Immunosuppressive metabolites of cyclosporine in the blood of renal allograft recipients

Correlations between Calcineurin Phosphatase Inhibition and Cyclosporine Metabolites Concentrations in Kidney Transplant Recipients: Implications for Immunoassays

Cyclosporine exhibits a wide spectrum of metabolites that vary considerably in the extent to which they interfere with the various parent drug monitoring immunoassays. There is no consensus regarding the clinical significance of metabolites. Cyclosporine exerts its immunosuppressive action by inhibiting the enzyme calcineurin phosphatase. Determination of the enzyme's activity is one of the most promising pharmacodynamic markers. It is unknown how calcineurin phosphatase inhibition correlates with various cyclosporine monitoring assays and what is the potential impact of metabolites in this perspective? The aim of the present study was to determine the concentration of cyclosporine (by means of three different assay methods) and the four most significant metabolites (AM1, AM4N, AM9, and AM1C) in relation to calcineurin phosphatase inhibition. Twelve randomly selected cyclosporine-treated renal transplant patients were included in the study. Blood samples were drawn before, 1, 2, 3, 4, 6, 8, and 12 hr after oral intake of cyclosporine. Parent drug and metabolites were determined by liquid chromatography/tandem mass spectrometry (LC/MSMS). Additionally, cyclosporine concentration was determined by the enzyme multiplied immunoassay technique (EMIT) and by the polyclonal fluorescence polarization immunoassay (pFPIA). Calcineurin phosphatase activity was measured by its ability to dephosphorylate a previously phosphorylated 19-amino acid peptide. We found that calcineurin phosphatase inhibition correlates strongly with parent cyclosporine metabolites concentrations determined by all three assay methods. Determination methods that took metabolites into consideration exhibit stronger correlations with calcineurin phosphatase inhibition (sum of cyclosporin plus metabolites r=-0.93, LC/MSMS; pFPIA r=-0.94, P<or=0.001), compared with methods that measure exclusively the parent drug (EMIT: -0.84; LC/MS-MS: -0.81, P<or=0.05). Our results indicate that the immunosuppressive role of cyclosporines metabolites should not be considered valueless per se. Further research is required in order to verify the potential clinical importance of our observations.

Cyclosporine A and adverse effects on organs: histochemical studies

The discovery that cyclosporine A (CsA) was a powerful immunosuppressant had a significant impact on transplant medicine. Its molecular mechanism of action has been well defined in T cells and involved inhibition of critical signalling pathways that regulated T-cell activation. In fact, CsA inhibited calcineurin phosphatase activity and thereby activation of the transcription factor nuclear factor of activated T cells. Over 10 years, its use is limited by side effects, determining nephro- and hepatotoxicity, gingival hypertrophy, tremor and increased blood pressure. These negative effects have been identified through morphological alterations and/or clinical parameters, i.e. variation in glomerular filtration rate for nephrotoxicity. Nevertheless, CsA remains a therapeutic valuable agent and it is normally utilized into clinical practice even if different dose adjustments or discontinuations in a significant percentage of patients must be used. This review focuses on the following topics: mechanisms of action and drug metabolism, interactions with other drugs, clinical and morphological evaluation of toxic effects on target organs. In particular, the morphological evaluation of negative effects has been considered reporting light and ultrastructural studies on target organs both in normal and immunosuppressive conditions. Moreover, the histochemical and immunohistochemical variations in cellular metabolism and antigenic properties of cells present in the parenchyma of these organs are discussed.

Cyclosporine and its metabolites before and 2 h post-dose: comparative measurements of a monoclonal and a polyclonal immunoassay

The aim of the study was to investigate the better accuracy of the 2-h post-dose (C2) levels of cyclosporine (CyA), compared with the pre-dose (C0) levels and to evaluate the results measured by a monoclonal or a polyclonal immunoassay. The parent compound of CyA in C2 (monoclonal2) was measured in 53 kidney transplant patients by the monoclonal fluorescence polarization method, as well as the parent compound plus metabolites (polyclonal2) by the polyclonal fluorescence polarization method. Also, the parent compound was measured in 21 of the patients for the C0 (monoclonal0), whereas the parent compound plus metabolites in 36, for the C0 (polyclonal0). As level of metabolites was considered the difference between polyclonal and monoclonal values (polyclonal-monoclonal), either in C0 (metabolites0) or in C2 (metabolites2). The ratio polyclonal2/monoclonal2 gave a mean value of 1.7+/-0.2 (mean+/-SD), whereas the mean value of the ratio polyclonal0/monoclonal0 was 2.3+/-0.6, with almost double variation. The mean value of the ratio metabolites2/monoclonal2 was 0.7+/-0.2 and of the ratio metabolites0/monoclonal0 was 1.3+/-0.6. The difference between the two ratios is very significant (p = 0.000001) and they are not correlated with each other (r = 0.18, p = 0.44). The measurements of monoclonal0 and polyclonal0 or monoclonal2 and polyclonal2 are very significantly correlated (r = 0.94, p = 0.000001 and r = 0.97, p = 0.000001, respectively). In C0 the proportion of metabolites is higher than in C2, with a double variation, as the degree of metabolism is diverse. Consecutively, in monoclonal methods, as cross-reactions occur with metabolites, it is more accurate to use the C2 measurement for the evaluation of CyA. The application of both methods, the polyclonal and the monoclonal, could be a useful tool as it gives an estimation of metabolites whose degree of contribution to the immunosuppressive result is difficult to ascertain. Finally, if for reasons of clinical experience, the polyclonal method is used, then the mean therapeutic levels of polyclonal2 are 1.5-1.7 compared with monoclonal2.

Lack of specificity of cyclosporine immunoassays. Results of a College of American Pathologists Study

OBJECTIVE

To evaluate the cross-reactivity of the 6 most abundant cyclosporine A (CsA) metabolites in commonly used assays for CsA.

