Meta-analysis of the association of the Trp64Arg polymorphism in the beta3 adrenergic receptor with body mass index

The β3-Adrenergic Receptor: Structure, Physiopathology of Disease, and Emerging Therapeutic Potential

The discovery and characterization of the signal cascades of the β-adrenergic receptors have made it possible to effectively target the receptors for drug development. β-Adrenergic receptors are a class A rhodopsin type of G protein-coupled receptors (GPCRs) that are stimulated mainly by catecholamines and therefore mediate diverse effects of the parasympathetic nervous system in eliciting "fight or flight" type responses. They are detectable in several human tissues where they control a plethora of physiological processes and therefore contribute to the pathogenesis of several disease conditions. Given the relevance of the β-adrenergic receptor as a molecular target for many pathological conditions, this comprehensive review aims at providing an in-depth exploration of the recent advancements in β3-adrenergic receptor research. More importantly, we delve into the prospects of the β3-adrenergic receptor as a therapeutic target across a variety of clinical domains.

The Association of Trp64Arg Polymorphism in the Beta-Adrenergic Receptor With Insulin Resistance: Meta-Analysis

BACKGROUND

Insulin resistance is a metabolic disorder that occurs in type 2 diabetes mellitus and obesity. Genetic factors such as β3-adrenoceptor polymorphism (Trp64Arg) may be involved in IR and insulin secretion. However, their association is controversial. Therefore, the current meta-analysis was conducted to clarify the relationship between the Trp64Arg and IR.

METHODS

The literature search was performed in PubMed, Embase, and Web of Science using the keywords "Receptors, Adrenergic, beta-3, Receptors, Adrenergic, Insulin Resistance, Protein-Coupled Receptor Kinase 3" from 2005 to February 7, 2021. We used a random-effects model to calculate the pooled effect size. We conducted subgroup analysis and regression analysis to identify sources of heterogeneity; and Egger's test and funnel plot were used to test publication bias. Finally, we conducted a sensitivity analysis.

RESULTS

We included eight papers with 1,586 subjects. There was a positive correlation between Trp64Arg mutation and insulin level (standardized mean difference = 0.20, 95% confidence intervals: 0.00 to 0.39, I² = 57.6%, p = 0.016). However, there was no association between Trp64Arg and the homeostasis model (HOMA-IR) assessment. Egger's tests showed no publication bias; the sensitivity analysis showed that our results were stable. Regression analysis revealed no source of heterogeneity.

CONCLUSION

Trp64Arg may be associated with IR. European ancestry, obesity, plasma insulin level, and test status may be potential factors affecting the relationship between Trp64Arg and IR.

Everything You Always Wanted to Know about β3-AR * (* But Were Afraid to Ask)

The beta-3 adrenergic receptor (β₃-AR) is by far the least studied isotype of the beta-adrenergic sub-family. Despite its study being long hampered by the lack of suitable animal and cellular models and inter-species differences, a substantial body of literature on the subject has built up in the last three decades and the physiology of β₃-AR is unraveling quickly. As will become evident in this work, β₃-AR is emerging as an appealing target for novel pharmacological approaches in several clinical areas involving metabolic, cardiovascular, urinary, and ocular disease. In this review, we will discuss the most recent advances regarding β₃-AR signaling and function and summarize how these findings translate, or may do so, into current clinical practice highlighting β₃-AR’s great potential as a novel therapeutic target in a wide range of human conditions.

Influence of ADRB2 Gln27Glu and ADRB3 Trp64Arg polymorphisms on body weight and body composition changes after a controlled weight-loss intervention

The β-2 and β-3 adrenergic receptors (ADRB2 and ADRB3) are thought to play a role in energy expenditure and lipolysis. However, the effects of the ADRB2 glutamine (Gln) 27 glutamic acid (glutamate) (Glu) and ADRB3 tryptophan (Trp) 64 arginine (Arg) polymorphisms on weight loss remain controversial. The aim of this study was to investigate the effect of these polymorphisms on changes in weight and body composition during a controlled weight-loss program. One hundred seventy-three healthy overweight and obese participants (91 women, 82 men) aged 18-50 years participated in a 22-week-long intervention based on a hypocaloric diet and exercise. They were randomly assigned to 1 of 4 groups: strength, endurance, strength and endurance combined, and physical activity recommendations only. Body weight, body mass index (BMI), and body composition variables were assessed before and after the intervention. Genetic analysis was carried out according to standard protocols. No effect of the ADRB2 gene was shown on final weight, BMI, or body composition, although in the supervised male group, Glu27 carriers tended to have greater weight (p = 0.019, 2.5 kg) and BMI (p = 0.019, 0.88 kg/m(2)) reductions than did noncarriers. There seems to be an individual effect of the ADRB3 polymorphism on fat mass (p = 0.004) and fat percentage (p = 0.036), in addition to an interaction with exercise for fat mass (p = 0.038). After the intervention, carriers of the Arg64 allele had a greater fat mass and fat percentage than did noncarriers (p = 0.004, 2.8 kg). In conclusion, the ADRB2 Gln27Glu and ADRB3 Trp64Arg polymorphisms may influence weight loss and body composition, although the current evidence is weak; however, further studies are necessary to clarify their roles.

From obesity genetics to the future of personalized obesity therapy

Obesity is a disorder characterized by an excess accumulation of body fat resulting from a mismatch between energy intake and expenditure. Incidence of obesity has increased dramatically in the past few years, almost certainly fuelled by a shift in dietary habits owing to the widespread availability of low-cost, hypercaloric foods. However, clear differences exist in obesity susceptibility among individuals exposed to the same obesogenic environment, implicating genetic risk factors. Numerous genes have been shown to be involved in the development of monofactorial forms of obesity. In genome-wide association studies, a large number of common variants have been associated with adiposity levels, each accounting for only a small proportion of the predicted heritability. Although the small effect sizes of obesity variants identified in genome-wide association studies currently preclude their utility in clinical settings, screening for a number of monogenic obesity variants is now possible. Such regular screening will provide more informed prognoses and help in the identification of at-risk individuals who could benefit from early intervention, in evaluation of the outcomes of current obesity treatments, and in personalization of the clinical management of obesity. This Review summarizes current advances in obesity genetics and discusses the future of research in this field and the potential relevance to personalized obesity therapy.

Brown adipose tissue in adult humans: a metabolic renaissance

Brown adipose tissue (BAT) plays a key role in energy homeostasis and thermogenesis in animals, conferring protection against diet-induced obesity and hypothermia through the action of uncoupling protein 1 (UCP1). Recent metabolic imaging studies using positron emission tomography computerized tomography (PET-CT) scanning have serendipitously revealed significant depots of BAT in the cervical-supraclavicular regions, demonstrating persistence of BAT beyond infancy. Subsequent cold-stimulated PET-CT studies and direct histological examination of adipose tissues have demonstrated that BAT is highly prevalent in adult humans. BAT activity correlates positively with increment of energy expenditure during cold exposure and negatively with age, body mass index, and fasting glycemia, suggesting regulatory links between BAT, cold-induced thermogenesis, and energy metabolism. Human BAT tissue biopsies express UCP1 and harbor inducible precursors that differentiate into UCP1-expressing adipocytes in vitro. These recent discoveries represent a metabolic renaissance for human adipose biology, overturning previous belief that BAT had no relevance in adult humans. They also have implications for the understanding of the pathogenesis and treatment of obesity and its metabolic sequelae.

Effect of β(3)-adrenergic receptor gene polymorphism on body weight change in middle-aged, overweight women

OBJECTIVES

To examine the effects of β(3)-adrenergic receptor gene polymorphism on body weight change during a weight reduction program for middle-aged, overweight women with careful consideration of their energy intake and expenditure.

METHODS

DESIGN

Intervention study of weight reduction for 12 weeks in a community setting.

SUBJECTS

Eighty overweight middle-aged women who completed the individualized lifestyle modification program.

MEASUREMENTS

β(3)-adrenergic receptor gene polymorphism was identified by polymerase chain reaction and consecutive restriction fragment-length polymorphism analysis. Anthropometrical parameters, lifestyle factors, blood lipid and glucose levels, physical activity level and energy intake were measured before and at the end of the program.

RESULTS

The numbers of subjects with the Trp64Trp, Trp64Arg, and Arg64Arg genotypes were 45, 30 and 5, respectively. Baseline characteristics among subjects with the 64Arg allele had significantly smaller decrease in body weight and energy intake than those without the 64Arg allele. The change of other clinical characteristics did not differ between the two groups. After adjusting for the %change of energy intake, the %change of body weight did not differ between the two groups.

