Biomedical subjects

Timothy M Wright

Publications and source records attributed to Timothy M Wright.

At least 19 recordsLinked to original sources

PubMed2006

T cell lines from systemic sclerosis patients and healthy controls recognize multiple epitopes on DNA topoisomerase I.

Anti-DNA topoisomerase I (topo-I) antibodies are exclusively detected in patients with systemic sclerosis (SSc). Participation of this topo-I-specific autoimmune response in the pathogenesis of SSc has been actively investigated, but remains unproven. Here we characterized the peripheral T cell proliferative response to recombinant topo-I (rtopo-I) in 16 SSc patients with circulating anti-topo-I antibody. A low level (cpm < 2000) T cell proliferation (SI > 3) was detected in 6 (38%) of 16 patients. This low level response was similar to those previously observed in healthy controls. We established 56 topo-I-specific T cell lines recognizing 13 distinct T cell epitopes on topo-I from 4 SSc patients and 2 healthy controls. These T cell lines were established from in vitro activated PBMC (CD25(+)) by rtopo-I antigen. However they did not have the phenotype of regulatory T cells. Notably, 40 (71%) of the 56 T cell lines recognizing a common epitope were established from one patient. DNA sequencing of the T cell receptor cDNA produced an identical sequence indicating these T cells were from a single topo-I-specific T cell precursor. These results suggest that topo-I-specific T cells can become clonally expanded in some patients and may contribute to the pathogenesis of this disease.

Amino Acid Sequence↗

PubMed2006

Cancellous bone adaptation to in vivo loading in a rabbit model.

Biophysical stimuli are important to the development and maintenance of cancellous bone, but the regulatory mechanisms need to be understood. We investigated the effects of mechanical loading applied in vivo to native cancellous bone in the rabbit on bone formation and trabecular realignment. A novel device was developed to apply controlled compressive loads to cancellous bone in situ. The effect of loading on cancellous bone volume fraction and architecture was quantified. A 4-week experiment was performed in rabbits with devices implanted bilaterally. Cyclic 1 MPa pressures were applied daily to the right limb for 10, 25, or 50 cycles at 0.5 Hz, and the left limb served as the control without any applied loading. Microcomputed tomography and histomorphometry were used to characterize the cancellous tissue within a 4-mm spherical volume located below the loading core. In vivo cyclic loading significantly increased the bone volume fraction, direct trabecular thickness, mean intercept length, and mineral apposition rate in the loaded limbs compared with contralateral limbs. Insufficient evidence was found to demonstrate an effect of number of cycles on the cancellous adaptation between loaded and control limbs. Using a rabbit model, we demonstrated that mechanical loading applied to cancellous bone in situ increased bone formation and altered trabecular morphology. This in vivo model will allow further investigation of cancellous functional adaptation to controlled mechanical stimuli and the influence of mechanical loading parameters, metabolic status, and therapeutic agents.

Adaptation, Biological↗

PubMed2006

Stair ascent kinematics affect UHMWPE wear and damage in total knee replacements.

Investigations were performed to characterize the wear patterns of tibial inserts in a load-controlled knee simulator by incorporating both normal gait and clinically acquired stair climbing kinematics and load conditions. Two different tibial insert designs were evaluated: the NexGen Cruciate Retaining Augmentable and NexGen Legacy Posterior Stabilized inserts. Two test conditions were run: standard gait only, and gait with bouts of stair climbing at a ratio of 70:1. Gravimetric wear measurements, damage and contact area assessments, and kinematic evaluations were performed. The addition of stair climbing kinematics significantly affected the wear behavior. Regardless of design, wear rates for standard gait tests were significantly higher than those that included bouts of stair climbing. The damage modes seen in both test conditions were primarily burnishing with secondary scratching and pitting. At 2 Mc, the damage areas were not significantly different between the two designs, but the damage area with stair climbing was significantly larger than that with gait alone. The fact that even small bouts of an additional activity of daily living could markedly impact wear simulator results calls into question the usefulness of studies that rely solely on kinematics and load inputs assumed from level gait.

Aged↗

PubMed2006

Retrieval, experimental, and computational assessment of the performance of total knee replacements.