DESIGN

Whole blood samples containing either only 62 ng/mL CsA (A) or 62 ng/mL CsA and between 49 and 86 ng/mL of 1 of the 6 most abundant CsA metabolites (B) were lyophilized. One sample of A and 1 of B were mailed to each of the laboratories participating in the College of American Pathologists Proficiency Testing Program quarterly during a 3-year period (1999-2001). Method means and coefficients of variation were calculated for each mailing.

RESULTS

The study showed significant cross-reactivity of metabolites in all the immunoassay systems studied. Overall degree of interference decreased from Abbott TDx polyclonal > Abbott TDx monoclonal > DiaSorin > Syva EMIT. High-performance liquid chromatography methods gave results close to those found using mass spectrometric techniques.

CONCLUSIONS

Significant metabolite interference was found to occur with the immunoassay systems studied.

Evaluation and comparison of therapeutic monitoring of whole-blood levels of cyclosporin A and its metabolites in renal transplantation by HPLC and RIA methods

BACKGROUND

The aim of the work was to evaluate the possibility to estimate the level of cyclosporin A (CyA) metabolites as the difference of radioimmunoassay (RIA) non-specific and RIA specific methods.

METHODS

Blood samples of renal transplant patients were analyzed by three different methods: RIA specific method (CYCLO-Trac, DiaSorin, USA) (RIA(SP)), RIA non-specific method (Immunotech, Czech Republic) (RIA(NS)), and high performance liquid chromatography (HPLC) method.

RESULTS

Although values obtained by RIA(SP) correlated well those obtained by HPLC (RIA(SP)=0.995.HPLC+9.68; r(2)=0.962, n=448), the results of HPLC methods were lower by 8%. The values obtained by RIA(NS) were 2.57 times higher than the values obtained by RIA(SP) (RIA(SP)=0.356RIA(NS); r(2)=0.713, n=448). The ratio (CyA+CyA metabolites)/(CyA) calculated as the ratio RIA(NS)/RIA(SP) values for 42 renal transplant patients was relatively stable for each particular patient. The sum of selected CyA metabolites (M1+M17+M21) measured by HPLC correlated well with that estimated from the difference of RIA(NS)-RIA(SP): HPLC(metab)=0.921.(RIA(NS)-RIA(SP))+21.3; (r(2)=0.746, n=448).

CONCLUSION

The combination of both the specific and non-specific methods for the determination of CyA presents an improved means for the TDM of CyA and CyA metabolites in renal transplant patients. Moreover, a combination of both methods can help to elucidate some unexpected events, such as the persistence of high cyclosporin blood levels.

High-performance liquid chromatographic method for therapeutic drug monitoring of cyclosporine A and its two metabolites in renal transplant patients

A novel fast HPLC method was developed for the determination of cyclosporine A (CyA) and its two metabolites M17 (AM1) and M21 (AM4N) in blood. Whole blood was precipitated with zinc sulphate, extracted with diethyl ether, evaporated, dissolved in aqueous methanol and partitioned twice with n-hexane. Chromatography was carried out using a microbore RP-column under isocratic elution with acetonitrile-methanol-water (200:80:140, v/v/v) at 70 degrees C and a detector set at 205 nm. Linearity for all three compounds was tested in the range of 1-1000 ng/ml. Recovery was 97-109%, and a coefficient of variation was 1.6-8.8% depending on the particular compound and its concentration. The method was used for a group of renal transplant patients having an inadequate response to CyA therapy in order to evaluate the possible role of CyA and its metabolites on the occurrence of hypertension and other toxicological events.

Effect of grapefruit juice on the pharmacokinetics of microemulsion cyclosporine and its metabolite in healthy volunteers: does the formulation difference matter?

This study was conducted to determine the effect of grapefruit juice on the pharmacokinetics of microemulsion cyclosporine and its major metabolites, M1 and M17, in 12 healthy volunteers. Each subject received two oral doses of microemulsion cyclosporine with water or grapefruit juice. Each subject also received intravenous cyclosporine on a separate occasion. Blood samples were collected for assay of cyclosporine, M1, and M17 during a 24-hour period, and were analyzed by a high-performance liquid chromatography method. Compared with water, administration with grapefruit juice significantly increased peak concentration (Cmax) and area under the concentration-time (AUC) of cyclosporine. Administration with grapefruit juice increased the absolute bioavailability of microemulsion cyclosporine by 45%. For cyclosporine metabolites, administration with grapefruit juice decreased the Cmax and AUC of M1 by 21% and 15%, respectively. These findings suggest that concurrent administration with grapefruit juice increases the bioavailability of microemulsion cyclosporine significantly compared with water in healthy volunteers. The grapefruit juice affects each metabolite formation and its pharmacokinetics differently, which suggests that the major site of its formation is different.

Cyclosporin A and hydroxycyclosporine (M-17) affect the secretory phenotype of human gingival fibroblasts

The responsiveness of human gingival fibroblast populations to cyclosporin A (CsA) and its principal metabolite, hydroxycyclosporine (M17), was evaluated in cell culture. Gingival fibroblasts exhibited a dose-dependent accumulation and bell-shaped distribution of dansylated CsA. A 100-fold excess of non-labeled CsA prevented the accumulation of the fluorescent probe in the fibroblasts. Both CsA (400 ng/ml) and M17 (100 ng/ml) stimulated mean gingival fibroblast cell number to 23.2% and 36.7% above controls, and reduced mean collagen production by 37.7% and 37.4% below controls, respectively; however, neither CsA nor M17 affected mean protein production in comparison to control cultures. Analyses of responses to CsA and M17 by ligand-accumulating and non-accumulating fibroblasts sorted out from the parent cultures did not provide consistent interstrain responses either by cells representing the upper quartile of fluorescence or cells representing the bottom quartiles of fluorescence. These data demonstrate that CsA is accumulated by gingival fibroblasts and that CsA and M17 are potent modulators of gingival fibroblast phenotype.

