The biological effects of oxidized LDL (oxLDL) may contribute to initiation and progression of the atherosclerotic process, and the association between cardiovascular disease and oxidation of LDL has been largely demonstrated. The objectives of this study were to establish the reference values of oxidative stress biomarkers in a young healthy Spanish population to determine the concentration of oxLDL and its relationship with lipid profile and with these biomarkers. oxLDL, F(2)-isoprostanes, protein carbonyls (PC), and 8-hydroxy-2'-deoxyguanosine (8-OHdG) were determinate by ELISA in 72 healthy subjects. Antioxidant enzymes, superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione reductase (GR) were carried out on a Hitachi 912 analyzer; lipid profile were assayed using automated systems (Cobas 711, Roche Diagnostics). All statistics were analyzed by using SPSS for Windows 15.0. SPSS Inc, Chicago, IL, USA. (Normal mean reference values): oxLDL (63.23 +/- 16.23 U/L), (Male/Female 68.06 +/- 17.69/58.39 +/- 13.6 U/L), F(2)-isoprostanes (2.26 +/- 0.9 microg/g creatinine), PC (0.34 +/- 0.15 nmol/mg), 8-OHdG (23.27 +/- 10.58 ng/ml), SOD (931.97 +/- 271.09 U/g Hb), GR (46.56 +/- 11.68 U/L), GPx (27.58 +/- 6.89 U/gHb (Male/Female 25.91 +/- 5.03/29.2 +/- 8.07 U/L)). OxLDL (63.23 U/L) was significantly (p < 0.05) positively correlated with BMI (22.53 Kg/m(2)), total cholesterol (175.79 mg/dl), triglycerides (87.58 mg/dl), LDL cholesterol (96.25 mg/dl), and uric acid (4.78 mg/dl), while negatively correlated with HDL-cholesterol (62.25 mg/dl). We have found different correlation between oxLDL and isoprostanes by gender with the rest of parameters. Normal reference values have been found significantly different for oxLDL and GPx by gender. Oxidized LDL is correlated with lipid profile but not with the oxidative stress biomarkers. Urinary isoprostanes are positively correlated with triglycerides and negatively with GR and GPx.

The soup contributed to increasing the concentration of each carotenoid by more than 100% after 3 and 4 weeks of consumption, the maximum increase being observed after 4 weeks. Oxidative markers did not show any variation except for GPx. Serum lycopene half-life was longer than that of β-carotene, which may be important for studies evaluating both carotenoids.

Presently, there is no clear consensus on the best approach to estimate carotenoid bioavailability. The best alternative would be to use human studies, but they are labour-intensive and expensive and can only be used to investigate a limited number of samples. Hence, a number of in vitro models have been developed to study pre-absorptive processes and factors affecting bioavailability. The question is, however, how well the results obtained by the various methods correlate to each other and to the in vivo situation. In the present paper, we have compared in vivo data from two human studies on differently processed soups containing carrots, tomato and broccoli, with results obtained by in vitro characterisation of the same soups. In vitro bioaccessibility was estimated by a static in vitro digestion investigating matrix release and micellarization of carotenoids and by uptake studies in a human intestinal cell line (Caco-2). In vivo data was obtained from clinical studies measuring total plasma carotenoid concentrations in human subjects after 4 weeks daily consumption of the soups. Comparison of the in vitro and in vivo results indicate that the combination of a two-step in vitro digestion and Caco-2 cells seems to be a useful tool for estimation of β-carotene bioaccessibility and screening of factors governing the release of β-carotene from this type of food. For lycopene the in vitro and in vivo results were less consistent, suggesting that reliable prediction of lycopene bioavailability might be more problematic.

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We developed a new method to evaluate the antioxidant effect of food products in a biological system. The antioxidant status of HepG2 cells was quantified after incubation with postprandial human chylomicrons after the intake of vegetable products. Three subjects consumed in a meal a vegetable soup containing 8.4 mg of β-carotene and 9 mg of lycopene. After 5 h, the subjects consumed a second meal without carotenoids. Blood samples were collected at basal time and every hour for 9 h. Chylomicrons were isolated from serum samples and used for both carotenoid quantification and HepG2 stimulation. Carotenoid in chylomicrons followed an inter-individual and bimodal carotenoid response. We demonstrated the antioxidant effect of postprandial chylomicrons in HepG2 at the time of maximum carotenoid concentration of chylomicrons with respect to basal time. This cell-based assay seems to be a useful method to evaluate the antioxidant effect of fruit and vegetable products in a biological system.

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