[The role of somatostatin on the cellular level].
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Adenylyl Cyclases↗
Biomedical subjects
F Raue
Publications and source records attributed to F Raue.
[Parathyroid hormone-related protein. A new calcium regulating hormone and its significance in tumor-associated hypercalcemia].
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Biomarkers, Tumor↗
[Diagnostic significance of parathyroid hormone-related protein in tumor patients with hypercalcemia].
The clinical utility of measuring parathormone-related protein (PTHrP) was investigated in 94 patients (48 men, 46 women, mean age 56 [18-82] years) with tumour-associated hypercalcaemia, using a radioimmunoassay directed against the middle portion (53-84) of PTHrP (reference range < 5-21 pmol/l). Increased levels of the middle portion of PTHrP were found in 44 of the 73 patients (60%) with hypercalcaemia associated with solid tumours (median 49 [22-333] pmol/l). There was a positive correlation between the serum calcium concentration and the PTHrP (P = 0.018). The frequency of a raised PTHrP, indicating hormone-induced hypercalcaemia, was similar in patients with and without bone metastases (48% vs 66%). Elevated PTHrP was particularly frequent in patients with squamous cell carcinomas (17 out of 21; 81%), while PTHrP levels were normal in 18 out of the 21 patients with hypercalcaemia associated with haematological malignancies. PTHrP levels were normal in 37 out of 38 normocalcaemic tumour patients and in 30 out of 32 patients with primary hyperparathyroidism. Hypercalcaemia associated with benign disease was found in only one case, a female with marked benign breast hypertrophy.--The measurement of PTHrP allows the demonstration of a pathogenetic factor in tumour-associated hypercalcaemia, and differentiation from other causes of hypercalcaemia, in particular primary hyperparathyroidism.
Adolescent↗
[The prognostic importance of calcitonin screening in familial medullary thyroid carcinoma].
In 34 of 139 patients (63 men, 76 women, mean age 41.2 +/- 15.6 years) with medullary thyroid carcinoma (MTC) the disease was of the familial variety. 13 of the 34 cases were discovered in the preclinical stage by screening (calcitonin stimulation with pentagastrin). This group was on average younger (16.8 +/- 10.7 years) than the 21 clinically manifest patients with MTC (28.0 +/- 11.9 years) or the 105 patients with sporadic MTC (45.7 +/- 13.6 years). The patients diagnosed through the screening programme had a more favourable tumour stage (12 in stage I or II) and were thus more likely to be cured. Their survival rate was higher (100% at both 5 and 10 years) than the survival rate of the patients with clinically manifest tumour (94 and 87%, respectively). But the group with manifest familial MTC did not differ from those with sporadic occurrence as regards the tumour stage (predominantly advanced stages), limited chance of cure and survival rate (5 years: 94%, 10 years: 81%). These data show that screening of family members decisively improves the prognosis of MTC of the familial variety.
Adult↗
Development and validation of an assay to measure bioactivity of human calcitonin in vitro using T47D cell membranes.
We have developed a "test-tube" assay to determine the biological activity of synthetic preparations of human calcitonin (hCT). The method is based on the dose-dependent accumulation of cyclic AMP in cell membrane preparations on stimulation with CT. As an unlimited cell source, we used the clonal cell line T47D, which possesses functional CT receptor-adenylate cyclase complexes. Half-maximal stimulation was achieved with 40-200 nmol/liter hCT. The method was able to precisely quantify the relative potencies of various hCT preparations. The intraassay and interassay coefficients of variation were 3.0 and 5.6%, respectively. The analytical performance, as estimated by additional recovery and specificity studies, was better than or comparable to the established in vivo rat hypocalcemia assay. Results obtained with these two methods were closely correlated (r = 0.83, P < 0.01). However, the in vitro membrane system allowed a higher throughput of samples, less preparation time, and better standardization and transportability of the assay, as large-scale membrane preparations were stable for at least 12 months in liquid nitrogen. This new in vitro membrane bioassay provides a convenient alternative to the currently performed in vivo rat hypocalcemia bioassays.
