Interaction of the NSAID cyclooxygenase inhibitor, acemetacin, with human serum albumin: an experimental and computational modelling investigation.

Acemetacin (ACM), a nonsteroidal anti-inflammatory drug (NSAID) used to treat chronic pain and inflammation, is known for its improved gastrointestinal tolerance compared to other NSAIDs. Clarifying how ACM associates with human serum albumin (HSA) is crucial for understanding its transport, distribution, and bioavailability. The ACM binding to HSA was examined through a combination of spectroscopic, microscopic, and computational methods. Fluorescence quenching confirmed spontaneous and moderate binding, with the binding constant (Ka) values of 7.52±0.03 × 104, 7.15±0.00 × 104, and 5.54±0.08 × 104 M-1 at 290, 300, and 310 K, respectively. Thermodynamic analysis (ΔH° = -11.35±0.49 kJ⋅mol-1; ΔS° = +54.53±1.64 J⋅mol-1⋅K-1) showed an enthalpy-driven process involving hydrogen bonds, van der Waals, and hydrophobic interactions. A 7.1% increase in the α-helical content, local perturbations around protein fluorophores and morphological alterations were noticed in the presence of ACM, as affirmed by circular dichroism, 3D fluorescence and atomic force microscopy. Molecular docking predicted the binding preference of ACM towards Site I over Site III, while the molecular dynamics simulation over 100 ns supported a stable ACM-HSA complex with an average RMSD of 0.32 nm and low RMSF fluctuations. This was well supported by competitive displacement results using site-specific probes, confirming Sudlow's Site I as the primary binding locus. The observed moderate binding affinity, site-selective binding behavior, and structural stability suggest effective serum transport and influence on tissue distribution, with potential implications for drug-drug interactions and therapeutic efficacy.