Ursolic acid treats renal tubular epithelial cell damage induced by calcium oxalate monohydrate via inhibiting oxidative stress and inflammation

Ursolic acid (UA) has been proved to have antioxidant and anti-inflammatory effects. However, it is not clear whether it has a protective impact on kidney damage induced by crystals of calcium oxalate monohydrate (COM). This work aimed to make clear the potential mechanism of UA protecting COM-induced kidney damage. The results manifested that high- and low-dose UA reduced COM crystals in COM rats' kidney, down-regulated urea, creatinine, and neutrophil gelatinase-associated lipocalin (NGAL) levels in rat plasma, declined kidney tissue and HK-2 cell apoptosis, inhibited Bax expression but elevated Bcl-2 expression. Additionally, UA alleviated renal fibrosis in COM rats, repressed α-SMA and collagen I protein expressions in the kidney and COM rats' HK-2 cells, depressed COM-induced oxidative damage in vivo and in vitro via up-regulating Nrf2/HO-1 pathway, up-regulated SOD levels and reduced MDA levels, down-regulated TNF-α, IL-1β, and IL-6 levels in vivo and in vitro via suppressing activation of TLR4/NF-κB pathway. In summary, the results of this study suggest that COM-induced renal injury can be effectively improved via UA, providing powerful data support for the development of effective clinical drugs for renal injury in the future.

Downregulation of inflammatory mediators by ethanolic extract of Bergenia ligulata (Wall.) in oxalate injured renal epithelial cells

ETHNOPHARMACOLOGICAL RELEVANCE

In the Indian traditional system of medicine, Bergenia ligulata (Wall.) Engl. has been used for treatment of urolithiasis. Its efficacious nature has led to its incorporation in various commercial herbal formulations such as Cystone and Neeri which are prescribed for kidney related ailments.

AIM OF THE STUDY

To assess whether ethanolic extract of B. ligulata can mitigate the cascade of inflammatory responses that cause oxidative stress and ultimately cell death in renal epithelial cells exposed to hyperoxaluric conditions.

MATERIAL AND METHODS

Bioactivity guided fractionation using solvents of varying polarities was employed to evaluate the potential of the extracts of B. ligulata to inhibit the crystallization process. Modulation of crystal morphology was visualized through Scanning electron microscopy (SEM) analysis. Cell death was assessed using flow cytometry based assays. Alteration in the inflammatory mediators was evaluated using real time PCR and immunocytochemistry. Phytochemical characterization of the ethanolic extract was carried out using FTIR, LC-MS and GC-MS.

RESULTS

Bioactivity guided fractionation for the assessment of antilithiatic activity revealed dose dependent inhibition of nucleation and aggregation process of calcium oxalate crystals in the presence of various extracts, however ethanolic extract showed maximum inhibition and was chosen for further experiments. Studies on renal epithelial NRK-52E cells showed, cytoprotective efficacy of B. ligulata extract against oxalate injury. SEM anaysis further revealed the potential of the extract to modulate the crystal structure and adhesion to renal cell surface. Exposure of the renal cells to the extract led to conversion of the calcium oxalate monohydrate (COM) crystals to the less injurious calcium oxalate dihydrate (COD) form. Expression analysis for oxidative stress and inflammatory biomarkers in NRK-52E cells revealed up-regulation of Mitogen activated protein kinase (MAPK), Osteopontin (OPN) and Nuclear factor- ĸB (NF-ĸB), in response to calcium oxalate insult; which was drastically reduced in the presence of B. ligulata extract. Flow cytometric evaluation pointed to caspase 3 mediated apoptotic cell death in oxalate injured cells, which was attenuated by B. ligulata extract.

CONCLUSION

Considering the complex multifactorial etiology of urolithiasis, ethanolic extract from B. ligulata can be a promising option for the management of kidney stones, as it has the potential to limit inflammation and the subsequent cell death.

Vitexin exerts protective effects against calcium oxalate crystal-induced kidney pyroptosis in vivo and in vitro

BACKGROUND

Nephrolithiasis is a common urinary disease with a high recurrence rate of secondary stone formation. Several mechanisms are involved in the onset and recurrence of nephrolithiasis, e.g., oxidative stress, inflammation, apoptosis, and epithelial-mesenchymal transition (EMT). Vitexin, a flavonoid monomer derived from medicinal plants that exert many biological effects including anti-inflammatory and anticancer effects, has not been investigated in nephrolithiasis studies. Moreover, pyroptosis, a form of programmed cell death resulting from inflammasome-associated caspase activation, has not been studied in mice with nephrolithiasis.

PURPOSE

We aimed to investigate the protective effect and underlying mechanisms of vitexin in nephrolithiasis, and the related role of pyroptosis in vivo and in vitro.

METHODS

Mouse models of nephrolithiasis were established via intraperitoneal injection of glyoxylate, and cell models of tubular epithelial cells and macrophages were established using calcium oxalate monohydrate (COM). Crystal deposition and kidney tissue injury were evaluated by hematoxylin and eosin, and von Kossa staining. Renal oxidative stress indexes including malondialdehyde (MDA), superoxide dismutase (SOD), glutathione (GSH), and catalase (CAT), were analyzed. The renal expression of interleukin-1 beta (IL-1β), gasdermin D (GSDMD), osteopontin (OPN), CD44, and monocyte chemotactic protein 1 (MCP-1), and EMT-related proteins in renal tubular epithelial cells was assessed. Cell viability and the apoptosis ratio were evaluated.

RESULTS

In vivo, vitexin alleviated crystal deposition and kidney tissue injury, and decreased the level of MDA, and increased the levels of SOD, GSH, and CAT. Vitexin also reduced the levels of the pyroptosis-related proteins GSDMD, NLRP3, cleaved caspase-1, and mature IL-1β, which were elevated in mice with nephrolithiasis, and repressed apoptosis and the expression of OPN and CD44. Moreover, vitexin mitigated F4/80-positive macrophage infiltration and MCP-1 expression in the kidneys. Furthermore, an in vitro study showed that vitexin increased the viability of HK-2 cells and THP-1-derived macrophages, which was impaired by treatment with COM crystals, decreased the medium lactate dehydrogenase (LDH) level, and inhibited the expression of pyroptosis-related proteins in HK-2 cells and macrophages. Vitexin repressed EMT of HK-2 cells, with increased expression of pan-cytokeratin (Pan-ck) and decreased expression of Vimentin and alpha-smooth muscle actin (α-SMA), and downregulated the Wnt/β-catenin pathway. Moreover, vitexin suppressed tumor necrosis factor-α (TNF-α) and IL-1β mRNA expression, which was upregulated by COM in macrophages.

