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: Dexamethasone ( Dex ) - induced hypertension is characterized by endothelial dysfunction associated with nitric oxide ( NO ) deficiency and increased superoxide ( O2 - ) production .
### Output Text:
<span class="chemical">Dexamethasone</span> ( <span class="chemical">Dex</span> ) - induced hypertension is characterized by endothelial dysfunction associated with <span class="chemical">nitric oxide</span> ( <span class="chemical">NO</span> ) deficiency and increased <span class="chemical">superoxide</span> ( <span class="chemical">O2 -</span> ) production . 