Delayed mTOR inhibition with low dose of everolimus reduces TGFβ expression, attenuates proteinuria and renal damage in the renal mass reduction model

A comprehensive update of the metabolic and toxicological considerations for immunosuppressive drugs used during pancreas transplantation

INTRODUCTION

Despite significant advancements in immunosuppressive regimens and surgical techniques, the prevalence of adverse events related to immunosuppression remains a major challenge affecting the long-term survival rates of pancreas and kidney allografts.

AREAS COVERED

This article presents a comprehensive review of the literature and knowledge (Jan/2012-Feb/2023) concerning glucose metabolism disorders and nephrotoxicity associated with tacrolimus and mammalian target of rapamycin inhibitors (mTORi). Novel signaling pathways potentially implicated in these adverse events are discussed. Furthermore, we extensively examine the findings from clinical trials evaluating the efficacy and safety of tacrolimus, mTORi, and steroid minimization.

EXPERT OPINION

Tacrolimus-based regimens continue to be the standard treatment following pancreas transplants. However, prolonged use of tacrolimus and mTORi may lead to hyperglycemia and nephrotoxicity. Understanding and interpreting experimental data, particularly concerning novel signaling pathways beyond calcineurin-NFAT and mTOR pathways, can offer valuable insights for therapeutic interventions to mitigate hyperglycemia and nephrotoxicity. Additionally, critically analyzing clinical trial results can identify opportunities for personalized safety-based approaches to minimize side effects. It is imperative to conduct randomized-controlled studies to assess the impact of mTORi use and steroid-free protocols on pancreatic allograft survival. Such studies will aid in tailoring treatment strategies for improved transplant outcomes.

Morphology of the male rat gonad after in Utero exposure to immunosuppressants

The protocol for immunosuppression of pregnant women is based on immunosuppressant panels. The aim of the study was to determine the influence of commonly applied combinations of immunosuppressants to pregnant rats on the morphology of the offspring' testes. Pregnant rats were treated with cyclosporin A (CsA), mycophenolate mofetil (MMF) and prednisone (Pred) (CMG); tacrolimus (Tc), MMF and Pred (TMG); CsA, everolimus (Ev) and Pred (CEG). Testes of mature offspring underwent morphological analysis. Mainly in the testes of CMG and TMG rats the morphological and functional changes were observed: immature germ cells (GCs) in the seminiferous tubule (ST) lumen, invaginations of the basement membrane, infolding to the seminiferous epithelium (SE), the ST wall thickening, increased acidophilia of Sertoli cells' (SCs) cytoplasm, large residual bodies near the lumen, dystrophic ST and tubules look like the Sertoli cell-only syndrome, Leydig cells with abnormal cell nucleus, hypertrophy of the interstitium, blurring of the boundary between ST wall and interstitium, a reduced number of GCs in the SE, vacuolation of the SE. In the CEG there were only a reduced number of GCs in some tubules and vacuolization of SCs. The safest combination of drugs was CEG, while the TMG and CMG were gonadotoxic.

The mTOR inhibitor everolimus attenuates tacrolimus-induced renal interstitial fibrosis in rats

AIMS

Tacrolimus-a widely used immunosuppressant to prevent allograft rejection after organ transplantation-is nephrotoxic, increasing the risk of kidney injury accompanied by kidney fibrosis. The mammalian target of rapamycin (mTOR) inhibitor, everolimus, is an immunosuppressant used together with tacrolimus. Although mTOR signaling inhibition has been demonstrated to exhibit antifibrotic effects, the efficacy of everolimus against tacrolimus-induced kidney fibrosis has not been explored. Therefore, we evaluated the protective effects of everolimus against tacrolimus-induced kidney fibrosis.

MAIN METHODS

To assess antifibrotic effect of everolimus against tacrolimus-induced kidney fibrosis, male Wistar rats were subcutaneously administered vehicle or tacrolimus (5 mg/kg per day) and/or everolimus (0.2 mg/kg per day) for 2 weeks after bilateral renal ischemia for 45 min. The antifibrotic effect of everolimus was also assessed using rat kidney fibroblast cell line (NRK-49F).

KEY FINDINGS

Tacrolimus administration increased predominant profibrotic cytokine transforming growth factor-β (TGF-β) and fibroblast activation marker α-smooth muscle actin (α-SMA) expression and promoted the infiltration of macrophages in the kidney cortex, resulting in renal interstitial fibrosis in rats. Tacrolimus increased serum creatinine, blood urea nitrogen, kidney injury molecule-1 (KIM-1), and kidney injuries, such as tubular dilation, vacuolization, and glomerular atrophy. Everolimus administration attenuated tacrolimus-induced kidney fibrosis and the associated abnormalities. Everolimus strongly suppressed TGF-β-induced kidney fibroblast activation and extracellular matrix protein expression by the mTOR signaling inhibition.

