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: In conclusion , the NF - kappaB inhibitor and antioxidant PDTC protected the piriform cortex , whereas it did not affect hilar neuronal loss .
### Output Text:
In conclusion , the NF - kappaB inhibitor and antioxidant <span class="chemical">PDTC</span> protected the piriform cortex , whereas it did not affect hilar neuronal loss . 