Urolithin A suppresses glucolipotoxicity-induced ER stress and TXNIP/NLRP3/IL-1β inflammation signal in pancreatic β cells by regulating AMPK and autophagy.

Background: Pancreatic inflammation plays a key role in diabetes pathogenesis and progression. Urolithin A (UA), an intestinal flora metabolite of pomegranate, has anti-diabetic, anti-inflammatory and kidney protection effects among others. However, its effects on pancreatic inflammation and the potential mechanisms have not been clearly established.

Purpose: This study aimed at investigating the molecular mechanisms of UA anti-pancreatic inflammation under a diabetic environment.

Methods: Diabetes induction in male C57BL/6 mice was achieved by a high fat diet and intraperitoneal streptozotocin injections. Then, diabetic mice were orally administered with UA for 8 weeks. In vitro, endoplasmic reticulum stress and MIN6 pancreatic β cell inflammation were induced using 25 mM glucose and 0.5 mM palmitic acid. The effects of UA were evaluated by immunohistochemistry, Western blot, and enzyme linked immunosorbent assays. Finally, the underlying mechanisms were elucidated using an autophagy inhibitor (chloroquine, CQ) and an AMPK inhibitor (dorsomorphin dihydrochloride).

Results: UA significantly inhibited IL-1β secretion and TXNIP/NLRP3 expression in the pancreas of diabetic mice and in MIN6 pancreatic cells. UA downregulated the ER stress protein, p-PERK, and promoted AMPK phosphorylation. UA activated autophagy to inhibit TXNIP/NLRP3 IL-1β inflammatory signal, an effect that was reversed by CQ. Dorsomorphin 2HCL, reversed the autophagy-activation and anti-inflammatory effects of UA. Verapamil, clinically applied as an antiarrhythmic drug, is a TXNIP inhibitor for prevention of beta cell loss and diabetes development, but limited by its cardiac toxicity. In this study, verapamil (as positive control) inhibited NLRP3 /IL-1β signaling in MIN6 cells. Inhibitory effects of UA on TXNIP and IL-1β were weaker than those of verapamil (both at 50 μM, p < 0.05, p < 0.01). Conversely, inhibitory effects of UA on p62 were stronger, relative to those of verapamil (p < 0.05), and there were no differences in AMPK activation and LC3 enhancement effects between UA and verapamil.

Conclusion: UA is a potential anti-pancreatic inflammation agent that activates AMPK and autophagy to inhibit endoplasmic reticulum stress associated TXNIP/NLRP3/IL-1β signal pathway.