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T F Taraschi

Publications and source records attributed to T F Taraschi.

At least 55 records · Page 3Linked to original sources
PubMed1991

The effect of chronic ethanol consumption on the fatty acid composition of phosphatidylinositol in rat liver microsomes as determined by gas chromatography and 1H-NMR.

Cell membranes and vesicles composed of extracted phospholipids isolated from rats chronically-fed ethanol develop a resistance to disordering by ethanol in vitro (membrane tolerance) and a decreased partitioning of ethanol into the membranes. The anionic lipid phosphatidylinositol (PtdIns) is the only microsomal phospholipid from the ethanol-fed rats that confers tolerance to vesicles of microsomal phospholipids from control rats in a paradigm where phospholipid classes are sequentially swapped. To investigate the molecular basis of this adaptation, the fatty acid content of microsomal PtdIns extracted from the livers of rats chronically fed ethanol for 5 weeks and their calorically-matched controls was analyzed by gas-liquid chromatography (GLC) and 1H-NMR spectroscopy. Chronic ethanol consumption caused an 8.4% decrease in arachidonic acid [20:4(n - 6)], a 20.0% increase in oleic acid [18: 1(n - 9)] and a 47.1% increase in the quantitatively minor fatty acid [20:3(n - 6)]. 1H-NMR was used to quantitatively assay compositional changes in the delta 5 olefinic moiety of the acyl chains in PtdIns, an approach that should be broadly applicable to other lipid systems. After chronic ethanol feeding PtdIns had decreased delta 5 unsaturates (-7.9% NMR, -8.2% GLC) and a corresponding increase in delta 5 saturates (+5.4% NMR, +5.3% GLC). In the other phospholipids, chronic ethanol feeding caused alterations in the fatty acid compositions specific for each phospholipid. PtdIns was the only microsomal phospholipid that exhibited a significant decrease in both the polyunsaturate pool and the ratio of the total olefinic content to the saturated fatty acid content. The major adaptive response in rat liver microsomal PtdIns to chronic ethanol administration involves a decrease in arachidonic acid [20:4 (n - 6)], which is partly compensated for by increases in oleic acid [18:1(n - 9)] and eicosatrienoic acid [20:3 (n - 6)], resulting in a depressed unsaturation and polyunsaturation index. The decreased unsaturation at the delta 5 position may have special functional relevance, due to the proximity of this position to the membrane surface, where ethanol is believed to reside. Whether these acyl changes are merely coincident with, or causative of, membrane tolerance requires further elucidation.

Alcoholism↗
PubMed1991

Modification of host cell membrane lipid composition by the intra-erythrocytic human malaria parasite Plasmodium falciparum.

