A simple enzyme-linked immunosorbent assay for testosterone

A new, enzyme-linked, immunosorbent assay for testosterone is described. The assay uses horseradish peroxidase coupled to testosterone as the tracer and offers the same sensitivity and reliability but greater convenience than radioimmunoassay. The assay is also simpler and more rapidly completed than previously described assays for testosterone.     

The conjugation of testosterone with horseradish peroxidase and a sensitive enzyme assay for the conjugate.

The formation of a horseradish peroxidase-testosterone conjugate for the enzyme-linked immunoassay of testosterone was investigated, using tritiated testosterone to follow the reaction. The formation of testosterone-3-(carboxymethyl) oxime-peroxidase by the mixed anhydride method was found to give a conjugate of high enzymatic activity and with three molecules of testosterone per molecule of peroxidase. The optimum conditions for the assay of peroxidase activity were studied and an assay capable of measuring 1 to 5 ng of the conjugate developed; the standard curve being virtually linear. The stability of the conjugate in solution and the effect of lyophilisation on enzymatic activity are also described. The peroxidase-testosterone conjugate was suitable for enzyme-linked immunoassay and the quantities measurable with the peroxidase assay covered the range necessary for a plasma testosterone assay. The stability of the conjugate was such that no particular precautions were necessary for its storage.     

A sensitive enzyme-linked immunosorbent assay (ELISA) for testosterone: use of a novel heterologous hapten conjugated to penicillinase.

A microplate enzyme-linked immunosorbent assay (ELISA) has been developed for the measurement of testosterone in plasma. The assay uses a heterologous system consisting of a novel hapten 4-(17 beta-hydroxy-3-oxoestra-4,9-dien-11 beta-yl)butanoic acid (1) conjugated to penicillinase (beta-lactamase). The key reaction in the synthesis of the hapten was the cuprate-mediated 1,4-conjugate addition on 3,3,17,17-bis-ethylenedioxy-5 alpha,10 alpha-oxido-estr-9(11)-ene by the Grignard reagent derived from trimethyl 4-bromoorthobutyrate; this regiospecifically introduces the 11 beta-butanoate function. The hapten-penicillinase conjugate was used in the assay in conjunction with the immunoglobulin G (IgG) fraction derived from a previously characterized, highly specific, antitestosterone serum raised against a testosterone-19-O-carboxymethyl ether-bovine serum albumin (T-19-O-CME-BSA) conjugate. This unique system represents one incorporating three elements of structural heterology: bridge, site, and ring heterology between the antigen hapten and enzyme-linked hapten. The limit of detection was 10 pg of testosterone with a sensitivity range between 15 and 1,000 pg. A low level of cross-reactivity with 5 alpha-dihydrotestosterone (6.17%) and 11 beta-hydroxytestosterone (1.03%) was noted. No interference was noted with other common androgens, estradiol, or progesterone. The sensitivity and selectivity observed in the assay may be attributable to the selection of penicillinase as the enzyme marker and the elements of conformational heterology between the antigen-linked and enzyme-conjugated steroid haptens.     

Detection and changes in levels of testosterone during spermatogenesis in the freshwater planarian Bdellocephala brunnea

It was reported recently that vertebrate-type steroids exist and control reproduction in several groups of invertebrates, including molluscs. Sexually reproductive freshwater planarians of the species Bdellocephala brunnea have a limited breeding season in their natural habitat. This phenomenon suggests that some endogenous reproductive hormones might play a role in vivo. However, to date, sex steroids such as androgen, estrogen, and progesterone have not been found in planarians. The goal of the present study was to determine whether androgen is present in sexual planarians such as B. brunnea. The presence of testosterone was detected by high-pressure liquid chromatography and, in sexually reproductive individuals in which no seminal vesicles were visible, the level of testosterone was about twice than that in individuals with visible seminal vesicles. An enzyme-linked immunosorbent assay revealed that the levels of testosterone during terminal spermatogenesis were three times higher than during the spermatocyte-building phase. Our results indicate that sexually reproductive freshwater planarians such as B. brunnea might have vertebrate-type steroids and show variation in testosterone levels during spermatogenesis.     

