Nitric oxide production from rat adipocytes is modulated by beta3-adrenergic receptor agonists and is involved in a cyclic AMP-dependent lipolysis in adipocytes

Hypoxia-Dependent Upregulation of VEGF Relies on β3-Adrenoceptor Signaling in Human Retinal Endothelial and Müller Cells

β-adrenoceptors (BARs) are involved in vascular endothelial growth factor (VEGF) production during retinal neovascularization. Here, using human retinal endothelial and Müller cells (hRECs and MIO-M1, respectively), we evaluated the effects exerted by hypoxia on BARs, hypoxia-inducible factor-1α subunit (HIF-1α) and VEGF, as well as the involvement of BAR3 and nitric oxide synthase (NOS) enzymes in hypoxia-induced VEGF production. We altered oxygen availability through a hypoxic incubator. BARs, HIF-1 α and VEGF levels were evaluated. Cells were treated with the BAR3 antagonist SR59230A, different NOS inhibitors or the NO donor SNAP. The influence of the BAR3/NOS axis on hypoxic VEGF production was assessed. Hypoxia upregulated BAR3, HIF-1α and VEGF in hRECs and MIO-M1 cells. SR59230A counteracted hypoxia-dependent VEGF increase in both cell lines, exerting no effect on HIF-1α upregulation. Treatments with NOS inhibitors prevented the hypoxia-dependent VEGF increase, while SNAP abrogated the effect of SR59230A in reducing hypoxia-induced VEGF upregulation. The present results corroborate the hypothesis that in the hypoxic retina, BAR3 influence on VEGF production is mediated by NO and suggest that, at least in endothelial and Müller cells, BAR3 activity is necessary to allow the HIF-1-mediated VEGF upregulation.

Dietary dibutyryl cAMP supplementation regulates the fat deposition in adipose tissues of finishing pigs via cAMP/PKA pathway

This study investigated potential mechanism of dibutyryl-cAMP (db-cAMP) on porcine fat deposition. (1) Exp.1, 72 finishing pigs were allotted to 3 treatments (0, 10 or 20 mg/kg dbcAMP) with 6 replicates. dbcAMP increased the hormone sensitive lipase (HSL) activity and expression of β-adrenergic receptor (β-AR) and growth hormone receptor (GHR), but decreased expression of peroxisome proliferator-activated receptor gamma 2 (PPAR-γ2) and adipocyte fatty acid binding protein (A-FABP) in back fat. dbcAMP upregulated expression of β-AR, GHR, PPAR-γ2 and A-FABP, but decreased insulin receptor (INSR) expression in abdominal fat. Dietary dbcAMP increased HSL activity and expression of G protein-coupled receptor (GPCR), cAMP-response element-binding protein (CREB) and insulin-like growth factor-1 (IGF-1), but decreased fatty acid synthase (FAS) and lipoprotein lipase (LPL) activities, and expression of INSR, cAMP-response element-binding protein (C/EBP-α) and A-FABP in perirenal fat. (2) Exp. 2, dbcAMP suppressed the proliferation and differentiation of porcine preadipocytes in a time- and dose-dependent manner, which might be associated with increased activities of cAMP and protein kinase A (PKA), and expression of GPCR, β-AR, GHR and CREB via inhibiting C/EBP-α and PPAR-γ2 expression. Collectively, dbcAMP treatment may reduce fat deposition by regulating gene expression related to adipocyte differentiation and fat metabolism partially via cAMP-PKA pathway.

l-Arginine supplementation regulates energy-substrate metabolism in skeletal muscle and adipose tissue of diet-induced obese rats

