Hormone immunoassays

Other biomedical and biological appHcations of mictocapsules continue to be developed. For example, the encapsulation of enzymes continues to attract interest even though loss of enzyme activity due to harshness of the encapsulation protocols used has been a persistent problem (59). The use of mictocapsules in antibody hormone immunoassays has been reviewed (60). The encapsulation of hemoglobin as a ted blood substitute has received much attention because of AIDS and blood transfusions (61). 

A.M. Pelkkikangas, S. Jaakohuhta, T. Lovgren, and H. Harma, Simple, rapid, and sensitive thyroid-stimulating hormone immunoassay using europium(III) nanoparticle label. Anal. Chim. Acta 517, 169-176 (2004). 

Immunoassays are subject to some effects and interferences unique to immunoassay and some common to all chemical assays (Wu 2000). Establishment of an assay should include some assessment of antibody interference, signal interference, and matrix and hook effects. Interference may be caused by cross-reactivity or by an endogenous metabolite (e.g., in steroid hormone immunoassays) or a xenobi-otic (or metabolite) with a similar structure this problem occurs more frequently... 

Chemiluminescence tracer used for steroid hormone immunoassays. 

Latex agglutination immunoassays are easily formatted into simple kits which can provide yes/no and semiquantitative estimates of antigen (or antibody) in a sample. The first such assay was developed in 1957 for rheumatoid factor (15) and assays are on the market for the deterrnination of many species of bacteria, fungi. Mycoplasma, parasites, ckettsia, and vimses, as well as for the deterrnination of autoimmune disease, hormones (qv), dmgs (see Pharmaceuticals), and blood proteins (16). Latex agglutination is also the basis of many home pregnancy tests. 

Most immunoassay kits and many commercial immunoassay analyzers are based on heterogenous EIA or FIA. These include an immunoassay system that uses FIA linked to radial partition chromatography of the antibody—antigen complex (39) a system that uses antibody-coated tubes for enzyme immunoassay of a variety of hormones and dmgs (40) and a system that uses either a sandwich or competitive FIA format to measure a variety of analytes (41). 

The singularity of MAbs and the ease of mass production appeared to be the answer to rapid development of highly specific immunoassays. Companies were formed to produce MAbs and incorporate them into assays. In fact, such assays have been developed and have proved very successful for infectious diseases, hormones, and other clinical analytes. 

ImmunO lSS iy. Chemiluminescence compounds (eg, acridinium esters and sulfonamides, isoluminol), luciferases (eg, firefly, marine bacterial, Benilla and Varela luciferase), photoproteins (eg, aequorin, Benilld), and components of bioluminescence reactions have been tested as replacements for radioactive labels in both competitive and sandwich-type immunoassays. Acridinium ester labels are used extensively in routine clinical immunoassay analysis designed to detect a wide range of hormones, cancer markers, specific antibodies, specific proteins, and therapeutic dmgs. An acridinium ester label produces a flash of light when it reacts with an alkaline solution of hydrogen peroxide. The detection limit for the label is 0.5 amol. 

Radiotracers have also been used extensively for the quantitative rnicrodeterrnination of blood semm levels of hormones (qv), proteins, neurotransmitters, and other physiologically important compounds. Radioimmunoassay, which involves the competition of a known quantity of radiolabeled tracer, usually I or H, with the unknown quantity of semm component for binding to a specific antibody that has been raised against the component to be deterrnined, is used in the rnicro deterrnination of physiologically active materials in biological samples (see Immunoassay). 

Applications. Immunoassays are used in many different disciplines, having clinical, industrial, agricultural, and environmental appHcations. This technique has made possible rapid analysis of such varied analytes as vimses, toxins, hormones, foreign proteins, dmgs, and insecticides. 

Immunochemical metliods drat utilize radioisotopic labeling can detect tire use of anabolic sex hormones drat increase die growdi in meat animals. Stilbene [588-59-0] trenbolone [10161 -33-8] and zeranol [55331-29-8] C gH2 0, can be successfully monitored by diese immunoassay techniques... 

Moroder, L., Nyfclcr, R., Gcmcincr, M., Kalbacher, H., and Wfinsch, E. (1983) Immunoassays of peptide hormones and their chemical aspects. BioBolymers 22, 481M86. 

Like FRET, today BRET is predominantly used in biological sciences, especially in the monitoring of protein-protein interactions such as hormone-receptor interaction [223, 224] and protein-DNA interaction in living systems. However, BL resonance energy transfer can also be applied in immunoassays by using for instance a peptide-tagged luciferase and a fluorescein-labeled antipeptide antibody [225]. The development of more BRET assays for small-molecule analytes is thus awaited. 

Immunoassay as an analytical technique was introduced by Rosalind Yalow and Solomon Berson in 1960 with their use of anti-insulin antibodies to measure the concentration of the hormone in plasma. This advance, for which Rosalind Yalow was awarded the Nobel prize, was probably the most important single advance in biological measurement of the following two decades. Examples of the use of immunoassay may now be found in almost all areas of analytical biochemistry. 

Time-resolved approaches for multi-analyte immunoassays have been described recently. Simultaneous determination of LH, follicle stimulating hormone (FSH), hCG, and prolactin (PRL) in a multisite manual strip format has been reported. 88 Four microtiter wells are attached to a plastic strip, two-by-two and back-to-back, such that the wells can be read on a microtiter plate reader. In a quadruple-label format, the simultaneous quantitative determination of four analytes in dried blood spots can be done using europium, samarium, dysprosium, and terbium. 89 In this approach, thyroid-stimulating hormone, 17-a-hydroxyprogesterone, immunoreactive trypsin, and creatine kinase MM (CK-MM) isoenzyme are determined from dried blood samples spotted on filter paper in a microtiter well coated with a mixture of antibodies. Dissociative fluorescence enhancement of the four ions using cofluorescence-based enhancement solutions enables the time-resolved fluorescence of each ion to be measured through four narrow-band interference filters. 

Y.-Y. Xu, K. Pettersson, K. Blomberg, I. Hemmila, H. Mikola, and T. Lovgren, Simultaneous quadruple-label fluorometric immunoassay of thyroid-stimulating hormone, 17 othydroxypro-gesterone, immunoreactive trypsin, and creatine kinase, Clin. Chem. 38, 2038-2043 (1992). 

Cell Culture-Derived Media-Derived Protein Impurities. Immunoassays can detect low impurity levels (<1 ppm).4 The ELISA is probably one of the most sensitive analytical methods. If bovine serum is used as a media component, then testing should include ELISAs for bovine serum albumin (BSA), bovine transferrin, bovine fetuin, and bovine IgG. Often hormones and growth factors, such as insulin or insulinlike growth factor, are used as media components. ELISAs should be used to detect and quantitate these residuals in the various production steps as well as in the final product. There are commercially available antibodies to most commonly used media components. If proprietary media components are used, then the same investment in time and effort is required for the production of specific antibodies, as described above for host cell impurities. 

Immunoassays have found wide applications in the field of clinical diagnostics for the detection and measurement of drugs, vitamins, hormones, proteins in general, metabolites, microorganisms, and other substances of interest in biological... 

M17. Miedema, K., Boelhouwer, J., and Otten, J. W., Determinations of proteins and hormones in serum by an immunoassay using antigen-enzyme conjugates. Clin. Chim. Ada 40, 187-192 (1972). 

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