Effect of gene polymorphisms on lipoprotein levels in patients with dyslipidemia of metabolic syndrome

Dyslipidemia in the metabolic syndrome (MS) is considered to be one of the most important risk factors for atherosclerosis. It is characterized by hypertriglyceridemia, low concentration of plasma HDL-cholesterol, predominance of small dense LDL particles and an increased concentration of plasma apolipoprotein B (apoB). The pathogenesis of this type of dyslipidemia is partially explained, but its genetic background is still unknown. To evaluate the influence of cholesterol ester transfer protein (CETP) TaqIB polymorphism, lipoprotein lipase (LPL) PvuII and HindIII polymorphisms, hepatic lipase (LIPC) G-250A polymorphism and apolipoprotein C-III (APOC3) SstI gene polymorphism on lipid levels in dyslipidemia of the metabolic syndrome, 150 patients with dyslipidemia of metabolic syndrome were included. 96 % of patients had type 2 diabetes. The patients did not take any lipid lowering treatment. The exclusion criterion was the presence of any disease that could affect lipid levels, such as thyroid disorder, liver disease, proteinuria or renal failure. Gene polymorphisms were determined using the polymerase chain reaction and restriction fragment length polymorphisms. The genotype subgroups of patients divided according to examined polymorphisms did not differ in plasma lipid levels with the exception of apoB. The apoB level was significantly higher in patients with S1S1 genotype of APOC3 SstI polymorphism when compared with S1S2 group (1.10+/-0.26 vs. 0.98+/-0.21 g/l, p=0.02). Similarly, patients with H-H- genotype of LPL HindIII polymorphism had significantly higher mean apoB, compared with H+H- and H+H+ group (1.35+/-0.30 vs. 1.10+/-0.26 g/l, p=0.02). In the multiple stepwise linear regression analysis, apoB level seemed to be influenced by APOC3 SstI genotype, which explained 6 % of its variance. The present study has shown that the S1 allele of APOC3 SstI polymorphism and the H- allele of LPL HindIII polymorphism might have a small effect on apoB levels in the Central European Caucasian population with dyslipidemia of metabolic syndrome.     

Restriction polymorphism in patients with lipid metabolism disorders and ischemic heart disease

Using the RELP analysis we studied the frequency of X2 allele of apoB gene in three groups of patients: 1) men at the age of 20-59 with lipid metabolism disorders revealed in population inspection of Oktyabrsky district in Moscow; 2) men with ischaemic heart disease and 3) healthy men. It was established that in individuals suffering from type IIa hyperlipidemia the frequency of X2 allele was significantly higher than in healthy donors from Moscow population. Homozygotes for X2 allele of XbaI RELP had 7-9% higher serum cholesterol levels, than homozygotes for X1 allele. The study suggests the X2 allele of the apoB gene to be associated with the development of high plasma cholesterol level. No significant difference in X2 allele frequencies was found between patients with ischaemic heart disease and healthy donors. There was also no association found between cholesterol and triglyceride levels and the presence of X2 allele in this group of patients.     

Apolipoprotein B signal peptide insertion/deletion polymorphism is associated with Ag epitopes and involved in the determination of serum triglyceride levels.

We have investigated the insertion/deletion polymorphism in the signal peptide region of the apoB gene in 106 Finnish individuals from North Karelia. The relative frequency of the insertion allele in this sample was 0.73. Strong linkage disequilibrium was detected between this apoB insertion/deletion polymorphism and the Ag(c/g) epitope pair of apoB, while weak linkage disequilibrium was detected between the polymorphism and the four other reported Ag epitope pairs [(a1/d), (x/y), (h/i) and (t/z)], as well as the apoB PvuII and the XbaI RFLPs. Using one-way analysis of variance there was a statistically significant association (P less than 0.05) between the apoB insertion/deletion polymorphism and serum triglyceride levels in this sample. Individuals homozygous for the insertion allele had higher triglyceride levels than individuals homozygous for the deletion allele, while individuals heterozygous for the polymorphism had intermediate levels. These differences were reduced when individuals were consuming a low fat diet but were statistically significant when the individuals returned to their normal diet. It is possible that insertion or deletion of three hydrophobic amino acids (leu-ala-leu) from the signal peptide of apoB may have a direct effect on plasma triglyceride levels by altering the intracellular processing of apoB or apoB-containing lipoproteins in the liver or intestine.     

