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C Hammer

Publications and source records attributed to C Hammer.

At least 37 records · Page 2Linked to original sources
PubMed2001

Xenotransplantation: perspectives and limits.

Xenotransplantation faces the dilemma of an unlimited supply of cells, tissues and organs on the one hand and severe obstacles and limits on the other. One reason for the limitations is that the source animal of choice, the pig, and the human recipient separated 90 million years ago during evolution, a time in which biological characteristics such as anatomy, physiology and immunology have had much time to drift far apart. The acceptance of such an evolutionary widely divergent organ, especially the heart of a pig, could evoke refusal of xenotransplantation in conservative and religious patients. New legal aspects of allocation of xenografts have therefore to be reflected upon and appropriate guidelines developed. Inquiries show, however, that the acceptance of all types of porcine organs would be high if the quality of life after receiving such a xenograft is comparable to that after receiving the same allograft. This individual benefit of a xenograft could lead to a disregard of the collective risk in terms of xenozoonoses, often presented as a catastrophic scenarium. Therefore, transplantation societies and ethics committees have published comments and even guidelines for handling future clinical xenotransplantation. All three monotheistic religions and Hinduism support the idea of saving and improving human life with the help of an animal organ.

Animals↗
PubMed2001

In vivo microscopic assessment of microcirculatory changes in a concordant xenogeneic primate experimental set up.

UNLABELLED: Organ transplantation is always connected with ischemia and thus reperfusion injury of the graft. One of the characteristics in this process is the temporary and permanent adherence of leukocytes to the endothelium of the graft. This cell-to-cell interaction allows the immunocompetent cells to interact in the sense of antigen recognition with mainly defect endothelial cells. It was the aim to study whether induction therapy with poly-clonal ATG's would reduce or even prohibit these early interactions. MATERIAL AND METHODS: The distal extremities of cynomolgus monkeys were flushed via the femoral vessels and reperfused with ABO-compatible human heparinised blood of a hct of 30%. Microcirculation was observed applying intra-vital microscopy. The images taken by a CCD-camera are recorded on video tapes for later off line evaluation. pATG 1 is directed against jurkat cells, pATG 2 against human thymocytes. In controls the blood vessels were perfused with untreated blood. In groups 2 and 3 the blood was treated with the amount of the ATG's used in clinical therapy 15 min. prior to perfusion. The total ischemia time was 1 hour. RESULTS: Five minutes after perfusion rolling was seen in the untreated animal, this increased to change into sticking after 30 min. The blood flow (RBC) in larger venoles remained almost normal. Both polyclonal ATG's inhibited the adhesion to a large extend. CONCLUSION: Ischemia reperfusion results in increasing adherence of leukocytes in the described model. pATG's suppress this phenomenon completely. This suggests that pATG's contain a number of antibodies directed against various types of cell surface molecules which are involved in reperfusion injury and that pATG's have a favourable influence on the early I/R-mechanisms after organ transplantation and a protective action when used as pre-operative induction therapy.

Animals↗
PubMed2000

IG-therasorb immunoapheresis in orthotopic xenotransplantation of baboons with landrace pig hearts.

