2). was inhibited by pifithrin-, an inhibitor of p53 transcriptional activity. Furthermore, 1,3-DNP brought on an unfolded protein response (UPR), as measured by an increased expression of CHOP, ATF4 and XBP1. Thus, other types of damage possibly linked to endoplasmic reticulum (ER)-stress and/or UPR could be involved in the induced apoptosis. Our results suggest that the stronger carcinogenic potency of 1 1,8-DNP compared to 1,3-DNP is usually linked to its higher genotoxic effects. This in combination with its lower potency to induce cell death may increase the probability of causing mutations. and 0.05 was considered significant. All calculations were executed with GraphPad Prism software. 3.?Results 3.1. Cell death BEAS-2B cells and Hepa1c1c7 cells were treated with 1,3-DNP and 1,8-DNP for 24 and 72 h, or DMSO only as control. Toxicity was examined by light microscopy (data not shown) and quantified after the staining of cells with Hoechst 33342 and PI. No major cytotoxic effects were observed in BEAS-2B cells after exposure to 1,3-DNP and CB-6644 1,8-DNP (Fig. 2). In Hepa1c1c7 cells (Fig. 2), however, 1,3-DNP caused a concentration-dependent increase in cell death starting at 3 M after 24 h exposure. The induced cell death was a mixture of apoptosis and necrosis. In contrast, 1,8-DNP did not induce any significant cell death after 24 h; after 72 h increased cell death was observed at the highest concentration (30 M; Fig. 2). Open in a separate window Fig. 2 Cell death determined by fluorescence microscopy. BEAS-2B or Hepa1c1c7 cells were exposed to various concentrations of 1 1,3-DNP, 1,8-DNP or DMSO (control) for up to 72 h. Cells were stained with Hoechst 33342 and propidium iodide (PI), and subsequently analyzed for apoptosis (Ap) (including apoptotic necrotic) and necrosis (Nec) using fluorescence microscopy. The third columns in the graphs are the sums of the two first. Data presents the mean SEM of at least 3 impartial experiments. * Significantly different from DMSO-treated controls ( 0.05). 3.2. Characterization of apoptosis We further characterized the 1,3- and 1,8-DNP-induced cell death in Hepa1c1c7 cells. After exposure to various concentrations of DNPs for 24 h, CB-6644 Hepa1c1c7 cells were sampled and analyzed by Western blotting. This revealed an increased cleavage of pro-caspase 3 and PARP at 10 and 30 M 1,3-DNP (Fig. 3A), while 1,8-DNP had no effects. Further, the pan-caspase inhibitor zVAD-FMK reduced 1,3-DNP-induced apoptosis from 31% to less than 15% (Fig. 3B), but the necrosis was somewhat increased. Open in a separate window Fig. 3 Effects of 1,3-DNP and 1,8-DNP apoptosis on cell cycle distribution. Hepa1c1c7 cells were exposed to various concentrations of 1 1,3-DNP, 1,8-DNP, or DMSO (control) for 24 h. (A) Levels of PARP and caspase 3 were analyzed by Western blotting (shown is usually one representative experiment out of three individual incubations). (B) Hepa1c1c7 cells were pre-treated for 1 h with zVAD-FMK Rabbit polyclonal to IL1R2 (20 M) followed by co-exposure with 1,3-DNP (30 M) or DMSO (control) for 24 h. Percentage of cell death was estimated by fluorescence microscopy counts. Data presents the mean SEM of 3 impartial experiments. * Significantly different from DMSO-treated controls ( 0.05). #Significantly different from treatments without zVAD-FMK ( 0.05). (C) Hepa1c1c7 cells were exposed to various concentrations of 1 1,3-DNP, 1,8-DNP or DMSO (control) for 24 h. Cells were stained with Hoechst 33258 and the cell cycle distribution was measured by flow cytometer. Data is usually presented as the relative proportions of cells (%) in the different cell cycle phases. Each bar represents the mean SEM of 3 impartial experiments. *Significantly different from DMSO-treated controls ( 0.05). Effects on cell cycle were analyzed by flow cytometry after 24 h of exposure (Fig. 3C). 1,3- and 1,8-DNP (10 M) both decreased the number of cells in G1, and increased the number of cells in S phase. 