SIGNIFICANCE

We demonstrated that everolimus attenuates tacrolimus-induced renal interstitial fibrosis in rats. Owing to its protective effect against tacrolimus-induced kidney fibrosis, everolimus may be useful when used concomitantly with tacrolimus.

mTOR-Inhibition and COVID-19 in Kidney Transplant Recipients: Focus on Pulmonary Fibrosis

Kidney transplant recipients are at high risk of developing severe COVID-19 due to the coexistence of several transplant-related comorbidities (e.g., cardiovascular disease, diabetes) and chronic immunosuppression. As a consequence, a large part of SARS-CoV-2 infected patients have been managed with a reduction of immunosuppression. The mTOR-I, together with antimetabolites, have been often discontinued in order to minimize the risk of pulmonary toxicity and to antagonize pharmacological interaction with antiviral/anti-inflammatory drugs. However, at our opinion, this therapeutic strategy, although justified in kidney transplant recipients with severe COVID-19, should be carefully evaluated in asymptomatic/paucisymptomatic patients in order to avoid the onset of acute allograft rejections, to potentially exploit the mTOR-I antiviral properties, to reduce proliferation of conventional T lymphocytes (which could mitigate the cytokine storm) and to preserve Treg growth/activity which could reduce the risk of progression to severe disease. In this review, we discuss the current literature regarding the therapeutic potential of mTOR-Is in kidney transplant recipients with COVID-19 with a focus on pulmonary fibrosis.

The Effects of Immunosuppressive Treatment during Pregnancy on the Levels of Potassium, Iron, Chromium, Zinc, Aluminum, Sodium and Molybdenum in Hard Tissues of Female Rats and Their Offspring

The ideal immunosuppressive regimen should provide for excellent immunosuppression with no side effects. Yet, current immunosuppressive therapy regimens commonly used in clinical applications fail to meet this criterion. One of the complications caused by immunosuppressive drugs is mineralization disorders in hard tissues. In this study, we evaluated the effects of three immunosuppressive therapies used after transplantation on the levels of potassium, iron, chromium, zinc, aluminum, sodium and molybdenum in the bones and teeth of female rats and their offspring. The study was conducted on 32 female Wistar rats, subjected to immunosuppressive regimens (cyclosporine A, mycophenolate mofetil and prednisone; tacrolimus, mycophenolate mofetil and prednisone; and cyclosporine A, everolimus and prednisone). The hard tissues of rats were analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES, ICAP 7400 Duo, Thermo Scientific) equipped with a concentric nebulizer and a cyclonic spray chamber. All the immunosuppressive regimens included in the study affected the concentrations of the studied minerals in hard tissues of female rats and their offspring. The therapy based on cyclosporine A, everolimus and prednisone led to a decline in the levels of iron in bone, zinc in teeth, and molybdenum in the bone and teeth of mothers, while in the offspring, it caused a decline of bone potassium, with a decrease in iron and increase of molybdenum in teeth. Moreover, the regimen caused an increase in aluminum and chromium in the teeth and aluminum in the bones of the offspring, and consequently, it seems to be the therapy with the most negative impact on the mineral metabolism in hard tissues.

Preventive effect of early introduction of everolimus and reduced-exposure tacrolimus on renal interstitial fibrosis in de novo living-donor renal transplant recipients

BACKGROUND

To improve the long-term outcomes following renal transplantation, prevention of renal-allograft interstitial fibrosis (IF), mainly due to calcineurin inhibitors, is an important therapeutic target. Everolimus (EVR) was reported to have antifibrotic effects. We aimed to investigate the safety, efficacy, and IF of our modified immunosuppressive regimen, which includes early introduction of EVR and reduced-exposure tacrolimus (Tac) (EVR group), and compare it with the standard-exposure tacrolimus-based regimen (Tac group) in de novo living-donor renal recipients.

METHODS

In this retrospective, single-center cohort study, we compared the 2-year clinical courses between the two groups according to intention to treat. Additionally, in patients in whom biopsies were obtained at 1 h, 3 months, and 12 months post-transplant, we compared IF between the groups using imaging analysis.

RESULTS

Overall, 47 patients were included (EVR group, n = 22; Tac group, n = 25). There were no significant differences in renal function and incidences of rejection and viral infections between the groups at the 2-year post-transplant follow-up. However, pathologic imaging analysis (n = 34) revealed chronological progression of IF in the Tac group during the first year post-transplant and no changes in the EVR group (fibrosis rate at 3 months: 20.8 vs. 13.6%, p < 0.001; at 12 months: 24.7 vs. 14.7%, p < 0.001, respectively).

CONCLUSION

Our modified immunosuppressive regimen may have an antifibrotic effect on transplanted kidneys without loss of safety and efficacy.

