Biomedical subjects

Jos Hoogmartens

Publications and source records attributed to Jos Hoogmartens.

At least 19 recordsLinked to original sources

PubMed2006

Racemization of aspartic acid from human dentin in the estimation of chronological age.

The estimation of chronological age in cadavers, human remains and in living human beings by various methods is discussed. These methods, which are based on the age dependent non-enzymatic changes of l-form amino acids to d-form amino acids, mainly aspartic acid, are among the most reliable and accurate methods to date. Most of these methods use gas chromatography (GC). In this review, results of aspartic acid racemization in dentin at different targets are discussed. In addition, pre-considerations and guidelines are given for the selection of dentin from teeth. A pilot project was run to evaluate the efficiency of high performance liquid chromatography (HPLC) coupled with fluorescence detection. New buffer conditions were found to obtain stable derivatives of aspartic acid enantiomers for the estimation of racemization.

Adolescent↗

PubMed2006

Recent advances in pharmaceutical applications of chiral capillary electrophoresis.

This review article summarizes developments and applications of chiral capillary electrophoresis (CE) in the pharmaceutical field published from January 2004 to June 2005. Due to the tremendous number of publications, this article is aimed to focus on major developments in chiral separations and some selected applications rather than to provide a descriptive overview of all published papers. Valuable information is also collected from several excellent reviews published during this period. Developments are classified according to CE modes, namely capillary zone electrophoresis (CZE), micellar electrokinetic capillary chromatography (MEKC), microemulsion electrokinetic chromatography (MEEKC). In the CZE section, different types of chiral selectors including cyclodextrins, oligo- and polysaccharides, crown ethers, macrocyclic antibiotics, ligand exchange systems and proteins are described. Nonaqueous capillary electrophoresis is also included in this section. Coupling CE to MS is discussed in a separate part, followed by a summary of selected pharmaceutical applications of enantioselective CE. Finally, some conclusions are drawn and prospects of CE in chiral analysis are also drafted.

Chemistry, Pharmaceutical↗

PubMed2006

Capillary electrophoresis method development for determination of impurities in sodium cysteamine phosphate samples.

A capillary electrophoresis method for determination of impurities in sodium cysteamine phosphate-an alternative drug to use in place of cysteamine (Cystagon), Mylan Laboratories Inc.) in the treatment of cystinosis-was developed. The administration of cysteamine, divided in four doses due to the short half-life of this drug, is a helpful treatment, but several patients show intolerance, due to the very unpleasant odor and taste of cysteamine. Sodium cysteamine phosphate is less organoleptic aversive and also has a larger active time, allowing the compression of the doses to 2 per day, increasing the acceptance of the drug. In the developed method the two main decomposition products of sodium cysteamine phosphate, cystamine and cysteamine, can be determined with LOQs of 30 microg/ml (0.2%) and 16 microg/ml (0.1%), respectively. The background electrolyte is 15 mM ammonium acetate (pH 8.85) with 10% methanol and the separation takes less than 4 min. UV detection is performed at 195 nm. This volatile method was developed with the purpose of further hyphenation to a mass spectrometer.

Cysteamine↗

PubMed2006

Advances in capillary electrophoretically mediated microanalysis: an update.

This review, as a continuation of an earlier report, gives an overview of recent developments, over the period from 2003 until now, in the use of capillary electrophoretic techniques for the in-line study of enzymatic reactions, derivatization, and chemical reactions. The article is divided into two parts: (i) in-line enzymatic reactions and (ii) in-line derivatization and chemical reactions. The first part introduces electrophoretically mediated microanalysis (EMMA) and discusses and illustrates the different modes of EMMA. A literature overview on enzymatic reactions is provided. The second part starts with an introduction of the procedures and the nomenclature used in the area of in-line derivatization and chemical reactions based on EMMA. Reported derivatization and chemical reaction procedures are discussed and summarized.

Electrophoresis, Capillary↗

PubMed2006

Analysis of unknown compounds in gentamicin bulk samples with liquid chromatography coupled with ion trap mass spectrometry.

