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Biomedical subjects

F H Silver

Publications and source records attributed to F H Silver.

At least 73 records · Page 4Linked to original sources
PubMed1986

Collagen-based wound dressing: effects of hyaluronic acid and fibronectin on wound healing.

Our previous studies have shown that a collagen-based wound dressing induces the spatial deposition of wound tissue. This study was conducted to determine the effects of hyaluronic acid and fibronectin on wound healing. These macromolecules play an important role in wound healing, embryonic development and cellular migration in vitro. The effects of the addition of varying levels of fibronectin and hyaluronate to a collagen sponge were studied. Low levels of both hyaluronate and fibronectin modified the structure of the implant, and resulted in increased chemoattraction, replication and collagen deposition in an in vivo wound healing model.

Animals↗
PubMed1985

The molecular structure and lubricating activity of lubricin isolated from bovine and human synovial fluids.

Lubricin was isolated from bovine ankle, metacarpophalangeal and knee and human knee synovial fluids. The lubricins isolated from the bovine joint fluids had the same amino acid and carbohydrate compositions, but differences were observed in the relative molecular masses. The Mr values of bovine metacarpophalangeal and ankle lubricin determined by light-scattering measurements were about 200 000, whereas values of 132 000 and 143 000 were obtained for the bovine knee lubricin. The human knee lubricin had a similar carbohydrate composition to bovine knee lubricin except for the higher glucosamine content, and the amino acid composition differed slightly. The human sample had a lower glutamic acid content and a leucine/isoleucine ratio of 2:1 compared with 1:1 in the bovine. The Mr value of the human knee lubricin (166 000) was also lower than that of the bovine metacarpophalangeal and ankle samples. The Mr value of the bovine knee lubricin determined by sedimentation-equilibrium measurements was 171 000. The length measurements determined by electron microscopy and also the sedimentation measurements showed considerable polydispersity and indicate that the degree of extension of lubricin molecules can vary. Friction measurements showed that the human knee synovial-fluid lubricin had equivalent lubricating ability in a test system in vitro to that observed for lubricin isolated from normal bovine synovial fluids. The lubricating ability of lubricin was concentration-dependent, and each lubricin sample was able to act as a lubricant in vitro in an equivalent manner to whole synovial fluid at concentrations that are thought to occur in vivo.

Amino Acids↗
PubMed1985

Collagen fiber formation in repair tissue: development of strength and toughness.

Dermal repair tissue shows a progressive increase in collagen content which may be related to the wound tensile strength. Wound strength and extensibility are lower than those found in normal skin. In animals, wounds closed by metal clips are chosen as a model to study the proliferative and remodeling phases of healing from a mechanical and morphological point of view. During the proliferative phase the low wound strength is associated with formation of collagen fibers of small diameter, later, (days 28-45) an acute change appears corresponding to the remodeling phase, with increased collagen fiber diameters observed by scanning electron microscopy and light microscopy, and increased tensile strength and toughness. By 180 days, wound strength and collagen fiber morphology were close to that observed in the normal skin. These observations show a direct relationship between collagen fiber diameter and tensile strength. In addition, packing density of collagen fibrils (determined by the birefringence retardation per unit thickness under polarized light) was unchanged until day 90, although collagen fiber diameters increased during this time.

Animals↗
PubMed1985

Mechanical analysis of hypertrophic scar tissue: structural basis for apparent increased rigidity.

The mechanical behavior of normal human skin and hypertrophic scar tissue (HST) is compared using constant-strain-rate and successive stress-relaxation uniaxial loading programs in vitro. HST is less extensible, requires more energy to be stretched in the physiologic range, and stores strain energy less efficiently than normal skin. The explanations for the differences observed between the mechanical behavior of normal skin and HST are based on the differences in their composition and structure. We suggest that the collagen fiber network is partially "prealigned" in a crimped tendon-like organization in HST, which reduces its extensibility and raises the strain energy required to stretch it. It is further hypothesized that an incomplete elastic fiber network, an abnormal glycosaminoglycan content, and/or abnormal collagen fiber slippage are responsible for the reduced capacity to return strain energy in the hypertrophic scar tissue. The results of these studies indicate that although HST has been described as stiffer than normal skin, the maximum stiffness of skin and HST are similar. The "apparent" increased rigidity of HST is a result of reduced extensibility rather than a change in its stiffness. This inexensibility may manifest itself by limiting joint mobility in the patient with HST.

Adolescent↗
PubMed1985

Collagen deposition during wound repair.

