Sirolimus delays renal allograft recovery

Urine metabolites reflect time-dependent effects of cyclosporine and sirolimus on rat kidney function

The clinical use of the immunosuppressant calcineurin inhibitor cyclosporine is limited by its nephrotoxicity. This is enhanced when combined with the immunosuppressive mTOR inhibitor sirolimus. Nephrotoxicity of both drugs is not yet fully understood. The goal was to gain more detailed mechanistic insights into the time-dependent effects of cyclosporine and sirolimus on the rat kidney by using a comprehensive approach including metabolic profiling in urine ((1)H NMR spectroscopy), kidney histology, kidney function parameters in plasma, measurement of glomerular filtration rates, the oxidative stress marker 15-F(2t)-isoprostane in urine, and immunosuppressant concentrations in blood and kidney. Male Wistar rats were treated with vehicle (controls), cyclosporine (10/25 mg/kg/day), and/or sirolimus (1 mg/kg/day) by oral gavage once daily for 6 and 28 days. Twenty-eight day treatment led to a decrease of glomerular filtration rates (cyclosporine, -59%; sirolimus, -25%). These were further decreased when both drugs were combined (-86%). Histology revealed tubular damage after treatment with cyclosporine, which was enhanced when sirolimus was added. No other part of the kidney was affected. (1)H NMR spectroscopy analysis of urine (day 6) revealed time-dependent changes of 2-oxoglutarate, citrate, and succinate concentrations. In combination with increased urine isoprostane concentrations, these changes indicated oxidative stress. After 28 days of cyclosporine treatment, urine metabonomics shifted to patterns typical for proximal tubular damage with reduction of Krebs cycle intermediates and trimethylamine-N-oxide concentrations, whereas acetate, lactate, trimethylamine, and glucose concentrations increased. Again, sirolimus enhanced these negative effects. Our results indicate that cyclosporine and/or sirolimus induce damage of the renal tubular system. This is reflected by urine metabolite patterns, which seem to be more sensitive than currently used clinical kidney function markers such as creatinine concentrations in serum. Metabolic profiling in urine may provide the basis for the development of toxicodynamic monitoring strategies for immunosuppressant nephrotoxicity.

Differences in proteinuria and graft function in de novo sirolimus-based vs. calcineurin inhibitor-based immunosuppression in live donor kidney transplantation

BACKGROUND

Calcineurin inhibitor(CNI)-free protocols using sirolimus (SRL) in kidney transplantation have proven effective, although reports have linked SRL to proteinuria. We sought to investigate this link and its impact on graft function.

METHODS

We retrospectively analyzed 184 live donor kidney transplant recipients who exclusively received de novo CNI-based (n = 106) or SRL-based (n = 78) regimens. Estimated glomerular filtration rate (GFR) and semi-quantitative dipstick proteinuria measurements were obtained at one, six, 12, and 24 months and six and 12 months, respectively.

RESULTS

SRL-treated patients had higher frequencies of proteinuria (> or =1+) at 6 months (40.8% vs. 21.4%, P = 0.006) and 12 months (37.8% vs. 18.4%, P = 0.004) than those treated with CNI. Independent predictors of proteinuria at 12 months were GFR at one month (OR 0.62 per 10 ml/min/1.73 m, P<0.001), delayed graft function (OR 11.5, P = 0.02), and a SRL-based regimen (OR 4.18, P=0.002). By univariable analysis, SRL vs. CNI patients had higher GFR at each point. SRL-treated patients without proteinuria had higher GFR at 12 months compared to CNI-treated patients with and without proteinuria (66 vs. 50 or 56 ml/min/1.73 m, P < 0.05). No difference in GFR was seen between SRL-treated patients with proteinuria vs. CNI-treated patients without proteinuria (57 vs. 56 ml/min/1.73 m, P > 0.05). Absence of proteinuria and a SRL-based regimen remained independently associated FS with higher GFR at 12 months by multivariable analyses.

CONCLUSIONS

De novo SRL-based immunosuppression is associated with a higher frequency of semi-quantitative proteinuria, however, estimated graft function at 1 year posttransplant remains superior to that of CNI-treated patients. Nevertheless, the long-term implications of these findings need to be determined.

