RESUMEN
One possible explanation for the growth failure in children with idiopathic short stature (ISS) is reduced peripheral responsiveness to GH. In Laron syndrome, growth retardation is caused by GH resistance due to GH receptor (GH-R) defects, which are associated in most cases with absent or low serum concentrations of the GH-R-related GH-binding protein (GHBP). We tested the hypothesis that some children with ISS have reduced serum concentrations of GHBP and that this may reflect decreased sensitivity to GH. A ligand-mediated immunofunctional assay was used to measure biochemically active GHBP in serum from 1549 children, including 773 controls, 573 with ISS, 107 with GH deficiency (GHD), and 96 with Turner syndrome (TS). Ages ranged from 1-17 yr. Serum GHBP concentrations in children with GHD, ISS, and TS were converted to SD scores and compared to controls by analysis of variance. In male and female ISS subjects, approximately 90% had GHBP concentrations below the age- and sex-adjusted mean for controls, and 20% had GHBP concentrations below the normal range. The mean serum GHBP SD score was lower in both males and females with GHD (-0.6) or ISS (-1.2) than in controls (both P < 0.005). The mean for ISS males was significantly lower than that for GHD males (P < 0.0001). The mean GHBP SD score for girls with TS (-0.3) did not differ significantly from that of the control females. The decreased levels of serum GHBP in some children with idiopathic short stature suggest that these children could have a defect at the level of the GH-R.
Asunto(s)
Proteínas Portadoras/sangre , Trastornos del Crecimiento/sangre , Hormona del Crecimiento/sangre , Adolescente , Biomarcadores/sangre , Estatura , Índice de Masa Corporal , Niño , Preescolar , Femenino , Hormona del Crecimiento/deficiencia , Humanos , Factor I del Crecimiento Similar a la Insulina/análisis , Factor I del Crecimiento Similar a la Insulina/metabolismo , Masculino , Valores de Referencia , Factores Sexuales , Síndrome de Turner/sangreRESUMEN
Human blood contains a high affinity GH binding protein (GHBP) which corresponds to the extracellular domain of he GH-receptor. It has been suggested that GHBP can modify the biological actions of GH, and alter the distribution of GH in the body. To study the hormonal regulation of growth, it is therefore necessary to measure GHBP as well as GH. We recently developed a ligand-mediated immunofunctional assay (LIFA) which allows separate quantitation of total GHBP (free and GH-bound) and the complex formed by GH and GHBP (GH/GHBP-complex) in human blood. We have now used the ligand-mediated immunofunctional assay to measure GHBP levels in plasma profiles from healthy children. GH was measured by immunoradiometric assay. Fifteen 24-h plasma profiles from 12 healthy children (3 girls and 9 boys) of different ages (6-15 yr), heights (-2.5 to +3.0 SD scores) and pubertal stages (1-4) were examined. Blood was withdrawn continuously for 24 h and collected in 20-min fractions. Time series for GH, GHBP, and GH/GHBP-complex were analyzed by cross-correlation and Fourier analysis. GH was secreted in a pulsatile fashion in all subjects. The concentration of the GH/GHBP-complex varied during the sampling period, and the changes correlated significantly with the GH pulses with correlation coefficients reaching maximum at zero time lag. In contrast, the changes in the total GHBP concentration were minor (coefficients of variation approximately 10%), and not correlated to GH pulses. Fourier analysis showed similar spectral power patterns for GH and GH/GHBP-complex, suggesting a diurnal rhythm (12- to 24-h periods) as well as components of higher frequencies (around 4-h periods). Although there were only subtle fluctuations in the total GHBP concentration, Fourier transformation revealed a diurnal rhythm with nadir during the night, while components of higher frequencies were much less abundant. We conclude that variations in total GHBP as measured by LIFA during a 24-h sampling period are small and that the concentration can be estimated from a single random blood sample.
