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Biomedical subjects

M Shinitzky

Publications and source records attributed to M Shinitzky.

At least 19 recordsLinked to original sources
PubMed1992

Improved chemotactic ability of neonatal polymorphonuclear cells induced by mild membrane rigidification.

Membrane lipid fluidity of peripheral blood polymorphonuclear cells (PMNs) of 24 newborn infants, 2-4 days after birth, was determined by steady-state fluorescence polarization with 1,6-diphenyl 1,3,5-hexatriene (DPH) as a probe and compared with that of PMNs from 23 adults. Measurements with intact cells, which correspond to all cellular lipid domains, did not display any statistically significant difference between PMNs of the two groups. However, application of bixinoyl glucosamine, a membrane-impermeable fluorescence quencher, revealed that the PMN plasma membrane of the newborn is about 23% more fluid than that of the adult. Total cholesterol-to-phospholipid ratio of newborn PMNs was found to be lower by about 10% than that of the adult, which could account for the difference in their plasma membrane fluidity. The possible implication of this finding for the deficit in chemotactic ability of leukocytes from newborns was tested with neonatal PMNs that have incorporated cholesteryl hemisuccinate (CHS), an efficient plasma membrane rigidifier. In all neonatal PMNs tested a mild incorporation of CHS (0.5-1 min incubation in 50 micrograms/ml dispersion) caused a significant improvement in their net chemotaxis, from an average value of 28 +/- 7 to 43 +/- 11. Longer incubations with CHS caused a gradual decrease in chemotactic ability that approached the basal level after about 5 min incubation. The net chemotaxis in adult PMNs was significantly higher than that of neonatal PMNs (72 +/- 13) and was gradually inhibited by incorporation of CHS without any initial augmentation. Based on these results it was estimated that about 27% of the chemotactic deficit of neonatal PMNs is mediated by their immature fluid membrane.

Adult↗
PubMed1991

Potentiation of delayed-type hypersensitivity response to syngeneic tumors in mice prevaccinated with cells modified by hydrostatic pressure and crosslinking.

Delayed-type hypersensitivity (DTH) to the chemically induced EL4 and virally induced ARadLV 136 leukemia cells was determined by the radioactive ear test. Prior to the DTH test, mice were prevaccinated with cells treated either with hydrostatic pressure or with the membrane-impermeant crosslinker adenosine dialdehyde or with a combination of these. For both tumor cells, DTH against unmodified cells was markedly potentiated by prevaccination with cells treated with hydrostatic pressure combined with adenosine dialdehyde. In vitro cytotoxicity data indicated that maximal lysis of target cells is induced by vaccination with adenosine-dialdehyde-treated cells, as well as by pressure in combination with adenosine dialdehyde treatment. In addition, increased [3H]thymidine uptake was observed in effector T cells induced by prevaccination with tumor cells modified by adenosine dialdehyde or pressure or both. This novel and innocuous potentiation of an antitumor immune response may have a practical utility in the treatment of human cancer.

Adenosine↗
PubMed1991

Resistance to NK cell-mediated cytotoxicity (in K-562 cells) does not correlate with class I MHC antigen levels.

Natural Killer (NK) cells probably function as an early line of defense against virus-infected cells and tumor cells. In all cases, the killing by NK cell-mediated cytotoxicity (NK-CMC) is not MHC-restricted and the factors which determine the sensitivity to NK-CMC have not yet been identified. A positive correlation between resistance to NK-CMC and the level of class I MHC antigen (MHC I) expression on target cells has been reported in many studies, and in some cases a functional linkage between the two has been claimed. Several other studies have shown that there is no such correlation. By employing several experimental systems, we demonstrate here a lack of correlation between the level of MHC I and the sensitivity of K-562 cells to NK-CMC. Transfer of MHC I to MHC I-negative cells via vesicles had no effect on their resistance to NK-CMC. In addition, a decrease in resistance to NK-CMC and increase of MHC I levels was observed following target-cell membrane modulation by both application of cholesterol and hydrostatic pressure. Finally, no correlation between sensitivity to NK-CMC and MHC I expression was found in three sublines of K-562 cells. Since NK-CMC is a multistage process, it is concluded that components other than class I MHC antigens have a more prominent role in modulating the sensitivity of target cells to NK-CMC.

