Glucocorticoids decrease the production of parathyroid hormone-related protein in vitro but not in vivo in the Walker carcinosarcoma 256 rat model

Adrenal effects of teriparatide in the treatment of severe postmenopausal osteoporosis

The aim of our study was to investigate the effects of teriparatide on the hypophysis-adrenal axis in postmenopausal women. Treatment with teriparatide increased plasmatic and urinary levels of cortisol after 6 and 12 months. Our paper demonstrates a possible direct secretagogue effect of teriparatide on adrenals in osteoporotic postmenopausal women.

INTRODUCTION

Teriparatide, recombinant human parathyroid hormone (1-34) (rhPTH [1-34]), is approved for the treatment of osteoporosis in men and postmenopausal women at high risk for fracture. In literature, data regarding the secretagogue effect of PTH on adrenocortical cells are present on in vitro, but not on in vivo, studies. The aim of our study was to investigate the effects of teriparatide on the hypophysis-adrenal axis in postmenopausal women.

METHODS

Twenty postmenopausal women with severe osteoporosis were treated with teriparatide in a regimen of 20 μg daily, self-administered injections at bedtime for 12 months and a calcium and vitamin D supplementation. At the same time, 20 osteopenic women matched for age and body mass index with the patients were enrolled and treated only with calcium and vitamin D. In all subjects, calcium, adrenocorticotropic hormone (ACTH), and plasmatic and urinary cortisol were evaluated at baseline and after 6 and 12 months.

RESULTS

Treatment with teriparatide increased plasmatic and urinary levels of cortisol after 6 and 12 months, reaching statistical significance only after 1 year. Plasmatic levels of ACTH did not change significantly.

CONCLUSIONS

Our paper, for the first time, demonstrates a possible direct secretagogue effect of teriparatide on adrenals in osteoporotic postmenopausal women.

The parathyroid hormone family of peptides: structure, tissue distribution, regulation, and potential functional roles in calcium and phosphate balance in fish

Parathyroid hormone (PTH) and PTH-related protein (PTHrP) are two factors that share amino acid sequence homology and act via a common receptor. In tetrapods, PTH is the main endocrine factor acting in bone and kidney to regulate calcium and phosphate. PTHrP is an essential paracrine developmental factor present in many tissues and is involved in the regulation of ossification, mammary gland development, muscle relaxation, and other functions. Fish apparently lack an equivalent of the parathyroid gland and were long thought to be devoid of PTH. Only in recent years has the existence of PTH-like peptides and their receptors in fish been firmly established. Two forms of PTH, two of PTHrP, and a protein with intermediate characteristics designated PTH-L are encoded by separate genes in teleost fish. Three receptors encoded by separate genes in fish mediate PTH/PTHrP actions, whereas only two receptors have so far been found in terrestrial vertebrates. PTHrP has been more intensively studied than PTH, from lampreys to advanced teleosts. It is expressed in many tissues and is present in high concentration in fish blood. Administration of this peptide alters calcium metabolism and has marked effects on associated gene expression and enzyme activity in vivo and in vitro. This review provides a comprehensive overview of the physiological roles, distribution, and molecular relationships of the piscine PTH-like peptides.

Cortisol and parathyroid hormone-related peptide are reciprocally modulated by negative feedback

In previous in vitro studies, we have shown that the N-terminal region of parathyroid hormone-related protein (PTHrP) can stimulate cortisol production in sea bream, Sparus auratus, interrenal tissue, possibly through a paracrine action. In the current study, the systemic interaction between cortisol and PTHrP was studied in vivo. Sustained elevated blood cortisol levels, induced either by cortisol injection or confinement stress, suppressed circulating PTHrP 6 and 24-fold, respectively, by comparison to control fish. Dexamethasone treatment reduced cortisol levels, prevented the decrease of plasma PTHrP observed in confined fish and raised plasma PTHrP levels in non-confined fish. In contrast, a single injection of (1-34) PTHrP caused a short-term (within 30 min and up to 2.5 h) decrease in plasma cortisol. The antagonistic effects between PTHrP and cortisol were substantiated by an overall (data pooled from all experiments) highly significant negative correlation (r0=-0.745, p<0.001, n=115) between the plasma levels of the two hormones. Although the underlying mechanism of the interaction still has to be determined, the high levels of PTHrP in circulation and the existence of systemic regulation favour the hypothesis that in fish PTHrP may act as an endocrine factor, although the gland that produces it still remains to be identified.

