[2,8-dihydroxyadenine nephrolithiasis: from diagnosis to therapy]

Adenine phosphoribosyltransferase (APRT, EC 2.4.2.7) deficiency is an enzymopathy of purine metabolism, which is inherited as an autosomal recessive trait. APRT is a salvage enzyme that normally catalyzes the conversion of adenine to adenosine monophosphate. APRT deficiency results in adenine accumulation with oxidation by xanthine dehydrogenase (XDH; EC 1.1.1.204) to 2,8-dihydroxyadenine (2,8-DHA) then excreted in urine. This compound is extremely insoluble and its crystallization can lead to stone formation and renal failure. The diagnosis of the disease is based on stone analysis by infrared spectroscopy or microscopic examination of urine, which may reveal typical 2,8-DHA crystals. The enzyme activity measurements in erythrocyte lysates will identify both homozygotes and heterozygotes for APRT deficiency. Molecular approach can identify mutations which are responsible of this inherited disease. Two types of deficit are commonly distinguished, depending on the level of residual APRT activity: type I, mainly observed in Caucasian subjects, in whom the enzyme activity is undetectable in homozygous patients and type II, found in Japanese patients who are able to form APRT but the enzyme activity is strikingly reduced because a low affinity for phosphoribosylpyrophosphate. The crystallization of 2,8-DHA and subsequent renal damages may be prevented with allopurinol therapy, a xanthine oxidase inhibitor. The role of the laboratory is crucial to detect APRT deficiency and to assess the efficacy of therapy, the objective being to avoid 2,8-DHA crystal formation.

Control of potassium excretion: a Paleolithic perspective

PURPOSE OF REVIEW

Regulation of potassium (K) excretion was examined in an experimental setting that reflects the dietary conditions for humans in Paleolithic times (high, episodic intake of K with organic anions; low intake of NaCl), because this is when major control mechanisms were likely to have developed.

RECENT FINDINGS

The major control of K secretion in this setting is to regulate the number of luminal K channels in the cortical collecting duct. Following a KCl load, the K concentration in the medullary interstitial compartment rose; the likely source of this medullary K was its absorption by the H/K-ATPase in the inner medullary collecting duct. As a result of the higher medullary K concentration, the absorption of Na and Cl was inhibited in the loop of Henle, and this led to an increased distal delivery of a sufficient quantity of Na to raise K excretion markedly, while avoiding a large natriuresis. In addition, because K in the diet was accompanied by 'future' bicarbonate, a role for bicarbonate in the control of K secretion via 'selecting' whether aldosterone would be a NaCl-conserving or a kaliuretic hormone is discussed.

SUMMARY

This way of examining the control of K excretion provides new insights into clinical disorders with an abnormal plasma K concentration secondary to altered K excretion, and also into the pathophysiology of calcium-containing kidney stones.

Association of Urokinase Gene 3′-UTR Polymorphism with Calcium Oxalate Nephrolithiasis

PURPOSE

Urokinase might play a role in the formation of kidney stones. The aim of this study was to investigate the role of the urokinase gene in calcium oxalate nephrolithiasis.

SUBJECTS AND METHODS

A control group of 150 healthy individuals having no history of stone formation (mean age 40 +/- 11.5 years) and a group of 130 patients (mean age 40.5 +/- 10.5 years) with recurrent calcium oxalate stones were examined. The C/T polymorphism of the urokinase gene was detected using polymerase chain reaction (PCR)-based restriction analysis.

RESULTS

A marginally significant difference (P = 0.035) was found in the distribution of the urokinase gene 3' untranslated region (UTR) C/T polymorphism between patients with stones and controls. The odds ratio for the risk of the T allele in stone patients was 1.006 (95% CI 0.63-1.62).

CONCLUSION

The T allele of 3' UTR of the urokinase gene may not be associated with a higher risk of stone formation.

Effects of potassium-magnesium citrate supplementation on cytosolic ATP citrate lyase and mitochondrial aconitase activity in leukocytes: A window on renal citrate metabolism

BACKGROUND

An increase in urinary citrate excretion is associated with a decrease in activity of renal cortical cytosolic ATP citrate lyase (ACL) and mitochondrial aconitase (m-aconitase). Because potassium-magnesium citrate causes an increase in urinary citrate excretion, we decided to assess its effects on ACL and m-aconitase in the leukocytes of renal stone patients.

METHODS

Twenty male renal stone patients were supplemented with potassium-magnesium citrate twice daily (i.e. 42 mEq potassium, 21 mEq magnesium, and 63 mEq citrate per day) for a period of 1 month. Two 24-h urine and one 15-mL heparinized blood samples were collected from each patient before and after supplementation. Urine samples were analyzed for relevant biochemical compositions. Leukocytes were separated from blood samples by centrifugation and assayed for ACL and m-aconitase activity.

RESULTS

Supplementation with potassium-magnesium citrate significantly increased urinary pH (P < 0.005) and excretions of potassium (P < 0.001), magnesium (P < 0.001) and citrate (P < 0.0001). The activity of both ACL and m-aconitase were significantly decreased (P < 0.004 and P < 0.02 respectively). The decrease in ACL activity was inversely correlated with an increase in urinary excretion of both potassium (r = -0.620, P < 0.0001) and citrate (r = -0.451, P < 0.004). A similar inverse correlation was observed between m-aconitase activity and urinary excretion of citrate (r = -0.322, P < 0.043).

CONCLUSION

Changes in enzyme activity, related to citrate metabolism in leukocytes, might reflect the status of renal tubular cells.

