The anti‑inflammatory activity of 2‑iminothiazolidines: the role of PPARγ and M2 macrophage subpopulations

Thiazolidine derivatives exert anti-inflammatory effects by inhibiting the NF-κB pathway and promoting macrophage polarization toward the anti-inflammatory M2 phenotype, partially through PPARγ activation. Our previous work identified thiazolidine derivative 13 [methyl 2-(benzoylimino)-3-methyl-4-(4-nitrobenzyl)-1,3-thiazolidine-4-carboxylate] as a potent immunomodulator that reduces pro-inflammatory mediators and enhances anti-inflammatory markers. However, its direct interaction with PPARγ remains unclear. This study aims to evaluate whether thiazolidine 13 activates PPARγ and contributes to M2 macrophage polarization using LPS-stimulated RAW 264.7 cells, cell transactivation assay and reporter gene (Hella cells), LPS-stimulated THP-1 cells, and molecular docking analysis. Compound 13 reduced NO₂⁻ production, CD80 expression, and pro-inflammatory cytokines while increasing IL-10, TGF-β, and CD206 in LPS-stimulated RAW 264.7 macrophages. Compound 13 also inhibited NO production in LPS-stimulated THP-1 cells. These effects were only partially reversed by PPARγ antagonists, suggesting additional PPARγ-independent mechanisms, while the induction of CD206 was closely linked to partial PPARγ activation. Docking studies supported this profile, showing that the (S) enantiomer of thiazolidine 13 adopts a binding mode typical of partial PPARγ agonists and exhibits a higher predicted affinity than the (R) enantiomer. Compound 13 acts as a partial PPARγ modulator capable of shifting macrophages from a pro-inflammatory toward an anti-inflammatory phenotype (M2-like). This dual action relies on the inhibition of NF-κB signaling and partial PPARγ activation. The predominance of the M2-like subpopulation, underscores its role in resolving inflammation and promoting tissue repair.