Cigarette smoke exposure potentiates bleomycin-induced lung fibrosis in guinea pigs

Abstract

The role of tobacco smoking in the development and outcome of pulmonary fibrosis is uncertain. To approach the effects of cigarette smoke on bleomycin-induced lung fibrosis, we studied five groups of guinea pigs: 1) controls, 2) instilled with bleomycin (B), 3) exposed to tobacco smoke for 6 wk (TS), 4) bleomycin instillation plus tobacco smoke exposure for 6 wk (B+TS), and 5) tobacco smoke exposure for 6 wk and bleomycin after smoking (TS/B). Guinea pigs receiving bleomycin and tobacco smoke exposure exhibited higher fibrotic lesions including a significant increase in the number of positive α-smooth muscle actin cells compared with bleomycin alone (B+TS, 3.4 ± 1.2%; TS/B, 3.7 ± 1.5%; B, 2.3 ± 1.5%; P < 0.01). However, only the TS/B group reached a significant increase in lung collagen compared with the bleomycin group (TS/B, 3.5 ± 0.7; B ± TS, 2.9 ± 0.4; B, 2.4 ± 0.2 mg hydroxyproline/lung; P < 0.01). Bronchoalveolar lavage (BAL) from TS/B showed an increased number of eosinophils and higher levels of IL-4 and tissue inhibitor of metalloproteinase-2 ( P < 0.01 for all comparisons) and induced a significant increase in fibroblast proliferation ( P < 0.05). Importantly, smoke exposure alone induced an increase in BAL neutrophils, matrix metalloproteinase-9, and fibroblast proliferation compared with controls, suggesting that tobacco smoke creates a profibrotic milieu that may contribute to the increased bleomycin-induced fibrosis.