401 - A Radical Pathway for Minocycline Toxicity: Role of Cytochrome c and Sulfite

Abstract

Minocycline (MC) is a second-generation semi-synthetic analogue of tetracycline. MC has been used as an antibiotic and for the treatment of various diseases such as acne vulgaris, sexually transmitted diseases, and rheumatoid arthritis. MC is currently being explored in various clinical trials for the treatment of cardiovascular diseases such as stroke, vascular aneurisms, and coronary by-pass surgery. However, the clinical use of MC has been associated with potential side effects. It has been demonstrated that MC interacts with cytochrome c (Cyt-c) and inhibits its peroxidase activity. However, molecular mechanism involved in the interaction between Cyt-c and MC is not studied. In this study, UV-visible spectroscopic measurements were carried out to understand the reaction between ferric cytochrome c (Fe3+Cyt-c) and MC. MC reduces Fe3+Cyt-c to ferrous cytochrome c (Fe2+Cyt-c). The reduction of Fe3+Cyt-c increases with increasing concentration of MC. Electron paramagnetic resonance (EPR) spin trapping studies using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) were performed with Fe3+Cyt-c, MC, and sulfite. An EPR spectrum corresponding to the sulfite radical adducts of DMPO (DMPO-SO3–) was obtained. The formation of DMPO-SO3– was very low in the absence of MC. Interestingly, the addition of MC enhanced the DMPO-SO3– adducts. Furthermore, the formation of DMPO-SO3– adducts increased with increasing concentration of MC. From these results, we propose a mechanism that the Fe3+Cyt-c oxidizes MC to MC radical, which subsequently oxidizes sulfite to sulfite radical. Our results suggest that Fe3+Cyt-c could have a novel role in the deleterious effects of MC in biological systems by increasing the production of sulfite radical.