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Biomedical subjects

A Dhondt

Publications and source records attributed to A Dhondt.

At least 19 recordsLinked to original sources
PubMed2003

Survival of hemodialysis patients and uremic toxin removal.

Uremic toxin removal based on diffusion and/or convection allows eliminating solutes with negative metabolic impact. Uremic solutes can be classified as small and water-soluble compounds, larger "middle" molecules, or protein bound solutes. The question arises whether more removal of each of these solute classes affects patient survival. Kt/V of urea is currently used as a surrogate for small water-soluble solute removal. There is ample evidence that Kt/V and survival are correlated, but the threshold Kt/V remains a matter of debate. Probably, the actually proposed threshold of 1.2 is too low. This impact of Kt/V is in contradiction with the low toxicity of urea and points to a role for other water-soluble solutes, e.g., potassium. More removal of middle molecules results in a lower morbidity and also in a lower mortality. In addition, a relationship has been demonstrated between the use of membranes with large pore size and a decrease of inflammatory status, by itself an important factor related to mortality. One of the problems is that large pore membranes are at the same time more biocompatible and reflect more dialysate impurities, compared to many small pore membranes, whereas they also reflect more dialysate impurities. It remains uncertain which one of these factors, if any, has a predominant effect. Recent studies point to a separate effect of pore size but await confirmation. Protein bound toxins inhibit several biochemical functions. Their removal pattern is totally different from that of classical markers such as urea. In analogy with drugs, it is essentially the free unbound fraction that exerts biological action; this free fraction is inversely related to serum albumin, another inflammatory marker related to survival. In a final section of this presentation, attention will be drawn to the relationship in uremic patients between inflammation, malnutrition, cardiovascular disease, and mortality, and some of the potential culprits are discussed. Virtually all of these molecules have a high molecular weight or are protein bound. It is concluded that both small and middle molecule removal have an impact on survival, so that more than urea removal alone should be pursued.

Humans↗
PubMed2002

The ionized fraction of serum total magnesium in hemodialysis patients: is it really lower than in healthy subjects?

AIM OF THE STUDY: Based on data in the literature, it remains unclear whether the ionized fraction of serum total magnesium (Mg) is lower in chronic hemodialysis (HD) patients compared to healthy subjects. PATIENTS AND METHODS: The ionized fraction of serum total Mg was investigated in 49 HD patients, pre- and post-dialysis, and compared to 30 healthy controls. The quality of the analytical performance of the Mg measurements has been emphasized by applying a reference method and/or rigorous internal quality control (IQC). In addition, the ionized fraction of serum total calcium (Ca) was measured in both populations, because the results for Mg should be related to those of Ca. RESULTS: In HD patients, the ionized fraction of serum total Mg was on average 65% (pre-dialysis 64.2% and post-dialysis 66.2%). In healthy controls, the ionized fraction was 64.9%. When the analytical variability was taken into account, no significant differences (p > 0.05) were observed between pre- and post-dialysis samples and controls. For Ca, an ionized fraction of 55.3% was found in HD patients, which was not significantly different from the fraction obtained in the control group (55.7%). CONCLUSION: The present study demonstrates that, compared to healthy controls, the ionized fraction of serum total Mg is not different in hemodialysis patients.

Aged↗
PubMed2001

The anti-proliferative effect of calcitriol on HL-60 cells is neutralized by uraemic biological fluids.

