Alteration of gastric functions and candidate genes associated with weight reduction in response to sibutramine

Precision medicine of obesity as an integral part of type 2 diabetes management - past, present, and future

Obesity is a complex and heterogeneous condition that leads to various metabolic complications, including type 2 diabetes. Unfortunately, for some, treatment options to date for obesity are insufficient, with many people not reaching sustained weight loss or having improvements in metabolic health. In this Review, we discuss advances in the genetics of obesity from the past decade-with emphasis on developments from the past 5 years-with a focus on metabolic consequences, and their potential implications for precision management of the disease. We also provide an overview of the potential role of genetics in guiding weight loss strategies. Finally, we propose a vision for the future of precision obesity management that includes developing an obesity-centred multidisease management algorithm that targets both obesity and its comorbidities. However, further collaborative efforts and research are necessary to fully realise its potential and improve metabolic health outcomes.

The Niche of n-of-1 Trials in Precision Medicine for Weight Loss and Obesity Treatment: Back to the Future

PURPOSE OF REVIEW

The n-of-1 clinical trials are considered the epitome of individualized health care. They are employed to address differences in treatment response and adverse events between patients, in a comparative effectiveness manner, extending beyond the delivery of horizontal recommendations for all.

RECENT FINDINGS

The n-of-1 design has been applied to deliver precision exercise interventions, through eHealth and mHealth technologies. Regarding personalized and precision medical nutrition therapy, few trials have implemented dietary manipulations and one series of n-of-1 trials has applied comprehensive genetic data to improve body weight. With regard to anti-obesity medication, pharmacogenetic data could be applied using the n-of-1 trial design, although none have been implemented yet. The n-of-1 clinical trials consist of the only tool for the delivery of evidence-based, personalized obesity treatment (lifestyle and pharmacotherapy), reducing non-responders, while tailoring the best intervention to each patient, through "trial and error". Their application is expected to improve obesity treatment and mitigate the epidemic.

Platform introducing individually tailored variability in nerve stimulations and dietary regimen to prevent weight regain following weight loss in patients with obesity

Prevention of weight regain following successful weight loss is a major challenge in the treatment of obesity, irrespective of the weight reduction method used. The majority of individuals regain the lost weight over time; thus, achieving long-term sustainability in weight loss remains an unresolved issue. A compensatory adaptation to the weight loss methods occurs in several body organs and partly explains the lack of sustainable effect. Variability is inherent in many biological systems, and patterns of variability constitute a body mechanism that is active at several levels, starting from the genes and cellular pathways through to the whole-organ level. This study aimed to describe a platform that introduces individually tailored variability in vagal nerve stimulation and dietary regimen to ensure prolonged and sustainable weight loss and prevent weight regain. The platform is intended to provide a method that can overcome the body's compensatory adaptation mechanisms while ensuring a prolonged beneficial effect.

Pharmacogenomics of Medication-Induced Weight Gain and Antiobesity Medications

Obesity is a chronic, multifactorial disease associated with a large number of comorbidities. The clinical management of obesity involves a stepwise integrated approach, beginning with behavioral and lifestyle modification, followed by antiobesity medications, endobariatric procedures, and bariatric surgery. Weight gain and subsequent obesity are common side effects of medications, such as prednisone or antipsychotics. In this era of precision medicine, it is essential to identify patients at the highest risk of weight gain as a result of medication use. Pharmacogenomics could play an important role in obesity management by optimizing use of antiobesity medications as well as minimizing adverse weight gain. This review aims to provide a comprehensive analysis of the current literature on the role of pharmacogenomics in obesity and medication-induced weight gain. In summary, there are more robust studies of medication associated with weight gain and pharmacogenomics, and more studies are needed to understand the role of pharmacogenomics in antiobesity medications.

Association of UCP-3 rs1626521 with obesity and stomach functions in humans

OBJECTIVE

To examine the association of gene variants of uncoupling proteins (UCP)-2 and -3 with obesity and gastrointestinal (GI) traits.

METHODS

In 255 overweight or obese adults, the associations of gene variants in UCP-2 (-3474, rs659366) and UCP-3 (rs1626521, rs2075577, rs15763) with body weight (BW) and GI traits were studied. Gene variants were genotyped by TaqMan® assay. The associations of genotypes with BW and GI traits (gastric emptying, gastric volume, satiety by buffet meal, satiation by nutrient drink test and GI hormones) were assessed using ANOVA corrected for false detection rate (FDR).

