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

Topical phenytoin effects on palatal wound healing

BACKGROUND

The clinical benefits of autogenous soft tissue grafts are countered by donor site morbidity. The aim of this prospective split-mouth clinical trial is to assess clinical, histological and patient outcomes following topical phenytoin (PHT) treatment of experimental palatal wounds.

METHODS

Systemically healthy adults were recruited. One 6 mm diameter wound (posterior) and one 4 mm diameter wound (anterior), each 1-1.5 mm deep, were created on both sides of the palate. Wounds on one randomly chosen side received 10% phenytoin USP and contralateral wounds received carrier alone. Biopsies were harvested from anterior wounds (Day 1 or Day 5) and were routinely processed for histology. Posterior wounds were left undisturbed to clinically evaluate healing (using photographs and Healing Score Index) on Days 1, 5, 14, and 21. Questionnaires were used to assess patient-centered outcomes. Data analysis was performed using generalized logistic and generalized linear mixed models.

RESULTS

Twenty participants completed all visits. 30% of participants reported more pain on control side than the PHT side at Day 1 (P = 0.014). PHT treated sites were more likely to not exhibit swelling (OR = 9.35; P = 0.009) and to not experience pain on palpation (OR = 6.278; P = 0.007). PHT significantly and time-dependently affected granulation tissue appearance (P = 0.004). Histologically, there were no significant differences between control and PHT, at any time point (P ≥ 0.853).

CONCLUSIONS

The results of the present study, the first one to report on topical PHT as palatal wound treatment, suggest that PHT application on palatal wounds could result in improved healing outcomes.

A model for one-dimensional morphoelasticity and its application to fibroblast-populated collagen lattices

The mechanical behaviour of solid biological tissues has long been described using models based on classical continuum mechanics. However, the classical continuum theories of elasticity and viscoelasticity cannot easily capture the continual remodelling and associated structural changes in biological tissues. Furthermore, models drawn from plasticity theory are difficult to apply and interpret in this context, where there is no equivalent of a yield stress or flow rule. In this work, we describe a novel one-dimensional mathematical model of tissue remodelling based on the multiplicative decomposition of the deformation gradient. We express the mechanical effects of remodelling as an evolution equation for the effective strain, a measure of the difference between the current state and a hypothetical mechanically relaxed state of the tissue. This morphoelastic model combines the simplicity and interpretability of classical viscoelastic models with the versatility of plasticity theory. A novel feature of our model is that while most models describe growth as a continuous quantity, here we begin with discrete cells and develop a continuum representation of lattice remodelling based on an appropriate limit of the behaviour of discrete cells. To demonstrate the utility of our approach, we use this framework to capture qualitative aspects of the continual remodelling observed in fibroblast-populated collagen lattices, in particular its contraction and its subsequent sudden re-expansion when remodelling is interrupted.

Assessment of the effect of phenytoin on cutaneous healing from excision of melanocytic nevi on the face and on the back

BACKGROUND

Topical phenytoin is a powerful skin wounds healing and it may be useful in clinical practice. The purpose of this study was to evaluate the effect of topical phenytoin 0.5%, by comparing it with cream (control) in wounds resulting from excision of two melanocytic nevi in the same patient. Our purpose was also to assess if phenytoin had better therapeutic and cosmetic outcomes when compared with cream (control).

METHODS

This study evaluated 100 patients with skin wounds from excision of melanocytic nevi. 50 patients with lesions on the face and 50 patients with lesions on the back, totalizing 200 lesions excised with modified punch. The resulting superficial skin wounds had the same diameter and depth, and second intention healing followed.Patients were followed for 60 days. Student's t-test, Mann Whitney nonparametric test, analysis of variance, LSD test, Shapiro-Wilks test and Fisher test were used to analyze the results, depending on the nature of the variables being studied.

