Cytoplasmic lipid droplets

Intracellular lipid droplets Cytoplasmic lipid droplets 14.6 45.8 20.9 11.9 6.8... 

Fonagy A., Yokoyama N. and Matsumoto S. (2001) Physiological status and change of cytoplasmic lipid droplets in the pheromone-producing cells of the silkmoth, Bombyx mori (Lepidoptera, Bombycidae). Arthr. Str. Fund. 30, 113-123. 

Figure 3. H NMR spectrum of myeloma cells that contained cytoplasmic lipid droplets. The protons in the triglycerides which give rise to the cross peaks in the spectrum are indicated. The conventional one-dimensional spectrum is shown at the top of the figure. From Callies et al., 1993, with permission.

As with the increase in phosphomonoester signal, these changes in the spectra of lipids are not necessarily indicative of a malignant cell. For example, mitogen-stimulated lymphocytes accumulate cytoplasmic lipid droplets (Tanaka et al., 1963) and show the high resolution H lipid signals (Mountford et al., 1982). 

Callies, R Sri-Pathmanathan, R.M., Ferguson, D.Y.P., Brindle, K.M. (1993). The appearance of neutral lipid signals in the H NMR spectra of a myeloma cell line correlates with the induced formation of cytoplasmic lipid droplets. Magn. Reson. Med. 29, 546-550. 

Figure 4.2. Electron micrograph showing a cytoplasmic lipid droplet (cld) in a cell fixed with potassium ferrocyanide. Dark-staining material of variable thickness coats the surface of the droplet (arrows). The alveolar lumen (1) is denoted. Bar = 1 p.m. From Dylewski et al. (1984a) with permission.

Figure 4.3. Electron micrograph showing a cytoplasmic lipid droplet (cld) and numerous microlipid droplets, some of which are denoted by arrows. An apparent fusion figure between the cld and a microlipid droplet is denoted by the arrow on the right. The specimen was fixed simultaneously with glutaraldehyde and osmium tetroxide. Bar = 0.5 p.m.

Studies in vitamin A replete animals suggest that most of the retinol is transferred from hepatocytes to the perisinusoidal stellate cells of the liver. Here, it is again esterified by LRAT to form mainly retinyl palmitate (76% to 80%), with smaller amounts of stearate (9% to 12%), oleate (5% to 7%), and linoleate (3% to 4%). The stellate cells contain 90% to 95% of hepatic vitamin A, as cytoplasmic lipid droplets that consist of between 12% to 65% retinyl esters (Batres and Olson, 1987). Studies with [ C]retinyl palmitate show that much of the recently ingested retinol appears more or less immediately in the... 

IC50S for the enzyme- (radioactive design) and cellular lipolysis inhibition by Aventis inhibitor 7600 were within one order of magnitude, strongly arguing for efficient penetration of the adipocyte plasma membrane and access to cytoplasmic lipid droplets. 

Russell TD, Palmer CA, Orlicky DJ, Fischer A, Rudolph MC, Neville MC, McManaman JL. Cytoplasmic lipid droplet accumulation in developing mammary epithelial cells roles of adipophilin and lipid metabolism. J Lipid Res 2007 48 1463-1475. 

Acetylated LDL bind to the scavenger receptor, are internalized via coated pits and coated vesicles, and are directed to lysosoines where the whole particle is degraded. The cholesterol moiety is transported to the cytoplasm and may be stored in the form of cytoplasmic lipid droplets or released from the cell. 

The interaction of HDL with the lipid droplets has been further investigated by morphological methods (Fig. 3). Upon lipid accumulation in the macrophage, an intimate contact between the endoplasmic reticulum (ER) and the margin of the lipid droplet can be observed. At the site of contact, due to the induction of phospholipid and apolipoprotein synthesis, lamellar bodies are formed which are surrounded by a newly synthesized membrane. These lamellar bodies consist of free cholesterol, phospholipids, and apolipoproteins including Apo E. From these lamellar bodies, HDL take up cholesterol, Apo E, and phosphoUpids on their route through the cell (Fig. 3b). In the absence of HDL, the lamellar bodies which originate from cytoplasmic lipid droplets, cannot be secreted from the cell. 

In another study using flash-frozen liver biopsies obtained from 37 insulin-resistant, obese, nondiabetic individuals [51], it was found that hepatic DAG content in cytoplasmic lipid droplets was the best predictor of insulin resistance y = 0.80, p<0.001), and it was responsible for 64% of the variability in insulin sensitivity. Mechanistic studies showed that hepatic DAG content was strongly correlated with activation of hepatic PKCe (y = 0.67, p< 0.001), which impairs insulin signaling, and that there was no significant association between insulin resistance and other putative lipid metabolites or plasma or hepatic markers of inflammation. The investigators concluded that hepatic DAG content in lipid droplets was the best predictor of insulin resistance in humans, and the data supported the hypothesis that NAFLD-associated hepatic insulin resistance is caused by an increase in hepatic DAG content, which results in activation of PKCe. 

TAGS in the adipose tissue serve as the main energy store of the body as well as carriers of fatty acids in lipoproteins. TAGs are also found in the cytoplasmic lipid droplets present in cells of many tissues. 

Millon et al. monitored plaque inflammation in atherosclerotic rabbits using a combined PET/MR scanner. Proton magnetic resonance metabolomic characterization of ovarian serous carcinoma was performed by Vettukattil et for diagnostic purposes. Pan et using NMR lipidomic approach, noticed increased unsaturation of lipids in cytoplasmic lipid droplets in DAOY cancer cells in response to cisplatin treatment. Akoudad et examined formation of cerebral microbleeds associated with the progression of ischemic vascular lesions, while Kos-tara et followed the progression of coronary heart disease NMR-based lipidomic analysis of blood lipoproteins. 

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