Biomedical subjects

J C Fruchart

Publications and source records attributed to J C Fruchart.

At least 163 records · Page 9Linked to original sources

PubMed1997

Subclasses of LpA-I in coronary artery disease: distribution and cholesterol efflux ability.

We analysed the distribution of LpA-I particles according to their molecular weight in 34 men with symptomatic coronary artery disease (CAD) and 11 men with no symptoms of CAD (control group). Using an original rapid and reproducible gradient gel electrophoresis technique, three LpA-I subclasses were defined: large (L-LpA-I), intermediate (I-LpA-I) and small LpA-I (S-LpA-I). The proportion of L-LpA-I was significantly lower in the CAD group (37.5 +/- 18.5%) than in the control group (58.9 +/- 15.0%) (P < 0.01). Conversely, a significantly (P < 0.05) higher proportion of I-LpA-I (31.9 +/- 20.7%) was observed in the CAD group compared with the control group (14.2 +/- 8.2%). Also, in the CAD group, the proportion of L-LpA-I was positively associated with the plasma level of LpA-I (P < 0.05) and, conversely, the proportion of S-LpA-I was negatively associated with LpA-I levels (P < 0.01). L-LpA-I and I-LpA-I from CAD patients and from control subjects were most effective in promoting cholesterol efflux from Fu5AH rat hepatoma cells, whereas S-LpA-I was ineffective in this regard. In conclusion, the decreased ratio in CAD patients of L-LpA-I, lipoprotein subspecies that are required for cholesterol efflux from cells, suggests a potential anti-atherogenic effect of these particles associated with the larger LpA-I subfractions.

Aged↗

PubMed1997

Fat ingestion is associated with increased levels of apoC-III- and apoE-B-containing lipoprotein particles in humans.

Apolipoprotein (apo) C-III and apoE have a major influence on post-prandial apoB-containing lipoprotein metabolism. The goal of the present study was to compare the post-prandial changes in particles containing apoB and apoC-III and those containing apoB and apoE. Twenty subjects consumed a fatty meal (1 g of fat kg-1). Human lipoprotein particles were measured by enzyme-linked immunosorbent assay (ELISA) using combinations of anti-apoC-III, -apoE and -apoB. Post-prandial lipaemia was associated with an increase in LpC-III:B (+100%) and LpE:B (+55%; P < 0.05), which occurred 4.07 +/- 1.2 and 4.7 +/- 0.8 h after the meal respectively (P < 0.05). Gel filtration chromatography showed that fasting plasma LpC-III:B and LpE:B eluted in two fractions consisting of large and smaller sized particles; 3 h after the meal, LpC-III:B and LpE:B increased in the very low-density lipoprotein (VLDL) + intermediate-density lipoprotein (IDL) fraction; at 6 h, LpC-III:B and LpE:B decreased in VLDL and LpE:B increased moderately in the low-density lipoprotein (LDL) size range; at 10 h, both concentrations of lipoprotein particles returned to fasting levels. In conclusion, apoC-III-B-containing and apoE-B-containing lipoproteins have different post-prandial metabolic fates. These differences may result in different atherogenic potential.

Adult↗

PubMed1997

Postprandial lipaemia is associated with increased levels of apolipoprotein A-IV in the triacylglycerol-rich fraction and decreased levels in the denser plasma fractions.

