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M J Chapman

Publications and source records attributed to M J Chapman.

At least 91 records · Page 5Linked to original sources
PubMed1995

Non-enzymatic glycation of lipoprotein(a) in vitro and in vivo.

Nonenzymatic glycation of lipoprotein may contribute to the premature atherogenesis of patients with diabetes mellitus by diverting lipoprotein catabolism from non-atherogenic to atherogenic pathways. It has been demonstrated that the proportion of apolipoprotein B-100 (apo B-100) in glycated form is significantly higher in diabetic patients than in non-diabetic controls, and equally that plasma lipoprotein(a) Lp(a) levels may be increased in diabetic patients. Consequently, we have evaluated the glycation of Lp(a) in vitro and in vivo, by use of a combination of m-aminophenylboronate affinity chromatography and enzyme-linked immunosorbent assay (ELISA) for apo B-100 and Lp(a). In vitro studies were performed on normolipodemic plasma samples containing elevated concentrations of Lp(a). These studies establish that Lp(a) can be glycated in vitro in the presence of high concentrations of glucose, although to a lesser extent than low density lipoprotein (LDL) (15.8% +/- 4.4% and 30.2% +/- 5.4% (P = 0.0001) after a 48 h incubation at 37 degrees C, respectively). We have also shown that apo B-100 was more glycated than apo(a) in the Lp(a) particle. In vivo studies have shown that the percentage of glycated Lp(a) in diabetic patients was significantly higher than in the control population (2.8% +/- 1.07% versus 2.0% +/- 0.43%, P = 0.017). The level of glycated Lp(a) is also positively correlated with that of HbA1c in diabetic patients (r=0.6, P=0.002). Since our results show that Lp(a) is less susceptible to glycation than LDL, we speculate that glycation of LDL may be more relevant to the cardiovascular risk associated with this particle than with Lp(a).

Apolipoprotein B-100↗
PubMed1995

Effects of dietary fat and L-methionine on the hepatic metabolism of very low density lipoproteins in the preruminant calf, Bos spp.

The effects of triglycerides (TG) from tallow (1.21 and 2.13 g TG/kg of body weight (BW) per meal, diets R and B respectively) and from tallow plus cream (2.50 g TG/kg of BW per meal, diet L) with or without L-methionine (2.6 g/kg dry matter) on hepatic apparent secretion of very low density lipoproteins (VLDL) were investigated in 3 groups of 4 preruminant calves fitted with chronic catheters and with electromagnetic blood-flow probes implanted in their hepatic vessels. Increasing TG concentrations stimulated the apparent VLDL secretion by the liver (1.02, -0.36 and -1.51 mg VLDL mass/min per kg of BW in diets L, B and R, respectively). L-Methionine increased this secretion when associated with the lipid-restricted (diet R; 0.25 and -1.51 mg VLDL/min per kg of BW) and basal (diet B; 0.35 and -0.36 mg VLDL/min per kg of BW) diets (non-significant). However, the VLDL apparent secretion decreased with the lipid-enriched diet (diet L), which suggests an insufficient dose of L-methionine compared with the level of TG intake, and a possible competition between liver and intestine for utilization of L-methionine for the synthesis of TG-rich lipoproteins.

Animals↗
PubMed1995

PAF-degrading acetylhydrolase is preferentially associated with dense LDL and VHDL-1 in human plasma. Catalytic characteristics and relation to the monocyte-derived enzyme.

