Immunosuppressive properties of methotrexate: apoptosis and clonal deletion of activated peripheral T cells

The anti-inflammatory actions of methotrexate are critically dependent upon the production of reactive oxygen species

1 The mechanism of action by which methotrexate (MTX) exerts its anti-inflammatory and immunosuppressive effects remains unclear. The aim of this study is to investigate the hypothesis that MTX exerts these effects via the production of reactive oxygen species (ROS). 2 Addition of MTX (100 nM-10 micro M) to U937 monocytes induced a time and dose dependent increase in cytosolic peroxide [peroxide](cyt) from 6-16 h. MTX also caused corresponding monocyte growth arrest, which was inhibited (P<0.05) by pre-treatment with N-acetylcysteine (NAC; 10 mM) or glutathione (GSH; 10 mM). In contrast, MTX induction of [peroxide](cyt) in Jurkat T cells was more rapid (4 h; P<0.05), but was associated with significant apoptosis at 16 h at all doses tested (P<0.05) and was significantly inhibited by NAC or GSH (P<0.05). 3 MTX treatment of monocytes (10 nM-10 micro M) for 16 h significantly reduced total GSH levels (P<0.05) independently of dose (P>0.05). However, in T-cells, GSH levels were significantly elevated following 30 nM MTX treatment (P<0.05) but reduced by doses exceeding 1 micro M compared to controls (P<0.05). 4 MTX treatment significantly reduced monocyte adhesion to 5 h and 24 h LPS (1 micro g ml(-1)) activated human umbilical vein endothelial cells (HUVEC; P<0.05) but not to resting HUVEC. Pre-treatment with GSH prevented MTX-induced reduction in adhesion. 5 In conclusion, ROS generation by MTX is important for cytostasis in monocytes and cytotoxicity T-cells. Furthermore, MTX caused a reduction in monocyte adhesion to endothelial cells, where the mechanism of MTX action requires the production of ROS. Therefore its clinical efficacy can be attributed to multiple targets.

Costimulating aberrant T cell responses by B7-H1 autoantibodies in rheumatoid arthritis

A pathogenic hallmark of rheumatoid arthritis (RA) is persistent activation of self-reactive CD4(+) T cells. The cause of this aberrant activity remains elusive. We report here detection of autoantibodies against B7-H1, a recently described member of the B7 family, in 29% of patients with RA versus 4% of healthy donors. High-level expression of cell surface B7-H1 are found on activated human CD4(+), CD8(+), and CD45RO(+) T cells. Immobilized autoantibodies to B7-H1 are capable of costimulating the proliferation of CD4(+) T cells in vitro, and the presence of these autoantibodies correlates with active disease status. Using immobilized B7-H1 mAb's and programmed death 1Ig, we demonstrate that engagement of B7-H1 on CD4(+) T cells costimulates proliferation and secretion of IL-10, and subsequently leads to programmed cell death, accompanied with upregulated expression of TNF-related apoptosis-inducing ligand and activation of caspase-3. Taken together with our previous findings, these data indicate a bidirectional signaling role of B7-H1 in T cell costimulation and apoptosis and implicate B7-H1 autoantibodies as contributing to the progression of RA by inducing aberrant T cell responses.

LF 15-0195 immunosuppressive agent enhances activation-induced T-cell death by facilitating caspase-8 and caspase-10 activation at the DISC level

The deoxyspergualin derivative LF 15-0195 has demonstrated some efficacy in animal models of autoimmune and graft-versus-host diseases and is currently tested in clinics. The molecular mechanisms of LF 15-0195 immunosuppressive activity remained unknown. We show that exposure to LF 15-0195 sensitizes Jurkat T cells to apoptosis induced by an agonistic anti-CD95 antibody (CH11 clone) and by the cytokine TNF-related apoptosis-inducing ligand. LF 15-0195 does not demonstrate any significant effect on the postmitochondrial activation of caspases, nor does it modify overall expression of CD95, Fas-associated death domain, and procaspase-8. The compound facilitates the recruitment of these molecules to the death-inducing signaling complex (DISC) and enhances caspase-8 and -10 activation, thus increasing cytochrome c and direct IAP binding with low pI (DIABLO)/Smac mitochondrial release. LF 15-0195 also sensitizes Jurkat T cells to CD3-mediated apoptosis, an in vitro model for activation-induced T-cell death (AICD). LF 15-0195-mediated sensitization to AICD was further confirmed in human peripheral T cells exposed to anti-CD3 antibodies, then cultured in the presence of interleukin-2. In these cells, LF 15-0195 increased apoptosis triggered by either anti-CD95 antibodies or CD3 restimulation, whereas no effect was observed on "passive apoptosis." Finally, in bone marrow recipient mice, LF 15-0195 enhanced allogeneic donor T-cell death, which required a functional CD95 pathway. These results suggest that LF 15-0195 sensitizes T cells to AICD by increasing caspase activation at the DISC level in response to CD95 engagement. This original mechanism, together with LF 15-0195 efficacy in various disease models, makes this compound a promising immunosuppressive drug.

T cell apoptosis by tryptophan catabolism

Indoleamine 2,3-dioxygenase (IDO) is a tryptophan-catabolizing enzyme that, expressed by different cell types, has regulatory effects on T cells resulting from tryptophan depletion in specific local tissue microenvironments. Different mechanisms, however, might contribute to IDO-dependent immune regulation. We show here that tryptophan metabolites in the kynurenine pathway, such as 3-hydroxyanthranilic and quinolinic acids, will induce the selective apoptosis in vitro of murine thymocytes and of Th1 but not Th2 cells. T cell apoptosis was observed at relatively low concentrations of kynurenines, did not require Fas/Fas ligand interactions, and was associated with the activation of caspase-8 and the release of cytochrome c from mitochondria. When administered in vivo, the two kynurenines caused depletion of specific thymocyte subsets in a fashion qualitatively similar to dexamethasone. These data suggest that the selective deletion of T lymphocytes may be a major mechanism whereby tryptophan metabolism affects immunity under physiopathologic conditions.

Apoptosis as a therapeutic tool in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory synovitis that is dominated by the presence of macrophages, lymphocytes and synovial fibroblasts, which leads to the destruction of bone and cartilage. The effectiveness of therapies that are directed against tumour-necrosis factor and interleukin-1 has identified macrophages as a crucial target for therapeutic intervention. However, not all patients respond to these therapies, and the benefits of this form of treatment are short lived. Recent work indicates that the insufficient apoptosis of inflammatory cells in the RA joint might contribute to pathogenesis. In this article, I characterize the mechanisms that prevent the apoptosis of chronic inflammatory cells in the RA joint, to identify potential new targets for the treatment of RA.

