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: Basic and clinical research has demonstrated that dementia of sporadic Alzheimer ' s disease ( sAD ) type is associated with dysfunction of the insulin - receptor ( IR ) system followed by decreased glucose transport via glucose transporter GLUT4 and decreased glucose metabolism in brain cells .
### Output Text:
Basic and clinical research has demonstrated that dementia of sporadic Alzheimer ' s disease ( sAD ) type is associated with dysfunction of the insulin - receptor ( IR ) system followed by decreased <span class="chemical">glucose</span> transport via <span class="chemical">glucose</span> transporter GLUT4 and decreased <span class="chemical">glucose</span> metabolism in brain cells . 