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Biomedical subjects

A L Boskey

Publications and source records attributed to A L Boskey.

At least 19 recordsLinked to original sources

Cell science and protein crystal growth research for the International Space Station.

The recent National Research Council report, Future Biotechnology Research on the International Space Station, evaluates NASA's plans for research in cell science and protein crystal growth to be conducted on the International Space Station. This report concludes that the NASA biotechnology programs have the potential to significantly impact relevant scientific fields and to increase understanding and insight into fundamental biological issues. In order to realize the potential impacts, NASA must focus its research programs by selecting specific questions related to gravitational forces' role in cell behavior and by using the microgravity environment as a tool to determine the structure of macromolecules with important biological implications. Given the time and volume constraints associated with space-based experiments, instrumentation to be used on the space station must be designed to maximize the productivity of researchers, and NASA's recruitment of investigators and support for space station experiments should aim to encourage and facilitate cutting-edge research.

Biotechnology↗

Type I collagen influences cartilage calcification: an immunoblocking study in differentiating chick limb-bud mesenchymal cell cultures.

Chick limb-bud mesenchymal cells, plated in high-density micro-mass culture, differentiate and form a matrix resembling chick epiphyseal cartilage. In the presence of 4 mM inorganic phosphate or 2.5 mM beta-glycerophosphate mineral deposits upon this matrix forming a mineralized tissue that, based on electron microscopy, x-ray diffraction and Fourier Transform Infrared microspectoscopy, is like that of chick calcified cartilage. In this culture system the initial mineral deposits are found on the periphery of the chondrocyte nodules. During differentiation of the cells in the high-density micro-mass cultures there is a switch from expression of type I collagen to type II, and then to type X collagen. However, type I collagen persists in the matrix. Because there is some debate about whether type I collagen influences cartilage calcification, an immunoblocking technique was used to determine the importance of type I collagen on the mineralization process in this system. Studies using nonspecific goat anti-chick IgG demonstrated that 1-100 ng/ml antibody added with the media after the cartilage nodules had developed (day 7) had no effect on the accumulation of mineral in the cultures. Nonspecific antibody added before day 7 blocked development of the cultures. Parallel solution based cell-free studies showed that IgG did not have a strong affinity for apatite crystals, and had no significant effect on apatite crystal growth. Type I collagen antibodies (1-200 ng/ml) added to cultures one time on day 9 (before mineralization started), or on day 11 (at the start of mineralization), slightly inhibited the accumulation of mineral. There was a statistically significant decrease in mineral accretion with 100 or 200 ng/ml collagen antibody addition continuously after these times. Fab' fragments of nonspecific and type I collagen antibodies had effects parallel to those of the intact antibodies, indicating that the decreased mineralization was not attributable to the presence of the larger, bulkier antibodies. The altered accumulation of mineral was not associated with cell death in the presence of antibody (demonstrated by fluorescent labeling of DNA) or with increased apoptosis (TUNEL-stain). In the immunoblocked cultures, EM analysis demonstrated that mineral continued to deposit on collagen fibrils, but there appeared to be fewer deposits. The data demonstrate that type I collagen is important for the mineralization of these cultures.

Animals↗

Two-dimensional vibrational correlation spectroscopy of in vitro hydroxyapatite maturation.

Two-dimensional (2-D) Raman and 2-D IR correlation spectroscopy are applied to analyze changes in the nu(4) region of the IR spectrum and in the nu(1) region of the Raman spectrum during the maturation of hydroxyapatite (HA) following the solution-mediated conversion of amorphous calcium phosphate (ACP) to HA. The nu(1) region of the Raman spectrum exhibits a frequency shift and sharpening during the maturation. Comparison of the experimental and simulated 2-D plots for this process suggests that the shift of a single peak, rather than a change in the relative intensity of two overlapped bands, is responsible for the observed spectral changes. The nu(4) mode of the PO(3-)(4) ion (T(2) symmetry in the free species) splits into a triplet with components near 563, 575, and 603 cm(-1) in HA. In addition, broad features appear at 540 and 617 cm(-1). During the latest stages of the maturation, an OH(-) librational mode develops at approximately 632 cm(-1). Changes in the relative intensities of three components of the nu(4) mode are not all correlated with each other. The synchronous 2-D plots reveal that the 563 and 603 cm(-1) pair are positively correlated while the feature at 575 cm(-1) is absent. A 587 cm(-1) mode arising from ACP is negatively correlated with the 563 and 603 cm(-1) pair and is both synchronously (positively) and asynchronously correlated with the 540 cm(-1) feature during the early stages of the maturation but is absent from 2-D plots of the later stages of the maturation. Cross correlations between the nu(4) mode and the nu(1),nu(3) contour generally confirm and extend previous assignments for the latter spectral region. Finally, the suitability of the 2-D approach for analysis of IR spectral images is examined through studies of HA crystallinity in a human iliac crest biopsy sample. Trabecular bone contains a fraction of HA that is more crystalline and mature than could be achieved in vitro during the room temperature ACP --> HA interconversion.