CONCLUSION

Vitexin exerts protective effects against nephrolithiasis by inhibiting pyroptosis activation, apoptosis, EMT, and macrophage infiltration. In addition, GSDMD-related pyroptosis mediates nephrolithiasis.

Fu-Fang-Jin-Qian-Cao herbal granules protect against the calcium oxalate-induced renal EMT by inhibiting the TGF-β/smad pathway

CONTEXT

Nephrolithiasis is a major public health problem worldwide and Fu-Fang-Jin-Qian-Cao granules (FFJQC) is a traditional Chinese herbal formula that is used to treat nephrolithiasis. The main component of nephrolithiasis is calcium oxalate (CaOx) and the epithelial-mesenchymal transition (EMT) shown to play a crucial role in CaOx-induced kidney injury. However, the mechanism underlying the therapeutic effect of FFJQC on the CaOx-induced renal EMT is unknown.

OBJECTIVE

This study explores the therapeutic benefits and mechanism of FFJQC in oxalate-induced kidney injury.

MATERIALS AND METHODS

60 male C57BL/6 mice were used in this experiment and divided into 6 groups. A mouse kidney stone model was created by intraperitoneal injection of glyoxylate at a dose of 100 mg/kg for 6 days. The standardized FFJQC was used to treat mouse crystal kidney injury by gavage at 1.35 and 2.7 g/kg, respectively. Western blotting and immunostaining for E-cadherin, cytokeratin 18 (CK18), vimentin, smooth muscle α-actin (α-SMA) and transforming growth factor β (TGF-β)/Smad pathway were conducted on renal tissues.

RESULTS

Following CaOx-induced kidney injury, the levels of E-cadherin and CK18 in kidney decreased, while vimentin and α-SMA levels increased. The FFJQC treatment increased the levels of E-cadherin and CK18 and decreased vimentin and α-SMA levels in varying degrees. What's more, the FFJQC reduced the expression of CaOx-induced fibrosis marker collagen II.

CONCLUSION

FFJQC alleviated the CaOx-induced renal EMT and fibrosis by regulating TGF-β/smad pathway. Therefore, the FFJQC is an important traditional Chinese medicine for the treatment of CaOx-induced renal injury and fibrosis.

Calcium Oxalate Monohydrate is Associated with Endothelial Cell Toxicity But Not with Reactive Oxygen Species Accumulation

One characteristic of ethylene glycol overdose is a cardiopulmonary syndrome including hypertension and pulmonary edema with pathology indicating damage to the endothelium of heart, lung and brain vessels. The mechanism of the cardiopulmonary toxicity is unknown, but has been linked with accumulation of the metabolite calcium oxalate monohydrate (COM) in the endothelium. These studies have evaluated the hypothesis that COM or the oxalate ion produces endothelial damage in vitro and that damage is linked with induction of reactive oxygen species (ROS). In cultured human umbilical vein endothelial cells (HUVEC), COM, but not the oxalate ion, produced cytotoxicity in a dose- and time-dependent manner. Using three ROS-sensitive dyes, HUVEC exposed to COM did not significantly increase ROS production. Additionally, co-treatment with three antioxidants that operate by different mechanisms did not reduce COM cytotoxicity. As such, an increase in ROS production does not explain cell death in endothelial cells. Aluminum citrate, uniquely among citrate compounds, significantly reduced COM cytotoxicity to endothelial cells and thus may act as an adjunct therapy for ethylene glycol poisoning to reduce endothelial damage. These results imply that accumulation of COM in endothelial cells is an important aspect of the cardiopulmonary toxicity from ethylene glycol.

Efficacy of Obcordata A from Aspidopterys obcordata on Kidney Stones by Inhibiting NOX4 Expression

Obcordata A (OA) is a polyoxypregnane glycoside derived from the Dai medicine Aspidopterys obcordata vines. This study aims to investigate the efficacy of OA on renal tubular epithelial cells exposed to calcium oxalate crystals. We incubated renal tubular cells with 28 μg·cm2 calcium oxalate crystals for 24 h with and without OA, GKT137831, phorbol-12-myristate-13-acetate (PMA), and tocopherol. The MTT [3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay, microscopic examination, flow cytometry, and immunofluorescence staining revealed that calcium oxalate crystals decreased cell viability and elevated reactive oxygen species (ROS) levels. OA, GKT137831, and tocopherol protected cells and decreased ROS levels. However, OA did not exhibit direct DPPH scavenging ability. In addition, immunoblotting illustrated that OA inhibited the NOX4 (nicotinamide adenine dinucleotide phosphate oxidases 4) expression and downregulated the protein expression in the NOX4/ROS/p38 MAPK (p38 mitogen-activated protein kinase) pathway. The findings suggest that the cytoprotective and antioxidant effects of OA can be blocked by the NOX4 agonist PMA. In conclusion, OA could be used as a NOX4 inhibitor to prevent kidney stones.

