Albuterol Isomers Modulate Platelet-Activating Factor Synthesis and Receptor Signaling in Human Bronchial Smooth Muscle Cells

Abstract

Background: 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. Methods: PAF binding and inositol phosphate (IP₃) 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. Results: 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 IP₃ 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 IP₃ release. (S)-albuterol stimulated PAFr protein expression. With PAF metabolism, (S)-albuterol treatment augmented PAF synthesis, but significantly inhibited PAF catabolism. Conclusions: 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.

Platelet-activating factor synthesis and receptor-mediated signaling are downregulated in ovine newborn lungs: relevance in postnatal pulmonary adaptation and persistent pulmonary hypertension of the newborn

“…TLC bands of the C-14-choline-PAF were scraped off, re-extracted and further purified by high-performance liquid chromatography, as we had reported previously, 9 and quantified by scintillation spectrometry with tritium and carbon-14 windows (Beckman LS 6500). Functional assessment of the purified radiolabeled PAF synthesized from the perinatal lamb lung membrane proteins was tested for bioactivity by the serotonin release method 25 with modifications, as we had recently reported, 26 and then normalized to tissue weight.…”

“…Functional assessment of the purified radiolabeled PAF synthesized from the perinatal lamb lung membrane proteins was tested for bioactivity by the serotonin release method 25 with modifications, as we had recently reported, 26 and then normalized to tissue weight.…”

“…Measurement of activity of the purified PAF PAF synthesized by perinatal lung parenchyma and pulmonary vessels was tested for biological activity after TLC and HPLC purification by the method of serotonin release using washed rabbit platelets with a modification of the method reported by Pinckard et al, 25 as we had previously reported. 26 In this quantification assay, authentic PAF standards were not added to the samples before lipid extraction or purification processes. Briefly, a calibration curve of 0.01 nM to 10.0 mM of authentic PAF in Tyrode's buffer was generated, and then the concentration of the purified PAF sample extracts in Tyrode's buffer (0.1 ml) was determined from the standard curve.…”

Lipid Mediators of Allergic Disease: Pathways, Treatments, and Emerging Therapeutic Targets

“…In addition, PAF has a proposed role in airway remodeling including specific effects on smooth muscle proliferation. A provocative recent report indicated that short acting beta 2 agonist (SABA) bronchodilators induce PAF release, possibly contributing to long-term airway inflammation and smooth muscle changes [21]. …”

Levosalbutamol as alternative to drugs on the basis of racemic salbutamol: Review of the results of pre-clinical research

“…Позднее упомянутой группой исследователей установлено, что S-сальбутамол может время-зависимо увеличивать связывание PAF с рецептором, коррелирующее с выбросом инозитолтрифосфата, в то время как левосальбутамол и рацемат не оказывают значимых эффектов. Более того, S-сальбутамол интенсифицирует синтез PAF и подавляет его катаболизм (Bae et al, 2012). PAF является важнейшим провоспалительным липидным медиатором, активно вовлекающимся в процессы развития аллергии и воспаления в легких (Roth et al, 1996;Honda et al, 2002).…”