Rheological properties and membrane fluidity of red blood cells and platelets in primary hyperlipoproteinemia

Age-related and atherosclerosis-related erythropathy in ApoE/LDLR-/- mice

In this work we applied a multimodal approach to define the age- and atherosclerosis-related biochemical and functional alterations in red blood cells (RBCs) in ApoE/LDLR^-/- mice. Our results revealed that age-related changes in RBCs, such as decreases in RBC deformability and mean height, were more pronounced in ApoE/LDLR^-/- mice than in age-matched control mice (C57BL/6J). The decreases in phospholipid content and level of lipid unsaturation were accompanied by an increase in cholesterol esters and esterified lipids in RBC membranes in aged C57BL/6J mice. The age-related decrease in the phospholipid content was more pronounced in ApoE/LDLR^-/- mice. In contrast, the increase in the total lipid content in RBC membranes occurred only in ApoE/LDLR^-/- mice with advanced atherosclerosis. The age-related alterations also included a decrease in the ratio of turns to α-helices in the secondary structure of hemoglobin (Hb) inside intact RBCs. On the other hand, an increase in the ratio of unordered conformations to α-helices of Hb was observed only in ApoE/LDLR^-/- mice and occurred already at the age of 5-weeks. This was related to hypercholesterolemia and resulted in an increased oxygen-carrying capacity. In conclusion, progressive mechanical and functional alterations of RBCs in aged ApoE/LDLR^-/- mice were more pronounced than in age-matched C57BL/6J mice. Although, several biochemical changes in RBCs in aged ApoE/LDLR^-/- mice recapitulated age-dependent changes observed in control mice, some biochemical features of RBC membranes attributed to hypercholesterolemia were distinct and could contribute to the accelerated deterioration of RBC function in ApoE/LDLR^-/- mice.

Molecular rotors report on changes in live cell plasma membrane microviscosity upon interaction with beta-amyloid aggregates

Amyloid deposits of aggregated beta-amyloid Aβ(1-42) peptides are a pathological hallmark of Alzheimer's disease. Aβ(1-42) aggregates are known to induce biophysical alterations in cells, including disruption of plasma membranes. We investigated the microviscosity of plasma membranes upon interaction with oligomeric and fibrillar forms of Aβ(1-42). Viscosity-sensing fluorophores termed molecular rotors were utilised to directly measure the microviscosities of giant plasma membrane vesicles (GPMVs) and plasma membranes of live SH-SY5Y and HeLa cells. The fluorescence lifetimes of membrane-inserting BODIPY-based molecular rotors revealed a decrease in bilayer microviscosity upon incubation with Aβ(1-42) oligomers, while fibrillar Aβ(1-42) did not significantly affect the microviscosity of the bilayer. In addition, we demonstrate that the neuroprotective peptide H3 counteracts the microviscosity change induced by Aβ(1-42) oligomers, suggesting the utility of H3 as a neuroprotective therapeutic agent in neurodegenerative disorders and indicating that ligand-induced membrane stabilisation may be a possible mechanism of neuroprotection during neurodegenerative disorders such as Alzheimer's disease.

Maintenance of Membrane Integrity and Permeability Depends on a Patched-Related Protein in Caenorhabditis elegans

Membrane integrity is critical for cell survival, defects of which cause pathological symptoms such as metabolic diseases. In this study, we used ethanol sensitivity of the nematode Caenorhabditis elegans to identify genetic factors involved in membrane integrity. InC. elegans, acute exposure to a high concentration (7% v/v) of ethanol changes membrane permeability, as measured by propidium iodide staining, and causes paralysis. We used the timing of complete paralysis as an indicator for alteration of membrane integrity in our genetic screen, and identified ptr-6 as a gene that confers ethanol resistance when mutated. PTR-6 is a patched-related protein and contains a sterol sensing domain. Inhibition of two PTR-encoding genes,ptr-15 and ptr-23, and mboa-1, encoding an Acyl Co-A: cholesterol acyltransferase homolog, restored ethanol sensitivity of the ptr-6 mutant, suggesting that these ptr genes and mboa-1 are involved in the maintenance of membrane integrity and permeability. Our results suggest that C. elegans can be used as a model system to identify factors involved in metabolic diseases and to screen for therapeutic drugs.

Estimation of cell membrane properties and erythrocyte red-ox balance in patients with metabolic syndrome

Metabolic syndrome (MS) is associated with occurrence of the many cardiovascular risk factors such as atherogenic dyslipidemia, visceral fat distribution, arterial hypertension and pro-thrombotic and pro-inflammatory status. In our study the effect of disorders that appear in MS on red-ox balance and erythrocyte cell membrane properties were estimated. The study comprised 50 patients with diagnosed MS and in 25 healthy subjects. Content of thiobarbituric acid reactive substances (TBARS) and catalase, superoxide dismutase and glutathione peroxidase activity were estimated in red blood cells. Moreover, conformation status of membrane proteins, membrane fluidity and osmotic fragility were evaluated. MS was found to manifest: (1) the increase of the concentration of TBARS in erythrocytes with no statistically significant differences in antioxidant enzymes activity, (2) disorders in the structure of erythrocyte cytoskeleton proteins, (3) the increase in membrane lipids fluidity at the depth of 5th and 12th carbon atom of fatty acid hydrocarbon chain and significantly decreased fluidity at the depth of 16th carbon atom, (4) increased erythrocyte osmotic fragility.

