Immunosuppressive properties of cyclosporin metabolites

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.

Monitoring cyclosporin in blood: between-assay differences at trough and 2 hours post-dose (C2)

With the introduction of a cyclosporin monitoring strategy based on the use of a sample collected 2 hours after dosing (C2) rather than the predose sample (C0), there was concern that the differences in blood cyclosporin results from the various assay systems would result in assay-specific target ranges for C2 monitoring. In addition, it was not known if the different proportion of cyclosporin metabolites in the blood 2 hours after dosing compared with that seen in predose samples would alter the relationship between the various assay methodologies. The aim of this study was to address these issues using blood samples from patients who had undergone kidney and liver transplantation. To do this, paired samples were collected predose and 2 hours after cyclosporin dosing at various periods following transplantation in kidney (88 paired samples) and liver (165 paired samples) transplant recipients. Cyclosporin was measured in these samples using five different immunoassays (radioimmunoassay, two fluorescent polarization immunoassays, and two homogeneous immunoassays) and high-performance liquid chromatography-mass spectrometry. The results of the study showed that when using these immunoassays to measure blood cyclosporin concentrations at C0, the cross-reactivity of the antibodies in the different immunoassay kits resulted in target therapeutic ranges that would need to vary between assays to maintain parity. However, when the same assays were used to measure the blood cyclosporin concentration at C2, the results were congruent, and assay-specific target therapeutic ranges should not be necessary. Thus, when adopting a C2 monitoring strategy, it is possible to use target therapeutic ranges that are independent of the assay system used.

Topical cyclosporin in the treatment of dermatologic diseases

Cyclosporine A (CsA) has been in clinical use for some decades, primarily for the prevention and treatment of organ transplant rejection and graft-versus-host disease. In more recent years, Cyclosporine has been recognized as beneficial in the treatment of dermatologic diseases, such as: psoriasis, lichen planus, Behcet disease, atopic dermatitis, pyoderma gangrenosum and epidermolysis bullosa acquisita. Above all, Cyclosporine is an important therapeutic modality for several dermatologic diseases that are refractory to other agents.

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.

Survey of cyclosporine therapeutic ranges, assay methodology, and use of 'sparing agents' in Australasian transplant centers

Since its introduction in the 1980s, cyclosporine has become the major immunosuppressive drug used in organ transplantation. Despite widespread experience with this expensive agent, a number of controversial issues remain. These include the use of sparing agents to allow a lower dose of cyclosporine to be prescribed, specificity of assay method, and values quoted as therapeutic ranges. The authors surveyed organ transplant centers in Australia and New Zealand to ascertain local practices and found considerable variability in the use and dosage of sparing agents, cyclosporine assay method, and therapeutic ranges. The implications of these differences are discussed.

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.

Anti-allergic activity of cyclosporin-A metabolites and their interaction with the parent compound and FK 506

The ability of cyclosporin-A (CSA) and four of its metabolites M1, M17, M18 and M21, to inhibit antigen-stimulated release of beta-hexoseaminidase from IgE-sensitized rat basophilic leukemia cells (RBL-2H3), as an in vitro correlate of anti-allergic effect, was studied Metabolites M17, M1 and M21 were effective in inhibiting enzyme release, though less potent than the parent compound. The concentrations achieving 50% inhibition (IC50 values) were 53.3, 315.5 and 875.7 ng/ml for CSA, M17 and M1, respectively. M21 had approximately same IC50 as M1 while M18 was essentially inactive. At the highest concentration tested (1000 ng/ml) the mean maximum percentage inhibitions were 98.6, 79.5, 53.9, 48.6 and 12.2 for CSA, M17, M1, M21 and M18, respectively. The relative anti-allergic potency of the metabolites was similar to their reported relative immunosuppressive potency. Combinations of low concentrations of CSA and its metabolites were synergistic in inhibiting enzyme release whereas at higher concentrations interactions were either additive or antagonistic. Even the concentrations of the metabolites that have little or no activity when used alone also potentiated the effect of CSA. The immunosuppressor FK 506 was found to be about three times more potent than CSA in this system and the interactions between FK 506 (3, 10 and 30 ng/ml) and CSA (10, 30 and 100 ng/ml) or M17 (20, 100 and 500 ng/ml) were synergistic at all combinations. Both CSA and M17 synergized more strongly with FK 506 than they did between themselves. These results show that some metabolites of CSA, like the parent compound, possess anti-allergic effects and that at concentrations that are obtainable in transplant patients, synergistic interaction occurs between CSA and its metabolites, and this may be of some therapeutic significance.

