The effect of cholesterol on the accumulation of intracellular calcium

Effects of Aster B-mediated intracellular accumulation of cholesterol on inflammatory process and myocardial cells in acute myocardial infarction

BACKGROUND

To investigate the effect of cholesterol accumulation in cells on the inflammatory process of acute myocardial infarction and cardiomyocytes and its mechanism.

METHODS

Blood samples of 15 patients with myocardial infarction were clinically collected to detect enzyme levels of cholesterol and related myocardial parameters in the serum. Correlation analysis was carried out. At the cellular level, simulation of cholesterol entry and exit from cells was conducted by a liposome-loaded cholesterol model in this study, and BNP and inflammatory factors were detected with enzyme-linked immunosorbent assay. Moreover, to investigate the molecular mechanism of myocardial damage caused by cholesterol, Gramd1b and Prkaca of HL-1 were knocked down with small interference RNA technique. Then, inhibitor C3 was used to weaken RhoA activity to explore the level of cardiac muscle cell BNP in order to identify key protein target sites that may be involved in the process of cholesterol damage to cardiac muscle cells.

RESULTS

Serum cholesterol concentration showed a significantly positive correlation with the levels of AST, CK, and LD in serum of patients with myocardial infarction. Cholesterol accumulation in cardiac muscle cells significantly increased the levels of BNP, inflammatory factors (IL-1β, IL-6, TNF-α, and CCL-2) in cardiac muscle cells, which exacerbated cardiomyocyte damage. Conversely, cholesterol excretion caused significant downregulation of BNP and inflammatory factors. Moreover, after knocking down Gramd1b, the accumulation of cholesterol in myocardial cells decreased, the levels of BNP and inflammatory factors significantly reduced, and the degree of myocardial cell damage was weakened. Knockdown of Prkaca inhibited RhoA activity and reversed cholesterol-induced elevation of BNP and inflammatory factors.

CONCLUSION

ASTER B-mediated intracellular accumulation of cholesterol in cardiac muscle cells may cause cardiomyocyte damage and inflammatory factor infiltration through PKA-Ca²⁺-RhoA pathways.

Cholesterol Stabilizes TAZ in Hepatocytes to Promote Experimental Non-alcoholic Steatohepatitis

Incomplete understanding of how hepatosteatosis transitions to fibrotic non-alcoholic steatohepatitis (NASH) has limited therapeutic options. Two molecules that are elevated in hepatocytes in human NASH liver are cholesterol, whose mechanistic link to NASH remains incompletely understood, and TAZ, a transcriptional regulator that promotes fibrosis but whose mechanism of increase in NASH is unknown. We now show that increased hepatocyte cholesterol upregulates TAZ and promotes fibrotic NASH. ASTER-B/C-mediated internalization of plasma membrane cholesterol activates soluble adenylyl cyclase (sAC; ADCY10), triggering a calcium-RhoA-mediated pathway that suppresses β-TrCP/proteasome-mediated TAZ degradation. In mice fed with a cholesterol-rich NASH-inducing diet, hepatocyte-specific silencing of ASTER-B/C, sAC, or RhoA decreased TAZ and ameliorated fibrotic NASH. The cholesterol-TAZ pathway is present in primary human hepatocytes, and associations among liver cholesterol, TAZ, and RhoA in human NASH liver are consistent with the pathway. Thus, hepatocyte cholesterol contributes to fibrotic NASH by increasing TAZ, suggesting new targets for therapeutic intervention.

