Cholesterol esters fibroblasts

One limitation of enzyme replacement therapy is the targeting of enzyme proteins to appropriate sites of substrate accumulation. Administration of a cholesterol esterase conjugated to albumin results in the degradation of pathologic cholesterol ester accumulations within the lysosomes of fibroblasts from a patient with cholesterol ester storage disease (246). 

It was possible for us to describe this clinical picture in detail from our own observations of a 13-year-old girl. We detected a very high content of cholesterol ester in the biopsy sample and a deficiency of lysosomal a-naphthyl-acetate esterase in the fibroblast culture. (205) (s. figs. 21.5 31.13, 31.14)... 

The helper effects of DOPE and cholesterol appear to be hydrocarbon chain-specific. This is demonstrated in studies of their mixtures with a series of alkyl acyl carnitine esters (alkyl 3-acyloxy-4-trimethylammonium butyrate chloride) tested with CV-1 cell culture (monkey fibroblast) [127]. The influence of the aliphatic chain length (n - 12-18) on transfection in vitro was determined using cationic liposomes prepared from these lipids and their mixtures with the helper lipids DOPE and cholesterol (Fig. 30). Both helper lipids provided for significant transfection enhancements in an apparently chain-specific manner, with the highest effects found for short-chain lipids with diC12 0 and diC14 0 chains in 1 1 mixtures with the respective helper lipid. 

Fig. 30 Transfection activity of lipoplexes consisting of alkyl/acyl carnitine esters, alone and with helper lipid (DOPE or cholesterol), on [1-galactosidase expression in CV-1 cell culture (monkey fibroblast) cationic lipid/DNA charge ratio 4 1 [127]...

LDL is oxidatively modified when incubated in vitro with three major cellular constituents of the vascular wall endothelial cells [35], vascular smooth muscle cells [35] and macrophages [35-37], The uptake of oxidised LDL occurs via the scavenger-receptor pathway, and expression of scavenger receptors has been demonstrated on macrophages, endothelial cells [38], fibroblasts [39] and smooth muscle cells [39]. Unlike the LDL receptor, expression of the scavenger receptor is not down-regulated by an increase in intracellular cholesterol [40]. Therefore, uptake of Ox-LDL contributes to the accumulation of cholesteryl esters in foam cells of atherosclerotic lesions [40]. Now, the question is Does oxidation of LDL-lipids influence the development of atherosclerosis ... 

More general information about the potential role of apoE in cellular lipoprotein uptake has come from studies with cultured cells (e.g., fibroblasts). Such cells manifest surface receptors for LDL that bind apoB, the protein component of LDL. This is followed by receptor-mediated endocytosis, fusion of the endo-cytic vesicles with lysosomes, and LDL degradation within the lysosomes (see Goldstein and Brown, 1979 Brown et al., 1981, for reviews and references). Cholesteryl esters taken into cells in this manner are hydrolyzed by a lysosomal acid lipase. The liberated cholesterol then leaves the lysosome and is used in the cell for membrane synthesis and as a regulator of intracellular cholesterol homeostasis. 

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