APO E gene and gene-environment effects on plasma lipoprotein-lipid levels

Apolipoprotein E4 as a target for developing new therapeutics for Alzheimer's disease

The identification of factors that influence the onset or progression of the sporadic form of Alzheimer's disease (AD) is a key step toward understanding its mechanism(s) and developing successful rational therapies. The apoE genotype has been identified as a powerful risk factor for AD that may account for as much as 50% of the sporadic form of the disease. As the major risk factor for late-onset AD, apolipoprotein E4 (apoE4) should be considered a good target for AD drug discovery. However, despite knowing for over a decade that apoE4 is detrimental to the disease process, we still remain uncertain about the molecular mechanisms subserving the risk-factor activity of apoE4. This, coupled with the fact that we know relatively little about the function(s) of apoE in brain, has presented a barrier to developing apoE-based therapeutics for AD. Progress has been made in understanding the neurobiology of apoE; a number of potentially overlapping functions have been ascribed, which include lipid transport, neuronal repair, dendritic growth, maintenance of synaptic plasticity, and anti-inflammatory activities. Until the gaps are filled in our understanding of the pathogenic function(s) of apoE4, therapeutic strategies targeting this protein will lag behind the development of other AD therapies. Putative pathological functions, or risk-factor activities, of apoE4 include its role in beta-amyloid deposition, neurofibrillary tangle formation, synaptic loss, lipid dysfunction, neuroinflammation, and oxidative stress.

Apolipoprotein E and renal disease

Apolipoprotein E (ApoE) is a major constituent of plasma lipoproteins with many biological actions of great significance. Beyond the known influence of ApoE polymorphisms on serum lipid profile, the pathogenesis of atherosclerosis, and the development of neurodegenerative disorders, ApoE also has a major role in the pathogenesis and progression of a variety of renal diseases, as well as in the atherosclerotic complications associated with them. Briefly, the polymorphisms of ApoE are major determinants of plasma lipid levels in uremic patients. They may affect the risk for cardiovascular disease in this population, predispose to the development of diabetic nephropathy, influence the severity of certain glomerulopathies, and regulate mesangial and glomerular functions locally in the kidney microenvironment. Finally, certain mutations of the ApoE gene are associated with a recently described nephropathy, termed lipoprotein glomerulopathy.

Meat‐Adaptive Genes and the Evolution of Slower Aging in Humans

The chimpanzee life span is shorter than that of humans, which is consistent with a faster schedule of aging. We consider aspects of diet that may have selected for genes that allowed the evolution of longer human life spans with slower aging. Diet has changed remarkably during human evolution. All direct human ancestors are believed to have been largely herbivorous. Chimpanzees eat more meat than other great apes, but in captivity are sensitive to hypercholesterolemia and vascular disease. We argue that this dietary shift to increased regular consumption of fatty animal tissues in the course of hominid evolution was mediated by selection for "meat-adaptive" genes. This selection conferred resistance to disease risks associated with meat eating also increased life expectancy. One candidate gene is apolipoprotein E (apoE), with the E3 allele evolved in the genus Homo that reduces the risks for Alzheimer's and vascular disease, as well as influencing inflammation, infection, and neuronal growth. Other evolved genes mediate lipid metabolism and host defense. The timing of the evolution of apoE and other candidates for meat-adaptive genes is discussed in relation to key events in human evolution.

Association of apolipoprotein E polymorphism with blood lipids and maximal oxygen uptake in the sedentary state and after exercise training in the HERITAGE family study

The relationship of apolipoprotein E (apo E) genotypes to plasma lipid and maximal oxygen uptake (Vo(2max)) was studied in the sedentary state and after a supervised exercise training program in black and white men and women. At baseline, the apo E 2/3 genotype was associated with the lowest, and apo E 3/4 and E4/4 with the highest low-density liporpotein (LDL) cholesterol and apo B levels in men and women of both races, while female (not male) carriers of apo E3 had higher high-density lipoprotein (HDL) cholesterol levels than carriers of other genotypes. Very-low-density lipoprotein (VLDL) cholesterol and triglyceride levels were significantly higher in carriers of both apo E2 and apo E4 in white men only. Racial and sex differences were noted in lipid responses to exercise training across genotypes with a significantly greater increase in HDL cholesterol observed only in white female carriers of apo E 2/3 and E3/3, as compared to apo E4/4. Apo E polymorphism was not found to be associated with Vo(2max) levels either in the sedentary state nor the Vo(2max) response to exercise training, contrary to previous reports.

