Background/Purpose:

Gout is associated with both multiple dietary triggers and metabolic co-morbidities, including obesity, metabolic syndrome, and diabates. AMP-activated protein kinase (AMPK) is a master regulator of energy homeostasis, and tissue AMPK activity is decreased by high fat diet and in diabetes, and is conversely increased by clarotic restraint, exercise, and several drugs in the clinic for arthritis (sodium salicylate, high dose aspirin, methotrexate) and by metformin. AMPK is a heterotrimeric complex compoased of an alpha catalytic subunit and two regulatory beta and gamma subunits. Phosphorylation at Thr-172 within the catalytic domain of the a subunit is critical for AMPK activity. Activation of AMPK exerts anti-inflamamtory effects partly by suppressing NF-kB activation. Thus, we assessed the function of AMPK in monsodium urate (MSU) crystal-induced inflammation in vitro and in vivo.

Methods:

We added MSU crystals (0.2 mg/ml) for 18 h to bone marrow derived macrophages (BMDMs) from AMPKa1 knockout (KO) mice and C57BL/6 mice, and pre-treated with AMPK activators AICAR (1 mM) or highly AMPK selective A-769662 (0.25 mM). We analyzed conditioned media by ELISA for cytokines that drive gout arthritis, and cell lysates by Western blot for AMPK activity (phosphorylation of AMPKa). We also injected A-769662 (0.5 mM) one hour prior to injection of MSU crystals (3 mg) into mouse SQ air pouches in vivo, and collected samples 6 hrs later.

Results:

MSU crystals decreased AMPK activity (phosphorylation of AMPKa Thr172) in BMDMs, and both AICAR and A-769662 inhibited IL-1b and CXCL1 induction by 75% (p=0.0006) and 88% (p=0.0009), respectively. Conversely, MSU crystal-induced production of IL-1b and CXCL1 was enhanced 1.5 to 2-fold in AMPKa1 knockout BMDMs. Colchicine at 10 nM concentration achieved by standard, low dose therapy for acute gout, up-regulated AMPK activity in BMDMs. Last, A-769662 attenuated inflammatory responses to MSU crystals in vivo by 72% reduction of number of infiltrating leukocytes (p=0.04) and decrease in IL-1b and CXCL1 in pouch fluid 60% (p=0.003) and 50% (p=0.025), respectively.

Conclusion:

AMPKa1 deficiency enhances MSU crystal-induced macrophage IL-1b and CXCL1 release in vitro. Conversely, selective activation of AMPK by A-769662 markedly suppresses MSU crystal-induced inflammatory responses both in vitro and in vivo. We also established that nanomolar colchicine, in addition to certain other agents in the clinic for arthritis and diabetes, has the capacity to suppress gouty inflammation partly via AMPK activation. Our results indicate a novel, diet and drug targetable mechanism by which high fat diet, diabetes and the urate crystal by itself, are linked with heightened inflammatory potential of urate crystals in gout through decreased tissue activity of the metabolic super-regulator AMPK.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/targeted-activation-of-the-metabolic-super-regulator-amp-activated-protein-kinase-ampk-blunts-gouty-inflammation/