CONCLUSION

The 64Arg allele of the β(3)-AR gene is not likely to be the factor determining the difficulty in losing body weight in Japanese middle-aged, overweight women. Lifestyle factors, such as the decrease in energy intake, might mask the effect of the 64Arg allele on body weight loss. Specific considerations for the management of energy intake would be needed to promote body weight loss for those with the 64Arg allele.

Association Between Body Fat Response to Exercise Training and MultilocusADRGenotypes

OBJECTIVE

To examine the contribution of adrenergic receptor (ADR) gene polymorphisms and their gene-gene interactions to the variability of exercise training-induced body fat response.

RESEARCH METHODS AND PROCEDURES

This was an intervention study that used a volunteer sample of 70 healthy, sedentary men (n = 29) and postmenopausal women (n = 41) 50 to 75 years of age, with a BMI < or = 37 kg/m2, from the Washington, DC, metropolitan area. Participants completed 6 weeks of dietary stabilization (American Heart Association diet) before 24 weeks of supervised aerobic exercise training. Diet was maintained throughout the intervention. Change in percent total body fat, percent trunk fat, and fat mass by DXA in ADR genotype groups (Glu12/Glu9 alpha2b-ADR, Trp64Arg beta3-ADR, and Gln27Glu beta2-ADR) at baseline and after 24 weeks of aerobic exercise training was measured.

RESULTS

In multivariate analysis (covariates: age, gender, and baseline value of phenotype), best fit models for percent total body and trunk fat response to exercise training retained main effects of all three ADR gene loci and the effects of each gene-gene interaction (p = 0.009 and 0.003, respectively). Similarly, there was a trend for the fat mass response model (p = 0.03). The combined genetic factors explained 17.5% of the overall model variability for percent total body fat, 22% for percent trunk fat, and 10% for fat mass.

DISCUSSION

The body fat response to exercise training in older adults is associated with the combined effects of the Glu12/Glu9 alpha2b-, Trp64Arg beta3-, and Gln27Glu beta2-ADR gene variants and their gene-gene interactions.

Meta-Analysis of the Association of the Trp64Arg Polymorphism in the β3 Adrenergic Receptor with Insulin Resistance

OBJECTIVE

To clarify the possible association between the Trp64Arg polymorphism and insulin resistance (IR).

RESEARCH METHODS AND PROCEDURES

Articles evaluating the effect of the Trp64Arg polymorphism on IR were identified on the MEDLINE and PubMed databases from 1995 to February, 2004. After extraction of relevant data, main and subgroup meta-analyses were performed to assess the differences in IR indices between Trp/Trp and Trp/Arg genotypes.

RESULTS

Forty eligible papers containing 56 subgroups were included in this meta-analysis. Among a total of 12,805 subjects, 21.9% had Trp64Arg mutation: 20.8%, heterozygotes and 1.1%, homozygotes. Significant associations were found between this mutation and some indices of IR. The weighted mean difference in fasting insulin, 120-minute insulin level after oral glucose tolerance test, and homeostasis model assessment between Arg64 and Trp64 was 0.23 [95% confidence interval (CI), 0.05 to 0.42] pM, 0.89 (95% CI, 0.30 to 1.48) pM, and 0.55 (95% CI, 0.14 to 0.96), respectively. Subgroup analysis further indicated that this significant association existed only in the Asian population (p < 0.01) and in the obese (p = 0.02) and diabetes subgroups (p = 0.03).

DISCUSSION

Numerous studies have been conducted to examine the relationship between the beta3-adrenergic receptor Trp64Arg polymorphism and components of IR syndrome. However, the results have been inconsistent and have led to controversy about whether this polymorphism is associated with these clinical features. The current meta-analysis demonstrated the moderate effects of the Trp64Arg polymorphism on IR in the Asian population and in obese and diabetic subgroups.

Historical perspectives in fat cell biology: the fat cell as a model for the investigation of hormonal and metabolic pathways

For many years, there was little interest in the biochemistry or physiology of adipose tissue. It is now well recognized that adipocytes play an important dynamic role in metabolic regulation. They are able to sense metabolic states via their ability to perceive a large number of nervous and hormonal signals. They are also able to produce hormones, called adipokines, that affect nutrient intake, metabolism and energy expenditure. The report by Rodbell in 1964 that intact fat cells can be obtained by collagenase digestion of adipose tissue revolutionized studies on the hormonal regulation and metabolism of the fat cell. In the context of the advent of systems biology in the field of cell biology, the present seems an appropriate time to look back at the global contribution of the fat cell to cell biology knowledge. This review focuses on the very early approaches that used the fat cell as a tool to discover and understand various cellular mechanisms. Attention essentially focuses on the early investigations revealing the major contribution of mature fat cells and also fat cells originating from adipose cell lines to the discovery of major events related to hormone action (hormone receptors and transduction pathways involved in hormonal signaling) and mechanisms involved in metabolite processing (hexose uptake and uptake, storage, and efflux of fatty acids). Dormant preadipocytes exist in the stroma-vascular fraction of the adipose tissue of rodents and humans; cell culture systems have proven to be valuable models for the study of the processes involved in the formation of new fat cells. Finally, more recent insights into adipocyte secretion, a completely new role with major metabolic impact, are also briefly summarized.

Influence of beta 3-adrenergic receptor Trp64Arg polymorphism on the improvement of metabolic syndrome by exercise-based intervention in Japanese middle-aged males

SUMMARY

OBJECTIVES

To date, there have been few intervention studies concerning the association of metabolic syndrome with beta 3-adrenergic receptor (ADRB3) Trp64Arg polymorphism, although ADRB3 Trp64Arg polymorphism has been reported to be associated with weight gain and insulin resistance by several intervention programs. We examined the influence of ADRB3 Trp64Arg polymorphism on the improvement of metabolic syndrome by an exercise-based intervention program.

METHODS

Thirty-six male employees who satisfied the metabolic syndrome criteria participated in a three-month exercise-based intervention program (average age, 49 ± 6 years old). The improvement rate of metabolic syndrome after the intervention was compared between subjects with and without ADRB3 Trp64Arg polymorphism. The Mantel-Haenszel test was employed to adjust the age, diet, and exercise in analysis of the influence of ADRB3 Trp64Arg polymorphism on metabolic syndrome. The Trp64Arg genotype of the β3-adrenoceptor gene was examined in peripheral blood leukocyte DNA by TaqMan PCR assay.

RESULTS

The distribution of polymorphism was 23 (Trp/Trp), 13 (Trp/Arg), and 0 (Arg/Arg). The metabolic syndrome improvement rates after intervention were 21.7% (Trp/Trp) and 53.8% (Trp/Arg) (p = 0.050). After adjustment individually for age, calorie limitation, and 10,000 or more and 12,000 or more steps of walking per day during intervention, the odds ratios of the Trp/Arg genotype for improvement of metabolic syndrome relative to that of the Trp/Trp genotype were 5.1 (p = 0.043), 4.9 (p = 0.051), 3.7 (p = 0.074), and 5.0 (p = 0.045), respectively.

CONCLUSION

The results suggested that ADRB3 Trp64Arg polymorphism influences the metabolic syndrome improvement rate by exercise-based intervention program.

Weight gain, schizophrenia and antipsychotics: new findings from animal model and pharmacogenomic studies

Excess body weight is one of the most common physical health problems among patients with schizophrenia that increases the risk for many medical problems, including type 2 diabetes mellitus, coronary heart disease, osteoarthritis, and hypertension, and accounts in part for 20% shorter life expectancy than in general population. Among patients with severe mental illness, obesity can be attributed to an unhealthy lifestyle, personal genetic profile, as well as the effects of psychotropic medications, above all antipsychotic drugs. Novel "atypical" antipsychotic drugs represent a substantial improvement on older "typical" drugs. However, clinical experience has shown that some, but not all, of these drugs can induce substantial weight gain. Animal models of antipsychotic-related weight gain and animal transgenic models of knockout or overexpressed genes of antipsychotic receptors have been largely evaluated by scientific community for changes in obesity-related gene expression or phenotypes. Moreover, pharmacogenomic approaches have allowed to detect more than 300 possible candidate genes for antipsychotics-induced body weight gain. In this paper, we summarize current thinking on: (1) the role of polymorphisms in several candidate genes, (2) the possible roles of various neurotransmitters and neuropeptides in this adverse drug reaction, and (3) the state of development of animal models in this matter. We also outline major areas for future research.

