High prevalence of brown adipose tissue in adult humans

CONTEXT

Positron emission tomography (PET)-computed tomography (CT) has identified metabolically active supraclavicular fat in adult humans based on uptake of labeled glucose and confirmed to be brown adipose tissue (BAT) histologically. However, PET-CT has estimated a prevalence of BAT as low as 5% in adult humans, casting doubt on its significance. The true prevalence of BAT is unknown because of the suboptimal sensitivity of standard PET-CT.

OBJECTIVE

The objective of the study was to determine whether BAT is present in PET-negative supraclavicular fat.

DESIGN

This was a prospective cohort study.

SETTING

The study was conducted at a tertiary referral hospital.

PATIENTS

Seventeen patients who underwent preoperative PET-CT for staging of head and neck malignancy participated in the study.

MAIN OUTCOME

The main outcome was signature BAT gene transcripts and protein in biopsies of supraclavicular fat with sc fat as negative control.

RESULTS

PET-CT was positive in three and negative in 14 patients. PET-positive fat harbored multilobulated lipid droplets and stained strongly for uncoupling protein 1 (UCP1). These features are absent in sc fat. By contrast, PET-negative fat contained a predominance of cells with unilobulated lipid droplets, with scattered cells containing multilobulated lipid droplets and variable UCP1 staining. Molecular analyses of fat biopsies showed lower but clear expression of UCP1, NDUFS3 (NADH dehydrogenase (ubiquinone) iron-sulfur protein 3), β₃-adrenoceptor, and PRDM16 (PR domain containing 16) transcripts.

CONCLUSIONS

BAT is present in supraclavicular fat, regardless of PET status. BAT is highly prevalent in adult humans, and its abundance determines PET status.

Intracellular fatty acids suppress β-adrenergic induction of PKA-targeted gene expression in white adipocytes

β-Adrenergic receptor (β-AR) activation elevates cAMP levels in fat cells and triggers both metabolic and transcriptional responses; however, the potential interactions between these pathways are poorly understood. This study investigated whether lipolysis affects β-AR-mediated gene expression in adipocytes. Acute β(3)-adrenergic receptor (β(3)-AR) stimulation with CL 316,243 (CL) increased expression of PKA-targeted genes PCG-1α, UCP1, and NOR-1 in mouse white fat. Limiting lipolysis via inhibition of hormone-sensitive lipase (HSL), a direct target of PKA, sharply potentiated CL induction of PCG-1α, UCP1, and NOR-1. CL also induced greater expression of PKA-targeted genes in white fat of HSL-null mice compared with wild-type littermates, further indicating that HSL activity limits PKA-mediated gene expression. Inhibiting HSL in 3T3-L1 adipocytes also potentiated the induction of PGC-1α, UCP1, and NOR-1 by β-AR activation, as did siRNA knockdown of adipose triglyceride lipase, the rate-limiting enzyme for lipolysis. Conversely, treatments that promote intracellular fatty acid accumulation suppressed induction of PGC-1α and UCP1 through β-AR stimulation. Analysis of β-adrenergic signaling indicated that excessive intracellular fatty acid production inhibits adenylyl cyclase activity and thereby reduces PKA signaling to the nucleus. Lastly, partially limiting lipolysis by inhibition of HSL increased the induction of oxidative gene expression and mitochondrial electron transport chain activity in white adipose tissue and facilitated fat loss in mice treated for 5 days with CL. Overall, our results demonstrate that fatty acids limit the upregulation of β-AR-responsive genes in white adipocytes and suggest that limiting lipolysis may be a novel means of enhancing β-AR signaling.

