Fibrin and wound healing

Activated platelets increase fibrinolysis of mesenchymal progenitor cells

Bone regeneration is initiated by the formation of a blood clot. Activated platelets within this fibrin-rich matrix release signaling molecules that can attract mesenchymal progenitor cells. To gain insight into the cellular mechanism by which activated platelets can support the immigration of mesenchymal progenitors, we have tested the hypothesis that platelet-released signaling molecules increase the capacity of bone marrow stromal cells (BMSC) to activate plasminogen. We report herein that platelet-released supernatants (PRS) elevate total urokinase-type plasminogen activator (uPA) and total plasminogen activator inhibitor-1 (PAI-1) levels in BMSC, as assessed by immunoassay. Quantitative polymerase chain reaction showed an upregulation of uPA, uPA receptor, and PAI-1. Zymography and kinetic analysis based on casein hydrolysis revealed enhanced activity of cell-associated uPA upon exposure of BMSC to PRS. Inhibiting c-Jun N-terminal kinase (JNK) and phosphatidylinositol 3-kinase (PI3K) signaling reduced uPA production and decreased plasminogen activation. Corresponding Western blot analysis showed increased phosphorylation of JNK and AKT in BMSC treated with PRS. These results suggest that activated platelets can enhance the plasminogen activation capacity of mesenchymal progenitors through the stimulation of uPA production, requiring JNK and PI3K/AKT signaling. By this mechanism platelets may contribute to the organization of the blood clot during bone regeneration.

Single and combined effects of alphavbeta3- and alpha5beta1-integrins on capillary tube formation in a human fibrinous matrix

The fibrinous exudate of a wound or tumor stroma facilitates angiogenesis. We studied the involvement of RGD-binding integrins during tube formation in human plasma-derived fibrin clots and human purified fibrin matrices. Capillary-like tube formation by human microvascular endothelial cells in a 3D plasma-derived fibrinous matrix was induced by FGF-2 and TNF-α and depended largely on cell-bound u-PA and plasmin activities. While tube formation was minimally affected by the addition of either the αvβ3-integrin inhibiting mAb LM609 or the α5-integrin inhibiting mAb IIA1, the general RGD-antagonist echistatin completely inhibited this process. Remarkably, when αvβ3- and α5β1-integrins were inhibited simultaneously, tube formation was reduced by 78%. It was accompanied by a 44% reduction of u-PA antigen accumulation and 41% less production of fibrin degradation products. αvβ5-integrin-blocking antibodies further enhanced the inhibition by mAb LM609 and mAb IIA1 to 94%, but had no effect by themselves. αv-specific cRGD only inhibited angiogenesis when α5β1-integrin was simultaneously blocked. Endostatin mimicked the effect of α5β1-integrin and inhibited tube formation only in the presence of LM609 or cRGD (73 and 80%, respectively). Comparable results were obtained when purified fibrin matrices were used instead of the plasma-derived fibrinous matrices. These data show that blocking of tube formation in a fibrinous exudate requires the simultaneous inhibition of αvβ3- and α5β1-integrins. This may bear impact on attempts to influence angiogenesis in a fibrinous environment.

Slow release of growth factors and thrombospondin-1 in Choukroun's platelet-rich fibrin (PRF): a gold standard to achieve for all surgical platelet concentrates technologies

Platelet concentrates for surgical topical applications are nowadays often used, but quantification of the long-term growth factor release from these preparations in most cases is impossible. Indeed, in most protocols, platelets are massively activated and there is no significant fibrin matrix to support growth factor release and cell migration. Choukroun's platelet-rich fibrin (PRF), a second generation platelet concentrate, is a leucocyte- and platelet-rich fibrin biomaterial. Here, we show that this dense fibrin membrane releases high quantities of three main growth factors (Transforming Growth Factor b-1 (TGFbeta-1), platelet derived growth factor AB, PDGF-AB; vascular endothelial growth factor, VEGF) and an important coagulation matricellular glycoprotein (thrombospondin-1, TSP-1) during 7 days. Moreover, the comparison between the final released amounts and the initial content of the membrane (after forcible extraction) allows us to consider that the leucocytes trapped in the fibrin matrix continue to produce high quantities of TGFbeta-1 and VEGF during the whole experimental time.

Potential cellular and molecular causes of hypertrophic scar formation

A scar is an expected result of wound healing. However, in some individuals, and particularly in burn victims, the wound healing processes may lead to a fibrotic hypertrophic scar, which is raised, red, inflexible and responsible for serious functional and cosmetic problems. It seems that a wide array of subsequent processes are involved in hypertrophic scar formation, like an affected haemostasis, exaggerated inflammation, prolonged reepithelialization, overabundant extracellular matrix production, augmented neovascularization, atypical extracellular matrix remodeling and reduced apoptosis. Platelets, macrophages, T-lymphocytes, mast cells, Langerhans cells and keratinocytes are directly and indirectly involved in the activation of fibroblasts, which in turn produce excess extracellular matrix. Following the chronology of normal wound healing, we unravel, clarify and reorganize the complex molecular and cellular key processes that may be responsible for hypertrophic scars. It remains unclear whether these processes are a cause or a consequence of unusual scar tissue formation, but raising evidence exists that immunological responses early following wounding play an important role. Therefore, when developing preventive treatment modalities, one should aim to put the early affected wound healing processes back on track as quickly as possible.

Ultrastructural localization of integrin subunits beta4 and alpha3 within the migrating epithelial tongue of in vivo human wounds

Subsequent to wounding, keratinocytes must quickly restore barrier function. In vitro wound models have served to elucidate mechanisms of epithelial closure and key roles for integrins alpha6beta4 and alpha3beta1. To extrapolate in vitro data to in vivo human tissues, we used ultrathin cryomicrotomy to simultaneously observe tissue ultrastructure and immunogold localization in unwounded skin and acute human cutaneous wounds. Localization of the beta4 integrin subunit in unwounded skin shows dominant hemidesmosomal association and minor basal keratinocyte lateral filopodic cell-cell expression. After wounding, beta4 dominantly localized to cytokeratin-rich regions (trailing edge hemidesmosomes) and minor association with lamellipodia (leading edge). beta4 colocalizes with alpha3 within filopodia juxtaposed to wound matrix, and increased concentrations of beta4 were found in cytoplasmic vesicles within basal keratinocytes of the migrating tongue. alpha3 integrin subunit dominantly localized to filopodia within basal keratinocyte lateral cell-cell interfaces in unwounded skin and both cell-cell and cell-matrix filopodic interactions in wounded skin. This study indicates that beta4 interacts with the extracellular environment through both stable and transient interactions and may be managed through a different endosomal trafficking pathway than alpha3. alpha3 integrin, despite its ability to respond to alternate ligands after wounding, does so through a single structure, the filopodia.

