Neurotoxicology and amino acid intake during development: the case of threonine

The use of ethylene glycol solution as the running buffer for highly efficient microchip-based electrophoresis in unmodified cyclic olefin copolymer microchips

An ethylene glycol solution was used as the electrophoretic running buffer in unmodified cyclic olefin copolymer (COC) microchips to minimize the interactions between the analytes and the hydrophobic walls of the plastic microchannels, enhance the resolution of the analytes and eliminate the uncontrollable dispersion caused by uneven liquid levels and non-uniform surfaces of the separation channels. Five amino acids that were labeled with fluorescein isothiocyanate (FITC) were used as model analytes to examine the separation efficiency. The effects of ethylene glycol concentration, pH and sodium tetraborate concentration were systematically investigated. The five FITC-labeled amino acids were effectively resolved using a COC microchip with an effective length of 2.5 cm under optimum conditions, which included using a running buffer of 20 mmol/L sodium tetraborate in ethylene glycol:water (80:20, v/v), pH 6.7. A theoretical plate number of 4.8 × 10(5)/m was obtained for aspartic acid. The system exhibited good repeatability, and the relative standard deviations (n=5) of the peak areas and migration times were no more than 3.4% and 0.7%, respectively. Furthermore, the system was successfully applied to elucidate these five amino acids in human saliva.

Safety assessment of N-acetyl-L-threonine

N-acetyl-L-threonine (NAT) is a dietary constituent that has been identified at low concentrations (< 1 microg/g fresh weight) in numerous foods. The current paper reports the outcome of toxicology studies conducted to assess the effects of NAT. No evidence of mutagenicity or genotoxicity was observed in in vitro bacterial or in vivo mammalian studies. No mortalities or evidence of adverse effects were observed in Sprague-Dawley (SD) rats following acute oral administration of 2000 mg of NAT/kg of body weight (kg of bw). A 28-day repeated dose toxicity study was conducted in SD rats by incorporating NAT into diets at concentrations targeting up to 1000 mg of NAT/kg of bw/day. All rats survived until scheduled sacrifice and no biologically significant differences were observed in any of the NAT treatment groups for body weights, feed consumption, clinical signs, behavioral, ophthalmology, hematology, coagulation, clinical chemistry, organ weights, or gross or microscopic changes. Based on these results, NAT does not represent a risk for mutagenicity or genotoxicity, is not acutely toxic, and the no-observed-adverse-effect-level (NOAEL) for systemic toxicity from repeated dose dietary exposure to NAT is 848.5 and 913.6 mg/kg of bw/day for male and female SD rats, respectively.

Threonine requirement of parenterally fed postsurgical human neonates

BACKGROUND

The threonine requirement of human neonates who receive parenteral nutrition (PN) has not been determined experimentally.

OBJECTIVE

The objective was to determine the parenteral threonine requirement for human neonates by using the minimally invasive indicator amino acid oxidation technique with L-[1-(13)C]phenylalanine as the indicator amino acid.

DESIGN

Nine postsurgical neonates were randomly assigned to 16 threonine intakes ranging from 10 to 100 mg . kg(-1) . d(-1). Breath and urine samples were collected at baseline and at plateau for (13)CO(2) and amino acid enrichment, respectively. The mean threonine requirement was determined by applying a 2-phase linear regression crossover analysis to the measured rates of (13)CO(2) release (F(13)CO(2)) and L-[1-(13)C]phenylalanine oxidation.

RESULTS

The mean threonine parenteral requirement determined by using phenylalanine oxidation was 37.6 mg . kg(-1) . d(-1) (upper and lower confidence limits, respectively: 29.9 and 45.2 mg . kg(-1) . d(-1)) and by using F(13)CO(2) oxidation was 32.8 mg . kg(-1) . d(-1) (upper and lower confidence limits, respectively: 29.7 and 35.9 mg . kg(-1) . d(-1)). Graded intakes of threonine had no effect on phenylalanine flux.

CONCLUSION

This is the first study to report on the threonine requirement for human neonates receiving PN. We found that the threonine requirement for postsurgical PN-fed neonates is 22-32% of the content of threonine that is presently found in commercial PN solutions (111-165 mg . kg(-1) . d(-1)).

Proton spectral editing for discrimination of lactate and threonine 1.31 ppm resonances in human brain in vivo

A single-voxel proton NMR J-difference editing method for discriminating between the 1.31 ppm resonances of lactate (Lac) and threonine (Thr) in human brain in vivo at 3 T is reported. One double-band and two triple-band Gaussian 180 degrees RF pulses, all with a bandwidth of 15 Hz, were employed within an adiabatic-refocused double-echo localization sequence to induce the target signals of Lac and Thr and simultaneously acquire a creatine singlet in each subscan. The optimum echo time and the editing efficiency were obtained by numerical analysis of the filtering performance. The Lac and Thr signals were extracted, without lipid contamination, from three subspectra. Using the calculated yields, the concentrations of Lac and Thr in the human occipital cortex were estimated to be 0.47+/-0.07 and 0.56+/-0.06 mM (mean+/-SD, N=7), respectively, with reference to Cr at 8 mM.

Effects of taurine deficiency and chronic methanol administration on rat retina, optic nerve and brain amino acids and monoamines

A chronic methanol (MeOH) intoxication scheme (2 g/kg/day ip for 2 weeks) was carried out in Sprague-Dawley rats, previously depleted of folates with methotrexate (MTX). beta-Alanine (beta-Ala), 5%, was also administered to some animals in the drinking water. Amino acids were determined in plasma, retina, optic nerve, hippocampus and posterior cortex by HPLC with fluorescence detection and monoamines in retina, hippocampus and posterior cortex by electrochemical detection. Beta-Ala administration reduced taurine (Tau) levels in plasma, hippocampus and posterior cortex, but not in retina and optic nerve. Aspartate (Asp) concentration in the optic nerve was increased in MTX-MeOH treated animals, and the administration of beta-Ala did not modify this elevation. The association of beta-Ala with MTX-MeOH produced an increase of threonine, and a decrease of 5-hydroxytryptamine (5-HT) in the retina without modifying 5-hydroxyindoleacetic acid, whereas in the hippocampus an elevation of asparagine was observed. We conclude that, in the retina, beta-Ala in combination with MTX-MeOH increased serotonin and decreased dopamine (DA) turnover rate, and resulted in changes in the amino acid balance, that could affect glycinergic activity. On the other hand, in the hippocampus, Asp metabolism could be affected by Tau depletion with beta-Ala.