Regulation of beta 3-adrenoceptor expression in white fat cells

Physiological and metabolic functions of the β3-adrenergic receptor and an approach to therapeutic achievements

A specific type of beta-adrenergic receptor was discovered in the decade of 1980s and subsequently recognized as a new type of beta-adrenergic receptor, called beta3-adrenoceptor (β3-AR). β3-AR expresses in different tissues, including adipose tissue, gall bladder, stomach, small intestine, cardiac myocytes, urinary bladder, and brain. Structurally, β3-AR is very similar to β1- and β2-AR and belongs to a G-protein coupled receptor that uses cAMP as an intracellular second messenger. Alternatively, it also activates the NO-cGMP cascade. Stimulation of the β3-AR increases lipolysis, fatty acid oxidation, energy expenditure, and insulin action, leading to anti-obesity and anti-diabetic activity. Moreover, β3-AR differentially regulates the myocardial contraction and relaxes the urinary bladder to balance the cardiac activity and delay the micturition reflex, respectively. In recent years, this receptor has served as an attractive target for the treatment of obesity, type 2 diabetes, congestive heart failure, and overactive bladder syndrome. Several β3-AR agonists are in the emerging stage that can exert novel pharmacological benefits in different therapeutic areas. The present review focuses on the structure, signaling, physiological, and metabolic activities of β3-AR. Additionally, therapeutic approaches of β3-AR have also been considered.

Genetic evidence for involvement of β2-adrenergic receptor in brown adipose tissue thermogenesis in humans

BACKGROUND

Sympathetic activation of brown adipose tissue (BAT) thermogenesis can ameliorate obesity and related metabolic abnormalities. However, crucial subtypes of the β-adrenergic receptor (AR), as well as effects of its genetic variants on functions of BAT, remains unclear in humans. We conducted association analyses of genes encoding β-ARs and BAT activity in human adults.

METHODS

Single nucleotide polymorphisms (SNPs) in β1-, β2-, and β3-AR genes (ADRB1, ADRB2, and ADRB3) were tested for the association with BAT activity under mild cold exposure (19 °C, 2 h) in 399 healthy Japanese adults. BAT activity was measured using fluorodeoxyglucose-positron emission tomography and computed tomography (FDG-PET/CT). To validate the results, we assessed the effects of SNPs in the two independent populations comprising 277 healthy East Asian adults using near-infrared time-resolved spectroscopy (NIRTRS) or infrared thermography (IRT). Effects of SNPs on physiological responses to intensive cold exposure were tested in 42 healthy Japanese adult males using an artificial climate chamber.

RESULTS

We found a significant association between a functional SNP (rs1042718) in ADRB2 and BAT activity assessed with FDG-PET/CT (p < 0.001). This SNP also showed an association with cold-induced thermogenesis in the population subset. Furthermore, the association was replicated in the two other independent populations; BAT activity was evaluated by NIRTRS or IRT (p < 0.05). This SNP did not show associations with oxygen consumption and cold-induced thermogenesis under intensive cold exposure, suggesting the irrelevance of shivering thermogenesis. The SNPs of ADRB1 and ADRB3 were not associated with these BAT-related traits.

CONCLUSIONS

The present study supports the importance of β2-AR in the sympathetic regulation of BAT thermogenesis in humans. The present collection of DNA samples is the largest to which information on the donor's BAT activity has been assigned and can serve as a reference for further in-depth understanding of human BAT function.

Transcriptome analysis of norepinephrine-induced lipolysis in differentiated adipocytes of Bama pig

Sympathetic innervation of white adipose tissue (WAT) plays a key role in the regulation of lipid metabolism. Sympathetic activation promotes release of norepinephrine (NE), which binds to adrenergic receptors on adipocytes, promoting adipocyte lipolysis and enhanced oxidative metabolism. However, the mechanism by which sympathetic nerves regulate lipid metabolism in pig adipose tissue remains unclear. We used NE to simulate the process of sympathetic driving in pig adipocytes. RNA sequencing (RNA-seq) was used to determine the gene expression profile of pig adipocytes responding to NE stimulation. Our data suggests that the lipolytic signaling pathway is activated in pig adipocytes upon acute stimulation of NE, resulting in enhanced lipid metabolism and lipolysis, consistent with the phenomena found in humans and mice. Specifically, differentially expressed protein coding genes (PCGs) (SIRT4, SLC27A1) are mainly associated with functions that inhibit fatty acid oxidation and promote lipid synthesis. Similarly, we investigated the changes in regulatory transcripts such as long non-coding RNAs (lncRNAs) and transcripts of uncertain coding potential (TUCP) in response to NE and found that differentially expressed lncRNAs (lncG47338, lncG30660, lncG29516, lncG3790) and TUCP (TUCP_G38001) were co-expressed with target genes related to the promotion of fatty acid β-oxidation, lipolysis and oxidative metabolism, thus acting as regulators. These results indicate a broad suite of gene expression alterations in response to NE stimulation and promote the understanding of the molecular mechanisms by which NE regulates lipid metabolism in pigs.