Phagocytosis of environmental or metabolic crystalline particles induces cytotoxicity by triggering necroptosis across a broad range of particle size and shape

In crystallopathies, crystals or crystalline particles of environmental and metabolic origin deposit within tissues, induce inflammation, injury and cell death and eventually lead to organ-failure. The NLRP3-inflammasome is involved in mediating crystalline particles-induced inflammation, but pathways leading to cell death are still unknown. Here, we have used broad range of intrinsic and extrinsic crystal- or crystalline particle-sizes and shapes, e.g. calcium phosphate, silica, titanium dioxide, cholesterol, calcium oxalate, and monosodium urate. As kidney is commonly affected by crystallopathies, we used human and murine renal tubular cells as a model system. We showed that all of the analysed crystalline particles induce caspase-independent cell death. Deficiency of MLKL, siRNA knockdown of RIPK3, or inhibitors of necroptosis signaling e.g. RIPK-1 inhibitor necrostatin-1s, RIPK3 inhibitor dabrafenib, and MLKL inhibitor necrosulfonamide, partially protected tubular cells from crystalline particles cytotoxicity. Furthermore, we identify phagocytosis of crystalline particles as an upstream event in their cytotoxicity since a phagocytosis inhibitor, cytochalasin D, prevented their cytotoxicity. Taken together, our data confirmed the involvement of necroptosis as one of the pathways leading to cell death in crystallopathies. Our data identified RIPK-1, RIPK3, and MLKL as molecular targets to limit tissue injury and organ failure in crystallopathies.

Protective Effects of Pistacia lentiscus L. fruit extract against calcium oxalate monohydrate induced proximal tubular injury

ETHNOPHARMACOLOGICAL RELEVANCE

The world prevalence of kidney stones is increasing and plants are frequently used to treat urolithiasis. Pistacia lentiscus L, a plant which freely grows around the Mediterranean basin areas, is widely used for various pathologies. P. lentiscus has an important impact as it has economical value on top of its pharmacological interest. Decoctions of its aerial parts and/or resin are used to treat kidney stones.

AIM OF THE STUDY

To in vitro assess the potential nephroprotective effect of Pistacia lentiscus ethanolic fruit extract (PLEF) on proximal tubular cells in response to the adhesion of calcium oxalate monohydrate (COM) crystals.

MATERIALS AND METHODS

Human Kidney [HK]-2 cells were incubated with and without COM in the presence or absence of PLEF. Cell viability was measured by the resazurin assay. The expression of E-cadherin was analyzed by PCR. The extracellular production of H₂O₂ was measured by Amplex® Red H₂O₂ Assay. The numbers of detached or non-adherent COM crystals in the presence of PLEF were microscopically captured and counted using ImageJ software. The interaction of PLEF with COM and the effect of PLEF on crystal size were analyzed by flow cytometry. The spectrophotometric measurement of turbidity was performed for assessing the COM concentration.

RESULTS

PLEF incubated with COM was able to increase the cell viability. The decrease of E-cadherin expression after incubation with COM was counteracted by PLEF. Overproduction of H₂O₂ induced by COM was also inhibited by PLEF. Observations using flow cytometry showed that interactions between PLEF and the COM crystals occurred. PLEF was also effective in reducing the particles size and in lowering COM concentration.

CONCLUSION

Our data show that COM tubulotoxicity can be significantly reversed by PLEF -at least in part- via an inhibition of COM crystals adhesion onto the apical membrane. This early beneficial effect of PLEF needs to be further investigated as a useful strategy in nephrolithiasis prevention.

Size-dependent cellular uptake mechanism and cytotoxicity toward calcium oxalate on Vero cells

Urinary crystals with various sizes are present in healthy individuals and patients with kidney stone; however, the cellular uptake mechanism of calcium oxalate of various sizes has not been elucidated. This study aims to compare the internalization of nano-/micron-sized (50 nm, 100 nm, and 1 μm) calcium oxalate monohydrate (COM) and dihydrate (COD) crystals in African green monkey renal epithelial (Vero) cells. The internalization and adhesion of COM and COD crystals to Vero cells were enhanced with decreasing crystal size. Cell death rate was positively related to the amount of adhered and internalized crystals and exhibited higher correlation with internalization than that with adhesion. Vero cells mainly internalized nano-sized COM and COD crystals through clathrin-mediated pathways as well as micron-sized crystals through macropinocytosis. The internalized COM and COD crystals were distributed in the lysosomes and destroyed lysosomal integrity to some extent. The results of this study indicated that the size of crystal affected cellular uptake mechanism, and may provide an enlightenment for finding potential inhibitors of crystal uptake, thereby decreasing cell injury and the occurrence of kidney stones.

Reinjury risk of nano-calcium oxalate monohydrate and calcium oxalate dihydrate crystals on injured renal epithelial cells: aggravation of crystal adhesion and aggregation

BACKGROUND

Renal epithelial cell injury facilitates crystal adhesion to cell surface and serves as a key step in renal stone formation. However, the effects of cell injury on the adhesion of nano-calcium oxalate crystals and the nano-crystal-induced reinjury risk of injured cells remain unclear.

METHODS

African green monkey renal epithelial (Vero) cells were injured with H2O2 to establish a cell injury model. Cell viability, superoxide dismutase (SOD) activity, malonaldehyde (MDA) content, propidium iodide staining, hematoxylin-eosin staining, reactive oxygen species production, and mitochondrial membrane potential (Δψm) were determined to examine cell injury during adhesion. Changes in the surface structure of H2O2-injured cells were assessed through atomic force microscopy. The altered expression of hyaluronan during adhesion was examined through laser scanning confocal microscopy. The adhesion of nano-calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD) crystals to Vero cells was observed through scanning electron microscopy. Nano-COM and COD binding was quantitatively determined through inductively coupled plasma emission spectrometry.

RESULTS

The expression of hyaluronan on the cell surface was increased during wound healing because of Vero cell injury. The structure and function of the cell membrane were also altered by cell injury; thus, nano-crystal adhesion occurred. The ability of nano-COM to adhere to the injured Vero cells was higher than that of nano-COD crystals. The cell viability, SOD activity, and Δψm decreased when nano-crystals attached to the cell surface. By contrast, the MDA content, reactive oxygen species production, and cell death rate increased.

CONCLUSION

Cell injury contributes to crystal adhesion to Vero cell surface. The attached nano-COM and COD crystals can aggravate Vero cell injury. As a consequence, crystal adhesion and aggregation are enhanced. These findings provide further insights into kidney stone formation.