Biopsy↗

A physical, chemical, and mechanical study of lumbar vertebrae from normal, ovariectomized, and nandrolone decanoate-treated cynomolgus monkeys (Macaca fascicularis).

Ovariectomized cynomolgus monkeys have previously been investigated as a nonhuman primate model of postmenopausal osteoporosis (Jerome et al., Bone Miner 9:527-540; 1994). In the present study, Fourier transform infrared microspectroscopy (FTIRM) was used to verify that differences in bone mineral quality and quantity in the vertebrae of mature intact (INT) and ovariectomized (ovx) monkeys were analogous to those seen in osteoporotic and nondiseased human bones. FTIRM spectra were acquired from 15 trabeculae per vertebra from three ovx and three INT adult monkeys (mean age 8 years). These spectra were compared with those of both trabecular and previously reported osteonal bone obtained from 3 "normal" and 11 postmenopausal osteoporotic human subjects. While variations in the mineral:matrix ratio (mineral content), carbonate:phosphate ratio, and crystallinity are typical for trabecular bone from iliac crests of normal human subjects, the values of these parameters were relatively static for trabecular bone from postmenopausal osteoporotic human subjects. In general, trabecular bone from postmenopausal osteoporotic human subjects exhibited decreased mineral content (1.0 +/- 0.5 vs. 2.9 +/- 0.6), increased crystallinity, and increased carbonate:phosphate relative to controls. Similarly, trabecular bone from ovariectomized monkeys exhibited lower mineral content (5.8 +/- 0.2) compared with the INT group (6.2 +/- 0.2; p </= 0.05) and contained larger/more perfect apatite crystals (increased crystallinity) with increased carbonate:phosphate ratios. Variations in absolute values were attributable to site differences (ilium vs. vertebrae). To appreciate the importance of mineral properties on mechanical properties, compression testing was performed using cores of monkey L-3 and L-4 vertebral bodies from a separate group of monkeys. Treating monkeys with the anabolic steroid nandrolone decanoate (ND) immediately after ovariectomy and for the next 24 months (ND group), or beginning 12 months after ovariectomy (dND group), increased the ultimate stress compared with an ovx treatment group, despite large interanimal variations in bone architecture and mechanical properties. These data support the hypothesis that ovariectomized adult monkeys are an excellent model for postmenopausal osteoporosis, and can be used for the evaluation of therapeutic modalities.

Animals↗

Complementary information on bone ultrastructure from scanning small angle X-ray scattering and Fourier-transform infrared microspectroscopy.

