The biochemical composition and metabolism of lipoproteins in type V hyperlipoproteinaemia.

The biochemical composition of lipoproteins in Type V hyperlipoproteinaemia was investigated with special reference to apolipoprotein-B. The in vivo metabolism of protein-labelled low density lipoprotein was also studied in five such patients (3 diabetic, 2 obese subjects). In association with pathologically elevated plasma levels of chylomicrons and very low density lipoproteins, low density lipoprotein concentration was significantly reduced. The proportions of triglyceride to apo-B and triglyceride to cholesterol were significantly increased in all lipoprotein classes, while the proportion of cholesterol to apo-B was significantly reduced. Disappearance of chylomicronaemia with treatment was associated with a prompt increase in low density lipoprotein concentration. The reduced low density lipoprotein concentration was accompanied by an accelerated fractional turnover rate, and by an absolute turnover rate which was subnormal. These results were interpreted as reduced synthesis of low density lipoprotein apoprotein and as a possible block in the conversion of very low density lipoprotein to low density lipoprotein in some Type V patients.