Endocrine Abstracts

In this study we explore and integrate a pathway for loss of functional beta cell mass in diabetes. Inflammatory cytokines induce human islet dysfunction, elevate expression of 12-lipoxygenase, increase cellular reactive species and induce NADPH oxidase. These pathways are elevated in islets from diabetic donors.

NADPH oxidase-1 (NOX-1) is significantly induced in either human donor islets, primary mouse islets or homogeneous beta cell lines following stimulation with a cocktail of inflammatory cytokines (TNFα, IL-1β, INFγ) (P<0.05). Beta cell dysfunction was concomitantly induced by the pro-inflammatory cytokine (PIC) stimulation as measured by the loss of glucose stimulated insulin response (P<0.05), elevated expression of MCP-1 (P<0.01), increase in cellular reactive oxygen species (ROS) (p<0.05) and induced cell death. Inhibitors of NADPH oxidase, apocynin, diphenylene iodonium or selective NOX1/4 inhibitors, block ROS generation (P<0.01) and inhibit expression of MCP-1 (P<0.05) induced by PICs. In islets from diabetic donors, expression of NOX-1 is elevated (P<0.05, n=5).

12-lipoxygenase (12-LO) has been shown to regulate NADPH oxidase in non-islet models. Does this linkage occur in islets? Stimulation with PICs increases the expression of 12-LO in human islets, and 12-HETE (12-hydroxyeicosatetraenoic acid), a product of 12-LO activity, stimulates NOX-1 expression 12±4 fold (P<0.05) in human islets. Validating an association between 12-LO and NOX-1 in islets, we show that a selective inhibitor of 12-LO (NCTT-956) blocks 80% of NOX-1 expression (P<0.01) and inhibits procaspase 3 cleavage (P<0.05) induced by PICs in homogeneous beta cells. An inactive structural analog (NCTT-695) did not exert these effects.

This report unifies 12-LO and NOX-1 in beta cell dysfunction induced by PICs, a pathway not previously described in islet beta cells. Inhibition of this pathway is a candidate target to preserve and protect beta cell mass in diabetes.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This work was supported, however funding details unavailable.