TNF inhibition as therapy for rheumatoid arthritis

The introduction of TNF- alpha -inhibiting biologicals has been a major therapeutic breakthrough in rheumatoid arthritis therapy. Against a background of conventional disease-modifying antirheumatic drug experience, this review focuses on present experiences and possible future developments. TNF inhibition results in profound improvement in the majority of rheumatoid arthritis patients, but non-response and adverse effects need attention. Adalimumab is being filed for approval. Other monoclonal antibodies or receptor constructs are in late development. Small molecule inhibitors of TNF production or signalling are a hot topic. One emerging target is nuclear factor kappa B and selective inhibition has proved effective in animal models of arthritis. Synovial proliferation in rheumatoid arthritis is characterised by diminished apoptosis of fibroblasts, whereas bone marrow precursor cells undergo accelerated apoptosis in active rheumatoid arthritis. Both abnormalities are seemingly ameliorated by TNF inhibition. Anti-apoptotic strategies will soon go into development for control of unresponsive rheumatoid arthritis.

Novel therapies for psoriasis

The T cell-driven immunopathogenesis of psoriasis has been well recognized since cyclosporine first revolutionized the treatment of psoriasis 20 years ago. Almost all investigative and clinical research subsequently, has concentrated on elucidating the specifics of antigen presentation, T cell interaction and the production of specific cytokines. The role of the keratinocyte, previously thought to be the primary target cell in psoriasis pathogenesis, has been relegated to a secondary role and the mechanism of action of systemic methotrexate in psoriasis has been challenged, the primary role of the T lymphocyte is now well known. While psoriasis has traditionally been treated "ab initio" with topical medications (corticosteroids, vitamin D(3), and retinoid derivatives), either singly, in combination, or with ultraviolet B (UVB) or psoralens and ultraviolet A (PUVA) therapy, the role of systemic medications has assumed greater prominence. Thus, three systemic medications currently are approved worldwide for the treatment of moderate to severe forms of psoriasis, namely cyclosporine, methotrexate and acitretin. The first two are likely to give significant clearing (greater than 75%) in the majority of cases, whereas acitretin is significantly less effective as monotherapy, but may approach methotrexate and cyclosporine in efficacy, if combined with PUVA or UVB phototherapy. The main limitations of these three drugs remain organ toxicity, especially hepatic toxicity with methotrexate, hypertension and nephrotoxicity with cyclosporine, and teratogenicity and mucocutaneous toxicity with acitretin. Thus, the need for more specific systemic therapy, targeting the T lymphocyte. This has become the major area of clinical research interest over the past 5 years, with the promise of longer-term disease control (improved remissions) and less organ toxicities. Currently, there are over 15 of these "biologic" drugs in various stages of development and clinical trials, either by the subcutaneous, intramuscular or intravenous route. The three main variables are the rapidity of onset, percentages of improvement and remission rates. Without exception, these new systemic agents appear to be remarkably free of systemic organ toxicities (liver, renal, bone-marrow, etc.), with adverse effects being limited to mild flu-like symptoms with the anticipated increase in infections (e.g., herpes simplex) being either equal to placebo or only marginally increased. Not all these agents under evaluation give clinical responses equal to methotrexate or cyclosporine (75% or greater clearing in 75% of cases). In addition, response rates may be slower with some therapies versus others. However, the need for intermittent administration even by the injectable route, longer remissions, lack of systemic organ toxicities and the potential for safer usage in females of child-bearing age, make a compelling argument for widespread acceptance by both patients and the dermatological community. Other modalities under clinical evaluation include vitamin D and retinoid drugs, topically and systemically, with effects on nuclear receptors, as well as more specific wavelengths (308 to 311 nm) of UVB phototherapy with application for more localized forms of psoriasis. For the 2 to 3% of the worldwide population of patients with psoriasis the future has never looked brighter.

Induction of apoptosis and modulation of activation and effector function in T cells by immunosuppressive drugs

Immunosuppressive drugs (ISD) are used for the prevention and treatment of graft rejection, graft-versus-host-disease (GVHD) and autoimmune disorders. The precise mechanisms by which ISD interfere with T cell activation and effector function or delete antigen-specific T cells are defined only partially. We analysed commonly used ISD such as dexamethasone (DEX), mycophenolic acid (MPA), FK506, cyclosporin A (CsA), rapamycin (RAP), methotrexate (MTX) and cyclophosphamide (CP) for apoptosis-induction and modulation of activation and effector function in human peripheral T cells, cytotoxic T cell lines (CTL) and Jurkat T cells. Of all drugs tested only CP and MTX prevented antigen-specific proliferation of T cells and decreased cytotoxicity of alloantigen specific CTL lines by direct induction of apoptosis. MTX and CP also slightly increased activation-induced cell death (AICD) and CD95-sensitivity. In contrast, all other drugs tested did not induce T cell apoptosis, increase CD95-sensitivity or AICD. CsA and FK506 even prevented AICD by down-modulation of CD95L. DEX, MPA, CsA, FK506 and RAP inhibited activation of naive T cells, but were not able to block proliferation of activated T cells nor decrease cytotoxic capacity of CTL lines. These results show that ISD can be classified according to their action on apoptosis-induction and inhibition of proliferation and would favour a rational combination therapy to delete existing reactive T cells and prevent further T cell activation.

Development of anti-TNF therapy for rheumatoid arthritis

The aetiology of systemic, autoimmune, chronic inflammatory diseases--such as rheumatoid arthritis--is not known, and their pathogenesis is complex and multifactorial. However, progress in the characterization of intercellular mediators--proteins that are now known as cytokines--has led to the realization that one cytokine, tumour-necrosis factor (TNF; previously known as TNF-alpha), has an important role in the pathogenesis of rheumatoid arthritis. This discovery heralded a new era of targeted and highly effective therapeutics for rheumatoid arthritis and, subsequently, other chronic inflammatory diseases.

Infliximab treatment induces apoptosis of lamina propria T lymphocytes in Crohn's disease

BACKGROUND AND AIMS

Treatment with infliximab induces remission in about 70% of patients with steroid refractory Crohn's disease. Because Crohn's disease is considered to be mediated by uncontrolled activation of mucosal T lymphocytes, we hypothesised that infliximab could induce apoptosis of T lymphocytes.

METHODS

Induction of apoptosis in vivo was studied in 10 patients with therapy refractory Crohn's disease. In vitro, resting or stimulated Jurkat T cells were incubated with infliximab.

RESULTS

Infusion of infliximab (5 mg/kg) in steroid refractory patients with Crohn's disease induced a clinical response in 9/10 patients but did not influence expression of activation markers, homing receptors, memory cells, Fas expression, or Bax/Bcl-2 expression on peripheral blood T lymphocytes. In contrast, a significant increase in CD3 and TUNEL positive cells within colonic biopsies was detected 24 hours after infusion of infliximab, suggesting that infliximab stimulates apoptosis of activated T lymphocytes but not of resting T cells. To test this hypothesis, the effects of infliximab on Jurkat T cells were investigated. We observed that infliximab induced apoptosis and an increase in the Bax/Bcl-2 ratio of CD3/CD28 stimulated Jurkat T cells but not of unstimulated Jurkat cells.

