The effect of partial replacements of membrane cholesterol by other steroids on the osmotic fragility and glycerol permeability of erythrocytes

Physical properties and stability mechanisms of poly(ethylene glycol) conjugated liposome encapsulated hemoglobin dispersions

Liposomes encapsulating hemoglobin (LEHs) surface-conjugated with 2000 and 550 Da poly(ethylene glycol) (PEG) were produced via extrusion through 400, 200 and 100 nm pore diameter membranes in two types of phosphate buffer with different ionic strengths. The lipid bilayers were composed of dimyristoyl-phosphatidylcholine (DMPC), cholesterol, dimyristoyl-phosphoethanolamine-PEG (DMPE-PEG), dimyristoyl-phosphatidylglycerol (DMPG), and alpha-tocopherol (in a 43:40:10:5:2 mole ratio). N-acetyl-L-cysteine was coencapsulated in order to suppress hemoglobin (Hb) oxidation. Various physical properties of PEG-LEH dispersions were determined: size distribution, encapsulation efficiency, P50 (partial pressure of O2 where half of the oxygen binding sites are saturated with O2), cooperativity coefficient, and encapsulated methemoglobin (MetHb) level. In order to study the stabilization mechanism of these dispersions, the effective bending constant (KB) and the spontaneous radius of curvature (R0) of PEG-LEHs were extracted by fitting a mathematical model describing the size distribution of a liposome dispersion to the experimentally measured size distributions. We observed that liposome dispersions extruded in phosphate buffer (PB) were more monodisperse than liposomes extruded in phosphate buffered saline (PBS), and higher molecular weight PEG promoted the formation of narrower size distributions. Moreover, extrusion in PB and lipid conjugation with higher molecular weight PEG imparted higher bilayer rigidity (high KB), and stabilized the liposome dispersions by the spontaneous curvature mechanism, whereas the other liposome dispersions were stabilized by thermal undulations (low KB). The P50 and cooperativity coefficient of PEG-LEHs extruded in PBS and PB was comparable to that of human blood, and the encapsulated MetHb levels were less than 5%. The highest encapsulation efficiencies obtained were 27%-36% (82-109 mg Hb/mL) for LEH dispersions extruded in PBS and grafted with 2000 Da PEG. These dispersions yielded KBs' ranging from 7kT to 27kT, which indicated that these dispersions were stabilized by spontaneous curvature. Whereas the same lipid combination extruded in PBS, however, instead conjugated with 550 Da PEG resulted in KBs' ranging from 2 kT to 2.7 kT, which indicated that these dispersions were stabilized by thermal undulations. Thermal undulations permitted Hb leakage through the lipid bilayers, which in turn lowered the encapsulation efficiency to 1%-10.7% (3-32 mg Hb/mL). Taken together, the experimentally measured size distributions and encapsulation efficiencies of PEG-LEH dispersions can be readily explained through analysis of the magnitude of KB, which dictates the stability mechanism of the liposome dispersion.

Non-cholesterol sterols in serum, lipoproteins, and red cells in statin-treated FH subjects off and on plant stanol and sterol ester spreads

BACKGROUND

Serum plant sterol levels are increased by consumption of statins and dietary plant sterols, and decreased by dietary plant stanols, but little is known about combination therapy of statin and plant sterols.

METHODS

We measured plant sterols in serum, lipoproteins, and red cells in subjects with familial hypercholesterolemia (FH) (n=18) treated with variable doses of statins off and on plant stanol (STA) and sterol ester (STE) spreads.

RESULTS

STA and STE spreads lowered LDL cholesterol approximately 15%. Plant sterols were decreased in serum, lipoproteins, and red cells by approximately 25% with STA and increased from 37% to 80% with STE, especially with high statin doses. The changes in serum were related to those in red cells. The baseline levels of serum plant sterols were negatively (r-range -0.639 to -0.935) and positively (r-range 0.526 to 0.598) correlated with the respective changes evoked by the STA and STE spreads.

CONCLUSIONS

STE reduces LDL cholesterol, but increases serum, lipoprotein, and red cell plant sterol levels in statin-treated FH subjects, while all the respective values are decreased with STA. Recent predictions that elevated serum plant sterols pose an increased coronary risk suggest that increases of serum plant sterol levels should be avoided, especially in atherosclerosis-prone individuals, such as subjects with FH.

Membrane properties of plant sterols in phospholipid bilayers as determined by differential scanning calorimetry, resonance energy transfer and detergent-induced solubilization

The increased use of plant sterols as cholesterol-lowering agents warrants further research on the possible effects of plant sterols in membranes. In this study, the effects of the incorporation of cholesterol, campesterol, beta-sitosterol and stigmasterol in phospholipid bilayers were investigated by differential scanning calorimetry (DSC), resonance energy transfer (RET) between trans parinaric acid (tPA) and 2-(6-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)hexanoyl-1-hexadecanoyl-sn-glycero-3-phosphocholine (NBD-PC), and Triton X-100-induced solubilization. The phospholipids used were 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), D-erythro-N-palmitoyl-sphingomyelin (PSM), and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). In DSC experiments, it was demonstrated that the sterols differed in their effect on the melting temperatures of both the sterol-poor and the sterol-rich domains in DPPC and PSM bilayers. The plant sterols gave rise to lower temperatures of both transitions, when compared with cholesterol. The plant sterols also resulted in lower transition temperatures, in comparison with cholesterol, when sterol-containing DPPC and PSM bilayers were investigated by RET. In the detergent solubilization experiments, the total molar ratio between Triton X-100 and POPC at the onset of solubilization (R(t,sat)) was higher for bilayers containing plant sterols, in comparison with membranes containing cholesterol. Taken together, the observations presented in this study indicate that campesterol, beta-sitosterol and stigmasterol interacted less favorably than cholesterol with the phospholipids, leading to measurable differences in their domain properties.

Metabolic effects of plant sterols and stanols (Review)

High serum LDL cholesterol concentration is a major risk factor for cardiovascular complications. This risk can be lowered by diet. In this respect foods containing plant sterol or stanol esters can be useful for mildly- and hypercholesteraemic subjects. Plant sterols and stanols, which are structurally related to cholesterol, decrease the incorporation of dietary and biliary cholesterol into micelles. This lowers cholesterol absorption. Furthermore, these components increase ABC-transporter expression, which may also contribute to the decreased cholesterol absorption. Consequently, cholesterol synthesis and LDL receptor activity increase, which ultimately leads to decreased serum LDL cholesterol concentrations. Animal studies have further shown that these dietary components may also lower atherosclerotic lesion development. Plant sterols and stanols also lower plasma lipid-standardized concentrations of the hydrocarbon carotenoids, but not those of the oxygenated cartenoids and tocopherols. Also, vitamin A and D concentrations are not affected. Although absorption of plant sterols and stanols (0.02-3.5%) is low compared to cholesterol (35-70%), small amounts are found in the circulation and may influence other physiological functions. However, there is no consistent evidence that plant sterols or stanols can change the risk of colon or prostate cancer, or immune status. In conclusion, plant sterols and stanols effectively reduce serum LDL cholesterol and atherosclerotic risk. In addition potential effects of plant sterols and stanols on other metabolic processes remain to be elucidated.

