Cholesterol-loading of peripheral tissues alters the interconversion of high density lipoprotein subfractions in rabbits.

High density lipoprotein (HDL) has been implicated in the process of reverse cholesterol transport,by which surplus cholesterol is removed from peripheral tissues and transported to the liver for excretion. It has been suggested that some subfractions of HDL may have a particular role in this process, though the underlying mechanism remains unclear. The present study was aimed at investigating the role of specific subfractions of HDL in reverse cholesterol transport. The interconversion of HDL subfractions in normal and cholesterol-loaded rabbits was studied in vivo. Rabbit HDL was separated by heparin-Sepharose affinity chromatography into six subfractions (HDL(I)-HDL(VI)), which were progressively enriched with apolipoprotein E (apo E), and varied in diameter and composition. Total HDL and its subfractions were individually labelled with 14C sucrose and injected in the rabbits. When rabbits which were not acutely loaded with [3H]cholesterol were injected with 14C-HDL(I), 70% of the label remained in this fraction while less than 5% was recovered in HDL(VI), containing the largest particles and those most enriched in apo E. No label was detectable in the liver of these animals. In rabbits which had received a prior loading of cholesterol, an average of only 18.3% of the 14C label was present in HDL(I) while approx. 40% of the label was recovered in HDL(VI). On average, 5.1% of the total 14C injected in these rabbits was recovered in the liver. It is concluded that two alternative routes for reverse cholesterol transport may be operative. While a continuous cholesterol-clearance route may be provided by particles of HDL of intermediate size, another route may be operative for clearance of excess cholesterol loaded into peripheral endothelial cells.

Receptor binding of an apolipoprotein E-rich subfraction of high density lipoprotein to rat and human brain membranes.

During nerve cell degeneration, cholesterol released from the degrading cells is conserved through the formation of a cholesterol-apolipoprotein (apo) E complex which is subsequently taken up by regenerating nerve cells. The aim of the present project was to identify the physiologically relevant lipoprotein receptor for this lipoprotein complex which has remained elusive. HDL was separated into apo E-rich and apo E-poor subfractions and labelled with [14C]-sucrose. Labelled apo E-rich HDL bound to rat brain membranes in a time- and ligand concentration-dependent manner and was a saturable process. Essentially no binding occurred with [14C]-apo E-poor HDL or with free apo E. Binding was partially inhibited by low density lipoprotein (LDL) and by alpha 2-macroglobulin. These results provide new evidence that native apoE-rich HDL particles resembling those present in the brain bind to rat brain membranes and that the binding may be due, at least in part, to the LDL receptor and to the LDL-receptor related protein. Evidence was also provided for the presence of a receptor which binds [14C]-sucrose human apoE-rich HDL in human brain. Characterisation of the receptor which mediates the uptake of cholesterol from HDL-like complexes by brain cells is important in understanding the role of apoE in the central nervous system and of the alterations which occur in disorders such as Alzheimer's disease.

Abnormal content of n-6 and n-3 long-chain unsaturated fatty acids in the phosphoglycerides and cholesterol esters of parahippocampal cortex from Alzheimer's disease patients and its relationship to acetyl CoA content.

The long-chain fatty acid composition of cholesterol esters, phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylinositol (PI) from parahippocampal cortex of Alzheimer's disease (AD) patients and control subjects was examined. In general the PC fraction contained less polyunsaturated long-chain fatty acids than did PE, PS or PI. Of the n-6 polyunsaturated long-chain fatty acids, PI contained the greatest incorporation of these acids followed by PE. There were significant differences between controls and AD patients in total n-6 EFAs. Arachidonic acid (C20:4n-6) was the predominant fatty acid of this family found to be present. In AD, PE and PS showed a deficit of adrenic acid (C22:4n-6) content and PE also contained less arachidonic acid. In AD subjects, the cholesterol esters contained significantly less n-3 polyunsaturated fatty acids with, specifically, a reduction in alpha-linolenic acid. Acetyl CoA content of hippocampal cortex was greater in AD patients than in control subjects indicating either an increased extent of oxidative metabolism or a failure to utilise acetyl CoA for anabolic processes. Abnormal magnitude of oxidative processes could give rise to the biosynthesis of PE and PS species containing less n-6 polyunsaturated fatty acids than occurs in control subjects.