BACKGROUND: The major problem of xenotransplantation is, that hyperacute xenograft rejection (HXR) causes graft failure within minutes or a few hours because of natural antibodies and activation of the complement system. As a preclinical model we transplanted pig hearts orthotopically into baboons. To prevent HXR after orthotopic xenotransplantation (oXHTx), the immunoglobulins (Ig) and natural antibodies were adsorbed to reusable Ig-Therasorb immunoadsorption (IA) columns. METHODS: We performed three oXHTx of landrace pig hearts into baboons (19+/-6.8 kg), using extracorporeal circulation (ECC) connected to the IA unit. After separating the recipient's blood into plasma and cellular fraction by a plasma filter, plasma flow was directed to the Ig-Therasorb column coated with polyclonal sheep-antibodies against human IgG, IgM, and IgA. Intraoperative treatment consisted of 4 cycles of IA. For a control, we transplanted one pig heart into a baboon (16.9 kg) without applying IA. Perioperatively, serum concentrations of Ig, anti-pig-antibodies, complement and cardiac enzymes were determined. Tissue samples of myocardium were collected at the end of the study for immunohistochemical examinations, light microscopic examination (LM) and electron microscopic examination (EM). For cardiac monitoring after oXHTx, we used ECG, echocardiography, and invasive measurement of cardiac output. To prevent a mismatch of donor and recipient heart size, the donor pig had a 30-40% lower body weight than the recipient baboon. RESULTS: Four cycles of IA removed >80% of IgG, IgM, and IgA from plasma. The graft of the control animal failed after 29 min. The first oXHTx with IA was intentionally terminated after 100 min, the second oXHTx after 11 hr and the third oXHTx after 21 hr. All xenografts showed no histological signs of HXR. After weaning off ECC, these donor hearts worked in sinus rhythm without electrocardiographic ST-segment elevation. An excellent cardiac output was measured by echocardiography and thermodilution (2 L/min). Serological parameters indicating cardiac damage were significantly lower after IA if compared with the control experiment. Macroscopically, the xenograft of the control animal showed massive hemorrhage in comparison with the almost inconspicuous grafts after IA. The myocardium of the IA group demonstrated fewer deposits of Ig and complement components compared with the control animal. CONCLUSION: Baboons do not hyperacutely reject a porcine xenograft after antibody depletion by the Ig-Therasorb column. In our experiment only 4 cycles of immunoapheresis effectively prevented HXR after oXHTx of baboons. The Ig-Therasorb column is a reusable device, which can be handled easily in combination with the ECC. IA must be tested in oXHTx longterm survival experiments, especially in combination with transgenic pig organs, which could be a reliable preclinical approach for future clinical xenotransplantation.

Animals↗
PubMed2000

Impact of hyperthermic preconditioning on postischemic hepatic microcirculatory disturbances in an isolated perfusion model of the rat liver.

Sublethal hyperthermia and the following recovery from this heat exposure, referred to as hyperthermic preconditioning, elicits a transient state of tolerance to oxidative insults through an intracellular protective response: stress response. The impact of hyperthermic preconditioning on hepatic microcirculatory disturbance, which is one of the determinants of ischemia/reperfusion-induced injury of the liver, was investigated by using intravital fluorescence microscopy. Thirty minutes of ischemia and a subsequent 120 minutes of reperfusion was induced in an in situ isolated perfusion model of Sprague-Dawley rats. Heat stress was given by whole-body hyperthermia, and a subsequent recovery was allowed for 18 or 48 hours, respectively. Postischemic decrease in sinusoidal perfusion rate and sinusoidal diameter, leukocyte stagnation in sinusoids, and leukocyte adhesion in postsinusoidal venules were significantly attenuated in both hyperthermia-pretreated groups. A recovery of bile production, a reduction of liver enzyme release, and an attenuation of tissue edema and histological damage were also observed. A marked expression of heat shock protein (HSP) 70 and heme oxygenase (HO-1)/HSP32 was correlatively observed in the liver tissue coincident with the induction of these protective effects. Hyperthermic preconditioning provides a continuous long-term and constant inhibitory effect (up to 48 hours after heat exposure) on postischemic injury of the liver through the attenuation of microcirculatory disturbances. These beneficial effects might be associated with a concomitant increase in HSP70 and HO-1/HSP32 expression.

Animals↗
PubMed2000

Influence of ischemic time on hyperacute xenograft rejection of pig hearts in a working heart perfusion model with human blood.

