Bubble cells: renal tubular cells in the urinary sediment with characteristics of viability

Urinary Vacuolar Casts Are a Unique Type of Casts in Advanced Proteinuric Glomerulopathies

Key Points

Vacuolar casts are a distinct type of casts identifiable by urinary sediment microscopy. Identification of urinary vacuolar casts is associated with the presence of an advanced and severe form of a proteinuric glomerular disease.

Background

Identification of casts by urinary sediment microscopy is a valuable diagnostic clinical tool for the evaluation of kidney disease. Vacuolar casts are an unrecognized unique type of casts characterized by the presence of nonpolarizable, clear vesicles of various sizes contained within a cast matrix, different from lipid casts, erythrocyte casts, or any other casts. We aimed to gain better understanding of the clinical relevance of these casts by establishing a multinational collaborative group to search for cases in which vacuolar casts were identified.

Methods

Leveraging an educational social media platform, we conducted a multinational observational study extracting cases of patients who presented with urinary vacuolar casts during evaluation for impaired kidney function. Parameters assessed included degree of proteinuria and kidney dysfunction, clinical and histopathological diagnosis, and severity of renal parenchymal scarring on biopsy. A control group of patients without vacuolar casts was included for comparison.

Results

Forty-six patients with urinary vacuolar casts were compiled from six countries. Nephrotic range proteinuria (82%), glomerular etiology (98%), and advanced CKD stage (62% 3B-5) were salient features. Histopathological diagnosis was available in 26 (57%) patients. Combining clinical and pathological diagnoses, diabetic nephropathy (48%), arterionephrosclerosis (30%), podocytopathies (15%), and proliferative glomerulonephritides (15%) accounted for most patients. Vacuolization of tubules or podocytes was present in 61% of the specimens. When compared with patients with histopathological diagnoses in which vacuolar casts were not found (n =186), patients with vacuolar casts more frequently had a glomerular etiology (100% versus 71%, P = 0.002), had greater proteinuria (median urine protein-to-creatinine 10.3 versus 2.2 g/g, P < 0.001), and had greater proportion of patients with ≥30% glomerular obsolescence (46% versus 20%, P = 0.003).

Conclusions

Thus, urinary vacuolar casts are strongly associated with advanced glomerulopathies with severe proteinuria. Future studies should examine their origin, composition, and prognostic value.

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Acute tubular necrosis and pre-renal acute kidney injury: utility of urine microscopy in their evaluation- a systematic review

BACKGROUND

Urine microscopy with examination of the urine sediment examination provides useful diagnostic information about the histology of the kidneys. While most nephrologists use urine microscopy to assess for the presence of glomerular diseases, they are less apt to use this diagnostic test when pre-renal acute kidney injury (AKI) or acute tubular necrosis (ATN) is clinically suspected. More often, tests such as fractional excretion of sodium (FeNa) and fractional excretion of urea (FeUrea) are used to differentiate these two causes of acute kidney injury.

DESIGN AND METHODS

A systematic search of Medline and the Cochrane Database, with no language restrictions, for studies in humans on urine microscopy with sediment examination for the differential diagnosis or risk stratification of acute kidney injury published between January 1960 and February 2009 was undertaken.

RESULTS

Based on the limited available data on urine microscopy reviewed in this paper, this test has merit in hospitalized patients with acute kidney injury to differentiate between pre-renal acute kidney injury and acute tubular necrosis. The presence and number of renal tubular epithelial cells and renal tubular epithelial cell casts and/or granular casts in the urine sediment appear beneficial in the diagnosis of ATN and may be useful in predicting more severe kidney damage that is reflected by non-recovery of AKI and need for dialysis.

CONCLUSIONS

Urine microscopy and urine sediment examination is widely available, easy to perform, and inexpensive. The clinical utility of urine microscopy in the differential diagnosis and prediction of outcome in AKI may be increased by using a simple urinary scoring system based on the number of renal tubular epithelial cells and renal tubular epithelial cell/granular casts.

