1892
AgNPs caused ROS formation in the cells , a reduction in their cell viability and mitochondrial membrane potential ( MMP ) , an increase in the proportion of cells in the sub - G1 ( apoptosis ) population , S phase arrest and down - regulation of the cell cycle associated proliferating cell nuclear antigen ( PCNA ) protein , in a concentration - and time - dependent manner .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 None