Rapamycin worsens renal function and intratubular cast formation in protein overload nephropathy

Exosomal‑miR‑1184 derived from mesenchymal stem cells alleviates cisplatin‑associated acute kidney injury

Acute kidney injury (AKI) poses a severe threat to human health. MicroRNAs (miRNAs/miRs) are known to be involved in the progression of AKI; however, the function of miR‑1184 in AKI remains unclear. Thus, the aim of the present study was to examine the role of this miRNA in kidney injury. In order to mimic AKI in vitro, HK‑2 cells were treated with cisplatin. Bioinformatics analysis was performed to explore the differentially expressed miRNAs in AKI. A Cell Counting Kit‑8 assay and flow cytometry were performed to examine cell viability and apoptosis, respectively. mRNA expression levels were detected via reverse transcription‑quantitative PCR, and protein levels were investigated by western blot analysis. ELISA was performed to examine the levels of IL‑1β and TNF‑α in the cell supernatants. The results revealed that miR‑1184 expression was downregulated in AKI. Exosomes derived from miR‑1184 agomir‑treated mesenchymal stem cells (MSCs) significantly reversed cisplatin‑induced cell growth inhibition by inhibiting apoptosis. Moreover, forkhead box O4 (FOXO4) was found to be the direct target of miR‑1184, and exosomes expressing miR‑1184 notably inhibited cisplatin‑induced inflammatory responses in HK‑2 cells via the mediation of IL‑1β and TNF‑α. Furthermore, exosomes derived from miR‑1184 agomir‑treated MSCs significantly induced G1 phase arrest in HK‑2 cells via the regulation of FOXO4, p27 Kip1 and CDK2. In conclusion, the present study demonstrated that exosomal‑miR‑1184 derived from MSCs alleviates cisplatin‑associated AKI. Thus, the findings presented herein may shed new light onto the exploration of novel strategies for the treatment of AKI.

Protective Role of Kynurenine 3-Monooxygenase in Allograft Rejection and Tubular Injury in Kidney Transplantation

Renal tubular epithelial cells (TECs) are the primary targets of ischemia-reperfusion injury (IRI) and rejection by the recipient's immune response in kidney transplantation (KTx). However, the molecular mechanism of rejection and IRI remains to be identified. Our previous study demonstrated that kynurenine 3-monooxygenase (KMO) and kynureninase were reduced in ischemia-reperfusion procedure and further decreased in rejection allografts among mismatched pig KTx. Herein, we reveal that TEC injury in acutely rejection allografts is associated with alterations of Bcl2 family proteins, reduction of tight junction protein 1 (TJP1), and TEC-specific KMO. Three cytokines, IFN γ , TNFα, and IL1β, reported in our previous investigation were identified as triggers of TEC injury by altering the expression of Bcl2, BID, and TJP1. Allograft rejection and TEC injury were always associated with a dramatic reduction of KMO. 3HK and 3HAA, as direct and downstream products of KMO, effectively protected TEC from injury via increasing expression of Bcl-xL and TJP1. Both 3HK and 3HAA further prevented allograft rejection by inhibiting T cell proliferation and up-regulating aryl hydrocarbon receptor expression. Pig KTx with the administration of DNA nanoparticles (DNP) that induce expression of indoleamine 2,3-dioxygenase (IDO) and KMO to increase 3HK/3HAA showed an improvement of allograft rejection as well as murine skin transplant in IDO knockout mice with the injection of 3HK indicated a dramatic reduction of allograft rejection. Taken together, our data provide strong evidence that reduction of KMO in the graft is a key mediator of allograft rejection and loss. KMO can effectively improve allograft outcome by attenuating allograft rejection and maintaining graft barrier function.

Renal Iron Accumulation and Oxidative Injury With Aging: Effects of Treatment With an Iron Chelator

Dysregulation of iron metabolism in the kidney may contribute to age-related increases in renal oxidative stress and dysfunction. This study assessed the effects of short-term iron chelation on markers of iron status, oxidative stress, inflammation, and autophagy in the kidneys of old rats. Old Fischer 344 rats (24 months) were treated with deferoxamine (DFO; 200 mg/kg, twice daily for 4.5 days); saline-treated young (6 months) and old rats served as controls. Renal nonheme iron was significantly higher in the old rats, with iron localized in the renal cortex. Ferritin levels were elevated in the kidneys of old rats, while expression of several antioxidant enzymes and mitochondrial proteins were reduced and protein carbonyls increased compared to young rats. DFO treatment significantly reduced ferritin levels, and increased transferrin receptor-1 protein, but did not affect nonheme iron content or protein carbonyls, nor did it reverse age-related changes in antioxidant enzymes and mitochondrial proteins. Although short-term DFO treatment did not mitigate the age-related increase in iron content and oxidative damage, this work demonstrates that old rats respond appropriately to DFO, suggesting that optimization of iron chelation regimens could be useful in improving renal homeostasis with aging.

