Biomedical subjects
Publications and source records attributed to M D Menger.
Using the thrombosis model of the hairless mouse ear, we demonstrate that intravenous application of hirudin significantly delays thrombus formation and increases the rate of vessel recanalization, thus, supporting its use in clinical microvascular surgery.
With the use of intravital microscopy, we demonstrate that the extent of bacterial contamination is a determinant for the microvascular response and consecutively the microvascular injury. The model of bacterial soft tissue infection used, ideally allows to study the influence of foreign materials on microvascular immune response.
With the use of intravital microscopy and computer-assisted image analysis systems the quantitative analysis of angiogenesis of freely transplanted islets of Langerhans shows that large islets compared with small islets become significantly better vascularized.
In a rat model of free flap transfer local heat shock-priming is able to prevent ischemia/reperfusion-induced inflammatory response by expression of heat shock protein-32.
In pedicled composite flaps critical perfusion-induced capillary flowmotion, which develops only in muscle, is calcium mediated and maintains adequate nutritive perfusion not only in muscle but also in skin and periost probably by blood flow redistribution.
Using the hairless mouse ear skin flap model we demonstrate that HSP-32 expression has to be considered as a significant mechanism of ischemic preconditioning-induced protection of critically perfused tissue.
Venous-systemic oxygen persufflation (VSOP) was performed in rat livers stored at 4 degrees C in either UW or HTK preservation solution. Since tissue anoxia is associated with a transformation of cellular NAD+ to NADH and the latter fluoresces upon UV-epiillumination, homogeneity and intensity of liver oxygenation could be analysed by intravital microscopic detection of NADH fluorescence. VSOP resulted in a significant decrease of the NADH signal, documenting effective tissue oxygenation in both UW and HTK. This effect was quite homogeneous (spatial variance < 15%). After 48 h of cold storage tissue levels of ATP (mumol/g dry weight) were increased upon VSOP in UW to 17.3 +/- 4.8 but only to 2.9 +/- 0.6 in HTK, while ATP amounted to less than 0.4 without VSOP in either of the groups. It is concluded that VSOP is an appropriate tool to prevent alterations of the hepatic redox status during ischemic preservation in UW and HTK. Metabolic preservation of energy-rich adenine nucleotides seems to be largely improved in combination with UW compared with HTK.
In endotoxin-exposed rat livers, G-CSF caused a reduction of CINC gene transcripts in the nonparenchymal cell fraction, which might be the mechanism for attenuation of microvascular leukocyte adherence and leukocyte-dependent tissue injury, as observed upon G-CSF application in a model of endotoxin-induced hepatotoxicity.
In a defect wound model in rats local application of hyaluronan improves proliferation of granulation tissue and epithelialization under diabetic conditions, thus, supporting its use in therapy of problem wounds in diabetes.
The effect of rG-CSF on wound healing in neutropenic mice was studied in the wound healing model on the ear of hairless mice. Animals were treated with a daily dose of rG-CSF (i.p.; 3 micrograms). rG-CSF significantly improved wound healing probably by modulation of the cellulary immune response.
BACKGROUND: Apart from rejection-related events, the manifestation of ischemia/reperfusion (I/R) injury remains a major problem, hampering success in human small bowel transplantation (SBTx). Therefore the aim of this study was to determine the potential of Carolina rinse (CR) to attenuate microvascular reperfusion injury in rat intestinal isografts. METHODS: After 18 hours of cold preservation in 4 degrees C University of Wisconsin solution (UW), rat SBTx was performed. Immediately before reperfusion the intestine was flushed with 4 degrees C or 37 degrees C Ringer's lactate (RL, groups 1 and 2) or CR (groups 3 and 4), respectively. In vivo fluorescence microscopy was used to analyze the grafts' microcirculation. RESULTS: In group 1 severe microvascular I/R injury was observed in mucosa and muscle layers. Microcirculatory deterioration was paralleled by enhanced leukocyte accumulation in submucosal venules and by impaired subserosal lymphatic capillary drainage (FCLD). Rinsing the grafts with 37 degrees C RL attenuated leukocyte-endothelial cell interaction and improved subserosal FCLD; however, it did not affect mucosal microvascular reperfusion damage. In contrast, 4 degrees C CR dramatically improved nutritive perfusion within muscle and mucosa (p < 0.05) and attenuated leukocyte adherence within submucosal venules (p < 0.05). Additional prewarming of CR almost completely prevented mucosal I/R injury (p < 0.05 versus group 3) and caused a fourfold increase of FCLD. CONCLUSIONS. With this study we demonstrate that CR in combination with rewarming of the graft before reperfusion is an effective regimen to prevent leukocyte accumulation and to counteract microvascular injury after SBTx.
