Review article: vitamin D and inflammatory bowel disease--established concepts and future directions

BACKGROUND

Understanding of the role of vitamin D in health and disease has increased markedly in the past decade, with its involvement extending well beyond traditional roles in calcium and phosphate homeostasis and musculoskeletal health. This conceptual expansion has been underpinned by identification and exploration of components of this axis including vitamin D-binding protein, key enzymes and receptors in multiple cell types, and a greater recognition of nonclassical autocrine and paracrine effects. Its influence in IBD remains uncertain.

AIM

To review the role of vitamin D in bone health, immune regulation and cancer prevention in IBD, and to outline practical issues and limitations of its use.

METHODS

An extensive online literature review including PubMed and Medline.

RESULTS

In patients with IBD, the vitamin D axis provides an important and often underutilised pathway to preserving bone health. Furthermore, an exciting body of clinical and basic science research demonstrates that these pathways may have an integral part to play in regulation of the immune response in IBD, through effects on the intestinal barrier, antigen presenting cells and adaptive T cells. The possibility of chemoprevention requires further study. The optimal target level of 25-hydroxy vitamin D in patients with IBD is currently uncertain, as is the best therapeutic modality.

CONCLUSIONS

Study of vitamin D pathways may result in the development of relatively inexpensive therapeutic options to optimise patient outcomes. Further prospective clinical research is required to address efficacy and long-term safety.

Optimizing thiopurine therapy in inflammatory bowel disease

Despite recent advances, the therapeutic armamentarium for inflammatory bowel disease (IBD) is still limited. In addition, a step-up approach is recommended for most IBD patients. Thus, optimizing each medical therapy before switching to another drug class is the rule in clinical practice. Conventional therapies for IBD have not received the same amount of attention as biologic therapies over the last decade. However, due to their efficacy, safety, and low cost the thiopurine drugs azathioprine and 6-mercaptopurine remain the backbone of therapy for IBD. Pharmacogenomic advances and increased knowledge of their metabolism are allowing dosage optimization. Herein, after describing the pharmacogenetics and pharmacokinetics of thiopurines, we will discuss how to optimize thiopurine therapy. We will then underscore the need to take into account safety issues when optimizing thiopurine treatment.

Clinical usefulness of therapeutic drug monitoring of thiopurines in patients with inadequately controlled inflammatory bowel disease

BACKGROUND

Circulating concentrations of 6-thioguanine nucleotide (6-TGN) and 6-methyl mercaptopurine (6-MMP) are associated with thiopurine efficacy and may predict toxicity. This study aimed to examine retrospectively the utility of measuring metabolite concentrations in patients with inflammatory bowel disease (IBD) who had continuing symptoms despite stable thiopurine treatment.

METHODS

Concentrations of 6-TGN and 6-MMP were measured in lysates of washed red cells by high-performance liquid chromatography in peripheral blood drawn from 63 symptomatic patients with IBD (63% men, mean age 37, range 14-74 years, 67% Crohn's disease, 33% ulcerative colitis) treated with azathioprine or 6-mercaptopurine. Short-term clinical outcomes were examined.

RESULTS

6-TGN concentrations weakly correlated with the thiopurine dose (r = 0.28, P = 0.08). On weight-based criteria, 50% of patients were underdosed. However, metabolite patterns suggested 7 (11%) patients were noncompliant, 18 (29%) were being underdosed, 33 (52%) were refractory to treatment with either appropriate (41%) or elevated (11%) metabolite concentrations, and 6 (10%) had a raised 6-MMP:6-TGN ratio consistent with aberrant thiopurine metabolism. The clinical outcome improved in 40 of 46 (87%) of patients in whom the course of action taken was as recommended by a metabolite-directed algorithm, while 3 of 17 patients (18%) improved where discordant actions were taken (P = 0.0001; Fisher's exact test). Fifteen patients (24%) avoided inappropriate escalation of therapy.

CONCLUSIONS

Dose-optimization or toxicity-avoidance strategies frequently result from metabolite testing in patients with inadequate efficacy from thiopurines, with evidence of better outcomes. Thiopurine metabolite testing is a potentially powerful tool for optimizing thiopurine usage in IBD.

