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Nutrition |
1 Nutrition and Genomics Laboratory, Jean Mayer-US Department of Agriculture Human Nutrition Research Center on Aging, Tufts University, Boston, MA.
2 Genetic and Molecular Epidemiology Unit and CIBER Fisiopatología de la Obesidad y Nutrición, School of Medicine, University of Valencia, Valencia, Spain.
3 Department of Epidemiology, School of Public Health, and Clinical Nutrition Research Center, University of Alabama at Birmingham, AL.
4 Laboratory of Medicine and Pathology, University of Minnesota, Minneapolis, MN.
5 Division of Epidemiology and Community Health, School of Public Health, University of Minnesota, MN.
6 Human Genetics Center, University of Texas Health Science Center, Houston, TX.
7 Experimental and Clinical Pharmacology Department, College of Pharmacy, University of Minnesota, Minneapolis, MN.
8 Division of Biostatistics, Washington University School of Medicine, St. Louis, MO.
aAddress correspondence to this author at: Nutrition and Genomics Laboratory, JM-USDA Human Nutrition Research Center on Aging at Tufts University, 711 Washington St., Boston, MA 02111-1524. Fax 617-556-3211; e-mail jose.ordovas{at}tufts.edu.
| Abstract |
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Methods: We studied the association between a functional APOA2 promoter polymorphism (265T>C) and plasma lipids (fasting and postprandial), anthropometric variables, and food intake in 514 men and 564 women who participated in the Genetics of Lipid Lowering Drugs and Diet Network (GOLDN) study. We obtained fasting and postprandial (after consuming a high-fat meal) measures. We measured lipoprotein particle concentrations by proton nuclear magnetic resonance spectroscopy and estimated dietary intake by use of a validated questionnaire.
Results: We observed recessive effects for this polymorphism that were homogeneous by sex. Individuals homozygous for the 265C allele had statistically higher body mass index (BMI) than did carriers of the T allele. Consistently, after multivariate adjustment, the odds ratio for obesity in CC individuals compared with T allele carriers was 1.70 (95% CI 1.022.80, P = 0.039). Interestingly, total energy intake in CC individuals was statistically higher [mean (SE) 9371 (497) vs 8456 (413) kJ/d, P = 0.005] than in T allele carriers. Likewise, total fat and protein intakes (expressed in grams per day) were statistically higher in CC individuals (P = 0.002 and P = 0.005, respectively). After adjustment for energy, percentage of carbohydrate intake was statistically lower in CC individuals. These associations remained statistically significant even after adjustment for BMI. We found no associations with fasting lipids and only some associations with HDL subfraction distribution in the postprandial state.
Conclusions: The 265T>C polymorphism is consistently associated with food consumption and obesity, suggesting a new role for APOA2 in regulating dietary intake.
| Introduction |
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30% drop in basal transcription activity (16)(17). In one of these studies, the 265T>C polymorphism was associated with waist circumference in men (16). Another study (18) reported an association between this polymorphism and abdominal fat depots in women. Although Castellani et al. (19) found increased body weight in mice overexpressing murine APOA2, the mechanism by which APOA2 may influence body weight is largely unknown. APOA2 is a member of the apolipoprotein multigene superfamily, which includes genes encoding soluble apolipoproteins (e.g., APOA1 and APOA4) that share genomic structure and several functions. Although all these apolipoprotein genes have been found to be related to obesity in at least one epidemiological study (20), only APOA4 has been subscribed in regulation of food intake, acting as a satiety signal (21). Therefore, we hypothesized that APOA2 may also be involved in regulating food intake. Overall, our aims were to study the effect of the 65T>C polymorphism in the APOA2 gene on body weight, food intake, and plasma lipid concentrations (fasting and postprandial) in a North American population. | Materials and Methods |
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The initially estimated sample size for the GOLDN study was
1200 individuals. Complete fasting and postprandial data were obtained from 1118 individuals. Individuals with inconsistent dietary data (total daily energy intake outside the range of 8005500 kcal in men or 6004500 in women) were excluded, resulting in a final sample size of 1078 individuals (514 men and 564 women).
