Biomedical subjects

D J Baylink

Publications and source records attributed to D J Baylink.

At least 37 records · Page 2Linked to original sources

PubMed2002

IGF-binding proteins are multifunctional and act via IGF-dependent and -independent mechanisms.

Traditionally, binding proteins are known to regulate the activity of ligands by prolonging their half-life, and insulin-like growth factor (IGF)-binding proteins (IGFBPs) are no exception to this. The IGFBP family contains six high-affinity members with variable functions and mechanisms of actions. In addition to functioning as simple carrier proteins, IGFBPs in serum function to regulate the endocrine actions of IGFs by regulating the amount of IGF available to bind to signaling IGF-I receptors, whereas locally produced IGFBPs act as autocrine/paracrine regulators of IGF action. Furthermore, recent in vitro and in vivo findings that IGFBPs function independently of the IGFs as growth modulators are particularly exciting. Regarding the role of IGFBPs as ligand-independent growth modulators, our recent data that IGFBP-5 stimulates markers of bone formation in osteoblasts lacking functional IGFs provide evidence that IGFBP-5 itself is a growth factor that can act independently of IGFs to regulate bone formation. In terms of the mechanism by which certain IGFBPs mediate their effects in a ligand-independent manner, the binding of IGFBP to its putative receptor on the cell membrane may stimulate the signaling pathway independent of an IGF receptor, to mediate the effects of IGFBPs in certain target cell types. IGFBPs may also exert IGF-independent effects by transcriptional activation of genes by IGFBPs transported into the nucleus via their nuclear localization signal. In conclusion, IGFBPs are unusually pleotrophic molecules with functions ranging from the traditional role of prolonging the half-life of the IGFs to functioning as growth factors independent of the IGFs. In this regard, it was surprising to find that the human genome contains only about 35 000 genes. One mechanism to account for such complexity with a relatively small number of genes is strikingly illustrated by the multifunctional IGFBP class of proteins.

Animals↗

PubMed2001

Quantitative assessment of forearm muscle size, forelimb grip strength, forearm bone mineral density, and forearm bone size in determining humerus breaking strength in 10 inbred strains of mice.

Bone strength is an important clinical endpoint of osteoporosis research. The evaluation of the relative importance of bone and muscle components to bone strength has widespread implications for the understanding and preventing of osteoporosis. The objectives of this study were to understand the interrelationship between the different components of the muscular skeletal system and to determine the effect of forearm muscle size, forelimb grip strength, forearm bone mineral density (BMD), and forearm bone size on the humerus breaking strength among 10 inbred strains of mice. The forearm muscle size was measured using a peripheral quantitative computed tomography (pQCT). The forearm BMD and forearm bone size were measured using a PIXIMUS Densitometer. The forelimb grip strength and humerus breaking strength were measured using an Instron Mechanical Tester. Significant correlations were found among the five regional phenotypes. All variables have a moderately high genetic component with heritability estimates of 0.83 for forelimb grip strength, 0.76 for forearm muscle size, 0.6 for forearm BMD, 0.63 for forearm bone size, and 0.68 for humerus breaking strength. Forward stepwise multiregression analysis showed that the forearm BMD, forelimb grip strength, and forearm bone size were three major determinants of bone strength and explained 61% of the variation in bone breaking strength. These data suggest that evaluation of these three parameters together, rather than BMD alone, is a more effective, noninvasive approach for predicting fracture risk.

Absorptiometry, Photon↗

PubMed2001

Structure and characterization of the human insulin-like growth factor binding protein (IGFBP)-6 promoter: identification of a functional retinoid response element.

The 1.7 kb human insulin-like growth factor binding protein (IGFBP)-6 gene 5'-flanking region was sequenced and found to have promoter activity in human osteoblasts. The sequence contains four clustered transcription start sites and three retinoic acid response elements (RAREs) with widely spaced half-sites. Only the proximal DR15 RARE was functional. Retinoids increased IGFBP-6 promoter activity up to 3-fold.

Animals↗

PubMed2001

Development of an MFG-based retroviral vector system for secretion of high levels of functionally active human BMP4.

