The inhibition of calcium oxalate monohydrate crystal growth by maleic acid copolymers

Inhibition of calcium oxalate crystallisation in vitro by an extract of Bergenia ciliata

OBJECTIVE

To evaluate the effectiveness of an extract obtained from the rhizomes of Bergenia ciliata (Saxifragaceae) on the inhibition of calcium oxalate (CaOx) crystallisation in vitro.

MATERIALS AND METHODS

A hydro-alcoholic extract (30:70, v/v) of rhizomes of B. ciliata was prepared at different concentrations (1-10 mg/mL). The crystallisation of CaOx monohydrate (COM) was induced in a synthetic urine system. The nucleation and aggregation of COM crystals were measured using spectrophotometric methods. The rates of nucleation and aggregation were evaluated by comparing the slope of the turbidity of a control system with that of one exposed to the extract. The results were compared with a parallel study conducted with a marketed poly-herbal combination, Cystone, under identical concentrations. Crystals generated in the urine were also analysed by light microscopy. Statistical differences and percentage inhibitions were calculated and assessed.

RESULTS

The extract of B. ciliata was significantly more effective in inhibiting the nucleation and aggregation of COM crystals in a dose-dependent manner than was Cystone. Moreover, the extract induced more CaOx dihydrate crystals, with a significant reduction in the number and size of COM crystals.

CONCLUSION

An extract of the traditional herb B. ciliata has an excellent inhibitory activity on crystalluria and therefore might be beneficial in dissolving urinary stones. However, further study in animal models of urolithiasis is needed to evaluate its potential anti-urolithiatic activity.

Green Nanotechnologies for Responsible Manufacturing

A perpetual increase in population and thus consumption of fossil fuels has led to increased pollution worldwide. Pollution in large metropolitan cities has reached an alarming level and is widely believed to be the leading contributor to chronic and deadly health disorders and diseases affecting millions of people each year. Although correlation between environmental pollution and global warming is debatable, the effects of pollution and its impact on human health are irrefutable and highly observable. Use of nanomaterials to generate energy, in an attempt to reduce environmental pollution, is in its preliminary stages and requires urgent and detailed investigation. This investigation focuses on three aspects of sustainability, (a): use of nanomaterials to monitor, detect, and remediate the environmental pollution, (b): responsible manufacturing of nanomaterials by employing principles of “green chemistry”, and (c): to drastically reduce waste and emission by-products employing use of nanomaterials as catalysts for enhanced efficiency. The synthesis of nanomaterials is accomplished by processes employing processes such as electrospinning, sol-gel, and MAPLE to drastically reduce and isolate emission and waste by-products. An exhaustive overview of the scope of our investigation and some specific applications relating to the use of nanomaterials in environmental friendly investigations, viz.; applications of nanomaterials as catalysts for enhanced efficiency, materials in CO2 sequestration, remediation of toxic metals in water streams, efficient thin film photovoltaic devices, fuel cells, and biodegradable consumable products is described. Fate and transport of nanomaterials in air, water, and soil; life-cycle analysis, and methodologies to conduct risk-assessment in the context of source reduction and conservation is discussed as a step towards sustainability.

Specific biofunctional performances of the hydroxyapatite-sodium maleate copolymer hybrid coating nanostructures evaluated by in vitro studies

The nanohybrid structures consisting of hydroxyapatite (HA) and sodium maleate-vinyl acetate copolymer (MP) deposited by Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique on Ti surfaces were investigated for specific biological qualities required in bone implantology. The data from in vitro studies demonstrated that human primary osteoblasts (OBs) firmly adhered to Ti coated with HA-MP as indicated by cytoskeleton and vinculin dynamics. OBs spread onto biomaterial surface and formed groups of cells which during their biosynthetic activity expressed OB phenotype specific markers (collagen and non-collagenous proteins) and underwent controlled proliferation.

Biocompatibility evaluation of a novel hydroxyapatite-polymer coating for medical implants (in vitro tests)

Nanocomposites consisting of hydroxyapatite (HA) and a sodium maleate copolymer (maleic polyelectrolyte), synthesized by hydrothermal method and deposited on titanium substrates by Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique were tested for the biological properties. Coating bioanalysis was carried out by triple staining of actin, microtubules and nuclei followed by immunofluorescence microscopy. Within 24 h cells that occupied the biomaterial surface displayed the morphology and cytoskeleton pattern similar to the controls. Cells grown on nanocomposite coated surfaces had a higher proliferation rate than their counterparts grown on Ti coated with HA alone, indicating that maleic polyelectrolyte improved surface bio-adhesive characteristics. The capacity to induce cell attachment, spreading and proliferation demonstrated the potential of Ti coated with HA-polymer nanocomposites to be used as scaffolds in dental or orthopedic implantology.

