Showing papers on "High-density lipoprotein published in 1993"

Moderate Alcohol Intake, Increased Levels of High-Density Lipoprotein and Its Subfractions, and Decreased Risk of Myocardial Infarction

Abstract: Background Previous studies have suggested that moderate alcohol intake exerts a protective effect against coronary heart disease. Alterations in plasma lipoprotein levels represent one plausible mechanism of this apparent protective effect. Methods We therefore examined the interrelation among alcohol consumption, plasma lipoprotein levels, and the risk of myocardial infarction in 340 patients who had had myocardial infarctions and an equal number of age- and sex-matched controls. The case patients were men or women less than 76 years of age with no history of coronary disease who were discharged from one of six hospitals in the Boston area with a diagnosis of a confirmed myocardial infarction. Alcohol consumption was estimated by means of a food-frequency questionnaire. Results We observed a significant inverse association between alcohol consumption and the risk of myocardial infarction (P for trend, <0.001 after control for known coronary risk factors). In multivariate analyses, the relative risk for ...

Effects of oleate-rich and linoleate-rich diets on the susceptibility of low density lipoprotein to oxidative modification in mildly hypercholesterolemic subjects.

Abstract: We report the results of feeding oleate- or linoleate-enriched diets for 8 wk to mildly hypercholesterolemic subjects and the resulting alterations in composition and functional properties of their plasma LDL and HDL. LDL isolated from subjects on oleate-enriched diets was less susceptible to copper-mediated oxidation, as measured by conjugated diene and lipid peroxide formation, and less susceptible to LDL-protein modification, as evidenced by reduced LDL macrophage degradation after copper- or endothelial cell-induced oxidation. For all subjects, the percentage of 18:2 in LDL correlated strongly with the extent of conjugated diene formation (r = 0.89, P < 0.01) and macrophage degradation (r = 0.71, P < 0.01). Oxidation of LDL led to initial rapid depletion of unsaturated fatty acids in phospholipids followed by extensive loss of unsaturated fatty acids in cholesteryl esters and triglycerides. Changes in HDL fatty acid composition also occurred. However, HDL from both dietary groups retained its ability to inhibit oxidative modification of LDL. This study demonstrates that alterations in dietary fatty acid composition can effectively alter the fatty acid distribution of LDL and HDL in hypercholesterolemic subjects and that susceptibility to LDL oxidation is altered by these changes. Substitution of monounsaturated (rather than polyunsaturated) fatty acids for saturated fatty acids in the diet might be preferable for the prevention of atherosclerosis.

Identification of a distinct human high-density lipoprotein subspecies defined by a lipoprotein-associated protein, K-45. Identity of K-45 with paraoxonase.

Abstract: In an attempt to provide immunological tools for subfractionation of high-density lipoproteins (HDL), monoclonal antibodies were raised against HDL complexes. Two clones identified a peptide, provisionally named K-45 (pI 4.5-4.9; molecular mass 45 kDa, range 42-48 kDa), whose plasma distribution and lipoprotein association were fully characterised. Gel filtration localised the peptide to the HDL region of human plasma where it co-eluted with apolipoprotein (apo) A-I, the structural protein of HDL. Complementary studies employing immunoabsorption with anti-(apo A-I) antibodies removed 90% of K-45 from plasma: conversely, anti-(apo A-II) antibodies eliminated only 10% of K-45. Immunoaffinity chromatography on an anti-(K-45) column revealed that the peptide was present in a distinct HDL subsepecies containing three major proteins: K-45, apo A-I and clusterin or apo J. The lipoprotein nature of the bound fraction was indicated by electron microscopy (diameter 9.6 +/- 3.3 nm) and quantification of lipids, the latter showing an unusually high triacyglycerol concentration. Plasma concentrations of K-45 were positively correlated with apo A-I and HDL-cholesterol and negatively correlated with apo B and total cholesterol. Thus, the peptide appears to be linked, directly or indirectly, to processes which give rise to an anti-atherogenic lipid profile. After completion of the present studies, an N-terminal sequence identical to that of K-45 was reported in recently isolated cDNA clones. These clones encode paraoxonase.

