Peripheral protein adsorption to lipid-water interfaces: the free area theory.

In fluid monolayers approaching collapse, phospholipids and their complexes with diacylglycerols hinder adsorption to the monolayer of the amphipathic protein, colipase. Herein, a statistical, free-area model, analogous to that used to analyze two-dimensional lipid diffusion, is developed to describe regulation by lipids of the initial rate of protein adsorption from the bulk aqueous phase to the lipid-water interface. It is successfully applied to rate data for colipase adsorption to phospholipid alone and yields realistic values of the two model parameters; the phospholipid excluded area and the critical free surface area required to initiate adsorption. The model is further developed and applied to analyze colipase adsorption rates to mixed monolayers of phospholipid and phospholipid-diacylglycerol complexes. The results are consistent with complexes being stably associated over the physiologically relevant range of lipid packing densities and being randomly distributed with uncomplexed phospholipid molecules. Thus, complexes should form in fluid regions of cellular membranes at sites of diacylglycerol generation. If so, by analogy with the behavior of colipase, increasing diacylglycerol may not trigger translocation of some amphipathic peripheral proteins until its abundance locally exceeds its mole fraction in complexes with membrane phospholipids.

Gastrointestinal stromal tumors (GIST).

BACKGROUND/AIMS: Gastrointestinal stromal tumors (GIST) are the most frequent non-epithelial tumors of the alimentary tract. The interstitial cells of Cajal or more primitive progenitor mesenchymal cells are suggested as their cells of origin. GIST's occur throughout the gastrointestinal tract but are generally located in the stomach and the intestine. About 70% of GIST's are immunohistochemically positive for CD34 and more than 90% for c-kit protein (CD117). About two thirds of GIST's are malignant. The tumor size, mitotic rate, cellularity and nuclear pleomorphism are the most important parameters characterizing the biological behavior of tumors. The diagnostic procedures are similar to those of other gastrointestinal neoplasms but only a half of the patients will have correct preoperative histological diagnosis. GIST's can be cured only by surgery. The procedure of choice, if possible, is resection without extended lymphadenectomy. Radiation and chemotherapy are generally ineffective. METHODOLOGY: 22 patients were operated on for GISTs in our department between 1996 and 2003. RESULTS: All but one proved to be benign. The patients were all asymptomatic after the operation except the malignant case. In his case an irresectable local recurrence developed later. CONCLUSIONS: GIST is a rare neoplasm of the GI tract. The only possibility for treatment of GISTs is surgical removal.

[The treatment of gastric tumours in our practice: a five year survey]. / Ein 5-Jahres-Uberblick über unsere Behandlung des Magenkarzinoms.

Between the 1st of January, 1998 and the 31st of December, 2002 we treated 111 patients for gastric cancer in the 2nd Department of Surgery, Semmelweis University, Budapest, Hungary. The majority of patients belonged to the advanced stages of the disease. In 65% of the cases a partial or total gastrectomy was performed. We combined the operation with D2 lymph node dissection if a R0 resection was possible, in the other cases with D1 lymphadenectomy. Postoperative morbidity rate ranged to 15%, the mortality 5.4%. 74 patients could be followed, 41 are dead and 33 still alive. According to the follow up examination the median survival time is 20.4 months at the moment. We observed a significantly shorter survival time, if vascular or lymphoid vessel invasion was present in the histologic specimen. The study has not been finished and the follow up will be continued.

Regulation of lipases by lipid-lipid interactions: implications for lipid-mediated signaling in cells.

