Apolipoprotein E genotype and response of lipid levels to postmenopausal estrogen use

Role of estrogen in women's Alzheimer's disease risk as modified by APOE

Alzheimer's disease (AD) is characterized by numerous sexual dimorphisms that impact the development, progression, and probably the strategies to prevent and treat the most common form of dementia. In this review, we consider this topic from a female perspective with a specific focus on how women's vulnerability to the disease is affected by the individual and interactive effects of estrogens and apolipoprotein E (APOE) genotype. Importantly, APOE appears to modulate systemic and neural outcomes of both menopause and estrogen-based hormone therapy. In the brain, dementia risk is greater in APOE4 carriers, and the impacts of hormone therapy on cognitive decline and dementia risk vary according to both outcome measure and APOE genotype. Beyond the CNS, estrogen and APOE genotype affect vulnerability to menopause-associated bone loss, dyslipidemia and cardiovascular disease risk. An emerging concept that may link these relationships is the possibility that the effects of APOE in women interact with estrogen status by mechanisms that may include modulation of estrogen responsiveness. This review highlights the need to consider the key AD risk factors of advancing age in a sex-specific manner to optimize development of therapeutic approaches for AD, a view aligned with the principle of personalized medicine.

Evaluation of UGT1A1 and SULT1A1 polymorphisms with lipid levels in women with different hormonal status

BACKGROUND

Estrogens influence many physiological processes including cardiovascular health. Polymorphisms in phase I and II estrogen metabolism enzymes are associated with lipid levels in women.

METHODS

A cross-sectional study was carried out with 269 postmenopausal women, 116 who received oral hormonal therapy (HT) (39-75 years) with estrogens or estrogens plus progestagen, 153 that did not receive any HT (38-85 years), and 155 premenopausal women (18-52 years). Polymorphisms in UGT1A1 (rs5839491) and SULT1A1 (rs1042028) were analysed by PCR-based methods. Adjusted lipid levels means were compared among genotypes by one-way analysis of variance, with corrections for multiple testing.

RESULTS

The UGT1A1*28 polymorphism was associated with total cholesterol (T-chol) (p = 0.030; corrected p = 0.060) and low-density lipoprotein cholesterol (LDL-C) levels (p = 0.011, corrected p = 0.022) in premenopausal women. The premenopausal and postmenopausal women, both carriers of SULT1A1*2/*2, had lower levels of T-chol and LDL-C means than carriers of the SULT1A1*1/*1 (p = 0.004, corrected p = 0.008 and 0.009, corrected p = 0.018, respectively).

CONCLUSION

The data showed the presence of an association between the UGT1A1*28/*28 and SULT1A1*2/*2 and T-chol and LDL-C levels in women with different hormonal status. No previous studies investigated the association of the polymorphisms examined in this study with lipoprotein levels in women separately by hormonal status.

Effects of apolipoprotein E genotype on blood cholesterol in adolescent girls

BACKGROUND

Few investigations have examined whether associations between the apolipoprotein E genotype (apo E) and total cholesterol or LDL-C are modified or explained by other characteristics. The objective of this study was to explore effects of behavioral characteristics, physical growth, body composition, sexual maturation, and endocrine function on age trajectories of total cholesterol and LDL-C by apo E in adolescent girls.

METHODS

Participants were 247 Caucasian adolescent girls followed for 4 years. Apo E genotyping and plasma lipid concentrations were determined from fasting blood samples using standard enzymatic methods. Age; gender; fat-free mass (FFM); BMI; percent body fat (PBF); sexual maturation (pubic hair, Tanner Stages 1-5); estradiol concentration (EST); energy intake; and physical activity were collected or calculated with standard methods.

RESULTS

In models including the proposed explanatory variables, apo E genotype remained strongly associated with total cholesterol and LDL-C. Girls with the epsilon (epsilon)3/3 and epsilon3/4 genotypes (where epsilon is the protein isoform of the apo E gene), relative to those with epsilon2/3, had total cholesterol and LDL-C values 16-23 mg/dL higher throughout adolescence. Age-apo E interaction terms remained significant. FFM, BMI, PBF, pubic-hair stage, and EST showed a significant effect on total cholesterol and LDL-C. When the combination of pubic-hair stage, EST, and one of FFM, BMI, and PBF was included in total cholesterol or LDL-C models, only EST was significant.

CONCLUSIONS

Adolescent girls with epsilon3/3 and epsilon3/4 genotypes had higher total cholesterol and LDL-C and showed different patterns of change, compared to those with epsilon2/3 genotype. These apo E effects were independent of behavioral characteristics, physical growth, body composition, sexual maturation, and endocrine function. Girls with epsilon3/3 or epsilon3/4 genotypes may be at risk for elevated total cholesterol and LDL-C later in life.

