A family of homozygous familial hyperalphalipoproteinemia with complete deficiency of cholesteryl ester transfer activity

The propositus was a 43-year-old Japanese male with a plasma total cholesterol (chol) level of 252 mg/dl and a high density lipoprotein (HDL)-chol of 169 mg/dl. His brother also had a markedly higher HDL-chol level of 149 mg/dl. In addition, his mother, sister and all 3 children had higher HDL-chol levels of 75-91 mg/dl. These data suggest that the propositus and his brother were homozygous for familial hyperalphalipoproteinemia (FHALP), whereas his mother, sister and 3 children were heterozygous for FHALP. None had any clinical signs of atherosclerosis. The propositus and his brother (homozygous FHALP) also showed markedly higher levels of apo AI (greater than or equal to 190 mg/dl) and E (greater than 16 mg/dl). Ultracentrifugal analysis disclosed an increase of HDL2-chol in the propositus. Cholesteryl ester transfer activity (CETA) was completely absent in the propositus (0.0% transfer/5 microliters/18 hr) and his brother (0.3% transfer/5 microliters/18 hr). It is concluded that this case is a family of homozygous FHALP probably caused by complete deficiency of CETA.     

Expression of the human apolipoprotein A-I gene in transgenic mice alters high density lipoprotein (HDL) particle size distribution and diminishes selective uptake of HDL cholesteryl esters.

Transgenic mice carrying the human apolipoprotein (apo) A-I gene (HuAITg mice) were used to examine the effects of overexpression of the human gene on high density lipoprotein (HDL) particle size distribution and metabolism. On a chow diet, control mice had HDL cholesterol and apo A-I levels of 49 +/- 2 and 137 +/- 12 mg/dl of plasma, respectively. HuAITg mice had HDL cholesterol, human apo A-I, and mouse apo A-I levels of 88 +/- 2, 255 +/- 19, and 16 +/- 2 mg/dl, respectively. Nondenaturing gradient gel electrophoresis revealed control mouse plasma HDL to be primarily monodisperse with a particle diameter of 10.2 nm, whereas HuAITg mouse plasma HDL was polydisperse with particles of diameter 11.4, 10.2, and 8.7 nm, which correspond in size to human HDL1, HDL2, and HDL3, respectively. In vivo turnover studies of HDL labeled with [3H]cholesteryl linoleyl ether (representing the cholesteryl ester pool) and 125I-apo A-I were performed. In control animals, the fractional catabolic rate (FCR) for HDL cholesteryl ester (0.197 +/- 0.010 pool/hr) was significantly (P less than 0.0005) more than the apo A-I FCR (0.118 +/- 0.006 pool/hr). In the HuAITg mice, the HDL cholesteryl ester FCR (0.124 +/- 0.008 pool/hr) was the same as the apo A-I FCR (0.126 +/- 0.010 pool/hr). There were no significant differences between control and HuAITg animals in the sites of tissue removal of HDL cholesteryl ester, with the liver extracting most of the injected radioactivity. Control and HuAITg animals had comparable liver and intestinal cholesterol synthesis and LDL FCR. In conclusion, HuAITg mice have principally human and not mouse apo A-I in their plasma. This apparently causes a change in HDL particle size distribution in the transgenic mice to one resembling the human pattern. The replacement of mouse by human apo A-I also apparently causes the loss of the selective uptake pathway of HDL cholesteryl esters present in control mice. These data imply that apo A-I primary structure has a profound influence on HDL particle size distribution and metabolism.     

Classical LCAT deficiency resulting from a novel homozygous dinucleotide deletion in exon 4 of the human lecithin: cholesterol acyltransferase gene causing a frameshift and stop codon at residue 144.