Oral management of the patient with end-stage liver disease and the liver transplant patient

The patient with end-stage liver disease who is in need of a liver transplant should have a pretransplant dental evaluation. Such a patient faces lifelong immunosuppression with an increased risk of infection. This article discusses both the need for control of oral diseases before liver transplantation and guidelines for oral care in the immediately postoperative and long-term transplant patient. Specific indications for antibiotic prophylaxis and antibiotic regimens are presented; in addition, adverse reactions and side effects of immunosuppressant drugs are discussed. Pertinent drug interactions salient to the dental management of patients with end-stage liver disease are reviewed, and specific management recommendations for these patients are presented.

Cyclosporine metabolite cross-reactivity in different cyclosporine assays

OBJECTIVES

There is a controversy regarding the role of cyclosporine (CsA) metabolites in both immunosuppression and toxicity, and measurement of the parent drug is commonly recommended. High performance liquid chromatography (HPLC) is the method commonly used for specific measurement of the parent drug, but is very time consuming. Antibody techniques are available but vary in specificity. Mixed lymphocyte culture assay (MLC) is a functional bioassay for the measurement of CsA which measures both parent drug and active metabolites. Because it is time consuming and labor intensive, it is not practical to use the MLC to monitor patient's CsA levels. The objective of this study is to evaluate the degree of cross-reactivity or interference among two different CsA immunoassays [(Immunoassay: CYCLO-Trac-RIA, Monoclonal-TDX; and two radioreceptor assays (RRA) (52 kDa immunophilin and cyclophilin)] with seven cyclosporine metabolites (AM19, AM1c9, AM4n9, AM1, AM9, AM1c, AM4n). The results are compared with a previously published MLC assay for the same metabolites.

METHODS

500 ng/mL of each of the CsA metabolites was assayed in spiked blood samples with both RRA using 52 kDa immunophilin and commercial cyclophilin and two commonly used commercial immunoassay procedures. The results were compared to those obtained with the previously published MLC assay.

RESULTS AND CONCLUSION

The CYCLO-Trac-radioimmunoassay showed minimal cross-reactivity with all of the seven CsA metabolites tested and is more specific to parent CsA than the current Abbott monoclonal procedure for the measurement of CsA. However the cross-reactivity of the seven metabolites using the Abbott monoclonal assay matched closely with their pharmacological potency as measured in the MLC assay. The RRAs showed greater cross-reactivity for most of the CsA metabolites tested than that found in the immunoassay procedures.

The determination of metabolite M17 and its meaning for immunosuppressive cyclosporin therapy

Cyclosporin A (CyA) is intensively metabolized by the hepatic cytochrome p450 III monooxygenase A system in the human liver, the most important metabolites being M1, M17, and M21. Because CyA and its metabolites have nephrotoxic, hepatotoxic, and neurotoxic side effects, CyA dosage must be calculated to avoid the risk of organ rejection through underdosage and toxic organ damage through overdosage or accumulation of metabolites. In this study, we determined the whole-blood concentrations of cyclosporin and metabolite M17 by high-pressure liquid chromatography (HPLC) and by monoclonal specific and polyclonal nonspecific fluorescence polarization immunoassay (Abbott) in patients after immunosuppressive treatment. Patients with different resorption and metabolization rates showed high individual variations. CyA concentrations in patients with good liver function and low concentrations of CyA metabolites showed a good correlation between the HPLC and the FPIA (TDx-monoclonal assay) methods in ranges between 25 and 180 ng/mL. TDx-monoclonal was not always as precise as HPLC. In cases of metabolic disorders, we found false high CyA concentrations assayed with the immunologic method, caused by a crossreaction of the elevated metabolite concentration. We found that HPLC rendered more information about the extent of immunosuppressive activity and the metabolization rate and showed a good correlation with the concentration of metabolite M17 and total metabolites measured with the Abbott CyA polyclonal kit.

An automated MALDI mass spectrometry approach for optimizing cyclosporin extraction and quantitation

A combinatorial extraction method and an automated matrix-assisted laser desorption/ionization (MALDI) mass spectrometry procedure were used to improve the clinical analysis of the immunosuppressant drug cyclosporin A. Cyclosporin extracts from whole blood were analyzed by MALDI and electrospray ionization (ESI) mass spectrometry, allowing for their identification and quantification. Due to limitations associated with the current multistep cyclosporin extraction procedure from whole blood, a combinatorial approach was devised to optimize this extraction. Optimization was performed by generating an array of solvent systems to be used for extraction from blood, and an automated analysis was carried out on a MALDI mass spectrometer to identify successful extractions. The first generation of experiments revealed four binary solvent systems to be effective for cyclosporin extraction (hexane/EtOH, ACN/H2O, ACN/MeOH, and hexane/CHCl3). A new array based on these solvent systems was generated, and a second iteration of these experiments was then performed. In the second generation of experiments, hexane/CHCl3 (70:30) was found to provide the most effective single-step extraction of these solvent systems for cyclosporin and its metabolites. The limits of detection were determined to be 15 ng/mL in whole blood for ESI/MS and MALDI-MS and could also be used for identifying major drug metabolites. In addition to applying this combinatorial approach to extraction procedures, this experimental design could easily be extended to examine other approaches, such as optimizing chemical reactions and screening inhibitors in enzymatic reactions.

