Effect of NAC on arsenic-induced gene expression. (A-B) Certain arsenic-induced gene expression changes can be blunted by at least 50% with NAC cotreatment (reversed). There are also genes whose expression is altered by arsenic but that remain unaffected by NAC (not reversed). Some genes were responsive (more than 2-fold) to NAC alone without arsenic and hence were categorized as being “not informative.” Values are averages of triplicates. Independent experiments were performed at least twice with similar results. (C) Schematic diagram showing that 6 of 26 genes tested are directly related to ROS production (common area of the 3 circles). Blue highlights down-regulated genes, and red highlights up-regulated genes by arsenic treatment. The 9 genes in the area common to the red and blue circles denote those with consensus change of expression after treatment with arsenic or hydrogen peroxide. The 12 genes in the area common to the red and black circles are those whose expression change after arsenic treatment could be reversed by NAC.