Relationship between the apolipoprotein E and angiotensin-converting enzyme genotypes and LDL particle size in Japanese subjects

Relationship Between the Apolipoprotein E Genotype and LDL Particle Size in Patients With Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is associated with dyslipidemia and increased cardiovascular risk. We assessed the effects of apolipoprotein E ( APOE) genotype on low-density lipoprotein (LDL) and high-density lipoprotein (HDL) particle size and lipid subclasses (separated by gradient gel electrophoresis) in patients with OSA. Stable patients (n = 181) prospectively recruited underwent full polysomnography. Both LDL particle size and LDL I proportion were reduced from ∊3∊3 homozygotes to ∊2 carriers and to ∊4 carriers (analysis of variance: P = .024; P = .040, respectively); carriers of the ∊4 allele of the APOE genotype had significantly lower LDL particle size and LDL I proportion compared to ∊3∊3 homozygotes ( P < .05 for both comparisons). Insulin resistance increased from patients with no OSA to those with mild–moderate and to those with severe OSA ( P < .001). In multivariate analysis, LDL size was independently predicted by APOE genotype, male gender, and the presence of metabolic syndrome (MetS; P = .001, P = .020, P = .027, respectively). The HDL particle size was not affected by APOE genotype. Our data demonstrate that both the ∊4 APOE genotype and MetS are independently related to smaller LDL size in patients with OSA.

Association of plasminogen activator inhibitor-1 4G/5G gene polymorphism with variations in the LDL particle size in healthy Japanese men

BACKGROUND

Several studies have supported the association between a predominance of small, dense low-density lipoprotein (LDL) and the risk of coronary artery disease. As another potentially atherogenic factor, impaired fibrinolytic activity due to increased plasminogen activator inhibitor-1 (PAI-1) concentrations has been shown. In addition, the 4G allele of the 4G/5G polymorphism in the promoter region of the PAI-1 gene is reported to be associated with the atherogenic lipid profile. We investigated the relation between the PAI-1 gene polymorphism and LDL particle size.

METHODS

A total of 156 healthy Japanese male subjects were recruited. The diameter of LDL particles was determined at their peak size using polyacrylamide gels using fresh plasma samples.

RESULTS

Fasting insulin and triglyceride concentrations were found to be significantly higher, and the LDL particle size was smaller in the homozygotes for the 5G allele than in the carriers of the 4G allele. An analysis of covariance (ANCOVA) adjusting for insulin and triglyceride concentrations showed a consistently significant difference in LDL particle size between the two groups. In the forward stepwise multiple regression analysis, triglycerides, insulin, and the PAI-1 5G/5G genotype remained in the model as independent and significant predictors capable of influencing the LDL particle size.

CONCLUSIONS

Our findings suggest that the 4G/5G polymorphism of the PAI-1 gene might be associated with LDL particle size in healthy Japanese males.

Genetics of LDL particle heterogeneity

Substantial evidence exists suggesting that small, dense LDL particles are associated with an increased risk of coronary heart disease. This disease-related risk factor is recognized to be under both genetic and environmental influences. Several studies have been conducted to elucidate the genetic architecture underlying this trait, and a review of this literature seems timely. The methods and strategies used to determine its genetic component and to identify the genes have greatly changed throughout the years owing to the progress made in genetic epidemiology and the influence of the Human Genome Project. Heritability studies, complex segregation analyses, candidate gene linkage and association studies, genome-wide linkage scans, and animal models are all part of the arsenal to determine the susceptibility genes. The compilation of these studies clearly revealed the complex genetic nature of LDL particles. This work is an attempt to summarize the growing evidence of genetic control on LDL particle heterogeneity with the aim of providing a concise overview in one read.

Evidence for a major quantitative trait locus on chromosome 17q21 affecting low-density lipoprotein peak particle diameter

BACKGROUND

Several lines of evidence suggest that small dense LDL particles are associated with the risk of coronary heart disease. Heritability and segregation studies suggest that LDL particle size is characterized by a large genetic contribution and the presence of a putative major genetic locus. However, association and linkage analyses have thus far been inconclusive in identifying the underlying gene(s).