Genome-wide linkage scan reveals multiple susceptibility loci influencing lipid and lipoprotein levels in the Quebec Family Study

A genome-wide linkage study was performed to identify chromosomal regions harboring genes influencing lipid and lipoprotein levels. Linkage analyses were conducted for four quantitative lipoprotein/lipid traits, i.e., total cholesterol, triglyceride, HDL-cholesterol (HDL-C), and LDL-C concentrations, in 930 subjects enrolled in the Québec Family Study. A maximum of 534 pairs of siblings from 292 nuclear families were available. Linkage was tested using both allele-sharing and variance-component linkage methods. The strongest evidence of linkage was found on chromosome 12q14.1 at marker D12S334 for HDL-C, with a logarithm of the odds (LOD) score of 4.06. Chromosomal regions harboring quantitative trait loci (QTLs) for LDL-C included 1q43 (LOD = 2.50), 11q23.2 (LOD = 3.22), 15q26.1 (LOD = 3.11), and 19q13.32 (LOD = 3.59). In the case of triglycerides, three markers located on 2p14, 11p13, and 11q24.1 provided suggestive evidence of linkage (LOD > 1.75). Tests for total cholesterol levels yielded significant evidence of linkage at 15q26.1 and 18q22.3 with the allele-sharing linkage method, but the results were nonsignificant with the variance-component method. In conclusion, this genome scan provides evidence for several QTLs influencing lipid and lipoprotein levels. Promising candidate genes were located in the vicinity of the genomic regions showing evidence of linkage.

High-density lipoprotein-cholesterol, its subfractions, and responses to exercise training are dependent on endothelial lipase genotype

Plasma high-density lipoprotein cholesterol (HDL-C) levels are an important independent risk factor for cardiovascular disease (CVD) that can be modified through exercise training. However, levels of HDL-C and its subfractions and their response to standardized exercise training are highly variable among individuals. Such variability suggests that levels of HDL-C, its subfractions, and their response to exercise training may be influenced by genetic variation and the interaction of that genetic variation with physical activity. The endothelial lipase gene (LIPG) may influence HDL-C metabolism and has several recently identified genetic variants. We hypothesized that the LIPG Thr111Ile polymorphism would be associated with variation in HDL-C levels and its subfractions and their response to exercise training. Eighty-three sedentary, healthy 50- to 75-year-old subjects were weight-maintained on an American Heart Association Step 1 Diet and then studied before and after aerobic exercise training. Sample size varied according to outcome measure as complete data was not available for all subjects. Initial age, body composition, and maximum oxygen consumption (V02max) did not differ between LIPG genotype groups (CC, n=41 to 44; CT/TT, n=37 to 39). Initial total cholesterol, low-density lipoprotein cholesterol (LDL-C), and triglyceride (TG) levels were not significantly different between groups. The CT/TT group had lower initial HDL(2NMR)-C (12 +/- 1.0 v 17 +/- 1.1 mg/dL; P =.002) and integrated HDL(1,2NMR)-C (13 +/- 1.0 v 18 +/- 1.1 mg/dL; P=.002) levels and somewhat higher initial levels of integrated HDL(3,4,5)-C (31 +/- 2.2 v 25 +/- 2.3 mg/dL; P=.06). With exercise training, Vo2max increased, and body weight, total body fat, and visceral adipose tissue decreased similarly in both groups. With training, HDL-C levels increased twice as much (4.4 +/- 0.8 v 1.9 +/- 0.9 mg/dL; P=.04), HDL3-C levels increased almost 2-fold greater (3.8 +/- 0.7 v 2.2 +/- 0.6 mg/dL; P=.07), and HDL(5NMR)-C levels increased more than 4 times as much (2.2 +/- 0.8 v 0.5 +/- 0.6 mg/dL; P=.08) in the CC compared to the CT/TT group. We conclude that the LIPG genotype is associated with interindividual variability in HDL-C and its subfractions and their response to exercise training.

