Increased cholesterol efflux potential of sera from ApoA-IMilano carriers and transgenic mice.
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The ability of HDL to remove cholesterol from peripheral cells and drive it to the liver for excretion is believed to explain most of the strong inverse correlation between plasma HDL cholesterol levels and coronary heart disease. Carriers of the ApoA-IMilano (A-IM) mutant have a severe hypoalphalipoproteinemia but are not at increased risk for premature of coronary heart disease. To explain this apparent paradox, we compared the capacity of serum from A-IM and control subjects to extract cholesterol from Fu5AH cells. Because the A-IM carriers are all heterozygotes for the mutation, we also compared the cholesterol efflux capacity of serum from transgenic mice expressing A-IM or wild-type ApoA-I (A-IWT), in the absence of murine ApoA-I. In the whole series of human or mouse sera, cholesterol efflux was significantly correlated with several HDL-related parameters; after adjustment for concomitant variables, the only parameter that remained significantly correlated with cholesterol efflux was the serum ApoA-I concentration (r2=0.85 in humans and 0.84 in mice). The same was true when samples from control subjects, A-IM carriers, A-IWT or A-IM mice were analyzed separately. Cholesterol efflux to sera from the A-IM carriers was only reduced slightly compared with control sera (25.0+/-4.2% versus 30.4+/-3.3%), although there was a large reduction (-45%) in the serum ApoA-I concentration in the former. Cholesterol efflux was also lower to sera from A-IM than A-IWT mice (15.6+/-3.8% versus 30. 1+/-7.1%), but less than expected from the 70% reduction in serum ApoA-I concentration. A relative efflux potential of serum was calculated in each group as the slope of the regression line fitting cholesterol efflux to ApoA-I concentrations. Therefore, the relative efflux potential reflects the relative efficiency of ApoA-I in determining cell cholesterol efflux. The relative efflux potential of mouse and human sera was in the following order: A-IM mice>A-IM carriers>A-IWT mice=control subjects, suggesting a gene-dosage effect of the A-IM mutation on the efficiency of serum to extract cholesterol from cells. The high efficiency of A-IM-containing HDL for cell cholesterol uptake would result in an improved reverse cholesterol transport in the A-IM carriers, possibly explaining the low susceptibility to atherosclerosis development. (+info)
Gemfibrozil for the secondary prevention of coronary heart disease in men with low levels of high-density lipoprotein cholesterol. Veterans Affairs High-Density Lipoprotein Cholesterol Intervention Trial Study Group.
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BACKGROUND: Although it is generally accepted that lowering elevated serum levels of low-density lipoprotein (LDL) cholesterol in patients with coronary heart disease is beneficial, there are few data to guide decisions about therapy for patients whose primary lipid abnormality is a low level of high-density lipoprotein (HDL) cholesterol. METHODS: We conducted a double-blind trial comparing gemfibrozil (1200 mg per day) with placebo in 2531 men with coronary heart disease, an HDL cholesterol level of 40 mg per deciliter (1.0 mmol per liter) or less, and an LDL cholesterol level of 140 mg per deciliter (3.6 mmol per liter) or less. The primary study outcome was nonfatal myocardial infarction or death from coronary causes. RESULTS: The median follow-up was 5.1 years. At one year, the mean HDL cholesterol level was 6 percent higher, the mean triglyceride level was 31 percent lower, and the mean total cholesterol level was 4 percent lower in the gemfibrozil group than in the placebo group. LDL cholesterol levels did not differ significantly between the groups. A primary event occurred in 275 of the 1267 patients assigned to placebo (21.7 percent) and in 219 of the 1264 patients assigned to gemfibrozil (17.3 percent). The overall reduction in the risk of an event was 4.4 percentage points, and the reduction in relative risk was 22 percent (95 percent confidence interval, 7 to 35 percent; P=0.006). We observed a 24 percent reduction in the combined outcome of death from coronary heart disease, nonfatal myocardial infarction, and stroke (P< 0.001). There were no significant differences in the rates of coronary revascularization, hospitalization for unstable angina, death from any cause, and cancer. CONCLUSIONS: Gemfibrozil therapy resulted in a significant reduction in the risk of major cardiovascular events in patients with coronary disease whose primary lipid abnormality was a low HDL cholesterol level. The findings suggest that the rate of coronary events is reduced by raising HDL cholesterol levels and lowering levels of triglycerides without lowering LDL cholesterol levels. (+info)
Hyperinsulinemic hypoalphalipoproteinemia as a new indicator for coronary heart disease.
