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Biomedical subjects

C Hammer

Publications and source records attributed to C Hammer.

At least 55 records · Page 3Linked to original sources
PubMed1999

Xenogeneic, extracorporeal liver perfusion in primates improves the ratio of branched-chain amino acids to aromatic amino acids (Fischer's ratio).

In fulminant hepatic failure (FHF), the development of hepatic encephalopathy is associated with grossly abnormal concentrations of plasma amino acids (PAA). Normalization of the ratio of branched-chain amino acids to aromatic amino acids (Fischer's ratio) correlates with clinical improvement. This study evaluated changes in PAA metabolism during 4 h of isolated, normothermic extracorporeal liver perfusion using a newly designed system containing human blood and a rhesus monkey liver. Bile and urea production were within the physiological range. Release of the transaminases AST, ALT and LDH were minimal. The ratio of branched (valine, leucine, isoleucine) to aromatic (tyrosine, phenylalanine) amino acids increased significantly. These results indicate that a xenogeneic extracorporeal liver perfusion system is capable of significantly increasing Fischer's ratio and may play a role in treating and bridging patients in FHF in the future.

Alanine Transaminase↗
PubMed1999

Scintigraphy and immunohistology of antimyosin-Fab during graft rejection.

Up to now, the cellular localization pattern of monoclonal antimyosin antibodies (AMA) during acute rejection has not been described. Focused on this the authors made immunohistochemical and scintigraphic studies (AMS) with AMA in an animal transplantation model. Heterotopic cervical heart transplantation was performed in 12 mongrel dogs. Immunosuppression consisted of triple drug therapy. As standard the grafts were examined by daily transmural biopsies and routine histology. Dependent on the daily biopsy results, 0.5 mg of indium 111 ((111)In)-labeled AMA-Fab was injected. Subsequently every 2 hours transmural biopsy cylinders were taken out of the right ventricle and examined in indirect peroxidase staining technique. Forty-eight hours after AMA injection, scintigraphy in single photon emission computed tomography (SPECT) technique (AMS) was carried out and the heart-to-lung ratio (H/L-ratio) was calculated. The immunohistochemical maximum of AMA accumulation could be found 20 to 72 hours after AMA injection. This means that a scintigraphic examination should be done earlier than 20 hours and later than 3 days after injection. Dependent on the grades of bioptic rejection diagnosis a specific morphologic AMA localization was seen (grade I+II intercellular and slightly intracellular detection of AMA, grade III strongly intracellular and in particular perinuclear accumulation of the antibody, p<0.01). Moreover, the authors found a good correlation between scintigraphic H/L-ratio results and the corresponding histologic findings (grade I: H/L = 2.1 +/- 0.2; grade II: H/L = 3.1 +/- 0.2; grade III: H/L = 3.5 +/- 0.3; n = 19; p<0.02). The recently described positive AMS scans even in cases of mild rejection seem to be subject to an intercellular AMA localization. This typical AMA morphology during mild rejection favors the theory of the pore-forming protein allowing the efflux of myosin fragments as effector mechanism of cytotoxic lymphocytes in the early phase of acute rejection. The immunohistochemical AMA examination could explain the present discrepancy between positive AMS results of an intracellular protein in cases of mild or moderate acute rejection when visible cellular damage in the corresponding routine histology is absent.

Animals↗
PubMed1999

Procalcitonin, a new indicator for non-viral infections in heart, lung or liver transplant patients.

PCT is a highly specific analyse which shows significant diagnostic validities when non-viral infections are compared with rejection episodes. PCT discriminates inflammatory events such as rejection or viral infections and non-viral infections including bacterial, fungal and protozoal infections. The half-life of PCT is 24 h indicating a clearly competent antibiotic treatment. PCT provides vital information early to clinicians and allows them to improve the management of bacterial/fungal infection in immunocompromised transplant patients. PCT thus facilitates and improves the outcome of survival rate and the quality of life in the postoperative period of patients with heart, lung or liver grafts.

Bacterial Infections↗
PubMed1998

Physiological obstacles after xenotransplantation.