Rat models of bone metastases

Bone metastases occur frequently in patients with advanced breast or prostate cancer. Bone metastases can be predominantly osteolytic, osteoblastic or mixed. Studies with animal models allow advances in understanding the molecular basis for bone metastases and provide new targets for therapy. Several animal models have been developed in rat with different pathophysiologies; they required injection or implantation of neoplastic cells into orthotopic locations, bones or the left ventricle of the heart. Several specific strains of rat have an increased incidence of spontaneous tumors. Carcinomas can be induced by either chemicals or physical agents. However, the most used and convenient way to induce bone metastases is a syngeneic transmission. MAT-Ly-Lu cells have been used in several models using Copenhagen rats to induce osteoblastic bone lesions. PA-III cells derived from Pollard tumors can also produce a combination of osteolytic and osteoblastic reactions at the site of transplantation. Osteolytic bone lesions can be obtained with an injection of Walker cells. The use of 13762 or c-SST2 cells allows also leads to osteolysis. Human xenografts can only be used in nude animals. It is essential to validate and correctly interpret the lesions in several models of bone metastasis. No animal model is sufficient by itself to represent the clinical findings observed in humans. The use of models developed in different species should be more predictive and bring a beam of arguments for a better knowledge of pathophysiological and therapeutic mechanisms.

Regulation of PTHrP and PTH/PTHrP receptor by extracellular Ca2+ concentration and hormones in the breast cancer cell line 8701-BC

It was previously reported that 8701-BC breast tumour cells express the gene for parathyroid hormone-related peptide (PTHrP) and PTH/PTHrP receptor (PTHrP-R) and release immunoreactive PTHrP (iPTHrP) into the extracellular medium. Since the regulation of PTHrP and PTHrP-R by breast cancer cells has been poorly investigated so far, we have chosen the 8701-BC cell line as a model system to investigate whether alterations in the extracellular Ca2+ concentration ([Ca2+]e) and treatment with some well-known differentiation agents for breast cells, such as dimethyl sulfoxide, hydrocortisone, progesterone, prolactin, all-trans retinoic acid and transforming growth factor-beta1 might (i) modulate quantitatively the release of iPTHrP, (ii) affect the PTHrP promoter usage and mRNA splicing patterns, and (iii) modify the expression of PTHrP-R. The data obtained indicate that 8701-BC cells are potentially able to utilise different start sites and mRNA splicing patterns for PTHrP transcription, and respond to variations of [Ca2+]e and to the addition of two hormones, hydrocortisone and progesterone, with modifications in the extracellular amount of iPTHrP. Moreover, expression of PTHrP-R is also modulated by changes of [Ca2+]e or treatment with hydrocortisone. This indicates that the 8701 -BC cell line is a suitable in vitro model for further studies on the complex molecular regulation of the PTHrP/PTHrP-R pair in breast cancer.

Extracellular matrix regulation of PTHrP and PTH/PTHrP receptor in a human breast cancer cell line

It was previously reported that 8701-BC breast cancer cells express the gene for parathyroid hormone-related peptide (PTHrP) and its cognate receptor (PTHrP-R), and release immunoreactive PTHrP in the extracellular medium; it was also found that PTHrP, in turn, exerts a role on the proliferative and invasive behavior in vitro of the same cell line. On the other hand, evidence has been produced that adhesion of 8701-BC cells onto different collagen substrates influences in various ways a number of phenotypic expressions, such as cell growth, motility, invasion of reconstituted basement membrane and production of lytic enzymes of the extracellular matrix (ECM). In light of these previous data, we have examined whether substrates of either reconstituted basement membrane or representative collagen components of the breast tumor stroma (type I, V and OF/LB) might (i) regulate the PTHrP promoter usage and mRNA splicing patterns, (ii) modulate quantitatively the extracellular release of immunoreactive PTHrP (iPTHrP), and (iii) affect the expression of PTHrP-R. The results obtained give evidence that (i) 8701-BC cells are able to utilize different start sites and mRNA splicing patterns for PTHrP transcription; (ii) 'structural' components of the stroma, such as collagens, are by themselves capable of controlling both the expression pattern of the PTHrP gene and the extent of extracellular release of iPTHrP, and (iii) PTHrP-R expression can be up- or down-regulated in response to the ECM substrate present. These data demonstrate that PTHrP and PTHrP-R expression by 8701-BC neoplastic cells can be modulated by ECM molecules, indirectly supporting the active participation of stromal collagen composition in the regulation of PTHrP-controlled circuits which may play a role in carcinogenesis.