Search PubMed⌕ Search

Biomedical subjects

G Schmitz

Publications and source records attributed to G Schmitz.

At least 235 records · Page 13Linked to original sources
PubMed1991

Cellular processes in atherogenesis: potential targets of Ca2+ channel blockers.

Atherosclerosis is characterized by increased endothelial permeability, monocyte infiltration, intimal smooth muscle cell (SMC) proliferation, platelet aggregation and the accumulation of lipids, calcium and extracellular matrix components in the vessel wall. In various animal studies and recently in humans it could be established that Ca2+ channel blockers delayed the progression of the atherosclerotic process at the stage of early lesions. This review surveys the interaction of Ca2+ channel blockers with various membrane proteins (purinergic receptors, nucleoside transporter, peripheral benzodiazepine receptors, multi-drug resistance protein) which are involved in signal transduction and their potential impact on the observed antiatherosclerotic effects. Although the precise mechanisms have yet to be fully elucidated, it has been clearly shown that these drugs inhibit smooth muscle cell proliferation and migration, improve cellular lipoprotein metabolism in vascular cells, alter phospholipid turnover, decrease platelet adhesion in the vessel wall, reduce extracellular matrix synthesis and protect against radical induced cell damage. Most of these effects are independent of Ca2+ flux across voltage-operated Ca2+ channels. However, all these processes are relevant to the pathogenesis of atherosclerosis and therefore the elucidation of the antiatherogenic mechanisms of Ca2+ channel blockers at the cellular level is of great interest. The future development of Ca2+ channel blockers with altered molecular structures optimized for their antiatherosclerotic targets may provide a useful tool in the therapy of atherosclerosis and risk factor intervention. The protective mechanisms are related to a stabilization of cell membrane integrity, the modulation of secretory activities and cell/cell communication processes rather than to a lowering of plasma lipoprotein levels.

Animals↗
PubMed1991

Nonradioactive HLA class II typing using polymerase chain reaction and digoxigenin-11-2'-3'-dideoxy-uridinetriphosphate-labeled oligonucleotide probes.

We describe a new, simple, rapid, and sensitive nonradioactive technique for the analysis of genetic variations. Genomic DNA was amplified using polymerase chain reaction and amplified DNA was hybridized, with digoxigenin (DIG)-labeled sequence-specific oligonucleotides. High specificity and sensitivity was achieved when labeling the sequence-specific oligonucleotide at the 3' end with only one DIG using digoxigenin-11-2',3'-dideoxy-uridine-5'-triphosphate and DNA deoxynucleotidylexotransferase. The hybridized probes were detected using antidigoxigenin alkaline phosphatase, fab fragments, and X-phosphate/NBT for visualization. This method was applied to the analysis of HLA-DR4-DRB1 alleles in polymerase chain reaction-amplified genomic DNA and resulted in highly specific and sensitive hybridization signals discriminating even in cases of a one-base-pair mismatch. This technique is particularly suited for HLA oligotyping because it allows the use of tetramethylammonium chloride for the simplification of hybridization and washing conditions.

Base Sequence↗
PubMed1991

Structure and function of lamellar bodies, lipid-protein complexes involved in storage and secretion of cellular lipids.