Apolipoprotein (apo) A-IV is primarily associated with HDL or with the lipoprotein-free fraction of plasma, and in small amounts with chylomicrons and VLDL. The aim of the present study was to assess the effect of a fatty meal on the postprandial variation in plasma apo A-IV and on its distribution among lipoprotein fractions following absorption of fat. Twenty healthy male subjects participated in the study. After an overnight fast, subjects were given a fatty breakfast containing 1 g fat/kg body weight (% energy: fat 65, carbohydrate 20; protein 15). Blood samples were taken every hour during the next 10 h. Apo A-IV was measured by ELISA. Postprandial lipaemia was associated with a moderate, although significant, increase in the plasma levels of apo A-IV. Apo A-IV increased from the median baseline value of 0.15 g/l to 0.165 g/l (median +17%; P < 0.01) 5 h after fat ingestion. The postprandial peak of apo A-IV occurred 1 h after the triacylglycerol peak. There were no statistically significant correlations between baseline lipids, baseline apo A-IV and postprandial changes in apo A-IV levels, or between postprandial changes in lipids and apo A-IV at any time. To assess apo A-IV distribution among lipoproteins, plasma was fractionated by fast performance liquid chromatography at baseline and 3, 6 and 10 h postprandially. There was a substantial heterogeneity in the apo A-IV distribution among lipoproteins following the fatty meal. At 3 h after fat ingestion, apo A-IV levels increased in the triacyglycerol-rich lipoprotein (TRL) fraction and decreased in the denser plasma fraction. At 6 h after the fatty meal, apo A-IV was still present in the TRL but was decreased in the HDL fractions. The findings of the present study support the concept that apo A-IV particles transfer from the denser plasma fraction to TRL during postprandial lipaemia.

Adult↗

PubMed1997

Circadian variation of postprandial lipemia.

The goal of the present study was to assess the influence of mealtime on postprandial lipemia. Thirteen healthy subject aged 19-32 y were given the same meal at night (0100) or during the day (1300) in random order: the meal contained 40% of estimated daily energy expenditure. Blood samples were drawn at baseline and hourly for 8 h after the meal. Serum total cholesterol, very-low-density-lipoprotein cholesterol (VLDL-C), low-density-lipoprotein cholesterol (LDL-C), high-density-lipoprotein cholesterol (HDL-C), triacylglycerols, VLDL-triacylglycerols, apolipoprotein (apo) A-I, and apo B were measured at each time point. In a subgroup of seven subjects a control fasting reference line was measured according to the same nocturnal and diurnal time schedule. The mean postprandial concentrations of triacylglycerol (P < 0.001), VLDL-triacylglycerol (P < 0.001), and VLDL-C (P < 0.001) were higher at night than during the day. In contrast, mean cholesterol (P < 0.01), LDL-C (P < 0.01), HDL-C (P < 0.001), apo A-I (P < 0.001), and apo B (P < 0.001) concentrations were lower after the night meal than after the day meal. The magnitude of the postprandial response was estimated by the area between the fasting and postprandial curves. The triacylglycerol and VLDL-triacylglycerol responses were not significantly different between night and day. The VLDL-C (P < 0.01) response was greater and LDL-C (P < 0.0001) and HDL-C (P < 0.01) responses were lower at night than during the day. These results indicate that circadian factors specifically affect serum cholesterol transport. Apo B (P < 0.01) and apo A-I (P < 0.01) responses followed LDL-C and HDL-C changes during the day but were dissociated from lipoprotein responses at night, suggesting that circadian apolipoprotein regulation is dissociated from that of serum lipids. The results of the present study indicate that postprandial lipid, lipoprotein, and apolipoprotein concentrations are affected by circadian factors.

Adult↗

PubMed1997

The role of a triplet repeat sequence of the very low density lipoprotein receptor gene in plasma lipid and lipoprotein level variability in humans.

The biological role of the very low density lipoprotein receptor (VLDL-R) in humans is not yet elucidated. This cellular receptor binds apolipoprotein E (apoE)-containing lipoparticles and is mainly expressed in peripheral tissues. The VLDL-R gene contains a polymorphic triplet (CGG) repeat located 19 bp upstream of the initiation codon. We explored the allelic distribution of this repeat in 1384 subjects of European Caucasian origin, 609 of them surviving a myocardial infarction. Six alleles corresponding to 5, 6, 7, 8, 9, and 11 repeats were detected in this population. The alleles 5, 8, and 9 were the most frequent, with frequencies of 0.413, 0.275, and 0.292, respectively. No association was found between the VLDL-R polymorphism and myocardial infarction. In controls without lipid lowering treatment, a statistically significant interaction between VLDL-R genotype and apoE phenotype was found for plasma triglycerides (P < .04), suggesting a gene-gene interaction. There was also a main effect of the VLDL-R polymorphism on LpE:B and LpA-I. The VLDL-R 9 allele was associated with lower levels of plasma LpE:B (P < .05) and higher concentrations of plasma LpA-I (P < .01) than the other alleles. These results suggest that VLDL-R has a modest influence on circulating lipoproteins in humans.