Rapeseed oil ingestion and exacerbation of hypertension-related conditions in stroke prone spontaneously hypertensive rats

Two groups of 20 stroke prone spontaneously hypertensive rats (SHRSP) at 5 weeks old were fed a diet containing 10 w/w% rapeseed (canola) oil or soybean oil as the only dietary fat, and given drinking water containing 1% NaCl. Life span of the canola oil group (62+/-2 days) was shorter than that of the soybean oil group (68+/-3 days). Stroke-related symptoms were observed in every animal, but the onset of those in the canola oil group, at 47+/-1 days after starting the administration was earlier than that in the soybean oil group, 52+/-2 days. Incidence of cerebral hemorrhage was similar in these groups, and no differences were found between lesions of organs in the groups. In another experiment, two groups of ten SHRSP at 5 weeks of age were fed the defatted diet and given canola oil or soybean oil by gavage at 10 w/w% of consumed food for 4 weeks without NaCl loading. After the 4-week administration, mean systolic blood pressure in the canola oil group and the soybean oil group were 233+/-2 and 223+/-0.3 mmHg, respectively. Phytosterol levels in both plasma and erythrocyte membranes reflected those contained in the oils ingested. Na(+), K(+)-ATPase activities in the brain, heart and kidney were enhanced in the canola oil group. These results indicate that promotion of hypertension-related deterioration in organs is likely to have relevance to the short life span in the canola oil group. Enhanced Na(+), K(+)-ATPase activity by phytosterols in the oil ingested may play a role in these changes.

Red cell and plasma plant sterols are related during consumption of plant stanol and sterol ester spreads in children with hypercholesterolemia

OBJECTIVE

To show whether the ratios of squalene and cholesterol precursor sterols to cholesterol and cholestanol and plant sterols to cholesterol change differently in plasma and especially in the red cells of hypercholesterolemic children during consumption of plant stanol and sterol ester spreads.

STUDY DESIGN

In a randomized, double-blind, crossover study, hypercholesterolemic children (n = 23) consumed low-fat plant stanol and sterol ester spreads for 5-week periods separated by a 5-week washout period. Plasma and red cell lipids, squalene, and noncholesterol sterols were measured before and at the end of each period.

RESULTS

The plant stanol and sterol ester spreads lowered plasma total (-9% and -6%, respectively) and low-density lipoprotein (-12% and -9%) cholesterol but had no effect on red cell cholesterol, high-density lipoprotein cholesterol, or plasma triglycerides. The ratios of plasma and red cell sitosterol and campesterol to cholesterol decreased by 32% to 36% (P <.001) with the plant stanol ester and increased by 40% to 52% (P <.001) with the sterol ester spread.

CONCLUSIONS

Consumption of plant sterols increases and consumption of plant stanols decreases the ratios of plant sterols to cholesterol in red cells of hypercholesterolemic children proportionately to the respective changes in plasma.

Structural features of sterols required to inhibit human sperm capacitation

Ejaculated mammalian sperm must undergo a final maturation (capacitation) before they can acrosome-react and fertilize eggs. Loss of cholesterol is an essential step in the capacitation of human sperm. Experimentally maintaining a high level of cholesterol inhibits capacitation, but the mechanism is unknown. The present study investigated the structural features that are required for cholesterol's inhibitory activity. Human sperm also contain much desmosterol, which is lost from sperm during capacitation. Preventing the loss of desmosterol inhibited capacitation (as assessed by acrosomal responsiveness), with an effectiveness approximately equal to cholesterol's inhibitory activity. Other structural analogs were added to the incubation medium to replace sperm cholesterol and desmosterol. Most inhibited capacitation, including those that lacked cholesterol's 3beta-OH group (cholesteryl methyl ether and epicholesterol) and those with modified C17 groups (ergosterol and diosgenin). Two steroids did not inhibit capacitation well. Coprostanol, which has a nonplanar steroid nucleus, had low inhibitory activity that could be explained by an elevated endogenous cholesterol concentration. Epicoprostanol, which has a nonplanar ring structure and a 3alpha-OH group, promoted rather than inhibited capacitation. The inhibitory activity of the analogs was correlated with their ability to promote order of egg phosphatidylcholine as measured by fluorescence anisotropy. In summary, a planar ring structure is required for sterol inhibitory activity, but a 3beta-OH group and a saturated cholesterol-like aliphatic tail on C17 are not required. The present results support the hypothesis that sperm sterols block capacitation by increasing order of phospholipids.

7-Dehydrocholesterol-dependent proteolysis of HMG-CoA reductase suppresses sterol biosynthesis in a mouse model of Smith-Lemli-Opitz/RSH syndrome

Smith-Lemli-Opitz/RSH syndrome (SLOS), a relatively common birth-defect mental-retardation syndrome, is caused by mutations in DHCR7, whose product catalyzes an obligate step in cholesterol biosynthesis, the conversion of 7-dehydrocholesterol to cholesterol. A null mutation in the murine Dhcr7 causes an identical biochemical defect to that seen in SLOS, including markedly reduced tissue cholesterol and total sterol levels, and 30- to 40-fold elevated concentrations of 7-dehydrocholesterol. Prenatal lethality was not noted, but newborn homozygotes breathed with difficulty, did not suckle, and died soon after birth with immature lungs, enlarged bladders, and, frequently, cleft palates. Despite reduced sterol concentrations in Dhcr7(-/-) mice, mRNA levels for 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the rate-controlling enzyme for sterol biosynthesis, the LDL receptor, and SREBP-2 appeared neither elevated nor repressed. In contrast to mRNA, protein levels and activities of HMG-CoA reductase were markedly reduced. Consistent with this finding, 7-dehydrocholesterol accelerates proteolysis of HMG-CoA reductase while sparing other key proteins. These results demonstrate that in mice without Dhcr7 activity, accumulated 7-dehydrocholesterol suppresses sterol biosynthesis posttranslationally. This effect might exacerbate abnormal development in SLOS by increasing the fetal cholesterol deficiency.

Thirteen-week dietary intake of rapeseed oil or soybean oil as the only dietary fat in Wistar Kyoto rats-change in blood pressure

Wistar Kyoto (WKY) rats were fed a diet containing 10% rapeseed (canola) oil or soybean oil as the only dietary fat for 13 weeks. From week 5 of feeding, systolic blood pressure of the canola oil group became higher than that of the soybean oil group. The 13-week canola oil intake increased plasma levels of Na(+) and lipids, and decreased the level of K(+) compared to those in the soybean oil group. The canola oil group also showed a high density of neutrophils and a low density of platelets compared to the soybean oil group. Moreover, the activities of catalase and superoxide dismutase in the hepatic cytosol were depressed in the canola oil group. The mechanisms for the higher blood pressure are unclear. However, an increase in body fluid via activation of Na(+) pump or Na(+), K(+)-ATPase and/or a blunt endothelium-dependent vasodilation by increased superoxide might have relevance to the elevated blood pressure. The increased plasma lipids and the changes in the densities of platelets and neutrophils appear not to be critical in WKY rats. However, these would tend to promote peripheral vascular lesions in the strains, such as spontaneously hypertensive rats and stroke-prone spontaneously hypertensive rats, which are prone to present atheroscrelotic vascular injury.

Blood coagulation and osmolar tolerance of erythrocytes in stroke-prone spontaneously hypertensive rats given rapeseed oil or soybean oil as the only dietary fat

The life-span of stroke-prone spontaneously hypertensive rats (SHRSP) has been reported to become shorter by ingestion of some vegetable oils, including rapeseed oil, when given as the sole dietary fat. The present study was undertaken to examine if the ingestion of rapeseed (canola) oil affects blood coagulating time and erythrocyte membranes. Namely, SHRSP were orally given canola oil or soybean oil as the only dietary fat (10% of diet) for 4 weeks. After the 4-week feeding, activated partial thromboplastin time (APTT) in the canola oil group (19.9+/-0.5 s, N=8) was significantly shorter than that in the soybean oil group (21.6+/-0.6 s, N=8, P<0. 05), though there were no between-group differences in plasma Ca(2+), platelet density and platelet aggregation. Erythrocytes from the canola oil group were less tolerant to low osmotic pressure than those from soybean oil group; the EC(50) values for NaCl concentration to cause hemolysis were 0.42+/-0.004 and 0.40+/-0.005% in the canola oil and the soybean oil groups, respectively (N=10, P<0.01). The canola oil-induced shortening of blood coagulation time and increased fragility in erythrocyte membranes may have relevance to the promotion of strokes in SHRSP.

