Fluorescence videomicroscopic assessment of xenogeneic microcirculation and impact of antibody removal by immunoadsorption

BACKGROUND

Alterations in microcirculation are considered central to the pathogenesis of hyperacute xenogeneic rejection (HXR) of vascularized xenografts, but currently there exist no data describing these microhemodynamic alterations.

METHODS

Rat livers were perfused in situ with either isogeneic rat blood or xenogeneic human blood. The microcirculation of these xenoperfused livers was investigated directly using intravital fluorescence microscopy, and compared with that of isogeneic hemoperfused livers. In addition, the impact of antibody depletion by immunoadsorption was investigated.

RESULTS

Although a homogenous microcirculation was found during isogeneic liver perfusion (index of acinar perfusion 90.4%/sinusoidal perfusion rate 93.6%), xenoperfusion resulted in a rapid breakdown of the microcirculation (47.5%/67.1%, respectively). Perfusion deficits were found predominantly in the periportal areas. Immunoadsorption reduced the total amount of IgM and IgG by 75.2% and 96.2%, respectively, and caused a significantly improved liver perfusion (80.2%/84.4%) and liver function, as indicated by bile production. In contrast, the massive hepatic leukocyte and platelet accumulation observed during perfusion with untreated xenogeneic blood was not altered by antibody depletion.

CONCLUSIONS

Thus, the combination of isolated rat liver perfusion and intravital fluorescence microscopy enables the observation and quantification of the early phase of HXR. This is an important step forward for sensitive characterization of the rejection process and will enable the mechanisms involved in HXR to be elucidated. Antibody depletion was shown to improve liver function and perfusion, but did not reconstitute liver viability to the level of the isogeneic perfusion. These findings highlight the need for additional therapeutic regimens in xenografting.

[Proliferative potential of nasal septum chondrocytes for in vitro culture of cartilage transplants]

BACKGROUND

Recent developments in the field of tissue engineering provide novel approaches in tissue repair and reconstructive surgery using the patients own cells. Isolated chondrocytes form new cartilage when seeded in appropriate scaffolds. Usually the number of cells from a cartilage biopsy is not sufficient. The present study investigates the potential of cell amplification of human nasal chondrocytes in monolayer culture.

METHODS

Nasal cartilage cells from seven healthy patients with age between 16 and 60 years were enzymatically isolated with collagenase and hyaluronidase. Subsequently, cells were seeded in 75 cm2 culture flasks. After confluency, cultures were trypsinized, counted, and again seeded at a concentration of 5 x 10(4) cells/ml. Dulbecco's MEM supplemented with 10% FCS was used as culture medium.

RESULTS

After enzymatic digest, an average of 5 x 10(5) cells per patient were isolated. At least 85% of the cells were vital. Within four to eight weeks, the cells number was increased 10(3) to 10(5) fold. No correlation between the proliferative activity and the age of the patient was observed in this study.

DISCUSSION

The observed increase in cell number resembles about 10 to 20 cell doublings. Although the doubling time appears to be longer during the second month, no definite limit of proliferative activity was seen during the time of study. Proliferating chondrocytes in monolayer lose their tissue-specific phenotype. For the de novo formation of cartilage transplants, redifferentiation of the expanded cells has to be stimulated.

CONCLUSION

This study shows that human nasal chondrocytes can be expanded sufficiently in monolayer for the engineering of autologous cartilage transplants.

Morphology of hDAF (CD55) transgenic pig kidneys following ex-vivo hemoperfusion with human blood

Discordant xenotransplantation of pig kidneys into man may be possible in the future using transgenic organs which regulate complement activity. It was the aim of this experimental study to characterize morphologic alterations of organs transgenic for human decay accelerating factor (hDAF/CD55) perfused with human blood since no data on function of these organs after exposure to human blood are available. An ex-vivo system was developed that allows computer driven pressure-controlled perfusion of kidneys including a separate cartridge oxygenator circuit. Following cold ischemia time of 1-4 hr, 8 kidneys from heterozygote transgenic animals (TG) and 9 control kidneys (C) were perfused with 500 ml freshly drawn heparinized human blood at physiological conditions. A histologic grading system from 0 to +4 was used to describe the histologic findings. Using a mouse antihuman DAF moAB, hDAF was stained on all TG kidneys both on glomerular capillary (4+) and vascular endothelium (2+), but there was no detectable hDAF-expression on controls. No difference in xenoantibody deposition on vascular endothelium was seen between both groups. There was comparable staining for complement fraction C4 in both groups, but significant reduction of C3 and C9 staining on glomerular and vascular endothelium in TG. P-selectin was expressed on a higher level in C (+4) compared with TG (+2). Neutrophil extravasation [NP-57 elastase] was higher in C (80.2 vs. 32.2 C vs. TG [values as n/high power field]). Tubular epithelial cell swelling and mild necrosis was paralleled by glomerular hemorrhage and platelet microthrombus formation in both groups as seen in transmission electron microscopy. The observed results allow the conclusion that hDAF expression on transgenic pig kidneys was sufficient to inhibit complement activation beyond C3 during xenoperfusion with human blood despite xenoantibody deposition.

