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R E Morris

Publications and source records attributed to R E Morris.

At least 73 records · Page 4Linked to original sources
PubMed1999

Feasibility of in vivo intravascular ultrasound tissue characterization in the detection of early vascular transplant rejection.

BACKGROUND: Unprocessed ultrasound radiofrequency (RF) signal analysis has been shown to distinguish different tissue structures more reliably than gray-scale interpretation of conventional ultrasound images. METHODS AND RESULTS: The objective of this study was to test the feasibility of in vivo intravascular ultrasound (IVUS) RF signal analysis in an animal model of allograft rejection. Six cynomolgus monkeys underwent transplantation of 3-cm aortic allograft segments distal to the renal arteries from immunologically mismatched donors. IVUS imaging with a 30-MHz system was performed 84 to 105 days after the operation. RF signals were acquired from cross sections of the recipient and the allograft aortas in real time with a digitizer at 500 MHz with 8-bit resolution. Sixty-five cross sections and 68 regions of interest (31 in host aorta and 37 in allograft) were analyzed in the adventitial layer with a total number of 8568 vectors processed. For each region of interest, a weighted-average attenuation was calculated on the basis of the attenuation and length for each individual vector. Histological examination was performed at every cross section imaged by IVUS. When the gray-scale images of conventional IVUS scored by an independent observer were compared, no distinction between adventitia of the native aorta and allograft was possible. Analysis of the average RF backscatter power also showed no significant difference (70.32+/-3.55 versus 70.72+/-3.38 dB). However, the average attenuation of allografts was significantly lower than that of the host aortas (2.64+/-1.38 versus 4.02+/-1.16 dB/mm, P<0.001). Histology demonstrated a marked adventitial inflammatory response in all allografts, with no inflammation observed in the host aortas. CONCLUSIONS: In vivo IVUS tissue characterization can be performed during routine imaging. In this model of transplant vasculopathy, RF attenuation measurements were more sensitive than visual or quantitative gray-scale analysis.

Animals↗
PubMed1999

Rapamycin reverses chronic graft vascular disease in a novel cardiac allograft model.

BACKGROUND: Chronic graft vascular disease (CGVD) in cardiac allografts has been defined as a slowly evolving vasculopathy unresponsive to conventional immunosuppression. We compared 4 rodent models of CGVD to evaluate the reproducibility of CGVD in heart allografts. Rapamycin (Rapa) and cyclosporine (CSA) were then used to treat CGVD. METHODS AND RESULTS: Hearts were harvested and placed heterotopically into allogenic recipients. CGVD scores of PVG allografts from ACI recipients treated with CSA on days 1 through 10 were significantly elevated on day 90 (n=16) compared with other models (immunosuppression used): (1) Lewis to F344 recipients (CSA), (2) Brown Norway to Lewis (FK506), and (3) DA to Wistar-Firth (methylprednisolone, azathioprine, CSA). Although delayed (day 60 to 90) CSA treatment had no effect (n=6), delayed Rapa (3 mg. kg-1. d-1 IP) reversed CGVD in PVG grafts (0.22+/-0.19 on day 90, n=6). ACI isografts showed no evidence of CGVD (n=6) at day 90. Immunohistochemistry of PVG grafts revealed perivascular infiltrates consisting of CD4(+) T cells and limited numbers of macrophages persisting up to day 90. Flow cytometry demonstrated increased levels of anti-donor antibody at day 90, which was significantly inhibited by Rapa treatment. CONCLUSIONS: PVG grafts developed a significant increase in CGVD without evidence of ongoing myocardial rejection. This CGVD appeared to be mediated by both cellular and humoral mechanisms, given CD4(+) perivascular infiltrates and increased levels of anti-donor antibody. The anti-CGVD effectiveness of Rapa during a period in which there was little myocardial cellular infiltrate supports a novel mechanism of effect such as smooth muscle or B-cell inhibition.

Animals↗
PubMed1999

Regulation of the macrophage vacuolar ATPase and phagosome-lysosome fusion by Histoplasma capsulatum.