In xenotransplantation long ischemic time of grafts is supposed to have a marked influence on hyperacute rejection (HXR). We investigated the influence of different cold ischemic times on HXR of ex vivo "working pig hearts" perfused with human blood. Xenoreactive natural antibodies (XNAb) as a trigger of HXR were eliminated by Ig-Therasorb immunoadsorption (IA). Explanted Landrace pig hearts of group G1 and group G3 (with additional IA) underwent 4 h of cold ischemia prior to xenoperfusion. Control groups G2 and G4 (with IA) were kept ischemic for only 46.6 +/- 15.8 and 51.2 +/- 4.2 min, respectively. Ischemic time prolonged the perfusion time in our working heart model (G1: 356 +/- 46.1 min; G2: 125 +/- 31 min; P < 0.05). IA had no additional impact on perfusion time but was effective by itself. The heart weight increased fourfold more in G2 as compared to the other groups. IA without ischemia significantly improved cardiac output in G4 (G3: 198.8 +/- 15.4 mL/min; G4: 338.5 +/- 16.0 mL/min). Coronary flow in G2 was significantly lower than in G1 (G1: 157.9 +/- 9.15 mL/min; G2: 59.4 +/- 20.1 mL/min). Histological signs of HXR (light and electron microscopy) could be found in G2 in contrast to the other groups. Parameters of serological damage showed a minimum in G4 and the maximum in G2. In G1 XNAb were nearly equally eliminated immediately after the start of xenoperfusion as in IA groups G4 and G3. Four hours of ischemic time showed beneficial effects in preventing HXR, possibly caused by changes of the endothelial cell surface (for example, glycosylation or loss of alpha1-3Gal epitopes with a hapten effect).

Acute Disease↗
PubMed2000

Prevention of hyperacute xenograft rejection in orthotopic xenotransplantation of pig hearts into baboons using immunoadsorption of antibodies and complement factors.

To prevent hyperacute xenograft rejection (HXR) caused by preformed natural antibodies (XNAb) after orthotopic heart xenotransplantation (oXHTx) of landrace pig hearts into baboons, we used immunoadsorption of immunoglobulins IgG, IgM and IgA and complement with the reusable Ig-Therasorb column. In addition to functional data, tissue was sampled for histological, immunohistochemical and electron microscopical analysis. We performed three oXHTx of landrace pig hearts to baboons using extracorporeal circulation (ECC) connected to the immunoadsorption unit. Intraoperative treatment consisted of four cycles of immunoabsorption (IA). One oXHTx of a baboon without IA served as a control. A mismatch of donor and recipient heart size was prevented by selecting a 30-40% lower body weight of donor pigs than recipients. Four cycles of IA removed more than 80% of IgG, IgM and IgA, 86% of antipig antibodies and 66% of complement factors C3 and C4 from plasma. The graft of the control animal failed after 29 min. Orthotopic xenotransplantation with IA was selectively terminated after 100 min, 11 h and 21 h, respectively without any histological signs of HXR in light and electron microscopy. After weaning off from ECC these donor xenografts showed sufficient function with normal ECG and excellent cardiac output in echocardiography and invasive measurement (1.93 +/- 0.035 l/min). The myocardium of the control xenograft demonstrated more deposits of Ig and complement components (C3, C4) than in the IA group. Baboons survive HXR after orthotopic pig heart xenotransplantation due to antibody depletion by reusable Ig-Therasorb column treatment. Long-term survival in an orthotopic baboon xenotransplantation model after IA, especially in combination with transgenic pig organs, could be a reliable preclinical trial for future clinical xenotransplantation programs.

Acute Disease↗
PubMed2000

The prevention and treatment of vascular graft infection with a Triclosan (Irgasan)-bonded Dacron graft: an experimental study in the pig.

OBJECTIVES: to evaluate the role of Triclosan (Irgasan(R)) in the prevention of prosthetic graft infection. MATERIAL AND METHODS: fifty-one pigs were assigned randomly to six groups. Group I (graft) and II (graft and Triclosan) were control groups. Groups III (graft) and IV (grafts and Triclosan) were contaminated with 2 x 10(7)CFU/ml S. aureus. Groups V (graft) and VI (graft and Triclosan) were intraoperatively contaminated with 2 x 10(7)CFU/ml S. aureus and reoperated on after 7 days. Remaining animals were sacrificed on day 28. The end point of the investigation was vascular graft infection, defined as the bacteriological and/or histological proof of infection. Results in both control groups no vascular graft infections were detected in Groups I and II. All of the group III animals presented but none of the group IV developed a graft infection (p <0.02). All of the group V animals presented and 10 of 12 animals developed a graft infection. CONCLUSION: in this animal model Triclosan bonding appears effective in preventing prosthetic graft infection. However, the in situ replacement of Triclosan-protected grafts was not successful in the treatment of graft infection.