Erlotinib attenuates the progression of chronic kidney disease in rats with remnant kidney

Background

Increasing evidence indicates that epidermal growth factor receptor (EGFR) has a pathogenic role in renal fibrosis. Currently no effective treatment can completely halt the progression of chronic kidney disease (CKD). This study was undertaken to investigate the renoprotective effects of erlotinib, a tyrosine kinase inhibitor that can block EGFR activity in the progression of CKD and the mechanisms involved.

Methods

Sprague Dawley rats with 5/6 nephrectomy were administered either erlotinib or vehicle from 2 weeks after surgery and for a period of 8 weeks. Blood pressure, proteinuria and serum creatinine were measured periodically. Renal morphological investigations were performed at sacrifice. In vitro, we used normal human mesangial cells (NHMCs) and human proximal tubular cells to investigate the inhibitory effects of erlotinib on renal fibrosis-associated signaling pathways by western blotting.

Results

Erlotinib treatment significantly blunted the progression of CKD as evidenced by reduced levels of serum creatinine, proteinuria and renal cortical profibrogenic genes and scores of glomerulosclerosis and tubulointerstitial damage. Tubulointerstitial macrophage infiltration and multiple pro-inflammatory cytokine gene expression levels were also attenuated by erlotinib treatment. In vitro, heparin-binding epidermal growth factor-like growth factor-induced Akt and extracellular-regulated kinase (ERK) 1/2 activation in normal human mesangial cells and human proximal tubular cells was inhibited by pretreatment with erlotinib.

Conclusions

EGFR blocking by erlotinib protected against renal fibrosis in 5/6 nephrectomized rats via inhibition of Akt and ERK 1/2 signaling pathways, which are associated with renal fibrosis. Erlotinib also has anti-inflammatory properties, which may contribute to its renoprotective effects. Erlotinib represents a potential novel therapeutic strategy for the treatment of CKD.

Cyclin G1 and TASCC regulate kidney epithelial cell G2-M arrest and fibrotic maladaptive repair

Fibrosis contributes to the progression of chronic kidney disease (CKD). Severe acute kidney injury can lead to CKD through proximal tubular cell (PTC) cycle arrest in the G₂-M phase, with secretion of profibrotic factors. Here, we show that epithelial cells in the G₂-M phase form target of rapamycin (TOR)-autophagy spatial coupling compartments (TASCCs), which promote profibrotic secretion similar to the senescence-associated secretory phenotype. Cyclin G1 (CG1), an atypical cyclin, promoted G₂-M arrest in PTCs and up-regulated TASCC formation. PTC TASCC formation was also present in humans with CKD. Prevention of TASCC formation in cultured PTCs blocked secretion of profibrotic factors. PTC-specific knockout of a key TASCC component reduced the rate of kidney fibrosis progression in mice with CKD. CG1 induction and TASCC formation also occur in liver fibrosis. Deletion of CG1 reduced G₂-M phase cells and TASCC formation in vivo. This study provides mechanistic evidence supporting how profibrotic G₂-M arrest is induced in kidney injury and how G₂-M-arrested PTCs promote fibrosis, identifying new therapeutic targets to mitigate kidney fibrosis.

The influence of exposure to immunosuppressive treatment during pregnancy on renal function and rate of apoptosis in native kidneys of female Wistar rats

Pregnancy puts a significant additional strain on kidneys. The aim of our study was to investigate the impact of immunosuppressive drugs on changes in native kidneys in female Wistar rats after exposure during pregnancy. The study was conducted on 32 dams, subjected to immunosuppressive regimens commonly used in the therapy of human kidney transplant recipients (cyclosporine A, mycophenolate mofetil and prednisone; tacrolimus, mycophenolate mofetil and prednisone; cyclosporine A, everolimus and prednisone). The animals received drugs for 2 weeks before pregnancy and during 3 weeks of pregnancy. In all treated dams lower body weight (but not kidney mass) and alterations in serum sodium and chloride ions were found; serum creatinine concentration was increased in dams treated with cyclosporine A, everolimus and prednisone. All treatment groups of dams showed increased apoptosis in the distal tubules. In histological examination the changed intensity of acidophilic or basophilic cytoplasm of epithelial cells was found in kidneys of rats treated with calcineurin inhibitors, mycophenolate mofetil and prednisone. All immunosuppressive regimens caused abnormalities affecting nephron tubules. Regimens containing calcineurin inhibitors and mycophenolate mofetil caused higher rate of apoptosis and more pronounced histopathological changes. Regimen based on everolimus despite the lower rate of apoptosis in the proximal tubules and lower accumulation of kidney injury markers revealed higher serum creatinine concentration. Thus, interpretation which combination of drugs is better or worse for long-lasting functioning of kidneys in pregnant females requires further studies.