The incompatibility of allografts is restricted to immunologic factors such as the MHC class I and class II antigens. Anatomic, physiological, and biochemical characteristics are identical. This is completely different in xenografts. The upright position of man is unique in nature. Gravity therefore exerts a different impact on the anatomic situation of organs such as lung, heart, liver, and kidney. More pronounced are differences on the humoral and enzymatic basis. Complex interactions existing in allografts are totally disturbed in xenogeneic situations. Up- and downregulation controlled by releasing factors on the one hand and inhibitors on the other must be species-specific. These actions of mainly proteases are both fast and in most cases depend on species-specific receptors. Examples are growth hormones which could stimulate the xenografts to unrestricted growth, as in pig hearts in the human patient. Enzymes not metabolized by the liver would constantly stimulate mechanisms to a level that is not compatible with life, and other reactions could be more expressed in the donor species than in man and thus disturb these interactions. Products like albumin are carriers for other molecules and need to be compatible for binding sites. Pig and human albumin have an amino acid identity of less than 65% erythropoetin (EPO) of less than 82%, and complement of less than 70%. All factors are obviously without specific function in the future recipient, the human patient. In contrast, pig complement would, as a foreign molecule, induce the alternative complement pathway in the human recipient, leading to unknown side effects. It is not sufficiently investigated whether under such physiological and anatomic differences a long-term survival of xenograft or recipient is possible--a chain is as strong as its weakest link.

Animals↗
PubMed1998

Cartilage reconstruction in head and neck surgery: comparison of resorbable polymer scaffolds for tissue engineering of human septal cartilage.

New cell culture techniques raise the possibility of creating cartilage in vitro with the help of tissue engineering. In this study, we compared two resorbable nonwoven cell scaffolds, a polyglycolic acid/poly-L-lactic acid (PGA/PLLA) (90/10) copolymer (Ethisorb) and pure PLLA (V 7-2), with different degradation characteristics in their aptitude for cartilage reconstruction. Chondrocytes were isolated enzymatically from human septal cartilage. The single cells were resuspended in agarose and transferred into the polymer scaffolds to create mechanical stability and retain the chondrocyte-specific phenotype. The cell-polymer constructs were then kept in perfusion culture for 1 week prior to subcutaneous transplantation into thymusaplastic nude mice. After 6, 12, and 24 weeks, the specimens were explanted and analyzed histochemically on the presence of collagen (azan staining), proteoglycans (Alcian blue staining), and calcification areas (von Kossa staining). Furthermore, different collagen types (collagen type I, which is found in most tissues, but not in hyaline cartilage matrix; and collagen type II, which is cartilage specific) were differentiated immunohistochemically by the indirect immunoperoxidase technique. Vascular ingrowth was investigated by a factor VIII antibody, which is a endothelial marker. Quantification of several matrix components was performed using the software Photoshop. Significant differences were found between both nonwoven structures concerning matrix synthesis and matrix quality as well as vascular ingrowth. Ethisorb, with a degradation time of approximately 3 weeks in vitro, showed no significant differences from normal human septal cartilage in the amount of collagen types I and II 24 weeks after transplantation. Thin fibrous tissue layers containing blood vessels encapsulated the transplants. V 7-2 constructs, which did not show strong signs of degradation even 24 weeks after transplantation, contained remarkably smaller amounts of cartilage-specific matrix components. At the same time, there was vascular ingrowth even in central parts of the transplants. In conclusion, polymer scaffolds with a short degradation time are suitable materials for the development of cartilage matrix products, while longer stability seems to inhibit matrix synthesis. Thus, in vitro engineering of human cartilage can result in a cartilage-like tissue when appropriate nonwovens are used. Therefore, this method could be the ideal cartilage replacement method without the risk of infection and with the possibility of reconstructing large defects with different configurations.

Adult↗
PubMed1998

Prevention of initial perfusion failure during xenogeneic ex vivo liver perfusion by selectin inhibition.

BACKGROUND: Endothelial cell activation triggered by xenoreactive antibodies and complement products is the main feature of discordant xenograft rejection. The contribution of early cell-mediated mechanisms to this rejection process is poorly understood, and the function of adhesion molecules in xenogeneic cell interactions in vivo is unclear. The aim of the study was to investigate the role of selectins in mediating cell-dependent initial perfusion failure and functional restrictions in xenoperfused guinea pig (GP) livers. METHODS: Isolated GP livers were hemoperfused in a flow-constant, recirculating perfusion system via the portal vein. Microhemodynamic parameters such as sinusoidal perfusion rate and leukocyte flux were analyzed using intravital fluorescence microscopy. Hepatic oxygen consumption and bile production, as well as liver enzymes, potassium level, and numbers of white blood cells and platelets in the perfusate, were determined. The GP livers were perfused either with GP blood (control perfusion), with unmodified rat blood (xenoperfusion), or with rat blood treated with the selectin-blocking polysaccharide Fucoidin. RESULTS: A significant sinusoidal perfusion failure was observed in the xenoperfusion group, which was accompanied by distinct signs of a functional restriction-like reduced oxygen consumption, bile production, and increased perfusion pressure. However, there were significantly fewer impairments in the Fucoidin group. Furthermore, fewer platelets were trapped and a smaller number of stagnant leukocytes were observed in this group. CONCLUSION: Fucoidin did not suppress complement activation during xenoperfusion. Considering that Fucoidin inhibits the selectin-dependent interactions among white blood cells, platelets, and sulfate-containing proteoglycans on the surface of vascular endothelium, these findings suggest an important role for early cellular interactions in the development of organ failure during xenogeneic rejection.