Six unknown compounds present in bulk gentamicin samples have been identified by ion-pairing reversed-phase liquid chromatography coupled with ion trap mass spectrometry. The structures of these unknown compounds were deduced by comparison of their fragmentation patterns with those of the available related substances and gentamicin reference substances. Seven other unknown components were partially identified.

Anti-Bacterial Agents↗

PubMed2005

Chiral capillary electrophoretic analysis of verapamil metabolism by cytochrome P450 3A4.

Cytochrome P450 (CYP), which is one of the most important enzymes in human liver, is responsible for a large portion of the first-pass metabolism of drugs. Many studies have focused on the determination of CYP activity by substrate assays. Most of them used liquid chromatography (LC) as analytical technique, while only a few studies used capillary electrophoresis (CE) for the separation and quantitation of reaction components. In this study, the feasibility of using CE in an in vitro metabolism study with CYP was tested. Verapamil was chosen as the substrate for CYP 3A4 isozyme (Supersome). A chiral capillary electrophoretic method was developed and validated for the simultaneous determination of R,S-verapamil (VER) and their major metabolites, R,S-norverapamil (NOR). A method for CYP 3A4 activity assay was proposed with VER as a probe. At the same time, the enantioselective metabolism of VER was studied. Michaelis-Menten constants of R- and S-VER were determined. S-VER was metabolised faster and more extensively than R-VER, with K(m)=167+/-23 microM, V(max)=3,418+/-234 pmol/min/mg for S-VER, and K(m)=168+/-35 microM, V(max)=2,502+/-275 pmol/min/mg for R-VER.

Cytochrome P-450 CYP3A↗

PubMed2005

Investigation of degradation products in a topical gel containing erythromycin and benzoyl peroxide by liquid chromatography-mass spectrometry.

Benzamycin, combining benzoyl peroxide and erythromycin, is a topical gel used in the treatment of acne vulgaris. Because of the reactivity of benzoyl peroxide, preparations containing both erythromycin and benzoyl peroxide might be unstable and degradation products could be formed. To investigate and identify these latter products, a gradient-based liquid chromatographic method using volatile mobile phase constituents was developed. Mass spectrometry data were acquired on solutions containing erythromycin and benzoyl peroxide and on freshly prepared, 2-month-old and 18-month-old samples of Benzamycin. With the reference spectra as interpretative templates, it was concluded that erythromycin undergoes oxidation, followed by benzoylation.

Benzoyl Peroxide↗

PubMed2005

Facilitated column selection in pharmaceutical analyses using a simple column classification system.

In this paper, the performance of a previously developed classification system applied to pharmaceutical chromatographic analyses, is investigated. The separation of seven different drug substances from their respective impurities was studied. The chromatographic procedure for acetylsalicylic acid, clindamycin hydrochloride, buflomedil hydrochloride, chloramphenicol sodium succinate, nimesulide and phenoxymethylpenicillin was performed according to the corresponding European Pharmacopoeia (Ph. Eur.) monograph. The separation of dihydrostreptomycin sulphate was performed according to the literature. It is shown that the column ranking system is a helpful tool in the selection of a suitable column in these analyses.

Aspirin↗

PubMed2005

Kinetic study of CYP3A4 activity on verapamil by capillary electrophoresis.

The use of capillary electrophoresis (CE) for the determination of CYP3A4 activity with verapamil as a substrate was investigated. CYP3A4 activity was determined by the quantitation of the product, norverapamil, based on separation by CE. The separation conditions were as follows: capillary, 80.5 cm (75 microm i.d., 72 cm effective length); 50 mM sodium phosphate buffer (pH 8.8); 20 kV (100 microA) applied voltage; UV detection at 200 nm; capillary temperature, 25 degrees C. With the developed CYP3A4 activity assay and the Lineweaver-Burk equation, the Michaelis-Menten parameters Km and Vmax for formation of norverapamil from verapamil in the presence of CYP3A4 were determined and were 22.8+/-2.5 microM and 7.67+/-0.26 pmol/min/pmol (or 983 pmol/min/mg) CYP3A4, respectively.

