Literatura científica selecionada sobre o tema "Clenbuterol"

Lynch, Gordon S., Alan Hayes, Siun P. Campbell, and David A. Williams. Effects of β2-agonist administration and exercise on contractile activation of skeletal muscle fibers. J. Appl. Physiol. 81(4): 1610–1618, 1996.—Clenbuterol, a β2-adrenoceptor agonist, has therapeutic potential for the treatment of muscle-wasting diseases, yet its effects, especially at the single-fiber level, have not been fully characterized. Male C57BL/10 mice were allocated to three groups: Control-Treated mice were administered clenbuterol (2 mg ⋅ kg−1 ⋅ day−1) via their drinking water for 15 wk; Trained-Treated mice underwent low-intensity training (unweighted swimming, 5 days/wk, 1 h/day) in addition to receiving clenbuterol; and Control mice were sedentary and untreated. Contractile characteristics were determined on membrane-permeabilized fibers from the extensor digitorum longus (EDL) and soleus muscles. Fast fibers from the EDL and soleus muscles of Treated mice exhibited decreases in Ca2+ sensitivity. Endurance exercise offset clenbuterol’s effects, demonstrated by similar Ca2+ sensitivities in the Trained-Treated and Control groups. Long-term clenbuterol treatment did not affect the normalized maximal tension of fast or slow fibers but increased the proportion of fast fibers in the soleus muscle. Training increased the proportion of fibers with high and intermediate succinate dehydrogenase activity in the EDL and soleus muscles, respectively. If clenbuterol is to be used for treating muscle-wasting disorders, some form of low-intensity exercise might be encouraged such that potentially deleterious slow-to-fast fiber type transformations are minimized. Indeed, in the mouse, low-intensity exercise appears to prevent these effects.

Clenbuterol and other β2-adrenergic agonists are effective at inducing muscle growth and attenuating muscle atrophy through unknown mechanisms. This study tested the hypothesis that clenbuterol-induced growth and muscle sparing is mediated through the activation of Akt and mammalian target of rapamycin (mTOR) signaling pathways. Clenbuterol was administered to normal weight-bearing adult rats to examine the growth-inducing effects and to adult rats undergoing muscle atrophy as the result of hindlimb suspension or denervation to examine the muscle-sparing effects. The pharmacological inhibitor rapamycin was administered in combination with clenbuterol in vivo to determine whether activation of mTOR was involved in mediating the effects of clenbuterol. Clenbuterol administration increased the phosphorylation status of PKB/Akt, S6 kinase 1/p70s6k, and eukaryotic initiation factor 4E binding protein 1/PHAS-1. Clenbuterol treatment induced growth by 27–41% in normal rats and attenuated muscle loss during hindlimb suspension by 10–20%. Rapamycin treatment resulted in a 37–97% suppression of clenbuterol-induced growth and a 100% reduction of the muscle-sparing effect. In contrast, rapamycin was unable to block the muscle-sparing effects of clenbuterol after denervation. Clenbuterol was also shown to suppress the expression of the MuRF1 and MAFbx transcripts in muscles from normal, denervated, and hindlimb-suspended rats. These results demonstrate that the effects of clenbuterol are mediated, in part, through the activation of Akt and mTOR signaling pathways.

