Differences in labelled triolein turnover after oral administration between liver and adipose tissue of rats

Is Oral Lipid-Based Delivery for Drug Targeting to the Brain Feasible?

This review outlines the feasibility of oral lipid-based targeted delivery of drugs to the brain, including permeation of the central nervous system's (CNS) protective blood-brain barrier (BBB). The structure of the BBB and disruption caused by varying disease states highlights the need for disease-specific approaches to alter permeation. Disruption during disease state, and the effects of certain molecules on the barrier, demonstrate the possibility of exploiting such BBB disruption for drug delivery. Many administration methods can be used to target the brain, but oral administration is considered ideal for chronic, long-term illnesses. Several lipids that have been shown to facilitate drug delivery into the brain after systemic administration, but could also be delivered orally are discussed, including oleic acid, triolein, alkylglycerol, and conjugates of linoleic and myristic acids. Current data reveal the potential for the use of such lipids as part of oral formulations for delivery to the brain by reaching sufficient plasma levels after administration to increase the permeability of the BBB. However, gaps in the literature remain regarding the concentrations and form of most lipids required to produce the desired effects. The use of lipids via oral delivery for brain targeting has not been investigated thoroughly enough to determine with certainty if similar permeability-enhancing effects would be observed as for parenteral administration. In conclusion, further research to fill research gaps is needed, but the limited evidence suggests that oral lipid-based drug delivery for brain targeting is potentially feasible.

Comparison of labeled acetate and glucose incorporations into lipids in the liver and adipose tissue after intravenous injection in rats

To compare incorporations of acetate and glucose in tissue total lipids and triacylglycerols (TAG), incorporations of labeled acetate and glucose in livers and epididymal adipose tissues (adipose tissue) were followed after their intravenous injection in the tail vein of individual rat fed a fat-free or 10% corn oil diet. The incorporation of acetate into total lipids (mostly TAG) in the liver reached maximum 2 h after the injection, while the incorporation of glucose decreased more quickly. Incorporation of glucose into total lipids and TAG was more greatly suppressed by dietary corn oil than that of acetate in the liver. In the adipose tissues, the incorporation of labeled acetate or glucose into total lipids was maximum 2-8 h after the injection, while the incorporation of glucose was very low, especially in rats fed the corn oil diet. Moreover, the time courses for labeled acetate and glucose incorporations into total lipids in the liver were parallel to those in plasma, but opposite to those in adipose tissue. TAG synthesized from acetate and glucose in the liver appeared to be mostly transported to adipose tissue. Thus, it is suggested that as the labeled glucose rapidly decreased in the liver, plasma and adipose tissue, TAG should be less derived from dietary carbohydrate than from dietary fat.

Caloric restriction and refeeding promoted different metabolic effects in fat depots and impaired dyslipidemic profile in rats

OBJECTIVE

We investigated the effects of severe caloric restriction and refeeding with a high-fat diet on lipid uptake by visceral adipose fat and lipid profile in rats.

METHODS

Rats were assigned to six groups: a chow diet (C), a high-fat diet (H), severe caloric restriction (SC and SH), and severe caloric restriction plus refeeding (SC-r and SH-r) during 8 wk. All animals were killed by decapitation 4 h after intragastric administration of [1-14C] triolein ( approximately 0.5 g, 0.3 muCi/rat). Liver; visceral retroperitoneal (RET), epididymal (EPI), and omental (VIS) white adipose tissues; brown adipose tissue; and intestine were immediately removed and weighed. The whole intestine was withdrawn and homogenized to determine lipid uptake. Total cholesterol, high-density lipoprotein (HDL), and triacylglycerol in plasma were determined enzymatically.

RESULTS

The SC and SH groups showed reduced visceral adiposity, although this effect was more evident in the SC group. The SC group had greater lipid absorption in the VIS than the C group. The SH treatment increased RET and VIS lipid uptake in relation to the H group. The SH-r treatment increased RET and VIS adiposity. HDL cholesterol decreased with caloric restriction in the SC and SH groups. The SH-r treatment did not increase HDL cholesterol.

CONCLUSION

Severe caloric restriction decreased visceral adiposity even in rats in the H group but did not reduce the risk of development of dyslipidemia. Therefore, food restriction plus refeeding with a high-fat diet increase the risk of development of visceral adiposity and dyslipidemia.