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

Abstract

BackgroundClinical 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.MethodologyThe 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 (14CO2 BACTEC®) detection system that quantifies mycobacterial growth as arbitrary “growth index units” (GI). Efficacy data are presented as “percent decrease in cumulative GI” (% −ΔcGI).Principal FindingsThe positive control antibiotic (clarithromycin) has ≥85% −ΔcGI at a concentration of 0.5 µg/ml. The negative control (ampicillin) has minimal inhibition at 64 µg/ml. MAP ATCC 19698 shows ≥80% −ΔcGI for both agents by 4 µg/ml. With the other three isolates, although more effective than ampicillin, 6-MP is consistently less effective than methotrexate.ConclusionsWe show that methotrexate and 6-MP inhibit MAP growth in vitro. Each of the four isolates manifests different % −ΔcGI. 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.

On the Action of 5-Amino-Salicylic Acid and Sulfapyridine on M. avium including Subspecies paratuberculosis

“…In this study (as previously [10]) we use four well-characterized strains of mycobacteria. Two are MAP, a bovine isolate, ATCC 19698 (ATCC Rockville MD) and “Dominic” a human isolate from an individual with Crohn's disease (originally isolated by R. Chiodini [17].)…”

“…Although controversial, there are increasingly compelling data that all [9], [10] or some of IBD may be caused by a single infectious agent Mycobacterium avium subspecies paratuberculosis (MAP.) [9]–[13] (& See [14] for review.)…”

“…[9]–[13] (& See [14] for review.) We have shown that two agents, methotrexate and 6-mercaptopurine (6-MP) [10], presumed to have “immunomodulatory” actions in IBD, [15], [16] are potent antiMAP antibiotics. We suggested that the decreases in pro-inflammatory cytokines in IBD “immunomodulatory” therapy might simply reflect a normal, secondary, physiological response, as the instigating MAP infection was effectively treated.…”

“…We concluded that henceforth methotrexate and 6-MP should be excluded from the placebo group when evaluating antiMAP therapies in IBD. [10] …”

Nanotechnology Based Therapeutics, Drug Delivery Mechanisms and Vaccination approaches for Countering Mycobacterium avium subspecies paratuberculosis (MAP) Associated Diseases

“…In addition, drugs such as amikacin, ciprofloxacin, levofloxacin, rifampicin posses varying degrees of susceptibility towards MAP (Krishnan et al, 2009). Greenstein et al (2007) showed that the accepted use of methotrexate and 6-mercaptopurine (6-MP) for therapy of IBD may be due to the inhibitory action of the drugs on MAP, instead of the generally prevailing idea that the primary mechanism of action is the drug's ability to decrease the production of pro-inflammatory cytokines. Nazareth et al (2015) investigated the growth of MAP in macrophages of CD patients under the influences of Infliximab treatment.…”