Individualization of Immunosuppressive Therapy. II. Sirolimus as a Less Nephrotoxic Alternative to Calcineurin Inhibitors

The nephrotoxic effects of chronic administration of calcineurin inhibitors have created a demand for a potent immunosuppressive drug free of this side effect. Sirolimus (SRL) clearly displays fewer and a lesser degree of adverse effects on renal function by itself. However, in combination with calcineurin antagonists, it tends to augment the nephrotoxicity due, at least in part, to a pharmacokinetic interaction. The use of SRL for de novo immunosuppression (even with adjunctive mycophenolate mofetil) is probably not sufficient to avert alloimmune reactions. A useful combination with SRL can be achieved by reducing calcineurin inhibitor exposure by 80% for immediately functioning kidneys or by delaying its inception until renal graft recovery. SRL proffers additional benefits as an inhibitor of endothelial and smooth muscle cell proliferation, serving as the foundation of chronic immunosuppressive therapy.

Rapamycin inhibits human renal epithelial cell proliferation: Effect on cyclin D3 mRNA expression and stability

BACKGROUND

Recent data have suggested that rapamycin use during the initial period after transplantation is associated with prolonged delayed graft function (DGF). Because of the known effects of rapamycin in other cell types, we speculated that this action may be secondary to human renal epithelial cells (HRECs) inhibition of proliferation.

METHODS

Primary cultures of HRECs were incubated with various concentrations of rapamycin. Cell proliferation was evaluated by cytotoxicity assays. The cell cycle was analyzed by flow cytometry. Protein expression levels were assessed by Western blot. Cyclin D3 mRNA levels were measured by quantitative real-time polymerase chain reaction (PCR). The transcriptional activity of the cyclin D3 gene was evaluated using transient transfection.

RESULTS

Rapamycin exerted a significant concentration-dependent antiproliferative effect on growing HRECs by inhibiting the G(1) to S transition. The p70(S6) kinase pathway leading to cell cycle progression was found to be active, and low concentrations of rapamycin dramatically reduced p70(S6) kinase phosphorylation. Rapamycin completely inhibited the increase in cyclin D3 protein expression and mRNA accumulation induced by fetal calf serum, but did not affect cyclin E or cdk-inhibitor expression levels. This regulation of cyclin D3 protein expression is mainly due to a destabilization of its mRNA. Rapamycin reduced the mRNA half-life by 26% (4.8 +/- 1.3 hours vs. 6.5 +/- 1.0 hours, P < 0.001).

CONCLUSION

Rapamycin inhibits the proliferative response of HRECs to mitogenic stimuli, and causes cell cycle arrest in the early G(1) phase, not only by a nonspecific process due to inhibition of the p70(S6k) pathway, but also by a direct effect on cyclin D3 mRNA stability.

The Selective Use of Basiliximab Versus Thymoglobulin in Combination with Sirolimus for Cadaveric Renal Transplant Recipients at Low Risk Versus High Risk for Delayed Graft Function

BACKGROUND

We previously reported that the use of basiliximab together with sirolimus permits a window of recovery from delayed graft function before the introduction of reduced-dose cyclosporine. The present study reviews our experience with the substitution of thymoglobulin for basiliximab as induction therapy for recipients at increased risk for early acute rejection episodes.

METHODS

We retrospectively reviewed 145 cadaveric renal allograft recipients who received either basiliximab (n=115) or thymoglobulin (n=30) in combination with sirolimus and prednisone, followed by delayed introduction of reduced doses of cyclosporine. Recipients were stratified as high immune responders if they were African American, a retransplant recipient, or a recipient with a panel-reactive antibody greater than 50%. All other recipients were considered low immune responders.

RESULTS

Basiliximab-treated high immune responders exhibited a higher incidence of acute rejection episodes (26%) than either basiliximab-treated low immune responders (10%, P=0.04) or thymoglobulin-treated high immune responders (3%, P=0.01). The median time to initiation of cyclosporine was 12 days; cyclosporine was initiated when the serum creatinine level was 2.5 mg/dL or less. Patients with early return of renal function displayed a lower incidence of acute rejection episodes than those with later recovery of function (P=0.003). High immune responders treated with basiliximab expressed a higher mean serum creatinine level at 3 months (P<0.01), 6 months (P=0.02) and 12 months (P=0.01) than either low immune responders treated with basiliximab or high immune responders treated with thymoglobulin.

