Deposition Of Cholesterol In Tissues Research Articles

Short Communication: Accumulation of Neutral Lipids in Liver and Aorta of Nef-Transgenic Mice.

HIV-infected individuals are at high risk of developing atherosclerosis and cardiovascular disease, in part, due to HIV-induced impairment of cholesterol metabolism. In vitro studies demonstrated that HIV-1 protein Nef inhibits activity of ABCA1, the main cellular cholesterol transporter, leading to cholesterol accumulation in macrophages and conversion of these cells into foam cells, characteristic for atherosclerosis. However, the mechanisms of Nef-mediated effects on cholesterol metabolism in vivo are not well characterized. In this study, we generated Nef-transgenic mice and evaluated the accumulation of neutral lipids in liver and aorta of these animals. Nef expression was low in all transgenic mice, with some mice carrying the Nef transgene, but not expressing the Nef RNA. Using Oil Red O staining, we demonstrated increased levels of neutral lipids in liver and aorta of mice expressing Nef relative to transgenic animals, with no detectable Nef expression or control wild-type mice. These results provide direct evidence that Nef promotes cholesterol deposition in tissues.

Mechanisms of Disease: genetic causes of familial hypercholesterolemia

Familial hypercholesterolemia (FH) is characterized by raised serum LDL cholesterol levels, which result in excess deposition of cholesterol in tissues, leading to accelerated atherosclerosis and increased risk of premature coronary heart disease. FH results from defects in the hepatic uptake and degradation of LDL via the LDL-receptor pathway, commonly caused by a loss-of-function mutation in the LDL-receptor gene (LDLR) or by a mutation in the gene encoding apolipoprotein B (APOB). FH is primarily an autosomal dominant disorder with a gene-dosage effect. An autosomal recessive form of FH caused by loss-of-function mutations in LDLRAP1, which encodes a protein required for clathrin-mediated internalization of the LDL receptor by liver cells, has also been documented. The most recent addition to the database of genes in which defects cause FH is one encoding a member of the proprotein convertase family, PCSK9. Rare dominant gain-of-function mutations in PCSK9 cosegregate with hypercholesterolemia, and one mutation is associated with a particularly severe FH phenotype. Expression of PCSK9 normally downregulates the LDL-receptor pathway by indirectly causing degradation of LDL-receptor protein, and loss-of-function mutations in PCSK9 result in low plasma LDL levels. Thus, PCSK9 is an attractive target for new drugs aimed at lowering serum LDL cholesterol, which should have additive lipid-lowering effects to the statins currently used.

Monogenic hypercholesterolemia: new insights in pathogenesis and treatment.

Monogenic hypercholesterolemia: new insights in pathogenesis and treatment.

Inhibition of acyl coenzyme A-cholesterol acyltransferase: a possible treatment of atherosclerosis?

Our full understanding of atherosclerosis and our ability to prevent its sequellae are incomplete. As a result, further investigation of novel antiatherosclerotic mechanisms and agents continues. Acyl coenzyme A-cholesterol acyltransferase (ACAT) inhibition has been evaluated as a potential mechanism by which the current treatment arsenal may be expanded. ACAT is present in a variety of tissues and is responsible for catalyzing the conversion of free cholesterol to the more readily stored cholesteryl esters. Impressive lipid effects demonstrated in animals have not generally been demonstrated in human clinical trials. Partial ACAT inhibition with specific agents has resulted in lesion regression and decreased progression, whereas complete ACAT inhibition via genetic alterations has led to an exacerbation of cholesterol deposition in tissues in animal models. No ACAT inhibitor has yet been fully evaluated in human clinical trials for its impact on atherosclerotic disease progression. Several hurdles, such as sample size requirements needed to detect effect over background therapy and lack of sensitive surrogate efficacy markers, have served as a deterrent to the development of this class of investigational drug. However, with recent technologic advancements, more sensitive methods of measuring disease progression may be available. Human clinical trials are currently underway, with several agents reported in Phase II clinical trials. Within the next few years, results from these trials may determine whether or not ACAT inhibitors will be added to the list of treatment options for the prevention of atherosclerotic disease progression.

Apolipoprotein E regulates dietary cholesterol absorption and biliary cholesterol excretion: studies in C57BL/6 apolipoprotein E knockout mice.