Association between accumulation of visceral fat and the combination of β3 adrenergic receptor Trp64Arg, β2 adrenergic receptor Arg16Gly and uncoupling protein 1 -3826A>G polymorphisms detected by Smart Amplification Process 2

β2 and β3 adrenergic receptors (β2AR, β3AR) and uncoupling protein 1 (UCP1) have been considered as candidate genes for obesity. Although each polymorphism of β3AR Trp64Arg, β2AR Arg16Gly and UCP1 -3826A>G is known to be associated with obesity, the interaction among these polymorphisms is not fully understood. We analyzed β3AR Trp64Arg, β2AR Arg16Gly and UCP1 -3826A>G polymorphisms by the Smart Amplification Process 2 in 222 Japanese subjects without the medication of hypertension, dyslipidemia or diabetes, and investigated the association between the physical and metabolic characteristics and the combination of these polymorphisms. In analysis of the genotypes combination, only the carriers of both β2AR Arg/Arg and UCP1 G/G genotypes had significantly higher waist to hip ratio (p=0.014). In analysis of the alleles combination, a significant difference was observed in waist to hip ratio among the groups stratified by the carrying number of the alleles of β3AR Arg, β2AR Arg and UCP1 G (p=0.026), and the waist to hip ratio was significantly higher in the carriers of four and five risk alleles than in the carriers from zero to three risk alleles (p=0.005). The present study demonstrated the interaction among β3AR Trp64Arg, β2AR Arg16Gly and UCP1 -3826A>G for the accumulation of visceral fat.

Relationship between Trp64Arg mutation in the β3-adrenergic receptor gene and metabolic syndrome: a seven-year follow-up study

BACKGROUND

It has been shown that the β3-adrenergic receptor (β3-AR) gene Trp64Arg mutation was closely related to obesity and insulin resistance, and may be related to the prevalence of metabolic syndrome (MS). The aim of this study was to investigate the relationship between the β3-AR gene mutation and the prevalence of MS.

METHODS

A seven-year follow-up study was initiated in 2000, with 496 samples of simplex obese subjects (body mass index ≥ 25 kg/m(2)) and 248 normal-weight subjects. According to the β3-AR genotypes, the subjects were classified as Trp64 homozygote group and Arg64 carrier group and after 7 years the prevalence of MS was determined.

RESULTS

According to the baseline profile, there were no significant differences in the adiposity, blood pressure, lipid profile, fasting plasma glucose and fasting insulin between Trp64 homozygote group and Arg64 carrier group either in obesity or normal-weight subjects. The results of follow-up study indicated that in obese men the prevalence rate of MS was much higher in Arg64 carrier group than that in Trp64 homozygote group (54.76% vs. 40.85%, P < 0.05), but there was no statistical difference in women of the above groups. The prevalence rate of MS in obese men of both Trp64 homozygote group and Arg64 carrier obese group were obviously higher than that in women of the above groups (40.85% vs. 18.27% and 54.76% vs 21.28%, all P < 0.005). Differences were not statistically significant in the prevalence of MS for normal weight Trp64 homozygote group and normal weight Arg64 carrier group, either between men, between women, or between men and women. Comparison of populations indicated that no matter with the β3-AR gene mutation or not, the prevalence of MS in obese subjects was significantly higher than normal weight subjects (χ(2) = 28.240 and χ(2) = 15.586, all P < 0.005). Logistic analysis showed that the mutation of β3-AR gene was associated with the prevalence of MS in men.

CONCLUSION

The mutation of β3-AR gene is the independent risk factor for the prevalence of MS in men.

Distribution of the Trp64Arg polymorphism in the ß 3-adrenergic receptor gene in athletes and its influence on cardiovascular function

BACKGROUND

The Trp64Arg polymorphism in the beta₃-adrenergic receptor (beta₃-AR) gene was extensively studied concerning the relationship with cardiovascular (CV) diseases, but few studies addressed this issue in athletes.

AIM

To examine the relationship between the Trp64Arg polymorphism in the beta₃-AR gene and several CV functions such as cardiac structure and function or blood biochemical parameters in Korean male controls and athletes.

METHODS

We recruited a total of 114 study subjects, including 81 male athletes (8 long distance runners, 17 soccer, 8 baseball, 10 basketball, 8 volleyball, 8 ice hockey, 8 judo, 6 taekwondo and 8 gymnastics) and 33 controls. Two dimensional echocardiography was performed in order to assess the cardiac structure and function and blood biochemical parameters were measured. Genotyping of Trp64Arg polymorphism in the beta₃-AR gene was also performed by the SNaPshot method.

