Apolipoprotein E3-Leiden (APOE*3-Leiden) transgenic mice have been studied to identify factors modulating chylomicron and VLDL remnant lipoprotein metabolism. Transient elevated levels of VLDL/LDL-sized lipoproteins occurred in these mice with maximal levels during the period of rapid growth (optimum at 45 d of age). After about 100 d of age, serum cholesterol and triglyceride levels stabilized to slightly elevated levels as compared to control mice. The expression of the APOE*3-Leiden transgene was not age-dependent. In young mice the in vivo hepatic production of VLDL-triglycerides was 50% increased as compared to older mice. This is sustained by in vivo VLDL-apo B turnover studies showing increased (75%) VLDL-apo B secretion rates in young mice, whereas the VLDL-apo B clearance rate appeared not to be age dependent.On a high fat/cholesterol diet, females displayed significantly higher cholesterol levels than males (10 versus 7.0 mmol/liter, respectively). Serum levels of VLDL/LDL sized lipoproteins increased upon administration of estrogens, whereas administration of testosterone gave the opposite result. As compared to male mice, in female mice the hepatic VLDL-triglyceride production rate was significantly elevated. Injection of estrogen in males also resulted in increased VLDL-triglyceride production, although not statistically significant. In vivo VLDL-apo B turnover experiments showed that the VLDL secretion rate tended to be higher in females. Although, the fractional catabolic rate of VLDLapo B is not different between males and females, administration of estrogens in males resulted in a decreased clearance rate of VLDL, whereas administration of testosterone in females resulted in an increased clearance rate of VLDL. The latter presumably due to an inhibiting effect of testosterone on the expression of the APOE*3-Leiden transgene.We conclude that hyperlipidemia in APOE*3-Leiden transgenic mice is strongly affected by age via its effect on hepatic VLDL production rate, whereas gender influences hyperlipidemia by modulating both hepatic VLDL production and clearance rate. ( J. Clin. Invest. 1996. 97:1184-1192.)

To investigate the quantitative requirement for apolipoprotein (apo) E in the clearance of lipoproteins via the non-low density lipoprotein (LDL) receptor mediated pathway, human APOE was overexpressed at various levels in the livers of mice deficient for both the endogenous Apoe and Ldlr genes ( Apoe Ϫ / Ϫ ؒ Ldlr Ϫ / Ϫ ) using adenovirusmediated gene transfer. We found that a low level of APOE expression, that was capable of reducing the hyperlipidemia in Apoe Ϫ / Ϫ mice, did not result in a reduction of the hyperlipidemia in Apoe Ϫ / Ϫ ؒ Ldlr Ϫ / Ϫ mice. Surpisingly, a very high level of APOE expression also did not result in a reduction of hypercholesterolemia in Apoe Ϫ / Ϫ ؒ Ldlr Ϫ / Ϫ mice, despite very high levels of circulating apoE ( Ͼ 160 mg/dl). Only a moderately high level of APOE expression resulted in a reduction of serum cholesterol level (from 35.2 ؎ 6.7 to 14.6 ؎ 2.3 mmol/l) and the disappearance of VLDL from the serum. Moreover, the very high level of APOE expression resulted in a severe hypertriglyceridemia in Apoe Ϫ / Ϫ ؒ Ldlr Ϫ / Ϫ mice and not Apoe Ϫ / Ϫ mice (25.7 ؎ 8.9 and 2.2 ؎ 1.8 mmol/l, respectively). This hypertriglyceridemia was associated with an APOE-induced increase in the VLDL triglyceride production rate and an inhibition of VLDL-triglyceride lipolysis. We conclude from these data that, for efficient clearance, the non-LDL receptor-mediated pathway requires a higher level of APOE expression as compared to the LDL receptor, but is more sensitive to an APOE-induced increase in VLDL production and inhibition of VLDL-triglyceride lipolysis. -van Dijk, K.

Studying the effects of dietary fish oil on VLDL metabolism in humans is subject to both large intra-and interindividual variability. In the present study we therefore used hyperlipidemic apolipoprotein (APO) E*3-Leiden mice, which have impaired chylomicron and very low density lipoprotein (VLDL) remnant metabolism, to study the effects of dietary fish oil on serum lipids and VLDL kinetics under highly standardized conditions. For this, female APOE*3-Leiden mice were fed a fat-and cholesterol-containing diet supplemented with either 0, 3 or 6% w/w (i.e. 0, 6, or 12% of total energy) of fish oil. Fish oil-fed mice showed a significant dose-dependent decrease in serum cholesterol (up to ؊ 43%) and triglyceride levels (up to ؊ 60%), mainly due to a reduction of VLDL ( ؊ 80%). LDL and HDL cholesterol levels were not affected by fish oil feeding. VLDL-apoB kinetic studies showed that fish oil feeding resulted in a significant 2-fold increase in VLDL-apoB fractional catabolic rate (FCR). Hepatic VLDL-apoB production was, however, not affected by fish oil feeding. VLDL-triglyceride turnover studies revealed that fish oil significantly decreased hepatic VLDL-triglyceride production rate ( ؊ 60%). A significant increase in VLDL-triglyceride FCR was observed ( ؉ 70%), which was not related to increased lipolytic activity.We conclude that APOE*3-Leiden mice are highly responsive to dietary fish oil. The observed strong reduction in serum very low density lipoprotein (VLDL) is primarily due to an effect of fish oil to decrease hepatic VLDL triglyceride production rate and to increase VLDL-apoB fractional catabolic rate.van Vlijmen, B.

The phospholipid composition of human and guinea pig skeletal muscle was determined. Virtually no autolytic changes occurred in the first half hour post‐mortem and after 12 hr only very small changes were detected. There were significant differences in the phospholipid composition of red and white muscle, especially in the diphosphatidyl glycerol (DPG) content,red muscle having over 50% more DPG than white muscle.