Scanning small angle X-ray scattering (scanning SAXS) and Fourier-transform infrared microspectroscopy (FT-IRM) have previously been utilized independently to characterize the structural properties of bone in an anatomical position-resolved fashion. Whereas SAXS provides a direct measure of the physical characteristics of apatitic crystals, FT-IRM assesses structure of both mineral and organic matrix at the molecular level. In the present study both methods were applied to examine the same developing bone tissue from the L-4 vertebra of a 14-month-old (accidental death). A 200-microm-thick section was processed for examination by scanning electron microscopy and SAXS. Spectra were collected at 200 microm spatial resolution at specific locations in cortical and cancellous bone. Parameters determined included total SAXS intensity, crystal thickness (T), and degree and direction of predominant crystal orientation. For FT-IRM analysis, a section 4 microm thick was cut longitudinally from the top of the sample. Spectra of regions 100 x 100 microm2 were acquired from the same locations as the SAXS spectra. Integrated areas of the phosphate nu(1,3) collagen amide I, and carbonate nu2 absorbances, were calculated to obtain mineral: matrix and carbonate:mineral ratios. The relative quantities of types A, B, and labile carbonate (substituted for apatite hydroxyl, phosphate, and surface positions, respectively) were also evaluated. Polarized FT-IRM data were collected to determine molecular orientation of the apatite and collagen components. The results of this study show that the information obtained from the two techniques is complementary. Both SAXS and FT-IRM data revealed that the crystals were significantly larger in the cancellous region compared with the cortical region, that mineralization was greater in the cortex, and that the crystals were oriented to a larger degree in the cancellous compared with the cortical bone. The scanning SAXS measure of crystal thickness was significantly correlated to the FT-IRM measures of crystallinity, type A carbonate substitution, and crystal orientation. In conclusion, it was found that the combined use of SAXS and FT-IRM provides valuable, unique information on structural changes in bone at both the microstructural and ultrastructural level. Although each method can be used individually, the combination of techniques provides additional insights into the mechanism of bone crystal maturation.

Apatites↗

Intermittent and continuous administration of the bisphosphonate ibandronate in ovariohysterectomized beagle dogs: effects on bone morphometry and mineral properties.

Bisphosphonates have emerged as a valuable treatment for postmenopausal osteoporosis. Bisphosphonate treatment is usually accompanied by a 3-6% gain in bone mineral density (BMD) during the first year of treatment and by a decrease in bone turnover. Despite low bone turnover, BMD continues to increase slowly beyond the first year of treatment. There is evidence that bisphosphonates not only increase bone volume but also enhance secondary mineralization. The present study was conducted to address this issue and to compare the effects of continuous and intermittent bisphosphonate therapy on static and dynamic parameters of bone structure, formation, and resorption and on mineral properties of bone. Sixty dogs were ovariohysterectomized (OHX) and 10 animals were sham-operated (Sham). Four months after surgery, OHX dogs were divided in six groups (n = 10 each). They received for 1 year ibandronate daily (5 out of 7 days) at a dose of 0, 0.8, 1.2, 4.1, and 14 microg/kg/day or intermittently (65 microg/kg/day, 2 weeks on, 11 weeks off). Sham dogs received vehicle daily. At month 4, there was a significant decrease in bone volume in OHX animals (p < 0.05). Doses of ibandronate >/= 4.1 microg/kg/day stopped or completely reversed bone loss. Bone turnover (activation frequency) was significantly depressed in OHX dogs given ibandronate at the dose of 14 microg/kg/day. This was accompanied by significantly higher crystal size, a higher mineral-to-matrix ratio, and a more uniformly mineralized bone matrix than in control dogs. This finding lends support to the hypothesis that an increase in secondary mineralization plays a role in gain in BMD associated with bisphosphonate treatment. Moreover, intermittent and continuous therapies had a similar effect on bone volume. However, intermittent therapy was more sparing on bone turnover and bone mineral properties. Intermittent therapy could therefore represent an attractive alternative approach to continuous therapy.

Animals↗

The material basis for reduced mechanical properties in oim mice bones.

Osteogenesis imperfecta (OI), a heritable disease caused by molecular defects in type I collagen, is characterized by skeletal deformities and brittle bones. The heterozygous and homozygous oim mice (oim/+ and oim/oim) exhibit mild and severe OI phenotypes, respectively, serving as controlled animal models of this disease. In the current study, bone geometry, mechanics, and material properties of 1-year-old mice were evaluated to determine factors that influence the severity of phenotype in OI. The oim/oim mice exhibited significantly smaller body size, femur length, and moment of area compared with oim/+ and wild-type (+/+) controls. The oim/oim femur mechanical properties of failure torque and stiffness were 40% and 30%, respectively, of the +/+ values, and 53% and 36% of the oim/+ values. Collagen content was reduced by 20% in the oim/oim compared with +/+ bone and tended to be intermediate to these values for the oim/+. Mineral content was not significantly different between the oim/oim and +/+ bones. However, the oim/oim ash content was significantly reduced compared with that of the oim/+. Mineral carbonate content was reduced by 23% in the oim/oim bone compared with controls. Mineral crystallinity was reduced in the oim/oim and oim/+ bone compared with controls. Overall, for the majority of parameters examined (geometrical, mechanical, and material), the oim/+ values were intermediate to those of the oim/oim and +/+, a finding that parallels the phenotypes of the mice. This provides evidence that specific material properties, such as mineral crystallinity and collagen content, are indicative and possibly predictive of bone fragility in this mouse model, and by analogy in human OI.

