The Role Of Interleukin-1β In Silica-induced Pulmonary, Cardiac And Renal Inflammation And Fibrosis

Objectives:Silica exposure primarily occurs in workplace such as metal or coal mining, construction, and glass and clay manufacturing industries. In addition to occupational exposures, environmental exposure occurs as a result of industrial contaminations, volcanic explosions and sandstorms. Prolonged inhalation of silica is classically associated with an occupational pulmanory disease called silicosis, which has been studied extensively. Additionally, epidemiological studies showed that silica exposure can also induce cardiovascular and renal diseases. Interleukin (IL)-1β is an important pro-inflammatory cytokine. It is evidenced that IL-1β is involved in many diseases such as diabetes, arthritis and the inflammation stage of silicosis. Our previous studies showed that IL-1β could be induced by the co-culture of macrophages and silica dust. In order to explore the role of IL-1β in silicosis and silica-induced cardiac and renal damages, we designed mice experiments in our study. The main objectives of this study are as follows:(1) to explore the role of IL-1β in silicosis and to study how IL-1β exerts its function in silicosis;(2) to observe the effects of inhalational silica dust on the heart and kidney tissues of mice;(3) to assess the role of IL-1β in silica-induced cardiac and renal inflammation and fibrosis.Methods:In this study, we generated a silicosis model by intratracheally instilled standard silica dust to mice and used an anti-IL-1β monoclonal antibody (mAb) to directly neutralize the silica-induced IL-1β in the mice. A total of128mice were randomly divided into four groups as the blank control group, physiological saline group, silica group and silica+IL-1β mAb group. On days1,7,28and84after instilled treatment,8mice of each group were sacrificed and the followed indicators were measured: (1) The IL-1β consentrations in BALF and serum were measure by enzyme linked immunosorbent assay (ELISA).(2) Lungs:the lung inflammation and fibrosis were scored by histological sections which were stained with H&E and Masson, respectively; the lung injury was assessed by measuring the total protein (TP), lactate dehydrogenase (LDH) and alkaline phosphatase (AKP) levels in BALF; to evaluate the lung inflammation, the numbers of total cell, macrophage, neutrophil and lymphocyte and the levels of tumor necrosis factor-a (TNF-a) and monocyte chemoattractant protein-1(MCP-1) in BALF were measured; to evaluate the lung fibrosis, the mRNA expression levels of transforming growth factor-β (TGF-β), collagen Ⅰ and fibronectin were measured by real-time quantitative PCR; to observe the changes of Thl/Th2balance, the representive Thl cytokine such as interferon-y (IFN-y) and Th2cytokine such as IL-4in BALF were measured by ELISA.(3) Hearts:to observe the inhalational silica-induced cardiac inflammation and fibrosis, we used real-time quantitative PCR to measure the mRNA levels of inflammatory indicators (IL-1β, IL-6, TNF-a and MCP-1), fibrotic indicators (TGF-β, collagen Ⅰ, collagen Ⅲ and fibronectin) and indicators of Thl/Th2balance (IFN-y and IL-13).(4) Kidneys:to investigate the inhalational silica-induced renal inflammation and fibrosis, we used real-time quantitative PCR to measure the mRNA levels of inflammatory indicators (IL-1β, IL-6and TNF-a), fibrotic indicators (TGF-P, collagen Ⅰ, collagen Ⅲ and fibronectin) and indicators of Thl/Th2balance (IFN-y and IL-4).Results:(1) The levels of IL-1β in BALF and serum of silica+IL-1β mAb group were significantly lower than those in silica group on days7,28and84(P<0.01).(2) The pathological sections of the lung tissues stained with H&E in the silica and silica+IL-1β groups showed obvious inflammation on days1,7,28and84(P<0.01), and the pathological sections of the lung tissues stained with Masson in the silica and silica+IL-1β groups showed significant collagen deposition on days28and84(P<0.01); anti-IL-1β significantly attenuated the inflammation and fibrosis mentioned above (P<0.05).(3) The levels of TP, LDH and AKP in BALF of the silica and silica+IL-1β mAb group mice were significantly increased on days1,7,28and84(P<0.01); the usage of anti-IL-1β mAb significantly decreased the levels of the above indicators (P<0.05). (4) The numbers of total cell, macrophage, neutrophil and lymphocyte and the contents of TNF-a and MCP-1in BALF of the silica and silica+IL-1β mAb group mice were significantly increased on days1,7,28and84(P<0.01); the numbers of total cell, macrophage and lymphocyte of the silica+IL-1β mAb group mice were significantly decreased that those of the silica group mice (P<0.01); the TNF-a content was also significantly decreased by the usage of anti-IL-1β mAb on days7,28and84(P<0.05); the consentration of MCP-1in BALF of the silica+IL-1β mAb group was significantly decreased on days1and7when compared with that in the silica group (P<0.01).(5) The mRNA levels of TGF-β, collagen Ⅰ and fibronectin of the lung tissues in the silica group were significantly increased on days28and84(P<0.01); the levels of these indicators were significantly decreased by anti-IL-1β mAb (P<0.01).(6) The ratio of IFN-y/IL-4was significantly decreased in the silica exposed mice on days7,28and84(P<0.01), however, the ratio in the silica+IL-1β mAb group was significantly higher than that in the silica group (P<0.05).(7) Significantly increased mRNA expression of TNF-α, MCP-1, collagen Ⅰ and fibronectin in heart tissues were shown on days7,28and84and significantly increased mRNA expression of IL-1β and IL-6were shown on days7and28(P<0.05); neutralization of IL-1β significantly decreased the mRNA levels of IL-6, TNF-a and MCP-1(P<0.05).(8) Significantly increased mRNA levels of IL-1β, IL-6, TGF-β, collagen Ⅲ and fibronectin in kidney tissues were shown on days7,28and84and obviously increased mRNA expression of TNF-a and collagen Ⅰ were shown on days7and28(P<0.05); the usage of IL-1β antibody significantly decreased the mRNA expressions of TNF-a, TGF-β, collagen Ⅰ, collagen Ⅲ and fibronectin (P<0.05).(9) Both of the IFN-y and IL-4mRNA levels in the kidneys of silica exposed mice were increased, and when compared with that in the silica group, the IFN-y mRNA level was significantly increased in the silica+IL-1β mAb group on days28and84(P<0.05).Conclusions:(1) IL-1β plays an important role in the silicosis progression. Depletion of IL-1β could attenuate the silica-induced lung inflammation and fibrosis.(2) The inhalational silica can induce the cardiac and renal inflammatory and fibrotic responses.(3) IL-1β exerts significant effects in the inhalational silica-induced cardiac inflammation, but exerts little effects in the inhalational silica-induced cardiac fibrosis.(4) IL-1β has an important function in the inhalational silica-induced renal inflammatory and fibrotic responses.