Animals↗
PubMed1998

Impact of immunoadsorption on complement activation, immunopathology, and hepatic perfusion during xenogeneic pig liver perfusion.

BACKGROUND: The impact of antibody adsorption by immunoapheresis on liver damage, complement activation, and hepatic perfusion was evaluated against the background of an application in extracorporeal pig liver perfusion for hepatic coma. METHODS: Eighteen pig livers were ex vivo perfused close to physiological conditions with fresh human blood for 4 hr. The influence of the perfusion circuit was investigated by perfusions of the circuit in the absence of livers (group 1 [G1]; n=5). Livers were xenoperfused without modifications in group 2 (G2; n=6). In group 3 (G3; n=6), pure Sepharose columns were used prior to liver perfusion. Immunoapheresis with Ig-Therasorb 100 columns was used in group 4 (G4; n=6). RESULTS: IgG was reduced by 95%, IgM by 72%, and IgA by 82% in G4, but only by about 30% in G3 (P<0.05). C4d, Bb fragment, and C3a levels were significantly lower in G4 than in G3 and G2 (P<0.05) after 180 min. Immunoadsorption diminished antibody and complement deposition as well as hepatocellular damage in G4. Portal angiographies demonstrated improved hepatic perfusion in G4. CONCLUSION: Immunoapheresis reduced organ damage as well as complement activation and improved hepatic perfusion during xenogeneic pig liver perfusion.

Acute Disease↗
PubMed1998

Cartilage tissue engineering with novel nonwoven structured biomaterial based on hyaluronic acid benzyl ester.

The aim of this study was to investigate the possibility of using the benzyl ester of hyaluronic acid (HYAFF 11), a recently developed semisynthetic resorbable material, as a scaffold for the culture of human nasoseptal chondrocytes in tissue-engineering procedures of cartilage reconstruction. Different techniques such as immunohistochemistry, scanning electron microscopy, and confocal laser scanning microscopy were used to study the behavior, morphology, and phenotype expression of the chondrocytes, which were initially expanded and then seeded on the material. The nonwoven cell carrier allowed good viability and adhesivity of the cells without any surface treatment with additional substances. Furthermore, the cultured cells expressed cartilage-specific collagen type II, indicating that they were able to redifferentiate within the scaffold of HYAFF 11 and were able to retain a chondrocyte phenotype even after a long period of in vitro conditions. Nevertheless, the expression of collagen type I, which was produced by dedifferentiated or incompletely redifferentiated chondrocytes, was noticeable. Additional data were obtained by subcutaneous implantation of samples seeded with human cells in the in vivo model of the athymic nude mouse. The results after 1 month revealed the development of tissue similar to hyaline cartilage. This study is promising for the use of this scaffold for tissue engineering of cartilage replacements.

Animals↗
PubMed1998

Monitoring of microhemodynamic changes during ex vivo xenogeneic liver perfusion using intravital microscopy.

The main targets of xenogeneic rejection mechanisms are the endothelial cells of the graft. Their activation and the consequent alteration of the organ's microcirculation lead to the destruction of the xenograft. Microhemodynamic changes occurring during this process are still poorly characterized. The aim of this study was to analyze the microcirculation during xenogeneic ex vivo hemoperfusion of rat livers and to monitor the impact of treatment strategies using intravital fluorescence microscopy. In contrast to the isogeneic control group, blood flow almost completely stopped within the first minutes of xenoperfusion. Simultaneously, perfusion pressure increased and bile production was reduced. Acetylsalicylate (Aspisol) and the platelet-activating factor antagonist WEB 2170 improved the microcirculation and function of the xenoperfused liver. The combination showed a synergistic effect. After apheresis of preformed xenogeneic antibodies, the parameters measured were comparable with those seen in isogeneic experiments. Complement degradation with cobra venom factor revealed a minor improvement in perfusion. A rapid, extensive, and irreversible leukocyte accumulation in terminal portal vessels was observed in all xenogeneic experiments. Blood counts of the perfusate confirmed the early trapping of leukocytes and platelets in the xenoperfused liver, indicating nonimmunological, cellular involvement in this rejection process.

