Effect of apolipoprotein E3/4 phenotype on postprandial triglycerides and retinyl palmitate metabolism in plasma from hyperlipidemic subjects in Japan

Quantile-dependent expressivity of postprandial lipemia

Purpose

“Quantile-dependent expressivity” describes an effect of the genotype that depends upon the level of the phenotype (e.g., whether a subject’s triglycerides are high or low relative to its population distribution). Prior analyses suggest that the effect of a genetic risk score (GRS) on fasting plasma triglyceride levels increases with the percentile of the triglyceride distribution. Postprandial lipemia is well suited for testing quantile-dependent expressivity because it exposes each individual’s genotype to substantial increases in their plasma triglyceride concentrations. Ninety-seven published papers were identified that plotted mean triglyceride response vs. time and genotype, which were converted into quantitative data. Separately, for each published graph, standard least-squares regression analysis was used to compare the genotype differences at time t (dependent variable) to average triglyceride concentrations at time t (independent variable) to assess whether the genetic effect size increased in association with higher triglyceride concentrations and whether the phenomenon could explain purported genetic interactions with sex, diet, disease, BMI, and drugs.

Results

Consistent with the phenomenon, genetic effect sizes increased (P≤0.05) with increasing triglyceride concentrations for polymorphisms associated with ABCA1, ANGPTL4, APOA1, APOA2, APOA4, APOA5, APOB, APOC3, APOE, CETP, FABP2, FATP6, GALNT2, GCKR, HL, IL1b, LEPR, LOX-1, LPL, MC4R, MTTP, NPY, SORT1, SULF2, TNFA, TCF7L2, and TM6SF2. The effect size for these polymorphisms showed a progressively increasing dose-response, with intermediate effect sizes at intermediate triglyceride concentrations. Quantile-dependent expressivity provided an alternative interpretation to their interactions with sex, drugs, disease, diet, and age, which have been traditionally ascribed to gene-environment interactions and genetic predictors of drug efficacy (i.e., personalized medicine).

Conclusion

Quantile-dependent expressivity applies to the majority of genetic variants affecting postprandial triglycerides, which may arise because the impaired functionalities of these variants increase at higher triglyceride concentrations. Purported gene-drug interactions may be the manifestations of quantile-dependent expressivity, rather than genetic predictors of drug efficacy.

Influence of Apolipoprotein E on the Lipid Profile and Postprandial Triglyceride Levels in Brazilian Postmenopausal Women With Artery Disease

This study confirms the association of risk factors for coronary artery disease (CAD) and the apoE polymorphisms, specifically related to the APOE*4 allele, with coronary disease in postmenopausal women. Significantly altered values of the lipid profile were found in patients when compared with controls, independent of the presence of the APOE*4 allele. However, the controls showed higher high-density lipoprotein cholesterol (HDL-C) levels and reduced triglyceride (TG) levels, differing significantly from patients. In this case, the study of subgroups, considering the APOE*3/3 and APOE*3/4 genotypes, suggests that the APOE*4 allele is not implicated in the variations of the lipid profile of patients and determined an increase in the production levels of HDL-C and a reduction in TG highly benefiting the control group compared with APOE*3/3 genotype. The metabolic kinetics of TG, although with the same pattern between groups, and the presence of the APOE*4 allele are suggested to be associated with accelerated clearance compared with APOE*3 allele in non-CAD group.

Disturbance in uniformly 13C-labelled DHA metabolism in elderly human subjects carrying the apoE ε4 allele