RESULTS

Phenytoin showed better therapeutic and cosmetic results, by healing faster, with more intense epithelization in wounds in comparison with cream (control). Phenytoin showed a statistically significant difference regarding the following parameters (p < 0.05): wounded area and healing time. Phenytoin application resulted in a smaller area and a shorter healing time. Also the intensity of exudates, bleeding, and the epithelization were more intense in phenytoin-treated wounds. Regarding the shape and thickness of the scar, injuries treated with phenytoin had round and flat shaped scars in most of the cases. Considering patient's gender and phototype, female patients presented smaller wounds and scar areas; and phototype I had the largest scar areas. Contact eczema was an adverse reaction in 7 injuries located on the back caused by cream (control) and hypoallergenic tape.

CONCLUSIONS

Phenytoin showed better therapeutic and cosmetic results compared with cream (control). Phenytoin is a low cost drug, which accelerates skin wounds healing in human patients.

TRIAL REGISTRATION

ISRCTN96539803.

Cell contraction forces in scaffolds with varying pore size and cell density

The contractile behavior of cells is relevant in understanding wound healing and scar formation. In tissue engineering, inhibition of the cell contractile response is critical for the regeneration of physiologically normal tissue rather than scar tissue. Previous studies have measured the contractile response of cells in a variety of conditions (e.g. on two-dimensional solid substrates, on free-floating tissue engineering scaffolds and on scaffolds under some constraint in a cell force monitor). Tissue engineering scaffolds behave mechanically like open-cell elastomeric foams: between strains of about 10 and 90%, cells progressively buckle struts in the scaffold. The contractile force required for an individual cell to buckle a strut within a scaffold has been estimated based on the strut dimensions (radius, r, and length, l) and the strut modulus, E(s). Since the buckling force varies, according to Euler's law, with r(4)/l(2), and the relative density of the scaffold varies as (r/l)(2), the cell contractile force associated with strut buckling is expected to vary with the square of the pore size for scaffolds of constant relative density. As the cell density increases, the force per cell to achieve a given strain in the scaffold is expected to decrease. Here we model the contractile response of fibroblasts by analyzing the response of a single tetrakaidecahedron to forces applied to individual struts (simulating cell contractile forces) using finite element analysis. We model tetrakaidecahedra of different strut lengths, corresponding to different scaffold pore sizes, and of varying numbers of loaded struts, corresponding to varying cell densities. We compare our numerical model with the results of free-floating contraction experiments of normal human dermal fibroblasts (NHDF) in collagen-GAG scaffolds of varying pore size and with varying cell densities.

Complex dependence of substrate stiffness and serum concentration on cell-force generation

Collagen is a widely used biomaterial in tissue engineering. Mechanical stimulation of cell-seeded collagen constructs and its effects on cell orientation, intracellular signaling, and molecular responses have been reported. Our aim was to study the transfer of applied mechanical load to resident cells in 3D collagen constructs. Stainless steel markers were embedded in constructs as reporters of micromovement and uniaxial (0-15%) strain was applied. Cell-seeded collagen constructs were also subjected to (0-15%) uniaxial strain and material responses recorded. The viscoelastic properties of collagen resulted in comparatively small movement of the marker bars relative to gel deformation. Cell seeding density of 1 million/mL had no significant effect on the viscoelastic properties of collagen for the range of strain tested. Our findings indicate that viscoelastic properties of collagen result in minimal force transfer of applied loads as recorded by movement of stainless steel markers. At higher strain rates as collagen got stiffer the movement decreased. These findings indicate that as cell-seeded collagen constructs mature in a bioreactor and become stiffer due to ECM production/deposition, mechanical stimulation will have to be tailored over time to account for increased stiffness of constructs in vitro to elicit predictable and consistent cellular responses.