RESULTS

A novel UCP-3 gene variant, rs1626521, was identified; it was associated with BW (P = 0.039), waist circumference (P = 0.035), and significantly higher postprandial gastric volume (P = 0.003) and calories ingested at buffet meal (P = 0.006, both significant with FDR). In a subgroup of 11 participants, rs1626521 was also associated with reduced mitochondrial bioenergetics efficiency in skeletal muscle (P = 0.051). In an in vitro study in HEK293 cells, rs1626521 reduced UCP-3 protein expression (P = 0.049). Associations detected between other genotypes and GI traits were nonsignificant with FDR.

CONCLUSIONS

A newly identified functional variant (rs1626521) in UCP-3 affects postprandial gastric functions and satiety and may contribute to weight gain and alter human mitochondrial function.

Gastrointestinal morbidity in obesity

Obesity is a complex disease that results from increased energy intake and decreased energy expenditure. The gastrointestinal system plays a key role in the pathogenesis of obesity and facilitates caloric imbalance. Changes in gastrointestinal hormones and the inhibition of mechanisms that curtail caloric intake result in weight gain. It is not clear if the gastrointestinal role in obesity is a cause or an effect of this disease. Obesity is often associated with type 2 diabetes mellitus (T2DM) and cardiovascular disease (CVD). Obesity is also associated with gastrointestinal disorders, which are more frequent and present earlier than T2DM and CVD. Diseases such as gastroesophageal reflux disease (GERD), cholelithiasis, or nonalcoholic steatohepatitis are directly related to body weight and abdominal adiposity. Our objective is to assess the role of each gastrointestinal organ in obesity and the gastrointestinal morbidity resulting in those organs from the effects of obesity.

Acute and chronic effects of desvenlafaxine on gastrointestinal transit and motility in dogs

BACKGROUND

Antidepressants are commonly used for treating functional gastrointestinal (GI) diseases. However, little is known whether antidepressants improve or impair GI motility. This study aimed at exploring possible effects of a serotonin-norepinephrine reuptake inhibitor, desvenlafaxine succinate (DVS), on GI motility in dogs.

METHODS

Eight dogs chronically implanted with a duodenal cannula and a colon cannula were used in the study. Experiments were performed to assess the effects of a single dose of DVS (50 or 100 mg) and DVS given 50 mg once a day for 2 weeks on gastric emptying of solid, small intestinal transit, and colon transit and contractions.

KEY RESULTS

(1) DVS significantly delayed gastric emptying of solid at a single dose of 50 or 100 mg. The inhibitory effect on gastric emptying was completely blocked by guanethidine (an adrenergic blocking agent). (2) DVS at a single dose of 50 or 100 mg accelerated colon transit, but showed no effects on small bowel transit. (3) DVS at a single dose of 50 mg enhanced colon contractions and guanethidine blocked the effect. (4) Surprisingly, DVS given at 50 mg once daily for 2 weeks did not alter gastric emptying, small bowel transit or colon transit.

CONCLUSIONS & INFERENCES

Acute DVS delays gastric emptying of solid and enhances the contractions of the colon, which may be mediated via the sympathetic mechanism. Acute DVS promotes the transit of the colon but not the small intestine. However, chronic administration of DVS does not seem to alter GI motility.

Obesity genetics: a monopoly game of genes

Obesity is a complex disease that affects all ethnic populations worldwide. The etiology of this disease is based on the interaction of genetic factors, environment and lifestyles indicators. Genetic contribution to the epidemic has gained attention from 2 sources: monogenic syndromes that display severe obesity, and the polygenic model of common obesity. Single mutations can render a syndrome with severe obesity resulting from alteration in central o peripheral appetite control mechanisms. The interaction of several polymorphisms and epigenetic modifications constitute the basic plot for common obesity, molecular ingredients that should not confuse the investigator-they make this riddle even harder to decipher.

The effects of weight loss strategies on gastric emptying and appetite control

The gastrointestinal tract plays an important role in the improved appetite control and weight loss in response to bariatric surgery. Other strategies which similarly alter gastrointestinal responses to food intake could contribute to successful weight management. The aim of this review is to discuss the effects of surgical, pharmacological and behavioural weight loss interventions on gastrointestinal targets of appetite control, including gastric emptying. Gastrointestinal peptides are also discussed because of their integrative relationship in appetite control. This review shows that different strategies exert diverse effects and there is no consensus on the optimal strategy for manipulating gastric emptying to improve appetite control. Emerging evidence from surgical procedures (e.g. sleeve gastrectomy and Roux-en-Y gastric bypass) suggests a faster emptying rate and earlier delivery of nutrients to the distal small intestine may improve appetite control. Energy restriction slows gastric emptying, while the effect of exercise-induced weight loss on gastric emptying remains to be established. The limited evidence suggests that chronic exercise is associated with faster gastric emptying, which we hypothesize will impact on appetite control and energy balance. Understanding how behavioural weight loss interventions (e.g. diet and exercise) alter gastrointestinal targets of appetite control may be important to improve their success in weight management.

