Natural Phosphodiesterase-4 Inhibitors with Potential Anti-Inflammatory Activities from Millettia dielsiana

The results of in silico screening of the 50 isolated compounds from Millettia dielsiana against the target proteins PDE4 (PDE4A, PDE4B, and PDE4D) showed binding affinity ranges from −5.81 to −11.56, −5.27 to −13.01, and −5.80 to −12.12 kcal mol(−1), respectively, with median values of −8.83, −8.84, and −8.645 kcal mol(−1), respectively. Among these compounds, Millesianin F was identified as the most promising PDE4A inhibitor due to its strongest binding affinity with the target protein PDE4A. (−11.56 kcal mol(−1)). This was followed by the compound 5,7,4′-trihydroxyisoflavone 7-O-β-d-apiofuranosyl-(1→6)-β-d-glucopyranoside (D50) with the binding affinity value of −11.35 kcal mol(−1). For the target protein PDE4B, compound D50 exhibited the strongest binding affinity value of −13.01 kcal mol(−1), while showing poorer inhibition ability for PDE4D. The 100 ns MD simulation examination (radius of gyration, Solvent Accessible Surface Area (SASA), Root-Mean-Square Deviation (RMSD), Root-Mean-Square Fluctuation (RMSF), and hydrogen bonding) was carried out to examine the overall stability and binding efficiency of the protein–ligand complex between compounds (Millesianin F, Millesianin G, Claclrastin-7-O-β-d-glucopyranoside, 7-hydroxy-4′,6 dimethoxyisoflavone-7-O-β-d-apiofuranosyl-(1→6)-β-d-glucopyranoside, 7-hydroxy-4′,8-dimethoxyisoflavone 7-O-β-d-apiofuranosyl-(1→6)-β-d-glucopyranoside, Odoratin-7-O-β-d-glucopyranoside, and 5,7,4′-trihydroxyisoflavone 7-O-β-d-apiofuranosyl-(1→6)-β-d-glucopyranoside) and PDE4 (A, B) subtype proteins. Compound D50 has shown strong anti-inflammatory activity, as evidenced by experimental results. It effectively inhibits PDE4B and PDE4D, with IC(50) values of 6.56 ± 0.7 µM and 11.74 ± 1.3 µM, respectively. Additionally, it reduces NO production, with an IC(50) value of 5.40 ± 0.9 µM. Based on these findings, it is promising and considered a potential novel anti-inflammatory drug for future development.