On the effect of thalidomide on Mycobacterium avium subspecies paratuberculosis in culture

Abstract

Without known mechanisms of action, thalidomide is used to treat a variety of non-malignant 'idiopathic' diseases. There is increasing concern that Mycobacterium avium subspecies paratuberculosis (MAP) may be zoonotic. Recently, methotrexate, azathioprine, 6-mercaptopurine (6-MP), 5-aminosalicylic acid (5-ASA), cyclosporine A, rapamycin, and tacrolimus have been shown to inhibit MAP growth in culture, indicating that, unknowingly, MAP infections may have been treated for decades. We herein test the hypothesis that thalidomide may inhibit MAP growth. Using the radiometric 14CO2 (Bactec) system we quantified growth kinetics of thalidomide (+/-), (+), and (-) and two components for thalidomide, phthalimide and 1-hydroxypiperidine-2,6-dione (HPD). We studied four MAP strains (three human isolates, 'Ben', 'Dominic', and UCF-4, and a bovine MAP isolate 19698) and three mycobacterial controls (Mycobacterium avium and bacillus Calmette-Guérin (BCG)). Growth was quantified as growth index (GI) and inhibition as percent decrease in cumulative GI (%-DeltacGI). Phthalimide had no dose-dependent inhibition on any strain. Neither thalidomide nor HPD inhibited M. avium or BCG. MAP inhibition varied; at 64 microg/ml, amongst human isolates, Dominic was most susceptible: thalidomide (+)=58%-DeltacGI and HPD=46%-DeltacGI. UCF-4 was next: thalidomide (-)=37%-DeltacGI and HPD=40%-DeltacGI. Ben was least susceptible: HPD=24%-DeltacGI. We have shown, in culture, the heretofore-undescribed inhibition of MAP growth by thalidomide and its enantiomers. Phthalimide was found to have no anti-MAP activity, whereas HPD was found to inhibit MAP growth. These data are compatible with the hypothesis that thalidomide, like other 'anti-inflammatories' and 'immunomodulators' may act, in part, as an anti-MAP antibiotic.