Collagen fiber diameters, amount of birefringent collagen (brightness) and birefringence retardation were measured in implanted collagen-based sponges containing hyaluronic acid (HA) and fibronectin (FN). In the presence of HA and FN, increased number of fibroblasts and brightness were observed 6 days after wounding. Increased brightness in the presence of HA and FN reflected increased deposition of oriented collagen fibers. From days 9 to 12, increased fiber diameters were similar in implanted collagen-based sponges with or without HA and FN. Increased birefringence retardation in sponges containing HA and FN was consistent with increased packing density of collagen fibers observed by scanning electron microscopy. Our results suggest that HA and FN are effective in promoting fibroblast movement into a collagen sponge and deposition of collagen fibers during the early phases of wound healing. Use of a collagen-based sponge containing HA and FN may enhance collagen deposition in situations where healing is compromised as in the case of dermal ulcers.

Animals↗
PubMed1984

Collagen fibrillogenesis in vitro: comparison of types I, II, and III.

The self-assembly of pepsin-extracted types I, II, and III collagen was studied to determine how differences in the triple-helical structure between collagen types influence in vitro collagen fibrillogenesis. Collagen types I, II, and III were extracted and purified from bovine sources, and were studied in solution by laser light scattering, pH titration, and determination of turbidity-time curves. The molecular weights were between 280,000 and 289,000, while the translational diffusion coefficients and particle scattering factors at 175.5 degrees were consistent with those expected for single collagen molecules. Titration of collagen types I, II, and III between pH 7.0 and 2.0 using HCl indicated that type I collagen had the most titratable carboxylic groups with type II and III having significantly fewer titratable groups. The self-assembly of these collagens was studied in vitro in phosphate-buffered saline. The time course and extent of fibril formation were studied turbidimetrically, and were found to be dependent on collagen type. Apparent rate constants were determined for both the lag and growth phases of fibril formation. The rates of both phases were greater for type III than for type I collagen, with the rates for type II collagen being intermediate. The extent of fibril formation was based on the turbidity per unit concentration (specific turbidity) extrapolated to zero concentration (intrinsic turbidity), which was found to be greater for type I than for type III collagen. Type II collagen had the smallest intrinsic turbidity. The specific and intrinsic turbidity values were consistent with the relative fibril diameters seen in dermis and cartilage by transmission electron microscopy. These observations indicate that helix-helix interactions are important in the regulation of the rate and extent of collagen fibrillogenesis and may be involved in the determination of fibril structure.

Animals↗
PubMed1984

On the structure of bovine articular cartilage high density proteoglycans. Isolation of the keratan sulfate and chondroitin sulfate side chains.

The structure of adult bovine articular cartilage high density proteoglycans (PG-I) was studied by degradation with Pronase, chondroitinase ABC, and alkaline borohydride treatments and fractionation and analysis of the products. The keratan sulfate (KS) peptides were rich in glutamic acid, proline, and serine and had a low glycine content. The chondroitin sulfate (CS) peptides had a high content of serine, glycine, and glutamic acid and a much lower proline content than the KS peptides. The data indicate that the KS and CS chains occur in more distinct regions of the protein core(s) than in bovine nasal cartilage PG. After alkaline borohydride treatment there was an almost quantitative conversion of xylose to xylitol and galactosaminitol was the only hexosaminitol detected in KS fractions. The results obtained indicated that the alkali-labile bonds linking the CS and KS chains are the same as those reported to occur in other cartilage PGs. The Mr of the KS chains calculated from the glucosamine and galactosaminitol contents gave values of 6,000-7,000, although gel chromatography and light scattering measurements indicated considerable heterogeneity. The KS and CS chains were quantitatively precipitated by cetylpyridinium chloride and the KS and a portion (15%) of the CS chains were found to be soluble in 1% cetylpyridinium chloride. The abnormal solubility properties of the CS chains in the presence of 1% cetylpyridinium chloride is thought to be due to their low sulfate content. The molecular weight of the remainder of the CS chains, based on the ratio of xylitol to galactosamine, varied from 6,500 to 16,000. The low Mr CS chains were rich in 6-sulfated disaccharides whereas the higher Mr chains had a higher content of 4-sulfated disaccharides. The ratio of galactose to xylitol also varied with Mr. These results indicate similarities in the structure of the adult bovine articular cartilage PG-Is to other cartilage high density PGs. The heterogeneities observed in the composition of the KS and CS chains, and their occurrence in relatively distinct regions of the protein core(s) indicate, however, that there is still much to be learned about the structure of these complex macromolecules.

Amino Acids↗
PubMed1984

Kinetic analysis of collagen fibrillogenesis: II. Corneal and scleral type I collagen.

