Reactive species can pose special problems needing special solutions: some examples

Abstract This chapter describes several situations in which free radicals/reactive species (RS) are especially problematic and require special protective mechanisms. The first is the gastrointestinal tract, which is exposed to pro-oxidants from the diet and must protect itself from oxidative damage using a range of antioxidants. It also produces some RS for useful purposes, including the regulation of bacterial colonization, by NADPH oxidase enzymes. The respiratory tract has to cope with inhaled air pollutants (O3, NO2, SO2, and O2 itself) and contains many antioxidants (especially GSH) in its lining fluids and cells. The relation of antioxidants (especially vitamin C) to asthma is also reviewed. Erythrocytes have special problems because of the haemoglobin they carry, which can oxidize to generate superoxide. Hence erythrocytes are rich in antioxidants. The effects of toxins (e.g. favism), glucose-6-phosphate dehydrogenase deficiency, and infection with malaria parasites on oxidative damage in erythrocytes are presented. Indeed, malaria can be treated with drugs that impose oxidative stress, such as artemisinin. Plants are discussed in detail, including the mechanisms of photosynthetic O2 production, how plants protect themselves against O2 toxicity (using many antioxidants, especially carotenoids), and how they can be damaged by poisons such as paraquat, air pollutants, atrazine, or oxyfluorfen. The problems of the ear and the involvement of RS in hearing loss are discussed. Conception (spermatozoa, ova), pregnancy, embryonic development, normal birth, and premature birth, and the action of teratogens are also considered in the free-radical/antioxidant context, as are the potential benefits and harm from exercise.