Azathioprine-related bone marrow toxicity and low activities of purine enzymes in patients with rheumatoid arthritis

Genomic Profiling for Predictive Treatment Strategies in Fibrotic Interstitial Lung Disease

Idiopathic pulmonary fibrosis (IPF) has traditionally been considered the archetype of progressive fibrotic interstitial lung diseases (f-ILDs), but several other f-ILDs can also manifest a progressive phenotype. Integrating genomic signatures into clinical practice for f-ILD patients may help to identify patients predisposed to a progressive phenotype. In addition to the risk of progressive pulmonary fibrosis, there is a growing body of literature examining how pharmacogenomics influences treatment response, particularly regarding the efficacy and safety profiles of antifibrotic and immunomodulatory agents. In this narrative review, we discuss current studies in IPF and other forms of pulmonary fibrosis, including systemic autoimmune disorders associated ILDs, sarcoidosis and hypersensitivity pneumonitis. We also provide insights into the future direction of research in this complex field.

Pharmacogenetics of Drug Therapies in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic systemic inflammatory disorder that can lead to severe joint damage and is often associated with a high morbidity and disability. Disease-modifying anti-rheumatic drugs (DMARDs) are the mainstay of treatment in RA. DMARDs not only relieve the clinical signs and symptoms of RA but also inhibit the radiographic progression of disease and reduce the effects of chronic systemic inflammation. Since the introduction of biologic DMARDs in the late 1990s, the therapeutic range of options for the management of RA has significantly expanded. However, patients' response to these agents is not uniform with considerable variability in both efficacy and toxicity. There are no reliable means of predicting an individual patient's response to a given DMARD prior to initiation of therapy. In this chapter, the current published literature on the pharmacogenetics of traditional DMARDS and the newer biologic DMARDs in RA is highlighted. Pharmacogenetics may help individualize drug therapy in patients with RA by providing reliable biomarkers to predict medication toxicity and efficacy.

Role of Pharmacogenomics in Kidney Disease and Injury

There has been considerable excitement in the kidney community surrounding the research findings on the genetic contributions to kidney diseases. However, positive outcomes of personalized therapeutic interventions can be circumvented by unpredictable pharmacokinetics of prescribed drugs. Furthermore, unpredictable drug disposition can result in toxicities such as kidney injury. Patient covariates, disease covariates, and pharmacogenetics all contribute to variability in drug disposition. Further treatment personalization and avoidance of drug- and biologic- induced kidney injury will require extensive knowledge and expertise in renal clinical pharmacology. The current review will focus on the pharmacogenetics of drugs and biologics used in the treatment of glomerular kidney diseases and drugs implicated in inducing kidney injury phenotypes.

Pharmacogenetics in rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic inflammatory arthritis leading to severe joint damage and associated with high morbidity and mortality. Disease-modifying antirheumatic drugs (DMARDs) are the mainstay of treatment in RA. DMARDs not only relieve the clinical signs and symptoms of RA but also inhibit the radiographic progression of disease. In the last decade, a new class of disease-modifying medications, the biologic agents, has been added to the existing spectrum of DMARDs in RA. However, patients' response to these agents is not uniform with considerable variability in both efficacy and toxicity. There are no reliable means of predicting an individual patient's response to a given DMARD prior to initiation of therapy. In this chapter, the current published literature on the pharmacogenetics of traditional DMARDS and the newer biologic DMARDs in RA is highlighted. Pharmacogenetics may help individualize drug therapy in patients with RA in the near future.

Genetic polymorphisms of NQO1, CYP1A1 and TPMT and susceptibility to acute lymphoblastic leukemia in a Tunisian population

Acute lymphoblastic leukemia (ALL) is the major pediatric cancer in developed countries. The etiology of ALL remains poorly understood, with few established environmental risk factors. These risks were influenced by co-inheritance of multiple low-risk genetic polymorphisms such as variants within cytochrome P450A1 (CYP1A1), NADPH: quinone oxidoreductase (NQO1) and Thiopurine methyltransferase (TPMT) genes. In this work, we conduct a case-control study to assess the impact of CYP1A1*2A (CYP1A1 T6235C); NQO1*2 (NQO1 C609T); TPMT*2 (TPMT G238C) and TPMT A719G polymorphisms on the risk of developing ALL. The frequencies of TPMT*2, TPMT A719G, NQO1*2 and CYP1A1*2 variants were examined in 100 patients with ALL and 106 healthy controls by allele specific PCR and/or PCR-RFLP methods using blood samples. We have found that NQO1 609CT genotype was overrepresented in patients and was associated with an aggravating effect compared to the reference group with NQO1 609CC genotype (p = 0.028, OR = 1.41; CI 95 %: 1.04-1.93). However, TPMT*2, TPMT 719*G and CYP1A1*2 variants did not appear to influence ALL susceptibility (p > 0.05). Moreover we have not found a significant correlation between the studied variants and Bcr-Abl transcript. In conclusion we retain that leukemogenesis of ALL is associated with carcinogens metabolism and consequently related to environmental exposures.

