LC−Biosensor System for the Determination of the Neurotoxin β-N-Oxalyl-l-α,β-diaminopropionic Acid

Identification and characterization of the key enzyme in the biosynthesis of the neurotoxin β-ODAP in grass pea

Grass pea (Lathyrus sativus L.) is a grain legume commonly grown in Asia and Africa for food and forage. It is a highly nutritious and robust crop, capable of surviving both droughts and floods. However, it produces a neurotoxic compound, β-N-oxalyl-L-α,β-diaminopropionic acid (β-ODAP), which can cause a severe neurological disorder when consumed as a primary diet component. While the catalytic activity associated with β-ODAP formation was demonstrated more than 50 years ago, the enzyme responsible for this activity has not been identified. Here, we report on the identity, activity, 3D structure, and phylogenesis of this enzyme—β-ODAP synthase (BOS). We show that BOS belongs to the benzylalcohol O-acetyltransferase, anthocyanin O-hydroxycinnamoyltransferase, anthranilate N-hydroxycinnamoyl/benzoyltransferase, deacetylvindoline 4-O-acetyltransferase superfamily of acyltransferases and is structurally similar to hydroxycinnamoyl transferase. Using molecular docking, we propose a mechanism for its catalytic activity, and using heterologous expression in tobacco leaves (Nicotiana benthamiana), we demonstrate that expression of BOS in the presence of its substrates is sufficient for β-ODAP production in vivo. The identification of BOS may pave the way toward engineering β-ODAP–free grass pea cultivars, which are safe for human and animal consumption.

Construction and application of β-(3-N-oxalyl-l-2,3-diaminopropanoic acid) biosensor based on carboxylated multiwalled carbon nanotubes/gold nanoparticles/chitosan/Au electrode

We describe the construction of a new enzyme electrode (GluOx/cMWCNT/AuNPs/CHIT/Au) and its application for the amperometric determination of β-ODAP (3-N-oxalyl-L-2,3-diaminopropanoic acid) in Lathyrus seeds.

Evaluation of hydrogel-coated glutamate microsensors

Glutamate microsensors form a promising analytical tool for monitoring neuronally derived glutamate directly in the brain. However, when a microsensor is implanted in brain tissue, many factors can diminish its performance. Consequently, a thorough characterization and evaluation of a microsensor is required concerning all factors that may possibly be encountered in vivo. The present report deals with the validation of a hydrogel-coated glutamate microsensor. This microsensor is constructed by coating a carbon fiber electrode (10-microm diameter; 300-500 microm long) with a five-component redox hydrogel, in which L-glutamate oxidase, horseradish peroxidase, and ascorbate oxidase are wired via poly(ethylene glycol) diglycidyl ether to an osmium-containing redox polymer. A thin Nafion coating completes the construction. Although this microsensor was previously used in vivo, information concerning its validation is limited. In the present study, attention was given to its selectivity, specificity, calibration, oxygen dependency, biofouling, operating potential dependency, and linear range. In addition, successful microsensor experiments in microdialysate, in vitro (in organotypic hippocampal slice cultures), and in vivo (in anesthesized rats) are shown.

Enantioselective determination of dencichine in rabbit plasma by high-performance liquid chromatography–electrospray mass spectrometry

An analytical method was developed for the determination of enantiomers of dencichine in plasma. Sample extraction from plasma was achieved by a solid-phase extraction (SPE) procedure using a C(18) cartridge, with carbocisteine as the internal standard. Plasma was deproteinized using inorganic acid and derivatizated before the SPE. Chiral separation of dencichine enantiomers was achieved by pre-column derivatization using o-phthaldialdehyde (OPA) and the chiral thiol N-isobutanoyl-L-cysteine (NIBC) to form diastereoisomeric isoindole derivatives that were separable by ODS column using a gradient solvent programme. The column eluent was monitored using mass spectrometry (MS). The conditions of MS detection were optimized, and selected ion monitoring was used to selectively detect D-dencichine and its arrangement isomer. High sensitivity and selectivity were obtained using this method. The limit of detection was determined to be 10 ng/ml for D-dencichine and 8 ng/ml for L-dencichine in plasma. The linearity was demonstrated over a wide range of concentrations, from 0.5 to 50 microg/ml for both enatiomers. The intra- and inter-day precision (C.V.), studied at four concentrations, was less than 7.0%. No interferences from endogenous amino acids and isomers of dencichine were found. The method was suitable for pharmacokinetic studies of dencichine enantiomers.