Effects of dietary cholesterol supplementation on growth and cholesterol metabolism of rainbow trout (Oncorhynchus mykiss) fed diets with cottonseed meal or rapeseed meal

This study was conducted to evaluate the effects of cholesterol on growth and cholesterol metabolism of rainbow trout (Oncorhynchus mykiss) fed diets with cottonseed meal (CSM) or rapeseed meal (RSM). Four experimental diets were formulated to contain 550 g kg(-1) CSM or 450 g kg(-1) RSM with or without 9 g kg(-1) supplemental cholesterol. Growth rate and feed utilization efficiency of fish fed diets with 450 g kg(-1) RSM were inferior to fish fed diets with 550 g kg(-1) CSM regardless of cholesterol level. Dietary cholesterol supplementation increased the growth rate of fish fed diets with RSM, and growth rate and feed utilization efficiency of fish fed diets with CSM. Similarly, dietary cholesterol supplementation increased the plasma total cholesterol (TC), high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and triiodothyronine levels, but decreased the plasma triglycerides and cortisol levels of fish fed diets with RSM or CSM. In addition, supplemental cholesterol increased the free cholesterol and TC levels in intestinal contents, but decreased the hepatic 3-hydroxy-3-methyl-glutaryl-CoA reductase activity of fish fed diets with RSM or CSM. These results indicate that 9 g kg(-1) cholesterol supplementation seems to improve the growth of rainbow trout fed diets with CSM or RSM, and the growth-promoting action may be related to the alleviation of the negative effects caused by antinutritional factors and/or make up for the deficiency of endogenous cholesterol in rainbow trout.

Improving the growth performance and cholesterol metabolism of rainbow trout (Oncorhynchus mykiss) fed soyabean meal-based diets using dietary cholesterol supplementation

A 9-week feeding trial was conducted to evaluate the effects of dietary cholesterol supplementation at different levels (0, 0·3, 0·6, 0·9, 1·2 and 1·5 %) on growth and cholesterol metabolism of rainbow trout (Oncorhynchus mykiss) fed soyabean meal (SBM)-based diets. Daily growth coefficient (DGC) steadily increased when the supplemental cholesterol was increased by up to 1·2 %, but declined upon further addition. The total cholesterol (TC), HDL-cholesterol (HDL-C) and LDL-cholesterol (LDL-C) levels in plasma generally increased when the supplemental cholesterol was increased by up to 1·2 %. Thereafter, the TC level reached a plateau, the LDL-C level showed a marked decline, whereas the HDL-C level continued to increase. Dietary cholesterol supplementation generally increased the total lipid and cholesterol levels in liver; the total lipid and TAG levels in muscle; the TC, free cholesterol, cholesteryl ester and total bile acid levels in intestinal contents; and the triiodothyronine and Ca levels in plasma. However, significant differences were mainly observed with high levels of supplemental cholesterol (0·9-1·5 %). Low levels of supplemental cholesterol (0·3-0·9 %) decreased hepatic 3-hydroxy-3-methyl-glutaryl-CoA reductase and cholesterol 7α-hydroxylase activities, but high levels of supplemental cholesterol (1·5 %) increased hepatic acyl-CoA:cholesterol acyl transferase and cholesterol 7α-hydroxylase activities. These results suggest that rainbow trout fed SBM-based diets have a certain 'cholesterol-buffering capacity', which in turn suggests the possibility of the inhibition of exogenous cholesterol absorption and/or inadequate endogenous production of cholesterol in trout fed SBM-based diets. DGC increased steadily with increasing supplemental cholesterol level up to 1·2 %, and the growth-promoting effects might be related to the alleviation of the negative effects caused by a soyabean diet and/or make up for the deficiency of endogenous cholesterol in rainbow trout.

Sphincter of Oddi dysfunction in hypercholesterolemic rabbits

BACKGROUND AND OBJECTIVES

The mechanisms that trigger gallbladder evacuation dysfunction, the key risk factor for gallstone formation, have not yet been fully elucidated. The sphincter of Oddi (SO) plays important roles in the regulation of gallbladder evacuation and maintenance of normal hydraulic pressure of the biliary tract. The aim of our study was to investigate the effects of hypercholesterolemia on the motility function of SO and the underlying mechanisms of SO dysfunction (SOD).

