RS-61443--a phase I clinical trial and pilot rescue study

Mycophenolic acid pharmacokinetics and related outcomes early after renal transplant

AIMS

The pharmacokinetics of mycophenolic acid and its glucuronide are complex. This study investigated the pharmacokinetics, pharmacodynamics and protein binding of mycophenolic acid and its glucuronide metabolite, early post-transplant in renal allograft recipients.

METHODS

Forty-two de novo renal transplant recipients receiving mycophenolate mofetil and concomitant cyclosporin (n = 32) or tacrolimus (n = 10) participated in the study. Blood samples were taken on day 5 post-transplant for measurement of free and total concentrations of mycophenolic acid, mycophenolic acid glucuronide and relevant biochemistry. Associations between free fraction and biochemistry were investigated. Free and total 6-h area under the concentration-time curve (AUC0-6) of mycophenolic acid was assessed relative to clinical outcomes in the first month post-transplant.

RESULTS

Kinetic variability of free and total mycophenolic acid and its glucuronide was greater in patients on cyclosporin (12- to 18-fold variation) than on tacrolimus (four- to fivefold) cotherapy. Cyclosporin-treated patients also had significantly lower predose total mycophenolic acid concentrations than tacrolimus-treated patients (median 0.8 mg l(-1) and 1.6 mg l(-1), respectively, P = 0.002). Mycophenolic acid glucuronide predose concentration correlated positively with mycophenolic acid glucuronide AUC0-6 (r > 0.95). Mycophenolic acid free fraction varied 11-fold, from 1.6% to 18.3%, whilst the glucuronide free fraction varied threefold, from 17.4% to 54.1%. Urea and creatinine concentrations correlated positively (r > 0.46), whilst albumin correlated negatively (r = -0.54) with free fraction of mycophenolic acid. Similar relationships were found for the free fraction of mycophenolic acid glucuronide. Mycophenolic acid free fraction was on average 70% higher in patients with albumin concentrations below a specified albumin cut-off concentration of 31 g l(-1)[free fraction = 7 +/- 4% for lower albumin and 4 +/- 3% for higher albumin, respectively; P = 0.001; 95% confidence interval (CI) for the difference 1.9, 4.2]. Neither free nor total mycophenolic acid AUC0-6 was related to rejection (P > 0.07). Free AUC0-6 was significantly higher in those patients with thrombocytopenic, leukopenic and/or infectious outcomes than in those without (mean +/- SD 1.9 +/- 0.3 mg h(-1) l(-1) and 1.1 +/- 0.1 mg h(-1) l(-1), P = 0.0043; 95% CI for the difference 0.3, 1.4).

CONCLUSIONS

The marked variability in mycophenolic acid/glucuronide pharmacokinetics occurring early post-transplant during the current study was greater in cyclosporin (12-18-fold) than in tacrolimus (four- to fivefold) treated patients. Concomitant cyclosporin was associated with total mycophenolic acid concentrations approximately half that of tacrolimus. Patients with marked renal impairment had the highest free fractions reported to date. The exposure to unbound mycophenolic acid was significantly related to infections and haematological toxicity.

Therapeutic Mycophenolic Acid Monitoring by Means of Limited Sampling Strategy in Orthotopic Heart Transplant Patients

Therapeutic drug monitoring (TDM) is essential to maintain the efficacy of many immunosuppressant drugs while minimizing their toxicity. TDM of mycophenolate mofetil requires area under the curve AUC determinations but appears laborious, costly, and clinically impractical. To overcome these problems, limited sampling strategies (LSS) have been proposed in adult and pediatric renal transplant patients. The purpose of this study was to develop an LSS in heart transplant patients. Forty-four mycophenolic acid (MPA) full AUC(0-12h) profiles were generated by high-performance liquid chromatography in nine heart transplant patients during the first 12 weeks posttransplant. Each patient received concomitant cyclosporine and prednisone therapy. Multiple stepwise regression analysis was used to define the time points of MPA levels to explain the MPA AUC(0-12h). Agreement between abbreviated AUC and the full AUC(0-12h) was tested by means of a Bland and Altman analysis. The highest coefficient of determination r(2) among MPA AUC and single concentrations (r(2) = .610) was observed with C(2), while C(12) provided the lowest one (r(2) = .003). Stepwise linear regression showed that the minimal model with the best estimation of MPA AUC(0-12h) was obtained at timed values of 1.25, 2, and 6 hours. The corresponding estimated model was AUC = 5.568 + 0.902 * C(1.25) + 2.022 * C(2) + 4.594 * C(6) (r(2) = .926). Bland and Altman analysis revealed good agreement between predicted AUC and full AUC. A further interesting model equation obtained by four samples was AUC = 3.800 + 1.015 * C(1.25) + 1.819 * C(2) + 1.566 * C(4) + 3.479 * C(6) (r(2) = .948).

Mycophenolate mofetil monotherapy in liver transplant recipients: a single center experience

The long-term use of calcineurin inhibitors (CIs) is associated with significant morbidity in liver transplant recipients. Although mycophenolate mofetil (MMF) is well tolerated, two small studies reported an unacceptable rate of acute allograft rejection in liver transplant recipients receiving MMF monotherapy. In this study, we retrospectively investigated the safety and efficacy of MMF monotherapy in liver transplant recipients. We reviewed the medical records of all patients who underwent liver transplant at our institution. Sixteen patients were identified who received MMF either as monotherapy (n = 13) or with corticosteroids (n = 3; 2 of them for other comorbid conditions), and these patients were studied to determine the efficacy and complications. Fifteen (15/16) patients were converted from a CI to MMF because of renal insufficiency. Patients were converted to MMF monotherapy after a median of 2,056 days (range, 606-5,893) after liver transplantation. The median postconversion follow-up was 668 days (range, 60-1,509). Four patients required dialysis despite conversion; of those patients not requiring dialysis, serum creatinine stabilized and showed a trend toward improvement (2.51 +/- 1.12 mg/dL to 1.85 +/- .58 mg/dL, P = .1). However, there were 3 episodes (47, 107, and 1,203 days after conversion) of severe, irreversible allograft rejection after conversion resulting in death in 2 patients and necessitating retransplantation in 1 patient. There were no patient characteristics, except perhaps African-American race, that predicted the development of rejection. In conclusion, MMF monotherapy was associated with a significant risk (19%) of unpredictable, severe, and irreversible allograft rejection even among long-term transplant survivors. Caution should be exercised before converting patients to MMF monotherapy.

The pharmacokinetics of mycophenolate mofetil in Thai kidney transplant recipients

Mycophenolate mofetil, in addition to cyclosporine and prednisolone significantly reduces the rate of acute rejection. The original recommended dose of MMF is fixed at 2 g/day. However, Thai patients cannot tolerate this dose due to gastrointestinal adverse effects. So the majority of patients are maintained on MMF at doses ranging from 0.5 to 2 g/day, according to their tolerability with an acceptable rate of acute rejection episodes. This study sought to determine the steady state pharmacokinetics of MMF in Thai kidney transplant recipients on stable doses of MMF. Forty-six kidney transplant patients more than 3 months on a stable MMF dose of 0.5, 1, 1.5, and 2 g/day together with cyclosporine and prednisolone underwent a single pharmacokinetic blood sampling for 12 hours following the morning dose of MMF. The analysis of plasma concentrations of mycophenolic acid (MPA), the sole pharmacologically active metabolite of MMF, was performed by using an high performance liquid chromatography method. Sparse efficient sampling strategies were employed to optimize the blood sampling schedule. Hence, blood samples were collected at 0, 0.5, 2, 12 hours after the MMF dose. The sampling time was designed to best estimate AUC(0-tau) at steady state. The initial MPA-Bayesian estimator were used for MPA concentrations that would allow the best estimation of Vc, CLt, and Ka. In this study, there is a high interindividual variability in the AUC. The median MPA AUC was 34.3 ug.h/mL (range 14.1-65.4). Thirty-one of 45 (68.9%) patients had a MPA AUC within 20 to 40 ug.h/mL, which is the most reasonable risk: benefit ratio in terms of preventing acute rejection episodes. Forty-one of 45 (91.1%) patients had MPA AUC within 20 to 60 ug.h/mL, which is the MPA therapeutic range. The highest Pearson correlation coefficient of determination between MPA AUC and a single concentration was observed with MPA 2 hours (r = 0.622) Without a fixed dosing regimen, most Thai kidney transplant recipients who receive MMF as part of a maintenance immunosuppressive regimen have the MPA AUC within the therapeutic window. The single drug concentration that correlates well with the AUC is MPA at 2 hours postdose.