Wear mechanisms in polyethylene components for total knee replacements are inherently mechanical; the local stresses or strains exceed some material limit. Retrieval analysis and knee simulators have provided the means to quantify the damage observed in vivo or in vitro. These results have been circumstantially linked to the material stresses obtained from computational simulations using finite element analysis, knee simulator tests, and computational simulations of two condylar knee designs. We hypothesize that if an equivalent loading environment is produced in the computational simulation, we can correlate the distribution of computed stresses with observed damage of simulator specimens and further relate design differences to in vivo performance from retrieval analyses. The finite element model agreed with the knee simulator kinematics and kinetics within 2-13%, and composite FEA contact areas matched 66-90% of the damage areas due to burnishing on the simulator specimens. Burnishing was the primary mode of damage for both the simulator and retrieval specimens corresponding with the relatively low magnitudes of contact stress observed. Both the computational and experimental techniques underpredicted the amount determined from retrieval analysis, but the differences between the two designs were consistent for all three methods. Combining these techniques strengthens the applicability of the computational simulation while highlighting the complementary approach of these methods for preclinical testing and assessing the link between material state and damage.

Arthroplasty, Replacement, Knee↗

PubMed2006

In vivo cyclic axial compression affects bone healing in the mouse tibia.

Abundant evidence exists that fracture healing can be influenced by mechanical loading. However, the specific loading parameters that are osteogenic remain unknown. We hypothesized that the bone healing response in mouse tibial osteotomies would be different with a short delay before loading compared to immediate load application, as well as with higher and lower load magnitudes applied. Eighty 12-week-old mice underwent osteotomy of the left tibia followed by intramedullary nailing. Mice were divided into six groups based on days delayed until application of load (0 days or 4 days) and amplitude of cyclic load (0.5N, 1N, or 2N). Loading regimens were applied at 1 Hz for 100 cycles per day, 5 days per week for 2 weeks, using an external device that applied axial compression to the tibia. Bone healing was assessed by both microcomputed tomography (CT) and four-point bend testing. A short delay followed by cyclic application of a relatively low load led to improved fracture healing, as determined by increased callus strength, but this enhancement disappeared as load amplitudes increased. Load initiation immediately following fracture inhibited healing, regardless of the magnitude of load applied. MicroCT measurements of calluses in the early healing stage did not predict the mechanical strength of the fractures. These findings confirm that controlled, noninvasive cyclic loading can improve the strength of healing callus. However, application of load immediately after fracture appears to be detrimental to healing. Load magnitude also plays a critical role, and must be taken into account in future studies and clinical applications. As the loading parameters necessary to enhance fracture healing become refined, external compression may be used as a potent stimulus for treating fractures with decreased biological capacity.

Animals↗

PubMed2006

Anti-th/to-positivity in a cohort of patients with idiopathic pulmonary fibrosis.

OBJECTIVE: To evaluate the presence and clinical relevance of anti-Th/To-positivity in patients with idiopathic pulmonary fibrosis (IPF). METHODS: Antinuclear antibody (ANA) testing was performed in 285 patients with a clinical diagnosis of IPF and surgical lung biopsy-proven usual interstitial pneumonia. Twenty-five subjects (8.8%) were found to have a positive ANA with a nucleolar-staining pattern and were followed for 10 years. Immunoprecipitation analysis indicated that 13 of the 25 subjects had autoantibodies against Th/To antigen. RESULTS: All subjects presented with worsening dyspnea. Pulmonary physiology and gas exchange did not differ between those with and those without a positive ANA, those with and without a nucleolar-staining ANA, and those with and without anti-Th/To antibody positivity. Retrospective review of the clinical record revealed that none of the 25 subjects with a nucleolar-staining ANA had the characteristic cutaneous features of systemic sclerosis (SSc). Four of the 13 Th/To-positive subjects had 3 of 5 criteria of limited cutaneous SSc (CREST variant), and 9 met proposed criteria for SSc sine scleroderma. None of the 12 Th/To-negative subjects had 3 or more criteria of limited cutaneous SSc (CREST variant), and only one met proposed criteria for SSc sine scleroderma. Of the 25 subjects with nucleolar-staining ANA, cumulative survival was similar between those who were Th/To-positive and those who were Th/To-negative (log-rank test, p = 0.73). Cumulative survival was similar between the 13 Th/To-positive subjects and all other 272 IPF subjects (log-rank test, p = 0.34). CONCLUSION: Our findings indicate that a nucleolar-staining ANA is a common finding in patients with IPF, and that antibodies against Th/To are responsible for the majority of these. Given the high specificity of Th/To-positivity for SSc, our data suggest that these subjects may have SSc sine scleroderma, and that their prognosis is no different from those with IPF.