Cell Death↗
PubMed1991

Platelet autoantibodies in dementia and schizophrenia. Possible implication for mental disorders.

Platelets isolated from blood of demented and schizophrenic patients were found to bear surface antibodies at a considerably higher titer than those found on platelets from normal age-matched groups or patients with affective disorders. The platelet count in demented and schizophrenic patients correlated inversely with the level of the platelet associated antibodies (PAA) which suggested an autoimmune route of opsonization. In most individual cases of dementia or schizophrenia PAA and platelet count were found to oscillate with time between high PAA-low platelet number and low PAA-high platelet number in approximately inverse correlation. PAA isolated from demented patients were found to cross-react with platelets from normals and with brain tissue from rats. Furthermore, molecular weights of specific brain antigens were identified by binding to PAA. These observations support the possibility that PAA might be implicated in the etiology of some mental dysfunctions associated with dementia and schizophrenia.

Adult↗
PubMed1979

Gross structural changes in isolated liver cell plasma membranes upon binding of insulin.

The addition of 10(-9) M insulin to a suspension of rat liver plasma membranes increases the overall lipid microviscosity, eta, by about 10--20%. The effect is confined to physiological concentrations of the hormone and is highly specific. The specificity was demonstrated in experiments where insulin analogues were added to liver plasma membranes and where insulin was added to human erythrocyte membranes. In both of these experiments practically no change in eta was detected. Upon in vitro enrichment of the membrane cholesterol, eta exceeded the level mediated by insulin binding, and the addition of 10(-9) M insulin to the cholesterol-enriched membranes did not further increase eta. Concomitant to the increase in eta upon insulin binding, the overall degree of exposure of the membrane protein, presumably to both sides of the membrane, is substantially increased. This effect is in line with the notion of vertical displacement of membrane proteins induced by changes in eta. The observed structural modulation can account for the effect of insulin on unrelated membrane responses, as well as for the negative cooperativity of insulin binding.

Animals↗
PubMed1979

Modulation of erythrocyte membrane proteins by membrane cholesterol and lipid fluidity.

Human erythrocyte membranes were enriched or depleted of cholesterol and effects on membrane proteins assessed with a membrane-impermeant sulfhydryl reagent, [35S]glutathione-maleimide. Reaction of the probe with intact cells quantifies exofacial sulfhydryl groups and reaction with leaky ghost membranes permits quantification of endofacial sulfhydryl groups. The mean endofacial sulfhydryl titer of cholesterol-enriched membranes exceeded that of cholesterol-depleted membrane by approximately 45 nmol/mg of protein or 64%. The corresponding exofacial titer of cholesterol-enriched cells was less than that of cholesterol-depleted cells by approximately 0.4 nmol/mg of protein, or 14%. Labeled membranes were examined by autoradiography of sodium dodecyl sulfate-polyacrylamide gel electropherograms to determine the labeling patterns of individual protein bands. Cholesterol enrichment enhanced the surface labeling of Coomassie brilliant blue stained bands 1,2,3, and 5, decreased the labeling of band 6, and did not change significantly that of band 4. The results demonstrate that changes in membrane cholesterol which influence lipid fluidity can alter the surface labeling of both intrinsic and extrinsic membrane proteins.

Cholesterol↗
PubMed1979

Possible role for glycosphingolipids in the control of immune responses.

