Biomedical subjects

C S Adams

Publications and source records attributed to C S Adams.

At least 19 recordsLinked to original sources

PubMed2006

Involvement of hydrogen peroxide in the differentiation and apoptosis of preosteoclastic cells exposed to arsenite.

Long-term exposure to sodium arsenite (AsO(2)) promotes the development of various cancers. Paradoxically, arsenic also induces pro-myelomonocytic leukemia cell differentiation, and at higher concentrations, apoptosis. The present study investigated the effects of AsO(2) on preosteoclasts. When treated with 2.5-5microM AsO(2), RAW264.7 cells underwent osteoclast differentiation as evidenced by an increase in the number of multinucleate cells expressing tartrate resistant acid phosphatase (TRAP). The appearance of these phenotypic markers was preceded by a low level increase in extracellular production of H(2)O(2) and was prevented by the addition of catalase (4.5microg/ml), an enzyme that removes H(2)O(2). Only at high concentrations (10-25microM) of AsO(2) was a significant loss of cell viability and a high level increase in H(2)O(2) production (1.5microM) observed. Apoptosis was blocked by pretreatment with diphenylene iodonium chloride (2microM), a NAD(P)H-flavoprotein inhibitor, suggesting the involvement of NADPH-oxidase. The data show that AsO(2), dose-dependently, stimulates increasing amounts of H(2)O(2) production. Moreover, at concentrations found in tissues of individuals exposed to geochemical AsO(2), osteoclasts underwent an H(2)O(2)-dependent differentiation. Therefore, chronic exposure to low-level amounts of AsO(2) could result in increased bone resorption and contribute to bone related pathologies.

Acid Phosphatase↗

PubMed2006

Active caspase-3 is required for osteoclast differentiation.

Based on our earlier observation that caspase-3 is present in osteoclasts that are not undergoing apoptosis, we investigated the role of this protein in the differentiation of primary osteoclasts and RAW264.7 cells (Szymczyk KH, et al., 2005, Caspase-3 activity is necessary for RANKL-induced osteoclast differentiation. The Proceedings of the 8th ICCBMT). We noted that osteoclast numbers are decreased in long bones of procaspase-3 knockout mice and that receptor activator of NF-kappaB ligand (RANKL) does not promote differentiation of isolated preosteoclasts. In addition, after treatment with inhibitors of caspase-3 activity, neither the wild-type primary nor the RAW264.7 cells express TRAP or became multinucleated. We found that immediately following RANKL treatment, procaspase-3 is cleaved and the activated protein is localized to lipid regions of the plasma membrane and the cytosol. We developed RAW264.7 procaspase-3 knockdown clonal cell lines using RNAi technology. Again, treatment with RANKL fails to induce TRAP activity or multinucleation. Finally, we evaluated NF-kappaB in procaspase-3 silenced cells. We found that RANKL treatment prevented activation and nuclear translocation of NF-kappaB. Together these findings provide direct support for the hypothesis that caspase-3 activity is required for osteoclast differentiation.

Animals↗

PubMed2005

Emergence and decay of turbulence in stirred atomic Bose-Einstein condensates.

We show that "weak" elliptical deformation of an atomic Bose-Einstein condensate rotating at close to the quadrupole instability frequency leads to turbulence with a Kolmogorov energy spectrum. The turbulent state is produced by energy transfer to condensate fragments that are ejected by the quadrupole instability. This energy transfer is driven by breaking the twofold rotational symmetry of the condensate. Subsequently, vortex-sound interactions damp the turbulent state leading to the crystallization of a vortex lattice.

Journal Article↗

PubMed2004

Controlled vortex-sound interactions in atomic Bose-Einstein condensates.

The low temperature dynamics of a vortex in a trapped quasi-two-dimensional Bose-Einstein condensate are studied quantitatively. Precession of an off-centered vortex in a dimple trap, embedded in a weaker harmonic trap, leads to the emission of sound in a dipolar radiation pattern. Sound emission and reabsorption can be controlled by varying the depth of the dimple. In a shallow dimple, the power emitted is proportional to the vortex acceleration-squared over the precession frequency, whereas for a deep dimple, periodic sound reabsorption stabilizes the vortex against radiation-induced decay.

