|Ph.D Student||Shulman Eliya|
|Subject||Studies towards Defining Biochemical Mechanism(s) for|
Aminoglycosides Induced Toxicity in Mammalian
|Department||Department of Chemistry||Supervisor||Professor Timor Baasov|
|Full Thesis text|
Aminoglycosides (AGs) are a powerful class of bactericidal antibiotics. These antibiotics target the 16S rRNA of the 30S ribosomal subunit and interfere with translational fidelity and the translocation step of protein synthesis, eventually resulting in bacterial cell death. Although a prokaryotic selectivity of action is crucial to the therapeutic utility of AGs as antibiotics, they are not entirely selective for the bacterial ribosome; they also bind to some extent to the eukaryotic cytoplasmic rRNA, and promote mistranslation. In fact, this lack of selectivity has been exploited as a treatment for genetic diseases that result from nonsense mutations.
However, a major drawback that limits AGs potential for suppression therapy is their high toxicity to mammals; they exhibit significant toxicity to mammalian cells (cytotoxicity) and most importantly they induce specific toxic events through kidney (nephrotoxicity) and through vestibular and auditory organs (ototoxicity).
The main objective of this research was to understand the origin of AG-induced toxicity, with special focus on cytotoxicity and ototoxicity. Particular emphasis was placed on the question of whether mitochondrial protein synthesis is a major cause in[CR1] AG-induced cytotoxicity and ototoxicity.
In this study we used standard AG antibiotics and synthetic derivatives of AGs that were developed in our laboratory (also named NB compounds) for the treatment of human genetic diseases. Preliminary cytotoxicity tests on synthetic AGs have shown that they exhibit significantly reduced cytotoxicity compered to standard AGs. In order to understand the origin of AG's toxicity, initially, by examining the ability of AGs to inhibit mitochondrial protein synthesis in vitro and ex vivo, we showed that the decreased specificity toward mitochondrial ribosome confers the lowered cytotoxicity of NB compounds. The same correlation was observed for ototoxic potential both in murine cochlear explants and the guinea pig in vivo. Finally, we provide insights on the mechanism of AG-induced toxicity. AGs inhibit mitochondrial protein synthesis in mammalian cells and perturb cell respiration, leading to a time- and dose-dependent increase in superoxide overproduction and accumulation of free ferrous iron in mitochondria caused by oxidative damage of mitochondrial aconitase, ultimately leading to cell apoptosis via the Fenton reaction. The results validate the power of rational design strategy to combat the adverse side effects of AGs and are therefore beneficial for further research in two directions: the design of new AG-based structures for the treatment of human genetic diseases and the design of new AG-based antibiotics with diminished deleterious effects on humans.