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Biomedical subjects

C Hammer

Publications and source records attributed to C Hammer.

At least 109 records · Page 6Linked to original sources
PubMed1996

[Xenogenic acceptance, a realistic fantasy?].

Over the last 5 years an unexpectedly fast progress has been achieved in the field of xenotransplantation. This gives cause for substantial hope. Thus, the wish to use animal grafts for the replacement of human organs could become a reality. However, no results exist at present to suggest a biological and immunological long term acceptance of xenografts in the near future. Xenotransplantation has the goal to improve the organ shortage dramatically and to solve the existing ethical problems of organ donation.

Animals↗
PubMed1995

Infections and immunological hazards of allogeneic bone transplantation.

Allogeneic transplantation of human cancellous and cortical bone is a controversially discussed concept in trauma and orthopaedic surgery. Biological and immunological arguments support transplantation of autologous material whenever this is technically possible. On the other hand, synthetic alloplastic materials for bone substitution are available free of immunological and hygienic hazards. In this context the value of allogeneic bone grafts is discussed, especially considering the problem of AIDS. If autologous corticospongious bone is to be used its supply is limited. On the other hand, alloplastic synthetic artificial bone does not meet all the requirements demanded for substitution of large osseous defects up to now. The problems of geometric and mechanical stability of these alloplastic materials still remain. Therefore, no alternative to allografting of large, stable, corticospongious fragments exists in some cases. Bone transplantation is performed without vital indication in nearly every case. Thus an optimum of hygienic security has to be claimed for recipients of allogeneic bone. The "Munich model" for bone transplantation is presented and discussed.

Acquired Immunodeficiency Syndrome↗
PubMed1995

Laryngeal reconstruction using allogeneic cartilages.

Preserved allogeneic cartilage has been used to reconstruct laryngeal defects. The most important problem with this approach has been graft resorption, which seems to be caused by devitalization of the grafts as a consequence of preservation. In this study, the authors compared the in vivo behavior of vital and nonvital preserved cartilage used to reconstruct the larynx of New Zealand white rabbits. The vital cartilage grafts were stored using organ culture procedures, and the nonvital grafts were stored in formaldehyde. While the formaldehyde-preserved cartilage showed inflammatory changes, the transplanted vital cartilage was well accepted and showed no evidence of immune cell infiltrations. The authors concluded that viable cartilage grafts are preferable to grafts of chemically preserved cartilage.

Animals↗
PubMed1995

Engineering of cartilage tissue using bioresorbable polymer fleeces and perfusion culture.

Replacement of injured or diseased skeletal tissues by either autograft or allograft cartilage has increased steadily during recent decades. The ideal method is to use autologous cartilage; however, this is extremely limited due to the scarcity of donor sites. We present a new approach to the in vitro formation of cartilage grafts for autologous grafting in reconstructive surgery. Bioresorbable polymer fleeces of polylactic acid were used as temporary cell carrier matrices to establish three-dimensional cultures of human chondrocytes. The polymer surface was coated with poly-L-lysine before cell integration. These cell-polymer tissue constructs were encapsulated with low melting point agarose and then placed in perfusion culture chambers to provide a constant supply of nutrients into the cultures. The culture medium consisted of Ham's F12 supplemented with 2% fetal calf serum and 50 micrograms/ml ascorbic acid. The cell-polymer tissues were harvested and frozen for toloudine and alcian blue staining as well as electron microscopic examination after different periods of time in culture. A monoclonal antibody specific for collagen type II was used to characterize the cell phenotype. With this culture procedure chondrocytes maintained a differentiated phenotype with synthesis of collagen and proteoglycan. Collagen fibrils with clear cross-striation were evident in electron microscopic images. The results show that our organotypic cell culture method allows the in vitro production of bioartificial cartilage for transplantation.

Biomedical Engineering↗
PubMed1995

[Cultivation of human cartilage tissue in a 3-dimensional perfusion culture chamber: characterization of collagen synthesis].