Gender differences in the validity of testosterone measured in saliva by immunoassay

We rigorously evaluated gender differences in the measurement validity of salivary testosterone. Matched serum, saliva, and finger stick blood spot specimens were collected from 40 (20 males) young adults (aged 18-27 years). Saliva was assayed for testosterone by two independent (isotopic and non-isotopic) immunoassay methods. Serum was assayed by commercially available immunoassay kits for free and total testosterone. An immunoassay was developed for the measurement of testosterone in dried blood spots and is presented in detail so as to be reproducible from this report. Regardless of assay method, salivary testosterone levels are modestly correlated with serum levels for males but not necessarily for females. Blood spot assay results were highly correlated with serum total and free testosterone for both males and females. Substitution of saliva assay results for serum values substantially underestimates known testosterone-behavior associations, and this effect is much more pronounced for females than for males. The findings have important implications for the use and potential misuse of noninvasive measures of testosterone, and with respect to statistical power, the probability of observing significant testosterone-behavior relationships.     

A highly specific heterologous enzyme-linked immunosorbent assay for measuring testosterone in plasma using antibody-coated immunoassay plates or polypropylene tubes.

A highly specific and sensitive enzyme-linked immunosorbent assay, using a heterologous combination of antiserum raised against testosterone-3-(O-carboxymethyl) oxime-bovine serum albumin and penicillinase-labeled testosterone-11 beta-carboxymethyl ether, was developed for measuring testosterone in human plasma. Immunoassay plates (96 wells) provided a sensitivity of 2.5 pg/well. This was achieved by maintaining the molar ratios of steroid to enzyme between 10 and 20. The assay was very specific for testosterone and did not show any cross-reaction with the related C19 steroids tested. Replacement of immunoassay plates with the locally available polypropylene tubes raised the detection limits to 25 pg/tube, but improved the range of doses of testosterone that could be measured up to 10,000 pg. The antiserum to testosterone derivative was linked to both immunoassay plates and polypropylene tubes through immunochemical bridges. Comparison of testosterone values of 52 plasma specimens obtained by both solid phase methods with those of radioimmunoassay showed good correlation.     

Improved sample preparation for the testosterone hydroxylation assay using disposable extraction columns

The preparation of samples for injection into a high-performance liquid chromatography from assay mixtures for the determination of cytochrome P-450-dependent testosterone hydroxylation has been substantially facilitated. By replacing the multiple cumbersome extraction steps of the conventional method with a single column extraction the time for sample preparation was reduced from hours to minutes. The new procedure also yields better recoveries for most of the testosterone metabolites than the original protocol. The use of extraction columns for sample preparation allows the simultaneous treatment of a large number of samples or even the automation of the whole assay procedure. The modified procedure is a straightforward, easy-to-perform method that should greatly facilitate the implementation of the testosterone hydroxylation assay for sharply discriminating between many individual cytochrome P-450 species in routine enzyme diagnostics.     

Effects of testosterone on cell-mediated and humoral immunity in non-breeding adult European starlings

One of the primary assumptions of the immunocompetence hypothesisis that testosterone is immunosuppressive. Although many studiesin birds and mammals have supported this assumption, conflictingresults have been reported in a variety of species. We investigatedthe effects of testosterone manipulation on both cell-mediatedand humoral immunity in adult songbirds, European starlings(Sturnus vulgaris). Male and female starlings were wild-caught,housed in the laboratory, and implanted with either empty silasticcapsules or capsules containing testosterone. Six weeks after implantation, humoral immunity was assessed by injecting thebirds with a novel antigen, keyhole limpet hemocyanin, andmeasuring specific antibody responses 10 and 15 days latervia an enzyme-linked immunosorbant assay. Cell-mediated immunitywas assessed 7 weeks after implantation via intradermal injectionof the T-cell mitogen phytohemagglutinin into the wing web and measuring the degree of swelling 24 h later. Antibody responsesto antigenic challenge were significantly suppressed in testosterone-treatedfemales 10 days post-injection and in both sexes 15 days post-injection.Furthermore, there was a significant inverse relationship betweenindividual variability in antibody responsiveness and plasmatestosterone concentrations. Cell-mediated responses to phytohemagglutininstimulation were also significantly suppressed in testosterone-treatedmales compared to same-sex controls. Testosterone treatmentsignificantly increased plasma corticosterone concentrations compared to controls, and the possibility of this effect mediatingthe immunosuppressive effects of testosterone is discussed.The present study is among the first to demonstrate testosterone-inducedsuppression of both cell-mediated and humoral immunity in aspecies of songbird.     

