Lipoprotein lipase gene polymorphism at the PvuII locus and serum lipid levels in Guangxi Hei Yi Zhuang and Han populations.

BACKGROUND: Hei Yi (which means "black worship" and "black dressing") Zhuang is a specific subgroup of the Zhuang nationality in China. Little is known about the relationship between genetic factors and lipid profiles in this population. Therefore, the present study was undertaken to compare the effects of lipoprotein lipase gene polymorphism at the PvuII locus on lipid levels in the Guangxi Hei Yi Zhuang and Han populations. METHODS: A total of 325 Hei Yi Zhuang subjects aged from 20 to 80 years were surveyed using stratified randomized cluster sampling. Serum levels of lipids and apolipoproteins were measured. Gene polymorphism was determined using polymerase chain reaction and restriction fragment length polymorphism. The results were compared with those for 331 matched Han subjects living in the same district. RESULTS: Serum levels of total cholesterol, triglycerides, low-density lipoprotein cholesterol and apolipoprotein B were significantly lower in Hei Yi Zhuang than in Han subjects (p<0.05-0.01), whereas the levels of high-density lipoprotein cholesterol and the ratio of apolipoprotein A1 to apolipoprotein B were significantly higher in Hei Yi Zhuang than in Han subjects (both p<0.01). The allelic frequencies for P+ and P- were 52.92% and 47.08% in Hei Yi Zhuang, and 58.46% and 41.54% in Han subjects (p<0.05), respectively. The frequencies of P+P+, P+P- and P-P- genotypes were 23.08%, 59.69% and 17.23% in Hei Yi Zhuang, and 29.31%, 58.31% and 12.38% in Han subjects (p>0.05), respectively. There were no significant differences or no significant correlation between serum lipid parameters and genotypes in Hei Yi Zhuang or Han subjects, or for the combined population of Hei Yi Zhuang and Han (all p>0.05). CONCLUSIONS: The allelic frequencies of the lipoprotein lipase gene at the PvuII locus in Hei Yi Zhuang were different from those in Han subjects, but the genotypic frequencies in Hei Yi Zhuang subjects were not different from those in Han subjects. There was no significant correlation between polymorphism of the lipoprotein lipase gene at the PvuII site and serum lipid levels in the two ethnic groups.     

Association of TaqIB polymorphism in the cholesteryl ester transfer protein gene with serum lipid levels in the Guangxi Hei Yi Zhuang and Han populations

BACKGROUND: Cholesteryl ester transfer protein (CETP) plays an important role in lipoprotein metabolism. The present study was undertaken to compare the difference in the CETP TaqIB gene polymorphism and its association with serum lipid levels between the Guangxi Hei Yi Zhuang and Han populations. METHODS: A total of 758 subjects of Hei Yi Zhuang and 778 participants of Han Chinese were surveyed. Genotyping of the CETP TaqIB was performed using polymerase chain reaction and restriction fragment length polymorphism and then confirmed using direct sequencing. RESULTS: The genotypic and allelic frequencies were significant differences between smokers and nonsmokers, or between hypertensives and normotensives in Hei Yi Zhuang, and between drinkers and nondrinkers in Han. The levels of high-density lipoprotein cholesterol (HDL-C) and apolipoprotein AI in Hei Yi Zhuang but not in Han were higher in B2B2 genotype than in B1B1 genotype (P < 0.01 for each). Higher HDL-C levels in Hei Yi Zhuang were found only in females, nondrinkers, nonsmokers, subjects with a body mass index of 24 kg/m or lesser, or normotensives in B2B2 genotype. Higher HDL-C levels in Han were found only in females in B2B2 genotype and in subjects with a body mass index of 24 kg/m or lesser or normotensives in B1B2 genotype. The levels of HDL-C in B1B1 and B1B2 individuals in both ethnic groups were higher in drinkers than in nondrinkers. CONCLUSIONS: There were significant differences in the interactions between the CETP TaqIB genotypes and several environmental factors in the Hei Yi Zhuang and Han populations. The polymorphism predicted differences in HDL-C and ApoAI in the Hei Yi Zhuang but not in the Han Chinese, even after adjustment for confounding variables. This means that the gene may not be truly involved in regulation of high-density lipoprotein metabolism or that there is an ethnic-specific effect.     