CONCLUSIONS

Our data indicate that infliximab treatment causes a rapid and specific increase in apoptosis of T lymphocytes in the gut mucosa. These findings may explain the rapid and sustained therapeutic effects of infliximab in Crohn's disease.

Molecular action of methotrexate in inflammatory diseases

Despite the recent introduction of biological response modifiers and potent new small-molecule antirheumatic drugs, the efficacy of methotrexate is nearly unsurpassed in the treatment of inflammatory arthritis. Although methotrexate was first introduced as an antiproliferative agent that inhibits the synthesis of purines and pyrimidines for the therapy of malignancies, it is now clear that many of the anti-inflammatory effects of methotrexate are mediated by adenosine. This nucleoside, acting at one or more of its receptors, is a potent endogenous anti-inflammatory mediator. In confirmation of this mechanism of action, recent studies in both animals and patients suggest that adenosine-receptor antagonists, among which is caffeine, reverse or prevent the anti-inflammatory effects of methotrexate.

Differential expression pattern of the antiapoptotic proteins, Bcl-2 and FLIP, in experimental arthritis

OBJECTIVE

To examine the relationship between apoptosis and the expression of antiapoptotic proteins in the pathogenesis of experimental inflammatory arthritis.

METHODS

Clinical and histologic assessment of adjuvant-induced arthritis (AIA) was performed over a 42-day period. The induction of apoptosis was measured by TUNEL analysis, and the antiapoptotic proteins, Bcl-2 and FLIP, were examined by immunohistochemistry with the use of monospecific antibodies. The percentage of Bcl-2- and FLIP-positive cells was correlated with histologic markers of AIA.

RESULTS

Arthritis developed by day 14 following adjuvant injection. Few TUNEL-positive cells were observed between days 0 and 21, indicating that apoptosis did not occur at these time points. An increase in the number of TUNEL-positive cells was observed at day 28, particularly outside sites of cartilage or bone erosion, which dramatically declined by day 35. Immunohistochemical analyses of Bcl-2 and FLIP revealed that the synovium was positive for Bcl-2 and FLIP on day 0. On day 14, Bcl-2 was present at the sites of early erosions and correlated with the erosion and inflammation scores. FLIP was also highly expressed at sites of erosion and was localized to the pannus starting on day 21. Although TUNEL positivity peaked at day 28, a time point in which Bcl-2 and FLIP were present, the areas that displayed intense positivity for expression of Bcl-2 and FLIP were TUNEL negative. In addition, the number of neutrophils in the synovial lining and pannus significantly decreased from day 28 to day 35, suggesting that the cells undergoing apoptosis were neutrophils. Furthermore, at day 42 when TUNEL-positive cells were absent, Bcl-2 expression was diminished, while FLIP remained highly expressed in the pannus.

CONCLUSION

The overall percentage of TUNEL-positive cells in the ankle was <1% except on days 28 and 35 post-adjuvant injection, suggesting that in AIA, similar to rheumatoid arthritis, a lack of apoptosis may contribute to disease progression. Furthermore, Bcl-2 and FLIP are temporally and differentially expressed during the pathogenesis of AIA. Inhibition of these molecules may augment synovial apoptosis and ameliorate the disease.

The effect of drugs and toxins on the process of apoptosis

In this review we examine the modifying effect of specific drugs on apoptosis. Apoptosis is a type of cell death prevalent during many physiological and pathological conditions, consisting of several steps, namely, initiating stimuli, transduction pathways, effector mechanisms, nuclear fragmentation, and phagocytosis. Pharmacological substances such as glucocorticoids can either induce or inhibit the process of apoptosis in various cells depending on the type of drug and its concentration. Understanding the mechanisms of interaction of drugs with cells undergoing apoptosis could encourage novel therapeutic approaches to human diseases in which apoptosis has a critical role.

Methotrexate suppresses NF-kappaB activation through inhibition of IkappaBalpha phosphorylation and degradation

Methotrexate (MTX), a folate antagonist, is a commonly used anti-inflammatory, antiproliferative, and immunosuppressive drug whose mode of action is not fully established. Due to the central role of NF-kappaB in these responses, we postulated that MTX must mediate its effects through suppression of NF-kappaB activation. We investigated the effects of MTX on NF-kappaB activation induced by TNF in Jurkat cells. The treatment of these cells with MTX suppressed TNF-induced NF-kappaB activation with optimum effects occurring at 10 microM MTX for 60 min. These effects were not restricted to Jurkat cells because other cell types were also inhibited. Besides TNF, MTX also suppressed the NF-kappaB activation induced by various other inflammatory stimuli. The suppression of TNF-induced NF-kappaB activation by MTX correlated with inhibition of IkappaBalpha degradation, suppression of IkappaBalpha phosphorylation, abrogation of IkappaBalpha kinase activation, and inhibition of NF-kappaB-dependent reporter gene expression. Because ecto 5' nucleotidase inhibitor (alpha,beta-methylene adenosine-5'-diphosphate) blocked the effect of MTX, adenosine mimicked the effect of MTX, and adenosine A2b receptor antagonist (3,7-dimethyl-1-propargylxanthine) reversed the inhibitory effect of MTX, we suggest that MTX suppresses NF-kappaB activation by releasing adenosine. A partial reversal of MTX-induced NF-kappaB suppression by thymidine and folinic acid indicates the role of the thymidylate synthase pathway also. Overall, our results clearly demonstrate that MTX suppresses NF-kappaB activation through the release of adenosine, which may contribute to the role of MTX in anti-inflammatory, immunomodulatory, and antiproliferative effects.

Anti-TNF alpha therapy of rheumatoid arthritis: what have we learned?

