Laminarin protects against hydrogen peroxide-induced oxidative damage in MRC-5 cells possibly via regulating NRF2.

Xue Liu,Yan Li,Wei Zhang,Huaman Liu,Yi Zhai,Xue Zhu

doi:10.7717/peerj.3642

Abstract

Oxidative damage is a major cause of lung diseases, including pulmonary fibrosis. Laminarin is a kind of polysaccharide extracted from brown algae and plays vital roles in various biological processes. However, the functions and mechanisms of laminarin in pulmonary oxidative damage are poorly understood. This study aimed at investigating the protective effect of laminarin against pulmonary oxidative damage and underlying mechanisms. Human lung fibroblasts MRC-5 cells were treated with hydrogen peroxide to induce oxidative damage. Laminarin treatment was performed before or after hydrogen peroxide treatment, and then major indexes of oxidative damage, including superoxide dismutase (SOD), malondialdehyde (MDA), reduced glutathione (GSH) and catalase (CAT), were quantified by biochemical assays. The expression of oxidation-related factor, nuclear factor erythroid 2 like 2 (NRF2) was analyzed by qPCR, Western blot and immunofluorescence assay. NRF2 knockdown and overexpression were performed by cell transfection to reveal possible mechanisms. Results showed that laminarin treatment of 0.020 mg/mL for 24 h, especially the pre-treatment, could significantly relieve changes in SOD, MDA, GSH and CAT that were altered by hydrogen peroxide, and promote NRF2 mRNA (P < 0.001). NRF2 protein was also elevated by laminarin, and nuclear translocation was observed. Factors in NRF2 signaling pathways, including KEAP1, NQO1, GCLC and HO1, were all regulated by laminarin. Roles of NRF2 were tested, suggesting that NRF2 regulated the concentration of SOD, MDA, GSH and CAT, suppressed KEAP1, and promoted NQO1, GCLC and HO1. These findings suggested the protective role of laminarin against pulmonary oxidative damage, which might involve the regulation of NRF2 signaling pathways. This study provided information for the clinical application of laminarin to pulmonary diseases like pulmonary fibrosis.

Highlights

As one of the vital respiratory organs of human, lungs play important roles in gas exchange as well as excretion, fluid exchange, regulation of acid–base balance and other biological processes
The aim of this study is to investigate the function of laminarin in hydrogen peroxideinduced pulmonary oxidative damage by nuclear factor erythroid 2 like 2 (NRF2)/antioxidant response element (ARE) signaling pathway
It was found that laminarin possessed strong antioxidant activity against hydroxyl free radical, and it had the similar consequence with Vitamin C (Vc) (Fig. S1A)

Summary

Introduction

As one of the vital respiratory organs of human, lungs play important roles in gas exchange as well as excretion, fluid exchange, regulation of acid–base balance and other biological processes. Oxides in lungs mainly derive from systemic circulation, gas inhalation and the pathological processes of the body. The enhancive oxygen consumption during respiratory burst induces the production of several oxides or enzyme like myeloperoxidase, hypochlorous acid and hydrogen peroxide, which oxidize sulfhydryl groups and cause cellular membrane damage (Goraca & Józefowicz-Okonkwo, 2007). Ozone inhalation may lead to inflammation and pulmonary oxidative damage, mediating the activity of factors such as toll-like receptor 4 (Connor, Laskin & Laskin, 2012; Li et al, 2011). Cigarette smoke activates the production of nitric oxide, further aggravating pulmonary oxidative damage (Ren et al, 2000; Turanlahti et al, 2000)

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