Relationship between change in femoral neck bone mineral density and hip fracture incidence during treatment with strontium ranelate

OBJECTIVE

Strontium ranelate (SR) increases bone mineral density (BMD) in postmenopausal osteoporotic women and reduces vertebral and non-vertebral fracture incidence. Hip fracture reduction has also been observed during 3-year treatment with SR in osteoporotic women at high risk of hip fracture. The objective of this study is to analyse the association between BMD changes and hip fracture incidence during treatment with SR.

MATERIAL AND METHODS

In this post-hoc analysis, 465 women aged over 74 years with low BMD at the femoral neck (T-score < or = -2.4 according to NHANES normative values) were selected from the population of a recently published study (the Treatment of Peripheral Osteoporosis Study - TROPOS). BMD was assessed at the femoral neck at baseline and after a follow-up of 3 years. Hip fractures were reported by study investigators.

RESULTS

After adjusting for age, body mass index, femoral neck BMD at baseline and number of prevalent vertebral fractures, we found that for each 1% increase in femoral neck BMD observed after 3 years, the risk to experience a hip fracture after 3 years decreased by 7% (95% CI: 1-14%) (p = 0.04). In patients experiencing a hip fracture over 3 years of treatment with SR, femoral neck BMD increased by (mean [SE]) 3.41 (1.02)% compared to 7.23 (0.81)% in patients without hip fracture (p = 0.02).

CONCLUSION

In this post-hoc analysis of women undergoing 3 years of SR treatment, an increase in femoral neck BMD is associated with a decrease in hip fracture incidence.

Over-expression of TIMP-1 in osteoblasts increases the anabolic response to PTH

Intermittent PTH treatment induces structural changes that affect cancellous bone mass and have led to its indication for the treatment of osteoporosis. PTH is also known to upregulate the expression of matrix metalloproteinases (MMP) in osteoblasts. We wanted to find out whether inhibiting osteoblastic MMPs can affect the anabolic action of PTH in vivo. We had shown previously that mice over-expressing TIMP-1 (tissue inhibitor of MMPs) specifically in osteoblasts display an increase in bone mineral density and bone mass combined with an overall decrease in bone turnover. In the present study, 10-week-old wild-type (WT) and transgenic (TG) mice were treated with PTH at 40 microg/kg/day for 1.5 months. DEXA analysis was performed before and after treatment, and histomorphometric and molecular analysis were carried out at the end of the experiment. Our findings indicate that the transgene boosted the anabolic action of PTH. The femurs of PTH-treated TG mice displayed a greater increase in bone mineral density and trabecular bone volume than treated WT mice. Interestingly, the positive effect of the transgene on the action of PTH resulted from both reduced bone resorption activity and an increase in the bone formation rate. Osteoclastic surfaces that were increased in PTH-treated WT mice remained unchanged in TG mice, suggesting a decrease in osteoclastic differentiation. Histomorphometric data also indicate that PTH administration increased osteoblast activity in TG mice and affected the number of osteoblasts in WT mice. In conclusion, we demonstrate that inhibiting osteoblastic MMPs can potentiate the anabolic effect of PTH by decreasing osteoclast activity and increasing osteoblast activity. Our data also suggest that osteoblastic MMPs have some role in mediating the anabolic effects of PTH in vivo and indicate that inhibitors of MMPs could constitute a new therapy for degenerative diseases.

Estradiol inhibits adhesion and promotes apoptosis in murine osteoclasts in vitro

Osteoporosis caused by estrogen deficiency is characterized by enhanced bone resorption mediated by osteoclasts. Adhesion to bone matrix and survival of differentiated osteoclasts is necessary to resorb bone. The aim of our study was to investigate the in vitro effects of estradiol on murine osteoclasts. RAW 264.7 cells treated with 30 ng/ml RANK-L were used as a model for osteoclastogenesis. Estradiol (10(-8)M) for 5 days induced an inhibition of osteoclast differentiation and beta3 expression. Estradiol inhibited significantly the adhesion of mature osteoclasts by 30%. Furthermore estradiol-induced apoptosis shown by with nuclear condensation and Bax/Bcl2 ratio. In addition, estradiol enhanced caspase-3, -8 and -9 activities. This effect completely disappeared using specific caspase-8 inhibitor. However, increased caspase-3 activity by estradiol was observed in the presence of caspase-9 inhibitor, indicating the preferential involvement of caspase-8 pathway. Fas and FasL mRNA expression was not regulated by estradiol. However, estradiol enhanced caspase-3 activity in Fas-induced apoptosis on mature osteoclasts, suggesting that this might interact with the Fas-signaling pathway. These data suggest that estradiol decreases bone resorption by several mechanisms including adhesion and apoptosis of osteoclasts.

LRP5 gene polymorphisms and idiopathic osteoporosis in men

Mutations in the low-density lipoprotein receptor-related protein 5 gene (LRP5) have demonstrated the role of LRP5 in bone mass acquisition. LRP5 variants were recently reported to contribute to the population-based variance in vertebral bone mass and size in males. To investigate whether LRP5 variants are implicated in idiopathic male osteoporosis, we studied 78 men with low BMD (<2.5 T score or < -2 Z score) aged less than 70 years (mean +/- SD: 50 +/- 16 years) in whom secondary causes of osteoporosis had been excluded and 86 controls (51 +/- 10 years). Genotypes and haplotypes were based on LRP5 missense substitutions in exons 9 (c.2047G > A, p.V667M) and 18 (c.4037C > T, p.A1330V), and their association with osteoporosis evaluated after adjustment for multiple clinical and environmental variables using logistic regression. The presence of osteoporosis was significantly associated with LRP5 haplotypes (P = 0.0036) independent of age (P = 0.006), weight (P = 0.004), calcium intake (P = 0.002), alcohol (P = 0.005) and tobacco (P = 0.004) consumption. Accordingly, the odds ratio for osteoporosis was 3.78 (95% CI 1.27-11.26, P < 0.001) in male carriers of haplotype 3 (c.2047A-4037T, n = 20 cases and 12 controls) versus homozygous carriers of haplotype 1 (c.2047G-4037C, n = 42 cases and 61 controls). In conclusion, these data indicate beyond a significant role for environmental factors, an association between LRP5 variants and idiopathic osteoporosis in males, pointing to a role of LRP5 in this disease.

[Calcimimetics, mechanisms of action and therapeutic applications]

The extracellular calcium-sensing receptor (CaR) on the parathyroid cell surface negatively regulates secretion of parathyroid hormone (PTH). Its activation by small changes in the extracellular concentration of ionized calcium (ec[Ca2+]) decreases PTH secretion and secondarily bone turnover. CaR is an ideal target for compounds that may be developed to modulate its activity - activating calcimimetics and inhibiting calcilytics. Calcimimetics can amplify the sensitivity of the CaR to ec(Ca2+), thereby suppressing PTH levels and in turn reducing blood Ca++. They dose-dependently reduce the secretion of PTH in cultured parathyroid cells, in animal models and in humans. In uremic animals, these compounds prevent parathyroid cell hyperplasia when given at the onset of the disease and stop cell proliferation if they are administered afterwards, when the hyperplasia already exists. They normalize plasma PTH levels and bone remodeling. In uremic patients undergoing hemodialysis, calcimimetics reduce plasma PTH concentrations in the short (12 weeks) and long (2 years) terms. They also reduce serum levels of calcium-phosphorus product. Calcimimetics are therefore an alternative for the treatment of secondary hyperparathyroidism, particularly in dialysis patients, when increased serum levels of calcium-phosphorus product, the attendant risk of cardiovascular calcification, and its lack of efficacy limit use of the standard treatment.