A biosensor based on co-immobilized l-glutamate oxidase and l-glutamate dehydrogenase for analysis of monosodium glutamate in food

A monosodium glutamate (MSG) biosensor made by co-immobilized L-glutamate oxidase (L-GLOD) and L-glutamate dehydrogenase (L-GLDH) as the bio-component based on substrate recycling for highly sensitive MSG or L-glutamate determination, has been developed. Regeneration of MSG by substrate recycling provided an amplification of the sensor response. Higher signal amplification was found in the presence of ammonium ion. The sensor was standardized to determine MSG in the range of 0.02-3.0 mg/L. Linearity was obtained from 0.02 to 1.2 mg/L in presence of ammonium ion (10 mM) and NADPH (reduced nicotinamide adenine dinucleotide phosphate) (2 mM), but in absence of L-GLDH, the detection limit of MSG is confined to 0.1 mg/L. The apparent Km for MSG with L-GLOD-L-GLDH coupled reaction was 0.4451 mM but 1.9222 mM when only L-GLOD was immobilized. Cross linking with glutaraldehyde in the presence of bovine serum albumin (BSA) as a spacer molecule has been used for the method of immobilization. The response time of the sensor was 2 min. The optimum pH and temperature of the biosensor has been determined as 7+/-2 and 25+/-2 degrees C, respectively. The enzyme immobilized on the membrane was used for over 50 measurements. The standard error of the sample measurement was 4-5%. The activity of the enzyme-immobilized membrane was tested over a period of 60 days.

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.

Hydrophilic interaction liquid chromatography with tandem mass spectrometry for the determination of underivatized dencichine (beta-N-oxalyl-L-alpha,beta-diaminopropionic acid) in Panax medicinal plant species

Dencichine (beta-N-oxalyl-L-alpha,beta-diaminopropionic acid) is a haemostatic agent present in important Chinese medicinal herbs such as Panax notoginseng, as well as other Panax species. It is also a reported neurotoxic agent found in Lathyrus sativus (grass pea seed). A selective analytical method incorporating hydrophilic interaction chromatography with positive electrospray ionization tandem mass spectrometry (HILIC/ESI-MS/MS), for the analysis of dencichine in Panax plant species, was developed. Using multiple reaction monitoring (MRM) mode, underivatized dencichine, a small and highly polar compound, was selectively detected and quantified. The contents of dencichine in raw and steamed Panax notoginseng roots, 11 pairs of raw and steamed P. notoginseng herbal products, Panax ginseng roots, and Panax quinquefolium roots, were analyzed and compared. Optimal sensitivity of 0.3 ppm (detection limit) and 1.5 ppm (quantification limit) was achieved. The method was rapid (< or =5 min), with the HILIC peak eluting at about 1 min. Steamed P. notoginseng samples were found to contain less dencichine than the corresponding raw samples, and there were also differences among the three Panax species; raw P. ginseng and P. quinquefolium contained less dencichine than the raw P. notoginseng species. This rapid and specific method may be applied to the quantification of dencichine in complex medicinal plants and their products.

Liquid chromatographic determination of total and beta-N-oxalyl-L-alpha,beta-diaminopropionic acid in lathyrus sativus seeds using both refractive index and bioelectrochemical detection

A further improved chromatographic method for the simultaneous determination of the total amount of ODAP, selectively the amount of its neurotoxic form, beta-ODAP, and free L-glutamate in raw Lathyrus sativus (grass pea) seed samples is described using post-column refractive index in combination with bioelectrochemical detection. The biosensor is based on crosslinking horseradish peroxidase (HRP) and an Os-containing mediating polymer with poly(ethyleneglycol)(400) diglycidyl ether (PEGDGE), forming an inner hydrogel layer and then immobilising L-glutamate oxidase (GlOx) as an outer layer on top of a graphite electrode. Addition of polyethylenimine (PEI) to the hydrogel is believed to have sensitivity and stability enhancing effect on the biosensor. The double-layer approach in the biosensor construction avoided direct electrical wiring of GlOx and resulted in a higher sensitivity of 4.6 mA/M cm2 with respect to beta-ODAP and a wider linear range (1-250 microM) for both L-glutamate and beta-ODAP when compared with a single-layer approach where GlOx, HRP, and Os-polymer are crosslinked together. The limit of detection for the chromatographic-biosensor system was found to be 2 microM with respect to beta-ODAP and 0.7 microM with respect to L-glutamate. The refractive index detection on-line with the biosensor enabled full control of the chromatographic system for the determination of the total amount of ODAP, selectively the amount of beta-ODAP and L-glutamate. Ten grass pea samples have been collected from Lathyrism prone areas of Ethiopia to test the applicability of the presently developed analytical system for real sample analysis. The toxin levels of grass pea collections were determined in an aqueous extracts and ranged from 0.52 to 0.76%, dry mass basis. Comparison of results of an established spectrophotometric assay and that of the present system has shown an extraordinary degree of agreement as revealed by parallel "t" test (90% confidence limit). The present system has operational stability of more than 50 h. Analysis time per sample is 10 min after extraction for 90 min.