Physical activity modulates effects of some genetic polymorphisms affecting cardiovascular risk in men aged over 40 years

BACKGROUND AND AIM

Several genetic polymorphisms have been found to be involved in cardiovascular risk, and many studies have documented the beneficial effect of systematic physical activity (PA) on the cardiovascular system. Our aim was to investigate the interactive effects of PA and genetic background on plasma lipids and homocysteine (tHcy) levels.

METHODS AND RESULTS

Clinical and metabolic parameters, dietary intakes and some polymorphisms of the genes involved in cardiovascular risk (Apo E, fatty acid binding protein-2, Apo AII, hepatic lipase and methylene tetrahydrofolate reductase) were determined in 100 men aged over 40 years who cycle 120-150 Km/week and 100 age-matched sedentary controls. The physically active subjects had lower concentrations of plasma LDL cholesterol (LDL-C), triglyceride (TG), Apo B, glucose and tHcy, and higher concentrations of plasma HDL cholesterol (HDL-C) and Apo AI than the sedentary men; they also had larger LDL particle sizes (LDLs). The LDL-C and Apo B raising effect of the Apo E epsilon 4 allele detectable in the sedentary subjects was totally absent in the cyclists, in whom the LDL-C and Apo B lowering effect of the epsilon 2 allele was observed. PA blunted the TG-raising effect of the Apo AII-265TT genotype, and amplified the HDL-C raising effect of the HL-250AA genotype. PA had a small but significant lowering effect on plasma tHcy adjusted for folate levels in subjects with the 677TT genotype of the MTHFR gene.

CONCLUSIONS

Extended high-intensity PA in men aged over 40 years may modify their metabolic cardiovascular risk factors even in the presence of some unfavourable genotypes.

Adherence to and dosing of beta-hydroxy-beta-methylglutaryl coenzyme A reductase inhibitors in the general population differs according to apolipoprotein E-genotypes

Discontinuation and poor adherence to therapy are major problems during long-term treatment, particularly with cholesterol lowering drugs. Several studies have indicated that the cholesterol lowering effect of statins differs according to apolipoprotein (apo)E genotypes. Low-density lipoprotein-cholesterol lowering capacity appears to be smaller in subjects with the epsilon(4) allele. To assess whether the use of statins in daily practice differs according to apoE genotypes, we used data from the Rotterdam Study, a population-based prospective cohort study in the Netherlands, which started in 1990 and included 7983 subjects aged 55 years or more. During follow-up, there were 798 subjects who started to use statins. We used a Cox proportional hazard model to determine the rate of discontinuation in the first 3 years of statin use. Subjects on statin therapy with epsilon(2)epsilon(2) and epsilon(4)epsilon(4) genotypes showed a trend towards higher dosages than subjects with the other genotypes. Relative to subjects with the epsilon(2)epsilon(3) genotype, those with the epsilon(4)epsilon(4) genotype had a risk of 2.28 [95% confidence interval (CI) 1.02-5.12] to discontinue statins within 3 years. In women, this relative risk was 1.70 (CI 0.53-5.42) versus 3.18 (CI 1.01-10.03) in men. The apoE genotype is associated with discontinuation of statins. This suggests that subjects who are genetically prone to develop hypercholesterolemia show the highest risk of discontinuation of treatment.

Quantitative trait loci influencing blood and liver cholesterol concentration in rats

OBJECTIVE

The LEW/OlaHsd and BC/CpbU rat inbred strains differ markedly in blood and hepatic cholesterol levels before and after a cholesterol-rich diet. To define loci controlling these traits and related phenotypes, an F2 population derived from these strains was genetically analyzed.

METHODS AND RESULTS

For each of the 192 F2 animals, phenotypes were determined, and genomic DNA was screened for polymorphic microsatellite markers. Significant quantitative trait loci (QTLs) were detected for basal serum cholesterol level on chromosome 1 (D1Rat335-D1Rat27: total population, lod score 9.6; females, lod score 10.3) and chromosome 7 (D7Rat69: males, lod score 4.1), for postdietary serum cholesterol level on chromosome 2 (D2Rat69: total population, lod score 4.4) and chromosome 16 (D16Rat6-D16Rat44: total population, lod score 3.3), for postdietary serum phospholipid level on chromosome 11 (D11Rat10: total population, lod score 4.1; females, lod score 3.6), and for postdietary serum aldosterone level on chromosome 1 (D1Rat14: females, lod score 3.7) and chromosome 18 (D18Rat55-D18Rat8: females, lod score 2.9). In addition, QTLs with borderline significance were found on chromosomes 3, 5 to 11, 15, and 18.

