Differentiation of cyclosporin A from isocyclosporin A by liquid chromatography/electrospray ionization mass spectrometry with post-column addition of divalent metal salt

RATIONALE

Cyclosporin A (CsA) rearranges to its isomer isocyclosporin A (isoCsA) upon acid hydrolysis and also during ionization in the ion source of the mass spectrometer. It has been reported that both compounds could not be differentiated by tandem mass spectrometry (MS/MS) using atmospheric pressure ionization (API) sources and ambiguously differentiated by using other sources. In order to analyze these compounds which are common fungal metabolites, it is relevant to develop a simple method for their differentiation.

METHODS

CsA and isoCsA were analyzed by liquid chromatography/mass spectrometry (LC/MS) with post-column addition of metal ion solutions in a quadrupole time-of-flight instrument equipped with an electrospray ionization (ESI) source.

RESULTS

Mass spectra of CsA obtained upon post-column addition of solutions of Ca(II), Cu(II) and Zn(II) showed complexes between cyclosporin and the metal, including [2CsA + Me](2+) and [CsA-H + Me](+). These complexes were not observed in the spectra of isoCsA. The same results were observed at different metal concentrations.

CONCLUSIONS

Differentiation via metal complexation in positive ion mode LC/ESI-MS was performed to simultaneously distinguish CsA and its isomer isoCsA.

[Complex of cyclosporins produced by Tolypocladium inflatum isolated from soil sample from Buriatiia]

A micromycete culture was isolated from a soil sample of Buryatiya and identified as Tolypocladium inflatum No. 2. The culture was shown to produce a complex of cyclosporins of unusual component structure: the content of cyclosporin A (55-60%) was the same as that in the substances produced by the majority of the described cultures, the content of cyclosporin B was much higher (about 40%) and the content of cyclosporin C was relatively low (about 3%). An appreciable content of cyclosporin (Leu4)Cs (3%) proved to be of interest.

Cyclosporins from Mycelium sterilae MS 2929

The structures of two new cyclosporins were elucidated by NMR and MS methods as cyclo[-MeBmt(1)-Abu(2)-Sar(3)-MeLeu(4)-Val(5)-MeLeu(6)-Ala(7)-d-Ala(8)-MeLeu(9)-MeNva(10)-MeVal(11)-] and cyclo[-MeBmt(1)-Abu(2)-Sar(3)-MeLeu(4)-Abu(5)-MeLeu(6)-Ala(7)-d-Ala(8)-MeLeu(9)-MeLeu(10)-MeVal(11)-].

Separation of peptides utilizing ultrahigh-temperature micellar electrokinetic chromatography

The use of ultrahigh column temperatures, up to 110 degrees C, in micellar electrokinetic capillary chromatography was investigated. The number of plates generated per unit time increased from 0.22 to 12.8 plates/s for separations at 15 degrees C and 110 degrees C, respectively. Ultrahigh-temperature micellar electrokinetic capillary chromatography was used for the separation of cyclic undecapeptides (cyclosporins). A minimum resolution of 1.39 was calculated for a critical peak pair at 110 degrees C, which is more than a 50% increase over resolution generated at 40 degrees C. During a run time of more than 90 min at 110 degrees C and at pH 9.3, no sample degradation or solvent boiling was observed.

Interaction of cyclophilin and cyclosporins monitored by affinity capillary electrophoresis

The affinity capillary electrophoretic separation of the complex of the enzyme cyclophilin (Cyp) with the immunosuppressive drug cyclosporin A (CsA) from uncomplexed Cyp and CsA in phosphate buffer (pH 8) under non-denaturing conditions by equilibrium-mixture analysis is reported. Using a new approach combining mobility-shift analysis and electrophoretically mediated microanalysis the binding constant of rhCyp18 to CsA and derivatives was estimated.