Animals↗
PubMed2000

Computer-assisted ex vivo, normothermic small bowel perfusion.

BACKGROUND: In the present study, a technique for computer-assisted, normothermic, oxygenated, ex vivo, recirculating small bowel perfusion was established as a tool to investigate organ pretreatment protocols and ischemia/reperfusion phenomena. A prerequisite for the desired setup was an organ chamber for ex vivo perfusion and the use of syngeneic whole blood as perfusate. METHODS: The entire small bowel was harvested from Lewis rats and perfused in an organ chamber ex vivo for at least 2 h. The temperature was kept at 37 degrees C in a water bath. Three experimental groups were explored, characterized by different perfusion solutions. The basic perfusate consisted of syngeneic whole blood diluted with either NaCl, Krebs' solution or Krebs' solution and norepinephrine to a hematocrit of 30%. In addition, in each group l-glutamine was administered intraluminally. The desired perfusion pressure was 100 mm Hg which was kept constant with a computer-assisted data acquisition software, which measured on-line pressure, oxygenation, flow, temperature and pH and adjusted the pressure by changing the flow via a peristaltic pump. The viability of the preparation was tested by measuring oxygen consumption and maltose absorption, which requires intact enzymes of the mucosal brush border to break down maltose into glucose. RESULTS: Organ perfusion in group 1 (dilution with NaCl) revealed problems such as hypersecretion into the bowel lumen, low vascular resistance and no maltose uptake. In contrast a viable organ could be demonstrated using Krebs' solution as dilution solution. The addition of norepinephrine led to an improved perfusion over the entire perfusion period. Maltose absorption was comparable to tests conducted with native small bowel. Oxygen consumption was stable during the 2-hour perfusion period. CONCLUSIONS: The ex vivo perfusion system established enables small bowel perfusion for at least 2 h. The viability of the graft could be demonstrated. The perfusion time achieved is sufficient to study leukocyte/lymphocyte interaction with the endothelium of the graft vessels. In addition, a viable small bowel, after 2 h of ex vivo perfusion, facilitates testing of pretreatment protocols for the reduction of the immunogenicity of small bowel allografts.

Absorption↗
PubMed2000

Impact of Ig-Therasorb immunoapheresis on stability of xenogeneic ex vivo porcine liver perfusion--value of aminotransferases and flow rates for the assessment of metabolic graft viability.

Due to growing shortage of donor organs, the concept of extracorporeal pig liver perfusion in the treatment of acute liver failure has been rediscovered. Immunomodulation, such as immunoapheresis or inhibition of complement, results in long-term perfusion without exact knowledge of the remaining metabolic graft viability. This study was aimed at the comparison of conventional parameters of graft stability such as perfusion rates and release of aminotransferases with parameters of metabolic graft function. Ig-Therasorb immunoapheresis (IA) of the xenogeneic perfusate was performed to protect the discordant pig livers from hyperacute rejection, mediated by preformed naturally occurring human xenogeneic antibodies. The application of IA created stable autologous graft reperfusion after a short time of xenoperfusion, but it was not able to prevent the livers from severe synthetic and functional damage. In the future, improvement of xenogeneic graft function, rather than pure prolongation of perfusion, must be the principal aim.

Animals↗
PubMed1999

The influence of antibody and complement removal with a Ig-Therasorb column in a xenogeneic working heart model.

