Mitogen-activated protein kinase signaling in human HepG2 cells treated with lidocaine (Lido). (A, B) Cells were treated with different concentrations of Lido (1 and 5 mM) for 3 h and with 5 mM Lido for 60, 120, and 180 min. Expression levels of mitogen-activated protein kinase (extracellular signal-regulated kinase [ERK] 1/2, p38, and c-Jun N-terminal kinase [JNK]) and their activated forms (phospho (p)-ERK1/2, p-p38, and p-JNK) were assessed by Western blot analysis and quantified using the ImageJ program. Glyceraldehyde-3-phosphate dehydogrenase (GAPDH) was used as a loading control (Con). Statistical differences were determined using a one-way ANOVA. (C) Cells were pretreated with or without the ERK1/2 inhibitor PD98059 (PD; 10 μM) or p38 inhibitor SB203580 (SB; 10 μM) for 2 h followed by exposure to Lido (5 mM) for 24 h. Expression levels of apoptosis-related proteins (caspase-3 and cleaved caspase-3) were assayed by Western blot analysis and quantified using the ImageJ program. β-actin was used as a loading Con. The image is representative of three independent experiments yielding similar results. (D) Cells were pretreated with or without the ERK1/2 inhibitor PD (10 μM) or p38 inhibitor SB (10 μM) for 2 h followed by exposure to Lido (5 mM) for 24 h. When caspase-3 was activated, chromophoric groups were freed from caspase substrates and detected with spectrophotometry. OD values obtained by spectrophotometry represent caspase-3 activity. Statistical differences were determined using a two-way ANOVA. These results are expressed as the mean ± SD of three independent experiments. *P < 0.05, **P < 0.01, and ***P < 0.001 different with the corresponding Con group; ##P < 0.01 Lido group versus Lido plus PD group or Lido plus SB group.