Reduced HDL-cholesterol Levels Research Articles

Genetic Susceptibility to Atherosclerosis

Atherosclerotic cardiovascular disease (ASCVD) frequently clusters in families. Although environmental factors such as diet, exercise, and smoking play a role in ASCVD, genetic factors are a major determinant of ASCVD risk. For example, in a study of Swedish twins, males with a dizygotic twin who died of premature coronary heart disease had a 4.3-fold increased risk of also dying from coronary heart disease, and if the twin was monozygotic, this risk increased to 14.9-fold.1 The genetic risk of ASCVD is conferred in part through known metabolic risk factors such as hypertension, dyslipidemia, and diabetes mellitus. However, these risk factors alone do not account for the entire genetic contribution to risk of ASCVD, and there remains substantial interest in the identification of additional genetic cardiovascular risk factors. Like humans, mouse strains differ considerably in their genetic predisposition to atherosclerosis.2 Most mouse strains are resistant to atherosclerosis even when fed an atherogenic diet; the C3H strain is a prototypical-resistant mouse strain. In contrast, C57BL/6J mice have been extensively studied as the mouse strain that is most susceptible to atherosclerosis when fed an atherogenic high-fat, high-cholesterol, cholic acid–containing diet.3 Initially, the focus on C57BL/6J mice centered on differences in plasma lipid levels, especially reduced HDL cholesterol levels, in response to the atherogenic diet4 and attempts to map gene loci linked to the phenotype of low HDL cholesterol.5 However, previous studies did not distinguish whether these differences in lipid profiles were restricted to particular dietary challenges or reflect an underlying genetic factor that contributes to atherosclerosis susceptibility. Furthermore, recent studies have suggested that C57BL/6J mice differ from less-susceptible strains in their response to inflammatory stimuli.6 7 Given the interest in atherosclerosis as an inflammatory disease,8 this has led to the hypotheses that C57BL/6J mice may be genetically …

HDL Cholesterol and TaqIB Cholesteryl Ester Transfer Protein Gene Polymorphism in Renal Transplant Recipients

Decreased serum levels of high-density lipoprotein cholesterol (HDL-C) are a well-known risk factor for coronary heart disease (CHD) in the general population and have been suggested as one of the best predictor of CHD after renal transplantation. However, very heterogeneous HDL-C levels have been reported in renal transplant recipients. In this patient population, serum HDL-C levels are determined by complex interactions between hormonal, environmental (such as a high amount of abdominal adipose tissue), and genetic factors and drugs (particularly glucocorticoids). We, therefore, evaluated the effects of the cholesteryl ester transfer protein (CETP) gene TaqIB polymorphism as well as of abdominal obesity on HDL-C levels in 78 male renal transplant recipients who were receiving azathioprine and/or ciclosporin A in combination with prednisone as immunosuppression. The patients were classified into genotypic groups according to the presence or absence of the restriction site (B1 allele or B2 allele, respectively). The distribution of CETP genotypes was similar to that previously described in the general population. Overall, HDL-C levels were 19 and 26% higher in B1B2 and B2B2 patients as compared with B1B1 homozygotes (p < 0.05), even after control for other lipid measurements. Patients with abdominal obesity (waist girth ≧93 cm) showed reduced HDL-C levels as compared with lean (waist girth <93 cm) patients (1.20 ± 0.28 vs. 1.42 ± 0.41 mmol/l, respectively, p < 0.01). Moreover, the HDL-C levels were markedly affected by the CETP TaqIB polymorphism in lean patients (+28 and +41% in B1B2 and B2B2 as compared with B1B1 patients, p < 0.05), but no significant difference was observed among obese patients. Significantly lower total cholesterol:HDL-C ratios were obtained in lean B2B2 homozygotes, suggesting that these patients could be less susceptible to atherosclerosis than lean B1B1 homozygotes. In addition, patients with the B1B1 genotype had more documented CHD as compared with patients carrying at least one B2 allele, supporting the protective effect of the B2 allele against CHD. In conclusion, considerable variation in HDL-C levels appears to be explained by the CETP TaqIB gene polymorphism in male renal transplant recipients, but this potential protective gene effect appears strongly reduced by concomitant abdominal obesity.