Adult↗

PubMed1997

In vivo glucosylated LpA-I subfraction. Evidence for structural and functional alterations.

This study compared the structural and functional properties of glucosylated and non-glucosylated LpA-I particle subfractions (GLpA-I and NGLpA-I, respectively) isolated from patients with poorly controlled type 1 (insulin-dependent) diabetes. Compared with NGLpA-I, GLpA-I showed an enrichment in triglycerides (P < .05) and a depletion in phospholipid (P < .05) content. Moreover, the triglycerides-to-cholesteryl esters ratio was increased (P < .05), suggesting an increased cholesteryl ester transfer protein activity and a possible transport defect that accelerates atherogenesis. The surface-to-core constituents ratio, an indirect estimate of particles size, is lower in GLpA-I (P < .01) than in NGLpA-I, correlating well with a larger median size (P < .05) as seen by electron microscopy. The apolipoprotein (apo) A-I conformation was evaluated through determination of the immunological accessibility of three different domains defining specific epitopes for anti-apo A-I monoclonal antibodies. We observed a marked decreased accessibility for two of these regions, which interestingly have already been implicated in the interaction with cells. Cell culture data suggest that nonenzymatic glycosylation occurring on apo A-I can modify lipoprotein function, since it results in a decreased binding of GLpA-I to HeLa cells and impaired cholesterol efflux from Fu5AH rat hepatoma cells.

Animals↗

PubMed1997

Regulation of lipoprotein metabolism by thiazolidinediones occurs through a distinct but complementary mechanism relative to fibrates.

Thiazolidinediones are antidiabetic agents, which not only improve glucose metabolism but also reduce blood triglyceride concentrations. These compounds are synthetic ligands for PPAR gamma, a transcription factor belonging to the nuclear receptor subfamily of PPARs, which are important transcriptional regulators of lipid and lipoprotein metabolism. The goal of this study was to evaluate the influence of a potent thiazolidinedione, BRL49653, on serum lipoproteins and to determine whether its lipid-lowering effects are mediated by changes in the expression of key genes implicated in lipoprotein metabolism. Treatment of normal rats for 7 days with BRL49653 decreased serum triglycerides in a dose-dependent fashion without affecting serum total and HDL cholesterol and apolipoprotein (apo) A-I and apo A-II concentrations. The decrease in triglyceride concentrations after BRL49653 was mainly due to a reduction of the amount of VLDL particles of unchanged lipid and apo composition. BRL49653 treatment did not change triglyceride production in vivo as analyzed by injection of Triton WR-1339, indicating a primary action on triglyceride catabolism. Analysis of the influence of BRL49653 on the expression of LPL and apo C-III, two key players in triglyceride catabolism, showed a dose-dependent increase in mRNA levels and activity of LPL in epididymal adipose tissue, whereas liver apo C-III mRNA levels remained constant. Furthermore, addition of BRL49653 to primary cultures of differentiated adipocytes increased LPL mRNA levels, indicating a direct action of the drug on the adipocyte. Simultaneous administration of BRL49653 and fenofibrate, a hypolipidemic drug that acts primarily on liver through activation of PPAR alpha both decreased liver apo C-III and increased adipose tissue LPL mRNA levels, resulting in a more pronounced lowering of serum triglycerides than each drug alone. In conclusion, both fibrates and thiazolidinediones exert a hypotriglyceridemic effect. While fibrates act primarily on the liver by decreasing apo C-III production, BRL49653 acts primarily on adipose tissue by increasing lipolysis through the induction of LPL expression. Drugs combining both PPAR alpha and gamma activation potential should therefore display a more efficient hypotriglyceridemic activity than either compound alone and may provide a rationale for improved therapy for elevated triglycerides.

