Profiling of urinary metabolites in human pregnancy
Christie, Elva Jean
Maternal urinary metabolites (organic acids and steroids) in human pregnancy were profiled by gas-chromatographic methods. Urine specimens were collected from pregnant women at two time intervals in gestation (12½-15½ weeks and 24½-27½ weeks). A group of nonpregnant women was also investigated. The 24-hour urinary creatinine excretion was used as a check of the completeness of urine collections. Urinary organic acids were isolated by anion-exchange chromatography (DEAE-Sephadex A-25). Urinary steroids and steroid conjugates were isolated by adsorption onto a neutral resin (Amberlite XAD-2). Steroid conjugates were hydrolyzed by enzymes from the digestive juice of the snail, Helix pomatia. Purified urinary organic acid and steroid extracts were methoximated and trimethylsilylated for gas-chromatographic analysis. Urinary acid profiles contained 50 recognizable peaks, 10 of which were unequivocally identified by mass spectral analysis (lactic acid, glycolic acid, sulfate, phosphate, erythronic acid, threonic acid, hippuric acid, citric acid, glucuronic acid, and uric acid). Urinary steroid profiles contained 16 recognizable, peaks, although only one peak was identified by mass spectral analysis (pregnanediol). The metabolite profiles were assessed for effects of diet, drugs, and intestinal microflora. Twelve acidic metabolites were excreted in greater amounts by pregnant women compared to nonpregnant women. Four acidic metabolites were excreted in greatly increasing amounts as pregnancy progressed: lactic acid, glycolic acid, the 4-deoxytetronic acids (only tentatively identified), and erythronic acid. Whereas lactic acid excretion was highly variable, the excretion of glycolic acid, the 4-deoxytetronic acids, and erythronic acid increased simultaneously. The possible significance of these alterations in the urinary acid profile in pregnancy was discussed. Organic acid excretion in several cases of high-risk pregnancy showed slight deviations from the normal profile. Urinary steroid excretion increased conspicuously as pregnancy progressed. The steroid metabolites could not be accurately quantified due to a lack of resolution with the present gas-chromatographic system. The present method would prove useful when large deviations in steroid excretion were to be confirmed. Urinary organic acid-steroid profiling may not find application in health assessment of the general population, but the technique holds exciting possibilities for the assessment of certain high-risk pregnancies. The present work provides reference profiles which form a basis for future comparisons.