Long-acting beta 2-adrenoceptor agonists: a new perspective in the treatment of asthma.

New long-acting beta 2-adrenoceptor agonists, formoterol and salmeterol, may soon appear in several European countries for treatment of asthma. This review examines currently available information and compares the basic pharmacology and describes the clinical effects of these new drugs. The long duration of bronchodilation seen in clinical studies seems to be similar, whereas in isolated tissues there might be a difference in the binding characteristics to the beta 2-adrenoceptor. Long-acting beta 2-agonists could have an inhibitory effect on inflammatory events related to asthma, but the clinical relevance of these effects is not clear at present. Long-term studies up to one year with both new drugs have not shown any unexpected side-effects, and no tachyphylaxis to beta-adrenoceptor stimulation has been reported. Patients appear to strongly prefer the new drugs compared to the short-acting beta 2-agonists. The potential place for these drugs in the treatment of asthma is discussed and some pitfalls pointed out. It is likely that the long-acting beta 2-agonists will be beneficial to many asthmatic patients.     

Acute and chronic regulation of ob mRNA levels by beta3-adrenoceptor agonists in obese Yellow KK mice.

The inhibitory effect of beta3-adrenoceptor agonists on the ob gene in brown adipose tissue (BAT) and white adipose tissue (WAT) is now well documented both in vivo in lean animals and in vitro, but the reported effects of beta3-adrenoceptor agonists on ob gene expression in obese animals remain controversial. We investigated whether ob gene expression in BAT and WAT is reduced by acute and chronic administrations of a beta3-adrenoceptor agonist, CL316,243 (CL). The ob gene mRNA levels in BAT, perimetric and inguinal WAT of obese Yellow KK mice were about 4-fold higher than those of lean controls. Acute exposure (6 h) to CL decreased ob gene mRNA levels in three fat depots in both animals. Chronic exposure (10 days) to CL also decreased ob gene mRNA levels in BAT, perimetric, and inguinal WAT in both animals. We concluded that acute and chronic regulation by a beta3-adrenoceptor agonist suppressed ob gene expression in obese Yellow KK mice and lean controls.     

Regulation of human airway mesenchymal cell proliferation by glucocorticoids and beta2-adrenoceptor agonists

Altered rates of cell proliferation play important roles in the pathogenesis of a variety of conditions, including cancer, inflammation and several airway and cardiovascular diseases. One of the most consistently observed changes in asthmatic airways is an increased volume of airway smooth muscle (ASM), that has been explained by proliferation, hypertrophy, extracellular matrix deposition within the smooth muscle bundles, and more recently, the migration of mesenchymal precursor cells to the airways. The best characterised of these is proliferation of ASM cells. In vitro studies suggest that the proliferation is driven by various mitogens, and ECM proteins found in asthma, such as collagen type I. Therefore, we compared the anti-mitogenic actions of two classes of anti-asthma agents, the glucocorticoids and the beta2-adrenoceptor agonists, in ASM cells grown on collagen type I. Culture on collagen type I prevented the anti-mitogenic actions of glucocorticoids, but not beta2-adrenoceptor agonists. In contrast, glucocorticoids are efficacious in regulating ASM production of GM-CSF, whereas beta2-adrenoceptor agonists are without effect. Therefore, combination therapy may have increased efficacy over glucocorticoids alone in controlling remodelling events due to complementary actions of the two classes of compounds.     

Immunohistochemical identification of the beta(3)-adrenoceptor in intact human adipocytes and ventricular myocardium: effect of obesity and treatment with ephedrine and caffeine

