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D T Baran

Publications and source records attributed to D T Baran.

At least 19 recordsLinked to original sources
PubMed2001

Insulin-like growth factor binding proteins in femoral and vertebral bone marrow stromal cells: expression and regulation by thyroid hormone and dexamethasone.

Insulin-like growth factor (IGF)-I is an important regulator of bone metabolism. Clinical observations suggest that different anatomic sites within the adult skeleton respond differently to hormonal and therapeutic treatment, and recent studies on bone marrow stromal cells in culture show that there are skeletal site-dependent differences in the gene expression of IGF-I. The actions of IGF-I and -II on bone cells are known to be modulated by the IGF binding proteins (IGFBP)-1 through -6 and the Type I and Type II IGF receptors. Therefore, we compared the expression of IGFBP-1 through -6 in adult female rat bone marrow stromal cell cultures derived from two separate skeletal sites: vertebrae and femurs. The cultures were maintained simultaneously under conditions that support osteoblast differentiation from osteoprogenitors present in the femoral and vertebral marrow cell populations. We also addressed whether IGFBP messenger RNA levels are regulated by thyroid hormone (T(3)) and dexamethasone (dex) treatment in femoral vs. vertebral marrow stromal cells in vitro, since steroid hormones play an important role in skeletal function. Northern blot analyses revealed that there are distinct skeletal site differences in the gene expression of IGFBPs. The vertebral marrow cultures express IGFBP-2 through -6 mRNAs, with IGFBP-2, IGFBP-4, and IGFBP-6 mRNAs predominating. The femoral marrow stromal cell cultures express only IGFBP-4 and IGFBP-6. Importantly, vertebral marrow cultures have much higher IGFBP mRNA steady-state levels than femoral cultures for all the detected IGFBP transcripts. IGFBP-1 is not detected in either femoral or vertebral cultures. In addition to a skeletal site difference, we show that T(3) and dex regulate the expression of specific IGFBP mRNAs. T(3) treatment also upregulates IGF-I protein secretion by vertebral marrow stromal cell cultures. Interestingly, the type I receptor for IGF-I was expressed equivalently in cultures from the two skeletal sites. These findings have important implications for the anatomical site specificities of hormonal responses that are noted in the skeleton.

Animals↗
PubMed2000

Binding of 1alpha,25-dihydroxyvitamin D(3) to annexin II: effect of vitamin D metabolites and calcium.

We have recently reported that annexin II serves as a membrane receptor for 1alpha,25-(OH)(2)D(3) and mediates the rapid effect of the hormone on intracellular calcium. The purpose of these studies was to characterize the binding of the hormone to annexin II, determine the specificity of binding, and assess the effect of calcium on binding. The binding of [(14)C]-1alpha,25-(OH)(2)D(3) bromoacetate to purified annexin II was inhibited by 1alpha, 25-(OH)(2)D(3) in a concentration-dependent manner. Binding of the radiolabeled ligand to annexin II was markedly diminished by 1alpha, 25-(OH)(2)D(3) at 24 microM, 18 microM, and 12 microM and blunted by 6 microM and 3 microM. At a concentration of 12 microM, 1beta, 25-(OH)(2)D(3) also diminished the binding of [(14)C]-1alpha, 25-(OH)(2)D(3) bromoacetate to annexin II, but cholecalciferol, 25-(OH)D(3), and 24,25-(OH)(2)D(3) did not. Saturation analyses of the binding of [(3)H]-1alpha,25-(OH)(2)D(3) to purified annexin II showed a K(D) of 5.5 x 10(-9) M, whereas [(3)H]-1beta,25-(OH)(2)D(3) exhibited a K(D) of 6.0 x 10(-9) M. Calcium, which binds to the carboxy terminal domain of annexin II, had a concentration-dependent effect on [(14)C]-1alpha,25-(OH)(2)D(3) bromoacetate binding to annexin II, with 600 nM calcium being able to inhibit binding of the radiolabeled analog. The inhibitory effect of calcium was prevented by EDTA. Homocysteine, which binds to the amino terminal domain of annexin II, had no effect on the binding of the bromoacetate analog to the protein. The data indicate that 1alpha,25-(OH)(2)D(3) binding to annexin II is specific and suggest that the binding site may be located on the carboxy terminal domain of the protein. The ability of 1beta,25-(OH)(2)D(3) to inhibit the binding of [(14)C]-1alpha, 25(OH)(2)D(3) bromoacetate to annexin II provides a biochemical explanation for the ability of the 1beta-epimer to inhibit the rapid actions of the hormone in vitro.

