Role of histone H3K36me3 in hepatic oxidative damage induced by arsenic in rats

Background Environmental pollutants can cause human health damage, which has become a research focus of domestic and foreign scholars. Histone H3 lysine 36 trimethylation (H3K36me3) is one of the sensitive targets of epigenetic modification due to arsenic exposure, and the mechanism of arsenic induced liver damage is still unclear.

Objective This experiment evaluates the association of H3K36me3 and hepatic oxidative damage induced by arsenic in rats, providing an epigenetic understanding of the mechanism and intervention of arsenic induced liver oxidative damage from the perspective of epigenetics.

Methods Thirty-two healthy weaned Wistar rats were randomly divided into a control group and three arsenic groups (low, medium, and high dose groups), with eight rats in each group. The median lethal dose (LD₅₀) of sodium arsenite in rats was 41 mg·kg^-1. According to the principle of dose design for subchronic toxicity test, the three arsenic dose groups were given 2.5 (1/16 LD₅₀), 5.0 (1/8 LD₅₀), and 10.0 (1/4 LD₅₀) mg·kg^-1 (calculated by body weight, thereafter) sodium arsenite solution respectively. The rats in the control group were given 10 mL·kg^-1 deionized water by intragastric administration, 6 d a week. After 4 months, urine and liver tissue samples were collected. The content of arsenic in liver was measured by inductively coupled plasma mass spectrometry (ICP-MS). Histone was extracted from the liver of rats by acid extraction, and the modification level of H3K36me3 was detected by enzyme-linked immunosorbent assay (ELISA). The level of urinary 8-hydroxy-2-deoxyguanosine (8-OHdG) was tested by the ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). The content of liver malondialdehyde (MDA) was determined by thiobarbituric acid (TBA) method. The linear relationships between liver arsenic, H3K36me3, 8-OHdG, and MDA were evaluated. A "liver arsenic-H3K36me3-8-OHdG/MDA" mediation model was established to explore potential mediating role of H3K36me3 in arsenic induced liver oxidative injury.

Results The levels of hepatic arsenic, urinary 8-OHdG, and hepatic MDA in the low, medium, and high arsenic groups were higher than the levels in the control group, while the level of hepatic H3K36me3 in the three arsenic dose groups were lower (P < 0.05). The levels of hepatic arsenic, urinary 8-OHdG, and hepatic MDA increased with higher arsenic doses (P_trend < 0.01), while the level of H3K36me3 in liver decreased with higher arsenic doses (P_trend < 0.01). Hepatic arsenic level had a positive correlation with urinary 8-OHdG and hepatic MDA levels (r=0.701, 0.748, P < 0.01), but had a negative correalation with liver H3K36me3 modification (r=-0.715, P < 0.01). Liver H3K36me3 modification was negatively correlated with urinary 8-OHdG and hepatic MDA levels (r=-0.660, -0.683, P < 0.01). Urinary 8-OHdG level was positively correlated with hepatic MDA level (r=0.778, P < 0.01). The mediating effect of H3K36me3 on arsenic induced 8-OHdG and MDA levels accounted for 30.97% and 38.91% of the total effect, respectively.

Conclusion The decreased H3K36me3 in rat liver induced by arsenic may be involved in the regulation of hepatic oxidative damage, suggesting that H3K36me3 may be used as a new target for studying the mechanism of hepatic oxidative damage.