APOE and Alzheimer's disease: advances in genetics, pathophysiology, and therapeutic approaches

The APOE ε4 allele remains the strongest genetic risk factor for sporadic Alzheimer's disease and the APOE ε2 allele the strongest genetic protective factor after multiple large scale genome-wide association studies and genome-wide association meta-analyses. However, no therapies directed at APOE are currently available. Although initial studies causally linked APOE with amyloid-β peptide aggregation and clearance, over the past 5 years our understanding of APOE pathogenesis has expanded beyond amyloid-β peptide-centric mechanisms to tau neurofibrillary degeneration, microglia and astrocyte responses, and blood-brain barrier disruption. Because all these pathological processes can potentially contribute to cognitive impairment, it is important to use this new knowledge to develop therapies directed at APOE. Several therapeutic approaches have been successful in mouse models expressing human APOE alleles, including increasing or reducing APOE levels, enhancing its lipidation, blocking the interactions between APOE and amyloid-β peptide, and genetically switching APOE4 to APOE3 or APOE2 isoforms, but translation to human clinical trials has proven challenging.

Dual functional liposomes carrying antioxidants against tau hyperphosphorylation and apoptosis of neurons

Quercetin (QU) and rosmarinic acid (RA) were loaded in phosphatidic acid-liposomes (QU/RA-PA-liposomes) with surface apolipoprotein E (ApoE) using a process of thin-film hydration, followed by covalent crosslinking to activate biological pathways for penetrating the blood-brain barrier (BBB) and redeeming the neuronal apoptosis from attack of β-amyloid 1-42 (Aβ1-42) and neurofibrillary tangles. The conjugation of liposomes with PA improved the activity of QU and RA against neurotoxicity of Aβ1-42. The fluorescent images of brain capillaries revealed that surface modification with ApoE improved the permeation ability of QU/RA-PA-ApoE-liposomes across the BBB. In addition, the highest therapeutic efficacy was obtained in the case of QU/RA-PA-ApoE-liposomes, compared to other QU/RA formulations studied using in vivo Aβ1-42-insulted rats mimicking Alzheimer's disease (AD). The cellular and molecular evidence from AD rats included the decrease in Aβ1-42 plaque formation and interleukin-6 secretion, increase in the neuronal count in Nissl staining, and reduction in the expression of phosphorylated extracellular signal-regulated kinase 1/2, c-Jun N-terminal kinase, p38 kinase and tau protein at serine 202 as well as caspase-3. The use of PA-ApoE-liposomes as a dual targeting formulation enhances the QU and RA ability to infiltrate the BBB, docks Aβ1-42 plaques and can be a potent approach to rescue degenerated neurons from AD.

Long-term exposure to ambient air pollution, APOE-ε4 status, and cognitive decline in a cohort of older adults in northern Manhattan

BACKGROUND

There is mounting evidence that long-term exposure to air pollution is related to accelerated cognitive decline in aging populations. Factors that influence individual susceptibility remain largely unknown, but may involve the apolipoprotein E genotype E4 (APOE-ε4) allele.

OBJECTIVES

We assessed whether the association between long-term exposure to ambient air pollution and cognitive decline differed by APOE-ε4 status and cognitive risk factors.

METHODS

The Washington Heights Inwood Community Aging Project (WHICAP) is a prospective study of aging and dementia. Neuropsychological testing and medical examinations occur every 18-24 months. We used mixed-effects models to evaluate whether the association between markers of ambient air pollution (nitrogen dioxide [NO2]), fine [PM2.5], and coarse [PM10] particulate matter) and the rate of decline in global and domain-specific cognition differed across strata defined by APOE-ε4 genotypes and cognitive risk factors, adjusting for sociodemographic factors and temporal trends.

RESULTS

Among 4821 participants with an average of 6 years follow-up, higher concentrations of ambient air pollution were associated with more rapid cognitive decline. This association was more pronounced among APOE-ε4 carriers (p < 0.001). A one interquartile range increase in NO2 was associated with an additional decline of 0.09 standard deviations (SD) (95%CI -0.1, -0.06) in global cognition across biennial visits among APOE-ε4 positive individuals and a 0.07 SD (95%CI -0.09, -0.05) decline among APOE-ε4 negative individuals. Results for PM2.5, PM10 and cognitive domains were similar. The association between air pollutants and rate of cognitive decline also varied across strata of race-ethnicity with the association strongest among White non-Hispanic participants.

CONCLUSIONS

These results add to the body of evidence on the adverse impact of ambient air pollution on cognitive aging and brain health and provide new insights into the genetic and behavioral factors that may impact individual susceptibility.

[Rapid determination of 28 pesticides and tetramine in whole blood by online gel permeation chromatography coupled with gas chromatography-mass spectrometry]

OBJECTIVE

To study the influences of carbon disulfide (CS2) exposureon fatty acid metabolism in apolipoprotein E (ApoE) knockout mice and C57BL/6J mice.

METHODS

Twenty-four male ApoE knockout mice were randomly and equally divided into four groups: a CS2-exposed normal diet group, a CS2-unexposed normal diet group, a CS2-exposed high-fat diet group, and a CS2-unexposed high-fat diet group. Twenty-four C57BL/6J male mice were divided into four groups in the same way. The CS2-exposed groups were exposed to CS2 (1 g/m³) by static inhalation for 5 hours a day, 5 days a week. After two weeks, the whole blood of mice was collected. Methyl ester derivatization of fatty acids was performed using an acid-catalyzed method. Fatty acid contents before and after exposure were compared by gas chromatography-mass spectroscopy.

RESULTS

There were significant differences in fatty acid contents of mice between the four groups. For the C57BL/6J mice, the arachidic acid contents in the CS2-exposed high-fat diet group were significantly lower than those in the CS2-unexposed high-fat diet group (P = 0.0450). For the ApoE knockout mice, the arachidonic acid contents in the CS2-exposed normal diet group were significantly lower than those in the CS2-unexposed control diet group (P = 0.0452). For the ApoE knockout mice, the γ-linolenic acid contents in the CS2-exposed high-fat diet group were significantly higher than those in the unexposed high-fat diet group (P = 0.0447).

CONCLUSION

Exposure to CS2 can induce fatty acid metabolism disorder in mice, indicating that CS2 may increase the risk of atherosclerosis and other cardiovascular diseases.

Suppressive effects of cacao polyphenols on the development of atherosclerosis in apolipoprotein E-deficient mice

Previous studies in humans have shown that the cacao polyphenols, (-)-epicatechin and its oligomers, prevent in vitro and ex vivo low-density lipoprotein oxidation mediated by free radical generators and metal ions and also reduce plasma LDL-cholesterol levels. The aim of this study was to examine the effects of cacao polyphenols on the development of atherosclerosis in apolipoprotein E-deficient (-/-) mice. Mice aged 8 weeks (n = 90) were randomized into three groups, and fed either normal mouse chow (controls) or chow supplemented with 0.25 or 0.40 % cacao polyphenols for 16 weeks. The mean plaque area in cross-sections of the brachiocephalic trunk was measured and found to be lower in the 0.25 % cacao polyphenol group than in the control group (p < 0.05). Pathological observations showed that accumulation of cholesterol crystals in the plaque area was greater in the control group compared with the 0.40 % cacao polyphenol group (p < 0.05). Immunochemical staining in the 0.25 and 0.40 % groups showed that expression of the cell adhesion molecules (VCAM-1 and ICAM-1) and production of oxidative stress markers (4-hydroxynonenal, hexanoyl-lysine, and dityrosine) were reduced in cross-sections of the brachiocephalic trunk. These results suggest that cacao polyphenols inhibit the development of atherosclerosis in apolipoprotein E-deficient (-/-) mice by reducing oxidative stress and inflammatory responses.