METHODS

Forty New Zealand white rabbits were divided randomly into the control group fed with standard chow and the experimental (Ch) group fed with a high-cholesterol diet for 8 weeks. Changes in the maximal gallbladder emptying rate, gallbladder evacuation with cholecystokinin-octapeptide (CCK-8) stimulation and SO functions of both groups were measured in vivo; B ultrasound examination was used for dynamic observation of peristaltic movements in vivo; SO pressure was measured using manometry; morphological characteristics were observed by electronic microscope; laser scanning confocal fluorescence microscopy was used to identify changes in [Ca]i and Ca oscillation in primary SO smooth muscle cells (SMCs).

RESULTS

Gallbladder cholestasis was observed during early stages of gallstone formation in Ch rabbits. CCK-8 could not improve the gallbladder cholestatic state in Ch group. Passive dilation of SO significantly improved the cholestatic state in Ch rabbits (P<0.05), although the maximal gallbladder emptying rate was still lower than that of the control group. Manometry data indicted a significant increase in the base pressure of the SO low-pressure ampulla segment and high-pressure segment (P<0.05) in Ch group. laser scanning confocal fluorescence microscopy assay data indicated that [Ca]i in SO cells of Ch group significantly increased and were in a state of overload (P<0.05); Ca oscillation signals in SO cells of Ch group were also abnormal.

CONCLUSION

Hypercholesterolemia initially induced SOD, leading to increased gallbladder evacuation resistance and cholestasis. We suggested that [Ca]i overload and/or Ca oscillation abnormality potentially play important roles in the pathogenesis of SOD.

Protein stability and the evolution of the cell membrane

Cholesterol has been shown to regulate the activity of several membrane proteins. Although this phenomenon represents an important factor in the regulation of ion homeostasis, insights are needed to fully understand the role of this lipid in cell function in order to better comprehend the effect of bilayer components upon membrane function. Since evolution has shaped the composition of the membrane bilayer, it becomes of interest to study these changes in parallel with the many functions of membranes such as ion transport. The present study employing a plasma membrane preparation obtained from calf ventricular muscle demonstrates that cholesterol partially inhibits the Ca(2+),Mg(2+)-ATPase as the catalytic function of the calcium pump, when incubation reaction temperatures are below 42 degrees C. In contrast, when incubation reaction temperatures are above 42 degrees C, cholesterol apparently promotes enzyme stabilization reflected in higher activity. Although the activation energy values for the enzyme are almost the same at ranges between 15 and 40 degrees C, the use of elevated temperatures promote higher enzyme inactivation rates in control than in cholesterol enriched membranes. Cholesterol apparently is promoting stabilization that in turn protects the enzyme against thermal inactivation. This protective effect is reflected in a decrease of inactivation rate values and energy released during enzyme catalysis. The modification of many membrane properties throughout million of years made it possible for new evolutionary driving forces to show themselves as new characteristics in eukaryotes such as the one discussed in this study, dealing with the presence of cholesterol in the cell membrane directly associated to the promotion of protein thermostability.

Activation of phospholipase C increases intramembrane electric fields in N1E-115 neuroblastoma cells

We imaged the intramembrane potential (a combination of transmembrane, surface, and dipole potential) on N1E-115 neuroblastoma cells with a voltage-sensitive dye. After activation of the B(2) bradykinin receptor, the electric field sensed by the dye increased by an amount equivalent to a depolarization of 83 mV. The increase in intramembrane potential was blocked by the phospholipase C (PLC) inhibitors U-73122 and neomycin, and was invariably accompanied by a transient rise of [Ca(2+)](i). A depolarized inner surface potential, as the membrane loses negative charges via phosphatidylinositol 4,5-bisphosphate (PIP(2)) hydrolysis, and an increase in the dipole potential, as PIP(2) is hydrolyzed to 1,2-diacylglycerol (DAG), can each account for a small portion of the change in intramembrane potential. The primary contribution to the measured change in intramembrane potential may arise from an increased dipole potential, as DAG molecules are generated from hydrolysis of other phospholipids. We found bradykinin produced an inhibition of a M-type voltage-dependent K(+) current (I(K(M))). This inhibition was also blocked by the PLC inhibitors and had similar kinetics as the bradykinin-induced modulation of intramembrane potential. Our results suggest that the change in the local intramembrane potential induced by bradykinin may play a role in mediating the I(K(M)) inhibition.

