The renal lesions of electrolyte imbalance. IV. The intranephronic calculosis of experimental magnesium depletion

Sulfated Undaria pinnatifida Polysaccharide Promotes Endocytosis of Nano-Calcium Oxalate Dihydrate by Repairing Subcellular Organelles in HK-2 Cells

The clinical manifestation of primary hyperoxaluria includes hyperoxaluria and recurrent urinary calculi. In this study, an oxidative damage model was constructed based on oxalate damage to the human renal proximal tubular epithelial cells (HK-2), and a comparative study was carried out on four different sulfated levels of Undaria pinnatifida polysaccharides (UPP0, UPP1, UPP2, and UPP3 with sulfate group [-OSO₃^-] contents of 1.59%, 6.03%, 20.83%, and 36.39%, respectively) on the repair of oxidatively damaged HK-2 cells. The results showed that after repair by UPPs, cell viability was enhanced, healing ability was improved, the intracellular superoxide dismutase level and mitochondrial membrane potential were increased, malondialdehyde, reactive oxygen species, and intracellular Ca²⁺ levels were reduced, cellular autophagy was reduced; lysosomal integrity was improved, and cytoskeleton and cell morphology were restored. The ability of repaired cells to endocytose nano-calcium oxalate dihydrate crystals (nano-COD) was enhanced. The activity of UPPs was closely related to their -OSO₃^- content. A too high or too low -OSO₃^- content was not conducive to polysaccharide activity, and only UPP2 exhibited the best cell repair ability and strongest ability to promote the cell endocytosis of crystals. UPP2 may be used as a potential agent to inhibit CaOx crystal deposition caused by high oxalate concentration.

Cell Protection and Crystal Endocytosis Inhibition by Sulfated Laminaria Polysaccharides Against Nano-COM-Induced Oxidative Damage in Renal Epithelial Cells

Background: The damage to renal tubular epithelial cells is closely related to the formation of kidney stones. At present, research on drugs that can protect cells from damage remains limited. Methods: This study aims to explore the protective effects of four different sulfate groups (-OSO₃ ^-) of Laminaria polysaccharides (SLPs) on human kidney proximal tubular epithelial (HK-2) cells and determine the difference in the endocytosis of nano-sized calcium oxalate monohydrate (COM) crystals before and after protection. COM with a size of 230 ± 80 nm was used to damage HK-2 cells to establish a damage model. The protection capability of SLPs (LP0, SLP1, SLP2, and SLP3) with -OSO₃ ^- contents of 0.73, 15, 23, and 31%, respectively, against COM crystal damage and the effect of SLPs on the endocytosis of COM crystals were studied. Results: Compared with that of the SLP-unprotected COM-injured group, the cell viability of the SLP-protected group was improved, healing capability was enhanced, cell morphology was restored, production of reactive oxygen species was reduced, mitochondrial membrane potential and lysosome integrity were increased, intracellular Ca²⁺ level and autophagy were decreased, cell mortality was reduced, and internalized COM crystals were lessened. The capability of SLPs to protect cells from damage and inhibit the endocytosis of crystals in cells enhanced with an increase in the -OSO₃ ^- content of SLPs. Conclusions: SLPs with a high -OSO₃ ^- content may become a potential green drug for preventing the formation of kidney stones.

Comparison of the adhesion of calcium oxalate monohydrate to HK-2 cells before and after repair using tea polysaccharides

Background: Kidney stone formation is closely related to renal epithelial cell damage and the adhesion of calcium oxalate crystals to cells. Methods: In this research, the adhesion of human kidney proximal tubular epithelial cells (HK-2) to calcium oxalate monohydrate crystals with a size of approximately 100 nm was studied. In addition, the inhibition of crystal adhesion by four tea polysaccharides (TPS0, TPS1, TPS2, and TPS3) with the molecular weights of 10.88, 8.16, 4.82, and 2.31 kDa, respectively were compared. Results: When oxalic acid-damaged HK-2 cells were repaired, cell viability increased. By contrast, reactive oxygen species level, phosphatidylserine eversion, and osteopontin expression decreased, thus indicating that tea polysaccharides have a repairing effect on damaged HK-2 cells. Moreover, after repairing the damaged cells, the amount of adherent crystals was reduced. The repair effect of tea polysaccharides is closely related to molecular weight, and TPS2 with the moderate molecular weight displayed the best repair effect. Conclusion: These results suggest that tea polysaccharides, especially TPS2, may inhibit the formation and recurrence of calcium oxalate kidney stones.