[Genetics of osteoporosis]

Osteoporosis is a multifactorial disease involving genetic component and several environmental factors. Some rare diseases that are associated with osteoporosis such as Lobstein disease or the "pseudoglial osteoporosis" syndrom are monogenetic. Nevertheless common osteoporosis is a polygenic affection resulting from the interaction between the polymorphism of different genes and the environmental factors. The genetic component of osteoporosis encompasses roughly 60 to 70% of bone mineral density, whereas the effect on fracture risk seems lower because of the importance of other environmental factors as falls. Many polymorphisms of candidate genes involved in the regulation of bone mass have been correlated to bone density. It is likely that many genes participate to the regulation of bone density although the existence of a major gene is highly suspected. Moreover linkage analysis after genome-wide search in populations with severe osteoporosis has focused on some regions of interest (QTL) on the chromosomes. This will allow to localize one or more specific genes. The current genetic studies on different populations affected by osteoporosis or not will be useful in order to better predict the fracture risk in association with bone density and biochemical markers of bone turnover. Moreover, this will lead to the development of new treatments of osfeoporosis and will help to adapt the therapy for individual patients.

Molecular characterization of two novel isoforms of the human calcitonin receptor

Calcitonin inhibits bone resorption by acting on osteoclasts via a specific receptor. The calcitonin receptor (CTR) is also found in many other normal and malignant tissues and cell lines. It has been cloned and sequenced in several species including humans. It belongs to a subclass of seven-transmembrane G protein-coupled receptors. Four human CTR (H-CTR) isoforms generated by alternatively spliced mRNA have previously been described. Two H-CTR encoding DNAs containing an unidentified 50-bp insert are now reported from T47D cells. The 50-bp insert corresponds to a DNA region located between exon 9 and exon 10, and appears to originate from an alternative splicing process. The two H-CTR cDNAs encode 274 and 290 aa long isoforms. Both are deleted from the putative fourth transmembrane domain to C-tail. They differ by the presence (H-CTR5) or absence (H-CTR6) of a previously known 16-aa insert in the putative first intracellular loop. Cell- and tissue-distribution analysis using RT-PCR demonstrates that the shorter one, HCTR6, is more prevalent. The mRNA of both isoforms was detected in giant cell tumor, whereas only H-CTR6 mRNA was detected in TT cells and kidney tissue. Neither H-CTR5 nor H-CTR6 could be detected in peripheral blood mononuclear cells cultured in the presence of RANKL, in MCF7 cells, and in cortical brain and ovarian tissues. When H-CTR6 was transiently expressed in HEK293 cells, CT failed to induce production of cAMP or to bind to the receptor. These suggest either an intrinsic loss of ligand binding function, or an altered intracellular trafficking. Our findings therefore indicate the existence of two novel splice variants of the H-CTR and confirm that multiple splicing patterns could be involved in the post-transcriptional regulation of the gene.

17beta-estradiol downregulates beta3-integrin expression in differentiating and mature human osteoclasts

The increased bone resorption observed after estrogen withdrawal is responsible for bone loss and may lead to osteoporosis. The mechanism by which estradiol inhibits bone resorption is known to involve decreased osteoclastogenesis, however, the effect on osteoclast adhesion remains unclear. We examined the in vitro effect of estradiol and raloxifene on human osteoclast differentiation and function. Human peripheral blood mononuclear cells were cultured with M-CSF/RANK-L for 18 days, and we evaluated bone resorption, the expression of the protein and mRNA of the integrins, c-jun and c-fos in the presence or absence of estradiol. In this human model, beta3-integrin expression increased at the mRNA and protein levels during osteoclast differentiation, whereas that of beta5-integrin did not. We found that estradiol and raloxifene directly inhibited bone resorption on bone slices by 50%, and decreased the expression of beta3-integrin mRNA (60%) and protein (20%) in a time-dependent manner. Moreover, the mRNAs of c-fos and c-jun were both diminished by estradiol and raloxifene, particularly in early osteoclasts, but also to a lesser extent in mature cells. These findings suggest that the direct inhibitory action of estradiol on bone resorption may affect human osteoclast differentiation through downregulation of c-fos and c-jun and adhesion through modulation of beta3-integrin.

Plasma bone-specific alkaline phosphatase changes in hemodialysis patients treated by alfacalcidol

Vitamin D derivatives correct high bone remodeling by decreasing plasma iPTH concentration in uremic patients with secondary hyperparathyroidism. However, without bone biopsy, plasma iPTH alone might not provide sufficient information regarding vitamin D-induced bone changes. Plasma bone-specific alkaline phosphatase (bAP) seems more sensitive than iPTH in assessing the degree of bone remodeling. We prospectively studied the evolution of iPTH and bAP in 14 adult hemodialysis patients treated for 1 year by i.v. alfacalcidol pulses. The mean total alfacalcidol dose was 0.08 +/- 0.02 g/kg/week. Ten patients completed the study, 2 patients had to be parathyroidectomized before week 24 because of hypercalcemia and uncontrolled hyperphosphatemia, and 2 other patients died before week 36. Mean iPTH levels diminished from 826 +/- 300 pg/ml (range 507 - 1,500 pg/ml) at baseline to 436 +/- 371 pg/ml (range 18 - 1,095 pg/ml) after 52 weeks of treatment (48% of decrease). Only 2 patients normalized plasma iPTH levels while 8/10 normalized bAP. Five patients remained with plasma iPTH concentrations higher than 5-fold the normal value. In contrast, plasma bAP levels declined from 47.6 +/- 32.2 ng/ml (range 15.4 - 130.0 ng/ml) at baseline to 17.8 +/- 9.9 ng/ml (range 8.0 +/- 38.0 ng/ml) at week 52 (63% of decrease). Bone histomorphometry was available in 6 patients after 15.8 +/- 5.1 months of alfacalcidol treatment. None of them met the criteria of adynamic bone disease as they had increased bone resorption and marrow bone fibrosis. Bone formation rate was normal in 2 patients and unmeasurable in the other 4. Two patients showed signs of osteomalacia. In conclusion, alfacalcidol preferentially reduced bone formation rate rather than the other histological parameters of secondary hyperparathyroidism. It reduced plasma bAP more efficiently than iPTH.

Effect of oestradiol on cytokine production in immortalized human marrow stromal cell lines

Oestrogen deficiency enhances bone osteoclastogenesis and bone resorption. Evidence of cooperation between stromal cells and osteoclast precursors in mice suggests that oestradiol acts by regulating cytokine release from stromal cells. Bone marrow stroma contains multipotent progenitors that give rise to many mesenchymal lineages, including osteoblasts that may regulate osteoclast differentiation. We immortalized and characterized six human bone marrow stromal cell lines (presence of Stro1, secretion of alkaline phosphatase, osteocalcin, formation of lipid droplets, and presence of alpha and beta oestrogen receptors). The response of cytokines to oestradiol was then evaluated in vitro, as were the phorbol myristate acetate (PMA)-stimulated cytokine levels. Cells had the characteristics of undifferentiated stromal cells (Stro1+, RANK-L+), and expressed alpha-oestrogen receptors. The osteoblast phenotype (amounts of alkaline phosphatase and osteocalcin) was weak and there was a poor capacity to differentiate into adipocytes. These cell lines did not respond to oestradiol by producing interleukin 6 (IL-6), IL-1 or tumour necrosis factor alpha (TNF-alpha) either constitutively or after stimulation with PMA. Moreover, RANK-L and osteoprotegerin expressions were not regulated by oestradiol in vitro. Thus, modulation of these cytokines by stromal cells do not appear to be the mechanism by which oestradiol regulates bone resorption in humans.