Lecithin: cholesterolacyltransferase (LCAT) transacylates the fatty acid at the sn-2 position of lecithin to the 3beta-OH group of cholesterol forming lysolecithin and the majority of cholesteryl ester found in plasma. LCAT participates in the reverse cholesterol transport pathway in man where it esterifies tissue-derived cholesterol following efflux from peripheral cells into HDL. Only 38 unique mutations in the human LCAT gene have been reported worldwide. Our French female proband presented with corneal opacity and no detectable plasma LCAT activity using either endogenous or exogenous assays. Her total plasma cholesterol and HDL cholesterol were low (2.34 mmol/l and 0.184 mmol/l, respectively) with a very high cholesterol/cholesteryl ester molar ratio (10.9:1). Plasma triglycerides were 0.470 mmol/l with low apo B (40.5 mg/dl), apo A-I (14.7 mg/dl), apo A-II (6.8 mg/dl) and apo E (2.1 mg/dl) levels. Plasma lipoprotein analysis by ultracentrifugation showed very low HDL concentrations and a characteristic shift of the lipoprotein profile towards larger, less dense particles. No proteinuria, renal dysfunction or signs of atherosclerosis were noted at age 45. Sequence analysis of her LCAT gene showed a novel homozygous TG-deletion at residues 138-139 that resulted in a frameshift causing the generation of a stop codon and premature termination of the LCAT protein at amino acid residue 144. Western blotting of the patient's plasma using a polyclonal IgY primary antibody against human LCAT failed to demonstrate the presence of a truncated LCAT protein. A 53 bp mismatched PCR primer was designed to generate an Fsp 1 restriction site in the wild type sequence of exon 4 where the mutation occurred. The 155 bp PCR product from the wild type allele produced a 103 bp and 52 bp fragment with Fsp 1 and no cleavage products with the mutant allele thus permitting rapid screening for this novel mutation.     

Cellular cholesterol efflux to plasma from moderately hypercholesterolaemic type 1 diabetic patients is enhanced, and is unaffected by simvastatin treatment

Aim/hypothesis Cellular cholesterol efflux to plasma is important in reverse cholesterol transport and may be affected by simvastatin in type 1 diabetes mellitus.Methods In 14 moderately hypercholesterolaemic type 1 diabetic and 13 healthy men we determined plasma (apo)lipoproteins, pre- HDL formation, cholesteryl ester transfer protein (CETP) activity, phospholipid transfer protein (PLTP) activity, cholesterol esterification, cholesteryl ester transfer and the capacity of plasma to induce cholesterol efflux out of Fu5AH cells and fibroblasts. After diet run-in, diabetic patients were randomly treated with simvastatin 10, 20, 40 mg and placebo, once daily each, for 6 weeks in a double-blind crossover design.Results Plasma very low density lipid protein (VLDL)+LDL cholesterol, LDL cholesterol, HDL phospholipids, apolipoprotein (apo) A-I, apo B, CETP activity, PLTP activity, cholesterol esterification, cholesteryl ester transfer and the capacity of plasma to induce cholesterol efflux from Fu5AH cells and fibroblasts were higher in diabetic patients. Pre- HDL formation was unaltered. Simvastatin treatment decreased VLDL+LDL cholesterol, LDL cholesterol, triglycerides and apo B, CETP activity, cholesterol esterification and cholesteryl ester transfer. HDL cholesterol increased and its change was correlated with the change in cholesteryl ester transfer. The ability to promote cholesterol efflux from Fu5AH cells and fibroblasts did not change after simvastatin.Conclusions/interpretation The capacity of plasma from moderately hypercholesterolaemic type 1 diabetic patients to induce cholesterol efflux out of Fu5AH cells and fibroblasts is enhanced, probably due to higher apo A-I, HDL phospholipids and PLTP activity. Simvastatin increases HDL cholesterol in type 1 diabetic patients via lowering of plasma cholesteryl ester transfer. The HDL changes after simvastatin do not increase cellular cholesterol efflux further.     

Cholesteryl ester transfer activity : Localization and role in distribution of cholesteryl ester among lipoproteins in man

The cholesteryl ester exchange/transfer protein is involved in the transport of cholesteryl ester from high density lipoproteins (HDL) to very low density lipoproteins (VLDL) and low density lipoproteins (LDL). Localization of cholesteryl ester transfer activity (CETA) in plasma was studied by measuring CETA in various delipidated fractions from a single step density ultracentrifugation gradient of plasma. CETA was measured in an in vitro system by calculating the exchange of cholesteryl ester in a standard mixture of [3H]CE-HDL and LDL. The method used for the delipidation of plasmas and fractions to be tested was critical. Optimal results were obtained by delipidation with diisopropylether-butanol (60: 40, v/v) at O degrees C. The bulk of CETA was detected in HDL3 (1.125 less than d less than 1.210 g/ml) when the lipoproteins were separated by single-step density gradient ultracentrifugation and in the 'lipoprotein-free' fraction (d greater than 1.250 g/ml) when the lipoproteins were separated by flotation ultracentrifugation including two washes. To determine whether CETA plays a role in the distribution of cholesteryl ester among the various lipoproteins, it was measured in whole plasma from normal and hyperlipidemic subjects. Plasma was delipidated before the assay in order to prevent bias due to variation of cholesterol content. CETA was higher in delipidated plasma of hyperlipidemic subjects (117.3 +/- 36.5 nmol CE/ml/h) than in delipidated plasma of normolipidemic controls (68.7 +/- 17.6 nmol CE/ml/h) (P less than 0.005). A positive correlation (r = 0.80, P less than 0.005) was found between CETA and (VLDL + LDL) cholesterol levels. A negative correlation (r = 0.57, P less than 0.05) existed between CETA and HDL cholesterol. This correlation was found both in the group as a whole and within the normal and the hyperlipidemic groups separately. The activity of the cholesteryl ester transfer appears to be a regulatory factor in the distribution of cholesteryl ester over the various lipoproteins.     