RESULTS

The genotype and allele distribution of Trp64Arg polymorphism in the beta₃-AR gene were significantly different among each sporting discipline, showing the highest Arg allele frequency in volleyball and gymnastics (p < 0.05). Also, this polymorphism was significantly associated with serum HDL-cholesterol and glucose level in athletes only (p < 0.05).

CONCLUSIONS

Our data showed the significant associations between the Trp64Arg polymorphism in the beta₃-AR gene and some CV parameters such as serum HDL-cholesterol and glucose levels in athletes. However, further studies of the precise mechanism behind these associations are needed.

Beta-adrenergic signals regulate adipogenesis of mouse mesenchymal stem cells via cAMP/PKA pathway

The adipogenic capacity of mesenchymal stem cells (MSCs) and the involvement of beta-adrenergic signals in lipolysis and thermogenesis have been well established. However, little is known about the development of beta-adrenergic receptor (beta-AR) systems and the role of beta-adrenergic signals in adipogenic differentiation of MSCs. In this study, we demonstrated that both the mRNA and protein levels of beta2- and beta3-AR were up-regulated following adipogenesis of mouse bone marrow derived MSCs. We also established that beta-AR agonists negatively while antagonists positively affected MSC adipogenesis. Both the beta2- and beta3-AR were involved in MSC adipogenesis, with beta3-AR being the predominant subtype. The effect of beta-ARs on MSC adipogenesis was at least partly mediated via the cAMP/PKA signaling pathway. These findings suggested that MSC is also a target for beta-adrenergic regulation, and beta-adrenergic signaling (major beta3-signaling) plays a role in MSC adipogenesis.

Independent predictive roles of eotaxin Ala23Thr, paraoxonase 2 Ser311Cys and beta-adrenergic receptor Trp64Arg polymorphisms on cardiac disease in Type 2 Diabetes--an 8-year prospective cohort analysis of 1297 patients

AIMS

To examine the independent and joint effects of multiple genetic variants on a cardiac end-point in an 8-year prospective study of a Chinese diabetic cohort.

METHODS

Seventy-seven single nucleotide polymorphisms (SNPs) of 53 candidate genes for inflammation, thrombosis, vascular tone regulation and lipid metabolism were genotyped in 1297 Chinese patients with no prior history of coronary heart disease (CHD) or heart failure at baseline. Cardiac end-point was defined by the occurrence of CHD and/or heart failure.

RESULTS

In Cox regression model, after adjustment for baseline confounding variables including age, sex, smoking status, duration of diabetes, glycaemic control, lipid levels, waist circumference, blood pressure, albuminuria and estimated glomerular filtration rate, genetic variants, including Ala/Ala of SCYA11 (eotaxin) Ala23Thr, Cys/Cys or Cys/Ser of PON2 (paraoxonase 2) Ser311Cys and Arg/Arg of ADRB3 (beta3-adrenergic receptor) Trp64Arg, were independently associated with incident cardiac end-point, with respective hazard ratios (95% confidence interval) of 1.70 (1.10-2.61, P=0.037), 1.42 (1.08-1.88, P=0.013) and 3.84 (1.18-12.50, P=0.025). Analysis of the joint effect of the risk alleles showed significant increased risk of the cardiac end-point with increasing number of risk alleles (P<0.001). The adjusted risk for the cardiac end-point was 4.11 (P=0.002) for patients carrying four risk alleles compared with those carrying one or no risk allele.

CONCLUSIONS

The independent risk conferred by genetic variants encoding pathways such as inflammation and lipid metabolism, not adequately reflected by conventional biomarkers, may identify high-risk individuals for intensified control of modifiable risk factors.