Mapping of autosomal dominant osteopetrosis type II (Albers-Schönberg disease) to chromosome 16p13.3

The osteopetroses are a heterogeneous group of conditions characterized by a bone-density increase due to impaired bone resorption. As well as the two or more autosomal recessive types, two autosomal dominant forms of osteopetrosis, differentiated by clinical and radiological signs, are described. Autosomal dominant osteopetrosis (ADO) type II, also known as "Albers-Schönberg disease," is characterized by sclerosis, predominantly involving the spine (vertebral end-plate thickening, or Rugger-Jersey spine), the pelvis ("bone-within-bone" structures), and the skull base. An increased fracture rate can be observed in these patients. By linkage analysis, the presence, on chromosome 1p21, of a gene causing ADO type II was previously suggested. However, analysis of further families with ADO type II indicated genetic heterogeneity within ADO type II, with the chromosome 1p21 locus being only a minor locus. We now perform a genomewide linkage scan of a French extended family with ADO type II, which allows us to localize an ADO type II gene on chromosome 16p13.3. Analysis of microsatellite markers in five further families with ADO type II could not exclude this chromosomal region. A summed maximum LOD score of 12.70 was generated with marker D16S3027, at a recombination fraction (straight theta) of 0. On the basis of the key recombinants in the families, a candidate region of 8.4 cM could be delineated, flanked by marker D16S521, on distal side, and marker D16S423, on the proximal side. Surprisingly, one of the families analyzed is the Danish family previously suggested to have linkage to chromosome 1p21. Linkage to chromosome 16p13.3 clearly cannot be excluded in this family, since a maximum LOD score of 4.21 at theta=0 is generated with marker D16S3027. Because at present no other family with ADO type II has proved to have linkage to chromosome 1p21, we consider the most likely localization of the disease-causing gene in this family to be to chromosome 16p13.3. This thus reopens the possibility that ADO type II is genetically homogeneous because of a single gene on chromosome 16p13.3.

Human osteopetrosis and other sclerosing disorders: recent genetic developments

Osteopetroses are rare human genetic disorders due to markedly decreased bone resorption. To date, the only gene whose inactivation was known to be responsible for human osteopetroses was that encoding carbonic anhydrase type II. Recessive malignant osteopetrosis is linked to decreased osteoclast function, unlike several osteopetroses in rodents that are caused by the inactivation of genes stimulating osteoclast differentiation. Recent advances in genetics have shown that some patients affected with recessive malignant osteopetrosis have inactivating mutations in a subunit of the vacuolar proton pump that is actively produced in the osteoclast brush border, but not in the lysosomes of other cells. The same gene is mutated in osteopetrotic oc/oc mice. The genes responsible for autosomal dominant osteopetrosis (ADO) have not yet been identified. Also, different localizations have been observed for ADO II, the type with sandwich vertebrae, and ADO I, presenting with diffuse osteocondensation. Less data than in malignant osteopetrosis are avaible on the cellular mechanism of decreased bone resorption in ADO but there is also genetic heterogeneity in ADO II. Pycnodysostosis is also due to a decreased resorption, and is quite close to osteopetrosis. Pycnodysostosis is linked to an inactivating mutation in the gene encoding cathepsin K, which is required for osteoclastic resorption. Decreased bone resorption is not the only defect inducing osteosclerosis, and Camurati-Engelmann disease is due to increased bone formation. Recently it has been shown that it is associated with a mutation in the propeptide of TGFbeta1. Thus, human osteosclerosing disorders have a wide range of phenotypes and genotypes and knowledge of them will contribute to a better understanding of the remodeling of normal bone.

New factors controlling bone remodeling

Two factors of crucial importance in bone cell differentiation were discovered within the last two years. One is the transcription factor Osf2/Cbfa1, which allows mesenchymal stem cells to differentiate into osteoblasts. Soluble factors, including bone morphogenetic proteins (BMPs), leptin, and TGF-beta, can modulate differentiation of mesenchymal stem cells to osteoblasts or to other cell types such as chondrocytes or adipocytes. The other recent discovery is osteoclast differentiating factor (ODF), which is specific for and indispensable to osteoclast differentiation. ODF belongs to the TNF family. Its soluble receptor, osteoprotegerin, prevents it from binding to osteoclasts, thus inhibiting its activity. A role of lymphocytes in bone remodeling has long been suspected, and it has now been shown that ODF is produced by activated T lymphocytes, which may therefore be implicated in bone loss accompanying inflammation. Finally, recent evidence supports a role for B lymphocytes in bone loss secondary to estrogen deprivation. In conclusion, these recent data may have important applications. Osteoprotegerin is a potent antiosteoclast agent that may prove useful in the treatment of bone disorders. Osf2/Cbfa1 and ODF are major targets in the treatment of osteoporosis.

Comparison of four morphometric definitions and a semiquantitative consensus reading for assessing prevalent vertebral fractures

The assessment of vertebral fracture in patients with osteoporosis by conventional radiography has been improved over the past 10 years using either the semiquantitative (SQ) method devised by Genant et al. or quantitative morphometry. However, there is still no internationally agreed definition for vertebral fracture and there have been few comparative studies between these different approaches. Our study assessed the reproducibility of the SQ method and of four commonly used morphometric algorithms (Melton's, Eastell's, Minne's and McCloskey's methods) for assessing prevalent vertebral fractures, and examined the agreement of each morphometric algorithm with a SQ consensus reading performed by three experts. With this consensus reading in place of a gold standard, we determined relative measures of sensitivity, specificity and optimal cutoff threshold for each morphometric algorithm. The study was conducted in 39 postmenopausal women who had at least one osteoporotic vertebral fracture. Normal values were derived from 84 healthy postmenopausal women with apparently normal vertebral bodies. Our results indicate that the concordance of SQ method was excellent (intraobserver agreement on serial radiographs = 96.4%, kappa = 0.91; agreement between individual readings and the consensus reading = 98%, kappa = 0.95). Three morphometric approaches demonstrated good intra- and interobserver concordance (Melton: intraobserver agreement on serial radiographs = 92.7%, kappa = 0.82, interobserver agreement = 91.1%, kappa = 0.79; Eastell: intraobserver agreement on serial radiographs = 87.6%, kappa = 0.66, interobserver agreement = 88.6%, kappa = 0.68; McCloskey: intraobserver agreement on serial radiographs = 91.5%, kappa = 0.72, interobserver agreement = 93.9%, kappa = 0.78). Except for McCloskey's method, the optimal cutoff thresholds defined in our study by highest kappa score or Youden index in comparison with the SQ consensus reading were near the cutoff thresholds that were arbitrarily fixed. The four morphometric algorithms provided a good agreement with the results of the SQ consensus reading, but the more complex algorithm did not provide better results and even if we adjusted the cutoff threshold, no morphometric algorithm agreed perfectly with the SQ consensus reading. We conclude that morphometric approaches currently used should not be employed alone to detect prevalent vertebral fractures in studies on osteoporosis, but should rather be used in combination with a visual assessment. The SQ approach that allows differential diagnosis of vertebral deformities and has demonstrated a better reproducibility can be employed alone when it is performed by experienced and well-trained readers.

Parathyroid hormone-related peptide stimulates proliferation of highly tumorigenic human SV40-immortalized breast epithelial cells

Parathyroid hormone-related protein (PTHrP) is the main mediator of humoral hypercalcemia of malignancy (HHM) and it is produced by many tumors, including breast cancers. Breast epithelial cells as well as breast cancer tumors and cell lines have been reported as expressing PTHrP and the PTH/PTHrP receptor, suggesting that PTHrP may act as an autocrine factor influencing proliferation or differentiation of these cell types. We investigated PTHrP gene expression, PTH/PTHrP receptor signaling, and PTHrP-induced mitogenesis in three immortalized human mammary epithelial cell lines that exhibit differential tumorigenicity. The most tumorigenic cells expressed the highest levels of PTHrP messenger RNA (mRNA) and protein. We used reverse-transcription polymerase chain reaction (RT-PCR) and immunoblotting to detect the PTH/PTHrP receptor transcripts and proteins in all of the three cell lines. Treatment with human PTHrP(1-34) [hPTHrP(1-34)] and hPTH(1-34) increased intracellular cyclic adenosine monophosphate (cAMP) but not free Ca2+ in the nontumorigenic line. These agonists increased both cAMP and free Ca2+ levels in the moderately tumorigenic line, but only increased free Ca2+ in the highly tumorigenic line. Application of the PTH/PTHrP receptor antagonist [Asn10,Leu11,D Trp12]PTHrP(7-34) or PTHrP antibodies reduced [3H]thymidine incorporation in a dose-dependent fashion in the highly tumorigenic cell line but did not affect the other lines. Thus, treatment with a PTH/PTHrP receptor antagonist reduced cell proliferation, suggesting that PTHrP signaling mediated by the phospholipase C (PLC) pathway stimulates proliferation of a highly tumorigenic immortalized breast epithelial cell line.

