Genetic factors affecting blood lipoproteins: the candidate gene approach

DNA polymorphisms at the lipoprotein lipase gene are associated with macroangiopathy in type 2 (non-insulin-dependent) diabetes mellitus

We studied the effect of variation at the lipoprotein lipase (LPL) gene locus on the susceptibility of individuals with Type 2 diabetes mellitus to atherosclerotic vascular disease in a population of 126 male and 114 female patients. The prevalence of any evidence of coronary heart disease (CHD) (presence of ischaemic ECG changes or definite myocardial infarction) was low in the patients who were homozygous for the presence of the PvuII restriction site (genotype 2-2) (40.9%) compared with those who were heterozygous (genotype 1-2) (57.9%; P = 0.05) or homozygous for the absence of it (genotype 1-1) (61.9%; P < 0.04). In men, a clear gene dosage effect on CHD was seen, the genotype 2-2 patients having the lowest (39.1%), the 1-2 patients an intermediate (49.3%) and the 1-1 patients the highest (61.1%) frequency of coronary disease. Patients with the genotype 2-2 of the HindIII polymorphism (absence of the restriction site) had the highest prevalence of any evidence of CHD (90.0%) compared with the genotype 1-2 (heterozygotes for the presence of the restriction site) (55.4%) or 1-1 (presence of the restriction site) (54.6%; P < 0.03). Stepwise discriminant analysis revealed that in the whole diabetic population the PvuII genotype of the LPL gene was independently and significantly associated with CHD but its effect decreased when the plasma lipids were taken into account. Overall, this study demonstrates the role of the PvuII polymorphism in the LPL gene to modulate the risk for diabetic macroangiopathy in patients with Type 2 diabetes mellitus.(ABSTRACT TRUNCATED AT 250 WORDS)

Elevated concentrations of plasma lipids and apolipoproteins B, C-III, and E are associated with the progression of coronary artery disease in familial hypercholesterolemic swine

We reported earlier that a complex familial hypercholesterolemia (c-FHC) phenotype characterized by elevated levels of total plasma cholesterol (TC) and apoB and reduced levels of HDL cholesterol (HDL-C) and apoA-I is associated with the development of spontaneous atherosclerotic lesions in swine. In this study, we investigated concentrations of plasma lipids and apolipoproteins B, C-III, and E in six parental animals of two cholesterol concentration phenotypes and their 32 offspring, which segregated into high, intermediate, and normal cholesterol phenotypes. Subsequently, we compared the extent of atherosclerotic lesion development in coronary arteries to the concentrations of plasma lipids and apolipoproteins in the parents and two offspring per family. Mean concentrations for the high (n = 23), intermediate (n = 13), and normal (n = 2) cholesterol level phenotypes at 4 months of age were TC, 316 +/- 62.2, 159 +/- 17.1, and 105 +/- 12 mg/dL; LDL cholesterol, 275 +/- 63.1, 113 +/- 16.4, and 67 +/- 18.4 mg/dL; HDL-C, 35 +/- 6.1, 41 +/- 5.7, and 33 +/- 6.4 mg/dL; triglycerides, 48 +/- 10.8, 39 +/- 8.0, and 29 +/- 5.7 mg/dL; apoB, 152 +/- 32.5, 80 +/- 7.2, and 48 +/- 5.7 mg/dL; apoC-III, 10 +/- 4.2, 8 +/- 1.7, and 3 +/- 0.1 mg/dL; and apoE, 17 +/- 3.4, 7 +/- 1.7, and 5 +/- 0.7 mg/dL, respectively. Histological analysis of the major coronary arteries from members of the three families showed considerable variation in the severity of lesions, ranging from foci of adaptive intimal thickening consisting of two to six layers of smooth muscle cells to advanced lesions containing necrotic cores, cholesterol clefts, calcification, and hemorrhage (type V). The most extensive lesions occurred only in animals of the high cholesterol phenotype (ie, c-FHC), in which the concentration of TC and apoB progressively increased after 4 months of age, apoC-III, apoE, and triglycerides increased or remained elevated, and HDL-C decreased, except for one animal. Data presented here show that the plasma cholesterol phenotypes in FHC animals are associated with levels of apolipoproteins B, C-III, and E and indicate that the increases in the studied parameters after 4 months of age correlate with the progression of coronary artery disease.

Cladistic analysis of the apolipoprotein AI-CIII-AIV gene cluster using a healthy French Canadian sample. I. Haploid analysis

A cladistic analysis was carried out to identify haplotypes hypothesized to differ for functional DNA sequence variations within the apolipoprotein (apo) AI-CIII-AIV gene cluster that affect plasma lipid, lipoprotein and apolipoprotein levels. A sample of unrelated healthy French Canadians was studied. First, a cladogram of the observed apo AI-CIII-AIV haplotypes was estimated. Then this cladogram was used to define a statistical analysis of the association between haplotype variation and variation in plasma lipid, lipoprotein and apolipoprotein levels. Three haplotypes were identified which were associated with small (5-12% of the total sum of squares) pleiotropic effects on plasma lipid, lipoprotein and apolipoprotein traits and these effects were context, i.e. gender, dependent.

Purification and characterization of recombinant human apolipoprotein A-II expressed in Escherichia coli

We have expressed recombinant human apolipoprotein A-II (apoA-II) in Escherichia coli, as a fusion protein with Schistosoma japonicum glutathione-S-transferase (GST). The GST-AII fusion protein was recovered by affinity chromatography using glutathione as a ligand. After thrombin cleavage and removal of the GST carrier, recombinant apoA-II was obtained in a highly purified form and was exclusively composed of dimeric apoA-II. Kinetics of association to dimyristoylglycerophosphocholine (Myr2GroPCho) vesicles showed that recombinant apoA-II exhibited the same pattern of association as human plasma apoA-II. Electron microscopic analysis of the complexes showed a typical pattern of rouleaux, characteristic of stacked discs, with a diameter similar to that determined by gradient-gel electrophoresis. Circular dichroism measurements showed that the alpha-helical content of both plasma and recombinant apoA-II increased similarly when the proteins associated with Myr2GroPCho vesicles, at the expense of a random-coil structure. Lipid-bound apoA-II consisted of 70-72% alpha helices, suggesting the presence of three 18-residue alpha helices/apoA-II monomer. Cross-linking experiments indicated that Myr2GroPCho complexes contained two molecules dimeric apoA-II/vesicle. Recombinant apoA-II was as efficient as plasma apoA-II in associating with HDL subclasses, and in displacing apoA-I from dipalmitoylglycerophosphocholine/cholesterol/apoA-I complexes, most likely due to its highly ordered secondary structure when associated with Myr2GroPCho vesicles. These findings demonstrate that recombinant apoA-II exhibits the same structural and functional properties as human plasma apoA-II. Thus, the expression system utilized is appropriate to produce mutagenized forms to further structure/function analysis.