Plasma lipoprotein abnormalities in heterozygotes for familial lecithin:cholesterol acyltransferase deficiency

Measurement of plasma lecithin:cholesterol acyltransferase (LCAT) activity was used to segregate unaffected family members (n = 8) from heterozygotes (n = 8) and homozygotes (n = 2) in a large LCAT-deficient kindred. The activity was absent in the homozygotes and was decreased to 50% of normal in the heterozygotes. Endogenous cholesterol esterification rate measurements did not differentiate the heterozygotes from the unaffected family members or normal subjects. The heterozygotes had significantly higher fasting plasma triglycerides, apo B, and lower HDL-cholesterol and apo AI than the unaffected family members. The HDL of the heterozygotes had the same mass of free cholesterol and triglyceride, but the mass of cholesteryl ester was reduced by 47%. The differences were not related to abnormal postheparin lipolytic activities. However, cholesteryl ester transfer activity in the lipoprotein-free (d greater than 1.21 bottom) fraction of plasma was significantly (P less than .05) decreased in the heterozygotes when compared to unaffected members. We conclude that the low LCAT activity is the likely cause of the qualitative and quantitative differences in the plasma lipoproteins of the heterozygotes in this family with LCAT deficiency. However, the low HDL and apo A-I levels are not associated with either a family or personal history of premature atherosclerosis.     

Lipids, lipoproteins, apolipoproteins, and other risk factors in Chinese men and women with and without myocardial infarction

One hundred and fifty-four male and 69 female Chinese patients, aged between 40 and 60 years, who had suffered myocardial infarction (MI) were investigated and compared with 216 men and 219 women who had no history or ECG evidence of coronary heart disease. The male MI patients had significantly raised levels of triglycerides (160 mg/dl), cholesterol (194 mg/dl), VLDL-CH (31 mg/dl), apolipoprotein B (122 mg/dl) and apolipoprotein E (4.7 mg/dl) and a lower apolipoprotein A-I level (126 mg/dl) than the control group (triglycerides 131, cholesterol 179, VLDL-CH 26, apo B 102, apo E4.2, and apo A-I 138 mg/dl). The women with MI also had higher values for the atherogenic lipids than the control group (triglycerides 175 vs. 134 mg/dl, cholesterol 218 vs. 186 mg/dl, LDL-CH 128 vs. 104 mg/dl, VLDL-CH 32 vs. 26 mg/dl, apo B 121 vs. 103 mg/dl and apo E 5.4 vs. 4.3 mg/dl), as well as lowered apolipoprotein A-I (128 vs. 144 mg/dl). The Lp(a) levels (men and women considered together) were significantly higher for the MI patients (34.3 mg/dl vs. 26.2 mg/dl). Anti-atherogenic lipoproteins such as HDL-cholesterol, HDL2-CH, HDL3-CH, phospholipids and apolipoprotein A-II, C-II and C-III showed no difference between the groups.     

Correlation of serum triglyceride and its reduction by omega-3 fatty acids with lipid transfer activity and the neutral lipid compositions of high-density and low-density lipoproteins

Serum triglyceride (TG) and high-density lipoprotein cholesterol (HDL-C) concentrations are inversely correlated and mechanistically linked by means of lipid transfer activities. Phospholipid transfer activity (PLTA) moves phospholipids among serum lipoproteins; cholesteryl ester transfer activity (CETA), which exchanges cholesteryl esters (CE) and TG among lipoproteins, is stimulated by nonesterified fatty acids (NEFA). The aims of this study were (a) to develop a quantitative model that correlates the neutral lipid (NL = CE + TG) compositions of HDL and LDL with serum TG concentration; (b) identify the serum lipid determinants of CETA and PLTA, and; (c) identify the effects of serum TG reductions on the neutral lipid compositions of HDL and LDL, serum NEFA concentrations, and on PLTA and CETA. These aims were addressed in 40 hypertriglyceridemic subjects before and after treatment with an 85% concentrate of omega-3 fatty acids (Omacor) and in 16 untreated normolipidemic subjects. In vivo, the NL compositions of LDL and HDL were described by a mathematical model having the form of adsorption isotherms: HDL - (TG/NL) = (0.90 +/- 0.07) serum TG/(7.0 +/- 1.2 mmol/l + serum TG) and LDL - (TG/NL) = (0.65 +/- 0.08) serum TG/(4.9 +/- 1.5 mmol/l + serum TG). Reduction of serum TG was associated with reductions in HDL - (TG/NL), serum NEFA concentration, and serum CETA but not PLTA. These data suggest that both hypertriglyceridemia and the attendant elevated serum CETA but not PLTA are determinants of HDL and LDL composition and structure and that serum TG concentrations are good predictors of the NL compositions of HDL and LDL.     

