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PubMed2006

Young-elderly differences in bone density, geometry and strength indices depend on proximal femur sub-region: a cross sectional study in Caucasian-American women.

Fragility fractures at the trochanter (TR) and the femoral neck (FN) have distinct etiologies, but the underlying age-related structural changes at these proximal femoral sub-regions are poorly understood. 28 young (41+/-3 years) and 124 elderly (74+/-3 years) healthy Caucasian women underwent volumetric quantitative computed tomography at the hip. Integral (i), cortical (c) and trabecular (t) bone mineral density and content (BMD, BMC) were measured. Geometric parameters included cross sectional area (CSA), and volumes of the integral, cortical and trabecular regions (VOL). Structural measures included indices of compressive (Compstr) and bending (BSI) strength. After adjusting for height and weight, an F-test was used to compare the TR and the FN mean values between young and elderly and to test for interaction to compare logarithmic difference of young and elderly (log(Young)-log(Elderly), Y/Ed) between the FN and the TR in an ANOCOVA model. All BMC, iBMD and tBMD values were significantly lower in elderly than in young women, with the largest Y/Ed in the FN tBMC and tBMD (P<0.0011 and P<0.0001). cBMD in young and elderly groups was not significantly different at the TR while at the FN it was greater (P=0.0075) in elderly than young women, showing significant Y/Ed (P=0.0003) dependence on skeletal site. Elderly women had significantly larger iVOL and CSA values (0.0001<P<0.0051), except for the FN iVOL. cVOL values were smaller in elderly than young women (P<0.0001). Y/Ed in bone geometry differed by sub-region only for cVOL measures (P=0.0267). Despite larger CSA and iVOL measures in elderly, the younger women had greater Compstr (P<0.0001) and BSI (P=0.0051). Thus, although both the TR and the FN appear to increase in size with age, this enlargement is insufficient to protect against loss of bone strength.

Adult↗
PubMed2006

The anabolic effect of PTH on bone is attenuated by simultaneous glucocorticoid treatment.

Glucocorticoids (GC) are used for the treatment of a wide spectrum of diseases because of their potent anti-inflammatory and immunosuppressive effects, and they are serious and common causes of secondary osteoporosis. Administration of intermittent parathyroid hormone (PTH) may induce formation of new bone and may counteract the bone loss induced by GC treatment. Effects of simultaneous PTH and GC treatment were investigated on bone biomechanics, static and dynamic histomorphometry, and bone metabolism. Twenty-seven-month-old female rats were divided randomly into the following groups: baseline, vehicle, PTH, GC, and PTH + GC. PTH (1-34) 25 mug/kg and GC (methylprednisolone) 2.5 mg/kg were injected subcutaneously each day for a treatment period of 8 weeks. The rats were labeled with fluorochromes 3 times during the experiment. Bone sections were studied by fluorescence microscopy. The PTH injections resulted in a 5-fold increase in cancellous bone volume. At the proximal tibia, PTH induced a pronounced formation of new cancellous bone which originated from the endocortical bone surfaces and from thin trabeculae. Formation and modeling of connections between trabeculae were observed. Similar but less pronounced structural changes were seen in the PTH + GC group. The compressive strength of the cancellous bone was increased by 6-fold in the PTH group compared with the vehicle group. GC partially inhibited the increase in compressive strength induced by PTH. Concerning cortical bone, PTH induced a pronounced increase in the endocortical bone formation rate (BFR) and a smaller increase in periosteal BFR. The combination of PTH + GC resulted in a partial inhibition of the PTH-induced increase in bone formation. Serum-osteocalcin was increased by 65% in the PTH group and reduced by 39% in the GC group. The pronounced anabolic effect of PTH injections on the endocortical and trabecular bone surfaces and less pronounced anabolic effect on periosteal surfaces were partially inhibited, but not prevented, by simultaneous GC treatment in old rats. Both cortical and cancellous bone possessed full mechanical competence after treatment with PTH + GC.

Animals↗
PubMed2005

Nanoscale mechanical and dynamical properties of DNA single molecules.

