Biomedical subjects

K S Boos

Publications and source records attributed to K S Boos.

At least 19 recordsLinked to original sources

PubMed2002

Use of a novel cation-exchange restricted-access material for automated sample clean-up prior to the determination of basic drugs in plasma by liquid chromatography.

A new kind of silica-based restricted-access material (RAM) has been tested in pre-columns for the on-line solid-phase extraction (SPE) of basic drugs from directly injected plasma samples before their quantitative analysis by reversed-phase liquid chromatography (LC), using the column switching technique. The outer surface of the porous RAM particlescontains hydrophilic diol groups while sulphonic acid groups are bound to the internal surface, which gives the sorbent the properties of a strong cation exchanger towards low molecular mass compounds. Macromolecules such as proteins have no access to the internal surface of the pre-column due to their exclusion from the pores and are then flushed directly out. The retention capability of this novel packing material has been tested for some hydrophilic basic drugs, such as atropine, fenoterol, ipratropium, procaine, sotalol and terbutaline, used as model compounds. The influence of the composition of the washing liquid on the retention of the analytes in the pre-column has been investigated. The elution profiles of the different compounds and the plasma matrix as well as the time needed for the transfer of the analytes from the pre-column to the analytical column were determined in order to deduce the most suitable conditions for the clean-up step and develop on-line methods for the LC determination of these compounds in plasma. The cationic exchange sorbent was also compared to another RAM, namely RP-18 ADS (alkyl diol silica) sorbent with respect to retention capability towards basic analytes.

Automation↗

PubMed2001

Evaluation of a multidimensional solid-phase extraction platform for highly selective on-line cleanup and high-throughput LC-MS analysis of triazines in river water samples using molecularly imprinted polymers.

A novel highly selective sample cleanup procedure based on the use of molecularly imprinted polymers (MIPs) as solid-phase extraction materials has been evaluated with respect to its applicability and routine use in environmental analysis. The method comprises the combination of a restricted access material (RAM) and a MIP allowing a selective sample preparation to be achieved in the online mode. This combination is called the size-selective sample separation and solvent switch (six-SPE). The RAM column combines size exclusion and adsorption chromatography, reducing the concentration of matrix molecules by a cutoff of 15 kDa. The MIP column selectively retains the triazine analytes whereas the residual matrix is not retained and separated completely. Thus, the automated RAM-MIP is capable of excluding all matrix and nontarget compounds. The cleaned and enriched extract is subsequently eluted to an HPLC column and analyzed by LC-MS. A complete on-line analysis cycle including multidimensional solid-phase extraction, separation, and detection takes less than 15 min. Terbuthylazine, atrazine, propazine, simazine, ametryn, prometryn, irgarol, and also the metabolites deethylatrazine and deisopropylatrazine can be determined without any matrix interferences, e.g., by humic acids. The whole setup is fully automated and may be continuously operated. Nonspecific interactions with the polymer are below 1% in all cases. The accuracy of the LC-MIP-LC-MS system was controlled using a certified reference material (Aquacheck). The applicability of the method to the cleanup of real samples was demonstrated by injection of contaminated river water samples. The stability of different polymers was tested by consecutive injections, and it was shown that the performance of the materials did not vary even after more than 300 enrichment and desorption cycles.

Journal Article↗

PubMed2001

Multidimensional on-line solid-phase extraction (SPE) using restricted access materials (RAM) in combination with molecular imprinted polymers (MIP).