Effect of cholesterol liposomes on calcium mobilization in muscle cells from the rabbit sphincter of Oddi

AIM: To analyze the influence of cholesterol liposome on the Ca²⁺ mobilization of cultured muscle cells in rabbit sphincter of Oddi’s.

METHODS: New Zealand rabbit was sacrificed and the sphincter of Oddi (SO) segement was obtained aseptically. The SO segment was cut into pieces and cultured in DMEM solution. Then the smooth muscle cells were subcultured, and the 4th-7th passage cells were used for further investigation. The intracellular Ca²⁺ increase was measured under confocal microscope after the addition of 20 mmol·L^-1 KCl, 10^-7 mol·L^-1 acetylcholine and 10^-7 mol·L^-1 cholecystokinin, and different antagonists were added to analyze the Ca²⁺ mobilization pathway. After the cells were incubated with 1 g·L^-1 cholesterol liposome (CL)(molar ratio was-2:1), the intracellular Ca²⁺ increase was measured again to determine the effect of CL on cellular Ca²⁺ mobilization.

RESULTS: The resting cellular calcium concentration of cultured SO cell was 108 nmol·L^-1± 21 nmol·L^-1. The intracellular Ca²⁺ increases induced by 20 mmol·L^-1 KCl, 10^-7 mol·L^-1 ACh and 10^-7 mol·L^-1 CCK were 183% ± 56%, 161% ± 52% and 130% ± 43%, respectively. When the extracellular Ca²⁺ was eliminated by 2 mmol·L^-1 EGTA and 5 μmol·L^-1 verapamil, the intracellular Ca²⁺ increases induced by KCl, ACh and CCK were 20% ± 14%, 82% ± 21% and 104% ± 23%, respectively. After the preincubation with heparin, the Ca²⁺ increases were 62% ± 23% and 23% ± 19% induced by ACh and CCK, as for preincubation with procaine they were 72% ± 28% and 85% ± 37% induced by ACh and CCK, respectively. Pretreatment with CL for 18 h, the resting cellular Ca²⁺ concentration elevated to 152 nmol·L^-1± 26 nmol·L^-1, however, the cellular Ca²⁺ increase percentages in response to these agonists were 67% ± 32%, 56% ± 33% and 34% ± 15%.

CONCLUSION: KCl elicite the SO cellular Ca²⁺ increase depends on influx of extracellular Ca²⁺, ACh evoked the SO celllular Ca²⁺ increase is through the mobilization of intracellular Ca²⁺ pool and influx of extracellular Ca²⁺ as well, CCK excites the SO cells mainly through mobilization of intracellular IP3-sensitive Ca²⁺ store. After the incorporation with cholesterol liposome, KCl,ACh and CCK induced cellular Ca²⁺ increase percentages decreased.

In situ localization of cholesterol in skeletal muscle by use of a monoclonal antibody

A common perception is that cholesterol, the major structural lipid found in mammalian membranes, is localized nearly exclusively to the plasma membrane of living cells and that it is found in much smaller quantities in internal membranes. This perception is based almost exclusively on cell fractionation studies, in which density gradient centrifugation is used for purification of discrete subcellular membrane fractions. Here we describe a monoclonal antibody, MAb 2C5-6, previously reported to detect purified cholesterol in synthetic membranes (Swartz GM Jr, Gentry MK, Amende LM, Blanchette-Mackie EJ, and Alving CR. Proc Natl Acad Sci USA 85: 1902-1906, 1988), that is capable of detecting cholesterol in situ in the membranes of skeletal muscle sections. Localization of cholesterol, the dihydropyridine receptor of the T tubule, and the Ca(2+)-ATPase of the sarcoplasmic reticulum (SERCA2) by means of double and triple immunostaining protocols clearly demonstrates that cholesterol is primarily localized to the sarcoplasmic reticulum membranes of skeletal muscle rather than the sarcolemmal or T tubule membranes. The availability of this reagent and its ability to spatially localize cholesterol in situ may provide a greater understanding of the relationship between membrane cholesterol content and transmembrane signaling in skeletal muscle.