Lipases are extracellular peripheral proteins that act at the surface of lipid emulsions stabilized, typically, by phospholipids. At a critical composition lipase activity toward substrates in phospholipid monolayers is discontinuously switched on by a small increase in substrate mole fraction. This occurs in part because lipase binding is inhibited by phospholipids. Binding of the lipase cofactor, colipase, is also inhibited by phospholipids. The initial rate of colipase binding increases abruptly at a substrate mole fraction that is approximately half the critical composition for lipase activity and just above that in substrate-phospholipid complexes. Moreover, complex collapse areas show an approximately 1:1 correlation with phospholipid excluded areas determined from an analysis of colipase adsorption rates. Thus, complexes inhibit colipase binding rate. Additionally, the switching of lipase activity likely occurs when uncomplexed substrate becomes the majority species in the interface. Lipase substrates, e.g. diacylglycerols, are typically the same lipids generated in the cytoplasmic surface of the plasma membrane of stimulated cells. As colipase binding is nonspecific and complexes involving lipase substrates form on the basis of lipid-lipid interactions alone, complexes should form in the plasma membrane of stimulated cells and may regulate protein translocation to the membrane.

Lipid lateral organization in fluid interfaces controls the rate of colipase association.

Colipase, a cofactor of pancreatic triacylglycerol lipase, binds to surfaces of lipolysis reactants, like fatty acid and diacylglycerol, but not to the nonsubstrate phosphatidylcholine. The initial rate of colipase binding to fluid, single-phase lipid monolayers was used to characterize the interfacial requirements for its adsorption. Colipase adsorption rates to phosphatidylcholine/reactant mixed monolayers depended strongly on lipid composition and packing. Paradoxically, reactants lowered colipase adsorption rates only if phosphatidylcholine was present. This suggests that interactions between phosphatidylcholine and reactants create dynamic complexes that impede colipase adsorption. Complex formation was independently verified by physical measurements. Colipase binding rate depends nonlinearly on the two-dimensional concentration of phosphatidylcholine. This suggests that binding is initiated by a cluster of nonexcluded surface sites smaller than the area occupied by a bound colipase. Binding rates are mathematically consistent with this mechanism. Moreover, for each phosphatidylcholine-reactant pair, the complex area obtained from the analysis of binding rates agrees well with the independently measured collapse area of the complex. The dynamic complexes between phosphatidylcholine and lipids, like diacylglycerols, exist independently of the presence of colipase. Thus, our results suggest that lipid complexes may regulate the fluxes of other proteins to membranes during, for example, lipid-mediated signaling events in cells.

Geometrical properties of gel and fluid clusters in DMPC/DSPC bilayers: Monte Carlo simulation approach using a two-state model.

In this paper the geometrical properties of gel and fluid clusters of equimolar dimyristoylphosphatidylcholine/distearoylphosphatidylcholine (DMPC/DSPC) lipid bilayers are calculated by using an Ising-type model (Sugar, I. P., T. E. Thompson, and R. L. Biltonen. 1999. Biophys. J. 76:2099-2110). The model is able to predict the following properties in agreement with the respective experimental data: the excess heat capacity curves, fluorescence recovery after photobleaching (FRAP) threshold temperatures at different mixing ratios, the most frequent center-to-center distance between DSPC clusters, and the fractal dimension of gel clusters. In agreement with the neutron diffraction and fluorescence microscopy data, the simulations show that below the percolation threshold temperature of gel clusters many nanometer-size gel clusters co-exist with one large gel cluster of size comparable with the membrane surface area. With increasing temperature the calculated effective fractal dimension and capacity dimension of gel and fluid clusters decrease and increase, respectively, within the (0, 2) interval. In the region of the gel-to-fluid transition the following geometrical properties are independent from the temperature and the state of the cluster: 1) the cluster perimeter linearly increases with the number of cluster arms at a rate of 8.2 nm/arm; 2) the average number of inner islands in a cluster increases with increasing cluster size, S, according to a power function of 0.00427 x S(1.3); 3) the following exponential function describes the average size of an inner island versus the size of the host cluster, S: 1 + 1.09(1 - e(-0.0072xS)). By means of the equations describing the average geometry of the clusters the process of the association of clusters is investigated.

[Gastrointestinal stromal tumors in our practice]. / Gasztrointesztinális stromális tumorok (GIST) elófordulása klinikánk anyagában.

