Photochemical Properties And Reactions With Biomolecules Of Gemifloxacin, Balofloxacin, And Tosufloxacin

Fluoroquinolones(FQs) are eutherapeutic and relatively inexpensive antibiotics that are proverbially applied in clinical medicine because of their wide antibacterial range. FQs have a common pyridine ketonic structure and block DNA replication by inhibiting DNA gyrase. However, the photosensitive toxicity of FQs has recently gained considerable research attention. Gemifloxacin(GEFX), balofloxacin(BFX), pazufloxacin(PAX), and tosufloxacin(TSFX) are members of FQ antibiotics, and the mechanisms of DNA and protein photodamage induced by these drugs remain unclear. The photochemical properties and photosensitive toxicities of GEFX, BFX, and TSFX were studied by means of laser flash photolysis, pulse radiolysis, UV-Vis absorption, steady irradiation, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis experiments(SDS-PAGE). The results obtained in this study may help in understanding the relationship between the molecular structure and photosensitive toxicity of FQs.Laser flash photolysis and pulse radiolysis were performed to investigate the photochemical properties of the triplet states of GEFX(3GEFX*) and TSFX(3TSFX*) in aqueous solutions. 3GEFX* and 3TSFX* absorption spectra showed maximum absorption at 510 and 460 nm, respectively. 3GEFX* and 3TSFX* were quenched by naproxen(NAP) via energy transfer with reaction rate constants of 1.2 × 108 and 1.3 × 109 dm3 mol-1 s-1, respectively. The energy of 3GEFX* was determined as 266 kJ mol-1. Transient absorption spectra showed direct evidence of electron transfer from 2ˊ-deoxyguanosine-5ˊ-monophosphate(d GMP), tryptophan(TrpH), tyrosine(TyrOH), N,N,Nˊ,Nˊ-tetramethyl-p-phenylenediamine(TMPD), and ferulic acid(FCA) to 3GEFX* and 3TSFX*. To identify the mechanism of electron transfer between the triplet states of FQs and dGMP more distinctly, a series of competition reactions was designed to investigate the formation of oxidized dGMP radicals based on the indication of electron donors TMPD and FCA. The reactions of GEFX with hydroxyl radicals(?OH), hydrate electrons(eaqˉ), and azide radicals(N3?) were investigated by pulse radiolysis. The characteristic absorption spectra of the neutral radical, radical anion, and radical cation of GEFX were obtained and the rate constants of the reactions of GEFX with ?OH and eaqˉ were found to be 1.5 × 1010 and 1.4 × 1010 dm3 mol-1 s-1, respectively. Steady irradiation and SDS–PAGE results proved that GEFX can damage specific proteins, such as Lyso, and trigger the crosslinking of Lyso molecules. Photosensitive damage to Lyso was enhanced by increasing oxygen concentration, GEFX concentration, and irradiation time.Laser flash photolysis revealed the mechanism of reactions of FCA and Lyso with the PAX triplet state(3PAX*), and the rate constants of these reactions were obtained. We designed an indirect experiment involving competition reactions to investigate the protective mechanism provided by FCA to Lyso. FCA, an active antioxidant, effectively inhibited FQ-induced cross-linking of proteins and reduced the photosensitive damage. These results help further elucidate the protective mechanism provided by antioxidants to proteins.The photochemical and photophysical properties of BFX were studied through UV-Vis absorption and fluorescence emission. The pKa value was determined and the absorption and emission spectra of BFX were observed to be pH-dependent. Photoionization of BFX was also studied using laser flash photolysis and the results indicated that this photoionization is a single photon process. Pulse radiolysis of the reactions of ?OH, eaqˉ, and N3? with BFX were employed to investigate the neutral radical, radical anion, and radical cation of BFX. An indirect experiment involving competition reactions was designed to study the photosensitive damage induced by BFX radical cations. Steady irradiation and SDS–PAGE results indicated that Lyso photodamage caused by BFX in aerobic conditions results from the combined actions of Type I and II reactions.The present study provided systematic results on the photochemical properties of GEFX, BFX, and TSFX; the photodynamic actions of these transient species were also investigated. The mechanisms of photooxidation of DNA, amino acids, and protein by FQs were proposed, and the relevant bimolecular reaction rate constants were determined. The obtained results further elucidate the protective mechanism provided by antioxidants to biomolecules.