Lifestyle factors affecting intrapair differences of serum apoproteins and cholesterol concentrations in adult identical twins

Ethanol-mediated upregulation of APOA1 gene expression in HepG2 cells is independent of de novo lipid biosynthesis

BACKGROUND

Moderate alcohol intake in human increases HDL-cholesterol, and has protective effects against cardiovascular disease (CVD). Although de novo lipid synthesis inhibitors are highly effective in lowering total and LDL-cholesterol they have only modest effects on raising HDL-C. A better understanding of the mechanism of ethanol-mediated HDL-C regulation could suggest new therapeutic approaches for CVD.

METHODS

Human hepatoblastoma (HepG2) and colorectal epithelial adenocarcinoma (Caco-2) cells were incubated in the presence of varying concentrations of ethanol in the culture medium, with or without addition of de novo lipid synthesis (DNLS) inhibitors (atorvastatin and/or TOFA). ApoA1 protein was measured by Western blot, and RNA of lipid pathway genes APOA1, APOC3, APOA4, APOB100, HMGCR, LDLR, and SREBF2 by quantitative RT-PCR. Lipoproteins (VLDL, LDL, and HDL) and lipids were also monitored.

RESULTS

Ethanol stimulated ApoA1 protein (both cytoplasmic and secreted) and APOA1 RNA levels in HepG2 cells in a dose sensitive way, with ~ 50% upregulation at 100 mM ethanol in the medium. The effect was not observed in intestinal-derived Caco-2 cells. DNLS inhibitors did not block the upregulation of ApoA1 RNA by ethanol; TOFA alone produced a modest increase in ApoA1 RNA. Ethanol had no effect on ABCA1 protein levels. Addition of ethanol to the cell medium led to modest increases in de novo synthesis of total cholesterol, cholesteryl esters and triglycerides, and as expected these increases were blocked when the lipid synthesis inhibitors were added. Ethanol stimulated a small increase in HDL and VLDL but not LDL synthesis. Ethanol in the cell medium also induced modest but measurable increases in the RNA of APOC3, APOA4, APOB, LDLR, and HMGCR genes. Unlike APOA1, induction of RNA from APOC3 and APOA4 was also observed in Caco-2 cells as well as HepG2 cells.

CONCLUSION

This study has verified the previously reported upregulation of APOA1 by exposure of HepG2, but not Caco-2 cells, to ethanol in the culture medium. It is shown for the first time that the effect is dependent on RNA polymerase II-mediated transcription, but not on de novo biosynthesis of cholesterol or fatty acids, and therefore is not a generalized metabolic response to ethanol exposure. Some other lipid pathway genes are also modulated by ethanol exposure of cells. The results reported here suggest that the proximal signaling molecule leading to increased APOA1 gene expression in response to ethanol exposure may be free acetate or acetyl-CoA.

TAKE HOME

Upregulation of ApoA1 gene expression in hepatoma cells in culture, upon exposure to moderate ethanol concentrations in the medium, occurs at the level of RNA and is not dependent on new cholesterol or fatty acid synthesis. The primary signaling molecule may be free acetate or acetyl-CoA. These results are important for understanding the mechanism by which moderate alcohol consumption leads to upregulation of serum HDL-cholesterol in humans, and suggests new approaches to targeting HDL as a risk factor for cardiovascular disease.

A higher glycemic response to oral glucose is associated with higher plasma apolipoprotein C3 independently of BMI in healthy twins

BACKGROUND AND AIMS

Plasma apolipoprotein C3 (ApoC3) is associated with higher plasma triglyceride and type 2 diabetes incidence. We evaluated whether body mass index (BMI) or glucose metabolism were associated with ApoC3 in healthy monozygotic (MZ) twins.

