The density and protein content of calcium oxalate crystals precipitated from human urine: a tool to investigate ultrastructure and the fractional volume occupied by organic matrix

Quantifying particle adhesion to the ureteral walls during peristaltic flow

In this paper, we investigate the motion of particle(s) under the action of peristaltic flow. The particle trajectories are simulated by considering sinusoidal peristaltic waves. The fluid flow is governed by a two-dimensional Navier-Stokes equation, whereas for the particle dynamics we use the Basset-Boussinesq-Oseen (BBO) equation. The particle trajectories computed for different characteristic peristaltic flows, that is, trapping flow, augmented flow, and backward flow, show that the net horizontal particle displacement is largest for the augmented flow case. In general, the particle motion depends on its location in the peristaltic channel because of the wall curvature, which directly affects the flow velocities. The reported results for a cluster of particles show that whilst a fraction of particles form a group and propagate along the wave, some particles are left behind that deposit on the channel wall. In many biological processes it is desirable to know the number of particles that accumulate on the channel walls. In the present work, we propose empirical relations which can be used to calculate particle adhesion as a function of time.

Method for CaOx crystals isolation from plant leaves

Although calcium oxalate (CaOx) crystals are present in many plants they are poorly studied. A possible limitation is the lack of methods for CaOx crystals isolation at high concentration and high purity, which is required for the analysis of their associated biomolecules such as proteins. To our knowledge, there are only four works that have isolated proteins from CaOx crystals. Those methods basically consist of grinding the plant material, filtration steps, enzymatic digestions, and density-based separation. However, they lack of steps to evaluate the quality and purity of the isolated crystals. Likewise, those works do not evaluate whether the crystals obtained carry contaminating proteins.

In the present work a detailed method for CaOx crystals isolation from amaranth leaves is described, which can be used to isolate crystals from other plant leaves. The present method is based on previous works with the addition of cleaning steps to removal contaminating protein, separation of crystals by size, and microscopic monitoring to validate the purification efficiency.

Main steps for CaOx crystals isolation:•

Plant leaves are ground and several washing steps, including enzymatic digestions and centrifugation, are carried out to remove cellular debris and contaminating proteins.

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CaOx crystals are enriched by centrifugation in sodium polytungstate.

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The different forms of crystals are separated by filtration.

Degraded Porphyra yezoensis polysaccharide protects HK-2 cells and reduces nano-COM crystal toxicity, adhesion and endocytosis

We studied the protection of degraded Porphyra yezoensis polysaccharide (PYP) on human proximal tubular epithelial cells (HK-2) from cytotoxicity of nano-calcium oxalate monohydrate (COM) crystal, and the regulation of adhesion and endocytosis of the COM crystal. Four degraded fractions, namely, PYP1, PYP2, PYP3, and PYP4, were successfully obtained, with molecular weights (Mws) of 576.2, 49.5, 12.6, and 4.02 kDa, respectively. PYP protection reduced the crystal toxicity, prevented the destruction of cell morphology and cytoskeleton, inhibited the production of reactive oxygen species and the decline of lysosomal integrity, and reduced the expression of osteopontin and transmembrane protein (CD44). PYPi inhibited the adhesion and endocytosis of HK-2 cells by nano-COM. Endocytic COM crystals were accumulated in the lysosomes. With decreasing molecular weight, the ability of PYP to reduce cell damage and inhibit cell adhesion and endocytosis increased. PYP4, which has the smallest molecular weight, weaker intramolecular hydrogen bonds and more reducing groups, showed the best biological activity. PYPi can reduce the oxidative damage of the crystal to the cell, inhibit the adhesion and endocytosis of the crystal, and reduce the risk of kidney stone formation. Therefore, PYP, especially PYP4, has potential for use as a green drug to inhibit the formation and recurrence of calcium oxalate stones.

In Vitro Evaluation of Stone Fragment Evacuation by Suction

Introduction: Contemporary, flexible stone baskets are unable to extract submillimeter stone fragments at the time of ureteroscopic laser lithotripsy. In this in vitro study, the feasibility of suctioning submillimeter fragments with a standard Luer Lock syringe through the working channel of a flexible ureteroscope was assessed. Materials and Methods: Phantom stones made from industrial plaster were mechanically fragmented into ≤1 and ≤0.5-mm groups. Both stone groups were divided into five preweighed trial samples. Each stone group was then mixed in a beaker filled with normal saline. A standard 10-mL Luer Lock syringe was connected to a fiber-optic ureteroscope with a 1.2-mm working channel. The syringe was then used to suction stone fragments from the beaker. The suctioned stone fragments and the stone fragments remaining in the beaker after removing the overlying solution were separated, centrifuged with supernatant removed, and dried in an incubator set at 33°C for 1 week. Dried weights were recorded. Results: Mean total weights for ≤0.5 and ≤1.0-mm stone groups at baseline were 0.807 and 0.806 g, respectively. The mean percentages of stone fragments suctioned through the ureteroscope for ≤0.5 and ≤1.0-mm groups were 86% and 86%, respectively (p = 0.973). During suctioning, 64% of stones in the ≤0.5-mm group were trapped in either the working channel of the ureteroscope or within the Luer Lock syringe compared with 78% of stones in the ≤1-mm group (p = 0.001) requiring cessation of the procedure to clear the channel. Conclusions: It is feasible to suction submillimeter stone fragments by connecting a Luer Lock syringe to the working channel of a flexible ureteroscope. The limiting factor for removing stone fragments appears to be the small working channel of flexible ureteroscopes as trapping of fragments during suctioning is common and requires time-consuming removal of the endoscope and clearing of the channel.

