A comparative analysis of strategies for isolation of matrix vesicles

Matrix vesicles (MVs) are extracellular organelles involved in the initial steps of mineralization. MVs are isolated by two methods. The first isolation method of MVs starts with collagenase digestion of osseous tissues, followed by two differential centrifugations. The second isolation method does not use proteases but rather starts with differential centrifugation, followed by a fractionation on a sucrose gradient. The first method results in a homogeneous population of MVs with higher cholesterol/lipid content, alkaline phosphatase activity, and mineral formation rate as compared with MVs isolated by the second method. The second method leads to higher protein diversity as compared with MVs isolated according to the first method. Due to their distinct protein composition, lipid-to-protein and cholesterol-to-phospholipid ratios, and differences in rates of mineral formation, both types of isolated MVs are crucial for proteomic analysis and for understanding the regulation of mineralization process at the molecular level.

New reporter cell line to evaluate the sequential emergence of multiple human cytomegalovirus mutations during in vitro drug exposure

We developed a new reporter cell line for human cytomegalovirus (HCMV) drug susceptibility testing. This cell line was obtained by incorporating the luciferase reporter gene under the control of an HCMV-specific promoter into the genome of astrocytoma cells (U373MG). We then used our reporter cell line to evaluate phenotypic changes conferred by the sequential emergence of HCMV UL54 and UL97 mutations following long-term drug exposure. The laboratory strain AD169 was passaged in the presence of increasing concentrations of ganciclovir (one viral line) or foscarnet (two viral lines). Resistant viruses were plaque purified at five different concentrations of ganciclovir and at three different concentrations of foscarnet. In addition to the previously described M460I and L595S UL97 mutations and the L545S and V812L UL54 mutations, exposition to ganciclovir (up to 3,000 microM) resulted in the selection of two unreported UL54 mutations (P829S and D879G). Passages in the presence of foscarnet (up to 3,000 microM) resulted in the selection of seven not previously described UL54 mutations (K500N, T552N, S585A, N757K, L802V, L926V, and L957F) in addition to the N408D mutation that has been associated with ganciclovir and cidofovir resistance. Long-term exposure of HCMV to either ganciclovir or foscarnet ultimately resulted in the selection of multiple UL54 mutations that conferred high levels of resistance to all approved HCMV DNA polymerase inhibitors, i.e., ganciclovir, cidofovir, and foscarnet. Emergence of each viral mutation conferred stepwise increases in drug 50% inhibitory concentrations that could be objectively measured with the new reporter cell assay.

Clinical impact of ganciclovir-resistant cytomegalovirus infections in solid organ transplant patients

Clinical consequences of ganciclovir resistant cytomegalovirus (CMV) infections were studied during 2 large prophylactic trials consisting of 100 days of valganciclovir or ganciclovir prophylaxis in solid organ transplant (SOT) recipients. The first one involved 301 high-risk (CMV donor seropositive/recipient seronegative) SOT recipients excluding lung transplants followed for 12 months, whereas the second one involved 80 lung transplant patients evaluated over 6 months. Among the 7 patients (4 non-lung and 3 lung transplant patients) carrying viruses with known ganciclovir-resistance [corrected] mutations in blood, adverse clinical outcome was only observed in the lung transplant recipients. Additionally, no CMV resistance mutations were observed in non-lung transplant patients receiving valganciclovir.

Human Metapneumovirus Infection in Adults with Community-Acquired Pneumonia and Exacerbation of Chronic Obstructive Pulmonary Disease

We tested nasopharyngeal aspirate specimens by real-time polymerase chain reaction assays and paired serum samples by enzyme-linked immunosorbent assays. Acute human metapneumovirus infections were identified in 6 (4.1%) of 145 adult patients who presented to the emergency department for pneumonia or acute exacerbation of chronic obstructive pulmonary disease during 2 winter/spring seasons in Quebec, Canada.