Journal Article↗

PubMed2004

Model surfaces engineered with nanoscale roughness and RGD tripeptides promote osteoblast activity.

Cell adhesion to biomaterials is a prerequisite for tissue integration with the implant surface. Herein, we show that we can generate a model silica surface that contains a minimal-length arginine-glycine-aspartic acid (RGD) peptide that maintains its biological activity. In the first part of this study, attachment of MC3T3-E1 osteoblast-like cells was investigated on silicon oxide, amine terminated substrates [i.e., 3-aminopropyl triethoxysilane (APTS)], grafted RGD, and physisorbed RGD control. The APTS layer exhibited nanoscale roughness and presented amine functional groups for grafting a minimal RGD tripeptide devoid of any flanking groups or spacers. Contact angle measurements indicated that the hydrophobicity of the APTS surface was significantly lower than that of the surface with grafted RGD (RGD-APTS). Atomic force microscopy showed that surfaces covered with RGD-APTS were smoother (Ra = 0.71 nm) than those covered with APTS alone (Ra = 1.59 nm). Focusing mainly on cell morphology, experiments showed that the RGD-APTS hybrid provided an optimum surface for cell adhesion, spreading, and cytoskeletal organization. Discrete focal adhesion plaques were also observed consistent with successful cell signaling events. In a second set of experiments, smooth, monolayers of APTS (Ra = 0.1 nm) were used to prepare arginine-glycine-aspartic acid-serine (RGDS)-APTS and arginine-glycine-glutamic acid-serine (RGES)-APTS (control) substrates. Focusing mainly on cell function, integrin and gene expression were all enhanced for rate osteosarcoma cells on surfaces containing grafted RGDS. Both sets of studies demonstrated that grafted molecules of RGD(S) enhance both osteoblast-like cell adhesion and function.

Animals↗

PubMed2004

Ionizing radiation sensitizes bone cells to apoptosis.

Osteoradionecrosis is a common sequelae of radiation therapy for head and neck cancer. To test the hypothesis that radiation induces osteoradionecrosis by induction of bone cell apoptosis, we exposed MC3T3-E1 osteoblast-like cells to gamma-radiation and evaluated cell viability. Twenty-four hours postirradiation, measurement of osteoblast dehydrogenase activity suggested that there was a small decrease in cell viability. However, TUNEL and flow cytometric analysis indicated that the viability loss was caused by inhibition of cell proliferation and not by induction of apoptosis. The effect of irradiation on osteoblast function was examined by Western blot and flow cytometric analysis. It was found that irradiated osteoblasts underwent G2 cell cycle arrest. In addition, we observed changes in expression of molecules that regulate the cell cycle. Thus, there was an increase in p53 transcription, a raised level of MDM2 dephosphorylation, and elevation in p21 and GADD153 protein levels. Since these proteins are concerned with the regulation of the cell cycle, the observed changes in expression would be expected to disturb cyclin activity and cause G2M arrest. The arrested cells displayed a dramatic increase in sensitivity to specific apoptogens. Thus, when irradiated, and then treated with Ca2+Pi or staurosporine, agents that cause mitochondrial dysfunction, more osteoblasts underwent apoptosis than with the apoptogen alone. In contrast, irradiated cells treated with anti-Fas antibody showed no change in apoptotic sensitivity; apoptosis was inhibited when osteoblasts were treated with etoposide. Similar alterations in sensitivity were observed when cells were arrested in G2/M by pretreatment with colchicine and then challenged with apoptogens. It was concluded that activation of radiation-induced G2 arrest sensitizes osteoblasts to agents that mediate apoptosis through a mitochondrial-dependent death pathway.

Animals↗

PubMed2004

Bone cell survival in microgravity: evidence that modeled microgravity increases osteoblast sensitivity to apoptogens.

