Department of Pediatrics, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, CA 90502, USA.
Int Arch Allergy Immunol. 2012;158(1):18-26. doi: 10.1159/000330029. Epub 2011 Dec 28.
Racemic albuterol is a 50:50 mixture of the (R)- and (S)-enantiomers of albuterol. Its clinical efficacy resides in the (R)-enantiomer (levalbuterol). Studies have shown that (S)-albuterol induces human bronchial smooth muscle cell (HBSMC) proliferation via a pathway linked to platelet-activating factor (PAF), but the underlying mechanism by which (S)-albuterol augments PAF effects is not clear. In this study, we compared effect of levalbuterol and (S)-albuterol on PAF receptor (PAFr)-mediated signaling and PAF metabolism by HBSMCs after incubation with the albuterol isomers.
PAF binding and inositol phosphate (IP(3)) release were studied on adherent cultured cells. PAFr protein expression was measured by Western blotting, PAF synthesis and catabolism were measured in membrane and cytosolic proteins of cells incubated with albuterol isomers.
Compared to control conditions, (S)-albuterol increased PAF binding by 70% after 30 min of preincubation and by 150% after 24 h of preincubation. Levalbuterol had no effect on PAF binding under both conditions. (S)-albuterol also augmented PAF stimulation of IP(3) release, while levalbuterol and the racemic mixture had no effect. WEB 2170, a PAFr antagonist, inhibited the ability of (S)-albuterol to increase PAF binding or stimulate IP(3) release. (S)-albuterol stimulated PAFr protein expression. With PAF metabolism, (S)-albuterol treatment augmented PAF synthesis, but significantly inhibited PAF catabolism.
Our data suggest that one mechanism by which (S)-albuterol stimulates HBSMC proliferation involves upregulation of PAFr-mediated effects including increased PAF synthesis and decreased PAF catabolism.
消旋沙丁胺醇是沙丁胺醇的（R）-和（S）-对映异构体的 50:50 混合物。其临床疗效存在于（R）-对映异构体（左沙丁胺醇）中。研究表明，（S）-沙丁胺醇通过与血小板激活因子（PAF）相关的途径诱导人支气管平滑肌细胞（HBSMC）增殖，但（S）-沙丁胺醇增强 PAF 作用的潜在机制尚不清楚。在这项研究中，我们比较了左沙丁胺醇和（S）-沙丁胺醇对 HBSMC 孵育沙丁胺醇异构体后 PAF 受体（PAFr）介导的信号转导和 PAF 代谢的影响。
研究了粘附培养细胞中的 PAF 结合和肌醇磷酸（IP（3））释放。通过 Western blot 测量 PAFr 蛋白表达，通过细胞孵育的膜和胞质蛋白测量 PAF 合成和分解代谢。
与对照条件相比，（S）-沙丁胺醇在预孵育 30 分钟后使 PAF 结合增加 70%，在预孵育 24 小时后增加 150%。在这两种情况下，左沙丁胺醇对 PAF 结合均无影响。（S）-沙丁胺醇还增强了 PAF 刺激的 IP（3）释放，而左沙丁胺醇和外消旋混合物则没有作用。PAFr 拮抗剂 WEB 2170 抑制了（S）-沙丁胺醇增加 PAF 结合或刺激 IP（3）释放的能力。（S）-沙丁胺醇刺激 PAFr 蛋白表达。用 PAF 代谢，（S）-沙丁胺醇处理增加了 PAF 合成，但显著抑制了 PAF 分解代谢。
我们的数据表明，（S）-沙丁胺醇刺激 HBSMC 增殖的一种机制涉及 PAFr 介导的效应上调，包括增加 PAF 合成和减少 PAF 分解代谢。
