Effects of calcitonin on 3',5'-cyclic adenosine monophosphate and calcium second messenger generation and osteoblast function in UMR 106-06 osteoblast-like cells

Change of urinary fluoride and bone metabolism indicators in the endemic fluorosis areas of southern China after supplying low fluoride public water

Background

Few studies have evaluated health impacts, especially biomarker changes, following implementation of a new environmental policy. This study examined changes in water fluoride, urinary fluoride (UF), and bone metabolism indicators in children after supplying low fluoride public water in endemic fluorosis areas of Southern China. We also assessed the relationship between UF and serum osteocalcin (BGP), calcitonin (CT), alkaline phosphatase (ALP), and bone mineral density to identify the most sensitive bone metabolism indicators related to fluoride exposure.

Methods

Four fluorosis-endemic villages (intervention villages) in Guangdong, China were randomly selected to receive low-fluoride water. One non-endemic fluorosis village with similar socio-economic status, living conditions, and health care access, was selected as the control group. 120 children aged 6-12 years old were randomly chosen from local schools in each village for the study. Water and urinary fluoride content as well as serum BGP, CT, ALP and bone mineral density were measured by the standard methods and compared between the children residing in the intervention villages and the control village. Benchmark dose (BMD) and benchmark dose lower limit (BMDL) were calculated for each bone damage indicator.

Results

Our study found that after water source change, fluoride concentrations in drinking water in all intervention villages (A-D) were significantly reduced to 0.11 mg/l, similar to that in the control village (E). Except for Village A where water change has only been taken place for 6 years, urinary fluoride concentrations in children of the intervention villages were lower or comparable to those in the control village after 10 years of supplying new public water. The values of almost all bone indicators in children living in Villages B-D and ALP in Village A were either lower or similar to those in the control village after the intervention. CT and BGP are sensitive bone metabolism indicators related to UF. While assessing the temporal trend of different abnormal bone indicators after the intervention, bone mineral density showed the most stable and the lowest abnormal rates over time.

Conclusions

Our results suggest that supplying low fluoride public water in Southern China is successful as measured by the reduction of fluoride in water and urine, and changes in various bone indicators to normal levels. A comparison of four bone indicators showed CT and BGP to be the most sensitive indicators.

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.

Prevention of osteocyte and osteoblast apoptosis by bisphosphonates and calcitonin

Glucocorticoid-induced osteoporosis may be due, in part, to increased apoptosis of osteocytes and osteoblasts, and bisphosphonates (BPs) are effective in the management of this condition. We have tested the hypothesis that BPs suppress apoptosis in these cell types. Etidronate, alendronate, pamidronate, olpadronate, or amino-olpadronate (IG9402, a bisphosphonate that lacks antiresorptive activity) at 10(-9) to 10(-6) M prevented apoptosis of murine osteocytic MLO-Y4 cells, whether it was induced by etoposide, TNF-alpha, or the synthetic glucocorticoid dexamethasone. BPs also inhibited apoptosis of primary murine osteoblastic cells isolated from calvaria. Similar antiapoptotic effects on MLO-Y4 and osteoblastic cells were seen with nanomolar concentrations of the peptide hormone calcitonin. The antiapoptotic effect of BPs and calcitonin was associated with a rapid increase in the phosphorylated fraction of extracellular signal regulated kinases (ERKs) and was blocked by specific inhibitors of ERK activation. Consistent with these in vitro results, alendronate abolished the increased prevalence of apoptosis in vertebral cancellous bone osteocytes and osteoblasts that follows prednisolone administration to mice. These results suggest that the therapeutic efficacy of BPs or calcitonin in diseases such as glucocorticoid-induced osteoporosis may be due, in part, to their ability to prevent osteocyte and osteoblast apoptosis.