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.

A review of assay methods for cyclosporin. Clinical implications

Cyclosporin is a unique immunosuppressive agent with a narrow therapeutic range. The pharmacokinetics of the drug present substantial within- and between-patient variability and drug interactions can significantly alter blood cyclosporin concentrations. Monitoring of cyclosporin concentrations in blood is an invaluable and essential aid in adjusting dosage to ensure adequate immunosuppression while minimising toxicity. The principal rationale behind therapeutic monitoring of cyclosporin is the fact that the incidence of rejection is higher at low cyclosporin concentrations and toxicity occurs more often at high concentrations. In renal transplant recipients, cyclosporin concentrations help to discriminate between insufficient immunosuppression and cyclosporin-induced nephrotoxicity. There are several methods available, both specific and nonspecific, for the routine measurement of cyclosporin. Radioimmunoassay and fluorescence polarisation immunoassay are most widely employed, while high performance liquid chromatography remains the reference procedure. The allegedly specific immunoassays tend to slightly overestimate the actual blood cyclosporin concentrations. There is a need for assay systems capable of measuring the biological activity of cyclosporin. Cyclosporin concentrations should be determined by a specific method, using whole blood as the sample matrix. The routine monitoring of individual cyclosporin metabolites is not warranted, but characterising the metabolite pattern of cyclosporin by concomitant use of a nonspecific and a specific assay can be clinically useful in patients with cyclosporin-associated toxicity or impaired liver function. In organ transplantation, measurement of blood cyclosporin concentration should be continued periodically as long as the therapy continues, whereas monitoring is only indicated in special circumstances in patients with autoimmune and other nontransplant diseases. The assessment of a 'therapeutic window' for cyclosporin is complicated for several reasons and definite target ranges cannot be given. Cyclosporin concentrations should always be interpreted in conjunction with the recent blood concentration history and other relevant clinical and laboratory data.

The synergistic immunosuppressive potential of cyclosporin metabolite combinations

Out of the 29 cyclosporin (CS) metabolites defined so far seven representatives were isolated from the bile of liver grafted patients, purified by HPLC and characterized by FAB-MS and/or 1H-NMR. These were used to determine the growth inhibitory effects on concanavalin A stimulated rat lymphocytes (LN). Metabolites diluted in culture medium at concentrations re-checked by HPLC at the respective assay time were added and proliferation determined by [3H]-thymidine incorporation after 48 h. A 50% growth inhibition of LN by single metabolites (AM) was achieved at the following concentrations (mg/l): CS: 0.023; primary metabolites AM1: 0.11; AM1c: 0.65; AM9: 1.05; secondary metabolites AM19: 1.02; AM4N9: 1.02; H355: 1.85; AM1A: 4.5. Although all metabolites were immunosuppressive at higher concentrations in vitro on a single metabolite level, only AM1 with 20% of the activity of native CS seemed to play a role in vivo. However, when we tested the antiproliferative effects of double or triple metabolite combinations, we found a strong synergism not only of primary metabolites, but even with combinations including secondary metabolites. The concentration of the participating metabolites necessary to decrease LN growth by 50% was far below the trough levels observed in vivo. Finally, to mimic to some extent the in vivo situation we determined the interaction of native CS with single metabolites or double combinations. In contrast to the clear synergism in the absence of CS the combinations of metabolites with native CS resulted in an additive growth inhibition. These results indicate an immunosuppressive potential of all metabolites tested and a clear synergism of metabolites in the absence of CS. Although up to double metabolite combinations did only additively enhance CS induced immunosuppression, the combination of 29 metabolites occurring in vivo might have significant immunosuppressive effects in situations where CS levels drop below active concentrations.

