Effects Of Erythromycin On Expression Of Smad3,Smad7 In Lung Fibroblasts From Rats Treated With Paraquat

Backgroud and objective: Paraquat intoxication is a common cause of death among intoxed patients. Due to the lack of an antidote or effective treatment, there is a high mortality of the paraquat-intoxicated patients. Severe paraquat intoxication is characterized by multiple organ failure, and the lungs are the most important target organs. The lungs present with early persistent alveolitis followed by later progressively pulmonary fibrosis. TGF-β/Smad signaling plays an important role in the process of pulmonary fibrosis. It has been indicated that some of macrolides including erythro-mycin have the property of anti-imflammatory independent of anti-microbial activity. The present study was undertaken to investigate the anti-fibrotic effects of erythromycin on an experimental model of paraquat-induced lung fibrosis in rats.Methods: Thirty SD rats were randomized to six groups: control group, paraquat group, erythromycin group, PQ+EM pre-treatment group, PQ+EM syn-treatment group and PQ+EM post-treatment group. PQ was intragastrically administraed at a dose of 80 mg/kg for once to the rats in all groups except for the NS and EM groups on day 0. EM was intragastrically administraed at a dose of 50 mg/kg once a day to the rats in EM group, PQ+EM pre-treatment group, PQ+EM syn-treatment group and PQ+EM post-treatment group from day 0, -3, 0, 7 to day 21 respectively. The rats in the NS group were intragastrically administraed equivalent volume of normal saline once a day. All the animals were sacrificed on day 21, and the lung specimens were obtained. The right upper lung was resected for measurement of collagen, the right lower lung was assessed histologically. The left lung was obtained to establish primary lung fibroblasts culture. MTT method and hydroxyproline alkaline hydrolysis were applied to evaluate the fibroblasts proliferation and collagen production respectively. Immunohistochemistry was applied to detect Smad3, Smad7. In situ hybridization was applied to detect Smad3 mRNA, Smad7 mRNA.Results: The area of alveolar septum and collagen in the lungs as well as the lung fibroblasts proliferation and collagen production increased in PQ group which were attenuated by erythromycin. There was no statistical significance between PQ+EM syn-treatment group and PQ+EM post-treatment group. Smad7, Smad7 mRNA expression were inhibited in PQ group, which were not affected by erythromycin. The expression of Smad3 mRNA was inhibited in PQ group but was enhanced by EM. The expression of Smad3 in plasma in PQ group was attenuated while in nucleus enhanced. Erythromycin inhibited Smad3 expression in nucleus but enhanced the expression in plasma. The change in PQ+EM pre-treatment group was the most obvious, while there was no statistical significance between PQ+EM syn-treatment group and PQ+EM post-treatment group.Conclusions: The lung fibroblasts proliferation and collagen production increased in paraquat intoxed rats, and Smad7, Smad7 mRNA, Smad3 mRNA expression were inhibited. The expression of Smad3 in plasma in paraquat intoxed rats was attenuated while in nucleus enhanced. Erythromycin can prevent lung fibrosis induced by paraquat, which might due to influce the signaling mediated by Smad3, and then inhibit the lung fibroblasts proliferation and collagen production.