Mycophenolate mofetil: Molecular mechanisms of action

Recent developments in the engineered biosynthesis of fungal meroterpenoids

Meroterpenoids are hybrid compounds that are partially derived from terpenoids. This group of natural products displays large structural diversity, and many members exhibit beneficial biological activities. This mini-review highlights recent advances in the engineered biosynthesis of meroterpenoid compounds with C15 and C20 terpenoid moieties, with the reconstruction of fungal meroterpenoid biosynthetic pathways in heterologous expression hosts and the mutagenesis of key enzymes, including terpene cyclases and α-ketoglutarate (αKG)-dependent dioxygenases, that contribute to the structural diversity. Notable progress in genome sequencing has led to the discovery of many novel genes encoding these enzymes, while continued efforts in X-ray crystallographic analyses of these enzymes and the invention of AlphaFold2 have facilitated access to their structures. Structure-based mutagenesis combined with applications of unnatural substrates has further diversified the catalytic repertoire of these enzymes. The information in this review provides useful knowledge for the design of biosynthetic machineries to produce a variety of bioactive meroterpenoids.

A GC-MS-based untargeted metabolomics approach for comprehensive metabolic profiling of mycophenolate mofetil-induced toxicity in mice

Background: Mycophenolate mofetil (MMF), the morpholinoethyl ester of mycophenolic acid, is widely used for maintenance immunosuppression in transplantation. The gastrointestinal toxicity of MMF has been widely uncovered. However, the comprehensive metabolic analysis of MMF-induced toxicity is lacking. This study is aimed to ascertain the metabolic changes after MMF administration in mice. Methods: A total of 700 mg MMF was dissolved in 7 mL dimethyl sulfoxide (DMSO), and then 0.5 mL of mixture was diluted with 4.5 mL of saline (100 mg/kg). Mice in the treatment group (n = 9) were given MMF (0.1 mL/10 g) each day via intraperitoneal injection lasting for 2 weeks, while those in the control group (n = 9) received the same amount of blank solvent (DMSO: saline = 1:9). Gas chromatography-mass spectrometry was utilized to identify the metabolic profiling in serum samples and multiple organ tissues of mice. The potential metabolites were identified using orthogonal partial least squares discrimination analysis. Meanwhile, we used the MetaboAnalyst 5.0 (http://www.metaboanalyst.ca) and Kyoto Encyclopedia of Genes and Genomes database (http://www.kegg.jp) to depict the metabolic pathways. The percentages of lymphocytes in spleens were assessed by multiparameter flow cytometry analysis. Results: Compared to the control group, we observed that MMF treatment induced differential expression of metabolites in the intestine, hippocampus, lung, liver, kidney, heart, serum, and cortex tissues. Subsequently, we demonstrated that multiple amino acids metabolism and fatty acids biosynthesis were disrupted following MMF treatment. Additionally, MMF challenge dramatically increased CD4+ T cell percentages but had no significant influences on other types of lymphocytes. Conclusion: MMF can affect the metabolism in various organs and serum in mice. These data may provide preliminary judgement for MMF-induced toxicity and understand the metabolic mechanism of MMF more comprehensively.

Immunosuppression, Compliance, and Tolerance After Orthotopic Liver Transplantation: State of the Art

Orthotopic liver transplantation is the treatment of choice for several otherwise irreversible forms of acute and chronic liver diseases. Early implemented immunosuppressant regimens have had disappointing results with high rejection rates. However, new drugs have reduced the daily immunosuppression requirements, thereby improving graft and patient survival as well as kidney function. Liver rejection is a T-cell-driven immune response and is the active target of immunosuppressive agents. Immunosuppressants can be divided into pharmacological or biological drugs: the gold standard is the calcineurin inhibitors, steroids, mycophenolate mofetil, and mechanistic target of rapamycin inhibitors. Compliance with these agents is essential, although they can increase the risk of infections and neoplastic diseases. In some patients, graft tolerance can be achieved. Graft tolerance is defined as the absence of acute and chronic rejection in a graft, with normal function and histology in an immunosuppression-free, fully immunocompetent host, usually as the final result of a successful attempt at immunosuppression withdrawal. The occurrence of immunosuppressive-related complications has led to new protocols aimed at protecting renal function and preventing de novo cancer and dysmetabolic syndrome. The backbone of immunosuppression remains calcineurin inhibitors in association with other drugs, mainly over the short-term period. To avoid rejection and the side effects on renal dysfunction, de novo cancer, and cardiovascular syndrome, optimal long-term immunosuppressive therapy should be tailored in liver transplant recipients.

Prediction of Free from Total Mycophenolic Acid Concentrations in Stable Renal Transplant Patients: A Population-Based Approach

BACKGROUND

A population pharmacokinetic (PK) protein-binding model was developed to (1) predict free mycophenolic acid (fMPA) based on total MPA (tMPA) concentrations in renal transplant patients, to establish the therapeutic range of fMPA through pharmacokinetic-pharmacodynamic studies; and (2) provide a guideline for dosing mycophenolate mofetil (MMF).

METHODS

Full PK profiles of 56 patients (from five different occasions) during the first year after transplantation who were treated with oral MMF and cyclosporine, or macrolides (either tacrolimus or sirolimus), were analysed. fMPA protein-binding was modelled using nonlinear mixed effects modelling (NONMEM). The influence of physiological factors and coadministered immunosupressant was studied.

RESULTS

A two-compartment model with first-order absorption and elimination, linear protein binding and enterohepatic circulation (EHC) best described the PK of MPA. Different recycling rate constants were considered depending on the coadministered immunosuppressant. The protein-binding rate constant (K_B [relative standard error, RSE%]) increased nonlinearly with renal function according to K _B = 43.1 (3.13)·(CL_CR/59.51)^0.394(10.66) h^-1. Furthermore, fMPA plasma clearance, given by clearance of the free mycophenolic acid (CL_fMPA), CL_fMPA = 410 (RSE%3.00)·(1+CsA·0.594 (22.39)) L/h, was 59.4% greater in cyclosporine-treated patients than in macrolide-treated patients, leading to lower MPA exposures. External evaluation proved acceptable area under the plasma concentration-time curve and trough concentration predictions.

CONCLUSIONS

A reliable protein-binding population PK model was developed for prediction of fMPA or tMPA from each other and for dose guiding in stable renal transplant recipients.