Buffers↗

PubMed2005

Development of a capillary electrophoretic method for the separation of diastereoisomers of a new human immunodeficiency virus protease inhibitor.

A capillary electrophoretic (CE) method was developed for the separation of diastereoisomers of a new human immunodeficiency virus (HIV) protease inhibitor TMC114. In total 16 isomers of this drug have been synthesized (eight pairs of enantiomers). We succeeded in the separation of the eight diastereoisomers, but no enantiomers could be separated. Because of the high similarity and water-insolubility of these isomers, the separation is a real challenge. Different CE modes were tried out: capillary zone electrophoresis (CZE), nonaqueous capillary electrophoresis (NACE), micellar electrokinetic capillary chromatography (MEKC), and microemulsion electrokinetic capillary chromatography (MEEKC). Only MEEKC offered resolution of these compounds.

Acetonitriles↗

PubMed2005

Gentamicin assay in human serum by solid-phase extraction and capillary electrophoresis.

We describe the development of a capillary electrophoresis method for the determination of gentamicin C1, C1a, C2a, and C2 components in human serum. Using a weak cation-exchanger with 20 mM phosphate buffer, pH 7.4, 200 mM borate buffer, pH 9.0, and ammonia/methanol, solid-phase extraction (SPE) of gentamicin components from the human sera was performed. The extract was derivatized with 1,2-phthalic dicarboxaldehyde/mercaptoacetic acid reagent. The derivatives were separated with a background electrolyte comprising 60 mM 2-(N-cyclohexylamino)ethanesulfonic acid (CHES) buffer at pH 9.5 containing 31.6% m/v methanol, and quantified with UV-light absorption detection at 230 nm. The identity of the gentamicin components was confirmed by mass spectrometry. The SPE recovery of the gentamicin ranged from 78% to 93%. The calibration curves were linear from the concentration limit of quantitation (LOQ) to 30 mg/L for the gentamicin mixture. The LOQ for gentamicin C1 was 0.33 mg/L, for C2a 0.23 mg/L, C2 0.25 mg/L, C1a 0.27 mg/L and the concentration limit of detection (LOD) for C1 was 0.15 mg/L, C2a 0.11 mg/L, C2 0.12 mg/L, C1a 0.13 mg/L. Intra-assay relative standard deviation (RSD) values were for C1 (5%), C1a (7%), C2 (6.5%) and C2a (9%); inter-assay RSD values were for C1 (11%), C1a (13.3%), C2 (15%) and C2a (14%). The Pearson's correlation between capillary electrophoresis and immunoassay revealed a linear relationship between these two techniques with r = 0.9. This method for determination of gentamicin C1, C1a, C2a, and C2 in human serum can thus be used in the entire therapeutic concentrations range of gentamicin.

Electrophoresis, Capillary↗

PubMed2005

Method development and validation for the analysis of didanosine using micellar electrokinetic capillary chromatography.

A selective MEKC method was developed for the analysis of didanosine in bulk samples. Successful separation of didanosine from 13 of its potential impurities, derived from the various synthetic preparation procedures, was achieved. As CZE gave poor separation selectivity, MEKC was preferable. The use of EKC allowed achievement of the separation in a significantly shorter time than conventional HPLC. An anionic long-chain surfactant, lithium dodecyl sulfate (LiDS), was used as the pseudostationary phase and sodium tetraborate buffer as the aqueous phase. In order to obtain the optimal conditions and to test the method robustness, a central composite response surface modeling experiment was performed. The optimized electrophoretic conditions include the use of an uncoated fused-silica capillary with a total length of 40 cm and an ID of 50 microm, a BGE containing 40 mM sodium tetraborate and 110 mM LiDS at pH 8.0, an applied voltage of 18.0 kV, and the capillary temperature maintained at 15 degrees C. The method was found to be robust. The parameters for validation such as linearity, precision, and sensitivity are also reported. Three commercial bulk samples were analyzed with this system.