Nanoscale variation of bioadhesive substrates as a tool for engineering of cell matrix assembly

Although molecular and physical mechanisms of fibroblast matrix assembly have been widely investigated, the role of adhesive ligand presentation on matrix assembly has only been recently probed (Pereira et al. Tissue Eng., 2007). In the present study, various-sized albumin-derived nanocarriers (ANCs) were fabricated as nanoscale organization units for functionalization with the cell adhesion domain of fibronectin. The adhesion, morphology, and matrix assembly of human dermal fibroblasts were compared on substrate-deposited, ligand-ANCs of varying size. At early time points, fibroblast attachment, stress fiber formation, and spreading were higher on functionalized, larger-sized carriers than on smaller carriers. Matrix assembly was greatest at the highest ligand density on larger nanocarriers but was undetectable at the same ligand density on smaller carriers. Tracking of fluorophore-encapsulated ANCs showed that larger carriers were displaced less than smaller carriers and that atomic force microscopy of ligand-ANCs binding to adherent cells demonstrated that the larger ligand-ANCs required larger dissociation forces. Taken together, these data suggest that the greater inertia of larger adhesive nanocarriers may generate more cellular tension, which in turn, promotes up-regulation of matrix assembly. Thus, the size of the nanocarrier and the density of ligand on that nanocarrier combine to dictate the early kinetics of fibroblast matrix assembly. These insights may be useful for understanding cell-matrix interactions, as well as for development of bioactive materials with defined cell-adhesive activities such as wound repair and matrix remodeling events.

A comparative study of tissue glue and vicryl suture for conjunctival and scleral closure in conventional 20-gauge vitrectomy

AIM

To describe the use of tissue glue to close scleral and conjunctival wounds, and to compare the clinical outcomes using tissue glue and vicryl suture for closing these areas in conventional 20-gauge (G) vitrectomy.

METHODS

Thirty eyes of 30 patients were included in this study. The indications for vitreoretinal surgery were diabetic vitreous haemorrhage with severe vitreoretinal traction in 10 eyes, retinal detachment and proliferative vitreoretinopathy in 14 eyes, and vitreous opacity in 6 eyes. Tissue glue (Tisseel, Baxter AG Industries, Vienna, Austria) was used to attach scleral and conjunctival wounds in 15 eyes and vicryl sutures in 15 eyes. The patients were allotted into two subgroups as tissue glue group (TG) and vicryl suture group (VG). The sclerotomy sites were evaluated with ultrasound biomicroscopy (UBM) postoperatively in TG. Follow-up period was 2 months. The groups were statistically compared for ocular signs and symptoms by Mann-Whitney U-test.

RESULTS

No scleral wound leakage and conjunctival reattachment were observed at the end of the surgical procedure and during the follow-up period. No adverse effects were seen in TG. Abnormal fibrous ingrowth was not detected at the sclerotomy sites by means of UBM in TG. Patient comfort was significantly higher in TG than VG (P<0.05).

CONCLUSIONS

Tissue glue has no adverse effects on ocular tissue and can be used as a substitute for suture materials, and the use of tissue glue decreases patient symptoms during the postoperative period after 20-G vitrectomy. Tissue glue can enable to perform sutureless surgery in the conventional 20-G vitrectomy.

Chemokines and diabetic wound healing

Chemokines are critical for white blood cell recruitment to injured tissues and play an important role in normal wound healing processes. In contrast, impaired wound healing in diabetic patients is accompanied by decreased early inflammatory cell infiltration but persistence of neutrophils and macrophages in the chronic, nonhealing wounds. These changes in inflammatory cell recruitment occur in conjunction with alterations in chemokine and growth factor expression. In addition to leukocyte trafficking, many different cell types, including endothelial cells, fibroblasts, and keratinocytes, produce and respond to chemokines, and these interactions are altered in diabetic wounds. Thus, the chemokine system may have both direct and inflammatory-mediated effects on many different aspects of diabetic wound healing. The potential roles of chemokines and inflammatory or immune cells in nonhealing diabetic wounds, including impairments in growth factor expression, angiogenesis, extracellular matrix formation, and reepithelialization, are examined.

The use of therapeutic gene eNOS delivered via a fibrin scaffold enhances wound healing in a compromised wound model

Diabetic healing is marked by a reduced nitric oxide (NO) production at the wound site. This study aimed to investigate whether a fibrin scaffold would enhance the delivery of adenovirus encoding endothelial nitric oxide synthase (eNOS), one of the enzymes responsible for NO production, resulting in more NO production, and enhanced healing. An alloxan rabbit ear ulcer model was used to investigate healing, in response to the following treatments: fibrin containing AdeNOS, AdeNOS alone, fibrin alone and no treatment. Immunohistochemistry to detect eNOS expression and histological evaluation of healing were assessed at 7 and 14 days. eNOS expression was significantly greater in the fibrin containing AdeNOS group at 14 days compared to all other groups. Furthermore, this group showed a significantly faster rate of epithelialisation than all other groups. The volume of inflammatory cells was highest in the fibrin containing AdeNOS group at 7 days, which dropped significantly by 14 days. Likewise, the surface area and length of vessels reduced significantly in the fibrin containing AdeNOS group between 7 and 14 days indicating tissue remodelling, but remained stable in all other groups. Regression analysis showed that the epithelialisation rate was significantly affected by change in eNOS expression, inflammation, and surface area and length of vessels over time in the fibrin containing AdeNOS group. It was concluded that fibrin delivery of AdeNOS resulted in enhanced eNOS expression, inflammatory response, and a faster rate of re-epithelialisation.