Clenbuterol, a compound classified as a β2-adrenoceptor (AR) agonist, has been employed in combination with left ventricular assist devices (LVADs) to treat patients with severe heart failure. Previous studies have shown that chronic administration of clenbuterol affects cardiac excitation-contraction coupling. However, the acute effects of clenbuterol and the signaling pathway involved remain undefined. We investigated the acute effects of clenbuterol on isolated ventricular myocyte sarcomere shortening, Ca2+ transients, and L-type Ca2+ current and compared these effects to two other clinically used β2-AR agonists: fenoterol and salbutamol. Clenbuterol (30 μM) produced a negative inotropic response, whereas fenoterol showed a positive inotropic response. Salbutamol had no significant effects. Clenbuterol reduced Ca2+ transient amplitude and L-type Ca2+ current. Selective β1-AR blockade did not affect the action of clenbuterol on sarcomere shortening but significantly reduced contractility in the presence of fenoterol and salbutamol ( P < 0.05). Incubation with 2 μg/ml pertussis toxin significantly reduced the negative inotropic effects of 30 μM clenbuterol. In addition, overexpression of inhibitory G protein (Gi) by adenoviral transfection induced a stronger clenbuterol-mediated negative inotropic effect, suggesting the involvement of the Gi protein. We conclude that clenbuterol does not increase and, at high concentrations, significantly depresses contractility of isolated ventricular myocytes, an effect not seen with fenoterol or salbutamol. In its negative inotropism, clenbuterol predominantly acts through Gi, and the consequent downstream signaling pathways activation may explain the beneficial effects observed during chronic administration of clenbuterol in patients treated with LVADs.

Aim: Follow-up investigations are often required for clenbuterol-positive cases. A method to distinguish doping abuse from meat contamination was developed. Materials & methods: A total of 26 volunteers were recruited to ingest clenbuterol contaminated-pork and clenbuterol tablets. Results: For 20 volunteers, after ingestion of contaminated-pork, R-(-)/S-(+)-clenbuterol ratio was <1.0, while the value was >1.0 after taking clenbuterol tablets. However, after taking clenbuterol tablets, some ratio points of the other six volunteers were between 0.9 and 1.0. A case of an abnormal cold and fever, which returned to normal after recovery, was also reported firstly. Conclusion: A change in R-(-)/S-(+)-clenbuterol was reported in the Chinese population initially. A ratio of 0.9 was recommended in doping related cases for the Chinese population.

Clenbuterol, a β2-selective adrenergic receptor agonist, is illicitly used in weight loss and performance enhancement and animal production. Increasing evidence demonstrates that clenbuterol induces various kinds of arrhythmias and QTc interval prolongation. However, little is known about the underlying mechanism. Most drugs are associated with QTc prolongation through interfering with human ether-a-go-go-related gene (hERG) K+ channels. The present study aims to investigate the effects and underlying mechanisms of clenbuterol on the hERG channel. HEK 293 cells were transfected with wild type and Y652A or F656A mutants of the hERG channel and treated with clenbuterol. The hERG current was recorded using whole-cell patch-clamp technique, and protein level was evaluated by Western blot. We found that clenbuterol decreases the mature form of the hERG protein at the cell membrane in a concentration- and time-dependent manner, without affecting the immature form. Correspondingly, clenbuterol chronic treatment reduced hERG current to a greater extent compared to acute treatment. In the presence of Brefeldin A (BFA), which was used to block hERG channel trafficking to cell membrane, clenbuterol reduced hERG on plasma membrane to a greater extent than BFA alone. In addition, the hERG channel’s drug binding sites mutant Y652A and F656A abolished clenbuterol-mediated hERG reduction and current blockade. In conclusion, clenbuterol reduces hERG channel expression and current by promoting the channel degradation. The effect of clenbuterol on the hERG channel is related to the drug-binding sites, Tyr-652 and Phe-656, located on the S6 domain. This biophysical mechanism may underlie clenbuterol-induced QTc prolongation or arrhythmia.