In human plasma, platelet activating factor (PAF)-degrading acetylhydrolase (acetylhydrolase) is principally transported in association with LDLs and HDLs; this enzyme hydrolyzes PAF and short-chain forms of oxidized phosphatidylcholine, transforming them into lyso-PAF and lysophosphatidylcholine, respectively. We have examined the distribution, catalytic characteristics, and transfer of acetylhydrolase activity among plasma lipoprotein subspecies separated by isopycnic density gradient ultracentrifugation; the possibility that the plasma enzyme may be partially derived from adherent monocytes has also been evaluated. In normolipidemic subjects with Lp(a) levels < 0.1 mg/mL, acetylhydrolase was associated preferentially with small, dense LDL particles (LDL-5; d = 1.050 to 1.063 g/mL) and with the very-high-density lipoprotein-1 subfraction (VHDL-1; d = 1.156 to 1.179 g/mL), representing 23.9 +/- 1.7% and 20.6 +/- 3.2%, respectively, of total plasma activity. The apparent Km values for PAF of the enzyme associated with such lipoproteins were 89.7 +/- 23.4 and 34.8 +/- 4.5 mumol/L for LDL-5 and VHDL-1, respectively: indeed, the Km value for LDL-5 was some 10-fold higher than that of the light LDL-1, LDL-2, and LDL-3 subspecies, whereas the Km of VHDL-1 was some twofold greater than those of the HDL-2 and HDL-3 subspecies. Furthermore, when expressed on the basis of unit plasma volume, the Vmax of the acetylhydrolase associated with LDL-5 was some 150-fold greater than that in LDL-1 (d = 1.019 to 1.023 g/mL). No significant differences in the pH dependence of enzyme activity or in sensitivity to protease inactivation, sulfydryl reagents, the serine protease inhibitor Pefabloc, or the PAF antagonist CV 3988 could be detected between apo B-containing and apo A-I-containing lipoprotein particle subspecies. Incubation of LDL-1 (Km = 8.4 +/- 2.6 mumol/L) and LDL-2 (d = 1.023 to 1.029 g/mL; Km = 8.4 +/- 3.3 mumol/L) subspecies with LDL-5, in which acetylhydrolase had been inactivated by pretreatment with Pefabloc, demonstrated preferential transfer of acetylhydrolase to LDL-5. Acetylhydrolase transferred to LDL-5 from the light LDL subspecies exhibited a Km of 9.4 +/- 2.2 mumol/L, a value characteristic of the particle donors. Finally, acetylhydrolase (Km = 23.4 +/- 7.6 mumol/L) released by adherent human monocytes in culture was found to bind preferentially to small, dense LDL subspecies upon incubation of Pefabloc-inactivated plasma with monocyte supernatant.(ABSTRACT TRUNCATED AT 400 WORDS)

Cells, Cultured↗
PubMed1995

Tissue factor pathway inhibitor activity associated with LDL is inactivated by cell- and copper-mediated oxidation.

Human plasma contains a multivalent, Kunitz-type proteinase inhibitor termed tissue factor pathway inhibitor (TFPI), which is a specific inhibitor of the action of the factor VII(a)-tissue factor complex in coagulation. A major fraction of plasma TFPI is transported in association with LDL. Because LDL may undergo oxidation in the arterial wall during atherogenesis, we examined the effect of copper- and cell-mediated oxidative modification on TFPI activity associated with LDL. Oxidation mediated by copper ions resulted in a significant inactivation of LDL-associated TFPI (60% to 72% at 24 hours with 2.5 mumol/l CuCl2). The inactivation of TFPI was strongly negatively correlated with both an increase in the net electrical charge of LDL (r = -.80, P < or = .0001) and with the production of thiobarbituric acid-reactive substances (r = -.78, P < or = .0001) and lipid peroxides (r = -.80, P < or = .0001). Cell-mediated oxidation, involving incubation of LDL for 48 hours with either monocyte-like THP1 cells or human monocytes in Ham's F-10 medium, effected a significant decrease (64% and 75%, respectively) in LDL-associated TFPI activity. By contrast, prolonged exposure of LDL to purified soybean lipoxygenase (5000 U/mL) was less effective in inactivating TFPI (47% reduction after incubation for 72 hours at 37 degrees C). We subsequently investigated the mechanism(s) that may underlie such inactivation. Oxidation of LDL is accompanied by the generation of various aldehydes, including malondialdehyde and 4-hydroxynonenal. Chemical modification with these aldehydes revealed a significant inverse correlation between the progressive loss of TFPI activity and both the increase in net electrical charge (r = -.90, P < or = .0001) and the derivatization of free amino acid residues of LDL (r = -.90, P < or = .0001). Specific chemical modification of lysine amino groups by acetylation similarly led to inactivation of LDL-associated TFPI activity. TFPI activity was almost totally abolished (< 1.4%) when the TNBS reactivities of acetylated LDL, malondialdehyde-modified LDL, and 4-hydroxynonenal-modified LDL were 31%, 21%, and 43% that of native LDL, respectively. Our data demonstrate that expression of LDL-associated anticoagulant activity is markedly decreased as a consequence of the oxidative process, and suggest that the progressive aldehydic derivatization of apo B of LDL, and of the associated TFPI protein, may contribute to this phenomenon. Because tissue factor is overexpressed in the atheromatous plaque, it may exert a marked local procoagulant effect.(ABSTRACT TRUNCATED AT 400 WORDS)

Blood Coagulation↗
PubMed1995

Pravastatin modulates cholesteryl ester transfer from HDL to apoB-containing lipoproteins and lipoprotein subspecies profile in familial hypercholesterolemia.