Evaluation of in vitro bone resorption: high-performance liquid chromatography measurement of the pyridinolines released in osteoclast cultures

None of the currently used methods to evaluate bone resorption by osteoclasts cultured on bone substrate measures directly the amounts of degraded bone collagen, which is a direct reflection of the osteoclast "work done." We therefore propose a reliable biochemical method to evaluate the in vitro collagenolysis process. Bone-resorbing activity was evaluated, after HPLC separation, by fluorimetric measurement of hydroxylysylpyridinoline (HP), a collagen cross-link molecule, released in culture supernatants. We first confirm previous data reporting that HP is released in the culture medium in a peptide-conjugated form. After acid hydrolysis, we show that HP is highly correlated with the lacunae area (r = 0.68, P<0.0001) and with the amounts of antigenic collagen fragments (Cross-laps for culture) released in culture medium (r = 0.77, P<0.0002). Using a cysteine protease inhibitor, we observed that lacunae areas are dramatically less inhibited (35% inhibition) than the release of bone-degraded products, including HP and antigenic collagen fragments (96 and 92% inhibition, respectively). Coupled to the resorbed area measurement, biochemical evaluations offer both quantitative and qualitative complementary measurements of the osteoclastic bone-resorbing process.

Dexamethasone increases RAMP1 and CRLR mRNA expressions in human vascular smooth muscle cells

A recent report has shown that in vitro the RAMP2/CRLR complex is a functional adrenomedullin receptor in human endothelial and vascular smooth muscle cells. However, in vivo, it is well known that CGRP receptors are expressed in human coronary arteries and that a beneficial effect is observed in patients after CGRP infusion of patients with congestive cardiac failure. This contrast may be explained by the in vivo impregnation of major hormones, so we have tested if glucocorticoids were able in vitro to enhance the expression of the RAMP1/CRLR expression leading to functional CGRP receptors. The expression of RAMP1, RAMP2, CRLR, and adrenomedullin was evaluated by semiquantitative reverse-transcriptase polymerase chain reaction (RT-PCR) using (33)P in human coronary arteries vascular smooth muscle cells (VSMC) cultured in the presence of dexamethasone. Under basal conditions, the CRLR mRNA was expressed, but RAMP2 mRNA was clearly more abundant than RAMP1 mRNA. Increases in CRLR and RAMP1 mRNA expressions occurred 4 h after treatment of VSMC with 10(-7) M dexamethasone and no change was found for RAMP2 mRNA. Adrenomedullin mRNA increased later, i.e., 8 and 16 h after dexamethasone treatment. The RAMP1 mRNA expression was elevated with doses of dexamethasone ranging from 10(-10) to 10(-7) M, thus a 5-fold increase in the ratio between RAMP1 and RAMP2 was observed with the lowest dose of dexamethasone and a 2-fold rise at 10(-7) M. CRLR mRNA levels were half-reduced with the two lowest doses of dexamethasone (10(-10) and 10(-9) M), but increased from 10(-8) to 10(-7) M. Thus, we suggest that, in vivo, glucocorticoids are involved in the expression of CGRP receptors by human coronary VSMC.

[Physiopathology of bone loss and pharmacologic approach of selective estrogen receptor modulators]

Osteoclastic resorption increases at menopause and remains high during aging. The complex mechanism responsible for this increase involves cytokines and growth factors secreted by stromal cells and/or by osteoblasts and cells in the hematopoietic microenvironment. Although estrogen receptors have been found mainly on osteoblasts and their precursors, the stromal cells, they have also been demonstrated on osteoclast precursors. Raloxifene is a selective estrogen receptor modifier (SERM) that has the beneficial effects of estrogens on bone tissue but no estrogen agonist effects on the breast and uterus. Although recent data have established that the mechanism of action of estrogens and SERMs is far more complex than was previously thought, the reason for the tissue selectivity of these molecules remains unknown.

A combination of low doses of 17 beta-estradiol and norethisterone acetate prevents bone loss and normalizes bone turnover in postmenopausal women

The effects of 17 beta-estradiol (E2) 1 mg combined with low doses of norethisterone acetate (NETA) on postmenopausal bone loss and turnover were investigated in a 2-year, randomized, double-masked, placebo-controlled trial. A total of 135 postmenopausal women with a lumbar spine bone mineral density (BMD) T-score between -2 and +2 were randomized to daily treatment with an oral tablet of either placebo, E2 1 mg/NETA 0.25 mg, or E2 1 mg/NETA 0.5 mg. Significant (p < 0.001) increases in BMD at the lumbar spine (L1-4) were observed with E2 1 mg/NETA 0.25 mg (5.2%) and E2 1 mg/NETA 0.5 mg (5.4%) compared with placebo (-0.9%). The total hip BMD increased significantly in the E2 1 mg/NETA 0.25 mg (3.1%) and E2 1 mg/NETA 0.5 mg groups (3.3%) compared with placebo. At the femoral trochanter, the increase in BMD in the E2 1 mg/NETA 0.5 mg group (6.3%) was significantly different from the placebo group (0.8%), while that in the E2 1 mg/NETA 0.25 mg group (3.3%) was not. No statistical differences were found between the active groups and placebo for the change in BMD at the femoral neck. Significant increases in BMD at the distal radius and total body were found for both E2 1 mg/NETA 0.25 mg (0.9% and 2.5%, respectively) and E2 1 mg/NETA 0.5 mg (2.1% and 3.0%, respectively) compared with placebo (-0.7% and 0.4%, respectively). At the end of the treatment, urinary pyridinoline type I collagen C-telopeptide had decreased by 65% and 60% in the E2 1 mg/NETA 0.25 mg and E2 1 mg/NETA 0.5 mg groups, respectively, while the mean serum concentrations of osteocalcin had decreased by 39% and 34%, bone-specific alkaline phosphatase by 32% and 29%, and C-terminal propeptide of type I collagen by 21% and 19% had decreased by 34-39%, 29-32%, and 19-21% in the E2 1 mg/NETA 0.25 mg and E2 1 mg/NETA 0.25 mg groups, respectively. In conclusion, combinations of E2 1 mg and NETA 0.25 or 0.5 mg prevent bone loss in postmenopausal women at the lumbar spine, hip, distal radius and total body, and normalize bone turnover.

Type II autosomal dominant osteopetrosis (Albers-Schönberg disease): clinical and radiological manifestations in 42 patients

Type II autosomal dominant osteopetrosis (ADO II, Albers-Schonberg disease) is a genetic condition characterized by generalized osteosclerosis predominating in some skeletal sites such as the spine and pelvis. ADO II is rare, and most available clinical descriptions are based on small numbers of patients. We report the clinical and radiological manifestations in 42 ADO II patients. To our knowledge, this is the largest series reported so far. Our inclusion criterion was presence on radiographs of the spine of vertebral endplate thickening, producing the classic sandwich vertebra appearance. We found various patterns of sandwich vertebra, of which we provide a description to assist physicians in diagnosing ADO II. The classic bone-within-bone appearance was present in most but not all skeletal sites. The radiological penetrance of the disease was high (90%) and increased after 20 years of age. As many as 81% of our patients experienced clinical manifestations. Fractures were common (78% of patients) and healed slowly. Hip osteoarthritis developed in 27% of patients and required arthroplasty in 9 of the 16 affected hips. Nonmandibular osteomyelitis occurred in 4 cases (11%). Twenty-four percent of patients had thoracic or lumbar scoliosis. Orthopedic surgery was performed in 52.8% of patients, of whom half had at least three surgical procedures for internal fracture fixation, arthroplasty, limb deformity correction, or treatment of surgical complications. There was a high rate of surgical complications including nonunion, infection, prosthesis loosening, and intraoperative fractures. Nearly two-thirds of patients (64%) had stomatologic manifestations, including mandibular osteomyelitis in 4 patients (11%). Cranial nerve involvement responsible for hearing loss, bilateral optic atrophy, and/or facial palsy was present in 14 patients but was clearly attributable to ADO II in only 6 cases (16%). This large series sheds new light on several aspects of ADO II, most notably the possibility of severe clinical complications. Although other forms of osteopetrosis are considerably more severe, the name "benign osteopetrosis" previously used for ADO II is probably a misnomer.

