Cellular lipids triglycerides

Obviously the interference of antihypertensive agents with cellular lipid metabolism may modify the atherosclerotic risk of individuals. Therefore, the effects of the Ca2+ antagonists, such as verapamil, diltiazem, nifedipine, and p-blockers, such as propanolol and metapralol on low density lipoprotein (LDL) receptor activity, cholesterol esterification time, oleate incorporation in triglycerides and sterol synthesis were studied in freshly isolated human leukocytes and in HEP G2 cells (Hepatoma cells). 

The purpose of this review is to compare the various approaches used to improve cellular lipid preservation and discuss the results obtained in the study of different lipid compounds in several tissues. This review will be confined mostly to metabolic studies performed in mammals in vivo or in vitro and will encompass the following lipid classes triglycerides, free fatty acids, cholesterol (free and ester), and phospholipids. No attempt will be made to review histo-chemical approaches to localization of lipids or radioautographic localization of steroid hormones, as these subjects were dealt with recently in a detailed way by Adams (1969) and by Stumpf (1970). 

Lipids encompass a wide class of amphiphilic molecules which, along with proteins, form the biological membranes necessary to support cellular function. While the simplest lipids, fatty acids and triglycerides, are not... 

ST 13 fibroblasts maintained in a medium containing insulin differentiate into adipose-like cells. This conversion is characterized by the appearance of lipid droplets in the cytoplasm and by an increase in synthesis and accumulation of cellular triglyceride. The insulin binding increases about 10-fold during differentiation. Tunicamycin inhibits the differentiation and suppresses insulin-binding activity.551... 

The accumulation of fat is a common cellular response to toxic compounds, which is normally reversible. Usually triglycerides accumulate, although sometimes phospholipids accumulate, as occurs after exposure to the drug chlorphentermine (see chap. 2). Steatosis is particularly common in the liver as this organ has a major role in lipid metabolism (Fig. 6.15). The lipid may appear in the cell as many small droplets or as one large droplet. Interference with lipid metabolism can occur at several points ... 

Cholesterol is an essential component of cellular membranes. In addition to dietary sources, we can also synthesize cholesterol. Cholesterol is transported in the blood as a lipoprotein, which is an aggregate of water-soluble proteins, cholesterol, and other lipids, including triglycerides. Proteins are denser than lipids,... 

The nascent HDL particles change shape and composition as they acquire additional free cholesterol by passive cellular diffusion of free cholesterol from cell membranes or from other plasma lipoproteins. HDL surface-localized LCAT progressively converts the free cholesterol on the surface of the particles to cholesterol ester, which occupies the core of the lipoprotein particle. This process converts the shape of the HDL particles from discoidal to spherical. The lipid unloading of HDL in the liver follows at least two pathways. In the first route, the cholesterol ester transfer protein (CETP) mediates cholesterol ester transfer from HDL to VLDL and LDL in exchange for triglyceride LDL in turn are taken up by the liver via the LDL receptor. In the second route, HDL binds to the scavenger receptor Bl, and cholesterol esters are selectively taken into the liver cells without internalization of HDL proteins (Fig. 15-2). 

The enterocytes of the small intestine can be isolated and used for study of intracellular aspects of intestinal lipid transport like triglyceride synthesis [52]. The disappearance of the mucus barrier during isolation of the epithelial cells results in plasma membrane disintegration and loss of cellular integrity when the cells are exposed to bile salts. As is the case for brush border vesicles, the system of isolated cells does not allow study of interaction between enterocytes and lipids dispersed in a form that resembles physiological conditions, i.e. solubilized in mixed bile salt micelles. 

These lipoproteins vary in size, density, relative composition of triglycerides, phospholipids, cholesterol, cholesterol ester, and proteins. In addition, each of these classes of lipoproteins may contain different apoproteins. These specific apoproteins are important for transformations within the lipid particle, and are signals for cellular receptors allowing uptake and/or endocytosis. 

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