Risk stratification in hypertension: new insights from the Framingham study

Five decades of epidemiologic research have established that blood pressure elevation is a common and powerful contributor to all of the major cardiovascular diseases, including coronary disease, stroke, peripheral artery disease, renal disease, and heart failure. The common variety of hypertension designated benign essential hypertension was not shown to be either benign or essential. Although clinicians favor the diagnosis and treatment of hypertension in terms of diastolic blood pressure elevation and categoric cut points, epidemiologic data show a more important influence of systolic blood pressure, and a continuous, graded influence of blood pressure even within what is regarded as the normotensive range. An important revelation in epidemiologic hypertension research is that hypertension usually occurs in conjunction with other metabolically linked risk factors; therefore, less than 20% occurs in isolation. The other risk factors that tend to accompany hypertension include glucose intolerance, obesity, left ventricular hypertrophy, and dislipidemia (elevated total, LDL, and small-dense LDL cholesterol levels, raised triglyceride, and reduced HDL cholesterol levels). Clusters of three or more of these additional risk factors occur at four times the rate expected by chance. This clustering is attributed to an insulin resistance syndrome promoted by abdominal obesity. The amount of risk factor clustering accompanying elevated blood pressure was observed to increase with weight gain. Based on Framingham Study data the prevalence of insulin resistance syndrome in the general population could be as high as 22% in men and 27% in women. Risk of coronary disease, the most common and most lethal sequel to hypertension, increased stepwise with the extent of risk factor clustering. Among persons with hypertension, about 40% of coronary events in men and 68% in women are attributable to the presence of two or more additional risk factors. Only 14% of coronary events in hypertensive men and 5% of those in hypertensive women occurred in the absence of additional risk factors. Other important features of risk stratification of hypertension are the presence of an elevated heart rate and left ventricular hypertrophy, and an elevated fibrinogen that often accompany hypertension. Recent population-based data reported suggest that elevated renin accompanying hypertension may independently enhance the risk of coronary events. Because clustering of other major risk factors with hypertension is the rule, the prudent physician should routinely screen for the presence of these other factors. Multivariate risk assessment profiles are now available for coronary disease, stroke, peripheral artery disease, and heart failure, to enable physicians to pool all the relevant risk factor information so as to arrive at a composite risk estimate. Hypertensive patients are more appropriately targeted for therapy by such risk stratification and the goal of the therapy should be to improve the multivariate risk profile.

Quantitative trait locus analysis of plasma lipoprotein levels in an autoimmune mouse model : interactions between lipoprotein metabolism, autoimmune disease, and atherogenesis.

The autoimmune MRL/lpr mouse strain, a model for systemic lupus erythematosus, exhibited an unusual plasma lipoprotein profile, suggesting a possible interaction of autoimmune disease and lipoprotein metabolism. In an effort to examine the genetic basis of such interactions, and to study their relationship to atherogenesis, we performed a quantitative trait locus analysis using a total of 272 (MRL/lprxBALB/cJ) second generation (F2) intercross mice. These mice were examined for levels of total plasma cholesterol, HDL cholesterol, VLDL and LDL cholesterol, unesterified cholesterol, autoantibodies, and aortic fatty streak lesions. Using a genome scan approach, we identified 4 quantitative trait loci controlling plasma lipoprotein levels on chromosomes (Chrs) 5, 8, 15, and 19. The locus on Chr 15 exhibited lod scores of 11.1 for total cholesterol and 6.7 for VLDL and LDL cholesterol in mice fed an atherogenic diet, and it contains a candidate gene, the sterol regulatory element binding protein-2. The locus on Chr 5 exhibited lod scores of 3.8 for total cholesterol and 4.1 for unesterified cholesterol in mice fed an atherogenic diet, and this locus has been observed in 2 previous studies. The locus on Chr 8 exhibited a lod score of 3.1 for unesterified cholesterol in mice fed a chow diet. This locus contains the lecithin-cholesterol acyltransferase gene, and decreased activity of the enzyme in the MRL strain suggests that this gene underlies the quantitative-trait locus. The locus on Chr 19 exhibited a lod score of 8.4 for HDL cholesterol and includes the Fas gene, which is mutated in MRL/lpr mice and is primarily responsible for the autoimmune phenotype in this cross. That the Fas gene is responsible for the HDL quantitative-trait loci is supported by the finding that autoantibody levels were strongly correlated with HDL cholesterol levels (rho=-0.37, P<0.0001) among the F2 mice. HDL cholesterol levels were in turn significantly associated with aortic fatty streak lesions among the F2 mice (rho=-0.17, P=0.006). Further, there was a threshold effect of autoantibody levels on the development of fatty streak lesions (rho=0.45, P=0.004 for 42 F2 mice with anti-dsDNA Ab over 0.5 OD). Our results support the concept that the high prevalence of coronary artery disease in systemic lupus erythematosus is due in part to a reduction of HDL cholesterol levels resulting from the autoimmune disease.