Purification and characterization of nuclear factors binding to the negative regulatory element D of human apolipoprotein A-II promoter: a negative regulatory effect is reversed by GABP, an Ets-related protein

We have previously shown that transcription of the human apolipoprotein A-II (apoA-II) gene is controlled by a complex set of regulatory elements [Cardot et al. (1993) Biochemistry 32, 9080-9093]. We have also identified previously described, as well as new activities which bind to these elements and influence to varying degrees the transcription of the apoA-II gene. DNA binding and competition assays indicated that element D binds three new activities, designated AIID1, AIID2, and AIID4, as well as an activity related to C/EBP. Activities AIID1, AIID2, and AIID4 were purified and characterized further in order to determine their function on the transcriptional regulation of human apoA-II gene. SDS-PAGE analysis as well as photoaffinity cross-linking of the affinity-purified AIID2 showed that it consists of three proteins with molecular masses ranging between 54 and 63 kDa. The amino acid sequence of tryptic peptides obtained from AIID2 protein bands revealed that it is homologous to GABP, an Ets-related protein. Similar analysis showed that affinity-purified AIID4 has an apparent molecular mass of 130 kDa. AIID1 activity was purified partially; in addition to binding to the apoA-II promoter, AIID1 also binds to the regulatory element C of apoCIII and may play a role in the transcriptional regulation of both genes. Methylation interference of G residues and permanganate modification of T residues indicated that the binding sites of AIID2 and AIID4 were contiguous on element D. However, the binding site of AIID1 overlaps with the binding sites of both AIID2 and AIID4. This suggests that the binding of AIID1 and AIID2 or of AIID1 and AIID4 may be mutually exclusive, whereas AIID2 and AIID4 may bind simultaneously. Transcription from a minimal promoter containing elements AB, C, and D of apoA-II increased 1.5- to 1.6-fold when element D is deleted, as well as by promoter mutations which eliminated the binding of both AIID1 and/or AIID4 to element D, but permitted the binding of AIID2/GABP. The findings suggest that element D has a negative regulatory role on apoA-II gene transcription when it is occupied by protein AIID1 and/or AIID4. This negative effect is reversed when element D is occupied only by the regulatory factor AIID2/GABP.

Associations of genotypes at the apolipoprotein AI-CIII-AIV, apolipoprotein B and lipoprotein lipase gene loci with coronary atherosclerosis and high density lipoprotein subclasses

Association studies were carried out in a sample of 86 patients from Sweden who had survived a myocardial infarction (MI) at a young age and 93 age-matched healthy individuals, to compare the impact of polymorphisms at the apolipoprotein (apo) AI-CIII-AIV gene cluster on among-individual differences in plasma lipid and lipoprotein traits, the five high density lipoprotein (HDL) subclasses (2b to 3c), lipoprotein lipase (LPL) activity and presence and progression of atherosclerosis. Individuals were genotyped for four polymorphisms; 5'apoAI (G/A-75), 3'apoAI (PstI; P +/-), apoCIII (C/T1100) and apoCIII (PvuII; V +/-), using PCR-based techniques. Allele frequencies were similar in healthy individuals and patients (frequencies of alleles in combined population: 5'apoAI-A-75 = 0.14, 3'apoAI-P- = 0.05, apoCIII-T1100 = 0.27 and apoCIII-V- = 0.18). In the healthy individuals, levels of low density lipoprotein (LDL) triglycerides were significantly associated with genotypes of the apoCIII-PvuII polymorphism (p = 0.02), but no other associations were found between lipids or HDL subclasses and single polymorphisms in the apoAI-CIII-AIV gene cluster. Levels of triglycerides and very low density lipoprotein (VLDL) triglycerides were significantly higher in the presence of the haplotype defined by the presence of apoCIII-T1100 and common alleles of the other three polymorphisms, explaining 5.8% and 7.8% (p = 0.03 and 0.01), respectively, of sample variance. In the patients, no associations were found between lipids or HDL subclasses and variation at the apoAI-CIII-AIV gene cluster. Associations were also examined between levels of HDL subclasses and variation at the apoE (common isoforms), apoB (signal peptide and XbaI polymorphisms) and lipoprotein lipase (PvuII, HindIII and Serine447/Stop polymorphisms) gene loci. In the patient group only, levels of protein in HDL2b, HDL2a and HDL3b subclasses were significantly associated with genotypes of the LPL-HindIII polymorphism (22.1, 19.3 and 11.4%, respectively, of sample variance; p < 0.05). Finally, associations were examined between genotypes at the apoAI-CIII-AIV gene cluster and the extent of coronary atherosclerosis. Global severity of atherosclerosis at the first angiography was weakly associated with genotypes of the apoCIII-C/T1100 polymorphism, presence of the T1100 allele being associated with 53% lower median score (1.6 vs 0.75; p = 0.09).(ABSTRACT TRUNCATED AT 400 WORDS)

Should children or young adults be screened for serum lipid levels to prevent adult coronary heart disease? Experience from the Cardiovascular Risk in Young Finns study

Coronary heart disease (CHD) has its origin in childhood. High cholesterol levels measured in children and adolescents are indicative of concurrent atherosclerotic changes and probably predict adult coronary heart disease. We review here the relevance of screening children, adolescents or young adults for serum lipid levels in order to efficiently prevent premature adult coronary heart disease. Data is presented in the light of the large Cardiovascular Risk in Young Finns study and other studies. The authors do not recommend universal screening strategies because of (i) the limited predictive power of serum lipid levels on an individual level, (ii) the limited knowledge on the safety of interventive measures on the growing child, and (iii) the limited knowledge on the ethical aspects of screening (labelling). However, the importance of measuring serum lipids to detect familial dyslipidaemic disorders such as familial hypercholesterolaemia, is stressed. The selection of children or adolescents for serum lipid measurements should be made on the basis of family history of early CHD or dyslipidaemia.