We sought to develop a retroviral vector system that would produce secretion of high levels of bone morphogenetic protein (BMP)-4 by optimizing the expression construct and developing an improved retroviral vector. Replacement of the propeptide domain of BMP4 with that of BMP2 increased the secretion level of mature BMP4 protein in transduced cells. The intact BMP2 pro-peptide sequence was essential, as deletion of a small part of the propeptide sequence of BMP2 from the BMP2/4 hybrid construct diminished BMP4 expression and secretion. Addition of a hemaglutinin tag to the carboxy terminus of BMP4 abolished the bioactivity of secreted BMP4. Transduction of rat marrow stromal cells (and fibroblasts) with an MFG-based retroviral vector pseudotyped with VSV-G envelope containing this BMP2/4 hybrid expression construct led to secretion of very high levels of mature BMP4 in conditioned medium (up to 1 microg/10(6) cells/24 hours). The secreted BMP4 was biologically active, as it induced alkaline phosphatase expression in C2C12 cells. The transduced rat marrow stromal cells expressing mature BMP4 induced de novo ectopic bone formation in syngenic immune-competent rats. We have developed an MFG-based retroviral vector system that causes secretion of high levels of functionally active human BMP4 protein.

Animals↗

PubMed2001

A new monoclonal antibody ELISA for detection and characterization of C-telopeptide fragments of type I collagen in urine.

Clinical studies have shown that measurements of urine concentration of degradation products of C-terminal telopeptides of type I collagen provide a selective marker to assess bone resorption. Assays for C-telopeptide fragments have been described using antibodies generated against an eight amino acid synthetic peptide EKAHDGGR. In this study, we describe development of a rat monoclonal antibody against a synthetic linear peptide, DFSFLPQPPQEKAHDGGR, which we isolated and characterized from Paget's urine by chromatographic methods. An ELISA procedure was developed to evaluate the efficacy of this monoclonal to measure bone resorption and characterize urinary degradation products of C-terminal type I collagen. The measuring range of ELISA was 10-1,000 ng/ml with a detection limit of 10 ng/ml. Averaged intraassay and interassay CVs were <7% (n = 8) and <11% (n = 3), respectively. Mean spike and dilution recoveries range between 90 and 116%. In assessing the clinical performance, we observed approximately 48% higher values for postmenopausal patients (n = 20) compared with premenopausal women (n= 19), Z score = 2.7 (P = 0.0091). The discriminatory power to assess subtle changes in bone turnover between pre- and postmenopausal women compares well with the commercially available markers of bone resorption. Comparison of C-telopeptide concentration in a population including normal and osteoporotic patients (n = 74) shows a strong correlation with DPYR r = 0.95 (P < 0.001). In addition, in postmenopausal osteoporotic patients, a 44% (P < 0.05) decrease in C-telopeptide concentration was observed after 3 months of treatment with Alendronate, as compared with basal values. The antibody developed in this study displays a slightly different epitope than that reported previously using eight amino acid residues EKAHDGGR. In addition, isolation and characterization of circulating forms of C-telopeptide from healthy children by immunoaffinity purification revealed the presence of two novel urinary fragments corresponding to amino acid sequence EKAHDGGR and EKAHDG, in addition to the previously known two fragments composed of two alpha-1 chains linked together by a pyridinium crosslinks. The origin of the fragment EKAHDG could not be explained by the known mechanisms involved in collagen degradation, indicating that it could be a product of renal handling of C-telopeptide fragments generated from bone. The preliminary clinical data suggest that the new assay may be useful for further investigation of the clinical importance of measurement of these type I collagen degradation products.

Adolescent↗

PubMed2001

Analysis of gene expression in the wound repair/regeneration process.

Wound repair/regeneration is a complex process consisting of three stages: inflammation, tissue regrowth, and remodeling, which together involve the action of hundreds of genes. In order to i) identity and analyze the genes that are expressed at the inflammatory stage of repair (i.e., 24 h after injury) and ii) evaluate the molecular basis of fast-wound repair/regeneration in adult mammals. we examined the expression of 8734 sequence-verified genes in response to ear punch in a fast wound-repair/regeneration strain, MRL/MpJ-Fas(lpr) mice, and a slow-wound-repair strain, C57BL/6J mice. Many differentially expressed genes can be assigned to wound-repairing pathways known to be active during the inflammatory phase. whereas others are involved in pathways not previously associated with wound repair. Many genes of unknown function (ESTs) exhibited a more than twofold increase in MRL/ MpJ-Fas(lpr) or C57BL/6J mice, suggesting that current understanding of the molecular events at the inflammatory stage of repair is still limited. A comparison of the differential expression profiles between MRL/MpJ-Fas(lpr) and C57BL/6J mice suggests that fast-wound-repair in MRL/MpJ-Fas(lpr) mice is mediated by a metabolic shift toward a low inflammatory response and an enhanced tissue repair.