Fasting insulin and apolipoprotein B levels and low-density lipoprotein particle size as risk factors for ischemic heart disease.

Epidemiological studies have established a relationship between cholesterol and low-density lipoprotein cholesterol (LDL-C) concentrations and the risk of ischemic heart disease (IHD), but up to half of patients with IHD may have cholesterol levels in the normal range. To assess the ability to predict the risk of IHD using a cluster of nontraditional metabolic risk factors that includes elevated fasting insulin and apolipoprotein B levels as well as small, dense LDL particles. Nested case-control study. Cases and controls were identified from the population-based cohort of the Quebec Cardiovascular Study, a prospective study conducted in men free of IHD in 1985 and followed up for 5 years. Incident IHD cases were matched with controls selected from among the sample of men who remained IHD free during follow-up. Matching variables were age, smoking habits, body mass index, and alcohol consumption. The sample included 85 complete pairs of nondiabetic IHD cases and controls. Ability of fasting insulin level, apolipoprotein B level, and LDL particle diameter to predict IHD events, defined as angina, coronary insufficiency, nonfatal myocardial infarction, and coronary death. The risk of IHD was significantly increased in men who had elevated fasting plasma insulin and apolipoprotein B levels and small, dense LDL particles, compared with men who had normal levels for 2 of these 3 risk factors (odds ratio [OR], 5.9; 95% confidence interval [CI], 2.3-15.4). Multivariate adjustment for LDL-C, triglycerides, and high-density lipoprotein cholesterol (HDL-C) did not attenuate the relationship between the cluster of nontraditional risk factors and IHD (OR, 5.2; 95% CI, 1.7-15.7). On the other hand, the risk of IHD in men having a combination of elevated LDL-C and triglyceride levels and reduced HDL-C levels was no longer significant (OR, 1.4; 95% CI, 0.5-3.5) after multivariate adjustment for fasting plasma insulin level, apolipoprotein B level, and LDL particle size. Results from this prospective study suggest that the measurement of fasting plasma insulin level, apolipoprotein B level, and LDL particle size may provide further information on the risk of IHD compared with the information provided by conventional lipid variables.

Correction of hypertriglyceridemia and impaired fat tolerance in lipoprotein lipase-deficient mice by adenovirus-mediated expression of human lipoprotein lipase.

Humans homozygous or heterozygous for mutations in the lipoprotein lipase (LPL) gene demonstrate significant disturbances in plasma lipoproteins, including raised triglyceride (TG) and reduced HDL cholesterol levels. In this study we explored the feasibility of adenovirus-mediated gene replacement therapy for LPL deficiency. A total of 5 x 10(9) plaque-forming units (pfu) of an E1/E3-deleted adenovirus expressing either human LPL (Ad-LPL) or the bacterial beta-galactosidase gene (Ad-LacZ) as a control were administered to mice heterozygous for targeted disruption in the LPL gene (n = 57). Peak expression of total postheparin plasma LPL activity was observed at day 7 in Ad-LPL mice versus Ad-LacZ controls (834 +/- 133 vs 313 +/- 89 mU/mL, P < .01), and correlated with human-specific LPL activity (522 +/- 219 mU/mL) and mass (9214 +/- 782 ng/mL), a change that was significant to 14 and 42 days, respectively. At day 7, plasma TGs were significantly reduced relative to Ad-LacZ mice (0.17 +/- 0.07 vs 1.90 +/- 0.89 mmol/L, P < .01) but returned to endogenous levels by day 42. Ectopic liver expression of human LPL was confirmed by in situ hybridization analysis and from raised LPL activity and mass in liver homogenates. Analysis of plasma lipoprotein composition revealed a marked decrease in VLDL-derived TGs. Severely impaired oral and intravenous fat-load tolerance in LPL-deficient mice was subsequently corrected after Ad-LPL administration and closely paralleled that observed in wild-type mice. These findings suggest that liver-targeted adenovirus-mediated LPL gene transfer offers an effective means for transient correction of altered lipoprotein metabolism and impaired fat tolerance due to LPL deficiency.

Passive cigarette smoking and reduced HDL cholesterol levels in children with high-risk lipid profiles.