Experimental evidence suggests DNA mechanical properties, in particular intrinsic curvature and flexibility, have a role in many relevant biological processes. Systematic investigations about the origin of DNA curvature and flexibility have been carried out; however, most of the applied experimental techniques need simplifying models to interpret the data, which can affect the results. Progress in the direct visualization of macromolecules allows the analysis of morphological properties and structural changes of DNAs directly from the digitised micrographs of single molecules. In addition, the statistical analysis of a large number of molecules gives information both on the local intrinsic curvature and the flexibility of DNA tracts at nanometric scale in relatively long sequences. However, it is necessary to extend the classical worm-like chain model (WLC) for describing conformations of intrinsically straight homogeneous polymers to DNA. This review describes the various methodologies proposed by different authors.

Cations, Divalent↗
PubMed2005

A new interpolation formula for semiflexible polymers.

A new formula for the force vs. extension relation is derived from the discrete version of the so-called Worm-like chain model. This formula correctly fits some recent experimental data on polymer stretching. Moreover, we have compared our formula with a Monte Carlo simulation of a semiflexible polymer.

Algorithms↗
PubMed2005

Local rigidity of a protein molecule.

Distribution of soft and rigid substructures within a protein molecule has been implicated in several occasions and most recently from the imaging and indentation experiments using an atomic force microscope. In this paper, previously reported result of mechanical extension experiments on the recombinant bovine carbonic anhydrase II, Q253C, is re-analyzed to estimate the distribution of Young's modulus, Y, in this protein. The force vs. extension curve of the enzymatically active, type I conformer gave an estimate of Y increasing from 40 to 220 MPa as the polypeptide chain was extended from 10 to 75 nm indicating the presence of a rigid core structure. The enzymatically inactive type II, in contrast, gave an almost constant modulus of 55+/-15 MPa in the same extension range in agreement with the previous proposal that it lacked a core structure.

Animals↗
PubMed2004

Positioning of cervical carcinoma and Burkitt lymphoma translocation breakpoints with respect to the human papillomavirus integration cluster in FRA8C at 8q24.13.

Molecular cytogenetic analysis frequently shows human papillomavirus (HPV) integration near translocation breakpoints in cervical cancer cells. We have recently described a cluster of HPV18 integrations in the distal end of the common fragile site FRA8C at 8q24 in primary cervical carcinoma samples. Chromosome band 8q24 contains the MYC gene (alias c-MYC), FRA8C, and FRA8D. The MYC gene is frequently deregulated--usually by translocation or amplification--in various tumor types. In the present study, we performed a molecular cytogenetic analysis of HPV18 integration patterns and the 8q24 translocation in a primary cervical carcinoma and in HeLa cells using combined binary ratio-fluorescence in situ hybridization. Our aim was to determine how the chromosomal breaks involved in these events relate physically to the MYC gene; whether they map to the FRA8C site, the FRA8D site, or both; and how they correlate with the occurrence of DNA flexibility domains. The 8q24 translocation breakpoints mapped between stretches of integrated HPV18 sequences in the distal end of FRA8C. This region contained DNA helix flexibility clusters, several of which mapped in the vicinity of HPV integration sites and translocation breakpoints in cervical carcinomas. DNA helix flexibility clusters were also found near known MYC translocation breakpoints in Burkitt lymphomas (BL), but most BL breakpoints mapped clearly outside FRA8C. Our data revealed that FRA8C is involved in HPV integration and chromosomal translocations in cervical carcinoma; however, this fragile site is not involved in classical MYC translocations in most BLs. In the context of the familial nature of cervical cancer, FRA8C may be considered a candidate susceptibility region for cervical carcinoma.

Burkitt Lymphoma↗
PubMed2004

Flexible chitin films: structural studies.

Chitin gels were transformed into thin, flexible chitin films with minimal dimensional shrinkage and maximum flexibility and thickness in the range of 25-80 microm by a cold-press process. Solvent residue was removed by heating the films at 50 degrees C for 12 h, followed by rinsing in 95% ethanol. The crystallinity and mechanical properties of the flexible chitin films were found to be a function of the amount of shrinkage from the gel to the final film that was obtained. For 28-microm thick films with 30% shrinkage, transparency of up to 90% was found. X-ray diffractometry (XRD) showed that the number of diffraction peaks appearing at 2theta;=23 degrees and 2theta;=27 degrees became increasingly sharper with shrinkage. Topographical information obtained from scanning electron microscopy (SEM) and atomic force microscopy (AFM) attributed the structural morphology of the films to the formation of sub-microscopic micelles. Scanning transmission electron microscopy (STEM) showed that shrinkage resulted in coarser microstructure, affecting tensile properties, where the ductility and toughness were proportional to the amount of shrinkage. These flexible chitin films have potential as wound dressing materials.

