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Biomedical subjects

A De Leenheer

Publications and source records attributed to A De Leenheer.

At least 19 recordsLinked to original sources
PubMed2005

Validation of 5 routine assays for serum free testosterone with a candidate reference measurement procedure based on ultrafiltration and isotope dilution-gas chromatography-mass spectrometry.

BACKGROUND/METHOD: The analytical validity of free testosterone (FTe) analog immunoassays is subject to much controversy. We revisited the validation of 4 analog assays and 1 FTe calculation procedure with a metrologically traceable reference measurement procedure (RMP) based on ultrafiltration and isotope dilution-mass spectrometry for direct measurement of Te in the ultrafiltrate. To this end, we performed split-sample measurements of 40 male sera. RESULTS: Deming regression showed that 3 of the immunoassays had moderate to good correlation (0.8474 < or = r < or = 0.9241) with the RMP; however, the slope was markedly below 1. The FTe calculation procedure was in good agreement with this result. The Sy/x values for all assays were higher than the combined imprecision values, which indicate their susceptibility to matrix-related effects. CONCLUSIONS: The study demonstrated substantial differences in analytical quality of FTe assays; however, the results suggested that after extending the validation with a larger variety of samples, recalibration of some analog assays might be worth further investigation.

Adult↗
PubMed2002

Chemometric detection of thermally degraded samples in the analysis of drugs of abuse with gas chromatography-Fourier-transform infrared spectroscopy.

We present a chemometric procedure for the identification of the reference standard chromatographic peak in cases where the GC-FTIR analysis of commercial standards results in the appearance of more than one peak in the GC chromatogram. The procedure has been designed for phenethylamines, which represent the class with the largest number of individual molecules on the illicit drug market, and which are abused for their stimulant and/or hallucinogenic effects. The similarity between their vapor-phase FTIR spectra was modeled using principal component analysis (PCA), and class identity was assigned on the basis of soft independent modeling of class analogy (SIMCA). Additional peaks could be assigned to impurities in the standards, but most often they were artifacts formed during the GC-FTIR analysis of thermolabile or chemically unstable compounds. The latter case is illustrated by the identification of the reference standard chromatographic peak and FTIR spectrum of the potent psychotropic amphetamine derivative N-methyl-1-(3,4-methylenedioxyphenyl)-2-butanamine (MBDB), and by the elucidation of the chemical changes that occur in the molecule of MBDB due to thermal degradation.

Chromatography, Gas↗
PubMed2000

Quantitative determination of paraquat in a fatal intoxication by HPLC-DAD following chemical reduction with sodium borohydride.

A fatality due to a massive ingestion of paraquat is presented. Screening by enzyme-multiplied immunoassay of postmortem blood and urine disclosed the presence of tricyclic antidepressants (in urine only), benzodiazepines, cotinine, and caffeine. Further analysis of blood, urine, and stomach contents with thin-layer chromatography, high-performance liquid chromatography (HPLC), and gas chromatography confirmed the results found in the preliminary routine screening. It also revealed the presence of paraquat in blood, urine, and stomach contents, of diethyl parathion in urine and stomach contents, and of mevinphos in blood and stomach contents. Quantitation of paraquat was performed using HPLC with diode-array detection. Sample preparation involved a protein-precipitation step using trichloroacetic acid (necessary only for blood and tissue homogenate), followed by a chemical reduction with sodium borohydride of the fully ionized paraquat to a diene, which is amenable to solvent extraction. Quantitative results were obtained for all postmortem matrices available: blood, 5.05 mg/L; urine, 6.00 mg/l; stomach contents, 17.2 g/L; liver, 4.86 mg/kg; and kidney, 80.6 mg/kg. The paraquat distribution in this case is compared with analytical findings reported in the literature. As would be expected, concentrations found in fatal paraquat intoxications display large differences. The data presented illustrate the outspoken lethal nature of the herbicide paraquat and the ongoing appearance of this compound in deadly accidental and suicidal poisonings.

