Mizoribine—An inosine monophosphate dehydrogenase inhibitor—acts synergistically with cyclosporine A in prolonging survival of murine islet cell and heart transplants across major histocompatibility barrier ☆ , ☆☆ Naohiko Fukami a, 1 , Vijay Subramanian a , Nataraju Angaswamy a , Wei Liu a , T. Mohanakumar a, ⁎, Kiyotaka Hoshinaga b a Department of Surgery, Washington University School of Medicine, St. Louis, MO, USA b Department of Urology, Fujita Health University School of Medicine, Toyoake, Aichi, Japan abstract article info Article history: Received 6 July 2011 Received in revised form 26 October 2011 Accepted 28 October 2011 Keywords: Mizoribine Cyclosporine Immunosuppression Murine heterotopic heart transplantation Murine islet transplantation Introduction: Mizoribine (MZR) is an inosine monophosphate dehydrogenase inhibitor. It has been widely used in Japan in the treatment of autoimmune diseases and is known to inhibit T and B cell proliferation. The aim of this study was to evaluate the efficacy of MZR as an immunosuppressive agent and determine its ability to synergize with a commonly used calcineurin inhibitor Cyclosporine A (CsA) in prolonging sur- vival of murine islet cells and heart transplanted across major histocompatibility barrier. Methods: Murine allogeneic islet cell transplantation between Balb/c donor mice and C57BL/6 recipient mice and heterotopic heart transplantation was done between C3H/He donor mice and Balb/c recipient mice. Recipients were divided into groups based on immunosuppression: Group 1—No immunosuppression, Group 2—MZR alone (20 mg/kg/day), Group 3—CsA alone (20 mg/kg/day), Group 4—MZR + CsA (20 mg/kg/day). Donor specif- ic IFN-γ, IL-10, IL-2, IL-4 secreting cells were enumerated by ELISpot. Serum cytokine and chemokine concentra- tion was measured by Luminex. Results: Islet cell allograft recipients treated with CsA and MZR had prolonged islet function compared to other groups [normoglycemia (blood glucose b 200 mg/dL) up to 32± 4 days, p b 0.05]. Similarly, heart allograft sur- vival was significantly improved in mice treated with CsA and MZR compared to other groups (50% 30-day sur- vival, p =0.04). Donor specific IFN-γ, IL-4, IL-2 secreting cells were significantly decreased in recipients treated with CsA and MZR with marked increase in IL-10 secreting cells (p b 0.05). There was also an increase in serum IL-10 with decrease in IFN-γ, IL-4, IL-2, MCP-1, and IL-6 in mice treated with CsA and MZR Conclusion: MZR and CsA when used in combination are potent immunosuppressive agents in murine islet cell and heart transplantation models. These agents lead to a decrease in donor specific IFN-γ with increase in IL-10 secreting cells leading to improved allograft survival and function. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Mizoribine (MZR) is an immunosuppressive agent that was initially isolated as an antibiotic from the mold Eupenicillium brefeldianum [1]. In its active form—mizoribine-5′-monophosphate, MZR acts as a competi- tive inhibitor of Inosine monophosphate dehydrogenase (IMPDH). IMPDH plays a role in the de novo synthesis of guanosine nucleotides especially in lymphocytes. Due to this MZR has a potent immunosup- pressive effect on both humoral and cellular immunity [2-4]. MZR was approved for clinical use in 1984 in Japan and has been used as a immu- nosuppressive agent in rheumatoid arthritis [5] and a variety of autoim- mune kidney diseases like lupus nephritis [6], IgA childhood nephropathy [7], steroid resistant nephritis [8] and even in renal trans- plantation [9]. It is also known to have anti-viral properties especially against respiratory syncytial, influenza and parainfluenza, measles and hepatitis C virus [10-12]. Cyclosporine A (CsA) is a widely used immunosuppressant that is used in both autoimmune diseases as well as in the setting of trans- plantation. As an inhibitor of calcineurin, it prevents the activation of both T-cells and B-cells [13]. Due to the different modes of action of MZR and CsA, we postulated that immunosuppressive properties of these two agents may synergize leading to better islet and heart al- lograft survival across MHC mismatches. Transplant Immunology 26 (2012) 140–145 Abbreviations: MZR, Mizoribine; MMF, Mycophenolate mofetil; CsA, Cyclosporine; IMPDH, Inosine monophosphate dehydrogenase; NFGB, Non-fasting blood glucose. ☆ Funding: TM is supported by the BJC Foundation. ☆☆ Authors have no relevant conflicts of interests to declare. ⁎ Corresponding author at: Washington University School of Medicine, Department of Surgery, Box 8109, 3328 CSRB, 660 S. Euclid Ave, St Louis MO 63110, USA. Tel.: +1 314 362 8463; fax: +1 314 747 1560. E-mail address: kumart@wustl.edu (T. Mohanakumar). 1 Naohiko Fukami is presently at Department of Urology, Fujita Health University School of Medicine, Toyoake, Aichi, Japan. 0966-3274/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.trim.2011.10.007 Contents lists available at SciVerse ScienceDirect Transplant Immunology journal homepage: www.elsevier.com/locate/trim