Bandages↗
PubMed2005

Structural insights into conformational flexibility at the peripheral site and within the active center gorge of AChE.

The peripheral anionic site on acetylcholinesterase (AChE), located at the active site gorge entry, encompasses overlapping binding sites for allosteric activators and inhibitors. Yet the molecular mechanisms coupling this site to the active center at the base of the gorge to modulate catalysis remain unclear. Crystal structures of mAChE bound with decidium, propidium and gallamine unveiled new determinants contributing to ligand interactions at the peripheral site. Subsequent studies using the syn and anti regioisomers of the click-chemistry inhibitor, TZ2PA6, that link propidium and tacrine moieties via distinctively substituted triazoles, revealed the inherent flexibility and a unique conformation of the peripheral site, along with substantial binding contributions from the triazoles with the Tyr337 region within the gorge. The recently solved structures of the mAChE mutant, Tyr337Ala, complexed with the TZ2PA6 isomers now reveals distinctive and time-dependent conformations of the complexes that are consistent with the triazole contribution to the energetics of inhibitor binding manifested in the respective dissociation rates of the complexes.

Acetylcholinesterase↗
PubMed2005

Acetylcholinesterase: pivotal roles of its long omega loop (Cys69-Cys96) in regulating substrate binding.

Acetycholinesterase (AChE) hydrolyses neuronal and non-neuronal acetylcholine (ACh) very efficiently, and this possibly prevents the mitogenic action of ACh. AChE activity was measured in twenty-three samples of non-small lung carcinomas (NSLCs) and in their adjacent normal tissue. Twelve out of them were adenocarcinoma (AC), 6 squamous cell carcinoma (SCC) and 5 large cell carcinoma (LCC). The mean AChE activity in healthy lung was 10.95 +/- 6.90 mU/mg; in AC, 8.13 +/- 5.84 (p = 0.774); in LCC, 9.57 +/- 7.47 mU/mg (p = 0.063); and in SCC, 2.25 +/- 0.67 (p = 0.028). AChE dimers and monomers were identified in healthy and tumoral tissues and their contribution was not affected by cancer. The fraction of AChE molecules reacting with the lectin Con A increased in squamous cell carcinoma when compared to control, adenocarcinoma and large cell carcinoma specimens. The increased level of ACh in lung cancers, resulting from the fall of AChE activity, may collaborate to lung cancer growth.

Acetylcholinesterase↗
PubMed2004

Exploring the range of protein flexibility, from a structural proteomics perspective.

Changes in protein conformation play a vital role in biochemical processes, from biopolymer synthesis to membrane transport. Initial systematizations of protein flexibility, in a database framework, concentrated on the movement of domains and linkers. Movements were described in terms of simple sliding and hinging mechanisms of individual secondary structural elements. Recently, the accelerated pace and sophistication of methods for structural characterization of proteins has allowed high-resolution studies of increasingly complex assemblies and conformational changes. New data emphasize a breadth of possible structural mechanisms, particularly the ability to drastically alter protein architecture and the native flexibility of many structures.

Pliability↗
PubMed2004

Structural and kinetic characterization of myoglobins from eurythermal and stenothermal fish species.