interventions and clinic visits
Participants were asked to fast for >12 h and abstain from using alcohol for >24 h before visiting the clinic. We measured weight with a beam balance, hip circumference at maximal hip girth, and waist circumference at the umbilicus. Body mass index (BMI) was calculated as weight (kg)/height (m)2, and obesity was defined as BMI
30 kg/m2. We administered clinical and lifestyle questionnaires and created an interviewer-administered, direct data entry system for the diet history questionnaire (DHQ) developed by the National Cancer Institute.
dietary intake
We estimated dietary intake by use of the DHQ, a food frequency questionnaire developed by staff at the Risk Factor Monitoring and Methods Branch. It consists of 124 food items and includes both portion size and dietary supplement questions. Two studies have been conducted to assess its validity (23)(24). The food list and nutrient database used with the DHQ are based on national dietary data [US Department of Agriculture (USDA) 199496 Continuing Survey of Food Intakes by Individuals, available from the USDA Food Surveys Research Group].
postprandial study fat challenge
The postprandial study fat challenge consisted of a meal formulated according to the protocol of Patsch et al. (25). The meal, which participants were instructed to consume within 15 min, had 700 calories/m2 body surface area (2.93 MJ/m2 body surface area); 3% of calories were derived from protein, 14% from carbohydrate, and 83% from fat sources. Cholesterol content was 240 mg and the ratio of polyunsaturated fat (PUFA) to saturated fat (SATFAT) was 0.06. The average person consumed 175 mL heavy whipping cream (39.5% fat) and 7.5 mL powdered, instant, nonfat dry milk, blended with ice and 15 mL chocolate- or strawberry-flavored syrup to increase palatability. We drew blood samples immediately before (time 0) and 3.5 and 6 h after the high-fat meal.
biochemical analyses
We drew venous blood after study participants had fasted overnight. Plasma samples were stored and analyzed together. We measured triglycerides by glycerol-blanked enzymatic method on the Roche COBAS FARA centrifugal analyzer (Roche Diagnostics). We measured cholesterol on the Hitachi 911 Automatic Analyzer (Roche Diagnostics) using a cholesterol esterase, cholesterol oxidase reaction (Chol R1; Roche Diagnostics). We used the same reaction to measure HDL cholesterol after precipitation of non-HDL cholesterol with magnesium/dextran. We measured LDL cholesterol by use of a homogeneous direct method (LDL Direct Liquid SelectTM Cholesterol Reagent; Equal Diagnostics) on the Hitachi 911. We measured lipoprotein particle concentrations and size by proton nuclear magnetic resonance spectroscopy (26)(27). Data were obtained from the measured amplitudes of their spectroscopically distinct lipid methyl group nuclear magnetic resonance signals. We measured the concentrations of the following subclasses: small LDL (diameter 18.021.2 nm), large LDL (21.223.0 nm), intermediate-density lipoprotein (IDL; 23.027.0 nm), large HDL (8.813.0 nm), medium HDL (8.28.8 nm), small HDL (7.38.2 nm), large VLDL (>60 nm), medium VLDL (35.060.0 nm), and small VLDL (27.035.0 nm). The small LDL subclass encompassed both intermediate small (19.821.2 nm) and very small (18.019.0 nm) particles.
dna isolation and apoa2 genotyping
DNA was isolated from blood samples using routine DNA isolation sets (Qiagen). We performed genotyping of the 265C>T polymorphism (rs5082) using a Taqman assay with allele-specific probes on the ABIPrism 7900HT Sequence Detection System (Applied Biosystems) according to routine laboratory protocols.