Absorption of bioactive molecules into OASIS wound matrix

OBJECTIVE

To examine the ability of OASIS Wound Matrix to absorb, retain, and protect bioactive molecules from solution.

DESIGN

Samples of OASIS Wound Matrix were incubated in solutions of bioactive molecules, specifically heparin, albumin, fibronectin, basic fibroblast growth factor 2, and platelet-derived growth factor (PDGF). Half of the samples were then rinsed, and all of the samples were evaluated using enzyme-linked immunosorbent assays (ELISAs) and dye-mediated spectrophotometric methods for absorption and retention of the bioactive molecules. Protection of PDGF was measured by placing PDGF-incubated and control samples into a degradation solution containing plasmin. Intact PDGF levels were then evaluated using a PDGF-specific ELISA.

MAIN OUTCOME MEASURES

The main outcome measures were the amount of each bioactive molecule that was absorbed after incubation in solutions and retained after rinses as well as the amount of PDGF remaining after plasmin degradation.

MAIN RESULTS

OASIS Wound Matrix absorbed bioactive molecules from solution, selectively absorbed PDGF from serum, and protected PDGF from protease degradation.

CONCLUSIONS

Although OASIS Wound Matrix potentially has multiple functions in wound healing, it likely promotes wound healing, in part, by absorbing, retaining, and protecting bioactive molecules from the wound environment.

A novel, tissue occlusive poly(ethylene glycol) hydrogel material

The use of guided bone regeneration (GBR) techniques requires new materials meeting the needs of clinical application. Design criteria for GBR devices are biocompatibility, tissue occlusion, space provision, and clinical manageability. This study evaluates a novel biodegradable poly (ethylene glycol) (PEG) based material as tissue occlusive membrane. A subcutaneous implant model in rats was developed to test the barrier function of the PEG hydrogels over time. Fourteen rats received three membrane implants and two positive controls each. Explants were collected over a period of 7 months. Histological analysis revealed that for at least 4 months cellular infiltration in the membrane explants was lower than 1% of that of the positive controls. Therefore, the PEG based hydrogel can be regarded as tissue occlusive during this period of time. A barrier function seems to be maintained for up to 6 months. In vitro degradation studies performed with the same PEG constructs confirm the in vivo result. In conclusion, our results indicate that this novel PEG-based material has potential for use as a GBR barrier membrane.

Delayed wound healing in Mac-1-deficient mice is associated with normal monocyte recruitment

The Mac-1 integrin is an important mediator of migration and inflammatory activation of neutrophils and monocytes. However, the role of Mac-1 in modulating macrophage emigration and activation and its subsequent impact on cutaneous wound healing have not been fully elucidated. To examine the significance of Mac-1 to murine wound healing, we measured epithelialization and granulation tissue formation in partial-thickness ear wounds and full-thickness head wounds, respectively, in Mac-1-deficient mice. Wounds were histologically analyzed at postwounding days 3, 5, and 7. The gap measured between the leading edges of inward-migrating granulation tissue was significantly increased in knockout mice compared with control animals at day 5 (3.8+/-0.3 vs. 2.6+/-0.5 mm; p<0.001) and day 7 (2.2+/-0.4 vs. 0.96+/-0.73 mm; p=0.005). Epithelial gap measurements were also increased in knockout mice vs. wild-type controls at days 3 (0.62+/-0.02 vs. 0.54+/-0.07 mm; p<0.05) and 5 (0.58+/-0.06 vs. 0.39+/-0.08 mm; p<0.001). Immunohistochemistry showed equal numbers of macrophages in knockout and control wounds. These findings show that Mac-1 is required for normal wound healing but that the attenuation in the deposition of granulation tissue and wound epithelialization in Mac-1 knockout mice is not associated with decreased monocyte migration into the wound.

Discrete crosslinked fibrin microthread scaffolds for tissue regeneration

In this study, we report on the development of discrete fibrin microthreads as well as novel scaffolds composed of arrays of fibrin threads. These scaffolds exhibit mechanical properties that are significantly greater than fibrin gels and cellular responses suggesting that the materials are conducive to the development of organized, aligned tissues. Fibrin microthreads were produced by coextruding solutions of 70 mg/mL fibrinogen and 6 U/mL thrombin through small diameter polyethylene tubing. Uncrosslinked fibrin microthreads averaged 55-65 microm in hydrated diameter and achieved ultimate tensile strengths approaching 4.5 MPa. The strengths and stiffnesses of the microthreads were approximately twofold greater when the materials were treated with exposure to ultraviolet (UV) light. Although UV crosslinking attenuated fibroblast proliferation, uncrosslinked fibrin microthreads supported fibroblast attachment, proliferation, and alignment, suggesting that they represent a viable biomaterial for the aligned regeneration of tissues. Because of the physiologic roles of fibrin matrices in the early phase of wound healing, we anticipate that these fibrin-based microthreads will direct the spatially and temporally complex processes of cell-mediated tissue ingrowth and regeneration.

Restoring hemostatic thrombin generation at the time of cutaneous wounding does not normalize healing in hemophilia B

BACKGROUND

We recently reported that wound healing is abnormal in hemophilia B (HB) mice [1]. The wounds show abnormal histology: s.c. hematoma formation; delayed re-epithelialization; delayed macrophage influx; and an increase in wound site angiogenesis.

OBJECTIVE

To test the hypothesis that restoring a hemostatic level of thrombin generation at the time of wounding would allow formation of an adequate platelet/fibrin plug and correct abnormalities of wound healing in HB.

METHODS

We placed a 3-mm cutaneous wound on the back of each HB or wild-type (WT) mouse. Some HB mice were treated just prior to wounding with either human factor IX (FIX) or FVIIa in a dose sufficient to normalize bleeding in a tail bleed model.

RESULTS

The average wound size over time in treated HB animals was intermediate between those in WT and untreated HB mice. However, the time to complete skin closure was not improved by treatment. Hematoma formation was decreased and macrophage influx began earlier in treated than in untreated HB animals. However, treated HB mice had evidence of ongoing low-level bleeding near the wound site, even after closure of the skin defect. Treatment also did not normalize the increased angiogenesis observed in HB mice.