Inhibition of salmon calcitonin on secretion of progesterone and GnRH-stimulated pituitary luteinizing hormone

The effects of salmon calcitonin (sCT) on the production of progesterone and secretion of luteinizing hormone (LH) were examined in female rats. Diestrous rats were intravenously injected with saline, sCT, human chorionic gonadotropin (hCG), or hCG plus sCT. Ovariectomized (Ovx) rats were injected with saline or sCT. In the in vitro experiments, granulosa cells and anterior pituitary glands (APs) were incubated with the tested drugs. Plasma LH levels of Ovx rats were reduced by sCT injection. Administration of sCT decreased the basal and hCG-stimulated progesterone release in vivo and in vitro. 8-Bromo-cAMP dose dependently increased progesterone production but did not alter the inhibitory effect of sCT. H-89 did not potentiate the inhibitory effect of sCT. Higher doses of 25-hydroxycholesterol and pregnenolone stimulated progesterone production and diminished the inhibitory effects of sCT. sCT did not decrease basal release of LH by APs, but pretreatment of sCT decreased gonadotropin-releasing hormone (GnRH)-stimulated LH secretion. These results suggested that sCT inhibits progesterone production in rats by preventing the stimulatory effect of GnRH on LH release in rat APs and acting directly on ovarian granulosa cells to decrease the activities of post-cAMP pathway and steroidogenic enzymes.

Expression of the CT/CGRP gene and its regulation by dibutyryl cyclic adenosine monophosphate in human osteoblastic cells

There is general agreement that calcitonin (CT) inhibits bone resorption by its effects on osteoclast function. CT was also found to have direct effects on osteoblast-like cells. In this study, we investigated the expression of CT and calcitonin gene-related peptide (CGRP), the two peptides encoded by the CT/CGRP gene, in human osteosarcoma cell lines and in normal human trabecular osteoblastic cells (HOB), and we studied the modulation of CT/CGRP gene expression by dibutyryl cyclic adenosine monophosphate ((Bu)2, cAMP), a cAMP analog. We first detected by Northern blot hybridization the presence of CT and CGRP mRNAs in different osteosarcoma cell lines (OHS-4, MG-63, Saos-2, HOS-TE85) and HOB cells. In the steady state, OHS-4 cells express slightly more CT and CGRP mRNAs than other cell lines or normal human osteoblasts, in parallel with messengers of differentiated osteoblasts, such as osteocalcin (OC) and alkaline phosphatase (ALP). OHS-4 cells also express CT and CGRP proteins, as demonstrated by immunocytochemistry. Stimulation of OHS-4 cells with 1 mM (Bu)2 cAMP induced a significant increase in mRNA levels for CT (x 2.5) and CGRP (x 3), as determined by a semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) procedure. The involvement of a transcriptional mechanism in this effect was evidenced by nuclear run-off transcription assay. In addition, (Bu)2 cAMP increased OC (x 4) and ALP (x 3) mRNA levels in OHS-4 cells. These effects were observed at 24 h and were maximal at 48 h, indicating that (Bu)2, cAMP induced cell differentiation and increased the transcription of the CT/CGRP gene in OHS-4 osteoblast-like cells. The results indicate that human osteosarcoma cells and primary human osteoblastic cells express CT and CGRP mRNA and proteins, and that (Bu)2 cAMP, an activator of protein kinase A, induces up-regulation of osteoblastic phenotypic genes and enhances CT and CGRP gene transcription, indicating that induction of osteoblastic differentiation by (Bu)2 cAMP is associated with enhanced expression of CT and CGRP in human osteoblastic cells.

Surface adhesion-mediated regulation of chondrocyte-specific gene expression in the nontransformed RCJ 3.1C5.18 rat chondrocyte cell line

Recent evidence suggests that decreased chondrocyte function in osteoarthritis and other articular disorders may be due to chondrocyte dedifferentiation produced by altered regulatory signals from the cartilage extracellular matrix (ECM). However, there are currently no mammalian chondrocytic cell line systems adapted to the study of this process. We therefore examined the effects of ECM growth conditions on markers of differentiated chondrocytic phenotype expression in the nontransformed rat RCJ 3.1C5.18 (RCJ) chondrocyte cell line, including type II collagen expression, aggrecan production, link protein gene expression, and parathyroid hormone (PTH) receptor number. RCJ cells grown in monolayer on plastic exhibited a dedifferentiated phenotype characterized by flattened cell morphology, with > 80% type I collagen and < 5% type II collagen production, as determined by two-dimensional gel mapping electrophoresis of collagen cyanogen bromide peptides. In addition, aggrecan production was low, and link protein mRNA was not expressed at detectable levels. After transfer to growth under minimal attachment conditions on the surface of a composite type I collagen/agarose (0.15%-0.8%) gel (CAG) for 7 days, RCJ cells developed a rounded, chondrocytic morphology and a pattern of differentiated, chondrocytic gene expression, with 79% type II and 8% type I collagen production. Steady-state type I and type II procollagen mRNA levels were altered in parallel with collagen protein expression. In cells grown on CAG, aggrecan production increased 6-fold, and there was a marked increase in both aggrecan core protein and link protein mRNA levels. In addition, maximal PTH-stimulated cAMP generation increased 15-fold in association with an increased PTH receptor number. Therefore, the RCJ chondrocyte cell line is highly sensitive to ECM regulation of chondrocyte-specific gene expression.