BACKGROUND: It has been demonstrated that uraemic serum/ultrafiltrate inhibits cell-mediated immune response in vitro, and that it suppresses calcitriol synthesis and its biological actions. METHODS: In the present in vitro study, the effect of calcitriol, uraemic ultrafiltrate (UUF) and a combination of both on the human promyelocytic leukaemia cell line, HL-60, was studied by evaluating bromodeoxyuridine (BrdU) incorporation into the DNA, luminol-amplified chemiluminescence (CL) production, expression of CD14, and levels of vitamin D receptor mRNA (VDR mRNA) and CD14 mRNA. RESULTS: The ability of calcitriol to block cell proliferation (37.4+/-5.4 to 30.5+/-5.6% cells incorporating BrdU, P:<0.01) was neutralized when UUF was applied together with calcitriol (53.4+/-21.3% cells incorporating BrdU, P:<0.01 vs calcitriol alone). Similarly to what was observed for BrdU incorporation, the CL production of HL-60 cells was enhanced in the presence of calcitriol (20126+/-10154 to 61528+/-24021 cpm, P:<0.01), and was suppressed again in the presence of calcitriol and UUF (20916+/-12075 cpm, P:<0.01 vs calcitriol alone); finally UUF also inhibited the calcitriol-induced CD14 expression (71.1+/-11.2 to 54.9+/-17.7% CD14 positive cells, P:<0.05). On the other hand, the calcitriol-induced CD14 mRNA levels were not significantly different in the presence of calcitriol and UUF compared to calcitriol alone. This points to an inhibition by UUF at a post-transcriptional level. Similar data were found for VDR mRNA levels. UUF was fractionated by HPLC in four fractions, hydrophilic uraemic solutes being eluted first (F1) and hydrophobic solutes being eluted last (F4); fractions 1, 2 and 3 simultaneously affected both BrdU incorporation and CL production in a significant way. CONCLUSIONS: It is concluded that UUF contains factors that impair calcitriol-activated function of HL-60 cells. Hence, the differentiation and immune response of these promyelocytic leukaemia cells, as induced by the supplementation of calcitriol, is neutralized in the presence of uraemic biological fluids. This may be of relevance for the propensity to infection and malignancy of the uraemic patient.

Biological Factors↗
PubMed2001

Heparin-induced release of protein-bound solutes during hemodialysis is an in vitro artifact.

BACKGROUND: Several studies have pointed to a release of drugs or protein-bound solutes from their binding sites during heparinization. The effect is attributed to the metabolism of triglycerides to free fatty acids (FFAs), which compete with drugs for protein binding sites. This study evaluated the impact of intradialytic heparin on the free concentration of the uremic toxin p-cresol and on FFAS: METHODS: Blood samples from hemodialysis (HD) patients, before and during HD, were collected with selected anticoagulation strategies. We assessed the effects of standing time, temperature, pH, and the addition of a lipase inhibitor, tetrahydrolipstatin (THL) to blood samples on the free p-cresol concentration. p-Cresol was analyzed by HPLC with fluorescence detection. We measured FFAs by gas chromatography, and the free fractions of added valproic acid and phenytoin were evaluated by fluorescence polarization immunoassay. RESULTS: In blood samples (n = 22) not submitted to a specific treatment, free p-cresol increased from 9.9 +/- 5.1 to 31.9 +/- 22.3 micromol/L after 30 min of heparin HD (P < 0.001) and correlated significantly with FFAs (r = 0.80; P = 0.002; n = 12). There was no increase in free p-cresol during heparin-free HD (n = 6) and trisodium citrate HD (n = 9). In addition, p-cresol in ultrafiltrates (n = 3) did not correspond to the free p-cresol in heparinized blood, suggesting that the increase in free p-cresol was artifactual. The release of p-cresol in the test tube was enhanced by standing time (n = 6), sample temperature (n = 6), and alkaline pH (n = 6). Inhibition of lipase activity with THL prevented the increase of FFAs (n = 6) and the release of free p-cresol during HD (n = 22). These results were corroborated by the study of the free fraction of valproic acid (n = 6) and phenytoin (n = 6). CONCLUSIONS: The free concentrations of protein-bound solutes in plasma of heparinized patients are influenced by external factors that alter the lipase activity in the test tube. The free fraction does not increase during HD when lipase activity is neutralized at the time of blood sampling, so that previously reported increases are probably artifacts.

Aged↗
PubMed2000

The removal of uremic toxins.

Three major groups of uremic solutes can be characterized: the small water-soluble compounds, the middle molecules, and the protein-bound compounds. Whereas small water-soluble compounds are quite easily removed by conventional hemodialysis, this is not the case for many other molecules with different physicochemical characteristics. Continuous ambulatory peritoneal dialysis (CAPD) is often characterized by better removal of those compounds. Urea and creatinine are small water-soluble compounds and the most current markers of retention and removal, but they do not exert much toxicity. This is also the case for many other small water-soluble compounds. Removal pattern by dialysis of urea and creatinine is markedly different from that of many other uremic solutes with proven toxicity. Whereas middle molecules are removed better by dialyzers containing membranes with a larger pore size, it is not clear whether this removal is sufficient to prevent the related complications. Larger pore size has virtually no effect on the removal of protein-bound toxins. Therefore, at present, the current dialytic methods do not offer many possibilities to remove protein-bound compounds. Nutritional and environmental factors as well as the residual renal function may influence the concentration of uremic toxins in the body fluids.