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Assessment of hepatic surface NADH fluorescence is complicated by questions concerning the relative contribution of Ito cell-associated vitamin A autofluorescence, which cannot be distinguished from each other using ultraviolet epi-illuminated microfluorographs. However, as presented herein, vitamin A autofluorescence can easily be eliminated due to its rapid photobleaching property. In line with in vitro studies on liver perfusion reported by Suematsu and coworkers (1993b), we assessed NADH fluorescence in liver surface regions, which were epi-illuminated for elimination of vitamin A autofluorescence and were allowed to recover for 20 min prior to onset of the experiment. To assess whether this procedure is stringent for accurate estimation of NADH fluorescence, we studied NADH fluorescence in non prebleached surface regions after a 30 sec and 60 sec epi-illumination period. Epi-illumination of these hepatic surface regions for more than 20 sec guaranteed also complete elimination of vitamin A autofluorescence (Vollmar et al., 1996) and further allowed to calculate the subsequent loss of NADH fluorescence due to a potential photobleaching effect after 30 sec and 60 sec of continuous light exposure. Corresponding data of the present study reveal a constant loss of NADH fluorescence of approximately 20% due to its photobleaching property over the time period from 20-60 sec of epi-illumination. Linear regression analysis of the kinetics of NADH fluorescence upon continuous light exposure allowed the calculation of the initial NADH fluorescence, excluding the interference with the Ito cell vitamin A-derived autofluorescence. The concurrency of this mathematically assessed value for the initial (non-bleached) NADH fluorescence within normal hepatic livers with the recovered value of NADH fluorescence allows the conclusion that the procedure for elimination of vitamin A autofluorescence, including ultraviolet epi-illumination with a subsequent NADH recovery period of at least 20 min, is not a prerequisite for the reliable assessment of intraindividual changes of hepatic NADH fluorescence in vivo. Thus, valid assessment of hepatic NADH fluorescence in vivo can be performed by analyzing initial NADH fluorescence bleaching kinetics, and does not necessarily require the 20 min recovery period after bleaching of the Ito cell vitamin A-derived autofluorescence.
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Postischemic reperfusion injury is caused by microcirculatory disturbances, including both nutritive perfusion failure (no reflow) and leukocyte activation (reflow paradox). Recent studies brought evidence that pentoxifylline (PTX) reduces tissue injury, decreases enzyme release, and improves survival after normothermic liver ischemia/reperfusion. The mechanisms of action, however, by which PTX protects postischemic tissue from injury have not been elucidated yet. With the use of fluorescence microscopy in a rat hepatic ischemia/reperfusion model, we studied in vivo the action of PTX on the manifestation of postischemic sinusoidal perfusion failure and microvascular leukocyte adherence. Microvascular reperfusion after 20 min portal triad cross-clamping was characterized by the cessation of blood flow within individual sinusoids (no reflow) and accumulation of leukocytes within the hepatic microvasculature, with stasis in sinusoids and rolling and firm adherence in postsinusoidal venules. PTX (20 mg/kg x hr i.v.) significantly (P < 0.05) attenuated microvascular leukocyte accumulation (44,600 +/- 1833 mm(-3) vs 67,684 +/- 2620 mm(-3) in saline-treated controls) and firm adherence of leukocytes in postsinusoidal venules (316.9 +/- 40.9 mm(-2) vs 522.9 +/- 95.0 mm(-2)); however, PTX did not influence manifestation of individual sinusoidal perfusion failure. Since reperfusion-induced parenchymal cell damage was found reduced in treated animals, we conclude that PTX attenuates postischemic injury in rat liver by reduction of leukocytic/inflammatory response but not by prevention of nutritive perfusion failure.