OBJECTIVE: Organ transplantation is limited by the number of brain-dead human donors. Xenotransplantation could be an alternative to guarantee a constant supply of organs. A major problem of xenotransplantation are xenogeneic natural antibodies (XNAb) directed against species-specific antigens of a discordant donor species (e.g. pig). They trigger the hyperacute xenograft rejection (HXR). Re-usable immunoapheresis (LA)-columns Ig-Therasorb (Therasorb, Baxter) were used to adsorb these XNAb. The effect of immunoapheresis of the perfusing human blood was investigated in ex vivo working pig hearts. METHODS: Hearts of 12 landrace pigs (body weight 14-31 kg) were explanted after inducing cardiac arrest with 4 degrees C Celsior solution. Human blood (500 ml, heparinized) was obtained from healthy volunteers. In group 1 (G1, n = 6), blood as perfusate remained untreated. In group 2 (G2, n = 6), native blood was separated by plasmapheresis into cellular components and plasma. The latter passed through the Ig-Therasorb column for removal of immunoglobulins (so-called immunoadsorption or immunoapheresis). After back-table preparation the hearts were mounted to the working heart model. After 20 min of reperfusion in Langendorff mode, the working heart mode was established. Blood samples were taken isochronously for measurement of: CK(-MB), LDH, ASAT, troponin, immunoglobulins, complement activity, anti-pig antibodies and others. After cessation of the heart, atrial and ventricular tissue samples were taken for histological examinations (light/electron microscopy and immunohistochemistry). RESULTS: Two cycles of immunoapheresis reduced the levels of IgG by 84%, IgM by 83.3% and IgA by 76%. In G2, the antibody immunoadsorption of blood prolonged the duration of the working heart mode significantly to 335+/-37.5 min. In contrast, hearts of group 1 (control) failed after 125+/-31.3 min. Heart rate was significantly different between both groups (G1, 77.3+/-6.1 beats/min; G2, 86.5+/-5.5 beats/min). In G2 cardiac output was 118% and mean coronary flow was 154.6% higher than in G1. CK, LDH and ASAT showed no differences in the two groups. Heart weight increased significantly more in group 1 than in G2. Histological examination indicated specific signs of HXR in G1 after 1.5 h, whereas in G2 only slight unspecific damages were found after 6 h. CONCLUSION: Antibody removal by means of immunoapheresis results in a significantly improved xenogeneic cardiac function. Immunoapheresis may, therefore, become an important adjunct in future pig-to-man clinical xenotransplantation.

Animals↗
PubMed1999

Effects of prolonged cold storage time in xenotransplantation.

BACKGROUND: Ischemia and reperfusion injury after prolonged ischemic time (IT) has a marked influence on hyperacute xenograft rejection (HXR). The aim of the study was to investigate the impact of different cold ischemic times on the HXR of ex vivo "working pig hearts" perfused with human blood. Xenoreactive natural antibodies (XNAb) as the trigger of HXR were reduced by immunoadsorption (IA) using an Ig-Therasorb column. METHODS: Hearts of 24 Landrace pigs (13-31 kg) were harvested after cardioplegia with Celsior-solution and split into 4 groups. In Group C1 (n = 6) the short ischemic time (IT) lasted 48.9+/-10 minutes on the average prior to start of xenoperfusion, in Group I1 IT lasted 4 hours instead. Groups C2 and 12 experienced the same IT as C1 and I1, respectively, but underwent 2 cycles of IA in addition. IA removed immunoglobulins IgG, IgM and IgA from the perfusate. In the working heart mode hemodynamic parameters were measured in defined intervals. Blood samples were collected at the same time to determine myocardial enzymes, immunoglobulins, complement and anti-pig-antibodies. At the end of the study (cardiac arrest) tissue was sampled for histologic examination (light/electron microscopy (LM/EM) and immunohistochemistry). RESULTS: Survival time of the control Group C1 was 125 minutes. IA resulted in an extension of perfusion time to 6.5 hours in C2. Four hours of IT (I1) prolonged the working time of hearts when compared with C1. IA had no additional impact (I2). Heart weight increased significantly in C1 without IA. Cardiac output and coronary flow in C1 were significantly lower when compared with the other 3 groups. IA improved cardiac output (CO) in C2 (vs C1, p < 0.001). Histologic signs of HXR (LM/EM) could be found in C1 in contrast to the other groups. Serologic parameters for myocardial damage were higher in groups with prolonged IT than in groups with short IT. CONCLUSION: Prolonged ischemia and reperfusion injury showed controversial effects in this specific xenogeneic heart transplant model. In contrast to observations in allogeneic transplantation 4 hours of IT showed a beneficial behaviour of the xenografts. Reasons could be either a protective effect of the Celsior solution or changes of the endothelial cell surface (in terms of glycosylation or loss of alpha1-3Gal-epitopes). Tolerance of prolonged IT would allow transportation of xenografts over long distances.

Animals↗
PubMed1999

Major carbohydrate epitopes in tissues of domestic and African wild animals of potential interest for xenotransplantation research.