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OBJECTIVES: The purpose of this study was to investigate the association among insulin resistance, high density lipoprotein cholesterol (HDL-C) and coronary heart disease (CHD), and to test the hypothesis that HDL-C may ameliorate the adverse effects of insulin. BACKGROUND: Serum low HDL-C (hypoalphalipoproteinemia) and hyperinsulinemia are independent predictors for CHD, but a strong negative correlation exists between them, as in patients with syndrome X. METHODS: Fifty-four pairs of cases (M/F: 49/5), defined as patients with angiographically proved CHD, and control subjects (M/F: 49/5) matched with cases with regard to gender and age were included. Insulin resistance was assessed by the homeostasis model assessment (HOMA). RESULTS: Cases had increased HOMA insulin resistance and lower serum levels of HDL-C than controls. A receiver operating characteristic (ROC) curve analysis indicated that HDL-C and insulin resistance were significant discriminators of CHD (area under ROC curve: 0.72 and 0.69, respectively). The interaction between HDL-C and the association of insulin resistance with CHD was significant: subjects with hyperinsulinemia and high HDL-C had no increased risk of CHD. Multivariate conditional logistic regression analysis showed that hyperinsulinemic hypoalphalipoproteinemia was a stronger indicator for CHD than either HDL-C or insulin resistance alone (-2 log likelihood: 19.0 vs. 12.6 or 15.7). CONCLUSIONS: Hyperinsulinemic hypoalphalipoproteinemia was a more potent indicator for CHD than either insulin resistance or low serum HDL-C levels alone, and the adverse effects of hyperinsulinemia seem to be ameliorated by high HDL-C levels. (+info)
Gemfibrozil, nicotinic acid and combination therapy in patients with isolated hypoalphalipoproteinemia: a randomized, open-label, crossover study.
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OBJECTIVES: To assess the effects of nicotinic acid (NA), gemfibrozil and combination therapy on the lipid profile of patients with clinical atherosclerotic disease and isolated hypoalphalipoproteinemia. BACKGROUND: Isolated hypoalphalipoproteinemia (low high density lipoprotein cholesterol [HDL-C] alone) accounts for a significant percentage of patients with premature atherosclerosis. However, it remains unclear whether currently available pharmacotherapy has the ability to favorably affect the lipid profile and therefore potentially reduce clinical events. METHODS: Twenty-three patients with clinically well-defined atherosclerosis and isolated hypoalphalipoproteinemia were prospectively randomized to receive gemfibrozil, NA or combination therapy in an open-label, crossover design trial to assess the effects on serum lipids. Lipid profiles and other relevant laboratory variables were monitored while the patients were on and off pharmacologic lipid-modulating therapy. RESULTS: In those 14 patients able to tolerate all forms of pharmacotherapy, HDL-C of 0.89 +/- 0.17 mmol/liter (34.5 +/- 6.5 mg/dl) increased by 15%, to 1.02 +/- 0.18 mmol/liter (39.7 +/- 7.1 mg/dl), while taking gemfibrozil (1,200 mg/day); by 35%, to 1.20 +/- 0.21 mmol/liter (46.5 +/- 8.1 mg/dl), while taking NA (mean dose 2,250 mg/day); and by 45%, to 1.29 +/- 0.19 mmol/liter (50.0 +/- 7.5 mg/dl), while taking combination therapy of gemfibrozil plus NA (p < 0.001 for all interventions as compared with baseline/washout; p < 0.005 NA vs. gemfibrozil; p < 0.001 combination therapy vs. gemfibrozil alone; p = 0.088 combination therapy vs. NA alone). Statistically significant favorable alterations were also observed with low density lipoprotein cholesterol (LDL-C), LDL-C/HDL-C, non-HDL-C/HDL-C, apolipoprotein (Apo) B and Apo B/Apo A1. CONCLUSIONS: In the majority of patients with clinical atherosclerotic disease and isolated hypoalphalipoproteinemia, pharmacologic therapy to raise HDL-C is not only feasible but is also effective with currently available agents, particularly when used in combination. (+info)
Complete genomic sequence of the human ABCA1 gene: analysis of the human and mouse ATP-binding cassette A promoter.
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The ABCA1 gene, a member of the ATP-binding cassette A (ABCA1) transporter superfamily, encodes a membrane protein that facilitates the cellular efflux of cholesterol and phospholipids. Mutations in ABCA1 lead to familial high density lipoprotein deficiency and Tangier disease. We report the complete human ABCA1 gene sequence, including 1,453 bp of the promoter, 146,581 bp of introns and exons, and 1 kb of the 3' flanking region. The ABCA1 gene spans 149 kb and comprises 50 exons. Sixty-two repetitive Alu sequences were identified in introns 1-49. The transcription start site is 315 bp upstream of a newly identified initiation methionine codon and encodes an ORF of 6,783 bp. Thus, the ABCA1 protein is comprised of 2,261 aa. Analysis of the 1,453 bp 5' upstream of the transcriptional start site reveals multiple binding sites for transcription factors with roles in lipid metabolism. Comparative analysis of the mouse and human ABCA1 promoter sequences identified specific regulatory elements, which are evolutionarily conserved. The human ABCA1 promoter fragment -200 to -80 bp that contains binding motifs for SP1, SP3, E-box, and AP1 modulates cellular cholesterol and cAMP regulation of ABCA1 gene expression. These combined findings provide insights into ABCA1-mediated regulation of cellular cholesterol metabolism and will facilitate the identification of new pharmacologic agents for the treatment of atherosclerosis in humans. (+info)
Ultrastructural changes in Bruch's membrane of apolipoprotein E-deficient mice.