Isoform-specific proteolysis of apolipoprotein-E in the brain

Apolipoprotein-E (apoE) plays important roles in neurobiology and the apoE4 isoform increases risk for Alzheimer's disease (AD). ApoE peptides are biologically active and may be produced in the brain. It is unclear if apoE proteolysis is dependent on isoform or AD status and this was addressed here. Hippocampus, frontal cortex, occipital lobe and cerebellum samples were homogenized into fractions that were soluble in Tris-buffered saline (TBS), Triton X-100 or guanidine hydrochloride and analysed for apoE fragmentation by Western blotting. Approximately 20% of apoE3 was detected as fragments and this was predominantly as a 25 kDa peptide in TBS-soluble fractions. The concentration of TBS-soluble apoE fragments was two- to three-fold higher in apoE3 compared to apoE4 subjects. This difference was observed in all areas of the brain examined and was not related to AD status. Cathepsin-D treatment generated apoE fragments that were very similar to those detected in brain, however, no apoE isoform-specific differences in susceptibility to cathepsin-D proteolysis were detected. This indicates that proteolytic processing of apoE to form soluble fragments in the human brain is dependent on apoE isoform but not AD status.

Genetic testing for heart disease susceptibility: potential impact on motivation to quit smoking

As genetic tests for common gene variants and multifactorial, lifestyle-related conditions become available, it will be increasingly important to determine the psychological and behavioral impact of this emerging class of genetic tests. Our aim was to examine the potential impact of genetic testing for heart disease susceptibility on psychological predictors of smoking cessation. Two hundred and sixty-one smokers were asked to imagine that they had undergone a test for heart disease risk. They were randomly assigned to a genetic test scenario (low- or high-risk result) or an oxidative test scenario (high-risk result). Smokers in the genetic test-high risk group reported greater intention to quit smoking than smokers in the oxidative test-high risk group (p = 0.009); 30% of this was mediated by their holding stronger beliefs that quitting would reduce their heart disease risk (outcome expectations) (p = 0.011). The effect of genetic test-high risk feedback on outcome expectations was greatest amongst smokers with no heart disease family history (p = 0.038). The results suggest that genetic testing for heart disease risk may enhance interventions designed to improve health via increasing smoking cessation rates. Whether the findings hold true in studies that use real rather than hypothetical genetic tests remains to be seen.

Chronic thrombin exposure results in an increase in apolipoprotein-E levels

Studies have shown that individuals with both a history of traumatic brain injury and inheritance of apolipoprotein E-4 (ApoE4) allele are associated with a poor neurologic outcome and an increased risk for Alzheimer's disease. We assessed the hypothesis that thrombin released during brain injury causes an increase in apolipoprotein-E levels and such increase in the levels of apolipoprotein-E4 isoform may have amyloidogenic effects. Rats received either thrombin (100 nm, 0.25 microl/hr, 28 days) or vehicle via intracerebroventricular (i.c.v.) infusion. Thrombin treatment increased apolipoprotein-E levels in hippocampus as compared to vehicle treatment (P < 0.001). Infusion of human apolipoprotein-E4 (0.6 ng/hr, i.c.v., 56 days) into rats resulted in beta-amyloid deposition and increased the number of GFAP-positive astrocytes. ApoE4 infusion also resulted in significant spatial memory deficits. These findings suggest that thrombin released during brain injury may contribute to an increase in apolipoprotein-E levels. Such increase in Apolipoprotein-E4 isoform facilitates beta-amyloid deposition and cognitive deficits.

Plasma phospholipid transfer protein activity is decreased in type 2 diabetes during treatment with atorvastatin: a role for apolipoprotein E?

Plasma phospholipid transfer protein (PLTP) plays an important role in lipoprotein metabolism. PLTP activity is elevated in patients with diabetes, a condition with strongly elevated risk for coronary heart disease. The aim of this study was to test the hypothesis that statins reduce PLTP activity and to examine the potential role of apolipoprotein E (apoE). PLTP activity and apoE were measured in patients with type 2 diabetes from the DALI (Diabetes Atorvastatin Lipid Intervention) Study, a 30-week randomized double-blind placebo-controlled trial with atorvastatin (10 and 80 mg daily). At baseline, PLTP activity was positively correlated with waist circumference, HbA(1c), glucose, and apoE (all P < 0.05). Atorvastatin treatment resulted in decreased PLTP activity (10 mg atorvastatin: -8.3%, P < 0.05; 80 mg atorvastatin: -12.1%, P < 0.002). Plasma apoE decreased by 28 and 36%, respectively (P < 0.001). The decrease in apoE was strongly related to the decrease in PLTP activity (r = 0.565, P < 0.001). The change in apoE remained the sole determinant of the change in PLTP activity in a multivariate model. The activity of PLTP in type 2 diabetes is decreased by atorvastatin. The association between the decrease in PLTP activity and apoE during statin treatment supports the hypothesis that apoE may prevent PLTP inactivation.

Cholesterol and apoe: a target for Alzheimer's disease therapeutics

Alzheimer's disease (AD) is a debilitating disease that affects many people. In order to reduce the number of people diagnosed with this disease, drug strategies need to be implemented that target early steps in disease pathogenesis. Elevated cholesterol levels and presence of the apolipoprotein E eta4 allele increase AD risk. How these two factors may contribute to AD pathogenesis and some therapeutic strategies for alleviating AD risk will be discussed.

Apolipoprotein E, cholesterol transport and synthesis in sporadic Alzheimer's disease

The discovery that the apolipoprotein E4 (apoE4) allele is genetically linked to both sporadic and familial late onset Alzheimer's disease (AD) raises the possibility that a dysfunction of the lipid transport system could seriously affect lipid homeostasis in the brain of AD subjects. The presence of the E4 allele has been associated with lower levels of apoE in both serum and brain tissues of normal and AD subjects. In an attempt to reverse the apoE deficit in AD, we identified and characterized several apoE inducer agents using a low throughput-screening assay. The most promising of these compounds is called probucol. Administration of probucol, an old cholesterol lowering drug, in mild to moderate sporadic AD led to significant increases in CSF apoE levels and a decrease of CSF beta amyloid 1-42 without significant modifications of CSF tau concentration or CSF lipid peroxides levels. These results are consistent with recent reports suggesting that the long term use of cholesterol lowering drugs that block 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) activity in the fourth and fifth decade of life may help reduce the risk of developing AD at later age. These results indicate that, in addition to lipid transport mediated by apoE, cholesterol homeostasis in the brain is markedly altered in response to changes in the HMGR pathway; suggesting a possible explanation for the potentially beneficial effect of statins in common AD.

Apolipoprotein E gene promoter -219G->T polymorphism increases LDL-cholesterol concentrations and susceptibility to oxidation in response to a diet rich in saturated fat

BACKGROUND

The apolipoprotein E (APOE) gene promoter polymorphism (-219G-->T) has been associated with increased risk of myocardial infarction, premature coronary artery disease, and decreased plasma apolipoprotein E concentrations.

OBJECTIVE

We aimed to determine in healthy subjects whether this polymorphism modifies the susceptibility of LDL to oxidation and the lipid response to the content and quality of dietary fat.

DESIGN

Fifty-five healthy men with the APOE3/E3 genotype (7 GG, 38 GT, and 10 TT) completed 3 dietary periods, each lasting 4 wk. The first was a saturated fatty acid (SFA)-rich diet [38% fat-20% SFA and 12% monounsaturated fatty acid (MUFA)-and 47% carbohydrates (CHO)], which was followed by a CHO-rich diet (30% fat-<10% SFA and 12% MUFA-and 55% CHO) or a MUFA-rich diet (38% fat-<10% SFA and 22% MUFA-and 47% CHO) in a randomized crossover design. At the end of each dietary period, LDL oxidation susceptibility, lipids, and lipoproteins were measured.

RESULTS

Compared with carriers of the G allele, TT subjects had a significantly (P < 0.05) shorter lag time after the SFA diet. The replacement of the SFA diet by the CHO or MUFA diet induced a greater increase (P < 0.05) in lag time in the TT subjects than in the GG or GT subjects. Carriers of the T allele had higher LDL-cholesterol (P < 0.05) and apolipoprotein B (P < 0.05) plasma concentrations after the SFA diet than did GG subjects. Compared with GG subjects, carriers of the T allele had a significantly (P < 0.05) greater decrease in LDL cholesterol and apolipoprotein B when they changed from the SFA to the CHO diet.

CONCLUSION

The -219G-->T polymorphism may partially explain differences in individual responses to diet.

