Noradrenaline protects neurons against H2 O2 -induced death by increasing the supply of glutathione from astrocytes via ß3 -adrenoceptor stimulation.

Oxidative stress has been implicated in a variety of neurodegenerative disorders, such as Alzheimer's and Parkinson's disease. Astrocytes play a significant role in maintaining survival of neurons by supplying antioxidants such as glutathione (GSH) to neurons. Recently, we found that noradrenaline increased the intracellular GSH concentration in astrocytes via ß3 -adrenoceptor stimulation. These observations suggest that noradrenaline protects neurons from oxidative stress-induced death by increasing the supply of GSH from astrocytes to neurons via the stimulation of ß3 -adrenoceptor in astrocytes. In the present study, we examined the protective effect of noradrenaline against H2 O2 -induced neurotoxicity using two different mixed cultures: the mixed culture of human astrocytoma U-251 MG cells and human neuroblastoma SH-SY5Y cells, and the mouse primary cerebrum mixed culture of neurons and astrocytes. H2 O2 -induced neuronal cell death was significantly attenuated by pretreatment with noradrenaline in both mixed cultures but not in single culture of SH-SY5Y cells or in mouse cerebrum neuron-rich culture. The neuroprotective effect of noradrenaline was inhibited by SR59230A, a selective ß3 -adrenoceptor antagonist, and CL316243, a selective ß3 -adrenoceptor agonist, mimicked the neuroprotective effect of noradrenaline. DL-buthionine-[S,R]-sulfoximine, a GSH synthesis inhibitor, negated the neuroprotective effect of noradrenaline in both mixed cultures. MK571, which inhibits the export of GSH from astrocytes mediated by multidrug resistance-associated protein 1, also prevented the neuroprotective effect of noradrenaline. These results suggest that noradrenaline protects neurons against H2 O2 -induced death by increasing the supply of GSH from astrocytes via ß3 -adrenoceptor stimulation.

ß3-Adrenoreceptors as ROS Balancer in Hematopoietic Stem Cell Transplantation.

In the last decades, the therapeutic potential of hematopoietic stem cell transplantation (HSCT) has acquired a primary role in the management of a broad spectrum of diseases including cancer, hematologic conditions, immune system dysregulations, and inborn errors of metabolism. The different types of HSCT, autologous and allogeneic, include risks of severe complications including acute and chronic graft-versus-host disease (GvHD) complications, hepatic veno-occlusive disease, lung injury, and infections. Despite being a dangerous procedure, it improved patient survival. Hence, its use was extended to treat autoimmune diseases, metabolic disorders, malignant infantile disorders, and hereditary skeletal dysplasia. HSCT is performed to restore or treat various congenital conditions in which immunologic functions are compromised, for instance, by chemo- and radiotherapy, and involves the administration of hematopoietic stem cells (HSCs) in patients with depleted or dysfunctional bone marrow (BM). Since HSCs biology is tightly regulated by oxidative stress (OS), the control of reactive oxygen species (ROS) levels is important to maintain their self-renewal capacity. In quiescent HSCs, low ROS levels are essential for stemness maintenance; however, physiological ROS levels promote HSC proliferation and differentiation. High ROS levels are mainly involved in short-term repopulation, whereas low ROS levels are associated with long-term repopulating ability. In this review, we aim summarize the current state of knowledge about the role of ß3-adrenoreceptors (ß3-ARs) in regulating HSCs redox homeostasis. ß3-ARs play a major role in regulating stromal cell differentiation, and the antagonist SR59230A promotes differentiation of different progenitor cells in hematopoietic tumors, suggesting that ß3-ARs agonism and antagonism could be exploited for clinical benefit.

ß3-Adrenergic receptor blockade reduces mortality in endotoxin-induced heart failure by suppressing induced nitric oxide synthase and saving cardiac metabolism.