Rheumatoid arthritis (RA), a systemic disease, is characterized by a chronic inflammatory reaction in the synovium of joints and is associated with degeneration of cartilage and erosion of juxta-articular bone. Many pro-inflammatory cytokines including TNF alpha, chemokines, and growth factors are expressed in diseased joints. The rationale that TNF alpha played a central role in regulating these molecules, and their pathophysiological potential, was initially provided by the demonstration that anti-TNF alpha antibodies added to in vitro cultures of a representative population of cells derived from diseased joints inhibited the spontaneous production of IL-1 and other pro-inflammatory cytokines. Systemic administration of anti-TNF alpha antibody or sTNFR fusion protein to mouse models of RA was shown to be anti-inflammatory and joint protective. Clinical investigations in which the activity of TNF alpha in RA patients was blocked with intravenously administered infliximab, a chimeric anti-TNF alpha monoclonal antibody (mAB), has provided evidence that TNF regulates IL-6, IL-8, MCP-1, and VEGF production, recruitment of immune and inflammatory cells into joints, angiogenesis, and reduction of blood levels of matrix metalloproteinases-1 and -3. Randomized, placebo-controlled, multi-center clinical trials of human TNF alpha inhibitors have demonstrated their consistent and remarkable efficacy in controlling signs and symptoms, with a favorable safety profile, in approximately two thirds of patients for up to 2 years, and their ability to retard joint damage. Infliximab (a mAB), and etanercept (a sTNF-R-Fc fusion protein) have been approved by regulatory authorities in the United States and Europe for treating RA, and they represent a significant new addition to available therapeutic options.

Localization of the murine reduced folate carrier as assessed by immunohistochemical analysis

The reduced folate carrier (RFC1) is a major route for the transport of folates in mammalian cells. The localization of RFC1 in murine tissues was evaluated by immunohistochemical analysis using a polyclonal antibody to the C-terminus of the carrier. There was expression of RFC1 in the brush-border membrane of the jejunum, ileum, duodenum and colon. RFC1 was localized to the basolateral membrane of the renal tubular epithelium. Carrier was detected on the plasma membrane of hepatocytes but not in bile duct epithelial cells. In the choroid plexus RFC1 was highly expressed at the apical surface. It was also expressed in axons and dendrites and on the apical membrane of cells lining the spinal canal. In spleen, RFC1 was detected only in the cells of the red pulp. These data provide insights into the role that RFC1 plays in folate delivery in a variety of tissues. In particular, the localization of carrier may elucidate the role of RFC1 in the vectorial transport of folates across epithelia. The data also indicate that in kidney tubules and choroid plexus the sites of RFC1 expression are different from what has been reported previously for the folate receptor; and while RFC1 is expressed in small intestine, folate receptor is not.

Western and Chinese antirheumatic drug-induced T cell apoptotic DNA damage uses different caspase cascades and is independent of Fas/Fas ligand interaction

Spontaneous or therapeutic induction of T cell apoptosis plays a critical role in establishing transplantation tolerance and maintaining remission of autoimmune diseases. We investigated the mechanisms of apoptosis induced by Chinese and Western antirheumatic drugs (ARDs) in human T cells. We found that hydroxychloroquine, Tripterygium wilfordii hook F, and tetrandrine (Tet), but not methotrexate, at therapeutic concentrations can cause T cell death. In addition, Tet selectively killed T cells, especially activated T cells. Although ARD-induced cytotoxicity was mediated through apoptotic mechanisms, Fas/Fas ligand interaction was not required. We further demonstrated that the processes of phosphatidylserine externalization and DNA damage along the ARD-induced T cell apoptotic pathway could operate independently, and that selective inhibition of DNA damage by caspase inhibitors did not prevent T cells from undergoing cell death. Moreover, we found that Tet- and Tripterygium wilfordii hook F-induced T cell DNA damage required caspase-3 activity, and hydroxychloroquine-induced T cell DNA damage was mediated through a caspase-3- and caspase-8-independent, but Z-Asp-Glu-Val-Asp-fluomethyl ketone-sensitive, signaling pathway. Finally, the observation that ARD-induced activation of caspase-3 in both Fas-sensitive and Fas-resistant Jurkat T cells indicates that Fas/Fas ligand interaction plays no role in ARD-induced T cell apoptosis. Our observations provide new information about the complex apoptotic mechanisms of ARDs, and have implications for combining Western and Chinese ARDs that have different immunomodulatory mechanisms in the therapy of autoimmune diseases and transplantation rejection.

Potential biologic agents for treating rheumatoid arthritis

The encouraging clinical results observed in trials using anti-TNF therapy clearly warrant further studies to determine whether TNF inhibitors are capable of modifying the destructive component of this disease in long-term follow-up studies as well as to assess the safety of long-term use (see the article by Keystone in this issue). It is also reasonable to propose that interfering with the cytokine cascade earlier in the course of disease may be of even greater therapeutic benefit. As the pathogenetic mechanisms in RA are more clearly defined, especially in early disease and in those individuals destined to develop severe disease, the potential of other biologic agents to specifically inhibit these critical pathways may provide better treatments for our patients. Many potential targets in the immune-mediated process of RA are currently being rigorously evaluated in clinical trials. Use of combinations of biologic therapies, perhaps in human patients with RA, should be of considerable interest in future trials.

Posttransplant administration of donor leukocytes induces long-term acceptance of kidney or liver transplants by an activation-associated immune mechanism

Donor leukocytes play a dual role in rejection and acceptance of transplanted organs. They provide the major stimulus for rejection, and their removal from the transplanted organ prolongs its survival. Paradoxically, administration of donor leukocytes also prolongs allograft survival provided that they are administered 1 wk or more before transplantation. Here we show that administration of donor leukocytes immediately after transplantation induced long-term acceptance of completely MHC-mismatched rat kidney or liver transplants. The majority of long-term recipients of kidney transplants were tolerant of donor-strain skin grafts. Acceptance was associated with early activation of recipient T cells in the spleen, demonstrated by a rapid increase in IL-2 and IFN-gamma at that site followed by an early diffuse infiltrate of activated T cells and apoptosis within the tolerant grafts. In contrast, IL-2 and IFN-gamma mRNA were not increased in the spleens of rejecting animals, and the diffuse infiltrate of activated T cells appeared later but resulted in rapid graft destruction. These results define a mechanism of allograft acceptance induced by donor leukocytes that is associated with activation-induced cell death of recipient T cells. They demonstrate for the first time that posttransplant administration of donor leukocytes leads to organ allograft tolerance across a complete MHC class I plus class II barrier, a finding with direct clinical application.

Overexpression of the apoptosis inhibitor FLIP in T cells correlates with disease activity in multiple sclerosis

The cellular caspase-inhibitory protein FLIP has been recently identified as a potent regulator of T lymphocyte susceptibility to Fas-mediated programmed cell death (apoptosis). Since impairment of apoptosis may be involved in multiple sclerosis (MS), we investigated the dynamics of cellular FLIP in unstimulated and activated T lymphocytes from MS patients, inflammatory and non-inflammatory neurological disorders, and healthy subjects. Cellular expression of the long and short forms of FLIP protein was similar in unstimulated T cells from MS patients and controls, but was significantly higher in activated T cells from patients with clinically active MS. This high FLIP expression in active MS correlated with cellular resistance to Fas-mediated apoptosis. In contrast, cellular expression of the anti-apoptotic protein Bcl-2 did not differ between active and stable disease, and was relatively similar between the MS group and controls. These findings suggest that cellular overexpression of the anti-apoptotic protein FLIP is a feature of clinically active multiple sclerosis.

