Tubular and interstitial nephrocalcinosis.

PURPOSE: We determined whether nephrocalcinosis is common and whether its detection is influenced by renal tissue processing. MATERIALS AND METHODS: Renal cortical and papillary tissue was obtained from the unaffected parts of 15 kidneys removed due to an oncological indication. The effect of tissue processing on the loss of crystals was studied in a kidney with nephrocalcinosis due to chronic pyelonephritis. Immediately frozen and formaldehyde fixed sections were analyzed by polarized light and Raman spectroscopy, and stained for calcium (Yasue) and hyaluronan. RESULTS: Although 13 of 15 snap-frozen sections from tumor kidneys contained birefringent particles (mean +/- SD 3.2 +/- 2.9 particles per cm(2)) in the renal tubules, this was not considered nephrocalcinosis because the crystals were not attached to the epithelial lining. Interstitial nephrocalcinosis was found on Yasue stain in 3 of 15 kidneys with tumor (20%). Calcium deposits were found in the papillary interstitium only, always together with hyaluronan. Formaldehyde fixed sections from the pyelonephritis kidney contained fewer renal tubular cell associated birefringent particles than immediately frozen sections (9.4 +/- 1.9 vs 41.6 +/- 1.2 per cm(2)). Particles were composed of calcium oxalate monohydrate (Yasue and Raman). CONCLUSIONS: There are 2 distinct forms of nephrocalcinosis, including tubular nephrocalcinosis, which seems to be reserved for specific conditions such as chronic pyelonephritis, and interstitial nephrocalcinosis. The incidence of tubular calcium oxalate nephrocalcinosis could be underestimated due to the loss of crystals during tissue processing for routine histology. The crystal binding molecule hyaluronan may have a role in the 2 forms of nephrocalcinosis.

Crystals cause acute necrotic cell death in renal proximal tubule cells, but not in collecting tubule cells.

BACKGROUND: The interaction between renal tubular cells and crystals generated in the tubular fluid could play an initiating role in the pathophysiology of calcium oxalate nephrolithiasis. Crystals are expected to form in the renal collecting ducts, but not in the proximal tubule. In the present investigation, we studied the damaging effect of calcium oxalate crystals on renal proximal and collecting tubule cells in culture. METHODS: Studies were performed with the renal proximal tubular cell lines, porcine proximal tubular cells (LLC-PK(1)) and Madin-Darby canine kidney II (MDCK-II) and the renal collecting duct cell lines, RCCD(1) and MDCK-I. Confluent monolayers cultured on permeable growth substrates in a two-compartment culture system were apically exposed to calcium oxalate monohydrate crystals, after which several cellular responses were studied, including monolayer morphology (confocal microscopy), transepithelial electrical resistances (TER), prostaglandin E(2) (PGE(2)) secretion, DNA synthesis ([(3)H]-thymidine), total cell numbers, reactive oxygen species [hydrogen peroxide (H(2)O(2))] generation, apoptotic (annexin V and DNA fragmentation), and necrotic (propidium iodide influx) cell death. RESULTS: Crystals were rapidly taken up by proximal tubular cells and induced a biphasic response. Within 24 hours approximately half of the cell-associated crystals were released back into the apical fluid (early response). Over the next 2 weeks half of the remaining internalized crystals were eliminated (late response). The early response was characterized by morphologic disorder, increased synthesis of PGE(2), H(2)O(2), and DNA and the release of crystal-containing cells from the monolayers. These released cells appeared to be necrotic, but not apoptotic cells. Scrape-injured monolayers generated even higher levels of H(2)O(2) than those generated in response to crystals. During the late response, crystals were gradually removed from the monolayers without inflammation-mediated cell death. Crystals did not bind to, were not taken up by, and did not cause marked responses in collecting tubule cells. CONCLUSION: This study shows that calcium oxalate crystals cause acute inflammation-mediated necrotic cell death in renal proximal tubular cells, but not in collecting tubule cells. The crystal-induced generation of reactive oxygen species by renal tubular cells is a general response to tissue damage and the increased levels of DNA synthesis seem to reflect regeneration rather than growth stimulation. As long as the renal collecting ducts are not obstructed with crystals, these results do not support an important role for crystal-induced tissue injury in the pathophysiology of calcium oxalate nephrolithiasis.