Ex vivo lymphocyte proliferative function is severely inhibited in renal transplant patients on mycophenolate mofetil treatment

Mycophenolate mofetil (MMF) is a recently introduced immunosuppressive drug. Its active form is mycophenolic acid (MPA). MPA specifically inhibits de novo purine synthesis, which is vital for T and B lymphocyte proliferation. We measured lymphocyte subset numbers and mitogen induced proliferation in kidney transplant recipients on different combinations of MMF, cyclosporin A (C), azathioprine (A) and prednisolone (P) (C+A n=70; C+A+P n=15; C+MMF n=45; C+MMF+P n=37) and normals (n=73). Patients on MMF had severely reduced phytohaemagglutinin A (PHA) induced proliferation compared to normals (Nml 2766+/-926 CPM/1000 lymphocytes [mean+/-S.D.]; C+MMF 282+/-406; C+MMF+P 195+/-496); non-MMF patients did not differ from normal. Similar inhibition of Poke Weed Mitogen and Staphylococcal enterotoxin B induced proliferation was observed. Cell cycle studies established that MMF patients had a significantly higher proportion of lymphocytes in the G0/G1 phase following PHA stimulation than the non-MMF patients. All transplant groups had significantly lower B cell numbers than the normal controls but no differences in CD4 and CD8 T cell numbers. All but the C+MMF group had significantly lower CD16+NK cell numbers than normal, while only the non-MMF groups had significantly lower CD56+NK cell numbers. The proliferation assay used was an ex vivo diluted whole blood technique. Removal of residual MPA by washing the plasma out prior to mitogen stimulation led to a significant increase in proliferation in six out of seven cases. In summary we have found that MMF treatment has a strikingly inhibitory effect on patient ex vivo lymphocyte mitogenic function.

Mycophenolate mofetil in solid-organ transplantation

This review focuses on the use of mycophenolate mofetil (MMF) as an immunosuppressive agent in solid-organ transplantation. MMF, a non-competitive inhibitor of inosine monophosphate dehydrogenase, blocks de novo purine synthesis in T and B lymphocytes, resulting in the selective inhibition of proliferation of these cells in response to antigenic stimuli. MMF may also promote apoptosis of these cells. The immunosuppressive ability of MMF is thought to derive mainly from the inhibition of inosine monophosphate dehydrogenase. The other effects of MMF include suppression of antibody synthesis by B lymphocytes, inhibition of proliferation of smooth muscle cells in culture and impaired glycosylation of adhesion molecules. MMF may exhibit anti-inflammatory effects resulting from decreased activity of the inducible form of nitric oxide synthase, a consequence of depletion of tetrahydrobiopterin, which leads to decreased generation of peroxynitrite, a pro-inflammatory molecule. The pharmacokinetics, pharmacodynamics and principles underlying therapeutic drug monitoring of MMF are reviewed. The results of the pivotal clinical trials of MMF in kidney and heart transplantation are discussed and a summary of the major studies demonstrating a positive effect of MMF on renal transplantation outcomes is presented. The use of MMF in the context of ABO-incompatible renal transplantation, renal transplantation in highly sensitised and cross-match positive recipients, humoral rejection of renal allografts, chronic allograft nephropathy and steroid/calcineurin inhibitor minimisation in renal transplantation are also discussed.

A neutropenia suggesting an interaction between valacyclovir and mycophenolate mofetil

Mycophenolate mofetil (MMF) is a drug which decreases the frequency of renal transplantation rejection. However, cytomegalovirus infections are a common feature of this treatment leading the physicians to prescribe antiviral prophylactic drugs like valacyclovir. During this association, neutropenia occur and the cause of this adverse effect is difficult to define. This report presents a case of neutropenia in a woman treated with MMF and valacyclovir. As the duration of the valacyclovir treatment exactly corresponds to the neutropenia duration, and the mycophenolate trough levels increased with the neutrophil count, the responsibility of this neutropenia was ascribed to valacyclovir. However, an examination of the literature for cases of neutropenia led to the suspicion of an interaction between MMF and valacyclovir. Mycophenolate may increase intracellular concentrations of valacyclovir up to haematotoxic levels. This mechanism may explain the interaction and further research is needed to confirm this interaction.

Experimental and clinical rationale for use of MMF in nontransplant progressive nephropathies

The incidence of progressive nephropathies and, consequently, the population suffering from end-stage renal disease have increased steadily in recent years, posing an ever-growing cost, in both human and financial terms, to society. There is mounting evidence that, in both immune-mediated and nonimmune-mediated chronic nephropathies, renal inflammatory events are key to the propagation and perpetuation of renal injury. Mycophenolate mofetil (MMF) is an antilymphocyte agent recently introduced in clinical practice for the prevention of allograft rejection. The present review discusses clinical and experimental evidence that the anti-inflammatory action of MMF can be advantageously used to arrest immune- and nonimmune-mediated progressive injury of native kidneys as well.

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.

Daclizumab induction, tacrolimus, mycophenolate mofetil and steroids as an immunosuppression regimen for primary kidney transplant recipients

BACKGROUND

Recent reports have demonstrated the efficacy of interleukin-2-receptor blockers in lowering the incidence of early acute rejection in cyclosporine-treated kidney recipients when compared to patients not induced with an antibody product. The addition of daclizumab to a tacrolimus-mycophenolate mofetil-based immunosuppressive protocol was tested to evaluate whether there might be an additional reduction of the risk of rejection after renal transplantation.

METHODS

Since March 1998, we studied the effect of daclizumab in a nonrandomized, prospective study of 233 sequential recipients of first renal transplant. They were retrospective compared with a control group of 225 renal transplant recipients receiving a 10-day course of OKT3 induction, and tacrolimus, mycophenolate mofetil, and methylprednisolone maintenance. The study group received the same immunosuppressive regimen with the addition of daclizumab at 1 mg/kg for five doses over 10 weeks in the place of OKT3 therapy. There was at least 1HLA DR antigen compatibility match present between all donors and recipients. Patients were followed for 1 year after renal transplantation for the incidence of biopsy-proven acute rejection, patient and graft survival, and adverse events.

RESULTS

At 12 months, patient and graft survival for the daclizumab was 98 and 96 vs. 96 and 94% for the OKT3 group, respectively, and were not statistically different. Acute rejection rates (<6 months) were lower in the daclizumab group as compared with the OKT3 group, i.e., 5 (2.1%) vs. 16 (7.1%) (P=0.011) respectively. The incidence of infection requiring hospitalization appeared to be lower with daclizumab (7.3 vs. 16%, P<0.0036) with a similar trend with cyclomegalovirus infection, i.e., 1.6 vs. 4%, respectively (P=0.14).

CONCLUSIONS

The combination of daclizumab, tacrolimus, mycophenolate mofetil, and steroids is safe and effective for kidney transplant recipients in lowering the incidence of early acute rejection and without any increase in morbidity when compared to our previous protocol, which may have an eventual impact in long-term graft survival.