Histoplasma capsulatum (Hc) maintains a phagosomal pH of about 6.5. This strategy allows Hc to obtain iron from transferrin, and minimize the activity of macrophage (Mo) lysosomal hydrolases. To determine the mechanism of pH regulation, we evaluated the function of the vacuolar ATPase (V-ATPase) in RAW264.7 Mo infected with Hc yeast or the nonpathogenic yeast Saccharomyces cerevisae (Sc). Incubation of Hc-infected Mo with bafilomycin, an inhibitor of the V-ATPase, did not affect the intracellular growth of Hc, nor did it affect the intraphagosomal pH. In contrast, upon addition of bafilomycin, phagosomes containing Sc rapidly changed their pH from 5 to 7. Hc-containing phagosomes had 5-fold less V-ATPase than Sc-containing phagosomes as quantified by immunoelectron microscopy. Furthermore, Hc-containing phagosomes inhibited phagolysosomal fusion as quantified by the presence of acid phosphatase, accumulation of LAMP2, and fusion with rhodamine B-isothiocyanate-labeled dextran-loaded lysosomes. Finally, in Hc-containing phagosomes, uptake of ferritin was equivalent to phagosomes containing Sc, indicating that Hc-containing phagosomes have full access to the early "bulk flow" endocytic pathway. Thus, Hc yeasts inhibit phagolysosomal fusion, inhibit accumulation of the V-ATPase in the phagosome, and actively acidify the phagosomal pH to 6.5 as part of their strategy to survive in Mo phagosomes.

Animals↗
PubMed1999

Flow cytometric analysis of the molecular mechanisms of immunosuppressive action of the active metabolite of leflunomide and its malononitrilamide analogues in a novel whole blood assay.

Malononitrilamides (MNAs) are a new class of immunomodulatory drug highly effective in in vivo models of allo- and xenotransplantation. Knowledge of their effects on immune cells, however, is limited and has been derived solely from investigations using isolated mononuclear cells. This use of purified cells to investigate drug activity is not ideal, so we have combined the analytical power of flow cytometry with our mitogen-driven, whole blood lymphocyte activation and proliferation assays to investigate the in vitro mechanism of action of MNAs. We first show that MNAs (A77 1726, HMR1279, and HMR1715), as well as brequinar (BQR) and cyclosporine (CsA), effectively inhibit cell activation antigen expression and lymphocyte proliferation. We next show that the inhibitory effects of MNAs and BQR, but not CsA, are reversed by the addition of uridine to the culture. These results suggest that inhibition of pyrimidine biosynthesis may be a mechanism by which MNAs suppress both lymphocyte activation and proliferation since these effects were reversed when uridine nucleotide pools were replenished. This novel finding of suppression of activation antigen expression by MNAs in whole blood expands our understanding of the effects of this new class of drug.

Acrylamides↗
PubMed1999

Coadministration of neoral and the novel rapamycin analog, SDZ RAD, to rat lung allograft recipients: potentiation of immunosuppressive efficacy and improvement of tolerability of staggered versus simultaneous treatment.

BACKGROUND: Neoral and rapamycin derivative (RAD) have complementary mechanisms for inhibition of lymphocyte activation and are substrates for the same pathways of drug metabolism. Therefore, we investigated treatment regimens designed to minimize pharmacokinetic interactions and to potentiate immunosuppressive efficacy in a highly stringent rat lung allograft model. METHODS: Lewis recipients of Brown Norway lungs received the following daily oral doses: (A) RAD at 2.5 mg/kg (n=9); (B) Neoral at 7.5 mg/kg (n=8); (C) RAD at 2.5 mg/kg + Neoral at 7.5 mg/kg simultaneously (n=8); or (D) RAD at 2.5 mg/kg + Neoral at 7.5 mg/kg (n=6) staggered 6 hr apart. Rats were assessed by daily weights, chest radiographs, drug trough levels (high-performance liquid chromatography/mass spectrometry), and blinded scoring of graft histology at death (day 21). RESULTS: Radiographs were completely opacified in all grafts of control and RAD monotherapy groups on days 7 and 14, respectively. Grafts were mildly opacified (Neoral monotherapy) and completely clear (both RAD + Neoral groups) on day 21. Simultaneous or staggered combined treatment dramatically reduced histologic rejection compared with treatment with either drug alone. Simultaneous treatment caused poor tolerability (poor grooming, lethargy) and significantly higher day-14 RAD and cyclosporine (CsA) trough levels (49+/-5 and 638+/-106 ng/ml; P<0.04) than in the staggered group (28+/-3 and 318+/-25 ng/ml) in which all animals were clinically normal. RAD and CsA day-14 trough levels in the staggered group were the same or lower than trough levels in animals treated with either drug alone (RAD 27+/-3/Neoral 815+/-67 ng/ml). CONCLUSIONS: (1) Administration of RAD + Neoral suppressed lung rejection more effectively than treatment with either drug alone. (2) Trough levels did not differ between monotherapy and staggered combination therapy for RAD but were lower for CsA. These results suggested that pharmacological, rather than pharmacokinetic, interactions between the parent drugs were responsible for the potentiation of immunosuppression when these drugs were coadministered. 3) Staggered administration of RAD+Neoral avoided the pharmacokinetic interactions that caused the elevated drug blood levels and poor tolerability caused by simultaneous administration. Thus, we could potentiate efficacy and improve tolerability by staggering administration of RAD and Neoral.