Studies were performed to evaluate the effects of modeled microgravity on the induction of osteoblast apoptosis. MC3T3-E1 osteoblast-like cells were cultured in alginate carriers in the NASA-approved high aspect ratio vessel (HARV). This system subjects the cells to a time-averaged gravitational field (vector-averaged gravity) to simulate low gravity conditions. Cells were cultured in the HARV for five days, and then examined for apoptosis. In simulated microgravity, the cells remained vital, although analysis of expressed genes indicated that there was loss of the mature osteoblast phenotype. Additionally, we noted that there was a loss of the mitochondrial membrane potential, a low level of the antiapoptotic protein Bcl-2, as well as Akt protein, and the redox status of the cells was disturbed. All of these parameters indicated that vector-averaged gravity disrupts mitochondrial function, thereby sensitizing osteoblasts to apoptosis. We then used a challenge assay to evaluate the apoptotic sensitivity of the cells subjected to vector-averaged gravity. When challenged with staurosporine, cells subjected to vector-averaged gravity evidenced elevated levels of cell death relative to control cell populations. Another objective of the study was to improve upon conventional carriers by using alginate encapsulation to support cells in the HARV. We have demonstrated that the alginate carrier system affords a more robust system than surface-seeded carriers. This new system has the advantage of shielding cells from mechanical damage and fluid shear stresses on cells in the HARV, permitting carefully controlled studies of the effects of vector-averaged gravity.

3T3 Cells↗

PubMed2003

Soliton-sound interactions in quasi-one-dimensional Bose-Einstein condensates.

Longitudinal confinement of dark solitons in quasi-one-dimensional Bose-Einstein condensates leads to sound emission and reabsorption. We perform quantitative studies of the dynamics of a soliton oscillating in a tight dimple trap, embedded in a weaker harmonic trap. The dimple depth provides a sensitive handle to control the soliton-sound interaction. In the limit of no reabsorption, the power radiated is found to be proportional to the soliton acceleration squared. An experiment is proposed to detect sound emission as a change in amplitude and frequency of soliton oscillations.

Journal Article↗

PubMed2003

Induction of apoptosis in skeletal tissues: phosphate-mediated chick chondrocyte apoptosis is calcium dependent.

In an earlier study, we have shown that Pi induced apoptosis of terminally differentiated hypertrophic chondrocytes. To ascertain whether Ca2+ modulates Pi-induced cell death, we asked the following two questions: First, can we prevent Pi-induced apoptosis by removing Ca2+ from the culture medium; alternatively, can we potentiate cell death by increasing the Ca2+ concentration? Second, can we inhibit chondrocyte apoptosis by blocking Pi transport? We also explored the mechanism of apoptosis by evaluating mitochondrial activity and reactive oxygen species (ROS) generation in cells treated with the ion pair. We noted that EDTA and EGTA blocked Pi-induced apoptosis in a dose-dependent manner. While high levels of Ca2+ alone had little effect on chondrocyte viability, the cation enhanced Pi-dependent cell death and greatly increased Pi uptake. When Pi transport was blocked, there was complete inhibition of cell killing. The process of cell death was characterized by mitochondrial hyperpolarization; two hours following apoptogen treatment, there was a significant decrease in the mitochondrial membrane potential. Coincident with the changes in mitochondrial function, there was an increase in intracellular Ca2+ that was maintained throughout the experimental period. A raised Ca2+ signal was observed in blebs at the cell membrane. Finally, we noted that, 75 minutes after treatment with the ion pair, there was a six-fold elevation in ROS levels. This increase declined to baseline values after three hours. Based on these observations, we suggest that, at the cartilage mineralization front, an elevation in local environmental Ca2+ and Pi concentrations modulates oxidative metabolism, and triggers apoptosis of terminally differentiated chondrocytes.

Animals↗

PubMed2003

Mechanisms by which extracellular matrix components induce osteoblast apoptosis.

