An enzyme immunoassay of estrone in swine serum

An enzyme immunoassay for estrone in swine serum was established. For this, beta-galactosidase from E. coli was conjugated through estrone-17 (O-carboxymethyl)oxime using a mixed anhydride reaction. The percentage of immunoreactive estrone-17 (O-carboxymethyl)oxime-beta-galactosidase conjugate was estimated to be about 70%. The recovery rate of estrone (25-500 pg) added to 0.05 ml of swine serum averaged 91.4%. The sensitivity of the present enzyme immunoassay was 5 pg/tube. The coefficients of variation (CV) were 5.9-8.2% (within assays) and 4.1-5.9% (between assays), respectively. Estrone values determined by the present enzyme immunoassay were highly correlated with those determined by radioimmunoassay (r = 0.99, P less than 0.005). This method of enzyme immunoassay was determined to be suitable for the routine assay of serum estrone.     

Preparation of specific antiserum to estriol 3-sulfate 16-glucuronide

The preparation and antigenic properties of estriol 3-sulfate 16-glucuronide-bovine serum albumin (BSA) conjugate in which the hapten is linked to the carrier through an (O-carboxymethyl)oxime bridge at the C-6 position on the steroid nucleus, have been described. Coupling of 6-oxoestriol 3-sulfate 16-glucuronide acetate-methyl ester 6-(O-carboxymethyl)oxime with BSA by the activated ester method followed by removal of the protecting groups with alkali provided the desired conjugate. The antisera raised against the conjugate in rabbits were highly specific to the double conjugate, estriol 3-sulfate 16-glucuronide, discriminating from ring A or D monoconjugated and unconjugated estrogens. The specificity of antisera elicited has been discussed on the basis of stereochemistry of the hapten-[C-6]-BSA conjugate.     

The use of homologous and hetebologous 125 I-radioligands in the radioimmunoassay of progesterone

Eight homologous and heterologous¹²⁵ I-radioligand systems for the radioimmunoassay of progesterone were examined. Using an antiserum raised to 11α-hydroxyprogesterone 11-succinyl-bovine serum albumin, standard curves were set up with the homologous radioligands, 11α-hydroxyprogesterone 11-succinyl-[¹²⁵I]-iodotyramine, -[¹²⁵I]-iodohistamine and -[¹²⁵I]-iodotyrosine methyl ester. Heterologous bridge systems were represented by progesterone-11α-oxycarbonyl-[¹²⁵I]-iodotyrosine methyl ester and 11α-hydroxyprogesterone 11-phthalyl-[¹²⁵I]-iodotyrosine methyl ester, and heterologous site systems by progesterone-3-(O-carboxymethyl)oxime-[¹²⁵I]-iodotyramine, progesterone-12-(O-carboxymethyl) oxime-[¹²⁵ I]-iodotyramine, and progesterone-20-(O-carboxymethyl) oxime-[¹²⁵I]-iodohistamine. The preparation of the steroid derivatives and iodination by a two-phase method are described. The curves obtained from the homologous radioligands were relatively insensitive compared with a tritiated system, with the tyrosine methyl ester derivative providing a more sensitive assay than the corresponding tyramine or histamine analogues. The heterologous bridge systems gave more sensitive curves than the homologous tracers whilst the 3- and 12-(O-carboxymethyl) oxime derivatives of progesterone furnished curves as sensitive as the tritiated reference. Progesterone-20-(O-carboxymethyl)oxime-[¹²⁵I]-iodohistamine was not bound by the antibody.     

Radioimmunoassay of 5 beta-cholestane-3 alpha,7 alpha,12 alpha,25-tetrol 3-glucuronide in serum of patients with cerebrotendinous xanthomatosis.

A rapid, convenient, and specific radioimmunoassay for 5 beta-cholestane-3 alpha,7 alpha,12 alpha,25-tetrol has been developed. Specific antiserum was obtained from rabbits immunized by the bile alcohol-bovine serum albumin conjugate, which was coupled by an (O-carboxymethyl)oxime bridge at the C-3 position. The assay produces values for serum concentrations of bile alcohol glucuronides in patients with cerebrotendinous xanthomatosis.     