Dyslipidaemia and obesity

Obesity is frequently associated with a dyslipidaemic state. Several metabolic and epidemiological studies published in the 1980s have, however, emphasized the importance of considering the regional distribution of body fat in the assessment of the health hazards of obesity. The development of imaging techniques such as computed tomography has also allowed it to be established that the fat located in the abdominal cavity, i.e. the visceral adipose tissue, was the critical correlate of the metabolic complications found in abdominal obesity which include insulin resistance and hyperinsulinaemia, glucose intolerance, hypertriglyceridaemia, hypoalphalipoproteinaemia and increased concentrations of dense LDL particles. Furthermore, since several genes are involved in the regulation of plasma lipoprotein-lipid levels and they have been reported to show polymorphism, visceral obesity should be considered as a permissive factor that exacerbates an individual's susceptibility to dyslipidaemia and premature coronary heart disease rather than a primary regulator of the dyslipidaemic state observed in visceral obese patients. Finally, as insulin resistance and the level of visceral adipose tissue are two main correlates of the dyslipidaemic state which characterizes abdominal obesity, treatment should be aimed at reducing visceral fat and improving insulin sensitivity. Prospective studies are clearly warranted to evaluate the potential benefits of such interventions on the incidence of coronary heart disease.

Traversing the biological complexity in the hierarchy between genome and CAD endpoints in the population at large

An emerging challenge facing those who are concerned about the efficacy of public health programs is to understand how information from the DNA revolution might be used to improve our ability to predict the initiation, progression and severity of a common disease having a complex multifactorial etiology. In the course of research to evaluate the role of information about DNA, combinations of genome types and environmental exposures that predispose to disease will be identified. Such information is expected to be useful in efforts to identify individuals and families at higher risk of disease and to predict their responses to a proposed therapy. This paper begins with a discussion of the features of a realistic biological model for the study of a common multifactorial disease. We present evidence for the complexity in the relationship between genome type variation and variation in risk of coronary artery disease (CAD) and review the preliminary results of our studies to determine whether information about genome type variation can improve our ability to predict the distribution of CAD among individuals in the population at large. Such studies make it apparent that new analytical strategies are necessary to deal with the plethora of genome type information available for the evaluation of risk of a common disease like CAD. This shift in the research paradigm will build upon new strategies to understand the organization of natural systems that are coming from outside the mainstream of genetic research.

Aging and genetic variation of plasma apolipoproteins. Relative loss of the apolipoprotein E4 phenotype in centenarians

We determined the common polymorphism of apolipoprotein E (E2, E3, and E4), apolipoprotein B Xba I polymorphism, and apolipoprotein C-III Sst I polymorphism in almost all Finnish centenarians alive in 1991 (n = 179/185). Plasma lipid and lipoprotein levels in different apolipoprotein genotypes were also measured. In comparison with younger Finnish populations studied previously, the frequency of the apolipoprotein E epsilon 2 allele was almost twice as high (7.0% versus 4.1%; P < .05) and that of the epsilon 4 allele only approximately one third as high (8.4% versus 22.7%; P < .001) in the centenarians. Plasma cholesterol and high-density lipoprotein cholesterol levels tended to be lowest in the group with the epsilon 2 allele (4.33 mmol/L and 1.41 mmol/L, respectively), intermediate in those with the epsilon 3 allele (4.57 mmol/L and 1.48 mmol/L, respectively), and highest in those with the epsilon 4 allele (4.82 mmol/L and 1.60 mmol/L, respectively). The frequencies of the apolipoprotein B X1 and X2 alleles (Xba I restriction site absent or present, respectively) among the centenarians and among the young Finns were not significantly different, whereas the apolipoprotein C-III S2 allele (Sst I restriction site present) occurred more often in the centenarians (frequency, 12.9%) than in the youngest reference population (frequency, 8.8%; P < .05). Centenarians with the apolipoprotein B X2X2 genotype and apolipoprotein E4 phenotype had a higher mean plasma cholesterol level than those with the X1X1 genotype and E2 phenotype (5.24 versus 3.43 mmol/L; P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Variability gene effects of DNA polymorphisms at the apo B, apo A I/C III and apo E loci on serum lipids: the Cardiovascular Risk in Young Finns Study

We studied the influence of selected genetic markers on the intra-individual long-term variability in serum lipid levels. The study cohort consisted of a sub-sample from a large follow-up study of atherosclerosis precursors in children and young adults. A total of 320 subjects had determinations of apo B XbaI RFLP genotypes, 305 subjects had apo AI/CIII SstI RFLP genotype determinations and 1581 subjects had their apo E phenotypes determined. Complete data on serum lipids were available at 3-year intervals over a 6-year follow-up period. The subjects were healthy and aged 3-18 years at baseline. Intra-individual variability was assessed with a nested analysis of variance procedure. Each of the genetic markers studied here significantly affected intra-individual variability of serum lipid levels. No clear sex influence was observed, although the differences in variability tended to be more significant in males. Apo B XbaI genotypes significantly influenced intra-individual variability of total and LDL-cholesterol levels in both sexes. A marked effect of the XbaI genotype was also found on triglyceride variability. In males the standardized intra-individual triglyceride variances were 0.71 and 0.34 in genotypes X1X1 and X2X2, respectively (p < 0.001), with a clear gene dosage effect. The apo AI/CIII genotype had an influence only on the variability of total cholesterol and LDL-cholesterol levels and only in males. The apo E phenotypes were associated with intra-individual variability in total and LDL-cholesterol levels but again, only in males.(ABSTRACT TRUNCATED AT 250 WORDS)

Apolipoprotein polymorphisms fail to define risk of coronary artery disease. Results of a prospective, angiographically controlled study

BACKGROUND

Because genetic factors are believed to contribute to the etiology of coronary artery disease (CAD), it has been suggested that DNA polymorphisms at candidate loci might identify individuals at high risk for developing disease. In this regard, apolipoprotein genes represent extremely promising loci because levels of apolipoproteins and their associated lipoproteins represent a major risk factor for CAD, and rare dysfunctional mutations in these genes result in a significant risk for CAD. To date, although some reports indicate that DNA polymorphisms at these loci are associated with increased risk of CAD, other reports have failed to find such associations.