Architecture-Guided Fluid Flow Directs Renal Biomineralization

Nephrocalcinosis often begins on a calcium phosphate deposit, at the tip of the medullo-papillary complex (MPC) known as Randall’s plaque (RP). Contextualizing proximally observed biominerals within the MPC has led us to postulate a mechanobiological switch that can trigger interstitial biomineralization at the MPC tip, remote from the intratubular biominerals. Micro X-ray computed tomography scans of human MPCs correlated with transmission and scanning electron micrographs, and X-ray energy dispersive spectrometry demonstrated novel findings about anatomically-specific biominerals. An abundance of proximal intratubular biominerals were associated with emergence of distal interstitial RP. The fundamental architecture of the MPC and mineral densities at the proximal and distal locations of the MPC differed markedly. A predominance of plate-like minerals or radially oriented plate-like crystallites within spheroidal minerals in the proximal intratubular locations, and core-shell type crystallites within spheroidal minerals in distal interstitial locations were observed. Based on the MPC anatomic location of structure-specific biominerals, a biological switch within the mineral-free zone occurring between the proximal and distal locations is postulated. The “on” and “off” switch is dependent on changes in the pressure differential resulting from changes in tubule diameters; the “Venturi effect” changes the “circumferential strain” and culminates in interstitial crystal deposits in the distal tubule wall in response to proximal tubular obstruction. These distal interstitial mineralizations can emerge into the collecting system of the kidney linking nephrocalcinosis with nephrolithiasis.

Nephrolithiasis in free-ranging North American river otter (Lontra canadensis) in North Carolina, USA

The North American river otter (Lontra canadensis) serves as an indicator species for environmental monitoring, is prized as a valuable furbearer, and is a popular display animal in zoologic collections. Nephrolithiasis has been reported as a frequent problem in other free-ranging and captive otter species but is rarely reported in North American river otters. In this study, we compared the prevalence of nephrolithiasis diagnosed using routine gross pathologic examination techniques with the use of computed tomography (CT) of excised kidneys. We also evaluated whether otter nephroliths could be accurately classified by their CT densities, and we examined the renal tissue uric acid concentrations in free-ranging otters in North Carolina, USA. Kidneys were collected from carcasses of legally trapped, free-ranging animals. Nephroliths were observed in 16.2% of the individuals (n = 229). Associations were found between age and nephrolith status and between capture location and nephrolith status (P = 0.026 and < 0.001, respectively). Computed tomography Hounsfield unit density measurements were not useful in determining nephrolith chemical composition in this study. Renal tissue uric acid concentrations were similar across genders, age groups, and stone status. The chemical composition of the nephroliths was determined by scanning electron microscopy-energy dispersive X-ray spectroscopy to be calcium phosphate in the carbonate form.

The tubular epithelium in the initiation and course of intratubular nephrocalcinosis

Intratubular nephrocalcinosis is defined as the histological observation of calcium oxalate and/or calcium phosphate deposits retained within the lumen of the renal tubules. As the tubular epithelium is the primary interaction partner of crystals formed in the tubular fluid, the role of the epithelial cells in nephrocalcinosis has been investigated intensively. This review summarizes our current understanding on how the tubular epithelium mechanistically appears to be involved both in the initiation and in the course of nephrocalcinosis, with emphasis on in vivo observations.

