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 tr iglyceride transfer protein (MTP) in the association of apolipoprotein (ape) B with lipid during intestinal lipoprotein assembly The MTP-inh ibiting 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-cont aining lipoproteins that were secreted from the cells. Secretion of ap oB-100 appeared to be more sensitive to BMS-200150 than apoB-48 secret ion, which appeared to be relatively insensitive. BMS-200150 caused a decrease in the triglyceride content of the secreted lipoproteins, com pared with control incubations without MTP inhibition. This indicated that, in Caco-2 cells, MTP is not only involved in the first step of l ipoprotein synthesis, i.e., the rescue of apoB from intracellular degr adation through early lipidation of the protein, but also in further s teps involving the association of lipoproteins with triglycerides. Whe n 0.5 mM oleic acid (18:1) was used to stimulate cellular lipid synthe sis, secreted lipoproteins were predominantly of chylomicron/VLDL dens ity 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, a s reported before (van Greevenbroek et al. 1995. J. Lipid Res. 36: 13- 24). Secretion of the lipoproteins at chylomicron/VLDL density was str ongly reduced by inhibition of MTP activity by BMS-200150, whereas the IDL/LDL density lipoproteins were relatively insensitive. In conclusi on, specific inhibition of MTP activity in Caco-2 cells with BMS-20015 0 resulted in reduced secretion of apoB-containing lipoproteins (predo minantly apoB-100) by Caco-2 cells and furthermore reduced the triglyc eride content of these lipoproteins. MTP inhibition preferentially red uced the secretion of triglyceride-rich lipoproteins (d < 1.006 g/ml).