Comparison of the in vitro and biophysical effects of cyclosporine A, FK-506, and mycophenolic acid on human peripheral blood lymphocytes

In Vitro Influence of Mycophenolic Acid on Selected Parameters of Stimulated Peripheral Canine Lymphocytes

Mycophenolic acid (MPA) is an active metabolite of mycophenolate mofetil, a new immunosuppressive drug effective in the treatment of canine autoimmune diseases. The impact of MPA on immunity is ambiguous and its influence on the canine immune system is unknown. The aim of the study was to determine markers of changes in stimulated peripheral canine lymphocytes after treatment with MPA in vitro. Twenty nine healthy dogs were studied. Phenotypic and functional analysis of lymphocytes was performed on peripheral blood mononuclear cells cultured with mitogens and different MPA concentrations– 1 μM (10⁻³ mol/m³), 10 μM or 100 μM. Apoptotic cells were detected by Annexin V and 7-aminoactinomycin D (7-AAD). The expression of antigens (CD3, CD4, CD8, CD21, CD25, forkhead box P3 [FoxP3] and proliferating cell nuclear antigen [PCNA]) was assessed with monoclonal antibodies. The proliferation indices were analyzed in carboxyfluorescein diacetate succinimidyl ester (CFSE)-labeled cells. All analyses were performed using flow cytometry. The influence of MPA on apoptosis was dependent on the mechanism of cell activation and MPA concentration. MPA caused a decrease in the expression of lymphocyte surface antigens, CD3, CD8 and CD25. Its impact on the expression of CD4 and CD21 was negligible. Its negative influence on the expression of FoxP3 was dependent on cell stimulation. MPA inhibited lymphocyte proliferation. In conclusion, MPA inhibited the activity of stimulated canine lymphocytes by blocking lymphocyte activation and proliferation. The influence of MPA on the development of immune tolerance–expansion of Treg cells and lymphocyte apoptosis–was ambiguous and was dependent on the mechanism of cellular activation. The concentration that MPA reaches in the blood may lead to inhibition of the functions of the canine immune system. The applied panel of markers can be used for evaluation of the effects of immunosuppressive compounds in the dog.

Mycophenolate mofetil (Cellcept)

Mycophenolate mofetil (MMF) is a new immunosuppressive drug designed to inhibit inosine monophosphate dehydrogenase (IMPDH). IMPDH is a key enzyme in the purine synthesis pathway of lymphocytes. IMPDH is crucially important for the proliferative responses of human T- and B-lymphocytes. Therefore, inhibition of IMPDH leads to selective lymphocyte suppression. Following successful testing in different in vitro and animal models, MMF entered clinical trials, where it has been used in combination with cyclosporin and steroids. MMF has rapid and complete absorption following oral administration. Pilot studies suggested a significant reduction in the incidence of rejection at doses of 1-3 g/day. These data led to the initiation of 3 pivotal trials, in which MMF was compared against different standard immunosuppressive protocols. Nearly 1500 patients were enrolled in these 3 randomised, double-blind, multicentre studies of the addition of MMF to standard immunosuppressive protocols for the prevention of acute renal allograft rejection. After six months, the rate of biopsy-proven rejection was significantly reduced. The adverse event profile resembles that of triple therapy with azathioprine: primarily involving the gastrointestinal (GI) tract, the haematopoietic system and the occurrence of opportunistic infections. MMF affords improved immunosuppressive therapy following renal, and probably other solid organ, transplantation. It is licensed for the prevention of acute renal allograft rejection in most countries around the world.

Mycophenolic Acid Interaction With Cyclosporine and Tacrolimus In Vitro and In Vivo