METHODS AND RESULTS

Forty-seven MZ twin-pairs (20 man, 27 women), aged 23-42 years, were divided in subgroups according to discordance or concordance for (a) BMI (within-pair difference (Δ) in BMI≥3.0 or<3.0 kg/m²), or (b) 2-h glucose iAUC, during oral glucose tolerance test (ΔGlucose iAUC ≥97.5 or<97.5 mmol × 120 minutes). Within these discordant or concordant subgroups, we tested (Wilcoxon signed-rank test) co-twin differences in ApoC3, adiposity measures, insulin-resistance and beta-cell function indices, and plasma and lipoprotein lipids. In BMI-Discordant (p = 0.92) or BMI-Concordant (p = 0.99) subgroups, ApoC3 did not differ between leaner and heavier co-twins. In the Glucose-Discordant subgroup, ApoC3 was significantly higher in twins with higher Glucose iAUC than in their co-twins with the lower Glucose iAUC (10.03 ± 0.78 vs. 8.48 ± 0.52 mg/dl; M ± SE; p = 0.032). Co-twins with higher Glucose iAUC also had higher waist circumference, body fat percentage, liver fat content, worse insulin-sensitivity and beta-cell function and higher cholesterol and triglyceride in plasma VLDL, IDL, and LDL. In Glucose-Concordant twin-pairs, no significant differences were observed in the explored variables. In all twin-pairs, ΔApoC3 correlated with Δ in lipids and glucose metabolism variables, the closest relationship being between ΔApoC3 and ΔVLDL triglyceride (r = 0.74, p < 0.0001).

CONCLUSIONS

While ApoC3 was not related to acquired differences in BMI, it associated with early dysregulation of glucose metabolism independently of obesity and genetic background.

Common genetic factors influence hand strength, processing speed, and working memory

BACKGROUND

It is important to detect cognitive decline at an early stage, especially before onset of mild cognitive impairment and dementia. Processing speed and working memory are aspects of cognitive function that are associated with cognitive decline. Hand strength is an inexpensive, easily measurable indicator of cognitive decline. However, associations between hand strength, processing speed, and working memory have not been studied. In addition, the genetic and environmental structure of the association between hand strength and cognitive decline is unclear. We investigated phenotypic associations between hand strength, processing speed, and working memory and examined the genetic and environmental structure of the associations between phenotypes.

METHODS

Hand strength, processing speed (digit symbol performance), and working memory (digit span performance) were examined in monozygotic and dizygotic twin pairs. Generalized estimating equations were used to identify phenotypic associations, and structural equation modeling was used to investigate the genetic and environmental structure of the association.

RESULTS

Generalized estimating equations showed that hand strength was phenotypically associated with digit symbol performance but not with digit span performance. Structural equation modeling showed that common genetic factors influenced hand strength and digit symbol and digit span performance.

CONCLUSIONS

There was a phenotypic association between hand strength and processing speed. In addition, some genetic factors were common to hand strength, processing speed, and working memory.

The Osaka University Aged Twin Registry: Epigenetics and Identical Twins Discordant for Aging-Dependent Diseases

The Osaka University Aged Twin Registry (OUATR) is the largest adult twin registry in Japan. Since its establishment in 1974, the OUATR has conducted a number of studies with particular focus on the environmental contribution to physical–cognitive–mental aging, longevity and aging-dependent diseases in later adulthood. The registry consists of 12,000 pairs of Japanese twins born between 1900 and 1935. Two hundred and fifty pairs of twins have undergone comprehensive medical examination to date. Follow-up questionnaires have been mailed out on a regular basis, for the purpose of checking current vital statuses, health conditions, and so forth. The main objective of this longitudinal twin study is to contribute to the prevention of lifestyle-related diseases and the promotion of successful aging.

Heritability of serum apolipoprotein concentrations in middle-aged Japanese twins

Background

Studies of the genetic and environmental influences on apolipoproteins have been conducted, but few have used data from Japanese twins. The aim of this study was to quantify and compare the genetic and environmental causes of individual differences in the serum concentrations of apolipoproteins in Japanese middle-aged twins.

Methods

Apo A-I, apo A-II, apo B, apo C-II, apo C-III, and apo E were studied. A total of 142 twin pairs, aged 45 through 65 years, were enrolled: 85 monozygotic pairs (59 male, 26 female) and 57 same-sexed dizygotic pairs (43 male, 14 female). The intraclass correlation coefficient and structural equation modeling were used to estimate the best-fitting model and heritability.

Results

Sixteen percent to 75% of the total variances of apo A-I, apo C-II, and apo C-III were attributable to genetic influence; apo A-I and apo C-II were influenced by dominant genetic factors. Twenty percent to 73% of the total variances of apo A-II, apo B, and apo E were attributable to additive genetic influence; apo B was clearly influenced by common environmental factors. Furthermore, the heritability of all apolipoproteins was higher among females than among males.