Mizoribine as an effective combined maintenance therapy with prednisolone in child-onset systemic lupus erythematosus

BACKGROUND

Systemic lupus erythematosus (SLE) is one of the major collagen diseases in childhood. However, the pathogenesis of this disease still remains unknown. The disease is known as a chronic inflammatory disease. Since oral and intravenous corticosteroid therapy has been introduced into the treatment of SLE, the prognosis of patients has improved significantly. However, it has now become clear that there are limitations in the effectiveness, as well as adverse reactions when corticosteroids therapy is administered for a long-term period. Therefore, we have been attempting to improve the maintenance therapy of child-onset SLE.

METHODS

We have proposed and tested a new type of combination therapy using prednisolone (PSL) and mizoribine (MZR) in pediatric patients with SLE for maintenance therapy after the induction of remission.

RESULTS

Our results showed that this combination therapy is more effective than the previous regimen. In addition, no significant side-effects were observed in our study.

CONCLUSION

This combination therapy is still not perfect. Efforts should be continued to establish an optimal therapy regimen for child-onset SLE.

Adverse gastrointestinal effects of mycophenolate mofetil: aetiology, incidence and management

Mycophenolate mofetil (MMF) is a relatively new immunosuppressive drug. It inhibits inosine monophosphate dehydrogenase, a key enzyme in the de novo pathway of purine synthesis, and thus causes lymphocyte-selective immunosuppression. Large clinical trials have revealed the efficacy of MMF in the prevention of allograft rejection when administered together with cyclosporin or tacrolimus and corticosteroids. Although the adverse effect profile of MMF is comparatively benign, gastrointestinal adverse effects are a major concern. These effects are partially explained by the increased immune suppression, by the mode of action and by interactions, particularly with other immunosuppressants. The aetiology of the rarest gastrointestinal adverse effects is still not completely clear. Therapy depends upon the clinical gravity of the adverse effects and is therefore a case of waiting and ob- serving. An adjustment of dosage of immunosuppressants according to the clinical situation and, particularly in the case of MMF, spreading the total dosage over more than 2 daily doses are often sufficient. Should adverse effects persist for a longer period of time and be of a more serious nature, a comprehensive invasive diagnostic process is necessary, including endoscopy and biopsy and the search for opportunistic infections. In this case, dosage reduction or the complete withdrawal of MMF seems to be unavoidable. Severe gastrointestinal complications with MMF are rare, but when they do occur they may require extensive diagnosis and treatment. In the future, therapeutic drug monitoring and, where necessary, pharmacological modifications of MMF could lead to a further reduction of adverse effects with an equal or even increased efficacy.

Mycophenolic acid levels in pediatric heart transplant recipients receiving mycophenolate mofetil

BACKGROUND

Mycophenolate mofetil (MMF) is an immunosuppressive agent that has shown promise in adult patients who have undergone heart transplantation. There have been a number of studies of the pharmacokinetics of MMF in adult solid organ transplant recipients, but there is very little information in the pediatric population. The purpose of this study was to review our experience with MMF dosing and the role of mycophenolic acid (MPA) levels for therapeutic drug monitoring in a population of pediatric heart transplant recipients.

METHODS

Data were obtained by review of the pediatric heart transplant database between November 1, 1997 and October 15, 1998. The data included all serum trough MPA levels, patient age, weight, height, indication for and dose of MMF, other medications, and details of all episodes of graft rejection.

RESULTS

Forty-four patients (27 males) had a total of 128 serum trough MPA levels. Median age at transplant was 2.7 years (7 days to 18.4 years), and at time of review was 6.3 years (29 days to 23.5 years). MMF treatment was used for induction in 18 patients, induction and rejection in 23 patients and graft vasculopathy in 3 patients. Dosing by body surface area (mg/m(2)), age and interval from transplantation were all independently associated with MPA level. There was a trend toward requiring higher doses to achieve desired levels (>3 ng/ml) in younger patients. The average dose to achieve desired levels was higher in the immediate post-transplant period. There was a trend that MPA levels for a given dose were higher in patients on concurrent tacrolimus therapy.

CONCLUSIONS

(1) There is marked individual variation in pharmacokinetics of MMF in pediatric patients; (2) dosing by body surface area may be advantageous; (3) higher MMF doses may be required at younger ages and in the early period after transplantation; (4) lower MMF doses may be required with concurrent tacrolimus therapy; and (5) serum trough MPA levels may relate to efficacy. Therefore, therapeutic drug monitoring of serum trough MPA levels may be required for individualized MMF dosing in pediatric cases.

Mycophenolate mofetil: suggested guidelines for use in kidney transplantation

Mycophenolate mofetil (MMF) is an immunosuppressive drug designed to inhibit inosine monophosphate dehydrogenase (IMPDH). IMPDH is a key enzyme in the de novo purine synthesis of lymphocytes. It is crucially important for proliferative responses of human T and B lymphocytes. The inhibition of IMPDH thus leads to selective lymphocyte suppression. After successful use in various in vitro and animal models, MMF was brought to clinical trial in patients undergoing transplantation. The drug is rapidly and completely absorbed following oral administration. Pilot studies of administration with cyclosporin and corticosteroids suggested a significant reduction in the incidence of organ rejection at dosages of 1 to 3 g/day. As a result of these studies, 3 pivotal randomised double-blind multicentre trials, involving nearly 1500 patients, were designed to investigate the effects of addition of MMF to different standard immunosuppressive protocols on the prevention of acute renal allograft rejection. After 6 months, the rates of biopsy-proven rejection were significantly reduced in patients receiving MMF. In combination with cyclosporin and corticosteroids, the adverse effect profile resembled that of azathioprine. Most adverse effects were associated with the gastrointestinal tract, the blood system and opportunistic infections. MMF offers improved immunosuppressive therapy following renal and probably other solid organ transplantation. MMF has been licensed since 1995 for the prevention of acute renal allograft rejection in most countries. It has been used in different combinations of immunosuppressive drugs and in various dosages and regimens.

Treatment of systemic lupus erythematosus with mycophenolate mofetil

Mycophenolate mofetil is an immunosuppressive drug that is of established efficacy in renal transplantation. It inhibits the de novo pathway of purine synthesis and therefore lymphocyte proliferation. Mycophenylate mofetil has been shown to ameliorate the severity of renal injury in murine models of lupus nephritis. Recent studies suggest that it may also be effective in the treatment of patients with lupus nephritis when used in conjunction with steroids. These observations need to be confirmed in adequately sized randomised-controlled studies.

Pharmacokinetics of mycophenolic acid after mycophenolate mofetil administration in liver transplant patients treated with tacrolimus

The pharmacokinetics of mycophenolic acid (MPA) was studied after oral administration of mycophenolate mofetil (MMF) in 8 liver transplant patients. The mean (+/- SD) maximum MPA plasma concentration of 10.6 (+/- 7.5) mg/ml was achieved within 0.5 to 5 hours. The mean (+/- SD) steady-state area under the plasma concentration versus time curve (AUC(0-12)) was 40 (+/- 30.9) mg/ml/h. The mean (+/- SD) half-life was 5.8 (+/- 3.8) hours. There was poor correlation between trough blood concentrations of tacrolimus (r = -0.004) or serum creatinine (r = 0.689) with MPA AUC, while the serum bilirubin concentrations correlated (r = 0.743) well with MPA AUC, suggesting impairment in MPA conjugation in patients with liver dysfunction. The mean (+/- SD) ratio of the AUC of mycophenolic acid glucuronide (MPAG) to MPA was 64 (+/- 84), which correlated significantly with serum creatinine (r = 0.72) but not with serum bilirubin concentrations (r = 0.309), indicating accumulation of MPAG in patients with renal dysfunction. In 7 primary liver transplant patients on the same dose of MMF, the trough plasma concentrations of MPA during the first week of therapy ranged from < 0.3 to 1.5 microg/ml. The MPA concentrations increased by several folds during the next few weeks, which correlates well with increases in serum albumin concentrations. Changes in albumin appear to partially contribute to the variations in the pharmacokinetics of MPA in liver transplant patients.