Efficacy of ciprofibrate in primary type II and IV hyperlipidemia: the Italian multicenter study

The 127 diet-resistant primary hyperlipidemic patients received 100 mg of ciprofibrate daily for 12 weeks. In the 63 patients with type IIa hyperlipidemia and 41 patients with type IIb hyperlipidemia, serum levels of total cholesterol, very-low-density lipoprotein cholesterol, low-density lipoprotein cholesterol, triglycerides, very-low-density lipoprotein triglycerides, and apolipoprotein (apo) B decreased significantly and levels of high-density lipoprotein cholesterol and apo A-I increased significantly. Similar changes occurred in the 23 type IV patients, except that high-density lipoprotein cholesterol levels increased significantly and apo B levels did not change. No clinically significant side effects or drug-related abnormal laboratory test results were noted. It is concluded that ciprofibrate is a safe and potent hypolipidemic agent.     

Detailed analysis of serum lipids and lipoproteins from Japanese type III hyperlipoproteinemia with apolipoprotein E2/2 phenotype

BACKGROUND: To clarify a detailed profile of serum lipids, lipoproteins and apolipoproteins (apo) in type III hyperlipoproteinemia (HLP) with apolipoprotein E (apo E) phenotype 2/2. METHODS: Nineteen consecutive Japanese type III HLP (9 men, 10 women) were studied. All had hypertriglyceridemia and 74% showed hypercholesterolemia. RESULTS: The degree of hyperlipidemia [total cholesterol (TC) 8.1 +/- 3.2 mmol/l, triglycerides (TG) 5.2 +/- 2.9 mmol/l] was milder than that in type III HLP in western countries. Lipoprotein fractions analyzed by ultracentrifugation showed that very low density lipoprotein cholesterol (VLDL-C) concentrations were considerably increased and that intermediate density lipoprotein cholesterol (IDL-C) concentrations were also increased, whereas low-density lipoprotein cholesterol (LDL-C) concentrations were low. Serum apo A-I, A-II and B concentrations were not increased, while apo C-II, C-III and E concentrations were considerably increased. However, the increase of apo E concentrations in the study subjects was far more pronounced than that of apo C-III, causing the ratio of apo E/C-III to be considerably higher than hyperlipidemia with other apo E phenotypes. CONCLUSION: By using this index apo E/C-III, it is possible to segregate type III HLP with apo E2/2 phenotype from other types of hyperlipidemia.     

Defective removal of cellular cholesterol and phospholipids by apolipoprotein A-I in Tangier Disease.

Tangier disease is a rare genetic disorder characterized by extremely low plasma levels of HDL and apo A-I, deposition of cholesteryl esters in tissues, and a high prevalence of cardiovascular disease. We examined the possibility that HDL apolipoprotein-mediated removal of cellular lipids may be defective in Tangier disease. With fibroblasts from normal subjects, purified apo A-I cleared cells of cholesteryl esters, depleted cellular free cholesterol pools available for esterification, and stimulated efflux of radiolabeled cholesterol, phosphatidylcholine, and sphingomyelin. With fibroblasts from two unrelated Tangier patients, however, apo A-I had little or no effect on any of these lipid transport processes. Intact HDL also was unable to clear cholesteryl esters from Tangier cells even though it promoted radiolabeled cholesterol efflux to levels 50-70% normal. Passive desorption of radiolabeled cholesterol or phospholipids into medium containing albumin or trypsinized HDL was normal for Tangier cells. Binding studies showed that the interaction of apo A-I with high-affinity binding sites on Tangier fibroblasts was abnormal. These results indicate that apo A-I has an impaired ability to remove cholesterol and phospholipid from Tangier fibroblasts, possibly because of a defective interaction of apo A-I with cell-surface binding sites. Failure of apo A-I to acquire cellular lipids may account for the rapid catabolism of nascent HDL particles and the low plasma HDL levels in Tangier disease.     