Afin de lutter efficacement contre les malversations du dopage, il apparaît essentiel de comprendre les mécanismes conduisant au remodelage musculaire. Dans ce but nous avons analysé les effets d’un β2-agoniste, le clenbutérol, sur le remodelage musculaire et les différentes voies de signalisation qui y sont associées. Nous nous sommes particulièrement intéressés au système des calpaïnes qui a souvent été associé à des phénomènes de remodelage musculaire, principalement dans des modèles d’atrophie. Nous avons montré une sollicitation précoce du système des calpaïnes lors d’un traitement chronique au clenbutérol chez le rat associé à une conversion phénotypique dans les muscles EDL et Soléaire et à une hypertrophie dans le muscle EDL uniquement. Puis, nous avons inhibé l’activité des calpaïnes en parallèle d’un traitement au clenbutérol. Les muscles ayant une activité des calpaïnes diminuée et soumis à un traitement au clenbutérol n’ont pas développé de remodelage musculaire. Ces premiers résultats renforcent l’idée d’une implication des calpaïnes dans le remodelage musculaire induit par un traitement chronique au clenbutérol
To fight doping in an effective manner, it is essential to understand the mechanisms leading to muscle remodeling. For this purpose we analyzed the effects of clenbuterol, on muscle remodeling and various associated signaling pathways. We were particularly interested with the calpain system which has often been associated with muscle remodeling phenomena, mainly in models of atrophy. We have shown that an early calpain system solicitation during chronic treatment with clenbuterol in rats was associated with a phenotypic conversion in the Soleus and EDL muscles and hypertrophy in the EDL muscle. We then inhibited the activity of calpains with a parallel clenbuterol treatment. The muscles with a reduced activity of calpain and treated with clenbuterol did not develop muscle remodeling. These initial results reinforce the idea of an involvement of calpain in the muscle remodeling induced by chronic treatment with clenbuterol

Clenbuterol Hydrochloride is a bronchodilator marketed as Spirospent® for Human Pharmaceuticals and as Ventipulmin® for Veterinary Pharmaceuticals by Boehringer Ingelheim.1 This research investigates formation of the 4-amino-α,α-dihydroxy-3,5-dichloroacetophenone impurity (Dihydroxy Impurity) in the synthesis of Clenbuterol Hydrochloride. The Dihydroxy Impurity has increased three-fold since the process was transferred to Boehringer Ingelheim Chemicals, Inc. in 1999.1 The Dihydroxy Impurity is proposed to be produced during an amination/reduction step from a reaction of water with the starting material.2 Additionally, the Dihydroxy Impurity can be formed by the reaction of water with an impurity, 4-amino-α,α-didibromo-3,5-dichloroacetophenone (Dibromo Impurity), that is generated in the previous step.2 The formation of the Dibromo Impurity was investigated through a series of Design of Experiments (DoE) analyses. The results from these analyses, presented within, determined the optimum bromination conditions to reduce the Dibromo Impurity. These conditions were able to reduce the Dibromo Impurity by 75%. A series of water spiking experiments with both the starting material of the amination/reduction step and the Dibromo Impurity were performed to investigate the formation of the Dihydroxy Impurity. Based on the results, a mechanism for the formation of the Dihydroxy Impurity is presented. The three-fold increase of the Dihydroxy Impurity was concluded to be due to ≥ 15% water in the amination reaction mixture reacting with the starting material. REFERENCES 1. Powner, T. H. Process Development Report: Preparation of Clenbuterol Hydrochloride USP, EP; Document No. DRCLEN Rev 0; Boehringer Ingelheim Chemicals, Inc.: Petersburg, VA, 2002; 1 – 194. 2. Brown, J. Clenbuterol Free Base C124A (Lot 1011974) Impurity; Boehringer Ingelheim Chemicals, Inc.: Petersburg, VA, 2007; 1 – 2.

Mitochondrial dysfunction is associated with numerous acute and chronic degenerative diseases. The beta-2 adrenergic receptor (beta(2)AR) agonist formoterol induces mitochondrial biogenesis (MB), but other beta(2)AR agonists, such as clenbuterol, do not. We sought to identify the MB signaling pathway of formoterol and the differences in signaling between these two ligands that result in the differential induction of MB. While formoterol and clenbuterol increased cAMP, only formoterol increased the phosphorylation of Akt and its downstream target eNOS. The increase in Akt phosphorylation was G beta gamma- and PI3K-dependent, and the increase in eNOS phosphorylation was G beta gamma- and Akt-dependent. Only formoterol increased cGMP. Formoterol induced MB as measured by increases in uncoupled cellular respiration and PGC-1 alpha and NDUFS1 mRNA expression and was blocked by inhibitors of G beta gamma, Akt, NOS, and soluble guanylate cyclase. To identify distinct receptor-ligand interactions leading to these differences in signaling, we docked formoterol and clenbuterol to six structures of the beta(2)AR. Compared to clenbuterol, the methoxyphenyl group of formoterol interacted more frequently with V114 and F193, while its formamide group interacted more frequently with C191. These data indicate that the unique structural features of formoterol allow it to interact with the beta(2)AR to activate the G beta gamma-Akt-eNOS-sGC pathway to induce MB.