Bone cell apoptosis is seen at sites of active turnover. We hypothesize that at these sites, factors released from resorbing bone induce apoptosis of vicinal cells. Related to this observation, earlier studies indicate that an elevation in the level of inorganic phosphate ions combined with a modest increase in the calcium (Ca2+) concentration, or a rise in the local concentration of RGD-containing peptides promote osteoblast apoptosis. The aim of the current investigation is to elucidate the mechanism by which these extracellular matrix components induce bone cell apoptosis. The data presented in this study clearly demonstrate that osteoblasts are sensitive to peptide fragments and solubilized mineral ions. It is reasonable to expect that these apoptogens would be generated by osteoclasts during resorption of the extracellular bone matrix. We suggest that these components conspire to regulate bone cell function. In terms of the mechanism by which these agents activate apoptosis, it is clear that while they share common pathways, there are some differences in the mechanism of apoptosis. These differences appear to be upstream of caspase activation. The observation that two such pathways exist lends strength to the notion that apoptosis is carefully regulated in bone and that signals from both matrix components act together to trigger the remodeling process.

Animals↗

PubMed2002

Cartilage viability after repetitive loading: a preliminary report.

OBJECTIVE: To assess matrix changes and chondrocyte viability during static and continuous repetitive mechanical loading in mature bovine articular cartilage explants. METHODS: Cartilage explants were continuously loaded either statically or cyclically (0.5 Hz) for 1-72 h (max. stress 1 megapascal). Cell death was assessed using fluorescent probes and detection of DNA strand breakage characteristic of apoptosis. Cell morphology and matrix integrity were evaluated using histology and transmission electron microscopy. RESULTS: Repetitive loading of articular cartilage at physiological levels of stress (1 megapascal) was found to be harmful to only the chondrocytes in the superficial tangential zone (STZ) and depended on the characteristics (static vs cyclic) and duration (1-72 h) of the applied load. The chondrocytes in the middle and deep zone remained viable at all times. Static loads caused cell death at an early time (3 h) as compared with cyclic loads (sinusoidal, 0.5 cycles per s for 6 h). The amount and extent of cell death peaked at 6 h of cyclic loading, and did not change in subsequent experiments run for longer periods of time (up to 72 h). There was no indication of fragmented nuclear DNA but there was evidence of injurious cell death (necrosis) by electron microscopy. Morphological analysis of cartilage repetitively loaded for 24 h showed matrix damage only in the uppermost superficial layer at the articular surface, reminiscent of the early stages of osteoarthritis. CONCLUSIONS: Cell death in mature cartilage explants occurred after 6 hours of continuous repetitive load or 3 h of static load. Cell death was directly related to the mechanical load, as control (free-swelling) explants remained viable at all times. The excessive, repetitive loading conditions imposed are not physiological, and demonstrate the deleterious effects of mechanical overload resulting in morphological and cellular damage similar to that seen in degenerative joint disease.

Animals↗

PubMed2002

RGD peptides immobilized on a mechanically deformable surface promote osteoblast differentiation.

The major objective of this work was to attach bone cells to a deformable surface for the effective transmission of force. We functionalized a silastic membrane and treated it with 3-aminopropyltriethoxysilane (APTS). A minimal RGD peptide was then covalently linked to the aminated surface. MC3T3-E1 osteoblast-like cells were cultured on the arginine-glycine-aspartic acid (RGD)-treated membrane for 3-15 days and cell attachment and proliferation was evaluated. We observed that cells were immediately bound to the membrane and proliferated. After 8 days on the material surface, osteoblasts exhibited high levels of ALP staining, indicating that the cells were undergoing maturation. Alizarin red staining and Fourier transform infrared (FTIR) analysis showed that the mineral formed by the cells was a biological apatite. The second objective was to apply a mechanical force to cells cultured on the modified silicone membrane. Dynamic equibiaxial strain, 2% magnitude, and a 0.25-Hz frequency were applied to bone cells for 2 h. Osteoblasts elicited increased phalloidin fluorescence, suggesting that there was reorganization of the cytoskeleton. Furthermore, the applied strain elicited increased expression of the alpha(v)beta3 integrin receptor. We concluded that the covalent binding of RGD peptides to a silicone membrane provides a compatible surface for the attachment and subsequent differentiation of osteoblasts. Moreover, the engineered surface transduces applied mechanical forces directly to the adherent cells via integrin receptors.