Intranasal salcatonin (salmon calcitonin). A review of its pharmacological properties and role in the management of postmenopausal osteoporosis

Osteoporosis is a common problem among postmenopausal women and is associated with significant morbidity, mortality and costs primarily resulting from osteoporotic fractures. Salcatonin (salmon calcitonin) inhibits osteoclastic bone resorption and is approximately 40 to 50 times more potent than human calcitonin. In most randomised trials in which intranasal salcatonin (usually 50 to 200 IU/day plus oral calcium supplements) was administered for 1 to 5 years to postmenopausal women for prevention of osteoporosis, bone mineral density or content of the lumbar spine increased by approximately 1 to 3% from baseline. In contrast, postmenopausal women receiving only oral calcium supplements typically had reductions in bone mineral density or content of about 3 to 6%. The difference between treatment groups was statistically significant in essentially all studies. Although changes in bone mineral density or content were broadly similar in studies of postmenopausal women with established osteoporosis to those in postmenopausal women receiving therapy for prevention of the disease, studies in women with established osteoporosis did not usually demonstrate statistically significant differences between treatment groups. Also in postmenopausal women with established osteoporosis, intranasal salcatonin reduced pain and/or analgesic consumption in some trials and, in a limited number of studies of relatively short duration (i.e. < or = 2 years), the incidence of osteoporotic fractures. A large multicentre 5-year study with adequate statistical power to confirm the effect of intranasal salcatonin on reducing osteoporotic fracture rates in postmenopausal women is currently under way. The intranasal formulation of salcatonin offers a more convenient and better tolerated alternative to the parenteral formulation of the drug which is administered by regular subcutaneous or intramuscular injections. Adverse events associated with the intranasal formulation are generally mild and transient, usually involving local reactions such as nasal discomfort, rhinorrhoea or rhinitis. Thus, for postmenopausal women unable or unwilling to tolerate long term hormone replacement therapy, intranasal salcatonin is an attractive alternative for the management of osteoporosis.

Calcitonin prevents bone loss but decreases osteoblastic activity in ovariohysterectomized beagle dogs

The antiresorptive effects of calcitonin are well documented. Recent in vitro and in vivo evidence points to an anabolic effect of calcitonin on osteoblasts. To assess the value of calcitonin in preventing the rapid and early bone loss after cessation of ovarian function and to investigate its effects on osteoblasts in vivo, 32 dogs were ovariohysterectomized (OHX) and 32 dogs were sham-operated (Sham). After the surgeries, half of the OHX and Sham dogs received every-other-day subcutaneous injections of human calcitonin (0.25 mg/dog/d), and the remaining dogs were given vehicle. Half of the animals had a bone biopsy at week 2 and were euthanized thereafter; the other half of the animals underwent a bone biopsy at month 1 and were euthanized at month 4. Blood drawings were done at baseline and at the time of each bone biopsy. Calcitonin prevented the increase in erosion depth seen in OHX animals and prevented the cancellous bone loss observed at 2 weeks and at 1 and 4 months. Calcitonin did not affect bone volume in Sham dogs. However, treatment with calcitonin induced a decrease in mineralizing surfaces and bone formation rates at the bone surface and cell level and an increase in mineralization lag time in both Sham and OHX animals without significantly affecting osteoblast number. This finding indicates that the negative effect of calcitonin on bone mineralization is not solely the result of a decrease in bone turnover. The data show that calcitonin, because of its antiresorptive effects, can prevent bone loss after cessation of ovarian function. However, short-term treatment with calcitonin does not stimulate osteoblast activity; on the contrary, it exerts a negative effect on osteoblastic bone formation and mineralization. Long-term studies are needed to investigate whether this unwanted effect of calcitonin on osteoblasts in vivo represents a transitory or persistent phenomenon.