Characterization of β-adrenergic receptors in bovine intramuscular and subcutaneous adipose tissue: comparison of lubabegron fumarate with β-adrenergic receptor agonists and antagonists

Chinese hamster ovary cell constructs expressing either the β ₁-, β ₂- or β ₃-adrenergic receptor (AR) were used to determine whether a novel β-AR modulator, lubabegron fumarate (LUB; Experior, Elanco Animal Health) might exert greater potency for a specific β-AR subtype. EC₅₀ values calculated based on cAMP accumulation in dose response curves indicate that LUB is highly selective for the β ₃-AR subtype, with an EC₅₀ of 6 × 10^–9 M, with no detectible agonistic activity at the β ₂-AR. We hypothesized that the accumulation of lipolytic markers would reflect the agonist activity at each of the β-receptor subtypes of the specific ligand; additionally, there would be differences in receptor subtype expression in subcutaneous (s.c.) and intrmuscular (i.m.) adipose tissues. Total RNA was extracted from adipose tissue samples and relative mRNA levels for β ₁-, β₂-, and β ₃-AR were measured using real-time quantitative polymerase chain reaction. Fresh s.c. and i.m. adipose tissue explants were incubated with isoproterenol hydrochloride (ISO; β-AR pan-agonist), dobutamine hydrochloride (DOB; specific β ₁-AA), salbutamol sulfate (SAL; specific β ₂-AA), ractopamine hydrochloride (RAC), zilpaterol hydrochloride (ZIL), BRL-37344 (specific β ₃-agonist), or LUB for 30 min following preincubation with theophylline (inhibitor of phosphodiesterase). Relative mRNA amounts for β ₁-, β ₂-, and β ₃-AR were greater (P < 0.05) in s.c. than in i.m. adipose tissue. The most abundant β-AR mRNA in both adipose tissues was the β ₂-AR (P < 0.05), with the β ₁- and β ₃-AR subtypes being minimally expressed in i.m. adipose tissue. ISO, RH, and ZH stimulated the release of glycerol and nonesterified fatty acid (NEFA) from s.c. adipose tissue, but these β-AR ligands did not alter concentrations of these lipolytic markers in i.m. adipose tissue. LUB did not affect glycerol or NEFA concentrations in s.c. or i.m. adipose tissue, but attenuated (P < 0.05) the accumulation of cAMP mediated by the β ₁- and β ₂-AR ligands DOB and SAL in s.c. adipose tissue. Collectively, these data indicate that bovine i.m. adipose tissue is less responsive than s.c. adipose tissue to β-adrenergic ligands, especially those that are agonists at the β ₁- and β₃-receptor subtypes. The minimal mRNA expression of the β ₁- and β ₃ subtypes in i.m. adipose tissue likely limits the response potential to agonists for these β-AR subtypes.

β3-Adrenergic receptors regulate human brown/beige adipocyte lipolysis and thermogenesis

β3-Adrenergic receptors (β3-ARs) are the predominant regulators of rodent brown adipose tissue (BAT) thermogenesis. However, in humans, the physiological relevance of BAT and β3-AR remains controversial. Herein, using primary human adipocytes from supraclavicular neck fat and immortalized brown/beige adipocytes from deep neck fat from 2 subjects, we demonstrate that the β3-AR plays a critical role in regulating lipolysis, glycolysis, and thermogenesis. Silencing of the β3-AR compromised genes essential for thermogenesis, fatty acid metabolism, and mitochondrial mass. Functionally, reduction of β3-AR lowered agonist-mediated increases in intracellular cAMP, lipolysis, and lipolysis-activated, uncoupling protein 1-mediated thermogenic capacity. Furthermore, mirabegron, a selective human β3-AR agonist, stimulated BAT lipolysis and thermogenesis, and both processes were lost after silencing β3-AR expression. This study highlights that β3-ARs in human brown/beige adipocytes are required to maintain multiple components of the lipolytic and thermogenic cellular machinery and that β3-AR agonists could be used to achieve metabolic benefit in humans.

Pharmacotherapeutic management of asthma in the elderly patient

INTRODUCTION

Asthma is a heterogeneous syndrome with variable phenotypes. Reversible airway obstruction and airway hyper-responsiveness often with an atopic or eosinophilic component is common in the elderly asthmatic. Asthma chronic obstructive pulmonary disease overlap syndrome (ACOS), a combination of atopy-mediated airway hyper-responsiveness and a history of smoking or other environmental noxious exposures, can lead to some fixed airway obstruction and is also common in elderly patients. Little specific data exist for the treating the elderly asthmatic, thus requiring the clinician to extrapolate from general adult data and asthma treatment guidelines.

AREAS COVERED

A stepwise approach to pharmacotherapy of the elderly patient with asthma and ACOS is offered and the literature supporting the use of each class of drugs reviewed.

