Oral octreotide capsules for the treatment of acromegaly: comparison of 2 phase 3 trial results.

PURPOSE: Results are presented from 2 to 3 trials investigating oral octreotide capsules (OOC) as an alternative to injectable somatostatin receptor ligands (iSRLs) in the treatment of acromegaly. METHODS: CH-ACM-01 was an open-label trial (N = 155) and CHIASMA OPTIMAL was a double-blind placebo-controlled (DPC) trial (N = 56), both investigating OOC as maintenance therapy for patients with acromegaly who were biochemical responders receiving iSRLs. RESULTS: Baseline characteristics in both trials reflected those expected of patients with acromegaly responding to treatment and were similar between trials, despite differences in inclusion criteria. OOC demonstrated a consistent degree of biochemical response across trials, with 65% of patients in CH-ACM-01 maintaining response during the core period and 64% of patients in CHIASMA OPTIMAL at the end of the DPC. Mean insulin-like growth factor I (IGF-I) levels remained within inclusion criteria at the end of treatment in both trials. Of 110 patients entering the fixed-dose phase in CH-ACM-01, 80% maintained or improved acromegaly symptoms from baseline to the end of treatment. Over 85% of patients in both trials elected to continue into the extension phases. OOC were found to be well tolerated across both trials, and no dose-related adverse events were observed. CONCLUSIONS: OOC demonstrated remarkably consistent results for biochemical response, durability of response, and preference to continue with oral treatment across these 2 complementary landmark phase 3 trials, despite differences in the design of each. Trial registration NCT03252353 (August 2017), NCT01412424 (August 2011).

Intraoperative indocyanine green videoangiography for identification of pituitary adenomas using a microscopic transsphenoidal approach.

PURPOSE: Initial successful surgical treatment of pituitary adenomas is crucial to reach long-term remission. Indocyanine green (ICG) videoangiography (VA) is well established in vascular neurosurgery nowadays and several reports described ICG application in brain tumor surgery. We designed this study to evaluate the feasibility of intravenous application of ICG and visualisation of a pituitary lesion via the fluorescence mode of the operation microscope. METHODS: 22 patients with pituitary adenomas were treated with transsphenoidal microsurgery and were included in this study. Intraoperatively 25 mg ICG was administered intravenously and visualized via the fluorescence mode of the operation microscope (Pentero/Zeiss). RESULTS: 22 patients qualified for transsphenoidal surgery presenting with different clinical symptoms (13 patients with acromegaly, 6 with M. Cushing and 3 with other symptoms like vision disorder or dizziness) and identification of a pituitary lesion (21 of 22 patients) in preoperative MR-imaging (mean diameter: 9 mm; SD 3.6; 6 macroadenomas, 15 microadenomas, 1 MR-negative). In all 22 patients ICG VA was performed during surgery. No technical failures or adverse events after drug administration occurred. Visualization was optimal approximately 2.4 min after intravenous application. In all patients the adenoma could be detected via two different types of visualization: direct visualization by fluorophore emission versus indirect detection of the adenoma by a lower ICG fluorescence compared to the surrounding tissue. CONCLUSION: Our data show that intraoperative ICG VA can be a useful and easily applicable additional diagnostic tool for visualization of pituitary lesions using the microscopic approach.

A consensus on the diagnosis and treatment of acromegaly complications.

In March 2011, the Acromegaly Consensus Group met to revise and update the guidelines on the diagnosis and treatment of acromegaly complications. The meeting was sponsored by the Pituitary Society and the European Neuroendocrinology Association and included experts skilled in the management of acromegaly. Complications considered included cardiovascular, endocrine and metabolic, sleep apnea, bone diseases, and mortality. Outcomes in selected, related clinical conditions were also considered, and included pregnancy, familial acromegaly and invasive macroadenomas. The need for a new disease staging model was considered, and design of such a tool was proposed.

Use of a GH receptor antagonist (GHRA) to explore the relationship between GH and IGF-I in adults with severe GH deficiency (GHD).