Calcium sulfate precipitation in the presence of water-soluble polymers

The effect of four different polymers on the precipitation of calcium sulfate was investigated in the present work. The degree of inhibition was estimated from measurements of the calcium ion activity and from specific solution conductivity measurements in the supersaturated solutions during the course of the precipitation process. The effects of polyacrylic acid (PAA, three different polymers with average molecular weight 2000, 50,000, and 240,000, respectively) and of a co-polymer of PAA with polystyrene sulfonic acid (PSA, average molecular weight<20,000) were investigated with respect to their effect on the kinetics of spontaneous precipitation of calcium sulfate salts. The results of the kinetics experiments suggested that the spontaneous precipitation from supersaturated calcium sulfate solutions at 25 degrees C yielded exclusively calcium sulfate dihydrate (gypsum) both in the absence and in the presence of the polymeric additives. The induction times, preceding the formation of the solid increased in all cases in the presence of the polymeric additives. Polymer concentrations as low as 2.0 ppm increased induction time from practically zero to 10 min. The rates of precipitation were reduced according to the solutions content in the polymers added and precipitation was completely suppressed in the presence of 6.0 ppm of the polymers tested, depending on their molecular weight. The lower the molecular weight of PAA, the more efficient was the threshold inhibition and the stronger the reduction of the rates of spontaneous precipitation. PSA yielded the poorest inhibition efficiency in comparison with the PAA, possibly because of the relatively lower affinity of the sulfonate groups for the calcium ions of the surface of the solid forming. The kinetics results analysis assuming Langmuir-type adsorption of the polymeric molecules on the growing supercritical gypsum nuclei showed different affinity for the polymers tested in agreement with the respective inhibition efficiency, in the order: PAA1>PAA2>PSA>PAA3. The presence of the polymers in the supersaturated solutions resulted in modification of the precipitated gypsum crystals morphology.

An interfacial energy mechanism for the complete inhibition of crystal growth by inhibitor adsorption

We present a unified model for complete crystal-growth inhibition based on the thermodynamics of interfaces. The premise for our model is that the adsorption of inhibitor leads to a reduction in interfacial tension or edge energy for the crystal surface or step, respectively. In our formulation, the work to add a layer or grow a step increases due to the difference in interfacial tensions or edge energies for surfaces with and without an adsorbed inhibitor. For a large enough difference in interfacial tensions or edge energies, complete inhibition of growth is realized when the total work does not decrease as more crystals are formed. We demonstrate that our model can provide a theoretical description of critical subcooling data for ice with antifreeze proteins and glycoproteins, critical subcooling data for hydrates and ionic crystals, and critical supersaturation data for various crystal systems.

Ecologically benign polymers: the case of maleic polyelectrolytes

The paper discusses a series of results that evidence the favorable effect of maleic polyelectrolytes in different fields in which a protective action of the environment is attained: (i) the exploitation of geothermal water, which is a cleaner source of energy; (ii) the improvement or preservation of the structure of agricultural soils; (iii) the substitution of phosphates in detergents; and (iv) the reduction of chromium load of effluents from tanning plants.

Calcium oxalate crystals in tomato and tobacco plants: morphology and in vitro interactions of crystal-associated macromolecules

Plants form calcium oxalate crystals with unique morphologies under well-controlled conditions. We studied the morphology of single calcium oxalate monohydrate (whewellite) crystals extracted from tomato and tobacco leaves. These crystals have a pseudotetrahedral shape. We identified the (101), (101) or (102), (110), and (hk0) faces as stable faces. The morphology is chiral with unique handedness. We also show that calcium oxalate monohydrate crystals isolated from tomato, tobacco, and bougainvillea leaves contain macromolecules rich in Gly, Glx, and Ser. Crystal-associated macromolecules extracted from tomato and tobacco influence the morphology of calcium oxalate monohydrate crystals grown in vitro, promoting preferential development of the [120] faces. Furthermore, crystal-associated macromolecules from tobacco promote nucleation of calcium oxalate monohydrate crystals, whereas model polypeptides do not have any significant effect on nucleation. These results imply an active role of the crystal-associated macromolecules in the formation of pseudotetrahedral shapes in vitro, and these properties may in part be responsible for the unique chiral morphology of the natural pyramidal-shaped crystals.

