Basic science Mycophenolic acid inhibits PMA-induced activation of the neutrophil respiratory burst B. Ju ¨ttner, M. Bencel, A. Weißig, A. Studzinski, K. Stenger, D. Scheinichen Department of Anesthesiology, Hannover Medical School, Hannover, Germany B. Jˇttner, M. Bencel, A.WeiÞig, A. Studzinski, K. Stenger, D. Scheinichen. Mycophenolic acid inhibits PMA-induced activation of the neutrophil respiratory burst. Transpl Infect Dis 2009: 11: 235^240. All rights reserved Abstract: Mycophenolate mofetil (MMF) is commonly used in immunosuppressive regimens for solid organ transplantation.There is evidence that the hydrolyzed active agent mycophenolic acid (MPA) causes the endothelial depletion of intracellular guanosine 5 0 - triphosphate (GTP) levels.This depletion may cause inactivation of nicotinamide adenine dinucleotide phosphate oxidase.The purpose of the present study was to examine the impact of MPA on the neutrophil respiratory burst and phagocytic activity using £ow cytometry. In whole blood of healthy volunteers, 2 di¡erent doses of MPA (1 and 10 mmol/L) did not alter hydrogen peroxide production of neutrophils induced by receptor-dependent activators. In contrast, MPA inhibits the protein kinase C (PKC)-mediated hydrogen peroxide production by phorbol 12-myristate 13-acetate (PMA) in a time-dependent manner (negative: 21.17  1.64 vs. 120 min: 14.46  1.28 mean £uorescence intensity, incubation with 1 mmol/L MPA). In conclusion, our results corroborated that the neutrophil respiratory burst activity of healthy volunteers, induced by either formyl-methionyl-leucylphenylalanine (fMLP), priming with tumor necrosis factor alpha followed by fMLP or Escherichia coli and neutrophil phagocytic capacity, were not signi¢cantly a¡ected after MPA treatment.We also could demonstrate that the hydrogen peroxide production of neutrophils decreased in response to the PKC activator PMA in a time-dependent manner.                                                                                                     Mycophenolate mofetil (MMF) is commonly used in immu- nosuppressive regimens for solid organ transplantation (1^3). Furthermore, MMF therapy is becoming more accepted as a treatment for various autoimmune disorders (4, 5). In addition to clinical e¡ectiveness, MMF use is also fostered by its favorable tolerability pro¢le, with main side e¡ects being nausea, diarrhea, headache, and less frequently, leukopenia. In vivo, MMF is rapidly hydrolyzed to the active agent mycophenolic acid (MPA). MPA reversibly inhibits the type II isoform of inosine monophosphate dehydrogenase (IMPDH) in activated Tand B lymphocytes more than the type I isoform, which is expressed in most cell types (6). IMPDH is a key enzyme in the de novo synthesis of guano- sine 5 0 -triphosphate (GTP). In phagocytes an activated GTP-binding protein is re- quired for a receptor-mediated and second messenger-in- duced superoxide anion (O 2  ) production by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (Nox) (7), in a process referred to as the respiratory burst. In this regard, Kr˛tz et al. (8) hypothesized that depletion of intra- cellular GTP levels may cause inactivation of Nox, because they found that MPA had an inhibitorye¡ect on endothelial O 2  generation and signi¢cantly impaired the respiratory burst in neutrophils. In contrast, Hochegger et al. (9) reported on a patient af- ter kidney transplantation, who developed an acute in£am- matory syndrome after increasing the MMF dosage. They demonstrated in vitro that the patient’s phorbol 12-myri- r 2009 John Wiley & Sons A/S Transplant Infectious Disease . ISSN 1398-2273 Abbreviations: DHR, dihydrorhodamine; FITC, £uorescein isothiocyanate; FL, £uorescence; fMLP, formyl-methionyl-leucylphenylalanine; GTP, guanosine 5 0 - triphosphate; IMPDH, inosine monophosphate dehydrogenase; mFI, mean £uorescence intensity; MMF, mycophenolate mofetil; MPA, mycophenolic acid; NADPH, nicotinamide adenine dinucleotide phosphate; Nox, NADPH oxidase; O 2  , superoxide anion; PBS, phosphate bu¡ered saline; PI, propidium iodide; PKC, protein kinase C; PMA, phorbol 12-myristate 13-acetate; TNF-a, tumor necrosis factor alpha Key words: mycophenolic acid; neutrophils; respiratory burst; phagocytosis Correspondence to: Bjo ¨rn Ju ¨ttner, MD, Department of Anesthesiology, Hannover Medical School, Carl-Neuberg-St. 1, D-30625 Hannover, Germany Tel: 1 49 511 532 3689 Fax: 1 49 511 532 3642 E-mail: juettner.bjoern@mh-hannover.de Received 3 November 2008, revised 20 November, 3 December 2008, accepted for publication 6 December 2008 DOI: 10.1111/j.1399-3062.2009.00382.x Transpl Infect Dis 2009: 11: 235–240 235