Animals↗
Prognostic factors in medullary thyroid carcinoma: evaluation of 741 patients from the German Medullary Thyroid Carcinoma Register.
A retrospective study of 741 patients with medullary thyroid carcinoma diagnosed between 1967 and 1991 was carried out by members of the German Medullary Thyroid Carcinoma Study Group to evaluate prognostic factors. A total of 559 patients (75%) were considered to have sporadic disease, and 182 (25%) had the familial type. The sex ratio (male to female) was 1:1.4 in sporadic disease patients, and the mean age at diagnosis was 45.9 years (range 5-81 years). For familial disease patients the sex ratio was 1:1.1, and the mean age at diagnosis was 33.4 (range 5-77 years). The follow-up time for 630 patients ranged from 1 month to 20.8 years (mean 13.0 years). The overall adjusted survival rate was 86.7% at 5 years and 64.2% at 10 years. In a univariate analysis the stage of disease at diagnosis, age, sex, and type of disease (sporadic, familial) were relevant prognostic factors, with a better prognosis for young female patients with familial disease and diagnosed at an early stage. In a multivariate proportional hazards analysis, the difference in the survival rate of patients with familial disease versus those with the sporadic form disappeared, while prognostic information provided by age and sex was still significant. The poorer prognosis of patients with sporadic medullary thyroid carcinoma may be related to the patients' older age at detection and more advanced tumor stage at diagnosis. There seems to be no difference in biological behavior between tumors of the sporadic and those of the familial type.
Adolescent↗
Levels of parathyroid hormone-related protein in hypercalcemia of malignancy: comparison of midregional radioimmunoassay and two-site immunoradiometric assay.
Overproduction of parathyroid hormone-related protein (PTHrP) is a major cause of hypercalcemia of malignancy in patients with solid tumors. We measured plasma levels of the protein by a radioimmunoassay (RIA) against PTHrP(53-84) and by an immunoradiometric assay (IRMA) against PTHrP (1-86). Of 16 affected patients 7 had elevated PTHrP levels in both assays and 4 had elevated levels in the RIA only. Median levels were about tenfold higher in these patients when measured by RIA (median of 34 versus 2.2 pmol/l). Measurements from both assays were, however, highly correlated with each other in this patient group (P < 0.01). PTHrP was not elevated in 10 normocalcemic patients with lung carcinoma. During long-term follow-up of a patient with a mesothelioma of the pleura, PTHrP levels measured with both assays decreased during chemotherapy in parallel with a normalization of serum calcium. In another hypercalcemic patient suffering from renal carcinoma, PTHrP measured by IRMA decreased by 40% within 12 h after nephrectomy, whereas PTHrP measured by RIA did not show a significant decline. Direct comparison of the assay results thus pointed to the existence of heterogeneity of circulating forms of PTHrP in plasma. In conclusion, both immunoassays detected elevated levels of PTHrP in a fraction of patients with hypercalcemia of malignancy and thus may be a tumor marker during treatment of malignancies.
Adult↗
Formation of neutralizing antibodies after treatment with human calcitonin.
PURPOSE: Calcitonin is used for the treatment of Paget's disease of bone, hypercalcemia, and postmenopausal osteoporosis. The formation of antibodies against heterologous calcitonins, such as salmon calcitonin (sCT), has been described frequently. Neutralizing effects of these antibodies have been demonstrated in many cases. As far as antibody formation against human calcitonin (hCT) is concerned, only a single case has been reported in the literature; however, investigations concerning the biologic activity of the antibodies were not performed. We have now assessed the sera of 33 patients treated with hCT for postmenopausal osteoporosis for a period of at least 12 months to evaluate the occurrence of hCT-binding and hCT-neutralizing antibodies. PATIENTS AND METHODS: Binding antibodies were detected by incubation of patient sera with 125I-labeled hCT; neutralizing activity was assessed in an in vitro bioassay that measured the impairment of the hCT-induced cyclic adenosine monophosphate (cAMP) formation in the human breast cancer cell line T47D. RESULTS: Prior to hCT treatment, none of the patients showed evidence of the presence of either binding or neutralizing antibodies. During the course of treatment, binding antibodies occurred in a single patient. These antibodies had a neutralizing activity characterized by 15% impairment of cAMP formation after 6 months and 27% impairment after 12 months of treatment compared with pretreatment control values. The neutralizing effect observed in this particular patient was comparatively mild compared with the effects seen after the formation of neutralizing antibodies against sCT, so major clinical sequelae were not expected in this patient. This may be due to the lower antigenicity of hCT as compared with sCT. CONCLUSION: Although antibody formation against hCT is a rare phenomenon, we nonetheless recommend monitoring of postmenopausal osteoporosis patients treated with sCT or hCT for neutralizing antibody formation in order to evaluate the therapeutic effect of treatment.
