C.J. STRASBURGER and F. KOHEN
A Blackburn, RA Dressendorfer, WF Blum, M Erhard, G Brem, CJ Strasburger and E Wolf
To study interactions between insulin-like growth factor-II (IGF-II) and growth hormone (GH) in vivo, we crossed hemizygous transgenic mice carrying phosphoenolpyruvate carboxykinase (PEPCK)-IGF-II fusion genes with hemizygous PEPCK-bovine GH (bGH) transgenic mice. Offspring harbouring both transgenes (IB), the IGF-II transgene (I) or the bGH transgene (B), and non-transgenic littermates (C) were obtained. Blood samples were taken before (end of week 12) and after (end of week 14) the mice had received a diet high in protein and low in carbohydrates to stimulate PEPCK promoter-controlled transgene expression. Mean serum GH concentrations of both B and IB mice corresponded to 900 ng/ml and increased more than twofold (P < 0.001) after 1 week of the high-protein diet. GH concentrations in controls and I mice were less than 20 ng/ml. Serum IGF-II concentrations in I and IB mice were three-to fourfold higher than those in C and B mice. Whereas IGF-II concentrations were not changed by the high-protein diet in the last two groups, serum IGF-II increased significantly in I (P < 0.001) and IB mice (P < 0.05). This increase was significantly (P < 0.05) less pronounced in IB than in C and I mice. Circulating IGF-I concentrations were about twofold (P < 0.001) higher in B and IB than in C and I mice, and showed a tendency to be lower in I than in C and in IB than in B mice when animals were maintained on the standard diet. The high-protein diet did not change circulating IGF-I concentrations in controls and B mice, but resulted in a significant reduction of serum IGF-I concentrations in I (P < 0.05) and IB mice (P < 0.001). Consequently, after PEPCK-IGF-II transgene expression was stimulated, serum IGF-I concentrations were significantly (P < 0.05) lower in I than in C and in IB than in B mice. Serum IGF-binding protein (IGFBP)-2 concentrations were significantly (P < 0.05) higher in I mice than in all other groups when mice were maintained on the standard diet, with a tendency to reduced IGFBP-2 concentrations in B mice. After the high-protein diet, serum IGFBP-2 concentrations did not change in C and I mice, but increased by two- to threefold in B and IB mice (P < 0.001). Serum IGFBP-3 concentrations tended to be greater in B and IB than in C and I mice, but these differences were mostly not significant. IGFBP-4 concentrations were significantly (P < 0.001) increased by GH overproduction in B and IB mice. Our data suggest that the reduction in circulating IGF-I concentrations by increased IGF-II is most probably due to the limited serum IGF binding capacity and the short half-life of free IGFs, rather than to a reduction in GH-dependent IGF-I production. Effects of GH overproduction on serum IGFBP-2 concentrations depend on dietary factors and may be both inhibitory and stimulatory.