Preparation and antigenic property of 3-dehydrolithocholylglycine 3-(O-carboxymethyl) oxime-bovine serum albumin conjugate

The preparation and antigenic property of 3-dehydrolithocholyglycine-bovine serum albumin (BSA) conjugate in which the hapten is linked to the carrier protein through an (O-carboxymethyl) oxime bridge at the C-3 position on the steroid nucleus is described. Antibody raised against antigen in the rabbit possessed high titer and specificity to lithocholylglycine, exhibiting no significant cross-reaction with free lithocholic acid or lithocholyltaurine.     

Preparation and antigenic property of methyl 3 beta-hydroxy-19-oxo-5-cholen-24-oate 19-(O-carboxymethyl) oxime-bovine serum albumin conjugate

The preparation and antigenic property of 3 beta-hydroxy-5-cholen-24-oic acid-bovine serum albumin (BSA) conjugate in which the hapten is linked to the carrier protein through an (O-carboxymethyl) oxime bridge at the C-19 position on the steroid nucleus is described. Antibody raised against antigen in the rabbit possessed high titer and specificity to 3 beta-hydroxy-5-cholen-24-oic acid, exhibiting no significant cross-reactions with various bile acids.     

Development of a direct microplate enzyme immunoassay for the determination of pregnanediol-3 alpha-glucuronide in urine

A sensitive direct enzyme immunoassay for urine pregnanediol-3 alpha-glucuronide was developed. The assay system involves the use of an antiserum against pregnanediol-3 alpha-glucuronide and an enzyme-labelled antigen chemically prepared by linking beta-D-galactosidase to 20 alpha-hydroxy-5 beta-pregnane 3(O-carboxymethyl)oxime. Free from antibody-bound antigen was separated by a solid-phase double antibody method, using a microplate coupled with goat anti-rabbit gamma-globulin. This solid-phase enzyme immunoassay for urine pregnanediol-3 alpha-glucuronide was validated in terms of specificity, accuracy and sensitivity. When urine samples were assayed for pregnanediol-3 alpha-glucuronide, the results obtained by the solid phase enzyme immunoassay and conventional radioimmunoassay methods agreed well (n = 30, r = 0.922). This assay system has an advantage over radioimmunoassay, because it does not require the use of radioisotopes. The procedure of this method is very simple, since it does not require purification steps of the biological samples.     

A convenient homogeneous enzyme immunoassay for estradiol detection

A convenient homogeneous enzyme immunoassay for estradiol is described. Unlike heterogeneous immunoassays, which require time-consuming separation steps or expensive automated systems, homogeneous immunoassays, wherein all reagents are freely suspended in bulk solution, can be simple and fast without costly instrumentation. The key component of this assay system, an estradiol-reporter enzyme conjugate, was prepared by covalently binding β-estradiol-6-(O-carboxymethyl)oxime to glucose-6-phosphate dehydrogenase (G6PDH) by an N-hydroxysuccinimide-enhanced, carbodiimide-mediated coupling reaction. The estradiol-G6PDH activity can be repressed up to 46% upon anti-estradiol antibody binding. The lower detection limit of the assay is 1 nM estradiol in aqueous solution, and the standard curve is linear on logit-log scale-up to 6.7 μM estradiol. A detection limit of 11.5 nM in estradiol-spiked human serum samples suggests the feasibility of applying this assay to monitor estradiol levels for the prediction and prevention of ovarian hyperstimulation syndrome.     

Preparation and antigenic properties of 5alpha-dihydrotestosterone-11-(O-carboxymethyl) oxime-BSA conjugate.

The C-11 (O-carboxymethyl) oxime derivative of 5-alphadihydrotestosterone (5alphaDHT) has been prepared. Due to steric hindrance at C-11, a novel two step procedure was used to introduce the (O-carboxymethyl) oxime at this position. Condensation of this oxime to bovine serum albumin afforded a conjugate which produced anti-5alphaDHT sera inoculated rabbits. Apart from a 30% cross reaction with testosterone, the antisera was reasonably specific for 5alphaDHT.     

