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Biomedical subjects

M Eastwood

Publications and source records attributed to M Eastwood.

At least 19 recordsLinked to original sources
PubMed2005

Cell proliferation rates in an artificial tissue-engineered environment.

Worldwide, and particularly in Europe, Japan and the USA, cardiovascular disease is a major killer. It can be treated using tissue or organ transplant surgery, but donor organs may be scarce. Tissue engineering is the integration of engineering principles and biology to produce satisfactory synthetic replacement body parts, using viable cells in a suitable matrix, for regenerative medicine. The aim of this study was to measure and compare cell proliferation kinetics after different time intervals of myofibroblasts in a synthetic matrix, thus to be able to deduce the period that a transplanted-cell population can be expected to survive in a tissue-engineered environment. Porcine aortic wall cells were grown in a porous sponge scaffold, that later could be fashioned into aortic or heart valve substitutes. Freshly acquired cells were seeded on identical sponges and were grown under normal culture conditions for a period of 4 weeks. Seeding concentration was a million cells per sponge. Cells progressively populated the sponges, both covering the surface and infiltrating the depth of the matrix, via sponge pores. Samples were taken at 1 week and at 4 weeks, and the rate of cell proliferation was determined by the metaphase arrest technique. Specimens were also taken for light and electron microscopy to determine whether these transplanted cells were capable of synthesizing their own extracellular matrix.

Algorithms↗
PubMed2004

AZD2563, a novel oxazolidinone: definition of antibacterial spectrum, assessment of bactericidal potential and the impact of miscellaneous factors on activity in vitro.

AZD2563, a new oxazolidinone targeted at Gram-positive bacteria, was evaluated and compared with linezolid and other agents against 802 aerobic bacterial isolates for spectrum of activity, bactericidal activity, and the effect of miscellaneous factors upon activity in vitro. At a concentration of 2 mg/L, AZD2563 inhibited 98% of all Gram-positive bacteria tested (100% at 4 mg/L), including susceptible and resistant isolates of Staphylococcus aureus, coagulase-negative staphylococci, Enterococcus spp., Streptococcus pneumoniae, other Streptococcus spp. and Corynebacterium spp. Conversely, all Enterobacteriaceae and non-fermenting Gram-negative bacteria had MICs > 128 mg/L, and only a few Haemophilus or Moraxella spp. had MICs < 8 mg/L. By conventional laboratory definition, AZD2563 and linezolid were bacteriostatic against staphylococci and enterococci, with variable bactericidal activity against Strep. pneumoniae. The in-vitro activity of AZD2563 was essentially unaffected by altering pH, inoculum size, the type of testing medium, or the inclusion of human serum up to 25% v/v.

Bacteria↗
PubMed2003

Heart valve and arterial tissue engineering.

In the industrialized world, cardiovascular disease alone is responsible for almost half of all deaths. Many of the conditions can be treated successfully with surgery, often using transplantation techniques; however, autologous vessels or human-donated organs are in short supply. Tissue engineering aims to create specific, matching grafts by growing cells on appropriate matrices, but there are many steps between the research laboratory and the operating theatre. Neo-tissues must be effective, durable, non-thrombogenic and non-immunogenic. Scaffolds should be bio-compatible, porous (to allow cell/cell communication) and amenable to surgery. In the early days of cardiovascular tissue engineering, autologous or allogenic cells were grown on inert matrices, but patency and thrombogenicity of grafts were disappointing. The current ethos is toward appropriate cell types grown in (most often) a polymeric matrix that degrades at a rate compatible with the cells' production of their own extracellular matrical proteins, thus gradually replacing the graft with a living counterpart. The geometry is crucial. Computer models have been made of valves, and these are used as three-dimensional patterns for mass-production of implant scaffolds. Vessel walls have integral connective tissue architecture, and application of physiological level mechanical forces conditions bio-engineered components to align in precise orientation. This article reviews the concepts involved and successes achieved to date.

Arteries↗
PubMed2001

Identification of a novel stretch-responsive skeletal muscle gene (Smpx).

Skeletal muscle is able to respond to a range of stimuli, including stretch and increased load, by increasing in diameter and length in the absence of myofiber division. This type of cellular growth (hypertrophy) is a highly complex process involving division of muscle precursor cells (myoblasts) and their fusion to existing muscle fibers as well as increased protein synthesis and decreased protein degradation. Underlying the alterations in protein levels are increases in a range of specific mRNAs including those coding for structural proteins and proteins that regulate the hypertrophic process. Seven days of passive stretch in vivo of tibialis anterior (TA) muscle has been shown to elicit muscle hypertrophy. We have identified a cDNA corresponding to an mRNA that exhibits increased expression in response to 7 days of passive stretch imposed on TA muscles in vivo. This 944-bp novel murine transcript is expressed primarily in cardiac and skeletal muscle and to a lesser extent in brain. Translation of the transcript revealed an open reading frame of 85 amino acids encoding a nuclear localization signal and two overlapping casein kinase II phosphorylation sites. This gene has been called "small muscle protein (X chromosome)" (Smpx; HGMW-approved human gene symbol SMPX) and we hypothesize that it plays a role in skeletal muscle hypertrophy.

