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Biomedical subjects

P N Demacker

Publications and source records attributed to P N Demacker.

At least 37 records · Page 2Linked to original sources
PubMed1999

Lipoprotein (a) concentrations in patients with familial combined hyperlipidemia and hypertension.

BACKGROUND: Lipoprotein (a) (Lp(a)) is an independent risk factor for coronary heart disease (CHD), and its association with hyperlipidemia and/or hypertension greatly increases the risk of premature CHD. METHODS: The present study assessed plasma concentrations of Lp(a) in hyperlipidemic subjects from families with well-defined familial combined hyperlipidemia (FCH) (n = 262) and from patients with hypertension (n = 168), and to compare it with Lp(a) plasma levels in healthy volunteers (n = 371). Lp(a) concentrations were measured using a specific radioimmunoassay. RESULTS: The Lp(a) plasma concentrations were similar in FCH patients (median 204 mg/l, range 16-2163 mg/l) and in the control group (155, 16-1846 mg/l; P > 0.05). The Lp(a) levels in patients with hypertension (157, 10-1985 mg/l) did not differ from those of controls (P > 0.05). The Lp(a) concentrations were similar in patients with essential hypertension (EH) and normal lipid levels, and in hyperlipidemic EH patients. A tendency towards higher levels of Lp(a) was observed in patients with secondary hypertension due to renal artery stenosis (RAS) (n = 26, Lp(a) 232, 16-1110 mg/l), but this was not statistically significant. CONCLUSIONS: Plasma concentrations of Lp(a) are similar in patients with FCH, with EH, either normo- or hyperlipidemic, and with RAS, when compared with healthy controls. However, measuring the Lp(a) levels in patients with either hyperlipidemia or hypertension remains important for assessing the risk potential for severe atherosclerosis in these patients.

Aged↗
PubMed1999

Integrin mediated adhesion of mononuclear cells from patients with familial hypercholesterolemia.

BACKGROUND: Low-density lipoproteins (LDL) can induce the adhesion of monocytes to endothelial cells. Monocytes of patients with familial hypercholesterolemia (FH) are exposed to high concentrations of LDL, and it has been reported that adhesiveness of these cells in hypercholesterolemic patients is enhanced. We investigated whether LFA-1 or VLA-4 mediated adhesion is altered in FH patients and whether HMG-CoA reductase inhibitors influence this adhesion. PATIENTS AND METHODS: LFA-1 and VLA-4 mediated adhesion to ICAM-1 and VCAM-1 coated beads was investigated using freshly isolated monocytes and T-lymphocytes from patients with homozygous FH, heterozygous FH (before and after cholesterol lowering treatment), and from controls. In addition, the expression of beta1- and beta2-integrins on these cells was determined. RESULTS: Both LFA-1 and VLA-4 mediated adhesion and integrin expression of monocytes and CD3+ cells from patients with homozygous FH and heterozygous FH was similar to that of monocytes from a control population. Treatment with HMG-CoA reductase inhibitors did not affect the adherence to ICAM-1 or VCAM-1, and did not influence the expression of integrins. CONCLUSIONS: In contrast to studies by others, we demonstrated in the present study that the actual LFA-1 and VLA-4 mediated adhesion of T-lymphocytes and monocytes is not altered in patients with FH.

Adolescent↗
PubMed1999

Infusion of lipoproteins into volunteers enhances the growth of Candida albicans.

Infusion of reconstituted high-density lipoproteins (rHDL) is being studied in clinical trials as an adjunctive therapy for gram-negative sepsis. Since no data are available on its possible effects in systemic candidiasis, we investigated the effect of rHDL infusion into volunteers on the growth of Candida albicans. C. albicans growth was 10- to 100-fold higher in the plasma of volunteers infused with 80 or 100 mg/kg rHDL than in plasma collected before infusion; administration of 60 mg/kg rHDL had marginal effects. In vitro, the isolated lipoprotein subfractions had a growth-promoting effect on C. albicans. These data suggest potential adverse effects of rHDL if infused into patients with systemic candidiasis. Thus, rHDL infusion into patients with sepsis caused by an unknown microorganism may be contraindicated.

Animals↗
PubMed1999

Evaluation of five different high-density lipoprotein cholesterol assays: the most precise are not the most accurate.