HDL cholesterol levels are known to be lower in smokers than in nonsmokers. Previous studies have demonstrated an association of decreased HDL cholesterol with passive smoking in children but have not adjusted for potential confounding factors. In a cross-sectional, pilot-scale study, we examined the relationship of HDL cholesterol levels to passive smoking in children and adolescents referred to a tertiary hyperlipidemia clinic. Eligibility criteria included (1) first visit to a lipid clinic, (2) LDL cholesterol >95th percentile for age or HDL cholesterol <5th percentile, (3) age between 2 and 18 years, and (4) absence of secondary causes of hyperlipidemia. Sociodemographic information, diet record, medical history, and fasting lipid profiles were obtained. Of 109 eligible patients, 103 (94%) were studied. Twenty-seven percent came from households with cigarette smokers. HDL cholesterol levels were 38.7+/-1.2 mg/dL (mean+/-SEM) in passive smokers versus 43.6+/-1.2 mg/dL in children without smoke exposure (P=.005). Smoking exposure was not significantly associated with other lipid values. The effect of smoking on HDL cholesterol was minimally affected by potential confounders. In multivariate regression adjusting for body mass index, age, sex, exercise, and dietary fat intake, passive smoking remained a significant risk factor for decreased HDL cholesterol (P=.012). Mean HDL cholesterol levels are lower in dyslipidemic children from households with smokers than in those without household smoke exposure. Passive smoking may worsen the risk profile for later atherosclerosis among high-risk young persons.

The pathogenetic role of impaired fatty acid trapping by adipocytes in generating the pleiotropic features of hyperapoB.

HyperapoB is the commonest dyslipoproteinaemiaassociated with coronary disease [1, 2] and is charac-terized by an increased LDL particle number due toincreased secretion of B100 lipoproteins by the liver[3]. The first feature of hyperapoB to be recognizedwas the elevated LDL particle number, many ofwhich are smaller and denser than normal [4]. In real-ity, though, the metabolism of all the lipoprotein clas-ses is demonstrably abnormal.At the onset, however, it must be appreciated thathyperapoB is a phenotype, not a genotype, and thereare multiple causes which produce increased hepaticsecretion of B100 lipoprotein particles. The focus inthis review, however, will be to outline how a reducedrate of fatty acid trapping by adipocytes can producethe pleiotropic features which characterize hyper-apoB. At the end of this line of reasoninglies the con-clusion that faults in fatty acid metabolism, not errorsin the LDL pathway, are the commonest causes forthe atherogenic dyslipoproteinaemias seen clinically.The features of hyperapoB to be explicated are: 1)increased hepatic VLDL secretion; 2) increased LDLparticle number; 3) smaller denser LDL particles; 4)reduced HDL cholesterol levels; 4) postprandial hy-perlipaemia with accumulation of triglyceride-richremnants; 5) elevated plasma non-esterified fattyacid levels (NEFA); and 6) insulin resistance.

A common substitution (Asn291Ser) in lipoprotein lipase is associated with increased risk of ischemic heart disease.

Lipoprotein lipase degrades triglycerides in plasma and as a byproduct produces HDL particles. Genetic variation in lipoprotein lipase may therefore affect cardiovascular risk. We tested 9,214 men and women from a general population sample and 948 patients with ischemic heart disease for the Asn291Ser substitution in lipoprotein lipase. The allele frequency in the general population was 0.024 and 0.026 for women and men, respectively. In comparison with noncarriers, female heterozygous probands had increased plasma triglycerides (delta = 0.23 mmol/liter), while HDL cholesterol was reduced in both female and male carriers (delta = 0.18 mmol/liter and delta = 0.11 mmol/liter, respectively). A similar phenotype was found in six homozygous carriers. On multiple logistic regression analysis, plasma triglycerides and HDL cholesterol were independent predictors of ischemic heart disease in both genders. On univariate analysis, odds ratios for ischemic heart disease in probands were 1.89 in women (95% CI: 1.19-3.01) and 0.90 in men (95% CI: 0.62-1.31), and on multivariate analysis were 1.98 in women (95% CI: 1.11-3.53) and 1.02 in men (95% CI: 0.65-1.60). This study demonstrates that a single common mutation in the lipoprotein lipase gene is associated with elevated plasma triglycerides and reduced HDL cholesterol levels, whereby carriers, in particular women, seem to be predisposed to ischemic heart disease. It cannot be excluded, however, that male carriers of this substitution may represent a subset of low-HDL individuals without raised triglycerides not predisposed to ischemic heart disease.

Impact of body mass index on coronary heart disease risk factors in men and women. The Framingham Offspring Study.

