Kidney injury molecule-1: more than just an injury marker of tubular epithelial cells?

Regardless of the original causes and etiology, the progression to renal function declines follows a final common pathway associated with tubulointerstitial injury, in which the proximal tubular epithelial cells (PTEC) are instrumental. Kidney injury molecule-1 (KIM-1) is an emerging biomarker, and its expression and release are induced in PTEC upon injury. KIM-1 plays the role as a double-edged sword and implicates in the process of kidney injury and healing. Expression of KIM-1 is also associated with tubulointerstitial inflammation and fibrosis. More importantly, KIM-1 expressing PTEC play the role as the residential phagocytes, contribute to the removal of apoptotic cells and facilitate the regeneration of injured tubules. The precise mechanism of KIM-1 and its sheded ectodomain on restoration of tubular integrity after injury is not fully understood. Other than PTEC, macrophages (Mø) also implicate in tubular repair. Understanding the crosstalk between Mø and the injured PTEC is essential for designing appropriate methods for controlling the sophisticated machinery in tubular regeneration and healing. This article will review the current findings of KIM-1, beginning with its basic structure, utility as a biomarker, and possible functions, with focus on the role of KIM-1 in regeneration and healing of injured PTEC.

The pathogenic role of the renal proximal tubular cell in diabetic nephropathy

A growing body of evidence indicates that the renal proximal tubular epithelial cell (PTEC) plays an important role in the pathogenesis of diabetic nephropathy (DN). Microalbuminuria that intensifies over time to overt proteinuria, a hallmark of DN, is already known to activate the PTEC to induce tubulointerstitial inflammation. In addition to proteins, a number of diabetic substrates including high glucose per se, advanced glycation end-products and their carbonyl intermediates, angiotensin II, and ultrafiltered growth factors activate a number of signaling pathways including nuclear factor kappa B, protein kinase C, extracellular signal-regulated kinase 1/2, p38, signal transducer and activator of transcription-1 and the generation of reactive oxygen species, to culminate in tubular cell hypertrophy and the accumulation in the interstitium of a repertoire of chemokines, cytokines, growth factors and adhesion molecules capable of orchestrating further inflammation and fibrosis. More recently, the kallikrein-kinin system (KKS) and toll-like receptors (TLRs) in PTECs have been implicated in this process. While in vitro data suggest that the KKS contributes to the progression of DN, there are conflicting in vivo results on its precise role, which may in part be strain-dependent. On the other hand, there are both in vitro and in vivo data to suggest a role for both TLR2 and TLR4 in DN. In this review, we offer a critical appraisal of the events linking the participation of the PTEC to the pathogenesis of DN, which we believe may be collectively termed diabetic tubulopathy.

Distinct role of matrix metalloproteinase-3 in kidney injury molecule-1 shedding by kidney proximal tubular epithelial cells

Tubulointerstitial injury is a common pathway in progressive renal impairment and human proximal tubular epithelial cells (PTEC) play a crucial role in this process. Kidney injury molecule-1 (KIM-1) has received increasing attention due to its potential utility as the therapeutic target and biomarker for kidney injury. This study aims to explore the underlying mechanism regulating the release of KIM-1. Cultured primary human PTEC expressed and released KIM-1 from the apical surface through an ectodomain shedding process mediated by matrix metalloproteinase (MMP), independent of gene expression and protein synthesis. The constitutive KIM-1 shedding by PTEC was enhanced in a dose- and time-dependent manner by human serum albumin (HSA) or tumor necrosis factor-α (TNF-α), two important physiological stimuli found during kidney injury. Data from PCR array screening of MMPs gene expression in PTEC following activation by HSA or TNF-α, and from blocking experiments using either synthetic MMP inhibitors or MMP gene knockdown by siRNA, revealed that the constitutive and accelerated shedding of KIM-1 in cultured PTEC was mediated by MMP-3. Furthermore, the up-regulation of MMP-3 and KIM-1 release by PTEC was associated with generation of reactive oxygen species. In a mouse model of acute kidney injury induced by ischemia and reperfusion, increased expression of MMP-3 and KIM-1 as well as their co-localization were observed in kidney from ischemic but not in sham-operated mice. Taken together, these in vitro and in vivo evidences suggest that MMP-3 plays an inductive role in KIM-1 shedding by PTEC.