This review article attempts to present an overview of the occurrence and function of lipid storage and secretory organelles: the lamellar bodies. Morphologically these organelles vary considerably in size (100 nm to 2400 nm); they are surrounded by a membrane and contain multilamellar lipid membranes. Lamellar bodies may also contain apolipoproteins and lytic enzymes and have an acidic pH, which confers on them a lysosomal character. Under normal physiological conditions, the main function of lamellar bodies is the supply of extracellular domains with specialized lipid components related to a specialized function. The lamellar bodies of the lung epithelium are best investigated in their functional and structural features and are the storage form of the lung surfactant. They provide a monomolecular lipid film of dipalmitoyl phosphatidylcholine (DPPC) on the surface of lung alveoli to lower surface tension necessary for optimal gas exchange and a hydrophobic protective lining against environmental influences. Additional cells of the respiratory system such as the mucosa of the human nose and the bronchi contain lamellar bodies. Lamellar bodies are also found in the gastrointestinal tract, in tongue papillae, oral epithelium, and mucosa cells of the stomach. The major phospholipid of lamellar bodies in mucosa cells of the stomach is DPPC, providing a hydrophobic protective lipid film against the tissue-damaging activities of gastric juice. The hydrophobic water-protective barrier of the skin, which consists mainly of neutral lipids, however, also originates from lamellar bodies secreted by epithelial cells. Lamellar bodies, mainly consisting of DPPC, also occur in mesodermal cell layers of sliding surfaces to provide the lubrication of joints, of the peritoneum, pericardium, and pleural mesothelium. In certain pathological conditions, such as atherosclerosis, Niemann-Pick disease, lecithin:cholesterol acyltransferase (LCAT) deficiency, cholestasis, degeneration of nerves and brain, and regeneration of nerves and wound healing, lipid-containing lamellar bodies have been observed in various cells, the function of which still remains to be elucidated. In early and late lesions of atherosclerotic plaques, lamellar bodies, consisting of unesterified cholesterol and phospholipids, are associated with the extracellular matrix of the intima. During regression of fatty streaks, lamellar bodies are seen intracellularly in macrophages and smooth muscle cells. Inherited metabolic disorders, such as Niemann-Pick disease type I and type II, result in the excessive accumulation of lamellar body-containing cells, for example in bone marrow, spleen, and lymphoid tissue. Type I is a deficiency in sphingomyelinase and type II is a defect in intracellular trafficking of lipoprotein-derived cholesterol.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

High-performance capillary electrophoresis of hydrophobic membrane proteins.

Hydrophobic membrane proteins, extrinsic and intrinsic ones, were separated by high-performance capillary zone electrophoresis (HPCZE) and high-performance capillary isotachophoresis (HPCITP). In the case of HPCZE with both coated and uncoated quartz capillaries the addition of 7 M urea to the separation buffers was necessary to achieve reproducible results. In the HPCITP experiments PTFE capillaries were used. When spacers were used, e.g., ampholytes, additional splitting of peaks was observed. The splitting was caused by the microheterogeneity of the investigated proteins, which are differently glycosylated and/or phosphorylated.

Animals↗
PubMed1990

Flow cytometric analysis of thiazole orange uptake by platelets: a diagnostic aid in the evaluation of thrombocytopenic disorders.

Thiazole orange (TO), a fluorescent dye originally synthesized for reticulocyte analysis, is characterized by a large fluorescence enhancement and high quantum yield on binding to nucleic acids, particularly RNA. In addition, the dye readily permeates live cell membranes. We applied TO staining, followed by fluorescence-activated flow cytometric analysis, to platelets in whole blood samples from hematologically normal subjects and patients with various quantitative platelet disorders. The percentage of TO-positive platelets in 50 control subjects was 8.6 +/- 2.8% (mean +/- SD) ranging from 2.8% to 15.8%. In 21 thrombocytopenic patients whose bone marrow contained normal to increased numbers of megakaryocytes, the percentage of fluorescently labeled platelets was significantly elevated (P less than .0001) to 26.9 +/- 10.9% (range, 13.3% to 57.1%). In contrast, the proportion of positively stained platelets in 23 patients with thrombocytopenia due to impaired platelet production (various conditions with reduced marrow megakaryocytes) did not significantly differ from the controls, whereas the absolute counts of TO-positive platelets were significantly lowered (P less than .0001). Differences in the distributions of the percentage values as well as of the absolute counts for TO-positive platelets between the two patient groups were again highly significant (P less than .0001). Both the sensitivity and the specificity of this method in distinguishing between these categories of thrombocytopenia were greater than or equal to 95%. We conclude that flow cytometric analysis of platelets after staining with TO is a sensitive and specific test that rapidly provides information on the thrombopoietic activity in thrombocytopenic disorders. Our data further suggest that increased amounts of residual RNA characterize platelets released under conditions of "stress thrombopoiesis."

Benzothiazoles↗
PubMed1990

MACOP-B chemotherapy for the treatment of high grade and intermediate grade non Hodgkin's lymphoma.

