Effects of rumen-protected methionine on plasma amino acid concentrations during a period of weight loss for late gestating beef heifers.

This study determined changes in plasma amino acid concentration in late-gestating (beginning 58 ± 1.02 days prior to calving), primiparous, winter-grazing range heifers receiving wheat middling-based supplement without (CON) or with rumen-protected methionine (MET) to provide 15 g DL-MET each day. Plasma was collected on days -2 and 0 (start of MET supplementation just prior to individually receiving supplement at 0700 hours). Plasma was sampled again on days 40, 42 and 44 prior to supplementation at 0700 and 1100 hours (4 h after receiving daily supplement). Data were analyzed with cow as the experimental unit. Continuous variables were analyzed by the main effects of treatment, date, or time and their interaction when appropriate. Comparable BW (P = 0.32) and BCS (P = 0.83) over the 44-day metabolism trial were found between both CON- and MET-fed heifers. MET-supplemented heifers had greater (P < 0.01) plasma concentrations of methionine indicating that the rumen-protection technology successfully delivered methionine to the small intestine. Supplementation with rumen-protected DL-MET caused a significant supplement × date interaction for glutamine (P = 0.03), glycine (P = 0.02), methionine (P < 0.01), and serine (P = 0.05). In addition, trends for supplement × date interactions were detected for leucine (P = 0.07), threonine (P = 0.09), valine (P = 0.08), total amino acids (TAA; P = 0.08), non essential amino acids (NEAA; P = 0.08), branched chain amino acids (BCAA; P = 0.08), and glucogenic amino acids (GLUCO; P = 0.08). These results suggest that the BCAA (leucine and valine) were utilized more efficiently with MET supplemented heifers compared to CON supplemented heifers. Plasma AA concentrations for glutamic acid (P < 0.01), histidine (P = 0.01), tyrosine (P < 0.01), and EAA (P < 0.01), all decreased throughout the study. These results further confirm methionine is a limiting amino acid in forage fed late-gestating heifers and further suggests the limitation when grazing dormant range forages as shown by improved utilization of other plasma amino acids when supplemental methionine was provided.

Determination of trace amino acids in human serum by a selective and sensitive pre-column derivatization method using HPLC-FLD-MS/MS and derivatization optimization by response surface methodology.

Analysis of trace amino acids (AA) in physiological fluids has received more attention, because the analysis of these compounds could provide fundamental and important information for medical, biological, and clinical researches. More accurate method for the determination of those compounds is highly desirable and valuable. In the present study, we developed a selective and sensitive method for trace AA determination in biological samples using 2-[2-(7H-dibenzo [a,g]carbazol-7-yl)-ethoxy] ethyl chloroformate (DBCEC) as labeling reagent by HPLC-FLD-MS/MS. Response surface methodology (RSM) was first employed to optimize the derivatization reaction between DBCEC and AA. Compared with traditional single-factor design, RSM was capable of lessening laborious, time and reagents consumption. The complete derivatization can be achieved within 6.3 min at room temperature. In conjunction with a gradient elution, a baseline resolution of 20 AA containing acidic, neutral, and basic AA was achieved on a reversed-phase Hypersil BDS C(18) column. This method showed excellent reproducibility and correlation coefficient, and offered the exciting detection limits of 0.19-1.17 fmol/µL. The developed method was successfully applied to determinate AA in human serum. The sensitive and prognostic index of serum AA for liver diseases has also been discussed.

Dynamic pH junction-sweeping technique for on-line concentration of acidic amino acids in human serum by capillary electrophoresis with indirect UV detection.

