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.

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.

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.

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.

Randomized controlled trial of antioxidants in intermittent claudication.

Epidemiological evidence suggests that antioxidants protect against the development of atherosclerosis. To determine the effectiveness of antioxidant therapy in patients with lower limb atherosclerosis, a randomized placebo-controlled trial was performed in 120 men and women with intermittent claudication and an ankle/brachial pressure index (ABPI) < or = 0.9. The study was analysed on an intention-to-treat basis. After 2 years, there were no significant differences between antioxidant and placebo groups in plasma cholesterol, lipoproteins, haemostatic or rheological factors. However, after 6 months, low density lipoprotein cholesterol was significantly lower in those taking antioxidant (108.0 mg/dl compared with 120.1 mg/dl, p < 0.05). There were no differences in the ABPI or walking distance, although both groups improved slightly with time. The incidence of cardiovascular events and death was nonsignificantly lower in the antioxidant compared with the placebo group: event rates per year were 5.5% (95% CI 2.4-8.6) in the first year and 9.6% (95% CI 6.8-12.4) in the second year for those on antioxidants; and 7.7% (95% CI 5.1-10.3) and 13.3% (95% CI 8.9-17.7) respectively for those on placebo. Significantly fewer serious adverse events occurred in the antioxidant than the placebo group: 21.8% (95% CI 16.2-27.4) compared with 40.0% (95% CI 33.9-46.1). This study therefore suggests that although antioxidants may prevent cardiovascular events in patients with peripheral atherosclerosis, they do not improve lower limb function.

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.

Uptake of apolipoprotein E-rich and apolipoprotein E-poor subfractions of high-density lipoprotein by liver membranes and HepG2 cells.

Apolipoprotein (apo) E plays an important role in mediating high-density lipoprotein (HDL) cholesterol transport and uptake by the liver. Evidence for and against the existence of conventional liver receptors for HDL containing apoE have been reported, although the selective uptake of the cholesterol moiety of HDL has been demonstrated. The present study investigated the hepatic uptake of subfractions of HDL separated on the basis of their apoE content. Rabbit HDL and its apoE-rich and apoE-poor subfractions, separated by heparin-Sepharose affinity chromatography, were labelled in their apoprotein moieties with [14C]sucrose and in their cholesteryl ester moiety with 3H. No binding of either subfraction to rabbit liver membranes could be detected. With cultured HepG2 cells, however, there was a high uptake of 3H but a very low uptake of 14C from both HDL subfractions, demonstrating that selective uptake was operating. Addition of unlabelled apoE-poor HDL inhibited the uptake of both labels from the two subfractions to the same extent. These studies, which differed from previously reported investigations by employing native homologous HDL subfractions of known apolipoprotein composition, demonstrated that apoE is not directly involved in the selective uptake of HDL cholesterol by the liver. In the absence of specific binding sites on liver membranes, it is suggested that an alternative mechanism might exist for the clearance of HDL cholesterol from the plasma.

Family communication patterns, rebelliousness, and adolescent reactions to anti-drug PSAs.

Research suggests that adolescents' family communication patterns should predict their reactions to anti-drug messages. The authors propose that the impact of such patterns is contingent upon the extent of adolescent rebelliousness. Fifty-one adolescents saw six anti-drug PSAs, and assessed whether they considered the messages believable and likely to persuade them and people they knew. Respondents were split into high/low groups with respect to conformity-orientation (authoritarian family communication patterns), conversation-orientation (open family communication patterns), and rebelliousness. As predicted, rebellious adolescents from the more authoritarian, conformity-oriented families considered the messages relatively less believable than did the non-rebellious adolescents from authoritarian, conformity-oriented families. Predicted negative relationships between family conversation-orientation and assessments of anti-drug PSA believability and persuasiveness were not found. Youth who had experimented with drugs, as predicted, did assess the anti-drug PSAs as less persuasive than those who did not.

High-density lipoprotein subclasses.

This review describes recent advances that have been made in the separation of HDL subfractions by physicochemical and immunological methods and the relationship between the particles obtained by the different procedures. The metabolic interconversions that occur as a result of cholesteryl ester transfer protein (CETP), lecithin:cholesterol acyltransferase (LCAT) and lipase activities and their role in the formation of mature HDL and in reverse cholesterol transport are discussed. Also considered are the alterations that occur in the HDL subpopulation profile in coronary heart disease and possible mechanisms by which HDL may protect against this condition.

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 role of subfractions of high density lipoprotein in the in vivo transport of cholesterol from cholesterol-loaded hepatic and peripheral endothelial cells in the New Zealand white rabbit.

1. High density lipoprotein (HDL) of the New Zealand White rabbit was separated by heparin-Sepharose affinity chromatography into six distinct subfractions of different composition and particle size. 2. When human acetyl LDL containing [3H]cholesteryl linoleate was injected intravenously into rabbits to prime the endothelial cells with labelled cholesterol, only 1-2% of the radioactivity remained in the plasma after 2 hr. 3. After 4 hr, 60.1% of the plasma radioactivity was present in HDL and 25% of this was recovered in the largest particles of HDL (fraction VI, mean particle diameter 11.6-11.8 nm). 4. The concentration of these largest particles of HDL, rich in apolipoprotein E, were also relatively increased in acetyl-LDL-treated rabbits when compared to controls (P < 0.01). 5. In control in vitro experiments, 62.2% of the radioactivity recovered in HDL was associated with subfractions IV and V (mean particle diameter 10.2-10.8 nm) while only 5% was present in fraction VI. 6. The results show that large HDL particles enriched with apo E contain a large proportion of cholesterol previously supplied to hepatic and peripheral endothelial cells. 7. This study demonstrated that the rabbit provides a useful animal model for the study of the metabolism of subfractions of HDL in relation to reverse cholesterol transport.

Differences in the fatty acid composition of the grey and white matter of different regions of the brains of patients with Alzheimer's disease and control subjects.

In the present study, a comparison was made of the fatty acid composition of the grey and white matter of the frontal, parietal and parahippocampal regions of post-mortem brains of patients who had died with Alzheimer's disease (n = 15) and control postmortem subjects (n = 10). Diagnosis of Alzheimer-type disease was based on the presence of senile plaques and neurofibrillary tangles in post-mortem sections. Several highly significant and specific differences were observed between the two groups. Adrenic acid (22:4 n-6) was three to four times higher in the grey matter but lower in the white matter in each of the three regions in the Alzheimer brains than in the control group. These alterations were compensated by reciprocal changes in 18:0 in the grey matter and 16:1 fatty acids in the white matter. There was no significant difference in the proportion of other fatty acids, including those of the n-6 and n-3 series, in either the grey or the white matter of any of the three regions of the two groups, except for a higher proportion of 22:6 n-3 in the parietal white matter in the Alzheimer patients. There was no significant relationship between the levels of the individual fatty acids and age at death. It is suggested that the alterations in the fatty acid composition observed in the brains of Alzheimer patients may be caused by an aberration in the system by which essential fatty acids are transported into the brain.

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).