Difficulties and possibilities with thiopurine therapy in inflammatory bowel disease--proceedings of the first Thiopurine Task Force meeting

BACKGROUND

Thiopurines, such as azathioprine and mercaptopurine, are of pivotal importance in the treatment of inflammatory bowel disease. Although these drugs have been used for several decades, still many questions remain unanswered.

AIM

To provide an overview of clinically and scientifically challenging topics concerning thiopurine therapy in inflammatory bowel disease treatment.

METHODS

The first meeting of the Thiopurine Task Force Interest Group was held during the 2009 United European Gastroenterology Week in London (GASTRO2009). The topics of this meeting were of particular clinical and scientific interest. Additional literature was identified by performing a Pubmed search using the search terms 'inflammatory bowel disease', 'azathioprine', '6-mercaptopurine' and 'thioguanine'.

RESULTS

The following topics were discussed: therapeutic drug monitoring; the synergy of thiopurines with aminosalicylates and allopurinol; serious adverse events such as opportunistic infections, hepatotoxicity, carcinogenicity and pancreatitis; prolongation of thiopurines during clinical remission; indications for thiopurines in the postoperative setting; and the potential use of thioguanine. Specific interesting and clinically relevant topics for potential future research are provided.

CONCLUSIONS

Thiopurines remain central to inflammatory bowel disease treatment, although future studies are required to substantiate a more personalised medicine approach to their use.

The use of azathioprine in Crohn's disease during pregnancy and in the post-operative setting: a worldwide survey of experts

BACKGROUND

Although thiopurines are considered safe in humans, they are still pregnancy FDA category D drugs. Prevention of post-operative recurrence is a challenge in clinical practice in Crohn's disease. The European Crohn's and Colitis Organisation consensus states that thiopurines should be considered in high-risk patients.

AIM

To perform a worldwide survey for evaluating the extent to which gastroenterologists who are experts in the field of IBD are utilising thiopurines during pregnancy and in the post-operative setting in Crohn's disease.

METHODS

This was a Web-based cross-sectional, statement-based survey, which was conducted among experts who have published at least once in the field of thiopurines in IBD.

RESULTS

Between 20 December 2009 and 9 April 2010, 175 questionnaires were received. The median number of IBD patients per physician per year was 400 (IQR 25-75th, 188-600) and the total number of IBD patients followed by all responders was 82,379. In a pregnant woman with a history of severe Crohn's disease in clinical remission after 1 year on azathioprine, 89% of experts usually continue azathioprine until delivery and 9% of physicians never administer azathioprine during pregnancy. After ileocecal resection for Crohn's disease, 39% of physicians initiate azathioprine only in high-risk patients, 28% of practitioners prescribe azathioprine according to endoscopic evaluation, 20% of gastroenterologists systematically initiate azathioprine and 13% have a different attitude.

CONCLUSIONS

Almost 9 of 10 physicians continue azathioprine throughout pregnancy. About 7 of 10 physicians prescribe azathioprine in the post-operative setting according to the European Crohn's and Colitis Organisation recommendations, whereas one-fifth of practitioners systematically initiate azathioprine after surgery.

The appropriateness of concomitant immunomodulators with anti-tumor necrosis factor agents for Crohn's disease: one size does not fit all

BACKGROUND & AIMS

There is no consensus on the appropriateness of concomitant immunomodulators with anti-tumor necrosis factor (TNF) therapy for Crohn's disease. Some patients benefit from concomitant immunomodulators, but concerns related to infections and lymphoma risk have dampened enthusiasm for this approach. We applied the RAND/University of California Los Angeles Appropriateness Method toward establishing appropriateness of concomitant immunomodulators and anti-TNF therapies for Crohn's disease.

METHODS

A literature review was conducted regarding efficacy and safety of concomitant immunomodulators in the setting of anti-TNF therapy for Crohn's disease and presented to the Building Research in Inflammatory Bowel Disease Globally group, a globally diverse panel of 13 gastroenterologists clinically experienced in inflammatory bowel disease. A total of 134 scenarios were constructed using several clinical variables. Panelists used a modified Delphi method to rate the appropriateness of concomitant immunomodulators, and met to discuss and re-rate appropriateness. Disagreement was assessed using a validated index.

