Sex difference in the regulation of plasma high density lipoprotein cholesterol by genetic and environmental factors

Association between high density lipoprotein (HDL) cholesterol concentration and restriction fragment length polymorphisms at the cholesteryl ester transfer protein (CETP) gene locus was studied in a random population-based cohort of 526 Caucasian subjects (259 men, mean age 50.9 years, and 267 women, mean age 51.8 years). HDL cholesterol concentration was adjusted for age, body mass index, alcohol consumption, smoking and plasma triglyceride and low density lipoprotein cholesterol levels. In females, the HDL cholesterol levels were associated withTagIB polymorphism (1.46 mmol/1 in the B1B1 genotype, 1.56 mmol/l in B 1B2 and 1.72 mmol/1 in B2B2,P = 0.0001 for the trend). In contrast, this was not observed in men (1.24, 1.20, 1.27 mmol/l, NS). The association was seen even in women who were current smokers (1.41, 1.56, 1.75 mmol/l,n = 72,P = 0.007), but not in male smokers (1.26, 1.19, 1.14 mmol/l,n = 102, NS). In male non-smokers the association was weak (1.22, 1.20, 1.32 mmol/l,n = 157,P = 0.05). In postmenopausal women not receiving hormone replacement therapy (n = 108), the association continued to be present, although weaker (1.50, 1.58, 1.70 mmol/l,P = 0.06). CETP activity (n = 101) tended to be lower in subjects with the 132132 genotype. In conclusion, a clear-cut sex difference was observed in the genotype effect on plasma HDL cholesterol levels. The slight attenuation of the gene dosage effect after menopause suggests that the gender difference may be, at least in part, due to sex hormones. A genetic subgroup (men with the 132132 genotype) particularly susceptible to the HDL cholesterol decreasing effect of smoking could be demonstrated.Part of this work was presented at the 67th Scientific Sessions of the American Heart Association, Dallas, Texas, USA, 14–17 November, 1994     

Distinction in the mode of receptor-mediated endocytosis between high density lipoprotein and acetylated high density lipoprotein: evidence for high density lipoprotein receptor-mediated cholesterol transfer

The interactions of high density lipoprotein (HDL) and acetylated high density lipoprotein (acetyl-HDL) with isolated rat sinusoidal liver cells have been investigated. Cellular binding of 125I-acetyl-HDL at 0 degrees C demonstrated the presence of a specific, saturable membrane-associated receptor. This receptor was affected neither by formaldehyde-treated albumin nor by low density lipoprotein modified either by acetylation or malondialdehyde, ligands known to undergo receptor-mediated endocytosis by the cells, indicating that the receptor for acetyl-HDL constitutes a distinct class among the scavenger receptors for chemically modified proteins. Parallel binding experiments using 125I-HDL also revealed the presence on these cells of a receptor for unmodified HDL. The ligand specificities of these two receptors were similar to each other except that the acetyl-HDL receptor was sensitive to polyanions such as dextran sulfate and fucoidin. Interaction of HDL with the cells at 37 degrees C was totally different from that of acetyl-HDL. Cellular binding of HDL was not accompanied by subsequent intracellular degradation of its apoprotein moiety, whereas its cholesterol moiety was significantly transferred to the cells. In contrast, acetyl-HDL was endocytosed and underwent lysosomal degradation as a holoparticle. This shift in receptor-recognition from the HDL receptor to the acetyl-HDL receptor was accomplished by acetylation of approximately 8% of the total lysine residues of HDL apoprotein. This unique difference in endocytic behavior between HDL and acetyl-HDL suggests a potential link of the HDL receptor to HDL-mediated cholesterol transfer in sinusoidal liver cells.     