OBJECTIVE: At diagnosis, approximately 50% of adults with severe GH deficiency (GHD) have an IGF-I within the reference range. It is unclear whether in such patients serum IGF-I levels are regulated by factors other than GH. DESIGN AND PATIENTS: We performed a double-blind, randomized, placebo-controlled, cross-over study to investigate the effect of the GH receptor antagonist - pegvisomant (20 mg daily for 14 days) on GH and IGF-I levels in three cohorts: patients with GHD and a normal IGF-I (NORMS); patients with GHD and a low IGF-I (LOWS) and healthy volunteers (CONS). RESULTS: Pegvisomant decreased IGF-I in CONS and NORMS [158.5 (101-206) vs. 103 (77-125) microg/l, P < 0.01; 124 (81-136) vs. 95 (51-113) microg/l, P < 0.01 respectively], but not in LOWS [31 (< 31-32) vs. 34.5 (< 31-38) microg/l], and this was associated with an increase in mean 24 h GH in CONS [0.49 (0.12-0.89) to 1.38 (0.22-2.45) microg/l (P = 0.03)] and in NORMS [69 (0-320)% from 0.1 (< 0.1-0.13) to 0.17 (0.11-0.42) microg/l (P = 0.03)], but not in the LOWS. The peak GH response to arginine was increased by pegvisomant in CONS and NORMS [6.1 (0.8-9) vs. 20.4 (13.1-28.8) microg/l, P = 0.03; 0.4 (0.1-0.5) vs. 0.5 (0.3-0.6) microg/l, respectively], but not in LOWS. CONCLUSIONS: These data indicate that patients with severe GHD with a normal IGF-I are able to increase GH secretion in response to a pegvisomant-induced fall in IGF-I, whereas those with low IGF-I levels are unable to increase GH secretion. Therefore circulating IGF-I appears to be GH-independent in GHD patients with a low IGF-I, but remains partially GH-dependent in GHD patients with a normal IGF-I.

Sex-specific regulation of ENaC and androgen receptor in female rat kidney.

With the beginning of puberty blood pressure increases and is persistently higher in men than in premenopausal women. Sex steroids are known to have complex effects on the renal and cardiovascular system and are involved in blood pressure regulation. The epithelial sodium channel (ENaC) modulates sodium reabsorption in the kidney, but little is known about sex-specific regulation of ENaC subunit expression. Regulation of the androgen receptor (AR) is known to be tissue-specific and age-dependent, but not well studied in the kidney. We investigated the effects of sex steroids on ENaC subunits and renal AR expression in an in vivo rat model. Ovariectomized female Wistar rats were treated with placebo, testosterone, 5 alpha-dihydrotestosterone (DHT) or 17 beta-estradiol (E2) for 14 days, and quantitative PCR and Western immunoblots were performed. DHT significantly decreased expression of all ENaC subunits in female rats, whereas testosterone showed only a trend to lower ENaC expression. These results are in contrast to previous studies where stimulating effects of androgens on the alpha-subunit of ENaC were seen. AR mRNA expression showed a trend to lower levels in females after testosterone treatment in this study. However, estrogen treatment significantly downregulated AR mRNA expression. In male control animals we were able to show a significantly increased expression of AR mRNA upon testosterone treatment. Our data demonstrate that AR and ENaC are regulated by sex steroids. That way sex steroids might modulate renal sodium reabsorption and therefore provide a possible explanation for sex differences in blood pressure.

Treatment of acromegaly with the GH receptor antagonist pegvisomant in clinical practice: safety and efficacy evaluation from the German Pegvisomant Observational Study.

OBJECTIVE: The GH receptor antagonist pegvisomant is a highly effective new treatment option in acromegaly. The German Pegvisomant Observational Study (GPOS) was started to monitor long-term safety and efficacy of pegvisomant as prescribed in clinical practice. DESIGN: GPOS is an observational, multi-center, surveillance study, which comprises non-interventional data collection. METHODS: Of the 229 patients included in the study, 90.4% had previous pituitary surgery, 43.2% were treated by radiation therapy, and 94.3% had previous medical therapy for acromegaly that had been discontinued mainly due to persistent IGF-I elevation or side effects. The intention-to-treat population included 177 patients with at least one post-baseline efficacy measurement. RESULTS: IGF-I levels decreased from 1.75+/-0.91-fold the upper limit of normal at baseline to 1.05+/- 0.62 at the 6-month visit, 0.96+/-0.60 at the 12-month visit, and to 0.89+/-0.41-fold after 24 months (P<0.0001). Mean duration of pegvisomant therapy was 51.8+/-35.8 weeks (median=51.9 weeks). IGF-I was normalized in 64.4% at 6 months with a median dose of 15.0 mg/day, in 70.9% at 12 months, and in 76.3% at 24 months. Fasting glucose levels improved from 114.4+/-45.9 to 101.5+/- 42.8 mg/dl after 6 months (P<0.01) and to 100.6+/-33.2 mg/ml after 12 months (P<0.01). General physical condition measured by specific signs and symptoms score improved significantly. Adverse events occurring in >1% were injection site reactions in 7.4%, elevated liver enzymes (>3 times of normal) in 5.2% (3.1% spontaneously normalized during continued treatment), reported increase of pituitary tumor volume in 5.2% (which was verified in 3.1%), and headache in 1.7%. CONCLUSIONS: Pegvisomant is generally well tolerated with a safety profile similar to that reported in clinical trials and can effectively reduce IGF-I in patients with acromegaly refractory to conventional therapy.

