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Biomedical subjects

K A Thomas

Publications and source records attributed to K A Thomas.

At least 73 records · Page 4Linked to original sources
PubMed1991

The structure of human acidic fibroblast growth factor and its interaction with heparin.

The secondary and tertiary structure of recombinant human acidic fibroblast growth factor (aFGF) has been characterized by a variety of spectroscopic methods. Native aFGF consists of ca. 55% beta-sheet, 20% turn, 10% alpha-helix, and 15% disordered polypeptide as determined by laser Raman, circular dichroism, and Fourier transform infrared spectroscopy; the experimentally determined secondary structure content is in agreement with that calculated by the semi-empirical methods of Chou and Fasman (Chou, P. Y., and Fasman, G. C., 1974, Biochemistry 13, 222-244) and Garnier et al. (Garnier, J. O., et al., 1978, J. Mol. Biol. 120, 97-120). Using the Garnier et al. algorithm, the major secondary structure components of aFGF have been assigned to specific regions of the polypeptide chain. The fluorescence spectrum of native aFGF is unusual in that it is dominated by tyrosine fluorescence despite the presence of a tryptophan residue in the protein. However, tryptophan fluorescence is resolved upon excitation above 295 nm. The degree of tyrosine and tryptophan solvent exposure has been assessed by a combination of ultraviolet absorption, laser Raman, and fluorescence spectroscopy; the results suggest that seven of the eight tyrosine residues are solvent exposed while the single tryptophan is partially inaccessible to solvent in native aFGF, consistent with recent crystallographic data. Denaturation of aFGF by extremes of temperature or pH leads to spectroscopically distinct conformational states in which contributions of tyrosine and tryptophan to the fluorescence spectrum of the protein vary. The protein is unstable at physiological temperatures. Addition of heparin or other sulfated polysaccharides does not affect the spectroscopic characteristics of native aFGF. These polymers do, however, dramatically stabilize the native protein against thermal and acid denaturation as determined by differential scanning calorimetry, circular dichroism, and fluorescence spectroscopy. The interaction of aFGF with such polyanions may play a role in controlling the activity of this growth factor in vivo.

Algorithms↗
PubMed1991

Conversion of cysteine to serine residues alters the activity, stability, and heparin dependence of acidic fibroblast growth factor.

Acidic fibroblast growth factor (aFGF) is a broad spectrum mitogen that is stabilized by complexation with heparin and heparan proteoglycans. The monomeric human protein contains 3 reduced cysteine residues of unknown function, the first 2 of which are conserved among all seven known fibroblast growth factors. The influence of these free sulfhydryl groups on the level, stability, and heparin dependence of the mitogenic activity at physiological temperature and pH is characterized using a complete set of site-directed mutants in which either any 1, 2, or all 3 of the cysteine residues are converted to serines. Mutants of aFGF in which either any 2 or all 3 cysteine residues are substituted by serines are more active, have longer activity half-lives, and are less heparin dependent than wild-type aFGF. In contrast, wild-type aFGF and the three mutants that each retain 2 cysteine residues inactivate more rapidly in the absence of heparin by a nonproteolytic mechanism but are markedly stabilized by heparin. This cysteine-mediated destabilization of aFGF not only diminishes its activity in the absence of heparin in tissue culture but also could functionally restrict its activity in vivo to the vicinity of mast cell-derived heparins and heparan proteoglycans associated with cell surfaces and basement membranes.

Blotting, Western↗
PubMed1991

Tissue growth into porous primary and revision femoral stems.

The authors studied 45 uncemented porous-coated femoral stems from 45 patients: 35 primary total hip arthroplasties and 10 revisions of either cemented (7) or uncemented (3) femoral components. Histologic sections were examined quantitatively for type, amount, and distribution of tissue ingrowth; these findings were correlated with clinical and radiographic data. Fibrous tissue ingrowth predominated in both groups. Of the primary arthroplasty group, the grade of bone ingrowth in 8 specimens was none, 14 minimal, 6 moderate, and 7 more extensive. In the revision cases, the grade of bone ingrowth in 5 was none, 3 minimal, and 2 moderate. Bone ingrowth was seen more frequently in the distal porous coating, particularly in the revision cases, and most often where direct stem-endosteal canal contact had occurred. While bone ingrowth can occur in uncemented revision stems, it generally appears less abundantly than in primary total hip arthroplasty.

Adult↗
PubMed1991

Activities of human acidic fibroblast growth factor in an in vitro dermal equivalent model.