In reconstructive head and neck surgery, there is a great need for cartilage transplants. Sufficient autologous graft is often not available. Heterologous cartilage is used frequently, although there is danger of transmitting viral infections and resorption rates are high. We have developed a three-dimensional model for the formation of cartilage in vitro. The aim of this study was to characterize the collagen synthesis under these culture conditions. Human chondrocytes were isolated by digesting septal cartilage matrix in the presence of type II collagenase, hyaluronidase, and Dnase II in Ham's F12 medium. The resulting cells were kept in monolayer culture for one week and then suspended in 2% ultra-low-melting agarose (1:1). The cell-agarose conglomerate was encapsulated with a 3% ultra-low-melting agarose solution and placed in a perfusion culture chamber. A permanent flow of fresh medium (Ham's F-12 supplemented with 50 micrograms/ml ascorbic acid and 2% fetal calf serum) was provided by a peristaltic pump which delivered 1 ml/h with on/off intervals of 30 min. Samples were recovered after two weeks. Using electron microscopy abundant collagen fibril formation was shown. The collagen fibrils were identified histologically as cartilage specific type II collagen. No mRNA expression of collagen type X was observed using in situ hybridization. The cells appeared in a round cell shape with round nucleus and only slight variations in form and size. The present results indicate that the chondrocytes maintain their differentiated phenotype and continue to synthesize typical matrix products in this three-dimensional perfusion culture chamber.(ABSTRACT TRUNCATED AT 250 WORDS)

Cartilage↗
PubMed1995

In vivo study of leukocyte-endothelium interaction in endotoxin-induced uveitis.

PURPOSE: To analyze leukocyte-endothelium interaction in iris venules of living rats and to quantify changes of leukocyte dynamics in endotoxin-induced uveitis (EIU). METHODS: Lewis rats received an intraperitoneal injection of 100 micrograms of lipopolysaccharide (LPS; Salmonella typhimurium). Using intravital fluorescence microscopy, the iris vessels were examined, 2, 4, 6, 10, 14, 24, and 72 hours after LPS injection. A setup for intravital fluorescence microscopy of iris venules in the rat is described. Images are recorded with a video camera and stored on S-VHS videotape for off-line analysis. For contrast enhancement, erythrocytes and plasma were stained with fluorescein isothiocyanate (FITC) and FITC-hydroxyethylstarch, respectively. Rhodamine 6G was used for intravital staining of leukocytes. Resolution and magnification (x850) of the system facilitates observation of individual cells in the bloodstream in real time. Leukocytes were either flowing in the center stream, rolling along the endothelium, or firmly adherent. Image analysis provided data on microvascular leukocyte flux and leukocyte velocity. RESULTS: The percentage of leukocytes rolling on postcapillary venular endothelium increased significantly (P < 0.05) 4 hours after endotoxin administration, as did the number of firmly adherent cells. Leukocyte-endothelium interaction reached its maximum 6 to 10 hours before an increase of inflammatory cells in the aqueous humor. The response to endotoxin was reversible, subsiding to near-normal values after 72 hours. CONCLUSIONS: Intravital fluorescence microscopy provides data on microvascular parameters, including the number of rolling and sticking leukocytes on vascular endothelium. Inflammation of the anterior uvea was characterized with regard to leukocyte recruitment from blood to the vessel wall.

Animals↗
PubMed1994

Beating neonatal rat cardiomyocytes as a model to study the role of xenoreactive natural antibodies in xenotransplantation.

The hyperacute rejection reaction of xenogeneic organs is supposed to be triggered by xenoreactive natural antibodies of the recipient organism. In an experimental set-up allowing for rapid medium exchange, primary cultures of spontaneously beating neonatal rat cardiomyocytes were challenged with dialyzed human serum containing xenoreactive natural antibodies. After adding the serum specimens, a reproducible pattern of disturbed contractility was observed: following an initial increase in beating frequency, spontaneous contractions stopped completely. This standstill was reversible in all experiments. No signs of permanent cytotoxicity were observed. The temporary cessation of contractions was prevented by raising extracellular calcium concentration, but not by extracellular electrical stimulation. After absorption of xenoreactive natural antibodies, cellular contractions ensued without interruption. Inactivated serum specimens produced similar effects on contractility, although the duration of the standstill period was significantly shorter. The same qualitative phenomenon occurred when sera of other xenogeneic species were used. These results point to a temporary functional disturbance of parenchymal cells by xenoreactive natural antibodies, whereas no chronic cytotoxicity was conspicuous in these experiments.

Animals↗
PubMed1994

Xenotransplantation and its future.

