not cultivated widely for human consumption due to the neurotoxin β-N-oxalyl-L-α, β-diaminopropionic acid (β-ODAP) and its association with neurolathyrism. Though some varieties with low β-ODAP have been developed through classical breeding, the β-ODAP content is increasing due to genotype x environment interactions. This review covers grass pea nutritional quality, β-ODAP biosynthesis, mechanism of paralysis, traditional ways to reduce β-ODAP, candidate genes for boosting sulfur-containing amino acids, and the potential and targets of gene editing to reduce β-ODAP content. Recently, two key enzymes (β-ODAP synthase and β-cyanoalanine synthase) have been identified in the biosynthetic pathway of β-ODAP. We proposed four strategies through which the genes encoding these enzymes can be targeted and suppressed using CRISPR/Cas9 gene editing. Compared to its homology in Medicago truncatula, the grass pea β-ODAP synthase gene sequence and β-cyanoalanine synthase showed 62.9% and 95% similarity, respectively. The β-ODAP synthase converts the final intermediate L-DAPA into toxic β-ODAP, whist β-cyanoalanine synthase converts O-Acetylserine into β-isoxazolin-5-on-2-yl-alanine. Since grass pea is low in methionine and cysteine amino acids, improvement of these amino acids is also needed to boost its protein content. This review contains useful resources for grass pea improvement while also offering potential gene editing strategies to lower β-ODAP levels.

A tale of four kingdoms – isoxazolin-5-one- and 3-nitropropanoic acid-derived natural products

The occurrence, structural diversity, (bio-)synthesis, properties and detoxification mechanisms of isoxazolinone- and 3-nitropropanoic acid-derived natural compounds are reviewed.

Effect of different levels of raw and heated grass pea seed (Lathyrus sativus) on nutrient digestibility, intestinal villus morphology and growth performance of broiler chicks

This study aimed to investigate chemical composition and effect of different levels (0%, 10% and 20%) of raw grass pea (RGP) and heat-treated (120 °C for 30 min) grass pea seed (HGP) on nutrient digestibility, dressing percentage, relative internal organ weights, intestinal villous morphology and broiler chicks' performance. A total number of 200 day-old male chicks were raised under similar condition for 10 days. On day 11, chicks were randomly assigned to five dietary treatments and four replicates of 10 birds each. The result of chemical analysis indicated that Iranian grass pea seed has low levels of total and condensed tannin, and it may be considered as a good source of protein (36.1%) and energy (17.09 kJ GE/g). Heat treatment reduced (p < 0.05) the total and condensed tannin to 21% and 78% respectively. Grass peas seed had higher levels of nitrogen-free extract, P, Na, Mg and Zn than soya bean meal. The apparent digestibility of gross energy and lipid was affected (p < 0.01) by the treatment diets, and it was the lowest after feeding 20% of HGP (p < 0.05). The relative weight of breast and pancreas (p < 0.05) was affected by treatments. Percentage weight of breast and pancreas increased (p < 0.05) after feeding high levels (20%) of RGP and HGP. Substitution of 20% of RGP and HGP increased the duodenal crypt depth (p < 0.05); however, it had no suppressive effect on villus height as the absorptive surface of intestine. The feed conversion ratio was not affected by the treatments in the total experimental period. This study showed that, although the high level of grass pea seed caused a remarkable increase in the relative weight of pancreas and decreased the apparent digestibility of gross energy and lipid, it had beneficial effect on breast relative weight. It seems that heat processing is not effective method for improving quality of Iranian grass pea seed.

Improvement of nutritive value of grass pea (Lathyrus sativus) seed meal in the formulated diets for rohu, Labeo rohita (Hamilton) fingerlings after fermentation with a fish gut bacterium

