The role of membrane skeletal-associated alpha-globin in the pathophysiology of beta-thalassemia

The beta-thalassemic mouse provides a useful model for testing hypotheses about the pathophysiology in human beta-thalassemia. The clinical picture of these mice and their red blood cell deformability characteristics are quite similar to those observed in human beta-thalassemia intermedia. The creation of transgenic mice that express human beta-globin (beta s) has provided an opportunity to study the effect of increasing the non-alpha-globin chain production on the thalassemic phenotype. A small increase in beta-globin production produces transgenic mice that are healthier, have almost normal hemoglobin values, and whose red blood cell deformability is increased. We quantified and characterized the membrane skeletal-associated globin in normal, transgenic thal/sickle, and thalassemic mice and showed that only alpha-globin was associated with the membrane skeleton in the pathologic red blood cells, and that the degree of rigidity as measured in the rheoscope correlated directly and closely with the amount of membrane skeletal-associated globin in these abnormal red blood cells.

Environmental diseases of the digestive system

Environmental factors are important mediators of many diseases of the digestive system, defined as the alimentary tract and the accessory organs of digestion, the liver and pancreas. In this review, we principally focus on the action of chemical agents which are classified as (1) naturally occurring compounds, (2) occupational hazards, (3) therapeutic drugs, and (4) constituents of substances of abuse. In addition, the putative role of dietary habits in the pathogenesis of malignant diseases of the digestive system is discussed.

Patient-initiated mobile mammography: analysis of the patients and the problems

Patient initiation of mammographic screening is one method of increasing compliance with screening mammography guidelines. A low-cost screening project using a mobile van was developed at the University of Alabama at Birmingham. Analysis of the first 2,099 patients revealed that the participants were generally white (92%), more likely to have had a previous mammogram than the norm (33% in this study vs 19% in a 1986 Gallup survey), and relatively high-risk (30% having a breast cancer risk factor). The cancer detection rate was 6.2 per 1,000 women screened, with a biopsy rate of 1.3% and a positive predictive value of 48%. More than half the cancers detected were in situ lesions or invasive carcinomas smaller than 1 cm. Our results suggest that low-cost mobile mammographic screening can operate at appropriate levels of sensitivity and specificity and is well accepted by participants. Such projects require considerable preliminary planning, significant financial and time commitment by the physicians involved, and meticulous follow-up. A mammography management software system was developed to facilitate tracking of patients for routine and diagnostic follow-up studies and rapid communication of results. Although most follow-up studies and biopsies were done in the community, resistance in the medical community was significant and is perhaps the greatest impediment to such screening endeavors.

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.

Cutaneous angiosarcoma of the breast 7 years after lumpectomy and radiation therapy

A case of angiosarcoma of the skin of the breast is described in a woman 7 years after a primary breast carcinoma was treated by means of lumpectomy and irradiation. On mammograms, the angiosarcoma showed redevelopment of skin thickening and increase in breast density. Clinically, the skin showed patchy discoloration. Although there is an established association of angiosarcoma with lymphedema and therapeutic irradiation, there have been few other reports of this rare complication of local therapy for breast carcinoma. Recognition of the mammographic and clinical manifestations may help in the earlier diagnosis of additional cases.