Current treatment practice in immunosuppression

New drugs have recently been added that may eventually replace the two-decade dominance of cyclosporin in solid organ transplantation. This cornerstone of immunosuppression was introduced by Borel [1] and Calne [2] in the mid-70s. In 1989, Starzl et al., after 2 years of preclinical experimentation, introduced tacrolimus (originally designated as FK506 by the Fujisawa Pharmaceutical Company of Japan) as a potent immunosuppressant for liver transplants [3]. Also, in recent years, a variety of novel purine and pyrimidine biosynthesis inhibitors have been tested for transplantation therapy. The leading agent which appears to be replacing the 35-year position occupied by azathioprine is the semi-synthetic morpholinoethyl ester of mycophenolic acid (MPA), mycophenolate mofetil (MMF), introduced by Allison [4] and Sollinger [5], and developed by the Syntex Corporation (now Roche Pharmaceuticals). Others, affecting different intra- or intercellular messages amplifying immunity, are in the pipeline.

Differentiation induction in non-lymphocytic leukemia cells upon treatment with mycophenolate mofetil

Inosine 5'-monophosphate (IMP) dehydrogenase catalyzes the rate-limiting reaction of guanine nucleotide biosynthesis and has been implicated in the reaction of cell growth and differentiation. We investigated the ability of mycophenolate mofetil, a prodrug of mycophenolic acid, to induce differentiation in HL-60 and U937 leukemic cells as well as in fresh leukemia cells from patients with non-lymphocytic leukemia. Treatment with mycophenolate mofetil reduced the intracellular guanosine 5'-triphosphate (GTP) levels and induced morphologic and functional differentiation in HL-60 and U937 cells dose-dependently. HL-60 and U937 cells developed macrophage-like cytoplasm as well as the expression of CD11b and CD14 antigens and the ability to oxidize nitroblue tetrazorium (NBT). These changes became evident when the intracellular GTP levels decreased to approximately 20-30% of the untreated control level and were abrogated by the addition of guanosine. In the fresh leukemic cells, differentiation induction was shown in the cells derived from seven of 13 patients. The fresh leukemia cells responding to mycophenolate mofetil revealed significant higher positivity to CD11b, CD14, and NBT before treatment and significantly reduced intracellular GTP levels after treatment compared to the non-responding cells. These findings suggest that mycophenolate mofetil induces differentiation in HL-60 and U937 cells and some fresh leukemia cells with moderate tendency to maturation, by causing a decrease in the intracellular GTP levels. Mycophenolate mofetil could be a promising differentiation inducer in vivo.

Mycophenolate mofetil reduces myofibroblast infiltration and collagen III deposition in rat remnant kidney

BACKGROUND

Myofibroblasts have been shown to play a pivotal role in the synthesis of extracellular matrix components in several animal models of renal fibrosis. The purpose of the present study was to investigate whether mycophenolate mofetil (MMF) reduces interstitial myofibroblast infiltration and collagen III deposition in 5/6 nephrectomized rats.

METHODS

Forty-five Wistar rats underwent 5/6 renal ablation and received by daily oral gavage either vehicle (N = 20) or MMF (N = 25) during the 60 days following surgery. Groups of five treated and five untreated rats were killed at two, four, and eight weeks after subtotal nephrectomy. Four untreated and three treated rats were killed at week 12, one month after treatment withdrawal. At the time of sacrifice, proteinuria, plasma, and urine creatinine were determined. Immunohistochemistry was performed on renal tissue for alpha-smooth muscle actin (alpha-SMA), a cytoskeletal marker of myofibroblasts, for type III collagen, and for proliferating cell nuclear antigen (PCNA). Moreover, in order to study the in vitro effects of MMF on fibroblast proliferation, rat fibroblasts were cultured in the presence or absence of mycophenolic acid (MPA).

RESULTS

At all periods studied, MMF treatment improved renal functional parameters and progressively decreased remnant kidney hypertrophy and glomerular volume increment. Proliferating cells in renal tubules, interstitium, and glomeruli, as well as interstitial myofibroblast infiltration and interstitial type III collagen deposition, were also significantly reduced by MMF treatment. In addition, MPA exhibited a dose-dependent inhibitory effect on in vitro proliferation of rat fibroblasts.

CONCLUSION

Reduction of interstitial myofibroblast infiltration may be an important event by which MMF significantly prevents renal injury following subtotal renal ablation. Thus, our results suggest that MMF could be useful to limit the progression of chronic renal disease toward end-stage renal failure.

The impact of routine mycophenolate mofetil drug monitoring on the treatment of cardiac allograft rejection

INTRODUCTION

Mycophenolate mofetil (MMF) is a unique immunosupressive agent that has been shown to be efficacious in the treatment of cardiac allograft rejection. The utility of therapeutic drug monitoring on rejection prophylaxis and treatment is inconclusive. This study was undertaken to evaluate the incidence of rejection in relation to MMF trough level following heart transplantation.

METHODS

Between May 1998 and February 1999, we retrospectively analyzed the clinical outcome of 215 heart transplant patients who had routine monitoring of MMF trough level at the time of scheduled endomyocardial biopsy. Patients were divided into three groups according to the time interval post transplant, and were evaluated in relation to the MMF trough level. Group I, 104 patients within 6 months of transplant; Group II, 90 patients, 6-12 months post transplant; and Group III, 71 patients beyond one year of transplant. Fifty patients had samples in more than one group. Rejection was defined as Grade > or = 3A based on ISHLT criteria. Mean follow-up period was 179+/-52 days.

RESULTS

A significantly decreased incidence of rejection was noted in the samples with MMF trough level > or = mg/l compared to those with less than 2 mg/l inpatients evaluated within the first year of transplant (Group I: 8.8% vs. 14.9%, Group II: 4.2% vs. 11.3%, both P=0.05). In the presence of therapeutic cyclosporine (CSA) or tacrolimus (FK) blood levels, the incidence of rejection decreased significantly when MMF trough level was > or = 2 mg/l compared to samples with MMF trough level <2 mg/l (3.6% vs. 14.4%, P=0.005). No significant difference was noted in the presence of subtherapeutic CSA or FK levels (15.4% vs. 13.9%, P=NS).

CONCLUSIONS

Monitoring of MMF trough levels may play a role in the management of cardiac transplant recipients during the first year post transplant.

Mycophenolate mofetil treatment reduces atherosclerosis in the cholesterol-fed rabbit

Immune/inflammatory responses of arterial vessel wall constituents to lipid metabolic disturbances have been postulated to contribute to the pathogenesis of atherosclerosis. Mycophenolate mofetil (MMF), an antiproliferative agent used in clinical transplantation, has been shown to inhibit smooth muscle cell (SMC) proliferation and decrease the recruitment of monocytes into sites of chronic inflammation. This study was conducted to determine the effect of MMF on atherosclerotic plaque development after cholesterol-induced injury. New Zealand white rabbits were fed a high-cholesterol diet containing 0.5% cholesterol and 8% peanut oil. The experimental group (n = 10) was given MMF (80 mg/kg/day subcutaneously); the control group (n = 10) received placebo injections. The aortas were harvested at 12 weeks for immunohistochemical analyses. SMCs were identified by reactivity with a monoclonal antibody (mAb) to alpha smooth muscle actin. Monocytes/macrophages were detected with mAb RAM 11. Cross-sectional areas of the media and neointima were measured using computer-assisted image analysis. The density of SMCs and macrophage/foam cells within the neointima was calculated by dividing the number of cells by the area of the plaque. Total cholesterol, triglyceride, high density lipoprotein, and low density lipoprotein were significantly increased compared with levels before the initiation of a high-cholesterol diet, but there were no significant differences between the MMF-treated and untreated groups. Neointimal area in aortic tissue sections of the MMF-treated group (0.586 +/- 0.602 mm(2)) was significantly lower when compared with that in control animals (1.082 +/- 0.621 mm(2)) (P < 0.05). The densities of neointimal SMCs and monocytes/macrophages in the control group were 778 +/- 293 and 341 +/- 90 cells/mm(2), respectively. MMF treatment significantly reduced the number of neointimal SMCs (506 +/- 185 cells/mm(2)) (P < 0.05). The number of monocytes/macrophages was also reduced after MMF treatment (260 +/- 124 cells/mm(2)) but not significantly. Our results demonstrate that the administration of MMF significantly reduced neointimal SMC accumulation and plaque development in a hypercholesterolemic model of atherosclerosis.

