title: Effects of beta-carotene on antioxidant enzyme activity, intracellular reactive oxygen and membrane integrity within post confluent Caco-2 intestinal cells.
abstract: As encountered with a plethora of other natural products, the antioxidant activity of beta-carotene has been proposed as one of the mechanisms by which diets rich in this pro-vitamin A active carotenoid apparently afford chemoprevention. Here, we report the ability of beta-carotene to alter endogenous reactive oxygen levels and antioxidant defences within non-stressed 'differentiated' monolayers of an intestinal epithelial cell line (Caco-2) and to subsequently effect resistance to general oxidative insult. The differentiated monolayers efficiently absorbed beta-carotene. Between 3 and 8 days post confluence, cultures exhibited a progressive increase in antioxidant enzyme activity and a corresponding reduction to intracellular ROS levels. The profile for antioxidant enzyme activity was unaffected by sustained daily supplementation with beta-carotene. However, after two daily treatments with 50 microM beta-carotene intracellular ROS levels were significantly reduced and there was a trend towards reduced intracellular ROS within monolayers subject to five daily treatments with 0.5 and 5 microM beta-carotene. Prolonged supplementation with 0.1 and 0.5 microM beta-carotene or short supplementation periods with 5 and 50 microM beta-carotene did not alter susceptibility to H(2)O(2). However, cultures treated daily between 3 and 8 days post confluence with 5 or 50 microM beta-carotene exhibited enhanced LDH release, increased non-adherence and enhanced Trypan blue staining when challenged with 10 mM H(2)O(2). In the absence of H(2)O(2), the beta-carotene treatments were not overtly toxic to the monolayers. These results indicate that beta-carotene does not enhance antioxidant defences within Caco-2 monolayers. The enhancement of H(2)O(2) toxicity by persistent, high doses of beta-carotene may contribute to the failure of this carotenoid to protect high risk individuals from certain degenerative conditions.
authors.affiliation: Antioxidant and Free-Radical Group, Cell Integrity Programme, Rowett Research Institute, Aberdeen, UK. csb@rri.sari.ac.uk
authors.forename: C S
authors.initials: CS
authors.lastname: Bestwick
authors.forename: L
authors.initials: L
authors.lastname: Milne
mesh_terms: D000975:Antioxidants / Q000494:pharmacology*; D018938:Caco-2 Cells; D002462:Cell Membrane / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D002470:Cell Survival; D004798:Enzymes / Q000032:analysis; D006801:Humans; D007527:Isoenzymes / Q000032:analysis; D018384:Oxidative Stress; D010100:Oxygen / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism; D019207:beta Carotene / Q000494:pharmacology*
chemical_list: D000975:Antioxidants; D004798:Enzymes; D007527:Isoenzymes; D017382:Reactive Oxygen Species; D019207:beta Carotene; D010100:Oxygen