Vegetable oils high in phytosterols make erythrocytes less deformable and shorten the life span of stroke-prone spontaneously hypertensive rats

Previous studies have shown that canola oil (CA), compared with soybean oil (SO), shortens the life span of stroke-prone spontaneously hypertensive (SHRSP) rats, a widely used model for hemorrhagic stroke. SHRSP rats are highly sensitive to dietary cholesterol manipulations because a deficiency of membrane cholesterol makes their cell membranes weak and fragile. Phytosterols, abundant in CA but not in SO, can inhibit the absorption of cholesterol and also replace a part of cholesterol in cell membranes. This study was performed to determine whether the high concentration of phytosterols in CA might account for its life-shortening effect on SHRSP rats. Male, 35-d-old SHRSP rats (n = 28/group) were fed semipurified diets containing CA, SO, CA fortified with phytosterols (canola oil + phytosterols, CA + P), SO fortified with phytosterols (soybean oil + phytosterols, SO + P), corn oil (CO), olive oil (OO) or a fat blend that mimicked the fat composition of a representative Canadian diet (Canadian fat mimic, CFM; 10 g/100 g diet). These fats provided 97, 36, 207, 201, 114, 27 and 27 mg phytosterols/100 g diet, respectively. Ten rats from each group were killed after 30-32 d for blood and tissue analyses. The remaining rats (18/group) were used for determination of life span. The life span of SHRSP rats fed the high phytosterol oils (CA, CA + P, SO + P and CO) was significantly (P<0.05) shorter than that of CFM- and SO-fed rats. At 30-32 d, the groups fed the high phytosterol oils had greater levels of phytosterols and significantly (P<0.05) higher ratios of phytosterols/cholesterol in plasma, RBC, liver and kidney, and a significantly (P<0.05) lower RBC membrane deformabilty index than the groups fed oils low in phytosterols (SO, OO and CFM). The mean survival times were correlated with RBC deformability index (r(2) = 0.91, P = 0.0033) and cholesterol concentration (r(2) = 0.94, P = 0.0016), and inversely correlated with RBC phytosterol concentration (r(2) = 0.58, P = 0.0798) and phytosterols/cholesterol (r(2) = 0.65, P = 0.0579), except in the OO group. This study suggests that the high concentration of phytosterols in CA and the addition of phytosterols to other fats make the cell membrane more rigid, which might be a factor contributing to the shortened life span of SHRSP rats.

Influence of sources of dietary oils on the life span of stroke-prone spontaneously hypertensive rats

In recent studies, the life span of stroke-prone spontaneously hypertensive (SHRSP) rats was altered by a variety of dietary fats. It was relatively shorter in rats fed canola oil as the sole source of fat. The present study was performed to find out whether the fatty acid profile and the high content of sulfur compounds in canola oil could modulate the life span of SHRSP rats. SHRSP rats (47 d old, n = 23/group) were matched by body weight and systolic blood pressure and fed semipurified diets containing 10% canola oil, high-palmitic canola oil, low-sulfur canola oil, soybean oil, high-oleic safflower oil, a fat blend that mimicked the fatty acid composition of canola oil, or a fat blend high in saturated fatty acids. A 1% sodium chloride solution was used as drinking water to induce hypertension. After consuming the diets for 37 d, five rats from each dietary group were killed for collection of blood and tissue samples for biochemical analysis. The 18 remaining animals from each group were used for determining their life span. The mean survival time of SHRSP rats fed canola oil (87.4+/-4.0 d) was not significantly different (P > 0.05) from those fed low-sulfur canola oil (89.7+/-8.5 d), suggesting that content of sulfur in canola oil has no effect on the life span of SHRSP rats. The SHRSP rats fed the noncanola oil-based diets lived longer (mean survival time difference was 6-13 d, P < 0.05) than those fed canola and low-sulfur canola oils. No marked differences in the survival times were observed among the noncanola oil-based groups. The fatty acid composition of the dietary oils and of red blood cells and liver of SHRSP rats killed after 37 d of treatment showed no relationship with the survival times. These results suggest that the fatty acid profile of vegetable oils plays no important role on the life span of SHRSP rat. However, phytosterols in the dietary oils and in liver and brain were inversely correlated with the mean survival times,indicating that the differential effects of vegetable oils might be ascribed, at least partly, to their different phytosterol contents.

Effect of dehydroepiandrosterone and its sulfate and fatty acid ester derivatives on rat brain membranes

The effects of dehydroepiandrosterone (DHEA) as well as its sulfate and fatty acid ester derivatives on rat brain membrane fluidity was investigated by fluorescence depolarization of a lipid probe 1,6-diphenyl-1,3,5-hexatriene and compared to its effect on phospholipid conformation investigated by Fourier transform infrared spectroscopy. In rat brain, membrane fluidity varied rostro-caudally, the frontal cortex showing the highest fluidity compared to the hypothalamus, hippocampus, striatum, thalamus, and hindbrain. As previously reported, it was observed that cholesteryl hemisuccinate and stearic acid rigidify striatal membrane whereas linoleic acid and L-alpha-phosphatidylcholine increase the membrane fluidity. Striatal fluidity was increased in vitro with increasing concentrations of DHEA, this effect was greater with the DHEA fatty acid ester derivatives (DHEA-L), DHEA-undecanoate, and DHEA-stearate, whereas no effect was observed with DHEA-sulfate (DHEA-S). In the frontal cortex only the two DHEA-L derivatives increased membrane fluidity, whereas DHEA and DHEA-S were without effect. The effect of DHEA-L on synthetic dimyristoylphosphatidylcholine-d54 phospholipid membranes indicates a disordering effect of DHEA-undecanoate and DHEA-stearate as reflected by increased trans-gauche isomerization of the acyl chains of the lipid. Hence, DHEA-L increase the disorder and/or fluidity of brain membranes; interestingly, these compounds are abundant in the brain where they are generally considered as storage compounds that slowly release the active unconjugated steroid hormone.

Selective modification of sterol composition of hepatomas: new opportunities for chemotherapy

The absence of feedback regulation of cholesterol biosynthesis in hepatomas suggests the possibility of substitution of cholesterol with its biosynthetic precursors (7-dehydrocholesterol or lanosterol) selectively in hepatomas without the accumulation of these precursors in liver and other normal tissues, by a combination of a high cholesterol diet and specific inhibitors of cholesterol biosynthesis (AY-9944 for accumulation of 7-dehydrocholesterol and ketoconazole for accumulation of lanosterol). We suggest: (1) using a selective accumulation of 7-dehydrocholesterol in hepatoma plasma membranes to increase the sensitivity of hepatoma cells to polyene antibiotics (amphotericin B, nystatin), because polyene antibiotics have higher affinity to 7-dehydrocholesterol compared to cholesterol; (2) using a selective accumulation of lanosterol in hepatoma cells to increase the sensitivity of hepatoma cells to different antitumor agents, because lanosterol is much less effective in supporting vital cell functions (including barrier properties of natural membranes) compared to cholesterol.

Fungicidal mechanism of action of D0870 against Cryptococcus neoformans under acidic conditions

The fungicidal mechanism of the triazole D0870 against Cryptococcus neoformans under acidic conditions was investigated. D0870 reduced the intracellular K+ content of C. neoformans at pH 4 to about half the value at pH 7 after 12 h of incubation. The 50% inhibitory concentrations of D0870 for ergosterol biosynthesis were almost the same at both pH 4 (0.017 microg/ml) and 7 (0.014 microg/ml); however, D0870 caused a marked accumulation of an unknown lipid and methylated sterols in C. neoformans cultured at pH 4. Extracted fractions containing the unknown lipid or methylated sterols showed strong fungicidal activities against C. neoformans both at pH 4 and 7 in phosphate-citrate buffer not containing D0870. Gas chromatographic-mass spectrometric analysis showed that the unknown lipid was obtusifolione. These results suggest that D0870 kills C. neoformans by disturbing the permeability of the cell membrane through the accumulation of obtusifolione and methylated sterols in the cell membrane under acidic conditions.