Pathogenesis of IgA nephropathy

Since its first description in 1968, IgA nephropathy has remained the most common form of idiopathic glomerulonephritis leading to chronic kidney disease in developed countries. The exact pathogenesis of IgA nephropathy is still not well defined. Current data implicate an important genetic factor, especially in promoting the overproduction of an aberrant form of IgA1. The immunochemical aberrancy of IgA nephropathy is characterized by the undergalactosylation of O-glycans in the hinge region of IgA1. However, such aberrant glycosylation alone does not cause renal injury. The next stage of disease development requires the formation of glycan-specific IgG and IgA antibodies that recognize the undergalactosylated IgA1 molecule. These antibodies often have reactivity against antigens from extrinsic microorganisms and might arise from recurrent mucosal infection. B cells that respond to mucosal infections, particularly tonsillitis, might produce the nephritogenic IgA1 molecule. With increased immune-complex formation and decreased clearance owing to reduced uptake by the liver, IgA1 binds to the glomerular mesangium via an as yet unidentified receptor. Glomerular IgA1 deposits trigger the local production of cytokines and growth factors, leading to the activation of mesangial cells and the complement system. Emerging data suggest that mesangial-derived mediators following glomerular deposition of IgA1 lead to podocyte and tubulointerstitial injury via mesangio-podocytic-tubular crosstalk. This Review summarizes the latest findings in the pathogenesis of IgA nephropathy.

Quantification of BK viral load in asymptomatic renal allograft recipients

INTRODUCTION

Polyoma BK virus (BKV) has recently been identified to cause renal allograft dysfunction, which manifests as polyomavirus-associated nephropathy (PVAN). However, the presence and level of BKV DNA in renal allograft patients with good and stable renal function have remained undetermined.

METHODS

In this prospective study, serum samples were collected from a total of 45 renal allograft recipients with serum creatinine <155 μmol/L. In 17 patients, whose duration of transplantation was under 2 years, samples were collected at 3-4-month intervals for up to 2 years after transplantation. BK viral load was quantified using quantitative polymerase chain reaction (Q-PCR).

RESULTS

The BK viral load in asymptomatic renal allograft recipients was independent of the duration of transplantation and did not correlate with allograft function. The mean (± SD) level of viremia was 552.80 ± 1931.00 genome copies/mL, with 92.9% of patients having low levels of viremia corresponding to <1 × 10(3) copies/mL. In contrast, patients with proven PVAN had levels in the range of 10(6) copies/mL.

CONCLUSIONS

The prevailing BK viral load in asymptomatic renal allograft patients is quantifiably low. Our findings may guide optimal immunosuppressive modulation in PVAN cases, where judicious manipulation of immunosuppression is required without inciting allograft rejection.

The role of leptin and its short-form receptor in inflammation in db/db mice infused with peritoneal dialysis fluid

BACKGROUND

In peritoneal dialysis (PD), the peritoneal membrane exhibits structural and functional changes following continuous exposure to the non-physiological peritoneal dialysis fluid (PDF). In this study, we examined the effect of PDF on peritoneal adipose tissue in a diabetic milieu.

METHODS

Six-week-old db/db mice and their non-diabetic littermates (db/m) were subjected to uninephrectomy. All animals then received intra-abdominal infusion of lactated Ringer's solution (Ringer) or 1.5% glucose-containing PDF (Dianeal) twice daily. Mice were sacrificed 4 weeks later. Parietal and visceral adipose tissues were harvested for examining gene and protein expression of adiponectin, leptin, monocyte chemotactic protein-1, vascular endothelial growth factor, tumor necrosis factor alpha (TNF-α), transforming growth factor beta and interleukin 6 (IL-6). Expression of TNF-α and F4/80+ macrophage accumulation in adipose tissues was assessed by immunohistochemical staining. Modulation of leptin synthesis and leptin receptors expression and the relevant signaling pathways were also determined by quantitative reverse transcription-polymerase chain reaction, immunoblotting or enzyme-linked immunosorbent assay.

RESULTS

Compared to Ringer infusion, Dianeal infusion significantly increased serum leptin but decreased adiponectin in db/db mice. Increased expression of leptin, TNF-α and IL-6 was observed in visceral but not in parietal adipose tissue. Dianeal infusion also increased F4/80+ macrophage accumulation and enhanced the expression of pro-inflammatory cytokines including IL-6 and TNF-α in the visceral adipose tissue. Compared to db/m mice, infusion with Dianeal exhibited a more deleterious effect on db/db mice, characterized by an upregulation of short-form leptin receptor ObRa and activation of the mitogen-activated protein kinase signaling pathway.