J Deladoey, G Gex, JM Vuissoz, CJ Strasburger, MP Wajnrajch and PE Mullis
OBJECTIVE: G to A transition at position 6664 of the growth hormone (GH-1) gene results in the substitution of Arg183 by His (R183H) in the GH protein and causes a new form of autosomal dominant isolated GH deficiency (IGHD type II). The aim of this study was to assess the bioactivity of this R183H mutant GH in comparison with both other GH variants and the 22-kDa GH in terms of GH-receptor gene regulation. DESIGN AND METHODS: The regulation of the GH-receptor gene (GH-receptor/GH binding protein, GHR/GHBP) transcription following the addition of variable concentrations (0, 12.5, 25, 50 and 500 ng/ml) of R183H mutant GH was studied in a human hepatoma cell line (HuH7) cultured in a serum-free hormonally defined medium. In addition, identical experiments were performed using either recombinant human GH (22-kDa GH) as a positive control or two GH-receptor antagonists (R77C mutant GH and pegvisomant (B-2036-PEG)) as negative controls. GHR/GHBP mRNA expression was quantitatively assessed by RT-PCR amplification after 0, 1, 3 and 6 h incubation. RESULTS: Following the addition of R183H mutant GH, GHR/GHBP mRNA changed at a similar rate to that seen in experiments where 22-kDa GH was added, indicating equal bioactivity. At all times and concentrations studied, the addition of R77C mutant GH, however, resulted in a significantly lower increase (P<0.001) of GHR/GHBP mRNA concentration compared with that caused by the addition of either 22-kDa GH or R183H mutant GH. Furthermore, in additional experiments, pegvisomant resulted in an absolute block of GHR/GHBP mRNA expression identical to that seen in control experiments where no 22-kDa GH was added at all. CONCLUSIONS: These data indicate that the R183H mutant GH, although causing an autosomal dominant form of IGHD has an identical effect on GHR/GHBP transcription as its wild-type, the 22-kDa GH. This implies that the IGHD caused by the R183H heterozygous mutation of the GH-1 gene is mainly due to a block of its regulated GH secretion. In addition, the R77C-GH variant and pegvisomant have an antagonistic effect at the level of GHR/GHBP transcription. All these data were confirmed by run-on experiments. In addition, these data highlight, as far as the GH variants are concerned, that a mutational alteration within the GH-1 gene might cause short stature also on the basis of an altered secretory pathway. This fact has to be taken into consideration when growth retardation is clinically diagnosed and studied at the molecular level. Secretory pathways and, therefore, cell-biological mechanisms are of importance and have to be considered in future not only at the scientific but also at the clinical level.
B Seidel, A Glasow, M Schutt, W Kiess, Z Wu, CJ Strasburger and J Kratzsch
OBJECTIVE: The human GH-binding protein (GHBP) is derived from the GH receptor (GHR) through proteolytic cleavage of its extracellular domain. Two isoforms of the GHBP exist, differing in the retention or exclusion of exon 3: E3(+)GHBP and E3(-)GHBP. Our study aimed to answer the questions whether the level of E3(+)GHBP in the serum correlates with the GHR exon 3 expression and whether or not the E3 genotype matches the mRNA expression pattern. METHODS: Since exon 3 retention/deletion can be detected at the protein level using epitope-specific antibodies, we were able to quantify the two isoforms by means of specific immunoassays in a total of 37 individuals. Additionally, these persons were also genotyped for exon 3 by genomic PCR and tested for GHR exon 3 mRNA expression by RT-PCR. RESULTS: We found a significant correlation between GHR exon 3 genotype and the ratio of E3(+)GHBP and E3(-)GHBP in the serum. Moreover, the genotype matched exactly the mRNA expression in fibroblasts and/or blood leukocytes in all samples investigated. The levels of E3(+)GHBP are more strongly correlated with body mass index, proinsulin and C-peptide than the levels of the E3(-) isoform. CONCLUSIONS: Our results show that the GHR exon 3 genotype is in accord with the type of GHBP isoforms found in the serum. Our data thus support the idea that the presence of exon 3-retaining and -excluding GHR/GHBP isoforms results from a genomic deletion rather than from alternative splicing.