Plasma high density lipoprotein subfractions in subjects with different coronary risk indices as assessed by plasma lipoprotein concentrations.

The distribution of plasma high density lipoprotein (HDL) subfractions was determined in 2 groups of healthy male subjects with different coronary risk indices (CI) as assessed by the ratio of total plasma cholesterol/HDL-cholesterol. The subjects in the 2 groups were of similar age and fitness (as assessed by VO2max). The higher risk group (CI greater than 4.0) contained a lower relative concentration of a specific HDL subfraction, HDL2b, separated by gradient gel electrophoresis, and a lower level of an apo E-rich HDL fraction, isolated by affinity chromatography, than the lower risk group (CI less than 4.0). The concentration of total HDL-cholesterol was higher in the lower risk group due to a difference in HDL2-cholesterol when separation was achieved by polyanion precipitation, but not when separation was made by ultracentrifugation. These observations suggest that the level of these specific HDL subfractions might, when taken in conjunction with plasma cholesterol concentration, provide a better index of coronary risk than that of total HDL as conventionally employed.

Alterations in plasma lipids, lipoproteins and high density lipoprotein subfractions in peripheral arterial disease.

The concentrations of the major lipoprotein classes and of high density lipoprotein (HDL) subfractions in 63 male patients with arteriosclerosis of the lower limbs (claudication) were determined and compared with values from 63 healthy controls. The patients with peripheral arterial disease (PAD) had reduced levels of total HDL-cholesterol and HDL2b of large particle size, increased levels of small HDL3c particles and a high ratio of total plasma-cholesterol to HDL-cholesterol (coronary risk factor). The PAD patients, however, had lower levels of low density lipoprotein (LDL)-cholesterol but higher concentrations of very low density lipoprotein (VLDL)-cholesterol and plasma triglyceride than healthy subjects. This study therefore suggests that in PAD, the protective effect of HDL may be more important than the atherogenic effect of LDL. It further suggests that while HDL-cholesterol HDL2b and the ratio of total plasma-cholesterol to HDL-cholesterol may provide valid indices for identifying individuals at risk of PAD, other factors, such as LDL and total cholesterol, may not provide such an appropriate risk indicator.

The effect of gammalinolenic acid on the subfractions of plasma high density lipoprotein of the rabbit.

The effect of dietary supplementation with evening primrose oil (containing 70% gammalinolenic acid) on the concentration of plasma lipids and lipoproteins of the New Zealand White rabbit was investigated. No significant changes were observed in the concentrations of plasma cholesterol or triglycerides during the treatment, although an increase in high density lipoprotein (HDL) cholesterol (P < 0.01) was observed at 4 weeks of evening primrose oil intake and 2 weeks after withdrawal. However, when HDL subpopulations were resolved by gradient gel electrophoresis, major alterations were observed in the distribution of HDL subfractions. These included an increase in HDL2b (P < 0.001) and HDL3c (P < 0.001) and the appearance of very large particles of HDL. These findings suggest that supplementation of diets with n-6 fatty acids may be effective in the long-term prevention of atherosclerosis.

The acute effect of prolonged walking and dietary changes on plasma lipoprotein concentrations and high-density lipoprotein subfractions.

The effect of diet on exercise-induced changes in the plasma concentrations of lipoproteins was examined in six healthy male subjects during walks of 37 km on each of four successive days. With a high-carbohydrate diet (85% of the calories as carbohydrate) there was an increase (P less than .05) in the concentration of very-low-density lipoprotein (VLDL)-cholesterol and VLDL-triglyceride and a decrease (P less than .01) in the concentration of high density lipoprotein (HDL)-cholesterol, due mainly to a decrease in HDL3-cholesterol (P less than .01), and HDL-protein (P less than .001). In contrast, a high-fat diet (75% fat) produced a decrease (P less than .01) in the concentration of VLDL-cholesterol and VLDL-triglyceride with increases (P less than .01) in HDL-protein concentration and in HDL-cholesterol concentrations that arose largely from an increase (P less than .001) in HDL2-cholesterol. Gradient gel electrophoretic analysis showed an increase (P less than .01) in the relative concentration of HDL2b (subspecies of diameter 10.57 nm) with a decrease (P less than .01) in the concentration of HDL2a (9.16 nm) plus HDL3a (8.44 nm) with the high-fat diet, but no significant or consistent change with the high-carbohydrate diet. There was no change in the level of the apolipoprotein E-rich HDL subfraction with either diet. Plasma lecithin:cholesterol acyltransferase activity decreased (P less than .05) with the high-fat diet but not with the high-carbohydrate diet. Thus, diet can strongly influence the changes that occur in plasma lipoprotein concentrations during prolonged low-intensity exercise.