The phospholipid and fatty acid compositions of the host infected erythrocyte plasma membrane (IEPM) have been determined for erythrocytes infected with the human malaria parasite Plasmodium falciparum. IEPM were prepared by selective lysis of the host erythrocyte (but not of the parasite membranes) with 0.1% saponin, followed by differential centrifugation. The purity of the IEPM was determined by measuring the membrane-specific enzyme markers acetylcholinesterase, glutamate dehydrogenase and lactate dehydrogenase, and by immunoelectron microscopy using monoclonal antibodies specific for human erythrocyte glycophorin A (4E7) and for a 195 kDa parasite membrane glycoprotein (Pf6 3B10.1). Both approaches demonstrated that the host erythrocyte plasma membrane preparation was free from contamination by parasite membranes. During intra-erythrocytic development of the parasite, the phospholipid composition of the erythrocyte membrane was strikingly altered. IEPM contained more phosphatidylcholine (38.7% versus 31.7%) and phosphatidylinositol (2.1% versus 0.8%) and less sphingomyelin (14.6% versus 28.0%) than normal uninfected erythrocytes. Similar alterations in phospholipid composition were determined for erythrocyte membranes of parasitized cells isolated by an alternative method utilizing polycationic polyacrylamide microbeads (Affigel 731). The total fatty acid compositions of the major phospholipids in IEPM were determined by g.l.c. The percentage of polyunsaturated fatty acids in normal erythrocyte phospholipids (39.4%) was much higher than in phospholipids from purified parasites (23.3%) or IEPM (24.0%). The unsaturation index of phospholipids in IEPM was considerably lower than in uninfected erythrocytes (107.5 versus 161.0) and was very similar to that in purified parasites (107.5 versus 98.5). Large increases in palmitic acid (C16:0) (from 21.88% to 31.21%) and in oleic acid (C18:1) (from 14.64% to 24.60%), and major decreases in arachidonic acid (C20:4) (from 17.36% to 7.85%) and in docosahexaenoic acid (C22:6) (from 4.34% to 1.8%) occurred as a result of infection. The fatty acid profiles of individual phospholipid classes from IEPM resembled in many instances the fatty acid profiles of parasite phospholipids rather than those of uninfected erythrocytes. Analysis of IEPM from P. falciparum-infected erythrocytes (trophozoite stage) revealed that, during intra-erythrocytic maturation of the parasite, the host erythrocyte phospholipid composition was markedly refashioned. These alterations were not dependent on the method used to isolate the IEPM, with similar results obtained using either a saponin-lysis method or binding to Affigel beads. Since mature erythrocytes have negligible lipid synthesis and metabolism, these alterations must occur as a result of parasite-directed metabolism of erythrocyte lipids and/or trafficking of lipids between the parasite and erythrocyte membranes.

Acetylcholinesterase↗
PubMed1991

The role of anionic phospholipids in membrane adaptation to ethanol.

In rats chronically fed-ethanol, liver microsomes and mitochondria, brain synaptosomes and reconstituted vesicles of their respective membrane phospholipids are resistant to disordering by ethanol in vitro (membrane tolerance) after 35 days of ethanol exposure. (Taraschi et al, 1986a; Rottenberg et al, 1981). Specific phospholipids from ethanol-fed rats, i.e. phosphatidylinositol (PI) from liver microsomes, cardiolipin (CL) from hepatic mitochondria and phosphatidylserine (PS) from brain synaptosomes confer tolerance to reconstituted vesicles of membrane phospholipids from control rats. In liver microsomes, PI was the only lipid that exhibited a significant decrease in both the polyunsaturate pool and the ratio of the total olefinic content to the saturated fatty acid content. The fatty acid composition of cardiolipin was perturbed by chronic ethanol administration as evidenced by a significant increase in oleic acid (18:1) and a significant decrease in linoleic acid (18:2). These alterations produced a more saturated cardiolipin with a decreased (4.4%) unsaturation index (UI) and a 60% reduction in the UI/saturated fatty acid index. These fatty acid modifications, which arise in response to long term ethanol ingestion, represent an adaptive shift in lipid metabolic pathways that do not appear to be (solely) responsible for membrane tolerance.

Alcoholism↗
PubMed1990

Phospholipase C activation by ethanol in rat hepatocytes is unaffected by chronic ethanol feeding.