Adaptive effects of the beta2-agonist clenbuterol on expression of beta2-adrenoceptor mRNA in rat fast-twitch fiber-rich muscles

Administration of the beta(2)-agonist clenbuterol has been shown to reduce the expression of beta(2)-adrenoceptor (AR) mRNA in fast-twitch fiber-rich (extensor digitorum longus, EDL) muscle without changing that in slow-twitch fiber-rich (soleus, SOL) muscle in rats. However, the regulatory mechanism for muscle fiber type-dependent down-regulation of the expression of beta(2)-AR mRNA induced by clenbuterol is still unclear. Therefore, mRNA expression of transcriptional and post-transcriptional regulatory factors for beta(2)-AR mRNA levels in fast-twitch fiber-rich (EDL and plantaris, PLA) and slow-twitch fiber-rich (SOL) muscles in clenbuterol-administered (1.0 mg/kg body weight/day for 10 days, subcutaneous) rats was studied by real-time reverse transcription-polymerase chain reaction. Administration of clenbuterol significantly reduced expression of beta(2)-AR mRNA in EDL and PLA muscles without changing that in SOL muscle. Administration of clenbuterol also significantly reduced the mRNA expression of transcriptional regulatory factor (glucocorticoid receptor) and mRNA stabilizing factor (Hu antigen R) in EDL and PLA muscles without changing those in SOL muscle. These results suggest that muscle fiber type-dependent effects of clenbuterol on expression of beta(2)-AR mRNA are closely related to the down-regulation of mRNA expression of transcriptional and post-transcriptional regulatory factors for beta(2)-AR mRNA levels.

Polymorphism Trp64Arg of beta 3 adrenoreceptor gene: allelic frequencies and influence on insulin resistance in a multicenter study of Castilla-León

BACKGROUND AND OBJECTIVE

The genetic variant (Trp64Arg) is a missense mutation located within the beta3 adrenoreceptor (Beta3AR). The aim of our study was to investigate the influence of Trp64Arg polymorphism in the Beta3AR gene on insulin resistance in obese patients and the allelic distribution of this polymorphismin a geographic area of Spain.

DESIGN

A population of 264 obese patients was analyzed. A bioimpedance, blood pressure, an assessment of nutritional intake, and biochemical parameters were measured. The beta 3 adrenoreceptor gene polymorphism(Trp64Arg) was genotyped.

RESULTS

Two hundred and twenty six patients (77 males/149 females) (85.6%) had the genotype Trp64/Trp64 (wild type group) with and average age of 41.12 +/- 13.1 years and 38 patients (16 males/22 females) Trp64/Arg64 (14.4%) (mutant type group) with an average age of 40.5 +/- 12.7 years. High frequencies of Arg64 allele were observed in Salamanca and Valladolid. In the mutant type group, HOMA (3.75 +/- 2.77 vs 5.27 +/- 5.4; p < 0.05) was higher than wild type group.

CONCLUSION

The finding of this study is the association of the Trp64/Arg64 Beta3AR with higher levels of HOMA. Frequencies of this polymorphism are different among geographic areas.

[Genetic predisposition to development of atrial fibrillation in patients with hypertensive disease]

We studied associations of genes of adrenoreceptor types 1, 2 and 3 (ADRB1, ADRB2, ADRB3), connexin (CX40) and voltage gated potassium channel type 2 (KCNH2) with development of atrial fibrillation (AF) in patients with hypertensive disease. We examined 102 patients with hypertensive disease which in 51 was complicated with AF. The groups were comparable by sex, age, Ketle index, presence of concomitant diseases. We determined alleles and genotypes of polymorphic markers G(-44)A and A71G of CX40 gene, Lys897Thr of KCNH2 gene, Ser49Gly of ADRB1 gene, Trp64Arg of ADRB3 gene with the help of PCR. Left atrial volume turned out to be significantly higher in patients with AF (88.7 +/- 4.13 ml and 65.4 +/- 3.96 ml, respectively, p = 0.001). No associations of genotypes of polymorphic markers Ser49Glu of ADRB1 gene, G(-44)A and A 71G of CX40 gene, Lys897Thr of KCNH2 gene, with emergence of AF in patients with arterial hypertension were revealed. For polymorphic marker Trp64Arg of ADRB3 gene frequency of Trp allele turned out to be significantly higher (OR 2.20, p = 0.0176), while frequency of Arg allele significantly lower (OR 0.43, p = 0.0176) in the group of patients with AF. In patients with AF frequency of Arg/ Arg genotype turned out to be significantly lower (OR 0.24, p = 0.0257).