Today at the beginning of the era of xenotransplantation, only simple and single observations about comparative physiology, biochemistry and anatomy are known. In addition, very few data exist which inform about the mechanisms after successful xenotransplantation. Nothing is known about the phenomena following successfully suppressed hyperacute xenogeneic rejection (HXR). Neither the elimination of a single factor nor the mitigation of whole systems has led to clinically relevant survival times (SVT). Pig organs transplanted into non-human primates survived a maximum of 22 days. The hope that transgenic manipulation and modification would be useful in prolonging the SVT of xenogeneic grafts still awaits supporting evidence. But within a short time, xenotransplantation could enable patients to receive a life saving animal organ as an alternative to an allograft. Xenotransplantation would, as a new dimension in medicine, shorten if not eliminate waiting lists. Therefore, scientists must vigorously develop xenografting as a viable alternative to allotransplantation. Xenotransplantation would not be the terrible danger that some individuals proclaim, and would also not simply be the extension of transplantation but would rather be a victory in medical research.

Animals↗
PubMed1994

Reduction of cyclosporine-induced nephrotoxicity by cilastatin following clinical heart transplantation.

The objective of this prospective, randomized, placebo-controlled, single-blinded study in 28 heart-transplanted patients was to investigate whether the dehydropeptidase inhibitor cilastatin reduces cyclosporine-induced nephrotoxicity. Cilastatin is available only in combination with imipenem, a beta-lactam antibiotic to which it is added for reduction of nephrotoxic side-effects of the antimicrobial agent. Patients received either 100 ml placebo (n = 12) or 100 ml (500 mg) imipenem/cilastatin (n = 16) twice perioperatively, and 4 times daily for the first 7 postoperative days. Serum creatinine and urea, as well as urine concentrations of N-acetyl-beta-D-glucosaminidase, which is directly correlated with tubular cell damage, were used as markers for renal function. Thromboxane B2 and 6-keto-prostaglandin F1-alpha serum concentrations were determined to investigate whether there is an imbalance in synthesis of thromboxane A2 and prostacyclin as a possible mechanism for cyclosporine-induced nephrotoxicity. Two placebo patients and 6 patients receiving imipenem/cilastatin had to be excluded from further analysis. Three of 10 placebo patients required hemofiltration, and 2 of them even required hemodialysis, as compared with none in the imipenem/cilastatin group. Creatinine concentrations increased significantly from the second to the fourth postoperative day in the placebo group, but remained nearly normal in cilastatin patients (P < 0.05 for intergroup comparison on postoperative days 2-4). The same trend was observed in urea and N-acetyl-beta-D-glucosaminidase concentrations, without the difference reaching statistical significance. For thromboxane B2 and 6-keto-prostaglandin F1-alpha no differences between the groups could be found. These results suggest that imipenem/cilastatin can counteract acute cyclosporine-induced nephrotoxicity, which appears to be associated with alterations of tubular cell function. The combined use of cyclosporine and imipenem/cilastatin appears to be advantageous in patients following heart transplantation during the initial postoperative period.

6-Ketoprostaglandin F1 alpha↗
PubMed1994

Intragraft events after heart transplantation: an experimental study comparing cytology in coronary sinus blood, peripheral blood, and daily histology.

Acute rejection is a frequent consequence after heart transplantation. To expand our knowledge of the rejection process and to investigate some intragraft events during acute rejection, the following experimental transplantation model was designed. Right cervical heart transplantation was performed in 12 mongrel dogs. Two experimental groups of six animals each received different immunosuppressive regimens. All animals were treated with daily triple drug therapy. In contrast to group 1, the animals in group 2 received high-dose steroids during rejection. The condition of the hearts was examined by daily transmural biopsies, graded according to the Billingham classification. To detect and quantify alterations in the mononuclear cell subsets of the myocardial venous return, blood samples from the coronary sinus blood (CS) and from peripheral blood (PB) were taken simultaneously with the biopsy. The total number of lymphoblasts and activated lymphocytes was determined and an activation index (AI) was calculated. The data referred to was established from 337 transmural biopsies. The AI of PB (n = 287) correlated well with the different stages of acute rejection (grade B0: AI = 2.2 +/- 2.1; grade B1 + 2: AI = 6.3 +/- 1.7; grade B3: AI = 10.0 +/- 4.7; P < 0.001). The rejection kinetics of both groups, including the rejection-free interval following high-dose steroid administration in group 2, could be expressed accurately by the AI. The time course of the total number of lymphoblasts in CS versus PB demonstrated that the lymphoproliferative response started 4 days prior to the first intramyocardial signs of rejection (mean = 3.8 +/- 0.7; n = 12).(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1994

Immunohistological studies of complement activation after xenogeneic perfusion of a working heart model.