The ß3-adrenergic receptor (ß3AR) is related to myocardial fatty acid metabolism and its expression has been implicated in heart failure. In this study, we investigated the role of ß3AR in sepsis-related myocardial dysfunction using lipopolysaccharide (LPS)-induced endotoxemia as a model of cardiac dysfunction. We placed mice into three treatment groups and treated each with intraperitoneal injections of the ß3AR agonist CL316243 (CL group), the ß3AR antagonist SR59230A (SR group), or normal saline (NS group). Survival rates were significantly improved in the SR group compared with the other treatment groups. Echocardiography analyses revealed cardiac dysfunction within 6-12 h of LPS injections, but the outcome was significantly better for the SR group. Myocardial ATP was preserved in the SR group but was decreased in the CL-treated mice. Additionally, quantitative PCR analysis revealed that expression levels of genes associated with fatty acid oxidation and glucose metabolism were significantly higher in the SR group. Furthermore, the expression levels of mitochondrial membrane protein complexes were preserved in the SR group. Electron microscope studies showed significant accumulation of lipid droplets in the CL group. Moreover, inducible nitric oxide synthase (iNOS) protein expression and nitric oxide were significantly reduced in the SR group. The in vitro study demonstrated that ß3AR has an independent iNOS pathway that does not go through the nuclear factor-κB pathway. These results suggest that blockading ß3AR improves impaired energy metabolism in myocardial tissues by suppressing iNOS expression and recovers cardiac function in animals with endotoxin-induced heart failure.NEW & NOTEWORTHY Nitric oxide production through stimulation of ß3-adrenergic receptor (ß3AR) may improve cardiac function in cases of chronic heart failure. We demonstrated that the blockade of ß3AR improved mortality and cardiac function in endotoxin-induced heart failure. We also determined that LPS-induced inducible nitric oxide synthase has a pathway that is independent of nuclear factor-κB, which worsened cardiac metabolism and mortality in the acute phase of sepsis. Treatment with the ß3AR antagonist had a favorable effect. Thus, the blockade of ß3AR could offer a novel treatment for sepsis-related heart failure.

TAS-303 Ameliorates Carbachol-Induced Detrusor Overactivity in Rats, Revealing Its Therapeutic Potential for Overactive Bladder.

Urinary incontinence is defined as an involuntary leakage of urine and is categorized into three types: stress urinary incontinence (SUI), urge urinary incontinence (UUI), and mixed urinary incontinence, which includes symptoms of SUI and UUI. As the underlying mechanisms of SUI and UUI are different, no drug is approved to treat all three types of urinary incontinence. TAS-303 is a selective norepinephrine reuptake inhibitor and has therapeutic potential for patients with SUI. In this report, we describe newly discovered pharmacological properties of TAS-303 and its effects on bladder function. Radioligand binding studies showed that TAS-303 inhibits M3 muscarinic receptor binding, with a Ki value of 547 nM. TAS-303 at 1, 3, and 10 mg/kg dose-dependently prolonged the intercontraction interval of carbachol-induced detrusor overactivity in rats, exhibiting a maximal effect that was comparable to tolterodine. These effects may result from coordinated regulation of bladder afferent activity via M3 muscarinic inhibition and ß3 adrenoreceptor activation by norepinephrine elevation due to norepinephrine transporter inhibition. Moreover, TAS-303 at the effective dose for bladder function did not induce dry mouth or constipation in rats, showing that this compound may have a lower risk of antimuscarinic side effects. Thus, TAS-303 is expected to be a new profile agent with therapeutic potential for all types of urinary incontinence. SIGNIFICANCE STATEMENT: Urinary incontinence is categorized into stress, urge, and mixed urinary incontinence, but because the underlying mechanisms of each differ, no drugs are available that treat all three. TAS-303 has therapeutic potential for stress urinary incontinence. This study describes newly discovered pharmacological properties of TAS-303, which ameliorated bladder afferent activity partly via M3 muscarinic inhibition, indicating improvement in urge urinary incontinence, and highlights the potential of TAS-303 as a new therapeutic agent for all types of urinary incontinence.

ß3-Adrenoreceptor Blockade Induces Stem Cells Differentiation in Melanoma Microenvironment.