The present study examined the role of apolipoprotein E (apoE) in the regulation of dietary cholesterol absorption and biliary cholesterol excretion. Increasing dietary cholesterol from 0.02% to 0.5% in C57BL/6 wild-type mice decreased the percentage of dietary cholesterol that is absorbed by 25%, and this decrease was associated with a 2-fold increase in gallbladder biliary cholesterol concentration. In contrast, increasing dietary cholesterol from 0. 02% to 0.5% in C57BL/6 apoE knockout mice produced no significant suppression of the percentage dietary cholesterol absorption and increased gallbladder biliary cholesterol concentration only 16%. Whereas in wild-type mice, the increase in dietary cholesterol increased the hepatic excretion of biliary cholesterol 4-fold, there was only a 2-fold increase in apoE knockout mice. On both the low- and the high-cholesterol diets, whole liver and isolated hepatocyte cholesterol content was higher in the apoE knockout mice. These results suggest that, in response to dietary cholesterol, apoE may play a critical role in decreasing the percentage absorption of dietary cholesterol and increasing biliary cholesterol excretion. These observations suggest a mechanism whereby the absence of apoE contributes to the propensity for tissue cholesterol deposition and accelerated atherogenesis in apoE knockout mice.

Apolipoprotein E regulates dietary cholesterol absorption and biliary cholesterol excretion: Studies in C57BL/6 apolipoprotein E knockout mice

The present study examined the role of apolipoprotein E (apoE) in the regulation of dietary cholesterol absorption and biliary cholesterol excretion. Increasing dietary cholesterol from 0.02% to 0.5% in C57BL/6 wild-type mice decreased the percentage of dietary cholesterol that is absorbed by 25%, and this decrease was associated with a 2-fold increase in gallbladder biliary cholesterol concentration. In contrast, increasing dietary cholesterol from 0. 02% to 0.5% in C57BL/6 apoE knockout mice produced no significant suppression of the percentage dietary cholesterol absorption and increased gallbladder biliary cholesterol concentration only 16%. Whereas in wild-type mice, the increase in dietary cholesterol increased the hepatic excretion of biliary cholesterol 4-fold, there was only a 2-fold increase in apoE knockout mice. On both the low- and the high-cholesterol diets, whole liver and isolated hepatocyte cholesterol content was higher in the apoE knockout mice. These results suggest that, in response to dietary cholesterol, apoE may play a critical role in decreasing the percentage absorption of dietary cholesterol and increasing biliary cholesterol excretion. These observations suggest a mechanism whereby the absence of apoE contributes to the propensity for tissue cholesterol deposition and accelerated atherogenesis in apoE knockout mice.

Decreased reverse cholesterol transport from Tangier disease fibroblasts. Acceptor specificity and effect of brefeldin on lipid efflux.

Tangier disease is characterized by HDL hypercatabolism and increased deposition of cholesterol in tissues. Tangier disease skin fibroblasts have decreased apoA-I-mediated cholesterol and phospholipid efflux, which may lead to the excess accumulation of cellular cholesterol. The mechanism of apolipoprotein-mediated cholesterol efflux and the apolipoprotein acceptor specificity for cholesterol efflux from normal and Tangier disease fibroblasts was investigated. Normal cells readily effluxed cholesterol and phospholipid to apoA-I and to all of the other apolipoproteins tested (apoA-II, AIV, C-I, C-II, C-III). In contrast, Tangier cells were almost completely defective in cholesterol efflux to apoA-I and to all of the other apolipoproteins tested. HDL was also less effective, by approximately 50%, in stimulating cholesterol efflux from Tangier cells compared with normal cells. In addition, Tangier cells also showed significantly reduced phospholipid efflux to both apolipoproteins and HDL. A similar rate of cholesterol efflux, however, was observed from normal and Tangier cells when phospholipid vesicles or cyclodextrin were used as acceptors. In contrast to normal cells, only phospholipid vesicles and cyclodextrin and not apoA-I or HDL depleted intracellular cholesteryl esters from Tangier cells. Brefeldin, an inhibitor of intracellular vesicular trafficking, decreased HDL-mediated cholesterol efflux by approximately 40% but almost completely blocked both cholesterol and phospholipid efflux to apoA-I from normal cells. Brefeldin also inhibited cholesteryl ester depletion by apoA-I and HDL from normal cells. Brefeldin, however, had no significant effect on cholesterol efflux from Tangier cells to HDL. In summary, Tangier cells were found to be defective in both cholesterol and phospholipid efflux to HDL and apoA-I. The defect in apolipoprotein-mediated lipid efflux was not specific for apoA-I but also occurred for other apolipoproteins, and brefeldin blocked HDL-mediated lipid efflux from normal but not Tangier disease cells. On the basis of these results, a model is proposed whereby decreased cholesterol efflux by apolipoproteins in Tangier cells is the result of a defect in a brefeldin-sensitive pathway of lipid efflux.