Human hepatic low-density lipoprotein receptors: associations of receptor activities in vitro with plasma lipid and apolipoprotein concentrations in vivo

The relationships of plasma lipid and apolipoprotein (apo) concentrations to hepatic low-density lipoprotein (LDL) receptor activity were examined in 21 subjects (16 females, 5 males), who were undergoing laparotomy for non-neoplastic disease (cholecystectomy in 16). None had familial hypercholesterolemia, or renal, endocrine or hepatic disease. Ages were 37-77 years (mean, 58 years), plasma cholesterol concentrations 4.09-6.72 mmol/l (5.38) and plasma triacylglycerol concentrations 0.75-2.35 mmol/l (1.36). Receptor activity was quantified in vitro as the total saturable binding and EDTA-suppressible binding (representing apoB,E receptors) of 125I-labelled human LDL (15 micrograms protein/ml) by liver homogenate at 37 degrees C. There were no significant differences between men and women in 125I-labeled LDL binding. In the pooled data, EDTA-suppressible binding averaged 50 ng 125I-LDL protein/mg cell protein (S.D., 15). Total saturable binding averaged 2-fold greater (mean, 101 ng/mg; S.D., 32). Plasma cholesterol, LDL cholesterol and apoB concentrations were negative functions of both EDTA-suppressible binding and total saturable binding, but the correlations with EDTA-suppressible binding were stronger (cholesterol: r = -0.59, P less than 0.01; LDL cholesterol: r = -0.48, P less than 0.05; apoB: r = -0.61, P less than 0.01). Plasma triacylglycerol, high-density lipoprotein cholesterol and apoA-I concentrations were not related to either measure of receptor activity. These results provide evidence that the activity of apoB,E receptors in the liver is a major determinant of the plasma LDL concentration in middle-aged and elderly humans.     

Molecular variation at the apolipoprotein B gene locus in relation to lipids and cardiovascular disease: a systematic meta-analysis

Apolipoprotein B (apoB) is the sole protein component of low-density lipoprotein (LDL) and is thought to play an important role in atherogenesis. We performed a meta-analysis of the associations between the three most frequently investigated polymorphisms (XbaI, signal peptide insertion/deletion, EcoRI) in the apolipoprotein B (APOB) gene, lipid parameters, and the risk of ischemic heart disease (IHD). We restricted our analysis to Caucasians. Homozygotes for the XbaI X+ allele had significantly elevated levels of LDL cholesterol (LDL-C) and apoB, but a decreased risk (OR=0.80; 95%CI: 0.66–0.96) of IHD. Homozygosity for the signal peptide deletion allele was associated with similarly increased levels of LDL-C and apoB, and with an increased risk of IHD (OR=1.30; 95%CI: 1.08–1.58). Subjects homozygous for the rare EcoRI allele had significantly decreased levels of total and LDL cholesterol, but unaltered risk of IHD. We conclude that all three polymorphic apoB sites are associated with altered lipid levels, but not necessarily with a consistently altered risk of IHD. These data suggest that the relationship between apoB levels, hypercholesterolemia and IHD risk cannot have a simple molecular basis in the apoB gene.     

New genetic variants in the apoA-I and apoC-III genes and familial combined hyperlipidemia

Linkage and association between the apolipoprotein (apo) A-I/C-III/A-IV gene region on chromosome 11 and familial combined hyperlipidemia (FCHL) has been observed previously. Using sequence analysis two new allelic variants were identified, C(317) -T in intron 2 of the apoA-I gene and C(1100)-T in exon 3 of the apoC-III gene. These variants were studied in 30 FCHL probands, 159 hyperlipidemic relatives, 327 normolipidemic relatives, and 218 spouses. The allele frequencies of both variants were significantly different in probands and spouses (P < 0.002 and P < 0.001, respectively), with increased frequency of the minor alleles in the probands. The minor genotypes (TT) were associated with elevated plasma triglyceride and apoC-III. Both variants were in strong, although not complete, linkage disequilibrium with each other and with the MspI site in the promoter region of the apoA-I gene and the SstI site in the 3' untranslated region of exon 4 of the apoC-III gene. Haplotypes based on these four variants were constructed and the distributions of haplotype combinations were significantly different (P < 0.0001). Two distinct haplotypes predisposing to FCHL were found: 2-2-1-2 and 1-2-2-2 (MspI, C(317) -T; SstI, C(1100)-T). The haplotype combinations carrying one of these high risk alleles are associated with elevated lipid levels in probands and in spouses. While these effects can be attributed to the presence of the M2 and S2 minor alleles, these results suggest that the importance of specific allelic haplotypes may be greater than single genotypic effects.     