Atherosclerosis in transgenic mice overexpressing apolipoprotein A-II.

Abstract: Concentrations of plasma high density lipoprotein (HDL) are inversely correlated with atherosclerotic coronary artery disease. The two most abundant protein constituents of HDL are apolipoproteins A-I and A-II (apoA-I and apoA-II). ApoA-I is required for assembly of HDL and, when overexpressed in transgenic mice, confers resistance to early atherosclerosis. The present studies reveal that transgenic mice that overexpress mouse apoA-II had elevated HDL-cholesterol concentrations but, nevertheless, exhibited increased atherosclerotic lesion development as compared to normal mice. The HDL in the transgenic mice was larger and had an increased ratio of apoA-II to apoA-I. Thus, both the composition and amount of HDL appear to be important determinants of atherosclerosis.

Triglyceride, High-Density Lipoprotein, and Coronary Heart Disease

Abstract: GREAT progress has been made over the past 30 years in identifying cardiovascular risk factors and in developing and implementing measures to correct them The Adult Treatment Panel of the National Cholesterol Education Program developed guidelines in 1988 that identified low-density lipoprotein (LDL) as the major atherogenic lipoprotein and high levels of LDL cholesterol (LDL-C) as the primary target for cholesterol-lowering therapy Since these guidelines were developed, the scientific database has significantly expanded Genetic investigations into familial dyslipidemias, advances in molecular biology, animal experiments, human observational studies, lipid metabolic studies, epidemiologic data, and the results of interventional clinical trials looking at mortality, cardiovascular end points, and angiographic changes in atheromatous lesions have created interest in further examination of the role of high-density lipoprotein cholesterol (HDL-C) and triglycerides (TGs) in the pathogenesis of coronary artery disease To address these questions, the National Heart, Lung, and Blood Institute and the Office of

The role of high-density lipoprotein and lipid-soluble antioxidant vitamins in inhibiting low-density lipoprotein oxidation.

Abstract: 1. The oxidation of low-density lipoprotein (LDL) is believed to play a central role in atherogenesis. We have compared the effect of antioxidant vitamins and high-density lipoprotein (HDL) on the Cu(2+)-catalysed oxidation of LDL. 2. Antioxidant vitamin supplementation significantly reduced conjugated diene formation but did not affect the formation of lipid peroxides. 3. Conversely, HDL did not affect conjugated diene formation but inhibited the formation of lipid peroxides by up to 90%. 4. The inhibition by HDL of lipid peroxide formation in oxidized LDL was dependent on the concentration of HDL and was not due to HDL chelating Cu2+. 5. Large interindividual variations in the inhibition of lipid peroxide formation by autologous HDL were evident, which were related to the rate of lipid peroxide generation in the LDL. 6. We conclude that HDL is a powerful antioxidant or more probably inhibitor of LDL oxidation in vitro and may play an important role in vivo in preventing atherosclerosis by inhibiting LDL oxidation in the artery wall.

Relationship of sex hormones to lipids and lipoproteins in nondiabetic men.

Abstract: Although many studies show that increased androgenicity is associated with increased triglyceride (TG) and decreased high density lipoprotein cholesterol in both pre- and postmenopausal women, relatively few data are available on the association of sex hormones to lipids and lipoproteins in men. We examined the association of sex hormone-binding globulin (SHBG), total and free testosterone, dehydroepiandrosterone sulfate (DHEA-SO4), and estradiol with lipids and lipoproteins in 178 nondiabetic men from the San Antonio Heart Study, a population-based study of diabetes and cardiovascular disease. The TG concentration was significantly inversely related to SHBG (r = -0.22), free testosterone (r = -0.15), total testosterone (r = -0.22), and DHEA-SO4 (r = -0.16). High density lipoprotein (HDL) cholesterol was significantly positively correlated to SHBG (r = 0.21), free testosterone (r = 0.15), total testosterone (r = 0.17), and DHEA-SO4 (r = 0.16). Total testosterone was significantly related to total cholesterol (r = -0.17) and low density lipoprotein cholesterol (r = -0.15). After adjustment for age, body mass index, waist to hip ratio, and glucose and insulin concentrations, TG concentrations remained significantly related to SHBG (r = -0.20), free testosterone (r = -0.15), and DHEA-SO4 (r = -0.18), and HDL cholesterol remained significantly associated with SHBG (r = 0.17), free testosterone (r = 0.15), total testosterone (r = 0.14), and DHEA-SO4 (r = 0.16). In conclusion, we observed a less atherogenic lipid and lipoprotein profile with increased testosterone concentrations. This was not explained by differences in glucose or insulin concentrations. However, sex hormones explained only a small percentage of the variation in total TG and HDL cholesterol concentrations. These findings are in striking contrast to data from women, in whom increased androgenicity is strongly associated with increased TG and decreased HDL cholesterol levels.