Animals↗

Surface analysis of human plasma fibronectin adsorbed to commercially pure titanium materials.

Protein binding on metallic implant surfaces, such as titanium, is governed by the physico-chemical nature of the metallic surface. Human plasma fibronectin (HPF) is an important matrix glycoprotein that mediates cell and protein attachment to each other or to the extracellular matrix present during wound healing. The objective of this study was to investigate the adsorption of HPF onto polished commercially pure titanium (cpTi) by using atomic force microscopy (AFM) and electron spectroscopy for chemical analysis (ESCA) and to measure the resultant surface contact angle before and after HPF binding. Two types of cpTi disks, one highly polished in our laboratory (HSS) and one commercially prepared (31), were reacted with HPF solutions of varying concentrations (1 microg/mL-10 ng/mL). ESCA survey spectra of samples coated with 1 microg/mL of fibronectin showed an increase in organic nitrogen and carbon compared with uncoated controls. Contact angle measurements of HSS and 31 cpTi disks showed no significant difference in average contact angle (36.3 degrees +/- 3.5 and 39.1 degrees +/- 3.1) despite differences in local root mean square (RMS) surface roughness (4.45 +/- 0.46 nm and 22.37 +/- 4.17 nm) as measured by AFM. Images obtained by AFM showed that 31 specimens were more irregular, with large parallel polishing grooves. Adsorbed HPF appeared in a globular form with an average length of 16.5 +/- 1.0 nm, a height of 2.5 +/- 0.5 nm, and a width of 9.6 +/- 1.2 nm. Fibronectin coating on both HSS and 31 cpTi specimens resulted in a significant increase in hydrophobicity compared to uncoated specimens. These results indicate the significance of HPF on cpTi and may explain how cpTi implants function in situ.

Adsorption↗

Identification of the oim mutation by dye terminator chemistry combined with automated direct DNA sequencing.

The homozygous oim/oim mouse, a model of moderate-to-severe human osteogenesis imperfecta, contains a G-nucleotide deletion in the Cola-2 gene (the murine pro alpha(I) collagen gene) that results in accumulation of alpha1(I) homotrimer collagen. Although these mice have a distinctive phenotype that includes multiple fractures and deformities, genotyping is necessary to distinguish them from their wildtype (+/+) and heterozygote (oim/+) littermates. In this study, the dye primer and dye terminator chemistry methods, in combination with automated direct DNA sequencing, were compared for accuracy and ease in genotyping. A total of 82 mice from 14 litters were bred and genotyped; this resulted in 18 +/+, 35 oim/+, and 29 oim/oim mice. The dye primer and dye terminator chemistry methods worked equally well for identification of the deletion mutation and thus the genotype of all of the mice. However, the dye terminator method was found to be superior on the basis of the reduced amount of sample handling and reduced quantity of reagent required.

Animals↗

Fourier transform infrared microspectroscopic analysis of bones of osteocalcin-deficient mice provides insight into the function of osteocalcin.