Prophylactic role of phycocyanin: a study of oxalate mediated renal cell injury

Oxalate induced renal calculi formation and the associated renal injury is thought to be caused by free radical mediated mechanisms. An in vivo model was used to investigate the effect of phycocyanin (from Spirulina platensis), a known antioxidant, against calcium oxalate urolithiasis. Male Wistar rats were divided into four groups. Hyperoxaluria was induced in two of these groups by intraperitoneal infusion of sodium oxalate (70 mg/kg) and a pretreatment of phycocyanin (100 mg/kg) as a single oral dosage was given, 1h prior to sodium oxalate infusion. An untreated control and drug control (phycocyanin alone) were also included in the study. We observed that phycocyanin significantly controlled the early biochemical changes in calcium oxalate stone formation. The antiurolithic nature of the drug was evaluated by the assessment of urinary risk factors and light microscopic observation of urinary crystals. Renal tubular damage as divulged by urinary marker enzymes (alkaline phosphatase, acid phosphatase and gamma-glutamyl transferase) and histopathological observations such as decreased tubulointerstitial, tubular dilatation and mononuclear inflammatory cells, indicated that renal damage was minimised in drug-pretreated group. Oxalate levels (P < 0.001) and lipid peroxidation (P < 0.001) in kidney tissue were significantly controlled by drug pretreatment, suggesting the ability of phycocyanin to quench the free radicals, thereby preventing the lipid peroxidation mediated tissue damage and oxalate entry. This accounts for the prevention of CaOx stones. Thus, the present analysis revealed the antioxidant and antiurolithic potential of phycocyanin thereby projecting it as a promising therapeutic agent against renal cell injury associated kidney stone formation.

Uric acid stone disease

The trend in uric acid stone formation appears to be on the rise again throughout much of the world. This is thought secondary to diet, body habitus, and social reasons. Uric acid stone disease has a rich and fascinating medical history and probably is the oldest known stone disease. Uric acid stone disease is strongly linked to the purine metabolic pathway, and its treatment is primarily medical. Uric acid stone disease can be prevented and these are one of the few urinary tract stones that can be dissolved successfully. Surgical intervention with uric acid stone disease represents a failure of medical therapy and a whole host of modern, minimally invasive methods are available for treating patients with this disease. Finally, uric acid nephrolithiasis is associated with a variety of inborn errors of metabolism based on mutations of key enzymes in the purine metabolic pathways. This review of uric acid stone formation will start with historical consideration, review basic biochemistry, and physiology and then focus upon specific clinical scenarios. The discussions will be heavily referenced for those interested in greater details.

Correction of an enzyme trafficking defect in hereditary kidney stone disease in vitro

In normal human hepatocytes, the intermediary-metabolic enzyme alanine:glyoxylate aminotransferase (AGT) is located within the peroxisomes. However, in approx. one-third of patients suffering from the hereditary kidney stone disease primary hyperoxaluria type 1, AGT is mistargeted to the mitochondria. AGT mistargeting results from the synergistic interaction between a common P11L (Pro11-->Leu) polymorphism and a disease-specific G170R mutation. The polymorphism generates a functionally weak mitochondrial targeting sequence, the efficiency of which is increased by the mutation. The two substitutions together, but not in isolation, inhibit AGT dimerization, highlighting the different structural requirements of the peroxisomal and mitochondrial protein-import machineries. In the present study, we show that treatments known to increase the stability of proteins non-specifically (i.e. lowering the temperature from 37 to 30 degrees C or by the addition of glycerol) completely normalize the intracellular targeting of mutant AGT expressed in transfected COS cells. On the other hand, treatments known to decrease protein stability (e.g. increasing the temperature from 37 to 42 degrees C) exacerbate the targeting defect. Neither of the treatments affects the relative efficiencies of the peroxisomal and mitochondrial protein-import pathways intrinsically. Results are discussed in the light of the known structural requirements of the two protein trafficking pathways and the formulation of possible treatment strategies for primary hyperoxaluria type 1.

Alanine:glyoxylate aminotransferase peroxisome-to-mitochondrion mistargeting in human hereditary kidney stone disease

The pyridoxal-phosphate (PLP)-dependent enzyme alanine:glyoxylate aminotransferase (AGT) is mistargeted from peroxisomes to mitochondria in patients with the hereditary kidney stone disease primary hyperoxaluria type 1 (PH1) due to the synergistic interaction between a common Pro(11)Leu polymorphism and a PH1-specific Gly(170)Arg mutation. The kinetic partitioning of newly synthesised AGT between peroxisomes and mitochondria is determined by the combined effects of (1) the generation of cryptic mitochondrial targeting information, and (2) the inhibition of AGT dimerization. The crystal structure of AGT has recently been solved, allowing the effects of the various polymorphisms and mutations to be rationalised in terms of AGT's three-dimensional conformation. Procedures that increase dimer stability and/or increase the rate of dimer formation have potential in the formulation of novel strategies to treat this otherwise intractable life-threatening disease.

Decreased renal vitamin K-dependent gamma-glutamyl carboxylase activity in calcium oxalate calculi patients

OBJECTIVE

To study the activity of vitamin K-dependent gamma-glutamyl carboxylase in patients with calcium oxalate (CaOx) urolithiasis compared with healthy individuals and to assess its relationship to the renal calcium oxalate urolithiasis.

METHODS

Renal parenchymas were harvested from urolithic patients and renal tumor patients undergoing nephrectomy. The renal carboxylase activity was evaluated as the radioactivity of [(14)C] labeled sodium bicarbonate in carboxylic reactions in vitro using beta-liquid scintillation counting.

