Ullrich T. Hopt

In vitro and in vivo degradation studies for development of a biodegradable patch based on poly(3-hydroxybutyrate).

For the development of a resorbable gastrointestinal patch, the in vitro degradation of solution-cast films of poly(3-hydroxybutyrate) (PHB), modifications of PHB expected to influence its degradation time, as well a poly(L-lactide) (PLLA) was examined. The molecular weight of pure PHB decreased by one-half after 1 year in buffer solution (pH 7.4, 37 degrees C). Acceleration in molecular weight decrease was observed by blending with atactic PHB, whereas no influence was found with low-molecular weight PHB. Leaching of a water-soluble additive led to a slight acceleration of PHB degradability. In contrast, a deceleration in degradation rate was observed with the addition of a hydrophobic plasticizer. In vitro tests indicated an accelerating effect of pancreatin on PHB degradation, whereas PLLA degradation remained essentially uninfluenced. In comparison to simple hydrolysis, the degradation rate of PHB was accelerated about threefold. From the in vitro results, a PHB/atactic PHB blend was selected for repair of a bowel defect in Wistar rats. A patch film was fabricated by a dipping/leaching method. Twenty-six weeks post-implantation, material remnants were found in only one of four animals. The bowel defects were closed in all cases. It could be assessed that the patch material resists the intestinal secretions for a sufficiently long time but that it finally degrades completely.

Impairment of pancreatic microcirculation in the early reperfusion period during simultaneous pancreas-kidney transplantation

Abstract The most likely cause of graft pancreatitis is the ischemia/reperfusion injury which can be a major problem in simultaneous pancreas‐kidney transplantation. Animal experiments suggest the important role in this process of an impaired microcirculation after reperfusion. We have investigated pancreatic microcirculation in the early reperfusion period during clinical pancreas‐kidney transplantation. Tissue PO2 (PO2ti) was monitored by a PO2‐sensitive electrode. After reperfusion (a. r.) samples were taken from the venous effluent of the pancreas and simultaneously from the radial artery. After an initial peak a transient fall of PO2 was found. Total blood flow and hemoglobin oxygen saturation (sHbO2) in the venous effluent increased until 90 min a. r. (107 ml/min, 97.1%) High venous sHbO2 and high PO2ti correlated with good graft outcome. These findings can be explained by an impairment of capillary perfusion (no reflow) and concomitant shunt perfusion. The data suggest the considerable relevance of pancreatic microcirculation in the early reperfusion period during clinical pancreas transplantation.

Characterization of microcirculatory disturbance in a novel model of pancreatic ischemia-reperfusion using intravital fluorescence-microscopy.

Introduction Microcirculatory disturbances caused by ischemia–reperfusion injury (IRI) are the crucial hallmarks of pancreatitis following pancreas transplantation. Aims To develop a novel rodent model of normothermic in situ ischemia of a pancreatic tail-segment that simulates the clinical situation of pancreas transplantation by flushing the organ via an inserted microcatheter and thus enables selective treatment of the organ via this access. Methodology Four experimental groups were investigated (n = 7 Wistar rats/group): sham animals without ischemia and dissection of the pancreas; control animals with dissection of a pancreatic tail segment pedunculated on the splenic vessels and flushing od this segment with saline via a microcatheter; and two groups of animals treated like controls with a pancreatic ischemia time of 1 hour or 2 hours. With use of intravital epifluorescence microscopy, the microcirculatory damage was characterized by investigation of functional capillary density (FCD) and leukocyte adherence in postcapillary venules (LAV) before ischemia and during a reperfusion time of 2 hours. Dry:wet ratio determinations, light microscopy, and electron microscopic investigations were performed to characterize the histologic organ damage. Results FCD decreased significantly (p < 0.05) 2 hours after reperfusion in the groups of 1-hour (−29.21%) and 2-hour ischemia (−42.73%), in comparison with baseline values. LAV increased significantly (p < 0.05), 4.3- and 5.8-fold, after 1-hour and 2-hour ischemia during the observation time. The histologic damage was similar to posttransplantation pancreatitis in humans 1 hour after reperfusion. In sham and control animals these alterations were not significant. Conclusions The rodent in situ model of pancreatic IRI showed standardized microcirculatory damage dependent on the ischemia time. Offering the possibility of selective treatment by the direct artery access to the ischemic pancreatic area, the model enables investigations of questions related to human pancreas transplantation.