Recent progress in the genetics of common obesity

The genetic contribution to interindividual variation in common obesity has been estimated at 40-70%. Yet, despite a relatively high heritability, the search for obesity susceptibility genes has been an arduous task. This paper reviews recent progress made in the obesity genetics field with an emphasis on established obesity susceptibility loci identified through candidate gene as well as genome-wide studies. For the last 15 years, candidate gene and genome-wide linkage studies have been the two main genetic epidemiological approaches to identify genetic loci for common traits, yet progress has been slow and success limited. Only recently have candidate gene studies started to succeed; by means of large-scale studies and meta-analyses at least five variants in four candidate genes have been found to be robustly associated with obesity-related traits. Genome-wide linkage studies, however, have so far not been able to pinpoint genetic loci for common obesity. The genome-wide association approach, which has become available in recent years, has dramatically changed the pace of gene discoveries for common disease, including obesity. Three waves of large-scale high-density genome-wide association studies have already discovered at least 15 previously unanticipated genetic loci incontrovertibly associated with body mass index and extreme obesity risk. Although the combined contribution of these loci to the variation in obesity risk at the population level is small and their predictive value is typically low, these recently discovered loci are set to improve fundamentally our insights into the pathophysiology of obesity.

Effect of the β3-adrenergic receptor gene polymorphism Trp64Arg on BMI reduction associated with an exercise-based intervention program in Japanese middle-aged males

OBJECTIVES

The β3-Adrenergic receptor gene polymorphism Trp64Arg (ADRB3 Trp64Arg) may be associated with weight gain, especially in the East Asian populations. To date, however, the results of various investigations aimed at determining whether ADRB3 Trp64Arg has any effect on weight reduction after intervention have been inconsistent. The aim of this study was to assess the effect of ADRB3 Trp64Arg on weight reduction in a non-pharmacological intervention program.

METHODS

Fifty-seven Japanese men (average age 48.1 ± 5.9 years) whose body mass index (BMI) was >23.0 kg/m(2) participated in an intervention program in which they were encouraged to exercise by walking with a pedometer for 12 weeks. The BMI was measured at the start of the intervention program and on weeks 4, 8, and 12 (end) of the intervention period. The reduction in the BMI (ΔBMI) was calculated as the BMI value obtained at each point in comparison to the baseline (initial) BMI. The participants were classified into two groups: Arg allele non-carriers (Trp/Trp) and Arg allele carriers (Trp/Arg or Arg/Arg), respectively.

RESULTS

Among the participants, 61.4% were Trp/Trp homozygous, 38.6% were Trp/Arg heterozygous, and 0.0% were Arg/Arg homozygous. There was no significant difference in the ΔBMI between Arg allele non-carriers and Arg allele carriers at week 4 [non-carrier mean ± standard deviation (SD) vs. carrier mean ± SD: 0.25 ± 0.43 vs. 0.24 ± 0.35, respectively; p = 0.954], week 8 (0.56 ± 0.68 vs. 0.58 ± 0.61, respectively; p = 0.913), and week 12 (0.70 ± 0.86 vs. 0.84 ± 0.80, respectively; p = 0.545).

CONCLUSIONS

Our results suggest that ADRB3 Trp64Arg does not influence BMI reduction after an exercise-based intervention program.

Lifestyle modifies the relationship between body composition and adrenergic receptor genetic polymorphisms, ADRB2, ADRB3 and ADRA2B: a secondary analysis of a randomized controlled trial of physical activity among postmenopausal women

Genetic variations in the adrenergic receptor (ADR) have been associated with body composition in cross-sectional studies. Recent findings suggest that ADR variants may also modify body composition response to lifestyle. We assessed the role of ADR variants in body composition response to 12 months of resistance training versus control in previously sedentary postmenopausal women. Randomized trial completers were genotyped for A2B (Glu9/12) by fragment length analysis, and B2 (Gln27Glu) and B3 (Trp64Arg) by TaqMan (n = 148, 54% hormone therapy users). Associations between genotypes and body composition, by dual energy X-ray absorptiometry, were analyzed using univariate models. There was no main effect of individual genes on change in body composition, however, gene x exercise interactions were observed for A2B (Glu9/12) and B2 (Gln27Glu) on change in lean soft tissue (LST, p = 0.02); exercisers on the A2B (Glu9-) background gained LST compared to a loss among controls over 12 months (p < 0.05), with no significant intervention effect on the A2B (Glu9+) background. Similarly, there was a significant LST gain with exercise on the B2 (Glu27+) background compared to loss among controls and no intervention effect on the B2 (Glu27-) background. A non-significant association between total body fat (TBF) and B3 (Trp64Arg) persisted among sedentary controls only when intervention groups were separated (%TBF gain with B3 (Arg64+) carriage, p = 0.03); exercisers lost TBF regardless of genotype. In summary, effect modification by lifestyle was demonstrated on ADRA2B, B2, and B3 genetic backgrounds. Individuals with certain ADR genotypes may be more vulnerable to adverse changes in body composition with sedentary behavior, thus these candidate genes warrant further study.

Trp64Arg polymorphism of the β3-adrenergic receptor gene, pre-pregnancy obesity and risk of pre-eclampsia

OBJECTIVE

Trp64Arg polymorphism of the beta3-adrenergic receptor (beta3-AR) gene was reported to be associated with increased risk of obesity and insulin resistance. Both traits have been implicated in the epidemiology and pathogenesis of pre-eclampsia. We investigated the relation of the beta3-AR gene to pre-pregnancy obesity and risk of pre-eclampsia. The present study is a case-control study of 87 Caucasian pre-eclampsia cases and 214 controls.

METHODS

Logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (CI), adjusted for maternal age and parity. Normotensive carriers of the variant allele (i.e. Arg64 allele) were 3.6 times more likely to be obese (body mass index (BMI) > or = 30 kg/m2) as compared with women not carrying the variant allele (OR = 3.6, 95% CI 0.8-15.0).

RESULTS

Arg64 allele was more frequent in controls as compared with pre-eclampsia cases (11.7 vs. 5.3%, p < 0.01). After adjusting for age and parity, carriers experienced a 60% reduction in risk of pre-eclampsia (OR = 0.4, 95% CI 0.2, 0.9) as compared with women not carrying this allele. The association between carriage of the variant allele and risk of pre-eclampsia appeared to be modified by maternal BMI. Compared with lean carriers, lean women without the variant allele experienced only a small increase in the risk of pre-eclampsia (OR = 1.5; 95% CI: 0.6, 3.9). The OR for overweight women without the variant allele was 7.3 (95% CI 2.7-19.2).

CONCLUSIONS

Our results suggest a puzzling relationship between the polymorphism and the risk of pre-eclampsia. Future studies are needed to confirm these findings.

No effect of the Trp64Arg variant of the beta3-adrenergic receptor gene on weight loss by diet and exercise intervention among Japanese adults

Controversy remains as to whether the presence of the tryptophan-to-arginine (Trp64Arg) variant of the beta(3)-adrenergic receptor gene impedes the magnitude of body weight loss by diet and exercise intervention. The objectives of the present study were to compare the changes in body weight between carriers and noncarriers of the Trp64Arg variant before and after 6 months of diet and exercise interventions for weight loss. A total of 37 middle-aged Japanese individuals (12 carriers and 25 noncarriers of the Trp64Arg variant) participated in the study. There were no significant differences in body weight between the 2 groups at the baseline. There were significant reductions in body weight both in carriers and noncarriers, but no significant differences between the 2 groups with respect to changes in these variables. The weight changes were -2.52 kg (95% confidence interval [CI], -3.56 to -1.48) among carriers and -1.89 kg (95% CI, -2.65 to -1.13) among noncarriers, and the change in the variant carrier group minus the change in the variant noncarrier group was -0.47 (95% CI, -1.97 to 1.02). These results suggest that the presence of the Trp64Arg variant of the beta(3)-adrenergic receptor gene may not play a major role as a hindrance to weight reduction.

Association of the beta3-adrenergic receptor Trp64Arg polymorphism with common metabolic traits: studies of 7605 middle-aged white people

AIM/HYPOTHESIS

The functional variant Trp64Arg in the beta(3)-adrenergic receptor has previously been examined for association with obesity and insulin resistance with ambiguous results. For further evaluation the present study examined the impact of the Trp64Arg variant on the pathogenesis of type 2 diabetes and obesity in a relatively large, homogenous study population.

METHODS

The Trp64Arg polymorphism was genotyped in 7605 Danish subjects using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Association was examined in case-control studies of obesity (1529 cases and 6049 controls) and type 2 diabetes (1373 cases and 4742 controls) and quantitative trait analyses among 5822 individuals. Furthermore, the association of Trp64Arg with type 2 diabetes was examined in a meta-analysis.