RESULTS

Significantly reduced activity of renal vitamin K-dependent gamma-glutamyl carboxylase was observed in the urolithic group as compared with normal controls (P < 0.01).

CONCLUSION

It suggests that the reduced carboxylase activity observed in the urolithic patients may play an important role in the course of renal calcium oxalate urolithiasis.

Urinary citrate excretion in patients with renal stone: roles of leucocyte ATP citrate lyase activity and potassium salts therapy

BACKGROUND

Hypocitraturia is a major metabolic abnormality in rural Northeast Thais with renal stones. These people also have low serum and urinary potassium and consume a high carbohydrate and low fat diet, which together might influence the intracellular metabolism and urinary excretion of citrate.

METHODS

In Study A, we measured plasma and urinary chemistries and assayed leucocyte ATP citrate lyase (ACL) activity in 30 normal urban control subjects (Group A1) and 30 rural renal stone patients (Group A2) in Northeast Thailand. Some of the subjects from both groups were also used to evaluate the intake of carbohydrate, protein and fat. In Study B, we examined the effects of potassium salts therapy with another group of 30 rural renal stone patients: Group B1 (n = 15) treated with potassium chloride and Group B2 (n = 15) with potassium-sodium citrate (with an aim to achieve 42 mEq potassium, 21 mEq sodium and 62 mEq citrate per day for 1 month).

RESULTS

In Study A, the leucocyte ACL activity of Group A1 was much lower than that of Group A2 (3.2 +/- 0.7 vs. 9.3 +/- 3.8 micromol acetylhydroxamate/mg protein/30 min, p < 0.0001). The plasma potassium, urinary excretions of potassium and citrate in Group A1 were higher than in Group A2. When data of the two groups were combined, urinary citrate excretion was inversely correlated with leucocyte ACL activity (r = 0.6783, p < 0.001). While the dietary protein intake did not differ between Groups A1 and A2, the carbohydrate intake by Group A1 was significantly lower (65.2 +/- 7.9% vs. 83.1 +/- 2.9%, p < 0.01) and fat higher (21.0 +/- 6.4% vs. 6.2 +/- 4.1%, p < 0.002) than Group A2. After treatment with potassium chloride (Group B1), only the potassium was increased (p < 0.001), while those treated with potassium-sodium citrate (Group B2) experienced a significant increase in urinary pH (p < 0.002), potassium (p < 0.001) and citrate (p < 0.001), and a decrease in leucocyte ACL activity (p < 0.001).

CONCLUSIONS

Compared to normal subjects, renal stone patients have low urinary citrate excretion with high leucocyte ACL activity. In Northeast Thailand, low potassium status and a high carbohydrate and low fat diet may cause the increased ACL activity. However, hypokaliuria, hypocitraturia and high leucocyte ACL activity can be corrected by potassium-sodium citrate salt therapy.

Correlation between Na, K-ATPase activity and potassium and magnesium contents in skeletal muscle of renal stone patients

Samples of external oblique muscles were surgically removed from 45 renal stone patients and analyzed for their K, Na and Mg content. The muscle samples were also measured for membrane Na, K-ATPase activity from the assay of its K+-dependent 3-0-methyl fluorescein phosphatase (K+-dependent 3-0-MFPase) activity. The results showed that the mean muscle contents +/- SEM of K, Na and Mg were 65.2 +/- 1.7 (range, 41.1 to 86.1), 45.5 +/- 2.0 (range, 23.5 to 73.2) and 6.3 +/- 1.0 (range, 4.1 to 8.5) micromol/g wet weight, respectively. The mean activity +/- SEM of the K+-dependent 3-0-MFPase or the Na, K-ATPase was calculated by subtracting the activity of the basal-form from that of the total-3-0-MFPase, which was 113 +/- 21 (range, 11 to 177) nmol/g wet weight/minute. The activity of the Na, K-ATPase showed a significant correlation with muscle K-content (r = 0.52, p<0.001) and Mg content (r = 0.45, p<0.002). Though the external oblique muscles of renal stone patients in our study, as compared to data from other sources, had a considerably low concentration of K and Mg, they exhibited a good correlation with membrane-Na, K-ATPase activity. Our results, therefore, support previous observations made by other investigators.

Altered gene expression in kidneys of mice with 2,8-dihydroxyadenine nephrolithiasis

BACKGROUND

We have developed a knockout mouse model for adenine phosphoribosyltransferase (APRT) deficiency, a condition that often leads to 2,8-dihydroxyadenine (DHA) nephrolithiasis in humans. Aprt knockout male mice develop severe renal damage by three months of age, but this is strain specific. Renal damage in female mice is less pronounced than in males. The gene level changes that promote renal injury in APRT-deficient mice are not known.

METHODS

We used mRNA differential display polymerase chain reaction (DD-PCR) to analyze renal gene expression changes in APRT-deficient male and female mice (strain C3H) compared with age- and sex-matched Aprt heterozygote controls. The differentially amplified bands were reamplified, cloned, sequenced, and queried against the National Center for Biotechnology Information nonredundant databases using the Basic Alignment Search Tool. Relative quantitative reverse transcription-polymerase chain reaction was used to confirm the results of DD-PCR for a selected number of genes in one-, three-, and six-month-old male and female mice.

