Toxic effects of PM_2.5 injection in air chamber on development of chicken embryo liver

Background The impact of fine particulate matter (PM_2.5) exposure on embryonic development and its toxic effects have attracted much attention. The mechanism of PM_2.5 to liver development is not clear.

Objective This study is designed to investigate the toxic effects of different doses of PM_2.5 on the development of chicken embryo liver and the potential mechanism.

Methods Sixty fertilized eggs were randomly divided into four groups:blank control group (0 mg·kg^-1 PM_2.5) and 0.2, 0.5, and 2 mg·kg^-1 PM_2.5 groups with egg weight balanced. A chicken embryo exposure model was established by injecting different doses of PM_2.5 into the air chamber, and then moving the eggs into the incubator for 21 d. After hatching, the chicks were weighed, calculated for liver index, and measured for selected biochemical indicators of liver function. HE staining was prepared for observing pathological changes of liver samples. Immunohistochemistry and Western blotting were used to detect the expressions of nuclear factor-κB (NF-κB) p65 and inducible nitric oxide synthase (iNOS) in liver tissues.

Results The hatched chickens' liver samples with HE staining showed that the 0.5 mg·kg^-1 PM_2.5 exposure led to disordered hepatocytes, with a small amount of inflammatory cell infiltration and slight fatty changes; the 2.0 mg·kg^-1 PM_2.5 exposure resulted in severely damaged hepatic lobular structure, with a lot of inflammatory infiltration and hepatic cell steatosis. Regarding the biochemical indicators of liver function, compared with the control group, the activity of alanine aminotransferase (ALT) was increased in the 0.5 or 2.0 mg·kg^-1 PM_2.5 group (P < 0.05), and the activity of aspartate aminotransferase (AST) was elevated in the 0.2, 0.5, or 2.0mg·kg^-1 PM_2.5 group (P < 0.05). The increase of PM_2.5 concentration was correlated with higher activities of ALT and AST (r=0.731 and 0.720, P < 0.05). The immunohistochemistry results showed that the expression levels of NF-κB p65 in the 0.5 and 2.0 mg·kg^-1 PM_2.5 groups were significantly higher than those in the control group and the 0.2 mg·kg^-1 PM_2.5 group (P < 0.05); and the expression level in the 2.0 mg·kg^-1 PM_2.5 group was higher than that in the 0.5 mg·kg^-1 PM_2.5 group (P < 0.05). The Western blotting results showed that compared with the control group, the expression levels of iNOS protein in the 0.5 and 2.0 mg·kg^-1 PM_2.5 groups were increased (P < 0.05).

Conclusion Chicken eggs exposed to PM_2.5 could cause liver steatosis and inflammatory injury in hatched chickens. The protein expression levels of NF-κB p65 and iNOS are increased with higher PM_2.5 doses, suggesting that inflammatory response may be one of the mechanisms of PM_2.5 induced developmental toxicity to chicken embryo liver.