Effect of magnesium on calcium oxalate urolithiasis

Proton pump inhibitors use is associated with a higher prevalence of kidney stones: NHANES 2007-2018

BACKGROUND

Proton pump inhibitors (PPIs) are widely used throughout the world as an effective gastrointestinal drug. Nevertheless, according to the existing literature, PPIs can reduce the excretion of magnesium, calcium and other components in urine, which may promote the formation of kidney stones. We used the National Health and Nutrition Examination Survey (NHANES) database to further investigate the association between the use of PPIs and the prevalence of kidney stones.

METHODS

We performed a cross-sectional analysis using data from 2007 to 2018 NHANES. PPIs use information of 29,910 participants was obtained by using prescription medications in the preceding month, and kidney stones were presented by a standard questionnaire. Multiple regression analysis and stratified analysis were used to estimate the association between PPIs use and kidney stones after an adjustment for potential confounders.

RESULTS

The multiple logistic regression indicated that the PPIs exposure group (P1) had a significantly higher risk of nephrolithiasis than the PPIs non-exposure group (P0) in Model 3 (OR 1.24, 95% CI 1.10-1.39, P < 0.001). The stratified analyses indicated there were significant statistical differences between PPIs use and kidney stones among females (OR 1.36, 95% CI 1.15-1.62, P < 0.001), non-Hispanic whites (OR 1.27, 95% CI 1.09-1.48, P = 0.002), individuals with an education level than 11th grade (OR 1.41, 95% CI 1.13-1.76, P = 0.002) and individuals with an annual family income of $0 to $19,999 (OR 1.32, 95% CI 1.06-1.65, P = 0.014) and $20,000 to $44,999 (OR 1.25, 95% CI 1.02-1.54, P = 0.033) in Model 3.

CONCLUSIONS

Our study revealed that PPIs use is associated with a higher prevalence of kidney stones for the US population, primarily among women, non-Hispanic whites, individuals with low education levels and individuals with low household income levels. Further studies are required to confirm our findings.

Association Between Serum Magnesium and the Prevalence of Kidney Stones: a Cross-sectional Study

Kidney stones, a painful and costly disease, have become a public health problem worldwide. The aim of this study was to evaluate the association between serum magnesium levels and the prevalence of kidney stones in a large population context. This study was conducted in Xiangya Hospital, Central South University in Changsha, Hunan, China, between October 2013 and December 2015. A total of 6228 subjects aged ≥ 18 years old were included. Kidney stones were diagnosed by (1) direct visualisation of stone(s) on the abdominal ultrasound examination, and (2) presence of stone(s) with a diameter ≥ 4 mm. The chemiluminescence method was used to measure the serum magnesium concentration. The association between serum magnesium and the prevalence of kidney stones was evaluated using logistic and spline regression in a cross-sectional study. The prevalence of kidney stones was 6.1% (7.5% in men and 4.2% in women). Compared with the lowest quartile, the crude odds ratio for kidney stones was 0.62 (95% CI 0.46-0.85) for the highest quartile of serum magnesium, and there was an inverse dose-response relationship (P for trend = 0.038). Similar results were observed for men and women separately. The findings were not materially altered by adjustment for potential confounders. In conclusion, subjects with relatively lower levels of serum magnesium, even though within the normal range, were subject to a higher prevalence of kidney stones in a dose-response relationship manner, indicating that magnesium may play a certain role in the prevention or treatment of kidney stones.

Alpha-enolase on apical surface of renal tubular epithelial cells serves as a calcium oxalate crystal receptor

To search for a strategy to prevent kidney stone formation/recurrence, this study addressed the role of α-enolase on apical membrane of renal tubular cells in mediating calcium oxalate monohydrate (COM) crystal adhesion. Its presence on apical membrane and in COM crystal-bound fraction was confirmed by Western blotting and immunofluorescence staining. Pretreating MDCK cells with anti-α-enolase antibody, not isotype-controlled IgG, dramatically reduced cell-crystal adhesion. Immunofluorescence staining also confirmed the direct binding of purified α-enolase to COM crystals at {121} > {100} > {010} crystal faces. Coating COM crystals with urinary proteins diminished the crystal binding capacity to cells and purified α-enolase. Moreover, α-enolase selectively bound to COM, not other crystals. Chemico-protein interactions analysis revealed that α-enolase interacted directly with Ca²⁺ and Mg²⁺. Incubating the cells with Mg²⁺ prior to cell-crystal adhesion assay significantly reduced crystal binding on the cell surface, whereas preincubation with EDTA, a divalent cation chelator, completely abolished Mg²⁺ effect, indicating that COM and Mg²⁺ competitively bind to α-enolase. Taken together, we successfully confirmed the role of α-enolase as a COM crystal receptor to mediate COM crystal adhesion at apical membrane of renal tubular cells. It may also serve as a target for stone prevention by blocking cell-crystal adhesion and stone nidus formation.