RESULTS

Sixty-three differentially amplified bands were identified, including 21 for known genes, and 8 of these were examined further. In three-month-old APRT-deficient male mice, the expression of C10 was increased tenfold, and there was a fourfold to sevenfold increase in the expression of a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS-1), MGP (matrix Gla protein), and lysyl oxidase (LOX). The expression of cholecystokinin-A receptor (CCKAR), imprinted multimembrane-spanning polyspecific transporter-like gene 1 (IMPT-1), and kidney androgen-regulated protein (KAP) was diminished twofold to fourfold, but there was little or no change in the expression of organic anion transporter (OATP). Except for a more than tenfold increase in C10 expression and up to tenfold decrease in KAP expression, APRT-deficient female mice did not show significant changes in gene expression compared with controls.

CONCLUSIONS

These findings suggest that (1) there are sex-related differences in gene expression in DHA lithiasis, possibly caused by increased deposition of DHA crystals in male compared with female kidneys; and (2) the expression of certain genes (for example, C10) may simply be an indication of nonspecific cellular stimulation and may not be related to renal injury.

Phospholipase A2 mediates immediate early genes in cultured renal epithelial cells: possible role of lysophospholipid

BACKGROUND

Exposure to high levels of oxalate induces oxidant stress in renal epithelial cells and produces diverse changes in cell function, ranging from cell death to cellular adaptation, as evidenced by increased DNA synthesis, cellular proliferation, and induction of genes associated with remodeling and repair. These studies focused on cellular adaptation to this oxidant stress, examining the manner by which oxalate exposure leads to increased expression of immediate early genes (IEGs). Specifically, our studies assessed the possibility that oxalate-induced changes in IEG expression are mediated by phospholipase A2 (PLA2), a common pathway in cellular stress responses.

METHODS

Madin-Darby canine kidney (MDCK) cells were exposed to oxalate in the presence or absence of PLA2 inhibitors: mepacrine and arachidonyl trifluoromethyl ketone (AACOCF3). Expression of IEG (c-jun, egr-1, and c-myc) mRNA was assessed by Northern blot analysis. PLA2 activity was determined by measuring the release of [3H]arachidonic acid (AA) from prelabeled cells.

RESULTS

Oxalate exposure (1 to 1.5 mmol/L) induced time- and concentration-dependent increases in IEG mRNA. Treatment with mepacrine resulted in a 75 to 113% reduction of oxalate-induced c-jun, egr-1, and c-myc mRNA, while AACOCF3 caused a 41 to 46% reduction of oxalate-induced c-jun and egr-1 mRNA. Of the two major byproducts of PLA2, only lysophosphatidylcholine (20 micromol/L) increased c-jun and egr-1 mRNA. In contrast, AA (25 micromol/L) attenuated the oxalate-induced increase in c-jun and egr-1 mRNA, presumably by inhibiting PLA2 activity.

CONCLUSIONS

These findings suggest that PLA2 plays a major role in oxalate-induced IEG expression in renal epithelial cells and that lysophospholipids might be a possible lipid mediator in this pathway.

The 1 alpha-hydroxylase locus is not linked to calcium stone formation or calciuric phenotypes in French-Canadian families

Calcium urolithiasis is often associated with increased intestinal absorption and urine excretion of calcium, and has been suggested to result from increased vitamin D production. The role of the enzyme 1 alpha-hydroxylase, the rate-limiting step in active vitamin D production, was evaluated in 36 families, including 28 sibships with at least a pair of affected sibs, using qualitative and quantitative trait linkage analyses. Sibs with a verified calcium urolithiasis passage (n = 117) had higher 24-h calciuria (P = 0.03), oxaluria (P = 0.02), fasting and postcalcium loading urine calcium/creatinine (Ca/cr) ratios (P = 0.008 and P = 0.002, respectively), and serum 1,25(OH)2 vitamin D levels (P = 0.02) compared with nonstone-forming sibs (n = 120). Markers from a 9-centiMorgan interval encompassing the VDD1 locus on chromosome 12q13-14 (putative 1 alpha-hydroxylase) were analyzed in 28 sibships (146 sib pairs) of single and recurrent stone formers and in 14 sibships (65 sib pairs) with recurrent-only (> or = 3 episodes) stone-forming sibs. Two-point and multipoint analyses did not reveal excess in alleles shared among affected sibs at the VDD1 locus. Linkage of stone formation to the VDD1 locus could be excluded, respectively, with a lambda d of 2.0 (single and recurrent stone formers) and 3.25 (recurrent stone formers). Quantitative trait analyses revealed no evidence for linkage to 24-h calciuria and oxaluria, serum 1,25(OH)2 vitamin D levels, and Ca/cr ratios. This study shows absence of linkage of the putative 1 alpha-hydroxylase locus to calcium stone formation or to quantitative traits associated with idiopathic hypercalciuria. In addition, there is coaggregation of calciuric and oxaluric phenotypes with stone formation.

[The effect of extracorporeal shockwave lithotripsy on the indices of urinary enzymes in nephrolithiasis patients]

Immediate and long-term effects of extracorporeal shock-wave lithotripsy (ESWL) on urine enzymes were studied in 200 patients with nephrolithiasis (NL). The patients had abnormally high urine excretion of AP, GGT, APA, LDH and NAG, whereas aminotransferases excretion was low. Pathobiochemical and diagnostic implications of these findings are discussed. Immediately after its conduction ESWL entails a mild injury to tubular portion of the nephron. The causes of long-term stay of enzymuria after ESWL in NL patients are discussed.

Does urokinase play a role in renal stone formation?