Quality of life in patients with vertebral fractures: validation of the Quality of Life Questionnaire of the European Foundation for Osteoporosis (QUALEFFO). Working Party for Quality of Life of the European Foundation for Osteoporosis

Vertebral fractures may be minor or lead to pain, decreased physical function, immobility, social isolation and depression, which together contribute to quality of life. A Working Party of the European Foundation for Osteoporosis has developed a specific questionnaire for patients with vertebral fractures. This questionnaire, QUALEFFO, includes questions in the domains pain, physical function, social function, general health perception and mental function. QUALEFFO was validated in a multicenter study in seven countries. The study was done in 159 patients aged 55-80 years with clinical osteoporosis, i.e., back pain and other complaints with at least one vertebral fracture and lumbar bone mineral density T-score <-1. Patients with a recent vertebral fracture were excluded because of unstable disease. Controls were age- and sex-matched, and did not have chronic back pain or vertebral fractures. Subjects with conditions exerting a major influence on quality of life were excluded. The QUALEFFO was administered twice within 4 weeks and compared with a generic questionnaire, the Short Form 36 of the Medical Outcomes Study (SF-36). Standard spinal radiographs were made for assessment of vertebral height. Seven questions were removed from the analysis because of low response rate, linguistic ambiguities or redundancy. The 41 remaining questions were analyzed for repeatability, internal consistency and the capacity to discriminate between patients with vertebral fractures and controls. Comparison with the SF-36 was performed within similar domains by conditional logistic regression and by receiver operating characteristic (ROC) curves. The repeatability of QUALEFFO was good (kappa statistics 0.54-0.90) and 26 of 41 questions had a kappa score >/=0.70. The internal consistency of the five domains was adequate, with Crohnbach alpha around 0.80. All except five questions discriminated significantly between patients and controls. The median scores of QUALEFFO were significantly higher in patients with vertebral fractures than in controls in all five domain (p<0. 001), which is consistent with decreased quality of life in patients with osteoporosis. Spinal radiographs were assessed using the McCloskey-Kanis algorithm. According to this, 124 patients (78%) had vertebral fractures of >/=3 SD severity, in contrast with 7 controls (4%). Significant correlations existed between scores of similar domains of QUALEFFO and the SF-36, especially for pain, physical function and mental function. All five domains within each questionnaire discriminated significantly between fracture cases and controls. The odds ratios for pain and social function were greater for QUALEFFO, while general health perception was more discriminating using the SF-36. The ROC curve analysis of QUALEFFO indicated that all five domains were significantly predictive of vertebral fractures. When comparing similar domains of the two questionnaires, QUALEFFO domains demonstrated significantly better performance for pain, physical function and social function. The QUALEFFO total score and SF-36 physical composite score showed similar performance. In conclusion, QUALEFFO is repeatable, coherent and discriminates well between patients with vertebral fractures and control subjects. The results of this study confirm the decreased quality of life in patients with vertebral fractures.

The visualization and evaluation of bone architecture in the rat using three-dimensional X-ray microcomputed tomography

Microcomputed tomography allows the true three-dimensional structure of bone to be assessed by a nondestructive analysis. This article describes how this technique has for the first time been applied to rat bone to determine the effects of aging, ovariectomy, and antiresorptive drugs on bone structure and how these results compare with those determined by histological and histomorphometric techniques. During the procedure, a micro X-ray source is directed toward the bone sample. Modifications in the X-ray beam induced by bone crystals are determined for a range of acquisitions before three-dimensional reconstruction of bone architecture is performed. Morphometric parameters determined were trabecular bone volume/tissue volume, trabecular number, and trabecular thickness. The results show that ovariectomy has a dramatic effect on rat bone structure. Following treatment with the bone resorption inhibitor tiludronate, the morphometric parameters were significantly improved. The results obtained with three-dimensional microcomputed tomography were in agreement with observations made using classical techniques. Microcomputed tomography should prove useful for evaluating the antiresorptive effects of bisphosphonates on bone architecture and in allowing between-drug comparisons.

Calcitonin receptor polymorphism is associated with a decreased fracture risk in post-menopausal women

High bone resorption by the osteoclast results in osteoporosis, a disease affecting 40% of women after the menopause. Calcitonin, used to treat osteoporosis, inhibits bone resorption via receptors located on the osteoclasts. Two alleles of the calcitonin receptor gene ( CTR ) exist: a base mutation T-->C in the third intracellular C-terminal domain changes a proline (CCG) at position 447 to a leucine (CTG). We therefore studied the distribution of these alleles in a cohort of 215 post-menopausal Caucasian women suffering or not from osteoporotic fractures. The region of interest within the point mutation was amplified by PCR and screened for single strand conformation polymorphism. This work was followed by DNA sequencing of the fragments amplified. We found that bone mineral density (BMD) at the femoral neck was significantly higher in heterozygous subjects with the Rr genotype compared with the homozygous leucine (RR) and homozygous proline (rr) genotypes. Also, a decreased fracture risk was observed in heterozygote subjects. In conclusion, our results suggest that polymorphism of CTR could be associated with osteoporotic fractures and BMD in a population of post-menopausal women. CTR heterozygotes could produce both alleles of the receptor. The heterozygous advantage effect of Rr subjects could explain their protection against osteoporosis: higher bone density and decreased fracture risk. Establishing the genotype of the CTR gene in post-menopausal women could be of value in evaluating their risk of developing fractures.

Markers of bone remodelling in metabolic bone disease

New specific markers of bone remodelling have been developed that allow the evaluation of bone formation (plasma levels of osteocalcin and bone alkaline phosphatases) or bone resorption (collagen crosslink levels in urine). These markers can be used to evaluate bone disease. Their best application is currently in renal osteodystrophy, where there is a broad spectrum of bone abnormalities. In patients with this disease, bone markers can obviate the need for bone biopsy. So far, bone alkaline phosphatase is the most sensitive and specific marker for predicting the type of bone disease and therefore for deciding treatment in dialysed patients, although it is not ideal. Bone markers have also allowed a dramatic improvement in the comprehensive approach to bone loss with aging in women. Monitoring of the marked increase in bone turnover, and its persistence, in older women after menopause may help in the design of treatment strategies for osteoporosis. There is some hope that the measurement of urinary levels of collagen crosslinks will help to predict the clinical outcome of osteoporosis with respect to fractures in postmenopausal women. Bone markers could, besides being a measurement of bone density, help to determine the optimal treatment of postmenopausal women. Bone markers could also be used to predict or ascertain the response to treatment of osteoporosis, but few data are currently available to judge the routine usefulness of these new applications.

Estrogen stimulates PTHrP but not PTH/PTHrP receptor gene expression in the kidney of ovariectomized rat

The aim of the present study was to test the hypothesis that the decreased renal tubular reabsorption of calcium observed in estrogen deficiency is associated with a local regulation of either PTHrP or PTH/PTHrP receptor genes in the kidney. Rats were randomly sham-operated (S) or ovariectomized receiving either vehicle (OVX) or 4 microg E2/kg/day (OVX+E4) or 40 microg E2/kg/d (OVX+E40) during 14 days using alzet minipumps. Plasma PTH and calcium levels were lower in untreated OVX animals than in all other groups (P < 0.01). Plasma PTH was higher in OVX+E40 than in OVX+E4 (P < 0.05). PTHrP mRNA expression in the kidney was unaffected by ovariectomy but was increased in OVX+E40 (0.984 +/- 0.452 for PTHrP/GAPDH mRNAs expression vs. 0.213 +/- 0.078 in sham, P < 0.01). PTH/PTHrP receptor mRNA expression and the cAMP response of renal membranes to PTH were unaffected by ovariectomy and estrogen substitution. In conclusion, renal PTHrP and PTH/PTHrP receptor mRNAs are not modified by ovariectomy. However, 17beta-estradiol increases renal expression of PTHrP mRNA without evident changes in its receptor expression and function. This may help to explain the pharmacological action of estrogen in the kidney, especially how it prevents the renal leak of calcium in postmenopausal women.