Increased plasma and renal clearance of an exchangeable pool of apolipoprotein A-I in subjects with low levels of high density lipoprotein cholesterol

Abstract: Plasma levels of HDL apo A-I are reduced in individuals with low HDL cholesterol (HDL-C) concentrations as a result of increased fractional catabolic rates (FCRs). To determine the basis for the high apo A-I FCRs, seven subjects with low HDL-C levels (31.0 +/- 4.3 mg/dl) were compared with three subjects with high HDL-C levels (72.0 +/- 4.5 mg/dl). Each subject received autologous HDL that was labeled directly by the iodine-monochloride method (whole-labeled) and autologous HDL that was labeled by exchange with homologous radiolabeled apo A-I (exchange-labeled). Blood was obtained for 2 wk, specific activities determined, and FCRs (d-1 +/- SD) estimated. In every subject, whether in the low or high HDL-C group, the exchange-labeled FCR was greater than the whole-labeled FCR. The exchange-labeled FCR was higher in the low HDL-C group (0.339 +/- 0.043) versus the high HDL-C group (0.234 +/- 0.047; P 1.210 (as percentage of total plasma counts per minute) with the exchange-labeled tracer than with the whole-labeled tracer (12.55 +/- 4.95% vs. 1.02 +/- 0.38%; P 1.210 in the low versus the high HDL-C groups. When apo A-I catabolism was studied by perfusing isolated rabbit kidneys with whole-labeled HDL, there was twice as much accumulation (cpm/g cortex) of HDL apo A-I isolated from subjects with low HDL-C than from subjects with high HDL-C (P < 0.0025). Finally, HDL that had been isolated from subjects with high levels of HDL-C was triglyceride enriched and exposed to partially purified lipases before perfusion through kidneys. Threefold more apo A-I from modified HDL accumulated in the cortex compared with the unmodified preparation (P < 0.007). The results of these in vivo and ex vivo studies indicate that individuals with low HDL-C levels have more loosely bound, easily exchanged apo A-I and that this exchangeable apo A-I is more readily cleared by the kidney.

Growth hormone treatment of growth hormone-deficient adults results in a marked increase in Lp(a) and HDL cholesterol concentrations.

Abstract: The effects of growth hormone treatment of adults with adult-onset pituitary insufficiency on lipoproteins and apolipoproteins were investigated. Nine patients, one women and eight men (age range, 34-58 years), who had been treated for pituitary tumors were studied. They had complete pituitary insufficiency with a duration of at least 1 year. All patients received replacement therapy with thyroid hormones, glucocorticoids, and gonadal steroids. The study had a double-blind, placebo-controlled, crossover design for active treatment with recombinant human growth hormone (0.25-0.5 units/kg per week s.c. given each evening) for 6 months. Fasting serum levels of cholesterol; triglycerides; high density lipoprotein and low density lipoprotein cholesterol; apolipoproteins A-I, B, and E; and lipoprotein (a) were measured before and after 6 and 26 weeks of treatment. Lipoprotein (a) concentrations increased markedly during treatment and were about twice as high compared with pretreatment levels. Serum cholesterol and low density lipoprotein cholesterol concentrations were decreased after 6 weeks of treatment, but levels had returned to pretreatment levels after 26 weeks. High density lipoprotein cholesterol concentrations increased during treatment and were significantly higher than pretreatment levels after 26 weeks of treatment. Serum triglyceride concentrations did not change significantly, but in two patients with marked hypertriglyceridemia, growth hormone treatment resulted in a marked decrease. Serum concentrations of apolipoproteins A-I, B, and E did not change significantly, but changes in apolipoprotein A-I and B concentrations were in parallel to those observed for high density lipoprotein cholesterol and low density lipoprotein cholesterol, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcohol consumption and insulin concentrations. Role of insulin in associations of alcohol intake with high-density lipoprotein cholesterol and triglycerides.

