Participation of the microsomal triglyceride transfer protein in lipoprotein assembly in Caco-2 cells: interaction with saturated and unsaturated dietary fatty acids.

This study was designed to gain insight into the role of microsomal triglyceride transfer protein (MTP) in the association of apolipoprotein (apo) B with lipid during intestinal lipoprotein assembly. The MTP-inhibiting compound BMS-200150 (Jamil et al. 1996. Proc. Natl. Acad. Sci. USA 93: 11991-11995) was used to inhibit the lipid transfer activity of MTP in Caco-2 cells. MTP inhibition reduced the number of apoB-containing lipoproteins that were secreted from the cells. Secretion of apoB-100 appeared to be more sensitive to BMS-200150 than apoB-48 secretion, which appeared to be relatively insensitive. BMS-200150 caused a decrease in the triglyceride content of the secreted lipoproteins, compared with control incubations without MTP inhibition. This indicated that, in Caco-2 cells, MTP is not only involved in the first step of lipoprotein synthesis, i.e., the rescue of apoB from intracellular degradation through early lipidation of the protein, but also in further steps involving the association of lipoproteins with triglycerides. When 0.5 mM oleic acid (18:1) was used to stimulate cellular lipid synthesis, secreted lipoproteins were predominantly of chylomicron/VLDL density and their secretion could be efficiently inhibited with BMS-200150. With 0.5 mm palmitic acid (16:0), lipoproteins of distinct densities (i.e., chylomicron/VLDL and IDL/LDL) were secreted by Caco-2 cells, as reported before (van Greevenbroek et al. 1995. J. Lipid Res. 36: 13-24). Secretion of the lipoproteins at chylomicron/VLDL density was strongly reduced by inhibition of MTP activity by BMS-200150, whereas the IDL/LDL density lipoproteins were relatively insensitive. In conclusion, specific inhibition of MTP activity in Caco-2 cells with BMS-200150 resulted in reduced secretion of apoB-containing lipoproteins (predominantly apoB-100) by Caco-2 cells and furthermore reduced the triglyceride content of these lipoproteins. MTP inhibition preferentially reduced the secretion of triglyceride-rich lipoproteins (d < 1.006 g/ml).