The classification of tumours originating from the wall of gastrointestinal organs changed dramatically since of electronmicroscopy and immunohystochemistry were introduced. Previously these tumours were classified as leiomyomas, leiomyosarcomas or schwannomas. With the new methods these disorders can be described in more details and unified, and so the change to provide correct prognosis improved. Still, there are some unanswered questions remaining for the pathologists. In our material in the past 5 year we treated 9 patients because of GIST. Most of them were found in the stomach (6), one developed in the oesophagus, one in the small bowel and another one in the rectum. With describe our patients and look at the related articles literature about this important diseases. Though the incidence is under 1% of patients operated on because of gastrointestinal diseases, we would like to share our experiences in treatment.

Isolated massive pleural effusion caused by pancreatico-pleural fistula.

BACKGROUND: Massive pleural effusions are uncommon but well-documented complications of chronic pancreatitis, usually caused by the development of a pancreaticopleural fistula. The mechanism of the fistula formation is thought to be rupture of the pancreatic duct or pseudocyst. MATERIAL AND METHODS: In the past 7 years we have treated 5 patients with massive pleural effusion of pancreatic origin in the Surgical Department of Semmelweis University Medical School. 4 patients were males; the average age was 52 years (range: 46-59 years). RESULTS: All 5 patients had a history of alcohol abuse and were admitted to the pulmonary department because of respiratory distress. Other symptoms such as abdominal pain, chest pain, or weight loss were not always present. The diagnosis was confirmed by a markedly elevated amylase level in the aspirated pleural fluid. Abdominal ultrasound, CT scan, and ERCP examinations were carried out in order to determine the cause of the pancreaticopleural fistula. Conservative (nonsurgical) treatment was effective within 3 weeks in only one case. The other 4 patients required surgical management. In 3 cases distal pancreatic resection with splenectomy and cholecystectomy was done. In one case cystojejunostomy was performed. All 5 patients have been cured with complete resolution of their pleural effusions. CONCLUSIONS: Patients with large pleural effusions may have underlying pancreatitis with a pancreaticopleural fistula. It is important to establish this diagnosis because treatment may require operative interventions.

[Acute gastrointestinal bleeding caused by a rare, benign tumor of the duodenum (gangliocytic paraganglioma)]. / A duodenum heveny vérzést okozó, ritka, benignus daganata (gangliocytic paraganglioma duodeni).

Diagnosis and treatment of massive gastrointestinal bleeding is sometimes very difficult problem in a surgical unit. Authors present a case of a 40 years old female with an atypical source of upper gastrointestinal bleeding. The origin of the bleeding was detected only by intraoperative enteroscopy. The source of the bleeding was a very rare benign tumour of the duodenum (Gangliocytic paraganglioma) which involved the papilla of Vater. During the operation resection of the pedunculated tumour was carried out, with choledochal--and Wirsungoplastyc, associated with external drainage of these ducts. According to the literature in preoperative diagnosis of this rare tumour endoscopy, angiography, and EUS are very useful. In case of malignancy, metastases radical operation-pancreatoduodenectomy--is indicated.

[Splenic rupture: a rare complication of colonoscopy]. / Kolonoszkópia ritka szövódménye: a lépruptura.

Splenic rupture due to colonoscopy is very rare. Only a few cases have been reported previously in the English literature. Authors present their own case and they call attention to the mechanism of this complication. They conclude consequences from the literature.

Monte Carlo simulation of two-component bilayers: DMPC/DSPC mixtures.

