Urolithin A suppresses glucolipotoxicity-induced ER stress and TXNIP/NLRP3/IL-1ß inflammation signal in pancreatic ß 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 ß 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-1ß 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-1ß 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-1ß signaling in MIN6 cells. Inhibitory effects of UA on TXNIP and IL-1ß 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-1ß signal pathway.

Urolithin A, a pomegranate metabolite, protects pancreatic ß cells from apoptosis by activating autophagy.

ETHNOPHARMACOLOGICAL RELEVANCE: Urolithin A is an active metabolite of plant polyphenol ellagic acid generated by intestinal flora, which is derived from strawberry or traditional anti-diabetic Chinese medicine such as Punica granatum L. and Phyllanthus emblica. The present study aimed to whether urolithin A can protect against glycolipid-toxicity-induced apoptosis of pancreatic ß-cells and the underlying mechanisms. MATERIALS AND METHODS: Apoptosis was induced in the pancreas of mice with type 2 diabetes and MIN6 pancreatic ß-cells. CC-8 assay was conducted to determine cell viability. Flow cytometry, JC-1 fluorescent probe, and western blot assays were performed to assess apoptosis. Immunofluorescence and western blot assays were used to detect changes in autophagy. The mechanism of apoptosis was elucidated using autophagy inhibitor chloroquine. RESULTS: Urolithin A intervention significantly reduced pancreatic cell apoptosis in diabetic mice and MIN6 ß cells. This was achieved by the downregulation of cleaved-caspase 3, cleaved-caspase 1, and restoration of cell viability, cell morphology and mitochondrial membrane potential, accompanied with the downregulation of autophagic protein SQSTM1/p62 and upregulation of LC3II. Chloroquine, an autophagy inhibitor, reversed the anti-glucolipotoxic and anti-apoptotic effects of urolithin A. CONCLUSION: These findings suggest that urolithin A protects against glucolipotoxicity-induced apoptosis in pancreatic ß-cells by inducing activation of autophagy.