Conclusions

Genetic factors, including additive genetic effects (A) and dominant effects (D), influence apolipoprotein levels. However, a common environment does not influence the variances of these apolipoproteins, with the exception of apo B. Furthermore, the heritability of apolipoprotein phenotypes differs by sex.

The nature of the association between diet and serum lipids in the community: a twin study

Diet is commonly thought to be an environmental influence on serum lipid concentrations. This study evaluated whether total caloric and fat intake predict total cholesterol (TC), low-density lipoprotein cholesterol (LDL), high-density lipoprotein cholesterol (HDL), and triglyceride (TRIG) concentrations for environmental, as compared with genetic, reasons among 137 monozygotic and 67 dizygotic young adult twins. When genetic influences were controlled by correlating differences between monozygotic co-twins, a significant association remained between diet and TC, LDL, and HDL, suggesting that these dietary and serum lipid measures correlate for environmental reasons. Twin structural equation modeling confirmed these results. Overall, these results provide additional support for the hypothesis that diet is an environmental influence on TC, LDL, and HDL.

The genetic background modifies the effects of the obesity mutation, 'fatty', on apolipoprotein gene regulation in rat liver

BACKGROUND

Obesity is associated with disorders of plasma lipid transport in many, but not in all obese subjects. The effects of obesity on the regulation of genes involved in plasma lipid transport may depend on specific mutations causing or contributing to obesity and/or on interactions of a specific obesity mutation with the genetic background. The 'fatty' (Glu269Pro) leptin receptor mutation causes severe obesity associated with hypertriglyceridaemia and altered hepatic apolipoprotein gene regulation in Zucker fatty rats.

OBJECTIVE

To determine whether the effects of the obesity mutation 'fatty' on apolipoprotein gene regulation in rat liver depend on the genetic background.

METHODS

We studied hepatic apolipoprotein (apo) A-IV, A-I, and C-III gene expression in obese rats carrying the 'fatty' mutation on the background of the Zucker or Wistar strain.

RESULTS

Basal apoA-IV gene expression was increased in fatty rats of both strains, whereas apoA-I and apoC-III gene expression differed between Wistar and Zucker fatty rats: apoA-I gene transcription was reduced to half and apoC-III mRNA was increased two-fold in Wistar fatty, but not in Zucker fatty rats vs lean controls. A fish oil diet suppressed apoA-IV, but not apoA-I gene transcription in Wistar fatty rats, whereas in Zucker fatty rats apoA-IV transcription was unaffected, but apoA-I transcription was suppressed.

CONCLUSIONS

Interactions of the 'fatty' leptin receptor mutation with the genetic background significantly affect the basal and diet-induced regulation of the apoA-IV, C-III and A-I genes in rat liver. The genetic background may therefore be a major determinant of the consequences of a specific obesity mutation for plasma lipid transport.

Dissecting the genetic architecture of lipids, lipoproteins, and apolipoproteins: lessons from twin studies

We review the ways in which twin studies have been used to investigate the genetic architecture of lipids, lipoproteins, and apolipoproteins. We focus on the age dependency of genetic effects and the importance of pleiotropy for the lipid system. Finally, consequences are discussed of age dependency and pleiotropy for the design and power of twin studies aimed at detecting the actual quantitative trait loci (QTLs) involved. It is concluded that twin studies have played an important role and will remain highly valuable for the elucidation of the genetic architecture of lipids, lipoproteins, and apolipoproteins. Twins can efficiently be used to identify the location and function of QTLs. Taking account of pleiotropy and age-dependent gene expression in study design and data analysis will improve the power and efficiency to find these QTLs for components of the lipid system.