We evaluated the accuracy and performance of four different test kits for the direct determination of high-density lipoprotein (HDL)-cholesterol and compared them with the phosphotungstic acid/MgCl2 assay. All four homogeneous assays were precise (within-run CV of < 2.0% and between-run CV of < 6.4%); both assays based on immuno-inhibition had the lowest CVs (within-run 1.3% and 0.9%; between-run 2.3% and 2.2%). Interference from haemolysis was negligible, but triglyceride concentrations gave a negative interference. The effects of conjugated and unconjugated bilirubin were opposite; conjugated bilirubin showed a negative interference of up to 40%; unconjugated bilirubin interfered positively up to 50%. Using the recently validated indirect phosphotungstic acid/MgCl2 method as a comparison, all four homogeneous assays did not fulfil the National Cholesterol Education Program total error standard, mainly due to the positive biases of 12 to 42%, apparently associated with improper calibrators. Both assays involving immuno-inhibition showed a concentration-dependent bias.

Bilirubin↗
PubMed1999

Survey of total error of precipitation and homogeneous HDL-cholesterol methods and simultaneous evaluation of lyophilized saccharose-containing candidate reference materials for HDL-cholesterol.

BACKGROUND: Standardization of HDL-cholesterol is needed for risk assessment. We assessed for the first time the accuracy of HDL-cholesterol testing in The Netherlands and evaluated 11 candidate reference materials (CRMs). METHODS: The total error (TE) of HDL-cholesterol measurements was assessed in native human sera by 25 Dutch clinical chemistry laboratories. Concomitantly, the suitability of lyophilized, saccharose-containing CRMs (n = 11) for HDL-cholesterol was evaluated. RESULTS: In the precipitation method group, which included 25 laboratories and four methods, the mean (minimum-maximum) TE was 11.5% (2.7-25.2%), signifying that 18 of 25 laboratories satisfied the TE goal of </=13% issued by the National Cholesterol Education Program (NCEP). In the homogeneous HDL-cholesterol method group, which included five laboratories, each performing two different methods, the mean (minimum-maximum) TE was 9.5% (6.0-17.3%) for the Boehringer assay and 15.7% (3.3-30.7%) for the Genzyme assay. For the Boehringer homogeneous assay, one of five laboratories did not meet the TE criterion, whereas for the Genzyme homogeneous assay, three of five laboratories exceeded the 13% criterion. The biases on the HDL-cholesterol values found by various precipitation methods were highly variable in all CRMs, irrespective of the quality, whereas the biases found by the homogeneous method from Boehringer were far less than +/-5% for the highest-quality CRMs (CRMs 4-6). CONCLUSIONS: The NCEP goal was met by 24 of 35 laboratories assessed by use of native human sera. Selectively pooled, lyophilized CRMs that are cryoprotected with 200 g/L saccharose have ample potential for use in the standardization of homogeneous HDL-cholesterol methods.

Chemical Precipitation↗
PubMed1999

Apolipoprotein E knock-out mice are highly susceptible to endotoxemia and Klebsiella pneumoniae infection.

Lipoproteins are able to neutralize bacterial lipopolysaccharide (LPS) and thereby inhibit the proinflammatory cytokine response. In a previous study, we demonstrated that hypercholesterolemic low density lipoprotein receptor knock-out (LDLr-/-) mice are protected against lethal endotoxemia and gram-negative infection. In the present study we investigated the susceptibility of apolipoprotein E knock-out mice (apoE-/-) to LPS and to Klebsiella pneumoniae. These mice have increased plasma lipoprotein concentrations in the very low density lipoprotein (VLDL)-sized fraction. Despite 8 -fold higher plasma cholesterol levels compared to controls, and in contrast to LDLr-/- mice, apoE-/- mice were significantly more susceptible to endotoxemia and to K. pneumoniae infection. Circulating TNFalpha concentrations after intravenously injected LPS were 4 - to 5-fold higher in apoE-/- mice, whereas IL-1alpha, IL-1beta, and IL-6 did not differ. This TNF response was not due to an increased cytokine production capacity of cells from apoE-/- mice, as ex vivo cytokine production in response to LPS did not differ between apoE-/- and control mice. The LPS-neutralizing capacity of apoE-/- plasma was significantly less than that of controls. Most likely, the absence of apoE itself in the knock-out mice explains the failure to neutralize LPS, despite the very high cholesterol concentrations.

Animals↗
PubMed1998

Bacterial lipopolysaccharide binds and stimulates cytokine-producing cells before neutralization by endogenous lipoproteins can occur.

