Human amniotic mesenchymal stem cells alleviate paraquat-induced pulmonary fibrosis in rats by inhibiting the inflammatory response

Abstract

Aims

To investigate the therapeutic effects of human amniotic mesenchymal stem cells (hAMSCs) on paraquat (PQ)-induced pulmonary fibrosis in rats and investigate the inflammatory mechanisms.

Main methods

hAMSCs were identified by morphological, flow cytometry and immunocytochemistry. A pulmonary fibrosis model was induced by administering PQ to rats. The hAMSCs group was treated with hAMSCs after 6 h of PQ poisoning. At 21 days after hAMSCs transplantation, lungs were harvested for H&E, Masson and immunohistochemical staining to evaluate pulmonary histopathology, collagen deposition, CD3+ cell infiltration and hAMSCs colonization. Arterial blood was used for lactic acid analysis and venous blood was used to detect TNF-α, IL-6, and TGF-β1 by ELISA method.

Key findings

hAMSCs can improve the lung structure and decrease collagen deposition induced by PQ. The membranes of CD3+ T cell in the PQ group were round and complete, while that in the hAMSCs group rats exhibited punctate or diffuse staining. In addition, the CD3+ cell was decreased by hAMSCs administration, and MAB1281-positive cells were detected in lung of hAMSCs group rats. The survival rate of the hAMSCs group was significantly higher than that of the PQ group at 21 days after injection. TNF-α, IL-6, TGF-β1 and lactic acid were significantly decreased by hAMSCs administration.

Significance

hAMSCs have a significant therapeutic effect on pulmonary fibrosis induced by acute PQ poisoning and can improve survival rate in rats. Furthermore, hAMSCs administration can improve lung histopathology and reduce collagen deposition by reducing inflammatory CD3+ T cell infiltration, inflammatory cytokine expression and lactic acid levels.

Introduction

Paraquat (1,1′-dimethyl-4,4′-bipyridinium dichloride; PQ) is a kind of herbicide widely used in China. PQ is a common cause of death by pesticide poisoning in developing countries. A 5- to 15-ml water solution containing 20% PQ (20–40 mg/kg) can cause death in adults, with a mortality rate of up to 80%. PQ absorbed through the digestive tract can cause damage to multiple organs, primarily the lungs, which can cause acute pulmonary inflammatory infiltration and rapid fibrosis development [[1], [2], [3]]. PQ can produce superoxide anions, resulting in lipid peroxidation, nuclear factor-κB activation, mitochondrial damage and apoptosis, which ultimately lead to lung injury and fibrosis. Presently, there are no clinically curative treatments except for gastric lavage, blood purification, immunosuppressive agent administration and lung transplantation [4,5].

In recent years, the therapeutic value of stem cell drugs for major diseases has been suggested [1]. Mesenchymal stem cells (MSCs) are pluripotent stem cells derived from the mesoderm that can differentiate into multiple mesenchymal lineages, such as chondrocytes, osteoblasts and adipocytes. The International Society for Cellular Therapy suggests defining MSCs on isolation by (i) their adherence to plastic; (ii) their expression of CD73, CD90 and CD105 on the cell surface; and (iii) the absence of several hematopoietic and endothelial markers [6]. MSCs have the potential to repair injured tissues by secreting growth factors and anti-inflammatory molecules, and MSCs derived from the bone marrow have been proven to be effective in the treatment of acute and chronic liver injury, acute myocardial infarction, spinal cord injury and autoimmune disease [[7], [8], [9]]. Recent studies have shown that umbilical cord-derived MSCs and amniotic epithelial cells (hAECs) can be used to prevent and treat pulmonary fibrosis induced by bleomycin in mice [[10], [11], [12]]. Human amniotic mesenchymal stem cells (hAMSCs) and hAECs are both derived from the human placenta chorion, which is generally discarded as medical waste, and have relatively few ethical issues [13]. hAMSCs and bone marrow MSCs have many similar biological characteristics, and normal bone marrow is relatively difficult to access as a tissue source for MSC isolation [14]. Because of the advantages of convenient access, low immunogenicity, strong proliferative ability and an increased original cell number for hAMSCs, these cells may be used widely in therapies for different diseases [15]. In regard to the current study, hAMSCs have not been studied in the treatment of acute pulmonary fibrosis caused by PQ poisoning. Therefore, in our study, pulmonary fibrosis induced by PQ in rats was established to investigate the therapeutic effect of hAMSCs transplantation. At the same time, the related inflammatory mechanisms involved in PQ pulmonary fibrosis were also investigated.