CONCLUSION

In conclusion, PD-induced hyperleptinemia amplifies the inflammatory response of adipose tissue through short-form leptin receptor when the long-form isotype is defective.

Impact of nephrotic edema of the lower limbs on obstructive sleep apnea: gathering a unifying concept for the pathogenetic role of nocturnal rostral fluid shift

BACKGROUND

Nocturnal rostral fluid shift has been suggested to be a risk factor for obstructive sleep apnea (OSA) in healthy subjects after lower body positive pressurization. It remains unclear whether this may apply to subjects with nephrotic lower limb edema and, if so, whether disease remission may reverse the accompanying OSA.

METHODS

Patients who presented with steroid-responsive primary nephrotic syndrome with lower limb edema as the predominant presenting clinical feature were recruited. They underwent one overnight polysomnography (PSG) before treatment and a repeat testing after achieving remission of the nephrotic edema.

RESULTS

Among 23 consecutive nephrotic subjects, 11 (48%) had polysomnographic evidence of sleep apnea [apnea-hypopnea index (AHI)≥5] upon presentation. After steroid-based treatment, there was remission of proteinuria associated with complete disappearance of lower limb edema, significant reduction of body mass index, waist, hip and calf circumferences and total body water mainly in the extracellular compartment. Repeat PSG, performed 8.1±2.6 months later, showed that the overall (N=23) respiratory disturbance index (RDI) and AHI fell from 17.3±5.0 to 8.7±2.5 (P<0.05) and from 16.3±5.1 to 7.8±2.3 (P=0.057), respectively. Among the 11 subjects with sleep apnea detected at baseline, their AHI and RDI fell from 33.4±7.8 to 15.0±3.7 (P<0.05) and from 34.8±7.6 to 16.5±4.0 (P<0.05), respectively. There was also concomitant improvement in sleep efficiency, mean nocturnal oxygen saturation, shorter duration during sleep with oxygen saturation<95 and <90% and reduced desaturation index. There was also subjective improvement in self-reported daytime sleepiness.

CONCLUSIONS

Nephrotic lower limb edema is associated with disturbed respiratory breathing and increased propensity to OSA, which was reversed upon remission of the nephrosis. This gathers a unifying concept for the role of nocturnal rostral fluid shift in the pathogenesis of OSA.

A study of the clinical and biochemical profile of peritoneal dialysis fluid low in glucose degradation products

OBJECTIVE

Although peritoneal dialysis (PD) is a widely accepted form of renal replacement therapy, concerns remain regarding the bioincompatible nature of standard PD fluid (PDF). Short-term studies of new biocompatible PDFs low in glucose degradation products (GDPs) reveal divergent results with respect to peritoneal integrity.

METHODS

We studied 125 patients on maintenance PD who were assigned, by simple randomization, to receive either conventional or low-GDP PDF at PD initiation. Parameters of dialysis adequacy and peritoneal transport of small solutes were determined at initiation and after a period of maintenance PD at the time when serum and overnight effluent dialysate were simultaneously collected and assayed for various cytokines, chemokines, adipokines, and cardiac biomarkers. All patients were further followed prospectively for an average of 15 months from the day of serum and effluent collection to determine patient survival and cardiovascular events.

RESULTS

Patients treated with conventional or low-GDP PDF were matched for sex, age, duration of dialysis, dialysis adequacy, and incidence of cardiovascular disease or diabetes. After an average of 2.3 years of PD treatment, the weekly total and peritoneal creatinine clearance, and the total and peritoneal Kt/V were comparable in the groups. However, urine output was higher in patients using low-GDP PDF despite there having been no difference between the groups at PD initiation. Patients using low-GDP PDF also experienced a slower rate of decline of residual glomerular filtration and urine output than did patients on conventional PDF. Compared with serum concentrations, effluent concentrations of tumor necrosis factor α, hepatocyte growth factor, macrophage migration inhibitory factor, interleukins 8 and 6, C-reactive protein, and leptin were found to be higher in both groups of patients after long-term PD, suggesting that the peritoneal cavity was the major source of those mediators. Compared with patients on low-GDP PDF, patients on conventional fluid showed elevated leptin and reduced adiponectin levels in serum and effluent. The effluent concentration of interleukin 8 was significantly lower in patients using low-GDP PDF. The survival rate and incidence of cardiovascular complications did not differ between these groups after maintenance PD for an average of 3.6 years.