METHODS AND RESULTS

To resolve the question of whether genetic polymorphisms at apolipoprotein loci can be used to identify individuals at increased risk for CAD, we evaluated the distribution of apolipoprotein genetic polymorphisms in a large series of subjects (n = 848) undergoing coronary angiography. Blinded assessment of angiograms was used to discriminate between patients with CAD (> or = 60% stenosis of any major branch, n = 444) and control subjects without disease (< or = 10% stenosis, n = 404). A total of 12 polymorphisms were evaluated at the following loci: apolipoprotein (apo) A-I/C-III/A-IV (five restriction site polymorphisms--Msp I, Pst I, Sst I, Pvu IIa, Pvu IIb), apo B (three restriction site polymorphisms--Xba I, EcoRI, Msp I, plus an insertion/deletion polymorphism), apo A-II (Msp I polymorphism), apo C-II (Taq I polymorphism), and apo E (protein isoforms revealed by DNA analysis). All subjects were of Northern European (primarily Angloscandinavian) descent, and, within each sex, patients and control subjects were of comparable age. All 12 loci were in Hardy-Weinberg equilibrium, with no indication of population heterogeneity. As expected, patients were distinguished from control subjects by their lipid profiles and a higher frequency of known risk factors for CAD. However, analysis by log-linear models indicated that there were no significant associations between apolipoprotein polymorphisms and the risk of CAD (P = .10 to .90). The lack of association was maintained irrespective of whether the analysis was carried out for the entire sample or the contrast was made more stringent by comparing patients most likely to have a genetic component to their disease (ie, young patients with early-onset CAD) with the control subjects least likely to have genetic susceptibility (ie, older control subjects who had ample time to develop CAD).

CONCLUSIONS

Despite the fundamental role of apolipoprotein genes in lipid metabolism, we find no evidence that common genetic polymorphisms of the major apolipoprotein loci have a significant influence on the risk of developing angiographically defined CAD in this representative population. Therefore, at this time we find no support for the hypothesis that mass screening for genetic polymorphisms at candidate loci can reduce the burden of CAD by identifying a substantial proportion of high-risk individuals. Instead, it appears more appropriate to direct attention toward modifying high-risk behaviors to alleviate the consequences of traditional environmental risk factors.

Characteristics of 46 heterozygous carriers and 57 unaffected relatives in five Danish families with familial defective apolipoprotein B-100

Plasma concentrations of cholesterol, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, apolipoprotein (apo) B, and lipoprotein(a) (Lp[a]) in 46 persons heterozygous for the apo B-3500 mutation causing familial defective apo B-100 (FDB) were compared with those in 57 non-FDB relatives. FDB patients had 50% to 70% higher mean concentrations of cholesterol, LDL cholesterol, and apo B than non-FDB relatives (P < 10(-4) for all three variables). Triglycerides were higher (P = .016) and HDL cholesterol was lower (P = .021) in FDB patients. The concentration ranges of these variables were broad in each family, and there was no between-family difference in means for cholesterol and LDL cholesterol. There was no phenotype-specific difference in Lp(a) concentrations between FDB patients and non-FDB relatives. Apo E4 is normally associated with higher concentrations of LDL and apo E2 with lower concentrations. This relation was partly reversed in FDB patients: apo E4 was associated with lower apo B concentrations and apo E2 with higher apo B concentrations. Tendon xanthomata were found in members of two of the five families. Six of 12 FDB patients > 50 years old had atherosclerotic disease. In contrast, all 18 non-FDB relatives > 50 years old were apparently healthy. A total of 8 FDB patients with atherosclerotic disease had 36% higher cholesterol concentrations, 28% higher apo B concentrations, 50% higher triglyceride concentrations, and 120% higher Lp(a) concentrations than FDB patients without clinical atherosclerosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipoprotein metabolism and its relationship to atherosclerosis

Lipoproteins are macromolecular complexes that transport cholesterol and triglycerides through the blood stream. The assembly and secretion of lipoproteins occurs in the liver and small intestine, but many modifications and transformations occur in the plasma. Plasma levels of cholesterol and triglycerides are regulated by both environmental effects on lipid metabolism and by genetic factors affecting both apoproteins on the surface of the lipoproteins and enzymes in plasma. Abnormalities of the lipoprotein transport system can increase an individual's risk for developing atherosclerosis.

Linkage between the APOB gene and serum ApoB levels in a large pedigree from the Bogalusa Heart Study

Maximum likelihood linkage analyses were performed to test for linkage between serum apoB levels and several candidate gene markers including apolipoprotein B, lipoprotein lipase, hepatic lipase, cholesterol ester transfer protein, and apolipoprotein AI in a large pedigree. Parameters of general Mendelian inheritance derived from maximum likelihood segregation analysis of the serum apoB levels were used in the linkage analysis. The highest two-point lod score between the quantitative trait and a marker defined by a single restriction digest was 1.86 at recombination fraction (theta) = 0. This was observed for linkage between serum apoB levels and the presence or absence of a PvuII digestion site in the apoB gene. Linkage between serum apoB levels and polymorphisms of the apoB gene defined by the two restriction digests EcoR1 and PvuII was supported by a lod score of 3.30, while inclusion of VNTR typings led to a lod score of 2.33. None of the other candidate genes gave positive evidence of linkage.

Adenine for guanine substitution -78 base pairs 5' to the apolipoprotein (APO) A-I gene: relation with high density lipoprotein cholesterol and APO A-I concentrations

A common mutation, adenine (A) for guanidine (G) substitution (G/A) has been located -78 bp 5' to the apo A-I gene. This region has been shown to be involved in the transcriptional regulation of the apo A-I gene. Previous studies have shown that this mutation is associated with altered high density lipoprotein cholesterol (HDL-C) levels, although these findings have not been consistent. We have studied the frequency of this mutation in 125 subjects (60 males and 65 females) selected because they had HDL-C levels below the 25th (low HDL) or above the 75th (high HDL) percentile of the population distribution. The presence of the mutation was detected by Msp I digestion of a 259 bp fragment of PCR amplified DNA. The allele frequency was similar in both groups (0.20 for the lowest HDL group and 0.28 for the highest HDL group, p > 0.05), although a non-significant trend was observed in a higher frequency of the A/A genotype in the highest HDL females (17.5%) vs only 6.7% in the lowest HDL female group. In conclusion, in this population the G/A mutation was not significantly associated with HDL-C or apo A-I plasma levels.

Genetic contributions to quantitative lipoprotein traits associated with coronary artery disease: analysis of a large pedigree from the Bogalusa Heart Study

A pedigree of a large family with high prevalence of heart disease is subjected to association and sib-pair linkage analysis to investigate the role of 5 candidate genes in the regulation of lipoprotein metabolism and the development of coronary artery disease. At the 5% nominal significance level, the apolipoprotein B locus (APOB) was found to be linked to high-density lipoprotein cholesterol level (HDL-C), low-density lipoprotein cholesterol level (LDL-C), the ratio HDL-C/LDL-C, and apolipoprotein AI level times this ratio (apoAI x LDL-C/HDL-C). APOB (PvuII) was strongly associated with apolipoprotein B levels (apoB) (P = 0.006) and the VNTR region of the APOB locus showed highly significant association between allele 7 and low triglyceride levels (P = 0.004). No significant linkage results were found with cholesterol ester transfer protein (CETP). At the 1% nominal significance level, CETP [TaqI(B)] showed significant association with LDL-C, apoB, and HDL-C/LDL-C. There was significant linkage of lipoprotein lipase (LPL) with very-low-density lipoprotein cholesterol and the ratio apoAI/HDL-C, and strong association results between LPL (HindIII) and triglyceride levels (P = 0.005). At the 5% nominal significance level, haptoglobin (HPA) was associated with HDL-C, HDL-C/LDL-C, apoAI/HDL-C and apoAI x LDL-C/HDL-C. The apolipoprotein AI locus did not show any significant linkages or associations. The study thus indicated that genetic variation of APOB, LPL, CETP, and lecithin cholesterol acyl transferase (which is linked to HPA and CETP) may play an important role in the regulation of lipoprotein metabolism and could contribute to the risk of coronary artery disease.

