Oxalobacter formigenes treatment confers protective effects in a rat model of primary hyperoxaluria by preventing renal calcium oxalate deposition

In primary hyperoxaluria, increased hepatic oxalate production sometimes leads to severe nephrocalcinosis and early end-stage kidney disease. Oral administration of Oxalobacter formigenes (O. formigenes), an oxalate-degrading bacterium, is thought to derive oxalate from systemic sources by inducing net enteric oxalate secretion. Here, the impact of O. formigenes on nephrocalcinosis was investigated in an ethylene glycol rat model mimicking hepatic oxalate overproduction in primary hyperoxaluria. Eighteen rats were administered ethylene glycol (0.75% in drinking water) for 6 weeks, of which 9 were treated by oral gavage with O. formigenes and 9 received vehicle. Five control rats did not receive ethylene glycol or O. formigenes. Plasma and urinary oxalate levels, calcium oxalate crystalluria, urinary volume, fluid intake, and serum creatinine were monitored during the study. On killing, nephrocalcinosis was quantified. Ethylene glycol intake induced pronounced hyperoxalemia, hyperoxaluria, calcium oxalate crystalluria and nephrocalcinosis. Concomitant O. formigenes treatment partially prevented the ethylene glycol-induced increase in plasma oxalate and completely prevented nephrocalcinosis. Urinary oxalate excretion was not reduced by O. formigenes treatment. Nevertheless, absence of crystals in renal tissue of O. formigenes-treated ethylene glycol animals indicates that the propensity for oxalate to crystallize in the kidneys was reduced compared to non-treated animals. This is supported by the lower plasma oxalate concentrations in O. formigenes-treated animals. This study shows a beneficial effect of O. formigenes treatment on ethylene glycol-induced hyperoxalemia and nephrocalcinosis, and thus supports a possible beneficial effect of O. formigenes in primary hyperoxaluria.

Early initiation of sodium-glucose linked transporter inhibitors (SGLT-2i) and associated metabolic and electrolyte outcomes in diabetic kidney transplant recipients

There is a paucity of data on the use of SGLT2 inhibitors on outcomes in kidney transplant recipients. There may be concern in initiating these agents, especially within the first year post-transplant when renal function is more labile and immunosuppression more intense, due to a presumed high risk of urinary infections and acute kidney injury. This is a retrospective study on 50 kidney transplant recipients, half of whom were started on therapy within the first year of transplant. Over a follow-up period of 6 months, overall patients had a statistically significant improvement in weight by -2.95 kg [SD 3.54, P = <.0001 (CI: 3.53, 1.50)] as well as hypomagnesemia 0.13 [SD 1.73, P = .0004 (CI: 0.06, 0.20)]. Overall insulin usage declined by -3.7 units [SD 22.8, P = .17]. 14% of patients had at least one urinary tract infection although this rate is not different (~20%) than that reported historically in this high-risk population.

Importance of magnesium sulfate supplementation in the prevention of hypomagnesemia and hypocalcemia during chemoradiation in head and neck cancer

In advanced squamous cell carcinoma of the head and neck, concomitant radiotherapy with cisplatin and/or cetuximab is frequently combined with cisplatin-based induction chemotherapy, which can cause severe hypomagnesemia, hypocalcemia, and hypokalemia. The aim of our study was to analyze the effects of magnesium sulfate supplementation on the incidence of hypomagnesemia, hypokalemia, and hypocalcemia during four cycles of TPF (docetaxel, cisplatin, and 5-fluorouracil) induction chemotherapy followed by concomitant radiotherapy (CRT) with cisplatin and cetuximab. Twenty-five patients included in a phase II prospective study received routine magnesium sulfate infusions before each cycle of cisplatin, and additional supplementation based on laboratory findings. During TPF, the incidence of grade 1/2 and grade 3/4 hypomagnesemia was 16% and 4%, respectively; and increased despite magnesium supplementation during CRT to 72% and 8%, respectively. During TPF, a grade 2 and grade 4 hypocalcemia occurred in 8% and 4%, respectively; and during CRT, it reached 36% (grade 1/2). Grade 1 hypokalemia only was observed during TPF (4%) and CRT (8%). The median amounts of supplemented magnesium sulfate during TPF and CRT were 20 mEq and 50 mEq, respectively. It appears that a low incidence of grade 3/4 hypomagnesemia and hypocalcemia in our patients resulted from intensive magnesium supplementation. Thorough measurements of magnesium and calcium during cisplatin-based chemoradiation protocols in patients with head and neck cancer are crucial in preventing the development of grade 3/4 hypomagnesemia and hypocalcemia.