[Myocardial hypertrophy in patients with hypertensive disease: the role of genetic polymorphism of beta-adrenoreactive structures]

Aim of the study was investigation of association of polymorphic markers Gly389Arg and Ser49Gly of ADRB1 gene, Gly1l6Arg and Glu27Gln of ADRB2 gene, Trp64Arg of ADRB3 gene, and 825 of GNB3 gene with structural and functional peculiarities of the left ventricular (LV) myocardium in patients with hypertensive disease. We examined 177 patients - 83 (46.9%) men and 94 (53.1%) women. Mean age was 60.6 +/- 0.76 years. In the studied group there were 19 patients (10.9%) with I degree arterial hypertension (AH), 57 patients (32.8%) with II degree AH, and 101 patients (56.3%) with III degree AH. Structural peculiarities of LV myocardium were investigated with the help of echocardiography. There turned out to be 40 patients without signs of LV hypertrophy and 137 patients with increase of LV myocardial mass index. patients with LV hypertrophy had higher frequency of genotype Arg/Arg of polymorphic maker Gly398Arg of ADRB1 gene (=0.008. OR 2.32 [CI 1.34 - 4.11]). In patients with concentric and eccentric hypertrophy significantly higher frequency of Arg/Arg genotype compared with patients with normal LV geometry and concentric LV remodeling was also noted. At conduction of multifactorial analysis independently connected with increase of LV myocardial mass turned out age of patients, level of systolic arterial pressure, presence of excessive body mass and carriage of Arg/Arg genotype of polymorphic marker Gly389Arg of ADRB1 gene.

Adverse ventricular remodeling and exacerbated NOS uncoupling from pressure-overload in mice lacking the beta3-adrenoreceptor

Stimulation of the beta-adrenergic system is important in the pathological response to sustained cardiac stress, forming the rationale for the use of beta-blockers in heart failure. The beta3-adrenoreceptor (AR) is thought to couple to the inhibitory G-protein, G(i), with downstream signaling through nitric oxide, although its role in the heart remains controversial. In this study, we tested whether lack of beta3-AR influences the myocardial response to pressure-overload. Baseline echocardiography in mice lacking beta3-AR (beta3(-/-)) compared to wild type (WT) showed mild LV hypertrophy at 8 weeks that worsened as they aged. beta3(-/-) mice had much greater mortality after transverse aortic constriction (TAC) than WT controls. By 3 weeks of TAC, systolic function was worse. After 9 weeks of TAC, beta3(-/-) mice also had greater LV dilation, myocyte hypertrophy and enhanced fibrosis. NOS activity declined in beta3(-/-)TAC hearts after 9 weeks, and total and NOS-dependent superoxide rose, indicating heightened oxidative stress and NOS uncoupling. The level of eNOS phosphorylation in beta3(-/-)TAC hearts was diminished, and nNOS and iNOS expression levels were increased. GTP cyclohydrolase-1 expression was reduced, although total BH4 levels were not depleted. 3 weeks of BH4 treatment rescued beta3(-/-) mice from worsened remodeling after TAC, and lowered NOS-dependent superoxide. Thus, lack of beta3-AR signaling exacerbates cardiac pressure-overload induced remodeling and enhances NOS uncoupling and consequent oxidant stress, all of which can be rescued with exogenous BH4. These data suggest a cardioprotective role for the beta3-AR in modulating oxidative stress and adverse remodeling in the failing heart.

The use of beta3-adrenergic receptor agonists in the treatment of heart failure

As the beta3-adrenergic receptor (beta3-AR) mediates a negative inotropic effect, upregulation of this receptor in patients with heart failure is considered to be harmful and associated with disease progression. The development of beta3-AR antagonists has therefore been proposed as a potential therapeutic option for heart failure. However, as increased intracellular myocyte Na+ levels represent a key adverse pathophysiological feature of heart failure, and the beta3-AR mediates the stimulation of the only export route for Na+ - the Na+-K+ pump - the upregulation of this receptor may also represent a useful compensatory mechanism. Data from animal studies and circumstantial observations from clinical trials suggest that beta3-AR activation is beneficial in severe heart failure, and that beta3-AR agonists are a promising therapeutic option for the treatment of this disease.