The extent of vacuolation in non-heart-beating porcine donor liver grafts prior to transplantation predicts their viability

Livers exposed to prolonged warm ischemia (WI), such as those from non-heart-beating donors (NHBDs), are at higher risk of primary graft nonfunction (PNF). In a pig model of liver transplantation (LTx) from NHBDs, hepatocellular vacuolation, focal hepatocyte dropout, congestion, and sinusoidal dilatation appeared on biopsies taken after exposure to WI. In functioning grafts, vacuolation and sinusoidal dilatation were reversible after LTx, in contrast to PNF grafts. We studied whether the extent of these morphological signs and particularly vacuolation, present on pre-LTx biopsies, was associated with WI length and able to predict PNF, hepatocellular damage, and survival. Pre-LTx biopsies from pig livers exposed to incremental periods of WI were reviewed retrospectively. The extent of vacuolation was quantified blindly by a pathologist's semiquantitative score, validated by stereological point counting and digital image analysis, and then used to predict PNF and hepatocellular damage. On biopsies taken after WI, stereological point counting and digital analysis scoring contributed significantly in predicting PNF (P = 0.027 and P = 0.043, respectively) versus the pathologist's semiquantitative score (P = 0.058). Stereological point counting and digital image analysis predicted the extent of hepatocellular damage (P < 0.0001 and P = 0.001) versus the pathologist's semiquantitative score (P = 0.085). In conclusion, the extent of parenchymal vacuolation present on WI liver grafts reflects the severity of hepatocellular damage and predicts pig liver graft viability before LTx. Further studies are now warranted to evaluate whether these anoxic changes that are associated with liver graft viability in pigs also apply to human NHBD liver biopsies.

Early diagnosis of acute kidney injury in critically ill patients

Acute kidney injury (AKI) is a common and serious problem in critically ill patients. Tests currently used to detect AKI (i.e., serum creatinine, serum urea and various urinary indices) often result in delayed detection of injury--becoming abnormal at 48-72 h after the initial insult. This delayed detection translates into a potential missed opportunity for therapeutic interventions at a time when kidney damage may be limitable or reversible. This may also, in particular, account for the poor clinical outcomes commonly associated with AKI. The development of novel serum and urinary biomarkers capable of detecting AKI at an earlier phase of illness is therefore vital. This article will review the pitfalls of current conventional testing in kidney injury and discuss the emergence of novel biomarkers with the potential to revolutionize the field of critical care nephrology.

Conventional markers of kidney function

Acute kidney injury remains a serious clinical problem for intensive care unit patients, and its incidence is rising. The detection and diagnosis of acute kidney injury in the intensive care unit currently require use of conventional markers of kidney function, specifically, serum creatinine and urea levels and, less frequently, other urinary tests. These conventional markers are familiar to clinicians and have long been used at the bedside. However, these markers are clearly not ideal, each has limitations, and none reflect real-time changes in glomerular filtration rate or a genuine acute injurious process to the kidney. More importantly, these conventional markers can contribute to delays in recognition of acute kidney injury and, hence, delays to appropriate supportive and therapeutic interventions. The early detection and diagnosis of acute kidney injury should be a clinical priority. A diagnostic test or panel of tests that are capable of evaluating aspects both of kidney function and acute injury are desperately needed in critical care nephrology. Cystatin C has been shown superior to conventional markers and may assume a greater role in intensive care unit patients for detecting both early changes in glomerular filtration rate and evidence of acute injury. Other newly characterized markers of kidney function or acute injury have the potential to revolutionized the field of critical care nephrology and greatly improve the supportive and therapeutic management of intensive care unit patients with acute kidney injury.