Renal stone formation is a complex multifactorial disease, and it is believed that the initial step in the pathogenesis of urolithiasis must be the precipitation of an organic matrix of mucoproteins followed by precipitation of minerals onto this matrix. An important factor in this process may be the activity and/or concentration of the urinary enzyme, urokinase, which would affect the level of urinary mucoproteins such as uromucoid. In support of this hypothesis, ELISA studies were conducted to investigate the urokinase concentrations in urine obtained from males (22-60 years) with and without renal stones. These results showed a significant decrease in urinary urokinase concentration of renal stone patients which, once again, underlines the possible involvement of urokinase in renal stone formation. Therefore, it seems logical to conclude that urokinase may play an integral role in this multifactorial disease.

Family study of 2,8-dihydroxyadenine stone formation: report of two cases of a compound heterozygote for adenine phosphoribosyltransferase deficiency (APRT*J/APRT*Q0)

The family members of 2 formers of 2,8-dihydroxyadenine stones were examined for history, adenine phosphoribosyltransferase (APRT) activity, genotype, urinary sediment, and urinary constituents. The patients' father showed a genotype of APRT*1/APRT*Q0, and their mother showed APRT*1/APRT*J. Patients 1 and 2 were compound heterozygotes for adenine phosphoribosyltransferase deficiency (APRT*J/APRT*Q0), and APRT activities were 4.5% and 4.0% of normal, respectively. 2,8-Dihydroxyadenine crystals could be seen in the urinary sediment. Treatment with allopurinol completely stopped new stone formation for 5 years in patient 1.

N-acetyl-beta-D-glucosaminidase excretion in calcium oxalate stone patients and its relation to the risk of stone formation

A tubular renal damage induced by crystals in the renal tubuli can be the triggering primary but also secondary cause of stone formation. In 72 calcium oxalate stone patients (45 men, 27 women) N-acetyl-beta-D-glucosaminidase [NAG] excretion in 24h-urine was investigated. 48 healthy test persons (27 men, 21 women) served as a control group and helped to establish reference values. In order to find out a possible relation between NAG reference values and the risks of urolithiasis, lithogenous and inhibitory substances were determined in both groups. In the following, relative calcium oxalate supersaturation, representing a risk of urinary stone formation, was analyzed and compared to NAG excretion values. The threshold value of pathologic NAG excretion was determined in the group of healthy test subjects (mean value +/- 2 standard deviation) and was fixed at 4.2 U/d (women 3.06 U/d, men 4.24 U/d). In our investigations on NAG excretion significantly (p < 0.05) increased values were found in stone patients (4.43 U/d +/- 4.27) as compared to healthy test persons (2.13 U/d +/- 1.02). In the case of increased NAG excretion in stone patients there was a positive correlation between NAG excretion and increased phosphate, sulphate, uric acid, oxalate, and creatinine excretion. Only in female patients there was a relation between relative calcium oxalate supersaturation and NAG excretion values. As a result, NAG determination is considered to be an appropriate means of tracing a certain risk group within calcium oxalate stone patients.

Low-molecular-weight variants of osteopontin generated by serine proteinases in urine of patients with kidney stones

Osteopontin (OPN) is a multifunctional glycosylated phosphoprotein found in body fluids, including urine, and has been implicated in urinary stone formation. We tested the hypothesis that OPN levels in urine of patients with kidney stones differed from normal individuals. To quantify OPN levels in the urine, we developed an ELISA using a combination of a mouse monoclonal and rabbit polyclonal antibodies raised against a recombinant glutathione-S-transferase-human OPN fusion protein. In a group of 34 patients diagnosed with kidney stones compared with a control group of 23 normal individuals, we found that OPN levels in urine of the patient and control groups ranged from 0.01 to 2.7 micrograms/ml, with no significant difference in their medians (P > 0.8, Mann-Whitney test). OPN in urine was qualitatively assessed by Western blotting using a biotinylated monoclonal antibody to detect various molecular forms. The urine of most individuals contained OPN species within in the 55- to 66-kDa electrophoretic mobility range. However, a significantly higher proportion of individuals in the patient group (13 of 34) was found to have aberrant urine OPN species (< or = 40 kDa) compared to 2 of 23 for the control group (P < 0.03, chi 2 test). Mixing experiments indicated that urine samples with aberrant OPN contain proteases inhibitable with phenylmethylsulfonyl fluoride. Such proteases could break down normal urine OPN in vitro. Therefore, urine from a high frequency of kidney stone patients contains serine proteases that contribute to proteolytic cleavage of OPN.

Clinical significance of urinary enzymes and beta 2-microglobulin following ESWL

To examine the renal damage caused by shock waves, urinary excretion of enzymes and beta 2-microglobulin were determined before and after ESWL. Urine samples were obtained from 35 patients with renal stone and 26 patients with ureteric stone treated with ESWL. Urinary lactate dehydrogenase (LDH) levels significantly increased on day 0, just after ESWL, in both groups. In the ureteric stone group the kidneys received less shock waves than in the renal stone group. Increased urinary lactate dehydrogenase was considered to have derived from erythrocytes in urine. Elevated urinary N-acetyl-beta-D-glucosaminidase (NAG) levels were also observed on day 0 after ESWL in both groups, due to unknown reasons. Indirect effect of ESWL through the sympathetic nervous system or humoral factors may contribute to increases in the urinary excretion of NAG. No significant increase was found in urinary gamma-glutamyl-transpeptidase (GGTP) levels for 5 days after ESWL. Urinary beta 2-microglobulin (BMG) levels increased on day 0 in the renal stone group alone. In our present study, the clinical significance of urinary enzymes and BMG was not well evaluated, because urinary excretion of these indicators following ESWL were transient and mild.