The role of honeydew in host searching of aphid hyperparasitoids

Foraging in many insect parasitoids is mediated by chemicals associated with hosts. For example, honeydew, the feces of feeding aphids, induces and/or prolongs searching behavior of aphid parasitoids. In the laboratory, we tested if aphid hyperparasitoids, which belong to a higher trophic level, also rely on aphid honeydew to locate their hosts. We used the potato aphid. Macrosiphum euphorbiae, the primary parasitoid, Aphidius nigripes, and four hyperparasitoids, Asaphes suspensus, Dendrocerus carpenteri. Alloxysta victrix, and Syrphophagus aphidivorus that possess different biological attributes and host ranges. We determined if foraging hyperparasitoid females could discriminate between (i) honeydew from a host and a non-aphid host (the potato aphid and the soft brown scale, Coccus hesperidum), and (ii) honeydew from healthy aphids and those parasitized by A. nigripes. Females of A. suspensus did not react to any of the honeydew treatments. While the presence of non-aphid honeydew did not modify the behavior of A. victrix, D. carpenteri, and S. aphidivorus females, they exhibited an increase in searching time and path length but not walking speed when in the presence of honeydew from aphids. However, there were no changes in host searching behaviors, such as antennation or ovipositor probing that have been reported for primary aphid parasitoids. There was no difference in the response of hyperparasitoid females to honeydew from healthy and parasitized aphids. These results indicate that hyperparasitoids may use aphid honeydew, a conspicuous cue from the second trophic level, as an infochemical to locate their hosts.

The degree of mineralization is a determinant of bone strength: a study on human calcanei

Strength of bones depends on bone matrix volume (BMV), bone microarchitecture, and also on the degree of mineralization of bone (DMB). We have recently shown in osteoporotic patients treated with alendronate that fracture risk decreased and bone mineral density increased with a parallel increase of the DMB due to prolonged secondary mineralization but without modifications of BMV or bone microarchitecture. DMB and strength were both measured at the tissue level in calcaneus bone samples taken at autopsy from 20 subjects (aged 78 +/- 8 years, 8 women, 12 men) who died suddenly without apparent bone disease. DMB parameters measured on microradiographs (mean DMB, distribution of DMB, most frequent maximum DMB value, and width at half maximum, an index reflecting the homogeneity of DMB) were compared with those reported in iliac cancellous bone samples of 43 human bones. Histomorphometric measurements of microarchitectural parameters (TbTh, TbN, and TbSp) were also measured. Compression tests were performed on contiguous samples of the same calcaneus on a universal screw-driven machine (Schenck RSA 250). A 5000-N load cell (TME, F 501 TC) measured the compressive load. The displacement was measured directly on the sample using a specific displacement transducer developed by the <<Laboratoire de Mécanique des Contacts et des Solides (LaMCoS).>> The apparent Young's modulus (E), the maximal strength (sigma(max)), and the work (W) until failure were measured. In human cancellous bone tissue, mean DMB (+/- SD) was higher in calcaneus (1.135 +/- 0.147 g/cm(3)) than in iliac crest (1.098 +/- 0.077 g/cm(3)). The mean most frequent maximum DMB values (mean DMB freq. max.) were 1.118 +/- 0.175 g/cm(3) in calcaneus and 1.108 +/- 0.095 g/cm(3) in iliac samples, and DMB was more heterogeneous in calcaneus than in iliac samples (mean width at half maximum were 0.270 +/- 0.127 versus 0.227 +/- 0.056 g/cm(3), respectively). Compression tests revealed significant positive linear correlations between DMB and both elastic modulus (r(2) = 0.69) and maximal strength (r(2) = 0.69). Correlations with DMB persisted (P < 0.003) even after adjustment for both calcified bone volume, for the Young's modulus (E), the maximal strength (sigma(max)) (r(2) = 0.44 and 0.41, respectively), and microarchitectural parameters (0.50 < r(2) < 0.56, P < 0.001). The same results were obtained with the work to fracture (W) (0.23 < r(2) < 0.46, P < 0.045). We conclude that the more the cancellous tissue was mineralized, the higher was its stiffness and compressive strength. This may explain the increase in bone strength when DMB is modified in a physiological range without necessary changes of BMV and bone microarchitecture. The impact of such modifications on fracture risk and the therapeutic implications of these data remain to be analyzed.