EXPERT OPINION

Inhaled, long-acting bronchodilators in combination with inhaled corticosteroids represent the backbone of treatment for the elderly patient with asthma or ACOS . Beyond these medications used as direct bronchodilators and topical anti-inflammatory agents, a stepwise approach to escalation of therapy includes multiple options such as oral leukotriene receptor antagonist or 5-lipoxygense inhibitor therapy, oral phosphodiesterase inhibitors, systemic corticosteroids, oral macrolide antibiotics and if evidence of eosinophilic/atopic component disease exists then modifying monoclonal antibody therapies.

The protective effects of the β3 adrenergic receptor agonist BRL37344 against liver steatosis and inflammation in a rat model of high-fat diet-induced nonalcoholic fatty liver disease (NAFLD)

BACKGROUND

Our objective was to investigate the efficacy of the beta-3 adrenergic receptor (β3-AR) agonist BRL37344 for the prevention of liver steatosis and inflammation associated with nonalcoholic fatty liver disease (NAFLD).

METHODS

Four groups were established: a control group (given a standard diet), a high-fat diet (HFD) group, an HFD + β3-AR agonist (β3-AGO) group, and an HFD + β3-AR antagonist (β3-ANT) group. All rats were fed for 12 weeks. The β3-AR agonist BRL37344 and the antagonist L748337 were administered for the last 4 weeks with Alzet micro-osmotic pumps. The rat body weights (g) were measured at the end of the 4th, 8th, and 12th weeks. At the end of the 12th week, the liver weights were measured. Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were analyzed with a Hitachi automatic analyzer. The lipid levels of the triglycerides (TGs), total cholesterol (TC), and low-density lipoprotein cholesterol (LDL-C) and the concentrations of free fatty acids (FFAs) were also measured. An oil red O kit was used to detect lipid droplet accumulation in hepatocytes. Steatosis, ballooning degeneration and inflammation were histopathologically determined. The protein and mRNA expression levels of β3-AR, peroxisome proliferator-activated receptor-alpha (PPAR-α), peroxisome proliferator-activated receptor-gamma (PPAR-γ), mitochondrial carnitine palmitoyltransferase-1 (mCPT-1), and fatty acid translocase (FAT)/CD36 were measured by western blot analysis and RT-qPCR, respectively.

RESULTS

After treatment with the β3-AR agonist BRL37344 for 4 weeks, the levels of ALT, AST, TGs, TC, LDL-C and FFAs were decreased in the NAFLD model group compared with the HFD group. Body and liver weights, liver index values and lipid droplet accumulation were lower in the HFD + β3-AGO group than in the HFD group. Decreased NAFLD activity scores (NASs) also showed that liver steatosis and inflammation were ameliorated after treatment with BRL37344. Moreover, the β3-AR antagonist L748337 reversed these effects. Additionally, the protein and gene expression levels of β3-AR, PPAR-α, and mCPT-1 were increased in the HFD + β3-AGO group, whereas those of PPAR-γ and FAT/CD36 were decreased.

CONCLUSION

The β3-AR agonist BRL37344 is beneficial for reducing liver fat accumulation and for ameliorating liver steatosis and inflammation in NAFLD. These effects may be associated with PPARs/mCPT-1 and FAT/CD36.

Perivascular adipose tissue phenotype and sepsis vascular dysfunction: Differential contribution of NO, ROS and beta 3-adrenergic receptor

AIMS

Vascular dysfunction plays a key role in sepsis but the role of perivascular adipose tissue (PVAT) in this condition is relatively unknown.

MAIN METHODS

Sepsis was induced by cecal ligation and puncture (CLP). The responses of the aorta and superior mesenteric artery to norepinephrine in the presence or absence of PVAT were evaluated. Fluorescent probes measured the production of nitric oxide (NO) and reactive oxygen species (ROS). NO synthases (NOS) and β3-adrenoceptor expression were detected by immunofluorescence and S-nitrosylation by the biotin switch assay.

KEY FINDINGS

Aorta and superior mesenteric arteries from septic animals with intact PVAT showed a worsened response to the vasoconstrictor compared to vessels without PVAT. PVAT from the aorta (APVAT) produced NO and ROS whereas PVAT from the superior mesenteric artery (MPVAT) produced only ROS. Septic APVAT exhibited a higher density of NOS-1 and NOS-3. S-nitrosylation was found in APVAT. Donor (PVAT obtained from normal or septic rats):Host (normal vessel without PVAT) experiments showed that L-NAME, ODQ and β3-adrenergic receptor antagonist blocked the septic APVAT anti-contractile effect. None of these compounds affected MPVAT; tempol, but not apocynin, blocked its anti-contractile effect.

SIGNIFICANCE

PVAT contributes to the anti-contractile effect in the aorta and mesenteric artery of septic rats through different pathways. β3-Adrenergic receptor and NO appear to be key mediators of this effect in APVAT, but not in MPVAT where ROS seem to be a relevant mediator. Therefore, PVAT is a relevant player of sepsis vascular dysfunction.