Impact of apolipoprotein E polymorphism in determining interindividual variation in total cholesterol and low density lipoprotein cholesterol in Hispanics and non-Hispanic whites

The extent of apolipoprotein E (apo E) polymorphism and its effect on eight quantitative risk factors for coronary heart disease (total cholesterol; low density lipoprotein (LDL) cholesterol; total high density lipoprotein and its subfractions, HDL2 and HDL3; triglycerides; fasting glucose and fasting insulin) has been determined in 238 randomly selected Hispanics (120 males and 118 females) and 201 non-Hispanic whites (NHWs) (105 males and 96 females) from the San Luis Valley, Colorado. The frequencies for the E * 2, E * 3 and E * 4 alleles were 0.048, 0.853 and 0.099, respectively, in Hispanics and 0.080, 0.783 and 0.137, respectively, in NHWs. Relatively low frequency of the E * 2 and E * 4 alleles in Hispanics compared with NHWs is consistent with the genetic and anthropologic data that Hispanics have substantial Amerindian admixture. The impact of apo E polymorphism on each quantitative trait was estimated after adjusting for concomitant variables including age, cigarette smoking and body mass index in both genders and pre- or post-menopause status in females. The distribution of eight quantitative traits was analyzed among three common apo E phenotypes, 3-2, 3-3 and 4-3. In Hispanics, significant variability among apo E phenotypes was observed for total cholesterol (P = 0.001) in females only and the apo E polymorphism accounts for 12.4% variation in total cholesterol and 15.2% variation in LDL-cholesterol. In NHWs, significant mean differences among apo E phenotypes were observed for total cholesterol in both males (P = 0.007) and females (P = 0.0004). In NHW males and females, the apo E polymorphism explained 9.2% and 12.4%, respectively, of the variation in total cholesterol, and 15.1% and 6.6%, respectively, of the variation in LDL-cholesterol. In NHWs, borderline significance levels were also noted for phenotype specific differences in HDL2-cholesterol in males (P = 0.04) and females (P = 0.05), for total HDL cholesterol in females (P = 0.02) and HDL3-cholesterol in females (P = 0.06). While the estimated effects of the apo E polymorphism on quantitative traits differ somewhat between Hispanics and non-Hispanic whites, this probably reflects the overall difference in frequencies of the less common alleles in the Hispanics rather than a biological difference in the effects of these alleles on lipid metabolism.

Association of a PvuII RFLP at the lipoprotein lipase locus with fasting insulin levels in Hispanic men

We present results from an association study between RFLPs in the lipoprotein lipase (LPL) gene and lipid and insulin levels. The study population consisted of 102 Hispanic men and 97 Hispanic women. The subjects were genotyped for two previously reported RFLPs detected with the restriction enzymes HindIII and PvuII. The frequencies of the RFLPs in the Hispanic population are similar to those seen in other Caucasian populations. Strong linkage disequilibrium was detected between the sites in Hispanics. Genotypes were used separately in analyses of variance with fasting serum triglycerides, total cholesterol, high density lipoprotein (HDL)-cholesterol, low density lipoprotein (LDL)-cholesterol, HDL2/HDL3-cholesterol, and insulin levels, as well as two measures of adiposity: waist-hip ratio and body mass index. Men and women were analyzed separately. Mean fasting insulin levels of the LPL PvuII genotypes were significantly different from each other in Hispanic men. The mean fasting insulin level of men who were homozygous for the presence of the PvuII site (+/+) was 9.20 +/- 0.24 mu units/ml, men who were heterozygous had a mean level of 10.54 +/- 0.20 mu units/ml, and men who were homozygous for the absence of the site (-/-) had a mean of 12.91 +/- 0.30 mu units/ml. This effect was not seen in Hispanic women. These results suggest that the regulation of LPL by insulin may be different in Hispanics with different LPL PvuII genotypes.

Influence of the apoA-II gene locus on HDL levels and fatty streak development in mice

Previous studies have shown that distal mouse chromosome 1 contains the apolipoprotein AII (apoAII) gene, encoding the second most abundant apolipoprotein in high density lipoproteins (HDLs), as well as a gene termed Ath-1 that controls aortic fatty streak development and HDL cholesterol levels in response to a high-fat, high-cholesterol diet. We report genetic studies confirming that the genes are distinct. Using molecular markers for mouse chromosome 1, we have further mapped the two genes, and our results indicate that they are separated by a minimum of 2 cM. We also report evidence that in mice on a low-fat chow diet, the apoAII gene locus influences HDL cholesterol levels. Thus, statistical analysis of two sets of recombinant inbred strains revealed concordant segregation patterns of HDL cholesterol levels and the apoAII gene locus. The effect of apoAII expression on HDL cholesterol levels was further tested by using a congenic strain that exhibits increased apoAII synthesis in comparison to the background strain. The results support the concept that increased synthesis of apoAII results in increased HDL cholesterol levels. Unexpectedly, increased expression of apoAII appeared to promote rather than retard aortic fatty streak development.