We investigated the main glycotopes expressed on the tissues of 44 animal species, including primates, nonprimate mammals, marsupials, birds, and a reptile. Paraffin-embedded tissue sections of kidney, heart, liver, pancreas, lung, brain and intestine of 24 domestic animal species were stained with seven fluorescent-labeled lectins. Testis sections of 20 African wild animal species were tested with the same lectins. Overall, three main immunofluorescence patterns were found in the vascular compartment. First, humans and Old World monkeys express genetically polymorphic ABH antigens and do not express alphaGal. Second, New World monkeys, other mammals, and marsupials do not express ABH antigens, but have large amounts of a genetically monomorphic alphaGal. Third, birds and reptiles do not express either ABH or alphaGal, but have monomorphic betaGal, probably different from the lactosamine precursor of ABH and alphaGal. Epithelial cells producing exocrine secretions also expressed carbohydrate epitopes. The fluorescence patterns of the cells of the exocrine compartment are similar, but not identical, to those expressed in the vascular compartment. All the animals tested have some ABH and betaGal in exocrine tissues, but New World monkeys and lower mammals are the only ones expressing alphaGal in exocrine tissues.

Animals↗
PubMed1999

Impact of immunoadsorption on xenogeneic extracorporeal pig liver perfusion: assessment of organ function during autologous reperfusion.

The shortage of liver grafts has resulted in an intensive search for alternative strategies of liver support in acute liver failure. Extracorporeal perfusion of pig livers (ECLP) is not a new concept, but recent improvements in cardiopulmonary bypass technology and new knowledge about xenogeneic immunologic mechanisms have made it a potential therapeutic modality. In previous suboptimal experimental and clinical models, no statements about the beneficial effect of long-lasting periods of ECLP were made. The aim of this study was to evaluate the capacity of pig liver for metabolic regeneration after xenogeneic ECLP under largely physiologic conditions. To delay hyperacute rejection (HAR), we utilized immunoadsorption (IA) of naturally preformed xenogeneic antibodies (XNAbs). This led to a stable xenogeneic ECLP for 45 min. However, IA was not able to prevent completely organ damage or loss of function resulting from insufficient autologous reperfusion. The inability to regenerate during autologous reperfusion provides a new measure of the function of a xenogeneic perfused pig liver. In addition, our results implicate that patients with fulminant liver failure will benefit from short perfusions with several fresh organs rather than from long perfusion with a single pig liver.

Animals↗
PubMed1999

Reduction of hepatic microcirculatory failure caused by normothermic ischemia/reperfusion-induced injury by means of heat shock preconditioning.

Transient sublethal hyperthermia and the recovery from this exposure to heat (heat shock preconditioning) provides a cytoprotective effect on oxidative insults through an intracellular protective response, heat shock response. The impact of heat shock preconditioning on hepatic microvascular failure, which is a causative determinant of ischemia/reperfusion-induced injury of the liver, was investigated by using intravital fluorescence microscopy. In Sprague-Dawley rats, normothermic ischemia was induced by totally clamping the hepatoduodenal ligament for 20 min, followed by 120 min of reperfusion. Heat shock preconditioning was performed by whole-body hyperthermia (42 degrees C for 15 min) and subsequent 48 h recovery. In accordance with the prominent induction of heat shock protein 70 in the liver tissue, the postischemic decrease in sinusoidal perfusion rate and sinusoidal diameter, and the postischemic increase in the number of stagnant leukocytes in sinusoids and adherent leukocytes in postsinusoidal venules were significantly attenuated in the heat shock-treated animals. Furthermore, liver enzyme release (glutamate pyruvate transaminase and alpha-glutathione S-transferase) was significantly reduced and postischemic deterioration of bile production was attenuated. The 7-day survival rate after 20-minute ischemia was significantly improved from 50% to 80% (heat shock-nontreated group vs. heat shock-treated group, P < 0.05). These results indicate that heat shock preconditioning attenuates ischemia/reperfusion-induced hepatic injury by preventing postischemic microvascular disturbances, and that its protective effect is circumstantially associated with the concomitant induction of heat shock protein 70.

Alanine Transaminase↗