Bile acid synthesis from cholesterol: regulatory and auxiliary pathways.

Bile acid synthesis from cholesterol can occur via two pathways, one initiated by sterol 27-hydroxylase activity or one initiated by that of cholesterol 7 alpha-hydroxylase. In contrast to cholesterol 7 alpha-hydroxylase, which is found in the liver, sterol 27-hydroxylase is a widely distributed mitochondrial enzyme with high activity in vascular endothelial cells. Although both pathways lead to the production of chenodeoxycholic and cholic acids, the key step, 7 alpha-hydroxylation, is governed by two different enzymes. Both 27-hydroxycholesterol and 3 beta-hydroxy-5-cholestenoic acid, the metabolites of cholesterol occurring via sterol 27-hydroxylase activity, normally circulate in plasma. After their uptake by the liver they are metabolized mostly to chenodeoxycholic acid, which down-regulates the activity of cholesterol 7 alpha-hydroxylase, the rate-limiting step for the production of bile acids in the liver. Because of this relationship and also in view of the accelerated atherosclerosis and cholesterol deposition in tissues that occur as a consequence of genetically determined sterol 27-hydroxylase deficiency and of the potent biologic effect of 27-hydroxycholesterol in cell culture, it is proposed that this metabolic pathway serves a regulatory function. The pathway beginning with cholesterol 7 alpha-hydroxylation is modulated by genetic, hormonal, and probably dietary factors, and becomes most prominent with the interruption of the enterohepatic circulation of bile acids.

Differential phenotypic expression by three mutant alleles in familial lecithin:cholesterol acyltransferase deficiency

Familial deficiency of lecithin:cholesterol acyltransferase (LCAT) is an autosomal recessive disorder characterised by abnormalities of all plasma lipoprotein classes and by abnormal deposition of unesterified cholesterol in tissues. To elucidate the molecular basis of the disease, the LCAT genes of three unrelated Japanese patients were amplified by means of the polymerase chain reaction. Direct sequencing of the amplified fragments covering all exons and junctions showed that the patients are homozygotes for separate gene mutations. In one patient a 3 bp insertion, which should cause a substantial change in the enzyme structure, was found in exon 4; he had near absence of LCAT mass and activity. Two separate missense mutations were identified in exon 6 of the other two patients, who produced functionally defective enzymes that differed widely in specific activity. The replacement of asparagine228 with positively charged lysine completely abolished enzyme activity, whereas the other, conservative, aminoacid substitution (methionine293→isoleucine) gave rise to a partially defective enzyme. These results show that distinct mutations cause differences in plasma LCAT activity and LCAT mass, ultimately leading to differential phenotypic expression of familial LCAT deficiency.

Effects of 2-(2,4-dimethylphenyl)indan-1,3-dione on serum lipoprotein and lipid metabolism of rodents.

2-(2,4-Dimethylphenyl)indan-1,3-dione was shown to be a potent hypolipidemic agent in rodents, lowering significantly both serum cholesterol and triglyceride levels at 20 mg/kg/day. The agent in vivo inhibited the enzymatic activities of ATP-dependent citrate lyase, acetyl-CoA synthetase, cholesterol-7-alpha-hydroxylase, acyl-CoA cholesterol acyl transferase, sn-glycerol-3-phosphate acyl transferase and phosphatidylate phosphohydrolase. Tissue lipid levels of liver and small intestine also were reduced by the agent. The rat serum lipoprotein lipid content was modulated by the drug, which should be favorable for the removable of cholesterol from peripheral tissue for conduction to the liver for clearance from the body. Low density lipoprotein (LDL) cholesterol levels were reduced after treatment, which suggests that the agent potentially reduces deposition of cholesterol in plaques. If chemotherapy for atherosclerosis is to be successful, then the high density lipoprotein (HDL) cholesterol level needs to be elevated more than 16% to 25%, the level produced by current hypolipidemic agents. 2-(2,4-Dimethylphenyl)indan-1,3-dione offers a 75% increase in HDL cholesterol levels and a 30% reduction of LDL cholesterol levels with a suppression of de novo synthesis of lipids and a reduction of tissue cholesterol deposition.

