E. Roy Skinner

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.

Features of the lipid transport system of fish as demonstrated by studies on starvation in the rainbow trout

SummaryA comparison was made of the processes involved in the transport and uptake of lipids in starved and fed trout in order to gain a fuller understanding of the underlying mechanisms of these processes and their control in fish. Trout that had been starved for 8 weeks showed significantly lower lipoprotein lipase activities than control fed fish in their adipose tissue (64±45 and 546±205 units±SEM for starved and fed, respectively;P<0.05) and liver (22±6 and 147±56;P<0.05) but no significant difference in red muscle (22±6 and 88±35) or heart (0.53±0.20 and 0.89±0.27). A similar difference in salt-resistant lipase, present in extra-hepatic tissues in trout, was found, i.e. adipose tissue: 200±105 and 1,327±190 (P<0.05); liver: 133±16 and 404±78 (P<0.01); red muscle: 101±32 and 105±20 (n.s.); heart: 2.43±0.38 and 1.92±0.37 (n.s.). The plasma cholesterol esterifying activity of starved trout (1.79±0.36 units) was significantly lower (P<0.001) than the fed fish (3.74±0.65). The concentrations of plasma VLDL and LDL were 67% and 47% lower (P<0.001 andP<0.05, respectively) in the starved than in the fed trout, while the concentration of HDL was the same (163±15 and 165±20 mg cholesterol/100 ml for starved and fed fish, respectively), as was the concentration of nonesterified fatty acids (0.303±0.039 and 0.333±0.035 mEq/l, respectively). These observations demonstrate that, in spite of differences in the distribution of lipases between the various tissues, fish possess systems for the transport and uptake of lipids that broadly parallel those of mammals and are consistent with the greater use of lipid as a major energy source in fish.

Changes in plasma lipoproteins and tissue lipoprotein lipase and salt-resistant lipase activities during spawning in the rainbow trout (salmo gairdnerii r.)

1. Lipoprotein lipase and salt-resistant lipase activities increased in the ovaries but decreased in the adipose tissue of female trout in the months leading up to spawning. 2. The activity of the plasma cholesterol esterifying enzyme increased significantly immediately prior to spawning. 3. Plasma lipoprotein concentrations decreased during the approach to spawning. 4. These studies suggest that the developing ovaries in the trout receive their nutrients by lipolysis of plasma lipoproteins as well as by vitellogenin uptake; differentiation of the roles of the lipid stores in different tissues is proposed.

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.

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.

The roles of the intestine and liver in the biosynthesis of plasma lipoproteins in the rainbow trout, Salmo gairdnerii Richardson

Abstract 1. 1. [3H]leucine and [35S]methionine incubated with trout intestinal mucosa or liver slices became incorporated into lipoproteins of d . 2. 2. Gel electrophoresis showed labelled chylomicrons/VLDL in the intestinal incubate, with small proportions of LDL and HDL also present in the liver incubate. 3. 3. Immunological procedures demonstrated that trout intestine, as well as liver, synthesizes apolipoproteins A-I and B. 4. 4. The study demonstrates that chylomicrons are synthesized in the intestine in trout while liver is the major site of lipoprotein synthesis.

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.

Fractionation of rat high density lipoprotein by affinity chromatography: Effect of prolonged ultracentrifugation on high density lipoprotein subspecies

Serum lipoproteins are usually prepared by sequential flotation at increasing solvent density in the ultracentrifuge [l] . It is known, however, that lipoproteins so prepared are modified during ultracentrifugation [2] . Rat HDL, isolated between densities 1.065 kg/l and 1.21 kg/l, contain several apolipoproteins [3,4] of which apo A-I (mol. wt 28 000), apo ARP (mol. wt 35 000) and apo A-IV (mol. wt 46 000) have been detected in the lipoprotein freed = 1.21 kg/l infranatant [5,8] . Of these, apo ARP appears in the greatest quantity and its appearance is dependant upon the force and duration of centrifugation [5,8] . This apo ARP may not be homogeneously distributed in rat HDL fractionated by gel filtration [ 193 . In this study, affinity chromatography of rat HDL using heparin-Sepharose has been employed to isolate an apo ARP-enriched HDL and to examine the effect of ultracentrifugation on this HDL.

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) ≤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% Cl 2.4–8.6) in the first year and 9.6% (95% Cl 6.8–12.4) in the second year for those on antioxidants; and 7.7% (95% Cl 5.1–10.3) and 13.3% (95% Cl 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% Cl 16.2–27.4) compared with 40.0% (95% Cl 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.

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 Alzheimers disease.