Increased body weight has been associated with an increased risk of morbidity and mortality from coronary heart disease (CHD) in several populations. We studied the distribution of body mass index (BMI, kg/m2) in men (n = 1566; mean age, 49 +/- 10 years) and women (n = 1627; mean age, 49 +/- 10 years) participating in the third examination cycle of the Framingham Offspring Study and the association of BMI with known CHD risk factors. In men, BMI increased with age until age 50 years, when it reached a plateau. In women, there was a trend toward an increase in BMI with age up to the seventh decade of life. Seventy-two percent of men and 42% of women had a BMI > or = 25.00, the cutoff point for the definition of overweight. In age-adjusted analyses, BMI was significantly and linearly associated with systolic blood pressure, fasting glucose levels, plasma total cholesterol, VLDL cholesterol, and LDL cholesterol levels and was inversely and linearly associated with HDL cholesterol levels (P < .001) in nonsmoking men and women. The association between BMI and apolipoprotein B and A-I was similar to that of LDL and HDL cholesterol, respectively. LDL size was also linearly associated with BMI: subjects with higher BMI had smaller LDL particles. Lipoprotein(a) levels were not associated with BMI in this population. Of all these risk factors for CHD, reduced HDL cholesterol levels and hypertension were those more strongly associated with higher BMI in both men and women. Elevated triglyceride levels and small LDL particles, and diabetes in women, were also strongly associated with higher BMI values in this population. Our results indicate that a high prevalence of adult Americans are overweight and support the concept that increased BMI is associated with an adverse effect on all major CHD risk factors. These results emphasize the importance of excess body fat as a public health issue.

Hypertriglyceridemia and low HDL cholesterol in Japanese patients with NIDDM.

Diabetes is frequently associated with the combination of hypertriglyceridemia and low HDL cholesterol level, a known risk factor for cardiovascular disease. We evaluated the frequency of elevated serum triglyceride and the reduced HDL cholesterol levels in Japanese male NIDDM patients. Hypertriglyceridemia (>1.69 mmol/l) and low HDL cholesterol level (<0.91 mmol/l) were frequently found in Japanese male (NIDDM patients (30.4 and 14.2%, respectively). The combined abnormality, i.e., hypertriglyceridemia with concomitant low HDL cholesterol level, was more common in patients with poor glycemic control. We observed that inpatient diet therapy markedly reduced serum triglyceride but serum HDL cholesterol did not change significantly. This is in marked contrast to primary hypertriglyceridemia, in which HDL cholesterol level generally increases in parallel with a reduction in serum triglyceride level. We discuss the defective removal of triglyceride-rich lipoproteins and ineffective HDL production caused by lipoprotein lipase (LPL) deficiency. We also discuss possible correction of this combined abnormality by certain maneuvers that increase LPL activity.

HDL subparticles and coronary artery disease in NIDDM

Decreased HDL cholesterol levels are associated with an increased risk of coronary artery disease (CAD) in non insulin dependent diabetes mellitus (NIDDM). The aim of this study was to compare HDL subparticles with apo A-I (LpAI) and those with apo A-I and apo A-II (LpAI/AII) in subjects with and without NIDDM and to study the relationship between HDL subparticles and CAD in NIDDM. Lipids, apo A-I and HDL subparticles were measured in 240 subjects with NIDDM and in 248 age and gender matched controls. Subjects with NIDDM had higher triglyceride levels (2.5 ± 1.8 vs. 1.4 ± 0.8 mmol/1, P < 0.001), lower HDL cholesterol (0.9 ± 0.3 vs. 1.2 ± 0.3 mmol/1, P < 0.001), apo A-I (124.7 ± 22.4 vs. 139.8 ± 24.1 mg/dl, P < 0.001) and LpAI/AII (82.4 ± 18.2 vs. 94.9 ± 16.7 mg/dl, P < 0.001) in comparison to controls. LpAI levels were similar in both groups. Diabetic subjects with CAD ( n = 109) had higher triglycerides (2.7 ± 1.9 vs. 2.3 ± 1.8 mmol/1, P = 0.02) and lower HDL cholesterol (0.8 ± 0.2 vs. 1.0 ± 0.3 mmol/1, P < 0.001), apo A-I (115.5 ± 20.1 vs. 132.3 ± 21.4 mg/dl, P < 0.001), LpAI (40.2 ± 9.1 vs. 44.4 ± 12.4 mg/dl, P = 0.06), and LpAI/AII levels (75.4 ± 18.0 vs. 88.3 ± 16.2 mg/dl, P < 0.001) in comparison to diabetic subjects without CAD ( n = 131). In a multivariate analysis, apo A-I was found to be the best predictor of CAD in subjects with NIDDM. In conclusion, reduced HDL cholesterol levels found in NIDDM are, principally, due to reduced concentrations of apo A-I and apo A-II-containing particles (LpAI/AII). While LpAI and LpAI/AII levels were lower in NIDDM subjects with CAD, plasma apo A-I is the best predictor of CAD in NIDDM.

