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: Overall , these findings indicate that VPA treatment results in oxidative stress , as measured by levels of 15 - F ( 2t ) - IsoP , which precedes the onset of necrosis , steatosis , and elevated levels of serum alpha - GST .
### Output Text:
Overall , these findings indicate that <span class="chemical">VPA</span> treatment results in oxidative stress , as measured by levels of <span class="chemical">15 - F ( 2t ) - IsoP</span> , which precedes the onset of necrosis , steatosis , and elevated levels of serum alpha - GST . 