ATP binding cassette G5 C1950G polymorphism may affect blood cholesterol concentrations in humans

Compliance with Nutritional Recommendations and Gut Microbiota Profile in Galician Overweight/Obese and Normal-Weight Individuals

Different research studies have identified specific groups or certain dietary compounds as the onset and progression of obesity and suggested that gut microbiota is a mediator between these compounds and the inflammation associated with pathology. In this study, the objective was to evaluate the dietary intake of 108 overweight (OW), obese (OB), and normal-weight (NW) individuals and to analyze their gut microbiota profile to determine changes and associations with Body Mass Index (BMI) and diet. When individuals were compared by BMI, significant differences in fiber and monounsaturated fatty acids (MUFAs) intake were observed, showing higher adequacy for the NW group. The analysis of gut microbiota showed statistical differences for 18 ASVs; Anaerostipes and Faecalibacterium decreased in the OW/OB group, whereas the genus Oscillospira increased; the genus was also found in the LEFSe analysis as a biomarker for OW/OB. Roseburia faecis was found in a significantly higher proportion of NW individuals and identified as a biomarker for the NW group. Correlation analysis showed that adequation to nutritional recommendation for fiber indicated a higher abundance of Prevotella copri, linearly correlated with F. prausnitzii, Bacteroides caccae, and R. faecis. The same correlation was found for the adequation for MUFAs, with these bacteria being more abundant when the intake was adjusted to or below the recommendations.

From Dietary Cholesterol to Blood Cholesterol, Physiological Lipid Fluxes, and Cholesterol Homeostasis

Dietary cholesterol (C) is a major contributor to the endogenous C pool, and it affects the serum concentration of total C, particularly the low-density lipoprotein cholesterol (LDL-C). A high serum concentration of LDL-C is associated with an increased risk for atherosclerosis and cardiovascular diseases. This concentration is dependent on hepatic C metabolism creating a balance between C input (absorption and synthesis) and C elimination (conversion to bile acids and fecal excretion). The daily C absorption rate is determined by dietary C intake, biliary C secretion, direct trans-intestinal C excretion (TICE), and the fractional C absorption rate. Hepatic C metabolism coordinates C fluxes entering the liver via chylomicron remnants (CMR), LDL, high-density lipoproteins (HDL), hepatic C synthesis, and those leaving the liver via very low-density lipoproteins (VLDL), biliary secretion, and bile acid synthesis. The knowns and the unknowns of this C homeostasis are discussed.

Effects of SNVs in ABCA1, ABCG1, ABCG5, ABCG8, and SCARB1 Genes on Plasma Lipids, Lipoproteins, and Adiposity Markers in a Brazilian Population

Several proteins are involved in cholesterol homeostasis, as scavenger receptor class B type I and ATP-binding cassette (ABC) transporters including ABCA1, ABCG1, ABCG5, and ABCG8. This study aimed to determine the effects of single nucleotide variants (SNVs) rs2275543 (ABCA1), rs1893590 (ABCG1), rs6720173 (ABCG5), rs6544718 (ABCG8), and rs5888 (SCARB1) on plasma lipids, lipoproteins, and adiposity markers in an asymptomatic population and its sex-specific effects. Volunteers (n = 590) were selected and plasma lipids, lipoproteins, and adiposity markers (waist-to-hip and waist-to-height ratios, lipid accumulation product and body adiposity index) were measured. Genomic DNA was isolated from peripheral blood cells according to the method adapted from Gross-Bellard. SNVs were detected in the TaqMan® OpenArray® Real-Time polymerase chain reaction platform and data analyses were performed using the TaqMan® Genotyper Software. The rs2275543*C point to an increase of high-density lipoprotein size in females while in males very-low-density lipoprotein, cholesterol, and triglycerides were statistically lower (P value < 0.05). The rs1893590*C was statistically associated with lower apolipoprotein A-I levels and higher activities of paraoxonase-1 and cholesteryl ester transfer protein (P value < 0.05). The rs6720173 was statistically associated with an increase in cholesterol and low-density lipoprotein cholesterol in males; moreover, rs6544718*T reduced adiposity markers in females (P value < 0.05). Regarding the rs5888, a decreased adiposity marker in the total population and in females occurred (P value < 0.05). Multivariate analysis of variance showed that SNVs could influence components of high-density lipoprotein metabolism, mainly through ABCG1 (P value < 0.05). The ABCA1 and ABCG5 variants showed sex-specific effects on lipids and lipoproteins, while SCARB1 and ABCG8 variants might influence adiposity markers in females. Our data indicate a possible role of ABCG1 on HDL metabolism.

The combination of single nucleotide polymorphisms rs6720173 (ABCG5), rs3808607 (CYP7A1), and rs760241 (DHCR7) is associated with differing serum cholesterol responses to dairy consumption

Existing evidence on the influence of genetic architecture on serum cholesterol responsiveness to dietary interventions focuses on individual single nucleotide polymorphisms and single nutrients. We associated the combination of ABCG5 rs6720173-C, CYP7A1 rs3808607-TT, and DHCR7 rs760241-GG genotypes with lower low-density lipoprotein cholesterol concentrations relative to the combination of rs6720173-GG, rs3808607-G, and rs760241-A genotypes (-0.37 ± 0.12 (n = 9) vs. +0.38 ± 0.14 mmol/L (n = 7), p = 0.0016) following a blended dairy (3 servings/day for 4 weeks) intervention.

Egg consumption and heart health: A review

Cardiovascular disease is the leading cause of death in the United States. Until recently, reducing dietary cholesterol has been a part of the American Heart Association (AHA) and American College of Cardiology (ACC) guidelines on lifestyle management, despite inconclusive evidence to support the recommendation. Considering eggs are a rich source of dietary cholesterol (typically containing 141-234 mg per egg), individuals with increased risk for CVD are advised not to consume eggs. Furthermore, based on the 2012 AHA/ACC guidelines, individuals with lower risk for CVD have previously been advised to avoid consuming eggs due to the high content of dietary cholesterol. Rather than strictly limiting cholesterol intake, the AHA and ACC guidelines now recommend dietary patterns that emphasize fruits, vegetables, whole grains, low-fat dairy products, poultry, fish, and nuts as an approach to favorably alter blood lipid levels. Of note, the 2015-2020 Dietary Guidelines for Americans have removed the recommendation of limiting cholesterol intake to no more than 300 mg per day; however, the guidelines advise that individuals should eat as little dietary cholesterol as possible while consuming a healthy eating pattern. The purpose of this review is to summarize the documented health risks of egg consumption in individuals with low and high risk for CVD and determine whether current recommendations are warranted based on the available literature. We also aim to provide guidance for future studies that will help further elucidate the health modulating effect of eggs.

Common Variants in Cholesterol Synthesis- and Transport-Related Genes Associate with Circulating Cholesterol Responses to Intakes of Conventional Dairy Products in Healthy Individuals

BACKGROUND

Dairy intake has been associated with varying impacts on circulating cholesterol concentrations across nutritional epidemiology and intervention studies, with findings attributed mainly to differences in the nature of dairy products consumed or study designs. The contribution of the genomic architecture to such observations has yet to be revealed.

OBJECTIVE

We assessed the impact of multiple common genetic variations in cholesterol-related genes on responses of serum cholesterol to the recommended amount of dairy product intake in Canada.