Animals↗
PubMed1998

Analysis of the microcirculation during xenogeneic liver perfusion in the guinea pig--rat model. The contribution of leukocytes to the rejection process.

Since the main feature of hyperacute rejection is a disturbance of the xenograft's microcirculation, we analyzed microhemodynamic parameters during xenogeneic hemoperfusion of the guinea pig (GP) liver and investigated the contribution of leukocytes to the rejection process using intravital fluorescence microscopy. Isolated GP livers were hemoperfused via the portal vein in a recirculating system with a constant flow of 1 ml/min per g liver. In contrast to isogeneic perfusion with heparinized GP blood, a disturbance in the microcirculation was observed during xenogeneic perfusion using heparinized rat blood, with significantly higher values of perfusion pressure, reduced sinusoidal perfusion rates, and a larger number of stagnant leukocytes. A complete breakdown of the microcirculation, with the highest values of perfusion pressure and the smallest perfusion index, was associated with 100% accumulated leukocytes when rat blood was anticoagulated with sodium citrate. Almost isogeneic perfusion values were obtained when fucoidin, which inhibits L-selectin-dependent cell interaction, was added to heparinized rat blood. These data indicate that leukocyte-endothelial cell interaction contributes to xenogeneic rejection.

Animals↗
PubMed1998

Xenogeneic rejection mechanisms shown by intravital microscopy.

The importance of this model is that it showed exactly where in the organ the xenogeneic damage occurred. The liver received the blood mainly via portal veins, which merge with the pulsatile arterioles in the Disse spaces. This periportal area is followed by the sinusoids and ends in the central or postsinusoidal vein. IVM enables us to differentiate between perfused and unperfused sinusoids and to calculate the ratio. Not all sinusoids are perfused at any time. It appears that 5% to 10% are unperfused. During xenoperfusion, only 65% of sinusoids show blood flow after a perfusion of 12 minutes. This is less than in hemorrhagic shock. Only the combined platelet inhibitors and apheresis resulted in remarkable improvement. The calculation of an index indicates the improvement of acinar perfusion. Thrombocytes and leukocytes remain, however, in the liver. In conclusion, the model used to analyze the dynamics of microvascular liver perfusion and sinusoidal perfusion is suitable for such investigations in a xenogeneic model. It has no major side effects, either on the perfusing blood or on the liver, as proved in the isogeneic control group. The important finding in our eyes is that the perfusion failure begins in the periportal fields, where the blood enters the foreign microvasculature and where the leukocytes first come in contact with the foreign endothelium. All previous manipulations had only a minor impact on this contact of cells with the foreign endothelium. The study indicates that the early events of xenogeneic hyperacute rejection are of unspecific character and involve leukocytes and thrombocytes to a major degree, thus being responsible for the dramatic decrease in the microcirculation in xenogeneic livers.

Animals↗
PubMed1998

Procalcitonin: a new marker for diagnosis of acute rejection and bacterial infection in patients after heart and lung transplantation.

UNLABELLED: The aim of the study was to investigate the reliability of procalcitonin (PCT), a new potential marker for detection of bacterial, fungal and protozoal infections, in order to differentiate these from viral infections and early rejections in heart, heart-lung and lung transplanted patients. PCT is a propeptide of calcitonin with unknown origin which is not detectable in plasma of healthy subjects. It increases rapidly and significantly under severe microbial infections. METHODS: PCT plasma levels were measured using an immuno-luminescence assay. C-reactive protein and white blood cells were quantified to validate the PCT values. RESULTS: Increased levels of PCT were found in all transplant patients with bacterial, fungal and protozoal infections. The magnitude of the values were clearly associated with the severity of the infection. Trauma of operation or inflammatory events such as viral infections and rejections did not trigger PCT-production. The release of PCT did not depend on the type of pathogens even though Aspergillum resulted in the highest levels measured. Sensitivity, specificity and prognostic value of PCT for systemic infections were higher than of the other parameters investigated. CONCLUSION: PCT is a highly specific analyte which shows significant diagnostic validities when nonviral infections are compared with rejection episodes. PCT discriminates between inflammatory events such as rejection or viral infections and nonviral-infections including bacterial, fungal and protozoal infections. The half-life of PCT is 24 h indicating clearly a competent antibiotic treatment. Unnecessary antibiotic therapy can be avoided due to the early exclusion of bacterial and fungal infections.

