Abstract
Kidney transplantation (KT) prolongs life in patients with kidney failure. KT requires the use of immunosuppressive agents such as tacrolimus (TAC) and mycophenolate mofetil (MMF) to prevent rejection of the donor kidney, which will result in graft loss. Drug levels for both TAC and MMF vary very widely in individual patients. Too high levels may increase the risk of complications such as infections and bone marrow suppression whereas too low can lead to KT rejection. MMF is a prodrug, which is hydrolyzed to mycophenolic acid (MPA) after oral administration. Quantification of MPA levels requires several measurements to construct an area under the curve over a 12 hr. period (AUC0-12) as a single trough level is a poor predictor of AUC. Because of the time constraint and cost, a full MPA AUC is rarely performed, and MMF is usually given as a fixed-dose combination. Unlike MPA, trough levels of TAC are an accepted method to estimate TAC AUC and are widely used in clinical practice. Trough levels vary widely between individuals after a fixed dose. Low trough levels of TAC has been shown to be related to the risk of rejection and decreased long-term outcome. Known genetic polymorphisms in enzymes related to MMF hydrolysis, MPA excretion, and reabsorption have been shown to contribute to the highly variable individual MPA AUC Similarly, several genes have been identified to account for variations in TAC trough levels. Previously, we have demonstrated the importance of polymorphisms of a few genes linked pharmacokinetics of MMF and TAC in Thais that differs in some aspects from the Western population. Nonetheless, all known genes that can influence drug levels have not been evaluated in Thais. Moreover, additional genetic polymorphisms as yet unknown may be important to determine drug pharmacokinetics and could predict the risk of transplant complications. A complete knowledge of gene polymorphisms and their frequency in the Thai population would lead to the development of a more accurate algorithm for individualized prescription of immunosuppressive agents, reducing complications and leading to improved patient care. Study objectives i) Collect DNA for whole genome sequencing of patients undergoing kidney transplantation for Genomic Thailand 2) To identify novel polymorphisms and evaluate contributions of known and unknown polymorphisms linked to trough-level tacrolimus in KT patients 3) To identify novel polymorphisms and evaluate contributions of known and unknown polymorphisms linked to area under the curve level of MPA in KT patients 4) To develop algorithms to dose MMF และ tacrolimus using clinical and genetic data 5) To evaluate risk of gene polymorphisms of alleles linked to MPA and TAC levels and complications of KT Methods This was planned as a retrospective and prospective study of patients with diseased-donor and living-related KT from Ramathibodi Hospital, Siriraj Hospital, and Chiangmai Hospital (n=1000) over a 2-year period. Relevant clinical details and drug details will be collected. Blood was collected for Genomics Thailand, and a separate sample will be kept for on-site analysis. Results We have enrolled 841 patients (in excess of the 500 planned for the first year). We have set up an assay of MPA and metabolite assay by ultra-high-performance liquid chromatography-tandem mass spectrometry. We measured AUC 12 hr. of MPA in 200 patients and are measuring known gene polymorphisms using a targeted high-evidence pharmacogenomic PCR array, which includes 2,000 variants in 150 genes in these patients. We will link MPA levels and TAC to these genotypes as well as develop a predictive algorithm in the first part of year 2. Conclusions and plan We have enrolled 841 patients (of target of 500 in year 1). In year 2, we requested to increase our enrollment to 1500 patients. (in total years 1 and 2). In the early part of Year 2, we will conclude an analysis of associations of known gene polymorphisms with MPA AUC and trough TAC levels using PCR array as well as develop an algorithm to predict outcomes. Later in Year 2, we will evaluate the relationship between MPA AUC and TAC levels in the rest of the patients once the Genomic Thailand data becomes available. In addition, we will link the risk of complications such as rejection and infection or marrow suppression with gene polymorphisms linked to drug metabolism.