Regulation on Calcium Oxalate Crystallization and Protection on HK-2 Cells of Tea Polysaccharides with Different Molecular Weights

The regulation on calcium oxalate (CaOx) crystallization and protective effect on human proximal tubular epithelial cells (HK-2) of four green tea polysaccharides (TPSs) with molecular weights of 10.88 (TPS0), 8.16 (TPS1), 4.82 (TPS2), and 2.3 kDa (TPS3) were comparatively studied. XRD, Fourier transform infrared spectroscopy, and scanning electron microscopy results revealed that TPS1, TPS2, and TPS3 can increase the percentage of the dihydrate crystalline phase in CaOx crystals and reduce the size of CaOx monohydrate crystals. TPSs increased the absolute value of the zeta potential of CaOx crystal and inhibited crystal nucleation and aggregation. The nucleation inhibition rates of TPS1, TPS2, and TPS3 to CaOx crystallization were 56.67%, 75.52%, and 52.92%, respectively, and their aggregation inhibition rates were 22.34%, 47.59%, and 21.59%, respectively. TPS preprotection can alleviate the oxidative damage of HK-2 cells caused by oxalate, increase cell viability, protect cell morphology, and reduce lactate dehydrogenase release and reactive oxygen species levels. The degraded TSPs, especially TPS2 with moderate molecular weight, may be used as a green drug to inhibit stone formation.

Low-power, low-cost urinalysis system with integrated dipstick evaluation and microscopic analysis

We introduce a coupled dipstick and microscopy device for analyzing urine samples. The device is capable of accurately assessing urine dipstick results while simultaneously imaging the microscopic contents within the sample. We introduce a long working distance, cellphone-based microscope in combination with an oblique illumination scheme to accurately visualize and quantify particles within the urine sample. To facilitate accurate quantification, we couple the imaging set-up with a power-free filtration system. The proposed device is reusable, low-cost, and requires very little power. We show that results obtained with the proposed device and custom-built app are consistent with those obtained with the standard clinical protocol, suggesting the potential clinical utility of the device.

Preparation, properties, formation mechanisms, and cytotoxicity of calcium oxalate monohydrate with various morphologies

Calcium oxalate monohydrate (COM) crystals with various morphologies, such as elliptical, hexagonal, peanut-like, spherical and flower-like structures with a size of about 10 μm, were prepared through varying the reactant concentration, stirring speed, reaction temperature, and additive.

Effect of Crystal Shape and Aggregation of Calcium Oxalate Monohydrate on Cellular Toxicity in Renal Epithelial Cells

Renal epithelial cell injury is a key step in inducing kidney stone formation. This injury induced by crystallites with different shapes and aggregation states has been receiving minimal research attention. To compare the shape and aggregation effects of calcium oxalate crystals on their toxicity, we prepared calcium oxalate monohydrate (COM) crystals with the morphology of a hexagonal lozenge, a thin hexagonal lozenge, and their corresponding aggregates. We then compared their toxicities toward human kidney proximal tubular epithelial (HK-2) cells. All four shapes of COM crystals caused cell-membrane rupture, upregulated intracellular reactive oxygen, and decreased mitochondrial membrane potential. This series of phenomena ultimately led to necrotic cell death. The overall damage in cells was determined in terms of both exterior and interior damage. Crystals with a large Ca2+ ion-rich (1̅01) active face showed the greatest toxicity in HK-2 cells and the largest extent of adhesion onto the cell surface. Crystals with sharp edges easily caused cell-membrane ruptures. The aggregation of sharp crystals aggravated cell injury, whereas the aggregation of blunt crystals weakened cell injury. Therefore, crystal shapes and aggregation states were important factors that affected crystal toxicity in renal epithelial cells. All of these findings elucidated the relationship between the physical properties of crystals and cytotoxicity and provided theoretical references for inhibiting stone formation.

