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Biomedical subjects

M Menger

Publications and source records attributed to M Menger.

At least 19 recordsLinked to original sources
PubMed2001

Temporary pancreatic duct occlusion by ethibloc: cause of microcirculatory shutdown, acute inflammation, and pancreas necrosis.

Temporary obliteration of the pancreatic duct has been suggested to be beneficial in chronic pancreatitis, segmental pancreatic transplantation, and following Roux-Y pancreaticojejunostomy. Little is known, however, as to whether obliteration of the duct alters exocrine pancreatic physiology. Therefore we studied in male inbred Lewis rats the immediate effects of Ethibloc-induced duct obliteration (Ethibloc: Ethicon, Norderstedt, Germany) on pancreatic microcirculation, inflammation, and tissue injury (n = 8), and compared these effects with those caused by experimental pancreatitis (4% sodium taurocholate; n = 8). Animals receiving an intraductal infusion of saline served as controls (n = 8). Duct occlusion with Ethibloc resulted in a marked decrease (p < 0.05) in capillary red blood cell (RBC) velocity and functional capillary density (FCD) to 88 +/- 39 microm/s (baseline 716 +/- 40 microm/s) and 72 +/- 33 cm(-1) (baseline 493 +/- 21 cm(-1)), respectively, which was even more pronounced when compared with that observed in experimental pancreatitis (333 +/- 62 microm/s and 195 +/- 44 cm(-1), respectively). In parallel, the manifestation of tissue damage was found to be more severe after Ethibloc; and chloracetate esterase staining showed a larger number of infiltrating leukocytes [555 +/- 86/high power field (HPF) versus pancreatitis: 160 +/- 12/HPF; p < 0.05). We conclude that intraductal application of Ethibloc induces significant microcirculatory failure and a marked inflammatory response, which are even more pronounced when compared with the changes observed with experimental pancreatitis. Based on these results and the fact that there is no direct proof for a benefit of temporary duct occlusion by Ethibloc, it is proposed that the procedure be reevaluated for its use in pancreatic surgery.

Animals↗
PubMed2000

Multiple conformational states of the hammerhead ribozyme, broad time range of relaxation and topology of dynamics.

The dynamics of a hammerhead ribozyme was analyzed by measurements of fluorescence-detected temperature jump relaxation. The ribozyme was substituted at different positions by 2-aminopurine (2-AP) as fluorescence indicator; these substitutions do not inhibit catalysis. The general shape of relaxation curves reported from different positions of the ribozyme is very similar: a fast decrease of fluorescence, mainly due to physical quenching, is followed by a slower increase of fluorescence due to conformational relaxation. In most cases at least three relaxation time constants in the time range from a few microseconds to approximately 200 ms are required for fitting. Although the relaxation at different positions of the ribozyme is similar in general, suggesting a global type of ribozyme dynamics, a close examination reveals differences, indicating an individual local response. For example, 2-AP in a tetraloop reports mainly the local loop dynamics known from isolated loops, whereas 2-AP located at the core, e.g. at the cleavage site or its vicinity, also reports relatively large amplitudes of slower components of the ribozyme dynamics. A variant with an A-->G substitution in domain II, resulting in an inactive form, leads to the appearance of a particularly slow relaxation process (tau approximately 200 ms). Addition of Mg(2+) ions induces a reduction of amplitudes and in most cases a general increase of time constants. Differences between the hammerhead variants are clearly demonstrated by subtraction of relaxation curves recorded under corresponding conditions. The changes induced in the relaxation response by Mg(2+) are very similar to those induced by Ca(2+). The relaxation data do not provide any evidence for formation of Mg(2+)-inner sphere complexes in hammerhead ribozymes, because a Mg(2+)-specific relaxation effect was not visible. However, a Mg(2+)-specific effect was found for a dodeca-riboadenylate substituted with 2-AP, showing that the fluorescence of 2-AP is able to indicate inner sphere complexation. Amplitudes and time constants show that the equilibrium constant of inner sphere complexation is 1.2, corresponding to 55% inner sphere state of the Mg(2+) complexes; the rate constant 6.6 x 10(3) s(-1) for inner sphere complexation is relatively low and shows the existence of some barrier(s) on the way to inner sphere complexes.

