Excessive Accumulation Of Cholesterol Research Articles

The effect of choline and myo-inositol on liver and carcass fat levels in aerobically trained rats.

Choline and myo-inositol are dietary supplements ingested under the premise that they facilitate the burning of stored fat. Choline and myo-inositol have been shown to prevent abnormal or excessive liver accumulation of cholesterol and triglycerides in choline and myoinositol deficient rats. The current study was designed to determine whether the consumption of choline and myoinositol by non-deficient aerobically trained rats affects the percent liver and carcass fat. Nineteen rats were trained aerobically for ten weeks then randomly assigned to an experimental group fed choline and myo-inositol mixed with their chow, or a control group fed only chow. Rats were sacrificed after 24 more days of aerobic training. Percent carcass and liver fat were determined by a lipid extraction procedure. There was a significant difference in the percent liver fat between groups, with the experimental group having less fat (6.69 +/- 2.23 vs 9.22 +/- 2.91 percent fat; r = 0.05). Percent carcass fat was not significantly different. There was a significant difference in the amount of weight gained during the 24 days of treatment, with the experimental group gaining less weight (5.1 +/- 9.2 vs 11.8 +/- 3.1 g; r < 0.05). The lack of an effect on percent carcass fat indicates that choline plus myoinositol supplements do not reduce adipose tissue mass but can inhibit weight gain while decreasing liver fat.

Regulation of intracellular cholesterol metabolism is defective in lymphoblasts from Niemann-Pick type C and type D patients

Regulation of intracellular cholesterol metabolism has been studied in Epstein-Barr virus-transformed lymphoblasts from patients with Niemann-Pick type C (NPC) and the Nova Scotia type D (NPD) disease. Addition of LDL to normal lymphoblasts cultured in lipoprotein-deficient medium increased cholesterol esterification 10-fold (to a maximum of 1.0 nmol/h/mg protein at 15 h), while little stimulation was seen in NPC cells. The response by NPD lymphoblasts was intermediate, reaching approximately half of normal values by 12–24 h. Lymphoblasts from both NPC and NPD obligate heterozygotes exhibited 50% of normal LDL-stimulated cholesterol esterification at 6 h, when activity was s 1 ̌ 0% of normal values in patient cells. Fluorescence staining with filipin indicated excessive intracellular accumulation of LDL-derived cholesterol in both NPC and NPD lymphoblasts. Downregulation of LDL receptor mRNA levels by LDL, measured by S1 nuclease protection assay, was also impaired in NP lymphoblasts and fibroblasts (NPC > NPD), although a similar rate of receptor protein down-regulation by LDL ( t 1 2 = 10–15 h ) was observed in normal and NP lymphoblasts. In contrast, LDL down-regulation of 3-hydroxy-3-methylglutaryl-CoA reductase mRNA did not appear to be affected in NP cells: LDL produced a 3-fold (lymphoblasts) of > 10-fold (fibroblasts) decrease by 12 h in both normal and affected cells. Thus, NPC and NPD lymphoblasts exhibit distinct defects in cholesterol esterification and storage, similar to those observed in mutant fibroblasts. Other regulatory responses are also impaired in NPC lymphoblasts but appear to be less affected in NPD cells. Lymphoblasts should provide a valuable immortalized cell line model for study of defective regulation of cholesterol esterification and transfort in Niemann-Pick type II disease, and may also suitable for diagnosis and carrier detection.

Effects of drugs on cholesterol esterification in normal and Niemann-Pick type C fibroblasts: AY-9944, other cationic amphiphilic drugs and DMSO

AY-9944 and other cationic amphiphilic drugs (CADs) have been reported to cause a reduction of acid sphingomyelinase activity in fibroblasts and various tissues in the rat, and DMSO has been known to correct a partial deficiency of acid sphingomyelinase activity in Niemann-Pick type C (NPC) fibroblasts. Furthermore, in the present study we demonstrated that AY-9944 and other CADs caused a marked reduction of cholesterol esterification in control fibroblasts and an excessive intracellular accumulation of unesterified cholesterol as in NPC cells, and that this reduction could partially be corrected by the addition of 2% DMSO to the medium. These characteristics of the drug-treated cells mimic the phenomena seen in NPC fibroblasts. Therefore, fibroblasts treated with CADs may be used as a model of drug-induced lipidosis of NPC. The effect of DMSO suggests the possibility of its usefulness in the treatment of NPC patients.