Dietary supplementation with l-arginine has been reported to reduce white fat mass in diet-induced obese rats and in obese humans. This study was conducted to test the hypothesis that the arginine treatment regulates glucose and fatty acid metabolism in insulin-sensitive tissues. Male Sprague–Dawley rats (4-week-old) were fed either low- or high-fat diets for 15 weeks ( n = 16/diet). Thereafter, lean or obese rats were fed their respective diets and received drinking water containing either 1.51% l-arginine-HCl or 2.55% alanine (isonitrogenous control) ( n = 8/treatment group). After 12 weeks of treatment, rats were euthanized and tissue samples were collected for biochemical assays. High-fat feeding increased the size of adipocytes isolated from retroperitoneal (RP) adipose tissue, while arginine treatment reduced their size. The total number of adipocytes in the adipose tissue did not differ among the four groups of rats. Glucose oxidation in extensor digitorum longus (EDL) muscle, soleus muscle, and RP adipose tissue were reduced in response to high-fat feeding. On the contrary, oleic acid oxidation in RP adipose tissue was enhanced in rats fed the high-fat diet. Arginine treatment stimulated both glucose and oleic acid oxidation in EDL and soleus muscles, while having no effect on glucose oxidation, oleic acid oxidation, or basal lipolysis per 106 adipocytes in RP adipose tissue. Collectively, these results indicate that oral supplementation with arginine to diet-induced obese rats promoted the oxidation of energy substrates in skeletal muscle, thereby reducing white fat in the body.

Towards Drug Repurposing in Cancer Cachexia: Potential Targets and Candidates

As a multifactorial and multiorgan syndrome, cancer cachexia is associated with decreased tolerance to antitumor treatments and increased morbidity and mortality rates. The current approaches for the treatment of this syndrome are not always effective and well established. Drug repurposing or repositioning consists of the investigation of pharmacological components that are already available or in clinical trials for certain diseases and explores if they can be used for new indications. Its advantages comparing to de novo drugs development are the reduced amount of time spent and costs. In this paper, we selected drugs already available or in clinical trials for non-cachexia indications and that are related to the pathways and molecular components involved in the different phenotypes of cancer cachexia syndrome. Thus, we introduce known drugs as possible candidates for drug repurposing in the treatment of cancer-induced cachexia.

A compendium of G-protein-coupled receptors and cyclic nucleotide regulation of adipose tissue metabolism and energy expenditure

With the ever-increasing burden of obesity and Type 2 diabetes, it is generally acknowledged that there remains a need for developing new therapeutics. One potential mechanism to combat obesity is to raise energy expenditure via increasing the amount of uncoupled respiration from the mitochondria-rich brown and beige adipocytes. With the recent appreciation of thermogenic adipocytes in humans, much effort is being made to elucidate the signaling pathways that regulate the browning of adipose tissue. In this review, we focus on the ligand-receptor signaling pathways that influence the cyclic nucleotides, cAMP and cGMP, in adipocytes. We chose to focus on G-protein-coupled receptor (GPCR), guanylyl cyclase and phosphodiesterase regulation of adipocytes because they are the targets of a large proportion of all currently available therapeutics. Furthermore, there is a large overlap in their signaling pathways, as signaling events that raise cAMP or cGMP generally increase adipocyte lipolysis and cause changes that are commonly referred to as browning: increasing mitochondrial biogenesis, uncoupling protein 1 (UCP1) expression and respiration.

iNOS as a metabolic enzyme under stress conditions

Nitric oxide (NO) is a free radical acting as a cellular signaling molecule in many different biochemical processes. NO is synthesized from l-arginine through the action of the nitric oxide synthase (NOS) family of enzymes, which includes three isoforms: endothelial NOS (eNOS), neuronal NOS (nNOS) and inducible NOS (iNOS). iNOS-derived NO has been associated with the pathogenesis and progression of several diseases, including liver diseases, insulin resistance, obesity and diseases of the cardiovascular system. However, transient NO production can modulate metabolism to survive and cope with stress conditions. Accumulating evidence strongly imply that iNOS-derived NO plays a central role in the regulation of several biochemical pathways and energy metabolism including glucose and lipid metabolism during inflammatory conditions. This review summarizes current evidence for the regulation of glucose and lipid metabolism by iNOS during inflammation, and argues for the role of iNOS as a metabolic enzyme in immune and non-immune cells.

Mechanistic Links Between Obesity, Diabetes, and Blood Pressure: Role of Perivascular Adipose Tissue

Obesity is increasingly prevalent and is associated with substantial cardiovascular risk. Adipose tissue distribution and morphology play a key role in determining the degree of adverse effects, and a key factor in the disease process appears to be the inflammatory cell population in adipose tissue. Healthy adipose tissue secretes a number of vasoactive adipokines and anti-inflammatory cytokines, and changes to this secretory profile will contribute to pathogenesis in obesity. In this review, we discuss the links between adipokine dysregulation and the development of hypertension and diabetes and explore the potential for manipulating adipose tissue morphology and its immune cell population to improve cardiovascular health in obesity.