A novel, multidimensional SPE sample-processing platform for complex fluids, which relies on the combination of small LC columns packed with restricted access materials (RAM) and molecular imprinted polymers (MIP) is described. It is called the Six-S ProcEdure (Six-SPE). Six-SPE involves a size-selective sample-separation step followed by a solvent-switch. Six-SPE efficiently removes interfering matrix components of complex aqueous samples and creates optimal conditions for selective recognition, i.e. binding of the imprinted target analyte(s). A Six-SPE analysis cycle consists of four distinct steps: 1. separation of a given sample (e.g. plasma, urine, saliva, milk, etc.) by adsorptive extraction (e.g. reversed-phase partitioning) of low molecular weight components on to the stationary phase of a RAM column and simultaneous size-exclusion, i.e. quantitative disposal of macromolecular matrix constituents to waste; 2. desorption and transfer of the extract from the RAM column on to a series-connected MIP column using a pure organic mobile phase (e.g. acetonitrile) [solvent switch]; 3. molecular recognition, i.e. selective binding of the target analyte(s) by a tailor-made MIP column; and 4. desorption and transfer of the analyte fraction on to a series-connected separation (e.g. HPLC) and/or detection system (e.g. UV, FD, MS). As a first application we coupled the Six-SPE platform to a conventional HPLC system for on-line analysis of the analgesic drug Tramadol in human plasma using LiChrospher ADS RP-18 as a RAM precolumn for the fractionation step in the first and second chromatographic dimension and a Tramadol imprinted polymer for the molecular recognition step, i.e. third chromatographic dimension.

Journal Article↗

PubMed2001

A simple turbidimetric assay designed for the routine screening as well as therapeutic monitoring of native LDL particles.

We describe the development and performance of a homogeneous assay for the direct turbidimetric determination of LDL particles in human serum. The assay is based upon the specific agglutination of LDL particles by the polyanion PAMPS. The co-agglutination of VLDL is avoided by the addition of a zwitterionic detergent. Yielding results within 10 min, the assay requires only a small sample volume taken directly from primary serum tubes, i.e., no pretreatment of the sample is necessary. It can be easily applied to routine clinical chemistry analyzers. The results are highly correlated with LDL cholesterol determinations by ultracentrifugation (r>0.95) and dextran sulfate precipitation (r>0.95), but an increased recovery of small, high density LDL particles is observed, which more adequately reflects the atherogenic risk of LDL. The assay provides excellent intra- and inter-assay CVs in the range of 0.6--1.6 and 1.7--2.4%, respectively, on Roche Diagnostics/Hitachi analyzers. The method is well suited to the high-throughput screening of LDL cholesterol levels.

Artifacts↗

PubMed2000

Analysis of neuropeptide Y and its metabolites by high-performance liquid chromatography-electrospray ionization mass spectrometry and integrated sample clean-up with a novel restricted-access sulphonic acid cation exchanger.

A novel restricted access cation exchanger with sulphonic acid groups at the internal surface was proven to be highly suitable in the sample clean up of peptides on-line coupled to HPLC-electrospray ionization (ESI)-MS. Neuropeptide Y (NPY) and several of its fragments in plasma were subjected to the sample clean-up procedure. The peptides were eluted by a step gradient from the restricted access column, applying 10 mM phosphate buffer pH 3.5 from 5 to 20% (v/v) of acetonitrile with 1 M NaCl and transferred to a Micra ODS II column (33x4.6 mm). The separation of the peptides and their fragments was performed by a linear gradient from 20 to 60% (v/v) acetonitrile in water with 0.1% formic acid and 0.01% trifluoroacetic acid in 4 min at a flow-rate of 0.75 ml/min. An integrated and completely automated system composed of sample clean up-HPLC-ESI-MS was used to analyze real life samples. The sample volumes ranged between 20 and 100 microl. Peaks due to the fragments NPY 1-36, 3-36 and 13-36 in porcine plasma were identified by ESI-MS. The limit of detection was in the 5 nmol/ml range. The total analysis required 21 min and allowed the direct injection of plasma.

Amino Acid Sequence↗

PubMed2000

Binding kinetics of triclosan (Irgasan) to alloplastic vascular grafts: an in vitro study.