Thymidine utilization abnormality in proliferating lymphocytes and hepatocytes of the woodchuck

Effective incorporation of tritiated thymidine ([(3)H]TdR) into proliferating lymphocytes is important because [(3)H]TdR is a standard label to study proliferate T-cell responses. We analyzed the thymidine utilization of woodchuck peripheral blood lymphocytes (PBL) since the [(3)H]TdR incorporation assay was not applicable to measure proliferative immune responses in the woodchuck, a current major virus/host model for human hepatitis B virus infection. Incorporation of [(3)H]TdR into DNA as well as the activity of the salvage pathway enzyme thymidine kinase (TK) of proliferating woodchuck PBL was low compared to human lymphocytes. Furthermore, [(3)H]TdR incorporation of proliferating woodchuck PBL remained residual regardless of the use of methotrexate, an inhibitor of the competitive deoxythymidine monophosphate de novo synthesis pathway. Using a human probe, specific for the proliferation-associated TK1, we proved the genomic presence and transcription of TK1 sequences in various species. TK1 sequences were detected in the genome of human, mouse, woodchuck, and chicken specimens. In contrast to proliferating human PBL and 3T3 mouse fibroblasts, no TK1 transcript was found in proliferating woodchuck PBL and hepatic cells. Transfection experiments with vectors containing the murine or human TK1 and selection assays demonstrated the ability of woodchuck cells to transcribe TK1 and to express functional TK1 proteins. Our study characterizes the unique failure of sufficient [(3)H]TdR incorporation into proliferating woodchuck cells and demonstrates tritiated adenine and serine as alternative labels to monitor PBL proliferation in the woodchuck.

Inhibition of dendritic cell differentiation by fumaric acid esters

Fumaric acid esters have proved to be effective for the systemic treatment of severe psoriasis vulgaris. These compounds have been shown to induce a Th2-like cytokine secretion pattern in T cells and to reduce keratinocyte proliferation in vitro. Dendritic cells seem to be of major importance as regulatory cells driving the psoriatic tissue reaction. Monocytes or CD34-positive myeloid progenitor cells are precursors of dendritic cells that can be generated in vitro by culture with granulocyte-macrophage colony-stimulating factor and interleukin-4. Using this model the effect of fumaric acid esters on granulocyte-macrophage colony-stimulating factor/interleukin-4-induced differentiation of monocyte-derived dendritic cells was investigated. The results of this study show that dimethylfumarate as well as methylhydrogenfumarate-calcium-salt (0.01-100 microg per ml) concentration-dependently inhibit monocyte-derived dendritic cell differentiation. This was reflected by an inhibition of CD1a, CD40, CD80, CD86, and HLA-DR expression as well as by a reduced capacity of dimethylfumarate-treated monocyte-derived dendritic cells to stimulate lymphocytes in the allogeneic mixed lymphocyte reaction. Other fumaric acid esters showed no effect on monocyte-derived dendritic cell-differentiation. At higher concentrations (30-100 microg per ml) dimethylfumarate, but not methylhydrogenfumarate calcium-salt induced apoptosis in monocyte-derived dendritic cells as measured by expression of Apo 2.7 and DNA fragmentation (TUNEL assay). These data point to a high susceptibility of the monocyte/dendritic cell system to dimethylfumarate and its main metabolite methylhydrogenfumarate. Other fumaric acid esters investigated were without effect. As the effects of fumarates on monocyte-derived dendritic cells observed occur at concentrations 20-fold lower compared with lymphocytes, our data seem to be of relevance in explaining the possible mode of action of these compounds in psoriasis.

Apoptosis and rheumatoid arthritis: past, present, and future directions

The current studies of apoptosis in rheumatoid arthritis (RA) suggest that molecules (Fas-related or TNF-related), pathways (activation of pro-apoptosis or anti-apoptosis pathway), cell types (lymphocytes or synovial fibroblast), and the mechanism that triggers apoptosis (tolerance induction-related, down-modulation of inflammation-related, or DNA damage-related) all play a fundamental role to determine the induction or prevention of RA. These series of defects at different levels and in different cells lead to hyperproliferation, defective apoptosis, or hyperapoptosis. This review summarizes the available knowledge of apoptosis and RA to help identify candidate target cells and target molecules for delivery of gene constructs or modified biological or chemical reagents to the target site for effective modification of these cells.

Inhibition of thymidine synthesis by folate analogues induces a Fas-Fas ligand-independent deletion of superantigen-reactive peripheral T cells

Methotrexate (MTX), a folate antagonist with multiple enzymatic targets, is used in the treatment of malignancies as well as in autoimmune and chronic inflammatory diseases, and ZD1694 (tomudex), a water-soluble quinazoline specific inhibitor of thymidylate synthase (TS), is used in the treatment of adenocarcinomas. In this study, we investigated the effects of these folate analogues on superantigen (SAg)-reactive peripheral T cells in vivo. In BALB/c mice, staphylococcal enterotoxin B (SEB)-induced cytokine secretion, IL-2R (CD25) expression and early deletion of a fraction of SEB-reactive V(beta)8(+) T cells were not impaired by either MTX (7 mg/kg/day) or tomudex (5 mg/kg/day). However, both MTX and tomudex prevented V(beta)8-selective T cell expansion and accelerated their peripheral elimination. Administration of thymidine (500 mg/kg/12 h) completely abrogated this effect, indicating that inhibition of TS but not that of other folate-dependent enzymes was the main mechanism involved. Furthermore, a marked increase of apoptotic cells restricted to the V(beta)8(+) T cell subset indicated that proliferation inhibition was associated with apoptosis. In contrast with peripheral V(beta)8(+) T cell deletion, MTX and tomudex did not prevent the increase of V(beta)8(+) thymocytes triggered by SEB. Experiments in C57BL/6-lpr/lpr mice further demonstrated that deletion of V(beta)8(+) T cells induced by folate analogues was independent of Fas-Fas ligand interaction. Our results provide evidence that folate analogues may selectively delete dividing peripheral T cells through TS inhibition, but do not interfere with other events triggered by SAg.

Computational predictions of binding affinities to dihydrofolate reductase: synthesis and biological evaluation of methotrexate analogues

The relative binding affinities to human dihydrofolate reductase of four new potential antifolates, containing ester linkages between the two aromatic systems, were estimated by free energy perturbation simulations. The ester analogue, predicted to exhibit the highest binding affinity to human dihydrofolate reductase, and a reference ester (more structurally related to methotrexate) were synthesized. As deduced from the measured IC(50) values, the calculated ranking of the ligands was correct although a greater difference in affinity was indicated by the experimental measurements. Among the new antifolates the most potent inhibitor exhibited a similar pharmacokinetic profile to methotrexate but lacked activity in a complex antiarthritic model in rat in vivo.

