Impact on Photophysical and Photochemical Properties of Fluoroquinolones by Interaction with Lysozyme in Aqueous Solutions

HUGO A. PÉREZ; FAUSTINO E. MORÁN VIEYRA; CLAUDIO D. BORSARELLI

Cordoba

Congreso; 16th International Congress on Photobiology; 2014

Fluoroquinolones (FQs) are broad-spectrum antibiotics that have beenused in the treatment of various infections [1]. They are capable of absorbingUV-VIS radiation generating excited states that can react with molecular oxygenor biomolecules such as proteins [2].In this work we studied the interaction between lysozyme (Lyz) and theFQs: ciprofloxacin (Cpx), norfloxacin (Nor) and levofloxacin (Lev) at differentpH conditions, using steady-state and dynamic absorption and emissionspectroscopies. UV-Vis and fluorescence spectra of the FQs were dependent onpH, indicating the formation of cationic, zwitterionic, and anionic species atpH 5, 7 and 10, respectively. At pH 5 and 7, a moderated fluorescence quenchingof FQs by Lyz is observed (Fig. 1), with KSV»104 M-1.Fluorescence lifetime measurements of FQs confirmed a static quenchingmechanism, indicating the formation of an antibiotic-enzyme adduct with Ka»104 M-1. Conversely, at pH 10, the addition of Lysincreases the FQs fluorescence intensity, suggesting that a different bindingsite is occupied. The Langmuir isotherm yielded Ka»106 M-1, two-order of magnitude larger than atlower pH, indicating the role of electrostatic attractive interactions betweenthe anionic form of FQs and the positively charged enzyme (pI@11.5).The photodegradation of FQs depends on O2 concentration. An efficient quenchingexists between FQs triplet states and O2 with a kQ=2-3x109 M s-1.  However, quantum yields of 1O2 for Nor and Cpx are lower than 6%. The presence of Lyz decreases thephotodegradation rate of the FQs through an efficient quenching of the FQstriplet states, kQ»7-10x109 M-1 s-1, evidencing a photoprotectiveeffect of Lyz.