CONCLUSIONS

Restoring initial hemostasis can modulate some of the parameters of wound healing. However, an extended period of adequate hemostatic function is necessary to achieve normal healing, probably because the risk of hemorrhage is increased by vascular remodeling and angiogenesis during the healing process.

Fibrin as a delivery vehicle for active macrophage activator lipoprotein-2 peptide: in vitro studies

Fibrin sealants have been used in hemostasis and tissue sealing for over 25 years and recent studies have shown them to be an ideal delivery vehicle for cells and bioactive substances. We examined the use of fibrin as a delivery vehicle for the macrophage activator lipoprotein peptide (MALP)-2. MALP-2, secreted by mycoplasma, plays an important role in an early influx of leukocytes and infiltration by monocytes and their subsequent activation into macrophages as detected by their secretion of cytokines and chemoattractants. We first showed that MALP-2 activated several monocytic cell lines by increasing the expression of cytokines and chemoattractants in these cells. Furthermore, using a reverse transcription-polymerase chain reaction approach, we found that MALP-2 affected the gene expression of its own receptors: TLR2 and TLR4 in various cell types including fibroblasts, keratinocytes, and endothelial cells. Furthermore, the conditioned medium, containing secreted cytokines and chemoattractants, collected from monocytes treated with MALP-2 enhanced fibroblast migration using a standard wound culture assay. Next, we examined MALP-2's effect on the human monocyte cell line when it is mixed with fibrin. Monocytes seeded on three-dimensional fibrin containing MALP-2 secreted more cytokines such as interleukin-6, tumor necrosis factor-alpha, and chemoattractants such as macrophage inflammatory protein 1 alpha and monocyte chemoattractant protein 1 when compared with monocytes seeded on three-dimensional fibrin in the absence of MALP-2. This study supports the use of fibrin to deliver MALP-2, and possibly other peptides, in an active form that might enhance wound healing.

Extracellular matrix as a strategy for treating chronic wounds

The dermis normally directs all phases of skin wound healing following tissue trauma or disease. However, in chronic wounds, the dermal matrix is insufficient to stimulate healing and assistance by external factors is needed for wound closure. Although the concept of the extracellular matrix directing wound healing is not new, ideas about how best to provide the extracellular matrix components required to 'jump-start' the healing process are still evolving. Historically, these strategies have included use of enzyme-inhibiting dressing materials, which bind matrix metalloproteinases and remove them from the chronic wound environment, or direct application of purified growth factors to stimulate fibroblast activity and deposition of neo-matrix. More recently, the application of a structurally intact, biochemically complex extracellular matrix, designed to provide the critical extracellular components of the dermis in a single application, has allowed for the reconstruction of new, healthy tissue and restoration of tissue integrity in the previously chronic wound. This review focuses on this third mechanism as an emerging tactic in effective wound repair. Intact extracellular matrix can quickly, easily, and effectively provide key extracellular components of the dermis necessary to direct the healing response and allow for the proliferation of new, healthy tissue. Its application may promote the healing of wounds that have been refractory to other, more conventional treatment strategies, and may eventually show utility when used earlier in wound healing treatment with the goal of preventing wounds from reaching a truly chronic, nonresponsive state.

Wound-healing activity of Morinda citrifolia fruit juice on diabetes-induced rats

OBJECTIVE

Morinda citrifolia L. is a traditional Polynesian medicinal plant which is apparently useful for bowel disorders, skin inflammation, infection, mouth ulcers and wound healing. This study aimed to evaluate the wound-healing activity of Morinda citrifolia fruit juice in streptozotocin-induced diabetic rats.

METHOD

An excision wound model was used. The animals were weight-matched and placed into three groups (n = 6 per group). Group 1 animals served as normal controls, while animals in groups 2 and 3 served as diabetic controls and experimental diabetic animals respectively. All animals were anaesthetised and a full-thickness excision wound (circular area of 300 mm2 and 2 mm deep) was created. Group 3 animals were given the juice of Morinda citrifolia fruit (100 ml per kilogram of body weight) in their drinking water for 10 days. Wound area measurements were taken on days 1, 5 and 11. Blood samples were collected simultaneously for glucose measurement. Granulation tissue that had formed on the wound was excised on day 11 and processed for histological and biochemical analysis.

RESULTS

The wound area of the Morinda citrifolia-treated group reduced by 73% (p < 0.001) when compared with the diabetic controls (63%). Significant increases in the weight of granulation tissue (p < 0.001) and hydroxyproline content (p < 0.00 1, 92.16 +/- 4.02) were observed. The protein content was moderately high. Histological studies showed that collagen was laid down faster in the experimental diabetic animals than in the normal control and diabetic control groups. Fasting blood glucose values in the diabetic experimental group had reduced by 29% (p < 0.00 1) compared with the diabetic control animals. There was a good correlation between the wound contraction rate and blood glucose values.

CONCLUSION

This study demonstrates that the juice of Morinda citrifolia fruit significantly reduces blood sugar levels and hastens wound healing in diabetic rats.

Effects of age of Holstein-Friesian calves on plasma cortisol, acute-phase proteins, immunological function, scrotal measurements and growth in response to Burdizzo castration