The influence of the parathyroid glands on the hypercalcemia of experimental magnesium depletion in the rat

Magnesium-deficient rats develop significant hypercalcemia, hypophosphatemia, and hyperphosphaturia. These changes suggest a state of hyperparathyroidism. This study examines the regulation of parathyroid gland activity in magnesium-deficient rats. Magnesium deficiency was induced in intact and chronically parathyroidectomized animals by feeding them a diet free of this cation. Control animals were pair fed and treated identically except for the inclusion of magnesium in their gavage solution.Magnesium-deficient rats with intact parathyroid glands developed significant hypercalcemia and hypophosphatemia. In addition, the concentration of ionic calcium in plasma was significantly elevated. In contrast, magnesium-deficient parathyroidectomized animals did not have a higher level of calcium in plasma than their nondeficient controls; they developed a decreased concentration of ionic calcium in the absence of a difference in the concentration of phosphate in plasma when compared with appropriate controls. The increased urinary excretion of phosphate was independent of the parathyriod status of the animals.It can be concluded that the hypercalcemia and hypophosphatemia of magnesium deficiency demands parathyroid gland activity and that the regulation of this activity is modified in the magnesium-deficient state to permit the maintenance of an elevated concentration of ionic calcium in plasma. Additional explanations must be found for the hyperphosphaturia.

Role of scanning electron microscopy in identifying drugs used in medical practice

Several plant preparations are administered for treatment of stone disease without scientific basis. This paper presents the results of in vitro and animal experimental studies using scanning electron microscopy (SEM) in the identification of the therapeutic properties of trial drugs in medicine. In the first set of the study, urinary crystals namely calcium oxalate monohydrate and calcium oxalate dehydrate were grown in six sets of Hane's tubes in silica gel medium. Trial drugs namely scoparia dulcis Lynn, musa sapiens and dolicos biflorus were incorporated in the gel medium to identify the dopant effect of the trial drugs on the size and extent of crystal column growth. The changes in morphology of crystals were studied using SEM. In the second set, six male Wistar rats each were calculogenised by administering sodium oxalate and ethylene glycol and diabetised using streptozotocin. The SEM changes of calculogenisation were studied. The rats were administered trial drugs before calculogenisation or after. The kidneys of the rats studied under the scanning electron microscope showed changes in tissue morphology and crystal deposition produced by calculogenisation and alterations produced by addition of trial drugs. The trial drugs produced changes in the pattern of crystal growth and in the crystal morphology of both calcium oxalate monohydrate and calcium oxalate dihydrate grown in vitro. Elemental distribution analysis showed that the crystal purity was not altered by the trial drugs. Scoparia dulcis Lynn was found to be the most effective anticalculogenic agent. Musa sapiens and dolicos biflorus were found to have no significant effect in inhibiting crystal growth. The kidneys of rats on calculogenisation showed different grades of crystals in the glomerulus and interstitial tissues, extrusion of the crystals into the tubular lumen, collodisation and tissue inflammatory cell infiltration. Scoparia dulcis Lynn exhibited maximum protector effect against the changes of calculogenisation. Musa sapiens and dolicos biflorus had only minimal effect in preventing crystal deposition, inflammatory cell infiltration and other changes of calculogenisation. SEM was found to be effective in assessing the effect of drugs on crystal growth morphology and tissue histology.

Animal models of kidney stone formation: an analysis

Calcific kidney stones in both humans and mildly hyperoxaluric rats are located on renal papillary surfaces and consist of an organic matrix and crystals of calcium oxalate and/or calcium phosphate. The matrix is intimately associated with the crystals and contains substances that can promote as well as inhibit calcification. Osteopontin, Tamm-Horsfall protein, bikunin, and prothrombin fragment 1 have been identified in matrices of both human and rat stones. Hyperoxaluria can provoke calcium oxalate nephrolithiasis in both humans and rats. Kidney-stone-forming rats are hypomagnesuric and hypocitraturic during nephrolithiasis. Human stone formers may have the same disorders. Males of both species are prone to develop calcium oxalate nephrolithiasis, whereas females tend to form calcium phosphate stones. Oxalate metabolism is considered to be almost identical between rats and humans. Thus, there are many similarities between experimental nephrolithiasis induced in rats and human kidney-stone formation, and a rat model of calcium oxalate nephrolithiasis can be used to investigate the mechanisms involved in human kidney stone formation.

