Biomedical subjects

M J Janssen

Publications and source records attributed to M J Janssen.

At least 19 recordsLinked to original sources

PubMed2001

A fluorescent receptor assay for benzodiazepines using coumarin-labeled desethylflumazenil as ligand.

This article describes a novel nonisotopic receptor assay for benzodiazepines with fluorescence detection. As labeled ligand (coumarin-labeled desethylflumazenil, CLDEF), a metabolite of the benzodiazepine antagonist flumazenil (desetheylflumazenil, Ro15-3890) has been coupled to a coumarin fluorophore, via a spacer. CLDEF had a Ki of 6.5 nM. To avoid the interference of the background fluorescence of the receptors in the measurement step, the bound CLDEF was dissociated from the receptors after the filtration step. This dissociation was achieved by incubating the CLDEF-bound to the receptors on the filters-with a weakly acetate buffer. The second filtrates then contained the previously bound CLDEF, which was then quantitated with a RP-HPLC system with a fluorescence detector. The results with a fluorescent receptor assay were very similar to those with a radioreceptor assay, in that the IC50 values of lorazepam were 7.2 +/- 0.5 and 6.6 +/- 0.7 nM, respectively.

Animals↗

PubMed2001

Bactericidal properties of group IIA and group V phospholipases A2.

Group V phospholipase A(2) (PLA(2)) is a recently characterized 14-kDa secretory PLA(2) of mammalian heart and macrophage-derived cells. Group IIA PLA(2), which is structurally close to group V PLA(2), has been shown to kill Gram-positive bacteria in vitro and to prevent symptoms of Gram-positive infection in vivo. We studied the antibacterial properties of fully active recombinant rat group IIA and V PLA(2)s. Both group IIA and V PLA(2)s were highly bactericidal against Gram-positive bacteria, including methicillin-resistant staphylococci and vancomycin-resistant enterococci. Only high concentrations of group IIA PLA(2) showed some bactericidal effect against the Gram-negative bacterium Escherichia coli. Our results confirm that group IIA PLA(2) is a potent antibacterial enzyme against Gram-positive bacteria. Moreover, we show here that group V PLA(2) is a novel antibacterial mammalian protein, but is less potent than group IIA PLA(2). Both enzymes may be considered as future therapeutic agents against bacterial infections.

Animals↗

PubMed2001

A systematic comparison of triple therapies for treatment of Helicobacter pylori infection with proton pump inhibitor/ ranitidine bismuth citrate plus clarithromycin and either amoxicillin or a nitroimidazole.

BACKGROUND: Triple therapies with proton pump inhibitor/ranitidine bismuth citrate (RBC), clarithromycin (C) and either amoxicillin (A) or a nitroimidazole (I) are widely accepted as treatment for Helicobacter pylori infection. However, it is not clear which of these antibiotic combinations should be preferred. AIM: To evaluate whether there is a difference in efficacy between triple therapies with proton pump inhibitor/RBC, clarithromycin and either amoxicillin or a nitroimidazole. METHODS: The literature was examined for randomized trials comparing proton pump inhibitor/RBC-C-A and proton pump inhibitor/RBC-C-I. Studies were grouped according to the type of acid inhibitor used (proton pump inhibitor or RBC) and differences between pooled cure rates were calculated. RESULTS: Forty-seven studies were identified: seven using RBC, 39 using proton pump inhibitor, one using both. RBC-C-I was somewhat superior to RBC-C-A, although this difference only reached statistical significance in intention-to-treat analysis. Overall, proton pump inhibitor-C-I and proton pump inhibitor-C-A were equally effective, but in nitroimidazole-susceptible strains, proton pump inhibitor-C-I performed better, in nitroimidazole-resistant strains, proton pump inhibitor-C-A performed better. No serious side-effects were reported and pooled drop-out rates were equal. CONCLUSIONS: In general, proton pump inhibitor-C-I and proton pump inhibitor-C-A are equally effective and therefore other factors such as local prevalence of resistant strains, cost of therapy and options for second-line treatment should determine which regimen should be preferred. When using RBC, the RBC-C-I combination is somewhat superior to RBC-C-A.