CONCLUSIONS

It appears that low-GDP PDF results in an improvement of local peritoneal homeostasis through a reduction of chronic inflammatory status in the peritoneum.

Hepatitis-related renal disease

Many glomerular diseases can be caused by viral infections based on the diagnostic criteria, including clinical and laboratory data, and molecular analysis of tissue. Operative pathogenetic mechanisms include kidney tropism of the virus, immune complex formation, direct cytopathogenic effect, and multi-organ failure. Chronic infection with hepatitis virus is etiologically linked to well-defined glomerulopathies. In endemic areas, HBV is associated with both membranous nephropathy and mesangiocapillary glomerulonephritis, while HCV is known to cause cryoglobulinemia-mediated glomerulonephritis and other forms of glomerulonephritis. Renal biopsy with appropriate serological and molecular testing helps to define virus-related glomerular lesions and provides a prognostic and therapeutic guide. Antiviral agents remain the mainstay of treatment.

Toll-like receptor 4 promotes tubular inflammation in diabetic nephropathy

Inflammation contributes to the tubulointerstitial lesions of diabetic nephropathy. Toll-like receptors (TLRs) modulate immune responses and inflammatory diseases, but their role in diabetic nephropathy is not well understood. In this study, we found increased expression of TLR4 but not of TLR2 in the renal tubules of human kidneys with diabetic nephropathy compared with expression of TLR4 and TLR2 in normal kidney and in kidney disease from other causes. The intensity of tubular TLR4 expression correlated directly with interstitial macrophage infiltration and hemoglobin A1c level and inversely with estimated glomerular filtration rate. The tubules also upregulated the endogenous TLR4 ligand high-mobility group box 1 in diabetic nephropathy. In vitro, high glucose induced TLR4 expression via protein kinase C activation in a time- and dose-dependent manner, resulting in upregulation of IL-6 and chemokine (C-C motif) ligand 2 (CCL-2) expression via IκB/NF-κB activation in human proximal tubular epithelial cells. Silencing of TLR4 with small interfering RNA attenuated high glucose-induced IκB/NF-κB activation, inhibited the downstream synthesis of IL-6 and CCL-2, and impaired the ability of conditioned media from high glucose-treated proximal tubule cells to induce transmigration of mononuclear cells. We observed similar effects using a TLR4-neutralizing antibody. Finally, streptozotocin-induced diabetic and uninephrectomized TLR4-deficient mice had significantly less albuminuria, renal dysfunction, renal cortical NF-κB activation, tubular CCL-2 expression, and interstitial macrophage infiltration than wild-type animals. Taken together, these data suggest that a TLR4-mediated pathway may promote tubulointerstitial inflammation in diabetic nephropathy.

Clinical pictures and novel mutations of WT1-associated Denys-Drash syndrome in two Chinese children

Denys-Drash syndrome (DDS) is characterized by early onset of nephropathy, genitalia malformation, and Wilms' tumor, where WT1 is the gene that is mutated in most patients. We report two de novo mutations in WT1 found in two Chinese DDS children. Patient 1 was a boy with complete DDS who was presented with progressive nephropathy, unilateral Wilms' tumor, bilateral cryptorchidism, and renal histology showing diffuse mesangial sclerosis (DMS). When the patient was 24 months old, a liver ultrasound showed multiple nodules, and the patient died of pneumonia 1 month later. The de novo novel mutation, c.1130A>T (p.His377Leu), was identified; the mutation replaces histidine with leucine in the zinc finger (Znf) structure and is predicted to change the local spatial structure of the protein. Patient 2 had 46 XX with incomplete DDS and presented with normal genitalia, proteinuria, unilateral Wilms' tumor with renal pedicle lymph node metastasis, and renal histology showing DMS. Her renal function remains normal after 48 months. A de novo mutation, c.1168C>T (p.Arg390Term), was identified; it truncates 60 amino acids at the C terminus, and it is predicted to result in loss of the DNA-binding capacities of the WT1 protein.