Aluminum citrate blocks toxicity of calcium oxalate crystals by preventing binding with cell membrane phospholipids

BACKGROUND/AIMS

Renal damage from ethylene glycol and primary hyperoxaluria is linked to accumulation of calcium oxalate monohydrate (COM) crystals in the renal proximal tubule (PT). In vitro studies have shown that aluminum citrate (AC), uniquely among citrate salts, blocks COM cytotoxicity to tubular cells. These studies were designed to evaluate the interaction of COM with membrane phospholipids and the ability of AC to reduce COM toxicity by interfering with this interaction.

METHODS

Interaction of COM with phospholipids was assessed using differential scanning calorimetric analysis of structural changes in specific liposomes. Interaction of COM with cell membranes was studied by measuring binding of radiolabeled crystals by human PT (HPT) cells.

RESULTS

Analysis of liposomes prepared from phosphatidylserine (PS) or phosphatidylcholine (PC) showed that COM interfered with the gel-liquid transition of PS liposomes, but not that of PC liposomes. AC reversed the COM-induced changes in liposomal structure. AC inhibited the binding of [(14)C]-COM by HPT cells in a concentration-dependent manner. AC blocked COM binding by interacting with the crystal surface and not the cell membrane.

CONCLUSION

These results indicate that AC blocks the binding of COM by PT cells, and consequently its cytotoxicity, by attaching to the surface of the crystal. Thus, AC, or a related compound that works by the same mechanism, could be a useful adjunct therapy to reduce the renal damage produced by severe hyperoxaluria.

[Study on processing for Rhizoma Pinelliae Praeparatum by comprehensive evaluation of multiple mark]

OBJECTIVE

To investigate the best processing technology of Rhizoma Pinelliae Praeparatum.

METHODS

L9(3(4)) orthogonal design was used with four factors: quantities of quick lime and Glycyrrhiza urallensis, processing time and temperature, the contents of Calcium oxalate crystals, Guanosine and Glycyrrhizic acid were determined by RP-HPLC, the irritation test was detected by swollen rabbits eyes with processing products.

RESULTS

The optimized processing technology was satisfied with some conditions as follows: the processing time was 48 hours, the processing temperature was 30 degrees C, quantities of quick lime and Glycyrrhiza uralensis were 10 g and 15 g.

CONCLUSION

The optimized processing method by orthogonal design has achieved the goal to reduce toxicity, the processing time and the processing temperature are confirmed respectively, and the processing time is significantly shortened comparing with Pharmacopoeia.

Dietary oxalate and calcium oxalate nephrolithiasis

PURPOSE

Patients with calcium oxalate kidney stones are advised to decrease the consumption of foods that contain oxalate. We hypothesized that a cutback in dietary oxalate would lead to a decrease in the urinary excretion of oxalate and decreased stone recurrence. We tested the hypothesis in an animal model of calcium oxalate nephrolithiasis.

MATERIALS AND METHODS

Hydroxy-L-proline (5%), a precursor of oxalate found in collagenous foods, was given with rat chow to male Sprague-Dawley rats. After 42 days rats in group 1 continued on hydroxy-L-proline, while those in group 2 were given chow without added hydroxy-L-proline for the next 21 days. Food and water consumption as well as weight were monitored regularly. Once weekly urine was collected and analyzed for creatinine, calcium, oxalate, lactate dehydrogenase, 8-isoprostane and H(2)O(2). Urinary pH and crystalluria were monitored. Rats were sacrificed at 28, 42 and 63 days, respectively. Renal tissue was examined for crystal deposition by light microscopy.

RESULTS

Rats receiving hydroxy-L-proline showed hyperoxaluria, calcium oxalate crystalluria and nephrolithiasis, and by day 42 all contained renal calcium oxalate crystal deposits. Urinary excretion of lactate dehydrogenase, 8-isoprostane and H(2)O(2) increased significantly. After hydroxy-L-proline was discontinued in group 2 there was a significant decrease in urinary oxalate, 8-isoprostane and H(2)O(2). Half of the group 2 rats appeared to be crystal-free.

CONCLUSIONS

Dietary sources of oxalate can induce hyperoxaluria and crystal deposition in the kidneys with associated degradation in renal biology. Eliminating oxalate from the diet decreases not only urinary oxalate, but also calcium oxalate crystal deposits in the kidneys and improves their function.

Calcium oxalate, and not other metabolites, is responsible for the renal toxicity of ethylene glycol

Ethylene glycol (EG) is nephrotoxic due to its metabolism. Many studies suggest that the toxicity is due to oxalate accumulation, but others have conversely suggested that toxicity results from effects of metabolites such as glycolaldehyde or glyoxylic acid on proximal tubule cells. In vivo studies have indicated that accumulation of calcium oxalate monohydrate (COM) corresponds closely with development of toxicity in renal tissue. The present studies were therefore designed to clarify the roles of various metabolites in the mechanism for EG toxicity in vitro by comparing the relative cytotoxicity of EG metabolites using three measures of cell death, ethidium homodimer uptake, lactate dehydrogenase (LDH) release and the conversion of the tetrazolium salt XTT to a colorimetric dye. Human proximal tubule cells in culture were incubated in physiologic buffers for 6h at 37 degrees C with COM (147-735microg/ml, an oxalate equivalence of 1-5mM), glycolate (5-25mM), glyoxylate (0.2-5mM) and glycolaldehyde (0.2-2mM). To assess the effects of acidity on the cytotoxicity, incubations were carried out at pH 6-7.4. The results show that COM dose-dependently increased LDH release and ethidium homodimer uptake, while the other metabolites did not. Conversely, COM had no effect on the XTT assay, while high concentrations of glycolaldehyde and glyoxylate decreased XTT activity, but the latter only at acidic pH. The correlation between the uptake of ethidium homodimer and the release of LDH suggest that COM is cytotoxic to human kidney cells in culture, while the XTT assay does not validly measure cytotoxicity in this system. These results indicate that COM, and not glyoxylate or glycolaldehyde, is the toxic metabolite responsible for the acute tubular necrosis and renal failure that is observed in EG-poisoned patients.

[Study on processing mechanism of Pinellia ternate]

OBJECTIVE

Elucidating the detoxification mechanism of the raw Pinellia ternata processed by alum solution or alkaline solution (pH > 12).