3T3 Cells↗

PubMed2002

The biohydrogenation of linoleamide in vitro and its effects on linoleic acid concentration in duodenal contents of sheep.

Previous studies showed that oleamide was protected from ruminal biohydrogenation and increased 18:1(n-9) concentration in milk when fed to lactating dairy cows. To appraise whether this protection extended to linoleamide, a rumen in vitro experiment was conducted to determine biohydrogenation of linoleamide followed by two sheep experiments to evaluate whether linoleamide could increase 18:2 (n-6) concentration in duodenal contents. Treatments for the in vitro and sheep studies consisted of three diets containing no added lipid (control), linoleic acid, or linoleamide. Lipids were added at 10% (DM basis) of the in vitro substrate (ground grass hay). The three substrates were incubated with mixed ruminal microbes in triplicate, and 5 mL of culture contents was taken at 0, 24, and 48 h for analysis of 18:2 (n-6) concentration by gas chromatography. The concentrations of 18:2 (n-6) (corrected for 18:2 (n-6) in the control cultures) at 0, 24, and 48 h were 2.51, 0.38, and 0.11 mg/5 mL for the linoleic acid cultures compared to 2.10, 1.35, and 1.08 mg/5 mL for the linoleamide cultures. Compared to linoleic acid, the cultures containing linoleamide had higher 18:1 (n-9) and lower concentrations of biohydrogenation products including trans-18:1 and 18:0. Three sheep with duodenal cannulas were fed the three diets in two separate 3 x 3 Latin squares each with 2-wk periods. The two squares only differed in the amount of added lipid (1.5 vs 5% of the ration DM). When the lipids were added at 1.5% of the ration DM, they had little effect on duodenal 18:2 (n-6) concentration (2.8, 3.6, and 4.3 mg/g DM for the control, linoleic acid, and linoleamide treatments, respectively). At 5% of the ration DM, both lipid supplements increased duodenal 18:2 (n-6) concentration over the control diet with a greater response observed for linoleamide (2.5, 12.2, and 16.8 mg/g DM for the control, linoleic acid, and linoleamide treatments, respectively). This study demonstrates reduced biohydrogenation of linoleamide based on its ability to maintain a higher concentration of 18:2 (n-6) in ruminal cultures and in duodenal contents of sheep compared to free linoleic acid.

Animals↗

PubMed2001

Matrix regulation of skeletal cell apoptosis. Role of calcium and phosphate ions.

Previously, we noted that inorganic phosphate (P(i)), a major component of bone extracellular matrix, induced osteoblast apoptosis (Meleti, Z., Shapiro, I. M., and Adams, C. S. (2000) Bone (NY) 27, 359-366). Since Ca(2+) along with P(i) is released from bone during the resorption process, we advanced the hypothesis that Ca(2+) modulates P(i)-mediated osteoblast apoptosis. To test this hypothesis, osteoblasts were incubated with both ions, and cell death was determined. We noted that a modest increase in the medium Ca(2+) concentrations ([Ca(2+)](e)) of 0.1-1 mm caused a profound and rapid enhancement in P(i)-dependent death of cultured osteoblasts. An elevation in [Ca(2+)](e) alone had no effect on osteoblast viability, whereas Ca(2+) channel blockers failed to inhibit killing of ion pair-treated cells. These results indicated that P(i)-mediated cell death is not dependent on a sustained increase in the cytosolic Ca(2+) concentration. Terminal dUTP nick-end labeling analysis and measurement of caspase-3 activity of the ion pair-treated cells suggested that death was apoptotic. Apoptosis was confirmed using caspase-3 and endonuclease inhibitors. The mitochondrial membrane potential and cytosolic Ca(2+) status of the treated cells were evaluated. After incubation with [Ca(2+) ](e) and P(i), a decrease in mitochondrial fluorescence was noted, suggesting that the ions decreased the mitochondrial transmembrane potential. Subsequent to the fall in mitochondrial membrane potential, there was a transient elevation in the cytosolic Ca(2+) concentration. Results of the study suggest that the ion pair conspire at the level of the plasma membrane to induce intracellular changes that result in loss of mitochondrial function. The subsequent increase in the cytosolic Ca(2+) concentration may trigger downstream events that transduce osteoblast apoptosis.