[Bone remodeling: evaluation methods]

Bone tissue undergoes continual renewal in order to keep the mechanical competence of the bone matrix. This is performed by two cells: osteoclasts which resorb the calcified matrix and osteoblast which synthetize a new bone matrix. Biochemical markers of bone remodelling allow the evaluation of the activity of each type of bone cells. An unbalance in this process induces modifications of the amount of calcified tissue and of the bone microarchitecture. Several technics based on X-ray and ultrasound allow a non invasive evaluation of these modifications.

Pamidronate corrects the down-regulation of the renal parathyroid hormone (PTH)/PTH-related peptide (PTHrP) receptor mRNA in rats bearing Walker tumors

Human hypercalcemia of malignancy (HHM) is generally due to the release into the circulation of parathyroid hormone-related peptide (PTHrP). PTHrP stimulates osteoclastic bone resorption and renal calcium reabsorption through the activation of a receptor similar to that of PTH (PTH-R). However, there is scarce information about the PTH-R regulation in the setting of the hypercalcemia. In the present study, we assessed the molecular basis of renal PTH-R regulation in Walker tumor-bearing rats either treated or not by a bisphosphonate, pamidronate. Twenty-seven 6-week-old rats were randomly divided into three experimental groups: WC- APD- (9 control rats), WC+ APD- (9 Walker tumor-bearing rats), and WC+ APD+ (9 Walker tumor-bearing rats receiving 15 mg/kg/day of sodium pamidronate every day for seven days). Pamidronate induced a significant decrease in the mean tumor weight (9.3+/-0.8 vs 6.3+/-0.6 g). Seven days after the subcutaneous implantation of the Walker cells, plasma total calcium was 10.8+/-0.4, 16.8+/-0.6, and 12.9+/-0.6 mg/dl in WC- APD-, WC+ APD-, and WC+ APD+, respectively. Plasma PTHrP concentration was undetectable, 15.9+/-2.6, and 7.2+/-1.4 pmol/l, respectively. Bone histomorphometric results showed high resorption in WC+ APD-, which returned below the basal level of the WC- APD- with pamidronate treatment. Densitometric analysis of Northern blots revealed that the renal PTH-R mRNA expression in WC+ WPD- rats was a quarter of the levels in the WC- APD- and WC+ APD+ groups. WC+ APD- also had a decreased PTH-stimulated cAMP production in renal membranes. The PTH-R was expressed in the Walker tumor and it was not modified by pamidronate treatment. In conclusion, the expression of PTH-R receptor mRNA is significantly reduced in the kidney of rats bearing Walker carcinoma tumor. Its regulation is tissue-specific: pamidronate, which partially corrected the hypercalcemia and elevated circulating PTHrP, normalized the PTH-R mRNA expression in the kidney but not in the tumor.

Cytokine release from marrow mononuclear cells is negatively correlated to cortical elasticity in non-osteoporotic postmenopausal women

Activation of bone remodeling is likely to be under the control of mechanical factors acting, in part, through soluble local factors. We therefore investigated a relationship between cytokine production by marrow cells and bone elasticity. We studied 36 non-osteoporotic postmenopausal women undergoing hip arthroplasty for hip arthrosis (mean age: 68 +/- 8 years; lumbar BMD Z-score: +0.54 +/- 0.33 SD). Adherent marrow mononuclear cells were cultured for 48 hours with autologous plasma, and supernatants were harvested for PGE2, IL-1, TNF-alpha, and IL-6 measurements. Femoral neck cortical bones were removed during surgery for cortical histomorphometric evaluation and determination of elasticity indices (C33) using ultrasonic transmission method. In this nonosteoporotic population, femoral neck longitudinal elasticity indices were inversely correlated to both cortical thickness (r = -0.58, P < 0.01) and cortical porosity (r = -0.33, P < 0.01). The longitudinal elasticity indices were also negatively correlated to basal IL-1 and TNF-alpha release by adherent mononuclear marrow cells (r = -0.59, P < 0.01; r = -0.60, P < 0.01, respectively). However, no relationship was found between the three cytokines tested and either cortical thickness or porosity. These data show a link between cortical biomechanical properties and local factors involved in bone remodeling. We suggest that increased bone elasticity decreases transmission of strain, which in turn decreases cytokine release from marrow cells. However, whether cytokines influence bone elasticity or vice versa remains to be demonstrated.

Effects of prostaglandins on human hematopoietic osteoclast precursors

The effect of prostaglandin E2 (PGE2) on osteoclast (OC) differentiation is unclear, either stimulator or inhibitor, depending on the in vitro system used. This probably reflects indirect mechanisms through intermediate cells. We have investigated the direct effect of PGE2 on human OC differentiation from cord blood monocytes (CBMs) in the absence of stromal cells. Macrophages and multinucleated cells (MNCs) resembling OCs form in cultures of CBMs stimulated by 1,25-dihydroxyvitamin D3. In the present study, CBMs were cultured for 3 weeks, as previously described, in the presence or absence of PGE2. The number of MNCs was significantly reduced in the presence of PGE2 as was the proliferation of cultured CBMs, assessed on day 7. Immunohistochemistry was performed to evaluate macrophage markers (CD11b and CD14) and OC marker (beta3-chain). PGE2 significantly increased the numbers of CD11b-positive and CD14-positive cells, whereas the number of beta3-chain-positive cells was significantly decreased. beta3-Chain, c-fos, and human calcitonin receptor (h-CTR) messenger RNA (mRNA) expressions were evaluated by reverse transcription-PCR with RNA extracted from cultured CBMs. In the presence of PGE2, expression of beta3-chain and c-fos mRNA was reduced from the first week of culture. h-CTR mRNA expression was also reduced, and only the h-CTR1 isoform was detected in the presence of PGE2. In addition, when PGE2 was added only during the last week of culture, when no CBM proliferation occurred, the number of CD11b- and beta3-positive cells was unchanged compared to that in the control culture, as were the proportion of MNCs, the fusion index, and the expression of c-fos mRNA. In conclusion, our results suggest that PGE2 has an inhibitory effect on human OC differentiation from CBMs, possibly by reducing precursor proliferation in these cultures. We also hypothesize that PGE2 may reduce OC differentiation by increasing the proportion of precursor cells that differentiate into macrophages. In addition, this may be the result of inhibition of the c-fos expression in CBMs.

1,25-dihydroxyvitamin D3 induces NAD(+)-dependent 15-hydroxyprostaglandin dehydrogenase in human neonatal monocytes

1,25-Dihydroxyvitamin D3 [1,25-(OH)2D3] induces the differentiation of monocytes into macrophage-like cells in vitro. To identify the genes expressed during this process, we performed differential display polymerase chain reaction on RNA extracted from cord blood monocytes (CBMs) treated with 1,25-(OH)2D3. Treated CBMs expressed type-I 15-hydroxyprostaglandin dehydrogenase (type-I 15-PGDH), the key enzyme of prostaglandin E2 (PGE2) catabolism and a 15-PGDH-related mRNA (15-PGDHr). This newly described 15-PGDH-related mRNA was constitutively expressed in adult monocytes. 15-PGDH gene(s) transcription was accompanied by the appearance of the 15-PGDH activity in treated CBMs. In addition, the cyclooxygenase 2 mRNA level was decreased and PGE2 levels in the culture mediums were lowered (50%). Our results stress that 1,25-(OH)2D3, at least in neonatal monocytes, can exert, directly or indirectly, a dual control on key enzymes of PGE2 metabolism. In conclusion, we suggest that modifications in prostaglandin metabolism, induced by the expression of type-I 15-PGDH and the downregulation of cyclooxygenase 2, could be involved in monocytic differentiation.