Proximal and overall gastric emptying of solids in patients with reduced gastric volume accommodation compared to matched controls

BACKGROUND

Interventions such as gastric surgery and erythromycin result in displacement of solids to the distal stomach and acceleration of overall and proximal gastric emptying. The effect of non-surgical impairment of gastric accommodation on gastric emptying is unclear. Non-surgical impairment of gastric accommodation is associated with accelerated gastric emptying.

AIM

To compare measurements of proximal and overall gastric emptying in patients with reduced postprandial gastric volume accommodation with the emptying rates in age- and gender-matched controls with normal postprandial gastric volume accommodation.

METHODS

We evaluated overall and proximal gastric emptying in nine patients with impaired gastric accommodation and age-equivalent and gender-matched controls. Gastric volumes and emptying were measured using validated SPECT and dual gamma camera scintigraphy, respectively. We compared group differences in overall and proximal gastric emptying t (1/2) by t test.

RESULTS

Patients with impaired postprandial gastric volume accommodation had greater fasting gastric volume. The proportion of food emptied from the proximal stomach immediately after meal ingestion was lower and t (1/2) of proximal gastric emptying correspondingly longer in the group with reduced postprandial gastric accommodation. In contrast, differences were not detected in overall gastric emptying in the two groups, and the ratio of overall to proximal gastric emptying t (1/2) was greater in the group with impaired volume accommodation.

CONCLUSIONS

Proximal stomach emptying is reduced in patients with impaired postprandial volume accommodation; this difference occurs predominantly during the time of meal ingestion. Compensatory mechanisms that result in normal overall gastric emptying require further elucidation.

Review article: the role of gastric motility in the control of food intake

BACKGROUND

From a classical point of view, gastric motility acts to clear the stomach between meals, whereas postprandial motility acts to provide a reservoir for food, mixing and grinding the food and to assure a controlled flow of food to the intestines.

AIM

To summarise findings that support the role of gastric motility as a central mediator of hunger, satiation and satiety.

METHODS

A literature review using the search terms 'satiety', 'satiation' and 'food intake' was combined with specific terms corresponding to the sequence of events during and after food intake.

RESULTS

During food intake, when gastric emptying of especially solids is limited, gastric distension and gastric accommodation play an important function in the regulation of satiation. After food intake, when the stomach gradually empties, the role of gastric distension in the determination of appetite decreases and the focus will shift to gastric emptying and intestinal exposure of the nutrients. Finally, we have discussed the role of the empty stomach and the migrating motor complex in the regulation of hunger signals.

CONCLUSIONS

Our findings indicate that gastric motility is a key mediator of hunger, satiation and satiety. More specifically, gastric accommodation and gastric emptying play important roles in the regulation of gastric (dis)tension and intestinal exposure of nutrients and hence control satiation and satiety. Correlations between gastric accommodation, gastric emptying and body weight indicate that gastric motility can also play a role in the long-term regulation of body weight.

Predictors of weight loss and maintenance in patients treated with antiobesity drugs

BACKGROUND

The prevalence of obesity and related diseases has increased enormously in the last few decades, becoming a very important medical and social issue. Because of the increasing number of people who need weight loss therapies and the high costs associated with these, the search for reliable predictors of success for weight loss and weight maintenance treatments has become a priority.

OBJECTIVE

A literature review was undertaken to identify possible predictors of outcome of weight loss and weight maintenance in patients treated with antiobesity drugs.

RESULTS

For the majority of variables, published data are not sufficient to define their role on final outcomes. Among all considered factors, only early response to treatment appeared to be a reliable positive predictor, and diabetes a negative predictor of weight loss and maintenance.

CONCLUSION

To date, no definitive results have been obtained. Due to the great benefits of reliable predictors of outcome associated to currently available antiobesity drugs and those under development, identifying these predictors has to be supported and encouraged.