Apolipoprotein-mediated cellular cholesterol/phospholipid efflux and plasma high density lipoprotein level in mice

Helical apolipoprotein(apo)s generate pre-beta-high density lipoprotein (HDL) by removing cellular cholesterol and phospholipid upon the interaction with cells. To investigate its physiological relevance, we studied the effect of an in vitro inhibitor of this reaction, probucol, in mice on the cell-apo interaction and plasma HDL levels. Plasma HDL severely dropped in a few days with probucol-containing chow while low density protein decreased more mildly over a few weeks. The peritoneal macrophages were assayed for apoA-I binding, apoA-I-mediated release of cellular cholesterol and phospholipid and the reduction by apoA-I of the ACAT-available intracellular cholesterol pool. All of these parameters were strongly suppressed in the probucol-fed mice. In contrast, the mRNA levels of the potential regulatory proteins of the HDL level such as apoA-I, apoE, LCAT, PLTP, SRB1 and ABC1 did not change with probucol. The fractional clearance rate of plasma HDL-cholesteryl ester was uninfluenced by probucol, but that of the HDL-apoprotein was slightly increased. No measurable CETP activity was detected either in the control or probucol-fed mice plasma. The change in these functional parameters is consistent with that observed in the Tangier disease patients. We thus concluded that generation of HDL by apo-cell interaction is a major source of plasma HDL in mice.     

Total cholesterol,low density lipoprotein cholesterol,and high density lipoprotein cholesterol and coronary heart disease in Scotland.

OBJECTIVE--To investigate long term changes in total cholesterol, high density lipoprotein cholesterol, and low density lipoprotein cholesterol concentrations and in measures of other risk factors for coronary heart disease and to assess their importance for the development of coronary heart disease in Scottish men. DESIGN--Longitudinal study entailing follow up in 1988-9 of men investigated during a study in 1976. SETTING--Edinburgh, Scotland. SUBJECTS--107 men from Edinburgh who had taken part in a comparative study of risk factors for heart disease with Swedish men in 1976 when aged 40. INTERVENTION--The men were invited to attend a follow up clinic in 1988-9 for measurement of cholesterol concentrations and other risk factor measurements. Eighty three attended and 24 refused to or could not attend. MAIN OUTCOME MEASURES--Changes in total cholesterol, high density lipoprotein cholesterol, and low density lipoprotein cholesterol concentrations, body weight, weight to height index, prevalence of smoking, and alcohol intake; number of coronary artery disease events. RESULTS--Mean serum total cholesterol concentration increased over the 12 years mainly due to an increase in the low density lipoprotein cholesterol fraction (from 3.53 (SD 0.09) to 4.56 (0.11) mmol/l) despite a reduction in high density lipoprotein cholesterol concentration. Body weight and weight to height index increased. Fewer men smoked more than 15 cigarettes/day in 1988-9 than in 1976. Blood pressure remained stable and fasting triglyceride concentrations did not change. The frequency of corneal arcus doubled. Alcohol consumption decreased significantly. Eleven men developed clinical coronary heart disease. High low density lipoprotein and low high density lipoprotein cholesterol concentrations in 1976, but not total cholesterol concentration, significantly predicted coronary heart disease (p = 0.05). Almost all of the men who developed coronary heart disease were smokers (91% v 53%, p less than 0.05). CONCLUSION--Over 12 years the lipid profile deteriorated significantly in this healthy cohort of young men. Smoking, a low high density lipoprotein concentration and a raised low density lipoprotein concentration were all associated with coronary heart disease in middle aged Scottish men, whereas there was no association for total cholesterol concentration. The findings have implications for screening programmes.     