Acidic fibroblast growth factor is a potent mitogen for human dermal fibroblasts in an in vitro three-dimensional collagen matrix, the "dermal equivalent." Both cell numbers and DNA synthesis are optimally stimulated by daily doses of 1 ng/ml of the pure human mitogen in the presence of heparin, which binds to, and stabilizes, the protein. Under daily treatment by 1 ng/ml aFGF, the fibroblast mitogenic response is marked but transient, and decreases steadily when fibroblasts mature in the collagen matrix. aFGF mitogenic stimulation also results in a decrease in cellular volume and inhibition of fibroblast-mediated contraction of the collagen gel. Various dosing regimes indicate that, although the greatest mitotic response was generated by daily dosing, nearly optimal responses can also be achieved with either a short duration of early daily dosing or longer-term intermittent treatment.

Cell Count↗
PubMed1991

Biomechanical evaluation of the anterior drawer test: the contribution of the lateral ankle ligaments.

The contributions of the lateral ankle ligaments to resisting anterior-posterior displacement of the talus were evaluated in eight unembalmed cadaveric ankles. While holding the distal tibia fixed, loads of 150 N were applied to the talus in the anterior and posterior directions in the neutral, dorsiflexed, and plantarflexed positions using an hydraulic test system. Tests were performed on the intact specimens then after sequential sectioning of the lateral ligaments of the ankle. Under strictly anteroposterior loading and without an axial (weight-bearing) load applied, no single ligament could be isolated as having a dominant stabilizing function.

Ankle Joint↗
PubMed1991

Fatigue failure of noncemented porous-coated implants. A retrieval study.

The causes of mechanical failure of five noncemented porous-coated components were studied. There were two cobalt-chromium alloy and three titanium alloy implants which fractured after 12 to 48 months. The implants included one acetabular component, and one femoral condylar, one patellar and two tibial components. Examination of the fractured surfaces revealed fatigue to be the mechanism of failure in all cases. The porous coating and the processes required for its fabrication had resulted in weakening and reduction of substrate thickness. Additional factors were stress concentration due to limited, localised bone ingrowth, and some features of the design of the implants.

Aged↗
PubMed1991

Enhanced bone ingrowth and fixation strength with hydroxyapatite-coated porous implants.

The effect of a hydroxyapatite (HA) coating on the interface attachment strength, rate of development of attachment strength, and degree of bone ingrowth of porous implants was investigated. Implants with ideal surgical fits and those having interface gap spaces were evaluated using femoral transcortical and intramedullary models. The application of a thin HA coating to porous implants significantly enhanced both interface attachment strength and bone ingrowth. The rate of development of interface strength and bone ingrowth was also more rapid with the HA-coated system. There was no evidence of any disruption, loss, or resorption of the HA coating.

Animals↗
PubMed1991

Survey of health care available to child athletes.

Surveys were sent to 84 children's hospitals and 397 sportsmedicine clinics to characterize the care available for the child athlete (aged 4 to 12 years); they were completed by 209 facilities (43% response rate). Fourteen of the facilities had a sportsmedicine clinic specifically for children; care was available for the child athlete in an additional 46 facilities, but less than 10% of the clinic visits were made by athletes aged 4 to 12 years. All responding clinics were further characterized by location, length of operation, composition, referral base, profitability and funding, etc. Although there are few sportsmedicine clinics specifically for children, many facilities provide experienced personnel in existing clinics to care for young athletes.

Athletic Injuries↗
PubMed1991

Experimental coating defects in hydroxylapatite-coated implants.

Defects in hydroxyapatite (HA)-coated metallic implant systems, including cracks, flakes, or scratches, may occur at the time of surgery or in time because of in vivo loading. Such defects may affect the bone-implant interface response because of increased local metallic corrosion and ion release. Using a canine transcortical push-out model, the interface mechanics and histology of HA-coated titanium and cobalt-chromium-molybdenum alloy implants with and without coating defects were evaluated. The coating defects extended through the HA material to the underlying metallic substrate. Interface mechanical testing and undecalcified histologic techniques were used to evaluate differences in interface response at three, five, six, ten, 12, and 32 weeks postimplantation. There were no statistically significant differences between the HA-coated implants with and without defects for either interface shear strength or stiffness; however, both HA-coated implant types developed significantly greater interface strength and stiffness when compared to uncoated metallic implants. Histologically, in all areas away from the defect, a progression to nearly complete mineralization of osseous tissue directly onto the HA-coated surface was observed with no interpositional fibrous tissue layer. At early time periods (up to six weeks) in the area of the coating defect, bone apposition and mineralization appeared to stop at the edge of the HA coating. At later time periods (greater than ten weeks), the area of the defect was filled with mineralized osseous tissue in approximately one-half of the specimens. A thin fibrous interpositional layer was observed at the interface of the exposed metal substrate.