RESULTS

Concomitant immunomodulators were generally rated appropriate for 63 scenarios, uncertain for 60 scenarios, and inappropriate for 11 scenarios. In general, concomitant immunomodulators were appropriate for those with extensive disease, shorter duration of disease, perianal involvement, prior surgery, females, and older patients (>26 y). Concomitant immunomodulators were generally rated inappropriate for young males, and in some scenarios involving uncomplicated disease. Smoking and the particular anti-TNF medication did not influence ratings. Disagreement was observed in 6 of 134 scenarios.

CONCLUSIONS

The appropriateness of concomitant immunomodulators with anti-TNF therapy for Crohn's disease was determined through a modified Delphi panel approach based on expert interpretation of the available literature. Clinicians should consider multiple factors when considering concomitant immunomodulators with anti-TNF treatment.

Optimizing conventional therapies for inflammatory bowel disease

Conventional therapies remain the mainstay of treatment for most patients with inflammatory bowel disease (IBD), with only a minority of patients requiring biologic therapies. Recently, attention has focused on optimizing dosing strategies for biologic agents; however, of equal importance are recent advances in the optimization of conventional IBD therapies. Newer aminosalicylate formulations demonstrate similar efficacy with a reduced pill burden and less frequent dosing, while new corticosteroid preparations may retain efficacy with a significantly improved safety profile. The limited indications for antibiotics and probiotics have been further refined by recent data, although uncertainties remain. Advances in the understanding of thiopurine metabolism continue to improve dose optimization and the potential for deliberate therapeutic manipulation with adjunctive therapies. An improved knowledge of intracellular methotrexate metabolism may translate to similar opportunities in the future. This article discusses recent advances relevant to clinical practice today.

Thiopurines, a previously unrecognised cause for fatigue in patients with inflammatory bowel disease

BACKGROUND

Active inflammatory bowel disease, anaemia, iron deficiency and depression, alone or in combination, are known contributing factors of fatigue in inflammatory bowel disease. However, in some patients, fatigue cannot be attributed to known causes. Thiopurines are not a recognized cause.

AIM

To describe the clinical scenario of a series of patients where thiopurines were the likely cause of fatigue.

METHOD

The clinical scenario of 5 patients was examined with specific reference to the temporal association of thiopurine therapy with fatigue, the effect of its withdrawal and rechallenge, and drug specificity.

RESULTS

The onset of severe fatigue was related to the introduction of azathioprine or 6-mercaptopurine, rapid relief was experienced on its withdrawal in all patients, and fatigue rapidly occurred on rechallenge. The speed of onset was rapid in two patients and in the context of gradual withdrawal of moderate steroid dose, but recurred rapidly on rechallenge when not on steroids.

CONCLUSIONS

Marked fatigue is a previously unrecognized adverse effect of thiopurines. It does not appear to be drug-specific. Its onset might be masked by concurrent steroid therapy.

Long term efficacy and safety of allopurinol and azathioprine or 6-mercaptopurine in patients with inflammatory bowel disease

BACKGROUND AND AIMS

We previously reported that IBD patients who are non-responders to thiopurines with preferential shunting of metabolites to hepatotoxic 6-methylmercaptopurine ribonucleotides compared to 6-thioguanine nucleotides can reverse the ratio of 6-MMP/6-TGN and respond to thiopurines with the addition of allopurinol. The objective of this study is to report long term efficacy and safety, along with results for an additional 11 patients.

METHODS

Retrospective chart review of patients at the University of Chicago IBD Center treated with allopurinol in addition to thiopurines.

RESULTS

Twenty five patients with Crohn's disease or ulcerative colitis were enrolled. Within the first month of therapy 6-TGN metabolite levels increased from a mean of 186.5±17.4 (SE) to 352.8±37.8 pmol/8×10(8) (p=0.0001). Over the same period 6-MMP levels decreased from a mean of 11,966±1697 to 2004±536 pmol/8×10(8) (p<0.0001). The mean daily dosage of prednisone decreased from 19.8±3.8 mg to 5.3±2.7 mg (p=0.03). Thirteen patients have a minimum of one year follow-up. Nine of these thirteen patients have continued on therapy for at least 2 years. All thirteen of these patients continue to be in clinical remission at the last follow-up visit. No patients have had evidence of sustained thrombocytopenia or abnormal liver enzymes.