Recent advances in IgA nephropathy--the glomerulopodocytic-tubular communication

IgA nephropathy (IgAN) is characterized by mesangial deposition of pathogenic polymeric IgA1 with rare deposits in the tubular epithelial cells (TEC). Recently, a novel mechanism involving a glomerulopodocytictubular cross-talk in the development of tubulointerstitial damage in IgAN has been revealed. Podocytes are positioned strategically along the glomerulotubular axis and plays an important role in mediating the glomerulotubular cross-talk. In IgAN, podocyte markers are reduced in the glomeruli. In vitro study implicates humoral factors (predominantly tumor necrosis factor-α and transforming growth factor-β) released from mesangial cells alter the glomerular permeability in the event of proteinuria and tubulointerstitial injury in IgAN. These mediators released from mesangial cells after IgA deposition further activate TEC leading to subsequent inflammatory changes in the renal tubulointerstitium.

Immunomodulatory agents against IgA nephropathy

Synthesis of aberrant IgA molecules as the key pathogenetic mechanism of immunoglobulin A nephropathy (IgAN) apparently forms a potential scientific rationale for applying immunomodulatory agents in the treatment of IgAN. There is evidence that corticosteroids can steadily reduce proteinuria and slow down renal progression. Evidence that pulse steroid plus intravenous or oral cyclophosphamide can retard the rate of progression of advanced IgAN was provided by several groups worldwide. Cyclosporin is generally not used to treat IgAN. The efficacy of azathioprine is equivocal. Mycophenolate mofetil reduces proteinuria by up to 30% and favorably impacts renal survival in Chinese patients with mild histologic lesions, but these results were not achieved in Caucasians with more advanced disease. In conclusion, the choice of immunomodulatory therapy remains controversial. We advocate the use of immunomodulatory agents as an adjunctive therapy in patients with proteinuria>1 g/day despite achieving target blood pressure with full renin-angiotensin blockade. More aggressive therapy should be reserved for patients with nephrotic-range proteinuria, crescentic lesions and/or rapidly progressive renal failure.

Severe hypocalcaemia and hyperphosphataemia caused by oral sodium phosphate fleet solution in a haemodialysis patient after parathyroidectomy

We report a case with severe electrolyte disturbance after the use of oral sodium phosphate solution (OSPS). A 69-year-old patient on haemodialysis received 45 mL of OSPS for bowel preparation. He had symptomatic hypocalcaemia with a serum calcium level of 0.95 mmol/L and serum phosphate level of 4.73 mmol/L. He was treated with haemodialysis and intravenous calcium supplementation. This patient had total parathyroidectomy recently leading to the absence of parathyroid hormone response. OSPS has been reported to cause life-threatening electrolyte disturbance especially in patients with renal failure. We suggest the use of safer alternatives for bowel preparations in renal failure patients.

Streptococcus bovis peritonitis complicating peritoneal dialysis--a review of 10 years' experience

OBJECTIVE

An association of Streptococcus bovis bacteremia with carcinoma of colon has been reported, but data regarding peritoneal dialysis (PD) peritonitis caused by S. bovis is scarce. In this study, we examined the clinical characteristics, associations, and outcomes of this disease entity.

METHODS

The case records of patients with S. bovis PD peritonitis presenting to 2 renal centers between January 2000 and September 2010 were reviewed. Clinical features and outcomes were identified and analyzed.

RESULTS

Of cultures from 23 episodes of S. bovis peritonitis in 20 patients (1.28% of all peritonitis episodes at our center), 19 (82.6%) showed S. bovis alone, and 4 (17.4%) showed mixed growth. In 7 episodes, the S. bovis was moderately resistant to penicillin G. Rates of resistance to clindamycin and erythromycin were 43.5% and 47.8% respectively. In 18 episodes (78.3%), a primary response was achieved with a first-generation cephalosporin and an aminoglycoside. In 4 episodes, a secondary response was achieved after a switch from cephalosporin to vancomycin, and in 1 episode with mixed growth, the Tenckhoff catheter had to be removed. Repeat peritonitis occurred in 3 patients at a mean of 50.0 months (range: 24.2 - 83.1 months). Of the 20 patients of S. bovis peritonitis, 10 (50%) underwent either a barium enema or a colonoscopy. One patient had history of colonic carcinoma 2 years before the peritonitis, and a subsequent work-up revealed no recurrence. Three patients had diverticulosis, and one had a concomitant sigmoid polyp. Findings in the other 6 patients were normal. No colorectal malignancy had developed in the remaining 10 patients after a mean follow-up of 76.6 months (range: 0.8 - 125.1 months).

CONCLUSIONS

Outcomes in S. bovis PD peritonitis were favorable, and an association with colorectal cancer was not found in our patients. Routine colonoscopy in these patients remains controversial and should be individualized.