Identification of SLC41A3 as a novel player in magnesium homeostasis

Regulation of the body Mg(2+) balance takes place in the distal convoluted tubule (DCT), where transcellular reabsorption determines the final urinary Mg(2+) excretion. The basolateral Mg(2+) extrusion mechanism in the DCT is still unknown, but recent findings suggest that SLC41 proteins contribute to Mg(2+) extrusion. The aim of this study was, therefore, to characterize the functional role of SLC41A3 in Mg(2+) homeostasis using the Slc41a3 knockout (Slc41a3(-/-)) mouse. By quantitative PCR analysis it was shown that Slc41a3 is the only SLC41 isoform with enriched expression in the DCT. Interestingly, serum and urine electrolyte determinations demonstrated that Slc41a3(-/-) mice suffer from hypomagnesemia. The intestinal Mg(2+) absorption capacity was measured using the stable (25)Mg(2+) isotope in mice fed a low Mg(2+) diet. (25)Mg(2+) uptake was similar in wildtype (Slc41a3(+/+)) and Slc41a3(-/-) mice, although Slc41a3(-/-) animals exhibited increased intestinal mRNA expression of Mg(2+) transporters Trpm6 and Slc41a1. Remarkably, some of the Slc41a3(-/-) mice developed severe unilateral hydronephrosis. In conclusion, SLC41A3 was established as a new factor for Mg(2+) handling.

Evaluation of calcium and magnesium in scalp hair samples of population consuming different drinking water: risk of kidney stone

The objective of this study was to examine the relationship between calcium (Ca) and magnesium (Mg) in underground water (UGW), bottled mineral water (BMW), and domestic treated water (DTW) with related to risk of kidney stones. The water samples were collected from different areas of Sindh, Pakistan. The scalp hair samples of both genders, age ranged 30-60 years, consuming different types of water, have or have not kidney disorders, were selected. The Ca and Mg concentrations were determined in scalp hair of study subjects and water by flame atomic absorption spectroscopy. The Ca and Mg contents in different types of drinking water, UGW, DTW, and BMW, were found in the range of 79.1-466, 23.7-140, and 45-270 mg/L and 4.43-125, 5.23-39.6, and 7.16-51.3 mg/L, respectively. It was observed that Ca concentration in the scalp hair samples of kidney stone patients consuming different types of drinking water was found to be higher (2,895-4721 μg/g) while Mg level (84.3-101 μg/g) was lower as compare to referents subjects (2,490-2,730 μg/g for Ca, 107-128 μg/g for Mg) in both genders. The positive correlation was found between Ca and Mg levels in water with related to kidney stone formations in population, especially who consumed underground water. A relative risk and odd ratio were calculated; the relative risk had a strong positive association with incidence of kidney stone which depends on types of drinking water.

Effects of drinking water quality on urinary parameters in men with and without urinary tract stones

OBJECTIVE

There is some controversy regarding the impact of water hardness on stone risk. Our study addresses this issue in a controlled setting.

MATERIAL AND METHODS

Fifteen stone-former (SF) and 14 non-stone-former (NSF) males participated in this study in 3 intervals of 2 days each. Subjects collected a 24-hour urine sample while consuming a self-selected diet. They were then administered controlled diets. During the first 2 days, patients consumed water of minimal hardness (WMH), followed by tap water (TW) with moderate hardness on days 3 and 4, and mineral water (MW) on the final 2 days. Calcium (Ca), phosphorus, uric acid, oxalate, citrate, magnesium (Mg), sodium, potassium, and creatinine (Cr) content were measured in 24-hour urine samples on days 2, 4, and 6.

RESULTS

Differences in water hardness and analytes were statistically significant among the different water types (P < .05). Urinary output in both groups increased during intervention with all 3 varieties of water (P < .05). Specific gravity of urine decreased in both groups drinking WMH and TW (P < .05) but not with MW. Mg/g Cr level was higher in NSF at baseline (P < .01), WMH (P < .05), and TW (P < .05). With the increase in drinking water hardness, Ca/g Cr ratio increased in SF but not in NSF (P < .05).