The pharmacogenetic basis of individual variation in thiopurine metabolism

Thiopurines are an important class of immunosuppressive therapy, which have been used in clinical practice for over 50 years. Despite this extensive experience many of the pharmacodynamic and pharmacokinetic properties of these drugs remain unknown. As a consequence there is often no clear explanation for the individual variation in response to treatment, both in terms of efficacy or adverse drug reactions. This review, which emphasizes practice in gastroenterology, summarizes the current understanding of thiopurine drug metabolism and highlights the role of nongenetic and genetic factors other than TPMT, which should be a focus for future research. Correlation of polymorphic variations in these genes with clinical outcomes is expected to clarify the basis for interindividual differences in thiopurine metabolism and enable a more personalized approach to therapy.

Pharmacogenetics: implications for therapy in rheumatic diseases

DMARDs not only improve the joint pain and swelling associated with rheumatoid arthritis (RA), but also slow down the joint damage associated with the disease. The efficacy of biologic therapies, introduced in the past decade for the treatment of RA, has been unequivocally established. Similarly, in addition to traditional drugs such as hydroxychloroquine, new biologic agents such as rituximab have been introduced for systemic lupus erythematosus in recent years. However, considerable variability occurs in the responses of patients to these therapies. Pharmacogenetics, the study of variations in genes encoding drug transporters, drug-metabolizing enzymes and drug targets, and their translation to differential responses to drugs, is a rapidly progressing field in rheumatology. Pharmacogenetic applications, particularly to the old vanguard DMARD, methotrexate, and the newer, more expensive biologic agents, might make personalized therapy in rheumatic diseases possible. The pharmacogenetics of commonly used DMARDs and of biologic therapies are described in this Review.

A pragmatic randomized controlled trial of thiopurine methyltransferase genotyping prior to azathioprine treatment: the TARGET study

AIM

To conduct a pragmatic, randomized controlled trial to assess whether thiopurine methyltransferase (TPMT) genotyping prior to azathioprine reduces adverse drug reactions (ADRs).

METHODS

A total of 333 participants were randomized 1:1 to undergo TPMT genotyping prior to azathioprine or to commence treatment without genotyping.

RESULTS

There was no difference in the primary outcome of stopping azathioprine due to an adverse reaction (ADR, p = 0.59) between the two study arms. ADRs were more common in older patients (p = 0.01). There was no increase in stopping azathioprine due to ADRs in TPMT heterozygotes compared with wild-type individuals. The single individual with TPMT variant homozygosity experienced severe neutropenia.

CONCLUSION

Our work supports the strong evidence that individuals with TPMT variant homozygosity are at high risk of severe neutropenia, whereas TPMT heterozygotes are not at increased risk of ADRs at standard doses of azathioprine.

Are patients with intermediate TPMT activity at increased risk of myelosuppression when taking thiopurine medications?

Thiopurine S-methyltransferase (TPMT) metabolizes thiopurine medications, including azathioprine and 6-mercaptopurine. Absent TPMT activity (i.e., in individuals homozygous for a variant TPMT allele) is associated with an increased risk of myelosuppression in patients taking thiopurine drugs. However, it is not clear if there is also an increased risk for patients with intermediate TPMT activity (i.e., in individuals heterozygous for a variant TPMT allele).

AIMS

To quantify the increased risk of myelosuppression for patients with intermediate TPMT activity.

MATERIALS & METHODS

A systematic review identified published studies, up to 29 September 2008, that explored the relationship between TMPT and hematological adverse drug reactions to thiopurines. Following a critical appraisal of the quality of published studies, a meta-analysis calculated the odds ratio of myelosuppression for patients with intermediate TPMT activity compared with wild-type.

RESULTS

A total of 67 studies were identified, the majority retrospective cohort in design. Patients with two TPMT variant alleles who are TPMT deficient have a substantial increase in their risk of myelotoxicity (86% of deficient patients developed myelosuppression). The increase in odds ratio of developing leukopenia for patients with intermediate TPMT activity or one TPMT variant allele compared with wild-type was 4.19 (95% CI: 3.20-5.48).

CONCLUSION

This meta-analysis suggests that individuals with both intermediate and absent TPMT activity have an increased risk of developing thiopurine-induced myelosuppression, compared with individuals with normal activity. However, there is significant variability in the quality of the reported studies and large prospective studies to clarify the size of the effect of TPMT variant alleles on the risk of myelosuppression should be conducted. Accurate risk assessments will provide important data to inform clinical guidelines.

Pharmacogenomics in the treatment of inflammatory bowel disease

In recent years, the benefits of early aggressive treatment paradigms for inflammatory bowel disease have emerged. Symptomatic improvement is no longer considered adequate; instead, the aim of treatment has become mucosal healing and altered natural history. Nonetheless, we still fail to achieve these end points in a large number of our patients. There are many reasons why patients fail to respond or develop toxicity when exposed to drugs used for inflammatory bowel disease, but genetic variation is likely to account for a significant proportion of this. Some examples, notably thiopurine methyltransferase polymorphism in thiopurine treatment, are already established in clinical practice. We present a review of the expanding literature in this field, highlighting many interesting developments in pharmacogenomics applied to inflammatory bowel disease and, where possible, providing guidance on the translation of these developments into clinical practice.

