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: Our results provide evidence that the AAP - induced hepatitis and its exacerbation by ethanol can either be reduced by end - product inhibition of PARP by NAA or by dietary depletion of the enzyme ' s substrate NAD .
### Output Text:
Our results provide evidence that the <span class="chemical">AAP</span> - induced hepatitis and its exacerbation by <span class="chemical">ethanol</span> can either be reduced by end - product inhibition of PARP by <span class="chemical">NAA</span> or by dietary depletion of the enzyme ' s substrate <span class="chemical">NAD</span> . 