Eight isonitrogenous (35% crude protein approximately) and isocaloric (4.0 kcalg(-1) approximately) diets were formulated incorporating raw and fermented grass pea (Lathyrus sativus) seed meal at 10%, 20%, 30% and 40% levels by weight into a fish meal based diet and fed to rohu, Labeo rohita, fingerlings for 80 days and fish performance was studied. A particular bacterial strain (Bacillus sp.) isolated from the intestine of adult common carp (Cyprinus carpio) reared in the wild having significant amylolytic, cellulolytic, lipolytic and proteolytic activities were used for fermentation of seed meal for 15 days at 37 degrees C. Fermentation of grass pea seed meal was effective in significantly reducing the crude fibre content and anti-nutritional factors, such as tannins, phytic acid and the neurotoxin, beta-ODAP and enhancing the available free amino acids and fatty acids. In terms of growth response, feed conversion ratio and protein efficiency ratio, 30% fermented grass pea seed meal incorporated diet resulted in significantly (P < 0.05) better performance of rohu fingerlings. In general, growth and feed utilization efficiencies of fish fed diets containing fermented seed meal were superior to those fed diets containing raw seed meal. The apparent protein digestibility (APD) values decreased with increasing levels of raw seed meal in the diets. The APD for raw seed meal was lower at all levels of inclusion in comparison to those for the fermented seed meals. The highest deposition of carcass protein was recorded in fish fed the diet containing 40% fermented seed meal. The results indicated that fermented grass pea seed meal can be incorporated in carp diets up to 30% level compared to 10% level of raw seed meal.

Neuroactive and other free amino acids in seed and young plants of Panax ginseng

The seeds and one to three years old plants of Asian ginseng (Panax ginseng C.A. Meyer) were analyzed for their free amino acid contents. The neuro-excitatory beta-ODAP (beta-N-oxalyl-L-alpha,beta-diaminopropionic acid), suggested to be the cause of the crippling neurolathyrism, was the major component in the seed extract (70% of the total free amino acids detected) and showed the highest concentration (0.43% by wt) compared to that in the different parts of young plants. beta-ODAP concentration was higher in the shoots as compared to roots and declined in older plants. The amount of beta-ODAP in the roots may be considered as an indirect measure of age and quality. Another neuro-active non-protein amino acid, GABA (gamma-aminobutyric acid), increased dramatically after germination and reached highest concentration in different parts of 3 year-old plants. Glutamine and arginine were the two major free proteinogenic amino acids in the ginseng plants and together they constituted over 50% of all the free amino acids detected in the root.

Identification and quantification of natural isoxazolinone compounds by capillary zone electrophoresis

A capillary zone electrophoresis (CZE) method that is specific, simple, rapid and also cheap was developed to analyse some natural UV-absorbing isoxazolinone compounds with toxic potential present in legume seedlings. The six most common natural isoxazolinone compounds were separated within 10 min with 25 mM potassium phosphate (pH 7.5) containing 8% 1-propanol as running buffer. A 60 cm coated fused-silica capillary (52.6 cm effective length x 75 microm I.D.), with an electric field of 375 V/cm at 30 degrees C was used. The limit of detection ranged from 0.01 mM (3.0 microg/ml) to 0.03 mM (7.7 microg/ml). Linearity between peak areas and concentrations ranging from 0.05 mM to 1.75 mM were determined for each isoxazolinone. The correlation coefficient was 0.9954 or greater. Both relative migration time and peak area were reproducible. The RSD of relative migration time is between 0.44 and 1.94% and RSD of peak area is between 1.26 and 6.86%. The concentrations of isoxazolinones in Lathyrus odoratus and L. sativus seedlings obtained by CZE were in agreement with the previous results from HPLC.

Amino acids in seeds and seedlings of the genus Lens

The amino acid content of seeds and 4-day-old seedlings were studied in five species of lentil: Lens culinaris, L. orientalis, L. ervoides, L. nigricans and L. odemensis. Free amino acid and also total protein amino acid content after HCl hydrolysis were determined by HPLC. The nonprotein UV-absorbing amino acids were determined by capillary zone electrophoresis (CZE). The content of free protein amino acids in seeds varied among species and increased dramatically after germination. Asparagine is quantitatively most important in both seed and seedling. The content of free nonprotein amino acids is variable in seeds and seedlings. gamma-Hydroxyarginine, gamma-hydroxyornithine, alpha-aminobutyric acid and taurine were found in both seeds and seedlings. Homoarginine was found in four species but not in L. orientalis while gamma-aminobutyric acid (GABA), alpha-aminoadipic acid (alpha-aaa) and three isoxazolinone derivatives: beta-(isoxazolin-5-on-2-yl)-alanine (BIA), gamma-glutamyl-BIA (gamma-glu-BIA) and 2-carboxymethyl-isoxazolin-5-one (CMI) were found exclusively in the seedlings. CMI was identified for the first time in lentil species. Lathyrine, beta-(2-amino-pyrimidine-4-yl)-alanine, which was reported to be in the seeds of some Lathyrus species was confirmed to be present also in the seedling of L. culinaris (trace amount), L. nigricans and L. odemensis. Trigonelline (N-methyl-nicotinic acid), a plant hormone, is present both in seeds and seedlings in different concentrations except in L. ervoides. The different combination of nonprotein amino acids among the species gives indication of their genetic relationship and might partly explain the varying compatibility for interspecies crossing.

