LTA4H exhibits dual hydrolase activity: it preferentially cleaves tripeptides at arginyl bonds and catalyzes the hydrolysis of the epoxide ring in leukotriene A4, producing leukotriene B4 with a hydroxyl group at the C-5 position.119 LTA4H inhibition is identified as the sole mechanism of action in the EMA Public Summary of Opinion on the orphan designation of bestatin for the treatment of pulmonary arterial hypertension in the EU. The gene discussed is LTA4H; the disease is pulmonary arterial hypertension.