Antioxidant activity of (all-E)-lycopene and synthetic apo-lycopenoids in a chemical model of oxidative stress in the gastro-intestinal tract

Abstract

Lycopene, the main pigment of tomato, is known to have protective effects on health. Its metabolites could also be involved in these effects. Potentially bioactive lycopene metabolites namely apo-10 0 -lycopenol, apo-10 0 -lycopenal, apo-14 0 -lycopenol, apo-14 0 -lycopenal, and apo-11-lycopenoids with alcohol, carboxylic acid, aldehyde and ethyl ester terminal groups were obtained by organic synthesis as (all-E) stereoisomers using HWE condensation reactions. The ability of (all-E)-lycopene and the synthesized apo-lycopenoids to inhibit lipid peroxidation was tested in a chemical model of postprandial oxidative stress in the gastric compartment. Oxidative stress was generated by metmyoglobin, the main form of dietary iron (from red meat), which is able to catalyse the peroxidation of linoleic acid under mildly acidic conditions. In this model, apo-6 0 -lycopenal and apo-8 0 -lycopenal were better inhibitors of lipid peroxidation than (all-E)-lycopene itself. For the apo-lycopenoids, a long unsaturated chain and a terminal carboxylic acid group both favour the antioxidant activity. The short-chain apo-lycopenoic acid, apo-14 0 -lycopenoic acid, was shown to behave like a hydrophilic antioxidant, i.e. by reducing hypervalent iron forms of metmyoglobin. Thus, besides the polyene chain length, the terminal group of the apo-lycopenoids is expected to deeply influence the lipophilic/hydrophilic balance of the molecule (and consequently its distribution between the aqueous and lipid phases) and its affinity for the heme cavity. It can thus be concluded that the polyene chain length and terminal group are two important parameters modulating the mechanism by which apo-lycopenoids express their antioxidant activity.

Analysis of microsamples of human faeces: a non-invasive approach to study the bioavailability of fat-soluble bioactive compounds

“…1a and peak (I) in Fig. 3a] displays a UV-VIS spectrum close to that reported for apo-10′-lycopenal [8], although we could not confirm its chromatographic behaviour due to the lack of authentic standard.…”

“…In this sense, different apo-carotenoids (i.e. β-apo-carotenals and apolycopenoids) have been reported to be formed under in vitro conditions and also to be present in foods and human tissues as a result of xanthophyll and lycopene metabolism [8,11,12]. Interestingly, under UPLC conditions, one of these "unknown" peaks [peak (II) in Fig.…”

“…While bioavailability of vitamin A and E may be relatively high, bioaccessibility of carotenoids from vegetables is low and several studies indicate that more than 70 % of the carotenoids may remain in the final digesta [1,[5][6][7]. Then, poorly bioavailable micronutrients like carotenoids may reach significant concentrations in the gastrointestinal tract where they may exert biological actions [8]. In this sense, the human colon is continuously exposed to a complex mixture of Abstract Introduction Bioavailability is a critical feature in the assessment of the role of micronutrients in human health.…”

Synthesis of apo-13- and apo-15-lycopenoids, cleavage products of lycopene that are retinoic acid antagonists

“…As has been observed by others (27), we found that homologation of 10 to ethyl apo-11-lycopenoate (13) by Wadsworth-Emmons reaction (Fig. 5) resulted in an approximately 3:1 isomeric mixture of the 2E/Z products.…”

Stability of bacterial carotenoids in the presence of iron in a model of the gastric compartment – Comparison with dietary reference carotenoids

“…Although xanthophylls having conjugated polyene chains with electro-withdrawing groups might be slightly less reducing than carotenes, this interpretation does not hold for the bacterial carotenoids. The polarity of carotenoids is another important factor to consider [19]. Indeed, xanthophylls in general and so glycosylated carotenoids in particular tend to be more localized at the edge of the micelles, thus being more exposed to oxidants in the aqueous phase.…”