statistical analysis
Triglyceride concentrations were log transformed and IDL and VLDL were square-root transformed for statistical testing. We used Pearson
2 and Fisher tests to test differences in percentages. We applied ANOVA and the Student t-test to compare crude means. We tested codominant, dominant, and recessive models for the APOA2 polymorphism. We carried out multivariate adjustments of the associations by analysis of covariance and estimated adjusted means. First, we adjusted analyses for demographic, clinical, and lifestyle variables and then for family relationships. To evaluate replication, we performed statistical analyses for the whole sample and for men and women separately. We also tested the statistical homogeneity of the effects by sex in the corresponding regression model with interaction terms. Obesity was defined as BMI
30 kg/m2. We fitted logistic regression models to estimate the odds ratio (OR) and 95% CI of obesity associated with the APOA2 polymorphism and to control for the effect of covariates and family relationships.
We performed ANOVA for repeated measures to analyze data obtained in the postprandial study. In this analysis, we studied the statistical effects of the APOA2 genotype alone, the effect of time (change in the variable after the high-fat load over the entire lipemic period), and the effect of the interaction of the 2 factors (genotype and time), which is indicative of the magnitude of the postprandial response in each group of individuals. We also carried out multivariate adjustment for covariates including demographic, clinical, lifestyle, and family relationships. We used routine regression diagnostic procedures to ensure the appropriateness of the models. Statistical analyses were done using SPSS 14.0 software (SPSS). All reported probability tests were 2-sided. Differences between means were considered significant at P <0.05.
bioinformatics analysis
Analysis of the genomic DNA sequence segment centered on the 265 variant was conducted with MAPPER (28) to identify potential transcription factor binding sites.
| Results |
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We next examined if the 265T>C APOA2 polymorphism may relate to food intake in this population. A recessive model of association was also found. Homogeneity of the associations was detected in both men and women; results for the overall sample are presented (Table 3
). Homozygous individuals for the CC allele had a statistically higher mean of energy intake than carriers of the T allele, which remained statistically significant even after multivariate adjustment for sex, age, tobacco smoking, alcohol consumption, diabetes, CVD, and familial relationships. Thus, daily energy intake was
900 KJ/d (200 Kcal/d) higher in CC homozygotes than in T allele carriers (P = 0.005). In terms of amount of food, CC homozygotes had significantly higher absolute intake than T allele carriers, even after multivariate adjustment. Total fat presented strong associations with the APOA2 polymorphism. Means of total fat intake (g/day) in men (Fig. 1A
) and women (Fig. 1B
) depending on the APOA2 polymorphism exemplify the recessive genetic effects and the internal replication of results. Moreover, when SATFAT, monounsaturated fat (MUFA), and PUFA as well as specific fatty acids were analyzed, significant differences were found even after multivariate adjustment. When macronutrients were expressed as percentage of daily energy intake, carbohydrate intake was statistically lower in CC homozygotes than in T allele carriers [mean (SE) 46.8% (1.7%) in TT + CT vs 44.9% (1.9%) in CC individuals, P = 0.012, in the multivariate adjusted model including sex, age, tobacco smoking, alcohol consumption, diabetes, CVD, and family relationships]. Likewise, after this multivariate adjustment, total fat intake expressed as percentage of daily energy intake was statistically higher in CC homozygotes than in T allele carriers [37.2% (1.4%) in TT + CT vs 38.6% (1.5%) in CC individuals; P = 0.023].
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Taking into account that CC individuals had higher BMI, we performed additional adjustment for BMI of the associations presented in Table 3
(results not shown). This additional adjustment slightly modified the P values and did not change the inference.