Quality of life as outcome in the treatment of osteoporosis: the development of a questionnaire for quality of life by the European Foundation for Osteoporosis

The morbidity of osteoporosis is caused by fractures. Vertebral fractures lead to pain and disability and a decrease in quality of life. A Working Party of the European Foundation for Osteoporosis has developed a specific questionnaire for patients with established vertebral osteoporosis. This questionnaire is intended for use in clinical trials. The questionnaire consists of questions and visual analogue scales in the following domains: pain, activities of daily living, jobs around the house, mobility, leisure and social activities, general health perception and mood. The questionnaire has been translated from English into French, German, Italian, Hebrew, Swedish and Dutch. The questionnaire is currently being validated in a multicentre study involving patients with stable osteoporosis and control subjects. Preliminary results indicate that the reproducibility is sufficient and that the questionnaire is able to discriminate between patients with vertebral osteoporosis and control subjects.

Inhibitory and stimulatory effects of prostaglandins on osteoclast differentiation

The effect of prostaglandins (PGs) on osteoclast differentiation, an important point of control for bone resorption, is poorly understood. After an initial differentiation phase that lasts at least 4 days, murine monocytes, cocultured with UMR106 osteoblastic cells (in the presence of 1,25-dihydroxyvitamin D3) give rise to tartrate-resistant acid phosphatase (TRAP) positive osteoclast-like cells that are capable of lacunar bone resorption. PGE2 strongly inhibits TRAP expression and bone resorption in these cocultures. To examine further the cellular mechanisms associated with this inhibitory effect, we added PGE2 to monocyte/UMR106 cocultures at specific times before, during, and after this initial 4-day differentiation period. To determine whether this PGE2 inhibition was dependent on the type of stromal cell supporting osteoclast differentiation, we also added PGE2 to cocultures of monocytes with ST2 preadipocytic cells. Inhibition of bone resorption was greatly reduced when the addition of PGE2 to monocyte/UMR106 cocultures was delayed until the fourth day of incubation; when delayed until the seventh day, inhibition did not occur. PGE2 inhibition of bone resorption was concentration-dependent and at 10(-6) M was also mediated by PGE1 and PGF2alpha. In contrast to its effects on monocyte/UMR106 cocultures, PGE2 stimulated bone resorption in monocyte/ST2 cocultures. Both ST2 cells and UMR106 cells were shown to express functional receptors for PGE2.These results show that PGs strongly influence the differentiation of osteoclast precursors and that this effect is dependent not only on the type and dose of PG administered, but also on the nature of the bone-derived stromal cell supporting this process.

PTH/PTHrP receptor mRNA is down-regulated in epiphyseal cartilage growth plate of uraemic rats

PTH/PTHrP receptor mRNA is down-regulated in epiphyseal cartilage growth plate of uraemic rats. Growth retardation, hypocalcaemia, hyperphosphataemia, and skeletal resistance to the action of PTH are well known features of advanced chronic renal failure (CRF). It has been suggested that the downregulation of renal and skeletal PTH receptors (PTH/PTHrP-R) could play an important role in the occurrence of these abnormalities. In the present study, four uraemic (4 weeks after 5/6 nephrectomy) and four control (sham-operated) rats were analysed for PTH/PTHrP-R mRNA expression at the proximal femoral and tibial growth plates by in situ hybridization. Uraemic rats had plasma biochemical abnormalities of advanced CRF including high creatinine, phosphate, and PTH, and low calcium and calcitriol levels. The femoral and tibial bones of uraemic animals were shorter in length than those of control rats, and had reduced width and cellularity of the epiphyseal cartilage growth plate. Mean (+/- SD) tibia growth plate width was 152 +/- 30 microns in uraemic rats, compared with 170 +/- 35 microns in control rats. The difference was mostly due to a marked reduction of the zone expressing PTH/PTHrP-R (mature chondrocytes) which was 30 +/- 5 microns in tibias from uraemic versus 44 +/- 10 microns in tibias from control rats. The hybridization signals of PTH/PTHrP-R per individual cell were quantified on dark field images using a computer-assisted image analysis system. The number of grains in PTH/PTHrP-R positive cells was also decreased in uraemic rats, 103 +/- 13 compared with 123 +/- 14 arbitrary units (dark pixel density)/cell in control rats (P < 0.005). In conclusion, these data indicate that rats with severe CRF and secondary hyperparathyroidism have reduced epiphyseal cartilage PTH/PTHrP-R mRNA expression. This alteration may be relevant in the pathogenesis of growth retardation in uraemia.

Dynamics of bone remodelling: biochemical and pathophysiological basis

Renewal of the bone matrix is induced by bone cells called osteoblasts and osteoclasts, which act sequentially on the bone surface. This "remodelling" depends on local factors, such as cytokines and growth factors which play an important role in the bone tissue as mediators of cell-to-cell and matrix-to-cell communication. Growth factors released from the bone matrix during the resorption are responsible for the refilling of the resorption cavity by osteoblasts. Cytokines also mediate locally the effect of several hormones on bone cells. Recent work is concerned with the modulation by oestradiol of osteoblastic cytokines acting on osteoclast differentiation. In mice, an increased production of interleukin-6 production by osteoblasts is responsible for the increased bone resorption occurring after ovariectomy. Other growth factors, such as transforming growth factor-beta, whose secretion is modified by oestradiol, may also be implicated. In women, an increase in cytokine production by blood mononuclear cells is associated with the occurence of menopause and reversed by oestrogen treatment. During osteoporosis and age-related bone changes, changes in the production of insulin-like growth factor I or of one of its binding proteins could be responsible for low bone formation. In addition to their role in bone remodelling, cytokines and growth factors are now implicated in osteoporosis.

Plasma total versus bone alkaline phosphatase as markers of bone turnover in hemodialysis patients

Plasma total versus bone alkaline phosphatase as markers of bone turnover in hemodialysis patients. Plasma bone-specific alkaline phosphatase (bAP) has been demonstrated to be more reliable than total alkaline phosphatases (tAP) in providing information about bone turnover in patients with metabolic bone diseases. This study surveyed 42 hemodialysis patients who underwent a systematic transiliac bone biopsy for histomorphometry study. Plasma bAP was determined by using a new immunoassay (Tandem-R Ostase, Hybritech, Liège, Belgium). Plasma bAP values were compared with those of two other plasma markers of bone metabolism, namely tAP and intact parathyroid hormone (iPTH), for the correlations with bone histomorphometric parameters. Patients with high-turnover bone disease (HTBD) (N = 32) had significantly higher plasma bAP levels than patients with normal or low bone turnover (N/LTBD) (N = 10) (66.9 +/- 63.5 ng/mL versus 10.8 +/- 4.2 ng/mL, respectively). Bone formation and resorption were highly correlated in these patients, and plasma bAP levels were positively correlated with bone resorption parameters, including osteoclast surface (r = 0.39, P < 0.0001) and osteoclast number/mm2 (r = 0.36, P < 0.001), and with bone formation parameters, osteoblast surface (r = 0.50, P < 0.005), and bone formation rate (r = 0.91, P < 0.0001). The bone formation rate was better correlated with plasma bAP levels than with either plasma tAP or iPTH concentrations. Plasma bAP level equal or higher than 20 ng/mL, either alone or combined with plasma iPTH of 200 pg/mL, had the highest sensitivity, specificity, and predictability values for the diagnosis of high-turnover bone disease, and formally excluded patients with normal or LTBD. In conclusion, plasma bAP can be measured with a reliable immunoassay in hemodialysis patients. It represents a highly sensitive and specific biochemical marker of skeletal remodeling in these patients. Therefore, both serum iPTH and bAP are complementary in diagnoses of the type of renal osteodystrophy.

Cytokines and osteoporosis

Bone remodeling is a complex process that involves cells from various lineages, the calcified extracellular bone matrix and a multitude of regulation factors that act at both the tissular and cellular levels. Resorption and formation of bone are regulated at various levels during the series of events that lead from stem cell proliferation to differentiation of mature cells. These events are controlled by calciotropic hormones, whose indirect cellular effects are mediated by the production of local factors. A host of cytokines and growth factors influence the proliferation and differentiation of bone cells, and their activities are modulated by a large number of hormones. Resorption by osteoclasts is regulated at various stages of the differentiation process by cytokines produced by osteoblasts or stromal cells. Experimental studies in mice suggest that these local factors play a role in postoophorectomy bone loss, although their exact mechanisms of action are not known. Evidence that these factors are involved in postmenopausal bone loss is beginning to accumulate, opening up a vast field of investigation.

