The potential of antioxidant enzymes as pharmacological agents in vivo.

1. Oxygen radicals have been associated with a number of unrelated pathological processes including ageing, radiation sickness, inflammation, oxygen toxicity, reoxygenation of ischaemic tissues, etc. The partial reduction of oxygen to superoxide anion (O2-.) and H2O2 leads to the formation of more deleterious species such as hydroxyl radical (OH.) starting a chain reaction ultimately causing lipid peroxidation and cell death. 2. To prevent the increased steady-state concentration of oxygen radicals many researchers have designed potential treatments including the i.v. injection of antioxidant enzymes or enzyme derivatives with longer half-life in circulation (i.e. enzymes encapsulated in liposomes or covalently modified). 3. Tissue distribution and half-life in circulation depend upon the type of enzyme being used as well as whether the enzyme is or is not in its native form. 4. This review comments on some of the scenarios where these enzymes have been utilized, and discusses relevant problems of stability of different enzymes in circulation.