Familial hypercholesterolemia (FH) results from genetic defects in the LDL receptor, and is characterized by a marked elevation in plasma LDL and by qualitative abnormalities in LDL particles. Because LDL particles are major acceptors of cholesteryl esters (CEs) from HDL, significant changes occur in the flux of CE through the reverse cholesterol pathway. To evaluate the effects of an HMG-CoA reductase inhibitor, pravastatin, on CE transfer from HDL to apo B-containing lipoproteins and on plasma lipoprotein subspecies profile in subjects with heterozygous FH, we investigated the transfer of HDL-CE to LDL subfractions and changes in both concentration and chemical composition of the apo B- and the apo AI-containing lipoproteins. After pravastatin treatment (40 mg/d) for a 12-week period, plasma LDL concentrations (mean +/- SD, 745.4 +/- 51.9 mg/dL) were reduced by 36% in patients with FH (n = 6). By contrast, the qualitative features of the density profile of LDL subspecies in patients with FH, in whom the intermediate (d = 1.029 to 1.039 g/mL) and dense (d = 1.039 to 1.063 g/mL) subspecies were significantly increased relative to a control group, were not modified by pravastatin. In addition, no significant effect on the chemical composition of individual LDL subfractions was observed. Furthermore, plasma HDL concentrations were not modified, although the density distribution of HDL was normalized. Indeed, the HDL density peak was shifted towards the HDL2 subfraction (ratios of HDL2 to HDL3 were 0.7 and 1.1 before and after treatment, respectively). Evaluation of plasma CE transfer protein (CETP) mass was performed with an exogenous CE transfer assay. Under these conditions, no modification of plasma CETP protein mass was induced by pravastatin administration. However, the rate of CE transfer from HDL to LDL was reduced by 24% by pravastatin (61 +/- 17 micrograms CE.h-1.mL-1 plasma; P < .0005), although intermediate and dense LDL subfractions again accounted for the majority (71%) of the total CE transferred to LDL. Thus, pravastatin induced reduction of plasma CETP activity without change in the preferential targeting of the transfer of HDL-CE towards the denser LDL subfractions. In conclusion, pravastatin reduces the elevated flux of CE from HDL to apo B-containing lipoproteins in subjects with heterozygous FH as a result of a reduction in the LDL particle acceptor concentration.

Adult↗
PubMed1994

Hypocortisolaemia and adrenocortical responsiveness at onset of septic shock.

OBJECTIVE: To characterise the plasma cortisol profile and adreno-cortial responsiveness (short Synacthen test) of patients in septic shock. DESIGN: Retrospective assessment using case-notes and ICU charts. SETTING: University teaching hospital ICU. PATIENTS: 68 septic shock patients with plasma cortisol and/or short Synacthen test measured at ICU-admission or onset of shock post ICU-admission. Patients were identified from a total population of 155 patients who had PCL and/or SST measured over a 4.5 year period. INTERVENTION: None. MEASUREMENTS AND RESULTS: Patients with septic shock had a plasma cortisol ranging from 210-8900 nmol/l and mortality of 56%. There were 22 (32%) below (low) and 46 (68%) above (high) a 'critical' plasma cortisol of 500 nmol/l. Using stepwise logistic regression, mortality was adequately predicted by and increased with, increasing plasma cortisol and onset of shock remote from ICU-admission. Short Synacthen tests were available in 33 patients: 11 responders (cortisol increment > 200 nmol/l above baseline 30 min after 0.25 mg intravenous Synacthen) and 22 hypo-responders. Mortality in patients was adequately predicted by and increased with a decrease in cortisol increment post-Synacthen. Thirteen patients (plasma cortisol 606 +/- [SD] 297 nmol/l) had complete haemodynamic profiles before inotropic therapy; no relationship was demonstrated between plasma cortisol and circulatory variables. Follow-up revealed no cases of Addison's disease. CONCLUSIONS: In septic shock, 'hypocortisolaemia' is not uncommon and does not predict a high mortality; adrenocortical hypo-responsiveness may be associated with poor outcome.

