Ulinastatin enhances autophagy against radiation-induced lung injury in mice

BACKGROUND: To investigate the enhancement of autophagy by ulinastatin for protecting against radiation-induced lung injury (RILI) in mice. METHODS: Forty C57BL/6 mice were equally divided into (I) control (C), (II) irradiation (R), (III) ulinastatin (U), (IV) 3-methyladenine (3-MA) (M), and (V) ulinastatin plus 3-MA (U+M) groups. Three mice in each group were infected with adeno-associated virus (AAV) carrying green fluorescent protein (GFP)-1A/1B-light chain 3 (GFP-LC3) in the lung for the marker of autophagy. All mice in R, U, M and U+M groups were given chest irradiation (1 Gy/min, 12 min), following injection with normal saline in C and U groups, ulinastatin (500,000 IU/kg·d, i.p., 7 d) in U group, 3-MA (10 mg/kg·d, i.p., 7 d) in M group, and ulinastatin plus 3-MA in U+M group. The effects of ulinastatin on lung injury and autophagy were evaluated by electron microscope (EM), immunohistochemistry, mRNA expression levels of collagen alpha-1 (COL1A1), collagen alpha-2 (COL1A2), α-smooth muscle actin (α-SMA) and transforming growth factor β1 (TGF-β1), and protein levels of LC3, α-SMA, COL1A2, TGF-β1, matrix metalloproteinase-2 (MMP-2) and MMP-9. RESULTS: EM observation revealed that the radiation caused the injury of type I and II alveolar epithelial cells, which was improved by ulinastatin treatment associated with increased the numbers of autophagosomes. GFP-LC3 signals was significantly enhanced by ulinastatin detected by immune histochemical tests. At transcriptional and/or translational levels, ulinastatin significantly enhanced the expression levels of TGF-β1 and LC3 but reduced COL1A1, COL1A2, α-SMA, MMP-2 and MMP-9 after radiation-induced RILI. CONCLUSIONS: Ulinastatin reduces RILI by enhancing autophagy, which might be a potential therapeutic drug in the protection against RILI.