Genetic studies of human apolipoproteins. XIII. Quantitative polymorphism of apolipoprotein C-III in the Mayans of the Yucatán Peninsula

Apolipoprotein C-III (APO C-III) is a structural component of very-low-density and high-density lipoprotein particles and is an inhibitor of lipoprotein lipase. In a study of genetic variation of apolipoproteins in the Mayan population of the Yucatán peninsula, we observed a quantitative polymorphism in APO C-III levels. This polymorphism is expressed as variation in immunoblot staining intensity following isoelectric focusing and as variation in plasma levels of APO C-III determined by radial immunodiffusion. This variation is consistent with the presence in Mayans of an allele associated with low levels of plasma APO C-III which we have designated APO C-III*D. Analysis of the distribution of APO C-III levels yields a gene frequency estimate for the deficiency allele of 0.59. There is a significant positive correlation between total plasma APO C-III levels and total plasma cholesterol and triglyceride levels, the lowest levels of cholesterol and triglycerides being seen in individuals homozygous for the deficiency allele. This observation is consistent with the proposed role of APO C-III in lipoprotein metabolism. Family data to determine whether this deficiency allele is due to mutation at the APO C-III structural locus were not available. However, molecular analysis using cloned probes from the APO A-I/C-III/A-IV gene cluster revealed no gross DNA rearrangement or deletion of sequences in this region in homozygous deficient individuals.     

Familial apolipoprotein A-I, C-III, and A-IV deficiency and premature atherosclerosis due to deletion of a gene complex on chromosome 11

The defect in a kindred with marked plasma high density lipoprotein (HDL) deficiency and premature atherosclerosis was examined. The homozygous proband died of coronary artery atherosclerosis at age 45 and had undetectable levels of plasma apolipoproteins A-I and C-III, proteins of HDL. In family studies 10 heterozygotes were identified whose mean apoA-I, apoC-III, apoA-IV, and HDL cholesterol levels were 67, 57, 65, and 62% of normal. These subjects were noted to have restriction fragment length polymorphisms following DNA digestion with a number of enzymes including BamHI, EcoRI, HindIII, XmnI, PstI, and PvuII, following hybridization with a probe spanning 1.1 kilobases approximately 2.5 kilobases 5' to the apoA-I gene. Cloning and sequence analysis of the abnormal allele indicated that the defect is due to the complete deletion of the apoA-I, -C-III, and -A-IV gene complex on chromosome 11, with both ends of the deletion being located in areas of highly repetitive DNA. The data support the concept of an independent role for HDL in the pathogenesis of atherosclerosis.     

The A-204C polymorphism in the cholesterol 7alpha-hydroxylase (CYP7A1) gene determines the cholesterolemia responsiveness to a high-fat diet

The aim of the study was to ascertain whether the A-204C polymorphism in the cholesterol 7 -hydroxylase (CYP7A1) gene plays any role in determining LDL-cholesterol (LDL-C) concentration responsiveness to a high-fat diet. The concentrations of total cholesterol and LDL-cholesterol were measured in eleven healthy men (age: 30.9+/-3.2 years; BMI: 24.9+/-2.7 kg/m(2);;) who were homozygous for either the -204A or -204C allele, after 3 weeks on a low-fat (LF) diet and 3 weeks on a high-fat (HF) diet. During both dietary regimens, the isocaloric amount of food was provided to volunteers; LF diet contained 22 % of energy as a fat and 2.2 mg of cholesterol/kg of body weight a day, HF diet 40 % of fat and 9.7 mg of cholesterol/kg of body weight a day. In six subjects homozygous for the -204C allele, the concentrations of cholesterol and LDL-cholesterol were significantly higher on HF than on LF diet (cholesterol: 4.62 vs. 4.00 mmol/l, p<0.05; LDL-C: 2.15 vs. 1.63 mmol/l, p<0.01, respectively); no significant change was observed in five subjects homozygous for the -204A allele. There were no other differences in lipid and lipoprotein-lipid concentrations. Therefore, the polymorphism in the cholesterol 7alpha-hydroxylase promotor region seems to be involved in the determination of cholesterol and LDL-C responsiveness to a dietary fat challenge.     