A monomeric human apolipoprotein E carboxyl-terminal domain

ApoE plays a critical role in lipoprotein metabolism and plasma lipid homeostasis through its high-affinity binding to the LDL-receptor family. In solution, apoE is an oligomeric protein and the C-terminal domain causes apoE's aggregation. The aggregation property presents a major difficulty for the structural determination of this protein. A high-level expression system of the apoE C-terminal domain is reported here. Using protein engineering techniques, we identified a monomeric, biologically active apoE C-terminal domain mutant. This mutant replaces five bulky hydrophobic residues in the region of residues 253-289 with either smaller hydrophobic or polar/charged residues (F257A, W264R, V269A, L279Q, and V287E). The solubility of the mutant is significantly increased ( approximately 10-fold). Cross-linking experiments indicate that this mutant is 100% monomeric even at 5 mg/mL. CD and guanidine hydrochloride denaturation results indicate that the mutant maintains an identical alpha-helical secondary structure and stability as compared with those of the wild-type protein. DMPC-binding assays demonstrate an identical vesicle clearance rate shared by both the mutant and the wild-type apoE C-terminal domain. In addition, electron microscopic results show identical recombinant HDL particles prepared with both the mutant and the wild-type proteins. These results indicate that residues F257, W264, V269, L279, and V287 are critical residues for aggregation but may not be important in maintaining the structure, stability, and lipid-binding activity of this apoE domain, suggesting that apoE may use different "epitopes" for its aggregation property, helical structure/stability, and lipid-binding activity. Finally, preliminary NMR data demonstrated that we have collected high-quality NMR spectra, allowing for an NMR structural determination of the apoE C-terminal domain.

Effects of acute lorazepam administration on aminergic activity in normal elderly subjects: relationship to performance effects and apolipoprotein genotype

The effects of acute lorazepam challenges on plasma (p) HVA, MHPG, and 5-HIAA, and their relationship to drug-induced cognitive and motor deficits and the apolipoprotein (APOE)-epsilon4 allele were examined. Eighteen healthy elderly (8 epsilon4 carriers) received placebo or acute oral lorazepam doses (0.5 mg or 1 mg) in random sequence, 1-week apart. Cognitive assessment and plasma levels of pHVA, pMHPG, and p5-HIAA were determined at baseline and at 1, 2.5, and 5 h postchallenge. There was no drug-to-placebo difference in monoamine levels and no consistent relationship between changes in monoamine levels and cognitive performance, regardless of epsilon4 status. However, the 1.0 mg dose increased p5-HIAA in epsilon4 carriers, whereas it caused a reduction in noncarriers. Higher baseline pMHPG and p5-HIAA levels were associated with better baseline memory. The epsilon4 allele may modulate the effect of lorazepam on p5-HIAA, but further studies are needed to confirm this finding and elucidate its possible significance.

Mice deficient in apolipoprotein E but not LDL receptors are resistant to accelerated atherosclerosis associated with obesity

The aims of this study were to determine whether mice induced to become obese also exhibited accelerated atherosclerosis, and to determine whether obesity itself or dyslipidemia associated with obesity enhanced atherosclerosis. Wild-type (C57BL/6) mice and mice deficient for the low density lipoprotein receptor (LDLR-/-) or apolipoprotein E (apoE-/-) were fed a low fat, rodent chow diet or a high fat, high sucrose (diabetogenic) diet to induce obesity. As compared with wild-type mice, diabetogenic diet-fed LDLR-/- mice became more obese and developed severe dyslipidemia. Consequently, atherosclerotic lesions were increased in the LDLR-/- mice 3.7-fold over chow fed values. ApoE-/- mice showed weight gain profiles similar to those observed for wild-type mice. However, no differences in plasma lipid levels, lipoprotein profiles or atherosclerotic lesion areas were observed between chow-fed and diabetogenic diet-fed apoE-/- mice. These data demonstrate that lipid storage and partitioning as mediated by the low density lipoproteins (LDL) receptor or apoE-/- have profound and opposing consequences for dyslipidemia and atherosclerosis susceptibility associated with obesity.

The recycling of apolipoprotein E and its amino-terminal 22 kDa fragment: evidence for multiple redundant pathways

A portion of apolipoprotein E (apoE) internalized by hepatocytes is spared degradation and is recycled. To investigate the intracellular routing of recycling apoE, primary hepatocyte cultures from LDL receptor-deficient mice and mice deficient in receptor-associated protein [a model of depressed expression of LDL receptor-related protein (LRP)] were incubated with human VLDL containing 125I-labeled human recombinant apoE3. Approximately 30% of the internalized intact apoE was recycled after 4 h. The N-terminal 22 kDa fragment of apoE was also resecreted, demonstrating that this apoE domain contains sufficient sequence to recycle. The 22 kDa fragment has reduced affinity for lipoproteins, suggesting that apoE recycling is linked to the ability of apoE to bind directly to a recycling receptor. Finally, apoE was found to recycle equally well in the presence of brefeldin A, a drug that blocks transport from the endoplasmic reticulum and leads to collapse of the Golgi stacks. Our studies demonstrate that apoE recycling occurs 1) in the absence of the LDL receptor or under conditions of markedly reduced LRP expression; 2) when apoE lacks the carboxyl-terminal domain, which allows binding to the lipoprotein; and 3) in the absence of an intact Golgi apparatus. We conclude that apoE recycling occurs through multiple redundant pathways.

Vitamins C and E downregulate vascular VEGF and VEGFR-2 expression in apolipoprotein-E-deficient mice

Anti-angiogenic therapy reduces both plaque growth and intimal neovascularization in apolipoprotein-E-deficient mice (apoE-/-). Vascular endothelial growth factor (VEGF) has been suggested as playing a role in the development of atherosclerosis. We examined the hypothesis that VEGF and VEGF receptor-2 (VEGFR-2) expression is upregulated in apoE-/- and, since it could be driven by oxidative stress, tested whether dietary supplementation with vitamins C and E could downregulate it.Two-month-old apoE-/- received vitamin C combined with alpha- or beta-tocopherol for 4 weeks. Aortic VEGF and VEGFR-2 expression were measured by RT-qPCR and western blot.ApoE-/- showed significantly higher expression of aortic VEGF and VEGFR-2 mRNA (P<0.001) and protein (P<0.001) than wild-type mice, as well as increased plasma VEGF (P<0.001). Vitamin C and alpha-tocopherol significantly reduced aortic VEGF and VEGFR-2 expression in apoE-/- (P<0.001), circulating VEGF (P<0.01) and plasma lipid peroxidation (P<0.01). apoE-/- receiving vitamin C and beta-tocopherol showed diminished lipid peroxidation and VEGFR-2, but only partial reduction of VEGF expression. These data demonstrate that augmented VEGF and VEGFR-2 expression in apoE-/- vasculature can be downregulated by vitamins C and E, at least partially through oxidative stress reduction. This novel mechanism could contribute to explaining the beneficial effects of antioxidant vitamins in experimental atherosclerosis.

Arsenic exposure accelerates atherogenesis in apolipoprotein E(-/-) mice

Epidemiologic studies have shown an association between elevated arsenic levels in drinking water and an increased risk of atherosclerosis and vascular diseases. The studies presented here were performed to evaluate the atherogenic potential of arsenic using a well-established and controlled animal model of human atherosclerosis, mice deficient in apolipoprotein E (ApoE), and in vitro systems including primary human vascular cells. Wild-type and ApoE-deficient mice were exposed to 20 or 100 microg/mL sodium arsenite in drinking water for 24 weeks. As assessed morphometrically, the size of grossly discernible lesions covering the intimal area of aorta were increased significantly in arsenic-treated ApoE-deficient mice compared with nontreated transgenic mice. This effect was not associated with increased levels of serum cholesterol but was accompanied by an accumulation of arsenic in the vessel wall. Introduction of cocoa butter into the diet for 2 weeks resulted in higher serum cholesterol levels and only slight increases in the lesion size in control or arsenic-exposed ApoE-deficient mice. There were no lesions observed in the wild-type C57BL6 mice, resistant to atherosclerosis, whether they received arsenic or control drinking water. In vitro studies, including primary aorta endothelial or smooth muscle cells, were conducted to evaluate whether arsenic induces cellular mechanisms relevant to atherogenesis such as endothelial dysfunction, lipid oxidation, and smooth muscle cell proliferation. Arsenic treatment does not modulate endothelial cell-mediated lipid oxidation or smooth muscle cell proliferation but induced the expression of genes coding inflammatory mediators, including interleukin-8. Induction of endothelial inflammatory activity may play a role in arsenic-related vascular effects.