Effect of micro- and macroporosity of bone substitutes on their mechanical properties and cellular response

The control of porosity morphology and physico-chemical characteristics of calcium phosphate bone substitutes is a key-point to guaranty healing success. In this work, micro- and macroporosity of materials processed with 70% Hydroxyapatite (HAP) and 30% beta-tricalcium phosphate (beta-TCP) were controlled by sintering temperature and porogen addition, respectively. Porosity was quantified by scanning electron microscopy (pore size) and mercury intrusion porosimetry (interconnection between pores). The content of macrointerconnections and their size were dependent on porogen content, shape, and size. Mechanical properties (compressive strength) were strongly dependent on macroporosity size and content, on the basis of exponential laws, whereas microporosity ratio was less influent. Relying on those results, three types of materials with contrasting porous morphologies were processed and assessed in vitro, in primary culture of human osteoblasts and fibroblasts. With both types of cells, an exponential cellular growth was effective. Cells colonized the surface of the materials, bridging macroporosity, before colonizing the depth of the materials. Cell migration across and into macroporosity occurred via the emission by the cells of long cytoplasmic extensions that hanged on microporosity. Both macroporosity and macrointerconnectivity size influenced the penetration of cells. An interconnection size of 15 microm appeared to be effective to support this invasion without bringing down mechanical strength.

Mechanisms of action of antiresorptive therapies of postmenopausal osteoporosis

In the treatment of osteoporosis, the aim of the antiresorptive therapy is to restore bone density by decreasing bone remodeling. The process of bone remodeling plays a role in plasma calcium homeostasis and serves to modify bone architecture in order to meet changing mechanical needs, to maintain osteocyte viability, and to repair microdamage in bone matrix. Estrogen deficiency results in a number of detrimental effects on bone, including suppression of osteocyte survival as well as impairment of osteoblast response to mechanical stimuli and repair of ageing bone. In this review, effects of available antiresorptive therapies on endocrine regulations of bone metabolism in postmenopausal osteoporosis are compared. The aim of antiresorptive treatment is to ensure adequate bone remodeling, reparation of microdamage of bone, and increased bone strength. Ideally, this effect should be maintained long-term. Several agents are approved for the treatment of osteoporosis. Calcitonin transiently inhibits osteoclast activity without decreasing osteoblast collagen synthesis. Aminobisphosphonates decrease bone remodeling by decreasing osteoclast activity and by inducing osteoclast apoptosis. This allows more time for secondary mineralization to proceed to completion in the existing bone tissue mass, so increasing the mechanical resistance of bone to loading. Estrogens and raloxifene (a selective estrogen receptor modulator that acts as an estrogen agonist in bone) suppress bone remodeling to the premenopausal range, maintaining the function of osteoblasts and osteocytes. In the placebo-controlled osteoporosis treatment trials, all the above treatments reduced the risk of fractures. Raloxifene therapy was also associated with a favorable or neutral effect in the cardiovascular system, and a reduced incidence of breast cancer. Selection of appropriate drug for treatment of postmenopausal osteoporosis should take into account the long-term effect of the antiresorptive agent on bone. Moreover, the effects on other tissues ++should also be considered, and this encompasses both safety concerns, as well as the potentially beneficial effects on other tissues. Further investigation is needed to evaluate the different modes of action of these agents, and their long-term effects on bone and other tissues.

Contribution of raloxifene and calcium and vitamin D3 supplementation to the increase of the degree of mineralization of bone in postmenopausal women

Raloxifene has been shown to increase bone mineral density and reduce the risk of vertebral fracture in postmenopausal women with osteoporosis. In this study, we report the results of the first prospective longitudinal study to evaluate the mean degree of mineralization of bone (MDMB) in a group of patients enrolled in the Multiple Outcomes of Raloxifene Evaluation trial. Patients were randomly assigned to one of three treatment groups: placebo (n = 24), raloxifene 60 mg/d (RLX60; n = 22), or raloxifene 120 mg/d (RLX120; n = 18). All patients received daily calcium (500 mg) and vitamin D(3) (400-600 IU) supplementation for the duration of the study. Iliac crest biopsies were taken at baseline and after 2 yr of treatment. Quantitative microradiography was used to analyze the biopsy specimens and revealed a statistically significant (P < 0.05) mean percentage increase in total MDMB of 7.0, 5.3, and 5% for RLX60-, RLX120-, and placebo-treated patients, respectively, compared with baseline. Raloxifene treatment was found to shift the distribution of total bone mineral to higher values of MDMB (RLX60, 29%; RLX120, 8%) with greater heterogeneity, compared with placebo. The profile of MDMB observed in biopsies after treatment with placebo and raloxifene, compared with baseline, closely resembles physiological premenopausal bone.

