Inhibitory Effects of Alkaline Extract of Citrus Reticulata on Pulmonary Fibrosis

Ethnopharmacological Relevance: The pericarp of Citrus reticulata possesses medical functions of regulating Qi and expelling phlegm, and has been clinically used for the treatment of lung related diseases in traditional Chinese medicine for a long time. Our previous research revealed that Citrus reticulata exhibited inhibitory effects on pulmonary fibrosis; however, its active principles are still unclear.

Aim Of The Study: To investigate the inhibitory effects on pulmonary fibrosis of alkaline extract from ethanol extract of Citrus reticulata and clarify its possible mechanism.

Materials And Methods: The citrus alkaline extract (CAE) was prepared from ethanol extract of Citrus reticulata and MRC-5 cells were used for the evaluation of inhibitory activity in vitro. CAE was further orally administrated to bleomycin (BLM)-induced pulmonary fibrosis rats. The rat body weight, hydroxyproline levels in serum and lung, pathological changes of lung, as well as mRNA and protein expressions of matrix metalloproteinase-9 (MMP-9), tissue inhibitor of metalloproteinase-1 (TIMP-1) and tumor necrosis factor-α (TNF-α) in rat lung tissues were analyzed.

Results: CAE dose-dependently inhibited the proliferation of MRC-5 cells, and the LDH assay clearly revealed that the inhibitory activity of CAE was not due to its cytotoxicity. CAE treatment significantly increased rat weight gain, ameliorated alveolitis and pulmonary fibrosis degree, and lowered hydroxyproline contents in both serum and lung tissues. RT-PCR and western blot revealed that mRNA and protein expressions of MMP-9 were significantly elevated, while mRNA and protein levels of TIMP-1 and TNF-α were markedly decreased in lung tissues of CAE treated rats.

Conclusions: The results collectively demonstrated that CAE possessed an inhibitory activity on the proliferation of MRC-5 and a preventive effect on BLM-induced pulmonary fibrosis in rats. The preliminary mechanisms of the effects may be through upregulation of MMP-9 expression and inhibition of the expressions of TNF-α and TIMP-1.