Hypertension is a characteristic complication of X-linked hypophosphatemia

X-linked hypophosphatemia (XLH) is a group of rare disorders caused by defective proximal tubular reabsorption of phosphate. Mutations in the PHEX gene are responsible for the majority of cases. There are very few reports of long-term complications of XLH other than skeletal and dental diseases. The aim of this study was to identify the phenotypic presentation of XLH during adulthood including complications other than skeletal and dental diseases. The clinical and biochemical phenotype of 22 adult patients with a PHEX gene mutation were examined retrospectively from their medical records. 6 patients had hypertension. The average age of hypertension onset was 29.0 years. Secondary hyperparathyroidism preceded the development of hypertension in 5 patients. 1 patient developed tertiary hyperparathyroidism. 15 patients had nephrocalcinosis. 2 patients had chronic renal dysfunction. Patients with hypertension had a significantly lower eGFR (p=0.010) compared to patients without hypertension. No significant difference was found in any other parameters. To examine the genotype-phenotype correlation, 10 adult males were chosen for analysis. No significant genotype-phenotype correlation analysis was revealed in any of the complications. However, there was a possibility that the age at nephrocalcinosis onset was younger in the non-missense mutation group than in the missense mutation group (p=0.063). This study corroborated the view that early-onset hypertension could be one of the characteristic complications seen in XLH patients. Considering the limited number of our patients, further study is necessary to address a potential cause of hypertension. XLH patients require careful lifelong treatment.

Hyperoxaluria is reduced and nephrocalcinosis prevented with an oxalate-degrading enzyme in mice with hyperoxaluria

BACKGROUND/AIMS

Hyperoxaluria is a major risk factor for recurrent urolithiasis and nephrocalcinosis. We tested an oral therapy with a crystalline, cross-linked formulation of oxalate-decarboxylase (OxDc-CLEC) on the reduction of urinary oxalate and decrease in the severity of kidney injury in two models: AGT1 knockout mice (AGT1KO) in which hyperoxaluria is the result of an Agxt gene deficiency, and in AGT1KO mice challenged with ethylene glycol (EG).

METHODS

Four different doses of OxDc-CLEC mixed with the food, or placebo were given to AGT1KO mice (200 mg/day, n = 7) for 16 days and to EG-AGT1KO mice (5, 25, and 80 mg, n = 11) for 32 days.

RESULTS

Oral therapy with 200 mg OxDc-CLEC reduced both urinary (44%) and fecal oxalate (72%) in AGT1KO mice when compared to controls. Similarly, in EG-AGT1KO mice, each of the three doses of OxDc-CLEC produced a 30-50% reduction in hyperoxaluria. A sustained urinary oxalate reduction of 40% or more in the 80 mg group led to 100% animal survival and complete prevention of nephrocalcinosis and urolithiasis.

CONCLUSION

These data suggest that oral therapy with OxDc-CLEC may reduce hyperoxaluria, prevent calcium oxalate nephrocalcinosis and urolithiasis, and can represent a realistic option for the treatment of human hyperoxaluria, independent of cause.

Does citrate prevent nephrocalcinosis in preterm neonates?

Nephrocalcinosis (NC) occurs frequently in preterm neonates. A high U-calcium/citrate is one of the contributing factors to the development of NC. In stone-forming children and adults citrate supplementation is a successful preventive therapy. In this randomized controlled trial the effect of citrate therapy was studied on the development of NC in preterm neonates with a gestational age <32 weeks. Thirty-eight preterm neonates (mean gestational age 29.8 weeks (SD 1.6), mean birth weight 1,300 g (SD 351) were treated with sodium citrate (0.52 mmol/kg/day in four doses) from day 8 of life until at term and 36 preterm neonates (mean gestational age 29.6 weeks (SD 1.6), mean birth weight 1,282 g (SD 256) were not treated. U-calcium, U-creatinine, U-citrate and U-pH were measured at day 7, 14, 21, 28 of life and at term. Renal ultrasonography (US) was performed at term. U-citrate/creatinine and U-pH were significantly higher and U-calcium/citrate was significantly lower in the citrate group at day 14, 21 and 28 compared with the control group (P<0.05). Complications of citrate administration were not encountered, however the incidence of NC was not significantly different in the treated (34%) compared with the control group (44%), P=0.37. Preterm neonates treated with citrate in the first months of life have higher U-citrate/creatinine and lower U-calcium/citrate compared with controls. Sodium citrate therapy in a dosage of 0.52 mmol/kg/day is safe but does not prevent NC. Whether a higher dose or potassium citrate decreases the incidence of NC should be evaluated in further studies.

