Low-dose rapamycin does not impair vascular integrity and tubular regeneration after kidney transplantation in rats

mTOR inhibitors offer advantages after kidney transplantation including antiviral and antitumor activity besides facilitating low calcineurin inhibitor exposure to reduce nephrotoxicity. Concerns about adverse effects due to antiproliferative and antiangiogenic properties have limited their clinical use particularly early after transplantation. Interference with vascular endothelial growth factor (VEGF)-A, important for physiologic functioning of renal endothelial cells and tubular epithelium, has been implicated in detrimental renal effects of mTOR inhibitors. Low doses of Rapamycin (loading dose 3 mg/kg bodyweight, daily doses 1.5 mg/kg bodyweight) were administered in an allogenic rat kidney transplantation model resulting in a mean through concentration of 4.30 ng/mL. Glomerular and peritubular capillaries, tubular cell proliferation, or functional recovery from preservation/reperfusion injury were not compromised in comparison to vehicle treated animals. VEGF-A, VEGF receptor 2, and the co-receptor Neuropilin-1 were upregulated by Rapamycin within 7 days. Rat proximal tubular cells (RPTC) responded in vitro to hypoxia with increased VEGF-A and VEGF-R1 expression that was not suppressed by Rapamycin at therapeutic concentrations. Rapamycin did not impair proliferation of RPTC under hypoxic conditions. Low-dose Rapamycin early posttransplant does not negatively influence the VEGF network crucial for recovery from preservation/reperfusion injury. Enhancement of VEGF signaling peritransplant holds potential to further improve outcomes

The mTOR inhibitor Rapamycin protects from premature cellular senescence early after experimental kidney transplantation

Interstitial fibrosis and tubular atrophy, a major cause of kidney allograft dysfunction, has been linked to premature cellular senescence. The mTOR inhibitor Rapamycin protects from senescence in experimental models, but its antiproliferative properties have raised concern early after transplantation particularly at higher doses. Its effect on senescence has not been studied in kidney transplantation, yet. Rapamycin was applied to a rat kidney transplantation model (3 mg/kg bodyweight loading dose, 1.5 mg/kg bodyweight daily dose) for 7 days. Low Rapamycin trough levels (2.1-6.8 ng/mL) prevented the accumulation of p16(INK4a) positive cells in tubules, interstitium, and glomerula. Expression of the cytokines MCP-1, IL-1 beta, and TNF-alpha, defining the proinflammatory senescence-associated secretory phenotype, was abrogated. Infiltration with monocytes/macrophages and CD8(+) T-lymphocytes was reduced and tubular function was preserved by Rapamycin. Inhibition of mTOR was not associated with impaired structural recovery, higher glucose levels, or weight loss. mTOR inhibition with low-dose Rapamycin in the immediate posttransplant period protected from premature cellular senescence without negative effects on structural and functional recovery from preservation/reperfusion damage, glucose homeostasis, and growth in a rat kidney transplantation model. Reduced senescence might maintain the renal regenerative capacity rendering resilience to future injuries resulting in protection from interstitial fibrosis and tubular atrophy

Investigations of pharmacokinetics and pharmacodynamics of mycophenolate mofetil in the first year after renal transplantation