Animals↗
PubMed1999

Potentiation of immunosuppressive efficacy by combining the novel leflunomide analog, HMR 279, with microemulsion cyclosporine in a rat lung transplant model.

BACKGROUND: The novel leflunomide (LFM) analog, HMR 279, potentiates the immunosuppressive efficacy of microemulsion cyclosporine (Neoral) in rodent heart transplantation. The present study was designed to evaluate the immunosuppressive efficacy of this combination in comparison to the combination of Neoral and LFM in a stringent allogeneic rodent lung transplant model. METHODS: Donor lungs from Brown Norway rats were implanted into Lewis recipients and were followed for 21 days. Postoperative monitoring included daily weight assessment, chest radiographs, drug trough levels measured by high-performance liquid chromatography (LFM/HMR 279) and high-performance liquid chromatography/mass spectrometry (Neoral), and blinded histology assessment of the transplanted lung on the day of death based on the International Society for Heart and Lung Transplantation working formulation. Untreated lung recipients served as controls (group I, n=5). Rats were assigned to the following treatment groups: II, 7.5 mg/kg/day Neoral (n=6); III, 10 mg/kg/day LFM (n=6); IV, 10 mg/kg/day HMR 279 (n=6); V, 10 mg/kg/day LFM plus 7.5 mg/kg/day Neoral given simultaneously (n=13); and VI, 10 mg/kg/day HMR 279 plus 7.5 mg/kg/day Neoral given simultaneously (n=6). Drugs were given daily by oral gavage. RESULTS: All rats except for one in the HMR 279 monotherapy group survived the follow-up period. The chest radiographs in the control, LFM, and HMR 279 monotherapy groups showed moderate to complete opacification of the left chest by postoperative day 7 (controls) and day 14 (LFM, 279). At postoperative day 21, the Neoral monotherapy and the combination groups showed no signs of opacification in the radiographs. Combination therapies of Neoral plus HMR 279 or Neoral plus LFM were most successful in preventing histologic allograft rejection. Combining Neoral and HMR 279 resulted in a significant decrease in the cyclosporine trough levels. Co-administration of LFM plus Neoral resulted in significantly higher LFM trough levels when compared to LFM monotherapy. Of all treatments studied, the combination of HMR 279 plus Neoral was tolerated best as assessed by percentage of weight change. CONCLUSIONS: This study showed for the first time in a stringent rodent lung transplant model that combined treatment of LFM or HMR 279 plus Neoral potentiates the immunosuppressive efficacies of these drugs and successfully prevents allograft rejection.

Amides↗
PubMed1999

High-performance liquid chromatographic assay with a simple extraction procedure for sensitive quantification of mycophenolic acid in rat and human plasma.

We describe a novel sensitive and simplified gradient HPLC assay for quantification of the immunosuppressant mycophenolic acid (MPA) in rat and human plasma. In contrast to previously reported MPA assays, our method used a single step extraction comprising addition of acetonitrile, which contained phenolphthalein glucoronic acid as internal standard, for protein precipitation. Linearity: 0.1-100 microg/ml (r2>0.999), mean recoveries: MPA 98.0%, internal standard 105.2%, mean intra-day precision: 4.3%, mean day-to-day precision: 4.3%, mean day-to-day accuracy: -1.5%. Sensitivity was sufficient to allow for quantification of mycophenolic acid in as little as 50 microl plasma.

Animals↗
PubMed1999

Mechanism of action for leflunomide in rheumatoid arthritis.