Although there is an increasing evidence that cancer stem cell (CSC) niches in the tumor microenvironment (TME) plays a crucial role in sustaining solid tumors progression, several molecular players involved in this regulation still remain unknown. The role of ß-adrenergic signaling in enhancing tumor growth through ß2-adrenoreceptors (ß2-ARs) has been confirmed in different cancer models, but the role played by the ß3-adrenergic receptor (ß3-AR) has recently emerged. Previous studies showed that ß3-AR promotes cancer growth through the activation of different stromal cells in the TME, and leads to melanoma malignancy progression through inflammation, angiogenesis, and immunotolerance. Here we show that in B16 melanoma-bearing mice, the pharmacological ß3-AR blockade is able to reduce the expression of CSC markers, and to induce a differentiated phenotype of hematopoietic subpopulations in TME. In particular, cytofluorimetric analysis (FACS) of the tumor mass shows that ß3-AR antagonist SR59230A promotes hematopoietic differentiation as indicated by increased ratios of lymphoid/hematopoietic stem cells (HSCs) and of myeloid progenitor cells/HSCs, and increases the number of Ter119 and natural killer (NK) precursor cells, and of granulocyte precursors, indicating active hematopoiesis within the tumor tissue. Moreover, pharmacological antagonism of ß3-AR induces mesenchymal stem cell (MSC) differentiation into adipocytes subtracting a potential renewal of the stem compartment by these cells. Here we demonstrate that ß3-AR blockade in the TME by inducing the differentiation of different stromal cells at the expense of stemness traits could possibly have a favorable effect on the control of melanoma progression.

ß3-Adrenoreceptor Blockade Reduces Hypoxic Myeloid Leukemic Cells Survival and Chemoresistance.

ß-adrenergic signaling is known to be involved in cancer progression; in particular, beta3-adrenoreceptor (ß3-AR) is associated with different tumor conditions. Currently, there are few data concerning ß3-AR in myeloid malignancies. Here, we evaluated ß3-AR in myeloid leukemia cell lines and the effect of ß3-AR antagonist SR59230A. In addition, we investigated the potential role of ß3-AR blockade in doxorubicin resistance. Using flow cytometry, we assessed cell death in different in vitro myeloid leukemia cell lines (K562, KCL22, HEL, HL60) treated with SR59230A in hypoxia and normoxia; furthermore, we analyzed ß3-AR expression. We used healthy bone marrow cells (BMCs), peripheral blood mononuclear cells (PBMCs) and cord blood as control samples. Finally, we evaluated the effect of SR59230A plus doxorubicin on K562 and K562/DOX cell lines; K562/DOX cells are resistant to doxorubicin and show P-glycoprotein (P-gp) overexpression. We found that SR59230A increased cancer cell lines apoptosis especially in hypoxia, resulting in selective activity for cancer cells; moreover, ß3-AR expression was higher in malignancies, particularly under hypoxic condition. Finally, we observed that SR59230A plus doxorubicin increased doxorubicin resistance reversion mainly in hypoxia, probably acting on P-gp. Together, these data point to ß3-AR as a new target and ß3-AR blockade as a potential approach in myeloid leukemias.

Role of adipokine zinc-α2-glycoprotein in coronary heart disease.

Zinc-α2-glycoprotein (AZGP1) is a newly identified adipokine that is associated with lipid metabolism and vascular fibrosis. Although adipokines contribute to lipid dysfunction and its related diseases, including stroke and coronary heart disease (CHD), the role of AZGP1 remains unclear. In this study, the role of AZGP1 in atherosclerosis and CHD was investigated. Serum AZGP1 levels from control (n = 84) and CHD (n = 91) patients were examined by ELISA and its relationship with various clinical parameters was analyzed. Immunohistochemistry and immunofluorescence were used to detect the expression of AZGP1 and its receptor in coronary atherosclerotic arteries. THP-1 and human embryonic kidney 293 cells were used to verify its anti-inflammatory role in atherosclerosis. Serum AZGP1 levels in CHD patients were lower than controls (P < 0.01) and independently associated with CHD prevalence (P = 0.021). AZGP1 levels also inversely correlated with the Gensini score. Immunohistochemistry and immunofluorescence showed that AZGP1 and its receptor ß3-adrenoceptor (ß3-AR) colocalized in lipid-rich areas of atherosclerotic plaques, particularly around macrophages. In vitro, AZGP1 had no effect on foam cell formation but showed anti-inflammatory effects through its regulation of JNK/AP-1 signaling. In summary, AZGP1 is an anti-inflammatory agent that can be targeted for CHD treatment.

