MMP9 and thromboangiitis obliterans: In addition, studies have shown that long-term cigarette exposure will lead to damage to the antioxidant defense system, which in turn increases the expression of MMP-9 and high mobility group box 1 (HMGB-1); high expression of MMP-9 and HMGB-1 also plays a role in TAO-related vascular lesions (136, 137).