Aged kidney: can we protect it? Autophagy, mitochondria and mechanisms of ischemic preconditioning

The anti-aging strategy is one of the main challenges of the modern biomedical science. The term "aging" covers organisms, cells, cellular organelles and their constituents. In general term, aging system admits the existence of nonfunctional structures which by some reasons have not been removed by a clearing system, e.g., through autophagy/mitophagy marking and destroying unwanted cells or mitochondria. This directly relates to the old kidney which normal functioning is critical for the viability of the organism. One of the main problems in biomedical studies is that in their majority, young organisms serve as a standard with further extrapolation on the aged system. However, some protective systems, which demonstrate their efficiency in young systems, lose their beneficial effect in aged organisms. It is true for ischemic preconditioning of the kidney, which is almost useless for an old kidney. The pharmacological intervention could correct the defects of the senile system provided that the complete understanding of all elements involved in aging will be achieved. We discuss critical elements which determine the difference between young and old phenotypes and give directions to prevent or cure lesions occurring in aged organs including kidney.

ABBREVIATIONS

AKI: acute kidney injury; I/R: ischemia/reperfusion; CR: caloric restriction; ROS: reactive oxygen species; RC: respiratory chain.

Activated renal tubular Wnt/β-catenin signaling triggers renal inflammation during overload proteinuria

Imbalance of Wnt/β-catenin signaling in renal cells is associated with renal dysfunction, yet the precise mechanism is poorly understood. Previously we observed activated Wnt/β-catenin signaling in renal tubules during proteinuric nephropathy with an unknown net effect. Therefore, to identify the definitive role of tubular Wnt/β-catenin, we generated a novel transgenic "Tubcat" mouse conditionally expressing stabilized β-catenin specifically in renal tubules following tamoxifen administration. Four weeks after tamoxifen injection, uninephrectomized Tubcat mice displayed proteinuria and elevated blood urea nitrogen levels compared to non-transgenic mice, implying a detrimental effect of the activated signaling. This was associated with infiltration of the tubulointerstitium predominantly by M1 macrophages and overexpression of the inflammatory chemocytokines CCL-2 and RANTES. Induction of overload proteinuria by intraperitoneal injection of low-endotoxin bovine serum albumin following uninephrectomy for four weeks aggravated proteinuria and increased blood urea nitrogen levels to a significantly greater extent in Tubcat mice. Renal dysfunction correlated with the degree of M1 macrophage infiltration in the tubulointerstitium and renal cortical up-regulation of CCL-2, IL-17A, IL-1β, CXCL1, and ICAM-1. There was overexpression of cortical TLR-4 and NLRP-3 in Tubcat mice, independent of bovine serum albumin injection. Finally, there was no fibrosis, activation of epithelial-mesenchymal transition or non-canonical Wnt pathways observed in the kidneys of Tubcat mice. Thus, conditional activation of renal tubular Wnt/β-catenin signaling in a novel transgenic mouse model demonstrates that this pathway enhances intrarenal inflammation via the TLR-4/NLRP-3 inflammasome axis in overload proteinuria.

Rapamycin Enhances Repressed Autophagy and Attenuates Aggressive Progression in a Rat Model of IgA Nephropathy

BACKGROUND

IgA nephropathy (IgAN) has been considered to be the most frequent form of primary glomerulonephritis that occurs worldwide with a variety of factors involved in its occurrence and development. The impact of autophagy in IgAN, however, remains partially unclear. This study was designed to investigate the effects of rapamycin in an IgAN model.

METHOD

After establishing an IgAN rat model, SD rats were divided into 4 groups: control, control + rapamycin, IgAN, IgAN + rapamycin. Proteinuria and the pathological changes and the level of autophagy of kidney were texted. Identify the expression of phosphorylation and total mammalian target of rapamycin (mTOR) and s6k1 as well as cyclin D1 in the kidney of rats through Western blot and immunohistochemistry.

RESULTS

With rapamycin treatment, we observed a significant reduction in the progression of proteinuria as well as alleviation of pathological lesions in IgAN rats. Besides, autophagy was inhibited, while the mTOR/S6k1 pathway was activated and expression of cyclin D1 was increased in IgAN. Rapamycin treatment increased autophagy and decreased the expression of cyclin D1.

CONCLUSION

These results may suggest that mTOR-mediated autophagy inhibition may result in mesangial cell proliferation in IgAN.

C5b-9 does not mediate tubulointerstitial injury in experimental acute glomerular disease characterized by selective proteinuria

AIM: To determine whether complement membrane attack complex (C5b-9) has a pathogenic role in tubulointerstitial injury in a renal disease model characterized by acute highly selective proteinuria.

METHODS: Protein-overload nephropathy (PON) was induced in adult female Piebald-Viral-Glaxo rats with or without complement C6 deficiency (C6^- and C6⁺) by daily intraperitoneal injections of bovine serum albumin (BSA, 2 g/d), and examined on days 2, 4 and 8.

