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Biomedical subjects

M D McKee

Publications and source records attributed to M D McKee.

At least 19 recordsLinked to original sources
PubMed2006

Chitosan-glycerol phosphate/blood implants elicit hyaline cartilage repair integrated with porous subchondral bone in microdrilled rabbit defects.

OBJECTIVE: We have previously shown that microfractured ovine defects are repaired with more hyaline cartilage when the defect is treated with in situ-solidified implants of chitosan-glycerol phosphate (chitosan-GP) mixed with autologous whole blood. The objectives of this study were (1) to characterize chitosan-GP/blood clots in vitro, and (2) to develop a rabbit marrow stimulation model in order to determine the effects of the chitosan-GP/blood implant and of debridement on the formation of incipient cartilage repair tissue. METHODS: Blood clots were characterized by histology and in vitro clot retraction tests. Bilateral 3.5 x 4 mm trochlear defects debrided into the calcified layer were pierced with four microdrill holes and filled with a chitosan-GP/blood implant or allowed to bleed freely as a control. At 1 day post-surgery, initial defects were characterized by histomorphometry (n=3). After 8 weeks of repair, osteochondral repair tissues between or through the drill holes were evaluated by histology, histomorphometry, collagen type II expression, and stereology (n=16). RESULTS: Chitosan-GP solutions structurally stabilized the blood clots by inhibiting clot retraction. Treatment of drilled defects with chitosan-GP/blood clots led to the formation of a more integrated and hyaline repair tissue above a more porous and vascularized subchondral bone plate compared to drilling alone. Correlation analysis of repair tissue between the drill holes revealed that the absence of calcified cartilage and the presence of a porous subchondral bone plate were predictors of greater repair tissue integration with subchondral bone (P<0.005), and of a higher total O'Driscoll score (P<0.005 and P<0.01, respectively). CONCLUSIONS: Chitosan-GP/blood implants applied in conjunction with drilling, compared to drilling alone, elicited a more hyaline and integrated repair tissue associated with a porous subchondral bone replete with blood vessels. Concomitant regeneration of a vascularized bone plate during cartilage repair could provide progenitors, anabolic factors and nutrients that aid in the formation of hyaline cartilage.

Animals↗
PubMed2006

Determinants of functional outcome after simple and complex acetabular fractures involving the posterior wall.

We have evaluated the functional, clinical and radiological outcome of patients with simple and complex acetabular fractures involving the posterior wall, and identified factors associated with an adverse outcome. We reviewed 128 patients treated operatively for a fracture involving the posterior wall of the acetabulum between 1982 and 1999. The Musculoskeletal Functional Assessment and Short-Form 36 scores, the presence of radiological arthritis and complications were assessed as a function of injury, treatment and clinical variables. The patients had profound functional deficits compared with the normal population. Anatomical reduction alone was not sufficient to restore function. The fracture pattern, marginal impaction and residual displacement of > 2 mm were associated with the development of arthritis, which related to poor function and the need for hip replacement. It may be appropriate to consider immediate total hip replacement for patients aged > 50 years with marginal impaction and comminution of the wall, since 7 of 13 (54%) of these required early hip replacement.

Acetabulum↗
PubMed2005

Tissue engineering of cartilage using an injectable and adhesive chitosan-based cell-delivery vehicle.

OBJECTIVE: Adult articular cartilage shows a limited intrinsic repair response to traumatic injury. To regenerate damaged cartilage, cell-assisted repair is thus viewed as a promising therapy, despite being limited by the lack of a suitable technique to deliver and retain chondrogenic cells at the defect site. DESIGN: We have developed a cytocompatible chitosan solution that is space-filling, gels within minutes, and adheres to cartilage and bone in situ. This unique combination of properties suggested significant potential for its use as an arthroscopically injectable vehicle for cell-assisted cartilage repair. The primary goal of this study was to assess the ability of this polymer system, when loaded with primary articular chondrocytes, to support cartilage formation in vitro and in vivo. The chitosan gel was cultured in vitro, with and without chondrocytes, as well as injected subcutaneously in nude mice to form subcutaneous dorsal implants. In vitro and in vivo constructs were collectively analyzed histologically, for chondrocyte mRNA and protein expression, for biochemical levels of glycosaminoglycan, collagen, and DNA, and for mechanical properties. RESULTS: Resulting tissue constructs revealed histochemical, biochemical and mechanical properties comparable to those observed in vitro for primary chondrocytes cultured in 2% agarose. Moreover, the gel was retained after injection into a surgically prepared, rabbit full-thickness chondral defect after 1 day in vivo, and in rabbit osteochondral defects, up to 1 week. CONCLUSIONS: The in situ-gelling chitosan solution described here can support in vitro and in vivo accumulation of cartilage matrix by primary chondrocytes, while persisting in osteochondral defects at least 1 week in vivo.