Haemodialyser biocompatibility and erythrocyte structure and function

There is controversy as to the clinical importance of providing haemodialysis (HD) with biocompatible versus non-biocompatible membranes. The effects of both acute and chronic dialysis with a biocompatible membrane (polyacrylonitrile, PAN) and a non-biocompatible membrane (cuprophane, CU) on the structural and functional properties of human erythrocytes have been examined. All 27 studied HD patients had increased erythrocyte osmotic fragility (OF) compared to controls; a single CU HD decreased mean OF (% lysis) by 13% without altering cell cholesterol. A single PAN HD decreased OF by a significantly greater amount (24%) and was associated with a 20% reduction in cell cholesterol. Chronic PAN HD for 6 months was associated with a sustained reduction in osmotic fragility compared to chronic CU HD (mean lysis 16% vs 45%) with no differences in mean pre-HD cell cholesterol. A single CU HD was associated with increased mean erythrocyte malonyldialdehyde (MDA) and reduced membrane content of spectrin and band 3 and this was significantly different from the effects of PAN. A single CU or PAN HD had no significant action on reduced glutathione (GSH), ankyrin, actin or sodium pump activity. Chronic HD was associated with increased GSH, and decreased ankyrin and band 3 protein compared with controls but the results for CU and PAN were not different. There was a non-significant tendency for higher MDA levels after chronic CU HD compared to PAN. These results indicate that the structural integrity of erythrocytes is improved by PAN HD with respect to CU but this difference cannot easily be ascribed to gross changes in structural proteins, ionic homeostasis or oxidation status.

Liposomes bearing platelet proteins: a model for surface functions studies

An improved procedure for the direct transfer of membrane proteins from human platelets to liposomes involving the treatment of platelets with linolenic acid was developed. The transfer of platelet proteins to liposomes prepared from the mixture of L-alpha-dimyristoyl-phosphatidylcholine/sphingomyelin in the molar ratio 80/20 appeared to be significantly enhanced compared with liposomes prepared from the same components mixed in other ratios. A wide range of platelet proteins was transferred, the most important being GPIb (170 kDa), GPIIb/IIIa (135 and 110 kDa). GPIV (90 kDa), GPIX (24 kDa) and the serotonin transporter (68 kDa). The recognition interactions between these proteoliposomes and specific protein antibodies clearly indicate that the non-invasive procedure used in this study ensured the reproducible transfer of platelet proteins without essentially altering their original conformation. The obtained results reveal also that the affinity of proteoliposomes to bind paroxetin was virtually the same as that of the native serotonin transporter. These results provide an indication of the possible use of such proteoliposomes as models to study at the molecular level the interaction of these proteins with their ligands.

The effect of side-chain analogues of cholesterol on the thermotropic phase behavior of 1-stearoyl-2-oleoylphosphatidylcholine bilayers: a differential scanning calorimetric study

In this study we have examined the effects of analogues of cholesterol differing with respect to alkyl side-chain length and structure on the thermotropic phase behavior of bilayers formed from 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC), an important subclass of naturally occurring phosphatidylcholines (PCs). The synthetic sterols we studied contained either a terminally unbranched (n-series) or a single methyl-branched (iso-series) side chain of 3 to 10 carbon atoms. The phase transition behavior was examined by high-sensitivity differential scanning calorimetry (DSC). The main phase transition endotherm of SOPC/sterol bilayers consists of superimposed sharp and broad components, which represent the hydrocarbon chain melting of sterol-poor and sterol-rich phospholipid domains, respectively. The transition temperature and the cooperativity of the sharp component are moderately reduced upon sterol incorporation and the enthalpy decreases to zero when sterol levels of 20-30 mol% are reached. The enthalpy of the broad component transition initially increases to a maximum around 25 or 25-30 mol% sterol and thereafter decreases with further increases in sterol concentration. However, the broad transition of SOPC bilayers containing both short (C-22, i-C5 and n-C3) and long (i-C9 and i-C10) side-chain sterols still persists at levels of 50 mol% sterol. Thus the effective stoichiometry of SOPC-sterol interactions varies with changes in sterol alkyl side-chain length. The incorporation of short linear or branched side-chain sterols (C-22, n-C3, n-C4, i-C5) causes the broad component transition temperature and cooperativity to decrease dramatically, whereas the incorporation of medium- and long-chain sterols in both the n- and iso-series has less effect on the transition temperature and cooperativity of the broad component. Overall, no significant differences were found between the n- and iso-series sterols for a given side-chain length. A comparison of the phase behavior of dipalmitoylphosphatidylcholine (DPPC)/sterol (McMullen et al. (1995) Biophys. J. 69, 169-176) and SOPC/sterol mixtures indicates that the primary factor responsible for changes in the thermotropic phase behavior of these systems is the extent of the hydrophobic mismatch between the sterol and the host lipid bilayer. However, sterol miscibility in PC bilayers, and thus the stoichiometry of lipid-sterol interactions, also appears to depend on the degree of unsaturation of the host lipid bilayer.

Studies in red blood cell preservation 10. 51Cr recovery of red cells after liquid storage in a glycerol-containing additive solution

The purpose of the present study was to compare the 24-hour recovery of red blood cells stored for 9 weeks in a hypoosmolar additive solution containing 150 mM glycerol to cells stored in Adsol. Seven units of packed red cells were split into 2 aliquots. To one sample, 100 ml of the experimental additive solution (EAS 25) was added, and to the other, 50 ml of Adsol. At the end of the storage period the cells were labeled with 51Cr. A double chromium technique was used to make it possible to perform comparative autologous studies in the same donor. The 24-hour 51Cr recovery value for EAS 25 was 73.0 +/- (SD) 4.2% and for Adsol 60.9 +/- 7.1. At 9 weeks the adenosine triphosphate levels were not significantly better compared to Adsol but the other in vitro measurements were better. New approaches to the study of red cell preservation are suggested.

Effect of sterol structure on molecular interactions and lateral domain formation in monolayers containing dipalmitoyl phosphatidylcholine

Molecular associations between different sterols and dipalmitoyl phosphatidylcholine (DPPC) were examined in monolayers at the air/water interface. The sterols examined included cholesterol, 5-cholesten-3- one, 4-cholesten-3 beta-ol, 4-cholesten-3-one, cholesteryl acetate, and cholesteryl methyl-and ethyl ether. Information about the long-range order in pure sterol monolayers, as well as lateral domain-formation in mixed sterol/DPPC monolayers was obtained from the lateral miscibility or distribution of NBD-cholesterol (present at 0.5 mol%), as determined by monolayer epifluorescence microscopy. It was observed that the miscibility of NBD-cholesterol with the host sterol was limited in all monolayers except those of 5-cholesten-3-one and 4-cholesten-3-one, suggesting that only these monolayers lacked a long-range order present in the other sterol monolayers. Note that the term long-range order does not necessarily imply that the monolayer is solid. In mixed monolayers containing 3 beta-OH sterols and DPPC, cholesterol formed laterally condensed domains whereas 4-cholesten-3 beta-ol did not. This finding suggest that the sterols/DPPC interaction is sensitive to the position of the double-bond of the sterol molecule (delta 5 versus delta 4). Neither of the 3-keto sterols formed laterally condensed domains with DPPC. Cholesteryl acetate, however, formed lateral domains with DPPC which were in part similar to those seen in the cholesterol/DPPC system. The domains formed were circular, indicating their fluid nature. Mixed monolayers containing either of the ether sterol derivatives failed to produce clearly defined condensed domains with DPPC, although both mixed monolayers had a surface texture which suggested some degree of nonuniform distribution of the fluorescent probe. In summary, these novel results directly demonstrate the selective importance of both the delta 5 double bond, as well as of specific functional groups at the 3-position, for the molecular association with DPPC, and consequently for the formation of sterol/phospholipid-rich lateral domains.

