| R-BM is a long actingβ2 adrenoceptor agonist which is used as a bronchiodilator agent in asthma and chronic obstructive pulmonary disease and it is the R enantiomer of bambuterol. Bambuterol is a chiral carbamate known as selective inhibitor of butyrylcholinesterase (BChE). The marked form of bambuterol is a racemic mixture composed of a 50:50 mixture of R and S isomers.Rac-BM has been marketed and widely used clinically for severals years .As the bis-dimethylcarbamate prodrug of terbutaline, bambuterol has more potent bronchospasmolytic activity than the latter upon oral administration and exhibits a duration of activity of more than 12 hours. Bambuterol released terbutaline into blood over a sustained period. In this respect,it is different from long acting beta agonists like salmeterol or formoterol. The drug has been demonstrated to have benefit in nocturnal symptoms. Bambuterol also exhibits a low degree of undesired cardiovascular side affects. In addition, bambuterol has lipid lowering effects in certain patients. It is known that the S-isomers ofβ2–agonists-including terbutaline are more toxic or less potent than the R-isomers, propeties which may be responsible for the side effects of racemic bambuterol in its clinical use.Among many drugs having chiral centers ,one enantiomer of a racemic pair is often more active than the other in treating a medical condition. For example,the levorotatory R-enantiomer of albuterol is approximately 80 times more potent as aβ2 receptor agonist than the dextrorotatory S-enantiomer,and the administration of the pure R-enantiomer offers improved therapeutic activity and fewer side effects.The United States Food and Durg Administration has approved R-albuterol hydrochloride as a new drug for the treatment of asthma. Blue from indigo plant is deeper than its origin .R-BM not only inherits the merits of rac-BM, but also has an advangtage over rac-BM.In the persent study, we compared the bronchodilating activity of R-BM and rac-BM in ashma model in three different condictions: the conscious and unrestrained guineas ,the anaesthetized guineas in vivo and the isolated guinea-pig trachea and pulmonary bar in vitro .To observe the main effect on pharmacology of R enantiomer bambuterol (R-BM) ,we compared inhibition to experimetal asthma between R-BM and racemic bambuterol (rac-BM),S enantiomer bambuterol(S-BM). First, Our study was aimed at investigating the potency of the bronchodilators action of the R-BM compared to rac-BM in three different conditions: the conscious and unrestrained guineas ; the anaesthetized guineas in vivo ; the isolated guinea-pig trachea and pulmonary bar in vitro .Then we make further researches into antiinflammatory effect of oral R-BM. At last, based on above experiments, further studies are necessary to evaluate inhibition to experimetal asthma between R-BM and S-BM.1. Inhibitory effect of R-BM on experimental asthma in guinea pigsIn the first condition ,we observe the latent period of period of ecpratory dyspnea,tic and falling down caused by histamine in normal guinea pigs or by egg albumin(OVA) in sensitized guinea pigs.①In the conscious and unrestrained guineas R-BM inhibited asthma induced by histamine in guinea-pig in a dose dependent manner . The results show that R-BM can inhibite asthmatic attacks of sensitized guinea pigs by 100% at the concentration of 4 mg/kg,8mg/kg. At the concentration of 2.0 mg/kg, the inhibitory rate was 75.0%. The mean effective does ED50 of R-BM,rac-BM were 1.625±0.876mg/kg, 2.639±1.329mg/kg,respectively. The peak value appeared about 4 hours after administration .meanwhile , the action could last 24 h .The effect of R-BM was much better than rac-BM and a significant difference between R-BM and rac-BM was observed ( P <0. 01) . ②The experiments show that R-BM can inhibite asthmatic attacks of sensitized guinea pigs by 100% at the concentration of 8 mg/kg.d. At the concentration of 4.0 mg/kg.d,2.0 mg/kg.d, the inhibitory rate was 75.0%,62.5%, respectively. At the concentration of 1.0,0.5mg/kg.d , the inhibitory rate was 37.5%和12.0%, but the rate of rac-BM at the same concentration were 12.0%,0 %. The effects of relieving asthma of rac-BM was weaker than R-BM and there was significant difference (P<0.01).The mean effective does ED50 of R-BM,rac-BM were 2.463±1.277mg/kg, 4.288±2.012mg/kg,respectively.The above results indicate that in the conscious and unrestrained condiction, R-BM inhibited asthma induced by histamine in guinea-pig or by OVA in sensitized guinea pigs . Through controlling asthma symptoms, the effect of R-BM was much better