Denervation as a tool for testing sympathetic control of white adipose tissue

This review summarizes the evidence derived from studies utilizing denervation procedures to demonstrate sympathetic control of white adipose tissue metabolism and body fat mass. A majority of the work demonstrating neural control of white fat was performed in the Bartness laboratory with Siberian hamsters as the predominant experimental model. These animals experience dramatic changes in body fat mass in response to changes in photoperiod, however, the mechanisms identified in hamsters have been reproduced or further elucidated by experiments with other animal models. Evidence for the role of sympathetic innervation contributing to the control of white adipocyte lipolysis and preadipocyte proliferation is summarized. In addition, evidence from denervation experiments for neural communication between different white fat depots as well as for a feedback control loop between sensory afferents from individual fat depots and sympathetic efferents to the same or distant white fat depots is discussed.

Role of Sympathetic Nerves and Adipocyte Catecholamine Uptake in the Vasorelaxant Function of Perivascular Adipose Tissue

OBJECTIVE

Healthy perivascular adipose tissue (PVAT) exerts an anticontractile effect on resistance arteries which is vital in regulating arterial tone. Activation of β₃-adrenoceptors by sympathetic nerve-derived NA (noradrenaline) may be implicated in this effect and may stimulate the release of the vasodilator adiponectin from adipocytes. Understanding the mechanisms responsible is vital for determining how PVAT may modify vascular resistance in vivo.

APPROACH AND RESULTS

Electrical field stimulation profiles of healthy C57BL/6J mouse mesenteric resistance arteries were characterized using wire myography. During electrical field stimulation, PVAT elicits a reproducible anticontractile effect, which is endothelium independent. To demonstrate the release of an anticontractile factor, the solution surrounding stimulated exogenous PVAT was transferred to a PVAT-denuded vessel. Post-transfer contractility was significantly reduced confirming that stimulated PVAT releases a transferable anticontractile factor. Sympathetic denervation of PVAT using tetrodotoxin or 6-hydroxydopamine completely abolished the anticontractile effect. β₃-adrenoceptor antagonist SR59203A reduced the anticontractile effect, although the PVAT remained overall anticontractile. When the antagonist was used in combination with an OCT3 (organic cation transporter 3) inhibitor, corticosterone, the anticontractile effect was completely abolished. Application of an adiponectin receptor-1 blocking peptide significantly reduced the anticontractile effect in +PVAT arteries. When used in combination with the β₃-adrenoceptor antagonist, there was no further reduction. In adiponectin knockout mice, the anticontractile effect is absent.

CONCLUSIONS

The roles of PVAT are 2-fold. First, sympathetic stimulation in PVAT triggers the release of adiponectin via β₃-adrenoceptor activation. Second, PVAT acts as a reservoir for NA, preventing it from reaching the vessel and causing contraction.

Adrenergic pathway activation enhances brown adipose tissue metabolism: a [¹⁸F]FDG PET/CT study in mice

OBJECTIVE

Pharmacologic approaches to study brown adipocyte activation in vivo with a potential of being translational to humans are desired. The aim of this study was to examine pre- and postsynaptic targeting of adrenergic system for enhancing brown adipose tissue (BAT) metabolism quantifiable by [(18)F]fluoro-2-deoxyglucose ([(18)F]FDG) positron emission tomography (PET)/computed tomography (CT) in mice.

METHODS

A β₃-adrenoreceptor selective agonist (CL 316243), an adenylyl cyclase enzyme activator (forskolin) and a potent blocker of presynaptic norepinephrine transporter (atomoxetine), were injected through the tail vein of Swiss Webster mice 30 minutes before intravenous (iv) administration of [(18)F]FDG. The mice were placed on the PET/CT bed for 30 min PET acquisition followed by 10 min CT acquisition for attenuation correction and anatomical delineation of PET images.

RESULTS

Activated interscapular (IBAT), cervical, periaortic and intercostal BAT were observed in 3-dimentional analysis of [(18)F]FDG PET images. CL 316243 increased the total [(18)F]FDG standard uptake value (SUV) of IBAT 5-fold greater compared to that in placebo-treated mice. It also increased the [(18)F]FDG SUV of white adipose tissue (2.4-fold), and muscle (2.7-fold), as compared to the control. There was no significant difference in heart, brain, spleen and liver uptakes between groups. Forskolin increased [(18)F]FDG SUV of IBAT 1.9-fold greater than that in placebo-treated mice. It also increased the [(18)F]FDG SUV of white adipose tissue (2.2-fold) and heart (5.4-fold) compared to control. There was no significant difference in muscle, brain, spleen, and liver uptakes between groups. Atomoxetine increased [(18)F]FDG SUV of IBAT 1.7-fold greater than that in placebo-treated mice. There were no significant differences in all other organs compared to placebo-treated mice except liver (1.6 fold increase). A positive correlation between SUV levels of IBAT and CT Hounsfield unit (HU) (R(2)=0.55, p<0.001) and between CT HU levels of IBAT and liver (R(2)=0.69, p<0.006) was observed.

