Peritubular ischemia contributes more to tubular damage than proteinuria in immune-mediated glomerulonephritis

The Natural History of Kidney Graft Cortical Microcirculation Determined by Real-Time Contrast-Enhanced Sonography (RT-CES)

Background

Kidney transplantation is the therapy of choice for end-stage kidney disease. Graft’s life span is shorter than expected due in part to the delayed diagnosis of various complications, specifically those related to silent progression. It is recognized that serum creatinine levels and proteinuria are poor markers of mild kidney lesions, which results in delayed clinical information. There are many investigation looking for early markers of graft damage. Decreasing kidney graft cortical microcirculation has been related to poor prognosis in kidney transplantation. Cortical capillary blood flow (CCBF) can be measured by real-time contrast-enhanced sonography (RT-CES). Our aim was to describe the natural history of CCBF over time under diverse conditions of kidney transplantation, to explore the influence of donor conditions and recipient events, and to determine the capacity of CCBF for predicting renal function in medium term.

Patients and Methods

RT-CES was performed in 79 consecutive kidney transplant recipients during the first year under regular clinical practice. Cortical capillary blood flow was measured. Clinical variables were analyzed. The influence of CCBF has been determined by univariate and multivariate analysis using mixed regression models based on sequential measurements for each patient over time. We used a first-order autoregression model as the structure of the covariation between measures. The post-hoc comparisons were considered using the Bonferroni correction.

Results

The CCBF values varied significantly over the study periods and were significantly lower at 48 h and day 7. Brain-death donor age and CCBF levels showed an inverse relationship (r: -0.62, p<0.001). Living donors showed higher mean CCBF levels than brain-death donors at each point in the study. These significant differences persisted at month 12 (54.5 ± 28.2 vs 33.7 ± 30 dB/sec, living vs brain-death donor, respectively, p = 0.004) despite similar serum creatinine levels (1.5 ± 0.3 and 1.5 ± 0.5 mg/dL). A sole rejection episode was associated with lower overall CCBF values over the first year. CCBF defined better than level of serum creatinine the graft function status at medium-term.

Conclusion

RT-CES is a non-invasive tool that can quantify and iteratively estimate cortical microcirculation. We have described the natural history of cortical capillary blood flow under regular clinical conditions.

A novel therapy to attenuate acute kidney injury and ischemic allograft damage after allogenic kidney transplantation in mice

Ischemia followed by reperfusion contributes to the initial damage to allografts after kidney transplantation (ktx). In this study we tested the hypothesis that a tetrapeptide EA-230 (AQGV), might improve survival and attenuate loss of kidney function in a mouse model of renal ischemia/reperfusion injury (IRI) and ischemia-induced delayed graft function after allogenic kidney transplantation. IRI was induced in male C57Bl/6N mice by transient bilateral renal pedicle clamping for 35 min. Treatment with EA-230 (20–50mg/kg twice daily i.p. for four consecutive days) was initiated 24 hours after IRI when acute kidney injury (AKI) was already established. The treatment resulted in markedly improved survival in a dose dependent manner. Acute tubular injury two days after IRI was diminished and tubular epithelial cell proliferation was significantly enhanced by EA-230 treatment. Furthermore, CTGF up-regulation, a marker of post-ischemic fibrosis, at four weeks after IRI was significantly less in EA-230 treated renal tissue. To learn more about these effects, we measured renal blood flow (RBF) and glomerular filtration rate (GFR) at 28 hours after IRI. EA-230 improved both GFR and RBF significantly. Next, EA-230 treatment was tested in a model of ischemia-induced delayed graft function after allogenic kidney transplantation. The recipients were treated with EA-230 (50 mg/kg) twice daily i.p. which improved renal function and allograft survival by attenuating ischemic allograft damage. In conclusion, EA-230 is a novel and promising therapeutic agent for treating acute kidney injury and preventing IRI-induced post-transplant ischemic allograft injury. Its beneficial effect is associated with improved renal perfusion after IRI and enhanced regeneration of tubular epithelial cells.