A family with autosomal dominant hypocalcaemia with hypercalciuria (ADHH): mutational analysis, phenotypic variability and treatment challenges

Autosomal dominant hypocalcaemia with hypercalciuria (ADHH) is an intriguing syndrome, in which activating mutations of the calcium sensing receptor (CaSR) have recently been recognised. We describe a kindred with seven affected individuals across three generations, including patients affected in the first decade of life. Age at diagnosis varied from birth to 50 years. Affected members had hypocalcaemia (1.53-1.85 mmol/l), hypercalciuria, low but detectable parathyroid hormone (PTH) and hypomagnesaemia. Four of seven affected individuals were symptomatic (seizures, abdominal pains and paraesthesias), unrelated to severity of hypocalcaemia. Additional complications include nephrocalcinosis (n = 3) and basal ganglia calcification, identified by CT scanning in all five individuals. Symptomatic individuals were treated with calcium and calcitriol to reduce the risk of hypocalcaemic seizures. DNA sequence analysis, identified a mutation in exon 3, codon 129 (TGC-->TAC) of the CaSR gene of seven affected family members, resulting in loss of a conserved cysteine residue, potentially disrupting CaSR receptor dimerisation. Thus, a novel mutation was identified in this family, who demonstrate variability of ADHH phenotype and also illustrate the complexities of clinical management. Optimal management of ADHH is difficult and we recommend judicious treatment to avoid an increased risk of nephrocalcinosis.

Hypocitraturia as a risk factor for nephrocalcinosis after kidney transplantation

Calcium-oxalate crystal deposition in kidney transplant biopsy specimen led us to investigate the impact of calcineurin inhibitor treatment on urinary excretion of lithogenic and stone inhibitory substances in 53 children after successful kidney transplantation (KTx) receiving cyclosporine A (CsA) or tacrolimus. We compared the values obtained with those of 12 patients with recurrent nephrotic syndrome under CsA and of 6 patients with Rasmussen encephalitis (RE) under tacrolimus therapy. Renal ultrasound examinations were repeatedly performed. Hypocitraturia was found in 69% of patients, with KTx patients having a significantly lower urinary citrate excretion than those receiving calcineurin inhibitors for other reasons. Secondly, we found hyperoxaluria in 35% of patients, again especially in those after KTx. No significant difference in urinary substances was seen comparing CsA with tacrolimus treatment. Urolithiasis was found in one and calcium-oxalate crystal deposition in biopsy specimen of three KTx patients. Calcineurin inhibitor treatment can lead to significant hypocitraturia, especially in patients after KTx receiving the highest dose of medication. Hyperoxaluria is primarily the result of a removal of significant body oxalate stores, deposited during dialysis, but may not be suspected as a specific side effect of calcineurin inhibitor therapy. Both findings can increase the risk for urolithiasis or nephrocalcinosis.

Effect of the calcimimetic NPS R-467 on furosemide-induced nephrocalcinosis in the young rat

BACKGROUND

Furosemide induces nephrocalcinosis in both humans and animals. We showed previously that parathyroidectomy protected against the development of furosemide-induced nephrocalcinosis in young rats, indicating a possible role for parathyroid hormone (PTH) in its pathogenesis. Calcimimetic agents such as NPS R-467 are potent and selective agonists at the calcium-sensing receptor in parathyroid glands and inhibit PTH secretion.

METHODS

To determine whether NPS R-467 could, like parathyroidectomy, prevent furosemide-induced nephrocalcinosis, we studied 35 6-week-old male Sprague-Dawley rats, divided into five groups. Group A served as control, group B received intraperitoneally furosemide (40 mg/kg), groups C, D, and E received furosemide and NPS R-467 intraperitoneally at doses of 10, 20, and 40 micromol/kg, respectively, daily for 8 days. During the last 3 days, animals were placed in metabolic cages for measurement of urine output, food, and water intake. Blood and kidneys were collected on day 8, 60 to 90 minutes after the last doses. Kidney calcium content was measured and nephrocalcinosis scoring (0 to 5) was assessed histologically.

