Exposure of airway epithelium to bile acids associated with gastroesophageal reflux symptoms: a relation to transforming growth factor-beta1 production and fibroblast proliferation.
BACKGROUND
Gastroesophageal reflux (GER) is common in patients with various airway diseases. Airway epithelial cells can release growth factors that promote fibroblast proliferation. Exposure of airway epithelium to bile acids may induce a fibrotic response.


OBJECTIVE
To determine how bile acids interact with airway epithelium; particularly, whether transforming growth factor-beta1 secretion and fibroblast proliferation are affected.


METHODS
Induced sputum from patients with asthma, GER, or asthma associated with GER symptoms, or from healthy control subjects was collected. Total bile acids were measured by a spectrophotometric enzymatic assay. The major components of bile acids, chenodeoxycholic acid (CD) and glycochenodeoxycholic acid (GCD), were used to stimulate primary airway epithelial cells. Quantitative polymerase chain reaction and Western blotting were applied for messenger RNA expression and signal pathway analysis, respectively. Conditioned medium following CD stimulation was coincubated with fibroblasts for proliferation study.


RESULTS
The amount of total bile acids in induced sputum was significantly higher in patients with GER and asthma-associated GER symptoms compared to that of healthy control subjects (p<0.005). CD, but not GCD, significantly induced TGF-beta1 production. TGF-beta1 messenger RNA expression was 2.5-fold increased compared to unstimulated cells. This occurred via p38 mitogen-activated protein (MAP) kinase and activating transcription factor-2 activation. Pretreatment with dexamethasone inhibited TGF-beta1 production at both messenger RNA and protein levels by inhibiting p38 MAP kinase phosphorylation. Conditioned medium from CD-treated epithelial cells enhanced fibroblast proliferation.


CONCLUSIONS
Aspiration of bile acids may induce airway fibrosis through the production of TGF-beta1 and fibroblast proliferation. Early intervention to attenuate these processes may reduce fibrogenesis in various airway diseases associated with GER.
Perng
Diahn-Warng
DW
Department of Chest Medicine, Taipei Veterans General Hospital and School of Medicine, Nathional Yang-Ming University, 201, Section 2, Shih-Pai Rd, Taipei 11217, Taiwan. dwperng@vghtpe.gov.tw
Chang
Kuo-Ting
KT
Su
Kang-Cheng
KC
Wu
Yu-Chung
YC
Wu
Mo-Tzu
MT
Hsu
Wen-Hu
WH
Tsai
Chun-Ming
CM
Lee
Yu-Chin
YC
D000704:Analysis of Variance; D001249:Asthma / Q000150:complications* / Q000473:pathology / Q000503:physiopathology; D001647:Bile Acids and Salts; D015153:Blotting, Western; D016022:Case-Control Studies; D049109:Cell Proliferation; D017077:Culture Media, Conditioned; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D005260:Female; D005347:Fibroblasts; D005355:Fibrosis / Q000473:pathology / Q000503:physiopathology; D005764:Gastroesophageal Reflux / Q000150:complications* / Q000473:pathology / Q000503:physiopathology; D006801:Humans; D020935:MAP Kinase Signaling System / Q000502:physiology; D008297:Male; D008875:Middle Aged; D020545:Respiratory Mucosa / Q000166:cytology / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D018709:Statistics, Nonparametric; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D001647:Bile Acids and Salts; D017077:Culture Media, Conditioned; D053773:Transforming Growth Factor beta1; D048051:p38 Mitogen-Activated Protein Kinases