Thiopurines: factors influencing toxicity and response

Thiopurines are the backbone of current anti-leukemia regimens and have also been effective immunosuppressive agents for the past half a century. Extensive research on their mechanism of action has been undertaken, yet many issues remain to be addressed to resolve unexplained cases of thiopurine toxicity or treatment failure. The aim of this review is to summarize current knowledge of the mechanism of thiopurine action in experimental models and put into context with clinical observations. Clear understanding of their metabolism will contribute to maximizing efficacy and minimizing toxicity by individually tailoring therapy according to the expression profile of relevant factors involved in thiopurine activation pathway.

Novel pharmacogenetic markers for treatment outcome in azathioprine-treated inflammatory bowel disease

BACKGROUND

Azathioprine (AZA) pharmacogenetics are complex and much studied. Genetic polymorphism in TPMT is known to influence treatment outcome. Xanthine oxidase/dehydrogenase (XDH) and aldehyde oxidase (AO) compete with TPMT to inactivate AZA.

AIM

To assess whether genetic polymorphism in AOX1, XDH and MOCOS (the product of which activates the essential cofactor for AO and XDH) is associated with AZA treatment outcome in IBD.

METHODS

Real-time PCR was conducted for a panel of single nucleotide polymorphism (SNPs) in AOX1, XDH and MOCOS using TaqMan SNP genotyping assays in a prospective cohort of 192 patients receiving AZA for IBD.

RESULTS

Single nucleotide polymorphism AOX1 c.3404A > G (Asn1135Ser, rs55754655) predicted lack of AZA response (P = 0.035, OR 2.54, 95%CI 1.06-6.13) and when combined with TPMT activity, this information allowed stratification of a patient's chance of AZA response, ranging from 86% in patients where both markers were favourable to 33% where they were unfavourable (P < 0.0001). We also demonstrated a weak protective effect against adverse drug reactions (ADRs) from SNPs XDH c.837C > T (P = 0.048, OR 0.23, 95% CI 0.05-1.05) and MOCOS c.2107A > C, (P = 0.058 in recessive model, OR 0.64, 95%CI 0.36-1.15), which was stronger where they coincided (P = 0.019).

CONCLUSION

These findings have important implications for clinical practice and our understanding of AZA metabolism.

Thiopurine-induced myelotoxicity in patients with inflammatory bowel disease: a review

AIM

Probably, the most important and potentially lethal adverse event of azathioprine (AZA) and mercaptopurine (MP) is myelosuppression. Our aim was to conduct a review of AZA/MP-induced myelotoxicity in inflammatory bowel disease (IBD) patients.

METHODS

Bibliographical searches were performed in MEDLINE/EMBASE. The studies evaluating thiopurine-induced myelotoxicity in patients with IBD were reviewed. The cumulative incidence and the incidence rate of AZA/MP-induced myelotoxicity were calculated by a meta-analysis.

RESULTS

In total, 66 studies (8,302 patients) were included. The cumulative incidence of AZA/MP-induced myelotoxicity was 7% (95% confidence interval [CI] 6-8%). The incidence rate (per patient and year of treatment) of the drug-induced myelotoxicity was 3% (95% CI 3-4%). The risk was roughly similar with AZA and with MP (7%vs 9%). The duration of AZA/MP treatment in patients with myelotoxicity ranged from 12 days to 27 yr. The cumulative incidence of infections among AZA/MP-induced myelotoxicity patients was 6.5%. The cumulative incidence of severe myelotoxicity was 1.1% (incidence rate 0.9%). Three deaths were reported due to myelotoxicity (cumulative incidence 0.06%, 95% CI 0.02-0.17%). The risk of death among patients who developed myelotoxicity was 0.94% (95% CI 0.32-2.70%).

CONCLUSION

The incidence rate of myelotoxicity in IBD patients receiving AZA/MP is approximately 3% per patient and year of treatment. Although bone marrow toxicity may develop at any time after starting the therapy, this happens more frequently during the first months. The incidence rate of severe myelotoxicity is less than 1% per patient and year of treatment, and the mortality risk is less than 0.1% (which means that the risk of death among IBD patients who develop myelotoxicity is approximately 1%).

The haemotoxicity of azathioprine in repeat dose studies in the female CD-1 mouse

Azathioprine (AZA) is a cytotoxic immunosuppressive drug used in the prevention of rejection in organ transplants and the treatment of auto-immune diseases. However, AZA is haemotoxic causing significant bone marrow depression. The present studies were to characterize the haemotoxicity of AZA in the female CD-1 mouse. In Experiment 1, a dose-ranging study, with AZA gavaged daily for 10 days, clinical evidence of toxicity was evident at 125 mg/kg and above. Experiment 2 was a dose-response study with AZA gavaged daily for 10 days at 40-120 mg/kg. At day 1 after the final dose, AZA induced a dose-related pancytopaenia, reduced femoral marrow cellularity, increases in serum levels of the cytokine fms-like tyrosine kinase 3 ligand, reduction in granulocyte-monocyte colony-forming units and erythroid colonies, and increased bone marrow apoptosis. Histology demonstrated hepatocyte hypertrophy, thymic atrophy, reduced splenic extramedullary haemopoiesis, and reduced cellularity of sternal bone marrow. In Experiment 3, AZA was dosed for 10 days at 100 mg/kg with autopsies at 1, 3, 9, 22, 29, 43 and 57 days postdosing. At 1, 3 and 9 days, haematological parameters reflected changes in Experiment 2. At 22/29 days, many blood parameters were returning towards normal; at 43/57 days, most parameters compared with controls. However, there was some evidence of a persistent (i.e. residual/late-stage) mild reduction in RBC and erythroid progenitor cell counts at day 43/57. We conclude that the CD-1 mouse provides an acceptable model for the haemotoxicity of AZA in man.