Animals↗
PubMed2005

Hierarchies of extracellular matrix and mineral organization in bone of the craniofacial complex and skeleton.

Structural hierarchies are common in biologic systems and are particularly evident in biomineralized structures. In the craniofacial complex and skeleton of vertebrates, extracellular matrix and mineral of bone are structurally ordered at many dimensional scales from the macro level to the nano level. Indeed, the nanocomposite texture of bone, with nanocrystals of apatitic mineral embedded within a crosslinked matrix of fibrillar and nonfibrillar proteins, imparts to bone the very mechanical properties and toughness it needs to function in vital organ protection, musculoskeletal movement and mastication. This article focuses on how hierarchies of extracellular matrix protein organization influence bone cell behavior, tissue architecture and mineralization. Additional attention is given to recent work on the molecular determinants of mineral induction in bone, and how the mineralization process is subsequently regulated by inhibitory proteins.

Animals↗
PubMed2005

Transglutaminase crosslinking of SIBLING proteins in teeth.

Transglutaminase 2 (TG2), a protein-crosslinking enzyme, participates in extracellular matrix maturation and cell adhesion in cartilage and bone. We hypothesized that TG2 has similar roles in teeth. A TG activity assay and immunoblotting of rat tooth extracts showed TG activity and the presence of high-molecular-weight forms of the SIBLING (Small Integrin-Binding LIgand N-linked Glycoprotein) proteins: dentin matrix protein 1 (DMP1), dentin phosphoprotein (DPP), and bone sialoprotein (BSP). DMP1 and BSP, each containing both glutamine and lysine residues critical for crosslink formation, readily formed polymers in vitro when incubated with TG2. The ability of glutamine-lacking DPP to form polymers in vitro and in vivo demonstrates that it could act as a lysine donor for crosslinking, potentially having protein crosslinking partner(s) in teeth. Consistent with a role in cell adhesion, the TG2 isoform was co-localized by immunohistochemistry with its substrates at cell-matrix adhesion sites, including along odontoblast tubules (DMP1 and DPP), in the pericellular matrix of cementocytes (DMP1), and in predentin (BSP).

Animals↗
PubMed2004

Tetrapolar measurement of electrical conductivity and thickness of articular cartilage.

A tetrapolar method to measure electrical conductivity of cartilage and bone, and to estimate the thickness of articular cartilage attached to bone, was developed. We determined the electrical conductivity of humeral head bovine articular cartilage and subchondral bone from a 1- to 2-year-old steer to be 1.14+/-0.11 S/m (mean+/-sd, n =11) and 0.306+/-0.034 S/m, (mean+/-sd, n =3), respectively. For a 4-year-old cow, articular cartilage and subchondral bone electrical conductivity were 0.88+/-0.08 S/m (mean+/-sd, n =9) and 0.179+/-0.046 S/m (mean+/-sd, n =3), respectively. Measurements on slices of cartilage taken from different distances from the articular surface of the steer did not reveal significant depth-dependence of electrical conductivity. We were able to estimate the thickness of articular cartilage with reasonable precision (<20% error) by injecting current from multiple electrode pairs with different inter-electrode distances. Requirements for the precision of this method to measure cartilage thickness include the presence of a distinct layer of calcified cartilage or bone with a much lower electrical conductivity than that of uncalcified articular cartilage, and the use of inter-electrode distances of the current injecting electrodes that are on the order of the cartilage thickness. These or similar methods present an attractive approach to the non-destructive determination of cartilage thickness, a parameter that is required in order to estimate functional properties of cartilage attached to bone, and evaluate the need for therapeutic interventions in arthritis.

Animals↗
PubMed2003

Purification of ovocalyxin-32, a novel chicken eggshell matrix protein.

The eggshell is a highly ordered structure resulting from the deposition of calcium carbonate and an organic matrix from the acellular uterine fluid. Characterization of the individual matrix components is necessary to determine their influence upon calcite crystal shape, size, and orientation during eggshell calcification. We have purified and sequenced a novel 32-kDa protein, ovocalyxin-32 (OCX-32), which is present at high levels in the uterine fluid during the terminal phase of eggshell formation, and is localized predominantly in the outer eggshell. Database searches identified expressed sequence tags (ESTs) whose alignment yielded the complete cDNA. OCX-32 protein possesses limited identity (32%) to two unrelated proteins: latexin, a carboxypeptidase inhibitor expressed in rat cerebral cortex and mast cells, and to a skin protein that is encoded by a retinoic acid receptor-responsive gene, TIG1. The timing of OCX-32 secretion into the uterine fluid suggests that it may play a role in the termination of mineral deposition.