Aliskiren combined with losartan in immunoglobulin A nephropathy: an open-labeled pilot study

BACKGROUND

Aliskiren is a relatively new oral direct renin inhibitor (DRI) that has been increasingly used for the treatment of diabetic nephropathy and hypertension. Its potential efficacy in nondiabetic chronic kidney diseases that are driven by renin-angiotensin system activation remains to be explored.

METHODS

From a teaching and regional hospital in Hong Kong between July 2009 and March 2010, patients with biopsy-proven immunoglobulin A nephropathy (IgAN) in whom the ratio of protein to creatinine, as measured in early morning urine samples, remained >113 mg/mmol (1000 mg/g), despite receiving the maximum recommended dose of losartan (100 mg daily) were recruited to receive additional DRI treatment. They were followed prospectively for 12 months with changes in proteinuria as the main outcome measure.

RESULTS

Twenty-five consecutive patients were enrolled. Treatment with aliskiren for 12 months reduced the mean urinary protein-to-creatinine ratio by 26.3% (95% confidence interval, 20.1-43.6; P = 0.001 versus baseline), with a reduction of ≥ 50% in 24% of patients. There were significant reductions in plasma renin activity (P < 0.0001) and serum interleukin-6 (P < 0.05) and transforming growth factor-β (P = 0.01) levels, compared with baseline. Two patients (8%) developed mild allergic reactions and six (24%) had transient hyperkalemia (K >5.5 mmol/L) during the study.

CONCLUSION

Aliskiren confers an antiproteinuric effect in IgAN patients with significant residual proteinuria, despite receiving the recommended renoprotective treatment. Further prospective randomized trials are warranted to examine its long-term renoprotective potential. This trial is registered with the ClinicalTrials.gov number NCT00922311.

Diabetic tubulopathy: an emerging entity

In chronic glomerulopathic disease, renal function correlates more with the degree oftubulointerstitial injury than that of the glomerular lesions. Proteinuria may be one of the pathologic links between these two intrarenal compartments. It is apparent that the proximal tubular epithelial cell (PTEC) assumes a proinflammatory and profibrotic role during proteinuria in which the PTEC expresses a variety of chemokines and injury signals that culminate in progressive interstitial inflammation and fibrosis. During diabetes, other substrates including advanced glycation end products (AGEs), AGE intermediates, and high glucose (HG) may provoke the PTEC even further. Glycated albumin, but not the equivalent dose of bovine serum albumin (BSA), stimulates tubular IL-8 and ICAM-1 expression via NF-κB-, MAPK- and STAT-1-dependent pathways. Human biopsies of diabetic nephropathy (DN) reveal colocalization of AGE and ICAM-1 in proximal tubules. The biologically active carbonyl intermediates methylglyoxal-BSA-AGE and AGE-BSA upregulate tubular expression of CTGF, TGF-β, and VEGF, whereas carboxymethyllysine-BSA stimulates tubular expression of IL-6, CCL-2, CTGF, TGF-β, and VEGF via RAGE activation and NF-κB signal transduction. Hyperglycemia (30 mM), but not the equivalent dose of mannitol, promotes proinflammatory (IL-6 and CCL-2), profibrotic (TGF-β) and angiogenic (VEGF) responses in tubular cells via MAPK and PKC signaling and induces epithelial mesenchymal transition, which is TGF-β1 mediated. It has recently been shown that toll-like receptor (TLR) is implicated in the diabetic kidney. In human DN biopsies and PTEC, TLR4is upregulated and plays a permissive role in HG-induced IL-6 and CCL-2 overexpression and monocyte transmigration. In streptozotocin-induced rat DN and PTEC, TLR2 appears to be upregulated. Other novel mediators that become activated in PTEC exposed to HG include macrophage inflammatory protein-3-α, Krüppel-like factor 6 and thioredoxin-interacting protein, which may be attenuated by peroxisome proliferator-activate dreceptor-γ activation. Collectively, these phenomena suggest that the renal tubules are heavily involved in the pathogenesis of DN. These pathophysiologic responses may be collectively described as diabetic tubulopathy.

