Search

Pathological calcifications may consist of calcium oxalate (CaOx), hydroxyapatite (HAP), and brushite (BRU). The objective of this study was to evaluate the effect of phytate (inositol hexakisphosphate, InsP6), InsP6 hydrolysates, and individual lower InsPs (InsP5, InsP4, InsP3, and InsP2) on the crystallization of CaOx, HAP and BRU in artificial urine. All of the lower InsPs seem to inhibit the crystallization of calcium salts in biological fluids, although our in vitro results showed that InsP6 and InsP5 were stronger inhibitors of CaOx crystallization, and InsP5 and InsP4 were stronger inhibitors of BRU crystallization. For the specific in vitro experimental conditions we examined, the InsPs had very weak effects on HAP crystallization, although it is likely that a different mechanism is responsible for HAP crystallization in vivo. For example, calciprotein particles seem to have an important role in the formation of cardiovascular calcifications in vivo. The experimental conditions that we examined partially reproduced the in vivo conditions of CaOx and BRU crystallization, but not the in vivo conditions of HAP crystallization.

Phytate has been classified as an anti-nutrient, but there are no adverse effects from the consumption of a balanced diet with 1 to 2 g of daily phytate (inositol-hexaphosphate, InsP6) as a calcium magnesium salt, the form naturally present in grains. Furthermore, recent research has shown that phytate consumption may prevent pathological calcifications, such as kidney stones and cardiovascular calcifications. However, many endogenous and exogenous enzymes can hydrolyze phytate to lower inositol phosphates (InsPs) that also have biological activity. We performed a controlled hydrolysis of phytate and identified the products (InsPs) using tandem mass spectrometry (MS/MS). The total level of all InsPs was measured using a non-specific methodology. In addition, we evaluated the effects of the InsP6 hydrolysates on calcium oxalate crystallization using scanning electron microscopy and measuring the time needed for the induction of crystallization. Our results indicate that InsP6 and its hydrolysis products functioned as effective inhibitors of calcium oxalate crystallization. Thus, even though InsP6 is hydrolyzed after consumption, the enzymatic products also have the potential to reduce pathological calcifications. Finally, although it is useful to measure the overall level of InsPs in biological fluids, such as urine, there is a need to develop simple analytical methods to quantify the level of individual InsPs.

Background: The likelihood of a Randall's plug composed of calcium oxalate monohydrate (COM) forming by the free particle mechanism in a model of kidney with a structure recently described by Robertson was examined at the most favourable conditions for the considered mechanism., Methods: The Robertson model of the kidney is used in the following development. The classical theory of crystallization was used for calculations., Results: Initial COM nuclei were assumed to form at the beginning of the ascending loop of Henle where the supersaturation with respect to COM has been shown to reach the threshold level for spontaneous nucleation. Nucleation proceeds by a heterogeneous mechanism. The formed particles are transported in the nephron by a laminar flow of liquid with a parabolic velocity profile. Particles travel with a velocity dependent on their position in the cross-section of the nephron assumed to be straight tubule with smooth walls and without any sharp bends and kinks. These particles move faster with time as they grow as a result of being surrounded by the supersaturated liquid. Individual COM particles (crystals) can reach maximum diameter of 5.2 × 10 -6  m, i.e. 5.2 μm, at the opening of the CD and would thus always be washed out of the CD into the calyx regardless of the orientation of the CD. Agglomeration of COM crystals forms a fractal object with an apparent density lower than the density of solid COM. The agglomerate that can block the beginning of the CD is composed of more crystals than are available even during crystaluria. Moreover the settling velocity of agglomerate blocking the opening of the CD is lower than the liquid flow and thus such agglomerate would be washed out even from upward-draining CD., Conclusions: The free particle mechanism may be responsible for the formation of a Randall's plug composed by COM only in specific infrequent cases such as an abnormal structure of kidney. Majority of incidences of Randall's plug development by COM are caused by mechanism different from the free particle mechanism.

Purpose: The main aim of the current study was to evaluate the effectiveness of mixtures of magnesium, citrate and phytate as calcium oxalate crystallization inhibitors., Materials and Methods: A turbidimetric assay in synthetic urine was performed to obtain induction times for calcium oxalate crystallization in the absence and presence of different mixtures of inhibitors. The morphology of calcium oxalate crystals in the absence or presence of inhibitors and mixtures of the inhibitors was evaluated in 2 crystallization experiments at low and high calcium oxalate supersaturation. The crystals formed were examined using scanning electron microscopy., Results: Examination of crystallization induction times revealed clear inhibitory effects of magnesium, citrate and phytate on calcium oxalate crystallization, supporting usefulness in the treatment and prevention of calcium oxalate nephrolithiasis. Significant synergistic effects between magnesium and phytate were observed. Scanning electron microscopy images revealed that phytate is a powerful crystal growth inhibitor of calcium oxalate, totally preventing the formation of trihydrate and monohydrate. In addition to crystallization inhibition capacity, citrate and magnesium avoided calcium oxalate crystallization by decreasing its supersaturation., Conclusions: The synergistic effect between magnesium and phytate on calcium oxalate crystallization suggests that a combination of these 2 compounds may be highly useful as antilithiasis therapy., (Copyright © 2015 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.)