M Tschop, H Lahner, H Feldmeier, H Grasberger, KM Morrison, OE Janssen, AF Attanasio and CJ Strasburger
OBJECTIVE: To determine if human growth hormone (hGH) replacement therapy alters pharmacokinetics of hydrocortisone (CS) substitution in hypopituitary adults. DESIGN: To this aim, we analysed serum and salivary CS profiles 270 min after oral CS administration at baseline and 6 and 12 months after initiation of hGH replacement therapy. METHODS: Serum IGF-I, cortisol-binding globulin (CBG), thyroxine-binding globulin (TBG) and sex hormone-binding hormone (SHBG) were measured using commercially available radioimmunoassays. In-house immunofluorometric assays were employed for measurements of CS and hGH. RESULTS: hGH replacement did not change total serum CS bioavailability (area under the serum cortisol profile curve). Interference of orally administered CS with salivary measurement of free CS (fCS) caused significant bias. Therefore, fCS levels were calculated from their total CS and cortisol-binding globulin (CBG) levels. CBG decreased by approximately 30% after both 6 and 12 months of hGH replacement therapy (n=20, P<0.01). A significant negative correlation between deltaCBG (CBG6months-CBGbaseline) and deltaIGF-I (IGF-I6months-IGF-Ibaseline) was observed (P=0.04). The calculated values of free CS tended to increase with physiological hGH replacement, but this effect was marginal and did not reach statistical significance. In contrast to the CBG concentrations, plasma levels of sex hormone-binding globulin and thyroxine-binding globulin were essentially stable. CONCLUSION: Given that no clinically relevant alterations in pharmacokinetics of CS were evoked by initiation of hGH replacement in hypopituitary adults, we conclude that CS substitution does not require dose adjustment after initiation of hGH replacement.
P Herschbach, G Henrich, CJ Strasburger, H Feldmeier, F Marin, AM Attanasio and WF Blum
BACKGROUND: Adults with growth hormone (GH) deficiency (GHD) may experience physical and psychological disturbances, which can affect their quality of life (QOL). OBJECTIVES: To develop and validate a disease-specific module from the previously published QOL measure Questions on Life Satisfaction Modules (QLS(M)): the QLS(M)-H that specifically addressed the needs of patients with hypopituitarism. A second aim was for the questionnaire to be applicable across different cultural backgrounds in order to evaluate the efficacy of therapy in large, international clinical trials, thus providing additional clinical endpoints for these studies. DESIGN: A preliminary German language version of the QLS(M)-H was developed from 26 semi-structured interviews of adults with GHD. The questionnaire was then independently translated into five other languages and applied in open, non-controlled, multicentre, longitudinal studies to patient (n=717) and normative populations (n=2700). METHODS: A revised, nine-item version of the questionnaire was developed, based on previously defined criteria, and was evaluated for reliability and validity. Sensitivity to detect changes after GH replacement was also assessed. RESULTS: The 16 items of the preliminary questionnaire were reduced to nine items on the basis of the correlation of items/factors from initial patient interviews. Psychometric analysis revealed the reliability of the nine-item scale. The Cronbach's alpha scores ranged from 0.81 to 0.89 and the test-retest correlations ranged from 0.76 to 0.88, all of which indicate reliability over time. Mean scores increased significantly during GH replacement therapy, with observed changes greater than those seen with the non-specific modules of the QLS(M), indicating the sensitivity of the scale. CONCLUSIONS: The QLS(M)-H questionnaire is concise, easy to complete, and can be effectively applied across different cultural backgrounds. Psychometric evaluation of the questionnaire reveals that it is a valid, reliable and sensitive tool useful for assessing impaired life satisfaction in adult patients with GHD and also for monitoring the efficacy of GH therapy.
EA Nijland, CJ Strasburger, C Popp-Snijders, PS van der Wal and EA van der Veen
The synthetic hexapeptide growth hormone-releasing peptide (GHRP)-2 specifically stimulates GH release in man. To determine the effects of prolonged treatment and whether response attenuation occurs in man, we administered to nine healthy subjects a daily s.c. injection of 100 microg GHRP-2 over 5 days. Every day blood samples were taken to determine GH, IGF-I, IGF-binding protein (IGFBP)-3 and osteocalcin levels. On days 1,3 and 5, GH was measured at -20,0,20,40,60,90,120 and 180 min using an immunometric and an immunofunctional assay. Mean-/+S.D). peak GH concentrations were 83+/-31, 59+/-22 and 51+/-13 microg/l on days 1, 3 and 5 respectively. Mean+/-S.D. areas under the curve for days 1, 3 and 5 were 6366+/-2514, 3987 +/- 1418 and 3392+/-1215 mU/l per min. Despite the maintained GH release, analysis of variance revealed that significant response attenuation occurred (P < 0.01). Mean serum IGF-I concentration did not increase after a 5 day treatment with GHRP-2. Mean basal levels were 22, 25,23,25,23,24 nmol/l measured on days 1 to 6. However, osteocalcin, another serum marker of GH activity in tissue, increased significantly from 3.2+/-1.0 to 4.2+/-0.4 microg/l (mean+S.D.) (P< 0.01).