Behaviour of human erythrocyte aggregation in presence of autologous lipoproteins

The aim of this work was to evaluate in vitro the effect of autologous plasma lipoprotein subfractions on erythrocyte tendency to aggregate. Aliquots of human blood samples were enriched or not (control) with their own HDL-C, LDL-C, or VLDL-C fractions obtained from the same batch by density gradient ultracentrifugation. Plasma osmolality and erythrocyte aggregation index (EAI) were determined. Blood aliquots enriched with LDL-C and HDL-C showed significant higher EAI than untreated aliquots, whereas enrichment with VLDL-C does not induce significant EAI changes. For the same range of lipoprotein concentrations expressed as percentage of osmolality variation, the EAI variation was positive and higher in presence of HDL-C than upon enrichment with LDL-C (P < 0.01). Particle size, up to LDL diameter values, seems to reinforce erythrocyte tendency to aggregate at the same plasma osmolality (particle number) range of values.

Damage to the structure of erythrocyte plasma membranes in patients with type-2 hypercholesterolemia

BACKGROUND

Hypercholesterolemia may decrease the deformability of red blood cells which impairs their hemorheological behavior and promotes atherosclerosis. The study involved 60 hypercholesterolemic patients and 30 healthy individuals as the control group.

METHODS

The membrane fluidity of erythrocytes was estimated by a spin-label method (5-doxylstearic acid (5-DSA)). The ratio of weakly to strongly (W/S) immobilized residues of erythrocyte membrane-bond maleimide-tempo spin label was studied in oxidative damage to membrane protein. Damage to erythrocyte proteins was also indicated by means of Na(+) K(+) ATPase activity.

RESULTS

The membranes of hyperlipidemia (hlp) patients contain larger concentrations of cholesterol 2.16+/-0.24 than do those of the normolipemic individuals 0.31+/-0.24 (P<0.001). The level of Na(+) K(+) ATPase in the erythrocyte membrane from the control group was higher 103.4+/-1.3 (nmolPi/(mgproteinsh)) than in the patient group 93.6+/-3.2 (nmolPi/(mgproteinsh)) (P<0.001). The order parameter S 5-DSA in the control group was 0.745+/-0.009 and in hlp patients was 0.755+/-0.009 (P<0.001). The W/S ratio in the control group amounted to 2.00+/-0.09 and in the hlp patient group was 2.50+/-0.11 (P<0.001).

CONCLUSION

Type-2 hypercholesterolemia causes changes in the structure and fluidity of erythrocyte plasma membranes since the excess of cholesterol affects the normal rheology of blood through its interaction with erythrocytes. It also impairs the function and structure of plasma membrane proteins.

Membrane microviscosity, blood pressure and cytosolic pH in Dahl rats: the influence of plasma lipids

OBJECTIVE

To determine the relationships between blood pressure, membrane microviscosity, plasma lipids and cytosolic pH in Dahl rats susceptible or resistant to salt hypertension.

DESIGN AND METHODS

Blood pressure, plasma triglycerides and total cholesterol, platelet cytosolic pH (pHi) and the microviscosity of both outer membrane leaflet (TMA-DPH fluorescence anisotropy) and membrane lipid core (DPH fluorescence anisotropy) were studied in platelets and erythrocyte ghosts of Dahl salt-sensitive (SS/Jr) and salt-resistant (SR/Jr) rats fed either a low-salt diet (0.3% NaCl) until the age of 9, 15 or 24 weeks or a high-salt diet (4% NaCl) for 5 or 10 weeks after weaning.

RESULTS

At low salt intake, DPH but not TMA-DPH anisotropy increased with age in platelets of SS/Jr rats. Chronic high salt intake was accompanied by an increase of DPH anisotropy in platelets but not in erythrocyte ghosts of SS/Jr rats. Platelet DPH anisotropy correlated positively with blood pressure of salt-loaded SS/Jr rats. Chronic high salt intake also reduced pHi in platelets, the regulation of which seemed to be related to the changes in TMA-DPH anisotropy. This especially concerns the thrombin-induced pHi rise which was inversely related to basal pHi, plasma lipids and TMA-DPH anisotropy. Altered membrane lipid composition might be the underlying mechanism because both membrane microviscosity and platelet pHi regulation were reported to correlate significantly with plasma triglycerides and/or cholesterol.