CONCLUSIONS

QTLs involved in blood and/or hepatic cholesterol concentrations (or related phenotypes) in the rat were identified. This contributes to the value of the rat as an animal model in studies researching the role of cholesterol in the pathogenesis of atherosclerosis and other cholesterol-related diseases.

Genetic polymorphisms: importance for response to HMG-CoA reductase inhibitors

Coronary artery disease is among the leading causes of death worldwide. Clinical trials show a protective effect of statins against the sequelae of coronary artery disease. The mean risk reductions for subjects using statins compared with placebo found in these trials is about 30%. These are average reductions for all patients included in the trials. Important factors in interpreting the variability in the outcome of drug therapy include the patient's health profile, prognosis, disease severity, quality of drug prescribing, compliance with prescribed pharmacotherapy and the genetic profile of the patient. This review aims to give an overview of the known polymorphisms (Cholesteryl Ester Transfer Protein polymorphism, Stromelysin-1 polymorphism, -455G/A and TaqI polymorphisms of the beta-fibrinogen gene, apoE4, Asp(9)Asn mutation in the lipoprotein lipase gene, the -514 CT polymorphism in the hepatic lipase gene and the ACE deletion type gene) that have an influence on the effects of statins in the general population. The expectation is that in the future a subject's genotype may determine whether he will be treated with statins or not. Determining the genotype will not deny therapy to a subject, but will help in deciding the therapy that will suit the patient best.

Effect of alcohol on lipids and lipoproteins in relation to atherosclerosis

Several studies indicate that light-to-moderate alcohol consumption is associated with a low prevalence of coronary heart disease. An increase in high-density lipoprotein (HDL) cholesterol is associated with alcohol intake and appears to account for approximately half of alcohol's cardioprotective effect. In addition to changes in the concentration and composition of lipoproteins, alcohol consumption may alter the activities of plasma proteins and enzymes involved in lipoprotein metabolism: cholesteryl ester transfer protein, phospholipid transfer protein, lecithin:cholesterol acyltransferase, lipoprotein lipase, hepatic lipase, paraoxonase-1 and phospholipases. Alcohol intake also results in modifications of lipoprotein particles: low sialic acid content in apolipoprotein components of lipoprotein particles (e.g., HDL apo E and apo J) and acetaldehyde modification of apolipoproteins. In addition, "abnormal" lipids, phosphatidylethanol, and fatty acid ethyl esters formed in the presence of ethanol are associated with lipoproteins in plasma. The effects of lipoproteins on the vascular wall cells (endothelial cells, smooth muscle cells, and monocyte/macrophages) may be modulated by ethanol and the alterations further enhanced by modified lipids. The present review discusses the effects of alcohol on lipoproteins in cholesterol transport, as well as the novel effects of lipoproteins on vascular wall cells.

Familial aggregation of blood lipid response to exercise training in the health, risk factors, exercise training, and genetics (HERITAGE) Family Study

BACKGROUND

Fasting levels of plasma lipids and lipoproteins are reported to improve with regular exercise training. However, little is known on whether the training responses are influenced by heritable factors.

METHODS AND RESULTS

The lipid profile was assessed in 115 black (224 individuals) and 99 white families (469 individuals), who participated in the HERITAGE Family Study, while in a sedentary state (baseline visit) and after exercise training for 20 weeks (post visit). Variables included total cholesterol, triglyceride, low-density lipoprotein cholesterol (LDL-C), apolipoprotein B (ApoB), high-density lipoprotein cholesterol (HDL-C), apolipoprotein A-I, and HDL-C subfractions 2 (HDL2-C) and 3 (HDL3-C). Familial correlations for the training responses (Delta=post-baseline) were significant for most variables, and the percent variance accounted for by familial factors (ie, maximal heritabilities) ranged from 25% to 38%. Exceptions were for higher heritabilities near 60% for DeltaApoB in blacks and DeltaHDL2-C in whites and a lower estimate of zero for DeltaLDL-C in blacks.