The influence of cellular and lipoprotein cholesterol contents on the flux of cholesterol between fibroblasts and high density lipoprotein

Previous studies indicate that free cholesterol moves passively between high density lipoprotein (HDL) and cell plasma membranes by uncatalyzed diffusion of cholesterol molecules in the extracellular aqueous phase. By this mechanism, the rate constants for free cholesterol influx (Cli) and efflux (ke) should not be very sensitive to the free cholesterol content of cells or HDL. Thus, at a given HDL concentration, the unidirectional influx and efflux of cholesterol mass (Fi, Fe) should be proportional to the cholesterol content of HDL and cells, respectively, and net efflux of cholesterol mass (Fe-Fi greater than 0) should occur when either cells are enriched with cholesterol or HDL is depleted of cholesterol. We have examined the influence of cell and HDL free cholesterol contents on the bidirectional flux of free cholesterol between HDL and human fibroblasts and also attempted to detect some dependence of flux on the binding of HDL to the cells. In the range of HDL concentrations from 1 to 1000 micrograms of protein/ml, ke for cell free cholesterol approximately doubled for every 10-fold increase in HDL concentration, reaching 0.04 h-1 at 1000 micrograms of HDL/ml. ke and Cli were not influenced by the doubling of fibroblast free cholesterol content (from 31 +/- 5 to 62 +/- 13 micrograms of cholesterol/mg of protein). There was an approximate exchange of cholesterol between HDL and the unenriched fibroblasts (e.g. at [HDL] = 100 micrograms/ml, Fe and Fi = 3.2 and 3.0 micrograms of cholesterol/[4 h.mg of cell protein], respectively). In contrast, there was substantial net efflux from the enriched cells (at [HDL] = 100 micrograms/ml, Fe and Fi = 5.5 and 3.1 micrograms of cholesterol/[4 h.mg of cell protein], respectively). The rate constants for cholesterol flux were not influenced by changing the free cholesterol content of HDL, so that there was net efflux of cell cholesterol in the presence of cholesterol-depleted HDL and net influx from cholesterol-rich HDL. The Kd of HDL binding to fibroblasts was reduced from 1.7 to 0.9 micrograms/ml by the enrichment of the cells with free cholesterol; this increase in affinity for HDL was not reflected in enhanced rate constants for cholesterol flux. The inhibition of specific HDL binding by treatment of the lipoprotein with dimethyl suberimidate did not affect cholesterol flux using either control or cholesterol-rich cells at any HDL concentration in the range 1-1000 micrograms/ml. The above results are consistent with the concept that net movement of free cholesterol between cells and HDL occurs by passive, mass-action effects.(ABSTRACT TRUNCATED AT 400 WORDS)     

Cholesterol efflux by acute-phase high density lipoprotein: role of lecithin: cholesterol acyltransferase

HDL plays an initial role in reverse cholesterol transport by mediating cholesterol removal from cells. During infection and inflammation, several changes in HDL composition occur that may affect the function of HDL; therefore, we determined the ability of acute-phase HDL to promote cholesterol removal from cells. Acute-phase HDL was isolated from plasma of Syrian hamsters injected with lipopolysaccharide. Cholesterol removal from J 774 murine macrophages by acute-phase HDL was less efficient than that by control HDL because of both a decrease in cholesterol efflux and an increase in cholesterol influx. LCAT activity of acute-phase HDL was significantly lower than that of control HDL. When LCAT activity of control HDL was inactivated, cholesterol efflux decreased and cholesterol influx increased to the level observed in acute-phase HDL. Inactivation of LCAT had little effect on acute-phase HDL. In GM 3468A human fibroblasts, the ability of acute-phase HDL to remove cholesterol from cells was also lower than that of normal HDL. The impaired cholesterol removal, however, was primarily a result of an increase in cholesterol influx without changes in cholesterol efflux. When control HDL in which LCAT had been inactivated was incubated with fibroblasts, cholesterol influx increased to a level comparable to that of acute-phase HDL, without any change in cholesterol efflux. These results suggest that the ability of acute-phase HDL to mediate cholesterol removal was impaired compared with that of control HDL and the lower LCAT activity in acute-phase HDL may be responsible for this impairment. The decreased ability of acute-phase HDL to remove cholesterol from cells may be one of the mechanisms that account for the well-known relationship between infection/inflammation and atherosclerosis.     

