Tubulointerstitial renal disease

Emerging biomarkers of chronic kidney disease in children

Chronic kidney disease (CKD) has become a significant public health concern, as it is associated with substantial morbidity. Prior research has evaluated multiple novel CKD biomarkers to supplement serum creatinine and proteinuria. The ultimate goal of this research is to find biomarkers that can be used to accurately predict CKD progression and to better time outpatient follow-up, and referral for transplant. Also, an optimal panel of biomarkers can augment the predictive value of proteinuria and serum creatinine by enriching patient enrollment in clinical trials. In this review, we discuss salient findings on 12 candidate plasma and urine biomarkers and their reported association with CKD. We explore the common pathways of CKD progression and the pathophysiologic processes of tubulointerstitial injury, inflammation, repair, and fibrosis that are potentially classified by specific biomarkers. We describe both pediatric and adult findings and highlight the paucity of pediatric research in CKD progression. It will be important for cohorts with longitudinal follow-up to evaluate these CKD biomarkers for potential use in pediatric clinical trials and routine CKD management.

Taurine ameliorates alloxan-induced diabetic renal injury, oxidative stress-related signaling pathways and apoptosis in rats

Hyperglycemia-induced oxidative stress plays a vital role in the progression of diabetic nephropathy. The renoprotective nature of taurine has also been reported earlier; but little is known about the mechanism of this beneficial action. The present study has, therefore, been carried out to explore in detail the mechanism of the renoprotective effect of taurine under diabetic conditions. Diabetes was induced in rats by alloxan (single i.p. dose of 120 mg/kg body weight) administration. Taurine was administered orally for 3 weeks (1% w/v in drinking water) either from the day on which alloxan was injected or after the onset of diabetes. Alloxan-induced diabetic rats showed a significant increase in plasma glucose, enhanced the levels of renal damage markers, plasma creatinine, urea nitrogen and urinary albumin. Diabetic renal injury was associated with increased kidney weight to body weight ratio and glomerular hypertrophy. Moreover, it increased the productions of reactive oxygen species, enhanced lipid peroxidation and protein carbonylation in association with decreased intracellular antioxidant defense in the kidney tissue. In addition, hyperglycemia enhanced the levels of proinflammatory cytokins (TNF-α, IL-6, IL-1β) and Na(+)--K(+)-ATPase activity with a concomitant reduction in NO content and eNOS expression in diabetic kidney. Investigation of the oxidative stress-responsive signaling cascades showed the upregulation of PKCα, PKCβ, PKCε and MAPkinases in the renal tissue of the diabetic animals. However, taurine administration decreased the elevated blood glucose and proinflammatory cytokine levels, reduced renal oxidative stress (via decrease in xanthine oxidase activity, AGEs formation and inhibition of p47phox/CYP2E1 pathways), improved renal function and protected renal tissue from alloxan-induced apoptosis via the regulation of Bcl-2 family and caspase-9/3 proteins. Taurine supplementation in regular diet could, therefore, be beneficial to regulate diabetes-associated renal complications.

Renal function in patients with β-thalassaemia major: a long-term follow-up study

BACKGROUND

Little information is available about the kidney's involvement in patients with β-thalassaemia major (TM). In particular, there are no studies reporting the outcome of renal function over time.

METHODS

In this retrospective study, we evaluated the changes in estimated glomerular filtration rate (eGFR) in 81 adult patients with TM followed for 10 years. Only patients who had an eGFR of >90 mL/min/1.73 m(2) at presentation were admitted to the study. All patients were regularly followed for at least 10 years.

RESULTS

At 10 years, 66 patients showed a mild decline in eGFR that remained, however, within a normal range (from 119.9 to 113.6 mL/min/1.73 m(2), P = 0.636). In the remaining 15 patients (18.5%), eGFR decreased to <90 mL/min (from 98.1 to 78.2 mL/min/1.73 m(2); P = 0.004). The repeated-measures models showed that the decline in eGFR over time was significantly higher (P = 0.0068) in patients with baseline phosphaturia >1000 mg/24 h (P = 0.0068), while eGFR tended to decline more rapidly in patients with baseline uricuria >700 mg/24 h than in those with lower uricuria (P = 0.0783). Univariate Cox's proportional regression models showed that abnormal levels of calcaemia were associated with the risk of kidney damage [hazard ratio (HR) 0.30, 95% confidence interval 0.09-0.97 for calcaemia 8.4-10.2 mg/dL versus HR not estimable for calcaemia <8.4 or >10.2 mg/dL].

