Central obesity in males affected by a dyslipidemia-associated genetic polymorphism on APOA1|[sol]|C3|[sol]|A4|[sol]|A5 gene cluster

Obesity has reached a globally epidemic level, and is forecasted to affect 800 million individuals by 2015.1, 2 Prolonged obesity increases risks of developing metabolic syndrome (MetS), type 2 diabetes and cardiovascular diseases.2 In particular, central obesity is considered more pathogenic than peripheral obesity, and often occurs in parallel with dyslipidemia and insulin resistance.3, 4 Central obesity can be defined by elevated waist-hip ratio (WHR) or waist circumference (WC), which has been designated to be the prerequisite factor for the MetS criteria by the International Diabetes Federation.5 Therefore, active weight-loss through weight-loss surgery or planned diet regime in centrally obese patients can improve their glycemic and lipidemic controls.6, 7 Interestingly, alterations in lipidemic control and ectopic fat deposition have been observed concurrently in patients during viral infections and associated treatments.8, 9 Moreover, mice models deficient in controlling lipid or glucose metabolism have developed lipodystrophic or obesogenic phenotypes.10, 11 Several genetic polymorphisms situated in the APOA1/C3/A4/A5 gene cluster are associated with dyslipidemia, insulin resistance and MetS. APOA1/C3/A4/A5 transcribes for apolipoproteins (apos) A1, C3, A4 and A5,12 which participate in plasma triglyceride (TG) and cholesterol metabolism. ApoA1 is the structural protein of high-density lipoprotein (HDL), which is involved in reverse cholesterol transport.13 Genetic polymorphisms in APOA1 are associated with fasting and postprandial plasma lipids, and responses to medication for dyslipidemia.14, 15 The promoter region-situated rs670 on APOA1 is correlated with HDL-cholesterol (HDL-C) levels, MetS and type 2 diabetes.16, 17, 18 ApoC3 inhibits plasma lipoprotein lipase activity, and is found on TG-rich lipoproteins and HDL.19 The single-nucleotide polymorphisms (SNPs) within APOC3 coding or promoter regions are associated with the altered TG metabolism.20, 21 Two SNPs situated in the insulin-responsive element of APOC3, rs2854116 and rs2854117 are known to be associated with postprandial plasma TG and fatty liver.20, 22 The function of apoA4 is less known, but in vitro studies suggest its participation in lipoprotein lipase activity and lecithin-cholesterol acyltransferase activity.23, 24 APOA4 rs675, a missense SNP that alters threonine347 to serine, is associated with response to fenofibrate treatment.25 ApoA5 regulates TG metabolism and is proposed to interact with lipoprotein lipase activity.26, 27 Thus, mutations and SNPs on APOA5, especially rs662799, rs3135506 and the Chinese-predominant rs2075291, are associated with dyslipidemia and MetS.12, 28, 29 The pathogenesis of metabolic conditions including central obesity, dyslipidemia and impaired glucose control are gender dependent.30 Central obesity is gender dependent, in that men are more susceptible to abdominal fat deposition than premenopausal women.31, 32 The complications of central obesity are also gender dependent, as it predisposes the highest risk in hypertriglycedemia in men, but poses more risk of IR in females.33 Gender-specific effects are also observed in genetic predispositions to central obesity, as genome-wide screening identified adipogenesis-associated SNPs favoring central obesity in women.34, 35 Reflectively, the risks for dyslipidemia predisposed by SNPs are gender specific.16, 27, 36, 37 APOA1 rs670-associated increase in poly-unsaturated fatty acid-induced HDL-C was observed only in females.16 APOC3 rs2854117 is correlated strongly with hypertriglyceridemia in men, whereas it is correlated with increased insulin resistance in women.36 Rs662799 and rs3135506 on APOA5 are associated with hypertriglyceridemia in men with greater effects,27 but associated with lower HDL-C levels only in women.37 Though the effect of APOA1/C3/A4/A5 gene cluster polymorphisms on dyslipidemia has been studied in great detail, the contributions these polymorphisms in central obesity are less known, especially in Asian populations. Furthermore, the effect of weight-loss in obese patients carrying APOA1/C3/A4/A5 SNPs in improving associated metabolic factors is not yet established. This study analyzes the contributions of APOA1/C3/A4/A5 SNPs to obesity-associated anthropometric and metabolic parameters in Taiwanese obese (BMI 25) patients and non-obese healthy (BMI <25) participants at baseline, and again in the obese patients 6 months after they have initiated weight-loss intervention. As gender has a vital role in the pathogenesis and pathophysiology of central obesity, the gender-specific contributions are examined. Gender-stratification of obese patients revealed that the overall association of APOA5 rs662799 C allele carriage with increased frequencies of central obesity