Added effects of dexamethasone and mesenchymal stem cells on early Natural Killer cell activation

Graft rejection and graft-versus-host disease are leading causes of transplant related mortality despite advancements in immunosuppressive therapy. Mesenchymal stem cells (MSCs) offer a promising addition to immunosuppressive drugs (ISD), while NK-cells are increasingly used as effector cells in graft-versus-leukemia. Combined therapy of ISD, NK-cells and/or MSCs is used in clinical practice. Here, we examined the effects of MSCs and selected ISD (tacrolimus, cyclosporin A, mycophenolic acid, dexamethasone) treatment on early NK-cell activation. We assessed STAT4 and STAT5 phosphorylation triggered by IL-12 and IL-2, respectively. Furthermore, we determined IFNγ, perforin production and the expression pattern of selected NK-cell receptors. Of all drugs tested, only dexamethasone inhibited NK-cell STAT4 and STAT5 phosphorylation. All ISD, with the exception of MPA, significantly inhibited IFNγ, and only dexamethasone inhibited upregulation of early activation markers CD69 and CD25 (IL-2 condition only). MSCs inhibited IL-2 induced NK cell STAT5 phosphorylation, IFNγ production and CD69 upregulation, and IL-12 induced IFNγ and perforin production. While MSCs mediated inhibition of CD69 expression was cell contact dependent, inhibition of IFNγ and perforin production, as well as STAT5 phosphorylation was cell-contact independent. Importantly, dexamethasone augmented MSCs mediated inhibition of both IL-12 and IL-2 induced CD69 expression and IFNγ production, as well as IL-2 induced STAT5 phosphorylation. Taken together, these novel insights may help the design of future NK-cell and MSCs based immunotherapy.

Mathematical equations to calculate true mycophenolic acid concentration in human plasma by using two immunoassays with different cross-reactivities with acyl glucuronide metabolite: comparison of calculated values with values obtained by using an HPLC-UV method

BACKGROUND

Both immunoassays and chromatographic methods are available for therapeutic drug monitoring of mycophenolic acid (MPA). Although chromatographic methods are more precise, immunoassays are widely used in clinical laboratories due to ease of adopting such assays on automated analyzers. We studied the possibility of using mathematical equations to calculate true MPA concentration by accounting for acyl glucuronide cross-reactivities with immunoassays by using two immunoassays with widely different cross-reactivities with the metabolite.

METHODS

We determined MPA concentrations in 20 specimens obtained from transplant recipients using cloned enzyme donor immunoassay (CEDIA) assay and a new particle enhanced turbidimetric inhibition immunoassay (PETINIA) assay. Then we developed mathematical equations to calculate true MPA concentration using values obtained by both immunoassays and reported cross-reactivity of acyl glucuronide with respective immunoassays. Calculated concentrations were compared with values obtained by using a high-performance liquid chromatography combined with ultraviolet detection (HPLC-UV) method.

RESULTS

We obtained good correlation between calculated MPA concentrations and corresponding MPA level obtained by using HPLC-UV method. Using x-axis as the MPA concentrations determined by the HPLC-UV method and y-axis as the calculated MPA level, we observed the following regression equation: y = 1.083x - 0.0995 (r = 0.99, n = 20).

CONCLUSIONS

Mathematical equations can be used to calculate true MPA concentrations using two immunoassays with different cross-reactivities with acyl glucuronide metabolite.

Positive bias in mycophenolic acid concentrations determined by the CEDIA assay compared to HPLC-UV method: is CEDIA assay suitable for therapeutic drug monitoring of mycophenolic acid?

BACKGROUND

Both immunoassays and chromatographic methods are available for therapeutic drug monitoring of mycophenolic acid (MPA), an immunosuppressant. We studied the suitability of cloned enzyme donor immunoassay (CEDIA) assay for routine monitoring of MPA by comparing values obtained by the CEDIA assay with corresponding values obtained by using a high-performance liquid chromatography combined with ultraviolet detection (HPLC-UV) method.

METHODS

We compared MPA concentrations obtained by a reference HPLC-UV method and CEDIA assay on Hitachi 917 analyzer (Roche Diagnostics, Indianapolis, IN) using 60 patient specimens (18 liver transplant recipient and 42 kidney transplant recipients).

RESULTS

When MPA concentrations in all 60 transplant recipients obtained by the HPLC-UV (x-axis) method were compared with corresponding values obtained by the CEDIA method (y-axis), the following regression equation was obtained: y = 1.1558x + 0.2876 (r = 0.97). Interestingly, much lower bias was observed in 42 renal transplant recipients as revealed by the following regression equation; y = 1.1181x + 0.2745 (r = 0.98). However, more significant positive bias was observed in 18 liver transplant recipients as following regression equation as observed: y = 1.3337x + 0.1493 (r = 0.94).

CONCLUSIONS

We conclude that MPA concentrations determined by the CEDIA assay showed significant positive bias compared to HPLC-UV method. Therefore, caution must be exercised in interpreting therapeutic drug monitoring result of MPA if CEDIA assay is used.

Enteric-coated mycophenolate sodium in combination with full dose or reduced dose cyclosporine, basiliximab and corticosteroids in Australian de novo kidney transplant patients

AIM

Cyclosporine (CsA), dosed to achieve C2 targets, has been shown to provide safe and efficacious immunosuppression when used with a mycophenolate and steroids for de novo kidney transplant recipients. This study examined whether use of enteric-coated mycophenolate sodium (EC-MPS) together with basiliximab and steroids would enable use of CsA dosed to reduced C2 targets in order to achieve improved graft function.

METHODS

Twelve-month, prospective, randomized, open-label trial in de novo kidney transplant recipients in Australia. Seventy-five patients were randomized to receive either usual exposure (n = 33) or reduced exposure (n = 42) CsA, EC-MPS 720 mg twice daily, basiliximab and corticosteroids.

RESULTS

There was no significant difference in mean Cockcroft-Gault CrCl (creatinine clearance) (60.2 ± 17.6 mL/min per 1.73 m(2) vs 63.2 ± 24.3, P = 0.64 for usual versus reduced exposure respectively) at 6 months. There was no significant difference between treatment groups in the incidence of treatment failure defined as biopsy proven acute rejection, graft loss or death (secondary endpoint: 30.3% full exposure vs 35.7% reduced exposure). At 12 months the incidence of overall adverse events was the same in both groups.