Early Conversion to Prednisolone/Everolimus as an Alternative Weaning Regimen Associates With Beneficial Renal Transplant Histology and Function: The Randomized-Controlled MECANO Trial

In renal transplantation, use of calcineurin inhibitors (CNIs) is associated with nephrotoxicity and immunosuppression with malignancies and infections. This trial aimed to minimize CNI exposure and total immunosuppression while maintaining efficacy. We performed a randomized controlled, open-label multicenter trial with early cyclosporine A (CsA) elimination. Patients started with basiliximab, prednisolone (P), mycophenolate sodium (MPS), and CsA. At 6 months, immunosuppression was tapered to P/CsA, P/MPS, or P/everolimus (EVL). Primary outcomes were renal fibrosis and inflammation. Secondary outcomes were estimated glomerular filtration rate (eGFR) and incidence of rejection at 24 months. The P/MPS arm was prematurely halted. The trial continued with P/CsA (N = 89) and P/EVL (N = 96). Interstitial fibrosis and inflammation were significantly decreased and the eGFR was significantly higher in the P/EVL arm. Cumulative rejection rates were 13% (P/EVL) and 19% (P/CsA), (p = 0.08). A post hoc analysis of HLA and donor-specific antibodies at 1 year after transplantation revealed no differences. An individualized immunosuppressive strategy of early CNI elimination to dual therapy with everolimus was associated with decreased allograft fibrosis, preserved allograft function, and good efficacy, but also with more serious adverse events and discontinuation. This can be a valuable alternative regimen in patients suffering from CNI toxicity.

Roles of mTOR complexes in the kidney: implications for renal disease and transplantation

The mTOR pathway has a central role in the regulation of cell metabolism, growth and proliferation. Studies involving selective gene targeting of mTOR complexes (mTORC1 and mTORC2) in renal cell populations and/or pharmacologic mTOR inhibition have revealed important roles of mTOR in podocyte homeostasis and tubular transport. Important advances have also been made in understanding the role of mTOR in renal injury, polycystic kidney disease and glomerular diseases, including diabetic nephropathy. Novel insights into the roles of mTORC1 and mTORC2 in the regulation of immune cell homeostasis and function are helping to improve understanding of the complex effects of mTOR targeting on immune responses, including those that impact both de novo renal disease and renal allograft outcomes. Extensive experience in clinical renal transplantation has resulted in successful conversion of patients from calcineurin inhibitors to mTOR inhibitors at various times post-transplantation, with excellent long-term graft function. Widespread use of this practice has, however, been limited owing to mTOR-inhibitor- related toxicities. Unique attributes of mTOR inhibitors include reduced rates of squamous cell carcinoma and cytomegalovirus infection compared to other regimens. As understanding of the mechanisms by which mTORC1 and mTORC2 drive the pathogenesis of renal disease progresses, clinical studies of mTOR pathway targeting will enable testing of evolving hypotheses.

The influence of intrauterine exposure to immunosuppressive treatment on changes in the immune system in juvenile Wistar rats

Background

In our study, we assessed the impact of immunosuppressive drug combinations on changes in the immune system of juvenile Wistar rats exposed to these drugs during pregnancy. We primarily concentrated on changes in two organs of the immune system – the thymus and the spleen.

Methods

The study was conducted on 40 (32+8) female Wistar rats administered full and half dose of drugs, respectively, subjected to regimens commonly used in therapy of human kidney transplant recipients ([1] cyclosporine A, mycophenolate mofetil, and prednisone; [2] tacrolimus, mycophenolate mofetil, and prednisone; [3] cyclosporine A, everolimus, and prednisone). The animals received drugs by oral gavage 2 weeks before pregnancy and during 3 weeks of pregnancy.

Results

There were no statistically significant differences in the weight of the thymus and spleen, but changes were found in the results of blood hematology, cytometry from the spleen, and a histologic examination of the examined immune organs of juvenile Wistar rats. In the cytokine assay, changes in the level of interleukine 17 (IL-17) after increasing amounts of concanavaline A were dose-dependent; the increase of IL-17 was blocked after administration of higher doses of immunosuppressive drugs. However, after a reduction of doses, its increase resumed.

Conclusion

Qualitative, quantitative, and morphological changes in the immune system of infant rats born to pharmacologically immunosuppressed females were observed. Thymus structure, spleen composition, and splenocyte IL-17 production were mostly affected in a drug regimen–dependent manner.

