Ameliorating effect of lithium chloride on damage of embryonic hippocampal neurons in rats induced by benzoapyrene exposure

Background Many studies have confirmed that benzoapyrene (BaP) can cause embryo neurotoxicity through placental barrier and blood-brain barrier, but there are few reports about the potential interventive effect of xenobiotics on BaP induced health damage. Lithium chloride is widely used in clinical emotion regulation, with neurotrophic and neuroprotective effects.

Objective This animal experiment investigates the ameliorating effect of lithium chloride on the damage of embryonic development and hippocampal neurons in rats exposed to BaP during pregnancy, so as to provide an experimental basis for the study of its specific mechanism.

Methods Ten-week-old pregnant SD rats were randomly divided into five groups with six rats in each group: a control group, a soybean oil group, a BaP group (20 mg·kg^-1 BaP), a LiCl group (40 mg·kg^-1 LiCl), and a LiCl intervention group (20 mg·kg^-1 BaP+40 mg·kg^-1 LiCl). From gestational day 8 (GD8) to GD14, mother rats were administered by gavage once a day for continuous 7 days, and their weights were recorded every day. On GD18, fetal rats were collected from pregnant rats, and the number, weight, body length, and tail length of the pups were recorded. The morphological changes of neurons in hippocampus were observed by HE staining. The expressions of glycogen synthasc kinase-3β (GSK-3β), pGSK-3β, and β-catenin in hippocampus were detected by Western blotting.

Results During the experiment, the control, soybean oil, and LiCl groups showed no differences in the body weight of pregnant rats and the development indexes of fetal rats (P>0.05). On GD14 and GD18, the weights of pregnant rats in the BaP group(323.34±5.71) g, (364.34±10.41) g were lower than those in the control group(339.17±7.10) g, (390.32±11.35) g (P < 0.05), and the weights of pregnant rats in the LiCl intervention group(345.05±7.72) g, (398.73±12.32) g were higher than those in the BaP group (P < 0.05). The body weight, body length, and tail length of fetal rats in the BaP group were (2.325±0.061) g, (3.072±0.077) cm, and (1.135±0.068) cm, respectively, which were lower than those in the control group(2.563±0.091) g, (3.284±0.078) cm, and (1.276±0.041) cm (all P < 0.05). The above development indexes of fetal rats in the LiCl intervention group were (2.669±0.096) g, (3.356±0.107) cm, and (1.206±0.041) cm, respectively, which were higher than those in the BaP group (P < 0.05). The morphological observation results showed that neurons in dentate gyrus of hippocampus in the BaP group shrank and stained deeply, which was improved in the LiCl intervention group. The Western blotting results showed that the expression level of pGSK-3β in the BaP group was decreased (gray value ratio: 0.87±0.04 in the control group, and 0.50±0.04 in the BaP group, F=19.64, P < 0.001), the expression level of GSK-3β was increased (gray value ratio: 1.53±0.14 in the control group, and 2.09±0.11 in the BaP group, F=5.90, P=0.011), and the expression level of β-catenin was decreased (gray value ratio: 1.41±0.14 in the control group, and 0.90±0.04 in the BaP group, F=11.16, P=0.001). LiCl intervention significantly reversed the decrease of pGSK-3β and β-catenin expressions and the increase of GSK-3β expression caused by BaP exposure (grey value for pGSK-3β was 0.69±0.08, P=0.036; for GSK-3β was 1.59±0.15, P=0.042; and for β-catenin was 1.33±0.08, P=0.006).

Conclusion LiCl intervention can improve embryonic growth retardation and hippocampal neuron damage in rats induced by BaP exposure during pregnancy. The mechanism may be related to the inhibition of GSK-3β activity and the increase of β-catenin expression by LiCl.