CONCLUSIONS

Heritable factors in part determine lipid profile responses to regular exercise. Maximal heritabilities were similar across ethnic groups and variables, except for DeltaLDL-C, DeltaApoB, and DeltaHDL2-C. Molecular studies to identify the markers and genes associated with these influences are currently underway.

Physical activity may modulate effects of ApoE genotype on lipid profile

Increased levels of physical activity may improve the lipid profile, but is this effect identical across apolipoprotein E (apoE) genotypes? A population-based cross-sectional survey conducted from 1999 to 2000 included 1708 randomly selected men and women aged 35 to 74 years. A validated physical activity questionnaire measured, for each participant, the total energy expenditure and its percentage used in high-intensity activities (%high-intensity activity), eg, brisk walking and sports. The effects of the apoEx%high-intensity activity interaction on the lipid profile were investigated by using multiple linear regression models. Among men, increased %high-intensity activity had greater protective effects in the apoE4 group regarding (1) high density lipoprotein (HDL) cholesterol (P<0.001), compared with either the apoE2 (interaction P=0.05) or apoE3 (interaction P<0.03) groups, and (2) triglycerides (P<0.03), compared with the apoE3 group (interaction P=0.07). A 10% increase of %high-intensity activity by an apoE4 man would correspond with a 0.07-mmol/L increase in HDL cholesterol and a -0.15-mmol/L decrease in triglycerides. Among women, only the protective effects of physical activity on HDL cholesterol in the apoE4 group versus the apoE2 group was statistically significant. Spending a larger fraction of the total energy expenditure in high-intensity activities may counteract the atherogenic effects of the epsilon4 allele on the lipid profile.

O componente genético da determinação dos lipídeos séricos

Os níveis de lipídeos séricos são características multifatoriais determinadas por um grande número de fatores genéticos e ambientais. A identificação do componente genético dessas características tem sido intensamente investigada nos últimos anos. Esses estudos têm enfocado principalmente polimorfismos nos genes que codificam proteínas estruturais e enzimas relacionadas com o metabolismo de lipídeos. Estudos mais recentes mostraram que o efeito desses polimorfismos depende em parte das interações dos diferentes genótipos com os fatores de risco clássicos tais como tabagismo, sobrepeso ou sedentarismo. A variabilidade encontrada nesses genes parece também influir na resposta a fármacos comumente utilizados no tratamento das hiperlipidemias.

Recent origin and spread of a common Lithuanian mutation, G197del LDLR, causing familial hypercholesterolemia: positive selection is not always necessary to account for disease incidence among Ashkenazi Jews

G197del is the most prevalent LDL receptor (LDLR) mutation causing familial hypercholesterolemia (FH) in Ashkenazi Jew (AJ) individuals. The purpose of this study was to determine the origin, age, and population distribution of G197del, as well as to explore environmental and genetic effects on disease expression. Index cases from Israel (n=46), South Africa (n=24), Russia (n=7), The Netherlands (n=1), and the United States (n=1) were enlisted. All trace their ancestry to Lithuania. A highly conserved haplotype (D19S221:104-D19S865:208-D19S413:74) was identified in G197del chromosomes, suggesting the occurrence of a common founder. When two methods were used for analysis of linkage disequilibrium (LD) between flanking polymorphic markers and the disease locus and for the study of the decay of LD over time, the estimated age of the deletion was found to be 20 +/- 7 generations (the 95% confidence interval is 15-26 generations), so that the most recent common ancestor of the mutation-bearing chromosomes would date to the 14th century. This corresponds with the founding of the Jewish community of Lithuania (1338 a.d.), as well as with the great demographic expansion of AJ individuals in eastern Europe, which followed this settlement. The penetrance of mutation-linked severe hypercholesterolemia is high (94% of heterozygotes have a baseline concentration of LDL cholesterol (LDL-C) that is >160 mg/dl), and no significant differences in the mean baseline lipid level of G197del carriers from different countries were found. Polymorphisms of apolipoprotein E and of scavenger-receptor class B type I were observed to have minor effects on the plasma lipid profile. With respect to determinative genetic influences on the biochemical phenotype, there is no evidence that could support the possibility of a selective evolutionary metabolic advantage. Therefore, the founder effect in a rapidly expanding population from a limited number of families remains a simple, parsimonious hypothesis explaining the spread of G197del-LDLR-linked FH in AJ individuals.