Changes in the Immune System of Female Wistar Rats After Exposure to Immunosuppressive Treatment During Pregnancy

This experimental study assessed the impact of medications frequently used after kidney transplantation on the immune system of pregnant female Wistar rats. The study evaluates medications, both approved and contraindicated during pregnancy in common therapeutic combinations. The study was conducted on 32 female Wistar rats, subjected to immunosuppressive regimens most commonly used in therapy of human kidney transplant recipients (cyclosporine A, mycophenolate mofetil and prednisone; tacrolimus, mycophenolate mofetil and prednisone; and cyclosporine A, everolimus and prednisone). The animals received drugs by oral gavage 2 weeks before pregnancy and at 3 weeks of pregnancy. We found drug regimen-dependent differences in cytometry from spleen. Many subpopulations of lymphocytes were suppressed in rats treated with cyclosporine A, mycophenolate mofetil and prednisone and tacrolimus, mycophenolate mofetil and prednisone; the number of NK cells was increased in group of rats treated with cyclosporine A, everolimus and prednisone. We also found changes in histological examination of thymus and spleen of all treated dams. In cytokine assay, we noticed increasing levels of IL-17 with increasing doses of concanavalin A in control group and in group of dams treated with cyclosporine A, mycophenolate mofetil and prednisone. This increase was blocked in rats treated with tacrolimus, mycophenolate mofetil and prednisone and cyclosporine A, everolimus and prednisone. Qualitative, quantitative and morphological changes of immune system in pharmacologically immunosuppressed females have been observed. Thymus structure, spleen composition and splenocytes IL-17 production were mostly affected in drug regimen-dependent manner.

Impact of Iodinated Contrast on Renal Function and Hemodynamics in Rats with Chronic Hyperglycemia and Chronic Kidney Disease

Iodinated contrast (IC) is clinically used in diagnostic and interventional procedures, but its use can result in contrast-induced acute kidney injury (CI-AKI). Chronic kidney disease (CKD) and chronic hyperglycemia (CH) are important predisposing factors to CI-AKI. The aim of this study was to investigate the impact of iodinated contrast on the renal function and hemodynamics in rats with chronic hyperglycemia and chronic kidney disease. A total of 30 rats were divided into six groups; Sham: control of chronic renal disease; Citrate: control of chronic hyperglycemia (CH); Nx5/6: rats with 5/6 nephrectomy; Chronic Hyperglycemia: rats receiving Streptozotocin 65 mg/kg; Nx5/6 + IC: rats Nx5/6 received 6 mL/kg of IC; CH + IC: Chronic hyperglycemia rats receiving 6 mL/kg of IC. Renal function (inulin clearance; urinary neutrophil gelatinase-associated lipocalin, NGAL) and hemodynamics (arterial blood pressure; renal blood flow; renal vascular resistance) were evaluated. Iodinated contrast significantly increased urinary NGAL and reduced inulin clearance, while the hemodynamics parameters showed changes in arterial blood pressure, renal blood flow, and renal vascular resistance in both CKD and CH groups. The results suggest that the iodinated contrast in risk factors models has important impact on renal function and hemodynamics. NGAL was confirmed to play a role of highlight in diagnosis of CI-AKI.

Dexmedetomidine Attenuates Bilirubin-Induced Lung Alveolar Epithelial Cell Death In Vitro and In Vivo

Objective:

To investigate bilirubin-induced lung alveolar epithelial cell injury together with the protection afforded by dexmedetomidine.

Design:

Prospective, randomized, controlled study.

Setting:

Research laboratory.

Subjects:

Sprague Dawley rats.

Interventions:

Alveolar epithelial A549 cell lines were cultured and received bilirubin (from 0 to 160 μM) to explore the protective pathway of dexmedetomidine on bilirubin-induced alveolar epithelial cell injury assessed by immunochemistry and flow cytometry. Sprague-Dawley rats were subjected to common bile duct ligation surgery to explore the protective effect of dexmedetomidine on hyperbilirubinemia-induced alveolar epithelial cell injury and respiratory failure in comparison with the Sham (subjected to the surgery procedure but without bile duct ligation) or dexmedetomidine control (only received intraperitoneal injection of dexmedetomidine).

Measurements and Main Results:

In vitro, dexmedetomidine reversed the collapse of mitochondrial membrane potential (Δψm), upregulation of cytochrome C, B cell leukemia 2 associated X protein, and cleaved-caspase 3 and 9 in A549 epithelial cells with bilirubin challenge. Furthermore, dexmedetomidine reversed the arrest of cell cycle and the downregulation of the transforming growth factorβ, phosphorylated mammalian target of rapamycin, and p42/44 mitogen-activated protein kinase induced by bilirubin. In vivo, pulmonary edema and inflammation were found after common bile duct ligation. Bilirubin and Paco₂ were significantly increased, and oxygen (Pao₂) was significantly decreased in the blood of common bile duct ligation rats from the postsurgery day 7 to day 21 when compared with those in the sham controls, respectively (p < 0.01). Daily intraperitoneal injection of dexmedetomidine significantly alleviated the lung edema and injury and prevented respiratory failure.

Conclusion:

Our data both in vitro and in vivo demonstrated that dexmedetomidine protected alveolar epithelial cell from bilirubin-induced injury. Dexmedetomidine may be a good choice of anesthetic/sedative for patients with chronic liver disease during the perioperative period.