CONCLUSIONS

In AZA/6-MP non-responders with increased 6-MMP/6-TGN ratios, addition of allopurinol continues to demonstrate safety and efficacy for long-term maintenance and steroid-sparing in IBD.

Thiopurine hepatotoxicity in inflammatory bowel disease: the role for adding allopurinol

BACKGROUND

Immunomodulator therapy with the thiopurine analogues azathioprine or 6-mercaptopurine is commonly prescribed for the treatment of inflammatory bowel disease (IBD). Drug adverse effects and the lack of efficacy, however, commonly require withdrawal of therapy. Allopurinol, a xanthine oxidase inhibitor, was recently evaluated in its role in modifying thiopurine metabolism and improving drug efficacy in IBD.

OBJECTIVE

This article reviews the role and safety of allopurinol co-therapy in the setting of thiopurine hepatotoxicity and/or non-responsiveness in IBD.

METHODS

Published articles on thiopurines in the treatment of IBD were examined.

CONCLUSION

The addition of low dose allopurinol to dose-reduced thiopurine analogue seems safe but careful monitoring for adverse effects and profiling of thiopurine metabolites is essential. There is evidence of improved immunomodulator efficacy and reduced hepatotoxicity clinically but further confirmatory studies are required before more definitive treatment recommendations can be given.

Current Controversies in Crohn's Disease: A Roundtable Discussion of the BRIDGe Group

In March 2008, a roundtable discussion was convened by the inflammatory bowel disease (IBD) specialist panel the BRIDGe (Building Resources and Research in IBD Globally) group, which consists of junior faculty gastroenterologists who have undergone advanced fellowship training at IBD referral centers in the United States, Canada, the United Kingdom, and Australia. An agenda was formulated to discuss three current controversies in Crohn's disease management: the role of 5-aminosalicylates, the use of biologic combination therapy versus monotherapy, and the use of step-up therapy versus top-down therapy for Crohn's disease. The aim of the meeting was three-fold: to review the data pertaining to each topic; to collect opinions from the participants as to their analysis of the literature and their current practice; and, where possible, to formulate recommendations of current best practice given the available evidence. This manuscript summarizes the discussions on these three areas of controversy in the current management of Crohn's disease.

Use of allopurinol to optimize thiopurine immunomodulator efficacy in inflammatory bowel disease

The thiopurine immunomodulators azathioprine and 6-mercaptopurine are integral to the management of inflammatory bowel disease (IBD), particularly as corticosteroid-sparing and maintenance agents; however, up to 50% of patients do not adequately respond to these agents. Advances in pharmacogenomics and an increased understanding of thiopurine metabolism have led to the practice of measuring the thiopurine metabolites 6-thioguanine (6-TGN) and 6-methylmercaptopurine (6-MMP) to help achieve optimal immunomodulator dosages. Metabolite profiles are also useful for categorizing the reasons for thiopurine treatment failures. A desirable metabolite profile favors 6-TGN production over 6-MMP formation; however, a significant subgroup of IBD patients, perhaps 15%, preferentially metabolizes thiopurines toward the inefficacious and potentially hepatotoxic metabolite 6-MMP. The xanthine oxidase inhibitor allopurinol has been shown recently to advantageously switch thiopurine metabolism toward 6-TGN production in this subgroup of patients, and small studies have shown this switch to be safe and clinically beneficial. This article reviews evidence describing the use of allopurinol to optimize immunomodulator metabolism, provides careful practice guidelines to clinicians considering this strategy, and briefly discusses the potential mechanisms by which this favorable interaction occurs.

