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: Similar to the remnant kidney model in PAN nephrosis the development of glomerular sclerosis may be related to " mesangial overloading . "
### Output Text:
Similar to the remnant kidney model in <span class="chemical">PAN</span> nephrosis the development of glomerular sclerosis may be related to " mesangial overloading . " 