CONCLUSIONS

NSF had significantly higher urinary Mg/g Cr excretion rate before intervention than SF (P < .01). Increasing drinking water hardness while controlling for all other factors increased Ca/g Cr ratio in SF, rendering them at least theoretically more inclined to stone formation.

Effects of 21 days of bed rest, with or without artificial gravity, on nutritional status of humans

Spaceflight and bed rest models of microgravity have profound effects on physiological systems, including the cardiovascular, musculoskeletal, and immune systems. These effects can be exacerbated by suboptimal nutrient status, and therefore it is critical to monitor nutritional status when evaluating countermeasures to mitigate negative effects of spaceflight. As part of a larger study to investigate the usefulness of artificial gravity as a countermeasure for musculoskeletal and cardiovascular deficits during bed rest, we tested the hypothesis that artificial gravity would have an effect on some aspects of nutritional status. Dietary intake was recorded daily before, during, and after 21 days of bed rest with artificial gravity (n = 8) or bed rest alone (n = 7). We examined body composition, hematology, general blood chemistry, markers of oxidative damage, and blood levels of selected vitamins and minerals before, during, and after the bed rest period. Several indicators of vitamin status changed in response to diet changes: serum alpha- and gamma-tocopherol and urinary 4-pyridoxic acid decreased (P < 0.001) and plasma beta-carotene increased (P < 0.001) in both groups during bed rest compared with before bed rest. A decrease in hematocrit (P < 0.001) after bed rest was accompanied by a decrease in transferrin (P < 0.001), but transferrin receptors were not changed. These data provide evidence that artificial gravity itself does not negatively affect nutritional status during bed rest. Likewise, artificial gravity has no protective effect on nutritional status during bed rest.

Strain differences in urinary factors that promote calcium oxalate crystal formation in the kidneys of ethylene glycol-treated rats

Ethylene glycol (EG)-induced hyperoxaluria is the most commonly employed experimental regimen as an animal model of calcium oxalate (CaOx) stone formation. The variant sensitivity to CaOx among different rat strains has not been fully explored, although the Wistar rat is known to accumulate more CaOx in kidney tissue after low-dose EG exposure than in the Fischer 344 (F344) rats. Supersaturation of CaOx in tubular fluid contributes to the amount of CaOx crystal formation in the kidney. We hypothesized that the urinary supersaturation of CaOx in Wistar rats is higher than that of F344 rats, thereby allowing for greater CaOx crystal deposition in the Wistar rat. Age-matched male Wistar and F344 rats were treated with 0.75% EG or drinking water for 8 wk. Twenty-four-hour urine was collected at 0, 2, 4, 6, and 8 wk for analysis of key electrolytes to calculate the CaOx supersaturation. Plasma oxalate level was also measured. Our data confirmed the different sensitivity to renal toxicity from EG between the two rat strains (Wistar > F344). After EG treatment, the plasma oxalate level and urine oxalate excretion were markedly greater in the Wistar rats than in the F344 rats, while urine calcium was slightly decreased in Wistars. Thus, the CaOx supersaturation in urine of Wistar rats was higher, which led to a greater crystal deposition in kidney in Wistar rats. These studies suggest that during EG treatment, changes in urine electrolytes and in CaOx supersaturation occur to a greater extent in the Wistar rat, in agreement with its greater sensitivity to EG toxicity.

Mechanism of urinary calcium regulation by urinary magnesium and pH

Urinary magnesium and pH are known to modulate urinary calcium excretion, but the mechanisms underlying these relationships are unknown. In this study, the data from 17 clinical trials in which urinary magnesium and pH were pharmacologically manipulated were analyzed, and it was found that the change in urinary calcium excretion is directly proportional to the change in magnesium excretion and inversely proportional to the change in urine pH; a regression equation was generated to relate these variables (R(2) = 0.58). For further exploration of these relationships, intravenous calcium chloride, magnesium chloride, or vehicle was administered to rats. Magnesium infusion significantly increased urinary calcium excretion (normalized to urinary creatinine), but calcium infusion did not affect magnesium excretion. Parathyroidectomy did not prevent this magnesium-induced hypercalciuria. The effect of magnesium loading on calciuria was still observed after treatment with furosemide, which disrupts calcium and magnesium absorption in the thick ascending limb, suggesting that the effect may be mediated by the distal nephron. The calcium channel TRPV5, normally present in the distal tubule, was expressed in Xenopus oocytes. Calcium uptake by TRPV5 was directly inhibited by magnesium and low pH. In summary, these data are compatible with the hypothesis that urinary magnesium directly inhibits renal calcium absorption, which can be negated by high luminal pH, and that this regulation likely takes place in the distal tubule.