Exercise training restores eNOS activation in the perivascular adipose tissue of obese rats: Impact on vascular function

OBJECTIVE

This study evaluated in obese rats the effect of exercise training on eNOS expressed in perivascular adipose tissue (PVAT) and its consequences on vascular function.

METHODS

Wistar rats were divided in 3 groups: control (standard diet), obese (high fat/high sucrose diet, HFS for 15 weeks), and exercised obese (HFS diet and exercise from week 6 to week 15, HFS-Ex) rats. The eNOS-adiponectin pathway and reactive oxygen species (ROS) were evaluated. Vascular reactivity was assessed on isolated aortic rings with or without PVAT and/or endothelium and exposed or not to the conditioned media of PVAT.

RESULTS

Obesity reduced eNOS level and phosphorylation on its activation site in the PVAT and had no impact on the vascular wall. Exercise training was able to increase eNOS and P-eNOS both in the vascular wall and in the PVAT. Interestingly, this was associated with increased level of adiponectin in the PVAT and to lower ROS in the vascular wall. Finally, PVAT of HFS-Ex aorta has eNOS-dependent anticontractile effects on endothelium denuded aortic rings and has beneficial effects on the endothelium-dependent vasorelaxation to ACh.

CONCLUSION

Exercise training in obese rats is able to impact PVAT eNOS with subsequent beneficial impact on vascular function.

β3 -Adrenoceptor stimulation of perivascular adipocytes leads to increased fat cell-derived NO and vascular relaxation in small arteries

Background and Purpose

In response to noradrenaline, healthy perivascular adipose tissue (PVAT) exerts an anticontractile effect on adjacent small arterial tissue. Organ bath solution transfer experiments have demonstrated the release of PVAT‐derived relaxing factors that mediate this function. The present studies were designed to investigate the mechanism responsible for the noradrenaline‐induced PVAT anticontractile effect.

Experimental Approach

In vitro rat small arterial contractile function was assessed using wire myography in the presence and absence of PVAT and the effects of sympathomimetic stimulation on the PVAT environment explored using Western blotting and assays of organ bath buffer.

Key Results

PVAT elicited an anticontractile effect in response to noradrenaline but not phenylephrine stimulation. In arteries surrounded by intact PVAT, the β₃‐adrenoceptor agonist, CL‐316243, reduced the vasoconstrictor effect of phenylephrine but not noradrenaline. K_v7 channel inhibition using XE 991 reversed the noradrenaline‐induced anticontractile effect in exogenously applied PVAT studies. Adrenergic stimulation of PVAT with noradrenaline and CL‐316243, but not phenylephrine, was associated with increased adipocyte‐derived NO production, and the contractile response to noradrenaline was augmented following incubation of exogenous PVAT with L‐NMMA. PVAT from eNOS^−/− mice had no anticontractile effect. Assays of adipocyte cAMP demonstrated an increase with noradrenaline stimulation implicating Gα_s signalling in this process.

Conclusions and Implications

We have shown that adipocyte‐located β₃‐adrenoceptor stimulation leads to activation of Gα_s signalling pathways with increased cAMP and the release of adipocyte‐derived NO. This process is dependent upon K_v7 channel function. We conclude that adipocyte‐derived NO plays a central role in anticontractile activity when rodent PVAT is stimulated by noradrenaline.

Neuroinflammation and Central Sensitization in Chronic and Widespread Pain

Chronic pain is maintained in part by central sensitization, a phenomenon of synaptic plasticity, and increased neuronal responsiveness in central pain pathways after painful insults. Accumulating evidence suggests that central sensitization is also driven by neuroinflammation in the peripheral and central nervous system. A characteristic feature of neuroinflammation is the activation of glial cells, such as microglia and astrocytes, in the spinal cord and brain, leading to the release of proinflammatory cytokines and chemokines. Recent studies suggest that central cytokines and chemokines are powerful neuromodulators and play a sufficient role in inducing hyperalgesia and allodynia after central nervous system administration. Sustained increase of cytokines and chemokines in the central nervous system also promotes chronic widespread pain that affects multiple body sites. Thus, neuroinflammation drives widespread chronic pain via central sensitization. We also discuss sex-dependent glial/immune signaling in chronic pain and new therapeutic approaches that control neuroinflammation for the resolution of chronic pain.