Apoptosis↗

PubMed2001

Sound emission due to superfluid vortex reconnections.

By performing numerical simulations based on the Gross-Pitaevskii equation, we make direct quantitative measurements of the sound energy released due to superfluid vortex reconnections. We show that the energy radiated expressed in terms of the loss of vortex line length is a simple function of the reconnection angle. In addition, we study the temporal and spatial distribution of the radiation and show that energy is emitted in the form of a sound pulse with a wavelength of a few healing lengths.

Journal Article↗

PubMed2001

Thermal activation of hydrocarbon C-H bonds by tungsten alkylidene complexes.

Thermal activation of CpW(NO)(CH(2)CMe(3))(2) (1) in neat hydrocarbon solutions transiently generates the neopentylidene complex, CpW(NO)(=CHCMe(3)) (A), which subsequently activates solvent C-H bonds. For example, the thermolysis of 1 in tetramethylsilane and perdeuteriotetramethylsilane results in the clean formation of CpW(NO)(CH(2)CMe(3))(CH(2)SiMe(3)) (2) and CpW(NO)(CHDCMe(3))[CD(2)Si(CD(3))(3)] (2-d(12)), respectively, in virtually quantitative yields. The neopentylidene intermediate A can be trapped by PMe(3) to obtain CpW(NO)(=CHCMe(3))(PMe(3)) in two isomeric forms (4a-b), and in benzene, 1 cleanly forms the phenyl complex CpW(NO)(CH(2)CMe(3))(C(6)H(5)) (5). Kinetic and mechanistic studies indicate that the C-H activation chemistry derived from 1 proceeds through two distinct steps, namely, (1) rate-determining intramolecular alpha-H elimination of neopentane from 1 to form A and (2) 1,2-cis addition of a substrate C-H bond across the W=C linkage in A. The thermolysis of 1 in cyclohexane in the presence of PMe(3) yields 4a-b as well as the olefin complex CpW(NO)(eta(2)-cyclohexene)(PMe(3)) (6). In contrast, methylcyclohexane and ethylcyclohexane afford principally the allyl hydride complexes CpW(NO)(eta(3)-C(7)H(11))(H) (7a-b) and CpW(NO)(eta(3)-C(8)H(13))(H) (8a-b), respectively, under identical experimental conditions. The thermolysis of 1 in toluene affords a surprisingly complex mixture of six products. The two major products are the neopentyl aryl complexes, CpW(NO)(CH(2)CMe(3))(C(6)H(4)-3-Me) (9a) and CpW(NO)(CH(2)CMe(3))(C(6)H(4)-4-Me) (9b), in approximately 47 and 33% yields. Of the other four products, one is the aryl isomer of 9a-b, namely, CpW(NO)(CH(2)CMe(3))(C(6)H(4)-2-Me) (9c) ( approximately 1%). The remaining three products all arise from the incorporation of two molecules of toluene; namely, CpW(NO)(CH(2)C(6)H(5))(C(6)H(4)-3-Me) (11a; approximately 12%), CpW(NO)(CH(2)C(6)H(5))(C(6)H(4)-4-Me) (11b; approximately 6%), and CpW(NO)(CH(2)C(6)H(5))(2) (10; approximately 1%). It has been demonstrated that the formation of complexes 10 and 11a-b involves the transient formation of CpW(NO)(CH(2)CMe(3))(CH(2)C(6)H(5)) (12), the product of toluene activation at the methyl position, which reductively eliminates neopentane to generate the C-H activating benzylidene complex CpW(NO)(=CHC(6)H(5)) (B). Consistently, the thermolysis of independently prepared 12 in benzene and benzene-d(6) affords CpW(NO)(CH(2)C(6)H(5))(C(6)H(5)) (13) and CpW(NO)(CHDC(6)H(5))(C(6)D(5)) (13-d(6)), respectively, in addition to free neopentane. Intermediate B can also be trapped by PMe(3) to obtain the adducts CpW(NO)(=CHC(6)H(5))(PMe(3)) (14a-b) in two rotameric forms. From their reactions with toluene, it can be deduced that both alkylidene intermediates A and B exhibit a preference for activating the stronger aryl sp(2) C-H bonds. The C-H activating ability of B also encompasses aliphatic substrates as well as it reacts with tetramethylsilane and cyclohexanes in a manner similar to that summarized above for A. All new complexes have been characterized by conventional spectroscopic methods, and the solid-state molecular structures of 4a, 6, 7a, 8a, and 14a have been established by X-ray diffraction methods.

