(S)-albuterol activates pro-constrictory and pro-inflammatory pathways in human bronchial smooth muscle cells

Background: Pro-constrictory and proinflammatory properties of (S)-albuterol have been widely reported both under in vivo and in vitro conditions. However, underlying mechanisms are unclear. Objective: We examined and compared the cellular effects of albuterol enantiomers on key intracellular molecules involved in constrictory and inflammatory pathways in human bronchial smooth muscle cells (hBSMCs). Methods: Primary hBSMCs were grown in culture and treated with various concentrations of albuterol enantiomers for various periods. Methacholine was used to stimulate cells. The expression and activity of G(s) and G(i) proteins, the intracellular free calcium concentration ([Ca2+](i)), the activity of phosphatidylinositol 3'-OH-kinase (PI3) kinase, and the transcriptional nuclear factor kappaB (NF-kappaB) level were examined. Results: There was a significant increase in the expression and activity of G(ialpha-1) protein and a decrease in the expression of G(s) protein in hBSMCs after 8 hours of treatment with (S)albuterol. These effects of (S)-albuterol were observed in a dose-dependent manner. Nonreceptor-mediated activation of adenylate cyclase by forskolin was attenuated with (S)albuterol. Treatment of the cells for 24 hours with (S)-albuterol significantly increased [Ca2+](i) on stimulation with methacholine. Interestingly, the effect of (R)-albuterol was opposite to that of (S)-albuterol. The effect of the racemic albuterol in some cases was similar to that of (S)-albuterol. (S)-Albuterol significantly activated both PI3 kinase and NF-kappaB in hBSMCs. Conclusion: These studies demonstrated an (S)albuterol-induced increase in the expression and activity of pro-constrictory pathways involving G(ialpha-1) protein and [Ca2+](i) and a decrease in the activity of the bronchodilatory pathway involving G(s) proteins in hBSMCs. Additionally, (S)-albuterol activated proinflammatory pathways involving PI3 kinase and NF-kappaB. Because (S)-albuterol metabolizes at least 10-fold slower than (R)-albuterol and has a longer elimination half-life, these cellular effects of (S)-albuterol might explain the detrimental effect seen with chronic administration of racemic albuterol in the treatment of airway diseases, such as bronchial asthma.