Abstract: BACKGROUNDThe relation between alcohol intake and insulin levels may explain, in part, the reported associations of alcohol with cardiovascular disease risk factors, including high-density lipoprotein (HDL) cholesterol, triglycerides, blood pressure, and glucose levels, each of which has been recognized as a component of the insulin resistance syndrome.METHODS AND RESULTSSubjects included nondiabetic participants of the Kaiser Permanente Women Twins Study (1989 through 1990). Usual alcohol intake was assessed as part of a food frequency questionnaire. For women from twin pairs in which both twins drank (n = 338), an increment of 12 g of alcohol per day (about one drink) was associated with an 8% lower 2-hour post-glucose-load insulin (P < .01) in a multiple regression analysis for twin data, adjusted for age, body mass index, waist-to-hip ratio, total caloric intake, and family history of diabetes. With genetic influences removed by matched analysis of the subset of 98 monozygotic twin pairs, an intrapair...

The novel compound NO-1886 increases lipoprotein lipase activity with resulting elevation of high density lipoprotein cholesterol, and long-term administration inhibits atherogenesis in the coronary arteries of rats with experimental atherosclerosis

Abstract: We have discovered a novel compound, NO-1886, which possesses a powerful lipoprotein lipase (LPL) activity-increasing action. Administration of NO-1886 increased LPL activity in the postheparin plasma, adipose tissue, and myocardium of rats, and produced a reduction in plasma triglyceride levels with concomitant elevation of HDL cholesterol levels. Administration of NO-1886 increased LPL enzyme mass in postheparin plasma and mRNA activity in epididymal adipose tissue, and it was concluded that the mode of action of this compound is stimulation of tissue LPL synthesis. We also conducted long-term studies to assess the impact of increases in LPL activity and HDL levels on the development of atherosclerotic lesions in rats. Administration of NO-1886 for as long as 90 d significantly decreased the degree of atherosclerotic changes in the coronary arteries of vitamin D2-treated, cholesterol-fed rats. Statistical analysis indicated that increased concentration of HDL is the factor contributing mostly to the prevention of coronary artery sclerosis. In summary, the results of our study indicate that compound NO-1886 increases LPL activity, causing an elevation in HDL levels, and that long-term administration of NO-1886 to rats with experimental atherosclerosis provides significant protection against the development of coronary artery lesions.

Hypertriglyceridemia and cholesteryl ester transfer protein interact to dramatically alter high density lipoprotein levels, particle sizes, and metabolism. Studies in transgenic mice.

