Local administration of 7 beta-hydroxycholesteryl-3-oleate inhibits growth of experimental rat C6 glioblastoma.

The effect of 7 beta-hydroxycholesteryl-3-oleate on rat brain C6 glioblastoma cells was studied. Three days after the inoculation of 2 x 10(5) C6 cells into the frontal cortex of 6-day-old Wistar rats, two types of liposomes [consisting of either phosphatidylcholine and monosialoganglioside (PG:GM1, 10:1 mol/mol) only, or containing 7 beta-hydroxycholesterol, 7 beta-hydroxycholesteryl-3-oleate, 7 alpha-hydroxycholesteryl-3-oleate, or 7-ketocholesteryl-3-oleate] were injected into the xenograft. Ten days later, the animals were sacrificed, the tumors were stained with cresyl violet or hematoxylin/eosin, their volumes determined by image analysis, and their development followed by magnetic resonance imaging. The mean (+/- SE) tumor volume was 4.4 +/- 1.0 mm3. The injection of liposomes without oxysterol had no effect on tumor growth, whereas injection of liposomes containing 7 beta-hydroxycholesteryl-3-oleate (36 nmol) gave rise to a marked decrease in tumor volume (from 4.4 +/- 1.0 to 0.7 +/- 0.4 mm3). Seven nmol had no effect on tumor growth, 72 nmol were as efficient as 36 nmol, and 144 nmol attenuated the tumor volume by 50% only. Liposomes containing 72 nmol of oleic acid enhanced the tumor volume 4-fold. These findings were confirmed by magnetic resonance imaging. Thus, following induction of tumors in both the right and left sides of the cortex and treatment of the right side, magnetic resonance imaging indicated a significant decrease in tumor volume on the right side only. When C6 cells and 7 beta-hydroxycholesteryl-3-oleate were simultaneously injected, tumors did not develop in 80% of the animals. The clearance of [3H]7 beta-hydroxycholesteryl-3-oleate, of which 75% was converted to cholesterol, reached 99% after 48 h. Other oxysterols did not affect the tumor volume except that 7-keto-cholesteryl-3-oleate decreased the tumor volume by 50%. Thus, the 3-fatty acyl ester and 7 beta-hydroxyl groups are apparently required for the antitumor growth effect. Taken together, these data suggest that 7 beta-hydroxycholesteryl-3-oleate might be useful for local glioblastoma chemotherapy.

Intracellular lipase activities in heart and skeletal muscle homogenates. The absence of trierucin cleavage by the heart: a possible biochemical basis for erucic acid lipidosis.

Rat heart and skeletal muscle homogenates were compared for their intracellular lipolytic activity towards a series of saturated and unsaturated triglycerides from trilaurin (C12:0) to trierucin (C22:1). It is shown that for all triglycerides esterified with fatty acids from C12 to C18, lipolytic activity in heart homogenates was higher than in skeletal muscle homogenates. For these triglycerides there was no relationship between the fatty acid chain length and the lipolytic activity. In both homogenates cleavage of unsaturated triglycerides was higher than cleavage of the homologous saturated triglyceride. Lipolysis of tri-delta-11-eicosenoin (C20:1) was similar in both homogenates but much lower than lypolysis of other triglycerides. Although cleavage of trierucin (C22:1) was very low in skeletal muscle homogenates, it was undetectable in heart homogenates, even when enzyme concentration was increased. A mixture of triglycerides did not show preferential hydrolysis of any simple triglyceride. Trierucin was the only triglyceride that did not complete for lipolytic activity and only with heart homogenates, which shows that that lipase(s) do not cleave trierucin. The absence of lipolytic activity towards trierucin in heart homogenates could explain the selective accumulation of erucic acid-rich triglycerides in hearts of animals fed a diet with a high erucic acid content.

Metabolism of 7 beta-hydroxycholesterol in astrocyte primary cultures and derived spontaneously transformed cell lines: correlation between the esterification on C-3 -OH by naturally occurring fatty acids and cytotoxicity.