Serum lipids, lipoproteins, and lipid metabolizing enzymes in identical twins discordant for obesity

Obesity is associated with adverse changes in plasma lipoprotein metabolism, but it is not known completely how this association is modified by genetic factors. We assessed the contribution of obesity to serum lipid and lipoprotein levels and lipid metabolizing enzyme activities by examining 23 identical twin pairs (9 male, 14 female) who had, on the average, an 18-kg intrapair difference in BW. Compared with lean co-twins, obese co-twins had approximately 20% higher low-density lipoprotein (LDL) cholesterol (P < 0.01), 20% lower high-density lipoprotein2 cholesterol (P = 0.010), and 90% (men) or 35% (women) higher (P < or = 0.06) total, very-low-density lipoprotein and LDL triglycerides. The pairs were divided into subgroups by the gender-specific median value of abdominal visceral fat (AVF) area in the obese co-twin and by apolipoprotein E 4 phenotype. The intrapair differences in serum cholesterol fractions were similar in twin pairs with high or low AVF, whereas only high AVF pairs showed significant differences in triglyceride fractions. The greatest intrapair differences in total, very-low-density lipoprotein and LDL triglycerides were observed in apolipoprotein E 4-positive pairs expressing high AVF. Compared with lean co-twins, lecithin cholesterol acyltransferase activity was 18% higher (P < 0.001) and hepatic lipase activity was 38% higher (P = 0.016) in obese co-twins with high AVF. When genetic factors are identical, obesity is associated with an atherogenic lipid profile, especially in subjects with high visceral fat accumulation.

Serum lipid profiles in Malay mothers and neonates: a cross-sectional study

OBJECTIVE

Preliminary epidemiological data suggest that dyslipidaemia contributes significantly to rising mortality due to atherosclerosis in Peninsular Malays. The aim of this study was to determine whether abnormal serum lipid profiles are present at birth in this population.

METHODOLOGY

The patients were 487 non-diabetic Malay women who had an uncomplicated antenatal course and delivered healthy singleton babies at term. Cord blood and maternal post-partum venous blood samples were taken for assay of serum cholesterol and triglyceride concentrations using standard enzymatic methods.

RESULTS

Maternal total serum cholesterol concentrations (mean +/- SD; 7.5 +/- 2.5 mmol/L) were higher than in other reported series (range of published means 5.2-6.5 mmol/L) with a correspondingly low high-density lipoprotein (HDL): total cholesterol ratio. The mean cord blood total serum cholesterol (1.7 +/- 1.0 mmol/L) was consistent with previously reported population means (1.5-1.9 mmol/L) but there was a relatively high low-density lipoprotein (LDL)-cholesterol and depressed HDL: cholesterol ratio. Significant correlations between maternal and neonatal serum total (P = 0.038) and especially HDL-cholesterol (P < 0.001) were observed. Maternal and cord blood serum triglyceride levels were comparable to those in other series.

CONCLUSIONS

These cross-sectional data provide evidence that abnormal serum cholesterol profiles are found in pregnant Malay women and their neonates which may have implications for the prevalence of macrovascular disease in the Malay population.

Intrapair differences of the blood cell components and lymphocyte subsets in monozygotic and dizygotic twins

We evaluated the relative influence of genetic and environmental factors on leukocytes, lymphocytes, neutrophils, monocytes, erythrocytes, reticulocytes, hemoglobin, platelets, T lymphocyte subsets, and NK marker cells in monozygotic (MZ) and dizygotic (DZ) twins. Peripheral blood components were measured in 154 healthy twin pairs (118 MZ pairs and 36 DZ pairs) and lymphocyte subsets in 48 healthy twin pairs (38 MZ pairs and 10 DZ pairs). Platelets and erythrocytes showed higher intraclass correlations in the MZ pairs than in the DZ pairs in the males. However, in the females, the intraclass correlations for these components were similar between the MZ and DZ pairs. Neutrophils and monocytes showed low intraclass correlations in the MZ pairs. The absolute number of CD4+ cells and the CD4+/CD8+ cell ratio showed high intraclass correlations regardless of age in the MZ pairs in both males and females. The intraclass correlation for the absolute number of CD3+ cells was low in pairs aged > or = 60 years in the MZ pairs. The absolute numbers of CD16+ cells and CD56+ cells showed high intraclass correlations regardless of age in the MZ pairs.

Genetic and environmental influences on serum lipid levels in twins

BACKGROUND

The extent to which serum lipid levels are affected by genetic and environmental factors remains a point of controversy. We examined both genetic and environmental influences on serum lipid levels in twins reared either together or apart who participated in the Swedish Adoption/Twin Study of Aging.

