ABSTRACT
Objective To explore the beneficial effects and mechanisms of neutrophil elastase (NE) and myeloperoxidase (MPO) on lead-induced hepatic inflammation in mice. Methods The specific pathogen free male C57BL/6 mice were randomly divided into four groups： control group, lead-exposed group, NE inhibitor group, and MPO inhibitor group, with three mice in each group. The mice in lead-exposed group, NE inhibitor group, and MPO inhibitor group were intraperitoneally injected with a dose of 10 mg/kg body mass of lead acetate solution, while the mice of control group received an equal volume of 0.9% saline three times per week for four weeks. In the last seven days, mice in both inhibitor groups were intraperitoneally injected with a dose of 40 mg/kg NE inhibitor sivelestat sodium or MPO inhibitor 4-aminobenzoic acid hydrazide (4-ABAH) once per day. Mouse body weight and liver histopathological changes were observed. The mRNA expression of genes associated with inflammation, such as tumor necrosis factor-α (Tnfa), interleukin-1β (Il1b), interleukin-6 (Il6), and nucleotide-binding oligomerization domain-like receptor protein 3(Nlrp3), apoptosis-associated speck-like protein (Asc) and cysteinyl aspartate specific proteinase (Caspase1) in the mouse liver tissues was detected by real-time quantitative polymerase chain reaction. The protein expression of NLRP3, ASC, and CASPASE-1 was detected using Western blotting. Results The activities of mice in all four groups were generally normal, and there was no significant difference in body weight (P>0.05). The results of hematoxylin-eosin staining showed that the cell size of hepatocytes varied in the lead-exposed mice, with indistinct cell boundaries, indicating early inflammatory responses in liver tissues. After intervention with NE or MPO inhibitors, the early inflammatory responses improved in the liver tissues of the mice in both inhibitor groups, with a better improvement observed in MPO inhibitor group compared with the NE inhibitor group. The mRNA expression of Tnfa, Il1b, Il6, Nlrp3, Asc, and Caspase1, as well as the protein expression of ASC, and CASPASE-1 in the livers of mice in the lead-exposed group was higher compared with those in the control group (all P<0.05). Compared with the lead-exposed group, the relative mRNA expression of Tnfa, Il1b, Il6, Nlrp3 and Asc was decreased in the liver tissues of mice in the NE inhibitor group (all P<0.05), while the relative expression of mRNA of Tnfa, Il1b, Il6, Caspase1 and the protein expression of ASC and CASPASE-1 were decreased in the liver tissues of mice in the MPO inhibitor group (all P<0.05). Conclusion Lead induce hepatic inflammation in mice by activating NLRP3 inflammasome. The inhibition of NE or MPO improve the lead-induced hepatic inflammatory responses in mice by alleviating NLRP3 inflammasome activation.