Potential of Noninvasive Serial Assessment of Acute Renal Allograft Rejection by 18F-FDG PET to Monitor Treatment Efficiency

We propose F-18-FDG PET as a method to monitor acute rejection of allogeneic renal transplants in a rat model. Methods: Allogeneically transplanted (aTX) rats (binephrectomized Lewis-brown Norway to Lewis) served as the renal transplant model. aTX rats treated with cyclosporine A (CSA) served as a therapy monitoring group. Healthy control rats, rats with acute CSA nephrotoxicity, rats with acute tubular necrosis, syngeneically transplanted (sTX) rats, and aTX rats treated with CSA since postoperative day 0 served as controls. After surgery, renal glucose metabolism was assessed in vivo serially up to postoperative day 7 by performing small-animal PET 3 h after intravenous injection of 30 MBq of F-18-FDG. Mean radioactivity (cps/mm(3) of tissue) was measured and the percentage injected dose calculated. Results were confirmed by histologic, functional, and autoradiographic analysis. Results: Renal F-18-FDG uptake was significantly elevated at postoperative day 4 in aTX rats, when compared with control, sTX, acute tubular necrosis, or CSA-treated rats (P < 0.05). In vivo F-18-FDG uptake correlated with the results of autoradiography and with inflammatory infiltrates observed on histologic examination. Notably, F-18-FDG PET assessed the response to therapy 48 h earlier than the time at which serum creatinine decreased and when histologic examination still showed signs of allograft rejection. In aTX rats, the CSA-susceptible graft infiltrate was dominated by activated cytotoxic T cells and monocytes/macrophages. Conclusion: F-18-FDG PET is an option to noninvasively assess early response to therapy in rat renal allograft rejection.