Interaction of peroxynitrite with carotenoids in human low density lipoproteins

Interaction of peroxynitrite, the product of the reaction between nitric ox ide and superoxide, with carotenes (lycopene, alpha-carotene, and beta-caro tene) and oxocarotenoids (beta-cryptoxanthin, zeaxanthin, and lutein) was s tudied both in homogeneous solution and in human low-density lipoproteins ( LDL), All carotenoids prevented the formation of rhodamine 123 from dihydro rhodamine 123 caused by peroxynitrite, suggesting that the carotenoids reac t with peroxynitrite. Oxocarotenoids were as effective as biothiols, known scavengers of peroxynitrite, whereas lycopene, alpha-carotene, and beta-car otene exhibited a considerably more pronounced effect, Moreover, peroxynitr ite caused a loss of carotenoids in LDL as was revealed by HPLC. The concen tration of peroxynitrite causing half-maximal loss of carotenoids in LDL ra nged from 13 +/- 3 to 68 +/- 3 mu M for lycopene and lutein, respectively. Again, oxocarotenoids were less reactive in this system. A correlation betw een efficiency of carotenoids in the competitive assay with dihydrorhodamin e 123 and the concentration of peroxynitrite causing half-maximal loss of c arotenoids in LDL was observed (r(2) = 0.91). These findings suggest that c arotenoids can efficiently react with peroxynitrite and perform the role of scavengers of peroxynitrite in vivo. (C) Academic Press.