Analysis of Variance↗
PubMed1990

Purification of a glycoprotein vascular endothelial cell mitogen from a rat glioma-derived cell line.

A growth factor that is mitogenic for vascular endothelial cells, with an ED50 of approximately 1 ng/ml, has been purified 170,000-fold to apparent homogeneity from tissue culture medium conditioned by a rat glioma-derived cell line. The pure protein is a 46-kDa dimer composed of two subunits of equivalent mass as established by comparison of migration in SDS/polyacrylamide gels with and without prior reduction. This glioma-derived growth factor is a glycoprotein and is not mitogenic for BALB/c 3T3 fibroblasts, properties that further distinguish it from other well-characterized vascular endothelial cell mitogens. In contrast to acidic and basic fibroblast growth factors and to platelet-derived endothelial cell growth factor, which have no secretory leader sequences and might only be released by leakage from damaged cells, the glycoprotein nature of this mitogen implies that it is processed through the glycosylating secretory pathway. This secretable growth factor could, therefore, be readily available in the extracellular space under normal physiological conditions in vivo to promote vascular endothelial cell proliferation associated with blood-vessel growth and maintenance.

Amino Acids↗
PubMed1990

Amino acid and cDNA sequences of a vascular endothelial cell mitogen that is homologous to platelet-derived growth factor.

Glioma-derived vascular endothelial cell growth factor (GD-VEGF) is a 46-kDa dimeric glycoprotein mitogen with apparently greater specificity for vascular endothelial cells than the well-characterized fibroblast growth factors. The GD-VEGF cDNA sequence encodes a 190-amino acid residue subunit that is converted, by removal of an amino-terminal hydrophobic secretory leader sequence, to the mature 164-residue subunit characterized by direct amino acid sequencing. The GD-VEGF homodimeric subunit is homologous to the platelet-derived growth factor A and B chains and its oncogene homologue v-sis.

Amino Acid Sequence↗
PubMed1990

Time-series analysis--spectral analysis and the search for cycles.

In summary, spectral analysis is one analytic strategy for analyzing time-series data. Specifically, spectral analysis enables researchers to detect cyclicity and determines the variance in the data accounted for by cyclic activity. Results describe cycle frequency, period, and amplitude. Unlike cosinor analysis (Lentz, 1990b), spectral analysis does not directly determine peak time nor directly indicate time-ordered relationships, as does autocorrelation (Taylor, 1990). Cyclic relationships between time-series data can be detected using coherency (Gottman & Ringland, 1981), an extension of spectral analysis which is beyond the scope of this article. A word of caution is in order for the uninitiated researcher. Spectral analysis, as well as autocorrelation and cosinor analysis, entails within-subject analysis of single variables. Currently, means of determining relationships between time series, such as cross-correlation and coherency, are bivariate. The need to analyze the pattern of individual variables within-subject, followed by examination of bivariate relationships between pairs of variables, is wisely balanced by limited numbers of variables and small sample size.

Nursing Research↗
PubMed1990

Disulfide bonds are neither required, present, nor compatible with full activity of human recombinant acidic fibroblast growth factor.

Human acidic fibroblast growth factor (aFGF) is a potent broad-spectrum mitogen that contains three Cys residues within its monomeric structure. We have found that site-directed mutants in which any one of these Cys residues is converted to serine remain highly active, although variably dependent on heparin, so none of the three possible intramolecular disulfide bonds that can be formed are required for mitogenic activity. Furthermore, a dispensable disulfide bond that might stabilize the active conformation is not present since all three Cys residues are accessible to chemical modification in recombinant as well as brain-derived aFGFs. Finally, formation of a disulfide bond between the two Cys residues conserved among all seven known members of the FGF family results in a virtually inactive product that can subsequently be reactivated by reduction. Thus, despite the extracellular function of aFGF, its Cys residues do not form intramolecular disulfide bonds in the active conformation.

Animals↗
PubMed1989

Stabilization by heparin of acidic fibroblast growth factor mitogenicity for human endothelial cells in vitro.