CONCLUSIONS

In most adults with TM, the eGFR tends to remain within a normal range after 10 years. However, patients with elevated phosphaturia, elevated uricuria and/or abnormal levels of calcaemia show a significant decline in eGFR over time, suggesting that tubular damage acquired in childhood caused by either TM or its treatment may eventually result in abnormal eGFR. Further studies in a larger cohort of TM patients are needed to further elucidate the long-term impact of TM on renal function.

Renal tubular fluid shear stress facilitates monocyte activation toward inflammatory macrophages

Modified urinary fluid shear stress (FSS) induced by variations of urinary fluid flow and composition is observed in early phases of most kidney diseases. Recently, we reported that renal tubular FSS promotes endothelial cell activation and subsequent adhesion of human monocytes, thereby suggesting that changes in urinary FSS can induce the development of inflammation (Miravète M, Klein J, Besse-Patin A, Gonzalez J, Pecher C, Bascands JL, Mercier-Bonin M, Schanstra JP, Buffin-Meyer B, BBRC 407: 813-817, 2011). Here, we evaluated the influence of tubular FSS on monocytes as they play an important role in the progression of inflammation in nephropathies. Human renal tubular cells (HK-2) were exposed to FSS 0.01 Pa for 30 min or 5 h. Treatment of human THP-1 monocytes with the resulting conditioned medium (FSS-CM) modified the expression of macrophage differentiation markers, suggesting differentiation toward the inflammatory M1-type macrophage. The effect was confirmed in freshly isolated human monocytes. In contrast to endothelial cells, the activation of monocytes by FSS-CM did not require TNF-α. Cytokine array analysis of FSS-CM showed that FSS modified secretion of cytokines by HK-2 cells, particularly by increasing secretion of TGF-β and by decreasing secretion of C-C chemokine ligand 2 (CCL2). Neutralization of TGF-β or CCL2 supplementation attenuated the effect of FSS-CM on macrophage differentiation. Finally, FSS-injured HK-2 cells expressed and secreted early biomarkers of tubular damage such as kidney injury molecule 1 and neutrophil gelatinase-associated lipocalin. In conclusion, changes in urinary FSS should now also be considered as potential insults for tubular cells that initiate/perpetuate interstitial inflammation.

Dendrimer-based macromolecular conjugate for the kidney-directed delivery of a multitargeted sunitinib analogue

The development of a macromolecular conjugate of a multitargeted tyrosine kinase inhibitor is described that can be used for renal-specific delivery into proximal tubular cells. A novel sunitinib analogue, that is, 17864, is conjugated to a NH(2) -PAMAM-G3 dendrimer via the platinum (II)-based Universal Linkage System (ULS™). The activity of 17864 is retained after coordination to the ULS linker alone or when coupled to NH(2) -PAMAM-G3. 17864-UlS-NH(2) -PAMAM-G3 is non-toxic to proximal tubular cells in vitro. After intravenous administration to mice, 17864-UlS-NH(2) -PAMAM-G3 rapidly and efficiently accumulates in the kidneys. These results are encouraging for future studies focusing on the development of novel therapeutics for the treatment of renal diseases.

Renal tubular fluid shear stress promotes endothelial cell activation

Modified urinary fluid shear stress (FSS) induced by variations of urinary fluid flow and composition is observed in early phases of most kidney diseases. In this study, we hypothesized that changes in urinary FSS represent a tubular aggression that contributes to the development of inflammation, a key event in progression of nephropathies. Human renal tubular cells (HK-2) were exposed to FSS for 30 min at 0.01 Pa. Treatment of human endothelial cells (HMEC-1) with the resulting conditioned medium (FSS-CM) increased C-C chemokine ligand 2 (CCL2) and tumor necrosis factor (TNF)-α protein secretion, increased endothelial vascular adhesion molecule-1 (VCAM-1) mRNA expression and stimulated adhesion of human (THP-1) monocytes to the endothelial monolayer. These effects were TNF-α dependent as they were abolished by neutralization of TNF-α. Interestingly, the origin of TNF-α was not epithelial, but resulted from autocrine endothelial production. However, in contrast to short term FSS, long term FSS (5h) induced the release of the key inflammatory proteins CCL2 and TNF-α directly from tubular cells. In conclusion, these results suggest for the first time that urinary FSS can contribute to the inflammatory state involved in initiation/perpetuation of renal diseases.

