Fractional removal rate of fat emulsion (K2) remains to be low in APOE3/3 phenotype subjects with serum triglyceride level above 180mg/dl.

The relation between fractional catabolic rate (K2) of an intravenously injected fat emulsion, Intralipid, and the level of serum triglyceride (TG) was evaluated to cast light on TG-rich lipoprotein metabolism in 182 subjects who were homozygotes for the most common form of apoE3/3. Both normolipidemic individuals and primary hyperlipidemic patients were included. To assess the influence of variation in the apoE phenotype on fat emulsion metabolism, 25 subjects with the apoE 4/3 phenotype and 21 with apoE 3/2 phenotype were also evaluated. In the apoE 3/3 subjects, K2 decreased with increasing TG level up to 180mg/dl, but above 180mg/dl, K2 remained at a constant level. This TG value was therefore concluded to be a cut off beyond which the TG-dependent decrease in K2 disappeared. No apparent correlation between K2 and serum TG was observed in subjects with apoE 4/3 or 3/2 phenotypes. In subjects with TG above 180mg/dl, presumably both accelerated synthesis and limited removal are involved in the development of their hypertriglyceridemia. Since K2 demonstrated little change with increase of TG over 180mg/dl in apoE 3/3 subjects, we concluded that the capacity to catabolize fat emulsion reaches a kinetic saturation. The TG value of 180mg/dl may be a physiological significance. The relation between K2 and TG was specific in apoE 3/3, as it was not observed in subjects having apoE 4/3 or 3/2 phenotypes.