Studies related to progesterone-induced hamster sperm acrosome reaction

Experiments were designed to characterize the effect of progesterone on the hamster sperm acrosome reaction (AR). Progesterone stimulated exocytosis of previously capacitated spermatozoa in a dose-dependent manner Progesterone-3-(O-carboxymethyl)oxime:BSA conjugate also induced AR when added to capacitated sperm suspensions. EGTA and La³⁺, added 10 min before progesterone, completely abolished the steroid-stimulatory effect. Benzamidine, a trypsin inhibitor, also inhibited AR when added to sperm cells 10 min before progesterone. This effect was avoided when spermatozoa were treated with the Ca2+ ionophore ionomycin. Conversely, the H+ ionophore PCCP, or the Na⁺/K⁺ ionophore nigericin, did not prevent the effect of the inhibitor. Results suggest that progesterone acts on the hamster sperm plasma membrane to stimulate exocytosis, which requires external Ca2+ and presumably Ca2+ influx. In addition, a sperm trypsin like protease may be part of the mechanism by which progesterone stimulates AR. Since the ionomycin-induced AR does not require this proteolytic activity, the possible involvement of such an enzyme in the progesterone-stimulated Ca2+ influx necessary for the occurrence of AR is discussed. © 1996 Wiley-Liss, Inc.     

An enzyme immunoassay for plasma betamethasone

A sensitive enzyme immunoassay for plasma betamethasone was developed using betamethasone-3-(O-carboxymethyl)oxime-β-D-galactosidase conjugate as a labelled antigen and 4-methylumbelliferyl-β-D-galactoside as a fluorescence substrate. The performances of the enzyme immunoassay were compared with that of a radioimmunoassay using ³H-betamethasone and the same antiserum. The minimal detectable level for the enzyme immunoassay was 0.15 pg/tube or 0.15 ng/ml of plasma, which was remarkably more sensitive than the radioimmunoassay level of 10 pg/tube or 2 ng/ml of plasma. The specificity was sufficient, in particular, the cross reactivity of cortisol was 0.008%. However, the precision of the enzyme immunoassay was inferior to that of the radioimmunoassay.     

Antibody binding characteristics of geometrical isomers of testosterone 3-(O-carboxymethyl)oxime.

Geometrical isomers of testosterone 3-(O-carboxymethyl)oxime and their histamine derivatives were purified on reverse-phase high pressure liquid chromatography, and their antibody binding characteristics were studied. Using a competitive testosterone enzyme immunoassay, the unfractionated mixture of the oximes showed 75% cross-reactivity with respect to testosterone, whereas the isolated 3Z- and 3E-isomers showed 124% and 26% cross-reactivity, respectively. The cross-reactivity was increased in the histamine derivatives, but the difference in cross-reactivity of the two isomers was reduced. Suppression of the ionization of the carboxyl group by lowering the pH of the incubation mixture in the antigen-antibody binding step raised the cross-reactivity of the mixture of free oximes to 128%, at pH 4.0. Thus, the geometry and ionization state of the carboxymethyl oxime group has a profound effect on the affinity of the isomers for the antibody.     

Homogeneous electrogenerated chemiluminescence immunoassay for the determination of digoxin employing Ru(bpy)(2)(dcbpy)NHS and carrier protein.

A highly sensitive homogeneous electrogenerated chemiluminescence (ECL) immunoassay for the determination of anti-digoxin antibody and digoxin hapten was developed employing Ru(bpy)(2)(dcbpy)NHS (bpy = 2,2'-bipyridyl; dcbpy = 2,2'-bipyridine-4,4'-dicarboxylic acid; NHS = N-hydroxysuccinimide ester) as an electrochemiluminescent label and bovine serum albumin (BSA) as a carrier protein. A digoxin hapten was indirectly heavily labelled with Ru(bpy)(2)(dcbpy)NHS through BSA to form Ru(bpy)(2)(dcbpy)NHS-BSA-digoxin conjugate. The ECL intensity of the immunocomplex of the conjugate with anti-digoxin antibody markedly decreased when the immunoreaction between Ru(bpy)(2)(dcbpy)NHS-BSA-digoxin conjugate and anti-digoxin antibody took place. Two formats, direct homogeneous immunoassay for anti-digoxin antibody and competitive immunoassay for digoxin, were developed to determine anti-digoxin antibody and digoxin, respectively. The anti-digoxin antibody concentration in the range 7.6 x 10(-8)-7.6 x 10(-6) g/mL was determined by direct homogeneous format. Digoxin hapten was determined throughout the range 4.0 x 10(-10)-1.0 x 10(-7) g/mL with a detection limit of 1.0 x 10(-10) g/mL by competitive format. The relative standard derivation for 6.0 x 10(-9) g/mL was 4.3%. The method has been applied to assaying digoxin in control human serum.     