Preconditioning of the distal tubular epithelium of the human kidney precedes nephrocalcinosis.

BACKGROUND: Preterm neonates and renal transplant patients frequently develop nephrocalcinosis. Experimental studies revealed that crystal retention in the distal nephron, a process that may lead to nephrocalcinosis, is limited to proliferating/regenerating tubular cells expressing hyaluronan and osteopontin at their luminal surface. Fetal and transplant kidneys contain proliferating and/or regenerating cells since nephrogenesis is not completed until 36 weeks of gestation, while ischemia and nephrotoxic immunosuppressants may lead to injury and repair in renal transplants. This prompted us to investigate the expression of hyaluronan and osteopontin and to correlate this to the appearance of tubular calcifications both in fetal/preterm and transplanted kidneys. METHODS: Sections of fetal/preterm kidneys and protocol biopsies of transplanted kidneys (12 and 24 weeks posttransplantation from the same patients) were stained for osteopontin, hyaluronan, and calcifications (von Kossa). RESULTS: Hyaluronan and osteopontin were expressed at the luminal surface of the epithelial cells lining the distal tubules of all fetal kidneys at birth and in all kidney graft protocol biopsies 12 and 24 weeks posttransplantation. In 7 out of 18 surviving (at least 4 days) preterm neonates crystal retention developed. In renal allografts a striking increase (from 2/10 to 6/10) in tubular crystal retention between 12 and 24 weeks posttransplantation was observed. In addition, crystals were selectively retained in distal renal tubules containing cells with hyaluronan and osteopontin at their luminal surface. CONCLUSION: The results of this study show that luminal expression of hyaluronan and osteopontin preceded renal distal tubular retention of crystals in preterm neonates and renal transplant patients. We propose that the presence of this crystal binding phenotype may play a general role in renal calcification processes.

Oxalate is toxic to renal tubular cells only at supraphysiologic concentrations.

BACKGROUND: Oxalate-induced tissue damage may play an initiating role in the pathophysiology of calcium oxalate nephrolithiasis. The concentration of oxalate is higher in the renal collecting ducts ( approximately 0.1 to 0.5 mmol/L) than in the proximal tubule ( approximately 0.002 to 0.1 mmol/L). In the present investigation, we studied the damaging effect of oxalate to renal proximal and collecting tubule cells in culture. METHODS: Studies were performed with the renal proximal tubular cell lines, LLC-PK1 and Madin Darby canine kidney II (MDCK-II), and the renal collecting duct cell lines, rat renal cortical collecting duct (RCCD1) and MDCK-I. Confluent monolayers cultured on permeable growth substrates in a two-compartment culture system were apically exposed for 24 hours to relatively low (0.2, 0.5, and 1.0 mmol/L) and high (5 and 10 mmol/L) oxalate concentrations, after which several cellular responses were studied, including monolayer morphology (confocal microscopy), transepithelial electrical resistances (TER), prostaglandin E(2) (PGE(2)) secretion, lactate dehydrogenase (LDH) release, DNA synthesis ([(3)H]-thymidine incorporation), total cell numbers, reactive oxygen species (H(2)O(2)) generation, apoptotic (annexin V and DNA fragmentation), and necrotic (propidium iodide influx) cell death. RESULTS: Visible morphologic alterations were observed only at high oxalate concentrations. TER was concentration-dependently decreased by high, but not by low, oxalate. Elevated levels of PGE(2), LDH, and H(2)O(2) were measured in both cell types after exposure to high, but not to low oxalate. Exposure to high oxalate resulted in elevated levels of DNA synthesis with decreasing total cell numbers. High, but not low, oxalate induced necrotic cell death without signs of programmed cell death. CONCLUSION: This study shows that oxalate is toxic to renal tubular cells, but only at supraphysiologic concentrations.

Hyaluronan is apically secreted and expressed by proliferating or regenerating renal tubular cells.