Amoxicillin↗

PubMed2000

Control of the chemical step by leucine-31 of pancreatic phospholipase A2.

A well-defined region of pancreatic and other secreted phospholipase A2 (PLA2), which we call the i-face, makes a molecular contact with the interface to facilitate and control the events and processivity of the interfacial catalytic turnover cycles. The structural features of the i-face and its allosteric relationship to the active site remain to be identified. As a part of the calcium binding (26-34) loop, Leu-31 is located on the surface near the substrate binding slot of PLA2. Analysis of the primary rate and equilibrium parameters of the Leu-31 substitution mutants of the pig pancreatic PLA2 shows that the only significant effect of the substitution is to impair the chemical step at the zwitterionic interface in the presence of added NaCl, and only a modest effect is seen on kcat at the anionic interface. Leu-31 substitutions have little effect on the binding of the enzyme to the interface; the affinity for certain substrate mimics is modestly influenced in W3F, L31W double mutant. The fluorescence emission results with the double mutant show that the microenvironment of Trp-31 is qualitatively different at the zwitterionic versus anionic interfaces. At both of the interfaces Trp-31 is not shielded from the bulk aqueous environment as it remains readily accessible to acrylamide and water. The NaCl-induced change in the Trp-31 emission spectrum of the double mutant on the zwitterionic interface is similar to that seen on the binding to the anionic interface. Together, the kinetic and spectroscopic results show that the form of PLA2 at the zwitterionic interface (Ez) is distinguishably different from the catalytically more efficient form at the anionic interface (Ea). This finding provides a structural basis for the two-state model for kcat activation by the anionic interface. In conjunction with earlier results we suggest that neutralization of certain cationic residues of PLA2 exerts a control on the calcium loop through residue 31.

Amino Acid Substitution↗

PubMed2000

Regulation of the expression of group IIA and group V secretory phospholipases A(2) in rat mesangial cells.

Rat mesangial cells synthesize and secrete a secretory phospholipase A(2) upon stimulation of the cells with cytokines, like IL-1beta and TNF and with cAMP elevating agents like forskolin. This enzyme was previously characterized to belong to group IIA sPLA(2). The discovery of several other low molecular weight phospholipases, like group IIC in murine testis and group V in human and rat heart, prompted investigations on the presence of group IIC and group V sPLA(2) in rat mesangial cells. This was done by isolating the RNA from stimulated cells and performing RT-PCR, using primers specific for group IIC and V sPLA(2). The results indicate that rat mesangial cells upon stimulation express next to group IIA also group V sPLA(2). No indications were obtained for the expression of group IIC sPLA(2). The regulation of the expression of group V sPLA(2) at the mRNA level was further investigated by examining the time-dependent expression, the influence of dexamethasone and the signaling route of the IL-1beta stimulation. The results show that the IL-1beta induced expression of group V sPLA(2) mRNA was time dependent and, similar to that of group IIA sPLA(2) mRNA, involves activation of NF-kappaB. However, in contrast to the group IIA sPLA(2), the expression of group V sPLA(2) was not influenced by the presence of dexamethasone. The expression of both phospholipases was also examined at the protein level in stimulated mesangial cells. Western blot analysis shows that stimulated mesangial cells synthesize both group IIA and group V sPLA(2) protein but the expression of group V is lower compared to that of group IIA sPLA(2). In addition, the extent of secretion into the medium appears to be considerably higher for group IIA than for group V sPLA(2).

Animals↗

PubMed2000

The phosphatidylcholine to phosphatidylethanolamine ratio of Saccharomyces cerevisiae varies with the growth phase.