CONCLUSION

This exploratory study suggests de novo renal transplant patients can safely receive a treatment regimen of either full or reduced exposure CsA in combination with EC-MPS, corticosteroids and basiliximab, with no apparent difference in efficacy or graft function during the first year after transplant.

Adaptive evolution of drug targets in producer and non-producer organisms

MPA (mycophenolic acid) is an immunosuppressive drug produced by several fungi in Penicillium subgenus Penicillium. This toxic metabolite is an inhibitor of IMPDH (IMP dehydrogenase). The MPA-biosynthetic cluster of Penicillium brevicompactum contains a gene encoding a B-type IMPDH, IMPDH-B, which confers MPA resistance. Surprisingly, all members of the subgenus Penicillium contain genes encoding IMPDHs of both the A and B types, regardless of their ability to produce MPA. Duplication of the IMPDH gene occurred before and independently of the acquisition of the MPAbiosynthetic cluster. Both P. brevicompactum IMPDHs are MPA-resistant, whereas the IMPDHs from a non-producer are MPA-sensitive. Resistance comes with a catalytic cost: whereas P. brevicompactum IMPDH-B is >1000-fold more resistant to MPA than a typical eukaryotic IMPDH, its kcat/Km value is 0.5% of 'normal'. Curiously, IMPDH-B of Penicillium chrysogenum, which does not produce MPA, is also a very poor enzyme. The MPA-binding site is completely conserved among sensitive and resistant IMPDHs. Mutational analysis shows that the C-terminal segment is a major structural determinant of resistance. These observations suggest that the duplication of the IMPDH gene in the subgenus Penicillium was permissive for MPA production and that MPA production created a selective pressure on IMPDH evolution. Perhaps MPA production rescued IMPDH-B from deleterious genetic drift.

Pharmacogenetics of the mycophenolic acid targets inosine monophosphate dehydrogenases IMPDH1 and IMPDH2: gene sequence variation and functional genomics

BACKGROUND AND PURPOSE

Inosine monophosphate dehydrogenases, encoded by IMPDH1 and IMPDH2, are targets for the important immunosuppressive drug, mycophenolic acid (MPA). Variation in MPA response may result, in part, from genetic variation in IMPDH1 and IMPDH2.

EXPERIMENTAL APPROACH

We resequenced IMPDH1 and IMPDH2 using DNA from 288 individuals from three ethnic groups and performed functional genomic studies of the sequence variants observed.

KEY RESULTS

We identified 73 single nucleotide polymorphisms (SNPs) in IMPDH1, 59 novel, and 25 SNPs, 24 novel, in IMPDH2. One novel IMPDH1 allozyme (Leu275) had 10.2% of the wild-type activity as a result of accelerated protein degradation. Decreased activity of the previously reported IMPDH2 Phe263 allozyme was primarily due to decreased protein quantity, also with accelerated degradation. These observations with regard to the functional implications of variant allozymes were supported by the IMPDH1 and IMPDH2 X-ray crystal structures. A novel IMPDH2 intron 1 SNP, G > C IVS1(93), was associated with decreased mRNA quantity, possibly because of altered transcription.

CONCLUSIONS AND IMPLICATIONS

These results provide insight into the nature and extent of sequence variation in the IMPDH1 and IMPDH2 genes. They also describe the influence of gene sequence variation that alters the encoded amino acids on IMPDH function and provide a foundation for future translational studies designed to correlate sequence variation in these genes with outcomes in patients treated with MPA.

Mycophenolic acid response biomarkers: a cell line model system-based genome-wide screen

Mycophenolic acid (MPA) is commonly used to treat patients with solid organ transplants during maintenance immunosuppressive therapy. Response to MPA varies widely, both for efficacy and drug-induced toxicity. A portion of this variation can be explained by pharmacokinetic and pharmacodynamic factors, including genetic variation in MPA-metabolizing UDP-glucuronyltransferase isoforms and the MPA targets, inosine monophosphate dehydrogenase 1 and 2. However, much of the variation in MPA response presently remains unexplained. We set out to determine whether there might be additional genes that modify response to MPA by performing a genome-wide association study between basal gene mRNA expression profiles and an MPA cytotoxicity phenotype using a 271 human lymphoblastoid cell line model system to identify and functionally validate genes that might contribute to variation in MPA response. Our association study identified 41 gene expression probe sets, corresponding to 35 genes, that were associated with MPA cytotoxicity as a drug response phenotype (p<1×10(-6)). Follow-up siRNA-mediated knockdown-based functional validation identified four of these candidate genes, C17orf108, CYBRD1, NASP, and RRM2, whose knockdown shifted the MPA cytotoxicity curves in the direction predicted by the association analysis. These studies have identified novel candidate genes that may contribute to variation in response to MPA therapy and, as a result, may help make it possible to move toward more highly individualized MPA-based immunosuppressive therapy.

Calcineurin inhibitor minimization in pediatric liver allograft recipients

The use of CNI in pediatric LTx has dramatically improved the outcome for children with end-stage liver disease by significantly reducing the rate of acute and chronic rejection. Long-term concerns about CNI-induced nephrotoxicity and other adverse effects remain an issue, particularly as the emphasis moves from short-term survival to long-term quality of life. This review summarizes lessons learnt from pediatric and adult solid organ transplantation in minimizing CNI use in immunosuppression protocols in children following LTx. There are three models for CNI minimization: dose reduction, withdrawal or avoidance, supplemented by the use of IL-2 receptor blocking antibodies in the peri-transplant period, and early transition to alternate drugs such as MMF or SRL. Prospective studies evaluating reduction or withdrawal protocols in adult and pediatric LTx indicate that rejection rates are comparable with traditional CNI-based immunosuppression and that two and five yr patient and graft survival are similar, with recovery in renal function. There are few studies evaluating complete avoidance of CNI, apart from that in renal transplantation, although the benefits of long-term reduction in cardiovascular, metabolic, and possibly neoplastic side effects may justify this approach. It is not clear yet how CNI minimization will affect the development of tolerance but experimental and preliminary clinical studies indicate that CNI and steroid avoidance or minimization in the peri-operative period may favor the development of long-term graft tolerance. In summary, CNI minimization may be safe and effective in the short term but large-scale pediatric randomized studies are required to evaluate the long-term efficacy of these regimes in the development of chronic rejection, PTLD, and graft tolerance.