Role of genetic variation at the apo AI-CIII-AIV gene cluster in determining plasma apo AI levels in boys and girls

We have investigated the effect of the G/A substitution in the promoter region of the apolipoprotein (apo) AI gene (-75 bp) on plasma lipid, lipoprotein and apolipoprotein levels in a sample of 204 children from central Italy. The subjects included 111 boys and 93 girls, aged 8-11 years old. The frequency of the A allele was 0.19 in the total sample, and 0.21 and 0.17 in boys and girls, respectively. Using analysis of variance, we found the G/A substitution was significantly associated with plasma levels of total cholesterol, LDL cholesterol, apo B, and apo AI in boys, accounting for 7.0, 4.2, 5.3, and 4.3% of the sample variance, respectively. Individuals with an A allele had higher mean levels of these lipid traits than individuals homozygous for the G allele. A dietary intervention study had been carried out in a subset of these children, and the effect of the G/A substitution on plasma apo AI levels remained when boys changed to a low fat low cholesterol diet. However, no significant association was observed in girls between any of the lipid traits and the G/A genotypes. We have previously reported in this sample of children that the two polymorphisms detected with restriction enzyme PvuII, with variable sites in the first intron of the apo CIII gene (Pvu II-CIII) and the apo CIII-AIV intergenic region (Pvu II-AIV), were associated with significant differences on plasma apo AI levels. We found that the association reached statistical significance in boys only in this study. Taking these three polymorphisms together, the effects on plasma apo AI levels were additive in boys, accounting for 20.0% of the sample variance. Boys having the genotype GG/V-V+ of the G/A substitution and the PvuII-AIV RFLP had mean apo AI levels 36 mg/dl lower than boys with the genotype GA + AA/V-V-. In girls, however, there was evidence of significant interaction of effects between the PvuII-AIV RFLP and the G/A substitution (P < 0.04), with the A allele being associated with higher levels of plasma apo AI only in girls having the rare allele (V+) of the PvuII-AIV RFLP. We conclude that genetic variation at the apo AI-CIII-AIV gene cluster is having a major impact on the determination of plasma apo AI levels in this sample of young boys, with additive effects due to functional changes at several places in this gene cluster detected directly (G/A) or in allelic association with the PvuII-CIII and PvuII-AIV polymorphisms.(ABSTRACT TRUNCATED AT 400 WORDS)

Genetic epidemiology of low-density lipoprotein subclass phenotypes

Heterogeneity in LDL particles can be described by two distinct phenotypes in individual subjects, denoted A and B, based on gradient gel electrophoresis. Phenotype A is characterized by a predominance of large, buoyant LDL particles, while phenotype B is characterized by a predominance of small, dense LDL particles. Several studies have demonstrated that LDL subclass phenotype B is associated with both increased risk of coronary heart disease and an atherogenic lipoprotein profile. Complex segregation analyses in families, heritability analyses in twins, and recent linkage analyses, uniformly support the presence of genetic influences on LDL subclass phenotypes. However, environmental and behavioural influences on LDL subclasses have also been documented. Understanding the mechanisms underlying LDL subclass phenotypes may lead to targeted intervention to reduce coronary heart disease (CHD) risk in genetically susceptible individuals. Thus, LDL subclass phenotypes represent a common, genetically-influenced risk factor for coronary heart disease.

Spontaneous hypercholesterolemia and arterial lesions in mice lacking apolipoprotein E

Apolipoprotein E (apoE) is a ligand for receptors that clear remnants of chylomicrons and very low density lipoproteins. Lack of apoE is, therefore, expected to cause accumulation in plasma of cholesterol-rich remnants whose prolonged circulation should be atherogenic. ApoE-deficient mice generated by gene targeting were used to test this hypothesis and to make a mouse model for spontaneous atherosclerosis. The mutant mice had five times normal plasma cholesterol, and developed foam cell-rich depositions in their proximal aortas by age 3 months. These spontaneous lesions progressed and caused severe occlusion of the coronary artery ostium by 8 months. The severe yet viable phenotype of the mutants should make them valuable for investigating genetic and environmental factors that modify the atherogenic process.

Lipid parameters and apolipoprotein B RFLP studies: comparison of normal and coronary heart disease groups as defined by angiography

We have compared the lipid and apolipoprotein values and the frequency of DNA polymorphisms of the apolipoprotein B gene detected with the restriction enzymes, Xba I and Eco RI in 122 patients with coronary heart disease (CHD) and 80 control subjects. The patients with coronary heart disease (CHD) were defined by > 70% stenosis in at least one major coronary artery whereas the controls showed no signs of coronary artery narrowing at angiography. When males and females were considered separately, differences in triglyceride, total cholesterol and high density lipoprotein-cholesterol (HDL-cholesterol) between CHD and control subjects were significant only for females. The polymorphism studies showed no significant differences between the control and CHD subjects except for a difference in the frequency in the females of the Xba I polymorphism (p < 0.05). The X1 allele (absence of the restriction enzyme cutting site) occurred significantly more often in the patient group than in the controls. Individuals with the X1X2 genotype had the highest serum total cholesterol whereas those with the X1X1 genotype had the lowest HDL-cholesterol value. Generally, the associations between the Xba I and Eco RI alleles and serum lipid levels were weak and inconsistent. Furthermore, even after careful selection of disease and control groups, a useful role for restriction fragment length polymorphism studies in assessing CHD risk in individual patients was not demonstrated.

Familial Mediterranean fever: analysis of inheritance and current linkage data

Familial Mediterranean fever (FMF) is a genetic disorder characterized by recurrent attacks of fever and inflammation of serosal surfaces. Unlike many mendelian disorders, the mode of transmission has been subject to some controversy as segregation analysis studies have always demonstrated fewer "observed" than "expected" affected individuals. Despite efforts to map the gene causing FMF, no definite linkage has been yet identified. This review analyses the epidemiologic and genetic characteristics in order to evaluate critically the inheritance of the disease and provide a perspective on the current biochemical and molecular genetic studies whose aim is to locate the gene for this disease.

Apolipoprotein B gene polymorphisms, lipoproteins and coronary atherosclerosis: a study of young myocardial infarction survivors and healthy population-based individuals

Association studies were carried out in a sample of 87 patients from Sweden who had survived a myocardial infarction (MI) before the age of 45, and 91 age-matched healthy individuals, to compare the impact of polymorphisms at the apolipoprotein (apo) E and B gene loci on among-individual differences in plasma lipid traits and progression of atherosclerosis. In the group of healthy individuals, polymorphisms creating the common apo E isoforms were, as expected, associated with significant differences in total and low density lipoprotein (LDL) cholesterol (11.7% and 11.6% of sample variance). For apo B, the polymorphism with the largest effect on apo B levels (16% of sample variance) was the C to T transition 265 bp 5' of the cap site, in the promoter (detectable by MspI). Both this polymorphism and the threonine2488 neutral substitution (detectable by XbaI) were associated with significant effects on LDL-cholesterol (8.3% and 9.3% of sample variance, respectively). The asparagine/serine4311 polymorphism was associated with a significant effect on high density lipoprotein (HDL) cholesterol alone, and there was no significant association with the glutamate/lysine4154 polymorphism (detectable by EcoRI) or the leucine-alanine-leucine (LAL) insertion/deletion polymorphism in the signal peptide. In the patients, polymorphisms creating the three common apo E isoforms were associated with large effects on cholesterol, apo B and triglyceride levels (19.9%, 20.3% and 23.9% of sample variance) of similar magnitude as in the healthy individuals. Apo B polymorphisms were found to be associated with much smaller effects on lipid traits than in the healthy individuals. The only significant association was between the asparagine/serine4311 polymorphism and HDL-triglyceride levels. However, global severity of coronary atherosclerosis at the first angiography was found to be significantly associated with the LAL insertion/deletion polymorphism (P = 0.008). Thus variation at the apo B gene locus is associated with the development of atherosclerosis, but the data suggests that this may act through mechanisms not directly related to effects on measured lipid traits.