The lethal effect of 7 beta-hydrocholesterol (7 beta-OHC) on spontaneously transformed cell lines, derived from neonatal rat astrocyte primary cultures and the extent of 7 beta-OHC esterification by naturally occurring fatty acids on C-3 -OH (metabolite) was investigated. The extent of cellular death and metabolite biosynthesis matched with the 7 beta-OHC concentrations. Incubation of the cells with 10 microM 7 beta-OHC in the presence of either lipoproteins depleted fetal calf serum or with increasing serum concentrations revealed proportionality between the degree of cellular cytotoxicity and metabolite levels. The use of tetracaine or progesterone as acyl-CoA: cholesterol acyltransferase (ACAT) inhibitors indicated that ACAT was involved in metabolite production; the inhibition of metabolite biosynthesis slowed down 7 beta-OHC lethal effect. Incubation of the cells with 1 mM db-cAMP, prior 7 beta-OHC treatment, enhanced both metabolite production and cellular death. These findings support the view that the metabolite is directly implicated in the cytotoxic action.

The nature of DT-diaphorase (EC 1.6.99.2) activity in plasma membrane of astrocytes in primary cultures.

This is the confirmation of an earlier indication (Mersel, M., Malviya, A.N., Hindelang, C. and Mandel, P. (1984) Biochim. Biophys. Acta 778, 144-154) that the plasma membrane of astrocytes in primary cultures is endowed with DT-diaphorase (EC 1.6.99.2) activity. It is observed that the NADPH-2,6-dichloroindophenol diaphorase activity found in the isolated plasma membrane is not inhibited by dicoumarol. DT-diaphorase-type activity is also observed on the cell surface employing dichloroindophenol as external electron acceptor and it is found to be a dicoumarol-sensitive NADH dehydrogenase.

Topological distribution of aminophospholipid fatty acids in trout intestinal brush-border membrane.

The transbilayer distribution of aminophospholipids in trout intestinal brush-border membrane has been investigated using trinitrobenzene sulfonic acid (TNBS). In the middle intestine, phosphatidylethanolamine (PE) is symmetrically distributed between the two leaflets while 68% of the phosphatidylserine (PS) are located in the inner membrane leaflet. In the posterior intestine, 64% of the PE and 69% of the PS are located in the inner membrane leaflet. When asymmetrically distributed, the inner species of PE and PS have a higher content of 22:6(n-3) than the outer ones. This asymmetric distribution of docosahexaenoic acid in trout intestinal brush-border membrane might be related to the rod-like shape of the microvillus membrane and to its metabolism to hydroxylated derivatives.

Plasma membrane isolated from astrocytes in primary cultures. Its acceptor oxidoreductase properties.

Rat astrocytes in primary cultures were employed to isolate the plasma membrane. The method for the isolation of plasma membrane was based on the capacity of the cytoskeleton to adhere to the substratum entrapping intracellular organelles during freezing-thawing cycle performed on the cell. By washing the 'surface adherent framework', the untrapped plasma membrane were recovered and density equilibrium centrifugation resulted in the isolated membrane. The isolated plasma membrane was characterized on the basis of a variety of marker enzymes positive to the plasma membrane such as (Na+ + K+)-ATPase or 5'-nucleotidase as well as the lack of conventional markers of other endomembranes. Ultrastructurally the membranes, as isolated here, were mainly vesicular in nature. The isolated plasma membrane was devoid of the dehydrogenase responsible for NADH-cytochrome c reductase activity. However, NADH-ferricyanide reductase activity and the dehydrogenase system catalyzing the transfer of reducing equivalents from NADH or NADPH to dichloroindophenol seems plasma membrane redox system. The identical specific activity employing dichloroindophenol as an electron acceptor with NADH or NADPH as donor indicate a DT-diaphorase (EC 1.6.99.2) like activity in the astrocytes plasma membrane.

A study on the topological distribution of phospholipids in microsomal membranes of chick brain using phospholipase C and trinitrobenzenesulfonic acid.

The transbilayer distribution of phospholipids in chicken brain microsomal membranes has been investigated using trinitrobenzenesulfonic acid and phospholipase C from Clostridium welchii. The exposure of intact microsomes to trinitrobenzenesulfonic acid showed that the labelling of aminophospholipids followed biphasic kinetics, indicating that these membranes contain a fast- and a slow-reacting pool of aminophospholipids. Use of microsomes radioiodinated on their surface led to the conclusion that the fast-reacting pool may be located on the outer leaflet of the microsomal vesicles. It contains about 35% of the phosphatidylethanolamine, 29% of the ethanolamine plasmalogens and 18% of the phosphatidylserine. The treatment of intact microsomes with the phospholipase C Cl. welchii produced the hydrolysis of 50% of the phospholipids without any loss of their permeability properties, indicating that they are not permeable to the hydrolase. Phospholipids extracted from the microsomes were hydrolyzed rapidly by the phospholipase C with the exception of phosphatidylserine and phosphatidylinositol. In intact microsomes about 90% of phosphatidylcholine, 32% of ethanolamine phospholipids and 60% of sphingomyelin were accessible to the phospholipase. These results suggest that the phospholipids have an asymmetric distribution in chicken brain microsomes, the external leaflet containing about 75% of the choline phospholipids and 25% of the aminophospholipids, whereas an opposite distribution is observed in the inner leaflet.