Normocholesterolemic Xanthomatosis

Hypercholesterolemia deadly culprit in the cause of coronary vascular disease, but is it always, or even commonly, the cause of atherosclerosis? The answer is clearly not always, as other factors also play a role in the complex problem of how lipids accumulate in the tissues. There is no question that hypercholesterolemia and hyperlipoproteinemia often result in the deposition of cholesterol in various tissues. This accumulation of cholesterol can take the form of either xanthomatosis or atherosclerosis. Cholesterol is carried in lipoproteins, particularly low-density lipoprotein (LDL) β-lipoprotein), very low-density lipoprotein (VLDL) (prebeta lipoprotein), and high-density lipoprotein (HDL) (α-lipoprotein). Various forms of xanthomas commonly develop in association with elevations in LDL and VLDL levels¹while HDL is thought to exert a protective effect against tissue cholesterol deposition by serving as a vehicle for transport of cholesterol from peripheral cells back to the liver. Low plasma concentration of HDL results in a defects of removal

Effects of Dietary Calcium and Fat on Cholesterol in Tissues and Feces of Young Goats

To examine the effects of amount of calcium and type of fat in the diet on distribution of cholesterol in plasma, several tissues and feces, 4-week-old goats (6 females and 18 males) were fed isocaloric diets consisting of goat milk supplemented with cholesterol and 1) soybean oil, 2) tallow, 3) soybean oil and CaCO3 or 4) tallow and CaCO3 for 20 weeks. Plasma cholesterol increased initially in all animals; plasma and lipoprotein cholesterol concentrations, however, were not affected by dietary fat or calcium. Goats fed CaCO3 excreted more calcium and ash in their feces and had greater cholesterol and fat concentrations in their livers. Neutral steroid, but not bile acid, excretion was greater in soybean oil-fed goats than in goats fed tallow. Soybean oil-fed goats had greater cholesterol concentrations in the viscera (minus liver) and tended to have greater cholesterol concentrations in the carcass and whole body. Aortas of soybean oil-fed goats exhibited greater fat deposition. In summary, dietary fat, but not calcium, significantly altered cholesterol disposition in young goats by affecting cholesterol deposition in tissues and excretion in feces, without a concomitant change in plasma cholesterol.

Diet- and hormone-induced lipid deposition in rat kidney: correlation with systolic blood pressure.

The influence of estradiol on deposition of cholesterol in tissues of ovariectomized rats on normal and high lipid diets was studied. Concomitantly the influence of a contraceptive steroid combination was studied in a similar manner in intact rats. It was found that the high lipid diet resulted in increased deposition of cholesterol in aorta, heart, liver and kidney. The presence of either endogenous or exogenous hormones accentuated the deposition of cholesterol in the kidney and resulted in significantly higher systolic blood pressures in these rats. In the rats on a high lipid diet, the concentration of cholesterol in the kidney correlated positively with systolic blood pressure. It is concluded that estrogen and high lipid diet exert a synergistic effect on deposition of cholesterol in kidney. The positive correlation between kidney cholesterol concentration and systolic blood pressure suggests a possible role for kidney lipid deposition in the hypertensive effect of estrogens.

Effect of soy versus beef diets on blood and tissue cholesterol and body composition of growing swine

Growing pigs were fed diets, similar in protein and fat content, based on soy protein isolate and soybean oil (soy) or ground beef containing 21% fat (beef). Ground corn, vitamins and minerals completed the diets. Egg yolk was added to balance the intake of cholesterol. No significant differences were seen in total plasma cholesterol or liver cholesterol concentrations. Soy-fed pigs had significantly greater concentrations of cholesterol in the viscera excluding the liver (p<.001), aorta (p<.04), carcass (p<.001) and whole body (liver + other viscera + carcass) (p<.001). No evidence of fatty streaking or plaque formation was seen in Sudan IV-stained aorta segments of either treatment group. Although pigs fed the soy diet gained weight at a slower rate, their carcasses contained a significantly greater (p<.02) concentration of fat. Our data show that the soy diet, as compared to the beef diet, increased the proportion of fat in the carcass and increased tissue cholesterol deposition.

High density lipoprotein-3 heterogeneity in subjects with the apo-AIMilano variant.

