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: Absence of PKC - alpha attenuates lithium - induced nephrogenic diabetes insipidus .
### Output Text:
Absence of PKC - alpha attenuates <span class="chemical">lithium</span> - induced nephrogenic diabetes insipidus . 