In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: The protection by overexpression of superoxide dismutase supports the hypothesis that oxidant stress plays a significant role in aminoglycoside - induced ototoxicity .
### Output Text:
The protection by overexpression of <span class="chemical">superoxide</span> dismutase supports the hypothesis that oxidant stress plays a significant role in <span class="chemical">aminoglycoside</span> - induced ototoxicity . 