RESULTS

The Trp64Arg polymorphism was not associated with obesity. However, the Arg-allele was associated with a slightly increased risk of type 2 diabetes (OR1.15 (CI: 1.01-1.31); p=0.04), increased insulin resistance estimated by homeostasis model assessment (p=0.01), higher fasting serum insulin levels (p=0.01), and higher levels of plasma glucose 2-h after glucose ingestion (p=0.02). After sex stratification these associations were only present among women. Furthermore, the Arg-allele was borderline associated with type 2 diabetes in a meta-analysis of the present and 26 previous studies (p=0.06, OR1.27 (CI: 0.99-1.63)) (n=18891).

CONCLUSION/INTERPRETATION

Trp64Arg does not confer an increased risk of obesity among Danes. Yet, in the present study of 7605 Danes the variant is associated with type 2 diabetes and quantitative traits related to type 2 diabetes.

Mutations in the beta1 adrenergic receptor gene and massive obesity in Japanese

Catecholamines strongly promote lipolysis and thermogenesis, and play a central role in the regulation of body fat content. The beta1 adrenergic receptor (BAR-1) is a major mediator of catecholamine-induced lipolysis and thermogenesis. To explore whether mutations in the BAR-1 gene contribute to morbid obesity in Japanese, we scanned for mutations in the coding sequence of the gene in 50 morbid obese [body mass index (BMI)>==35.0kg/m(2); 99.7th percentile] Japanese subjects. Direct DNA sequencing was performed following polymerase chain reaction (PCR) amplification. Two common polymorphisms, Gly49Arg and Arg389Ser, were detected in these subjects. The frequencies of these polymorphisms, as determined by PCR-restriction fragment length polymorphism (RFLP) analysis, showed no significant difference between 180 severely obese subjects (BMI>==30.0kg/m(2); 97th percentile) and 132 control (BMI<25.0kg/m(2)) subjects. This study represents the first investigations of genetic variations of BAR-1 in relationship to morbid obesity and suggests mutations in the BAR-1 coding sequence is not likely a major cause of morbid obesity at least in Japanese.

Metabolic syndrome and ADRB3 gene polymorphism in severely obese patients from South Italy

OBJECTIVE

To evaluate the prevalence of beta(3)-adrenergic receptor (ADRB3) Trp64Arg polymorphism and its relationship with the metabolic syndrome in severe obesity.

DESIGN

Cross-sectional outpatients study.

PATIENTS AND METHODS

In 265 (100 men) severely obese non-diabetic subjects and 78 (25 men) healthy volunteers, genomic DNA was isolated from peripheral leukocytes. In obese patients, plasma concentrations of leptin, lipids, glucose and insulin, the homeostasis model assessment index and blood pressure have been measured. The Trp64Arg mutation was identified with the real-time TaqMan method.

RESULTS

Neither genotype distribution nor allele frequency differed between the two groups. The metabolic syndrome prevalence was 59% in obese subjects, and was higher in men than in women (65 vs 55%: P=0.03). The body mass index (BMI) was related to age tertiles (beta=0.08; P<0.001; multiple linear regression) in Trp64Arg-positive obese subjects.

CONCLUSION

We confirm the high prevalence of the metabolic syndrome among severely obese subjects. ADRB3 polymorphism was significantly related to insulin resistance only in obese male subjects. Moreover, increased BMI was related to age in obese subjects with the ADRB3 polymorphism.

The Emerging Pharmacogenomics of the β‐Adrenergic Receptors

Beta-adrenergic signaling mechanisms are of central importance to cardiovascular health and disease. Modulation of these pathways represents an important pharmacologic approach to the treatment of heart failure and hypertension. Advances in molecular genetics have identified genetic polymorphisms in the human beta-adrenergic receptor genes; some of this variation predicts changes in protein sequence/structure, and potentially changes in function, of the b-adrenergic receptors. This article reviews the current state of knowledge and understanding of the genetic variation present in the three human beta-adrenergic receptor genes. Already, variation in these genes has been associated with observed differences in several cardiovascular phenotypes. This work has led to the demonstration of functional differences in activity between receptors with certain known polymorphisms and "wild-type" receptors. An understanding of these polymorphisms is key to the development of studies of how differences in drug response/effects may be mediated by these polymorphisms. Such studies are anticipated to provide a foundation for the development of novel pharmacologic approaches where selection of and dosing of cardiovascular therapy is tailored to individuals on the basis of each patient's specific genetic makeup.

Impact of variation in ADRB2, ADRB3, and GNB3 genes on body mass index and waist circumference in a Brazilian population

The potential effect of variants in three catecholaminergic pathway genes (ADRB2, ADRB3, and GNB3) on obesity-related traits was investigated in an European-derived Brazilian population. Three-hundred and thirty-five individuals were screened for the ADRB2 Arg16Gly and Gln27Glu, ADRB3 Trp64Arg, and GNB3 814G-->A and 825C-->T polymorphisms using PCR-based methods. The association of the polymorphisms with quantitative variables was tested separately in each sex by analysis of covariance using general linear models, including age as a covariate. Only the ADRB2 Arg16Gly polymorphism was associated with higher body mass index and waist circumference. This association was restricted to the male sample. As the number of studies increases, it becomes clear that the genetic bases of obesity are complex, with sex-specific effects a playing an important role in its etiology. In the context of this European-derived population, the ADRB2 gene accounts for a significant part of obesity-related phenotypes in males.

Energy expenditure, body composition and insulin response to glucose in male twins discordant for the Trp64Arg polymorphism of the beta3-adrenergic receptor gene

AIM

The tryptophan to arginine change in position 64 (Trp64Arg) polymorphism of the beta3-adrenergic receptor (beta3AR) gene has been associated with an increased prevalence of obesity, insulin resistance and type 2 diabetes. In this, decreased rates of energy expenditure and impaired insulin secretion could play a role.

METHODS

In 10 male twin pairs discordant for the Trp64Arg polymorphism, we examined insulin response to glucose by an oral glucose tolerance test (OGTT), a frequently sampled intravenous glucose tolerance test (FSIGT), body composition by the bioimpedance method, dual-energy X-ray absorptiometry scanning and energy expenditure by indirect and direct calorimetry.

RESULTS

Twins heterozygous for the Trp64Arg polymorphism showed significantly lower fat mass independent of the method used, and significantly lower fasting insulin and glucose concentrations compared with their homozygous wild-type co-twins. Correspondingly, insulin resistance and insulin secretion determined by homeostasis model assessment were significantly lower in twins carrying the Trp64Arg polymorphism. However, there were no significant differences in adiponectin levels, insulinogenic index assessed by OGTT, or insulin sensitivity, acute insulin response to glucose, glucose effectiveness or insulin disposition index assessed by minimal modelling of the FSIGT. Furthermore, there were no differences in sleeping, resting or post-prandial energy expenditure.

CONCLUSIONS

In male twins with a high similarity in genetic and environmental background, the Trp64Arg polymorphism of the beta3AR gene is associated with lower fat mass, fasting insulin levels and an appropriate insulin response to glucose. Thus, heterozygosity for the Trp64Arg variant is unlikely to increase the risk of obesity, insulin resistance or type 2 diabetes.

Pharmacogenetics of the human beta-adrenergic receptors

The beta-adrenergic receptors (ADRBs) are cell surface receptors that play central roles in the sympathetic nervous system. Pharmacological targeting of two of these receptors, ADRB1 and ADRB2, represents a widely used therapeutic approach for common and important diseases including asthma, hypertension and heart failure. Genetic variation in both ADRB1 and ADRB2 has been linked to both in vitro and clinical disease phenotypes. More recently, interest has shifted to studies that explore potential interaction between variation in ADRBs and medications directed at these important receptors. This paper reviews the current state of knowledge and understanding of ADRB genetic variation and explores the likely direction of future studies in this area.