Scanning electron microscopy of 2,8-dihydroxyadenine crystals and stones

The lack of purine salvage enzyme, adenine phosphoribosyltransferase (APRT), leads to 2,8-dihydroxyadenine stone formation and/or crystalluria because it is insoluble in urine. Urolithiasis composed of 2,8-dihydroxyadenine is not only formed in a complete defect of APRT, but also in a partial deficiency of this enzyme. The defect is inherited as an autosomal recessive trait, the homozygous state is associated with high urinary levels of 2,8-dihydroxyadenine and with crystalluria, calculus formation, and potential nephrotoxicity. Determination of the APRT activity will facilitate quantification of the enzyme deficiency and elucidation of the hereditary history. 2,8-dihydroxyadenine excretion in the 24-hour urine and its circadian rhythm were determined using a new method of high performance liquid chromatography determination. By means of a standard case presentation, we illustrate the analysis of urinary sediments and calculi as well as the scanning electron microscopic images of this kind of stone.

A missense mutation in the hypoxanthine phosphoribosyltransferase gene in a pediatric patient with hyperuricemia

We have identified a mutation in the gene coding for the enzyme hypoxanthine phosphoribosyltransferase in a pediatric patient with hyperuricemia and nephrolithiasis. The mutation is a nucleotide substitution causing an amino acid substitution in the hypoxanthine phosphoribosyltransferase protein. In this patient, fibroblasts but not lymphocytes showed resistance to 6-thioguanine, and reduced enzyme activity was detected in lymphocytes. These results are consistent with the intermediary phenotype associated with partial hypoxanthine phosphoribosyltransferase enzyme deficiency. Altogether, six males in this family suffered from hyperuricemic symptoms, and small differences in phenotype were seen.

A review of new concepts in renal stone research

Clinical and basic research in the field of urolithiasis has developed rapidly in recent years. Progress in extracorporeal shock wave lithotripsy (ESWL) and percutaneous nephrolithotomy (PNL) has brought about a revolution in the surgical treatment of urolithiasis and research at the cellular and molecular level is now expanding. In spite of these advances, however, clinical treatment of urolithiasis remains far from satisfactory. Stone recurrence in many patients cannot be predicted and is beyond control of urologists mainly because the mechanisms of stone formation are still not fully understood. It is necessary to study the process of stone-formation more intensely at the cellular and molecular level, and to strengthen the links between basic and clinical research in the field. In this review, the processes involved in the formation of stones are compared with those involved in normal bio-mineralization and a model of urolithiasis is put forward based on modern systems science. Attention is concentrated on: (a) Directions of research based on physico-chemical theories of stone formation; (b) The role of renal tubular defects in urolithiasis; (c) The role of free radical reactions in stone formation; and (d) Macromolecular abnormalities and their correction.

Adenine phosphoribosyltransferase deficiency with renal deposition of 2,8-dihydroxyadenine leading to nephrolithiasis and chronic renal failure

Homozygous adenine phosphoribosyltransferase deficiency is a genetic defect that is associated with 2,8-dihydroxyadenine urolithiasis. Since the prevalence of the heterozygous state is found in 0.4% to 1.2% of the population, it is surprising that more cases of 2,8-dihydroxyadenine urolithiasis have not been reported. Herein we describe a patient with complete adenine phosphoribosyltransferase deficiency with 2,8-dihydroxyadenine urolithiasis leading to chronic renal failure. Gene sequencing revealed that the patient is a compound heterozygote. One of the mutations (a T insertion between bases 346 and 347) has been encountered before, but the second (a G-to-A substitution at base 1356) has not been previously reported. Possible explanations for the unexpected rarity of 2,8-dihydroxyadenine urolithiasis are discussed.

Urinary type IV collagenase: elevated levels are associated with bladder transitional cell carcinoma

Accumulating experimental evidence has linked the overproduction of extracellular matrix-degrading metalloproteinases with tumor cell invasion. In the present study one member of the metalloproteinase family, type IV collagenase (M(r) 72,000 gelatinase), is shown to be elevated in the urine of patients with transitional cell carcinoma of the bladder. The form of the enzyme in the urine was studied by three independent methods: enzyme-linked immunosorbent assay, Western immunoblotting; and gelatin zymography. Immunoblotting revealed that the enzyme was present as a series of fragments, each retaining the amino terminus of the mature proenzyme. A prominent M(r) 43,000 fragment was associated with the transitional cell carcinoma cases. Zymography demonstrated that multiple enzyme species with gelatinase activity were present in urine and that high-molecular-weight bands of substrate lysis corresponded to complexes between type IV collagenase and tissue inhibitor of metalloproteinases 2. The total amount of type IV collagenase antigen was significantly elevated in the urine of 37 transitional cell carcinoma patients (range, 0-1081 ng/ml; mean, 318.4 +/- 147.3) compared to 19 normal controls (P < or = 0.004) and 17 inflammatory disease controls (P < or = 0.011). Immunohistochemical staining of bladder tumor biopsies verified that the transitional cell carcinoma cells were producing the M(r) 72,000 enzyme. Thus, M(r) 72,000 type IV collagenase, which is present in the urine in many forms including fragments and complexes with inhibitors, may be a useful marker for bladder cancer diagnosis or prognosis.