METHODS

In a multicenter, randomized crossover design, 101 normolipidemic adults (n = 29 men and 72 women), with a mean ± SD age of 41.7 ± 16.7 y and a body mass index (BMI, in kg/m(2)) of 25.9 ± 4.3 consumed 3 servings/d of dairy [375 mL 1% milk-fat (MF) milk, 175 g 1.5% MF yogurt, and 30 g of 34% MF cheese] or energy-matched control products (juice, cashews, and cookies) provided within a prudent background diet for 4 wk each, separated by a 4- to 8-wk washout period. Serum lipid variables were determined by standard enzymatic methods by using an autoanalyzer. Candidate single nucleotide polymorphisms were assessed by TaqMan genotyping assay.

RESULTS

The responsiveness of serum total cholesterol (TC) and LDL cholesterol to the dairy compared with the control diet was associated with individuals' genotypes. The cholesterol transport gene ATP-binding cassette subfamily G, member 5 (ABCG5) rs6720173-GG homozygotes had higher concentrations of TC (+0.18 mmol/L; P = 0.0118) and LDL cholesterol (+0.17 mmol/L; P = 0.0056) relative to C-allele carriers (-0.07 and -0.06 mmol/L, respectively). The bile acid synthesis gene cholesterol 7α-hydroxylase (CYP7A1) rs3808607-G-allele carriers had higher TC (+0.20 to +0.28 mmol/L; P = 0.0026) and LDL cholesterol (+0.19 mmol/L for GT genotype; P = 0.0260) relative to TT homozygotes (-0.11 and -0.03 mmol/L, respectively). In addition, the cholesterol synthesis gene 7-dehydrocholesterol reductase (DHCR7) rs760241-A-allele carriers had higher LDL cholesterol (+0.26 mmol/L; P = 0.0399) relative to GG homozygotes (+0.06 mmol/L).

CONCLUSION

Genetic variations in ABCG5, CYP7A1, and DHCR7 may contribute to differing responses of serum cholesterol to dairy intake among healthy adults. This trial was registered at clinicaltrials.gov as NCT01444326.

The role of the gut in reverse cholesterol transport--focus on the enterocyte

In the arterial intima, macrophages become cholesterol-enriched foam cells and atherosclerotic lesions are generated. This atherogenic process can be attenuated, prevented, or even reversed by HDL particles capable of initiating a multistep pathway known as the macrophage-specific reverse cholesterol transport. The macrophage-derived cholesterol released to HDL is taken up by the liver, secreted into the bile, and ultimately excreted in the feces. Importantly, the absorptive epithelial cells lining the lumen of the small intestine, the enterocytes, express several membrane-associated proteins which mediate the influx of luminal cholesterol and its subsequent efflux at their apical and basolateral sides. Moreover, generation of intestinal HDL and systemic effects of the gut microbiota recently revealed a direct link between the gut and the cholesterol cargo of peripheral macrophages. This review summarizes experimental evidence establishing that the reverse cholesterol transport pathway which initiates in macrophages is susceptible to modulation in the small intestine. We also describe four paths which govern cholesterol passage across the enterocyte and define a role for the gut in the regulation of reverse cholesterol transport. Understanding the concerted function of these paths may be useful when designing therapeutic strategies aimed at removing cholesterol from the foam cells which occupy atherosclerotic lesions.

ATP-binding cassette transporter G5 and G8 polymorphisms and several environmental factors with serum lipid levels

Background

The association of ATP-binding cassette (ABC) transporter single nucleotide polymorphisms (SNPs) and serum lipid profiles is inconsistent. The present study was undertaken to detect the association of ABCG5/G8 SNPs and several environmental factors with serum lipid levels.

Methodology/Principal Findings

Genotyping of the ABCG5 (rs4131229 and rs6720173) and ABCG8 (rs3806471 and rs4148211) SNPs was performed in 719 unrelated subjects of Mulao nationality and 782 participants of Han nationality. There were no differences in the genotypic and allelic frequencies of four SNPs between the two ethnic groups besides the genotypic frequencies of rs4131229 SNP in Han. The levels of triglyceride (TG), apolipoprotein (Apo) A1, and ApoA1/ApoB ratio (rs4131229); low-density lipoprotein cholesterol (LDL-C) and ApoB (rs6720173); high-density lipoprotein cholesterol (HDL-C), ApoA1, ApoB, and ApoA1/ApoB ratio (rs3806471); and HDL-C, ApoA1, and ApoA1/ApoB ratio (rs4148211) in Han were different among their genotypes (P<0.05–0.001). The levels of LDL-C (rs6720173) and ApoA1 (rs3806471) in Mulao were also different among their genotypes (P<0.05 for each). The levels of TC, TG, HDL-C, ApoA1, and ApoA1/ApoB ratio (rs4131229); LDL-C and ApoB (rs6720173); HDL-C, ApoA1, and ApoA1/ApoB ratio (rs3806471); and TG, HDL-C, ApoA1, and ApoA1/ApoB ratio (rs4148211) in Han males; and ApoA1/ApoB ratio (rs4131229); LDL-C, ApoB, and ApoA1/ApoB ratio (rs3806471); HDL-C, ApoA1, and ApoA1/ApoB ratio (rs4148211) in Han females were different between the genotypes (P<0.05–0.001). The levels of LDL-C in Mulao females were also different between GG and GC/CC genotypes of rs6720173 (P<0.05). The correlation between serum lipid parameters and genotypes of four SNPs was observed in Han, especially in Han males. Serum lipid parameters were also correlated with several environmental factors.

Conclusions

The associations of four ABCG5/G8 SNPs and serum lipid levels are different between the Mulao and Han populations, or between males and females, suggesting that there may be a racial/ethnic- and/or sex-specific association between ABCG5/G8 SNPs and some serum lipid parameters.

Association of ATP binding cassette transporter G8 rs4148217 SNP and serum lipid levels in Mulao and Han nationalities

Background

The association of ATP binding cassette transporter G8 gene (ABCG8) rs4148217 single nucleotide polymorphism (SNP) and serum lipid profiles is still controversial in diverse racial/ethnic groups. Mulao nationality is an isolated minority in China. The aim of this study was to evaluate the association of ABCG8 rs4148217 SNP and several environmental factors with serum lipid levels in the Guangxi Mulao and Han populations.

Methods

A total of 634 subjects of Mulao nationality and 717 participants of Han nationality were randomly selected from our previous samples. Genotyping of the ABCG8 rs4148217 SNP was performed by polymerase chain reaction and restriction fragment length polymorphism combined with gel electrophoresis, and then confirmed by direct sequencing.

Results

The genotypic and allelic frequencies of ABCG8 rs4148217 SNP were different between the two nationalities (P < 0.01 for each), the frequency of A allele was higher in Mulao than in Han. The A allele carriers in Han had lower high-density lipoprotein cholesterol (HDL-C) and apolipoprotein (Apo) A1 levels than the A allele noncarriers (P < 0.05 for each), whereas the A allele carriers in Mulao had lower ApoA1 levels than the A allele noncarriers (P < 0.05). Subgroup analyses showed that the A allele carriers in Han had lower HDL-C and higher triglyceride (TG) levels in females but not in males than the A allele noncarriers (P < 0.05 for each), and the A allele carriers in Mulao had lower ApoA1 levels in females but not in males than the A allele noncarriers (P < 0.05). The levels of TG and HDL-C in Han, and ApoA1 in Mulao were associated with genotypes in females but not in males (P < 0.05-0.01). Serum lipid parameters were also correlated with several environmental factors (P < 0.05-0.001).

