Genotoxicity Of Cement Dust Alone And The Combination With BaP

Cement is one of the most important building materials in the world. There are a great variety of cement. Among them Portland cement is most widely used. Cement manufacture is one of the sources of industrial dust. Exposure of humans to cement dust in production and use causes adverse effects on the upper respiratory tract, including airway obstruction and malignant tumor, specifically larynx carcinomas In contrast, some studies indicated that exposure of human to cement dust had no health effects on the respiratory tract. Because of a lack of toxicological publications on cement dust, two questions are uncertain and waiting for the explanation: 1) whether cement dust has carcinogenicity and 2) if yes, what is the mechanism of respiratory tract carcinogenesis of cement dust, especially laryngeal cancers?It was reported that the relative risk for larynx carcinoma in cement workers was increased with their smoking habits. Whether we can explain this phenomenon by the synergistic effect between cement dust and smoking? Benzo[a]pyrene is one of the most typical carcinogens in cigarettes smoking and one of the polycyclic aromatic hydrocarbons (PAH) which were discovered as carcinogens earliest. Because occupational co-exposure to cement dust and BaP may induce complex influence on health, in the present study, we exposed the target cells to BaP and cement dust alone or together to investigate the genotoxicity caused by cement dust and BaP alone or combined action.Considering the fact that the alveolar epithelium is probably the mostly common position of cement dust exposure in the respiratory tract, so in the first part of this research, human lung epithelial carcinoma cells (A549 cells) were used as target cells. The micronuclei test and comet assay were applied to evaluate the genotoxic effect of cement dust in A549 cells and to investigate whether cement dust can enhance BaP-induced genotoxicity. Based on studies that building and construction workers were at higher risk for developing laryngeal carcinoma than other cancers in upper respiratory tract, the region of pharynx oralis may be more sensitive to cement dust than the other part of the upper respiratory tract. Therefore, in the second part of this research, human epithelial oropharyngeal cells, which were derived from the healthy throat tissue of patients with or without laryngeal cancer, were used as target cells to evaluate the genotoxicity of cement dust in human epithelial oropharyngeal cells by comet assay.This paper is consisted of two parts:Part IGenotoxic effect of cement dust alone and its combination with BaP in A549 cells Portland cement (cement dust A), portland cement pozzolan dust (cement dust B) and BaP were selected as test substances. A549 cells were treated with the cement dust A and cement dust B (50, 100, 200μg/cm2), and BaP (25μmol/l) alone or together for 48 h, respectively. In the experiment of substance treating alone, silica (DQ12 100μg/cm2) and titanium oxide (TiO2 200μg/cm2) were used as positive and negative controls for particles, and cell medium was used as solvent control. In the experiment of substence treating together, DMSO was used as solvent control. The cytokinesis block micronucleus (CBMN) test was used for analysis of micronucleus formation in cells. Meanwhile, micronuclei frequency and nucleus division index (NDI) were calculated. Furthermore, comet assay was used for analysis genotoxicicity of cement dust at high concentration of 200μg/cm2 by measuring the DNA Olive tail moment (OTM). Our results showed that exposure of A549 cells to the cement dusts A and B alone did not increase micronuclei frequency. High concentration of cement dust (200μg/cm2) had no significant effect on OTM. But when the cells were treated simultaneously with cement dust A (100 and 200μg/cm2) or cement dust B (200μg/cm2) with BaP (25μmol/L), micronuclei frequencies were significantly higher in combination treatment of cement dust and BaP than BaP treated alone (P<0.05). The present study indicated that cement dust is not genotoxic, but has promoting effects on BaP-induced genotoxicity in A549 cells.Part IIThe genotoxic effect of cement dust in cultivated human epithelial oropharyngeal cells Human epithelial oropharyngeal cells were isolated from the healthy tissue of the upper respiratory tract of 24 patients with laryngeal cancer and 31 patients without laryngeal cancer. The cells were identified to come from healthy tissues by biopsy. These cells were treated by cement dust A and B at concentrations of 50, 100 and 200μg/cm2. DQ12 (100μg/cm2) and TiO2 (200μg/cm2) were used as positive and negative controls for particles, respectively. Medium and BaP are also used as controls. Comet assay were applied to evaluate the DNA damage induced by cement dust in human epithelial oropharyngeal cells. Our results showed that cement dust A and B caused significant DNA damage in cultivated human epithelial oropharyngeal cells compared to cell medium control (P<0.05), depending on the sensitivity of individual cells to cement dust. No differences in DNA damage in human epithelial oropharyngeal cells could be observed between patients with and without carcinoma, which suggested that oropharyngeal cells from the persons suffered from laryngeal cancer seem to be not more sensitive to genotoxicity of cement dust than persons without laryngeal cancer (P>0.05).In summery we conclude that cement dust is genotoxic in, cultivated human epithelial oropharyngeal cells but not in A549 cells, which suggested that different kinds of cells has different sensitivity to the genotoxicity induced by cement dust. No differences in DNA damage sensitivity were observed between patients suffered from laryngeal cancer and patient without tumor. In A549 cells, Cement dust can increase BaP-induced MN frequency, which suggested that cement dust has the promoting effect on genotoxicity of BaP.