RESULTS: Groups with PON developed equivalent levels of heavy proteinuria within 24 h of BSA injection. In C6⁺ rats with PON, the tubulointerstitial expression of C5b-9 was increased and localized predominantly to the basolateral surface of tubular epithelial cells (TECs), whereas it was undetectable in C6^- animals. TEC proliferation (as assessed by the number of BrdU+ cells) increased by more than 50-fold in PON, peaking on day 2 and declining on days 4 to 8. There was a trend for a reduction in the number of BrdU+ TECs on day 4 in the C6^- PON group (P = 0.10 compared to C6⁺) but not at any other time-point. Kidney enlargement, TEC apoptosis (TUNEL⁺ cells) and markers of tubular injury (tubule dilatation, loss of TEC height, protein cast formation) were not altered by C6 deficiency in PON. Interstitial monocyte (ED-1+ cell) accumulation was partially reduced in C6^- animals with PON on day 4 (P = 0.01) but there was no change in myofibroblast accumulation.

CONCLUSION: These data suggest that C5b-9 does not mediate tubulointerstitial injury in acute glomerular diseases characterized by selective proteinuria.

Induction monotherapy with sirolimus has selected beneficial effects on glomerular and tubulointersititial injury in nephrotoxic serum nephritis

Background

The study aimed to test the hypothesis that therapeutic treatment with a mammalian target of rapamycin complex 1 inhibitor reduces renal cell proliferation and attenuates glomerular and tubulointerstitial injury in the early phase of nephrotoxic serum nephritis (NSN) in rats.

Methods

Male Wistar-Kyoto rats received a single tail-vein injection of sheep anti-rat glomerular basement membrane serum (day 0) and were treated with vehicle or sirolimus (0.25 mg/kg/day by subcutaneous injection) from day 1 until day 14.

Results

Treatment with sirolimus attenuated kidney enlargement by 41% (P<0.05), improved endogenous creatinine clearance by 50% (P<0.05), and reduced glomerular and tubulointerstitial cell proliferation by 53% and 70%, respectively, (P<0.05 compared to vehicle) in rats with NSN. In glomeruli, sirolimus reduced segmental fibrinoid necrosis by 69%, autologous rat immunoglobulin G deposition, glomerular capillary tuft enlargement, and periglomerular myofibroblast (α-smooth muscle actin-positive cells) accumulation (all P<0.05) but did not significantly affect glomerular crescent formation (P=0.15), macrophage accumulation (P=0.25), or the progression of proteinuria. In contrast, sirolimus preserved tubulointerstitial structure and attenuated all markers of injury (interstitial ED-1- and α-smooth muscle actin-positive cells and tubular vimentin expression; all P<0.05). By immunohistochemistry and Western blot analysis, sirolimus reduced the glomerular and tubulointerstitial expression of phosphorylated (Ser 235/236) S6-ribosomal protein (P<0.05).

Conclusion

Induction monotherapy with sirolimus suppressed target of rapamycin complex 1 activation, renal cell proliferation, and injury during the early stages of rodent NSN, but the degree of histological protection was more consistent in the tubulointerstitium than the glomerular compartment.

Potential role of Akt signaling in chronic kidney disease

Renal fibrosis, particularly tubulointerstitial fibrosis, is the common final outcome of almost all chronic kidney diseases. However, the mechanisms involved in the development of renal fibrosis are poorly understood. The Akt (also known as protein kinase B, PKB) family is serine/threonine protein kinases that play critical roles in regulating growth, proliferation, survival, metabolism and other cellular activities. Cytokines, high-glucose medium, transforming growth factor-β1 or advanced glycation end-products activate Akt in different renal cells. Increased Akt activation has been found in experimental tubulointerstitial fibrosis. In addition, Akt activation is also an important node in diverse signaling cascades involved in kidney damage. These data give evidence for a role for Akt in renal fibrosis, but no reviews are available on the role of Akt in the process. Thus, our aim is to review the role of Akt activation and signaling in renal fibrosis.

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.

CDK4/6 inhibition induces epithelial cell cycle arrest and ameliorates acute kidney injury

Acute kidney injury (AKI) is common and urgently requires new preventative therapies. Expression of a cyclin-dependent kinase (CDK) inhibitor transgene protects against AKI, suggesting that manipulating the tubular epithelial cell cycle may be a viable therapeutic strategy. Broad spectrum small molecule CDK inhibitors are protective in some kidney injury models, but these have toxicities and epithelial proliferation is eventually required for renal repair. Here, we tested a well-tolerated, novel and specific small molecule inhibitor of CDK4 and CDK6, PD 0332991, to investigate the effects of transient cell cycle inhibition on epithelial survival in vitro and kidney injury in vivo. We report that CDK4/6 inhibition induced G0/G1 cycle arrest in cultured human renal proximal tubule cells (hRPTC) at baseline and after injury. Induction of transient G0/G1 cycle arrest through CDK4/6 inhibition protected hRPTC from DNA damage and caspase 3/7 activation following exposure to the nephrotoxins cisplatin, etoposide, and antimycin A. In vivo, mice treated with PD 0332991 before ischemia-reperfusion injury (IRI) exhibited dramatically reduced epithelial progression through S phase 24 h after IRI. Despite reduced epithelial proliferation, PD 0332991 ameliorated kidney injury as reflected by improved serum creatinine and blood urea nitrogen levels 24 h after injury. Inflammatory markers and macrophage infiltration were significantly decreased in injured kidneys 3 days following IRI. These results indicate that induction of proximal tubule cell cycle arrest with specific CDK4/6 inhibitors, or "pharmacological quiescence," represents a novel strategy to prevent AKI.

