Cyclosporin A-induced changes in endogenous metabolites in rat urine: a metabonomic investigation using high field 1H NMR spectroscopy, HPLC-TOF/MS and chemometrics

The model nephrotoxin cyclosporin A was administered to male Wistar-derived rats daily for 9 days at a dose level of 45 mg/kg per day. Urine samples were collected daily and the excretion pattern of low molecular mass organic molecules in the urine was studied using 1H NMR spectroscopy and HPLC-TOF/MS. Distinct changes in the pattern of endogenous metabolites, as a result of the daily administration of cyclosporin A, were observed by 1H NMR from day 7 onwards. The NMR-detected markers included raised concentrations of glucose, acetate, trimethylamine and succinate and reduced amounts of trimethylamine-N-oxide. In parallel studies by HPLC-TOF/MS a reduction in the quantities of kynurenic acid, xanthurenic acid, citric acid and riboflavin present in the urines was noted, together with reductions in a number of as yet unidentified compounds. In addition, signals resulting from the polyethylene glycol, present in the dosing vehicle, and cyclosporin A metabolites were detected by MS. However, these were excluded from the subsequent multivariate data analysis in order to highlight only changes to the endogenous metabolites. Analysis of both the 1H NMR and HPLC-MS spectroscopic data using pattern recognition techniques clearly identified the onset of changes due to nephrotoxicity.

Comparison of bioavailability and metabolism with two commercial formulations of cyclosporine a in rats

The bioavailability and metabolism of cyclosporine A (CsA) capsules were compared with two bioequivalent (Food and Drug Administration approved) preparations in rats. Two groups of Wistar-Kyoto rats were given 10 mg/kg q.d. of Sandimmun Neoral (NEO), Novartis Pharma, and CsA (United States Pharmacopeia modified), Eon Labs (EON), as capsules dissolved in water by oral gavage. After reaching steady-state (SS), rats were euthanized 2, 4, 8, 12, and 24 h after dosing. Parallel to this investigation, a single dose (SD) study was also performed. CsA and CsA metabolite concentrations of AM1, AM4N, and AM9 were determined by high-performance liquid chromatography in kidney, whole blood, and urine. The bioavailability of EON was 15% lower [area under the curve (AUC)(SS blood CsA), 27.9 +/- 3.69 mg. h/l] in the blood and was 40% lower (AUC(SS kidney CsA), 136.2 +/- 21.2 mg. h/l) in the kidney in contrast to NEO (AUC(SS blood CsA), 32.1 +/- 4.32 mg. h/l and AUC(SS kidney CsA), 220.8 +/- 29.5 mg. h/l). In contrast, the plasma AM4N level was significantly elevated in group receiving EON (AUC(SS blood AM4N), 4.1 +/- 0.42 mg. h/l) compared with the other group treated with NEO (AUC(SS blood AM4N), 2.9 +/- 0.39 mg. h/l). In the kidneys, no significant differences were observed concerning the AM4N concentrations of NEO (AUC(SS kidney AM4N), 11.8 +/- 1.87 mg. h/l) versus EON (AUC(SS kidney AM4N), 12.1 +/- 2.14 mg. h/l), but AM1 was increased (AUC(SS kidney AM1), 54.3 +/- 11.2 mg. h/l) in comparison to NEO (AUC(SS kidney AM1), 20.5 +/- 3.56 mg. h/l). Furthermore, EON produced a larger amount of AM4N in the urine (5.8 +/- 0.85 mcirog/24 h versus 2.2 +/- 0.95 microg/24 h). Similar results were obtained with the SD study. Although the clinical consequences of our results remain at present unknown, the data suggest differences in CsA disposition that may affect drug efficacy and safety and merit further investigation in humans.

Acidosis and weight loss are induced by cyclosporin A in uninephrectomized rats

The effects of cyclosporin A (CyA, 50 mg/kg body weight) or its commercial vehicle (cremophor) on the acid-base regulation of uninephrectomized rats were assessed for 7 days and in non-nephrectomized rats for 15 days. CyA induced a marked systemic acidosis, accompanied by decreases in blood PCO(2) and plasma bicarbonate. Untreated uninephrectomized rats did not show the acidosis. In CyA-treated rats the urine pH decreased (control 6. 65+/-0.06 vs. CyA 6.18+/-0.08; P<0.01) as well as urinary bicarbonate (non-nephrectomized rats 7.50+/-1.88 mM vs. uninephrectomy plus CyA 0.75+/- 0.06 mM; P<0.01), suggesting partial renal compensation of systemic acidosis. Titratable acidity increased in CyA-treated rats (control 21.6+/-1.2 vs. CyA 63.3+/-12.0 microEq/l; P<0.001). Phosphate, glucose, and osmolar clearances were not significantly altered in non-nephrectomized rats treated with CyA for 15 days. There was a striking decrease in body weight in CyA-treated rats (control 274.0+/-3.8 vs. CyA 225.0+/-5.1 g; P<0. 01), but compensatory growth of the remaining kidney was not prevented by this drug or by its vehicle. In summary, CyA induced a severe metabolic acidosis in uninephrectomized rats that was not compensated by the remaining kidney, in spite of the well-preserved compensatory weight gain of this organ. Loss of body weight was significant in CyA-treated animals.

