Inhibiting the soluble epoxide hydrolase increases the EpFAs and ERK1/2 expression in the hippocampus of LiCl-pilocarpine post-status epilepticus rat model

Purpose

This study aimed to investigate the enzyme activity of soluble epoxide hydrolase (sEH) and quantify its metabolic substrates, namely epoxygenated fatty acids (EpFAs), and products of sEH in the hippocampus after administering TPPU [1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl)urea], an inhibitor of sEH. Furthermore, it explored whether the extracellular signal-activated protein kinase 1/2 (ERK1/2) is involved in the anti-seizure effects of TPPU in the lithium chloride (LiCl)-pilocarpine induced post-status epilepticus (SE) rat model.

Methods

The rats were intraperitoneally (I.P.) injected with LiCl and pilocarpine to induce SE and then spontaneous recurrent seizures (SRS) were observed. Rats were randomly assigned into SRS + TPPU group (intragastrically administering 0.1 mg/kg/d TPPU), SRS + Vehicle group (administering the vehicle instead), and Control group. Enzyme-linked immunosorbent assay, Western-blot analysis, and ultra-high-performance liquid chromatography/mass spectrometry (LC/MS) were performed to measure the enzyme activity of sEH, the protein level of sEH and ERK1/2, and the concentration of TPPU and polyunsaturated fatty acids (PUFAs) metabolisms in the hippocampus.

Results

The frequency of SRS events of Racine stage 3 or higher ranged from 0 to 19 per week in the SRS + Vehicle group, compared to 0–5 per week in the SRS + TPPU group. sEH enzyme activity and protein levels were significantly elevated in the SRS + Vehicle group compared to the Control group. After TPPU administration, the hippocampal TPPU concentration reached 10.94 ± 4.37 nmol/kg. sEH enzyme activity was significantly reduced in the LiCl-pilocarpine-induced post-SE rat model, although sEH protein levels did not decrease significantly. The regioisomers 8,9-, 11,12-, and 14,15-EETs, total EETs, the EETs/DHETs ratio, other EpFAs including 16(17)-EpDPA, and the 19(20)-EpDPA/19,20-DiHDPA ratio in the hippocampus were significantly increased. Additionally, the p-ERK1/2 to ERK1/2 ratio in the hippocampus was significantly elevated following TPPU administration.

Conclusion

This study demonstrates that inhibiting sEH with TPPU increases the levels of EETs, other EpFAs, and ERK1/2 expression in the hippocampus of a LiCl-pilocarpine-induced post-SE rat model. These findings suggest that the anti-seizure effect of TPPU may be mediated through the EETs-ERK1/2 pathway.