Comparison of cyclophilin binding assay and radioimmunoassay in monitoring of blood cyclosporine

Cyclosporine binds with cyclophilin, an abundant protein found in almost all tissues, and the resulting complex interacts with calcineurin diminishing T-cell activation. Cyclophilin can be regarded as a cellular "receptor" for cyclosporine. Measuring cyclosporine binding to cyclophilin may offer a link between pharmacokinetics and pharmacodynamics that could improve monitoring of cyclosporine therapy. The authors investigated the feasibility of the cyclophilin binding assay and compared the results with a standard specific monoclonal radioimmunoassay in 100 blood samples taken for therapeutic drug monitoring. The results obtained with these methods were related closely with each other (r = 0.96; p < 0.001) but the mean (+/-SEM) concentrations were approximately two-fold higher in cyclophilin binding assay than in radioimmunoassay (520.4 +/- 49.9 ng/ml versus 257.7 +/- 28.6 ng/ml, respectively, p < 0.001). The shapes of the cyclosporine concentration versus time curves in two patients after a liver and heart transplantation, respectively, were similar after both methods but cyclophilin binding assay gave higher values than radioimmunoassay. Before firm conclusions on the clinical value of cyclophilin binding assay can be made, comparative studies in patients linking cyclosporine concentrations measured with cyclophilin binding assay and standard methods to the therapeutic outcome are needed.

Reversal activity of cyclosporin A and its metabolites M1, M17 and M21 in multidrug-resistant cells

Cyclosporin A (CSA) is an effective inhibitor of the P-glycoprotein (P-gp) activity and has been shown to modulate multidrug resistance (MDR) in in vitro experimental models. During degradation of CSA, the metabolites arising from the parental compound reach high levels in the serum of patients, and it is not clear whether these metabolites maintain the reversal activity of the parental compound, like the metabolites of verapamil. In an in vitro experimental model, we compared the reversal activity of CSA and 3 CSA metabolites (M1, M17, and M21) in the range of concentrations obtained in whole blood during a clinical trial with CSA used as a revertant agent. As experimental model we used LoVo-resistant cells. Our in vitro studies indicated that the metabolic hydroxylation and demethylation of CSA lead to molecules that greatly differ from the parent drug in their reversal activity. In the range of concentration detected in the whole blood of the patients (1-3 microM), CSA had a significant reversal activity. It decreased the IC50 of antineoplastic drugs involved in MDR (vincristine, taxol, doxorubicin and etoposide) but not the IC50 of platinum or methotrexate. CSA increased intracellular doxorubicin content and inhibited P-gp 3[H]azidopine photolabeling. Conversely, CSA metabolite concentrations superimposable to those observed in the patients (0.5-2.2 microM) had no sensitizing effects on the cytotoxicity of MDR-related anti-neoplastic drugs, nor did they affect 3[H]azidopine photolabeling or doxorubicin uptake. This study demonstrates that, during degradation of CSA, metabolite derivatives arise that have a very different reversal activity from that of the parental compound.

Rapid, sensitive high-performance liquid chromatographic method for the determination of cyclosporin A and its metabolites M1, M17 and M21

Cyclosporin A (CyA) and its metabolites seem to have nephro-, hepato- and neurotoxic side effects. Immunosuppressive therapy is a narrow path between the risk of rejection by underimmunosuppression and toxic organ damage by overdosage. Thus CyA dosage must be calculated to avoid the risks of organ rejection through underdosage and toxic organ damage through overdosage or accumulation of metabolites. In routine monitoring of CyA therapy, it can be important to measure not only the parent drug but also the metabolites. We describe a rapid and isocratic high-performance liquid chromatographic method for measurement of CyA and its metabolites M1, M17 and M21 in whole blood. CyA was detected by ultraviolet absorption at 212 nm with a CN analytical column maintained at 50 degrees C and recycling of hexane-isopropanol as mobile phase for improved long-term column stability and efficiency. The minimum detectable concentration of CyA and the three metabolites was 10 ng/ml blood. Our modified HPLC method for the determination of CyA and its metabolites is a simple (isocratic), rapid (the retention times were 7.1 min for CYD, internal standard, 8.9 min for CyA, 11.0 min for M21, 12.9 min for M17 and 16.3 min for M1) and economical method suitable for measuring the concentration of the major metabolite, M17, and for routine monitoring of CyA-treated patients.

Receptor assays in the clinical laboratory

OBJECTIVE

To review the relative advantages/disadvantages of receptor assays versus immunoassays.

REVIEW OF CURRENT LITERATURE RESULTS

The history of immunoassays is evaluated. Current shortcomings are emphasized. The present and future role of receptor assays is assessed.

CONCLUSION

The author predicts a shift away from immunoassays to receptor assays for certain analytes such as Vitamin B12, folic acid and drugs that undergo extensive metabolism.

Cytokines and cell surface markers in prediction of cardiac allograft rejection

Endomyocardial biopsy is generally used to quantify heart allograft rejection and guide immunotherapy. Biopsy, however, is invasive, costly, and risky. Since rejection requires lymphocyte activation, the purpose of this study was to assess alternative methods to evaluate rejection dynamics by investigating serum levels of cytokines and cell surface markers after heart transplantation. Interleukin-2-receptor bearing CD4+T (IL-2R/CD4) cell levels were higher in the peripheral blood of human transplant recipients with rejection grade 2 (p < 0.02). HLA-DR/CD3 levels were somewhat higher in rejection grade 2. There was no correlation between biopsy scores and serum levels of tumor necrosis factor (TNF-alpha), IL-2, or percentage of T cell, NK cell, B cell, CD4+T cell, CD8+T cell, HLA-DR/CD4, HLA-DR/CD8, IL-2R/CD3, IL-2R/CD8. Interleukin-1 (IL-1 beta) was not detectable in all of the samples. The current studies suggest that monitoring lymphocyte IL-2R/CD4 and HLA-DR/CD3 levels is useful in predicting cardiac transplant rejection.

