Doxycycline (DOXY) is an antibiotic routinely prescribed in human and veterinary medicine for antibacterial treatment, but it has also numerous side effects that include oxidative stress, inflammation, cancer or hypoxia-induced injury. Endogenously produced hydrogen sulfide (H₂S) and polysulfides affect similar biological processes, in which reactive oxygen species (ROS) play a role. Herein, we have studied the interaction of DOXY with H₂S (Na₂S) or polysulfides (Na₂S₂, Na₂S₃ and Na₂S₄) to gain insights into the biological effects of intermediates/products that they generate. To achieve this, UV-VIS, EPR spectroscopy and plasmid DNA (pDNA) cleavage assay were employed. Na₂S or Na₂S₂ in a mixture with DOXY, depending on ratio, concentration and time, displayed bell-shape kinetics in terms of producing/scavenging superoxide and hydroxyl radicals and decomposing hydrogen peroxide. In contrast, the effects of individual compounds (except for Na₂S₂) were hardly observable. In addition, DOXY, as well as oxytetracycline and tetracycline, interacting with Na₂S or other studied polysulfides reduced the •cPTIO radical. Tetracyclines induced pDNA cleavage in the presence of Na₂S. Interestingly, they inhibited pDNA cleavage induced by other polysulfides. In conclusion, sulfide and polysulfides interacting with tetracyclines produce/scavenge free radicals, indicating a consequence for free radical biology under conditions of ROS production and tetracyclines administration.
Keywords: DNA cleavage; EPR spectroscopy; doxycycline; hydrogen sulfide; hydroxyl radical; oxytetracycline; polysulfides; superoxide; tetracycline; •cPTIO radical.