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U Christians

Publications and source records attributed to U Christians.

At least 19 recordsLinked to original sources
PubMed1995

A risk-benefit assessment of tacrolimus in transplantation.

Tacrolimus is a new macrolide immunosuppressant that was isolated from Streptomyces tsukubaensis in 1984. In vitro, on a molecular basis, tacrolimus is 50 to 100 times more potent that cyclosporin. Since 1989, numerous clinical trials have been completed comparing the usefulness of tacrolimus with that of cyclosporin for baseline immunosuppression in solid organ transplantation. Almost all of these studies demonstrated the superior immunosuppressive potency of tacrolimus. However, in most of these trials, tacrolimus-based immunosuppression was associated with a higher overall frequency of drug-related adverse effects compared with cyclosporin. Based on the efficacy and tolerability profile of tacrolimus that has been demonstrated in the various clinical trials so far, tacrolimus is a relevant alternative to cyclosporin for baseline immunosuppression in liver transplantation. In addition to primary immunosuppression, conversion from cyclosporin to tacrolimus should be performed during episodes of severe graft rejection (e.g. resistant to steroid bolus therapy). The future role of tacrolimus for baseline immunosuppression in kidney and thoracic organ transplantation has yet to be defined by ongoing studies.

Humans↗
PubMed1994

Comparison of different assays for the quantitation of FK 506 levels in blood or plasma.

In a prospective study, we evaluated the analytical performance of different assays for the quantitation of FK 506 in blood and plasma. The new whole blood IMX assay was compared with four modifications (liquid/liquid or solid/liquid extraction of blood or plasma respectively) of the standard enzyme-linked immunosorbent assay (ELISA). Both assays utilize the same monoclonal antibody for detection of FK 506. Using isolated FK 506 metabolites generated in vitro, this antibody was shown to recognize not only the unmodified parent drug but also FK 506 metabolites. In stable liver-grafted patients, sensitivity of both modifications of the whole blood ELISA was adequate. In contrast, in some stable patients, plasma ELISA was not able to detect FK 506; this was observed mainly after liquid/liquid extraction of FK 506. Sensitivity of the IMX assay was also low; in six of 10 stable liver-grafted patients, IMX levels were below the limit of detection. In all assays, FK 506 levels were found to be elevated during episodes of liver dysfunction; a possible explanation for this effect would be that of accumulation of cross-reacting FK 506 metabolites. As FK 506 metabolites are known to be less immunosuppressive than the parent drug, liver function should always be taken into account if IMX or ELISA levels are used for drug monitoring.

Antibodies, Monoclonal↗
PubMed1994

Measurement of blood concentrations of FK506 (tacrolimus) and its metabolites in seven liver graft patients after the first dose by h.p.l.c.-MS and microparticle enzyme immunoassay (MEIA).

1. Blood and urine concentrations of the macrolide immunosuppressant FK506 and its metabolites were measured in seven orthotopic liver transplant patients after the first oral dose of FK506 (0.04 +/- 0.02 mg kg-1) used as primary immunosuppressant. A specific h.p.l.c.-MS assay was used, allowing the measurement of parent drug and eight metabolites. Results were compared with those obtained using a microparticle enzyme immunoassay (MEIA). 2. Blood drug concentrations were described by an open two compartment model with first-order absorption giving the following mean data: tmax: 1.9 (h), Cmax: 17.4 (microgram l-1), AUC: 328.1 (microgram l-1 h), t1/2,1: 0.74 (h). The terminal elimination half-life was estimated at about 26 h using the h.p.l.c.-MS assay. 3. The metabolites found in blood were demethyl-FK506 and demethyl-hydroxy-FK506, while in urine FK506 and eight of its metabolites were detected.

Adult↗
PubMed1994

Use of organotypical cultures of primary hepatocytes to analyse drug biotransformation in man and animals.