RESULTS

Furosemide increased urine output and fluid intake, and decreased body weight gain similarly in all groups. Serum PTH levels (mean +/- SD) were significantly higher in furosemide-treated control animals (276 +/- 226 pg/mL vs. 64 +/- 21 pg/mL); NPS R-467 induced a dose-dependent decrease in PTH levels (52 +/- 51 pg/mL, 18 +/- 7 pg/mL, and 13 +/- 3 pg/mL in groups C, D, and E, respectively). Plasma Ca(2+) was slightly, but significantly lower in all three NPS R-467 treated groups (5.1 +/- 0.4 mg/dL, 4.8 +/- 0.3 mg/dL, and 4.5 +/- 0.3 mg/dL in groups C, D, and E, respectively) compared to 5.7 +/- 0.1 mg/dL and 5.5 +/- 0.2 mg/dL in groups A and B, respectively. Furosemide treatment induced a substantial increase in kidney calcium content (1819 +/- 664 microg/g dry weight vs. 126 +/- 26 microg/g dry weight) and nephrocalcinosis scoring (5.0 +/- 0.0 vs. 0.0 +/- 0.0). Treatment with NPS R-467 ameliorated the furosemide-induced increase in kidney calcium content (673 +/- 312 microg/g, 361 +/- 188 microg/g, and 563 +/- 291 microg/g) and nephrocalcinosis scoring (2.2 +/- 1.2, 0.7 +/- 0.8, and 1.0 +/- 1.2) in groups C, D, and E, respectively.

CONCLUSION

The calcimimetic agent NPS R-467 prevents the development of hyperparathyroidism and attenuates nephrocalcinosis in the furosemide-treated young rat.

Activating mutations of the calcium-sensing receptor: management of hypocalcemia

Activating mutations of the calcium-sensing receptor (CaR) can cause isolated hypoparathyroidism. Treatment of hypocalcemia in these patients remains to be optimized, because the use of 1-hydroxylated vitamin D3 derivatives can cause hypercalciuria and nephrocalcinosis. We identified activating CaR mutations in 8 (42%) of 19 unrelated probands with isolated hypoparathyroidism. The severity of hypocalcemic symptoms at diagnosis was independent of age, mutation type, or mode of inheritance but was related to the degree of hypocalcemia; serum Ca was 1.97 +/- 0.08, 1.82 +/- 0.14, and 1.54 +/- 0.22 mmol/liter, respectively, in asymptomatic (n = 7), mildly symptomatic (n = 8), and severely symptomatic patients (n = 6). Hypocalcemia segregated with the CaR mutation, but no phenotype-genotype relationships were identified. Fourteen patients received regular 1-hydroxylated vitamin D3 treatment (mean duration, 7.2 +/- 4.9 yr). Nine had hypercalciuric episodes, which were associated with nephrocalcinosis in eight cases. Serum Ca during treatment predicted hypercalciuria and nephrocalcinosis poorly, because either or both of the latter could develop in hypocalcemic patients. Thus, mutational analysis of the CaR gene should be considered early in the work-up of isolated hypoparathyroidism. Treatment options should be weighed carefully in patients with serum Ca below 1.95 mmol/liter. The risk of nephrocalcinosis during treatment can be minimized by carefully monitoring urinary Ca excretion.

Renal cortical calcification in syngeneic intact rats and those receiving an infrarenal thoracic aortic graft: possible etiological roles of endothelin, nitrate and minerals, and different preventive effects of long-term oral treatment with magnesium, citrate and alkali-containing preparations

Renal cortical nephrocalcinosis (C-NC) is a rare disorder of uncertain etiology. Using highly inbred (syngeneic) male Lewis rats, we describe the spontaneous occurrence of histologically detectable C-NC in sham operated control rats (Sham; n=12), its aggravation following grafting of the ascending thoracic aorta from a donor rat to the infrarenal aorta of a recipient (ATx; n=12), and differences in C-NC inhibition after 12 weeks of oral administration of magnesium (Mg), citrate and alkali. C-NC is characterized by Kossa-positive areas located in cells of the proximal tubule close to blood vessels and also, to a lesser extent, within glomeruli. After ATx there was vascular overproduction of endothelin (ET-1) but decreased production of nitrate; in renal cortical tissue there was an excess of calcium over Mg and phosphorus and oxalate over citrate. In plasma there was an increase in calcium and creatinine within the normal range. Calcification of tubular cells was eliminated by a preparation containing potassium, sodium and bases (from citrate degradation and bicarbonate) in addition to Mg. Less effective than the latter was Mg-potassium citrate and least effective, Mg citrate. The former treatment also normalized calcemia and urinary nitrate, but only incompletely suppressed ET-1 and had no significant effect on glomerular calcification or tissue and urinary oxalate. Urinary ET-1 excess appeared directly related to the cortical tissue calcium/Mg ratio, and urinary excretion of Mg, citrate and total protein appeared to be inversely related to the severity of C-NC. It was concluded that (1) the highly inbred rat is prone to precipitation of calcium phosphate in the renal cortex; (2) this type of C-NC occurs in close proximity to and within renal vascular tissue and is associated with an imbalance of vasoconstrictors and vasodilators of endothelial origin; (3) effective inhibition of C-NC can be achieved by an alkalinizing combination of Mg, potassium, sodium and citrate, underscoring its utility in the prophylaxis of pathological calcium phosphate deposition. The significance of these findings for the etiology and treatment of clinical disorders with renal and vascular calcification is uncertain and requires further investigation.

