Research has suggested that lycopene may be metabolized by eccentric cleavage, catalyzed by β-carotene oxygenase 2 (BCO2), resulting in the generation of apo-lycopenals. Apo-6′-lycopenal and apo-8′-lycopenal have been reported previously in raw tomato. We now show that several other apolycopenals are also present in raw and processed foods, as well as in human plasma. Apo-lycopenal standards were prepared by in vitro oxidation of lycopene, and a high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method using atmospheric pressure chemical ionization in negative mode was developed to separate and detect the apo-6′-, 8′-, 10′-, 12′-, 14′-, and 15′-lycopenal products formed in the reaction.Hexane/acetone extracts of raw tomato, red grapefruit, watermelon, and processed tomato products were analyzed, as well as plasma of individuals who had consumed tomato juice for eight weeks. Apo-6′-, 8′-, 10′-, 12′-, and 14′-lycopenals were detected and quantified in all food products tested, as well as plasma. The sum of apo-lycopenals was 6.5 µg/100 g 'Roma' tomato, 73.4 µg/100 g tomato paste, and 1.9 nmol/L of plasma. We conclude that several apo-lycopenals, in addition to apo-6′-and 8′-lycopenal, are present in lycopene containing foods. In addition, the presence of apo-lycopenals in plasma may derive from the absorption of apo-lycopenals directly from food and/or human metabolism.

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The dihydroceramide desaturase (DES) enzyme is responsible for inserting the 4,5-trans-double bond to the sphingolipid backbone of dihydroceramide. We previously demonstrated that fenretinide (4-HPR) inhibited DES activity in SMS-KCNR neuroblastoma cells. In this study, we investigated whether 4-HPR acted directly on the enzyme in vitro. N-C8:0-D-erythrodihydroceramide (C 8 -dhCer) was used as a substrate to study the conversion of dihydroceramide into ceramide in vitro using rat liver microsomes, and the formation of tritiated water after the addition of the tritiated substrate was detected and used to measure DES activity. NADH served as a cofactor Sphingolipids are known to be modulators of various cell functions. They are not only components of cell membranes but also play a role in cell survival, apoptosis, senescence, and differentiation (1, 2). Ceramide, a central molecule in the metabolism of sphingolipids and glycosphingolipids, is involved in these regulatory cellular events. Intracellulary, ceramide is generated by different pathways. De novo synthesis of ceramide starts with condensation of L-serine with palmitoylCoA. Further reduction and subsequent N-acylation generates dihydroceramide. Ceramide is finally generated by introduction of the 4,5-double bond into dihydroceramide by dihydroceramide desaturase (DES) 2 (3). The DES enzyme was characterized previously, and an in vitro assay was developed to determine its activity (4). In subsequent studies, a family of sphingolipid ⌬4-desaturases (homologs of the Drosophila melanogaster degenerative spermatocyte gene 1 (des-1)) were identified via a bioinformatics approach (5). These proteins contain three His-containing consensus motifs that are characteristic of a group of membrane fatty acid desaturases. The human homolog of des-1 is now referred to as DEGS-1, although it was first cloned in 1997 and named as membrane lipid desaturase because its physiologic substrate was not determined at the time (6). DEGS-1 is the only dihydroceramide desaturase reported to be present in human cells, and its mouse homolog (mDES1) was shown to have desaturase activity (7). hDES2, the human homolog of the mouse DES2 (mDes2) gene, like mDES2 has dihydroceramide hydroxylase activity (8). Although mDES2 has been reported to have both desaturase and hydroxylase activity, no desaturase activity was detected in HEK 293 human embryonic kidney cells overexpressing hDES2 (8). In this work, we refer to enzyme as DES in experiments with rat liver microsomes and as DEGS-1 in experiments with human SMS-KCNR cells.We previously developed an assay to evaluate the in situ activity of DEGS-1 using cell-permeable dihydroceramidoids (dhCCPS analogs) (9). We showed in these studies that the

Background:The human enzyme ␤-carotene 15,15Ј-oxygenase (BCO1) produces vitamin A from carotenoids in food. Results: BCO1 catalyzes the oxidative cleavage of the 15-15Ј double bond of major dietary provitamin A carotenoids, ␤-apocarotenals, and lycopene. Conclusion: BCO1 reacts only with carotenoids and apocarotenoids that yield retinal or acycloretinal. Significance: Elucidating the substrate specificity of BCO1 is crucial for understanding how humans metabolize carotenoids.

4-Oxo-N-(4-hydroxyphenyl)retinamide (4-oxo-4-HPR) is a recently identified metabolite of fenretinide (4-HPR). We explored the effectiveness of 4-oxo-4-HPR in inducing cell growth inhibition in ovarian, breast, and neuroblastoma tumor cell lines; moreover, we investigated the molecular events mediating this effect in two ovarian carcinoma cell lines, one sensitive