Alcohol and membrane-associated signal transduction

In recent years, ethanol has been shown to interact with membrane-associated signal transduction mechanisms which rely on the reaction of phospholipases with their phospholipid substrates in the membrane. In several cell and membrane preparations, ethanol activates the polyphosphoinositide-specific phospholipase C and triggers the complete battery of intracellular signalling responses that are characteristic for hormones acting through this pathway, including the formation of inositol-1,4,5-trisphosphate, the release of Ca2+ from intracellular storage sites with the consequent activation of cytosolic Ca2(+)-dependent enzymes, and the formation of diacylglycerol leading to the stimulation of protein kinase C. The activation of phospholipase C appears to be due to an interaction of ethanol with the intramembrane complex of receptor-G-protein-phospholipase C, presumably promoting the release of bound GDP and the binding of GTP to activate the G-protein which controls phospholipase C activity. In many intact cells, the phospholipase C is subject to a feedback inhibitory control by protein kinase C. In liver cells, ethanol also triggers this feedback inhibition, leading to a rapid decline in the phospholipase C activation; at the same time, ethanol also causes the desensitization of the response to vasopressin and other phospholipase C-linked agonists. At hormone concentrations in the physiological range, the heterologous desensitization by ethanol of the agonist-mediated phospholipase C activation may be a significant factor at ethanol concentrations that are readily attained in vivo. Further interaction of ethanol with the intracellular second messenger system is mediated through a hormone-sensitive phospholipase D. This enzyme uses phosphatidylcholine to generate phosphatidic acid which can be further converted to diacylglycerol. In the presence of ethanol the enzyme catalyzes the transphosphatidylation to phosphatidylethanol. It is not clear, however, under what conditions this process could affect the normal pattern of formation of second messenger molecules. After chronic ethanol intake, a tolerance can develop at the cellular level to the effects of ethanol on agonist-induced signal transduction processes. However, the mechanism by which this tolerance develops is currently a matter of conjecture. Studies on liver cells indicate that the activity of protein kinase C may play a role in the development of this type of tolerance to ethanol. A better understanding of the interaction of ethanol with these phospholipid-dependent signal transduction processes could point to mechanisms by which ethanol could interfere with physiological control mechanism in a variety of cells and tissues.

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.

Primary pulmonary hypertension. Vascular structure, morphometry, and responsiveness to vasodilator agents

The use of pharmacologic agents in the treatment of pulmonary hypertension has not proved to be uniformly successful or predictable. One possible reason for the vagaries in response is that the pulmonary vascular lesions are not consistent. We examined the relation between the structure of the pulmonary resistance vessels in unexplained (primary) pulmonary hypertension and the response to pulmonary vasodilators. Our study involved 19 patients with clinically unexplained pulmonary hypertension (mean pressure, 59 +/- 14 mm Hg). After characterizing them clinically and performing control hemodynamic measurements, we determined the acute effects of a series of vasodilator agents that have different mechanisms of action. In 16 patients, lung biopsy material was related to the hemodynamic studies; in nine patients, including six who had undergone open lung biopsy, the hemodynamic studies were related to the pathologic changes found at autopsy. Histologic specimens from all 19 patients were evaluated qualitatively and sorted into three subsets of hypertensive pulmonary arteriopathy: medial hypertrophy (with minimal intimal proliferation), arteriopathy with plexiform lesions (associated predominantly with concentric laminar intimal proliferation and fibrosis), and arteriopathy with microthrombotic lesions (associated predominantly with eccentric intimal proliferation and fibrosis). The 16 lung biopsies were also quantitated by morphometric techniques. Using a decrease in calculated pulmonary vascular resistance of more than 30% accompanied by a decrease in mean pulmonary arterial pressure of at least 10% to define vasodilation, only four patients were responders. The patients varied considerably in their responses to different vasodilator agents. Patients with similar clinical and hemodynamic profiles differed considerably with respect to the nature of their pulmonary vascular obstructive lesions and their responses to vasodilator agents. Qualitative histologic examination of lung tissue did not provide a basis for predicting how individual patients would respond to vasodilator agents. However, quantitative morphologic analysis of the initial open lung biopsy specimens did prove helpful in predicting acute responsiveness to vasodilator agents and the subsequent clinical course of these patients with unexplained (primary) pulmonary hypertension. An intimal area of more than 18% of the vascular cross-sectional area had an 85% predictive value for identifying the patients who did poorly during the first 36 months of follow-up.