Animals↗
PubMed2000

Reconciling quantitative ultrasound of the calcaneus with X-ray-based measurements of the central skeleton.

Osteoporosis is frequently undiagnosed before fracture because of the lack of availability of instruments to quantitate bone mass. To evaluate the utility of quantitative ultrasound (QUS) of the calcaneus to diagnose osteoporosis, we determined bone mineral density (BMD) of the posterior-arterior spine, total hip, and femoral neck by dual-energy X-ray absorptiometry (DXA) and QUS in 312 women aged 50 years and older. A risk factor assessment (simple calculated osteoporosis risk estimation [SCORE]) also was quantitated in all women. Ninety-four of the 312 women were diagnosed as osteoporotic based on T scores < or = -2.5 at the spine, total hip, and/or femoral neck. The sensitivity of the individual central sites for the diagnosis of osteoporosis was 49% at the spine (46 of 94 women), 32% at the total hip (30 of 94 women), and 81% at the femoral neck (76 of 94 women). At a QUS T score < or = -1, the peripheral technique had a sensitivity of 62% and a specificity of 72%. Combining a QUS T score of < or = -1 followed by a risk factor assessment of women with a QUS T score > or = -0.99 using a cut point of 11 increased sensitivity to 81% (comparable with femoral neck DXA) but decreased specificity to 58%. If peripheral QUS measurements and risk factor assessment are the only tools employed before initiation of therapy, the benefits of increased ease of diagnosis will need to be balanced against potentially unnecessary treatment in some normal patients and lack of treatment in some osteoporotic patients.

Absorptiometry, Photon↗
PubMed2000

Osteoporosis: which current treatments reduce fracture risk?

Randomized controlled trials showed that several antiosteoporosis drugs decrease the incidence of fractures, which is a better measure of efficacy than are changes in bone mineral density or serum markers of bone turnover. With effective agents available, physicians should make osteoporosis treatment a priority, especially for patients at high risk, such as those who have already had a fracture.

Aged↗
PubMed2000

Annexin II is the membrane receptor that mediates the rapid actions of 1alpha,25-dihydroxyvitamin D(3).

1alpha,25-Dihydroxyvitamin D(3) has been shown to exert its effects by both genomic (minutes to hours) and rapid (seconds to minutes) mechanisms. The genomic effects are mediated by interaction with the nuclear vitamin D receptor. We show that the vitamin D analog, [(14)C]-1alpha,25-dihydroxyvitamin D(3) bromoacetate, is specifically bound to a protein (molecular weight 36 kDa) in the plasma membrane of rat osteoblastlike cells (ROS 24/1). The plasma membrane protein labeled with the bromoacetate analog was identified as annexin II by sequence determination and Western blot. Partially purified plasma membrane proteins (PI 6.9-7.4) and purified annexin II exhibited specific and saturable binding for [(3)H]-1alpha, 25-dihydroxyvitamin D(3). Antibodies to annexin II inhibited [(14)C]-1alpha,25-dihydroxyvitamin D(3) bromoacetate binding to ROS 24/1 plasma membranes, immunoprecipitated the ligand-protein complex, and inhibited 1alpha,25-dihydroxyvitamin D(3)-induced increases in intracellular calcium in ROS 24/1 cells. The results indicate that annexin II may serve as a receptor for rapid actions of 1alpha, 25-dihydroxyvitamin D(3).