The aim of this study was to investigate the binding kinetics of triclosan (Irgasan) to alloplastic vascular grafts and to examine its antimicrobial activity against various microbial pathogens in vitro. Vascular grafts made by Intergard (Intervascular), Fluoropassiv (Vascutek), and Gore-tex (Gore) were examined. Grafts were incubated in 10 g/L triclosan (Irgasan), dried, sterilized, and incubated in RPMI medium. One-centimeter segments of the grafts were resected under sterile conditions at intervals of minutes, then hours, followed by days and up to 4 weeks. Samples were stored frozen at -20 degrees C for the measurement of triclosan bound to the vascular graft by high-performance liquid chromatography (HPLC). The binding kinetics under perfusion conditions were determined for Intergard grafts, which were perfused with 50 mL of nutrient medium for 24 hr. Samples were taken at various time intervals for the measurement of triclosan. The antimicrobial activity of triclosan against Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans as well as Enterococcus faecium was determined. Triclosan effectively binds to vascular graft without the use of intermediate binding substances. It stayed on the graft for the duration of 4 weeks. Under both static and perfusion conditions, the binding kinetics are similar. Triclosan binds most effectively to Intergard grafts, less so to Fluoropassiv grafts, and not at all to Gore-tex material. Antimicrobial activity of triclosan is very effective against S. aureus and E. faecium but not against P. aeruginosa.

Anti-Infective Agents, Local↗

PubMed1998

HELP apheresis in the treatment of sepsis.

Heparin induced extracorporeal lipoprotein fibrinogen precipitation (HELP) is an established procedure for removal of low-density lipoprotein (LDL) cholesterol, lipoprotein (a), and fibrinogen in patients with severe hypercholesterolemia. In vitro studies revealed that HELP also removes endotoxin, tumor necrosis factor alpha (TNF-alpha) and C-reactive protein (CRP). With the intention to treat, we applied this procedure to 4 patients with severe gram-negative sepsis with highly elevated endotoxin blood levels. Nine treatments were performed, 6 using the standard HELP precipitating buffer and 3 without addition of heparin to the precipitating buffer. Heparin was omitted from the precipitating buffer to avoid fibrinogen depletion in patients at risk (low fibrinogen, postoperative). The average processed plasma volume was 3,386 ml in the standard and 2,963 ml in the modified treatment. Mean reductions (%) in plasma solute concentrations were (standard/ modified procedure) as follows: endotoxin, 50/57; TNF-alpha, 25/5; CRP, 49/55; fibrinogen, 49/6; total cholesterol, 38/5; and apolipoprotein B (Apo B), 41/2. Both treatment modalities were equally effective in removing endotoxin and CRP. With the modified precipitation buffer, fibrinogen was not removed. To further simplify the extracorporeal treatment, we have designed a closed-loop circuit with 2 adsorbers in series, one for removal of TNF-alpha (dextran sulfate modified cellulose) and the other for removal of endotoxin (DEAE-cellulose). In vitro evaluation confirmed very efficient endotoxin and TNF-alpha removal from plasma. This system is very simple, operates at physiological pH, and uses adsorbers already in clinical use for other purposes.

Apolipoproteins B↗

PubMed1997

Evaluation of liquid chromatographic behavior of restricted-access media precolumns in the course of direct injection of large volumes of plasma samples in column-switching systems.

The chromatographic behavior of an alkyl-diol silica (ADS, 25 x 4 mm I.D.) and a semipermeable surface (SPS, 10 x 10 mm I.D.) supports two types of restricted-access media (RAM), which served as precolumns in column-switching systems for direct injection of large volumes of plasma samples (500 microl), was studied with regard to peak performance, retention and column back pressure. The adsorption of matrix proteins both on sealings (porous frits and sieves) and packings was also examined. Columns of ADS and SPS were unchanged after the injection of 10-20 ml human plasma under normal working conditions. Even when changes occurred on the precolumns (>50 ml of plasma in total), it was still possible to regenerate the column performance by replacing the column sieves, or by washing and removing columns from the system for a period, since the changes were more related to the blockage of sealings and/or the adsorption of proteins on the hydrophilic surfaces. Proteins could eventually be unspecifically adsorbed on the hydrophobic ligand of the support. It was found on one ADS column that the retention decreased by 20% and the pressure increased 30 bar after an intensive loading of 75 ml plasma (injection volume, 500 microl) without reconditioning procedure. Studies showed that the column sealings played the most important role for the lifetime of RAM columns. For ADS columns, using sieves without polytetrafluoroethylene (PTFE) nets were the best. No significant difference in column life span between SPS and ADS was found.

Adsorption↗

PubMed1997

Liquid chromatography-mass spectrometry with on-line solid-phase extraction by a restricted-access C18 precolumn for direct plasma and urine injection.