Pharmacogenomics in rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic inflammatory arthritis that leads to severe joint damage and is associated with high morbidity and mortality. Disease-modifying antirheumatic drugs (DMARDs) are the mainstay of treatment in RA. DMARDs not only relieve the clinical signs and symptoms of RA but also inhibit the radiographic progression of disease. Recently, a new class of disease-modifying medications, the biologic agents, has been added to the existing spectrum of DMARDs in RA. However, patients' response to these agents is not uniform, with considerable variability in both efficacy and toxicity. There are no reliable means of predicting an individual patient's response to a given DMARD prior to initiation of therapy. In this chapter, the current published literature on the pharmacogenomics of traditional DMARDs and the newer biologic DMARDs in RA is highlighted. Pharmacogenomics may help individualize drug therapy in patients with RA in the near future.

[Monitoring of thiopurine methyltransferase and thiopurine metabolites to optimize azathioprine therapy in inflammatory bowel disease]

Determination of the activity of thiopurine methyltransferase (TPMT) and of thiopurine metabolites (6-thioguanine and 6-methylmercaptopurine nucleotides) could be useful for individualized monitoring of azathioprine (AZA) and 6-mercaptopurine (6-MP) doses. TPMT activity in the general population follows a trimodal distribution, in which approximately 0.3% of the population is homozygotic for the low-activity allele. A notable correlation has been observed between the low TPMP activity genotype or phenotype and the risk of myelotoxicity. Patients with a high TPMT activity genotype or homozygous phenotype should receive immunosuppressive doses that have clearly been demonstrated to be effective. In contrast, in patients with a low TPMT activity genotype or homozygous phenotype, the use of AZA/6-MP should be contraindicated or only very small doses should be administered. Importantly, TPMP deficiency explains only some cases of myelotoxicity and consequently periodic laboratory testing should be performed in patients receiving AZA/6-MP, even though TPMP function may be normal. Currently, the utility of routine thiopurine metabolite determinations in patients undergoing AZA/6-MP therapy has not been established and this practice should be limited to specific situations such as lack of response to thiopurine therapy or the occurrence of thiopurine-related adverse effects. Randomized trials comparing the routine strategy of AZA/6-MP dosing (based exclusively on the patient's weight) versus individualized monitoring (based on quantification of TPMP activity and/or thiopurine metabolites) are required before definitive conclusions on the most effective alternative can be drawn.

Role of 5'-nucleotidase in thiopurine metabolism: enzyme kinetic profile and association with thio-GMP levels in patients with acute lymphoblastic leukemia during 6-mercaptopurine treatment

Thiopurines are used for treatment of several diseases. Cytotoxicity is caused by the derived compounds 6-thioguanine nucleotides (TGNs) and methyl-6-thioinosine monophosphate (methylthio-IMP). The 6-thiopurine mononucleotides 6-thio-IMP (thio-IMP), 6-thio-GMP (thio-GMP) and methylthio-IMP can be catabolized by purine 5'-nucleotidase. It has been shown that the various 5'-nucleotidases are key enzymes for (6-thio)-purine metabolism. We aimed to investigate whether the overall 5'-nucleotidase (5'NT) activity is correlated with the efficacy and toxicity of 6-thiopurine nucleotides. Substrate affinity of 5'NT for IMP, GMP, AMP, thio-IMP, thio-GMP and methylthio-IMP was studied in human lymphocytes. For each of the substrates, the pH for optimal overall enzyme activity has been determined at a pH range between 6 and 10. At the optimal pH, assays were performed to establish Km and Vmax values. Optimal pH values for the various substrates were between 7 and 8.5. Km values ranged from 33 to 109 microM, Vmax ranged from 3.99 to 19.5 nmol/10(6) peripheral mononuclear cells (pMNC) h, and Vmax/Km ratios ranged from 105 to 250. The results did not show a distinct preference of 5'NT activity for any of the tested thiopurine nucleotides. The enzyme kinetic studies furthermore revealed substrate inhibition by thio-IMP and thio-GMP as a substrate. Inhibition by thio-GMP also seems to occur in patients treated with 6-mercaptopurine (6 MP); subsequently, this may lead to toxicity in these patients.