BACKGROUND: Hyaluronan has diverse biologic functions in the body, varying from structural tasks to cell stress-induced CD44-mediated activation of intracellular signaling pathways. Hyaluronan biology is relatively unexplored in the kidney. Previously, we identified hyaluronan as binding molecule for crystals in the renal tubules. Crystal retention is a crucial early event in the etiology of kidney stones. The present study was performed to determine the polarized distribution of hyaluronan and CD44 by renal tubular cells. METHODS: Madin-Darby canine kidney (MDCK) strain I and primary cultures of human renal tubular cells were grown on permeable supports in a two-compartment culture system. Studies were performed during growth and after scrape-injury. Metabolic labeling studies and an enzyme-linked hyaluronan -binding assay were used to measure the molecular mass and the amount of secreted hyaluronan in apical and basal medium. Confocal microscopy was applied to detect membrane hyaluronan and CD44. Hyaluronan synthase (HAS) mRNA expression was studied with reverse transcriptase-polymerase chain reaction (RT-PCR). The in vitro expression profile of hyaluronan was compared with that in biopsies of transplanted human kidneys with acute tubular necrosis. RESULTS: Proliferating cells produced more hyaluronan (M(r) > 10(6) Da) than growth-inhibited cells in intact monolayers and up to 85% was targeted to the apical compartment, which was accompanied by increased HAS2 mRNA expression and slightly decreased HAS3 mRNA, while HAS1 mRNA remained undetectable. Hyaluronan and CD44 were exclusively expressed at the apical surface of proliferating/regenerating cells. After (re)establishment of tight junctions, hyaluronan was no longer detectable while CD44 was targeted to basolateral membrane domains. In vivo in inflamed human kidneys hyaluronan was abundantly expressed in the cortical tubulointerstitial space as well as at the luminal surface of regenerating renal tubular cells. CONCLUSION: These results demonstrate that the production of hyaluronan by renal tubular cells is activated during proliferation and in response to mechanical injury and that hyaluronan and CD44 expression is highly polarized. The targeted delivery of hyaluronan to the apical compartment suggests that hyaluronan produced by renal tubular cells supports proliferation/regeneration in the renal tubules, but that it does not contribute to hyaluronan accumulation in the renal interstitium. These data further support the concept that mitogen/stress-induced hyaluronan deposition in the renal tubules increases the risk for crystal retention and stone formation.

Percutaneous nephrolithotomy for treating renal calculi in children.

OBJECTIVE: To report our experience with the percutaneous management of renal stone disease in children. PATIENTS AND METHODS: The medical and radiological records of children up to 18 years old who were treated for renal calculi by percutaneous nephrolithotomy (PCNL) at our institution between March 1995 and April 2003 were reviewed. For stone removal a special paediatric 18 F access sheath was used. RESULTS: In all, 26 PCNLs were used in 23 patients (10 boys and 13 girls, aged 1.7-16.8 years). The presenting symptoms were urinary tract infection, abdominal pain and/or haematuria. Of the 23 patients, 17 (75%) had associated metabolic disease or underlying urological anatomical abnormalities. Urinary tract infections were found in 15 patients (65%). The mean (range) stone burden was 6.0 (0.5-18.2) cm2, and the operative duration 127 (50-260) min. The primary stone-free rate was 58%, which increased to 81% after treating residual fragments. One blood transfusion was required and one patient developed urosepsis after PCNL, which was treated with antibiotics. CONCLUSION: PCNL is an effective alternative for treating renal stones in children, and is the treatment of choice for stones refractory to extracorporeal shock wave lithotripsy.

Calcium oxalate crystal adherence to hyaluronan-, osteopontin-, and CD44-expressing injured/regenerating tubular epithelial cells in rat kidneys.