In vitro evaluation of apical microleakage following canal filling with a coated carrier system compared with lateral and thermomechanical Gutta-Percha condensation techniques

AIM

The apical sealing ability of a coated carrier system was evaluated in extracted human teeth and compared with lateral and thermomechanical condensation techniques using dye penetration.

METHODOLOGY

Sixty-four extracted single-rooted teeth were instrumented to an apical size 30 using 4% taper Hero 642 trade mark instruments (Micromega, Besançon, France). The sample was divided into three experimental groups. Twenty teeth were randomly obturated with lateral condensation, 20 with thermomechanical compaction and 20 teeth with the Herofill trade mark Soft-Core system. Four teeth were used as positive and negative controls. The teeth were covered with nail varnish up to 2 mm from the apical foramen and immersed in a 2% aqueous methylene blue dye solution for 1 week and then washed, dehydrated and embedded in resin. The apical 1 mm of each tooth was removed to reveal the apical limit of the preparation. Transverse sections of the teeth were taken at 500, 1000 and 1500 micro m from this point and evaluated for apical leakage. Significant differences between the preparations were analysed with a semiautomatic analyser and the ratio of the dye-penetrated surface to the total dentinal surface was calculated.

RESULTS

Statistical analysis of the results demonstrated significantly less leakage for the Herofill trade mark Soft-Core system compared to lateral condensation in terms of total mean dentinal surface and at the 500 micro m level. No other differences were noted between Herofill trade mark Soft-Core and thermomechanical or lateral condensation, either for the total mean value or at each level.

CONCLUSIONS

The Herofill trade mark Soft-Core system was a reliable obturation system in the apical portion and compared favourably with other gutta-percha filling techniques.

Changes in bone remodeling rate influence the degree of mineralization of bone

Mineralization of bone matrix implies two successive steps, a primary mineralization on the calcification front followed by a slow process of secondary mineralization progressively adding about 50-60% of the mineral content on bone matrix. Our model is that antiresorptive agents prolong the lifetime of the basic structural units (BSUs) by causing a marked reduction in the birth rate of basic multicellular units (BMUs), and increase the degree of mineralization of bone (DMB) by allowing a more complete secondary mineralization. Conversely, agents or events provoking an augmentation of the birthrate of BMUs and a decrease of the lifetime of BSUs lead to resorption of new BSUs before they have fully completed their secondary mineralization, leading to the presence of incompletely mineralized BSUs and a low mean DMB value, as measured by quantitative microradiography. Measurements of DMB (distribution and mean value) under circumstances with various remodeling activities favor our model. In postmenopausal osteoporotic women treated during 2 or 3 years with alendronate (10 mg/day), an increase of the mean DMB of approximately 7 to 10% was found, due to a marked reduction in the bone remodeling. In contrast, an activation of bone remodeling as in primary hyperparathyroidism lowered the mean DMB.

[Cellular culture of osteoblasts and fibroblasts on porous calcium-phosphate bone substitutes]

PURPOSE OF THE STUDY

Calcium phosphate ceramics are synthetic bone substitutes able to fill in bone destruction as a support of the bone growth. This work consisted in an in vitro assessment of osteoblasts and fibroblasts cultures on macroporous calcium-phosphate bone substitutes to analyze the interaction between cells and bone substitute.

MATERIALS AND METHODS

The macroporous ceramic was composed of 70% hydroxyapatite and 30% tri-calcium phosphate with known mechanical and physico-chemical properties. Three compounds were processed with different size of macropore and with or without microporosity on their surface. Cells were seeded on discs measuring 10 mm in diameter and 2 mm in thickness. Cellular viability was evaluated by the MTT test for every stage of observation. An histological study to observe the invasion in the depth of discs was performed. Scanning electron microscopy was used to analyze the cellular comportment in contact with the surface of substitutes.

RESULTS

An exponential cellular growth was effective on each substitute with the two cellular types. Cells spread on the surface of the compounds covering macropores and colonized the depth of the discs. A size of macropore of 300 microm or more seemed to support this invasion. 15 microm sized interconnections appeared to be effective to allow cell migration between macropores. The cell proliferation was similar on substitutes with or without microporosity.

CONCLUSION

Biomaterials currently used as bone substitute are more or less osteoconductive but they have no osteoinductive property. A hybrid association of calcium-phosphate ceramic with osteogenic cells should promote the development of a calcium phosphate compound with osteoinductive capacity.