Gene by sex interaction in the etiology of coronary heart disease and the preceding metabolic syndrome

BACKGROUND

Despite decades of research, the genetic basis of coronary heart disease and its metabolic risk factors is poorly understood. Few studies consider that sex may modify the effect of gene variants on disease. Investigation of gene by sex interaction may help to elucidate underlying genetic susceptibilities and explain the sexual dimorphism of these complex traits.

AIMS

The aim of this review is to summarize evidence for gene by sex interaction in the etiology of coronary heart disease and the metabolic syndrome.

DATA SYNTHESIS

Published literature was examined in the areas of familial aggregation of coronary heart disease; heritability of body mass, insulin resistance, hypertension and dyslipidemia; genome-wide linkage analysis in humans and rodents; and large-scale genetic association studies. Possible mechanisms of gene by sex interaction are discussed including X-linked inheritance, confounding by risk factors and the effect of sex hormones.

CONCLUSIONS

The strongest evidence for gene by sex interaction in relation to coronary heart disease and the metabolic syndrome is in the etiology of body mass, insulin resistance and possibly dyslipidemia. Genetic studies of these traits would benefit from taking sex differences into account. Alternative mechanisms underlying gene by sex interaction, besides obvious sex hormone differences, should be considered.

Do long-term HDL-C declines associated with a first birth vary by apo E phenotype? The Coronary Artery Risk Development in Young Adults (CARDIA) study

BACKGROUND

High-density lipoprotein cholesterol (HDL-C) levels in premenopausal and postmenopausal women are differentially affected by exogenous sex hormones depending on their apolipoprotein E (apo E) genotype. Because endogenous sex hormones markedly increase during pregnancy, we examined whether HDL-C declines after a first birth varied by apo E polymorphisms.

METHODS

In 1147 nulliparas (416 black, 731 white), fasting blood samples (nonpregnant) were drawn at baseline and at follow-up years 5, 7, and 10. Time-dependent pregnancy groups included 0 pregnancies (P0), 1+ short pregnancy (P1+), 1 birth (B1), 2 or more births (B2+). ApoE groups by alleles identified with a phenotype method included E4 (4/3 and 4/4), E3 (3/3), and E2 (2/2 and 3/2). Differences in adjusted mean HDL-C changes among pregnancy groups and ApoE groups were examined using repeated measures multiple linear regression.

RESULTS

HDL-C declines associated with parity (one or more births) depended on ApoE group (ApoE*Pregnancy Interaction; p < 0.002). For B1 and B2+ vs. P0, HDL-C declines were -2.4 to -2.7 mg/dl in E4 and -3.4 to -4.1 mg/dl in E3. In E2, HDL-C declines were -6.6 mg/dl for one birth, and -11.5 mg/dl for two or more births, each relative to the 0 pregnancies (P0) group (linear trend, p < 0.001).

CONCLUSIONS

The degree to which childbearing adversely affects long-term HDL-C declines varies by apo E phenotype, based on a method that accurately classifies genotype. Our findings show that 2/2 and 3/2 genotypes are associated with larger parity-related HDL-C declines than 3/3, 4/3, and 4/4 genotypes.

ESR1 and APOE gene polymorphisms, serum lipids, and hormonal replacement therapy

OBJECTIVES

The risks and benefits of hormone replacement therapy (HRT) are, at least in part, mediated by the metabolic individuality of women. Therefore, we investigated the association between polymorphisms at the estrogen receptor 1 gene (ESR1) and at the apolipoprotein E gene (APOE) with lipid and lipoprotein levels in order to verify whether these concentrations are modulated by these gene variants in women with different hormonal status.

METHODS

One hundred and eighteen postmenopausal women using oral HRT with estrogen or estrogen plus progestagen (HRT+, mean age=56+/-6.7 years, 39-75 years) and 167 postmenopausal women that were not on HRT (HRT-, mean age=58+/-9.8 years, 38-85 years) participated in the study. The polymorphisms were genotyped by PCR-RFLP methods.

RESULTS

No significant effect of ESR1 genotypes or haplotypes and ESR1*HRT interactions were detected on lipid levels in two-way analysis of variance. Postmenopausal women HRT nonusers carriers of the APOE*4 allele had higher T-chol and LDL-C levels than postmenopausal women HRT nonusers carriers of the APOE*3 and APOE*2 allele. T-chol and LDL-C concentrations in postmenopausal users of HRT that were APOE*4 carriers were similar to those in postmenopausal women nonusers of HRT homozygotes for APOE*3 and APOE*2 carriers. A significant APOE*4/HRT interaction was detected on T-chol and LDL-C levels by multiple regression analysis.