Endotoxin preconditioning in pancreatic ischemia/reperfusion injury.

Objectives Prospective organ donors are exposed to various stress types. The effect of endotoxin pretreatment (ETX) on pancreatic ischemia/reperfusion injury (IRI) is unclear. We investigated, using a rat model of pancreatic IRI of an in situ isolated pancreatic tail segment, the effect of ETX on postischemic microcirculation and organ damage. Methods Twenty-four hours before pancreatic dissection, either intraperitoneal application of ETX (1 mg/kg in 0.9% NaCl) or saline only (control) was performed. Two-hour normothermic ischemia of the pancreatic tail was induced by clamping the splenic vessels and was followed by a reperfusion period of 2 hours. Microcirculatory parameters were measured by intravital epifluorescence microscopy [functional capillary density (FCD), adherent leukocytes (ALs), and histology]. The presented data represent the mean ± SEM/SD as appropriate. Results ETX pretreatment caused a significantly greater decrease in FCD (497 ± 6 cm/cm2 baseline versus 326 ± 15 cm/cm2 2 hours of reperfusion) compared with controls (498 ± 8 versus 258 ± 15 cm/cm2) 2 hours after reperfusion (P < 0.01). Two hours after reperfusion, ALs were significantly decreased in ETX animals compared with controls (ETX: 141 ± 37 versus 273 ± 36 cells/mm2, P < 0.05). Histologic damage was less in ETX (6.4 score points ± 0.32 versus 8.8 ± 0.33 control, P < 0.05). Conclusion ETX preconditioning decreases microcirculatory deterioration caused by IRI by means of less loss of nutritive tissue perfusion, decrease in ALs, and less histologic damage. This indicates a protective effect of ETX preconditioning in pancreatic IRI.

Ischemic preconditioning attenuates capillary no-reflow and leukocyte adherence in postischemic pancreatitis

Background and aimsIschemic preconditioning (IPC) has been shown to protect several organs from ischemia–reperfusion injury. Postischemic microvascular dysfunction is considered to be the key mechanism of early graft pancreatitis after transplantation. The aim of the study was to determine whether brief ischemia and reperfusion before prolonged ischemia followed by reperfusion is protective in respect to microcirculatory derangement in postischemic pancreatitis.MethodsIn an in-situ model of ischemia–reperfusion was induced in the isolated pancreatic tail segment. Wistar rats were randomized to one group (n=7/group) with 2-h ischemia and reperfusion (I/R) and another group with 10-min ischemia and 10-min reperfusion (IPC) before the prolonged ischemia time. Microcirculation was observed for 2xa0h by intravital-fluorescence microscopy that analyzed functional capillary density and leukocyte adherence in postcapillary venules. Histological damage was quantified by a semiquantitative score (edema, vacuolization, PMN infiltration, necrosis).ResultsIPC resulted in a significant improvement of functional capillary density (248±20 vs 372±8xa0cm−1, P<0.001), a significant reduction in leukocyte adherence in postcapillary venules (476±79 vs 179±15 cells/mm2, P<0.001) and in significantly lower histological damage (score 9±0.8 vs 5±1.4, P<0.001), when compared with the ischemia–reperfusion group.ConclusionIPC reduces pancreatic inflammatory reaction by preservation of postischemic microcirculation. Therefore, it might become a useful procedure before organ procurement in pancreas transplantation.

Caspase-Inhibition senkt signifikant die Apoptoserate im experimentellen Pankreastransplantationsmodell an der Ratte

Objectives nApoptosis is activated during the early phase of reperfusion after liver transplantation and during warm ischemia of different organs in small animals. In addition, recent published data indicate that ischemia-reperfusion (I/R) injury induces apoptotic cell death in experimental pancreas transplantation. One strategy aimed at reducing I/R injury in organ transplantation focused on protection from apoptosis by caspase inhibition (CI). The aim of the present study was to examine the impact of caspase inhibition on pancreatic cell apoptosis in experimental pancreas transplantation.