Efficacy and safety of mycophenolate mofetil monotherapy in liver transplant patients with renal failure induced by calcineurin inhibitors

OBJECTIVE

To assess the efficacy and safety of mycophenolate mofetil (MMF) monotherapy in liver transplant recipients with renal failure secondary to the use of calcineurin inhibitors (CNIs).

MATERIALS AND METHODS

Thirty-one patients on MMF monotherapy with creatinine levels >1.3 mg/dL, previously immunosuppressed with CNIs and MMF, were analyzed. Conversion was started in patients with no acute or chronic rejection episodes and stable liver chemistry. CNI doses were reduced by 25% every 2 to 3 months, or to 50% if the dose was lower than 1 mg/d of tacrolimus or 50 mg/d of cyclosporine. Different variables were recorded from the time that conversion to monotherapy was decided, on the discontinuation day of the calcineurin inhibitor, and during the follow-up.

RESULTS

Mean times from transplant to conversion ranged from 14 to 186 months. The minimum follow-up time in monotherapy was 12 months. Renal function improved at 6 months in 70% of cases and at 12 months in 69.6%. Patients with no renal function improvement maintained stable creatinine values. There were no rejection episodes, graft losses, or deaths. No leukopenia occurred, and triglyceride and uric acid values improved.

CONCLUSIONS

MMF monotherapy is a safe alternative in patients with posttransplant renal failure secondary to the use of CNIs. Renal function improvement was achieved in almost 70% of patients at 12 months, and creatinine values were maintained in all other patients. The risk of rejection due to the slow tapering of CNIs is minimum.

Enzyme immunoassay for mycophenolic acid in milk and cheese

Mycophenolic acid (MPA) was reacted with N-hydroxysuccinimide and conjugated to keyhole limpet hemocyanin (KLH), and to horseradish peroxidase (HRP), respectively. The MPA-KLH was used to produce anti-MPA antiserum in rabbits. A competitive direct enzyme immunoassay (EIA) for MPA was established with anti-MPA antiserum and MPA-HRP conjugate. The mean 50% inhibition and detection limit of MPA standard curves (n = 103) were 197 +/- 67 and 81 +/- 48 pg/mL, respectively. The EIA was specific for MPA and its synthetic 2-morpholinoethyl ester, mycophenolate mofetil (91% relative cross-reactivity). Raw bulk milk and pasteurized milk, with and without beta-glucuronidase pretreatment, were analyzed by EIA. No MPA was found in milk, at a detection limit of 100 pg/mL (recovery 58-66% at 0.125-2 ng/mL). Blue-veined cheese from the German market (n = 53) was analyzed by EIA, and the detection limit was at 0.5 ng/g (recovery 68-79% at 5-100 ng/g). All but two cheeses contained MPA, although mostly (66%) at levels of <10 ng/g. MPA at 400-1200 ng/g was found in Roquefort cheeses. Highest levels (4-11 microg/g) were found in a German soft cheese preparation. MPA levels in mycelium-rich parts of cheese were 3 times higher than in mycelium-free parts.

Effects of adenosine monophosphate-activated kinase activators on bovine oocyte nuclear maturation in vitro

The purpose of this study was to examine the effects of an activator of AMPK (5-aminoimidazole-4-carboxamide 1-beta-D-ribofuranoside (AICAR)) on bovine oocyte nuclear maturation in vitro. After 7 hr of culture, AICAR (1 mM) significantly increased the percentages of cumulus-enclosed oocytes (CEO) and denuded oocytes (DO) remaining at the germinal vesicle stage. After 22 hr of culture, AICAR significantly reduced the percentage of CEO reaching metaphase II (MII). AICAR at 1.0 mM also increased the inhibitory effect of the adenylate cyclase activator forskolin in CEO; however, at 0.05 mM, AICAR increased the percentage of oocytes at MII after 22 hr of culture compared to forskolin alone. The adenosine kinase inhibitor 5'-aminodeoxyadenosine reversed the effect of AICAR in CEO and DO showing that phosphorylation of AICAR by adenosine kinase is required for its inhibitory activity. GMP, but not AMP, inhibited meiosis in CEO and DO; however, inhibition of guanyl and adenyl nucleotides synthesis did not reverse the effect of AICAR suggesting that the inhibitory effect of AICAR is not due to increased synthesis of these nucleotides. Metformin, another activator of AMPK, also inhibited GVBD in CEO and DO. The alpha-1 isoform of the catalytic subunit of AMPK was detected in oocytes and cumulus cells, and reverse transcription-polymerase chain reaction experiments showed the presence of transcripts for alpha-1, alpha-2, beta-1, and gamma-3 isoforms of the regulatory subunits in cumulus cells and oocytes. These data show that the AMPK activator AICAR is inhibitory to nuclear maturation in bovine oocytes due to activation of AMPK.

Liver transplantation()

Orthotopic liver transplantation (OLT) involves the substitution of a diseased native liver with a normal liver (or part of one) taken from a deceased or living donor. Considered an experimental procedure through the 1980s, OLT is now regarded as the treatment of choice for a number of otherwise irreversible forms of acute and chronic liver disease.The first human liver transplantation was performed in the United States in 1963 by Prof. T.E. Starzl of the University of Colorado. The first OLT to be performed in Italy was done in 1982 by Prof. R. Cortesini. The procedure was successfully performed at the Policlinico Umberto I of the University of Rome (La Sapienza).The paper reports the indications for liver transplantation, donor selection and organ allocation in our experience, surgical technique, immunosuppression, complications and results of liver transplantation in our center.

Mycophenolate mofetil promotes prolonged improvement of renal dysfunction after pediatric liver transplantation: experience of a single center

Few studies have evaluated the long-term use of MMF in liver transplanted children with renal dysfunction. The aim of this study is to report the experience of a pediatric transplantation center on the efficacy and security of long-term use of a MMF immunosuppressant protocol with reduced doses of CNIs in stable liver transplanted children with renal dysfunction secondary to prolonged use of CsA or Tac. Between 1988 and 2003, 191 children underwent OLT and 11 patients developed renal dysfunction secondary to CNIs toxicity as evaluated by biochemical renal function parameters. The interval between liver transplantation and the introduction of the protocol varied from one to 12 yr. Renal function was evaluated by biochemical parameters in five phases: immediately prior to MMF administration; 3, 6, 12 and 24 months after the introduction of MMF. Among the patients, nine of them (82%) showed improvement of renal function parameters in comparison with the pretreatment values. The two patients that did not show any improvement were patients in whom the interval of time between OLT and the introduction of MMF was longer. All parameters of liver function remained unchanged. No episodes of acute or chronic rejection or increases in infection rates during the period were detected. Two patients developed transitory diarrhea and leukopenia that were reverted with reduction of MMF dosage. In conclusion, in liver transplanted pediatric patients with CNI-induced chronic renal dysfunction, the administration of MMF in addition to reduced doses of CNIs promotes long-term improvement in renal function parameters with no additional risks.