The effect of mycophenolic acid (MPA) in combination with either cyclosporine (CsA) or tacrolimus (TRL) on whole-blood lymphocyte function was assessed in vitro as well as in vivo. For the in vitro studies, rat whole blood was incubated with different concentrations of MPA together with CsA or TRL. In vivo, rats (n = 6 per group) were orally treated with 2.5 or 5 mg/kg of mycophenolate mofetil (MMF), either alone or in combination with 5 mg/kg CsA or 4 mg/kg TRL. Blood was obtained before and at different times after dosing. For both in vitro and in vivo studies, mitogen-stimulated whole blood was analyzed by flow cytometry to determine inhibition of expression of lymphocyte proliferation (proliferating cell nuclear antigen, PCNA) and T-cell activation (eg, CD25). Plasma MPA concentrations were measured by HPLC, and whole-blood CsA and TRL concentrations were quantified using LC-MS/MS. In vitro, low concentrations of 250 and 500 nM MPA acted additively with CsA and overadditively with TRL to suppress lymphocyte function, whereas higher MPA concentrations (1000 nM) in these combinations did not further increase inhibition compared with monotherapy with CsA or TRL alone. In vivo, the MPA AUC0-24 showed a dose-dependent increase. CsA and TRL AUC0-24 were not influenced by the MMF dose. Combination therapy increased inhibition of lymphocyte function compared with MMF monotherapy with a pronounced effect on PCNA compared with CD25. Significant differences between 2.5 and 5 mg/kg MMF in the combination groups were observed at 2 or 6 hours after dosing because of the maximal inhibitory effect on PCNA and CD25 expression (P < 0.05, ANOVA). However, in combination with TRL no different effects on the inhibition of CD25 expression were found between the 2 MMF doses. These novel data indicate that measurement of pharmacodynamic parameters of lymphocyte function in whole blood may help to monitor drug combination therapy and provide a rationale for drug reduction to minimize toxicity without compromising efficacy.

Assessment of immunosuppressive drug interactions: inhibition of lymphocyte function in peripheral human blood

Cyclosporin (CsA) or tacrolimus (TRL) is routinely combined with either sirolimus (SRL) or mycophenolate mofetil (MMF) in immunosuppressive regimes in organ transplantation. The aim of our study was to establish a specific human blood assay of lymphocyte function in order to assess interactions of these drug combinations. Different concentrations (10(6)-10(9) nM) of CsA, TRL, SRL or mycophenolic acid (MPA, the active metabolite of MMF) was added to whole blood of five human volunteers. Drug combinations were studied by adding 250, 500 or 1000 nM of MPA to different concentrations of CsA, TRL, or SRL or by adding 1, 10 or 25 nM of SRL to different concentrations of CsA or TRL. After concanavalin-A stimulation, whole blood cultures were analyzed by flow cytometry detecting lymphocyte proliferation and activation by bivariate expression of proliferating cell nuclear antigen (PCNA)/DNA content and T cell-surface activation antigens (e.g. CD25, CD95, and CD154). We found an order of potency inhibiting lymphocyte function with SRL>TRL>CsA>MPA. In addition, we observed enhanced inhibition of PCNA, CD25, CD95 or CD154, if either CsA or TRL was combined with low concentrations of MPA, or SRL alone or if SRL was combined with low concentrations of MPA. Data analysis revealed an independent functional synergism or partial agonism in most combinations. This human blood assay is able to assess lymphocyte function and to monitor immunosuppressive therapy. The assay also permits pharmacological analysis of drug interactions, which will lead to improved safety and therapeutic efficacy in transplanted patients.

Mycophenolate mofetil inhibits differentiation, maturation and allostimulatory function of human monocyte-derived dendritic cells

We have studied the effect of mycophenolate mofetil (MMF), a new drug used in prevention of transplant rejection, on differentiation, maturation and allostimulatory activity of human monocyte-derived dendritic cells (MDDC). MDDC were generated in vitro with granulocyte macrophage-colony stimulating factor (GM-CSF) and interleukin (IL)-4 in the presence or absence of MMF. MMF reduced the number of immature MDDC in culture, dose-dependently, by inducing apoptosis and inhibited their stimulatory activity on allogeneic lymphocytes. These changes correlated with down-regulation of co-stimulatory and adhesion molecules such as CD40, CD54, CD80 and CD86. No differences were observed in mannose receptor (MR)-mediated endocytosis, measured by the uptake of fluorescein isothiocyanate (FITC)-dextran. MDDC differentiated in the presence of MMF showed significantly reduced maturation upon stimulation with lipopolysaccharide, as judged by lower expresson of CD83 and co-stimulatory molecules, lower production of tumour necrosis factor (TNF)-alpha, IL-10, IL-12 and IL-18 as well as lower stimulation of alloreactive T cells including naive CD4+ CD45RA+ T cells. In contrast, MDDC matured in the presence of MMF showed a more marked decrease in the FITC-dextran uptake than mature MDDC cultivated without MMF and the phenomenon correlated with down-regulation of the MR expression. These results suggest that MMF impairs differentiation, maturation and function of human MDDC in vitro, which is an additional mechanism of its immunosuppressive effect.