Calcium oxalate monohydrate (COM) papillary calculi can be initiated by subepithelial calcification of the renal papillae. Hydroxyapatite disruption of the papillary epithelial layer can become the nidus of a COM papillary calculus. This study evaluated the causes of papillary tissue calcifications in 60 patients with calcium oxalate lithiasis, 30 with COM papillary and 30 with calcium oxalate dihydrate (COD) calculi. Urinary redox potential was higher in the COM than the COD group, suggesting that the former is more deficient in antioxidants due to increased oxidative stress. Urinary calcium was significantly higher in the COD group, whereas urinary oxalate was significantly higher in the COM group, suggesting a greater degree of oxidative injury of renal cells. Evaluations of their diets showed that both groups consumed low amounts of phytate-rich products. Of chronic diseases possibly associated with urolithiasis, only the prevalence of gastroduodenal ulcer differed significantly, being higher in the COM group and suggesting that epithelial lesions are common to gastroduodenal ulcers and COM papillary renal stones. Occupational exposure to cytotoxic products occurred in 47 % of the COM and 27 % of the COD group, but this difference was not statistically significant. These findings indicate that oxidative stress is associated with injury to papillary tissue and that this is the origin of intrapapillary calcifications. The continuation of this process is due to modulators and/or deficiencies in inhibitors of crystallization. Identifying and eliminating the causes of injury may prevent recurrent episodes in patients with papillary COM calculi.

Most renal calculi can be classified using well-established criteria in a manner that reflects both composition and fine structure under specific pathophysiological conditions. However, when a large patient population is considered, rare renal calculi invariably appear, some of which have never been classified; careful study is required to establish stone etiology in such cases. The patient in the present case report formed two types of calculi. One was attached on the wall of the renal pelvis near the ureter and part of the calculus was embedded inside pelvic renal tissue. The calculus developed on an ossified calcification located in the pelvis tissue. Current knowledge on the development of calcification in soft tissues suggests a pre-existing injury as an inducer of its development. A mechanism of calculus formation is proposed. The second stone was a typical jack-stone calculus., (© 2011 The Japanese Urological Association.)

Objectives: Subepithelial hydroxyapatite calcification of renal papilla is thought to be involved in the formation of calcium oxalate monohydrate (COM) papillary calculi. To assess the mechanism of formation, we sought to correlate the fine structure of papillary renal calculi with specific pathophysiologic conditions and urinary alterations., Methods: The study included 831 COM papillary renal calculi with established fine inner structures. A total of 24 patients with chronic stone formation were randomly selected, and their urine was collected and analyzed. The case history and lifestyle habits of these patients were obtained., Results: The 831 papillary calculi could be classified into 1 of 4 main groups. Type I included small calculi in which COM columnar crystals begin to develop in the concave zone in close contact with papillary tissue. Type II calculi contained a hydroxyapatite core located in or near the concave zone. Type III consisted of calculi that developed on the tip of the papillae and in the concave zone, containing hydroxyapatite, calcified tissue, and calcified tubules. Type IV consisted of papillary calculi in which the core, which is situated near, but not in, the concave zone, is formed by intergrown COM crystals and organic matter. Many factors, including urinary alterations (eg, hyperoxaluria), associated diseases (eg, hypertension, diabetes), and consumption or exposure to cytotoxic substances (eg, analgesic abuse) were associated with these types of calculi., Conclusions: Our findings have indicated that injury is the first cause of papillary COM calculus formation, with the location of the injury determining the morphology of the resulting calculus., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Background: The use of herbal medicines (medicinal plants or phytotherapy) has recently gained popularity in Europe and the United States. Nevertheless the exact mechanism of the preventive effects of these products is still far to be clearly established, being its knowledge necessary to successfully apply these therapies to avoid stone formation., Methods: The effect of oral lemon juice administration on calcium oxalate urolithiasis was studied in male Wistar rats. Rats were rendered nephrolithic by providing drinking water containing 0.75% ethylene glycol [v/v] (EG) and 2% ammonium chloride [w/v] (AC) for 10 days. In addition to EG/AC treatment, three groups of rats were also gavage-administered solutions containing 100%, 75% or 50% lemon juice [v/v] (6 microl solution/g body weight). Positive control rats were treated with EG/AC but not lemon juice. Negative control rats were provided with normal drinking water, and were administered normal water by gavage. Each group contained 6 rats. After 10 days, serum samples were collected for analysis, the left kidney was removed and assessed for calcium levels using flame spectroscopy, and the right kidney was sectioned for histopathological analysis using light microscopy., Results: Analysis showed that the rats treated with EG/AC alone had higher amounts of calcium in the kidneys compared to negative control rats. This EG/AC-induced increase in kidney calcium levels was inhibited by the administration of lemon juice. Histology showed that rats treated with EG/AC alone had large deposits of calcium oxalate crystals in all parts of the kidney, and that such deposits were not present in rats also treated with either 100% or 75% lemon juice., Conclusion: These data suggest that lemon juice has a protective activity against urolithiasis.

Objective: This paper deals with the mechanism by which uric acid affects calcium oxalate crystallization and the role of crystallization inhibitors in this process., Material and Methods: Pure uric acid crystals and fragments of uric acid renal calculi were used to induce calcium oxalate crystal formation and development. These studies were performed in flow systems, using synthetic urine and similar conditions to those found in real renal situations. The type and size of the developed crystals were evaluated by scanning electron microscopy and the amount of calcium oxalate crystallized was quantitated by means of inductively coupled plasma atomic emission spectroscopy., Results: The presence of uric acid crystals in a flow system provoked calcium oxalate monohydrate (COM) crystallization at a rate of 3.3 microg/h/mg uric acid. When uric acid renal calculi fragments were used, the amount of COM crystallized varied between 0.048 and 0.161 microg/h/mg of renal calculi depending on the porosity of the calculus. At particular concentrations (3.03 microM phytate, 28.75 microM pyrophosphate, 40 mg/l chondroitin sulphate) the crystallization inhibitors assayed produced a maximum decrease of approximately 50% in the amount of COM crystallized on uric acid crystals. Mucin (a glycoprotein) caused only slight effects., Conclusion: Uric acid crystals can clearly induce the development of COM crystals on them through a heterogeneous nucleation process and some crystallization inhibitors can notably delay such a process.

