Effect of caffeine on hyperoxic lung injury of premature rats and its relationship with p38 motigen-activated protein kinase signal pathway

Abstract

Objective To study the effect of caffeine on hyperoxic lung injury of premature rats and its relationship with p38 motigen-activated protein kinase(MAPK) signal pathway. Methods Sixty Wistar premature rats were divided into 4 groups(n=15) according to the random number table: air + normal saline group(A+ N group), air + caffeine group(A+ C group), hyperoxia + normal saline group(H+ N group), and hyperoxia + caffeine group(H+ C group). Among them, H+ N group and H+ C group were continually exposed to hyperoxia(oxygen concentration was 60%~70%). For A+ C group and H+ C group, the premature rats were injected with caffeine of 29 mg/(kg·d) into their peritoneal cavities every day after birth.For A+ N group and H+ N group, the premature rats were injected with normal saline of the same volume into their peritoneal cavities.In each group, the lung tissues of 5 premature rats were randomly selected on the third, seventh and fourteenth day respectively.The pathological changes of lung tissue, radiated alveolar count(RAC) and collagen content in lung tissue were observed under a light microscope.The wet/dry ratio(W/D) was measured.Two-step immunohistochemistry was used to detect the distribution of p38MAPK in lung tissue.The content of phosphorylated p38MAPK(p-p38MAPK) protein was detected by western blot. Results Compared with the air groups, the lung tissues of premature rats in high oxygen exposure groups showed different degree of inflammatory changes on the third, seventh, and fourteenth day.The changes were more obvious with the prolonged exposure to hyperoxia.Pulmonary fibrosis was visible on the fourteenth day, which was improved after caffeine intervention.The RAC value of premature rats in hyperoxia exposure groups was significantly lower than that in air-exposure groups(P<0.05), and the W/D ratio and collagen content in lung tissue increased significantly(P<0.05), which were improved after caffeine intervention(P<0.05). The results of two-step immunohistochemistry showed that the number of p-p38MAPK positive cells in the lung tissue of premature rats in hyperoxia exposure groups increased and widely distributed, but decreased after caffeine intervention.The results of western blot showed that the content of p-p38MAPK protein in lung tissue of premature rats in hyperoxia exposure groups was significantly higher than that of air groups(P<0.05), but it decreased after caffeine intervention(P<0.05). Conclusion Hyperoxia can promote the formation of pulmonary fibrosis by activating p38MAPK signal pathway.Caffeine can interdict the expression of p38MAPK to alleviate the fibrosis of lung tissue exposed to hyperoxia and thus protects the lung tissue. Key words: Hyperoxia; Lung injury; Caffeine; p38 motigen-activated protein kinase; Premature rats