2-Aminopurine↗
PubMed2000

Motor neuron cell death in a mouse model of FALS is not mediated by the p53 cell survival regulator.

Mutant Cu/Zn superoxide dismutase (SOD1) associated with familial amyotrophic lateral sclerosis (FALS) causes selective motor neuron loss through unknown mechanisms of cell damage. Damaged neurons frequently undergo apoptosis mediated by the p53 cell survival regulator. We therefore studied whether motor neuron disease (MND) in mice expressing the human SOD1 mutant G93A is dependent on p53 by crossing G93A mice with p53-knockout mice. Since p53-/- mice's life expectance is usually shorter (160+/-49 days, n=11) than the time at which the G93A mice die from MND (212+/-50 days, n=7), only a few of the G93A/p53-/- double transgenics were expected to live to experience MND. Nevertheless, four of the 22 G93A/p53-/- mice succumbed to MND after 160+/-28 days, as expected under these conditions of competing death risks if the absence of p53 fails to protect from MND. Thus, MND in mice expressing G93A does not require p53. This conclusion is supported by histology: pre-symptomatic G93A mice display disease-associated vacuoles within the dendrites of motor neurons regardless of p53 status.

Aging↗
PubMed2000

Dynamics of the RNA hairpin GNRA tetraloop.

The dynamics of RNA hairpin tetraloops of the GNRA type [sequence G- any ribonucleotide (N)-purine (R)-A] was analyzed by fluorescence spectroscopy and by fluorescence-detected temperature-jump relaxation, using RNA oligomers with 2-aminopurine (2AP) substituted in two different positions of the loop sequence, Gp2APpApA (HP1) and GpAp2APpA (HP2), as indicator. The fluorescence of HP1 is much higher than that of HP2, indicating a lower degree of 2AP-stacking in HP1. Addition of Mg(2+) or Ca(2+) ions leads to an increase of fluorescence in HP1, whereas a decrease of fluorescence is observed in HP2. In both cases at least two ion-binding equilibria are required to fit titration data. T-jump experiments using fluorescence detection show a relaxation process with a time constant of 22 micros for HP1, whereas two relaxation processes with time constants 5 and 41 micros, are found for HP2. These results clearly demonstrate the existence of more than the single conformation state detected by NMR analysis. The T-jump amplitudes decrease with increasing bivalent ion concentration, indicating that one of the states is favored in the presence of bivalent ions. The loop relaxation processes are slower than standard stacking processes, probably because of activation barriers imposed by a restricted mobility of loop residues, and are assigned to a stacking rearrangement, probably between the 5' and the 3'-side. A similar process has been observed previously for the anticodon loop of tRNA(Phe). The rate constants of the transition are in the range of 10(4) s(-1) in the case of HP1. The data demonstrate the existence of structures that are not resolved by standard NMR because of fast exchange and are not found by X-ray analysis because of restrictions by crystal packing.

2-Aminopurine↗
PubMed1999

ET-1 induces pancreatitis-like microvascular deterioration and acinar cell injury.

Using in vivo microscopy red blood cell (RBC) velocities, functional capillary density (FCD) and capillary diameters were estimated after inducing acute pancreatitis by intraductal infusion of sodium taurocholate (0.8 ml; 4%) or after topical superfusion of the pancreas with ET-1 (100 pmol). Sodium taurocholate mediated a significant decrease in RBC velocities between 50 and 70%, transient decrease in capillary diameters by 10%, and a sustained decrease in FCD between 60 and 70% paralleled by a dramatic heterogeneity in blood flow. Topical superfusion of the exteriorized pancreas with ET-1 caused a significant decrease in RBC velocities between 65 and 75%, a sustained decrease in capillary diameters by 10%, and a decrease in FCD by 45% accompanied by an increase in flow heterogeneity. Following sodium taurocholate infusion pancreas histology revealed a severe edema and sublobular acinar cell necrosis, while topical ET-1 application displayed a severe edema of the pancreas with focal acinar cell necrosis. Thus, ET-1 mediated a deterioration of the pancreatic microcirculation, which is similar to the microcirculatory failure found in sodium taurocholate-induced experimental pancreatitis and was associated with focal acinar cell necrosis. We are thus inclined to hypothesize that endothelin released by injured endothelial cells during acute biliary pancreatitis promotes microcirculatory failure and ischemia in acute pancreatitis, eventually leading to acinar cell necrosis.