Renal manifestations of systemic illness in children

Kidney disease may be associated with a systemic disorder or found in isolation. With advances in the understanding of the pathophysiology of glomerular disorders, the distinction between primary and secondary glomerular disease is no longer valid. A wide spectrum of glomerular, vascular, and tubulointerstitial diseases may accompany autoimmune disorders, nephritogenic pharmaceuticals, infections, or complement dysregulation. This article focuses on renal manifestations of systemic diseases such as vasculitis, drug- and infection-related tubulointerstitial injury, and thrombotic disorders.

Fibrotic mechanisms in idiopathic rapidly progressive glomerulonephritis: the role of TGF-beta1 and C5b-9

BACKGROUND

Idiopathic IRPGN is a form of renal vasculitis in which a high chronicity index is present despite minimal impairment of renal function. The present study investigated the mechanisms underlining the relatively early appearance of fibrosis.

METHODS

In all, 34 patients (17 males) with biopsy proven idiopathic RPGN were included. On light microscopy, the percentage and evolution stage of crescents, the presence of glomerular necrosis, the degree or severity of arteriosclerosis, as well as the extent of tubulointerstitial (TIN) infiltration, interstial fibrosis, and tubular atrophy were assessed. Monoclonal antibodies were used to identify infiltrating macrophages, HLA-DR (+), alpha-SMA (+), and PCNA (+) cells, the expression of the adhesion molecule ICAM-1, the growth factor TGF-beta1, and the terminal complement component C5b-9.

RESULTS

The presence of glomerular necrosis correlated positively with the number of SMA (+) cells in TIN (p = 0.036). Glomerular TGF-beta1 expression had positive correlation with tubular C5b-9 expression. The tubulointerstitial TGF-beta1 expression correlated with tubular C5b-9 expression (p = 0.001) and TGF-beta1 expression (p = 0.009). Independent factors predicting the severity of renal function impairment were the CRP levels (p = 0.002) and the degree of arteriosclerosis (p = 0.01). CRP levels correlated with the severity of interstitial infiltration and fibrosis (p = 0.02), the expression of TGF-beta1 in the glomeruli (p = 0.009) and the interstitial space (p = 0.001), and the intensity of tubular ICAM-1 and C5b-9 expression (p = 0.023, p = 0.002, respectively). The severity of proteinuria showed a significant correlation with the expression of TGF-beta1 in the glomeruli (p = 0.033) and the tubulointerstitium (p = 0.019).

CONCLUSIONS

The activation of interstitial fibroblasts seems to be an early phenomenon that is related to the extent of glomerular necrosis. Glomerular TGF-beta1 may induce tubular expression of C5b-9. Increased tubular C5b-9 expression may result in interstitial fibrosis through increased TGF-beta1 production.

Predictors of outcome in idiopathic rapidly progressive glomerulonephritis (IRPGN)

Background

Small vessel vasculitides are known to follow a devastating course towards end-stage renal disease, unless treated with immunosuppressive regiments. We investigated the value of clinical, histological and immunohistochemical parameters as predictors of outcome at diagnosis in patients with pauci immune necrotizing glomerulonephritis.

Methods

In 34 patients the percentage and evolution stage of crescents, the presence of glomerular necrosis, the degree or severity of arteriosclerosis, as well as the extent of tubulointerstitial infiltration, interstial fibrosis and tubular atrophy were assessed. Monoclonal antibodies were used to identify infiltrating macrophages, α-SMA(+) and PCNA(+) cells, the expression of integrins α3β1 and LFA-1β, the adhesion molecule ICAM-1, the growth factor TGF-β1 and the terminal complement component C5b-9.

Results

24 pts (70.6%) showed a complete or partial response to the treatment. The follow-up period was 20 ± 22 months. At multivariate analysis, serum CRP (p = 0.024), the intensity of tubular expression of C5b-9 (p < 0.0001) as well as the extent of glomerular and tubular expression of α3β1 integrin (p = 0.001 and 0.008 respectively) independently predicted the response to treatment. The response rate was better in ANCA(+) pts (p = 0.008). The extent of interstitial infiltrate (p < 0.0001), the severity of tubulointerstitial fibrosis (p < 0.0001) and the severity of tubular TGF-β1 expression (p < 0.0001) were independent predictors of long term outcome of renal function.