Adrenal Cortex↗
PubMed1994

Identifiability and indistinguishability of nonlinear pharmacokinetic models.

Three nonlinear model structures of interest in pharmacokinetics are analyzed to determine whether the unknown, independent, model parameters can be deduced if perfect input-output data were available. This is the problem of identifiability. The method used is based on the local state isomorphism theorem. In certain circumstances, the modeler may be undecided between several model structures and it is then of interest to determine whether different model structures can be distinguished from perfect input-output data. This is the problem of model indistinguishability. The technique used, again based on the local state isomorphism theorem, parallels the similarity transformation approach for linear systems described previously in this journal. The analysis is performed on three two-compartment examples having one linear and one nonlinear (Michaelis-Menten) elimination pathway. In each model there is, on physiological and other grounds, some uncertainty over the precise location (central compartment or peripheral compartment) of one of the elimination pathways.

Models, Biological↗
PubMed1994

Lipoprotein (a): implication in atherothrombosis.

Substantial experimental evidence now implicates lipoprotein (a) as an independent risk factor for premature cardiovascular disease. Both plasma Lp(a) levels and apo(a) phenotype are strong predictors of risk for ischaemic heart disease. The accumulation of apo(a) in vascular wall tissue and in atherosclerotic plaques and the potential inhibition of fibrinolysis by Lp(a) underlie the enhanced risk of premature cardiovascular disease associated with this cholesterol-rich particle. Recent studies of the capacity of purified Lp(a) isoforms to inhibit fibrinolysis in an in vitro system have revealed that small isoforms of Lp(a) (< or = 500 kDa) are efficient inhibitors of plasminogen activation and bind with high affinity to fibrin. Conversely, large isoforms exert little or no inhibitory effect in this system (> 500 kDa). These data suggest that the potential, high affinity interaction of Lp(a) particles containing small isoforms with fibrin introduces a new, third dimension to the atherothrombotic risk associated with these cholesterol-rich particles.

Apolipoproteins A↗
PubMed1994

Indistinguishability for a class of nonlinear compartmental models.

Indistinguishability, as applied to nonlinear compartmental models, is analyzed by means of the local state isomorphism theorem. The method of analysis involves the determination of all local, diffeomorphic transformations connecting the state variables of two models. This is then applied to two two-compartment models, in the first instance with linear eliminations, and then with the addition of eliminations with Michaelis-Menten kinetics. In the nonlinear example, the state transformation turns out to be linear or possibly affine. It is found that the nonlinear analysis could be eased by splitting the state isomorphism equations into those of the initial linear models together with extra equations due to the nonlinearities.

Kinetics↗
PubMed1994

A new in vitro method for the simultaneous evaluation of cholesteryl ester exchange and mass transfer between HDL and apoB-containing lipoprotein subspecies. Identification of preferential cholesteryl ester acceptors in human plasma.

To date, several methods have been developed to determine the activity of plasma lipid transfer proteins. These methods have largely involved the addition of the transfer protein in question to labeled substrates, followed by prolonged incubation (4 to 18 hours) and subsequent evaluation of the radioactivity transferred to precipitated low-density lipoprotein (LDL). While adequate for determining the activity of cholesteryl ester transfer protein (CETP), these methods generally do not take into account the composition or levels of lipoproteins present within a given individual plasma because pools of high-density lipoprotein (HDL) are labeled and used for the transfer experiments. Both the direction and the extent of lipid transfer are dependent on the composition and relative abundance of both donor and acceptor particles as well as the activity of the lipid transfer protein(s). Here we describe a new method for the determination of the capacity of plasma samples to facilitate cholesteryl ester transfer from HDL to LDL and very-low-density lipoprotein (VLDL), a method that has several advantages. First, the subject's HDL is labeled and used for transfer. Second, the labeled HDL, in a quantity equivalent to 1% of the plasma HDL mass, is added to the subject's plasma, and therefore the relative abundance of both donor and acceptor particles is preserved at their physiological levels. Third, both cholesteryl ester mass and radioactivity are determined, allowing the net mass transfer of cholesteryl ester and cholesteryl ester exchange to be quantified separately.(ABSTRACT TRUNCATED AT 250 WORDS)

Apolipoproteins↗
PubMed1994

PAF-acether-degrading acetylhydrolase in plasma LDL is inactivated by copper- and cell-mediated oxidation.