Adult↗

PubMed2005

Impingement in total hip arthroplasty a study of retrieved acetabular components.

Impingement can damage the acetabular liner, create polyethylene wear, and cause dislocation. We determined the prevalence of impingement, its relation with dislocation, and the influence of patient, surgical, and design factors in 162 components randomly selected from a larger group retrieved between 1990 and 1999. Impingement arc, severity, and wear damage were measured; patient data were obtained from medical records, and component position was determined from radiographs. More than half (56%) showed impingement, including 94% of those removed for dislocation. The occurrence of impingement was significantly increased if the revision diagnosis was dislocation, if the component had a large outer diameter or an elevated rim, and if the femoral component had an extended flanged neck. Implant design, in particular head/neck ratio, can help reduce the prevalence of impingement.

Acetabulum↗

PubMed2005

Mechanisms for pumping fluid through cementless acetabular components with holes.

The pumping of fluid and polyethylene wear debris from the joint space to the retroacetabular bone is implicated in the pathogenesis of osteolysis. Three possible mechanisms for this pumping: pressure gradients, diaphragm pumping, and piston pumping were studied in vitro in a laboratory model. The simulated activities of rising from a chair and climbing stairs produced high-pressure gradients and high angles of loading that could pump fluid through the apical hole to the retroacetabular bone. A noncongruent liner acted as a diaphragm pump, producing pressures 6 times higher than that seen with a congruent liner. Pistoning motion of the liner produced pressures 8 times higher than when no pistoning occurs. These pumping mechanisms could be mitigated by the use of acetabular components without holes.

Acetabulum↗

PubMed2005

Impingement of acetabular cups in a hip simulator: comparison of highly cross-linked and conventional polyethylene.

We hypothesized that the reduction in toughness that accompanies elevated levels of cross-linking in ultrahigh-molecular weight polyethylene would lead to increased wear and damage in acetabular cups under conditions of impingement with the neck of the femoral component. Test cups were exposed to 2.8, 10, and 20 Mrad of gamma irradiation and were tested in a simulator, incorporating impingement during every wear cycle. Wear behavior was compared based on wear rate, observations of damage, and the number and morphology of wear particles. The 10-Mrad cups had the lowest rate (15.2 +/- 5.1 mg/Mc), followed by the 2.8-Mrad (40.1 +/- 4.2 mg/Mc) and 20-Mrad (67.9 +/- 24.2 mg/Mc) groups. The wear damage was most severe in the 20-Mrad cups, although all 3 groups showed pitting and delaminating. Wear rates and damage of highly cross-linked polyethylene cups were significantly higher in an impingement wear test than in previous simulator studies.

Acetabulum↗

PubMed2005

Biomechanics of nonfusion implants.

Although spine fusion is a versatile and effective technique in the treatment of spinal disorders, increased stresses on adjacent unfused levels lead to symptomatic adjacent level degeneration in many patients. The goal of nonfusion devices in spine surgery is to ablate or unload painful structures while preserving segmental motion. The intended performance of nonfusion devices such as disc replacement, nucleus pulposus replacement, and posterior stabilization devices can be understood from the biomechanics of the functional spinal unit in health and disease and the interplay between the motion segment and the device. Implant design issues can also markedly affect performance.

Animals↗

PubMed2005

Cancellous bone strains indicate efficacy of stem augmentation in constrained condylar knees.