Effect of 7 beta-hydroxycholesterol on astrocyte primary cultures and derived spontaneously transformed cell lines: cytotoxicity and metabolism.

The lethal effect of 7 beta-hydroxycholesterol (7 beta-OHC) on neonatal rat astrocyte primary cultures and spontaneously transformed cell lines derived from them was investigated. Confluent astrocyte primary cultures were not affected by 30 microM 7 beta-OHC over a period of 72 h. In contrast, spontaneously transformed cells were killed by 20 microM 7 beta-OHC within the first 48 h. Further studies indicated that the cell lines metabolized 7 beta-OHC to a product the polarity of which was less than that of 7 beta-OHC. The metabolite was identified as 7 beta-OHC esterified on C-3 by naturally occurring fatty acids. Incubation of the cell lines with 0.5 microM metabolite markedly affected the cells within 24 h. These observations suggest that the 7 beta-OHC metabolite is implicated in the mechanism of action of 7 beta-OHC cytotoxicity on spontaneously transformed cells.

Effect of 7 beta-hydroxycholesterol on growth and membrane composition of Mycoplasma capricolum.

7 beta-OH cholesterol in a cholesterol rich growth medium (5-10 micrograms/ml) extended the lag period and slowed down the growth rate of Mycoplasma capricolum cells. In a cholesterol poor medium (0.5 micrograms/ml) inadequate to support growth, 7 beta-OH cholesterol exerts a synergistic effect on growth. The 7 beta-OH cholesterol was incorporated unchanged from the growth medium and could be recovered exclusively in the membrane fraction. The incorporation of the 7 beta-OH cholesterol has no effect on the total phospholipid content but the DPG to PG ratio was markedly decreased. Exchange studies with lipid vesicles revealed that whereas most of the cholesterol underwent exchange, only about 20% of the 7 beta-OH cholesterol was exchanged.

Ethanolamine base exchange enzymatic activities in spontaneous transformed glial cell lines. Effect of dibutyryl cyclic AMP treatment.

Cultured astrocytes derived from neonatal rats (normal cells) displayed maximal ethanolamine base exchange enzymatic activity (EBEE) when cultures reached confluency and cells almost ceased to divide. At this stage, ethanolamine phosphotransferase (EPT) and choline base exchange enzyme (CBEE) activities reached a plateau. In spontaneously transformed glial cells, no differential activity variation either between EPT and CBEE, or between EPT and EBEE was observed. The EBEE activity was mainly localized in the microsomal fraction and was completely absent from plasma membranes. Dibutyryl cyclic AMP (db-cAMP) treatment of the transformed cells reversed the pattern of these activities to that of normal cells. Moreover, treatment of the transformed cells with medium conditioned by normal astroblasts markedly increased EBEE activity. This study demonstrates that (i) variation of EBEE activity during cell growth differs in normal and in transformed cultured glial cells. (ii) EBEE activity may be modulated via both db-cAMP and normal cell conditioned medium. Our findings suggest a possible implication of EBEE in the maturation and contact inhibition of cell growth.

Effect of 7 beta-hydroxycholesterol on astrocyte primary cultures and derived spontaneously transformed cell lines. Cytotoxicity and cholesterogenesis.

The correlation between the lethal effect of 7 beta-hydroxycholesterol (7 beta-OH-CH) on spontaneously transformed cell lines derived from rat astrocyte primary cultures (normal cells) and de novo cholesterogenesis was investigated. Both 7 beta-OH-CH and 7-keto-CH were not cytotoxic on normal cells but 7 beta-OH-CH affected markedly the viability of the transformed cells. The use of [14C]acetate or [14C]mevalonate indicated that 7-keto-CH inhibits de novo cholesterogenesis upstream of 3-hydroxy-3-methylglutaryl CoA reductase (HMGR) in both cell types whereas 7 beta-OH-CH also inhibits downstream of HMGR. The accumulation of two radiolabelled products X1 and X2 between mevalonate and CH was found in unsaponifiable neutral lipids extracted from 7 beta-OH-CH treated transformed cells. HPLC and GC-MS revealed that X1 and X2 are not lanosterol and 24,25-epoxylanosterol, respectively. Incubation of the transformed cells with X1 and X2 did not affect their viability. Our data demonstrate that, under our experimental conditions, 7 beta-OH-CH cytotoxicity is not linked to the inhibition of de novo cholesterogenesis in cultured glial transformed cells.