Osteocalcin, the gamma-carboxyglutamic acid-containing protein, which in most species is the predominant noncollagenous protein of bone and dentin, has been postulated to play roles in bone formation and remodeling. Recently, genetic studies showed that osteocalcin acts as an inhibitor of osteoblast function. Based on von Kossa staining and measurement of mineral apposition rates in tetracycline-labeled bones, osteocalcin knockout animals were reported to have no detectable alterations in bone mineralization. To test the hypothesis that, in addition to regulating osteoblastic activity, osteocalcin is involved in regulating mineral properties, a more sensitive assay of mineralization, Fourier transform infrared microspectroscopy (FT-IRM) was used to study thin sections of femora of 4-week-, 6-month- (intact and ovariectomized), and 9-month-old wild-type and osteocalcin-knockout mice. FT-IRM spectra provided spatially resolved measures of relative mineral and carbonate contents, and parameters indicative of apatite crystal size and perfection. No differences were detected in the mineral properties of the 4-week-old knockout and wild-type mice indicating that the mineralization process was not altered at this time point. Six-month-old wild-type animals had higher mineral contents (mineral:matrix ratios) in cortical as compared with trabecular bones; mineral contents in knockout and wild-type bones were not different. At each age studied, carbonate:phosphate ratios tended to be greater in the wild-type as compared with knockout animals. Detailed analysis of the phosphate nu1,nu3 vibrations in the spectra from 6-month-old wild-type animals indicated that the crystals were larger/more perfect in the cortical as opposed to the trabecular bones. In contrast, in the knockout animals' bones at 6 months, there were no differences between trabecular and cortical bone in terms of carbonate content or crystallite size and perfection. Spectral parameters of the cortical and trabecular bone of the knockout animals resembled those in the wild-type trabecular bone and differed from wild-type cortical bone. In ovariectomized 6-month-old animals, the mineral content (mineral:matrix ratio) in the wild-type cortices increased from periosteum to endosteum, whereas, in the knockout animals' bones, the mineral:matrix ratio was constant. Ovariectomized knockout cortices had lower carbonate:phosphate ratios than wild-type, and crystallite size and perfection resembled that in wild-type trabeculae, and did not increase from periosteum to endosteum. These spatially resolved data provide evidence that osteocalcin is required to stimulate bone mineral maturation.

Age Factors↗

Infrared microspectroscopic imaging of biomineralized tissues using a mercury-cadmium-telluride focal-plane array detector.

A 64 x 64 mercury-cadmium-telluride focal-plane array detector attached to a Fourier transform infrared microscope was used to spectroscopically image 5 microm sections of canine alveolar bone tissue in the fingerprint region of the infrared spectrum. By ratioing the relative intensities of specific bands across the images, it is possible to obtain spatial distributions of the mineral-to-matrix ratio and mineral maturity as a function of distance from an osteon.

Animals↗

Biomineralization: conflicts, challenges, and opportunities.

Biomineralization is the process by which mineral crystals are deposited in an organized fashion in the matrix (either cellular or extracellular) of living organisms. Over the past 25 years, new insights into the mechanisms that control these processes have been obtained, yet questions asked then still persist, especially in terms of vertebrate mineralization. Specifically, there are still debates concerning the chemical nature of the first mineral crystals formed in bone, dentin, and cementum; the factors leading to the initial deposition of these crystals; and the functions of macromolecules found associated with these crystals. In this review, emphasis is placed on the currently accepted answers to these questions, drawing insight from nonvertebrate systems. It is suggested that there are redundant calcification mechanisms and that, by taking advantage of our current knowledge of these mechanisms, opportunities will be provided for therapeutic manipulation of diseases in which biomineralization is impaired.

Animals↗

Effects of proteoglycan modification on mineral formation in a differentiating chick limb-bud mesenchymal cell culture system.

In the presence of 4 mM inorganic phosphate, differentiating chick limb-bud mesenchymal cells plated in micromass cultures form a mineralized matrix resembling that of chick calcified cartilage. To test the hypothesis that cartilage proteoglycans are inhibitors of cell mediated mineralization, the synthesis, content, and turnover of proteoglycans were altered in this system, and the extent of mineralization and properties of the mineral crystals examined. In all cases where the proteoglycan synthesis or proteoglycans present were modified to provide fewer or smaller molecules, mineralization was enhanced. Specifically, when proteoglycan synthesis was blocked by treatment with 10(-10) M retinoic acid, extensive mineral deposition occurred on a matrix devoid of both proteoglycans and cartilage nodules. The crystals, which formed rapidly, were relatively large in size based on analysis by X-ray diffraction or FT-1R microspectroscopy, and were more abundant than in controls. When 2.5 or 5 mM xylosides were used to cause the synthesis of smaller proteoglycans, the extent of mineral accretion was also increased relative to controls; however, the matrix was less affected, and the extent of mineral deposition and the size of the crystals were not as markedly altered as in the case of retinoic acid. Modification of existing proteoglycans by either chondroinase ABC or hyaluronidase treatment similarly resulted in increased mineral accretion (based on 45Ca uptake or total Ca uptake) relative to cultures in which the proteoglycan content was not manipulated. Crystals were more abundant and larger than in control mineralizing cultures. In contrast, when proteoglycan degradation by metalloproteases was inhibited by metal chelation with o-phenanthroline, the Ca accretion at early time points was increased, but as mineralization progressed, Ca accumulation decreased. These data provide evidence that in this culture system, proteoglycans are inhibitors of mineralization.