This study compares the effect of the growth phase on the phospholipid composition and the activity of several phospholipid biosynthetic enzymes in a wild-type yeast grown in fermentable (glucose) and non-fermentable (lactate) semi-synthetic and complete synthetic media. Several distinct differences as well as similarities were found. The cellular phosphatidylcholine: phosphatidylethanolamine (PC:PE) ratio was found to vary with the growth phase, with increases in PC levels at the expense of PE during the transition to stationary phase. The variation was most pronounced in semi-synthetic lactate medium, which is routinely used for the isolation of mitochondria, where the PC:PE ratio changed from 0.9 to 2.2 during this transition. Similar growth phase-dependent changes in PC and PE content were observed in isolated organelles such as mitochondria, mitochondria-associated membranes and microsomes. Phosphatidylinositol (PI) levels were much higher in cells grown on lactate compared to cells grown on glucose (20% vs. 5-10%). Irrespective of the medium, PI levels increased upon entering stationary phase. The activities of the phospholipid biosynthetic enzymes phosphatidylserine synthase and the phospholipid-N-methyltransferases were found to be maximal at the end of logarithmic growth and to decrease upon entering stationary phase in all media. Cells grown on lactate displayed a significantly higher phospholipid:protein ratio than cells grown on glucose. The results are discussed in terms of regulation of phospholipid biosynthesis and membrane biogenesis in response to growth phase and carbon source.

Carbon↗

PubMed2000

Fluorescent-labeled ligands for the benzodiazepine receptor. Part 1: Synthesis and characterization of fluorescent-labeled benzodiazepines.

Because radioactive labeled ligands in receptor assays have several disadvantages, we synthesized a number of fluorescent-labeled benzodiazepines. Several fluorophores were attached at different positions of 1,4-benzodiazepine molecules in order to assess the impact of the fluorophores and their coupling position on the affinity for the benzodiazepine receptor. Besides the 1,4-benzodiazepines, the 1,2-annelated 1,4-benzodiazepines were also used for labeling. A metabolite of flumazenil (18), desethylflumazenil (Ro15-3890, 19), was labeled with the fluorophore 4-bromomethyl-7-methoxycoumarin, with and without the incorporation of a spacer chain, yielding the methyl-methoxycoumarin (Mmc) derivatives Mmc-Ro15-3890 (20a) and Mmc-O-CO-(CH2)3-Ro15-3890 (20b), respectively. After the synthesis, the fluorescent-labeled benzodiazepines were purified by HPLC, using an analytical RP-C18 column. For the purification of 20b, the chromatographic system was optimized, using multi-criteria decision making (MCDM) techniques. The binding affinities for the benzodiazepine receptor and the fluorescence characteristics were determined for the resulting products.

Animals↗

PubMed2000

Fluorescent-labeled ligands for the benzodiazepine receptor. Part 2: The choice of an optimal fluorescent-labeled ligand for benzodiazepine receptor assays.

In this article, the binding affinities of the fluorescent-labeled benzodiazepines described in Part 1 are compared to assess the influence of the labeling position and the choice of fluorophore on the binding affinity. This comparison was extended by taking into account the data of other fluorescent-labeled benzodiazepines in the literature. The differences in the binding affinities observed could partly be explained by structure-activity relationships (SAR). On the basis of this comparison, fluorescent-labeled desethylflumazenil (Ro15-3890, 19) derivatives were selected as the most suitable labeled ligands in fluorescent receptor assays. A methyl-methoxycoumarin derivative (Mmc-O-CO-(CH2)3-Ro15-3890) (20b) had a Ki-value of 6.5 nM, and a 7-nitrobenz-2-oxa-1,3diazole derivative (NBD-NH-(CH2)3-Ro15-3890, 21) had a Ki-value of 5.7 nM. In order to yield sufficient sensitivity in the final receptor assay, a suitable fluorescent labeled ligand should have a Ki < 10 nM. A further advantage of the above two ligands is that the benzodiazepine moiety has no receptor affinity of its own. Thus, if some hydrolysis of the labeled ligand were to occur, the resulting Ro15-3890 (18) would hardly affect the outcome of the assay. In the second part of this paper the prerequisites of the fluorophore are being examined. In this regard, 20b is preferred, because the coumarin derivative has higher fluorescence intensities in aqueous media than the NBD-derivative. Therefore, 20b was selected as a fluorescent-labeled ligand in the development of a non-radioactive receptor assay for benzodiazepines.