CONCLUSIONS

The three pharmacologic approaches reported here enhanced BAT metabolism by targeting different sites in adrenergic system as measured by [(18)F]FDG PET/CT.

Role of leptin resistance in the development of obesity in older patients

Obesity is a global epidemic associated with aging-like cellular processes; in both aging and obesity, resistance to hormones such as insulin and leptin can be observed. Leptin is a circulating hormone/cytokine with central and peripheral effects that is released mainly by subcutaneous white adipose tissue. Centrally, leptin controls food intake, energy expenditure, and fat distribution, whereas it controls (among several others) insulin sensitivity, free fatty acids (FFAs) oxidation, and lipolysis in the periphery. Aging is associated with important changes in both the distribution and the composition of adipose tissue. Fat is redistributed from the subcutaneous to the visceral depot and increased inflammation participates in adipocyte dysfunction. This redistribution of adipose tissue in favor of visceral fat influences negatively both longevity and healthy aging as shown in numerous animal models. These modifications observed during aging are also associated with leptin resistance. This resistance blunts normal central and peripheral functions of leptin, which leads to a decrease in neuroendocrine function and insulin sensitivity, an imbalance in energy regulation, and disturbances in lipid metabolism. Here, we review how age-related leptin resistance triggers metabolic disturbances and affects the longevity of obese patients. Furthermore, we discuss the potential impacts of leptin resistance on the decline of brown adipose tissue thermogenesis observed in elderly individuals.

Testosterone modulation of cardiac β-adrenergic signals in a rat model of heart failure

In this study, we examined the effects of castration and testosterone replacement on β-adrenoceptor and G protein expression in rats subjected to doxorubicin-induced heart failure. Five groups were included in this report: control, sham-castration with heart failure, castration with heart failure, castration+testosterone replacement with heart failure and castration+testosterone replacement and flutamide with heart failure. At 4 weeks post-treatment, echocardiography, hemodynamics and histopathology were assessed. Castration led to a further deterioration in myocardial performance, apoptosis and fibrosis, while testosterone replacement ameliorated these effects. Data obtained from Western blots revealed that testosterone upregulated the expression of β(2)-adrenoceptor, Gs, Gi(2) and bcl2 levels, downregulated the expression of β(3)-adrenoceptor, Gi(3) and GRK2 levels, and did not modify the expression of β(1)-adrenoceptor levels in the hearts of castrated rats subjected to doxorubicin-induced heart failure. Analyses of serum 17β-estradiol concentrations test confirmed that these effects of testosterone were exerted through the androgen pathway. Thus our findings suggest that testosterone may have beneficial effects for male heart failure patients with androgen deficiency and this protection involves modulation of the cardiac β-adrenergic system.

Brown versus white adipose tissue: a mini-review

BACKGROUND

Brown adipose tissue (BAT) is abundant in small mammals and in newborns and helps them to survive cold temperatures. In adults, it had long been considered to be absent or at least of no relevance. Recent investigations, however, have fuelled interest in adult BAT.

OBJECTIVE

We aimed at (1) summarizing structural and physiological characteristics of BAT versus white adipose tissue (WAT); (2) discussing the development of the two adipose tissue types; (3) reviewing the data available from human studies on BAT, and (4) discussing the impact of aging.

METHODS

We summarize recent descriptions of BAT and WAT based on the original literature and reviews in the field, with emphasis on human BAT.

RESULTS

WAT and BAT have essentially antagonistic functions: WAT stores excess energy as triglycerides and BAT is specialized in the dissipation of energy through the production of heat. Considerable amounts of BAT are present in a substantial proportion of adult humans and relatively high quantities of BAT are associated with lower body weight. With increasing age, BAT decreases and body weight increases.

CONCLUSIONS

Although the available cross-sectional data do not allow definite conclusions to be drawn concerning a causal relationship between loss of BAT and increasing body weight with advancing age or obesity-related metabolic disorders of older age, stimulation of BAT appears to be an attractive novel candidate target for the treatment of age-related obesity.

Role of beta3-adrenoceptors for intrahepatic resistance and portal hypertension in liver cirrhosis

Increased intrahepatic resistance and splanchnic blood flow cause portal hypertension in liver cirrhosis. Nonselective beta-adrenoceptor (beta-AR) antagonists have beneficial effects on hyperdynamic circulation and are in clinical use. In this context, the role of the beta(3)-AR is undefined. Here we investigated their expression and role in portal hypertension in patients and rats with liver cirrhosis. We analyzed cirrhotic human and rat tissues (liver, splanchnic vessels) and primary rat cells. Protein expression of beta(3)-AR was determined by western blot and messenger RNA (mRNA) levels by reverse-transcription polymerase chain reaction (RT-PCR). Activities of Rho-kinase and the nitric oxide (NO) effector protein kinase G (PKG) were assessed by way of substrate phosphorylation (moesin, vasodilator-stimulated phosphoprotein [VASP]). Cyclic 3',5' adenosine monophosphate (cAMP) accumulation was determined by an enzyme-immunoassay kit. The effects of selective beta(3)-AR agonists (CGP12177A, BRL37344) and antagonist (SR59230A) were investigated by collagen matrix contraction of hepatic stellate cells (HSCs), in situ liver perfusions, and in vivo hemodynamic parameters in bile duct ligation and carbon tetrachloride intoxication in cirrhotic rats. In cirrhosis of humans and rats, beta(3)-AR expression is markedly increased in hepatic and in splanchnic tissues. Stimulation of beta(3)-AR leads to relaxation of HSCs by way of cAMP accumulation, and by inhibition of Rho-kinase activity; any role of NO and its effector PKG was not observed. beta(3)-AR agonists decrease intrahepatic resistance and portal pressure in cirrhotic rats.