Tipping the balance from angiogenesis to fibrosis in CKD

Chronic progressive renal fibrosis leads to end-stage renal failure many patients with chronic kidney disease (CKD). Loss of the rich peritubular capillary network is a prominent feature, and seems independent of the specific underlying disease. The mechanisms that contribute to peritubular capillary regression include the loss of glomerular perfusion, as flow-dependent shear forces are required to provide the survival signal for endothelial cells. Also, reduced endothelial cell survival signals from sclerotic glomeruli and atrophic or injured tubule epithelial cells contribute to peritubular capillary regression. In response to direct tubular epithelial cell injury, and the inflammatory reaction that ensues, capillary pericytes dissociate from their blood vessels, also reducing endothelial cell survival. In addition, direct inflammatory injury of capillary endothelial cells, for instance in chronic allograft nephropathy, also contributes to capillary dropout. Chronic tissue hypoxia, which ensues from the rarefaction of the peritubular capillary network, can generate both an angiogenic and a fibrogenic response. However, in CKD, the balance is strongly tipped toward fibrogenesis. Understanding the underlying mechanisms for failed angiogenesis in CKD and harnessing endothelial-specific survival and pro-angiogenic mechanisms for therapy should be our goal if we are to reduce the disease burden from CKD.

Kidney injury molecule-1 expression in IgA nephropathy and its correlation with hypoxia and tubulointerstitial inflammation

Tubulointerstitial injury plays an important role in the development and progression of chronic kidney disease (CKD). Kidney injury molecule (KIM)-1 is induced in damaged proximal tubules in both acute renal injury and CKD. However, the dynamics of KIM-1 in CKD and effects of KIM-1 expression on disease progression are unknown. Here, we aimed to determine the associations between tubular KIM-1 expression levels, renal function, and inflammation in CKD. The relationships between levels of KIM-1 and clinicopathological parameters were analyzed in patients with progressive and nonprogressive IgA nephropathy. KIM-1 expression was increased in patients with IgA nephropathy, and its expression was significantly correlated with the decrease of renal function. KIM-1 was particularly evident at the site with reduced capillary density, and KIM-1-positive tubules were surrounded by infiltrates of inflammatory cells. Using in vitro cell models, we showed that cellular stressors, including hypoxia, induced KIM-1 expression. KIM-1-expressing cells produced more chemokines/cytokines when cultured under hypoxic conditions. Furthermore, we showed that tubular cells with KIM-1 expression can regulate the immune response of inflammatory cells through the secretion of chemotactic factors. These data suggest that KIM-1-expressing epithelial cells may play a role in the pathogenesis of tubulointerstitial inflammation during chronic renal injury through the secretion of chemokines/cytokines.

A Rare Case of Type I RenalTubular Acidosis with Membranous Nephropathy Presenting as Hypokalemic Paralysis

Type 1 renal tubular acidosis (RTA), or distal RTA (dRTA), is a disorder of renal tubular acidification, which is generally asymptomatic but may rarely present as hypokalemic paralysis. Here, we report the case of a young male who presented with sudden onset weakness of all 4 limbs and a 2-month history of swelling of the legs. An investigation revealed hypokalemia, metabolic acidosis, and nephrotic syndrome. Additional analyses revealed normal anion gap metabolic acidosis with a positive urine anion gap and dRTA. Renal biopsy showed evidence of membranous nephropathy (MN). The patient's weakness improved with potassium supplements. Normalization of the serum potassium level and disappearance of proteinuria were established with an ACE inhibitor and potassium supplementation. This case is an unusual combination of dRTA with MN coupled with the rare presenting symptoms of hypokalemic paralysis and medullary nephrocalcinosis.

Effect of treatment on urinary kidney injury molecule-1 in IgA nephropathy

Background

Kidney injury molecule-1 (KIM-1) is a biomarker useful for detecting early tubular damage and has been recently reported as a useful marker for evaluating kidney injury in IgA nephropathy (IgAN). We therefore investigated whether treatment decreases urinary KIM-1 excretion in IgAN.