METHODS

We studied 302 pairs of twins (mean age, 65.6 years; range, 52 to 86); 146 pairs had been reared apart. We simultaneously compared the twins on the basis of both zygosity and rearing status, which allowed joint estimation of genetic and environmental influences on serum lipid levels. Genetic influence was expressed in terms of heritability, the proportion of the population variation attributable to genetic variation (a value of 1.0 indicates that all of the population variation is attributable to genetic variation). The serum lipids and apolipoproteins measured included total cholesterol, high-density lipoprotein cholesterol, apolipoproteins A-I and B, and triglycerides.

RESULTS

Structural-equation analyses revealed substantial heritability for the serum levels of each lipid measured, ranging from 0.28 to 0.78. Comparisons of the twins reared together with those reared apart suggested that the environment of rearing had a substantial impact on the level of total cholesterol (accounting for 0.15 to 0.36 of the total variance). Sharing the same environment appeared to affect the other lipid measures much less, however, than did genetic factors and unique environmental factors not shared by twins. Comparisons of younger with older twins suggested that heritability for apolipoprotein B and triglyceride levels decreased with age.

CONCLUSIONS

The effect of genetic factors on the serum levels of some but not all lipids appears to decrease with age. Early rearing environment appears to remain an important factor in relation to levels of total cholesterol later in life, but it has less effect on other serum lipids and apolipoproteins in the elderly.

Risk factors for cognitive aging in adult twins

Monozygotic (MZ) and dizygotic (DZ) twins in later adulthood were studied in order to examine genetic and environmental contributions to the decline of cognitive performance. In this study, 118 twin pairs took a comprehensive medical examination at a university hospital. Cognitive function was measured by the Wechsler Adult Intelligence Scale (WAIS). The intraclass correlation coefficients on Digit Span (D) and Digit Symbol (DS) subtests of the WAIS did not show any significant difference between MZ and DZ twins although Block Design (BD) showed a significant difference. The values of the intraclass correlation coefficients were mostly around 0.5 and showed significant within-pair similarity of test scores. The mean score of D, DS and BD declined with advancing age. The intraclass correlation coefficients for D, DS and BD were around 0.2 in the MZ twins reared apart, and around 0.6 in the MZ twins reared together. These results indicated a significant environmental influence on cognitive aging in later adulthood.

Intrapair differences of physical aging and longevity in identical twins

The genetic and environmental contributions to physical aging (hair graying, balding, presbyopia) and longevity (age at death) were examined by within-pair comparison in monozygotic (MZ) and dizygotic (DZ) twins in later adulthood. Physical aging was investigated on 135 pairs of adult twins aged over 50. Hair graying and hair loss (baldness) showed significantly higher rates of concordance in the MZ twins than in the DZ twins. The intrapair difference of the degree of hair graying was negligible in 79%, slight in 15% and striking in 5% among the MZ pairs; while negligible in 40%, slight in 50% and striking in 10% among the DZ pairs. The intrapair difference of the degree of hair loss was negligible in 92%, slight in 8% (and striking in none) among the MZ pairs; while negligible in 69%, slight in 25% and striking in 6% among the DZ pairs. The age at onset of presbyopia showed a slightly higher rate of concordance in the MZ than in the DZ pairs. Longevity (age at death) was surveyed on 184 pairs of twins who died at over 40 years of age. The intrapair difference of longevity was 6.65 +/- 5.6 years (maximum 18.0; minimum 0.04) in the MZ pairs, and 8.66 +/- 7.2 years (maximum 18.6; minimum 2.9) in the DZ pairs. The MZ pairs showed a slightly smaller within-pair difference of longevity than the DZ pairs.