Incorporation of cholesterol into high density lipoprotein recombinants.

Apo-A-1, the principal apoprotein of high density lipoprotein, was incubated with cholesterol containing liposomes of dimyristoyl lecithin, lecithin from high density lipoprotein or sphingomyelin. Conditions were chosen to give 100% conversion of cholesterol-free liposomes into recombinants which were isolated by density gradient ultracentrifugation. For all phospholipids, there was a progressive decrease in incorporation of lipid into recombinants with increasing cholesterol/phospholipid ratio. The cholesterol/phospholipid ratio of recombinants was ～ 45% of unreacted liposomes, for all initial cholesterol/phospholipid ratios. The reduced cholesterol content suggests exclusion of cholesterol from a fraction of recombinant phospholipid, probably a boundary layer in contact with apo A-1.     

Regulation of high density lipoprotein receptors in cultured macrophages: role of acyl-CoA:cholesterol acyltransferase

The interaction of human serum high density lipoproteins (HDL) with mouse peritoneal macrophages and human blood monocytes was studied. Saturation curves for binding of apolipoprotein E-free [125I]HDL3 showed at least two components: non-specific binding and specific binding that saturated at approximately 40 micrograms HDL protein/ml. Scatchard analysis of specific binding of apo E-free [125I]-HDL3 to cultured macrophages yielded linear plots indicative of a single class of specific binding sites. Pretreatment of [125I]HDL3 with various apolipoprotein antibodies (anti apo A-I, anti apo A-II, anti apo C-II, anti apo C-III and anti apo E) and preincubation of the cells with anti-idiotype antibodies against apo A-I and apo A-II prior to the HDL binding studies revealed apolipoprotein A-I as the ligand involved in specific binding of HDL. Cellular cholesterol accumulation via incubation with acetylated LDL led to an increase in HDL binding sites as well as an increase in the activity of the cytoplasmic cholesterol esterifying enzyme acyl-CoA:cholesterol acyltransferase (ACAT). Incubation of the cholesterol-loaded cells in the presence of various ACAT inhibitors (Sandoz 58.035, Octimibate-Nattermann, progesterone) revealed a time- and dose-dependent amplification in HDL binding and HDL-mediated cholesterol efflux. It is concluded that the homeostasis of cellular cholesterol in macrophages is regulated in part by the number of HDL binding sites and that ACAT inhibitors enhance HDL-mediated cholesterol efflux from peripheral cells.     

The role of high-density lipoprotein cholesterol in the prevention and possible treatment of cardiovascular diseases

Despite significant progress in the management of atherosclerosis and its resultant complications, cardiovascular disease remains the principal cause of death in the world. The National Cholesterol Education Project Adult Treatment Panel III (NCEP ATP III) recognizes low levels of high-density lipoprotein cholesterol (HDL) as a risk factor for coronary heart disease (CHD) and high levels of HDL as a risk-reducing factor; however, the elevation of HDL as a specific therapeutic target for the prevention and treatment of CHD has yet to be accepted on the same level as low-density lipoprotein (LDL)-reducing therapies. Current HDL elevators including nicotinic acid, fibric acid derivatives, peroxisome proliferator activated receptor (PPAR) agonists and statins also affect other lipid constituents which make interpretation of the clinical trials of these drugs difficult in teasing out the independent effect of HDL elevation. Ample laboratory investigation suggests that HDL elevation would reduce atherosclerotic burden through multiple independent mechanisms. In this review, we explore HDL biology, its potential mechanisms in the treatment of atherosclerotic disease, and promising new drugs with HDL-raising activity.     

