Objective: To observe the effects of Benzo(a)pyrene (BaP) on apoptosis of neuronal cells and expression of Bcl-2 and Bax proteins and to explore the mechanism of neurotoxicity induced by BaP in rats.
Methods: A total of 32 SD rats were divided randomly into 4 groups, i.e. 3 BaP (126.2, 63.1 and 31.5 µg/kg) groups and a solvent control (50 µg/kg olive oil) group. All rats were exposed to BaP or olive oil by lateral cerebral ventricle micro-injection 1 time a week for 3 weeks. The apoptosis of neuronal cells was detected with TdT-mediated dUTP-biotin nicked labeling (TUNEL) assay and the expression levels of Bcl-2 and Bax were measured with SABC immunohistochemistry in the cerebral cortex and hippocampus tissues of rats.
Results: The results of TUNEL assay showed that apoptosis bodies on the surface of the neurons in the cerebral cortex and hippocampus were clearly observed and the number of apoptosis bodies increased with BaP. Apoptosis indexes (AIs) of the rat cerebral cortex and hippocampus in high exposure group were significantly higher than those in control group (P < 0.05 or P < 0.01). The analysis of immunohistochemistry showed that the Bcl-2 expression levels significantly decreased, the Bax expression levels obviously increased and the ratio of Bcl-2 to Bax decreased in the rat cerebral cortex and hippocampus of medium and high exposure groups, as compared with control group (P < 0.05 or P < 0.01). In the rat cerebral cortex and hippocampus, there were the negative correlation (r = -0.927, P < 0.01; r = -0.934, P < 0.01) between AI and Bcl-2, the positive correlation (r = 0.858, P < 0.01; r = 0.847, P < 0.01) between AI and Bax and the negative correlation (r = -0.939, P < 0.01; r = -0.942, P < 0.01) between AI and Bcl-2/Bax.
Conclusion: BaP could induce the apoptosis of neuronal cells in the rat cerebral cortex and hippocampus. Bcl-2 and Bax protein expression may play an important role in the apoptosis of neuronal cells induced by BaP.