Abstract: Several types of transgenic mice were used to study the influence of hypertriglyceridemia and cholesteryl ester transfer protein (CETP) expression on high density lipoprotein (HDL) levels, particle sizes, and metabolism. The presence of the CETP transgene in hypertriglyceridemic human apo CIII transgenic mice lowered HDL-cholesterol (HDL-C) 48% and apolipoprotein (apo) A-I 40%, decreased HDL size (particle diameter from 9.8 to 8.8 nm), increased HDL cholesterol ester (CE) fractional catabolic rate (FCR) 65% with a small decrease in HDL CE transport rate (TR) and increased apo A-I FCR 15% and decreased apo A-I TR 29%. The presence of the CETP transgene in hypertriglyceridemic mice with human-like HDL, human apo A-I apo CIII transgenic mice, lowered HDL-C 61% and apo A-I 45%, caused a dramatic diminution of HDL particle size (particle diameters from 10.3 and 9.1 to 7.6 nm), increased HDL CE FCR by 107% without affecting HDL CE TR, and increased apo A-I FCR 35% and decreased apo A-I TR 48%. Moreover, unexpectedly, hypertriglyceridemia alone in the absence of CETP was also found to cause lower HDL-C and apo A-I levels primarily by decreasing TRs. Decreased apo A-I TR was confirmed by an in vivo labeling study and found to be associated with a decrease in intestinal but not hepatic apo A-I mRNA levels. In summary, the introduction of the human apo A-I, apo CIII, and CETP genes into transgenic mice produced a high-triglyceride, low-HDL-C lipoprotein phenotype. Human apo A-I gene overexpression caused a diminution of mouse apo A-I and a change from monodisperse to polydisperse HDL. Human apo CIII gene overexpression caused hypertriglyceridemia with a significant decrease in HDL-C and apo A-I levels primarily due to decreased HDL CE and apo A-I TR but without a profound change in HDL size. In the hypertriglyceridemic mice, human CETP gene expression further reduced HDL-C and apo A-I levels, primarily by increasing HDL CE and apo A-I FCR, while dramatically reducing HDL size. This study provides insights into the genes that may cause the high-triglyceride, low-HDL-C phenotype in humans and the metabolic mechanisms involved.

Oxidative tyrosylation of high density lipoprotein by peroxidase enhances cholesterol removal from cultured fibroblasts and macrophage foam cells.

Abstract: Lipoprotein oxidation is thought to play a pivotal role in atherogenesis, yet the underlying reaction mechanisms remain poorly understood. We have explored the possibility that high density lipoprotein (HDL) might be oxidized by peroxidase-generated tyrosyl radical. Exposure of HDL to L-tyrosine, H2O2, and horseradish peroxidase crosslinked its apolipoproteins and strikingly increased protein-associated fluorescence. The reaction required L-tyrosine but was independent of free metal ions; it was blocked by either catalase or the heme poison aminotriazole. Dityrosine and other tyrosine oxidation products were detected in the apolipoproteins of HDL modified by the peroxidase/L-tyrosine/H2O2 system, implicating tyrosyl radical in the reaction pathway. Further evidence suggests that tyrosylated HDL removes cholesterol from cultured cells more effectively than does HDL. Tyrosylated HDL was more potent than HDL at inhibiting cholesterol esterification by the acyl-CoA:cholesterol acyltransferase reaction, stimulating the incorporation of [14C]acetate into [14C]cholesterol, and depleting cholesteryl ester stores in human skin fibroblasts. Moreover, exposure of mouse macrophage foam cells to tyrosylated HDL markedly diminished cholesteryl ester and free cholesterol mass. We have recently found that myeloperoxidase, a heme protein secreted by activated phagocytes, can also convert L-tyrosine to o,o'-dityrosine. This raises the possibility that myeloperoxidase-generated tyrosyl radical may modify HDL, enabling the lipoprotein to protect the artery wall against pathological cholesterol accumulation.

Induction of murine macrophage growth by modified LDLs.

Abstract: We previously reported that cell membrane components and lipoproteins were able to induce the growth of murine peritoneal macrophages. The aim of the present study was to examine whether macrophage growth could also be induced by chemically modified lipoproteins, such as acetylated low density lipoprotein (acetyl-LDL) or oxidized LDL, ligands known to be endocytosed by the macrophage scavenger receptors. When murine peritoneal exudate macrophages were cultured in vitro with 25-100 micrograms/mL acetyl-LDL or oxidized LDL, significant growth was induced. On comparing the dose-response curves of these LDLs, a more potent effect was seen with oxidized LDL than acetyl-LDL, especially on resident macrophages. On the other hand, growth of these cells was not stimulated by native (unmodified) LDL or high density lipoprotein. These in vitro data revealed a new function of chemically modified LDLs as effective inducers of macrophage cell growth. This aspect may be physiologically relevant to the growth of macrophage foam cells in situ in the development of atherosclerosis.

Effects of simvastatin on apoB metabolism and LDL subfraction distribution.