Separation of cyclosporins by high-performance liquid chromatography and mass spectrometric study of cyclosporin metabolites

A semi-preparative (high-performance liquid chromatography) method for separation of cyclosporin metabolites in a fungal fermentation sample was developed. By using the optimized chromatographic separation, 20 cyclosporin metabolites in a process sample were isolated, and their molecular masses measured by double focusing sector mass spectrometry. The structures of some of the cyclosporin congeners were investigated by tandem sector mass spectrometry using fast atom bombardment ionization. The isobaric cyclosporins D ([Val2] CS) and G ([Nva2] CS) were differentiated by significantly different relative intensities of a fragment ion at m/z 30 [CH4N]+ from a precursor ion at m/z 72 [C4H10N]+. Otherwise the tandem mass spectrometry (MS/MS) spectra of the fragment ions of the two isomers are very similar. Cyclosporin A and iso-cyclosporin A were also analysed by high energy MS/MS. No significant fragment ions were found to provide distinctions between them. Relatively good overviews of process samples containing very similar structures were achieved by combining LC separation, molecular ion recognition and MS/MS characterization.

Cyclosporin C is the main antifungal compound produced by Acremonium luzulae

A strain of Acremonium luzulae (Fuckel) W. Gams was selected in screening new microorganisms for biological control of fruit postharvest diseases, especially gray and blue mold diseases on apples and strawberries. This strain manifests a very strong activity against a large number of phytopathogenic fungi. In this work, the product responsible for this antifungal activity was isolated from modified Sabouraud dextrose broth cultures of A. luzulae. It was purified to homogeneity by reverse-phase column chromatography. On the basis of UV, infrared, and 1H and 13C nuclear magnetic resonance spectra, mass spectral analysis, and the amino acid composition of the acid hydrolysates, the antibiotic was determined to be cyclosporin C. Cyclosporin C showed a broad-spectrum activity against filamentous phytopathogenic fungi but no activity against bacteria or yeasts. Its antifungal activity is only fungistatic. In contrast to Tolypocladium inflatum, another cyclosporin-producing strain, A. luzulae, did not produce additional cyclosporins. This was confirmed by in vivo-directed biosynthesis.

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.

Cyclosporins from Tolypocladium terricola

New natural cyclosporins were isolated from the mycelium of surface cultivated fungus Tolypocladium terricola. The chemical structures of [Leu4] CS and [MeLeu1] CS = cyclosporin-J, were deduced from the NMR and mass spectral data. Biological activity of new cyclosporins is reported based on the proliferative mitogen stimulation test.

Substrate specificities of cyclosporin synthetase and peptolide SDZ 214-103 synthetase. Comparison of the substrate specificities of the related multifunctional polypeptides

The recently discovered multifunctional polypeptide cyclosporin synthetase is capable of synthesizing the cyclic undecapeptide cyclosporin A in a batch reaction. Substrates are the unmethylated constitutive amino acids of cyclosporin A. Exchange of one or more of these by various amino acids gives a picture of the substrate specificity of the enzyme in vitro, which is different from the known picture obtained by in vivo studies. The uncommon amino acid butenylmethylthreonine in position 1 of the cyclosporin ring can be exchanged by an unexpected large spectrum of different amino acids, showing a great flexibility of this site. Position 2, on the other hand, which shows the greatest variability in vivo, has an only slightly lower specificity in vitro. Position 3 has a very high degree of specificity; positions 4, 6, 7, 9, and 10 have marginally less. The variability of positions 5 and 11 is moderate, whereas position 8 shows only low substrate specificity in vitro. In general, most sites of SDZ 214-103 synthetase appear to be more specific than those of cyclosporin synthetase. Site 11 has nearly identical substrate specificity compared with that of cyclosporin synthetase. The D-2-hydroxy acid position (position 8) can be occupied by a large spectrum of substrates varying from D-lactic acid to D-2-hydroxyisocaproic acid. Within the limits of the present data, the addition of further functional groups to the D-2-hydroxy acid moiety are apparently not tolerated by the enzyme.

