A new perspective on fungal metabolites: identification of bioactive compounds from fungi using zebrafish embryogenesis as read-out

There is a constant need for new therapeutic compounds. Fungi have proven to be an excellent, but underexplored source for biologically active compounds with therapeutic potential. Here, we combine mycology, embryology and chemistry by testing secondary metabolites from more than 10,000 species of fungi for biological activity using developing zebrafish (Danio rerio) embryos. Zebrafish development is an excellent model for high-throughput screening. Development is rapid, multiple cell types are assessed simultaneously and embryos are available in high numbers. We found that 1,526 fungal strains produced secondary metabolites with biological activity in the zebrafish bioassay. The active compounds from 39 selected fungi were purified by liquid-liquid extraction and preparative HPLC. 34 compounds were identified by a combination of chemical analyses, including LCMS, UV-Vis spectroscopy/ spectrophotometry, high resolution mass spectrometry and NMR. Our results demonstrate that fungi express a wide variety of biologically active compounds, consisting of both known therapeutic compounds as well as relatively unexplored compounds. Understanding their biological activity in zebrafish may provide insight into underlying biological processes as well as mode of action. Together, this information may provide the first step towards lead compound development for therapeutic drug development.

A specific method for the measurement of cyclosporin A in human whole blood by liquid chromatography-tandem mass spectrometry

Therapeutic monitoring of the immunosuppressant cyclosporin A (CsA) is routinely performed by immunoassays to make individual dosage adjustments for patients after organ transplantation. High-performance liquid chromatography with ultraviolet detection (HPLC-UV) has been used as the reference method. However, HPLC-UV methods frequently suffer from chromatographic interferences that affect accuracy and reproducibility. A sensitive, specific HPLC-tandem mass spectrometry (HPLC/MS/MS) method for the quantitation of CsA has been developed. One hundred microliters CsA whole blood sample containing cyclosporin C (CsC) as the internal standard was extracted with ethyl ether. High-performance liquid chromatography separation was accomplished on an RP-C18 narrow-bore column at 50 degrees C with a linear gradient elution followed by on-line ion-spray ionization MS/MS analysis. The standard curve was established in the range of 10 to 1000 microg/l (r = 0.9989, n = 8). Limits of detection and quantitation were 1 microg/l and 5 microg/l, respectively. Imprecision was <4% across three control levels. Cyclosporine A recovery averaged 88%. Six metabolites: AM1, AM9, AM4N, Am1c, AM1a, and AM19 were identified with this method. AM1, AM9, and AM1c were further differentiated with a modification to the MS/MS conditions. This method was used in a comparison study with an HPLC-UV method: HPLC = 1.055 LC/MS/MS + 7.05 (microg/l), (Sy/x = 25.7), r2 = 0.982. With its high degree of sensitivity and specificity, this LC/MS/MS method offers a valuable reference method for immunoassay evaluation and a tool for metabolite investigation.

Simultaneous quantification of cyclosporin A and its major metabolites by time‐of‐flight secondary‐ion mass spectrometry and matrix‐assisted laser desorption/ionization mass spectrometry utilizing data analysis techniques: Comparison with high‐performance liquid chromatography

Simultaneous quantification of cyclosporin A (CsA) and its major metabolite (AM1) in blood has been achieved using time‐of‐flight secondary‐ion mass spectrometry (TOF‐SIMS) and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI/TOF‐MS). Previous investigations indicated that spectral interferences exist in the analysis of CsA blood samples by the above methods. In TOF‐SIMS, interference is caused by overlap of the Ag‐cationized internal standard, cyclosporin D (CsD), with the Ag‐cationized metabolite, AM1. To resolve this interference and obtain quantitative information, cross‐correlation analysis was applied to the TOF‐SIMS data. Application of damped non‐linear least squares curve‐fitting was carried out to resolve an interference in the MALDI/TOF‐MS data due to multiple cationization products (i.e. Na and K). Measurement of standard samples indicates that the minimum accuracy (95% confidence level) of the TOF‐SIMS method was better than 9% for CsA and 13% for AM1 using only one standard curve'. Similarly, the minimum accuracy of the MALDI/TOF‐MS method was determined to be 14% for CsA and better than 25% for AM1. Blood samples obtained from transplant patients receiving CsA were analyzed by polyclonal fluorescence polarization immunoassay, high‐performance liquid chromatography (HPLC), and by both TOF‐MS methods. Both TOF‐MS results for CsA and mono‐hydroxylated CsA are in good agreement with the HPLC results.

Hydrolysis of cyclosporin A: identification of 1,11 seco-cyclosporin A and 4,5 seco-isocyclosporin A by FAB-MS/MS

We have previously reported that treatment of CsA with aqueous HCI gives rise to the formation of a number of water-soluble compounds. Two of these were identified from their FAB-MS/MS spectra as open-chain nona- and decapeptides. We describe here the identification of two other main compounds deriving from the same treatment. Identification was rendered possible from the comparison of their FAB-MS/MS spectra with those of methyl and acetyl derivatives. The two compounds are water-soluble, open-chain undecapeptides corresponding to 1.11 seco-CsA and of 4.5 seco-isoCsA, respectively.

Cyclosporin metabolism in transplant patients

The immunosuppressant cyclosporin, a cyclic undecapeptide, is metabolized to more than 30 metabolites. Cytochrome P450IIIA enzymes located in liver and small intestine are responsible for the biotransformation of cyclosporin and its metabolites and are the site of several drug interactions. It is still under discussion, whether the cyclosporin metabolites are involved in the immunosuppressive and/or toxic activities of cyclosporin. While isolated metabolites show not more than 10-20% of the activity of the mother compound in vitro, metabolite combinations have additive and synergistic effects. Isolated metabolites show no toxic effects in rat models while there is an association between metabolite blood concentrations and cyclosporin toxicity in several clinical studies. Possible mechanisms for the toxic effect of cyclosporin metabolites are covalent binding to macromolecules in liver and kidney, alteration of the cytochrome P450 pattern in liver and kidney, increased endothelin production in the kidney and synergistic effects of cyclosporin combinations on mesangial cells. Liver dysfunction leads to an alteration of the metabolite patterns and to increased concentrations of cyclosporin metabolites in blood. In conclusion there is evidence that cyclosporin metabolites may contribute to cyclosporin toxicity and high metabolite blood concentrations in patients should not be tolerated.