OBJECTIVES: To investigate whether the beta(3)-adrenoceptor could be identified by immunohistochemistry in intact human white and brown adipocytes and other human tissues, and to investigate the influence of obesity and its treatment with ephedrine and caffeine on the expression of the beta(3)-adrenoceptor in adipocytes. METHODS: Morbidly obese patients were given a hypoenergetic diet (70% of energy expenditure) and some were also treated with ephedrine and caffeine (20/200 mg, three times daily) for 4 weeks. Adipose tissue and other tissues were taken during surgery. Immunohistochemistry was carried out using a monoclonal antibody raised against the human beta(3)-adrenoceptor. RESULTS: Staining was localized to the periphery of cells. All white adipocytes were stained. Those from lean subjects and obese subjects treated with ephedrine and caffeine showed more intense staining than those from untreated obese subjects. Staining was more intense in brown than in white adipocytes in perirenal adipose tissue from phaeochromocytoma patients. Staining was also seen in ventricular myocardium, and in smooth muscle of the prostate, ileum, colon and gall bladder. DISCUSSION: The tissue and subcellular distribution of staining was consistent with it being due to binding of the antibody to the human beta(3)-adrenoceptor. The presence of the beta(3)-adrenoceptor in human white adipocytes is consistent with evidence that it can mediate lipolysis in human white adipocytes. The increased expression of the beta(3)-adrenoceptor in obese subjects treated with caffeine and ephedrine supports the potential of beta(3)-adrenoceptor agonists in the treatment of obesity and type 2 diabetes. Its expression in ventricular myocardium is consistent with evidence that the beta(3)-adrenoceptor mediates a negative inotropic effect in this tissue.     

Alpha1- and beta1-adrenoceptor signaling fully compensates for beta3-adrenoceptor deficiency in brown adipocyte norepinephrine-stimulated glucose uptake

To assess the relative roles and potential contribution of adrenergic receptor subtypes other than the beta3-adrenergic receptor in norepinephrine-mediated glucose uptake in brown adipocytes, we have here analyzed adrenergic activation of glucose uptake in primary cultures of brown adipocytes from wild-type and beta3-adrenergic receptor knockout (KO) mice. In control cells in addition to high levels of beta3-adrenergic receptor mRNA, there were relatively low alpha1A-, alpha1D-, and moderate beta1-adrenergic receptor mRNA levels with no apparent expression of other adrenergic receptors. The levels of alpha1A-, alpha1D-, and beta1-adrenergic receptor mRNA were not changed in the beta3-KO brown adipocytes, indicating that the beta3-adrenergic receptor ablation does not influence adrenergic gene expression in brown adipocytes in culture. As expected, the beta3-adrenergic receptor agonists BRL-37344 and CL-316 243 did not induce 2-deoxy-d-glucose uptake in beta3-KO brown adipocytes. Surprisingly, the endogenous adrenergic neurotransmitter norepinephrine induced the same concentration-dependent 2-deoxy-D-glucose uptake in wild-type and beta3-KO brown adipocytes. This study demonstrates that beta1-adrenergic receptors, and to a smaller degree alpha1-adrenergic receptors, functionally compensate for the lack of beta3-adrenergic receptors in glucose uptake. Beta1-adrenergic receptors activate glucose uptake through a cAMP/protein kinase A/phosphatidylinositol 3-kinase pathway, stimulating conventional and novel protein kinase Cs. The alpha1-adrenergic receptor component (that is not evident in wild-type cells) stimulates glucose uptake through a phosphatidylinositol 3-kinase and protein kinase C pathway in the beta3-KO cells.     

Positive inotropic effects of the beta2-adrenoceptor agonist terbutaline in the human heart: Effects of long-term beta1-adrenoceptor antagonist treatment

Objectives. This study was conducted to determine whether activation of cardiac beta₂-adrenoceptors increases contractility in humans and whether this is affected by long-term beta₁-adrenoceptor antagonist treatment.Background. Coexistence of beta₁- and beta₂-adrenoceptors in the human heart is generally accepted. The functional importance of cardiac beta₂-adrenoceptors for increases in contractility in humans, however, has not been completely established.Methods. We studied 1) the beta-adrenoceptor subtype mediating positive inotropic effects of the beta₂-adrenoceptor agonist terbutaline in vitro (on right atrial and left ventricular preparations from nonfailing human hearts) and increases in contractility (by measurement of systolic time intervals) in vivo in seven healthy male volunteers; and 2) in vivo whether long-term treatment of volunteers with the beta₁-adrenoceptor antagonist bisoprolol affects terbutaline-induced increases in contractility.Results. In vitro terbutaline caused a concentration-dependent increase in atrial and ventricular adenylate cyclase activity and force of contraction. Terbutaline effects were antagonized only by the beta₂-adrenoceptor antagonist ICI 118,551, indicating that they were mediated by beta₂-adrenoceptor stimulation. In vivo intravenous infusions of terbutaline (dose range 25 to 300 ng/kg body weight per min for 15 min) dose dependently increased heart rate and shortened the pre-ejection period and heart rate-corrected electromechanical systole (QS₂) time. These effects are mediated predominantly by beta₂-adrenoceptor stimulation because they were only marginally affected by the beta₁-adrenoceptor antagonist bisoprolol (1 × 10 mg orally), either given 2 h before infusion or long term for 3 weeks.Conclusions. Stimulation of cardiac beta₂-adrenoceptors in humans causes not only in vitro but also in vivo positve inotropic effects. Long-term beta₁-adrenoceptor antagonist treatment does not considerably affect beta₂-adrenoceptor-mediated in vivo increases in contractility. Thus, it may be possible to treat patients with chronic heart failure and long-term beta₁-adrenoceptor antagonist therapy with beta₂-adrenoceptor agonists if immediate inotropic support is needed.     

