Anti-inflammatory action of exendin-4 in human islets is enhanced by phosphodiesterase inhibitors: potential therapeutic benefits in diabetic patients.
OBJECTIVE
Exendin-4, a glucagon-like peptide-1 (GLP-1) analogue, is reported to have modest anti-inflammatory effects in addition to that of improving beta cell survival. We therefore sought to determine whether exendin-4 decreases expression of the gene encoding chemokine (C-X-C motif) ligand (CXCL)10, which plays a role in initiating insulitis in type 1 diabetes.


METHODS
The expression of CXCL10 in human islets was determined at the mRNA level by real-time RT-PCR analysis and at the protein level by western blotting. The level of CXCL10 in culture medium was measured by ELISA. Pathway-specific gene expression profiling was carried out to determine the expression of a panel of genes encoding chemokines and cytokines in human islets exposed to cytokines.


RESULTS
IFN-γ induced expression of CXCL10 through activation of signal transducer and activator of transcription-1 (STAT-1). A combination of cytokines (IL-1β, TNF-α and IFN-γ) showed strong synergy in the induction of numerous chemokines and cytokines through nuclear factor kappa B and STAT-1. Exendin-4 suppressed basal expression of several inflammatory mediators. In combination with phosphodiesterase inhibitors, exendin-4 also decreased IFN-γ-induced CXCL10 expression in human islets and in MIN6 cells (a mouse beta cell line), and its secretion into the culture medium. Exendin-4 action was mimicked by forskolin, an activator of adenylyl cyclase, and by dibutyryl cyclic AMP. Protein kinase A was not involved in mediating exendin-4 action on CXCL10. The mechanism of exendin-4's anti-inflammatory action involved decreases in STAT-1 levels.


CONCLUSIONS
These findings suggest that the GLP-1-cyclic AMP pathway decreases islet inflammation in addition to its known effects on beta cell survival.
Pugazhenthi
U
U
Department of Medicine, University of Colorado Denver, Mail Stop 8106, 12801 E 17th Ave, Aurora, CO 80045, USA.
Velmurugan
K
K
Tran
A
A
Mahaffey
G
G
Pugazhenthi
S
S
D000704:Analysis of Variance; D000893:Anti-Inflammatory Agents / Q000494:pharmacology* / Q000627:therapeutic use; D015153:Blotting, Western; D002460:Cell Line; D002478:Cells, Cultured; D054357:Chemokine CXCL10 / Q000235:genetics / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism / Q000494:pharmacology; D003920:Diabetes Mellitus / Q000188:drug therapy* / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D000077270:Exenatide; D006801:Humans; D066298:In Vitro Techniques; D007371:Interferon-gamma / Q000494:pharmacology; D053583:Interleukin-1beta / Q000494:pharmacology; D007515:Islets of Langerhans / Q000187:drug effects* / Q000378:metabolism*; D016328:NF-kappa B; D010455:Peptides / Q000494:pharmacology* / Q000627:therapeutic use; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D012333:RNA, Messenger; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050794:STAT1 Transcription Factor / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D014688:Venoms / Q000494:pharmacology* / Q000627:therapeutic use
D000893:Anti-Inflammatory Agents; C114753:CXCL10 protein, human; D054357:Chemokine CXCL10; D053583:Interleukin-1beta; D016328:NF-kappa B; D010455:Peptides; D010726:Phosphodiesterase Inhibitors; D012333:RNA, Messenger; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D014409:Tumor Necrosis Factor-alpha; D014688:Venoms; D007371:Interferon-gamma; D000077270:Exenatide; D000242:Cyclic AMP