Carrying the apoE ε4 allele (E4+ ) is the most important genetic risk for Alzheimer’s disease. Unlike non-carriers (E4- ), E4+ seem not to be protected against Alzheimer's disease when consuming fish. We hypothesised that this may be linked to a disturbance in n-3 DHA metabolism in E4+. The aim of the present study was to evaluate [13C]DHA metabolism over 28 d in E4+ v. E4-. A total of forty participants (twenty-six women and fourteen men) received a single oral dose of 40 mg [13C]DHA, and its metabolism was monitored in blood and breath over 28 d. Of the participants, six were E4+ and thirty-four were E4-. In E4+, mean plasma [13C]DHA was 31% lower than that in E4-, and cumulative b-oxidation of [13C]DHA was higher than that in E4- 1–28 d post-dose (P ≤0·05). A genotype x time interaction was detected for cumulative b-oxidation of [13C]DHA (P ≤ 0·01). The whole-body half-life of [13C]DHA was 77% lower in E4+ compared with E4- (P ≤0·01). In E4+ and E4-, the percentage dose of [13C]DHA recovered/h as 13CO2 correlated with [13C]DHA concentration in plasma, but the slope of linear regression was 117% steeper in E4+ compared with E4- (P ≤ 0·05). These results indicate that DHA metabolism is disturbed in E4+, and may help explain why there is no association between DHA levels in plasma and cognition in E4+. However, whether E4+ disturbs the metabolism of 13C-labelled fatty acids other than DHA cannot be deduced from the present study.

Effect of the fat composition of a single high-fat meal on inflammatory markers in healthy young women

The aim of the present study was to examine the effect of a single high-fat meal with different fat quality on circulating inflammatory markers and gene expression in peripheral blood mononuclear cells (PBMC) to elucidate the role of fat quality on postprandial inflammation. A postprandial study with fourteen healthy females consuming three test meals with different fat quality was performed. Test days were separated by 2 weeks. Fasting and postprandial blood samples at 3 and 6 h after intake were analysed. The test meal consisted of three cakes enriched with coconut fat (43 % energy as saturated fat and 1 % energy as α-linolenic acid (ALA)), linseed oil (14 % energy as ALA and 30 % energy as saturated fat) and cod liver oil (5 % energy as EPA and DHA and 5 % energy as ALA in addition to 31 % energy as saturated fat). In addition, ex vivo PBMC experiments were performed in eight healthy subjects investigating the effects of EPA and ALA on release and gene expression of inflammatory markers. The IL-8 mRNA level was significantly increased after intake of the cod liver oil cake at 6 h compared with fasting level, which was significantly different from the effect observed after the intake of linseed cake. In contrast, no effect was seen on circulating level of IL-8. In addition, ALA and EPA were shown to elicit different effects on the release and mRNA expression levels of inflammatory markers in PBMC cultured ex vivo, with EPA having the most prominent pro-inflammatory potential.

Apolipoprotein E polymorphisms and postprandial triglyceridemia before and after fenofibrate treatment in the Genetics of Lipid Lowering and Diet Network (GOLDN) Study

BACKGROUND

Although much is known about the effect of Apolipoprotein E (APOE) alleles on fasting lipid concentrations, less is known about the effect of APOE alleles on postprandial triglyceridemia or the triglyceride response to fenofibrate.

METHODS AND RESULTS

We evaluated the effects of the APOE locus on fasting and postprandial triglyceride concentrations as part of the Genetics of Lipid Lowering and Diet Network (GOLDN) study. Participants were evaluated after a high-fat meal challenge before (n=1072) and after 3 weeks of daily treatment with 160 mg of fenofibrate (n=738). Mixed models adjusted for sex, age, waist circumference, and family relationship were used to examine the association of the ε4 carrier and ε2 carrier status versus ε3 homozygotes with fasting triglycerides and the area under the curve (AUC) for triglycerides during the high-fat meal challenge. Compared with the ε3/ε3 genotype, ε2 carriers had on average higher fasting triglyceride concentrations (130.5 mg/dL versus 109.3 mg/dL, P<0.001). After fenofibrate treatment, the APOE genotype differences persisted in the fasting state (ε2 carriers: 85.1 mg/dL versus ε3/ε3: 75.9 mg/dL, P<0.05). Carriers of the ε4 allele had significantly higher fasting triglyceride concentrations only prefenofibrate (120.9 mg/dL versus 109.3 mg/dL, P=0.008). APOE alleles did not have an effect on response to fenofibrate. Postprandial triglycerides were significantly higher for ε2 carriers versus ε3 homozygotes (but not ε4 carriers) both before and after fenofibrate treatment (P=0.01 and P=0.005, respectively).

CONCLUSIONS

APOE polymorphisms are important determinants of triglyceride concentrations, especially in the fasting state.