Levels of mycophenolic acid and its glucuronide derivative in the plasma of liver, small bowel and kidney transplant patients receiving tacrolimus and cellcept combination therapy

In order to help assess the usefulness of mycophenolate mofetil (MMF) as an immunosuppressive agent in recipients of organs other than kidneys, we measured the trough levels of the active metabolite of MMF, mycophenolic acid (MPA), and its inactive glucuronide derivative (MPAG), in the plasma of liver (n = 83) and small bowel transplant patients (n = 15) receiving MMF in combination with tacrolimus. These levels were compared with a group of renal transplant patients (n = 25) receiving the same drug regimen. All patient groups were otherwise comparable except the small bowel patient group which contained more pediatric patients (average age 18.7 +/- 3.9 years), and, therefore, received a higher average drug dose (in mg/kg). Despite this, these patients displayed the lowest levels of MPA of any group (0.39 +/- 0.08 microg/ml, P < 0.001 vs. 1.10 +/- 0.17 microg/ml for liver transplant patients, P < 0.001 or 2.46 +/- 0.37 microg/ml for renal transplant patients, P < 0.001). There were no statistically significant differences in MPAG levels between any of the groups. Although preliminary, these data demonstrate significant transplanted organ-specific differences in MMF pharmacology and/or bioavailability, and suggest the need for separate evaluation of MMF dosing for each transplant type.

The use of mycophenolate mofetil in transplant recipients

With the development of new immunosuppressive agents, the focus of anti-rejection therapy has shifted from prevention of acute allograft rejection to an emphasis on sufficient immunosuppression with minimal toxicity. Mycophenolate mofetil (MMF) is a recently developed immunosuppressive drug, which acts to inhibit T and B cell proliferation by blocking the production of guanosine nucleotides required for DNA synthesis. It also prevents the glycosylation of adhesion molecules that are involved in attachment of lymphocytes to endothelium and potentially in leukocyte infiltration of an allograft during an immune response. High-quality randomized clinical trials have demonstrated that MMF, when used with cyclosporine (CsA) and steroids, reduces the frequency and severity of acute rejection episodes in kidney and heart transplants, improves patient and graft survival in heart allograft recipients and increases renal allograft survival at 3 years. It has also been effective in reversing acute and resistant rejection episodes in heart, kidney and liver recipients. The ability of MMF to facilitate sparing of other immunosuppressive agents, particularly in CsA-related nephrotoxicity, is also promising. By permitting reduction in CsA doses, MMF may stabilize or improve renal graft function in patients with CsA-related nephrotoxicity or chronic allograft nephropathy. Early results of phase I and II trials evaluating MMF therapy in liver and combined pancreas/kidney transplant recipients are encouraging. The main adverse effects associated with oral or intravenous MMF are gastrointestinal and hematologic in nature. Although the direct costs of using MMF vs. azathioprine (AZA) are higher, the decreased incidence and treatment of acute rejection in patients treated with MMF supports its use as a cost-effective option during the first year following transplantation.Thus, MMF has become an important therapeutic tool in the transplant clinician's armamentarium. Ongoing issues to be resolved in clinical trials include the role of MMF in the absence of other potent agents, e.g., as monotherapy or with a steroid but without calcineurin inhibitor; whether MMF will have an impact on chronic allograft dysfunction; and the cost-effectiveness of treatment following the first year of transplantation.

Coadministration of tacrolimus and mycophenolate mofetil in stable kidney transplant patients: pharmacokinetics and tolerability

The tolerance and pharmacokinetics (PK) of tacrolimus (T) by the addition of mycophenolate mofetil (MMF) in stable kidney transplant patients (6/group) on long-term tacrolimus-based therapy were investigated. Patients received combination T and MMF therapy at three MMF doses: 1, 1.5, and 2 g/day administered twice daily. A 12-hour blood PK profile for T was obtained prior to MMF dosing; concomitant 12-hour profiles for T, mycophenolic acid (MPA), and mycophenolic acid glucuronide (MPAG) were obtained after 2 weeks of administration. Tolerance was monitored through 3 months. The intra- and intergroup PK of T were variable. The mean AUC0-12 of T for each group was increased after 2 weeks of concomitant MMF administration, but the increase was not statistically significant. Both drugs were well tolerated. Gastrointestinal events were of interest as such have been attributed to both T and MMF. Events reported were diarrhea, nausea, dyspepsia, and vomiting. Other common adverse events were headache, hypomagnesemia, and tremors. Most were mild, although a few were considered to be moderate. There was no apparent relationship between the incidence of any adverse event and MMF treatment group. In the present study, the coadministration of T and MMF did not significantly alter T pharmacokinetics.

Mycophenolate mofetil increases cytomegalovirus invasive organ disease in renal transplant patients

The impact of cytomegalovirus (CMV) infection post-transplantation is in part influenced by the degree of immunosuppression. While mycophenolate mofetil (MMF) does not increase the overall incidence of CMV infection, we have questioned whether or not it increases its severity. Using a case control study design in which 29 renal transplant patients developed CMV disease [17 (59%) of which received azathioprine (AZA) and 12 (41%) received MMF], increases in the frequency of organ involvement with CMV (58 vs. 18%; p = 0.03) and in the number of organs involved with CMV were noted in the MMF versus the AZA group (2.0 vs. 1.0; p = 0.015). These results indicate that the increased immunosuppressive activity of MMF impacts the morbidity of CMV infection, thus warranting the use of effective anti-CMV preventive regimens while patients are treated with MMF.

Pharmacokinetics of mycophenolate mofetil in patients with end-stage renal failure

BACKGROUND

Mycophenolate mofetil (MMF) acts as a prodrug for the immunosuppressive drug mycophenolic acid (MPA). It is rapidly converted to MPA following oral ingestion. MPA is metabolized to MPA glucuronide (MPAG), which is renally excreted. This study examines the pharmacokinetics of MPA and MPAG in patients with end-stage renal failure who were on hemodialysis (N = 10) or peritoneal dialysis (N = 10) treatment.

METHODS

After an overnight fast, a single oral dose of 1 g MMF was given. Plasma concentrations of MPA and MPAG were measured from 0 (predose) to 36 hours after administration, using high-performance liquid chromatography (HPLC). The area under the concentration time curve (AUC) from 0 to 36 hours was calculated using the trapezoidal rule.

RESULTS

Mean (+/- SD) AUC for MPA was 55.7 +/- 32.6 mg/L.h for hemodialysis patients and 44.7 +/- 14.7 mg/L.h for peritoneal dialysis patients, which is similar to expected values for subjects with normal renal function. The mean (+/- SD) maximum plasma concentration (Cmax) for MPA was lower than would be expected for subjects with normal renal function (16.01 +/- 10.61 mg/L for hemodialysis, 11.48 +/- 4.98 mg/L for peritoneal dialysis). MPAG clearance was prolonged with AUC approximately five times what would be expected in subjects with normal renal function (1565 +/- 596 mg/L.h for hemodialysis, 1386 +/- 410 mg/L.h for peritoneal dialysis). There was no significant difference for any of the pharmacokinetic parameters between subjects on hemodialysis and those on peritoneal dialysis. Plasma concentrations of MPA and MPAG did not fall significantly during hemodialysis. No MPA was detectable in hemodialysis or peritoneal dialysis fluid, but small amounts of MPAG were detected in hemodialysis fluid in 1 out of 10 subjects and in peritoneal dialysis fluid in 3 out of 10 subjects.