Between Nov. 1985 and Nov. 1988, sixty-three patients with high grade malignant (hg) and intermediate grade malignant (img) Non Hodgkin's Lymphoma (NHL) were treated with MACOP-B (methotrexate, doxorubicin, cyclophosphamide, vincristine, prednisone and bleomycin). Thirty-seven patients received MACOP-B as an upfront treatment modality, whereas twenty-six patients had relapsed disease and received MACOP-B as a salvage protocol. Four weeks after termination of therapy, 75% of patients with de novo NHL and 72% of the patients with relapsed NHL were in complete remission (CR). In the group of newly diagnosed NHL, 22% achieved partial remission (PR) and 3% no change (NC), whereas in the group with relapsed disease 14% had PR and 14% had progressive disease (PD). At a medium follow-up of 12 months (range 1 month to 33 months), 74% of patients with de novo NHL continued to be in CR whereas the continuous CR rate in patients with relapsed disease was 35%. Overall survival after 30 months of observation for the patient group with de novo NHL was 75% and 40% for patients with relapsed NHL. The mean duration for completion of the projected 12 chemotherapy cycles, given in weekly intervals, was 12.9 and 13.5 weeks in upfront or salvage therapy, respectively. With low incidence of major toxicities, application of drugs on an outpatient basis, and high efficacy, MACOP-B shows substantial advantages for therapy of de novo and relapsed NHL.

Adult↗
PubMed1990

Regulation of phospholipid biosynthesis during cholesterol influx and high density lipoprotein-mediated cholesterol efflux in macrophages.

We have studied the rate of phospholipid synthesis and turnover in mouse peritoneal macrophages in reaction to cholesterol influx and high density lipoprotein (HDL)-mediated cholesterol efflux, using three different radioactive precursors, 32PO4(3-), [3H]choline, and [14C]oleic acid. The cells were loaded with cholesterol for up to 18 h with acetyl-low density lipoprotein (LDL), and phospholipid synthesis was measured at various time intervals and compared with nonloaded macrophages. In the first 2 h of cholesterol loading, a twofold increase in the rate of synthesis for sphingomyelin, phosphatidylcholine, phosphatidylserine-inositol, and phosphatidylethanolamine was observed. After this initial up-regulation, the rate of phospholipid synthesis continuously declined upon further cholesterol loading, while the turnover rate of cellular phospholipids was not affected under the same conditions. The lysosomal inhibitor chloroquine abolished the down-regulation, revealing a strong correlation between phospholipid synthesis and lysosomal enzyme activity which was presumably dependent on the release of cholesterol from the lysosome. The reduction in phospholipid synthesis induced by cholesterol loading is reversible by the addition of HDL3 to the cells. When HDL3 was added to the culture medium, a two- to threefold increase in phosphatidylcholine synthesis and a twofold increase in sphingomyelin formation was observed after 3 h. Ca2+ antagonists of the dihydropyridine type, which down-regulate HDL-receptor activity and promote the formation and cellular release of lamellar bodies derived from the lysosomal compartment (Schmitz, G., et al. 1988. Arteriosclerosis. 8: 46-56, and Robenek, H., and G. Schmitz. 1988. Arteriosclerosis. 8: 57-67), specifically enhance the synthesis of sphingomyelin in cholesterol-loaded macrophages. Inhibitors of acyl-CoA:cholesterol acyltransferase (Octimibate, progesterone) increase both the synthesis of sphingomyelin and phosphatidylcholine, and enhance HDL-receptor activity. The results indicate that cholesterol and phospholipid metabolism are coordinately regulated in macrophages. Moreover, the formation of phosphatidylcholine and sphingomyelin seems to be an important factor for the promotion of HDL-receptor-mediated cellular cholesterol efflux.

Animals↗
PubMed1990

Macrophage interaction of HDL subclasses separated by free flow isotachophoresis.