Background: The use of extracorporeal shock wave lithotripsy (ESWL) to treat calcium oxalate dihydrate (COD) renal calculi gives excellent fragmentation results. However, the retention of post-ESWL fragments within the kidney remains an important health problem. This study examined the effect of various urinary conditions and crystallization inhibitors on the regrowth of spontaneously-passed post-ESWL COD calculi fragments., Methods: Post-ESWL COD calculi fragments were incubated in chambers containing synthetic urine varying in pH and calcium concentration: pH = 5.5 normocalciuria (3.75 mM), pH = 5.5 hypercalciuria (6.25 mM), pH = 6.5 normocalciuria (3.75 mM) or pH = 6.5 hypercalciuria (6.25 mM). Fragment growth was evaluated by measuring increases in weight. Fragment growth was standardized by calculating the relative mass increase., Results: Calcium oxalate monohydrate (COM) crystals formed on COD renal calculi fragments under all conditions. Under pH = 5.5 normocalciuria conditions, only COM crystals formed (growth rate = 0.22 +/- 0.04 microg/mg x h). Under pH = 5.5 hypercalciuria and under pH = 6.5 normocalciuria conditions, COM crystals and a small number of new COD crystals formed (growth rate = 0.32 +/- 0.03 microg/mg x h and 0.35 +/- 0.05 microg/mg x h, respectively). Under pH = 6.5 hypercalciuria conditions, large amounts of COD, COM, hydroxyapatite and brushite crystals formed (growth rate = 3.87 +/- 0. 34 microg/mg x h). A study of three crystallization inhibitors demonstrated that phytate completely inhibited fragment growth (2.27 microM at pH = 5.5 and 4.55 microM at pH = 6.5, both under hypercalciuria conditions), while 69.0 microM pyrophosphate caused an 87% reduction in mass under pH = 6.5 hypercalciuria conditions. In contrast, 5.29 mM citrate did not inhibit fragment mass increase under pH = 6.5 hypercalciuria conditions., Conclusion: The growth rate of COD calculi fragments under pH = 6.5 hypercalciuria conditions was approximately ten times that observed under the other three conditions. This observation suggests COD calculi residual fragments in the kidneys together with hypercalciuria and high urinary pH values may be a risk factor for stone growth. The study also showed the effectiveness of specific crystallization inhibitors in slowing calculi fragment growth.

Calcium oxalate monohydrate (COM) renal calculi can be classified into two groups: papillary and nonpapillary. In this paper, a comparative study between etiologic factors of COM papillary and nonpapillary calculi is performed. The study included 40 patients with COM renal calculi. The urine of these individuals was analyzed. Case history, lifestyle, and dietetic habits were obtained. No significant differences between urinary biochemical data of both groups were observed; 50% of COM papillary stone formers and 40% of COM nonpapillary stone formers had urolithiasis family history. A low consumption of phytate-rich products was observed for both groups. A relationship between profession with occupational exposure to cytotoxic products and COM papillary renal lithiasis was detected. The results suggest that COM papillary calculi would be associated to papillary epithelium alterations together with a crystallization inhibitors deficit, whereas COM nonpapillary calculi would be associated to the presence of heterogeneous nucleants and a crystallization inhibitors deficit.

Objectives: The monohydrate calcium oxalate lithiasis (MCO) is divided in two groups depending on the morphologic-crystal structure: papillary (anchorage point on a renal papilla lesion) and cavity (formed in a cavity with low urodynamic capacity). The minimal differences between urinary biochemistry of MCO makers in comparison with healthy population suggests that other factors different than urine biochemistry (professional activity, dietetic habits, systemic diseases) may be related with lithogenesis. The objective of this work is to study such factors, and compare them in both groups of MCO lithiasis (papillary and cavity)., Methods: We study 40 patients with MCO lithiasis (20 patients papillary and 20 patients cavitary). Medical history was performed (family history of lithiasis; associated diseases such as high blood pressure, diabetes, hyperuricemia, hypercholesterolemia, peptic ulcer disease; dietetic survey to evaluate phytate consumption; professions with high-risk of exposure to toxic agents); 24-hour urine biochemical tests, two-hour urine (pH), and serum biochemical profile were performed. Statistical analysis was performed using student's t test and chi-square., Results: There is a high prevalence of family history of renal lithiasis (45%) without differences between groups. There are not differences in urine or blood biochemical tests. There is a low consumption of phytate-containing foods in both groups, without significant differences. There is a trend to a greater exposure to cytotoxic agents in the papillary group (45%) vs. the cavity group (25%). Hypertension and hyperuricemia are more prevalent in the cavity MCO group (alpha = 0.025 and alpha = 0.010, respectively). Peptic ulcer disease is more prevalent in the papillary MCO group (alpha = 2.025). There are no significant differences in prevalence of hypercholesterolemia or diabetes mellitus between groups., Conclusions: Papillary MCO calculi are associated with a deficit of crystallization inhibitors (phytates), and disorders of the epithelium covering the renal papilla (cytotoxic agents exposure, peptic ulcer disease). Cavity MCO calculi are associated with a deficit of crystallization inhibitors (phytates) and a greater amount of heterogeneous nucleants (organic material induced by diseases such as hypertension, hyperuricemia, hyperglycemia, and hypercholesterolemia).