Transplantation of organs from one species to another leads to immediate hyperacute rejection. Activation of complement is one important factor involved in this process. Whether complement activation is induced by preformed natural antibodies (PNAbs) via the classical pathway or by an "activator surface" via the alternative pathway is unclear. In order to simulate the relevant clinical situation of animal donor/human recipient we perfused working porcine hearts ex vivo with human blood. This also offered the possibility to study the process of complement activation in a precisely defined system with human complement proteins. PNAb titer and complement lytic activity of the plasma were measured. Immunohistological stainings for IgG, IgM, C1q, C4, C3d, C5-9, factor B, and properdin were performed on tissue sections of the left ventricle. PNAb titer almost totally disappeared within the first 5 min of perfusion. Complement lytic activity of the classical pathway decreased similarly within the first 3 h of xenogeneic and autologous perfusion from 70% to 40%. More detailed immunohistological studies revealed positive staining for C3d on endothelium and myocardium of ex vivo perfused xenogeneic hearts. Complement-induced cytotoxicity was proven by the presence of C5-9 (membrane attack complex). However, hardly any C1q and C4 could be found in the ex vivo xenogeneic perfused hearts. Staining for factor B was positive and proved activation via the alternative pathway. Beyond that, the presence of properdin binding even indicated an upregulation of the alternative pathway C3 convertase.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Engineering of cartilage tissue using bioresorbable polymer carriers in perfusion culture.

Bioresorbable polymer fleeces with a high internal surface area were used as temporary matrices to establish three-dimensional cultures of isolated human articular chondrocytes. The polymer surface was coated with poly-L-lysine to support cell attachment. The resulting cell-polymer tissues were cultured in perfusion culture chambers to achieve a constant supply of nutrients by diffusion. Retention and accumulation of extracellular matrix components synthesized by the chondrocytes were improved by encapsulation of the cell-polymer integrate in agarose gel. The cell-polymer tissues formed abundant collagen fibrils in vitro with a typical cross-triation clearly visible in electron microscopy analysis. Chondrocytes and intercellular matrix stained positively with monoclonal antibodies specific for differentiated chondrocytes and type II collagen. Synthesis of proteoglycans and collagen was also evident by further analysis with alcian blue and azan staining of cell-polymer tissue sections. The presented experimental tissue culture technique offers a novel concept for the in vitro formation of vital cartilage implants for reconstructive surgery or treatment of destructive joint diseases and possibly for the in vitro engineering of human tissues in general, with applications in drug testing and replacement of animal experiments.

Adult↗
PubMed1994

Cytoimmunological monitoring after homograft valve replacement.

Examination results concerning immunological reactions in cryopreserved allograft valves during the early postoperative course are so far not available. Cytoimmunological monitoring (CIM) is a well established method to prove rejection reaction after allograft transplantation and was used in this study. Allograft valves were harvested from patients who underwent heart transplantation, and did not require sterilizing in antibiotic solutions. The valves were dissected, conserved and subsequently frozen to -40 degrees C and stored in a freezing system at -196 degrees C. During the first 3 weeks following allograft implantation, CIM was performed daily. An activation index (AI) was determined from the cytological evaluation of the mononuclear concentrate in the peripheral blood. An increase of the AI > 1 was defined as an immunological reaction. As control we performed 98 CIM examinations in eight patients who underwent bioprosthetic valve replacement in the aortic position. Echocardiography (TTE and TEE) was used postoperatively as function control. Out of 16 patients who underwent cryopreserved aortic valve implantation in the aortic position, 336 CIM-results were obtained. An immunological reaction could be detected in all patients, starting on the 5th day on average. Comparing ABO-compatible (group I, n = 9) with ABO-incompatible (group II, n = 7) allografts, the AI-maximum in group I was 1.4 with a mean duration of 1.5 days. Group II was characterized by more intensive immunoreactions (mean = 2.3) which proved to be even more prolonged (mean = 3.3 days, P < 0.05). Nevertheless it became apparent that all observed immunological events were completely reversible without the need for immunosuppressive drugs.(ABSTRACT TRUNCATED AT 250 WORDS)

ABO Blood-Group System↗