Evidences on three relevant obesogenes: MC4R, FTO and PPARγ. Approaches for personalized nutrition

Obesity is a complex disease that results from the interaction between lifestyle (dietary patterns and sedentary habits) and genetic factors. The recognition of a genetic basis for human obesity has driven to identify putative causal genes to understand the pathways that control body mass and fat deposition in humans as well as to provide personalized treatments and prevention strategies to fight against obesity. More than 120 candidate genes have been associated with obesity-related traits. Genome-wide association study has so far identified over 20 novel loci convincingly associated with adiposity. This review is specifically focused on the study of the effects of melanocortin 4 receptor, Peroxisome proliferator-activated receptor γ and fat mass and obesity associated (FTO) gene variants and their interactions with dietary intake, physical activity or drug administration on body weight control. The advances in this field are expected to open new ways in genome-customized diets for obesity prevention and therapy following personalized approaches.

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

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.

A common variant in the adiponectin gene on weight loss and body composition under sibutramine therapy in obesity

In this study, we aimed to explore whether a common single nucleotide polymorphism (SNP), rs266729 (-11,377C > G), in the adiponectin C1Q and collagen domain containing (ADIPOQ) gene could influence weight reduction and fat change under sibutramine therapy in an obese population. There were 131 obese Taiwanese patients, including 44 in the placebo group and 87 in the sibutramine (10 mg daily) group. We assessed the measures of weight loss and body fat reduction at the end of the 12-week treatment period by analysis of covariance (ANCOVA) models using gender, baseline weight, and baseline percent body fat as covariates. By comparing the placebo and sibutramine groups with ANCOVA, our data revealed a strong effect of sibutramine on percent body fat loss (1.9 ± 0.3 vs 4.6 ± 0.5%; P < 0.001) and on weight reduction (2.8 ± 2.0 vs 7.9 ± 1.6 kg; P < 0.001) for subjects with the CC genotype. On the contrary, sibutramine had no significant effect on percent body fat loss or on weight loss in the GG and GC individuals. The results suggest that the SNP rs266729 of the ADIPOQ gene may contribute to weight reduction and fat loss in response to sibutramine therapy in Taiwanese obese patients.

A preliminary candidate genotype-intermediate phenotype study of satiation and gastric motor function in obesity

Stomach motility contributes significantly to fullness sensation while eating and cessation of food intake in humans. Genes controlling adrenergic and serotonergic mechanisms (ADRA2A, GNB3, and SLC6A4) affect gastric emptying (GE), volume (GV), and satiation. Fat mass and obesity-associated gene (FTO) is linked with satiety. Our aim was to examine the association of these candidate genes with stomach functions that signal postprandial fullness: GE, GV, and maximum tolerated volume (MTV). These biomarkers constitute a component of the intermediate phenotype of satiation. A total of 62 overweight or obese participants underwent genotyping of the candidate genes, and validated measurements of GE of solids and liquids by scintigraphy, fasting and postprandial change in GV by SPECT (single photon emission computed tomography), and MTV by nutrient drink test. These markers of satiation were compared for 38 genetic variants in ADRA2A, ADR2C, ADRB3, uncoupling protein (UCP)-2 and -3, GNB3, FTO, and SLC6A4 using a recessive model of inheritance. ADRA2A, ADR2C, UCP-3, GNB3, and FTO loci were significantly associated with the intermediate phenotype markers of satiation: ADR2C (Ins-Del322_325) with accelerated GE; GNB3 (rs1047776) with delayed GE; ADRA2A (rs491589 and rs553668) and GNB3 (rs2269355, rs10849527, and rs3759348) with decreased postprandial GV; ADRA2A (rs3750625) and GNB3 (rs4963517 and rs1129649) with increased postprandial GV; UCP-3 (rs1685356) with increased MTV, and FTO (rs9939609) decreased MTV. Genetic susceptibility to postprandial satiation can be identified through intermediate phenotype markers. With independent validation, these markers may guide patient selection of weight-loss therapies directed at gastric motor functions.

Genetic variants influencing effectiveness of weight loss strategies

Body weight excess has an increasingly high prevalence in the world. Obesity is a complex disease of multifactorial origin with a polygenic condition affected by environmental factors. Weight loss is a primary strategy to treat obesity and its morbidities. Weight changes through life depend on the interaction of environmental, behavioral and genetic factors. Interindividual variation of weight loss in response to different types of interventions (behavioral, caloric restriction, exercise, drug or surgery) has been observed. In this article, currently available data on the role of candidate gene polymorphisms in weight loss are reviewed. Even though control of weight loss by genotype was described in twin and family studies, it is premature to recommend use of genotyping in the design of therapeutic diets or drug treatment. Future studies will have to be large in order to assess the effects of multiple polymorphisms, and will have to control factors other than diet.

