Enzyme immunoassay for serum dexamethasone using 4-(carboxymethylthio)dexamethasone as a new hapten

Development of an Enzyme-Linked Immunosorbent Assay for Serum 11-Dehydrocorticosterone in Rat and Mouse

We have developed an enzyme-linked immunosorbent assay (ELISA) for serum 11-dehydrocorticosterone (4-pregnen-21-ol-3,11,20-trione). The antiserum against 11-dehydrocorticosterone 21-hemisuccinate-conjugated bovine serum albumin was raised in rabbits. As an enzyme-labeled antigen, 11-dehydrocorticosterone 21-hemisuccinate was conjugated to horseradish peroxidase. Two ELISA systems were established: one without the extraction of steroids from serum (direct method), and another that used an HPLC purification step (HPLC method). The cross-reactivity of all steroids tested against the antibody was low except cortisone (92%); however, since cortisone levels in rats and mice are negligible, cortisone does not interfere with this direct ELISA. The measurable range of serum 11-dehydrocortiocosterone in both the direct and HPLC methods was 0.3-250 ng/ml and 0.78-400 ng/ml, respectively. Both methods displayed satisfactory parallel dilution, recovery and reproducibility; moreover, the values obtained with each method significantly correlated with the alternate method. To evaluate the two ELISA systems, the serum concentrations of 11-dehydrocorticosterone in normal rats and mice were determined by these two systems. The levels in Wistar rats fluctuated from 3 to 14 weeks of age (7.8+/-2.6 ng/ml) but at 1 week (1.7+/-1.2 ng/ml) were significantly low compared to other ages. No sex differences were found in rats and mice. Further, using the proposed direct method, chronological changes of rat serum 11-dehydrocorticosterone levels after 11-dehydrocorticosterone administration have been investigated together with corticosterone levels. These results verify that the proposed ELISA for 11-dehydrocorticosterone is useful for measuring 11beta-HSD activities in combination with the determination of serum corticosterone in rats and mice.

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.