The status of PAI-1 as a risk factor for arterial and thrombotic disease: a review

Plasminogen activator inhibitor-1 (PAI-1) is a rapid inhibitor of tissue plasminogen (tPA) in vivo. Evidence suggests that the level of plasma PAI-1 activity is responsible for the regulation of the whole fibrinolytic process through this tPA/PAI-1 interaction. Levels of PAI-1 have therefore emerged as a candidate for a thrombotic risk factor. Recent epidemiological data supports the view that high plasma levels of PAI-1 may be important in the pathogenesis of arterial and thrombotic disease. These data are reviewed and their significance discussed. PAI-1 expression has been shown to be regulated by many different factors in vitro and the relevance of these data to in vivo physiology is addressed. The current knowledge of the biochemistry, expression and genetics of PAI-1 is also presented and the significance of this to disease pathogenesis is discussed.

Molecular cloning and sequence analysis of the cDNA encoding human apolipoprotein H (beta 2-glycoprotein I)

Apolipoprotein H, also known as beta-2-glycoprotein I, was purified from human serum, and antiserum produced to denatured apolipoprotein H detected a cDNA clone from a lambda gt11 library derived from human liver. This cDNA coded for the complete sequence of the mature protein. The cDNA insert, along with a polymerase chain reaction product which extended the 5' end of the message, were subcloned and both strands were sequenced. The apolipoprotein H precursor was found to code for 345 amino acids, 326 of which appear in the mature protein. The deduced amino acid sequence of human apolipoprotein H differs from its rat homologue by the presence of a 48-amino acid stretch which is absent from the rat protein. The remainder of the proteins share a greater than 80% similarity. The amino acid sequence of apolipoprotein H consists largely of repeated units approximately 60 amino acids in length. These repeats are comparable to "sushi structures" found in a large number of diverse proteins, including complement components, receptors and regulators of complement activation, serum proteins, membrane-associated adhesion proteins, and other structural and catalytic proteins. Apolipoprotein H was shown to be transcribed by human hepatoma cell lines Hep 3B and Hep G2, and rat liver by detection of mRNA using northern blot analysis.

Familial lipoprotein disorders in patients with premature coronary artery disease

BACKGROUND

Genetic lipoprotein disorders have been associated with premature coronary artery disease (CAD).

METHODS AND RESULTS

The prevalence of such disorders was determined in 102 kindreds (n = 603 subjects) in whom the proband had significant CAD documented by angiography before the age of 60 years. Fasting plasma cholesterol, triglyceride, low density lipoprotein (LDL) cholesterol, apolipoprotein (apo) B, and lipoprotein (a) [Lp(a)] values above the 90th percentile and high density lipoprotein (HDL) cholesterol and apo A-I below the 10th percentile of age- and sex-specific norms were defined as abnormal. An abnormality was noted in 73.5% of probands compared with 38.2% in age-matched controls (p less than 0.001), with a low HDL cholesterol level (hypoalphalipoproteinemia) being the most common abnormality (39.2% of cases). In these kindreds, 54% had a defined phenotypic familial lipoprotein or apolipoprotein disorder. The following frequencies were observed: Lp(a) excess, 18.6% (includes 12.7% with no other dyslipidemias); hypertriglyceridemia with hypoalphalipoproteinemia, 14.7%; combined hyperlipidemia, 13.7% (11.7% with and 2.0% without hypoalphalipoproteinemia); hyperapobetalipoproteinemia (elevated apo B only), 5%; hypoalphalipoproteinemia, 4%; hypercholesterolemia (elevated LDL only), 3%; hypertriglyceridemia, 1%; decreased apo A-I only, 1%. Overall, 54% of the probands had a familial dyslipidemia; unclassifiable lipid disorders (spouse also affected) were found in 3%. No identifiable familial dyslipidemia was noted in 43% of kindreds of those; nearly half (45%) had a sporadic lipid disorder. Parent-offspring and proband-spouse correlations for these biochemical variables revealed that lipoprotein and apolipoprotein levels are in part genetically determined, with Lp(a) showing the highest degree of parent-offspring correlation.

CONCLUSIONS

Our data indicate that more than half of patients with premature CAD have a familial lipoprotein disorder, with Lp(a) excess, hypertriglyceridemia with hypoalphalipoproteinemia, and combined hyperlipidemia with hypoalphalipoproteinemia being the most common abnormalities.

The genetic basis of lipoprotein disorders. Introduction and overview

In order to elucidate the genetic abnormalities underlying lipoprotein disorders associated with susceptibility to coronary heart disease, researchers have looked for candidate genes. The studies have focused particularly on the lipoprotein transport genes. Relatively common as well as rare mutations have already been identified in several of these genes. In addition, further metabolic and genetic studies indicate that some of these loci harbour significant, but as yet undefined, genetic variation. In the next few years, it is not unreasonable to expect that all or most of the significant mutations at these loci will be catalogued. It is too early to know whether this will be sufficient to explain the genetic basis of altered lipoprotein levels, or whether new loci will need to be investigated. Additional candidate gene loci might be those coding for genes involved in intracellular cholesterol metabolism, cholesterol absorption or insulin resistance. New loci may also be revealed by the technique of reverse genetics. A more complete understanding of the genetics of susceptibility to atheroscerosis will probably also entail the identification of variants at genetic loci that control both the reaction of the blood vessel wall to atherogenic lipoproteins and the thrombosis system. Investigation of the genetic basis of susceptibility to coronary heart disease remains a worthwhile and lively field, with important implications for clinical and public health.

Association of a polymorphism in the Apo AI gene promoter with hyperalphalipoproteinemia

The distribution of a polymorphism due to an Adenine to Guanine transition in the ApoAI gene has been studied in 136 women and 108 men, through amplification of the promoter region of the gene and allele-specific oligonucleotide hybridization. The allelic frequencies for the A allele were 0.10, 0.14 and 0.27 in women and 0.08, 0.17 and 0.14 in men for the lowest decile, intermediate group and the highest decile of HDL-cholesterol levels, respectively. Statistical analysis showed that the A allele was associated with high HDL-cholesterol levels in women, but not in men.