Borohydrides↗
PubMed1998

Analysis of the DNA damage induced by phenyl glycidyl ether using capillary zone electrophoresis-electrospray mass spectrometry.

The in vitro adduct formation between phenyl glycidyl ether (PGE) and calf thymus DNA was investigated. Agarose slab gel electrophoresis of DNA incubated with PGE revealed that nearly all high-molecular-weight species were degraded after 10 h of incubation. After DNA precipitation the reaction products present in the supernatant were subjected to a solid-phase extraction on a polystyrene divinylbenzene copolymer, enabling analysis on capillary zone electrophoresis (CZE), using sample stacking. These reaction products were mainly produced during the first 10 h of incubation, indicating that these products result from the DNA degradation. On the other hand, analysis of the adducts present in the enzymatic digest of the DNA pellet revealed that these adducts were formed only after 10 h of incubation. The reaction products present in the DNA supernatant were identified by on-line coupling of CZE to electrospray tandem mass spectrometry. Three major reaction products resulted from phosphate alkylation, as proven by the analysis of the corresponding low-energy CAD product ion mass spectra. This phosphate alkylation results in phosphotriesters which readily hydrolyze, resulting in DNA strand breaks.

Animals↗
PubMed1998

Preparative capillary zone electrophoresis in combination with off-line graphite furnace atomic absorption for the analysis of DNA complexes formed by a new aminocoumarine platinum (II) compound.

Calf thymus DNA was incubated in vitro with a new aminocoumarin platinum (II) complex in order to study its interaction with DNA. The platinated DNA was hydrolyzed enzymatically to the 5'-mononucleotide level using DNAase I and nuclease P1. Analysis of the DNA hydrolysate with capillary zone electrophoresis (CZE), using sample stacking, revealed the presence of unhydrolyzed oligonucleotides in the platinated DNA. A homemade system, using only some plastic pipet tips, was constructed to collect the oligonucleotide fraction during CZE analysis. The platinum content of this fraction was determined using graphite furnace atomic absorption with Zeeman background correction. This system proved to be a useful tool to detect platinated DNA species (with a quantifiable detection limit for the detection of platinum of 0.78 ng). Subsequent gel filtration experiments confirmed the presence of high molecular weight oligonucleotides that were platinated. This was proven by reversal of the platination using thiourea and subsequent enzymatic hydrolysis to 5'-mononucleotides.

Animals↗
PubMed1998

Assessment of the state-of-the-art trueness and precision of serum total-calcium and glucose measurements in Finnish laboratories--the QSL-Finland study.

The purpose of the QSL-Finland study was to assess the state-of-the-art trueness and precision of serum total-calcium and glucose measurements in Finnish clinical laboratories. For this purpose, 21 hospitals and clinical institutes were selected. They measured six single donation sera, the total-calcium (t-calcium) and glucose content of which had been determined by ion chromatography and isotope dilution-gas chromatography-mass spectrometry (ID-GC-MS) reference methods. The results were interpreted in light of specifications for imprecision, bias and total error of routine methods that have been proposed in the past. The data revealed that the performance of t-calcium and glucose methods is generally acceptable in Finnish clinical laboratories. This study did not lead to a separation of laboratories according to accreditation. In consequence, it seems that accreditation, in its present form, cannot substitute dedicated quality assurance practices.

Blood Glucose↗
PubMed1998

Analysis of the DNA adducts of phenyl glycidyl ether in a calf thymus DNA hydrolysate by capillary zone electrophoresis-electrospray mass spectrometry: evidence for phosphate alkylation.