Butyrate stimulates adipose lipolysis and mitochondrial oxidative phosphorylation through histone hyperacetylation-associated β3 -adrenergic receptor activation in high-fat diet-induced obese mice

NEW FINDINGS

What is the central question of this study? Butyrate can prevent diet-induced obesity through increasing energy expenditure. However, it is unclear whether β₃ -adrenergic receptors (ARβ3) mediate butyrate-induced adipose lipolysis. What is the main finding and its importance? Short-term oral administration of sodium butyrate is effective in alleviating diet-induced obesity through activation of ARβ3-mediated lipolysis in white adipose tissue. Butyrate can prevent diet-induced obesity through increasing energy expenditure. However, it is unclear whether ARβ3 mediates butyrate-induced adipose lipolysis. In this study, weaned mice were were fed control (Con) or high-fat (HF) diet for 8 weeks to establish obesity. High-fat diet-induced obese mice maintained on the HF diet were divided into two subgroups; the HFB group was gavaged with 80 mg sodium butyrate (SB) per mouse every other day for 10 days, whereas the HF group received vehicle. Chromatin immunoprecipitation assay was performed to determine the status of histone H3 lysine 9 acetylation (H3K9Ac) on the promoter of the β₃ -adrenergic receptor (ARβ3) gene in epididymal white adipose tissue. It was shown that five gavage doses of SB significantly alleviated HF diet-induced obesity and restored plasma leptin concentration to the control level. Protein contents of ARβ3 and PKA, as well as ATGL and p-HSL (Ser563), were significantly upregulated in the HFB group compared with the HF group. Mitochondrial oxidative phosphorylation was enhanced by SB treatment. Sodium butyrate significantly increased the expression of four out of 13 mitochondrial DNA-encoded genes and significantly upregulated the protein contents of peroxisome proliferator-activated receptor-γ coactivator 1α and COX4. Moreover, SB administration enhanced the expression of ARβ3 and its downstream signalling. The G protein-coupled receptor 43 and p-CREB (Ser133) were significantly stimulated by SB. In addition, an active transcription marker, H3K9Ac, was significantly enriched on the promoter of the ARβ3 gene. Our results indicate that short-term oral administration of SB is effective in alleviating diet-induced obesity through activation of the ARβ3-mediated lipolysis in the epididymal white adipose tissue.

AG. Persistent Catechol-O-methyltransferase-dependent Pain Is Initiated by Peripheral β-Adrenergic Receptors

BACKGROUND

Patients with chronic pain disorders exhibit increased levels of catecholamines alongside diminished activity of catechol-O-methyltransferase (COMT), an enzyme that metabolizes catecholamines. The authors found that acute pharmacologic inhibition of COMT in rodents produces hypersensitivity to mechanical and thermal stimuli via β-adrenergic receptor (βAR) activation. The contribution of distinct βAR populations to the development of persistent pain linked to abnormalities in catecholamine signaling requires further investigation.

METHODS

Here, the authors sought to determine the contribution of peripheral, spinal, and supraspinal βARs to persistent COMT-dependent pain. They implanted osmotic pumps to deliver the COMT inhibitor OR486 (Tocris, USA) for 2 weeks. Behavioral responses to mechanical and thermal stimuli were evaluated before and every other day after pump implantation. The site of action was evaluated in adrenalectomized rats receiving sustained OR486 or in intact rats receiving sustained βAR antagonists peripherally, spinally, or supraspinally alongside OR486.