Methods

We prospectively enrolled 37 patients with biopsy-proven IgAN. Urinary KIM-1 was assessed before and after treatment, which included low salt diet, blood pressure control, pharmacotherapy with angiotensin receptor blockers and/or angiotensin converting enzyme inhibitors, and immunosuppressive agents as necessary. The median treatment duration was 24 months.

Results

Urinary KIM-1/creatinine (Cr) was significantly decreased in patients with IgAN after treatment compared to baseline (P < 0.0001, 1.16 [0.51-1.83] vs 0.26 [0.12-0.65] ng/mg). There was a decrease in the amount of proteinuria after treatment, but it was not statistically significant (P = 0.052, 748.1 [405-1569.7] vs 569.2 [252.2-1114] g/d). Estimated glomerular filtration rate (eGFR) did not change with treatment (P = 0.599, 79.28 ± 30.56 vs 80.98 ± 32.37 ml/min/1.73 m²). Urinary KIM-1 was not correlated with proteinuria baseline or follow up (pre-: R = - 0.100, P = 0.577, post-: R = 0.001, P = 0.993). In patients with higher baseline urinary KIM-1, both urinary KIM-1 level and proteinuria were significantly decreased following treatment.

Conclusions

Treatment decreases urinary KIM-1/Cr in patients with IgAN. It also reduces proteinuria in patients with higher baseline urinary KIM-1. These results suggest a potential role for urinary KIM-1 as a biomarker for predicting treatment response in IgAN, however, further study is needed to verify this.

Protective effects of L-type fatty acid-binding protein (L-FABP) in proximal tubular cells against glomerular injury in anti-GBM antibody-mediated glomerulonephritis

Background. In glomerulonephritis (GN), an overload of free fatty acids (FFA) bound to albumin in urinary protein may induce oxidative stress in the proximal tubules. Human liver-type fatty acid-binding protein (hL-FABP) expressed in human proximal tubules, but not rodents, participates in intracellular FFA metabolism and exerts anti-oxidative effects on the progression of tubulointerstitial damage. We examined whether tubular enhancement of this anti-oxidative action modulates the progression of glomerular damage in immune-mediated GN in hL-FABP chromosomal gene transgenic (Tg) mice.

Methods. Anti-glomerular basement membrane antibody-induced glomerulonephritis (anti-GBM GN) was induced in Tg and wild-type mice (WT). Proteinuria, histopathology, polymorphonuclear (PMN) influx, expression of tubulointerstitial markers for oxidative stress 4-hydroxy-2-Nonenal (HNE) and fibrosis (α-smooth muscle actin), proximal tubular damage (Kim-1), Peroxisome Proliferator-Activated Receptor γ (PPAR γ) and inflammatory cytokines [Monocyte Chemotactic Protein-1, tumor necrosis factor-alpha (TNF-α) and Transforming growth factor beta (TGF-β)] were analyzed. The mice were also treated with an angiotensin type II receptor blocker (ARB).

Results. The urinary protein level in Tg mice decreased significantly during the acute phase (∼Day 5). Tg mice survived for a significantly longer time than WT mice, with an attenuation of tubulointerstitial damage score and expression of each tubulointerstitial damage marker observed at Day 7. Expression of inflammatory cytokines on Day 7 was higher in WT mice than Tg mice and correlated strongly with PPARγ expression in WT mice, but not in Tg mice. Interestingly, Tg mice showed insufficient PMN influx at 3 and 6 h, with simultaneous elevation of urinary L-FABP and reduction in HNE expression. The two strains of mice showed different types of glomerular damage, with mild mesangial proliferation in Tg mice and severe endothelial swelling with vascular thrombosis in WT mice. The glomerular damage in Tg mice was improved by administration of an ARB.

Conclusions. The present experimental model suggests that tubular enhancement of L-FABP may protect mice with anti-GBM GN from progression of both tubulointerstitial and glomerular injury.