Lipoprotein(a), apolipoprotein A-I and B serum levels in young families from Tallinn,Estonia. Relationships with other cardiovascular risk factors and nationality

Serum lipid, lipoprotein(a) (Lp(a)), apolipoprotein (apo) A-I and B concentrations were studied in young families of Tallinn: 157 husbands, 81 wives and 149 newborns participated in the study; 48% of subjects were Estonians, 39% Russians and 13% other nationalities. As previous studies among middle-aged men and school children of Estonia revealed clear national differences in serum lipoprotein profiles, our special interest was to study lipoprotein parameters in relation to ethnic origin. Body mass index (BMI), blood pressure (BP) and smoking habits were determined. In newborns, maturity by physical and neurological criteria and Apgar score after birth were assessed. At the age of 18-30 years, Estonian men had significantly higher serum total cholesterol, LDL cholesterol, triglyceride and Lp(a) levels than did Russian men. Estonian newborns had higher serum triglyceride concentration than Russian ones. Among women no national differences were recorded in the measured parameters. Lp(a) levels were not statistically correlated with age, BMI, BP or current smoking. Negative associations were revealed between Lp(a) and serum level of apo A-I (in men) or triglycerides (in newborns). Lp(a) concentrations correlated positively with LDL cholesterol (in women) and apo B (in newborns). Lp(a) levels of newborns were not associated with birthweight or health status, but correlated strongly with the sum of parental and fathers' Lp(a) concentrations, demonstrating that a genetic factor(s) is involved in the values of plasma Lp(a) levels.     

Lipoprotein(a), apolipoprotein A-I and B serum levels in young families from Tallinn, Estonia. Relationships with other cardiovascular risk factors and nationality.

Serum lipid, lipoprotein(a) (Lp(a)), apolipoprotein (apo) A-I and B concentrations were studied in young families of Tallinn: 157 husbands, 81 wives and 149 newborns participated in the study; 48% of subjects were Estonians, 39% Russians and 13% other nationalities. As previous studies among middle-aged men and school children of Estonia revealed clear national differences in serum lipoprotein profiles, our special interest was to study lipoprotein parameters in relation to ethnic origin. Body mass index (BMI), blood pressure (BP) and smoking habits were determined. In newborns, maturity by physical and neurological criteria and Apgar score after birth were assessed. At the age of 18-30 years, Estonian men had significantly higher serum total cholesterol, LDL cholesterol, triglyceride and Lp(a) levels than did Russian men. Estonian newborns had higher serum triglyceride concentration than Russian ones. Among women no national differences were recorded in the measured parameters. Lp(a) levels were not statistically correlated with age, BMI, BP or current smoking. Negative associations were revealed between Lp(a) and serum level of apo A-I (in men) or triglycerides (in newborns). Lp(a) concentrations correlated positively with LDL cholesterol (in women) and apo B (in newborns). Lp(a) levels of newborns were not associated with birthweight or health status, but correlated strongly with the sum of parental and fathers' Lp(a) concentrations, demonstrating that a genetic factor(s) is involved in the values of plasma Lp(a) levels.     

Quantitative analysis of apolipoprotein E secretion by human monocyte-derived macrophages in culture

Apolipoprotein E (apo E) has an impact on lipid metabolism and its production by macrophages is considered to play a protective role against atherosclerosis. Apo A-I stimulates secretion of apo E from macrophages. We developed a new method to evaluate the ability of human monocyte-derived macrophages to secrete apo E, and the effects of factors such as apo A-I were examined. Monocytes separated from peripheral venous blood were cultured. The levels of apo E in macrophage-conditioned medium were quantified by immunoblotting with an anti-human apo E antiserum conjugated with alkaline phosphatase. The basal levels of apo E secretion and the response to exogenous apo A-I in macrophages from 10 healthy volunteers were measured. Sufficient accuracy and sensitivity were confirmed and coefficient of variation of the method was 18 +/- 11% (n = 10). It was confirmed that macrophage secreted apo E in a concentration-dependent manner in response to M-CSF and apo A-I. The average apo E concentration in the conditioned medium of macrophages from 10 healthy subjects was 30.9 +/- 14.7 ng/mg cell protein. After the addition of apo A-I, the average apo E concentration increased, by about 60%, to 49.4 +/- 29.7 ng/mg cell protein (p < 0.05). There was a positive correlation between the apo A-I-induced increase and plasma LDL cholesterol levels (r = +0.54, p < 0.05).     