To determine the effect of age at castration on physiological and immunological stress indices, 60 Holstein-Friesian bull calves were sourced so that they were in one of five age groups for Burdizzo castration on day 0 (16 July 2002; no. = 10 per treatment) : 1·5, 2·5, 3·5, 4·5, and 5·5 months of age (mean body weight ± s.e. = 63 ± 2·5, 89 ± 3·7, 104 ± 3·7, 142 ± 3·6, 169 ± 8·1 kg, respectively), or were sham castrated at 5·5 months of age (171 ± 2·9 kg body weight) to serve as intact controls specific to this age group. Blood samples were collected at 15- to 30-min intervals from 2 h before until 8 h after treatment, with further samples collected at 10 and 12 h on day 0, and on days 1, 2 and 3, and weekly from days 7 to 35 after treatment. Following castration, peak plasma cortisol responses were significantly greater in 5·5-month-old castrates than intact calves, and all calves castrated at a younger age had reduced peak responses, with the greatest reduction in 1·5-month-old castrates. Overall, the integrated cortisol responses for the first 3 h after castration were three-fold greater in 5·5-month-old castrates than intact calves. While the integrated cortisol responses were reduced by proportionately 0·46 and 0·35 in 1·5- and 4·5-month-old castrates, the lower responses observed in 2·5- and 3·5- month-old castrates were not significantly different from the 5·5-month-old castrates. The integrated cortisol responses for the next 9 h after castration were not different among treatment groups. On day 3 after castration, peak plasma haptoglobin and fibrinogen concentrations were significantly greater in 5·5-month-old castrates than intact calves, but the concentrations were markedly reduced in calves castrated at 1·5 and 2·5 months than when castrated at 5·5 months of age. On day 1, phytohaemagglutinin-inducedin vitrointerferon-γ production was suppressed in 5·5-month-old castrates compared with intact calves. Scrotal circumferences increased in all castrates on day 1 and 7 and were greater in 5·5- month-old castrates than intact calves, but the swelling was reduced in the 1·5- compared with 5·5-month-old castrates. The temperature differences between the core body and scrotal skin were greater on day 2 and 3 in the 1·5-month-old than all other castrates. There was no effect of castration on the overall 42-day growth rates of calves. In conclusion, the physiological stress and inflammation caused by Burdizzo castration, indicated by increased plasma cortisol, acute-phase proteins, scrotal swelling, and depressed temperature differences between the core body and scrotal skin were reduced by castrating calves at 1·5 months rather than at 5·5 months of age.

Fibrin/platelet plug counteracts cutaneous wound contraction: The hypothesis of “skipping stone”

Cutaneous wound contraction and epithelialization act collaboratively to minimize the exposed wound surface. However excessive wound contraction is undesirable due to the resultant disfigurement and scarring. Fibrin clot has greater stiffness than surrounding tissue and mechanical strain further enhances its stiffness. On the contrary, skin exhibits diminished stiffness when affected by high strain rates. Therefore during early stages of wound healing, the contractile wound border is confronted by fibrin clot forming a high strain region in the interface of contractile tissue and fibrin clot--which is evidenced by computer simulation. Due to the stress relaxation property of skin, the contractile strain is partly neutralized. Meanwhile, gradually the stiffness of fibrin clot decreases which is followed by another cycle of wound contraction. This cyclic pattern of contraction resembles the movement of a stone over water or "skipping stone". The stone bounces repeatedly when thrown across the surface of water with reduction of jumping altitude with each bounce till the stone stops completely. This hypothesis is further supported by the observed initial delay in wound contraction and the chronological correlation of enhanced wound contraction with loss of superficial eschar and substitution of fibrin clot with granulation tissue. Also there is evidence that fibrin inhibits fibroblast-mediated contraction of collagen. Furthermore, modest increase in wound contraction rate in fibrinogen deficient mice and fibrin-mediated diminished wound contraction are agreement with the proposed hypothesis.

Decorin Modulates Fibrin Assembly and Structure

Emerging evidence indicates that fibrin clotting is regulated by different external factors. We demonstrated recently that decorin, a regulator of collagen fibrillogenesis and transforming growth factor-beta activity, binds to the D regions of fibrinogen (Dugan, T.A., Yang, V. W.-C., McQuillan, D.J., and Höök, M. (2003) J. Biol. Chem. 278, 13655-13662). We now report that the decorin-fibrinogen interaction alters the assembly, structure, and clearance of fibrin fibers. Relative to fibrinogen, substoichiometric amounts of decorin core protein modulated clotting, whereas an excess of an active decorin peptide was necessary for similar activity. These concentration-dependent effects suggest that decorin bound to the D regions sterically modulates fibrin assembly. Scanning electron microscopy images of fibrin clotted in the presence of increasing concentrations of decorin core protein showed progressively decreasing fiber diameter. The sequestration of Zn(2+) ions from the N-terminal fibrinogen-binding region abrogated decorin incorporation into the fibrin network. Compared with linear thicker fibrin fibers, the curving thin fibers formed with decorin underwent accelerated tissue-type plasminogen activator-dependent fibrinolysis. Collectively, these data demonstrate that decorin can regulate fibrin organization and reveal a novel mechanism by which extracellular matrix components can participate in hemostasis, thrombosis, and wound repair.

The immune-body cytokine network defines a social architecture of cell interactions

Background

Three networks of intercellular communication can be associated with cytokine secretion; one limited to cells of the immune system (immune cells), one limited to parenchymal cells of organs and tissues (body cells), and one involving interactions between immune and body cells (immune-body interface). These cytokine connections determine the inflammatory response to injury and subsequent healing as well as the biologic consequences of the adaptive immune response to antigens. We informatically probed the cytokine database to uncover the underlying network architecture of the three networks.

Results

We now report that the three cytokine networks are among the densest of complex networks yet studied, and each features a characteristic profile of specific three-cell motifs. Some legitimate cytokine connections are shunned (anti-motifs). Certain immune cells can be paired by their input-output positions in a cytokine architecture tree of five tiers: macrophages (MΦ) and B cells (BC) comprise the first tier; the second tier is formed by T helper 1 (Th1) and T helper 2 (Th2) cells; the third tier includes dendritic cells (DC), mast cells (MAST), Natural Killer T cells (NK-T) and others; the fourth tier is formed by neutrophils (NEUT) and Natural Killer cells (NK); and the Cytotoxic T cell (CTL) stand alone as a fifth tier. The three-cell cytokine motif architecture of immune system cells places the immune system in a super-family that includes social networks and the World Wide Web. Body cells are less clearly stratified, although cells involved in wound healing and angiogenesis are most highly interconnected with immune cells.

Conclusion

Cytokine network architecture creates an innate cell-communication platform that organizes the biologic outcome of antigen recognition and inflammation. Informatics sheds new light on immune-body systems organization.

Reviewers

This article was reviewed by Neil Greenspan, Matthias von Herrath and Anne Cooke.