Thiazide diuretics arrest the progression of nephrocalcinosis in children with X-linked hypophosphatemia

OBJECTIVE

X-linked hypophosphatemia (XLH) is characterized clinically by rickets, hypophosphatemia, and hyperphosphaturia. Conventional treatment of XLH with oral phosphate and vitamin D is associated with increased urinary calcium excretion and nephrocalcinosis. Thiazide diuretics decrease urinary calcium excretion. The objective of this study was to determine the effect of thiazide diuretics on the clinical and radiologic course of nephrocalcinosis in children with XLH.

METHODS

The effect of hydrochlorothiazide (HCTZ) on clinical and radiologic progression of nephrocalcinosis was evaluated in 11 children with XLH. All patients had been treated previously with vitamin D and oral phosphate and had radiologic evidence of nephrocalcinosis. The average age of the patients at the start of HCTZ was 6.6 +/- 1.0 years. The effect of oral HCTZ at 0.8 +/- 0.1 mg/kg body weight per day given for 3.3 +/- 0.6 years on the progression of nephrocalcinosis and urinary calcium excretion was evaluated.

RESULTS

There was no change in serum phosphorous, calcium, potassium, and chloride after HCTZ therapy. HCTZ therapy increased serum bicarbonate and decreased urinary calcium excretion. The grade of nephrocalcinosis increased from 0.4 +/- 0.2 to 1.5 +/- 0.3 in the 2.3 +/- 0.3 years before initiation of HCTZ therapy, whereas the degree of nephrocalcinosis was stable after 3.3 +/- 0.6 years of HCTZ therapy (1.5 +/- 0.3 vs 3.0 +/- 0.3).

CONCLUSION

HCTZ decreased urinary calcium excretion but did not result in the resolution of nephrocalcinosis. However, when compared with the control period, HCTZ prevented the progression of nephrocalcinosis in children with XLH.

Urinary kidney stone inhibitors. What is the news?

Supersaturation with respect to calcium salts (oxalate and phosphate) is the driving force leading to crystalluria and nephrolithiasis. High-molecular-weight urinary inhibitors are recently described molecules capable of altering the process of kidney stone formation. By inhibition of crystal nucleation, growth and aggregation and by inhibition of crystal interaction with tubular cells, these proteins efficiently prevent stone formation and retention in the urinary tract. But in spite of considerable efforts, characterization of these proteins is still under way. Besides the pathophysiology of risk factors for calcium salts supersaturation such as idiopathic hypercalciuria or hyperoxaluria, the renal involvement of protein inhibitors is the most exciting field in the comprehensive approach of nephrolithiasis, a disease that affects up to 10% of people in Western countries.

Reappraisal of the quantity and nature of renal calcifications and mineral metabolism in the magnesium-deficient rat. Effects of treatment with potassium citrate or the combination magnesium citrate and potassium citrate