Aim: The presence of uric acid in the beginning zone of different types of 'pure' calcium oxalate renal calculi was evaluated with the aim of establishing the degree of participation of uric acid crystals in the formation of such calculi., Methods: The core or fragment of different types of 'pure' calcium oxalate renal calculi was detached, pulverized and uric acid extracted. Uric acid was determined using a high-performance liquid chromatography/mass spectrometry method., Results: In calcium oxalate monohydrate (COM) papillary calculi with a core constituted by COM crystals and organic matter, 0.030+/-0.007% uric acid was found in the core. In COM papillary calculi with a core constituted by hydroxyapatite, 0.031+/-0.008% uric acid was found in the core. In COM unattached calculi (formed in renal cavities) with the core mainly formed by COM crystals and organic matter, 0.24+/-0.09% uric acid was found in the core. In COM unattached calculi with the core formed by uric acid identifiable by scanning electron microscopy (SEM) coupled to X-ray microanalysis, 20.8+/-7.8% uric acid was found in the core. In calcium oxalate dihydrate (COD) unattached calculi containing little amounts of organic matter, 0.012+/-0.004% uric acid was found. In COD unattached calculi containing little amounts of organic matter and hydroxyapatite, 0.0030+/-0.0004% of uric acid was found., Conclusions: From these results it can be deduced that uric acid can play an important role as inducer (heterogeneous nucleant) of COM unattached calculi with the core formed by uric acid identifiable by SEM coupled to X-ray microanalysis (these calculi constitute the 1.2% of all calculi) and in COM unattached calculi with the core mainly formed by COM crystals and organic matter (these calculi constitute the 10.8% of all calculi).

Urine contains variable amounts of organic matter derived from cell degradation. The cellular detritus is composed by membranous and cytosolic glycoproteins, etc. The aim of this paper was to study the role of organic matter in calcium oxalate crystal development and to evaluate the action of some crystallization inhibitors on this process. Crystallization studies were carried out on urine in stagnant urine as well as under flow conditions, in presence and absence of cellular debris. Low amounts of cellular debris (when batch conditions were used), exhibited some inhibitory activity on heterogeneous nucleation of calcium oxalate monohydrate crystals, probably due to glycoproteins. Increasing amounts of cellular debris, however, promoted the nucleation of calcium oxalate monohydrate crystals. When cellular debris was retained in a cavity with a urine flow, this organic matter effectively induced the development of primary aggregates of calcium oxalate monohydrate crystals (crystallization range 2.8 mg/h per mg of organic matter). Presence of crystallization inhibitors prevented or minimized crystal development. These findings show that cell debris provides the necessary elements for the development of oxalate crystals and that this process can be effectively inhibited by presence of crystallization inhibitors.

Objective: The exact mechanism of renal stone formation is still not totally understood. Thus, the role of crystallization inhibitors at different stages of stone development, the influence of preexisting solid particles and the effects of variations in urine composition require further clarification. The aim of this paper is to clarify some of these questions by studying the regrowth achieved by real spontaneously passed post-extracorporeal shock wave lithotripsy (post-ESWL) fragments of calcium oxalate monohydrate (COM) renal calculi., Material and Methods: An in vitro system was used to study the regrowth of post-ESWL fragments of COM calculi, which was defined as the relative increase in weight of the fragments., Results: It was found that new columnar zones of COM crystals were formed under normal calcium and oxalate urinary conditions and no calcium phosphates were observed, in spite of the urinary pH being >6. The presence of 3.03 microM phytate totally blocked these crystal growth processes. When hypercalciuric urine was used at a pH of 6.5, large brushite crystals and zones totally covered by hydroxyapatite were observed for short periods, and zones containing calcium oxalate dihydrate crystals could be observed for longer periods. In such cases, 9.09 microM phytate totally blocked the growth processes, 69.0 microM pyrophosphate caused a reduction in calculi growth of 93% and 5.35 mM citrate caused no inhibitory effects., Conclusion: The results show that when crystallization inhibitors were absent, the growth of calcium oxalate calculi fragments took place even under normal urine conditions, clearly demonstrating the importance of crystallization inhibitors in avoiding or delaying calculi development.

Objective: To assess the effects of a glycoprotein (mucine) on calcium oxalate crystal development in different conditions and situations, to clarify some of its possible effects., Materials and Methods: Crystallization was assessed using a batch system in presence of mucine suspensions, by kinetic-turbidimetric measurements, and using a flow system in the presence of retained agglomerates of mucine, evaluating the precipitated calcium oxalate., Results: In batch conditions low mucine concentrations (<15 mg/L) inhibited calcium oxalate nucleation and higher concentrations (<250 mg/L) inhibited calcium phosphate nucleation, whereas at high concentrations there was also promotion. The presence of an aggregate of mucine in the flow system provoked calcium oxalate monohydrate crystallization at 0.691 microg/h per mg of mucine. In flow conditions pyrophosphate at 11.5 micromol/L caused a decrease of 84% in the calcium oxalate crystallized on mucine, 1.32 mmol/L of citrate a decrease of a 83%, 20 mg/L of pentosan polysulphate a decrease by 80%, and 7.58 micromol/L phytate totally prevented the crystallization of calcium oxalate on mucine., Conclusion: All substances inhibiting calcium oxalate crystallization with the capacity to interact with calcium ions also have crystallization promoting properties when they are at sufficiently high concentrations, because of their capacity to form agglomerates or the insolubility of their calcium salts.