Diet-induced obese mice are leptin insufficient after weight reduction

Behavioral therapies aimed at reducing excess body fat result in limited fat loss after dieting. To understand the causes for maintenance of adiposity, high-fat (HF) diet-induced obese (DIO) mice were switched to a low-fat chow diet, and the effects of chow on histological and molecular alterations of adipose tissue and metabolic parameters were examined. DIO mice reduced and stabilized their body weights after being switched to chow (HF-chow), but retained a greater amount of adiposity than chow-fed mice. Reduction in adipocyte volume, not number, caused a decrease in fat mass. HF-chow mice showed normalized circulating insulin and leptin levels, improved glucose tolerance, and reduced inflammatory status in white adipose tissue (WAT). Circulating leptin levels corrected for fat mass were lower in HF-chow mice. Leptin administration was used to test whether reduced leptin level of HF-chow mice inhibited further fat loss. Leptin treatment led to an additional reduction in adiposity. Finally, HF-HF mice had lower mRNA levels of beta(3) adrenergic receptor (beta(3)-AR) in epididymal WAT (EWAT) compared to chow-fed mice, and diet change led to an increase in the WAT beta(3)-AR mRNA levels that were similar to the levels of chow-fed mice, suggesting an elevation in sympathetic activation of WAT during diet switch relative to HF-HF mice leading to the reduced leptin level and proinflammatory cytokine content. In summary, HF-chow mice were resistant to further fat loss due to leptin insufficiency. Diet alteration from HF to low fat improved metabolic state of DIO mice, although their adiposity was defended at a higher level.

Reversal of high pancreatic islet and white adipose tissue blood flow in type 2 diabetic GK rats by administration of the beta3-adrenoceptor inhibitor SR-59230A

Previous studies have shown that the Goto-Kakizaki (GK) rat, a nonobese type 2 diabetes model, has an increased white adipose tissue (WAT) and islet blood flow when compared with control rats. The aim of the study was to examine if these increased blood flow values in GK rats could be affected by the beta(3)-adrenoceptor antagonist SR-59230A. We measured organ blood flow with a microsphere technique 10 min after administration of SR-59230A (1 mg/kg body wt), or the corresponding volume of 0.9% NaCl solution (1 ml/kg body wt) in rats anaesthetized with thiobutabarbital. The GK rat had an increased blood flow in all intra-abdominal adipose tissue depots except for the sternal fat pad compared with Wistar-Furth (WF) rats. However, no differences were seen in the blood perfusion of subcutaneous white or brown adipose tissue. The blood flow was also increased in both the pancreas and in the islets in the GK rat compared with WF rats. SR-59230A treatment affected neither WAT nor pancreatic blood flow in WF rats. In GK rats, on the other hand, SR-59230A decreased both WAT and islet blood flow values to values similar to those seen in control WF rats. The whole pancreatic blood flow was not affected by SR-59230A administration in GK rats. Interestingly, the brown adipose tissue blood flow in GK rats increased after SR-59230A administration. These results suggest that beta(3)-adrenoceptors are involved in regulation of blood flow both in islet and in adipose tissue.

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.

Diverse evolutionary histories for beta-adrenoreceptor genes in humans

In humans, three genes--ADRB1, ADRB2 and ADRB3--encode beta-adrenoreceptors (ADRB); these molecules mediate the action of catecholamines in multiple tissues and play pivotal roles in cardiovascular, respiratory, metabolic, and immunological functions. Genetic variants in ADRB genes have been associated with widespread diseases and conditions, but inconsistent results have often been obtained. Here, we addressed the recent evolutionary history of ADRB genes in human populations. Although ADRB1 is neutrally evolving, most tests rejected neutral evolution for ADRB2 in European, African, and Asian population samples. Analysis of inferred haplotypes for ADRB2 revealed three major clades with a coalescence time of 1-1.5 million years, suggesting that the gene is either subjected to balancing selection or undergoing a selective sweep. Haplotype analysis also revealed ethnicity-specific differences. Additionally, we observed significant deviations from Hardy-Weinberg equilibrium (HWE) for ADRB2 genotypes in distinct European cohorts; HWE deviation depends on sex (only females are in disequilibrium), and genotypes displaying maximum and minimum relative fitness differ across population samples, suggesting a complex situation possibly involving epistasis or maternal selection. Overall, our data indicate that future association studies involving ADRB2 will benefit from taking into account ethnicity-specific haplotype distributions and sex-based effects. With respect to ADRB3, our data indicate that the gene has been subjected to a selective sweep in African populations, the Trp64 variant possibly representing the selection target. Given the previous association of the ancestral ADRB3 Arg64 allele with obesity and type 2 diabetes, dietary adaptations might represent the underlying selective force.