Abstract: Seven moderately hypercholesterolemic subjects were studied before and after 10 weeks of simvastatin therapy (20 mg/day). Therapy reduced low density lipoprotein (LDL) cholesterol by 39% (p < 0.001), whereas high density lipoprotein and very low density lipoprotein (VLDL) cholesterol were unchanged. Apolipoprotein (apo) B-containing lipoproteins were divided into VLDL1 (Sf 60-400), VLDL2 (Sf 20-60), intermediate density lipoprotein (IDL) (Sf 12-20), and LDL (Sf 0-12), and metabolic changes were sought in dual-tracer VLDL1 and VLDL2 turnover studies. VLDL1 apoB pool size was unaltered by therapy, as were its rates of synthesis, catabolism, and delipidation to VLDL2. Similarly, the VLDL2 apoB pool size was unchanged, but its metabolic fate was altered. The IDL pool size fell significantly (27%, p < 0.01) due entirely to an increased fractional catabolism of the lipoprotein. In our subjects, the circulating mass of LDL apoB decreased (49%, p < 0.01) primarily due to a reduction in its synthesis. Before therapy, 30% of the apoB entering the delipidation cascade in these hyperlipidemic subjects was converted to LDL. On therapy the input remained the same, but direct catabolism from VLDL2 and IDL was increased (p < 0.05), and as a result only 16% eventually appeared in LDL. These kinetic changes were associated with a fall in particle cholesteryl ester content throughout the delipidation cascade. We also observed a link between LDL kinetics and its subfraction distribution. Simvastatin influences the metabolism of LDL, IDL, and VLDL2 but not VLDL1.

Dietary fat increases high density lipoprotein (HDL) levels both by increasing the transport rates and decreasing the fractional catabolic rates of HDL cholesterol ester and apolipoprotein (Apo) A-I. Presentation of a new animal model and mechanistic studies in human Apo A-I transgenic and control mice.

Abstract: In humans, diets high in saturated fat and cholesterol raise HDL-cholesterol (HDL-C) levels. To explore the mechanism, we have devised a mouse model that mimics the human situation. In this model, HuAITg and control mice were studied on low fat (9% cal)-low cholesterol (57 mg/1,000 kcal) (chow) and high fat (41% cal)-high cholesterol (437 mg/1,000 kcal) (milk-fat based) diets. The mice responded to increased dietary fat by increasing both HDL-C and apo A-I levels, with a greater increase in HDL-C levels. This was compatible with an increase in HDL size observed by nondenaturing gradient gel electrophoresis. Turnover studies with doubly labeled HDL showed that dietary fat both increase the transport rate (TR) and decreased the fractional catabolic rate of HDL cholesterol ester (CE) and apo A-I, with the largest effect on HDL CE TR. The latter suggested that dietary fat increases reverse cholesterol transport through the HDL pathway, perhaps as an adaptation to the metabolic load of a high fat diet. The increase in apo A-I TR by dietary fat was confirmed by experiments showing increased apo A-I secretion from primary hepatocytes isolated from animals on the high fat diet. The increased apo A-I production was not associated with any increase in hepatic or intestinal apo A-I mRNA, suggesting that the mechanism of the dietary fat effect was posttranscriptional, involving either increased translatability of the apo A-I mRNA or less intracellular apo A-I degradation. The dietary fat-induced decrease in HDL CE and apo A-I fractional catabolic rate may have been caused by the increase in HDL particle size, as was suggested by our previous studies in humans. In summary, a mouse model has been developed and experiments performed to better understand the paradoxical HDL-raising effect of a high fat diet.

Cell-derived unesterified cholesterol cycles between different HDLs and LDL for its effective esterification in plasma.

