ABSTRACT
Lycopene, like other lipophilic dietary components, is absorbed from the intestine in chylomicrons. These large, triacylglycerol-rich lipoproteins are metabolized in the blood by removal of some of the triacylglycerol, leaving smaller chylomicron remnants particles that deliver the remaining lipids to the liver. Lycopene may then re-enter the circulation and is transported in low density lipoprotein. The proportion of dietary lycopene absorbed in chylomicrons is relatively low and is influenced by a number of factors. It is increased by the consumption of tomato products rather than the raw fruit, as well as by the presence of fat in the diet, and the cis isomer is more easily incorporated into chylomicrons than the all-trans form. Conversely, absorption is reduced by non-absorbable fat substitutes such as sucrose polyester, and in older as compared to younger subjects. In addition, other carotenoids in the diet may compete with lycopene for absorption in chylomicrons, although this does not appear to influence its bioavailability in the medium term. Some studies have suggested that lycopene may protect against atherosclerosis, possibly because its antioxidant properties protect low density lipoprotein from oxidation. However, the presence of lycopene in chylomicron remnants, which are also known to be atherogenic, has been found to increase their induction of macrophage foam cell formation and decrease their uptake by the liver, thus potentially promoting atherosclerotic lesion development. The type of 160lipoprotein carrier of lycopene, therefore, may be important for its effects on atherosclerosis, with its presence being beneficial in low density lipoprotein, but deleterious in chylomicron remnants. Since chylomicron remnants are normally rapidly cleared from the blood, the beneficial effect may predominate in healthy subjects. However, remnant particles accumulate in the blood in some conditions, including obesity and diabetes, and the potentially detrimental effects may be more important in these circumstances. Despite the potential protective effects of dietary lycopene against cardiovascular and other diseases, the mechanisms regulating its absorption in chylomicrons are not completely understood, and more research is essential to establish the optimum conditions for the dietary intake of lycopene in order to obtain the maximum benefit for health.