Adipose Tissue↗

PubMed1997

Is cholesterol the major lipoprotein risk factor in coronary heart disease?--a Franco-Scottish overview.

There has been much debate over the past three decades concerning the role of hyperlipidaemia in coronary heart disease (CHD) and the efficacy of reducing plasma lipids levels. Although reduction in plasma cholesterol has been associated with a favourable effect on both primary and secondary CHD, there is a growing feeling that cholesterol may not be the only significant lipoprotein risk factor to be involved. Only relatively recently has the true role of triglycerides become apparent. Studies have indicated that the greatest reduction in CHD with some treatments has been found in those patients in whom high triglyceride levels accompany hypercholesterolaemia. In particular, in younger patients who have suffered a myocardial infarction, hypertriglyceridaemia is more common than hypercholesterolaemia. Nevertheless, recent large studies have shown that reduction of low-density lipoprotein (LDL) is beneficial, even in post-infarction patients with a relatively normal total cholesterol level. Furthermore, studies with fibrates and with HMG Co-A reductase inhibitors have indicated that progression of atheromatous lesions can be halted and in may cases there is evidence of regression. Continuing research on the pathophysiology of atherosclerosis, including the role of macrophages and thrombotic involvement, will further define the role of hypolipidaemics in the prevention and management of coronary heart disease.

Adult↗

PubMed1996

Interstitial fluid apolipoprotein A-II: an association with the occurrence of myocardial infarction.

A sample of male patients aged 25-64 years, survivors of myocardial infarction (MI) taken from the Lille MONICA register, and age-matched control subjects from the general population were recruited in Lille and its surroundings in the North of France. Diabetics and subjects taking hypolipidemic drugs were excluded from the analysis, so that 73 MI and 144 control subjects were included. Lipids, apolipoprotein (apo) A-I, apo A-II, apo A-IV and apo B, and apo A-I-containing particles such as lipoproteins containing both apo A-I and apo A-II (LpA-I:A-II) and those containing apo A-I but not apo A-II (LpA-I) were measured in interstitial fluid by applying mild suction, and in plasma. Univariate analysis showed that plasma triglycerides, very low density lipoprotein (VLDL)-cholesterol and apo B were significantly higher, while high density lipoprotein (HDL)-cholesterol, apo A-I, LpA-I and LpA-I:A-II were lower in MI survivors compared to controls after adjustment for age, body mass index (BMI), alcohol and tobacco consumption. In interstitial fluid, cholesterol and apo A-II were higher in MI than in controls before adjustment for covariates. However, after adjustment, triglycerides became significant while cholesterol and apo A-II remained significantly higher in MI, at 43.8 and 7.5 mg/dl, respectively, than in control subjects, at 38.6 and 5.9 mg/dl, respectively. Taking into account only the plasma parameters, the multivariate analysis reveals that triglycerides and apo A-I appear to be independent factors indicative of the presence of a MI. When plasma and interstitial fluid parameters were taken together in the multivariate analysis, the measurement of apo A-II in interstitial fluid increased the level of prediction of MI over the information provided by the plasma parameters. These data raise the possibility that interstitial fluid apo A-II levels may be associated with the occurrence of MI.

Adult↗

PubMed1996

Potential gene therapy for lecithin-cholesterol acyltransferase (LCAT)-deficient and hypoalphalipoproteinemic patients with adenovirus-mediated transfer of human LCAT gene.