How are Azathioprine and 6-mercaptopurine dosed by gastroenterologists? Results of a survey of clinical practice

BACKGROUND

Azathioprine (AZA) and 6-mercaptopurine (6-MP) are accepted as effective therapy for Crohn's disease and ulcerative colitis. Although general guidelines have been suggested for weight-based dosing of thiopurines, no standard of care has been established. Clinical trials have demonstrated efficacy for weight-based dosing of AZA at 2.5 mg/kg/day and 6-MP at 1.5 mg/kg/day. Escalation of dosing is recommended within 2 weeks of initiating therapy. The aim was to determine the prescribing practices of community practice gastroenterologists with respect to 6-MP/AZA dosing.

METHODS

Questionnaires were distributed via a mail database or during gastroenterology society meetings to gastroenterologists in NY, NJ, and CT. Questionnaires ascertained starting doses of AZA/6-MP, use of thiopurine methyltransferase (TPMT) enzyme testing, and strategy for dose optimization.

RESULTS

A total of 145 questionnaires were collected. Twenty-four percent of gastroenterologists escalated the dose within 2 weeks after initiating therapy. The majority used weight-based dosing as their target of therapy. Thirty-five percent reported measuring TPMT levels and 46% used metabolite monitoring.

CONCLUSIONS

Most gastroenterologists take longer than recommended to raise the dose of AZA/6-MP. Although the majority of gastroenterologists reported maximal dosages based on weight, there may be a delay in achieving this goal. Optimizing dosing of AZA/6-MP may improve efficacy and reduce the need to use additional therapy.

Review article: appropriate use of corticosteroids in Crohn's disease

BACKGROUND

Corticosteroids are a well-established treatment for active Crohn's disease and have been widely used for decades. It has become apparent, however, that a proportion of patients either fails to respond to corticosteroids or is unable to withdraw from them without relapsing. Furthermore, their use is associated with a range of side effects, such that long-term treatment carries unacceptable risk.

AIM

To review the evidence regarding the appropriate use of corticosteroids in Crohn's disease, along with their side effects, safety and alternatives.

METHODS

To collect relevant articles, a PubMed search was performed from 1966 to November 2006 using the terms 'steroid', 'corticosteroid', 'glucocorticoid', 'prednisolone', 'prednisone', 'methylprednisolone', 'hydrocortisone', 'dexamethasone' and 'budesonide' in combination with 'Crohn(s) disease'. Relevant articles were reviewed, as were their reference lists to identify further articles.

RESULTS

When used correctly, corticosteroids are a highly effective, well tolerated, cheap and generally safe treatment for active Crohn' disease. Nevertheless, approximately 50% of recipients will either fail to respond (steroid-resistant) or will be steroid dependent at 1 year. Newer alternatives to corticosteroids are not, however, without risk themselves and, moreover, are not necessarily available universally.

CONCLUSIONS

Steroids are used widely to treat Crohn's disease, a situation that is unlikely to change in the near future. Accordingly, efforts should be made to ensure that they are used correctly and that their side effects are minimized. Reference is made to recently published guidelines and a simplified 'users guide' is presented.

[The role of translational research in inflammatory bowel disease]

The idiopathic inflammatory bowel diseases, broadly classified as either Crohn's disease or ulcerative colitis, are caused by a dysregulated mucosal immune response to a luminal antigen, possibly a bacterium, in a genetically predisposed host. A rapid expansion of knowledge in recent years has greatly increased our understanding of the pathophysiology of these disorders. For example, the relatively recent discovery of the NOD2 gene, a protein involved in bacterial sensing, has provided further evidence of the complex interplay between hosts and microbes in Crohn's disease. Significant recent advances have also occurred with the discovery of the role of Toll-like receptors and dendritic cells in the development of gut inflammation, and the role of proinflammatory cytokines in the development and potentiation of gut inflammation. This article presents an update on these key developments and emphasizes the translational aspects of research that are directly related to patient care.

Effect of allopurinol on clinical outcomes in inflammatory bowel disease nonresponders to azathioprine or 6-mercaptopurine

BACKGROUND & AIMS

Many IBD patients not responding to azathioprine (AZA) or 6-mercaptopurine (6-MP) preferentially metabolize 6-MP to 6-methylmercaptopurine (6-MMP). We describe the use of allopurinol in AZA/6-MP nonresponders to deliberately shunt metabolism of 6-MP toward 6-thioguanine (6-TGN) and improve clinical responses.

