Post-Rapamycin Proteinuria: Incidence, Evolution, and Therapeutic Handling at a Single Center

Podocytes maintain high basal levels of autophagy independent of mtor signaling

While constant basal levels of macroautophagy/autophagy are a prerequisite to preserve long-lived podocytes at the filtration barrier, MTOR regulates at the same time podocyte size and compensatory hypertrophy. Since MTOR is known to generally suppress autophagy, the apparently independent regulation of these two key pathways of glomerular maintenance remained puzzling. We now report that long-term genetic manipulation of MTOR activity does in fact not influence high basal levels of autophagy in podocytes either in vitro or in vivo. Instead we present data showing that autophagy in podocytes is mainly controlled by AMP-activated protein kinase (AMPK) and ULK1 (unc-51 like kinase 1). Pharmacological inhibition of MTOR further shows that the uncoupling of MTOR activity and autophagy is time dependent. Together, our data reveal a novel and unexpected cell-specific mechanism, which permits concurrent MTOR activity as well as high basal autophagy rates in podocytes. Thus, these data indicate manipulation of the AMPK-ULK1 axis rather than inhibition of MTOR as a promising therapeutic intervention to enhance autophagy and preserve podocyte homeostasis in glomerular diseases.

Abbreviations: AICAR: 5-aminoimidazole-4-carboxamide ribonucleotide; AMPK: AMP-activated protein kinase; ATG: autophagy related; BW: body weight; Cq: chloroquine; ER: endoplasmic reticulum; ESRD: end stage renal disease; FACS: fluorescence activated cell sorting; GFP: green fluorescent protein; i.p.: intra peritoneal; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; NPHS1: nephrosis 1, nephrin; NPHS2: nephrosis 2, podocin; PLA: proximity-ligation assay; PRKAA: 5ʹ-AMP-activated protein kinase catalytic subunit alpha; RPTOR/RAPTOR: regulatory associated protein of MTOR, complex 1; RFP: red fluorescent protein; TSC1: tuberous sclerosis 1; ULK1: unc-51 like kinase 1

Safety of mTOR inhibitors in adult solid organ transplantation

INTRODUCTION

Mammalian target of rapamycin (mTOR) inhibitors (sirolimus and everolimus) are a class of immunosuppressive drugs approved for solid organ transplantation (SOT). By inhibiting the ubiquitous mTOR pathway, they present a peculiar safety profile. The increased incidence of serious adverse events in early studies halted the enthusiasm as a kidney sparing alternative to calcineurin inhibitors (CNI).

AREAS COVERED

Herein we review mTOR inhibitors safety profile for adult organ transplantation, ranging from acute side effects, such as lymphoceles, delayed wound healing, or cytopenias, to long-term ones which increase morbidity and mortality, such as cancer risk and metabolic profile. Infection, proteinuria, and cutaneous safety profiles are also addressed.

EXPERT OPINION

In the authors' opinion, mTOR inhibitors are a safe alternative to standard immunosuppression therapy with CNI and mycophenolate/azathioprine. Mild adverse events can be easily managed with an increased awareness and close monitoring of trough levels. Most serious side effects are dose- and organ-dependent. In kidney and heart transplantation mTOR inhibitors may be safely used as either low-dose de novo or through early-conversion. In the liver, conversion 4 weeks post-transplantation may reduce long-term chronic kidney disease secondary to calcineurin nephrotoxicity, without increasing hepatic artery/portal vein thrombosis.

Current trends in immunosuppressive therapies for renal transplant recipients

PURPOSE

Current trends in immunosuppressive therapies for renal transplant recipients are reviewed.

SUMMARY

The common premise for immunosuppressive therapies in renal transplantation is to use multiple agents to work on different immunologic targets. The use of a multidrug regimen allows for pharmacologic activity at several key steps in the T-cell replication process and lower dosages of each individual agent, thereby producing fewer drug-related toxicities. In general, there are three stages of clinical immunosuppression: induction therapy, maintenance therapy, and treatment of an established acute rejection episode. Only immunosuppressive therapies used for maintenance therapy are discussed in detail in this review. The most common maintenance immunosuppressive agents can be divided into five classes: (1) the calcineurin inhibitors (CNIs) (cyclosporine and tacrolimus), (2) costimulation blockers (belatacept), (3) mammalian target of rapamycin inhibitors (sirolimus and everolimus), (4) antiproliferatives (azathioprine and mycophenolic acid derivatives), and (5) corticosteroids. Immunosuppressive regimens vary among transplantation centers but most often include a CNI and an adjuvant agent, with or without corticosteroids. Selection of appropriate immunosuppressive regimens should be patient specific, taking into account the medications' pharmacologic properties, adverse-event profile, and potential drug-drug interactions, as well as the patient's preexisting diseases, risk of rejection, and medication regimen.