Correlation between the ratio of serum low-density lipoprotein cholesterol and high-density lipoprotein cholesterol with that of serum apolipoproteins B and A-I

Summary Phosphowolframate/magnesium chloride, a commonly used precipitation method for the determination of high-density lipoprotein cholesterol in human serum, yields a supernatant containing almost all of the lipoproteins apo A-I and apo A-II but no lipoprotein apo B. The correlation between high-density lipoprotein cholesterol and apo A-I was very high (r=0.94), as well as that between the precipitation method and ultracentrifugal analysis (r>0.95,P<0.001). In contrast, detergent precipitation (for the determination of low-density lipoprotein cholesterol in human serum) produced sediments which contained the major proportion of apo B and only minor amounts of apo A-I and apo A-II. The precipitation method for low-density lipoprotein cholesterol showed very good agreement with ultracentrifugal analysis (r=0.99). Yields of 80.2% were obtained for apo B with both methods. Results obtained using the precipitation methods showed excellent agreement with those obtained using the Friedewald formula (r>0.99). Results were also very similar when hypertriglyceridemic serum samples were briefly centrifuged before analysis of cholesterol, high-density lipoprotein cholesterol and triglyceride values. The present study shows highly significant correlations between cholesterol/high-density lipoprotein cholesterol or low-density lipoprotein cholesterol/high-density lipoprotein cholesterol and apo B/apo A-I ratios (P<0.001). Apo B and apo A-I levels could be used in addition to low- and high-density lipoprotein cholesterol values when assessing the risk of cardiovascular disease, if the methods for determining serum apolipoproteins have been properly standardized.     

Activity of low-density lipoprotein receptors as estimated from concentrations of apolipoprotein B and C-II in serum

The correlation between low-density lipoprotein (LDL) receptor activity and concentrations of lipids and apolipoproteins in serum was examined in 12 subjects with heterozygous familial hypercholesterolemia (FH) and in four with non-FH type II hyperlipoproteinemia. Concentrations of high-density lipoprotein cholesterol and of apolipoproteins (apo) A-I, C-II, and C-III were significantly positively correlated with LDL receptor activity, whereas LDL receptor activity was significantly inversely correlated with LDL cholesterol and apo B concentrations, and with apo ratios B/A-I and B/A-II. Neither total serum cholesterol, triglyceride, phospholipid, apo A-I, nor apo E concentrations correlated significantly with LDL receptor activity. Multiple regression analysis, with LDL receptor activity as the dependent variable, revealed concentrations of apo B and apo C-II to be the principal determinant factors. To confirm this, we subsequently calculated the LDL receptor activities before and after administration of CS-514, an inhibitor of hydroxymethylglutaryl-CoA reductase (EC 1.1.1.88), which increases the hepatic LDL receptor activity and decreases the concentration of cholesterol in serum. This drug increased calculated LDL receptor activities significantly, with a significant decrease in serum cholesterol.     

The full induction of human apoprotein A-I gene expression by the experimental nephrotic syndrome in transgenic mice depends on cis-acting elements in the proximal 256 base-pair promoter region and the trans-acting factor early growth response factor 1.

To identify molecular factors regulating apo A-I production in vivo, we induced in transgenic mice the experimental nephrotic syndrome, which results in elevated levels of HDL cholesterol (HDL-C), plasma apo A-I, and hepatic apo A-I mRNA. Human (h) apo A-I transgenic mice with different length 5' flanking sequences (5.5 or 0.256 kb, the core promoter for hepatic-specific basal expression) were injected with nephrotoxic (NTS) or control serum. With nephrosis, there were comparable (greater than twofold) increases in both lines of HDL-C, h-apo A-I, and hepatic h-apo A-I mRNA, suggesting that cis-acting elements regulating induced apo A-I gene expression were within its core promoter. Hepatic nuclear extracts from control and nephrotic mice footprinted the core promoter similarly, implying that the same elements regulated basal and induced expression. Hepatic mRNA levels for hepatocyte nuclear factor (HNF) 4 and early growth response factor (EGR) 1, trans-acting factors that bind to the core promoter, were measured: HNF4 mRNA was not affected, but that of EGR-1 was elevated approximately fivefold in the nephrotic group. EGR-1 knockout (EGR1-KO) mice or mice expressing EGR-1 were injected with either NTS or control serum. Levels of HDL-C, apo A-I, and hepatic apo A-I mRNA were lowest in nonnephrotic EGR1-KO mice and highest in nephrotic mice expressing EGR-1. Although in EGR1-KO mice HDL-C, apo A-I, and apo A-I mRNA levels also increased after NTS injection, they were approximately half of those in the nephrotic EGR-1-expressing mice. We conclude that in this model, basal and induced apo A-I gene expression in vivo are regulated by the trans-acting factor EGR-1 and require the same cis-acting elements in the core promoter.     

Characterization of apolipoprotein A-I- and A-II-containing lipoproteins in a new case of high density lipoprotein deficiency resembling Tangier disease and their effects on intracellular cholesterol efflux.