Teleost myoglobin (Mb) proteins from four fish species inhabiting different temperature environments were used to investigate the relationship between protein function and thermal stability. Mb was isolated from yellowfin tuna (homeothermal warm), mackerel (eurythermal warm), and the Antarctic teleost Notothenia coriiceps (stenothermal cold). Zebrafish (stenothermal tropical) myoglobin was expressed from cloned cDNA. These proteins differed in oxygen affinity, as measured by O2 dissociation rates and P50 values, and thermal stability as measured by autooxidation rates. Mackerel Mb had the highest P50 value at 25 degrees C (3.7 mmHg), corresponding to the lowest O2 affinity, followed by zebrafish (1.0 mmHg), yellowfin tuna (1.0 mmHg), and N. coriiceps (0.6 mmHg). Oxygen dissociation rates and Arrhenius plots were similar between all teleost species in this study, with the exception of mackerel myoglobin, which was two-fold faster at all temperatures tested. Myoglobin from the Antarctic teleost had the highest autooxidation rate (0.44 h(-1)), followed by mackerel (0.26 h(-1)), zebrafish (0.22 h(-1)), and yellowfin tuna (0.088 h(-1)). Primary structural analysis revealed residue differences distributed throughout the polypeptide sequences, making it difficult to identify, which, if any, residues contribute to structural flexibility. However, analysis of molecular dynamics trajectories indicates that Mb from the eurythermal mackerel is predicted to be the most flexible protein within the D loop and FG turn. At the same time, it has the lowest O2 affinity and the highest O2 dissociation rates when compared to myoglobins from teleosts that appear to be less flexible in our dynamics simulations.

Adaptation, Physiological↗
PubMed2004

Acceptance of flexible sigmoidoscopy screening for colorectal cancer.

This study was conducted in the Kaiser Permanente Medical Care Program of Northern California to identify patient characteristics that explain interest in flexible sigmoidoscopy (FS) screening. A mailed screening invitation to 6837 age-eligible patients elicited responses from 49%. Efforts to reach and interview both eligible respondents and non-respondents resulted in 2728 computer-assisted telephone interviews (CATI), with 60% indicating interest in FS screening. Five components of the Integrated Behavioral Model were measured with respect to FS screening: attitude, affect, social influence, facilitators/barriers, and perceived risk of colorectal cancer. All five model components were significantly and independently associated with interest in FS, with patient attitude being the strongest predictor. Of the 32 items comprising the model components, nine items having the highest correlations with FS interest were identified as potentially important issues to address by efforts to increase interest in screening. Six of these were attitudinal beliefs. The findings from this theory-driven study provide specific targets for the design of interventions to increase FS interest and screening rates.

Adult↗
PubMed2003

Inhibitor specificity via protein dynamics: insights from the design of antibacterial agents targeted against thymidylate synthase.

Structure-based drug design of species-specific inhibitors generally exploits structural differences in proteins from different organisms. Here, we demonstrate how achieving specificity can be aided by targeting differences in the dynamics of proteins. Thymidylate synthase (TS) is a good target for anticancer agents and a potential target for antibacterial agents. Most inhibitors are folate-analogs that bind at the folate binding site and are not species specific. In contrast, alpha156 is not a folate-analog and is specific for bacterial TS; it has been shown crystallographically to bind in a nonconserved binding site. Docking calculations and crystal structure-based estimation of the essential dynamics of TSs from five different species show that differences in the dynamics of TSs make the active site more accessible to alpha156 in the prokaryotic than in the eukaryotic TSs and thereby enhance the specificity of alpha156.

Anti-Bacterial Agents↗
PubMed2006

Microtubule mechanics: a little flexibility goes a long way.

Microtubules are the least flexible of the cytoskeletal filaments, yet they are occasionally seen to be severely buckled in cells. A recent analysis suggests these buckles are evidence of high contractile forces throughout the cytoplasm, and that the other elements of the cytoskeleton laterally reinforce microtubules to help prevent their collapse.

Biomechanical Phenomena↗
PubMed2004

Strength, fracture toughness and microstructure of a selection of all-ceramic materials. Part II. Zirconia-based dental ceramics.