Lipoproteins are able to bind to lipopolysaccharide (LPS) and neutralize its deleterious effects. However, it is not clear why the LPS-binding capacity of circulating lipoproteins, which is 10- to 10 000-fold above the maximal LPS concentrations found in septic patients, is not sufficient to inhibit the effects of LPS during an infection, whereas infusion of exogenous lipoproteins has a potent inhibitory action. In this study, the kinetics of LPS-neutralization by VLDL, LDL, and HDL were investigated, at lipoprotein-to-LPS ratios found in severe Gram-negative sepsis. At least 4-8-h preincubation of LPS with either LDL or HDL were necessary to inhibit 50% of the LPS-induced TNF-alpha production by human peripheral blood mononuclear cells (PBMC), whereas after 24 h of preincubation LDL or HDL strongly inhibited the TNF-alpha synthesis (70-90%, P<0.01). VLDL was the least effective lipoprotein fraction. In contrast, FITC-LPS bound to PBMC much more rapidly, with 70% of the total binding after 30 min, and 90% after 1-h incubation. The increase of LDL or HDL concentrations up to 10-fold (as in experimental models of hyperlipoproteinaemia) was able not only to further decrease TNF-alpha production after long LPS-lipoproteins preincubation periods, but also to improve the kinetics of LPS neutralization. In conclusion, LPS binds and stimulates the mononuclear cells in circulation before neutralization by endogenous lipoproteins can occur. Additional increase in the lipoprotein-to-LPS molar ratio (e.g. by infusion of exogenous lipoproteins) accelerates the kinetics of LPS neutralization, and may be useful as adjunctive therapy in severe Gram-negative infections.

Dose-Response Relationship, Drug↗
PubMed1998

Gender-related association between the -93T-->G/D9N haplotype of the lipoprotein lipase gene and elevated lipid levels in familial combined hyperlipidemia.

Familial combined hyperlipidemia (FCHL) is a frequent cause of premature coronary artery disease. Affected family members are characterized by different combinations of elevated cholesterol and/or triglyceride levels. A reduction in lipoprotein lipase (LPL) activity has been observed in a subgroup of FCHL patients. Recently, we have demonstrated an increased frequency of mutations in the LPL gene in Dutch FCHL patients compared to normolipidemic controls. In the present study, we have applied a pedigree-based maximum likelihood method to study the effect of LPL mutations on the phenotypic expression of FCHL in families. In 40 FCHL probandi, three different previously reported mutations in the LPL gene were identified resulting in amino acid changes, D9N, N291S, and S447X. The D9N mutation in exon 2 appeared to be in strong linkage disequilibrium with a T-->G substitution at position -93 in the promoter region of the LPL gene. We present data that the -93T-->G/D9N haplotype is associated with significantly higher levels of LDL and VLDL cholesterol, and VLDL triglycerides. Interestingly, the effect was only observed in male carriers. In line with our previous observations, these results further sustain that the LPL gene is a susceptibility gene for dyslipidemia which explains part of the variability in the phenotype observed among FCHL family members.

Adult↗
PubMed1998

Beta-VLDL accumulation in familial dysbetalipoproteinemia is associated with increased exchange or diffusion of chylomicron lipids to apo B-100 containing triglyceride-rich lipoproteins.

To gain more insight into the accumulation of beta-very low density lipoprotein (beta-VLDL) in familial dysbetalipoproteinemia (FD), we followed the courses of the levels of retinyl palmitate (rp), alpha-tocopherol (alpha-T) and apolipoprotein (apo) B-48 in various lipoprotein fractions for up to 48 h in eight patients with FD and six normolipidemic control subjects after an oral fat load (50 g fat/m2 containing 150000 IU of rp and 5000 IU of alpha-T). Alpha-T was added because of its rapid transfer to other lipoproteins. Fasting apo B-48 concentration in FD was normal to strongly elevated, dependent on the fasting lipid concentrations. 3 h after fat loading, total apo B-48 content did not abnormally increase; while the apo B-100 content in the triglyceride-rich lipoprotein fraction remained stable. The levels of both vitamins increased considerably, especially in the remnant fraction (Sf 15-100), which in due course exclusively contained apo B-100 in most hyperlipidemic patients. This, together with the observation that peaks for rp and alpha-T were observed 3-6 h later than for apo B-48 strongly suggests that both vitamins transfer or diffuse rapidly towards the apo B-100 containing VLDL. RP is thus more a marker for this process, which also comprises chylomicron lipids, than a specific marker for chylomicrons. This process, first described here, appears decisive in the pathogenesis of FD.

