Mechanical and biocompatible characterization of a cross-linked collagen-hyaluronic acid wound dressing.

Collagen scaffolds have been widely employed as a dermal equivalent to induce fibroblast infiltrations and dermal regeneration in the treatment of chronic wounds and diabetic foot ulcers. Cross-linking methods have been developed to address the disadvantages of the rapid degradation associated with collagen-based scaffolds. To eliminate the potential drawbacks associated with glutaraldehyde cross-linking, methods using a water soluble carbodiimide have been developed. In the present study, the glycosaminoglycan (GAG) hyaluronic acid (HA), was covalently attached to an equine tendon derived collagen scaffold using 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) to create ntSPONGE The HA was shown to be homogeneously distributed throughout the collagen matrix. In vitro analyses of the scaffold indicated that the cross-linking enhanced the biological stability by decreasing the enzymatic degradation and increasing the thermal denaturation temperature. The material was shown to support the attachment and proliferation of mouse L929 fibroblast cells. In addition, the cross-linking decreased the resorption rate of the collagen as measured in an intramuscular implant model in rabbits. The material was also shown to be biocompatible in a variety of in vitro and in vivo assays. These results indicate that this cross-linked collagen-HA scaffold, ntSPONGE has the potential for use in chronic wound healing.

Demineralized bone matrix as an osteoinductive biomaterial and in vitro predictors of its biological potential.

The osteoinductivity of demineralized bone matrix (DBM) varies from donor to donor as a result of varying levels of multiple growth factors, matrix integrity, and artifacts from material processing. Many in vitro assays are currently used for screening the osteoinductivity of DBM. The objectives of this study were to determine the correlation of specific growth factors and in vitro mitotic stimulation to in vivo ectopic bone formation capacity with a large number of DBM samples. Samples were assayed using ELISA methods for BMP-2/4 and TGF-beta1 (n = 304) and cell proliferation using SAOS-2 osteoblasts (n = 239). All samples were then implanted intramuscularly in the abdomen of nude rats. All in vitro assays showed significant variability for any particular level of ostoinductivity determined by in vivo model. A significant, but only very weak, positive correlation to in vivo results was found for TGF-beta1 (r(2) = 0.016), BMP 2/4 (r(2) = 0.065), and SAOS-2 cell proliferation (r(2) = 0.053). The results of this study amplify the notion that a multitude of factors and their relative interplay, rather than a single factor are likely to determine the potency of any particular lot of DBM.

Reperfusion-induced neutrophil CD18 polarization: effect of hyperbaric oxygen.

BACKGROUND: Hyperbaric oxygen (HBO) inhibits ischemia reperfusion (IR) -induced neutrophil adhesion to endothelium through an unknown mechanism. This study evaluates the effect of HBO on IR-stimulated neutrophil adhesion and polarization of expressed CD18 adhesion molecules using a novel in vitro adhesion assay and confocal microscopy. MATERIALS AND METHODS: Neutrophils from normal animals were isolated from whole blood and incubated with plasma from rat gracilis muscle flaps on coverslips pretreated with ICAM. Percent adherence to ICAM and CD18 polarization was evaluated in the following five groups: (1) Nonischemic control, n = 15; (2) 4 h ischemia (IR, n = 15); (3) 4 h ischemia with HBO treatment (100% oxygen at 2.5 atmospheres absolute (IR + HBO, n = 15)); (4) 4 h ischemia with 100% oxygen at room temperature and pressure (RTP) (IR + normobaric hyperoxia, n = 5); and (5) 4 h ischemia with 8% oxygen at 2.5 atmospheres absolute (IR + hyperbaric normoxia, n = 5). Direct HBO treatment of neutrophils was also evaluated. RESULTS: Neutrophils exposed to IR plasma showed a significant increase in percent adherent (0.8 +/- 0.1% versus 16.7 +/- 2.2%, P < 0.05) and polarized cells (6.2 +/- 1.7% versus 43.9 +/- 12.2%, P < 0.05) compared to controls. Hyperbaric oxygen significantly reduced the adhesion and polarization to 1.6 +/- 0.3 and 4.1 +/- 2.5%, respectively (P = < 0.05). Normobaric hyperoxia and hyperbaric normoxia did not affect neutrophil adherence or CD18 polarization following IR. Direct HBO treatment of neutrophils did not change the percent of polarized cells in IR. CONCLUSIONS: Hyperbaric oxygen inhibits IR-induced neutrophil adhesion by blocking CD18 surface polarization and requires plasma exposure to HBO. Treatment with oxygen or pressure alone is not effective.

Extracellular Wound Matrices: Novel Stabilization and Sterilization Method for Collagen-based Biologic Wound Dressings.

Biologic extracellular matrix (ECM)-based wound dressings offer promise in the treatment of chronic wounds. A variety of animal and human tissue derived dressings are currently available. These products are processed and/or sterilized by a range of chemical and mechanical processes, which will impact the final quality of the matrices--ultimately affecting the overall wound healing process. A novel method is described to prepare a sterile and biocompatible biological wound dressing. The advantages and the clinical implications of this wound dressing preparation are also discussed.

A quantitative method for determining polarization of neutrophil adhesion molecules associated with ischemia reperfusion.