[Two cases of 2.8-dihydroxyadenine stone with a partial deficiency of adenine phosphoribosyltransferase]

We report two cases of 2.8-dihydroxyadenine stones due to partial deficiency of adenine phosphoribosyltransferase. The first patient is a 41-year-old female. Radiologic examination revealed left radiolucent renal stones and contracted kidney. Left nephrectomy was performed. Infrared spectrometric analysis of the stones revealed 2.8-dihydroxyadenine calculi. The adenine phosphoribosyltransferase activity in lymphocyte (T cell) was 19.5% of the control level. After the operation, the patient was given 300 mg/day of alloprinol. There have been no signs of recurrence. The second patient was a 52-year-old male. Radiologic examination revealed radiolucent stones of the right kidney and the urine bladder. Percutaneous nephrolithotomy and cystolithotripsy were performed. Infrared spectrometric analysis of the stones revealed 2.8-dihydroxyadenine calculi. The adenine phosphoribosyltransferase activity in the lymphocytes (T cell) was 21% of the control level. After the operation the patient was given 200 mg/day of alloprinol and put on a low purine diet. There have been no signs of recurrence.

Immunohistochemical detection of renal carbonic anhydrase of patients with recurrent urolithiasis

In renal exploratory excisions the isoenzyme C of the carbonic anhydrase was detected in 51 operative treated patients with recurrent urolithiasis and in 6 patients with ren mobilis or stenosis of the ureteral pelvic junction by using the immunohistochemical PAP-method. In the distal tubules and collecting ducts there is an alternating occurrence of cells with small and those with strong reactivity. This correlates with the distribution of mean or principal (P-, small reaction) and intercalated (I-, strong reaction) cells. The number of carbonic anhydrase rich cells and the degree of their cytoplasmic reaction to this enzyme seem to correlate with the ability of the urine to acidify. The patients were divided into four groups according to the mean urine pH estimated for a period of two weeks. The third group with predominantly acid urine (pH less than 5.8) showed a significantly increased number of carbonic anhydrase rich cells (mean = 63% +/- 6, n = 18) as compared to the first group (controls) without urolithiasis and normal urine (pH 5.8-6.8, mean = 46% +/- 8, n = 6) or the second group with urolithiasis and normal urine (pH 5.8-6.8, mean = 46% +/- 8, n = 28). The fourth group with predominant alkaline urine (pH greater than 6.8) showed a significantly decreased number of intercalated cells (mean = 42% +/- 16, n = 5) in comparison to the third group. Indeed, the difference with the control group is not significant but the cytoplasmic reaction of I-cells decreases distinctly in comparison to all other groups.

[Localization and extent of tissue damage caused by extracorporeal lithotripsy (ESWL)]

Extracorporeal shock wave lithotripsy (ESWL) causes proteinuria. In our study we investigated the protein fractions and the electrolyte composition of the urine in patients who had been treated with ESWL. The aim was to obtain information on the degree and the localisation of the glomerular, tubular or vascular destruction caused by ESWL in humans. A total of 34 patients with stones had been treated with ESWL. As parameters we used: urine output, creatinine clearance, total protein, albumin, immunoglobulin G, N-acetyl-beta-D-glucosaminidase (beta-NAG), alpha-1-microglobulin, the fractional excretion of Na+ and apolipoprotein-A-1. After ESWL treatment proteinuria and albuminuria are found. Our parameters show no deterioration of the glomerula or the tubulus. The increase in apolipoprotein-A-1, a postglomerular parameter, however, is interpreted as a manifestation of vascular destruction after ESWL; this is normally temporary, leaving no permanent damage.

Increased serum alkaline phosphatase activity: a possible indicator of renal damage

Increased levels of serum alkaline phosphatase (ALP) (E.C.3.1.3.1.) were observed in 25 patients with various urological conditions involving the kidneys: malignancy, complicated nephrolithiasis, and surgical and percutaneous manipulations. Other possible sources for increased ALP level, mainly hepatic and osseous, were excluded by history, laboratory tests, and liver and bone imaging. Studies of isoenzymes of ALP did not show a distinctive pattern. ALP levels returned to the normal range by treating the underlying lesions involving the kidney: nephrectomy, complete removal of stones, or removal of nephrostomy. The increase in serum ALP activity may be derived from the injury to the brush border membrane of the renal tubular cells. Renal function impairment and contrast media induced nephrotoxicity may also be responsible for the increased serum ALP. Serum ALP may be a marker for involvement of the kidneys in pathological processes and an indicator of complete treatment. This clinical observation is worthy of further study.

Identification of a splice mutation at the adenine phosphoribosyltransferase locus in a German family

We examined the molecular basis of adenine phosphoribosyltransferase (APRT) deficiency in homozygous-deficient, identical twin brothers who were born to non-consanguineous German parents. DNA was isolated from blood, and the APRT gene was amplified by PCR, subcloned into M13, and sequenced completely. A single T insertion between bases 1831-1832 or 1832-1833 was identified. This alters the consensus sequence at the exon 4 - intron 4 spice donor site and leads to aberrant splicing. The same mutation has been described previously in two affected brothers from Belgium, and the Indianapolis group has also identified it in two other, unrelated Caucasian patients. Thus, this mutation may be a common cause of APRT deficiency in the Caucasian population.