The structure of high density lipoproteins (HDL) isolated from subjects with the AIMilano (AIM) apoprotein variant was studied by the use of the cross-linking reagent dimethylsuberimidate. The HDL2 subfraction is markedly reduced, as compared to control subjects; the HDL3 subfraction, on the other hand, shows a marked heterogeneity, being characterized by at least three particle subpopulations, identified as HDL3-I, HDL3-II, and HDL3-III. The HDL3 fraction purified from the AI Milano subjects eluted as a symmetrical peak from a 6% agarose column, corresponding to a unimodal particle size distribution. The content of the different HDL3 particles, detected by cross-linking, varied widely along the elution profile, the tail of the peak being enriched in anomalous particles of very small size (HDL3-III). Apoprotein compositional studies indicated that these small HDL3-III may be enriched in the AIM monomer, the larger particles containing more AIM-AII complexes and AIM dimers. All the anomalous HDL3 particles are triglyceride enriched, with a decreased cholesterol ester content. They may be an intermediate product in the cholesterol transfer chain between HDL and very low density lipoproteins, or be generated during interconversion of HDL. These particles may have a functional role in tissue cholesterol homeostasis; their unusual compositional changes may help explain the protection of the studied subjects from tissue cholesterol deposition, in spite of the marked decrease of the total HDL fraction.

Ischaemic disease in men and women with familial hypercholesterolaemia and xanthomatosis A comparative study of genetic and environmental factors in 274 heterozygous cases

The incidence of ischaemic diseases in familial hypercholesterolaemia and xanthomatosis (familial Type II) was studied in a group of 158 men and 116 women. 1. (1) Men and women did not differ with regard to the inherited metabolic disease. Levels of serum cholesterol, the marker of the genetic defect, were not statistically different, and cholesterol deposition in tissues, visualized by skin and tendon xanthomas, was not sex related. 2. (2) Men and women were different with regard to ischaemic diseases. The incidence was much lower in women, and the mean age of onset 9 years later. Moreover, there was a sex difference in the nature of the ischaemic disease, with a high male predominance of myocardial infarction. 3. (3) Since the major risk factor hypercholesterolaemia could not explain such a difference, the role of other risk factors was investigated. It was shown that the incidence of ischaemic diseases was increased in women by cigarette smoking and hypertension, and that the difference in age of onset between males and females was no longer seen in smoking women. It is suggested that the genetic factor is responsible for the atherosclerotic lesion in both sexes and that other factors playing a role in ischaemic complications including tobacco and hypertension may explain the difference between men and women.

Effect of vitamin D, sucrose, corn oil and endocrines on tissue cholesterol in rats.

A diet containing 65 per cent sucrose with added cholesterol resulted in hypercholesteremia and increased tissue cholesterol deposition in rats. Ten per cent corn oil with added cholesterol in Purina laboratory chow had no apparent effect on the serum total cholesterol but increased cholesterol deposition in tissues. Ovariectomy was without significant effect. Thyroidectomy or hypophysectomy aggravated the hypercholesteremia and the increased tissue cholesterol deposition induced by the sucrose diet. The effect of hypophysectomy was not due to the loss of thyrotrophic hormone alone. Addition of vitamin D aggravated hypercholesteremia and increased liver cholesterol deposition in normal, thyroidectomized or hypophysectomized rats fed the sucrose diet. In ovariectomized rats, the tissue cholesterol deposition was also augmented. When corn oil diet was fed, the supplementary vitamin D increased the serum total cholesterol level of the thyroidectomized rat.

Food Intake and Estrogenic Hormone Effects on Serum and Tissue Cholesterol

Cholesterol-fed male rats have shown greater variations in liver cholesterol with different levels of protein intake than have females (Okey and Lyman, '54, '56). In young rats, the sex differences became apparent at the time when males showed the heightened food consumption and growth rate associated with the attainment of puberty. Moreover, they were most marked when the diets contained barely enough good protein to support optimal growth if the total food (and hence calorie) consumption was high. An investigation seemed indicated, to test whether the sex difference was the result of a specific hormone effect or only a corollary of the differ ence in food intake and growth rate of males and females. Human males are known to have a higher incidence of dis eases associated with abnormal tissue cholesterol deposition, whereas human females (as well as female rats) tend to have higher serum cholestA©rolsthan males of the same age and diet groups (Gillum et al., '55). It was therefore also con sidered desirable to find out something about the relationship between circulating and stored cholesterol.