Preparative isotachophoresis (ITP) was used for the fractionation of fasting and postprandial high density lipoproteins (HDL) according to their net charge in the absence of molecular sieve effects. Three major HDL subpopulations with fast, intermediate, and slow mobility have been recognized. Particle size analysis by gradient gel electrophoresis has shown that in the fast-migrating subpopulation particles dominate with a size of HDL3a and HDL2b. The subpopulation with intermediate mobility contains particles with a size between HDL2a and HDL3b, while in the slow migrating subpopulation particles dominate with a size of HDL2b, HDL3a, and HDL3c. The fast-migrating subpopulation is rich in apoA-I and phosphatidylcholine. The particles of this fraction bind at 4 degrees C to HDL receptors on macrophages with high affinity (KD = 7.71 micrograms/ml; Bmax = 245.6 ng). The subpopulations with intermediate mobility is rich in apoA-II, apoE, C apolipoproteins, cholesteryl esters, and sphingomyelin. Its affinity to HDL receptors (KD = 17.7 micrograms/ml; Bmax = 198.4 ng) is lower than that of the HDL particles in the fast-migrating subfraction. The slow-migrating subpopulation consists of particles rich in apoA-IV and is associated with a high LCAT activity. This fraction expresses the highest nonspecific binding to mouse peritoneal macrophages compared to the other HDL fractions and contains only a small amount of particles that interact with HDL receptors by high affinity binding (KD = 7.3 micrograms/ml; Bmax = 95.9 ng). In 37 degrees C binding experiments the fast-migrating subfraction reveals the highest total cell-associated activity. 72% of which is trypsin-resistant. The other subfractions express a lower total cell-associated activity and 45% of the activity of the intermediate- and 43% of the activity of the slow-migrating fraction is trypsin-sensitive. When the HDL fractions are isolated from postprandial sera of the same donor, the fast-migrating particles bind at 4 degrees C with a higher affinity (KD = 4.6 micrograms/ml) while no significant changes are observed in the intermediate- and slow-migrating subpopulations. The slow- and the fast-migrating HDL subpopulations isolated from fasting serum have a high capacity to promote cholesterol removal from macrophages. We hypothesize that the HDL subpopulations rich in apoA-I promote cholesterol removal predominantly via the interaction with HDL receptors, while apoA-IV-rich HDL particles receive their driving force for cholesterol efflux from the concomitant action of LCAT via a predominantly nonspecific interaction of the particles with the cell surface.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

[Peripheral remnant metabolism].

Although in cross-sectional studies of men with premature CHD plasma triglycerides as well as LDL-cholesterol levels are almost invariably increased, the atherogenicity of plasma triglycerides has remained controversial, mainly because in most prospective studies triglycerides have failed to survive the test of multivariate analysis as an independent risk factor. On the other hand the atherosclerotic risk is increased in some genetic disorders associated with elevated triglyceride levels and also in patients with remnant hyperlipidemia coexistence of non-functional apo E isoforms with a genetic or acquired disorder of VLDL/IDL metabolism lead to the accumulation of remnant lipoproteins (beta-VLDL) with a prolonged half life which are finally metabolized in macrophages leading to foam cell formation. Similar remnant particles have been described as hypertriglyceridemic-VLDL1 (HTG-VLDL1) in patients with hypertriglyceridemia. At least two metabolic pathways are involved in the cellular uptake of remnant lipoproteins. One is identical with the classical LDL-Apo B, E receptor, which binds these particles by either the apo B or apo E moiety. The other binding site may be related to the LRP-type (LDL-receptor-like protein) remnant receptor which recognizes functional apo E isoforms. In addition beta-VLDL and oxidatively modified remnant lipoproteins are recognized by the scavenger receptor of macrophages leading to cholesterylester accumulation. The oxidized remnant lipoproteins may be also cytotoxic for endothelial cells as it has been shown extensively for the atherogenic oxidized LDL. Among the peripheral cells macrophages, endothelial cells and also vascular smooth muscle cells are the major cell types which are affected by atherogenic remnant lipoprotein particles.(ABSTRACT TRUNCATED AT 250 WORDS)

Apolipoproteins E↗
PubMed1990

[The effect of Ca++ antagonists on cellular lipid metabolism].

The antiatherogenic effects of Ca2(+)-antagonists have been proved in animal studies and in man. It is suggested that drugs of this class--unlike lipid-lowering drugs--do not exert their effects by decreasing lipoprotein plasma levels but by a modulation of signal transducers. Ca2(+)-antagonists inhibit the extracellular matrix synthesis and thereby decrease cell adhesion and the modification of matrix-bound low density lipoproteins (LDL). Thus less modified LDL are produced, which are catabolized by scavenging or by phagocytosis of macrophages, leading to a reduction of foam cell production. Ca2(+)-antagonists also enhance the synthesis of membrane phospholipids, e.g. sphingomyelin (SPM), thereby increasing the membrane turnover and fluidity. In addition they positively influence the formation and catabolism of radicals. The resulting membrane protective effects possibly delay the general ageing process and improve the integrity of the cytoskeleton as well as of the adjacent membranes. In various studies it has been established that the use of Ca2(+)-antagonists leads to a reversal of atherosclerotic processes at the stage of early lesions. The effects of this class of drugs on a molecular level will be a focal point of future research. Of special importance will be the study of the cell specific signal transducing processes in those types of cells involved in atherosclerosis and the understanding of their role in the process as a whole.