Glutamic acid (Glu) and aspartic acid (Asp), as two important neurotransmitters, have been the focus of increasingly intense research over the past several years. Glu and Asp are present in biological fluids such as serum at trace levels, but complex components in biological matrices make it difficult to determine them in biological samples. In this paper, a sensitive and simple method coupled with indirect UV detection, using benzoic acid (BA) as the UV-absorbing probe, was developed and validated for the quantitative determination of Glu and Asp in human serum and Compound Amino Acid Injection-18 AA. The method combines a dynamic pH junction with a sweeping technique using ß-cyclodextrin (ß-CD) as the complexing agent for sweeping. Employing this proposed method, low detection limits of 0.061µg/mL for Glu and 0.032µg/mL for Asp were obtained. The sensitivity was improved 30- and 55-fold for Glu and Asp compared to conventional CE method. Standard curves were linear (r>0.999) over the concentration range of 0.1-8.0µg/mL. To further improve the resolution of Asp from interfering substances in human serum, 6% (v/v) methanol was added to the sample matrix, and resulted in the detection limits of 0.125µg/mL for Glu and 0.057µg/mL for Asp. With a simple precipitation of protein, the method has been successfully applied to the analysis of human serum, and the recoveries (82% for Glu and 87% for Asp) were achieved with relative standard deviations of 1.9% and 2.0%, respectively.

Photoluminescent sensing for acidic amino acids based on the disruption of graphene quantum dots/europium ions aggregates.

A simple mix-and-detect photoluminescence method was developed for the turn-on detection of acidic amino acids. To achieve this, graphene quantum dots (GQDs), which emit both down-conversion and up-conversion photoluminescence were prepared by solvothermal synthesis. The carboxylic acid-rich surface not only increases the water solubility of the prepared GQDs, but also makes Eu(3+)-triggered GQDs aggregation possible, thus causing the photoluminescence quenching of GQDs. The quenched photoluminescence can be recovered by the competition between acidic amino acids and GQDs for Eu(3+). Under optimized conditions, sensitive and specific acidic amino acids quantitation can be achieved by utilizing the changes in either down-conversion or up-conversion photoluminescence. Up-conversion mode gives a little lower detection limit than the down-conversion one. Nearly overlapped calibration curves were obtained for the two acidic amino acids, glutamic acid (Glu) and aspartic acid (Asp), thus suggesting that the proposed method can be used not only for the quantitation of individual acidic amino acids, but also for the detection of total amount of them.

Colon-specific prodrugs of 5-aminosalicylic acid: synthesis and in vitro/in vivo properties of acidic amino acid derivatives of 5-aminosalicylic acid.

5-aminosalicyl-L-aspartic acid (5-ASA-Asp) and 5-aminosalicyl-L-glutamic acid (5-ASA-Glu) were synthesized and their properties as colon-specific prodrugs of 5-aminosalicylic acid (5-ASA) were investigated employing rats as test animals. Incubation of 5-ASA-Asp and 5-ASA-Glu with the homogenates of tissue and contents of stomach or small intestine released no 5-ASA, indicating that they were stable in this condition. Incubation of 5-ASA-Asp with the cecal contents released 5-ASA 37%, whereas 5-ASA-Glu released only 8% of the dose in 16 h. Plasma concentration of 5-ASA-Asp after intravenous administration decreased rapidly and became undetectable in 60 min. No 5-ASA was detected in the blood, which indicated 5-ASA-Asp was stable in the plasma. After oral administration of 5-ASA-Asp, concentration of 5-ASA, its metabolite N-acetyl-5-ASA, and 5-ASA-Asp in the plasma, feces, and urine was determined. In the plasma, 5-ASA-Asp was not detected and the concentration of 5-ASA or N-acetyl-5-ASA was very low. About 33% of the administered dose was recovered as 5-ASA and N-acetyl-5-ASA and 43% as 5-ASA-Asp from feces, and 20% as 5-ASA and N-acetyl-5-ASA and 1% as 5-ASA-Asp from urine in 24 h. These results suggested that most of 5-ASA-Asp was delivered to the large intestine and about half of the administered dose was activated to liberate 5-ASA. After oral administration of free 5-ASA, fecal recovery was only 7% of the dose in 24 h and more than 80% was recovered from urine. Comparing 5-ASA-Asp and free 5-ASA, the amount of 5-ASA available in the large intestine was much larger, while the amount of 5-ASA in urine, which might be related to the systemic toxicity of 5-ASA, was much lower by the administration of 5-ASA-Asp than free 5-ASA.