Animals↗
PubMed1999

Expression of multiple thyroid hormone receptor isoforms in rat femoral and vertebral bone and in bone marrow osteogenic cultures.

Thyroid hormones influence both bone formation and bone resorption. Clinical data and animal studies provide evidence of skeletal site heterogeneity (hip vs. spine) of bone responses to thyroid hormones. In vitro studies also demonstrate direct effects of thyroid hormones on cells of the osteoblast lineage. Transcriptional regulation by thyroid hormone is mediated by ligand-dependent transcription factors called thyroid hormone receptors (TRs). Two genes, c-ErbAalpha and c-ErbAbeta, generate at least four TR isoforms in the rat: TRalpha(1), c-erbAalpha(2), TRbeta(1), and TRbeta(2). Although functional TRs have been identified in cells of the osteoblast lineage, it is still not known if TR isoform expression in bone differs depending upon which skeletal site is examined. We have used ribonuclease protection assay and Northern blot analysis to simultaneously examine the expression of TR isoform mRNAs in adult rat femoral and vertebral bone. TRalpha(1), c-erbAalpha(2), and TRbeta(1) are expressed in both femur and vertebra whole bone. Bone marrow cells from both skeletal sites were also cultured under conditions whereby the osteoprogenitors differentiated into osteoblasts and formed a mineralized extracellular matrix. TRalpha(1), c-erbAalpha(2), and TRbeta(1) mRNAs are each expressed in both femoral and vertebral osteoblast cultures. The presence of TRalpha(1), c-erbAalpha(2), and beta(1) proteins was confirmed by Western analysis of nuclear protein extracts from femoral and vertebral cell cultures. These results indicate that the three predominant TR isoforms are highly expressed in bone and osteoblasts from femurs and vertebrae. Whether there are distinct mechanisms of thyroid hormone action mediated by TRalpha(1), c-erbAalpha(2), and TRbeta(1) at these separate skeletal sites remain to be shown.

Animals↗
PubMed1999

Practical clinical application of biochemical markers of bone turnover: Consensus of an expert panel.

Biochemical markers of bone turnover have emerged as powerful tools to aid in managing osteoporosis. The newer bone markers have been intensively studied for more than a decade. As a result, we can now confidently report their clinical utility in assessing risk of rapid bone loss and fracture, and monitoring therapy in postmenopausal women with or at risk of osteoporosis. In this review, we will provide a comprehensive foundation for this utility. While there are still questions remaining to be answered, bone marker technology has matured to play an essential role in patient management. We will describe, in practical terms, how bone markers can be appropriately incorporated into clinical practice today.

Aged↗
PubMed1998

Dexamethasone stimulates osteogenic differentiation in vertebral and femoral bone marrow cell cultures: comparison of IGF-I gene expression.

Osteoblast-like cell cultures have been established from the marrow of adult rat vertebrae. We have simultaneously examined the response to dexamethasone (dex) treatment in cultures of young adult female vertebral and femoral marrow cells. Alkaline phosphatase (AP) activity was analyzed as well as the expression of mRNAs for osteocalcin (OC) and insulin-like growth factor I (IGF-I). The vertebral and femoral marrow cells were maintained for 7 days in primary culture with or without 10(-8) M dex and then 6 days in secondary culture without dex or with 10(-8) M or 10(-7) M dex. All cells were examined on day 6 of secondary culture. Vertebral and femoral cultures each expressed the highest AP enzyme levels when grown with dex in primary culture (10(-8) M) and secondary culture (10(-7) M). Under all experimental conditions, vertebral cultures had lower AP enzyme activity than femoral cultures. When dex was omitted from secondary culture, OC gene expression was not detected in either vertebral or femoral passaged cells even if dex was present in primary culture. For dex conditions where OC was expressed, vertebral cultures had higher OC mRNA steady-state levels than femoral cultures. IGF-I gene expression was detected by Northern analysis in both vertebral and femoral secondary cultures. However, vertebral marrow cultures had much higher IGF-I mRNA levels compared to femoral cultures whether or not dex was present in primary culture. These findings demonstrate that dex supports the differentiation of both vertebral and femoral adult marrow osteogenic cells into osteoblasts. Our results support the hypothesis that osteoblastic marrow cultures differ depending upon which location in the skeleton they are from and that there are skeletal site-dependent differences in the insulin-like growth factor system components.

