Effects of Hyperthermic Conditions on the Reactivity of Oxygen Radicals

Abstract

Generation and reactivity of superoxide (0₂⁻) and hydroxyl (OH') radicals in enzymatic and radiolytic systems were investigated over the temperature range from 20^o-50^oC. The generation rate and reaction kinetics of both enzymatically and radiolytically produced superoxide radicals were determined by a cytochrome c reduction assay. For OH' radical reaction studies the degradation of hyaluronic acid was assayed. An increase in temperature leads to a greater reactivity of both radicals, but in the case of an enzymatic source a disproportionate increase in the rate of generation is observed. In the pulse radiolysis system, the reactivity of superoxide radicals was found to be stimulated 15-fold over the temperature range from 20^oC to 60^oC, although the activity of superoxide dismutase was only minimally increased (about 1.6-fold). The results are discussed with respect to the possible importance of active oxygen species to the biological effects of hyperthermia.

Key Words:

• Oxygen activation
• Superoxide radicals
• Hydroxyl radicals
• Hyperthermia
• Hyaluronic acid degradation