Targeting ß3-adrenergic receptor signaling inhibits neuroblastoma cell growth via suppressing the mTOR pathway.

Neuroblastoma (NB), the most common extracranial solid tumor in childhood, always leads to an unfavorable prognosis. ß3-adrenergic receptor (ß3-AR) signaling plays an important role in lipid metabolism. Although previous studies have focused mainly on the role of ß2-AR in tumor cells; there are few studies about the cancer-related function of ß3-AR. Herein, we showed that ß3-AR expression was significantly increased in clinical NB tissue compared with that in the less malignant ganglioneuroma (GN) and ganglioneuroblastoma (GNB) tissues. Further cellular assays demonstrated that treatment of NB cells with SR59230A (a specific ß3-AR antagonist) suppressed NB cells growth and colony formation, and siRNA knockdown of ß3-AR expression also inhibited NB cell proliferation. The mechanistic study revealed that ß3-AR knockdown and SR59230A inhibited the phosphorylation and thereby the activation of the mTOR/p70S6K pathway. Activation of the mTOR pathway with the activator MHY1485 reversed the inhibitory effect of SR59230A on NB cell growth. Above all, our study clarifies a novel regulatory role of ß3-AR in NB cell growth and provides a potent therapeutic strategy for this disease by specific targeting of the ß3-AR pathway.

Perivascular Adipose Tissue Contributes to the Modulation of Vascular Tone in vivo.

BACKGROUND: Perivascular adipose tissue (PVAT) reduces vascular tone in isolated arteries in vitro, however there are no studies of PVAT effects on vascular tone in vivo. In vitro adipocyte ß3-adrenoceptors play a role in PVAT function via secretion of the vasodilator adiponectin. OBJECTIVE: We have investigated the effects of PVAT on vessel diameter in vivo, and the contributions of ß3-adrenoceptors and adiponectin. METHOD: In anaesthetised rats, sections of the intact mesenteric bed were visualised and the diameter of arteries was recorded. Arteries were stimulated with electrical field stimulation (EFS), noradrenaline (NA), arginine-vasopressin (AVP), and acetylcholine (Ach). RESULTS: We report that in vivo, stimulation of PVAT with EFS, NA, and AVP evokes a local anti-constrictive effect on the artery, whilst PVAT exerts a pro-contractile effect on arteries subjected to Ach. The anti-constrictive effect of PVAT stimulated with EFS and NA was significantly reduced using ß3-adrenoceptor inhibition, and activation of ß3-adrenoceptors potentiated the anti-constrictive effect of vessels stimulated with EFS, NA, and AVP. The ß3-adrenoceptor agonist had no effect on mesenteric arteries with PVAT removed. A blocking peptide for adiponectin receptor 1 polyclonal antibody reduced the PVAT anti-constrictive effect in arteries stimulated with EFS and NA, indicating that adiponectin may be the anti-constrictive factor released upon ß3-adrenoceptor activation. CONCLUSIONS: These results clearly demonstrate that PVAT plays a paracrine role in regulating local vascular tone in vivo, and therefore may contribute to the modulation of blood pressure. This effect is mediated via adipocyte ß3-adrenoceptors, which may trigger release of the vasodilator adiponectin.

Nesfatin-1 Acts Centrally to Induce Sympathetic Activation of Brown Adipose Tissue and Non-Shivering Thermogenesis.

Nesfatin-1 has originally been established as a bioactive peptide interacting with key hypothalamic nuclei and neural circuitries in control of feeding behavior, while its effect on energy expenditure has only recently been investigated. Hence, the aim of this study was to examine whether centrally acting nesfatin-1 can induce ß3-adrenergic stimulation, which is a prerequisite for the activation of thermogenic genes and heat release from interscapular brown adipose tissue, key physiological features that underlie increased energy expenditure. This question was addressed in non-fasted mice stereotactically cannulated to receive nesfatin-1 intracerebroventricularly together with peripheral injection of the ß3-adrenoceptor antagonist SR 59230 A, to assess whole-body energy metabolism. Using a minimally invasive thermography technique, we now demonstrate that the thermogenic effect of an anorectic nesfatin-1 dose critically depends on ß3 adrenergic stimulation, as the co-administration with SR 59230 A completely abolished heat production from interscapular brown adipose tissue and rise in ocular surface temperature, thus preventing body weight loss. Moreover, through indirect calorimetry it could be shown that the anorectic concentration of nesfatin-1 augments overall caloric expenditure. Plausibly, central administration of nesfatin-1 also enhanced the expression of DIO2 and CIDEA mRNA in brown adipose tissue critically involved in the regulation of thermogenesis.