METHODS

Twenty outpatients who were AZA/6-MP nonresponders and had high 6-MMP metabolite levels were included. Subjects were commenced on allopurinol 100 mg daily, and the dose of 6-MP/AZA was reduced to 25%-50% of the original dose.

RESULTS

After allopurinol was started, mean 6-TGN levels increased from 191.3 (+/- standard error of the mean) +/- 17.1 to 400.3 +/- 36.9 pmol/8 x 10(8) red blood cells (P < .001), whereas mean 6-MMP levels decreased from 10,604.7 +/- 1278.2 to 2000.6 +/- 437.1 pmol/8 x 10(8) red blood cells (P < .001). The addition of allopurinol led to a reduction in the mean partial Harvey Bradshaw Index in Crohn's disease patients from 4.9 +/- 1.0 to 1.5 +/- 0.3 points (P = .001), and in ulcerative colitis patients mean Mayo Scores decreased from 4.1 +/- 0.7 to 2.9 +/- 0.7 points (P = .13). The addition of allopurinol enabled a reduction in mean daily prednisone dosage from 17.6 +/- 3.9 to 1.8 +/- 0.7 mg (P < .001) and led to normalization of transaminase levels, with mean AST levels reducing from 42.5 +/- 8.1 to 23.5 +/- 1.6 IU (P = .12) and mean ALT levels reducing from 101.6 +/- 26.9 to 33.9 +/- 5.2 IU (P = .01).

CONCLUSIONS

The addition of allopurinol to thiopurine nonresponders with high 6-MMP metabolite levels is an effective and safe means of optimizing 6-TGN production, leading to improved disease activity scores, reduced corticosteroid requirements, and normalization of liver enzymes.

Effect of allopurinol on clinical outcomes in inflammatory bowel disease nonresponders to azathioprine or 6-mercaptopurine

BACKGROUND & AIMS

Many IBD patients not responding to azathioprine (AZA) or 6-mercaptopurine (6-MP) preferentially metabolize 6-MP to 6-methylmercaptopurine (6-MMP). We describe the use of allopurinol in AZA/6-MP nonresponders to deliberately shunt metabolism of 6-MP toward 6-thioguanine (6-TGN) and improve clinical responses.

METHODS

Twenty outpatients who were AZA/6-MP nonresponders and had high 6-MMP metabolite levels were included. Subjects were commenced on allopurinol 100 mg daily, and the dose of 6-MP/AZA was reduced to 25%-50% of the original dose.

RESULTS

After allopurinol was started, mean 6-TGN levels increased from 191.3 (+/- standard error of the mean) +/- 17.1 to 400.3 +/- 36.9 pmol/8 x 10(8) red blood cells (P < .001), whereas mean 6-MMP levels decreased from 10,604.7 +/- 1278.2 to 2000.6 +/- 437.1 pmol/8 x 10(8) red blood cells (P < .001). The addition of allopurinol led to a reduction in the mean partial Harvey Bradshaw Index in Crohn's disease patients from 4.9 +/- 1.0 to 1.5 +/- 0.3 points (P = .001), and in ulcerative colitis patients mean Mayo Scores decreased from 4.1 +/- 0.7 to 2.9 +/- 0.7 points (P = .13). The addition of allopurinol enabled a reduction in mean daily prednisone dosage from 17.6 +/- 3.9 to 1.8 +/- 0.7 mg (P < .001) and led to normalization of transaminase levels, with mean AST levels reducing from 42.5 +/- 8.1 to 23.5 +/- 1.6 IU (P = .12) and mean ALT levels reducing from 101.6 +/- 26.9 to 33.9 +/- 5.2 IU (P = .01).

CONCLUSIONS

The addition of allopurinol to thiopurine nonresponders with high 6-MMP metabolite levels is an effective and safe means of optimizing 6-TGN production, leading to improved disease activity scores, reduced corticosteroid requirements, and normalization of liver enzymes.