METHOD

Raw Pinellia ternata was immersed in alum solution and alkaline solution according to Chinese pharmacopoeia. Observed the shape's changing of needle-like calcium oxalate crystals by scanning electro-microscopy. Determinating the contents of calcium oxalate crystals by applying oxidation reduction titration. Measured the irritations of raw P. ternata and various processing products on the model of rabbits'eyes.

RESULT

After processed by 8% alum solution prescribed in Chinese pharmacopoeia or 10% sodium carbonate solution, the needle-like shape of raphides in raw Pinellia ternata were changing and the sting barb of raphides were rusted and dissolved, the contents of calcium oxalate crystal in raw Pinellia ternata were sharply declined from more than 1% to less than 0.5%. the decline of contents is relative to the irritation decline of P. ternata on rabbit's eyes. Less than 0.5% calcium oxalate crystals of P. ternata almost had no irritation.

CONCLUSION

After processed by 8% alum solution or sodium carbonate solution (pH > 12) , the irritation components in raw P. ternata could be rusted and dissolved, the needle point of raphides was broken, which led to the raphides'content declining and the irritation disappearing. The micro-structures, shapes and contents of calcium oxalate crystals in different medicine plants were not same. These properties of calcium oxalate crystal in India Madder Root and yam et al were very different from those in raw P. ternata.

Calcium oxalate crystals and methyl salicylate as toxic principles of the fresh leaves from Palicourea longiflora, an endemic species in the Amazonas state

The species of the genus Palicourea (Rubiaceae family) is well-known for its toxicity towards animals, particularly livestock. This work reports the occurrence of skin irritation during the manipulation of Palicourea longiflora, considering the prevalence of the monofluoracetic acid (MFAA) and another toxic compound: methyl salicylate. The MFAA was identified by 19F-NMR and methyl salicylate by gas chromatography linked to mass spectrometry (GC/MS) analysis. Additionally, an anatomical study of leaves had been used to explain the mechanism of penetration of the toxic principles.

[Study on irritation of calcium oxalate crystal in raw Pinellia ternata]

OBJECTIVE

Confirm the irritation of needle-like calcium oxalate crystals in raw Pinellia ternata.

METHOD

Comparing the irritations of raw P. ternate containing calcium oxalate crystals, the raw P. ternate no containing calcium oxalate crystals, the pure needle-like calcium oxalate crystals isolated from raw P. ternata, the extracts of water and various solvents from raw P. ternate. by using the model of rabbits' eyes. Studying the quantity effect relationship of different concentration suspensions of needle-like calcium oxalate crystal isolated from raw P. ternate on rabbits' eyes. Observing the shape and appearance of calcium oxalate crystals in raw P. ternate and raw India Madder Root by the electro microscope and comparing their irritation degrees with the same contents of calcium oxalate crystals.

RESULT

Calcium oxalate crystals in raw P. ternata showed very strong irritation property. Under the same content of calcium oxalate crystals, the irritation of raw P. ternata and pure needle-like calcium oxalate crystals isolated from raw P. ternate had no significant difference. The concentrations of needle-like calcium oxalate crystals were do relative to the degree of irritation on rabbits' eyes and they showed undoubted quantity-effect relationship.

CONCLUSION

Calcium oxalate crystal is the irritation component in raw P. ternata.

Impact of hypoxia and hypercapnia on calcium oxalate toxicity in renal epithelial and interstitial cells

Although there is an ongoing controversy about the primary site of calcium oxalate stone (CaOx) formation, there is some evidence for extratubular crystallization. However, the mechanisms leading to such interstitial calcifications are not clear. Anatomical studies have demonstrated a close association between the renal vasculature and renal tubules. It has been hypothesized that disorders of the vasculature may contribute to renal stone formation. The exceptional papillary environment with low oxygen and high carbon dioxide is of interest in this context and its impact on CaOx toxicity to renal cells has to be evaluated. LLC-PK1, Madin-Darby canine kidney (MDCK), human umbilical vein endothelial (HUVEC) and fibroblast cell lines were exposed to hypoxia (3% O2) alone, hypercapnia combined with hypoxia (3% O2, 18% CO2) or standard culture conditions (20% O2) for 72 h. Cell survival rates were determined microscopically after 4 h of incubation with CaOx at final concentrations of 1, 2 and 4 mM. DAPI staining and western blot were used to evaluate the induction of apoptosis. We confirmed that CaOx leads to concentration-dependent effects on the viability of the cell lines. HUVECs were most vulnerable to CaOx among the four cell lines. Incubation under hypoxia alone had no impact on CaOx toxicity to any of the cell lines in terms of survival. However, under combined hypoxic and hypercapnic conditions, all cell lines displayed a significant reduction of cell survival compared to room air incubation. Again, this effect was most pronounced for HUVECs. The induction of apoptosis could not be demonstrated in any experimental setting. Combined hypoxia and hypercapnia clearly aggravate CaOx toxicity to renal cell lines. As we could not demonstrate the induction of apoptosis, this effect may be a result of toxic necrosis. Especially the CaOx effect on interstitial cell lines might be of interest in the chronic ischemic papillary environment. An increased toxicity may lead to recurrent stone formation, and vice versa, diseases of the vasculature, like arteriosclerosis, may further promote stone formation by induction of local ischemia. This issue has to be clarified by further studies.

Expression Profiling of Crystal-Induced Injury in Human Kidney Epithelial Cells

BACKGROUND

Deposition of crystals within tubular lumens is a feature of many kidney stone diseases, including crystals of calcium oxalate monohydrate (COM) in primary hyperoxaluria and of 2,8-dihydroxyadenine (DHA) in adenine phosphoribosyltransferase deficiency. Crystals are injurious to renal epithelial cells, but the molecular bases of cell injury have not been well characterized.

METHODS

We used a cDNA microarray to identify the time-dependent changes in gene expression associated with the interaction of COM or DHA crystals with primary cultures of normal human kidney cortical epithelial cells.

RESULTS

We observed gene expression changes that were common to both crystal types, as well as a number of crystal-specific responses. A subset of genes known to be aberrantly expressed in kidney tissue from stone formers also showed an altered expression in COM- or DHA-treated normal human kidney cortical epithelial cells.