Animals↗

PubMed2001

Genetic variation in bone-regenerative capacity among inbred strains of mice.

Genetic variation in bone-regenerative capacity has not been studied in any animal model system. We developed a "drill-hole" model in the tail vertebra of inbred strains of mice that allows us to reproducibly introduce an injury with a defined boundary and quantify the rate of bone healing using the combination of high-resolution Faxitron X-ray imaging and the ChemiImager 4000 Low Light Imaging System. Using this model, we demonstrate that bone-regenerative capacity is a genetically controlled trait with an estimated heritability of 72%, and that it differs significantly among inbred strains of mice. Of the 12 inbred strains tested, Sencar/PtJ was identified as the most suitable model for the study of hard-tissue regeneration. This strain regained 73% of bone loss 30 days after injury, in contrast to the slow healer, CBA/J, which recovered only 25% of the bone loss during the same period. Bone-regenerative capacity was not correlated with soft-tissue-regenerative capacity, suggesting that different sets of genes may regulate soft- and hard-tissue regeneration. It was, however, significantly correlated with total bone mineral density (R = 0.49, p < 0.01), indicating that high bone density is associated not only with prevention of bone fracture, but also with promotion of bone regeneration.

Animals↗

PubMed2001

Circadian and longitudinal variation of serum C-telopeptide, osteocalcin, and skeletal alkaline phosphatase in C3H/HeJ mice.

Inbred strains of mice are increasingly being used as an animal model to investigate skeletal disorders relevant to humans. In the bone field, one of the most convenient endpoints for evaluating genetic, physiological, or pharmaceutical perturbations is the use of biochemical markers. To apply biochemical markers in an effective manner, it is of key importance to establish the biological variation and appropriate sampling time. In this study, we evaluate two components: (i) circadian changes, and (ii) longitudinal variation for three serum markers, osteocalcin, C-telopeptide, and skeletal alkaline phosphatase (sALP), using 6-week-old C3H/HeJ (C3H) mice. To study circadian rhythms, the mice were randomly divided into eight groups of 15 mice each. Blood was collected at 3 h intervals, starting at 9:00 A.M. and continuing until 6:00 A.M. the next day. To determine whether circadian rhythm is intrinsically regulated or influenced by restricted food intake, it was also studied after a 12 h fasting period. Serum osteocalcin and C-telopeptide levels were measured by enzyme-linked immunoassay (ELISA) and skeletal alkaline phosphatase by a kinetic assay. The results demonstrated significant circadian variations in osteocalcin and C-telopeptide levels with a peak value between 0900 and 1200 h during daytime and a nadir between 15:00 and 18:00 h. The peak levels of C-telopeptide and osteocalcin were 26%-66% higher as compared with 24 h mean values. The pattern of the circadian variation of C-telopeptide and osteocalcin was similar in female and male animals and was not significantly affected by restricted food intake. The sALP levels were only marginally affected by the circadian rhythm. Longitudinal variations, expressed as coefficient of variation (CV), for osteocalcin, C-telopeptide, and sALP concentrations were 17%, 14%, and 16%, respectively. In addition, the longitudinal variations were not significantly influenced by the time of blood collection in sALP and osteocalcin levels, whereas C-telopeptide levels showed significantly higher within-subject day-to-day variation in morning samples, as compared with blood samples collected in the afternoon. The results highlight the importance of: (i) the timing of sample collection for appropriate interpretation of the bone marker data; and (ii) using the appropriate number of samples based on the variance obtained herein.

Alkaline Phosphatase↗

PubMed2001

Genetic control of the rate of wound healing in mice.

