Lipid intestinal transport

In this equation, FB is defined as the bioaccessibility coefficient, z. e., fraction of lipid released from the food matrix into juices of the gastrointestinal tract FT is defined as the transport coefficient, i.e., fraction of the released lipid component transported across the intestinal epithelium and Fm is the fraction of the lipid component that reaches the systemic circulation without being metabolized. It is usually important to measure the concentration of a bioactive component at a particular location to establish its efficacy. Thus, the concentration-time profile of a specific bioactive component at a particular site of action may be helpful in the... 

Plasma Lipoproteins. The plasma lipids are transported by four major lipoprotein classes. The plasma lipoproteins are synthesized and secreted only in the intestine and liver. Chylomicrons, the richest in triglyceride, are synthesized in the small intestine and transport dietary (exogenous) triglyceride and cholesterol. Very low density (prebeta) lipoproteins (VLDL)... 

Hui, D. Y., Labonte, E. D., and Howies, P. N. (2008) Development and physiological regulation of intestinal lipid absorption III. Intestinal transporters and cholesterol absorption. Am. J. Physiol. Gastrointest. Liver Physiol. 294, 839-843. 

Synthetic allithiamin derivatives, such as thiamin propyl and tetrahydro-furfuryl disulfides, have been used for the prevention and treatment of thiamin deficiency. Because they are lipid soluble, and are not subject to the normal control of thiamin absorption by saturation of the intestinal transport system, they have potential benefits in the treatment of thiamin-deficient alcoholics, whose absorption of thiamin is impaired. 

Lipoproteins are macromolecules comprising proteins (= apolipoproteins, apoproteins) and lipids. They transport water-insoluble lipids in the blood, with the exception of the albumin-bound free fatty acids. Only short-chain fatty acids are dissolved in plasma. The lipoproteins are formed in the liver and in the mucosa of the small intestine. (14)... 

Constantinides, P.P. and Wasan, KM. (2007) Lipid formulation strategies for enhancing intestinal transport and absorption of P-glycoprotein (P-gp) substrate drugs in vitro/in vivo case studies. Journal of Pharmaceutical Sciences, 96 (2), 235-248. 

Plasma lipoproteins are complex lipids that transport other lipids through the bloodstream. Chylomicrons carry dietary triglycerides from the intestine to other tissues. Very low density lipoproteins carry triglycerides synthesized in the liver to other tissues for storage. Low-density lipoproteins carry cholesterol to peripheral tissues and help regulate blood cholesterol levels. High-density lipoproteins transport cholesterol from peripheral tissues to the liver. 

Lipoproteins are soluble complexes of proteins (apolipoproteins) and lipids that transport lipids in the circulation of all vertebrates and even insects. Lipoproteins are synthesized in the liver and the intestines, arise from metabolic changes of precursor lipoproteins, or are assembled at the cell membranes from cellular lipids and exogenous lipoproteins or apolipoproteins. In the circulation, lipoproteins are highly dynamic. They undergo enzymatic reactions of their lipid components, facilitated and spontaneous lipid transfers, transfers of soluble apolipoproteins, and conformational changes of the apolipoproteins in response to the compositional changes. Finally, lipoproteins are taken up and catabolized in the liver, kidney, and peripheral tissues via receptor-mediated endocytosis and other mechanisms. This chapter deals with the composition and structure of human lipoproteins. 

An alternative explanation for the decrease of RER and Golgi membranes of absorptive cells may lie with the simple assumption that de novo membrane synthesis does not keep pace with membrane utilization or turnover in this cell type. The importance of membrane containers and de novo membrane synthesis in the intestinal transport of lipid was emphasized by a study in which ribosomal protein synthesis was inhibited with puromycin (Friedman and Cardell, 1972a). In this... 

HDL and VLDL are assembled primarily in the endoplasmic reticulum of the liver (with smaller amounts produced in the intestine), whereas chylomicrons form in the intestine. LDL is not synthesized directly, but is made from VLDL. LDL appears to be the major circulatory complex for cholesterol and cholesterol esters. The primary task of chylomicrons is to transport triacylglycerols. Despite all this, it is extremely important to note that each of these lipoprotein classes contains some of each type of lipid. The relative amounts of HDL and LDL are important in the disposition of cholesterol in the body and in the development of arterial plaques (Figure 25.36). The structures of the various... 

Lipoprotein metabolism is the process by which hydrophobic lipids, namely triglycerides and cholesterol, are transported within the interstitial fluid and plasma. It includes the transport of energy in the form of triglycerides from intestine and liver to muscles and adipose, as well as the transport of cholesterol both from intestine and liver to peripheral tissues, as well as from peripheral tissues back to the liver. 

In addition to the described lipid pathways mainly operative in macrophages, two further ABC-transporteis, ABCG5 and ABCG8 have been implicated in the efflux of dietary sterols from intestinal cells back into the gut lumen and from liver to the bile duct (Fig 1). Both ABC-transporters form a functional heterodimer with highest expression levels in liver and intestine and are regulated... 

By definition, chylomicrons are found in chyle formed only by the lymphatic system draining the intestine. They are responsible for the transport of all dietary lipids into the circulation. Small quantities of VLDL... 

FIG. 2 Mechanisms of drug transfer in the cellular layers that line different compartments in the body. These mechanisms regulate drug absorption, distribution, and elimination. The figure illustrates these mechanisms in the intestinal wall. (1) Passive transcellular diffusion across the lipid bilayers, (2) paracellular passive diffusion, (3) efflux by P-glycoprotein, (4) metabolism during drug absorption, (5) active transport, and (6) transcytosis [251]. 

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