Einleitung Die Mycophenolsäure (MPA) gehört zur standardmäßigen immunsuppressiven Therapie nach Nierentransplantation. Es gibt nur wenige prospektive Studien zur Überprüfung der Eignung von Dosisschemata für eine Therapie mit Mycophenolatmofetil. Mit dieser Arbeit sollte überprüft werden, ob durch Therapeutisches Drug Monitoring der Mycophenolsäure im ersten Jahr nach Nierentransplantation das klinische Outcome verbessert werden kann. Außerdem wurde im Rahmen einer Substudie die Bedeutung der IMPDH-Aktivität für das Monitoring der MPA-Pharmakodynamik untersucht. Methodik Die Untersuchungen erfolgten im Rahmen einer offenen, prospektiven, randomisierten, kontrollierten, multizentrischen Studie (FDCC-Studie). Alle Patienten wurden zentral randomisiert (1:1 in den Arm, der eine feste MMF-Dosis (FD) und den Arm, der eine konzentrationskontrollierte MMF-Dosis (CC) erhielt). Die MPA-AUC wurde an den Tagen 3 und 10, in der Woche 4 und in den Monaten 3, 6 und 12 nach Transplantation aus 3 MPA-Konzentrationen (C0, C0,5, C2) kalkuliert (Ziel-AUC: 45 mg*h/l). Primäre Endpunkte waren Therapieversagen durch akute Rejektion, Transplantatverlust, Tod oder Unterbrechung der MMF-Therapie. Sekundäre Endpunkte waren die Inzidenz opportunistischer Infektionen und maligner Erkrankungen, die Nierenfunktion und das Auftreten unerwünschter Ereignisse. Im Rahmen der Substudie wurde die mononukleäre und die erythrozytäre IMPDH- Aktivität bestimmt. Ergebnisse Es wurden 56 Patienten randomisiert, wobei 31 Patienten dem CC-Arm (AUC- gesteuerte MMF-Dosierung) und 25 Patienten dem FD-Arm (MMF-Standard-Dosis) zugeordnet wurden. Insgesamt konnte kein signifikanter Unterschied der MPA-AUC-Werte zwischen den beiden Behandlungsgruppen dokumentiert werden. Es wurden keine statistisch signifikanten Unterschiede der Endpunkte nachgewiesen. Auffällig war, dass die MPA-AUC-Werte am Tag 10 nach Transplantation bei beiden beobachteten Patientengruppen zu mehr als 65% unterhalb von 30 mg*h/l lagen. 41,7% der Patienten mit einer MPA-AUC<30 mg*h/l am Tag 3 nach Transplantation erlitten eine akute Rejektion, dagegen nur 23,5% der Patienten mit einer MPA-AUC>30 mg*h/l. Sämtliche akuten Rejektionen traten während der ersten 20 Tage des gesamten Beobachtungszeitraums auf. Die mononukleäre IMPDH-Aktivität fiel während des Beobachtungszeitraums kontinuierlich ab. Lediglich am 10. postoperativen Tag kam es zu einem einmaligen, statistisch signifikanten Anstieg. Zu allen Visiten waren jeweils den höheren MPA-AUC- Werten niedrigere IMPDH-Aktivitäten zuzuordnen. Die erythrozytäre IMPDH-Aktivität stieg bis Monat 9 kontinuierlich an. Schlussfolgerung Es wurde kein signifikanter Unterschied der MPA-AUC-Werte zwischen den Patienten beider Behandlungsarme festgestellt. Somit war ein Effektivitätsunterschied nicht erreichbar. Vor allem in der Frühphase nach Transplantation ist möglicherweise eine intensivierte MPA-Exposition wichtig, um akute Rejektionen zu vermeiden. Die mononukleäre IMPDH-Aktivität scheint ein guter pharmakodynamischer Parameter für das biologische Ansprechen einer MMF-Therapie zu sein. Der Anstieg der erythrozytären IMPDH-Aktivität muß weiter untersucht werden.Background Mycophenolic acid (MPA) is a part of standard immunosuppressive therapy after renal transplantation. There are only spare prospective studies investigating different dose schemes of MMF therapy. This dissertation intents to examine whether patients outcome in the first year after renal transplantation could be improved by therapeutic drug monitoring of MPA. Moreover within the context of a substudy the value of IMPDH activity for monitoring MPA pharmacodynamics was verified. Methods Investigations were performed within the context of an open, prospective, randomized, controlled, multicentre study (FDCC study). Patients were randomized centrally (1:1 into the fixed dose arm (FD) and the concentration controlled arm (CC)). MPA-AUC was calculated (target AUC 45mg*h/l) on day 3 and 10, in week 4 and in month 3, 6 and 12 after transplantation out of 3 MPA-concentrations (C0, C0,5, C2). Primary endpoints were treatment failure by acute rejection, graft loss, death or discontinuation of MMF therapy. Secondary endpoints were the incidence of opportunistic infections and malignancies, renal function and the incidence of adverse events. Within the context of the substudy IMPDH activity of monocytes and erythrocytes were measured. Results 56 patients were randomized (31 patients were assigned to the CC-arm (concentration- controlled) and 25 to the FD-arm (fixed dose)). There were neither significant differences in MPA-AUC values between both treatment groups, nor in primary and secondary endpoints. 10 days after transplantation more than 65% of all patients had MPA-AUC values below 30 mg*h/l. 41.7% of the patients with MPA-AUC<30mg*h/l on day 3 after transplantation were experiencing an acute rejection. In contrast, only 23.5% of the patients with an MPA-AUC>30 mg*h/l had an acute rejection. All acute rejections occurred during the first 20 days after transplantation. Except a significant increase on day 10, mononuclear IMPDH activity decreased continuously. Higher MPA-AUC values could always be assigned to lower IMPDH activity at any time of the study. IMPDH activity of erythrocytes increased continuously until month 9. Conclusions There were no significant differences between MPA-AUC levels in the FD-arm and the CC-arm. Therefore, no difference in efficacy could be achieved. To prevent acute rejections an intensified MPA exposure may be important especially in the early phase after transplantation. Mononuclear IMPDH activity seems to be an appropriate pharmacodynamic parameter for the biological efficacy of MMF therapy. The rise in erythrocyte’s IMPDH activity needs further investigation