CONCLUSIONS

Our results show that cultured epithelial cells exposed to COM or DHA crystals demonstrate cellular responses that may be physiologically relevant, thus suggesting that this experimental system may be useful for elucidating the mechanisms of crystal-induced renal cell injury.

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.

Characterization of glycosaminoglycans in tubular epithelial cells: calcium oxalate and oxalate ions effects

BACKGROUND

The interaction between tubular epithelial cells and calcium oxalate crystals or oxalate ions is a very precarious event in the lithogenesis. Urine contains ions, glycoproteins and glycosaminoglycans that inhibit the crystallization process and may protect the kidney against lithogenesis. We examined the effect of oxalate ions and calcium oxalate crystals upon the synthesis of glycosaminoglycans in distal [Madin-Darby canine kidney (MDCK)] and proximal (LLC-PK1) tubular cell lines.

METHODS

Glycosaminoglycan synthesis was analyzed by metabolic labeling with (35)S-sulfate and enzymatic digestion with specific mucopolysaccharidases. Cell death was assessed by fluorescent dyes and crystal endocytosis was analised by flow cytometry.

RESULTS

The main glycosaminoglycans synthesized by both cells were chondroitin sulfate and heparan sulfate most of them secreted to the culture medium or present at cellular surface. Exposition of MDCK cells to oxalate ions increased apoptosis rate and the incorporation of (35)S-sulfate in chondroitin sulfate and heparan sulfate, while calcium oxalate crystals were endocyted by LLC-PK1, induced necrotic cell death, and increased (35)S-sulfate incorporation in glycosaminoglycans. These effects seem to be specific and due to increased biosynthesis, since hydroxyapatite and other carboxylic acid did not induced cellular death or glycosaminoglycan synthesis and no changes in sulfation degree or molecular weight of glycosaminoglycans could be detected. Thapsigargin inhibited the glycosaminoglycan synthesis induced by calcium oxalate in LLC-PK1, suggesting that this effect was sensitive to the increase in cytosolic calcium.

CONCLUSION

Tubular cells may increase the synthesis of glycosaminoglycans to protect from the toxic insult of calcium oxalate crystals and oxalate ions, what could partially limit the lithogenesis.

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.

The cytotoxicity of oxalate, metabolite of ethylene glycol, is due to calcium oxalate monohydrate formation

Oxalate is a minor, but important metabolite of ethylene glycol and has been directly linked with acute and subchronic renal toxicity in ethylene glycol poisoning. Numerous studies have characterized the cytotoxicity of oxalate as including plasma membrane damage and organelle injury. Oxalate has two forms in vivo: oxalate ions and calcium oxalate monohydrate (COM) crystals that readily form in the presence of calcium. The present study was designed to compare the cytotoxicity of the oxalate ion and COM crystals in human and rat cells. In rat red blood cells, the oxalate ion did not increase hemolysis, while COM crystals produced hemolysis with a concentration-dependent increase. In human proximal tubule (HPT) cells in culture, COM suspensions, at concentrations >3 mM but with no oxalate ion, caused cytotoxicity as evidenced by the release of lactate dehydrogenase (LDH) into media. Cytotoxicity was not observed in HPT cells treated with oxalate solutions that contained no COM because EDTA prevented its formation. The cytotoxic effects of COM to HPT cells were potentiated by acidosis (pH 6.5), but not by glycolate, the major metabolite of ethylene glycol. The toxicity of COM to HPT cells and to proximal tubule cells from Wistar and F-344 rats, compared using both ethidium homodimer uptake and LDH leakage, increased in human and rat cells in a concentration-dependent manner. Rat cells were more sensitive to COM than HPT cells, but there were no apparent differences between the effects in Wistar cells and F-344 cells. These results demonstrate that COM crystals, and not the oxalate ion, are responsible for the membrane damage and cell death observed in normal human and rat PT cells and suggest that COM accumulation in the kidney is responsible for the renal toxicity associated with ethylene glycol exposure.

Calcium Oxalate Monohydrate, a Metabolite of Ethylene Glycol, Is Toxic for Rat Renal Mitochondrial Function

Ethylene glycol poisoning can produce acute renal failure, requiring long-term hemodialysis to restore function. The mechanism of the renal failure is unknown, but is associated with tubular cell necrosis and ethylene glycol metabolism. The end metabolite of ethylene glycol is oxalic acid, the precipitation of which as calcium oxalate monohydrate (COM) crystals in the tubular lumen has been linked with the renal toxicity. Our recent studies suggest that COM is an intracellular toxicant to normal human proximal tubule cells in culture. The present studies were designed to assess whether COM or ionic oxalate alters mitochondrial function so as to lead to renal cell death. In isolated rat kidney mitochondria, COM produced a dose-dependent decrease in State 3 respiration (40% decrease at 0.05 mM COM with either succinate or glutamate/malate as substrate), without affecting either State 4 respiration or the ADP/O ratio. COM, from 0.01-0.05 mM also dose-dependently increased mitochondrial swelling, which was completely blocked by cyclosporin A. The inhibition of State 3 respiration, however, was not reversed by cyclosporin A administration. Potassium oxalate, at concentrations up to 5 mM did not inhibit mitochondrial respiration or induce swelling. These results suggest that COM, and not the oxalate ion, damages rat kidney mitochondria and induces the mitochondrial permeability transition, which may then lead to renal cell death. Since COM is transported intracellularly by kidney cells, the renal toxicity of ethylene glycol may result from inhibition of mitochondrial respiratory function in proximal tubular cells by COM crystals.