Cholesterol metabolism and violence: a study of individuals convicted of violent crimes.

To examine the relationship between plasma lipoproteins and apolipoproteins in men with convictions for violent offences, blood was obtained from 15 men with a history of violence who were serving prison sentences for violent offences, and 25 age-matched male controls from the staff of the Argyll and Bute Psychiatric Hospital, who had no criminal records. The two groups did not differ in plasma total cholesterol concentrations, HDL-C, LDL-C, VLDL-C or in HDL subfractions. The most significant differences in the offenders were higher apoprotein AIV (3.62 vs 0.85: p = < 0.000001) and higher apoprotein E (7.70 vs 5.19: p = < 0.0002).

High density lipoprotein fatty acids in dementia.

High density lipoproteins (HDL) are small plasma particles which may be able to pass through the blood-brain barrier. We have therefore studied the fatty acids of HDL in patients with dementia to determine whether the changes are consistent with those previously reported in brain tissue. The HDL phospholipid and the HDL cholesteryl ester both showed reduced concentrations of arachidonic acid (20:4n6) as compared to normal controls. HDL may be a useful plasma fraction for study of lipids in neurodegenerative diseases.

Tin and fatty acids in dementia.

Serum elements and fatty acids of red cell and plasma phospholipids, cholesterol esters and high density lipoproteins, were studied in patients with Alzheimer's disease (SDAT) and with multi-infarct dementia (MID). Increased 20:4n6 in MID was the finding most consistent in the different tissues. The red cell phospholipids were more unsaturated in MID than in SDAT but in SDAT the plasma phospholipids were more saturated. Serum Al, Sn and V concentrations were higher in SDAT than in MID while serum Mn concentrations were higher in MID. Sn and V correlated negatively with the unsaturation index of the red cell phospholipids and Sn showed a striking pattern of correlations with the red cell phospholipid fatty acids in SDAT: it was significantly positively correlated with 16:0 and 18:1n-9 and negatively correlated with 20 and 22 carbon n-3 and n-6 essential fatty acids. Since we have shown elevated tin levels in patients with Alzheimer's disease, and since organic tin compounds given to animals produce a syndrome with similarities to Alzheimer's disease, there is a need for investigation of the role of tin in lipid metabolism in dementia.

Alterations in the concentration of an apolipoprotein E-containing subfraction of plasma high density lipoprotein in coronary heart disease.

The concentrations of high density lipoprotein (HDL) subfractions in 100 healthy male subjects were compared with 100 newly presenting patients with myocardial infarction (MI) within 12 h of the onset of chest pain. A subfraction of HDL enriched in apolipoprotein E (apo E), separated by heparin-Sepharose affinity chromatography, was present in lower concentrations (P < 0.001) in the plasma of the coronary patients than in the control subjects. This finding was confirmed by a lower content (P < 0.02) of apo E, measured by ELISA, in the total HDL fraction isolated from the coronary patients. Gradient gel electrophoresis of the total HDL demonstrated that the coronary patients had a significantly decreased concentration of the large HDL particles, HDL2b, of mean diameter 10.57 nm and a higher concentration of the smaller-sized HDL3, especially HDL3c, of mean diameter 7.62 nm. The coronary patients had a lower concentration of HDL cholesterol than the control subjects, attributable to the HDL2 fraction, with no difference in HDL2a between the two groups. There was no difference in the concentration of plasma cholesterol or triglyceride. The distribution of apo E phenotypes was similar in the two groups. HDL2b produced the highest discriminant power between the two groups, followed by apo E-rich HDL, HDL2 and HDL3c Plasma cholesterol correlated strongly with apo E-rich HDL for control subjects but not for MI survivors. This study demonstrates that the inverse relationship between HDL cholesterol and coronary risk shown in epidemiological studies is attributable to the large, apo E-containing HDL subspecies which under some circumstances are implicated in cholesterol removal by reverse cholesterol transport. This study also suggests that the concentration of the large, apo E-containing HDL may provide a sensitive predictor for subjects at risk of developing coronary heart disease.