Amino Acid Sequence↗
PubMed2000

Aortic root characteristics of human pulmonary autografts.

BACKGROUND: After pulmonary autograft replacement of the aortic valve and root, the pulmonary artery (PA) wall is subjected to higher pressures. Concern exists that this may lead to structural and functional changes in the implanted autograft and subsequent aortic root dilatation and neoaortic regurgitation. We therefore assessed root dimensions and neoaortic regurgitation, morphological structure, and mechanical behavior in patients who underwent the Ross operation. METHODS AND RESULTS: Seventy-four patients who were randomized to undergo aortic valve replacement with an aortic homograft or a pulmonary autograft were followed up echocardiographically for up to 4 years and had their aortic root dimensions measured at the level of the annulus, sinuses, and sinotubular junction. In a separate series of 18 patients who underwent pulmonary autograft surgery and 8 normal organ donors, samples from the PA and aorta were analyzed for medial wall thickness, distribution of the staining of collagen and elastin, and elastin fragmentation. Finally, stress-strain curves were obtained from samples of the PA and aorta from 9 patients who underwent pulmonary autograft surgery and from 1 patient in whom a 4-month-old autograft was explanted. No patient in either group had aortic dilatation at any level of >20% or more than mild aortic regurgitation at up to 4 years of follow-up. The aortic media was thicker in both autografts and normal donors (P:<0.01), and there was a trend for the PA media to be thicker in the autograft group. Elastic fiber in all aortas showed little or no variation, whereas in the PA, there was considerable variation in fragmentation. Patients with higher preoperative PA pressures tended to have lower fragmentation scores (chi(2) P:<0.01). The lower stiffness modulus, higher stiffness modulus, and maximum tensile strength of the aorta was 34% to 38% higher than that of the PA (P:<0.01); however, the 4-month-old autograft appeared to show adaptation in mechanical behavior. CONCLUSIONS: In our series of patients, there was no significant progressive dilatation of the aortic root. We demonstrated differences in the anatomic structure and mechanical behavior of the PA in vitro and highlighted histological and mechanical modes of adaptation.

Adolescent↗
PubMed2000

Molecular responses of human dermal fibroblasts to dual cues: contact guidance and mechanical load.

Fibroblast contraction in wound healing involves the interaction of several cell types, cytokines, and extracellular matrix molecules. We have previously developed fibroblast alignment models using precise uniaxial mechanical loads in 3D culture and using contact guidance on fibronectin strands. Our aim here was to use contact guidance to place fibroblasts in their potentially most sensitive configuration, i.e., perpendicular to the axis of loading, to present cells with conflicting guidance cues. Gene expression at the mRNA level of cells recovered from different zones of the 3D collagen gel (with distinct orientation) was determined by quantitative RT-PCR for the matrix proteases MMP1, 2, and 3, and inhibitors TIMP1 and 2. Our results show a 2-, 4-, and 3-fold increase in MMP1, 2, and 3, respectively, in the non-aligned strain zone, relative to the aligned strain zone. These results suggest that cells unable to align to applied loads remodel their matrix far more rapidly than orientated cells. Where fibroblasts were held in an alignment perpendicular to the applied load by contact guidance, the fall in MMP mRNA expression was largely abolished, indicating that these cells remained in a mechano-activated state. The protease inhibitors TIMP1 and 2 were poorly mechano-responsive, further suggesting that changes in MMP expression result in functional matrix remodelling. These results indicate how mechanical loading in tissues may influence matrix remodelling, particularly under conflicting guidance cues.

Cell Adhesion↗
PubMed1998

Effect of precise mechanical loading on fibroblast populated collagen lattices: morphological changes.

The contraction of a collagen lattice by resident fibroblasts causes strains to be developed within that lattice. These strains can be increased or decreased by altering the aspect ratio (ratio of length/width/thickness) of the fibroblast populated collagen lattice, as the cross-sectional area resisting the strain is changed and by the application of an external load. The fibroblasts align themselves with the direction of the maximum principle strain; in effect, these cells are "hiding" from the perceived strain. The direction of the maximum principle strain can be predetermined by the use of a computational finite element analysis. Using the tensioning-Culture Force Monitor to apply pre-determined loading patterns of known repeatable magnitudes, as calculated by the finite element analysis, we have succeeded in aligning fibroblasts into a deliberate predicted orientation. This study has shown that the resident fibroblast population will respond to changes in strain resulting from the most subtle of mechanical loads. This may be an important mechanism in development and repair of connective tissue.

