Caco-2 cells, an intestinal cell line derived from a human colorectal carcinoma that spontaneously differentiates under standard culture conditions, lends itself to the in vitro study of human gut in view of its efficient intestinal transport processes. Among its multiple biological functions are those related to the absorption, transport, and metabolism of lipids and lipoproteins. Despite their intestinal origin, confluent Caco-2 cell monolayers primarily express L-FABP for the uptake of apical dietary long chain fatty acids, incorporating them into triglycerides by the glycerol 3-phosphate pathway, and assembling very-low-density lipoprotein, high-density lipoprotein, and low-density lipoprotein. The monoacyl-glycerol pathway is inactive in Caco-2 cells. Furthermore, the secretion of newly synthesized triglyceride-rich lipoproteins is very restricted, despite abundant production of apolipoprotein (apo) B. The regulation of apoB synthesis and its mRNA editing at the enterocyte level has been intensively examined in Caco-2 cells. Luminal fatty acids, calcium ion, as well as vitamins and hormones are known to modulate the apoB-48/apoB-100 at the transcriptional and/or translational level. The regulation of 3-hydroxy-3-methylglutaryl-CoA reductase and acyl-CoA: (cholesterol acyltransferase), the key enzymes governing intracellular cholesterol handling, have also been extensively examined in Caco-2 cells. In many respects this cell line provides an excellent in vitro model for the investigation of intestinal lipoprotein metabolism; however, their limited secretion capacity remains a potential drawback to comparisons with the in vivo physiological state.

Shiga toxin (Stx)-producing Escherichia coli (STEC) causes hemorrhagic colitis and hemolytic-uremic syndrome (HUS).

Although Caco-2 cells are frequently employed for the study of enterocyte lipid metabolism, variable results have been reported regarding their ability to synthesize and secrete lipids and apolipoproteins. The major goal of this investigation is to examine the capacity of Caco-2 cells to elaborate and secrete lipids, lipoproteins, and apolipoproteins at different degrees of morphological and functional differentiation. Cells were cultured in medium with 5% fetal bovine serum (FBS), on permeable polycarbonate filters from 2 to 30 d in the presence of 14C-oleate or 35S-methionine. Cellular differentiation, as assessed by morphology (light and electron microscopy), transepithelial resistance, free fatty acid flux, and sucrase activity, progressed steadily up to 20 d of culture. Caco-2 cells esterified oleic acid mainly into phospholipids, triglycerides (TG), and smaller amounts of cholesterol esters. Lipid synthesis began as early as 2 d, and TG secretion was enhanced with increased duration of culture. However, very low efficiency of lipid export was observed at all levels of differentiation, reaching a maximum of only 6% of intracellular lipids. VLDL and LDL were the dominant lipoproteins secreted, with HDL comprising < 20% of the total. VLDL secretion increased, while LDL decreased, whereas the lipid composition of lipoproteins varied little with increasing duration of culture. Apoprotein B and A-I synthesis and secretion increased markedly from 11 to 20 d of culture. The ratio of apo B-100/B-48 decreased between 11 and 30 d, consistent with enhanced apo B editing of more mature enterocytes. Taken together, our data suggest that from 20 d of culture, Caco-2 cells are morphologically and functionally mature, capable of lipid esterification, and lipoprotein and apolipoprotein synthesis. However, despite their functional and morphological similarities to mature enterocytes, Caco-2 cells have a very limited lipid export capacity.