CONCLUSION

There is a marked hepatic and mesenteric up-regulation of beta(3)-ARs in human cirrhosis and in two different animal models of cirrhosis. The beta(3)-AR-agonists should be further evaluated for therapy of portal hypertension.

Body fat mass reduction and up-regulation of uncoupling protein by novel lipolysis-promoting plant extract

We have found natural products exhibiting lipolysis-promoting activity in subcutaneous adipocytes, which are less sensitive to hormones than visceral adipocytes. The activities and a action mechanisms of a novel plant extract of Cirsium oligophyllum (CE) were investigated in isolated adipocytes from rat subcutaneous fat, and its fat-reducing effects by peroral administration and topical application were evaluated in vivo. CE-induced lipolysis was synergistically enhanced by caffeine, a phosphodiesterase inhibitor, and was reduced by propranolol, a β adrenergic antagonist. The peroral administration of 10% CE solution to Wistar rats for 32 days reduced body weight gain, subcutaneous, and visceral fat weights by 6.6, 26.2, and 3.0%, respectively, as compared to the control group. By the topical application of 2% of this extract to rats for 7 days, weight of subcutaneous fat in the treated skin was reduced by 23.2%. This fat mass reduction was accompanied by the up-regulation of uncoupling protein 1 (UCP), a principal thermogenic mitochondrial molecule related to energy dissipating, in subcutaneous fat and UCP3 in skin except for the fat layer. These results indicate that CE promotes lipolysis via a mechanism involving the β adrenergic receptor, and affects the body fat mass. This fat reduction may be partially due to UCP up-regulation in the skin including subcutaneous fat. This is the first report showing that repeated lipolysis promotion through CE administration may be beneficial for the systematic suppression of body fat accumulation or the control of fat distribution in obesity.

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.

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.

Pregnancy Effects on Rat Adipose Tissue Lipolytic Capacity are Dependent on Anatomical Location

Pregnancy is characterized by changes in maternal adiposity. The aim of this study was to carry out a detailed analysis of the different steps of the adrenergic pathway, lipoprotein lipase (LPL) levels and adipocyte size, in order to evaluate the response of white adipose tissue (WAT) to the metabolic changes during pregnancy depending on the anatomical location. In general, the levels of the proteins of the lipolytic pathway decreased with pregnancy. In retroperitoneal WAT adenylate cyclase (AC) levels decreased from 100% in controls to 44% by day 13 and 11% by day 20. In mesenteric WAT the alpha (2A)/beta (3)-adrenergic receptor balance seemed to be one of the main regulatory points of the lipolytic pathway and the reduction in the postreceptor element levels was clearly lower than for the other two depots (PKA levels reduced from 100% in controls to 72% by day 20, while in the other two depots it decreased to 30%, and AC and HSL levels did not show statistically significant changes in this depot). In contrast, the LPL-to-HSL ratio may be a major regulatory point in gonadal WAT. In summary, we describe regional differences in the regulation of WAT metabolism throughout pregnancy, which may be of great importance to determine the role of the different fat depots during late pregnancy. Thus, gonadal and mesenteric WAT changed to a lipolytic state to sustain the rapid foetal growth, although with differences between them in the main regulatory points, while retroperitoneal WAT could have a role later on, during lactation.

Potential use of beta(3)-adrenoceptor antagonists in heart failure therapy

Recently, a functional, negatively inotropic, beta(3)-adrenoceptor was characterized in the human heart. Several studies now suggest that this receptor might play an important role in the pathophysiology of heart failure, by counterbalancing the effects of a beta(1)- and beta(2)-stimulation. Therefore, this review summarizes the rationale and effects of beta-adrenergic blockade in chronic heart failure and specifically addresses the question of the potential use of beta(3)-adrenoceptor antagonists in the treatment of heart failure and other pathophysiological conditions associated with a decreased cardiac contractility.

