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: Among all animals , glomerular and tubular injury were inversely correlated with mtDNA levels , mtDNA - encoded respiratory chain activities and with the expression of the mtDNA - encoded respiratory chain subunit COX - I .
### Output Text:
Among all animals , glomerular and tubular injury were inversely correlated with mtDNA levels , mtDNA - encoded respiratory chain activities and with the expression of the mtDNA - encoded respiratory chain subunit COX - I . 