Association of aging with bleomycin-induced pulmonary fibrosis in rats and treatment by cyclophosphamide combined with methylprednisolone Running title: Role of MP and CTX combination in the aging of pulmonary fibrosis

Abstract

Background:Aging is a natural process characterized by a progressive functional impairment and reduced capacity to respond adaptively to environmental stimuli.Idiopathic pulmonary fibrosis(IPF)has been found to increase considerably with age.Immunosenescence,oxidative stress,abnormal shortening of telomeres, apoptosis, and epigenetic changes affecting gene expression have been proposed to contribute to the aging process,and aging-associated diseases.We used oxidative stress and immune senescence to identify the relationship between aging and pulmonary fibrosis(PF).In clinical studies,the combination of methylprednisolone(MP) and cyclophosphamide(CTX) has great benefits for patients with IPF,but the mechanisms involved in aging are not well understood. Methods:PF rat models were induced by bleomycin(BLM) and treated with MP or MP/CTX combination.Transmission electron microscope, hematoxylin and eosin (H&E) and Masson staining were used to measure the morphology of PF.Malondialdehyde(MDA),myeloperoxidase(MPO),lutathione peroxidase(GSH-PX) and superoxide dismutase(SOD) levels were determined using commercial kits.T cells were analyzed with flow cytometry. Results: We found that the combined use of MP and CTX can reduce collagen deposition,decreased the level of MDA,while increased the level of MPO and the activities of SOD and GSH-PX.Further,MP and CTX combination inhibited T cell senescence in lung tissues, such as decreasing CD4+CD27-CD28-cells. Conclusions: Aging was associated with PF.The combination of MP and CTX improved the degree of PF by reducing oxidative stress and inhibiting T cell senescence.These findings provide novel insights into the mechanisms by which MP and CTX combination affects PF.