CONCLUSION

Advancements in transplant immunosuppression have resulted in a significant reduction in acute cellular rejection and a modest increase in long-term patient and graft survival. Because the optimal immunosuppression regimen is still unknown, immunosuppressant use should be influenced by institutional preference and tailored to the immunologic risk of the patient and adverse-effect profile of the drug.

mTOR inhibitor-associated proteinuria in kidney transplant recipients

The use of mammalian target of rapamycin inhibitor (mTOR-I) after kidney transplantation has been associated with a higher incidence of proteinuria compared with calcineurin inhibitors (CNIs). This review will focus on mTOR-I-associated proteinuria in different settings after kidney transplantation: de novo mTOR-I treatment in combination with CNI, de novo mTOR-I-containing and CNI-free treatment, early conversion from a CNI-based regimen to an mTOR-I-based regimen, and late conversion. Some possible mechanisms of mTOR-I-induced proteinuria will also be reviewed.

Sirolimus in pediatric renal transplantation

SRL, an mTOR inhibitor that inhibits cell cycle progression, represents an important alternative to CNIs, which are still the cornerstones of pediatric solid organ tx. Because there are still limited data on SRL use among pediatric solid organ recipients, further studies are needed to verify the efficacy and safety of SRL. It has unique pharmacokinetic characteristics concerning dosing intervals and reduction of the dose in combination with other immunosuppressants. SRL also has antineoplastic, antiviral, and antiatherogenic advantages over other immunosuppressive agents. The adverse effects of SRL including thrombocytopenia, hyperlipidemia, proteinuria, impaired wound healing, mouth ulcers, edema, male hypogonadism, TMA, and interstitial pneumonitis must be considered carefully in pediatric population. This article reviews the most recent data on SRL application in the field of pediatric renal tx.

Proteinuria after conversion to sirolimus in kidney transplant recipients: impact of pre-existing proteinuria, graft function, and angiotensin-converting enzyme inhibitors/angiotensin-receptor antagonists

BACKGROUND

Proteinuria is a known side effect of therapy with sirolimus. The effect of angiotensin-converting enzyme inhibitors or angiotensin-receptor blockers (ACEI/ARB ) on sirolimus-associated proteinuria has not yet been assessed.

PATIENTS AND METHODS

A retrospective cohort study of renal transplant patients treated with sirolimus (n = 55) was performed.

RESULTS

Of 55 patients, 24 (44%) had no proteinuria (<0.15 g/d) prior to conversion. Of 24 patients, 11 (46%) showed de novo proteinuria >0.15 g/d after 12 months, only 2 developed proteinuria > 1 g/d. The total number of proteinuria >1 g/d after 12 months including patients with pre-existing proteinuria >1 g/d (n = 3) was seven of 55 patients (13%). Multivariate regression analysis revealed pre-existing proteinuria > 0.15 g/d and reduced glomerular filtration rate as independent predictors for the development of proteinuria after conversion to sirolimus.

CONCLUSION

Reduced glomerular filtration rate and pre-existing proteinuria but not therapy with ACEI/ARB are independent predictors for proteinuria after conversion to sirolimus. Treatment with ACEI/ARB did not reduce pre-existing proteinuria after conversion except in single cases with severe proteinuria.

Conversion to sirolimus in renal transplant recipients: a single-center experience

Maintenance immunosuppression with calcineurin inhibitors (CNI) following renal transplantation is associated with nephrotoxicity and accelerated graft loss. Sirolimus (SRL) is a nonnephrotoxic immunosuppressive agent. We retrospectively analyzed our experience with kidney transplant recipients who were converted from CNI to SRL. A total of 58 renal transplant recipients were converted from CNI to SRL. SRL was started at a dose of 0.075 mg/kg and, at the same time, CNI dose was reduced by 50% daily for 3 days. SRL trough levels were targeted between 8 and 12 ng/mL. When target trough levels were achieved, CNI was withdrawn. The main indications for switching were posttransplant malignancies (n = 32) and chronic allograft nephropathy (CAN) (n = 10). The mean time from transplantation to conversion was 84 +/- 71 months. Mean serum creatinine level was 1.63 +/- 0.52 mg/dL before conversion. Serum creatinine levels at the 1, 3, 6 months, and 1, 2, 3 years after conversion were 1.64 +/- 0.58 mg/dL (P = 0.67), 1.52 +/- 0.53 mg/dL (P = 0.414), 1.62 +/- 0.62 mg/dL (P = 0.734), and 1.48 +/- 0.58 mg/dL (P = 0.065), 1.58 +/- 0.53 mg/dL (P = 0.854), 1.88 +/- 0.77 mg/dL (P = 0.083), respectively. Daily proteinuria levels increased from 0.04 +/- 0.11 g/day at baseline to 0.55 +/- 1.33 g/day (P = 0.037) after conversion, in the responders group. In the nonresponders group, baseline proteinuria was 0.13 +/- 0.25 g/day, and increased to 1.44 +/- 2.44 g/day after conversion (P = 0.008). SRL was discontinued in 16 patients (31%) because of the occurrence of severe side effects. The proportion of patients remaining on SRL therapy over time was 43.1% at 1 year, 15.5% at 2 years after conversion, and 10.3% at 3 years after conversion. SRL conversion may be very useful in patients suffering from neoplasia; however, frequent side effects related with this intervention should be considered, and routine conversion from CNI to SRL to reduce nephrotoxicity should be discouraged.