Enzyme immunoassay for serum 18-hydroxycorticosterone and its clinical application

An enzyme immunoassay for serum 18-hydroxycorticosterone was established using alkaline phosphatase as a label. The antiserum for 18-hydroxycorticosterone was produced by immunization of rabbits with 18-hydroxycorticosterone 3-(O-carboxymethyl)oxime conjugated to bovine serum albumin. Sephadex LH-20 column chromatography was used to separate 18-hydroxycorticosterone from other steroids in serum samples. The minimal detectable amount of 18-hydroxycorticosterone was 50 pg/tube and the measurable range was from 5 to 1000 ng/dl when a 1.0 ml serum sample was used. Intra- and inter-assay coefficients of variance were 5.0% (n=6) and 5.8% (n=6), respectively. Four of 5 patients with aldosterone-producing adenoma had above-normal serum 18-hydroxycorticosterone levels.     

Enzyme immunoassay of testosterone in plasma, with use of polyethylene glycol to separate antibody-bound and free hormone.

We describe an enzyme immunoassay for testosterone in which we use a testosterone-3-(carboxymethyl)oxime horseradish peroxidase conjugate as the label and an antiserum, raised in rabbits, to testosterone-3-(carboxymethyl)oxime-bovine serum albumin conjugate. Polyethylene glycol (Carbowax 6000) is used to separate antibody-bound and free steroid. The assay has a sensitivity of 12 pg/assay tube and satisfies the usual criteria of specificity, precision and accuracy. The results agree well with those obtained with a comparable radioimmunoassay.     

Cell surface-binding sites for progesterone mediate calcium uptake in human sperm.

Recent studies (e.g. Blackmore, P. F., Beebe, S. J., Danforth, D. R., and Alexander, N.) (1990) J. Biol. Chem. 265, 1376-1380) have shown that in human sperm, progesterone produces a rapid increase in intracellular free calcium ([Ca2+]i) and an induction of the acrosome reaction (e.g. Osman, R. A., Andria, M. L., Jones, A. D., and Meizel, S. (1989) Biochem, Biophys. Res. Commun. 160, 828-833). In this study, the location of progesterone receptors on the cell surface of human sperm was identified using progesterone immobilized on bovine serum albumin (BSA) (progesterone 3-(O-carboxymethyl)oxime:BSA) as well as progesterone and its 3-O-carboxymethyloxime derivative. Using fluorescence microscopy, BSA-fluorescein isothiocyanate was shown to be excluded from intact sperm, thus validating the use of progesterone 3-(O-carboxymethyl)oxime:BSA to identify cell surface-binding sites for progesterone. The immobilized progesterone and the 3-O-carboxymethyloxime derivative rapidly increased [Ca2+]i and were full agonists, although they were approximately 1.5 orders of magnitude less potent than progesterone. They also displayed an identical time course to increase [Ca2+]i as free progesterone, and the entire increase in [Ca2+]i was due to the influx of Ca2+. This progesterone-mediated response displayed different steroid receptor characteristics since the very potent inhibitors of genomic progesterone responses, RU38486 and ZK98.299, were very ineffective at inhibiting the progesterone-mediated increase in [Ca2+]i. Also the synthetic progestins megestrol, medroxyprogesterone acetate, norgestrel, norethynodrel, norethindrone, R5020, and cyproterone acetate did not mimic the effects of progesterone to increase [Ca2+]i. It is proposed that a distinct nongenomic cell surface receptor for progesterone exists in human sperm.     

A simple procedure for enzyme labelling of progesterone derivatives: application of active esters formed using N,N'-disuccinimidyl carbonate

N,N'-Disuccinimidyl carbonate was used to synthesize N-hydroxysuccinimide esters of 11 alpha-hydroxyprogesterone 11-[1,4-14C]hemisuccinate (P11-HS) and 11 alpha-hydroxyprogesterone 11-glucuronide (P11-Glu) in a one-step procedure at room temperature. Enzyme-labelled progesterone was subsequently formed by reaction of the ester, without purification, with alkaline phosphatase. Labels produced by this simple procedure compared favourably with those formed using an established method of ester synthesis when assessed in enzyme immunoassay (EIA).     

