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Biomedical subjects

R Wyss

Publications and source records attributed to R Wyss.

At least 37 records · Page 2Linked to original sources
PubMed1996

Determination of the arotinoid mofarotene in human, rat and dog plasma by high-performance liquid chromatography with automated column switching and ultraviolet detection.

A sensitive and specific high-performance liquid chromatographic method was developed and validated for the determination of the third-generation retinoid (arotinoid) mofarotene (Ro 40-8757) in human, rat and dog plasma, using direct injection of deproteinated plasma samples, automated column switching (on-line solid-phase extraction) and ultraviolet detection. Plasma (0.5 ml) was deproteinated by adding ethanol (1 ml) containing the internal standard Ro 42-8659 (200 ng/ml). After centrifugation, 0.9 ml of the supernatant were directly injected onto a precolumn packed with C18 Corasil 37-50 microns. Polar plasma components were washed out from the precolumn using 1% ammonium acetate-acetic acid-acetonitrile (900:9:100, v/v/v). After valve switching, the pre-concentrated compounds were transferred to the analytical column (C18) in the backflush mode, separated by gradient elution and detected at 300 nm. The retention times (total run times) were approximately 15 and 20 min for the internal standard and mofarotene, respectively. The method was linear in the range 10-1000 ng/ml with a limit of quantification of 10 ng/ml. The mean recoveries were 80.4%, 81.7% and 77.8% (range 10-1000 ng/ml) and the inter-assay precision was 2.7% (range 20-1000 ng/ml), 1.5% and 2.0% (both range 100-1000 ng/ml) for human, rat and dog plasma, respectively. Mofarotene was found to be stable in human, rat and dog plasma stored at -20 degrees C for 3 months and 22 degrees C for 24 h. The method was successfully applied to clinical, pharmacokinetic and toxicokinetic studies.

Animals↗
PubMed1995

Chromatographic and electrophoretic analysis of biomedically important retinoids.

The determination of retinol (vitamin A) and its metabolites, as well as synthetic retinoids, in biological samples is a challenging task due to the sensitivity of these compounds to light, heat and oxygen, high protein binding, separation of geometric isomers and determination of low endogenous levels. Numerous procedures for sample preparation have been published for biological fluids and tissues, consisting of solvent extraction, solid-phase extraction (off-line) and HPLC with column switching (on-line solid-phase extraction). The last-mentioned technique has several advantages, including a high degree of automation, no evaporation of extraction solvents, protection from light and higher sensitivity. Due to the favourable UV characteristics of most retinoids, HPLC with UV detection is most often employed, and photodiode array detection is becoming more and more popular. Fluorescence and electrochemical detection have found only a limited field of application, but the use of LC-MS resulted in a few highly sensitive methods. Reconsideration of GC through the use of better deactivated columns and cold on-column injection and evaluation of new promising separation methods, such as supercritical fluid chromatography and capillary electrophoresis, have shown preliminary encouraging results, but appear to reach the required sensitivity only by coupling to MS. Therefore, HPLC with UV detection is still the method of choice for highly sensitive and selective retinoid determination, as well as for high sample throughput and robustness.

Chromatography, Gas↗
PubMed1995

Hybrid scanning transmission electron/scanning tunneling microscope system for the preparation and investigation of biomolecules.

A hybrid scanning transmission electron/scanning tunneling microscope vacuum system is introduced, which allows freeze drying and metal coating of biological samples and their simultaneous observation by scanning transmission electron microscopy and scanning tunnelling microscopy (STM). Different metal coatings and STM tips were analysed to obtain the highest possible resolution for such a system. Bovine liver catalase was used as a test sample and the STM results are compared to a molecular scale model.

Animals↗
PubMed1995

Metabolism of mofarotene in hepatocytes and liver microsomes from different species. Comparison with in vivo data and evaluation of the cytochrome P450 isoenzymes involved in human biotransformation.

The arotinoid mofarotene is a novel potent anticancer compound. The metabolic profiles obtained from rat, dog, and human plasma showed a good correlation with the corresponding in vitro profiles observed with liver microsomes and hepatocytes. Interspecies differences in its metabolism were investigated using microsomes prepared from the livers of the mouse, rat, dog, cynomolgus monkey, and humans. These in vitro experiments showed that, both qualitatively and quantitatively, the metabolic profiles obtained with cynomolgus monkey liver samples were similar to those observed with human liver material. However, rat and dog were also confirmed to be suitable species for assessing the safety of mofarotene, and were used in toxicology. The involvement of cytochrome P450 (CYP) in the metabolism of mofarotene was examined with human liver microsomes. CYP3A4 plays a major role in the metabolism, and CYP1A2 might be responsible for a minor pathway. Finally, the potential induction by mofarotene of four major CYP isoenzymes was investigated in rats. These experiments showed that CYP1A1 was clearly induced, whereas a slight induction of CYP3A and CYP2B was observed. Repeated administration of mofarotene had no effect on CYP2E1. These studies with liver microsomes and hepatocytes aided the selection of appropriate species for toxicology, and have provided information that will help to predict potential drug-drug interactions in clinical trials.

Animals↗