OBJECTIVE: The present study is the second part of an investigation of strength, fracture toughness and microstructure of nine all-ceramic materials. In the present study, DC Zirkon, an experimental yttria partially stabilized zirconia, In-Ceram Zirconia slip and In-Ceram Zirconia dry-pressed were compared. METHODS: Strength was appraised on ten bar-shaped specimens for each material (20 x 4 x 1.2 mm) with the three-point bending method. The fracture toughness (Indentation Strength) was measured on twenty specimens (20 x 4 x 2 mm) for each ceramic. The volume fraction of each phase, the dimensions and shapes of the grains and the crack pattern were investigated with SEM. Phase transformation was investigated with X-ray diffraction. Data were compared with an ANOVA and Sheffé post hoc test (p = 0.05). RESULTS: Means of strength (MPa) and fracture toughness (MPa m(1/2)) values and their standard deviation were: In-Ceram Zirconia dry-pressed 476 (50)1, 4.9 (0.36)1; In-Ceram Zirconia slip 630 (58)2, 4.8 (0.50)1; the experimental yttria partially stabilized zirconia 680 (130)2, 5.5 (0.34)2; DC-Zirkon 840 (140)3, 7.4 (0.62)3. Values with the same superscript number showed no significant statistical difference. Microscope investigation and X-ray diffraction revealed the important role played by the tetragonal to monoclinic phase transformation and by the relationship between the glassy matrix and the crystalline phase in the strengthening and toughening mechanisms of these ceramics. SIGNIFICANCE: the zirconia-based dental ceramics are stronger and tougher materials than the conventional glass-ceramics. Better properties can have positive influence on the clinical performance of all-ceramic restorations.

Analysis of Variance↗
PubMed2004

Strength, fracture toughness and microstructure of a selection of all-ceramic materials. Part I. Pressable and alumina glass-infiltrated ceramics.

OBJECTIVE: The present study, divided into two parts, aimed to compare the strength, fracture toughness and microstructure of a range of all-ceramic materials. In part I, three hot-pressed glass-ceramics (IPS-Empress, Empress 2 and a new experimental ceramic) and alumina glass-infiltrated ceramics (In-Ceram Alumina), processed by both slip casting and dry pressing, were compared. METHODS: Tensile strength was appraised on 10 bar-shaped specimens (20 x 4 x 1.2 mm3) for each material with the three-point bending method; the fracture toughness was measured from 20 specimens (20 x 4 x 2 mm3), by using the indentation strength technique. Data were compared with ANOVA and the Sheffé post hoc test (p = 0.05). The volume fraction of each phase, the dimensions and shapes of the grains, porosity and the crack patterns were investigated using SEM. RESULTS: The average and standard deviation in strength (MPa) and fracture toughness (MPa m(1/2)) were: IPS-Empress 106(17)1, 1.2(0.14)1; Empress 2 306(29)2, 2.9(0.51)2, new experimental ceramic 303(49)2, 3.0(0.65)2, In-Ceram Alumina dry-pressed 440(50)2, 3.6(0.26)2, In-Ceram Alumina slip 594(52)3, 4.4(0.48)3. Values with the same superscript number showed no significant statistical difference. Microscopy revealed the relationship between the glass matrix and the crystalline phase and the characteristics of the latter were correlated to the strengthening and toughening mechanisms of these glass-ceramics. SIGNIFICANCE: The mechanical properties and microstructure of core materials have been advocated as crucial to the clinical long-term performance of all-ceramic dental restorations. This investigation provides the clinician with data regarding strength, fracture toughness and microstructure of a broad range of current materials.

Aluminum Silicates↗
PubMed2004

Tooth deformation patterns in molars after composite restoration.

OBJECTIVE: Residual stresses from polymerization shrinkage in composite restorations deform a tooth. This may cause debonding, enamel crack propagation, and post-operative sensitivity. Deformation due to shrinkage has been measured previously at a few discrete points. The purpose of this study was to analyze cuspal deformation pattern of the occlusal portion of molars for various cavity types and sizes after restoration with a light-initiated composite. METHODS: Five extracted human molars were successively prepared as Class I, Class II OM, large Class II OM, and large Class II MOD. The cavities were filled with a light-curing composite using a dentin adhesive system. The occlusal portion of the unrestored cavity and the restoration were digitized with a profilometer. The digitized data of the unrestored and restored tooth were used to calculate the cuspal contour change with Cumulus software. Deformation was visualized as a color contour map. RESULTS: Cuspal deformation showed up in the contour map as a reduction of buccal and lingual contour perpendicular to the surface. Large Class II MODs exhibited the highest cuspal deformation, followed by large OM restorations. Cuspal deformations in Class I and small Class II OM restorations were not significantly different. SIGNIFICANCE: When a composite restoration was cured, the surrounding tooth deformed due to polymerization shrinkage. Cavity type and size affected how much cusps moved inward as a result of polymerization shrinkage. This study quantified and visualized the pattern of cuspal deformation.

Analysis of Variance↗