The investigators used subcutaneous murine air pouch inflammatory responses to MSU crystals for their animal model of gout. The subcutaneous air pouches were generated by repeated injection of sterile air into 6-week-old and 8-week-old mice. The researchers found that the AMPKα1 knockout mice had significantly increased MSU crystal-induced leukocyte infiltration in air pouch cavities when compared to wild-type mice (see Figure 1). The MSU crystal-induced inflammation in wild-type mice was inhibited by treatment with the AMPK activator A-769662 (see Figure 2). Western blot analysis of the tissues lining the air pouch confirmed that A-769662 increased phosphorylation of AMPKα. The investigators documented the consequent decreased inflammatory response through IL-1β and CXCL release both in vitro and in vivo.
A-769662 also promoted AMPK-dependent macrophage antiinflammatory M2 polarization in vitro. In particular, A-769662 inhibited MSU crystal-induced phosphorylation of the NF-ҡB p65 subunit in BMDMs. Moreover, treatment with A-769662 inhibited NLRP3 gene expression and activation of caspase-1 and IL-1β.
The latest research suggests that colchicine is an effective treatment for gout because it activates the nutritional biosensor AMPK.
Colchicine Inhibits Inflammatory Response
The team then treated BMDMs that had been stimulated by MSU crystals with a low concentration of colchicine (10 nM). The colchicine dose was selected to mimic the peak plasma concentrations clinically achieved in dosing for gout flare prophylaxis. The investigators observed no significant change in cell viability at this concentration of colchicine. The low dose did, however, promote the phosphorylation of AMPKα as well as macrophage M2 polarization. The polarization was documented by an increase in the ratio of arginase-1 to NOS2 mRNA expression and was observed in the BMDMs from wild-type mice, but not in the BMDMs from AMPKα1 knockout mice. Treatment with colchicine also inhibited the inflammatory response and reduced activation of caspase-1, as well as the release of IL-1β and CXCL1 by wild-type BMDMs, but not knockout BMDMs.
Thus, a decrease in mouse macrophage AMPK activity promotes a state of increased inflammatory responsiveness to MSU crystals. Conversely, AMPK activation and colchicine are able to polarize macrophages in vitro to favor the antiinflammatory M2 population.
Future of Gout Research
The results of the current study open the door to new lines of research in gout pathophysiology and gout treatment. Robert Terkeltaub, MD, professor of medicine at UCSD and a senior investigator on the study, also suggested the possibility that future studies might use an AMPK biomarker in order to better understand the risk of gout flares and elucidate how best to manage the risk of flare. The results of the current study also point to the possibility that additional gout drug therapies might be developed that have an improved ability to increase AMPK activity.