In peripheral blood, native low-density lipoprotein (LDL) is a major carrier of acetylhydrolase, the enzyme that hydrolyzes the sn-2 acetate of PAF-acether, converting it to lyso PAF-acether. By controlling the level of PAF-acether, the acetylhydrolase may regulate the biologic effects of this potent inflammatory and thrombotic mediator. The biologic oxidation of LDL appears to underlie its atherogenicity. We report here that oxidative modification of LDL led to progressive loss of associated acetylhydrolase activity. Reductions of approximately 90% and 40% of acetylhydrolase activity occurred respectively in LDL oxidized for 24 hours by copper ions (2.5 mumol/L) in phosphate-buffered saline and in LDL incubated with human monocyte-like THP1 cells in Ham's F-10 medium. Acetylhydrolase activity decreased as a function of the degree of LDL oxidation and was correlated with an increase in net negative charge and in the content of thiobarbituric acid-reactive substances (r = -.94 and r = -.88, respectively; P < or = .001). The acetylhydrolase of mildly oxidized LDL displayed a similar Km for PAF-acether compared with native LDL, whereas its Vmax was lower. Thus, acetylhydrolase conserved its affinity for PAF-acether, whereas a nondefined and noncompetitive inhibitor, apparently produced during oxidation, might account for the observed loss in enzymatic activity. Acetylhydrolase activity was totally recovered in LDL modified by both acetylation and malondialdehyde.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Alkyl-2-acetylglycerophosphocholine Esterase↗
PubMed1994

Preferential cholesteryl ester acceptors among the LDL subspecies of subjects with familial hypercholesterolemia.

Elevated cholesteryl ester transfer protein-mediated transfer of cholesteryl ester (CE) from high-density lipoprotein (HDL) to low-density lipoprotein (LDL) may contribute to the atherogenicity of LDL in subjects with familial hypercholesterolemia (FH). To identify the major CE acceptors among LDL subspecies, we investigated the qualitative and quantitative features of CE transfer and exchange to LDL on incubation of plasma under physiological conditions. LDL subspecies were fractionated by density-gradient ultra-centrifugation. Both mass transfer and exchange of HDL CE to and with very-low-density lipoprotein plus intermediate-density lipoprotein and LDL were linear for the first 6 hours of incubation. Thereafter mass transfer ceased, but exchange continued at a comparable rate. The rate of CE mass transfer to apolipoprotein B-containing lipoproteins was significantly enhanced in heterozygous FH subjects compared with normolipidemic individuals (91.6 +/- 28.2 versus 52.9 +/- 19.6 micrograms CE/h per milliliter plasma, FH versus normal subjects, P < .02). In FH subjects the predominant LDL subspecies (LDL 3 and 4, d = 1.029 to 1.050 g/mL) accounted for 59.7 +/- 9.2% of the total CE transferred to LDL from HDL. By contrast, expression of CE mass transfer relative to the mass of each lipoprotein acceptor showed the triglyceride (TG)-rich (10.7% to 17.3%), light LDL subspecies (LDL 1 and 2, d = 1.019 to 1.029 g/mL) to represent the preferential CE acceptors (LDL 1 and 2, 94.8 to 136.5 micrograms CE/mg LDL mass; LDL 3 through 5 [d = 1.029 to 1.063 g/mL], 47.1 to 64.1 micrograms CE/mg LDL mass).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Lipoprotein metabolism in the preruminant calf: effect of a high fat diet supplemented with L-methionine.