Sirolimus reduces vasculopathy but exacerbates proteinuria in association with inhibition of VEGF and VEGFR in a rat kidney model of chronic allograft dysfunction

BACKGROUND

Use of the mTOR inhibitor (mTORi) sirolimus to replace calcineurin inhibitors in kidney transplantation has been associated with improved renal function but, in a proportion of cases, also with de novo or exacerbated proteinuria. Experimental deficiency of vascular endothelial growth factor (VEGF) induces proteinuria and mTOR is required for VEGF production and signalling. We therefore explored the impact of sirolimus on the development of chronic allograft dysfunction (CAD) in the rat, with a focus on VEGF biology.

METHODS

Lewis rats received F344 kidney allografts and were treated with 24 weeks of cyclosporine or sirolimus. Controls included allografts treated with cyclosporine for 10 days only and isografts treated with cyclosporine or sirolimus for 24 weeks. Kidney injury (proteinuria and histology) and expression of VEGF and VEGF-receptor (VEGFR; immunohistochemistry, laser capture micro-dissection and quantitative RT-PCR) were assessed.

RESULTS

Allograft controls developed proteinuria, tubulointerstitial fibrosis and atrophy, glomerulosclerosis, vasculopathy and leucocyte accumulation. Proteinuria was significantly reduced in both treatment groups but significantly more in cyclosporine treated animals. Tubulointerstitial damage, glomerulosclerosis and leucocyte accumulation were significantly attenuated in both treatment groups; however, vasculopathy was reduced only by sirolimus. Significantly diminished expression of VEGF and VEGFR mRNA and protein was evident in the sirolimus group. In vitro, sirolimus reduced VEGF production by podocytes (P < 0.05) and inhibited VEGF-induced proliferation of podocytes, endothelial and mesangial cells.

CONCLUSIONS

Cyclosporine and sirolimus retard development of CAD in this rat model. Sirolimus exhibits greater protection against vasculopathy but induces proteinuria; effects are likely to be related to inhibition of VEGF signalling.

Preconditioning donor with a combination of tacrolimus and rapamacyn to decrease ischaemia-reperfusion injury in a rat syngenic kidney transplantation model

Reperfusion injury remains one of the major problems in transplantation. Repair from ischaemic acute renal failure (ARF) involves stimulation of tubular epithelial cell proliferation. The aim of this exploratory study was to evaluate the effects of preconditioning donor animals with rapamycin and tacrolimus to prevent ischaemia-reperfusion (I/R) injury. Twelve hours before nephrectomy, the donor animals received immunosuppressive drugs. The animals were divided into four groups, as follows: group 1 control: no treatment; group 2: rapamycin (2 mg/kg); group 3 FK506 (0, 3 mg/kg); and group 4: FK506 (0, 3 mg/kg) plus rapamycin (2 mg/kg). The left kidney was removed and after 3 h of cold ischaemia, the graft was transplanted. Twenty-four hours after transplant, the kidney was recovered for histological analysis and cytokine expression. Preconditioning treatment with rapamycin or tacrolimus significantly reduced blood urea nitrogen and creatinine compared with control [blood urea nitrogen (BUN): P < 0·001 versus control and creatinine: P < 0·001 versus control]. A further decrease was observed when rapamycin was combined with tacrolimus. Acute tubular necrosis was decreased significantly in donors treated with immunosuppressants compared with the control group (P < 0·001 versus control). Moreover, the number of apoptotic nuclei in the control group was higher compared with the treated groups (P < 0·001 versus control). Surprisingly, only rapamycin preconditioning treatment increased anti-apoptotic Bcl2 levels (P < 0·001). Finally, inflammatory cytokines, such as tumour necrosis factor (TNF)-α and interleukin (IL)-6, showed lower levels in the graft of those animals that had been pretreated with rapamycin or tacrolimus. This exploratory study demonstrates that preconditioning donor animals with rapamycin or tacrolimus improves clinical outcomes and reduce necrosis and apoptosis in kidney I/R injury.

Fresh and cryopreserved, uncultured adipose tissue-derived stem and regenerative cells ameliorate ischemia-reperfusion-induced acute kidney injury

Background. Acute kidney injury (AKI) represents a major clinical problem with high mortality and limited causal treatments. The use of cell therapy has been suggested as a potential modality to improve the course and outcome of AKI.

Methods. We investigated the possible renoprotection of freshly isolated, uncultured adipose tissue-derived stem and regenerative cells (ADRCs) before and after cryopreservation in a rat ischemia–reperfusion (I–R) model of AKI.