Cyclic AMP-independent relaxation mediated by beta3-adrenoceptors on guinea pig gastrointestine

In this study, we investigated the signal transduction pathway involved in beta(3)-adrenoceptor-mediated relaxations of guinea pig gastric fundus and duodenum. In the presence of beta1- and beta2-adrenoceptor blockade, the potency (pD2 value) of catecholamines ((-)-isoprenaline, (-)-noradrenaline and (-)-adrenaline) and beta(3)-adrenoceptor agonists ((R*, R*)-(+/-)-4-[2-[(2-(3-chlorophenyl)-2-hydroxyethyl)amino]propyl]phenoxyacetic acid sodium (BRL37344) and (+/-)-[4-[3-[(1,1-dimethylethyl)amino]-2-hydroxypropoxy]-1,3-dihydro-2H-benzimidazol-2-one] hydrochloride ((+/-)-CGP12177A)) to induce relaxation was not affected by the adenylate cyclase inhibitor, 9-(tetrahydro-2-furanyl)-9H-purin-6-amine (SQ-22,536, 100 microM). Catecholamines induced an elevation of cyclic AMP and SQ-22,536 significantly abolished the responses of gastric fundus. However, cyclic AMP levels were unaltered by the beta3-adrenoceptor agonists in gastric fundus and by the five agonists in duodenum. Furthermore, the relaxant responses to catecholamines and to beta3-adrenoceptor agonists were unaffected by the cyclic AMP-dependent protein kinase inhibitor, N-(2-[p-bromocinnamylamino]ethyl)-5-isoquinolinesulfonamide (H-89, 10 microM) in gastric fundus. These results suggest that beta3-adrenoceptor-induced relaxation is mediated through both cyclic AMP-dependent and cyclic AMP-independent pathways in gastric fundus and through a cyclic AMP-independent pathway in duodenum.

Effect of oleoyl-estrone treatment on the expression of beta1- beta2- and beta3-adrenoreceptors in rat adipose tissues

Adult female rats received a constant i.v. infusion of oleoyl-estrone (3.5 pmol/kg day) in a lipidic suspension for 14 days. On days 0 (no treatment), 3, 6, 10 and 14, as well as on day 14 for controls (receiving only the lipid); the rats were killed and the expression of the beta1-, beta2- and beta3-adrenoceptor genes, in brown adipose tissue and in subcutaneous and periovaric white adipose tissue, were measured by RNA protection assay, and compared with that of cyclophyllin. The beta3-adrenoceptor was the most expressed in all adipose tissues, whereas beta2 was the less expressed in brown adipose tissue. Oleoyl-estrone significantly, but moderately, increased the expression of beta-adrenoceptors in the three adipose tissues: beta1 increased in subcutaneous, beta2 and beta3 in periovaric and beta3 in brown adipose tissue. Oleoyl-estrone also decreased beta3 expression in subcutaneous white adipose tissue. On day 10, adipocytes isolated from periovaric white adipose tissue of oleoyl-estrone-treated rats showed higher cAMP response to an isoproterenol challenge than the controls. The mechanism by which oleoyl-estrone elicits the wasting of fat reserves could be mediated by adrenergic pathways, at least in part.

Beta3-adrenoceptors in the cardiovascular system

beta-Adrenoceptors of the beta1 and beta2 subtypes classically mediate the effects of catecholamines on the contractility of cardiac muscle and the relaxation of vascular smooth muscle. Since the molecular characterization of the beta3-adrenoceptor in 1989, most studies of this adrenoceptor subtype have focused on its control of lipolysis in adipose tissues. However, more recent studies have investigated the involvement of beta3-adrenoceptors in the physiological control of cardiac and vascular contractility. In this article, the pharmacological and molecular evidence that supports the functional role of beta3-adrenoceptors in cardiovasculartissues of various species, including humans, will be discussed. These data might provide new insights into our understanding of the abnormal responsiveness of the cardiovascular system to catecholamines in heart failure and its treatment with beta3-adrenoceptor antagonists.

Peripheral cardiovascular actions of SR 58611 A, a beta 3-adrenoceptor agonist, in the dog: lack of central effect

In order to investigate the putative role of beta3-adrenoceptors in central and peripheral cardiovascular regulations, the effects of intracisternal (i.c.) and intravenous (i.v.) injections of SR 58611 A (10, 50, 100 and 200 nmol kg-1), a selective beta3-adrenoceptor agonist, were investigated in chloralose anaesthetized dogs. In normal dogs, i.v. SR 58611 A (100 and 200 nmol kg-1) induced a dose-dependent increase in heart rate with no change in blood pressure. After i.c. injection, SR 58611 A failed to modify blood pressure and heart rate (except at the highest dose 200 nmol kg-1 which induced a positive chronotropic effect). The positive chronotropic effect of SR 58611 A (200 nmol kg-1) appeared earlier and was significantly more pronounced after i.v. than i.c. administration. The positive chronotropic effect of i.v. SR 58611 A (200 nmol kg-1) was reduced by pretreatment with beta-adrenoceptor antagonists [propranolol, nadolol, bupranolol or the beta3-adrenoceptor selective antagonist, SR 59230 A (2 mg kg-1 i.v.)] and suppressed after sinoaortic denervation (i.e. after removal of vagal tone to the heart). These experiments do not show evidence for a primary central cardiovascular effect of SR 58611 A. The positive chronotropic effect of i.v. SR 58611 A is mainly of peripheral origin and can be attributed to a baroreceptor-mediated reflex due to the beta3-adrenoceptor mediated vasodilation with an increase in sympathetic tone and a reduction in vagal tone to the heart.

