Quantitation of methylated basic amino acids in biological fluid

Determination of N(G),N(G)-dimethylarginine in human plasma by high-performance liquid chromatography

N(G),N(G)-Dimethylarginine (asymmetric dimethylarginine, ADMA) can be directly separated and measured from deproteinized human plasma using o-phthaldialdehyde-mercaptoethanol (OPA reagent) as a fluorogenic reagent by reversed-phase high-performance liquid chromatography. The mean recovery of ADMA was over 96% and the inter- and intra-assay coefficients of variation of amounts were lower than 3.80% and those of retention time were below 0.37% for five runs. The detection limit of the assay is 1 pmol when the signal-to-noise ratio is 3:1. It was observed that the concentration of ADMA was significantly elevated in plasma of patients with pregnancy induced hypertension (PIH) in contrast to healthy pregnant women.

Determination of methylated amino acids in human serum by high-performance liquid chromatography

Employing high-performance liquid chromatography with isocratic elution using a two-column system (mu Bondapak C18 and mu Bondapak CN) and phenyl isothiocyanate as a fluorogenic reagent, NG-monomethylarginine (MMA). NG-dimethylarginines, and epsilon-N-trimethyllysine (TML) can be quatitatively separated from human serum samples. The recoveries of these amino acids were over 90%. It was observed that the serum concentrations of MMA, DMA and TML were significantly elevated in sera obtained from patients suffering from diabetes mellitus, hepatitis or hyperthyroidism, particularly the last condition.

Measurement of epsilon-N-trimethyllysine in human blood plasma and urine

A method for measurement of epsilon-N-trimethyllysine in human blood plasma and urine is described. An internal standard, delta-N-trimethylornithine, was added to plasma and urine specimens and the mixtures were deproteinized and/or hydrolyzed. Preliminary purification of epsilon-N-trimethyllysine and delta-N-trimethylornithine was achieved by sequential cation-exchange--anion-exchange chromatography. Amino acids in the column eluates were derivatized with o-phthalaldehyde and mercaptoethanol, and were separated by isocratic reversed-phase high-performance liquid chromatography in the presence of an ion-pairing reagent. Quantitation was achieved by post-column fluorometry. The limit of detection was 5 pmol of epsilon-N-trimethyllysine injected into the chromatograph. The procedure was suitable for determination of epsilon-N-trimethyllysine in 1 ml of plasma or 0.2-0.4 ml of urine. The method was applied to measurements of epsilon-N-trimethyllysine in plasma and urine of four systemic carnitine deficiency patients and six normal subjects. Plasma epsilon-N-trimethyllysine concentration was significantly lower in systemic carnitine deficiency patients compared to normal individuals, but no significant difference in urinary epsilon-N-trimethyllysine excretion was observed between the two groups.

Determination of 6-N-trimethyllysine in urine by high-performance liquid chromatography

A method for determination of 6-N-trimethyllysine in urine is described. Trimethyllysine and the chemically analogous 6-N-triethyllysine internal standard were isolated from aqueous samples by microcolumn ion-exclusion chromatography. The specimens were derivatized by reaction with 1-fluoro-2,4-dinitrobenzene and reaction byproducts extracted by organic solvents. The trimethyllysine and internal standard derivatives were separated easily from other sample constituents by reversed-phase paired-ion high-performance liquid chromatography with spectrophotometric detection at 405 nm. Standard curves were linear over a sample concentration range of 10-150 nmol/ml; the detection limit corresponded with 0.1 nmol trimethyllysine injected into the chromatograph. The procedure was used for determination of trimethyllysine in human urine.