CONCLUSION

The results from this study suggest that the HRT influence on T-chol and LDL-C levels is modulated by APOE isoforms but not by ESR1 polymorphisms.

Apolipoprotein E polymorphism in Saudis

Apolipoprotein E (apoE) genotypes were determined in 165 Saudis. The prevalence of genotype, E3/E3, E3/E4 and E4/E4 was found to be 71, 27 and 2% respectively. The E3/E3 was the most prevalent genotype among the Saudis followed by E3/E4. However, other genotypes E2/E2, E2/E3 and E2/E4 were absent showing the absence of E2 allele in the test population. The high frequencies of the E3 allele (0.845) and E3/E3 genotype (0.71) and absence of E2 allele in Saudis under study are similar to those reported earlier for Native Americans, Mexican-Americans, Mayans, Cayapa, Mazatecan Indians and Mexican Mestizos populations.

Modification of the effects of estrogen therapy on HDL cholesterol levels by polymorphisms of the HDL-C receptor, SR-BI: the Rancho Bernardo Study

BACKGROUND

Previous studies have found polymorphisms of the HDL receptor, SR-BI, to be associated with plasma HDL-C in women, but not men, suggesting a modifying role of estrogen. We examined whether the association between SR-BI genotypes and HDL-C is modified by use of unopposed estrogen in community-dwelling postmenopausal Caucasian women.

METHODS

Common polymorphisms in Intron5 and Exon8 of the SR-BI gene were evaluated in 689 women from the Rancho Bernardo Study. Multiple linear regression analysis was carried out adjusting for confounders.

RESULTS

HDL-C levels did not differ significantly by genotype in the aggregate population. However, significant interaction was found between estrogen use and Exon8 (p=0.03), Intron5 (p=0.03) and Intron5/Exon8 diplotypes (p=0.01). SR-BI genotype was associated with HDL-C levels only among estrogen users (p=0.05) and explained 5.3% of the variance in HDL-C in this group. Consistent with prior studies, individuals heterozygous at both Intron5 and Exon8 loci had the lowest HDL-C levels. Among women with symptomatic CHD, the interaction between estrogen use and SR-BI genotype became even stronger.

CONCLUSIONS

The effect that unopposed estrogen use has on HDL-C may depend on a woman's SR-BI genotype.

Estrogen receptor 2 and progesterone receptor gene polymorphisms and lipid levels in women with different hormonal status

Sex steroid hormones have multiple effects on lipid metabolism. We investigated the association between two common single nucleotide polymorphisms of the estrogen receptor 2 gene (ESR2), 1082G>A and 1730A>G, and PROGINS polymorphism of the progesterone receptor gene (PGR) with lipoprotein levels in a cross-sectional study with 472 women of European descent. The women were classified into three subgroups according to hormonal status, premenopausal women (n=187; mean age=34+/-9.7 years), postmenopausal women exposed to hormone replacement therapy (HRT) (n=118; 56+/-6.7 years) and postmenopausal women unexposed to HRT (n=167; 58+/-9.8 years). The premenopausal and postmenopausal women exposed to HRT, both carriers of G/A genotype, exhibited LDL-C (P=0.027 and 0.001, respectively) and T-chol levels (P=0.035 and 0.001, respectively) lower than carriers of G/G genotype. This association was not observed in postmenopausal women unexposed to HRT. These results suggest that ESR2 1082G>A genotype may influence LDL-C levels in women with abundant estrogen levels, due to either endogenous or exogenous sources.

Apolipoprotein and apolipoprotein receptor genes, blood lipids and disease

PURPOSE OF REVIEW

Apolipoproteins and their receptors are the main controllers of lipid metabolism and, as such, have a major impact not only on the risk of cardiovascular disease but also on the development and degeneration of the central nervous system. Variations in the genes coding for these apolipoproteins and their receptors and the interaction with the environment determine individual susceptibility to metabolic disturbances, the response to dietary or pharmacological intervention and, finally, to disease.

RECENT FINDINGS

This review will focus on recent findings, such as the latest concepts regarding apolipoprotein E in neurodevelopment, the newly identified apolipoprotein A-V and its influence in triglyceride metabolism, and the improved understanding of apolipoprotein A-I and HDL metabolism in the light of the discovery of the ABC family of transporters. Other key aspects of lipoprotein metabolism and cardiovascular disease risk such as apolipoprotein B-100, the LDL receptor, apolipoprotein C-III or apolipoprotein (a) will be updated.

SUMMARY

Variations in these genes will be analysed in relation to plasma lipid levels, their interactions with diet, treatment or other environmental stimuli, and their influence on the risk of cardiovascular disease and neurological disorders.