There have been few studies of the inheritance of wound healing in mammals. In this study, we demonstrate that inbred strains of mice differ significantly in the rate of wound healing. Of the 20 strains tested, fast healers (MRL/MpJ-Fas(lpr) and LG/J) healed wounds four times faster than slow healers (Balb/cByJ and SJL/J). The genetic basis underlying the difference in the healing capacity was analysed using F2 populations of two different crosses. We show that the wound healing is a polygenically determined quantitative trait with an average estimated heritability of 86%. The modes of gene action in these two crosses are different. In the (MRL/MpJ x SJL/J) cross, genes regulating fast healing in MRL/MpJ mice exhibited additive effects, whereas these effects were suppressed by a dominant repressor gene in CBA/J mice in the (MRL/MpJ-Fas(lpr) x CBA/J) cross. Information gained from this investigation provides insight into further study of molecular mechanisms underlying the rate of wound healing in mammals.

Analysis of Variance↗

PubMed2001

Inhibition of human osteoblast marker gene expression by retinoids is mediated in part by insulin-like growth factor binding protein-6.

All-trans -retinoic acid (atRA) inhibits osteoblast marker gene expression and markedly increases expression of insulin-like growth factor binding protein-6 (IGFBP-6) in human osteoblasts. The possibility that IGFBP-6 inhibits the osteoblast phenotype and also mediates the inhibitory effect of atRA on osteoblast marker gene expression was explored using an antisense approach. Stable human osteoblast-like osteosarcoma SaOS-2 cells were prepared that expressed antisense IGFBP-6 RNA under basal and atRA-stimulated conditions. The functional expression of IGFBP-6 antisense RNA was confirmed by measuring IGFBP-6 mRNA by Northern analysis or by measuring IGFBP-6 protein in the conditioned media (CM) by radioimmunoassay. Antisense clones produced less mRNA and had less IGFBP-6 protein in the CM than controls. IGFBP-6 protein levels in the CM were inversely correlated with alkaline phosphatase (ALP) activity, whereas IGFBP-3 and IGFBP-4 protein levels were not. We reasoned that atRA would have little or no effect on ALP activity in IGFBP-6 antisense clones if atRA mediated its inhibitory effects by recruiting IGFBP-6. In the majority of IGFBP-6 antisense clones with the lowest IGFBP-6 mRNA and CM protein levels and only modest changes in other IGF system components, atRA did not significantly decrease ALP activity. These findings provide evidence that atRA recruits IGFBP-6 to inhibit the human osteoblast phenotype.

Alkaline Phosphatase↗

PubMed2001

Identification of wound healing/regeneration quantitative trait loci (QTL) at multiple time points that explain seventy percent of variance in (MRL/MpJ and SJL/J) mice F2 population.

Studies on genetic mechanisms of wound healing in mammals are very few, although injury is a leading cause of the global burden of disease. In this study, we performed a high-density, genome-wide scan using 633 (MRL/MPJ x SJL/J) F(2) intercross at multiple time points (days 15, 21, and 25) to identify quantitative trait loci (QTL) involved in wound healing/regeneration. The hypothesis of the study was that QTL and unique epistatic interactions are involved at each time point to promote wound healing/regeneration. Ten QTL were identified from chromosomes 1, 4, 6, 7, 9, and 13. Of the 10 QTL, eight from chromosomes 1, 4, 6, and 9 were novel as compared to QTL identified in the study. The 10 QTL altogether explained 70% of variance in F(2) mice. The same QTL were identified at each time point, with simple linear correlation between days 15, 21, and 25, showing very high significant relationships (R >0.92, P <0.0001). Unique epistatic interactions were identified at each time point except those from chromosomes 4, 6, 9, and 13 that were found at all three time points, showing that some loci are involved at all the three time points of wound healing (days 15, 21, and 25). Therefore, loci-to-loci interactions may play a major role in wound healing. Information from these studies may help in the identification of genes that could be involved in wound healing/regeneration.

Analysis of Variance↗

PubMed2001

Evidence that IGF-binding protein-5 functions as a growth factor.

