SUN-LB124 Novel Elisa Assays Demonstrate Specificity of Islet and Intestinal Processing of Proglucagon

Circulating proglucagon peptides (PGP) are produced in islet α-cells, enteroendocrine L-cells. Release of PGP is thought to be tissue specific, e.g. α-cells make glucagon and L-cells make GLP-1 through predominant actions of proconvertases 2 and 1/3 (PC2 and PC1/3). However, this dichotomous model has recently been challenged. To address the contribution of the gut and pancreas to plasma PGP we developed 4 novel sandwich ELISA assays and applied them in studies with PGP stimulation from the islet (IV arginine) and intestine (meal). Monoclonal antibodies were raised in mice with genetic ablation of proglucagon transcription. Clones were screened and selected for affinity and specificity, and assays for glucagon, GLP-1, glicentin and oxyntomodulin developed. Eight healthy humans received 5 g arginine intravenously after a 12 hour fast and had blood sampled for 15 minutes; an additional 10 consumed a liquid mixed nutrient meal and prandial blood was taken for 180 minutes. None of the assays registered signal in plasma from proglucagon null mice, and specificity, background and cross-reactivity were acceptable in each. In response to IV arginine plasma glucagon increased 4-fold, and GLP-1 1.5-fold, with significant increases in 15-minute AUC; there was no significant change in either glicentin or oxyntomodulin. In response to meal ingestion there was no change in circulating glucagon, but oxyntomodulin, GLP-1 and glicentin increased 2, 3, and 4-fold respectively. These findings are generally compatible with PC1/3 dominant processing of PGP in the gut, but raise the possibility that α-cells produce both PC2 (glucagon) and PC1/3 (GLP-1) products.