Comparison of Body Fat Distribution and Blood Lipid Profiles according to Trp64Arg Polymorphism for the .BETA.3-Adrenergic Receptor Gene in Korean Middle-Aged Women

The aim of this study was to determine whether there was an association between body fat distribution, blood lipid profiles, and beta 3-adrenergic receptor gene polymorphism in Korean middle-aged women. Subjects were grouped according to BMI as obese (> or = 5 BMI, n = 95) or non-obese (BMI<25, n = 93). The Trp64Arg mutation of the beta 3-adrenergic receptor gene was detected by PCR-RFLP. Skinfold thickness, body circumference, intra-abdominal fat area by CT, and blood lipid profiles were also measured. Data were compared using ANOVA, Bonferroni t-test, and Chi-square. Significance for statistical analyses were set at p<0.05. In the obese group, 63.16% were Trp64Trp homozygotes and 36.84% were Trp64Arg heterozygotes, compared to 80.65% who were Trp64Trp homozygotes and 19.35% who were Trp64Arg heterozygotes in the non-obese group. These results indicated a significant (chi-square = 4.943, p<0.05) difference between the two groups. Frequency of the Arg64 allele in the obese group (16.84%) showed a significant (chi-square = 4.185, p<0.05) difference as compared to the non-obese group (9.68%). Skinfold thickness and body circumference of the Trp64Arg heterozygote group showed a consistent increase as compared to the Trp64Trp homozygote group. Visceral fat area and VSR of Trp64Arg heterozygote group showed a higher tendency than Trp64Trp homozygotes in the obese group, but these differences were not statistically significant. In conclusion, the Trp64Arg polymorphism of the beta 3-adrenergic receptor gene is associated with obesity in middle-aged Korean women, but it is difficult to suggest the prominent association of the Trp64Arg polymorphism of the beta 3-adrenergic receptor gene with prevalence of abdominal obesity or dyslipidemia in Korean middle-aged women.

The frequency of Trp64Arg polymorphism of the β3-adrenergic receptor gene in healthy and obese Hungarian children and its association with cardiovascular risk factors

OBJECTIVE

To estimate the frequency of Arg64 allele of the beta(3)-adrenergic receptor (3-BAR) gene in healthy (H) and obese (O) Hungarian children, and to look for possible associations between this polymorphism and some clinical and metabolic characteristics of obese children.

PATIENTS/METHODS

In all, 147 healthy (male: 68) and 295 obese (male: 168) children were examined. The average age of the children in the two groups was 12.4+/-1.7 vs 12.6+/-3.2, respectively. Exon 1 of 3-BAR was amplified by polymerase chain reaction and the fragments were digested with BstN1. In obese children, oral glucose tolerance test was carried out and blood pressure (BP) was checked.

RESULTS

The frequency of Trp64Arg polymorphism in normal and obese Hungarian children was similar (H vs O: n=14/9.5% vs n=35/11.8%). Obese children carrying the Arg64 allele (n=35, male: 23) were compared to randomly chosen, obese children without the Arg64 allele (n=35, male: 20). A significant difference was found between the body weight (81.2+/-23.2 vs 75.6+/-17.7 kg; mean+/-s.d.; P<0.01), body fat (38.8+/-3.9 vs 36.5+/-2.3%; mean+/-s.d.; P<0.05), mean fasting insulin levels (31.4+/-16.7 vs 16.9+/-7.6 microIU/ml; P<0.001) and mean systolic BP values (125.2+/-10.1 vs 114.5+/-8.3 mmHg; P<0.001) of the two obese groups.

CONCLUSIONS

The frequency of Trp64Arg polymorphism was similar in Hungary as compared to other European countries. Although the prevalence of this polymorphism was similar in H and O children, the presence of Arg64 allele seems to be associated with increased adiposity, elevated systolic BP and higher fasting insulin levels.

Association between β-adrenergic receptor polymorphisms and their G-protein-coupled receptors with body mass index and obesity in women: a report from the NHLBI-sponsored WISE study

OBJECTIVES

The beta-adrenergic receptor (betaAR) genes are candidate genes for obesity because of their roles in energy homeostasis and promotion of lipolysis in human adipose tissue. Objective is to determine the association between obesity and polymorphisms in genes of the beta(1)AR (ADRB1), beta(2)AR (ADRB2), beta(3)AR (ADRB3), Gs protein alpha (GNAS1), to which all three beta-receptors couple and the G protein beta3 subunit (GNB3), to which beta(3)ARs couple.

DESIGN

A case-control genetic association study.

SUBJECTS

A total of 643 black or white women enrolled in Women's Ischemia Syndrome Evaluation (WISE) study.

MEASUREMENTS

Genotypes were determined by PCR with single primer extension. Associations between genotype and body mass index (BMI), waist-to-hip ratio (WHR), waist circumference, and obesity were made.

RESULTS

Polymorphisms in the three betaAR genes, GNAS1, and GNB3 were not associated with BMI, WHR, waist circumference, or obesity. Linear and logistic regression analyses found no contribution of either genotype or haplotype with anthropometric measurements or obesity.

CONCLUSIONS

Our study suggests that among American women with suspected coronary heart disease, polymorphisms in the betaARs and their G-protein-coupled receptors do not contribute to increased BMI, WHR, waist circumference, or obesity. Given that 50% of all women die from coronary heart disease, and a higher percentage have heart disease during their lifetime, our results are likely generalizable to many American women.

No association of the Trp 64 Arg mutation of the beta3-adrenergic receptor gene with obesity, type 2 diabetes mellitus, hyperlipidemia, and hypertension in Japanese patients with schizophrenia

OBJECTIVE

This study was conducted to address the question of whether the beta3-adrenergic receptor gene mutation (Trp 64 Arg) is associated with metabolic disease in Japanese patients with schizophrenia.

METHODS

In a cross-sectional study, 89 participants were grouped into three genotypes. The 64 Arg allelic frequency in patients with or without metabolic disease was analyzed. Anthropometrics variables and biochemical parameters were compared among the genotypes.

RESULTS

The 64Arg allele, which had a frequency of 0.22, was not associated with obesity, type 2 diabetes mellitus, dyslipidemias, or hypertension. No significant differences among the genotypes were found in current age, age at diagnosis with schizophrenia, body mass index, waist-hip ratio, plasma glucose, plasma insulin, triglycerides, free fatty acids. Patients with the 64 Arg allele had greater 24-h excretion of norepinephrine than those lacking the variant (p = 0.019).

CONCLUSION

The 64 Arg allelic mutation is not associated with obesity, type 2 diabetes mellitus, lipid metabolism dysfunction, or hypertension in Japanese patients with schizophrenia.

Pharmacogenetics of antipsychotic-induced weight gain

RATIONALE

Antipsychotic medications have been associated with considerable weight gain. The degree of inter-individual variability and known genetic contributions to obesity suggest a combination of genetic and environmental factors. In the absence of established mechanisms and valid predictors for this relevant adverse effect, pharmacogenetic studies may provide the basis for the development of individualized treatment and preventive interventions.

OBJECTIVE

The aim of the present review is to analyze the theoretical and empirical knowledge base for the selection of the most promising target genes that may contribute to antipsychotic-induced weight gain.

METHODS

Examination of the preclinical and clinical literature that can inform the rational choice of target genes that may play a role in the development of adverse changes in body composition associated with antipsychotic treatment.

RESULTS

Theoretically, candidate gene selection can be guided by knowledge about molecular pathways associated with obesity, receptors modulated by antipsychotic drugs, and enzymes implicated in their metabolism and bioavailability. While most available data relate to the general mechanisms of obesity and few studies have directly examined the genetic contributions to antipsychotic-induced weight gain, several genes warrant further investigation. These include the 5-HT(2C), pro-opiomelanocortin, leptin, ghrelin, tumor necrosis factor alpha, adiponectin, dopamine D(2) receptor, histamine-H(1) receptor, and alpha(1), beta(2) and beta(3) adrenergic receptor genes.

CONCLUSIONS

Pharmacogenetic studies can provide powerful tools for the pre-treatment identification of individuals at high risk for antipsychotic-induced weight gain, to uncover biological mechanisms that may even generalize to non-drug-induced weight gain, and to isolate novel targets for treatments of weight gain and obesity. To enhance power, future studies should pay close attention to population selection and avoidance/control of confounds, particularly past treatment exposure.

Melanocortin-4 receptor gene variant I103 is negatively associated with obesity

Several rare mutations in the melanocortin-4 receptor gene (MC4R) predispose to obesity. For the most common missense variant V103I (rs2229616), however, the previously reported similar carrier frequencies in obese and nonobese individuals are in line with in vitro studies, which have not shown a functional implication of this variant. In the present study, we initially performed a transmission/disequilibrium test on 520 trios with obesity, and we observed a lower transmission rate of the I103 allele (P=.017), which was an unexpected finding. Therefore, we initiated two large case-control studies (N=2,334 and N=661) and combined the data with those from 12 published studies, for a total of 7,713 individuals. The resulting meta-analysis provides evidence for a negative association of the I103 allele with obesity (odds ratio 0.69; 95% confidence interval 0.50-0.96; P=.03), mainly comprising samples of European origin. Additional screening of four other ethnic groups showed comparable I103 carrier frequencies well below 10%. Genomic sequencing of the MC4R gene revealed three polymorphisms in the noncoding region that displayed strong linkage disequilibrium with V103I. In our functional in vitro assays, the variant was indistinguishable from the wild-type allele, as was the result in previous studies. This report on an SNP/haplotype that is negatively associated with obesity expands the successful application of meta-analysis of modest effects in common diseases to a variant with a carrier frequency well below 10%. The respective protective effect against obesity implies that variation in the MC4R gene entails both loss and gain of function.