Calcium oxalate nephrolithiasis, a free or fixed particle disease

The chances of stone formation occurring through a free particle mechanism were calculated using the approach of Finlayson and Reid [1]. For these calculations we used new data on nephron dimensions, supersaturation and crystal growth rates in urine, and also incorporated the size increasing effect of crystal agglomeration. The calculations were performed assuming different levels of oxalate excretion, simulating the diurnal variation and acute hyperoxaluria following a dietary load. In addition urinary flow conditions were varied according to changes in daily urinary volume. It is shown that during the normal transit time of urine through the nephron, particles can obtain a size big enough to be retained in the nephron. This is mainly due to the size-increasing effect of the agglomeration process. The precipitable amount of oxalate present is not limiting for the maximum attainable particle size. However, acute increases in oxalate excretion do pose a risk because supersaturation is reached earlier in the nephron and consequently the crystal particles are allowed more time to increase in size. In conclusion, the present calculations demonstrate that during the normal transit time through the kidney, crystalline particles can be formed which are large enough to be retained because of their size and thus form the nidus of a stone. The highest risk is encountered at the end of those collecting ducts where crystals formed in nephrons with a long loop of Henle meet and agglomerate.

Multielement analysis of kidney tissue with renal calculi

Tissue distribution and concentration gradients of macro- and micro-elements in the papilla, medulla, and cortex of human kidney with renal calculi were measured with spectrometer. An uninvolved portion of the hypernephroma kidney was used as control. Cadmium (Cd), cobalt (Co), and molybdenum (Mo) were least in amount in renal papilla as compared with the cortex and medulla in renal stone kidney. Overall there was less Mo in stone kidney tissue, and also significantly less when compared with that of control renal papilla. Considering the reported fact that Mo was found in high concentrations in urinary tract stones and our data that Mo was less in stone kidney, it is speculated that Mo may play some unexplained but significant role in certain stage(s) of the stone formation.

The evaluation of urinary protein patterns in a stone-forming animal model using two-dimensional polyacrylamide gel electrophoresis

The exact role of urinary proteins in kidney stone formation remains an area of controversy. Some investigators believe that urinary proteins are selectively incorporated within urinary calculi and as such have an active role in stone formation. Other investigators believe that urinary proteins are nonspecifically adsorbed into urinary crystals and thus have only a passive role in stone formation. In the current investigation a previously described stone-forming animal model (hyperoxaluric rat) was utilized along with an animal model for renal tubular injury (gentamicin nephrotoxicity) in an effort to clarify the role of urinary proteins in kidney stone formation. Urine specimens were collected before and after the induction of stone formation and after the induction of renal tubular injury. The purified proteins from each urine specimen were separated in two dimensions by electrophoresis resulting in a characteristic "map" of protein spots for each urine specimen. All animals in the stone-forming group had pathologic evidence of early stone formation (diffuse intranephronic calculosis). Early stone formation was consistently associated with a reduction in the excretion of low molecular weight urinary proteins (30,000 dalton and less than 20,000 dalton ranges). Alcian blue staining confirmed the presence of matrix within clumps of intranephronic calcium oxalate crystals. Renal tubular injury was associated with an increase in the excretion of low molecular weight proteins (approximate 20,000 dalton range) consistent with classical tubular proteinuria. These results suggest that low molecular weight urinary proteins are selectively incorporated within the crystalline structure of the stone early during its formation.