Calf thymus DNA was reacted in vitro with phenyl glycidyl ether (PGE) and was hydrolysed enzymatically, to the 5'-monophosphate nucleotides using deoxyribonuclease I (DNA-ase I) and nuclease P1. The adducts were concentrated using solid phase extraction (SPE), on a polystyrene divinylbenzene copolymer in order to remove the unmodified nucleotides. The adducts could be identified using capillary zone electrophoresis-electrospray tandem mass spectrometry (CZE ES-MS/MS), using sample stacking. In addition to the base alkylated 2'-deoxynucleotides present in the DNA-hydrolysate, also phosphate alkylated 2'-deoxynucleotide adducts were identified for TMP and dAMP. An additional adduct, dUMP alkylated on the uridine moiety was found originating from the hydrolytic deamination of dCMP alkylated on N3 of the cytosine moiety. Enzymatic hydrolysis using nuclease P1 was incomplete as shown by the presence of dinucleotides alkylated on the base moiety. They were successfully hydrolysed to the corresponding 2'-deoxynucleotides by snake venom phosphodiesterase (SVP). Data are shown indicating that alkylations on the pyrimidine bases were more resistant to enzymatic hydrolysis with nuclease P1 than the purine alkylated products.

Alkylation↗
PubMed1993

Between-country comparability of clinical chemistry results: an international quality assessment survey of 17 analytes in six European countries through existing national schemes.

Two lyophilized control sera were distributed through seven national external quality assessment schemes in six European countries--Belgium, Switzerland, France, The Netherlands, Sweden and the United Kingdom--participated in the study. The results for 17 routine analytes were obtained from almost 5000 laboratories for the two sera. The organizers of the schemes were asked to process the results according to a common outlier removal procedure, and submit method-related data if available. The two sera were also distributed through the external/internal scheme of The Netherlands, and the within-laboratory standard deviations calculated in this scheme have been used in a scaling procedure for the external mean values and between-laboratory standard deviations of the participating countries. The results show remarkable agreement in the national mean values for practically all analytes, but considerable differences in the between-laboratory variation. Data from comparable method groups was obtained for 12 analytes from Belgium, France, The Netherlands and the UK. Though revealing some specific differences between methods and countries, the method-related data are generally in agreement with the all-method data. In this study reference method values were only available for cholesterol. The high degree of agreement found suggests, however, that mutual recognition of all-method mean values in national schemes could be acceptable, especially for analytes for which reliable reference methods are not available. The major element of variation is between-laboratory rather than between-country.

Animals↗
PubMed1992

The distribution of cis- and trans-acitretin in human epidermis.

The concentrations of trans-acitretin and its principal metabolite, cis-acitretin, were measured by h.p.l.c. after single and multiple dosing (50 mg orally for 13 days) in plasma, blister fluid and epidermal samples from four healthy male volunteers. Within-day epidermal concentrations of trans-acitretin exceeded those of the cis-form which were at the limit of assay sensitivity. No accumulation of trans-acitretin was observed in plasma or blister fluid but AUC values for the drug in blister roof cells tended to be higher after multiple dosing.

Acitretin↗
PubMed1991

Development, validation, and certification by isotope dilution gas chromatography-mass spectrometry of lyophilized human serum reference materials for cortisol (CRM 192 and 193) and progesterone (CRM 347 and 348).

The Community Bureau of Reference of the European Communities has produced four batches of lyophilized serum Certified Reference Materials, two for cortisol (CRM 192 and 193) and two for progesterone (CRM 347 and 348). For cortisol, one of the pools consisted of serum from healthy blood donors, whereas the second batch was supplemented with pure cortisol. The progesterone Reference Materials contained only endogenous hormone concentrations. Assessment of vial-to-vial variability in the cortisol and progesterone concentrations showed no between-sample inhomogeneity, and the materials were stable. The quality of the materials was therefore considered sufficient for certification of the values for the cortisol and progesterone concentrations by a collaborative study involving several laboratories from the European Communities, using isotope dilution gas chromatography-mass spectrometry. Inaccuracy in reconstitution of the lyophilized materials was less than 0.3%; imprecision of sampling was less than 0.2%. For determinations of cortisol and progesterone concentrations, the mean within-laboratory coefficients of variation (CVs) were 1.76% (CRM 192), 1.19% (CRM 193), 1.64% (CRM 347), and 1.75% (CRM 348). The between-laboratory CVs were greater: CRM 192, 1.79%; CRM 193, 1.48%; CRM 347, 2.08%; and CRM 348, 2.16%. The concentrations in the reconstituted Reference Materials were certified to be 273 nmol/L in CRM 192 and 763 nmol/L in CRM 193 for cortisol and 10.13 nmol/L in CRM 347 and 40.3 nmol/L in CRM 348 for progesterone. Uncertainties at the 0.95 confidence level--6 (CRM 192), 14 (CRM 193), 0.21 (CRM 347), and 1.0 nmol/L (CRM 348)--were considered compatible with the intended use of the materials.

