Genetic Predisposition-Chronic Nephrotoxicity From CI-Liver Transplant Recipients-Potential Correlation-Urinary Biomarkers

Study Design:

This study will be a cross-sectional investigation of liver transplant recipients who received a liver transplant and have at least 6 months of follow-up. This study will be conducted at Northwestern Memorial Hospital, Northwestern Medical Faculty Foundation and Northwestern University.

Patients who underwent liver transplantation and have at least 6 months of follow-up receiving a maintenance immunosuppression (which consists of calcineurin inhibitors (CI), cyclosporine (CsA), or tacrolimus (Tac)) during the entire post-transplant follow-up period will be included in the analysis.

For each patient, the following information will be collected:

• Date of transplantation, age, gender, race, causes of liver failure, past medical history including incidence of hypertension, diabetes mellitus, post-operative complications, post-operative infections, number of acute liver rejection episodes, death, CsA and Tac trough levels at different time points post-transplant and sCr levels before liver transplant, at 1, 6, 12, 24 months, and yearly post-transplant.
• GFR (Glomerular Filtration Rate) with MDRD equation before liver transplant, at 1, 6, 12, 24 months, and yearly post-transplant.
• In the attempt to rule out all patients with pre-existing CRF before liver transplant, only the patients with sCr<1.0mg/dL before liver transplant will be included in our analysis.

Genotyping:

• DNA will be extracted using blood buffy coat from liver transplant recipients.
• Determination of ACE genotypes will be performed by using polymerase chain reaction sequence-specific primers (PCR-SSP) and polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP).
• Based on GRF calculation by MDRD equation liver transplant patients will be categorized into three groups based on NKF staging of chronic kidney disease:

Group I->normal GFR (>90ml/min/1.73m2). Stage I CKD Group II->GFR between 30-59ml/min/1.73m2. Stage III CKD Group III->GFR between 15-29ml/min/1.72m2. Stage IV CKD

• Urine (80cc) will be collected from all patients in the 3 groups and analyzed for biomarkers of interstitial fibrosis and proximal tubule injury. Specific biomarkers that will be tested are: urinary TGF-beta1, kidney injury molecule-1 and angiotensinogen. Urinary biomarkers will be normalized to creatinine and analyzed using an ELISA assay.
• Blood (20cc)will be taken at one visit.
• An additional blood draw (18cc) will be requested from all subjects. This blood will be used to study organ transplant tolerance in subjects who are currently using immunosuppressant medications.

Statistical Plan-Statistical tests to be performed:

Once liver transplant patients are genotyped and urine samples are collected we will compared the development of CKD post liver transplant for associations with urinary biomarkers and polymorphisms of the ACE gene. Two sample t tests will be used to compare differences in continuous variables between liver patients with different degree of CKD; chi square tests will be used to compare differences in discrete variables. Multivariable logistic regression analysis will be also performed to identify the combination of clinical variable and gene polymorphisms that are significantly associated with the development of post liver transplant renal dysfunction.

This study will enable us to learn and evaluate potential genetic predisposition for the development of renal dysfunction after exposure to CI. If our hypothesis is correct, testing of the component of the RAS genotypes may help identify patients at risk for CI nephrotoxicity and help in the pre-selection of liver transplant candidates in whom the use of CI as primary immunosuppression should be avoided.

Furthermore, the data generated from this study might serve as a strong basis for a prospective NIH-founded project to look at the role of agents that block the renin-angiotensin system for the prevention of CI-induced chronic nephrotoxicity.

Inclusion criteria

• Informed consent
• Males and females > 18 years old
• Liver transplant recipients who have received a liver transplant at least 6 months ago
• Liver transplant recipients receiving a maintenance immunosuppression.

Exclusion criteria

• Legal incapacity and/or other circumstances rendering the patient unable to understand the nature, scope and possible consequences of the study
• Pre-existing known kidney disease before liver transplantation
• Multi-organ transplant