Determination of the effects of mycophenolic acid on the nucleotide pool of human peripheral blood mononuclear cells in vitro by high-performance liquid chromatography

Pharmacodynamic assessment of mycophenolic acid in resting and activated target cell population during the first year after renal transplantation

Aims

To explore the pharmacodynamics of mycophenolic acid (MPA) through inosine monophosphate dehydrogenase (IMPDH) capacity measurement and purine levels in peripheral blood mononuclear cells (PBMC) longitudinally during the first year after renal transplantation (TX).

Methods

PBMC were isolated from renal recipients 0–4 days prior to and 6–9 days, 5–7 weeks and 1 year after TX (before and 1.5 hours after dose). IMPDH capacity and purine (guanine and adenine) levels were measured in stimulated and nonstimulated PBMC.

Results

Twenty‐nine patients completed the follow‐up period, of whom 24 received MPA. In stimulated PBMC, the IMPDH capacity (pmol 10⁻⁶ cells min⁻¹) was median (interquartile range) 127 (95.8–147) before TX and thereafter 44.9 (19.2–93.2) predose and 12.1 (4.64–23.6) 1.5 hours postdose across study days after TX. The corresponding IMPDH capacity in nonstimulated PBMC was 5.71 (3.79–6.93), 3.35 (2.31–5.62) and 2.71 (1.38–4.08), respectively. Predose IMPDH capacity in nonstimulated PBMC increased with time, reaching pre‐TX values at 1 year. In stimulated PBMC, both purines were reduced before (median 39% reduction across days after TX) and after (69% reduction) dose compared to before TX. No alteration in the purine levels was observed in nonstimulated PBMC. Patients needing dose reductions during the first year had lower pre‐dose IMPDH capacity in nonstimulated PBMC (1.87 vs 3.00 pmol 10⁻⁶ cells min⁻¹, P = .049) at 6–9 days.

Conclusion

The inhibitory effect of MPA was stronger in stimulated PBMC. Nonstimulated PBMC became less sensitive to MPA during the first year after TX. Early IMPDH capacity appeared to be predictive of dose reductions.

The role of the Hint1 protein in the metabolism of phosphorothioate oligonucleotides drugs and prodrugs, and the release of H2S under cellular conditions

Phosphorothioate oligonucleotides (PS-oligos) containing sulfur atom attached in a nonbridging position to the phosphorus atom at one or more internucleotide bond(s) are often used in medicinal applications. Their hydrolysis in cellular media proceeds mainly from the 3'-end, resulting in the appearance of nucleoside 5'-O-phosphorothioates ((d)NMPS), whose further metabolism is poorly understood. We hypothesize that the enzyme responsible for (d)NMPS catabolism could be Hint1, an enzyme that belongs to the histidine triad (HIT) superfamily and is present in all organisms. We previously found that (d)NMPS were desulfurated in vitro to yield (d)NMP and H₂S in a Hint1-assisted reaction. Here, we demonstrate that AMPS/GMPS/dGMPS introduced into HeLa/A549 cells are intracellularly converted into AMP/GMP/dGMP and H₂S. The level of the released H₂S was relative to the concentration of the compounds used and the reaction time. Using RNAi technology, we have shown decreased levels of AMPS/GMPS desulfuration in HeLa/A549 cells with reduced Hint1 levels. Finally, after transfection of a short Rp-d(A_PSA_PSA) oligomer into HeLa cells, the release of H₂S was observed. These results suggest that the metabolic pathway of PS-oligos includes hydrolysis into (d)NMPS (by cellular nucleases) followed by Hint1-promoted conversion of the resulting (d)NMPS into (d)NMP accompanied by H₂S elimination. Our observations may be also important for possible medicinal applications of (d)NMPS because H₂S is a gasotransmitter involved in many physiological and pathological processes.

A sensitive method for the separation and quantification of low-level adenine nucleotides using porous graphitic carbon-based liquid chromatography and tandem mass spectrometry