Chronic glial activation, neurodegeneration, and APP immunoreactive deposits following acute administration of double-stranded RNA

Several neurodegenerative disorders, including Alzheimer's and Parkinson's diseases, are associated with immunocompetent microglia, leading to the suggestion that chronic glial-mediated inflammation contributes to the neurodegeneration seen in these diseases. Little direct evidence supports this hypothesis, and no suitable rodent models exist that do not involve the use of blunt trauma or ischaemia, events that are infrequently encountered in the human disease state. In the present study, we report that administration of double-stranded RNA, a classical inducer of interferon-gamma (IFN-gamma), causes rapid and persistent activation of microglia and astrocytes, as well as induction of interleukin-1beta (IL-beta) and nitric oxide synthase. In close temporal succession to glial activation, there is neurodegeneration, with neuron loss involving apoptosis in selected brain regions including the septal nucleus, hippocampus, cortex and thalamus, along with hippocampal atrophy. This neuronal loss is accompanied by punctate deposits of material that are immunoreactive for amyloid precursor protein, beta-amyloid peptide (Abeta), and apolipoprotein E. The findings may have clinical relevance, since the administration of the nonsteroidal antiinflammatory agent (NSAID) ibuprofen markedly reduces the neurodegeneration observed in the absence of significant glial inhibition. These findings may be relevant to the pathogenesis of Alzheimer's disease in particular, and to other neurodegenerative diseases involving inflammation.

Increased binding of LDL and VLDL to apo B,E receptors of hepatic plasma membrane of rats treated with Fibernat

BACKGROUND

Research has focussed on the hypocholesterolemic effects of certain types of dietary fiber such as enhancing conversion of hepatic cholesterol to bile acids or increase in catabolism of low density lipoprotein (LDL) via the apo B,E receptor.

AIM OF THE STUDY

The effect of oral administration of a unique fibre cocktail of fenugreek seed powder, guar gum and wheat bran (Fibernat) and its varied effects on some aspects of lipid metabolism and cholesterol homeostasis in rats were examined.

METHODS

Rats were administered Fibernat along with the atherogenic diet containing 1.5 % cholesterol and 0.1 % cholic acid. Amounts of hepatic lipids, hepatic and fecal bile acids and activity of hepatic triglyceride lipase (HTGL) were determined. Transmission electron microscopic examination of the liver tissue and extent of uptake of (125)I-LDL and (125)I-VLDL by the hepatic apo B,E receptor was carried out.

RESULTS

Food intake and body weight gain were similar between the 3 different dietary groups. Fibernat intake significantly increased apo B,E receptor expression in rat liver as reflected by an increase in the maximum binding capacity (B(max)) of the apo B,E receptor to (125)I-LDL and (125)I-VLDL. The activity of HTGL was increased by approximately 1.5-fold in Fibernat-fed rats as compared to those fed the atherogenic diet alone. A marked hypocholesterolemic effect was observed. Cholesterol homeostasis was achieved in Fibernat-fed rats.

CONCLUSION

Two possible mechanisms are postulated to be responsible for the observed hypocholesterolemic effect a) an increase in conversion of cholesterol to bile acids and b) possibly by intra-luminal binding which resulted in increased fecal excretion of bile acids and neutral sterols. The resulting reduction in cholesterol content of liver cells coupled with upregulation of hepatic apo B,E receptors and increased clearance of circulating atherogenic lipoproteins-LDL and very low density lipoprotein (LDL and VLDL)-is the main mechanism involved in the hypocholesterolemic effect of Fibernat. The results suggest that Fibernat's effect on plasma LDL concentration is also possibly mediated by increased receptor-mediated catabolism of VLDL. Thus, Fibernat therapy is an effective adjunct to diet therapy and might find potential use in the therapy of hyperlipidemic subjects.

Effectiveness and tolerability of a new lipid-altering agent, gemcabene, in patients with low levels of high-density lipoprotein cholesterol

This study evaluated the efficacy and tolerability of gemcabene, a new lipid-altering agent, in a double-blind, randomized, dose-response study of 161 patients with high-density lipoprotein (HDL) cholesterol of <35 mg/dl and serum triglyceride (TG) levels of either >/=200 (n = 94) or <200 mg/dl (n = 67). After a 6-week, placebo, dietary lead-in period, patients were administered either 150, 300, 600, or 900 mg of gemcabene or placebo once daily for 12 weeks. In the TG >/=200 mg/dl stratum, gemcabene significantly increased serum HDL cholesterol by 18% with corresponding significant increases of 6% in both apolipoprotein A-I and A-II levels at the 150-mg dose. HDL cholesterol levels also increased 12% at the 300-mg dose; however, this did not reach statistical significance. Also, in the TG >/=200 mg/dl stratum, serum TG levels were significantly reduced by 27% and 39% at the 150- and 300-mg doses of gemcabene, respectively. No significant differences were found in serum HDL cholesterol or TG levels in the TG >/=200 mg/dl groups that received 600 or 900 mg of gemcabene, or in TG <200 mg/dl groups administered any dose of gemcabene. However, at these higher 600- and 900-mg doses, gemcabene significantly reduced serum low-density lipoprotein (LDL) cholesterol levels by 15% to 25%, respectively, in both TG strata, with proportionate decreases in the levels of apolipoprotein B. Gemcabene was well tolerated with a frequency of adverse events similar to that of placebo. In conclusion, at the lower doses, gemcabene significantly increased HDL cholesterol and reduced TG serum levels in patients with low HDL cholesterol and TG >/=200 mg/dl. At the higher doses, gemcabene significantly reduced LDL cholesterol levels in all patients with low HDL cholesterol.

Fenofibrate induces HDL-associated PAF-AH but attenuates enzyme activity associated with apoB-containing lipoproteins

Human plasma platelet-activating factor acetylhydrolase (PAF-AH) is an enzyme associated mainly with the apolipoprotein B (apoB)-containing lipoproteins and primarily with LDL. A small proportion of enzymatic activity is also associated with HDL. Plasma paraoxonase 1 (PON1) is an esterase exclusively associated with HDL. The effect of fenofibrate on PAF-AH and PON1 activities in patients with dyslipidemias of Types IIA, IIB, and IV were studied. Fenofibrate reduced plasma PAF-AH activity in all patient groups. In Type IIA patients, this reduction was mainly due to a fall in enzyme activity associated with the dense LDL subspecies, whereas in Type IIB and Type IV patients, it was due to the decrease in PAF-AH activity associated with both the VLDL+IDL and dense LDL subspecies. Drug therapy in Type IIB and Type IV patients significantly increased the HDL-associated PAF-AH activity due to the increase in enzyme activity associated with the HDL-3c subfraction. Fenofibrate did not affect serum PON1 activities toward paraoxon and phenylacetate in either patient group. The fenofibrate-induced elevation of HDL-associated PAF-AH activity in dyslipidemic patients of Type IIB and Type IV, as well as the reduction in enzyme activity associated with atherogenic apoB-containing lipoproteins in all patient groups, may represent a new and important antiatherogenic effect of this potent lipid-modulating agent.

Effect of apoE genotype on the hypolipidaemic response to pravastatin in an outpatient setting

BACKGROUND

Considerable variability exists in the plasma lipid and lipoprotein response to statin treatment due, in part, to genetic factors. The gene for apolipoprotein E (ApoE) is polymorphic and the different genotypes modulate baseline lipid levels. The objective of the present study was to evaluate the effect of the apoE genotype on the lipoprotein response to pravastatin treatment in an outpatient population followed-up in several different clinics across Spain. Subjects and methods. Subjects (n=401; 56% female; mean age 57 years), who were hypercholesterolaemic despite a diet poor in saturated fat and cholesterol, were treated according to NCEP-ATP II guidelines. Plasma lipids and lipoproteins were measured centrally before and after 16 weeks of treatment with 20 mg day-1 of pravastatin.

RESULTS

ApoE genotype distributions were 3.2% with varepsilon2/3, 73.1% with varepsilon3/3 and 22.4% with varepsilon3/4 or varepsilon4/4. ApoE genotype did not have any effect on baseline lipid levels except on triglycerides such that the carriers of the varepsilon2 allele had concentrations significantly greater than those subjects with varepsilon3/3 genotype and carriers of the varepsilon4 allele after adjustment for age, gender and body mass index (BMI) (P < 0.001). Once adjusted for age, gender, BMI and baseline lipid levels, the apoE polymorphism did not significantly influence the plasma lipid and lipoprotein response to pravastatin.