CONCLUSION

A strategy combining sirolimus with basiliximab for low-immunologic risk recipients and thymoglobulin for high-risk recipients leads to prompt recovery of renal function with a low risk of acute rejection episodes.

Acute Nephrotoxicity of Tacrolimus and Sirolimus in Renal Isografts: Differential Intragraft Expression of Transforming Growth Factor-??1 and ??-Smooth Muscle Actin

BACKGROUND

Renal dysfunction early after kidney transplantation has multiple causes including ischemia-reperfusion (I/R) injury and drug-induced nephrotoxicity. This study assesses the acute nephrotoxicity of tacrolimus (Tac) and sirolimus (Sir) in a rat renal isograft model.

METHODS

Lewis renal isografts and uninephrectomized rats that did not undergo transplantation were treated with various doses of Tac (0.5-5.0 mg/kg/d) or Sir (0.5-6.5 mg/kg/d). Kidneys were examined on day 14 by routine histology and immunohistochemistry for transforming growth factor (TGF)-beta1 and alpha-smooth muscle actin (SMA).

RESULTS

Both Tac and Sir demonstrated evidence of nephrotoxicity in the early posttransplant period including increased serum creatinine and morphologic changes in the graft including interstitial inflammation, fibrosis, and tubular vacuolization. Nephrotoxicity was most prominent in the high-dose treatment groups for both drugs and was more severe in transplanted kidneys than in uninephrectomized animals that did not undergo transplantation, suggesting an additive effect of I/R injury and drug nephrotoxicity. Both Tac and Sir increased intragraft TGF-beta1 and alpha-SMA, but there were distinct differences in the patterns of TGF-beta1 expression. Both demonstrated TGF-beta1 in tubular epithelial cells, but Sir was associated with proximal tubular TGF-beta1 localization in a bright granular pattern, whereas Tac was associated with diffuse distal tubular staining.

CONCLUSIONS

Both Tac and Sir may be nephrotoxic in the early posttransplant period, especially at high doses and when combined with I/R injury. Immunohistochemical localization of TGF-beta1 in the tubular cells was distinctly different with each drug, suggesting possible differences in the mechanism(s) of nephrotoxicity requiring further study.

Immunosuppression for Long-Term Maintenance of Renal Allograft Function

The incidence and severity of acute rejection episodes was markedly reduced by the introduction of new immunosuppressive drug regimens for renal transplantation, resulting in improved graft survival at 1 year. However, only modest improvement has been shown in long-term graft function rates. This overview evaluates the efficacy of currently used immunosuppressive drugs and drug combinations for long-term maintenance therapy. Prospective controlled trials rarely extend beyond 5 years; therefore, registry data and retrospective reports have also been employed. From currently available data it may be concluded that the initial beneficial effect of ciclosporin (cyclosporin) is lost 10 years after transplantation. Tacrolimus is an alternative to ciclosporin with a different profile of adverse effects and a higher efficacy in acute rejection treatment. For long-term maintenance, projected half-lives of kidney graft function are in favour of tacrolimus. Mycophenolate mofetil (MMF) has been shown to significantly reduce the incidence of early rejections. However, the improved long-term graft survival reported in retrospective studies has still to be confirmed in controlled trials. There is no convincing evidence for superiority of triple therapy including prednisone (or prednisolone), calcineurin inhibitors and azathioprine/MMF over dual therapy without azathioprine/MMF with respect to long-term outcome. Withdrawal of corticosteroids or calcineurin inhibitors clearly reduces adverse drug effects but carries the risk of acute rejection episodes. Avoidance of corticosteroids by using new immunosuppressive drug combinations may be an option to minimise toxic adverse effects in the future. At present, it seems unjustified to convert renal transplant recipients with stable graft function and tolerable adverse effects from one drug to another solely in expectation of future benefits. Acute early or late rejection episodes and intolerable adverse effects are good reasons for conversions between calcineurin inhibitors or cytotoxic agents. Chronic allograft nephropathy with slowly deteriorating graft function remains an unresolved problem.