The mineralization of bone tissue: a forgotten dimension in osteoporosis research

Osteoporosis treatment should not only prevent the loss of bone tissue, not interfere with apatite and avoid bone mineral changes at the crystal level, but should also increase the mechanical resistance of bone and thus protect the skeleton against new fractures. Mineral substance is crystallized as nonstoichiometric carbonated apatite ionic crystals of small size and extended specific surface. Consequently, they have a very large interface with extracellular fluids, and numerous interactions between ions from the extracellular fluid and ions constituting apatite crystals are thus possible. It is generally agreed that bone strength depends on the bone matrix volume and the microarchitectural distribution of this volume, while the degree of mineralization of bone tissue is almost never mentioned as a determinant of bone strength. We now have evidence that the degree of mineralization of bone tissue strongly influences not only the mechanical resistance of bones but also the bone mineral density. In adult bone, our model is based on the impact of changes in the bone remodeling rate on the degree of mineralization of bone tissue. The purpose of this paper is to report the main results concerning the interactions of strontium (Sr) with bone mineral in animals and in osteoporotic women treated with strontium ranelate (SR). These studies aimed to evaluate using X-ray microanalysis, X-ray diffraction and computerized quantitative contact microradiography: (1) the relative calcium and Sr bone content, (2) the distribution of Sr in compact and cancellous bone, (3) the dose dependence of the deposition of Sr in bone, (4) the interactions between Sr and mineral at the crystal level (in monkeys), (5) the influence of Sr on the mean degree of mineralization of bone tissue and on the distribution of the degree of mineralization of bone tissue, and (6) the bone clearance of Sr over short periods of time (6 and 10 weeks) after cessation of SR administration (monkeys treated for 13 and 52 weeks, respectively). In monkeys killed at the end of exposure (13 or 52 weeks), Sr was taken up in a dose-dependent manner into compact and cancellous bone, with a higher content in new bone than in old bone. The Sr content greatly decreased (about 2-fold) in animals killed 6 or 10 weeks after the end of treatment but this affected new bone almost exclusively. After SR treatment, there were no significant changes in crystal characteristics. Easily exchangeable in bone mineral, Sr was slightly linked to crystals by ionic substitution (generally 1 calcium ion substituted by 1 Sr ion in each unit cell). The degree of bone mineralization was not significantly different in the various groups of monkeys. Thus, at the end of long-term SR treatment and after a period of withdrawal, Sr was taken up in a dose-dependent manner into new bone without alteration of the degree of bone mineralization and with no major modification of bone mineral at the crystal level. In postmenopausal osteoporotic women treated with SR (0.5, 1 and 2 g/day) for 2 years, Sr was dose-dependently deposited into new bone without changes in the degree of mineralization of bone tissue. These findings could reflect dose-dependent stimulation of bone formation and are of potential value for the use of SR in the treatment of osteoporosis. In conclusion, the different studies performed on bone samples from monkeys and humans treated with various doses of SR showed that Sr was heterogeneously distributed between new and old bone but in a dose-dependent manner without alteration of the crystal characteristics and the degree of mineralization of bone tissue, even after long-term administration of often high doses of SR (the highest therapeutic dose used in humans is 4-fold lower than the lowest experimental dose administered to monkeys). This emphasizes the value, as antiosteoporotic treatment, of SR, which is safe at the bone mineral level.