BACKGROUND: Overexpression of human lecithin-cholesterol acyltransferase (LCAT) in transgenic mice results in an increase of the antiatherogenic HDLs. METHODS AND RESULTS: To investigate the potential use of LCAT for gene therapy, a recombinant adenovirus was constructed in which the human LCAT cDNA was expressed under the control of the human cytomegalovirus immediate/early promoter followed by a chimeric intron (AdCMV human LCAT). Human apolipoprotein (apo) A-I transgenic mice infected with AdCMV human LCAT by intravenous injection accumulated reactive LCAT in the plasma. LCAT activity was increased 201-fold in the plasma of mice infected with 1 x 10(6) pfu AdCMV human LCAT, from 45 +/- 2 to 9068 +/- 812 nmol.mL-1.h-1, in comparison with basal LCAT activity measured in control mice, 5 days after injection. Plasma HDL cholesterol levels rose from 117 +/- 12 to 797 +/- 48 mg/dL, and plasma human apo A-I concentrations increased from 247 +/- 14 to 616 +/- 17 mg/dL, in AdCMV human LCAT infected mice compared with control mice. HDL particles were larger and had a different electrophoretic mobility. Studies of cholesterol efflux by incubation of serum with cholesterol-loaded Fu5AH cells showed that serum from AdCMV human LCAT-infected mice promoted a significantly higher efflux than did that of the controls. CONCLUSIONS: These data establish the potential of this approach for treatment of subjects with LCAT gene defects as well as patients with low plasma levels of apo A-I and HDL cholesterol.

Adenoviridae↗

PubMed1996

Two regulatory elements of similar structure and placed in tandem account for the repressive activity of the first intron of the human apolipoprotein A-II gene.

Recent reports indicate that apolipoprotein (apo) A-II, the second most abundant protein of high-density lipoproteins, plays a crucial role in counteracting the beneficial effect of apo A-I against atherogenesis. Transcription of the human apo A-II gene is controlled by an enhancer comprising 14 regulatory elements located upstream of its promoter whereas the first intron of this gene behaves as a silencer. Here we show that two sequence elements account for the repressive activity of this intron and correspond to negative regulatory elements termed NRE I and NRE II. The activity of intron I and the nuclear proteins binding to NRE I and II are encountered in hepatic cells but not in non-hepatic cells studied here. Both NREs form nucleoprotein complexes of very similar physicochemical characteristics and bind the same or closely related proteins. Site-directed mutagenesis, transient transfection and gel-shift analysis experiments indicate that both NREs exhibit similar structures, being composed of two sites required for maximal activity and optimal binding of transcription factors. Therefore two negative regulatory elements of similar structure and function, placed in tandem, account for the repressive activity of the first intron of the human apo A-II gene. These NREs do not exhibit structural similarity with known NREs of other genes.

Animals↗

PubMed1996

Protection against atherogenesis in mice mediated by human apolipoprotein A-IV.

Apolipoproteins are protein constituents of plasma lipid transport particles. Human apolipoprotein A-IV (apoA-IV) was expressed in the liver of C57BL/6 mice and mice deficient in apoE, both of which are prone to atherosclerosis, to investigate whether apoA-IV protects against this disease. In transgenic C57BL/6 mice on an atherogenic diet, the serum concentration of high density lipoprotein (HDL) cholesterol increased by 35 percent, whereas the concentration of endogenous apoA-I decreased by 29 percent, relative to those in transgenic mice on a normal diet. Expression of human apoA-IV in apoE-deficient mice on a normal diet resulted in an even more severe atherogenic lipoprotein profile, without affecting the concentration of HDL cholesterol, than that in nontransgenic apoE-deficient mice. However, transgenic mice of both backgrounds showed a substantial reduction in the size of atherosclerotic lesions. Thus, apoA-IV appears to protect against atherosclerosis by a mechanism that does not involve an increase in HDL cholesterol concentration.

Animals↗

PubMed1996

Inhibition of atherosclerosis development in cholesterol-fed human apolipoprotein A-I-transgenic rabbits.