Leflunomide (Arava) has recently been approved by the Food and Drug Administration for the treatment of rheumatoid arthritis (RA). This approval was based on data from a double-blind, multicenter trials in the United States (leflunomide versus methotrexate versus placebo) in which leflunomide was superior to placebo and similar to methotrexate (Strand et al., Arch. Intern. Med., in press, 1999). In a multicenter European trial, leflunomide was similar to sulfasalazine in efficacy and side effects (Smolen et al., Lancet 353, 259-266, 1999). Both methotrexate and leflunomide retarded the rate of radiolographic progression, entitling them to qualify as disease-modifying agents (Strand et al., Arch. Intern. Med., in press, 1999). Leflunomide is an immunomodulatory drug that may exert its effects by inhibiting the mitochondrial enzyme dihydroorotate dehydrogenase (DHODH), which plays a key role in the de novo synthesis of the pyrimidine ribonucleotide uridine monophosphate (rUMP). The inhibition of human DHODH by A77 1726, the active metabolite of leflunomide, occurs at levels (approximately 600 nM) that are achieved during treatment of RA. We propose that leflunomide prevents the expansion of activated and autoimmune lymphocytes by interfering with the cell cycle progression due to inadequate production of rUMP and utilizing mechanisms involving p53. The relative lack of toxicity of A77 1726 on nonlymphoid cells may be due to the ability of these cells to fulfill their ribonucleotide requirements by use of salvage pyrimidine pathway, which makes them less dependent on de novo synthesis.

Animals↗
PubMed1999

Suppression of acute rejection in allogeneic rat lung transplantation: a study of the efficacy and pharmacokinetics of rapamycin derivative (SDZ RAD) used alone and in combination with a microemulsion formulation of cyclosporine.

BACKGROUND: The novel immunosuppressant SDZ RAD, 40-0 (2-hydroxyethyl)rapamycin, is an orally active rapamycin analogue developed for use in combination with cyclosporine (Neoral). The present study was designed to evaluate the efficacy of SDZ RAD, Neoral, or a combination of both drugs for suppression of acute rejection in an allogeneic, unilateral rat lung transplant model. METHODS: Brown-Norway (RT1n) donor lungs were implanted into Lewis (RT1l) recipients that were observed for 21 days. Postoperative evaluation included daily weights, serial chest radiographs, drug trough levels, and histology scores of the transplanted lung on the day of sacrifice. Treatment groups were comprised of rats treated orally with the RAD vehicle as controls (n = 6); SDZ RAD 2.5 mg/kg/day (n = 9); Neoral 7.5 mg/kg/day (n = 8); Neoral 2.5 mg/kg/day (n = 6); SDZ RAD 2.5 mg/kg/day plus Neoral 7.5 mg/kg/day (n = 7); and Neoral 2.5 mg/kg/day plus SDZ RAD 2.5 mg/kg/day (n = 6). RESULTS: The results of this study showed that neither monotherapy with 2.5 mg/kg/day of Neoral, nor 2.5 mg/kg/day of SDZ RAD prevented severe acute rejection in unilateral lung transplant recipients. Furthermore, despite high dose (7.5 mg/kg/day) Neoral treatment, graft histology showed moderate rejection. However, addition of 2.5 mg/kg/day of SDZ RAD to 7.5 mg/kg/day of Neoral completely prevented histologic rejection in four of seven grafts, although the remaining 3 grafts showed minimal rejection. This combination resulted in significantly higher RAD trough levels when compared to SDZ RAD treatment alone. Combining a lower dose of Neoral (2.5 mg/ kg/day) with 2.5 mg/kg/day of SDZ RAD resulted in less weight loss and improved animal health; however, the histology of lung grafts in these rats showed mild rejection. CONCLUSIONS: This is the first study on the efficacy of the novel rapamycin derivative SDZ RAD for the control of acute lung allograft rejection. Results showed that acute unilateral rat lung allograft rejection is refractory to monotherapy with either high dose Neoral or SDZ RAD. The two regimens of combined treatment with Neoral plus SDZ RAD used in these studies produced either minimal rejection and reduced tolerability or mild rejection and better tolerability and showed potentiation of immunosuppression when both drugs were used together. Additional investigation of these two drugs is needed, however, to devise regimens that produce both high immunosuppressive efficacy and good tolerability.

Acute Disease↗
PubMed1999

The histology of subcutaneously implanted donor bronchial rings correlates with rejection scores of lung allografts in a primate lung transplant model.