Effect of mycophenolate mofetil therapy on lymphocyte activation in heart transplant recipients

BACKGROUND

Mycophenolic acid is reported to provide effective immunosuppression by inhibiting inosine monophosphate dehydrogenase. In an attempt to monitor the effects of therapy with mycophenolate mofetil, we measured the expression of the activation markers CD25, CD38, CD69 and HLA-DR on lymphocytes of patients after heart transplantation.

METHODS

Thirty-six patients enrolled in the study were randomly assigned to one of two groups. Patients in the control group (n = 15) received cyclosporine, azathioprine and prednisone. Patients in the study group (n = 21) were switched from azathioprine to mycophenolate mofetil (MMF) 3 months after heart transplantation. The expressions of the activation markers CD25, CD38, CD69 and HLA-DR on B cells, T cells and natural killer (NK) cells in peripheral blood were determined by flow cytometry.

RESULTS

In patients treated with MMF a significant reduction of the B-cell count was observed in comparison to a healthy control group and patients under therapy with azathioprine. The decline of B cells in the MMF group started 3 months after onset of therapy and, after 1 year, was nearly halved. In addition, the percentages of CD38-positive B cells, activated T cells (CD4(+)/CD25(+), CD8(+)/CD38(+)) and HLA-DR-expressing NK cells were reduced during therapy with MMF.

CONCLUSIONS

Our studies have shown administration of MMF to be associated with a reduction of B lymphocytes and a downregulation of activation markers on B cells. In contrast to in vitro findings, our data indicate that the immunosuppressive effect of MMF in vivo is exhibited mainly on B cells.

Novel assays of multiple lymphocyte functions in whole blood measure: new mechanisms of action of mycophenolate mofetil in vivo

The antiproliferative effects of MMF are believed to be the mechanism of its immunosuppressive action. We further investigated the mechanisms of action by assessing the pharmacodynamics (PD) of MMF in treated animals using whole blood assays not only of lymphocyte proliferation but also of activation. In vitro, different MPA concentrations were added to rat whole blood. In vivo, Lewis rats were treated with single doses of 5, 10 or 20 mg/kg MMF (n = 6 rats/dose group). Blood was obtained before and at different times after drug administration. For both in vitro and in vivo studies, different mitogens with calcium-dependent (TCR) or -independent (co-stimulatory) pathways of lymphocyte activation were added to the blood for stimulation. Proliferation was measured by [3H]TdR incorporation and by flow cytometric detection of DNA content. Activation was measured by changes in T cell surface expression of CD25, CD134, CD71, CD11a and CD54. In vitro and in vivo studies showed a dose-dependent inhibition by MPA and MMF, respectively, of lymphocyte proliferation and surface antigen expression. We observed high correlations between MMF PD effects over time with both MMF dose and MPA plasma concentrations in vivo. We show that MMF, apart from its antiproliferative effect, induced a dose-dependent suppression of calcium-dependent and -independent stimulated expression of important lymphocyte cell surface antigens. These data suggest that the ex vivo assessment of immune function in whole blood can uncover new mechanisms of MMF action. Our results demonstrated that the measurement of the PD is a means to assess the functional effects of MMF after its administration in vivo.

Cyclosporin A induces the opening of a potassium-selective channel in higher plant mitochondria

The immunosuppressive drug, cyclosporin A (CsA), induces the generation of a transmembrane electrical potential difference (deltapsi) in deenergized plant mitochondria incubated in sucrose-based media. Build up of deltapsi is prevented by external monovalent cations in the order K+ > Rb+ = Li+ > Na+, or by the protonophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone, which also collapses the deltapsi generated by CsA. Entry of K+ into mitochondria can be monitored as swelling by incubating the organelles in a medium containing KCl to maintain constant osmolarity. This swelling is inhibited by ATP and stimulated by CsA or valinomycin. In addition, in mitochondria energized by succinate, KCl causes a dissipation of deltapsi, with sigmoidal kinetics, which is favored by CsA. Therefore, plant mitochondria appear to possess a K+ selective, voltage-dependent channel, which is opened by CsA, regulated by the redox state, and inhibited by nucleotides. The hypothetical roles of this new K+ATP channel are discussed in relation to its potential involvement in mitochondrial volume regulation, thermogenesis, apoptosis, and/or prevention of reactive oxygen species formation in plants.

Modulation of Multidrug Resistance in Cancer by Immunosuppresive Agents. Preclinical Studies

This is a brief summary of the status of known immunosuppressive drugs describing their potential and mode of action to reverse the function of the MDR1 gene product, the P glycoprotein. Different aspects of these immunosuppressors have been reviewed in the recent literature. This summary will focus only on those studies which relate to the effect of these drugs on the P-glycoprotein. In addition, studies which may explain the mode of action, but do not deal directly with P-glycoprotein, are also summarized.