Genotyping of Thiopurine Methyltransferase Using Pyrosequencing

Thiopurine methyltransferase (TPMT) metabolizes thiopurine drugs which are used in the treatment of leukemia and some autoimmune diseases. Previously, 11 mutant alleles of TPMT gene (TPMT*1S, *2, *3A, *3B, *3C, *3D, *4, *5, *6, *7, and *8) have been reported. These mutant alleles may cause life-threatening toxicity in patients exposed to thiopurine drugs, 6-mercaptopurine and azathioprine. We have developed a rapid and accurate protocol for TPMT genotype determination using Pyrosequencing(TM) technology in 96 Japanese subjects. Five fragments of the TPMT gene (exon 4, 5, 7, 8, 10) were amplified by PCR, and the 10 single-nucleotide polymorphisms (SNPs) for TPMT*1S, *2, *3A, *3B, *3C, *3D, *4, *5, *6, *7, and *8 were sequenced. The results of this pyrosequencing method corresponded exactly with those of the DNA sequencing method using BigDye terminator chemistry. We have demonstrated that typing of 10 SNPs can be performed within 30 min. Pyrosequencing has a wide application in the large-scale identification of individual TPMT genotypes.

Clinical utility of thiopurine S-methyltransferase genotyping

Thiopurine S-methyltransferase (TPMT) is a cytosolic enzyme that plays a major role in the metabolism of thiopurine drugs such as mercaptopurine and azathioprine. The interindividual differences in response to thiopurine administration is in part due to the presence of genetic polymorphisms in the gene that regulates TPMT activity. TPMT genotype correlates well with the in vivo enzyme activity within erythrocytes. Patients with genetically determined decreased TPMT activity develop severe myelosuppression when treated with standard doses of thiopurine drugs because an excess of thioguanine nucleotides accumulates in hematopoietic tissues. TPMT genotyping provides clinicians with a reliable method for identifying TPMT-deficient patients who can benefit from low doses of thiopurine drugs in order to reduce the risk of developing adverse effects. Moreover, the administration of higher doses of the drug could improve therapeutic response in patients in whom the TPMT genotyping demonstrates the absence of mutated alleles.

RT-PCR permits simultaneous genotyping of thiopurine S-methyltransferase allelic variants by multiplex induced heteroduplex analysis

Thiopurine-based drugs are a widely prescribed group of medications. Their tolerance and effectiveness is dependent on an individual's ability to metabolize these compounds. An essential enzyme for the metabolism of these drugs is thiopurine S-methyltransferase (TPMT), whose activity is subject to genetic variation. Genotyping of the most frequent allelic variants in TPMT affords an extremely accurate prediction of the three clinical phenotypes: high, intermediate, and low enzyme activity. One constraint of most genotyping methods is the inability to demonstrate physical linkage between two sequence variants that occur in different exons, e.g., c.460G>A and c.719A>G, which give rise to TPMT*3, the most common defective allele in Caucasian populations. Using mRNA/cDNA as a template enables analysis of both sequence variants in a single assay. This approach could be applicable to other genes where allelic variation (in-cis and in-trans) is due to alterations in different exons. Induced heteroduplex generator analysis has previously been shown to discriminate in-cis and has also been suitable for multiplexing. In this method we have exploited both these features and for the first time have applied them to a RT-PCR analysis. The primary reagent developed allows unequivocal resolution of TPMT*3A and the alleles carrying the c.719A>G allelic variant, TPMT*3C, as well as the silent alteration c.474T>C. The TPMT*3B variant has not been observed. A secondary reagent, which can be multiplexed, identifies the TPMT*2 allele.

[Thiopurine methyltransferase activity and myelosuppression in inflammatory bowel disease patients treated with azathioprine and 6-mercaptopurine]

BACKGROUND AND OBJECTIVE

We aimed at assessing whether there exists a relationship between thiopurine methyltransferase (TPMT) activity and the incidence of adverse events, especially myelotoxicity, in patients with inflammatory bowel disease treated with azathioprine (AZA) or 6-mercaptopurine (6-MP).

PATIENTS AND METHOD

By means of a radiochemical method, we determined the TPMT activity in erythrocytes of patients with inflammatory bowel disease who had received previously or at the time of the study AZA or 6-MP (n = 97). A group of 37 patients who had never been treated with these drugs was included. We studied the relationship between several variables and TPMT values as well as their correlation with adverse events.

RESULTS

Mean (SD) TPMT value was 20.8 (5) U/ml erythrocytes (from 7.8 to 32.7). There was no patient with low TPMT levels (< 5); 9% patients had intermediate levels (from 5 to 13.7 U/ml), while 91% displayed high levels (>= 13.8 U/ml). There were no differences when comparing TPMT values according to several variables such as age, gender, tobacco consumption, weight, type of inflammatory bowel disease, and treatment with 5-aminosalicylates, steroids or AZA/6-MP. Side effects were seen in 13 out of 97 (13%) patients administered AZA/6-MP. None patient with side effects exhibited low TPMT levels (< 5 U/ml), nor even intermediate levels (5-13.7 U/ml). There were no differences when comparing mean TPMT values in patients with side effects and in those without side effects.

CONCLUSIONS

In this study, the usefulness of the determination of the TPMT activity to identify patients with inflammatory bowel disease at risk of myelotoxicity due to AZA or 6-MP has not been confirmed. Therefore, even when the TPMT enzymatic activity is normal, it is necessary to continue performing the periodic laboratory analysis.

