Osteoblast-osteoclast interaction in bone resorption. Preliminary results

Osteoclastic bone resorption has been evaluated in vitro by release of tritiated collagen fragments from 3H-proline prelabeled bone particles incubated for 48 hours in presence of avian isolated osteoclasts. Cells were co-incubated with periosteum-free chick calvarial fragments by interposition of 0.4 micron millipore membrane transwells, in presence or absence of 10(-8) M 1.34 bovine parathyroid hormone (PTH). Results demonstrated that i) calvaria exert a stimulating effect over osteoclastic bone resorption which was 1.8 fold enhanced with respect to controls (p less than 0.001). ii) the stimulating effect is exerted by calvarium-derived soluble molecules capable of crossing the 0.4 micron millipore membrane interposed between calvarial fragments and osteoclasts, iii) in this experimental system no further enhancement of calvarial stimulating effect is operated by PTH treatment.     

Biotrickling filtration of isopropanol under intermittent loading conditions

This paper investigates the removal of isopropanol by gas-phase biotrickling filtration. Two plastic packing materials, one structured and one random, have been evaluated in terms of oxygen mass transfer and isopropanol removal efficiency. Oxygen mass transfer experiments were performed at gas velocities of 104 and 312 m h^?1 and liquid velocities between 3 and 33 m h^?1. Both materials showed similar mass transfer coefficients up to liquid velocities of 15 m h^?1. At greater liquid velocities, the structured packing exhibited greater oxygen mass transfer coefficients. Biotrickling filtration experiments were carried out at inlet loads (IL) from 20 to 65 g C m^?3 h^?1 and empty bed residence times (EBRT) from 14 to 160 s. To simulate typical industrial emissions, intermittent isopropanol loading (16 h/day, 5 day/week) and intermittent spraying frequency (15 min/1.5 h) were applied. Maximum elimination capacity of 51 g C m^?3 h^?1 has been obtained for the random packing (IL of 65 g C m^?3 h^?1, EBRT of 50 s). The decrease in irrigation frequency to 15 min every 3 h caused a decrease in the outlet emissions from 86 to 59 mg C Nm^?3 (inlet of 500 mg C Nm^?3). The expansion of spraying to night and weekend periods promoted the degradation of the isopropanol accumulated in the water tank during the day, reaching effluent concentrations as low as 44 mg C Nm^?3. After a 7-week starvation period, the performance was recovered in less than 10 days, proving the robustness of the process.     

Trabecular bone density and loading history: regulation of connective tissue biology by mechanical energy

The method of considering a single loading condition in the study of stress/morphology relationships in trabecular bone is expanded to include the multiple loading conditions experienced by bone in vivo. The bone daily loading histories are characterized in terms of stress magnitudes or cyclic strain energy density and the number of loading cycles. Relationships between local bone apparent density and loading history are developed which assume that bone mass is adjusted in response to strength or energy considerations. Three different bone maintenance criteria are described which are formulated based upon: (1) continuum model effective stress, (2) continuum model fatigue damage accumulation density, and (3) bone tissue strain energy density. These approaches can be applied to predict variations in apparent density within bone and among bones. We show that all three criteria have similar mathematical forms and may be related to the density (or concentration) of bone strain energy which is transferred (dissipated) in the mineralized tissue. The loading history and energy transfer concepts developed here can be applied to many different situations of growth, functional adaptation, injury, and aging of connective tissues.     

Relationship between bone tissue strain and lattice strain of HAp crystals in bovine cortical bone under tensile loading

Cortical bone is a composite material composed of hydroxyapatite (HAp) and collagen. As HAp is a crystalline structure, an X-ray diffraction method is available to measure the strain of HAp crystals. However, HAp crystals in bone tissue have been known to have the low degree of crystallization. Authors have proposed an X-ray diffraction method to measure the lattice strain of HAp crystals from the diffusive intensity profile due to low crystallinity. The precision of strain measurement was greatly improved by this method. In order to confirm the possibility of estimating the bone tissue strain with measurements of the strain of HAp crystals, this work investigates the relationship between bone tissue strain on a macroscopic scale and the lattice strain of HAp crystals on a microscopic scale. The X-ray diffraction experiments were performed under tensile loading. Strip bone specimens of 40x6x0.8mm in size were cut from the cortical region of a shaft of bovine femur. A stepwise tensile load was applied in the longitudinal direction of the specimen. By detecting the diffracted X-ray beam transmitted through the specimen, the lattice strain was directly measured in the loading direction. As a result, the lattice strain of HAp crystals showed lower value than the bone tissue strain measured by a strain gage. The bone tissue strain was described with the mean lattice strain of the HAp crystals and the elastic modulus.     

