Colchicine inhibits monosodium urate crystal-mediated inflammation by influencing F-actin formation

To understand the mechanism by which colchicine inhibits the inflammatory properties of monosodium urate (MSU) crystal deposits and tophi.

We investigated the effects of colchicine on the inflammatory properties of monosodium urate (MSU) crystal deposits in several models: (i) In vitro tophus formation by MSU and neutrophils; (ii) MSU-induced peritonitis model; (iii) Alpha-1-antitrypsin-induced peritoneal MSU flare model; (iv) MSU-induced arthritis model. We measured neutrophil numbers, NET formation, IL-1β production and F-actin generation by MSU crystals. In addition, we tested the effect of actin inhibitors SMIFH2, Cytochalasin B and Latrunculin B in the models.

Colchicine did not affect neutrophil numbers in all these models. However, colchicine was highly effective to inhibit NET formation, IL-1β production and F-actin generation indicating less pronounced tophus formation, lower inflammatory properties of tophi and reduced conversion from G-actin into F-actin, respectively. F-actin was shown to accumulate in tophi without presence of colchicine and being resistant to degradation by DNase I. Actin inhibitors SMIFH2 and Cytochalasin B significantly reduced IL-1β and neutrophil elastase levels and mitigated MSU-induced arthritis.

Colchicine effects on gout flares are not based on reducing neutrophil numbers but on changing the functional properties of tophi by reducing their DNase-resistant F-actin concentrations and thereby reducing the negative impact of NETs on IL-1β production and the pro-inflammatory state of tophi. Actin inhibitors may be interesting tools to convey anti-inflammatory properties and reduction of flares in gout patients.