[Cytotoxicity and genomic damage of benzo[a]pyrene in gene transformed cell model]

To investigate cytotoxicity and genotoxicity of benzo(a)pyrene (B(a)P) by 16HBE-CYP1A1 cells which are human bronchial epithelial cell with CYP1A1 transformed.

Expression of CYP1A1 and mEH of cell models were tested by real-time quantitative polymerase chain reaction. Cells were treated with 0, 1, 5, 10 and 20 micromol/L B(a)P for 24 h. Adverse effects of B(a)P were tested by cytokinesis-block micronucleus (CBMN) cytome assays. Cytotoxicity was assessed by the nuclear division index (NDI), frequency of necrotic and apoptotic cells. Genetic damages were assessed by frequencies of CBMN, nucleoplasmic bridges (NPBs) and nuclear buds (NBUDs).

High levels of CYP1A1 and mEH were found in 16HBE-CYP1A1 cells (relative mRNA content was 7.8 x 10(-4) and 0.030 respectively). In 16HBE-CYP1A1 cells, NDI were decreased in 1, 5, 10 and 20 micromol/L B(a)P treated groups, 1.92 +/- 0.04, 1.71 +/- 0.01, 1.61 +/- 0.04, and 1.41 +/- 0.01, respectively; and lower than control group (2.08 +/- 0.03). Compared with control group ((82.67 +/- 6.66)%), the binucleated cells ratios were decreased, (76.33 +/- 3.51)%, (66.33 +/- 0.58)%, (51.67 +/- 1.53)% and (39.0 +/- 1.0)% respectively.Necrotic cells ratios were (1.93 +/- 0.42)%, (2.20 +/- 0.53)%, (8.07 +/- 0.90)% and (15.27 +/- 2.80)%, respectively, higher than control group ((0.47 +/- 0.11)%). The differences were significant (F values were 899.94, 303.33, 240.87, P < 0.01). Apoptotic cells were increased at lower groups and decreased to normal at higher groups treated by B(a)P. They were (1.20 +/- 0.53)%, (2.00 +/- 0.20)%, (1.47 +/- 0.12)%, (1.20 +/- 0.00)% and (1.20 +/- 0.00)%, respectively. Analysis on biomarkers of genetic damage, the significant dose-effect relationship were observed in NPBs and NBUDs (F values were 50.23, 121.09, P < 0.01, respectively). Frequencies of NPBs were (4.67 +/- 2.89) per thousand, (7.33 +/- 1.53) per thousand, (10.67 +/- 2.08) per thousand and (11.00 +/- 1.00) per thousand respectively. Frequencies of NBUDs were (2.33 +/- 0.58) per thousand, (4.00 +/- 1.00) per thousand, (5.00 +/- 1.00) per thousand, and (7.67 +/- 1.16) per thousand respectively. However, the dose-relationship of CBMN last only to 10 micromol/L B(a)P treated groups in 16HBE-CYP1A1 cells, and frequencies of CBMN were (8.33 +/- 3.21) per thousand, (14.67 +/- 1.15) per thousand, respectively. Frequency of CBMN was (16.67 +/- 2.88) per thousand in 20 micromol/L B(a)P treated group, lower than 10 micromol/L B(a)P treated group ((17.67 +/- 2.08) per thousand). In 16HBEV control cells, the cytotoxicity was found only in higher B(a)P treated groups and frequencies of CBMN, NPBs and NBUDs were increased also. While no significant differences were observed between 5, 10, 20 micromol/L B(a)P treated groups (they were (6.37 +/- 2.08) per thousand, (9.33 +/- 1.52) per thousand, (9.33 +/- 3.21) per thousand; (4.33 +/- 1.53) per thousand, (6.00 +/- 2.65) per thousand, (5.33 +/- 1.53) per thousand and (2.33 +/- 0.58) per thousand, (3.33 +/- 1.16) per thousand, (3.67 +/- 1.16) per thousand, respectively).

The genetic damages were more severe after treated with activated B(a)P, which may be induced by decreased NDI, increased necrotic cells and inhibition of apoptosis.