Neutrophil-mediated mechanisms of damage and in vitro protective effect of colchicine in non-vascular Behçet's syndrome

Behçet's syndrome (BS) is a systemic vasculitis with several clinical manifestations. Neutrophil hyperactivation mediates vascular BS pathogenesis, via both a massive reactive oxygen species (ROS) production and neutrophil extracellular traps (NETs) release. Here, we investigated neutrophil-mediated mechanisms of damage in non-vascular BS manifestations and explored the in vitro effects of colchicine in counteracting these mechanisms. NETs and intracellular ROS production was assessed in blood samples from 80 BS patients (46 with active non-vascular BS, 34 with inactive disease) and 80 healthy controls. Moreover, isolated neutrophils were incubated for 1 hour with an oxidating agent (2,2'-azobis (2-amidinopropane) dihydrochloride; 250nM), and the ability of pure colchicine pre-treatment (100ng/ml) to counteract oxidation-induced damage was assessed. Patients with active non-vascular BS showed remarkably increased NET levels [21.2 (IQR 18.3-25.9) mU/ml] compared to patients with inactive disease [16.8 (13.3-20.2) mU/ml] and to controls [7.1 (5.1-8.7) mU/ml], p<0.001]. Also, intracellular ROS tended to increase in active BS, although not significantly. In active non-vascular BS, NETs correlated with neutrophils ROS production (p<0.001) and were particularly increased in patients with active mucosal (p<0.001), articular (p=0.004), and gastrointestinal symptoms (p=0.006). In isolated neutrophils, colchicine significantly reduced oxidation-induced NET production and cell apoptosis, though not via an antioxidant activity. Neutrophil-mediated mechanisms might be directly involved in non-vascular BS, and NETs, more than ROS, might drive the pathogenesis of mucosal, articular and intestinal manifestations. Colchicine might be effective in counteracting neutrophils-mediated damage in BS, although further studies are needed.