The origins and regulation of tissue tension: identification of collagen tension-fixation process in vitro

The absence of a controllable in vitro model of soft tissue remodeling is a major impediment, limiting our understanding of collagen pathologies, tissue repair and engineering. Using 3D fibroblast-collagen lattice model, we have quantified changes in matrix tension and material properties following remodeling by blockade of cell-generated tension with cytochalasin D. This demonstrated a time-dependent shortening of the collagen network, progressively stabilized into a built-in tension within the matrix. This was differentially enhanced by TGFB1 and mechanical loading to give subtle control of the new, remodeled matrix material properties. Through this model, we have been able to identify the 'tension remodeling' process, by which cells control material properties in response to environmental factors.

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.

3-D in vitro model of early skeletal muscle development

An understanding of the mechanical and mechano-molecular responses that occur during the differentiation of mouse C2C12 [corrected] myoblasts in 3-D culture is critical for understanding growth, which is important for progress towards producing a tissue-engineered muscle construct. We have established the main differences in force generation between skeletal myoblasts, dermal fibroblasts, and smooth muscle cells in a 3-D culture model in which cells contract a collagen gel construct. This model was developed to provide a reproducible 3-D muscle organoid in which differences in force generation could be measured, as the skeletal myoblasts fused to form myotubes within a collagen gel. Maintenance of the 3-D culture under sustained uni-axial tension, was found to promote fusion of myoblasts to form aligned multi-nucleate myotubes. Gene expression of both Insulin Like Growth Factor (IGF-1 Ea) and an isoform of IGF-1 Ea, Mechano-growth factor (IGF-1 Eb, also termed MGF), was monitored in this differentiating collagen construct over the time course of fusion and maturation (0-7 days). This identified a transient surge in both IGF-1 and MGF expression on day 3 of the developing construct. This peak of IGF-1 and MGF expression, just prior to differentiation, was consistent with the idea that IGF-1 stimulates differentiation through a Myogenin pathway [Florini et al., 1991: Mol. Endocrinol. 5:718-724]. MGF gene expression was increased 77-fold on day 3, compared to a 36-fold increase with IGF-1 on day 3. This indicates an important role for MGF in either differentiation or, more likely, a response to mechanical or tensional cues.

[Surgical treatment of hand deformities in hereditary dystrophic bullous epidermolysis]

In the period 1996-2001 in the Clinic for Plastic Surgery and Burns of the Military Medical Academy, 18 patients. 12 male and 6 female, with hereditary dystrophic epidermolysis bullosa (HDEB) and hand deformities were surgically treated, to achieve the complete separation of fingers, correction of the thumb adduction contracture and flexion or extension contracture of finger joints. The period of wound healing on flat surfaces after surgery, and the period between two operations was estimated. The most common deformity was the flexion contractures of metacarpophalangeal (MP) joints (45%) and one or both interphalangeal (IP) joints (types A1, A2). In 20% of the hands MP joint was stretched with the flexion contracture in distal interphalangeal (DIP) or both IP joints (types B1, B2). In 35% of hands MP joint was in hyperextension with folded proximal interphalangeal (PIP) or both IP joints (C1 i C2). The adduction deformity of the thumb type 1, without the possibility of abduction, was present in 15%, type 2, when the thumb was placed above the palm in 60% and type 3, when the thumb was fused in the palm in 25%. Pseudosyndactyly of the first degree (till PIP joint) was found in 30% of hands, the second degree (till DIP joint) in 25%, and the third degree (the whole finger length) in 45% of hands. Fingers were completely separated and stretched surgically. The period of spontaneous healing was 15 days on the average. EBDC represents great medical and social problem that requires multidisciplinary approach of physicians of various specialties (surgeons, dermatologists, pediatrists, geneticists, nutritionists, physiatrists, ophthalmologists, dentists, ENT, as well as specially trained persons and families). The efficient specific systemic therapy aiming to increase the skin resistance to mechanical trauma does not exist yet, and should be developed in the field of gene therapy. The surgical correction of hand deformities, acrylate glove use in the longer post operative period combined with physiotherapy, the active use of hands, the protection of injuries and skin care are the measures which prolong the period between the recurrence of contractures.

