Role of tobacco smoke on lung response to crystalline silica exposure in rats

Previous studies have shown that smoking induces oxidative stress and inflammation, known factors that coincide with the development and progression of lung toxicity in response to crystalline silica exposure. Nevertheless, the precise role of tobacco smoke exposure on the lung response to tobacco smoke exposure and the underlying mechanisms remain largely elusive. Therefore, the objective of the present study was to determine the effect of smoking, if any, on silica-induced pulmonary toxicity and the underlying molecular mechanisms. Pulmonary toxicity and lung gene expression profiles were determined in rats exposed to air, crystalline silica, tobacco smoke, or crystalline silica plus tobacco smoke. Silica exposure resulted in significant pulmonary toxicity which was further exacerbated by tobacco smoke exposure in the rats. Significant differences in the gene expression profiles were detected in the lungs of the rats exposed to tobacco smoke, silica or a combination of both compared with the air exposed control rats. Overall design: Approximately 3 months old male Fischer rats (Charles River Laboratories, Wilmington, MA) were used in this study which was conducted in an Association for Assessment and Accreditation of Laboratory Animal Care International approved animal facility (NIOSH, Morgantown, WV) following a protocol approved by the Animal Care and Use Committee. The rats were housed in groups of 3 rats/cage and maintained on a 12-hour light-dark cycle in a temperature (68-72oF) and humidity (30-70%) controlled room with free access to filtered tap water and Teklad rodent diet (Envigo, Indianapolis, IN). The rats were divided into 4 groups (n=6) and exposed to air (control) tobacco smoke (80 mg/m3, twice weekly, 12 months), crystalline silica (15 mg/m3, 6 hours/day, 5 days) or crystalline silica (15 mg/m3, 6 hours/day, 5 days) followed by tobacco smoke (80 mg/m3, twice weekly, 12 months) by whole-body inhalation. Approximately 12 months following initiation of the exposures, the rats were euthanized, and lung gene expression profiles determined by RNA sequencing. Total RNA isolated using the miRNeasy Kit (Qiagen, Inc, Valencia, CA) and next generation sequencing libraries prepared using TruSeq Stranded mRNA Library Prep Kit (Illumina, Inc, San Diego, CA) were used in the sequencing.