A general procedure for screening inhibitory antibodies: application for identifying anti-protein kinase C antibodies

In this communication we describe a microfiltration assay to identify monoclonal antibodies that interfere with the activity of enzymes. This method is quick and sensitive to small changes in the activity of the enzyme and does not require highly purified enzyme or large quantities of antibodies. It has been applied to identify anti-protein kinase C antibodies which would have been impossible to identify by classical assays such as enzyme-linked immunosorbent assay.     

A sensitive enzyme-linked immunosorbent assay for dihydrofolate reductase.

A competitive enzyme-linked immunosorbent assay (ELISA) has been developed for the enzyme, dihydrofolate reductase. The sensitivity of the assay system approximates 3 ng of immunoreactive enzyme protein which is comparable to the sensitivity achieved in the radioimmunoassay (RIA) for this enzyme. The mean coefficient of variation for within--and between--assay precision was less than 13%. The assay appears to be specific and valid as the concentration of the enzyme is the same whether measured by ELISA or [3H]-methotrexate binding. Since this method, like the RIA, measures the mass concentration of enzyme protein, in conjunction with a [3H]-methotrexate binding assay it will be useful for quantitating functional as well as non-functional immunoreactive forms of the enzyme.     

Enzyme-Linked Immunosorbent Assay for Quantitative Detection of Bacillus thuringiensis Crystal Protein

Accurate measurement of the toxic protein crystal produced during deep-tank fermentation of Bacillus thuringiensis is critical for optimum process yield. The currently accepted method is a bioassay that requires more time to generate data than to complete the fermentation itself. A noncompetitive enzyme-linked immunosorbent assay has been developed with purified B. thuringiensis crystals to generate rabbit antiserum. This technique gives a quantitative crystal protein value with a colorimetric endpoint for either liquids or powders within 4 h of sampling. Reproducibility of this enzyme-linked immunosorbent assay satisfies criteria for use in a commercial process.     

Determination of serum testosterone using radioimmunoanalysis without previous extraction

A modification to the radiochemical assay method to measure testosterone in serum, that renders unnecessary the extraction of testosterone from a serum sample is described. The serum is heated at 60 degrees C for 1 hour, thereby testosterone binding proteins are destroyed, then radioimmunoassay follows as usual.     

Rapid and sensitive quantitative immunoassay for the large simian virus 40 T antigen

A quantitative, enzyme-linked immunoadsorbent assay has been developed for the simian virus 40 large T antigen. When hamster anti-simian virus 40 tumor serum was used, this method permitted specific identification of large T antigen and its analog, the D2 hybrid protein, a molecule with the same C-terminal approximately 600 amino acids as large T antigen. The sensitivity limit of this test was 0.63 ng of protein. The slopes of the regression lines of the enzyme-linked immunosorbent assay titrations performed with highly purified D2 or simian virus 40 large T antigen and with crude extracts of simian virus 40-infected monkey and transformed human cells were identical. Thus, the curve generated with a purified protein, such as D2, can serve as a quantitative standard for the measurement of large T antigen in a wide variety of extracts. Furthermore, solutions containing high salt concentrations and buffers containing up to 0.1% Nonidet P-40 did not interfere with the assay, making it applicable to the measurement of large T antigen in a variety of chromatographic fractions. The enzyme-linked immunosorbent assay was three times more sensitive, was significantly faster to perform, and was quantitatively valid over a much broader large-T-antigen concentration range than the complement fixation test. As such, it should be useful in future studies of the structure and function of this protein.     

Induction of vitellogenin synthesis in an Atlantic salmon (Salmo salar) hepatocyte culture: a sensitive in vitro bioassay for the oestrogenic and anti-oestrogenic activity of chemicals.