Inhibition of Ca2+ uptake into A7r5 vascular smooth muscle cells by farnesol: lack of effect on membrane fluidity and Ca2+-ATPase activities

BACKGROUND

Previous studies have shown that farnesol, a 15-carbon nonsterol derivative of mevalonic acid, inhibits vasoconstriction. Because of its lipophilic properties, we hypothesized that farnesol increased membrane dynamics, thus reducing uptake of Ca2+ and contraction.

OBJECTIVE

To characterize the effect of farnesol on cell membrane fluidity.

DESIGN

The study was conducted using A7r5 cells, a rat aortic vascular smooth muscle cell line. Inhibition of Ca2+ uptake by farnesol was first established in these cells. Then, the effect of farnesol on membrane dynamics was determined. Finally, to ascertain that activation of Ca2+ extrusion and reuptake processes by farnesol did not occur, Ca2+-ATPase activity was examined.

METHODS

Membrane fluidity in cell homogenates was estimated using two fluorescent dyes (1,6-diphenyl-1,3,5-hexatriene) and (1-[-(trimethylamino)-phenyl]-6-phenyl-1,3,5-hexatriene). Ca2+ uptake was determined by monitoring the changes in cytosolic Ca2+ concentration ([Ca2+]i) in fura-2-loaded cells after addition of KCI. Ca2+-ATPase activity was measured in 100000 x g cell fractions.

RESULTS

Farnesol reduced KCI-induced (Ca2+]i transients significantly (P < 0.001), but did not modify membrane dynamic properties [0.214+/-0.007 versus 0.218+/-0.007 (n = 10) and 0.142+/-0.002 versus 0.146+/-0.003 (n = 5) for 1 -[-(trimethylamino)-phenyl]-6-phenyl-1,3,5-hexatriene and 1,6-diphenyl-1,3,5-hexatriene anisotropies, respectively; NS]. Administration of up to 30 micromol/l farnesol did not affect Ca2+-ATPase activity.

CONCLUSION

Farnesol inhibits KCI-dependent rise of [Ca2+]i in A7r5 cells. This effect of farnesol is not related to a global change in plasma membrane lipid organization or to activation of Ca2+ pumps. Other mechanisms such as direct inhibition of voltage-dependent Ca2+ channels could therefore explain the biologic action of farnesol in the vascular tissue.

Alteration of lymphocyte membrane phospholipids and intracellular free calcium concentrations in hyperlipidemic subjects

Hypercholesterolemia has been proposed to influence cell functions via changes in membrane composition. The aim of the present study was to determine whether the membrane phospholipid composition of human lymphocytes is modified in hypercholesterolemia and whether these changes are accompanied by functional modifications. The phospholipid fatty acid contents and intracellular free calcium concentrations were determined in peripheral blood lymphocytes from 13 subjects with serum total cholesterol levels ranging from 4.6 to 8.8 mmol/l. The spontaneous basal rate of thymidine incorporation in lymphocyte of hypercholesterolemic individuals increased, while its relative stimulation by ConA was less effective. Important changes in membrane lipid composition, consisting mainly of decrease of the mass of phospholipids, and of associated polyunsaturated fatty acids were observed in hypercholesterolemia. In contrast, the cell cholesterol content was significantly increased. The intracellular free calcium concentration was enhanced and strongly associated with circulating cholesterol levels, cell cholesterol content and phospholipid fatty acids. These results indicate that hypercholesterolemia is accompanied by profound changes in lymphocyte membrane lipid composition and Ca(2+) handling.

