Fat emulsion catabolism in vitro and in vivo--sex related differences

Acylation stimulating protein: a female lipogenic factor?

Acylation stimulating protein (ASP) is a potent lipogenic factor produced from adipocytes. Plasma ASP levels were shown to increase in obesity, diabetes mellitus type II and dyslipidemia, and decrease after weight loss and fasting. Growing evidence suggests that ASP may significantly contribute to subcutaneous fat storage in females. In vitro, ASP stimulated triglyceride synthesis to a larger extent in subcutaneous compared with omental adipocytes. The ASP receptor binding affinity to plasma membranes prepared from adipose tissue showed higher binding affinity to plasma membranes from female adipose tissue compared with male adipose tissue, and was more pronounced to subcutaneous compared with omental plasma membranes. Human studies demonstrated that postprandial triglyceride clearance predicted by ASP levels was more efficient in women than in men. In mice, postprandial triglyceride clearance, with intraperitoneal ASP administration, was faster in females compared with males. The ASP deficient mice were resistant to weight gain and had reduced fat mass that was more pronounced in females. Recent findings in humans and mice point to a significant association between progesterone and ASP variations in females. In this review, we highlight findings, to date, linking ASP to physiological and hormonal alterations that may contribute to subcutaneous fat distribution typical to females.

Acylation stimulating protein (ASP) deficiency alters postprandial and adipose tissue metabolism in male mice

Acylation stimulating protein (ASP) is a potent stimulator of triglyceride synthesis in adipocytes. In the present study, we have examined the effect of an ASP functional knockout (ASP(-/-)) on lipid metabolism in male mice. In both young (14 weeks) and older (26 weeks) mice there were marked delays in postprandial triglyceride clearance (80% increase at 14 weeks and 120% increase at 26 weeks versus wild type (+/+)). Postprandial nonesterified fatty acids were also increased in ASP(-/-) mice versus ASP(+/+) mice by 37% (low fat 10% Kcal) and by 73% (high fat 40% Kcal) diets, although there were no differences in fasting lipid levels. The ASP(-/-) mice had moderately increased energy intake (16% +/- 2% p < 0.0001) and reduced feed efficiency (33% increase in calories/g of body weight gained on low fat diet) versus wild type. The ASP(-/-) mice also had modest changes in insulin/glucose metabolism (30% to 40% decrease in insulin.glucose product), implying increased insulin sensitivity. As well, there were decreases in leptin (29% shift in leptin to body weight ratio) and up to a 26% decrease in specific adipose tissue depots versus the wild type mice on both low fat and high fat diets. These results demonstrate that ASP plays an important role in adipose tissue metabolism and fat partitioning.

Antimalarial properties of soy-bean fat emulsions

Intralipid and Ivelip are commercial preparations of soy-bean lipid extracts used for intravenous supplementation of lipids in various clinical conditions. They were found to inhibit the growth of Plasmodium falciparum in culture with an IC50 of 8.07 +/- 2.13 and 13.32 +/- 2.05 mg.ml-1, respectively. Intralipid rapidly and efficiently inhibited nucleic acid synthesis in cultured P. falciparum, exhibiting full inhibitory activity in less than 2 h. Ivelip injected intraperitoneally, was found by the 4-day suppressive test to be active in vivo against P. vinckei petteri within the normal recommended regimen for dietary lipid supply (0.5-4 g.kg-1), but it was impossible to obtain a radical cure even with very high doses (6.4 g.kg-1). Ivelip was less effective against P. berghei and P. yoelii nigeriensis. As Ivelip showed no interference with the antimalarial activity of chloroquine, it could be considered for use in the treatment of severe human malaria in association with 4-aminoquinolines to expedite the clearance of parasites.

Effects of hypertonic glucose on the rates of plasma clearance and CO2 production of intravenously administered intralipid emulsion in dogs

Simultaneous infusion of glucose and Intralipid was carried out on dogs to evaluate the effect of glucose on utilization of the fat emulsion. For control experiments, normal saline was used in place of glucose. Results of these studies revealed that clearance of Intralipid and also of triglyceride and free fatty acid (FFA) from the plasma did not differ between the dogs receiving glucose and those receiving saline infusion. The rates of Intralipid clearance were 0.049 +/- 0.003 and 0.047 +/- 0.003 per minute (n = 16), respectively. Study with radioactive [14C]Intralipid also gave similar rates of 14C clearance from the plasma, 0.037 +/- 0.003 and 0.040 +/- 0.003 per minute (n = 4), respectively for the two groups. These suggested that clearance of Intralipid from the plasma was not affected by glucose. However, data on expired 14CO2 revealed that oxidation of the fat, which yielded CO2 as end product, was inhibited by glucose. The amount of 14CO2 expired in 2 hours was 10.4 +/- 1.4% for the saline group, which was significantly reduced to 3.0 +/- 0.4% (n = 4; p less than 0.01) for the glucose group. In each group, CO2 production was much delayed as compared to fat clearance from the plasma. Thus, the rate of clearance of Intralipid from plasma does not reflect the actual utilization of fat emulsion. In accordance with an experiment with insulin, it appears that suppression of CO2 production is directly related to plasma insulin levels.