Aminoacid composition of amniotic fluid in central-nervous-system malformations

Mid-second trimester organic acids in severe open neural tube defects

OBJECTIVE

To investigate amnioic fluid organic concentrations at 16 weeks gestation from normal fetuses and those affected by severe neural tube defects.

METHODS

Amniotic fluid collected from normal, anencephalic and severe open spina bifida fetuses was analysed for up to 24 organic acids by gas liquid chromatography.

RESULTS

Significant increase in organic acids similar to those observed in defects of phenylalanine and tyrosine metabolism were identified when compared with the normal fetuses. Significant differences in organic acid concentrations were also identified within the two neural tube defect groups.

CONCLUSION

A relationship between phenylalanine and tyrosine metabolism, closure rate of the neural tube and folate metabolism is proposed.

Quantification of human amniotic fluid constituents by high resolution proton nuclear magnetic resonance (NMR) spectroscopy

We have investigated the ability of high-resolution proton NMR spectroscopy to provide a biochemical constituent screening of human amniotic fluid (AF). Proton NMR spectra were obtained at 300 MHz on AF from patients undergoing amniocentesis in the mid-trimester. Only AF from normal pregnancies (normal fetal karyotype, normal alpha-fetoprotein levels, normal birth outcome) was used in this study. The AF supernatant was lyophilized and resuspended in deuterated water containing 0.1 mM phosphate buffer and 6.02 mM disodium maleate. Identification of low molecular weight compounds was confirmed by two-dimensional NMR spectra (primarily correlated spectroscopy, or COSY) and standard addition techniques. A broad profile of compounds were 'NMR visible' in a single proton spectrum, including creatinine, glucose, organic acids (acetate, citrate, and lactate) and several amino acids (alanine, histidine, leucine, phenylalanine, tyrosine and valine). The proton spectrum was unaffected by prior freezing/thawing of AF samples. We were able to quantify compounds by comparison with an added concentration standard (maleate) at concentrations as low as 30 microM. Good agreement with literature values based on other analytical techniques was obtained.

Comparison of amino acid concentrations in amniotic fluid from fetal neural tube defective and normal pregnancies

Amniotic fluid collected during the second trimester of pregnancy was analysed for amino acid and protein concentrations. The composition of amniotic fluid from pregnancies complicated by fetal anencephaly or spina bifida was investigated for variance from normal amniotic fluid. In spina bifida the hydroxy amino acids were raised whilst the branched chain amino acids were lower in concentration. In anencephaly the total amino acid and the protein concentrations were raised, and a wider range of concentrations for most of the amino acids was apparent.

Amino acid composition of amniotic fluid in intrahepatic cholestasis of pregnancy, pre-eclampsia and rhesus incompatibility

The levels of free amino acids in amniotic fluid were determined in twenty patients with normal pregnancy, five with intrahepatic cholestasis of pregnancy, twelve with pre-eclampsia, and four with rhesus incompatibility. In pre-eclampsia there was no significant change in the amino acid composition of the amniotic fluid. In recurrent intrahepatic cholestasis the concentration of 15 out of the 22 amino acids studied was significantly higher than normal and the mean concentration of 4 others was more than 20 per cent above normal without this being statistically significant. In rhesus incompatibility there was a significant decrease in the concentration of 13 amino acids, and a decrease of more than 20 per cent in the mean concentration of 5 others.