Adult↗
PubMed1998

LPS-induced cytokine production and expression of LPS-receptors by peripheral blood mononuclear cells of patients with familial hypercholesterolemia and the effect of HMG-CoA reductase inhibitors.

Inflammatory processes play an important role in atherogenesis, and proinflammatory cytokines such as interleukin-1beta (IL-1beta), IL-6, and tumour necrosis factor alpha (TNFalpha) are thought to be mediators in this phenomenon. We have previously established that peritoneal macrophages of LDL-receptor knock-out mice, which are hypercholesterolemic and are prone to atherosclerosis, have an increased LPS-induced cytokine production capacity, ex vivo. The aim of the present study was to investigate whether the process leading to atherosclerosis in patients with familial hypercholesterolemia (FH) is associated with increased cytokine production capacity of peripheral blood mononuclear cells (PBMC) and/or increased expression of adhesion molecules on monocytes and lymphocytes. Furthermore, we assessed the effect of cholesterol lowering on the production capacity of PBMC, as these drugs are beneficial with regard to cardiovascular diseases. LPS-induced IL-1beta and TNFalpha production by PBMCs of 21 heterozygous FH patients appeared to be similar to the production by PBMCs of 21 healthy volunteers. In addition, expression of the LPS-receptors CD14 and beta2-integrins in nine patients and controls did not differ either. In a second series of experiments, HMG-CoA synthesis inhibitors were ineffective to change the LPS-induced production by PBMC of IL-1alpha, IL-1beta, IL-1 receptor antagonist (IL-1ra), IL-6, and TNFalpha. In conclusion, cytokine production capacity of blood cells or the expression of LPS-receptors on circulating PBMC do not deviate in subjects with FH and also do not change as a result of treatment with cholesterol synthesis inhibitors.

Animals↗
PubMed1998

LPS-induced cytokine production and expression of beta2-integrins and CD14 by peripheral blood mononuclear cells of patients with homozygous familial hypercholesterolemia.

It has been suggested that proinflammatory cytokines such as tumor necrosis factor-alpha (TNF) and interleukin-1beta (IL-1), as well as adhesion molecules such as beta2-integrins and CD14, play a role in the pathogenesis of atherosclerosis. Familial hypercholesterolemia (FH) is an autosomal disease in which defective or absent LDL receptors are the cause for extreme LDL concentrations and early development of atherosclerosis. We studied lipopolysaccharide-induced cytokine production and the expression of adhesion molecules by mononuclear cells of three homozygous FH patients and compared them with first-degree relatives and healthy controls. There was a tendency towards increased cytokine production by cells of FH patients, whereas the expression of adhesion molecules was not modified compared to controls. In addition, LDL-apheresis inhibited IL-1 and TNF production and the expression of CD11a, CD11b, CD11c and CD14 by the mononuclear cells of FH patients and this may be an additional beneficial effect of LDL-apheresis apart of decreasing LDL concentrations.

Adolescent↗
PubMed1998

Fat loading experiments with the vitamins A and E suggest that in postprandial lipemia transfer/diffusion of chylomicron lipids to VLDL contributes to beta-VLDL formation.

Vitamins A and E differ in hydrophobicity. When added to a fat load more or less specific labeling of chylomicrons and their remnants can be expected and this allows to approach the mechanism of postprandial lipemia from a new sight of view. Applied in a study in which 20 patients participated (eight patients with familial dysbetalipoproteinemia (FD), six patients with familial combined hyperlipidemia (FCH) and six controls) we found that vitamin A, no longer paralleled the apo B-48 concentrations from 9 h after a fat load, especially in the remnant fraction with Sf 15-100. Qualitatively, the distribution of vitamin A to the more dense fractions mirrored that of vitamin E, but the latter was more rapid. Both vitamins at the maximum of remnant-accumulation, at 14 h after the fat load, correlated with the cholesterol content of the remnant fraction. For vitamin E there was a similar concentration dependent distribution to all other lipoprotein fractions. The results confirm our view that the lipoprotein mechanism can be regarded as a dynamic system. During regular episodes following the meals, exogenous fat is, like the vitamins, distributed over all endogenously formed lipoproteins. This transfer process results in the formation of beta-VLDL and contributes to the pathogenesis of FCH and FD.

Chylomicrons↗
PubMed1998

Increased interleukin-1alpha and interleukin-1beta production by macrophages of low-density lipoprotein receptor knock-out mice stimulated with lipopolysaccharide is CD11c/CD18-receptor mediated.