A variety of organic compounds have been documented to bind to the oestrogen receptor and induce oestrogenic effects in different vertebrates. The presence of these environmental oestrogens or oestrogen mimics in the aquatic environment has been suspected of disrupting the normal endocrinology of wild populations of fish. In this study, induction of vitellogenin synthesis in primary hepatocytes from Atlantic salmon (Salmo salar) was optimized and validated as an oestrogenic in vitro bioassay using a sensitive capture vitellogenin enzyme-linked immunosorbent assay. After proper optimization (cell media supplements, cell density, temperature and exposure time), this assay gave a sensitive and reproducible response to both endogenous steroids (relative potency: 17beta-oestradiol>oestriol>oestrone>17alpha-oestradiol) and a range of common oestrogen mimics (relative potency: ethynyloestradiol and diethylstilboestrol>genistein and zearalenone>bisphenol A and 4-t-octylphenol>4-n-nonylphenol and 2'-chloro,4-chloro-diphenyltrichloroethane (o,p'-DDT). However, the androgen testosterone and the putative oestrogen mimics dieldrin and toxaphene were not shown to be oestrogenic using this hepatocyte bioassay. Oestrogen-induced vitellogenin synthesis was efficiently inhibited by the anti-oestrogen ZM 189.154, suggesting that this bioassay may be used for testing both the oestrogenic and the anti-oestrogenic properties of chemicals.     

First Assessment of the Sex Ratio for an East Pacific Green Sea Turtle Foraging Aggregation: Validation and Application of a Testosterone ELISA

Determining sex ratios of endangered populations is important for wildlife management, particularly species subject to sex-specific threats or that exhibit temperature-dependent sex determination. Sea turtle sex is determined by incubation temperature and individuals lack external sex-based traits until sexual maturity. Previous research utilized serum/plasma testosterone radioimmunoassays (RIA) to determine sex in immature/juvenile sea turtles. However, there has been a growing application of enzyme-linked immunosorbent assay (ELISA) for wildlife endocrinology studies, but no study on sea turtles has compared the results of ELISA and RIA. This study provides the first sex ratio for a threatened East Pacific green sea turtle (Chelonia mydas) foraging aggregation, a critical step for future management of this species. Here, we validate a testosterone ELISA and compare results between RIA and ELISA of duplicate samples. The ELISA demonstrated excellent correspondence with the RIA for providing testosterone concentrations for sex determination. Neither assay proved reliable for predicting the sex of reproductively active females with increased testosterone production. We then applied ELISA to examine the sex ratio of 69 green turtles foraging in San Diego Bay, California. Of 45 immature turtles sampled, sex could not be determined for three turtles because testosterone concentrations fell between the ranges for either sex (females: 4.1–113.1 pg/mL, males: 198.4–2,613.0 pg/mL) and these turtles were not subsequently recaptured to enable sex determination; using a Bayesian model to predict probabilities of turtle sex we predicted all three ‘unknowns’ were female (> 0.86). Additionally, the model assigned all turtles with their correct sex (if determined at recapture) with 100% accuracy. Results indicated a female bias (2.83F:1M) among all turtles in the aggregation; when focusing only on putative immature turtles the sex ratio was 3.5F:1M. With appropriate validation, ELISA sexing could be applied to other sea turtle species, and serve as a crucial conservation tool.     

Rapid isotyping of murine monoclonal antibodies by enzyme-linked immunofiltration assay

Summary As a part of the initial characterization of monoclonal antibodies, the isotype is routinely identified by enzyme-linked immunosorbent assay (ELISA). In the present study, we describe an isotyping methodology that uses the technique referred to as enzyme-linked immunofiltration assay (ELIFA) for greatly accelerating the assay compared with ELISA. In the ELIFA method, solutions are filtered through a nitrocellulose membrane using a controlled flow rate to bind proteins. By using this technology, the time required to isotype a monoclonal antibody was reduced from a minimum of 4 to 8 hr using a standard ELISA assay to 30 min with ELIFA.     

Testosterone deficiency impairs glucose oxidation through defective insulin and its receptor gene expression in target tissues of adult male rats

