BETA-CAROTENE AND LUTEIN PROTECT HEPG2 HUMAN LIVER-CELLS AGAINST OXIDANT-INDUCED DAMAGE

Numerous epidemiological studies support a strong inverse relationship between consumption of carotenoid-rich fruits and vegetables and the incidence of some degenerative diseases. One proposed mechanism of pro tection by carotenoids centers on their putative antioxidant activity, although direct evidence in support of this contention is limited at the cellular level. The antioxidant potential of beta-carotene (BC) an d lutein (LUT), carotenoids with or without provitamin A activity, res pectively, was evaluated using the human liver cell line HepG2. Pilot studies showed that a 90-min exposure of confluent cultures to 500 mu mol/L tert-butylhydroperoxide (TBHP) at 37 degrees C significantly (P < 0.05) increased lipid peroxidation and cellular leakage of lactate d ehydrogenase (LDH), and decreased the uptake of H-3-alpha-aminoisobuty ric acid and H-3-2-deoxyglucose. Protein synthesis, mitochondrial acti vity and glucose oxidation were not affected by TBHP treatment, sugges ting that the plasma membrane was the primary site of TBHP-induced dam age. Overnight incubation of cultures with greater than or equal to 1 mu mol/L dl-alpha-tocopherol protected cells against oxidant-induced c hanges. In parallel studies, overnight incubation of HepG2 in medium c ontaining micelles with either BC or LUT (final concentrations of 1.1 and 10.9 mu mol/L, respectively), the cell content of the carotenoids increased from < 0.04 to 0.32 and 3.39 nmol/mg protein, respectively. Carotenoid-loaded cells were partially or completely protected against oxidant-induced changes in lipid peroxidation, LDH release and amino acid and deoxyglucose transport. These data demonstrate that BC and LU T or their metabolites protect HepG2 cells against oxidant-induced dam age and that the protective effect is independent of provitamin A acti vity.