Ethanol inhibits electrically-induced calcium transients in isolated rat cardiac myocytes

The fluorescent Ca2+ indicator fura-2 was used to follow cytosolic Ca2+ transients during excitation-contraction coupling in suspensions of isolated rat heart cells induced to beat synchronously by electrical field stimulation. The Ca2+ transient reached a maximum at about 30 ms after application of the electrical stimulus and then relaxed to the basal level over the following 200 ms. Treatment of the myocytes with 0.25 to 2.0% ethanol (40 to 340 mM) caused a decrease in the peak of the Ca2+ transient, with no apparent change in the time to peak. This effect of ethanol occurred progressively over a period of about 1 min before a new stable state was achieved. At 1% ethanol the peak Ca2+ level was reduced by 50%. Ethanol reversed the stimulatory effect of isoproterenol on peak Ca2+ and at high levels of ethanol the beta-adrenergic agonist no longer caused any enhancement of the Ca2+ transient. Ethanol did not cause any marked change in the basal Ca2+ level between beats. The effects of ethanol were readily reversible. These results suggest that the negative inotropic effect of ethanol observed in intact cardiac muscle preparations may result in part from interference with the Ca2+ fluxes responsible for excitation-contraction coupling in ventricular myocytes.

Very low dose alpha-2b interferon for the treatment of hairy cell leukemia

Alpha-2b interferon (alpha-2b IFN), administered at 2 x 10(6) U/m2 three times per week is highly effective in the treatment of progressive hairy cell leukemia (HCL) and in the retreatment of patients who have relapsed after previous IFN therapy. To determine if a lower interferon dose would induce a comparable antileukemic effect with less toxicity, a-2b IFN was administered at 2 x 10(5) U/m2 subcutaneously three times per week to 17 patients with progressive HCL. Thirteen patients had HCL in relapse after a previous response to alpha-2b IFN; four patients were previously untreated. The median duration of treatment was 9 months. Toxicity consisted only of transient, mild flu-like symptoms in two patients. Of the 13 previously IFN-treated patients, four had a minimal response, one had no response, and eight had progressive disease. Of four previously untreated patients, one had a partial response, two had a minimal response, and one had no response. In seven of eight patients whose disease progressed on low-dose IFN, the dose was escalated to 2 x 10(6) U/m2 three times per week, and all seven patients demonstrated hematologic response within 3 months to the dose escalation. We conclude that alpha-2b IFN at 2 x 10(5) U/m2 three times per week is relatively ineffective for the treatment of relapse after previous IFN therapy.

Subcutaneous granulocyte-macrophage colony-stimulating factor in patients with myelodysplastic syndrome: toxicity, pharmacokinetics, and hematological effects

The toxicity, pharmacokinetics, and hematologic effects of granulocyte-macrophage colony-stimulating (GM-CSF) were studied in a phase I/II trial of 16 patients with myelodysplastic syndrome (MDS). The GM-CSF was administered subcutaneously (SC) daily so as to achieve prolonged blood levels and to establish an outpatient treatment regimen. Four dose levels were administered for ten days: 0.3 microgram/kg/d (three patients), 1.0 microgram/kg/d (three), 3.0 micrograms/kg/d (four), and 10.0 micrograms/kg/d (six). The most common toxicities were fever and a flu-like syndrome, which were dose-dependent. The maximum-tolerated dose was 10.0 micrograms/kg/d, which induced severe rigors (two patients), fever greater than 40 degrees C (one), severe bronchospasm (one), and WBC 60,000 (one). In one patient, refractory anemia with excess blasts in transformation (RAEB-T) progressed to acute nonlymphocytic leukemia after two doses of GM-CSF, and the patient died of leukemia that did not respond to chemotherapy. After doses of 3.0 and 10.0 micrograms/kg, serum GM-CSF levels peaked at 3.8 to 6.3 hours, and persisted for 14 and 24 hours, respectively. Circulating granulocytes (neutrophils and bands) increased in a dose-dependent manner, as 11 of 13 patients who received greater than or equal to 1.0 microgram/kg/d responded with a two- to 194-fold increase. Although the neutrophils usually returned to pretreatment levels shortly after stopping GM-CSF, two patients continue to exhibit an elevation of neutrophils for 6 months. Dose-related increases in circulating monocytes and eosinophils were also noted. Transient increases in platelet and reticulocyte counts were observed in two and three patients, respectively. Five of the 16 patients later received maintenance GM-CSF at 3 micrograms/kg/d for 2 to 9 weeks. All showed a dramatic increase in neutrophils after 2 weeks. Thereafter, despite continued therapy, the neutrophil count in four patients declined markedly. In conclusion, GM-CSF is well tolerated by the SC route and induces striking, but usually temporary, improvement in the neutropenia of MDS. Larger prospective phase III trials will determine the duration of hematologic responses and the impact on infection, morbidity, and mortality.