Arteriosclerosis↗
PubMed1990

Characterization of apolipoprotein B-containing lipoproteins separated by preparative free flow isotachophoresis.

Preparative free flow isotachophoresis (ITP) was used for the fractionation of apoB-containing lipoproteins (d less than 1.063 g/ml) from fasting and postprandial sera derived from normolipidemic individuals. According to their net electric mobility, four major particle groups (I-IV) have been recognized. The fast-migrating particles in group I, which correspond predominantly to very low density lipoproteins (VLDL), are rich in triglycerides, free cholesterol, phosphatidylcholine, and apoE and C apolipoproteins. This group expresses nonspecific binding to fibroblasts but binds to HepG2 cells with high affinity (KD = 3.6 micrograms/ml, Bmax = 37 ng) to a single class of binding sites. The particles migrating in group II, which are related to intermediate density lipoproteins (IDL), are richer in cholesteryl esters and apoB than those in group I. They interact specifically with a single site on fibroblasts (KD = 7.8 micrograms/ml, Bmax = 54 ng) while on HepG2 cells two binding sites, one with a higher (KD = 3.5 micrograms/ml, Bmax = 22 ng) and one with a lower affinity component (KD = 16.9 micrograms/ml, Bmax = 53 ng), are involved. The particles migrating in groups III and IV correspond to low density lipoproteins (LDL). The protein moiety of both fractions consists almost exclusively of apoB. Group III represents cholesteryl ester-rich LDL particles, while the particles in group IV contain smaller amounts of cholesteryl esters. The lipoproteins of both groups are ligands for apoB,E-receptors. However, the particles in group IV interact with fibroblasts with the highest affinity (KD = 2.3 micrograms/ml, Bmax = 58 ng) and with the biphasic HepG2 cell binding sites with the lowest affinity of all analyzed groups (KD1 = 11.2 micrograms/ml, Bmax1 = 58 ng, KD2 = 68 micrograms/ml, Bmax2 = 170 ng). When apoB-containing lipoproteins were isolated from postprandial sera of the same individuals, significant changes in the lipid composition were observed only in particle groups I and II, where the triglyceride and phospholipid content was enhanced. Group I particles from postprandial serum bind to HepG2 cells with a higher affinity (KD = 2.5 micrograms/ml) than group I particles from fasting serum. Postprandial group II particles bind with the same affinity to the biphasic HepG2 cell receptor as fasting group II particles, while the affinities of postprandial group III (KD1 = 4.1 micrograms/ml, KD1 = 47 micrograms/ml) and group IV particles (KD1 = 3.9 micrograms/ml, KD2 = 38 micrograms/ml) to the high affinity binding site of the biphasic receptor are enhanced.(ABSTRACT TRUNCATED AT 400 WORDS)

Apolipoproteins B↗
PubMed1989

[Para-pelvic cysts: difficulties in differential diagnosis].

According to their different etiology, parapelvic cysts must be differentiated from simple renal cysts, pararenal pseudocysts, intramural renal pelvis cysts and suprarenal pseudocysts. An important criterium of parapelvic cysts is their epithelial lining. According to their radiological features, these cysts must be described as "parapelvically located cysts" until the definite histological diagnosis is made by the pathologist. The exact differentiation between a parapelvic cyst and a pararenal pseudocyst may be of forensic importance in posttraumatic patients.

Adult↗
PubMed1988

Purification of monoclonal antibodies against the low-density lipoprotein receptor by preparative isotachophoresis.

A preparative free-flow isotachophoretic method for the purification of monoclonal antibodies from mouse ascites fluid and tissue culture media is described. This high-resolution method allows the direct separation of monoclonal antibodies from antibody-containing tissue culture media or ascites fluid and gives a better separation from the major contaminant protein fractions and a higher recovery of the monoclonal antibodies than anion-exchange chromatography. The purification can run continuously and without any time-consuming regeneration procedures; the monoclonal antibody is obtained under mild conditions in a small electrolyte volume.

Animals↗