Animals↗

PubMed1999

Transbilayer movement of phosphatidylcholine in the mitochondrial outer membrane of Saccharomyces cerevisiae is rapid and bidirectional.

The process of transmembrane movement of phosphatidylcholine (PC) across the outer membrane of mitochondria was investigated in vitro in mitochondrial outer membrane vesicles (OMV) from the yeast Saccharomyces cerevisiae. Phosphatidylcholine-transfer protein (PC-TP) was used to extract radiolabeled PC from OMV, with small unilamellar vesicles serving as acceptor system. Endogenously radiolabeled PC synthesized either via the CDP-choline pathway or via methylation of phosphatidylethanolamine can be extracted completely from the OMV with a t(1/2) of 1 min or less at 30 degrees C. The size of the pool of PC in OMV available for exchange by PC-TP is not affected by pretreatment of the OMV with proteinase K or sulfhydryl reagents. In the reverse experiment where radiolabeled PC was introduced into the OMV, similar characteristics for the exchange were found. The accessibility of labeled PC to externally added phospholipase A(2) was used as a measure for its transmembrane distribution. It was found that PC is not exclusively located in the outer leaflet of the OMV. Only 30-35% can be degraded in intact OMV by phospholipase A(2), irrespective of whether the PC is introduced by PC-TP or endogenously synthesized via either of the pathways of biosynthesis. The results demonstrate the occurrence of rapid bidirectional transbilayer movement of both endogenous and in vitro introduced PC in OMV. Furthermore, there appears to be no preference for mitochondrial import of PC synthesized by either of the pathways in vivo.

Carbon Radioisotopes↗

PubMed1999

Enzymatic properties of rat group IIA and V phospholipases A(2) compared.

Group IIA and V phospholipases A(2) (PLA(2)s) are known to play a role in inflammatory responses. We have constructed a bacterial expression vector for rat group IIA and V PLA(2)s, over-expressed, folded and purified the proteins with the aim to study and compare the properties of the enzymes in detail. For zwitterionic phospholipid micelles, both enzymes display optimum activity at pH 8. 0 and absolutely require Ca(2+) for enzymatic activity. In the presence of substrate, group V PLA(2) has a high affinity for Ca(2+) (K(Ca2+)=90 microM) while K(Ca2+) of group IIA PLA(2) was found to be 1.6 mM. The absence of substrate only marginally influences the Ca(2+) affinities. In contrast to group IIA PLA(2), group V PLA(2) does not show a jump in the activity profile at substrate concentrations around the critical micelle concentration. Direct binding studies using n-alkylphosphocholines indicate that group V PLA(2) forms protein-lipid aggregates at pre-micellar lipid concentrations in a cooperative and Ca(2+)-dependent manner. This behavior, which is comparable to that observed for the PLA(2) from Naja melanoleuca snake venom, reflects the high affinity of this enzyme for zwitterionic phospholipids. Competitive inhibition by the substrate analogues (R)-2-dodecanoylaminohexanol-1-phosphocholine and its phosphoglycol derivative was tested on zwitterionic micelles as substrate. Group IIA PLA(2) shows a preference for the phosphoglycol inhibitor whereas the phosphocholine inhibitor binds stronger to the active site of group V PLA(2). The enzymatic activity was also measured on zwitterionic liposomes which appear to be much better substrates for group V PLA(2) than for group IIA PLA(2). The overall results suggest that group V PLA(2) is better suited for action on biological membranes than group IIA PLA(2).