Mycophenolate mofetil. A review of its pharmacodynamic and pharmacokinetic properties and clinical efficacy in renal transplantation

Mycophenolate mofetil is an ester prodrug of the active immunosuppressant mycophenolic acid. It is a noncompetitive, selective and reversible inhibitor of inosine monophosphate dehydrogenase, an important enzyme in the de novo synthesis of guanosine nucleotides in T and B lymphocytes. Mycophenolate mofetil and/or mycophenolic acid inhibit the proliferation of lymphocytes and the production of antibodies induced by a variety of mitogens and antigens. Mycophenolate mofetil is also active in several animal models of transplantation and has produced effects in animals that indicate that it may inhibit the chronic rejection process. Mycophenolate mofetil has been compared with azathioprine or placebo in 3 large, randomised, double-blind, multicentre trials as part of combination immunosuppression therapy with cyclosporin and corticosteroids. Compared with either placebo or azathioprine (1 to 2 mg/kg/day or 100 to 150 mg/day), mycophenolate mofetil 2 or 3 g/day was associated with a significantly lower proportion of patients experiencing acute rejection or treatment failure during the first 6 months after transplantation. Mycophenolate mofetil also tended to be associated with a lower proportion of patients who required a full course of antirejection therapy. However, the proportion of patients who died or who had graft loss was similar between all of the treatment groups. There are currently no data regarding the effects of mycophenolate mofetil on long term patient or graft survival, which are important clinical outcomes in assessing its place in the management of renal transplantation. Clinical trials are also needed to evaluate mycophenolate mofetil in specific patient populations (e.g. repeat renal transplant patients or highly sensitised patients), to determine its efficacy in alternative immunosuppressive protocols and to investigate its use in the transplantation of other solid organs. In summary, mycophenolate mofetil appears to be an attractive new agent in the prevention of graft rejection in renal transplant recipients that has shown superior efficacy to azathioprine. Although long term clinical outcome data are required, mycophenolate is a potentially important advance in transplant immunosuppression.

FK-506 and cyclosporine A (CsA) immunomodulation of the human gut mucosal immune system

FK-506 and cyclosporine A (CsA) are two immunosuppressive drugs used in the treatment of patients after liver and small intestine transplantation. A clinical advantage of FK-506 over CsA has been observed in these patients. Although the immunomodulation of both drugs has been well documented in the circulatory immune system, their effect on the mucosal immune system is not well established. In this study, the effect of FK-506 on the human gut mucosal immune system was compared to CsA. Proliferation of human colonic lamina propria lymphocytes (LPL) was measured by DNA synthesis and ornithine decarboxylase (ODC) activity. Results show that FK-506 and CsA suppress LPL DNA proliferation in a dose-dependent manner. FK-506 had a stronger antiproliferative effect compared to CsA. Moreover, the antiproliferative effect of both drugs was not dependent on monocytes or monocyte-associated factors (IL-1 beta, IL-6). In addition, exogenous addition of IL-2 did not restore the suppressive effect of either drug on LPL DNA synthesis. We conclude that: (1) both drugs have an antiproliferative effect on the human mucosal immune system; and (2) the stronger effect of FK-506 on human LPL compared to CsA may explain its superior clinical response observed in patients after liver/small intestine transplantation.

The interaction of immunosuppressive compounds in tandem stimulated peripheral human lymphocytes

We have developed an in vitro system to model the interactions of drugs used to treat transplant rejection. This system consists of stimulation of human lymphocytes with a primary mitogen (anti-T-cell receptor complex antibodies (OKT3 or wt31)) and treatment with a primary immunosuppressive drug (ISD) (Cyclosporine A (CsA) or FK-506)). This is later followed by stimulation with a secondary mitogen (Interleukin-2 or anti-CD28), and treatment with a second ISD. This system allows a variety of concentrations and compounds to be rapidly tested. We have used this system to study the effect of various compounds when used as either primary or secondary ISDs. Our results show that when CsA is used as the primary ISD, further proliferation can be inhibited by rapamycin, mycophenolic acid, or suramin. When FK-506 is the primary ISD, inhibition of proliferation by rapamycin is variable depending on the primary and secondary mitogens. If rapamycin is the primary ISD, both CsA and FK-506 show antagonistic interactions. These results suggest that the order in which combinations of ISDs are administered in transplantation may have significant effects on the clinical outcome.