Characterization of glucuronidated phase II metabolites of the immunosuppressant cyclosporine in urine of transplant patients using time-of-flight secondary-ion mass spectrometry

The immunosuppressant, cyclosporine, is metabolized in the liver and small intestine to > 30 metabolites. Metabolism and immunosuppressive and toxic potentials of the metabolites are still unclarified. Therefore, search and determination of new metabolites remain an important part of cyclosporine research. In this study, cyclosporine metabolites were determined in 42 urine samples of transplant patients using time-of-flight secondary-ion MS. Besides the known metabolites of phase I and phase II, other groups of new phase II metabolites were detected, and most of them were identified as glucuronidated phase I metabolites. All metabolites were found in the urine of heart, kidney, and bone marrow graft patients, with frequencies in the range of 74% and 12%. The most intensive group of these metabolites was also detected in a HPLC fraction, together with the known glucuronidated AM1c. The concentration of this new metabolic group could be estimated to < or = 5/ml. In conclusion, this work demonstrated that time-of-flight secondary-ion MS is a powerful tool in pharmacological investigations. Furthermore this study showed that phase II metabolism is an important metabolic pathway of cyclosporine in transplant patients.

Diltiazem increases blood concentrations of cyclized cyclosporine metabolites resulting in different cyclosporine metabolite patterns in stable male and female renal allograft recipients

1. Six male and six female stable renal allograft recipients under cyclosporine immunosuppression and without concomitant therapy with drugs known either to induce or inhibit CYP3A enzymes were included in the study and received 180 mg day-1 diltiazem for 1 week in a two-period cross-over fashion. Cyclosporine (352 +/- 56 mg day-1) was given in two daily oral doses. The daily doses were not changed during the study. Blood samples were collected for 12 h after receiving cyclosporine alone and after receiving diltiazem in addition for 1 week. Cyclosporine and nine of its metabolites were quantified using h.p.l.c. 2. Co-administration of diltiazem caused a 1.6 fold increase of the AUC (0, 12 h) of cyclosporine and a 1.7 fold increase of the AUC(0, 12 h) of its metabolites. Analysis of the metabolite patterns showed an over-proportional increase of the AUC(0, 12 h) of the cyclized metabolites AM1c (2.6 fold) and AM1c9 (2.2 fold). The AUC(0, 12 h) values of cyclosporine and the hydroxylated metabolites increased less than two fold. 3. Differences of the AUC(0, 12 h) values of cyclosporine with and without diltiazem were significantly higher in female than in male patients (P < 0.02). The differences in the AUC(0, 12 h) values of the metabolites, especially AM1c, tended to be higher in female patients as well. 4. It is concluded that coadministration of diltiazem not only increases the blood concentration of cyclosporine but also those of its metabolites, leads to a shift of the metabolite pattern towards cyclized metabolites, and that the pharmacokinetic changes under diltiazem administration are more prominent in female than in male patients.

Metabolism of cyclosporin G in the mouse, rat, and dog

Cyclosporin G (CsG; Sandoz compound OG 37-325) is a cyclic undecapeptide with potent, immunosuppressive activity and is currently in clinical testing for prevention of transplanted solid organ rejection. Although structurally similar to cyclosporin A (CsA), results in animals suggest that CsG has a reduced potential for nephrotoxicity when compared with CsA, while retaining equivalent therapeutic efficacy. In the present study, the major metabolic pathways of CsG in the mouse, rat, and dog were investigated using radiolabeled drug substance to determine if interspecies differences in metabolism exist. The results indicated that the major metabolic pathways in these animal species are similar to those previously reported for CsA, including oxidative modifications at amino acids 1, 4, and 9, and concomitant cyclization of amino acid 1 in two of these metabolites. Moreover, the seven major CsG metabolites (designated GM19, GM1c9, GM4N9, GM1, GM9, GM1c, and GM4N) observed in animal excreta and/or blood were identical to those identified in humans. The major circulating metabolite in blood was GM9 (9-hydroxylated CsG) in all species. In addition, numerous unidentified minor metabolites were observed. Renal excretion was a minor elimination pathway, with the majority of drug-related material excreted via the fecal route. In conclusion, CsG was found to proceed through the same metabolic pathways in three animal species and humans, and that species differences in metabolism were primarily because of differences in the relative importance of the pathways observed.