AF Muller, SW Lamberts, JA Janssen, LJ Hofland, PV Koetsveld, M Bidlingmaier, CJ Strasburger, E Ghigo and AJ Van der Lely
OBJECTIVES: In humans, fasting leads to elevated serum GH concentrations. Traditionally, changes in hypothalamic GH-releasing hormone and somatostatin release are considered as the main mechanisms that induce this elevated GH secretion during fasting. Ghrelin is an endogenous ligand of the GH secretagogue receptor and is synthesized in the stomach. As ghrelin administration in man stimulates GH release, while serum ghrelin concentrations are elevated during fasting in man, this increase in ghrelin levels might be another mechanism whereby fasting results in stimulation of GH release. DESIGN AND SUBJECTS: In ten healthy non-obese males we performed a double-blind placebo-controlled crossover study comparing fasting with and fasting without GH receptor blockade. GH, ghrelin, insulin, glucose and free fatty acids were assessed. RESULTS: While ghrelin levels do not vary considerably in the fed state, fasting rapidly induced a diurnal rhythm in ghrelin concentrations. These changes in serum ghrelin concentrations during fasting were followed by similar, profound changes in serum GH levels. The rapid development of a diurnal ghrelin rhythm could not be explained by changes in insulin, glucose, or free fatty acid levels. Compared with fasting without pegvisomant, fasting with pegvisomant did not change the ghrelin rhythm. CONCLUSIONS: These data indicate that ghrelin is the main driving force behind the enhanced GH secretion during fasting.
M Maccario, F Tassone, C Gauna, SE Oleandri, G Aimaretti, M Procopio, S Grottoli, CD Pflaum, CJ Strasburger and E Ghigo
OBJECTIVE: To verify the hypothesis of an increased sensitivity to GH in obesity (OB) and Cushing's syndrome (CS). DESIGN: We studied the effects of short-term administration of low-dose rhGH on circulating IGF-I levels in patients with simple OB or CS and in normal subjects (NS). METHODS: Nineteen women with abdominal OB aged (mean +/- s.e.m.) 38.2+/-3.1 years, body mass index 40.7+/-2.5 kg/m(2), waist to hip ratio 0.86+/-0.02, ten with CS (50.4+/-4.2 years, 29.7 +/- 3.3 kg/m(2)) and 11 NS (35.0+/-3.6 years, 20.5+/-0.5 kg/m(2)) underwent s.c. administration of 5 microg/kg per day rhGH at 2200 h for four days. Serum IGF-I, IGF-binding protein-3 (IGFBP-3), GH-binding protein (GHBP), insulin and glucose levels were determined at baseline and 12 h after the first and the last rhGH administration. RESULTS: Basal IGF-I levels in NS (239.3+/-22.9 microg/l) were similar to those in OB (181.5+/-13.7 microg/l) and CS (229.0+/-29.1 microg/l). Basal IGFBP-3, GHBP and glucose levels in NS, OB and CS were similar while insulin levels in NS were lower (P<0.01) than those in OB and CS. In NS, the low rhGH dose induced a sustained rise of IGF-I levels (279.0+/-19.5 microg/l, P<0.001), a non-significant IGFBP-3 increase and no change in GHBP, insulin and glucose levels. In OB and CS, the IGF-I response to rhGH showed progressive increase (246.2+/-17.2 and 311.0+/-30.4 microg/l respectively, P<0.01 vs baseline). Adjusting by ANCOVA for basal values, rhGH-induced IGF-I levels in CS (299.4 microg/l) were higher than in OB (279.1 microg/l, P<0.01), which, in turn, were higher (P<0.05) than in NS (257.7 microg/l). In OB, but not in CS, IGFBP-3 and insulin levels showed slight but significant (P<0.05) increases during rhGH treatment, which did not modify glucose levels in any group; thus, in the OB patient group a significant fall in glucose/insulin ratio was observed. CONCLUSIONS: Short-term treatment with low-dose rhGH has enhanced stimulatory effect on IGF-I levels in OB and, particularly, in hypercortisolemic patients. These findings support the hypothesis that hyperinsulinism and hypercortisolism enhance the sensitivity to GH in humans.