The activation of phosphoinositide-specific phospholipase C by ethanol was compared in hepatocytes isolated from ethanol-fed rats and from pair-fed control animals. Ethanol (100-300 mM) caused a dose-dependent transient increase in cytosolic free Ca2+ levels in indo-1-loaded hepatocytes from both groups of animals. The rate of Ca2+ increase was similar in hepatocytes from control and ethanol-fed rats, but the decay of the Ca2+ increase was somewhat slower in the latter preparation. The ethanol-induced Ca2+ increase caused activation of glycogen phosphorylase, with 50% response at 50 mM-ethanol and a maximal response at 150-200 mM-ethanol, not significantly different in hepatocytes from control and ethanol-fed animals. Ins(1,4,5)P3 formation in response to ethanol (300 mM) or vasopressin (2 nM or 40 nM) was also similar in the two preparations. It is concluded that long-term ethanol feeding does not lead to an adaptive response with respect to the ethanol-induced phospholipase C activation in rat hepatocytes. The ability of ethanol in vitro to decrease membrane molecular order in liver plasma membranes from ethanol-fed and control rats was measured by e.s.r. Membranes from ethanol-fed animals had a significantly lower baseline order parameter compared with control preparations (0.313 and 0.327 respectively), indicative of decreased membrane molecular order. Addition of 100 mM-ethanol significantly decreased the order parameter in control preparations by 2.1%, but had no effect on the order parameter of plasma membranes from ethanol-fed rats, indicating that the plasma membranes had developed tolerance to ethanol, similar to other membranes in the liver. Thus the membrane structural changes associated with this membrane tolerance do not modify the ethanol-induced activation of phospholipase C. The transient activation of phospholipase C by ethanol in hepatocytes may play a role in maintaining an adaptive phenotype in rat liver.

Alcoholism↗
PubMed1990

1H NMR dipolar echo decay spectroscopy: a sensitive probe of membrane structure.

The structural and motional properties of membrane lipids in various physical states and macroscopic organizations are elucidated by 1H NMR dipolar echo decay spectroscopy (DECODE). Multilamellar lipid dispersions in the gel (L beta') and liquid-crystalline (L alpha) states and a nonbilayer, hexagonal (HII) phase are readily distinguished, a dynamic profile within these phases is identified, and dipolar order parameters are obtained in the fluid phases. The method is suitable for any pulsed NMR spectrometer. DECODE provides the first depth-dependent assay of lipid order that does not rely on isotopic labeling or exogenous probe.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1990

Rats withdrawn from ethanol rapidly re-acquire membrane tolerance after resumption of ethanol feeding.

The time course for the re-acquisition of membrane tolerance to the disordering effects of ethanol in vitro has been determined for liver microsomes obtained from chronically ethanol-fed rats that were withdrawn from ethanol for 2-4 days (during which tolerance is lost) followed by resumption of ethanol feeding. Naive rats require 28-35 days of chronic ethanol feeding to develop membrane tolerance. Microsomal membranes regain partial sensitivity to ethanol disordering after 2-3 days of withdrawal and regain the complete sensitivity observed in membranes from untreated control rats after 4 days of withdrawal. The period of ethanol re-feeding required for the re-acquisition of membrane tolerance was dependent on the withdrawal period, with tolerance appearing sooner if the withdrawal period was shorter. The time course for the re-development of tolerance in previously tolerant animals was considerably faster (4-14 days) than in naive rats being administered the ethanol diet for the first time (35 days). Microsomes from rats that were withdrawn for 2 days (which retained partial tolerance) and then re-fed the ethanolic-diet required only 4 days to re-acquire membrane tolerance. Microsomes from rats withdrawn 3 days required 8 days and those withdrawn 4 days required 15 days for full tolerance to re-develop. The same time-course for the re-acquisition of membrane tolerance was observed in either intact microsomes or in liposomes prepared from extracted microsomal total phospholipids. Phosphatidylinositol (PI) has previously been reported to be responsible for conferring membrane tolerance to liver microsomes in ethanol-fed rats (Taraschi, T.F., Ellingson, J.S., Wu, A., Zimmerman, R. and Rubin, E. (1986) Proc. Natl. Acad. Sci. USA 83, 9398-9402). The time course for re-acquisition of membrane tolerance by liver microsomes following ethanol withdrawal and resumption of ethanol feeding correlated with the ability of PI to confer tolerance.

Animals↗
PubMed1989

On the use of N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)phosphatidylethanolamine in the study of lipid polymorphism.

