Stereoselective Inhibition of Human Butyrylcholinesterase by the Enantiomers of Bambuterol and Their Intermediates

Abstract

This work describes the sequential hydrolysis of bambuterol enantiomers and their monocarbamate metabolites (MONO) catalyzed by human butyrylcholinesterase (BChE) as well as the enzyme inhibition resulting from this process. Particular emphasis is given to the contribution given by MONO to the enzyme inhibition because it was not fully characterized in previous works. Bambuterol and MONO enantiomers displayed the same time-and concentrationdependent mechanism of interaction with the enzyme. The hydrolysis kinetics of both bambuterol and MONO was enantioselective, and the (R)-enantiomer of each compound was hydrolyzed fourfold faster than the respective (S)-enantiomer. Even though the enzyme inhibition rates of (R)-and (S)-MONO were much slower than those of their respective bambuterol enantiomers (∼15-fold), both MONO enantiomers showed a significant BChE inhibition when physiologically relevant concentrations of enzyme and inhibitors were used (∼50% of their respective bambuterol enantiomers). The kinetic constants obtained by testing each single compound were used to model the contribution given by MONO to the enzyme inhibition observed for bambuterol. The hydrolysis of MONO enantiomers enhanced the inhibitory power of bambuterol enantiomers of about 27.5% (R) and 12.5% (S) and extended more than 1 hour the duration of inhibition. The data indicate that MONO contribute significantly to the inhibition of BChE occurring in humans upon administration of normal doses of bambuterol. In addition, the hydrolysis of MONO resulted in the rate-limiting step in the conversion of bambuterol in its pharmacologically active metabolite terbutaline; therefore, MONO concentrations should always be monitored during pharmacokinetic studies of bambuterol.

Chiral analysis of bambuterol, its intermediate and active drug in human plasma by liquid chromatography–tandem mass spectrometry: Application to a pharmacokinetic study

“…3 and Table 3 were consistent with the previous report. According to our previous study, the hydrolysis kinetics of both bambuterol and monocarbamate bambuterol was enantioselective and the R-enantiomer of each compound was hydrolyzed 4-fold faster than the respective S-enantiomer [6]. Therefore, t 1/2s of all R-form analytes in Table 3 were smaller than their S-forms, which meant for all the analytes, the metabolic rates of R-enantiomers were faster than those of S-enantiomers.…”

“…Because S-bambuterol was hydrolyzed slower than R-bambuterol, C max and AUC 0 − t of S-bambuterol were larger than those of R-bambuterol in this study. However, although R-monocarbamate bambuterol was hydrolyzed faster than Smonocarbamate bambuterol, the hydrolysis of R-bambuterol was much faster than that of R-monocarbamate bambuterol [6], which led to the accumulation of R-monocarbamate bambuterol. Therefore, C max and AUC 0 − t of R-monocarbamate bambuterol in Table 3 were much larger than the S-enantiomer.…”

“…Rac-bambuterol hydrochloride and rac-terbutaline sulphate were purchased from the National Institute for the Control of Pharmaceutical and Biological Products (Beijing, China). R-monocarbamate bambuterol hydrochloride and S-monocarbamate bambuterol hydrochloride (purity ≥ 98.9%, determined by HPLC analysis) were prepared in our laboratory according to a procedure reported elsewhere [6]. The test drugs were bambuterol tablets containing 10 mg of bambuterol hydrochloride, which were provided by Dongguan Key-Pharma Biomedical Co., Ltd. (Guangdong, China).…”

“…Both bambuterol and monocarbamate bambuterol are BChE inhibitors, inhibiting their own hydrolysis [3][4]. Our previous studies showed that monocarbamate bambuterol contributed significantly to the inhibition of BChE in humans after the administration of normal doses of bambuterol, which resulted in the rate-limiting step during the conversion of bambuterol into its active drug terbutaline [5][6]. Therefore, monocarbamate bambuterol concentrations should always be monitored during the pharmacokinetic studies of bambuterol [6].…”

In vivo metabolism study of (R)‐bambuterol in humans using ultra high performance liquid chromatography with tandem mass spectrometry

“…( R )‐Bambuterol hydrochloride and ( R )‐terbutaline sulfate were obtained from Dongguan Key‐Pharma Biomedical (Guangdong, China). ( R )‐Monocarbamate bambuterol hydrochloride (purity ≥98.9%, determined by HPLC analysis) was prepared in our laboratory according to a reported procedure . The test drugs were bambuterol tablets containing 10 mg of ( R )‐bambuterol hydrochloride, provided by Dongguan Key‐Pharma Biomedical.…”