Ethanol enhances de novo synthesis of high density lipoprotein cholesterol

Male squirrel monkeys fed ethanol at variable doses were used to assess whether alcohol enhances de novo synthesis of high density lipoprotein (HDL) cholesterol in vivo. Monkeys were divided into three groups: 1) Controls fed isocaloric liquid diet; 2) Low Ethanol monkeys fed liquid diet with vodka substituted isocalorically for carbohydrate at 12% of calories; and 3) High Ethanol animals fed diet plus vodka at 24% of calories. High Ethanol primates had significantly higher levels of HDL nonesterified cholesterol than Control and Low Ethanol animals while serum glutamate oxaloacetate transaminase was similar for the three treatments. There were no significant differences between the groups in HDL cholesteryl ester mass or specific activity following intravenous injection of labeled mevalonolactone. By contrast, High Ethanol monkeys had significantly greater HDL nonesterified cholesterol specific activity with approximately 60% of the radioactivity distributed in the HDL3 subfraction. This report provides the first experimental evidence that ethanol at 24% of calories induces elevations in HDL cholesterol in primates through enhanced de novo synthesis without adverse effects on liver function.     

Location and motion of free cholesterol molecules in high density lipoprotein

Human high density lipoprotein (HDL₃) was reconstituted with the free cholesterol molecules replaced with 4-[¹³C]-cholesterol. 90 MHz [¹³C]-NMR spectra were obtained and two cholesterol resonances at chemical shifts of 41.73 and 42.20 ppm could be resolved. The former signal arises from the C-4 atom of cholesterol molecules associated with phospholipids and located in the surface of the HDL₃ particle while the latter resonance is due to cholesterol molecules associated with cholesterol ester and triglyceride molecules in the core. HDL₃ reconstituted without any cholesterol ester or triglyceride gave a single resonance at 41.73 ppm indicating that all the free cholesterol molecules are in the surface. 60% of the free cholesterol molecules present in normal HDL₃ are in the phospholipid monolayer around the surface where they undergo relatively restricted motion compared to the remaining 40% situated in the liquid core. The free cholesterol molecules can equilibrate between the two pools in the timescale 10ms–700s.     

Interaction of high density lipoprotein particles with membranes containing cholesterol

In this study, free cholesterol (FC) efflux mediated by human HDL was investigated using fluorescence methodologies. The accessibility of FC to HDL may depend on whether it is located in regions rich in unsaturated phospholipids or in domains containing high levels of FC and sphingomyelin, known as "lipid rafts." Laurdan generalized polarization and two-photon microscopy were used to quantify FC removal from different pools in the bilayer of giant unilamellar vesicles (GUVs). GUVs made of POPC and FC were observed after incubation with reconstituted particles containing apolipoprotein A-I and POPC [78A diameter reconstituted high density lipoprotein (rHDL)]. Fluorescence correlation spectroscopy data show an increase in rHDL size during the incubation period. GUVs made of two "raft-like" mixtures [DOPC/DPPC/FC (1:1:1) and POPC/SPM/FC (6:1:1)] were used to model liquid-ordered/liquid-disordered phase coexistence. Through these experiments, we conclude that rHDL preferentially removes cholesterol from the more fluid phases. These data, and their extrapolation to in vivo systems, show the significant role that phase separation plays in the regulation of cholesterol homeostasis.     

The effects of apolipoprotein F deficiency on high density lipoprotein cholesterol metabolism in mice

Apolipoprotein F (apoF) is 29 kilodalton secreted sialoglycoprotein that resides on the HDL and LDL fractions of human plasma. Human ApoF is also known as Lipid Transfer Inhibitor protein (LTIP) based on its ability to inhibit cholesteryl ester transfer protein (CETP)-mediated transfer events between lipoproteins. In contrast to other apolipoproteins, ApoF is predicted to lack strong amphipathic alpha helices and its true physiological function remains unknown. We previously showed that overexpression of Apolipoprotein F in mice reduced HDL cholesterol levels by 20-25% by accelerating clearance from the circulation. In order to investigate the effect of physiological levels of ApoF expression on HDL cholesterol metabolism, we generated ApoF deficient mice. Unexpectedly, deletion of ApoF had no substantial impact on plasma lipid concentrations, HDL size, lipid or protein composition. Sex-specific differences were observed in hepatic cholesterol content as well as serum cholesterol efflux capacity. Female ApoF KO mice had increased liver cholesteryl ester content relative to wild type controls on a chow diet (KO: 3.4+/-0.9 mg/dl vs. WT: 1.2+/-0.3 mg/dl, p<0.05). No differences were observed in ABCG1-mediated cholesterol efflux capacity in either sex. Interestingly, ApoB-depleted serum from male KO mice was less effective at promoting ABCA1-mediated cholesterol efflux from J774 macrophages relative to WT controls.     