The genetics of obesity

Obesity prevalence has increased markedly over the past few decades. The obesity pandemic has huge implications for public health and our society. Although multiple studies show that the genetic contribution to obesity is significant, our genes have not changed appreciably over this time period. It was hypothesized that natural selection favors genotypes that result in a thrifty metabolism because individuals who carry these genotypes would be more likely to survive times of nutrient scarcity and to pass these genotypes to successive generations. Now that most of the world has adopted an increasingly "obesigenic" lifestyle of excess caloric intake and decreased physical activity, these same genes contribute to obesity and poor health. With the exception of the rare mutations that cause severe morbid obesity, it seems that numerous genes, each with modest effect, contribute to an individual's predisposition toward the more common forms of obesity. Variants in several candidate genes have been identified: association analyses and functional studies show that they contribute to modest obesity and related phenotypes. More recently, insights regarding gene-gene interactions have begun to emerge. Genome-wide scans for obesity phenotypes have led to the identification of several chromosome regions that are likely to harbor obesity susceptibility genes. Because of the increasing number of genome scans, several regions of replication have emerged. Positional cloning of these genes will undoubtedly unveil new insights into the molecular and pathophysiologic mechanisms of energy homeostasis and obesity.

The Trp(64)Arg polymorphism of the beta(3)-adrenergic receptor gene is not associated with body weight or body mass index in Japanese: a longitudinal analysis

The beta(3)-adrenergic receptor (ADRB3) is expressed mainly in visceral adipose tissue and is thought to contribute to lipolysis and the delivery of free fatty acids to the portal vein. Although many studies have examined the relationship between the Trp(64)Arg mutation of ADRB3 and obesity, the results have been inconsistent. We examined the cross-sectional relationship of ADRB3 variants with indexes of obesity, and their longitudinal changes over 10 yr, in men and women, aged 40-69 yr, who were randomly selected from the Japanese rural population. The study considered both dietary energy intake and physical activity levels. Among the 746 participants, the genotype frequencies of the Trp(64)Trp, Trp(64)Arg, and Arg(64)Arg variants were 483, 224, and 39, respectively. The cross-sectional analysis showed no significant differences in height, weight, body mass index, blood pressure, serum total and high density lipoprotein cholesterols, and hemoglobin A(1c) among the genotype groups even after adjustments for gender, age, smoking, alcohol drinking, physical activity, and energy intake. No significant differences in the weight changes between the genotype groups were evident in the longitudinal analysis. We conclude that the Trp(64)Arg mutation of ADRB3 has little or no influence on either body weight or body mass index in the general Japanese population.

Beta-adrenoceptor polymorphisms

There can be no doubt that beta(1)-, beta(2)- and beta(3)-adrenoceptor genes have genetic polymorphisms. Two single nucleotide polymorphisms have been described for the beta(1)- (Ser49Gly; Gly389Arg), three for the beta(2)- (Arg16Gly; Gln27Glu; Thr164Ile) and one for the beta(3)-adrenoceptor subtype (Trp64Arg) that might be of functional importance. The possibility that changes in expression or properties of the beta-adrenoceptors due to single nucleotide polymorphisms might have phenotypic consequences influencing their cardiovascular or metabolic function or may contribute to the pathophysiology of several disorders like hypertension, congestive heart failure, asthma or obesity is an idea that has attracted much interest during the last 10 years. At present, it appears that these beta-adrenoceptor polymorphisms are very likely not disease-causing genes, but might be risk factors, might modify disease and/or might influence progression of disease. The aim of this review is to provide an overview of the functional consequences of such beta-adrenoceptor polymorphisms in vitro, ex vivo and in vivo.

Obesity--is it a genetic disorder?

Obesity is one of the most pressing problems in the industrialized world. Twin, adoption and family studies have shown that genetic factors play a significant role in the pathogenesis of obesity. Rare mutations in humans and model organisms have provided insights into the pathways involved in body weight regulation. Studies of candidate genes indicate that some of the genes involved in pathways regulating energy expenditure and food intake may play a role in the predisposition to obesity. Amongst these genes, sequence variations in the adrenergic receptors, uncoupling proteins, peroxisome proliferator-activated receptor, and the leptin receptor genes are of particular relevance. Results that have been replicated in at least three genome-wide scans suggest that key genes are located on chromosomes 2p, 3q, 5p, 6p, 7q, 10p, 11q, 17p and 20q. We conclude that the currently available evidence suggests four levels of genetic determination of obesity: genetic obesity, strong genetic predisposition, slight genetic predisposition, and genetically resistant. This growing body of research may help in the development of anti-obesity agents and perhaps genetic tests to predict the risk for obesity.

Difficulty in losing weight by behavioral intervention for women with Trp64Arg polymorphism of the beta3-adrenergic receptor gene

OBJECTIVE

Trp64Arg mutation in the beta(3)-adrenergic receptor (beta(3)AR) gene is relatively common in Japanese people. However, it has not been clear whether persons with Trp64Arg mutation in the beta(3)AR gene tend to have obesity and difficulty in losing weight even with a restricted diet and exercise. We investigated the response of body weight and metabolic factors to behavioral intervention in Japanese women with Trp64Arg mutation in the beta(3)AR gene.

DESIGN

A 3-month behavioral intervention study using a combination of diet and exercise programs.

SUBJECTS

A total of 76 perimenopausal women with no clinical symptoms (age: 54.7+/-7.7 y, body mass index (BMI): 21.0-33.0 kg/m(2)).

MEASUREMENTS

Anthropometric measurements (weight, height, body fat, waist circumference, hip circumference, skin fold, resting energy expenditure and blood pressure) and metabolic measurements (serum levels of cholesterol, triglyceride, phospholipid, nonesterified fatty acid, glucose, insulin and leptin) and determination of the beta(3)AR genotype by polymerase chain reaction followed by BstNI digestion.

RESULTS

At the baseline of BMI, body weight, body fat, waist circumference, hip circumference, the arm skin fold, resting energy expenditure, or blood lipid and glucose profiles, there was no significant difference in participants with/without mutation of the beta(3)AR gene. The intervention yielded a body weight reduction in 69 and 48%, and induced a significant difference in weight loss (-0.74 and -0.01 kg) for women with wild-type and Trp64Arg mutation, respectively. Significant differences of anthropometric parameters were found in body weight, BMI, waist and hip circumferences and blood pressure of wild type by the intervention. However, women with Trp64Arg mutation did not show significant changes in these anthropometric parameters, except for hip circumference. A significant difference was found in high-density lipoprotein cholesterol (HDL-C) and in the low-density lipoprotein cholesterol/HDL-C ratio in both genotypes.

CONCLUSION

The results of the present study suggest that the Trp64Arg mutation of the beta(3)AR gene is associated with difficulty in losing weight through behavioral intervention, although it is not related to obesity-related phenotypes and resting energy expenditure before the intervention.

Interactions among the beta2- and beta3- adrenergic receptor genes and total body fat and abdominal fat level in the HERITAGE Family Study

OBJECTIVE AND SUBJECTS

Interactions between markers in the beta2- and beta3-adrenergic receptor (ADR) genes and total body fat and computerized tomography-measured abdominal fat phenotypes were studied in the HERITAGE Family Study cohort of Black (n=205; 81 males and 124 females) and White (n=415; 198 males and 217 females) subjects before and after an endurance training program.

RESULTS

In Black subjects, beta2- and beta3-ADR gene variants showed evidence of interactions on changes in total body fat mass and abdominal fat area (P<0.005 and =0.010, respectively). Black subjects who were carriers of both beta2-ADR Arg16 and beta3-ADR Arg64 alleles had a greater decrease in total fat mass as well as abdominal total and subcutaneous, but not visceral fat areas in response to endurance training than subjects with other genotype combinations (P from 0.011 to 0.047). After correction for multiple tests, the findings remained essentially unchanged for total body fat mass and abdominal fat area, but became nonsignificant for subcutaneous fat area. The changes in abdominal fat correlated positively with the changes in fat mass (P<0.0001). The interactions between beta2 and beta3-ADR gene markers accounted for a maximum of 3% of the variances in the response of total fat mass and abdominal fat area to endurance training in Black subjects but it was not significant in White subjects.