Evidence for sequential utilization of fibronectin, vitronectin, and collagen during fibroblast-mediated collagen contraction

Contraction plays a major role in wound healing and is inevitably mediated through the mechanical interaction of fibroblast cytoskeleton and integrins with their extracellular matrix ligands. Cell-matrix attachment is critical for such events. In human dermal fibroblasts most such interactions are mediated by the beta1-type integrins. This study investigated the role played by key components in this system, notably fibronectin, vitronectin, and integrin subcomponents alpha2 and alpha5, which recognize collagen and fibronectin. Inhibition of adhesion through these ligands was studied either by antibody blocking or with fibronectin and/or vitronectin depletion. Functional effects of inhibition were monitored as force generation in collagen-glycosaminoglycan (IntegraTM) sponges, over 20 hours using a culture force monitor. Dose and time-course inhibition studies indicated that initial attachment and force generation (approx. 0-5 hours postseeding) was through fibronectin receptors and this was followed by vitronectin ligand and receptor utilization (4 hours onward). Utilization of the collagen integrin subcomponent alpha2 appeared to be increasingly important between 6 and 16 hours and dominant thereafter. Additionally, there was evidence for functional interdependence between the three ligand systems fibronectin, vitronectin, and collagen. We propose that there is a short cascade of sequential integrin-ligand interactions as cells attach to, extend through, and eventually contract their matrix. (WOUND REP REG 2002;10:-408)

Contraction-mediated pinocytosis of RGD-peptide by dermal fibroblasts: inhibition of matrix attachment blocks contraction and disrupts microfilament organisation

Force generation in collagen and matrix contraction are basic functions of fibroblasts and important elements of tissue repair. Cell-matrix attachment is critical to this contraction, involving RGD-binding integrins. We have investigated how this process operates, in terms of force generation (in the Culture Force Monitor) and cytoskeletal structure, using a synthetic RGD-decapeptide. The RGD-peptide blocked force generation over the first 6 h, followed by near complete recovery by 20 h. However, dose response was complex indicating multiple processes were operating. Analysis of cytoskeletal structure after treatment with RGD-peptide indicated major disruption with condensed aggregates of actin and microtubular fragmentation. Fluorescent labeling and tracking of the RGD-peptide demonstrated intracellular uptake into discrete cytoplasmic aggregates. Critically, these RGD-peptide pools co-localised with the condensed actin microfilament aggregates. It is concluded that RGD-peptide uptake was by a form of contraction-mediated pinocytosis, resulting from mechanical tension applied to the untethered RGD-peptide-integrin, as contractile microfilament were assembled. These findings emphasize the importance of sound mechanical attachment of ligand-occupied integrins (e.g., to extracellular matrix) for normal cytoskeletal function. Conversely, this aspect of unrestrained cytoskeletal contraction may have important pathogenic and therapeutic applications.

Tissue engineering of biological cardiovascular system surrogates

Cardiovascular diseases are common in ageing communities globally. This fact is most striking in the industrialised world where the aged population makes up a large proportion of society. Elderly patients are frequently treated surgically with grafts to replace damaged tissues and vessels. The number of human-donated components is insufficient and synthetic surrogates are sought. These might be wholly mechanical, wholly biological, or tissue engineered complexes of cells and their products growing in a scaffold. At present, many such composites exist with potential for use as substitutes for specific blood vessels. The challenges of producing tissue engineered heart valves are now being widely explored. Neotissues must provide an effective, durable, non-thrombogenic and non-immunogenic substitute that will fulfil the purpose of the natural tissue. The aims and scope of this paper are to review current and novel concepts in the field of tissue engineering of biological cardiovascular system surrogates. Mechanical stresses and strains on cardiovascular cells in vitro have been recognised and can be measured by a culture force monitor. Physiological stresses can be generated by a tensioning culture force monitor and applied to engineered tissue, aligning the cells and mimicking arterial wall architecture. The hydrostatic forces a vessel experiences and mechanical parameters of blood vessels can be studied in the tubular culture system of a multi-cue bioreactor.