The kallikrein-kinin system

Emerging evidence suggests a role of the kallikrein-kinin system (KKS) in the pathogenesis of diabetic nephropathy (DN). Tissue kallikrein 1 is a member of the tissue kallikrein family that is mainly responsible for the generation of kinins, and bradykinin (BK) is the principal kinin responsible for the biologic actions of the KKS that acts through the ubiquitous BK 2receptor (B2R) and the inducible B1R. In the kidney, all KKS components are expressed. In particular, kallikrein 1 that is traditionally thought to be solely confined to the distal nephron has recently been identified in the proximal tubule of the human diabetic kidney. Current evidence suggests conflicting roles of the KKS in DN. For a renoprotective role of the KKS, BK reduces mesangial cell proliferation under the diabetic milieu; Akita B2R-/- or STZ-induced KLK-/- mice (T1DM) have more severe albuminuria and glomerulosclerosis, while antagonizing the B2R with icatibant attenuates the antiproteinuric effect of ramiprilin db/db mice (T2DM). For a detrimental role of the KKS, BK upregulates tubular cell IL-6, CCL-2, and TGF-β expression via ERK1/2 activation; the B2R-/- status protects against the development of DN lesions in STZ-injected mice, while blocking B2R with icatibant alleviates biochemical and histologic injuries in uninephrectomized db/db mice. These opposite findings may arise from multiple factors and call for further evaluation to clarify the role of the KKS in DN and diabetic tubulopathy.

The renin-angiotensin system

Diabetic nephropathy (DN) is a leading cause of end-stage renal disease in developed countries where type 2 diabetes mellitus has reached epidemic proportions. Although the exact pathogenesis of DN is not fully understood and is likely diverse in nature, there are convincing data that the renin-angiotensin system (RAS) is a major mediator of renal injury. Angiotensin II (Ang II), traditionally playing a central role as a mediator of glomerular hemodynamic adaptation and injury, is now recognized to exert proinflammatory action leading to upregulation of chemokines, adhesion molecules, and other fibrogenic growth factors that culminate in a decline of renal function. Hyperglycemia and mechanical stress deriving from glomerular hypertension are the key factors underlying pathogenesis of DN. The common signaling pathways stimulated by high glucose and mechanical insult may act synergistically, thereby accelerating the cell damage. Podocytes are subjected not only to the load of filtered glucose but also to diverse mechanical forces. Both high glucose and mechanical stress may impair the protein systems anchoring the podocyte foot processes in the glomerular basement membrane, therefore blunting resistance of these cells to mechanical forces in addition to the inflammatory insults. Loss of the podocytes is irreversible due to their inability to proliferate and to replenish damaged cells. Podocytes are injured early in the course of DN, which, most likely, underlies further glomerular and renal damage in diabetes. Under normal physiological conditions, podocytes play a specific role in the maintenance of intraglomerular RAS balance with enzymatic activities that predominantly lead to ANG1-7 and ANG1-9 formation, as well as Ang II degradation. ANG1-7 counteracts the proinflammatory actions of Ang II. These enzymatic activities are altered in a nonphysiological environment such as hyperglycemia that mimics diabetic kidney disease. An understanding of the local intraglomerular RAS will provide a novel approach for early stages of DN.

Renal cell carcinoma of native kidney in Chinese renal transplant recipients: a report of 12 cases and a review of the literature

Objectives

To present and discuss the epidemiological and clinical aspects, as well as therapeutic options and outcome of de novo renal cell carcinoma (RCC) of the native kidneys in a series of Chinese renal transplant recipients.

Patients and Methods

A retrospective, cohort study examining all renal transplant recipients with the diagnosis of RCC of native kidney followed up in two major regional hospitals in Hong Kong between January 2000 and December 2009. Clinical data included age, gender, cause of renal failure, symptoms at presentation, duration of transplantation, immunosuppressive therapy, and history of acquired cystic kidney disease (ACKD). Laboratory, radiographic, operative, and pathology reports were used to assess the tumor extent.

Results

Among the 1,003 renal transplant recipients recruited, 12 transplant recipients had a nephrectomy for a total of 13 RCC. The prevalence of de novo RCC was 1.3%. The mean age at diagnosis of RCC was 48.4 years, and the median time from transplantation to diagnosis was 6.1 years. ACKD was found in 6 (50%) of the patients. All patients except one were asymptomatic. pT1 disease was found in ten patients with a mean tumor size of 3.2 cm. All patients were treated successfully with radical nephrectomy. After a median follow-up of 38 months, two patients (16.7%) died. One died of sepsis, and the other died of metastatic carcinoma.

Conclusions

With increasing data showing a better prognosis if RCC is detected early by screening, it is time to consider screening all kidney transplant recipients for ACKD and RCC.

