Protective role of human insulin against the cytotoxicity associated with human mutant S20 G islet amyloid polypeptide.

Aims/Introduction Islet amyloid polypeptide ( IAPP) is a main component of islet amyloid in type 2 diabetes and cosecreted from β-cell with insulin. Clinical evidence from the patients with S20 G mutation of the IAPP gene, as well as experimental evidence that insulin could inhibit amyloid formation of IAPP, suggests that a gradual reduction of insulin could be related to the cytotoxicity associated with S20 G- IAPP through long-term deterioration of β-cells in type 2 diabetes. Our objective was to show an effect of human insulin on S20 G- IAPP associated cytotoxicity. Materials and Methods We analyzed the cytotoxicity associated with S20 G- IAPP by controlling human insulin expression using adenovirus vectors with micro ribonucleic acid specifically against human insulin in endocrine At T-20ins cells, which express human insulin permanently. Additionally, we carried out a follow-up study of circulating IAPP and insulin in type 2 diabetic patients. Results S20 G- IAPP expression was associated with a decrease in viability and an increase in terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling-positive cells in At T-20ins cells. Furthermore, downregulation of human insulin enhanced the cytotoxicity associated with S20 G- IAPP, and induced the cytotoxicity associated with wild-type ( WT)- IAPP. Reduction of ubiquitin carboxy-terminal hydrolase L1 activity enhanced cytotoxicity under the downregulation of human insulin expression in both S20 G- and WT- IAPP transduced cells. A 5-year follow up of type 2 diabetic patients showed a disproportionate increase of serum fasting IAPP-to-insulin ratio from baseline. Conclusions Human insulin plays a protective role against the cytotoxicity associated with S20 G- IAPP, as well as WT- IAPP. The findings could suggest long-term deterioration of insulin secretion associates with IAPP linked cytotoxicity in type 2 diabetes. [ABSTRACT FROM AUTHOR]