Acute Disease↗
PubMed1999

Isolation and characterization of the eighth component of the bovine complement system.

OBJECTIVE: To isolate and characterize the eighth component of the complement system (C8) in cattle. SAMPLE POPULATION: Fresh plasma obtained from beef cattle. PROCEDURES: Plasma samples were fractionated, using sequential precipitation and ion-exchange and gel-filtration chromatography, to yield C8. The protein was identified throughout the procedure on the basis of its hemolytic function. Electrophoresis in polyacrylamide gels was used to determine molecular weight and composition of polypeptide chains. Reconstitution of classical and alternative complement pathways was used to characterize the hemolytic function of bovine C8. RESULTS: The bovine C8 protein consisted of a disulfide-bonded alpha-gamma heterodimer that was noncovalently associated with a beta chain. Apparent molecular weight of the alpha, beta, and gamma chains under reducing conditions were 66, 61, and 23 kd, respectively. In the classical pathway of activation, bovine C8 and the ninth component of the complement system (C9) had species incompatibility with human C8 and C9 on sheep erythrocyte target cells. CONCLUSIONS: A simple 4-step fractionation procedure provided good yield of bovine C8 from plasma. The isolated protein was structurally comparable to C8 from other species. Purified bovine C8 may be useful in functional hemolytic assays to investigate the roles of complement-mediated lysis in the pathogenesis of inflammatory diseases and the killing of susceptible microorganisms.

Animals↗
PubMed1997

Childhood leukemia and electromagnetic fields: results of a population-based case-control study in Germany.

The investigation of an association between increased exposure to residential extremely-low frequency electromagnetic fields (ELF-EMF) and childhood leukemia was part of a population-based case-control study carried out between 1992 and 1995 in the northwestern part of Germany. A total of 129 children with leukemia and 328 controls participated in the EMF-study. Exposure assessment comprised measurements of the magnetic field over 24 hours in the child's bedroom at the residence where the child had been living for the longest period before the date of diagnosis, and spot measurements at all residences where the child had been living for more than one year. The median of the 24h-measurement in the child's bedroom was regarded as the most valid exposure variable. For children exposed to more than 0.2 microT, an elevated but not significant odds ratio (OR) was observed (OR = 3.2, 95 percent confidence interval = 0.7-14.9). These figures are based on only four leukemia cases and three controls since only 1.5 percent of the study population was classified as highly exposed. Exploratory analyses revealed ORs that were not statistically significantly increased for other characteristics of the magnetic field at varying cut-points. The results are comparable with those from other studies. Although not statistically significant, they may indicate a positive association between EMF and childhood leukemia.

Adolescent↗
PubMed1996

Mg(2+)-dependent conformational changes in the hammerhead ribozyme.

Conformational changes of the hammerhead ribozyme were examined by fluorescence changes of 2-aminopurine riboside incorporated either in the substrate or in the ribozyme. Fluorescence changes could be observed for both the substituted substrate and ribozyme upon complex formation, indicating a different environment for the 2-aminopurine in the complex. Ribozyme-substrate constructs for ciscleavage containing 2-aminopurine at various sites were used for the determination of binding constants of Mg2+ and Ca2+. Depending upon the site of 2-aminopurine substitutions, the fluorescence intensity upon addition of Mg2+ or Ca2+ was reduced by 0-50%. The measurements were performed in high ionic strength buffers such that base pairing in the helical regions is expected to be complete. With three of the ribozymes, the dependence of the fluorescence emission as a function of Mg2+ concentration could be fitted by single binding processes, whereas for the two remaining ribozymes a second binding process needed to be included. The binding constants range from 7600 M-1 down to 12 M-1 in 75 mM Tris-HCl (pH 7.5) and indicate the presence of multiple binding sites in the ribozymes with varying degrees of affinity toward the metal ions. Mg2+ binding constants determined in the same buffer from the Mg2+ dependence of the cleavage rate are of the order of 100 M-1; thus, Mg2+ sites directly involved in catalysis are of intermediate affinity. The ribozyme containing 2-aminopurine in loop III demonstrated the highest binding constant whereas the ribozyme with a 2-aminopurine next to a 2'-deoxy-2'-aminocytosine at the cleavage site exhibited only low metal ion affinity. The data obtained for Ca2+ are very similar to those found for Mg2+. This approach provides a first set of data describing a Mg2+ binding topography to hammerhead RNA molecules and should be useful for the analysis of other RNA molecules.