Creatinine↗
PubMed2000

Vitamin E-bonded cellulose membrane and hemodialysis bioincompatibility: absence of an acute benefit on expression of leukocyte surface molecules.

Dialysis with unmodified cellulose membranes is associated with such bioincompatibility phenomena as leukopenia, increased expression of adhesion molecules on leukocytes, and release of reactive oxygen species. Dialysis biocompatibility can be improved by modifications in the structure of the cellulose membrane to diminish leukocyte activation and/or protect against the released free oxygen radicals. Excebrane (Terumo Corp, Tokyo, Japan) is a vitamin E-modified cellulose membrane. In the present study, the effect of dialysis with Excebrane membranes on granulocyte and monocyte counts; CD11b, CD11c, and CD45 expression on the surface of granulocytes; and CD14 expression on monocytes was evaluated and compared with low-flux polysulfone membranes. Fifteen minutes after the start of dialysis, granulocytopenia and monocytopenia were more pronounced with the Excebrane membrane compared with polysulfone. The increase in basal expression of CD11b and CD45 on circulating granulocytes was more pronounced during dialysis with Excebrane than polysulfone membranes. Regarding the increased expression on in vitro stimulation with phorbol myristate acetate, blunted upregulation was obtained during dialysis using Excebrane membranes for CD11c and CD45 expression on granulocytes and CD14 expression on monocytes. In conclusion, such indices of membrane bioincompatibility as leukocyte counts and expression of leukocyte surface molecules show more profound alterations with Excebrane than the standard low-flux polysulfone membrane in both basal and in vitro activated states.

Biocompatible Materials↗
PubMed2000

Intradialytic removal of protein-bound uraemic toxins: role of solute characteristics and of dialyser membrane.

BACKGROUND: The efficiency of dialysis membranes is generally evaluated by assessing their capacity to remove small, water-soluble and non-protein-bound reference markers such as urea or creatinine. However, recent data suggest that protein-bound and/or lipophilic substances might be responsible for biochemical alterations characterizing the uraemic syndrome. METHODS: In the present study, the total concentrations of four uraemic retention compounds (indoxyl sulphate, hippuric acid, 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid (CMPF) and p-cresol) and of tryptophan, the only protein-bound amino acid and a precursor of indoxyl sulphate, were compared with those of urea and creatinine in pre- and post-dialysis serum and in dialysate of 10 patients; two high-flux (HF) membranes (cellulose triacetate (CTA) and polysulphone (PS)) and a low-flux polysulphone (LFPS) membrane were compared in a crossover design, using HPLC. RESULTS: Except for hippuric acid (67.3+/-17.5% decrease), major differences were found in the percentage removal of the classical uraemic markers on one hand (creatinine 66.6+/-7.0% and urea 75.5+/-5.8% decrease) and the studied protein-bound and/or lipophilic substances on the other (indoxyl sulphate, 35.4+/-15.3% and p-cresol 29.0+/-14.2% decrease; tryptophan, 27.5+/-40.3%, and CMPF, 22.4+/-17.5% increase; P<0.01 vs urea and creatinine in all cases). Hippuric acid removal was more pronounced than that of the remaining protein-bound compounds (P<0. 01). After correction for haemoconcentration, per cent increase of tryptophan and CMPF was less substantial, while per cent negative changes for the remaining compounds became more important. There was a correlation between creatinine and urea per cent removal at min 240 (r=0.51, P<0.01), but all the other compounds showed no significant correlation with either of these two. The three membranes were similar regarding the changes of total solute concentrations from the start to the end of dialysis. CONCLUSIONS: Urea and creatinine are far more efficiently removed than the other compounds under study, except for hippuric acid. There are no striking differences between the HF membranes. Moreover, compared with the LF membrane these HF membranes do not appear to be superior in removing the studied compounds.

Aged↗
PubMed2000

Effect of regional citrate anticoagulation on leukopenia, complement activation, and expression of leukocyte surface molecules during hemodialysis with unmodified cellulose membranes.