Amino Acid Sequence↗

PubMed1999

Improved benzodiazepine radioreceptor assay using the MultiScreen Assay System.

In this article, an improved benzodiazepine radioreceptor assay is described, which allows substantial reduction in assay time. The filtration in this method was performed by using the MultiScreen Assay System. The latter consists of a 96-well plate with glass fibre filters sealed at the bottom, which allows both the incubation and the filtration of the specimen in the same plate. After the filtration, the filters were punched out for quantitation of the bound labeled ligand [3H]flunitrazepam. The results obtained with the MultiScreen Assay System did not differ significantly from the data obtained with the conventional filtration manifold (48S): The Ki's of lorazepam were 2.4 +/- 0.30 and 1.9 +/- 0.15 nM, respectively. In case a radioactive label is replaced by a fluorescent label, the bound labeled-ligand usually cannot be determined in the presence of the receptor material. Here, the bound labeled-ligand has to be dissociated after the filtration step. To dissociate the ligand-receptor complex, Tris- HCl buffer, containing 10 microM flumazenil, was added to the filters and the second filtrates were collected containing the previously bound fractions in the absence of receptor material. This approach showed the same Ki for lorazepam, 2.5 +/- 0.04 nM as without dissociation, when using the radio-labeled benzodiazepine [3H]flunitrazepam.

Filtration↗

PubMed1999

Effect of folic acid and betaine on fasting and postmethionine-loading plasma homocysteine and methionine levels in chronic haemodialysis patients.

OBJECTIVES: To study fasting and postmethionine-loading (increment and decrement) plasma homocysteine levels in end-stage renal disease (ESRD) patients in relation to B-vitamin status and after folic acid treatment without or with betaine. DESIGN: Plasma total homocysteine (tHcy) and methionine levels were measured in chronic haemodialysis patients after an overnight fast, and 6 and 24 h after an oral methionine load (0.1 g kg-1). The patients were subsequently randomized to treatment with folic acid 5 mg daily with or without betaine 4 g daily, and the loading test was repeated after 12 weeks. The patients were then re-randomized to treatment with 1 or 5 mg folic acid daily for 40 weeks, after which a third loading test was performed. SETTING: Haemodialysis unit of university hospital and centre for haemodialysis. SUBJECTS: Twenty-nine consecutive maintenance (> 3 months) haemodialysis patients, not on folic acid supplementation, 26 of whom completed the study. RESULTS: At baseline, the mean fasting, the 6 h postload and the 6 h postload increment plasma tHcy levels were increased as compared with those in healthy controls (46.8 +/- 6.9 (SEM), 92.8 +/- 9.1 and 46.0 +/- 4.2 mumol L-1, respectively) and correlated with serum folate (r = -0.42, P = 0.02; r = -0.61, P = 0.001 and r = -0.54, P = 0.003, respectively), but not with vitamin B6 or vitamin B12. At week 12, these variables had all decreased significantly. Betaine did not have additional homocysteine-lowering effects. At week 52, fasting and postload tHcy levels did not differ significantly between patients on 1 or 5 mg folic acid daily. Plasma tHcy half-life and plasma methionine levels after methionine loading were not altered by folic acid treatment. CONCLUSIONS: In chronic haemodialysis patients, fasting as well as postmethionine-loading plasma tHcy levels depend on folate status and decrease after folic acid therapy. Increased postload homocysteine levels in these patients therefore do not necessarily indicate an impaired transsulphuration capacity only; alternatively, folate may indirectly influence transsulphuration. The elucidation of the complex pathogenesis of hyperhomocysteinaemia in chronic renal failure requires further investigation.

Adult↗

PubMed1999

Engineering the disulphide bond patterns of secretory phospholipases A2 into porcine pancreatic isozyme. The effects on folding, stability and enzymatic properties.