Retention of crystals in the kidney is an essential early step in renal stone formation. Studies with renal tubular cells in culture indicate that hyaluronan (HA) and osteopontin (OPN) and their mutual cell surface receptor CD44 play an important role in calcium oxalate (CaOx) crystal binding during wound healing. This concept was investigated in vivo by treating rats for 1, 4, and 8 d with ethylene glycol (0.5 and 0.75%) in their drinking water to induce renal tubular cell damage and CaOx crystalluria. Tubular injury was morphologically scored on periodic acid-Schiff-stained renal tissue sections and tissue repair assessed by immunohistochemical staining for proliferating cell nuclear antigen. CaOx crystals were visualized in periodic acid-Schiff-stained sections by polarized light microscopy, and renal calcium deposits were quantified with von Kossa staining. HA was visualized with HA-binding protein and OPN and CD44 immunohistochemically with specific antibodies and quantified with an image analyzer system. Already after 1 d of treatment, both concentrations of ethylene glycol induced hyperoxaluria and CaOx crystalluria. At this point, there was neither tubular injury nor crystal retention in the kidney, and expression of HA, OPN, and CD44 was comparable to untreated controls. After 4 and 8 d of ethylene glycol, however, intratubular crystals were found adhered to injured/regenerating (proliferating cell nuclear antigen positive) tubular epithelial cells, expressing HA, OPN, and CD44 at their luminal membrane. In conclusion, the expression of HA, OPN, and CD44 by injured/regenerating tubular cells seems to play a role in retention of crystals in the rat kidney.

Pericellular matrix formation by renal tubule epithelial cells in relation to crystal binding.

BACKGROUND/AIM: Retention of crystals in the kidney ultimately leads to renal stone formation. Hyaluronan (HA) has been identified as binding molecule for calcium oxalate monohydrate crystals. The association of high molecular mass (M(r)) HA with cell surface receptors such as CD44 gives rise to pericellular matrix (PCM) formation by many eukaryotic cells in culture. Here, we study the ability of several renal tubular cell lines to assemble PCMs and to synthesize high-M(r) HA during proliferation in relation to crystal retention. METHODS: PCM assembly by MDCK-I, MDCK-II, and LLC-PK1 cells was visualized by particle exclusion assay. Metabolic labeling studies were performed to estimate the cellular production of HA. The expression of CD44 and HA was studied using fluorescent probes, and crystal binding was quantified with radiolabeled calcium oxalate monohydrate. RESULTS: PCMs were formed, and HA was expressed by most MDCK-I and some MDCK-II, but not by LLC-PK1 cells. All cell types expressed CD44 at their apical surface. MDCK-I and MDCK-II cells secreted, respectively, 14.7 +/- 1.6 and 0.5 +/- 0.2 pmol [3H]glucosamine incorporated in high-M(r) HA, whereas LLC-PK1 cells did not secrete HA. Streptomyces hyaluronidase treatment significantly decreased crystal binding (microg/cm2) to MDCK-I cells (from 8.6 +/- 0.4 to 3.9 +/- 0.9), but hardly to MDCK-II cells (from 10.2 +/- 0.2 to 9.6 +/- 0.1) or LLC-PK1 cells (from 10.2 +/- 0.8 to 9.9 +/- 0.3). CONCLUSIONS: There are various forms of crystal binding to renal tubular cells in culture. Crystal attachment to MDCK-I and some MDCK-II cells involves PCM assembly that requires high-M(r) HA synthesis. HA production and PCM formation do not play a role in crystal binding to LLC-PK1 and the majority of MDCK-II cells. It remains to be determined which form of binding is involved in renal stone disease.

Internalization of calcium oxalate crystals by renal tubular cells: a nephron segment-specific process?

BACKGROUND: Crystal retention in the kidney is caused by the interaction between crystals and the cells lining the renal tubules. These interactions involve crystal attachment, followed by internalization or not. Here, we studied the ability of various renal tubular cell lines to internalize calcium oxalate monohydrate (COM) crystals. METHODS: Crystal-cell interactions are studied by light-, electron-, and confocal microscopy with cells resembling the renal proximal tubule [porcine kidney (LLC-PK1)], proximal/distal tubule [Madin-Darby canine kidney II (MDCK-II)], and distal tubule and/or collecting ducts [(Madin-Darby canine kidney I (MDCK-I), rat cortical collecting duct 1 (RCCD1)]. Crystal-binding strength and internalization are characterized and quantified with radiolabeled COM. RESULTS: Microscopy studies showed that crystals were firmly embedded in the membranes of LLC-PK1 and MDCK-II cells to be subsequently internalized. On the other hand, crystals bound only loosely to MDCK-I and RCCD1 and were not taken up by these cells. Crystal uptake by LLC-PK1 and MDCK-II, expressed in microg/10(6) cells, is temperature-dependent and gradually increases from 0.88 and 0.15 in 30 minutes, respectively, to 4.70 and 3.85, respectively, after five hours, whereas these values never exceeded background levels in MDCK-I and RCCD1 cells. CONCLUSION: The adherence of COM crystals to renal cells with properties of the proximal tubule is inevitable and actively followed by their uptake, whereas crystals attached to cells resembling the distal tubule and/or collecting duct are not internalized. Since crystal formation usually occurs in segments beyond the renal proximal tubule, crystal uptake may be of less importance in the etiology of idiopathic calcium oxalate stone disease.