BACKGROUND: Dialysis with complement-activating membranes is associated with leukopenia, which is related to an increased expression of adhesion molecules on leukocytes. Citrate chelates calcium and has been claimed to attenuate leukopenia. METHODS: In this study, the effects of citrate anticoagulation on leukocyte and granulocyte counts, complement activation, and the expression of CD11b, CD11c, and CD45 on the surface of granulocytes were evaluated during hemodialysis with unmodified cellulose membranes. Standard heparin was compared to citrate in three different schedules: citrate was infused to obtain a concentration of either 7 or 10 mmol/l blood. CaCl(2) was administered into the dialyzer outlet at 8. 25 mmol Ca(2+)/h (citrate 10 mmol/l) or at 11 mmol Ca(2+)/h (citrate 7 and 10 mmol/l) to reconstitute the calcium levels in the blood returning to the patient. RESULTS: The use of citrate at a high concentration (10 mmol/l) was associated with a blunted upregulation of CD11b, both at the inlet and at the outlet bloodline; for CD11c a reduced upregulation was observed on granulocytes harvested from the inlet bloodline. No effects of citrate were observed on leukopenia, granulocytopenia, or complement activation. A positive correlation between the decrease in systemic ionized Ca(2+) concentration and the increase in CD11b and CD11c expression was found. CONCLUSION: Citrate/CaCl(2) administration affects leukocyte adhesion molecule expression in a dose-dependent way; however, no significant effect could be demonstrated on leukopenia and complement activation.

Adult↗
PubMed1999

Acute isoniazid intoxication: seizures, acidosis and coma.

Isoniazid (INH) is the most widely used of the antituberculosis drugs. An acute overdose is potentially fatal and is characterized by the clinical triad of repetitive seizures unresponsive to the usual anticonvulsants, metabolic acidosis with a high anion gap and coma. The diagnosis of INH overdose should be considered in any patient who presents with an unexplained metabolic acidosis and convulsions. The cornerstone of therapy consists in pyridoxine (vitamin B6) and the dose should be equal to the amount of INH ingested. When conservative therapy fails or in case of renal insufficiency, dialysis must be considered. Severe central nervous toxicity can also be caused by chronic ingestion of higher than therapeutic doses of INH. In those cases pyridoxine-therapy can be useful as well. In the present paper a case of acute overdose of INH is reported, followed by a review of the literature.

Acidosis↗
PubMed1998

A sensitive HPLC method for the quantification of free and total p-cresol in patients with chronic renal failure.

Para-cresol (4-methylphenol) is a volatile phenolic compound which is retained in chronic renal failure. Several recent studies suggest that p-cresol interferes with various biochemical and physiological functions at concentrations currently observed in uremia. Only a few methods are available for the determination of p-cresol concentration in serum. In addition, these methods have only been used for the determination of total p-cresol. In particular, the evolution of free (non-protein bound) p-cresol is of concern, because conceivably this is the biologically active fraction. The concentration of free p-cresol, is, however, markedly lower than that of total p-cresol, in view of its important protein binding. We report a method enabling the measurement of total and free p-cresol concentration in serum of healthy controls and uremic patients. Deproteinization, extraction and HPLC procedure are efficient, without interference of other protein bound ligands and/or precursors of p-cresol or phenol. By means of spiking experiments, the measurement of the UV absorbance over the 200-400 nm wavelength range, and capillary gas chromatography-mass spectrometry, the considered compound is identified as p-cresol. With a fluorescence detection at 284/310 nm as extinction/emission wavelengths the detection limit of p-cresol is 1.3 micromol/l (0.14 microg/ml). Recovery of added p-cresol to normal serum is 95.4+/-4.1%. For free p-cresol and total p-cresol determinations, intra-assay and day-to-day variation co-efficients are 3.2%, 4.2%, 6.9% and 7.3%, respectively. Compared to healthy controls, the serum p-cresol levels are 7-10 times higher in continuous ambulatory peritoneal dialysis patients (CAPD), uremic outpatients, and hemodialysis patients: 8.6+/-3.0 vs. 62.0+/-19.5, 87.8+/-31.7 and 88.7+/-49.3 micromol/l (0.93+/-0.32 vs. 6.70+/-2.11, 9.49+/-3.43, and 9.60+/-5.30 microg/ml) (p<0.05), respectively. The difference is even more important if free p-cresol is considered. This corresponds to a decreased protein binding in uremic patients. We conclude that the present method allows an accurate measurement of both total and free p-cresol, and that the measured concentrations in uremia are in the range which may cause biochemical alterations.