Antialbuminuric actions of calcilytics in the remnant kidney

Hyperphosphatemia accelerates the progression of chronic kidney diseases. In the present study, the effects of ronacaleret, a calcilytic agent, on renal injury were assessed in the following four groups of rats: 5/6-nephrectomized Wistar rats as a control (C group), rats treated with ronacaleret (3 mg·kg(-1)·day(-1); R group), rats treated with calcitriol (30 ng·kg(-1)·day(-1); V group), and rats treated with both ronacaleret and calcitriol (R + V group). Three months later, rats were euthanized under anesthesia, and the remnant kidneys were harvested for analysis. Albuminuria was lower in the R and V groups than in the C group (P < 0.05). Creatinine clearance was elevated in the R and V groups compared with the C group (P < 0.05). Serum Ca(2+) and renal ANG II were higher in the R + V group than in the C group (P < 0.05 for each), and serum phosphate was reduced in the R group compared with the C group (P < 0.05). Fibroblast growth factor-23 was lower in the R group and higher in the V and R + V groups than in the C group. However, parathyroid hormone did not differ significantly among the four groups. Renal klotho expression was elevated in the R and V groups compared with the C group (P < 0.05). The present data indicate that ronacaleret preserves klotho expression and renal function with reductions in serum phosphate and albuminuria in 5/6-nephrectomized rats. Our findings demonstrate that vitamin D prevents declines in klotho expression and renal function, suppressing albuminuria.

Functional and histological improvement after everolimus rescue of chronic allograft dysfunction in renal transplant recipients

Background

We tested the strategy of mTOR inhibitors with calcineurin inhibitor minimization in renal transplant recipients with known chronic allograft dysfunction.

Methods

In this open-label, single-arm study, renal transplant patients were recruited after biopsy-confirmed chronic allograft dysfunction in the absence of acute rejection episode within 2 months, with proteinuria <0.8 g/day, and serum creatinine <220 μmol/L or estimated glomerular filtration rate >40 mL/min/1.73 m². They were converted to everolimus (aiming for trough everolimus level 3–8 ng/mL) with cyclosporine minimization, to assess the effect on renal function, rate of glomerular filtration rate decline, and longitudinal transplant biopsy at 12 months.

Results

Seventeen Chinese patients (median transplant duration, 4.2 years) were recruited; no patients discontinued study medication. The mean slope of the glomerular filtration rate over time was −4.31±6.65 mL/min/1.73 m² per year in the year before everolimus, as compared with 1.29±5.84 mL/min/1.73 m² per year in the 12 months of everolimus therapy, a difference of 5.61 mL/min/1.73 m² per year (95% confidence interval [CI], 0.40–10.8) favoring everolimus therapy (P=0.036). Serial renal biopsy histology showed significant decrease of tubular atrophy (15.7%±11.3% versus 7.1%±7.3%, P=0.005) and interstitial fibrosis (14.8%±11.5% versus 7.2%±8.2%, P=0.013). Intrarenal expression of TGF-β1 mRNA showed a nonsignificant decrease after everolimus treatment.

Conclusion

In renal transplant recipients with biopsy-confirmed chronic allograft dysfunction, we found a significant beneficial effect of everolimus rescue therapy and calcineurin inhibitor minimization strategy on the improvement of glomerular filtration rate decline rate. In secondary analysis, everolimus was shown to slow down the disease progression by reducing the tubular atrophy and interstitial fibrosis scoring.

Recent advances in renal interstitial fibrosis and tubular atrophy after kidney transplantation

Although kidney transplantation has been an important means for the treatment of patients with end stage of renal disease, the long-term survival rate of the renal allograft remains a challenge. The cause of late renal allograft loss, once known as chronic allograft nephropathy, has been renamed “interstitial fibrosis and tubular atrophy” (IF/TA) to reflect the histologic pattern seen on biopsy. The mechanisms leading to IF/TA in the transplanted kidney include inflammation, activation of renal fibroblasts, and deposition of extracellular matrix proteins. Identifying the mediators and factors that trigger IF/TA may be useful in early diagnosis and development of novel therapeutic strategies for improving long-term renal allograft survival and patient outcomes. In this review, we highlight the recent advances in our understanding of IF/TA from three aspects: pathogenesis, diagnosis, and treatment.