Lack of specificity of antibodies directed against human beta-adrenergic receptors

The present study was designed to investigate if antibodies against beta-adrenergic receptors (betaARs) can be used to determine expression of betaAR in human myocardium. Western blotting was performed to investigate the specificity of antibodies directed against beta(1)AR and beta(2)AR in human left ventricular tissue. A comparison was made between cardiac tissue from patients with idiopathic dilated cardiomyopathy and ischemic heart disease and nonfailing donors. The antibodies directed against beta(1)AR and beta(2)AR recognized several protein bands at different molecular weights. Moreover, both antibodies also recognized multiple proteins in Chinese hamster ovary cells expressing beta(1)AR, beta(2)AR, and even beta(3)AR. betaAR antibodies are not specific and are not suited to study expression of betaAR in human myocardium.

Beta 3 adrenergic receptors: molecular, histological, functional and pharmacological approaches

Different classes of receptors mediate norepinephrine and epinephrine effects, one of the most recently discovered being the beta 3 adrenergic ones. The paper has proposed itself to present the history of the discovery of beta 3 adrenergic receptors, different techniques for their identification, their structure, localization, genetic data and also the mechanism of regulation of their functions. It also contains an exhaustive approach regarding the histological localization and functions of beta 3 adrenergic receptors in different apparatus and systems, making evident their effect on glucidic, lipidic and energetic metabolism. The substances that influence beta 3 adrenergic receptors activities, especially the agonists, have been studied regarding their practical applications in the treatment of diabetes mellitus and of the disturbances of lipid metabolism.

Do gene polymorphisms alone or in combination affect the function of human beta3-adrenoceptors?

BACKGROUND AND PURPOSE

beta(3)-Adrenoceptors mediate many important physiological functions, for example, in the urinary bladder. The corresponding gene is polymorphic, and the W64R (Trp64Arg) single nucleotide polymorphism has been associated with disease states such as obesity, type 2 diabetes and bladder dysfunction. While these clinical data suggest that the 64R variant is hypofunctional, previous in vitro studies in which this variant was generated by site-directed mutagenesis and subsequent transfection have not consistently confirmed this.

EXPERIMENTAL APPROACH

We transfected the wild-type human beta(3)-adrenoceptor and the 64R variant and also the more recently discovered 265M and 306F variants as well as 64R/265M and 64R/306F double mutants into human embryonic kidney cells and selected clones expressing the receptors at a density of about 100 fmol mg protein(-1). Receptor activation was measured by cAMP accumulation and ligand affinity by radioligand binding. Desensitisation was assessed as alterations of cAMP responses after prolonged agonist treatment.

KEY RESULTS

Neither mutated receptor exhibited alterations in efficacy or potency for cAMP accumulation for any of five agonists (isoprenaline, noradrenaline, YM 178, FK 4664, CGP 12 177). In competition binding studies, the mutations did not affect the ability of any agonist to bind to the receptor. Wild-type receptors and the 64R variant exhibited similar isoprenaline-induced functional desensitization during a 24 h treatment.

CONCLUSIONS AND IMPLICATIONS

None of the polymorphisms tested here significantly altered the interaction of isoprenaline, noradrenaline, YM 178, FK 4664 or CGP 12 177 with the human beta(3)-adrenoceptor when expressed at near physiological levels in a human cell line.