Aged↗
Cyclic AMP formation in rat bone and kidney cells is stimulated equally by parathyroid hormone-related protein (PTHrP) 1-34 and PTH 1-34.
Parathyroid hormone-related protein (PTHrP) plays a major role in the pathogenesis of humoral hypercalcemia of malignancy. It interacts with the PTH receptor and has therefore a nearly identical effect on bone cells as PTH. However, PTHrP is thought to be less potent than PTH in stimulating adenylate cyclase in canine renal membranes, leading to the hypothesis of a differential efficiency in signal transduction by PTHrP with respect to bone vs kidney. In a homologous model with intact osteoblast-like cells (UMR 106) and primary kidney cells, both from the rat, we have tested N-terminal peptide fragments, based on the rat amino acid sequence 1-34, of PTH and PTHrP. Compared with PTHrP(1-34), rat PTH(1-34) had a similar relative potency in bone cells (85%) and in kidney cells (140%) in its ability to stimulate adenylate cyclase. Human PTH(1-34) was 5.6- to 6.5-fold less potent than rat PTH(1-34) in both cell types. In human osteoblast-like cells (SaOS-2), rat and human PTH were essentially equally potent compared to PTHrP(1-34) (identical sequence in rat and human) in stimulating cAMP accumulation. In conclusion, our study revealed the equipotency of rat PTH(1-34) and PTHrP(1-34) in stimulating intracellular cAMP formation in a homologous system of rat bone and kidney cells. There seemed to be no unique signal transduction mechanism of PTHrP to the adenylate cyclase in rat kidney cells compared with bone cells.
Adenylyl Cyclases↗
Levels of parathyroid hormone-related protein (PTHrP) in hypercalcemia of malignancy are not lowered by treatment with the bisphosphonate BM 21.0955.
Parathyroid hormone-related protein (PTHrP) is a major cause of hypercalcemia in malignancy and serum levels are elevated in many patients suffering from this syndrome. In 10 patients with hypercalcemia of malignancy the levels of the midregional fragment of PTHrP in serum were determined by radioimmunoassay over 7 days during a calcium-lowering treatment with a single dose of the bisphosphonate BM 21.0955. PTHrP concentrations remained unchanged 6 days after administration of the drug as compared with pretherapeutic values, thus apparently excluding an effect of either the drug itself or the rapid fall in serum calcium on the release of PTHrP by the tumors or on its clearance from the circulation. In the patients with elevated midregional PTHrP levels (n = 6), the calcium-lowering effect of the drug was significantly less pronounced than in patients with normal PTHrP (n = 4) (mean serum calcium of 2.89 vs. 2.51 mmol/l at day 6), despite similar pretherapeutic concentrations. Of the six patients with elevated PTHrP, five were still hypercalcemic, whereas in the group with normal PTHrP one out of four patients remained hypercalcemic. In conclusion, PTHrP levels in hypercalcemia of malignancy remained unchanged after calcium-lowering therapy with bisphosphonates. High serum PTHrP levels were, however, predictive of a lesser effectiveness of the drug in lowering serum calcium.
Adult↗
Diminished calcitonin secretion after ovariectomy without apparent reduction in calcitonin content in the rat.
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Animals↗
Regulation of calcitonin secretion in vitro.