Impaired Fas-independent apoptosis of T lymphocytes in patients with multiple sclerosis

The homeostasis of the immune system is maintained by apoptotic (programmed cell death) elimination of potentially pathogenic, autoreactive mononuclear cells. There is emerging evidence that apoptosis mediated by the cell death receptor Fas is impaired in activated lymphocytes from patients with multiple sclerosis (MS), but other forms of apoptosis have not yet been fully evaluated. To further explore the dynamics of programmed cell death in MS, spontaneous and induced apoptosis of both peripheral and intrathecal mononuclear cells was investigated in clinically active MS patients and appropriate controls. In the MS group, spontaneous apoptosis of unfractionated mononuclear cells was significantly reduced, and activated intrathecal and peripheral T cells were found to be predominantly resistant to Fas-independent apoptosis. These results indicate that in clinically active MS, the reduced susceptibility of mononuclear cells to apoptosis is partly due to impairment of Fas-independent apoptotic pathways.

Effects of methotrexate on nucleotide pools in normal human T cells and the CEM T cell line

It has been proposed that the clinical utility of methotrexate (MTX) in the treatment of rheumatoid arthritis may be due, in part, to inhibition of 5-amino imidazole-4-carboxamide ribonucleotide formyltransferase (AICARFT) by polyglutamated forms of MTX. AICARFT is the second folate dependent enzyme in de novo purine biosynthesis. In this study, the effects of MTX on de novo purine biosynthesis as well as total nucleotide pools were evaluated in both the human T cell line, CEM, and phytohemagglutinin-activated normal human T lymphocytes. De novo synthesized purines were metabolically labeled with 14C-glycine after MTX treatment and analyzed by HPLC. In normal T cells, MTX produced a dose-dependent reduction in de novo adenosine and guanosine pools with maximal effects (>50%) at 1 microM MTX. In CEM cells, de novo purine synthesis was almost completely blocked by 1 microM MTX. Total purine pools were also reduced in both cell types after MTX treatment. Since 1 microM MTX caused almost complete growth inhibition in CEM cells, we evaluated whether growth could be reconstituted with exogenous purine bases and pyrimidine nucleosides which can be utilized via salvage pathways. The combination of hypoxanthine and thymidine substantially reversed growth inhibition with 1 microM MTX in CEM cells. Taken together, these results demonstrate that MTX inhibits de novo nucleotide synthesis in T cells and suggest that AICARFT inhibition may be one aspect of the multi-site mechanism of MTX action in the treatment of rheumatoid arthritis.

Chronic neutropenia mediated by Fas ligand

Chronic neutropenia, often associated with rheumatoid arthritis, is a characteristic finding in large granular lymphocyte (LGL) leukemia. The mechanism of neutropenia is not known. Normal neutrophil survival is regulated by the Fas–Fas ligand apoptotic system. We hypothesized that neutropenia in LGL leukemia is mediated by dysregulated expression of Fas ligand. Levels of Fas ligand in serum samples from patients with LGL leukemia were measured with a Fas ligand enzyme-linked immunosorbent assay. The effects of serum from patients with LGL leukemia on apoptosis of normal neutrophils were determined by flow cytometry and morphologic assessment. High levels of circulating Fas ligand were detected in 39 of 44 serum samples from patients with LGL leukemia. In contrast, Fas ligand was undetectable in 10 samples from healthy donors. Serum from the patients triggered apoptosis of normal neutrophils that depended partly on the Fas pathway. Resolution of neutropenia was associated with disappearance or marked reduction in Fas ligand levels in 10 of 11 treated patients. These data suggest that high levels of Fas ligand are a pathogenetic mechanism in human disease.

Chronic neutropenia mediated by Fas ligand

Chronic neutropenia, often associated with rheumatoid arthritis, is a characteristic finding in large granular lymphocyte (LGL) leukemia. The mechanism of neutropenia is not known. Normal neutrophil survival is regulated by the Fas–Fas ligand apoptotic system. We hypothesized that neutropenia in LGL leukemia is mediated by dysregulated expression of Fas ligand. Levels of Fas ligand in serum samples from patients with LGL leukemia were measured with a Fas ligand enzyme-linked immunosorbent assay. The effects of serum from patients with LGL leukemia on apoptosis of normal neutrophils were determined by flow cytometry and morphologic assessment. High levels of circulating Fas ligand were detected in 39 of 44 serum samples from patients with LGL leukemia. In contrast, Fas ligand was undetectable in 10 samples from healthy donors. Serum from the patients triggered apoptosis of normal neutrophils that depended partly on the Fas pathway. Resolution of neutropenia was associated with disappearance or marked reduction in Fas ligand levels in 10 of 11 treated patients. These data suggest that high levels of Fas ligand are a pathogenetic mechanism in human disease.

Immunosuppressive drugs: the first 50 years and a glance forward

During the past 50 years, many immunosuppressive drugs have been described. Often their mechanisms of action were established long after their discovery. Eventually these mechanisms were found to fall into five groups: (i) regulators of gene expression; (ii) alkylating agents; (iii) inhibitors of de novo purine synthesis; (iv) inhibitors of de novo pyrimidine synthesis; and (v) inhibitors of kinases and phosphatases. Glucocorticoids exert immunosuppressive and anti-inflammatory activity mainly by inhibiting the expression of genes for interleukin-2 and other mediators. Cyclophosphamide metabolites alkylate DNA bases and preferentially suppress immune responses mediated by B-lymphocytes. Methotrexate and its polyglutamate derivatives suppress inflammatory responses through release of adenosine; they suppress immune responses by inducing the apoptosis of activated T-lymphocytes and inhibiting the synthesis of both purines and pyrimidines. Azathioprine metabolites inhibit several enzymes of purine synthesis. Mycophenolic acid and mizoribine inhibit inosine monophosphate dehydrogenase, thereby depleting guanosine nucleotides. Mycophenolic acid induces apoptosis of activated T-lymphocytes. A leflunomide metabolite and Brequinar inhibit dihydroorotate dehydrogenase, thereby suppressing pyrimidine nucleotide synthesis. Cyclosporine and FK-506 (Tacrolimus) inhibit the phosphatase activity of calcineurin, thereby suppressing the production of IL-2 and other cytokines. In addition, these compounds have recently been found to block the JNK and p38 signaling pathways triggered by antigen recognition in T-cells. In contrast, rapamycin inhibits kinases required for cell cycling and responses to IL-2. Rapamycin also induces apoptosis of activated T-lymphocytes. Immunosuppressive and anti-inflammatory compounds in development include inhibitors of p38 kinase and of the type IV isoform of cyclic AMP phosphodiesterase which is expressed in lymphocytes and monocytes.A promising future application of immunosuppressive drugs is their use in a regime to induce tolerance to allografts. The role of leukocytes in grafts, and the induction of apoptosis of clones of responding T-lymphocytes, is discussed.