Regulation of LTP-I secretion from human monocyte-derived macrophages by differentiation and cholesterol accumulation in vitro

Human macrophages in vitro synthesize and secrete the cholesteryl ester (CE) transfer protein, LTP-I. The effect of differentiation of monocyte-to-macrophage on the synthesis and secretion of LTP-I cholesteryl ester transfer activity was investigated. One marker of macrophage differentiation is expression of the ‘scavenger’ receptor, which mediates macrophage uptake and degradation of acetylated low-density lipoprotein. Monocytes secreted very little detectable CE transfer activity in the first 24 h following cell isolation. Both CE transfer activity and scavenger receptor activity increased with time in culture. Thus, although circulating monocytes probably do not secrete CE transfer activity, tissue macrophages such as hepatic Kupffer cells may contribute to plasma CE transfer activity. Resident macrophages of the arterial wall are derived from circulating monocytes which enter the vessel wall where they differentiate into macrophages. Such macrophages are the principal source of lipid-laden foam cells of the atherosclerotic plaque. Cholesterol accumulation results when uptake of lipoprotein cholesterol overwhelms the capacity of macrophages to excrete cholesterol. Since LTP-I is postulated to function in reverse cholesterol transport, the effect on LTP-I secretion of loading macrophages with cholesterol was determined after exposure of macrophages to acetylated-LDL or free cholesterol (FC). Cholesterol loading by both these maneuvers resulted in dose-dependent increases in macrophage secretion of CE transfer activity, and there was a significant positive correlation between CE transfer activity secreted and accumulation of CE. Thus, LTP-I may function at the cellular level in maintenance of lipid homeostasis: macrophage LTP-I secretion may be a protective mechanism in response to excess cholesterol accumulation in resident macrophages of the arterial wall.

Type C Niemann-Pick disease: dimethyl sulfoxide moderates abnormal LDL-cholesterol processing in mutant fibroblasts

Biochemical and cytochemical studies have revealed that abnormal processing of low-density-lipoprotein (LDL) cholesterol can be reversed in mutant Niemann-Pick C (NP-C) fibroblasts when 2% dimethyl sulfoxide (DMSO) is added to the culture medium. Both the excessive lysosomal accumulation of LDL cholesterol and the delayed induction of cellular homeostatic responses associated with the uptake of LDL by the mutant cells were substantially reversed by DMSO. DMSO appears to accelerate the intracellular mobilization of LDL-derived cholesterol through effects that may reflect enhanced membrane permeability or cholesterol solubilization.

Type-C Niemann-Pick disease: low density lipoprotein uptake is associated with premature cholesterol accumulation in the Golgi complex and excessive cholesterol storage in lysosomes.

Incubation of fibroblasts derived from patients with type-C Niemann-Pick disease with low density lipoprotein results in excessive intracellular accumulation of unesterified cholesterol. Cytochemical techniques revealed that this abnormal cholesterol accumulation is associated not only with a massive storage of cholesterol in lysosomes but also with a premature cholesterol enrichment of the Golgi complex. Cholesterol appeared also in the Golgi complex of some normal fibroblasts after 24 hr of low density lipoprotein loading. These findings indicate that components of the Golgi complex play a role in the intracellular translocation of exogenously derived cholesterol and that disruptions of the cholesterol transport pathway at the Golgi may, in part, be responsible for the deficiency in cholesterol utilization in type-C Niemann-Pick fibroblasts.

1 Lipid transport through the plasma: the metabolic basis of hyperlipidaemia

Plasma lipid abnormalities derive their importance from their association with coronary artery disease. Elevated cholesterol levels accentuate risk, and clinical trials have shown that reductions lead to a decline in coronary events. The major plasma lipids, cholesterol and triglyceride, circulate in association with specific proteins as lipid-protein or lipoprotein complexes. The proteins direct and regulate the metabolism of these complexes by interacting with tissue enzymes and receptors. The metabolic fate of circulating triglyceride is governed by the activity of the enzyme lipoprotein lipase, situated in adipose tissue and skeletal muscle. Cellular demand for cholesterol, on the other hand, is met by activation of a specific receptor which mediates the delivery of sterol-rich lipoproteins to lysosomal degradation in liver and peripheral tissues. In order to prevent excess cholesterol accumulation at the periphery, there is a system of reverse cholesterol transport which involves assimilation and trapping of the sterol in the plasma lipoproteins through the action of the enzyme lecithin:cholesterol acyltransferase. Thereafter, the cholesterol is delivered to the liver, the only organ capable of excreting it in significant amounts. Disturbances in these processes may produce gross changes in the plasma lipid profile, clearly recognizable as hyperlipidaemia. However, it is becoming increasingly clear that a number of inherited traits can subtly perturb the lipoprotein spectrum and increase coronary risk even in subjects whose plasma lipoprotein profile would be considered normal.