6. ZUSAMMENFASSUNG Charakterisierung b-adrenerger Rezeptoren auf Pferdelymphozyten und deren Regulation unter dem Einfluß von Clenbuterol und Dexamethason Getu Abraham Institut für Pharmakologie, Pharmazie und Toxikologie, Veterinärmedizinische Fakultät, Universität Leipzig, Deutschland Juni, 2001 86 S., 205 Lit., 7 Tab., 23 Abb. Über Vorkommen und Eigenschaften von b-Adrenozeptoren auf Pferdelymphozyten und ihre pharmakologische Regulation liegen bisher keine Untersuchungen vor. Mit der vorliegenden Arbeit sollten b-adrenerge Rezeptoren an intakten Pferdelymphozyten in Bindungsstudien mit dem Radioliganden (-)-(125I)-Iodocyanopindolol (ICYP), einem potenten b2-selektiven Adrenozeptorenantagonisten, charakterisiert und deren funktionelle Ansprechbarkeit durch Messung des Isoprenalin-induzierten Anstiegs des intrazellulären cAMP-Gehaltes mittels Radioimmunoassay bestimmt werden. Die Bindung von ICYP an intakten Pferdelymphozyten war schnell, sättigbar (maximale Anzahl der Bindungsstellen 320 ± 20 ICYP Bindungsstellen/Zelle, Mittelwert±SEM, n = 12) ) und hochaffin (KD-Wert für ICYP 14,37 ± 1,66 pmol/l, Mittelwert±SEM, n = 12). Verdrängungsexperimente mit Agonisten und Antagonisten zeigten eine Affinität und Stereoselektivität, wie sie bei b-Adrenozeptoren zu erwarten waren. Der nicht radioaktiv markierte b2-selektive Adrenozeptorantagonist ICI 118,551 verdrängte den Radioliganden ICYP aus seiner Bindung mit mehr als 1500fach höherer Affinität als der nicht radioaktiv markierte b1-selektive Adrenozeptorantagonist CGP 20712A. In Pferdelymphozyten können somit mehr als 90 % der b-Adrenozeptoren dem b2-Subtyp zugeordnet werden. Ein Anteil von weniger als 10 % an b1-Adrenozeptoren kann allerdings nicht ausgeschlossen werden. Die Bindungsstellen waren stereospezifisch, da das biologisch aktive (-)-Propranolol die Bindung von ICYP mit 40fach höherer Affinität verdrängte als (+)-Propranolol. b-adrenerge Agonisten verdrängten ICYP aus seiner spezifischen Bindung in der Rangfolge ihrer pharmakologischen Wirkungstärke, die typisch für den b2-Subtyp des Adrenozeptors ist: (-)-Isoprenalin > (-)-Adrenalin > (-)-Noradrenalin. Eine ähnliche Rangfolge wurde auch für die Agonist-induzierte cAMP-Bildung in Lymphozyten festgestellt. Aufgrund der dargestellten Befunde kann die Schlußfolgerung gezogen werden, daß ICYP ein geeigneter Radioligand ist, um b-adrenerge Rezeptoren an Pferdelymphozyten zu identifizieren und zu charakterisieren. Die Bindung von ICYP an intakte Lymphozyten stellt somit ein geeignetes Modell dar, um wichtige Informationen über die Funktion und Regulation des b-adrenergen Systems beim Pferd sowohl unter physiologischen (pathophysiologischen) Bedingungen als auch über Arzneimittel-induzierte Veränderungen in vivo zu gewinnen. Ausgehend von den beschriebenen Grundlagenuntersuchungen wurden in einer weiteren Versuchsreihe bei zwölf klinisch gesunden Pferden der Einfluß von Clenbuterol und Dexamethason lymphozytäre b2-Adrenozeptoren, hinsichtlich ihrer Dichte, ihrer Affinität zum Radioliganden und ihrer cAMP-Bildung (als Maß für die funktionelle Ansprechbarkeit der b2-Adrenozeptoren bestimmt über Stimulation durch 10 µmol/l Isoprenalin) untersucht. Während der 12tägigen Clenbuterolbehandlung (2 Ž 0,8 µg/kg/Tag, i. v.) fielen die Anzahl der b2-Adrenozeptoren an Lymphozyten und der durch (-)-Isoprenalin-induzierte Anstieg