Clevudine attenuates bleomycin-induced early pulmonary fibrosis via regulating M2 macrophage polarization

Pulmonary fibrosis (IPF) is a chronic, progressive interstitial lung disease. It is a growing clinical problem which can result in breathlessness or respiratory failure and has an average life expectancy of 3 years from diagnosis. Predominantly accumulation of M2 macrophages accelerates fibrosis progression by secreting multiple cytokines that promote fibroblast to myofibroblast transition and aberrant wound healing of epithelial cells. Targeting activated macrophages to inhibit the pro-fibrotic phenotype is considered as an approach for the potential treatment of PF. Clevudine is s a purine nucleoside analogue which in an oral formulation is approved for treatment of patients with hepatitis B virus (HBV). Here, we found that clevudine is capable of suppressing profibrotic phenotype (i.e., CD206, Arg1 and YM1) of M2 macrophages while enhancing anti-fibrotic phenotype (i. e., CD86, IL-6 and IL-10) by inhibiting PI3K/Akt signaling pathway. This effect further alleviates M2-induced myofibroblast activation and epithelial-to-mesenchymal transition (EMT), thus resulting in a decline of collagen deposition, pro-fibrotic cytokines secretion, with a concomitant recover of pulmonary functions in vivo. Less infiltration of M2 macrophages between alpha-SMA + cells was also found in clevudine treated mice. Our findings indicate a potential anti-fibrotic effect of clevudine by regulating macrophage polarization and might be meaningful in clinical settings.