Degradation of extracellular matrix proteins (fibronectin, vitronectin and laminin) by serine-proteinases isolated from Lonomia achelous caterpillar hemolymph

Lonomia achelous is a caterpillar distributed in southern Venezuela and in northern Brazil that causes an acute hemorrhagic syndrome in people who have contact with its bristles. The effect of the crude hemolymph and its chromatographic fractions (FDII, Lonomin V and Lonomin V-2) on extracellular matrix proteins was studied. The chromatographic fractions show activities similar to plasmin and urokinase. In sodium dodecyl sulfate-polyacrylamide gel electrophoresis, both lonomins appear as a protein band of 25 kDa under reduced conditions. By exclusion chromatography, the molecular weights of Lonomin V and Lonomin V-2 were 26.5 and 24.5 kDa, respectively. Fibronectin, laminin and vitronectin were degraded by all venom components. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis, under reduced conditions, shows that lonomins degrade fibronectin in four main fragments of 116, 60, 50 and 30 kDa. Molecular exclusion chromatography in native conditions shows that the molecular masses of these fragments are > or = 300, 62 and 27 kDa. The proteolytic effect of lonomins was abolished by benzamidine/HCl, iodoacetic acid and aprotinin. The extracellular matrix protein degradation together with the fibrino(geno)lytic activity of hemolymph and its fractions could explain, in part, the hemorrhagic syndrome, and the wound dehiscence in persons who have had contact with the L. achelous caterpillar.

Cecropia peltata L(Cecropiaceae) has wound-healing potential: a preclinical study in a Sprague Dawley rat model

The plant Cecropia peltata is used in traditional medicine to treat a variety of disorders. The objective of the study presented in this report was to screen the extracts of this plant leaf for its wound-healing properties based on its traditional use for wound healing. Aqueous and ethanol extracts were prepared for topical and oral administration. The dose studied was 150 mgkg(-1)day(-1) for 10 days, using the excision wound model in rats. Carboxymethyl cellulose (1%) was used as control in topical and oral route studies. Animals were randomized to treatment or control, the experiment being done with prior ethical approval from the university. Wound areas were measured. On day 11, tissue was excised to determine the contents of protein, hydroxyproline, and hexosamine. Wound areas reduced statistically significantly in all treatment groups compared to respective controls (P < .001). Biochemistry and tissue histology outcomes were consistent with changes in the treatment groups. No differences were detected within the treatment groups. The study permits the conclusion that Crecopia peltata has wound-healing potential.

Enhancement of osseointegration by generating a dynamic implant surface

Preparations of autologous plasma rich in growth factors (PRGF) are used to promote healing and tissue regeneration. We seek to determine whether covering the titanium implant surface with this preparation could enhance osseointegration. The interaction of PRGF with the surface of titanium implants was examined by environmental scanning electron microscopy (ESEM). A total of 23 implants were placed in the tibiae and radii of 3 goats; 13 implants were inserted after covering the surface and filling the alveolus with PRGF, and 10 more implants were inserted following a conventional protocol and served as controls. Histomorphometric analysis of the bone-implant interface was performed after 8 weeks. Finally, 1391 implants were placed in 295 patients after bioactivating the surface with PRGF. Stability and implant survival were evaluated. The implant surface adsorbed the protein-rich material as shown by ESEM. In the animal study, osseointegration was enhanced when the surface was covered with PRGF as shown by histomorphometry (bone-implant contact: 51.28% +/- 4.7% vs 21.89% +/- 7.36%; P < .01). Finally, studies in patients showed that 99.6% of the implants treated with PRGF were well osseointegrated. Clinical use of this technique in oral implantology can improve the prognosis.

Sutureless Amniotic Membrane Fixation Using Fibrin Glue for Ocular Surface Reconstruction in a Rabbit Model

PURPOSE

Amniotic membrane transplantation has become an important treatment option for corneal surface reconstruction. However, suture fixation of the transplant has various disadvantages like corneal irritation, scarring, graft loss due to membrane shrinkage, and the need for subsequent suture removal. Replacement of sutures by bioadhesives might be an advantageous alternative. This controlled study was designed to evaluate a new sutureless technique for amniotic membrane fixation onto the corneal surface by using fibrin glue.

METHODS

Standardized disks of cryopreserved amniotic membranes were transplanted onto the deepithelialized cornea of 12 rabbits using either conventional suture fixation or a new fibrin glue technique. The rabbits were followed-up with slit-lamp examination and fluorescein staining until epithelialization was completed. Consecutively, the rabbits were killed and the eyes processed for histology and immunohistochemistry for cytokeratin-3.

RESULTS

All membranes of both groups stayed in place throughout the follow-up time and showed a progressive graft epithelialization that was completed after 12 days. Whereas suture-fixated membranes showed progressive tissue shrinkage, fibrin-glued sheets remained unaltered. In the bioadhesive group, histology revealed a smooth fibrin layer in the graft-host interface and a continuous, stratified layer of cytokeratin-3 expressing corneal epithelial cells on the membrane surface. In contrast, suture-fixated membranes showed contracted and prominent membrane edges with epithelial ingrowth into the submembrane interface.

CONCLUSION

Our results demonstrate the general feasibility of reproducible and reliable sutureless amniotic membrane fixation onto the corneal surface in rabbits. Stable adherence is maintained until epithelialization is completed. The sutureless technique gives sufficient manipulation time for the sheet before the final cross-linking process is completed. Furthermore, several advantageous characteristics could be demonstrated as increased biocompatibility, better epithelialization pattern and the lack of membrane shrinkage.

Platelet-rich fibrin (PRF): a second-generation platelet concentrate. Part V: histologic evaluations of PRF effects on bone allograft maturation in sinus lift

OBJECTIVE

Platelet-rich fibrin (PRF) belongs to a new generation of platelet concentrates, with simplified processing and without biochemical blood handling. The use of platelet gel to improve bone regeneration is a recent technique in implantology. However, the biologic properties and real effects of such products remain controversial. In this article, we therefore attempt to evaluate the potential of PRF in combination with freeze-dried bone allograft (FDBA) (Phoenix; TBF, France) to enhance bone regeneration in sinus floor elevation.

STUDY DESIGN

Nine sinus floor augmentations were performed. In 6 sites, PRF was added to FDBA particles (test group), and in 3 sites FDBA without PRF was used (control group). Four months later for the test group and 8 months later for the control group, bone specimens were harvested from the augmented region during the implant insertion procedure. These specimens were treated for histologic analysis.

RESULTS

Histologic evaluations reveal the presence of residual bone surrounded by newly formed bone and connective tissue. After 4 months of healing time, histologic maturation of the test group appears to be identical to that of the control group after a period of 8 months. Moreover, the quantities of newly formed bone were equivalent between the 2 protocols.

