A group of doctors have confirmed that 12-lipoxygenase (12-LO) is indeed found in human islets and that its pro-inflammatory lipid products can lead to lower insulin production and beta-cell death, which gives rise to type 1 diabetes. The team, from Eastern Virginia Medical School's (EVMS) Strelitz Diabetes Center, studied human islets from individuals who had donated their bodies to science through the Juvenile Diabetes Research Foundation (JDRF) Islet Resource Center Consortium.
The research was led by Jerry Nadler, M.D., professor and chair of internal medicine and director of the center. It is published in the February issue of The Journal of Clinical Endocrinology and Metabolism.
Prior research has established that 12-LO, a protein-based enzyme found in beta cells, produces specific lipids that cause inflammation and can lead to the death of beta cells in laboratory models. Yet, little is known about the differential effect of the various hydroxyeicosatetraenoic acids (HETEs) that result from LO activity in human islets, the EVMS team explains. Their study thus focused on comparing the effects of 12-LO products on human islet viability and function.
One challenge has been to validate that 12-LO and its pro-inflammatory lipid products have a role in human diabetes. Gaining access to human beta cells can be difficult, but the school was able to leverage resources from JDRF’s Islet Resource Center Consortium, Dr. Nadler explains.
Human islets were treated with stable compounds derived from LOs: 12(S)-HETE, 15HETE, 12HPETE, and 12RHETE. The islets were then examined for insulin secretion and islet viability. The p38-MAPK and JNK stress-activated pathways were investigated as mechanisms of 12-LO-mediated islet inhibition in rodent and human islets.
They found that insulin secretion was consistently reduced by 12(S)-HETE and 12HPETE. 12(S)-HETE at 1 nM reduced viability activity by 32% and increased cell death by 50% at 100 nM in human islets. These effects were partially reversed with lisofylline, a small molecule anti-inflammatory compound that protects mitochondrial function.
Additionally, 12(S)-HETE increased phosphorylated p38-MAPK protein activity in human islets, the scientists report. Injecting 12-LO siRNA into C57BL/6 mice reduced 12-LO and phosphorylated p38-MAPK protein levels in mouse islets. The addition of pro-inflammatory cytokines increased phosphorylated p38 levels in normal mouse islets but not in siRNA-treated islets.
“We are currently working with investigators in California and the National Institutes of Health to identify ideal medications that would target 12-LO as a new treatment to halt immune damage to human insulin-producing cells,” says David A. Taylor-Fishwick, Ph.D., associate professor.