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

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.

Prevention of hyperacute rejection by human decay accelerating factor in xenogeneic perfused working hearts

As a potential source of organs for xenotransplantation, pigs that are transgenic for human decay accelerating factor (DAF) have been bred in order to overcome hyperacute rejection. We investigated the protective effect of human DAF in a porcine working heart model perfused by human blood. Hearts of normal landrace pits served as controls. The following parameters were measured: stroke work index, coronary flow and arteriovenous oxygen consumption, 6-keto prostaglandin F1alpha and prostaglandin E2 as markers of endothelial cell activation; creatine phosphokinase and lactate dehydrogenase for evaluation of the extent of myocardial damage; TNFalpha and IL-6 as markers of mononuclear cell activation. Histological and ultrastructural investigations from myocardial tissue sections were done at the end of perfusion. Human (h) DAF appeared to inhibit complement-mediated endothelial cell activation of transgenic pig hearts successfully. This was in contrast to landrace pig hearts, which had a sixfold increase of prostaglandin levels during perfusion with human blood. The cardiac weight increase during perfusion time due to interstitial edema tended to be less in the hDAF group. Myocardial damage was minimal in transgenic hearts, whereas normal pig hearts produced a threefold increase of creatine phosphokinase and lactate dehydrogenase levels. In these hearts, electron microscopy revealed single cell necrosis of myocytes and vacuolization of mitochondria with cristae rupture. According to the results obtained in the working heart model, the breeding of pigs that are transgenic for hDAF represents a promising step to making heart xenotransplantation a clinical reality in the future.

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.

Xenoreactive natural antibodies and induced antibodies--their effects of beating cardiomyocytes as a model of a xenograft

Xenotransplantation has been complicated by hyperacute rejection reactions, which are supposedly triggered by preformed natural antibodies (PNAb) of the recipient organism, whereas the role of antibodies specifically induced by previous antigen contact (IAb) is less clear. Primary cultures of spontaneously beating neonatal rat cardiomyocytes were used as a model of the heart to elaborate the effects of both PNAb and IAb from xenogeneic species and to investigate into their mechanisms of action. An experimental setup allowing for rapid medium exchange under continuous observation was employed. Sera containing PNAb reproducibly bring about a stereotype pattern of altered contractility including an initial increase in beating frequency followed by a temporary cessation of beating within the first minutes after administration. After recovery of spontaneous contractions, the cells within the monolayer exhibited a dissociation of the synchronicity of the beating persisting for several hours. The temporary pause in beating was prevented by a very high extracellular calcium concentration, but not by extracellular electrical stimulation sufficient to trigger contractions in control cells. Electrophysiological measurements carried out in adult ventricular guinea pig heart muscle cells under the same experimental conditions revealed an increase of the excitation threshold of the cells after application of sera containing PNAb due to an enhanced input resistance. These results indicate that the effect of PNAb is the consequence rather of a generally reduced excitability of the cell than of the inhibition of a singular ionic conductance. After specific absorption of PNAb directed against rat antigens beating of neonatal rate cardiomyocytes ensued without interruption. Sera specimens devoid of complement produced similar effects on contractility, although the duration of the standstill period was significantly shorter. The increase in input resistance visualized in guinea pig myocytes was absent after removing PNAb against guinea pig antigens but not after absorbing PNAb directed against rat epitopes. Signs of a permanent cytotoxicity after the administration of PNAb were lacking in all experiments. IAb against rat heart tissue raised in rabbits stopped the contractions of neonatal rat cardiomyocytes within 30 min after administration irreversibly and lead concentration-dependently to a destruction of the cells.

In vivo monitoring of splenocytes in NMRI nu/nu- and nu/+,- mice during Lewis lung tumor progression or regression

Splenocytes of T-cell deficient NMRI nu/nu- mice (n=15) and of inbred immunocompetent NMRI nu/+,littermates (n=18) significantly (p<0.05) increased during Lewis lung (LL) tumor growth and eventually decreased. Half of the heterozygous NMRI nu/+,- mice rejected the tumors (LL-regressors). Zymosan-induced and lucigenin-amplified chemiluminescence (CL) of splenic polymorphonuclear leukocytes (PMN) and -precursors significantly (p<0.05) increased in NMRI nu/+,- mice with progressing tumors (LL-progressors) on the 3rd and in LL-regressors and nude mice on the 7th day after tumor inoculation. It subsequently decreased although numbers of PMN/- precursors further multiplied predominantly in the LL-progressors. Another peak of CL was found in those animals after the 20th day. Splenic lymphocytes significantly (p<0.05) increased in all mice from day 5 forward and dropped to original numbers between the 20th and 25th days. Maximal lymphocyte counts were significantly (p<0.05) lower in nude mice as compared to the NMRI nu/+,- littermates. The splenic T-/B-ratio significantly (p<0.005) correlated in LL-regressors and did not in LL-progressors. This correlation could be a suitable marker for tumor progression in NMRI nu/+ mice bearing LL-tumors.

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.