Urinary mononuclear cell and disease activity of systemic lupus erythematosus

Mononuclear cells play a cardinal role in the pathogenesis of systemic lupus erythematosus (SLE). A high urine cytology score has been reported to be associated with lupus nephritis in relapse. The objective of this study was to examine the urinary mononuclear cell population of patients with lupus nephritis, and explore its correlation with lupus disease activity. We studied 12 patients with active lupus nephritis, 17 patients with lupus nephritis in remission, 12 SLE patients with no history of renal disease and 13 healthy subjects. Clinical disease activity was quantified by the SLE Disease Activity Index (SLEDAI). Mononuclear cell species in the urinary sediment were examined by immunocytochemistry. Patients with active lupus nephritis had significantly more mononuclear cells in the urinary sediment. The number of CD3+ cell was significantly elevated in the active lupus nephritis than the others (P < 0.001), while there was no significant difference in the number of CD20+ and CD56+ cell among patient groups. The total urinary mononuclear cell correlated significantly with the overall SLEDAI score (r = 0.58, P < 0.001) as well as the renal score (r = 0.57, P < 0.001). The number of urinary CD3+, but not CD20+ or CD56+, cell significantly correlated with the overall SLEDAI score (r = 0.46, P = 0.003) as well as the renal score (r = 0.40, p = 0.011). In nine patients with renal biopsy, the histological activity index correlated with the total urinary mononuclear cell (r = 0.75, P = 0.02), CD3+ (r = 0.69, P = 0.04) and CD20+ cell (r = 0.69, P = 0.04). We conclude that urinary mononuclear cell was markedly elevated in patients with active lupus, and the urinary mononuclear cell count correlated significantly with the SLEDAI score and histological activity. CD3+ and CD20+ cells are the major component of urinary mononuclear cell in SLE patients and their number correlates with lupus disease activity.

Urinary Biochemistry and Microscopy in Septic Acute Renal Failure: A Systematic Review

BACKGROUND

Biochemistry and microscopy of urine are widely published diagnostic activities in patients with acute renal failure (ARF). However, their scientific basis in patients with septic ARF has not been assessed systematically.

METHODS

We performed a systematic review of MEDLINE, EMBASE, CINHAL, and PubMed databases and bibliographies of retrieved articles for all studies describing urinary biochemistry, indices, and microscopy in patients with septic ARF.

RESULTS

We identified 27 articles (1,432 patients). Because of substantial heterogeneity, no formal quantitative analysis could be performed. Urinary biochemistry or derived indices were reported in 24 articles (89%), and microscopy, in 7 articles (26%). The majority were small single-center reports and had serious limitations. For example, only 52% of patients were septic, only 54% of patients had ARF, many studies failed to include a control group, time from diagnosis of sepsis or ARF to measure of urinary tests was variable, and there were numerous potential confounders. Urinary sodium, fractional excretion of sodium, urinary-plasma creatinine ratio, urinary osmolality, urinary-plasma osmolality ratio, and serum urea-creatinine ratio showed variable and inconsistent results. Low-molecular-weight proteinuria was described in only 22% of articles. A few reports of urinary microscopy described muddy brown/epithelial cell casts and renal tubular cells in patients with septic ARF, whereas others described normal urinary sediment.

CONCLUSION

The scientific basis for the use of urinary biochemistry, indices, and microscopy in patients with septic ARF is weak. More research is required to describe their accuracy, pattern, and time course in patients with septic ARF.

Biomarkers of acute renal injury and renal failure

Acute renal failure (ARF) is a frequent problem in the intensive care unit and is associated with a high mortality. Early recognition could help clinical management, but current indices lack sufficient predictive value for ARF. Therefore, there might be a need for biomarkers in detecting renal tubular injury and/or dysfunction at an early stage before a decline in glomerular filtration rate is noted by an increased serum creatinine. A MEDLINE/PubMed search was performed, including all articles about biomarkers for ARF. All publication types, human and animal studies, or subsets were searched in English language. An extraction of relevant articles was made for the purpose of this narrative review. These biomarkers include tubular enzymes (alpha- and pi-glutathione S-transferase, N-acetyl-glucosaminidase, alkaline phosphatase, gamma-glutamyl transpeptidase, Ala-(Leu-Gly)-aminopeptidase, and fructose-1,6-biphosphatase), low-molecular weight urinary proteins (alpha1- and beta2-microglobulin, retinol-binding protein, adenosine deaminase-binding protein, and cystatin C), Na+/H+ exchanger, neutrophil gelatinase-associated lipocalin, cysteine-rich protein 61, kidney injury molecule 1, urinary interleukins/adhesion molecules, and markers of glomerular filtration such as proatrial natriuretic peptide (1-98) and cystatin C. These biomarkers, detected in urine or serum shortly after tubular injury, have been suggested to contribute to prediction of ARF and need for renal replacement therapy. However, excretion of these biomarkers may also increase after reversible and mild dysfunction and may not necessarily be associated with persistent or irreversible damage. Large prospective studies in human are needed to demonstrate an improved outcome of biomarker-driven management of the patient at risk for ARF.