RESULTS

The authors found that male (N = 6) and female (N = 6) rats receiving sustained OR486 exhibited decreased paw withdrawal thresholds (control 5.74 ± 0.24 vs. OR486 1.54 ± 0.08, mean ± SEM) and increased paw withdrawal frequency to mechanical stimuli (control 4.80 ± 0.22 vs. OR486 8.10 ± 0.13) and decreased paw withdrawal latency to thermal heat (control 9.69 ± 0.23 vs. OR486 5.91 ± 0.11). In contrast, adrenalectomized rats (N = 12) failed to develop OR486-induced hypersensitivity. Furthermore, peripheral (N = 9), but not spinal (N = 4) or supraspinal (N = 4), administration of the nonselective βAR antagonist propranolol, the β2AR antagonist ICI-118,511, or the β3AR antagonist SR59230A blocked the development of OR486-induced hypersensitivity.

CONCLUSIONS

Peripheral adrenergic input is necessary for the development of persistent COMT-dependent pain, and peripherally-acting βAR antagonists may benefit chronic pain patients.

Functional G894T (rs1799983) polymorphism and intron-4 VNTR variant of nitric oxide synthase (NOS3) gene are susceptibility biomarkers of obesity among Tunisians

OBJECTIVE

The endothelial nitric oxide synthase (NOS3) has been shown to play a role in the modulation of lipolysis. The goal of this study was to examine the impact of the G894T (rs1799983) and a 27 bp variable number of tandem repeats (VNTR 4a/b) of NOS3 gene on obesity in a sample of the Tunisian population.

RESEARCH METHODS AND PROCEDURES

The study included 211 normal weight subjects and 183 obese patients. NOS3 G894T and 4a/b variants were determined by PCR analysis and examined for association with obesity-related traits. The effect of obesity on forearm skin blood flow (FSBF) response to acetylcholine, an endothelium-dependent vasodilator was determined by laser Doppler iontophoresis.

RESULTS

In case-control studies, both G894T and 4a/b variants were associated with obesity. A significantly increased risk of obesity was found with the NOS3(G894T) TT genotype (OR:2.62, P=0.04). This association remains significant after adjustments for age and gender (OR: 2.93, P=0.03). A higher risk was also observed for carriers of the G894T allele (OR: 1.72, P=0.001). Stratified analysis by gender revealed that obese men (but not women) had significantly higher frequency of TT genotypes compared to controls (9.9% vs. 2.9%, P=0.01). Carriers of the 4b allele presented a significantly higher risk of obesity than non-carriers even after adjustments for age and gender (OR (95%CI): 1.72 (1.16-2.56), P=0.004). Correlations with anthropometric parameters revealed that carriers of TT and bb genotypes had significantly higher body mass index compared to those homozygous for the G and a alleles (P=0.0004).

CONCLUSION

This study provides the first evidence for the association of G894T and 4a/b variants with body mass index and the risk of obesity in Tunisians. These polymorphisms did not exhibit, however any significant association with both metabolic traits and vascular function.

β2- and β3-adrenergic receptors drive COMT-dependent pain by increasing production of nitric oxide and cytokines

Decreased activity of catechol-O-methyltransferase (COMT), an enzyme that metabolizes catecholamines, contributes to pain in humans and animals. Previously, we demonstrated that development of COMT-dependent pain is mediated by both β2- and β3-adrenergic receptors (β2ARs and β3ARs). Here we investigated molecules downstream of β2- and β3ARs driving pain in animals with decreased COMT activity. Based on evidence linking their role in pain and synthesis downstream of β2- and β3AR stimulation, we hypothesized that nitric oxide (NO) and proinflammatory cytokines drive COMT-dependent pain. To test this, we measured plasma NO derivatives and cytokines in rats receiving the COMT inhibitor OR486 in the presence or absence of the β2AR antagonist ICI118,551+β3AR antagonist SR59320A. We also assessed whether the NO synthase inhibitor L-N(G)-nitroarginine methyl ester (L-NAME) and cytokine-neutralizing antibodies block the development of COMT-dependent pain. Results showed that animals receiving OR486 exhibited higher levels of NO derivatives, tumor necrosis factor α (TNFα), interleukin-1β (IL-1β), interleukin-6 (IL-6), and chemokine (C-C motif) ligand 2 (CCL2) in a β2- and β3AR-dependent manner. Additionally, inhibition of NO synthases and neutralization of the innate immunity cytokines TNFα, IL-1β, and IL-6 blocked the development of COMT-dependent pain. Finally, we found that NO influences TNFα, IL-1β, IL-6, and CCL2 levels, whereas TNFα and IL-6 influence NO levels. Altogether, these results demonstrate that β2- and β3ARs contribute to COMT-dependent pain, at least partly, by increasing NO and cytokines. Furthermore, they identify β2- and β3ARs, NO, and proinflammatory cytokines as potential therapeutic targets for pain patients with abnormalities in COMT physiology.

