Interaction of peroxynitrite with carotenoids in human low density lipoproteins

Interaction of peroxynitrite, the product of the reaction between nitric oxide and superoxide, with carotenes (lycopene, alpha-carotene, and beta-carotene) and oxocarotenoids (beta-cryptoxanthin, zeaxanthin, and lutein) was studied both in homogeneous solution and in human low-density lipoproteins (LDL). All carotenoids prevented the formation of rhodamine 123 from dihydrorhodamine 123 caused by peroxynitrite, suggesting that the carotenoids react with peroxynitrite. Oxocarotenoids were as effective as biothiols, known scavengers of peroxynitrite, whereas lycopene, alpha-carotene, and beta-carotene exhibited a considerably more pronounced effect. Moreover, peroxynitrite caused a loss of carotenoids in LDL as was revealed by HPLC. The concentration of peroxynitrite causing half-maximal loss of carotenoids in LDL ranged from 13 +/- 3 to 68 +/- 3 microM for lycopene and lutein, respectively. Again, oxocarotenoids were less reactive in this system. A correlation between efficiency of carotenoids in the competitive assay with dihydrorhodamine 123 and the concentration of peroxynitrite causing half-maximal loss of carotenoids in LDL was observed (r(2) = 0.91). These findings suggest that carotenoids can efficiently react with peroxynitrite and perform the role of scavengers of peroxynitrite in vivo.