The effects of heparin and other glycosaminoglycans (GAGs) on the mitogenicity and stability of acidic fibroblast growth factor (aFGF) were studied. The mitogenic activity of aFGF was assayed utilizing cultured adult human endothelial cells (AHECs) isolated from iliac arteries and veins as target cells. In most experiments, aFGF purified from bovine brain was employed; in some experiments recombinant bovine aFGF was used and qualitatively similar results were obtained. In the presence of heparin, bovine aFGF at doses between 0.5 and 1.0 ng/ml (30-60 pM) elicited half the maximum AHEC growth over a 4-day period depending on the cell line tested; in the absence of heparin, significant growth was not observed at aFGF concentrations less than 10-20 ng/ml. This effect of heparin was dose-dependent over the range 0.1-10 micrograms/ml (half-maximum dose, 2 micrograms/ml). The mitogenic activity of bovine aFGF for AHECs decreased by 50% after preincubation in culture medium without cells at 37 degrees C for 2 1/2 to 3 hours. In contrast, the mitogenic activity of bovine aFGF preincubated in the presence of heparin-containing culture medium without cells was dramatically stabilized (half-life 24-29 hours). These effects also were observed in serum-free medium. Several GAGs structurally related to heparin such as chondroitin-4-sulfate, chondroitin-6-sulfate, dermatan sulfate, and hyaluronic acid neither potentiated nor stabilized aFGF mitogenic activity. However, heparan sulfate from bovine lung was found to be nearly as active as heparin in both these effects. These data suggest that the binding and stabilization of mitogens by extracellular and tissue-associated heparan sulfates might play important roles in the regulation of AHEC growth.

Cell Division↗
PubMed1989

Quantitative histologic analysis of tissue growth into porous total knee components.

Histologic and radiographic analysis was performed on 85 porous-coated, uncemented knee components (26 femoral, 34 tibial, and 25 patellar) retrieved from 45 patients for malposition or instability, unexplained pain, late infection, postmortem or postamputation, and posttrauma. No component was clinically or radiographically loose at the time of removal. The average patient age at removal was 62.1 years (range, 39-85 years), and the average time in situ was 12.4 months (range, 2 weeks to 53 months). Radiographs from 31 of the 45 patients (69%) were examined for implant alignment, fit, subsidence, loose beads, and the presence of sclerotic and lucent lines. Histologic and microradiographic sections of the implant and adherent tissue were examined for type, amount, and anatomic location of tissue ingrowth. Overall, 52% of the components showed no evidence of bone ingrowth, 29% showed minimal (less than 2%), 12% showed moderate (2-5%), and 7% showed extensive (5-10%) bone ingrowth. In no case was bone present in more than 10% of the available pore volume of any component. There were no significant differences in the incidence or extent of bone ingrowth among femoral, tibial, and patellar components, nor in the extent of bone ingrowth observed in comparing different implant designs, materials, or porous coating types. When bone ingrowth was observed, the anatomic location was consistent in each type of component. The presence of a lucent line radiographically was indicative of fibrous encapsulation, while a sclerotic line or absence of any radiographic abnormality was seen with both fibrous tissue and bone ingrowth.

Aged↗
PubMed1989

Biologic response to hydroxylapatite-coated titanium hips. A preliminary study in dogs.

Hydroxylapatite (HA)-coated and uncoated Ti-6A1-4V alloy femoral endoprostheses were evaluated in adult dogs. The femoral stems had proximal anterior, posterior, and medial pockets of either a commercially pure titanium porous coating or a grooved macrotexture. They also had a medial collar, with an inferior surface pocket of either the porous coating or the grooved macrotexture. HA-coated and uncoated specimens of each type were evaluated. The devices were placed as unilateral hemiarthroplasties in 12 dogs and remained in function for up to 52 weeks. Histologic sections from the uncoated grooved implants showed no direct bone-implant apposition in the proximal regions after up to 10 weeks; the HA-coated grooved implants demonstrated extensive direct bone-coating apposition after 5 weeks. Sections from uncoated porous implants evaluated after 10 weeks demonstrated approximately equivalent in-growth to those sections from the HA-coated devices after 6 weeks. All HA-coated implants demonstrated consistent bone-implant apposition with no fibrous tissue interposition. The HA-coated surfaces were associated with increased bone deposition and proliferation at early implantation periods. In no histologic section examined was there any evidence of deterioration of the HA coating, nor was any separation of the coating from the substrate material observed.

Alloys↗