Osteoblast hydraulic conductivity is regulated by calcitonin and parathyroid hormone

It is our hypothesis that osteoblasts play a major role in regulating bone (re)modeling by regulating interstitial fluid (ISF) flow through individual bone compartments. We hypothesize that osteoblasts of the blood-bone membrane lining the bone surfaces are capable of regulating transosseous fluid flow. This regulatory function of the osteoblasts was tested in vitro by culturing a layer of rat calvarial osteoblasts on porous membranes. Such a layer of osteoblasts subjected to 7.3 mm Hg of hydrostatic pressure posed a significant resistance to fluid flow across the cell layer similar in magnitude to the resistance posed by endothelial monolayers in vitro. The hydraulic conductivity, the volumetric fluid flux per unit pressure drop, of the osteoblast layer was altered in response to certain hormones. Hydraulic conductivity decreased approximately 40% in response to 33 nM parathyroid hormone, while it exhibited biphasic behavior in response to calcitonin: increased 40% in response to 100 nM calcitonin and decreased 40% in response to 1000 nM calcitonin. Further, activation of adenylate cyclase by forskolin dramatically increased the hydraulic conductivity, while elevation of intracellular calcium, [Ca2+]i, by the calcium ionophore A23187 initially decreased the hydraulic conductivity at 5 minutes before increasing conductivity by 30 minutes. These results suggest that cyclic adenosine monophosphate (cAMP) and [Ca2+]i may mediate changes in the osteoblast hydraulic conductivity. The increase in hydraulic conductivity in response to 100 nM calcitonin and the decrease in response to PTH suggest that the stimulatory and inhibitory effects on bone formation of calcitonin and parathyroid hormone, respectively, may be due in part to alterations in bone fluid flow.

Ineffectiveness of calcitonin on a local-disuse osteoporosis in the sheep: a histomorphometric study

Local immobilization is a good model for studying disuse-induced bone loss and to appreciate the effects of drugs, especially preventive action of antiresorptive therapy. In fact, increased osteoclastic activity is the main point of such a bone loss. The effect of salmon calcitonin was investigated on immobilization-induced osteoporosis in the sheep. Twenty-four nonovariectomized, adult, female, Welsh mountain sheep were submitted, by an external fixator procedure, to hock joint immobilization from the tibia to the the metatarsus for 12 weeks. The sheep were randomized into two groups receiving either an injection of placebo or salmon calcitonin (100 IU) three times per week, for 12 weeks. Histomorphometric analysis was performed on pre- and posttherapeutic transiliac bone biopsies, and on immobilized (left) and nonimmobilized calcanei removed after sacrifice. Results showed a 29% significant decrease of cancellous bone volume in the placebo group due to a significant reduced trabecular thickness when we compared immobilized versus nonimmobilized calcaneus. This structural adaptation appeared to be the consequence of an overall increased bone turnover. In the calcitonin group, same changes were observed, with a 23% reduction of bone mass in the immobilized calcaneus. By comparing calcitonin with placebo groups in both left and right calcanei, no difference was found. On the other hand, a significant increase of mineralization parameters in the iliac crest was only observed in the calcitonin group. In conclusion, salmon calcitonin, at a dose of 100 IU/day three times a week, was ineffective in preventing local disuse osteoporosis in this sheep model.