Inhibitory activity of a naturally occurring heterocyclic beta-substituted alanine, beta-(isoxazolin-5-on-4-yl)-L-alanine, on the L-glutamate/L-aspartate transporter (GLAST) expressed in Xenopus oocytes

Excitatory amino acid (EAA) transporters are of physiological importance in the regulation of the extracellular concentration of excitatory amino acids and the neuroexcitation in CNS. Among four identified transporters, the Na+-dependent high-affinity L-glutamate/L-aspartate transporter (GLAST) is highly expressed in glial cells. Here, we report a naturally occurring inhibitor of GLAST, derived from bovine retina, using the Xenopus oocyte expression system. Beta-(isoxazolin-5-on-4-yl)-L-alanine (TAN), an antifungal antibiotic, inhibited [14C]L-glutamate (L-Glu) transport into GLAST-expressing oocytes. TAN also served as a substrate for this transporter in voltage-clamp experiments measuring the current coupled to the EAA transport. The maximum current of TAN itself was approximately 1/3 of that of L-glutamate, and its apparent affinity was almost the same as L-Glu. In combination with L-Glu, TAN antagonized L-glutamate transport. In radioisotope experiments, the inhibitory potency of this compound against [14C]L-Glu uptake into oocytes was approximately 1/6 of that of L-(-)-threo-3-hydroxyaspartate (THA). The glucoside of TAN (TANG), occurring in seedlings of the garden pea, the lentil and some Lathyrus species, did not show any electrophysiological activity nor was it transported into oocytes. It is proposed that TAN is a novel type antagonist of natural origin on GLAST. By affecting such transport system, naturally occurring compounds may affect the regulation of the extracellular level of endogenous EAA.

Effects of β-ODAP and its biosynthetic precursor on the electrophysiological activity of cloned glutamate receptors

3-N-Oxalyl-l-2,3-diaminopropanoic acid (β-ODAP) induces neurolathyrism, a motor neuron disease. To elucidate the pathogenic mechanism of this process, the action of β-ODAP on the excitatory amino acid (EAA) receptor-mediated currents was examined using cloned EAA receptors expressed in Xenopus oocytes. On the voltage-clamp recordings of an AMPA receptor (α (1)α (2) heterooligomer), β-ODAP was a strong agonist on this receptor, the potency being almost the same as l-glutamate. On the other hand, β-ODAP had little effect on the glutamate-evoked currents through the expressed NMDA receptor (NR1(A)/NR2A), but showed a weak inhibitory effect on the glycine-modulatory site. β-ODAP may cause the neurodegenerative disease, neurolathyrism, mainly through the excitotoxic interaction with AMPA receptors.

Toxic models of upper motor neuron disease

Although neurotoxic models for progressive degeneration of both the anterior horn cell and the Betz cell do not exist, (neuro)lathyrism and neurocassavism (konzo) are examples of self limiting neurotoxic disorders that predominantly target the Betz cell. Both disorders are caused by the continuous intake of neurotoxic plant products (Lathyrus sativus and Manihot esculenta, respectively) which result in a virtually identical clinical picture of spastic paraparesis. A neurotoxic excitatory amino acid and AMPA agonist (beta-N-oxalylamino-1-alanine, BOAA) is held largely responsible for lathyrism. Epidemics of konzo are strongly associated with increased intake of the cyanide-liberating glycoside linamarin by protein-poor subjects. Whereas an animal model for neurocassavism does not exist, macaques fed Lathyrus sativus or BOAA develop central motor deficits with corticospinal tract involvement. Estimated dosages of Lathyrus sativus used to induce beginning lathyrism in well-nourished primates are 10-20 fold greater than those associated with irreversible human neurolathyrism. Major unexplained aspects of both diseases are the factors which allow the suspected toxins to target Betsz cells (blood-brain barrier, receptor distribution, cellular energy metabolism), the latency to onset in both diseases, and how two separate etiologic factors trigger clinically similar disorders.