The estimation of the plasma free fraction of cyclosporine in rabbits and heart transplant patients: the application of a physiological model of renal clearance

We estimated the free fraction (fu) of cyclosporine (CyA) in the plasma from concentrations of CyA in urine (Cu) and plasma (Cp), urine flow rate (UF), and glomerular filtration rate in rabbits and in heart transplant patients. Following intravenous administration of CyA (5-30 mg kg-1) in ten NZW rabbits and oral administration of CyA (4.8-12.1 mg kg-1) in nine heart transplant patients, CyA concentrations in urine and plasma were measured by HPLC. The ratios of Cu to Cp and UF data were fitted to a physiological model of renal clearance using NONMEM. The free fraction of cyclosporine in the rabbits and the heart transplant patients was 0.0122 and 0.14, respectively. Because of the relatively low permeability of CyA across the tubular epithelium, no apparent equilibrium between Cu and Cp at any urine flow rate was reached and, therefore, the Cu to Cp ratio will not be equal to fu.

Urinary protein excretion and the diagnosis of graft rejection or renal dysfunction in renal transplant patients

Urinary proteins have been found to be a sensitive marker of renal damage caused by nephrotoxic agents. An electrophoretic method was used to investigate the potential value of the pattern of urinary protein excretion in 14 cyclosporin-treated renal transplant patients, to differentiate between graft rejection episodes and other causes of renal dysfunction. Urinary protein excretion consistent with renal damage was observed in all of the patients studied, with no marked differences between those with signs of graft rejection, those with renal dysfunction, or those with stable renal function.

Preparative chromatographic purification of cyclosporine metabolites

Polar and primary metabolites of cyclosporin A (CsA) have successfully been isolated by a novel separation protocol. An efficient, easy-to-scale-up chromatographic adsorption/desorption operation recovers polar and primary CsA metabolite pools from large volumes of urine; purified CsA metabolites are subsequently obtained by high-resolution preparative elution chromatography of the semipurified metabolite pools. Separations performed on a semipreparative scale [with a 250 x 9.4 mm (i.d.) reversed-phase HPLC column] yielded microgram quantities of CsA metabolites at > 97% purity, as determined by fast atom bombardment mass spectrometry. These separations also yielded two previously unreported CsA metabolites, similar to AM1A but with an additional hydroxylation. The yield of metabolites was increased to several milligrams by performing the separations with a preparative-scale [250 x 21.2 mm (i.d.)] reversed-phase column. The production rate of purified primary CsA metabolites was greatly increased by performing the separation with the preparative-scale column under conditions of severe mass overloading. In a single chromatographic run, we successfully isolated 11.0 and 5.0 mg of AM1 and AM1c, respectively, at a purity of > 97%. As expected, this increase in the yield of purified metabolites was accompanied by a decrease in the overall recovery. This separation scheme enables the rapid processing of large volumes of urine for isolation of the milligram quantities of CsA metabolites necessary to assess their biological activity. The procedure is applicable to small- or large-scale metabolite isolation and provides a ready source of purified metabolites for in vitro and whole-animal studies.

NMR spectroscopy as a novel approach to the monitoring of renal transplant function

