Abstract

Mycophenolate mofetil (MMF) is commonly prescribed after transplantation and has proven advantages over other immunosuppressive drugs but gastrointestinal (GI) side effects frequently limit its use. The pathways involved in the metabolism of the prodrug MMF and the bioactive derivative mycophenolic acid (MPA) are well characterized but the mechanism responsible for toxicity is unknown. Here we extend our previous observation that an intact gut microbiome is required for MMF-induced toxicity and demonstrate that gut bacterial metabolism is responsible for the GI inflammation and weight loss associated with MMF exposure. In mice consuming MMF, the introduction of vancomycin alone was sufficient to prevent or reverse MMF-induced weight loss and colonic inflammation. MMF induced the expansion of bacteria expressing {beta}-glucuronidase (GUS) in the cecum and proximal colon. GUS activity, which is responsible for the catabolism of glucuronidated MPA (MPAG) to free MPA, was increased in the presence of MMF and eliminated by vancomycin. Vancomycin eliminated multiple Bacteroides spp. that flourished in the presence of MMF and prevented the breakdown of MPAG without negatively affecting serum MPA levels. Human data suggests that increased stool GUS activity can be associated with MMF-related toxicity. Our work provides a mechanism for the GI toxicity associated with MMF and a future direction for the development of therapeutics.