Acute renal insufficiency after high-dose melphalan in patients with primary systemic amyloidosis during stem cell transplantation

BACKGROUND

Patients with primary systemic amyloidosis (AL) have a poor prognosis. Median survival time from standard treatments is only 17 months. High-dose intravenous melphalan followed by peripheral blood stem cell transplant (PBSCT) appears to be the most promising therapy, but treatment mortality can be high. The authors have noted the development of acute renal insufficiency immediately after melphalan conditioning. This study was undertaken to further examine its risk factors and impact on posttransplant mortality.

METHODS

Consecutive AL patients who underwent PBSCT were studied retrospectively. Acute renal insufficiency (ARI) after high-dose melphalan was defined by a minimum increase of 0.5 mg/dL (44 micromol/L) in the serum creatinine level that is greater than 50% of baseline immediately after conditioning. Urine sediment score was the sum of the individual types of sediment identified on urine microscopy.

RESULTS

Of the 80 patients studied, ARI developed in 18.8% of the patients after high-dose melphalan. Univariate analysis identified age, hypoalbuminemia, heavy proteinuria, diuretic use, and urine sediment score (>3) as risk factors. Age and urine sediment score remained independently significant risk factors in the multivariate analysis. Patients who had ARI after high-dose melphalan underwent dialysis more often (P = 0.007), and had a worse 1-year survival (P = 0.03).

CONCLUSION

The timing of renal injury strongly suggests melphalan as the causative agent. Ongoing tubular injury may be a prerequisite for renal injury by melphalan as evidenced by the active urinary sediment. Development of ARI adversely affected the outcome after PBSCT. Effective preventive measures may help decrease the treatment mortality of PBSCT in AL patients.

Site-specific alteration of actin assembly visualized in living renal epithelial cells during ATP depletion

Disruption of normal actin organization in renal tubular epithelial cells is an important element of renal injury induced by ischemia. Studies of fixed cells indicate that the cytoskeleton is disrupted by both ischemia and ATP depletion in a site-specific manner. However, few studies have examined these effects in living cells, and the relationship between the time course of ATP reduction and alteration of the cytoskeleton remains unclear. Here, time-lapse video images of cultured renal epithelial cells expressing an enhanced green fluorescent protein (EGFP)-actin fusion protein were obtained, and the kinetics of fluorescence actin distribution before and during ATP depletion is quantified and compared with measured ATP levels. This study found that assembly of lamellar actin is inhibited rapidly as cellular ATP levels are reduced, whereas disruption of actin in stress fibers is more gradual and persistent. Actin associated with focal adhesions is largely resistant to ATP depletion in these experiments, and, consistent with previous studies, particulate aggregates of actin were formed within the cytoplasm of ATP-depleted cells. Most surprisingly, time-lapse imaging of EGFP-actin distribution, quantitative fluorescence imaging of phalloidin-stained cells, and ultrastructural studies indicate that assembly of actin filaments occurs at sites of epithelial cell-cell attachment in ATP-depleted cells. This assembly is initiated early during ATP depletion and continues after ATP levels are maximally reduced. Assembly of actin at sites of cell-cell attachment may be an element of the pathology of injury induced by ischemia, or alternatively, could reflect the function of a protective mechanism. These studies directly demonstrate site-specific alteration of actin assembly in living epithelial cells during ATP depletion. The results also reveal that actin reorganization continues after ATP levels are maximally decreased and that epithelial cell-cell attachments are sites of actin assembly in ATP-depleted cells.