Journal Article↗

PubMed2001

Phosphate ions mediate chondrocyte apoptosis through a plasma membrane transporter mechanism.

In a previous investigation we showed that phosphate ions (Pi) induced apoptosis of terminally differentiated hypertrophic chondrocytes. To explore the mechanism by which Pi induces cell death, we asked the following two questions. First, can we prevent Pi-induced apoptosis by inhibiting plasma membrane Na-Pi cotransport? Second, which specific Na-Pi transporters are expressed in chondrocytes and are they developmentally regulated? Terminally differentiated hypertrophic chondrocytes were isolated from chick tibial cartilage and cell death was measured in the presence of 3-7 mmol/L Pi. To ascertain whether apoptosis was linked to a rise in cellular Pi loading, we examined the effect of phosphonoformic acid (PFA), a competitive inhibitor of Na-Pi cotransport on Pi-induced apoptosis in chondrocytes. We found that 1 mmol/L PFA blocked anion-induced cell death and prevented an increase in the cell Pi content. In a parallel study, we determined that the bisphosphonate, alendronate, also protected chondrocytes from death, albeit at a lower concentration than PFA. Using a DNA end-labeling procedure, we showed that the Pi-treated cells were apoptotic and, as might be predicted, the presence of PFA blocked induction of the death sequence. Next, we examined the expression of two Pi transporters in relation to chondrocyte maturation and anion treatment. We noted that there was expression of the constitutive transporter, Glvr-1, and a type II cotransporter in chick growth plate cells. Although these transport systems are active in terminally differentiated cells, it is probable that the initiation of apoptosis may require the induction of other Pi-transport systems. It is concluded that, at the mineralization front, cell death is linked directly to the elevation in environmental anion concentration and the concomitant rise in intracellular Pi levels.

Alendronate↗

PubMed2001

A novel mechanism of body mass regulation.

While significant attention has been devoted to the identification of hormonal factors that control body mass, little attention has been paid to the role of mechanical loading on animal mass. Here, we provide evidence that intraperitoneal implantation of metabolically inert mass results in a compensatory reduction in tissue mass. Deer mice (Peromyscus maniculatus) were surgically implanted with weights of 1, 2 or 3 g. There was a resulting loss of tissue mass (total body mass minus implant mass) that was proportional to the mass of the implant. This reduction in tissue mass followed a reduction in food intake in animals with 3 g implants. Evaluation of body composition failed to identify any single component that contributed to the loss of tissue mass. Removal of implants led to a transient restoration of body mass to levels similar to the total body mass of those control animals in which the implant had not been removed. However, within 12 days of implant removal, body mass again declined to the level seen before implant removal. These results suggest the existence of a set point that is sensitive to changes in the perception of mass and that is transduced via neural pathways.

Animals↗