Cardioprotective Effects of Beta3-Adrenergic Receptor (ß3-AR) Pre-, Per-, and Post-treatment in Ischemia-Reperfusion.

The ß3-AR (beta3-adrenergic receptor) is resistant to short-term agonist-promoted desensitization and delivers a constant intracellular signal, making this receptor a potential target in acute myocardial infarction (AMI). AIM: To investigate whether selective modulation of ß3-AR prior to or during ischemia and/or reperfusion may be cardioprotective. METHODS: Isolated perfused rat hearts were exposed to 35-min regional ischemia (RI) and 60-min reperfusion. The ß3-AR agonist (BRL37344, 1 µM) or antagonist (SR59230A, 0.1 µM) was applied: (i) before RI (PreT) or (ii) last 10 min of RI (PerT) or (iii) onset of reperfusion (PostT) or (iv) during both PerT+PostT. Nitric oxide (NO) involvement was assessed, using the NOS inhibitor, L-NAME (50 µM). Endpoints were functional recovery, infarct size (IS), cGMP levels, and Western blot analysis of eNOS, ERKp44/p42, PKB/Akt, and glycogen synthase kinase-3ß (GSK-3ß). RESULTS: Selective treatment with BRL significantly reduced IS. L-NAME abolished BRL-mediated cardioprotection. BRL (PreT) and BRL (PerT) significantly increased cGMP levels (which were reduced by L-NAME) and PKB/Akt phosphorylation. BRL (PostT) produced significantly increased cGMP levels, PKB/Akt, and ERKp44/p42 phosphorylation. BRL (PerT+PostT) caused significant eNOS, PKB/Akt, ERKp44/p42, and GSK-3ß phosphorylation. CONCLUSION: ß3-AR activation by BRL37344 induced significant cardioprotection regardless of the experimental protocol. However, the pattern of intracellular signaling with each BRL treatment differed to some degree and suggests the involvement of cGMP, eNOS, ERK, GSK-3ß, and particularly PKB/Akt activation. The data also suggest that clinical application of ß3-AR stimulation should preferably be incorporated during late ischemia or/and early reperfusion.

ß3-adrenergic receptor activation induces TGFß1 expression in cardiomyocytes via the PKG/JNK/c-Jun pathway.

In heart failure, the expression of cardiac ß3-adrenergic receptors (ß3-ARs) increases. However, the precise role of ß3-AR signaling within cardiomyocytes remains unclear. Transforming growth factor ß1 (TGFß1) is a crucial cytokine mediating the cardiac remodeling that plays a causal role in the progression of heart failure. Here, we set out to determine the effect of ß3-AR activation on TGFß1 expression in rat cardiomyocytes and examine the underlying mechanism. The selective ß3-AR agonist BRL37344 induced an increase in TGFß1 expression and the phosphorylation of c-Jun N-terminal kinase (JNK) and c-Jun in ß3-AR-overexpressing cardiomyocytes. Those effects of BRL37344 were suppressed by a ß3-AR antagonist. Moreover, the inhibition of JNK and c-Jun activity by a JNK inhibitor and c-Jun siRNA blocked the increase in TGFß1 expression upon ß3-AR activation. A protein kinase G (PKG) inhibitor also attenuated ß3-AR-agonist-induced TGFß1 expression and the phosphorylation of JNK and c-Jun. In conclusion, the ß3-AR activation in cardiomyocytes increases the expression of TGFß1 via the PKG/JNK/c-Jun pathway. These results help us further understand the role of ß3-AR signaling in heart failure.

ß-Adrenoceptor Blockade for Infantile Hemangioma Therapy: Do ß3-Adrenoceptors Play a Role?