CONCLUSIONS

Platelets of salt hypertensive Dahl rats are characterized by an increased microviscosity of membrane lipid core which correlated positively with blood pressure. The major influence of plasma triglycerides on DPH anisotropy should be taken into consideration when investigating the links between membrane microviscosity and blood pressure. On the other hand, the changes in microviscosity of the outer membrane leaflet might be involved in pHi regulation (probably through control of the Na+/H+ exchanger).

Effect of dietary versus pharmacological correction of hypertriglyceridemia on red blood cell membrane sodium/lithium countertransport activity

An elevated red blood cell Na/Li countertransport (Na/Li CT) is often associated with high blood pressure and metabolic abnormalities. Recent studies suggested that a reduction in serum TG levels is associated with a decrease in Na/Li CT activity. However, it is still unclear if this phenomenon could be originated from systemic metabolic alterations or from modifications of the membrane dynamic properties. Aim of the present study was to investigate whether dietary or pharmacological TG lowering therapy might have a different effect on Na/Li CT activity and related metabolic parameters. Twenty normotensive hyper-TG patients were recruited from the Lipid outpatient Clinic: they had a baseline Na/Li CT activity significantly higher compared with age- and BMI-matched normolipidemic controls (386+/-33 vs 274+/-39 umol/l RBC/h, p<0.05). The patients were randomly prescribed one of the following two-months treatment: Group 1)-triglyceride lowering diet; Group 2)-lipid lowering drug (Gemfibrozil 600 mg b.i.d.). Na/Li CT and metabolic and anthropometric variables were measured at baseline and after 1 and 2 months of treatment. At the end of intervention, there was in both groups a significant and comparable fall in plasma triglyceride (group 1: -2.61+/-0.73 mmol/l p<0.01; group 2: -4.29+/-1.20 mmol/l p<0.01). In the diet-treated group there were, in addition small but significant reductions in body weight (-3.7+/-0.8 kg p<0.01), fasting glucose (-0.36+/-0.14 mmol/l p<0.05) and insulin levels (-2.1+/-0.5 mU/l, p<0.01), while no such changes were observed in the fibrate treated patients. Na/Li CT activity was significantly and comparably reduced at the end of treatment in both groups (group 1: -97+/-28 umol/l cell/h, p<0.01; group 2: -89+/-30 umol/l cell/h, p<0.01). In conclusion, these results indicate that the decrease in Na/Li CT associated with both dietary and drug treatment of hypertriglyceridemia is to be traced to a direct effect of plasma TG concentration on this transport system (probably as a result of modification in the membrane lipid environment) rather than to changes in plasma insulin levels or insulin resistance.

Erythrocyte membrane cholesterol/phospholipid changes and hemorheological modifications in familial hypercholesterolemia treated with lovastatin

Fourteen patients with familial hypercholesterolemia treated with lovastatin (40 mg/day) for three months were studied to find out whether the expected changes in plasma lipids are accompanied by modifications in the lipid composition of the erythrocyte membrane and whether these in turn induce changes in the rheological behavior of the red blood cell. Our results demonstrate the efficacy of lovastatin in reducing the plasma concentration of cholesterol and LDL cholesterol. The changes observed in the plasma lipids correlate with a significant decrease in the cholesterol/phospholipid ratio of the red blood cell membrane, from 1.19 +/- 0.19 in a basal situation to 0.92 +/- 0.23 (p < 0.01) at the end of treatment. These changes in the lipid composition of the cell are statistically related to a decrease in erythrocyte aggregability and an improvement in blood filterability, which means beneficial change in the patients' hemorheological situation.

Cell calcium handling and intracellular pH regulation in hereditary hypertriglyceridemic rats: reduced platelet response to thrombin stimulation

Multiple cell membrane alterations have been described in humans and animals with various genetic forms of hypertension and/or dyslipidemia. The aim of our study was to characterize some properties of platelets and/or erythrocytes (cytosolic calcium handling, intracellular pH regulation and thrombin responsiveness) in a new model of genetic hypertension associated with hyperlipidemia-Prague hereditary hypertriglyceridemic (HTG) rats. There were no differences in basal cytosolic Ca2+ values in platelets or erythrocytes of HTG rats and control Wistar rats. Ca2+ influx into erythrocytes was also similar in HTG and control rats. In both strains Ca2+ influx correlated positively with plasma triglycerides. The slope of this relationship was less steep in HTG than in Wistar rats. Cytosolic Ca2+ response to thrombin stimulation was smaller in HTG platelets, which were also characterized by a major reduction of thrombin-induced Mn2+ entry through receptor-operated Ca2+ channels. Platelets of HTG rats had the same basal intracellular pHi values and similar buffering capacity as control rats but their pHi response to thrombin stimulation was substantially reduced. It can be concluded that reduced responsiveness to thrombin stimulation is a major alteration found in platelets of hypertensive hereditary hypertriglyceridemic rats.