The relationship of magnesium intake to serum and urinary calcium and magnesium levels in Trinidadian stone formers

BACKGROUND

The present study was undertaken to investigate the relationship between the dietary intake of magnesium and the serum and urinary levels of calcium and magnesium in a group of Trinidadian stone formers.

METHODS

A group of 102 confirmed stone formers presenting to urological clinics were interviewed using a questionnaire designed to obtain a semi-quantitative estimate of their oral magnesium intake. Patients were invited to give blood samples for serum calcium and magnesium levels and to provide 24-h urine specimens for the measurement of urinary levels of these minerals, as well as total urinary volumes. A group of 102 controls was subjected to a similar interview and blood and urinary testing. Chi-square tests and Student's t-tests were used to examine group demographic differences. The Mann-Whitney test investigated differences in biochemical indices. Binary logistic regression was used to identify predictors of stone formation.

RESULTS

Blood samples were obtained from 60 patients and 98 controls. Urine samples were returned by 34 patients and 97 controls. Only 10 stones were retrieved from patients. Patients had a significantly lower magnesium intake, but higher median serum and urinary calcium levels, and higher serum calcium to magnesium ratios than controls. Independent variables capable of predicting stone formation included total magnesium intake and serum and urinary calcium levels.

CONCLUSIONS

Increased serum and urinary calcium levels, calcium to magnesium ratios, and a low magnesium intake were predictive of stone formation in this Trinidadian population.

The nutritional status of astronauts is altered after long-term space flight aboard the International Space Station

Defining optimal nutrient requirements is critical for ensuring crew health during long-duration space exploration missions. Data pertaining to such nutrient requirements are extremely limited. The primary goal of this study was to better understand nutritional changes that occur during long-duration space flight. We examined body composition, bone metabolism, hematology, general blood chemistry, and blood levels of selected vitamins and minerals in 11 astronauts before and after long-duration (128-195 d) space flight aboard the International Space Station. Dietary intake and limited biochemical measures were assessed during flight. Crew members consumed a mean of 80% of their recommended energy intake, and on landing day their body weight was less (P = 0.051) than before flight. Hematocrit, serum iron, ferritin saturation, and transferrin were decreased and serum ferritin was increased after flight (P < 0.05). The finding that other acute-phase proteins were unchanged after flight suggests that the changes in iron metabolism are not likely to be solely a result of an inflammatory response. Urinary 8-hydroxy-2'-deoxyguanosine concentration was greater and RBC superoxide dismutase was less after flight (P < 0.05), indicating increased oxidative damage. Despite vitamin D supplement use during flight, serum 25-hydroxycholecalciferol was decreased after flight (P < 0.01). Bone resorption was increased after flight, as indicated by several markers. Bone formation, assessed by several markers, did not consistently rise 1 d after landing. These data provide evidence that bone loss, compromised vitamin D status, and oxidative damage are among critical nutritional concerns for long-duration space travelers.

Intestinal transport of an obdurate anion: oxalate

In this review, we focus on the role of gastrointestinal transport of oxalate primarily from a contemporary physiological standpoint with an emphasis on those aspects that we believe may be most important in efforts to mitigate the untoward effects of oxalate. Included in this review is a general discussion of intestinal solute transport as it relates to oxalate, considering cellular and paracellular avenues, the transport mechanisms, and the molecular identities of oxalate transporters. In addition, we review the role of the intestine in oxalate disease states and various factors affecting oxalate absorption.

Effects of angiotensin II subtype 1 receptor blockade by losartan on tubulointerstitial lesions caused by hyperoxaluria

PURPOSE

Hyperoxaluria is a recognized cause of tubulointerstitial lesions and this circumstance could contribute to cause chronic renal disease. The renin-angiotensin system has a critical role in the development of interstitial fibrosis, mostly by angiotensin II type 1 receptor stimulation of pro-fibrotic mechanisms. We evaluated whether angiotensin II type 1 receptor blockade prevents oxalate renal lesions.