Objective: It is well known that all renal stones are associated with a high recurrence rate. The aim of this paper is to study the different types of renal calculi recurrence., Material and Methods: The study included 220 patients who had produced two or more renal calculi over a period of <5 years (total 634 calculi). The procedure used to study renal calculi involved appropriate combinations of stereoscopic microscopy with infrared spectrometry and scanning electron microscopy coupled with X-ray microanalysis., Results and Conclusion: Recurrent stone-formers can be classified into two large groups: those who always produce the same type of calculus (the most common type of recurrence was calcium oxalate dihydrate, followed by calcium oxalate monohydrate non-papillary and calcium oxalate monohydrate papillary calculi); and those who produce different types of renal calculi (the most frequent recurrences in this group were the changes calcium oxalate dihydrate-->calcium oxalate dihydrate/hydroxyapatite and calcium oxalate monohydrate-->calcium oxalate dihydrate).

The phytate urinary levels in a group of active calcium oxalate stone formers were studied and compared with those found in healthy people. Urinary phytate was significantly lower for stone formers. If deficit of the capacity to inhibit crystallization of calcium salts is considered an important factor related to calcium stone formation, the excretion of low phytate amounts could be an important risk factor in the development of this type of renal calculi. The influence of dietary phytate on urinary excretion was also studied. Clearly maintenance of a phytate-free diet significantly decreased the urinary excretion of phytate (about 50% after 36 h). This demonstrated the importance of dietary phytate in maintaining adequate urinary levels to permit effective crystallization inhibition of calcium salts and consequently preventing renal stone development.

The effects of free radicals on the development of crystals attached to the living epithelium have been studied using an experimental model that enables close simulation of the conditions prevailing in the kidney. The results obtained clearly demonstrate that free radical-damaged cells produce a favorable environment for crystal development. At low free radical concentrations, crystals develop on calcium-enriched zones, whereas at higher concentrations, crystals develop on areas with a destroyed monolayer of superficial cells. Evaluation of the action of some products with antioxidant action and/or crystallization-inhibitory capacity is also included. Antioxidants, such as ascorbic acid and mannitol, exerted the most remarkable effects in avoiding calcium oxalate crystal development, whereas crystal inhibitors, such as citric acid, did not produce any remarkable reduction in calcium oxalate crystallization. Phytic acid notably decreased calcium oxalate crystal development. The ability of phytic acid to diminish calcium oxalate crystallization must be attributed to the combination of its inhibitory capacity of calcium oxalate crystallization and its preventive antioxidant action.

We have studied the early stages of calcium oxalate monohydrate (COM) crystallization, mainly heterogeneous nucleation, on fixed particles. Experiments were performed using a flow system that closely simulates the human renal conditions related to COM heterogeneous nucleation. The effects of citrate, phytate, aescin and glycyrrhinic acid in the COM heterogeneous nucleation on different solid surfaces as calcium phosphate, a mixture of mucin and calcium phosphate and wax were studied. The presence of citrate at normal urinary concentrations (1.85.10(-3) M) totally inhibited the development of COM crystals only on the most hydrophobic assayed material (wax). Saponins (aescin and glycyrrhinic acid) only exhibited important inhibitory effects of COM crystallization on the hydrophobic wax substrate but in no case the formation of COM crystals was totally prevented. Phytate exerted the most remarkable effects on the heterogeneous nucleation of COM crystals, thus, when it was present at 1.43.10(-7) M, it totally prevented the development of COM crystals on the three assayed solid substrates.

A comparative study between different etiological factors of calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD) is presented. The most frequent alteration in COD urolithiasis was associated with hypercalciuria, whereas in COM urolithiasis was associated with urinary pH. A comparison between COM and COD groups of stone formers that exhibited 1, 2 or 3 alterations was performed. Thus, in individuals with two simultaneous alterations, the association between altered urinary pH and hypomagnesiuria was the most frequent in the COM group, whereas the association between hypercalciuria and altered urinary pH was most frequent in the COD group. In individuals with three simultaneous alterations, the association between hypercalciuria, hyperphosphaturia and hyperuricuria was most frequent in both COM and COD stone formers.

Density and content of mineral constituents were determined for 33 human calcium oxalate monohydrate (hereafter COM) uroliths whose external appearance and inner structure were described in part I and II respectively. Studied stones contained 0.13-0.42 wt.% of struvite, 0.68-4.12 wt.% of hydroxyapatite, 73-96 wt.% of COM and 3-10 wt.% of water unbound in a crystallohydrate 10 to 20 wt.% of calculus mass is not accounted for by chemical analysis. Density of COM calculi varying between 1.67 and 2.06 g cm-3 is not a function of any single stone parameter. Around 30% of stone volume is not occupied by crystalline components. The mulberry stones of sedimentary origin contained higher amount of organic matter than papillar and mulberry stones displaying site of attachment to epithelium.

The inner fine structure of 30 human uroliths composed predominantly of calcium oxalate monohydrate was studied in detail. Each type of stone distinguished on the basis of qualitative parameters, viz. M1, M2, S1 and S2 (see Part I), exhibited a specific and characteristic inner structure different in several well-defined aspects from the other types. The inner structure suggests a sedimentary origin of the M1 type stone whereas the fixed particle origin of the M2, S1 and S2 stones, 3 types of core on which M2, S1 and S2 calculi developed were identified. The A type was represented by a void cavity with walls covered by an organic matter, the B type was formed by loosely arranged COM crystals and the C type was represented by a layer of an organic matter. Clinical observations lend support to the sedimentary origin of the M1 stones.