BACKGROUND: Prospective epidemiological studies support the hypothesis that high levels of high-density lipoprotein (HDL) cholesterol and apolipoprotein (apo) A-I limit atherosclerosis development. However, more data from studies with animal models of atherosclerosis that resemble the human disease are required to demonstrate the effect of apo A-I in the inhibition of atherogenesis. The rabbit is a good animal model for human atherosclerosis. METHODS AND RESULTS: Human apo A-I-transgenic rabbits have been produced, and we have evaluated the effect of apo A-I on the development of atherosclerosis in transgenic rabbits fed a cholesterol-rich diet for 14 weeks. Plasma cholesterol levels of atherogenic apo B-containing lipoproteins were similar for transgenic and control rabbits (> 1000 mg/dL), while plasma levels of HDL cholesterol in the transgenic group were always about twice that of the control group (68 +/- 11 versus 37 +/- 3 mg/dL at 14 weeks; P < .001). At the end of the experiment, the amount of aortic surface area covered by lesions as well as the amount of lipid accumulation in the aorta were significantly less in transgenic rabbits compared with the control group (15 +/- 12% versus 30 +/- 8%, P < .0027 for the surface area of the thoracic aorta; 116 +/- 31 versus 247 +/- 39 mumol/g aorta, P < .0068 for cholesterol content in total aorta). CONCLUSIONS: Overexpression of human apo A-I in rabbits inhibits the development of atherosclerosis in this animal model that resembles, in many respects, human atherosclerosis.

Analysis of Variance↗

PubMed1996

Transcriptional induction of rat liver apolipoprotein A-I gene expression by glucocorticoids requires the glucocorticoid receptor and a labile cell-specific protein.

Treatment with glucocorticoids increases the concentration of plasma high-density lipoprotein (HDL), which is inversely correlated to the development of atherosclerosis. Previously, we demonstrated that repeated administration of glucocorticoids increases apolipoprotein (apo) A-I gene expression and decreases apoA-II gene expression in rat liver. In the present study, the mechanism of glucocorticoid action on hepatic apoA-I and apoA-II expression was studied. A single injection of rats with dexamethasone increased hepatic apoA-I mRNA levels within 6 h and further increases were observed after 12 h and 24 h. In contrast, liver apoA-II mRNA levels gradually decreased after dexamethasone treatment to less than 25% control levels after 24 h. In rat primary hepatocytes and McARH8994 hepatoma cells, addition of dexamethasone increased apoA-I mRNA levels in a time-dependent and dose-dependent manner, whereas apoA-II mRNA levels were unchanged. Simultaneous addition of the glucocorticoid antagonist RU486 prevented the increase in apoA-I mRNA levels after dexamethasone treatment, which suggests that the effects of dexamethasone are mediated through the glucocorticoid receptor. Inhibition of transcription by actinomycin D and nuclear-run-on experiments in McARH8994 cells and primary hepatocytes showed that dexamethasone induced apoA-I, but not apoA-II, gene transcription. Transient-transfection assays in McARH8994 cells with a chloramphenicol acetyl transferase vector driven by the rat-apoA-I-gene promoter demonstrated that the proximal apoA-I promoter could be induced by dexamethasone, and this effect could be abolished by simultaneous treatment with RU486. However, in COS-1 cells, apoA-I promoter transcription was not induced by dexamethasone or cotransfected glucocorticoid receptor. In addition, the induction of apoA-I gene transcription by dexamethasone was blocked by the protein-synthesis inhibitor cycloheximide, which suggests the presence of a labile protein involved in apoA-I gene activation by dexamethasone. In conclusion, our results demonstrate that dexamethasone regulates rat apoA-I, but not apoA-II, gene expression through direct action on the hepatocyte. The induction of apoA-I gene transcription by dexamethasone requires the glucocorticoid receptor and a labile cell-specific protein.

