Iron-ascorbate alters the efficiency of Caco-2 cells to assemble and secrete lipoproteins

Although oxidative stress has been implicated in development of gut pathologies, its role in intestinal fat transport has not been investigated. We assessed the effect of Fe2+-ascorbate-mediated lipid peroxidation on lipid synthesis, apolipoprotein biogenesis, and lipoprotein assembly and secretion. Incubation of postconfluent Caco-2 cells with iron(II)- ascorbate (0.2 mM/2 mM) in the apical compartment significantly promoted malondialdehyde formation without affecting sucrase activity, transepithelial resistance, DNA and protein content, and cell viability. However, addition of the oxygen radical-generating system reduced 1)[C-14] oleic acid incorporation into cellular triglycerides (15%, P< 0.0002) and phospholipids (16%, P< 0.0005); 2) de novo synthesis of cellular apolipoprotein A-I (apo A-I) (18%, P< 0.05), apo A-IV (38%, P< 0.05), and apo B-48 (45%, P< 0.003) after [S-35] methionine addition; and 3) production of chylomicrons (50%), VLDL (40%), LDL (37%), and HDL (30%) (all P< 0.0001). In contrast, increased total cellular cholesterol formation (96%, P< 0.0001), assayed by [C-14] acetate incorporation, was noted, attributable to marked elevation (70%, P<0.04) in activity of DL-3-hydroxy-3-methylglutaryl-CoA reductase, the rate-limiting enzyme in cholesterol synthesis. The ratio of Acyl-CoA to cholesterol acyltransferase, the esterifying cholesterol enzyme, remained unchanged. Fe2+-ascorbate-mediated lipid peroxidation modifies intracellular fat absorption and may decrease enterocyte efficiency in assembling and transporting lipids during gut inflammation.