A liquid chromatography coupled to heated electrospray ionization/tandem mass spectrometry (LC-HESI-MS/MS) method was developed for the simultaneous quantitative analysis of low nanomolar level adenine nucleotides AMP, ADP, ATP, cyclic AMP (cAMP), and the nucleoside adenosine. For analyte retention and separation, reverse phase chromatography using porous graphitic carbon (PGC) was employed as it provided full resolution. The erratic chromatographic behaviour characteristic of PGC, including deterioration of analyte resolution and increased peak tailing (leading to decreased sensitivity), was mitigated by incorporating acidic equilibration within runs using a quaternary gradient. Analyte resolution and chromatographic sensitivity were still lost after a period of column inactivity; hence a pre-conditioning protocol was implemented between batches to regenerate the column. These column regeneration measures also allowed elution of AMP, ADP and ATP in the sequence of mono- to tri- nucleotides, differing from conventional reverse phase elution where analytes elute with decreasing polarity. This nucleotide elution sequence has the advantage of overcoming potential mis-annotation and inaccurate quantification of smaller nucleotides caused by in-source fragmentation of ATP. The method was validated in granulosa cell conditioned media, with the LLOQs ranging between 10-50nM for most analytes. To verify the method using biological samples, nucleotide secretion was measured in granulosa cell conditioned media under various treatments known to alter their levels. Moreover, the method was applied to cumulus-oocyte complex cell lysates to examine its linearity in a complex matrix.

The Immunosuppressant Mycophenolic Acid Alters Nucleotide and Lipid Metabolism in an Intestinal Cell Model

The study objective was to elucidate the molecular mechanisms underlying the negative effects of mycophenolic acid (MPA) on human intestinal cells. Effects of MPA exposure and guanosine supplementation on nucleotide concentrations in LS180 cells were assessed using liquid chromatography-mass spectrometry. Proteomics analysis was carried out using stable isotope labeling by amino acids in cell culture combined with gel-based liquid chromatography-mass spectrometry and lipidome analysis using ¹H nuclear magnetic resonance spectroscopy. Despite supplementation, depletion of guanosine nucleotides (p < 0.001 at 24 and 72 h; 5, 100, and 250 μM MPA) and upregulation of uridine and cytidine nucleotides (p < 0.001 at 24 h; 5 μM MPA) occurred after exposure to MPA. MPA significantly altered 35 proteins mainly related to nucleotide-dependent processes and lipid metabolism. Cross-reference with previous studies of MPA-associated protein changes widely corroborated these results, but showed differences that may be model- and/or method-dependent. MPA exposure increased intracellular concentrations of fatty acids, cholesterol, and phosphatidylcholine (p < 0.01 at 72 h; 100 μM MPA) which corresponded to the changes in lipid-metabolizing proteins. MPA affected intracellular nucleotide levels, nucleotide-dependent processes, expression of structural proteins, fatty acid and lipid metabolism in LS180 cells. These changes may compromise intestinal membrane integrity and contribute to gastrointestinal toxicity.

Use of designed experiments for the improvement of pre-analytical workflow for the quantification of intracellular nucleotides in cultured cell lines

The present study is focused on the development of a pre-analytical strategy for the quantification of intracellular nucleotides from cultured cell lines. Different protocols, including cell recovery, nucleotide extraction and purification, were compared on a panel of nucleoside mono-, di- and triphosphates from four cell lines (adherent and suspension cells). The quantification of nucleotides was performed using a validated technique with on-line solid-phase extraction coupled with liquid chromatography-triple quadrupole tandem mass spectrometry (LC-MS/MS). Designed experiments were implemented to investigate, in a rigorous and limited-testing experimental approach, the influence of several operating parameters. Results showed that the technique used to harvest adherent cells drastically affected the amounts of intracellular nucleotides. Scraping cells was deleterious because of a major leakage (more than 70%) of intracellular nucleotides during scraping. Moreover, some other tested conditions should be avoided, such as using pure methanol as extraction solvent (decrease over 50% of intracellular nucleotides extracted from NCI-H292 cells) or adding a purification step with chloroform. Designed experiments allowed identifying an interaction between the percentage of methanol and the presence of chloroform. The mixture methanol/water (70/30, v/v) was considered as the best compromise according to the nucleoside mono-, di-, or triphosphates and the four cell lines studied. This work highlights the importance of pre-analytical step combined with the cell lines studied associated to sensitive and validated assay for the quantification of nucleotides in biological matrices.

Simultaneous quantification of IMPDH activity and purine bases in lymphocytes using LC-MS/MS: assessment of biomarker responses to mycophenolic acid

BACKGROUND

The development of biomarkers describing the individual responses to the immunosuppressant mycophenolic acid (MPA) has focused on the target enzyme activity [inosine 5'-monophosphate dehydrogenase (IMPDH)]. An extended strategy is to quantify the metabolic consequences of IMPDH inhibition. The aim of this study was to develop an assay for quantification of IMPDH activity and related purine bases and to provide preliminary data on the behavior of these biomarkers during clinical exposure to MPA.

