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: Their ototoxicity is a serious health problem and , as their ototoxic mechanism involves the production of NO , we need to assess the use of NO inhibitors for the prevention of aminoglycoside - induced sensorineural hearing loss .
### Output Text:
Their ototoxicity is a serious health problem and , as their ototoxic mechanism involves the production of <span class="chemical">NO</span> , we need to assess the use of <span class="chemical">NO</span> inhibitors for the prevention of <span class="chemical">aminoglycoside</span> - induced sensorineural hearing loss . 