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: It has also been suggested that sirolimus directly causes increased glomerular permeability / injury , but evidence for this mechanism is currently inconclusive .
### Output Text:
It has also been suggested that <span class="chemical">sirolimus</span> directly causes increased glomerular permeability / injury , but evidence for this mechanism is currently inconclusive . 