Effect of dibutyryl cyclic AMP and isoproterenol on 7 beta-hydroxycholesterol cytotoxicity and esterification in spontaneous transformed cell lines derived from astrocyte primary cultures.

Incubation of spontaneous transformed cells derived from astrocyte primary cultures with 30 microM 7 beta-hydroxycholesterol (7 beta-OH-CH) which is lethal to the cells or with 150 microM isoproterenol reduces the intracellular level of cAMP (4- and 2-fold respectively). Treatment of the cultures with 0.5 mM dibutyryl (db)-cAMP and 7 beta-OH-CH increases 3-fold the intracellular level of cAMP and both, db-cAMP and isoproterenol, raise the lethal effect of 7 beta-OH-CH and its esterification on C-3-OH by naturally occurring fatty acids (metabolite). Kinetic studies of net steryl-3-esters hydrolysis revealed that db-cAMP and isoproterenol lower that of cholesteryl-3-esters (2-fold) whereas the opposite is found for the metabolite. These data demonstrate that (i) high cAMP intracellular levels modulate differently the net hydrolysis of cholesteryl-3-esters and metabolite, (ii) isoproterenol acts otherwise than cAMP on 7 beta-OH-CH esterification, (iii) the cytotoxicity of 7 beta-OH-CH is linked to its own esterification. The accumulation of metabolite subsequent to db-cAMP or isoproterenol treatment as a result of acyl-CoA:cholesterol acyl transferase activation is discussed.

7 beta-hydroxycholesterol and 7 beta-hydroxycholesteryl-3-esters reduce the extent of reactive gliosis caused by an electrolytic lesion in rat brain.

Electrolytic lesions performed in brain cortex of six-day-old or adult rats resulted in the appearance of many reactive astrocytes around the injury site after a postoperative delay of eight days. They were revealed by immunohistochemistry using antibodies against glial fibrillary acidic protein. Injection of tritiated thymidine 24 h prior to autopsy indicated that, in neonates, 50% of the reactive astrocytes were proliferating. Infusion of 2 microliters of liposome suspension made of phosphatidylcholine and a monosialoganglioside, in the injury site, immediately after the electrolytic lesion did not modify the extent of the reactive gliosis. Liposomes containing 3 nmol of either 7 beta-hydroxycholesterol, 7 beta-hydroxycholesteryl-3-stearate or 7 beta-hydroxycholesteryl-3-oleate reduced by about 50% the intensity of the reactive gliosis in the frontal cortex of six-day-old rats and by 40% the number of dividing astrocytes. In the adult rat cortex the intensity of the glial reaction was also decreased by 30% by 15 nmol 7 beta-hydroxycholesteryl-3-oleate. Further investigations demonstrated that it is the 7 beta-hydroxy function which is needed for the biological activity of these oxysterols. These findings, which demonstrate anti-proliferative and anti-inflammatory properties of 7 beta-hydroxycholesterol on astrocytes, facilitate the future investigation of the influence of reactive gliosis on functional recovery following brain injury. This anti-proliferative property could also be used in other kinds of pathologies involving glial cell proliferation, such as glioblastomas.

Kinetic characterisation and solubilisation of gamma-hydroxybutyrate receptors from rat brain.

The solubilisation of the gamma-hydroxybutyrate (GHB) receptors from rat brain membranes was undertaken as the first step for their molecular characterisation and purification. Treatment of crude brain membranes with high concentrations of NaCl and Triton X-100 resulted in solubilisation of proteins which retain specific GHB binding activity. Ionic detergents do not solubilise and/or inactivate the receptors. Measurements of kinetic parameters of GHB binding showed that the solubilised receptor, in the presence of detergent, exhibited a reduction of affinity for GHB and its endogenous brain analogue trans-4-hydroxycrotonate (T-HCA). The membrane protein extract, submitted to chromatography by gel filtration, showed a single peak of protein with [3H]GHB binding activity. Association and dissociation constants of GHB for its membrane binding site were in accordance with the Kd determined by the Scatchard method.