and MetS was contributed mainly by obese males (Table 5). Obese male C allele carriers had increased odds of elevated WHR by 6.52-fold (95% CI=1.87–22.73, P=0.003) as compared with non-C allele carriers after adjustments for age, BMI and TG (Table 5). Though the frequency of MetS increased in obese males APOA5 rs662799 C allele carriers as compared with non-C allele carriers, the effect was diminished after additional adjustment for WHR (Table 5). In addition, the correlation of APOA5 rs662799 C allele with WHR and central obesity in obese males remained strong and significant after further adjustment for APOA5 rs2075291 (Supplementary Table 4). On the other hand, the carriage of APOA5 rs662799 C allele in obese females did not statistically increase the occurrence of central obesity, MetS or low-HDLC after appropriate adjustments (Table 5). APOA5 rs662799 C allele carriage increased odds of hyper-TG in both obese males and obese females, however, after adjustment for age, BMI plus WHR only that in obese females remained statistically significant (odds ratio=5.63, 95% CI=1.89–16.78, P=0.002, Table 5). Similarly, additional adjustment for APOA5 rs2075291 did not diminish the correlation of APOA5 rs662799 C allele carriage with hyper-TG in obese females (Supplementary Table 4). Consistent with the baseline findings of the current study, baseline WHR of obese male APOA5 rs662799 C allele carriers was higher than that of non-C allele carriers (0.98±0.05 vs 0.93±0.05 unit, P=0.005, Figure 2b). Interestingly, significant improvements in WHR was achieved in APOA5 rs662799 C allele carriers (0.98±0.05 to 0.94±0.05, P=0.001, Figure 2b). On the contrary, the changes in WHR were not evident in APOA5 rs662799 non-C allele males (0.93±0.05 to 0.92±0.07, P=0.267). Of note, significant improvements of male APOA5 rs662799 C allele and non-C allele carriers were observed in both WC (P<0.001 and P=0.004) and HC (P<0.001 and P=0.002). The significant improvement in WHR at 6 months after weight-loss intervention resulted in the comparable WHR (P=0.240, Figure 2b) between male APOA5 rs662799 C allele and non-C allele carriers at study endpoint. In contrast, APOA5 rs662799 C allele carriage was not associated with difference in baseline or post-intervention WHR in females, and no significant improvement was observed in APOA5 rs662799 C allele carriers (Supplementary Figure 2B). Additionally, TG improvements were observed in both males (P<0.001, Figure 2c) and females (P=0.009 Supplementary Figure 2C). This study has analyzed the effects of APOA1/C3/A4/A5 dyslipidemia-associated SNPs on central obesity using cross-sectional and longitudinal methods. In particular, APOA5 rs662799 has been found to exhibit gender-specific associations with metabolic parameters in obese individuals. Obese males carrying APOA5 rs662799 minor variant had increased WHR and TG, and thus have increased odds in central obesity, hypertriglycedemia and MetS. Importantly, after comparable reductions in BMI, weight-loss intervention significantly improved the gender-specific impairments predisposed by APOA5 rs662799 polymorphism. APOA5 rs662799’s effect on dyslipidemia has been widely studied, and its association with plasma lipid has exhibited gender-specificities.27, 37, 41 The present study confirmed APOA5 rs662799’s significant impact on TG and hypertriglycedemia in obese patients of both genders. One of the first relevant publications found that the effect of APOA5 rs662799 on increased plasma TG was significant in Caucasian males but not their female counterparts.27 Moreover, in both Turkish and German participants, APOA5 rs662799 minor variant was associated with isolated hypertriglycedemia in males, whereas in females accompanying lower HDL-C levels were observed.37, 41 This observation is echoed by our data, which showed APOA5 rs662799 minor allele linearly-correlated with TG only in obese males, but associated with low HDL-C accompanied hypertriglycedemia in females (Table 5). Of particular interest, our results indicated APOA5 rs662799 minor variant associated with WHR and central obesity as reflected by greater WHR in obese males. The effect of APOA5 rs662799 on central obesity was evident only in obese males, but was not observed in obese females and non-obese participants. Interestingly, men’s higher tendency of adipose accumulation in the central region did not conceal the contribution of APOA5 rs662799 on central obesity. The findings were consistent after adjustments for TG, age and BMI, showing an independent nature of the association. According to a recent meta-analysis study, APOA5 rs662799 have displayed a persistent and cross-ethnic association with MetS.12 Correspondingly, our results indicated that APOA5 rs662799 was associated with MetS risk in obese males, particularly through the correlation with WHR and TG. This observation further emphasizes the importance of APOA5 rs662799, as central obesity