Activation of the purine salvage pathway in mononuclear cells of cardiac recipients treated with mycophenolate mofetil

BACKGROUND

The objective of this study was to investigate purine nucleotide metabolism in peripheral blood mononuclear cells (PBMC) of cardiac transplant recipients switched from azathioprine to mycophenolate mofetil (MMF).

METHODS

Concentrations of guanosine 5'triphosphate (GTP) and adenosine 5'triphosphate (ATP), the activities of inosine monophosphate dehydrogenase (IMPDH), guanine phosphoribosyltransferase (GPRT), and hypoxanthine phosphoribosyltransferase (HPRT) were determined in PBMC of 27 cardiac transplant recipients before switch to MMF and 3, 6, and 12 months thereafter.

RESULTS

There was no difference in the activities of IMPDH and salvage pathway enzymes GPRT and HRPT as well as in intracellular GTP and ATP concentrations between the patients before switch to MMF and healthy controls. The GTP and ATP concentrations in PBMC of cardiac recipients did not change during the entire observation period. Although the MPA trough level remained similar, IMPDH activity declined from 897 to 316 pmol/10(6)PBMC/h 3 months after MMF onset, was almost completely inhibited after 6 months, and partially restored to 143 pmol/10(6)PBMC/h 12 months after switch to MMF. In contrast, GPRT activity increased after 3, 6, and 12 months of MMF therapy and HPRT activity 3 and 6 months after switch to MMF.

CONCLUSIONS

We demonstrated for the first time an induction of salvage pathway enzyme activities in PBMC under MMF therapy. This probably accounts for the maintenance of intracellular purine nucleotide pools and prevents the GTP depletion.

Mycophenolate mofetil monotherapy in liver transplantation

AIM

Calcineurin inhibitors (CI) are associated with significant morbidity in transplant recipients. The aim of this study was to evaluate the effectiveness and safety of mycophenolate mofetil (MMF) monotherapy in liver transplantation (LT).

METHODS

We analysed 32 patients (24 males, 8 female, of mean age 55.7 years) who underwent LT between 1994 and 2003. In 29 patients immunosuppressive therapy was cyclosporine; in three patients it was tacrolimus. Eleven patients were submitted for LT due to hepatitis B cirrhosis; eight for hepatitis C cirrhosis, six for alcoholic cirrhosis, and seven for other diseases. In these patients, MMF was added gradually, simultaneously reducing the dosage of CI up to complete withdrawal. We considered the efficacy (decrease in serum creatinine) and the incidence of complications (acute and chronic rejection, leukopenia, diarrhea).

RESULTS

Patients were converted to MMF after a median of 50 months after LT. MMF monotherapy was started after a median of 9 months in association with CI. Indications for switch to MMF monotherapy were adverse effects of CI (renal disfunction in 30 patients) and de novo tumoral evidence after LT in two patients. Median dosage of MMF was 750 mg twice daily (500-1500 mg). There was a statistically significant decrease in serum creatinine levels (2.02-1.7 mg/dL; P = .0001). Side effects were: leukopenia in five of 32 patients (15.6%), diarrhea in four of 32 patients (12.5%), and one acute rejection.

CONCLUSION

MMF monotherapy improved renal function and was not associated with a significant risk of allograft rejection. Side effects were mild with dose regimens up to 750 mg twice daily.

Effect of Cyclosporine, Mycophenolate Mofetil, and Their Combination With Steroids on Apoptosis in a Human Cultured Monocytic U937 Cell Line

Transplant patient plasma produces an increased rate of mononuclear cell apoptosis despite a normal serum creatinine value. Immunosuppressive medications may be one factor that causes an altered apoptotic pattern. We evaluated the in vitro effects of various doses of cyclosporine, mycophenolate mofetil, and steroids on apoptosis of a cultured human monocytic U937 cell line, using estimates by fluorescence microscopy and annexin V assays. Increasing cyclosporine concentrations (100 to 800 ng/mL) progressively increased apoptosis rates (16% to 32%). The combination of steroid (0.01 microg/mL) and cyclosporine increased the apoptosis rate to 45%. Mycophenolate mofetil alone (0.3 microg/mL) led to an apoptosis rate of 34%. Therapeutic levels of mycophenolate mofetil from 3 to 7 microg/mL led to apoptosis rates from 56% to 67%. The combination of cyclosporine, steroid, and mycophenolate mofetil increased the rate of apoptosis to 95%. Immunosuppressive therapy may contribute to the high rate of apoptosis observed among mononuclear cells of transplanted patients. This effect may alter patient susceptibility to infections and contribute to a unique mechanism of immunosuppression.

Mycophenolate mofetil for renal dysfunction after pediatric liver transplantation

BACKGROUND

Cyclosporine A (CsA) and tacrolimus (Tac) provide effective immunosuppression after orthotopic liver transplantation (OLT) but can cause renal dysfunction that may progress to end-stage renal failure (ESRF). Mycophenolate mofetil (MMF) is a newer immunosuppressant that does not affect renal function. Its long-term use in children with renal dysfunction after OLT has not yet been fully evaluated.

METHODS

A retrospective analysis was performed of all children begun on MMF for renal dysfunction and followed up for at least 1 year. Renal dysfunction was defined as calculated glomerular filtration rate (cGFR) of less than 65 mL/min/1.73 m2. cGFR and liver function were measured before and after transfer. Data were analyzed using the Wilcoxon signed rank test.