HGF promotes adhesion of ATP-depleted renal tubular epithelial cells in a MAPK-dependent manner

Hepatocyte growth factor (HGF) has been shown to enhance recovery from renal tubular ischemia. We investigated the possibility that HGF improves recovery by preventing ischemia-induced loss of cell adhesion. Murine inner medullary collecting duct-3 (mIMCD-3) cells subjected to 90% ATP depletion demonstrated a 55% decrease in adhesion, an effect that was completely reversed by the addition of HGF. Assays examining release of adherent cells revealed similar results with 30 min of ATP depletion causing loss of adhesion of 25% of mIMCD-3 cells and HGF completely reversing this effect. In contrast, HGF was unable to reverse the loss of adhesion of cells exposed to 99% ATP depletion. Examination of the mitogen-activated protein kinase (MAPK) signaling pathway revealed that HGF could induce extracellular signal-regulated kinase (ERK) phosphorylation in control and 90% ATP-depleted cells but not in 99% ATP-depleted cells. Inhibition of ERK activation with U0126 completely blocked the HGF-dependent reversal of ATP-depleted cell adhesion. Thus ATP-depleted cells demonstrate a marked decrease in cell adhesion that is reversible by the addition of HGF. This effect of HGF requires activation of the MAPK pathway.

Mouse proximal tubular cell-cell adhesion inhibits apoptosis by a cadherin-dependent mechanism

Adhesion of epithelial cells to matrix is known to inhibit apoptosis. However, the role of cell-cell adhesion in mediating cell survival remains uncertain. Primary cultures of mouse proximal tubular (MPT) cells were used to examine the role of cell-cell adhesion in promoting survival. When MPT cells were deprived of both cell-matrix and cell-cell adhesion, they died by apoptosis. However, when incubated in agarose-coated culture dishes (to prevent cell-matrix adhesion) and at high cell density (to allow cell-cell interactions), MPT cells adhered to one another and remained viable. Expression of E-cadherin among suspended, aggregating cells increased with time. A His-Ala-Val (HAV)-containing peptide that inhibits homophilic E-cadherin binding prevented cell-cell aggregation and promoted apoptosis of MPT cells in suspension. By contrast, inhibition of potential beta(1)-integrin-mediated interactions between cells in suspension did not prevent either aggregation or survival of suspended cells. Aggregation of cells in suspension activated phosphatidylinositol 3-kinase (PI3K), an event that was markedly reduced by the presence of the HAV peptide. LY-294002, an inhibitor of PI3K, also inhibited survival of suspended cells. In summary, we provide novel evidence that MPT cells, when deprived of normal cell-matrix interactions, can adhere to one another in a cadherin-dependent fashion and remain viable. Survival of aggregated cells depends on activation of PI3K.

Effect of nitric oxide donors on renal tubular epithelial cell-matrix adhesion

BACKGROUND

Nitric oxide (NO) and its metabolite, peroxynitrite (ONOO-), are involved in renal tubular cell injury. We postulated that if NO/ONOO- has an effect to reduce cell adhesion to the basement membrane, this may contribute to tubular obstruction and may be partially responsible for the harmful effect of NO on the tubular epithelium during acute renal failure (ARF).

METHODS

We examined the effect of the NO donors (z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1- ium-1, 2-diolate (DETA/NO), spermine NONOate (SpNO), and the ONOO- donor 3-morpholinosydnonimine (SIN-1) on cell-matrix adhesion to collagen types I and IV and fibronectin using three renal tubular epithelial cell lines: LLC-PK1, BSC-1, and OK.

RESULTS

In LLC-PK1 cells, DETA/NO (500 microM) had no effect, and SpNO (500 microM) had a modest effect on cell adhesion compared with controls. Exposure to SIN-1 caused a dose-dependent impairment in cell-matrix adhesion. Similar results were obtained in the different cell types and matrix proteins. The effect of SIN-1 (500 microM) on LLC-PK1 cell adhesion was not associated with either cell death or alteration of matrix protein and was attenuated by either the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, the superoxide scavenger superoxide dismutase, or the ONOO- scavenger uric acid in a dose-dependent manner.

CONCLUSIONS

These results therefore support the possibility that ONOO- generated in the tubular epithelium during ischemia/reperfusion has the potential to impair the adhesion properties of tubular cells, which then may contribute to the tubular obstruction in ARF.

