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Biomedical subjects

M Shinitzky

Publications and source records attributed to M Shinitzky.

At least 91 records · Page 5Linked to original sources
PubMed1980

Correlations between membrane viscosity, serum cholesterol, lymphocyte activation and aging in man.

Membrane microviscosity, serum cholesterol and lymphocyte stimulation in man were examined in relation to aging. A direct correlation was found between the mole ratio of cholesterol to phospholipids in the serum and the membrane microviscosity of the peripheral blood lymphocyte membranes, both of which increase progressively with age. The increase in membrane microviscosity with age is also concomitant with the decrease in response of the lymphocytes to concanavalin A stimulation. The data suggest that increase in lymphocyte membrane microviscosity is a prominent factor which may lead to the overt reduction of proliferative responses of lymphocytes with aging.

Adolescent↗
PubMed1980

Lipid fluidity markedly modulates the binding of serotonin to mouse brain membranes.

The binding of [3H]serotonin to mouse brain crude membrane and synaptosomal membrane preparations was investigated as a function of membrane fluidity changes by lipids. The microviscosity (eta) of the synaptic membranes was increased by in vitro incubation with either cholesteryl hemisuccinate or stearic acid, resulting in an up to 5-fold increase in the specific binding of [3H]serotonin. Serotonin binding increased progressively until it reached a maximum at 1.75 relative eta units; then it declined. Fluidization of membrane lipids, by treatment with lecithin or linoleic acid, caused a small but significant decrease in serotonin binding. These observations are compatible with the concept of vertical displacement of membrane proteins, indicating that in the untreated brain tissue the accessibility (Bmax) of serotonin receptor binding sites constitutes only a fraction (about 20%) of the potential binding capacity stored in the membrane. Scatchard plots of [3H]serotonin binding, at different eta values, indicate a continuous change in the binding affinity (Kd) of serotonin to its receptor, concomitant with changes in its accessibility. These results may have important implications for physiological processes in the central nervous system, which are associated with modulation of membrane lipids, such as aging. In addition, the regional heterogeneity and plasticity of receptors may be accounted for by differences in membrane lipid fluidity. It was found here that various brain regions differ markedly in their membrane lipid viscosity.

Animals↗
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↗
PubMed1978

Microviscosity changes during differentiation of neuroblastoma cells.

Microviscosity (eta) of the plasma-membrane lipid matrix was measured in exponentially growing and differentiating C1300 mouse neuroblastoma cells, attached to a glass substratum, by fluorescence polarisation of 1,6-diphenyl-1,3,5-hexatriene. Upon differentiation eta decreases progressively, reaching values below those observed in the growth phase. Treatment of the cells with dipalmitoyl phosphatidylcholine vesicles reversibly inhibits morphological differentiation. The results show that a high membrane fluidity is a prerequisite for differentiation.

Cell Differentiation↗
PubMed1978

Determination of fetal lung maturity by fluorescence polarization of amniotic fluid.

The degree of fluorescence polarization (P value) of 1,6-diphenyl-1,3,5-hexatriene has been shown to be an excellent indicator of the lecithin/sphingomyelin (L/S) ratio in laboratory prepared liposomal dispersions. In order to test the validity of this technique in amniotic fluid, the L/S ratio and P value of 161 amniotic fluid specimens were determined. In 127 the P value was less than or equal to 0.336 and the L/S ratio was greater than or equal to 2. In 26 the P value was greater than 0.336 and the L/S ratio was less than 2 (P less than 0.05). The amniotic fluid P value is affected by blood or meconium but not by surgical lubricants or bilirubin. We concluded that the degree of fluorescence polarization of amniotic fluid indicates fetal lung maturity as reliably as the L/S ratio. However, this method has important technical and practical advantages that make it more applicable for a clinical laboratory.

Amniotic Fluid↗