In this paper, the on-line coupling of solid-phase extraction, based on a restricted-access support with liquid chromatography-mass spectrometry (LC-MS), for the analysis of biological samples is described. The system was tested with cortisol and prednisolone for plasma analysis and arachidonic acid for urine analysis. A precolumn packed with a 25-micron C18 alkyl-diol support is used for direct plasma or urine injection. Using column-switching techniques, the analytes enriched on the precolumn are eluted to the analytical column without transfer loss. An on-line heart-cut technique was employed and only the analyte-containing fraction eluting from the LC column is directed to the MS to protect the LC-MS interface and ion-source from contamination. The whole system is operated in a parallel mode, that is, sample pre-treatment and LC-MS analysis are performed simultaneously to provide the shortest possible analysis time. The only off-line sample pre-treatment step required was centrifugation to remove particulate matter. With the fully automated system, total analysis times of 5 and 9.5 min were achieved for cortisol in serum and arachidonic acid in urine, respectively. Cortisol and related compounds were quantitatively recovered from plasma with a detection limit for prednisolone (direct injection of 100 microliters on restricted-access precolumn) of 2 ng/ml.

Arachidonic Acid↗

PubMed1997

Determination of methotrexate and its metabolite 7-hydroxymethotrexate by direct injection of human plasma into a column-switching liquid chromatographic system using post-column photochemical reaction with fluorimetric detection.

A simple, sensitive and fully automated column-switching system by direct injection of plasma samples for determination of methotrexate and its metabolite 7-hydroxymethotrexate was developed. The system utilized a C8 alkyl-diol silica precolumn coupled with a LiChrospher RP-18 analytical column, followed by a photoreactor and fluorimetric detection. The photo-oxidative irradiation was accomplished at UV 254 nm in the presence of 0.1% hydrogen peroxide in the eluent. Studies showed that the fluorimetric response was influenced by the reaction time, the degree of the reactor's transparency and the choice of the working wavelengths. By optimizing the content of acetonitrile in the eluent, methotrexate can be separated from 7-hydroxymethotrexate completely. The method validation revealed quantitative recoveries (> or = 94%) with coefficients of variation < or = 4.4%. The limits of detection and quantitation for determination of methotrexate were 0.20 and 0.36 ng, respectively, corresponding to 2.0 and 3.6 ng/ml for an injection volume of 100 microliters. It was possible to enhance the sensitivity further by injecting larger plasma volumes, up to 500 microliters.

Antirheumatic Agents↗

PubMed1996

Cross-linked iron dextran is an efficient oral phosphate binder in the rat.

BACKGROUND: There is a need for alternative oral phosphate binders. In-vitro studies showed that iron(III)oxide-hydroxide-modified cross-linked dextran is a promising, insoluble phosphate-binding agent. The present study was designed to assess its in-vivo efficacy and safety in the rat. STUDY, DESIGN AND METHODS: Iron(III)oxide-hydroxide modified dextran beads were mixed with normal rat feed in a proportion of 8% by weight. With this formula rats were fed for 4 weeks. A control group received the same diet without added phosphate binder. Samples of blood, urine, and faeces were taken from each animal before the phosphate binder was administered, 2 weeks later, and at the end of the examination period (day 29). Phosphate, calcium, iron were analysed in the blood samples. Calcium and phosphate concentrations were determined in the urine, phosphate, calcium, and iron concentrations in the excrements. Stability of the material in the duodenum was also simulated. RESULTS AND CONCLUSIONS: The results demonstrate an excellent phosphate-binding capacity of the material and a good tolerance during the intestinal passage. No significant chemical or enzymatic degradation, histological alterations, or other treatment-related macroscopic findings were recorded. The present efficacy and toxicity study has shown effective phosphate binding with no toxicity and no iron release after ingestion of this novel phosphate binding agent. We propose clinical evaluation studies to assess whether similar efficacy and safety can be shown in humans.

Administration, Oral↗

PubMed1995

Evaluation and routine application of the novel restricted-access precolumn packing material Alkyl-Diol Silica: coupled-column high-performance liquid chromatographic analysis of the photoreactive drug 8-methoxypsoralen in plasma.