Artifacts↗
PubMed1998

Citrate anticoagulation does not correct cuprophane bioincompatibility as evaluated by the expression of leukocyte surface molecules.

BACKGROUND: Citrate, used for the anticoagulation of the extracorporeal dialysis circuit, reduces ionized calcium by chelation and has been claimed to attenuate dialyser membrane bioincompatibility. Dialysis with complement-activating cuprophane membranes is associated with leukopenia which has been related to an increase in adhesion molecule expression on the surface of circulating leukocytes. METHODS: The effect of citrate anticoagulation on the expression of CD11b, CD11c and CD45 on the surface of granulocytes and CD14 on monocytes during haemodialysis with cuprophane membranes, was evaluated by flow cytometric analysis. A comparison of standard heparin vs citrate was performed in 14 chronic haemodialysis patients. During citrate anticoagulation a calcium-free dialysate was used and citrate was infused to obtain a concentration of 4.3 mmol/l blood. The unchallenged 'baseline state' expression of the surface molecules and the increase after ex vivo stimulation with phorbol 12-myristate 13-acetate (delta-PMA) or formyl-methionyl-leucyl-phenylalanine (delta-fMLP) was studied. RESULTS: With heparin, as well as with citrate, a sharp fall in granulocyte and monocyte count was observed after 15 min of dialysis, followed by a recovery at the end of the session. The expression of CD11b, CD11c and CD45 on granulocytes increased markedly during cuprophane dialysis with a peak at 15 min; there were no differences in response between heparin and citrate anticoagulation. Delta-PMA and delta-fMLP for CD45, CD11c and CD14 showed a decrease during cuprophane dialysis vs t0; again there were no differences between heparin and citrate. CONCLUSION: We conclude that the use of citrate was not associated with reduced leukocyte activation as measured by the expression of surface molecules during cuprophane dialysis and that no effect on dialysis leukocytopenia could be registered.

Aged↗
PubMed1998

The haematopoietic effect of recombinant human erythropoietin in haemodialysis is independent of the mode of administration (i.v. or s.c.).

BACKGROUND: Previous studies comparing intravenous (i.v.) and subcutaneous (s.c.) administration of recombinant human erythropoietin (rHuEpo) often did not achieve optimal iron reserve, were restricted to a limited follow-up period (not allowing equilibration) and/or did not exclude the role of other confounding factors. In addition all papers focused on the conversion from i.v. to s.c. METHODS: In this study, 30 equilibrated patients on s.c. rHuEpo were randomized into two groups, one converting to i.v. after 6 months of follow-up and one remaining on s.c. rHuEpo. In both groups rHuEpo was administered three times weekly. Only patients completing a further 6 months follow-up were considered for statistical evaluation. Serum ferritin was targeted at 200 ng/ml and haematocrits between 28 and 36% were pursued. RESULTS: The average haematocrit levels before conversion were 31.9 +/- 1.1% in the conversion group and 31.4 +/- 1.6% at the same time point in the nonconversion group (P = NS). After 6 months haematocrits were 31.5 +/- 0.5% in the conversion group and 31.1 +/- 0.9% in the non-conversion group (P = NS). Ferritin concentration in the conversion group was 219 +/- 49 ng/ml before and 230 +/- 83 ng/ml after the conversion. For the non-conversion group ferritin was 224 +/- 25 ng/ml and 236 +/- 52 ng/ml respectively (P = NS). The weight-standardized average rHuEpo dose per injection remained the same in the conversion group before and after conversion (44.0 +/- 1.8 U/kg/injection vs 45.4 +/- 4.7 U/kg/injection) (P = NS). In the non-conversion group the corresponding rHuEpo doses were 32.9 +/- 4.2 U/kg/injection and 39.6 +/- 7.0 U/kg/injection respectively (P = NS). There were no differences in serum PTH, aluminium, vitamin B12, folic-acid levels, and intake of co-trimoxazole, ACE inhibitors or theophylline. CONCLUSION: No changes in rHuEpo dose were observed after conversion from s.c. to i.v. There were no significant differences between the conversion and non-conversion group. These results are in contrast to some earlier studies suggesting lower rHuEpo requirements in case of s.c. administration.