Adolescent↗
PubMed1998

Intravital microscopic investigation of xenogeneic microcirculation and impact of complement depletion by cobra venom factor.

Discordant xenografts are hyperacutely rejected within minutes. Disturbances in the microcirculation are considered to be the central mechanisms of hyperacute xenogeneic rejection (HXR). In this study intravital fluorescence microscopy was applied to investigate the dynamics of microcirculatory alterations in a setting in which HXR was inhibited by complement (C) depletion. Blood flow was measured as rat livers were perfused with isogeneic rat or xenogeneic human blood to assess the pattern of either physiological isogeneic hemoperfusion or in the course of HXR. Next, the complement system of the perfusate was inactivated by cobra venom factor (CVF) in order to inhibit HXR. Liver sinusoids of the isogeneic group were homogeneously perfused (sinusoidal perfusion rate 93.6+/-0.3%), whereas in the xenogeneic group the sinusoidal perfusion rate dropped to 67.1+/-3%. The perfusion in the periportal zone of an acinus was significantly lower ( 59.0+/-3.3%) than in the pericentral zone (76.2+/-3.1%). Treatment with CVF improved the sinusoidal perfusion to a value of 85.6+/-2.3%, physiological perfusion, however could not be reached. In contrast to the isogeneic group, massive white blood cell (WBC) and platelet accumulation was found in the xenogeneic group, especially in the terminal portal vessels and in the periportal zone of liver acini. WBC and platelet counts show that the adherence of these cells appears rapidly in the first 5 min after reperfusion as firm adherence. CVF was not able to inhibit WBC and platelet accumulation, indicating that WBC endothelial interactions do not require an intact complement system. Bile flow, a parameter of liver function, decreased only slightly during isogeneic perfusion. The addition of CVF to the rat blood reduced the bile flow to one half of the untreated isogeneic flow, indicating a hepatotoxic side-effect of CVF. In xenogeneic perfusion the bile flow dropped to 62.6% and with the addition of CVF to 37.5% in the first 15 min after reperfusion. The bile flow of the CVF treated groups recovered during the perfusion but could not reach isogeneic values.

Acute Disease↗
PubMed1998

Organs from animals for man.

In the following review some of the problems of xenotransplantation shall be discussed, based on the few experimental data available so far and on reports in the literature describing investigations which may be of importance for xenotransplantation. The impact of gravity on the upright posture of man versus almost all other mammals, the dysfunction between enzymes and hormones in different species and the lack of interactions between interleukins, cytokines and vasoactive substances will be taken into consideration. The question must be asked whether different levels of carrier molecules or serum proteins play a role in the physiological network. Even though the development of transgenic animals or other imaginative manipulations may lead to the acceptance of any type of xenografted organ, it has to be established for how long the products of the xenografts are able to act in the multifactorial orchestra. We are far from understanding xenogeneic molecular mechanisms involved in toxicity, necrosis and apoptosis or even reperfusion injury and ischemia in addition to the immediate mechanisms of the hyperacute xenogeneic rejection. Here, cell adhesion, blood clotting and vasomotion collide and bring micro- and macrocirculation to a standstill. All types of xenogeneic immunological mechanisms studied so far were found to have a more serious impact than those seen in allogeneic transplantation. In addition we are now only beginning to understand that so-called immunological parameters in allogeneic mechanisms act also in a true physiological manner in the xenogeneic situation. These molecular mechanisms occur behind the curtain of hyperacute, accelerated, acute or chronic xenograft rejection of which only some folds have been lifted to allow glimpses of part of the total scene. Other obstacles are likely to arise when long-term survival is achieved. These obstacles include retroviral infections, transfer of prions and severe side effects of the massive immunosuppression which will be needed. Moral, ethical and religious concerns are under debate and the species-specific production of proteins of the foreign donor species developed for clinical use suddenly appears to be a greater problem than anticipated.

Animals↗
PubMed1998

Redesigning nucleic acids.

A research program has applied the tools of synthetic organic chemistry to systematically modify the structure of DNA and RNA oligonucleotides to learn more about the chemical principles underlying their ability to store and transmit genetic information. Oligonucleotides (as opposed to nucleosides) have long been overlooked by synthetic organic chemists as targets for structural modification. Synthetic chemistry has now yielded oligonucleotides with 12 replicatable letters, modified backbones, and new insight into why Nature chose the oligonucleotide structures that she did.

Catalysis↗