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: Serum hemoglobin , haptoglobin and angiogenesis markers of vascular endothelial growth factor and angiopoetin - 2 were investigated before and after therapy .
### Output Text:
Serum hemoglobin , haptoglobin and angiogenesis markers of vascular endothelial growth factor and angiopoetin - 2 were investigated before and after therapy . 