β3-adrenergic receptor activity modulates melanoma cell proliferation and survival through nitric oxide signaling

We have recently shown in B16F10 melanoma cells that blockade of β3-adrenergic receptors (β3-ARs) reduces cell proliferation and induces apoptosis, likely through the involvement of nitric oxide (NO) signaling. Here, we tested the hypothesis that the effects of β3-AR blockade on melanoma cells are mainly mediated by a decrease in the activity of the NO pathway, possibly due to reduced expression of inducible NO synthase (iNOS). B16F10 cells were used. Nitrite production, iNOS expression, cell proliferation, and apoptosis were evaluated. β3-AR blockade with L-748,337 reduced basal nitrite production, while β3-AR stimulation with BRL37344 increased it. The effects of β3-AR blockade were prevented by NOS activation, while the effects of β3-AR activation were prevented by NOS inhibition. Treatments increasing nitrite production also increased iNOS expression, while treatments decreasing nitrite production reduced iNOS expression. Among the different NOS isoforms, experiments using L-748,337 or BRL37344 with activators or inhibitors targeting specific NOS isoforms demonstrated a prominent role of iNOS in nitrite production. β3-AR blockade decreased cell proliferation and induced apoptosis, while β3-AR activation had the opposite effects. The effects of β3-AR blockade/activation were prevented by iNOS activation/inhibition, respectively. Taken together, these results demonstrate that iNOS-produced NO is a downstream effector of β3-ARs and that the beneficial effects of β3-AR blockade on melanoma B16F10 cell proliferation and apoptosis are functionally linked to reduced iNOS expression and NO production. Although it is difficult to extrapolate these data to the clinical setting, the targeted inhibition of the β3-AR-NO axis may offer a new therapeutic perspective to treat melanomas.

β2-adrenoceptor agonists can both stimulate and inhibit glucose uptake in mouse soleus muscle through ligand-directed signalling

The β-adrenoceptor agonists BRL37344 and clenbuterol have opposite effects on glucose uptake in mouse soleus muscle, even though the β2-adrenoceptor mediates both effects. Different agonists may direct the soleus muscle β2-adrenoceptor to different signalling mechanisms. Soleus muscles were incubated with 2-deoxy[1-(14)C]-glucose, β-adrenoceptor agonists, other modulators of cyclic AMP, and inhibitors of intracellular signalling. The adenylyl cyclase activator forskolin (1 μM), the phosphodiesterase inhibitor rolipram (10 μM) and BRL37344 (10, but not 100 or 1,000, nM) increased, whereas clenbuterol (100 nM) decreased, glucose uptake. Forskolin increased, whereas clenbuterol decreased, muscle cyclic AMP content. BRL37344 (10 nM) did not increase cyclic AMP. Nevertheless, protein kinase A (PKA) inhibitors prevented the stimulatory effect of BRL37344. Nanomolar but not micromolar concentrations of adrenaline stimulated glucose uptake. After preincubation of muscles with pertussis toxin (100 ng/ml), 100 nM clenbuterol, 0.1-10 μM adrenaline and 100 nM BRL37344 stimulated glucose uptake. Clenbuterol increased the proportion of phosphorylated to total β2-adrenoceptor. Inhibitors of phosphatidylinositol 3-kinase (PI3K) and the stress-activated mitogen-activated protein kinase (MAPK), but not of the classical MAPK pathway, prevented stimulation of glucose uptake by BRL37344. Elevation of the cyclic AMP content of soleus muscle stimulates glucose uptake. Clenbuterol, and high concentrations of adrenaline and BRL37344 direct the β2-adrenoceptor partly to Gαi, possibly mediated by β2-adrenoceptor phosphorylation. The stimulatory effect of 10 nM BRL37344 requires the activity of PKA, PI3K and p38 MAPK, consistent with BRL37344 directing the β2-adrenoceptor to Gαs. Ligand-directed signalling may explain why β2-adrenoceptor agonists have differing effects on glucose uptake in soleus muscle.

