Protective effects of diallyl sulfide on pulmonary oxidative damage and the underlying molecular mechanisms

• Main Authors: Cheng-Ying Ho, 何承穎
• Other Authors: 顏國欽
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/27407180270822594826

博士 === 國立中興大學 === 食品暨應用生物科技學系所 === 103 === The lung is constantly challenged with oxidative damage due to gas exchange and exposure to exogenous air pollutants. Oxidative stress-aggravated chronic inflammatory diseases of the airway are well documented. Although the lung has a well-developed antioxidant system to protect itself against exposure to endogenous or exogenous oxidants, excessive levels of ROS can still cause inflammation in the lung. Treatment with antioxidants to ameliorate oxidative stress might be an effective strategy to reduce airway complications. Diallyl sulfide (DAS), which is enriched in garlic, is one of the natural organosulfuric compounds that are beneficial to human health. The aim of this study was to evaluate the anti-inflammatory and immunomodulation effects and mechanism of DAS in pulmonary disorders. Nuclear factor-erythroid 2 related factor 2 (Nrf2) is a redox sensitive transcription factor, which binds to an antioxidant response element (ARE) in the promoter region of genes encoding several phase-II detoxifying/antioxidant enzymes and related stress-responsive proteins. In this study, we first investigated the promotive role of DAS in lung by evaluating the effect of DAS on expressions of antioxidant enzymes in vivo and the Nrf2 modulation in vitro in normal condition. DAS at a dosage of 500 mg/kg body weight significantly increased the pulmonic total level of Nrf2 and nuclear translocation of Nrf2. The mRNA levels of heme oxygenase-1, catalase, superoxide dismutase, glutathione peroxidase and NAD(P)H:quinone oxidoreductase 1, and GSH/GSSG ratio were also elevated. DAS level was measured in the plasma after 7 days of oral administration, and the Cmax value was 15 ± 4.2 μM. Furthermore, DAS could induce nuclear translocation of Nrf2 via extracellular signal-regulated kinase (ERK)/p38 signaling pathway in human embryonic lung fibroblasts MRC-5 cells. Our results demonstrate that DAS administration can significantly induce antioxidant enzymes in rat lung, and gives scientific support to the possible use of DAS as a dietary preventive agent against oxidative stress-induced lung injury. Due to the inflammatory events can be inhibited via a reduction in oxidative stress by antioxidant enzymes, thus, we further investigated the inhibitory effect of DAS on TNF-α- or histamine induced inflammation in rat aortic smooth muscle A7r5 cells and explored the molecular mechanism underlying this inhibition. DAS significantly blocked the accumulation of the nuclear p65 protein in TNF-α-induced rat aortic smooth muscle A7r5 cells by attenuating TNF-α receptor complex through the dissociation of the TNF receptor-associated death domain and TNF receptor-associated factor 2. Moreover, DAS inhibited histamine-induced inflammation through decreasing ROS levels by enhancing the Nrf2-related antioxidative enzyme. DAS also inhibited inflammation by suppressing interleukin-1β and TNF-α through the inhibition of ROS-induced PI3K/Akt and the downstream nuclear factor-κB (NF-κB) and activator protein 1. Our results demonstrate that DAS is a potential phytochemical to inhibit TNF-α- and histamine-induced inflammation, suggesting that DAS might be an effective dietary agent for the prevention of oxidative stress-induced inflammation of the airway. We next investigated the protective effect and mechanism of DAS against ovalbumin (OVA)-induced allergic asthma in an animal model. DAS markedly decreased the number of infiltrated inflammatory cells and the levels of type 2 T-helper cell (Th2) cytokines in bronchoalveolar lavage (BAL) fluid. The OVA-specific immunoglobin E levels in sera were also reduced by DAS. The report of lung histopathological examinations showed that the OVA-induced inflammatory cell infiltration and mucus hypersecretion were inhibited by DAS administration. Also, increased generation of ROS, 8-iso-prostaglandin F2 α and 8-hydroxy-2''-deoxyguanosine in BAL fluid as well as NF-κB nuclear translocation in lungs, by inhalation of OVA was diminished by DAS. Moreover, DAS enhanced the OVA-induced downregulation of Nrf2 activation and antioxidant enzyme mRNA levels. We further found that DAS-modulated Nrf2 activation was through regulating microRNA-144, -34a and -34b/c. These findings indicate that the pathogenesis of OVA-induced bronchial asthma is highly associated with oxidative stress, and DAS may be an effective supplementation to alleviate the disease. Excessive levels of ROS impair the cellular redox level, abnormal production of collagen and induction of extracellular matrix (ECM) accumulation, which resulting in pulmonary fibrosis. We finally investigated the effect and molecular mechanism DAS on the inhibition of transforming growth factor-beta (TGF-β)-induced fibrosis in MRC-5 cells. The results showed that DAS significantly suppressed the production of collagen in TGF-β-induced MRC-5 cells by attenuating Sma and Mad homologue (Smad) 2/3 phosphorylation through enhancing HO-1 levels. Moreover, DAS inhibited TGF-β-induced myofibroblast formation by decreasing ROS through enhancing Nrf2-related antioxidative enzyme and by promoting myofibroblast apoptosis. Our results demonstrate that DAS is a potential phytochemical to inhibit TGF-β-induced fibrosis, which suggesting that DAS might be a dietary agent to prevent oxidative stress-induced pulmonary fibrosis. This study reveals for the first time that garlic organosulfuric compound possess the promoting effect of Nrf2 activation, and the immunomodulating effects. It suggests that DAS supplementation may be useful as an adjuvant therapy for the treatment of pulmonary disorder involved bronchial asthma and pulmonary fibrosis.