Myeloperoxidase: the yin and yang in tumour progression

Myeloperoxidase (MPO) is a heme- containing enzyme abundantly expressed in neutrophils. It catalyzes the reaction between chloride and hydrogen peroxide to generate a potent oxidant, hypochlorous acid (HOCl). It plays an important role in innate immune defense mechanism. However, excessive generation of MPO-derived oxidants has been linked to tissue damage and in the initiation and progression of diseases such as cancer which arise from chronic inflammation. The oxidant activity of MPO is believed to promote the metabolism of chemical carcinogens, cause DNA damage and compromise the repair process. It is also considered as important mediators of gastric ulcers caused by Helicobacter pylori (H. pylori) through its ability to catalyze the generation of reactive oxidants. A G-463 a polymorphism located in the promoter of the MPO gene plays an important role in its transcription. Moreover the reactive oxidants produced by neutrophilic enzyme have the potential to interact with tumour cells and contribute to their metastasis. There has been a considerable interest in the screening of plant extracts and compounds isolated from them for their potential use as HOCl scavengers. This review will discuss the role of MPO in tumour progression and provide an overview of its part in tumour metastasis and ulcer.