METHODS

Liquid chromatography-mass spectrometry was used to determine xanthine (IMPDH activity in incubated cell lysate), hypoxanthine, guanine, and adenine derived from free nucleotides in lymphocytes. Analytical performance was assessed, and the biomarkers were examined in CD4⁺ cells from 2 groups: Healthy individuals in a single-dose MPA study (n = 5) and liver transplant recipients on MPA therapy (n = 15).

RESULTS

Coefficients of variation between series were below 10% and 15% for measurement of the purines and IMPDH activity, respectively. Although IMPDH was inhibited, the purine levels increased in response to MPA in 3 of the 5 healthy individuals, and this positive response seemed to be associated with IMPDH1 c.579 + 119 G/G and c.580 - 106 G/G. In the liver transplant study, guanine was not reduced in response to the transient drop in IMPDH activity after MPA dosing. However, there were trends toward decrease in guanine and elevation of hypoxanthine during prolonged MPA therapy. The guanine/hypoxanthine ratio (median) was 37% lower and the adenine level was 21% lower at day 17 compared with day 4 after transplantation.

CONCLUSIONS

The assay allows precise quantification of IMPDH activity, hypoxanthine, guanine, and adenine in lymphocytes. Some individuals may possess a counteracting purine response to the MPA-mediated inhibition of IMPDH. Reduction of the guanine/hypoxanthine ratio may be related to prolonged inhibition of IMPDH and seems as an intriguing pharmacodynamic biomarker for MPA.

Expression of IMPDH mRNA after mycophenolate administration in male volunteers

Background. Mycophenolic acid (MPA) is the first-line antimetabolic immunosuppressants used in solid organ transplantation. Here, in vivo expressions of the pharmacodynamic marker IMPDH mRNA were analyzed to investigate its usefulness in assessing drug effects. Materials and Methods. Six healthy male volunteers who had the same genotype for genes known to be associated with drug metabolism and effects were selected to remove the confounding effect of these genotypes. Mycophenolate mofetil (MMF, 1 g) was administered once to each subject, and blood samples were collected with certain interval before and after MMF administration to measure lymphocyte expression levels of IMPDH1 and IMPDH2 mRNA. One week later, the experiment was repeated. Results. Whereas IMPDH1 mRNA expression was stable, IMPDH2 mRNA expression showed 2 peaks in the first week. Both IMPDH1 and IMPDH2 mRNA expression in the second week remarkably decreased from the first week. Conclusion. The temporary increase in IMPDH2 mRNA expression in the first week might be due to a reactive reaction against the plasma MPA concentration. In the second week, the intracellular guanosine monophosphate might be depleted, rendering IMPDH2 mRNA synthesis inactive. When MPA is regularly administered to reach a steady state, the IMPDH2 mRNA expression may be kept low and may effectively reflect biological responses regardless of drug intake.

A new class of dual-targeted antivirals: monophosphorylated acyclovir prodrug derivatives suppress both human immunodeficiency virus type 1 and herpes simplex virus type 2

BACKGROUND

Human immunodeficiency virus type 1 (HIV-1) and herpes simplex virus type 2 (HSV-2) are responsible for 2 intersecting epidemics in which the disease caused by 1 virus facilitates the transmission of and pathogenesis by the other. Therefore, suppression of one virus infection will affect the other. Acyclovir, a common antiherpetic drug, was shown to directly suppress both viruses in coinfected tissues. However, both antiviral activities of acyclovir are dependent on phosphorylation by the nucleoside kinase activity of coinfecting human herpesviruses.

METHODS

We developed acyclovir ProTides, monophosphorylated acyclovir with the phosphate group masked by lipophilic groups to allow efficient cellular uptake, and investigated their antiviral potential in cell lines and in human tissues ex vivo.

RESULTS

Acyclovir ProTides suppressed both HIV-1 and HSV-2 at median effective concentrations in the submicromolar range in ex vivo lymphoid and cervicovaginal human tissues and at 3-12 micromol/L in CD4(+) T cells. Acyclovir ProTides retained activity against acyclovir-resistant HSV-2.

CONCLUSIONS

Acyclovir ProTides represent a new class of antivirals that suppress both HIV-1 and HSV-2 by directly and independently blocking the key replicative enzymes of both viruses. Further optimization of such compounds may lead to double-targeted antivirals that can prevent viral transmission and treat the 2 synergistic diseases caused by HIV-1 and HSV-2. To our knowledge, the acyclovir ProTides described here represent the first example of acyclic nucleoside monophosphate prodrugs being active against HIV-1.