Testosterone and insulin interact in their actions on target tissues. Most of the studies that address this issue have focused on the physiological concentration of testosterone, which maintains normal insulin sensitivity but has deleterious effects on the same when the concentration of testosterone is out of this range. However, molecular basis of the action of testosterone in the early step of insulin action is not known. The present study has been designed to assess the impact of testosterone on insulin receptor gene expression and glucose oxidation in target tissues of adult male rat. Adult male albino rats were orchidectomized and supplemented with testosterone (100 microg/100 g b. wt., twice daily) for 15 days from the 11th day of post orchidectomy. On the day after the last treatment, animals were euthanized and blood was collected for the assay of plasma glucose, serum testosterone and insulin. Skeletal muscles, such as gracilis and quadriceps, liver and adipose tissue were dissected out and used for the assay of various parameters such as insulin receptor concentration, insulin receptor mRNA level and glucose oxidation. Testosterone deprivation due to orchidectomy decreased serum insulin concentration. In addition to this, insulin receptor number and its mRNA level and glucose oxidation in target tissues were significantly decreased (p<0.05) when compared to control. However, testosterone replacement in orchidectomized rats restored all these parameters to control level. It is concluded from this study that testosterone deficiency-induced defective glucose oxidation in skeletal muscles, liver and adipose tissue is mediated through impaired expression of insulin and its receptor gene.     

A new method for the simultaneous determination of androstenedione, testosterone, 11-oxotestosterone and 11 beta-OH-testosterone in fish plasma using combined techniques of Celite chromatography and radioimmunoassay

A new method for the simultaneous determination of androstenedione, testosterone, 11-oxotestosterone and 11 beta-hydroxy-testosterone in teleost plasma has been developed. Steroids extracted from the plasma were first separated by Celite chromatography using ethanediol as the stationary phase and different concentrations of ethyl acetate in iso-octane as the eluting solvents. Androstenedione, testosterone, 11-oxotestosterone and 11 beta-OH-testosterone were eluted successively with 0, 10, 15 and 40% of ethyl acetate in iso-octane. The eluted steroid fractions were then quantatively determined by radioimmunoassay. Data on the accuracy, precision, and sensitivity were presented showing that this new assay system was precise and reproducible. As an illustration of its application, this method was used in the present study to determine the plasma androgen levels in Monopterus albus and in methyl-testosterone treated Tilapia mossambicus.     

Determination of testosterone concentrations in rat plasma using liquid chromatography-atmospheric pressure chemical ionization mass spectrometry combined with ethyl oxime and acetyl ester derivatization

A quantitative method for measuring testosterone (T) concentrations in rat plasma was developed using ethyl oxime and acetyl ester derivatization and liquid chromatography-atmosphere pressure chemical ionization tandem mass spectrometry (LC-APCI-MS/MS). The method utilizes a solid phase extraction with Varian Bond Elut C18, a derivatization process to form testosterone ethoxime acetate and LC-APCI-MS/MS with a reversed phase LC and a C8 column. This method is capable of detecting testosterone concentrations as low as 0.2 ng/ml in a 0.05 ml sample of rat plasma. This method can be used as a sensitive chromatography-based assay for small sample volumes of rat blood.     

Determination of testosterone and 6β-hydroxytestosterone by gas chromatography–selected ion monitoring–mass spectrometry for the characterization of cytochrome p450 3A activity

A method for the determination of testosterone and its metabolite, 6β-hydroxytestosterone, in liver microsomal incubates employing gas chromatography with selected ion monitoring mass spectrometric detection (GC–SIM–MS) has been developed. The method is more rapid than previously reported methods. Testosterone and its metabolites are extracted from the incubation mixture in a single step with methylene chloride. The method does not require derivatization and testosterone and its metabolites are separated on a HP-5MS fused-silica capillary column in less than 15 min. The retention times of testosterone (m/z 288), methyltestosterone (m/z 302), and 6β-hydroxytestosterone (m/z 304) are approximately 12.7, 12.8, and 13.4 min, respectively. There are no interferences from other known CYP450 metabolites of testosterone. In addition, the selectivity and specificity of the mass spectrometer helps eliminate possible interferences from drugs and new chemical entities evaluated using this methodology. Calibration curves for testosterone and 6β-hydroxytestosterone are linear from 0.25 to 100 μM. Extraction recoveries are better than 92% for both analytes and the internal standard, methyltestosterone. Over the course of five separate runs, within-day and inter-day precision (expressed as relative standard deviation) was less than 5% for all concentrations of testosterone and 6β-hydroxytestosterone. Accuracies ranged from 95.8 to 105.8% for testosterone and 94.6 to 104.2% for 6β-hydroxytestosterone. The assay has been used to characterize the CYP3A metabolic activity of multiple preparations of human, rat, and dog liver microsomes.