A fully automated coupled-column HPLC method for on-line sample processing and determination of the photoreactive drug 8-methoxypsoralen (8-MOP) in plasma has been developed. The method is based on the novel internal-surface reversed-phase precolumn packing materials Alkyl-Diol Silica (ADS). This new family of restricted-access materials has a hydrophilic, electroneutral outer particle surface and a hydrophobic internal pore surface. The supports tolerate the direct and repetitive injection of proteinaceous fluids such as plasma and allow a classical C18-, C8- or C4-reversed-phase partitioning at the internal (pore) surface. The total protein load, i.e. the lifetime of the precolumn used in this study (C8-Alkyl-Diol Silica, 25 microns, 25 x 4 mm I.D.), exceeds more than 100 ml of plasma. 8-MOP was detected by its native fluorescence (excitation 312 nm, emission 540 nm). Validation of the method revealed a quantitative and matrix-independent recovery (99.5-101.3% measured at five concentrations between 21.3 and 625.2 ng of 8-MOP per milliliter of plasma), linearity over a wide range of 8-MOP concentrations (1.2-3070 ng of 8-MOP/ml, r = 0.999), low limits of detection (0.39 ng of 8-MOP/ml) and quantitation (0.79 ng of 8-MOP/ml) and a high between-run (C.V. 1.47%, n = 10) and within-run (C.V. 1.33%, n = 10) reproducibility. This paper introduces coupled-column HPLC as a suitable method for on-site analysis of drug plasma profiles (bedside-monitoring).

Calibration↗

PubMed1995

Coupled-column liquid chromatographic analysis of epirubicin and metabolites in biological material and its application to optimization of liver cancer therapy.

A specific, sensitive and fully automated coupled-column LC method for the determination of the anthracycline cytostatic epirubicin and four metabolites in the biological materials human plasma, liver homogenate and liver tumour homogenate has been developed. System-integrated sample processing was achieved using a new restricted access silica precolumn packing. This porous Alkyl-Diol Silica (ADS) was specially designed for the direct and repetitive injection of proteinaceous samples. It consists of a hydrophilic and electroneutral external particle surface (glyceryl-residues) and a hydrophobic reversed-phase internal surface (butyryl-, octanoyl- or octadecyl-residues). These bimodal chromatographic properties allow retention of low molecular analytes by classical RP-chromatography exclusively at the lipophilic pore surface. Macromolecular constituents of the sample matrix (e.g. proteins) are size-excluded by 5 nm pores and quantitatively eliminated in the interstitial void volume. On-line analysis was performed by coupling a C4-Alkyl-Diol precolumn (20 x 4 mm i.d., particle size 25 microns) and LiChrospher RP Select B analytical column (250 x 4 mm i.d., particle size 5 microns) via an electrically driven six-port valve. Separation of the parent compound and its metabolites was achieved with a mobile phase consisting of water (0.1% triethylamine, v/v, pH 2.0 adjusted with trichloroacetic acid)-acetonitrile (70:30, v/v) at a flow rate of 1 ml min-1. The analytes were detected using their natural fluorescence (excitation 445 nm, emission 560 nm). The method described is used for the determination of pharmacokinetics of epirubicin and its metabolites in order to evaluate and optimize treatment regimen of liver cancer chemoembolization therapy.

Chromatography, Liquid↗

PubMed1994

Reduction of the incidence of rejection by adjunct immunosuppression with photochemotherapy after heart transplantation.