Borates↗

PubMed2005

Mass spectrometric study to characterize thioisoindole derivatives of aminoglycoside antibiotics.

Aminoglycoside antibiotics are widely used to treat serious Gram-negative and Gram-positive bacterial infections. The lack of a UV chromophore presents a problem in the analysis of aminoglycosides. Derivatization with 1,2-phthalic dicarboxaldehyde (OPA) in the presence of a thiol made it possible to introduce a UV chromophoric thioisoindole moiety. A qualitative mass spectrometry study was carried out to confirm the molecular identity of the products formed. The conditions described earlier to derivatize gentamicin and kanamycin yielded products in which all primary amino groups are fully derivatized. On the other hand, with tobramycin and amikacin, there was also formation of incompletely derivatized products that contained one thioisoindole group less than the fully derivatized product. This study has therefore brought an additional insight into the nature of the OPA-aminoglycoside derivatives studied.

Aminoglycosides↗

PubMed2005

Determination of hypericin in human plasma by high-performance liquid chromatography after intravesical administration in patients with transitional cell carcinoma of the bladder.

In the present study, the systemic absorption of hypericin was investigated after intravesical instillation of the compound in nine patients with superficial transitional cell carcinoma (TCC) bladder tumors. Hypericin (8 microM) was instilled in the bladder for 2-3 h before photodynamic diagnosis of bladder tumors. Blood was then collected from a peripheral vein 1 h after termination of the instillation. Solid phase extraction with ammonium acetate buffer and methanol was used to extract hypericin from the plasma. A reversed-phase high performance liquid chromatographic method with fluorescence detection was used to identify and quantify hypericin in the extracts from plasma samples. Analysis of standard plasma samples, which were spiked with known amounts of hypericin, indicated that the pH of the buffer was a determining factor in the extraction yield. The results obtained using ammonium buffer (pH 3.5) and methanol showed the mean extraction recovery of hypericin to be 64% (RSD=12%, n=6). The limits of detection and quantification were 6 and 20 nM, respectively. Extraction and analysis of the plasma of patients after intravesical administration showed hypericin concentrations below the detection limit (<6 nM). In addition, photodynamic treatment of in vitro cultured HeLa cells incubated with 1-100 nM hypericin concentrations showed that lower concentrations (1-20 nM) of hypericin do not induce significant photocytotoxic effects. Taken together, these results imply that photosensitization or other systemic side effects in patients are not to be expected after photodynamic diagnosis of TCC bladder tumors with hypericin.

Administration, Intravesical↗

PubMed2004

Liquid chromatography-mass spectrometry study towards the pH and temperature-induced N-acyl migration in polymyxin B.

In the course of the synthesis and purification of new polymyxins and analogues, formation of a by-product with identical mass was observed and it was believed that this might be the result of acyl migration from the Nalpha- to the Ngamma-position of residue alpha,-gamma-diaminobutyric acid 1 (Dab1) under acidic conditions. Therefore, a LC-MS/MS study was initiated to establish the stability of polymyxin B3 in aqueous solution at room temperature and 60 degrees C, as well as different pH values (i.e. 1.4, 4.4 and 7.4). It was shown that the by-product, which is actually formed in the course of the purification of polymyxin B3 after evaporation in acidic medium, has a retention time similar to Ngamma-polymyxin B3. Acyl-migration occurred most rapidly at 60 degrees C and pH 7.4. Furthermore, it was established that migration of the acyl from the Nalpha- to the Ngamma-position of residue Dab1 is reversible and that the equilibrium seems to be in favor of the Nalpha-acylated compound.

Amino Acid Sequence↗

PubMed2004

Identification of impurities in erythromycin by liquid chromatography-mass spectrometric detection.