CONCLUSION

ApoE genotype appears not to influence the hypolipidaemic effect of pravastatin in patients monitored in a general outpatient setting.

Anti-atherosclerotic effect of simvastatin depends on the presence of apolipoprotein E

Low density lipoprotein receptor deficient (LDLR-KO) and apolipoprotein E deficient (apo E-KO) mice both develop hyperlipidemia and atherosclerosis by different mechanisms. The aim of the present study was to compare the effects of simvastatin on cholesterol levels, endothelial dysfunction, and aortic lesions in these two models of experimental atherosclerosis. Male LDLR-KO mice fed a high cholesterol (HC; 1%) diet developed atherosclerosis at 8 months of age with hypercholesterolemia. The addition of simvastatin (300 mg/kg daily) to the HC diet for 2 more months lowered total cholesterol levels by approximately 57% and reduced aortic plaque area by approximately 15% compared with the LDLR-KO mice continued on HC diet alone, P<0.05. Simvastatin treatment also improved acetylcholine (ACh)-induced endothelium-dependent vasorelaxation in isolated aortic rings, which was associated with an increase in NOS-3 expression by approximately 88% in the aorta measured by real time polymerase chain reaction (PCR), P<0.05. In contrast, in age-matched male apo E-KO mice fed a normal diet, the same treatment of simvastatin elevated serum total cholesterol by approximately 35%, increased aortic plaque area by approximately 15%, and had no effect on endothelial function. These results suggest that the therapeutic effects of simvastatin may depend on the presence of a functional apolipoprotein E.

Oxysterol-induced activation of macrophage NADPH-oxidase enhances cell-mediated oxidation of LDL in the atherosclerotic apolipoprotein E deficient mouse: inhibitory role for vitamin E

In the present study we provide evidence, both direct and circumstantial, that macrophage oxysterols induce translocation of p47phox from the cytosol to the cell's plasma membrane, forming an active NADPH-oxidase complex which produces superoxide anion and facilitates cell-mediated oxidation of LDL. The study was performed on macrophages from atherosclerotic apolipoprotein E deficient (E(0)) mice, which are under oxidative stress. The oxysterol content in peritoneal macrophages (MPM) from E(0) mice was significantly higher (by 50-80%) than that observed in MPM from control (C57BL6) mice. E(0) MPM release 2-fold more superoxide anions and oxidize LDL by 2.5-fold more than control MPM. Furthermore, macrophage protein kinase C (PKC) activity and arachidonic acid (AA) release (which are both involved in NADPH-oxidase activation) were elevated by 60 and 70%, respectively, in E(0) MPM compared with control MPM. Dietary supplementation of vitamin E (40 mg/kg per day for 2 months) to E(0) mice resulted in a reduction in MPM total oxysterols content (-27%) and this effect was associated with a reduction in PKC activity (-36%), AA release (-39%), cytosolic p47phox translocation to the plasma membrane (-30%), superoxide anion release (-25%) and MPM-mediated LDL oxidation (-28%), compared with unsupplemented E(0) mice. Enrichment of MPM from control mice with the major oxysterols found in E(0) MPM (7-ketocholesterol, beta-epoxycholesterol and 7beta-hydroxycholesterol) resulted in a dose-dependent increase (60-80%) in PKC activity, AA release, p47phox translocation, superoxide anion release and cell-mediated oxidation of LDL. These data clearly demonstrate for the first time that under oxidative stress, cellular lipids are oxidized, and that macrophage enrichment with oxysterols (as exists in E(0) mice) activates the NADPH-oxidase system and enhances cell-mediated oxidation of LDL, a key event during early atherogenesis.

Chronic treatment with sulfhydryl angiotensin-converting enzyme inhibitors reduce susceptibility of plasma LDL to in vitro oxidation, formation of oxidation-specific epitopes in the arterial wall, and atherogenesis in apolipoprotein E knockout mice

The effects of chronic treatment with the new sulfhydryl angiotensin-converting enzyme (ACE)-inhibitor, zofenopril, in comparison with the classical sulfhydryl ACE-inhibitor captopril or enalapril or placebo on the development of atherosclerosis were determined in apolipoprotein-E knockout (apoE(-/-)) mice. Groups of 2-month-old male mice received either placebo (N=10), 0.05 mg/kg/day of zofenopril (N=10), 1 mg/kg/day of zofenopril (N=10), 5 mg/kg/day of captopril (N=10) or 0.5 mg/kg/day of enalapril (N=8). After 29 weeks of treatment, computer-assisted imaging analysis revealed that zofenopril reduced the aortic cumulative lesion area by 78% at 0.05 mg/kg/day and by 89% at 1 mg/ml/day of zofenopril compared to that of the placebo (P<0.0001). Captopril reduced by 52% aortic lesions compared to placebo (P<0.01 vs. placebo; P<0.05 vs. zofenopril at both doses). Enalapril did not reduce aortic lesions. Furthermore, 0.05 mg/kg/day of zofenopril reduced susceptibility of plasma LDL to in vitro oxidation compared to captopril, enalapril or placebo, as shown by significant reduction of malondialdehyde content (P<0.001 vs. placebo or enalapril; P<0.05 vs. captopril), as well as by the prolongation of lag-time (P<0.01 vs. placebo or enalapril P<0.05 vs. captopril). More importantly, mice treated with 1 mg/ml/day of zofenopril had a significant decrease in the intimal immunohistochemical presence of oxidation-specific epitopes on oxLDL (NA59 monoclonal antibody, P<0.01), macrophages derived foam cells (F4/80 monoclonal antibody, P<0.05) and native LDL (NP monoclonal antibody, P<0.01) compared to placebo, captopril or enalapril. Thus, chronic treatment with the new sulfhydryl ACE-inhibitor zofenopril has antiatherosclerotic and antioxidant effects in the arterial wall of hypercholesterolemic apoE(-/-) mice. This protection was significantly higher than that reached with captopril and at lower doses of the drug. Treatment with 0.5 mg/kg/day of enalapril did not provide any protective effect.

Regulation of apolipoprotein E secretion in rat primary hippocampal astrocyte cultures

Apolipoprotein E isoforms may have differential effects on a number of pathological processes underlying Alzheimer's disease. Recent studies suggest that the amount, rather than the type, of apolipoprotein E may also be an important determinant for Alzheimer's disease. Therefore, understanding the regulated synthesis of apolipoprotein E is important for determining its role in Alzheimer's disease. We show here that in rat primary hippocampal astrocyte cultures, dibutyryl-cAMP increased apolipoprotein E secretion with time in a dose-dependent manner (to 177% at 48 h) and that retinoic acid potentiated this effect (to 298% at 48 h). Dibutyryl-cAMP also gave a rapid, albeit transient, increase of apolipoprotein E mRNA expression (to 200% at 1 h). In contrast, the protein kinase C activator phorbol 12-myristate 13-acetate decreased both apolipoprotein E secretion (to 59% at 48 h) and mRNA expression (to 22% at 1 h). Phorbol 12-myristate 13-acetate also reversed the effects of dibutyryl-cAMP. Apolipoprotein E secretion was also modulated by receptor agonists for the adenylyl cyclase/cAMP pathway. Isoproterenol (50 nM, a beta-adrenoceptor agonist) enhanced, while clonidine (250 nM, an alpha2-adrenoceptor agonist) decreased, secreted apolipoprotein E. We also analysed the effects of agonists for the phospholipase C/protein kinase C pathway. Arterenol (1 microM, an alpha1-adrenoceptor agonist) and serotonin (2.5 microM) enhanced, whereas carbachol (10 microM, an acetylcholine muscarinic receptor agonist) decreased secreted apolipoprotein E. The effects of these non-selective receptor agonists were modest, probably due to effects on different signalling pathways. Arterenol also potentiated the isoproterenol-mediated increase. We also show that phorbol 12-myristate 13-acetate and dibutyryl-cAMP have opposite effects on nerve growth factor, as compared to apolipoprotein E, secretion, suggesting that the results obtained were unlikely to be due to a general effect on protein synthesis. We conclude that astrocyte apolipoprotein E production can be regulated by factors that affect cAMP intracellular concentration or activate protein kinase C. Alterations in these signalling pathways in Alzheimer's disease brain may have consequences for apolipoprotein E secretion in this disorder.