des intrazellulären cAMP-Gehaltes signifikant (p < 0,05, n = 8) unter die Ausgangswerte unbehandelter Tiere ab. Clenbuterol bewirkte in der therapeutischen Dosis bereits 48 Stunden nach der Behandlung einen Abfall der Anzahl der b2-Adrenozeptoren bzw. der cAMP-Bildung um etwa 30 - 40 %. Während der restlichen Behandlungsdauer unter Clenbuterol blieb die Rezeptorendichte auf diesem niedrigen Niveau. Bei einer weiteren Versuchsgruppe wurde der Effekt des Glukokortikoids Dexamethason auf die Clenbuterol-induzierte Desensibilisierung von b2-Adrenozeptoren untersucht. Dexamethasonverabreichung (1 Ž 0,1mg/kg/d, i. v.) unmittelbar nach der letzten Clenbuteroldosis über 5 Tage beschleunigte die Wiederherstellung der down-regulierten Anzahl der lymphozytären b2-Adrenozeptoren und des Isoprenalin-induzierten Anstiegs des intrazellulären cAMP-Gehaltes (p < 0,05, n = 4). Schon 24 Stunden nach der ersten Dexamethasongabe waren beide Parameter von den Durchschnittswerten am Tag vor Behandlungsbeginn statistisch nicht zu unterscheiden. Die Anzahl der lymphozytären b2-Adrenozeptoren stieg sogar ab dem dritten Tag der Dexamethasonbehandlung bis auf das Doppelte bei unbehandelten Tiere an. Nach dem Absetzen der Dexamethasonbehandlung kam es zu einer langsam Abnahme der Rezeptorendichte und ihrer Ansprechbarkeit, wobei die vor der Clenbuterolbehandlung gemessenen Werte erst nach 4 Tagen erreicht wurden. Bei gleichzeitiger Behandlung der Tiere mit Clenbuterol und Dexamethason konnte durch das Glukokortikoid die Clenbuterol-induzierte Abnahme der b2-Adrenozeptorendichte und deren Ansprechbarkeit vollständig verhindert werden. Weder durch die Clenbuterol-abhängige Down-Regulation noch durch die Dexamethason-bedingte Hochregulation kam es zu signifikanten Veränderungen der Dissoziationskonstante (KD) und somit der Affinität von ICYP zu b2-Adrenozeptoren. Die Ergebnisse zeigen, daß es unter Behandlung mit Clenbuterol zu einer schnell einsetzenden, umfangreichen Down-Regulation der b2-Adrenozeptorendichte an Lymphozyten des Pferdes kommt und daß diese Toleranzentwicklung durch Glukokortikoide vollständig wieder aufgehoben oder verhindert werden kann. Zur Therapie der COB von Pferden scheint somit die kombinierte Anwendung von b2-Mimetika und Glukokortikoiden von Vorteil zu sein
7. Summary Characterization of b-adrenergic Receptors on Equine Lymphocytes and their Regulation under the Influence of Clenbuterol and Dexamethasone Getu Abraham Institute of Pharmacology, Pharmacy and Toxicology, Faculty of Veterinary Medicine, University of Leipzig, Germany June, 2001 86 pp., 205 ref., 7 tab., 23 fig. b-Adrenoceptors and their regulation by pharmacological active substances have not yet been characterized in equine lymphocytes. In this study, b-adrenoceptors were identified and subclassified by (-)-[125I]-iodocyanopindolol (ICYP) binding, a potent b2-adrenergic antagonist, as well as by their isoprenaline-induced responsiveness using radioimmunoassay in intact viable equine lymphocytes. The specific ICYP binding was rapid, saturable (maximum number of binding sites 320 ± 20 ICYP binding sites/cell, means±SEM, n = 12) and of high affinity (KD-value for ICYP 14.37 ± 1.66 pmol/l, means±SEM, n = 12). The competition binding studies with agonists and antagonists showed the affinity and stereoselectivity to be expected for b-adrenergic receptors. The