Establishing PDE4 as a Novel Target of Urolithin-A in Mitigating LPS-induced Inflammation in Retinal Pigmented Epithelium Cells.

Ocular inflammation is a major contributor to vision-threatening disorders, with phosphodiesterase 4 (PDE4), a key regulator of cAMP playing a central role in pro-inflammatory signaling. Although investigational PDE4 inhibitors like Rolipram (RP) show therapeutic promise, their systemic toxicity limits clinical application, underscoring the need for safer, targeted alternatives. Urolithin A (UA), a gut-derived metabolite of ellagic acid with emerging anti-inflammatory properties, was evaluated as a novel PDE4 inhibitor. Molecular docking revealed that UA binds with high affinity to the A-chain of PDE4A (-8.79 kcal/mol), forming unique π-π stacking and multiple hydrogen bonds. In contrast, RP binds preferentially to the B-chain with slightly lower affinity (-8.42 kcal/mol) and fewer stabilizing interactions. While both ligands engage similar catalytic residues, UA exhibited a more extensive binding profile, suggesting enhanced stability and specificity. In lipopolysaccharide (LPS)-stimulated human retinal pigment epithelial cells (ARPE-19), UA significantly inhibited PDE4A activity, elevated intracellular cAMP, and reduced key inflammatory mediators (NF-κB, IL-6, TNF-α), as demonstrated by immunofluorescence, ELISA, and gene expression analysis. These findings support UA's function as an anti-inflammatory agent by inhibiting PDE4A, highlighting its potential as a safer systemic or localized therapy for ocular inflammatory diseases.