Journal Article

On the Action of Methotrexate and 6-Mercaptopurine on M. avium Subspecies paratuberculosis

Greenstein, Robert J., Brown, Sheldon T., Su, Liya, Haroutunian, Vahram, Shahidi, Azra

2007

Overview

Clinical improvement in inflammatory bowel disease (IBD) treated with methotrexate and 6-mercaptopurine (6-MP) is associated with a decrease in pro-inflammatory cytokines. This has been presumed to indicate the mechanism of action of methotrexate and 6-MP. Although controversial, there are increasingly compelling data that Mycobacterium avium subspecies paratuberculosis (MAP) may be an etiological agent in some or all of IBD. We hypothesized that the clinical efficacy of methotrexate and 6-MP in IBD may be to simply inhibit the growth of MAP. The effect on MAP growth kinetics by methotrexate and 6-MP were evaluated in cell culture of two strains each of MAP and M. avium using a radiometric ((14)CO(2) BACTEC detection system that quantifies mycobacterial growth as arbitrary \"growth index units\" (GI). Efficacy data are presented as \"percent decrease in cumulative GI\" (% -DeltacGI). The positive control antibiotic (clarithromycin) has >or=85% -DeltacGI at a concentration of 0.5 microg/ml. The negative control (ampicillin) has minimal inhibition at 64 microg/ml. MAP ATCC 19698 shows >or=80% -DeltacGI for both agents by 4 microg/ml. With the other three isolates, although more effective than ampicillin, 6-MP is consistently less effective than methotrexate. We show that methotrexate and 6-MP inhibit MAP growth in vitro. Each of the four isolates manifests different % -DeltacGI. These data are compatible with the hypothesis that the clinical improvement in patients with IBD treated with methotrexate and 6-MP could be due to treating a MAP infection. The decrease in pro-inflammatory cytokines, thought to be the primary mechanism of action, may simply be a normal, secondary, physiological response. We conclude that henceforth, in clinical studies that evaluate the effect of anti-MAP agents in IBD, the use of methotrexate and 6-MP should be excluded from any control groups.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: 6-Mercaptopurine / Ampicillin / Ampicillin - pharmacology / Ampicillin - therapeutic use / Animals / Anti-Bacterial Agents - pharmacology / Anti-Bacterial Agents - therapeutic use / Antibiotics / Cattle / Cell culture / Clarithromycin / Crohn's disease / Crohns disease / Cytokines / Cytokines - immunology / Deoxyribonucleic acid / Detection equipment / Dihydrofolate reductase / DNA / Drug dosages / E coli / Escherichia coli / Etiology / Gastroenterology and Hepatology/Gastrointestinal Infections / Gastroenterology and Hepatology/Inflammatory Bowel Disease / Growth kinetics / Humans / Hypotheses / Immunosuppressive Agents - pharmacology / Immunosuppressive Agents - therapeutic use / Infections / Infectious Diseases/Antimicrobials and Drug Resistance / Infectious Diseases/Bacterial Infections / Infectious Diseases/Gastrointestinal Infections / Inflammatory bowel disease / Inflammatory bowel diseases / Inflammatory Bowel Diseases - drug therapy / Inflammatory Bowel Diseases - immunology / Inflammatory Bowel Diseases - microbiology / Intestine / Johne's disease / Kinetics / Laboratories / Lymphoma / Mercaptopurine / Mercaptopurine - pharmacology / Mercaptopurine - therapeutic use / Methotrexate / Methotrexate - pharmacology / Methotrexate - therapeutic use / Microbial Sensitivity Tests / Microbiology/Environmental Microbiology / Microbiology/Medical Microbiology / Mycobacterium / Mycobacterium avium / Mycobacterium avium subsp. paratuberculosis - drug effects / Mycobacterium avium subsp. paratuberculosis - immunology / Mycobacterium avium subsp. paratuberculosis - pathogenicity / Paratuberculosis / Pasteurization / Pathogens / Physiological aspects / Political aspects / Public Health and Epidemiology/Infectious Diseases / R&D / Research & development / Salmonella / Surgery/Gastrointestinal Surgery