is recognized as the precedent factor promoting the other components of MetS. Two separate studies have found the association of WC with APOA5 rs3135506 in Hispanics,42 and BMI with APOA5 rs2075291 in Chinese.43 However, APOA5 rs3135506 genotype was found to be ubiquitous among our study group, while APOA5 rs2075291 was associated with increased TG but not BMI. Genotype–dietary fat interactions on APOA5 rs662799’s effect on central obesity has been reported, as the variant carriers consuming Mediterranean low-fat diet have increased WC than non-carriers.44 The pathogenic mechanism of APOA5 rs662799 in WHR is outside the scope of our study. Nevertheless, recent studies reported treatment of apoA5 in in vitro-differentiated human adipocytes have specific regulation on the amount of intracellular lipid content,45 and that APOA5-transgenic mice have increased inguinal fat pads.46 Of specific importance, a decrease in hepatic apoA5 was shown to accompany improvements in liver steatosis in individuals who underwent bariatric surgery.47 Furthermore, several reports illustrated the effect of apoA5 on intracellular lipid droplet in hepatoma cell lines,48 and that APOA5-transgenic mice have increased hepatic TG.49 As central obesity is associated with the exacerbation of liver steatosis in obese individuals,50 the results of ours and others stress the importance of weight control for APOA5 rs662799 variant carriers in maintaining a healthy profile. The response of APOA5 rs662799-associated metabolic disorders to weight-loss intervention has not been thoroughly analyzed previously. Only two studies have focused on the post hocs of weight reduction in APOA5 rs662799 minor variant carriers.51, 52 Examination of obese males undergoing restricted diet intervention found APOA5 rs662799 minor variant carriers had comparable BMI and lipid parameters, yet significant greater reduction in BMI was achieved than their counterparts at 3 months after intervention.51 The other study found that female carriers of APOA5 rs662799 minor variants had a significantly higher baseline TG; 9 weeks after life-style intervention, the variant carriers achieved a greater reduction of TG than their control counterparts.52 During a longer regular visit period (6 months) achieved in this study, our results indicated weight loss can ameliorate the unfavorable metabolic profiles in risk carriers of APOA5 rs662799 polymorphisms. Moreover, although WHR of the risk variant carriers were higher than those of non-risk counterparts at baseline, the difference became insignificant after a comparable reduction in BMI after a 6-month period. Analysis of normal weight individuals further strengthened this finding, as APOA5 rs662799 showed no significance in correlation with metabolic parameters. In sum, this study demonstrates the importance of weight management in individuals carrying APOA5 rs662799 polymorphisms, as intervention can reduce the unfavorable metabolic profile predisposed by these SNPs. In conclusion, this study conducted a systematic and through longitudinal analysis on the effects of the well-known SNPs on APOA1/C3/A4/A5 in gender-stratified obese patients undergoing weight-loss intervention. We showed that APOA5 rs662799 polymorphism (C allele carriers: T/C and C/C) was unfavorable in obese patients; however, this predicament was improved prominently by weight management. Despite our relatively small sample size, appropriate statistical adjustments demonstrated the consistency of our main findings. Moreover, baseline observations and preliminary analysis in normal weight volunteers supported the intervention outcome of the patients, despite the varied intervention methods among the patients. This pioneering study supports the generally accepted view of weight maintenance in maintaining a healthy metabolic profile. Results of this study provide further insight into the benefits of weight-loss intervention in Asian obese patients with central obesity and dyslipidemia. The authors declare no conflict of interest. We are grateful for Miss Ting-Yu Hou’s technical assistance and Miss Yu-Chen Shih for her administrative assistance. This study is supported by the National Science Council, Taiwan (grant no. NSC 100-2321-B-006 -015 -MY3, NSC-100-2320-B-006 -007 -MY3) and NCKUH (NCKUH-9801002). Author Contributions: M-C Hsu designed research, performed experiments, analyzed data and wrote the paper; C-S Chang and K-T Lee participated in research design, collection of clinical data and patient samples; Y-S Tsai and P-H Kuo participated in research design and collection of patient samples; H-Y Sun participated in research design and discussion; K-C Young participated in research design, discussion and paper-editing; C-H Wu contributed to research design, discussion and paper-editing, collection of clinical data and patient samples. Supplementary Information accompanies the paper on the Nutrition & Diabetes website