Effect of egg cholesterol and dietary fats on plasma lipids, lipoproteins, and apoproteins of normal women consuming natural diets

Nine normal women, 22 to 37 years old, consumed controlled quantities of natural foods to test their responses to dietary cholesterol and saturated fat. All diets contained, as percentage of calories, 14% protein, 31% fat, and 55% carbohydrate. The main sources of polyunsaturated and saturated fats were corn oil and lard, respectively, and egg yolk was used for cholesterol supplementation. All subjects participated in four diet protocols of 15 days duration, and each diet period was separated by 3 weeks without diet control. The first diet (corn) was based on corn oil, had a polyunsaturated to saturated fat ratio (P/S) of 2.14, and contained 130 mg of cholesterol. The second diet (corn+) was identical to the first but contained a total of 875 mg of cholesterol. The third diet (lard) was based on lard, had a P/S ratio of 0.64, and contained 130 mg of cholesterol. The fourth diet (lard+) was identical to the third, but contained 875 mg of cholesterol per day. Changes of the plasma lipid, lipoprotein and apoprotein parameters relative to the corn diet were as follows: the corn+ diet significantly increased total plasma cholesterol, HDL-cholesterol, LDL-cholesterol, and apoB levels; the lard diet significantly increased total cholesterol, HDL-cholesterol, and apoB; and the lard+ diet significantly increased the total cholesterol, HDL-cholesterol, LDL-cholesterol, and apoA-I and apoB levels. There were no significant variations in VLDL-cholesterol, triglyceride, or apoE levels with these diets. The diets affected both the number of lipoprotein particles as well as the composition of LDL and HDL. Compared to the corn diet, cholesterol and saturated fat each increased the number of LDL particles by 17% and 9%, respectively, and the cholesterol per particle by 9%. The combination of saturated fat and cholesterol increased particle number by 18% and particle size by 24%. Switching from lard+ to lard, corn+, or corn diets reduced LDL-cholesterol of the group by 18%, 11%, and 28%, respectively, while a large inter-individual variability was noted. In summary, dietary fat and cholesterol affect lipid and lipoprotein levels as well as the particle number and chemical composition of both LDL and HDL. There is, however, considerable inter-individual heterogeneity in response to diet.     

Apolipoprotein E polymorphism in the Finnish population: gene frequencies and relation to lipoprotein concentrations

ApoE phenotypes were determined in 615 unrelated Finnish individuals. The apoE gene frequencies observed (epsilon 2, 0.041; epsilon 3, 0.733; epsilon 4, 0.227) differ significantly from those in other populations. The frequency of the allele epsilon 2 was lower and that of epsilon 4 higher than in all other studied populations. Plasma lipids and apolipoproteins A-I, A-II and B were recorded in 207 of the typed subjects. By comparison with the most frequent homozygous apoE 3/3 phenotype, it was found that total cholesterol, LDL-cholesterol, and apoB concentrations were all markedly higher in apoE 4/4 and to a lesser degree in apoE 4/3 phenotypic groups. On the other hand, these lipid and apolipoprotein levels tended to be lower in E-2 heterozygotes. These data confirm and extend, in a different ethnic group, previous results of an effect of apoE genes on plasma lipoprotein concentrations. The data suggest that the apoE gene locus may be one factor responsible for the high LDL cholesterol concentrations in the Finnish population.     

Synthesis of plasma lipoproteins by the isolated perfused liver from the fasted and fed pig.