1. In conventional single-gel culture systems for primary hepatocytes, rapid loss of drug metabolizing capacities is a common feature and parallels general loss of function. An organotypical (double gel) culture technique for primary hepatocytes is established by enclosing the cells within two layers of extra cellular matrix. This serves to imitate the in vivo microenvironment within the space of Dissé. Using rat hepatocytes, this technique has been shown previously to maintain protein synthetic functions in vitro and to allow more efficient P450A-dependent biotransformation of drugs than a standard single-gel culture system. 2. The aim was to test the capacity of this organotypical culture model for primary rat and human hepatocytes to generate drug metabolites in a typical species-dependent pattern. 3. Urapidil, an antihypertensive drug, was used as a test compound, since it is metabolized in vivo in a species-dependent manner in rat and man. 4. Primary rat and human hepatocytes were cultured within two layers of collagen and exposed to 2.25 micrograms/ml urapidil for periods of 1-24 h at 3 days in culture. Urapidil metabolites were measured using hplc. 5. Metabolite M1 (hydroxylated product) was produced preferentially in human hepatocyte cultures, and metabolites M2/M3 (O-demethylated, N-demethylated product) were preferentially generated in rat cultures. This corresponded to the in vivo pattern found in man and rat, respectively. 6. Since in vitro urapidil metabolism by human and rat hepatocytes cultured in a double-gel system reflects that in vivo, it is suggested that information from such a system may be useful to predict the metabolic pathway of novel xenobiotics and to direct further toxicological evaluation.

Adult↗
PubMed1993

Reversal of multidrug resistance in Chinese hamster ovary cells by the immunosuppressive agent rapamycin.

The ability of cyclosporin A, FK506, and rapamycin to overcome multidrug resistance was investigated in Chinese hamster ovary cells in vitro by growth inhibition experiments. 1-30 microM of immunosuppressant sensitized drug-resistant cells and their drug-sensitive parents in a dose-dependent manner to adriamycin (2-2000-fold), colchicine (2-260-fold), and vinblastine (2-120-fold). The multidrug resistance-reversing activity increased in the order rapamycin < FK506 < cyclosporin A, irrespective of whether the resistant cells overexpressed hamster or human P-glycoprotein. The interaction of the three macrolides with P-glycoprotein was characterized by their ability to competitively inhibit the photoaffinity labelling of plasma membranes of resistant CHRB30 cells by iodomycin. The three immunosuppressants bound with high affinity to P-glycoprotein.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1993

Cyclosporine metabolite pattern in blood from patients with acute GVHD after BMT.

The cyclosporine (CYA) metabolite patterns in blood were evaluated in patients with liver dysfunction after allogeneic BMT. Fifty-five BMT patients were included in the study until discharge from hospital. Blood trough levels of CYA and 12 of its metabolites were quantified using HPLC. The patients were assigned to three groups: group I (no acute GVHD, n = 23), group II (acute GVHD of the skin and good liver function, overall acute GVHD: grade I: n = 18, grade II: n = 2) and group III (acute GVHD and liver dysfunction, overall acute GVHD: grade II: n = 2, grade III/IV: n = 8). Analysis of the trough blood concentrations of CYA and its metabolites revealed higher concentrations of metabolite AM19 in group III than in the other groups without reaching statistical significance. During acute GVHD of the liver, the metabolites AM19 (p < 0.01), AM1c9 (p < 0.05) and AM1A (p < 0.05) were significantly elevated compared with patients with normal liver function while CYA and all other metabolites did not differ. The CYA metabolite pattern in patients with acute GVHD and liver involvement was identical with that of liver graft patients during acute graft rejection, while the metabolite patterns of the patients without acute GVHD paralleled that of kidney grafted patients with normal liver function. Acute GVHD of the liver leads to an impaired elimination of CYA with increased blood concentrations of single CYA metabolites.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1992

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.

Bile↗
PubMed1992

Specific and sensitive measurement of FK506 and its metabolites in blood and urine of liver-graft recipients.

A specific and sensitive assay for quantifying the immunosuppressant FK506 and its metabolites in blood and urine was developed. 32-O-Acetyl FK506 was synthesized and used as internal standard. FK506 and its metabolites were purified from the samples by solid-liquid extraction and were injected into a high-performance liquid chromatographic (HPLC) system linked to a mass spectrometer (MS) by particle-beam interface. The FK506 derivatives were separated from interfering material by use of a 100 x 4 mm C8 analytical column and water/acetonitrile or water/methanol gradient elution; they were detected by negative chemical ionization with methane as reagent gas. The limit of detection was 25 pg in a standard solution, and the limit of quantification in blood was 250 pg (extracted from 1 mL of blood). The CV was 11.3% at 5 ng, and no interferences with other drugs were found.

Chromatography, High Pressure Liquid↗
PubMed1991

FK 506.

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Anti-Bacterial Agents↗
PubMed1991

Ciclosporin metabolite pattern in blood and urine of kidney graft patients in relation to liver function.