The change in the fluorescence properties of dioleoyl-N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)phosphatidylethanola mine (N-NBD-PE) as an indicator of the (liquid-crystalline) bilayer-to-non-bilayer hexagonalII (HII) phase transition has been investigated. Lipid bilayer systems which are known to undergo the bilayer-to-HII phase transition on addition of Ca2+ were compared with systems which can undergo aggregation and fusion but not HII phase formation. The former included Ca2+-triggered non-bilayer transitions in cardiolipin and in phosphatidylethanolamine mixed with phosphatidylserine. The latter type of system investigated included the addition of polylysine to cardiolipin and Ca2+ to phosphatidylserine. Freeze-fracture electron microscopy was used to confirm that under the experimental conditions used, the formation of HII phase was occurring in the first type of system, but not in the second, which was stable in the bilayer state. It was found that the fluorescence intensity of N-NBD-PE (at 1 mol% of the phospholipids) increased in both types of system, irrespective of the formation of the HII phase. A dehydration at the phospholipid head group is a common feature of the formation of the HII phase, the interaction of divalent cations with phosphatidylserine and the interaction of polylysine with lipid bilayers, suggesting that this may be the feature which affects the fluorescence properties of the NBD. The finding of a fluorescence intensity increase in systems lacking HII phase involvement clearly indicates that the effect is not unique to the formation of the HII phase. Thus, while offering high sensitivity and the opportunity to follow kinetics of lipid structural changes, changes in the N-NBD-PE fluorescence properties should be interpreted with caution in the study of the bilayer-to-HII phase transition.

Calcium↗
PubMed1988

The captured volume of multilamellar vesicles.

Characterization of classical 'hand-shaken' multilamellar lipid vesicles (MLVs) confirmed that these systems exclude solute during formation thus confounding previous captured volume measurements which typically have utilized solute as a merker of the occluded aqueous space. We used solvent rather than solute to determine the captured volume of these systems and obtained values at least twice those previously reported. We present here a captured volume and lamellarity profile of 'hand-shaken' MLVs and suggest that these parameters are dependent on the lipid concentration present during hydration.

Electron Spin Resonance Spectroscopy↗
PubMed1988

Cardiolipin from ethanol-fed rats confers tolerance to ethanol in liver mitochondrial membranes.

In rats chronically consuming ethanol, the liver mitochondrial membranes develop resistance to the disordering effects of ethanol in vitro, so-called "membrane tolerance". To investigate the molecular basis of this tolerance in the inner mitochondrial membrane, multilamellar vesicles were produced by recombining the mitoplast phospholipids (quantitatively separated by preparative HPLC) from control and ethanol-fed animals in various combinations. The effect of in vitro ethanol on the physical properties of these vesicles was determined by electron spin resonance. Vesicles composed of all mitoplast phospholipids from control rats were disordered by 50-100 mM ethanol, whereas those made of the phospholipids from ethanol-fed animals were resistant. When phosphatidylcholine (46 mol %) or phosphatidylethanolamine (42 mol %) from ethanol-fed rats replaced the corresponding phospholipids of control rats, the vesicles were disordered by ethanol. By contrast, when as little as 2.5 mol % of cardiolipin (one-fourth the naturally occurring amount) from ethanol-fed rats replaced that phospholipid from control rats, vesicles were rendered entirely resistant to disordering by ethanol. The same amount of cardiolipin from ethanol-fed rats also conferred membrane tolerance to vesicles composed of bovine phospholipids, demonstrating that this effect is not restricted to rat mitoplast phospholipids. In vesicles composed of a single mitoplast-phospholipid class, only vesicles composed of cardiolipin from ethanol-fed rats resisted disordering. Phosphatidylinositol from liver microsomes of ethanol-fed rats also confers membrane tolerance and was the only microsomal phospholipid that formed tolerant vesicles. Thus, in livers of rats chronically fed ethanol, anionic phospholipids are selectively converted into potent promoters of membrane tolerance in both mitochondrial and microsomal membranes.

Alcoholism↗
PubMed1986

Perturbation of red cell membrane structure during intracellular maturation of Plasmodium falciparum.