ATP binding cassette transporter ABCA1 modulates the secretion of apolipoprotein E from human monocyte-derived macrophages

Apolipoprotein E (apoE) produced by macrophages in the arterial wall protects against atherosclerosis, but the regulation of its secretion by these cells is poorly understood. Here we investigated the contribution of the adenosine triphosphate binding cassette transporters ABCA1 and ABC8 to the secretion of apoE from either primary human monocyte-derived macrophages (HMDM) or human THP1 macrophages. During incubations of up to 6 h, apoE secretion from both THP1 macrophages and HMDM was stimulated by 8-Br-cAMP, which activates ABCA1 expression. The putative ABCA1 inhibitor glyburide and antisense oligonucleotides directed against ABCA1 mRNA significantly reduced apoE secretion from THP1 macrophages and HMDM. Antisense oligonucleotides directed against ABC8 mRNA also inhibited apoE secretion, although this inhibition was less pronounced and consistent than in the case of ABCA1. ApoE secretion from HMDM of ABCA1-deficient patients with Tangier disease was also decreased. ApoE mRNA expression was not affected by inhibition of ABCA1 or ABC8 in normal HMDM or the lack of functional ABCA1 in HMDM from Tangier disease patients. Inhibition of ABCA1 in HMDM prevented the occurrence of anti-apoE-immunoreactive granular structures in the plasma membrane. We conclude that ABCA1 and, to a lesser extent, ABC8 both promote secretion of apoE from human macrophages.

Puromycin-induced lipid peroxidation in the cochlea of ApoE knockout mice

Puromycin-treated apolipoprotein E (ApoE)-deficient mice were used to study lipid peroxidation (LPO) in the cochlea. Puromycin causes accelerated peroxidation of lipids and induces both inner ear and renal lesions in experimental animals presenting with abnormally high serum cholesterol. To prevent LPO, we used probucol, an effective inhibitor of LPO, and, simultaneously, also a lipid-lowering drug. The mice were given a single injection of the aminonucleoside of puromycin (25 mg/100 g). Polyclonal malondialdehyde and 4-hydroxynonenal antibodies were used to localize the LPO products. LPO products were mainly found in the stria vascularis of puromycin-treated mice. No LPO products were observed in the hair cells. LPO product immunoreactivity was clearly diminished in the animal group treated with both puromycin and probucol. In the cochlea of the ApoE-deficient mouse, puromycin affects mainly the stria vascularis due to the accelerated peroxidation of structural lipids. Probucol treatment prevented the formation of LPO products.

Effect of apolipoprotein AII on the interaction of apolipoprotein E with beta-amyloid: some apo(E-AII) complexes inhibit the internalization of beta-amyloid in cultures of neuroblastoma cells

Apolipoprotein (apo) E and its polymorphism are linked to the pathogenesis of late-onset and sporadic Alzheimer's disease (AD). ApoE facilitates the deposition and fibrillogenesis of beta-amyloid (Abeta), and may participate in Abeta clearance. We recently found that apo(E-AII) complex binds to Abeta much more strongly than does monomeric apoE. Here, we investigated the effect of apoAII on the interaction between apoE and Abeta. Addition of apoAII to apoE monomers increased the binding of apoE2 and apoE3 to Abeta(1-42), presumably following the formation of apo(E3-AII), apo(E2-AII), and apo(AII-E2-AII) complexes. This increased binding was not seen in the case of apoE4. When neuroblastoma cells were cultured in media containing Abeta(1-42) and a mixture of apoE3 and apoAII, intracellular Abeta was significantly reduced and cell viability was maintained at a higher level than in cells cultured without apoAII. ApoE2 itself seemed to act as an inhibitor of the endocytosis of Abeta, and we did not observe a significant effect of apoAII on the movement of Abeta in apoE2-containing medium. However, cell viability could be maintained at a higher level (as with apoE3) by adding apoAII to apoE2, despite the reduced viability of cells incubated without apoAII. In medium containing apoE4, both the amount of Abeta accumulated into cells and the cell viability were unchanged by the presence of apoAII in the medium. In addition, apoE4 itself was toxic, as previously suggested. These findings demonstrate that the type of apo(E-AII) complex present could underlie the isoform-specific role of apoE in the pathogenesis of AD.

Sodium dodecyl sulfate-resistant complexes of Alzheimer's amyloid beta-peptide with the N-terminal, receptor binding domain of apolipoprotein E

Immunocytochemical, biochemical, and molecular genetic studies indicate that apolipoprotein E (apoE) plays an important role in the process of amyloidogenesis-beta. However, there is still no clear translation of these data into the pathogenesis of amyloidosis-beta. Previous studies demonstrated sodium dodecyl sulfate (SDS)-resistant binding of apoE to the main component of Alzheimer's amyloid-A beta and modulation of A beta aggregation by apoE in vitro. To more closely characterize apoE-A beta interactions, we have studied the binding of thrombolytic fragments of apoE3 to A beta in vitro by using SDS-polyacrylamide gel electrophoresis and intrinsic fluorescence quenching. Here we demonstrate that SDS-resistant binding of A beta is mediated by the receptor-binding, N-terminal domain of apoE3. Under native conditions, both the N- and C-terminal domains of apoE3 bind A beta; however, the former does so with higher affinity. We propose that the modulation of A beta binding to the N-terminal domain of apoE is a potential therapeutic target for the treatment of amyloidosis-beta.

Postprandial concentrations and distribution of apo C-III in type 2 diabetic patients. Effect Of bezafibrate treatment

Apo C-III plays a key role in the metabolism of triglyceride-rich lipoproteins. It has recently been implicated as a potential determinant of the triglyceride (TG) lowering effect of fibrates, which down-regulate its expression. This hypothesis has been explored in ten moderately hypertriglyceridemic (TG 4.50+/-2.40 mmol/l) male type 2 diabetic patients tested with a lipid load before and after 4 weeks of treatment with 400 mg bezafibrate daily. Treatment lowered apo C-III concentrations by 20%, mainly in VLDL. Postprandially, apo C-III was transferred to chylomicrons in proportion to their TG content exclusively from HDL. VLDL retained their apo C-III and the apo C-III:TG ratio decreased as TG contents increased. At the end of the absorptive period (8 h) HDL did not recover the totality of their apo C-III (net loss 19 and 28% respectively before and after treatment, P<0.0001 for time effect). Bezafibrate lowered apo E by 33% (P<0.03). The apo C-III:apo E ratio did not vary significantly under treatment but underwent a postprandial decrease: 13% before and 18% (P=0.01) after treatment. These results indicate that repression of apo C-III expression and lowering of the apo C-III:E ratio are not likely mechanisms for the lipid-lowering effects of fibrates in type 2 diabetic patients. The potent effects on postprandial lipemia are suggestive of an apo C-III-independent stimulation of lipolysis.

Heparin specifically inhibits binding of apolipoprotein E to amyloid beta-peptide

Apolipoprotein E (apoE) binds to non-fibrillar amyloid beta-peptide with high affinity. We find here that heparin specifically inhibits apoE-amyloid beta-peptide (1-40) interaction. Low molecular weight heparins reduce the affinity of this interaction 3-fold as it was estimated by surface plasmon resonance. The binding is not affected by high salt concentration, which prevents heparin-induced changes of apoE conformation. We propose that rigid protein conformation, induced by high affinity heparin binding to apoE, is unfavorable for its interaction to amyloid beta-peptide. Using thioflavin T assay, we find that heparin promotes fibrillogenesis of amyloid beta-peptide whereas apoE abolishes this effect. The data suggests that the relationship between apoE and glycosaminoglycans may be important for amyloid beta-peptide fibril formation.

Probucol

The purpose of this review article is twofold. It seeks to present an overview of research studies conducted on the many effects of probucol, and it demonstrates the interest in pursuing studies on probucol"s multiple specific actions and its future as a therapeutic agent. Within this article, the results of animal studies, experimental human studies, and clinical human studies are detailed, as is information on toxicology studies and on the side effects of the drug.