Conclusions

The ABCG8 rs4148217 SNP is associated with serum TG, HDL-C and ApoA1 levels in our study populations, but this association is different between the Mulao and Han populations. There is a sex (female)-specific association in both ethnic groups.

Variation and evolution of the ABC transporter genes ABCB1, ABCC1, ABCG2, ABCG5 and ABCG8: implication for pharmacogenetics and disease

The ATP-binding cassette (ABC) transporter genes are ubiquitous in the genomes of all vertebrates. Some of these transporters play a key role in xenobiotic defense and are endowed with the capacity to efflux harmful toxic substances. A major role in the evolution of the vertebrate ABC genes is played by gene duplication. Multiple gene duplication and deletion events have been identified in ABC genes, resulting in either gene birth or gene death indicating that the process of gene evolution is still ongoing in this group of transporters. Additionally, polymorphisms in these genes are linked to variations in expression, function, drug disposition and drug response. Single nucleotide polymorphisms in the ABC genes may be considered as markers of individual risk for adverse drug reactions or susceptibility to complex diseases as they can uniquely influence the quality and quantity of gene product. As the ABC genes continue to evolve, globalization will yield additional migration and racial admixtures that will have far reaching implications for the pharmacogenetics of this unique family of transporters in the context of human health.

Frequencies of four ATP-binding cassette transporter G8 polymorphisms in patients with ischemic vascular diseases

ATP-binding cassette transporter G8 (ABCG8) was found to participate in plant sterol and cholesterol (CHOL) transport; however, the potential associations of ABCG8 genetic variants and ischemic vascular diseases are largely unknown. Determinations of allele frequencies of four common ABCG8 polymorphisms (D19H, Y54C, T400K, and A632V) were carried out in 241 unrelated patients with ischemic stroke, 148 patients with coronary heart disease, and 191 blood donors (controls). Allele frequencies of the investigated polymorphisms in patient groups showed no significant differences compared with controls. There was a tendency toward reduced 54YY-genotype frequency among male patients with stroke. On stratification by age at disease onset, male patients with stroke under the age of 50 (n = 62) showed significantly reduced 54YY-frequency compared with male controls (n = 92; 24.2% vs. 41.3%; odds ratio: 0.45 [95% confidence intervals: 0.22-0.93]; p = 0.038). No such associations were found among women. In healthy controls, CHOL levels of individuals with the 54YY genotype (n = 71; median: 4.51 mM, 25th-75th percentiles: 4.19-5.43) were significantly reduced compared with 54YC and 54CC individuals combined (n = 120; median: 4.95 mM, 25th-75th percentiles: 4.42-5.88, p = 0.009). Further, we identified a new ABCG8-variant, T401S, in a control subject. In conclusion, ABCG8 54YY-genotype may be a potential protecting factor against ischemic stroke in young men and may influence plasma CHOL levels.

ABCG5/G8 polymorphisms and markers of cholesterol metabolism: systematic review and meta-analysis

Genetic variation at the ABCG5/G8 locus has been associated with markers of cholesterol homeostasis. As data originate from small-scale studies, we performed a meta-analysis to study these associations in a large dataset. We first investigated associations between five common ABCG5/G8 polymorphisms (p.Q604E, p.D19H, p.Y54C, p.T400K, and p.A632V) and plasma sterol levels in 245 hypercholesterolaemic individuals. No significant associations were found. Subsequently, our data were pooled into a meta-analysis that comprised 3,364 subjects from 16 studies (weighted mean age, 46.7 ± 10.5 years; BMI, 23.9 ± 3.5 kg/m(2)). Presence of the minor 632V allele correlated with reduced LDL-C concentrations (n = 367) compared with homozygosity for the 632A variant [n = 614; -0.11 mmol/l (95% CI, range: -0.20 to -0.02 mmol/l); P = 0.01]. The remaining polymorphisms were not associated with plasma lipid levels. Carriers of the 19H allele exhibited lower campesterol/TC (n = 83; P < 0.001), sitosterol/TC (P < 0.00001), and cholestanol/TC (P < 0.00001), and increased lathosterol/TC ratios (P = 0.001) compared with homozygous 19D allele carriers (n = 591). The ABCG8 632V variant was associated with a clinically irrelevant LDL-C reduction, whereas the 19H allele correlated with decreased cholesterol absorption and increased synthesis without affecting the lipid profile. Hence, associations between frequently studied missense ABCG5/G8 polymorphisms and markers of cholesterol homeostasis are modest at best.

Hepatic cholesterol transporter ABCG8 polymorphisms in gallstone disease in an Indian population

BACKGROUND AND AIM

Gallstone formation is characterized by the abnormal regulation of cholesterol trafficking and solubilization. The prevalence of gallstone disease (GSD) differs between ethnic groups sharing the common environment. These differences can be explained by a genetic predisposition to gallstone formation. Studies have identified single nucleotide polymorphisms (SNP) D19H and T400K in the cholesterol transporter gene ATP-binding cassette, subfamily G, member 8 (ABCG8) in patients with cholesterol gallstones. The aim of this study was to analyze the relationship between D19H and T400K polymorphisms in the ABCG8 gene and GSD in an Indian population, and the effects of these polymorphisms on cholesterol levels in sera and bile.

METHODS

A total of 226 patients with GSD were analyzed for their lipid profile in plasma and bile. A total of 289 controls were recruited, and their plasma lipid profile was analyzed by standard protocols. The genotype of SNP D19H and T400K of ABCG8 was analyzed in 226 patients and 222 control samples. SNP D19H was analyzed by direct sequencing, and SNP T400K genotyping was assayed by the amplification refractory mutation system-polymerase chain reaction.

RESULTS

There was no significant difference in the allelic distribution of SNP T400K between the GSD and gallstone-free groups (P > 0.05), but the distribution of the SNP variant, D19H, was significantly higher (P = 0.017, odds ratio = 2.274) in patients compared to controls. The analysis of serum and bile cholesterol followed a strong association with genotypes.

CONCLUSION

SNP D19H, but not SNP T400K, in the ABCG8 gene is significantly associated with GSD in an Indian population.

Genetic causes of high and low serum HDL-cholesterol

Plasma levels of HDL cholesterol (HDL-C) have a strong inherited basis with heritability estimates of 40-60%. The well-established inverse relationship between plasma HDL-C levels and the risk of coronary artery disease (CAD) has led to an extensive search for genetic factors influencing HDL-C concentrations. Over the past 30 years, candidate gene, genome-wide linkage, and most recently genome-wide association (GWA) studies have identified several genetic variations for plasma HDL-C levels. However, the functional role of several of these variants remains unknown, and they do not always correlate with CAD. In this review, we will first summarize what is known about HDL metabolism, monogenic disorders associated with both low and high HDL-C levels, and candidate gene studies. Then we will focus this review on recent genetic findings from the GWA studies and future strategies to elucidate the remaining substantial proportion of HDL-C heritability. Comprehensive investigation of the genetic factors conferring to low and high HDL-C levels using integrative approaches is important to unravel novel pathways and their relations to CAD, so that more effective means of diagnosis, treatment, and prevention will be identified.