The concentration of extracellular calcium rightly regulates calcitonin secretion by calcium influx through dihydropyridine-sensitive voltage-dependent calcium channels; the result is an increase in intracellular calcium. There also exists a cAMP-dependent pathway of calcitonin release activated by glucagon or growth hormone releasing hormone. In thyroid C-cells, as in all cells, there is dual regulation of adenylate cyclase, mediated by inhibitory or stimulatory G proteins; glucagon stimulated cAMP production can be inhibited by somatostatin via pertussis toxin sensitive inhibitory G proteins. Somatostatin inhibits not only cAMP dependent but also calcium-dependent calcitonin secretion. Furthermore, somatostatin inhibits voltage dependent calcium channel currents thereby lowering cytosolic calcium. These actions also involve a pertussis toxin-sensitive inhibitory G protein but they occur independently of changes in the cytosolic cAMP concentration. Thus multiple interactions between second messenger systems at different cellular levels modulate calcitonin secretion.
Animals↗
Neutralizing antibodies against calcitonin.
The use of calcitonin (CT) is established as a treatment of Paget's disease of bone and postmenopausal osteoporosis (PMO). Salmon calcitonin (sCT), which differs in 14 of the 32 amino acids from human calcitonin, has found a wider distribution world wide, although antibody formation against sCT has been reported in more than 70% of the patients on continuous sCT treatment. The clinical significance of these antibodies has been discussed controversially, because the occurrence of antibodies is not always associated with the development of secondary resistance. Using an in vitro bioassay, based on the CT-mediated increase of the cyclic AMP (cAMP) production of the human breast cancer cell line T 47 D we could identify a neutralizing activity against sCT in the serum of a subset of patients with formation of antibodies against sCT which was related to the development of secondary resistance. Antibody formation against human calcitonin (hCT) has been reported only once before. Binding and neutralizing antibodies were now observed in 1 of 33 patients with PMO treated with hCT. Due to a low neutralizing activity, clinical sequelae were not to be expected in this patient. The formation of neutralizing antibodies against calcitonin is common after treatment with salmon but a rare phenomenon after treatment with human calcitonin. We recommend monitoring of patients with postmenopausal osteoporosis and Paget's disease of bone on long term treatment with sCT or hCT for neutralizing antibody formation in order to evaluate the therapeutic effect of treatment.
Antibodies↗
Long-term exposure to SMS 201-995 inhibits proliferation and calcitonin release in neoplastic C-cells.
The effect of the long-acting somatostatin analogue SMS 201-995 on cellular proliferation and calcitonin production was examined in rMTC 6-23 cells. A dose-dependent inhibition of calcitonin release and cellular calcitonin content was obtained in cells exposed to SMS 201-995 for 72 hrs. The dose-dependent antiproliferative effect of SMS 201-995 (10(-8)-10(-6) M) was significant after 72 hrs of exposure. SMS 201-995 has an inhibitory effect on calcitonin secretion and synthesis as well as on the growth of C-cells.
Animals↗
The potential value of somatostatin receptor scintigraphy in medullary thyroid carcinoma.
In a prospective study, ten patients with recurrent medullary thyroid carcinoma (markedly elevated calcitonin levels) were investigated by means of somatostatin receptor scintigraphy (SRS) with 111Inpentetreotide. Scintigraphically, 30 sites of pathological uptake were found, mostly located in the neck and upper mediastinum. So far, 18 suspected tumour sites underwent histological examination and 14 of them could be verified as metastases of medullary thyroid carcinoma (MTC). The remaining four putative tumour lesions turned out to be false positive scintigraphic findings caused by chronic inflammation and somatostatin receptor positive tumours other than MTC. We conclude that SRS is a promising imaging modality for localization of MTC recurrence and may thus make a contribution to better management of this patient group.
Adult↗
Major role of dihydropyridine-sensitive Ca2+ channels in Ca(2+)-induced calcitonin secretion.
