Enzyme and cytokine effects on the impaired onset of the murine foreign-body reaction to dermal sheep collagen

The effect of collagen-chitosan porous scaffold thickness on dermal regeneration in a one-stage grafting procedure

Dermal substitutes are used as dermal regeneration templates to reduce scar formation and improve wound healing. Unlike autografts, dermal substitutes lack normal vascular networks. The increased distance required for diffusion of oxygen and nutrients to the autograft following interpositioning of the substitute dramatically affects graft survival. To evaluate the effect of collagen-chitosan scaffold thickness on dermal regeneration, single-layer collagen-chitosan porous scaffolds of 0.5-, 1- and 2-mm thicknesses were fabricated and used to treat full-thickness wounds in a one-stage grafting procedure in a rat model. Skin-graft viability, wound contraction, histological changes, and wound tensile strength were evaluated. The results indicated that the distance for the diffusion of oxygen and nutrients to the autograft in the 2-mm-thick scaffold provided less support for graft take, which resulted in graft necrosis, extensive inflammatory reaction, marked foreign-body reaction (FBR), rapid scaffold degradation, and abnormal collagen deposition and remodeling. In contrast, the thinner scaffolds, especially of that 0.5-mm thickness, promoted earlier angiogenesis, ensuring skin-graft viability with a mild FBR, and ordered fibroblast infiltration and better collagen remodeling. It can be concluded that collagen-chitosan porous scaffolds with a thickness of <1mm are more suitable for dermal regeneration and can be used as dermal templates for treatment of dermal defects using a one-stage grafting procedure.

The correlation between difference in foreign body reaction between implant locations and cytokine and MMP expression

The foreign body reaction (FBR) differs between subcutaneously and supra-epicardially implanted materials. We hypothesize that this is a result of differences in cytokine, chemokine and matrix metalloproteinase (MMP) dynamics. Therefore we applied collagen disks subcutaneously and on the epicardium in mice and analyzed the FBR from day 1 to 21. Both the influx of leukocytes and implant degradation were higher in supra-epicardially implanted collagen than in subcutaneously implanted material. This correlated with a higher gene expression of pro-inflammatory cytokines such as IL-1 and IL-6, and a lower expression of the anti-inflammatory cytokine IL-10. Furthermore, the higher supra-epicardial expression of PMN attractants CXCL1/KC and CXCL2/MIP2 correlated with a higher and prolonged PMN influx. The gene expression levels of collagen degrading MMPs, i.e. MMP8, MMP13 and MMP14 were similar in subcutaneous and supra-epicardial disks. However, the activity of these enzymes was markedly higher supra-epicardially. In addition, the MMP9 expression was higher supra-epicardially, suggesting a role for this enzyme in the degradation process. In conclusion, a strong pro-inflammatory milieu is generated after supra-epicardial implantation that enables prolonged PMN presence and activation. This, together with the high supra-epicardial MMP9 level, could explain the observed difference in Col-I degradation between locations.

Cellular and Molecular Dynamics in the Foreign Body Reaction

Intracorporally implanted materials, such as medical devices, will provoke the body to initiate an inflammatory reaction. This inflammatory reaction to implanted materials is known as the foreign body reaction (FBR) and is characterized by 3 distinct phases: onset, progression, and resolution. The FBR proceeds in the creation of a dynamic microenvironment that is spatially well organized. The progression of the FBR is regulated by soluble mediators, such as cytokines, chemokines, and matrix metalloproteinases (MMPs), which are produced locally by tissue cells and infiltrated inflammatory cells. These soluble mediators orchestrate the cascade of cellular processes in the microenvironment that accompanies the FBR, consisting of cellular activation, angiogenesis, extravasation, migration, phagocytosis, and, finally, fibrosis. The nature of the FBR requires that the soluble mediators act in a spatial and temporally regulated manner as well. This regulation is well known for several inflammatory processes, but scarce knowledge exists about the intricate relationship between the FBR and the expression of soluble mediators. This review discusses the key processes during the initiation, progression, and resolution phase, with emphasis on the role of soluble mediators. Besides other sites of implantation, we focus on the subcutaneous implantation model.

Prolactin (PRL) up-regulates Indoleamine 2,3-dioxygenase (IDO) expression in CD14+ cells

Indoleamine 2,3-dioxygenase (IDO), one of the enzymes of tryptophan catabolism, has been shown to play an essential role for successful pregnancy through the inhibition of allogenic fetus-induced T-cell proliferation, and interferon-gamma (IFN-gamma) induces the expression of IDO in CD14-positive (CD14(+)) cells. On the other hand, prolactin (PRL) is the hormone whose serum levels drastically elevate during pregnant period and is shown to play an important role in the early stages of pregnancy including implantation. However little is known about the physiological significance of the elevation of PRL from second trimester except for its fundamental role in lactation. Since receptors of PRL and IFN-gamma share their structure and the signal transduction pathway, we hypothesized the potential crosstalk between two substances. To test this idea, we examined the effect of PRL on IFN-gamma-induced IDO expression in CD14(+) cells. CD14(+) cells were prepared from peripheral blood of 12 healthy controls who had informed consent, and IDO expression and transcriptions were analyzed by flow cytometry and RT-PCR. The results showed that although PRL by itself had little effect on IDO expression, PRL significantly enhanced the IFN-gamma-induced IDO expression at comparable to those seen in a pregnant period. In contrast, no such effect was observed with PRL at lower concentrations comparable to those seen in a non-pregnant period. These findings suggest that PRL may contribute to the maintenance of pregnancy by augmenting IFN-gamma induction of IDO expression.