Conclusion

Patients with ANCA-associated renal vasculitis seem to respond better to the treatment. Acute phase reactants, such as CRP, implying a more intense parenchymal inflammatory reaction, as well as the intensity of the de novo expression of C5b-9 and the glomerular and tubular expression of α3β1 integrin predict the response to therapy. The severity of TIN lesions and of the tubulo-interstitial TGF-β1 and C5b-9 expression predict an unfavourable outcome.

The renal antifibrotic effects of angiotensin-converting enzyme inhibition involve bradykinin B2 receptor activation in angiotensin II-dependent hypertension

OBJECTIVE

The renoprotective action of angiotensin I-converting enzyme inhibitors (ACE-Is) is well established, but the role played by bradykinin (BK) remains unclear. We therefore investigated whether an enhanced BK effect on B2 receptor subtype mediated the antifibrotic effect of ACE-Is and whether neutral endopeptidase (NEP) inhibition, which can blunt BK degradation more effectively than ACE inhibition, provided further renoprotection in a rat model of angiotensin (Ang) II-dependent renal damage.

METHODS

Five-week-old Ren-2 transgenic rats (TGRen2) received, for 8 weeks, a placebo, ramipril (5 mg/kg body weight) or the dual ACE + NEP inhibitor MDL 100,240 (MDL) (40 mg/kg body weight). After 4 weeks, the B2 receptor antagonist icatibant (0.5 mg/kg body weight) was administered on top of active treatment for 4 weeks to 50% of the TGRen2 rats. Blood pressure was measured weekly by a tail-cuff method and, after sacrifice, kidney weight, glomerular volume, density of glomerular profiles were measured; tubulo-interstitial fibrosis, glomerular and perivascular fibrosis were quantified by histomorphometry.

RESULTS

The development of hypertension and tubulo-interstitial fibrosis was prevented by both ramipril and MDL (P = 0.0001 versus placebo); icatibant annulled the latter effect. Glomerular and perivascular fibrosis were unaffected by either ramipril or MDL alone; however, combined treatment with icatibant enhanced glomerular fibrosis (P = 0.0001 versus placebo).

CONCLUSION

Enhanced BK effect on B2 subtype receptors is essential for the prevention of tubulo-interstitial fibrosis with ACE or dual ACE + NEP inhibition in TGRen2 rats.

Rho/Rho kinase pathway regulates maintenance of the differentiated tubular epithelial cell phenotype on laminin-1

BACKGROUND

Maintenance of a polarized tubular epithelium by appropriate intracellular signaling and extracellular matrix is critical both in normal renal function as well as in acute and chronic tubular injury. We examined the hypothesis that maintenance of a differentiated epithelial phenotype on the basement membrane glycoprotein laminin-1 is controlled by the Rho/Rho kinase pathway.

METHODS

Using the tubular epithelial cell lines LLC-PK1 and MDCK which were cultured on laminin-1 vs. collagen IV, we analyzed cell morphology and motility (cohort migration assay) as well as expression of differentiation and dedifferentiation markers (immunofluorescence microscopy).

RESULTS

Cohort migration of LLC-PK1 cells was significantly slowed down on laminin-1 (10.7 +/- 2.2 m.u. (migratory units)) compared with collagen IV (16.6 +/- 2.3 m.u.; BSA control: 2.8 +/- 2.5 m.u.). Inhibition of the Rho/Rho kinase pathway by C3 exotoxin (1 mug/ml) or the Rho kinase inhibitor Y27632 (10 microM) significantly augmented cohort migration on laminin-1 (14.5 +/- 1.4 and 16.0 +/- 1.8 m.u. vs. 10.7 +/- 2.2 m.u.). In parallel to the increased migratory activity, inhibition of the Rho/Rho kinase pathway resulted in a more mesenchymal phenotype of LLC-PK1 cells on laminin-1 with increased formation of lamellopodia and filopodia, distinct loss of focal contacts and stress fibers, upregulation of the dedifferentiation marker vimentin, and loss of cell-cell contacts with translocation of beta-catenin from the adherens junctions to the cytosol and nucleus. Similarly, cohort migration of MDCK cells was retarded on laminin-1 when compared with collagen IV, and addition of the Rho kinase inhibitor Y27632 resulted in enhanced motility and a change in cell morphology.

CONCLUSION

The study demonstrates that the Rho/Rho kinase pathway is required to maintain a non-migratory epithelial phenotype of cultured renal tubular LLC-PK1 and MDCK cells on the basement membrane glycoprotein laminin-1.