Two Novel Molecular Defects in theLCATGene Are Associated With Fish Eye Disease

A 53-year-old man with a severely reduced HDL cholesterol level, dense corneal opacities, normal renal function, and premature coronary artery disease was investigated together with 16 members of his family. The proband was diagnosed with fish eye disease. As in previously reported patients with fish eye disease, the endogenous plasma cholesterol esterification rate was near normal, yet lecithin:cholesterol acyltransferase (LCAT) activity was almost absent when measured with exogenous HDL analogues used as substrate. Direct sequencing of the LCAT gene revealed two novel missense mutations in exon 1 and exon 4, resulting in the substitution of Pro10 with Gln (P10Q) and Arg135 with Gln (R135Q), respectively. Both missense mutations were located on different alleles. Genetic analysis by polymerase chain reaction revealed 4 carriers of the P10Q and 3 carriers of the R135Q defect. Functional assessment of both missense mutations revealed that when exogenous HDL analogues were used as substrate, the specific activity of rLCAT p10Q was 18% of wild type (WT); however, when LDL was used as substrate, the activity was 146% of WT. By contrast, rLCATR135Q was inactive against both substrates. Thus, we conclude that the LCATR135D mutation is causative for complete LCAT deficiency and that the clinical phenotype of fish eye disease seen in this patient is due to the Pro10 mutation. The presence of premature coronary artery disease in the absence of other risk factors in this new case of fish eye disease raises questions regarding the risk of atherosclerosis, which has previously been reported to be nonexistent.

Triglycerides and HDL-cholesterol as risk factors for ischemic heart disease. Results from the Québec cardiovascular study

The relative importance of reduced plasma high density lipoprotein-cholesterol (HDL-C) levels and elevated plasma triglyceride (TG) concentrations as risk factors for ischemic heart disease (IHD) was examined in a sample of 2177 men from the Québec City suburbs. The sample included 202 men with known IHD. The relationship between HDL-C and TG levels, although significant ( r = −0.49, P < 0.0001), was not linear, as most of the variation in HDL-C levels was observed within TG levels below 2.5 mmol/1. Reduced HDL-C (<0.9 mmol/l) was a prevalent condition in men with IHD (50%) compared to those without IHD (30%). On the other hand 26% and 20% of men with and without IHD, respectively, had elevated TG levels (TG > 2.3 mmol/l). A 2-fold increase in prevalence odds ratio (OR) was observed in men with TG levels > 2.3 mmol/1 (95% confidence intervals (CI) [1.2;3.3]). No residual association between elevated TG levels and IHD was found, however, after adjustment for HDL-C concentrations (OR 1.2, 95% CI 0.7;2.1). On the other hand, HDL-C remained a significant predictor of IHD after adjustment for other risk factors (OR 0.3, 95%, CI 0.2;0.6). Men with reduced HDL-C levels were also characterized by a cluster of risk factors such as obesity, diabetes mellitus and hypertension, which may contribute to increase the risk of IHD. Finally, the independent interpretation of cholesterol, TG or LDL-C levels may lead to an inadequate prediction of risk, as a large number of IHD patients showed a cluster of risk factors which included low HDL-C concentrations.

A new molecular defect in the lecithin: cholesterol acyltransferase (LCAT) gene associated with fish eye disease.

We report a new genetic defect in the lecithin:cholesterol acyltransferase (LCAT) gene associated with classical clinical and biochemical features of fish eye disease. The 63-year-old Australian female proband also suffers from non-insulin-dependent (type II) diabetes mellitus. She presented with corneal opacities, markedly reduced HDL-cholesterol (0.1 mmol/L; < 10% of normal controls), and elevated plasma triglycerides. The presence of diabetes did not explain the lipoprotein profile, which differed markedly in comparison to two female hypertriglyceridemic diabetic subjects. Cholesterol esterification in HDL-like particles was minimal but plasma cholesterol esterification was maintained due to LCAT activity in non-HDL-containing lipoprotein fractions. DNA sequence analysis of the proband's LCAT gene showed two C to T transitions resulting in the substitution of Thr123 with Ile and Tyr144 with Cys. Allele-specific PCR amplification procedures were used to confirm the presence of the mutations in this proband and to screen for additional carriers in her family. Three first degree relatives (mother, brother, son) were heterozygous for the Thr123 --> Ile mutation and her daughter had the Tyr144 --> Cys mutation. Apart from a reduction in HDL-cholesterol levels to half the normal concentration and a 20% reduction in apoA-I levels, their plasma lipids were unremarkable. The proband's son and daughter were further investigated. Both had normal cholesterol esterification rates in plasma and VLDL/LDL-depleted plasma, but reduced LCAT activity (50% that of normal). Thus, the biochemical and phenotypic expression for fish eye disease in the heterozygote subjects was similar, irrespective of the underlying LCAT mutation.