Interactions between age and apoE genotype on fasting and postprandial triglycerides levels

OBJECTIVE

The influences of genetic determinants on the magnitude of postprandial lipaemia are presently unclear. Here the impact of the common apolipoprotein (apo)E epsilon mutation on the postprandial triglyceride (TG) response is determined, along with an assessment of genotype penetrance according to age, body mass index and gender.

METHODS AND RESULTS

Healthy adults (n=251) underwent a postprandial investigation, in which blood samples were taken at regular intervals after a test breakfast (0 min, 49 g fat) and lunch (330 min, 29 g fat) until 480 min after the test breakfast. There was a significant impact of apoE genotype on fasting total cholesterol (TC), (P=0.027), LDL-cholesterol (LDL-C), (P=0.008), and %LDL(3) (P=0.001), with higher and lower levels in the E4 and E2 carriers respectively relative to the E3/E3 genotype. Reflective of a higher fasting TG (P=0.001), a significantly higher area under the curve for the postprandial TG response (TG AUC) was evident in the E4 carriers relative to the E3/E3 group (P=0.038). In the group as a whole, a significant age×genotype interaction was observed for fasting TC (P=0.021). In the participants>50 years there was a significant impact of genotype on TC (P=0.005), LDL-C (P=0.001) and TAG AUC (P=0.028).

CONCLUSIONS

It is possible that an exaggerated postprandial lipaemia contributes to the increased coronary heart disease risk associated with carriers of the E4 allele; an effect which is more evident in older adults.

Decreased post-prandial triglyceride response and diminished remnant lipoprotein formation in cholesteryl ester transfer protein (CETP) deficiency

Plasma cholesteryl ester transfer protein (CETP) mediates CE/TG exchange among various lipoproteins. CETP deficiency results in low LDL and high HDL phenotype including apoE-rich large HDL. Large HDL could provide apoE to chylomicron/VLDL during lipolysis in post-prandial state, accelerating remnant lipoprotein uptake in the liver. To determine the effects of low CETP levels on post-prandial lipoprotein metabolism, lipid levels of plasma remnant-like lipoprotein particles (RLP) fraction were determined in one homozygous and three heterozygous CETP deficiency and controls with apoE3/3 phenotype. After oral fat-load, the area under curve (AUC) of TG levels were remarkably decreased in CETP deficiency as compared to controls (423+/-187 [S.D.] mg/dl x h in three heterozygous CETP deficiency and 926+/-268 [S.D.] in 10 controls, P=0.012). Similarly, the homozygote had a low AUC of TG levels (416 mg/dl x h). Plasma RLP-cholesterol levels were decreased in heterozygotes, but not significantly as compared to controls (P=0.14). HPLC analysis showed that increased RLP-cholesterol level was not due to conventional VLDL-LDL size RLP, but to those in large HDL size in the homozygote. In heterozygotes, bimodal distribution of RLP-cholesterol level was found in lipoprotein sizes of conventional VLDL-LDL and large HDL. Subjects with CETP deficiency appeared to have low levels of TG response and diminished remnant lipoprotein formation after fat-load.

Diabetic lipemia with eruptive xanthomatosis in a lean young female with apolipoprotein E4/4

Eruptive xanthomas in adults are usually indicative of chylomicronemia. Although diabetes mellitus is the most common secondary cause of chylomicronemia, which is designated as diabetic lipemia, the clinical characteristics of diabetes with regard to development of xanthomas are not well defined. In this paper, we describe a young female who displayed eruptive xanthomas as an initial manifestation of diabetic lipemia. The patient was a 20-year-old female with a body mass index of 18.9 kg/m2 and Marfanoid appearance. Her past history was unremarkable, except for patent ductus arteriosus and mild mental retardation. She was admitted to our division for eruptive xanthomas on the extremities and marked hyperglycemia (random glucose, 520 mg/dl) and hypertriglyceridemia (6880 mg/dl). She was diagnosed with Type 2 diabetes based on the positive family history of diabetes, residual secretory capacity of insulin, and absence of autoantibodies related to Type 1 diabetes. Based on the increase in the concentrations of both chylomicrons and very low density lipoproteins, type V hyperlipoproteinemia was diagnosed. After the initiation of insulin therapy, both hypertriglyceridemia and eruptive xanthomas subsided, without administering any hypolipidemic agents. Minimal model analysis of a frequently sampled intravenous glucose tolerance test revealed severe insulin resistance, despite the absence of obesity. Post-heparin lipoprotein lipase (LPL) activity was moderately decreased, and common mutations in the LPL gene were not demonstrated by genetic screening. The apolipoprotein E phenotype was E4/4, which is known to be associated with type V hyperlipoproteinemia. Hypoadiponectinemia of 1.7 microg/ml was also revealed, which may, in part, account for the insulin resistance and decreased LPL activity. In conclusion, the clustering of apolipoprotein E4/4 and hypoadiponectinemia, in addition to insulin resistance and poor glycemic control, might have resulted in hypertriglyceridemia with eruptive xanthomatosis in this subject.

