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: In pre - nephrotic stage the plasma level of fatty acids , triacylglycerol and VLDL decreased while that of phospholipid , cholesteryl esters and HDL remained constant .
### Output Text:
In pre - nephrotic stage the plasma level of <span class="chemical">fatty acids</span> , <span class="chemical">triacylglycerol</span> and VLDL decreased while that of phospholipid , <span class="chemical">cholesteryl esters</span> and HDL remained constant . 