199 - Oxygen Effect on Protection of Human Lymphoid Cells Against Free Radicals by the Carotenoid Lycopene

Abstract

Carotenoids are known to act as dietary antioxidants and so are of wide interest for their health benefits. Dietary lycopene, the carotenoid pigment in tomatoes, has been shown to protect against human lymphoid cell membrane damage from free radicals produced by gamma radiation and also by the nitrogen dioxide radical, generated photolytically. This protective effect is dramatically reduced as the oxygen concentration increases, particularly for damage due to gamma radiolysis – becoming near zero at 100% oxygen from 5-fold protection at 20% oxygen and 50-fold protection at zero per-cent oxygen. The effect is less pronounced for nitrogen dioxide-induced cell killing falling from 17-fold protection in the absence of oxygen to 9-fold at 100% oxygen. Non-cellular gamma radiation and laser studies were also carried out to support the molecular mechanisms suggested for the effect of oxygen. The remarkable reduction in protection by lycopene against gamma radiation at high oxygen concentrations could be exploited to enhance radiation procedures for therapy and preliminary studies have also been undertaken for irradiations with high energy protons.