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: Acute treatment with metformin has a protective effect in myocardial infarction by suppression of inflammatory responses due to activation of AMP - activated protein kinase ( AMPK ) .
### Output Text:
Acute treatment with <span class="chemical">metformin</span> has a protective effect in myocardial infarction by suppression of inflammatory responses due to activation of <span class="chemical">AMP</span> - activated protein kinase ( AMPK ) . 