(A) Plots of dose (AuNP mg/L) versus intracellular lipid peroxidase activity in Ap/En cells (% of control) at day 16. A 5 to 60 mg/L dose of all AuNPs exhibited comparable response. Only 100 mg/L dose caused significant but variable increase in enzyme activity (AuNPKG-50 exhibited lowest, while AuNPG-50 exhibited highest activity in response to 100 mg/L dose). Values are mean ± SD; (B) Plots of dose (AuNP mg/L) versus intracellular lipid peroxidase activity in Ap/Ep cells (% of control) at day 16. Different AuNPs yielded variable response, but maximum protection was provided by AuNPKG-50 at 20 to 60 mg/L dose. Values are mean ± SD. *: p < 0.05 when Ap/En or Ap/Ep values were compared with An/En values. X, # or @: p < 0.05, when enzyme activity of Ap/Ep cells exposed to a given dose of and AuNP compared with enzyme activity of Ap/Ep cells exposed to the same dose of other AuNPs; (C) The time course of change in enzyme activity of Ap/En (broken line) and Ap/Ep (solid line) cell pre-exposed to a 20 mg/L dose of AuNPKG-50. *: p < 0.05 when exposed to day 0 values, and x: p < 0.05 when Ap/En and Ap/Ep values were compared at each time interval.