Immune mechanisms, including production of pro-inflammatory cytokines such as interleukin-1 (IL-1) and tumour necrosis factor (TNF), play an important role in early atherogenesis. The study of the mechanisms responsible for the increased cytokine production capacity of hypercholesterolemic hosts is therefore crucial for finding new strategies aimed to stop the development of atherosclerosis. We assessed the lipopolysaccharide (LPS)-induced cytokine production of macrophages from low-density lipoproteins (LDL)-receptor knock-out (LDLR-/-) mice, which have a seven- to ninefold higher plasma LDL concentration. Macrophages of LDLR-/- mice produced approximately twofold more IL-1alpha and IL-1beta in response to LPS when compared with macrophages of control mice (LDLR+/+). TNF-alpha synthesis was only slightly increased. Removal of CD14 by phospholipase C treatment of cells decreased cytokine production by 50% (IL-1) to 80% (TNF), but the differences between LDLR-/- and LDLR+/+ remained the same. In contrast, treatment of cells with anti-CD11c monoclonal antibody inhibited the IL-1alpha and IL-1beta production in LDLR-/- mice towards normal values, while no effect could be seen on TNF. In conclusion, LDLR-/- macrophages stimulated with LPS synthesize more IL-1alpha and IL-1beta than controls and this phenomenon is mediated by the CD11c/CD18 receptor.

Animals↗
PubMed1998

A common genetic mechanism determines plasma apolipoprotein B levels and dense LDL subfraction distribution in familial combined hyperlipidemia.

Familial combined hyperlipidemia (FCH) is a common lipid disorder characterized by elevations of plasma cholesterol and/or triglyceride in first-degree relatives. A predominance of small, dense LDL particles and elevated apolipoprotein B (apoB) levels is commonly found in members of FCH families. Many studies have investigated the genetic mechanisms determining individuals' lipid levels, in FCH families. Previously, we demonstrated a major gene effect on LDL particle size and codominant Mendelian inheritance involved in determination of apoB levels in a sample of 40 well-defined FCH families. An elevation of apoB levels is associated metabolically with a predominance of small, dense LDL particles in FCH. To establish whether a common gene regulates both traits, we conducted a bivariate genetic analysis to test the hypothesis of a common genetic mechanism. In this study, we found that 66% of the total phenotypic correlation is due to shared genetic components. Further bivariate segregation analysis suggested that both traits share a common major gene plus individual polygenic components. This common major gene explains 37% of the variance of adjusted LDL particle size and 23% of the variance of adjusted apoB levels. Our study suggests that a major gene that has pleiotropic effects on LDL particle size and apoB levels may be the gene underlying FCH in the families we studied.

Apolipoproteins B↗
PubMed1998

Posttranscriptional down-regulation of tumor necrosis factor-alpha and interleukin-1beta production in acute meningococcal infections.

The regulation of tumor necrosis factor-alpha (TNF) and interleukin-1beta (IL-1beta) production was studied in patients with meningococcal disease. Circulating TNF and IL-1beta normalized within 1 day. TNF mRNA and IL-1beta mRNA in white blood cells decreased over 3-4 days. During the acute stage, TNF and IL-1beta production in stimulated whole blood cultures was down-regulated. After 4-5 days, this production was restored. The down-regulation was unlikely to be caused by circulating IL-6 and IL-10, as these cytokines normalized within 2-3 days. TNF mRNA in stimulated cultures during the acute stage, with down-regulated production, did not differ from that at recovery, with restored production. In contrast, the down-regulated production of IL-1beta was associated with significantly lower IL-1beta mRNA levels. Thus, TNF and IL-1beta production are differentially regulated. Whereas TNF production is regulated posttranscriptionally, IL-1beta production is also regulated at the mRNA level.

Anti-Bacterial Agents↗
PubMed1998

Lipoprotein(a) inhibits lipopolysaccharide-induced tumor necrosis factor alpha production by human mononuclear cells.

Lipoproteins can bind lipopolysaccharide (LPS) and decrease LPS-stimulated cytokine production. Lipoprotein(a) [Lp(a)] was as potent as low-density lipoproteins (LDL) in inhibiting LPS-stimulated tumor necrosis factor synthesis by human mononuclear cells. The kinetics of LPS inhibition by Lp(a) was similar to that of LDL. This suggests that circulating Lp(a) may be an important factor determining the amplitude of the response to LPS in humans.

Humans↗