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: Mechanistic studies in both in vivo and in vitro systems showed that the Nrf2 - mediated protection against diabetic nephropathy is , at least , partially through inhibition of transforming growth factor - beta1 ( TGF - beta1 ) and reduction of extracellular matrix production .
### Output Text:
Mechanistic studies in both in vivo and in vitro systems showed that the Nrf2 - mediated protection against diabetic nephropathy is , at least , partially through inhibition of transforming growth factor - beta1 ( TGF - beta1 ) and reduction of extracellular matrix production . 