Relationship of high density lipoprotein cholesterol to cholesterol metabolism in the baboon (Papio sp.)

Genetic effects on serum high density lipoprotein (HDL) cholesterol concentration and several parameters of a two-pool model of cholesterol metabolism were investigated in 79 baboons, the progeny of 6 sires. Significant differences (P less than 0.05) were observed among the sire progeny groups for HDL cholesterol (HDL-C), cholesterol production rate, cholesterol mass of pool A, and the rate constants KA and KAB. Rank correlations (rs) revealed that the sire progeny group means for HDL-C are closely correlated with those for the cholesterol mass of pool A (rs = 0.89), KA (rs = -0.78), and KAB (rs = -0.94). These strong correlations suggest that pool A, KA, and KAB are influenced to a large degree by the same genes that regulate HDL-C concentration. The strong inverse relationship (rs = -0.78) between HDL-C and KA suggests that the differences among these sire progeny groups for HDL-C are due chiefly to those metabolic processes which regulate cholesterol excretion from pool A. This conclusion is consistent with reports that HDL-C is a preferred precursor for bile acid synthesis.     

Trans-intestinal cholesterol efflux is not mediated through high density lipoprotein

Transintestinal cholesterol efflux (TICE) provides an attractive target to increase body cholesterol excretion. At present, the cholesterol donor responsible for direct delivery of plasma cholesterol to the intestine is unknown. In this study, we investigated the role of HDL in TICE. ATP-binding cassette protein A1 deficient (Abca1(-/-)) mice that lack HDL and wild-type (WT) mice were intravenously injected with chylomicron-like emulsion particles that contained radiolabeled cholesterol that is liberated in the liver and partly reenters the circulation. Both groups secreted radiolabeled cholesterol from plasma into intestinal lumen and TICE was unaltered between the two mouse models. To further investigate the role of HDL, we injected HDL with radiolabeled cholesterol in WT mice and Abca1(-/-)×Sr-b1(-/-) mice that lack HDL and are also unable to clear HDL via the liver. The intestines of both mice were unable to take up and secrete radiolabeled cholesterol from HDL via TICE. Although a generally accepted major player in the hepatobiliary route-based cholesterol excretion, HDL plays no significant role in TICE in mice.     

Interaction of cholesterol,phospholipid and apoprotein in high density lipoprotein recombinants