Methotrexate suppresses the interleukin-6 induced generation of reactive oxygen species in the synoviocytes of rheumatoid arthritis

Various cytokines and reactive oxygen species (ROS) play a fundamental role in the inflammatory and immunologic processes of rheumatoid arthritis (RA). Methotrexate (MTX) is one of the disease-modifying anti-rheumatic drugs and its effect may be partly due to the modulation of immunologic or inflammatory reactions by some cytokines. In the present study, we investigated the effects of MTX on the gene expression and synthesis of interleukin-6 (IL-6), and the proliferative activity and the production of ROS in the fibroblast-like synoviocytes (FLSs) obtained from the patient of RA. The expression or production of IL-6 was induced spontaneously, and augmented by the addition of recombinant human IL-6 or recombinant human IL-1 beta and TNF-alpha in FLSs. These spontaneous and augmented IL-6 expressions or productions were suppressed by treatment with low-concentration of MTX (1 microg/ml). Also, IL-6 stimulated the proliferation of FLSs, and this IL-6 driven proliferation was inhibited with the treatment of MTX or N-acetylcysteine (NAC, 1 mM). Furthermore, ROS production in FLSs was increased significantly by IL-6, and its effect was also abrogated in the presence of MTX or NAC. These results suggest that inflammatory reaction in the synovium of RA patients could be augmented by the autocrine or other cytokine-induced production of IL-6 with subsequent generation of ROS in the synoviocytes, and the modulations of IL-6 synthesis and ROS production may contribute to the therapeutic effects of MTX for RA.

Effect of methotrexate on blood purine and pyrimidine levels in patients with rheumatoid arthritis

OBJECTIVE

The mechanism of anti-inflammatory effects of methotrexate (MTX) at low dose may relate to a decrease in availability of the purine precursor or it may depend on accumulation of 5-aminoimidazole-4-carboxamide (AICAR) and the anti-inflammatory nucleoside adenosine. The aim of this study was to evaluate the possible mechanism of action by analysis of changes in blood concentrations of purine and pyrimidine metabolites during MTX treatment.

METHODS

Venous blood samples were collected from rheumatoid arthritis patients before and at different times for up to 7 days after the start of MTX treatment. Whole blood concentrations of adenosine, uridine, hypoxanthine, uric acid and erythrocyte nucleotides were measured by HPLC.

RESULTS

The initial blood adenosine concentration was 0.073 +/- 0.013 microM and no differences were observed during MTX treatment. However, a decrease in uric acid concentration was observed from 205.5+/-13.5 to 160. 9+/-13.5 microM (P<0.05) within 24 h after MTX administration. The hypoxanthine concentration decreased in parallel with uric acid, while the uridine concentration decreased 48 h after MTX administration. No accumulation of AICAR-triphosphate (ZTP) was observed in the erythrocytes.

CONCLUSIONS

MTX decreases circulating purine and pyrimidine concentrations, and their availability for DNA and RNA synthesis, which may affect immune cell proliferation and protein (cytokine) expression. The absence of adenosine concentration changes and lack of ZTP formation is evidence against an AICAR/adenosine mechanism, although localized adenosine concentration changes cannot be excluded.

Tumour necrosis factor (TNF) production by T cell receptor-primed T lymphocytes is a target for low dose methotrexate in rheumatoid arthritis

Methotrexate (MTX) is an effective immunosuppressive agent in various chronic inflammatory diseases such as rheumatoid arthritis (RA). However, its mechanisms of action are only partially understood. In this study, we assessed the effects of MTX on the differentiation of peripheral blood (PB) CD4+CD45RA 'naive' and CD4+CD45RO 'memory' T cells from healthy controls and patients with RA. Accordingly, purified T cells were primed and restimulated in vitro via the T cell receptor (TCR) in the presence of IL-2 to generate effector T cells secreting large amounts of Th1 and Th2 cytokines. We observed that low doses of MTX strongly suppress TNF and to a lesser extent interferon-gamma (IFN-gamma) production by T cells from both healthy donors and RA patients when present during T cell priming via the TCR. Similar data were obtained for TCR-primed synovial fluid mononuclear cells in RA. In contrast, production of IL-4 by TCR-primed CD45RA T cells was significantly increased upon MTX treatment. Interestingly, MTX did not enhance IL-4 production when present during restimulation of effector CD45RO T cells, although it still suppressed TNF production. The results indicate that MTX effects depend on the stage of T cell activation and identify TNF production by TCR-primed T lymphocytes as a target for low-dose MTX treatment in RA. These findings could explain the delayed clinical effects of MTX and may contribute to its potent anti-inflammatory and immunoregulatory properties.

Review article: targeting TNF alpha as a key cytokine in the inflammatory processes of Crohn's disease--the mechanisms of action of infliximab

Crohn's disease is a chronic, debilitating gastrointestinal disorder in which a variety of cellular processes and pro-inflammatory mediators influence the pathogenesis of the disease. Although the potential roles and functions of the pro-inflammatory mediators continue to be debated, several mediators, specifically tumour necrosis factor-alpha, have been clearly identified as having a pivotal role in the inflammation of the bowel mucosa of these patients. Therapies specifically focusing on the inflammatory process underlying Crohn's disease have the potential for providing disease modification and prolonged remission. Infliximab, an antitumour necrosis factor-alpha monoclonal antibody, has been demonstrated to neutralize tumour necrosis factor-alpha and restore and reset the immunological dysbalance of the inflamed mucosa. Preliminary studies with infliximab suggested that treatment resulted in a rapid and almost complete inhibition of multiple inflammatory pathways. In clinical studies of infliximab, patients with Crohn's disease achieved rapid reduction in clinical signs and symptoms, substantiated by both endoscopic and microscopic evaluation.

Methotrexate inhibits the first committed step of purine biosynthesis in mitogen-stimulated human T-lymphocytes: a metabolic basis for efficacy in rheumatoid arthritis?