Animals↗

Matrix vesicles promote mineralization in a gelatin gel.

Extracellular matrix vesicles (MVs) are associated with initial calcification in a variety of tissues, but the mechanisms by which they promote mineralization are not certain. In this study, MVs isolated from fourth passage rat growth plate chondrocyte cultures were included within a gelatin gel into which calcium and phosphate ions diffused from opposite ends. In this gel, apatite formation occurs by 3.5 days in the absence of mineralization promoters, allowing measurement of the ability of different factors to "nucleate" apatite before this time or to assess the effects of molecules which modulate the rate and extent of mineral deposition. Mineral ion accumulation and crystal type are assayed at 5 days. In this study, MV protein content in the central band of a 10% gelatin gel was varied by including 100 microliters of a Tris-buffered solution containing 0-300 micrograms/ml MV protein. There was a concentration-dependent increase in mineral accretion. Whereas 10 micrograms MV protein in the gel did not significantly promote apatite formation as compared with vesicle-free gels, 20 and 30 micrograms MV protein in the gel did promote apatite deposition. Inclusion of 10 mM beta-glycerophosphate in the gels, along with MVs, did not significantly increase apatite formation despite the demonstrable alkaline phosphatase activity of the MVs. In contrast, MVs at all concentrations significantly increased apatite accumulation when proteoglycan aggregates or ATP, inhibitors of apatite formation and proliferation, were included in the gel. Slight increases in calcium, but not phosphate accumulation, were also noted when an ionophore was included with the MVs to facilitate Ca ion transport into the vesicles. FT-IR analysis of the mineral formed in the vesicle-containing gels revealed the presence of a bone-like apatite. These data suggest that MVs facilitate mineralization by providing enzymes that modify inhibitory factors in the extracellular matrix, as well as by providing a protected environment in which mineral ions can accumulate.

Adenosine Triphosphate↗

Effects of bone CS-proteoglycans, DS-decorin, and DS-biglycan on hydroxyapatite formation in a gelatin gel.

The small leucine-rich bone proteoglycans, biglycan and decorin, can be purified by chromatography on hydroxyapatite columns, demonstrating their potential affinities for bone apatite. To determine their effects on in vitro apatite formation and growth, a mixture of the chondroitin-sulfate (CS) bone proteoglycans, or purified fractions of the dermatan sulfate (DS) containing proteoglycans, DS-decorin and DS-biglycan obtained from skin and articular cartilage, respectively, were analyzed in a gelatin gel diffusion system in which apatite formation occurs in the absence of proteins in a 3.5 day period. Low concentrations of the bone CS-proteoglycan mixture and low DS-biglycan concentrations (5-25 microg/ml) increased apatite formation relative to proteoglycan-free controls at 3.5 days. The CS-proteoglycan mixture was less effective at 50 microg/ml than at 10 microg/ml. DS-biglycan was similarly most effective at 5-25 microg/ml. At 5 days, when apatite growth and proliferation were assessed, 10 and 50 microg/ml of both CS-bone proteoglycan and DS-biglycan increased mineral yields. DS-decorin, in contrast, had no significant effect on mineral accumulation at any of these concentrations. In seeded growth experiments, 1 and 10 microg/ml CS-proteoglycan and 10 and 50 microg/ml DS-biglycan were significant effective inhibitors of mineral accretion, whereas DS-decorin showed no tendency to inhibit seeded growth. Using molar extinction coefficients to determine concentrations, the binding of DS-biglycan and DS-decorin to apatite (specific surface 54 m2/g) was determined using a Langmuir adsorption isotherm model. DS-biglycan had a greater affinity for apatite than DS-decorin (0.285 ml/micromol versus 0.0098 ml/micromol). DS-biglycan binding was more specific with fewer binding sites (3.5 micromol/m2 compared with 18. 2 micromol/m2 for DS-decorin). Data suggest that of the small proteoglycans, biglycan may play a more significant role than decorin in the regulation of mineralization.

Animals↗