Immunopharmacodynamic studies of cyclosporine in patients awaiting renal transplantation

The immunopharmacodynamics of cyclosporine were investigated in eight hemodialysis patients awaiting renal transplantation. Cyclosporine was administered orally (10 mg/kg) and intravenously (4 mg/kg), with both administrations separated by at least one week. Plasma samples were processed at 37 degrees C and analyzed for specific cyclosporine and its four major metabolites (AM1, AM1c, AM9, and AM4N) using high-performance liquid chromatography. In addition, the in vitro immunosuppressive activity of these serial plasma samples was estimated as a relative percentage inhibition of third party mitogenic lymphocyte proliferation stimulated with phytohemagglutinin. The relationships between concentration and effect of cyclosporine versus time were noted. These results suggest that unchanged cyclosporine concentrations in plasma correlate with mitogen-induced lymphocyte suppression yielding significant immunosuppressant activity of cyclosporine. Control studies with plasma from healthy volunteers spiked with cyclosporine in the concentration range of 0-10,000 ng/mL were developed. A sigmoidal Emax model was fitted to the effect versus plasma concentration data. The ratio of effect versus predicted effect were calculated for intravenous cyclosporine dosing. There was a good correlation between the observed and predicted inhibitory effect.

Pharmacokinetics of orally and intravenously administered cyclosporine in pre-kidney transplant patients

The pharmacokinetics of cyclosporine (CSA) and four metabolites were evaluated in eight hemodialysis subjects awaiting renal transplantation to compare metabolic patterns with those observed in post-transplant patients and normal volunteers. Each subject received a single 4-mg/kg intravenous and a single 10-mg/kg oral dose separated by a 1-week washout period. Blood samples were collected before and at .5, 1, 1.5, 2, 2.5, 3, 4, 6, 8, 10, 12, 14, and 24 hours after CSA dosing. Cyclosporine blood, plasma, and metabolite (M17, M1, M18, M21) levels were determined by high-pressure liquid chromatography. Mean (+/- standard deviation) CSA blood clearance was .47 +/- .15 L/hour/kg, steady-state volume of distribution (Vss) was 1.9 +/- .5 L/kg, and mean residence time (MRT) was 4.4 +/- 1.8 hours after intravenous dosing. With plasma, mean clearance was .70 +/- .31 L/hour/kg, Vss was 2.4 +/- 1.2 L/kg, and MRT was 3.7 +/- 2.2 hours. Cyclosporine bioavailability (F) averaged 24 +/- 11 and 24 +/- 15%, using blood and plasma, respectively. Values for clearance and Vss were approximately 30 to 100% greater than comparable estimates in healthy volunteers, but F and MRT were not altered to this extent. These changes might be explained on the basis of decreased protein binding in uremic patients. The area under the curve ratio for M17 and M1 to CSA increased an average of 1.7- and 3.9-fold, respectively, after oral dosing compared with intravenous administration, indicating increased conversion during first-pass metabolism.

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.

Therapeutic monitoring of cyclosporin--an update

The success of organ transplantation is closely related to clinical use of the immunosuppressive drug cyclosporin (CsA). The dosage of CsA is complicated by the large intra- and interindividual variability in its pharmacokinetics, as well as by the narrow concentration range between insufficient immunosuppression and toxicity. Potential sources of error in the sampling procedure and the advantages and disadvantages of the available analytical methods are discussed. Traditionally, 12 or 24 hour trough concentrations of CsA are monitored. Recently, peak concentrations or estimation of AUCs by a limited sampling strategy have been tried to improve the relatively weak concentration-effect and concentration-toxicity relationships found with trough CsA concentration monitoring. Studies of the CsA concentration-effect relationships for various treatment indications are reviewed.

Synergistic and antagonistic effects of combinations of cyclosporine A and its metabolites on inhibition of phytohemagglutinin-induced lymphocyte transformation in vitro

Cyclosporine A (CsA) and purified CsA metabolites were tested alone and in combination in cell culture to determine their effects on phytohemagglutinin (PHA)-induced lymphocyte proliferation. CsA was significantly more inhibitory than its metabolites at all concentrations tested (0-1000 ng/mL). CsA exerted maximum inhibition (70% decrease in [methyl-3H]thymidine incorporation) at concentrations of 300 ng/mL or greater; metabolites M1, M17, and M21 depressed the response 46, 39, and 23%, respectively, at 300 ng/mL. Metabolites M8, M18, M26, M25, M13, and M203-218 were non-inhibitory. When combinations of M17 and CsA were tested for the effects on PHA-induced lymphocyte transformation, a synergistic effect occurred at combinations of low concentrations of M17 and CsA and an antagonistic effect at the higher concentrations. Of the 49 combinations of CsA and M17 tested, 30 were antagonistic, 16 synergistic and 3 undecided (approaching addition). When 49 combinations of CsA and the non-immunosuppressive metabolite M8 were tested, 29 of the 49 combinations were synergistic, 17 antagonistic, 1 additive and 2 undecided (approaching addition). Of the 29 synergistic combinations, 14 were strongly synergistic. The importance of the interaction of CsA and metabolites to the immunopharmacology of CsA therapy is discussed.

The kinetics of cyclosporine and its metabolites in bone marrow transplant patients

1. The pharmacokinetics of cyclosporine (CsA) and the time course of CsA metabolites were studied in five bone marrow transplant patients after intravenous (i.v.) administration on two separate occasions and once after oral CsA administration. 2. Cyclosporine and cyclosporine metabolites were measured in whole blood by h.p.l.c. 3. Cyclosporine clearance after i.v. administration decreased from 3.9 +/- 1.7 ml min-1 kg-1 to 2.0 +/- 0.6 ml min-1 kg-1 after 14 days of treatment. The mean +/- s.d. absolute oral bioavailability of cyclosporine was 17 +/- 11%. 4. Hydroxylated CsA (M-17) was the major metabolite in blood. There were no significant differences in the mean metabolite/CsA AUC ratios between the first and second i.v. studies. 5. After oral administration, the metabolite to CsA AUC ratios were higher for most metabolites compared to those observed in the second i.v. study, suggesting a contribution of intestinal metabolism to the clearance of CsA.