Preparations of gangliosides from bovine brain contain material which acts as a strong mitogen on murine spleen cells. This material is highly lipophilic and co-purifies with the ganglioside fraction. It contains saccharides of a similar composition to those found in monosialogangliosides, as well as a spinogsine base and an appreciable amount of peptide. The common brain gangliosides GM1, GD1a and GD1b, on the other hand, are not mitogenic and act as suppressors of the mitogenic activity of bacterial lipopolysaccharide on murine spleen cells. Both the mitogenically active and suppressive fractions of bovine brain glycosphingolipid were found to act exclusively on B lymphocytes. Since gangliosides and related compounds are components of plasma membranes and of amphipathic nature, they may passively migrate between the lymphocyte subpopulations and thus act as physiological modulators of immune responses.

Animals↗
PubMed1979

Cholestryl-phosphoryl-choline in lipid bilayers.

Cholesteryl-phosphoryl-choline (CPC), a hybrid between cholesterol and lecithin, is incorporated into sonicated liposomes and erythrocyte membranes similarly to cholesterol. The effect of CPC on lipid microviscosity and degree of order is smaller, but not significantly than that of cholesterol. It is proposed that CPC may be employed as an efficient modulator of lipid dynamics.

Blood↗
PubMed1979

Viscosity of lymphocyte plasma membrane in aging mice and its possible relation to serum cholesterol.

Lymphocyte membrane fluidity was examined in aged mice and characterized as a qualitative and effective change which takes place in the aging process. Fluorescence polarization of diphenylhexatriene-labelled mouse spleen cells is substantially higher in cells from old mice (20--36 months) than young mice (2--7 months). A similar difference was also observed with isolated plasma membranes from spleen cells of old and young mice. The overall estimate is that the lipid microviscosity in the lymphocyte plasma membrane from old mice is about 20% higher than that of young mice. The cholesterol/phospholipid ratio determined for the isolated plasma membrane preparations was 0.68 and 0.9, respectively, which is probably the main cause for the difference in membrane viscosity. An elevated cholesterol/phospholipid ratio was also observed in the blood serum of old mice. It is plausible that the source of excess membrane cholesterol in the old mouse lymphocytes originates in the high serum cholesterol.

Aging↗
PubMed1979

Effective tumor immunization induced by cells of elevated membrane-lipid microviscosity.

The immunogenicity of a series of mouse tumor lines propagated in vivo (T and B lymphomas and mammary adenocarcinoma) was tested after alteration of the cell membrane-lipid microviscosity. Tumor cells used for immunization were first treated to alter the lipid content, then irradiated and injected intraperitoneally into syngeneic mice. A second identical immunization was performed 14 days later. The degree of immunization in the treated mice was assessed by survival time after challenge with untreated viable tumor cells of the same origin as the immunizing cells. For all tumors tested, enrichment of the immunizing cells with cholesterol or cholesteryl hemisuccinate, which increased the membrane-lipid microviscosity significantly, afforded a marked increase in immunization, compared to that obtained with cells that were only irradiated. Furthermore, in over 90% of the mice that were pretreated with cholesteryl hemisuccinate-enriched cells, tumor growth after the challenge was not detectable. Because the lipid-modifying treatments of the immunizing cells involve no toxic substances, these results may provide the basis for a potent approach to immunotherapy of human cancer.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1979

Passive modulation of blood-group antigens.

Rh-positive erythrocytes were enriched and depleted of membrane cholesterol, and the mediated change in the degree of exposure of the D antigens was determined by fluorescence-activated cell sorting, using indirect fluorescent antibody labeling. The results are compatible with a model in which the expression of the D antigens can be modulated significantly by the lipid microviscosity (eta). At a high cholesterol-to-phospholipid ratio (C/PL) of 1.55, which corresponds to eta (25 degrees C) = 7.5 poise (1 poise = 0.1 Pa.sec), the relative detectable number of D antigens was about double than that at C/PL = 0.65, eta (25 degrees C) = 4.1 poise. In analogous experiments similar fluidity changes resulted in only about 20% modulation of expression of the A1 antigen, suggesting that in the native state this antigen is already well exposed on the erythrocyte surface. This type of antigenic modulation may also operate in vivo, and may thus bear some fundamental implications on tumor immunology and autoimmune diseases.