CONCLUSIONS

The accumulation of MPAG may be responsible for the poor gastrointestinal tolerance of this drug in dialysis patients and probably limits the maximum dose of MMF that can be tolerated.

Risk for posttransplant Diabetes mellitus with current immunosuppressive medications

With improvements in the practice of transplantation and the introduction of new immunosuppressive medications, there has been a substantial increase in 1-year allograft survival rates. Consequently, the pool of potential candidates for organ transplants continues to grow and a greater preponderance of older patients with more comorbidities are undergoing transplantation. As a result, there is interest in such medical complications as posttransplantation diabetes mellitus (PTDM) that develop after the transplantation of a successful allograft. PTDM is an undesirable consequence of transplantation because of its associated morbidity and impairment of both patient and graft survival. Although some controversy exists, it is likely that glucose intolerance after transplantation results in both macrovascular and microvascular disease, and there is an increasing risk for infectious and cardiovascular diseases, to which transplant recipients are already at increased susceptibility. Both experimental and clinical observations have shown that immunosuppressive agents currently used in transplantation account for a large degree of the increased risk for PTDM. Consequently, improved understanding of the effects of currently used immunosuppressive medicines on glycemic tolerance is of interest in clinical transplantation.

Newer immunosuppressive drugs: a review

In recent years, many new immunosuppressive drugs have been discovered and developed for clinical use in transplantation. This review focuses on those drugs (leflunomide, mycophenolate mofetil, sirolimus, tacrolimus) that have been shown to have immunosuppressive activity in patients. Different anti-interleukin-2 receptor antibodies are also reviewed as an example of a resurgence of development in the area of monoclonal antibodies. The price for reducing the incidence of allograft rejection by improved immunosuppression was thought to be a proportional increase in the incidence of infection and malignancy. Data from Phase III clinical trials of new immunosuppressants, however, show a statistically significant reduction in the incidence of acute rejection produced by these new drugs, which has not been accompanied by increases in infection and malignancy rates. The wide array of new drugs offers the opportunity to use combinations that block different pathways of immune activation while at the same time selecting drug combinations with nonoverlapping toxicity profiles so that doses of each single drug can be reduced below toxicity levels. The immunosuppressive therapy for patients can be tailored according to their individual needs.

Mycophenolate mofetil, microemulsion cyclosporine, and prednisone as primary immunosuppression for pediatric liver transplant recipients

Triple immunosuppressive therapy using mycophenolate mofetil (MMF), microemulsion cyclosporine (me-CsA), and prednisone offers the potential for potent immunosuppression without intravenous drug therapy or anti-T-cell antibody induction therapy. This report describes the application of an immunosuppressive protocol (CNp) using MMF, me-CsA, and prednisone as primary immunosuppression for pediatric liver transplant recipients at the University of California at San Francisco. From August 1995 through December 1996, 26 children (17 boys, 9 girls) aged 1 month to 16 years (mean +/- standard deviation, 58 +/- 62 months; median, 31 months) underwent liver transplantation at our institution, receiving CNp as primary immunosuppression. Posttransplantation renal function, incidence of leukopenia, and drug tolerance within the group receiving CNp as primary immunosuppression were compared with those of 19 children who received primary immunosuppression consisting of azathioprine, oil-based gel-encapsulated cyclosporine, and prednisone with anti-T-cell antibody induction therapy at the same institution from October 1993 through July 1995. No significant difference was observed between immunosuppressive protocols in serum creatinine level or incidence of leukopenia requiring medical therapy during the first year posttransplantation. Whereas gastrointestinal symptoms were observed in approximately 30% of CNp recipients during initial immunotherapy, tolerance of CNp primary immunotherapy was routinely achieved by the dose reduction of MMF. At 1 year posttransplantation, 20 children (77%) remained on CNp primary immunotherapy, 5 children (19%) were receiving tacrolimus-based immunotherapy secondary to rejection, and 1 patient (4%) converted to tacrolimus-based immunotherapy secondary to persistent gastrointestinal intolerance. In conclusion, CNp provides an alternative immunosuppressive protocol that eliminates the necessity of intravenous and induction immunosuppressive therapy with no increased incidence of posttransplantation renal dysfunction or leukopenia and is well tolerated in children.

Combination therapy with tacrolimus and mycophenolate mofetil following cardiac transplantation: importance of mycophenolic acid therapeutic drug monitoring

BACKGROUND

Interest has recently been expressed in tacrolimus and mycophenolate mofetil (MMF), two potent immunosuppressants, for a variety of transplant indications. The efficacy of this combination was assessed as primary therapy following cardiac transplantation.

METHODS

Forty-five patients were enrolled; 15 into Phase I and 30 to Phase II of the study. Intravenous tacrolimus was administered for 2-3 days to all patients prior to conversion to oral therapy; target blood concentrations were 10-15 ng/mL. Treatment also consisted of steroids and MMF. During Phase I, a fixed 2 g/day dose of MMF was given whilst doses were adjusted according to mycophenolic acid (MPA) plasma levels during Phase II (target range 2.5-4.5 microg/mL). Mean follow-up was 696 +/- 62 days and 436 +/- 88 days for Phases I and II, respectively.

RESULTS

Phase I: Patient survival was 100%. Rejection was diagnosed in 66.7% of patients (mean number of episodes per patient 1.33 +/- 1.18). Retrospective analyses indicated that whereas mean MPA plasma levels >3.0 microg/mL were not associated with rejection, no correlation was found with tacrolimus blood concentrations. Phase II: A survival rate of 96.7% was evident, one patient having died from aspergillosis. Diagnoses of rejection were made in 10.0% of patients (0.10 +/- 0.31 episodes per patient) and confounding factors were present in all 3 cases. MPA trough levels were 1.0 +/- 0.3 microg/mL at this time. Resolution was apparent following pulse steroid therapy. Steroids were successfully withdrawn from all patients who completed 6 months' treatment.

CONCLUSIONS

Combination therapy with tacrolimus and MMF is associated with suppression of acute myocardial rejection; however, this is dependent upon routine therapeutic drug monitoring.

Mycophenolate mofetil: therapeutic applications in kidney transplantation and immune-mediated renal disease

The immunosuppressant mycophenolate mofetil (MMF) inhibits the enzyme inosine-5' monophosphate dehydrogenase and thus interferes with cellular GTP synthesis. MMF suppresses the cellular and humoral immune response and has antiproliferative effects on vascular smooth muscle and mesangial cells in vitro and in vivo. In large multicenter trials with almost 1500 patients MMF has been proven highly efficacious for transplant rejection prophylaxis with the main side-effects of gastrointestinal disorders and a slightly increased incidence of viral infections. Recent investigations suggest MMF as an alternative immunosuppressant in cyclosporin A nephrotoxicity. Preliminary observations show promising results for MMF in the treatment of autoimmune-mediated renal disease. The rationale for its use in this patient group and evidence from experimental studies are discussed. As current therapy of this disease entity is still unsatisfactory, future clinical trials are necessary to investigate the efficacy and safety of MMF for this new indication.

Long-term composite tissue allograft survival in a porcine model with cyclosporine/mycophenolate mofetil therapy

BACKGROUND

Low-dose cyclosporine (CsA)/mycophenolate mofetil (MMF) therapy has significantly reduced the frequency of rejection and drug-induced side effects in rat hindlimb allograft recipients. With an eye toward direct clinical application, we developed a large-animal extremity composite tissue allograft model to assess the antirejection efficacy and systemic toxicity of combination CsA/MMF treatment.