Lipid homeostasis and apolipoprotein E in the development and progression of Alzheimer's disease

Extracellular amyloid plaques, intracellular neurofibrillary tangles, and loss of basal forebrain cholinergic neurons in the brains of Alzheimer's disease (AD) patients may be the end result of abnormalities in lipid metabolism and peroxidation that may be caused, or exacerbated, by beta-amyloid peptide (Abeta). Apolipoprotein E (apoE) is a major apolipoprotein in the brain, mediating the transport and clearance of lipids and Abeta. ApoE-dependent dendritic and synaptic regeneration may be less efficient with apoE4, and this may result in, or unmask, age-related neurodegenerative changes. The increased risk of AD associated with apoE4 may be modulated by diet, vascular risk factors, and genetic polymorphisms that affect the function of other transporter proteins and enzymes involved in brain lipid homeostasis. Diet and apoE lipoproteins influence membrane lipid raft composition and the properties of enzymes, transporter proteins, and receptors mediating Abeta production and degradation, tau phosphorylation, glutamate and glucose uptake, and neuronal signal transduction. The level and isoform of apoE may influence whether Abeta is likely to be metabolized or deposited. This review examines the current evidence for diet, lipid homeostasis, and apoE in the pathogenesis of AD. Effects on the cholinergic system and response to cholinesterase inhibitors by APOE allele carrier status are discussed briefly.

Apolipoprotein E gene polymorphism alters lipids before pancreas transplantation

BACKGROUND

Pancreas transplantation (PTX) improves lipids in patients with type 1 diabetes mellitus. However, there are patients who have persistent abnormal lipids or develop new hyperlipidemia despite PTX. One factor that may influence the lipid profile is apolipoprotein E (Apo E) genotype. Apo E polymorphism, particularly E2 and E4 alleles, increases the risk of dyslipidemia. Apo E2 has also been found to increase risk of diabetic nephropathy and so may be more prevalent in PTX candidates.

METHODS

This study evaluated fasting-lipid profiles in type 1 diabetes patients who were pancreas transplant candidates to prospectively evaluate the impact of Apo E genotype on dyslipidemia before and after PTX.

RESULTS

Presence of one or more E4 alleles resulted in higher triglycerides ( =0.0446), lower HDL ( =0.0247), and a higher cholesterol-to-HDL (C/H) ratio ( =0.0405) before PTX when compared with those with E3/3 genotype. After PTX, lipids improved so there was no longer a difference in fasting lipids between patients with an E4 allele and E3/3 genotype. Presence of an E2 allele had no significant impact on fasting lipids before or after PTX.

CONCLUSIONS

Presence of an Apo E4 allele worsened HDL, triglycerides, and C/H ratio before PTX compared with those with E3/3 genotype, whereas the presence of an Apo E2 allele had no significant effect on lipids before or after PTX. Thus, Apo E4 has a larger impact than Apo E2 on fasting-lipid profile in PTX candidates, and Apo E gene polymorphism does not worsen lipid dyslipidemia after PTX, despite introduction of immunosuppressant medications known to cause dyslipidemia.

Apolipoprotein E and diets: a case of gene-nutrient interaction?

Apolipoprotein E has key functions in lipoprotein metabolism, and polymorphisms in the apolipoprotein E gene are associated with distinct lipoprotein patterns. The possibility of gene-nutrient interactions for apolipoprotein E has been addressed in many studies. Although results have generally been mixed, the indications for such an interaction have been more common in studies employing a metabolic challenge. Studies directly designed to examine apolipoprotein E gene-nutrient interactions are needed.