To examine the effect of incorporation of cholesterol into high density lipoprotein (HDL) recombinants, multilamellar liposomes of ³H cholesterol/¹⁴C dimyristoyl phosphatidylcholine were incubated with the total apoprotein (apoHDL) and principal apoproteins (apoA-1 and apoA-2) of human plasma high density lipoprotein. Soluble recombinants were separated from unreacted liposomes by centrifugation and examined by differential scanning calorimetry and negative stain electron microscopy. At 27°C, liposomes containing up to approx. 0.1 mol cholesterol/mol dimyristoyl phosphatidylcholine (DMPC) were readily solubilized by apoHDL, apoA-1 or apoA-2. However, the incorporation of DMPC and apoprotein into lipoprotein complexes was markedly reduced when liposomes containing a higher proportion of cholesterol were used. For recombinants prepared from apoHDL, apoA-1 or apoA-2, the equilibrium cholesterol content of complexes was approx. 45% that of the unreacted liposomes. Electron microscopy showed that for all cholesterol concentrations, HDL recombinants were predominantly lipid bilayer discs, approx. $\text{160 × 55}\text{A}\text{?}$. Differential scanning calorimetry of cholesterol containing recombinants of DMPC/cholesterol/apoHDL or DMPC/cholesterol/apoA-1 showed, with increasing cholesterol content, a linear decrease in the enthalpy of the DMPC gel to liquid crystalline transition, extrapolating to zero enthalpy at 0.15 cholesterol/DMPC. The enthalpy values were markedly reduced compared to control liposomes, where the phospholipid transition extrapolated to zero enthalpy at approx. 0.45 cholesterol/DMPC. The calorimetric and solubility studies suggest that in high density lipoprotein recombinants cholesterol is excluded from 55% of DMPC molecules bound in a non-melting state by apoprotein.     

Determination of high density lipoprotein cholesterol in venous and capillary whole blood

A procedure is presented and evaluated for separation of plasma high density lipoprotein from either capillary or venous whole blood. The lipoprotein is separated by adding 50 microliter of sample to 250 microliter of 0.15 M NaCl solution containing 99.9 g/l polyethyleneglycol 6000, 0.0374 g/l dextran sulfate (Mr 15,000) and 2.6 mM Mg2+. After gentle mixing for a few minutes and standing 10 min at room temperature, mixtures are centrifuged (1,500 g) for 10 min and cholesterol is measured on 200 microliter of supernatant by an enzymatic-colorimetric method. Comparison studies demonstrate a good correlation between high density lipoprotein cholesterol in plasma and capillary or venous whole blood. The procedure is simple, has the advantage of using either K3-EDTA-anticoagulated whole blood, without the need of centrifugation, or capillary whole blood which can also be collected away from the laboratory.     

Incorporation of cholesterol into serum high density lipoprotein apoprotein and recombinants

The uptake of cholesterol (CHL) by serum high density lipoprotein (HDL) delipidated apoproteins and phospholipid-apoprotein recombinants has been studied with two methods; by incubation with Celite-dispersed cholesterol or with cholesterol crystals. The apoproteins bind very small amounts of cholesterol with a maximum of about 6 micrograms/mg apoprotein. Recombinants with dimyristoyl phosphatidylcholine (DMPC) or egg phosphatidylcholine (EPC) as phospholipid component gave similar values for cholesterol uptake. The initial rate for uptake from Celite-cholesterol by recombinants was high (0.1 mol cholesterol/mol phospholipid/h) and somewhat higher than that for phospholipid vesicles. The maximal uptake was by gel filtration shown to depend on the size of the complexes with values about 0.95 mol cholesterol per phospholipid for vesicular complexes, 0.75 for discoidal complexes and between 0.5 and 0.2 for small 'protein-rich' complexes. During the incubation of recombinants with cholesterol there was considerable decomposition of discoidal complexes and formation of larger ones. The results show that phospholipid-apoprotein complexes are efficient acceptors for cholesterol but also that about 25% of the phospholipid in the discoidal complexes is excluded from interaction with cholesterol by interaction with apoprotein.     

Association between plasma high density lipoprotein cholesterol and antipyrine metabolism in alcoholics

Seven patients entering an alcoholic detoxification and treatment unit exhibited elevated levels of plasma high density lipoprotein cholesterol (HDLC) and enhanced metabolic disposal of antipyrine. Followig a 2-week abstinence treatment, the HDLC levels were reduced by 28% (from 64 to 47 mg/100 ml) and the $\text{t}\text{1}\text{2}$ of antipyrine was extended from 12.4 to 13.7 hours. The extent of the HDLC reduction correlated with the antipyrine $\text{t}\text{1}\text{2}$ changes (r = ?0.753, P = 0.05).