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: These results suggest that 1 ) both SOD and DMTU have protective effects on GM - mediated nephropathy , 2 ) the mechanisms for the protective effects differ for SOD and DMTU , and 3 ) superoxide anions play a critical role in GM - induced renal vasoconstriction .
### Output Text:
These results suggest that 1 ) both SOD and <span class="chemical">DMTU</span> have protective effects on <span class="chemical">GM</span> - mediated nephropathy , 2 ) the mechanisms for the protective effects differ for SOD and <span class="chemical">DMTU</span> , and 3 ) <span class="chemical">superoxide</span> anions play a critical role in <span class="chemical">GM</span> - induced renal vasoconstriction . 