Results. We demonstrated that ADRC therapy drastically reduced mortality (survival 100% vs. 57%, ADRC vs. controls, respectively) and significantly reduced serum creatinine (sCr on Day 3: 3.03 ± 1.58 vs. 7.37 ± 2.32 mg/dL, ADRC vs. controls, respectively). Histological analysis further validated a significantly reduced intratubular cast formation, ameliorated acute tubular epithelial cell necrosis and mitigated macrophage infiltration. Furthermore, a reduced RNA expression of CXCL2 and IL-6 was found in the ADRC group which could explain the reduced macrophage recruitment. Use of cryopreserved ADRCs resulted in an equally high survival (90% vs. 33% in the control group) and similarly improved renal function (sCr on Day 3: 4.64 ± 2.43 vs. 7.24 ± 1.40 mg/dL in controls).

Conclusions. Collectively, these results suggest a potential clinical role for ADRC therapy in patients with AKI. Importantly, cryopreservation of ADRCs could offer an autologous treatment strategy for patients who are at high risk for AKI during planned interventions.

Prospects for mTOR inhibitor use in patients with polycystic kidney disease and hamartomatous diseases

Mammalian target of rapamycin (mTOR) is the core component of two complexes, mTORC1 and mTORC2. mTORC1 is inhibited by rapamycin and analogues. mTORC2 is impeded only in some cell types by prolonged exposure to these compounds. mTOR activation is linked to tubular cell proliferation in animal models and human autosomal dominant polycystic kidney disease (ADPKD). mTOR inhibitors impede cell proliferation and cyst growth in polycystic kidney disease (PKD) models. After renal transplantation, two small retrospective studies suggested that mTOR was more effective than calcineurin inhibitor-based immunosuppression in limiting kidney and/or liver enlargement. By inhibiting vascular remodeling, angiogenesis, and fibrogenesis, mTOR inhibitors may attenuate nephroangiosclerosis, cyst growth, and interstitial fibrosis. Thus, they may benefit ADPKD at multiple levels. However, mTOR inhibition is not without risks and side effects, mostly dose-dependent. Under certain conditions, mTOR inhibition interferes with adaptive increases in renal proliferation necessary for recovery from injury. They restrict Akt activation, nitric oxide synthesis, and endothelial cell survival (downstream from mTORC2) and potentially increase the risk for glomerular and peritubular capillary loss, vasospasm, and hypertension. They impair podocyte integrity pathways and may predispose to glomerular injury. Administration of mTOR inhibitors is discontinued because of side effects in up to 40% of transplant recipients. Currently, treatment with mTOR inhibitors should not be recommended to treat ADPKD. Results of ongoing studies must be awaited and patients informed accordingly. If effective, lower dosages than those used to prevent rejection would minimize side effects. Combination therapy with other effective drugs could improve tolerability and results.

PKC-delta promotes renal tubular cell apoptosis associated with proteinuria

Proteinuria may contribute to progressive renal damage by inducing tubulointerstitial inflammation, fibrosis, and tubular cell injury and death, but the mechanisms underlying these pathologic changes remain largely unknown. Here, in a rat kidney proximal tubular cell line (RPTC), albumin induced apoptosis in a time- and dose-dependent manner. Caspase activation accompanied albumin-induced apoptosis, and general caspase inhibitors could suppress this activation. In addition, Bcl-2 transfection inhibited apoptosis and attenuated albumin-induced Bax translocation to mitochondria and cytochrome c release from the organelles, further confirming a role for the intrinsic pathway of apoptosis in albuminuria-associated tubular apoptosis. We observed phosphorylation and activation of PKC-delta early during treatment of RPTC cells with albumin. Rottlerin, a pharmacologic inhibitor of PKC-delta, suppressed albumin-induced Bax translocation, cytochrome c release, and apoptosis. Moreover, a dominant-negative mutant of PKC-delta blocked albumin-induced apoptosis in RPTC cells. In vivo, we observed activated PKC-delta in proteinuric kidneys of streptozotocin-induced diabetic mice and in kidneys after direct albumin overload. Notably, albumin overload induced apoptosis in renal tubules, which was less severe in PKC-delta-knockout mice. Taken together, these results suggest that activation of PKC-delta promotes tubular cell injury and death during albuminuria, broadening our understanding of the pathogenesis of progressive proteinuric kidney diseases.

Rapamycin has dual opposing effects on proteinuric experimental nephropathies: is it a matter of podocyte damage?

BACKGROUND

In clinical renal transplantation, an increase in proteinuria after conversion from calcineurin inhibitors to rapamycin has been reported. In contrast, there are studies showing a nephro-protective effect of rapamycin in proteinuric diseases characterized by progressive interstitial inflammatory fibrosis.

METHODS

Because of the contradictory reports concerning rapamycin on proteinuria, we examined proteinuria and podocyte damage markers on two renal disease models, with clearly different pathophysiological mechanisms: a glomerular toxico-immunological model induced by puromycin aminonucleoside, and a chronic hyperfiltration and inflammatory model by mass reduction, both treated with a fixed high rapamycin dose.

