Interaction of amikacin and tobramycin with melanin in the presence of Cu2+ and Zn2+ ions.

Aminoglycoside antibiotics such as amikacin and tobramycin are the most commonly used treatment against Gram-negative bacterial infections. The widely used aminoglycosides have the unfortunate side-effect of targeting sensory hair cells of the inner ear, so that treatment often results in permanent hair cell loss. Because melanin can act as an antioxidant as well as drug and metal chelator, evidence for its role in protecting the stria and organ of Corti against noise, ototoxins, and aging has long been sought. Protective properties of melanin may derive from its ability to bind cations and metals and to scavenge free radical. The aim of the presented work was to examine the amikacin and tobramycin binding to melanin in the presence of Cu2+ and Zn2+ ions. It has been demonstrated that amikacin and tobramycin form stable complexes with melanin in the presence of metal ions and the amount of aminoglycoside antibiotics bound to melanin increases with the increasing of initial drugs concentration. For amikacin and tobramycin complexes with [melanin-Cu2+] and [melanin-Zn2+] one class of binding sites with the association constant K 10(3)M(-1) has been found. It has been also shown that Cu2+ and Zn2+ ions administered to melanin before complexing with drugs decrease the amount of aminoglycosides bound to melanin, probably by blocking some active centers in the melanin molecule.