Modulating the sEH/EETs Axis Restrains Specialized Proresolving Mediator Impairment and Regulates T Cell Imbalance in Experimental Periodontitis.

Epoxyeicosatrienoic acids (EETs) and other epoxy fatty acids are short-acting lipids involved in resolution of inflammation. Their short half-life, due to its metabolism by soluble epoxide hydrolase (sEH), limits their effects. Specialized proresolving mediators (SPMs) are endogenous regulatory lipids insufficiently synthesized in uncontrolled and chronic inflammation. Using an experimental periodontitis model, we pharmacologically inhibited sEH, examining its impact on T cell activation and systemic SPM production. In humans, we analyzed sEH in the gingival tissue of periodontitis patients. Mice were treated with sEH inhibitor (sEHi) and/or EETs before ligature placement and treated for 14 d. Bone parameters were assessed by microcomputed tomography and methylene blue staining. Blood plasma metabololipidomics were carried out to quantify SPM levels. We also determined T cell activation by reverse transcription-quantitative PCR and flow cytometry in cervical lymph nodes. Human gingival samples were collected to analyze sEH using ELISA and electrophoresis. Data reveal that pharmacological sEHi abrogated bone resorption and preserved bone architecture. Metabololipidomics revealed that sEHi enhances lipoxin A4, lipoxin B4, resolvin E2, and resolvin D6. An increased percentage of regulatory T cells over Th17 was noted in sEHi-treated mice. Lastly, inflamed human gingival tissues presented higher levels and expression of sEH than did healthy gingivae, being positively correlated with periodontitis severity. Our findings indicate that sEHi preserves bone architecture and stimulates SPM production, associated with regulatory actions on T cells favoring resolution of inflammation. Because sEH is enhanced in human gingivae from patients with periodontitis and connected with disease severity, inhibition may prove to be an attractive target for managing osteolytic inflammatory diseases.

Occlusion Heightened by Metal Crown Cementation is Aggressive for Periodontal Tissues.

PURPOSE: To investigate the effect of experimental traumatic occlusion (ETO) induced by metal crowns on alveolar bone loss. MATERIALS AND METHODS: Metal crowns were custom-made for the lower first molars with occlusal discrepancy of 0.4 and 0.7 mm from the maximum intercuspation. Thirty-six animals were randomly divided into three groups (n = 12 animals per group): 0.4-mm hyperocclusion group, 0.7-mm hyperocclusion group and the sham group (no metal crown). Twenty-eight days after crown cementation, the animals were euthanized and gingival tissue was collected to assess cytokine levels of IL-17, IL-6, and TNF-α using enzyme-linked immunosorbent assay (ELISA). Mandibles were stained with 1% methylene blue and alveolar bone levels were quantified. Western blotting was used to quantify the expression of receptor activator of nuclear factor κ B (RANK), and its ligand (RANKL), secreted osteoclastogenic factor of activated T cells (SOFAT) and TNF-α-converting enzyme (TACE). Also, mandibles were histologically processed and stained with hematoxylin and eosin, from which the presence of osteoclast-like cells, multinucleated cells containing ≥3 nuclei was counted at 100× magnification. The data were analyzed using one-way ANOVA and Tukey tests. RESULTS: Experimental occlusal trauma for 28 consecutive days significantly increased alveolar bone loss and multinucleated cell counts (p < 0.05). RANK, RANKL, SOFAT, TACE, IL-6, and TNF-α were significantly higher in gingival tissues of ETO groups (p < 0.05). IL-17 titers were unchanged among the groups (p > 0.05). CONCLUSION: Experimental traumatic occlusion activates and sustains bone resorption pathways in the periodontium inducing alveolar bone resorption. As the intensity of occlusal trauma increased, alternative osteoclastic pathways were activated, such as TACE and SOFAT.

Soluble Epoxide Hydrolase Pharmacological Inhibition Decreases Alveolar Bone Loss by Modulating Host Inflammatory Response, RANK-Related Signaling, Endoplasmic Reticulum Stress, and Apoptosis.

Epoxyeicosatrienoic acids (EETs), metabolites of arachidonic acid derived from the cytochrome P450 enzymes, are mainly metabolized by soluble epoxide hydrolase (sEH) to their corresponding diols. EETs but not their diols, have anti-inflammatory properties, and inhibition of sEH might provide protective effects against inflammatory bone loss. Thus, in the present study, we tested the selective sEH inhibitor, 1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea (TPPU), in a mouse model of periodontitis induced by infection with Aggregatibacter actinomycetemcomitans Oral treatment of wild-type mice with TPPU and sEH knockout (KO) animals showed reduced bone loss induced by A. actinomycetemcomitans This was associated with decreased expression of key osteoclastogenic molecules, receptor activator of nuclear factor-κB/RANK ligand/osteoprotegerin, and the chemokine monocyte chemotactic protein 1 in the gingival tissue without affecting bacterial counts. In addition, downstream kinases p38 and c-Jun N-terminal kinase known to be activated in response to inflammatory signals were abrogated after TPPU treatment or in sEH KO mice. Moreover, endoplasmic reticulum stress was elevated in periodontal disease but was abrogated after TPPU treatment and in sEH knockout mice. Together, these results demonstrated that sEH pharmacological inhibition may be of therapeutic value in periodontitis.

Soluble epoxide hydrolase inhibition enhances production of specialized pro-resolving lipid mediator and promotes macrophage plasticity.

BACKGROUND AND PURPOSE: Epoxyeicosatrienoic acids (EETs) and other epoxy fatty acids (EpFA) are lipid mediators that are rapidly inactivated by soluble epoxide hydrolase (sEH). Uncontrolled and chronic inflammatory disorders fail to sufficiently activate endogenous regulatory pathways, including the production of specialized pro-resolving mediators (SPMs). Here, we addressed the relationship between SPMs and the EET/sEH axis and explored the effects of sEH inhibition on resolving macrophage phenotype. EXPERIMENTAL APPROACH: Mice were treated with a sEH inhibitor, EETs, or sEH inhibitor + EETs (combination) before ligature placement to induce experimental periodontitis. Using RT-qPCR, gingival samples were used to examine SPM receptors and osteolytic and inflammatory biomarkers. Maxillary alveolar bone loss was quantified by micro-CT and methylene blue staining. SPM levels were analysed by salivary metabolo-lipidomics. Gingival macrophage phenotype plasticity was determined by RT-qPCR and flow cytometry. Effects of sEH inhibition on macrophage polarization and SPM production were assessed with bone marrow-derived macrophages (BMDMs). KEY RESULTS: Pharmacological inhibition of sEH suppressed bone resorption and the inflammatory cytokine storm in experimental periodontitis. Lipidomic analysis revealed that sEH inhibition augmented levels of LXA4, RvE1, RvE2, and 4-HDoHE, concomitant with up-regulation of LTB4R1, CMKLR1/ChemR23, and ALX/FPR2 SPM receptors. Notably, there is an impact on gingival macrophage plasticity was affected suggesting an inflammation resolving phenotype with sEH inhibition. In BMDMs, sEH inhibition reduced inflammatory macrophage activation, and resolving macrophages were triggered to produce SPMs. CONCLUSION AND IMPLICATIONS: Pharmacological sEH inhibition increased SPM synthesis associated with resolving macrophages, suggesting a potential target to control osteolytic inflammatory disorders.