BACKGROUND: Venous systemic oxygen persufflation of the liver (i.e., gaseous insufflation of oxygen via the venous vascular system) has proven to be an effective tool for preventing anoxic tissue injury during extended time periods of ischemic preservation. It also allows for an improved recovery of the persufflated organ after orthotopic transplantation. METHODS: Biophysical aspects of the persufflation technique with regard to persufflation pressure (9 mmHg versus 18 mmHg) and oxygen concentration (pure oxygen versus air) in the persufflation gas were investigated in rat livers, using epi-illumination microscopic detection of autofluorescence of NADH, which accumulates in anoxic tissue. RESULTS: We demonstrated that a low-pressure persufflation (9 mmHg) is as sufficient as a higher pressure persufflation (18 mmHg) in oxygenating the ischemic organ. Moreover, oxygenation of the liver was found to be complete and rather homogeneous upon the pure oxygen persufflation, irrespective of the insufflation pressure used. In contrast, insufflation of air instead of pure oxygen resulted in insufficient aeration of the liver, even at the higher persufflation pressure of 18 mmHg. CONCLUSIONS: Our results indicate that the oxygen concentration of the persufflation gas rather than the persufflation pressure is a determinant of successful tissue oxygenation during cold storage.
Inadequate vascularization and microvascular rejection are major limitations for successful free pancreatic islet xenotransplantation. Commonly used immunosuppressive regimens may alter the process of vascularization, and are ineffective at preventing graft rejection. In this study, we investigated, in vivo, the action of the new immunosuppressive agent RS-61443 on angiogenesis and microvascular rejection of rat pancreatic islets after xenogeneic transplantation into the dorsal skinfold of Syrian golden hamsters. In nontreated xenografts, intravital fluorescence microscopy demonstrated a regular process of vascularization during the first 6 days after transplantation. On days 10, 14, and 20, graft rejection was observed, characterized by microvascular leukocyte accumulation (244+/-59 mm(-2)), loss of endothelial integrity, and capillary perfusion failure. Islet xenografts of animals treated with RS-61443 (40 mg/kg per day) demonstrated inhibition of vascularization with the consequence of a markedly reduced size of the grafts' microvascular network (0.05+/-0.007 mm2), when compared with that of nontreated xenografts (0.09+/-0.015 mm2; P< 0.05). However, treatment with RS-61443 effectively prevented microvascular graft rejection, as indicated by the absence of leukocyte accumulation (24+/-9 mm(-2); P<0.01), endothelial damage, and nutritive perfusion failure. Thus, RS-61443 treatment may represent an interesting approach for improving the outcome of pancreatic islet xenotransplantation.
Angiotensin-converting enzyme (ACE) inhibitors have proven to be effective in the reduction of ischemia/reperfusion damage after myocardial ischemia. Whether this favorable effect can be related to other models of ischemia and reperfusion has not yet been investigated. Therefore, we studied in a model of syngeneic liver transplantation in the rat the effect of recipient enalapril treatment on postischemic liver injury. Untreated animals served as the control group. Treatment with enalapril was started 5 minutes before reperfusion by intravenous infusion of enalapril at a dosage of 5 mg/kg/h. By means of in vivo microscopy, the sinusoidal perfusion rate and leukocyte adherence in sinusoids and postsinusoidal venules were analyzed during 45 to 60 minutes of reperfusion. Liver function was monitored by measuring bile output over a period of 60 minutes. Analysis of coagulation factors (prothrombin time, factor V, fibrinogen) and liver enzymes (alanine transaminase [ALT], aspartate transaminase [AST]) served for the evaluation of organ dysfunction and damage secondary to ischemia/reperfusion injury. The sinusoidal perfusion rate was significantly improved by enalapril treatment (94.7% [1.0] vs. 75.3% [3.8]; mean [SEM]; P = .005). In addition, leukocyte-sticking in both liver sinusoids and postsinusoidal venules was remarkably reduced in enalapril-treated animals as compared with controls (stickers/lobule: 21.0 [3.3] vs. 59.2 [2.1]; P = .0004; stickers/mm2 venular surface: 20.5 [4.7] vs. 110.3 [18.1]; P = .0004). Moreover, bile output was increased (1.13 [0.35] vs. 0.43 [0.18] g bile/60 min x 100 g liver; P = .06). Values for PT (22.5% [2.1] vs. 9.7% [1.8]; P = .005), factor V 99.4% [9.5] vs. 49.5% [8.5]; P = .007), and fibrinogen (64.1% [7.7] vs. 12.8% [3.2]; P = .001) were significantly improved, paralleled by a remarkable reduction in serum ALT (1,428 U/L [190] vs. 2,315 [248]; P = .02). Our data show for the first time that ACE inhibition in the liver recipient by enalapril attenuates hepatic ischemia/reperfusion damage after experimental liver transplantation. Our results may offer a novel approach to reduce ischemia/reperfusion injury in clinical liver transplantation.