Abstract: Pulse-chase incubations of human plasma with [3H]cholesterol-laden skin fibroblasts or low density lipoproteins (LDL) and nondenaturing two-dimensional electrophoresis were used to study the transfer and esterification of cell-derived unesterified cholesterol (UC) in human plasma lipoproteins. Specific radioactivities ([3H]UC per microgram of UC) were calculated, and net cholesterol mass transfer was quantified using a fluoro-enzymatic assay to validate productive transfers of UC between high density lipoprotein (HDL) and LDL. Cellular UC was initially taken up by pre-beta 1-HDL and subsequently transferred in the sequence pre-beta 2-HDL-->pre-beta 3-HDL-->alpha-HDL-->LDL. During the first 5 minutes of this process, only 5% of cellular cholesterol was esterified in pre-beta 3-HDL and alpha-HDL; the remainder reached LDL as UC. Cellular UC accumulating in LDL was then redistributed to various HDL particles via two pathways: 1) the partially LDL receptor-mediated uptake and re-secretion of UC by cells and 2) the direct transfer of UC to HDL, mostly to alpha-HDL and a small amount to pre-beta-HDL. UC was not transferred from LDL to HDL after inhibition of lecithin:cholesterol acyltransferase (LCAT). The esterification of cellular [3H]cholesterol in plasma was competitively inhibited by the addition of excess unlabeled LDL but not of excess HDL. However, both excess LDL and excess HDL prevented the esterification of cell-derived cholesterol in apolipoprotein B-free plasma. This demonstrated that LDL is the major source of UC to the LCAT reaction and that the transfer of UC from LDL to HDL is LCAT dependent. In conclusion, the effective esterification of cell-derived cholesterol in plasma involves a rapid transfer of UC via HDL particles to LDL, from which it is distributed to pre-beta-HDL and alpha-HDL. Furthermore, we hypothesize that the transfer per se of cellular UC to LDL forms a cholesterol concentration gradient between cell membranes and HDL and thus a second, reverse cholesterol transport mechanism in addition to the esterification of cholesterol by LCAT.

Thyroxine replacement therapy and circulating lipid concentrations.

Abstract: OBJECTIVE Hypothyroidism is a common disorder and while the association of overt hypothyroidism with hypercholesterolaemia is clear, the effect upon lipids of the minor abnormalities of thyroid function often found in those receiving T4 replacement therapy is unclear. The aim of the present studies was to define in those with hypothyroidism the effect upon circulating lipids of subtle changes in thyroid status, indicated by serum TSH values below or above the normal range. DESIGN (i) Prospective study of short-term T4 treatment of those with subclinical hypothyroidism. (ii) Cross-sectional study of long-term T4 treatment, comparing non-T4 treated controls and T4 treated patients with serum TSH values either below or within the normal range. PATIENTS Short-term T4 therapy was examined in 11 post-menopausal females with subclinical hypothyroidism (high TSH, normal free T4) studied before therapy and 6 weeks after T4 at incremental doses (50, 100, 150 micrograms/day). Long-term T4 treatment for hypothyroidism was investigated in 105 females on therapy for at least 1 year compared with 105 controls matched for age and menopausal status. MEASUREMENTS Fasting levels of total cholesterol, low density lipoprotein (LDL) cholesterol, high density lipoprotein (HDL) cholesterol and HDL subfractions were determined in patients and controls. RESULTS (i) T4 treatment of subjects with subclinical hypothyroidism resulted in reductions in total and LDL cholesterol with increasing T4 dose (P < 0.001). Comparison of lipid results pretreatment with those when TSH was restored to normal revealed no significant difference in lipids; in contrast, comparison of lipids in those with normal TSH compared with the same subjects when TSH was suppressed revealed reductions in total and LDL cholesterol. (ii) Long-term T4 treatment was associated with a reduction in total and LDL cholesterol measurements in those over 55 years receiving suppressive doses of T4 but no significant difference in lipids in those with normal serum TSH compared with non-T4 treated controls. CONCLUSION Effects of T4 upon lipid measurements suggest that patients with subclinical hypothyroidism should receive replacement therapy. Doses of T4 which suppress TSH to below normal may have a more significant influence upon lipids than doses of T4 which restore TSH to the normal range.