Alkaline Phosphatase↗
PubMed1998

Thyroid hormone excess increases insulin-like growth factor I transcripts in bone marrow cell cultures: divergent effects on vertebral and femoral cell cultures.

Thyroid hormones (T3 and T4) regulate bone development, growth, and turnover. Studies have suggested that different skeletal sites respond differently to thyroid hormones. Therefore, we examined the in vitro T3 responsiveness of cells committed to the osteoblast lineage as a function of skeletal location. Bone marrow cells derived from female rat femurs and vertebrae were cultured using conditions that induce osteogenic differentiation. Cells from both sites formed mineralized bone nodules in primary and secondary culture. In femoral cultures, collagen type I (coll I) and osteocalcin (OC) messenger RNA (mRNA) levels increased from the earliest time point examined (day 3) to a maximum on day 12 and thereafter declined to undetectable levels. T3 increased both OC and coll I mRNA, resulting in a continuous expression throughout the culture period. Insulin-like growth factor I (IGF-I) gene expression was detected at very low levels by Northern analysis of femoral total RNA, and T3 only marginally enhanced IGF-I mRNA levels. In vertebral cultures, OC and coll I mRNA levels also increased with time in culture, but remained expressed throughout the culture period. OC and coll I mRNA levels were not markedly altered in response to T3. In contrast to femoral cells, IGF-I gene expression was easily visualized in Northern blots from untreated vertebral cultures and was markedly increased by the addition of T3. The continuous presence of T3 (10(-7) M) in the medium for 18 days caused a marked decrease in the number of alkaline phosphatase-positive colonies formed in femoral secondary cultures, but only a slight decrease in the number in vertebral cultures. In addition, short term (6 days) exposure to T3 (10(-7) M) at the beginning of the culture period decreased alkaline phosphatase activity in femoral cultures, but not in vertebral cultures. These findings indicate that there are skeletal site-dependent differences in the in vitro responses of cells of the osteoblastic lineage to thyroid hormone.

Alkaline Phosphatase↗
PubMed1998

Bone mineral density and broadband ultrasound attenuation with estrogen treatment of postmenopausal women.

The purpose of the current study was to determine the changes in lumbar spine, hip, and calcaneus bone mineral density (BMD), and in calcaneus broadband ultrasound attenuation (BUA) in early menopausal women and to assess the effects of estrogen replacement therapy (ERT) on bone mass at these sites over a 2-yr period. Fifty-three Caucasian women who were at least 6 mo postmenopausal were divided into two groups based on estrogen use. Twenty-one women, average age 53.0 +/- 0.6 yr and 2.9 +/- 0.3 yr since menopause, had been receiving estrogen in combination with progesterone for at least 6 mo prior to enrollment in the study. Thirty-two women, average age 52.7 +/- 0.8 yr and 2.8 +/- 0.3 yr since menopause, had never received ERT. During the 2-yr study, women not receiving ERT had significant decreases in BMD of the spine -2.3 +/- 0.6%, femoral neck -2.2 +/- 0.8%, and calcaneus -4.7 +/- 0.9%, and in BUA of the calcaneus -14.3 +/- 1.8%. ERT prevented the decreases in BMD at the spine +0.4 +/- 0.6% and calcaneus -2.3 +/- 1.1%, but did not prevent a significant decrease in bone mass at the femoral neck -1.9 +/- 0.8% and BUA at the calcaneus -17.8 +/- 3.2%. Neither group had significant decreases in total hip BMD. This study demonstrates again that ERT prevents the menopause-associated decreases in spine BMD. However, in this group of women, ERT did not prevent loss in femoral neck BMD or BUA. The results suggest that women being treated with estrogen for maintenance of BMD in early menopause need to be monitored to ensure efficacy of therapy, especially in the maintenance of femoral neck BMD.