Sphingomyelinase and cell-permeable ceramide analogs increase the release of plasminogen activator inhibitor-1 from cultured endothelial cells

We investigated the effect of exogenous staphylococcal sphingomyelinase (SMase) on the release of tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1) from cultured human umbilical vein endothelial cells (HUVEC). Addition of SMase (2 units/ml) to the culture medium induced an approx. 15-fold increase in the extracellular level of PAI-1 antigen at 3 h. No significant increase in the level of t-PA antigen was detected. Treatment of HUVEC with SMASE (2 units/ml) for 3 h resulted in a significant decrease in the cellular sphingomyelin (SM) level, accompanied by a corresponding increase in the ceramide level. Cell-permeable ceramide analogs also enhanced the release of PAI-1 from cultured HUVEC in concentration- and time-dependent manners. A 6-fold increase in PAI-1 antigen level was observed after incubation for 3 h with 10 microM N-acetylsphingosine. Similar effect was noted as early as 2 h with 10 microM N-hexyanoylsphingosine. Addition of sphingosine failed to affect the release of PAI-1 from cultured HUVEC, indicating that the effects of ceramide analogs were independent of sphingosine generation. Pretreatment with cycloheximide or actinomycin D abated the response of HUVEC to N-acetylsphingosine in the increased levels of both extracellular and intracellular PAI-1. These results suggest that ceramide, generated via "SM cycle", acts as a lipid mediator of PAI-1 release from vascular endothelial cells, and may contribute to a better understanding of the pathogenesis of the PAI-1-associated thrombotic disorders.

Erythrocyte membrane fatty acid composition as a marker of dietary compliance in hyperlipidaemic subjects

Dietary intervention is the first treatment step in management of hyperlipidaemia, but there are few objective criteria of compliance. Whether intensive dietary intervention would produce a detectable change in erythrocyte membrane fatty acid composition which could be used as a marker of compliance was examined in 31 new hyperlipidaemic patients. Over a 6 month period, body mass index fell from 29.0 to 26.9 kg/m2 (P < 0.001) and total cholesterol by 19% from 8.16 to 6.58 mmol/l (P < 0.001). The energy derived from fat was reduced from 38.5% to 29.6% (P < 0.001), and the ratio of dietary polyunsaturated to saturated (P:S) fatty acids in the diet increased from 0.45 to 0.66 (P < 0.01). Small but significant changes were recorded in several red cell membrane fatty acids, and the P:S ratio increased from 0.91 to 1.13 (P < 0.001). It would appear, therefore, that red cell membrane changes parallel dietary changes and hence are a potential marker for compliance with dietary changes.

Insulin Receptor Processing and Lipid Composition of Erythrocyte Membrane in Patients with Hyperlipidemia

The aim of this study was to determine whether the common forms of dyslipidemia could affect either the lipid composition or insulin receptor processing (down-regulation) of erythrocytes. The study included 22 patients with type IIa hypercholesterolemia, 15 patients with type IV hypertriglyceridemia and 12 patients with type IIb hyperlipidemia. Ten normolipidemic subjects were used as controls. Their erythrocyte membranes were analyzed for lipid composition and insulin receptor down-regulation. The results show that all the hyperlipidemias investigated were characterized by significant increases in the cholesterol to phospholipid molar ratio (0.56 +/- 0.08 in controls and 1.11 +/- 0.13, 1.09 +/- 0.14, 1.04 +/- 0.15, p < 0.001, in types IIa, IIb and IV, respectively). Surface insulin receptors of type IIa and IIb patients did not appear to down-regulate when compared to normal subjects, but rather up-regulated (+65.2% in controls, -1.0% and -8.7%, p < 0.001, in type IIa and IIb patients, respectively). Patients with type IV hypertriglyceridemia showed a residual capacity for insulin receptor internalization (10.7% down-regulation). Membranes of all the patients contained a higher proportion of phosphatidylethanolamine; the molar ratio of sphingomyelin to phosphatidylcholine was significantly higher in types IIb than in controls (1.22 +/- 0.11 and 1.12 +/- 0.10, p < 0.05, respectively); all the patients showed a lower content of polyunsaturated fatty acids in the major glycerophospholipid classes. However, type IV hypertriglyceridemics showed less variations, especially in the phosphatidylserine fraction. These results indicate that the alterations in lipoprotein pattern may affect both the lipid membrane equilibria and the processing ability of surface insulin receptors. Copyright 1995 S. Karger AG, Basel

Platelet cytosolic Ca2+ and membrane dynamics in patients with primary hypercholesterolemia. Effects of pravastatin