Significance of a polymorphism (G-->A transition) in the -75 position of the apolipoprotein A-I gene promoter on serum high density lipoprotein-cholesterol levels in Japanese hyperlipidemic subjects

High density lipoprotein-cholesterol (HDL-C) levels are inversely related to the incidence of coronary artery disease. We studied the influence of a G(-75)-->A transition in the promoter of the apolipoprotein (apo) A-I gene, a major protein component of HDL, on serum HDL-C levels in hyperlipidemic subjects. Seventy three hyperlipidemic subjects with serum levels of high HDL-C (HDL-C > or = 70 mg/dl, Group H) were compared with hyperlipidemic subjects with levels of HDL-C between 40 and 70 mg/dl (Group N) and those with HDL-C < 40 mg/dl (Group L). Group H showed a higher incidence (45.2%) of low plasma cholesteryl ester transfer protein (CETP) activity than Groups N (9.1%) and L (5.3%) (p < 0.001). Group H had a higher incidence of the G(-75)-->A transition (0.275) than Groups N (0.117, p < 0.05) and L (0.056, p < 0.01), among subjects with normal CETP activities. The HDL-C levels in subjects with the transition (84 +/- 16 mg/dl) were higher than those in subjects without the transition (56 +/- 12 mg/dl) (p < 0.05). These data suggest that a G(-75)-->A transition of the apo A-I gene promoter, in addition to the common mutation of CETP gene, contributes to high HDL-C levels among hyperlipidemic patients in Japan.     

Small polydisperse low density lipoproteins in familial hyperalphalipoproteinemia with complete deficiency of cholesteryl ester transfer activity

Lipoprotein abnormalities were analyzed in 3 cases of marked hyperalphalipoproteinemia caused by complete deficiency of cholesteryl ester transfer activity. The probands were all men, aged 34, 43 and 48 years, respectively. The serum high density lipoprotein (HDL)-cholesterol levels of these patients were higher than 150 mg/dl (157-254 mg/dl), while serum total cholesterol levels ranged from 227 to 360 mg/dl. Sequential flotation-ultracentrifugation analysis disclosed that low density lipoprotein (LDL)-cholesterol was slightly decreased and that cholesteryl ester accumulated solely in the HDL2 fraction, which was also enriched with apolipoprotein E. Cholesteryl ester transfer activity was completely absent in all of these cases. High-performance liquid chromatography showed a decrease of LDL particle size in combination with a marked enlargement of HDL particle size. Analytical ultracentrifugation disclosed heterogeneity of LDL with the presence of small LDL subpopulations. We conclude that hyperalphalipoproteinemia due to complete deficiency of cholesteryl ester transfer activity is characterized by the presence of both small polydisperse LDL and markedly large HDL enriched with cholesteryl ester and apolipoprotein E.     

Inhibition of cholesteryl ester transfer protein increases serum apolipoprotein (apo) A-I levels by increasing the synthesis of apo A-I in rabbits

BACKGROUND: Inhibition of cholesteryl ester transfer protein (CETP) is an effective way to increase HDL levels in animals and humans. The effects of a CETP inhibitor, JTT-705, on the in vivo kinetics of apolipoprotein (apo) A-I and apo A-I gene expression in the liver and intestine were investigated. METHODS: Japanese White rabbits were randomly fed normal rabbit chow LRC-4 (n=10, control) or a food admixture of LRC-4 and 0.75% JTT-705 (n=10, treated) for 7 months. An in vivo kinetics study of apo A-I was performed by injecting rabbit 125I-apo A-I, and apo A-I mRNA levels were quantified by RT-PCR. RESULTS: JTT-705 significantly inhibited CETP activities, increased serum levels of HDL-cholesterol (C), HDL2-C, HDL-phospholipid, and apo A-I, and decreased HDL-triglyceride levels. The synthetic rate of apo A-I was higher in the treated rabbits than in control rabbits (13.7 +/- 2.6 versus 9.5 +/- 1.3 mg/kg per day, P < 0.05), while the fractional catabolic rate was similar in the two groups. JTT-705 increased apo A-I mRNA levels in the liver without affecting those in the intestine. CONCLUSION: Inhibition of CETP activity by JTT-705 increases HDL levels by increasing the synthesis of apo A-I, suggesting that it could be a promising therapeutic approach for atherosclerosis.     