Practical aspects in the use of cyclosporin in paediatric nephrology

Many factors must be considered for the effective and safe use of cyclosporin A (CsA) in paediatric nephrology. Detailed knowledge of the variable bioavailability, tissue distribution, and metabolism, as well as causes which lead to their alteration are necessary. Factors which affect the activity of the mixed function oxidase system cytochrome P-450 must be considered, i.e. liver dysfunction and many drugs. Precise knowledge of the CsA determination method and the spectrum of metabolites is essential. In children with renal transplants, a body surface area-related dose will better meet the dose requirements than a body weight related-dose. For drug level monitoring whole blood rather than plasma should be used, and the parent drug level should be the main determinant; elevated metabolite levels may be important in suspected nephrotoxicity or liver dysfunction. Pharmacokinetic profiles are necessary to discover absorption problems or increased CsA clearance rates which necessitate shorter dosing intervals. In children with steroid-dependent minimal change nephrotic syndrome, remission without steroids is maintained as long as CsA is given. The appropriate starting dosage is 150 mg/m2 per day; trough level monitoring is mandatory to prevent nephrotoxicity and to confirm adequate immunosuppressive drug levels which should be 80-160 ng/ml (parent drug level). Although the benefit of CsA has been reported in some cases of lupus erythematosus, its use should be restricted to severe cases only until its efficacy and safety has been confirmed in controlled trials.

Contribution of cyclosporin metabolites to immunosuppression in liver-transplanted patients with severe graft dysfunction

The aim of this study was to analyse the immunosuppressive contribution of cyclosporin metabolites in liver-grafted patients. Therefore the immunosuppressive potency of 17 metabolites, alone and in combination, was tested in human mixed lymphocyte cultures, and the results were correlated with metabolite blood levels in liver-grafted patients. Of the 17 metabolites tested only six highly lipophilic metabolites showed a detectable immunosuppressive activity of up to 10% of the activity of cyclosporin; the effect of combining metabolites was additive. For calculation of the in vivo activity, blood levels of seven major cyclosporin metabolites were determined in liver-grafted patients with normal liver function (group A, 43 episodes) and with severe hyperbilirubinaemia (group B, 66 episodes). Both patient groups had comparable levels of parent drug (122.9 +/- 17.4 vs. 111.1 +/- 23.5 ng/ml by HPLC) and similar blood levels of the highly lipophilic metabolites 17, 1 and 18. By contrast, blood levels of the less lipophilic metabolites 8, 9, 26 and 203-218 were substantially increased in group B (P less than 0.05). High overall metabolite blood levels in group B were also indicated by a non-specific monoclonal RIA (520 +/- 199 ng/ml for group A vs. 1318 +/- 407 ng/ml for group B). Despite the very high levels in group B, however, the overall contribution of the metabolites to immunosuppression was similar in both groups (12.6 +/- 5.0% for group A vs. 13.8 +/- 5.6% for group B). These findings indicate that, despite a marked accumulation of cyclosporin metabolites in patients with severe cholestatic liver dysfunction, their immunosuppressive contribution remains low.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of the immunosuppressant cyclosporine on the circulation of heart transplant recipients

The effect of cyclosporine on the systemic circulation and on heart rate is unknown for heart transplant recipients. Thirty-four heart transplant recipients were studied by right-sided cardiac catheterization after endomyocardial biopsy. A direct linear relation was found between systemic and pulmonary vascular resistance and cyclosporine trough blood levels, which were negatively related to heart rate. The effect of cyclosporine on pulmonary vascular resistance, however, was not statistically significant by multivariate analysis when patient age was considered. In contrast, renal function appeared unrelated to systemic vascular resistance or heart rate. It appears that cyclosporine trough blood levels may have a direct effect on systemic vascular resistance as well as an unexplained negative chronotropic effect on heart rate.

The clinical significance of cyclosporine metabolites

Cyclosporine (CsA) is extensively metabolized, with over 14 metabolites having been characterized to date. The confirmation of structure and purity is a prerequisite for studies involving CsA metabolites. Analytical techniques such as fast atom bombardment/mass spectroscopy (FAB/MS), tandem mass spectrometry (MS), 1H- and 13C-nuclear magnetic resonance (NMR) can be used for such purposes. In vitro experiments indicate that metabolites are considerably less immunosuppressive and toxic than CsA. In vivo studies have been hampered by sufficient quantities of metabolites and a suitable animal model. Preliminary results in the rat suggest that CsA metabolites are less immunosuppressive and toxic than CsA, although these results must be confirmed using a more suitable animal model. Present data indicate that the routine monitoring of metabolites is not warranted in transplant patients, although additional information is required to confirm these findings.