An investigation into the role of ascorbic acid in renal calculogenesis in albino rats

Neither stone nor calcium oxalate crystal deposition was observed in the kidneys of rats after oral ingestion of 60 mg. L-ascorbic acid daily for three months, although urinary excretion of stone inhibitors (magnesium and citrate) was decreased and oxalate increased. The highly acidic pH of urine and reduced calcium excretion might have prevented their deposition.

Kidney function in rats with corticomedullary nephrocalcinosis: effects of alterations in dietary calcium and magnesium

Single-nephron and whole-kidney function were studied in female rats with corticomedullary nephrocalcinosis, and in animals where the lesion had been prevented either by a dietary magnesium supplement or by using a diet with a calcium:phosphorus ratio in excess of 1. At the single-nephron level, rats with nephrocalcinosis had prolonged tubular fluid transit times. Proximal transit time was 19.42 +/- 1.98 (mean +/- S.E. of mean) vs. 11.58 +/- 0.19 s for controls; distal transit time was 62.64 +/- 9.16 vs. 31.50 +/- 1.03 s for controls. Although single-nephron function is altered in nephrocalcinosis, data obtained from rats in metabolism cages indicate that whole-kidney function is largely unaffected by the lesion.

Etiopathogenesis, clinical manifestations, and management of canine calcium oxalate urolithiasis

Calcium oxalate uroliths are commonly called metabolic uroliths because they are sequelae of a variety of metabolic abnormalities that alter the composition of body fluids and urine. Factors incriminated in the etiopathogenesis of calcium oxalate urolithiasis include hypercalciuria, hyperoxaluria, and hyperuricosuria. The predominant type of calcium oxalate urolith encountered in dogs is the monohydrate form; however, the dihydrate form may also occur. Male dogs have been more frequently affected than female dogs. Medical therapy should be formulated with the goal of reducing urine concentration of calculogenic substances.

Renal papillary changes in patient with calcium oxalate lithiasis

We report the case of a white woman with bilateral renal calculi that were removed by bilateral nephrolithotomies. The morphology of renal tubular stones and the changes in papillary tissue were studied by light microscopy and scanning and transmission electron microscopy. The stones were made of calcium oxalate and were intratubular. Large calcium phosphate deposits were present in the interstitium. There was a marked interstitial fibrosis and tubular epithelial hyperplasia.

Effects of magnesium deficiency on intratubular calcium oxalate formation and crystalluria in hyperoxaluric rats

Previous studies have shown that magnesium deficiency accelerates renal tubular calcium oxalate monohydrate deposition in rats on chronic hyperoxaluric, lithogenic protocols. The present study was conducted to investigate the effect of magnesium deficiency on intratubular calcium oxalate formation in rats from the 1st day of administration of a hyperoxaluric agent. The objectives were to delineate early ultrastructural features of the formation, mechanisms of retention, and development of renal tubular crystal deposits and to characterize the crystalluria in rats on the hyperoxaluric/hypomagnesuric protocol. Intratubular calcium oxalate monohydrate deposits were found in magnesium deficient rats after only 24 hours of ad libitum administration of 1 per cent ethylene glycol drinking water. Animals on regular food diet did not display renal tubular deposition after 11 days of ethylene glycol administration. Strand- and sheet-like organic material emanating from the luminal wall of the tubules was adherent to the crystals, thereby serving to immobilize them within the tubule. Calcium oxalate monohydrate crystals predominated in the urines of hyperoxaluric/hypomagnesuric animals with intratubular deposits while dihydrate crystals were the primary constituent of urines from rats administered ethylene glycol alone (no intratubular deposition). The results support the supposition that under certain conditions magnesium deficiency is a significant risk factor for intrarenal calcium oxalate deposition and stone formation. Furthermore the identification of calcium oxalate monohydrate crystalluria may be an important indicator of the propensity toward intranephronic calcium oxalate formation and urolithiasis.

Calcium and oxalate concentrations in human renal tissue: the key to the pathogenesis of stone formation?