Polarity, integrin, and extracellular matrix dynamics in the postischemic rat kidney

Acute renal failure (ARF) as a consequence of ischemic injury is a common disease affecting 5% of the hospitalized population. Despite the fact that mortality from ARF is high, there has been little improvement in survival rates over the last 40 years. The pathogenesis of ARF may be related to substantial changes in cell-cell and cell-extracellular matrix interactions mediated by beta1-integrins. On the basis of in vitro and in vivo studies, reorganization of beta1-integrins from basal to apical surfaces of injured tubular epithelia has been suggested to facilitate epithelial detachment, contributing to tubular obstruction and backleak of glomerular filtrate. In this study, we examine integrin and extracellular matrix dynamics during epithelial injury and repair using an in vivo rat model of unilateral ischemia. We find that, soon after reperfusion, beta1-integrins newly appear on lateral borders in epithelial cells of the S3 segment but are not on the apical surface. At later times, as further injury and regeneration coordinately occur, epithelia adherent to the basement membrane localize beta1 predominantly to basal surfaces even while the polarity of other marker proteins is lost. At the same time, amorphous material consisting of depolarized exfoliated cells fills the luminal space. Notably, beta1-integrins are not detected on exfoliated cells. A novel finding is the presence of fibronectin, a glycoprotein of plasma and the renal interstitium, in tubular spaces of the distal nephron and to a lesser extent S3 segments. These results indicate that beta1-integrins dramatically change their distribution during ischemic injury and epithelial repair, possibly contributing to cell exfoliation initially and to epithelial regeneration at later stages. Together with the appearance of large amounts of fibronectin in tubular lumens, these alterations may play a significant role in the pathophysiology of ARF.

Two novel probes reveal tubular and vascular Arg-Gly-Asp (RGD) binding sites in the ischemic rat kidney

We have previously demonstrated that RGD peptides prevent tubular obstruction in ischemic acute renal failure (ARF) suggested that exposed unoccupied integrin receptors represent the target for such therapy. The present study investigated the topography of RGD binding sites and integrin receptors in ischemic rat kidneys. Two RGD peptides were synthesized: a cyclic biotinylated (Bt) RGD peptide and a linear RGD peptide (GRGDSP) labeled with rhodamine green (RhoG). Rats were subjected to 45 minutes of renal artery occlusion kidneys were harvested at different times post-ischemia, and stained with RGD peptides and a panel of antibodies to integrins. In control, Bt-RGD staining was undetectable in alkaline phosphatase histochemistry, whereas immunofluorescence detection with Rho-streptavidin conjugate as well as RhoG-GRGDSP staining faintly decorated the basolateral aspect of the proximal tubular cells in a punctate fashion. In contrast, ischemic kidneys showed binding to the basolateral and apical aspects of proximal tubules, peritubular capillaries, and desquamated cells within tubular lumen. The most conspicuous staining of ischemic kidneys was obtained with antibodies to the beta 1 (labeling of the apical aspect of proximal and distal tubules, as well as desquamated cells obstructing tubular lumen) and the alpha V (glomeruli, tubular epithelia, intima of blood vessels stained faintly, while the obstructing cellular conglomerates showed intense staining) subunits. Double staining with Bt-RGD and antibodies against the beta 1 and alpha V beta 3 integrins showed co-localization of staining within the tubules and vasculature, respectively. In vitro attachment of HL-60 leukocytes to the endothelial cells was inhibited by the cyclic RGD peptide. In conclusion, expression of RGD binding sites and beta 1 integrin subunits along the apical aspect of tubular epithelia and on the surface of desquamated cells is in concert with the hypothesis on the pathogenetic role of RGD-recognizing integrins in tubular obstruction. The expression of RGD binding sites along the intimal surface of blood vessels in ischemic kidneys suggests an additional target for RGD peptides in vascular endothelial cells.