Journal Article↗
PubMed1997

Site selectivity of osteoblast gene expression response to thyroid hormone localized by in situ hybridization.

We have previously reported that thyroid-stimulating hormone (TSH)-suppressive doses of L-thyroxine (L-T4) decrease femoral, but not vertebral, bone mineral density (BMD) in rats. L-T4-induced decreases in BMD were associated with increased expression of genes, reflecting osteoblast activity in mRNA extracted from whole femurs but not from vertebrae. To document that this skeletal selectivity reflected altered osteoblast activity, we studied gene expression by in situ hybridization in 8-wk-old rats treated with L-T4 (20 microg x 100 g body wt(-1) x day(-1)) for 4 wk. TSH-suppressive doses of L-T4 were associated with decreased femoral (0.299 +/- 0.005 vs. 0.273 +/- 0.005 g/cm2, P < 0.01), but not vertebral (0.222 +/- 0.004 vs. 0.218 +/- 0.003 g/cm2), BMD. In situ hybridization documented that L-T4 administration for 4 wk increased expression of osteocalcin and alkaline phosphatase mRNA in femoral, but not vertebral, osteoblasts. This study demonstrates a differential gene expression response of vertebral and femoral osteoblasts to L-T4. This altered degree of gene expression markers of osteoblast activity documented by in situ hybridization may in part explain the apparent clinical differences in the effect of L-T4 on femoral and vertebral BMD.

Alkaline Phosphatase↗
PubMed1996

Effects of the vitamin D3 analog 1 alpha, 25-dihydroxyvitamin D3-3 beta-bromoacetate on rat osteosarcoma cells: comparison with 1 alpha, 25-dihydroxyvitamin D3.

The actions of the hormonal form of vitamin D, 1 alpha, 25-dihydroxyvitamin D3 [1 alpha, 25-(OH)2 D3], are mediated by both genomic and nongenomic mechanisms. Several vitamin D synthetic analogs have been developed in order to identify and characterize the site(s) of action of 1 alpha, 25-(OH)2D3 in many cell types including osteoblastic cells. We have compared the effects of 1 alpha, 25-(OH)2D3 and a novel 1 alpha, 25-(OH)2D3 bromoester analog (1,25-(OH)2-BE) that covalently binds to vitamin D receptors. Rat osteosarcoma cells that possess (ROS 17/2.8) or lack (ROS 24/1) the classic intracellular vitamin D receptor were studied to investigate genomic and nongenomic actions. In ROS 17/2.8 cells plated at low density, the two vitamin D compounds (1 x 10(-8) M) caused increased cell proliferation, as assessed by DNA synthesis and total cell counts. Northern blot analysis revealed that the mitogenic effect of both agents was accompanied by an increase in steady-state osteocalcin mRNA levels, but neither agent altered alkaline phosphatase mRNA levels in ROS 17/2.8 cells. ROS 17/2.8 cells responded to 1,25-(OH)2-BE but not the natural ligand with a significant increase in osteocalcin secretion after 72, 96, 120, and 144 hr of treatment. Treatment of ROS 17/2.8 cells with the bromoester analog also resulted in a significant decrease in alkaline phosphatase-specific activity. To compare the nongenomic effects of 1 alpha, 25-(OH)2D3 and 1,25-(OH)2-BE intracellular calcium was measured in ROS 24/1 cells loaded with the fluorescent calcium indicator Quin 2. At 2 x 10(-8) M, both 1 alpha,25-(OH)2D3 and 1, 25-(OH)2-BE increased intracellular calcium within 5 min. Both the genomic and nongenomic actions of 1,25-(OH)2-BE are similar to those of 1 alpha,25-(OH)2D3, and since 1,25-(OH)2-BE has more potent effects on osteoblast function than the naturally occurring ligand due to more stable binding, this novel vitamin D analog may be useful in elucidating the structure and function of cellular vitamin D receptors.