A simple, isocratic liquid chromatographic (LC) method using volatile mobile phase constituents for the identification of related substances in erythromycin samples is described. For method development, evaporative light scattering detection (ELSD) was used. An XTerra RP18 column was used at 70 degrees C with a mobile phase consisting of acetonitrile-isopropanol-0.2M ammonium acetate pH 7.0-water (165:105:50:680). Mass spectral data were acquired on an ion trap mass spectrometer equipped with an electrospray interface operated in the positive ion mode. First, a library was created using MS/MS and MS(n) spectra of reference substances available in the laboratory. Using these reference spectra as interpretative templates, eight novel related substances in erythromycin samples were identified: N-demethylerythromycin E, erythromycin E N-oxide, anhydroerythromycin C, N-demethylerythromycin B, anhydro-N-demethylerythromycin A, pseudoerythromycin E enol ether, EF lacking the neutral sugar and EA lacking the neutral sugar.

Chromatography, Liquid↗

PubMed2004

Bioanalysis of tobramycin for therapeutic drug monitoring by solid-phase extraction and capillary zone electrophoresis.

A method based on solid-phase extraction (SPE) and capillary zone electrophoresis (CZE) for the analysis of tobramycin in human serum is presented. An off-line SPE employing a carboxypropyl bonded phase (CBA) cartridge was used for the extraction of tobramycin from human serum. Adsorbed tobramycin was eluted from the CBA cartridge using a mixture of NH(3) (25%, w/v)-methanol (30:70, v/v). After evaporation, the analyte was reconstituted and derivatized with o-phthaldialdehyde (OPA)/3-mercaptopropionic acid (MPA). The resulting tobramycin-OPA/MPA derivative was purified, and then identified by mass spectrometry. The tobramycin-OPA/MPA derivative was then analysed by CZE with a background electrolyte (BGE) comprising of 30 mM sodium tetraborate pH 10.0-acetonitrile (ACN) (80:20, v/v) with ultraviolet detection at 230 nm. A linear response was observed in the range of 0.3-30 microg/ml with r(2) = 0.992. The sensitivity of the method was determined by its limit of quantitation (LOQ) and limit of detection (LOD) of 0.3 microg/ml and 0.1 microg/ml, respectively. SPE recovery ranged from 68 to 79% at the trough levels to 98% at the peak levels found in serum. Furosemide has been added as internal standard (IS) to improve precision. For the therapeutic range of tobramycin in serum (2-10 microg/ml) the relative standard deviation (R.S.D.) was less than 11% for the entire SPE/CE process. The method demonstrated excellent selectivity as shown by the lack of interference from a total of 20 drugs investigated. The method was then used in therapeutic drug monitoring of patients receiving the drug.

Anti-Bacterial Agents↗

PubMed2004

Chiral capillary electrophoretic method for quantification of apomorphine.

A new method for chiral determination of apomorphine enantiomers was developed and validated. Seven different neutral and charged cyclodextrins were tested for enantioselectivity on R,S-apomorphine. Sulfobutylether-beta-cyclodextrin was found to offer the best resolution, but with this system, four peaks were detected from a solution of the two enantiomers, which was suggested to be the result of different forms of the complex between the selector and apomorphine. A complexation constant was estimated for a complex of 1:1 ratio for the second and the fourth peak, whereas the other two peaks were fitted to a model ratio of 1:2 (analyte-selector). To avoid this phenomenon, hydroxypropyl-beta-cyclodextrin was then chosen as the chiral selector. An optimisation study was performed on three factors: concentration of the chiral selector, pH of the buffer, and applied voltage. Optimum conditions were: 14 mM of hydroxypropyl-beta-cyclodextrin, pH 3.0, and 16 kV. UV detection was at 200 nm. The method was validated at the chosen conditions, offering a limit of detection of 0.2 microM and a limit of quantification of 0.5 microM. The validated method was applied for the determination of R,S-apomorphine in a transport study with an in vitro cell culture model of the intestinal mucosa (Caco-2).

Apomorphine↗