CELLULAR PROCESSING OF APOLIPOPROTEIN B-CONTAINING LIPOPROTEINS FROM YOUNG POSTINFARCTION PATIENTS AND HEALTHY CONTROLS

3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase activity was measured in fibroblasts incubated with large (Sf > 60) and small (Sf 20-60) very low density lipoprotein (VLDL), intermediate density lipop rotein (IDL) and low density lipoprotein (LDL) particles, at similar p rotein concentrations, from young post-infarction patients and healthy controls. The results showed that apolipoprotein (ape) B-containing l ipoproteins (VLDL, IDL, LDL) from patients suppressed HMG-CoA reductas e activity to a similar extent compared to apo B-containing lipoprotei ns from controls. When all subjects taken together were grouped accord ing to triglyceride levels, it was found that small VLDL from hypertri glyceridaemic individuals suppressed the HMG-CoA reductase activity mo re than small VLDL from normotriglyceridaemic individuals. The opposit e pattern was seen for LDL. The lipoprotein composition was related to the respective HMG-CoA reductase activity. In addition to a positive association between the cholesterol content of small VLDL and LDL, and the inhibition of HMG-CoA reductase activity, the apo C I and C II co ntent of small VLDL and IDL was inversely related to the suppression o f HMG-CoA reductase activity. This study shows that the cellular proce ssing of apo B-containing lipoproteins in young post-infarction patien ts and healthy controls is heterogeneous and dependent on the composit ion of the lipoprotein.