Translational research in inflammatory bowel disease

The idiopathic inflammatory bowel diseases (IBDs), broadly classified as either Crohn's disease (CD) or ulcerative colitis (UC), are caused by a dysregulated mucosal immune response to a luminal antigen, possibly a bacterium, in a genetically predisposed host. A rapid expansion of knowledge in recent years has greatly increased our understanding of the pathophysiology of these disorders. For example, the relatively recent discovery of the NOD2 gene, a protein involved in bacterial sensing, has provided further evidence of the complex interplay between hosts and microbes in Crohn's disease. Significant recent advances have also occurred with the discovery of the role of Toll-like receptors and dendritic cells in the development of gut inflammation, and the role of proinflammatory cytokines in the development and potentiation of gut inflammation. This article presents an update on these key developments and emphasizes the translational aspects of research that are directly related to patient care.

Allopurinol safely and effectively optimizes tioguanine metabolites in inflammatory bowel disease patients not responding to azathioprine and mercaptopurine

BACKGROUND

Many non-responders to azathioprine or mercaptopurine (6-mercaptopurine) have high normal thiopurine methyltransferase activity and preferentially metabolize mercaptopurine to produce 6-methylmercaptopurine instead of the active 6-tioguanine (6-tioguanine) metabolites.

AIM

To describe the use of allopurinol in mercaptopurine/azathioprine non-responders to deliberately shunt metabolism of mercaptopurine towards 6-tioguanine.

METHODS

Fifteen thiopurine non-responders whose metabolites demonstrated preferential metabolism towards 6-methylmercaptopurine are described. Subjects were commenced on allopurinol 100 mg po daily and mercaptopurine/azathioprine was reduced to 25-50% of the original dose. Patients were followed clinically and with serial 6-tioguanine and 6-methylmercaptopurine metabolite measurements.

RESULTS

After initiating allopurinol, 6-tioguanine levels increased from a mean of 185.73 +/- 17.7 to 385.4 +/- 41.5 pmol/8 x 10(8) red blood cells (P < 0.001), while 6-methylmercaptopurine decreased from a mean of 10 380 +/- 1245 to 1732 +/- 502 pmol/8 x 10(8) RBCs (P < 0.001). Allopurinol led to a decrease in white blood cell from a mean of 8.28 +/- 0.95 to 6.1 +/- 0.82 x 10(8)/L (P = 0.01).

CONCLUSIONS

The addition of allopurinol to thiopurine non-responders with preferential shunting to 6-methylmercaptopurine metabolites appears to be an effective means to shift metabolism towards 6-tioguanine.

Spatial and temporal distribution of nerves, ganglia, and smooth muscle during the early pseudoglandular stage of fetal mouse lung development

Neural tissue and smooth muscle appear early in the developing fetal lung, but little is known of their origin and subsequent distribution. To investigate the spatial and temporal distribution of nerves, ganglia, and airway smooth muscle during the early pseudoglandular stage, fetal mouse lungs at embryonic days (E) 11 to 14 were immunostained as whole-mounts and imaged by confocal microscopy. At E11, the primordial lung consisted of the future trachea and two budding epithelial tubules that were covered in smooth muscle to the base of the growing buds. The vagus and processes entering the lung were positive for the neural markers PGP 9.5 (protein gene product 9.5) and synapsin but no neurons were stained at this stage. An antibody to p75NTR revealed neural crest cells on the future trachea as well as in the vagus and in processes extending from the vagus to the lung. This finding indicates that even though neuronal precursors are already present at this stage, they are still migrating into the lung. By E12, neural tissue was abundant in the proximal part of the lung and nerves followed the smooth muscle-covered tubules to the base of the growing buds. At E13 and E14, a neural network of interconnected ganglia, innervated by the vagus, covered the trachea. The postganglionic nerves mainly followed the smooth muscle-covered tubules, but some extended out into the mesenchyme beyond the epithelial buds. Furthermore, we show in a model of cultured lung explants that neural tissue and smooth muscle persist and continue to grow and differentiate in vitro. By using fluorescent markers and confocal microscopy, we present the developing lung as a dynamic structure with smooth muscle and neural tissue in a prime position to influence growth and development.