Pharmacodynamics of mycophenolic acid in CD4+ cells: a single-dose study of IMPDH and purine nucleotide responses in healthy individuals

Mycophenolate mofetil is used in rejection prophylaxis after allograft transplantation. The highly variable pharmacokinetics and pharmacodynamics (PD) of the active moiety mycophenolic acid (MPA) render this drug attractive for therapeutic monitoring. The aim of this study was to characterize the exposure-response relationship for MPA to guide future strategies for individualized therapy based on PD monitoring. A single-dose (100, 250, 500, and 1000 mg mycophenolate mofetil) crossover exposure-response study of MPA PD in CD4 cells was performed in 5 healthy individuals. The activity of inosine 5'-monophosphate dehydrogenase (IMPDH) at time 0 ranged from 1.2 to 7.2 pmol per 10 cells/min. IMPDH was strongly inhibited by MPA; MPA EC50 (concentration required for 50% inhibition) of 2.3 mg/L was determined by a pooled data analysis. Decreased IMPDH gene expression was associated with the exposure to MPA. There were no immediate reductions of guanine nucleotides. On the contrary, a trend toward increased guanosine triphosphate was observed. IMPDH activity AUC0-12h approached maximum reduction at MPA AUC0-12h 22 mg x h/L (corresponding to the 500 mg dose), whereas plasma concentrations exceeding approximately 6 mg/L did not further increase the IMPDH inhibition. The results suggest that guanine nucleotides in circulating lymphocytes may not serve as immediate response biomarkers to MPA. Strategies for preventing over- or underexposure to MPA may be developed by means of IMPDH activity combined with MPA concentration measurement.

IMP dehydrogenase basal activity in MOLT-4 human leukaemia cells is altered by mycophenolic acid and 6-thioguanosine

OBJECTIVE

Depletion of guanine and deoxyguanine nucleotides by inhibition of inosine 5'-monophosphate dehydrogenase (IMPDH, EC 1.1.1.205) or introduction of 6-thioguanine nucleotide antimetabolites are two principles of retarding cell proliferation by interference with the cellular purine nucleotide pool. IMPDH activity may be a promising pharmacodynamic biomarker during immunosuppressive and anticancer pharmacotherapy. The aim of the study was to investigate the impact of mycophenolic acid (MPA) and 6-thioguanosine (tGuO) on IMPDH basal activity.

MATERIAL AND METHODS

We studied the IMPDH basal activity (i.e. the enzyme activity following inhibitor exposure, but measured in absence of the inhibitor) in response to increasing concentrations of the IMPDH inhibitor MPA and the antimetabolite tGuO in MOLT-4 human leukaemia cells. In parallel, IMPDH gene expression and cellular purine nucleotide concentrations were examined.

RESULTS

A biphasic concentration-dependent influence of MPA on the IMPDH basal activity was observed. At concentrations < or =IC50, MPA increased the IMPDH basal activity. The increase was associated with elevated expression of IMPDH2. Despite increased expression, the basal enzyme activity decreased following exposure to high MPA concentrations. The IMPDH2 expression increased modestly in response to tGuO exposure. However, the IMPDH basal activity decreased when the cells were exposed to a proliferation-blocking tGuO concentration.

CONCLUSIONS

These findings demonstrate that IMPDH basal activity is influenced by MPA and tGuO, and suggest that reduced IMPDH basal activity is related to the proliferation-blocking effects of these agents.

Assessing biomarkers of oxidative stress: analysis of guanosine and oxidized guanosine nucleotide triphosphates by high performance liquid chromatography with electrochemical detection

Oxidation of the guanosine moiety in DNA has become a hallmark biomarker in assessing oxidative stress. The oxidation of guanosine in the nucleotide triphosphate pool has been overlooked due to the lack of a reliable methodology. This method describes a sample processing and high performance liquid chromatography with electrochemical detection protocol for the analysis of the cellular pool of guanosine triphosphates and oxidized guanosine triphosphates. Validation of this method is demonstrated along with evaluation of these analytes in control and oxidizing conditions in vitro and in HEK 293T cells. Oxidation of this triphosphate pool occurred independently of oxidation to DNA.