Prediction of acute graft rejection in renal transplantation: the utility of cyclosporine blood concentrations

While cyclosporine is recommended to be used only in conjunction with monitoring of its blood concentrations, the utility of these measurements in preventing treatment failure is not established. In a group of 52 patients trough levels and steady-state concentrations were monitored in serum and whole blood by specific (SP) and nonspecific (NS) assays (polyclonal radioimmunoassay, PR; fluorescence polarization immunoassay, FP; high-pressure liquid chromatography, HP). From as many as 10 determinations of trough level and steady state concentrations during the first 40 days after renal transplantation, the lowest measurement was selected. In the case of an acute rejection episode within that time period, only values until that event were considered. Trough level measurements in serum by PR/NS and by FP/NS and in whole blood by HP/SP were not significantly different between patients with and patients without rejection episodes. However, simultaneously measured steady-state values (serum/PR/NS and serum/FP/NS) were significantly lower in patients suffering from rejection (with rejection SS/serum/PR/NS mean = 127 ng/ml, SD = 41 ng/ml; without rejection mean = 163 ng/ml, SD = 60 ng/ml; P = 0.027, t test). This difference could not be demonstrated for steady state/whole blood/HP/SP measurements. A logistic regression analysis demonstrated that the probability of rejection can be decreased by up to 40% if steady state/serum/PR/NS or steady state/serum/FP/NS values never drop below 250 ng/ml early after renal transplantation.

The immunosuppressive activity of the aldehydic transformation of cyclosporine on alloreactive T-cells

Cyclosporine (CsA) is a potent immunosuppressive compound, and its metabolites have previously been shown to have pharmacologic activity. The aldehydic metabolites have been isolated and are a metabolic intermediate after the conversion of CsA to its most active hydroxylated metabolite. The in vitro sensitivity of alloreactive T-lymphocytes, which are generated from a mixed lymphocyte reaction and propagated from organ transplant biopsy specimens to the aldehydic metabolites of CsA, was tested. In secondary proliferative assays in the presence of varying concentrations of CsA and the aldehydes, the concentration required to inhibit proliferation by 50% was 50 to 150 ng/mL for CsA and 3150 to 3500 ng/mL for the aldehydes. Pretreatment of alloreactive cells with CsA or the aldehydes did not alter cell viability, as tested with dye exclusion, or cell reactivity on reculturing. These studies concluded that the structural modification formed by metabolism of CsA to the aldehydic structure eliminates its antiproliferative activity on T-lymphocytes.

Inter- and intra-subject variation of the suppression of mitogen-induced proliferation of human lymphocytes by cyclosporin-A: reduction of response with delayed addition may be relevant to timing of therapy

In vitro, CsA is capable of suppressing mitogen-stimulated growth of human peripheral blood lymphocytes. Dose--response studies on lymphocytes from normal volunteers have shown that the variation between subjects is greater than the variation between repeated studies on the same subject in the 72 h uptake of 3H-TdR. The tests are easy to perform and they could be used to help in deciding, prior to transplantation, the dose of CsA to be used and whether other immunosuppressive therapy is needed. Activation of lymphocyte proliferation in vivo is a continuous process and recruitment to growth in vitro takes place over 24 h after mitogen stimulation. CsA was most effective in suppressing the replicative growth of lymphocytes in vitro when added up to 4 h after the start of the culture, but it was much less effective when added at 8 h. The experiments suggest that 8 hourly administration of CsA will optimise suppression of activation of the lymphocytes in vivo. If the suppressive activity of the metabolite M17 and the individual variation in sensitivity of the patients' lymphocytes to CsA are also taken into account it may be possible to reduce the dose of CsA to achieve effective immunosuppression and thereby minimise toxicity.

Assessment of immunosuppression by serum inhibition of alloreaction and measurement of cyclosporin A (CyA) serum levels in kidney graft recipients under CyA

The immunosuppressive effect of kidney graft recipient sera was studied on T-lymphocyte alloreactive line (4H) proliferation and compared to native cyclosporin A (CyA) and CyA metabolite concentrations determined by radioimmunoassay (RIA) using specific or nonspecific monoclonal antibodies. Three clinical groups were studied: (1) patients experiencing acute renal rejection episodes (CyA-R), (2) patients experiencing CyA-dependent nephrotoxicity episodes (CyA-TOX) and (3) patients in a clinically steady state (CyA-ST), according to their therapeutic regimen i.e., monotherapy (CyA alone) or polytherapy (CyA associated with prednisolone and/or azathioprine). Regardless of the clinical state, sera of patients in polytherapy displayed more inhibitory activity than those of monotherapy patients (24% and 40% inhibition of 4H proliferation, respectively, at sera dilution of 1:2), something which was no doubt due to the inhibitory activity of prednisolone on T-lymphocyte growth. In the two therapeutic regimens, CyA-ST patient sera exhibited the lowest inhibitory activity on the 4H line (45% and 65% inhibition of 4H proliferation in mono- and polytherapy, respectively, at sera dilution of 1:2). Sera from CyA-TOX patients were highly inhibitory (74% and 86% inhibition of 4H proliferation in mono- and polytherapy, respectively, at sera dilution of 1:2), in agreement with RIA assays showing increased native circulating CyA and CyA metabolites and daily CyA intake in this group as compared to CyA-ST. Surprisingly, CyA-R patient sera were no less inhibitory than those of CyA-ST patients on 4H-line, antigen-induced proliferation.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetic drug interactions with cyclosporin (Part II)

Part I of this article, which appeared in the previous issue of the Journal, considered the potential mechanisms of drug interactions with cyclosporin, and divided the interacting drugs into 2 categories. Drugs that decrease cyclosporin concentrations (e.g. anti-convulsants, rifampicin, etc.) were dealt with first; the authors then moved on to consider the second category, those that increase cyclosporin concentration (macrolide antibiotics, azole antifungal drugs). Part II continues the survey of this category.

Assay methods for cyclosporine monitoring following liver transplantation

This article reviews therapeutic drug monitoring for cyclosporine in liver transplantation. Brief descriptions of various immunoassay methods include sample matrix selection, assay reagents, and metabolite cross-reactivity information. Multiple comparisons of the various methods are outlined. Examples of the method-dependent relationship between clinical events and changes in cyclosporine concentration are presented. Other potential predictors of liver allograft function are listed.