METHODS AND RESULTS

An autosomal genome-wide scan for LDL peak particle diameter (LDL-PPD) was performed in the Québec Family Study. A total of 442 markers were genotyped, with an average intermarker distance of 7.2 cM. LDL-PPD was measured by gradient gel electrophoresis in 681 subjects from 236 nuclear families. Linkage was tested by both sib-pair-based and variance components-based linkage methods. The strongest evidence of linkage was found on chromosome 17q21.33 at marker D17S1301, with an LOD score of 6.76 by the variance-components method for the phenotype adjusted for age, body mass index, and triglyceride levels. Similar results were obtained with the sib-pair method (P<0.0001). Other chromosomal regions harboring markers with highly suggestive evidence of linkage (P< or =0.0023; LOD > or =1.75) include 1p31, 2q33.2, 4p15.2, 5q12.3, and 14q31. Several candidate genes are localized under the peak linkages, including apolipoprotein H on chromosome 17q, the apolipoprotein E receptor 2, and members of the phospholipase A2 family on chromosome 1p as well as HMG-CoA reductase on chromosome 5q.

CONCLUSIONS

This genome-wide scan for LDL-PPD indicates the presence of a major quantitative trait locus located on chromosome 17q and others interesting loci influencing the phenotype.

The polymorphism of the beta3-adrenergic receptor gene is associated with reduced low-density lipoprotein particle size

People with a predominance of small, dense low-density lipoprotein (LDL) particles appear to be at increased risk for coronary disease, independent of LDL cholesterol levels. The Trp64Arg variant of the beta3-adrenergic receptor gene is reported to be associated with abdominal obesity and resistance to insulin, and as a consequence, this variant may be a genetic factor in the development of atherosclerosis. Therefore, we investigated whether the beta3-adrenergic receptor polymorphism contributes to the distribution of LDL particle size in 136 Japanese subjects, aged 33 to 59 years, who visited for a routine annual checkup. None of these subjects were taking any medication. The diameter of LDL particles was determined at their peak size using nondenaturing 2% to 16% polyacrylamide gradient gels using fresh plasma samples. The genotype frequencies were: Trp/Trp, 71.3%; Try/Arg, 22.1%; and Arg/Arg, 6.6%, with allele frequencies of 0.82 for Trp64 and 0.18 for Arg64. The subjects with the Arg/Arg genotype had significantly higher levels of fasting plasma insulin and triglycerides and an insulin resistance index of homeostasis model assessment (HOMA-R), and significantly smaller LDL particle size than did the subjects with the Trp/Trp genotype. After adjusting for fasting insulin, body mass index (BMI), and HOMA-R index, there was no longer an observed difference in LDL particle size. The number of the Arg64 allele in individuals was significantly related with fasting insulin, BMI, triglycerides, glycosylated hemoglobin (HbA1c), and fasting glucose, and it was inversely related with LDL particle size. After adjusting for triglyceride, fasting insulin levels, and HOMA-R index, LDL particle size was no longer inversely correlated with the Arg allele. These findings suggest that the Trp64Arg variant in the beta3-adrenergic receptor gene may be associated with reducing LDL particle size, probably due to insulin resistance.

Therapeutic modulation of low-density lipoprotein size

Small, dense LDL particles have been linked to atherosclerosis, often in a cluster of risk factors and affecting approximately 20% of adults. Over the past year, studies confirmed that small dense LDL is an autosomal dominant trait, influenced mainly by hypertriglyceridaemia and obesity, insulin resistance and diabetes mellitus and some incompletely investigated genetic loci. Compositional and functional differences have been observed in small LDL. Evidence is emerging that lifestyle as well as pharmacological intervention can modulate LDL size, but there is no proof yet that this is of clinical benefit.