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: MMP - TIMP and ADAM mRNAs were semi - quantitatively analyzed and protein expressions were determined by immunohistochemistry .
### Output Text:
MMP - TIMP and ADAM mRNAs were semi - quantitatively analyzed and protein expressions were determined by immunohistochemistry . 