Crystal retention capacity of cells in the human nephron: involvement of CD44 and its ligands hyaluronic acid and osteopontin in the transition of a crystal binding- into a nonadherent epithelium.

Nephrolithiasis requires formation of crystals followed by their retention and accumulation in the kidney. Crystal retention can be caused by the association of crystals with the epithelial cells lining the renal tubules. The present study investigated the interaction between calcium oxalate monohydrate (COM) crystals and primary cultures of human proximal (PTC) and distal tubular/collecting duct cells (DTC). Both PTC and DTC were susceptible to crystal binding during the first days post-seeding (4.9 +/- 0.8 micro g COM/cm2), but DTC lost this affinity when the cultures developed into confluent monolayers with functional tight junctions (0.05 +/- 0.02 micro g COM/cm2). Confocal microscopy demonstrated the expression of the transmembrane receptor protein CD44 and its ligands osteopontin (OPN) and hyaluronic acid (HA) at the apical membrane of proliferating tubular cells; at confluence, CD44 was expressed at the basolateral membrane and OPN and HA were no longer detectable. In addition, a particle exclusion technique revealed that proliferating cells were surrounded by HA-rich pericellular matrices or "cell coats" extending several microns from the cell surface. Disintegration of these coats with hyaluronidase significantly decreased the cell surface affinity for crystals. Furthermore, CD44, OPN, and HA were also expressed in vivo at the luminal side of tubular cells in damaged kidneys. These results suggest (1) that the intact distal tubular epithelium of the human kidney does not bind crystals, and (2) that crystal retention in the human kidney may depend on the expression of CD44-, OPN-, and-HA rich cell coats by damaged distal tubular epithelium.

Urinary crystallization inhibitors do not prevent crystal binding.

PURPOSE: Renal stone formation requires the persistent retention of crystals in the kidney. Calcium oxalate monohydrate (COM) crystal binding to Madin Darby canine kidney strain I (MDCK-I), a cell line that resembles the epithelium in the renal distal tubule/collecting duct, is developmentally regulated, while LLC-PK1 cells (American Type Tissue Collection), which are widely used as a model of the renal proximal tubule, bind crystals irrespective of their stage of epithelial development. Whereas to our knowledge the binding molecules for COM at the surface of LLC-PK1 cells are still unknown, crystals adhere to the hyaluronan (HA) rich pericellular matrix transiently expressed by mobile MDCK-I cells. In the current study we investigated whether crystal binding to either cell type is influenced by urinary substances, including glycoprotein inhibitors of crystallization MATERIALS AND METHODS: We studied crystal binding to MDCK-I cells during wound repair, to confluent LLC-PK1 cells and to HA immobilized on a solid surface using [14C] COM pretreated or not pretreated with urine from healthy male volunteers. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis were performed to assess whether the crystals became coated with urine derived proteins RESULTS: Western blot analysis demonstrated that pretreated COM crystals were covered with protein inhibitors of crystallization. However, this protein coat had no significant effect on the level of crystal binding to either cell type. In contrast, the adherence of urine treated crystals to immobilized HA was significantly reduced CONCLUSIONS: The adherence of crystals to pericellular matrixes may encompass more than their simple fixation to the polysaccharide HA. Calcium oxalate crystal retention is not prevented by coating crystals with urinary constituents such as glycoproteins and, therefore, may predominantly depend on the surface properties of the renal tubular epithelium.