On the basis of what we know about urinary supersaturation and particle growth inhibitors stone formation is unlikely to start from free crystalluric particles in the renal tubule. Therefore, the object of this study is to report data on the intrarenal distribution of calcium and oxalate in man and to examine a possible relationship between calcium and oxalate concentrations in the renal tissue and stone formation. Fresh human renal tissue was obtained at operation from 7 subjects. The calcium concentrations in the papilla, medulla and cortex were measured by atomic absorption spectrophotometry. A radioenzymatic procedure was used to determine the corresponding oxalate concentrations. Significantly higher concentrations of calcium and oxalate were observed in the papilla compared to the medulla. The medulla, in turn, contained higher concentrations than the cortex. Calcium and oxalate concentrations were 6 and 25 times higher in the normal papilla than in the urine, respectively. The ion product of calcium oxalate concentrations in the human renal tissue have not been investigated, although the frequent finding of calcification in the renal papilla suggests that they may exist. The observed intrarenal calcium and oxalate concentration gradients seem to be a significant mechanism in the pathogenesis of papillary calcification and a strong indication for renal stone formation to start from fixed crystalluric particles in the papilla.

The effect of magnesium and fluoride on nephrocalcinosis and aortic calcification in rats given high sucrose diets with added phospnates

The study was conducted to observe in rats the possible modification of ectopic calcification by magnesium-orthophosphate-fluoride combinations, used as additives of diet for reduction of the cariogenicity of the sucrose. In rats, fed low magnesium diets, extra dietary orthophosphate (2%) considerably elevated the calcification of kidneys. Further additions of magnesium and fluoride partially reduced this adverse effect of phosphate. While the calcium content of the aorta in rats, fed low magnesium-high phosphate diet, was considerably elevated, the further addition of magnesium (40 ppm) partially reduced the calcifying effect of phosphate in aorta. Fluoride (15 ppm) together with magnesium (40 ppm) completely reduced it. The appearance of renal calculi caused by a low magnesium diet or by extra phosphate were similar according to light and electron microscopy except for the larger size in the latter case and occasional extratubular calculi found in groups with high phosphate-low magnesium and high phosphate with added magnesium diets.

Hypomagnesemia due to renal disease of unknown etiology

A young man, investigated because of tetanic convulsions and arthritic pains, was shown to have hypomagnesemia, hypermagnesuria, hypokalemia, hypercalciuria, progressive nephrocalcinosis and chondrocalcinosis. In this syndrome, renal function was normal except for the abnormal excretion of electrolytes. Renal sodium conservation was normal. Light and electron microscopic studies of renal biopsy specimens showed the presence of several abnormal tubules. Immunofluorescent staining showed deposits of immunoglobulins in the glomeruli and tubules. Magnesium therapy was started under balance study conditions and resulted in decreased calciuria and complete remission of subjective symptoms. The progression of nephrocalcinosis was halted, and there was some decrease in the intra-articular calcium deposits after two years of continuous oral magnesium therapy. The administration of spironolactone decreased urinary magnesium but did not normalize it, whereas triamterene administration was without effect in this respect. The results of the morphologic and electrolyte balance studies are discussed. The patient was found to exhibit several features which have not been described before in connection with hypomagnesemia of unknown origin.

The site of calcification in the human renal papilla

In a study of kidneys obtained from adult human subjects at necropsy, the specificity and sensitivity of the alizarin red S method for detecting calcification is confirmed.

A survey of the relevant literature indicates that, while calcification is frequently found in the human renal papilla at necropsy, conflicting opinions have been expressed regarding its anatomical site. In the present study of 62 adult human kidneys, in which specific renal disease had been excluded, papillary calcification was present in 43 (69 per cent). A detailed histological study of the papilla, using thin and thick sections, demonstrates the predominant site of calcification to be in the walls of the long loops of Henle, where it is closely related to the basement membrane.

The nature of papillary calcification and its possible relationship to the physiology of the renal medulla are briefly discussed. The question is raised as to the possible part played by the loops of Henle in the genesis of renal calculi.