Calcitonin inhibits testosterone and luteinizing hormone secretion through a mechanism involving an increase in cAMP production in rats

Effects of calcitonin peptides, including human calcitonin (hCT), salmon calcitonin (sCT), and calcitonin gene-related peptide (CGRP), on the secretion of testosterone and luteinizing hormone (LH) in male rats were studied. Male rats were injected intravenously with human chorionic gonadotropin (hCG), calcitonin peptides, or hCG plus calcitonin peptides. Blood samples were collected at several intervals following hormone challenge. In an in vitro experiment, testis blocks were incubated with hCG (0, 0.05, 0.5, or 5 IU/ml) or hCG (0.5 IU/ml) plus calcitonin peptides (0-10(-9) or 10(-6) M) at 34 degrees C for 30 minutes. Both medium and plasma samples were extracted by ether and analyzed for testosterone by radioimmunoassay (RIA). The concentration of calcium in each plasma sample was measured by an automatic calcium analyzer. The anterior pituitary gland (AP) was incubated with or without calcitonin peptides (0-10 nM) at 37 degrees C for 30 minutes. They were then incubated with gonadotropin releasing hormone (GnRH, 10 nM) for a further 30 minutes. The concentration of LH in AP medium was measured by RIA. The accumulation of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) in both testicular tissues and APs were measured by RIA. A single intravenous injection of calcitonin peptides decreased the basal and hCG-stimulated levels of plasma testosterone gradually from 60 to 180 or 360 minutes after challenge. The plasma calcium was not altered by the injection of calcitonin peptides and/or hCG. Administration of calcitonin peptides in vitro resulted in a dose-dependent inhibition of both basal and hCG-stimulated release of testosterone.(ABSTRACT TRUNCATED AT 250 WORDS)

Responsiveness of gene expression markers of osteoblastic and osteoclastic activity to calcitonin in the appendicular and axial skeleton of the rat in vivo

We have previously shown that calcitonin (CT), an inhibitor of bone resorption, increases vertebral, but not femoral bone density in the rat. To address the physiologic responses associated with these effects on bone mineral density (BMD), we assessed mRNA transcripts reflecting activities of osteoblasts (type I collagen, osteocalcin, osteopontin, and alkaline phosphatase), osteoclasts [tartrate-resistant acid phosphatase (TRAP)], and cell proliferation (histone H4) in the spine and femur of these rats. CT increased spine BMD while increasing type I collagen and decreasing TRAP and histone mRNAs. In the femur, where CT had no effect on BMD, it decreased type I collagen and histone H4 mRNA but did not affect TRAP. CT had no effect on the gene expression of osteocalcin, osteopontin, or alkaline phosphatase at either site. The results indicate that selective alterations in gene expression, as reflected by steady state mRNA levels, are consistent with the changes observed by BMD measurement, and can more clearly define the specific contribution from osteoblast and osteoclast activity. This study demonstrates a heterogeneity in response of the axial and appendicular skeleton to CT, reflected by alterations in gene expression that provide a basis for understanding the observed BMD responses to various pharmacologic interventions.

Calcitonin induces a decreased Na+ conductance in identified neurons of Aplysia

The ionic mechanism of the effect of extracellularly ejected calcitonin (CT) on the membrane of identified neurons R9 and R10 of Aplysia was investigated with voltage-clamp, micropressure ejection, and ion substitution techniques. Micropressure-ejected CT caused a marked hyperpolarization in the unclamped neuron. Heat-inactivated CT was without effect. Clamping the same neuron at its resting potential level (-60 mV) and re-ejecting CT with the same dose produced a slow outward current (Io(CT), 30-40 sec in duration, 4-6 nA in amplitude) associated with a decrease in input membrane conductance. Io(CT) was decreased by depolarization and increased by hyperpolarization. The extrapolated reversal potential of Io(CT) was approximately +10 mV. Io(CT) was sensitive to changes in the external Na+ concentration but not to changes in K+, Ca2+, and Cl- concentrations. Micropressure-ejected forskolin produced a slow outward current, which, like the current to CT, was associated with a decrease in input membrane conductance, and was sensitive to changes in the external Na+ concentration. Io(CT) was prolonged by bath-applied isobutylmethylxanthine (IBMX) but was not affected by 1-oleoyl-2-acetylglycerol (OAG) and calphostin C. Neither superfusion of the neuron with nordihydroguaiaretic acid (NDGA) nor superfusion with indomethacin caused any changes in Io(CT). These results suggest that extracellular CT can induce a slow outward current associated with a decrease in Na+ conductance, mediated by a receptor-controlled increase in intracellular cyclic adenosine 3',5'-monophosphate.