Biomechanical Phenomena↗
PubMed1998

Tensional homeostasis in dermal fibroblasts: mechanical responses to mechanical loading in three-dimensional substrates.

Many soft connective tissues are under endogenous tension, and their resident cells generate considerable contractile forces on the extracellular matrix. The present work was aimed to determine quantitatively how fibroblasts, grown within three-dimensional collagen lattices, respond mechanically to precisely defined tensional loads. Forces generated in response to changes in applied load were measured using a tensional culture force monitor. In a number of variant systems, resident cells consistently reacted to modify the endogenous matrix tension in the opposite direction to externally applied loads. That is, increased external loading was followed immediately by a reduction in cell-mediated contraction whilst decreased external loading elicited increased contraction. Responses were cell-mediated and not a result of material properties of the matrices. This is the first detailed characterisation of a tensional homeostatic response in cells. The maintained force, after 8 h in culture, was typically around 40-60 dynes/million cells). Maintenance of an active tensional homeostasis has widespread implications for cells in culture and for whole tissue function.

Cells, Cultured↗
PubMed1998

Fibroblast responses to mechanical forces.

The repair and maintenance of connective tissues is performed predominately by a mesenchymal cell known as a fibroblast. The activity of this cell is regulated, in part, by changes in the mechanical environment in which it resides. The authors have addressed some of the questions related to the fibroblast and how it responds to mechanical stimulation. An in vitro model, the 'culture force monitor', and its derivative, the tensioning culture force monitor have been developed enabling quantitative investigations to be performed on fibroblasts in a collagen lattice. Results have shown that a fibroblast can generate a force of approximately 10(-10) N, as a result of change in cell shape and attachment, while in a three-dimensional collagen lattice. Application of a physiologically similar mechanical load has shown that fibroblasts have the ability to maintain a tensional homeostasis of approximately 40-60 x 10(-5) N per million cells, change cellular morphology in a predictable manner and biochemically modify their resident environment.

Animals↗
PubMed1997

Hospital food.

Explore the source record for details and available documents.

Eating↗
PubMed1997

The effect of burn blister fluid on fibroblast contraction.

Burns of the hand seem to be followed by more stiffness and contractures than other injuries. This study was aimed at examining whether burn exudate contributes to this difference. Five cell strains of human dermal fibroblasts were each treated with three samples of burn blister fluid and the effect compared with the rate of contraction of free floating fibroblast populated collagen lattices (FPCL). In addition, the response of fibroblasts from the dermis, fascia and peritendinous sheath of the hand to burn fluid were compared both in FPCLs and by the tensile forces they generated in the culture force monitor. Results of this study consistently show that the addition of burn fluid to culture medium stimulates fibroblasts to contract to a greater degree in the first 24-48 h. It is proposed that the presence of burn blister fluid provides materials which promote contraction. This in turn may contribute to the postburn stiffness seen clinically.

Adolescent↗
PubMed1997

Phenytoin reduces the contraction of recessive dystrophic epidermolysis bullosa fibroblast populated collagen gels.

Recessive dystrophic epidermolysis bullosa (RDEB) is a group of genetic disorders in which blistering occurs below the basement membrane, in many cases resulting in extensive scar formation, contractures and mitten deformities. Our aim was to compare quantitatively the contraction forces generated by normal and RDEB fibroblats and to investigate the effect of Phenytoin (5,5-diphenyl-2,4-imidazolidinedione, sodium salt; PHT). PHT is an anticonvulsant agent, that causes fibrosis as a side effect. This study utilised conventional untethered fibroblast populated collagen lattice contraction and a quantitative force measurement instrument, the culture force monitor (CFM). The RDEB cell lines were hypercontractile, generating 2.5 times the force of normal fibroblasts, though they appeared morphologically normal. In untethered collagen gels PHT (20 micrograms/ml) significantly reduced contraction of both normal and RDEB fibroblasts over 7 days. Pre-treatment of RDEB cells for 5 days also produced a 40% reduction in contraction as measured in the CFM. One suggested mechanism of PHT action is through inhibition of matrix metalloproteinase activity, but the similar effects of PHT and Colchicine (an inhibitor of microtubule polymerisation) in the CFM, indicate that it may act on contraction through disruption of microfilaments and changes to cell shape. These findings show that isolated RDEB fibroblasts retain the hypercontractile features of many of the patient's lesion sites and imply that local application of PHT may have a therapeutic effect in controlling contraction.

Biomechanical Phenomena↗
PubMed1996

Quantitative analysis of collagen gel contractile forces generated by dermal fibroblasts and the relationship to cell morphology.