The potential influence of genetic variants in genes along bile acid and bile metabolic pathway on blood cholesterol levels in the population

The liver is currently known to be the major organ to eliminate excess cholesterol from our body. It accomplishes this function in two ways: conversion of cholesterol molecules into bile acids (BAs) and secretion of unesterified cholesterol molecules into bile. BAs are synthesized in the hepatocytes, secreted into bile and delivered to the lumen of the small intestine where they act as detergents to facilitate absorption of fats and fat-soluble vitamins. About 95% of BAs are recovered in the ileum during each cycle of the enterohepatic circulation. Five percent are lost and replaced by newly synthesized BAs, which amounts to approximately 500 mg/day in adult humans. In contrast to the efficiency of the BAs' enterohepatic circulation, 50% of the 1000 mg of cholesterol secreted daily into bile is lost in feces. It is known that rare human mutations in certain genes in bile acid and bile metabolic pathway influence blood cholesterol levels. With the recent success of genome-wide association studies, we are convinced that common genetic variants also play a role in the genetic architecture of plasma lipid traits. In this review, we summarized the current state of knowledge about genetic variations in bile acid and bile metabolic pathway, and assessed their impact on blood cholesterol levels and cholesterol metabolic kinetics in the population.

Single nucleotide polymorphisms in ABCG5 and ABCG8 genes in Chilean subjects with polygenic hypercholesterolemia and controls

BACKGROUND

The excretion of cholesterol from liver and intestine is regulated by ATP-binding cassette half-transporters ABCG5 and ABCG8. Polymorphisms in their genes have been related to higher levels of plasma lipids. Thus, the aim of the present study was to evaluate the possible association between the 1950C > G (ABCG5) and the 251A > G (ABCG8) polymorphisms and the presence of hypercholesterolemia (HC) in Chilean subjects.

METHODS

A total of 118 non-related individuals with HC (total cholesterol, TC > or = 6.2 mmol/L) and 104 normolipidemic subjects (controls, TC < or = 5.17 mmol/L), aged 18 to 65 years old, were included in this study. The ABCG5 1950C>G and ABCG8 251A>G genotypes were assessed by polymerase chain reaction-restriction fragment length polymorphism.

RESULTS

The genotype distribution of the ABCG5/ABCG8 polymorphisms was in Hardy-Weinberg equilibrium in both groups. The frequency of CC homozygous genotype for ABCG5 1950C > G polymorphism was higher in HC patients than in controls (42% vs. 10%, p < 0.001). On the other hand, no significant differences for the 251A > G polymorphism of the ABCG8 gene were observed (p=NS). Nevertheless, HC subjects carrying the GG genotype for the 251A > G variant exhibited higher values of high-density lipoprotein cholesterol when compared to other genotypes (p=0.020).

CONCLUSIONS

Our data showed that the ABCG5 1950C > G polymorphism is associated with HC in the studied population. Nevertheless, this study is limited by its sample size.

Understanding the nutrigenomic definitions and concepts at the food-genome junction

The marked differences in individual response to dietary factors have led to major controversies in nutrition and puzzled nutrition scientists over the last century. The emerging field of nutrigenomics helps us to understand the basis for some of these differences and also promises us the ability to tailor diet based on individual genetic makeup. Great advances in Human Genome Project, documentation of single nucleotide polymorphisms (SNPs) in candidate genes and their association with metabolic imbalances have gradually added new tests to the nutrigenomic panel. Studies based on ethnopharmacology and phytotherapy concepts showed that nutrients and botanicals can interact with the genome causing marked changes in gene expression. This has led to the commercial development of nutraceuticals and functional foods that can modify negative health effects of individual genetic profile bringing the field to the "food/genome" junction. Despite the promise of nutrigenomics to personalize diet, there is skepticism whether it can truly bring about meaningful modification of the risk factors connected to chronic diseases, due to the lack of large scale nutrition intervention studies. Several intervention studies currently underway in the United States and abroad (Israel, Spain, and France) will further help validate nutrigenomic concepts. France has already introduced a National Nutrition and Health Program to assess nutritional status and risk of major metabolic diseases. As the field(s) related to nutritional genomics advance in their scope, it is essential that: (a) strict guidelines be followed in the nomenclature and definition of the subdisciplines; and (b) the state/federal regulatory guidelines be updated for diagnostic laboratories, especially for those offering tests directly to the public (without a physician's request) to help protect the consumer.

The effects of ABCG5/G8 polymorphisms on plasma HDL cholesterol concentrations depend on smoking habit in the Boston Puerto Rican Health Study

Low HDL-cholesterol (HDL-C) is associated with an increased risk for atherosclerosis, and concentrations are modulated by genetic factors and environmental factors such as smoking. Our objective was to assess whether the association of common single-nucleotide polymorphisms (SNPs) at ABCG5/G8 (i18429G>A, i7892T>C, Gln604GluC>G, 5U145A>C, Tyr54CysA>G, Asp19HisG>C, i14222A>G, and Thr400LysC>A) genes with HDL-C differs according to smoking habit. ABCG5/G8 SNPs were genotyped in 845 participants (243 men and 602 women). ABCG5/G8 (i7892T>C, 5U145A>C, Tyr54CysA>G, Thr400LysC>A) SNPs were significantly associated with HDL-C concentrations (P < 0.001-0.013) by which carriers of the minor alleles at the aforementioned polymorphisms and homozygotes for the Thr400 allele displayed lower HDL-C. A significant gene-smoking interaction was found, in which carriers of the minor alleles at ABCG5/G8 (Gln604GluC>G, Asp19HisG>C, i14222A>G) SNPs displayed lower concentrations of HDL-C only if they were smokers (P = 0.001-0.025). Also, for ABCG8_Thr400LysC>A SNP, smokers, but not nonsmokers, homozygous for the Thr400 allele displayed lower HDL-C (P = 0.004). Further analyses supported a significant haplotype global effect on lowering HDL-C (P = 0.002) among smokers. In conclusion, ABCG5/G8 genetic variants modulate HDL-C concentrations, leading to an HDL-C-lowering effect and thereby a potential increased risk for atherosclerosis only in smokers.

Genetic variation in ABC G5/G8 and NPC1L1 impact cholesterol response to plant sterols in hypercholesterolemic men

ATP-binding cassette hetero-dimeric transporters G5 and G8 (ABCG5/G8) have been postulated to mediate intestinal cholesterol efflux, whereas Niemann-Pick C1 Like 1 (NPC1L1) protein is believed to be essential for intestinal cholesterol influx. The individual or combined genetic markers, such as single nuclear polymorphisms (SNPs), of these two transporter genes may explain inter-individual variations in plasma cholesterol response following plant sterol (PS) intervention. The present study was aimed at investigating the association between ABCG5/G8 and NPC1L1 genotype SNPs with sterol absorption and corresponding plasma concentrations. The study used a 4-week crossover design with 82 hypercholesterolemic men characterized by high vs. low basal plasma PS concentrations consuming spreads with or without 2 g/day of PS. For the ABCG8 1289 C > A (T400 K) polymorphism, the A allele carriers with high basal plasma PS concentrations demonstrated a 3.9-fold greater reduction (p < 0.05) in serum low density lipoprotein cholesterol (LDL-C) than their low basal plasma PS counterparts. For the NPC1L1 haplotype of 872 C > G (L272L) and 3929 G > A (Y1291Y), individuals carrying mutant alleles showed a 2.4-fold greater (p < 0.05) reduction in LDL-C levels, compared to wild type counterparts. Results suggest that genetic and metabolic biomarkers together may predict inter-individual lipid level responsiveness to PS-intervention, and thus could be useful in devising individualized cholesterol lowering strategies.

