Impact on photophysical and photochemical properties of fluoroquinolones by interaction with lysozyme in aqueous solutions

HUGO A. PÉREZ, FAUSTINO E. MORÁN VIEYRA Y CLAUDIO D. BORSARELLI

Cordoba

Congreso; 16th International Congress on Photobiology (16vo Congreso Internacional de Fotobiología); 2014

Fluoroquinolones (FQs) are broad-spectrum antibiotics that have been used in the treatment of various infections [1]. They are capable of absorbing UV-VIS radiation generating excited states that can react with molecular oxygen or biomolecules such as proteins [2]. In this work we studied the interaction between lysozyme (Lyz) and the FQs: ciprofloxacin (Cpx), norfloxacin (Nor) and levofloxacin (Lev) at different pH conditions, using steady-state and dynamic absorption and emission spectroscopies. UV-Vis and fluorescence spectra of the FQs were dependent on pH, indicating the formation of cationic, zwitterionic, and anionic species at pH 5, 7 and 10, respectively. At pH 5 and 7, a moderated fluorescence quenching of FQs by Lyz is observed (Fig. 1), with KSV = 104M-1. Fluorescence lifetime measurements of FQs confirmed a static quenching mechanism, indicating the formation of an antibiotic-enzyme adduct with Ka = 104M-1. Conversely, at pH 10, the addition of Lys increases the FQs fluorescence intensity, suggesting that a different binding site is occupied. The Langmuir isotherm yielded Ka =106M-1, two-order of magnitude larger than at lower pH, indicating the role of electrostatic attractive interactions between the anionic form of FQs and the positively charged enzyme (pI = 11.5).  The photodegradation of FQs depends on O2 concentration. An efficient quenching exists between FQs triplet states and O2 with a kQ=2-3x109M-1s-1. However, quantum yields of 1O2 for Nor and Cpx are lower than 6%. The presence of Lyz decreases the photodegradation rate of the FQs through an efficient quenching of the FQs triplet states, kQ = 7-10x109M-1s-1, evidencing a photoprotective effect of Lyz.