MATERIALS AND METHODS

We divided 2-month-old male Sprague-Dawley rats into 4 groups, namely group 1-control, group 2-hyperoxaluria, group 3-hyperoxaluria plus losartan and group 4-losartan. For 4 weeks groups 2 and 3 received 1% ethylene glycol (precursor for oxalates) in drinking water. Losartan (40 mg./kg. body weight) was administered in groups 3 and 4 daily. At the end of the study renal lesions were evaluated using anti-alpha-smooth muscle actin, anti-collagen type III, anti-monocytes/macrophages and anti-transforming growth factor-beta1 antibodies. To evaluate oxidative stress in renal tissue total glutathione and thiobarbituric acid reactive substances in kidney homogenates were determined. Regarding renal functional parameters, creatinine clearance and urinary albumin excretion were also studied.

RESULTS

Despite similar urinary oxalate levels compared with group 2 group 3 rats showed fewer tubulointerstitial lesions, consisting of significant lower scores for tubular atrophy, unspecific inflammatory cell infiltrate, ED1 mouse anti-rat monoclonal antibody (Serotec, Ltd., Oxford, United Kingdom) (monocytes/macrophages), crystal deposits, interstitial fibrosis, alpha-smooth muscle actin, collagen type III and tubulointerstitial transforming growth factor-beta1. Moreover, urinary albumin excretion and creatinine clearance were significantly improved in group 3 (p <0.01). Higher total glutathione and lower thiobarbituric acid reactive substances were also observed in this group (p <0.01). Thiobarbituric acid reactive substances were the most important and significant independent variable correlating with interstitial fibrosis (t ratio 4.867, p <0.04).

CONCLUSIONS

We believe that the renal-angiotensin system interaction by losartan produces a beneficial effect against renal lesions caused by hyperoxaluria through a number of actions, including a reduction in crystal formation in the tubular fluid, inflammatory reaction control and interaction with oxidative stress. These factors lead concurrently to preserve tubular epithelial cell and renal interstitium integrity. In addition, these results suggest that the principal mechanism of action should be mediated by angiotensin II type 1 receptors.

Calcium nephrolithiasis: effect of water hardness on urinary electrolytes

OBJECTIVES

To analyze the impact of water hardness from public water supplies on calcium stone incidence and 24-hour urine chemistries in patients with known calcium urinary stone formation. Patients are frequently concerned that their public water supply may contribute to urinary stone disease. Investigators have documented an inverse relationship between water hardness and calcium lithogenesis. Others have found no such association.

METHODS

Patients who form calcium stones (n = 4833) were identified geographically by their zip code. Water hardness information from distinct geographic public water supplies was obtained, and patient 24-hour urine chemistries were evaluated. Drinking water hardness was divided into decile rankings on the basis of the public water supply information obtained from the Environmental Protection Agency. These data were compared with patient questionnaires and 24-hour urine chemistries. The calcium and magnesium levels in the drinking water were analyzed as independent variables.

RESULTS

The number of total lifetime stone episodes was similar between patients residing in areas with soft public water and hard public water. Patients consuming the softest water decile formed 3.4 lifetime stones and those who consumed the hardest water developed 3.0 lifetime stones (P = 0.0017). The 24-hour urine calcium, magnesium, and citrate levels increased directly with drinking water hardness, and no significant change was found in urinary oxalate, uric acid, pH, or volume.

CONCLUSIONS

The impact of water hardness on urinary stone formation remains unclear, despite a weak correlation between water hardness and urinary calcium, magnesium, and citrate excretion. Tap water, however, can change urinary electrolytes in patients who form calcium stones.

Rethinking the role of urinary magnesium in calcium urolithiasis

BACKGROUND AND PURPOSE

The role of magnesium in urinary stone formation remains undefined. In vivo, magnesium inhibits stone formation in hyperoxaluric rats, and small clinical studies suggest a protective effect of magnesium supplementation in calcium oxalate stone formers. We performed a retrospective review of more than 7,000 stone patients to see if there is a relation between urinary magnesium and other stone risk variable constituents.

MATERIALS AND METHODS

A national database of stone formers categorized by residential ZIP code was queried, and, using strict inclusion criteria, 2,147 patients having pure calcium oxalate stones were identified. There were 1,912 (89%) eumagnesuric (43-246 mg/24 hours) and 235 (11%) hypomagnesuric (<43 mg/24 hours) patients.