Recent studies support the concept that IGF-binding protein-5 (IGFBP-5) stimulates bone formation, at least in part, via IGF-independent mechanisms. To evaluate this hypothesis further, we evaluated in vitro and in vivo effects of IGFBP-5 on bone formation parameters using the IGF-I knockout (KO) mouse. Treatment of serum-free cultures of osteoblast clones derived from IGF-I KO mice with recombinant human IGFBP-5 increased both proliferation and alkaline phosphatase (ALP) activity in a dose-dependent manner, an effect comparable to that seen with IGF-I. IGF-II levels from media conditioned by osteoblasts derived from IGF-I KO mouse were below those detectable by RIA. To eliminate possible actions of IGF-II, if any was produced by osteoblasts derived from IGF-I knockout mice, the IGFBP-5 effect was studied in the presence of exogenously added IGFBP-4, a potent inhibitor of IGF-II actions in bone cells. Addition of IGFBP-4 blocked IGF-I- but not IGFBP-5-induced cell proliferation in osteoblasts derived from IGF-I knockout mice. Consistent with in vitro results, a single local injection of IGFBP-5 to the outer periosteum of the parietal bone of IGF-I KO mice increased ALP activity and osteocalcin levels of calvarial bone extracts. The magnitudes of IGFBP-5-induced increases in ALP and osteocalcin in parietal bone extracts of IGF-I KO mice were comparable to those seen in C3H mice. In contrast to IGFBP-5, local administration of IGFBP-4 had no significant effect on bone formation in C3H and IGF-I KO mice. These results provide the first direct evidence to our knowledge that IGFBP-5 functions as a growth factor that stimulates its actions in part via an IGF-independent mechanism.

Alkaline Phosphatase↗

PubMed2001

Evidence that anabolic effects of PTH on bone require IGF-I in growing mice.

Although it has been established that PTH exerts potent anabolic effects on bone in animals and humans, the mechanism of PTH action on bone remains controversial. Based on the previous findings that PTH treatment increased production of IGF-I in bone cells and that PTH effects on bone cells in vitro were blocked by IGF-I-blocking antibodies, we proposed that IGF-I action is required for the stimulatory effects of PTH on bone formation. To test this hypothesis, we evaluated the effects of PTH on bone formation parameters in growing mice lacking functional IGF-I genes. Five-week-old IGF-I(-/-) mice and wild-type littermates were given daily sc injections of 160 microg/kg body weight of PTH (1-34) or vehicle for 10 d. In wild-type animals, PTH caused a significant increase in serum osteocalcin levels (113%), serum alkaline phosphatase activity (48%), and alkaline phosphatase activity in femoral bone extracts (>80%), compared with the vehicle-treated control group. In contrast, in IGF-I(-/-) mice, there was no significant effect of PTH on any bone formation parameters. PTH treatment increased total bone mineral density, as evaluated by peripheral quantitative computer tomography, at the distal metaphysis of the femur by 40% in wild-type mice, but it had no effect on bone mineral density in mice lacking functional IGF-I genes. In vitro studies using osteoblasts derived from control and IGF-I(-/-) mice revealed that PTH treatment increased cell number in osteoblasts derived from IGF-I knockout mice in the presence of exogenously added IGF-I but not without IGF-I. These data to our knowledge provide the first direct evidence that the anabolic effects of PTH on bone formation in vivo require IGF-I action in growing mice.

Animals↗

PubMed2001

Systemic administration of insulin-like growth factor (IGF)-binding protein-4 (IGFBP-4) increases bone formation parameters in mice by increasing IGF bioavailability via an IGFBP-4 protease-dependent mechanism.

Insulin-like growth factor (IGF)-binding protein-4 (IGFBP-4) is a potent inhibitor of IGF actions in vitro. However, we found that systemic administration of IGFBP-4 at pharmacological doses caused a significant increase in bone formation parameters in mice by a mechanism that may involve increased IGF bioavailability via proteolysis of IGFBP-4. To evaluate the hypothesis that proteolysis of IGFBP-4 is essential for the stimulatory effects of systemically administered IGFBP-4, we produced wild-type, protease-resistant, and IGFBP-4 proteolytic fragments and evaluated their effects using biochemical markers. Protease-resistant IGFBP-4 was more potent than wild-type IGFBP-4 in inhibiting IGF-I-induced mouse osteoblast cell proliferation in vitro and in inhibiting IGF-I-induced increase in alkaline phosphatase (ALP) activity in bone extract after local administration in vivo. Systemic administration of wild-type IGFBP-4, but not protease-resistant IGFBP-4, increased serum osteocalcin, serum ALP, and ALP in skeletal extracts in a dose-dependent manner, with a maximal effect of 40% (P < 0.05) at 1.25 nmol/mouse. Systemic administration of wild-type, but not protease-resistant, IGFBP-4 increased free IGF-I levels in serum in normal mice. IGF-I, but not wild-type IGFBP-4, increased bone formation parameters in IGF-I-deficient mice. This study demonstrates that systemic administration of IGFBP-4 increases bone formation parameters in mice by increasing IGF bioavailability in the circulation via an IGFBP-4 protease-dependent mechanism.