Shape, colour, surface features and external appearance were determined from 33 human uroliths composed predominantly of calcium oxalate monohydrate (COM). Based on these properties COM renal stones were classified into mulberry (M) and spheroid (S) type, each of which was further divided into two well defined subtypes, M1-fused globules, M2-loose globules, S1-corrugated surface and S2-even surface. This classification indicates that only specific combinations of external characteristics could occur on COM renal uroliths. No apparent correlation between the stone type and respective biochemical urinary data transpired from available information.

Available information relevant to stone genesis on both calcium oxalate monohydrate crystallization and fine inner structure of papillary calculi is reviewed. Integration of attained facts facilitated formulating a feasible mechanism of papillary calculi formation and development. Medical implications of this mechanism are assessed.

The effects on the calcium oxalate urolithiasis urinary risk factors of Herniaria hirsuta L. (Carryophyllaceae) and Agropyron repens L. (Gramineae), in herb infusion form, combined with different diets (standard, high glucidic, high protein) have been studied using Wistar rats. From this study it is deduced that the possible effects of the A. repens infusion can not be assigned to any positive effects on the main urolithiasis risk factors. The tentative antilithiasic effects of the H. hirsuta infusion clearly depends on the diet. Thus, a clear increase in the citraturia was only detected when such infusion was administered with the high protein diet.

A procedure to evaluate the global inhibitory capacity of heterogeneous nucleation for a given urine without any modification of its composition was developed. The procedure is based on the use of flat solid substrates that are submerged in urine. The quantification of the amount of formed crystals on the substrate permits to evaluate the crystallization inhibitory capacity for a whole urine. The proposed method was applied to study the inhibitory capacity of urines belonging to stone-formers and healthy people, before and after the ingestion of a dietary complement containing phytate in order to prove its reliability. A clear increase of the inhibitory capacity of the urine was detected in most cases when the dietary complement was consumed. Moreover, lack of crystallization inhibitory capacity was more frequent in stone-formers than in healthy people.

Objective: To study the initial steps of calcium oxalate monohydrate (COM) stone formation and the influence of the inhibitor substances citrate and phytic acid, using an in vitro model., Materials and Methods: Experiments were performed using a device to simulate renal stone formation in conditions similar to those found in humans., Results: COM crystal formation took place directly on the solid substrate in contact with the urine but no previous formation occurs in the liquid with subsequent attachment. The first COM crystals appeared after 3 h, in the presence of citrate at a physiological concentration of 1.7 x 10(-3) M. A decrease in the total amount of COM was observed during the next 9 h. After 24 h the quantity of COM crystals was the same irrespective of the presence or absence of citrate. In the presence of phytic acid (6 x 10(-3) M) the appearance of the first COM crystals was delayed by > 24 h. At 78 h a few small COM crystals were detected., Conclusion: A fixed solid surface, irrespective of its composition, in contact with normal urine sooner or later develops stone-forming compounds on its surface. The composition of these compounds depends on the supersaturated salts that are present. Under the experimental conditions citrate had only a limited capacity to inhibit COM crystal development. In contrast, phytic acid exhibited a much higher capacity for inhibition even at a considerably lower concentration than that of citric acid.

A simple model to study calcium oxalate monohydrate (COM) crystallization on different substrates is presented and the action of different potential inhibitors is evaluated and discussed. COM heterogeneous nucleation was assayed on solid surfaces as calcium phosphate, mixtures of mucin with calcium phosphate, and wax. In the presence of a non-protected non-renewed solid surface in contact with normal urine, COM crystal formation could be detected at short intervals (3 h). The most active heterogeneous nucleation capacity corresponded to calcium phosphate. In the presence of 10% mucin, owing to the renewal of the surface layer no COM crystal were detected on the pellet's surface. The study of citrate and pentosan polysulphate (a semisynthetic polysaccharide) on COM heterogeneous nucleation demonstrated some important inhibitory effects when concentration increased and time decreased. Maximum effects were selectively manifested on calcium phosphate surfaces. Only phytic acid at adequate concentration exhibited a total inhibitory capacity of COM formation, even during longer intervals (15 h).

A very simple analytical procedure with dimethylmethylene blue as photometric reagent was applied for the evaluation of glycosaminoglycan (GAG) urinary excretions and concentrations in both sexes, calcium oxalate stone formers, and a control group. The GAG concentrations varied significantly in stone formers (males and females) and in the control group; moreover, in some individual cases, a deficit of urinary GAGs was clearly detected. Apart from important inhibitory effects of GAGs on heterogenous calcium oxalate nucleation, the low urinary GAG content could be the cause of a pathological epithelium, favoring stone formation. The dimethylmethylene blue method is recommended as a quick screening procedure to determine a GAG deficit.

A scanning electron microscopy study of the ultrastructure of 18 calcium oxalate monohydrate papillary calculi was performed with the purpose of establishing the main steps in calculus formation. It is concluded that these calculi originate in a "core" located near the central part of the calculus. Significant quantities of organic matter as well as calcium phosphates can be found in the "core" and at the surface of adhesion to the papilla and, in some cases, fibers and calcified tubules can also be found in the contact zone. In no case did this material affect the crystalline structure of the calculi, indicating that its formation follows the calculus genesis. The study of the compact columnar zone revealed that its formation starts in a practically continuous surface formed by organic matter and crystals that surround the core. This layer favors the growth of oriented calcium oxalate monohydrate crystals upon it. Based on these observations, a feasible mechanism of papillary calcium oxalate monohydrate calculus formation is proposed.