An acetylcholinesterase/choline oxidase-based amperometric biosensors as a liquid chromatography detector for acetylcholine and choline determination in brain tissue homogenates

A liquid chromatography (LC) detector based on a fast response and sensitive bienzyme amperometric biosensor for acetylcholine (ACh) and choline (Ch) is described. The detector fabrication consisted of glutaraldehyde co-crosslinking of acetylcholinesterase and choline oxidase with bovine serum albumin on the Pt working electrode of a conventional thin-layer electrochemical flow cell. The influence of some experimental parameters (e.g., enzyme loading, thickness of the bienzyme layer, flow rate) on the detector characteristics has been studied in order to optimize the analyte response while minimizing band-broadening and distortion. A mobile phase consisting of a phosphate buffer (I, 0.1 M; pH, 6.5) containing 5 mM sodium hexane sulfonate and 10 mM tetramethylammonium phosphate was found to give very satisfactory resolution and peak shape in ion-pair, reversed-phase LC. Linear responses were observed over at least four decades and absolute detection limits (at a signal-to-noise ratio of 3) were 12 and 27 fmol injected for Ch and ACh, respectively. After one month of intensive use in the LC system, the detector retained about 70% of its initial sensitivity. The potential of the described approach is demonstrated by the simultaneous determination of Ch and ACh in rat brain tissue homogenates.

Analysis of beta-N-oxalyl-L-alpha,beta-diaminopropionic acid and homoarginine in Lathyrus sativus by capillary zone electrophoresis

A simple capillary zone electrophoresis (CZE) method has been developed for the simultaneous quantitative determination of beta-N-oxalyl-L-alpha,beta-diaminopropionic acid (beta-ODAP) and homoarginine in Lathyrus sativus (LS; grass pea). A new Na2B4O7-Na2SO4 run buffer was used and the pH was 9.20, contents of beta-ODAP and homoarginine in crude extracts of LS plant material were determined with this method, the RSDs of peak areas of beta-ODAP and homoarginine were 2.62% and 3.61%, respectively. It was found that the equilibrium concentration ratio of alpha- and beta-ODAP decreased from 34.5/65.5 to 28.6/71.4 when the pH of the solution increased from pH 3.0 to pH 11.0.

Redox hydrogel based bienzyme electrode for L-glutamate monitoring

Amperometric bienzyme electrodes based on coupled L-glutamate oxidase (GlOx) and horseradish peroxidase (HRP) were constructed for the direct monitoring of L-glutamate in a flow injection (FI)-system. The bienzyme electrodes were constructed by coating solid graphite rods with a premixed solution containing GlOx and HRP crosslinked with a redox polymer formed of poly(1-vinylimidazole) complexed with (osmium (4-4'-dimethylbpy)2 Cl)II/III. Poly(ethylene glycol) diglycidyl ether (PEGDGE) was used as the crosslinker and the modified electrodes were inserted as the working electrode in a conventional three electrode flow through amperometric cell operated at -0.05 V versus Ag¿AgCl (0.1 M KCl). The bienzyme electrode was optimized with regard to wire composition, Os-loading of the wires, enzyme ratios, coating procedure, flow rate, effect of poly(ethyleneimine) addition, etc. The optimized electrodes were characterized by a sensitivity of 88.36 +/- 0.14 microA mM(-1) cm(-2), a detection limit of 0.3 microM (calculated as three times the signal-to-noise ratio), a response time of less than 10 s and responded linearly between 0.3 and 250 microM (linear regression coefficient = 0.999) with an operational stability of only 3% sensitivity loss during 8 h of continuous FI operation at a sample throughput of 30 injections h(-1).

Characterisation of a thermophilic L-glutamate dehydrogenase biosensor for amperometric determination of L-glutamate by flow injection analysis

Carbon paste wax electrodes incorporating thermophilic L-glutamate dehydrogenase, NADP and a polymeric toluidine blue O (poly-TBO) mediator have been characterised for the amperometric determination of L-glutamate at 313-318 K in a flow injection analysis (FIA) system. The biosensors exhibit good sensitivity, mechanical stability and reproducibilty, unlike carbon paste- or carbon wax-based electrodes under the same conditions. The carbon paste wax electrode responds linearly to L-glutamate up to 40 mM, the detection limit is 0.3 mM and the RSD (n = 10) for 5 mM L-glutamate was 7.6%. The response to some potential interferents has been quantified. Addition of finely ground hexaammineruthenium (III) trichloride ([Ru(NH3)6]Cl3) to the carbon paste wax electrodes decreases the FIA peak width and increases the peak current. The metal complex appears to accelerate the rate of oxidation of NAD(P)H by poly-TBO.