Pulmonary toxicity and global gene expression changes in response to sub-chronic inhalation exposure to crystalline silica in rats

Exposure to crystalline silica results in serious adverse health effects, most notably, silicosis. An understanding of the mechanism(s) underlying silica-induced pulmonary toxicity is critical for the intervention and/or prevention of its adverse health effects. Rats were exposed by inhalation to crystalline silica at a concentration of 15 mg/m³, 6 hr/day, 5 days/week for 3, 6 or 12 weeks. Pulmonary toxicity and global gene expression profiles were determined in lungs at the end of each exposure period. Crystalline silica was visible in lungs of rats especially in the 12-week group. Pulmonary toxicity, as evidenced by an increase in lactate dehydrogenase (LDH) activity and albumin content and accumulation of macrophages and neutrophils in the bronchoalveolar lavage (BAL), was seen in animals depending upon silica exposure duration. The most severe histological changes, noted in the 12-week exposure group, consisted of chronic active inflammation, type II pneumocyte hyperplasia, and fibrosis. Microarray analysis of lung gene expression profiles detected significant differential expression of 38, 77, and 99 genes in rats exposed to silica for 3-, 6-, or 12-weeks, respectively, compared to time-matched controls. Among the significantly differentially expressed genes (SDEG), 32 genes were common in all exposure groups. Bioinformatics analysis of the SDEG identified enrichment of functions, networks and canonical pathways related to inflammation, cancer, oxidative stress, fibrosis, and tissue remodeling in response to silica exposure. Collectively, these results provided insights into the molecular mechanisms underlying pulmonary toxicity following sub-chronic inhalation exposure to crystalline silica in rats.

接触结晶型二氧化硅会引发严重的有害健康效应，其中最为突出的是矽肺病（silicosis）。阐明二氧化硅诱导肺毒性的潜在机制，对于干预乃至预防其健康危害至关重要。本研究采用吸入暴露方式，将大鼠暴露于浓度为15 mg/m³的结晶型二氧化硅环境中，每日暴露6小时、每周5天，分别持续3、6或12周。在每个暴露周期结束时，检测大鼠肺部的肺毒性情况，并分析其全基因组表达谱。大鼠肺部可见结晶型二氧化硅沉积，尤以12周暴露组最为显著。根据暴露时长的不同，实验动物出现了程度不一的肺毒性，表现为乳酸脱氢酶（lactate dehydrogenase, LDH）活性升高、白蛋白含量增加，以及支气管肺泡灌洗液（bronchoalveolar lavage, BAL）中巨噬细胞与中性粒细胞的聚集。12周暴露组可见最为严重的组织病理学改变，包括慢性活动性炎症、Ⅱ型肺泡上皮细胞增生以及纤维化。基因芯片（microarray）分析结果显示，与时间匹配的对照组相比，分别暴露3、6、12周的大鼠肺部分别有38、77和99个基因出现显著差异表达。在上述显著差异表达基因（significantly differentially expressed genes, SDEG）中，有32个基因在所有暴露组中均存在差异表达。对显著差异表达基因进行生物信息学富集分析，发现其功能、调控网络及经典通路显著富集于炎症反应、肿瘤发生、氧化应激、纤维化与组织重塑等与二氧化硅暴露相关的生物学过程。综上，本研究结果为阐明大鼠经亚慢性吸入暴露结晶型二氧化硅后肺毒性的分子机制提供了重要见解。