Asunto(s)
Proteínas Portadoras/sangre , Ritmo Circadiano , Hormona del Crecimiento/sangre , Adolescente , Niño , Femenino , Análisis de Fourier , Humanos , Técnicas para Inmunoenzimas , Ensayo Inmunorradiométrico , Ligandos , MasculinoRESUMEN
Interleukin-8 (IL-8), a potent neutrophil chemotactic peptide, has been found in association with human disease, but its contribution to chemotactic activity in humans is not yet known. We asked whether IL-8 is present in inflammatory human pleural effusions, and to what extent it contributes to pleural liquid neutrophil chemotactic activity. Because tumor necrosis factor alpha (TNF-alpha) is a strong inducer of IL-8, we also asked whether TNF-alpha was present. For this prospective study, we collected pleural liquid from 51 patients (empyema, 14; parapneumonic, four; tuberculous, eight; malignant, nine; miscellaneous exudative, seven; and transudative, nine), counted pleural neutrophils, and measured IL-8 and TNF-alpha concentrations in the supernatant. To determine the contribution of IL-8 to chemotactic activity in empyema, we measured the neutrophil migration induced by empyemic liquids before and after addition of anti-IL-8 F(ab')2 antibody fragments or control anti-IL-6 F(ab')2. We found that IL-8 concentrations were higher in empyema (61.3 +/- 21.0 ng/ml [SEM]) than in all other effusions (1.1 +/- 0.5 ng/ml) (p = 0.0001). All empyema liquids had IL-8 concentrations above 2.5 ng/ml, which was true for only three of the other 37 effusions (two parapneumonic, one tuberculous). IL-8 levels correlated with the pleural neutrophil count (r = 0.46; p = 0.007) and the neutrophil chemotactic activity of pleural liquid (r = 0.43; p = 0.008). Anti-IL-8 antibodies decreased chemotactic activity in empyema liquids by 65 +/- 5%, whereas the control antibody had no effect (0 +/- 5% decrease) (p = 0.0005).(ABSTRACT TRUNCATED AT 250 WORDS)
Asunto(s)
Quimiotaxis de Leucocito/fisiología , Empiema Pleural/metabolismo , Interleucina-8/fisiología , Derrame Pleural/química , Empiema Pleural/epidemiología , Ensayo de Inmunoadsorción Enzimática , Femenino , Humanos , Interleucina-8/análisis , Masculino , Persona de Mediana Edad , Neutrófilos/fisiología , Derrame Pleural/citología , Derrame Pleural/epidemiología , Estudios Prospectivos , Factor de Necrosis Tumoral alfa/análisis , Factor de Necrosis Tumoral alfa/fisiologíaRESUMEN
The natriuretic peptide receptors (NPRs) are a family of three cell surface glycoproteins, each with a single transmembrane domain. Two of these receptors, designated NPR-A and NPR-B, are membrane guanylyl cyclases that synthesize cGMP in response to hormone stimulation. The third receptor, NPR-C, has been reported to function in the metabolic clearance of ligand and in guanylyl cyclase-independent signal transduction. We engineered three chimeric proteins consisting of the natriuretic peptide receptor extracellular domains fused to the Fc portion of human IgG-gamma 1. These molecules provide material for detailed studies of the human receptor's extracellular domain structure and interaction with the three human natriuretic peptides, atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and type-C natriuretic peptide (CNP). The homodimeric fusion proteins, designated A-IgG, B-IgG, and C-IgG, were secreted from Chinese hamster ovary cells and purified by protein-A affinity chromatography. We present here the primary characterization of these fusion proteins as represented by the intrinsic hormone affinities measured by saturation binding and competition assays. The dissociation constant of 125I-ANP for A-IgG was 1.6 pM and for C-IgG, 1.2 pM. The dissociation constant of 125I-Y0-CNP (CNP with addition of tyrosine at the amino terminus) for B-IgG was 23 pM. The rank order of potency in competitive binding for A-IgG was ANP greater than BNP much greater than CNP, whereas for B-IgG the ranking was CNP much greater than ANP greater than BNP. For C-IgG, we observed ANP greater than CNP greater than or equal to BNP. These data demonstrate that the receptor-IgG fusion proteins discriminate among the natriuretic peptides in the same manner as the native receptors and provide a basis for future structural studies with these molecules. The purified fusion proteins have a variety of potential applications, one of which we illustrate by a solid phase screening assay in which rabbit sera from a series of synthetic-peptide immunizations were titered for receptor reactivity and selectivity.
Asunto(s)
Inmunoglobulina G/metabolismo , Natriuréticos/metabolismo , Receptores de Superficie Celular/metabolismo , Proteínas Recombinantes de Fusión/metabolismo , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Unión Competitiva , Western Blotting , Células CHO , Cricetinae , ADN , Electroforesis en Gel de Poliacrilamida , Femenino , Humanos , Sueros Inmunes , Inmunoglobulina G/genética , Datos de Secuencia Molecular , Natriuréticos/genética , Conejos , Receptores del Factor Natriurético Atrial , Receptores de Superficie Celular/genética , Receptores de Superficie Celular/inmunología , Receptores de Superficie Celular/aislamiento & purificación , Proteínas Recombinantes de Fusión/genética , Proteínas Recombinantes de Fusión/inmunología , Proteínas Recombinantes de Fusión/aislamiento & purificaciónRESUMEN
In order to identify residues required for the binding of interleukin-8 (IL-8) to its receptor, mutants were constructed in which clusters of charged amino acids were systematically replaced with alanine along the entire IL-8 sequence. The mutants were tested for their ability to induce a receptor-mediated rise in cytosolic free Ca2+, a property of wild-type IL-8 which can readily be detected by flow cytometry using neutrophils loaded with the calcium probe Indo-1. Eleven of the 12 mutants caused neutrophil calcium mobilization at 5 nM; the exception being a triple alanine mutant at positions K3, E4, and R6, which was inactive at all concentrations tested (150 nM maximum). A second set of mutants was generated in which residues 1-15 were individually mutated to alanine. Mutants E4A, L5A, or R6A were all inactive in the Ca2+ assay at 5 nM and competed poorly with 125I-IL-8 for neutrophil receptor binding; I10A, E4A, L5A, and R6A had approximately 30-, 100-, 100-, and 1000-fold reduced affinity, as compared with control IL-8, respectively. The nuclear magnetic resonance structure of IL-8 indicates that, in solution, the side chains of E4, L5, R6, and I10 point away from the core of the protein and do not participate in any intramolecular hydrogen bonds or salt bridges (Clore, G. M., and Gronenborn, A. M. (1991) J. Mol. Biol. 217, 611-620).