beta-carotene as a high-potency antioxidant to prevent the formation of phospholipid hydroperoxides in red blood cells of mice.

In order to investigate the antioxidant effect of beta-carotene in vivo, phospholipid hydroperoxides and beta-carotene isomers in red blood cells (RBC), plasma and tissue organelles were quantitatively measured after the oral administration of beta-carotene (94.8% all-trans-beta-carotene) to mice. Three groups of 24 mice each were fed for 1 week on a semisynthetic diet supplemented with either 0.6% or 3.0% beta-carotene/diet or maintained on a control (beta-carotene-unsupplemented) diet. The RBC phospholipid hydroperoxides showed a significant decrease followed by an increase of beta-carotene intakes; i.e., 201, 16 and 4 pmol of phosphatidylcholine hydroperoxide/ml packed RBC, and 108, 22 and 8 pmol of phosphatidylethanolamine hydroperoxide/ml packed RBC, in the mice given the control diet, 0.6% carotene diet and 3.0% carotene diet, respectively. The RBC beta-carotene increased from 14 to 43 pmol/ml packed RBC as followed by the increase of beta-carotene intakes. Such a potent antioxidant effect of beta-carotene as observed in RBC was not confirmed in the plasma, liver or lungs, although their beta-carotene contents increased. The beta-carotene ingestion increased the all-trans-beta-carotene and retinol contents in RBC, plasma, liver and lungs, but the alpha-tocopherol content decreased. In the beta-carotene-supplemented (6 g and 30 g/kg diet) mice, cis-beta-carotene content was relatively higher in the RBC (25-35% of total beta-carotene) than that in the plasma, liver and lungs. The present findings indicate that not only does beta-carotene act as a potent antioxidant in vivo but also its antioxidant effect is very specific in the RBC phospholipid bilayers rather than in the plasma and other tissue organelles.