Short chain alcohols activate guanine nucleotide-dependent phosphoinositidase C in turkey erythrocyte membranes

The ability of alcohols to regulate inositol lipid-specific phospholipase C (phosphoinositidase C) was examined in turkey erythrocyte ghosts prepared by cell lysis of erythrocytes which were prelabeled with [3H] inositol. Guanosine 5'-[gamma-thiotriphosphate] GTP[S] stimulated the production of both [3H]inositol bisphosphate (18-fold) and [3H]inositol trisphosphate (6-fold) in this system. The accumulation of [3H]inositol bisphosphate and [3H]inositol trisphosphate was linear up to 8 min following an initial lag period of 1-2 min. Ethanol (300 mM) reduced the lag period for [3H]inositol phosphate accumulation at submaximal GTP[S] concentrations and caused a shift to the left (3-fold) in the dose-response curve. Other short chain alcohols, methanol (300 mM), 1-propanol (200 mM), and 1-butanol (50 mM) also enhanced the accumulation of [3H] inositol phosphates in the presence of submaximal GTP[S] concentrations. Receptor activation by the purinergic agonist adenosine 5'-[beta-thio]disphosphate (ADP[S]) (10 microM) also reduced the lag period for [3H] inositol phosphate formation and shifted the GTP[S] dose response to the left (10-fold). In addition, ADP[S] increased the response to maximal GTP[S] concentrations. The formation of [3H]inositol phosphates induced by GTP[S] was associated with a concomitant decrease in labeling of both [3H]phosphatidylinositol monophosphate and [3H]phosphatidylinositol bisphosphate, but no decrease in [3H]phosphatidylinositol was observed. All of the alcohols tested enhanced the breakdown of [3H]polyphosphoinositides in the presence of GTP[S]. The dose response to guanosine 5'-[beta gamma-imino]triphosphate for [3H]inositol phosphate formation was displaced to the left by ethanol (300 mM) and ADP[S] (10 microM) (2- and 7-fold), respectively. ADP[S] also enhanced the maximal response to guanosine 5'-[beta gamma-imino]triphosphate. The [3H]inositol phosphate formation produced in response to NaF was unaffected by either ethanol or receptor activation. These results indicate that alcohols initiate an activation of phosphoinositidase C, mediated at the level of the regulatory guanine nucleotide-binding protein.

CT and MR imaging in the evaluation of retroperitoneal fibrosis

We have performed CT and MR on five patients with biopsy proven retroperitoneal fibrosis (RPF). Magnetic resonance (MR) accurately displayed a retroperitoneal mass of low signal intensity on T1-weighted scans and of heterogeneous medium signal intensity on T2-weighted scans. The coronal MR views demonstrated a retroperitoneal mass: the shape, signal intensity, and effects on the ureters and major vessels appear characteristic of RPF.