Animals↗
PubMed2003

Cartilage formation and calcification in arteries of mice lacking matrix Gla protein.

Matrix Gla protein (MGP/Mgp) is a protein expressed predominantly by vascular smooth muscle cells (VSMCs) and by chondrocytes. Transgenic mice lacking Mgp die 1-3 months after birth due to calcification of elastic fibers and rupture of large elastic arteries such as the aorta. Here, we report on cartilage formation that commonly occurs in calcified arteries of Mgp-/- mice. Using histology, von Kossa staining, immunohistochemistry, and Western blotting, together with examination of cellular markers for VSMCs and extracellular matrix markers for cartilage, we provide evidence for cell transformation from VSMC to chondrocyte in the arterial media in the absence of Mgp. At 2 weeks of age in the aorta of Mgp-/- mice, VSMCs lose immunostaining for smooth muscle alpha-actin concomitant with the appearance of cartilage molecules as shown by immunohistochemical staining and Western blotting for aggrecan, link protein, and type II collagen. These data provide evidence that the absence of Mgp, and/or calcification of the ECM, in the arterial media can trigger chondrocyte differentiation and cartilage formation in blood vessels.

Actins↗
PubMed2002

Osteopontin deficiency increases mineral content and mineral crystallinity in mouse bone.

Fourier transform infrared microspectroscopy (FTIRM) and infrared imaging (FTIRI) were used to characterize the mineral in bones of two different lines of Opn-deficient (Opn-/-) mice and their background-matched wild-type controls (Opn+/+). Sections of tibia and femur from 12-week-old and 16-week-old mice were evaluated with a spatial resolution between 10 microm (FTIRM) and 7 microm (FTIRI). FTIRI was used to examine 400 microm x 400 microm areas in cortical bone and trabecular bone and FTIRM examined selected 20 microm x 20 microm areas at sites within these anatomically defined areas. Despite the absence of an obvious phenotype in Opn-deficient mice, being undetectable by radiographic and histological methods, FTIRM analyses revealed that the relative amount of mineral in the more mature areas of the bone (central cortical bone) of Opn-knockout mice was significantly increased. Moreover, mineral maturity (mineral crystal size and perfection) throughout all anatomic regions of the Opn-deficient bone was significantly increased. The 2-dimensional, color-coded data (images) produced by FTIRI showed similar increases in mineral maturity in the Opn-/- bone, however, the crystallinity parameters were less sensitive, and significance was not achieved in all areas analyzed. Nonetheless, the findings of increased mineral content and increased crystal size/perfection in both lines of Opn-deficient mice at both ages are consistent with in vitro data indicating that Opn is a potent inhibitor of mineral formation and mineral crystal growth and proliferation, and also support a role for Opn in osteoclast recruitment and function.

Animals↗
PubMed2002

Homotypic interactions of soluble and immobilized osteopontin.

Osteopontin (OPN) is an extracellular matrix protein found in bones and teeth, where it accumulates at matrix-matrix interfaces. We postulate that OPN interacts homotypically and heterotypically in the adhesion of apposing matrices. Using suspensions of OPN-coupled aldehyde/sulfate latex spheres, we measured the strength of homotypic OPN-OPN binding in vitro. Doublets formed through shear-induced collisions in a cone and plate rheoscope were subjected to shear stresses >0.6 Nm(-2) and the fraction broken up determined over 60 s. Rapid initial breakup of 35% of doublets was followed by very slow breakup of the remaining 65%. Monte Carlo simulation of the breakup kinetics pointed to the existence of low and high bond strength populations of doublets. Dynamic light scattering spectroscopy of soluble OPN showed that 27% by mass existed as dimers. We postulate that OPN dimers binding to monomers account for the low strength bonds since a strong bond has already formed between the molecules of the dimer. In contrast, OPN-OPN monomer bonds had higher tensile strength than bonds between the high-affinity interaction of IgG and protein G, previously studied. Antibody blocking studies showed that the self-binding region of OPN resides in the C-terminus. These data suggest that homotypic OPN-OPN bonds have physiologically significant strength, supporting the hypothesis that OPN-OPN binding and self-assembly participate in adhesion within mineralized tissues.