Animals↗
PubMed1996

A prospective study of proximal femur bone mass following cemented and uncemented hip arthroplasty.

Cross-sectional studies have demonstrated significant decreases in bone mass in femoral cortical bone adjacent to prostheses. Thirty-six patients who had undergone 31 cemented and 9 uncemented primary total hip arthroplasties (THA) were prospectively studied to define further the natural history of this femoral cortical bone loss. Dual-energy X-ray absorptiometry (DXA) was employed to quantify bone mineral density (BMD) changes in four subregions around the femoral prostheses. Femoral BMD loss (average 12.3%) was observed in the three proximal subregions 2 months postoperatively. This loss increased to 21.2% by 6 months postoperatively, and by 2 years postoperatively it averaged 25.5% in the same three subregions. There were no significant BMD changes in the subregion distal to the prosthesis tip or in the contralateral hip. Subgroups were compared based on prosthesis size and cement use. Statistically significant differences in BMD loss were observed between the large cemented cobalt chrome prosthesis group (n = 8) and the large uncemented titanium prosthesis group (n = 8). These differences were only present in the most proximal medial subregion where the large cemented groups had twice the bone loss in this area as compared with the large uncemented group. The data indicate that bone loss occurs adjacent to femoral prosthesis within 2 months of surgery and that DXA is a useful technique to quantify prospectively femoral cortical bone loss following THA.

Adult↗
PubMed1996

Differential responses of femoral and vertebral bones to long-term excessive L-thyroxine administration in adult rats.

Recent studies suggest that thyroid-stimulating hormone suppressive doses of thyroid hormone decrease bone mass in humans and growing rats. To determine the long-term effects of excessive L-thyroxine administration on the femur and vertebrae in an adult rat model, 20 male Sprague-Dawley rats (20 weeks old) were randomized into two groups. Group 1 received L-thyroxine (20 micrograms/100 g body weight ip daily), and group 2 received normal saline ip daily for 20 weeks. Femoral and lumbar vertebral bone mineral density measurements were performed at 0, 6, 15, 18 and 20 weeks of treatment. After 20 weeks of treatment, total RNA was isolated from both femoral and lumbar bones. Northern hybridization was performed with 32P-labeled DNA probes for osteocalcin, osteopontin, alkaline phosphatase and tartrate-resistant acid phosphatase. Significant decreases in bone mineral density in the femur of L-thyroxine-treated rats were observed after 15 weeks (p < 0.03). Lumbar bone mineral density was not affected. Both osteoblast (osteocalcin, osteopontin, alkaline phosphatase) and osteoclast (tartrate-resistant acid phosphatase) gene expression markers were increased significantly in the femoral bone (p < 0.001), but not in the lumbar vertebrae of the L-thyroxine-treated rats. We conclude that long-term administration of excessive doses of L-thyroxine to the adult rat preferentially affects femoral but not vertebral bone. This is manifested by decreased bone mineral density as well as increased gene expression markers for osteoblast and osteoclast activity in the femur.

Acid Phosphatase↗
PubMed1995

Quantitative ultrasound: a technique to target women with low bone mass for preventive therapy.

Assessment of bone mass is the best predictor of fracture. The current challenge is to develop a strategy to determine which women should be targeted for preventive therapy. The cost of dual-energy x-ray absorptiometry equipment precludes its widespread availability in physicians' offices and clinics. Quantitative ultrasound appears to offer a low-cost alternative method to assess bone mass and fracture risk. In addition, ultrasound is radiation free. Quantitative ultrasound values decrease with age, are lower in osteoporotic women, and are influenced by estrogen treatment. The associations observed between quantitative ultrasound and fracture indicate that it is comparable to densitometry in predicting fracture risk. This association remains significant after correction for bone mineral density, suggesting that ultrasound measures additional properties of bone that are determinants of strength. Quantitative ultrasound may prove to be a technique that will allow bone mass testing to become more readily available to the population. The ability of quantitative ultrasound to discriminate those women at greatest risk for fracture will allow physicians to target those women for preventive therapy.

Bone Density↗