The yeast cyclophilin multigene family: purification, cloning and characterization of a new isoform

Cyclophilins (Cyps) constitute a highly conserved family of proteins present in a wide variety of organisms. Historically, Cyps were first identified by their ability to bind the immunosuppressive agent cyclosporin A (CsA) with high affinity; they later were found to have peptidyl-prolyl cis-trans isomerase (PPIase) activity, which catalyzes the folding of oligopeptides at proline-peptide bonds in vitro and may be important for protein folding in vivo. Cells of Saccharomyces cerevisiae contain at least two distinct Cyp-related PPIases encoded by the genes CYP1 and CYP2. A yeast strain (GL81) containing genomic disruptions of three known yeast PPIase-encoding genes [CYP1, CYP2 and RBP1 (for rapamycin-binding protein); Koltin et al., Mol. Cell. Biol. 11 (1991) 1718-1723] was previously constructed and found to be viable. Soluble fractions of these cells possess residual CsA-sensitive PPIase activity (2-5% of that present in wild-type cells as assayed in vitro). We have purified an approx. 18-kDa protein exhibiting PPIase activity from a soluble fraction of GL81 cells and determined that its N-terminal amino acid (aa) sequence exhibits significant homology (but nonidentity) to the Cyp1 and Cyp2 proteins. We designate the gene for this new protein, CYP3. Using a degenerate oligodeoxyribonucleotide (oligo) based on the N-terminal aa sequence, plus an internal oligo homologous to a conserved region within the portion of CYP1 and CYP2 that had been deleted in the genome, a CYP3-specific DNA fragment was generated by the polymerase chain reaction (PCR) using GL81 genomic DNA as a substrate. This PCR fragment was used as a probe to isolate CYP3 genomic and cDNA clones.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective 13C-labelling of cyclosporin A

Cyclosporin A is biosynthetically labelled with 13C by growing an overproducing strain of Tolypocladium inflatum on minimal media containing either [1-13C]-, [2-13C]-, [3-13C]- or [6-13C]glucose as the only carbon source. NMR analysis of the 13C-labelled peptide showed a labelling pattern in which 13C occurs at specific sites. These can be predicted by consideration of the relevant biosynthetic pathways. Quantitation of the site-specific enrichments revealed that the 13C-label incorporation is efficient and selective. Metabolic fluxes through alternative pathways can also be estimated from these results. Isotopically labelled peptides will be a very useful tool for the study of molecular interactions with their receptors.

The isolation, structural characterization, and immunosuppressive activity of cyclosporin G (NVa2-cyclosporine) metabolites

Seven cyclosporin G metabolites were isolated by high-performance liquid chromatography from the urine of normal subjects receiving the drug. The structure and purity of the metabolites were assessed by fast atom bombardment/mass spectroscopy, by proton nuclear magnetic resonance (NMR), and by 13C-NMR. The structural modifications of the cyclosporin G metabolites consisted primarily of hydroxylation and demethylation, as is the case for cyclosporin A metabolites. The immunosuppressive activities of the metabolites were tested in three separate in vitro systems: a primary and secondary mixed lymphocyte system, as well as a mitogen stimulated system. In general, the metabolites have immunosuppressive activity of less than 10% of cyclosporin G. The significance of these findings in relation to the therapeutic monitoring of cyclosporin G is discussed.

Isolation and structural identification of 9hydroxy-9desmethyl-cyclosporine

A metabolite of cyclosporine has been isolated and its structure identified through use of HPLC and tandem mass spectroscopy. Fast atom bombardment mass spectrometry of an HPLC fraction co-eluting with 1 eta hydroxy-cyclosporine (M17) indicated that the mass of this metabolite was 2 Da greater than that of cyclosporine. Further isolation by HPLC yielded a pure fraction, which we analyzed with tandem mass spectrometry. Linear acyl fragment ions originating from the metabolite under collision-induced dissociation were consistent with the difference in mass being associated with amino acid 9 in the cyclosporine backbone. We propose a nomenclature system for future discussion of cyclosporine metabolites.