Carotid arteriosclerosis in identical twins discordant for cigarette smoking

From a nationwide twin panel, identical twin pairs with highest discordance in cigarette smoking were selected for a study of arteriosclerosis (49 pairs with a mean age of 52 years). Smoking history was obtained in 1975, 1981, and 1986. The mean life-long smoking dose of the smoking cotwins was 20 package-years. The smoking and nonsmoking cotwins had similar systolic and diastolic blood pressures, total plasma cholesterol level, body mass index, and some psychosocial factors; the only difference was found in use of alcohol, which was greater among smoking cotwins. Duplex sonography of carotid arteries was performed. Carotid artery stenoses (narrowing of area of the lumen with 15-60%) were found in nine pairs: in nine smoking twins and in two of their nonsmoking cotwins (p = 0.036). The total area of carotid plaques was 3.2 times larger in smoking cotwins (p less than 0.001). The thickness of the inner layer of carotid arteries was more marked in smoking cotwins (p less than 0.001). The size of plaques and the degree of inner layer thickening correlated with the dose of smoking (NS). The association of smoking with carotid arteriosclerosis was highly significant even after the adjustment for age, total plasma cholesterol level, diastolic blood pressure, and body mass index in multiple logistic regression analyses.

Factors associated with high density lipoprotein cholesterol in a population with high high density lipoprotein cholesterol levels

A cross-sectional study of a random sample of 976 coloureds (mixed race) of the Cape Peninsula, ages 15 to 64 years old, revealed a population with unexpectedly high levels of high density lipoprotein (HDL) cholesterol. The mean level for men was 55.4 +/- 16.1 mg/dl (SD) and for women, 60.8 +/- 16.0 mg/dl. The ratio of HDL cholesterol to total cholesterol expressed as a percentage was 26.3% +/- 9.5% for men and 28.1% +/- 9.3% for women. The HDL cholesterol levels were apparently lower than those of black and Negro populations, yet higher than those of Caucasian populations. Men with levels of HDL cholesterol above the median reported a personal history and a family history of coronary heart disease less frequently than did men with lower levels, while women with high levels of HDL cholesterol were less likely to have a history of hypertension or diabetes. Stepwise multiple regression analysis of variables significantly associated with HDL cholesterol levels showed that they explained 29.7% and 24.7%, respectively, of the variation in HDL cholesterol in men and women. Those variables independently associated with HDL cholesterol in both men and women were: serum triglyceride (-), cigarette consumption (-), alcohol, body mass index (-), age, and serum low density lipoprotein cholesterol levels (-). The reasons for the relatively high HDL cholesterol levels in this population are unknown. However, it would seem possible that these levels offer some protection against the high risk factors of smoking, hypertension, and hypercholesterolemia.

Anthropometric and lifestyle correlates of serum lipoprotein and apolipoprotein levels among normal non-smoking men and women

The relationship between serologic predictors of coronary risk and anthropometric as well as lifestyle characteristics was investigated in 61 men (37.5 +/- 8.5 yrs) and 33 women (40.1 +/- 9.0 yrs). All subjects were healthy non-smokers, mostly middle-class bank employees. In bivariate analysis, among both genders the ratio of waist-to-hip circumference (WHR) was the single best predictor of levels of serum LDL-cholesterol, apolipoprotein B, VLDL-cholesterol and triglycerides (positive association) as well as HDL-cholesterol and apolipoprotein A-I (inverse association). In men, body fat as estimated from bioelectrical impedance measurement was the second best predictor of lipoprotein and apoprotein concentrations, whereas in women it was the body mass index (BMI). The additional independent predictive power of WHR and body fat for the lipid profile was tested in multivariate analysis by adding WHR and body fat sequentially to regression models containing already BMI, endurance capacity, exercise, alcohol consumption and age. For example, explained variance of triglyceride distribution rose from 26.3 to 35.1% (P = 0.01 for increase) when body fat was entered into the regression equation, or inclusion of WHR into a model already containing age, the behavioral variables, BMI, and body fat increased the explained variance of LDL/HDL-cholesterol ratio from 20.9 to 27.6% (P = 0.04 for increase). In women, the same regression models were even slightly more predictive for the serum lipid profile. Endurance capacity was related to a low atherogenic risk lipid profile in bivariate analysis but lost much of its predictive power in multivariate analysis, which confirms that the effect of fitness on lipid levels is probably mediated in part by a low body fat content. It is concluded from this cross-sectional investigation that studies which focus on associations between lifestyle and serologic predictors of atherogenic risk should possibly include the WHR and a measure of body fat, since the latter two appear to be closer correlates of serum lipoprotein and apolipoprotein levels than BMI or single behavioral factors, at least among male non-smokers.