Higher level of plasma cholesteryl ester transfer activity from high-density lipoprotein to Apo B-containing lipoproteins in subjects with angiographically detectable coronary artery disease

Background and hypothesis: Plasma high-density lipoprotein cholesterol (HDL-C) levels correlate inversely with the incidence of coronary artery disease. In order to ascertain whether the transfer activity is related to coronary atherosclerosis, we studied plasma cholesteryl ester transfer activity (CETA) from HDL to apo B-containing lipoproteins in a consecutive series of 64 Japanese men aged <60 years who had undergone diagnostic coronary angiography. Methods: The subjects were divided into two groups: those who had ≥50% luminal stenosis in one or more coronary arteries (Group 1) and those who had <50% stenosis (Group 2). Results: CETA was 20.8±6.0%/2h in 38 subjects in Group 1. significantly higher than 17.4±6.9%/2h in 26 subjects in Group 2(p<0.05). Plasma HDL-C levels in Group 1 were significantly lower than those in Group 2(p<0.05). CETA correlated inversely with HDL-C levels (r = ?0.46, p<0.001). Plasma total cholesterol, low-density lipoprotein cholesterol (LDL-C), triglyceride (TG), and Lp(a) levels did not differ significantly between the two groups. There was no significant correlation between CETA and either LDL-C or TG levels. Conclusion: Results suggest that high CETA is realted to low plasma HDL-C levels and may lead to the development of coronary atherosclerosis. Also, CETA was independent of plasma LDL-C or TG levels.     

A new labeling approach using stable isotopes to study in vivo plasma cholesterol metabolism in humans.

A method to study reverse cholesterol transport in humans was developed using stable isotopes and kinetic analysis. Three normolipidemic subjects received simultaneous intravenous infusions of deuterated leucine and (13)C-acetate for 14 and 8 hours, respectively. Deuterium enrichment was measured in protein-bound leucine in apolipoproteins (apo) B-100 and A-I (using gas chromatography coupled with mass spectrometry [GCMS]) and (13)C-enrichment in unesterified cholesterol and cholesteryl ester (using gas chromatography coupled to isotope ratio mass spectrometry [GC-C-IRMS]) in very-low-density lipoprotein (VLDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL) during the tracer infusion. Curves were analyzed using multicompartmental analysis. This protocol is suitable to quantify the different processes involved in reverse cholesterol transport (RCT) in humans, including cholesterol esterification, transfer of cholesteryl ester from HDL towards apo B-100-containing lipoproteins, and the contribution of VLDL, LDL, and HDL in the final steps of RCT. In agreement with previous data from kinetic analysis of radiotracer experiments, our results suggest that in fasting normolipidemic subjects the major fraction of cholesteryl ester enters plasma through esterification in HDL (more than 95%). The major fraction of cholesteryl ester disappears through apo B-100-containing lipoproteins (VLDL and LDL) catabolism (mean of 82%) rather than through removal from HDL (mean of 18% with approximately an equal part for apo AI-dependent and independent catabolism, respectively, 7% and 11%). We conclude that this protocol could be applied to study the modulation of these processes by nutrition, diseases, or pharmacologic treatments.     