Isolation of 10 cyclosporine metabolites from human bile

Ten metabolites of cyclosporine were isolate from the ethyl ether extract of bile from four liver transplant patients receiving cyclosporine. Two of the metabolites were unique and previously unidentified. Liquid-liquid partitioning into diethyl ether with subsequent defatting with n-hexane was used for the initial extraction from bile. Separation of the individual metabolites (A-J) was performed using a Sephadex LH-20 column and a gradient high performance liquid chromatographic method. The molecular weights of the isolated metabolites were determined by fast atom bombardment/mass spectrometry. Gas chromatography with mass spectrometric amino acid analysis was also used to identify the amino acid composition and the hydroxylation position of metabolites A, B, C, D, and G. Proton nuclear magnetic resonance spectra were utilized to distinguish the chemical shifts of N-CH3 singlets and NH doublets of metabolites A, B, C, and D. Metabolites A, E, F, H, I, and J were reported previously in human urine and animal bile. Metabolites C and D are dihydroxylated compounds which cannot be clearly described as previously isolated compounds. Metabolites B and G are novel metabolites with a mass fragment which corresponded to a loss of 131 Da from the protonated molecular ion (MH+) in the fast atom bombardment/mass spectrometry, suggesting that the double bond in amino acid 1 has been modified. Metabolites B and G were primarily isolated from the bile of one of the liver transplant patients which contained abnormally high concentrations of these two metabolites. The method described is an efficient procedure for isolating milligram quantities of the major metabolites with greater than 95% purity.

Cyclosporins--new analogues by precursor directed biosynthesis

Cyclosporin A (ciclosporin), a potent and clinically important immunosuppressive drug (Sandimmun), represents the main component of a group of over 25 closely related, cyclic undecapeptides produced by the fungus Tolypocladium inflatum. By feeding experiments using DL-alpha-allylglycine as precursor, specific incorporation in position 2 was attained leading to [Allylgly2]cyclosporin A. Exogenously supplied L-beta-cyclohexylalanine results in the almost exclusive production of [MeCyclohexylala1]cyclosporin A (replacement of methylbutenyl-methylthreonine-1). D-Alanine in position 8 can be successfully substituted by D-serine. The new [D-Ser8] analogues of the cyclosporins A, C, D and G as well as [Allylgly2]cyclosporin A exhibit high immunosuppressive effects.

Isolation and in vitro characterization of a novel immunosuppressive cyclosporine metabolite

A novel metabolite (M-E) was identified by high-performance liquid chromatography in the serum of cyclosporine-treated renal transplant recipients during a second wave of immunosuppressive activity after disappearance of the initial wave due to the direct effect of CsA. M-E was identified in human serum and porcine bile both by HPLC and by a preparative thin-layer chromatography (TLC). It demonstrated homogeneity with characteristic retention times on C8 and C18 column HPLC systems using a variety of elution systems, and distinctive TLC mobility (Rf 0.35). Metabolite E (M-E) was documented to be a CsA metabolite by radioactive tracer studies, by crossreactivity with a polyclonal sheep antibody in radioimmunoassay, and by the presence of a characteristic mass spectrum. Further, in vitro immunosuppressive assays documented effects of M-E similar to those of CsA. The relative activity of M-E versus CsA was quantitated by potency ratios: for inhibition of normal human mixed lymphocyte culture reactions, the ratio was 0.79 +/- 0.23. Interindividual differences were observed in patient susceptibility to MLR inhibition not only by CsA, as previously reported by others, but also by M-E. There was a lesser effect of M-E compared with CsA in inhibiting proliferation of, and IL-2 generation by, C3H murine splenocytes stimulated with concanavalin A: the potency ratios for both systems were about 0.5, possibly reflecting an interspecies variability in generation of or susceptibility to M-E. These studies suggest that heretofore unidentified metabolites--including, but not limited to, M-E--may play an important role in the immunosuppressive effect of CsA in man.

A simple improved method for the measurement of cyclosporin by liquid-liquid extraction of whole blood and isocratic HPLC

The current HPLC methods of cyclosporin measurement have been reviewed and all aspects assessed. A simple isocratic C-18 reverse phase HPLC method with improved efficiency is described for the routine measurement of cyclosporin in whole blood. An alkaline ether extraction is followed by an acid wash, solvent evaporation and two hexane washes of the reconstituted extract. The turn-round time for a single sample is 1 h. Daily batches of up to 40 patient samples can be easily measured with this method. The results are compared with those from the Sandoz radioimmunoassay (RIA) method.

