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: The possible relationship between mesangial dysfunction and development of glomerular sclerosis was studied in the puromycin aminonucleoside ( PAN ) model .
### Output Text:
The possible relationship between mesangial dysfunction and development of glomerular sclerosis was studied in the <span class="chemical">puromycin aminonucleoside</span> ( <span class="chemical">PAN</span> ) model . 