Modular augmented stems of a constrained condylar knee implant are intended to improve tibial fixation under increased varus/valgus loads, but conflicting studies have not yet indicated the factors determining stem usage and performance. To address this, we combined a paired-tibiae, cadaveric experiment of unstemmed and stemmed tibial components with specimen-specific computational models. We hypothesized that the stem would improve implant stability by decreasing implant motion and compressive strains in the proximal cancellous bone due to load transfer by the stem. The models also would indicate the important factors governing stem performance. Large variations of the displacements arose because of loading and biologic variability indicating the inconclusive effects of a stem. Despite these variations, the models showed that a stem augment consistently decreased the strains (30%-50%) in the bone beneath the tray. In tibiae of sufficient stiffness, the supporting cancellous bone did not approach yield, suggesting that a stem augment may not always be necessary. On the other hand, tibial specimens with reduced bone quality and lower stiffness benefited from a stem augment that transferred load to the distal cortical bone. Therefore, patient selection and proper sizing of the implant were identified as important factors in the analyses.

Aged↗

PubMed2005

Polyethylene in knee arthroplasty: what is the future?

Ultra-high molecular weight polyethylene remains the gold standard as a bearing surface for total knee arthroplasty. But problems of oxidative degradation and wear have prompted new sterilization techniques and new forms of more highly cross-linked polyethylene. The value of these solutions can be shown initially from laboratory data, but in the end their usefulness will be confirmed through clinical performance. The significance of new polyethylenes cannot be established on the basis of a single type of test or even on a single goal such as improved wear resistance. Rather, a range of requirements dictated by design goals (function, fixation, and wear) must be considered. The requirements can be competing, so that matching one compromises matching another that, if not taken into account, can lead to failure in clinical use. Previous improvements to polyethylene ultimately failed because not all the requirements were met. The same concern exists with highly cross-linked polyethylenes; improvements in wear resistance are tempered by a decrease in toughness. A case can be made for and against these polyethylenes, but early clinical results in hip arthroplasty show significantly improved wear, raising the possibility of also improving wear performance in knee arthroplasties.

Arthroplasty, Replacement, Knee↗

PubMed2005

The mechanical behavior of locking compression plates compared with dynamic compression plates in a cadaver radius model.

OBJECTIVE: The purpose of this cadaveric study was to compare the mechanical behavior of a locked compression plate, which uses threaded screw heads to create a fixed angle construct, with a dynamic compression plate construct in a cadaver radius model. DESIGN: Mechanical study with cyclic testing and high-speed optical motion analysis. SETTING: Biomechanics laboratory at an academic institution. PATIENTS/PARTICIPANTS: Eighteen pairs of fresh-frozen human cadaver radii were divided into 3 groups of 6 to be tested as a group in each of the following force applications: anteroposterior (AP) bending, mediolateral bending, or torsion. INTERVENTION: Each bone was osteotomized leaving a 5-mm fracture gap and then fixed with a plate. For each pair, 1 radius received a standard plate (limited-contact dynamic compression plates; LC-DCP), the contralateral radius was fixed with a locking compression plate (LCP), and specimens underwent cyclic loading. Normalized stiffness, average energy absorbed, and Newton-cycles to failure were calculated. In addition, a 3-dimensional, high-speed, infrared motion analysis system was used to evaluate motion at the fracture site. MAIN OUTCOME MEASUREMENTS: Construct stiffness, fracture site motion, cycles to failure, and energy absorption. Repeated measures ANOVA were used to detect differences between groups with time. RESULTS: In the torsion group, LCP specimens failed at 60% greater Newton-cycles than the LC-DCP (1473 vs. 918; P < 0.05). In the AP group, the LC-DCP absorbed significantly greater energy during 10,000 cycles compared with the LCP group (P < 0.05). The 2 constructs demonstrated different biomechanical behavior with time. As cycling progressed in the LC-DCP specimens under torsion testing, stiffness (measured at the actuator at the bone ends) did not change significantly; however, fracture motion (measured at the fracture surfaces) decreased significantly (P = 0.04). The LCP specimens did not display similar behavior. CONCLUSIONS: Our findings indicated that LCP constructs may demonstrate subtle mechanical superiority compared with the LC-DCP. The LCP specimens had less energy absorption in the AP group and survived longer in the torsion group. Discordance of motion between measurement regions was observed only in the LC-DCP torsion group, and may have been caused by plate-bone slippage or bone-screw subcatastrophic failure. However, many other compared parameters were found to be similar, and the clinical significance of the few differences found between constructs mandates further investigation.