The Trp64Arg polymorphism of the beta 3-adrenergic receptor gene is not associated with obesity or type 2 diabetes mellitus in a large population-based Caucasian cohort

The beta3-adrenergic receptor (3-BAR) is assumed to play a role in the regulation of energy balance by increasing lipolysis and thermogenesis. A recently detected allelic polymorphism (Trp64Arg polymorphism) has been suggested to contribute to the development of obesity and non-insulin-dependent diabetes mellitus. We examined the prevalence of the two 3-BAR alleles in Germany and looked for associations between 3-BAR genotype and metabolic disorders (obesity and type 2 diabetes mellitus). From over 6450 participants in the Diabetomobile Study, a nationwide epidemiologic study on the prevalence of metabolic disorders (carried out from 1993 to 1996 in Germany), 1259 participants were randomly chosen. The 3-BAR genotype status was determined by 3-BAR gene-specific genomic PCR and consecutive restriction fragment length polymorphism analysis. The frequencies of the different genotypes in the examined cohort were as follows: Trp64/Trp64, 88.3%; Trp64/Arg64, 10.8%; and Arg64/ Arg64, 0.8%. No significant differences between the different genotypes were found when comparing age, body mass index, weight, total and high-density lipoprotein (HDL) cholesterol, fasting insulin, HbA11, and blood pressure; neither did the type 2 diabetes mellitus participants in the different genotype groups differ significantly in terms of age of diabetes onset or HbA11. This is the largest population-based study on the Trp64Arg polymorphism reported yet. The Arg64 allele of the 3-BAR gene was found commonly in Germany. In our cohort, no significant associations between the Arg64 allele and metabolic disorders (e.g. obesity, type 2 diabetes mellitus, dyslipidemia, or hypertension) were detected.

Effects of chronic treatment with noradrenaline or a specific beta3-adrenergic agonist, CL 316 243, on energy expenditure and epididymal adipocyte lipolytic activity in rat

1. The effects of 7 days exposure to a specific beta3-adrenergic agonist, CL 316 243 (1 mg/kg x 24 hr), or to the physiological hormone, noradrenaline (5 mg/kg x 24 hr), were tested on energy expenditure and on in vitro lipolysis in male Sprague-Dawley rats. 2. At the second day of treatment, the total energy expenditure and the resting metabolic rate were increased by 20 and 30%, respectively, in the CL-treated group. Under the same conditions, a dose five times higher of NA increased the resting metabolic rate by 11% without any significant change in the total daily energy expenditure. 3. The CL-treated group showed a lower weight gain, correlated with a significant reduction in retroperitoneal adipose tissue weight. Both treatments resulted in a marked desensitization (increased EC50 values) of the NA stimulated lipolysis of epididymal adipocytes. The effects of both treatments on maximal lipolysis were opposite. Indeed, chronic NA-treatment decreased the responsiveness of lipolysis while chronic treatment with CL increased the maximal stimulation of lipolysis to NA. Furthermore, dose-response curve for CL on lipolysis showed a marked functional desensitization of beta3-adrenergic response. 4. Our results demonstrate the high selectivity of beta3-adrenergic agonists to stimulate whole body energy expenditure and lipid mobilization in rodents. The present results point out for the first time an adrenergic desensitization of the lipolytic response after chronic administration of a beta3-agonist.

Tissue-specific modulation of insulin receptor mRNA levels in adrenaline-treated rats

Insulin receptor (IR) gene expression at the mRNA level was investigated in liver, hindlimb skeletal muscle, and epididymal adipose tissue of rats exposed to prolonged in vivo administration of adrenaline in relation to control rats. In the liver of adrenaline-treated rats, there were no differences in relation to controls when DNA and protein content were measured. In skeletal muscle, only a slight decrease in protein concentration was detected. By contrast, a clear increase in both protein and DNA content was observed in the adipose tissue of treated animals. Northern blot assays revealed two IR mRNA species of approximately 9.5 and 7.5 Kb in the three tissues from controls. Adrenaline treatment induced an increase of approximately 60% in the levels of both RNAs in adipose tissue but not in liver or skeletal muscle. These results provide evidence for an in vivo tissue-specific regulation of IR gene expression at the mRNA level in rats under an experimental condition of excess of catecholamines.

Fat cells

The adipocyte is a metabolically active cell that functions to store energy for times of energy deprivation or enhanced need. Obesity is characterized by increased lipid accumulation and turnover compared with the nonobese state. Both triglyceride synthesis and lipolysis are regulated metabolic processes in the adipocyte. Current research on the metabolic activities of the human adipocyte focus on plasma triglyceride hydrolysis and uptake of fatty acids by LPL, esterification of these fatty acids, and the subsequent triglyceride breakdown by hormone-sensitive lipase in response to stimulation of adrenergic receptors. These topics are discussed in relationship to the development of obesity.