Chromatographic methods as tools in the field of mycotoxins

Achievements in the applications of chromatographic techniques in mycotoxicology are reviewed. Historically, column chromatography (CC) and paper chromatography (PC) were applied first, followed by thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC) and gas chromatography (GC). Although PC techniques are no longer used in the analysis of mycotoxins, selected applications of PC are included to underline historical continuity. The most important achievements published from 1980 onwards are described. They include clean-up methods, TLC, CC, HPLC and GC of mycotoxins in environmental samples, foods, feeds, body fluids and in studies on biosynthesis and biotransformations of mycotoxins. Advantages and disadvantages of chromatographic techniques used in mycotoxicology are also evaluated.

Liver transplantation

Liver transplantation has become an established form of therapy for patients with almost any type of irreversible and severe liver disease. The remarkable success of liver transplantation has resulted from recent advances in immunosuppressive therapy, surgical techniques, and patient selection. Additional progress has been made in the management of the complex postoperative medical complications that may occur. Indeed, liver transplantation has contributed significantly to an improved quantity and quality of life for many patients with liver disease.

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.

Serum cyclosporine concentration and risk of acute graft-versus-host disease after allogeneic marrow transplantation

To determine the relation between the serum cyclosporine concentration and the risk of acute graft-versus-host disease (GVHD), we studied 179 recipients of bone marrow grafts from HLA-identical sibling donors who received prophylaxis with cyclosporine, either by itself or combined with methotrexate. Cyclosporine was given either orally or intravenously at full doses from the day before transplantation until day 50; it was then tapered off and discontinued on day 180. Trough concentrations of serum cyclosporine were measured by radioimmunoassay. The relation between patients' characteristics and the risk of acute GVHD was analyzed with a relative-risk regression model. In 66 patients (37 percent), grades II to IV of acute GVHD developed 7 to 66 days (median, 13) after transplantation. The trough cyclosporine concentration for a given week was significantly associated with the risk that acute GVHD would develop during the following week. The relative risks were 0.7 (i.e., there was a 30 percent reduction in risk) for every increase of 100 ng per milliliter in cyclosporine concentration and 1.0, 0.60, and 0.20 for concentrations of less than 100, 100 to 199, and 200 or more ng per milliliter, respectively (P less than 0.01). A patient's age, prophylaxis regimen, and year of transplantation also influenced the risk of acute GVHD significantly. These data indicate that low cyclosporine concentrations can be a cause of treatment failure and that concentrations should be monitored in recipients of marrow transplants.

High-performance liquid chromatographic column-switching method for two cyclosporine metabolites in blood

Cyclosporine (CSA) is biotransformed to many metabolites which may contribute to its immunosuppressive and nephrotoxic activity. We report a rapid and sensitive, automated column-switching high-performance liquid chromatographic (HPLC) method for measuring CSA-M17 in whole blood; the method also separates CSA-M1. CSA metabolite standards were isolated by a preparative-scale HPLC method. Samples were prepared by protein precipitation with acetonitrile followed by dilution with water. CSA-M17 was initially separated on a C8 column; final separation was on a C18 column. The inter-day relative standard deviation at 50 ng/ml was 8% (n = 3). Limit of detection was 20 ng/ml.

Adverse reactions and interactions of cyclosporin

Cyclosporin is a potent, widely used specific immunosuppressive agent which affects T-helper cells, and has little myelotoxicity. Its pharmacokinetics are complex and many of its actions remain poorly understood. Numerous side effects have been reported, affecting most organs. Most troublesome have been renal injury, systemic hypertension and vascular changes. Oral use is more effective than intramuscular and safer than the intravenous route. Interactions with other drugs include those which affect hepatic metabolism and those which reduce clearance. Aminoglycosides, macrolide antibiotics, imidazole derivatives, calcium channel blockers, sulphonamides and steroids are included in such interactions. Other metabolic effects of cyclosporin are more subtle and include hyperchloraemic alkalosis, changes in serum potassium and magnesium and effects on testosterone and prolactin levels. Acute poisoning with cyclosporin has been reported, again without myelosuppression. Cyclosporin is an important agent with multisystem toxicity, which requires precise monitoring of drug concentrations, liver and renal function, haemoglobin levels and plasma electrolytes. Cyclosporin pharmacodynamics and interactions with other drugs need to be carefully considered if lower rates of toxicity are to be achieved.

Sensitivity of activated human lymphocytes to cyclosporine and its metabolites

Alloreactive T cells generated as clones from mixed lymphocyte cultures, or propagated from heart or liver transplant biopsies, were tested for secondary proliferation measured in the primed lymphocyte test in the presence of Cyclosporine A and metabolites fractionated from human bile. Significant differences were observed in Cyclosporine A sensitivity between various cell cultures ranging as high as 100-fold. The liver is the primary site of Cyclosporine A metabolism, which yields a number of hydroxylated and N-dimethylated derivatives that are eventually secreted into the bile. Bile was collected from adult liver transplant patients on Cyclosporine A therapy and following extraction with diethyl ether, separated by high pressure liquid chromatography. Thirteen fractions were tested for their effect on lymphocyte proliferation in concanavalin A activation, mixed lymphocyte cultures and primed lymphocyte test assays. The strongest immunosuppressive effect was found with fraction 8, which contained metabolite M17, which has a single hydroxylation in position 1. Only three other fractions 9, 10, and 13, which contained metabolites M1, M18, and M21, respectively, exhibited immunosuppressive activity, albeit much lower than that of Cyclosporine A. Differences in Cyclosporine A sensitivity among alloreactive T cells followed similar patterns with Cyclosporine A metabolites. Thus, the assessment of the Cyclosporine A effect must consider differences in drug sensitivity of lymphocytes involved in transplant immunity and the generation of metabolites with immunosuppressive activity.