than rac-BM and a significant difference between R-BM and rac-BM was observed.2. Ovalbumin-induced changes of RL and Cdyn in sensitized guinea pigComparision with baseline value before aerosol challenge of antigen, bronchial challenge of ovalbumin-sensitized guinea pigs induced 219% in crease of RL and 62% reduction of Cdyn with maximal response at 2 min. Mean value increase of RL and mean value reduction of Cdyn from 1 to 30 min after antigen challenge were up to 149%±97% and 52%±13%, respectively in saline group. R-BM 1.0, 2.0 and 4.0 mg/kg, administered by ig, induced dose-related inhibition of the bronchoconstrictive response to aerosolised ovalbumin. Maximal increase of RL and reduction response of Cdyn at 2 min were 58%, 29%, and 17%,and 38%, 23%, and 21%; Mean increase of RL and reduction response of Cdyn from 1 to 30 min were 34%±9%, 18%±4%, and 8%±3% and 127%±6% ,15%±14% and 4%±10%; rac-BM 1.0, 2.0 and 4.0mg/kg administered by ig produced dose-related inhibition of the bronchoconstrictive responses to aerosolised ovalbumin. Maximal increase of RL and reduction response of Cdyn at 5 min were 78% ,51%, 24%, and and 43% ,36% and, 16%. Mean increase of RL and reduction response of Cdyn from 1 to 30 min were 56%±5%, 36%±8%, and 19%±4% and 34%±4%, 25%11%, and 12%±12%. ID50 of R-BM and rac-BM about RL were 1.22, 2.16 mg/kg at maximal response ,respectively. ID50 of R-BM and rac-BM about Cdyn were 0.91, 1.14 mg/kg at mean response ,respectively.The above results indicate that in the anaesthetized guineas R-BM induced does-related inhibition of the bronchoconstrictive responses to aerosolized ovalbumin. R-BM as prodrug of terbutaline metabolized in body has a better effect than rac-BM on the model of experimental asthma in guinea pigs.3. Inhibitory effect of R-BM on experimental asthma in isolated guinea pigs lung parenchymal and trachealstripIn vitro study,the whole trachea and the whole lung were excised from guinea pigs,and then cut into proper size preparations.After an equilibration period of 60min,histamine was administered to preparations at a concentration that in preliminary experiments had been shown to produce 80-90% of maximal contraction. Data were recorded by means of a MedLab system. Then medicinal serum of test drug was administered to histamine-precontracted preparations and left in contact with the tissue until complete inhibition was attained. Research the spasmolytic action in trachea and the inhibitory effect in pulmonary bar.The above results indicate that R-BM showed obvious inhibitory effect of tracheal contraction within the terminal concentration 0.01-0.04mg/ml. The results were significantly different from rac-BM group.4. Ovalbumin-induced airway inflammation in sensitized miceTo compare the antiinflammatory effects of oral R-BM and rac-BM, the counts of total leukocyteand neutrophils and eosinophil granuloeyte in bronchoalveolar lavage fluid (BALF). In sensitized mice,after 7 days ovalbumin-aerosol challenge, antigen induced a significant increase of inflammatory cells in BALF. The number of inflammatory cells in BALF in antigen challenged group was significantly higer than that in control group(p<0.01).R-BM caused a dose-dependent inhibition and the effect is stronger than rac-BM.5. Comparative Research on the Treatment Effect of R-BM and S-BM to AsthmaRac-BM contains two chiral carbons and, therefore, the synthetic molecular product contains two enantiomers (R and S) . Since rac-BM is a 50:50 mixture of the two enantiomers, the distomer (S-BM) is inactive at the same dose of the eutomer which showed activity, the result is exactly to be expected. We carry out this experiment for the purpose of giving a further study on comparing the treatment effect of R-BM and S-BM to asthma.①In the experiment of lung function, R-BM 1.0, 2.0 and 4.0 mg/kg, administered by ig, induce dose-related inhibition of the bronchoconstrictive response to aerosolised ovalbumin. But S-BM don't show the inhibiton in a dose-dependent manner at concentrations between 1.0 mg/kg and 4.0 mg/kg. Moreover, high dose of S-BM group(4.0mg/kg) markedly promote bronchoconstriction from asthma compared with model group. It is because S-BM can enhance the sensitivity of airway tissues to antigen.②In the experiment of receptor regulation, continuous administration of R-BM or S-BM could down-regulate the expression ofβ2- receptor. And S-BM is more serious than R-BM.The above results indicate that the administration of the pure R-enantiomer offers improved therapeutic activity and fewer side effects.
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