Animals↗

PubMed1996

Branched synthetic constructs that mimic the physico-chemical properties of apolipoprotein AI in reconstituted high-density lipoproteins.

Amphipathic helical repeats are considered as the structural units of numerous apolipoproteins and have been described as being responsible for the interaction of apolipoproteins with phospholipids in high-density lipoproteins (HDL). Furthermore, apolipoproteins, and especially apolipoprotein AI (apoAI), are involved in various biological functions of these circulating particles in plasma. Studies with synthetic peptides corresponding to domains of the apoAI sequence have however shown that short 39-residue fragments do not interact strongly enough with phospholipids to generate particles that correctly mimic the physico-chemical properties of HDL reconstituted with native apoAI [Vanloo, B., Demoor, L., Boutillon, C., Lins, L., Baert, J., Fruchart, J. C., Tartar, A. & Rosseneu, M. (1995) Association of synthetic peptide fragments of human apolipoprotein A-I with phospholipids, J. Lipid Res. 36, 1686-1696.]. Here we show that synthetic branched multimeric peptides, often used as carriers for the design of synthetic vaccines (multiple-antigen peptides), can be used to mimic the physiochemical properties of apoAI in HDL. This type of molecule is obtained by using a small core matrix of Lys residues bearing radially branched synthetic peptides as dendritic arms. We compared the lipid-binding capacities and the structural properties of a linear peptide corresponding to residues 145-183 of apoAI [apoAI-(145-183)-peptide] with those of two multimeric peptides consisting respectively of three [trimeric apoAI-(145-183)] and four copies [tetrameric apoAI-(145-183)] of the selected sequence, branched on a covalent core matrix. This paper provides evidence for the increased abilities of the multimeric peptides to associate with phospholipids compared with the short linear peptides. Moreover, the trimeric apoAI-(145-183) peptide was most efficient in mimicking the physico-chemical and structural properties of native apoAI in reconstituted HDL. As tools adequate to unravel the structure/function relationship of separate apolipoprotein domains are still missing, these multimeric peptides might constitute an alternative approach to linear peptides which are poor mimetics and to protein mutants which are difficult to produce and only provide information about the total sequence.

Amino Acid Sequence↗

PubMed1996

Entry of polyunsaturated fatty acids into the brain: evidence that high-density lipoprotein-induced methylation of phosphatidylethanolamine and phospholipase A2 are involved.

The conversion of phosphatidylethanolamine (PE) into phosphatidylcholine (PC) by a sequence of three transmethylation reactions is shown to be stimulated by the apolipoprotein E-free subclass of high-density lipoprotein (HDL3) in isolated bovine brain capillary (BBC) membranes, HDL3-induced stimulation of BBC membranes pulsed with [methyl-14C]methionine causes a transient increase in each methylated phospholipid, i.e. phosphatidyl-N-monomethylethanolamine (PMME), phosphatidyl-NN-dimethylethanolamine (PDME) and PC. PC substrate arising from the activation of PE N-methyltransferase (PEMT) is hydrolysed by a phospholipase A2 (PLA2), as demonstrated by the accumulation of lysophosphatidylcholine (lyso-PC). When PE containing [14C]arachidonic acid in the sn-2 position ([14C]PAPE) is incorporated into BBC membranes, HDL3 stimulation induces the formation of PMME, PDME, PC and lyso-PC and the release of [14C]arachidonic acid, which correlates with the previous production of lyso-PC, suggesting that HDL3 stimulates a PLA2 that can release polyunsaturated fatty acids (PUFA). Both PEMT and PLA2 activities depend on a HDL3 concentration in the range 0-50 micrograms/ml and are strictly dependent on HDL3 binding, because HDL3 modified by tetranitromethane is no longer able to bind to specific receptors and to trigger PEMT and PLA2 activation. Moreover, HDL3 prelabelled with [14C]PAPE can stimulate PDME and lyso-PC synthesis in BBC membranes in the presence of S-adenosylmethionine, suggesting that HDL3 can supply BBC membranes in polyunsaturated PE and can activate enzymes involved in PE N-methylation and PUFA release. The results support the hypothesis of a close relationship between HDL3 binding, PE methylation and PUFA release, and suggest that the PC pool arising from PE could be used as a pathway for the supply of PUFA to the brain.