Polymorphisms in ABCG5/G8 transporters linked to hypercholesterolemia and gallstone disease

ATP-binding cassette (ABC) transporters function in the homeostasis of lipids. Dysfunction of ABC transporters is frequently associated with disease. This review examines links between polymorphisms of ABC G5 (ABCG5) and G8 (ABCG8) transporter genes to hypercholesterolemia and to gallstone disease risk. Various polymorphisms (A632V, T400K, D19H, M429V, and C54Y) in the ABCG8 and ABCG5 (Q604E) gene have been found to be associated with several facets of cholesterol metabolism, including baseline cholesterol level, cholesterol kinetics, individual responsiveness of plasma cholesterol to dietary and pharmaceutical interventions for hypercholesterolemia, and increased risk of gallstones. Clearly, the ABCG5 and ABCG8 genes play an important role in cholesterol homeostasis. However, more research is needed to establish how specific polymorphisms of these genes confer to higher risk of these diseases.

Association between non-responsiveness to plant sterol intervention and polymorphisms in cholesterol metabolism genes: a case-control study

Plant sterol (PS) consumption decreases low-density lipoprotein cholesterol (LDL-C) levels; however, high variability of responsiveness of lipid levels to PS intervention has been observed. We hypothesized that common single-nucleotide polymorphisms (SNPs) in the genes for the ATP binding cassette proteins G5 (ABCG5) and G8 (ABCG8), Niemann-Pick C1-like 1 (NPC1L1), or other proteins of the cholesterol pathway, would underline inter-individual variations in response to PS. Twenty-six hyperlipidemic subjects completed a randomized trial of 3 PS phases and a control phase. Three non-responders were identified who failed on 3 consecutive occasions to decrease either total cholesterol or LDL-C level vs. control. It was observed that after 3 PS phases compared with a control phase, cholesterol absorption changed to a lesser degree (–7.7% ± 10.8%) in the non-responders than in the top 3 responders (–22.1% ± 8.8%); however, cholesterol synthesis rates did not differ between sub-groups. No common polymorphisms in ABCG8, ABCG5, or NPC1L1 were demonstrated between the 3 top responders and the non-responders. Yet, 1 non-responsive subject did demonstrate a rare SNP in NPC1L1. Results indicate PS intake did not decrease cholesterol absorption rates to the same degree in certain subjects, possibly clarifying the inter-individual variability in the cholesterol-lowering effect; hence, this work should be expanded.

Significant association of ABCG8:D19H gene polymorphism with hypercholesterolemia and insulin resistance

The absorption efficiency of cholesterol is closely correlated to dietary phytosterol content and determined by genetic factors. The ATP-binding cassette (ABC) transporters ABCG5 and ABCG8 act as a sterol efflux pump to regulate the absorption of cholesterol and phytosterol. The levels of cholesterol and phytosterol associated with a Chinese diet are very different from those associated with a Western diet. This study aims to explore the association between serum total cholesterol/LDL-C levels and ABCG5/ABCG8 polymorphisms in a Taiwanese population consuming an ordinary Chinese diet. A total of 1,046 subjects (894 men and 152 women) were recruited in a hospital-based health check-up center in Kaohsiung Medical University Hospital. Five nonsynonymous polymorphisms of Q604E (ABCG5), D19H, C54Y, T400 K and A632 V (ABCG8) were analyzed by TaqMan genotyping assay. Analysis showed that the D19H polymorphism of the ABCG8 gene was significantly associated with serum total cholesterol, LDL-C levels and HOMA-IR index. Adjusting for sex and age, subjects with the D19H (GC) genotype were significantly associated with a threefold higher risk of high cholesterol and LDL-C levels than subjects with D19 (GG). These results suggest that the D19H polymorphism of ABCG8 could be considered a susceptible gene marker indicating an increased likelihood of developing high cholesterol and LDL-C levels in Taiwanese consuming an ordinary Chinese diet. It is supposed that the coexistence of higher insulin resistance and hypercholesterolemia for carriers of the D19H polymorphism may result in a greater risk of cardiovascular disease.

Single nucleotide polymorphisms in ABCG5 and ABCG8 are associated with changes in cholesterol metabolism during weight loss

The purpose of this study was to examine whether changes in cholesterol metabolism after weight loss were affected by single nucleotide polymorphisms (SNPs) in ABCG5 and ABCG8 genes. Thirty-five hypercholesterolemic women lost 11.7 +/- 2.5 kg (P < 0.001). Cholesterol kinetics were assessed using stable isotope techniques. TaqMan PCR was used to detect SNPs in ABCG5/G8. Homozygous Q604E variants in ABCG5 had larger (P < 0.05) reductions in cholesterol absorption and greater increases (P < 0.05) in synthesis in contrast to heterozygous and homozygous wild-type carriers. Heterozygous C54Y carriers had smaller declines (P = 0.047) in synthesis compared with homozygous variant individuals. The presence of at least one Y54 variant was associated with higher (P = 0.042) post-weight-loss synthesis compared with carriers of the C54 genotype. The direction of the results is consistent with cross-sectional studies on the effects of Q604E and C54Y polymorphisms on plasma cholesterol. SNPs in ABCG5/G8 were found to be associated with the response of cholesterol metabolism to weight loss. The evidence for associations between SNPs in ABCG5/G8 and various parameters of cholesterol metabolism indicates the potential effectiveness of establishing genetic screening tools to determine optimal lipid-lowering treatment routes for individuals during weight reduction.

Intestinal cholesterol transport proteins: an update and beyond

PURPOSE OF REVIEW

Various studies have delineated the causal role of dietary cholesterol in atherogenesis. Strategies have thus been developed to minimize cholesterol absorption, and cholesterol transport proteins found at the apical membrane of enterocytes have been extensively investigated. This review focuses on recent progress related to various brush-border proteins that are potentially involved in alimentary cholesterol transport.

RECENT FINDINGS

Molecular mechanisms responsible for dietary cholesterol and plant sterol uptake have not been completely defined. Growing evidence, however, supports the concept that several proteins are involved in mediating intestinal cholesterol transport, including SR-BI, NPC1L1, CD36, aminopeptidase N, P-glycoprotein, and the caveolin-1/annexin-2 heterocomplex. Other ABC family members (ABCA1 and ABCG5/ABCG8) act as efflux pumps favoring cholesterol export out of absorptive cells into the lumen or basolateral compartment. Several of these cholesterol carriers influence intracellular cholesterol homeostasis and are controlled by transcription factors, including RXR, LXR, SREBP-2 and PPARalpha. The lack of responsiveness of NPC1L1-deficient mice to ezetimibe suggests that NPC1L1 is likely to be the principal target of this cholesterol-lowering drug.

SUMMARY

The understanding of the role, genetic regulation and coordinated function of proteins mediating intestinal cholesterol transport may lead to novel ways of treating cardiovascular disease.

Similar serum plant sterol responses of human subjects heterozygous for a mutation causing sitosterolemia and controls to diets enriched in plant sterols or stanols

OBJECTIVE

We investigated the serum phytosterol responses of heterozygous relatives of sitosterolemia patients to diets enriched in phytosterols or stanols.

DESIGN

Randomized double-blind crossover design.

SETTING

Muenster, Germany.

SUBJECTS

Eight heterozygous and 13 control subjects were recruited. One heterozygote and three controls dropped out.

INTERVENTIONS

Seven heterozygotes and 10 controls received daily portions of margarine containing 2 g of plant sterols, 2 g of stanols or a control margarine for 6 weeks each in a randomized order. These phases were intercepted by wash-out periods of 6 weeks each.