CD40: A Mediator of Pro- and Anti-Inflammatory Signals in Renal Tubular Epithelial Cells

Infiltration of immune cells into the renal interstitium is characteristic of chronic inflammatory kidney diseases. CD4+ T cells and platelets express CD40 ligand (CD40L) and are reported to mediate proinflammatory events in renal proximal tubular epithelial cells (RPTEC) via interaction with CD40. In other cell types, CD40 signals can also induce protective genes. Here, human RPTEC were treated with sCD40L to ligate CD40, and a significant increase in the generation of proinflammatory reactive oxygen species was found; however, CD40-activated cells did not undergo apoptosis. This suggests that CD40 signals may simultaneously induce antiapoptotic genes for cytoprotection of RPTEC. Heme oxygenase-1 (HO-1) expressed in RPTEC serves as a protective gene, but it is not known whether it is regulated by CD40. Next, RPTEC were transiently transfected with a full-length HO-1 promoter-luciferase construct and were treated with sCD40L. CD40 ligation was found to significantly increase HO-1 promoter activity. By electrophoretic mobility shift assay, it was confirmed that CD40 signaling induced the transcriptional activation of HO-1 through the binding of NF-kappaB to its promoter. By Western blot analysis, a marked increase in HO-1 protein expression following CD40 ligation was also found. These observations are of clinical significance because it was found that CD40 and HO-1 are induced in expression in vivo in inflamed rejecting kidney biopsies and co-expressed in renal tubules. Therefore, ligation of CD40 in RPTEC promotes both inflammatory and anti-inflammatory processes. Regulating the balance between these two events may be of importance in the prevention of tubular injury associated with renal disease.

Relaxin-1–deficient mice develop an age-related progression of renal fibrosis

BACKGROUND

Relaxin (RLX) is a peptide hormone that stimulates the breakdown of collagen in preparation for parturition and when administered to various models of induced fibrosis. However, its significance in the aging kidney is yet to be established. In this study, we compared structural and functional changes in the kidney of aging relaxin-1 (RLX-/-) deficient mice and normal (RLX+/+) mice.

METHODS

The kidney cortex and medulla of male and female RLX+/+ and RLX-/- mice at various ages were analyzed for collagen content, concentration, and types. Histologic analysis, reverse transcription-polymerase chain reaction (RT-PCR) of relaxin and relaxin receptor mRNA expression, receptor autoradiography, glomerular isolation/analysis, and serum/urine analysis were also employed. Relaxin treatment of RLX-/- mice was used to confirm the antifibrotic effects of the peptide.

RESULTS

We demonstrate an age-related progression of renal fibrosis in male, but not female, RLX-/- mice with significantly (P < 0.05) increased tissue dry weight, collagen (type I) content and concentration. The increased collagen expression in the kidney was associated with increased glomerular matrix and to a lesser extent, interstitial fibrosis in RLX-/- mice, which also had significantly increased serum creatinine (P < 0.05) and urinary protein (P < 0.05). Treatment of RLX-/- mice with relaxin in established stages of renal fibrosis resulted in the reversal of collagen deposition.

CONCLUSION

This study supports the concept that relaxin may provide a means to regulate excessive collagen deposition during kidney development and in diseased states characterized by renal fibrosis.

Secretion of collagen type IV by human renal fibroblasts is increased by high glucose via a TGF- -independent pathway

BACKGROUND

Tubulointerstitial fibrosis is an important component of diabetic nephropathy, which is characterized by increased expression of interstitial extracellular matrix components and aberrant expression of the basement membrane component collagen type IV. The present study examined the effect of high ambient glucose and transforming growth factor-beta1 (TGF-beta1) on collagen secretion by human renal fibroblasts and proximal tubular epithelial cells (PTECs).

METHODS

Human renal fibroblasts (TK173) and PTECs (HK2) were used to examine the effects of high glucose (25 mM d-glucose) and TGF-beta1 (1 ng/ml) on collagen type I, III and IV secretion compared with control medium (5.5 mM glucose). Matrix components were measured by enzyme-linked immunosorbent assay (ELISA) and reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Renal fibroblasts are the main producers of the interstitial components collagen type I and type III, while collagen type IV was secreted predominantly by PTECs. However, renal fibroblasts were also able to secrete collagen type IV. Secretion of collagen type IV by fibroblasts was increased upon stimulation with TGF-beta1, reaching levels comparable with those secreted by TGF-beta1-induced PTECs. Moreover, high glucose stimulated increased collagen type IV secretion. Importantly, this could not be attenuated by neutralizing pan-specific anti-TGF-beta antibodies.