Effect of aqueous extract from Herniaria hirsuta L. on experimentally nephrolithiasic rats

Despite considerable progress in medical therapy, there is no satisfactory drug to treat kidney stones. Therefore, this current study is aimed to look for an alternative treatment by using Herniaria hirsuta on nephrolithiasic rats as a preventive agent against the development of kidney stones. The experiment was conducted in normal and calcium oxalate (CaOx) nephrolithiasic rats during 3 weeks. Several parameters were followed weekly including water intake, urinary volume and pH, some urinary chemistries, and crystalluria. At the end, kidneys were analyzed by light microscope. The results showed that water intake and urinary volume increased in nephrolithiasic rats, but their urinary pH decreased especially in the third week of treatment. Urinary oxalate increased significantly during the second week for untreated rats and remained constant in rats treated with Herniaria decoction. However, urinary calcium decreased significantly in week 2 in untreated rats and remained constant in treated rats. Qualitative analysis of crystalluria showed that untreated rats excreted large CaOx monohydrate and few dihydrate crystals while treated animals excreted mostly small CaOx dihydrate crystals. The examination of kidney sections revealed that CaOx deposition was limited in treated rats when compared to untreated ones. These results obtained in vivo confirmed the beneficial effect of Herniaria hirsuta and may justify its use as a preventive agent against the formation of calcium oxalate kidney stones.

[Study of stinging crystals in tian nanxing]

OBJECTIVE

To test whether the raphides in Tian Nanxing (Pinellia pedatisecta Schott) caused irritation.

METHOD

Scan Electron Microscope and Microscope Oberservation; Animal experimental study.

RESULT

Through the comparision of unprocessed Tian Nanxing to processed ones which included 36 h, 72 h, 120 h processed samples, the great modifications in the structure of raphides, especially for the ones with barbs in the processed samples was observed with time course study. A further animal experimental study went to show that the rate of change for raphides with barbs existed a dose-reponse relationship to irritation.

CONCLUSION

Investigations of the causes of these reactions showed that raphides of calcium oxalate are, at least in part, responsible for the Tian Nanxing's irritation.

Mitochondrial superoxide production during oxalate-mediated oxidative stress in renal epithelial cells

Crystals of calcium oxalate monohydrate (COM) in the renal tubule form the basis of most kidney stones. Tubular dysfunction resulting from COM-cell interactions occurs by mechanism(s) that are incompletely understood. We examined the production of reactive oxygen intermediates (ROI) by proximal (LLC-PK1) and distal (MDCK) tubular epithelial cells after treatment with COM (25-250 microg/ml) to determine whether ROI, specifically superoxide (O(2)(*-)), production was activated, and whether it was sufficient to induce oxidative stress. Employing inhibitors of cytosolic and mitochondrial systems, the source of ROI production was investigated. In addition, intracellular glutathione (total and oxidized), energy status (ATP), and NADH were measured. COM treatment for 1-24 h increased O(2)(*-) production 3-6-fold as measured by both lucigenin chemiluminescence in permeabilized cells and dihydrorhodamine fluorescence in intact cells. Using selective inhibitors we found no evidence of cytosolic production. The use of mitochondrial probes, substrates, and inhibitors indicated that increased O(2)(*-) production originated from mitochondria. Treatment with COM decreased glutathione (total and redox state), indicating a sustained oxidative insult. An increase in NADH in COM-treated cells suggested this cofactor could be responsible for elevating O(2)(*-) generation. In conclusion, COM increased mitochondrial O(2)(*-) production by epithelial cells, with a subsequent depletion of antioxidant status. These changes may contribute to the reported cellular transformations during the development of renal calculi.

[Studies on stimulating components of raw Pinellia ternata (Thunb.) (banxia)]

OBJECTIVE

To study the stimulating components of raw Pinellia ternata (Banxia).

METHODS

Used the methods of extracting with various organic solvents; x-ray fluorescence spectrometer; scanning electron microanalyzer; oxidation and reduction titrations; and ultraviolet spectrophotometry.

RESULTS

Experiments showed that calcium oxalate hydrate (C2CaO4 x H2O) was one of the stimulating components of raw Pinellia ternata, and its shape, and contents related to the stimulation of raw Pinellia ternata. After processing, the shape and contents of calcium oxalate changed, decreased respectively, and the stimulation of Pinellia ternata decreased.

CONCLUSION

The needle crystal of calcium oxalate is one of the stimulating components in raw Pinellia ternata.

Crystal-cell interaction and apoptosis in oxalate-associated injury of renal epithelial cells

Two renal epithelial cell lines, LLC-PK1 and Madin-Darby canine kidney (MDCK), were grown in monolayers and exposed to oxalate (Ox) and/or calcium oxalate (CaOx) crystals to investigate cellular responses to these challenges. In addition, LLC-PK1 cells were exposed to high concentrations of Ox for various time periods to investigate the role of apoptosis in Ox-associated cell injury. Both cell types showed signs of damage when exposed to Ox. However, LLC-PK1 cells appeared more sensitive than MDCK cells. There was a significant increase in release of lactate dehydrogenase into the medium and decrease in trypan blue exclusion by cells in the monolayer. Most noticeable was the detachment of cells from the substrate. Exposure of cells to CaOx crystals resulted in their attachment to cell surfaces followed by internalization. Using flow cytometry for quantification of apoptotic cells, transmission electron microscopy for morphology, and electrophoresis for DNA laddering detection, we observed significant apoptotic changes including condensation and margination of nuclear chromatin, DNA fragmentation, and migration of phosphatidylserine of the plasma membrane from inside to the cell surface. However, these cells also showed some necrotic changes such as loss of plasma membrane integrity and release of lactate dehydrogenase, indicating that the apoptotic process was interrupted.