Additive effect of PPAR-γ agonist and ARB in treatment of experimental IgA nephropathy

Our recent in vitro study demonstrated peroxisome proliferator-activated receptor-γ (PPAR-γ) agonist potentiated the anti-inflammatory effect of angiotensin receptor blocker (ARB) in tubular epithelial cell under milieu mimicking IgA nephropathy (IgAN). Here we studied the therapeutic effect of combining a PPAR-γ agonist, rosiglitazone (Ros), with an ARB, losartan (Los), in experimental IgAN induced in Lewis rats by oral and intravenous immunization with bovine gamma-globulin (BGG). The rats were randomly divided into six groups: control, IgAN, IgAN with unilateral nephrectomy (IgAN/1K), and IgAN/1K receiving Ros, Los, or Ros + Los. Medication was given 1 week after nephrectomy until killing. Rats developing IgAN had hematuria, mesangial hypercellularity with IgA deposition, glomerular damage, and tubulointerstitial infiltration of CD25+ leukocytes accompanied by increased renal expression of TGF-β, AngII receptor subtype-1 (ATR1) and ICAM-1. The renal histopathology, albuminuria, and renal expression of TGF-β, ATR1 and ICAM-1 worsened with unilateral nephrectomy. Ros or Los reduced the renal expression of PCNA, TGF-β, ATR1, and ICAM-1 in IgAN rats with nephrectomy. Despite no difference between rats treated with monotherapy, combined therapy offered additive effect with decreased renal expression of TGF-β, ATR1 and ICAM-1 and attenuation of renal injury. Our animal study suggests combined PPAR-γ agonist and ARB holds promise for future therapy for IgAN.

CT angiography versus conventional digital angiography in preoperative assessment for Chinese living kidney donors

BACKGROUND

Computed tomography (CT) angiography is used for preoperative evaluation of living kidney donors, but its correlation with intraoperative findings during the transplant operation remains unknown.

METHODS

Between April 1997 and October 2008, 34 consecutive pairs of living kidney transplants were carried out. Conventional digital angiography was employed for the preoperative assessment in the first 19 pairs, and CT angiography in the subsequent 15 pairs. The radiological reports and operative findings during kidney harvest were carefully examined and compared.

RESULTS

Among the 34 cases in our cohort, we found 9 early branching renal arteries (26.4%) and 6 double renal arteries (17%). Venous and ureteral anomalies were rare, with only 1 case (2.9%) of each. CT angiography offered excellent and equal accuracy (accuracy 100%) when compared with conventional digital angiography for renal arterial anatomy. CT angiography showed superior performance compared with conventional angiography in the domain of venous and collecting system anomalies (accuracy 100% vs. 94.7%, respectively). No contrast nephropathy or allergy was documented in our series.

CONCLUSIONS

CT angiography showed excellent correlations with surgical findings in the Chinese population. It is associated with minimal risk of contrast nephropathy as well as lower cost and therefore should be adopted as the standard preoperative assessment of living kidney donors.

Essential role for Smad3 in angiotensin II-induced tubular epithelial-mesenchymal transition

Angiotensin II (Ang II) is a key mediator of chronic kidney disease, in which epithelial-mesenchymal transition (EMT) is a critical process mediated by the TGFbeta/Smad signalling pathway. The present study examined the specific role of Smads in Ang II-induced EMT in vitro and in vivo. We found that Ang II signalled through the receptor of AT1, not AT2, to activate Smad2/3 and induce EMT in a normal rat tubular epithelial cell line (NRK52E). Activation of Smads by Ang II was attributed to degradation of an inhibitory Smad7, which was mediated by the AT1-Smurf2-dependent ubiquitin degradation mechanism because blockade of AT1 receptor or knockdown of Smurf2 inhibited Smad7 loss, thereby reducing Smad2/3 activation and EMT in response to Ang II. In contrast, over-expression of Smad7 inhibited Ang II-induced Smad2/3 activation and EMT in NRK52E cells and in a rat model of remnant kidney disease. Moreover, knockdown of Smad3, not Smad2, attenuated Ang II-induced EMT. In conclusion, Ang II activates Smad signalling to induce EMT, which is mediated by a loss of Smad7 through the AT1-Smurf2-dependent ubiquitin degradation pathway. Smad3, but not Smad2, may be a mediator of EMT, while Smad7 may play a protective role in EMT in response to Ang II.