Blood Chemical Analysis↗
PubMed1990

Comparison of cyclosporin A measurement in whole blood by six different methods.

In a multicentre trial, we analyzed and compared the cyclosporin concentrations in whole blood specimens (trough values) from renal and bone marrow transplant patients using six different methods: high-performance liquid chromatography (n-butyl reversed-phase column) as reference, and 5 immunoassay procedures using monoclonal specific or non-specific antibodies, or polyclonal antibodies, for measuring cyclosporin with and without its cross-reacting metabolites. Results obtained by the 2 specific RIAs show good correlations (r-values of 0.945 and 0.921) versus the HPLC method, with average assay ratios of: 1.52 for 3H-RIA/HPLC and 1.26 for 125I-RIA/HPLC. In contrast, ratios for non-specific immunoassay/HPLC show multiple-fold overestimations of cyclosporin with very wide variations: 4.58 for 3H-RIA/HPLC, 3.97 for 125I-RIA/HPLC and 3.87 for fluorescence polarization immunoassay (FPIA)/HPLC. These findings indicate 1) that the 'specific' 3H- and 125I-RIAs can be used for cyclosporin measurements in whole blood using normal therapeutic ranges established by HPLC, 2) that the important disparity and variable overestimations by 'non-specific' RIA or fluorescence polarization immunoassay, compared with HPLC, require adjustments in therapeutic ranges, and 3) that the available 'specific' and 'non-specific' immunoassays should enable establishment of within-house reference 'therapeutic/toxic' ranges for cyclosporin in individual centres, based on these 'specific' versus 'non-specific' assays.

Antibodies, Monoclonal↗
PubMed1989

Synthesis of 11C-labelled thymidine for tumor visualization using positron emission tomography.

A no-carrier added synthesis of [11C]thymidine from cyclotron produced [11C]methyl iodide is presented. The bis-silylated derivative of the lithium salt of 5-bromo-2'-deoxyuridine is treated with [11C]methyl iodide in THF at -50 degrees C giving 20-30 mCi [11C]thymidine in a 40-70% radiochemical yield. Purification is performed by reversed phase chromatography on a C18 column. The whole procedure takes 25 min and the specific activity is about 20-30 mCi/mumol at the end of the synthesis.

Carbon Radioisotopes↗
PubMed1983

Steroid profiles of body fluids other than urine, obtained by capillary gas chromatography.

Steroid profiling by capillary gas chromatography has been applied to the analysis of free and conjugated steroids in serum, ovarian follicles, lutein cyst and peritoneal fluids. Sep-Pak C18 octadecylsilica was used for extraction, whereas the separation of free and different conjugates was accomplished by successive hydrolysis and liquid extraction steps.

Ascitic Fluid↗
PubMed1983

The production in high yield of N'-(4-[11C]methyl)-imipramine.

A method for the routine production in high yield of N'-(4-[11C]methyl)-imipramine is presented. The label is incorporated by reaction of C-11 methyl iodide (11CH3I) upon desipramine in dimethylsulfoxide. Quaternization of the tertiary amine by 11CH3I is minimized by using an excess of desipramine. The reaction proceeds at room temperature for 10 min and the product is isolated by means of high-performance liquid chromatography (HPLC). The entire production takes only 40 min and results in a radiochemical yield of 60%. About 60 mCi of labeled product are available for medical application; the specific activity, at the time of use, is 50 mCi/mumole. The product was characterized by chromatographic and spectrometric methods.

Carbon Radioisotopes↗