The effect of clomipramine treatment on plasma lipoproteins and high density lipoprotein subfractions in healthy subjects.

The effect of clomipramine on plasma lipoproteins, including high density lipoprotein (HDL) subfractions in five healthy males was investigated. The concentrations of total plasma cholesterol and low density lipoprotein cholesterol decreased slightly while that of total HDL-cholesterol showed a small increase, giving a decrease (p less than 0.05) in the ratio of total plasma cholesterol to HDL-cholesterol. The level of HDL2-cholesterol increased (p less than 0.01) with clomipramine treatment while there was no significant change in the concentration of HDL3-cholesterol. Gradient gel electrophoresis showed that administration of the drug was associated with an increase in the relative concentration of HDL2a as well as of HDL2b and a decrease in that of HDL3b/3c. The plasma concentration of apolipoprotein (Apo) A-I showed a small but insignificant increase. These changes in lipoprotein profile are characteristic of those associated with a decrease in coronary risk.

The composition and concentration of umbilical cord plasma lipoproteins; their relationship to the birth weight and other clinical factors of the newborn.

The present studies confirmed that plasma obtained from individual umbilical cords contains very low density, low density and high density lipoprotein particles whose mean compositions are similar to those of the adult, though they are present in considerably lower concentrations. A fairly wide variation in both composition and concentration was found between different individuals. For full-term deliveries, a positive correlation (p less than 0.01) was found between the cholesteryl ester: free cholesterol ratio of the high density lipoprotein fraction and the birth weight, suggesting differences in the distribution of the particles that constitute this lipoprotein fraction. Otherwise, no correlation was found between the composition or concentration of any lipoprotein fraction and birth weight, gestation, sex or other factor investigated. Premature newborns (30-36 weeks) had concentrations of high density lipoproteins and cholesteryl ester: free cholesterol ratios of the high density lipoprotein that were markedly high in relation to their birth weights and in the same range as full-term newborns (37-40 weeks).

Randomized controlled trial of gamma-linolenic acid and eicosapentaenoic acid in peripheral arterial disease.

BACKGROUND AND AIMS: epidemiological studies suggest polyunsaturated fatty acids protect against the development of atherosclerosis. The aim of this study was to perform a randomized controlled trial of gamma-linolenic and eicosapentaenoic acids in patients with lower limb atherosclerosis. Main outcome measures were: cholesterol and lipoprotein concentrations; haemostatic and rheological variables; the ankle brachial pressure index; walking distance; and cardiovascular events and death. METHODS: 120 men and women with stable intermittent claudication were randomized to 2 years treatment with either a combination of gamma-linolenic and eicosapentaenoic acids, or placebo. RESULTS: 39 (65.0 cent) of those taking fatty acids and 36 (60.0 cent) of those taking placebo completed the trial. Lipid concentrations did not differ significantly during the trial. In those taking fatty acids, haematocrit was significantly higher than in the placebo group after 6 months (46.1 cent compared with 44.6 cent, P 0.05). CONCLUSIONS: a combination of polyunsaturated fatty acids produced a statistically significant reduction in systolic blood pressure, but no other significant benefits on risk factors. The trend towards fewer coronary events in those taking fatty acids warrants further investigation.

1H-NMR relaxation times and water content of red blood cells from chronic alcoholic patients during withdrawal.

Red blood cell proton nmr, T1 and T2 times, and water content were measured for normal control subjects and thirteen patients with chronic alcoholism during the withdrawal phase. T1 and T2 were significantly increased without significant alteration in cell water content. The relaxation times were more markedly affected in those with symptoms of delirium tremens. These findings suggest that the intracellular free:bound water states rather than water content is the more likely explanation for these changes. The results are discussed in relation to similar findings obtained from in vivo studies in man and in vitro studies in animals.