Cation-independent mannose 6-phosphate receptor inhibitor (PXS25) inhibits fibrosis in human proximal tubular cells by inhibiting conversion of latent to active TGF-beta1

Hyperglycemia and hypoxia have independent and convergent roles in the development of renal disease. Transforming growth factor-β(1) (TGF-β(1)) is a key cytokine promoting the production of extracellular matrix proteins. The cationic-independent mannose 6-phosphate receptor (CI-M6PR) is a membrane protein that binds M6P-containing proteins. A key role is to activate latent TGF-β(1). PXS25, a novel CI-MPR inhibitor, has antifibrotic properties in skin fibroblasts, but its role in renal fibrosis is unclear. The aim was to study the role of PXS25 in matrix protein production under high glucose ± hypoxic conditions in human proximal tubule (HK-2) cells. HK-2 cells were exposed to high glucose (30 mM) ± 100 μM PXS25 in both normoxic (20% O(2)) and hypoxic (1% O(2)) conditions for 72 h. Cellular fibronectin, collagen IV, and matrix metalloproteinase-2 (MMP-2) and MMP-9 were assessed. Total and active TGF-β(1) were measured by ELISA. High glucose and hypoxia independently induced TGF-β(1) production. Active TGF-β(1), but not total TGF-β(1) was reduced with concurrent PXS25 in the presence of high glucose, but not in hyperglycemia+hypoxia conditions. Hyperglycemia induced fibronectin and collagen IV production (P < 0.05), as did hypoxia, but only hyperglycemia-induced increases in matrix proteins were suppressed by concurrent PXS25 exposure. High glucose induced MMP-2 and -9 in normoxic and hypoxic conditions, which was not modified in the presence of PXS25. High glucose and hypoxia can independently induce endogenous active TGF-β(1) production in human proximal tubular cells. PXS25 inhibits conversion of high glucose-induced release of active TGF-β(1), only in the absence of hypoxia.

Renal tubular angiogenic dysregulation in anti-Thy1.1 glomerulonephritis

Peritubular vascular changes and hypoxia after glomerular injury may explain subsequent tubulointerstitial injury and fibrosis. Several studies suggested that the expected tubulointerstitial angiogenic response is actively suppressed in this setting. The mechanism of this aberrant response has not been clearly identified. We used a common model of glomerular injury in rats to assess vascular changes and to identify potential factors associated with this aberrant response. Anti-Thy1.1 antibody administration (1 or 4 weekly doses) led to a dose-dependent renal damage characterized by elevated urea and tubulointerstitial fibrosis as assessed by Picro-Sirius Red staining. We quantified peritubular capillaries using CD31 and CD34 immunohistochemistry and showed that tubular angiogenic dysregulation was associated with peritubular capillary rarefaction. Using laser capture microdissection, we demonstrated an early induction of fibrogenic and angiogenic factors in the glomeruli and a subsequent dysregulated angiogenic response in the tubulointerstitial compartment. Proximal tubules of anti-Thy1.1-treated animals had increased pigment epithelial-derived factor (PEDF) expression by immunohistochemistry. Protein taken by laser capture microdissection also showed that PEDF was upregulated. Temporally associated with PEDF expression was a transient downregulation of tubular hypoxia-inducible factor (HIF)1α. In a human proximal tubular cell culture, we show that PEDF downregulates HIF1α protein and gene expression in cells exposed to 1% oxygen. In anti-Thy1.1 glomerulonephritis, there is aberrent tubular angiogenesis associated with glomerular injury and tubulointersititial fibrosis. We showed that PEDF may be involved by downregulating HIF1α. Further work is needed to elucidate the mechanism of PEDF upregulation and action in the tubules.

'Cannibalism' (cell phagocytosis) does not differentiate reactive renal tubular cells from urothelial carcinoma cells

OBJECTIVE

Cannibalism of one cell by another in voided urine cytology has been considered a cytological feature for differentiating urothelial carcinoma (UC) from benign lesions. Recently, however, we observed cannibalism in voided urine obtained from patients with renal glomerular disease (RGD). The purpose of this study was to determine the cytomorphological and immunocytochemical characteristics of cannibalism in voided urine from RGD.