CONCLUSIONS

Sinus floor augmentation with FDBA and PRF leads to a reduction of healing time prior to implant placement. From a histologic point of view, this healing time could be reduced to 4 months, but large-scale studies are still necessary to validate these first results.

Aggregated IgG inhibits the differentiation of human fibrocytes

Fibrocytes are fibroblast-like cells, which appear to participate in wound healing and are present in pathological lesions associated with asthma, pulmonary fibrosis, and scleroderma. Fibrocytes differentiate from CD14+ peripheral blood monocytes, and the presence of serum delays this process dramatically. We previously purified the factor in serum, which inhibits fibrocyte differentiation, and identified it as serum amyloid P (SAP). As SAP binds to Fc receptors for immunoglobulin G (IgG; Fc gammaRs), Fc gammaR activation may be an inhibitory signal for fibrocyte differentiation. Fc gammaR are activated by aggregated IgG, and we find aggregated but not monomeric, human IgG inhibits human fibrocyte differentiation. Monoclonal antibodies that bind to Fc gammaRI (CD64) or Fc gammaRII (CD32) also inhibit fibrocyte differentiation. Aggregated IgG lacking Fc domains or aggregated IgA, IgE, or IgM do not inhibit fibrocyte differentiation. Incubation of monocytes with SAP or aggregated IgG inhibited fibrocyte differentiation. Using inhibitors of protein kinase enzymes, we show that Syk- and Src-related tyrosine kinases participate in the inhibition of fibrocyte differentiation. These observations suggest that fibrocyte differentiation can occur in situations where SAP and aggregated IgG levels are low, such as the resolution phase of inflammation.

Platelet-rich fibrin (PRF): a second-generation platelet concentrate. Part I: technological concepts and evolution

Platelet-rich fibrin (PRF) belongs to a new generation of platelet concentrates geared to simplified preparation without biochemical blood handling. In this initial article, we describe the conceptual and technical evolution from fibrin glues to platelet concentrates. This retrospective analysis is necessary for the understanding of fibrin technologies and the evaluation of the biochemical properties of 3 generations of surgical additives, respectively fibrin adhesives, concentrated platelet-rich plasma (cPRP) and PRF. Indeed, the 3-dimensional fibrin architecture is deeply dependent on artificial clinical polymerization processes, such as massive bovine thrombin addition. Currently, the slow polymerization during PRF preparation seems to generate a fibrin network very similar to the natural one. Such a network leads to a more efficient cell migration and proliferation and thus cicatrization.

Platelet-rich fibrin (PRF): a second-generation platelet concentrate. Part II: platelet-related biologic features

Platelet-rich fibrin (PRF) belongs to a new generation of platelet concentrates, with simplified processing and without biochemical blood handling. In this second article, we investigate the platelet-associated features of this biomaterial. During PRF processing by centrifugation, platelets are activated and their massive degranulation implies a very significant cytokine release. Concentrated platelet-rich plasma platelet cytokines have already been quantified in many technologic configurations. To carry out a comparative study, we therefore undertook to quantify PDGF-BB, TGFbeta-1, and IGF-I within PPP (platelet-poor plasma) supernatant and PRF clot exudate serum. These initial analyses revealed that slow fibrin polymerization during PRF processing leads to the intrinsic incorporation of platelet cytokines and glycanic chains in the fibrin meshes. This result would imply that PRF, unlike the other platelet concentrates, would be able to progressively release cytokines during fibrin matrix remodeling; such a mechanism might explain the clinically observed healing properties of PRF.

Engineered spatial patterns of FGF-2 immobilized on fibrin direct cell organization

The purpose of this study was to initiate the exploration of cell behavioral responses to inkjet printed spatial patterns of hormones biologically immobilized on biomimetic substrates. This approach was investigated using the example of preosteoblastic cell response in vitro to fibroblast growth factor-2 (FGF-2) printed on fibrin films. Concentration modulated patterns of FGF-2, including continuous concentration gradients, were created by overprinting dilute FGF-2 bioinks with a custom inkjet printer. The immobilized FGF-2 was biologically active and the printed patterns persisted up to 10 days under cell culture conditions. Cell numbers increased in register to printed patterns from an initial random uniform cell distribution across the patterned and non-patterned fibrin substrate. Patterned immobilized FGF-2, not cell attachment directed cell organization because the fibrin substrate was homogeneous. The capability to engineer arbitrary and persistent hormone patterns is relevant to basic studies across various fields including developmental biology and tissue regeneration. Furthermore, since this hormone inkjet printing methodology is extensible to create complex three-dimensional structures, this methodology has potential to create therapies for tissue engineering using spatial patterned delivery of exogenous hormones.

Overview: acute and chronic wounds

Knowledge of normal wound healing and the changes associated with chronic wounds have advanced significantly. Distinct characteristics identified through basic and clinical studies are found in nonhealing wounds, including bacterial and growth factor imbalances, increased inflammatory responses, and proteolytic forces that tip the balance toward tissue degradation rather than repair. This article describes the alterations that reduce healing and that also have important implications for the management of chronic wounds and presents a focus for future developments in wound therapy.

Enhancement of implantable glucose sensor function in vivo using gene transfer-induced neovascularization

The in vivo failure of implantable glucose sensors is thought to be largely the result of inflammation and fibrosis-induced vessel regression at sites of sensor implantation. To determine whether increased vessel density at sites of sensor implantation would enhance sensor function, cells genetically engineered to over-express the angiogenic factor (AF) vascular endothelial cell growth factor (VEGF) were incorporated into an ex ova chicken embryo chorioallantoic membrane (CAM)-glucose sensor model. The VEGF-producing cells were delivered to sites of glucose sensor implantation on the CAM using a tissue-interactive fibrin bio-hydrogel as a cell support and activation matrix. This VEGF-cell-fibrin system induced significant neovascularization surrounding the implanted sensor, and significantly enhanced the glucose sensor function in vivo. This model system, for the first time, provides the "proof of principle" that increasing vessel density at the sites of implantation can enhance glucose sensor function in vivo, and demonstrates the potential of gene transfer and tissue interactive fibrin bio-hydrogels in the development of successful implants.