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PURPOSE: To examine the histologic and ultrastructural changes in Bruch's membrane (BM) in apolipoprotein E deficient [ApoE(-)] mice in comparison with age-matched control animals. METHODS: Two-month-old (group 1) and 8-month-old (group 2) normal control C57BL/6 mice and 2-month-old (group 3) and 8-month-old (group 4) ApoE(-) mice were studied. All groups of mice were fed a standard rodent diet. The mice were killed, serum lipid levels were determined, and the eyes were ultrastructurally examined using standard techniques to measure the thickness of BM. The area fraction of electron-lucent (EL) particles in BM was quantified using point-counting stereology. RESULTS: The serum cholesterol levels of the ApoE(-) mice were significantly higher than those of the control mice (P = 0.0001). There was a significant thickening and EL particle accumulation in BM associated with age in the control animals. Group 2 had a thicker BM and more EL particle accumulation than group 1 (P = 0.0410 for thickness; P = 0.0042 for particle accumulation). Age-related changes were not seen in ApoE(-) mice; thickness and accumulation were similar in groups 3 and 4 (P = 0.50, thickness; P approximately/= 1.0, accumulation). Significant thickening and accumulation were seen in young ApoE(-) mice (group 3) versus young control animals (group 1; P = 0.008, thickening; P < 0.0001, EL particle accumulation). Group 4 ApoE(-) mice did not have a thicker BM or more EL particles than group 2 control animals (P = 0.2910, thickness; P = 0.35, EL particle accumulation). "Membrane-bounded" material (material between two membranes) was present significantly more frequently in ApoE(-) mice. CONCLUSIONS: ApoE(-) mice exhibit accumulation of EL particles at an earlier age and have more membrane-bounded material in BM than control mice. This material has ultrastructural similarities to basal linear deposit, which accumulates in age-related maculopathy. (+info)
Common and rare ABCA1 variants affecting plasma HDL cholesterol.
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Mutations in ABCA1, a member of the ATP-binding cassette family, have been shown to underlie Tangier disease (TD) and familial hypoalphalipoproteinemia (FHA), which are genetic disorders that are characterized by depressed concentrations of plasma high density lipoprotein (HDL) cholesterol. An important question is whether common variants within the coding sequence of ABCA1 can affect plasma HDL cholesterol in the general population. To address this issue, we developed a screening strategy to find common ABCA1 variants. This strategy involved long-range amplification of genomic DNA by using coding sequences only, followed by deep sequencing into the introns. This method helped us to characterize a new set of amplification primers, which permitted amplification of virtually all of the coding sequence of ABCA1 and its intron-exon boundaries with a single DNA amplification program. With these new sequencing primers, we found 3 novel ABCA1 mutations: a frameshift mutation (4570insA, A1484S-->X1492), a missense mutation (A986D) in a TD family, and a missense mutation (R170C) in aboriginal subjects with FHA. We also used these sequencing primers to characterize 4 novel common amino acid variants in ABCA1, in addition to 5 novel common silent variants. We tested for association of the ABCA1 I/M823 variant with plasma HDL cholesterol in Canadian Inuit and found that M823/M823 homozygotes had significantly higher plasma HDL cholesterol compared with subjects with the other genotypes. The results provide proof of principle of the effectiveness of this approach to identify both rare and common ABCA1 genomic variants and also suggest that common amino acid variation in ABCA1 is a determinant of plasma HDL cholesterol in the general population. (+info)
Proteolytic degradation and impaired secretion of an apolipoprotein A-I mutant associated with dominantly inherited hypoalphalipoproteinemia.
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We have devised a combined in vivo, ex vivo, and in vitro approach to elucidate the mechanism(s) responsible for the hypoalphalipoproteinemia in heterozygous carriers of a naturally occurring apolipoprotein A-I (apoA-I) variant (Leu(159) to Arg) known as apoA-I Finland (apoA-I(FIN)). Adenovirus-mediated expression of apoA-I(FIN) decreased apoA-I and high density lipoprotein cholesterol concentrations in both wild-type C57BL/6J mice and in apoA-I-deficient mice expressing native human apoA-I (hapoA-I). Interestingly, apoA-I(FIN) was degraded in the plasma, and the extent of proteolysis correlated with the most significant reductions in murine apoA-I concentrations. ApoA-I(FIN) had impaired activation of lecithin:cholesterol acyltransferase in vitro compared with hapoA-I, but in a mixed lipoprotein preparation consisting of both hapoA-I and apoA-I(FIN) there was only a moderate reduction in the activation of this enzyme. Importantly, secretion of apoA-I was also decreased from primary apoA-I-deficient hepatocytes when hapoA-I was co-expressed with apoA-I(FIN) following infection with recombinant adenoviruses, a condition that mimics secretion in heterozygotes. Thus, this is the first demonstration of an apoA-I point mutation that decreases LCAT activation, impairs hepatocyte secretion of apoA-I, and makes apoA-I susceptible to proteolysis leading to dominantly inherited hypoalphalipoproteinemia. (+info)