Purine enzymes in patients with rheumatoid arthritis treated with methotrexate

OBJECTIVES

To study (a) purine metabolism during treatment with methotrexate (MTX) in patients with rheumatoid arthritis (RA) and (b) the relation of purine metabolism with efficacy and toxicity of MTX treatment.

METHODS

One hundred and three patients with active RA who started treatment with MTX were included. The initial MTX dosage was 7.5 mg/week and raised to a maximum of 25 mg weekly if necessary. The purine enzymes 5'-nucleotidase (5'NT), purine-nucleoside-phosphorylase (PNP), hypoxanthine-guanine-phosphoribosyltransferase (HGPRT), and adenosine-deaminase (ADA) were measured before the start, after six weeks, and after 48 weeks or at study withdrawal. The laboratory results were related to measures of efficacy and toxicity of MTX treatment.

RESULTS

Baseline values of 5'NT and PNP (16.9 and 206.8 nmol/10(6) mononuclear cells/h, respectively) were similar to those in former studies. Activities of HGPRT and ADA were relatively low at the start (8.7 and 80.3 nmol/10(6) mononuclear cells/h, respectively). After six weeks purine enzyme activities showed no important changes from baseline. After 48 weeks of MTX treatment a decrease of the enzyme activities of ADA (-21.6 nmol/10(6) mononuclear cells/h; 95% CI -28.6 to -14.7), PNP (-78.9 nmol/10(6) mononuclear cells/h; 95% CI -109.0 to -48.7), and HGPRT (-2.0 nmol/10(6) mononuclear cells/h; 95% CI -3.1 to -0.9) was found. No association was shown between the enzyme activities of ADA, PNP, and HGPRT, and the efficacy or toxicity of MTX treatment. In contrast, enzyme activity of 5'NT showed a decrease in the subgroup of patients discontinuing MTX treatment because of hepatotoxicity.

CONCLUSION

MTX treatment in patients with RA leads to a significant decrease of the purine enzyme activities of ADA, PNP, and HGPRT that is not related to the anti-inflammatory efficacy or toxicity of MTX. Hepatotoxicity was related to a decrease in the enzyme activity of 5'NT. These changes may be explained by direct or indirect (via purine de novo and salvage metabolism and the homocysteine pathway) effects of MTX.

Allelic variants of the thiopurine S-methyltransferase deficiency in patients with ulcerative colitis and in healthy controls

OBJECTIVE

Thiopurine S-methyltransferase (TPMT) is a cytosolic enzyme that catalyzes the inactivation of mercaptopurine, azathioprine, and thioguanine. The genetic polymorphisms in the TPMT gene that regulate TPMT activity are inherited as an autosomal recessive trait and patients with genetically determined low levels of TPMT activity develop severe myelosuppression when treated with standard doses of the above-mentioned drugs. We have analyzed the frequencies of the allelic variants of the TPMT gene in a white European population of healthy blood donors from Spain and The Netherlands, and in a group of patients suffering from ulcerative colitis (UC) with a similar genetic background.

METHODS

Two hundred and thirteen unrelated healthy individuals (HC) and 146 UC patients were typed for the polymorphic sites at positions 460 (G-->A) and 719 (A-->G) of the TPMT gene using specific polymerase chain reaction-restriction fragment-length polymorphism (PCR-RFLP) methods.

RESULTS

There were no significant differences between the allele frequencies observed in the group of UC patients and those of the control group (10% of cases were heterozygous carriers of a TPMT mutant allele). The most frequent mutant allele in both UC and HC groups was TPMT3A (A460-->G719) (60% of carriers). TPMT3B (A460-->A719) and TPMT3C (G460-->G719) alleles were more often found in our study than in previously reported studies, reflecting the different genetic backgrounds of the European populations analyzed.

CONCLUSIONS

Genotyping methods provide a simple and reliable screening to identify patients with a high risk of developing severe bone marrow toxicity if treated with thiopurine drugs. In UC patients, TPMT genotype should be determined before the initiation of azathioprine therapy.

Methylation pharmacogenetics: catechol O-methyltransferase, thiopurine methyltransferase, and histamine N-methyltransferase

Methyl conjugation is an important pathway in the biotransformation of many exogenous and endogenous compounds. Pharmacogenetic studies of methyltransferase enzymes have resulted in the identification and characterization of functionally important common genetic polymorphisms for catechol O-methyltransferase, thiopurine methyltransferase, and histamine N-methyltransferase. In recent years, characterization of these genetic polymorphisms has been extended to include the cloning of cDNAs and genes, as well as a determination of the molecular basis for the effects of inheritance on these methyltransferase enzymes. The thiopurine methyltransferase genetic polymorphism is responsible for clinically significant individual variations in the toxicity and therapeutic efficacy of thiopurine drugs such as 6-mercaptopurine. Phenotyping for the thiopurine methyltransferase genetic polymorphism represents one of the first examples in which testing for a pharmacogenetic variant has entered standard clinical practice. The full functional implications of pharmacogenetic variation in the activities of catechol O-methyltransferase and histamine N-methyltransferase remain to be determined. Finally, experimental strategies used to study methylation pharmacogenetics illustrate the rapid evolution of biochemical, pharmacologic, molecular, and genomic approaches that have been used to determine the role of inheritance in variation in drug metabolism, effect, and toxicity.