In vitro modulation of rat adipocyte ghost membrane fluidity by cholesterol oxysterols

The effects of cholesterol and cholesterol-derived oxysterols (cholestanone, cholestenone, coprostanone and epicoprostanol) on adipocyte ghost membrane fluidity were studied using a fluorescence depolarization method. The fluorescence anisotropy of the treated membranes was determined using 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH). Cholestanone and cholesterol decreased membrane fluidity at both the concentrations tested (10 & 50 microM) while the rest of the sterols did not exert any significant effect on membrane fluidity. In the presence of epinephrine, cholestanone partitioned more towards the lipid core but cholesterol partitioning was not affected. The fusion activation energies (delta E) obtained for membranes preincubated with cholestanone (8.6 kcal/mol) and cholesterol (8.2 kcal/mol) were not significantly different from that of untreated membranes (8.3 kcal/mol). Membranes preincubated with cholestanone and cholesterol did not exhibit any change in lipid phase throughout the temperature range (10-45 degrees C) tested. The sterols were found to inhibit fisetin-induced phospholipid methylation in isolated rat adipocytes in the rank order of cholesterol > epicoprostanol > cholestanone = cholestenone = coprostanone, while basal methylation was unaffected. When adipocytes were preincubated with the sterols before the addition of fisetin, cholestanone and cholestenone showed 74% and 66% inhibition of maximal methylation respectively. These results indicated that cholesterol oxysterols interact differently with rat adipocyte membranes, with cholestanone interacting more with phospholipids located at the inner lipid bilayer (e.g. phosphatidylethanolamine) while cholesterol interacts more with phosphatidylcholine located at the outer lipid bilayer. This differential interaction may cause selective changes in membrane fluidity at different depths of the bilayer and thus may modulate the activities of membrane-bound proteins such as enzymes and receptors.

Differential scanning calorimetric study of the effect of sterol side chain length and structure on dipalmitoylphosphatidylcholine thermotropic phase behavior

We have investigated the thermotropic phase behavior of dipalmitoylphosphatidylcholine (DPPC) bilayers containing a series of cholesterol analogues varying in the length and structure of their alkyl side chains. We find that upon the incorporation of up to approximately 25 mol % of any of the side chain analogues, the DPPC main transition endotherm consists of superimposed sharp and broad components representing the hydrocarbon chain melting of sterol-poor and sterol-rich phospholipid domains, respectively. Moreover, the behavior of these components is dependent on sterol side chain length. Specifically, for all sterol/DPPC mixtures, the sharp component enthalpy decreases linearly to zero by 25 mol % sterol while the cooperativity is only moderately reduced from that observed in the pure phospholipid. In addition, the sharp component transition temperature decreases for all sterol/DPPC mixtures; however, the magnitude of the decrease is dependent on the sterol side chain length. With respect to the broad component, the enthalpy initially increases to a maximum around 25 mol % sterol, thereafter decreasing toward zero by 50 mol % sterol with the exception of the sterols with very short alkyl side chains. Both the transition temperature and cooperativity of the broad component clearly exhibit alkyl chain length-dependent effects, with both the transition temperature and cooperativity decreasing more dramatically for sterols with progressively shorter side chains. We ascribe the chain length-dependent effects on transition temperature and cooperativity to the hydrophobic mismatch between the sterol and the host DPPC bilayer (see McMullen, T. P. W., Lewis, R. N. A. H., and McElhaney, R. N. (1993) Biochemistry 32:516-522). Moreover, the effective stoichiometry of sterol/DPPC interactions is altered by a significantly large degree of hydrophobic mismatch between the sterol and the DPPC bilayer. Thus the short chain sterols appear to exhibit considerable immiscibility in gel state DPPC bilayers, effectively limiting their interaction with adjacent phospholipid molecules.

Binding and iron delivering of ovotransferrin to cholesterol-depleted chick-embryo red blood cells

Binding and iron delivering of ovotransferrin (OTf) were evaluated using 14-day old chick-embryo red blood cells (CERBC) and cholesterol-depleted by treatment with chicken egg phosphatidyl choline (E-PC) liposomes. Liposome-treated CERBC assayed for their cholesterol content showed a cholesterol depletion depending on the incubation time, being 25% (w/w) of the maximum cellular removal of cholesterol seen after 22 h incubation at 37 degrees C. Total phosphorus content did not change either for the various samples or during the different incubation times, indicating that specific cholesterol removal occurred, as confirmed also by the increased membrane fluidity revealed through fluorescence anisotropy measurements. The apparent dissociation constant (Kd) of control and treated CERBC was almost of the same value at the same incubation time, ranging from 0.30 microM after 0.25 h incubation to 0.19 microM after 14 or 22 h incubation. In all experiments, the maximum value of bound OTf molecules per cell (Bmax) notably decreased as incubation time increased. But, in cholesterol partly depleted CERBC, the decrease of the Bmax values was less pronounced as the incubation time increased. As far as binding experiments were concerned, iron uptake studies showed that uptaking capacities decreased as incubation time increased. Considering both binding and iron uptake, at the same incubation time, liposome-treated CERBC were slightly more efficient with respect to untreated samples. In any case a passive iron delivering could be evidenced after 22 h incubation. It is suggested that cholesterol may tune binding and iron uptake by either regulating or affecting the expression or mobility of the OTf receptor.

Comparative differential scanning calorimetric and FTIR and 31P-NMR spectroscopic studies of the effects of cholesterol and androstenol on the thermotropic phase behavior and organization of phosphatidylcholine bilayers

We have investigated the comparative effects of the incorporation of increasing quantities of androstenol and cholesterol on the thermotropic phase behavior of aqueous dispersions of members of a homologous series of linear saturated diacyl PCs1 using high sensitivity DSC. We have also employed FTIR and 31P-NMR spectroscopy to study the comparative effects of androstenol and cholesterol incorporation on the organization of the host PC bilayer in both the gel and liquid-crystalline states. The effects of androstenol and cholesterol incorporation on the thermotropic phase behavior of shorter chain PCs like 14:0 PC are generally similar but not identical. The incorporation of either sterol progressively decreases the temperature and enthalpy, but not the cooperativity, of the pretransition and completely abolishes it at sterol concentrations above 5 mol%. Moreover, at sterol concentrations of 1 to 20-25 mol%, both androstenol and cholesterol incorporation produce DSC endotherms consisting of superimposed sharp and broad components, the former due to the hydrocarbon chain melting of sterol-poor and the latter to the melting of sterol-rich 14:0 PC domains. The temperature and cooperativity of the sharp component are reduced slightly with increasing concentration of androstenol or cholesterol, and the enthalpy of the sharp component decreases progressively and becomes zero at 20-25 mol% sterol. As well, at cholesterol or androstenol concentrations above 20-25 mol%, the enthalpy of the broad component also decreases linearly with increasing sterol incorporation and becomes zero at sterol levels of about 50 mol%. However, whereas cholesterol incorporation progressively increases the temperature of the broad component of the DSC endotherm, androstenol incorporation decreases the temperature of this component. In contrast, the effects of androstenol and cholesterol incorporation on the thermotropic phase behavior of the intermediate and longer chain PCs studied here are considerably different. Although the incorporation of cholesterol increases the main phase transition temperature of 16:0 PC slightly and decreases the phase transition of 18:0 PC and 21:0 PC, androstenol incorporation decreases the main phase transition temperatures of all three PCs rather markedly. Moreover, androstenol is less effective in reducing the enthalpy and cooperativity of the broad component of the DSC endotherm of 16:0 PC and especially 18:0 PC bilayers in comparison to cholesterol. Androstenol incorporation (> 5 mol%) also results in the appearance of a second, low temperature endotherm in the DSC traces of the intermediate and longer chain PC dispersions that is not observed in similar cholesterol/PC dispersions. FTIR and 31P-NMR results suggest that this endotherm arises from a temperature-induced dissolution of androstenol in the gel phase PC bilayers. This second endotherm occurs at lower androstenol concentrations and increases in area at a given androstenol level as the chain length of the host PC bilayer increases. We ascribe the increasing immiscibility of androstenol in both the gel and liquid-crystalline states of PC bilayers of increasing thickness to an increasing degree of hydrophobic mismatch between the androstenol molecule and the host phospholipid bilayer.

