DT-13 Mediates Ligand-Dependent Activation of PPARγ Response Elements In Vitro

Activation of inflammatory pathways releases a storm of cytokines. Moreover, unregulated cytokines contribute to chronic inflammatory disorders. However, ligand-activated peroxisome proliferator-activated receptor gamma (PPARγ) is involved in suppressing inflammatory cytokines via transrepression of nuclear factor kappa B (NFκB). Therefore, in this study, the anti-inflammatory saponin DT-13 is explored as a ligand of PPARγ. DT-13 upregulated the expression of PPARγ in lipopolysaccharide (LPS)-stimulated RAW264.7 cells in comparison to treatment with LPS alone. Applying a HEK transfection model, we observed a DT-13 dose-dependent increase in ligand-dependent activation of PPARγ, which was compared with troglitazone and rosiglitazone. DT-13 was not able to compete with the synthetic fluoromone tracer for binding to PPARγ as observed in a fluorescence polarization binding assay, whereas molecular docking showed a possible binding interaction of DT-13 with the PPARγ nuclear receptor. We proved the expression of PPARγ protein in the presence of DT-13 using a robust cell-based HEK293FT transfection model. More in-depth analysis needs to be performed to evaluate the efficiency of the binding of DT-13 to PPARγ. A possible binding interaction of DT-13 to PPARγ was observed, similar to that of rosiglitazone. This study revealed a novel mechanism for anti-inflammatory effects by DT-13 through PPARγ-dependent transrepression of NFκB.