Structural and Geometrical Isomers of Carotenoids in Human Plasma

Abstract

We have quantitatively analyzed human plasma for the following carotenoids: all-trans-lutein, all-trans-zeaxanthin, α-cryptoxanthin, β-cryptoxanthin, the sum of all-trans-lycopene and its cis isomers, α-carotene and β-carotene. In addition, we have tentatively identified and quantified 13-cis-lutein and 13-cis-zeaxanthin in human plasma. The latter two cis isomers are also apparent in samples of two common food items, spinach and corn meal. We have analyzed the ratios of all of the members of the β,β family of carotenoids (zeaxanthin, β-cryptoxanthin and β-carotene) to their corresponding β,ɛ structural isomers (lutein, α-cryptoxanthin and α-carotene) in human plasma. There are marked differences in these ratios, with β-carotene and β-cryptoxanthin predominating in the carotene and monohydroxy-xanthophyll classes and lutein predominating in the dihydroxy-xanthophyll class. These differences could be attributable to dietary intake or to specific mechanisms in the way humans absorb and utilize these compounds.