Livers from fasted or fed pigs were perfused for 5 h with Krebs-Ringer bicarbonate buffer containing human erythrocytes, bovine serum albumin, glucose, and amino acids. Liver viability was estimated by color, consistency, portal pressure, bile flow, electrolyte changes, and glucose levels in the perfusate, urea synthesis, [1-14C]leucine incorporation into protein, oxygen uptake, and histological examination. It was shown that the liver was maintained in good condition throughout the perfusions. The apolipoprotein B (apoB) and apolipoprotein A-I (apoA-I) in the perfusate were measured by solid phase radioimmunoassay. In the fasted state, the amount of apoB released was greatest in the low density lipoprotein (LDL) fraction and the amount was especially high during the 1st h. There was no increase of apoB in this fraction by feeding. The apoB in the very low density lipoprotein (VLDL) fraction was less than that in the LDL fraction in the fasted state, and it increased more than 2-fold in the fed animals. The amount of apoA-I was greatest in the 1.21 bottom fraction and was relatively small in the high density lipoprotein (HDL) fraction. The HDL fraction contained approximately one-twentieth as much apoA-I as the 1.21 bottom fraction in the fasted condition. In the fed state, apoA-I in the HDL fraction increased markedly, although the amount was still less than in the 1.21 bottom fraction.     

Effect of apoC-III gene polymorphisms on the lipoprotein-lipid profile of viscerally obese men

Abdominal visceral adipose tissue (AT) accumulation is associated with an atherogenic metabolic profile that includes increased plasma triglyceride (TG), low HDL cholesterol levels, and an insulin-resistant hyperinsulinemic state. Whereas the apolipoprotein (apo) C-III C3238G gene variant, often referred to as the SstI polymorphism, has been related to variations in plasma TG concentrations, another variation within the insulin responsive element (C-482T) of the apoC-III gene has been associated with greater glucose and insulin responses to an oral glucose tolerance test (OGTT); however, these results were obtained in nonobese individuals. We therefore investigated the effects of three apoC-III gene polymorphisms, namely SstI, C-482T, and T-455C, on fasting plasma lipoprotein-lipid levels and response to a 75 g OGTT in a sample of 122 viscerally obese men (abdominal visceral AT area >or=130 cm(2)). Among the three gene variants that were examined, the SstI variation was the only one found to be associated with hypertriglyceridemia. Indeed, S1/S2 heterozygotes (n = 24) were characterized by increased fasting plasma TG concentrations compared with S1/S1 homozygotes (n = 98) (mean +/- SD: 3.03 +/- 1.58 vs. 2.34 +/- 0.95 mmol/l respectively, P < 0.05). The higher TG concentrations in S1/S2 were associated with the presence of smaller, denser LDL particles compared with S1/S1 subjects (LDL peak particle diameter: 24.8 +/- 0.5 nm vs. 25.1 +/- 0.5 nm respectively, P < 0.05). Furthermore, there was no association between the response to the OGTT and any of the apoC-III gene variants (SstI, T-455C, or C-482T) examined. Results of the present study support the notion of a hypertriglyceridemic effect associated with the apoC-III SstI polymorphism that could modulate the magnitude of the dyslipidemic state in abdominally obese patients.     

A novel and simple method for quantification of small,dense LDL

A preponderance of small, dense (sd) LDL is strongly associated with the development of coronary heart disease, but the method for the measurement of sd LDL is too laborious for clinical use. We report a simple method for the quantification of sd LDL that is applicable to an autoanalyzer. This method consists of two steps: first, to precipitate the lipoprotein of density (d) <1.044 g/ml using heparin-magnesium; and second, to measure LDL-cholesterol in the supernatant by the homogeneous method or apolipoprotein B (apoB) by an immunoturbidometric assay. The cholesterol and apoB values obtained by the precipitation method (45 +/- 26 and 33 +/- 20 mg/dl, respectively) were similar to those obtained in the lipoprotein (d = 1.044-1.063) separated by ultracentrifugation (42 +/- 22 and 31 +/- 17 mg/dl, respectively), and there was an excellent correlation between the two methods for sd LDL-cholesterol (y = 1.05X + 1, r = 0.88, n = 69) and apoB (y = 1.07X, r = 0.90). Sd LDL values had a significant inverse correlation with LDL size. A high correlation was found between sd LDL-cholesterol and apoB values (r = 0.94). Sd LDL value was related to triglyceride, apoB, and LDL-cholesterol, but not to the buoyant LDL level. These results suggest that this precipitation method is a simple and rapid method for the measurement of sd LDL concentration.     