Ischemia-reperfusion-induced neutrophil adhesion to endothelium is CD18-dependent, but information regarding polarity of CD18 adhesion molecules remains speculative. This study evaluated neutrophil adhesion using an in vitro cell adhesion assay and introduces a quantitative method of measuring CD18 membrane distribution using confocal microscopy. Neutrophils from normal animals were isolated from whole blood and incubated with plasma from rat gracilis muscle flaps with no ischemia and reperfusion (nonischemic control, n = 10) or 4 hours of ischemia and 90 minutes of reperfusion (ischemia/reperfusion, n = 10), on coverslips pretreated with and without (phosphate-buffered saline) soluble intercellular adhesion molecules. Coverslips without intercellular adhesion molecules represented a negative control (intercellular adhesion molecules were required for adhesion). Percent adherence to intercellular adhesion molecules was expressed as a ratio of adherent cells/total cells. CD18 polarization was assessed by staining neutrophils with fluorescein isothiocyanate-labeled anti-CD11b, followed by confocal microscopy and Z-stack analysis. Membrane-associated CD18 was expressed as fluorescence intensity units in three equal areas of the cell membrane. Capping was defined as twice as much fluorescence in 33 percent of the cell membrane as in the remaining 67 percent. Neutrophils exposed to ischemia and reperfusion plasma showed a significant increase in adhesion (0.8 +/- 0.1 percent versus 16.7 +/- 2.2 percent, p < 0.001) and CD18 polarization (6.2 +/- 1.7 percent versus 43.9 +/- 12.2 percent, p = 0.0206) compared with controls. This article describes an in vitro assay that reliably reproduces the neutrophil adhesion phenomenon associated with ischemia-reperfusion injury. Results from confocal microscopy allowed for quantitative estimation of membrane-associated receptor polarization.

The chemokine CX3CL1 regulates NK cell activity in vivo.

In vitro, chemokines can both activate and induce migration of NK cells. However, little is known about how chemokines influence NK cell activity in vivo. We studied the role of CX(3)CL1 and its receptor, CX(3)CR1, in modulating NK cell activity in an established in vivo model of tumour cell clearance. Radiolabelled YAC-1 target cells intravenously injected into C57BL/6 mice rapidly localize to the lungs and are cleared by NK cells. In mice pre-treated with blocking anti-CX(3)CL1 or anti-CX(3)CR1 Ab, target cell clearance decreased by four- to fivefold (p<0.001). In vitro, we found no effect of anti-CX(3)CL1 or anti-CX(3)CR1 Ab on NK lysis of target cells. We further examined adhesion of NK cells to Py-4-1 endothelial cells. NK cell binding to activated endothelial monolayers was significantly inhibited by anti-CX(3)CR1 Ab or soluble CX(3)CL1 (p<0.001). These studies identify a critical role for CX(3)CL1 in modulating NK cell activity in vivo.

Proinflammatory actions of thromboxane receptors to enhance cellular immune responses.

Metabolism of arachidonic acid by the cyclo-oxygenase (COX) pathway generates a family of prostanoid mediators. Nonsteroidal anti-inflammatory drugs (NSAIDs) act by inhibiting COX, thereby reducing prostanoid synthesis. The efficacy of these agents in reducing inflammation suggests a dominant proinflammatory role for the COX pathway. However, the actions of COX metabolites are complex, and certain prostanoids, such as PGE(2), in some circumstances actually inhibit immune and inflammatory responses. In these studies, we examine the hypothesis that anti-inflammatory actions of NSAIDs may be due, in part, to inhibition of thromboxane A(2) synthesis. To study the immunoregulatory actions of thromboxane A(2), we used mice with a targeted disruption of the gene encoding the thromboxane-prostanoid (TP) receptor. Both mitogen-induced responses and cellular responses to alloantigen were substantially reduced in TP(-/-) spleen cells. Similar attenuation was observed with pharmacological inhibition of TP signaling in wild-type splenocytes, suggesting that reduced responsiveness was not due to subtle developmental abnormalities in the TP-deficient mice. The absence of TP receptors reduced immune-mediated tissue injury following cardiac transplant rejection, an in vivo model of intense inflammation. Taken together, these findings show that thromboxane augments cellular immune responses and inflammatory tissue injury. Specific inhibition of the TP receptor may provide a more precise approach to limit inflammation without some of the untoward effects associated with NSAIDs.

Rho kinase promotes alloimmune responses by regulating the proliferation and structure of T cells.

Coordinated rearrangements of the actin-myosin cytoskeleton facilitate early and late events in T cell activation and signal transduction. As many important features of cell shape rearrangement involve small GTP-binding proteins, we examined the contribution of Rho kinase to the functions of mature T cells. Inhibitors of the Rho kinase pathway all had similar actions to inhibit the proliferation of primary lymphocyte cultures. Likewise, transfection of the human Jurkat T cell line with a dominant negative, kinase-defective mutant of Rho kinase diminished Jurkat cell proliferation. Furthermore, inhibition of Rho kinase substantially attenuated the program of cytokine gene expression that characterizes T cell activation, blocked actomyosin polymerization, and prevented aggregation of the TCR/CD3 complex colocalized with lipid rafts. These actions are relevant to immune responses in vivo, as treatment with a Rho kinase inhibitor considerably prolonged the survival of fully allogeneic heart transplants in mice and diminished intragraft expression of cytokine mRNAs. Thus, Rho GTPases acting through Rho kinase play a unique role in T cell activation during cellular immune responses by promoting structural rearrangements that are critical for T cell signaling.