Fig. 2. Changes in 8-OHdG, MDA and NO contents in the lung. The contents of NO (free radical), 8-OHdG (marker of oxidative damage to DNA), and MDA (LPO marker) are significantly increased in the NiCl₂-treated groups. The letters A, B, C, and D represent a significant difference (p < 0.01) among the four groups; the letters a, b, c, and d represent a difference (p < 0.05) among the four groups.