In this paper, we describe a relatively simple lattice model of a two-component, two-state phospholipid bilayer. Application of Monte Carlo methods to this model permits simulation of the observed excess heat capacity versus temperature curves of dimyristoylphosphatidylcholine (DMPC)/distearoylphosphatidylcholine (DSPC) mixtures as well as the lateral distributions of the components and properties related to these distributions. The analysis of the bilayer energy distribution functions reveals that the gel-fluid transition is a continuous transition for DMPC, DSPC, and all DMPC/DSPC mixtures. A comparison of the thermodynamic properties of DMPC/DSPC mixtures with the configurational properties shows that the temperatures characteristics of the configurational properties correlate well with the maxima in the excess heat capacity curves rather than with the onset and completion temperatures of the gel-fluid transition. In the gel-fluid coexistence region, we also found excellent agreement between the threshold temperatures at different system compositions detected in fluorescence recovery after photobleaching experiments and the temperatures at which the percolation probability of the gel clusters is 0.36. At every composition, the calculated mole fraction of gel state molecules at the fluorescence recovery after photobleaching threshold is 0.34 and, at the percolation threshold of gel clusters, it is 0.24. The percolation threshold mole fraction of gel or fluid lipid depends on the packing geometry of the molecules and the interchain interactions. However, it is independent of temperature, system composition, and state of the percolating cluster.

Role of the sterol superlattice in the partitioning of the antifungal drug nystatin into lipid membranes.

Nystatin isolated from Streptomyces is a polyene antibiotic that is frequently used in the treatment and prophylaxis of fungal infections. Here, the fractional sterol concentration dependencies of the partition coefficient for partitioning of nystatin into ergosterol/dimyristoyl-L-alpha-phosphatidylcholine (DMPC), cholesterol/DMPC, ergosterol/1-palmitoyl-2-oleoyl-L-alpha-phosphatidylcholine (POPC), and ergosterol/POPC/1-palmitoyl-2-oleoyl-L-alpha-phosphatidylethano lam ine (POPE) multilamellar vesicles have been determined fluorometrically at 37 degrees C using approximately 0.3-1.0 mol % sterol concentration increments over a wide concentration range (e.g., 18-54 mol % sterol). This unconventional approach of varying membrane sterol content, in contrast to previous studies using large sterol concentration increments (e.g., 10 mol %), leads to a striking observation. The partition coefficient of nystatin changes dramatically with membrane sterol content in a well-defined alternating manner, displaying a local minimum at or very close to the critical sterol mole fractions (e.g., 20.0, 22.2, 25.0, 33.3, 40.0, and 50.0 mol % sterol) predicted for sterols regularly distributed in either hexagonal or centered rectangular superlattices. In ergosterol/DMPC bilayers, for example, there is a >3-fold increase in nystatin partitioning with a minute change (approximately 1 mol %) in sterol content on either side of the critical sterol mole fraction, 25.0 mol %. These results provide semifunctional evidence supporting the sterol regular distribution model [Chong, P. L.-G. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 10069-10073]. More importantly, these results reveal a new membrane phenomenon, that is, that nystatin partitioning is affected by the extent of sterol regular distribution in the plane of the membrane. This phenomenon occurs not only in saturated (e.g., DMPC) but also in unsaturated (e.g., POPC) lipid membranes, and persists in the presence of polar headgroup heterogeneity (e.g., POPC/POPE). This membrane property points to a new method for studying the interactions of polyene antibiotics with sterol-containing membranes, and the need to consider the membrane sterol content of the target cells when administering nystatin or other polyene antibiotics.

Cholesterol and ergosterol superlattices in three-component liquid crystalline lipid bilayers as revealed by dehydroergosterol fluorescence.

We have examined the fractional sterol concentration dependence of dehydroergosterol (DHE) fluorescence in DHE/cholesterol/dimyristoyl-L-alpha-phosphatidylcholine (DMPC), DHE/ergosterol/DMPC and DHE/cholesterol/dipalmitoyl-L-alpha-phosphatidylcholine (DPPC) liquid-crystalline bilayers. Fluorescence intensity and lifetime exhibit local minima (dips) whenever the total sterol mole fraction, irrespective of the DHE content, is near the critical mole fractions predicted for sterols being regularly distributed in hexagonal superlattices. This result provides evidence that all three of these naturally occurring sterols (e.g., cholesterol, ergosterol, and DHE) can be regularly distributed in the membrane and that the bulky tetracyclic ring of the sterols is the cause of regular distribution. Moreover, at the critical sterol mole fractions, the steady-state anisotropy of DHE fluorescence and the calculated rotational relaxation times exhibit distinct peaks, suggesting that membrane free volume reaches a local minimum at critical sterol mole fractions. This, combined with the well-known sterol condensing effect on lipid acyl chains, provides a new understanding of how variations in membrane sterol content change membrane free volume. In addition to the fluorescence dips/peaks corresponding to hexagonal superlattices, we have observed intermediate fluorescence dips/peaks at concentrations predicted by the centered rectangular superlattice model. However, the 22.2 mol% dip for centered rectangular superlattices in DHE/ergosterol/DMPC mixtures becomes diminished after long incubation (4 weeks), whereas on the same time frame the 22.2 mol% dip in DHE/cholesterol/DMPC mixtures remains discernible, suggesting that although all three of these sterols can be regularly distributed, subtle differences in sterol structure cause changes in lateral sterol organization in the membrane.