The excretion of carbonic anhydrase isozymes CA I and CA II in the urine of apparently healthy subjects and in patients with kidney disease

Carbonic anhydrase isozymes CA I and CA II were assayed by a radio-immunosorbent technique in the plasma and urine of apparently healthy subjects and of patients with renal disease. The concentrations (mean +/- SD, n = 8) of CA I and CA II in the plasma of healthy subjects were 2.3 +/- 2.3 and 0.8 +/- 0.5 mg/l, respectively. The urinary excretion values were 3.8 +/- 2.0 and 3.5 +/- 1.9 micrograms/24 h, and the apparent renal clearances were 21 +/- 17 and 52 +/- 44 microliters/min, respectively, values that are similar to those of other low molecular weight proteins. CA I and CA II have mol. wt of 28,850 and 29,300, respectively, they are globular in shape and have a Stoke-Einstein radius of 25 A. They could, therefore, be expected to be filtered at the glomeruli and thereafter reabsorbed by the proximal tubules. CA II is also present in the cytoplasm of renal proximal and distal tubular cells. A study of the pattern of urinary excretion of CA I and CA II could permit detection of damage to renal tubular cells in two ways--either from defective reabsorption of filtered CA I and CA II by the proximal tubular cells, or from leakage of CA II from the proximal or distal tubules into the urine. Some patients with hypercalcuria and renal tubular acidosis showed increased excretion of these enzyme proteins and of beta 2-microglobulin (BMG) into the urine, but the prevalence was rather low (27%). Further studies of patients with more severely damaged kidneys are required.

[NAG (N-acetyl-beta-D-glucosaminidase)--a sensitive marker for disorders of kidney function]

In a clinical study we tested the use of the lysosomal enzyme NAG as a parameter of kidney function. Following prospective randomization, we examined NAG excretion during cisplatin treatment with/without nephroprotection, after intravenous urography with ionic/non-ionic contrast media, during lower/upper urinary tract infections and before/after extracorporeal shockwave lithotripsy for intrarenal calculi (first-generation equipment used). Measurements were performed in 3-h urine specimens and in urine collected over 24 h, using a simple method of analysis. A correlation between NAG leakage and functional disorder of the renal tubular cells seemed likely on the basis of additional clinical and experimental data. Increases, in some cases dramatic, in NAG excretion were observed after the administration of cisplatin and ionic contrast media, in acute pyelonephritis, and after extracorporeal shockwave lithotripsy. However, the increase in NAG excretion was less impressive during cisplatin therapy when nephroprotective amino acids were infused, and in the urography group when non-ionic contrast media were used. Infections of the lower urinary tract did not increase NAG excretion. The results indicate that NAG is a sensitive marker of occult renal dysfunction, which can be checked by non-invasive techniques and can be used in a clinic setting to detect functional disorders of the kidney.

[2,8-dihydroxyadenine urinary calculus: the significance of exact physical calculus analysis]

A 21-year-old female patient was treated with Uralyt-U for 3 months for a radiolucent kidney stone. During this therapy the stone increased significantly in volume. After treatment by ESWL, the stone was analyzed by a chemical method and by X-ray diffraction. Calcium phosphate and urate were detected by the chemical method and 2,8-dihydroxyadenine by X-ray diffraction. This case report emphasizes the importance of precise stone analysis for medical treatment is emphasized.

[The proteolysis-ion theory of the pathogenesis of nephrolithiasis]

A study was made of urinary proteolysis. This parameter turned to be decreased in patients with nephrolithiasis versus normal subjects. The authors developed an original proteoclastic-ion theory of nephrolithiasis pathogenesis, based on the two main risk factors triggering the disease: low levels of urinary proteolysis leading to the formation of a calculous matrix; the urine pH values optimal for the sedimentation of lithiasic salts. The combination of both risk factors was responsible for the development of calculous crisis and the formation of microlith. The decreased index of urinary proteolysis calculated with the formula offered could be regarded as a risk indication to the microlith formation. A possible elimination of the both risk factors was demonstrated. The technique of microlithiasis metaphylaxis was developed with regard to the major and minor risk factors and the possibility of their elimination. The values of urinary proteolysis were the criteria for a successful therapeutic response. With regard to the number of risk factors the risk of primary nephrolithiasis or lithiasis relapses could be predicted.

2,8-dihydroxyadenine urolithiasis: report of a case first diagnosed after renal transplant

We report a case of homozygous adenine phosphoribosyl transferase (APRT) deficiency associated with 2,8-dihydroxyadenine stones recurrent in a patient with a renal transplant. The disease was diagnosed 23 years after the initial episode of renal colic. At that time the disease was unknown. Our patient is only the second case of this disorder reported from the United States. Correct diagnosis is important because long-term maintenance with allopurinol and a low purine diet can effectively prevent stone formation and renal failure.

2,8-Dihydroxyadenine lithiasis

2,8-Dihydroxyadenine (2,8-DHA) lithiasis is a form of kidney stone previously mistaken for uric acid because of identical reactivity in non-specific tests used routinely in stone analysis. Unlike uric acid, the stones crush easily and do not react with uricase. The biochemical basis for the defect is a deficiency of the enzyme adenine phosphoribosyltransferase (APRT). A complete deficiency has been reported in 29 patients from 11 countries. The number of stone formers reported in Japan (10 homozygotes, 16 heterozygotes) Austria (3), and Switzerland (2) suggests more efficient diagnosis in those countries. The defective enzyme in heterozygotes in Japan is a kinetic mutant demonstrable in intact not lysed cells. 20% of APRT-deficient subjects have been asymptomatic. An equal number have presented in acute renal failure, three of whom are now on dialysis. Formation of the nephrotoxic 2,8-DHA can be prevented by allopurinol. This underlines the importance of early diagnosis, since such severe renal damage should be avoidable.

[Clinico-biochemical and morphological changes in obstructive calculous pyelonephritis in children]

The article presents results of a comparative study of clinico-biochemical and morphological alterations in 38 patients with obstructive calculous pyelonephritis before and after operation. The data obtained show considerably elevated activity of LDG and other enzymes, content of cholesterin, total phospholipids followed by histomorphological alterations in the kidney.

Deficient urinary fibrinolysis in renal stone disease

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