Brain serotonin transporter occupancy by oral sibutramine dosed to steady state: a PET study using (11)C-DASB in healthy humans

Sibutramine is a centrally acting monoamine reuptake inhibitor prescribed as an appetite suppressant in the management of obesity. Its effects are mostly attributable to serotonin and norepinephrine transporter (SERT and NET, respectively) inhibition by its potent metabolites mono-desmethylsibutramine (M1) and di-desmethylsibutramine (M2). However, there is a paucity of in vivo data in humans about mechanisms underlying both clinical efficacy and the dose-independent non-response observed in a minority of patients. Twelve healthy male patients (mean age 41 years) completed a double-blind, placebo-controlled, within-subject crossover investigation of brain SERT occupancy by sibutramine 15 mg daily at steady state. Correlations were measured between occupancy and (i) plasma concentrations of sibutramine, M1 and M2; (ii) appetite suppression. (11)C-DASB PET scans were performed on the HRRT camera. Binding potentials (BP(ND)) were calculated by the Logan reference tissue (cerebellum) method. SERT occupancy was modest (mean 30+/-10%), was similar across brain regions, but varied widely across subjects (15-46%). Occupancy was correlated positively (p=0.09) with M2 concentration, but not with sibutramine or M1. No significant appetite suppression was seen at <25% occupancy and greatest suppression was associated with highest occupancy (25-46%). However, several subjects with occupancy (36-39%) in the higher range had no appetite suppression. SERT occupancy by clinical doses of sibutramine is of modest magnitude and may be mediated predominantly by M2 in humans. 5-HT reuptake inhibition may be necessary but is not sufficient for sibutramine's efficacy in humans, supporting preclinical data suggesting that the hypophagic effect requires the co-inhibition of both SERT and NET.

Weight loss and body fat reduction under sibutramine therapy in obesity with the C825T polymorphism in the GNB3 gene

The relationship between weight reduction after sibutramine treatment and a single nucleotide polymorphism, rs5443 (C825T), in the guanine nucleotide binding protein beta polypeptide 3 (GNB3) gene is currently inconsistent. In this study, we aimed to reassess whether the GNB3 rs5443 single nucleotide polymorphism could influence weight reduction and body composition change under sibutramine therapy in 131 obese Taiwanese patients. By comparing the sibutramine and placebo groups with analysis of covariance, our data showed a strong effect of sibutramine on weight reduction (7.4+/-1.4 vs. 3.4+/-1.2 kg; P<0.001) and on body fat percentage loss (4.2+/-0.1 vs. 2.1+/-0.1%; P<0.001) in the combined TT+TC carriers. In contrast, sibutramine caused no significant additional effect on weight loss (P = 0.078) or on body fat percentage loss (P = 0.441) in homozygous C allele carriers.

Feasibility and application of 3-dimensional ultrasound for measurement of gastric volumes in healthy adults and adolescents

OBJECTIVES

Abnormal gastric accommodation to a meal results in dyspepsia. Current methods to measure gastric volume (GV) are invasive or involve ionizing radiation. The aims of this study were to compare fasting and postprandial (PP) GVs measured by (99m)Tc-single photon emission computed tomography (SPECT) and 3-dimensional ultrasound (3D-US) in adults, to assess the performance characteristics of 3D-US measurement of GV during fasting and postprandially, and to develop normative data of GVs in 24 healthy adolescents.

PATIENTS AND METHODS

Eleven adults underwent SPECT and 3D-US simultaneously to measure GV, and a second 3D-US alone within 1 week of the first study. Twenty-four adolescents underwent 1 3D-US measurement. Each study included fasting, a 300-mL Ensure meal, and 0 to 30-minute PP GV measurements.

RESULTS

3D-US identifies GV accommodation to 300mL Ensure. Delta (0-30 minutes average PP fasting) GV was 444mL (median, interquartile range [IQR]=422, 534) for 3D-US and 543mL (median, IQR=486, 564) for SPECT (P=0.15). There were larger interindividual coefficients of variation for GV by 3D-US (60.3% fasting and 21.3% average PP) compared with 19% fasting and 9.2% PP for SPECT. Intraindividual coefficients of variation for the 2 3D-US measurements in adults were 84% fasting and 44% average PP. The estimated GVs for the adolescent group (median [25th-75th IQR]) were 33 (18-53)mL fasting, 330 (284-357)mL 30 minutes PP, and 281 (240-324)mL for delta GV.