RESULTS

Compared to the control period, serum phytosterol concentrations increased overall by more than 20% when subjects consumed the plant sterol margarine (F((1,15))=8.719, P=0.01), with no significant difference between heterozygotes (mean +14.5 (s.d. 17.2) micromol/l, +23.0%) and controls (+4.9 (9.9) micromol/l, +20.5%; F((1,15))=2.168, P=0.162), but decreased when subjects consumed the stanol-enriched margarine (F((1,15))=12.124, P=0.003), again to a similar extent in heterozygotes (-34.2 (41.2) micromol/l, -54.2%) and controls (-12.2 (9.2) micromol/l, -50.6%; F((1,15))=2.729, P=0.119). The lowest total serum concentrations of cholesterol and phytosterols were seen after the diet enriched in stanols. Serum stanol concentrations increased on this diet, but on a very low level and never exceeded 0.05% of serum cholesterol levels in any subject.

CONCLUSIONS

Serum phytosterol concentrations increased only moderately in heterozygotes consuming a diet enriched in phytosterols, indicating that they retained considerable capacity to excrete phytosterols even at higher intakes.

Are plasma lipid levels related to ABCG5/ABCG8 polymorphisms? A preliminary study in siblings with gallstones

BACKGROUND

The role of ABCG5 and ABCG8 genes in the determination of plasma lipid levels is currently under intensive investigation. The aim of this study was to evaluate plasma lipid levels in sibling pairs with gallstones and to assess their correlation with common gene polymorphisms in the ABCG5/ABCG8 genes.

METHODS

Plasma levels of cholesterol, HDL-cholesterol, and triglycerides were measured in 68 patients belonging to 34 sibling pairs with gallstones (affected sibling pairs, mean age 56.3 years) and in 68 gallstone carriers with stone-free siblings (age/gender-matched controls in a ratio of 2:1 with the index patients of the study group). Four and one non-synonymous sequence variants in ABCG8 and ABCG5 genes, respectively, were determined in the affected sibling pairs, employing allelic discrimination with 5' nuclease assays.

RESULTS

Plasma triglyceride levels were higher and HDL-cholesterol levels lower in the index patients than in controls. Plasma lipid levels were correlated in the members of the affected sibling pairs. Triglyceride levels were higher in carriers of the common alleles for ABCG5 Q604E and ABCG8 D19H sequence variants, and HDL-cholesterol was lower in carriers of the common alleles for ABCG5 Q604E than in carriers of the rare alleles.

CONCLUSIONS

The significantly different plasma lipid levels in siblings with gallstones versus controls, as well as the correlation of plasma lipids in affected sibling pairs, confirm the genetic influence in gallstone disease. Polymorphisms in ABCG5/ABCG8 genes might contribute to the genetic variation in plasma lipid levels and in cholesterol saturation of the bile.

Plasma Concentrations of Plant Sterols: Physiology and Relationship with Coronary Heart Disease

Recently, it has been questioned whether elevated levels of circulating plant sterols increase the risk of coronary heart disease (CHD). To date, no definitive conclusions regarding such a relationship have been reached, nor have there been any studies summarizing the factors that contribute to the observed elevations in plant sterol concentrations in plasma. Thus, the purpose of this review is to systematically compare the plant sterol levels of subjects from the general population and to describe factors that contribute to the variations observed. The question of whether elevated plasma concentrations of plant sterols are associated with an increased risk of CHD was also assessed. Results indicate that the key factors accounting for variations in circulating plant sterol concentrations include: apolipoprotein E phenotypes, ATP-binding cassette transporter polymorphisms, use of statin drugs, presence of metabolic syndrome, dietary intake of plant sterols, gender, and analytical techniques used in the measurement of plant sterols in the plasma. An analysis of the studies examining the relationship between circulating levels of plant sterols and CHD risk in non-sitosterolemic populations revealed no clear associations. Furthermore, it was shown that the above-mentioned factors play an important role in determining the levels of plant sterols in plasma. Since these factors may act as potential confounders, they must be controlled for before more solid conclusions can be reached.

Cholesterol and saturated fat intake determine the effect of polymorphisms at ABCG5/ABCG8 genes on lipid levels in children

PURPOSE

Analysis of mutations in genes of the cholesterol metabolic pathway has not completely explained the interindividual variability of blood cholesterol concentrations attributed to gene-nutrient interactions. Thus, we analyzed polymorphisms in the ABCG5 and ABCG8 genes, involved in the regulation of intestinal cholesterol absorption, with special interest in a potential interaction with diet to determine lipid levels.

METHODS

The polymorphisms ABCG5 C1950G (Gln604Glu) and ABCG8 C1895T (Ala640Val) were determined by polymerase chain reaction and restriction analysis in 1227 healthy school children, aged 6 to 8 years.

RESULTS

No significant differences were found in blood lipid levels between subjects with different genotypes of the two analyzed polymorphisms. However, important differences appeared when separating subjects by their different lipid intake. The presence of the ABCG8 C1895T and ABCG5 C1950G polymorphisms was associated with different plasma total cholesterol, low-density lipoprotein cholesterol complex, and apolipoprotein B levels only in low-cholesterol consumers (significantly for the C1895T polymorphism), and among children within the lower tertile of saturated fat intake (significantly for the C1950G polymorphism).

CONCLUSION

Polymorphisms at the half-transporter ABCG5 and ABCG8 genes affect blood cholesterol concentrations in prepubertal children by influencing dietary responsiveness. This highly significant gene-nutrient interaction could explain the great individual differences in the plasma lipid response to cholesterol and fat intake.

The ABCG5 polymorphism contributes to individual responses to dietary cholesterol and carotenoids in eggs

The ATP binding cassette G5 (ABCG5) polymorphisms have been postulated to play a role in the response to dietary cholesterol. The objective of this study was to examine the contribution of the ABCG5 polymorphism on the plasma response to consumption of cholesterol and carotenoids from eggs. For this purpose, genotyping was conducted for 40 men and 51 premenopausal women who were randomly assigned to consume an egg (EGG, 640 mg/d additional dietary cholesterol and 600 microg lutein+ zeaxanthin) or placebo (SUB, 0 mg/d cholesterol, 0 microg lutein + zeaxanthin) diet for 30 d. The two arms of the dietary intervention were separated by a 3-wk washout period. Plasma concentrations of total cholesterol, LDL cholesterol (LDL-C), and HDL cholesterol were determined. Because eggs are an excellent source of lutein and zeaxanthin, the plasma levels of these carotenoids were also measured in a subset of subjects to determine whether the response to carotenoid intake was similar to that seen for dietary cholesterol and to evaluate the contribution of ABCG5 polymorphism to both responses. Individuals possessing the C/C genotype experienced a greater increase in both LDL-C (P < 0.05) and a trend for lutein (P = 0.08) during the EGG period compared with those individuals with the C/G (heterozygote) or G/G genotypes (homozygotes). These results, although obtained from a small number of subjects, suggest that the ABCG5 polymorphism may play a role in the plasma response to dietary cholesterol and carotenoids.

A detailed Hapmap of the Sitosterolemia locus spanning 69 kb; differences between Caucasians and African-Americans

Background

Sitosterolemia is an autosomal recessive disorder that maps to the sitosterolemia locus, STSL, on human chromosome 2p21. Two genes, ABCG5 and ABCG8, comprise the STSL and mutations in either cause sitosterolemia. ABCG5 and ABCG8 are thought to have evolved by gene duplication event and are arranged in a head-to-head configuration. We report here a detailed characterization of the STSL in Caucasian and African-American cohorts.