Polymorphisms of the gene encoding cholesterol ester transfer protein and serum lipoprotein levels in subjects with and without coronary heart disease

Summary We determined TaqI-A, TaqI-B and EcoNI genotypes at the cholesteryl ester transfer protein (CETP) locus in 111 healthy volunteers and in 187 hyperlipidemic men of whom 72 had suffered a myocardial infarction. There were no significant differences in the allele distributions at these polymorphic loci either between the population sample and the hyperlipidemic subjects, or between patients with and without previous myocardial infarction. To detect the associations between the CETP polymorphisms and serum lipid and apoprotein levels, we determined the serum concentrations of total cholesterol, triglycerides, high density lipoprotein (HDL)-cholesterol, apoA-I, apoA-II and apoB in the subjects studied and correlated them to the 3 RFLPs. No significant differences were observed in the serum levels of apoproteins and lipid parameters between subjects with different genotypes in any of these polymorphic CETP loci, either in the population sample or in hyperlipidemic men. Multivariate analyses did not reveal a significant independent role for any of the 3 polymorphisms in determining serum HDL-cholesterol or apoA-I levels after adjusting for triglyceride and low density lipoprotein cholesterol concentrations. This was evident for the group of healthy volunteers and for hyperlipidemic subjects, including those who had survived a myocardial infarction. We conclude that, in Finns, the CETP RFLPs are not useful markers for the risk of coronary heart disease.     

Lipoprotein composition of human suction-blister interstitial fluid

Interstitial fluid (IF) was obtained in 27 apparently healthy subjects (12 males, 15 females) by applying mild suction (200-250 mm Hg) on the skin either on the midvolar forearm or on the paraumbilical region of the abdomen. The IF concentrations of lipids and apolipoproteins (apo) were studied and compared with those of serum (S). The mean ratio between interstitial fluid and serum (IF/S ratio) varied from 0.14 for forearm apoE to 0.29 for apoA-II on the abdomen. This ratio was consistently lower for apoE, C-II, C-III, and B than for apoA-I and A-II, and significantly lower on the arm than on the abdomen for all apolipoproteins studied. The IF/S ratios showed marked variations among individuals. However, interstitial fluid apolipoprotein concentrations at different blister sites were highly correlated within each individual. Studies with agarose gel electrophoresis and density gradient ultracentrifugation revealed that large triglyceride-rich particles were virtually lacking in interstitial fluid and that the relation between the low density lipoproteins (LDL) and high density lipoproteins (HDL) was shifted towards a greater proportion of HDL. The lipoprotein distribution in the HDL range of interstitial fluid differed from that of serum showing one maximum at a density of about 1.070 g/ml (serum HDL2 about 1.090 g/ml) and one at a density of 1.130-1.140 g/ml (serum HDL3, 1.110-1.120 g/ml). The former subfraction contained most of the lipoprotein-bound apoE while the latter contained the major part of apoA-I and apoA-II. Studies of the lipoproteins of interstitial fluid may add to our understanding of the development of atherosclerosis and xanthomatosis and may also provide valuable information on the permeability of the capillary membrane in normo- and pathophysiological states.     

Both Serum Apolipoprotein B and the Apolipoprotein B/Apolipoprotein A-I Ratio Are Associated with Carotid Intima-Media Thickness

Background

Previous studies indicated that apolipoprotein measurements predicted cardiovascular disease (CVD) risk; however, associations between apolipoproteins and carotid intima-media thickness (CIMT) were less explored.

