Nicotinic acid inhibits glucose-stimulated insulin secretion via the G protein-coupled receptor PUMA-G in murine islet ß cells.

OBJECTIVES: Chronic administration of nicotinic acid (NA), a potent antilipidemic compound, aggravates glycemic control in diabetic patients. It is not known if NA has direct effects on islet ß cells. METHODS: Real-time reverse transcriptase-polymerase chain reaction, in situ hybridization, and immunofluorescence techniques were used to examine the expression of NA receptor PUMA-G, a member of the G protein-coupled receptor (G-PCR) family, in murine islet ß cells. Calcium transient was measured using confocal microscopy, whereas the intracellular cyclic adenosine monophosphate and glucose-stimulated insulin secretion (GSIS) from isolated islets were determined by the enzyme-linked immunosorbent assay. RESULTS: High levels of PUMA-G transcripts and protein were detected in all ß cells, and about 40% of α cells. PUMA-G transcripts increased more than 3-fold in islets incubated with interferon γ. Cyclic adenosine monophosphate accumulation, induced by IBMX/forskolin, was inhibited by NA; however, the inhibition was completely abolished by pretreatment of the culture with pertussis toxin. No calcium transient was detected in islet cells in the presence of NA. Static incubation of islets with NA led to an approximately 30% reduction of GSIS. CONCLUSIONS: The results indicated that PUMA-G stimulation by NA in islet ß cells inhibited GSIS likely via activation of the Gi signaling pathway.

Intra-arterial targeted islet-specific expression of Sirt1 protects ß cells from streptozotocin-induced apoptosis in mice.

Gene therapy provides a promising approach to curing diabetes. However, an effective route for islet-specific targeting has yet to be established. Toward this end, the pancreatic blood circulation system in Balb/c mice was determined by the injection of rhodamine-containing beads. The efficiency of islet targeting was then measured by the injection of adenoviral vectors carrying a green fluorescence gene via the celiac trunk (C.T.). The results showed that >95% of islets and about 60% of ß cells within the pancreatic body and tail could be labeled 3 days after surgery. α-Cell labeling was not as efficient, whereas labeling of nonendocrine tissues was barely detectable. For proof of principle, adenoviral vectors carrying a Sirtuin transgene were injected similarly to test the islet protection effect in the streptozotocin (STZ)-induced type 1 diabetic model. The results demonstrated that overexpression of Sirtuin in STZ-treated mice reduced the level of ß-cell death and extent of glucose intolerance. This study reports on efficient islet-specific targeting by using adenoviral injection. This procedure could be invaluable to the treatment of diabetes and the study of islet biology.