Kinetic studies of desensitization and resensitization of the relaxation response to beta-2 adrenoceptor agonists in isolated guinea pig trachea.

Activation of beta-2 adrenoceptors (BAR) in smooth muscle preparations is associated with a rapid, reversible and incomplete receptor desensitization, resulting in a steady-state relaxation response to BAR agonists. Based on results from cell culture studies, we hypothesize that, in the isolated guinea pig trachea, this steady state is a result of a concurrent resensitization of desensitizing BAR. In tracheal segments maintained at mechanical tone (4-6 g), isoproterenol (ISO) and the partial BAR agonist salbutamol (SALB) elicited a monotonic, rapid (1-3 min) and reproducible relaxation response that could be maintained for up to 45 min and was completely reversed by propranolol. Similarly, tissues preconstricted with 0.1 microM carbachol (CARB) responded with a sustained relaxation response to ISO. In contrast, in tissues preconstricted with 0.3 to 10 microM CARB or with 75 mM KCl, the relaxation elicited by ISO was followed by a slow (20-30 min) and partial restoration of muscle tone ("fade"). The relaxation and fade were observed when CARB-constricted tissues were relaxed with SALB (0.2 or 10 microM) or 10 microM salmeterol. No response to SALB was observed when tissues were preconstricted with KCl. The fade met criteria for its classification as a homologous desensitization of the relaxation response at the BAR level. In desensitized washed tissues, a complete recovery of the original relaxation response could be detected within 60 min of drug removal. A propranolol- and ICI 118-551-sensitive steady state was achieved 30 to 35 min after the addition of BAR agonists to the isolated tissues. A three-compartment phenomenological kinetic model accurately described the observed data, defining one steady-state and three rate constants, describing relaxation (k1), desensitization (k2) and resensitization (k3). The values of k2 and k3 for the response to SALB and to salmeterol were significantly larger than those observed for ISO. In the presence of KCl, the values of k2 and k3 for the response to ISO were indistinguishable from those measured in the presence of CARB. Given the parameters defined by our model, we propose that desensitization and resensitization of BAR in the isolated guinea pig trachea are distinct concurrent processes whose net result actively maintains a sustained partial relaxation response to ISO, SALB or salmeterol. The component of resensitization in the presence of agonist may account for the clinical efficacy of inhaled BAR agonists.

The use of modified Baylor score in the prediction of rebleeding in peptic ulcer hemorrhage.

The upper gastrointestinal bleeding is still an everyday problem. 40-50% of these bleedings are originating from peptic ulcer. The rate of rebleeding after initial hemostasis is 30-50%. In this group of patients we can observe the highest morbidity and mortality. The aim of this work is to select those patients who belong to the high risk group from the point of rebleeding. For this purpose we introduced after a retrospective analysis the modified Baylor score. In this scoring system the age, the number and severity of parallel illnesses, the hemostatus by the admittance, the ulcer size and location and the stigmata of recent hemorrhage are taken into consideration. On the basis of this every patient gets a score between 0 and 31. Based on our retrospective analysis we could establish three grades of risk groups: low risk (0-7), middle risk (8-11) and high risk (12 and over). In the low risk group there was no rebleeding. In the middle risk group we observed 4 rebleedings in 19 patients, while in the high risk group there were 32 rebleedings out of 36 cases. As a conclusion we can state, that the modified Baylor score is capable for the selection of high risk patients for rebleeding. With the early elective operations in these cases the high morbidity and mortality can be reduced.