Fibril formation of neutral salt soluble and pepsin-treated type I collagen from rabbit corneal stroma or sclera was compared using a turbidimetric analysis which permits the determination of apparent rate constants and activation energies for the lag and growth phase of collagen fibrillogenesis. Information regarding the lateral growth of fibrils was obtained from the final turbidity values. Neutral salt soluble corneal collagen had smaller rate constants for both the lag and growth phases of fibrillogenesis than scleral collagen. Pepsin treatment decreased the rate constants for both collagens proportionately. The activation energies were higher for type I collagen from cornea than sclera. Pepsin treatment increased the activation energy for both phases of corneal fibril formation but only the growth phase of scleral collagen fibrillogenesis was affected. The extent of lateral fibril growth was compared using the intrinsic turbidity values which are related to the mass per unit fibril length. Neutral salt soluble scleral type I collagen had a significantly higher intrinsic turbidity than did neutral salt soluble corneal collagen indicating that scleral collagen formed thicker fibrils; however, this difference was not retained after pepsin treatment, demonstrating that a helical-telopeptide interaction occurs in corneal type I collagen which influences fibril diameter. The observed differences in the rate constants, activation energies and intrinsic turbidity values indicates that there are molecular differences which are responsible for fibrillar differences of corneal and scleral type I collagens.

Animals↗
PubMed1984

Fibroblast-collagen sponge interactions and the spatial deposition of newly synthesized collagen fibers in vitro and in vivo.

Fibroblast-collagen sponge interactions were studied in cell culture and dermal wound systems. In both models fibroblasts appear to adhere, attach and orient in the presence of type I collagen fibrils. In the presence of fibronectin, purified from bovine blood, adhesion and alignment of fibroblasts appeared to be enhanced as well as the deposition of thick collagen fibers. When collagen sponges were grafted onto full thickness dermal wounds the granulation tissue that was laid down within the collagen sponge appeared to differ from granulation tissue laid down below the collagen sponge or on similar wounds in the absence of a sponge. In the absence of a collagen sponge the granulation tissue is characterized by wavy collagen fibers that exhibit an extinction pattern characteristic of crimped fibers found in tendon when examined under polarized light. In contrast, collagen fibers laid down within the sponge appear to be highly oriented and lack evidence of crimp. These results suggest that the presence of a collagen matrix acts as a template that allows for the organized spatial deposition of newly synthesized collagen fibers. The enhanced biosynthesis of thick collagen fibers in the presence of a collagen sponge containing fibronectin may decrease the remodeling phase that is associated with dermal scarring.

Animals↗
PubMed1983

A two step model for lateral growth of collagen fibrils.

A two step model of lateral growth of type I collagen fibrils is presented which is an extension of a previous model. Step I of lateral growth involves interactions between pairs of opposite charges which form dipoles perpendicular to the molecular axis and results in removal of loosely bound water between collagen molecules in solution. During step II of lateral aggregation, rearrangement of the inner hydration layer occurs as a result of intermolecular interactions between dipoles parallel to the molecular axis, unpaired charges and hydrophobic residues. It is proposed that differences in fibril diameters between types I, II and III collagen reflect differences in the extent of step II lateral aggregation. Type III collagen which forms thinner fibrils than type I, is shown to have fewer theoretical step II charge-charge interactions consistent with the model that fibril diameters are dependent on secondary lateral growth. Based on this model the fibril forming ability of collagen is in part a result of interactions between dipoles oriented perpendicular to the molecular axis whereas the extent of fibril diameter growth reflects secondary charge-charge and hydrophobic interactions.

Chemical Phenomena↗
PubMed1983

Kinetic analysis of collagen fibrillogenesis: I. Use of turbidity--time data.

A method is presented for analyzing turbidity-time curves characterizing biological assembly and disassembly processes. The method allows for the determination of apparent rate constants for the turbidity lag and growth phases of collagen fibrillogenesis. Plots of concentration/lag time versus concentration for type I collagen and concentration/(time to complete growth phase) versus concentration are shown to be straight lines. The slopes of these plots are defined as the apparent rate constants for the lag and growth phases. Activation energies are obtained from the temperature dependence of these slopes. The slopes of the growth portion of turbidity-time curves as well as the final turbidity are directly proportional to the collagen concentration. These observations are consistent with the hypothesis that the rate limiting steps for both lag and growth phases are apparent first order with respect to collagen concentration. Sample calculations based on light scattering theory suggest that the turbidimetric growth phase begins when the number of collagen molecules per unit length is greater than 100 and that the extent of fibril formation is proportional to the turbidity per unit concentration. These studies indicate that the turbidimetric lag phase involves both linear and lateral growth of collagen linear aggregates.

Animals↗
PubMed1983

Model conformations of the carboxyl telopeptides in vivo based on type I collagen fibral banding patterns.