Pegvisomant treatment in gigantism caused by a growth hormone-secreting giant pituitary adenoma.

BACKGROUND: Gigantism is rare with the majority of cases caused by a growth hormone (GH)-secreting pituitary adenoma. Treatment options for GH-secreting pituitary adenomas have been widened with the availability of long-acting dopamine agonists, depot preparations of somatostatin analogues, and recently the GH receptor antagonist pegvisomant. CASE REPORT: A 23-year-old male patient presented with continuous increase in height during the past 6 years due to a GH-secreting giant pituitary adenoma. Because of major intracranial extension and failure of octreotide treatment to shrink the tumour, the tumour was partially resected by a trans-frontal surgical approach. At immunohistochemistry, the tumour showed a marked expression of GH and a sparsely focal expression of prolactin. Somatostatin receptors (sst) 1-5 were not detected. Tumour tissue weakly expressed dopamine receptor type 2. The Gs alpha subunit was intact. Conversion from somatostatin analogue to pegvisomant normalized insulin-like-growth-factor-I (IGF-I) levels and markedly improved glucose tolerance. CONCLUSION: Pegvisomant is a potent treatment option in patients with pituitary gigantism. In patients who do not respond to somatostatin analogues, knowledge of the SST receptor status may shorten the time to initiation of pegvisomant treatment.

Elevated transaminases during medical treatment of acromegaly: a review of the German pegvisomant surveillance experience and a report of a patient with histologically proven chronic mild active hepatitis.

OBJECTIVE: The new GH receptor antagonist pegvisomant is the most effective medical therapy to normalize IGF-I levels in patients with acromegaly. Based on currently available data pegvisomant is well tolerated; however, treatment-induced elevation of transaminases has been reported and led to the necessity for drug discontinuation in some patients in the pivotal studies. The aim of this study was to evaluate and characterize the prevalence of elevated transaminases and to describe in detail the findings in a single case who required drug discontinuation because of elevation of transaminases which emerged during treatment and who underwent liver biopsy. DESIGN AND METHODS: Retrospective safety analyses were carried out on 142 patients with acromegaly receiving pegvisomant treatment in Germany between March 2003 and the end of 2004. Of these patients, 123 were documented in a post-marketing surveillance study, one case of elevated transaminases was reported spontaneously and the other patients were treated in a clinical study. RESULTS: Mean treatment duration with pegvisomant in the ongoing observational study at the end of 2004 was 28.3 +/- 19.9 (S.D.) weeks. Twelve out of the 142 patients had elevated transaminases above three times the upper limit of normal, likely caused by biliary obstruction in five of the patients. All patients but one affected by elevated transaminases had been previously treated with somatostatin analogues. In six out of 142 (4%) of patients, pegvisomant was permanently withdrawn because of elevated transaminases. The same number of patients showed a transient increase of transaminases with either spontaneous remission without dose modification (n = 4) or no re-increase of transaminases after temporary discontinuation and re-exposure (n = 2). The liver biopsy of one patient who was permanently withdrawn showed a chronic mild hepatitis with a mixed portal inflammation including eosinophilic granulocytes. CONCLUSIONS: Liver function tests should be regularly followed on pegvisomant treatment. Biliary complications, which may arise from restitution of normal gall bladder motility after cessation of somatostatin analogue treatment, need to be differentiated from pegvisomant-induced abnormalities. The histological pattern of the liver biopsy performed in one of the patients showed a mild chronic active hepatitis. The lack of dose dependency and rather low frequency of elevated transaminases in those cases where a biliary disorder was excluded render this reaction an idiosyncratic drug toxicity.