Cancer cells activate p53 in response to 10-formyltetrahydrofolate dehydrogenase expression

A folate enzyme, FDH (10-formyltetrahydrofolate dehydrogenase; EC 1.5.1.6), is not a typical tumour suppressor, but it has two basic characteristics of one, i.e. it is down-regulated in tumours and its expression is selectively cytotoxic to cancer cells. We have recently shown that ectopic expression of FDH in A549 lung cancer cells induces G1 arrest and apoptosis that was accompanied by elevation of p53 and its downstream target, p21. It was not known, however, whether FDH-induced apoptosis is p53-dependent or not. In the present study, we report that FDH-induced suppressor effects are strictly p53-dependent in A549 cells. Both knockdown of p53 using an RNAi (RNA interference) approach and disabling of p53 function by dominant-negative inhibition with R175H mutant p53 prevented FDH-induced cytotoxicity in these cells. Ablation of the FDH-suppressor effect is associated with an inability to activate apoptosis in the absence of functional p53. We have also shown that FDH elevation results in p53 phosphorylation at Ser-6 and Ser-20 in the p53 transactivation domain, and Ser-392 in the C-terminal domain, but only Ser-6 is strictly required to mediate FDH effects. Also, translocation of p53 to the nuclei and expression of the pro-apoptotic protein PUMA (Bcl2 binding component 3) was observed after induction of FDH expression. Elevation of FDH in p53 functional HCT116 cells induced strong growth inhibition, while growth of p53-deficient HCT116 cells was unaffected. This implies that activation of p53-dependent pathways is a general downstream mechanism in response to induction of FDH expression in p53 functional cancer cells.

Determination of fifteen nucleotides in cultured human mononuclear blood and umbilical vein endothelial cells by solvent generated ion-pair chromatography

The paper describes the development of a method for the determination of 15 nucleotides in cultured mononuclear blood and umbilical vein endothelial cell lysates by solvent generated ion-pair chromatography. The phase system is generated via a mobile phase of 100 mM phosphoric acid adjusted to pH 6.2 with triethylamine. Nucleotides are eluted by applying a linear magnesium ion gradient. The method is robust, highly reproducible and easily adaptable to other cell lysates and allows the separation and quantitation of the nucleotides with detection limits in the range from 17 (ADP) to 126 (CDP) pmol in 20-microl aliquots.

Quantification of the influence of mycophenolic acid on the release of endothelial adhesion molecules

BACKGROUND

Mycophenolic acid selectively inhibits inosine 5'-monophosphate dehydrogenase leading to a shortage of guanosine nucleotides. Since GTP is required for the synthesis of glycoproteins, this immunosuppressive drug also influences the production of several cell adhesion molecules.

METHOD

Soluble endothelial cell adhesion molecules released into cell culture supernatants after an incubation period of 16 h are assessed via a standard ELISA procedure applying test kits for E-selectin, VCAM-1 and ICAM-1.

RESULTS

Treatment with TNF-alpha leads to the induction of E-selectin and causes a significant increase in VCAM-1 and ICAM-1 content in the supernatant in relation to the level of unstimulated cells. Due to the inhibitory effects of MPA-applied either alone or in combination with cyclosporin A and prednisolone-sE-selectin is significantly reduced and sVCAM-1 is slightly but not significantly decreased, whereas sICAM-1 levels remain unchanged.

CONCLUSIONS

We demonstrate that the influence of MPA on endothelial cell adhesion molecules can readily be determined via ELISA. The results indicate that the immunosuppression by MPA is also achieved by slightly reducing the expression and consequent release of E-selectin, a pivotal molecule in the first step of leucocyte-endothelial interactions.

Influence of mycophenolic acid on inosine 5'-monophosphate dehydrogenase activity in human peripheral blood mononuclear cells

BACKGROUND

Inosine 5'-monophosphate dehydrogenase (IMPDH) catalyses the oxidation of inosine 5'-monophosphate (IMP) to xanthosine 5'-monophosphate (XMP). Thus, this enzyme plays an important role in the rate-limiting step of the de novo guanine nucleotide biosynthesis, making it a potent target for immunosuppressive drugs. Mycophenolic acid (MPA) is the most potent and specific inhibitor of IMPDH.

METHOD

IMPDH activity is determined via evaluation of XMP formation and the inhibitory influence of MPA in human peripheral blood mononuclear cells (PBMCs) is assessed by means of high-performance liquid chromatography (HPLC). For this objective, we have optimised a method based on solvent-generated ion exchange chromatography by cautiously varying mobile phase parameters.

RESULTS

The optimised method renders it possible to separate 18 analytes in 54 min in a single isocratic experiment and to measure the IMPDH activity in the lysate of human PBMCs in dependence on incubation time, substrate, co-substrate and inhibitor concentrations. In this way, we have determined the Michaelis-Menten constants K(M) and V(max) for IMP and beta-NAD+ and the inhibitor constant K(i) for MPA.