Rat liver chromatin phospholipids.

To shed light on the question whether the phospholipids present in chromatin are native or are due to contamination from nuclear membranes, we labeled the phospholipids of isolated nuclei and determined the amount of phospholipids (PL) and PL fatty acid composition in nuclei and chromatin. The hepatocyte nuclei were isolated and radioiodinated by the lactoperoxidase method under saturating and nonsaturating conditions, and the radioactivity associated with chromatin extracted from these nuclei was monitored. Whereas 97% the label was recovered in the nuclear membranes, only 0.08-0.6% was found in chromatin. The PL present in chromatin were relative to the amounts present in the entire nuclei and calculated as percentage of total, phosphatidylethanolamine (10%), phosphatidylserine (22%), phosphatidylinositol (19%) phosphatidylcholine (14%), and sphingomyelin (35%). In sphingomyelin of chromatin-associated PL an enrichment in polyunsaturated fatty acids was seen. The data indicated that the PL found in isolated chromatin do not seem to be due to contamination from the nuclear membrane.

Growth-associated protein 43 is down-regulated in cultured astrocytes.

Growth-associated protein 43 (GAP-43: other designations--pp46, F1, B-50, p-57) is an abundant, neural, membrane-associated protein involved in synaptic plasticity and regeneration. We recently reported that GAP-43 is present in plasma membranes of cultured rat astrocytes. In the present study the level of astrocytic GAP-43 was assessed by indirect immunofluorescence labeling of cells with a specific anti-GAP-43 serum and immunoblotting of plasma membrane proteins. The results indicate that all astrocytes from 1-day-old cortex contained GAP-43 and those differentiated in culture did not. Furthermore, GAP-43 decreased dramatically during 3 weeks in culture. These results are consistent with the developmental down-regulation of GAP-43 in vivo.

[Differential action of 7 beta-hydroxycholesterol on myocardial cells and fibroblasts. Obtaining primary cultures of pure myocardial cells]. / Action différentielle du 7 beta-hydroxycholestérol sur des cellules myocardiales et des fibroblastes. Obtention de cultures primaires de cellules myocardiales pures.

Newborn rat myocardial cells, grown in primary cultures, beat synchronously. Addition of 7 beta-hydroxycholesterol, at a 2.5 microM concentration, impairs this synchrony and may even stop any contraction. The associated fibroblasts no longer adhere to the support, and can be washed away by fresh culture medium. This restores the synchronous beatings of the myocardial cells, the viability of which is then even improved while they grow in the absence of fibroblasts.

Fast-heating mass spectrometry of phosphatidylcholine, lysophosphatidylcholine, phosphatidylethanolamine, and sphingomyelin.

A fast-heating probe and chemical ionization have been used to obtain mass spectra of the synthetic glycerophospholipids 1,2-diacyl-sn-glycero-3-phosphocholine, 1,2-diacyl-sn-glycero-3-phosphoethanolamine, and 1-monoacyl-2-lyso-sn-glycero-3-phosphocholine. The phospholipids investigated gave quasimolecular peaks and fragment ions, with preferential cleavage of the C-O bond (beta position to the phosphorus atom) and loss of phosphoethanolamine or phosphocholine. This technique makes possible the analysis of mixtures of intact phosphatidylethanolamine, phosphatidylcholine, 2-lysophosphatidylcholine, and sphingomyelin isolated from natural sources such as egg yolk or brain. Only minor and inexpensive modifications of a standard mass spectrometer are required.

Studies on oxygen and volume restriction in cultured cardiac cell: possible rearrangement of sarcolemmal lipid moieties during anoxia and ischemia-like states.

Cultured heart cells have been shown useful for investigating states of oxygen and volume restrictions, simulating anoxia and ischemia-like states at cellular levels. The sarcolemma has been implicated as one of the early sites of ischemic damage; therefore, lactoperoxidase catalyzed radioiodination was used to study accessibility of the sarcolemmal lipid moieties to this enzymatic probe, reflecting their exposure to the extracellular environment, hence the biophysical state of the sarcolemma. These studies have shown that within one hour of 'ischemic' injuries: (1) The degree of labelling in the total phospholipid fraction is considerably increased; and (2) Profound changes in the relative extent of labelling of different phospholipid classes were observed. The PE/PC labelling ratio increases dramatically with the progress of ischemia-like state. We suggest that early during ischemic injury, reorganization of the cell surface phospholipids occurs and discuss possible relations to the energy charge of the cell.