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: RESULTS : Urinary NGF , PGE2 and PGF2alpha were significantly increased in patients with OAB compared with controls ( p < 0 . 05 ) .
### Output Text:
RESULTS : Urinary NGF , <span class="chemical">PGE2</span> and <span class="chemical">PGF2alpha</span> were significantly increased in patients with OAB compared with controls ( p < 0 . 05 ) . 