METHODS

Radial forelimb osteomyocutaneous flap transplants were performed between size-matched, outbred pigs assigned to one of two groups: 5 control pigs received no immunosuppression, and 10 pigs received a once-daily oral CsA/MMF/prednisone regimen. Rejection was assessed by visual inspection of flap skin and correlated with serial histopathologic examination of skin biopsies.

RESULTS

In all control pigs, the flap was completely rejected on day 7. Of the 10 pigs receiving treatment, one died from pneumonia and an another from an anesthetic complication on days 19 and 30, respectively, without signs of rejection. Two flaps were lost on days 25 and 29 from severe rejection. Three pigs were free of rejection at the end of the 90-day follow-up period, and three had stable mild-to-moderate rejection at 90 days (P= 0.0007 vs. controls). White blood cell and platelet counts, serum creatinine values, and liver function tests remained normal in all animals receiving immunosuppressive therapy.

CONCLUSIONS

Our results, to our knowledge, demonstrate for the first time that rejection can be significantly delayed in a large-animal composite tissue allograft model including skin using only orally administered agents dosed according to clinically relevant strategies without significant drug-specific systemic side effects.

Inosine-5'-monophosphate dehydrogenase: regulation of expression and role in cellular proliferation and T lymphocyte activation

Guanine nucleotide synthesis is essential for the maintenance of normal cell growth and function, as well as for cellular transformation and immune responses. The expression of two genes encoding human inosine-5'-monophosphate dehyrogenase (IMPDH) type I and type II results in the translation of catalytically indistinguishable enzymes that control the rate-limiting step in the de novo synthesis of guanine nucleotides. Cellular IMPDH activity is increased more than 10-fold in activated peripheral blood T lymphocytes and is attributable to the increased expression of both the type I and type II enzymes. In contrast, abrogation of cellular IMPDH activity by selective inhibitors prevents T lymphocyte activation and establishes a requirement for elevated IMPDH activity in T lymphocytic responses. In order to assess the molecular mechanisms governing the expression of the IMPDH type I and type II genes in resting and activated peripheral blood T lymphocytes, we have cloned the human IMPDH type I and type II genes and characterized their genomic organization and their respective 5'-flanking regions. Both genes contain 14 highly conserved exons that vary in size from 49 to 207 base pairs. However, the intron structures are completely divergent, resulting in disparities in gene length (18 kilobases for type I and 5.8 kilobases for type II). In addition, the 5'-regulatory sequences are highly divergent; expression of the IMPDH type I gene is controlled by three distinct promoters in a tissue specific manner while the type II gene is regulated by a single promoter and closely flanked in the 5' region by a gene of unknown function. The conservation of the IMPDH type I and type II coding sequence in the presence of highly divergent 5'-regulatory sequences points to a multifactorial control of enzyme expression and suggests that tissue-specific and/or developmentally specific regulation of expression may be important. Delineation of these regulatory mechanisms will aid in the elucidation of the signaling events that ultimately lead to the synthesis of guanine nucleotides required for cellular entry into S phase and the initiation of DNA replication.

Prolonged depletion of guanosine triphosphate induces death of insulin-secreting cells by apoptosis

Inhibitors of IMP dehydrogenase, such as mycophenolic acid (MPA) and mizoribine, which deplete cellular GTP, are used clinically as immunosuppressive drugs. The prolonged effect of such agents on insulin-secreting beta-cells (HIT-T15 and INS-1) was investigated. Both MPA and mizoribine inhibited mitogenesis, as reflected by [3H]thymidine incorporation. Cell number, DNA and protein contents, and cell (metabolic) viability were decreased by about 30%, 60%, and 80% after treatment of HIT cells with clinically relevant concentrations (e.g. 1 microg/ml) of MPA for 1, 2, and 4 days, respectively. Mizoribine (48 h) similarly induced the death of HIT cells. INS-1 cells also were damaged by prolonged MPA treatment. MPA-treated HIT cells displayed a strong and localized staining with a DNA-binding dye (propidium iodide), suggesting condensation and fragmentation of DNA, which were confirmed by detection of DNA laddering in multiples of about 180 bp. DNA fragmentation was observed after 24-h MPA treatment and was dose dependent (29%, 49%, and 70% of cells were affected after 48-h exposure to 1, 3, and 10 microg/ml MPA, respectively). Examination of MPA-treated cells by electron microscopy revealed typical signs of apoptosis: condensed and marginated chromatin, apoptotic bodies, cytosolic vacuolization, and loss of microvilli. MPA-induced cell death was almost totally prevented by supplementation with guanosine, but not with adenosine or deoxyguanosine, indicating a specific effect of GTP depletion. An inhibitor of protein isoprenylation (lovastatin, 10-100 microM for 2-3 days) induced cell death and DNA degradation similar to those induced by sustained GTP depletion, suggesting a mediatory role of posttranslationally modified GTP-binding proteins. Indeed, impeding the function of G proteins of the Rho family (via glucosylation using Clostridium difficile toxin B), although not itself inducing apoptosis, potentiated cell death induced by MPA or lovastatin. These findings indicate that prolonged depletion of GTP induces beta-cell death compatible with apoptosis; this probably involves a direct impairment of GTP-dependent RNA-primed DNA synthesis, but also appears to be modulated by small GTP-binding proteins. Treatment of intact adult rat islets (the beta-cells of which replicate slowly) induced a modest, but definite, death by apoptosis over 1- to 3-day periods. Thus, more prolonged use of the new generation of immunosuppressive agents exemplified by MPA might have deleterious effects on the survival of islet or pancreas grafts.

Anesthesia for Renal Transplantation

Renal transplantation is the preferred mode of replace ment therapy for most patients with end-stage renal disease (ESRD) and accounts for nearly 60% of all organ transplants in the United States. While as many as 35,000 people remain on the list waiting to receive a cadaveric kidney, living-related renal transplantation offers a shorter waiting period and greater survival. Maximization of the health of the kidney recipient before transplantation can improve ultimate outcome. Proper anesthetic management is facilitated by under standing the physiology and pharmacology of ESRD. Maintaining intraoperative blood volume is a key to good graft function, especially the living-related pediat ric kidney recipient. Recent improvements in combined immnosuppression therapy have improved the overall outcome in transplant recipients. The average 3-year survival is nearly 75%.

Transplantation of vascularized allogeneic skeletal muscle for scalp reconstruction in a renal transplant patient

BACKGROUND

We report the case of a vascularized allogeneic skeletal muscle transplant (VASM) and autologous skin grafting as rescue therapy for refractory squamous cell carcinoma of the scalp.

METHODS

A renal transplant recipient with recurrent squamous carcinoma of the scalp underwent an excision that resulted in a 11 x 14 cm2 scalp defect with exposed cranium. At the time of multiorgan procurement, a section of rectus abdominis and external oblique muscle and fascia with its independent vascular bundle was isolated and stored in cold University of Wisconsin solution. The patient received methylprednisolone and rabbit antithymocyte globulin intravenously during scalp preparation, before single-vessel anastomosis of the deep inferior epigastric vascular bundle from the donor muscle to the recipient neck vessels. An autologous split-thickness skin graft was secured to the surface of the allogeneic muscle.

RESULTS

Immunosuppression was maintained with prednisone and cyclosporine. Serial VASM biopsies were used to evaluate acute rejection. Perivascular lymphocytic infiltrates and rare focal myonecrosis were evident on biopsy at 2 weeks postoperatively, and mycophenolate mofetil was added. Subsequent VASM biopsies showed predominately interstitial and perivascular T-cell lymphocytic infiltrates interpreted as consistent with mild rejection, but the allograft appeared intact without clinical evidence of rejection. On postoperative week 18, the mycophenolate mofetil was discontinued. There has been no evidence of recurrence or metastasis. The patient remains ambulatory with a healed scalp 12 months after the VASM.

CONCLUSION

The success of this first allogeneic skeletal muscle transplant is encouraging and provides another reconstruction option for wounds in transplant patients on chronic immunosuppression.