Infantile hemangiomas (IH) are frequent (4-5% of the childhood population) benign vascular tumors that involve accumulation, proliferation, and differentiation of aberrant vascular cells. Typically, IH are innocuous and spontaneously disappear, but they represent a potential risk for harmful effects in the body (e.g., permanent disfigurement) and health (e.g., ulcerations) in some patients. From a serendipitous discovery, the nonselective ß-adrenoceptor blocker propranolol (which blocks ß1-adrenoceptors, ß2-adrenoceptors, and ß3-adrenoceptors) emerged as an alternative therapy to treat this pathology and it quickly became a first-line treatment for IH. Nevertheless, its specific mechanisms of action remain thus far unknown. In this respect, several studies have suggested that ß1-adrenoceptors and ß2-adrenoceptors play a role in proliferative and angiogenic mechanisms. However, current basic research studies suggest that ß3-adrenoceptors could be also involved. Notably, ß3-adrenoceptors stimulate multiple intracellular pathways related to vascular function (e.g., blood flow, angiogenesis, etc.). This review compiles some lines of evidence suggesting that ß3-adrenoceptors may: (1) play a role in the pathophysiology of IH and (2) represent a potential therapeutic target for IH treatment. Hence, clinical evidence is mandatory to decide whether incorporation of ß3-adrenoceptor blockers into the therapeutic armamentarium may increase effectiveness in the treatment of IH and other vascular anomalies.

Inhibition of cholinergic neurotransmission by ß3-adrenoceptors depends on adenosine release and A1-receptor activation in human and rat urinary bladders.

The direct detrusor relaxant effect of ß3-adrenoceptor agonists as a primary mechanism to improve overactive bladder symptoms has been questioned. Among other targets, activation of ß3-adrenoceptors downmodulate nerve-evoked acetylcholine (ACh) release, but there is insufficient evidence for the presence of these receptors on bladder cholinergic nerve terminals. Our hypothesis is that adenosine formed from the catabolism of cyclic AMP in the detrusor may act as a retrograde messenger via prejunctional A1 receptors to explain inhibition of cholinergic activity by ß3-adrenoceptors. Isoprenaline (1 µM) decreased [3H]ACh release from stimulated (10 Hz, 200 pulses) human (-47 ± 5%) and rat (-38 ± 1%) detrusor strips. Mirabegron (0.1 µM, -53 ± 8%) and CL316,243 (1 µM, -37 ± 7%) mimicked isoprenaline (1 µM) inhibition, and their effects were prevented by blocking ß3-adrenoceptors with L748,337 (30 nM) and SR59230A (100 nM), respectively, in human and rat detrusor. Mirabegron and isoprenaline increased extracellular adenosine in the detrusor. Blockage of A1 receptors with 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 100 nM) or the equilibrative nucleoside transporters (ENT) with dipyridamole (0.5 µM) prevented mirabegron and isoprenaline inhibitory effects. Dipyridamole prevented isoprenaline-induced adenosine outflow from the rat detrusor, and this effect was mimicked by the ENT1 inhibitor, S-(4-nitrobenzyl)-6-thioinosine (NBTI, 30 µM). Cystometry recordings in anesthetized rats demonstrated that SR59230A, DPCPX, dipyridamole, and NBTI reversed the decrease in the voiding frequency caused by isoprenaline (0.1-1,000 nM). Data suggest that inhibition of cholinergic neurotransmission by ß3-adrenoceptors results from adenosine release via equilibrative nucleoside transporters and prejunctional A1-receptor stimulation in human and rat urinary bladder.

CNS ß3-adrenergic receptor activation regulates feeding behavior, white fat browning, and body weight.