This study was designed to evaluate the relationships between platelet cytosolic Ca2+ concentration ([Ca2+]i) and plasma lipids in patients with primary hypercholesterolemia. In a double-blind, placebo-controlled trial, we determined platelet [Ca2+]i in the presence and virtual absence of extracellular Ca2+ and the effects of prolonged treatment with pravastatin, a selective inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase. Platelet [Ca2+]i and membrane microviscosity were determined in 22 normotensive hypercholesterolemic men. Platelet [Ca2+]i was observed to vary with in vivo plasma lipid characteristics: in untreated patients, [Ca2+]i determined at low extracellular Ca2+ concentration was significantly associated with plasma triacylglycerols (P = .008) and with the total cholesterol to HDL cholesterol ratio (P = .044). Triacylglycerol levels also correlated inversely with the external Ca(2+)-dependent [Ca2+]i rise. Pravastatin treatment reduced plasma total cholesterol (-20 +/- 3%), LDL cholesterol (-30 +/- 3%), triacylglycerols (-17 +/- 6%), and apoB levels (-25 +/- 4%) and simultaneously decreased platelet [Ca2+]i measured in a low-Ca2+ medium by 14 +/- 6% (P = .03). However, [Ca2+]i values remained positively correlated with the total cholesterol to HDL cholesterol ratio (P = .04). Prvastatin treatment did not induce marked changes in membrane microviscosity, although the changes in trimethylaminodiphenylhexatriene anisotropy were inversely correlated with those of HDL cholesterol. These results indicate that plasma lipids can modulate cytosolic Ca2+ in platelets by affecting Ca2+ transport pathways that are dependent and independent of Ca2+ influx.

Monocytes from patients with combined hypercholesterolemia-hypertriglyceridemia and isolated hypercholesterolemia show an increased adhesion to endothelial cells in vitro: II. Influence of intrinsic and extrinsic factors on monocyte binding

One of the primary risk factors for atherosclerosis is hypercholesterolemia. Patients with isolated hypercholesterolemia or combined hypercholesterolemia-hypertriglyceridemia are at risk to develop premature atherosclerosis. Diet-induced hypercholesterolemia in animals leads to an increased adhesion of monocytes to and transmigration through the intact endothelium of the vessel wall. In the present study, we investigated in vitro binding of freshly isolated monocytes from patients and healthy controls to a monolayer of endothelial cells obtained from human umbilical vein. All four diagnosed patient groups with isolated or combined hypercholesterolemia showed a significant increase in monocyte binding as compared with the control group (familial hypercholesterolemia [FH], +41%; polygenic hypercholesterolemia [PH] +35%; familial combined hypercholesterolemia [FCH], +47%; nonfamilial combined hypercholesterolemia-hypertriglyceridemia [CHH], +67%). In a longitudinal study it was observed that diet or medication induced a decrease in cholesterol and triglycerides; however, these therapeutic conditions did not diminish in vitro monocyte binding in the patient groups. There was no correlation between monocyte binding and plasma cholesterol, low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, triglycerides, or lipoprotein(a) within hyperlipidemic patient groups. The presence of heart and vessel disease in hyperlipidemic patients was not associated with a change in monocyte binding. The adhesion to endothelial cells of monocytes from smoking patients with combined hypercholesterolemia (27%) was significantly higher (+23%) than that of monocytes from nonsmoking patients. Cytofluorimetric analysis of monocytes from FCH and CHH patients for specific monocyte differentiation markers and integrins did not show differences as compared with monocytes from healthy controls.

Increased number of high sensitive platelets in hypercholesterolemia, cardiovascular diseases, and after incubation with cholesterol

The number of low density platelets was found to be increased in patients with hypercholesterolemia, as compared with the number in controls. The percentage increase of the low density platelet subpopulation was even more pronounced in patients with hypercholesterolemia when compared with that in patients suffering from myocardial infarction or angina. In vitro studies with control platelets incubated with cholesterol rich liposomes showed also an increase in the subpopulation of low density platelets. After incubation of control platelets with cholesterol rich liposomes, a higher membrane anisotropy and a higher cholesterol to phospholipid (C/P) molar ratio of the plasma membrane were found. Furthermore, cholesterol-enriched platelets were more sensitive upon thrombin stimulation. The results suggest that a shift of platelet subpopulations to a higher number of low density platelets could be caused by either the level of plasma cholesterol or an in-vitro incubation with cholesterol rich liposomes.

Spontaneous platelet aggregation in whole blood is increased in non-insulin-dependent diabetes mellitus and in female but not male patients with primary dyslipidemia

Increased platelet aggregability has been shown in hypercholesterolemia, and stirring-induced spontaneous aggregation in whole blood is increased in insulin-dependent diabetes mellitus (DM). We have determined spontaneous aggregation in citrated (10 mM) whole blood, from 27 primary dyslipidemic patients (DYS; 14F, 13M), 16 male non-insulin-dependent DM (NIDDM) patients, and 17 normolipidemic controls (N; 6F, 11M), using platelet counting to quantify aggregation. Spontaneous aggregation was significantly higher, both in the female DYS group (median 30% [interquartile range 25,50], P < 0.005) and the NIDDM group (33% [25,41], P < 0.005), than in the N group (17% [12,27]), but did not differ significantly in the male DYS group (23% [10,33]). Similar results were obtained in the presence of indomethacin (25 mumol/l) to prevent artefactual thromboxane (TX) A2 formation, indicating that increased spontaneous aggregation was TXA2-independent. Interestingly, increased spontaneous aggregation appeared to be independent of serum cholesterol and triglyceride concentrations, as well as age and sex per se. We conclude that spontaneous platelet aggregation was increased both in female primary dyslipidemic patients and NIDDM patients, but not in male DYS patients. The clinical significance of increased spontaneous platelet aggregability is that it may favour shear-induced aggregation which may occur at critical arterial stenoses in vivo leading to thrombus formation.

