Objective      To determine the effect of astaxanthin (AX) on bleomycin (BLM)-induced lung fibrosis in SD rats and explore the underlying mechanism. Methods     Thirty-two healthy male SD rats (weighing 200～220 g) were randomly divided into 4 groups

that is

Sham

BLM

AX

and AX+BLM groups. After intratracheal administration of BLM (5 mg/kg) or normal saline (Sham)

the rats were orally administered with AX (2 mg/kg) oil solution or vegetable oil daily for the AX group and AX+BLM group or BLM group respectively for 14 consecutive days. All rats were sacrificed in 24 h after the last administration and the lung tissues were harvested. Lung pathological changes were evaluated by lung coefficient calculation

hematoxylin-eosin staining

Masson trichrome staining and hydroxyproline assay. The expression of αSMA in the lung tissue was determined by immunohistochemical assay

and the serum level of TGFβ1 was measured by enzyme linked immunosorbent assay (ELISA). The expression of Smad2/3 and ERK1/2 in the lung tissues were determined by Western blotting. Results      Compared with the Sham and AX groups

the BLM group showed severe lung injury

with obvious formation of lung fibrosis. But the AX+BLM group had notably alleviated lung inflammation and fibrosis (P0.01)

reduced collagen deposition

decreased hydroxyproline content (P0.01)

lower expression of α-SMA

declined level of TGF-β1 (P0.05)

and decreased expression levels of Smad2/3 and p-ERK1/2. Conclusion     AX exerts obvious inhibitory effect on BLM-induced lung fibrosis

which may be related with its decreasing the TGF-β1 level and thus down-regulating Smads/ERK signaling pathway.