Postoperative evaluation of patients with acromegaly: clinical significance and timing of oral glucose tolerance testing and measurement of (free) insulin-like growth factor I, acid-labile subunit, and growth hormone-binding protein levels.

CONTEXT: It is not exactly known when patients with acromegaly should be evaluated for cure after transsphenoidal adenomectomy (TA). OBJECTIVE: The objective of this study was to define the optimal time point of postoperative evaluation by serial measurements of glucose-suppressed GH levels [oral glucose tolerance test (OGTT)] and the GH-dependent parameters IGF-I, free IGF-I, acid labile subunit (ALS), and GH-binding protein (GHBP). DESIGN: We describe a prospective study with 1-yr follow-up. SETTING: The study was conducted at a university hospital. PATIENTS: Seventeen patients with acromegaly were included in the study. MAIN OUTCOME MEASURES: The main outcome measures were OGTT results at 1, 2, 3, 8, and 12 wk after TA; weekly measured GH, (free) IGF-I, ALS, and GHBP levels up to 12 wk; and total IGF-I levels measured at 52 wk. RESULTS: Postoperatively, nine patients were in remission with an OGTT GH nadir of less than 0.5 microg/liter and normalized IGF-I levels, whereas eight patients had persistent acromegaly. In both cured and noncured patients, OGTT results at 1 wk after TA were highly reproducible over time. In contrast, early postoperative IGF-I levels fluctuated and only stabilized at 12 wk. In all cured patients, free IGF-I levels rapidly normalized within 2 wk after TA (specificity, 100%). Preoperative ALS levels were elevated in all patients and normalized only in the cured patients after TA (specificity, 89%). Preoperative GHBP levels were low and increased from 2 wk after surgery. CONCLUSIONS: We show that in the postoperative evaluation of patients with acromegaly, already 1 wk after surgery, an OGTT using 0.5 microg as the GH nadir cutoff value has a high predictive value for cure, whereas early IGF-I levels show varying patterns toward stabilization. Therefore, IGF-I should be measured as a predictive parameter not within 3 months after surgery. Free IGF-I and ALS levels may have an additional value in the postoperative assessment of disease activity.

Deficient insulin-like growth factor I in chronic heart failure predicts altered body composition, anabolic deficiency, cytokine and neurohormonal activation.

BACKGROUND: Recent studies of growth hormone supplementation in chronic heart failure have been associated with variable results. Acquired abnormalities of biochemical parameters of the growth hormone insulin-like growth factor I axis have been associated with severe chronic heart failure. There are suggestions of an acquired growth hormone resistance with deficient insulin-like growth factor I in some patients. OBJECTIVES: Therefore, we set out to investigate the clinical and functional status and the degree of cytokine and neurohormonal alteration of chronic heart failure patients with deficient insulin-like growth factor I responses. METHODS: Patients with chronic heart failure were divided into two groups according to their insulin-like growth factor I levels (classified according to the manufacturer's assay range in normal controls): low insulin-like growth factor I <104 (n = 20; 89 +/- 9.6 ng/ml), and normal/high >104 ng/ml (n = 32; 169 +/- 52 ng/ml). Between groups there was no difference in age (low versus high: 65.3 +/- 12.1 versus 61.6 +/- 9.1 years, p = 0.21), body mass index, aerobic capacity (peak oxygen consumption: low versus high: 15.5 +/- 5.2 versus 17.3 +/- 6.3 mL/kg/min, p = 0.23), left ventricular ejection fraction, New York Heart Association classification. RESULTS: During quadriceps strength testing, patients with low insulin-like growth factor I had reduced absolute strength (-24%), and strength per unit area muscle (- 14%) than patients with normal/high insulin-like growth factor I. Leg muscle cross-sectional area was lower in the low insulin-like growth factor I group (-12% and -13% for right and left legs, respectively). These alterations were accompanied by increased levels of growth hormone (+145%), tumor necrosis factor-alpha (+46%), cortisol/ dehydroepiandrosterone ratio (+60%), noradrenaline (+49%) and adrenaline (+136%) (all at least p < 0.05). CONCLUSIONS: Patients with low insulin-like growth factor I levels show signs of altered body composition, cytokine and neuroendocrine activation, to a greater extent than patients with normal/high levels.

