Cell culture and PM exposure
Chinese hamster ovary (CHO) cells were purchased from theCell Bank of the Chinese Academy of Medical Science(Beijing, China). Cells were grown in Dulbecco’s modifiedEagle medium (DMEM) supplemented with 10 % (v/v) fetalbovine serum (FBS) plus 2 mM L-glutamine and 1 % (v/v)penicillin-streptomycin (100 U/ml penicillin and 0.1 mg/mlstreptomycin) and incubated at 37 °C in a 5 % CO2humidifiedenvironment. PM solutions were diluted to the appropriateconcentrations with culture medium for each experiment andwere then used to treat the cells.