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: Oxidative stress was determined by measuring the oxidation of lipids and proteins and diminution in renal Nrf2 levels .
### Output Text:
Oxidative stress was determined by measuring the oxidation of lipids and proteins and diminution in renal Nrf2 levels . 