RESULTS

In puromycin groups, rapamycin provoked significant increases in proteinuria, together with a significant fall in podocin immunofluorescence, as well as clear additional damage to podocyte foot processes. Conversely, after mass reduction, rapamycin produced lower levels of proteinuria and amelioration of inflammatory and pro-fibrotic damage. In contrast to the puromycin model, higher glomerular podocin and nephrin expression and amelioration of glomerular ultrastructural damage were found.

CONCLUSIONS

We conclude that rapamycin has dual opposing effects on subjacent renal lesion, with proteinuria and podocyte damage aggravation in the glomerular model and a nephro-protective effect in the chronic inflammatory tubulointerstitial model. Rapamycin produces slight alterations in podocyte structure when acting on healthy podocytes, but it clearly worsens those podocytes damaged by other concomitant injury.

Adverse effects of nicotine and immunosuppression on proximal tubular epithelial cell viability, tissue repair and oxidative stress gene expression

BACKGROUND

Renal dysfunction in non-renal transplantation is a major arbiter of poor late allograft outcomes. Tobacco recidivism is an important modifiable risk marker for cardiac allograft loss, but its effects on renal dysfunction remain poorly studied.

METHODS

In a 96-well plate, 10(-5) proximal tubular epithelial (PTE) cells (HK-2, American Type Culture Collection) were cultured overnight and treated with sirolimus (SRL; 100 nmol/liter), nicotine (N; 10(-7) mol/liter) and mycophenolate mofetil (MMF; 10 micromol/liter), alone or in combination for 24 hours. Cell viability was quantified by treatment with tetrazolium salt WST-1 and calculated as the difference in percent inhibition with respect to the optical densitometry (OD) of treated and untreated cells. Gene and protein expression was analyzed using real-time polymerase chain reaction and Western blot techniques.

RESULTS

OD decreased with SRL (-52.7 +/- 2.85%), N (-47.3 +/- 3.84%) and MMF (-53.3 +/- 2.4%) in isolation. Further reduction in OD occurred when N was combined with SRL (-63 +/- 2.3%, p < 0.04), MMF (-64.3 +/- 1.45%, p < 0.02) or the combination of SRL and MMF (-78.2%, p < 0.007). Compared with control, treatment of PTE cells with N increased mRNA expression of transforming growth factor-beta (TGF-beta; 10-fold), connective tissue growth factor (CTGF; 25-fold), osteopontin (OPN; 10-fold) and NADPH oxidase components (p22(phox), NOX-1 and Rac-1 at 18-, 16- and 12-fold, respectively). The pre-treatment of cells with inhibitor of superoxide generator diphenylene iodonium (DPI) reversed these effects.

CONCLUSIONS

Nicotine adversely amplified the effects of SRL and MMF on tissue repair and oxidative stress markers, subsequently modulating PTE viability. However, caution is advised in extrapolating these in vitro findings to the human model.

Everolimus: an update on the mechanism of action, pharmacokinetics and recent clinical trials

BACKGROUND

A growing body of evidence suggests that everolimus might offer effective immunosuppressive activity together with antiproliferative effects that may address some of the unmet needs in the long-term therapeutic management of the post-transplant patient.

OBJECTIVE

To summarize the emerging evidence for employing everolimus-based immunosuppression.

METHODS

A systematic review was conducted of the Medline, Embase and Renal Health Library (Cochrane Collaboration) databases, and of the summary publications from international transplant meetings and congresses during 2000-2008.

RESULTS

This article summarizes this analysis, with special focus on the pharmacokinetic characteristics of everolimus and on the results of its use in renal transplantation. Some data has also been included about the efficacy of the drug in other solid organ transplantation and in tumours.

CONCLUSIONS

Everolimus is an immunosuppressant drug with proven efficacy in transplantation. When used in combination with cyclosporin, better results are obtained in renal function with low cyclosporin doses. Adverse events related to this drug are frequent and lead to moderate dropout rates.

mToR inhibitors-induced proteinuria: mechanisms, significance, and management

Massive urinary protein excretion has been observed after conversion from calcineurin inhibitors to mammalian target of rapamycin (mToR) inhibitors, especially sirolimus, in renal transplant recipients with chronic allograft nephropathy. Because proteinuria is a major predictive factor of poor transplantation outcome, many studies focused on this adverse event during the past years. Whether proteinuria was due to sirolimus or only a consequence of calcineurin inhibitors withdrawal remained unsolved until high range proteinuria has been observed during sirolimus therapy in islet transplantation and in patients who received sirolimus de novo. Podocyte injury and focal segmental glomerulosclerosis have been related to mToR inhibition in some patients, but the pathways underlying these lesions remain hypothetic. We discuss herein the possible mechanisms and the significance of mToR blockade-induced proteinuria.

Effect of seliciclib (CYC202, R-roscovitine) on lymphocyte alloreactivity and acute kidney allograft rejection in rat

BACKGROUND

T cell stimulation by alloantigens is followed by cell cycle progression, an event that is critically dependent on cyclin-dependent kinases.

