Myristic acid increases dense lipoprotein secretion by inhibiting apoB degradation and triglyceride recruitment

Fatty acids of varying lengths and saturation dif- ferentially affect plasma apolipoprotein B-100 (apoB-100) levels. To identify mechanisms at the level of production, rat hepatoma cells, McA-RH7777, were incubated with ( 35 S)methionine and either fatty acid-BSA complexes or BSA alone. There were increases in labeled apoB-100 secre- tion with saturated fatty acids palmitic and myristic (MA) (153 � 20% and 165 � 11%, respectively, relative to BSA). Incubation with polyunsaturated docosahexaenoic acid (DHA) decreased secretion to 26 � 2.0%, while monounsat- urated oleic acid (OA) did not change it. In pulse-chase studies, MA treatment resulted in reduced apoB-100 degra- dation, in agreement with its promotion of secretion. In triglyceride (TG) studies, synthesis was stimulated equally by OA, MA, and DHA, but TG secretion was relatively de- creased with MA and DHA. With OA, the majority of newly secreted apoB100-lipoproteins was d � 1.006, but with MA, they were much denser (1.063 � d). Furthermore, the rela- tive recruitment of newly synthesized TG to lipoproteins was impaired with MA. We conclude that mechanisms for effects of specific dietary fatty acids on plasma lipoprotein levels may include changes in hepatic production. In turn, hepatic production may be regulated by specific fatty acids at the steps of apoB-100 degradation and the recruitment of nascent TG to lipoprotein particles. —Kummrow, E., M. M. Hussain, M. Pan, J. B. Marsh, and E. A. Fisher. Myristic acid increases dense lipoprotein secretion by inhibiting apoB degradation and triglyceride recruitment. J. Lipid Res. 2002. 43: 2155-2163.