CONCLUSION

Interactions between sequence variants in the beta2-beta3-ADR gene contributed to the changes in fat mass and abdominal adiposity in response to endurance training in Black subjects.

TRP64ARG polymorphism of the beta 3-adrenergic receptor gene and obesity risk: effect modification by a sedentary lifestyle

AIM

We performed a case-control study to assess the association between obesity risk and the Trp64Arg polymorphism of the beta 3-adrenergic receptor gene.

METHODS

Obese subjects [n = 159; body mass index (BMI) > 30 kg/m2] and controls (n = 154; BMI < 25 kg/m2) were compared using multivariable logistic regression to control for potential confounders.

RESULTS

A higher obesity risk (adjusted OR: 2.98; 95% CI: 1.00-8.56; p = 0.05) was associated with the Trp64Arg polymorphism among sedentary, but not among more active people.

CONCLUSIONS

Our results suggest that the TRP64ARG polymorphism of the ADRB3 seems to be a risk factor for obesity that is dependent on a sedentary lifestyle.

The peroxisome proliferator-activated receptor-gamma2 Pro12Ala polymorphism

Peroxisome proliferator-activated receptor (PPAR)-gamma is a transcription factor with a key role in adipocyte differentiation. The Ala allele of the common Pro12Ala polymorphism in the isoform PPAR-gamma2 is associated with reduced risk for type 2 diabetes. The effect on the individual is weak, but because of a prevalence of >75% of the high-risk Pro allele, the population-attributable risk is enormous. The in vivo effects of the polymorphism are secondary to alterations in adipose tissue, where PPAR-gamma2 is predominantly expressed. Moderate reduction in transcriptional activity of PPAR-gamma as a result of the polymorphism modulates production and release of adipose-derived factors. Both decreased release of insulin-desensitizing free fatty acids, tumor necrosis factor-alpha, and resistin and increased release of the insulin-sensitizing hormone adiponectin result in secondary improvement of insulin sensitivity of glucose uptake and suppression of glucose production. The population effect of this polymorphism may be modulated by environmental or genetic factors such as obesity, ethnicity, ratio of unsaturated to saturated fatty acids, and genetic background. Once diabetes has developed, the protective effect of the Ala allele may be lost, since increased vascular complications and more pronounced beta-cell dysfunction have been reported. These observations, however, are currently unexplained. In conclusion, the Pro12Ala polymorphism in PPAR-gamma2 represents the first genetic variant with a broad impact on the risk of common type 2 diabetes. The precise understanding of its mechanism may lead to novel diagnostic, preventive, and therapeutic approaches for improving the management of type 2 diabetes.

beta(3)-Adrenoceptor agonists: potential, pitfalls and progress

beta(3)-Adrenoceptor agonists are very effective thermogenic anti-obesity and insulin-sensitising agents in rodents. Their main sites of action are white and brown adipose tissue, and muscle. beta(3)-Adrenoceptor mRNA levels are lower in human than in rodent adipose tissue, and adult humans have little brown adipose tissue. Nevertheless, beta(3)-adrenoceptors are expressed in human white as well as brown adipose tissue and in skeletal muscle, and they play a role in the regulation of energy balance and glucose homeostasis. It is difficult to identify beta(3)-adrenoceptor agonist drugs because the pharmacology of both beta(3)- and beta(1)-adrenoceptors can vary; near absolute selectivity is needed to avoid beta(1/2)-adrenoceptor-mediated side effects and selective agonists tend to have poor oral bioavailability. All weight loss is lipid and lean may actually increase, so reducing weight loss relative to energy loss. beta(3)-adrenoceptor agonists have a more rapid insulin-sensitising than anti-obesity effect, possibly because stimulation of lipid oxidation rapidly lowers intracellular long-chain fatty acyl CoA and diacylglycerol levels. This may deactivate those protein kinase C isoenzymes that inhibit insulin signalling.

No evidence for an association between genetic polymorphisms of beta(2)- and beta(3)-adrenergic receptor genes with body mass index in Aymara natives from Chile

OBJECTIVE

We assessed the association between Gln27Glu and Trp64Arg genetic polymorphisms of the beta(2) (ADRB2) and beta(3) (ADRB3) adrenergic receptor genes with body mass index and other cardiovascular risk factors.

METHODS

In a cross-sectional study, adult Aymara subjects (n = 152) living in the Andean regions of northern Chile were characterized with respect to their ADRB2 and ADRB3 genotypes, body mass index, plasma leptin and insulin levels, fasting glucose concentration, blood pressure, and plasma lipid profile.

RESULTS

The frequency of the Glu27 allele of the ADRB2 gene was estimated to be 0.04, and the allele frequency of the Arg64 variant of the ADRB3 gene was estimated as 0.13. No associations were found between the Trp64Arg polymorphism of the ADRB3 gene and body mass index or other cardiovascular risk factors. The small number of subjects with the allele encoding Glu27 in the ADRB2 gene seriously limited the analysis of the association between genotype and phenotype with the use of this polymorphism, although no clear associations were found.

CONCLUSION

We found insufficient evidence to support an association between polymorphisms Gln27Glu and Trp64Arg of the ADRB2 and ADRB3 genes, respectively, with body mass index and other cardiovascular risks in the rural Aymara population from Chile.

Genetic variation and obesity in Australian women: a prospective study

OBJECTIVE

A number of candidate genes have been implicated in the pathogenesis of obesity in humans. This study examines associations between longitudinal changes in body mass and composition and the presence of polymorphisms in the beta-3 adrenergic receptor, tumor necrosis factor-alpha, leptin, and leptin receptor (Lepr) in a cohort of Australian women.

RESEARCH METHODS AND PROCEDURES

Healthy white Australian women (n = 335) were randomly selected from the Barwon region of Victoria and underwent baseline anthropometry and double-energy X-ray absorptiometry for assessment of body mass and adiposity. These measurements were repeated again at 2-year follow-up. Genomic DNA was extracted and used for polymerase chain reaction-based genotyping of all polymorphisms.

RESULTS

The Pro1019Pro Lepr polymorphism was associated with longitudinal increases in body weight (p = 0.02), fat mass (p = 0.05), and body mass index (p = 0.01) in this study, and individuals homozygous for the A allele at this locus had a greater propensity to gain body fat over time. The largest effects on body composition seemed to be in individuals already obese at baseline. Changes in body weight, fat mass, percent body fat, and body mass index over a 2-year period were not associated with genetic variation in the beta-3 adrenergic receptor (Trp64Arg), tumor necrosis factor-alpha promoter, or leptin genes in non-obese or obese women.

DISCUSSION

These results suggest that a Lepr polymorphism is involved in the regulation of body mass and adiposity in obese Australian white women, which may have implications for the treatment of obesity in this population.

Association of BMI with the beta3-adrenergic receptor gene polymorphism in Japanese: meta-analysis

OBJECTIVE

To assess the effect of the Trp64Arg polymorphism in the beta3-adrenergic receptor gene (ADRB3) on body mass index (BMI) in the Japanese population.

RESEARCH METHODS AND PROCEDURES

We selected studies that evaluated the association between BMI and ADRB3 polymorphism among Japanese, using MEDLINE and PubMed. After data collection, an extension of ANOVA was performed to assess the differences according to the genotype.

RESULTS

In a total of 35 subgroups including 2316 subjects with the Trp64Arg variant and 4266 subjects without this variant, the weighted mean difference in BMI was 0.26 kg/m(2) (95% confidence interval: 0.18 to 0.42; p < 0.01), indicating that variant carriers exhibited higher BMI than did normal homozygous subjects.

DISCUSSION

Although it is known that the allele frequency of the ADRB3 polymorphism differs among races, this study focuses on the Japanese population, which has a high allele frequency of ADRB3 polymorphism. We assumed that statistical errors would be prevented due to the sufficient number of subjects. In conclusion, the results support the hypothesis that ADRB3 gene polymorphism is associated with BMI.

Beta-2 adrenergic receptor variants are associated with subcutaneous fat accumulation in response to long-term overfeeding

OBJECTIVE

The effects of alpha-2A (A2A)-, beta-2 (B2)- and beta-3 (B3)-adrenergic receptor (ADR) gene polymorphisms on adiposity, fat distribution and plasma insulin and leptin changes in response to long-term overfeeding were explored.