A new technique simulating some of the conditions experienced by papillar and caliceal oxalocalcic stones during the early stages of their generation was developed. This technique enables the study of how conditions prevailing at calculogenesis, such as pH, composition of urine and presence of admixtures, influence the rate of formation and development, the crystalline texture and the composition of the concretion formed. Results achieved with this technique demonstrate that: (1) an appropriate substrate always gives rise to a crystalline concretion if it is in contact with supersaturated urine; (2) primary agglomeration plays a significant role in concretion development whereas secondary agglomeration is of minor importance; and (3) citrate and pyrophosphate exert a considerable influence on the shape and composition of particles constituting the concretion.

In this paper a thorough study on the composition and structure of calcium oxalate monohydrate (COM) papillary calculi is presented. In 86.4% of these calculi, small amounts of phosphates were detected and generally located at the calculi core. This demonstrates the importance of phosphates as the heterogeneous nucleus of 'pure' COM calculi. Study of the main biochemical parameters of these patients showed that the most frequent biochemical alteration was associated with hypocitraturia (25%), whereas hypercalciuria and/or hyperoxaluria were detected in very few cases. With respect to the urinary pH values, 70% of the patients presented values lower than 6 and 30% higher than 6. These facts indicate that in a number of cases the formation of phosphates is not the result of persistent high urinary pH values, and the presence of occasional papillary microinfections must be suspected. It is clear that, by avoiding the formation of heterogeneous phosphate nuclei, 'pure' COM calculi would not develop, and consequently therapies for these individuals under these conditions must take this into account.

Fine structure, location and size of the core of 12 calcium oxalate monohydrate (COM) papillar calculi from different 'idiopathic' stone-formers were studied by an optical and scanning electron microscope equipped with the EDAX analytical device. Each individual core exhibited a unique overall structure composed of loosely arranged twined and intergrown crystals of plate-like and/or columnar shape and particles of 'rosette' structure with considerable void space among crystals in some cases or compact structure in others. Crystals were covered by a thin layer or organic material mostly invisible to the microscope. Sometimes debris of organic origin in a core was observed. A substantial amount of organic matrix appeared at the core boundary, often in the form of amorphous plates. The outer striated layer of COM stone consisting of tightly packed columnar crystals originated on this matrix. The stone core was located near the stone surface that was attached to the kidney wall and contained foreign particles that act as heterogeneous nucleants of calcium oxalate crystals.

The possible effects of Zn and Cu in oxalocalcic urolithiasis were investigated. The formation of calcium oxalate crystals in the presence of Zn and Cu demonstrated that their morphology is clearly affected by these ions. Thus, when such ions were present in a number of higher concentrations, a notable increase in the primary aggregation was clearly detected. On the other hand, Zn and Cu urinary levels were determined in groups of stone-formers and healthy people. Zinc urinary concentration was significantly lower for lithiasic than for healthy people and the copper urinary concentration was lower for lithiasic than healthy males, but both female groups had a similar copper urinary concentration. The mentioned differences disappeared when serum levels were considered. These obtained results have been comparatively evaluated with those obtained by other authors. When considering all the commented aspects, it is concluded that no important direct action of zinc and copper on oxalocalcic calculi genesis takes place.

Based on reconsideration of the contemporary knowledge on calcium oxalate urolithiasis a feasible mechanism of calculi generation is suggested. Experimental findings and clinical aspects supporting the suggested mechanism are presented. The ways of urolithiasis treatment and areas of future research are indicated.

The effects on the calcium oxalate urolithiasis urinary risk factors of "Rosa Canina", in herb infusion form, and magnesium chloride have been studied using female Wistar rats under balanced dietary conditions. No significant effects on the volume of liquids drunk or on creatinine, phosphate, and oxalate urinary concentrations and excretions were observed. The herb infusion did not cause any diuretic effect. Calciuria decreased and citraturia increased when taking the herb infusion, and vice versa when taking magnesium chloride. Magnesium chloride decreased the urinary pH value, but this effect was not observed when magnesium chloride was administered with herb infusion. In conclusion, the same beneficial effects of the studied infusion herb on calcium oxalate urolithiasis urinary risk factors can be clearly detected. An interesting fact is that it seems that some possible effects depend on dietary components, thus, i.e., an increase in the urinary pH was only detected when the intake of the herb infusion was studied in a magnesium chloride-supplemented diet.

The development of agglomerated particles of calcium oxalate monohydrate (COM) on the semi-batch precipitation from a synthetic urine carried out at physiological conditions (37 degrees C, pH = 5.5) was studied by optical and electron scanning microscopy. COM agglomerates develop by primary and secondary agglomeration proceeding simultaneously; the latter mechanism is, however, less important than the former. Citrate ions modify slightly the COM crystal shape and inhibit primary agglomeration. Mucin particles serve as a substrate for preferential formation (nucleation) of new COM crystals. The structure of formed agglomerates closely resembles that of a certain type of COM renal calculi. A combination of primary agglomeration of crystals forming stones and nucleation of new crystals on a mucoprotein layer partially covering their surface constitutes the possible mechanism of such stone development. Experimental data support this mechanism.

Formation of agglomerates of calcium oxalate monohydrate (COM) crystals on semi-batch precipitation performed at conditions relevant to urolithiasis (37 degrees C, pH = 6, initial ratio [Ca]/[Ox] = 10), but without any specific admixture, was followed by both optical and electron microscopy. COM crystals formed on precipitation developed into large agglomerates consisting of intergrown crystals by a mechanism of primary agglomeration. Primary agglomeration of COM crystals represents an important mechanism of COM renal calculi growth.