High density lipoprotein metabolism in endurance athletes and sedentary men

BACKGROUND. Endurance athletes have higher high density lipoprotein (HDL) concentrations than sedentary controls. To examine the mechanism for this effect, we compared HDL apoprotein metabolism in 10 endurance athletes aged 34 +/- 6 years (mean +/- SD) and 10 sedentary men aged 36 +/- 8 years. METHODS AND RESULTS. Subjects were maintained on controlled diets for 4 weeks, and metabolic studies using autologously labeled 125I HDL were performed during the final 2 weeks. Lipids and lipoproteins were measured daily during these 2 weeks, and the average of 14 values was used in the analysis. HDL cholesterol (58 +/- 14 versus 41 +/- 10 mg/dl), HDL2 cholesterol (26 +/- 10 versus 12 +/- 8 mg/dl), and apolipoprotein A-I (apo A-I) (144 +/- 18 versus 115 +/- 22 mg/dl) were higher in the athletes, whereas triglyceride concentrations (60 +/- 18 versus 110 +/- 48 mg/dl) were lower (p less than 0.01 for all). Postheparin lipoprotein lipase activity was not different, but hepatic triglyceride lipase activity was 27% lower (p less than 0.06) in the athletes. The athletes' mean clearance rate of triglycerides after an infusion of Travamulsion (1 ml/kg) was nearly twofold that of the inactive men (5.8 +/- 1.5 versus 3.2 +/- 0.9%/min, p less than 0.001). There was no differences in HDL apoprotein synthetic rates, whereas the catabolic rates of both apo A-I (0.15 +/- 0.02 versus 0.22 +/- 0.05 pools per day, p less than 0.01) and apolipoprotein A-II (apo A-II) (0.15 +/- 0.02 versus 0.20 +/- 0.04 pools per day, p less than 0.05) were reduced in the trained men. Apo A-I and apo A-II half-lives correlated with HDL cholesterol in each group (r greater than 0.76, p less than 0.05 for all) but not consistently with lipase activities or fat clearance rates. This relation between apoprotein catabolism and HDL cholesterol was strongest at HDL cholesterol concentrations of less than 60 mg/dl. CONCLUSIONS. We conclude that higher HDL levels in active men are associated with increased HDL protein survival. The mechanisms mediating this effect require better definition, and other factors appear to contribute to HDL cholesterol and protein concentrations among individual subjects.     

A novel mutation of the apolipoprotein A-I gene in a family with familial combined hyperlipidemia

We report a large family in which four members showed a plasma lipid profile consistent with the clinical diagnosis of familial combined hyperlipidemia (FCHL). One of these patients was found to have markedly reduced HDL cholesterol (HDL-C) (0.72 mmol/l) and Apo A-I (72 mg/dl) levels, a condition suggestive of the presence of a mutation in one of the HDL-related genes. The analysis of APOA1 gene revealed that this patient was heterozygous for a cytosine insertion in exon 3 (c.49–50 ins C), resulting in a frame-shift and premature stop codon at position 26 of pro-Apo A-I (Q17PFsX10). This novel mutation, which prevents the synthesis of Apo A-I, was also found in four family members, including three siblings and the daughter of the proband. Carriers of Apo A-I mutation had significantly lower HDL-C and Apo A-I than non-carriers family members (0.77 ± 0.15 mmol/l vs. 1.15 ± 0.20 mmol/l, P < 0.005; 71.4 ± 9.1 mg/dl vs. 134.0 ± 14.7 mg/dl, P < 0.005, respectively). Two of the APOA1 mutation carriers, who were also heavy smokers, had fibrous plaques in the carotid arteries causing mild stenosis (20%). The intimal-media thickness in the two other adult carriers was within the normal range. The other non-carriers family members with FCHL had either overt vascular disease or carotid atherosclerosis at ultrasound examination. This observation suggests that the low HDL-C/low Apo A-I phenotype may result from a genetic defect directly affecting HDL metabolism, even in the context of a dyslipidemia which, like FCHL, is associated with low plasma HDL-C.     

Chronic hypothyroidism induces abnormal structure of high-density lipoproteins and impaired kinetics of apolipoprotein A-I in the rat

Abnormal levels of plasma high-density lipoproteins (HDL) commonly reflect altered metabolism of the major HDL-apolipoprotein A-I (apo A-I). It is well known that thyroid hormones are involved in the regulation of lipoprotein metabolism, inducing significant changes in the concentration, size, and composition of plasma HDL. The purpose of this study was to evaluate the mechanisms responsible of the decreased HDL-apo A-I in chronic thyroidectomized rats (Htx) and to assess the role of HDL structure in apo A-I turnover. Htx rats were found to have a 3-fold increase in low-density lipoprotein-cholesterol (LDL-C), whereas HDL-C and apo A-I showed a 25.9% and 22.6% decrease compared to controls (P <.05), thus suggesting a defect in HDL metabolism. Turnover studies of apo A-I incorporated into normal HDL, using exogenous (125)I-radiolabeling, confirmed an altered fractional catabolic rate (FCR) in Htx rats (0.097 +/- 0.009 d(-1) v 0.154 +/- 0.026 d(-1) for Htx and control rats, respectively, P <.005). Apo A-I production rates calculated with autologous HDL data showed that apo A-I synthesis was decreased to a higher extent than the already reduced apo A-I catabolism, thus explaining the low apo A-I plasma levels in Htx rats. Composition analysis of HDL-Htx revealed increased phospholipid and apo E content, whereas apo A-IV was diminished. Such structural changes contribute to the reduced apo A-I catabolism as demonstrated with further kinetic turnover studies in normal rats treated with (125)I-radiolabeled apo A-I reincorporated into HDL isolated from plasma of Htx rats (FCR, 0.102 +/- 0.017 v 0.154 +/- 0.026 d(-1), for Htx and normal rats, respectively, P <.005). In summary, chronic hypothyroidism in rat a species that lacks cholesteryl ester transfer protein (CETP) activity is characterized by low HDL-C and apo A-I plasma levels as a result of a low apo A-I production rate that exceeds a decreased FCR. Both structural abnormalities of HDL and changes induced in the animal that affect HDL catabolism contribute to the low FCR of apo A-I in the hypothyroid state.     