CONCLUSIONS

The chromatographic method presented in this report allows a rapid, reliable and reproducible quantification of IMPDH activity in PBMCs and therefore represents an attractive tool for the pharmacodynamic monitoring of the effects of MPA in patients under immunosuppressive therapy.

In vitro effects of mycophenolic acid on the nucleotide pool and on the expression of adhesion molecules of human umbilical vein endothelial cells

The immunosuppressive drug mycophenolate mofetil (MMF) and its active metabolite mycophenolic acid (MPA) selectively inhibit inosine 5'-monophosphate dehydrogenase (IMPDH), and therefore interfere with cellular guanine nucleotide biosynthesis. IMPDH is additionally involved in the synthesis of membrane glycoproteins, some of which are adhesion receptors known to play an active part in the regulation of cell-cell contacts, which are crucial in the process of recruitment and transendothelial infiltration of activated leucocytes in the transplanted organ. As a consequence, MPA leads to a reduction of cellular infiltrates in the course of transplant rejection. In the present study, the effects of MPA on human umbilical vein endothelial cells (HUVEC) are investigated at both molecular and cellular levels. In our experiments, HUVECs are treated with tumor necrosis factor-alpha (TNF-alpha; 10 ng/ml) in order to mimic activation occurring at a rejection crisis. The dose-dependent influence of concomitant incubation with MPA (5-20 micromol/l; 48 h, 37 degrees C, 5% CO2) on their intracellular nucleotide profile is observed by determining the concentrations of purine and pyrimidine nucleotides, using a HPLC method based on solvent generated ion-exchange. The possibility of synergistic effects is investigated by incubating endothelial cells with mixtures of three different immunosuppressants (mycophenolic acid; cyclosporin A, 100 ng/ml; prednisolone, 1 micromol/l)--a combination commonly used after transplantation--varying the amount of MPA (5-20 micromol/l). Stimulation with TNFalpha does not significantly modulate the intracellular levels of nucleotides quantitated. In the presence of MPA concentrations of at least 5 micromol/l, GTP levels (68+/-12%) are significantly decreased compared to controls (100%). At a concentration of 20 micromol/l MPA, the GTP amount is reduced to 58+/-7%. In contrast to these observations, the levels of UDP and UTP are increasing significantly under coincubation with MPA concentrations greater than 5 micromol/l. At 20 micromol/l MPA, UDP and UTP are increased to 147+/-19% and 114+/-11%, respectively. All other nucleotides (CTP, ADP, ATP) reveal no significant alterations in their intracellular concentrations under the conditions applied. Incubation of TNFalpha-treated HUVEC monolayers, with a mixture of three immunosuppressive drugs varying the amount of MPA, show no significant differences compared with the data observed after incubation with MPA alone. In addition, the influence of MPA (10 micromol/l) on a cellular level is observed by measuring the cell surface expression of adhesion molecules on cytokine-stimulated HUVECs, using TNFalpha (10 ng/ml), interferon-gamma (100 ng/ml), interleukin-1beta (10 ng/ml) and interleukin-8 (20 ng/ml). Expression of the intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), endothelial leucocyte adhesion molecule-1 (ELAM-1) and platelet endothelial cell adhesion molecule-1 (PECAM-1) was assessed by flow cytometry. Activation of endothelial cell monolayers with TNFalpha significantly increases the mean fluorescence intensity of VCAM-1 (361+/-14%) and ICAM-1 (429+/-47%) surface expression, compared to controls, and additionally induces E-selectin expression (2919+/-134%). The same tendencies, but in a lesser degree, are observed under stimulation of cells with either IFNgamma or IL-1beta. Incubation with a combination of TNFalpha and MPA leads to a significant reduction in VCAM-1 (329+/-13%) and E-selectin (2613+/-167%) expression, compared to the values obtained for HUVEC incubated with the cytokine alone. Treatment of the cells with IL-1beta/MPA also reduces the expression of VCAM-1 to a level significantly lower than the level observed after stimulation with IL-1beta. Incubation with MPA alone reveals no significant modulation in the expression of all surface molecules tested compared to the values of unstimulated HUVECs. The experiments show that the immunosuppressive action of MPA not only inhibits lymphocyte proliferation but also decreases the expression of adhesion molecules on endothelial cells, which are the first target of the cellular rejection process.