The osteopontin-controlled switching of calcium oxalate monohydrate morphologies in artificial urine provides insights into the formation of papillary kidney stones

The protein osteopontin (OPN) plays an important role in preventing the formation of calcium oxalate monohydrate (COM) kidney stones. To gain insight into these mechanisms, crystallization was induced by addition of human kidney OPN to artificial urine (ionic strength comparable to urine; without citrate), and the OPN-COM interaction studied using a combination of scanning electron (SEM) and confocal microscopy. By SEM, we found that increasing OPN concentrations formed large monoclinic penetration twins (no protein added) and, at higher concentrations (1-, 2μg/ml OPN), super and hyper twins with crystal habits not found in previous studies. For instance, the hyper twins indicate well-facetted gearwheel-like habits with "teeth" developed in all crystallographic <h0l> directions. At OPN concentrations ≥2μg/ml, a switching to small dumbbell-shaped COM habits with fine-textured surfaces occurred. Confocal microscopy of these dumbbells indicates protein incorporation in almost the entire crystal structure (in contrast to facetted COM), proposing a threshold concentration of ∼2μg/ml OPN for the facetted to the non-facetted habit transformation. Both the gearwheel-like and the dumbbell-shaped habit are again found side-by-side (presumably triggered by OPN concentration gradients within the sample) in in-vitro formed conglomerates, which resemble cross-sections of papillary kidney stones. The abrupt transformation from facetted to non-facetted habits and the unique compliance of the two in-vitro formed habits with the two main morphologies found in papillary kidney stones propose that OPN is a main effector in direct stone-forming processes. Moreover, stone structures which exhibit these two morphologies side-by-side might serve as a novel indicator for OPN concentrations surrounding those structures.

The effect of intracrystalline and surface-bound osteopontin on the degradation and dissolution of calcium oxalate dihydrate crystals in MDCKII cells

In vivo, urinary crystals are associated with proteins located within the mineral bulk as well as upon their surfaces. Proteins incarcerated within the mineral phase of retained crystals could act as a defence against urolithiasis by rendering them more vulnerable to destruction by intracellular and interstitial proteases. The aim of this study was to examine the effects of intracrystalline and surface-bound osteopontin (OPN) on the degradation and dissolution of urinary calcium oxalate dihydrate (COD) crystals in cultured Madin Darby canine kidney (MDCK) cells. [(14)C]-oxalate-labelled COD crystals with intracrystalline (IC), surface-bound (SB) and IC + SB OPN, were generated from ultrafiltered (UF) urine containing 0, 1 and 5 mg/L human milk OPN and incubated with MDCKII cells, using UF urine as the binding medium. Crystal size and degradation were assessed using field emission scanning electron microscopy (FESEM) and dissolution was quantified by the release of radioactivity into the culture medium. Crystal size decreased directly with OPN concentration. FESEM examination indicated that crystals covered with SB OPN were more resistant to cellular degradation than those containing IC OPN, whose degree of disruption appeared to be related to OPN concentration. Whether bound to the crystal surface or incarcerated within the mineral interior, OPN inhibited crystal dissolution in direct proportion to its concentration. Under physiological conditions OPN may routinely protect against stone formation by inhibiting the growth of COD crystals, which would encourage their excretion in urine and thereby perhaps partly explain why, compared with calcium oxalate monohydrate crystals, COD crystals are more prevalent in urine, but less common in kidney stones.

Particle motion in unsteady two-dimensional peristaltic flow with application to the ureter

Particle motion in an unsteady peristaltic fluid flow is analyzed. The fluid is incompressible and Newtonian in a two-dimensional planar geometry. A perturbation method based on a small ratio of wave height to wavelength is used to obtain a closed-form solution for the fluid velocity field. This analytical solution is used in conjunction with an equation of motion for a small rigid sphere in nonuniform flow taking Stokes drag, virtual mass, Faxén, Basset, and gravity forces into account. Fluid streamlines and velocity profiles are calculated. Theoretical values for pumping rates are compared with available experimental data. An application to ureteral peristaltic flow is considered since fluid flow in the ureter is sometimes accompanied by particles such as stones or bacteriuria. Particle trajectories for parameters that correspond to calcium oxalates for calculosis and Escherichia coli type for bacteria are analyzed. The findings show that retrograde or reflux motion of the particles is possible and bacterial transport can occur in the upper urinary tract when there is a partial occlusion of the wave. Dilute particle mixing is also investigated, and it is found that some of the particles participate in the formation of a recirculating bolus, and some of them are delayed in transit and eventually reach the walls. This can explain the failure of clearing residuals from the upper urinary tract calculi after successful extracorporeal shock wave lithotripsy. The results may also be relevant to the transport of other physiological fluids and industrial applications in which peristaltic pumping is used.