A 48-yr-old Caucasian female of central European origin (subject IM) with low plasma cholesterol and normal plasma triglyceride (TG) had extremely low apo A-I (6 mg/dl), A-II (5 mg/dl), and HDL cholesterol (2 mg/dl) levels. She had most of the clinical symptoms typically associated with Tangier disease, including early corneal opacities, yellow-streaked tonsils, hepatomegaly, and variable degrees of peripheral neuropathy, but had no splenomegaly. She had a myocardial infarction at age 46. Since HDL are postulated to be involved in the transport of excess cholesterol from peripheral tissues to the liver for degradation, and the ability of an HDL particle to promote cellular cholesterol efflux appears to be related to its density, size, and apo A-I and A-II contents, we isolated and characterized the HDL particles of this patient and all her first degree relatives (mother, a brother, and two children). The plasma A-I, A-II, and HDL cholesterol levels of all five relatives were either normal or high. Using anti-A-I and anti-A-II immunosorbents, we found three populations of particles in IM: one contained both apo A-I and A-II, Lp(AI w AII); one contained apo A-I but no A-II, Lp(AI w/o AII); and the third (an unusual one) contained apo A-II but no A-I, Lp(AII). Two-thirds of her plasma A-I and A-II existed in separate HDL particles, i.e., in Lp(AI w/o AII) and Lp(AII), respectively. Only Lp(AI w AII) and Lp(AI w/o AII) were present in the plasma of the relatives. All three populations of the patient's HDL particles had a normal core/surface lipid ratio, but the cores were enriched with TG. The apo A-I-containing particles, however, were considerably smaller and contained much less lipid than Lp(AII). Despite these unusual physicochemical characteristics, the apo A-I-containing particles and Lp(AII) were effective suppressors of intracellular cholesterol esterification in cholesterol-loaded human skin fibroblast. The patient's plasma apo D and lecithin cholesterol acyltransferase levels were reduced, with an increased proportion located in non-HDL plasma fractions. These findings are discussed in light of Tangier disease and other known HDL-deficiency cases, and the role of HDL in the maintenance of cell cholesterol homeostasis.     

HDL and clinical and biochemical correlates in Italian non-smoker women.

High-density lipoprotein (HDL)-cholesterol levels, inversely related to the risk of myocardial infarction, are determined by genetic and environmental factors. The aim of this study was to evaluate the prevalence of low and high HDL plasma levels and the influence of environmental factors and lipid profile in an Italian non-smoker female population. HDL, apolipoprotein A-I, apolipoproteins, lipids and estrogen plasma levels were measured in a population of 1471 women with a mean age of 45 +/- 14 years. HDL values < or = 35 mg/dl were noted in 11.2% of the subjects, showing 2.4% coronary heart disease (CHD) prevalence. The 90th percentile was characterized by HDL levels > or = 66 mg/dl and the absence of coronary atherosclerosis. Total cholesterol, apolipoprotein B and triglycerides (r = -0.31, p < 0.0001) were the main determinants of HDL levels; apolipoprotein E, estrogen use, body mass index (BMI), alcohol consumption and age showed a weaker correlation. Apolipoprotein A-I concentration was influenced more notably by estrogen use, total cholesterol and apolipoprotein E; levels of triglycerides, apolipoprotein B, BMI, age and alcohol consumption are less important. The parameters considered here, taken together, explain HDL and apolipoprotein A-I variability of approximately 31% and 24%, respectively. A surprisingly high prevalence of very low (< or = 35 mg/dl) and high (> or = 66 mg/dl) HDL levels in Italian women further confirms the importance of studies on the HDL distribution in different population groups.     

Plasma concentrations of apolipoprotein A-I containing particles in normolipidaemic young men