The relationship between portal venous and hepatic arterial blood flow. I. Experimental liver transplantation.

The relationship between the changes in portal venous and hepatic arterial blood flows, in the liver is a much disputed question, it has tremendous significance in the practice of transplantation, and an explanation has been available since 1981, when Lautt published the so-called "adenosine washout theory". According to our earlier observations the decrease of portal pressure or flow consistently led to an increase in hepatic artery flow. At the same time changes in hepatic artery flow or pressure seemed to produce only inconsistent effects on the portal circulation. In the present experiments liver transplantation (OLTX) was carried out on mongrel dogs by Starzl's method. Electromagnetic flow probes were placed on the hepatic artery and the portal vein before removal of recipient's liver, and after completion of all vascular anastomoses to the newly inserted liver, during the recirculatory phase of OLTX. The flow probes were connected to a Hellige electromagnetic flowmeter, portal venous and systemic arterial pressures were also recorded. The control HAF was 241 +/- 23 ml/min, the average PVF was 517 +/- 47 ml/min before removal of the recipient's liver. In the recirculatory phase of HAF increased, by 71 +/- 12% (p < 0.001). The PVF decreased in most animals after OLTX. The decrease was in average -40.2 +/- 3.5% (p < 0.001). The THBF calculated by adding the HAF and PVF showed a small, but not significant decrease recirculation. The systemic arterial pressure decreased slightly and portal vein pressure rose in most animals after OLTX. There was a substantial increase in portal inflow resistance and prehepatic arteriolar resistance and a decrease in hepatic artery resistance. The decrease of PVF after OLTX can be explained by progressive fluid accumulation in the liver parenchyma and increased sinusoidal and portal inflow resistance. The prolonged and continuous increase in hepatic artery flow during the recirculatory phase of OLTX may be due to the decrease of portal flow. The exact mechanism, by which a change in portal flow leads to arteriolar dilatation, can be most probably explained by the "adenosine washout theory" of Lautt.

Fluorescence evidence for cholesterol regular distribution in phosphatidylcholine and in sphingomyelin lipid bilayers.

Our previous studies indicated that sterols (including cholesterol and dehydroergosterol) can be regularly distributed into hexagonal superlattices in the plane of liquid-crystalline phosphatidylcholine bilayers. It was suggested that regular and irregular regions coexist in the membrane. In the present study, we report supporting evidence for our sterol regular distribution model. We have examined the fractional concentration dependencies of dehydroergosterol (a naturally occurring cholesterol analogue) fluorescence intensity and lifetime in various phosphatidylcholine and sphingomyelin bilayers. Fluorescence intensity and lifetime dips have been observed at specific sterol mole fractions. At those mole fractions, the acrylamide quenching rate constant of dehydroergosterol fluorescence reaches a local maximum. Those mole fractions match the critical sterol mole fractions at which sterol molecules are expected to be regularly distributed into hexagonal superlattices. The results support the idea that the sterols in the regular region are embedded in the bilayer less deep than those in the irregular regions. We have also examined the fractional cholesterol concentration dependencies of diphenylhexatriene (DPH) fluorescence intensity, lifetime, and polarization in DMPC vesicles. DPH fluorescence intensity and polarization also exhibit distinct dips and peaks, respectively, at critical sterol mole fractions for hexagonal superlattices. However, DPH lifetime changes little with sterol mole fraction. As a comparison, the fluorescence properties of DHE and DPH behave differently in response to the formation of sterol regular distribution. Furthermore, finding evidence for sterol regular distribution in both phosphatidylcholine and sphingomyelin membranes raises the possibility that sterol regular distribution may occur within phospholipid/cholesterol enriched domains of real biological membranes.