The aim of this work is to evaluate the role and importance of inhibitors and promoters in urolithiasis. Carrying in mind theoretical considerations, we conclude that in urolithogenic processes, inhibitors and promoters could only play a decisive role in the "idiopathic" oxalocalcic urolithiasis. We classify the "idiopathic" oxalocalcic stone-formers into three main groups, considering inhibitory and promoting factors. It is shown that such classification is in good agreement with the clinical results observed in a group of 88 "idiopathic" oxalocalcic stone-formers.

An animal model involving rats fed with different diets (high protein, high carbohydrate, high lipid, high fiber and control balanced diet) was used to evaluate the dietary effects on the main oxalocalcic urolithogenic parameters. It was found that the inhibitory factors that prevent calcium oxalate stone formation (citrate and magnesium) were clearly more favorable in the group of rats fed with a balanced diet. However, factors favouring the heterogeneous calcium phosphate nucleation were also found in the balanced diet. On the other hand, factors facilitating the heterogeneous uric acid nucleation were found in rats treated with high protein, high lipid, high carbohydrate and high fiber diets. In conclusion it seems that the balanced diet appears to be the less lithogenic one.

In urolithogenic processes both, promoters and deficit of inhibitors, play an important role. The inhibitory action of added inhibitors (magnesium, citrate, pyrophosphate and chondroitin sulphate) was investigated using the urine of 72 patients with calcium urolithiasis. It was concluded that the deficit of inhibitors seems to be an important cause of stone formation in idiopathic oxalocalcic urolithiasis. Nevertheless, when that specific heterogeneous nucleation takes place it becomes an important factor and the inhibitor plays a complementary role in calcium oxalate urolithiasis.

The interaction between calcium and glycosaminoglycans (GAGs) was studied using a calcium ion-selective electrode. The Ca-binding capacity of GAGs involved 16% of total calcium in the presence of chondroitin sulphate and 28% in the presence of pentosan polysulphate. The action of GAGs on the nucleation of uric acid and sodium urate was examined and inhibitory effects were observed. The action of uric acid as a heterogeneous nucleant of calcium oxalate was studied, and considerable promotion of the heterogeneous nucleation of calcium oxalate by uric acid was found, which could be inhibited by the action of GAGs. From these summarised in vitro results, we conclude that uric can constitute an important risk factor for calcium oxalate urolithiasis through heterogeneous nucleation and the GAGs can play an important role as preventive agents.

The effects of diet on the formation of calcium oxalate stones were studied in 150-day-old rats by measuring the diuresis, pH, and urinary and blood concentrations of promoting and inhibitory substances. An increase in phosphate (promoting) and magnesium (inhibiting), and a decrease in citrate (inhibiting) and pH were found in the urine of rats fed with a high protein diet. No differences were observed in the plasma concentrations of calcium, magnesium, and phosphate. These results confirm epidemiological and clinical studies in humans that have shown that any diet rich in protein can change the concentrations of these substances in urine.

A study was made of the effects of citrate, pentosan polysulphate (a glycosaminoglycan) and mucin (a mucoprotein) upon crystalline growth and aggregation of calcium oxalate in synthetic urine. It was found that citrate inhibited aggregation. Pentosan polysulphate had no perceptible effect on aggregation but favoured the formation of calcium oxalate dihydrate crystals. Mucin enhanced the formation of large characteristic aggregates and also led to the formation of calcium oxalate dihydrate crystals. Particles of mucin in a solution served as a substrate on which several crystals of calcium oxalate dihydrate were formed by heterogeneous nucleation; the subsequent growth of these crystals resulted in the formation of large agglomerates.

The part played by hyperoxaluria in the formation of calcium oxalate urinary calculi was studied in 153 patients who had each been diagnosed as having calcium oxalate urinary calculi on one or more occasions. Seventy-seven of the patients excreted normal amounts of calcium (less than 6.2 mmol/d), and 76 had hypercalciuria (excretion greater than or equal to 6.2 mmol/d); each group was divided into a further two groups depending on whether the oxalate concentration was above or below 0.16 mmol/l. Pure calcium oxalate stones were more common in patients whose calcium excretion was normal, and mixed calcium oxalate and phosphate stones were more common among hypercalciuric patients. Urinary concentrations/day of magnesium, citrate, and phosphorus were significantly lower in the two groups in which the oxalate concentrations were below 0.16 mmol/l than in a normal control group, and magnesium and phosphorus were significantly lower in the two groups in which oxalate concentrations were less than 0.16 mmol/l than in the two in which they were above that value. The concentration of citrate was also lower, but not significantly so. In addition, the pH of the urine in patients with mixed stones was significantly higher in all groups than when the stones were composed of pure calcium oxalate.

In calcium oxalate urolithiasis, the monohydrate and dihydrate forms can be found. The aim of this paper is to examine a group of patients with calcium oxalate calculi to determine the calcium oxalate form and the possible relationship with calcium and other urinary biochemical parameters. It was found that calcium oxalate monohydrate is more frequent in the normocalciuric group and also is associated with a lack of inhibitory capacity, while a mixed calculus of calcium oxalate and phosphate or calcium oxalate dihydrate can be related with hypercalciuria.

Different mathematical expressions have been proposed in the literature with the aim to reflect the risk of calcium oxalate urolithiasis. Such expressions, as well as a number of new relationships proposed by us, have been evaluated in 76 patients and 34 normal subjects. Stone-formers were divided into two groups: patients with normal calcium and oxalate excretion and patients with hypercalciuria and/or hyperoxaluria. The results obtained were comparatively evaluated. Several formulae gave some acceptable results, but none of them were excellent. This can be explained by the fact that these discrimination indexes more or less reflect supersaturation and/or inhibition deficit, but none of them reflect promoting factors such as heterogeneous nucleation and/or aggregation capacity.