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Biomedical subjects

C Hammer

Publications and source records attributed to C Hammer.

At least 91 records · Page 5Linked to original sources
PubMed1996

Quantitative analysis of the microcirculation of xenogeneic haemoperfused rat livers by intravital microscopy.

Livers from male Sprague-Dawley rats were perfused with heparinised, unmodified isogeneic rat blood (n = 6) or xenogeneic human blood. The microcirculation of these livers, as the primary manifestation of hyperacute xenogeneic rejection, was directly observed and quantified by using fluorescence videomicroscopy. Bile flow and enzyme release of the isogeneic perfused livers were in the physiological range, whereas bile flow was significantly reduced and enzyme release increased during xenogeneic perfusion. In contrast to an almost physiological acinar (90.4%) and sinusoidal (93.6%) perfusion rate in the isogeneic group, a rapid breakdown of microcirculation with an acinar perfusion index of 47.5% and a sinusoidal perfusion rate of 67.1% were found in the xenogeneic group. This direct quantification of microcirculatory parameters is a step forward towards sensitive and early characterisation of the severity of the xenogeneic rejection of the liver.

Animals↗
PubMed1996

Microsurgical reconstruction of the lymphatic and nerve system in small bowel transplantation: the rat model, first results.

The goal in tissue transplantation is the restoration of all natural (physiological) communication pathways between the host and the graft. To this end, the effects of microsurgical reconstruction of artery, vein, lymphatic vessel, and nerve during grafting were investigated. Allogenic (MHC class II incompatible) and isogenic orthotopic (graft in functional continuity) small bowel recipients with immediate microsurgical lymphatic and nerve anastomosis were observed clinically as well as by immunological and histological examination. To explain the influence of the lymphatic system in allograft survival, short-term therapy was applied with the immunosuppressant cyclosporin A (10 mg/kg i.m.) for only 5 postoperative days. Average allograft survival ended in the control group after 10 days without any therapy, increased up to 20 days after immunosuppressive therapy (in both groups acute rejection and graft-versus-host disease were seen) and increased further to more than 200 days following lymphatic connection of the host and the graft during allografting. In this group no lymphatic edema of the graft was seen. To determine the optimal location of nerve anastomoses between the host and the graft without irritating the host nerve system, isografts in the same model were investigated. No paralysis of graft neighboring tissues was seen when the last ganglion function, and its following nerve plexus, of the host is saved. Nerve reconstruction must be undertaken after this last crossing of regional nerve fibers before entering the organ. The same rule is effective for organ explantation.

Anastomosis, Surgical↗
PubMed1996

Expression of human decay accelerating factor (hDAF) in transgenic pigs regulates complement activation during ex vivo liver perfusion--immunopathological findings.

Ex vivo perfusions of human decay accelerating factor-expressing transgenic (n = 3), and nontransgenic (n = 6) porcine livers with human blood revealed a higher degree of organ damage in non-transgenic pig livers. Transgenic livers were protected from immunohistologically detectable complement deposition, despite corresponding IgM and IgG deposits in both groups. Complement activation and consumption of C3 and C4 turned out to be lower in transgenic pig livers. In contrast to livers of normal landrace pigs, livers from genetically manipulated pigs showed no morphological alterations after perfusion.

Animals↗
PubMed1996

The function of transgenic human DAF-expressing porcine livers during hemoperfusion with human blood.

Extracorporal pig liver perfusion could bridge the deadly problem of acute human liver failure. However, preformed natural antibodies and complement activation (CA) are the predominant mechanisms of hyperacute xenogeneic rejection. The blockade of both pathways of CA in the xenograft, using transgenic livers expressing human decay accelerating factor on the endothelial surface results in prolonged graft survival and lower release of mediators.

Animals↗
PubMed1996

Effect of growth factors on matrix synthesis by human nasal chondrocytes cultured in monolayer and in agar.

Reconstructive surgery of multiple areas of the body may require replacement bone or cartilage transplants to repair defects or lesions of skeletal tissue. Advances in cell and tissue culture techniques now permit synthesis of autologous human cartilage in vitro. Several growth factors regulate the metabolism and activation of cartilage cells. To enhance culture conditions and effectiveness for in vitro cartilage engineering, the aim of our investigations was to characterize the influence of transforming growth factor (TGF)-beta and basic fibroblast growth factor (bFGF) on human nasal septal chondrocytes. The isolated cells were cultured as monolayers on plastic and in soft agar. The biological effects of the growth factors were assessed by determining synthesis of total protein and proteoglycan. TGF-beta caused a dose-dependent stimulation of total protein as well as glycosaminoglycan synthesis by all chondrocytes cultured. This stimulatory effect of TGF-beta was greater for chondrocytes cultured in soft agar than for chondrocytes cultured on plastic. No stimulatory effects of matrix synthesis was observed for bFGF in either culture condition. Our results show that TGF-beta can be employed to enhance in vitro production of cartilage grafts for reconstructive surgery.

Cartilage↗
PubMed1996

Monoclonal antibodies against human chondrocytes.