The immunosuppressive and anti-inflammatory effects of low-dose methotrexate (MTX) have been related directly to inhibition of folate-dependent enzymes by polyglutamated derivatives, or indirectly to adenosine release and/or apoptosis and clonal deletion of activated peripheral blood lymphocytes in S-phase. In this study of phytohaemagglutinin-stimulated primary human T-lymphocytes we show that MTX (20 nM to 20 microM) was cytostatic not cytotoxic, halting proliferation at G(1). This stasis of blastogenesis was associated with an inhibition of purine ribonucleotide synthesis but a stimulation of pyrimidine biosynthesis, the normal mitogen-induced expansion of ATP and GTP pools over 72 h being restricted to concentrations of unstimulated T-cells, whereas the increment in UTP pools exceeded that of controls. Decreased incorporation of H(14)CO(3) or [(14)C]glycine into purine ribonucleotides, with no radiolabel accumulation in any de novo synthetic intermediate but enhanced H(14)CO(3) incorporation into UTP, supported these MTX-related effects. Exaggerated [(14)C]hypoxanthine salvage (which normalized the purine and UTP pools) confirmed the increased availability of 5-phosphoribosyl-1-pyrophosphate (PP-ribose-P) as the molecular mechanism underlying these disparate changes. These results provide the first substantive evidence that the immunosuppressive effects of low-dose MTX in primary blasting human T-lymphocytes relate not to the inhibition of the two folate-dependent enzymes of purine biosynthesis but to inhibition of the first enzyme, amidophosphoribosyltransferase, thereby elevating PP-ribose-P and stimulating UTP synthesis. Varying cell types or incubation conditions employed by other workers, especially malignant/activated cells with high basal metabolic rates, might mask the effects noted in primary human T-lymphocytes. The findings imply the involvement of low-dose MTX in the inhibition of T-lymphocyte proliferation and proliferation-dependent processes in rheumatoid arthritis.

Hodgkin's disease and B cell lymphoproliferation in rheumatoid arthritis patients treated with methotrexate: a kinetic study of lymph node changes

We describe 2 patients with seropositive rheumatoid arthritis treated with methotrexate (MTX) who developed Hodgkin's disease (HD) and non-Hodgkin's lymphoma. Followup allowed a lymph node biopsy at 4 different time points in 1 patient and at 2 in the other. In the first patient, the steps included a long history of benign follicle hyperplasia, a polymorphic diffuse B cell lymphoproliferation, and finally HD unassociated with Epstein-Barr virus (EBV). In the second patient, a polymorphic diffuse lymphoproliferation was followed by a monomorphic large B cell lymphoproliferation associated with EBV. The cytogenetic analysis showed a monoclonal proliferation associated with the same chromosomal abnormalities found in 1 of the clones observed in the initial biopsy. These 2 cases illustrate the complexity of the role of MTX in the outbreak of such manifestations.

Selective expression of folate receptor beta and its possible role in methotrexate transport in synovial macrophages from patients with rheumatoid arthritis

OBJECTIVE

To investigate the expression of folate receptors (FR) and reduced folate carrier (RFC) and determine their relevance to methotrexate (MTX) transport in synovial mononuclear cells (SMC) from patients with rheumatoid arthritis (RA).

METHODS

Levels of FR and RFC messenger RNA (mRNA) were examined by reverse transcriptase-polymerase chain reaction (RT-PCR) in SMC from RA patients and peripheral blood mononuclear cells from healthy donors. Expression of FR-beta mRNA and protein was determined by Northern blot and Western blot analyses in RA SMC and monocyte/macrophage-lineage cells. FR-beta expression and folic acid binding capacity on the cell surface were examined by flow cytometric analysis and 3H-folic acid binding analysis. Studies of the inhibition of 3H-MTX uptake in the presence of unlabeled folic acid were performed to investigate the uptake of MTX through FR in RA SMC.

RESULTS

RT-PCR, Northern blot, and Western blot analyses showed that FR-beta mRNA and protein were expressed selectively in activated monocytes and CD14+ RA SMC. These cells exhibited folic acid binding capacity. Furthermore, the FR-beta protein was shown to have folic acid binding capacity. Uptake of 3H-MTX through RA SMC was significantly inhibited in the presence of unlabeled folic acid.

CONCLUSION

These results demonstrate that FR-beta expression is selectively elevated in RA synovial macrophages and suggest that MTX is transported through FR-beta in RA synovial macrophages. The findings suggest that folate antagonists with higher affinity for FR-beta would be useful in the treatment of RA.

Pharmacokinetics, safety, and efficacy of combination treatment with methotrexate and leflunomide in patients with active rheumatoid arthritis

OBJECTIVE

To examine the safety and pharmacokinetics of and clinical response to leflunomide, a de novo pyrimidine synthesis inhibitor, when administered to patients with active rheumatoid arthritis (RA) who have been receiving long-term methotrexate therapy.

METHODS

This was an open-label, 52-week study in which 30 patients with RA that remained active despite therapy with methotrexate at 17+/-4 mg/week (mean +/- SD) for > or =6 months were given leflunomide, 10-20 mg/day. Patients were assessed for adverse effects, pharmacokinetic measurements of leflunomide and methotrexate, and clinical response by American College of Rheumatology (ACR) 20% response criteria.

RESULTS

Twenty-three patients completed 1 year of treatment. No significant pharmacokinetic interactions between leflunomide and methotrexate were noted. This combination therapy was generally well tolerated clinically, with the exception of elevations of liver enzyme levels. Seven patients withdrew from the treatment regimen: 2 withdrawals were voluntary, 3 were due to persistent elevation of plasma transaminase levels, and 2 were due to lack of efficacy. Of the patients, 16 (53%) met ACR 20% response criteria. Two met ACR criteria for remission after 1 year.

CONCLUSION

The combination of methotrexate and leflunomide has therapeutic potential in RA.

Medical therapy for inflammatory bowel disease

CD and UC represent a spectrum of chronic IBD that present in protean ways and are accompanied by a variety of systemic sequelae. Sulfasalazine and the newer 5-aminosalicylates are important in the management of mild-to-moderate disease, whereas corticosteroids remain the primary therapy for most patients with moderate-to-severe disease (Tables 2-5). The toxicities associated with long-term steroid therapy, combined with their ineffectiveness as maintenance medications, have led to increased use of immunomodulators, such as azathioprine and 6-MP, for the treatment of steroid-dependent and steroid-resistant IBD. Infliximab is a novel therapeutic adjunct for chronically active and fistulizing CD that will herald a new era of biologic therapy for IBD. Meanwhile, CSA remains an alternative to urgent colectomy in severe UC unresponsive to corticosteroids and also for CD patients with severe disease or refractory fistulas. Finally, continued insights into the etiopathogenic pathways in IBD will provide evolving and innovative approaches until the eventual causes and cures are elucidated. In the meantime, clinicians should remain optimistic regarding current ability to reduce the morbidity and maintain the quality of life for patients suffering with these frustrating diseases.

Molecular and cellular effects of methotrexate

In 1998, knowledge about the mechanisms of action of methotrexate (MTX) in immunoinflammatory disorders further increased. The most interesting results to date came from studies showing that most of the anti-inflammatory actions of MTX are mediated by adenosine, which may account for the profound effects of MTX on cytokines, cytokine inhibitors, and cell differentiation. Finally, potential novel pharmacologic strategies are discussed based on actual knowledge about the molecular and cellular actions of MTX.