Aernoud Fiolet

373 Clinical implications and future perspectives Inflammasome inhibition The biochemical effects of colchicine are broad, but the microtubule inhibitory properties of the drug specifically affect inflammasome activity, localised in many immune cells, and monocytes in particular. Activation of the nucleotide-binding oligomerisation domain–, leucine-rich repeat–, and pyrin domain–containing protein 3 (NLRP3) inflammasome leads to caspase 1 activation and subsequent interleukin-1 β and interleukin-18 expression. 23 These cytokines have a flywheel effect in the inflammatory response and increase cell activation and recruitment. 24 In Chapter 3, we have demonstrated how crystalloid structures contribute to NLRP3 inflammasome activation and how crystallisation of cholesterol can initiate NLRP3 inflammasome activation and interleukin-1 β expression in the atherosclerotic plaque. 25 Subsequently, we have confirmed in Chapter 11 that low- dose colchicine leads to lower levels of expression of the NLRP3 inflammasome, which may partially explain the protective effects of the drug in atherosclerosis. These data are however conducted in a highly experimental setting. Additional in vivo confirmation and assessment of the dose-response curve could also improve understanding of the mechanisms of action of colchicine in atherosclerosis. Platelet morphological changes and aggregation Microtubules support the shape of nonactivated platelets and contribute to the internal reorganisation for shape change after activation. Microtubules and filaments are also structural parts of the pseudopodia of the platelet, used for motility and aggregation. Future mechanistic research of colchicine in atherosclerosis should certainly entail further elucidation of the effects of the drug on platelets, as contemporary evidence is limited. Historical in vitro experiments show how moderate doses of colchicine impair internal transformation and late aggregation of platelets. High-dose colchicine leads to complete microtubule dissolution and fully halts platelet aggregation. 26 More recently, colchicine was shown to reduce maximal platelet aggregation even after prior cyclooxygenase 1 and P2Y12 adenosine diphosphate receptor inhibition with acetylsalicylic acid and clopidogrel. 27 Leukocyte/platelet aggregation, rather than platelet/platelet aggregation, seems to be preferentially affected. 28 In vivo evidence of such mechanisms is not yet available. There are no clinical studies that have specifically addressed haemostasis or bleeding events associated with colchicine, and such events are rare. Data on bleeding events need to be collected in in future clinical trials. Secondly, it will be worthwhile to combine data on such events in aggregate analyses.