A review of the receptor-binding properties of p-synephrine as related to its pharmacological effects

Bitter orange (Citrus aurantium) extract and its primary protoalkaloid p-synephrine are used widely in weight loss/weight management and sports performance products. Because of structural similarities, the pharmacological effects of p-synephrine are widely assumed to be similar to those of ephedrine, m-synephrine (phenylephrine), and endogenous amine neurotransmitters as norepinephrine and epinephrine. However, small structural changes result in the receptor binding characteristics of these amines that are markedly different, providing a plausible explanation for the paucity of adverse effects associated with the wide-spread consumption of p-synephrine in the form of dietary supplements as well as in various Citrus foods and juices. This paper summarizes the adrenoreceptor binding characteristics of p-synephrine relative to m-synephrine, norepinephrine, and other amines as related to the observed pharmacological effects.

Measurement of inverse agonism in β-adrenoceptors

Increasing numbers of compounds, previously classified as antagonists, were shown to inhibit this spontaneous or constitutive receptor activity, instead of leave it unaffected as expected for a formal antagonist. In addition, some other antagonists did not have any effect by themselves, but prevented the inhibition of constitutive activity induced by thought-to-be antagonists. These thought-to-be antagonists with negative efficacy are now known as "inverse agonists." Inverse agonism at βAR has been evidenced for both subtypes in wild-type GPCRs systems and in engineered systems with high constitutive activity. It is important to mention that native systems are of particular importance for analyzing the in vivo relevance of constitutive activity because these systems have physiological expression levels of target receptors. Studies of inverse agonism of β blockers in physiological setting have also evidenced that pathophysiological conditions can affect pharmacodynamic properties of these ligands. To date, hundreds of clinically well-known drugs have been tested and classified for this property. Prominent examples include the beta-blockers propranolol, alprenolol, pindolol, and timolol used for treating hypertension, angina pectoris, and arrhythmia that act on the β₂ARs, metoprolol, and bisoprolol used for treating hypertension, coronary heart disease, and arrhythmias by acting on β₁ARs. Inverse agonists seem to be useful in the treatment of chronic disease characterized by harmful effects resulting from β₁AR and β₂AR overactivation, such as heart failure and asthma, respectively.

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.

Folic Acid Supplementation Modifies β-Adrenoceptor–Mediated In Vitro Lipolysis of Obese/Diabetic (+db/+db) Mice

The effects of folic acid (5.7 and 71 μg/kg, 4 weeks) consumption on the β-adrenoceptors (β-ARs)–elicited lipolysis in vitro of the abdominal adipocytes of lean/control (+ m/+ db) and obese/diabetic (+ db/+ db) mice (female) were investigated. β-AR agonists (salbutamol, a β2-AR agonist; BRL 37344 and CGP 12177, β3-AR agonists; adrenaline, a β-AR agonist)–mediated lipolysis, β2-, and β3-ARs protein expression of the adipose tissues after folic acid consumption were evaluated. Our results demonstrate that a smaller magnitude of the basal (spontaneous) and the β-AR agonists–triggered lipolysis was observed in + db/+ db mice, and folic acid supplementation (71 μg/kg) resulted in an improvement of both the baseline and the β-ARs–mediated lipolysis. In controls, a lower β2-and β3-ARs protein expression of the adipose tissues was detected in + db/+ db mice, compared to + m/+ db mice. In both strains fed with folic acid (71 μg/kg), a reduction of β2-AR protein expression was observed compared to the respective controls. In + db/+ db mice, folic acid (5.7 and 71 μg/kg) consumption caused a dose-dependent increase of β3-AR protein expression compared to controls. We demonstrate that lipolysis elicited by β-AR (β2- and β3-ARs) agonists was blunted in + db/+ db mice. Folic acid consumption has significant modulatory effects on β-ARs protein expression and lipolysis.