ABO Blood-Group System↗
PubMed1979

Modulation of transferrin receptors in bone marrow cells by changes in lipid fluidity.

The hypothesis that modulation of transferrin receptors during haematopoiesis is mediated by changes in the lipid fluidity of the cell membranes was tested in this study with bone marrow cells. Binding conditions were first established, under which internalization of fluorescently-labelled transferrin was reduced to a minimum during the binding assays. Cholesterol depletion, which was achieved by a mild physiological treatment, and which increased the membrane-lipid fluidity, resulted in a substantial increase in the average number of the available transferrin receptors per bone marrow cell. Cholesterol enrichment mediated a converse effect. These findings correlate well with the changes observed in the availability of transferrin receptors and membrane microviscosity during differentiation of erythroid cells. In line with the notion of passive modulation, it is proposed that the transferrin receptor is a cross-membrane protein with a substantial portion facing the cytoplasm.

Animals↗
PubMed1979

Microviscosity of amniotic fluid phospholipids, and its importance in determining fetal lung maturity.

Fluorescence polarization measurements of microviscosity (apparent viscosity within the hydrophobic center of lipid bilayers) of amniotic fluid correlate well with lecithin/sphingomyelin ratios determined by thin-layer chromatography. In addition to lecithin, phosphatidylglycerol and phosphatidylinositol are important for determining fetal lung maturity, but the lecithin/sphingomyelin ratio gives no information concerning these other phospholipids. The microviscosity of sphingomyelin significantly exceeded that of lecithin over the temperature range 25--37 degrees C; values for phosphatidylglycerol, phosphatidylinositol, and phosphatidylserine were lower. Phosphatidylglycerol, phosphatidylinositol, and phosphatidylserine, added individually, significantly decreased the microviscosity of dispersions with lecithin/sphingomyelin ratios corresponding either to fetal lung immaturity or maturity. Phosphatidylglycerol caused the greatest decrease in both. Mixtures of the three phospholipids in the proportions found in term amniotic fluid decreased the microviscosity of fluids with either mature or immature lecithin/sphingomyelin ratios by 23--27%. When each was present in the proportion found in tracheal aspirate (twice that of term amniotic fluid), the decreases uere 46--50%. This technique quickly and precisely indicates not only fetal lung maturity but also the presence of important phospholipids other than lecithin and sphingomyelin.

Amniotic Fluid↗
PubMed1978

A differential interaction of daunomycin, adriamycin and their derivatives with human erythrocytes and phospholipid bilayers.

Drug-membrane association of daunomycin, adriamycin and three of its derivatives, adriamycin-14-octanoate (AD-14-OCTA), adriamycin-14-acetate (AD-14-ACE) and N-trifluoroacetyladriamycin-14-valerate (AD32), was studied using phospholipid bilayers and human erythrocytes. The various drugs exhibited a differential affinity to membrane-lipid domains. Lipid-incorporated drugs exhibit a marked change in the shape of the emission spectrum which was utilized for the evaluation of the apparent dielectric constant, epsilon, of the environment surrounding the anthracycline moiety, as well as for the determination ofthe partitioning constant. By measuring the fluorescence polarization and the fluorescence lifetime of the incorporated drugs, rotational relaxation times of 4--8 ns were derived. These parameters provide a supportive evidence of the association of the fluorophore of the drugs with membrane-lipid domains. The anthracycline derivatives interact to a different degree with dipalmitoyl phosphatidylcholine and phosphatidylserine as reflected by changes in their thermotropic properties assessed by differential scanning calorimetry. Daunomycin was the most effective in decreasing the temperature of the phase transition and brought about a comparable reduction in the enthalpy of melting as AD32 and AD-14-OCTA. Adariamycin was the least potent of the series. AD-14-ACE and AD32 protected erythrocytes against hypotonic lysis, adriamycin and daunomycin had no significant effect on the susceptibility to hypotonic lysis, whereas AD-14-OCTA proved to be hemolytic even at low concentration (approx. 10(-7M).

Calorimetry, Differential Scanning↗