Alkaline Phosphatase↗

PubMed2001

Prevention of bone loss with tibolone in postmenopausal women: results of two randomized, double-blind, placebo-controlled, dose-finding studies.

Tibolone, a novel compound with tissue-specific effects, has been found to have antiresorptive properties in bone. To confirm the efficacy of tibolone and determine its minimum effective dose for prevention of bone loss in early postmenopausal women, two randomized, double-blind, placebo-controlled, dose-finding studies were performed. Seven hundred seventy healthy women postmenopausal within 1-4 yr, with normal bone density for their age, were treated for 2 yr with 0.3, 0.625, 1.25, or 2.5 mg tibolone daily or placebo. All subjects took supplemental calcium carbonate (500 mg daily). Bone mineral density (BMD) of the lumbar spine and right proximal femur was measured by dual-energy x-ray absorptiometry for up to 2 yr. At each dose level, except the lowest (0.3 mg), tibolone produced a progressive increase in lumbar spine and total hip BMD over the 2-yr treatment period; at 0.3 mg, total hip density was maintained. However, only the doses 1.25 mg and 2.5 mg produced a progressive increase in femoral neck BMD. The differences in mean percent change from baseline in spine and total hip density were significant (P < 0.05) for all tibolone dose groups compared with placebo at all time points. Tibolone was well tolerated, with a similar overall incidence of adverse events compared with placebo. Tibolone 1.25 mg per day is recommended because it shows a positive and statistically significant change in BMD of spine and femoral neck.

Aged↗

PubMed2001

Pregnancy-associated plasma protein-A accounts for the insulin-like growth factor (IGF)-binding protein-4 (IGFBP-4) proteolytic activity in human pregnancy serum and enhances the mitogenic activity of IGF by degrading IGFBP-4 in vitro.

Pregnancy-associated plasma protein-A (PAPP-A) has been identified as the insulin-like growth factor (IGF)-dependent IGF-binding protein-4 (IGFBP-4) protease produced by human fibroblasts. Recently, we found that serum proteases induced during human pregnancy cleaved IGFBP-4 in both an IGF-II-dependent and an IGF-II-independent fashion. This study sought to determine whether PAPP-A is the predominant IGFBP-4 protease in human pregnancy serum (PS) and to assess the in vitro role of serum PAPP-A. Immunoprecipitation with PAPP-A antibody effectively depleted PAPP-A from the PS and completely abolished both IGF-II-dependent and IGF-II-independent IGFBP-4 proteolytic activity in PS. Direct addition of PAPP-A antibody to PS completely blocked IGFBP-4 proteolysis and partially blocked IGFBP-5 proteolysis, but had no effect on IGFBP-3 proteolysis. To evaluate the role of serum PAPP-A, we tested whether PAPP-A in PS modulated the inhibitory activity of IGFBP-4 on IGF-II-induced cell proliferation in human osteosarcoma MG63 cells. The wild-type IGFBP-4 (WTBP-4; 200 ng/mL) failed to inhibit proliferation of the cells treated with PS (0.1% or 0.3%) alone or in combination with IGF-II (40 ng/mL), whereas the inhibitory effect of WTBP-4 was observed in the cells treated with nonpregnancy serum alone or in combination with IGF-II (P < 0.05). In contrast to WTBP-4, a protease-resistant IGFBP-4 was able to inhibit proliferation of the cells treated with PS alone or in combination with IGF-II (P < 0.05). In the presence of PAPP-A neutralizing antibody, the inhibitory effect of WTBP-4 on proliferation of the cells treated with IGF-II and PS was restored. In summary, these data demonstrate 1) that PAPP-A represents the predominant IGFBP-4 protease in PS; 2) that PAPP-A may in part contribute to IGFBP-5, but not IGFBP-3, proteolytic activity in PS; and 3) that PAPP-A enhances the bioactivity of IGFs in vitro by degrading IGFBP-4.