Secretory phospholipases A2 (PLA2s) are small homologous proteins rich in disulphide bridges. These PLA2s have been classified into several groups based on the disulphide bond patterns found [Dennis, E. A. (1997) Trends Biochem. Sci. 22, 1-2]. To probe the effect of the various disulphide bond patterns on folding, stability and enzymatic properties, analogues of the secretory PLA2s were produced by protein engineering of porcine pancreatic PLA2. Refolding experiments indicate that small structural variations play an important role in the folding of newly made PLA2 analogues. Introduction of a C-terminal extension together with disulphide bridge 50-131 gives rise to an enzyme that displays full enzymatic activity having increased conformational stability. In contrast, introduction of a small insertion between positions 88 and 89 together with disulphide bridge 86-89 decreases the catalytic activity significantly, but does not change the stability. Both disulphide bridges 11-77 and 61-91 are important for the kinetic properties and stability of the enzyme. Disulphide bridge 11-77, but not 61-91, was found to be essential to resist tryptic breakdown of native porcine pancreatic PLA2.

Animals↗

PubMed1999

Introduction of a C-terminal aromatic sequence from snake venom phospholipases A2 into the porcine pancreatic isozyme dramatically changes the interfacial kinetics.

Porcine pancreatic phospholipase A2 (PLA2) was modified by single and multiple site-directed mutations at sites thought to be involved in interfacial binding. Charged and polar residues in the C-terminal region were replaced by aromatic residues on the basis of an analogy with snake venom PLA2s, which display high affinity for a zwitterionic interface. The PLA2 variants constructed were N117W, N117W/D119Y and K116Y/N117W/D119Y. Titration with micelles of a zwitterionic substrate suggests that the variants N117W and K116Y/N117W/D119Y possess improved ability to bind to the micellar substrate interface, relative to the wild-type enzyme. Improved interfacial binding was confirmed by direct binding studies with micelles of a zwitterionic substrate analogue, indicating up to five times higher affinity for both variants. Interfacial binding is not improved for the variant N117W/D119Y. Maximal enzyme velocities (Vapp./max) with the zwitterionic substrate were between 25 and 75% of that of the wild-type enzyme. However, competitive inhibition and direct binding studies with a strong inhibitor revealed that the affinity for substrate present at the interface (Km*) is perturbed by the mutations made. For the variant N117W, the slight decrease observed in Vapp./max is most likely made up of a 24-fold reduction in catalytic turnover (kcat) and 18-fold improved substrate binding (Km*).

Amino Acid Substitution↗

PubMed1999

Catalytic role of the active site histidine of porcine pancreatic phospholipase A2 probed by the variants H48Q, H48N and H48K.

The catalytic contribution of His48 in the active site of porcine pancreatic phospholipase A2 was examined using site-directed mutagenesis. Replacement of His48 by lysine (H48K) gives rise to a protein having a distorted lipid binding pocket. Activity of this variant drops below the detection limit which is 10(7)-fold lower than that of the wild-type enzyme. On the other hand, the presence of glutamine (H48Q) or asparagine (H48N) at this position does not affect the structural integrity of the enzyme as can be derived from the preserved lipid binding properties of these variants. However, the substitutions H48Q and H48N strongly reduce the turnover number, i.e. by a factor of 10(5). Residual activity is totally lost after addition of a competitive inhibitor. We conclude that proper lipid binding on its own accelerates ester bond hydrolysis by a factor of 10(2). With the selected variants, we were also able to dissect the contribution of the hydrogen bond between Asp99 and His48 on conformational stability, being 5.2 kJ/mol. Another hydrogen bond with His48 is formed when the competitive inhibitor (R)-2-dodecanoylamino-hexanol-1-phosphoglycol interacts with the enzyme. Its contribution to binding of the inhibitor in the presence of an interface was found to be 5.7 kJ/mol.

Animals↗

PubMed1998

The effect of renal transplantation on hyperhomocysteinaemia in dialysis patients, and the estimation of renal homocysteine extraction in patients with normal renal function.