Pharmacological ß3-adrenergic receptor (ß3AR) activation leads to increased mitochondrial biogenesis and activity in white adipose tissue (WAT), a process commonly referred to as "browning", and transiently increased insulin release. These effects are associated with improved metabolic function and weight loss. It is assumed that this impact of ß3AR agonists is mediated solely through activation of ß3ARs in adipose tissue. However, ß3ARs are also found in the brain, in areas such as the brain stem and the hypothalamus, which provide multisynaptic innervation to brown and white adipose depots. Thus, contrary to the current adipocentric view, the central nervous system (CNS) may also have the ability to regulate energy balance and metabolism through actions on central ß3ARs. Therefore, this study aimed to elucidate whether CNS ß3ARs can regulate browning of WAT and other aspects of metabolic regulation, such as food intake control and insulin release. We found that acute central injection of ß3AR agonist potently reduced food intake, body weight, and increased hypothalamic neuronal activity in rats. Acute central ß3AR stimulation was also accompanied by a transient increase in circulating insulin levels. Moreover, subchronic central ß3AR agonist treatment led to a browning response in both inguinal (IWAT) and gonadal WAT (GWAT), along with reduced GWAT and increased BAT mass. In high-fat, high-sugar-fed rats, subchronic central ß3AR stimulation reduced body weight, chow, lard, and sucrose water intake, in addition to increasing browning of IWAT and GWAT. Collectively, our results identify the brain as a new site of action for the anorexic and browning impact of ß3AR activation.

Targeting ß3-Adrenergic Receptors in the Heart: Selective Agonism and ß-Blockade.

Cardiac diseases, such as heart failure, remain leading causes of morbidity and mortality worldwide, with myocardial infarction as the most common etiology. HF is characterized by ß-adrenergic receptor (ßAR) dysregulation that is primarily due to the upregulation of G protein-coupled receptor kinases that leads to overdesensitization of ß1 and ß2ARs, and this clinically manifests as a loss of inotropic reserve. Interestingly, the "minor" ßAR isoform, the ß3AR, found in the heart, lacks G protein-coupled receptor kinases recognition sites, and is not subject to desensitization, and as a consequence of this, in human failing myocardium, the levels of this receptor remain unchanged or are even increased. In different preclinical studies, it has been shown that ß3ARs can activate different signaling pathways that can protect the heart. The clinical relevance of this is also supported by the effects of ß-blockers which are well known for their proangiogenic and cardioprotective effects, and data are emerging showing that these are mediated, at least in part, by enhancement of ß3AR activity. In this regard, targeting of ß3ARs could represent a novel potential strategy to improve cardiac metabolism, function, and remodeling.

Repeated Cold Stress Enhances the Acute Restraint Stress-Induced Hyperthermia in Mice.

The rodents exposed to repeated cold stress according to a specific schedule, known as specific alternation of rhythm in temperature (SART), exhibit autonomic imbalance, and is now used as an experimental model of fibromyalgia. To explore the susceptibility of SART-stressed animals to novel acute stress, we tested whether exposure of mice to SART stress for 1 week alters the extent of acute restraint stress-induced hyperthermia. Mice were subjected to 7-d SART stress sessions; i.e., the mice were alternately exposed to 24 and 4°C at 1-h intervals during the daytime (09:00-16:00) and kept at 4°C overnight (16:00-09:00). SART-stressed and unstressed mice were exposed to acute restraint stress for 20-60 min, during which rectal temperature was monitored. Serum corticosterone levels were measured before and after 60-min exposure to restraint stress. SART stress itself did not alter the body temperature or serum corticosterone levels in mice. Acute restraint stress increased the body temperature and serum corticosterone levels, both responses being greater in SART-stressed mice than unstressed mice. The enhanced hyperthermic responses to acute restraint stress in SART-stressed mice were significantly attenuated by SR59230A, a ß3 adrenoceptor antagonist, but unaffected by diazepam, an anxiolytic, mifepristone, a glucocorticoid receptor antagonist, or indomethacin, a cyclooxygenase inhibitor. These results suggest that SART stress enhances the susceptibility of mice to acute restraint stress, characterized by increased hyperthermia and corticosterone secretion, and that the increased hyperthermic responses to acute stress might involve accelerated activation of sympathetic ß3 adrenoceptors, known to regulate non-shivering thermogenesis in the brown adipose tissue.

ß3 adrenergic receptor in the kidney may be a new player in sympathetic regulation of renal function.