In this study, photochemotherapy (PCT) was used for adjunct immunosuppression in the first six months after heart transplantation (HTx). Fifteen patients after orthotopic HTx were included in the study; all received standard triple-drug immunosuppression including cyclosporine, azathioprine and glucocorticoids, but no adjunct therapy with mono- or polyclonal antibodies. The patients were divided into three groups: group I served as control with no additional treatment; group II received adjunct treatment with 10 courses of PCT (single-day treatments); and group III received 20 PCT courses since it was given each time on two consecutive days. PCT was started in both groups on day one after HTx; it was applied with a higher frequency in the early postoperative period and thereafter continued at four-week intervals for a total of 6 months. The photopheresis method for PCT included extracorporeal UVA irradiation of mononuclear cells that were treated with the photosensitive drug 8-methoxypsoralen (8-MOP) and subsequently retransfused to the patient. A new liquid form of 8-MOP was added directly to the buffy coat, resulting in reliable and sufficient drug levels in the cell suspension during the irradiation period; problems caused by oral application due to unpredictable variations in gastrointestinal absorption were thus prevented. Analysis of the total numbers of acute rejection episodes (AREs) within the first four weeks after HTx revealed a more impressive decrease by double PCT (group III, 3 AREs) than by single PCT (group II, 5 AREs) in comparison with the control (group I, 6 AREs). Over the total observation time (mean: 9.6 months), however, both PCT schedules reduced the total number of AREs observed in the control group (20 AREs) equally by more than 50% (9 AREs each in groups II and III) (P = 0.007). Furthermore, PCT treated patients had significantly fewer infections (6 infections in each group) than control group patients (15 infections) (P = 0.026); this, however, may be accounted for by the higher number of acute rejections in the control group and consequent increase in unspecific immunosuppression treatment. Our results suggest that PCT is a safe and effective method of adjunct immunosuppression that can be applied early in the postoperative period; it reduces the number of rejection episodes and does not increase the risk of infections.

Adult↗

PubMed1994

Characterization and extracorporeal application of a new phosphate-binding agent.

A new phosphate-binding agent which does not cause any severe side effects in vivo was developed by modifying a crosslinked dextran with polynuclear iron(III)oxide-hydroxide. Its particle size ranges from 150 to 300 microns, and the iron content was about 18% by dry weight. The oxidation state of iron was characterized by ESCA and Mössbauer spectroscopy. The maximum phosphate binding capacity of the iron(III)oxide-hydroxide-modified dextran was determined with respect to aqueous phosphate solutions, human serum and whole blood. The effects on whole blood count, haemolysis, protein concentration and enzyme activities were examined. In addition, the influence of phosphate concentration, pH and temperature on the phosphate uptake of the material was determined. The results show that this new adsorbent might provide an alternative to conventional phosphate-binding agents. This paper also describes the first experiments on the therapeutic application of the material in an extracorporeal blood perfusion system for the treatment of hyperphosphataemia during haemodialysis.

Adsorption↗

PubMed1992

Coupled-column high-performance liquid chromatographic method for the determination of 1-hydroxypyrene in urine of subjects exposed to polycyclic aromatic hydrocarbons.

A coupled-column high-performance liquid chromatographic system for integrated, on-line sample processing and the determination of free and conjugated 1-hydroxypyrene in urine has been developed. The method is based on a "tailor-made" copper phthalocyanine-modified porous-glass precolumn packing material, which allows a direct and repeated injection of urine samples and a selective enrichment of trace amounts of particular components. The fully automated method has a low detection limit (0.01 pmol), a quantitative and matrix-independent recovery and a highly reliability, as shown by an interlaboratory comparison of methods.

Chromatography, High Pressure Liquid↗

PubMed1988

On-line sample processing and analysis of diol compounds in biological fluids.

We developed a coupled dual column system with an optional post-column derivatization for on-line sample processing, trace enrichment and analysis of aromatic 1,2-diol and aliphatic cis-diol biomolecules (e.g. catecholamines, ribonucleosides). The fully automated high-performance liquid chromatography analyzer tolerates the direct injection of proteinaceous fluids by use of a unique bonded-phase precolumn material which allows the simultaneous performance of covalent affinity and size-exclusion chromatography.

Catecholamines↗

PubMed1988

A minimum structured adenine nucleotide for ADP/ATP transport in mitochondria.

An ADP analogue, i.e. 3H- or 14C-labeled 5'-diphosphate of 6-(beta-D-ribofuranosyl-methyl)-4-pyrimidinamine, was synthesized, the structure of which was deduced from structure-activity studies on the substrate specificity of the nucleotide-binding center of the inner mitochondrial membrane integrated ADP/ATP carrier protein. Bearing only the minimal but substrate-essential recognition structures, minimum structured ADP (msADP) is bound to the cytosol-facing active center and transported by the highly specific carrier system across the inner mitochondrial membrane.

Adenosine Diphosphate↗