Effects of sub-chronic exposure to SO2 on lipid and carbohydrate metabolism in rats

Sulfur dioxide (SO2) is a ubiquitous air pollutant, present in low concentrations in the urban air, and in higher concentrations in the working environment. While toxicological reports on SO2 have extensively dealt with the pulmonary system, essentially no data are available on the effects of chronic exposure to this pollutant on intermediary metabolism, although some biochemical changes in lipid metabolism have been detected. The present investigation was aimed at evaluating the effects of sub-chronic exposure to SO2 on concentrations of serum lipids/lipoproteins and on glucose metabolism, in animal models of hypercholesterolemia and diabetes. A specially designed control-inert atmosphere chamber was used, where male Sprague-Dawley rats fed on either standard or cholesterol enriched (HC) diets, as well as streptozotocin diabetics, were exposed to SO2 at 5 and 10 ppm, 24 h per day for 14 days. In rats, both on a standard diet and on a HC regimen, SO2 exposure determined a significant dose-dependent increase in plasma triglycerides, up to +363% in the 10 ppm HC exposed animals. This same gas concentration significantly reduced HDL cholesterol levels. In contrast, exposure of diabetic animals to 10 ppm SO2 resulted in a fall (-41%) of plasma and liver triglycerides and in a concomitant increase (+62%) of plasma HDL cholesterol. This discrepancy could apparently be related to diverging effects of SO2 exposure on plasma insulin levels in the different animal groups. Kinetic analyses of triglyceride synthesis carried out in rats on a standard diet revealed, in exposed animals, a significant reduction in the secretory rate, in spite of the concomitant hypertriglyceridemia. These findings suggest that SO2 exposure can markedly modify major lipid and glycemic indices, also indicating a differential response in normo/hyperlipidemic versus diabetic animals.

Decreased early atherosclerotic lesions in hypertriglyceridemic mice expressing cholesteryl ester transfer protein transgene.

The human cholesteryl ester transfer protein (CETP) facilitates the transfer of cholesteryl ester from HDL to triglyceride-rich lipoproteins. The activity of CETP results in a reduction in HDL cholesterol levels, but CETP may also promote reverse cholesterol transport. Thus, the net impact of CETP expression on atherogenesis is uncertain. The influence of hypertriglyceridemia and CETP on the development of atherosclerotic lesions in the proximal aorta was assessed by feeding transgenic mice a high cholesterol diet for 16 wk. 13 out of 14 (93%) hypertriglyceridemic human apo CIII (HuCIII) transgenic (Tg) mice developed atherosclerotic lesions, compared to 18 out of 29 (62%) controls. In HuCIII/CETPTg, human apo AI/CIIITg and HuAI/CIII/CETPTg mice, 7 of 13 (54%), 5 of 10 (50%), and 5 of 13 (38%), respectively, developed lesions in the proximal aorta (P < .05 compared to HuCIIITg). The average number of aortic lesions per mouse in HuCIIITg and controls was 3.4 +/- 0.8 and 2.7 +/- 0.6, respectively in HuCIII/CETPTg, HuAI/CIIIg, and HuAI/CIII/CETPTg mice the number of lesions was significantly lower than in HuCIIITg and control mice: 0.9 +/- 0.4, 1.5 +/- 0.5, and 0.9 +/- 0.4, respectively. There were parallel reductions in mean lesion area. In a separate study, we found an increased susceptibility to dietary atherosclerosis in nonhypertriglyceridemic CETP transgenic mice compared to controls. We conclude that CETP expression inhibits the development of early atherosclerotic lesions but only in hypertriglyceridemic mice.