The effects of alcoholism on skeletal and cardiac muscle

To determine the prevalence of alcoholic myopathy and cardiomyopathy, we studied a group of 50 asymptomatic alcoholic men (mean age, 38.5 years) entering an outpatient treatment program. Studies performed included an assessment of muscle strength by electronic myometer, muscle biopsy, echocardiography, and radionuclide cardiac scanning, with comparison to healthy control subjects of similar age. The patients' mean (+/- SEM) daily alcohol consumption was 243 +/- 13 g over an average of 16 years. These patients had no clinical or laboratory signs of malnutrition or electrolyte imbalance. Forty-two percent of the patients, as compared with none of the controls, had strength of less than 20 kg as measured in the deltoid muscle. Muscle-biopsy specimens from 23 patients (46 percent) had histologic evidence of myopathy. In the cardiac studies, when the alcoholic patients were compared with 20 healthy controls, the patients had a significantly lower mean ejection fraction (59 vs. 67 percent), a lower mean shortening fraction (33 vs. 38 percent), a greater mean end-diastolic diameter (51 vs. 49 mm), and a greater mean left ventricular mass (123 vs. 106 g per square meter of body-surface area). One third of the alcoholics had an ejection fraction of 55 percent or less, as compared with none of the controls. Endomyocardial biopsy specimens from six patients with ejection fractions below 50 percent showed histologic changes of cardiomyopathy. The estimated total lifetime dose of ethanol correlated inversely with muscular strength (r = -0.65; P less than 0.001). In an analysis that also included six patients with symptomatic alcoholic cardiomyopathy, the estimated total lifetime dose of ethanol correlated inversely with the ejection fraction (r = -0.58; P less than 0.001) and directly with the left ventricular mass (r = 0.59; P less than 0.001). We conclude that myopathy of skeletal muscle and cardiomyopathy are common among persons with chronic alcoholism and that alcohol is toxic to striated muscle in a dose-dependent manner.

Ethanol causes decreased partitioning into biological membranes without changes in lipid order

One of the adaptive responses of cell membranes to chronic ethanol consumption is the acquisition of a resistance to fluidization or disordering of the lipids by ethanol in vitro and a reduced partitioning of ethanol into the membrane (membrane tolerance). The degree to which the effects on partitioning and lipid disordering share common features has not previously been explored and in addition the relevance of the value of lipid order in the absence of added ethanol (baseline lipid order) to membrane tolerance has not been established. The location in the bilayer and the nature of the modification underlying these effects is also unknown. The effect of chronic ethanol treatment was examined using 5-doxyl decane as a model hydrophobic compound. Its partitioning into the membranes was determined by utilizing its ability to quench fluorophores (1,6-diphenyl-2,3,5-hexatriene and 3- and 12-anthroyl stearates) by collisional quenching. The partition coefficient of 5-doxyl decane into the bilayer central region was reduced as a result of the chronic ethanol treatment. The effect could also be demonstrated in vesicles of phospholipids and was lost 4 days after withdrawal of the ethanol from the diet. These results closely parallel those relating to resistance to lipid disordering and suggest that both techniques detect a common modification. Lipid order was assessed using fluorescence anisotropy measurements of a range of fluorophores, including those used to determine the partitioning properties of the membrane. No effect of chronic ethanol treatment on lipid order was found, either in the intact membranes or in vesicles of extracted phospholipids. This suggests that changes in baseline order are not critical features of membrane tolerance in liver microsomes. In addition it appears that the altered partitioning of the 5-doxyl decane into the central region of the membrane is not related to lipid order changes in this region. The reduced partitioning of 5-doxyl decane may be a reflection of a redistribution in the lipid bilayer, perhaps due to modifications in other locations in the membrane, such as the lipid head group region.