RESULTS

Forty-eight children (23 males) began MMF at a median age of 11.1 (0.9-18.1) years and at a median of 4.0 (0.3-12.4) years postOLT. Median baseline cGFR was 54 (range 29-65) mL/min/1.73 m2. Immunosuppression after transfer was MMF monotherapy in 36, MMF with steroids, in 4 and MMF with low-dose CsA or Tac in 8. In 44 (92%) patients, there was a statistically significant increase to a median cGFR of 69 (28-114) mL/min/1.73 m2 by 1 month and a further increase to a median cGFR of 77 (24-105) mL/min/1.73 m2 by 2 months of MMF treatment, after which time cGFR was maintained. Children aged less than 3 years at OLT or who were less than 5 years postOLT when MMF was begun demonstrated greater increases in cGFR. Four children with a median baseline cGFR of 34 (range 31-49) mL/min/1.73 m2 did not respond and progressed to ESRF. Mild side effects occurred in seven (15%) and gastrointestinal bleeding requiring discontinuation of MMF in one (2%). Liver function abnormalities occurred in seven (15%): transient transaminitis in three, acute rejection in two, and chronic rejection in two, of whom one required retransplantation.

CONCLUSIONS

In 92% children with renal dysfunction after OLT, MMF treatment provided safe and effective immunosuppression and allowed CsA or Tac to be discontinued or reduced, leading to improvement of renal function. The improvement was greatest in younger children and those who began MMF early postOLT. Side effects were uncommon. Additional steroid cover during the transfer to MMF should be considered to prevent liver-allograft rejection.

Effects of mycophenolate mofetil on key pattern of coronary restenosis: a cascade of in vitro and ex vivo models

Background

Mycophenolate mofetil (MMF), the prodrug of mycophenolic acid (MPA), is a rationally designed immunosuppressive drug. The current study investigates the effect of MMF on key pattern of restenosis in a cascade of in vitro and ex vivo models.

Methods

Part I of the study investigated in northern blot and cytoflow studies the effect of MMF (50, 100, 150, 200, 250, and 300 μg/mL) on TNF-α induced expression of intercellular adhesion molecule 1 (ICAM-1) in human coronary endothelial cells (HCAEC) and human coronary medial smooth muscle cells (HCMSMC). Part II of the study applied a human coronary 3D model of leukocyte attack, the 3DLA-model. HCAEC and HCMSMC were cultured on both sides of a polycarbonate filters, mimicking the internal elastic membrane. Leukocyte attack (LA) was carried out by adding human monocytes (MC) on the endothelial side. The effect of MMF (50 μg/mL) on adhesion and chemotaxis (0.5, 1, 2, 3, 4, 6, and 24 h after LA) and the effect on proliferation of co-cultured HCMSMC (24 h after LA) was studied. In part III of the study a porcine coronary organ culture model of restenosis (POC-model) was used. After ex vivo ballooning MMF (50 μg/mL) was added to the cultures for a period of 1, 2, 3, 4, 5, 6, and 7 days. The effect on reactive cell proliferation and neointimal thickening was studied at day 7 and day 28 after ballooning.

Results

Expression of ICAM-1 in northern blot and cytoflow studies was neither clearly inhibited nor stimulated after administration of MMF in the clinical relevant concentration of 50 μg/mL. In the 3DLA-model 50 μg/mL of MMF caused a significant antiproliferative effect (p < 0.001) in co-cultured HCMSMC but had no effect on MC-adhesion and MC-chemotaxis. In the ex vivo POC-model neighter reactive cell proliferation at day 7 nor neointimal hyperplasia at day 28 were significantly inhibited by MMF (50 μg/mL).

Conclusion

Thus, the data demonstrate a significant antiproliferative effect of clinical relevant levels of MMF (50 μg/mL) in the 3DLA-model. The antiproliferative effect was a direct antiproliferative effect that was not triggered via reduced expression of ICAM-1 or via an inhibition of MC-adhesion and chemotaxis. Probably due to technical limitations (as e.g. the missing of perfusion) the antiproliferative effect of MMF (50 μg/mL) could not be reproduced in the coronary organ culture model. A cascade of focused in vitro and ex vivo models may help to gather informations on drug effects before large experimental studies are initiated.

The functional basis of mycophenolic acid resistance in Candida albicans IMP dehydrogenase

Candida albicans is an important fungal pathogen of immunocompromised patients. In cell culture, C. albicans is sensitive to mycophenolic acid (MPA) and mizoribine, both natural product inhibitors of IMP dehydrogenase (IMPDH). These drugs have opposing interactions with the enzyme. MPA prevents formation of the closed enzyme conformation by binding to the same site as a mobile flap. In contrast, mizoribine monophosphate, the active metabolite of mizoribine, induces the closed conformation. Here, we report the characterization of IMPDH from wild-type and MPA-resistant strains of C. albicans. The wild-type enzyme displays significant differences from human IMPDHs, suggesting that selective inhibitors that could be novel antifungal agents may be developed. IMPDH from the MPA-resistant strain contains a single substitution (A251T) that is far from the MPA-binding site. The A251T variant was 4-fold less sensitive to MPA as expected. This substitution did not affect the k(cat) value, but did decrease the K(m) values for both substrates, so the mutant enzyme is more catalytically efficient as measured by the value of k(cat)/K(m). These simple criteria suggest that the A251T variant would be the evolutionarily superior enzyme. However, the A251T substitution caused the enzyme to be 40-fold more sensitive to mizoribine monophosphate. This result suggests that A251T stabilizes the closed conformation, and this hypothesis is supported by further inhibitor analysis. Likewise, the MPA-resistant strain was more sensitive to mizoribine in cell culture. These observations illustrate the evolutionary challenge posed by the gauntlet of chemical warfare at the microbial level.

Mycophenolate mofetil in pediatric liver transplant patients with renal dysfunction: preliminary data

The prolonged use of CNI has been associated with nephrotoxicity. MMF is a new immunosuppressive agent. In the present study, the consequences of introducing MMF and reduction of CNI in liver-transplant children were analysed. The present study included eight pediatric liver-transplant patients who had transplantation at least 5 yr previously, had stable graft function and had renal dysfunction as a probable side-effect of CNI therapy. CNI was replaced with MMF in all patients and serum creatinine, uric acid concentration, azotemia and creatinine clearance before and 6 months after study entry were measured. The patients were monitored closely for side-effects of MMF as well as graft function. Six months after study entry serum creatinine, uric acid concentration, azotemia and creatinine clearance improved in all the patients at the last follow-up. The aspartate aminotransferase and alanine aminotransferase concentrations were stable during the study period and did not observe any serum bilirubin increased as well. No side-effects were reported in patients on MMF. Only one patient reported temporary pruritus and nausea. The results indicate that renal dysfunction significantly improved when MMF therapy is started and CNI reduced. Furthermore present data suggest that the risk of acute allograft rejection is very low when the CNI desired reduction is achieved in not too short time and absolutely when the MPA levels are strictly monitored.