Animals↗

PubMed1996

Opposite regulation of human versus mouse apolipoprotein A-I by fibrates in human apolipoprotein A-I transgenic mice.

The regulation of liver apolipoprotein (apo) A-I gene expression by fibrates was studied in human apo A-I transgenic mice containing a human genomic DNA fragment driving apo A-I expression in liver. Treatment with fenofibrate (0.5% wt/wt) for 7 d increased plasma human apo A-I levels up to 750% and HDL-cholesterol levels up to 200% with a shift to larger particles. The increase in human apo A-I plasma levels was time and dose dependent and was already evident after 3 d at the highest dose (0.5% wt/wt) of fenofibrate. In contrast, plasma mouse apo A-I concentration was decreased after fenofibrate in nontransgenic mice. The increase in plasma human apo A-I levels after fenofibrate treatment was associated with a 97% increase in hepatic human apo A-I mRNA, whereas mouse apo A-I mRNA levels decreased to 51%. In nontransgenic mice, a similar down-regulation of hepatic apo A-I mRNA levels was observed. Nuclear run-on experiments demonstrated that the increase in human apo A-I and the decrease in mouse apo A-I gene expression after fenofibrate occurred at the transcriptional level. Since part of the effects of fibrates are mediated through the nuclear receptor PPAR (peroxisome proliferator-activated receptor), the expression of the acyl CoA oxidase (ACO) gene was measured as a control of PPAR activation. Both in transgenic and nontransgenic mice, fenofibrate induced ACO mRNA levels up to sixfold. When transgenic mice were treated with gemfibrozil (0.5% wt/wt) plasma human apo A-I and HDL-cholesterol levels increased 32 and 73%, respectively, above control levels. The weaker effect of this compound on human apo A-I and HDL-cholesterol levels correlated with a less pronounced impact on ACO mRNA levels (a threefold increase) suggesting that the level of induction of human apo A-I gene is related to the PPAR activating potency of the fibrate used. Treatment of human primary hepatocytes with fenofibric acid (500 microM) provoked an 83 and 50% increase in apo A-I secretion and mRNA levels, respectively, supporting that a direct action of fibrates on liver human apo A-I production leads to the observed increase in plasma apo A4 and HDL-cholesterol.

Analysis of Variance↗

PubMed1996

Chymase in exocytosed rat mast cell granules effectively proteolyzes apolipoprotein AI-containing lipoproteins, so reducing the cholesterol efflux-inducing ability of serum and aortic intimal fluid.

Degranulated mast cells are present in human fatty streaks. Chymase in granules released from degranulated rat serosal mast cells, i.e., in granule remnants, proteolyzes human high density lipoprotein3 (HDL3), and so reduces its ability to induce cholesterol efflux from macrophage foam cells in vitro. In this study we found that remnant chymase, by proteolyzing human serum and human aortic intimal fluid, prevents these two physiologic fluids from effectively inducing cholesterol efflux from cultured macrophage foam cells. Inhibition was strongest when remnants were added to apolipoprotein AI (apoAI)-containing lipoproteins; the remnants had no effect on the weaker efflux produced by apoAI-deficient serum. Western blot analysis showed that granule remnants degrade apoAI in serum and in internal fluid. When released from remnants, chymase lost its ability to proteolyze HDL3 in the presence of serum. Thus, remnant chymase (but not isolated chymase) was able to resist the natural protease inhibitors present in serum and in intimal fluid. The results imply participation of exocytosed mast cell granules in foam cell formation in atherogenesis.

Animals↗