Acquired growth hormone resistance in patients with chronic heart failure: implications for therapy with growth hormone.

OBJECTIVES: We aimed to determine whether growth hormone (GH) resistance is present in patients with chronic heart failure (CHF) and whether it may be linked to the biochemical response to GH treatment. BACKGROUND: Acquired GH resistance is a feature of severe illness, in particular, cachexia. In patients with CHF, the response to GH therapy appears to be variable. METHODS: Biochemical markers of the GH-insulin-like growth factor-I (IGF-I) axis were compared in 21 cachectic patients with CHF, 51 noncachectic patients and 26 healthy control subjects. In separate studies, the predictive value of baseline biochemical variables for the IGF-I response to GH treatment was analyzed. RESULTS: Cachectic patients showed an increase of total GH and immunologically intact GH (p < or = 0.0002) and a decrease of GH-binding protein (BP) (p = 0.005), IGF-BP3 (p = 0.01) and IGF-I (p = 0.06), compared with noncachectic patients. Similar changes were found when the cachectic group was compared with the control group. No differences were found between noncachectic patients and control subjects. Levels of GH-BP correlated with the IGF-I/GH ratio in all subgroups (all p < or = 0.002). Baseline GH-BP levels were related to the increase of IGF-I levels in response to GH treatment in patients with CHF after 24 h (r = 0.83, p = 0.005; n = 9; study 2), 44 days (r = 0.52, p = 0.007; n = 25; study 3) and 96 days (r = 0.54, p = 0.006; n = 24; study 3). CONCLUSIONS: Most cachectic and some noncachectic patients with CHF show features of acquired GH resistance. The principal predictors of the biochemical features of GH resistance and of the poor biochemical response to short-term and longer-term GH treatment are GH-BP plasma levels. The presence of GH resistance is potentially a major factor determining the response to GH therapy in patients with CHF.

Circulating insulin-like growth factor binding protein-3 predicts one-year outcome after ischemic stroke.

BACKGROUND: Insulin-like Growth Factor-1 (IGF-1) and Insulin-like Growth Factor Binding Protein-3 (IGFBP-3) have been ascribed neuroprotective effects. We sought to determine whether levels of IGF-1 and IGFBP-3 predict functional outcome after ischemic stroke. METHODS: IGF-1 and IGFBP-3 levels were measured in the first week after stroke in patients with first ischemic stroke who were enrolled in the Berlin Cream&Sugar Study. National Institutes of Health Stroke Scale (NIHSS) was collected at admission. Lesion volume was determined from acute MRI if available. Functional outcome according to the modified Rankin Scale (mRS) was assessed after one year. In multivariate analyses we identified parameters associated with unfavourable functional outcome (mRS>2). RESULTS: We included 100 patients. 21 patients had an unfavourable functional outcome. IGF-1 levels were<- 2 standard deviation score (SDS) in 7 patients, and>2 SDS in 12 patients. IGFBP-3 levels werethe 95(th) percentile. Low levels of IGFBP-3 (p=0.002), NIHSS at admission (p=0.043) and age (p=0.001) were associated with unfavourable functional outcome in the univariate analyses. In multivariate analysis including IGFBP-3, IGF-1, age, thrombolysis and NIHSS only low IGFBP-3 levels (OR 7.2, 95%CI 1.8-29.0, p=0.006) were associated with unfavourable functional outcome. If lesion volume was incuded (n=71), only IGFBP-3 levels (OR 7.2, 95%CI 1.5-35.5, p=0.015) were associated with unfavourable functional outcome. CONCLUSION: IGFBP-3 levels after ischemic stroke may independently predict functional outcome after one year.

Systemic regulation of distraction osteogenesis: a cascade of biochemical factors.

