Special issue on “Peroxidase”

In this special issue of Free Radical Research, we have organized 9 articles or reviews from contributors of the “8th International Human Peroxidase Meeting,” which was held in Sydney (Australia) between September 9 and 12, 2013. The next meeting will be held at Koln (Germany) between September 14 and 17, 2015. The themes of this meeting were the roles, functions, physiopathological impacts of enzymes from the peroxidase–cyclooxygenase superfamily and especially those of Chordata peroxidases including myeloperoxidase (MPO), eosinophil peroxidase (EPO), lactoperoxidase (LPO), and thyroid peroxidase. The articles of this special issue cover a large panel of research topics from laboratories that contribute to the peroxidase field.

Two research articles are related to the detection of halogenating activity by dyes. The research for these specific and sensitive markers is of importance to detect and/or quantify the peroxidase activity in vitro or ex vivo. The research article written by Arnhold et al. focuses on the detection of the halogenating activity in neutrophils and eosinophils by a fluorescent dye, namely aminophenyl fluorescein [1]. This method could be applied not only to flow cytometry but also to detect production of hypohalogenous acids by MPO and EPO from their respective leukocytes. Sokolov et al. validate celestine blue B as an interesting probe for the measurement of MPO activity, and demonstrate its suitability for assessing MPO inhibition [2].

A third article by Franck et al. validates a combined assay for the quantity and the activity of MPO in biological fluids. Using the immunocapture of the enzyme, they first specifically quantify the amount of MPO by a second antibody before measuring its activity by the Amplex Red method in a second step [3].

In the research article entitled “Interaction of ceruloplasmin with eosinophil peroxidase (EPO) as compared to its interplay with myeloperoxidase: reciprocal effect on enzymatic properties,” Sokolov et al. propose a comprehensive study of the interaction between EPO and ceruloplasmin [4]. Ceruloplasmin is a plasma protein that can interact with peroxidases and modulate their activity. As this interaction has been already observed for MPO, the authors compare ceruloplasmin interaction with both peroxidases.

Thiocyanate is a pseudohalogenous anion, which is a substrate for peroxidases such as MPO, EPO, and LPO. Hypothiocyanous acid, which is the product of the reaction of thiocyanate and peroxidases, specifically oxidizes thiol (Cys) residues of proteins, resulting in the formation of reversible thiol oxidation products including sulfenic acids. These products can be reduced back to Cys by antioxidant enzyme systems. In the review entitled “Biochemical mechanisms and therapeutic potential of thiocyanate in human health,” Chandler and Day explore the oxidation of thiocyanate by Chordata peroxidases and underline the potential role of thiocyanate as therapeutical agent that could modulate peroxidase's deleterious activity [5].

Interestingly, Morgan et al. demonstrate that the thiocyanate supplementation decreases the atherosclerotic plaque development in human MPO transgenic mice [6]. These authors emphasize the specific reversible oxidative modifications generated by hypothiocyanous acid compared with those of hypochlorous acid also produced by MPO, which produces irreversible oxidation products.

Konradi et al. explore the role of reactive oxygen species (ROS) in vascular dysfunction [7]. This condition is generally admitted as an initial step in the development of heart failure and leukocyte peroxidases seem to be one of the promoting factors. The authors propose new therapeutical approaches that could include peroxidases as interesting drug targets.

There is significant evidence that peroxidases contribute to the production of ROS in vivo. In this context, the review of Carroll et al. entitled “Reaction of low molecular mass organoselenium compounds (and their sulfur analogues) with inflammation-associated oxidants” provides a comprehensive overview of the role of selenium as an antioxidant [8]. Selenium has similar chemical properties to sulfur but in general, organoselenium compounds have a higher reactivity toward ROS. This exhaustive review explores the benefits of such compounds in the struggle against ROS, notably those produced by peroxidases.

Finally, Van Antwerpen and Zouaoui Boudjeltia propose a review entitled “Rational drug design applied to myeloperoxidase inhibition” [9]. As MPO was pointed out as a therapeutical target, many authors are trying to develop specific MPO inhibitors. This review illustrates the rational drug design approach applied to MPO inhibition and its benefit for the research of new MPO inhibitors.

In summary, the 9 articles in this special issue of Free Radical Research will bring readers new insights into the interesting world of human peroxidases, a subfamily of enzymes which contribute to the production of ROS and hypohalous acids. These articles cover technologies, comprehensive reviews, and fundamental research related to these heme-containing enzymes. We hope that readers of Free Radical Research will enjoy reading this special issue.

Declaration of interest

The authors report no declarations of interest. The authors alone are responsible for the content and writing of the paper.