Associations of serum total cholesterol, different types of stroke, and stenosis distribution of cerebral arteries. The Akita Pathology Study

BACKGROUND AND PURPOSE

The relation between serum total cholesterol levels and stroke is controversial. The Akita Pathology Study provides data on the association of serum total cholesterol, different types of stroke, and distribution of stenosis in cerebral arteries.

METHODS

The data are based on 750 autopsied men aged 30 years and older who were admitted to a local hospital in northeast Japan between 1966 and 1984. The overall autopsy rate was 88%. The grade of stenosis in the cerebral arteries was determined blindly by one pathologist using Baker's method for basal cerebral arteries (atherosclerosis scores) and using microscopic examination of a single basal ganglion slide for the intracerebral penetrating arteries (arteriolosclerosis scores).

RESULTS

The age-adjusted mean value of serum total cholesterol concentration was 164 mg/dL for cerebral hemorrhage, 177 mg/dL for infarction in penetrating artery regions, and 200 mg/dL for infarction in cortical artery regions. Mean serum cholesterol was lower in deaths caused by cerebral hemorrhage than in those caused by myocardial infarction and other cardiovascular disease. Mean atherosclerosis score of basal cerebral arteries was low for cerebral hemorrhage, intermediate for penetrating artery infarction, and high for cortical artery infarction. Stenosis of both basal and penetrating arteries was minimum or absent in cases of cerebral hemorrhage. Only the basal arteries were stenotic in cases of cortical artery infarction, whereas both basal and penetrating arteries were stenosed in cases of penetrating artery infarction. There were positive associations of serum cholesterol with stenosis of basal and penetrating arteries. Among cases of cerebral hemorrhage, serum total cholesterol levels were even lower in men with no significant stenosis in either basal or penetrating arteries than in men with stenosis in either type of artery.

CONCLUSIONS

The association of serum cholesterol with pathogenesis varies among stroke types. Elevated serum cholesterol levels were associated with the presence of cortical artery infarction, while low serum cholesterol levels were associated with cerebral hemorrhage.

The effect of dietary N-3 fatty acids on osmotic fragility and membrane fluidity of human erythrocytes

Sixteen healthy females were randomly assigned to receive fish oil or corn oil double blind in a 28 days intervention period. Osmotic fragility of erythrocytes was decreased in the fish-oil supplemented group and not affected in the corn-oil group. The decrease in osmotic fragility was maximal after 14 days and approached the pre-intervention level after 24 and 28 days of n-3 supplementation. No change was observed in erythrocyte membrane fluidity in either of the groups. The level of n-3 fatty acids increased significantly in erythrocytes from the fish oil supplemented subjects, mainly at the expense of linoleic acid (18:2, n-6) and oleic acid (18:1). No significant change was seen in the relative amount of arachidonic acid (20:4,n-6) or in the phospholipid/cholesterol ratio in erythrocytes, while the ratio between the sum of phoshatidylcholine and sphingomyeline/phosphatidylethanolamine (PC+SM/PE) increased during the intervention period. This study does not verify the hypothesis of a relationship between osmotic fragility and membrane fluidity. It is concluded that increased level of n-3 fatty acids in erythrocyte membranes decreases osmotic fragility, and that this effect is counteracted by increased PC+SM/PE ratio.

Report of the Conference on Low Blood Cholesterol: Mortality Associations

BACKGROUND

A National Heart, Lung, and Blood Institute (NHLBI) Conference was held October 9-10, 1990, to review and discuss existing data on U-shaped relations found between mortality rates and blood total cholesterol levels (TC) in some but not other studies. Presentations were given from 19 cohort studies from the United States, Europe, Israel, and Japan. A representative of each study presented its findings and also submitted tables of proportional hazards regression coefficients for entry TC levels in regard to death, and these were incorporated into a formal statistical overview adjusted for age, diastolic blood pressure, cigarette smoking, body mass index, and alcohol intake, as available.

METHODS AND RESULTS

The U-shape for total mortality in men and the flat relation in women resulted largely from a positive relation of TC with coronary heart disease death and an inverse relation with deaths caused by some cancers (e.g., lung but not colon), respiratory disease, digestive disease, trauma, and residual deaths. Risk for combined noncardiovascular, noncancer causes of death decreased steadily across the range of TC. The conference considered possible explanations for the statistical associations found between low TC levels or active TC lowering and certain causes of death. One is that TC is lowered by some disease conditions themselves, such as wasting in chronic pulmonary disease or reduced production and secretion of cholesterol-bearing lipoproteins with liver disease. In this sort of situation, the TC:mortality association found in observational studies may be due to preexisting disease. This was addressed by excluding early deaths from the analysis, which did not change the results. The conference considered as well the biological function of cholesterol, which, if seriously deranged, might hypothetically cause a wide variety of diseases and dysfunction. The conference also considered the biological functions that might provide plausible mechanisms for the associations found.

CONCLUSIONS

Definitive interpretation of the associations observed was not possible, although most participants considered it likely that many of the statistical associations of low or lowered TC level are explainable by confounding in one form or another. The conference focused on the apparent existence and nature of these associations and on the need to understand their source rather than on any pertinence of the findings for public health policy. Further research is recommended to explain the observed associations of low TC levels (and TC lowering) with certain noncardiovascular diseases. This includes studies of the time course of TC change in disease, the relation of TC to morbidity, further studies of possible epidemiological confounding, monitoring of population trends in TC and mortality, further studies of the relations in women, auditing of noncardiovascular events in trials, studies of cell membrane, genetic and molecular links to cholesterol metabolism, TC level and disease, studies of disease manifestations in specific lipid disorders, and further study of the proposed causal mechanisms linking low TC and hemorrhagic stroke.

Sterically stabilized liposomes

Many recent reports have demonstrated that rapid uptake of liposomes in vivo by cells of the mononuclear phagocytic system (MPS), which has restricted their therapeutic utility, can be overcome by incorporation of lipids derivatized with the hydrophilic polymer polyethylene glycol (PEG). The structure-function relationship of PEG-derivatized phosphatidylethanolamine (PEG-PE) has been examined by measurement of blood lifetime and tissue distribution in both mice and rats. The results are reviewed and contrasted with those from liposomes without PEG-PE or other surface modifications. With a PEG molecular weight in the range of 1000 to 5000, prolonged circulation and reduced MPS uptake is achieved. After 24 h, up to 35% of the injected dose remains in the blood and less than 10% is taken up by the two major organs of the MPS, liver and spleen, compared with 1% and up to 50%, respectively, for liposomes without PEG-PE. Other important advantages of PEG-PE have been identified: prolonged circulation is independent of liposome cholesterol content, degree of hydrocarbon chain saturation in either the PC or the PE lipid anchor, lipid dose, or addition of most other negatively charged lipids. This versatility in lipid composition and dose is important for controlling drug release in a liposome-based therapeutic agent. Steric stabilization has been proposed as a theoretical basis for the results and some initial results testing this hypothesis have been reported. A description of a theoretical model is presented here and evaluated with the data available. The results are compared with other particulate drug carriers and the range of potential applications are considered.

