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: While AAP caused a 117 - fold elevation of serum transaminase activities in mice kept on a standard laboratory diet , which was significantly exacerbated by ethanol and inhibited by nicotinic acid amide ( NAA ) , adverse effects were noted in animals fed a diet free of precursors of NAD .
### Output Text:
While <span class="chemical">AAP</span> caused a 117 - fold elevation of serum transaminase activities in mice kept on a standard laboratory diet , which was significantly exacerbated by <span class="chemical">ethanol</span> and inhibited by <span class="chemical">nicotinic acid amide</span> ( <span class="chemical">NAA</span> ) , adverse effects were noted in animals fed a diet free of precursors of <span class="chemical">NAD</span> . 