METHODS

Twenty four men (mean (+/-s.d.) age 21+/-2 y) who constituted 12 pairs of identical twins ate a 4.2 MJ/day energy surplus, 6 days a week, for a period of 100 days. Total body fat was assessed by hydrodensitometry and total subcutaneous fat by the sum of eight skinfolds. Abdominal fat areas were measured by computerized tomography (CT). Plasma glucose and insulin during fasting and in response to an oral glucose tolerance test (OGTT) were assayed. The insulin and glucose areas were computed using the trapezoidal method. Plasma leptin was measured with an enzyme-linked immunosorbent assay. The ADR polymorphisms were identified by PCR or Southern blot technique.

RESULTS

The ADRB2 Gln27Gln genotype (n=10) was associated with a larger gain (percentage change) in weight (P<0.001) and total subcutaneous (P<0.005) fat than the Glu27Glu/Gln27Glu genotype (n=14). In addition, overfeeding induced greater increases in the insulin areas under the curve during the OGTT and the fasting plasma level of leptin (P<0.01 and <0.03, respectively) among Gln27Gln than in the Glu27Glu/Gln27Glu subjects. The body composition and metabolic changes among the ADRB2 BanI 3.7/3.4 kb subjects (n=10) were similar to those of Gln27Gln subjects. ADRA2A DraI (n=4) 6.3/6.3 kb subjects experienced a decrease (-8%) while 6.7/6.3 kb subjects (n=20) registered an increase (+10%; P=0.017) of OGTT glucose area after the 100-day caloric surplus. The four carriers of the ADRB3 variant (Trp64Arg) experienced the same magnitude of changes as the 20 homozygotes for the Trp allele. In general, comparisons based on the 24 subjects considered as unrelated men and the mean values for each of the 12 pairs yielded similar results.

CONCLUSION

The ADRB2 Gln27Gln subjects gained more weight and total subcutaneous fatness and also experienced a greater increase in insulin resistance than Glu27Glu/Gln27Glu subjects with exposure to long-term overfeeding. Similar differences were observed between carriers and non-carriers of the ADRB2 3.7/3.4 kb BanI variant. Genetic variation at the ADRB2 locus could thus be one of the factors responsible for the large inter-individual differences observed in the response to long-term alterations in energy balance and should be further investigated.

Beta(3)-adrenergic receptor gene variant is associated with upper body obesity only in obese Japanese-American men but not in women

We investigated gender differences in the relationships between the Trp64Arg variant of the beta(3)-adrenergic receptor (AR) gene in obesity and insulin resistance in nondiabetic subjects. In 476 nondiabetic Japanese-Americans (M/F=204/272), the Trp64Arg variant of the beta(3)-AR gene was examined. The presence or absence of the Trp64Arg mutation was examined in DNA separated from leukocytes in peripheral blood using the PCR-RFLP method. The frequency of abnormal allele of the beta(3)-AR gene was 0.18 for males and 0.17 for females, almost the same as the reported values in Japanese. There was no difference in the frequency of the beta(3)-AR gene variant between obese and non obese subjects for each gender. However, among obese males (body mass index > or =24.2 kg/m(2)), with the beta(3)-AR gene mutation, the waist-to-hip ratio, fasting insulin, 2-h insulin, total insulin, and HOMA, an index of insulin resistance, were all significantly higher than obese males without the mutation. In females, the index of obesity, insulin resistance, or lipid metabolism did not differ significantly between the subjects with or without the beta(3)-AR gene variant either in the obese and non-obese group. We suggest that the beta(3)-AR gene variant is not important as an obesity-inducing factor in Japanese. However, in males, when obesity becomes obvious, the beta(3)-AR gene variant is considered to influence the enhancement of insulin resistance, in association with visceral obesity.

Gender specific associations of the Trp64Arg mutation in the beta3-adrenergic receptor gene with obesity-related phenotypes in a Mediterranean population: interaction with a common lipoprotein lipase gene variation

OBJECTIVE

To investigate the association between the Trp64Arg beta3-adrenergic receptor (ADRB3) mutation and obesity-related phenotypes in a Mediterranean Spanish population considering the effect of other genetic and environmental factors. DESIGN AND SUBJECT: Cross-sectional study in 1063 (476 men and 587 women) randomly selected from this population (aged: 18-68 years).

MEASUREMENTS

Anthropometric (weight, height and waist-to-hip ratio), blood pressure, biochemical (lipids, fasting glucose, and uric acid), life-style variables, and the Trp64Arg, HindIII-Lipoprotein lipase (LPL) and apolipoprotein E polymorphism.

RESULTS

Frequency of the Arg64 allele was low (0.051; 95% CI: 0.042-0.060). We found gender-specific associations between the Trp64Arg mutation and obesity related phenotypes. In men, carriers of the Arg64 variant had higher body mass index (BMI) (27.63 +/- 3.81 vs. 26.34 +/- 3.57 kg m-2, P=0.049) and total cholesterol (5.85 +/- 1.45 vs. 5.28 +/- 1.06 mmol L-1; P=0.011) compared with wild-type individuals. Logistic regression analysis, revealed that the risk of overweight was two times higher in male carriers of the Arg64 allele. In women, the Arg64 variant was only associated with higher fasting glucose (P=0.031). These genotype effects persisted after adjustment for age, genetic and life-style variables. For the LPL polymorphism, the H-/H- genotype was associated with lower BMI and with lower risk of overweight (OR: 0.49; 95% CI: 0.30-0.81) in both men and women. However, after adjustment for covariates, these associations only remained statistically significant (P < 0.02) in women. Moreover, in women, a statistically significant interaction (P=0.026) between the LPL and the ADRB3 gene loci in determining BMI was found. Thus, the Arg64 allele was associated with a higher BMI only in H+/H+ women.

CONCLUSIONS

The Trp64Arg mutation was associated with BMI and lipids in men. In women, an additional gene-gene interaction with the LPL-HindIII polymorphism may explain the results.

A new gene related to human obesity identified by suppression subtractive hybridization

OBJECTIVE

The aim of the research was to identify genes specially expressed in the obese state and potentially involved in the pathogenesis of obesity.

DESIGN AND SUBJECTS

We used the technique of suppression subtractive hybridization (SSH), which combines subtractive hybridization with PCR, to generate a population of PCR fragments enriched for transcripts of high or low abundance from differentially expressed genes. PolyA+ mRNA was isolated from subcutaneous abdominal adipose tissue of five massively obese (>35 kg/m(2)) and five normal-weight (<25 kg/m(2)) women. cDNA generated from RNA pooled from the obese subjects was contrasted by SSH with an excess of pooled cDNA from the normal-weight women.

RESULTS

Seventy-nine clones were obtained among which one showed by RT-PCR a higher expression in obese than in normal-weight subjects. This gene was shown to be predominantly expressed in adipose tissue in contrast to brain, liver, kidney, heart and skeletal muscle, and was called "Adipogene". No expression was detected in lung, pancreas and placenta. The cDNA was 1.5 kb long with an open reading frame of 1004 nucleotides encoding a protein of 334 amino acids (37 kDa). No significant sequence similarity was found in databanks, except for weak amino acid homologies with prokaryotic AraC/XylS transcriptional regulator family. Adipogene is encoded on chromosome 8, less than 1 centiMorgan (cM) from the beta3 adrenergic receptor (ADRB3) locus. Weak linkages were observed with body mass index (BMI) and three microsatellite markers located within 10 cM of Adipogene, whereas no linkage was observed with Trp64Arg ADRB3 polymorphism using the Québec Family Study database.

CONCLUSION

Using the SSH technique, we have identified a new gene, called Adipogene, which is overexpressed in the adipose tissue of the obese individuals and could be involved in obesity.

The Trp64Arg polymorphism of the beta3-adrenergic receptor gene is not associated with training-induced changes in body composition: The HERITAGE Family Study

OBJECTIVE

To investigate the association between the Trp64Arg polymorphism of the beta3-adrenergic receptor gene and changes in body composition in response to endurance training.

RESEARCH METHODS AND PROCEDURES

Adult sedentary white and black subjects participating in the HERITAGE Family Study were measured before and after 20 weeks on endurance training for the body mass index, fat mass, percentage of body fat, fat-free mass, sum of eight skinfolds, and subcutaneous, visceral, and total abdominal fat areas. The association between the Trp64Arg polymorphism and the response phenotypes, computed as the difference between pre- and post-training values, was tested by analysis of covariance separately in men and women. The gene by race interaction term was also tested.

RESULTS

No race differences were observed for allelic and genotype frequencies. Training resulted in significant reduction of body fat in both men and women. No association of the Trp64Arg polymorphism was observed with training-induced changes for any of the body composition phenotypes in both men and women.

DISCUSSION

These results suggest that the Trp64Arg polymorphism of the beta3-adrenergic receptor gene is not related to changes in body composition in response to exercise training.