Pharmacokinetics of cyclosporine in hyperlipidaemic long-term survivors of heart transplantation. Lack of interaction with the lipid-lowering agent, fenofibrate

Cyclosporine (Cy) binds to lipoproteins in plasma. In order to test if its pharmacokinetics would be modified when efficient lipid-lowering treatment is introduced, a study has been done of Cy pharmacokinetics and any interaction with the lipid-lowering agent fenofibrate in hyperlipidaemic long-term, survivors of heart transplantation. Fenofibrate 200 mg once daily significantly reduced blood lipids (cholesterol 6.5 vs 7.7 mmol/l; apoprotein B 1.2 vs 1.6 g/l) but did not modify mean whole blood Cy trough levels (113 before fenofibrate vs 103 ng.ml-1), Cmax (812 ng.ml-1 by RIA and 757 ng.ml-1 by HPLC before fenofibrate versus 865 and 741 respectively, during fenofibrate); tmax (1.6 and 1.7 h before fenofibrate versus 1.4 and 1.4 h respectively), and t1/2 (13.9 and 11.1 h versus 9.5 and 10.7 h). The only adverse effect was an increase in creatinine (157 vs 145 mmol/l). Further studies are needed to investigate the mechanism of Cy-fenofibrate nephrotoxicity and to evaluate the long-term efficiency and safety of fenofibrate after heart transplantation.

Protective effects of diltiazem and the prostazycline analogue iloprost in human renal transplantation

To test the hypothesis that calcium antagonists decrease the incidence and severity of delayed graft function, we conducted three separate, prospective, randomized trials. In these trials, we investigated the effects of diltiazem and those of the prostacycline analogue iloprost. In the first study, 22 control patients and 20 diltiazem patients received grafts perfused with either vehicle or diltiazem 20 mg/L in the Euro-Collins solution. Subsequently, the diltiazem subjects were given the drug as a bolus of 0.28 mg/kg, followed by a continuous infusion of 0.002 mg/min/kg for the following 2 days. Thereafter, diltiazem 60 mg was given to the treated subjects orally for up to 4 years. In the second study, 11 control subjects and 10 diltiazem subjects received the same postoperative regimen, but all grafts were harvested without addition of diltiazem to the perfusion solution. In the third protocol, four groups were studied as follows: 19 control subjects who received no specific treatment, 16 subjects who received diltiazem, 16 subjects who were given iloprost, and 14 subjects who received both iliprost and diltiazem. The donor kidney of treated patients was perfused with either diltiazem, iloprost, or both drugs. Primary graft function occurred more commonly in the groups receiving diltiazem. Further, in the first study the number of hemodialyses per patient was reduced in those patients with delayed graft function. Fewer rejection episodes occurred in patients receiving diltiazem. Plasma levels of soluble interleukin-2 receptors decreased significantly during diltiazem treatment. Moreover, renal biopsies showed less severe signs of cyclosporin-A (CyA) nephrotoxicity in diltiazem-treated patients compared to controls, even though these patients also exhibited higher CyA trough levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetic interaction between cyclosporin and diltiazem

Previous reports have indicated that administration of the calcium antagonist diltiazem results in major changes in the pharmacokinetics of cyclosporin A (CyA). A new clinical trial was undertaken in 22 renal transplant patients receiving a constant dose of cyclosporin to further explore this interaction. Coadministration of diltiazem for one week produced an increase in the blood concentration of CyA and its metabolites 17 and 18 in almost all patients, but no increase in CyA metabolites 1 and 21. The mean whole blood CyA trough level determined by HPLC rose from 117 ng.ml-1 to 170 ng.ml-1 after one week on diltiazem, and the mean trough level of metabolite 17 rose similarly from 184 ng.ml-1 before to 336 ng.ml-1. Based on experiments with microsomes from human liver the effect of diltiazem was due to noncompetitive inhibition of CyA-metabolism by diltiazem, and the increased concentration of metabolite 17 might have been due to stronger inhibition of its secondary metabolism steps.