Effect of chronic ethanol ingestion on pancreatic protein synthesis

The effect of chronic ethanol feeding on pancreatic protein synthesis was assessed by studying the rate of incorporation of [3H]leucine into proteins in isolated rat pancreatic acini in vitro. Chronic ethanol feeding increased the rate of protein synthesis (2-3-fold) compared to controls fed an isocaloric diet. The onset of the increase in protein synthesis was detectable 2 days after the beginning of ethanol feeding, reached a maximum after 7 days and remained constant for up to 4 months. The increased incorporation of [3H]leucine was not due to an increased turnover of proteins as measured in pulse-chase experiments. After separation of individual digestive enzymes by SDS-polyacrylamide gel electrophoresis and determination of the distribution of radioactivity in different proteins, a general increase in the rate of incorporation of the label into all of the proteins was observed. In contrast to the observations made with isolated acini, there was no significant difference between the control and ethanol-fed groups when the rate of pancreatic protein synthesis was measured in vivo. However, overnight withdrawal of ethanol led to an increase of approx. 70% in protein synthesis in the ethanol-fed group. These results suggest that chronic ethanol ingestion modifies the control of pancreatic protein synthesis; the enhanced protein synthesis is expressed in isolated acini, i.e., in the absence of physiological factors present during chronic ethanol ingestion and in vivo after ethanol withdrawal.

Proliferative disease and atypia in biopsies performed for nonpalpable lesions detected mammographically

A recent study of risk factors for breast cancer indicated elevated risks of 5.3 and 1.9 times, respectively, for women with biopsy specimens showing atypical hyperplasia (AH) and proliferative disease without atypia. These risks increase to 11 and 3.2 times, respectively, in women who also have a family history of breast cancer. This study reviews lesions detected mammographically in a series of patients with documented risk factors. The pathologic specimens of 100 consecutive localization breast biopsies performed for nonpalpable abnormalities detected mammographically were reviewed and classified according to the criteria of Dupont and Page in order to determine the incidence of AH and proliferative breast disease. The mammographic characteristics and historical risk factors of these women also were correlated. Twenty percent of the biopsy specimens showed carcinomas, 55% of which were noninvasive. AH was found in an additional 10% of the biopsy specimens, whereas proliferative disease without atypia occurred in 21% of the biopsy specimens. Forty-nine percent of the biopsy specimens showed nonproliferative changes. This study demonstrated that mammography, in addition to its ability to detect small nonpalpable cancers, identifies a high percentage (31% in this series) of women with pathologic lesions known to have an elevated risk for subsequent breast cancer. The current impetus for large-scale mammographic screening of asymptomatic women mandates the development of rational therapeutic protocols to accommodate the widening spectrum of high-risk pathologic lesions found in these selected populations.

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.

Ethanol-induced modifications to membrane lipid structure: effect on phospholipase A2-membrane interactions

Chronic ethanol intoxication leads to the development of a resistance to lipid disordering by ethanol, a phenomenon known as "membrane tolerance". In the absence of the added ethanol, the lipid order, as measured by ESR and fluorescence techniques, does not necessarily change as a result of chronic ethanol ingestion (as in liver microsomes, for example). This suggests that the spectroscopic techniques detect tolerance somewhat indirectly, in that the modification responsible may reside in a region distinct from that being probed and also raises the question of whether membrane tolerance is necessarily associated with an alteration in the membrane lipid structure. Here we show that liver microsomes from rats treated chronically with ethanol are rendered relatively resistant to the hydrolytic action of exogenous phospholipase A2, compared to preparations from control animals. This resistance persists in reconstituted lipid vesicles prepared from extracted phospholipids. Since the same substrate (1-palmitoyl-2-N-(4-nitrobenzo-2-oxa-1,3-diazole)amino caproylphosphatidylcholine) was used in both membranes from ethanol-treated animals and controls, the modification appears to reside in the structure and/or organization of the membrane. Further evidence that the lipid structure is modified by chronic ethanol treatment is provided by the observation that perturbance of the membrane structural integrity by increasing levels of oleic acid led to a progressive loss of the ethanol-induced relative resistance to hydrolysis by phospholipase A2. The results of this study support the idea that membrane tolerance involves a modification to lipid structure probably at the bilayer surface. The use of exogenous phospholipase A2 provides a new method for probing the structural modifications induced by chronic ethanol ingestion.