Recently, some ELISA kits have been developed to specifically measure "active" GIP and GLP-1, but it is unclear if these kits can accurately quantify all bioactive forms.  Thus, we evaluated our novel receptor-mediated incretin bioassays in comparison to commercially available ELISA kits using plasma samples from healthy subjects before and after DPP-4 inhibitor administration.


 We utilized cell lines stably co-transfected with human GIP or GLP-1 receptors and a cAMP-inducible luciferase expression construct for the bioassays and commercially available ELISA kits. 
ELISA kits
Strikingly, at 15 min, active GIP levels as determined by the bioassay reached levels approximately 20-fold higher after the DPP-4 inhibitor treatment, while total and active GIP levels determined by ELISA were increased just 1.5 and 2.1-fold, respectively.  Following administration of a DPP-4 inhibitor there was an observable peak of active GLP-1 levels as determined by the bioassay at 15 min after oral glucose load, reaching 11.0 ± 0.62 pmol/l, 1.4-fold greater than levels obtained without DPP-4 inhibitor treatment.  In contrast, total GLP-1 levels determined by ELISA were decreased after DPP-4 inhibitor treatment.



DPP-4 inhibitor treatment