Cholesterol effects on nonelectrolyte membrane transport in human erythrocytes: NMR magnetization transfer studies

The cholesterol content of human erythrocytes was altered by incubating them with sonicated dispersions of cholesterol/phosphatidylcholine at 37 degrees C. 31P NMR saturation transfer experiments were used to measure the rate constant for efflux of dimethyl methylphosphonate (DMMP) from the cells, and thereby gain an estimate of the permeability coefficient. It was shown that up to 39% depletion of membrane cholesterol (cholesterol/phospholipid molar ratio of 0.46) increased the efflux rate constant and permeability coefficient of DMMP 1.55- and 1.86-fold, respectively. Enrichment of the membranes with cholesterol by 45% (cholesterol/phospholipid molar ratio of 1.57) on the other hand, decreased the efflux rate constant and permeability coefficient 1.63- and 1.79-fold, respectively. It was concluded that DMMP may be used as a probe molecule to study the functional consequences of changes in the lipid composition of erythrocytes in diseases that are associated with disorders of lipid metabolism.

Increased erythrocyte aggregation in insulin-dependent diabetes mellitus and its relationship to plasma factors: a multivariate analysis

Red blood cell aggregation in vitro (kinetics and shear resistance) was studied in 13 healthy controls and 13 type I (insulin-dependent) diabetic patients free of severe degenerative complications who were matched for age, sex, and body mass index. Measurements were performed with a device that analyzes the laser light backscattered by a blood suspension. Both the velocity of rouleau formation and the cohesion of the rouleau network were significantly increased in diabetic patients. Plasma viscosity and whole-blood viscosity measured at low shear rate (0.95 s-1) were also significantly elevated in the diabetic group. Multivariate analyses of the whole population sample and the diabetic patients confirmed the influence of plasma proteins on the kinetics of aggregation. Fibrinogen levels, which were close to normal, affected mainly the shear resistance of the aggregates. Triglyceride and apolipoprotein (apo) B levels and indexes of metabolic control or protein glycation (fasting blood glucose and fructosamine) also appeared to influence markedly both the kinetics of rouleau formation and the cohesion of the rouleau networks. These rheological abnormalities occurred in diabetic patients before the appearance of any severe degenerative complications. We suggest that these rheological abnormalities are linked to plasma or erythrocyte factors, and are not due to angiopathy.

Lovastatin decreases plasma and platelet cholesterol levels and normalizes elevated platelet fluidity and aggregation in hypercholesterolemic patients

The lipid composition of whole platelets and the fluidity of platelet membranes, as well as the sensitivity of the cell to aggregation, were studied in type IIA hypercholesterolemic human subjects before and after treatment with lovastatin. Fourteen patients with primary hypercholesterolemia having initial cholesterol levels of 383 +/- 52 mg/dL (mean +/- standard deviation) were studied and compared with 21 control subjects having cholesterol levels of 187 +/- 32 mg/dL. Lovastatin was administered orally at a starting dose of 40 mg daily. The dose was increased to 80 mg daily for eight patients who did not achieve the target cholesterol level of 200 mg/dL at 6 weeks. Serum cholesterol level was decreased by 37% following 20 weeks' administration of the drug. The fluidity of platelet membranes expressed in terms of the fluorescence anisotropy parameter was determined using the probe 1,6-diphenyl-1,3,5-hexatriene (DPH). When compared with platelets obtained from normocholesterolemic controls, platelets from hypercholesterolemic patients had a higher molar ratio of cholesterol to phospholipids ([C/PL] 0.86 +/- 0.15 v 0.57 +/- 0.06 for controls) and of phosphatidylcholine to sphingomyelin ([PC/SM] 2.64 +/- 0.87 v 2.00 +/- 0.15 for controls), enhanced fluidity (anisotropy parameter at 37 degrees C of 0.892 +/- 0.066 v 0.977 +/- 0.065 for controls), and a greater tendency to aggregate (aggregation of 84.2% +/- 6.3% v 78.5% +/- 7.6% for controls).(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo shear flow and erythrocyte membrane fluidity in hypertensive patients

1. To evaluate the response of red blood cells subjected to the shear flow in hypertension, the relationships between wall shear phenomena determined in vivo in the brachial artery of hypertensive patients and the modifications of the membrane dynamics measured in vitro in erythrocyte ghosts of 32 patients were investigated. 2. Two fluorescent probes, diphenylhexatriene (DPH) and its trimethylamino-derivative (TMA-DPH), localized respectively in the lipid membrane core and at the lipid-water interface, were used. 3. Shear rate, shear stress and blood velocity were positively correlated with TMA-DPH anisotropy (P = 0.015, 0.005 and 0.026, respectively), but not with that of DPH. This indicates that wall shear forces were associated with the microviscosity of the outer part of the cell membrane. 4. The changes in wall shear forces and erythrocyte membrane microviscosity probed by TMA-DPH or DPH were observed to vary in parallel under nitrendipine therapy. 5. These results suggest that in vivo shear forces participate in the control of erythrocyte membrane fluidity or that erythrocytes adapt their membrane properties to blood flow conditions.