Methotrexate in rheumatoid arthritis: an update with focus on mechanisms involved in toxicity

OBJECTIVES

To provide an update of the current knowledge of the mechanism of action of low-dose methotrexate (MTX) in the treatment of patients with rheumatoid arthritis (RA), with an emphasis on the mechanisms involved in toxicity. We also considered strategies currently used to prevent or decrease toxicity of MTX.

METHODS

We reviewed the literature dealing with the subjects of MTX treatment of RA, the mechanisms of action of low-dose MTX regarding efficacy and toxicity, and strategies used to prevent or decrease MTX toxicity.

RESULTS

MTX is a fast working and effective second-line antirheumatic agent (SLA). Its use is limited mainly because of side effects. The mechanisms of action regarding efficacy and toxicity are probably determined by different metabolic pathways. Recent data indicate that the antiinflammatory effect of MTX is mediated by adenosine. However, MTX side effects can only partly be explained by folate antagonism and may also depend on its action on other related metabolic pathways. The latter include the homocysteine-methionine-polyamine pathway and purine metabolism. Variants in these metabolic routes (ie, the C677T mutation in the methylene-tetrahydrofolate reductase [MTHFR] gene), may predispose to the development of side effects. Currently the most promising strategy to decrease or prevent toxicity of MTX is concomitant prescription of folic acid or folinic acid. Other strategies are currently under investigation.

CONCLUSIONS

MTX benefits a majority of RA patients. Approximately 30% of patients, however, abandon treatment because of drug-related side effects. Folic acid or folinic acid likely reduces MTX toxicity. More data, however, are needed to evaluate a potential detrimental effect on the antirheumatic efficacy of MTX.

Steroid-sparing alternative treatments for sarcoidosis

Alternatives to corticosteroids for the treatment of sarcoidosis are reviewed. These include cytotoxic agents such as methotrexate, azathioprine, and cyclophosphamide. In addition, agents such as hydroxychloroquine and cyclosporine are reviewed. The efficacy, toxicity, and timing of these drugs in the management of sarcoidosis is discussed.

Azathioprine-induced severe pancytopenia due to a homozygous two-point mutation of the thiopurine methyltransferase gene in a patient with juvenile HLA-B27-associated spondylarthritis

Severe pancytopenia due to azathioprine (AZA) toxicity in patients with autoimmune diseases is not uncommon. We describe a 14-year-old girl with HLA-B27+ spondylarthritis who was treated with AZA 3 mg/kg/day and who suddenly developed severe pancytopenia in the seventh week of treatment. Analysis of the catabolic pathway of AZA revealed a homozygous deficiency of thiopurine methyltransferase (TPMT) on the basis of a combined 2-point mutation at nucleotide positions 460 and 719 in the gene for TPMT, causing a toxic level of the metabolic active 6-thioguanine nucleotides (6-TGN) (2,394 pmoles/8 x 10(8) red blood cells). The patient was transfusion dependent and finally recovered 8 weeks after the development of the pancytopenia. At that time, 6-TGN had already returned to normal therapeutic levels. Family studies revealed another homozygous deficiency in the mother, while the other family members were heterozygous.

Hematologic complications of rheumatic disease therapies

Hematologic side effects of rheumatic disease therapies are generally mild and reversible; however, the clinician must be alert for potential profound and life-threatening toxicities. A knowledge of the toxicity patterns for the individual drugs is necessary to anticipate potential complications. Management of acute leukemias and lymphomas arising in patients with connective tissue disorders is particularly challenging. Further data are needed to define the best treatment options and thus enrollment in clinical trials is encouraged for these patients.

Immunosuppressant therapy during gestation

Use of immunosuppressants during pregnancy is indicated for anti-rejection therapy in transplantation patients and treatment of autoimmune diseases. Maternal side effects include nephrotoxocity and hepatotoxicity. All immunosuppressant drugs cross the placenta. Immunosuppressant use during the first trimester is not strongly associated with an increased risk of congenital anomalies, although some agents (eg, azathioprine) may be associated with slightly increased frequencies of birth defects. Effects of exposure to this class of drugs during the second and third trimesters affects the fetus' immune system. The result is an infant with a transiently compromised immune system at an increased risk of slightly lower birth weight. Other direct toxic effects of the drugs on the infant's pancreas, liver, and lymphocytes are reported. Certain agents (eg, penicillamine, chloroquine) should be avoided during pregnancy, if possible. However, their use cannot be discontinued during pregnancy given the life-threatening nature of the indication for use of immunosuppressants.

Purine enzyme activities in recent onset rheumatoid arthritis: are there differences between patients and healthy controls?

OBJECTIVE

Purine enzyme activities may predict the effectiveness of azathioprine treatment and be associated with increased deaths from infectious diseases. In rheumatoid arthritis, patients show variable responses to azathioprine and a higher percentage of death is caused by infections. The aim of the study was to investigate possible rheumatoid arthritis associated abnormalities of purine enzyme activities by measuring several of these enzymes in patients with recent onset rheumatoid arthritis before treatment with disease modifying antirheumatic drugs or prednisone.