There is an urgent need for drugs capable of inhibiting renal calcifications, nephrocalcinosis and stones included, in humans. Current anticalcification medication is based mainly on alkalinization of the metabolism using potassium-containing citrate alone, despite the fact that calcium stone patients suffer marginally from both magnesium and potassium deficiency. We investigated the anticalcification efficacy of oral potassium citrate versus the combined administration of this drug and magnesium citrate in the magnesium-deficient rat developing corticomedullary nephrocalcinosis and luminal microliths in the long term. Among other things we employed specific stains for calcium and oxalate, light microscopy and element analysis for renal tissue and calcifications, respectively. In addition, minerals in renal tissue, urine and plasma were determined, as well as the state of extracellular calcium homeostasis. Magnesium deficiency caused pure calcium phosphate tissue deposits, containing no magnesium, but no deposition of calcium oxalate in the tubular lumen; tissue magnesium, calcium and phosphorus were increased, and there was marked potassium wastage via urine; despite mild hypercalcemia other signs of hyperparathyroidism were not found. Alkalinization with the two kinds of medication evoked an increase in urinary pH, citrate, and potassium; however, potassium citrate alone tended to aggravate renal concretions, whereas the combination of this drug with magnesium citrate completely prevented concretions. It was concluded that: (1) magnesium deficiency-induced calcifications are oxalate-free and are not sensitive to mobilization by alkalinization with potassium citrate, which might explain the failure of the drug to prevent stone recurrence in clinical stone patients, and (2) the combination of potassium citrate and magnesium citrate, which shows enormous anticalcification efficacy, deserves high priority in clinical trials aimed at evaluating strategies for the prevention of stones.

Crystalluria: a clinically useful investigation in children with primary hyperoxaluria post-transplantation

Primary hyperoxaluria type I (PH I) is a congenital error of metabolism that can be manifested by an increased oxalate production, and ultimately result in kidney failure. After a combined liver/kidney transplantation, children with PH I have persistent excretion of oxalate that causes crystal formation in the urinary tract, and could result in systemic oxalosis and eventual graft failure. We speculated that crystalluria may be predictive of this nephrolithogenic tendency and thus investigated the effect of an intensive therapeutic strategy to prevent crystal formation in 13 children at our hospital. Oxalate crystal volume (OCV) measurements were performed at regular intervals for 36 months, and compared with urine supersaturation measurements. We found that crystalluria with the OCV measurement is non-invasive, easily performed, and gives feedback on the efficacy of PH I therapy within one hour. Further study is needed to determine whether this method is a better predictor of nephrocalcinosis than is supersaturation alone.

Medical management and complications of X-linked hypophosphatemic vitamin D resistant rickets

To improve the growth failure, bowed legs, and biochemical and radiological abnormalities in patients with X-linked hypophosphatemic vitamin D resistant rickets (XLH), combined therapy of phosphate and calcitriol is the best therapeutic approach at present. However, the complications involving combined therapy, such as hypercalcemia, nephrocalcinosis and hyperparathyroidism, are not fully solved. To achieve better control, new therapeutic approaches have been reported recently, for example, growth hormone (GH) or new vitamin D analogs. GH improved linear growth, decreased phosphate reabsorption and increased 1-alpha-hydroxylase activity. Furthermore, 24R,25-dihydroxyvitamin D3 (24,25) improved the bone lesions in hypophosphatemic (Hyp) mice, and also in XLH, without the adverse effects such as hypercalcemia or hypercalciuria compared with 1,25-dihydroxyvitamin D3. These new approaches should be considered for the treatment of patients with XLH.

Nephrocalcinosis

The routine use of ultrasonography has resulted in an explosion in the number of conditions reported to be associated with nephrocalcinosis. It has also been increasingly recognized that urolithiasis and nephrocalcinosis can coexist in the same patient. The two conditions most commonly associated with nephrocalcinosis in childhood are the use of furosemide in infancy and the treatment of patients with hypophosphatemic rickets with phosphate and vitamin D preparations. Although originally thought to be related to hypercalciuria, more recent studies in humans and research animals indicate a multifactorial etiology for furosemide-related nephrocalcinosis. In patients with hypophosphatemic rickets, it seems that the dose of phosphate and in particular the development of secondary hyperparathyroidism play a central role in the development of nephrocalcinosis. Among the entities recently reported to be associated with nephrocalcinosis are some that characteristically include Fanconi's syndrome. These findings dispute the previous teaching of lack of renal calcifications in this syndrome, which involves proximal renal tubular acidosis. The diagnosis of nephrocalcinosis requires a metabolic work-up to identify the offending factor. When identified, appropriate intervention should be instituted.

Neonatal Bartter syndrome--use of indomethacin in the newborn period and prevention of growth failure

Neonatal Bartter syndrome differs from the classical Bartter syndrome in the occurrence of antenatal presentation with polyhydramnios. Nephrocalcinosis and severe growth retardation are common sequelae. Indomethacin has been reported to improve linear growth, but its use in the early newborn period has been infrequently described. In this paper we report normal growth and development and the absence of nephrocalcinosis in an infant now aged 19 months with neonatal Bartter syndrome treated from day 3 of life with indomethacin. With early diagnosis and treatment with indomethacin plus adequate water, calories, and sodium, normal growth can be achieved and nephrocalcinosis may be prevented in children with neonatal Bartter syndrome.