The effects of dietary lipid and L-Met supplementation on plasma lipids and lipoproteins were investigated in 16-wk-old preruminant calves. Four calves received the basal milk diet (2.0 g of lipid/kg of BW per meal) for 8 d followed by the same diet supplemented with L-Met (2.6 g/kg of dietary DM) for 5 d. Similarly, seven calves received successively the basal diet supplemented with cream (2.7 g of lipid/kg of BW per meal) and the same diet supplemented with L-Met. The diet with cream induced higher triglyceridemia than the basal diet because of a marked increase in chylomicra and in very low density lipoproteins, which suggested stimulation of intestinal lipoprotein secretion. Moreover, this lipid-enriched diet stimulated the formation of very light high density lipoproteins to the detriment of heavy high density lipoproteins. These particles, the bovine counterpart of mammalian high density lipoproteins of type 1, were distributed within the density range of low density lipoproteins. Addition of L-Met in the diets increased plasma concentrations of chylomicra and very low density lipoproteins, suggesting direct stimulation of the intestinal secretion of both of these lipoproteins and of the hepatic very low density lipoproteins. No effect of L-Met was observed on the concentrations and the physicochemical properties of low and light high density lipoproteins.

Animals↗
PubMed1993

Does apolipoprotein(a) heterogeneity influence lipoprotein(a) effects on fibrinolysis?

High plasma levels of lipoprotein(a) [Lp(a)] are considered to be an independent risk factor for premature cardiovascular disease and are inversely associated with apolipoprotein(a) [apo(a)] isoform sizes. The contribution of apo(a) polymorphism to the inhibition of fibrinolysis, a mechanism that may favor thrombus development, was therefore evaluated by measuring the ability of Lp(a) particles of distinct apo(a) isoform content to compete with plasminogen for fibrin binding during plasminogen activation by fibrin-bound tissue-type plasminogen activator. The rate of plasmin generation was most efficiently inhibited by an isoform with a molecular weight (M(r)) of approximately 540 Kd. An isoform with M(r) approximately 590 Kd produced a less pronounced effect, whereas the isoform with M(r) approximately 610 Kd failed to inhibit plasminogen activation. These effects were directly proportional to the amount of Lp(a) bound to the carboxy-terminal lysine residues of degraded fibrin. The relative affinity of the binding (kd range, 16 to 180 nmol/L) reflected the ability of individual Lp(a) isoforms to inhibit the binding of plasminogen (kd, 600 nmol/L). The question of the influence of kringle sequence variability on the binding to fibrin was not addressed by the present work. These data suggest that apo(a) isoform types with high affinity for fibrin may influence the ability of Lp(a) to interfere with fibrinolysis and contribute thereby to the association of elevated levels of Lp(a) with atherosclerotic and thrombotic risks.

Apolipoproteins A↗
PubMed1993

Management of atrial tachyarrhythmias in the critically ill: a comparison of intravenous procainamide and amiodarone.

OBJECTIVE: To compare the efficacy and safety of intravenous (IV) amiodarone and procainamide for the treatment of atrial tachyarrhythmias (AT) in the critically ill. DESIGN: In this prospective study, patients were allocated to drug treatment on the basis of hospital identification number, even for procainamide and odd for amiodarone. SETTING: Patients were recruited from a teaching hospital ICU and did not include postoperative cardiac patients. PATIENTS AND PARTICIPANTS: 26 patients with AT sustained for at least 1 h and failure to respond to correction of possible precipitating factors were entered in the study. Exclusion criteria were systolic blood pressure (SBP) < 80 mmHg, and known hypersensitivity to either drug. Two patients with chronic atrial fibrillation (who received amiodarone) were later excluded from the analysis. In the final analysis, 14 patients received procainamide and 10 amiodarone. INTERVENTIONS: IV amiodarone (3 mg/kg followed by 10 mg/kg/24 h, with repeat dose of 3 mg/kg at 1 h if no response) or i.v. procainamide (10 mg/kg at 1 mg/kg/min followed by infusion of 2-4 mg/min for 24 h, with repeat dose of 5 mg/kg at 1 h if no response). MEASUREMENTS AND RESULTS: In the procainamide group 10/14 (71%) and in the amiodarone group 7/10 (70%) had converted to sinus rhythm by 12 h. There was no significant difference in response between the groups. SBP was not significantly different from baseline after administration of either drug. CONCLUSIONS: Procainamide and amiodarone appear to be safe and equally effective in the treatment of AT in the critically ill.

Aged↗
PubMed1993

Heterogeneity of cellular cholesteryl ester accumulation by human monocyte-derived macrophages.

