Background Benzoapyrene (BaP) is neurotoxic and can cause neuronal damage by oxidative stress. Proanthocyanidin (PC) has antioxidant activity, and its mechanism may related to nuclear factor-erythroid 2-related factor 2 (Nrf2)-heme oxygenase-1 (HO-1) signaling pathway.

Objective To explore potential protective effect of PC on hippocampal neuron injury induced by BaP oxidative stress.

Methods Hippocampal neurons of neonatal SD rats delivered within 24 h were isolated and cultured, and cell activity was detected by cell counting kit-8 (CCK-8) method. According to the pre-experimental results, a control group and three BaP groups of 10, 20 and 40 µmol·L⁻¹ were set up for Stage I experiment. The length of neurites and number of branches of hippocampal neurons in each group were observed by immunofluorescence method. Reactive oxygen species (ROS) fluorescence probe method was used to measure ROS levels in cells. Real-time quantitative fluorescent polymerase chain reaction (qRT-PCR) and Western blotting were used to detect the mRNA and protein expression of Nrf2, Kelch-like epichlorohydrin associated protein-1 (Keap1), HO-1, B-cell lymphoma-2 (Bcl-2), and Bcl-2-associated X (Bax) in hippocampal neurons of each group, respectively. According to the results of Stage I experiment, three group were set up, including control group, BaP alone treatment group (BaP 20 µmol·L⁻¹), and PC intervention group (BaP 20 µmol·L⁻¹ + PC 2.5 µg·mL⁻¹) for Stage II experiment, with the same protocol as Stage I.

Results For Stage I experiment, compared with the control group, the 10, 20, and 40 µmol·L⁻¹ BaP groups showed gradually shortened length of neurites (177.60±3.49), (142.40±6.52), and (100.50±19.40) µm (P<0.05) and decreased number of branches (8.00±1.00, 6.33±1.53, 4.33± 0.58) of hippocampal neurons (P<0.05); increased ROS production (2.38±0.33, 8.08±0.26, 9.86±0.19) (P<0.05); the qRT-PCR results showed that the mRNA expression levels of Nrf2 (0.35±0.03, 0.25±0.01, 0.13±0.03), Keap1 (0.70±0.01, 0.47±0.03, 0.15±0.02), HO-1 (0.77±0.02, 0.60±0.02, 0.32±0.01), and Bcl-2 (0.65±0.03, 0.47±0.02, 0.18±0.02) gradually decreased, and the mRNA expression level of Bax gradually increased (1.24±0.01, 2.25±0.15, 4.98±0.30) (P<0.05); the Western blotting results showed that the protein expression trends of Nrf2, Keap1, HO-1, Bcl-2, and Bax were consistent with the mRNA results. For Stage II experiment, compared with the BaP alone treatment group, the length of neurites in the PC intervention group became longer, (149.90±3.01) μm vs (202.00±4.45) μm (P<0.05), the number of branches increased, (4.67±0.58) vs (8.33±0.58) (P<0.05); the ROS production reduced, (10.81±0.63) vs (7.31±0.70) (P<0.05); the mRNA expression levels of Nrf2, Keap1, HO-1, and Bcl-2 increased (P<0.05), and the mRNA expression levels of Bax decreased (P<0.05); the Nrf2, Keap1, HO-1, and Bcl-2 protein expression levels increased (P<0.05), and Bax protein expression level decreased (P<0.05).

Conclusion PC may exert neuroprotective effects by activating the Nrf2-HO-1 signaling pathway, inhibiting BaP-induced oxidative stress in neuronal cells, and reducing cytotoxicity.