ABSTRACT
Objective To investigate whether Toll-like receptor 4 (TLR4) inhibition affects liver regeneration during acetaminophen (APAP)-induced liver injury in mice, as well as the mechanism of TLR4 involved in liver regeneration. Methods A total of 78 male CD-1 mice were divided into nine groups using a random number table, i.e., three control groups (normal control group, solvent control group, inhibitor control group) with 6 mice in each group and six experimental groups (APAP 24-hour group, TAK-242+APAP 24-hour group, APAP 48-hour group, TAK-242+APAP 48-hour group, APAP 72-hour group, TAK-242+APAP 72-hour group) with 10 mice in each group. The mice in the experimental groups were given a single dose of intraperitoneally injected APAP (300 mg/kg), and TAK-242 was intraperitoneally injected at a dose of 3 mg/kg at 3 hours before APAP administration. Serum and liver tissue samples were collected at different time points. The biochemical method was used to measure the serum level of alanine aminotransferase (ALT); HE staining was used to observe liver pathological changes; RT-PCR, Western blot, and immunohistochemistry were used to measure the expression levels of Cyclin D1, PCNA, Ki-67, STAT3, and p-STAT3. The t -test was used for comparison of normally distributed continuous data between two groups; a one-way analysis of variance was used for comparison between multiple groups, and the least significant difference t -test was used for further comparison between two groups. The Mann-Whitney U test was used for comparison of non-normally distributed continuous data between two groups, and the Kruskal-Wallis H test was used for comparison between multiple groups and further comparison between two groups. Results Compared with the normal control group, the APAP 24-hour and 48-hour groups had a significantly higher serum level of ALT (both P < 0.05), and the TAK-242+APAP 24-hour and 48-hour groups had a significantly higher serum level of ALT than the APAP group at the same time point (both P < 0.05). HE staining showed typical central lobular necrosis in the liver of APAP-treated mice, and the TAK-242+APAP 24-hour and 48-hour groups had a significantly larger necrotic area than the APAP group at the same time point (both P < 0.05). RT-PCR, Western blot, and immunohistochemistry showed that the TAK-242+APAP 24-hour, 48-hour, and 72-hour groups had significantly lower mRNA and protein expression levels of Cyclin D1 than the APAP group at the same time point (all P < 0.05); the TAK-242+APAP 24-hour, 48-hour, and 72-hour groups had a significantly lower mRNA expression level of PCNA than the APAP group at the same time point (all P < 0.05), and the TAK-242+APAP 24-hour and 48-hour groups had a significantly lower protein expression level of PCNA than the APAP group at the same time point (all P < 0.05); the TAK-242+APAP 24-hour and 72-hour groups had a significantly lower mRNA expression level of Ki-67 than the APAP group at the same time point (all P < 0.05), and the TAK-242+APAP 24-hour, 48-hour, and 72-hour groups had a significantly lower protein expression level of Ki-67 than the APAP group at the same time point (all P < 0.05). In addition, the TAK-242+APAP 24-hour and 48-hour groups had a significantly lower phosphorylation level of STAT3 than the APAP group at the same time point (both P < 0.05). Conclusion TLR4 may promote liver regeneration by increasing the phosphorylation level of STAT3 during APAP-induced liver injury in mice.