Low levels of plasma high-density lipoprotein (HDL)-cholesterol and apolipoprotein (apo)-A-I are associated with premature coronary heart disease. However, particles in the density range of HDL are heterogeneous. Two main types of apo A-I-containing particles can be identified, one species containing both apo A-I and apo A-II (Lp A-I:A-II) and the other apo A-I but no apo-A-II (Lp A-I). This study was designed to measure HDL cholesterol, apo A-I, and, using a new procedure, Lp A-I in 233 healthy normolipidaemic young men (cholesterol less than 250 mg dl-1 and triglycerides less than 200 mg dl-1). Among these subjects, the composition of HDL was very variable as indicated by the 10th and the 90th percentiles of the HDL-cholesterol/apo A-I ratios which were 0.32 and 0.49, respectively. The 10th and 90th percentiles of apo A-I and Lp A-I:A-II were 126 and 167 mg dl-1 and 83 and 116 mg dl-1, respectively. On the other hand, Lp A-I showed a much larger variation, the 10th and 90th percentiles being at 33 and 62 mg dl-1, respectively. The distribution of individual values of Lp A-I showed that this fraction of apo A-I-containing particles was very variable among subjects, the Lp A-I/apo A-I ratio extending from 0.18 to 0.58. Triglycerides, Lp A-I and Lp A-I:A-II were correlated with HDL cholesterol, but no correlation between apo A-I containing subfractions and plasma triglycerides was noticed. Since preliminary results from angiographic and clinical studies show that Lp A-I could exert a protective role for atherosclerosis, it would seem that the measurement of Lp A-I might help in the future to characterize better the individual's risk for atherosclerosis.     

Effects of pindolol on serum lipids, apolipoproteins, and lipoproteins in patients with mild to moderate essential hypertension

The effects of 12 weeks' administration of the beta-blocker pindolol (5 mg twice daily) on serum lipids, apolipoproteins (apo), and lipoproteins were studied in 20 normolipidemic patients with mild to moderate essential hypertension (WHO I-II). Pindolol significantly increased both high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C), while very-low-density lipoprotein cholesterol (VLDL-C) was significantly decreased. Apo A-II levels were increased significantly and the apo B/apo A-I ratio, which is one of the atherogenic indexes, was decreased significantly after pindolol therapy. Total cholesterol, HDL subfraction cholesterols, the LDL-C/HDL-C ratio, triglycerides, apo A-I, apo B, apo C-II, apo C-III, and apo E did not change significantly.     

Sustained expression of human apo A-I following adenoviral gene transfer in mice

Elevation of HDL cholesterol, following adenoviral apolipoprotein A-I (apo A-I) gene transfer, may delay or revert ischemic cardiovascular disease, provided transgene expression is persistent. The choice of promoter may have significant impact on persistence of transgene expression. Human apo A-I expression was compared after adenoviral gene transfer with a cytomegalovirus promoter (CMV) driven construct (AdCMV/A-I.gA-I) and with a construct (AdA-I.gA-I.4xapoE) containing the endogenous 256 bp apo A-I promoter (A-I), the genomic human apo A-I DNA (gA-I) and 4 human apo E enhancers (4xapoE) in three different mouse strains: C57BL/6, Balb/c and Fvb. After gene transfer with 5 x 10(8) p.f.u. of AdCMV/A-I.gA-I, human apo A-I expression was observed for 35 days in C57BL/6 mice, but declined below 1 mg/dl within 14 days both in Balb/c and Fvb mice, due to a strong humoral immune response against human apo A-I. In contrast, after transfer with AdA-I.gA-I.4xapoE, human apo A-I expression persisted for 6 months in all three strains and no antibodies against human apo A-I occurred in Fvb or Balb/c mice. Human apo A-I transgene DNA level 35 days after transfer with AdA-I.gA-I.4xapoE was 4.6- to 5.5-fold higher than with AdCMV/A-I.gA-I. CMV promoter attenuation occurred in all three strains, but promoter attenuation was not observed in any strain after transfer with AdA-I.gA-I.4xapoE. In conclusion, gene transfer with AdA-I.gA-I.4xapoE is associated with absence of an immune response against human apo A-I, improved transgene DNA persistence and absence of promoter shut-off, resulting in human apo A-I expression for up to 6 months in three different mouse strains. Possibly, the absence of human apo A-I expression in antigen-presenting cells with the liver-specific apo A-I promoter containing construct abrogated the immune response against human apo A-I in Balb/c and Fvb mice.     

A frameshift mutation in the human apolipoprotein A-I gene causes high density lipoprotein deficiency, partial lecithin: cholesterol-acyltransferase deficiency, and corneal opacities.