Effects of estrogen replacement on plasma lipoproteins and apolipoproteins in postmenopausal, dyslipidemic women.

The effects of oral estrogen replacement (ethinyl estradiol 0.02 mg/d) on plasma triglyceride, total cholesterol, very-low-density lipoprotein (VLDL) cholesterol, low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, and apolipoprotein (apo) A-I and B levels and LDL particle size were assessed in 20 postmenopausal women with a previous hysterectomy and various forms of dyslipidemia (LDL cholesterol > or = 4.14 mmol/L [160 mg/dL] and/or HDL cholesterol < or = 1.03 mmol/L [40 mg/dL]). All subjects were studied while on a standard cholesterol-lowering diet, and were sampled in the fasting state before beginning estrogen therapy and after a mean of 13 weeks of estrogen therapy. Lipids were measured by standardized enzymatic techniques, apos were measured by enzyme-linked immunoassays, and LDL particle size was measured by gradient gel electrophoresis. Mean values for plasma lipid parameters (mmol/L) at baseline and during estrogen replacement were as follows: triglyceride, 2.11 and 2.75 (30% increase); total cholesterol, 7.45 and 6.52 (13% decrease); VLDL cholesterol, 1.09 and 1.22 (12% increase); LDL cholesterol, 5.09 and 3.70 (27% decrease); and HDL cholesterol, 1.27 and 1.58 (24% increase). Mean values for apo A-I were 163 and 254 mg/dL (56% increase), and for apo B they were 170 and 148 mg/dL (13% decrease). The LDL particle score was 4.09 and 4.52 (11% smaller). Changes in all parameters were statistically significant (P = .05) except for VLDL cholesterol. These data indicate that estrogen replacement is effective in decreasing LDL cholesterol and apo B concentrations and increasing HDL cholesterol and apo A-I concentrations in dyslipidemic postmenopausal women, but it should not be used in patients with baseline fasting triglyceride levels higher than 2.82 mmol/L (250 mg/dL) unless it is accompanied by a progestin. Our data indicate that this form of estrogen replacement could lower the risk of coronary artery disease (CAD) by more than 50% in these women, based on favorable alterations in plasma lipoproteins.     

Selective reduction of cholesterol in HDL2 fraction by probucol in familial hypercholesterolemia and hyperHDL2 cholesterolemia with abnormal cholesteryl ester transfer

Long-term treatment with probucol induced marked regression of xanthoma in patients with both homozygous and heterozygous familial hypercholesterolemia despite a substantial accompanying decrease in high-density lipoprotein (HDL) cholesterol. Furthermore, a close correlation was found between the extent of the regression and the reduction of HDL cholesterol, which suggests that the probucol-induced decrease in HDL may not be an atherogenic change, but may reflect a favorable change for lipoprotein metabolism. The present study also evaluated the effects of probucol on HDL metabolism in patients with familial hyperHDL2 cholesterolemia who had extremely high levels of HDL cholesterol ranging from 130 to 280 mg/dl. Premature corneal opacities were present in 2 patients, 1 of whom also had coronary artery disease despite high HDL cholesterol levels. In the 2 cases, the net transfer of cholesteryl ester from HDL to very low density lipoprotein and LDL was impaired, and low hepatic triglyceride lipase activity was observed, but cholesteryl ester transfer protein was not deficient. Administration of probucol to these patients caused a marked reduction of serum cholesterol, which was accounted for exclusively by a reduction in the HDL2 fraction. The size of the HDL2 particles, which had been much larger, decreased to normal, and the net transfer rate of cholesteryl ester was normalized. In the other 3 cases of hyperHDL2 cholesterolemia, the cholesteryl ester transfer activity was completely deficient. Unlike its effect in the first 2 cases, probucol did not cause any change in lipid and apoprotein in the 3 patients with complete deficiency of cholesteryl ester transfer activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Levels of serum lipids, apolipoproteins A-I and B and pseudocholinesterase activity and their discriminative values in patients with coronary by-pass operation