This study investigates the systemic biochemical regulation of fracture healing in distraction osteogenesis compared with rigid osteotomy in a prospective in vivo study in humans. To further clarify the influence of mechanical strain on the regulation of bone formation, bone growth factors (insulin-like growth factor [IGF] I, IGF binding protein [IGFBP] 3, transforming growth factor [TGF] beta1, and basic FGF [bFGF]), bone matrix degrading enzymes (matrix-metalloproteinases [MMPs] 1, 2, and 3), human growth hormone (hGH), and bone formation markers (ALP, bone-specific ALP [BAP], and osteocalcin [OC]) have been analyzed in serum samples from 10 patients in each group pre- and postoperatively. In the distraction group, a significant postoperative increase in MMP-1, bFGF, ALP, and BAP could be observed during the lengthening and the consolidation period when compared with the baseline levels. Osteotomy fracture healing without the traction stimulus failed to induce a corresponding increase in these factors. In addition, comparison of both groups revealed a significantly higher increase in TGF-beta1, IGF-I, IGFBP-3, and hGH in the lengthening group during the distraction period, indicating key regulatory functions in mechanotransduction. The time courses of changes in MMP-1, bone growth factors (TGF-beta1 and bFGF), and hGH, respectively, correlated significantly during the lengthening phase, indicating common regulatory pathways for these factors in distraction osteogenesis. Significant correlation between the osteoblastic marker BAP, TGF-beta1, and bFGF suggests strain-activated osteoblastic cells as a major source of systemically increased bone growth factors during callus distraction. The systemic increase in bFGF and MMP-1 might reflect an increased local stimulation of angiogenesis during distraction osteogenesis.

The antigenic epitopes of human grown hormone as mapped by monoclonal antibodies.

The antigenic epitopes of human GH (hGH) have been investigated using monoclonal antibodies (Mabs) to hGH. A panel of 12 Mabs was incorporated into two-site binding assays in order to investigate the antigenic surface of hGH. Nine reaction patterns were observed. The Mabs were further characterized in terms of their cross-reactivity with human placental lactogen, human PRL, with recombinant hGH molecules (MetLeu8hGH, Met14hGH), and with fragments derived from enzymatic or chemical digestion of hGH. These studies provided information on the antigenic sites that are shared with human placental lactogen and on the N-terminal and C-terminal regions of the hGH molecule. Based upon these findings, we tentatively suggest the epitope model for hGH comprising at least 10 antigenic sites (epitopes) which may be grouped into five antigenic regions.

Insulin-like growth factor I is an independent coregulatory modulator of natural killer (NK) cell activity.

We aimed to investigate the natural killer (NK) cell activity in hGH-deficient adults and to analyze the effect of insulin-like growth factor (IGF)-I in vivo and in vitro on NK cell activity. NK cell activity was measured in a 4-h nonisotopic assay with europium-labeled and cryopreserved K-562 cells. NK-cell numbers were measured after incubation with murine monoclonal CD3 and CD16 antibodies by flow cytometry analysis. In a cross-sectional study, the basal and interferon-beta (IFN-beta) stimulated (1000 IU/ml) NK cell activity of 15 hGH-deficient patients and 15 age- and sex-matched controls was measured. The percentages and absolute numbers of CD3-/16+ NK-cells were not significantly different in the patient vs. control group. The basal and IFN-beta stimulated NK cell activity however was significantly decreased in the patient vs. control group at all effector/target (E/T) cell ratios from 12.5-100 (e.g. 17 +/- 3 vs. 28 +/- 3% lysis without IFN-beta, P < 0.05, and 42 +/- 4 vs. 57 +/- 4% lysis with IFN-beta, P < 0.05; both at E/T 50). IGF-I levels of patients and controls showed a significant positive correlation with NK cell activity (r = 0.37; P < 0.05). In an IGF-I in vitro study (IGF-I in vitro 250-1250 microg/L), the basal and IFN-beta stimulated NK cell activity of 13 hGH-deficient patients and of 18 normal subjects was significantly enhanced by IGF-I in vitro (e.g. GH-deficient patients: 9 +/- 2 vs. 10 +/- 2% lysis without IFN-beta, P < 0.05 and 25 +/- 4 vs. 30 +/- 4% lysis with IFN-beta, P < 0.005; and normal subjects: 15 +/- 3 vs. 23 +/- 3% lysis without IFN-beta, P < 0.001 and 35 +/- 4 vs. 44 +/- 5% lysis with IFN-beta, P < 0.001; both at IGF-I 500 microg/L). In summary, in our cross-sectional study, adult GH-deficient patients showed a significantly lower basal and IFN-beta stimulated NK cell activity than matched controls, despite equal NK cell numbers. IGF-I levels of patients and controls showed a weak positive correlation with NK cell activity. In an in vitro study, IGF-I significantly enhanced basal and IFN-beta stimulated NK cell activity of hGH-deficient patients and also of normal subjects. The decreased NK cell activity in GH-deficient patients may be caused at least in part by low serum IGF-I levels. IGF-I appears to be an independent coregulatory modulator of NK cell activity.

