Determination of delta-aminolevulinic acid in blood plasma and urine by gas-liquid chromatography

Urinary 5-aminolevulinic acid in lead-exposed children

Lead intoxication can interfere with haem synthesis and alter the concentration of haem precursors, such as the neurotoxin 5-aminolevulinic acid, in plasma and urine. The relationship between blood lead concentration (PbB), a biomarker of lead exposure, and 5-aminolevulinic acid concentration in urine (ALAU), a biomarker of the early biological effect of lead, was examined in lead-exposed children. ALAU was assayed by chemical derivatization and high performance liquid chromatography with fluorescence detection. The study subjects were 79 children with moderate to high lead exposure recruited from a lead-poisoning prevention clinic. Their urine had been previously analysed for creatinine (CR) concentration and the benzene metabolite trans,trans- muconic acid, and their blood had been analysed for lead. We found that ALAU was not correlated with PbB (Spearman r=0.088, p=0.44), but the ratio ALAU/CR was correlated with PbB (Spearman r=0.22, p=0.054). Creatinine and ALAU concentrations were higher in urine samples collected in the afternoon than those collected in the morning, a finding that is consistent with known diurnal variation. However the ratio ALAU/CR was not different in morning and afternoon urines, supporting the use of creatinine adjustment of ALAU analysis of spot urine samples. In view of the neurotoxic properties of ALA, future validation studies of biomarkers of lead exposure and effect in children should include ALAU or ALAU/CR as potential markers of lead effect.

Identification of ninhydrin-positive caprolactam metabolites in the rat

Caprolactam (2-oxohexamethylenimine) is metabolized in the rat partly to 4-hydroxycaprolactam or the corresponding free acid. The 4-hydroxy metabolite rearranges spontaneously in acidic aqueous medium to an equilibrium mixture of which 6-amino-gamma-caprolactone is the major component and 6-amino-4-hydroxyhexanoic acid is a minor component. Approximately 16% of the caprolactam ingested daily by rats fed a diet containing 3% caprolactam was excreted as the 4-hydroxy metabolite and a small amount was excreted as the non-hydroxylated acid, 6-aminohexanoic acid. The metabolites were isolated by ion-exchange chromatography and identified by gas chromatography-mass spectroscopy and infra-red and nuclear magnetic resonance spectroscopy.

Determination of delta-aminolaevulinic acid in biological fluids by gas-liquid chromatography with electron-capture detection

A derivative of delta-aminolaevulinic acid (AmLev), 2-methyl-3-acetyl-4-(3-propionic acid pentafluorobenzyl ester)pyrrole, with favourable properties for g.l.c. with electron-capture detection, was synthesized. Less than 1 pg could be detected on the column. 6-Amino-5-oxohexanoic acid formed the analogous derivative under similar conditions and was used as the internal standard in the development of a highly sensitive and specific assay for AmLev. The method has been applied to peripheral-venous and umbilical-cord plasma and to cerebrospinal fluid of normal and porphyric subjects.