Carotenoids are yellow, red and orange pigments that accumulate in the chloroplasts of plants. Carotenoids play an important role in plant physiology, where that act to harvest light in the 400 to 500 nm range which aids the plant in times of low light availability. During times of high light availability, carotenoids protect the plant from over exposure to sunlight by dissipating excess energy as heat and thus prevent cellular damage. In mammal, dietary carotenoids act as singlet oxygen scavengers and can accumulate in lipid membranes where they interact with other antioxidant chemicals. Lycopene is the most abundant carotenoid in Western diets on account of its high concentrations in tomatoes. Lycopene has a C40 acyclic structure with a high number of conjugated double bonds in the trans configuration. This structure absorbs energy from singlet oxygen and dissipates it as heat without chemical change.
Although many plant compounds have been tested for their antioxidant capacity in vitro, less data is available from humans studies. In order to be an effective in vivo antioxidant, the chemical must survive digestion and first pass metabolism, and be absorbed to the plasma in a form that maintains its radical scavenging ability. Researchers1 have investigated the bioavailability and antioxidant capacity of isolated lycopene from tomato and found that it is both bioavailable, and a strong antioxidant in humans. In a double-blind randomised study, 82 healthy adults were supplemented with 0, 6.5, 15 or 30mg of isolated lycopene for 8 weeks while consuming a lycopene restricted diet. Lycopene plasma levels increased in all subjects when compared to the placebo, and the comet assay revealed a significant reduction in DNA damage with 30mg supplementation per day compared to the placebo.
These results suggest that lycopene is bioavailable in humans and is able to prevent DNA damage, presumable through a decrease in oxidative stress as estimated through a significant reductions in urinary 8-hydroxy deoxoguanosine (8-OHdG; a marker of oxidative stress to DNA). Other studies have previously shown that similar lycopene intakes (6.5, 15 and 30mg) from tomato products are bioavailable in humans, but this study demonstrated that isolated lycopene is also bioavailable in humans. Markers for lipid peroxidation (urinary F2-isoprostane, LDL oxidation, malondialdehyde and hydroxynonenals) were not significantly different from the placebo group. This null effects in this study of lycopene against lipid peroxidation are in contrast to previous studies that have shown benefits in humans. This may suggest that isolated carotenoids cannot protect from lipid peroxidation to the same extent as whole food carotenoids.
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