Manipulation of cholesterol and cholesteryl ester synthesis has multiple effects on the metabolism of apolipoprotein B and the secretion of very-low-density lipoprotein by primary hepatocyte cultures

Inhibition of esterified and non-esterified cholesterol synthesis by lovast atin in primary rat hepatocytes suppressed the net synthesis and very-low-d ensity lipoprotein (VLDL) secretion of apolipoprotein B (apoB)-48 and apoB- 100. Lovastatin did not alter the rates of apoB-48 and apoB-100 post-transl ational degradation. 25-Hydroxycholesterol, which inhibited nonesterified c holesterol synthesis but increased the synthesis of cholesteryl ester, show ed differential effects on the metabolism of apoB-48 and apoB-100. Whereas the secretion of apoB-48 VLDL was suppressed there was no effect on the sec retion of apoB-100 VLDL. The post-translational degradation of apoB-48, but not of apoB-100, was enhanced by 25-hydroxycholesterol. The net synthesis rates of apoB-48 and apoB-100 were unaffected by 25-hydroxycholesterol. The inhibitory effect of lovastatin alone on the net synthesis of apoB-48 and apoB-100 was reversed by the simultaneous presence of 25-hydroxycholesterol , suggesting a role for newly synthesised cholesteryl ester. Prevention of the reversal effect by the acyl-CoA: cholesterol acyltransferase (ACAT) inh ibitor YM 17E supported this interpretation. In the presence of lovastatin, restoration of the net synthesis of apoB by 25-hydroxycholesterol was not accompanied by an increased VLDL output of apoB-48 and apoB-100. However, u nder these conditions there was an increased post-translational degradation of apoB-48 and apoB-100. These results suggest that interference with intr acellular cholesterol and cholesteryl ester metabolism interrupts VLDL asse mbly at sites of both apoB net synthesis and post-translational degradation . (C) 1999 Elsevier Science B.V. All rights reserved.