Different action of xenoreactive natural and immune antibodies on functioning cardiomyocytes

PNAB and IAB have totally different action on BCM. PNAB inhibit the contractile function of BCM by producing a reversible standstill and by disturbing the synchronization of the BCM-monolayer. IAB are cytotoxic and depend on the presence of complement.

Defects of the respiratory chain in various tissues of old monkeys: a cytochemical-immunocytochemical study

The aim of the present study was to evaluate if defects of the respiratory chain known to occur in humans, also exist in lower primates. Cytochemical-immunocytochemical studies of the respiratory chain enzymes in five monkeys (10-25 years of age) showed defects of ubiquinone cytochrome-c-oxidoreductase (complex III), of cytochrome-c-oxidase (complex IV) and of ATP-synthase (complex V) in the limb muscles, diaphragm, heart muscle and extraocular muscles of three old animals (about 25 years) and also in the heart muscle of two younger animals (10 and 15 years). Characteristically, the defects were randomly distributed and there was no loss of succinate-dehydrogenase (complex II) in the fibres. Ultracytochemistry-immunocytochemistry of complex IV disclosed that in an involved fibre segment all the mitochondria exhibited the defect. The highest number of defects was observed in the extraocular muscle (up to 340/cm2) while the lowest defect density was present in the limb muscles (2-5/cm2). Defects of complex IV occurred two to three times more often than defects of complex III and besides isolated defects of complex III and IV, combined defects of both complexes were also observed. Defects of complex V occurred exclusively in combination and were rarely seen. Using subunit specific antisera against complex IV, it could be demonstrated at light and electron microscopic level that loss of activity of cytochrome-c-oxidase was associated with a loss both of mitochondrially and nuclearly coded subunits of the enzyme. In summary, aging in lower primates and humans is characterised by a highly similar defect expression of the respiratory chain enzymes, with intercellular and interorgan differences of the aging process, underlining the universal nature of the involved pathogenetic mechanisms.

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.

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.

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.

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.

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.

Resorbable polyesters in cartilage engineering: affinity and biocompatibility of polymer fiber structures to chondrocytes

The resorbable polymers polyglycolic acid (PGA) and polylactic acid (PLA) are gaining increasing importance in tissue engineering and cell transplantation. The present investigation was focused on the biocompatibility and cell retaining behavior of PGA/poly-L-lactide (PLLA) (90/10) and PLLA nonwoven structures for the in vitro development of chondrocyte-polymer constructs. The effect of the relevant monomers to chondrocytes was analyzed. Type II collagen and poly-L-lysine were compared to improve loading of PGA/PLLA and PLLA polymer nonwovens with chondrocytes. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetra-zoliumbrom ide (MTT) test was applied for quantification. At concentrations above 2 mg/mL, glycolic acid was more cytotoxic than lactic acid. As shown by pH equilibration, the cytotoxic effect is not due merely to the acidity of the alpha-hydroxy acids. Regarding the degradation products, glycolic acid, and L(+) lactic acid, nonwovens of PLLA are more biocompatible with chondrocytes than nonwovens of polyglycolide. Collagen type II and poly-L-lysine generally improved cell seeding on resorbable polymers in tissue engineering; however, their efficiency varies depending on the type of fiber structure.

[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.

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.

Na-K/2Cl transporter inhibition for reduction of postischemic kidney failure tested in autologous reperfusion

Postischemic kidney function may be influenced by donor conditioning. The sulfamoyl-benzoate "piretanide" (P) is a diuretic agent with an inhibitory effect on the luminal Na-K-2CL-transporter system in the ascending part of the loop of Henle. A clinical pilot study demonstrated a lower rate of organ dysfunction following transplantation in humans when the donor organs were pretreated with piretanide. In an experimental ex vivo model the effect of piretanide on immediate organ function following long or short cold ischemia was studied. Porcine kidneys (n = 36) were removed after in situ transaortal hypothermic flushing with 21 Eurocollins solution. Following short storage (1 h, n = 18) or long storage (24 h, n = 18) the kidneys were reperfused with intraoperatively drawn heparinized autologous blood diluted with Ringer's lactate to a hematocrit of 25%. Urine flow was higher in the piretanide-pretreated group (p), especially after long storage. The electrolyte loss was comparable in both groups. Postischemic endogenous creatinine clearance was significantly elevated in the treatment group (4.45 +/- 0.6 ml/min per 100 mg in P vs 1.91 +/- 0.4 ml/min per 100 mg, in control, P < 0.05 Mann-Whitney test). Renal hemodynamics were improved by piretanide, resulting in significantly lower resistance and allowing higher flow during pressure-controlled perfusion. O2 consumption, representing general metabolic activity, was higher after long storage, indicating an earlier recovery from cold ischemia. In this ex vivo model, autologous reperfusion of porcine kidneys could be improved by piretanide pretreatment. Autoregulation of kidney vasculature was maintained as well as functional parameters such as creatinine clearance or gluconeogenesis. Therefore, piretanide may be used in larger clinical trials to further improve organ quality in times of donor shortage.

[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)

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.

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.

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.

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.

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.

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.