High field 1H NMR spectroscopy was used for the rapid multicomponent analysis of low molecular wt compounds in urine in order to investigate the patterns of metabolic changes associated with early renal allograft dysfunction. Urine samples were collected daily for 14 days from 33 patients who underwent primary renal allograft transplantation, and analyzed by 500 and/or 600 MHz 1H NMR spectroscopy. All patients received 20 mg prednisolone and 5 mg/kg b.d. oral cyclosporin A (CsA) solution. In this study no patient showed clinical or histopathological evidence of CsA nephrotoxicity. For each patient the NMR-generated metabolite data were correlated with the clinical observations, graft biopsy pathology, and data from conventional laboratory techniques for assessing renal function. The NMR spectra of urine from patients with immediate functioning grafts were similar with respect to their patterns of amino acids, organic acids and organic amines, whereas the patients with delayed or non-functioning grafts showed significantly different metabolite excretion patterns. In longitudinal studies on individual patients there were increased urinary levels of trimethylamine-N-oxide (TMAO), dimethylamine (DMA), lactate, acetate, succinate, glycine and alanine during episodes of graft dysfunction. However, only the urinary concentration of TMAO was statistically significantly higher (P < 0.025) in the urine collected from patients during episodes of graft dysfunction (410 +/- 102 microM TMAO/mM creatinine) than in patients with good graft function (91 +/- 18 microM TMAO/mM creatinine) or healthy control subjects (100 +/- 50 microM TMAO/mM creatinine). These findings suggest that graft dysfunction is associated with damage to the renal medulla which causes the release of TMAO into the urine from the damaged renal medullary cells. This provides a possible novel urinary marker for post-transplant graft dysfunction. This study shows that NMR spectroscopy of biofluids, when used in combination with conventional laboratory techniques, is a valuable aid to renal transplant monitoring.

Cholestasis and kidney dysfunction in liver transplant patients reduces cyclosporine metabolite excretion

Cyclosporin A (CsA) is metabolized principally by the hepatic cytochrome P 450-dependent microsomal enzyme system and eliminated virtually entirely as metabolites, mainly in the bile. Only less than 1% of the oral dose is excreted unmetabolized in the urine or bile. Metabolites account for 50-70% of the total CsA in whole blood. Some of the metabolites have been shown to possess an immunosuppressive and even toxic effect but the role of this effect remains uncertain. In order to evaluate the effect of liver and kidney failure on the metabolism of CsA, we studied twelve patients who had undergone liver transplantation. The samples were collected during the first 4 postoperative weeks. The aim of the study was threefold: to evaluate (1) whether an impairment of liver function, as measured by standard biochemical liver function tests, decreased the metabolism or excretion of CsA; (2) whether an induction of either the CsA metabolites or the parent compound took place in the first postoperative period; and (3) whether kidney failure, as measured by serum creatinine, correlated with blood levels of CsA or its metabolites.

Ciclosporin metabolite pattern in blood and urine of liver graft recipients. I. Association of ciclosporin metabolites with nephrotoxicity

Blood ciclosporin (Cs) metabolite pattern in 58 liver grafted patients was routinely monitored by HPLC from the first Cs dose after transplantation until discharge from hospital. Eighteen patients with normal kidney function were allocated to Group I and 14 patients in Group II suffered Cs nephrotoxicity during their clinical course. There were no significant differences between both groups in blood Cs level, kidney function before transplantation, liver function or co-administration of other potentially nephrotoxic drugs. A correlation matrix involving both groups showed a significant correlation between the blood concentration of metabolite M1c9 and serum creatinine and urea, and an inverse correlation with creatinine clearance. During a nephrotoxic episode the blood concentrations of metabolites M1c9 and M1A were significantly elevated in patients in Group II. Analysis of the time course revealed significantly higher blood levels of M19 and M1c9 in Group II patients compared with those in Group I for the first 10 days after transplantation. Serum creatinine and urea concentrations remained significantly elevated, the creatinine clearance being significantly reduced throughout the period of observation. The elevated blood concentrations of ciclosporin metabolites M1c9 and M19 during nephrotoxic episodes suggest that these metabolites are associated with ciclosporin nephrotoxicity. It could not be decided if the elevated metabolite concentrations were the result of and/or the reason for impaired kidney function.

Ciclosporin metabolite pattern in blood and urine of liver graft recipients. II. Influence of cholestasis and rejection

The pattern of metabolites of ciclosporin in blood and 24 h-urine of 58 liver graft recipients was routinely monitored by HPLC from transplantation until discharge from hospital. Liver function and ciclosporin metabolite pattern in patients with an uncomplicated clinical course and in those with cholestasis or acute rejection were compared. During cholestasis M19 and M1A, and during acute rejection M19, in blood were significantly elevated compared to the control group. Blood M19 was significantly correlated with bilirubin concentration and gamma-glutamyl transferase activity in serum, and M1A with the serum bilirubin concentration. Analysis of the metabolite pattern over the observation period showed higher concentrations of M19 and M1A in blood from patients with cholestasis and acute rejection than in the control group; concentrations were lower in the rejection group than in the cholestasis group. The metabolite pattern in 24 h-urine showed similar alterations in ciclosporin metabolite pattern to those in blood. Cholestasis and rejection shift the ciclosporin metabolite pattern in blood and urine to higher concentrations of M19 and M1A, whereas the concentrations of other metabolites and ciclosporin were not significantly affected.