Antioxidant activities of natural 9-CIS and synthetic all-trans β- carotene assessed by human neutrophil chemiluminescence

Much attention has been focused on the biological activity of geometrical isomers of β-carotene. In the present study, the in vitro antioxidant activities of a natural 9-cis β-carotene purified from Dunaliella bardawil and synthetic all-trans β-carotene were studied using enhanced human neutrophil chemiluminescence upon stimulation with opsonized zymosan. Lucigenin-dependent chemiluminescence was used for largely measuring superoxide anion (O₂) production, luminol-dependent chemiluminescence with sodium azide (NAN₃) and horseradish peroxidase (HRP) was used for measuring hydrogen peroxide (H₂O₂) production, and luminol-dependent chemiluminescence without oxidant metabolism modulator was used for determination of myeloperoxidase (MPO)-mediated production. With β-carotene concentration of 1.4 μ M, neutrophils showed a decrease in lucigenin- dependent chemiluminescence to 75% and 78% of controls (p<0.05) by natural 9- cis β-carotene and synthetic all-trans β-carotene, respectively. With β- carotene concentration of 1.86 μ M, neutrophils also showed a decrease in luminol-dependent chemiluminescence in the presence of NaN₃ and HRP to 86% and 81% of controls (p<0.05) by natural 9-cis β -carotene and synthetic all- trans β -carotene, respectively. On the other hand, neutrophils did not show a statistically significant difference in any chemiluminescence assay by the same concentration of natural 9-cis β-carotene and synthetic all-trans β - carotene. These results suggest that, up to the concentration of 1.86 μ M, natural 9-cis β -carotene and synthetic all-trans β-carotene exert equal antioxidant activities assessed by enhanced human neutrophil chemiluminescence.