CONCLUSIONS

These data show that renal fibroblasts secrete collagen type IV, which can be increased by high glucose independent of endogenous TGF-beta. This suggests that as well as the increased expression of interstitial components, renal fibroblasts can contribute to the increased expression of the basement membrane component collagen type IV in tubulointerstitial fibrosis observed during diabetic nephropathy.

Angiotensin II-induced hypertrophy of proximal tubular cells requires p27Kip1

BACKGROUND

Angiotensin II (Ang II), as a single factor, induces hypertrophy of cultured proximal tubular cells of various species. Cells undergoing hypertrophy are arrested in the G1 phase of the cell cycle. Ang II also stimulated the expression of p27Kip1, an inhibitor of cyclin-dependent kinases (CDK). Although previous studies inhibiting p27Kip1 expression with antisense oligonucleotides suggested that this CDK inhibitor is important for Ang II-induced hypertrophy of proximal tubular cells, nonspecific effects of antisense technology, and the inability to transfect 100% of cells raised concerns about the true role of p27Kip1 in tubular hypertrophy.

METHODS

Proximal tubular cells were isolated and cultured from wild-type (p27Kip1+/+) and knockout (p27Kip1-/-) mice. p27Kip1 genomic and protein expression was evaluated. Proximal tubular cell origin was confirmed by expression of various markers [3M-1 antigen, gamma-glutamyltransferase, angiotensin-converting enzyme (ACE)]. Cell proliferation (cell number, 3[H]thymidine incorporation) and hypertrophy (de novo protein synthesis as measured by 3[H]leucine incorporation, hypertrophy index, cell size) were evaluated. CDK2 and CDK4 activities were determined by an in vitro kinase assay. In addition, cell cycle analysis was performed by flow cytometry. p27Kip1 expression was reconstituted in two different clones of p27Kip1-/- proximal tubular cells using an inducible vector system based on ecdysone response elements.

RESULTS

In accordance with previous studies, 10-7 mol/L Ang II induces hypertrophy and cell cycle arrest of p27Kip1+/+ proximal tubular cells. In contrast, Ang II facilitated cell cycle progression of two p27Kip1-/- proximal tubular cell lines without inducing hypertrophy. Ang II activates CDK4/cyclin D kinase activity in p27Kip1+/+ and -/- tubular cells, but stimulates CDK2/cyclin E activity only in wild-type cells. However, in the presence of Ang II, reconstituting p27Kip1 expression in p27Kip1-/- tubular cells using an inducible expression system, restored G1 phase arrest and the hypertrophic phenotype. Ang II did not induce apoptosis of either p27Kip1+/+ or -/- tubular cells.

CONCLUSION

Our findings are the first clear evidence that p27Kip1 is required for Ang II-induced hypertrophy of proximal tubular cells. However, although p27Kip1 expression is an absolute requirement for this hypertrophy, reconstitution experiments revealed that other factors induced by Ang II contribute to this hypertrophy.

Stem cell factor and crescentic glomerulonephritis

BACKGROUND

Numerous cells and cytokines have been implicated in the pathogenesis of crescentic glomerulonephritis (CGN). Recently, there has been growing awareness of the role of mast cells and their growth factor, stem cell factor (SCF), in the process of tissue inflammation and fibrosis.

METHODS

In this study, renal biopsy specimens from 28 patients with a histopathologic diagnosis of CGN were evaluated immunohistochemically for the presence of mast cells, SCF, and its receptor (c-kit). In addition, CD34+ hematopoietic cells, monocytes (CD68+ cells), and myofibroblasts (alpha-smooth muscle actin-positive [alpha-SMA+] cells) were counted. Renal biopsy specimens from cadaveric kidney donors and kidneys removed for hypernephroma (n = 6) served as controls. Point counting of positive immunostaining for SCF, alpha-SMA, and collagens III and IV was undertaken. Glomerular and interstitial fibrosis (IF) scores were determined.

