Chapter 6 Mechanisms of cell injury by free radicals

Abstract

Publisher Summary This chapter discusses the role of free radical in diseases. The vast majority of these diseases involve two basic and recurring mechanisms of free-radical production: activated inflammatory cells and injury resulting from ischemia and reperfusion. Chemically, a free radical is any molecule containing a single, unpaired electron. Because a covalent bond is formed when a pair of electrons occupies a single molecular orbital, free radicals may be viewed as molecular fragments formed by homolytic cleavage of a bond. The unpaired electron imparts paramagnetic character to the radical, which displays a characteristic absorption spectrum in a magnetic field, which is detectable by electron paramagnetic resonance spectroscopy (EPR). Molecular oxygen is somewhat of an electronic oddity in that its ground state is a diradical, with two unpaired electrons of like spin. The superoxide radical has a dual personality—a good side and a bad side. Studies suggest that cellular redox status, determined in part by rates of superoxide generation and scavenging, may play important roles in regulating cellular proliferation. Overproduction of the radical has long been associated with increased lipid peroxidation, but it was found that over-scavenging of the radical could paradoxically lead to the same end. This is because free radicals can initiate chain reactions, and they can terminate them. Hence, the relative rates of free-radical production, reaction, and scavenging produce a rather delicate and precarious balance in the healthy cell.