2-Aminopurine↗
PubMed1995

Impact of vitamin E supplement in standard laboratory animal diet on microvascular manifestation of ischemia/reperfusion injury.

Aimed at improving animal fertility and health, diets for farm and laboratory animals have over the last few years been supplemented with increasing amounts of the antioxidant vitamin E. We now demonstrate by intravital microscopy that feeding hamsters with a vitamin E-supplemented "standard" rodent diet (60 ppm vitamin E) significantly reduces the microvascular manifestations of ischemia/reperfusion injury when compared to animals fed a nonsupplemented diet. Postischemic leukocyte adhesion to venular endothelium was reduced from 770 +/- 204 cells/mm2 at 24 h after reperfusion in control animals on the nonsupplemented diet to 403 +/- 105 cells/mm2 in animals on the "standard" rodent diet (means +/- SD, n = 7 animals per group, p < 0.01). Animals on the nonsupplemented diet showed a dramatic loss of capillary perfusion density until 7 days after reperfusion (to 21 +/- 13% of preischemic baseline values), whereas this loss was significantly attenuated (to 71 +/- 12% of preischemic values, p < 0.01) in animals on the "standard" rodent diet. No difference in the extent of reperfusion injury was seen between animals on the "standard" rodent diet and animals on diets with substantially higher vitamin E supplements (300 ppm-30,000 ppm). Besides underscoring the benefit of vitamin E in reducing the extent of ischemia/reperfusion injury, this study raises the concern that vitamin E supplements in "standard" laboratory animal diets may have a far-reaching impact on biomedical research by jeopardizing established animal models of disease.

Animals↗
PubMed1992

Reduction by superoxide dismutase of leukocyte-endothelial adherence after liver transplantation.

One hour after orthotopic rat liver transplantation, hepatic microcirculation and adhesion characteristics of leukocytes to the endothelial wall were studied with intravital microscopy. Cold storage for 1 and 8 hours in Euro-Collins solution resulted in reduction of perfused sinusoids to 83% and 48% and a decrease of leukocyte velocity from 417 microns/sec in controls to 311 microns/sec and 269 microns/sec, respectively. Additionally, the number of permanently adherent leukocytes rose from 4% in controls to 33% and 43% after cold storage for 1 and 8 hours. Intravenous injection of the free radical scavenger human recombinant superoxide dismutase (40 mg/kg) during reperfusion resulted in marked improvement of the hepatic microcirculation after both 1 and 8 hours of cold storage (91% and 69% perfused sinusoids; 420 microns/sec and 350 microns/sec leukocyte velocity; p less than 0.05). Furthermore, the percentage of permanently adherent leukocytes decreased to 13% and 28% after 1 and 8 hours of cold ischemia, respectively. These results support the hypothesis that oxygen-derived free radicals contribute to leukocyte adherence and microcirculatory failure after cold liver ischemia and transplantation. Thus, application of oxygen free radical scavengers during liver transplantation procedures might be useful to improve graft function.

Animals↗
PubMed1991

Microcirculatory disturbances and leucocyte adherence in transplanted livers after cold storage in Euro-Collins, UW and HTK solutions.

