Parathyroid hormone in the treatment of osteoporosis

ELISA array-based immunoassay for multiplex detection of osteoporosis-relevant biomarkers

Aim: This study aimed to develop an ELISA array-based immunoassay for the simultaneous detection of osteoporosis-relevant biomarkers. Methods: ELISA array was constructed and its performance was evaluated using commercial antigens. The validity was further confirmed using traditional ELISA. Results: The constructed ELISA array showed good repeatability. The linear ranges and limits of detection for the four markers mentioned above were 0.01-8 ng/ml (1 pg/ml), 5.0-1000 ng/ml (1 ng/ml), 0.5-400 ng/ml (0.1 ng/ml) and 1-100 ng/ml (1 ng/ml), respectively. The measured concentrations of serum samples by ELISA array showed high correlation with those from traditional ELISA. Conclusion: ELISA array-based immunoassay provided a feasible and productive method to multiplex measure markers for osteoporosis.

HMGB1 expression and release by bone cells

Immune and bone cells are functionally coupled by pro-inflammatory cytokine intercellular signaling networks common to both tissues and their crosstalk may contribute to the etiologies of some immune-associated bone pathologies. For example, the receptor activator of NF-kappaB ligand (RANKL)/osteoprotegerin (OPG)/receptor activator of NF-kappaB (RANK) signaling axis plays a critical role in dendritic cell (DC) function as well as bone remodeling. The expression of RANKL by immune cells may contribute to bone loss in periodontitis, arthritis, and multiple myeloma. A recent discovery reveals that DCs release the chromatin protein high mobility group box 1 (HMGB1) as a potent immunomodulatory cytokine mediating the interaction between DCs and T-cells, via HMGB1 binding to the membrane receptor for advanced glycation end products (RAGE). To determine whether osteoblasts or osteoclasts express and/or release HMGB1 into the bone microenvironment, we analyzed tissue, cells, and culture media for the presence of this molecule. Our immunohistochemical and immunocytochemical analyses demonstrate HMGB1 expression in primary osteoblasts and osteoclasts and that both cells express RAGE. HMGB1 is recoverable in the media of primary osteoblast cultures and cultures of isolated osteoclast precursors and osteoclasts. Parathyroid hormone (PTH), a regulator of bone remodeling, attenuates HMGB1 release in cultures of primary osteoblasts and MC3T3-E1 osteoblast-like cells but augments this release in the rat osteosarcoma cell line UMR 106-01, both responses primarily via activation of adenylyl cyclase. PTH-induced HMGB1 discharge by UMR cells exhibits similar release kinetics as reported for activated macrophages. These data confirm the presence of the HMGB1/RAGE signaling axis in bone.

Bone loss induced by ovariectomy in rats is prevented by gene transfer of parathyroid hormone or an Arg-Gly-Asp-containing peptide

Osteoporosis is a major and growing healthcare concern as the population ages. The genes of both a Arg-Gly-Asp (RGD)-containing peptide and parathyroid hormone (PTH) were used to reduce bone loss induced by ovariectomy (OVX) in rats. Plasmids with either RGD or PTH gene were delivered into the quadriceps of OVX rats. The expression of the genes was detected by RT-PCR and radioimmunoassay. Analysis of bone mineral density, bone mechanical testing and bone mineral content indicated an improvement in bone properties in both RGD-transferred and PTH-transferred rats compared to OVX rats. Gene transfer of either RGD or PTH is therefore a possible approach to prevent bone loss in OVX rats thus providing a potential method to prevent osteoporosis in clinical situations.

Association of Otosclerosis With Sp1 Binding Site Polymorphism in COL1A1 Gene: Evidence for a Shared Genetic Etiology With Osteoporosis

HYPOTHESIS

There is an association between otosclerosis and osteoporosis.

BACKGROUND

Both osteoporosis and otosclerosis are common bone diseases to which relatively large portions of the population are genetically predisposed. Recently, a strong association has been described between osteoporosis and an Sp1 binding site of putative functional significance in the first intron of the COL1A1 gene.

METHODS

We applied polymerase chain reaction-based restriction enzyme analysis to determine the polymorphic distribution of the Sp1 site in 100 patients with otosclerosis and 108 control subjects.

RESULTS

This study showed a significant association between otosclerosis and the COL1A1 first intron Sp1 site. The allelic frequency of the Sp1 site is very similar between otosclerosis and osteoporosis.

CONCLUSION

Some cases of otosclerosis and osteoporosis could share a functionally significant polymorphism in the Sp1 transcription factor binding site in the first intron of the COL1A1 gene.

Autoregulation in the parathyroid glands by PTH/PTHrP receptor ligands in normal and uremic rats

BACKGROUND

The secretion of parathyroid hormone (PTH) from the parathyroid glands might be regulated by autocrine/paracrine factors. We have previously shown that N-terminal parathyroid hormone-related protein (PTHrP) enhanced the secretory PTH response to low calcium in vivo and in vitro in rat parathyroid glands. N-terminal PTHrP fragments are equipotent to N-terminal PTH as ligands for the PTH/PTHrP receptor that is demonstrated in parathyroid tissue. This supports the possibility that the parathyroid cells respond to PTH/PTHrP receptor ligands and as such are target for an autoregulatory action of PTH and PTHrP. Our aim was to search for the PTH/PTHrP receptor in rat parathyroid glands and to examine the effects of PTHrP 1-40 on PTH secretion in in vivo models of secondary hyperparathyroidism (HPT) in uremic rats.