unlabelled selective b2-adrenoceptor antagonist ICI 118,551 was about 1500 times more potent in inhibiting ICYP binding than was the b1-selective adrenoceptor antagonist CGP 20712A. It is, therefore, concluded that in intact equine lymphocytes ICYP labels a class of functional b-adrenoceptors, that belong predominantly (> 90 %) to the b2-adrenoceptor subtype. A minor (< 10 %) b1-adrenoceptor component, however, cannot be completely ruled out. The binding sites were stereoselective, as the (-)-isomer of propranolol was about 40 times more potent to inhibit ICYP binding than was the (+)-isomer. Agonists competed for specific binding with a rank order of potency (-)-isoprenaline > (-)-adrenaline > (-)-noradrenaline, which is typical for a b2-subtype of adrenergic receptor; the same order of potency was obtained for agonist-induced stimulation of lymphocyte cyclic AMP content. Thus, it can be concluded that ICYP is a promising compound for the reliable determination of the binding characteristics of b-adrenoceptors of equine lymphocytes and besides that, this might give an insight in providing physiologically significant information about the regulation of the b-adrenergic receptor system. Based upon this study, we further investigated, in 12 healthy thoroughbred horses, the effects of the b2-agonist clenbuterol and the glucocorticoid dexamethasone on the lymphocyte b2-adrenenergic receptor density and affinity as well as on its responsiveness (assessed by lymphocyte cyclic AMP responses to 10 µmol/l (-)-isoprenaline). Clenbuterol (2Ž0.8µg/kg/d, i. v. for 12 days) decreased ICYP binding sites only 48 h after application by ~30-40 %; concomitantly, lymphocyte cAMP response to (-)-isoprenaline was significantly reduced (p < 0.05, n = 8). The values remained at these low levels throughout the following 10 days of treatment. After withdrawal of clenbuterol the density and responsiveness of b2-adrenoceptors gradually increased, reaching pre-drug levels after 4 days. Next the effects of dexamethasone on clenbuterol-induced desensitisation were studied. Administration of dexamethasone (1Ž0.1mg/kg/d, i. v. for five days) immediately after clenbuterol withdrawal accelerated b2-adrenergic receptor recovery (p < 0.05, n = 4): only 24 hours after administration dexamethasone restored the number of binding sites and cAMP response to (-)-isoprenaline to levels statistically indistinguishable from the values before starting clenbuterol treatment. Three days after dexamethasone administration the density of lymphocyte b2-adrenoceptors was further increased about two fold the pre-treatment values, and this increase declined gradually after dexamethasone withdrawal, reaching baseline values after 4 days. Furthermore, in groups simultaneously exposed to both drugs dexamethasone completely prevented clenbuterol-induced decrease in lymphocyte b2-adrenoceptor density and responsiveness. No significant change was observed in the dissociation constant and, thus, in the affinity of ICYP to b-adrenoceptors remained unchanged during or after treatment with either clenbuterol or dexamethasone. It is concluded that dexamethasone (glucocorticoids) can reverse and prevent clenbuterol-induced down-regulation of the lymphocyte b2-adrenoceptors and thus, a combined therapy with clenbuterol and dexamethasone may be potentially beneficial in COPD of horses