Effects of temperature and pH on osmotic fragility of erythrocytes of the domestic fowl (Gallus domesticus) and guinea-fowl (Numida meleagris)

The effects of temperature and pH on the osmotic behaviour of erythrocytes of the domestic fowl and guinea-fowl were studied. Erythrocytes of the guinea-fowl were observed to be more osmotically fragile than those of the domestic fowl at 29 degrees C and pH 7.7. The osmotic fragility of erythrocytes of both species decreased as the temperature (at constant pH of 7.7) or pH (at constant temperature of 29 degrees C) increased. The erythrocyte count, packed cell volume, haemoglobin concentration and mean corpuscular volume were identical in both species.

Mitochondrial and microsomal cholesterol mobilization after oxidative stress induced by adriamycin in rats fed with dietary olive and corn oil

The influence of three different dietary fats (8%) and of endogenous lipid peroxidation with regard to cholesterol concentrations in liver mitochondria and microsomes and in serum has been investigated in the rat. Although the different diet fat used did not produce any effect on serum cholesterol, it was possible to show that each experimental diet differently influenced the microsomal and mitochondrial levels of cholesterol. The highest mitochondrial and microsomal cholesterol content was found in case of diet supplemented with virgin olive oil and the lowest with rectified olive oil. An endogenous oxidative stress induced by adriamycin was able to produce a clear decrease in microsomal and mitochondrial cholesterol level and a sharp increase in serum concentration in all three groups. However, dietary fats and adriamycin had no effect on the microsomal and mitochondrial membrane viscosity as detected by fluorescence polarization. These results are consistent with the hypothesis that mitochondrial and microsomal cholesterol can exchange with exogenous pools when phospholipid peroxidation occurs.

Interaction of cholesterol with synthetic sphingomyelin derivatives in mixed monolayers

To study the structural requirements of the molecular interactions between cholesterol and sphingomyelins in model membranes, sphingomyelin derivatives were synthesized in which (a) the 3-hydroxy group was replaced with a hydrogen atom or with a methoxy, ethoxy, or tetrahydropyranyloxy group, (b) the N-acyl chain length was varied, and (c) the N-acyl chain length contained an alpha-hydroxy group. The chemical syntheses of these derivatives from DL-erythro-sphingosine are reported. The properties of these sphingomyelin derivatives were examined in monolayer membranes at the air/water interface. The mean molecular area of the pure N-stearoylsphingomyelin derivatives was determined, and the effects of cholesterol on the condensation of sphingomyelin packing in the monolayer were recorded. It was observed that replacement of the 3-hydroxy group of sphingomyelin with a hydrogen atom or its substitution with a methoxy or ethoxy group did not affect the ability of cholesterol to condense the molecular packing in monolayers. Even when a bulky tetrahydropyranyloxy group was introduced at the 3-hydroxy position of egg sphingomyelin, cholesterol was still able to condense the molecular packing of this derivative. The condensing effect of cholesterol on derivatives of N-stearoyl-SPMs was significantly larger than the comparable effect observed with 1,2-distearoyl-sn-glycero-3-phosphocholine or 1,2-dipalmitoyl-sn-glycero-3-phosphocholine. Our results with 3-hydroxysphingomyelins having differing N-acyl chain lengths (i.e., N-stearoyl, N-myristoyl, and N-lauroyl), and with 3-hydroxy-N-(alpha-hydroxypalmitoyl)sphingomyelin also indicated that cholesterol was able to induce condensation of the molecular packing.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of membrane cholesterol levels: effects on endothelial cell function

The endothelial cell lining of blood vessels is now recognized as an active interface between blood and the underlying tissue. Modulation of cholesterol levels in several cell types has resulted in altered cell function. We have removed cholesterol from the endothelial cell membrane and have observed corresponding alterations in endothelial cell function. Following depletion of cholesterol from the endothelial cells, polymorphonuclear leukocyte adhesion to the cells was decreased. Angiotensin-converting enzyme activity of the endothelial cells was increased following removal of cholesterol from the endothelial cell membranes. The results of fluorescence polarization measurements suggest that these changes may be partially explained by altered membrane order.

Electron spin resonance studies of erythrocyte membrane in spinocerebellar degeneration

Erythrocyte membrane fluidity was examined by electron spin resonance spectra using nitroxide fatty acid spin labels in spinocerebellar degeneration (SCD). Subjects with SCD, motor neuron disease (MND) and controls did not differ in fluidity of the deep site (hydrophobic region) of the erythrocyte membrane. However, the fluidity of the shallow site (hydrophilic region) in the erythrocyte membrane was significantly less fluid in SCD than in controls and MND (outer hyperfine splitting of 5-nitroxide stearic acid: SCD 54.70 +/- 0.43 G, controls 53.57 +/- 0.41 G, MND 53.54 +/- 0.35 G, P less than 0.001). Serum HDL-cholesterol and membrane fluidity correlated significantly in controls, but not in SCD. A significant negative correlation between age and membrane fluidity was found in SCD, but not in controls. These data suggest that membrane abnormality exists in SCD and may be concerned with aging.

Serum cholesterol levels and six-year mortality from stroke in 350,977 men screened for the multiple risk factor intervention trial

We examined the relation between the serum total cholesterol level and the risk of death from stroke during six years of follow-up in 350,977 men, 35 to 57 years of age, who had no history of heart attack and were not currently being treated for diabetes mellitus. The diagnosis of stroke and the type of stroke were obtained from death certificates. Using proportional-hazards regression to control for age, cigarette smoking, diastolic blood pressure, and race or ethnic group, we found that the six-year risk of death from intracranial hemorrhage (International Classification of Diseases, ninth edition [ICD-9], categories 431 and 432) was three times higher in men with serum cholesterol levels under 4.14 mmol per liter (160 mg per deciliter) than in those with higher cholesterol levels (P = 0.05 by omnibus test across five cholesterol levels). On the other hand, a positive association was observed between the serum cholesterol level and death from nonhemorrhagic stroke (P = 0.007). The inverse association of the serum cholesterol level with the risk of death from intracranial hemorrhage was confined to men with diastolic blood pressure greater than or equal to 90 mm Hg, in whom death from intracranial hemorrhage is relatively common. We conclude that there is an inverse relation between the serum cholesterol level and the risk of death from hemorrhagic stroke in middle-aged American men, but that its public health impact is overwhelmed by the positive association of higher serum cholesterol levels with death from nonhemorrhagic stroke and total cardiovascular disease (ICD-9 categories 390 through 459).

Trends for coronary heart disease and stroke and their risk factors in Japan

Disease surveillance and population surveys of risk characteristics in a northeast rural community of Japan (1965 census population, 7,030) are combined in an attempt to relate morbidity and risk factor trends for coronary heart disease and stroke during the last 2 decades. Between 1964 and 1983, the incidence of coronary heart disease (i.e., combined myocardial infarction, angina pectoris, and sudden death) did not change significantly among men and women ages 40-69, and was lower than that for stroke. The incidence of all stroke declined about 60% for both men and women, ages 40-69, with a significant decrease in cerebral hemorrhage for both sexes and in cerebral infarction for men. Between 1963-1966 and 1980-1983, significant upward shifts occurred in the means and distributions of serum total cholesterol and serum total protein in every age and sex group, primarily during the 1st decade. Age-adjusted mean cholesterol levels rose 22 mg/dl to the 1980-1983 mean of 179 mg/dl in men ages 40-69. In women ages 40-69, the mean rose 29 mg/dl to 192 mg/dl. Among nutrients, animal fat intake doubled in men ages 40-59 from 4.5% of daily calories in 1969 to 9.6% in 1980-1983. Animal protein intake also increased, from 5.8% to 7.1%. Most of this increase occurred between 1969 and 1972-1975 and may be attributable to an increased intake of meat, eggs and dairy products. From 1963-1966 to 1980-1983, mean relative weight index rose significantly for all age-sex groups except men ages 50-69. Mean systolic and diastolic blood pressure levels declined for every age-sex group, with a 15-mm Hg age-adjusted decrease in systolic, 4-mm Hg decrease in diastolic pressure among men ages 40-69, and a 11-mm Hg systolic and 4-mm Hg diastolic decrease for women. Two cohorts of men and women ages 40-69 at baseline were followed for disease incidence: an early cohort (2,257 persons) followed from 1963-1966 to 1973 and a later cohort (2,711 persons) followed from 1972-1975 to 1983. In these cohorts, significant risk prediction for cerebral hemorrhage and infarction was obtained with blood pressure level and end organ effects in the electrocardiogram and fundus photographs. Serum cholesterol was inversely associated with cerebral hemorrhage in the early cohort but not in the later.(ABSTRACT TRUNCATED AT 400 WORDS)