mTOR inhibitors and renal allograft: Yin and Yang

Mammalian target of rapamycin inhibitors (mTOR-I), everolimus and sirolimus, are immunosuppressive drugs extensively used in renal transplantation. Their main mechanism of action is the inhibition of cell signaling through the PI3 K/Akt/mTOR pathway. This interesting mechanism of action confers to these medications both great immunosuppressive potential and important anti-neoplastic properties. Although the clinical utility of this drug category, as with other antineoplastic/immunosuppressants, is clear, the use of mTOR-I commonly results in the development of several complications. In particular, these agents may determine severe renal toxicity that, as recent studies report, seems clearly correlated to dose and duration of drug use. The mTOR-I-induced renal allograft spectrum of toxicity includes the enhanced incidence of delayed graft function, nephrotoxicity in particular when co-administered with calcineurin inhibitors (CNI) and onset of proteinuria. The latter effect appears highly frequent in patients undergoing mTOR-I treatment and significantly associated with a rapid graft lost. The damage leading to this complication interests both the glomerular and tubular area. mTOR-I cause an inhibition of proliferation in podocytes and the epithelial-to-mesenchymal transition in tubular cells. Interestingly, all these side effects are mostly reversible and dose related. Therefore, it is unquestionable that these particular drugs should be administered at the lowest dose able to maintain relatively low trough levels, in order to maximize their important and specific therapeutic effects while minimizing or avoiding drug toxicities. Utilization of low dosages of mTOR-I should be encouraged not only in CNI-combined schemas, but also when administered alone in a CNI-free immunosuppressive protocol.

Influence of conversion from calcineurin inhibitors to everolimus on fibrosis, inflammation, tubular damage and vascular function in renal transplant patients

BACKGROUND

Conversion from calcineurin inhibitor (CNI) to mTOR inhibitors may reduce and even halt the progression of chronic allograft dysfunction (CAD) which is the most important cause of renal allograft loss. We aimed to investigate the effects of conversion from CNI to everolimus on parameters of fibrosis, inflammation, glomerulotubular damage and vascular functions in renal transplant recipients.

METHODS

Fifteen stable renal transplant recipients who were under CNI treatment (male/female 13/2, mean age 41 ± 10 years) were enrolled and switched to everolimus. Serum and urinary transforming growth factor-β (TGF-β), urinary neutrophil gelatinase-associated lipocalin (NGAL) and monocyte chemoattractant protein-1 (MCP-1) were measured as markers of fibrosis, tubular damage and inflammation. As parameters of vascular functions, pulse wave velocity (PWV), augmentation index (AIx), serum asymmetric dimethyl-arginine and fibroblast growth factor-23 (FGF-23) were measured. All these measurements were repeated at the 3rd month of conversion.

RESULTS

Estimated GFR (52 ± 7-57 ± 11 ml/min/l.73 m(2), p = 0.02) (was increased after conversion to everolimus. However, serum uric acid levels were significantly decreased (6.21 ± 1.21-5.50 ± 1.39 mg/dL, p = 0.01). Serum TGF-β levels (8727 ± 2897-1943 ± 365 pg/mL, p = 0.03) and urinary NGAL levels (26 ± 10-12 ± 2 ng/mg creatinine, p = 0.05) were significantly decreased. However, urinary MCP-1, FGF-23, PWV and AIx did not change. Urinary TGF-β was associated with urinary NGAL (r = 0.62, p = 0.01), urinary MCP-1 (r = 0.68, p = 0.005) and proteinuria (r = 0.50, p = 0.05).

CONCLUSION

Conversion from CNI to everolimus resulted in significant decreases of serum TGF-β and urinary NGAL which may represent less fibrosis and tubular damage. Association of urinary TGF-β with NGAL and MCP-1 suggests that tubular damage, fibrosis and inflammation may act together for progression of CAD.

Correlation between TGF-β1 expression and rapamycin-induced liver fibrosis improvement in rats

AIM: To investigate the role of transformation growth factor-β1 (TGF-β1) in the therapeutic effect of rapamycin on liver fibrosis in rats.

METHODS: Rats were divided into three groups: a normal control group, a liver fibrosis model group and a rapamycin treatment group. Rats were treated with carbon tetrachloride to induce liver fibrosis. Eight weeks after treatment, liver histological changes and the expression of TGF-β1 in the liver were detected. In addition, serum TGF-β1 levels were dynamically monitored.

RESULTS: After immunohistochemical and HE staining, image-pro plus 6 image analysis software was used to analyze the integrated absorbance (IA). The IA values were 9891.4 ± 1725.7, 104239.9 ± 20890.6, and 27853.6 ± 2031 in the normal control group, liver fibrosis model group and rapamycin treatment group, respectively. The expression of TGF-β1 in liver tissue was significantly different among the three groups (P < 0.01).

CONCLUSION: Rapamycin can significantly reduce the levels of TGF-β1 in liver tissue and serum, which may be involved in the therapeutic effect of rapamycin on liver fibrosis.

Everolimus-induced epithelial to mesenchymal transition in immortalized human renal proximal tubular epithelial cells: key role of heparanase

BACKGROUND

Everolimus (EVE) is a drug widely used in several renal transplant protocols. Although characterized by a relatively low nephrotoxicity, it may induce several adverse effects including severe fibro-interstitial pneumonitis. The exact molecular/biological mechanism associated to these pro-fibrotic effects is unknown, but epithelial to mesenchymal transition (EMT) may have a central role. Additionally, heparanase, an enzyme recently associated with the progression of chronic allograft nephropathy, could contribute to activate this machinery in renal cells.