Lipoproteins and their genetic variation in subjects with and without angiographically verified coronary artery disease

To examine the concentration of serum lipoproteins and the association of their genetic variation with the occurrence of coronary artery disease (CAD), composite serum lipoprotein profiles including lipoprotein(a) (Lp[a]), apolipoprotein (apo) E phenotypes, and apo B Xba I genotypes were determined in patients with angiographically verified CAD (CAD+ group, n = 111) and in subjects with no angiographic evidence of CAD (CAD- group, n = 46). In addition, we determined the concentrations of serum lipids, lipoproteins, and apolipoproteins in 96 healthy controls. Both CAD- and CAD+ groups had lower concentrations of apos A-I and A-II but higher concentrations of serum total and very low density lipoprotein triglyceride and very low density lipoprotein cholesterol than did healthy controls. The mean concentrations of serum total and low density lipoprotein cholesterol and the median values of Lp(a) were similar in the CAD+ and CAD- groups, both having higher concentrations of low density lipoprotein cholesterol and apo B than the healthy controls. Irrespective of gender, patients with CAD had significantly lower serum high density lipoprotein cholesterol than did those without CAD (1.48 +/- 0.40 versus 1.16 +/- 0.29 mmol/l, p less than 0.001). In women, the mean serum total and very low density lipoprotein triglyceride concentration was also higher in the CAD+ than in the CAD- group. The frequency of the apo E4 allele (epsilon 4) was significantly higher in the CAD+ group (0.293) than in the CAD- group (0.174; p less than 0.001). The frequencies of the two apo B alleles, X1 (Xba I restriction site absent) and X2 (Xba I restriction site present), were similar in the two groups. Stepwise discriminant analysis revealed that in men, serum high density lipoprotein cholesterol had the highest power to discriminate for CAD. In addition, the concentration of plasma apo B levels and the occurrence of apo E phenotypes were independently associated with CAD in men. In women, the only independent factor associated with CAD after adjustment for beta-blocker and diuretics usage was the concentration of serum triglycerides.

Polymorphisms in the apolipoprotein (apo) AI-CIII-AIV gene cluster: detection of genetic variation determining plasma apo AI, apo CIII and apo AIV concentrations

We have examined the associations between levels of plasma apolipoprotein (apo) AI, apo CIII and apo AIV and genetic variation in the apo AI-CIII-AIV gene cluster in 162 boys and young men from Belgium aged from 7 to 23 years. Genotypes were determined for six restriction enzymes XmnI, PstI, SstI, PvuIIA-CIII, PvuIIB-AIV and XbaI, and for the G to A substitution at -75 bp in the 5' region of the apo AI gene. The polymorphism most strongly associated with apo AI levels was the G to A substitution (P = 0.025, R2 x 100 = 3.6%) confirming previous observations. The polymorphism most strongly associated with apo CIII levels was that of PvuIIA-CIII (P = 0.023, R2 x 100 = 2.9%) in the apo CIII gene. This novel association must be interpreted with caution until it has been confirmed in an independent sample. The polymorphism associated with the largest effect on apo AIV levels was that detected with XbaI in the apo AIV gene, but this association was not statistically significant. Previously reported associations between the SstI polymorphism and triglyceride levels, and between the PstI polymorphism and apo AI levels, were weakly detected in the present sample. Our results show that variation associated with some of the polymorphisms in the apo AI-CIII-AIV cluster makes a small, but statistically significant, contribution to the determination of apo AI and apo CIII levels in this sample of young men and boys. These observations may, in part, explain reported associations between polymorphisms in this gene cluster, differences in plasma lipid and lipoprotein levels, and prevalence of coronary artery disease.

Association of apolipoprotein B gene variants with plasma apoB and low density lipoprotein (LDL) cholesterol levels

The contribution of the variants of the apolipoprotein (apo) B locus to the total variance in plasma apoB and cholesterol levels was examined in four independent populations, two that were composed of normal controls (n = 77 and 85) and two with coronary heart disease (n = 115 and 159). A correlation between genotype at the apoB-XbaI locus and apoB levels was observed. The effects of the (+; presence of restriction site) and (-) alleles were to increase or decrease the apoB and cholesterol levels by approximately 3.5 mg/dl, respectively. None of the 274 individuals in the coronary heart disease (CHD) groups was found to be a carrier of the apoB allele Arg3500----Gln, previously shown to be associated with an apoB protein defective in binding to the low density lipoprotein receptor (LDL-R). No DNA sequence variants were found in the region encoding amino acid residues 3129-3532 within the putative LDL-R binding domain among 35 individuals with apoB levels above the 94th percentile (141 mg/dl).

Dietary fatty acids, lipoproteins, and cardiovascular disease

Dietary fat quality and quantity significantly affect the metabolism of all the plasma lipoproteins and probably constitute the most significant dietary determinants of plasma lipoprotein levels. Since the major role of the plasma lipoproteins is the transport of exogenous and endogenous fat, this would be expected of a highly regulated, metabolically homeostatic system. The data clearly show that dietary fat saturation affects all aspects of lipoprotein metabolism, from synthesis to intravascular remodeling and exchanges to receptor-mediated and nonspecific catabolism. The experimental data regarding dietary fatty acid effects on lipoprotein metabolism are complicated and at times contradictory due to the large degree of metabolic heterogeneity in the population, which, when coupled with the known abnormalities of lipoprotein metabolism associated with certain types of hyperlipoproteinemia, can present responses from A to Z. It is clear that the same dietary pattern has different effects in different individuals and that complicating factors of individuality raise some concerns regarding generalized dietary recommendations. As new knowledge of the role of dietary factors and CVD risk develops, and our abilities to characterize the individual patient's response to dietary interventions become more refined, it may be possible to specify dietary fat intervention from a patient-oriented concept rather than a single all-purpose diet approach. Thus it would be possible to design dietary interventions to match patient needs and gain both efficacy and compliance. With the spectrum of approaches possible--low fat, moderate fat with MUFA, n-3 PUFA, etc.--we should be able to approach dietary interventions to reduce CVD risk at both a population-based level and a patient-specific level. There remains much to learn regarding the effects of dietary fatty acids on the synthesis, intravascular modifications, and eventual catabolism of the plasma lipoproteins. The area of lipoprotein metabolism in health and disease, of its modifications by diets and drugs, and of the contributions of genetic heterogeneity to these processes is one of notable advances over the past two decades and continues to be an area of intense investigation.