Methods

Caucasian and African-American DNA samples were genotypes for polymorphisms at the STSL locus and haplotype structures determined for this locus

Results

In the Caucasian population, 13 variant single nucleotide polymorphisms (SNPs) were identified and resulting in 24 different haplotypes, compared to 11 SNPs in African-Americans resulting in 40 haplotypes. Three polymorphisms in ABCG8 were unique to the Caucasian population (E238L, INT10-50 and G575R), whereas one variant (A259V) was unique to the African-American population. Allele frequencies of SNPs varied also between these populations.

Conclusion

We confirmed that despite their close proximity to each other, significantly more variations are present in ABCG8 compared to ABCG5. Pairwise D' values showed wide ranges of variation, indicating some of the SNPs were in strong linkage disequilibrium (LD) and some were not. LD was more prevalent in Caucasians than in African-Americans, as would be expected. These data will be useful in analyzing the proposed role of STSL in processes ranging from responsiveness to cholesterol-lowering drugs to selective sterol absorption.

Identification, Sequence Analysis and mRNA Tissue Distribution of the Bovine Sterol Transporters ABCG5 and ABCG8

The family of ATP-binding cassette (ABC) transporters consists of several transmembrane proteins that use ATP hydrolysis as an energy source for the transport of a variety of substances through cellular membranes. Two members of this family, ABCG5 and ABCG8, are implicated in the intestinal absorption and biliar excretion of sterols. Cholesterol content in milk is highly variable among species, breeds, and individuals of the same species, but a potential application of these genes in lipid homeostasis in the mammary gland has never been addressed. In the present work, expression of ABCG5 and ABCG8 in the bovine was demonstrated for the first time and characterized by quantitative PCR. The entire coding region and promoter area were sequenced and screened for motifs involved in lipid homeostasis. Both ABCG5 and ABCG8 presented a high level of length and sequence identity with other mammalian species. In the intergenic promoter region, 2 GATA boxes, a liver receptor homolog-1 response element, and a nuclear factor-kappaB response element, important factors in other lipid regulatory processes, were identified. As expected, high expression levels of both ABCG5 and ABCG8 were present in liver and digestive tract samples, and interestingly, in the mammary gland, opening new avenues for further investigation about their potential role in lipid trafficking and excretion during lactation.

Dietary cholesterol provided by eggs and plasma lipoproteins in healthy populations

PURPOSE OF REVIEW

Extensive research has not clearly established a link between egg consumption and risk for coronary heart disease. The effects of egg intake on plasma lipids and low-density lipoprotein (LDL) atherogenicity in healthy populations need to be addressed.

RECENT FINDINGS

The lack of connection between heart disease and egg intake could partially be explained by the fact that dietary cholesterol increases the concentrations of both circulating LDL and high-density lipoprotein (HDL) cholesterol in those individuals who experience an increase in plasma cholesterol following egg consumption (hyperresponders). It is also important to note that 70% of the population experiences a mild increase or no alterations in plasma cholesterol concentrations when challenged with high amounts of dietary cholesterol (hyporesponders). Egg intake has been shown to promote the formation of large LDL, in addition to shifting individuals from the LDL pattern B to pattern A, which is less atherogenic. Eggs are also good sources of antioxidants known to protect the eye; therefore, increased plasma concentrations of lutein and zeaxanthin in individuals consuming eggs are also of interest, especially in those populations susceptible to developing macular degeneration and eye cataracts.

SUMMARY

For these reasons, dietary recommendations aimed at restricting egg consumption should not be generalized to include all individuals. We need to acknowledge that diverse healthy populations experience no risk in developing coronary heart disease by increasing their intake of cholesterol but, in contrast, they may have multiple beneficial effects by the inclusion of eggs in their regular diet.

No genetic association between ATP binding cassette proteins and Japanese sporadic Alzheimer's disease

The identification of the epsilon4 variant of apolipoprotein E as a genetic risk factor for late-onset Alzheimer's disease (AD) suggests that cholesterol may play a direct role in the pathogenesis of the disease. Recent studies have suggested that the ATP-binding cassette (ABC) protein G5 (ABCG5) may be involved in the regulation of intestinal cholesterol absorption. Furthermore, genetic variation of this locus may affect blood cholesterol concentrations. We therefore studied whether the ABCG5 C1950G (Gln640Glu) polymorphism affects the risk of AD. In addition, there was no difference in mean baseline cholesterol concentrations between individuals with the C/C genotype and carriers of the G allele. Recent studies have shown that genetic regions including the ABCA12 gene might also be associated with the risk of AD. The ABCA12 gene, located <1 Mb from the peak marker on chromosome 2q34, is also a member of the ABC transporter superfamily. In the current study, two common polymorphisms of the ABCA12 gene, rs952718 (T/G) and rs956133 (A/G), were analyzed in our subjects. These polymorphisms showed no association with the risk of AD. Furthermore, we observed weak linkage disequilibrium between these two single nucleotide polymorphisms. These results indicate that the common polymorphisms of the ABCG5 and ABCA12 genes investigated here are not associated with AD.

Single nucleotide polymorphisms modify the transporter activity of ABCG2

Single nucleotide polymorphism (SNP) analyses of the ABCG2 gene have revealed three nonsynonymous SNPs resulting in the amino acid changes at V12M, Q141K and D620N. To determine whether the SNPs have an effect on drug transport, human embryonic kidney cells (HEK-293) were stably transfected with full length ABCG2 coding wild-type or SNP variants of ABCG2. In 4-day cytotoxicity assays with mitoxantrone, topotecan, SN-38 or diflomotecan, cells transfected with wild-type R482 ABCG2 showed IC50 values up to 1.2-fold to 5-fold higher than cells expressing comparable levels of Q141K ABCG2, suggesting that the Q141K SNP affects drug transport. FTC-inhibitable mitoxantrone efflux normalized to ABCG2 surface expression as assayed by the anti-ABCG2 antibody 5D3 was significantly lower in cells transfected with Q141K ABCG2 than in those transfected with wild-type R482 ABCG2 (P = 0.0048). Values for V12M and D620N ABCG2 were comparable to those for wild-type R482 ABCG2. The vanadate-sensitive ATPase activity of ABCG2 was assayed in Sf9 insect cells infected with wild-type or SNP variants of ABCG2. Basal ATPase activity in cells transfected with Q141K ABCG2 was 1.8-fold lower than in cells transfected with wild-type ABCG2, but was comparable among cells expressing wild-type, V12M or D620N ABCG2. Confocal studies of ABCG2 localization revealed higher intracellular staining in the Q141K transfectants than in cells transfected with wild-type or V12M ABCG2. Decreased transport of Hoechst 33342 was observed in Sf9 cells expressing V12M ABCG2; however, this was not true in HEK-293 cells expressing V12M ABCG2. These results suggest that the Q141K SNP affects the transport efficiency of ABCG2 and may result in altered pharmacokinetics or drug-resistance profiles in clinical oncology.