Adult↗
PubMed1998

Inhibition of calcitriol-induced monocyte CD14 expression by uremic toxins: role of purines.

End-stage renal disease is associated with a defect in immunologic functions. Previous studies have demonstrated that uremic ultrafiltrate (UUF) contains factors that suppress calcitriol synthesis and its biological actions. In the present study, the effect of UUF on basal and calcitriol-induced membrane bound CD14 expression of monocytes activated by phorbol 12-myristate 13-acetate was evaluated. CD14 acts as a receptor for the complexes of lipopolysaccharide and lipopolysaccharide-binding protein. Monocytes isolated from normal donors were used for the assay of monocyte CD14 expression. A calcitriol induced rise in monocyte CD14 expression (1966+/-423 to 2421+/-436 fluorescence intensity) was found. However, UUF not only suppressed basal CD14 expression of monocytes (from 1966+/-423 to 1240+/-203, P < 0.05) but also significantly blunted calcitriol-induced CD14 expression (from 2421+/-436 to 1744+/-229, P < 0.05). HPLC fractionated UUF collected from 8 to 16 min (fraction 1, F1) and from 25 to 40 min (fraction 3, F3) also significantly suppressed the expression of CD14. Because purine derivatives coeluted within F1, their effect on monocyte CD14 expression was also tested. Uric acid, xanthine, and hypoxanthine was found to suppress basal as well as calcitriol-induced CD14 expression of monocytes in a dose-dependent manner. In conclusion, UUF contains factors that impair calcitriol activated function of monocytes.

Calcitriol↗
PubMed1998

Pain at the injection site of subcutaneously administered erythropoietin: phosphate-buffered epoetin alpha compared to citrate-buffered epoetin alpha and epoetin beta.

Patients may complain of pain at the injection site after subcutaneous (s.c.) administration of erythropoietin (EPO). Local pain due to s.c. EPO into the thigh was evaluated in 60 hemodialysis patients in a double-blind, placebo-controlled study. Identical volumes and concentrations (2000 IU in 0.5 ml) of phosphate-buffered epoetin-alpha (EPO-alpha ph), citrate-buffered epoetin-alpha (EPO-alpha ci) and epoetin-beta (EPO-beta) were compared to 0.5 ml of 0.9% saline (SAL), used as placebo. The patients received the 4 injections at the same occasion. For pain evaluation, a verbal scale ranging from no pain (0) to extremely painful (5) and a 10 cm ungraduated visual analogue score (VAS) (0 = no pain, 10 = maximal pain) were used. Treatment acceptance was assessed (yes/no) and expressed as a percentage of the population. Ranking of the preparations from 1 to 4 according to increasing local discomfort was performed. Median verbal pain scores and interquartile ranges were 1.0 (0-2) for SAL, 0.0 (0-2) for EPO-beta, 1.5 (0-3) for EPO-alpha ph (p < or = 0.05 vs SAL and EPO-beta) and 3.0 (2-4) for EPO-alpha ci (p < or = 0.001 vs EPO-alpha ph). VAS was 0.9 (0.5-2.5) for SAL, 0.9 (0.4-2.4) for EPO-beta, 2.7 (0.8-5.7) for EPO-alpha ph (p < or = 0.001 vs SAL and EPO-beta) and 4.2 (1.7-6.4) for EPO-alpha ci (p < or = 0.001 vs EPO-alpha ph). Treatment acceptance was 73% for SAL, 78% for EPO-beta, 60% for EPO-alpha ph (p < or = 0.05 vs EPO-beta) and 32% for EPO-alpha ci (p < or = 0.05 vs EPO-alpha ph). Ranking was 2 (1-3) for SAL, 2 (1-2) for EPO-beta, 3 (1-4) for EPO-alpha ph (p < or = 0.05 vs SAL and EPO-beta) and 4 (3-4) for EPO-alpha ci (p < or = 0.05 vs SAL and EPO-beta) and 4 (3-4) for EPO-alpha ci (p < or = 0.001 vs EPO-alpha ph). In conclusion, s.c. EPO-alpha ph is better accepted than s.c. EPO-alpha ci. However, s.c. EPO-beta is less painful.

Aged↗