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To understand copper - induced cytotoxicity at the molecular level , we employed several cellular and biochemical assays after exposure to copper , and found a significant induction of enzyme activities of antioxidant proteins with increased intracellular reactive oxygen species ( ROS ) as well as an increase of TUNEL - positive cells , but a decrease of BrdU - positive cells .
 Chemical: copper; Chemical: copper; Chemical: oxygen; Chemical: BrdU
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: copper; Chemical: copper; Chemical: oxygen; Chemical: BrdU