Methodology and Principal Findings

The cross-sectional study included 6069 participants aged 40 years or older with NGT from Shanghai, China. Serum fasting traditional lipids (total cholesterol [TC], low-density lipoprotein cholesterol [LDL-C], high-density lipoprotein cholesterol [HDL-C] and triglycerides [TG]), apoA-I and apoB were assessed. A high-resolution B-mode ultrasonography was performed to measure CIMT. We found CIMT increased progressively across the quartiles of serum apoB (p for trend <0.0001). In logistic regression, concentrations of apoB (odds ratio [OR] 1.27, 95% confidence interval [CI] 1.18–1.36), TC (OR 1.23, 95% CI 1.14–1.32), LDL-C (OR 1.25, 95% CI 1.16–1.34) and TG (OR 1.11, 95% CI 1.04–1.20) were significantly related to elevated CIMT after adjusted for age and sex. Meanwhile, the apoB/apoA-I ratio (OR 1.25, 95% CI 1.17–1.34) related to elevated CIMT. ApoB (OR 1.23, 95% CI 1.00–1.51) and the apoB/apoA-I ratio (OR 1.19, 95% CI 1.04–1.36) remained significantly associated with elevated CIMT, after adjusted for the traditional CVD risk factors including traditional lipids.

Conclusions and Significance

There were significant associations between serum apoB, the apoB/apoA-I ratio and elevated CIMT. Serum apoB and the apoB/apoA-I ratio might be independent predictors of early atherosclerosis in NGT.     

Apolipoprotein A-IV polymorphism and its effect on plasma lipid and apolipoprotein concentrations

Recently, we determined the apolipoprotein E (apoE) phenotype distribution in 2,000 randomly selected 35-year-old male individuals by slab gel isoelectric focusing of delipidated plasma samples, followed by immunoblotting using anti-apoE antiserum. These blots have been successfully re-used for immunovisualization of apoA-IV isoelectric focusing patterns. In a population sample of 1,393 individuals, four distinct apoA-IV isoforms were detected, encoded by the alleles A-IV*0, A-IV*1, A-IV*2, and A-IV*3 with gene frequencies of 0.002, 0.901, 0.079, and 0.018, respectively. The mean of plasma cholesterol, triglyceride, apoB and E levels did not differ significantly among the different apoA-IV phenotype groups. For these lipoprotein parameters, less than 0.1% of the total phenotypic variance could be accounted for by the APOA-IV gene locus. Our results did not show any effect of apoA-IV polymorphism on plasma apoA-I levels nor could we find any correlation between plasma levels of apoA-I and apoA-IV within the different apoA-IV phenotype groups. The plasma level of apoA-IV in subjects bearing the A-IV*3 allele is significantly lower than in subjects without the A-IV*3 allele (5 mg/dl versus 14 mg/dl). We therefore conclude that, in contrast to the apoE polymorphism, the polymorphism at the APOA-IV locus does not influence any of the levels of the lipoprotein parameters considered except apoA-IV.     

Intracellular apoA-I and apoB distribution in rat intestine is altered by lipid feeding

Intracellular forms of chylomicrons, very low density lipoprotein (VLDL) and high density lipoprotein (HDL) have previously been isolated from the rat intestine. These intracellular particles are likely to be nascent precursors of secreted lipoproteins. To study the distribution of intracellular apolipoprotein among nascent lipoproteins, a method to isolate intracellular lipoproteins was developed and validated. The method consists of suspending isolated enterocytes in hypotonic buffer containing a lipase inhibitor, rupturing cell membranes by nitrogen cavitation, and isolating lipoproteins by sequential ultracentrifugation. ApoB and apoA-I mass are determined by radioimmunoassay and newly synthesized apolipoprotein characterized following [3H]leucine intraduodenal infusion. Intracellular chylomicron, VLDL, low density lipoprotein (LDL), and HDL fractions were isolated and found to contain apoB, and apoA-IV, and apoA-I. In the fasted animal, less than 10% of total intracellular apoB and apoA-I was bound to lipoproteins and 7% of apoB and 35% of apoA-I was contained in the d 1.21 g/ml infranatant. The remainder of intracellular apolipoprotein was in the pellets of centrifugation. Lipid feeding doubled the percentage of intracellular apoA-I bound to lipoproteins and increased the percentage of intracellular apoB bound to lipoproteins by 65%. Following lipid feeding, the most significant increase was in the chylomicron apoB and HDL apoA-I fractions. These data suggest that in the fasting state, 90% of intracellular apoB and apoA-I is not bound to lipoproteins. Lipid feeding shifts intracellular apolipoprotein onto lipoproteins, but most intracellular apolipoprotein remains non-lipoprotein bound. The constant presence of a large non-lipoprotein-bound pool suggests that apolipoprotein synthesis is not the rate limiting step in lipoprotein assembly or secretion.