The force generated in granulation tissue during wound contraction is thought to be cell mediated; however, it is unclear whether contractile forces are generated by fibroblast locomotion or contraction of myofibroblasts. To help clarify this question the force of this contraction can now be determined accurately in a human dermal fibroblast collagen lattice system using a novel instrument known as a Culture Force Monitor. Three distinct phases of contraction of such collagen gels could be identified over the first 24 hours. Most of the force generated by human dermal fibroblasts was produced during the first stage in parallel with cell attachment and associated changes in cell shape, and the appearance of cell processes. During this initial 24 hours no evidence could be found for the presence of myofibroblasts, but stereoscopic and electron microscopic analysis at a range of time points indicated that migratory fibroblasts were present in the system. Comparison of the contraction profiles of cells extracted from other tissues (tendon and articular cartilage), and extracted by different means from the same tissue specimen, indicated that different populations of fibroblasts can be distinguished on the basis of their pattern of contractions. It would seem that most of the force generated in this model is a result of fibroblast attachment and movement within the collagen lattice. Furthermore, different groups of fibroblasts, even within the same tissue, may vary in their contraction (hence locomotory) activity.

Animals↗
PubMed1996

Balanced mechanical forces and microtubule contribution to fibroblast contraction.

Fibroblast locomotion is thought to generate tractional forces which lead to contraction and reorganisation of collagen in tissue development and repair. A culture force monitor device (CFM) was used to measure changes in force in fibroblast populated collagen lattices, which resulted from cytoskeletal reorganisation by cytochalasin B, colchicine, vinblastine, and taxol. Microfilament disruption abolished contraction forces, microtubule disruption elicited a new peak of contraction, while taxol stabilisation of microtubules produced a gradual fall in measured force across the collagen gel. Based on these measurements, it is suggested that the cell can be viewed as an engineering structure in which residual intracellular forces, from contractile microfilaments, exert compressive loading on microtubular elements. This microtubular structure appears to act as a "balanced space frame" (analogous to an aeroplane chassis), maintaining cell shape and consequently storing a residual internal tension (RIT). In dermal fibroblasts this hidden RIT was up to 33% of the measurable force exerted on the collagen gel. Phenotypic differences between space frame organisation and RIT levels could explain site and pathological variations in fibroblast contraction.

Actin Cytoskeleton↗
PubMed1996

An association between maternal diet and colonic diverticulosis in an animal model.

BACKGROUND/AIMS: Maternal diet may have an effect on the health of the offspring in middle and later life. This study used the laboratory rat as an animal model to examine whether the fibre content of the maternal diet during pregnancy affected subsequent development of colonic diverticula in the offspring fed lifelong fibre deficient or higher fibre diets. METHODS: The parents of experimental animals were fed either a diet that was known to predispose to colonic diverticulosis or a control diet for one month prior to mating. The offspring were fed one of these diets for 18 months. The incidence of colonic diverticulosis, submucosal collagen content, collagen solubility in weak acid, and the composition of intestinal contents were then measured. RESULTS: Offspring of rats fed a higher fibre diet from higher fibre diet fed parents had 0% incidence of colonic diverticulosis. When offspring (regardless of parental diet) were fed a low fibre diet for life the acid solubility was lowered compared with rats fed lifelong higher fibre diet mean (SD) (0.044 (0.0007) v 0.073 (0.0015) sigmoid colon (ratio of soluble:insoluble collagen)); 21.1% had diverticulosis and there was reduced fibre fermentation. However, when the diet of the parents of the fibre deficient diet fed rats was considered, the animals whose mothers had a fibre deficient diet had lower acid solubility (0.032 (0.0007)) and an increased incidence of colonic diverticulosis (42.1%) than the animals fed a fibre deficient diet from higher fibre diet fed parents (p < 0.01 in all instances). CONCLUSION: Maternal diet and the subsequent nutrition of the progeny seem to be of importance in the development of colonic diverticulosis in the rat.

Animals↗
PubMed1994

A culture force monitor for measurement of contraction forces generated in human dermal fibroblast cultures: evidence for cell-matrix mechanical signalling.

Non-contractile cells are able to exert 'tensional' forces on collagen substrate. Although such forces have been implicated in contraction during tissue repair their importance and mechanism of action are difficult to assess without quantitative data. Currently, the most widely used model is not a direct measure of force and has serious deficiencies as a model of wound contraction. A Culture Force Monitor, CFM, has been developed in this study, to measure directly the forces generated by fibroblasts and other cell types in culture. Under model conditions, a peak force of 1 x 10(-10) Newton/cell was generated (assuming participation of all cells) over a range of cell densities. Contraction of a collagen gel over 2 days was in 3 phases; initial contraction, linear increase and equilibrium. The final, maximum force was produced at the equilibrium phase (24 h) and balanced the restraining force of the CFM. Cell force responses during the initial and linear phases (corresponding to cell attachment) indicated that contraction of the cells responded in a rapid and subtle manner to changes in the mechanical properties of their substrate.

Cells, Cultured↗