Epidemiologic data of recent years have identified an important role of HDL deficiency in the etiology of atherosclerosis. Biochemical data suggest that some of these deficiencies may be a consequence of defects in the structural genes of HDL apolipoproteins or of plasma enzymes that modify HDL. We analyzed the genetic defect in a 42-yr-old patient suffering from corneal opacities and complete absence of HDL cholesterol but not of coronary artery disease, thus clinically resembling fish eye disease. The observation of an abnormal immunoblot banding pattern of apolipoprotein A-I (apo A-I) and of reduced lecithin: cholesterol acyltransferase (LCAT) activity in plasma led to sequence analysis of the genes for apo A-I and LCAT in this patient and his family. Direct sequencing of polymerase chain reaction amplified DNA segments containing the exons of the candidate genes, resulted in the identification of a frameshift mutation in apo A-I while the LCAT sequence was identical to the wild type. The apo A-I mutation was predictive for an extensive alteration of the COOH-terminal sequence of the encoded protein. Evidence for the release of this mutant protein into the plasma compartment and for the absence of normal apo A-I was derived from ultraviolet laser desorption/ionization mass spectrometry analysis. Our results suggest that a defective apo A-I is the causative defect in this case of HDL deficiency with corneal opacities.     

Apo A-I inhibits foam cell formation in apo E–deficient mice after monocyte adherence to endothelium

We have previously shown that expression of the human apo A-I transgene on the apo E-deficient background increases HDL cholesterol and greatly diminishes fatty streak lesion formation. To examine the mechanism, prelesional events in atherosclerotic plaque development were examined in 6- to 8-week-old apo E-deficient and apo E-deficient/human apo A-I transgenic mice. A quantitative assessment of subendothelial lipid deposition by freeze-fracture and deep-etch electron microscopy indicated that elevated apo A-I did not affect the distribution or amount of aortic arch subendothelial lipid deposits. Immunohistochemical staining for VCAM-1 demonstrated similar expression on endothelial cells at prelesional aortic branch sites from both apo E-deficient and apo E-deficient/human apo A-I transgenic mice. Transmission electron microscopy revealed monocytes bound to the aortic arch in mice of both genotypes, and immunohistochemical staining demonstrated that the area occupied by bound mononuclear cells was unchanged. Serum paraoxonase and aryl esterase activity did not differ between apo E-deficient and apo E-deficient/human apo A-I transgenic mice. These data suggest that increases in apo A-I and HDL cholesterol inhibit foam cell formation in apo E-deficient/human apo A-I transgenic mice at a stage following lipid deposition, endothelial activation, and monocyte adherence, without increases in HDL-associated paraoxonase.     

Familial apolipoprotein A-I variants

Apolipoprotein (apo) A-I is the major apolipoprotein of HDL and is a single polypeptide chain with 243 amino acid residues. Familial apo A-I deficiency is a rare metabolic disorder of which 13 cases have been characterized at the molecular level. However, in subjects with apo A-I deficiency, coronary artery disease is not always present. To date, more than 40 genetically determined structural variants of apo A-I have been identified. Seven apo A-I mutations have been identified to cause hereditary amyloidosis. In our laboratory, we characterized ten apo A-I variants, including apo A-I(Vall56Glu) Oita. A minority of structural variants were associated with altered HDL cholesterol levels or increased risk for cardiovascular disease.     

In vivo metabolism of a mutant form of apolipoprotein A-I, apo A-IMilano, associated with familial hypoalphalipoproteinemia.

Apo A-IMilano is a mutant form of apo A-I in which cysteine is substituted for arginine at amino acid 173. Subjects with apo A-IMilano are characterized by having low levels of plasma HDL cholesterol and apo A-I. To determine the kinetic etiology of the decreased plasma levels of the apo A-I in these individuals, normal and mutant apo A-I were isolated, radiolabeled with either 125I or 131I, and both types of apo A-I were simultaneously injected into two normal control subjects and two subjects heterozygous for apo A-IMilano. In the normal subjects, apo A-IMilano was catabolized more rapidly than the normal apo A-I (mean residence times of 5.11 d for normal apo A-I vs. 3.91 d for apo A-IMilano), clearly establishing that apo A-IMilano is kinetically abnormal and that it has a shortened residence time in plasma. In the two apo A-IMilano subjects, both types of apo A-I were catabolized more rapidly than normal (residence times ranging from 2.63 to 3.70 d) with normal total apo A-I production rates (mean of 10.3 vs. 10.4 mg/kg per d in the normal subjects). Therefore, in the subjects with apo A-IMilano, the decreased apo A-I levels are caused by rapid catabolism of apo A-I and not to a decreased production rate, and the abnormal apo A-IMilano leads to the rapid catabolism of both the normal and mutant forms of apo A-I in the affected subjects.