Common sequence variations in ABCG8 are related to plant sterol metabolism in healthy volunteers

Polymorphisms in the ATP binding cassette (ABC) transporters ABCG5 and ABCG8 are related to plasma plant sterol concentrations. It is not known whether these polymorphisms are also associated with variations in serum plant sterol concentrations during interventions affecting plant sterol metabolism. We therefore decided to study changes in serum plant sterol concentrations with ABCG5/G8 polymorphisms after consumption of plant stanol esters, which decrease plasma plant sterol concentrations. Cholesterol-standardized serum campesterol and sitosterol concentrations were significantly associated with the ABCG8 T400K genotype, as were changes in serum plant sterol concentrations after consumption of plant stanols. The reduction of -57.1 +/- 38.3 10(2) x micromol/mmol cholesterol for sitosterol in TT subjects was significantly greater compared with the -36.0 +/- 18.7 reduction in subjects with the TK genotype (P = 0.021) and the -16.9 +/- 13.0 reduction in subjects with the KK genotype (P = 0.047). Changes in serum campesterol concentrations showed a comparable association. No association with serum LDL cholesterol was found. Genetic variation in ABCG8 not only explains cross-sectional differences in serum plant sterol concentrations but also determines a subject's responsiveness to changes in serum plant sterols during interventions known to affect plant sterol metabolism.

Sterol transporters: targets of natural sterols and new lipid lowering drugs

Recent insights in the role of ATP-binding cassette (ABC) transporters ABCG5 and ABCG8, the discovery of ezetimibe, the first approved direct cholesterol absorption inhibitor, as well as the identification of Niemann-Pick C1 Like 1 (NPC1L1) protein as sterol transporter in the gut, focused attention on sterol transport processes in the small intestine and the liver. The identification of defective structures in the ABCG5 or ABCG8 transporters in patients with the rare disease of sitosterolemia elucidated their role as sterol efflux pumps regulating at least in parts the intestinal sterol absorption and the hepatic sterol output. ABCG5 and ABCG8 themselves are regulated by cholesterol via liver X receptors (LXRs), which are also activated by oxysterols and some derivatives of plant sterols. NPC1L1 could recently be identified as a major sterol transporter for the intestinal uptake of cholesterol as well as plant sterols. Studies in NPC1L1 knockout mice indicate that this transporter is essential for the intestinal uptake of sterols and that NPC1L1 might also be involved in the mechanism of action of ezetimibe. However, studies with photoreactive cholesterol as well as with photoreactive ezetimibe analogues suggest that other processes might also be involved in the mechanism of action of ezetimibe.

Primary hypercholesterolemia: genetic causes and treatment of five monogenic disorders

Coronary heart disease is a major cause of death in Europe and the USA. Insudation of atherogenic lipoproteins, including low-density lipoprotein (LDL), into the artery wall is integral to atherosclerosis. It is clear that numerous genetic loci contribute to increased plasma levels of LDL. However, five specific monogenic disorders, three of which have been reported recently, are known to increase LDL. These are familial hypercholesterolemia (LDL receptor gene: LDLR); familial ligand-defective apoB- 100 (apoB gene: APOB); autosomal recessive hypercholesterolemia (ARH gene); sitosterolemia (ABCG5 or ABCG8 genes) and cholesterol 7alpha-hydroxylase deficiency (CYP7A1 gene). This review relates the mechanisms underlying these five disorders with specific therapeutic interventions.

Plant sterols: factors affecting their efficacy and safety as functional food ingredients

Plant sterols are naturally occurring molecules that humanity has evolved with. Herein, we have critically evaluated recent literature pertaining to the myriad of factors affecting efficacy and safety of plant sterols in free and esterified forms. We conclude that properly solubilized 4-desmetyl plant sterols, in ester or free form, in reasonable doses (0.8-1.0 g of equivalents per day) and in various vehicles including natural sources, and as part of a healthy diet and lifestyle, are important dietary components for lowering low density lipoprotein (LDL) cholesterol and maintaining good heart health. In addition to their cholesterol lowering properties, plant sterols possess anti-cancer, anti-inflammatory, anti-atherogenicity, and anti-oxidation activities, and should thus be of clinical importance, even for those individuals without elevated LDL cholesterol. The carotenoid lowering effect of plant sterols should be corrected by increasing intake of food that is rich in carotenoids. In pregnant and lactating women and children, further study is needed to verify the dose required to decrease blood cholesterol without affecting fat-soluble vitamins and carotenoid status.

ATP binding cassette transporter G5 and G8 genotypes and plasma lipoprotein levels before and after treatment with atorvastatin

The mechanisms responsible for interindividual variation in response to statin therapy remain uncertain. It has been shown that hepatic cholesterol synthesis is associated with ATP binding cassette transporter G5 and G8 (ABCG5/8) activities. To test the hypothesis that genetic variation in ABCG5/8 might influence the plasma lipid response to statin therapy, we examined five nonsynonymous polymorphisms at the ABCG5/8 loci (Q604E, D19H, Y54C, T400K, and A632V) in 338 hypercholesterolemic patients treated with 10 mg atorvastatin. In carriers of the D19H variant, means of posttreatment values and adjusted percent reductions in LDL cholesterol (LDLC) were significantly lower (P = 0.028) and greater (P = 0.036) (112 mg/dl, 39.7%) than those of noncarriers (119 mg/dl, 36.2%), respectively, while no significant difference was observed in percent reductions in total cholesterol. Stepwise multiple regression analysis revealed significant and independent associations with absolute or percent reduction between D19H genotype and posttreatment LDL cholesterol levels. The other polymorphisms were not significantly associated with treatment effects. These results suggest that, in patients with hypercholesterolemia, the ABCG8 D19H variant is associated with greater LDLC-lowering response to atorvastatin therapy.

ABCG5 and ABCG8 are expressed in gallbladder epithelial cells

Gallbladder epithelial cells (GBEC) are exposed to high biliary cholesterol concentrations on their apical (AP) surface. The mechanisms of cholesterol absorption and efflux by these cells are not known. We hypothesized that ABCG5 and ABCG8 are expressed in GBEC and mediate AP cholesterol efflux. Human gallbladder cDNA expressed message for ABCG5 and ABCG8. Cultured murine GBEC also expressed abcg5 and abcg8 mRNA and protein, as did cultured canine GBEC. Interestingly, treatment with model bile containing supersaturating concentrations of cholesterol, or treatment with LXRalpha/RXR ligands, did not lead to differences in expression of ABCG5 or ABCG8 in the murine or the canine cells. The subcellular localization of ABCG5 and ABCG8 did show alterations, with predominantly intracellular localization at baseline and predominantly AP localization following treatment with model bile or LXRalpha ligand. GBEC therefore express ABCG5 and ABCG8; these sterol transporters may play a role in mediating AP cholesterol efflux in the gallbladder epithelium.

Sitosterolemia: a gateway to new knowledge about cholesterol metabolism

Sitosterolemia (OMIM 210250) is a rare, autosomal recessive lipid disorder initially described almost 30 years ago. The disease is characterized by elevated plasma levels of plant sterols due to increased intestinal absorption and reduced biliary secretion of neutral sterols. Patients with sitosterolemia are frequently hypercholesterolemic, and develop xanthomas and premature coronary heart disease (CHD). Hemolysis, arthralgias and arthritis are also frequently associated with the disorder. Recently, sitosterolemia has been revealed to be due to mutations in either of the two ATP-binding cassette (ABC) half-transporters. ABCG5 or ABCG8. These two genes are expressed almost exclusively in the liver and intestine, and are co-regulated by the nuclear hormone receptor, liver X receptor (LXR). Genetically modified mice, which express either high levels or no ABCG5 and ABCG8 have been developed. Analyses of these mice confirm that these two transporters play key roles in regulating the absorption of dietary and biliary sterols, and in mediating the excretion of neutral sterols from the liver to the bile. The elucidation of the gene defects responsible for sitosterolemia provides potential therapeutic targets for the treatment of hyperlipidemias in the general population.