Animals↗
PubMed2002

Interobserver and intraobserver variation in the assessment of the healing of tibial fractures after intramedullary fixation.

The reliability of the radiological assessment of the healing of tibial fractures remains undetermined. We examined the inter- and intraobserver agreement of the healing of such fractures among four orthopaedic trauma surgeons who, on two separate occasions eight weeks apart, independently assessed the radiographs of 30 patients with fractures of the tibial shaft which had been treated by intramedullary fixation. The radiographs were selected from a database to represent fractures at various stages of healing. For each radiograph, the surgeon scored the degree of union, quantified the number of cortices bridged by callus or with a visible fracture line, described the extent and quality of the callus, and provided an overall rating of healing. The interobserver chance-corrected agreement using a quadratically weighted kappa (kappa) statistic in which values of 0.61 to 0.80 represented substantial agreement were as follows: radiological union scale (kappa= 0.60); number of cortices bridged by callus (kappa = 0.75); number of cortices with a visible fracture line (kappa= 0.70); the extent of the callus (kappa = 0.57); and general impression of fracture healing (kappa = 0.67). The intraobserver agreement of the overall impression of healing (kappa = 0.89) and the number of cortices bridged by callus (kappa = 0.82) or with a visible fracture line (kappa = 0.83) was almost perfect. There are no validated scales which allow surgeons to grade fracture healing radiologically. Among those examined, the number of cortices bridged by bone appears to be a reliable, and easily measured radiological variable to assess the healing of fractures after intramedullary fixation.

Bony Callus↗
PubMed2001

Ovocalyxin-32, a novel chicken eggshell matrix protein. isolation, amino acid sequencing, cloning, and immunocytochemical localization.

The eggshell is a highly ordered structure resulting from the deposition of calcium carbonate concomitantly with an organic matrix upon the eggshell membranes. Mineralization takes place in an acellular uterine fluid, which contains the ionic and matrix precursors of the eggshell. We have identified a novel 32-kDa protein, ovocalyxin-32, which is expressed at high levels in the uterine and isthmus regions of the oviduct, and concentrated in the eggshell. Sequencing of peptides derived from the purified protein allowed expressed sequence tag sequences to be identified that were assembled to yield a full-length composite sequence whose conceptual translation product contained the complete amino acid sequence of ovocalyxin-32. Data base searches revealed that ovocalyxin-32 has limited identity (32%) to two unrelated proteins: latexin, a carboxypeptidase inhibitor expressed in the rat cerebral cortex and mast cells, and a skin protein, which is encoded by a retinoic acid receptor-responsive gene, TIG1. High level expression of ovocalyxin-32 was limited to the isthmus and uterus tissue, where immunocytochemistry at the light and electron microscope levels demonstrated that ovocalyxin-32 is secreted by surface epithelial cells. In the eggshell, ovocalyxin-32 localizes to the outer palisade layer, the vertical crystal layer, and the cuticle of the eggshell, in agreement with its demonstration by Western blotting at high levels in the uterine fluid during the termination phase of eggshell formation. Ovocalyxin-32 is therefore identified as a novel protein synthesized in the distal oviduct where hen eggshell formation occurs.

Amino Acid Sequence↗
PubMed2001

Outcome of foot injuries in multiply injured patients.

In the past, foot injuries in patients with multiple trauma were thought to be of lesser importance than fractures of long bones. In one prospective study from the authors' institutions, however, multiple-trauma patients with foot injuries were shown to have a poorer functional outcome compared with matched controls. To address these concerns, this article has two parts. The first part is an overview of general principles in the treatment of foot injuries in polytrauma patients. The treatment of specific injuries is beyond the scope of this article, but an approach is highlighted that can be remembered when decisions are made regarding these severely injured patients. The second part reviews the findings from the authors' study, focusing on functional outcomes of multiple-trauma patients with foot injuries.

Calcaneus↗
PubMed2001

Tardy posterolateral rotatory instability of the elbow due to cubitus varus.