Biomechanical Phenomena↗

PubMed2005

Fibromyalgia syndrome.

The objectives of the first OMERACT Fibromyalgia Syndrome (FM) Workshop were to identify and prioritize symptom domains that should be consistently evaluated in FM clinical trials, and to identify aspects of domains and outcome measures that should be part of a concerted research agenda of FM researchers. Such an effort will help standardize and improve the quality of outcomes research in FM. A principal assumption in this workshop has been that there exists a clinical syndrome, generally known as FM, characterized by chronic widespread pain typically associated with fatigue, sleep disturbance, mood disturbance, and other symptoms and signs, and considered to be related to central neuromodulatory dysregulation. FM can be diagnosed using 1990 American College of Rheumatology criteria. In preparation for the workshop a Delphi exercise involving 23 FM researchers was conducted to establish a preliminary prioritization of domains of inquiry. At the OMERACT meeting, the workshop included presentation of the Delphi results; a review of placebo-controlled trials of FM treatment, with a focus on the outcome measures used and their performance; a panel discussion of the key issues in FM trials, from both an investigator and regulatory agency perspective; and a voting process by the workshop attendees. The results of the workshop were presented in the plenary session on the final day of the meeting. A prioritized list of domains of FM to be investigated was thus developed, key issues and controversies in the field were debated, and consensus on a research agenda on outcome measure development was reached.

Delphi Technique↗

PubMed2004

Molecular recognition patterns of serum anti-DNA topoisomerase I antibody in systemic sclerosis.

Autoreactive anti-DNA topoisomerase I (anti-Topo I) Abs are commonly detected in sera of systemic sclerosis (SSc) patients. Our studies have established a positive correlation between the levels of serum anti-Topo I Abs and both disease severity and activity of SSc. The molecular targets of anti-Topo I Ab on Topo I domains remain to be further defined. In this report, we studied the molecular recognition pattern of serum anti-Topo I Ab in 52 SSc patients. The highest reactivity of serum anti-Topo I Abs was against the core subdomains I and II (aa 207-441) and, to a lesser extent, against the core subdomain III (aa 433-636) of Topo I. The linker domain (aa 636-712) and the C-terminal domain (aa 713-765) had much less reactivity than the core domain (aa 207-636). Strikingly, very little reactivity was directed against the N-terminal domain (aa 1-213) by serum anti-Topo I Ab. This molecular recognition pattern was consistent among all SSc serum samples studied. Results from patients with serial serum samples indicated that this pattern remained unchanged over time. Interestingly, some naive B cells from healthy controls, upon transformation by EBV, produced IgM Abs against Topo I. These Abs had low affinity for Topo I and reacted equally to all domains of Topo I. The molecular recognition pattern of serum anti-Topo I Ab in SSc suggests the presence of a unique antigenic stimulation in vivo in this disease.

Antibodies, Antinuclear↗

PubMed2004

Autocrine activation by interleukin 1alpha induces the fibrogenic phenotype of systemic sclerosis fibroblasts.

OBJECTIVE: To explore the cellular localization of interleukin 1alpha (IL-1alpha) in cultured fibroblasts from lesional skin of patients with systemic sclerosis (SSc) and to study the role of intracellular IL-1alpha in the activation of fibroblasts. METHODS: Dermal fibroblasts were derived from 12 patients with SSc. Expression of IL-1alpha mRNA was examined using reverse transcriptase-polymerase chain reaction (RT-PCR). The cellular distribution of IL-1alpha was examined by subcellular fractionation, flow cytometry, and immunocytochemistry. A full-length IL-1alpha cDNA was subcloned into the pcDNA3 vector to create sense and antisense-encoding constructs. Normal and SSc fibroblasts were stably transfected with the sense and antisense-encoding constructs, respectively. Stably transfected fibroblast clones were analyzed for the production of procollagen and IL-6 protein by ELISA, alpha1(I) procollagen mRNA by Northern blot hybridization, and proliferation by [3H]thymidine incorporation. RESULTS: SSc-affected fibroblasts constitutively expressed intracellular IL-1alpha, which was predominantly located in the nucleus. Inhibition of IL-1alpha expression in SSc-affected fibroblasts using antisense constructs resulted in decreased proliferation, IL-6 production, and procollagen synthesis. Conversely, overexpression of IL-1alpha in normal fibroblasts resulted in development of the SSc fibroblast phenotype. CONCLUSION: IL-1alpha is an important autocrine fibrogenic factor in SSc, suggesting that inhibition of intracellular IL-1alpha may be a novel strategy for the treatment of SSc.