Impact of polymorphisms of the human beta2-adrenoceptor gene on obesity in a French population

OBJECTIVE: To investigate the impact of two common polymorphisms in the human beta2-adrenoceptor gene (Gly16Arg and Gln27Glu substitutions) on obesity and anthropometric measurements as well as blood variables in a large sample of a French population. DESIGN AND SUBJECTS: Within the framework of the WHO-MONICA project, a population study composed of 1195 subjects aged 35-64 y was randomly sampled from the electoral rolls of the Urban Community of Lille, in northern France. Subjects without any medical treatment (for hypercholesterolaemia, hypertension or diabetes mellitus) susceptible to interfere with body weight and biological variables were selected (n = 836, 419 men/417 women, age = 49.5+/-8.1 y, body mass index (BMI) = 25.7+/-4.4 kg/m2). Subjects with a body mass index > or = 30 kg/m2 were considered as obese (n = 119, age = 49.5+/-8.2 y, BMI = 33.9+/-3.3 kg/m2 range 30-44). MEASUREMENTS: Genotyping was carried out with allele-specific oligonucleotides hybridization. Association between genotypes and various obesity markers (body weight, body mass index, waist and waist-to-hip ratio), lipid, glucose and insulin variables were studied. RESULTS: The Gly16Arg and Gln27Glu polymorphisms were in complete linkage disequilibrium. Gln27Gln subjects had an increased risk of obesity (odds ratio (OR) = 1.77, 95% CI 1.19-2.62, P = 0.005). This effect was mainly detected in men (OR = 2.40, 95% CI 1.34-4.27, P = 0.003). Men bearing the Gln27Gln genotype had higher body weight, BMI, waist and hip circumferences and waist-to-hip ratio than others. Moreover, if Gln27Gln men carried in addition the Arg16 allele, the increase in body weight, BMI and waist-to-hip ratio was more important. CONCLUSION: Our results suggest that genetic variability of the beta2-adrenoceptor gene is implicated in body weight regulation and in the onset of obesity in French men.     

Duration of action of inhaled vs. Intravenous beta(2)-adrenoceptor agonists in an anaesthetized guinea-pig model

We compared the duration of action of the short-acting alpha(2)-adrenoceptor agonist salbutamol and the long-acting alpha(2)-adrenoceptor agonists salmeterol and formoterol when administered iv or by inhalation in a histamine-induced bronchoconstriction model in the guinea-pig. Following aerosol dosing, maximal bronchoprotector effects were seen for salbutamol, salmeterol and formoterol at concentrations of 1 mg/ml, 100 microg/ml and 30 microg/ml respectively, giving a potency order of formoterol > salmeterol > salbutamol. All displayed similar maximum effects in this system. A maximal concentration of salbutamol showed bronchoprotection at 1 h but not at 3 h post-dosing whereas maximal concentrations of formoterol and salmeterol showed protection up to 5 h post-aqueous-aerosol dosing, giving a duration order of salmeterol > formoterol > salbutamol. All three alpha(2)-adrenoceptor agonists showed dose-dependent bronchoprotection and duration of action following intravenous administration; salbutamol and salmeterol were equipotent and both were less potent than formoterol. Bronchoprotection obtained with sub-maximal concentrations of all three alpha(2)-adrenoceptor agonists faded within 30 min following iv administration, but this could be extended by increasing the doses. These results demonstrate that the route of administration is important in determining the duration of action of alpha(2)-adrenoceptor agonists in the lung. Furthermore, such findings lend support to the suggestion that the physico-chemical characteristics of salmeterol govern its duration of action rather than sustained binding of this agonist to a alpha(2)-adrenoceptor exo-site.     