Effects of bisphosphonates on matrix mineralization

Bone strength is determined not only by the volume of bone tissue and the microarchitectural organization of this bone, but also by the degree of mineralization of bone matrix. The mineralization process consists of a primary deposition of mineral substance on the calcification front, followed by a slow and progressive increase of the mineral deposition named secondary mineralization. In osteoporosis, there is a negative imbalance between bone resorption and bone formation, resulting in bone loss, and microarchitectural deterioration of the trabecular network. Therapeutic agents for osteoporosis could increase bone strength by three separate, but interrelated effects on bone tissue: 1) the prevention of bone loss and thus the preservation of bone microarchitecture, 2) an increase in the volume of bone matrix, and 3) an increase in the degree of mineralization to a level similar to that seen in healthy premenopausal women, through a prolongation of the duration of secondary mineralization. Therefore the use of antiresorptive agents that reduce bone turnover, as bisphosphonates, provide a rational approach to treatment of osteoporosis. Extensive phase III clinical trials have shown that osteoporotic women treated orally with alendronate (ALN) for 3 years or more had substantial increases in bone mineral density (BMD) of approximately 10% at the spine together with reductions of about 50% in the incidence of vertebral fractures. Since a marked reduction in activation frequency was evidenced in the transiliac biopsies taken after treatment with ALN compared to placebo (PLA), without detectable increase in cancellous bone volume, it was hypothesized that the increase in BMD and the reduction in the incidence of fragility fractures were due, in a substantial part, to an increase in the degree of mineralization of bone (DMB). The mean DMB was measured by quantitative microradiography on transiliac bone biopsies taken from 53 postmenopausal osteoporotic women who had been treated with ALN (10 mg/day) during 2 (9 patients) or 3 years (16 patients) or with PLA (15 and 13 patients, respectively). In the same patients, BMD values were obtained by dual-energy X-ray absorptiometry on lumbar spine at the beginning and end of treatment. Histomorphometric parameters and activation frequency of new remodeling units were also measured on the biopsies. After 2 years of ALN, mean DMB in compact bone was 9.3% (p=0.0035) and in cancellous bone was 7.3% (p=0.0009) higher, respectively, versus PLA. After 3 years of ALN, mean DMB in compact bone was 11.6% (p=0.0002) and in cancellous bone was 11.4% (p=0.0001) higher, respectively, versus PLA. After 2 and 3 years of ALN and compared to the corresponding PLA, the distribution of the DMB clearly showed a shift towards the highest mineralization values and a decrease of the number of bone structure units having low values of mineralization. The between group differences in mean DMB were similar to those of BMD at the lumbar spine level (+8.7% after 2 years +9.6% after 3 years, respectively), suggesting that mean DMB augmentation probably accounts for the major part of the increase in BMD seen with ALN. These results support our model that the reduction in the activation frequency caused by the antiresorptive effect of ALN is followed by a prolonged secondary mineralization which increases the percentage of bone structure units having reached a maximum degree of secondary mineralization and, through this mechanism, mean DMB. That these effects contribute to improved bone strength is demonstrated by the reduction in fracture incidence previously demonstrated in these patients. In conclusion, quantitative microradiography gives access to the mineral dimension of bone tissue which has been insufficiently taken into account until now as an important determinant of bone strength and quality of bone.

Synchrotron radiation microtomography allows the analysis of three-dimensional microarchitecture and degree of mineralization of human iliac crest biopsy specimens: effects of etidronate treatment

Quantitative microcomputed tomography using synchrotron radiation (SR microCT) was used to assess the effects of a sequential etidronate therapy on both three-dimensional (3D) microarchitecture and degree of mineralization of bone (DMB) in postmenopausal osteoporosis. Thirty-two iliac crest biopsy specimens were taken from 14 patients with osteoporosis (aged 64 +/- 1.8 years) before (baseline) and after 1 year of etidronate treatment, and after 2 years of treatment for four of the patients. The samples were imaged at high spatial resolution (voxel size = 10 microm) using the microtomography system developed at the European Synchrotron Radiation Facility (ESRF), Grenoble, France. Three-dimensional microarchitecture parameters were calculated and compared with those obtained from conventional histomorphometry. In addition, the DMB was evaluated also in 3D. No significant statistical changes regarding bone mass and structural parameters were observed in histomorphometry or 3D analyses. The distribution of the DMB in cortical and trabecular bone showed a trend to a shift toward highest mineralization values after 1 year of etidronate treatment (3.88% and 1.24% in cortical and trabecular bone, respectively). This trend was more evident after 2 years. The study also showed that SR microCT is an accurate technique and the only one for quantifying both the mineralization and the microarchitecture of bone samples at the same time in 3D.