BACKGROUND: The diagnosis of acute rejection in lung transplantation generally relies on transbronchial biopsies. This invasive procedure may be associated with bronchial bleeding or pneumothorax and may not be feasible in patients with severely compromised lung function. The hypothesis of the current study was that histopathological findings of donor bronchial segments implanted into the subcutaneous tissue of lung allograft recipients would predict lung tissue rejection scores, thus providing the clinician with an alternate source of information. METHODS: Unilateral left lung transplantation was performed in 34 cynomolgus monkeys as part of a drug efficacy study. After completion of the transplant procedure, 4 bronchial ring segments of the explanted recipient left lung and 4 bronchial ring segments of the non-transplanted right donor lung were implanted subcutaneously in the abdominal region. Lung allograft rejection was evaluated by open lung biopsies of the allograft performed on postoperative (PO) Day 14 and during sacrifice on PO Day 28. At the time of each biopsy, 2 donor and 2 recipient subcutaneous bronchial rings were explanted. Histologic evaluation of the lung tissue samples was performed according to the working formulation of the International Society for Heart and Lung Transplantation. Bronchial rings were independently evaluated by assessing the degree of airway narrowing; percentage of intact epithelial coverage as well as its specific histology (respiratory ciliated, flattened cuboidal, squamous); presence of lymphocytes, macrophages or spindle cells; and presence of peribronchial inflammation, luminal fibrosis, lymphocytic bronchitis or luminal mucous. Statistical analysis was performed by logistic regression. RESULTS: In the recipient bronchial rings, there was no evidence of airway narrowing. There was 98% epithelial coverage, 71% that were respiratory ciliated cells, and there was no inflammation. Donor bronchial rings showed no airway narrowing for monkeys with grade A0 to A2 rejection in tissue biopsies and a maximum narrowing (41.2%) with A4 rejection. Epithelial cell coverage was approximately 100% with grade A0-A2 and 44+/-11% with A4 rejection. Lymphocytic bronchitis was most severe in A4 rejection and minimal in A0 to A2 rejection. By logistic regression analysis, independent predictors of a likelihood of rejection were the degree of airway obliteration, the percentage of epithelial cell coverage, the degree of lymphocytic bronchitis and the product of respiratory and flattened cuboidal cell coverage. CONCLUSIONS: The current data show that histologic alterations of subcutaneously implanted donor bronchial rings correlate with lung tissue biopsy scores based on the ISHLT working formulation. Because subcutaneous bronchial rings can be explanted under local anesthesia, they may provide useful information for the diagnosis of acute allograft rejection in patients with impaired lung function, patients that obtaining lung tissue samples may not be feasible.

Acute Disease↗
PubMed1999

The therapeutic prescription for the organ transplant recipient: the linkage of immunosuppression and antimicrobial strategies.

Infection and rejection, the two major barriers to successful organ transplantation, are closely linked, with immunosuppressive therapy being central to the pathogenesis of both. After almost two decades when azathioprine and prednisone, supplemented by antilymphocyte antibody therapy, were the cornerstones of post-transplant immunosuppressive programs, there has been a major increase in the therapeutic armamentarium available to treat rejection: cyclosporine, tacrolimus, mycophenolate mofetil, rapamycin, and antibodies directed against the interleukin-2 receptor. These agents are potent inhibitors of microbial specific T cell function, thus potentiating opportunistic infection with herpes group viruses, fungal and mycobacterial species, Strongyloides stercoralis, and a variety of intracellular pathogens. The mechanisms by which each of these drugs exerts its effects are an important determinant of the antimicrobial strategies that will be necessary to combat infection. Indeed, strategies to limit these infections are being linked to the nature of the immunosuppressive therapy required in a particular patient. Thus, the therapeutic prescription for the transplant patient is said to have two components: an immunosuppressive component to prevent and treat rejection, and an antimicrobial one to make it safe. In addition to using antimicrobial agents therapeutically, in the transplant patient prevention is stressed in which antibiotics are deployed prophylactically or preemptively.

Anti-Infective Agents↗
PubMed1999

Normal surfactant pool sizes and inhibition-resistant surfactant from mice that overexpress surfactant protein A.