Dietary phosphorus restriction to half the minimum required amount slightly reduces weight gain and length of tibia, but sustains femur mineralization and prevents nephrocalcinosis in female kittens

The effects of dietary P restriction to half the recommended minimum level on growth, bone and renal mineralization and urinary composition were studied in female kittens. In two separate experiments, 8-week-old weanling kittens were fed on purified diets containing either 4.6 or 9.2 mmol P/MJ (2.8 or 5.6 g P/kg diet). In the second experiment there was an additional low-P diet in which the Ca concentration was reduced from 9.5 to 4.8 mmol/MJ (7.5 v. 3.8 g Ca/kg diet). P restriction slightly but systematically reduced weight gain (to a maximum of 16%) and growth of the tibia (by 1-4%); the former effect was statistically significant (P < 0.05) between the ages of 15 and 20 weeks in Expt 1 only, and the latter did not reach statistical significance at any time point (P > or = 0.13). No adverse effect of P restriction was found on mineralization of femur at the age of 39 weeks. Kidney Ca concentrations were significantly lowered (Expt 1, 6 v. 20 mumol/g dry weight, P < 0.001; Expt 2, 7 v. 16 mumol/g dry weight, P < 0.01) in cats fed on the low-P diets, this effect not being affected by the dietary Ca:P ratio. Urinary P concentration was significantly depressed (by 50-96%) after feeding the low-P diets (P < 0.001). P intake did not influence P, Ca and Mg retention during the period of 15 to 39 weeks of age.

Effects of insulin and 1 alpha-hydroxy vitamin D3 on streptozotocin-induced diabetic rats fed a low zinc diet

Streptozotocin-induced diabetic rats (LZ-DM rats) developed nephrocalcinosis after being fed a low zinc diet for 4 weeks. However, administration of 1 alpha-hydroxy vitamin D3 (1-OHD3) or insulin inhibited the formation of nephrocalcinosis. The urinary calcium level increased when 1-OHD3 was administered to these rats, but decreased in the group receiving insulin. It was also observed that the femur recovered its hardness when insulin was administered, although the hardness in the LZ-DM rats remained lower than that of the control rats. Rat femur hardness, however, did not completely recover with 1-OHD3 treatment. These results indicate that the effects of insulin and 1-OHD3 differ, even though nephrocalcinosis was reduced by administration of either insulin or 1-OHD3. It appears that insulin assists bone formation, and the 1-OHD3 hastens calcium excretion.

Long-term phosphorus restriction prevents corticomedullary nephrocalcinosis and sustains reproductive performance but delays bone mineralization in rats

In a long-term experiment with three successive generations of rats, the influence of dietary phosphorus restriction (2 instead of 4 g phosphorus/kg diet) on nephrocalcinosis, reproduction and bone mineralization was studied. Nephrocalcinosis in female rats, as based on kidney calcium concentration and histological examination, was prevented by phosphorus restriction. The low phosphorus diet caused reduced femur concentrations of magnesium, calcium and phosphorus in rats of the first and second generation aged 4 to 12 wk. The low phosphorus diet resulted in lower plasma phosphorus concentrations. In the kidneys of female rats, immediately after lactation, a higher degree of tubular hyperplasia was seen after the low phosphorus diet was fed. Reproductive performance was not affected by phosphorus restriction. We conclude that 0.2% phosphorus in the diet prevents nephrocalcinosis in female rats while it sustains reproduction but delays bone mineralization.

Prophylactic role of extracorporeal shock wave lithotripsy in the management of nephrocalcinosis

Electromagnetic extracorporeal shock wave lithotripsy (ESWL) was performed with a standard Siemens Lithostar on parenchymal calcifications in 10 medullary sponge kidneys in order to evaluate the eventual benefit of preventive lithotripsy. The results of shock wave lithotripsy on precaliceal calcifications were disappointing and have been related to the lack of expansion during shock wave interaction and to the impaired drainage of particles. Three patients also had large impacted ureteric stones and in such cases ESWL remains the treatment of choice.

