Mycophenolic acid AUC in Thai kidney transplant recipients receiving low dose mycophenolate and its association with UGT2B7 polymorphisms

Manop Pithukpakorn,1 Tiwat Tiwawanwong,2 Yupaporn Lalerd,3 Anunchai Assawamakin,3,4 Nalinee Premasathian,2 Adis Tasanarong,5 Wanna Thongnoppakhun,3 Attapong Vongwiwatana2 1Division of Medical Genetics, 2Division of Nephrology, Department of Medicine, 3Division of Molecular Genetics, Department of Research and Development, Faculty of Medicine Siriraj Hospital, 4Department of Pharmacology, Faculty of Pharmacy, Mahidol University, 5Department of Medicine, Faculty of Medicine, Thammasat University, Bangkok, Thailand Background: Despite use of a lower mycophenolate dose in Thai kidney transplant patients, acceptable graft and patient outcomes can be achieved. We therefore examined the pharmacokinetics of mycophenolic acid (MPA) by area under the curve (AUC) and investigated genetic contribution in mycophenolate metabolism in this population. Methods: Kidney transplant recipients with stable graft function who were receiving mycophenolate mofetil 1,000 mg/d in combination with either cyclosporine or tacrolimus, and prednisolone were studied. The MPA concentration was measured by fluorescence polarization immunoassay (FPIA), at predose and 1, 1.5, 2, 4, 6, 8, 10, and 12 hours after dosing. Genetic polymorphisms in UGT1A8, UGT1A9, and UGT2B7 were examined by denaturing high-performance liquid chromatography (DHPLC)-based single-base extension (SBE) analysis. Results: A total 138 patients were included in study. The mean AUC was 39.49 mg-h/L (28.39–89.58 mg-h/L), which was in the therapeutic range. The correlation between the predose MPA concentration and AUC was poor. The mean AUC in the tacrolimus group was higher than that in the cyclosporine group. Polymorphisms in UGT2B7 showed significant association with AUC. Conclusion: Most of our patients with reduced mycophenolate dose had the AUC within the therapeutic range. Genetic polymorphisms in UGT2B7 may play a role in MPA metabolism in Thai kidney transplant patients. Keywords: UGT, MPA, pharmacokinetic, immunosuppressiv

Deficiency of C4 from Donor or Recipient Mouse Fails to Prevent Renal Allograft Rejection

Complement effector products generated in the transplanted kidney are known to mediate transplant rejection, but which of the three main activation pathways of complement trigger this response is unclear. Here we assessed the role of the classical and lectin pathways by studying the common component C4 in mouse kidney transplant rejection. We transplanted wild-type or C4-null H-2(b) donor kidneys into H-2(k) or H-2(d) recipients, or vice-versa, to assess the roles of donor kidney and recipient expression of complement. Intragraft C4 gene expression rose substantially during rejection. However, we found no significant association between graft acceptance and the presence of C4 in either the donor kidney or recipient mouse. At the time of rejection, we found no significant differences in alloantibody response in the different groups. Tubular deposition of C3 to C9 occurred regardless of the absence or presence of C4 in either the donor or recipient mouse, indicating that C4 was dispensable for complement activation at this site. These data suggest that complement activation and renal allograft rejection are independent of the classical and lectin pathways in these models, implying that in the absence of these pathways the alternative pathway is the main trigger for complement-mediated rejection

Identifying compartment-specific non-HLA targets after renal transplantation by integrating transcriptome and “antibodyome” measures

We have conducted an integrative genomics analysis of serological responses to non-HLA targets after renal transplantation, with the aim of identifying the tissue specificity and types of immunogenic non-HLA antigenic targets after transplantation. Posttransplant antibody responses were measured by paired comparative analysis of pretransplant and posttransplant serum samples from 18 pediatric renal transplant recipients, measured against 5,056 unique protein targets on the ProtoArray platform. The specificity of antibody responses were measured against gene expression levels specific to the kidney, and 2 other randomly selected organs (heart and pancreas), by integrated genomics, employing the mapping of transcription and ProtoArray platform measures, using AILUN. The likelihood of posttransplant non-HLA targets being recognized preferentially in any of 7 microdissected kidney compartments was also examined. In addition to HLA targets, non-HLA immune responses, including anti-MICA antibodies, were detected against kidney compartment-specific antigens, with highest posttransplant recognition for renal pelvis and cortex specific antigens. The compartment specificity of selected antibodies was confirmed by IHC. In conclusion, this study provides an immunogenic and anatomic roadmap of the most likely non-HLA antigens that can generate serological responses after renal transplantation. Correlation of the most significant non-HLA antibody responses with transplant health and dysfunction are currently underway