METHODS

Several biomolecular strategies (RT-PCR, immunofluorescence, zymography and migration assay) have been used to assess the capability of EVE (10, 100, 200 and 500 nM) to induce an in vitro heparanase-mediated EMT in wild-type (WT) and Heparanase (HPSE)-silenced immortalized human renal epithelial proximal tubular cells (HK-2). Additionally, microarray technology was used to find additional biological elements involved in EVE-induced EMT.

RESULTS

Biomolecular experiments demonstrated a significant up-regulation (more than 1.5 fold increase) of several genes encoding for well known EMT markers [(alpha-smooth muscle actin (α-SMA), Vimentin (VIM), Fibronectin (FN) and matrix metalloproteinase-9 (MMP9)], enhancement of MMP9 protein level and increment of cells motility in WT HK2 cells treated with high concentrations of EVE (higher than 100 nM). Similarly, immunofluorescence analysis showed that 100 nM of EVE increased α-SMA, VIM and FN protein expression in WT HK2 cells. All these effects were absent in both HPSE- and AKT-silenced cell lines. AKT is a protein having a central role in EMT. Additionally, microarray analysis identified other 2 genes significantly up-regulated in 100 nM EVE-treated cells (p < 0.005 and FDR < 5%): transforming growth factor beta-2 (TGFβ2) and epidermal growth factor receptor (EGFR). Real-time PCR analysis validated microarray.

CONCLUSIONS

Our in vitro study reveals new biological/cellular aspects of the pro-fibrotic activity of EVE and it demonstrates, for the first time, that an heparanase-mediated EMT of renal tubular cells may be activated by high doses of this drug. Additionally, our results suggest that clinicians should administer the adequate dosage of EVE in order to increase efficacy and reduce adverse effects. Finally heparanase could be a new potential therapeutic target useful to prevent/minimize drug-related systemic fibrotic adverse effects.

TGF-β/Smad3 activates mammalian target of rapamycin complex-1 to promote collagen production by increasing HIF-1α expression

Transforming growth factor (TGF)-β is a major mediator of kidney fibrosis. In the past decade it was recognized that, besides canonical Smad signaling, many other signaling pathways participate in the process of TGF-β-induced fibrogenesis. One such pathway involves mammalian target of rapamycin complex (mTORC)1. We recently reported that the hypoxia-inducible factor (HIF)-1 is essential for TGF-β-induced collagen expression regardless of ambient oxygen tension. A modulator of HIF expression other than oxygen tension is mTORC1. We therefore sought to evaluate a possible role for mTORC1 activity in TGF-β-induced fibrogenesis. mTORC1 activity was increased in human mesangial cells treated with TGF-β in a TGF-β receptor-dependent manner. Short hairpin (sh)RNA to Smad3 decreased, while overexpression of Smad3 increased, the mTORC1 activity, suggesting that TGF-β stimulation of mTORC1 also requires Smad3. Pretreatment with rapamycin or shRNA for a regulatory molecule of mTORC1, Raptor, reduced TGF-β-induced COL1A2-luc activity and collagen I protein expression. mTORC1 inhibition also prevented the TGF-β-stimulated increase in both hypoxia-responsive element (HRE) activity and HIF-1α protein expression, while activation of mTORC1 by active Rheb increased basal but not TGF-β-induced HRE activity. shRNA to Smad3 reduced HRE activity, while overexpression of Smad3 increased HIF-1α protein expression and activity in an mTORC1-dependent manner. Lastly, overexpression of HIF-1α bypassed the inhibitory effect of mTORC1 blockade on collagen expression. These results suggest that Smad3/mTORC1 interaction to promote HIF-1 expression is a key step in normoxic kidney fibrogenesis.

Transforming growth factor-beta and the glomerular filtration barrier

The increasing burden of chronic kidney disease worldwide and recent advancements in the understanding of pathologic events leading to kidney injury have opened up new potential avenues for therapies to further diminish progression of kidney disease by targeting the glomerular filtration barrier and reducing proteinuria. The glomerular filtration barrier is affected by many different metabolic and immune-mediated injuries. Glomerular endothelial cells, the glomerular basement membrane, and podocytes—the three components of the filtration barrier—work together to prevent the loss of protein and at the same time allow passage of water and smaller molecules. Damage to any of the components of the filtration barrier can initiate proteinuria and renal fibrosis. Transforming growth factor-beta (TGF-β) is a pleiotropic cytokine strongly associated with the fibrogenic response. It has a known role in tubulointerstitial fibrosis. In this review we will highlight what is known about TGF-β and how it interacts with the components of glomerular filtration barrier and causes loss of function and proteinuria.