MINERAL-INDUCED FORMATION OF REACTIVE OXYGEN SPECIES

Abstract

This chapter explores the role of minerals in the formation of reactive oxygen species. Five different mechanisms by which minerals may promote the formation and transformation of ROS species are explored (Fig. 1). These are: 1. Mineral release of metal ions: Metals that are released into body "uids via congruent or incongruent mineral dissolution can act as catalysts. In this mechanism minerals are a source of metals, but are not directly involved in any of the reactions. 2. Surface-bound metal-promoted reactions: Insoluble metal-containing minerals can catalyze formation of ROS from molecular oxygen. In this mechanism the conversion of molecular oxygen takes place on the mineral surface, with the mineral surface itself, or adsorbed species, acting as an electron donor. 3. Intrinsic or mechanically-induced surface defects: Defects on the mineral surface, either intrinsic to the mineral structure or generated by crushing, can react to form ROS. In this mechanism, highly reactive defects combine with water, molecular oxygen, or carbon dioxide to form ROS. 4. In!ammatory cell/mineral interactions: Insoluble particles that deposit in the airways and alveoli of the lung may activate airway epithelial cells or macrophages as a result of binding to the cell surface or engulfment mechanisms that bring the particles into the cell interior; these processes can lead to production of secondary cellular ROS, including hydroxyl radicals and other very reactive entities. Hence, minerals that do not promote ROS formation via the !rst three mechanisms in vitro may still show upregulation of ROS in vivo.​