The nature of renal cell injury

The main functional change in patients with acute renal failure (ARF) is a decrease in glomerular filtration rate (GFR). The virtual complete recovery of renal function in those patients who survive ARF, as well as the minimal renal histological abnormalities during ARF when the GFR is less than 10 ml/min, suggest that a major component of the renal tubular cell injury is sublethal or reversible. Experimental models of acute tubular necrosis frequently have placed the emphasis on irreversible proximal tubular cell death. The nature of the renal tubular cell injury in ischemic acute renal failure, however, includes not only cell death (necrosis or apoptosis) but also sublethal injury causing cell dysfunction. The role of intracellular calcium, the calcium-dependent enzymes calpain, phospholipase A2 and nitric oxide synthase (NOS), in the pathophophysiology of this renal tubular cell injury during hypoxia/ischemia is described. The effects of calpain and nitric oxide (NO) on the cytoskeleton and cell adhesion are discussed. Potential mechanisms whereby tubular injury leads to a profound fall in GFR, including increased tubuloglomerular feedback and increased distal tubular obstruction, in ischemic acute renal failure are proposed.

Cyclic RGD peptides ameliorate ischemic acute renal failure in rats

Renal tubular obstruction is an important contributor to the pathophysiology of acute renal failure. Based on the previous findings of the role played by arginine-glycine-aspartic acid (RGD) recognizing integrins in tubular obstruction, this study examined the effect of RGD peptides on the course of ischemic acute renal failure in rats. For in vivo studies, animals were subjected to 45 minutes of unilateral renal ischemia with contralateral nephrectomy, and cyclic RGD peptides or a linear biotinylated RGD peptide were injected systemically after the release of renal artery clamp. In vitro studies compared the potency of the peptides in inhibiting BS-C-1 cell-matrix and cell-cell adhesion. Two novel cyclic RGD peptides utilized in these studies showed different inhibitory potency in preventing cell-matrix adhesion: cyclic RGDDFV was a highly potent in vitro inhibitor of BS-C-1 cell-matrix adhesion, whereas cyclic RGDDFLG was less potent. In cell-cell adhesion assays, however, both peptides were equipotent. Despite the differences in inhibiting cell-matrix adhesion, a single systemic administration of either peptide improved creatinine clearance postoperatively and accelerated recovery of renal function with a rank order: cyclic RGDDFV > or = RGDDFLG >> RDADFV (inactive control). These findings represent the first in vivo demonstration of the effectiveness of cyclic RGD peptides in ameliorating ischemic acute renal failure, and suggest that in this setting RGD peptides predominantly inhibit cell-cell adhesion, whereas inhibition of cell-matrix adhesion is of lesser significance.

Expression of clusterin in human renal diseases

Clusterin, a glycoprotein with potent cohesive properties, is induced in a wide variety of acute and chronic experimental renal diseases. The purpose of this study was to examine clusterin expression in human renal diseases. Clusterin immunostaining was examined in nephrectomy specimens from patients with autosomal-dominant polycystic kidney disease (N = 5), autosomal-recessive polycystic kidney disease (N = 3), multilocular cyst of the kidney (N = 2), renal hypoplasia/dysplasia (N = 7), Wilms' tumor (nephroblastoma) (N = 6), renal cell carcinoma (N = 9), and acute and/or chronic renal transplant rejection (N = 15). No clusterin staining was detected in normal renal tissue distant from renal cell carcinomas. Increased expression of clusterin was found in epithelial cells lining cysts in all of the cystic disorders studied. Clusterin expression was found in some immature tubules in hypoplastic/dysplastic kidneys and in tubules of rejected renal allografts, but was not a prominent finding in renal neoplasms, although some renal cell carcinomas expressed clusterin in a focal manner. Common features of clusterin induction included exclusively epithelial production of clusterin in cysts, immature nephrons, and injured tubules, heterogeneity of clusterin expression, with only some tubules and/or cysts in a given area staining for clusterin, and uniform clusterin staining of epithelial cells in a given tubule or cyst in most cases. Based on its cohesive properties, we speculate clusterin functions to maintain cell-cell and cell-substratum interactions which become perturbed in the setting of renal injury and cystic diseases.

Macroscopic hematuria as a presenting manifestation of oliguric acute tubular necrosis

Macroscopic hematuria associated with acute renal failure usually results from glomerulonephritis or structural abnormalities (stones, tumors, or infections). Acute tubular necrosis is rarely associated with macroscopic hematuria in the absence of other genitourinary abnormalities. We describe a patient who presented with macroscopic hematuria, in whom only acute tubular necrosis could be identified as a causative factor.