Red blood cell aggregation and primary hyperlipoproteinemia

Erythrocyte aggregation (EA) was determined in a Myrenne aggregometer at stasis (EAMo) and low shear (EAM1) in 102 patients suffering from primary hyperlipoproteinemia (PHLP)-46 with familial hypercholesterolemia (FH); 28 with familial combined hyperlipemia (FCHL); 28 with primary hypertriglyceridemia (PHTG)-and in a control group (CG) of healthy matched subjects. EA was also determined in FH after the autologous plasma had been replaced by a control plasma. The following parameters were also measured: fibrinogen (Fbg), plasmatic lipids, apolipoproteins, glucose, HbA1 c and membrane erythrocyte lipids: cholesterol (C) and phospholipids (PL). An increase in both EAMo and EAM1 was observed in all the studied groups of patients. When erythrocytes of FH were resuspended in control plasma, EA normalized, but only in 75% of them. Fbg was elevated only in FH and FCHL. Membrane C was increased mainly in FH and FCHL. EA correlates with both Fbg and apolipoproteins. In FH, EA also correlates with membrane C/PL. In addition, a high significant correlation exists between EA and HbA1 c in FCHL. The results obtained suggest that not only Fbg and apolipoproteins but also possible changes in erythrocyte membrane could encourage EA in PHLP.

Human lymphocyte sodium-hydrogen exchange. The influences of lipids, membrane fluidity, and insulin

The relation between serum lipids, membrane fluidity, insulin, and the activity of the sodium-hydrogen exchanger was investigated in human lymphocytes from 83 subjects. Subjects had a wide range of serum lipids and no concurrent disease. Lymphocyte membrane anisotropy (inversely related to membrane fluidity) was measured with a fluorescence polarization method. Sodium-hydrogen exchange maximal proton efflux rate, affinity for external sodium, and resting pH were determined with the intracellular pH-sensitive fluorochrome 2',5'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Sodium-hydrogen exchange maximal proton efflux rate was negatively correlated with the age of the subject (p = 0.03). Membrane anisotropy correlated with serum triglyceride (p = 0.04). Multiple regression analysis demonstrated that the maximal proton efflux rate in human lymphocytes was significantly related to age (p = 0.005), systolic blood pressure (p = 0.04), membrane anisotropy (p = 0.03), and serum cholesterol (p = 0.03). Incubation of lymphocytes with insulin failed to affect sodium-hydrogen exchange kinetics, intracellular buffering power, or resting intracellular pH. These results suggest that membrane-bound transport proteins may be influenced by serum lipids and the fluidity of the lipid membrane in which they are bound, but they are unlikely to be affected by insulin.

Changes of membrane phospholipid composition of human erythrocytes in hyperlipidemias. I. Increased phosphatidylcholine and reduced sphingomyelin in patients with elevated levels of triacylglycerol-rich lipoproteins

The composition of red blood cell membrane and plasma phospholipids has been analyzed in patients with hyperlipidemias. In red cells of patients with elevated levels of triacylglycerol-rich lipoproteins, phosphatidylcholine (PC) was raised and sphingomyelin (SM) reduced, resulting in a 20% increase of the membrane PC/SM ratio. In plasma phospholipids of these patients PC and SM levels were also higher and lower, respectively and the plasma PC/SM ratio was elevated by more than 50%. Close positive correlations between plasma and membrane phospholipids were obtained for PC, SM and the PC/SM ratio in normolipidemic and hyperlipidemic donors. Plasmalogen phosphatidylethanolamine (PE), a supposed endogenous protector against lipid oxidation, was reduced by about 20% in red cell membrane lipids in hyperlipidemic patients. Also plasmalogen-PE in plasma tended to be reduced in hyperlipidemic donors. Plasma HDL levels were positively related to the content of plasmalogen PE in the red cell membrane. In conclusion, there are closely related increases in PC/SM ratios in plasma and the red cell membrane in patients with elevated levels of triacylglycerol-rich lipoproteins. It is speculated that decreases in red cell membrane plasmalogen-PE in hyperlipidemic patients could be related to impaired antioxidant protection, possibly as a consequence of reductions in plasma HDL levels.