Endocrine cells are known to possess multiple types of Ca2+ channels. In neurons, omega-conotoxin-sensitive N-type Ca2+ channels have been shown to play a dominant role in neurotransmitter release, but uncertainty remains about the types of Ca2+ channels involved in stimulus-secretion coupling in endocrine cells. We investigated the relative contribution of 1,4-dihydropyridine-sensitive and omega-conotoxin-sensitive Ca2+ channels to Ca(2+)-induced calcitonin release in parafollicular cells of the thyroid (C cells). In whole cell voltage-clamp experiments, both 1,4-dihydropyridine-sensitive and omega-conotoxin-sensitive Ca2+ channel currents were identified. The dihydropyridine isradipine (1 microM) but not omega-conotoxin (1 microM) inhibited the steady-state Ca2+ influx at physiological membrane potentials, the spontaneous electrical activity, and calcitonin secretion (at 2-h incubations). Moreover, suppression of the spontaneous electrical activity by the Na+ channel blocker tetrodotoxin did not affect calcitonin release. We conclude that 1,4-dihydropyridine-sensitive Ca2+ channels play a major role in Ca(2+)-dependent calcitonin release and that calcitonin secretion due to Ca2+ influx proceeds even in the absence of action potentials.
Animals↗
Parathyroid hormone-related protein (PTHrP) does not regulate 1,25-dihydroxyvitamin D serum levels in hypercalcemia of malignancy.
We investigated in humoral hypercalcemia of malignancy whether parathyroid hormone-related protein (PTHrP) elevation causes a rise in 1,25-dihydroxyvitamin D (1,25-(OH)2 D) serum levels. We assessed 41 patients with hypercalcemia of malignancy in a prospective study. There were 19 patients who had serum PTHrP levels in the normal range; 22 patients had elevated serum PTHrP levels. All patients were treated with the bisphosphonate pamidronate resulting in a drop of serum calcium (p < 0.0001) and serum phosphate (p < 0.0023) within 12 days, independent of the group. Parathyroid hormone (PTH) was suppressed at the start of therapy and rose to within the normal range during therapy (p < 0.0001), regardless of the PTHrP levels. PTHrP levels were not influenced by calcium lowering therapy. The serum levels of 1,25-(OH)2 D were either suppressed or in the low normal range at the beginning of the study, without any significant difference between both groups. All patients showed a rise in 1,25-(OH)2 D during bisphosphonate therapy (p < 0.0001), independent of their PTHrP levels. Thus PTHrP did not influence the calcium, phosphate-, or PTH-dependent regulation of 1,25-(OH)2 D during calcium lowering therapy. We conclude, that PTHrP does not stimulate renal 1-hydroxylase activity in humoral hypercalcemia of malignancy.
Adult↗
Homologous desensitization of calcitonin receptors and calcitonin-dependent adenylate cyclase in T47D cells.
Prolonged use of calcitonin (CT) in vivo leads to a loss of biological response (escape). To understand the molecular basis of this phenomenon, we examined desensitization of calcitonin receptors and down-regulation of adenylate cyclase response to CT in T47CD cells after a preincubation with CT. Preincubation with salmon or human CT (sCT, hCT) for 3 h led to a concentration-dependent loss of [125I]-sCT binding and a similar loss of adenylate cyclase response to a maximal stimulatory dose of sCT. At the same time there was an increased basal activity of the adenylate cyclase. After 24 h preincubation with sCT, basal cAMP levels fell considerably but not to basal levels. Time course experiments showed a delayed decline of maximally sCT-stimulated cAMP levels, which started after 1 h, while binding values declined over the first 60 min to one-third of the original values. Upon removal of CT from the medium, recovery of hormone binding occurred in parallel with the recovery of the adenylate cyclase response to sCT. T47D cells incubated with 25 mumol/l monensin, a lysosomal inhibitor, showed a persistent [125I]-sCT binding after removal of hormone, consistent with diminished intracellular receptor degradation. However, despite persistent binding to the cells, basal and stimulated cAMP levels dropped in the same manner as seen in controls. Our experiments support the view that tight binding of CT to its receptor stimulates adenylate cyclase in T47D cells, until receptors are removed by internalization. The physiological role of internalization of the CT receptor might be to end continuous stimulation of the adenylate cyclase, which occurs after binding.
Adenylyl Cyclases↗