An experimental approach, which in this study was applied to the malarial system, can be used to analyze the molecular structure and organization of individual phospholipids in a wide variety of biological membranes. Electron spin resonance spectroscopy was used to investigate the structural modifications of the major red cell phospholipids that occur in erythrocyte membranes infected with the human malarial parasite, Plasmodium falciparum. These modifications were correlated with the intracellular developmental stage of the parasite. Phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine were increasingly disordered (fluidized) as infection progressed. This disordering occurred at different rates and to varying extents.

Animals↗
PubMed1986

Membrane tolerance to ethanol is rapidly lost after withdrawal: a model for studies of membrane adaptation.

The structural properties of liver microsomes and erythrocytes obtained from rats that had been chronically administered ethanol were examined by electron spin resonance (ESR) following ethanol withdrawal for 1-10 days. Membranes obtained from control animals exhibited considerable molecular disordering upon the addition of ethanol in vitro (50-100 mM). Conversely, microsomal and erythrocyte membranes from alcoholic animals were resistant to this disordering by ethanol (membrane tolerance). These membrane properties were also apparent in lipid bilayers comprised of either total lipids or phospholipids isolated from the control and alcoholic animals. While several weeks of ethanol administration were required for both erythrocytes and microsomes to develop membrane tolerance, erythrocytes from alcoholic animals were disordered by ethanol in vitro after the animals had been withdrawn from ethanol for only 1 day. The same rapid loss of tolerance was observed in microsomes after 2 days of withdrawal. The same time course for the loss of tolerance was observed in lipid bilayers prepared from the total lipid and phospholipid extracts. No significant differences in the cholesterol/phospholipid ratio were observed between the microsomal or erythrocyte membranes isolated before and after withdrawal. Thus, alterations in the microsomal and erythrocyte phospholipids, and not cholesterol content, were responsible for conveying membrane tolerance. Membrane structural properties can be rapidly adjusted in a mammalian system in response to the withdrawal of the external membrane perturbant ethanol. The withdrawal model, which begins with established membrane tolerance and leads to rapid and complete loss of tolerance, provides a model to analyze the compositional changes responsible for this tolerance to disordering by ethanol.

Adaptation, Physiological↗
PubMed1986

Phosphatidylinositol from ethanol-fed rats confers membrane tolerance to ethanol.

The presence of ethanol disorders (fluidizes) biological membranes, but its chronic administration confers resistance to this perturbation (membrane tolerance). The latter effect has been invoked as an explanation for behavioral tolerance in alcoholics, but the molecular basis for membrane tolerance is obscure. To study the molecular mechanisms of this acquired resistance to disordering, we fed rats ethanol (36% of total calories) for 35 days, after which we quantitatively separated the phospholipids of hepatic microsomal membranes by high-performance liquid chromatography. Multilamellar vesicles were prepared from the recombined phospholipid classes, and their physical properties were examined by electron spin resonance. Vesicles composed of phospholipids from untreated rats were disordered (fluidized) in the presence of ethanol, whereas those made from phospholipids of ethanol-fed rats were resistant to this effect. When phosphatidylcholine (66.5 mol %), phosphatidylethanolamine (21 mol %), or phosphatidylserine (4.0 mol %) from ethanol-fed rats replaced their corresponding phospholipids in vesicles prepared from microsomal phospholipids from untreated rats, the membranes were still disordered by ethanol. In contrast, when 2.5-8.5 mol % phosphatidylinositol from ethanol-fed rats replaced phosphatidylinositol from untreated rats, the reconstituted membranes were rendered resistant to ethanol-induced disordering. Liver microsomal phosphatidylinositol (2.5-8.5 mol %) from ethanol-fed rats also conferred membrane tolerance to vesicles composed of bovine liver and brain phospholipids, an effect which demonstrates that the ability of phosphatidylinositol to confer membrane tolerance is not restricted to the microsomal membrane.

Alcoholism↗