An accurate determination of human growth hormone content in different pituitary extracts, using a radioimmunoassay with polyacrylamide gel electrophoresis as a bound-free separation system

Ultrasensitive in vivo bioassay detects bioactive human growth hormone in transduced primary human keratinocytes

An improved in vivo body weight gain bioassay for the potency determination of human growth hormone (hGH) has been set up in "little" mice (lit/lit), a mutant derived from the C57BL/6J strain. This improved assay now has a detection limit of the order of 0.05 micrograms/mouse/day, which corresponds to a sensitivity about 20-fold higher than that of the most sensitive in vivo assay reported up to now: the tibia test in hypophysectomized rats or mice. This sensitivity was achieved mainly by introduction of a careful pre-assay selection and of a three injections per day schedule. The utilization of these conditions in a 2x2 factorial assay design allowed the potency determination of recombinant DNA-derived hGH (rec-hGH) in bacterial extracts with acceptable accuracy and precision, together with the greatest economy of material, only 0.24 mg of unknown and standard hormone preparation being sufficient for an entire 10-animal assay. This contrasts to a minimum of 2.7 mg that are necessary for an economical assay in hypophysectomized rats. The same assay procedure was also used to demonstrate the in vivo bioactivity of hGH secreted into a culture medium from transduced human primary keratinocytes. The growth curve constructed with n = 8 little mice presented a highly significant correlation (r = 0.939, p < 0.001) and a slope = 0.016 g/mouse/day. It was thus possible to prove, for the first time, the in vivo bioactivity of rec-hGH secreted by transplantable human epidermal cells, utilized as an experimental model for somatic gene therapy.

The use of recombinant human growth hormone for radioiodination and standard preparation in radioimmunoassay

Recombinant human growth hormone (rec-hGH) obtained by cloning hGH precursor gene, bacterial expression and periplasmic secretion of the authentic, mature form of the hormone was used, after purification and characterization, for the preparation of radioimmunoassay (RIA) reagents. 125I-rec-hGH was prepared by the classical chloramine-T iodination technique, while an internal standard of the same rec-hGH was used and calibrated against pituitary hGH reference preparation (NIDDK-hGH-RP-1) with the use of a reference antiserum (NIDDK-anti-hGH-2). In both cases the behavior of the recombinant preparation was identical to that of the pituitary hormone. This confirms previous data on bacterial correct processing and folding of the protein, as far as its immunological behavior is concerned and indicates its suitability for the preparation of immunoassay reagents.

Ultraviolet scanning densitometry for detection, quantitation, and preparative elution of protein bands from unstained gels

Ultraviolet scanning of gel rods was used to identify and quantify protein bands in a nondestructive manner with good precision and sensitivity. This same technique, applied on a preparative scale, allowed quantitative protein elution, by reversed electrophoresis, from gel slices completely sealed in a dialysis bag. Protein recovery approached the theoretical yield (93.5 +/- 5%), with practically no interfering substances, and the entire preparative process (first electrophoresis, densitometric scanning, and reversed electrophoresis) could be performed in approximately 6 h. Its application to human growth hormone has shown no alteration in the biological activity of this protein.

Stokes radius determination of radioiodinated polypeptide hormones by gel filtration

A simple technique for determination of the molecular (Stokes) radius of radioiodinated proteins was developed using the same column and chromatographic conditions employed in routine radioimmunoassay tracer purification. The calibration curve for five radioiodinated standard proteins presented a highly significant correlation (r = -0.996; P less than 0.001) and allowed precise molecular radius determination for labeled human growth hormone (hGH), luteotropin (hLH), follicle-stimulating hormone (hFSH), thyrotropin (hTSH), prolactin (hPRL), and corticotropin (hACTH), enabling detection of differences of the order of +/- 3%. The validity of the method was verified by determining the molecular radius of hGH in both "cold" (unlabeled standards and unknowns) and "hot" (radioiodinated standards and unknowns) systems. The technique can be applied in a very simple manner, requiring just one simple additional calibration run before Sephadex G-100 tracer purification. Furthermore, it can be applied to any protein, even when only extremely limited amounts are available. Since the standards and unknowns are labeled and chromatographed under identical conditions, potential common alterations of the molecule due to oxidation, iodine incorporation, tracer-carrier interactions, etc., are automatically corrected for.

Human growth hormone radioiodination using different batches of 125I of various ages

The reproducibility and the influence of the batch and decay level of Na125I on the radioiodination of human growth hormone (hGH) were examined by a polyacrylamide gel electrophoresis (PAGE) technique. The between-day coefficient of variation (CV) exhibited a value of 11.9% for labelling yields and 14.3% for antibody specific binding. The within-day variation for different shipments and isotope decay-levels was similar to that for the control experiment, carried out under the same conditions, using Na125I from a single lot. The results indicate that the decay-level and batch do not significantly influence either the yields or the immunological properties of the labelled product. The suitability of this PAGE technique as a control test for radioiodinated proteins is established by comparison with gel chromatography on Sephadex G-100.

Radioiodination of human growth hormone with characterization and minimization of the commonly defined "damaged products"

The radioiodination and chromatographic purification of human growth hormone (hGH) has been studied in order to better define and control the so-called "preparation damage", which is often a cause of interferences, loss in specific activity and sensitivity, misclassification errors in radioligand assays, and a source of misinterpretation when the tracer is used in receptors or in vivo studies. A series of labelings and false labelings, with and without protein carrier in the buffer used for Sephadex purification, indicate that the "preparation damage" peak is made up of two components: aggregated 125I-hGH and BSA-carried radioactivity. The former can be minimized by the use of recently extracted non-lyophilized hGH, and the latter by enzymatic labeling. Both components can be better resolved, and thus eliminated, when Sephadex G-100 is employed rather than G-75.