Densitometric scans of high resolution banding patterns of uranyl acetate-stained, type I collagen fibrils teased from rat tail tendon were correlated with sequence derived model scans. The best model for the alpha 1 carboxyl telopeptide has the first 15 residues in a "S fold" or "random coil" with a net axial displacement of 7 residues (a contracted region) and the last 10 residues extended along the fibril axis. The correlation of both models with experimental scans is significantly improved when two 4D-staggered intermolecular crosslinks are modeled by eliminating four charges in band a3: the two lysines in the alpha 1 carboxyl telopeptides and two hydroxylysines at residues 87 and 88 in the triple helix. The alpha 2 carboxyl telopeptide is modeled as being folded back on the triple helix. Also, as previously found for type I segment long spacing crystallites, the highest correlation of models with the experimental data is obtained when the alpha 2 chain is in the A or reference position of the triple helix (alpha 2, alpha 1, alpha 1). It is further hypothesized that unfolding of the "S fold" or "random coil" in the alpha 1 carboxyl telopeptide may be a reversible mechanism for low strain energy dissipation in tendon and other connective tissues.

Animals↗
PubMed1983

Viscoelastic behavior of human connective tissues: relative contribution of viscous and elastic components.

Stress-relaxation tests were performed at successive strain levels on strips of human aorta, skin, psoas tendon, dura mater, and pericardium. The elastic fraction, the equilibrium force divided by the initial force, was calculated at each strain increment. In the aorta, the elastic fraction decreased with strain and was modeled as the transfer of stress from elastic to collagen fibers, while in skin it increased with strain, probably due to the rearrangement of individual collagen fiber orientations, resulting in an aligned collagen network at high strains. The strain-independent elastic fractions for tendon, dura mater, and pericardium were similar, and approximately equal to the values found for aorta and skin at high strains. It was hypothesized that the elastic fraction is related to the type of fiber loaded, and the tissue geometry. This analysis may be useful in studying disease-induced changes in the mechanical properties of connective tissues.

Aged↗
PubMed1982

Measurements of reducing end groups on bovine vitreous-humour hyaluronic acid by reaction with [14C]cyanide.

Bovine vitreous-humour sodium hyaluronate was purified by precipitation with cetylpyridinium chloride, CsCl-density-gradient sedimentation and gel-permeation chromatography. The number of reducing end groups in two similarly prepared hyaluronate samples was determined by reaction with K14CN, and measurements of intrinsic viscosity were performed to determine whether this reaction caused degradation of the hyaluronate. The intrinsic viscosity of one hyaluronate sample was 192ml/g, compared with a value of 187ml/g after reaction with [14C]cyanide, which indicates that the labelling reaction did not cause depolymerization of the hyaluronate. The Mr calculated from these viscosity values is approx. 60000. Fractionation of the [14C]cyanide-labelled hyaluronate by gel chromatography showed that it was composed of a polydisperse population of molecules with calculated chain lengths, based on the ratio of [14C]cyanide to uronic acid, ranging in molecular weight from 9000 to 264000, with an average Mr of 63200. On the basis of these measurements it is concluded that reaction with [14C]cyanide does not cause degradation of bovine vitreous-humour hyaluronate polysaccharide chains and that reaction with [14C]cyanide can be used to determine the molecular weight of this hyaluronate.

Animals↗
PubMed1982

Type I collagen segment long spacing banding patterns. Evidence that the alpha 2 chain is in the reference or A position.

Densitometric scans of electron micrographs of type I collagen segment long spacing crystallites stained with uranyl acetate or phosphotungstic acid and uranyl acetate have been correlated with computer-synthesized scans derived from the sequence of the alpha 1(I) and alpha 2 chains. Three models that differ in the location of the alpha 2 chain were used in the computer synthesis; Models A, B, and C have the alpha 2 chain in the A, B, and C chain positions, respectively. For all 13 experimental scans, the order of decreasing correlation with the models was found to be A,B,C. The probability of getting the same order of decreasing correlation all 13 times is 6/6(13). It was also determined at the 0.99 confidence level that the mean of the differences in the correlation coefficients among the models is greater than 0, supporting the conclusion that sequence-derived models best fit the experimental data when the alpha 2 chain is in the A position. Our results also agree with recent studies that show that uranyl ions bind to both positively and negatively charged residues on collagen type I.

Animals↗
PubMed1982

A molecular model for linear and lateral growth of type I collagen fibrils.

A model is proposed for Type I collagen fibrillogenesis in which linear and lateral growth are directed by attractive charged pair interactions. It is suggested that linear growth decreases the rate of rotational motion resulting in an increased rate of lateral collisions. The mechanism of linear aggregation involves interactions between sets of unusual charged pairs located at positions 53, 54 and 56 and positions 990 and 992 as well as in the non-helical ends. These charged pairs attract each other electrostatically as well as form a hydrophobic pocket between the molecules. Lateral growth occurs by attractions between D-staggered, charged pairs which alternate between intra- and interchain states. Interchain interactions lead to lateral association of neighboring molecules and formation of a D-staggered unit containing five trimers. Rotational motion of the triple-helical backbone as well as the ability of charged pairs in their interchain state to interact by several different possible combinations between alpha-chains suggest that lateral packing of collagen molecules into fibrils at least in vitro may not need to be specific.

Amino Acid Sequence↗