Background/Purpose: Monosodium urate (MSU)-induced inflammation is caused by the deposition of MSU crystals in the joints and periarticular tissues under conditions of hyperuricemia. These deposits can activate primed joint resident macrophages which form the NOD-, LRR- and pyrin-containing protein 3 (NLRP3) inflammasome, cleaving pro-IL-1β and causing inflammation. NLRP3 formation relies on TGF-β Activated Kinase 1 (TAK1) and its downstream effectors for both production of pro-IL-1β during the priming phase and phosphorylation of NLRP3 before inflammasome formation during activation. Pentagalloyl glucose (PGG) is a hydrolysable polyphenolic natural compound that has widely been shown to have anti-inflammatory and anti-cancer properties and has recently been shown to inhibit TAK1. Here we tested the efficacy of PGG in MSU-induced inflammasome activation and elucidated its mechanism of action in THP-1-derived macrophages in vitro and a mouse model of MSU-induced inflammation.

Methods: MSU crystal-activated THP-1 macrophages were used to investigate the signaling mechanisms modulated by PGG to elicit its anti-inflammatory activity by Western blotting and ELISA methods. The effect of PGG on inflammasome activity was investigated using immunofluorescence to determine ASC speck formation. The efficacy of PGG was compared with a known irreversible inhibitor of TAK1, 5Z-7-oxozeaneol (5z7o). For in vivo evaluation, we treated C57BL6/J mice with potassium oxonate (a uricase inhibitor; 300 mg/kg; intraperitoneally (i.p.)) daily for 7 days. On the 7^th day, mice were pretreated with PGG (30 mg/kg; i.p.) for 2 hours followed by a single intraarticular injection of MSU crystals into the right ankle of each mouse to mimic an acute gout flare. Ankle diameters were measured each day until the flares resolved.

Results: Pretreatment of THP-1 macrophages with PGG (0.1-10 µM) caused a dose-dependent inhibition in the phosphorylation of TAK1 (p-TAK1^184/187) and p-NF-κBp65. PGG treatment significantly reduced the production of pro-IL-1β during the priming phase. Analysis of cell culture supernatant by ELISA showed a dose-dependent decrease in chemokine (IL-8, MCP-1 and RANTES) production and a significant decrease in soluble IL-1β production, which correlated with a similar inhibition of NLRP3 inflammasome formation by PGG. Daily injections of PGG significantly reduced the diameter of ankles of mice injected with MSU by 40% on day 1, and rapidly resolved the inflammation compared to the untreated ankles.

Conclusion: PGG significantly reduced MSU-induced proinflammatory mediators and inhibited the formation of NLRP3 inflammasomes. Our finding suggests that treatment with TAK1 inhibitors may help reduce the onset and severity of acute gout flares.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/tgf-%ce%b2-activated-kinase-1-inhibition-by-pentagalloyl-glucose-inhibits-nlrp3-inflammasome-formation-and-ameliorates-msu-induced-inflammation/