Microproteins in amniotic fluid as an index of changes in fetal renal function during development

Abstract

Protein content and protein composition were studied in amniotic fluid obtained from 171 healthy pregnant women between the 16th and 38th week of gestation, using microgradient gel electrophoresis to separate proteins according to their molecular size into albumin (68 KD), proteins of low molecular weight (LMW proteins, less than 68 KD), and proteins of high molecular weight (HMW proteins, greater than 68 KD). Additionally alpha-1-microglobulin (alpha-1-MG, 33 KD) and beta-2-microglobulin (beta-2-MG, 11,8 KD) were analysed as micromolecular marker proteins. Concentrations of LMW proteins were 0.15-0.22 g/l, of alpha-1-MG 28.4-34.5 mg/l, and of beta-2-MG 7.2-11.6 mg/l during the second trimester of gestation, and thereafter decreased progressively to 0.03 g/l, 14.1 mg/l and 2.4 mg/l respectively near term. The same developmental trends were confirmed by calculating the protein/creatinine ratios in amniotic fluid. The concentrations of LMW proteins found in the first postnatal urine of 73 healthy infants born prematurely or at term were similar to those in amniotic fluid of corresponding fetal age. Concentrations of albumin and HMW proteins in postnatal urine were about 5% and 15% respectively when compared with amniotic fluid concentrations. No strong correlation existed between gestational age and either of the analysed proteins which would allow accurate assessment of fetal maturation by protein analysis in amniotic fluid. It is concluded that fetal urinary excretion is the major determinant of the microprotein content of amniotic fluid. Microproteins seem to reflect an increasing tubular reabsorption capacity, which accelerates rapidly after the second trimester of gestation.

Structural characterization of the oligosaccharide chains of human α1‐microglobulin from urine and amniotic fluid

“…Urine of patients with renal failure represents a typical source for the isolation of adult a 1 -m, which is present in plasma in quite low concentration, representing only 0.03±0.04% of the total protein content. On the other hand, the protein is relatively more abundant in the amniotic fluid, in which the fetal urinary excretion is the major determinant of a 1 -m content, especially during the second trimester of gestation [26,27]. In this period its level is 28.4±34.5 mg´L…”

“…, which represents about 0.8% of the total protein amount, and thereafter decreases progressively to 14.1 mg´L 21 near term [26], as a consequence of an increasing tubular reabsorption capacity.…”

Maternal Tobacco Smoking and Lung Epithelium-Specific Proteins in Amniotic Fluid

“…The strongest correlations were found with LMWP, which are assumed to derive largely from fetal urinary excretion and to reflect the function and maturation of the fetal kidney tubules (27)(28)(29)(30). By contrast, CC16 in AF was much less correlated with HMWP, which are largely retained by the fetal glomerular filter (26).…”

“…Levels of CC16 and SP-A in AF were also compared with those of albumin and transferrin, two HMWP originating from the fetal liver. By contrast with CC16 and SP-A, which are secreted at the surface of the epithelium lining the airways and the alveoli, these nonpulmonary LMWP and HMWP are components of the fetal urine, and their levels in AF reflect the maturity of the fetal kidney (27)(28)(29)(30). Because glucocorticoids play an important role in the pulmonary development and are considered to mediate the well-known acceleration of the fetal lung maturation in smoke-exposed mothers, the level of free cortisol was determined in AF and its relationship with the other parameters in AF studied (31).…”

SDS-PAGE as an Additional Test to Determine Fetal Kidney Function prior to Intrauterine Diversion of Urinary Tract Obstruction

“…Furthermore only a little pro tein is required and proteins with a molecu lar weight of less than 60,000 daltons such as ci|-antitrypsin, retinol-binding protein, d|-and fo-microglobulin, which are critical for the evaluation of tubular reabsorption ca pacity, can easily be detected. a r and P2-microglobulins as an index of changes in fetal renal function can also be assessed in amniotic fluid [11], but needling of the di lated bladder in cases of fetal obstructive uropathies still offers the additional advan tage of also being able to evaluate the electro lyte and neutral amino acid concentration as well as the osmolarity of the urine. If the pre dictive value of SDS-PAGE, as an additional part of the biochemical test profile to deter mine residual renal function in utero as sug gested by this case report, can be substan tiated by careful long-term follow-up of other cases we would recommend perform ing this test in addition to the previously described useful parameters before attempt ing permanent vesicoamniotic drainage for diversion of fetal urinary tract obstruction.…”