METHODS

23 patients with recent onset rheumatoid arthritis and 28 healthy controls were studied. Activities of the enzymes 5'-nucleotidase, purine nucleoside phosphorylase (PNP), hypoxanthine guanine phosphoribosyltransferase (HGPRT), and thiopurine methyltransferase (TPMT) were measured. Assessment of disease activity and blood sampling for routine measurements and HLA typing were done simultaneously.

RESULTS

Purine enzyme activities did not differ between patients and healthy controls. Enzyme activities had no significant relations with indices of disease activity or rheumatoid factor titre or with the rheumatoid arthritis associated HLA types. Activity of 5'nucleotidase decreased with age (P < or = 0.05) and was lower by about 27% (P = 0.007) in males than in females.

CONCLUSIONS

In rheumatoid arthritis patients, neither the variability in azathioprine effectiveness nor the increased death rate from infections can be explained by pre-existing abnormalities in the activities of the purine enzymes 5'-nucleotidase, PNP, HGPRT, or TPMT at an early stage of the disease, before disease modifying antirheumatic drugs or prednisone treatment. Besides adjustment for age, results of studies involving purine 5' nucleotidase activity should also be adjusted for sex.

Acute febrile toxic reaction in patients with refractory rheumatoid arthritis who are receiving combined therapy with methotrexate and azathioprine

OBJECTIVE

To assess the frequency and clinical features of an acute febrile toxic reaction (AFTR) in patients with refractory rheumatoid arthritis (RA) receiving combined therapy with methotrexate (MTX) and azathioprine (AZA).

METHODS

A cohort of 43 RA patients being treated with MTX/AZA combination therapy were studied. In all of them, RA had been refractory to single-therapy disease-modifying antirheumatic drugs. We analyzed the frequency and clinical features of AFTR, which consisted mainly of the development of fever, leukocytosis, and cutaneous leukocytoclastic vasculitis when AZA was added to the MTX regimen.

RESULTS

Four of the 43 patients (9.3%) who had been receiving long-term, well-tolerated treatment with MTX (mean +/- SD 375.5 +/- 159.5 days, range 227-561 days) developed AFTR shortly (mean +/- SD 25.7 +/- 13.6 days, range 17-46 days) after the addition of AZA to the regimen. The AFTR resolved rapidly (3 +/- 1.4 days) after discontinuation of AZA and MTX. In 2 cases, rechallenge with AZA and MTX was linked to a new flare of AFTR.

CONCLUSION

The knowledge of this side effect is particularly important because it mimics a severe infectious complication related to immunosuppressive therapy, and because rechallenge can produce severe toxicity. Most of the new combined therapies for RA do not seem to be more toxic than single-drug treatment. Nevertheless, clinicians should be aware of a possible increase in side effects due to drug interactions or some other unidentified mechanism.

The use of therapeutic drug monitoring to optimise immunosuppressive therapy

Most experience of the therapeutic drug monitoring of immunosuppressive agents has been acquired in the field of solid organ transplantation; however, agents such as cyclosporin (cyclosporin A) are being increasingly utilised for the management of autoimmune diseases. Cyclosporin is the most widely studied immunosuppressant, but in spite of this many controversies still exist as to the optimum strategy for monitoring this drug. Owing to its widely variable pharmacokinetics and metabolism, and the absence of a simple method to measure therapeutic effectiveness, many factors should be considered. In most circumstances, measuring whole blood through concentrations of cyclosporin with a specific assay methodology is warranted. In addition, knowledge of other factors that may alter the pharmacokinetics (such as liver function, concomitant food or medications, gastrointestinal status, and time since transplantation) should be taken into account so that therapy can be appropriately adjusted. Other methods of monitoring have been investigated, such as AUC (area under the concentration-time curve) monitoring and immunological monitoring. However, further refinement of these techniques and greater experience with their efficacy must be accumulated before their role in the monitoring of cyclosporin can be defined. Tacrolimus, like cyclosporin, shares many of the difficulties in monitoring for efficacy and toxicity due largely to the variable pharmacokinetics; similarly to cyclosporin, whole blood through concentration monitoring should be utilised in combination with knowledge of the factors that may affect the pharmacokinetics. Muromonab CD3 (OKT3) is a monoclonal antibody used for the treatment and prophylaxis of acute allograft rejection. Several immunological monitoring techniques have been investigated for this agent. Monitoring CD3+ levels can assist clinicians in determining therapeutic efficacy, while measuring antimuromonab CD3 antibody titres can help determine if xenosensitisation has occurred, causing therapeutic ineffectiveness. The clinical monitoring of azathioprine, one of the first immunosuppressive agents used in transplantation, has historically been limited to monitoring complete blood counts for bone marrow suppression. However, newer techniques measuring intracellular DNA nucleotides appear to be promising. The new immunosuppressants on the horizon include mycophenolate mofetil and rapamycin. The clinical experience with therapeutic drug monitoring of these 2 compounds is scant in the literature; however, both agents have demonstrated efficacy in preventing or treating allograft rejection while maintaining a relatively well tolerated toxicity profile in recent clinical trials. Routine monitoring does not appear to be warranted for immunosuppressive therapy in autoimmune diseases.