Inhibition of inosine monophosphate dehydrogenase (IMPDH) by the antiviral compound, 2-vinylinosine monophosphate

A new enzyme-mediated synthesis of 2-vinylinosine, a compound with broad-spectrum RNA antiviral activity, is described. In order to understand the mechanism of action of this compound, we synthesized its monophosphate and investigated the behavior of that compound toward the enzyme, inosine monophosphate dehydrogenase (IMPDH), a key enzyme involved in the biosynthesis of nucleotides. 2-Vinylinosine monophosphate is a potent inhibitor of IMPDH with a K(i) of 3.98 microM (k(inact)=2.94 x 10(-2) s(-1)). The antiviral activity of 2-vinylinosine may be explained by its cellular conversion to the monophosphate through the sequential action of PNP and HGPRT and subsequent inhibition of IMPDH by the cellularly produced 2-vinylinosine 5'-monophosphate.

Rapid determination of mycophenolic acid in plasma by reversed-phase high-performance liquid chromatography

A simple, accurate and sensitive high-performance liquid chromatographic method with UV detection was carried out to measure plasma concentrations of mycophenolic acid. Following a simplified acid hydrolysis of the sample, the separation was carried out in 4 min using a Zorbax Eclipse C(8) reversed-phase column with a flow-rate of 1.5 ml/min, and monitoring the absorbance at 250 nm. Throughput was up to 100 samples in 24 h. Within the investigated concentration ranges of mycophenolic acid (0-100 mg/l), good linearity (r>0.99) was obtained. The method is sensitive (the limit of detection was about 20 microg/l) and precise (for 0.49 mg/l added to plasma, within-run C.V. was 2% and between-run was 4.2%; for 2.88 mg/l, within-run C.V. was 0.35% and between-run C.V. was 0.69%; for 24.38 mg/l, within-run C.V. was 0.77% and between-run C.V. was 3.1%). Analytical recoveries were 96% for 0.5 mg/l mycophenolic acid added to plasma, 100% for 12 mg/l and 102.5% for 24 mg/l.

Pharmacodynamics of mycophenolate mofetil after heart transplantation: new mechanisms of action and correlations with histologic severity of graft rejection

The primary mechanism of action in vivo of mycophenolate mofetil (MMF) is believed to be inhibition of lymphocyte proliferation. We used novel assays of lymphocyte functions (pharmacodynamics, PD) in whole blood collected from rat heart allograft recipients treated with MMF to investigate the mechanisms of action of the active metabolite of MMF, mycophenolate acid (MPA) in vivo. Allograft recipients were treated orally once daily with 3 different doses of MMF. Seven days after transplantation, blood was collected 24h after the penultimate dose and several timepoints after the last dose, after which grafts were removed for microscopic grading of rejection. Lymphocytes in whole blood samples were mitogen stimulated through calcium-dependent and -independent signaling pathways. Inhibition of PD was measured by lymphocyte proliferation and expression of several surface antigens on T cells, and was calculated as area under the time-inhibition of immune function effect curve (AUE0-24h). We found that inhibition of lymphocyte proliferation and antigen expression by MPA correlated highly with MMF-dose, MPA level and with the histologic severities of graft rejection (p <0.05). In summary, MPA suppressed lymphocyte proliferation and expression of T-cell surface antigens in whole blood collected from MMF-treated allograft recipients, thus demonstrating the multiple mechanisms of suppression of rejection on peripheral blood T cells after MMF treatment.

Down-regulation of experimental allergic encephalomyelitis in DA rats by tiazofurin

The immunomodulatory potential of tiazofurin (TR) on experimental autoimmune encephalomyelitis (EAE) was investigated. Given continuously, TR dose-dependently suppressed the development of EAE in Dark Agouti (DA) rats immunized with either rat spinal cord homogenate (SCH) or myelin oligodendrocyte glycoprotein (MOG). Amelioration of clinical signs was also obtained when the drug was administered during the inductive phase only (day 0 to 8), or during the effector phase (day 10 to 20) of the disease. Efficacy of TR was further evaluated by adoptive transfer of the disease with myelin basic protein (MBP)-sensitized draining lymph node cells (DLNC). Cells from TR-protected rats failed to transfer the disease into naive syngeneic recipients; in addition, TR treatment of recipient rats that had received MBP-sensitized lymphoid cells diminished the adoptively transferred EAE. A reduction of clinical EAE in TR-treated rats was accompanied with the absence of mononuclear infiltration in the spinal cord and defective adhesive cell-cell interactions. The anti-MOG autoAb production was also decreased. Importantly, no evidence for a generalized impairment of the T cell activity, nor decreased in vitro proliferative antigen specific response of LNC from TR-treated animals was found. These results suggest that TR exerts its EAE protective and suppressive effects by limiting adhesive interactions involved in the autoimmune pathogenic process, and due to the lack of general immunosuppressive activity, it should be considered as a candidate drug for the treatment of neuroinflammatory diseases like multiple sclerosis (MS).

Novel mycophenolic adenine bis(phosphonate) analogues as potential differentiation agents against human leukemia

Novel mycophenolic adenine dinucleotide (MAD) analogues have been prepared as potential inhibitors of inosine monophosphate dehydrogenase (IMPDH). MAD analogues resemble nicotinamide adenine dinucleotide binding at the cofactor binding domain of IMPDH; however, they cannot participate in hydride transfer and therefore inhibit the enzyme. The methylenebis(phosphonate) analogues C2-MAD and C4-MAD were obtained by coupling 2',3'-O-isopropylideneadenosine 5'-methylenebis(phosphonate) (22) with mycophenolic alcohols 20 and 21 in the presence of diisopropylcarbodiimide followed by deprotection. C2-MAD was also prepared by coupling of mycophenolic methylenebis(phosphonate) derivative 30 with 2',3'-O-isopropylideneadenosine. Compound 30 was conveniently synthesized by the treatment of benzyl-protected mycophenolic alcohol 27 with a commercially available methylenebis(phosphonic dichloride) under Yoshikawa's reaction conditions. C2-MAD and C4-MAD were found to inhibit the growth of K562 cells (IC(50) = 0.7 microM and IC(50) = 0.1 microM, respectively) as potently as mycophenolic acid (IC(50) = 0.3 microM). In addition, C2-MAD and C4-MAD triggered vigorous differentiation of K562 cells an order of magnitude more potently than tiazofurin, and MAD analogues were resistant to glucuronidation in vitro. These results show that C2-MAD and C4-MAD may be of therapeutic interest in the treatment of human leukemias.

