Effects of beta-carotene on antioxidant enzyme activity, intracellular reactive oxygen and membrane integrity within post confluent Caco-2 intestinalcells

As encountered with a plethora of other natural products, the antioxidant a ctivity of beta-carotene has been proposed as one of the mechanisms by whic h diets rich in this pro-vitamin A active carotenoid apparently afford chem oprevention. Here, we report the ability of beta-carotene to alter endogeno us reactive oxygen levels and antioxidant defences within non-stressed 'dif ferentiated' monolayers of an intestinal epithelial cell line (Caco-2) and to subsequently effect resistance to general oxidative insult. The differen tiated monolayers efficiently absorbed beta-carotene. Between 3 and 8 days post confluence, cultures exhibited a progressive increase in antioxidant e nzyme activity and a corresponding reduction to intracellular ROS levels. T he profile for antioxidant enzyme activity was unaffected by sustained dail y supplementation with beta-carotene. However, after two daily treatments w ith 50 mu M beta-carotene intracellular ROS levels were significantly reduc ed and there was a trend towards reduced intracellular ROS within monolayer s subject to five daily treatments with 0.5 and 5 mu M beta-carotene. Prolo nged supplementation with 0.1 and 0.5 mu M beta-carotene or short supplemen tation periods with 5 and 50 mu M beta-carotene did not alter susceptibilit y to H2O2. However, cultures treated daily between 3 and 8 days post conflu ence with 5 or 50 mu M beta-carotene exhibited enhanced LDH release, increa sed non-adherence and enhanced Trypan blue staining when challenged with 10 mM H2O2. In the absence of H2O2, the beta-carotene treatments were not ove rtly toxic to the monolayers. These results indicate that beta-carotene doe s not enhance antioxidant defences within Caco-2 monolayers. The enhancemen t of H2O2 toxicity by persistent, high doses of beta-carotene may contribut e to the failure of this carotenoid to protect high risk individuals from c ertain degenerative conditions. (C) 1999 Elsevier Science B.V. All rights r eserved.