Biochemical and functional alterations associated with hypercholesterolemia in platelets from hypertensive patients

Hypercholesterolemia and hypertension are two of the major risk factors associated with increased atherosclerotic vascular disease. An abnormal platelet function is one of the mechanisms proposed to participate in atherogenesis. This study was undertaken to find out whether hypercholesterolemia in hypertensive patients can change platelet lipid composition and reactivity. Twenty-nine untreated hypertensive patients were distributed into 3 age, body mass index and blood pressure-matched groups according to their plasma cholesterol levels (normal, borderline or elevated, group NC, BC and HC respectively). Their platelet lipid composition, cytosolic Ca2+ concentration, cyclic AMP content and aggregating response to ADP and collagen were determined. Platelet from group HC patients were characterized by reduced cyclic AMP content (evaluated in the presence and absence of a platelet phosphodiesterase inhibitor) and aggregating responses to ADP and collagen, increased palmitic acid content and decreased arachidonic, eicosapentaenoic and docosatetraenoic and pentaenoic acid content, resulting in a lowered polyunsaturated to saturated fatty acid ratio (P less than 0.001). In contrast, platelet cytosolic Ca2+ concentration, DPH steady-state anisotropy and cholesterol to phospholipid molar ratio were not significantly changed. This indicates that hypercholesterolemia is accompanied in hypertensive patients by marked changes in platelet fatty acid composition, cyclic AMP content and response to aggregating agents. These changes, which clearly differ from those induced by in vitro cholesterol loading, could reflect not only the balance between LDL and HDL stimulation but also an adaptation to hemodynamic perturbations.

Effects of dietary fish oil supplementation on platelet aggregability and platelet membrane fluidity in normolipemic subjects with and without high plasma Lp(a) concentrations

The purpose of this study was to compare the relative effect of n-3 fatty acids on plasma lipids and platelet function in normolipemic subjects (n = 8) with plasma Lp(a) levels greater than 30 mg/dl and normolipemic subjects (n = 7) without detectable plasma Lp(a) concentrations. Six weeks of dietary supplementation (3.8 g EPA and 2.9 g DHA/d) significantly reduced (P less than 0.005) plasma TGs in both groups whereas no changes of plasma TC, LDL-C, HDL-C, and Lp(a), respectively, were found. Collagen- or thrombin-stimulated platelet aggregation and collagen- or thrombin-induced TXB2 generation from platelets decreased by approx. 45% in Lp(a)-negative and Lp(a)-positive platelet donors after a 6 week dietary intake. Four more weeks without n-3 supplementation restored the pretreatment values of TGs, platelet aggregability and TXB2 release. The biophysical properties of platelets from normolipemics with and without high plasma Lp(a) concentrations revealed a similar structural order of platelets at 37 degrees C using DPH, TMA-DPH, or 6-AS as fluorescent probes. Also similar temperature-dependent changes in platelet fluidity from 37 degrees C to 17 degrees C were observed in platelet preparations from Lp(a)-positive and Lp(a)-negative subjects. However, no subtle changes in the structural order of platelets due to nutrient intakes were found in all subjects (n = 15, 19-28 yrs) using fluorescence polarization technique. The present data suggest a similar in vitro platelet behaviour from normolipemic subjects with and without high plasma levels of Lp(a) (which is considered a risk for premature atherosclerosis) in contrast to platelet aggregability and platelet fluidity in certain hyperlipidemic stages.

Platelet membrane fluidity in type IIA, type IIB and type IV hyperlipoproteinemia

Fluorescence spectroscopy, a very sensitive index for measuring the biophysical properties of living cell systems, was used to examine the structural order of intact, resting, gel-filtered platelets from hyperlipidemic subjects (n = 48, 25-70 years) and normolipemic subjects (n = 34, 19-68 years). Fluorescence anisotropy (r[s]), which is inversely related to membrane fluidity, was estimated using 3 different fluorescent dyes, DPH, TMA-DPH, and 6-AS, known to label different regions of biological membranes. Increased membrane fluidity was observed in type IIB (n = 24, 36-62 yrs; r[s] = 0.0692 +/- 0.09) and type IV (n = 10, 33-57 yrs; r[s] = 0.058 +/- 0.006) hyperlipidemics in comparison to type IIA (n = 14, 25-70 yrs; r[s] = 0.086 +/- 0.019) and control subjects (n = 24, 28-68 yrs; r[s] = 0.079 +/- 0.012). The temperature dependency of r[s]-DPH values was significantly different (P less than 0.01) in platelets from type IIB and type IV patients compared to type IIA and control subjects of similar age. A significant positive correlation (P less than 0.005) between membrane fluidity and age was found only in healthy control subjects (n = 34, 19-68 yrs). Despite significant (P less than 0.01) differences in plasma lipid concentrations in hyperlipidemic patients and controls, significant ex vivo relations between membrane fluidity and lipoprotein concentrations, free fatty acid distribution, and increased age were found only in healthy control subjects. Plasma levels of thromboxane as well as serum selenium concentrations did not significantly differ between hypercholesterolemic, hypertriglyceridemic, and control subjects.