Anna Maria Ploch-Jankowska, Ewa Długosz

Evaluation of the effect of 2-acetyl-6-methoxynaphthalene on naproxen binding to human serum albumin. Spectroscopic studies

2025-12-01

Study subject. Human serum albumin is the major plasma protein that plays a key role in transporting endogenous and exogenous compounds, including drugs. Naproxen, a widely used non-steroidal anti-inflammatory drug, exhibits high affinity for albumin. Under environmental conditions, naproxen undergoes photodegradation, forming by-products such as 2-acetyl-6-methoxynaphthalene, whose effect on drug binding to albumin has not yet been sufficiently investigated. It has therefore become important to determine whether degradation products affect drug transport in the body and whether they induce structural modifications and functional changes of albumin.

Objective. The aim of this study was the spectroscopic characterization of the competition mechanism between naproxen and its photodegradation product, 2-acetyl-6 methoxynaphthalene, during binding to human serum albumin, both native and defatted. The analysis sought to determine the effect of the presence of the degradation product and of physicochemical conditions (temperature, presence of fatty acids) on binding parameters, the secondary structure of albumin, and mutual molecular interactions in model drug–carrier systems.

Materials and methods. The study was performed in vitro using three spectroscopic techniques: UV/Vis spectrophotometry, infrared spectroscopy, and nuclear magnetic resonance spectroscopy. Binary and ternary protein systems were examined: NAP – (d)HSA and NAP – (d)HSA with AMN at 10% and 20%.

Results. The presence of the naproxen degradation product was shown to affect the association constants of naproxen with albumin, decreasing the drug’s affinity and increasing the concentration of its free fraction in plasma. In ternary model systems, competition for binding sites within albumin was observed. The presence of 2-acetyl-6-methoxynaphthalene also significantly affected the protein’s secondary structure, especially the content of α-helix and β-structures, particularly in defatted albumin. NMR results confirmed differences in the local environment of naproxen protons and weaker interactions of its degradation product with albumin, suggesting its lower affinity for the transport protein.

Conclusions. The photodegradation product of naproxen (2-acetyl-6-methoxynaphthalene), even at pharmacopoeial permissible concentrations, can markedly influence the drug’s binding to albumin and thus its bioavailability and safety of use. The study underscores the need to consider drug degradation products in pharmacokinetic evaluation, particularly for over-the-counter preparations. The applied ternary model and integrated spectroscopic approach provide a valuable contribution to research on drug–protein interactions in the context of pharmaceutical stability and drug quality.

Keywords: naproxen, 2-acetyl-6-methoxynaphthalene, human serum albumin, spectroscopic methods.

© Farm Pol, 2025, 81(3): 135–147