Generation of human soluble leptin receptor by proteolytic cleavage of membrane-anchored receptors.

The leptin receptor (ObR) exists in multiple isoforms. In rodents, a soluble isoform is generated by alternative splicing; but in humans, there is no mRNA encoding soluble receptor (leptin binding protein). We investigated the hypothesis that human leptin binding protein can be generated by proteolytic cleavage of membrane-anchored leptin receptors (ObRb and ObRa). Leptin binding protein of similar size to that previously detected in human serum was detected by HPLC in medium of cells transfected with ObRa. ObRa exhibited higher expression at the cell surface than ObRb and generated greater levels of leptin binding protein. Ligand-mediated immunofunctional and immunofluorometric assays revealed that the leptin binding protein in medium bound both leptin and an ObR-specific antibody and that the level of leptin binding protein correlated with receptor expression at the cell surface. Phorbol 12-myristate-13-acetate and N-ethylmaleimide increased the accumulation of leptin binding protein, an indication that the production of leptin binding protein was up-regulated by PKC and sulfhydryl group activation. The protease inhibitors, TNFalpha protease inhibitor 1 and Immunex compound 2, could inhibit the production of leptin binding protein, indicating that the enzyme responsible for leptin binding protein cleavage belongs to the metalloprotease family. In conclusion, human leptin binding protein is generated by proteolytic cleavage of membrane-anchored leptin receptor by a metalloprotease.

Growth hormone and its receptor are expressed in human thymic cells.

GH has been shown to modulate various functions of the thymus. We now demonstrate the production of human GH (hGH) by human thymic cells, and the expression of GH receptors in thymic epithelial cells (TEC) and in thymocytes at different stages of differentiation. The presence of hGH messenger RNA was shown by RT-PCR in both human thymocytes and in primary cultures of TEC. Moreover, immunoreactive hGH material was detected in culture media of thymocytes and TEC with the use of a sensitive immunoradiometric assay. GH receptor gene expression was shown in TEC in primary cultures and in fetal and postnatal TEC lines as well as in thymocytes. By immunocytochemistry, the presence of GH receptors in the various TEC preparations was confirmed. In cytofluorometric studies with the use of a biotinylated anti-GH receptor monoclonal antibody, we could show that GH receptors are predominantly expressed by immature thymocytes: over 90% of CD3- CD4- CD8- CD19- CD34+ CD2- cells (a phenotype characterizing the most immature T cell progenitors in the thymus) were GH receptor positive. Our results provide a molecular basis for an autocrine/paracrine mode of action of GH in the human thymus.

Immunofunctional assay of human growth hormone (hGH) in serum: a possible consensus for quantitative hGH measurement.

Confirmation of the diagnosis of GH deficiency in adults and children involves provocative testing for human (h) GH. Different commercially available immunoassays yield largely discrepant results in the measurement of GH levels in human serum. These discrepancies result in doubtful relevance of cut-off levels proposed for GH provocative testing. We have developed an immunofunctional assay method that allows quantitation of only those GH forms in circulation that possess both binding sites of the hormone for its receptor and thus can initiate a biological signal in target cells. An anti-hGH monoclonal antibody recognizing binding site 2 of hGH is immobilized and used to capture hGH from the serum sample. Biotin-labeled recombinant GH-binding protein in a second incubation step forms a complex with those hGH molecular isoforms that have both binding sites for the receptor. The signal is detected after a short third incubation step with labeled streptavidin. The assay is sensitive (detection range, 0.1-100 micrograms/L) and has average inter- and intraassay precisions of 10.3% and 7.3% respectively. Endogenous GH-binding protein does not interfere with the hGH result; placental lactogen slows no detectable cross-reaction in this immunofunctional assay. The degree of immunofunctionally active hGH forms in serum samples, calculated by comparison of immunofunctional assay and RIA results, varied between 52-93%. We propose this immunofunctional assay for GH measurement as a new reference method for hGH quantitation in serum. The immunofunction assay translates only hGH forms into an assay signal that are capable of dimerizing GH receptors and, thus, of initiating a biological effect in target cells.