Ciclosporin, an immunosuppressant, is metabolized by the liver cytochrome P450 system. Changes in the pattern of its metabolites in blood and urine in patients with disturbed liver function have been studied. Forty seven kidney graft patients receiving 2.9 mg/kg/d ciclosporin b.i.d., and no additional medication that would interfere with ciclosporin metabolism, were allocated to three groups according to liver function: I with normal liver function (n = 19), II with elevated liver enzyme activity or bilirubin concentration in serum (n = 20), and III with cholestasis (n = 8). Ciclosporin and 17 metabolites were determined in blood and 24 h-urine. In blood the trough concentrations of metabolites M19 and M1A were significantly higher in group III than in groups I and II. The total quantity of metabolites excreted in 24 h-urine was significantly different for H230, M4N69 and M1A (group III greater than I = II). Renal excretion of the daily dose of ciclosporin in patients in group I was 2.7%, group II 3% and group III 5.7%. In group III compared to group I the ciclosporin metabolite pattern was shifted to a relatively higher concentration of M19 in blood and of H 230, M19 and M1A in urine. Since high ciclosporin metabolite concentrations appear to be associated with nephrotoxicity, the metabolite pattern in patients with impaired liver function should be monitored.

Alanine Transaminase↗
PubMed1991

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.

Adult↗
PubMed1991

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.

Cholestasis↗
PubMed1991

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)

Cyclosporins↗
PubMed1991

Isolation of an immunosuppressive metabolite of FK506 generated by human microsome preparations.

Metabolism of FK506, a 23 member macrolide under clinical investigation as immunosuppressant after transplantation, was studied using human liver microsomes. Two fractions isolated by semi-preparative HPLC were identified by negative fast atom bombardment mass spectrometry as FK506 metabolites with mass peaks at m/z = 790 indicating demethylation of the mother compound. The immunosuppressive activity of one metabolite was evaluated in a ConA-stimulated peripheral rat lymphocyte assay. FK506 had an IC50 of 0.186 nmol/L and the metabolite tested of 1.89 nmol/L.

Animals↗
PubMed1991

Additive and synergistic effects of cyclosporine metabolites on glomerular mesangial cells.

Out of the 29 cyclosporin (Cs) metabolites defined so far, 10 representative ones were isolated from bile of liver grafted patients, purified by HPLC, and their structure specified by FAB-MS and 1H NMR. These were used to determine the growth inhibitory effects on Sprague Dawley rat glomerular mesangial cells (MC). Metabolite dilutions were added to cultured MC for 72 hours and [3H]-thymidine incorporation was measured. A 50% growth inhibition by single metabolites (M) on MC was achieved at the following concentrations (mg/liter): Cs: 1.25; M21: 6.0; M18: 9.0; M26: 10.5; M1: 10.8; M8: 10.8; M17: 12.5; M13: greater than 20.0; M25: greater than 25.0; M203-218: greater than 50.0; H355: greater than 50.0. The activity was correlated to the degree of metabolization as the group of six "active" compounds included four primary metabolites (hydroxylated or demethylated derivatives of Cs: M21, M18, M1, M17), whereas the four "inactive" compounds exclusively were secondary metabolites (demethylated, hydroxylated and/or oxidized primary metabolites: M13, M25, M203-218, H355). Combinations of active metabolites with or without Cs resulted in an additive antiproliferative effect. Although single metabolite activities are not relevant in vivo, already combinations of three (M1 + M17 + M18) or four metabolites (M17 + M18 + M21 + H355) resulted in a significant growth inhibition at concentrations of the participating metabolites measured in urine of liver transplanted patients. Moreover, significant synergistic activities were determined with combinations including secondary metabolites. A final set of experiments discharged unspecific cytotoxic effects. The inhibition of MC [3H]-thymidine incorporation was completely reversible and moreover, direct mesangiolysis was excluded for both single and combined metabolite actions. Thus, considering rat MC proliferation as an initial kidney cell model system for subsequent, more detailed studies measuring functional parameters, we have demonstrated that activities of single metabolites are related to their chemical structure. More importantly, mimicking to some extent the patients' situation, combinations of metabolites at concentrations occurring in vivo reduced MC proliferation in culture in an at least an additive fashion, suggesting that side effects of Cs treatment might be attributed to combined Cs metabolite actions.

Animals↗