Enzymatic synthesis of cyclosporin A

An enzyme fraction, isolated from crude extracts of the fungus Tolypocladium inflatum, strain 7939/F, is able to synthesize the undecapeptide cyclosporin A. The formation of cyclosporin A was monitored by incorporation of the radiolabeled constituent amino acids of cyclosporin A or by using S-adenosyl-L-[14C-methyl] methionine. The structure of cyclosporin A, synthesized enzymatically in vitro, was confirmed by chromatographic comparison with the authentic compound and by amino acid analyses. Replacement of L-2-aminobutyric acid in the reaction mixture by L-alanine, L-threonine, L-valine, or L-norvaline yields the naturally occurring cyclosporins B, C, D, and G. Also, D-alanine could be replaced by D-serine to yield [D-Ser8]cyclosporin A.

Thin-layer chromatographic detection of cyclosporine and its metabolites in whole blood using rhodamine B and alpha-cyclodextrin

High-performance thin-layer chromatography (HPTLC) has advantages for the analysis of cyclosporine (CsA) and its metabolites in peripheral blood not shared by the radioimmunoassay (RIA) or high-performance liquid chromatography (HPLC) methods. While separation by HPTLC and HPLC is based on relative hydrophobicity, HPTLC (unlike HPLC) is capable of concurrent multisample analysis without expensive instrumentation. As distinguished from RIA, HPTLC detects CsA and metabolites as separate components, and does not use radioactive reagents. A novel rhodamine B/alpha-cyclodextrin stain was developed and the characteristic retention factors (Rf values), as determined by the ratio of the migration distance of a component in relation to the solvent front, were determined for the mobile phase heptane: pyridine: ethyl acetate (100: 75: 1, v/v) on aminopropyl-bonded silica gel HPTLC plates: 0.65, cyclosporin D (CsD); 0.60, CsA; 0.50, dihydrocyclosporin C (dhCsC); 0.42, metabolites M-21 and M-17; 0.40, M-1; 0.35, M-E; 0.25, M-D; and 0.22, M-A. Metabolite M-18 showed migration similar to that of M-17 using a mobile phase of heptane: pyridine: acetonitrile (5:2:1, v/v) in the 0.60-0.50 range. The metabolite profiles were obtained in 8 patients receiving the drug for the first time. The HPTLC analytical technique identifies CsA and its metabolites in peripheral blood and offers advantages for pharmacologic monitoring of transplant patients.

Isolation and liquid chromatographic determination of the cyclic peptide mycotoxin cyclosporin A from rice

A simple method for determination and quantitation of a cyclic peptide mycotoxin, cyclosporin A, in rice is presented. Rice inoculated with Trichoderma polysporum (Link ex Pers.) was extracted with methylene chloride after 4 weeks of incubation. Cyclosporin A was isolated from extracts by using open bed gel filtration column chromatography (LH-20, acetonitrile) and monitored with thin layer chromatography and reverse phase liquid chromatography coelution with a standard. Preliminary thin layer chromatographic methods were developed. Cyclosporin A was detected by iodine and after partial acid hydrolysis by ninhydrin and UV light. A liquid chromatographic method was developed that used a reverse phase disposable cartridge cleanup and isocratic chromatography with a reverse phase octadecylsilica column and a UV detector set at 212 nm. Recovery of cyclosporin A from spiked rice samples (mg/g range) was 85%.

Preparation, extraction and high performance liquid chromatography of cyclosporin A from plasma that contains interfering compounds

Cyclosporin A (CyA) in human plasma-containing interfering compounds was determined by high performance liquid chromatography (HPLC) after the plasma had been subjected to incubation with proteinase K. This hydrolytic enzyme did not hydrolyse the cyclosporins and was therefore an ideal aid in eliminating interfering peptides selectively. The use of Extrelut as an extraction aid contributed much to higher yields of cyclosporins. Ethyl acetate, the extraction solvent used, gave less complex profiles on HPLC chromatograms than other solvents (eg diethyl ether and methanol) and contributed to a shorter chromatographic period per sample, an advantage in repetitive determinations.

[Search for new antibiotics of the cyclosporin group]

A total of 160 fungal cultures belonging to Trichoderma were isolated from soil samples collected in various regions of the USSR. The cultures were tested for production of antibiotics of the cyclosporin group, having a narrow antifungal spectrum. It was found that 7 cultures produced substances having a selective inhibitory effect on Asp. niger and no activity against gram-positive and gram-negative organisms. An antibiotic substance close by its physicochemical properties to cyclosporins was isolated from T. viride 122.