RESULTS

Patients who developed progressive chronic kidney failure showed a significant increase in percentage of crescents, number of interstitial c-kit+ cells, and glomerular CD68+ cells compared with those with a favorable outcome. Analysis showed a significant elevation of tryptase+ mast cells in the interstitium of renal biopsy specimens of patients with CGN compared with controls. SCF and c-kit+ cells were found in glomeruli and interstitium, with occasional immunostaining of the crescent with SCF. Both glomerular and interstitial SCF immunostaining was significantly higher in biopsy specimens of patients compared with controls. Glomerular and interstitial SCF showed a significant positive correlation with 24-hour urinary protein level. There were a few CD34+ cells in both glomeruli and interstitium, but their numbers did not differ between patients and controls. Colocalization of CD34+ and c-kit+ was seen in some rounded interstitial and spindle-shaped cells. Number of interstitial mast cells proved to be a strong predictor of IF. Glomerular SCF correlated negatively with creatinine clearance and positively with glomerular CD68+ cells. Interstitial immunostainable SCF correlated positively with interstitial CD68+ cells and interstitial collagen III. On double antigen labeling, SCF was shown in the vicinity of alpha-SMA+ cells.

CONCLUSION

These results show the potential involvement of mast cells and their growth factor SCF/c-kit in CGN.

A novel mechanism of nephron loss in a murine model of crescentic glomerulonephritis

BACKGROUND

Nephron loss is a major determinant of renal failure in glomerular diseases. The prevalent concept stresses the role of the toxicity of filtered proteins and/or of interstitial inflammation in tubular degeneration. However, whether that concept is compatible with the actual histopathological features of nephron loss has not been investigated specifically.

METHODS

We investigated the morphological aspects of tubular degeneration in crescentic glomerulonephritis in mice. Glomerulonephritis was induced by intravenous injection of anti-glomerular basement membrane antiserum in presensitized mice. Kidneys were fixed by perfusion and examined by light- and electron microscopy and by immunohistochemistry.

RESULTS

Tubular degeneration started with cellular hypotrophy in the proximal tubule. Hypotrophy appeared to follow obstruction of the initial proximal tubule by a cellular crescent. Whereas induction of intercellular adhesion molecule-1 (ICAM-1) was diffuse in glomerulonephritic mice, expression of CD44 and vascular cell adhesion molecule-1 (VCAM-1) appeared to be restricted to degenerating tubules. Interstitial inflammation developed in the vicinity of degenerating tubules. Inflammatory infiltration of tubules themselves was observed only in late stages of tubular degeneration.

CONCLUSION

In a similar manner as described earlier for focal segmental glomerulosclerosis, in crescentic glomerulonephritis nephron loss can be initiated by the progression of a glomerular lesion into the proximal tubule. Interstitial inflammation might be rather a consequence than the cause of tubular degeneration.

TGF-beta signaling in renal disease

Since discovery over a decade ago of a role for the cytokine TGF-beta as key mediator of glomerular and tubulointerstitial pathobiology in chronic kidney diseases, studies of TGF-beta signaling in the kidney have focused on the molecular biology of fibrogenesis. In recent years, glomerular and tubular epithelial cell apoptosis and cellular transdifferentiation have been proposed as putative primary pathomechanisms that may underlie progression of renal disease. This review describes evidence in support of nonlinear models and functional roles of TGF-beta signaling in mediating apoptosis and epithelial-to-mesenchymal transdifferentiation (EMT) in chronic progressive renal disease. Emphasis is placed on cell context-dependent models of TGF-beta signaling providing a conceptual framework to consolidate seemingly distinct pathomechanisms of progression of glomerular and tubulointerstitial disease.

An atypical pattern of Epstein-Barr virus infection in a case with idiopathic tubulointerstitial nephritis

Recently, Epstein-Barr virus (EBV) received attention because a latent form of its infection in renal proximal tubular epithelial cells was found to cause idiopathic, chronic tubulointerstitial nephritis. In this report, we describe the case of a patient with a replicative form of EBV infection, chronic active EBV infection (CAEBV), who developed acute tubulointerstitial nephritis and minimal change nephrotic syndrome. A renal biopsy revealed papillary infoldings of atypical tubular epithelium and adjacent dense infiltration of lymphocytes. Using in situ polymerase chain reaction methods, we detected the EBV genome in some of the infiltrating lymphocytes, but not in the tubular epithelial cells. EBV-infected T cells are thought to activate other educated T cells, as well as secrete an unrestricted variety of cytokines, thus playing a pivotal role in CAEBV and its end organ disease. Therefore, in our case, the CAEBV activated, educated T cells may have followed the EBV-infected lymphocytes as they infiltrated into the peritubular interstitium, and promoted focal tubular epithelial atypia and minimal change nephrotic syndrome. The long-term observation of such patients is important because CAEBV may progress into lymphoproliferative diseases.