Conversion to sirolimus for chronic allograft nephropathy and calcineurin inhibitor toxicity and the adverse effects of sirolimus after conversion

BACKGROUND

Chronic allograft nephropathy and calcineurin inhibitor toxicity may cause graft loss. After kidney transplantation, especially among those patients with chronic allograft nephropathy, sirolimus may be a good alternative to calcineurin inhibitors. Unlike calcineurin inhibitors, sirolimus is devoid of significant nephrotoxicity, but approximately 30% to 50% of patients on sirolimus therapy display mild or severe adverse effects. We sought to report our experience with sirolimus conversion among patients with chronic allograft nephropathy as well as the mild versus severe adverse effects that limit the drug's use.

MATERIALS AND METHODS

We analyzed the outcomes of 88 patients (64 men and 24 women) of overall mean age of 35.9 +/- 9.9 years (range, 21-59 years) who had undergone kidney transplantation. Immunosuppressive therapy had been converted from a calcineurin inhibitor to sirolimus because of biopsy-proven chronic allograft nephropathy, calcineurin inhibitor toxicity, or presence of malignancy. We excluded patients with prior acute rejection episodes. Subjects were divided into two groups with respect to their creatinine levels: Group A < 2 mg/dL and Group B >or= 2 mg/dL. After conversion to sirolimus, possible adverse effects of sirolimus were evaluated at the follow-up inset. Each patient underwent a physical examination, and estimation of serum lipid and electrolyte levels as well as hemoglobin concentration.

RESULTS

At the time of conversion of the 88 renal transplant patients, their mean duration after grafting was 48 +/- 15 months (range, 4-296). The prior treatment consisted of a calcineurin inhibitor, prednisolone, and mycophenolate mofetil. After conversion, the calcineurin inhibitor was stopped and sirolimus was begun. The 48 Group 2 patients (34 men, 14 women) of overall mean posttransplant time of 22.7 +/- 14.6 months who underwent conversion displayed a mean serum creatinine increase to 3.2 +/- 1.4 mg/dL, including 17 subjects who underwent rejection. The 40 Group 1 patients (30 men, 10 women) with a mean overall posttransplant period of 67.6 +/- 49.9 months showed an fall in serum creatinine level to 1.4 +/- 0.5 mg/dL among only 3 patients. While 5/88 patients showed no increase in proteinuria (5.6%); 83 (94.4%) did experience it. Proteinuria increased from a mean of 192 +/- 316 to 449 +/- 422 mg/d. Only three patients displayed heavy proteinuria (>3 g/d); sirolimus was discontinued for this reason. Proteinuria was well controlled in the other patients with angiotensin-converting enzyme and/or angiotensin II receptor inhibitor agents. After sirolimus conversion, serum cholesterol levels increased from 187 +/- 42 to 214 +/- 52 mg/dL, and serum triglyceride levels increased from 161 +/- 61 to 194 +/- 102 mg/dL. All but four patients responded to statin therapy, with serum lipid levels falling to acceptable levels. Another four patients developed unilateral lower extremity edema with sirolimus discontinued for this reason. One patient displayed generalized arthralgia.

CONCLUSION

Chronic allograft nephropathy or calcineurin inhibitor toxicity can lead to loss of graft kidney function. Calcineurin inhibitor toxicity can lead to chronic allograft nephropathy. Patients with a low baseline serum creatinine level who undergo sirolimus conversion showed stabilized kidney function. Late conversion of patients with a serum creatinine above 2 mg/dL face a risk of graft failure. Sirolimus displayed a limited incidence of serious adverse effects; mild or moderate adverse effects, such as hyperlipidemia and proteinuria, were easily controlled with countermeasure therapy.

Chronic allograft nephropathy

PURPOSE OF REVIEW

Despite dramatic declines in acute rejection and early graft failure, long-term outcomes after kidney transplantation have improved little during the past 25 years. Most late allograft failure is attributed to chronic allograft nephropathy, but this is a clinicopathological description and not a diagnosis, and its pathogenesis and treatment are largely unknown.

RECENT FINDINGS

Recent studies suggest that acute rejection during the first few months, and calcineurin inhibitor toxicity thereafter, may both contribute to chronic allograft nephropathy. There is also accumulating evidence that injury from antibody-mediated rejection may play an important pathogenic role in at least some patients with chronic allograft nephropathy, particularly those with transplant glomerulopathy. Therapeutic measures, including protocols to reduce calcineurin inhibitor exposure, remain largely unproven.

SUMMARY

Understanding why so many kidney allografts fail, despite effective preventive measures for early acute rejection, is one of the most important areas of research in kidney transplantation today.