Atherosclerosis alters the composition, structure and function of arterial smooth muscle cell plasma membranes

The object of this study was to examine changes in plasma membranes of arterial smooth muscle (ASM) during atherogenesis obtained from cholesterol-fed (2%) rabbits. A microsomal fraction highly enriched with plasma membrane markers was prepared by subcellular organelle fractionation from ASM freshly isolated from the thoracic aorta. The membranes were analyzed for unesterified (free) cholesterol (FC) content, membrane bilayer structural parameters (X-ray diffraction), phospholipid (PL) composition, and Na+/K(+)-ATPase activity and kinetics. Following 8 weeks on diet, membrane FC content increased 67.1%. Small angle X-ray diffraction demonstrated an increase in membrane hydrocarbon core electron density and an increase in overall lipid bilayer width (56-62 A). This increase in bilayer width was highly correlated with the membrane FC content (r = 0.992). Both membrane FC content And bilayer width independently correlated with time on cholesterol diet. The phospholipid profile of the membrane revealed a 16.4% increase in phosphatidylcholine (PC), 19.3% decrease in phosphatidylethanolamine (PE) and 62.8% increase in sphingomyelin (SM) content with no change in total PL content. Na+/K(+)-ATPase activity was decreased 52.2% (P < 0.005), and [3H]ouabain binding kinetics demonstrated a 27.6% decrease in maximum binding sites (Bmax) (P < 0.01) while the dissociation constant (Kd) remained unaltered. Membranes obtained from control ASM cells enriched with FC in culture demonstrated changes similar to those in atherosclerotic ASM membranes including an increase in membrane FC content, an increase in bilayer width, and a decrease in Na+/K(+)-ATPase activity with decreased ouabain Bmax. These data demonstrate marked compositional, structural and functional changes in ASM cell membrane characteristics in dietary atherosclerosis. These changes were highly correlated with cholesterol accumulation in the plasma membrane bilayer and were observed before the appearance of visible lesions. We suggest that these membrane defects may be linked with early atherogenesis.

Cholesterol oxidation reduces Ca(2+)+MG (2+)-ATPase activity, interdigitation, and increases fluidity of brain synaptic plasma membranes

These experiments examined effects of cholesterol oxidation on Ca(2+)+Mg(2+)-ATPase activity, Na(+)+K(+)-ATPase activity, and membrane structure of brain synaptic plasma membranes (SPM). Cholesterol oxidase [E.C.1.1.3.6 from Brevibacterium sp.] was used to oxidize cholesterol. Two cholesterol pools were identified in synaptosomal membranes based on their accessibility to cholesterol oxidase. A rapidly oxidized cholesterol pool was observed with a 1t1/2 of 1.19 +/- 0.09 min and a second pool with a 2t1/2 of 38.30 +/- 4.16 min. Activity of Ca(2+)+Mg(2+)-ATPase was inhibited by low levels of cholesterol oxidation. Ten percent cholesterol oxidation, for example, resulted in approximately 35% percent inhibition of Ca(2+)+Mg(2+)-ATPase activity. After 13% cholesterol oxidation, further inhibition of Ca(2+)+Mg(2+)-ATPase activity was not observed. Activity of Na(+)+K(+)-ATPase was not affected by different levels of cholesterol oxidation (5%-40%). SPM interdigitation was significantly reduced and fluidity was significantly increased by cholesterol oxidation. The relationship observed between SPM interdigitation and Ca(2+)+Mg(2+)-ATPase activity was consistent with studies using model membranes [7]. Brain SPM function and structure were altered by relatively low levels of cholesterol oxidation and is a new approach to understanding cholesterol dynamics and neuronal function. The sensitivity of brain SPM to cholesterol oxidation may be important with respect to the proposed association between oxygen free radicals and certain neurodegenerative diseases.