Analytic validation of the enzyme multiplied immunoassay technique for the determination of mycophenolic acid in plasma from renal transplant recipients compared with a high-performance liquid chromatographic assay

The analysis of mycophenolic acid (MPA) has proved a valuable adjunct to the clinical care of organ transplant recipients. The analytic validation of the enzyme multiplied immunoassay technique (EMIT) for the determination of MPA in plasma is described. The EMIT MPA standard curve was 0 to 15.0 microg/mL, and curve storage was maintained for 4 weeks. The MPA EMIT assay proved reliable and reproducible, as shown by the intra-assay and interassay coefficients of variation (1.58-3.68% and 1.23-7.57%, respectively). Excellent linear correlation ( r = 0.999) was observed for dilution linearity. The sensitivity of the assay was 0.01 microg/mL. Recoveries of 99.4% to 104.2% were obtained by spiking aliquots of three controls of known MPA concentrations with MPA. No interference was observed for endogenous substances and coadministered immunosuppressant drugs, and no cross-reactivity from the major metabolite MPA glucuronide was found. The high-performance liquid chromatography (HPLC) assay used protein precipitation and C18 ion-pair chromatography with ultraviolet detection at 304 nm. Plasma concentrations of MPA were measured using EMIT and HPLC. A linear relationship was observed between EMIT and HPLC (EMIT = 1.091 x HPLC - 0.089; r 2 = 0.990, n = 129). These results indicate that EMIT is a simple, rapid, and sensitive assay method for the measurement of MPA in plasma.

Determination of mycophenolic acid and its phenol glucuronide metabolite in human plasma and urine by high-performance liquid chromatography

Simultaneous determination of mycophenolic acid (MPA) and mycophenolate phenol glucuronide (MPAG) in plasma and urine was accomplished by isocratic HPLC with UV detection. Plasma was simply deproteinated with acetonitrile and concentrated, whereas urine was diluted prior to analysis. Linearity was observed from 0.2 to 50 microg/ml for both MPA and MPAG in plasma and from 1 to 50 microg/ml of MPA and 5 to 2000 microg/ml MPAG in urine with extraction recovery from plasma greater than 70%. Detection limits using 0.25 ml plasma were 0.080 and 0.20 microg/ml for MPA and MPAG, respectively. The method is more rapid and simple than previous assays for MPA and MPAG in biological fluids from patients.

Implications of selective type II IMP dehydrogenase (IMPDH) inhibition by the 6-ethoxycarbonyl-3,3-disubstituted-1,5-diazabicyclo[3.1.0]hexane-2,4-diones on tumor cell death

It was shown previously that three 1,5-diazabicyclo[3.1.0]hexane-2,4-diones selectively inhibited human Type II IMP dehydrogenase (IMPDH) from Tmolt4 cell leukemia [Barnes et al., Biochemistry 2000;39:13641-50]. The agents acted as competitive inhibitors of this isoform, yet when tested against human Type I at concentrations ranging from 0.5 to 500 microM, Type I was not inhibited. This study focuses on the antineoplastic activity and cellular effects of one of these agents and two new derivatives containing ethoxycarbonyl substitution at position C6. Agents were studied for antiproliferative activity in human Tmolt4 leukemia (EC(50) 3.3 to 9.2 microM) and alterations in the levels of enzymes involved with cellular metabolism, including DNA and RNA syntheses due to IMPDH inhibition. Results reported here demonstrate that 6-ethoxycarbonyl-3,3-disubstituted-1,5-diazabicyclo[3.1.0]hexane-2,4-diones are effective inhibitors of DNA synthesis (30-66% inhibition) due to reductions in dGTP pool levels. Collectively, the three agents proved to be selective inhibitors of human IMPDH Type II activity (K(i) 11-33 microM), leading to cytotoxicity in a number of suspended and solid tumor lines, notably MCF-7 (EC(50) 0.7 to 6.0 microM). In addition, negative cytotoxic actions of these agents on WI-38 cell growth, a normal rapidly growing human line, suggest that specific targeting of Type II IMPDH would help to eliminate cell killing in lines where Type I predominates. Furthermore, effects of agents on DNA synthesis and cell death could be reversed by the addition of exogenous guanosine to the medium. Results from in vitro studies suggest that the 6-ethoxycarbonyl-3,3-disubstituted-1,5-diazabicyclo[3.1.0]hexane-2,4-diones may be used as effective isozyme-selective chemotherapeutic agents.

Replacement of calcineurin inhibitors with mycophenolate mofetil in liver-transplant patients with renal dysfunction: a randomised controlled study

BACKGROUND

Renal dysfunction is a major complication of long-term immunosuppressive therapy with calcineurin inhibitors (CNI) in liver-transplant recipients. We undertook a randomised study to assess the safety and efficacy of CNI withdrawal and replacement by mycophenolate mofetil.

METHODS

28 people who had had renal dysfunction attributable to suspected CNI toxicity after liver transplantation participated in the study. We replaced CNI with mycophenolate mofetil in a stepwise pattern in half the group (study patients); the other half (controls) stayed on CNI immunosuppression. Renal function, blood pressure, uric acid, and blood lipids were measured before and 6 months after study entry. Side-effects of medication and graft function were recorded throughout the study.

FINDINGS

At the end of the study, mean (SD) serum creatinine had fallen by 44.4 (48.7) micromol/L in study patients compared with 3.1 (14.3) micromol/L in controls; a mean difference of 41.3 micromol/L (95% CI 12.4-70.2). Moreover, systolic and diastolic blood pressure, and serum uric acid decreased significantly in the study group but not in the control group (mean [95% CI] between group differences 10.8 mm Hg [3.0-18.6], 5.0 mm Hg [0.9-9.2], and 83.1 micromol/L [12.7-153.6], respectively). There were no changes in cholesterol or triglyceride concentrations in either group. Side-effects were reported by eight of the study patients. Three reversible episodes of acute graft rejection occurred in study patients during mycophenolate mofetil monotherapy, whereas none occurred in the control group.

INTERPRETATION

Substitution of CNI by mycophenolate mofetil can improve renal function, blood pressure, and uric acid concentration of liver-transplant patients, but there is an increased rejection risk with mycophenolate mofetil monotherapy.