We investigated the effect of the 265T>C APOA2 polymorphism on fasting plasma lipids, lipoproteins, and particle size in both men and women. No heterogeneity by sex was found. Neither in the crude model nor in the multivariate-adjusted model (Table 4
) were statistically significant differences between APOA2 genotypes found. Considering that a high-fat intake increases APOA2 concentrations, a postprandial study of fat challenge was also performed in the 1078 participants. Blood samples were drawn before time 0 and at 3.5 and 6 h after consuming the high-fat meal. After multivariate adjustment, no statistically significant genotype effects or genotype*time interactions were observed for total cholesterol, LDL cholesterol, HDL cholesterol, triglycerides, small LDL particles, large LDL particles, mean LDL particle size, mean VLDL particle size, or mean HDL particle size (results not shown). Statistically significant genotype effects were observed for HDL and VLDL particles (Fig. 2A
F). The amount of small HDL particles, which decreased after the fat load, was significantly higher in CC homozygotes over the entire postprandial period than in carriers of the T allele (P = 0.029) and reached its highest statistical significance (P = 0.014) at 3.5 h after the fatty meal. Conversely, the amount of medium-sized HDL particles increased and was lower in CC homozygotes over the entire period (P = 0.049). The fat-loading test increased postprandial large VLDL particles, which were lower in homozygous individuals for the 265C allele. These results suggested a faster clearance in CC homozygotes than in carriers of the T allele.
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The bioinformatic analysis of the APOA2 gene control (upstream) region indicates the potential for a CEBPA [CCAAT/enhancer binding protein (C/EBP)
] binding site that is not predicted with the minor C allele.
| Discussion |
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Despite the scarcity of previous data supporting a role of APOA2 in regulating food intake, copious experimental evidence demonstrates a pivotal role of another apolipoprotein, APOA4, as a satiety signal (20)(21)(39)(40). Fujimoto et al. (39) were the first to report that APOA4 is a satiety factor secreted by the intestine after fat absorption and that this function of APOA4 is not shared by gut APOA1. Unfortunately, Fujimoto et al. (39) did not test the effects of APOA2, and its potential effects remain to be elucidated. If APOA2 acts as a satiety signal, taking into account that the 265T>C polymorphism results in lower APOA2 concentrations, individuals homozygous for 265C can have a higher food intake than carriers of the T allele. A direct consequence of the involvement of APOA2 in regulating food intake is its influence in body weight regulation. Only 2 population studies have examined the association between the 265T>C polymorphism and anthropometric measures, with controversial results (16)(18). In this American population, we have found that in both men and women, homozygous individuals for the 265C allele had higher obesity risk than carriers of the T allele. Our findings are in agreement with Lara-Castro et al. (18), who reported statistically higher amounts of visceral adipose tissue in white women carriers of the 265C allele. Neither of these studies examined the influence of the 265T>C polymorphism in determining food intake. Vant Hooft et al. (16) studied the association between this polymorphism and fasting plasma glucose, insulin, lipids, and lipoproteins and found no significant associations, in agreement with our results. Moreover, they also carried out an oral fat tolerance test and found that the overall response of plasma triglycerides during the entire 6-h period was unassociated with the APOA2 265T>C polymorphism. Interestingly, postprandial APOB-100 concentrations in the Sf >60 of triglyceride-rich protein (a measure of large VLDL particles) were significantly lower in individuals homozygous for the 265C allele, suggesting that the reduced plasma APOA2 concentrations associated with the C allele enhances the ability to remove large VLDL from circulation during alimentary lipemia. In our study, we measured large VLDL particles and obtained results in agreement with these observations. In addition, we measured HDL particle size in the postprandial period and observed a significant increase in the small HDL subfraction associated with the 265C allele.
In conclusion, in this population study the 265T>C polymorphism has no significant role in determining fasting plasma lipids and particle size. Postprandial state increases the effects of this polymorphism, and significant differences were observed in HDL subfraction distribution as well as borderline effects on large VLDL particles. However, the most consistent effects of this polymorphism were observed on anthropometric variables and food intake. Homozygous individuals for the 265C allele had higher obesity risk than carriers of the T allele. CC individuals also had statistically higher total energy and fat intake. As these effects were consistently found in both men and women, we suggest a new role for APOA2 in regulating food intake. More population studies are needed to replicate these findings.
| Acknowledgments |
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Financial disclosures: None declared.
| Footnotes |
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2 Human genes: APOA2, apolipoprotein A-II; HTR2A, 5-hydroxytryptamine (serotonin) receptor 2A. ![]()
| References |
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