Effect of experimental hyperoxaluria on renal calcium oxalate monohydrate binding proteins in the rat

OBJECTIVE

To determine the functional role of calcium oxalate binding proteins in the nucleation, aggregation and retention of calcium oxalate crystals under physiological and hyperoxaluric conditions. Materials and methods Hyperoxaluria was induced in rats using 0.75% of ethylene glycol in drinking water. Calcium oxalate binding proteins were isolated and fractionated by cellulose column chromatography. Three major protein peak fractions were obtained (73 kDa in Tris-HCl buffer, 20 kDa in 0.05 mol/L NaCl buffer and 23 kDa in 0.3 mol/L buffer). Oxalate binding and the inhibition of crystal nucleation and aggregation by these fractions were determined.

RESULTS

The adsorption of calcium oxalate monohydrate (COM) was ubiquitous in rat tissues and subcellular organelles, but the percentage adsorption varied; maximum absorption occurred in kidneys and pancreas, with microsomes showing maximal adsorption in the kidney. Hyperoxaluric rat tissues showed a greater percentage adsorption. Microsomes were enriched with the 20 kDa protein, while nuclei contained the 23 kDa protein in higher concentrations. COM-binding proteins derived from hyperoxaluric rat kidney had a greater content of 74 kDa and 23 kDa proteins with increased oxalate-binding activities. In the crystal-growth studies, the 74 kDa protein was a promoter, while the other protein fractions inhibited crystallization. In hyperoxaluria, the crystal-growth promoting activity of the 74 kDa protein was further increased, while the inhibition by the 20 and 23 kDa proteins was decreased. The 74 kDa protein derived from control rats formed single COM crystals in a crystal growth system, while the hyperoxaluric rat fraction induced the aggregation of COM crystals.

CONCLUSION

COM-binding proteins (the 74 and 23 kDa fractions) were expressed more in hyperoxaluric rats. In hyperoxaluria the 74 kDa protein tended to promote crystal nucleation and aggregation, and the 20 and 23 kDa proteins were less inhibitory, which increases the risk of stone formation.

A novel basic protein from human kidney which inhibits calcium oxalate crystal growth

OBJECTIVES

To isolate calcium oxalate-binding proteins from human kidney and characterize the functional properties.

MATERIALS AND METHODS

Calcium oxalate crystals were prepared and allowed to interact at two different pH values with Triton-extracted human kidney homogenate. The proteins in the homogenate were isolated and fractionated on a cellulose column, and purified by high-performance liquid chromatography. The protein with the greatest oxalate binding activity at pH 4.5 was analysed for its amino-acid composition and characterized by Scatchard plot analysis, crystal growth, nucleation and aggregation studies.

RESULTS

Three major protein fractions were eluted when calcium oxalate monohydrate was adsorbed at both pH values (designated as fractions I-III, according to their order of elution). The yield of fraction I and III was increased when adsorbed at an acidic pH. However, only fraction III had maximum oxalate binding activity at pH 4.5. When purified, this protein had maximum oxalate binding activity of approximately 270 pmol/mg protein and a molecular weight of approximately 23 kDa. Amino acid analysis showed that 18% of the total molar proportion was of basic amino acids, e.g. lysine and arginine, while acidic amino acids accounted for only 11%. Both alanine and glycine constituted approximately 41% of the total molar proportion. Modifications to the lysine group abolished oxalate-binding activity of the protein. The protein inhibited crystal growth by 82% at 0.8 micromol/L, while it inhibited the nucleation and aggregation of the crystals by 6% and 28%, respectively, at 49 nmol/L. The inhibition of both nucleation and aggregation was higher at pH 5.7 than at pH 7.4. Significantly, the protein induced the formation of intertwined calcium oxalate dihydrate crystals in a medium known to induce the formation of individual dihydrate crystals.

CONCLUSION

The protein described here is the first reported basic inhibitor of calcium oxalate crystal growth with oxalate-binding activity at pH 4.5 that modulates calcium oxalate crystallization. It is suggested that this protein may play a physiologically significant role in inhibiting stone formation in acidic urine.