Liposome-encapsulated hemoglobin as an artificial red blood cell: characterization and scale-up

Encapsulation methods using high pressure extrusion and homogenization were developed which produce hemoglobin-containing liposomes, approximately one micron or less in diameter with an oxygen-carrying capacity of more than half that of red blood cells (RBCs). These methods were developed for scaling-up liposome-encapsulated hemoglobin (LEH) production. Previously, the lack of adequate scale-up methods has been a serious barrier to full scale efficacy and toxicity testing for all the researchers engaged in such investigations. The scale-up methods and characterization of the resulting LEH preparations are presented.

Equilibrium uptake of D-glucose by osmotically stressed unilamellar phospholipid vesicles

The assumptions inherent in the use of osmotic manipulation to determine the extent of solute binding to brush border membrane vesicles (the ideal osmotic responsiveness of the vesicles and the independence of solute binding from the incubation medium osmotic pressure) were examined in a model system (large unilamellar lipid vesicles). The equilibrium uptake of D-glucose by unilamellar vesicles composed of egg lecithin (PC), phosphatidic acid (PA), and cholesterol (Chol) was measured as a function of the osmotic concentration of the incubation medium. The variation of the encapsulated aqueous volume of PC:PA and PC:PA:Chol vesicles with the osmotic stress was directly determined by a fluorescence self-quenching technique. Encapsulated volume changes of both PC:PA and PC:PA:Chol vesicles were found to be resistant to the osmotic stress, exhibiting positive deviations from ideal behavior. Equilibrium uptake experiments with these vesicles showed that glucose was taken up in excess of that amount predicted on the basis of the encapsulated volume when the vesicles were subjected to osmotic stress less than 0.25 osmol/kg. At osmotic stresses greater than 0.75 osmol/kg, equilibrium uptake could be predicted solely on the basis of the encapsulated volume. These results, based on a model vesicle system, strongly suggest that osmotic manipulation may be an inappropriate method to assess the extent of solute binding to natural membrane vesicle preparations, such as brush border membrane vesicles, without more direct evidence.

Calcium diphosphatidate membrane traversal is inhibited by common phospholipids and cholesterol but not by plasmalogen

Phosphatidate-mediated Ca2+ membrane traversal is inhibited by phospholipids (PL) such a phosphatidylcholine (PC), phosphatidylinositol (PI), phosphatidylserine (PS), sphingomyelin and lysoPC, but not by PC-plasmalogen. Kinetics of Ca2+ traversal through a 'passive' bilayer consisting of OH-blocked cholesterol show competition between PC and phosphatidic acid (PA); it appears likely that a Ca(PA.PC) complex is formed which is not a transmembrane ionophore but will reduce the amount of phosphatidic acid available for the formation of the ionophore, Ca(PA)2. PS and PI may inhibit Ca2+-traversal in the same manner by forming Ca(PA.PL) complexes. We suggest that PC-plasmalogen, with one of the Ca2+-chelating ester CO groups missing, cannot engage in calcium cages, i.e., Ca(PA.PL) complexes, and thus does not interfere with Ca(PA)2 formation. Double-reciprocal plotting of Ca2+ traversal rates in cholesterol-containing liposomes vs. calcium concentration suggests that cholesterol inhibits Ca2+ traversal by competing with Ca2+ for PA. The inhibition does not seem to be caused by a restructuring or dehydration of the membrane 'hydrogen belts' affected by cholesterol; most probably, it is due to hydrogen bonding of the cholesterol-OH group to a CO group of PA; this reduces the amount of PA available for the calcium ferry. The inhibition by sphingomyelin and lysoPC may also be explained by their OH group interacting with PA via hydrogen bonding. The pH dependence of Ca2+ traversal suggests that H[Ca(PA)2]- can serve as Ca2+ cross-membrane ferry but that at physiological pH, [Ca(PA)2]2- is the predominant ionophore. In conclusion, the results indicate that Ca2+ traversal is strongly dependent on the structure of the hydrogen belts, i.e., the membrane strata occupied by hydrogen bond acceptors (CO of phospholipids) and donors (OH of cholesterol, sphingosine), and that lipid hydrogen belt structures may regulate storage and passage of Ca2+.

Sterol depletion reduces receptor-mediated low-density lipoprotein binding in NS-1 mouse myeloma cells

NS-1 mouse myeloma cells, a cholesterol auxotrophic cell line with a lesion in the cholesterol biosynthetic pathway at the demethylation of lanosterol to C-29 sterol, were depleted of cholesterol by incubation in cholesterol-free medium for 24 to 48 h. The low-density lipoprotein receptor activities in untreated and in cholesterol-depleted cells were then compared. The cholesterol-depleted NS-1 cells consistently exhibited a 75 to 90% reduction in receptor-mediated low-density lipoprotein binding compared to untreated cells. The decline of the low-density lipoprotein binding of cholesterol-free medium-incubated NS-1 cells was prevented by addition of free cholesterol or its biosynthetic intermediate, demosterol, to the medium. The addition of lanosterol, an intermediate upstream to the lesion site in the cholesterol biosynthetic pathway, was completely ineffective. The results indicate that proper membrane cholesterol content is necessary for the maintenance of normal low-density lipoprotein receptor function in NS-1 cells.

Lipid acyl chain-dependent effects of sterols in Acholeplasma laidlawii membranes

Acholeplasma laidlawii was grown with different fatty acids for membrane lipid synthesis (saturated straight- and branched-chain acids and mono- and di-unsaturated acids). The ability of 12 different sterols to affect cell growth, lipid head group composition, the order parameter of the acyl chains, and the phase equilibria of in vivo lipid mixtures was studied. The following two effects were observed with respect to cell growth: with a given acyl chain composition of the membrane lipids, growth was stimulated, unaffected, reduced, or completely inhibited (lysis), depending on the sterol structure; and the effect of a certain sterol depended on the acyl chain composition (most striking for epicoprostanol, cholest-4-en-3-one, and cholest-5-en-3-one, which stimulated growth with saturated acyl chains but caused lysis with unsaturated chains). The three lytic sterols were the only sterols that caused a marked decrease in the ratio between the major lipids monoglucosyldiglyceride and diglucosyldiglyceride and hence a decrease in bilayer stability when the membranes were enriched in saturated (palmitoyl) chains. With these chains correlations were found for several sterols between the glucolipid ratio and the order parameter of the acyl chains, as well as the lamellar-reversed hexagonal phase transition, in model systems. A shaft experiment revealed a marked decrease in the ratio of monoglucosyldiglyceride to diglucosyldiglyceride with the lytic sterols in unsaturated (oleoyl) membranes. The two cholestenes induced nonlamellar phases in in vivo mixtures of oleoyl A. laidlawii lipids. The order parameters of the oleoyl chains were almost unaffected by the sterols. Generally, the observed effects cannot be explained by an influence of the sterols on the gel-to-liquid crystalline phase transition.