We have studied cholesteryl ester accumulation in human monocyte-derived macrophages, which together with smooth muscle cells, represent the major cell types that accumulate cholesterol in atherosclerotic lesions. Monocyte-derived macrophages were incubated with either acetylated low density lipoprotein (AcLDL) or non-lipoprotein cholesterol and the question as to whether all of the cells, or specific cell subpopulations could accumulate cholesteryl ester was examined. We stained cholesteryl ester in monocyte-macrophages with the fluorescent probe filipin. Cholesteryl ester accumulated as lipid droplets that were widely dispersed in the cell cytoplasm. Interestingly, no more than 65% of monocyte-macrophages accumulated cholesteryl ester during the 1st day of incubation with non-lipoprotein cholesterol. By 2 days of incubation, greater than 90% of cells displayed cholesteryl ester deposition. The cholesteryl ester which accumulated during the 2nd day of incubation was derived from unesterified cholesterol that had accumulated during the 1st day of incubation. This finding was substantiated by the following: (1) chemical measurements showed that the total cholesterol content of monocyte-macrophages did not increase further after the 1st day of incubation, and (2) all monocyte-macrophages had accumulated fluorescent tagged cholesterol during the 1st day of incubation. In contrast to the results obtained with non-lipoprotein cholesterol, more than 90% of monocyte-macrophages incubated with AcLDL for 1 day accumulated cholesteryl ester in two experiments. However, less than 62% of monocyte-macrophages accumulated cholesteryl ester in two other experiments, thereby resembling results obtained with non-lipoprotein cholesterol. Again, the lack of cholesteryl ester accumulation with AcLDL was not due to a lack of uptake of AcLDL, as greater than 90% of monocyte-macrophages accumulated fluorescent tagged AcLDL. The observed heterogeneity in cholesterol esterification among human monocyte-macrophages suggests that functional subpopulations of these cells may exist with respect to cholesterol processing. However, heterogeneity in cholesteryl ester accumulation did not seem to correlate with expression of HLA-DR antigen, a marker of immunological activation of macrophages. Other sources of heterogeneity most likely result from inter-cellular variation at one or more levels of regulation of the cholesterol trafficking and esterification process.

Acetylation↗
PubMed1993

Ciprofibrate therapy normalises the atherogenic low-density lipoprotein subspecies profile in combined hyperlipidemia.

The effect of ciprofibrate treatment on the atherogenic profile of low-density lipoprotein (LDL) subspecies in combined hyperlipidemia (CHL) has been investigated in six patients displaying elevated plasma triglyceride and cholesterol levels (> 200 and > 250 mg/dl, respectively). The E2E2 phenotype was excluded; four patients possessed familial antecedents of premature coronary heart disease (CHD). Analysis of five LDL subclasses separated by isopycnic density gradient ultracentrifugation showed a predominance of dense LDL subspecies (LDL-4 and LDL-5, d 1.039-1.063 g/ml; 51% of total LDL mass) in the asymmetric LDL density profile characteristic of CHL patients at baseline. Ciprofibrate treatment (100 mg/day for 1 month) effected marked reductions in both total plasma LDL and apo B-100 levels (approximately 19% and approximately 23%, respectively). Equally, the plasma profile of LDL subspecies was normalised to a significant degree as a result of preferential reduction in the elevated levels of both dense subspecies (LDL-4 and LDL-5; -43% and -54%, respectively; P < 0.03 and P < 0.006 [corrected], respectively). The circulating concentrations of light LDL (LDL-1, d 1.019-1.023 g/ml) were also diminished significantly by ciprofibrate (-30%; P < 0.006 [corrected]). Furthermore, ciprofibrate not only effected reductions in the elevated triglyceride content of the hydrophobic core of all LDL subspecies but also normalised their common deficiency in free cholesterol. In addition, the abnormally small particle diameters of LDL-4 and -5 were increased to normal. Plasma levels of both apo B-100 and triglycerides were significantly and positively correlated with those of LDL-4 and LDL-5, suggesting not only that the degree of triglyceride elevation is intimately linked to the extent of shift in LDL subclass profile towards denser subspecies, but also that triglyceride reduction upon treatment strongly influences LDL-4 and LDL-5. In conclusion, our findings indicate that ciprofibrate treatment in combined hyperlipidemia results in marked reduction in plasma triglyceride levels (-33%), and that such reduction is intimately linked to normalisation of both the qualitative and quantitative features of the atherogenic LDL subspecies profile typical of this disorder.

Adult↗