A lipoprotein lipase mutation (Asn291Ser) is associated with reduced HDL cholesterol levels in premature atherosclerosis

A reduction of high density lipoprotein cholesterol (HDC) is recognized as an important risk factor for coronary artery disease (CAD). We now show in approximately 1 in 20 males with proven atherosclerosis that an Asn291Ser mutation in the human lipoprotein lipase (LPL) gene is associated with significantly reduced HDL levels (P = 0.001) and results in a significant decrease in LPL catalytic activity (P < 0.0009). The relative frequency of this mutation increases in those patients with lower HDL cholesterol levels. In vitro mutagenesis and expression studies confirm that this change is associated with a significant reduction in LPL activity. Our data support the relationship between LPL activity and HDL-C levels, and suggest that a specific LPL mutation may be a factor in the development of atherosclerosis.

Remodelling of lipoproteins in transgenic mice expressing human cholesteryl ester transfer protein.

Cholesteryl ester transfer protein (CETP) facilitates the transfer of reciprocal exchange of neutral lipids between lipoproteins. To better understand the function of CETP and its role in atherogenic pathways, transgenic mice which express human CETP were generated. The transgene encoding human CETP was under the control of the mouse alpha-fetoprotein enhancer and mouse albumin gene promoter and was expressed exclusively in the liver. The level of human CETP activity in transgenic mouse plasmas was found to be 1- to 5-fold greater than in normolipidemic human plasma. Human CETP induced an approx. 30 and 40% reduction of HDL cholesterol levels in plasma from female and male transgenic mice, respectively, when compared to controls. In addition, multiple alterations in mouse lipoprotein composition were observed in the transgenic mice. Diminished HDL cholesterol levels and disappearance of the apo E-rich HDL1 moiety account for the dramatic reduction in plasma cholesterol. The decrease in HDL cholesterol was accompanied by a marked reduction in HDL particle size and apo A-I content. The cholesterol content and the size of LDL particles increased, but only modestly, in transgenic mouse plasma. In conclusion, human CETP induces a significant remodelling of mouse lipoproteins which results in dramatic reduction in plasma cholesterol levels.

Effects of an American Heart Association step I diet and weight loss on lipoprotein lipid levels in obese men with silent myocardial ischemia and reduced high-density lipoprotein cholesterol

Reduced plasma concentrations of high-density lipoprotein cholesterol (HDL-C) are a risk factor for coronary artery disease (CAD). In this study, we examined the sequential effects of an isocaloric American Heart Association (AHA) step I diet and a hypocaloric AHA step I diet (AHA step I diet + weight loss) on lipoprotein lipid levels in 14 middle-aged and older (60 ± 6 years, mean ± SD) obese (body mass index [BMI] > 27 kg/m 2) nondiabetic men with exercise-induced silent myocardial ischemia (SI) and reduced HDL-C levels (0.85 ± 0.14 mmol/L). Nine men of comparable age and obesity and with no evidence of exercise-induced ischemia that were evaluated longitudinally served as metabolic controls. In men with SI, after 3 months on the isocaloric AHA step I diet plasma triglyceride (TG) levels decreased by 26% (2.25 ± 0.66 to 1.67 ± 0.69 mmol/L, P < .005), cholesterol by 12% (5.24 ± 0.84 to 4.62 ± 0.78 mmol/L, P < .01), and low-density lipoprotein cholesterol (LDL-C) by 10% (3.40 ± 0.69 to 3.05 ± 0.70 mmol/L, P < .01). However, plasma HDL-C levels also decreased by 7% (0.85 ± 0.14 to 0.79 ± 0.13 mmol/L, P < .05). Subsequent weight loss (11 ± 4 kg) in conjunction with the AHA step I diet resulted in an additional decrease of 24% in TG ( P < .005), 10% in cholesterol ( P < .05), and 10% in LDL-C ( P < .05). Plasma HDL-C levels increased by 8% ( P < .01), thereby correcting the decline seen on the AHA step I diet alone. Postheparin hepatic lipase (HL) activity decreased with weight loss ( P < .005), with no significant change in lipoprotein lipase (LPL) activity. There were no significant changes in lipoprotein lipids or postheparin lipolytic activity in the metabolic controls. Therefore, in men with SI, the sequential interventions of an isocaloric AHA step I diet and an AHA step I diet with weight loss decreased plasma TG levels by 44% ( P < .0001), LDL-C levels by 18% ( P < .0001), and the LDL-C to HDL-C ratio by 19% ( P < .005), with no significant change in HDL-C levels. Additional treatment modalities that include supervised exercise programs and drug therapy may be warranted in older obese subjects whose HDL-C levels do not normalize with diet and weight-loss interventions alone.