Transglutaminase-mediated oligomerization of the fibrin(ogen) alphaC domains promotes integrin-dependent cell adhesion and signaling

Interactions of endothelial cells with fibrin(ogen) are implicated in inflammation, angiogenesis, and wound healing. Cross-linking of the fibrinogen alphaC domains with factor XIIIa generates ordered alphaC oligomers mimicking polymeric arrangement of the alphaC domains in fibrin. These oligomers and those prepared with tissue transglutaminase were used to establish a mechanism of the alphaC domain-mediated interaction of fibrin with endothelial cells. Cell adhesion and chemical cross-linking experiments revealed that oligomerization of the alphaC domains by both transglutaminases significantly increases their RGD (arginyl-glycyl-aspartate)-dependent interaction with endothelial alphaVbeta3 and to a lesser extent with alphaVbeta5 and alpha5beta1 integrins. The oligomerization promotes integrin clustering, thereby increasing cell adhesion, spreading, formation of prominent peripheral focal contacts, and integrin-mediated activation of focal adhesion kinase (FAK) and extracellular signal-regulated kinase (ERK) signaling pathways. The enhanced integrin clustering is likely caused by ordered juxtaposition of RGD-containing integrin-binding sites upon oligomerization of the alphaC domains and increased affinity of these domains for integrins. Our findings provide new insights into the mechanism of the alphaC domain-mediated interaction of endothelial cells with fibrin and imply its potential involvement in cell migration. They also suggest a new role for transglutaminases in regulation of integrin-mediated adhesion and signaling via covalent modification of integrin ligands.

A novel in vitro dermal wound-healing model incorporating a response to mechanical wounding and repopulation of a fibrin provisional matrix

Previously our laboratory, and others, described an in vitro model for the study of fibroblast wound repopulation. The so-called punch-wounded, fibroblast-populated collagen lattice has been used extensively in tissue repair research. We now identify certain shortcomings with this model, which have led to its enhancement by the introduction of a provisional matrix fabricated in situ from fibrinogen and alpha-thrombin. In the previous model, fibroblasts repopulate the wound defect (WD) as a monolayer of cells and on reaching confluence, a process reminiscent of fibroplasia fills the wound space. The enhanced model, with fibrin acting as a provisional matrix, allowed fibroblasts to repopulate the WD as a three-dimensional network of cells that were morphologically different from cells migrating over the collagen substratum of the previous model. Fibroblast repopulation of the fibrin matrix was typically around double the rate of repopulation of the empty wound space. We propose this model as an enhanced, yet sufficiently reproducible, model for the study of fibroblast responses to tissue damage. It can be further enhanced by the addition of other cell types and matrix components.

Is Vacuum Assisted Closure a valid technique for debriding chronic leg ulcers?

OBJECTIVE

Between May 2001 and October 2002 a prospective controlled open non-comparative study was performed to assess the effectiveness of topical negative pressure in the fibrinous debridement of chronic leg ulcers.

METHOD

Fifteen leg ulcers that had not responded to several other treatment modalities were treated with the Vacuum Assisted Closure system (KCI) for six days.

RESULTS

The median percentage reduction in fibrinous tissue was 28% on day three and 40% on day six. Between days one and three the percentage change was > or = 50% in four patients and > or = 25% in six patients. Between days three and six percentages of fibrin in the wound were lower in all patients, except for two who had higher percentages and two who had the same percentage.

CONCLUSION

VAC therapy was rapidly efficacious, promoting angiogenesis and the formation of healthy tissue.

Colloid surface chemistry critically affects multiple particle tracking measurements of biomaterials

Characterization of the properties of complex biomaterials using microrheological techniques has the promise of providing fundamental insights into their biomechanical functions; however, precise interpretations of such measurements are hindered by inadequate characterization of the interactions between tracers and the networks they probe. We here show that colloid surface chemistry can profoundly affect multiple particle tracking measurements of networks of fibrin, entangled F-actin solutions, and networks of cross-linked F-actin. We present a simple protocol to render the surface of colloidal probe particles protein-resistant by grafting short amine-terminated methoxy-poly(ethylene glycol) to the surface of carboxylated microspheres. We demonstrate that these poly(ethylene glycol)-coated tracers adsorb significantly less protein than particles coated with bovine serum albumin or unmodified probe particles. We establish that varying particle surface chemistry selectively tunes the sensitivity of the particles to different physical properties of their microenvironments. Specifically, particles that are weakly bound to a heterogeneous network are sensitive to changes in network stiffness, whereas protein-resistant tracers measure changes in the viscosity of the fluid and in the network microstructure. We demonstrate experimentally that two-particle microrheology analysis significantly reduces differences arising from tracer surface chemistry, indicating that modifications of network properties near the particle do not introduce large-scale heterogeneities. Our results establish that controlling colloid-protein interactions is crucial to the successful application of multiple particle tracking techniques to reconstituted protein networks, cytoplasm, and cells.

Inhibition of fibrocyte differentiation by serum amyloid P

Wound healing and the dysregulated events leading to fibrosis both involve the proliferation and differentiation of fibroblasts and the deposition of extracellular matrix. Whether these fibroblasts are locally derived or from a circulating precursor population is unclear. Fibrocytes are a distinct population of fibroblast-like cells derived from peripheral blood monocytes that enter sites of tissue injury to promote angiogenesis and wound healing. We have found that CD14(+) peripheral blood monocytes cultured in the absence of serum or plasma differentiate into fibrocytes within 72 h. We purified the factor in serum and plasma that prevents the rapid appearance of fibrocytes, and identified it as serum amyloid P (SAP). Purified SAP inhibits fibrocyte differentiation at levels similar to those found in plasma, while depleting SAP reduces the ability of plasma to inhibit fibrocyte differentiation. Compared with sera from healthy individuals and patients with rheumatoid arthritis, sera from patients with scleroderma and mixed connective tissue disease, two systemic fibrotic diseases, were less able to inhibit fibrocyte differentiation in vitro and had correspondingly lower serum levels of SAP. These results suggest that low levels of SAP may thus augment pathological processes leading to fibrosis. These data also suggest mechanisms to inhibit fibrosis in chronic inflammatory conditions, or conversely to promote wound healing.