BACKGROUND: Cubitus varus has long been considered merely a cosmetic deformity. The purpose of this paper is to demonstrate a causal relationship between cubitus varus and instability of the elbow. METHODS: In twenty-four patients (twenty-five limbs) with a cubitus varus deformity following a pediatric distal humeral fracture or resulting from a congenital anomaly (three limbs of two patients), tardy posterolateral rotatory instability of the elbow developed approximately two to three decades after the deformity occurred. All patients presented with lateral elbow pain and recurrent instability. The average varus deformity was 15 degrees (range, 0 degrees to 35 degrees ). Surgery was performed in twenty-one patients (twenty-two limbs). Treatment consisted of reconstruction of the lateral collateral ligament and osteotomy in seven limbs, ligament reconstruction alone in ten, osteotomy alone in four, and total elbow arthroplasty in one. RESULTS: In three patients, the triceps muscle was dynamically stimulated intraoperatively to contract while resisting extension of the elbow. This produced posterolateral rotatory subluxation of the elbow, which was reversed by corrective osteotomy and lateral transposition of a portion of the medial head of the triceps that originally had been attached to the elongated, deformed medial aspect of the olecranon. At an average of three years (minimum, one year) after the operation, the result was good or excellent for nineteen of the twenty-two limbs that had undergone an operation; three limbs had persistent instability. CONCLUSIONS: With cubitus varus, the mechanical axis, the olecranon, and the triceps line of pull are all displaced medially. The repetitive external rotation torque on the ulna permitted by these deformities can stretch the lateral collateral ligament complex and lead to posterolateral rotatory instability. Thus, cubitus varus deformity secondary to supracondylar malunion or congenital deformity of the distal part of the humerus may not always be a benign condition and may have important long-term clinical implications. Operative correction can relieve symptoms of instability. The indications for preventive corrective osteotomy remain to be determined.

Adolescent↗
PubMed2001

Predictors of follow-up of atypical and ASCUS papanicolaou tests in a high-risk population.

OBJECTIVE: Our goals were to assess adherence to the National Cancer Institute clinical practice guideline for the management of atypical squamous cells of uncertain significance (ASCUS) Papanicolaou (Pap) test results in a community at high risk of cervical cancer. We also hoped to identify predictors of adherence to the guideline. STUDY DESIGN: We used an historical cohort and collected data by chart abstraction. POPULATION: Our study included women receiving care in 7 urban community health centers who had an initial ASCUS or atypical Pap test result in 1996. We excluded women with a history of cervical dysplasia or human immunodeficiency virus infection, yielding a final sample of 387 women. OUTCOMES: measured The outcome measured was the level of adherence to the guideline, defined as falling within 1 of 3 mutually exclusive categories (complete, moderate, or low). RESULTS: Care providers recommended colposcopy after an initial atypical Pap test result in 12% of cases and repeat cytology in 67%. Failure to document a plan for management was found in 19% of cases. Complete adherence was achieved for 27% of subjects, moderate adherence for 28%, and low adherence for 45%. The factors associated with complete versus moderate or low adherence included site of care, description of the abnormality (ASCUS vs atypia), availability of on-site colposcopy, and discussing the plan at a visit. CONCLUSIONS: Adherence with the National Cancer Institute clinical practice guideline in this setting was disappointing and varied substantially by site. Factors amenable to change that may improve follow-up include good communication of results with patients and providing colposcopy at the site of primary care.

Cohort Studies↗
PubMed2000

Phosphate regulation of vascular smooth muscle cell calcification.

Vascular calcification is a common finding in atherosclerosis and a serious problem in diabetic and uremic patients. Because of the correlation of hyperphosphatemia and vascular calcification, the ability of extracellular inorganic phosphate levels to regulate human aortic smooth muscle cell (HSMC) culture mineralization in vitro was examined. HSMCs cultured in media containing normal physiological levels of inorganic phosphate (1.4 mmol/L) did not mineralize. In contrast, HSMCs cultured in media containing phosphate levels comparable to those seen in hyperphosphatemic individuals (>1.4 mmol/L) showed dose-dependent increases in mineral deposition. Mechanistic studies revealed that elevated phosphate treatment of HSMCs also enhanced the expression of the osteoblastic differentiation markers osteocalcin and Cbfa-1. The effects of elevated phosphate on HSMCs were mediated by a sodium-dependent phosphate cotransporter (NPC), as indicated by the ability of the specific NPC inhibitor phosphonoformic acid, to dose dependently inhibit phosphate-induced calcium deposition as well as osteocalcin and Cbfa-1 gene expression. With the use of polymerase chain reaction and Northern blot analyses, the NPC in HSMCs was identified as Pit-1 (Glvr-1), a member of the novel type III NPCs. These data suggest that elevated phosphate may directly stimulate HSMCs to undergo phenotypic changes that predispose to calcification and offer a novel explanation of the phenomenon of vascular calcification under hyperphosphatemic conditions. The full text of this article is available at http://www.circresaha.org.

Arteries↗