W Doehner, CD Pflaum, M Rauchhaus, IF Godsland, K Egerer, M Cicoira, VG Florea, R Sharma, AP Bolger, AJ Coats, SD Anker and CJ Strasburger
OBJECTIVE: Regulation of growth hormone (GH) receptor expression and hence tissue GH sensitivity may be important for the conflicting results found in treatment studies with recombinant growth hormone in chronic heart failure (CHF). Growth hormone-binding protein (GHBP) corresponds to the extracellular domain of the GH receptor and is closely related to measures of body composition and, specifically, to size of visceral fat tissue. Leptin, the adipocyte specific (ob) gene product, has been proposed as the signal linking adipose tissue and GHBP/GH-receptor expression. CHF has recently been shown to be a hyperleptinaemic and insulin-resistant state regardless of aetiology. This study aimed to examine the influence of leptin on GHBP in CHF patients with and without cardiac cachexia compared with healthy control subjects. METHODS: We studied 47 male patients with CHF (mean age 61+/-2 years, New York Heart Association (NYHA)-class 2.7+/-0.1, left ventricular ejection fraction (LVEF) 28+/-2%, peak oxygen consumption 16.8+/-0.9 ml/kg/min) and 21 male healthy controls of similar age. Of the CHF patients, 19 were cachectic (cCHF; non-oedematous weight loss >7.5% over at least 6 months) and 28 non-cachectic (ncCHF; similar for age and LVEF). Insulin sensitivity was assessed by an intravenous glucose tolerance test using the minimal model approach. RESULTS: Compared with healthy controls, patients had elevated levels of leptin (7.6+/-0.7 vs 4.8+/-0.7 ng/ml, P<0.05), insulin (76.2+/-8.9 vs 41.4+/-6.0 pmol/l, P<0.01), and reduced insulin sensitivity (2.43+/-0.2 vs 3.48+/-0.3 min(-1).microU.ml(-1).10(4), P<0.005) but similar GHBP levels (901+/-73 vs 903+/-95 pmol/l). Leptin levels were increased in ncCHF (9.11+/-1.0 ng/ml, P=0.001) but were not different from normal in cCHF (5.32+/-0.7 ng/ml, P>0.5). After correction for total body fat mass, both ncCHF and cCHF were hyperleptinaemic (41.8+/-3.8 and 37.9+/-0.38 vs 24.4+/-2.1 ng/ml/100 g, ANOVA P=0.001). In both patients and controls there was a direct correlation between leptin levels and GHBP (r=0.70 and r=0.71 respectively, both P<0.0001). This relationship was stronger than between GHBP and several parameters of body composition (body mass index (BMI), total and regional body fat mass or % body fat) and held true when sub-groups were tested individually (ncCHF r=0.62, P<0.001; cCHF r=0.79, P<0.0001). In multivariate regression analysis in all CHF patients, serum leptin levels emerged as the strongest predictor of GHBP, independent of age, BMI, total and regional fat mass or % body fat, fasting insulin level and insulin sensitivity. CONCLUSION: Fat mass corrected leptin levels are elevated in CHF patients with and without cachexia. Reduced total fat mass may account for lower leptin levels in cachectic CHF patients compared with non cachectic patients. Leptin strongly predicts GHBP levels in CHF regardless of its hyperleptinaemic state or severely altered body composition as in cardiac cachexia. Leptin could be the signalling link between adipose tissue and GHBP/GH receptor expression in CHF.