Risk/benefit ratio of long-term treatment withβ 2-adrenoceptor agonists

Optimal control of chronic obstructive airway disorders is usually achieved with therapy based onβ ₂-adrenoceptor agonist administration. Aerosols are highly effective, have few side effects, allow for fine adjustment of dosage to titrate symptoms, and result in reduction in hyperreactivity. Equivalent bronchodilating doses of oral agents cause side effects that limit acceptability. With oral agents, cardiohemodynamic disturbances are usually minor, while tremor and restlessness diminish with continued drug use. In chronic regimens, an aerosolβ ₂-adrenergic agent should be chosen whose overall incidence of side effects is less than 5%, and an oral agent that produces no more than a 10% incidence of tremor. Suboptimal oral dosages in combination with maximal dosages ofβ ₂-agonist aerosol, with or without other bronchodilator drugs, are advisable for chronic therapy. An optimal risk/benefit ratio with broxaterol therapy will probably be achieved by using an aerosol-oral combination. Thus, broxaterol, a newβ ₂-agent, should be studied further to determine its value in chronic bronchospastic disorders.     

Advantages and disadvantages of alpha 2-adrenoceptor agonists for systemic hypertension

Alpha 2-receptor agonists are effective antihypertensive drugs that reduce sympathetic activity by both central and peripheral mechanisms. Plasma noradrenaline and renin concentrations are reduced. Hemodynamic disturbances are minor with a near-normal cardiovascular response to standing, exercise and volume depletion. The main problems are due to central adverse effects, particularly sedation, and a syndrome of sympathetic overactivity on sudden withdrawal. These problems can be minimized by using lower doses, while therapy with a useful antihypertensive drug is maintained. Clonidine and its analogs have a low toxicity and very few contraindications. They remain a useful part of the therapeutic armamentarium in hypertension.     

Potential value of oral beta 2-adrenoceptor agonists in congestive heart failure: a haemodynamic and metabolic study

This study was designed to investigate and compare the haemodynamic and metabolic responses to pirbuterol and salbutamol in patients with congestive heart failure and coronary artery disease. Attention was directed towards the effects these beta 2-adrenoceptor agonists have on left ventricular systolic function, systemic and coronary haemodynamics and myocardial substrate metabolism. Sixteen patients were randomly allocated to treatment with either pirbuterol 20 mg or salbutamol 6 mg. Since no statistically significant differences between the responses to these drugs were observed, combined data for both agents are presented. Ninety minutes after the drug intervention cardiac index increased from 2.2 +/- 0.1 to 2.9 +/- 0.2 1/min per m2 (P less than 0.001) in association with marked reductions in systemic vascular resistance (from 22 +/- 1 to 15 +/- 1 units, P less than 0.001) and increments in left ventricular dp/dtmax (from 1074 +/- 85 to 1422 +/- 133 mm Hg/sec, P less than 0.05). Modest reductions in left ventricular end-diastolic pressure (from 21 +/- 1 to 15 +/- 1 mm Hg, P less than 0.01) were observed. Heart rate increased from 82 +/- 5 to 91 +/- 4 beats/min (P less than 0.01) but the small fall in mean arterial pressure (from 86 +/- 3 to 78 +/- 3 mm Hg) was not significant. Drug-induced coronary vasodilatation reduced coronary coronary vascular resistance from 0.65 +/- 0.06 to 0.47 +/- 0.04 units (P less than 0.01) and led to a marked increase in coronary sinus blood flow (from 124 +/- 9 to 155 +/- 9 ml/min, P less than 0.05). Arterial levels of free fatty acids increased from 0.78 +/- 0.13 to 1.05 +/- 0.18 mmol/l (P less than 0.05) resulting in the preferential utilization of this substrate as a myocardial energy source. Despite the substantial haemodynamic improvement, however, no significant increase in myocardial oxygen uptake or lactate production was observed. Thus, in patients with coronary artery disease and congestive heart failure pirbuterol and salbutamol improve left ventricular function by a combination of afterload reduction and positive inotropism such that no appreciable deterioration in myocardial energetics occurs.     