Clinical pharmacokinetics of mycophenolate mofetil

The pharmacokinetics of the immunosuppressant mycophenolate mofetil have been investigated in healthy volunteers and mainly in recipients of renal allografts. Following oral administration, mycophenolate mofetil was rapidly and completely absorbed, and underwent extensive presystemic de-esterification. Systemic plasma clearance of intravenous mycophenolate mofetil was around 10 L/min in healthy individuals, and plasma mycophenolate mofetil concentrations fell below the quantitation limit (0.4 mg/L) within 10 minutes of the cessation of infusion. Similar plasma mycophenolate mofetil concentrations were seen after intravenous administration in patients with severe renal or hepatic impairment, implying that the de-esterification process had not been substantially affected. Mycophenolic acid, the active immunosuppressant species, is glucuronidated to a stable phenolic glucuronide (MPAG) which is not pharmacologically active. Over 90% of the administered dose is eventually excreted in the urine, mostly as MPAG. The magnitude of the MPAG renal clearance indicates that active tubular secretion of MPAG must occur. At clinically relevant concentrations, mycophenolic acid and MPAG are about 97% and 82% bound to albumin, respectively. MPAG at high (but clinically realisable) concentrations reduced the plasma binding of mycophenolic acid. The mean maximum plasma mycophenolic acid concentration (Cmax) after a mycophenolate mofetil 1 g dose in healthy individuals was around 25 mg/L, occurred at 0.8 hours postdose, decayed with a mean apparent half-life (t1/2) of around 16 hours, and generated a mean total area under the plasma concentration-time curve (AUC infinity) of around 64 mg.h/L. Intra- and interindividual coefficients of variation for the AUC infinity of the drug were estimated to be 25% and 10%, respectively. Intravenous and oral administration of mycophenolate mofetil showed statistically equivalent MPA AUC infinity values in healthy individuals. Compared with mycophenolic acid, MPAG showed a roughly similar Cmax about 1 hour after mycophenolic acid Cmax, with a similar t1/2 and an AUC infinity about 5-fold larger than that for mycophenolic acid. Secondary mycophenolic acid peaks represent a significant enterohepatic cycling process. Since MPAG was the sole material excreted in bile, entrohepatic cycling must involve colonic bacterial deconjugation of MPAG. An oral cholestyramine interaction study showed that the mean contribution of entrohepatic cycling to the AUC infinity of mycophenolic acid was around 40% with a range of 10 to 60%. The pharmacokinetics of patients with renal transplants (after 3 months or more) compared with those of healthy individuals were similar after oral mycophenolate mofetil. Immediately post-transplant, the mean Cmax and AUC infinity of mycophenolic acid were 30 to 50% of those in the 3-month post-transplant patients. These parameters rose slowly over the 3-month interval. Slow metabolic changes, rather than poor absorption, seem responsible for this nonstationarity, since intravenous and oral administration of mycophenolate mofetil in the immediate post-transplant period generated comparable MPA AUC infinity values. Renal impairment had no major effect on the pharmacokinetic of mycophenolic acid after single doses of mycophenolate mofetil, but there was a progressive decrease in MPAG clearance as glomerular filtration rate (GFR) declined. Compared to individuals with a normal GFR, patients with severe renal impairment (GFR 1.5 L/h/1.73m2) showed 3-to 6-fold higher MPAG AUC values. In rental transplant recipients during acute renal impairment in the early post-transplant period, the plasma MPA concentrations were comparable to those in patients without renal failure, whereas plasma MPAG concentrations were 2- to 3-fold higher. Haemodialysis had no major effect on plasma mycophenolic acid or MPAG. Dosage adjustments appear to not be necessary either in renal impairment or during dialysis. (ABSTRACT TRUN

Myoblast transplantation in non-dystrophic dog

Dog myoblasts obtained from muscle biopsies were infected in vitro with a defective retroviral vector containing a cytoplasmic beta-galactosidase (beta-Gal) gene. These myoblasts were initially transplanted in the irradiated muscles of SCID mice and beta-Gal positive muscle fibers were observed. beta-Gal myoblasts were also transplanted back either in the donor dogs (autotransplantation model) or in unrelated recipient dogs (allotransplantation model). Following these myoblast injections, a rapid inflammatory reaction developed within the muscle as indicated by an expression of P-selectin and of pro-inflammatory cytokine mRNAs (interleukin 6 (IL-6) and transforming growth factor beta (TGF-beta), and by a neutrophil infiltration. Following either auto- or allotransplantation in inadequately or non-immunosuppressed dogs, a specific immune reaction also developed within 2 weeks as indicated by the infiltration of CD4+ and of CD8+ lymphocytes, the increased expression of IL-10 and granzyme B mRNAs and the presence of antibodies reacting with the injected cells. Some dogs were immunosuppressed with several combinations of FK506, cyclosporine (CsA) and RS-61443. In dogs immunosuppressed with CsA combined with RS-61443, only a few myoblasts and myotubes expressing beta-Gal were observed 1-2 weeks after the transplantation, but no muscle fibers expressing beta-Gal were observed after 4 weeks, and antibodies against the injected cells were formed. In dogs immunosuppressed with FK506 alone, although no antibodies against the injected cells were produced, there were no small cells and no muscle fibers expressing beta-Gal 1 month after the transplantation. However, FK506 triggered diarrhea and vomiting in dogs. When the dogs were immunosuppressed with FK506 combined with CsA and RS-61443, muscle fibers expressing beta-Gal were present 4 weeks after the transplantation and no antibodies reacting with donor myoblasts were detected. These results indicate that the combination of three immunosuppressive agents (i.e., FK506, CsA and RS-61443) is effective in controlling the specific immune reactions following myoblast transplantation in dogs and they underline that the outcome of myoblast transplantation is dependent in part on an adequate immunosuppression. These results obtained here in normal dogs may justify myoblast transplantation in dystrophic dogs despite the side effects of FK506.

A placebo controlled study of mycophenolate mofetil used in combination with cyclosporine and corticosteroids for the prevention of acute rejection in renal allograft recipients: 1-year results. The European Mycophenolate Mofetil Cooperative Study Group

PURPOSE

We performed a randomized, double-blind, multicenter, placebo controlled study to compare the efficacy and safety of 2 oral doses of mycophenolate mofetil with placebo for prevention of acute rejection episodes following first or second cadaveric renal allograft transplantation.

MATERIALS AND METHODS

A total of 491 patients were enrolled in the study and randomly allocated to receive placebo (166), 1 gm. mycophenolate mofetil twice daily (165) or 1.5 gm. mycophenolate mofetil twice daily (160). Patients were given concomitant immunosuppression with cyclosporine and corticosteroids. Treatment with mycophenolate mofetil was initiated within 72 hours of transplantation and was continued for at least 1 year.

RESULTS

The percentages of patients who experienced biopsy proved rejection or withdrew early from the trial for any reason were significantly reduced with 2 gm. (30.3%) and 3 gm. (38.8%) mycophenolate mofetil compared to placebo (56.0%) (p < 0.001). The biopsy proved rejection rates of the placebo, and 2 gm. and 3 gm. mycophenolate mofetil treatment arms were 46.4, 17.6 and 13.8%, respectively. There were fewer patients in the 2 gm. (28.5%) and 3 gm. (24.4%) mycophenolate mofetil groups compared to the placebo (51.8%) group, who received full courses of corticosteroids or antilymphocyte agents for treatment of rejection episodes in the first 6 months after renal transplantation. There was a greater incidence of gastrointestinal adverse events, leukopenia and opportunistic events in the mycophenolate mofetil treatment groups.

CONCLUSIONS

Mycophenolate mofetil was shown to reduce significantly the number of patients who experienced biopsy proved rejection episodes or treatment failure during the first year after renal transplantation, and was well tolerated.