To date, the study of the sympathetic regulation of renal function has been restricted to the important contribution of ß1- and ß2-adrenergic receptors (ARs). Here we investigate the expression and the possible physiologic role of ß3-adrenergic receptor (ß3-AR) in mouse kidney. The ß3-AR is expressed in most of the nephron segments that also express the type 2 vasopressin receptor (AVPR2), including the thick ascending limb and the cortical and outer medullary collecting duct. Ex vivo experiments in mouse kidney tubules showed that ß3-AR stimulation with the selective agonist BRL37344 increased intracellular cAMP levels and promoted 2 key processes in the urine concentrating mechanism. These are accumulation of the water channel aquaporin 2 at the apical plasma membrane in the collecting duct and activation of the Na-K-2Cl symporter in the thick ascending limb. Both effects were prevented by the ß3-AR antagonist L748,337 or by the protein kinase A inhibitor H89. Interestingly, genetic inactivation of ß3-AR in mice was associated with significantly increased urine excretion of water, sodium, potassium, and chloride. Stimulation of ß3-AR significantly reduced urine excretion of water and the same electrolytes. Moreover, BRL37344 promoted a potent antidiuretic effect in AVPR2-null mice. Thus, our findings are of potential physiologic importance as they uncover the antidiuretic effect of ß3-AR stimulation in the kidney. Hence, ß3-AR agonism might be useful to bypass AVPR2-inactivating mutations.

Nebivolol ameliorates asymmetric dimethylarginine-induced vascular response in rat aorta via ß3 adrenoceptor-mediated mechanism.

BACKGROUND: Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase (NOS) inhibitor, induces endothelial dysfunction. Nebivolol, a highly selective ß1-adrenergic receptor (AR) blocker, is the only beta-blocker known to induce vascular production of nitric oxide. OBJECTIVE: The present study was designed to evaluate the effect and mechanism of nebivolol on ADMA-induced vascular response in rat aorta in vitro. METHODS: In vitro, the effects of nebivolol and ADMA on resting tone or contraction induced by phenylephrine (PE, 10(-6 )mol/L) and relaxation induced by acetylcholine (Ach, 10(-10)-10(-5 )mol/L) were evaluated. RESULTS: ADMA in a concentration-dependent manner increased the resting and PE-induced tone and reduced Ach-induced relaxation. Nebivolol inhibited the ADMA-induced enhancements in tone and reversed the effects of ADMA on Ach-induced relaxation. These effects of nebivolol were blocked by selective ß3 receptor blocker cyanopindolol (1 µM), but not by selective ß2 receptor blocker butoxamine (50 µM). CONCLUSIONS: Nebivolol ameliorates the ADMA-induced vascular responses in rat aorta, at least in part, by mechanisms involving ß3 adrenoceptor.

The odd sibling: features of ß3-adrenoceptor pharmacology.

ß3-Adrenoceptor agonists have recently been introduced for the treatment of overactive urinary bladder syndrome. Their target, the ß3-adrenoceptor, was discovered much later than ß1- and ß2-adrenoceptors and exhibits unique properties which make extrapolation of findings from the other two subtypes difficult and the ß3-adrenoceptor a less-understood subtype. This article discusses three aspects of ß3-adrenoceptor pharmacology. First, the ligand-recognition profile of ß3-adrenoceptors differs considerably from that of the other two subtypes, i.e., many antagonists considered as nonselective actually are ß3-sparing, including propranolol or nadolol. Many agonists and antagonists classically considered as being ß3-selective actually are not, including BRL 37,344 ((±)-(R*,R*)-[4-[2-[[2-(3-chlorophenyl)-2-hydroxyethyl]amino]propyl]phenoxy] acetic acid sodium hydrate) or SR 59,230 (3-(2-ethylphenoxy)-[(1S)-1,2,3,4-tetrahydronaphth-1-ylamino]-(2S)-2-propanol oxalate). Moreover, the binding pocket apparently differs between the human and rodent ß3-adrenoceptor, yielding considerable species differences in potency. Second, the expression pattern of ß3-adrenoceptors is more restricted than that of other subtypes, particularly in humans; this makes extrapolation of rodent findings to the human situation difficult, but it may result in a smaller potential for side effects. The role of ß3-adrenoceptor gene polymorphisms has insufficiently been explored and may differ even between primate species. Third, ß3-adrenoceptors lack the phosphorylation sites involved in agonist-induced desensitization of the other two subtypes. Thus, they exhibit downregulation and/or desensitization in some, but not other, cell types and tissues. When desensitization occurs, it most often is at the level of mRNA or signaling molecule expression. All three of these factors have implications for future studies to better understand the ß3-adrenoceptor as a novel pharmacological target.