The tissue distribution of the human beta3-adrenoceptor studied using a monoclonal antibody: direct evidence of the beta3-adrenoceptor in human adipose tissue, atrium and skeletal muscle

OBJECTIVE: To develop a monoclonal antibody that recognises an epitope of the native beta3-adrenoceptor expressed on the extracellular surface of human cells and tissues. DESIGN: A high affinity monoclonal antibody, Mab72c, was raised against the human beta3-adrenoceptor expressed on a transfected mammalian cell line. RESULTS: In CHO (Chinese hamster ovary) cells transfected with beta3-adrenoceptor cDNA, antibody labelling was found to be proportional to receptor density measured by the binding of the radiolabelled beta-adrenoceptor antagonist, [125I]-iodocyanopindolol. The use of Mab 72c has demonstrated the expression of the beta3-adrenoceptor in a variety of human tissues, including gall bladder, prostate and colon, where a mRNA signal had been detected previously. This study also provides the first direct demonstration of the expression of beta3-adrenoceptors in human skeletal muscle, atrium and adipose tissue. CONCLUSION: The development of this antibody represents an important addition to the armentarium of reagents that are available to study the localisation of beta3-adrenoceptors in human tissues.     

G-protein beta3 subunit gene splice variant in obesity and overweight.

OBJECTIVE: To determine whether the C825T polymorphism of the G-protein beta3 subunit gene (GNB3) is associated with overweight and obesity. This polymorphism leads to a splice variant (Gbeta3-s) with higher activity and very strong association with essential hypertension. DESIGN: A cross-sectional case-control study. SUBJECTS: The sets of affected and control British/European Caucasian subjects used were: (i) an obesity clinic group most of whom had "morbid obesity" (mean body mass index (BMI) for group=43+/-8 kg/m(2)) and non-obese controls (BMI< or =30); (ii) a group of overweight/obese healthy normotensive community volunteers (BMI>25; mean 29+/-5) and controls (BMI< or =25; mean 23+/-1); (iii) a group of overweight/obese hypertensive patients (BMI>25; mean 30+/-4) and lean hypertensive controls (BMI< or =25; mean=23+/-2). MEASUREMENTS: BMI, blood pressure, serum lipids, alleles of GNB3 polymorphism. RESULTS: Compared with control, frequency of the T allele in obese subjects was higher by 12% in (i), 17% in (ii) and 28% in (iii), but the differences were not statistically significant. Slight tracking of the T allele with elevation in BMI was, however, observed, in the obesity clinic group (P=0.018). CONCLUSION: The C825T splice variant of GNB3 makes little if any contribution to obesity in the groups we tested.     

Involvement of beta1- and beta2- but not beta3-adrenoceptor activation in adrenergic PYY secretion from the isolated colon

The secretion of PYY by endocrine L cells of the terminal gut is under the control of nutrients, the autonomic nervous system and hormones. Catecholamines, and the non-specific beta-adrenergic agonist isoproterenol induce PYY secretion from rat isolated colon or ileum. Because beta3-adrenergic receptors now appear to mediate many of the effects of catecholamines in the gastrointestinal tract, we investigated the involvement of beta1-, beta2-, and beta3-adrenoceptor stimulation in PYY secretion from the isolated, vascularly perfused rat colon. Infusion of 10(-6) M isoproterenol induced a transient increase in PYY secretion (from 36+/-4 to 87+/-20 fmol/2 min; n=7, P<0.05), that was abolished by a previous infusion of the beta1- and beta2-adrenergic blocker (and partial beta3-agonist) alprenolol (10(-6) M). The beta1-adrenergic agonist dobutamine and the beta-2 agonist terbutaline also (both at 10(-5) M) significantly stimulated PYY secretion, from 29+/-1 to 79+/-12 fmol/2 min and from 19+/-1 to 73+/-13 fmol/2 min respectively (n=7, P<0.05). Neither of the beta3-adrenergic agonists tested (BRL 37 344 (10(-5), 10(-6) M) and SR 58 611A (10(-6) M)) significantly stimulated PYY secretion, thus confirming the exclusive involvement of beta1- and beta2-receptors in beta-adrenergic agonist induced hormone secretion.