Autocrine Communication↗

PubMed2003

A nuclear target for interleukin-1alpha: interaction with the growth suppressor necdin modulates proliferation and collagen expression.

There is growing evidence for the intracellular role of cytokines and growth factors, but the pathways by which these activities occur remain largely obscure. Previous work from our laboratory identified the constitutive, aberrant expression of the 31-kDa IL-1 alpha precursor (pre-IL-1 alpha) in the nuclei of fibroblasts from the lesional skin of patients with systemic sclerosis (SSc). We established that pre-IL-1 alpha expression was associated with increased fibroblast proliferation and collagen production. Further investigation has led to the identification of a mechanism by which nuclear expression of pre-IL-1 alpha affects fibroblast growth and matrix production. By using a yeast two-hybrid method, we found that pre-IL-1 alpha binds necdin, a nuclear protein with growth suppressor activity. We mapped the region of pre-IL-1 alpha responsible for necdin binding and found it to be localized near the N terminus, a region that is present on pre-IL-1 alpha, but not the mature 17-kDa cytokine. Expression studies demonstrated that pre-IL-1 alpha associates with necdin in the nuclei of mammalian cell lines and regulates cell growth and collagen expression. Our results provide the first evidence, to our knowledge, of a nuclear target for pre-IL-1 alpha. Based on these findings, we propose that the constitutively up-regulated expression of pre-IL-1 alpha in the nuclei of SSc fibroblasts up-regulates proliferation and matrix production of SSc fibroblasts through binding necdin, and by counteracting its effects on cell growth and collagen production.

Amino Acid Sequence↗

PubMed2003

Identification of an IL1A gene segment that determines aberrant constitutive expression of interleukin-1 alpha in systemic sclerosis.

OBJECTIVE: To further explore the mechanisms of transcriptional regulation of the IL1A gene in fibroblasts from the affected skin of patients with systemic sclerosis (SSc). METHODS: The transcription activity of IL1A was estimated by nuclear run-on assay. A reporter construct (pLuc.-1437) was prepared that contained a 1.5-kb genomic fragment extending from -1437 to +39 relative to the transcription start site of the IL1A gene inserted upstream of the luciferase gene. The DNA protein binding activity for the cis-element of the IL1A gene was determined by electrophoretic mobility shift assay (EMSA). RESULTS: Affected fibroblasts exhibited a strong nuclear run-on signal, indicative of constitutive transcription activity of the IL1A gene. Luciferase assay indicated high levels of transcription activity of pLuc.-1437 in transiently transfected fibroblasts from affected skin; this was absent in transiently transfected control fibroblasts. Analysis of constructs containing a series of 5' deletions of pLuc.-1437 revealed that the sequence between -96 and -82 (nuclear factor-interleukin-1 alpha [NF-IL-1 alpha]) was the most important for transcription of the IL1A gene in affected SSc fibroblasts. NF-IL-1 alpha contains a 5'-GGAA-3' sequence that is essential for specific binding of members of the Ets nuclear protein family. Using EMSA, a DNA protein complex was detected in samples containing nuclear extracts from affected fibroblasts and the NF-IL-1 alpha probe, whereas no specific band was detected in samples from normal fibroblasts. The DNA protein complex disappeared with the use of NF-IL-1 alpha probes that had mutations of the Ets binding sites. CONCLUSION: These findings suggest that a DNA binding protein containing the Ets domain is constitutively expressed only in fibroblasts from the affected skin of SSc patients and regulates the transcription of the IL1A gene, which contributes to the fibrogenic phenotype of fibroblasts in SSc.

Adult↗