B-016 Development of a novel immunoassay that measures only the CELA3B Isoform of Fecal Pancreatic Elastase: A potentially more sensitive method to detect exocrine pancreatic insufficiency

Background Measurement of fecal pancreatic elastase 1 (PE-1) is used as a convenient/non-invasive way to determine exocrine pancreatic insufficiency (EPI) in stool. EPI is caused by a deficiency of exocrine pancreatic enzymes (including PE-1) that results in a lack of normal digestion.[1] This deficiency of exocrine pancreatic enzymes can be caused by chronic pancreatitis, cystic fibrosis, celiac disease, diabetes, pancreatic resection and cancer.[1,2] In humans, PE-1 consists of two isoforms, CELA3A and CELA3B.[3] Current commercially available fecal PE-1 immunoassays measure both isoforms simultaneously without being able to distinguish between them.[1,3] For this study, we created an ELISA that specifically measures only CELA3B to complement our commercially available PE kit that measures both isoforms simultaneously. In doing so, we can directly measure CELA3B and deduce 3A levels. The goal for measuring individual isoforms is to determine whether there are differences in their quantities in normal vs EPI suspected individuals and secondarily to determine whether this information could lead to better detection of EPI. Methods A novel sandwich ELISA was created using homemade mouse monoclonal antibodies specific for CELA3B. Human recombinant CELA3A and 3B were made to test isoform specificity. Our commercially available fecal PE ELISA measures both CELA3A and 3B simultaneously and was used to measure total PE levels. As a preliminary approach, human fecal PE (both total and CELA3B) was measured in control and individuals with suspected EPI. Results All patients tested had CELA3A and 3B in their stool. In the control group (n=34), CELA3A and 3B consisted of 69% and 31% of total PE, respectively, with average concentrations of CELA3A (472 ug/g), 3B (279 ug/g) and total (751 ug/g). For the suspected EPI group (n=19), CELA3A consisted of 77% and 3B 23% of total PE, with average concentrations of CELA3A (83 ug/g), 3B (28 ug/g) and total (111 ug/g). Conclusions With the use of our novel CELA3B specific and commercial total PE immunoassays, we measured the levels of both CELA3A and 3B human PE isoforms in a cohort of control and EPI suspected subjects. Intriguingly, CELA3A was the predominant isoform measured in both cohorts, which is at odds with current literature that states 3B is the main isoform that survives intestinal transit.[3] Our data also demonstrated an 8% drop in CELA3B in patients with suspected EPI vs control, which may make it a more sensitive isoform to examine. Whether measurement of a single isoform has clinical significance to earlier detection of EPI and its associated diseases is unknown, but this preliminary data suggests the topic merits further investigation.