Andreas Grauer

A case of neuroendocrine oncogenic osteomalacia associated with a PHEX and fibroblast growth factor-23 expressing sinusidal malignant schwannoma

Oncogenic osteomalacia is a rare paraneoplastic syndrome that is characterized biochemically by hypophosphatemia and low plasma 1,25-dihydroxyvitamin D3, and clinically by osteomalacia, pseudofractures, bone pain, fatigue, and muscle weakness. We present a patient with a malignant schwannoma as the underlying cause of this disorder. A permanent cell line (HMS-97) derived from this tumor showed evidence of neuroendocrine differentiation by immunohistochemistry and of neurosecretory activity by electron microscopy. The cell line did express PHEX (phosphate-regulating gene with homologies to endopeptidases located on the X-chromosome) and FGF-23 (fibroblast growth factor-23) transcripts on northern hybridization; however, none of the known mutations from the related mendelian disorders of X-linked hypophosphatemic rickets or autosomal-dominant hypophosphatemic rickets could be detected. Tumor cell (HMS-97)-derived conditioned medium did not inhibit phosphate transport in a standard opossum kidney cell assay and in animal experiments. The medium also showed no PTH1- or PTH2-receptor-stimulating bioactivity. HMS-97 cells might be useful for further studies that aim to determine the genetic mechanism that leads to the observed PHEX and FGF-23 expression, both of which might have a direct role in the pathogenesis of oncogenic osteomalacia. In addition, these cells might be a useful tool for the investigation of neuroendocrine Schwann cell function and autoimmune peripheral nerve disease.

Formation of Neutralizing Antibodies After Treatment With Human Calcitonin

PURPOSE Calcitonin is used for the treatment of Pagets 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.

1,25-Dihydroxyvitamin D3 suppresses dexamethasone effects on calcitonin secretion

1,25-Dihydroxyvitamin D3 (1,25(OH)2D3) and dexamethasone (DEX) influence synthesis and secretion of various hormones. Recent reports concerning the interaction of the two steroids revealed opposite--agonistic as well as antagonistic--effects in different biological systems. As calcitonin (CT) gene expression is affected by both agents, inhibited by 1,25(OH)2D3 and stimulated by DEX, we utilized CT secretion and storage as a model to study the combined effects of the two hormones. A human C cell carcinoma cell line (TT) was used, incubating the cells for a period of 4 days with 1,25(OH)2D3 and DEX alone and in combination. 1,25(OH)2D3 resulted in a decrease, whereas DEX resulted in a increase of CT secretion and content. Combining the two steroids, 1,25(OH)2D3 surprisingly abolished the stimulation of DEX on CT secretion and content. The underlying mechanism is yet unclear and could be envisioned to include steroid receptor regulation or gene transcription.

Neuron-specific enolase in medullary thyroid carcinoma: immunohistochemical demonstration, but no significance as serum tumor marker

SummaryNeuron-specific enolase (NSE) is an enzyme detectable in nervous and neuroendocrine tissue. Increased serum levels of NSE are found in small cell lung cancer and in patients with neuroblastoma, in whom NSE is used as a serum tumor marker. We have investigated 32 patients with histologically proven medullary thyroid carcinoma, a tumor of neuroendocrine origin, in which the classical tumor marker calcitonin (CT) was pathologically elevated. Positive immunocytochemistry for NSE and CT in C-cells was obtained in all cases. Increased serum NSE levels were found in only 5 of 32 patients, there was no correlation between NSE and CT concentrations. We also compared NSE and CT serum levels during long-term follow-up and again found no correlation between NSE and CT. After i.v. stimulation tests with pentagastrin and calcium, no correlation was found between NSE and CT serum levels. We conclude, therefore, that in medullary thyroid carcinoma NSE is useful for immunocytochemistry but not a reliable serum tumor marker.

A new in vitro bioassay for human calcitonin : validation and comparison to the rat hypocalcemia bioassay

The human breast cancer cell line T 47 D expresses calcitonin (CT) receptors that are coupled to adenylate cyclase and which reveal a dose-dependent cyclic AMP response to CT. We used this model to establish an in vitro bioassay for synthetic human CT (hCT) preparations to overcome some of the obstacles of the standard rat hypocalcemia in vivo bioassay. The detection limit of the in vitro bioassay was 1 x 10(-10) M hCT (EC 50: 8.7 pM +/- 26%) compared to 7.3 x 10(-9) M (EC 50: 7.2 microM +/- 32%) for the in vivo bioassay. The relative potencies of test preparations revealed a good correlation (r = 0.89) and several hCT-related substances produced comparable results when tested by the two methods. The standard deviations of precision and accuracy, however, were significantly smaller (P less than 0.05) for the in vitro bioassay. According to these data the T 47 D in vitro bioassay is more sensitive, superior in precision and accuracy, and comparable in specificity to the rat hypocalcemia bioassay.