Serum lipids and apoproteins A-I and B were measured in 115 male patients and serum pseudocholinesterase activity (PChE) was determined in 83 patients with 3 vessel coronary artery disease (CAD). The control subjects were matched according to sex, smoking, relative weight and age and were free from heart disease. The CAD patients had significantly higher serum VLDL cholesterol and triglyceride levels and lower HDL cholesterol and apo A-I levels and lower HDL to total cholesterol ratio than the controls. The concentrations of serum total cholesterol and LDL cholesterol were only slightly (6.4% and 8.8%, on an average) higher in CAD patients than in controls. The apo B levels of CAD patients were also slightly lower in patients than in controls. The CAD patients had slightly higher PChE activities than controls. The ratios of apo A-I to PChE and HDL cholesterol to PChE were significantly (about 30%, P less than 0.001) lower in patients than in controls. In discriminant analysis between the groups HDL cholesterol and apo A-I showed the best (74% success in reclassifying the patients to correct groups), and total cholesterol, triglycerides, LDL cholesterol and apo B remarkably weak discriminating power among the single variables of serum lipids and lipoproteins. In discriminating analysis the apo A-I/PChE and HDL cholesterol/PChE ratios showed relatively high (77.1 and 71.1% success from the patients to correct groups) and serum PChE activity weak discriminating power. These results indicate that low levels of HDL cholesterol and apo A-I and the low ratio of HDL cholesterol to total cholesterol are the most potent metabolic risk factors for 3 vessel coronary artery disease in a population with relatively high serum total cholesterol level. The determinations of apo A-I/PChE and HDL cholesterol/PChE ratios may be an additional, valuable tool in discriminating the risk for CAD.     

Influence of serum amyloid A on the decrease of high density lipoprotein-cholesterol in active sarcoidosis

OBJECTIVE: We have previously observed low levels of high density lipoprotein (HDL) cholesterol in active sarcoidosis. The aim of this study was to analyze the role of serum amyloid A (SAA) on this lipid disorder. METHODS: Eighty five untreated sarcoid patients, 40 with active disease and 45 with inactive disease, were recruited. Sarcoidosis activity was evaluated by means of clinical, chest X-ray, gallium-67 scan, serum angiotensin converting enzyme (peptidyl-dipeptidase A) values, and pulmonary function tests. Analysis of lipoprotein metabolism included: serum cholesterol, low density lipoprotein (LDL)-cholesterol, HDL-cholesterol, HDL(2)-cholesterol, HDL(3)-cholesterol, apolipoprotein A-I (apo A-I), apolipoprotein B (apo B), and triglyceride concentrations. Serum amyloid A protein and lecithin-cholesterol acyltransferase (LCAT) activity were measured. RESULTS: In active sarcoidosis we found significantly reduced levels of HDL-cholesterol (1.17+/-0.36 vs. 1. 44+/-0.39 mmol/l, P=0.002), HDL(3)-cholesterol (0.78+/-0.23 vs. 1. 02+/-0.21 mmol/l, P<0.0001), and apo A-I (1.36+/-0.29 vs. 1.61+/-0. 27 g/l, P<0.0001) and significantly increased levels of triglyceride (1.51+/-0.64 vs. 1.03+/-0.46 mmol/l, P<0.0001), and apo B (1.14+/-0. 25 vs. 0.99+/-0.27 g/l, P=0.012) versus inactive sarcoidosis. Serum amyloid A concentrations were significantly increased in the patients with active disease (155.45+/-154.01 mg/ml) compared to the inactive sarcoid patients (89.70+/-65.36 mg/ml) (P=0.011). There were no significant differences in cholesterol, LDL-cholesterol, HDL(2)-cholesterol or LCAT values between groups. Multivariate logistic regression analysis showed that HDL-cholesterol (regression coefficient b=-1.96; S.E.=0.87; P=0.02) and SAA (regression coefficient b=0.01; S.E.=0.004; P=0.01) were the two variables independently associated with disease activity. Moreover, a significant negative correlation was observed between SAA levels and both HDL-cholesterol (r=-0.39; P=0.01) and apo A-I (r=-0.35; P=0.03) levels, in the active sarcoid group. Conversely, no correlation was found in the inactive sarcoid group. CONCLUSION: The low HDL-cholesterol and apo A-I concentrations seen in active sarcoid patients are associated with a significant increase of SAA levels. We suggest that the displacement of apo A-I by SAA on HDL accounts for the lower level of HDL-cholesterol seen in active sarcoidosis.