Cell Division↗

PubMed2001

Effect of combined risedronate and hormone replacement therapies on bone mineral density in postmenopausal women.

Both hormone replacement therapy (HRT) and bisphosphonates are efficacious in the prevention and treatment of postmenopausal osteoporosis. Combined therapy with bisphosphonate and HRT is likely to be used in clinical practice, and limited data are available regarding its efficacy and safety. This was a 1-yr, double blind, placebo-controlled study in which 524 postmenopausal women received daily treatment with conjugated equine estrogens (0.625 mg) alone or in combination with risedronate (5 mg). Women who had not undergone hysterectomy received medroxyprogesterone acetate (up to 5 mg, daily or cyclically) at the discretion of the investigator. The primary efficacy end point was the percent change from baseline in mean lumbar spine bone mineral density (BMD) at 1 yr. Changes in BMD at the proximal femur and forearm, bone turnover markers, and histology and histomorphometry were also assessed. At 12 months, significant (P < 0.05) increases from baseline in lumbar spine BMD were observed in both treatment groups (HRT-only, 4.6%; combined risedronate-HRT, 5.2%); the difference between the two groups was not statistically significant. Both therapies led to significant increases in BMD at 12 months at the femoral neck (1.8% and 2.7%, respectively), femoral trochanter (3.2% and 3.7%), distal radius (1.7% and 1.6%), and midshaft radius (0.4% and 0.7%). The differences between groups were statistically significant (P < 0.05) at the femoral neck and midshaft radius. Both combined risedronate-HRT and HRT-only produced significant decreases in the biochemical markers of bone turnover, with somewhat greater decreases in the combined treatment group. Bone biopsy data showed normal bone structure and normal mineralization with either treatment. Expected decreases in bone turnover were observed and were greater in the combined treatment group (68-79% reduction relative to baseline values, P < 0.005). Overall, combined treatment had a safety profile similar to that of HRT-only, including bone and gastrointestinal safety profiles. In conclusion, the combined treatment with risedronate and HRT had a favorable effect on BMD similar to that of HRT alone at the lumbar spine and slightly, but significantly, greater than that of HRT alone at the femoral neck and midshaft radius. The combined treatment was well tolerated, and there were no adverse effects on the skeleton.

Aged↗

PubMed2001

Antisense oligodeoxynucleotide evidence that a unique osteoclastic protein-tyrosine phosphatase is essential for osteoclastic resorption.

This study tested the hypothesis that a unique osteoclastic transmembrane protein tyrosine phosphatase (PTP-oc) is involved in osteoclastic resorption by determining whether suppression of PTP-oc expression with a specific phosphorothioated 20-mer PTP-oc antisense oligodeoxynucleotide (oligo) would inhibit basal, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]-stimulated, and PTH-stimulated osteoclastic resorption. Treatment of rabbit osteoclasts with 1 microM of the antisense oligo for up to 4 days showed a time-dependent reduction in PTP-oc protein level, indicating that this PTP-oc antisense oligo was effective. To assess the effect of PTP-oc antisense oligo on osteoclastic resorption, rabbit osteoclasts were pretreated for 3 days with 1 microM of the antisense, a scramble oligo, or vehicle, respectively, followed by a 3-day treatment with vehicle, 10 nM of 1,25(OH)2D3, or 10 nM of parathyroid hormone (PTH). 1,25(OH)2D3 and PTH each alone increased PTP-oc cellular level and stimulated resorptive activity of rabbit osteoclasts. The antisense oligo treatment, but not the scramble oligo, decreased the basal and the stimulated resorption activity and reduced the PTP-oc protein level. Treatment with the PTP-oc antisense oligo, but not the scramble oligo, also markedly increased the Y527 phosphorylation level of c-src in rabbit osteoclasts. In conclusion, these results provide the first antisense oligo evidence that PTP-oc plays an essential role in osteoclastic resorption.

Animals↗