METHODS

We conducted a study to evaluate whether the cyclin-dependent kinase inhibitor seliciclib affected rat lymph node cells (LNc) activation and proliferation induced by either concanavalin A or allogeneic splenocytes in vitro and studied the mechanisms underlying the suppressive effect. We also investigated the immunosuppressive properties of seliciclib in vivo.

RESULTS

Seliciclib completely inhibited in vitro proliferation of LNc and CD8 T cells, in response to either concanavalin A or allogeneic splenocytes. The percentage of activated LNc was lower in mixed leukocyte reactions (MLR) added with seliciclib than in MLR added with vehicle. The percentages of viable and apoptotic cells at the end of MLR with seliciclib were comparable to those of MLR with vehicle. LNc pre-exposed in MLR to seliciclib did not respond to further stimulation with alloantigens, and neither IL-2 nor IL-15 restored proliferation. These data indicate that the inhibitory effect of seliciclib on T cell alloreactivity is not because of cytotoxic effect but is associated with induction of profound T cell anergy. LNc harvested at the end of the primary MLR with seliciclib did not suppress the proliferation of syngeneic LNc cells toward allogeneic splenocytes, thus excluding that seliciclib induced the formation of regulatory cells. Finally, seliciclib partially prolonged grafted animal survival in a rat model of fully major histocompatibility complex-mismatched kidney transplantation.

CONCLUSIONS

Altogether these results document that seliciclib regulates lymphocyte reactivity and may exert an immunosuppressive effect in vivo in the setting of transplantation.

Development of proteinuria after switch to sirolimus-based immunosuppression in long-term cardiac transplant patients

Calcineurin-inhibitor therapy can lead to renal dysfunction in heart transplantation patients. The novel immunosuppressive (IS) drug sirolmus (Srl) lacks nephrotoxic effects; however, proteinuria associated with Srl has been reported following renal transplantation. In cardiac transplantation, the incidence of proteinuria associated with Srl is unknown. In this study, long-term cardiac transplant patients were switched from cyclosporine to Srl-based IS. Concomitant IS consisted of mycophenolate mofetil +/- steroids. Proteinuria increased significantly from a median of 0.13 g/day (range 0-5.7) preswitch to 0.23 g/day (0-9.88) at 24 months postswitch (p = 0.0024). Before the switch, 11.5% of patients had high-grade proteinuria (>1.0 g/day); this increased to 22.9% postswitch (p = 0.006). ACE inhibitor and angiotensin-releasing blocker (ARB) therapy reduced proteinuria development. Patients without proteinuria had increased renal function (median 42.5 vs. 64.1, p = 0.25), whereas patients who developed high-grade proteinuria showed decreased renal function at the end of follow-up (median 39.6 vs. 29.2, p = 0.125). Thus, proteinuria may develop in cardiac transplant patients after switch to Srl, which may have an adverse effect on renal function in these patients. Srl should be used with ACEi/ARB therapy and patients monitored for proteinuria and increased renal dysfunction.

Can mTOR inhibitors reduce the risk of late kidney allograft failure?

The most frequent causes of late kidney allograft failure are chronic rejection, nonalloimmune injury and death, all of which may depend on the characteristics of the donor and recipient, but may also be influenced by the type of immunosuppression. Combining calcineurin inhibitors (CNIs) and corticosteroids offers potent immunosuppression, but may also cause side effects leading to progressive graft dysfunction or an increased risk of death. New immunosuppressive strategies may come from the availability of inhibitors of mTOR, a downstream effector of phosphatidylinositol-3 kinase that provides the signal for cell proliferation by phosphorylating a cascade of kinases. Recent trials have shown that it is possible to minimize the dose or withdraw CNIs a few weeks after transplantation when they are combined with mTOR inhibitors and their combination may also make it possible to minimize or avoid the use of corticosteroids. Moreover, by inhibiting the signal for cell proliferation, mTOR inhibitors may reduce the replication of cytomegalovirus inside host cells, prevent transplant vasculopathy, and exert anti-oncogenic activity. All of these characteristics offer a ray of hope for reducing the risk of long-term allograft failure.

Sirolimus is not always responsible for new-onset proteinuria after conversion for chronic allograft nephropathy

An eight-yr-old combined liver and kidney transplant recipient for hyperoxaluria type I developed significant proteinuria and hypertension after conversion of a Tacrolimus, MMF, and corticosteroids-based immunosuppression to Sirolimus, low-dose Tacrolimus, and corticosteroids six and a half yr after the transplant for chronic allograft nephropathy. There was only one class I HLA match and the recipient had multiple blood exposures prior to transplantation. The patient was treated with combined hemodialysis and peritoneal dialysis while awaiting transplantation to reduce the oxalate load. A renal biopsy revealed a de novo transplant glomerulopathy that was associated with specific HLA antibodies unrelated to the donor (HLA DR 17 and 18). After reintroduction of MMF, these antibodies became undetectable and the proteinuria completely resolved. We hypothesize that HLA antibodies may cause transplant glomerulopathy even if they are not donor-specific. Their production appears more susceptible to MMF therapy. A thorough work-up of new-onset proteinuria after conversion to Sirolimus should be performed, including an immunological work-up and a renal biopsy.