The degree of mineralization of bone tissue measured by computerized quantitative contact microradiography

Strength of bones depends on bone matrix volume (BMV), bone microarchitecture, but also bone mineralization, and we have recently shown in osteoporotic patients treated with alendronate that fracture risk and bone mineral density (BMD) were changed without modifications of BMV or bone microarchitecture. Mineralization of bone matrix implies two successive steps: a rapid primary mineralization on the calcification front followed by a slow process of secondary mineralization progressively adding about one-half of the mineral content on bone matrix. These two steps are clearly illustrated by microradiographs of compact and cancellous bone tissue from transiliac human biopsies. Our working hypothesis is based on the impact of changes in bone remodeling rate on the degree of mineralization of bone, i.e., on the BMD measured at the tissue level. Contact quantitative microradiography using a computerized microdensitometric method, is described and allows the measurement of the mean degree of mineralization of bone (MDMB). This parameter may be quantitatively evaluated by exposing an aluminum calibration step-wedge and a plane-parallel calcified tissue section simultaneously to the same beam of X-rays, then determining, from the resulting microradiograph, the thickness of aluminum that produces the same X-ray absorption as a given region of the bone tissue section. To be used as a control group, iliac bone samples were taken at necropsy from 43 subjects (30 women aged 48.4 +/- 3.7 years and 13 men aged 66.0 +/- 4.4 years) who died suddenly showing no apparent bone disease. A control MDMB, which does not change with age, and a control distribution of these values are thus established. These control values are necessary for interpreting the changes in MDMB observed in bone conditions untreated or treated.

Relationships between trabecular bone remodeling and bone vascularization: a quantitative study

Beside its well-known role in bone development, vascularization plays a major role in bone cell migration for bone remodeling and metastatic tumor invasion. However, the various techniques used to identify vessels in bone have never been tested for trabecular bone vessel quantification, whereas bone remodeling quantitative parameters are commonly assessed. In this context, we developed and compared various histological techniques used to visualize blood vessels in rat bone in order to quantify them. First, several products were tested by intracardiac infusion to opacify the bone vascular network. The best results were obtained using either an India ink-1% agarose solution or an India ink-saturated barium sulfate solution followed by X-ray microradiography. Second, to identify the types of vessels, we also performed histoenzymology and immunohistochemistry stainings. Neither alkaline phosphatase (for endothelial cells) nor adenosine triphosphatase (ATPase) stainings (for smooth muscle cells) provided a low enough background to allow for vessel identification and quantification. For immunohistochemistry, various specific vessel constituents were analyzed: laminin, smooth muscle cell alpha-actin, factor VIII, and lectin Griffonia simplifolia. Anti-laminin and anti-smooth muscle cell alpha-actin antibodies gave the best results for quantification. Third, after optimization of these techniques, we performed quantitative bone and vessel histomorphometry on two groups of 12 rats each, for which bone remodeling and vessel number and area parameters were measured. No statistical differences were observed between the two groups, confirming the reproducibility of our measurements. A significant relationship was found between vessel number and histodynamic parameters; that is, bone formation rate correlated positively with India ink-positive vessel area (p < 0.009, r2 = 0.54) and alpha-actin-positive vessel number (p < 0.05, r2 = 0.66). Furthermore, we report reproducible techniques for visualization and quantification of vessels in bone that also allowed for simultaneous conventional bone histomorphometry. This methodology should help researchers to better understand the functional and anatomical relationship between trabecular bone and its vascularization during normal or pathological processes.

Rate of emergence of cytomegalovirus (CMV) mutations in leukocytes of patients with acquired immunodeficiency syndrome who are receiving valganciclovir as induction and maintenance therapy for CMV retinitis

The emergence of mutations conferring ganciclovir resistance was evaluated in an open-label randomized clinical trial that compared oral valganciclovir with intravenous ganciclovir as induction therapy, followed by maintenance with valganciclovir, for newly diagnosed cytomegalovirus (CMV) retinitis in 148 patients with acquired immunodeficiency syndrome. The presence of CMV mutations was directly assessed in patient leukocytes by polymerase chain reaction, followed by restriction fragment-length polymorphism (RFLP) for detection of the most common UL97 mutations associated with ganciclovir resistance and by sequencing of the viral UL97 gene. The cumulative percentages of patients with UL97-mutant viruses at 3, 6, 12, and 18 months (based on the number of patients on treatment at each time point) was 2.2%, 6.5%, 12.8%, and 15.3%, respectively. Of the 20 relevant UL97 mutations found by sequencing in 14 patients, 14 (70%) were detected by RFLP analysis. The rate of emergence of ganciclovir-resistant viruses with use of oral valganciclovir is no greater than that reported with use of intravenous ganciclovir.