Pulmonary surfactant protein-A (SP-A) has been reported to regulate the uptake and secretion of surfactant by alveolar type II cells, to stabilize large surfactant aggregates including tubular myelin, and to protect the surface activity of surfactant from protein inhibitors. In this study we investigated the consequences of overexpression of SP-A on pulmonary homeostasis and surfactant function in transgenic mice. The human SP-C promoter was used to direct synthesis of rat surfactant protein A (rSP-A) in alveolar type II cells and nonciliated bronchiolar cells of the distal respiratory epithelium. Levels of SP-A measured through enzyme-linked immunosorbent assay were 7- to 8-fold higher in lung homogenates and alveolar lavage fluid of the rSP-A mice than in those of transgene-negative littermates. The swimming exercise tolerance and lung compliance of mice bearing the transgene were unchanged. Mean air space sizes seen in randomly selected light-microscopic fields were not significantly different in the transgene-positive and -negative mice by morphometric analysis, but 15% of transgenic animals had scattered foci containing dilated alveoli and alveolar ducts without evidence of inflammation or fibrosis. Some alveolar macrophages contained bar-shaped osmophilic inclusions that had a highly ordered ultrastructure. There were no differences between the transgene-positive and -negative mice in the tissue or alveolar pool sizes of saturated phosphatidylcholine or in the large-aggregate composition of alveolar surfactant. The surface activity of surfactant isolated from the rSP-A mice was similar to that of the controls, but in the presence of protein inhibitors, the surface tension-reducing properties of the rSP-A surfactant were better preserved (P < 0.05). We conclude that overexpression of SP-A does not affect resting surfactant phospholipid levels, but that it enhances the resistance of surfactant to protein inhibition.

Animals↗
PubMed1999

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.

Animals↗
PubMed1999

Effect of anesthesia on a whole blood lymphocyte proliferation assay in the rat.

Lymphocyte proliferation assays are commonly used to quantify the effects of immunosuppressive drugs in animal models, but the influence of anesthetic agents on those assays is not well understood. We used a whole blood proliferation assay to compare lymphocyte proliferation in blood drawn from normal male Lewis rats that were sedated using three common methods. Rats (n = 12) were serially bled from the orbital plexus while anesthetized with diethyl ether, methoxyflurane, or carbon dioxide. Before the beginning of the anesthetic trials, a random subset of the rats (n = 6) was bled via the jugular vein using only manual restraint to provide a baseline control group. A comparison of the lymphocyte proliferation results obtained under these four conditions (manual restraint, diethyl ether, methoxyflurane, or CO2) showed no significant differences. The only hematological variation seen was an elevation of the number of circulating lymphocytes when ether was used. We conclude that there is no justification for withholding sedation when bleeding rats for this type of lymphocyte proliferation. Furthermore, when considering the use of one of the agents examined in this study, the method can be chosen based on factors other than potential adverse effects on the assay results.

Anesthetics↗
PubMed1999

Pharmacodynamics of immunosuppression by mycophenolic acid: inhibition of both lymphocyte proliferation and activation correlates with pharmacokinetics.

Mechanisms of immunosuppressive action of mycophenolic acid (MPA) on rat lymphocytes and correlations among MPA plasma concentrations (pharmacokinetics) and its suppression of immune functions (pharmacodynamics) were studied in vitro and in vivo. In vitro, MPA inhibited concanavalin A-stimulated lymphocyte proliferation in blood [tritium-labeled thymidine ([(3)H]TdR) incorporation, percentage of lymphocytes positive for proliferating cell nuclear antigen, and in S-G(2)M by flow cytometry] and activation (percentage of lymphocytes expressing CD25 or CD134). Maximum percent inhibitions (I(max)) of lymphocyte functions and concentrations of MPA (mg/l in blood) inhibiting 50% of I(max) (IC(50)) were 99%/0.14 mg/l for [(3)H]TdR, 93%/0.28 mg/l for S-G(2)M, 74%/0.29 mg/l for CD25, and 83%/0.24 mg/l for CD134. Blood sampled at different times after single or multiple oral MPA administrations at four dose levels was assayed for lymphocyte functions and MPA plasma concentrations. I(max) (%) and IC(50) (mg/l in plasma by HPLC) were 98 to 99%/0.18 to 0.19 mg/l for [(3)H]TdR, 88 to 98%/0.70 to 0.83 mg/l for S-G(2)M, 60 to 63%/0.65 to 0.81 mg/l for CD25, and 72 to 77%/0.61 to 0.74 mg/l for CD134. IC(50) values for S-G(2)M, CD25, and CD134 were higher after multiple daily treatments than after a single dose. There were clear and direct relationships among MPA dose levels, kinetics of MPA plasma concentrations, and dynamics of lymphocyte functions. MPA treatment in vitro and in vivo inhibits not only mitogen-stimulated lymphocyte proliferation in whole blood but also lymphocyte expression of cell surface cytokine receptors. These two different mechanisms of action may contribute to the therapeutic efficacy of MPA in vivo.

Animals↗