Altered kidney graft high-energy phosphate metabolism in kidney-transplanted end-stage renal disease type 1 diabetic patients: a cross-sectional analysis of the effect of kidney alone and kidney-pancreas transplantation

OBJECTIVE

Diabetes, hypertension, dyslipidemia, obesity, nephrotoxicity of certain immunosuppressive drugs, and the persistence of a chronic alloimmune response may significantly affect graft survival in end-stage renal disease (ESRD) type 1 diabetic patients who have undergone kidney transplant. The aim of this study was to ascertain the impact of kidney alone (KD) or combined kidney-pancreas (KP) transplantation on renal energy metabolism.

RESEARCH DESIGN AND METHODS

We assessed high-energy phosphates (HEPs) metabolism by using, in a cross-sectional fashion, 31P-magnetic resonance spectroscopy in the graft of ESRD type 1 diabetic transplanted patients who received KD (n = 20) or KP (n = 20) transplant long before the appearance of overt chronic allograft nephropathy (CAN). Ten nondiabetic microalbuminuric kidney transplanted patients and 10 nondiabetic kidney transplanted patients with overt CAN were chosen as controls subjects.

RESULTS

Simultaneous KP transplantation patients showed a higher beta-ATP/inorganic phosphorus (Pi) ratio (marker of the graft energy status) versus the other groups, and a positive correlation between beta-ATP/Pi phosphorus ratio and A1C was found. In the analysis limited to the subgroup of normoalbuminuric patients, the difference in beta-ATP/Pi was still detectable in KP patients compared with KD transplantation.

CONCLUSIONS

KP transplantation was associated with better HEPs than in KD transplantation, suggesting that restoration of beta-cell function positively affects kidney graft metabolism.

Proteinuria following conversion from azathioprine to sirolimus in renal transplant recipients

Recent studies have reported a significant increase of proteinuria in kidney transplant recipients who were switched from a calcineurin inhibitor (CI) to sirolimus. This has (partly) been ascribed to the hemodynamic renal effects of CI withdrawal. We have evaluated the evolution of proteinuria in renal transplant recipients who underwent conversion from azathioprine to sirolimus. In a randomized, prospective, multicenter study called RESCUE (Recurrent cutanEous Squamous cell Carcinoma Under RapamunE) the efficacy and safety is investigated of conversion to sirolimus in stable renal transplant recipients with a cutaneus squamous cell carcinoma (SCC). In our center 25 patients have been included in this study of which 13 patients were randomized to continue their current immunosuppressive treatment and 12 to conversion to sirolimus. After a mean follow-up of 360 days mean proteinuria increased from 0.37+/-0.34 to 1.81+/-1.73 g/24 h after conversion to sirolimus (P<0.005). In the control group there was no change in proteinuria. A significant increase of proteinuria was observed in all seven patients with proteinuria before conversion, whereas proteinuria remained absent in all patients without previous proteinuria. Two of the patients with proteinuria were converted from cyclosporine and five were converted from azathioprine to sirolimus. Sirolimus was discontinued in five patients with proteinuria, and in all of them proteinuria declined to baseline values. Our study demonstrates that conversion from azathioprine to sirolimus after kidney transplantation may cause a reversible increase of proteinuria. Sirolimus-induced proteinuria therefore cannot be ascribed to the hemodynamic renal effects of withdrawal of CI.

Sirolimus-Associated Proteinuria and Renal Dysfunction

Sirolimus is a novel immunosuppressant with potent antiproliferative actions through its ability to inhibit the raptor-containing mammalian target of rapamycin protein kinase. Sirolimus represents a major therapeutic advance in the prevention of acute renal allograft rejection and chronic allograft nephropathy. Its role in the therapy of glomerulonephritis, autoimmunity, cystic renal diseases and renal cancer is under investigation. Because sirolimus does not share the vasomotor renal adverse effects exhibited by calcineurin inhibitors, it has been designated a 'non-nephrotoxic drug'. However, clinical reports suggest that, under some circumstances, sirolimus is associated with proteinuria and acute renal dysfunction. A common risk factor appears to be presence of pre-existing chronic renal damage. The mechanisms of sirolimus-associated proteinuria are multifactorial and may be due to an increase in glomerular capillary pressure following calcineurin inhibitor withdrawal. It has also been suggested that sirolimus directly causes increased glomerular permeability/injury, but evidence for this mechanism is currently inconclusive. The acute renal dysfunction associated with sirolimus (such as in delayed graft function) may be due to suppression of compensatory renal cell proliferation and survival/repair processes. Although these adverse effects occur in some patients, their occurrence could be minimised by knowledge of the molecular effects of sirolimus on the kidney, the use of sirolimus in appropriate patient populations, close monitoring of proteinuria and renal function, use of angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers if proteinuria occurs and withdrawal if needed. Further long-term analysis of renal allograft studies using sirolimus as de novo immunosuppression along with clinical and laboratory studies will refine these issues in the future.