The importance of mechanical loading in bone biology and medicine

This paper discusses the premise that the skeleton is primarily a mechanical organ, and reviews the reasons that mechanical factors play a major role in bone biology. It begins by considering three basic observations: (1) Galileo's observation that bone proportions become more robust as the species' overall size increases; (2) da Vinci's observation that larger structures are inherently weaker than smaller structures subjected to the same stress; and (3) the general observation that each unit of bone mass provides structural support for about 15 units of soft tissue organ mass. Together, these observations lead to the concept that it can be advantageous to minimize bone mass, consistent with constraints on other factors. This premise is discussed here in relation to the phenomenon of bone remodeling, which is seen to serve two purposes: the adjustment of bone mass and geometry to maintain peak bone strains at their maximum tolerable values, and the continual removal of fatigue damage produced at those strain levels. Finally, it is observed that bone remodeling apparently originated approximately 250 million years ago when the first vertebrates of substantial size became weight-bearing on land, suggesting that mechanical forces associated with weight-bearing were instrumental in the evolution of bone remodeling.     

The modulating effect of amino acids on an organotypic culture of lymphoid tissue

The effect of 20 essential and nonessential L-amino acids on the dynamics of development of spleen explants from 1- and 21-day-old rats on an organotypic tissue culture was studied. The hydrophilic amino acids with a higher molecular mass (asparagine, lysine, arginine, and glutamic acid) induced an inhibitory effect on the growth zone of explants of immature tissue from 1-day-old animals and an opposite, stimulating effect on the mature spleen tissue of 21-day-old rats. An immunohistochemical analysis revealed a reciprocal correlation between the expression of the proapoptotic protein p53 and the cell proliferation upon the action of lysine, asparagine, and glutamic acid. The role of polar amino acids in the modulation of cell proliferation and apoptosis in dependence on the period of ontogenesis was determined. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2006, vol. 32, no. 3; see also http://www.maik.ru.     

The modulating effect of amino acids on an organotypic culture of lymphoid tissue

The effect of 20 essential and nonessential L-amino acids on the dynamics of development of spleen explants from 1-and 21-day-old rats on an organotypic tissue culture was studied. The hydrophilic amino acids with a higher molecular mass (asparagine, lysine, arginine, and glutamic acid) induced an inhibitory effect on the growth zone of explants of immature tissue from 1-day-old animals and an opposite, stimulating effect on the mature spleen tissue of 21-day-old rats. An immunohistochemical analysis revealed a reciprocal correlation between the expression of the proapoptotic protein p53 and the cell proliferation upon the action of lysine, asparagine, and glutamic acid. The role of polar amino acids in the modulation of cell proliferation and apoptosis in dependence on the period of ontogenesis was determined.     

Local bone formation due to combined mechanical loading and intermittent hPTH-(1-34) treatment and its correlation to mechanical signal distributions

We evaluated the local response of cortical bone in the rat tibia due to combined treatment with synthetic parathyroid hormone, hPTH-(1-34), and mechanical stimulation by four-point bending. Forty-eight female retired breeder Sprague-Dawley rats were divided into six groups. Mechanically stimulated animals included the following groups: (1) Bend+PTH, (2) Sham+PTH, (3) Bend+Vehicle, (4) Sham+Vehicle. Non-mechanically stimulated animals included a (5) Control group that received neither loading nor injections, and a (6) PTH group that received only hPTH-(1-34) injections. The right limbs of mechanically loaded animals were exposed to a peak force of 50 N for 36 cycles at 2 Hz, three days per week for four weeks, and PTH-treated animals received injections equivalent to 50 μg/kg BW. Fluorochrome labeling was used to measure local formation at 12 sectors about the endocortical periphery. The distributions of endocortical bone formation were compared to the local formation differences between treatment groups and to a variety of potential mechanical stimuli signals. Results indicated that hPTH-(1-34) exerted a potent anabolic effect with near-uniform formation about the endocortical surface, and that localized formation peaks due to bending were further augmented in the presence of hPTH-(1-34) treatment. Correlation of formation patterns to mechanical signal distributions highlighted several candidate signals including the mid-principal stress, the dilatational strain, and the radial gradient of the local radial strain.