Calcification and silicification: a comparative survey of the early stages of biomineralization

Most of the studies on biomineralization have focused on calcification and silicification, the two systems that predominate in nature in the construction of skeletal or integumental hard tissues. They have, however, been studied separately, as if they were completely distinct processes, in spite of their several points of contact, especially as far as the organic-inorganic relationships during the early mineralization stages are concerned. A very tight association of the inorganic substance with organic macromolecules, in fact, initially characterizes both systems. Although the mechanism of biomineralization remains elusive, a number of old and new findings, which have been taken into account in this review, support the view that, both in calcification and in silicification, genetically controlled organic macromolecules induce the formation of composite, organic-inorganic nanoparticles, behave as templates for the subsequent assemblage of the nanoparticles into micro- to macroarchitectures of complex pattern, and, eventually, are mostly reabsorbed. There are still many gaps left in our knowledge of this process. Comparative studies of the two biomineralization systems may help to fill them.

How does bovine serum albumin prevent the formation of kidney stone? A kinetics study

To attain a better understanding of the crystallization of calcium oxalate crystals under the influence of the protein bovine serum albumin, we examined not only the nucleation kinetics but also the structural synergy between the biomineral and the biosubstrate. It follows that during the crystallization process of calcium oxalate crystals bovine serum albumin inhibits the nucleation of calcium oxalate by increasing the kink kinetics barrier. The results of scanning electron microscopy and X-ray diffraction show, however, that bovine serum albumin promotes the formation of calcium oxalate dihydrate. Apart from this, bovine serum albumin facilitates the ordered calcium oxalate crystal assembly by suppressing the supersaturation-driven interfacial structure mismatch. The physics questions behind the mentioned effects have been addressed from the kinetics point of view. This may explain why bovine serum albumin plays an important role in suppressing urine stone formation.

The importance of a clean face: the effect of different washing procedures on the association of Tamm-Horsfall glycoprotein and other urinary proteins with calcium oxalate crystals

This study was undertaken to determine whether the use of different washing procedures could explain dissident findings in published studies examining the role of urinary macromolecules in urolithiasis. Calcium oxalate monohydrate (COM) crystals were deposited from or added to the same sieved urine, washed with copious or limited amounts of distilled water, or with methanol, and examined by field emission scanning electron microscopy (FESEM). Demineralized extracts were analysed by SDS-PAGE and Western blotting for Tamm-Horsfall glycoprotein (THG), human serum albumin (HSA), osteopontin (OPN) and prothrombin fragment 1 (PTF1). Synchrotron X-ray diffraction (SXRD) with Rietveld whole-pattern peak fitting and profile analysis was used to determine non-uniform crystal strain and crystallite size in crystals generated from inorganic solutions in the presence of increasing concentrations of THG and prothrombin (PT). HSA and PTF1 were present in all demineralized crystal extracts, confirming their inclusion within COM. OPN was present in all extracts except those derived from pure inorganic COM crystals, because of its occlusion within small numbers of calcium oxalate dihydrate (COD) crystals contaminating the COM population. THG was absent from the demineralized extracts of all crystals washed copiously with water, but present in those washed with methanol or limited amounts of water. FESEM showed extraneous organic material associated only with crystals whose extracts contained THG, confirming that the protein does not bind permanently to the COM crystal surface and is not occluded within the mineral bulk. This was confirmed by SXRD, which showed that non-uniform strain and crystallite size remained unaltered in crystals grown in the presence of increasing THG concentrations. However, non-uniform strain increased and crystallite size decreased with increasing PT concentrations, demonstrating unambiguously that PT is included in COM crystals. It was concluded that scrupulous care must be taken to ensure the complete removal of extraneous THG adventitiously associated with CaOx crystals in order to avoid inaccurate analysis of crystal matrix protein content and possible misinterpretation of experimental data.

The association of different urinary proteins with calcium oxalate hydromorphs. Evidence for non-specific interactions

It has been proposed that various urinary proteins interact specifically with different calcium oxalate hydromorphs and these interactions have important implications regarding the understanding of the onset and progress of kidney stone disease. Calcium oxalate monohydrate and dihydrate crystals were grown and characterised thoroughly to establish sample purity. These crystals were then incubated in artificial urine samples containing isolated urinary macromolecules. Crystal growth was prevented by saturating the incubation mix with calcium oxalate, and this was confirmed through electron microscopy and calcium measurements of the incubation mix. The surface interactions between the different calcium oxalate hydrates and urinary proteins were investigated by the use of Western blots and immunoassays. The same proteins, notably albumin, Tamm-Horsfall protein, osteopontin and prothrombin fragment 1, associated with both hydrates. There was a trend for more protein to associate with calcium oxalate dihydrate, and greater quantities of different proteins associated with both hydrates when Tamm-Horsfall protein was removed from the incubation mix. There is no evidence from this study to indicate that particular proteins interact with specific calcium oxalate hydrates, which in turn suggests that these protein-mineral interactions are likely to be mediated through non-specific charge interactions.