Study On The Phototoxicity And Inhibition Mechanism Of Fluoroquilonones

Fluoroquinolone(FQs)is a world-widely used group of antibiotic drugs that have basic structure of quinolone,this kind of antibiotics have significant advantages such as broad antibacterial spectrum,good efficacy,and relatively lower slighter effects.However,FQs also cause several types of side effects like central neurotoxicity,phototoxicity and light induced cell mutations.Despite the low incidence,there are considerable patients suffering from these side effects due to the large numbers of patients taking FQs.The study of the formation mechanism of its phototoxicity has attracted the efforts of many researchers,and substantial numbers of meaningful results have been obtained,but until now,the structural factors that cause the phototoxicity of FQs have not been clarified systematically and convincingly.The thesis combine transient research methods such as laser flash photolysis and pulse radiolysis and steady-state methods including gel electrophoresis,HPLC,UV-Vis absorption spectra,fluorescence emission spectra,as well as theoretical calculation,to investigate the structure-phototoxicity relationship of FQs.Despite revealing the cause of phototoxicity from chemical structure perspective,this thesis attempts to develop novel exogenous protective agents to reduce FQs induced phototoxicity as well,and improve the commonly used detection methods for reactive oxygen species(ROS)to make the research results more reliable.By comparing the photochemical properties and phototoxicity of pefloxacin and difloxacin,the thesis investigated the influence to phototoxicity of substituents in position 1 of FQs.It is found that the maximum excitation wavelength of FQs is blue shifted from UVA band to UVB band,along with the substituent in position 1 changing from ethyl group to fluoro phenyl group.In consideration that majority energy of the UV region which arrives at the surface of the earth locates in UVA band,the blue shift is beneficial to the reduction of phototoxicity.The results obtained by this thesis shows that the blue shift effect of the excitation wavelength caused by the steric effect is more significant to phototoxicity than that of defluorination reaction.By analyzing the photochemical properties and phototoxicity of antofloxacin(ANT)and levofloxacin(LEV),the thesis investigated the influence to phototoxicity of substituents in position 5 of FQs.It is found that if the number 5 position is an amino group(ANT),the theoretical calculation shows that the excitation from the ground state to the excited state of the FQs requires lower energy and a higher probability of transition compared with LEV,which substituent in position 5 is H atom.The addition of amino group changes the intramolecular charge transfer processes thus leads to the non radiative deactivation passway of ANT-related transient products,in consequence,no triplet states was found under experimental condition and no photosensitive damage of biomolecules was found in our study.The thesis also tried to introduce antioxidants from the external point of view to mitigate the damage of biomolecules.Our results shows that graphene oxide can protect biomolecules from UV-induced photosensitive damage through physical shielding,charge transfer and energy transfer processes.Meanwhile,it can donate electrons to impaired biomolecules and repaire them.Due to the aforementioned mechanisms,graphene oxide exhibits excellent protective effects to proteins in our study.Since graphene oxide has been applied as drug carrier in numerous reports,it is feasible to use graphene oxide as the carrier of FQs,playing the role of drug delivery and reducing phototoxicity simultaneously.In view of the key role of reactive oxygen species(ROS)in the cause of photosensitivity,we have studied the commonly used detection methods of ROS.As the parent compound of ROS,most fluently used probing methods of superoxide anion radical is tetrazolium salts colorimetry methodology.For the first time,this thesis found that the Colorimetric agent exhibits strong oxidizability under UV irradiation and is no longer the specific probe of detecting superoxide anion radical.Furthermore,by adding superoxide dismutase(SOD)in the detection process,the probing method is improved and the calculation formulas of superoxide anion free radical yield are obtained accurately.These finding is helpful in analyzing the FQs phototoxicity accurately,as well as detecting the origin of nanotoxicity caused by nanomaterials effectively.