Alcohol and molecular regulation of protein glycosylation and function

Chronic alcohol exposure leads to the appearance of carbohydrate-deficient transferrin (CDT), a N-glycosylated protein and sialic acid-deficient apolipoprotein E (apoE), an O-glycosylated protein. We show that chronic ethanol treatment destabilizes sialyltransferase (ST) mRNA resulting in a concomitant decreased steady-state level of ST mRNA. As a result, alcohol markedly decreases the hepatic synthetic rate of ST. This leads to impaired sialylation of transferrin and apoE. Consequently, apoE content in plasma high-density lipoproteins (HDL) is decreased. ApoE plays a significant role in the delivery of HDL cholesterol to the liver via apo B/E receptor, a process called reverse cholesterol transport (RCT). Desialylation of apoE results in its decreased association with HDL. Thus, the dissociation constant of HDL for binding to sialo-apoE is 90 +/- 35 nM, whereas that for desialo-apoE is 1010 +/- 250 nM. More importantly, the uptake of labeled cholesterol by human HepG2 cells is decreased by 30-40% from reconstituted HDL particles (rHDL)-containing desialo-apoE compared to rHDL with sialo-apoE. We conclude that chronic alcohol exposure down-regulates the expression of sialyltransferase genes resulting in impaired sialylation of apoE. This leads to its decreased binding to plasma HDL and thereby, impairs the RCT function of HDL.

Phenotyping of porcine apolipoprotein E using isoelectric focusing and localization of the APOE gene within the halothane-susceptibility linkage group

A method has been developed for the phenotyping of pig apolipoprotein E. It was based on isoelectric focusing of sialidase-treated and delipidated blood plasma followed by immunoblotting. As the first antibody the anti-human apolipoprotein E antibody was used. The genetic polymorphism of pig apolipoprotein E appeared to be controlled by three alleles at one locus. A two-point linkage analysis was performed between certain loci belonging to the halothane linkage group and the APOE locus on material comprising 9 Zlotnicka Spotted boars, 30 Polish Large White sows, and their 160 offspring. A tight linkage between the A1BG and the APOE loci was documented (theta = 0.038).

Effect of simvastatin on the lipid profile of hemodialysis patients

BACKGROUND

Simvastatin, a 3-hydroxy 3-methylglutaryl co-enzyme A (HMG-CoA) reductase inhibitor, is used widely for treatment of hypercholesterolemia. Simvastatin may be a suitable treatment for dyslipidemia in hemodialysis (HD) patients. However, investigation of the side-effects and safety of long-term administration of simvastatin to HD patients has been limited. In this study, we investigated the effects and safety of simvastatin and its effects on lipoprotein metabolism in hypercholesterolemic patients on HD.

METHODS

Simvastatin was administered at a dosage of 5 mg/day for 24 weeks to 38 HD patients with high serum total cholesterol (TC) levels (200 mg/dl) or low high-density lipoprotein cholesterol (HDL-C) levels (35 mg/dl). Every four weeks, serum lipids, apolipoprotein, lipoprotein (a) [Lp(a)] and malondialdehyde (MDA) levels were measured. In addition, lipid levels were determined in each lipoprotein fraction separated by ultracentrifugation.

RESULTS

After 24 weeks of simvastatin administration, TC significantly decreased by 25.7%, and low-density lipoprotein cholesterol (LDL-C) was significantly decreased by 33.6%. Triglyceride (TG) and HDL-C showed no significant changes. Apolipoprotein (apo) B significantly decreased by 24.5% and apo E by 30.0%. No significant changes were observed in the other apolipoproteins. MDA was also significantly decreased, whereas Lp(a) was not significantly altered. In the lipoprotein fractions, very LDL cholesterol (VLDL-C), intermediate-density lipoprotein cholesterol (IDL-C), LDL1 cholesterol (LDL1-C), and LDL2 cholesterol (LDL2-C) showed significant decreases. No particular side-effects were observed during the 12 months of simvastatin administration.

CONCLUSIONS

These results suggest that simvastatin appears to be safe and effective in HD patients with hypercholesterolemia.

Tetracycline-regulatable expression vectors tightly regulate in vitro gene expression of secreted proteins

The regulation of gene expression by the tetracycline system has attracted a high level of interest in the recent past. However, expression of secreted proteins has not been evaluated precisely. In this study, we constructed two versions of a one-plasmid system containing the elements necessary for the regulation of gene expression. The regulatable elements and the selectable marker (Neor) were set up in two different configurations, pTRIN31 and pTRIN76. With these two regulatable versions, the levels of protein expression after transfection into the NIH/3T3 cell line were measured by insertion of three different genes encoding the secreted proteins (hGH, ApoE3, hGM-CSF). The maximum levels of gene expression obtained with the pTRIN76-derived plasmids were 100ng/24h/106 cells for hGH, 427ng/24h/106 cells for ApoE3 and 108ng/24h/106 cells for hGM-CSF. For the pTRIN31-derived plasmids the maximum levels were 2.7ng/24h/106 cells for hGH and 47ng/24h/106 for ApoE3. Both plasmids give rise to an expression of the transfected gene that can be tightly regulated by three different molecules: tetracycline, minocycline and doxycycline. The levels of the secreted proteins are below the detectable level when the reporter genes are repressed. This repression is reversible within 48h after the regulator has been removed from the medium.

Trifluoroethanol induces the self-association of specific amphipathic peptides

We have examined the effect of trifluoroethanol (TFE) on the solution behaviour of three amphipathic peptides. One of the peptides, containing three heptad repeat units (Ac-YS-(AKEAAKE)3GAR-NH2), remained monomeric under conditions where TFE induced a two-state transition from a random coil to an alpha-helix. In contrast, the TFE-induced alpha-helical formation of two peptides derived from human apolipoproteins C-II and E was accompanied by the formation of discrete dimers and trimers, respectively. The apolipoprotein C-II peptide further aggregated to form beta-sheet at higher concentrations of TFE (50% v/v). The results suggest a class of peptides capable of discrete self-association in the presence of cosolvents which favour intramolecular hydrogen bonding.

Regulation of lipoprotein metabolism by estrogen in inbred strains of mice occurs primarily by posttranscriptional mechanisms

Estrogen protects against developing premature coronary artery disease. However, the mechanism of protective effects of estrogen still remains poorly understood. One mechanism by which estrogen can have protective effects appears to be through modulation of plasma lipoproteins. We showed that the mouse can be used as animal model to study estrogen-mediated synthesis and secretion of lipoproteins since, unlike the rat, the mouse does not up-regulate LDL receptors (Srivastava et al. [4]). Since inbred strains of mice differ in their genetic background and show differing responsiveness to dietary lipids, we examined how various inbred strains of mice respond to estradiol administration, and whether some mouse strains show responses similar to rats. 17beta-estradiol was administered to male mice from 15 different inbred strains, and the changes in plasma levels of lipids, apoB, apoAI, and apoE were examined. Total cholesterol decreased in all but one strain, apoAI levels decreased in all but 3 strains while apoB levels and apoB/apoAI ratios increased in all but 2 strains, suggesting that in contrast to rats, the apoB-containing lipoproteins increased relative to HDL in all strains of mice examined. Basal and estradiol-induced changes in total cholesterol were significantly correlated with changes in apoAI, but not apoB, reflecting the predominance of HDL over other lipoproteins in mouse plasma. The effects of estrogen on plasma apoE levels varied among various inbred strains of mice tested. Plasma apoE levels increased in seven strains treated with estrogen, and remained unchanged in the rest. To examine whether changes of plasma apoproteins are associated with the changes in the respective hepatic mRNA levels, apoAI, B and E mRNA were quantified by RNase protection assay. Hepatic apoE mRNA did not show correlation with either basal or post treatment plasma apoE levels in any of the strains. Similarly, most of the mouse strains did not show correlation of plasma apoAI and apoB levels with the corresponding hepatic mRNA levels. These results suggest that estrogen regulates plasma lipoprotein concentrations primarily by posttranscriptional mechanisms, and there were strain-related differences in the estrogen-mediated regulation of lipoprotein metabolism.

