Metabolism of pregnenolone and pregnenolone sulphate in human foetal liver tissue in vitro

Steroidogenic enzyme expression in the human fetal liver and potential role in the endocrinology of pregnancy

The human feto-maternal unit produces large amounts of steroid hormones, particularly estrogens, during the second and third trimesters. The fetal adrenal gland and the placenta are considered the principal tissues driving steroid production but the fetal liver is likely to play an essential role in this process. This study was designed to measure transcript expression of proteins involved in steroid synthesis, metabolism, conjugation and signalling in the human fetal liver and to examine sex differences and effects of maternal smoking. Liver samples were taken from 55 normal fetuses from women undergoing second trimester elective termination. Levels of 23 mRNA transcripts encoding steroid synthesis/metabolic/conjugation enzymes and steroid receptors were measured by real-time PCR. The expression of representative proteins was confirmed by western blotting and immunohistochemistry. The human fetal livers expressed high levels of CYP19A1, SULT2A1, SULT1E1, HSD17B2, SRD5A3 and CYP3A7. Lower levels of SULT1A1, STS, UGT2B17, GPER, AKR1C3, UGT2B15, AR, CYP11A1, CYP21A2, HSD17B3, HSD17B1 and SRD5A1 were also detectable. The expression of ESR, ESR2, CYP17A1 and HSD3B transcripts was undetectable in most fetal livers, although HSD3B was shown to be present by western blotting. Sex differences were limited to SRD5A3 (lower in females) and UGT2B17 (higher in females). Maternal smoking increased the expression of CYP19A1, SULT2A1, UGT2B17, HSD17B2 and AKR1C3 and reduced the expression of SRD5A3 in the male fetal liver. This study shows that the human fetal liver is likely to have an extensive effect on circulating steroid levels in the human fetus and mother. The most important of these effects will be alterations to the species, conjugation and availability of estrogens in the fetus. Maternal smoking is likely to reduce circulating androgen bioactivity in male fetuses.

Development of an enzyme immunoassay for serum 16-dehydropregnenolone

We have developed an enzyme immunoassay (EIA) for serum 16-dehydropregnenolone (3beta-hydroxy-5,16-pregnadien-20-one; 16-DHP). The antiserum against 16-DHP-3-hemisuccinate conjugated bovine serum albumin (16-DHP-3HS-BSA) was raised in rabbits. For use as an enzyme labeled antigen, 16-DHP-3HS was conjugated to alkaline phosphatase. The minimal amount of 16-DHP detected was 4 pg (0.013 pmol)/assay and the measurable range was from 0.06-60 ng/ml (0.191-191 nmol/l). The intra-assay coefficient of variation (C.V.) was 4.1% (0.73+/-0.03 ng/ml, mean+/-S.D., n=6), and inter-assay C.V. was 7.7% (0.13+/-0.01 ng/ml, n=6). A liner relation was observed between the serum sample dilution and the 16-DHP concentration. For the recovery study, authentic 16-DHP was added to a serum sample (original concentration: 0.10-0.14 ng/ml), and the recovery was found to be 94.4-96.8% (final 16-DHP concentrations calculated: 0.29-16.3 ng/ml). To investigate the reliability of the present EIA, the values from our EIA were compared with those obtained by GC-MS. The 16-DHP concentration could not be measured in serum by GC-MS because of its sensitivity. Therefore, the conjugated steroid, 16-DHPS, was first enzymatically hydrolysed and then the 16-DHP measured by both methods. There was a good correlation between the levels determined by these methods (Pearson's correlation coefficient: r=0.927, p<0.001, y=0.74x+3.61, n=27). The serum concentrations of 16-DHP in neonates and umbilical vein were 0.53+/-0.09 ng/ml and 0.88+/-0.61 ng/ml, respectively. No 16-DHP was detected in serum from normal healthy adults using the present EIA. These results suggest that 16-DHP originates from the fetus and neonate.

Distributional variation of P-450 immunoreactive hepatocytes in human liver disorders

Implications of P-450 in human hepatic disorders were immunohistochemically examined. We first confirmed that an antibody against P-450-HM1, an isozyme of cytochrome P-450 which was purified from human livers at autopsy, detects only P-450 on immunoblots. In a study of 79 consecutive autopsied livers using the avidin-biotin-peroxidase complex method, the antibody reacted strongly with fetal hepatocytes, the reaction being more intense in the left lobe than in the right lobe. In normal livers, immunoreactivity was confined to centrilobular hepatocytes, decreasing in the periportal zone. Enhanced expression was occasionally found in scattered hepatocytes and in hepatocytes surrounding sublobular veins; this enhancement was related to longterm steroid therapy. No specific induction was observed in patients with toxic hepatitis. In patients with fibrosis, cirrhosis, or regenerative nodules, however, P-450-positive hepatocytes were observed in the periportal and middle zones as well as in the central zone. In contrast, hepatocellular carcinomas were devoid of P-450 immunoreactivity. These results suggest that P-450-HM1, which is abundant in the fetal liver, is reexpressed in regenerating hepatocytes but not in cancers.