1,3-DNP seemed to be slightly more potent than 1,8-DNP, and also gave a significant G2 increase even at 3 M. 3.3. Cellular mechanisms.3B), but the necrosis was somewhat increased. Open in a separate window Fig. the other hand, 1,3-DNP-induced apoptosis was inhibited by pifithrin-, an inhibitor of p53 transcriptional activity. Furthermore, 1,3-DNP brought on an unfolded protein response (UPR), as measured by an increased expression of CHOP, ATF4 and XBP1. Thus, other types of damage possibly linked to endoplasmic reticulum (ER)-stress and/or UPR could be involved in the induced apoptosis. Our results suggest that the stronger carcinogenic potency of 1 1,8-DNP compared to 1,3-DNP is usually linked to its higher genotoxic effects. This in combination with its lower potency to induce cell death may increase the probability of causing mutations. and 0.05 was considered significant. All calculations were executed with GraphPad Prism software. 3.?Results 3.1. Cell death BEAS-2B cells and Hepa1c1c7 cells were treated CB-6644 with 1,3-DNP and 1,8-DNP for 24 and 72 h, or DMSO only as control. Toxicity was examined by light microscopy (data not shown) and quantified after the staining of cells with Hoechst 33342 and PI. No major cytotoxic effects were observed in BEAS-2B cells after exposure to 1,3-DNP and 1,8-DNP (Fig. 2). In Hepa1c1c7 cells (Fig. 2), however, 1,3-DNP caused a concentration-dependent increase in cell death starting at 3 M after 24 h exposure. The induced cell death was a mixture of apoptosis and necrosis. In contrast, 1,8-DNP did not induce any significant cell death after 24 h; after 72 h increased cell death was observed at the highest concentration (30 M; Fig. 2). Open in a separate window Fig. 2 Cell death determined by fluorescence microscopy. BEAS-2B or Hepa1c1c7 cells were exposed to various concentrations of 1 1,3-DNP, 1,8-DNP or DMSO (control) for up to 72 h. Cells were stained with Hoechst 33342 and propidium iodide (PI), and subsequently analyzed for apoptosis (Ap) (including apoptotic necrotic) and necrosis (Nec) using fluorescence microscopy. The third columns in the graphs are the sums of the two first. Data presents the mean SEM of at least 3 impartial experiments. * Significantly different from DMSO-treated controls ( 0.05). 3.2. Characterization of apoptosis We further characterized the 1,3- and 1,8-DNP-induced cell death in Hepa1c1c7 cells. After exposure to various concentrations of DNPs for 24 h, Hepa1c1c7 cells were sampled and analyzed by Western blotting. This revealed an increased cleavage of pro-caspase 3 and PARP at 10 and 30 M 1,3-DNP (Fig. 3A), while 1,8-DNP had no effects. Further, the pan-caspase inhibitor zVAD-FMK reduced 1,3-DNP-induced apoptosis from 31% to less than 15% (Fig. 3B), but the necrosis was somewhat increased. Open in a separate window Fig. 3 Effects of 1,3-DNP and 1,8-DNP apoptosis on cell cycle distribution. Hepa1c1c7 cells were exposed to various concentrations of 1 1,3-DNP, 1,8-DNP, or DMSO (control) for 24 h. (A) Levels of PARP and caspase 3 were analyzed by Western blotting (shown is one representative experiment out of three separate incubations). (B) Hepa1c1c7 cells were pre-treated for 1 h with zVAD-FMK (20 M) followed by co-exposure with 1,3-DNP (30 M) or DMSO (control) for 24 h. Percentage of cell death was estimated by fluorescence microscopy counts. Data presents the mean SEM of 3 independent experiments. * Significantly different from DMSO-treated controls ( 0.05). #Significantly different from treatments CB-6644 without zVAD-FMK ( 0.05). (C) Hepa1c1c7 cells were exposed to various concentrations of 1 1,3-DNP, 1,8-DNP or DMSO (control) for 24 h. Cells were stained with Hoechst 33258 and the cell cycle distribution was measured by flow cytometer. Data is presented as the relative proportions of cells (%) in the different cell cycle phases. Each bar represents the mean SEM of 3 independent experiments. *Significantly different from DMSO-treated controls ( 0.05). Effects on cell cycle were analyzed by flow cytometry after 24 h of exposure (Fig. 3C). 1,3- and 1,8-DNP (10 M) both decreased the number of cells in G1, and increased the number of cells in S phase. 1,3-DNP seemed to be slightly more potent than 1,8-DNP, and also gave a significant G2 increase even at 3 M. 3.3. Cellular mechanisms involved in the cytotoxicity ROS may be formed during nitro-PAHs metabolism as well as during the cell death process as a result of mitochondrial damage. As it has been suggested that ROS is an important determinant both with regard to induced cytotoxicity and genotoxicity, we measured ROS formation in BEAS-2B and Hepa1c1c7 cells after exposure to various concentrations of 1 1,3- and 1,8-DNP for 2 and 24 h (Fig. 4; Supplementary Fig. 1). Both compounds increased the level of ROS as.