BACKGROUND: The pathophysiology of hyperhomocysteinaemia in chronic renal failure (CRF) is unknown. Possible mechanisms are decreased renal homocysteine (Hcy) catabolism or inhibition of extrarenal Hcy metabolism by uraemic toxins. METHODS: We studied the short-term effect on plasma Hcy concentration of improvement of renal function after successful kidney transplantation (n = 8), and determined renal Hcy extraction by measurement of total Hcy in arterial and renal venous blood in 7 cardiac patients with normal renal function. RESULTS: Post-transplantation, plasma Hcy decreased with improving renal function. In the cardiac patients, no significant renal Hcy extraction could be demonstrated, but tubular disposal of the filtered load could not be excluded. CONCLUSIONS: Because loss of such renal metabolism could lead to hyperhomocysteinaemia in CRF, it is necessary to determine the renal extraction of free Hcy in subjects with normal renal function to further investigate renal homocysteine metabolism.

Adult↗

PubMed1998

No change in impaired endothelial function after long-term folic acid therapy of hyperhomocysteinaemia in haemodialysis patients.

BACKGROUND: Hyperhomocysteinaemia is frequent in chronic haemodialysis patients. Because of its potential role in athero- and thrombogenesis, the effects of long-term homocysteine-lowering treatment on endothelial function are of interest. METHODS: We conducted a randomized, controlled trial in 35 haemodialysis patients. In phase 1, patients were treated with 5 mg folic acid or 5 mg folic acid and 4 g betaine per day for 12 weeks, and in phase 2 with 1 or 5 mg folic acid daily for 40 weeks. In phase 3, all patients received 15 mg folic acid daily for four weeks. Endothelial function was assessed before and after 52 weeks of treatment by determination of flow-mediated vasodilatation of the brachial artery, and by measuring plasma levels of endothelium-derived proteins. RESULTS: Non-fasting predialysis plasma total homocysteine was markedly elevated at baseline (46.9 +/- 6.3 mumol/l) and decreased rapidly after initiation of therapy. Significant differences in plasma homocysteine between the groups were found neither during phase 1 nor phase 2. Plasma total homocysteine had normalized in only two out of 30 patients at the end of phase 2. Increasing the daily folic acid dose to 15 mg did not further reduce plasma total homocysteine. Endothelial function parameters did not improve. CONCLUSIONS: We concluded that betaine is not effective in conjunction with folic acid in the treatment of hyperhomocysteinaemia in haemodialysis patients. Normalization of plasma total homocysteine is seldom achieved with 1, 5 or 15 mg folic acid daily, which may explain why long-term homocysteine-lowering treatment with 1 or 5 mg folic acid does not ameliorate endothelial function.

Adult↗

PubMed1998

Endothelium-dependent vasodilatation is impaired in peritoneal dialysis patients.

BACKGROUND: Peritoneal dialysis (PD) patients have a high risk of cardiovascular mortality, which is not completely explained by conventional risk factors. Other factors related to chronic renal failure and/or dialysis treatment might lead to endothelial dysfunction, which is associated with an adverse cardiovascular outcome. One such factor is hyperhomocysteinaemia, which has a high prevalence in PD patients. METHODS: A vessel wall movement detector system was used to investigate endothelium-dependent, flow-mediated, and endothelium-independent, glyceryl trinitrate-induced, vasodilatation of the brachial artery in 29 PD patients and 29 control subjects. RESULTS: Endothelium-dependent vasodilatation was markedly reduced in the PD group: 5.7 +/- 1.0% vs 10.4 +/- 1.3% in the control group (P = 0.004). Endothelium-independent vasodilatation was not impaired. Plasma total homocysteine was elevated in the PD patients (45.2 +/- 6.2 micromol/l), but was not related to endothelium-dependent vasodilatation. CONCLUSION: Chronic peritoneal dialysis patients have impaired endothelium-dependent vasodilatation, which may reflect an increased susceptibility for the development of atherosclerosis and thrombosis.

Arteriosclerosis↗