RESULTS

Patients with decreased urinary magnesium excretion had significantly less daily urine excretion of citrate, calcium, oxalate, uric acid, and sodium than the eumagnesuric group (p < 0.0001). Stone recurrence was slightly more common in the hypomagnesuric group, although the difference was not statistically significant. The percentage of patients voiding <1 L of urine per day was significantly higher in the hypomagnesuric group. In the eumagnesuric group, males outnumbered females 2:1, whereas hypomagnesuric patients showed a female predominance of 1.4:1.

CONCLUSION

The beneficial effects of urinary magnesium on stone formation may be less than previously reported. The role of oral magnesium supplementation and the subsequent increase in urinary magnesium in calcium urinary stone formation remains unknown. Our data suggest that its effect on or interaction with citrate may be influential on urinary citrate concentrations. If magnesium has a protective effect, it may work through pathways that enhance citrate excretion.

Gahat: a Napalese cure for urolithiasis?

OBJECTIVES

Gahat (Vigna unguiculata) is a legume used for centuries in Nepal and Pakistan to treat the symptoms associated with urinary calculi. We prospectively evaluated the effect of Gahat consumption on 24-hour urine parameters in an attempt to assess its in vivo effect in normal volunteers.

METHODS

Eight non-stone-forming volunteers collected 24-hour urine specimens while on their routine diets for baseline data. Urine was analyzed for pH, volume, calcium, citrate, phosphate, sodium, magnesium, uric acid, and oxalate. The Gahat was prepared according to local custom. No additives were used to enhance flavor. The pureed mixture (8 ounces) was ingested three times daily for 2 days. Subjects were instructed to maintain their normal diet, including fluid intake and activity during the study period. Twenty-four hours after the start of Gahat intake, a second 24-hour urine collection was initiated while volunteers continued the Gahat. Results of the urine samples before and after Gahat intake were analyzed, using the paired Student t test.

RESULTS

There were no significant differences in urinary electrolytes between the urine samples before and after Gahat intake. Magnesium, urine volume, and uric acid differences approached clinical significance.

CONCLUSIONS

Gahat increased urinary magnesium through an unknown mechanism and had no effect on other routine 24-hour urine electrolytes. The increase in urinary volume is attributed to the increase in fluid consumption by the subjects. If this legume is effective in preventing or dissolving urinary calculi, it may act through mechanisms not identified in 24-hour urine electrolytes.

Effects of calcium and magnesium on urinary oxalate excretion after oxalate loads

PURPOSE

Urinary oxalate is a primary determinant of the level of calcium oxalate saturation and the formation of calcium oxalate crystals, a key event in kidney stone formation. The primary objective of this study was to compare the effects of calcium carbonate and magnesium oxide on oxalate absorption.

MATERIALS AND METHODS

An experimental model was used that allowed differentiation between endogenously and oxalate load-derived urinary oxalate. Twenty-four healthy subjects (10 males, 14 females) participated in three oxalate load (OL) tests: control (OL alone), calcium carbonate (OL with concomitant calcium carbonate ingestion), and magnesium oxide (OL with concomitant magnesium oxide ingestion). Oxalate loads consisted of 180 mg. unlabeled and 18 mg. 1,2[13C2] oxalic acid. Timed urine samples were collected after the OL for analysis of oxalate, calcium, magnesium, and creatinine.

RESULTS

Both the calcium carbonate and magnesium oxide treatments were associated with significantly lower load-derived oxalate levels at all time points within the initial 24-hour post-oxalate ingestion period compared with levels observed for the control treatment. There were no treatment effects on endogenous oxalate levels. The efficiency of oxalate absorption for the calcium carbonate (5.1%) and magnesium oxide (7.6%) treatments was significantly lower than that for the control treatment (13.5%).

CONCLUSIONS

The results suggested that magnesium was nearly as effective as calcium in reducing oxalate absorption and urinary excretion. Higher levels of urinary oxalate, calcium, and magnesium in males appeared to be largely a function of body size since gender differences either disappeared or were reversed when a correction was made for urinary creatinine excretion.

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.