Investigation of plasma membrane-associated apolipoprotein E in primary macrophages

Our previous studies identified the lysosome as the compartment for degradation of newly synthesized apoE in primary macrophages. Lysosomal degradation of newly synthesized apoE is extensive and rapid (> 50% in 60 min). In the present study we tested the hypothesis that the macrophage cell surface is part of the itinerary of apoE in its path to the lysosomes. We therefore examined the existence and size of the apoE pool associated with the macrophage cell surface. Such a pool may not only provide a mechanism of targeting apoE for lysosomal degradation, by endocytosis, but also have important implications for the metabolism of lipoproteins by macrophages. Treatment of macrophages with heparin (10 micrograms/ml and 5 mg/ml) and heparinase I (1 U/ml), which releases substantial amounts of apoE from HepG2 cells, results in no additional release of apoE from macrophages. Treatment of macrophages with xyloside (1 mM) or GRGDTP (500 micrograms/ml) does not decrease the extent of cell-associated apoE. Both immunogold labeling, followed by electron microscopy, and immunofluorescent labeling and light microscopy further confirm the lack of significant amounts of cell surface-associated apoE in macrophages. In contrast, immunolabeled apoE is readily observed in permeabilized cells. Taken together, these data indicate the absence of significant apoE-glycosaminoglycan interaction at the macrophage cell surface. The lack of such an interaction is likely due to paucity of heparan sulfate proteoglycans on the macrophage cell surface, when compared to hepatocytes. Along with our previous observations. (Deng. J., V. Rudick, and L. Dory, 1995. J. Lipid Res. 36:2129-2140), these results suggest direct targeting of a portion of newly synthesized apoE from trans-Golgi network to lysosomes for degradation, without involving the plasma membrane and endocytosis.

Astrocytes and microglia respond to estrogen with increased apoE mRNA in vivo and in vitro

This study examined the regulation of apolipoprotein E (apoE) by 17beta-estradiol (E2) in brain glia, using rats with regular ovulatory cycles as an in vivo model and cultured astrocytes and mixed glia as in vitro models. Two brain regions were examined which had demonstrated transient synaptic remodeling during the estrous cycle. In the hippocampal CA1 region and the hypothalamic arcuate nucleus, apoE mRNA was elevated at proestrus when plasma E2 was high and synaptic density was increasing. Both astrocytes and microglia contributed to this increase in apoE mRNA. In vitro, E2 treatment had no effect on apoE mRNA levels in monotypic cultures of either astrocytes or microglia. In contrast, mixed glial cultures responded to E2 with increased apoE mRNA and protein, suggesting that heterotypic cellular interactions are important in the brain response to estrogens. In situ hybridization in combination with cell-specific markers showed that E2 increased apoE mRNA levels in both astrocytes and microglia. These results, which are the first evidence of apoE mRNA localization to microglia in vivo and the control of apoE expression in brain cells by estrogens, are discussed in terms of the possible protective role of E2 in Alzheimer's disease and prior findings that emphasize the expression of apoE mRNA in astrocytes within the brain.

Functional characterization of two different Kupffer cell populations of normal rat liver

BACKGROUND

Kupffer cells of the liver represent the largest population of tissue macrophages. Small and large Kupffer cells were distinguished in normal liver, leading to the suggestion that they have different functions. This study intends to further characterize small and large Kupffer cells of normal rat liver in vivo and in vitro.

METHODS

Sections of rat liver were investigated by double-staining immunofluorescence with the monoclonal antibodies ED1 and ED2. Isolated nonparenchymal liver cells were separated according to size to obtain small and large Kupffer cells. In culture, phagocytosis was studied by zymosan ingestion and cell proliferation by incorporation of 3H-thymidine. Synthesis of the proteins C1-inhibitor, apolipoprotein E and interleukin-1 was studied by endogenous labeling of newly synthesized proteins, immunoprecipitation and sodium dodecylsulfate-polyacrylamide gel electrophoresis.

RESULTS

ED1+ ED2+ Kupffer cells were located in the liver along the sinusoids. ED1+ ED2+ cells were found mainly located around the central vein and portal vessels. By counterflow elution, small ED1+ ED2- cells were separated from larger ED1+ ED2+ cells and cultured. The larger cells abundantly synthesized C1-inhibitor and apolipoprotein E, while the small cells synthesized only trace amounts of these proteins. Interferon-gamma increased C1-inhibitor synthesis in small (5-fold) and large cells (1.5-fold). 3H-thymidine incorporation was 11-fold higher in small than in large cells. However, lipopolysaccharide-induced pro-interleukin-1 alpha and pro-interleukin-1 beta synthesis and phagocytic activity were similar in both populations.

CONCLUSIONS

The data demonstrate two different populations of mononuclear phagocytes in normal rat liver well distinguished by immunocytochemical and functional markers.

Apolipoprotein E1-Hammersmith (Lys146-->Asn;Arg147-->Trp), due to a dinucleotide substitution, is associated with early manifestation of dominant type III hyperlipoproteinaemia

Apolipoprotein E (apoE) is one of the major protein constituents of chylomicron and very low density lipoprotein (VLDL) remnants and plays a central role as a ligand in the receptor-mediated uptake of these particles by the liver. Here we describe a new variant of apoE, apoE1-Hammersmith, which is associated with dominantly expressed type III hyperlipidaemia. The propositus, aged 26, developed tubero-eruptive xanthomas at the age of 3, her daughter developed similar lesions at age 7 but her son, aged 3, shows no clinical abnormality so far. All three cases had an apoE3E1 phenotype and a broad beta band on lipoprotein electrophoresis. Cysteamine modification resulted in a shift of apoE1 to the apoE2 isoform position, indicating that the mutation leading to apoE1-Hammersmith occurred on an apoE3 background. ApoE genotyping confirmed these results. Sequence analysis of DNA of the propositus was performed for exons 3 and 4 and revealed a dinucleotide substitution causing two amino acid changes at adjacent positions (Lys146-->Asn) and (Arg147-->Trp).

Effects of hormone replacement modalities on low density lipoprotein composition and distribution in ovariectomized cynomolgus monkeys

This study was designed to determine the effect of several hormone replacement therapies on LDL size, density, heterogeneity, and composition in surgically postmenopausal cynomolgus monkeys fed an atherogenic diet. Groups (n = 5 each) of ovariectomized cynomolgus monkeys were untreated (control), or treated with conjugated equine estrogens, medroxyprogesterone acetate (progesterone), combined estrogen-progesterone, or tamoxifen for 9 weeks. There were no differences among treatment groups in total plasma, LDL, or HDL cholesterol or triglyceride concentrations. Plasma LDL were isolated by ultracentrifugation and size exclusion chromatography and subfractionated by density gradient centrifugation for subsequent chemical analysis. Estrogen treatment was associated with significantly smaller (measured as LDL molecular weight, 3.9 +/- 0.2 g/mu mol) and denser plasma LDL (1.034 g/ml peak density) compared with control (4.5 +/- 0.1 g/mu mol; 1.030 g/ml peak density) or progesterone-treated animals (4.6 +/- 0.2; 1.029 g/ml peak density). LDL from the estrogen group were relatively enriched in protein and triglyceride and poor in cholesteryl ester and apolipoprotein F (apoE) compared to the control group. Triglyceride enrichment with estrogen treatment occurred predominantly in the lighter, larger LDL subfractions (d = 1.015-1.025 g/ml), which were reduced in concentration (26 +/- 10 mg cholesterol/dl) compared to control (61 +/- 19 mg/dl) or progesterone treated animals (67 +/- 16 mg/dl). Combined estrogen-progesterone or tamoxifen treatment resulted in changes in LDL that followed the same trend as those observed with estrogen treatment. We conclude that short-term estrogen treatment of ovariectomized cynomolgus monkeys results in changes in plasma LDL size, density, and composition while having no apparent effect on overall plasma lipid concentrations.

Pupil dilatation assay by tropicamide is modulated by apolipoprotein E epsilon 4 allele dosage in Alzheimer's disease

The mydriatic response to dilute tropicamide was studied in 25 Japanese patients with Alzheimer's disease (AD), 13 patients with non-AD neurological diseases (non-AD) and 11 normal elderly subjects (control). Although the changes in resting pupil diameter and area over baseline were significantly greater (p < 0.05) in AD patients than in non-AD patients and controls, there was considerable overlap between the three groups. The change in resting pupil area was significantly greater (p < 0.05) in AD patients homozygous for ApoE epsilon 4 than in AD patients heterozygous for or without this allele. Despite a limited sample size in the present study, our results indicate that the pupil dilation assay by tropicamide is not an effective diagnostic tool for AD, and it may be modulated by different gene dosage of ApoE epsilon 4.