Rationale and design of the Department of Veterans Affairs high-density lipoprotein cholesterol Intervention Trial (HIT) for secondary prevention of coronary artery disease in men with low high-density lipoprotein cholesterol and desirable low-density lipoprotein cholesterol

Abstract: Although a large body of epidemiologic evidence suggests that low levels of high-density lipoprotein (HDL) cholesterol are strongly associated with an increased risk of coronary artery disease (CAD), no large-scale clinical trials focusing on this association have been reported. This report describes the rationale and design of the Department of Veterans Affairs HDL Intervention Trial (HIT), a multicenter, randomized, controlled clinical trial designed to determine whether lipid therapy reduces the combined incidence of CAD death and nonfatal myocardial infarction in men with established CAD who have low levels of HDL cholesterol with "desirable" levels of low-density lipoprotein (LDL) cholesterol. Twenty-five hundred men with CAD and HDL cholesterol < or = 40 mg/dl, LDL cholesterol < or = 140 mg/dl, and triglycerides < or = 300 mg/dl are being recruited at 20 Department of Veterans Affairs medical centers, randomized to either gemfibrozil or placebo, and followed in a double-blind manner for an average of 6 years. In this population, gemfibrozil is expected to increase HDL cholesterol by 10 to 15%, have a negligible effect on LDL cholesterol, and lower triglycerides by 30 to 40%. Because an estimated 20 to 30% of patients with CAD have a low HDL cholesterol as their primary lipid abnormality, the results of this trial are expected to have far-reaching clinical implications.

Low density lipoprotein- and high density lipoprotein-mediated signal transduction and exocytosis in alveolar type II cells.

Abstract: Low density lipoproteins (LDL) and high density lipoproteins (HDL) from serum stimulate signal-transduction pathways and exocytosis in rat alveolar type II cells. Both LDL and HDL stimulated primary cultures of type II cells to secrete phosphatidylcholine (PtdCho), the major phospholipid component of pulmonary surfactant. The effects on secretion were preceded temporally by stimulation of inositol phospholipid catabolism, calcium mobilization, and translocation of protein kinase C from cytosolic to membrane compartments. Heparin, which blocks the binding of ligands to the LDL receptor, completely inhibited the effects of LDL on signal transduction and PtdCho secretion but did not inhibit the effects of HDL. Unilamellar PtdCho liposomes the size of native LDL had no effect on type II cells; however, PtdCho complexes containing either apolipoproteins E or A-I stimulated both signal transduction and PtdCho secretion. LDL receptors were present in type II cell membranes by immunoblotting. In contrast to findings with hepatic membranes, type II cells exhibited two major bands of 130 kDa and 120 kDa and a minor band at 230 kDa that also was present under reducing conditions. These results are consistent with our hypothesis that the LDL-receptor pathway functions in vivo to deliver cholesterol to type II cells and that this process is coupled to surfactant assembly and secretion via signal-transduction pathway(s). HDL elicits similar responses independent of the LDL receptor, suggesting that type II cells may use the selective uptake pathway to obtain cholesterol or that HDL triggers signal transduction by mechanisms unrelated to lipid delivery.

Low levels of total cholesterol, high‐density lipoprotein, and apolipoprotein a1 in association with anticardiolipin antibodies in patients with systemic lupus erythematosus

Abstract: Objective. To determine if there is an association between low levels of high-density lipoprotein cholesterol (HDL), apolipoprotein A1 (Apo A1), total cholesterol, and anticardiolipin antibody (aCL) in patients with systemic lupus erythematosus (SLE) who are not taking corticosteroids. Methods. We studied 75 outpatients with documented SLE who were attending our hospital clinics: 57 were aCL positive and 18 were aCL negative. Both IgG and IgM aCL levels were determined by enzyme-linked immunosorbent assay. Lipid fractions (total cholesterol, HDL, low-density lipoprotein, very–low-density lipoprotein, and triglycerides) were determined by standard enzymatic techniques. Apo A1 and Apo B levels were determined by nephelometry. Results. Patients with SLE who were IgG aCL + had low levels of serum cholesterol (mean ± SD 173.6 ± 34.6 mg/dl) and HDL (43.9 ± 16.3 mg/dl) compared with aCL– SLE patients, normal donors, and patients with other diseases. Apo A1 levels were also low in the aCL + group (95.5 ± 50.9 mg/dl) compared with the aCL– group (152.7 ± 32.6 mg/dl). There was no association of total cholesterol level or aCL titer with clinical activity. Conclusion. These data indicate that in SLE patients, there is an association between antibody against the phospholipid cardiolipin and low levels of cholesterol, HDL, and Apo A1.