Idiopathic calcium oxalate urolithiasis and endogenous oxalate production

Despite the great effort that has gone into investigating urolithiasis, this condition still persists as one of the major ailments of the urinary tract. Calcium oxalate urolithiasis is the most common form, accounting for some 60 to 80% of total stones. This review examines the elements (i.e., urine volume and pH and urinary excretion of calcium, oxalate, citrate, urate, magnesium, pyrophosphate, and glycosaminoglycans) that give rise to idiopathic calcium oxalate urolithiasis. Treatment strategies for idiopathic calcium oxalate urolithiasis, including lithotripsy, also are discussed. Urinary oxalate excretion is a major risk factor for calcium oxalate urolithiasis, with 85 to 95% of the urinary load derived endogenously. The factors controlling endogenous oxalate production are reviewed, including pathways for the diversion of glyoxylate from oxalate production. The use of beta-aminothiols and other substances to reduce endogenous oxalate production in subjects with idiopathic calcium oxalate urolithiasis is also discussed. A review of current methodologies for the determination of urinary oxalate is also included.

Role of urinary physiology and chemistry in bladder carcinogenesis

Urine is a complex mixture of numerous substances, only some of which are described above. Literally thousands of substances have been identified in normal urine, including a variety of ions, non-ionic substances and macromolecules. Their presence and concentrations are highly variable, dependent on fluid intake and on nutritional, physiological and biochemical influences. Marked diurnal variations exist. Methodologies involved in the collection and analysis of these components can greatly influence the interpretation of the results. The influence of these various parameters in the urine on bladder carcinogenicity can be either direct or indirect. A major difficulty in studying this aspect of urothelial carcinogenesis is that it is essentially impossible to alter only one variable in the urine at a time. Alteration of any one variable results in physiological alteration of several other of the constituents in the urine. In addition, the processes involved in urothelial carcinogenesis frequently involve a complex interaction of multiple variables, such as volume, osmolality, cationic concentration, anionic concentration, quantitative and qualitative differences in protein, and generation of precipitate, crystals or calculi. Thus, it is likely that the actual mechanisms involved in the carcinogenic process with many of these chemicals, particularly those that are non-genotoxic, will involve a complex interaction of several constituents of the urine. Although this poses a formidable obstacle to our understanding in experimental situations as well as in extrapolating to humans, the role of specific factors appears to be discernible and should offer insight into the risk assessment process (Cohen and Ellwein, 1991 a,b and 1992).

Magnesium oxide administration and prevention of calcium oxalate nephrolithiasis

We studied the effect of oral administration of magnesium oxide (MgO) on calcium oxalate (CaOx) nephrolithiasis in rats. Nephrolithiasis was induced by administration of 1.0% ethylene glycol (EG) in drinking water. Magnesium oxide was given mixed with food at 500 mg./100 g. rat chow. Dispensation of MgO resulted in a significant increase of urinary pH and a modest increase in urinary excretion of citrate. Urinary excretion of oxalate started to decline by day 14 and was significantly reduced on days 21 and 28. All rats receiving EG displayed crystalluria. From the group receiving EG only, 3 of 4 rats sacrificed on day 15 and 2 of 4 rats sacrificed on day 29 had CaOx crystal deposits in their kidneys. None of the 8 rats who received both EG and MgO had CaOx nephrolithiasis. Thus our findings indicate that dispensation of magnesium as MgO can be beneficial against calcium oxalate nephrolithiasis.

Uninephrectomy enhances urolithiasis in ethylene glycol treated rats

Uninephrectomy (uNX) usually induces compensatory hyperfunction of the remaining kidney in an attempt to preserve the homeostasis of body fluid composition. The present study used uninephrectomized Sprague-Dawley rats on a lithogenic diet (0.5% ethylene glycol, EG) to evaluate the influence on urinary stone formation and calcium oxalate crystal deposition of compensatory excretion of lithogenic substances in the remnant kidney. The results showed that there were no urinary stones or calcium oxalate crystal deposits in the intact or uNX rats fed a normal diet. In the EG feeding groups, the incidence of massive (grade 3) crystal deposits was significantly higher in the uNX rats (87.5%) than that in the intact rats (37.5%; P less than 0.05). The incidence of urinary stone formation was also higher in the uNX rats as compared to that of the intact rats, although the difference did not achieve statistical significance. The serum magnesium, phosphorus and creatinine increased significantly, whereas creatinine clearance (CCr), 24-hour urinary excretions of citrate, sodium, potassium and chloride decreased significantly in the uNX rats fed EG. These data indicate that uninephrectomy increases the vulnerability of the contralateral remnant kidney to urolithiasis and crystal deposition when the lithogenic risk factors are present. Furthermore, once the remnant kidney forms urolithiasis or massive calcium oxalate crystal deposits, the renal function is severely compromised.