Cell-specific antigens are mainly found in cells or membrane surfaces rather than in the surrounding matrix. However, until now it was not possible to produce antibodies specific for cellular structures of chondrocytes. In 1989, Lance (Immunol. Lett. 21:63-73; 1989) first established specific monoclonal antibodies for human articular chondrocytes tested only by immunofluorescence. Studies describing the specificity of these five antibodies (HUMC 1-5) and their relevance for immunohistological analysis of cartilage tissue were not available until now. Therefore, the aim of the following study was to investigate the distribution of HUMC 1, 2, 3, 4, and 5 in mesenchymal cells in vivo and in vitro immunohistochemically. Further investigations concentrate on the localization of chondrocyte specific antigens using immunoelectron microscopy. Immunohistological studies showed positive immunostainings with all five antibodies in human chondrocytes in vivo and in vitro. A cross-reaction with human fibroblasts and osteoblasts for the antibodies HUMC 2 and HUMC 5 was observed. Furthermore, a parallel loss of immunoreactivity for HUMC 1, HUMC 3, and HUMC 4 was observed in cultured chondrocytes indicating that the specific antigens vanish during differentiation observed in vitro. Subsequent immunoblot analysis employing collagens as antigens did not show any reactivity. Using immunoelectron microscopy, gold particle labeling was observed in intracytoplasmatic vesicles of isolated chondrocytes. Our results indicate that HUMC 1, HUMC 3, and HUMC 4 are specific for cartilage cells and might be suitable for immunohistological analysis of different cartilage tissues and pathologically altered chondrocytes.

Antibodies, Monoclonal↗
PubMed1996

Expression of ICAM-1 on intact cartilage and isolated chondrocytes.

A major factor in cellular cytotoxicity is the interaction between LFA-1 on leukocytes and ICAM-1 on targets. Because several inflammatory cartilage diseases are characterized by the presence of leukocyte infiltrates, the expression of ICAM-1 on human cartilage, cultured chondrocytes, and transplanted cartilage was investigated using monoclonal antibodies. Frozen tissue sections, chondrocytes in suspension, as well as total cellular mRNA were prepared from human cartilage samples. ICAM-1 expression was studied with two different monoclonal antibodies directed against ICAM-1 by immunohistochemical APAAP-staining and additional flow cytometric analyses. The expression of ICAM-1-mRNA in cartilage tissue was analyzed using the northern blot hybridization technique. Furthermore, chondrocytes were treated in culture with interleukin-1 (IL-1) and gamma-interferon (gamma-IFN). ICAM-1 expression after culture was quantified using flow cytometric analysis. We could detect ICAM-1 mRNA in cartilage tissue, however, the immunostaining of tissue sections using monoclonal antibodies did not give clear positive reactions. Isolated chondrocytes showed strongly positive staining patterns in comparison with adequate negative controls as assessed by flow cytometry. A dose-dependent increase of the expression of ICAM-1 on chondrocytes was observed when stimulated with IL-1 and gamma-IFN. Finally, two of the three studied transplanted autologous cartilage samples with advanced resorption showed the presence of ICAM-1 molecules as assessed by immunohistochemistry. This expression of ICAM-1 suggests that the molecule plays a role in severe cartilage inflammatory processes, where tissue damage leads to the exposure of chondrocyte surfaces.

Cell Division↗
PubMed1996

[Apparent wall shear rate and leukocyte-endothelium interaction in iris blood vessels in endotoxin-induced uveitis].

UNLABELLED: Inflammatory stimuli induce the expression of adhesion molecules on leukocytes and endothelial cells. The adhesive forces between leukocytes and the vascular endothelium are antagonized by the shear stress of the flowing blood. The aim of this study was to examine how differences in the apparent wall shear rate measured in iris venules with varying caliber affect leukocyte-endothelium interaction. METHODS: The microvasculature of the iris in Lewis rats (n = 6) was examined using intravital fluorescence microscopy [2]. Blood flow was visualized with FITC-HES and leukocytes were stained with rhodamine 6G. Venules (n = 110) ranging in diameter from 20-60 microns were analysed with regard to the following parameters: Flux of leukocytes, velocity of leukocytes in the center stream, number of rolling and adherent leukocytes. The apparent wall shear rate was calculated from the center stream velocity and the vessel diameter. Animals were examined 4 h after administration of endotoxin from S. typhimurium (500 mg/kg body wt i.p.), when leukocyte-endothelium interaction is strongly enhanced. RESULTS: The flux of leukocytes, the absolute number of rolling leukocytes and the velocity of leukocytes in the center stream was higher in larger than in smaller venules. The apparent wall shear rate decreased with increasing vessel diameter. Calculated values were 806 +/- 59 s-1 for vessels 20-30 microns in diameter and 483 +/- 34 s-1 for vessels of 50-60 microns (mean +/- SEM). The number of adherent leukocytes per mm2 endothelial surface and the rolling fraction did not show significant differences between vessels with varying caliber. CONCLUSION: Although the shear rate declined with increasing vessel diameter, we could not observe an increase in rolling and adherent leukocytes. The effects of vessel diameter on leukocyte adhesion to the vascular endothelium in postcapillary iris venules are minimal.

Animals↗
PubMed1996

Quantitative analysis of interleukin-1-alpha gene expression in middle ear cholesteatoma.

Regardless of its origin, cholesteatoma is characterized by the presence of a keratinizing epithelium with an hyperproliferative behavior leading to a very important bone resorption. Previous studies have demonstrated overexpression of interleukin-1 (IL-1 protein in middle ear cholesteatoma by immunohistochemistry and enzyme-linked immunosorbent assay, suggesting a significant role for IL-1-alpha. In this study, the presence of IL-1-alpha messenger ribonucleic acid (mRNA) was quantified by in situ hybridization on frozen sections (n = 10) and by computer-assisted image analysis. Human skin obtained from the external ear canal (n = 10) was used as the control. A higher percentage of cells hybridized for the antisense probes IL-1-alpha mRNA was found in cholesteatoma epithelium. Furthermore, keratinocytes of the suprabasal cell layers were also found to contain specific hybridizations. Some cells in cholesteatoma stroma also contained IL-1-alpha mRNA transcripts. The results of this study confirm the central role of IL-1-alpha in the epithelium hyperproliferation and bone resorption observed in middle ear cholesteatoma.

Cholesteatoma, Middle Ear↗