METHODS

Seventy cytology specimens of voided urine were examined and the findings were compared with the histological findings. In addition, we compared the cytomorphological and immunocytochemical differences in cannibalism found in RGD and cases of UC selected as showing cannabilism.

RESULTS

Cannibalism in voided urine was found in three (5.5%) of 55 RGD cases. The finding was measured as (1+) < 5 cells, (2+) 5-20 cells, and (3+) > 20 cells and was (1+) in all three RGD cases, compared with 6.7%, 60% and 33.3% respectively in 15 UC cases. Differences in low cellularity cases (1+) and moderate to high cellularity cases (2+ or 3+) were statistically significant between RGD (3 and 0) and UC (1 and 14) (P=0.005). The maximum diameter of cannibalized cells in RGD was 24.3-33.0 microm (mean 29.8 microm) versus 18.0-30.4 microm (mean 23.3 microm) in UC (P=0.004). Necrosis and isomorphic erythrocytes were absent in RGD, but were found in 46.7% and 86.7%, respectively, of UC cases (P=0.245 and P=0.012). Dysmorphic erythrocytes were identified in all three cases with RGD and 13.3% of UC (P=0.012). Vimentin reactivity was found in all cases with cannibalism in RGD, but never in UC (P=0.001).

CONCLUSIONS

Our results demonstrated that cannibalism in voided urine is present not only in UC but also in RGD. Furthermore, we showed that cellularity of cannibalism, vimentin reactivity and background differed significantly and can be used for differential diagnosis between the two groups.

Peritubular capillaries are rarefied in congenital nephrotic syndrome of the Finnish type

Congenital nephrotic syndrome of the Finnish type (NPHS1) is associated with the rapid development of glomerular and tubulointerstitial fibrosis. Here we measured morphologic and molecular changes in the peritubular capillaries of the kidney in patients with NPHS1. Immunohistochemical analysis for the endothelial cell marker CD31 showed marked narrowing and a moderate but significant reduction in peritubular capillary density, especially in areas of increased collagen I and alpha-smooth muscle actin content. No evidence of endothelial-mesenchymal transformation was found. There was increased expression (up to 43-fold) of hypoxia inducible factor-1alpha suggesting tubulointerstitial hypoxia. Double-labeling for CD31 and vimentin showed small foci of peritubular capillary loss and tubular cell damage. While the amount of intercellular adhesion molecule-1 was upregulated in endothelial cells, other adhesion molecules were only modestly expressed. Vascular endothelial growth factor expression was reduced by up to half and decreased endothelial progenitor cell marker CD34 expression indicated lack of vascular repair. Our results suggest that hypoxia in the tubulointerstitium caused by hypoperfusion of glomerular and tubulointerstitial capillaries and rarefaction of the latter may be important for the rapid progression of fibrosis in the kidneys of patients with NPHS1.

Urinary fatty acid-binding protein 1: an early predictive biomarker of kidney injury

In the development of novel therapeutic strategies for kidney disease, new renal biomarkers for early detection and accurate evaluation of renal injury are urgently required for both acute kidney injury (AKI) and chronic kidney disease (CKD). Fatty acid-binding protein 1 (FABP1) is expressed in renal proximal tubule cells and shed into urine in response to hypoxia caused by decreased peritubular capillary blood flow. To clarify the role of urinary FABP1 in kidney disease, we established human FABP1 transgenic mice and evaluated the responses of FABP1 to several AKI and CKD models. Moreover, there are accumulating clinical data that urinary FABP1 can detect human AKI earlier than serum creatinine and can distinguish the risk population for AKI. Investigation with "humanized" FABP1 transgenic mice and measurement of clinical samples allowed us to develop urinary FABP1 as a new renal biomarker. Further clinical studies are necessary to confirm the potential of urinary FABP1 for clinical application.