Cells of proximal and distal tubular origin respond differently to challenges of oxalate and calcium oxalate crystals

LLC-PK1 and Madin-Darby canine kidney (MDCK) cells were used to study the role of free radicals in renal epithelial injury during exposure to oxalate ions (Ox) and calcium oxalate monohydrate (COM) crystals. The cell cultures were exposed for 120 or 240 min to 1.0 mmol Ox or 1.0 mmol Ox plus 500 microg/ml of COM crystals averaging 1.0 microm in size. Exposure of both LLC-PK1 and MDCK cells to Ox alone increased the leakage of lactate dehydrogenase, which was further enhanced when cells were exposed to Ox + COM crystals. The release of lactate dehydrogenase from the LLC-PK1 cell line, however, was significantly higher than that from MDCK cells. LLC-PK1 cells also showed a significant increase in malondialdehyde (MDA) content on Ox challenge. MDA content was even higher when LLC-PK1 cells were challenged with Ox + COM crystals. However, in MDCK cells, the elevated MDA content was similar in both treatment groups, suggesting that these cells may be more resistant to the calcium oxalate crystals. Glutathione peroxidase activity was decreased in both LLC-PK1 and MDCK cells. Challenging cells with Ox + COM resulted in decreased catalase activity in LLC-PK1, but increased catalase activity in MDCK cells. Superoxide dismutase activity and reduced glutathione content were not significantly different in either cell type when challenged with Ox or Ox + COM. Previous in vivo animal studies yielded indirect evidence for the increased lipid peroxidation during hyperoxaluria-induced nephrolithiasis. However, in an animal model, it is difficult to separate the effect of Ox from Ox in combination with COM crystals. This study suggests that the injury to renal tubular epithelial cells is accompanied by lipid peroxidation when exposed to Ox. The injury is augmented when COM crystals are included. LLC-PK1 cells are more susceptible to Ox-associated injury than MDCK cells.

Oxalate and calcium oxalate crystals are injurious to renal epithelial cells: results of in vivo and in vitro studies

Calcium oxalate (CaOx) nephrolithiasis was induced in male Sprague-Dawley rats by administration of 0.75% ethylene glycol. Urinary excretion of lactate dehydrogenase (LDH) was used as a marker of cellular injury. Lipid peroxides (LP), as marker for free radical injury, were measured as malondialdehyde (MDA) in urine and the kidneys. Urinary oxalate (Ox), LDH, LP, CaOx crystals, and renal LP and CaOx crystal deposits were examined on day 0, 5, 30 and 60 of the experiment. There were significant differences between control and experimental rats in all the parameters except LDH which did not show a significant increase after 15 days. Subconfluent cultures of MDCK and LLCPK1 cells were exposed to various concentrations of oxalate and/or 500 fg/ml CaOx crystals. Cell viability was assayed by trypan blue exclusion, cellular injury was determined by measuring LDH in the media, and free radical injury was measured as MDA contents of the cells. On exposure to both Ox and/or CaOx crystals trypan blue exclusion decreased and LDH and MDA increased significantly in both tissue cultures. LLC-PK1 appeared more sensitive. The results indicate that both oxalate and calcium oxalate crystals are injurious to renal epithelial cells in the kidneys as well as in culture.

Alterations in MDCK and LLC-PK1 cells exposed to oxalate and calcium oxalate monohydrate crystals

Structural analysis of human kidney stones reveals the presence of cellular membranes and other cell fragments. Experimentally, calcium oxalate crystallization is facilitated when an exogenous nephrotoxin is given with ethylene glycol, thus providing cellular degradation products to act as heterogeneous nuclei. In this report, we tested whether oxalate alone could act as a cell toxin capable of producing damaged cells without the presence of an exogenous agent. Cultured LLC-PK1 and MDCK cells, when exposed to 1.0 mmol KOx, a concentration at the limit of metastability for calcium oxalate nucleation, were severely damaged as measured by specific lactate dehydrogenase (LDH) release in the spent media and by trypan blue exclusion. This effect was magnified by the addition of pre-formed calcium oxalate monohydrate crystals; the injury was significantly amplified when compared to exposure to oxalate alone. Scanning electron microscopy studies illustrated attachment of crystals to cells with loss of cell-to-cell and cell-to-substrate contact, as cells were released from the monolayer. In both oxalate and combined crystal-oxalate studies, more cells were released from the monolayer and exhibited considerably more damage when compared to controls. Oxalate, at the limit of metastability for calcium oxalate, is a cell toxin and can produce cellular degradation products. This effect is increased significantly by the addition of calcium oxalate monohydrate crystals.

Madin-Darby canine kidney cells are injured by exposure to oxalate and to calcium oxalate crystals

The reaction of Madin-Darby canine kidney cells (MDCK) to potassium oxalate (KOx), calcium oxalate monohydrate (COM) crystals, or a combination of the two was studied. The most noticeable effect of exposure of the cells to either KOx or COM crystals was loss of cells from the monolayer ranging from 20% to 30%, depending upon the particular treatment. Cellular enzyme values in the media were elevated significantly by 12 h of exposure, although in specific instances, elevated levels occurred at earlier time periods. As regards the monolayer, trypan blue exclusion was decreased significantly, although amounting to only a 4-5% reduction. Specific tritiated release occurred at 4 and 12 h after exposure to KOx and at 12 h after exposure to crystals. Structurally, COM-cell interactions were complex and extensive endocytosis was noted. Cells were released from culture either as cell-crystal complexes or from the intercellular spaces after exocytosis. When treatments were combined the effects were only slightly additive, but the two treatments potentiated each other: all media enzyme levels (with one exception) were elevated at 2 h, tritiated adenine release was present at 4 h, and there was more extensive cell loss from the culture monolayer. These data suggest that both KOx and COM crystals damage MDCK cells when applied alone, and in concert they act synergistically.

Pulmonary oxalate deposition associated with Aspergillus niger infection. An oxidant hypothesis of toxicity

Tissue injury by Aspergillus niger infection is associated with the deposition of calcium oxalate crystals. Oxalate is recognized to function as a ligand for numerous metal cations and will react with ferric ion to form a coordination complex. We describe oxalate deposition in the lung of a patient with A. niger infection and quantify surface-complexed Fe3+. Crystals collected from lung tissue demonstrated considerable concentrations of surface iron. In addition, we tested the hypothesis that this surface coordination of Fe3+ by oxalate is associated with increased in vitro oxidant generation. Calcium oxalate crystals (1.0 mg/ml) complexed all available Fe3+ from solutions of ferric chloride to concentrations of as much as 1.0 mM. Oxidant generation in both a chemical and a cellular system, measured as thiobarbituric-acid-reactive products of deoxyribose and chemiluminescence, respectively, increased with coordination of higher concentrations of inorganic iron. We conclude that calcium oxalate associated with A. niger infection complexes iron cations onto the crystalline surfaces and may generate oxidants at the solid-solution interface, which could result in tissue injury.