Lack of emergence of cytomegalovirus UL97 mutations conferring ganciclovir (GCV) resistance following preemptive GCV therapy in allogeneic stem cell transplant recipients

Fifty allogeneic stem cell transplant recipients were enrolled in a prospective cytomegalovirus pp65 antigenemia-guided preemptive therapy trial. Among these, 10 of 34 patients who received ganciclovir exhibited sustained and/or recurrent antigenemia despite treatment. Thirteen leukocyte preparations from these 10 subjects were screened for the presence of the most frequent cytomegalovirus UL97 mutations conferring ganciclovir resistance. None of these mutations were detected after mean and median ganciclovir exposures of 31.6 and 28.0 days, respectively.

Case study: rapid emergence of a cytomegalovirus UL97 mutant in a heart-transplant recipient on pre-emptive ganciclovir therapy

A cytomegalovirus (CMV) strain containing a mutation in the UL97 gene (Leu595Ser), which is known to confer ganciclovir resistance, emerged rapidly in a heart-transplant recipient after 54 days of antigenaemia-guided ganciclovir therapy. The emergence of this viral mutant, while the patient was receiving oral ganciclovir 1000 mg three times daily, was associated with increasing CMV pp65 antigenaemia levels despite the re-instatement of intravenous ganciclovir 5 mg/kg twice daily. The antiviral regimen was then switched to intravenous foscarnet 90 mg/kg, administered either twice daily, once daily or every other day, which resulted in a rapid decrease of CMV antigenaemia levels and prevented the development of CMV-associated disease. Frequent monitoring of the CMV viral load and/or mutational studies are warranted in highly immunocompromised transplant recipients to prevent the development of CMV disease caused by ganciclovir-resistant strains.

Molecular evolution of influenza A/H3N2 viruses in the province of Québec (Canada) during the 1997-2000 period

In this study, we compared antigenic (hemagglutination inhibition (HI) assay) and molecular (sequencing of the hemagglutinin (HA1) gene) characterization of influenza isolates collected in the Province of Québec (Canada) during the last three flu seasons (1997-2000). Twenty-three isolates were tested by a standard HI assay and 37 by sequencing of the HA1 gene for their homology to the A/H3N2 vaccine strains A/Wuhan/359/95 (1997-1998) and A/Sydney/5/97 (1998-1999 and 1999-2000). By HI, two isolates were antigenically similar to A/Wuhan/359/95 (both from 1997 to 1998), 16 were similar to A/Sydney/5/97 (1997-2000) and no conclusions could be inferred for the other five isolates due to identical HI titers for the two vaccine strains (n=4) or insufficient viral titer (n=1). Sequence analysis revealed that four isolates from 1997 to 1998 were related to A/Wuhan/359/95 whereas the others (n=4) from 1997 to 1998, as well as all isolates from 1998 to 1999 (n=18) and 1999 to 2000 (n=11) were closer to A/Sydney/5/97. The mean number of amino acid differences for the 33 A/Sydney/5/97-like isolates compared with the homologous vaccine strain was 6.3 (1.9%), 9.2 (2.8%) and 13.6 (4.1%) for those collected in 1997-1998, 1998-1999, and 1999-2000, respectively. Phylogenetic analysis confirmed that a progressive drift occurred among our A/H3N2 influenza isolates over the last three flu seasons. Furthermore, it revealed that isolates collected during the last two flu seasons were in fact more related to A/Panama/2007/99 (2000-2001 vaccine strain) than to A/Sydney/5/97. Our studies suggest that molecular analysis of the HA1 gene should complement the HI assay for a more accurate analysis of influenza A virus drift.

Mechanisms of action and therapeutic potential of strontium in bone

The processes of bone resorption and formation are tightly governed by a variety of systemic and local regulatory agents. In addition, minerals and trace elements affect bone formation and resorption through direct or indirect effects on bone cells or bone mineral. Some trace elements closely chemically related to calcium, such as strontium (Sr), have pharmacological effects on bone when present at levels higher than those required for normal cell physiology. Indeed, strontium was found to exert several effects on bone cells. In addition to its antiresorptive activity, strontium was found to have anabolic activity in bone, and this may have significant beneficial effects on bone balance in normal and osteopenic animals. Accordingly, strontium has been thought to have potential interest in the treatment of osteoporosis. This review summarizes the mechanisms of action of strontium on bone cells, the evidence for its beneficial effects on bone mass in vivo, and its potential therapeutic effects in osteopenic disorders.