CONCLUSIONS

3D-US is a promising method to measure GV accommodation to a meal. Large coefficients of variation reflect the learning stage in development of this promising technique.

Public health genomics: translating obesity genomics research into population health benefits

We examine how a public health genomics framework can be used to move genomic discoveries into clinical and public health practice for obesity prevention and treatment. There are four phases of translational research: T1: discovery to candidate health application; T2: health application to evidence-based practice guidelines; T3: practice guidelines to health practice; and T4: practice to population health impact. Types of multidisciplinary research and knowledge synthesis needed for each phase, as well as the importance of developing and disseminating evidence-based guidelines, are discussed. Because obesity genomics research is mostly in the discovery phase or in the very early phases of translation (T1), the authors present this framework to illustrate the range of translation activities needed to move genomic discoveries in obesity to actual applications that reduce the burden of obesity at the population level.

A controlled pharmacogenetic trial of sibutramine on weight loss and body composition in obese or overweight adults

BACKGROUND & AIMS

Weight loss in response to sibutramine is highly variable. We assessed the association of specific markers of polymorphisms of candidate alpha2A adrenoreceptor, 5-HT transporter, and GNbeta3 genes and weight loss with sibutramine.

METHODS

We conducted a randomized, double-blind, pharmacogenetic study of behavioral therapy and sibutramine (10 or 15 mg daily) or placebo for 12 weeks in 181 overweight or obese participants. We measured body weight, body mass index, body composition, gastric emptying, and genetic variation (alpha2A C1291G, 5-HTTLPR, and GNbeta3 C825T genotypes). Analysis of covariance was used to assess treatment effects on and associations of the specific markers of candidate genes with weight loss and body composition.

RESULTS

Sibutramine, 10 and 15 mg, caused weight loss (P = .009); there was a statistically significant gene by dose interaction for GNbeta3 genotype. For each candidate gene, significant treatment effects at 12 weeks were observed (P < .017) for all specific genotype variants (Delta weight loss in the 2 sibutramine doses vs placebo): alpha2A CC (Delta, approximately 5 kg), GNbeta3 TC/TT (Delta, approximately 6 kg), and 5-HTTLPR LS/SS (Delta, approximately 4.5 kg). Gene pairs resulted in significantly greater sibutramine treatment effects on weight (both P < .002): in participants with 5-HTTLPR LS/SS with GNbeta3 TC/TT; Delta, approximately 6 kg and those with alpha2A CC with GNbeta3 TC/TT; Delta, approximately 8 kg; however, effects were not synergistic. Treatment with sibutramine also resulted in significantly greater reduction of body fat for specific alpha2A CC and GNbeta3 TC/TT genotype variants individually (both P < .02).

CONCLUSIONS

Patient selection based on candidate genes may enhance response to multidimensional sibutramine and behavioral therapy for obesity.

Pharmacogenetics: potential role in the treatment of diabetes and obesity

BACKGROUND

Common genetic variation is associated with increased risk of common metabolic diseases such as type 1 and type 2 diabetes, and obesity. Increasing experience with genetic association studies has led to an understanding of the large sample sizes required to detect a weak to moderate genetic predisposition to disease, the need to reproduce such associations in independent cohorts, and the statistical criteria required to detect a true association. This approach has been used successfully to identify disease-associated gene variation usually in representative populations of large numbers.

OBJECTIVE

To review the current understanding of how common genetic variation influences predisposition to, and treatment of, metabolic disease.

METHODOLOGY

Review of scientific literature.

RESULTS

While there has been progress in understanding how genetic variation predisposes to diabetes and obesity, and how candidate genes may alter drug response, several caveats limit the interpretation and significance of pharmacogenetic studies published to date: those caveats typically include relatively small numbers of participants and choice of endpoints in determining gene-associated differences in response, which may not be clinically significant or relevant as a biomarker or predictor of a desired clinical effect. The genetic variants studied at a given locus are often limited in number and may not represent a comprehensive map of the region under study.

CONCLUSIONS

The pharmacogenetic associations in diabetes and obesity that have been reported to date have had limited impact on the choice of individual treatments. We perceive, however, that this field is in its infancy in these multifactorial metabolic diseases, and with further advances and future drug intervention trials designed in a way that allows a more clear interpretation of the impact of genetic variation on differences in drug response in obesity and diabetes, it is anticipated that pharmacogenetics will have a significant impact on individualizing medical care.