METHODS

PTH secretion was examined during ethyleneglycol tetraacetic acid (EGTA)-induced hypocalcemia both with and without PTHrP. Five groups, each of six normal rats, received a bolus of increasing doses of 0.1, 1.0, 10, and 100 microg of PTHrP 1-40, or vehicle only. Chronic renal failure (CRF) was induced by 5/6 nephrectomy. One group of 12 CRF rats received a standard diet, while another CRF group of 18 rats received a high phosphorus diet to induce more severe HPT. After 8 weeks of uremia, the rats were infused with EGTA and PTHrP 1-40 or vehicle. The presence of the PTH/PTHrP receptor in the rat parathyroid glands was examined by reverse transcription-polymerase chain reaction (RT-PCR) technique. PTH was measured by a rat PTH assay that does not cross-react with PTHrP.

RESULTS

In a dose-related manner, PTHrP enhanced the PTH response to hypocalcemia in normal rats. A similar rate of decrease of plasma Ca++ was induced by EGTA in all experimental groups. In CRF rats, plasma creatinine (0.99 +/- 0.10 mmol/L vs. 0.33 +/- 0.01 mmol/L, P < 0.001) and plasma PTH (226 +/- 32 pg/mL vs. 69 +/- 16 pg/mL, P < 0.001) levels were significantly increased. The CRF rats on high phosphorus diet had significant hypocalcemia (Ca++, 1.04 +/- 0.02 mmol/L vs. 1.28 +/- 0.03 mmol/L, P < 0.001), hyperphosphatemia (3.48 +/- 0.3 mmol/L vs. 2.25 +/- 0.1 mmol/L, P < 0.001) and severe secondary HPT, PTH (984 +/- 52 pg/mL vs. 226 +/- 32 pg/mL, P < 0.001) compared to CRF rats on a standard phosphorus diet. The maximal PTH response to hypocalcemia was enhanced in CRF rats (maximum PTH 382 +/- 58 pg/mL vs. 196 +/- 29 pg/mL in normal rats, P < 0.01) and further enhanced by PTHrP 1-40 to 826 +/- 184 pg/mL (P < 0.01). The secretory capacity of the parathyroid glands in response to low Ca++ was severely diminished in uremia. In CRF rats given a high phosphorus diet, the basal PTH levels were at the upper part of the calcium/PTH curve, and the induction of more marked hypocalcemia did not stimulate PTH secretion further (maximum PTH 1475 +/- 208 pg/mL vs. basal 1097 +/- 69 pg/mL, NS). PTHrP, however, further enhanced the maximal PTH levels significantly (maximum PTH 3142 +/- 296 pg/mL, P < 0.01). The presence of the PTH/PTHrP receptor in the rat parathyroid glands was confirmed by RT-PCR technique.

CONCLUSION

PTHrP enhanced significantly, in a dose-related manner, the low Ca++-stimulated PTH secretion in normal rats. The PTH/PTHrP receptor is present in rat parathyroid glands. The impaired secretory capacity of the parathyroid glands in uremic rats is significantly enhanced by PTHrP. An autocrine/paracrine role in the parathyroid glands of the PTH/PTHrP receptor targeting peptides, PTHrP and PTH, is suggested. Thus, it is hypothesized that PTH during hypocalcemia might have a positive auto-feedback regulatory role on its own secretion.

Does PTH have a direct effect on intestine?

Dogma for the past three decades has dictated that parathyroid hormone (PTH) has no direct effect on intestine with regard to calcium or phosphate absorption, but rather that PTH acts to promote the synthesis of a hormonally active form of vitamin D, namely 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)]. However, diverse laboratories have each provided some evidence to suggest PTH does indeed have a direct effect on intestine. We will briefly review the evidence for biological effects, biochemical effects, and the presence of intestinal receptors for PTH, and conclude with the implications for biomedical research.

Bone remodelling in osteoarthrosic subjects undergoing a physical exercise program

BACKGROUND

The connection between osteoarthritis (OA) and osteoporosis (OP) has attracted considerable attention but reports about bone mass density (BMD) in OA are often contradictory. Some data indicate that BMD is higher in OA patients than in healthy subjects, whereas other studies showed no differences. It has been observed that mud pack treatment (MPT) induces a decrease in cytokines with bone-resorbing effects. The aim of this study is to evaluate the response of bone and connective tissue to physical exercise and thermal treatment.

METHODS

Forty osteoarthrosic patients were divided in group A (physical exercise and MPT), and group B (physical exercise alone). Blood and urine samples were collected before and after the treatments to assay blood metabolic markers and urinary hydroxyproline.

RESULTS

In group A, some parameters show statistically significant differences before and after mud pack treatment (MPT). In group B, all parameters present no statistical significant changes before and after the physical exercise program.

CONCLUSIONS

Few studies established the importance of exercise to maintain normal cartilage and bone metabolism. In group A of the present study, an influence on all the parameters of bone metabolism is evident. It is possible that physical exercise only if combined with MPT stimulates physiologic bone metabolism and favors skeletal health.