Effect of the Common-866G/A Polymorphism of the Uncoupling ...

Mol Diagn Ther 2010; 14 (2): 101-106 1177-1062/10/0002-0101/$49.95/0

ORIGINAL RESEARCH ARTICLE

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Effect of the Common –866G/A Polymorphism of the Uncoupling Protein 2 Gene on Weight Loss and Body Composition under Sibutramine Therapy in an Obese Taiwanese Population Tun-Jen Hsiao,1 Lawrence Shih-Hsin Wu,2,3 Yuchi Hwang,2 Shih-Yi Huang4 and Eugene Lin2 1 2 3 4

College of Public Health and Nutrition, Taipei Medical University, Taipei, Taiwan Vita Genomics, Inc., Taipei, Taiwan Institute of Medical Sciences, Tzu Chi University, Hualien, Taiwan School of Nutrition and Health Sciences, Taipei Medical University, Taipei, Taiwan

Abstract

Background: Sibutramine, a serotonin and norepinephrine reuptake inhibitor, is used as an anti-obesity drug. Several pharmacogenetic studies have shown correlations between sibutramine effects and genetic variants, such as the 825C/T (rs5443) single nucleotide polymorphism (SNP) in the guanine nucleotide binding protein beta polypeptide 3 (GNB3) gene. Objective: In this study, our goal was to investigate whether a common SNP, -866G/A (rs659366), in the uncoupling protein 2 (UCP2) gene could influence weight reduction and body composition under sibutramine therapy in an obese Taiwanese population. Methods: The study included 131 obese patients, 44 in the placebo group and 87 in the sibutramine group. We assessed the measures of weight loss and body fat reduction at the end of a 12-week treatment period by analysis of covariance (ANCOVA) models using gender, baseline weight, and body fat percentage at baseline as covariates. Results and Conclusion: By comparing the placebo and sibutramine groups with ANCOVA, our data showed a strong effect of sibutramine on weight loss in the combined UCP2 -866 AA + GA genotype groups (p < 0.001). Similarly, a strong effect of sibutramine on body fat percentage loss was found for individuals with the AA or GA genotypes (p < 0.001). In contrast, sibutramine had no significant effect on weight loss (p = 0.063) or body fat percentage loss (p = 0.194) for individuals with the wild-type GG genotype, compared with the placebo group of the same genotype. Moreover, a potential gene-gene interaction between UCP2 and GNB3 was identified by multiple linear regression models for the weight loss (p < 0.001) and for the percent fat loss (p = 0.031) in response to sibutramine. The results suggest that the UCP2 gene may contribute to weight loss and fat change in response to sibutramine therapy in obese Taiwanese patients.

Background Sibutramine is a serotonin and norepinephrine reuptake inhibitor, which is used as an anti-obesity drug to support weight loss in patients with obesity.[1] Weight reduction and changes in body composition with sibutramine treatment in obese patients have been associated with some genetic variants, including the -1291C/G single nucleotide polymorphism (SNP) in the adrenergic alpha-2A-receptor (ADRA2A) gene,[2] the 825C/T (rs5443) SNP in the guanine nucleotide binding protein

beta polypeptide 3 (GNB3) gene,[2-4] and the serotonin transporter gene linked polymorphic region (5-HTTLPR) variant in the solute carrier family 6 member 4 (SLC6A4; serotonin neurotransmitter transporter) gene.[2,5] The uncoupling protein 2 (UCP2) gene encodes a mitochondrial transporter protein, which is highly expressed in adipose tissue, skeletal muscle, and pancreatic islets.[6] A common SNP, -866G/A (rs659366), located in the promoter of the UCP2 gene, has received much attention. The UCP2 -866G/A SNP is not conclusively associated with obesity per se,

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although a previous study[7] revealed that UCP2 -866G/A was associated with fat reduction after a very low-calorie diet among overweight female participants. Moreover, the variant A allele of the UCP2 -866G/A polymorphism was identified to be associated with decreased risk of obesity in adults[8,9] and in children.[10] It has also been shown that the UCP2 -866G/A polymorphism was linked with energy metabolism.[11] Furthermore, there have been contradictory reports regarding its role in type 2 diabetes mellitus, with A allele carriers described as being at increased[9,12] or reduced[13,14] risk. Additionally, the UCP2 -866G/A variant allele has been reported to enhance UCP2 mRNA expression levels in human fat cells.[8,9] Taken together, all of these data indicate that UCP2 is a plausible candidate gene for pharmacogenetic studies of sibutramine therapy. Association studies based on individual SNPs may overlook the associations that can only be found when the combinations of multiple genomic regions are investigated.[15,16] Therefore, it is essential to address gene-gene interactions for defining a trait that implicates complex pharmacokinetic and pharmacodynamic mechanisms, particularly when each involved variant only manifests a minor marginal effect.[17-19] Our previous report[4] mainly described findings from association studies of the GNB3 825C/T polymorphism and sibutramine. The aim of the current study was to test whether UCP2 -866G/A could influence weight reduction and fat loss in response to sibutramine treatment among obese Taiwanese individuals. Furthermore, we extended the previous research to assess the gene-gene interactions based on the UCP2 and GNB3 genes for sibutramine treatment in obese patients.

diseases or with concomitant medications were excluded from the study. The study cohort consisted of 131 patients, 87 in the sibutramine (10 mg daily) group and 44 in the placebo group. Five patients in the sibutramine group and seven in the placebo group dropped out before the study period was completed. In addition, SNP genotyping for one patient in the sibutramine group was undetermined. In this study, the first endpoint was weight loss after 12 weeks versus baseline. The second endpoint was body fat percentage loss at the end of 12 weeks compared with baseline. Total body fat was measured by dual energy x-ray absorptiometry (Lunar Corp., Madison, WI, USA). Genotyping

DNA was isolated from blood samples, using a QIAamp DNA blood kit (Qiagen, Valencia, CA, USA) according to the manufacturer’s instructions. To extract DNA, we used 200 mL of blood, which was further diluted in 200 mL of distilled water.[22] Before the PCR reaction, part of the extracted DNA was diluted to a concentration of 10 mg/mL. The quality of the isolated genomic DNA samples was checked using agarose gel electrophoresis, and the quantities were determined using spectrophotometry. All SNP genotyping was performed using the Taqman SNP genotyping assay (Applied Biosystems Inc. [Life Technologies], Foster City, CA, USA). The primers and probes of SNPs were from the ABI Assay-On-Demand kit (Applied Biosystems). Reactions were carried out according to the manufacturer’s protocol. The probe fluorescence signal detection was performed using the ABI Prism 7900 real-time PCR system (Applied Biosystems).

Materials and Methods Statistical Analysis Patients

Patients participating in the study were originally enrolled in our previous study[4] and have been described in detail elsewhere. Briefly, obese Taiwanese patients were recruited from the Taipei Medical University Hospital in Taipei, Taiwan, in 2008. Before conducting the study, approval was obtained from the Institutional Review Board of the Taipei Medical University Hospital. The approved informed consent form was signed by each subject. We used Asian-adapted definitions[20,21] of obesity, based on the body mass index (BMI): non-obese BMI