Acute generalized exanthematous pustulosis, a clue to neutrophil-mediated inflammatory processes orchestrated by T cells

PURPOSE OF REVIEW

Circumstantial evidence exists that certain neutrophilic inflammatory processes are regulated by T cells, but how this occurs is not well understood. The present review presents data on how T cells may directly orchestrate a neutrophilic inflammation by specific release of the neutrophil-attracting chemokine CXCL8 (formerly known as interleukin-8).

RECENT FINDINGS

Acute generalized exanthematous pustulosis (AGEP) is an uncommon cutaneous eruption that is most often provoked by drugs, by acute infections with enteroviruses, or by mercury. It is characterized by acute, extensive formation of nonfollicular sterile pustules on an erythematous background, fever and elevated numbers of blood neutrophils. Involvement of T cells in drug-induced AGEP was suggested by positive patch tests and lymphocyte transformation tests. Moreover, drug-specific CD4+ and CD8+ T cells could be isolated and propagated in vitro from patch test sites and blood from AGEP patients. Their main characteristic is a high level of CXCL8 production.

SUMMARY

T cells are involved even in some neutrophil-rich inflammatory responses, and they may orchestrate the immune reaction directly by high CXCL8 production or indirectly via interleukin-17 production, which induces CXCL8 production in various cell types. AGEP serves as a valuable model for characterizing T cells with a particular function--namely production of CXCL8--leading to neutrophilic inflammation. It is tempting to speculate that elucidation of this pathomechanism will help to improve our understanding of similar neutrophilic eruptions (e.g. pustular psoriasis) and may reveal new targets for pharmacotherapeutic interventions in such diseases.

Effect of combining ACE inhibitor and statin in severe experimental nephropathy

BACKGROUND

Angiotensin-converting enzyme (ACE) inhibitor therapy given soon after disease induction uniformly prevents proteinuria in virtually all models of disease progression. This does not necessarily apply to patients with proteinuric nephropathies, who might be referred late in the course of their disease. Here we used a severe rat model of passive Heymann nephritis (PHN), which may mimic advanced phases of human membranous nephropathy, to study the response to ACE inhibitor alone or in combination with a HMG CoA reductase inhibitor (statin) that independently of the cholesterol-lowering effect influences pathways involved in inflammatory and fibrogenic processes. Therapies started when animals had massive proteinuria and renal lesions.

METHODS

PHN was accelerated by uninephrectomy seven days after IV injection of rabbit anti-FX1A antibody. Four months later, when massive proteinuria and renal lesions were present, the rats were divided into five groups and daily given orally: vehicle; lisinopril 40 mg/L; lisinopril 400 mg/L; simvastatin 2 mg/kg b.i.d; or lisinopril 40 mg/L plus simvastatin. Six normal rats served as controls. Animals were sacrificed at 10 months.

RESULTS

By the end of the study three PHN rats died in the vehicle group, four in the group given lisinopril at 40 mg/L and two in the group at 400 mg/L, whereas all rats on simvastatin or combined therapy were alive. Blood pressure increased during time in PHN and was normalized by treatment with ACE inhibitor and combined therapy. Even at the high dose lisinopril failed to reduce proteinuria. Simvastatin only partially affected proteinuria. However, combining lisinopril with simvastatin had a remarkable antiproteinuric effect, such that at 10 months the urinary proteins were comparable to pre-treatment values and significantly lower than either the vehicle or lisinopril groups. Hypercholesterolemia of PHN rats was limited by combined therapy, and a positive correlation was found between serum cholesterol and proteinuria. Renal function was only partially ameliorated by simvastatin but significantly improved by combined therapy. Drug combination significantly limited glomerulosclerosis, tubular damage and interstitial inflammation, compared to vehicle or drugs alone. Up-regulation of monocyte chemoattractant protein-1 (MCP-1) mRNA in PHN kidneys was not affected by lisinopril, it was inhibited by 30% after simvastatin, and almost completely normalized by lisinopril plus simvastatin.

CONCLUSIONS

These data suggest that a combined ACE inhibitor and statin approach could represent a therapeutic option for patients with advanced renal disease in whom ACE inhibitors alone fail to lower proteinuria and injury to any substantial extent.