Distinct electric potentials in soma and neurite membranes

Structurally similar voltage-dependent ion channels may behave differently in different locations along the surface of a neuron. A possible reason could be that channels experience nonuniform electrical potentials along the plasmalemma. Here, we map the electrical potentials along the membrane of differentiated N1E-115 neuroblastoma cells with a potential-sensitive dye. We find that the intramembrane potential gradient is indeed more positive in the membranes of neurites than in the membranes of somata. This is not attributable to differences in ion conductances or surface charge densities between the membranes of neurites and somata; instead, it can be explained by differences in lipid composition. The spatial variation in intramembrane electrical potential may help account for electrophysiological and functional differences between neurites and somata.

The induction of apoptosis is a common feature of the cytotoxic action of ether-linked glycerophospholipids in human leukemic cells

The ability of 2 recent ether-lipid derivatives, aza-phospholipids BN52205 and BN52211, to induce apoptosis in different leukemia cell lines was investigated using I-octadecyl-2-methyl-rac-glycero-3- phosphocholine (ET-18-OCH3) as a positive control. HL60, K562, Molt-4 and U937 cells were exposed for 24 hr to 20 microM of drug. The 2 aza-derivatives were as cytotoxic as ET-18-OCH3: BN52205 and BN52211 selectively induced apoptotic death in HL60, Molt-4 and U937 cells, but not in the K562-resistant cell line. Around 50% of DNA was fragmented in HL60 cells after exposure to the aza-derivatives, and 34% and 20% of DNA was fragmented in Molt-4 and U937 cells respectively. Similar results were obtained when cells were exposed to ET-18-OCH3. Our data confirm that ether lipids induce apoptosis in a variety of human leukemic cells, providing a possible explanation for their selectivity and mechanism of action.

Unusual low proton permeability of liposomes prepared from the endogenous myelin lipids

In contrast with most other lipid substrates, in this article we show that liposomes prepared from the total myelin lipids exhibited a negligible proton permeability. Neither the generation of valinomycin-induced potassium diffusion potentials as high as -177 mV nor the imposition of large pH gradients (up to three units) was able to produce a substantial flux of protons through liposomal membranes, as determined by the distribution of [14C]-methylamine, or the changes in the fluorescence of the probes 9-aminoacridine, acridine orange, and pyranine. The presence of cations (Na+, K+, Ca2+) did not alter this behavior. Voltage clamping did not increase the transmembrane delta pH-driven proton permeability. However, liposome diameter was found to be critical because small unilamellar vesicles displayed a much higher proton permeability than large unilamellar or multilamellar vesicles. This abnormally low proton permeability is interpreted by virtue of the characteristic biochemical composition of myelin lipid matrix, with a high content of cholesterol and sphingolipids and a very low level of free fatty acids. These results could be important for elucidating the role of myelin in the regulation of pH in the brain. In addition, the myelin lipid extract could be useful for reconstituting proteins that participate in the transport of H+ through the membrane.

Induction of apoptosis in human leukemic cells by the ether lipid 1-octadecyl-2-methyl-rac-glycero-3-phosphocholine. A possible basis for its selective action

Ether-linked glycerophospholipids (ether lipids, EL) are membrane-interactive drugs selectively cytotoxic toward neoplastic cells compared with normal cells. No conclusive explanation has yet been provided for this selectivity. We now present data indicating that the drug 1-octadecyl-2-methyl-rac-glycero-3-phosphocholine (ET-18-OMe) induces apoptosis, or programmed cell death, in human leukemic cells. Apoptotic death is induced selectively by ET-18-OMe in HL60 cells, which are sensitive to the drug's cytotoxic action, but not in the resistant K562 cell line. Enrichment of HL60 cells with cholesterol (HL60-CHOL cells) significantly protects the cells from the cytotoxic effect and from the induction of apoptosis by ET-18-OMe; the percentage of fragmented DNA is only 17% for HL60-CHOL, compared with 50% in native HL60 cells after exposure to 20 microns ET-18-OMe for 24 hr. Our study provides a possible explanation for differences in sensitivity to EL among different cell types and illustrates an indirect interaction of EL with cellular DNA.