The development of a European questionnaire for quality of life in patients with vertebral osteoporosis

The complaints of vertebral osteoporosis usually result from wedge or crush fractures and biconcave deformities. These are caused by a decrease of bone mass and deterioration of bone structure leading to loss of strength. Treatment of osteoporosis should result in an increase of bone mass, and the incidence of new vertebral fractures should diminish. However, new vertebral fractures are not always accompanied by pain, and disability does not well correlate with the number of vertebral fractures. Patients with osteoporosis often have other problems e.g. with taking a shower, preparing meals, gardening, walking stairs, visiting friends and attending social activities. In addition, pain and disability may influence mood and lead to depression. The assessment of quality of life should be a primary endpoint in clinical trials in patients with osteoporosis and in individual patients care. Recently, the European Foundation for Osteoporosis (EFFO) has decided a develop a questionnaire for patients with vertebral osteoporosis, i.e. patients with vertebral deformities. The questionnaire is meant for use in clinical trials. A questionnaire was made including 48 questions and 6 visual analogue scales. The questions concern the following domains: pain, activities of daily living, jobs around the house, moving, leisure and social activities, general health perception and mood. The questionnaire ("Qualeffo") has now entered the validation phase. The first study in 8 centres concerns the within-subject reproducibility, the internal coherence, and the specificity by comparing osteoporotic patients with a control group not suffering from osteoporosis or backpain.

Sequence of a novel mRNA coding for a C-terminal-truncated form of human NAD(+)-dependent 15-hydroxyprostaglandin dehydrogenase

We amplified, using the polymerase chain reaction (PCR) and NAD(+)-dependent 15-hydroxyprostaglandin dehydrogenase (type-I 15-PGDH)-specific primers, RNA extracted from the HL-60 cell line. Two bands, differing in size by approx. 160 bp, were detected with ethidium bromide staining after electrophoresis of amplification products and hybridization with a 15-PGDH-specific probe. Sequencing these DNA bands revealed that the largest corresponded to the 15-PGDH cloned from human placenta [Ensor et al., J. Biol. Chem. 265 (1990) 14888-14891]. The smaller sequence coded for a predicted C-terminal-truncated form of 15-PGDH. This subtype of the type-I 15-PGDH mRNA was also found using RT-PCR in human liver, placenta and a cell line derived from a human medullary thyroid carcinoma (TT cells). Hybridization studies using specific probes indicated that this new mRNA form probably corresponded to the 3.4-kb mRNA, one of the two 15-PGDH mRNAs previously detected in Northern blot analysis.

1,25 dihydroxyvitamin D and dexamethasone decrease in vivo Walker carcinoma growth, but not parathyroid hormone related protein secretion

Parathyroid hormone related protein (PTHrP) is produced by several breast cancers. 1,25 dihydroxyvitamin D (1,25[OH]2D) and Dexamethasone (DEX) have been shown to decrease PTHrP mRNA expression in several cell lines. We therefore tested the in vivo effect of both steroids on PTHrP secretion and tumor development of the Walker carcinoma (WC). WC cells were injected subcutaneously in Fisher rats which were simultaneously treated with either vehicle, or 1,25(OH)2D (0.5 micrograms/kg/d) or DEX (2 mg/kg/d). After 7 days, tumor weight was significantly decreased in the 2 treated-groups as compared to the control group. Vehicle treated-rats developed hypercalcemia, which was also observed in rats treated with 1,25(OH)2D; by contrast, the plasma calcium was significantly decreased in the DEX-treated group compared to vehicle-treated rats. In a dose-effect experiment, this dose of 1,25(OH)2D induced marked hypercalcemia in rats not implanted with WC, but was required to decrease the tumor weight in implanted rats. In both 1,25(OH)2D and DEX-treated groups, plasma PTHrP levels were significantly decreased, but there was a similar correlation between PTHrP plasma level and tumor weight in the three groups. Indeed, the cytosolic PTHrP content/mg tumor was identical in the 3 groups. By contrast, the PTHrP/Actin mRNA in the tumor was significantly decreased in the 1,25(OH)2D group, comparatively to the vehicle and DEX groups. Our results show that Dexamethasone and 1,25(OH)2D decrease WC tumor development in vivo, but do not change the PTHrP secretion by the remaining tumor although steady state PTHrP mRNA content level is decreased by 1,25(OH)2D.

Cytokine-mediated bone resorption in patients with the hyperimmunoglobulin E syndrome

Hyperimmunoglobulin E syndrome (HIES) is a rare immunodeficiency disorder characterized by increased serum immunoglobulin E levels. Bone fragility is part of this syndrome, which has recently been reported to be also associated with an imbalance in cytokine-secreting lymphocyte subpopulation. It has recently been shown that some cytokines can play a role in the bone fragility following menopause. We therefore investigated six patients (mean age 16.5 +/- 8.5 years) affected by this rare syndrome in order to study their bone remodeling and the possible involvement of cytokines in causing the bone fragility associated with this disease. Three of six patients had suffered long bone fractures; in four of six patients the cortical bone mass measured at the distal radius was two standard deviations below that of the aged-matched controls. Urinary pyridinoline excretion, a marker of bone resorption, was markedly increased in the two youngest patients. Adherent mononuclear cells derived from these patients were cultured in vitro and the bone resorbing activity (BRA) of the culture supernatant was measured by means of a fetal rat long bone assay. The BRA was up to 28% above the basal value. We compared the BRA and the cytokine production by the mononuclear cells of these patients to that of postmenopausal women. The BRA, and the IL1 beta, IL6, and TNF alpha levels in the mononuclear cell culture supernatants were identical for both HIES and postmenopausal women. However, the levels of PGE2 were higher and the levels of interferon-gamma were lower in the HIES patients. In conclusion, increased bone resorption in young patients with the HIES is responsible for the cortical bone loss that leads to a higher incidence of fractures. The high BRA secreted by the mononuclear cells of these patients is similar to that found in mononuclear cells from postmenopausal women. These data provide evidence of potent mononuclear cell activation leading to bone loss in HIES, which could be related to IgE-dependent mechanisms.

Osteoclast formation from human cord blood mononuclear cells co-cultured with mice embryonic metatarsals in the presence of M-CSF

Investigating the potentiality of cord monocytes to differentiate toward osteoclast-like cells (OCL) in vitro, we previously reported that in the presence of 1,25(OH)2 vitamin D3 (1,25-(OH)2D3), multinucleated-cells generated by cord monocyte cultures though displaying morphological features of OCL failed to resorb devitalized bones. We thus hypothesized that full differentiation of cord monocytes toward bone-resorbing cells may require the presence of factors released from and/or direct interactions with living osteogenic cells. In the present study, we tested these hypotheses using two culture systems supporting the development of bone-resorbing cells in the presence of bone matrix. First, cord mononuclear cells were co-cultured with murine fetal metatarsals depleted of osteoclast progenitor cells (stripped metatarsals) in the presence of 1,25-(OH)2D3. We found that cord mononuclear cells failed to differentiate toward OCL as indicated by the absence of the release of 45Ca previously incorporated in fetal bones and by the absence of formation of TRAP-positive (TRAP[+]) multinucleated cells which have invaded mineralized cartilage during the co-culture period. In the same model, we then investigated the effect of some soluble factors known as stimulators of osteoclast differentiation. Whereas exogenous rhIL6 and rhIL3 were ineffective in this assay, rhM-CSF consistently increased both the number of TRAP(+) multinucleated cells inside the mineralized cartilage and the release of 45Ca into the culture media. The effects of rhM-CSF were time-dependent reaching the maximum after 3 weeks of culture.(ABSTRACT TRUNCATED AT 250 WORDS)