Effects of naproxen and methotrexate on the extent of aortic lesions and cholesterol concentrations in cholesterol-fed rabbits

In this study rabbits were fed a hypercholesterolemic diet for 8 weeks with and without drug additives. Extent of aortic lesions was determined by planimetry and cholesterol concentrations by chemical analysis. Results in the naproxen-treated group were not significantly different from those in the untreated group. Methotrexate, a DNA synthesis inhibitor, resulted in significantly less extensive lesions and in lower aortic cholesterol concentrations. We have previously shown that two other compounds, hydroxyurea and mercaptopurine, that interfere with DNA synthesis have a similar beneficial effect. Aortic tissue cholesterol and extent of lesions were shown in this study (and previously) to be significantly correlated. Since drugs frequently have multiple metabolic effects these drugs might produce their effects on the lesion by retarding cholesterol accumulation in the aorta. However, it seems more likely that the effect was produced by retardation of proliferation of smooth muscle cells (either by preventing entry into the DNA synthesis phase or by death in the peridivision phase). The lower cholesterol accumulation in the aorta could be secondary perhaps because fewer cells were present that were susceptible to excessive cholesterol accumulation.

HYPERCHOLESTEROLEMIA AND LIPOPROTEIN-X(LP-X) IN INFANTS DURING INTRALIPID INFUSION

Ten infants of gestational ages 26-40 weeks with G.I. defects, but without cholestasis, received total parenteral nutrition with intralipid (2-4g/kg/day) during the first 6 weeks of life. Within 24 hrs there was an increase in plasma free cholesterol of 38 ± 4mg% (mean±SEM, n=10). In 3 infants, infused for 1-3 weeks the increases in free cholesterol were 105, 115 and 117mg%. Cholesterol esters remained constant. The rise in free cholesterol occurred exclusively in the density range 1.006-1.063g/m. corresponding to low density Lipoproteins (LDL). Fractionation of this LDL on hydroxyapatite yielded 2 components, one corresponding to LP-X and the other an LDL-like particle with Apo B but increased cholesterol and phospholipid concentrations. LP-X, indistinguishable from that seen in cholestatic states, was confirmed by chromatographic and electrophoretic techniques; and on analysis contained free cholesterol (26%), phospholipid (65%), albumin and Apo C proteins (6%). Using agar electrophoresis LP-X appeared in the plasma within 8hrs of starting the Intralipid infusion and disappeared within 48hrs of stopping. LP-X appeared despite close monitoring of plasma Intralipid levels which were maintained at 100mg% or less. Because LP-X is associated with excessive tissue cholesterol accumulation, this Intralipid induced dysliproproteinemia cannot be viewed as a trivial metabolic complication.

Response of the Liver to Prolonged Protein Depletion: V. Neutral Glycerides and Cholesterol; Production of Fatty Livers by Certain Amino Acids Fed in a Protein-Free Ration

The influence of prolonged protein deprivation followed by protein repletion in the adult male rat upon liver neutral glycerides and cholesterol was studied. Neutral glyceride and cholesterol concentrations increased for 8 weeks. Thereafter neutral glycerides decreased to normal and cholesterol to below normal after 14 weeks of deficiency. Attempts to alleviate the slightly fatty liver produced in the simple protein deficiency by including 0.3% DL-methionine in the protein-free ration produced a marked increase in these liver lipids. These excessive accumulations also reached a maximum after 8 weeks, followed by a decline towards normal. Reintroduction of protein into the rations at the terminal stages of protein deficiency caused a rebound of neutral glycerides and cholesterol to far above normal levels. The exact pattern of this response, however, was influenced markedly by whether methionine had been included in the ration during development of the protein deficiency. Cystine and methionine produced very fatty livers when added individually to the protein-free ration, whereas valine increased neutral glycerides and cholesterol to some extent. Leucine was quite lipotropic, however, and maintained the concentrations of these liver lipids normal or below. Phenylalanine was also somewhat lipotropic. Other essential amino acids had no effect. Omission of the dietary source of lipids (corn oil) had no effect on the excessive accumulation of neutral glycerides or cholesterol produced by methionine in the protein-free ration.