Diazoxide enhances basal metabolic rate and fat oxidation in obese Zucker rats

Persistent suppression of hyperinsulinemia in genetically obese (fa/fa) Zucker rats by diazoxide (DZ) reduces food intake and weight gain; improves insulin sensitivity, glycemic control, and lipid profile; and enhances beta(3)-adrenergic function and lipolysis in adipose tissue. The aim of this study was to elucidate the effects of DZ on basal metabolic rate (BMR), fat oxidation, and adrenergic function of lean and obese Zucker rats. Diazoxide (150 mg/kg/d) or vehicle (control) was administered for 4 weeks in 7-week-old obese and lean Zucker rats (n = 8-9 per subgroup). Animals underwent indirect calorimetry, body composition analysis, and determination of uncoupling proteins (UCPs) messenger RNA (mRNA) in brown and white adipose tissues (BAT and WAT) and skeletal muscle (SM), beta(3)-adrenergic receptor (AR) mRNA in BAT and WAT, beta(2)-AR in SM as well as WAT, and SM adenylate cyclase (AC) activity at the completion of study. Diazoxide treatment decreased food intake, weight gain, and body fat in obese rats (P < .01). Although DZ treatment lowered fasting plasma glucose, insulin, leptin, adiponectin, and lipids in obese rats (P < .01), it increased adiponectin-leptin ratio (P < .01). Plasma adiponectin-leptin ratio was inversely correlated with fat mass in obese and lean rats (r = -0.86, P < .0001). Diazoxide treatment resulted in higher BMR and fat oxidation rate in obese compared with control animals (P < .01), without any effect in lean animals. Furthermore, plasma adiponectin was inversely correlated with BMR (-0.56, P < .001) and lipid oxidation rate (-0.61, P < .0005) and was positively correlated with nonprotein respiratory quotient (r = 0.41, P < .01) in obese and lean rats. This was associated with increased beta(3)-AR mRNA expression in BAT and WAT (P < .01), UCP-1 and UCP-3 in BAT and AC activity in WAT (P < .02), and AC activity in SM of DZ obese rats compared with controls (P < .01), without significant change in SM beta(2)-AR mRNA expressions. Diazoxide attenuation of hyperinsulinemia decreased the rate of weight gain but enhanced insulin sensitivity, BMR, and fat oxidation in obese rats. This was associated with increased receptor- and non-receptor-mediated adrenergic function in adipose and muscle tissues in obese rats, respectively. These metabolic changes in obese Zucker rats suggest that antiobesity effects of DZ appear to be not only through its anorectic effect, modification of disturbed insulin metabolism, and inhibition of lipogenesis, but also due to augmentation of adrenergic function, energy expenditure, and fat utilization.

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.

[A prospective study of the relationship between Trp64Arg beta(3)-adrenergic receptor gene polymorphism and metabolic syndrome]

OBJECTIVE

To investigate the relationship between Trp64Arg mutation in beta(3)-adrenergic receptor (beta(3)-AR) gene and the incidence of metabolic syndrome (MS).

METHODS

A seven-year follow-up study was conducted in 386 simple obese subjects and 175 normal weight subjects in whom geno-typing of Trp64Arg mutation in beta(3)-AR gene was examined in 2000.

RESULTS

There were no differences between a Trp64Trp homozygote group and a Trp64Arg heterozygote group of whether obese or normal weight subjects with respect to adiposity, blood pressure, lipid profile, fasting blood glucose and fasting insulin in the baseline. The results of follow-up indicated that the incidence of MS in the Trp64Arg heterozygote group was higher than that in the Trp64Trp homozygote group of obese males (54.76% vs 40.85%, P < 0.05) but not in the group of obese females. The incidences of MS both in the Trp64Trp homozygote group and Trp64Arg heterozygote group were higher in obese males than in obese females (40.85% vs 18.27% and 54.76% vs 21.28%, all P < 0.01). No significant differences were found in incidences of MS both in the Trp64Trp homozygote group and Trp64Arg heterozygote group of normal weight subjects whether the comparison was made between males and females respectively or between males and females. The overall incidence of MS in the obese subjects were significantly increased than that in the normal weight subjects whether there was gene variant or not (31.30% vs 6.03% and 42.75% vs 12.73%, all P < 0.01). Logistic analysis showed that beta(3)-AR gene variant was associated with increased incidence of MS in males.

CONCLUSION

beta(3)-AR gene Trp64Arg mutation is an independent risk factor for the incidence of MS in males.