Integrity of the hepatic microcirculation and maintenance of endothelial cell viability are critical components in preventing primary non-function after liver transplantation. Therefore, hepatic microcirculation and leucocyte-endothelial interaction were studied in rat livers stored for 1 h in Euro-Collins (EC), University of Wisconsin (UW), and histidine-tryptophan-ketoglutarate (HTK) solutions and subsequently transplanted. One hour after transplantation surgery, the livers were exposed under an intravital fluorescence microscope. After injection of the leucocyte marker acridine orange (1 mumol/kg), six pericentral fields were observed for 30 s and experiments were recorded continuously. The percentage of perfused sinusoids was reduced in the livers in the EC group (82.9%) in contrast to the UW (93.2%) and HTK groups (91.0%). Livers in the EC group showed a reduction in the diameters of pericentral sinusoids (7.3 +/- 0.2 microns; mean +/- SEM) compared with the UW group (9.5 +/- 0.2 microns; P less than 0.05) and HTK group (10.2 +/- 0.8 microns; P less than 0.05), indicating substantial cell swelling in livers stored in EC solution. Permanent adherence of leucocytes was most frequently observed in the EC group (33.5 +/- 1%), while this phenomenon was less pronounced in the UW group (14.5 +/- 1.1%; P less than 0.05) and HTK group (16.3 +/- 0.7%; P less than 0.05). Conversely, temporary adherence of leucocytes was reduced in the EC group (19.7 + 1.3%) compared with the UW group (30.5 + 2.1%) and the HTK group (34.4 + 0.8%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1988

Potentiation of leukotriene production following sequestration of neutrophils in isolated lungs: indirect evidence for intercellular leukotriene A4 transfer.

Granulocyte (polymorphonuclear leukocyte, PMN) sequestration in the microvascular bed with release of different mediators has been implicated in the pathogenesis of inflammatory and allergic disorders in many organs including the lung. In the present study, we investigated the profile and quantity of leukotriene (LT) generation in isolated blood-free perfused rabbit lungs, in isolated PMNs in vitro and in rabbit lungs, following administration of PMNs, mimicking pulmonary leukostasis. Following stimulation with increasing concentrations of the calcium ionophore A 23137 (0.1 to 2 mumol/L), LTs were detected in the buffer fluid by their chromatographic mobility in different high-performance liquid chromatography (HPLC) systems, by on-line peak spectrum analysis, and by post-HPLC radioimmunoassay (RIA). In isolated lungs, a dose-dependent generation of cysteinyl LTs greater than LTB4, in the complete absence of omega-oxidation products of LTB4 as well as nonenzymatic hydrolysis products of LTA4, was evoked. PMNs in vitro showed a typical profile of LT liberation (LTB4, 20-OH-, and COOH-LTB4, nonenzymatic LTA4 metabolites). In the model of pulmonary leukostasis, the presence of omega-oxidation products of LTB4 indicated metabolic integrity of the trapped PMNs. Nonenzymatic hydrolysis products of LTA4 were, however, not detected in the combined system, whereas the cysteinyl LTs increased markedly. This profile suggests intercellular transfer of PMN-derived LTA4 to lung cells in the microenvironment. In addition, at 2 mumol/L A23187, the sum of all LTA4-derived products surpassed the arithmetic sum of the isolated preparations more than threefold. This potentiation of an LT generation under conditions of pulmonary leukostasis may be of biologic significance for amplification of inflammatory events.

Animals↗
PubMed1987

A cobra venom factor (CVF)-induced C3 convertase activity in the hemolymph of Galleria mellonella.

A cobra venom factor (CVF)-induced C3 convertase has been generated from the hemolymph of Galleria mellonella. CVF was immobilized on Sepharose 4B and treated with cell-free hemolymph obtained from either unvaccinated G. mellonella larvae or larvae immunized with formalized Pseudomonas aeruginosa. The C3-cleaving activity was detected by the ability to cleave the alpha-chain of bovine C3 in a manner analogous to the CVF-induced mammalian C3 convertase, CVF,Bb. The insect-derived C3 convertase formed at 28 degrees C but not at 37 degrees C, then once formed was active at both 28 degrees C and 37 degrees C. EDTA did not inhibit the formation and action of the insect derived C3 cleaving activity.

Animals↗