The biosynthesis of cyanogenic glucosides in higher plants. The (E)- and (Z)-isomers of p-hydroxyphenylacetaldehyde oxime as intermediates in the biosynthesis of dhurrin in Sorghum bicolor (L.) Moench

The biosynthesis of the tyrosine-derived cyanogenic glucoside dhurrin has been studied with a microsomal preparation obtained from etiolated seedlings of sorghum. The biosynthetic pathway involves tyrosine, N-hydroxytyrosine, and p-hydroxyphenylacetaldehyde oxime as early intermediates (M?ller, B. L. and Conn, E. E. (1980) J. Biol. Chem. 254, 8575-8583). The use of deuterium-labeled tyrosine and mass spectrometric analyses demonstrate that the alpha-hydrogen atom of tyrosine is retained in the conversion of tyrosine to p-hydroxyphenylacetaldehyde oxime. This excludes p-hydroxyphenylpyruvic acid oxime as intermediate in the pathway. A high pressure liquid chromatography method was developed to separate the (E)- and (Z)-isomers of p-hydroxyphenylacetaldehyde oxime. The microsomal enzyme system was found to produce initially the (E)-isomer of p-hydroxyphenylacetaldehyde oxime. An isomerase then converts the (E)-isomer to the (Z)-isomer, which is the isomer preferentially utilized by the microsomal enzyme system in the subsequent biosynthetic reactions. The (E)-isomer produced in situ is more efficiently converted to the (Z)-isomer than exogenously added (E)-isomer and may thus be metabolically channeled.     

A direct antigen heterologous enzyme immunoassay for measuring progesterone in serum without using displacer

An antigen heterologous enzyme-linked immunosorbent assay (ELISA) for directly measuring progesterone in serum is described. Six combinations of antigens and enzyme conjugates were tested; the enzyme conjugate 17-alphaOH-progesterone-3-O-carboxymethyloxime-alkalinephosphatase (17-alphaOH-P-3-CMO-ALP) and the immunogen progesterone-3-carboxymethyloxime-bovine serum albumin (P-3-CMO-BSA) were found to be best. Fifty microliters of standard or serum sample and 100 microL of the 17-alphaOH-P-3-CMO-ALP enzyme conjugate were added to the antibody coated wells, and incubated for 1 h at 37 degrees C. Bound enzyme activity was measured by using p-nitrophenyl phosphate as substrate. The sensitivity of the assay was 0.11 ng/mL, and intra- and inter-assay CVs ranged from 5.1% to 9.6%. The analytical recoveries were 97-105%. The serum progesterone values obtained by this method correlated well with those obtained by radioimmunoassay; r=0.97 (n=44). Moreover, in this ELISA no displacing agent was used or special means was required to displace progesterone from corticosteroid binding globulin (CBG). Serum progesterone concentrations of subjects, with histories of recurrent spontaneous abortions were also measured, and correlated well with clinical history.     

Preparation of specific antisera to estrone-3-glucuronide and estriol-3-glucuronide

The preparation and antigenic properties of estrone-3-glucuronide- and estriol-3-glucuronide-bovine serum albumin conjugates in which the hapten is linked to the carrier protein through an (O-carboxymethyl)oxime bridge at the C-6 position on the steroid nucleus, have been described. Antibodies raised against the two immunogens in the rabbit possessed high specificity to estrone-3-glucuronide and estriol-3-glucuronide, respectively, exhibiting little cross-reactivities with other estrogen conjugates and no cross-reactions with related steroids except for free estrogens, their 3-methyl ethers and 3-sulfates. The cross-reactive antibodies were eliminated by partial immunoadsorption on affinity chromatographic media using the estrone-3-methyl ether 17-(O-carboxymethyl)oxime- and estriol-3-methyl ether 16 (or 17)-hemisuccinate-aminohexyl Sepharose conjugates, respectively. The purified antisera exhibited no cross-reactivities with free estrogens and ring A conjugates of estrone and estriol.