Vitamin adipocytes

In vitro and ex vivo studies have shown that FATPs transport LCFAs and very long-chain fatty acids (VLCFAs) but no medium-chain fatty acids, fatty acid esters, or lipid-soluble vitamins [4]. LCFA transport is inhibited by prior protease treatment. Synthetic substrates for FATPs include 14C-labeled fatty acids and the fluorescently labeled fatty acid analogue C1 -BODEP Y-Cl 2. Using the latter substrate, differences in fatty acid uptake kinetics between FATP expressing 3T3 LI adipocytes and 3T3 LI fibroblasts, which are devoid of FATPs, can be readily appreciated (Fig. 2). 

Adipocytes have vitamin D receptors, and there is evidence that vitamin D may act as a suppressor of adipocyte development (Kawada et al., 1996). It has been suggested that vitamin D inadequacy may be a factor in the development of the metabolic syndrome ( syndrome X, the combination of insulin resistance, hyperlipidemia, and atherosclerosis associated with abdominal obesity). Sunlight exposure, and hence vitamin D status, may be a factor in the difference in incidence of atherosclerosis and myocardial infarction between northern and southern European countries in addition to effects on adipocyte development, calcitriol also enhances insulin secretion through induction of calbindin-D (Section 3.3.7.1), and there is some evidence vitamin D supplements can improve glucose tolerance (Boucher, 1998). 

Kawada T, Kamei Y, and Sugimoto E (1996) The possibility of active form of vitamins A and Das suppressors on adipocyte development via ligand-dependent transcriptional regulators. International Journal of Obesity and Related Metabolic Disorders 20(Suppl 3),S52-7. 

Lipids are a class of nonpolar molecules that include the fats, cholesterol, fatty acids, lipid-soluble vitamins, waxes, soaps, glycerophospholipids, sphingolipids, and others. Lipids are found in the membranes of cells, the endoplasmic reticulum, and in specialized fat storage cells called adipocytes. 

In general, the greater the amount of vitamin E fed and/or length of feeding period, the higher the tissue concentration of a-tocopherol (Table 8.2). Plasma levels of a-tocopherol are used to monitor intake of the vitamin, but are considered an adequate indicator of tissue vitamin status only during steady-state conditions (Arnold et al., 1992b). Within plasma, vitamin E is associated with lipoproteins, while in cells it is found as part of biomembranes. Traber and Kayden (1987) have reported that in human adipose tissue, tocopherol is associated primarily with adipocyte contents and not the plasmalemma. 

Chylomicrons are assembled from TAG in the intestine. Their apoprotein components are synthesized and modified in the rough endoplasmic reticulum but the chylomicron itself is assembled in the Golgi. Chylomicrons are synthesized with a unique apoB48 on their surface, but also acquire apoE and apoCII once they are in the circulation. The apoCII allows the chylomicrons to interact with lipoprotein in the capillaries of the adipose tissue to release most of the triglyceride. Lipoprotein lipase hydrolyses chylomicron TAG to monoacylglycerol, FA and glycerol so that they can enter the adipocyte where TAG is re-synthesized and stored. Chylomicron remnants containing cholesterol and fat soluble vitamins are removed from the circulation by the liver. 

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