Dietary fluoride prevents phosphorus-induced nephrocalcinosis in female rats

The effect of dietary fluoride (F) on nephrocalcinosis was studied in young, female rats. Nephrocalcinosis was induced by a diet rich in phosphorus (P). F in the diet effectively counteracted P-induced nephrocalcinosis in a dose-dependent fashion. The feeding of increasing amounts of F caused decreasing calcium (Ca) and F concentrations in kidney. This suggests that the amount of Ca in kidney determines F accumulation in this organ, rather than F intake. Increasing amounts of F in the diet caused increasing rates of urinary and fecal excretion and whole-body retention of F. Dietary F did not influence urinary and fecal excretion and plasma concentrations of Ca, magnesium (Mg), and P. The metabolic basis for the protective effect of F against the development of nephrocalcinosis remains to be established.

Effects of sodium citrate, potassium citrate, and citric acid in preventing experimental calcium oxalate urolithiasis in rats

Male Wistar-strain rats which had been fed a glycolic-acid diet developed severe nephrocalcinosis with urinary calculi within 4 weeks. Rats fed the same diet with citrate salts added had, however, either slight or no nephrocalcinosis without any stones in the urinary system. Nephrocalcinosis intermediate between those in the citrate groups and the glycolic-acid group, with some urinary calculi, was observed in the citric-acid group. During the experiment, the urinary oxalate concentration increased markedly and was higher in the citrate and citric-acid than in the glycolic-acid group. The urinary citrate concentration was significantly higher in the citrate groups and lower in the citric acid and glycolic-acid groups. Therefore, citrate salts can be concluded to inhibit nephrocalcinosis and calculi formation as a result of decreased urinary saturation by means of increase in urinary citrate, in spite of a slight increase in the urinary oxalate.

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.

Inhibition of experimental nephrocalcinosis with a prostaglandin synthetase inhibitor

Nephrocalcinosis was induced in a group of experimental rats by means of intraperitoneal injections of 10% calcium gluconate. Two further groups of rats were treated with indomethacin and flurbiprofen (Froben) before receiving the i.p. calcium gluconate, to study the effects of prostaglandin inhibition on the process of renal parenchymal calcification. Tissue calcification was studied by means of contact microradiography and histology. Quantitative calcium analysis was by means of energy dispersive analysis of X-rays (EDAX). There was a marked inhibition of cortical nephrocalcinosis and a significantly reduced calcium concentration (P less than 0.005) in the animals treated with a prostaglandin inhibitor compared with the animals given i.p. calcium gluconate alone. This study suggests that prostaglandins are involved in the process of renal parenchymal calcification and may be aetiologically significant in the pathogenesis of stone formation.

The protective effect of sulfur-containing steroids against nephrocalcinosis induced by mercuric chloride in rats

1. Experiments were conducted on rats and structure-activity correlations were performed using sulfur-containing steroids against nephrocalcinosis induced by mercuric chloride (HgCl2). 2. The protective effect of spironolactone has been described previously and we have now demonstrated the activity of 7-mercapto-17-hydroxy-3-oxo-4-androsten-17-propionic acid-lactone. 3. The activity of the sulfhydryl radical present in this molecule has been shown to be slightly lower than that of the thioacetyl radical present in spironolactone. 4. The importance of the steroid structure to which a specific radical is attached has become evident during these experiments with the inactivity of 7-mercapto-3,20-dioxo-4-pregnene-16-carbothiamineacetate which possesses a thioacetyl group in the same position as spironolactone (i.e. only the two lateral chains in position 16 and 17 are different between these two steroids). 5. Thus, both the composition of the sulfur-containing radical and the steroid moiety are important for protection against inorganic mercury poisoning.

Natural history of primary distal renal tubular acidosis treated since infancy

Clinical and pathophysiologic studies were performed in five unrelated children with primary distal renal tubular acidosis who were diagnosed during infancy and followed for 3 to 9 1/2 years. All patients had permanent defects in hydrogen ion secretion, sodium reabsorption, and concentrating capacity. A transient, age-related, proximal tubular defect in sodium and bicarbonate reabsorption was also present. Renal bicarbonate wasting was mainly observed during the first years of life and progressively decreased with advancing age. Glomerular filtration rate remained within normal limits. Following sustained therapy with sodium and potassium bicarbonate, the patients had optimal growth, arrest of progression of nephrocalcinosis, and lack of other characteristic features of the disease with the exception of polyuria. Dosage of alkali was mainly determined by the magnitude of the renal bicarbonate loss and decreased progressively from a maximum of 3.9 to 10.0 mEq/kg/day during the first year of life to about 3 mEq/kg/day at or beyond 6 years of age. The total dosage of alkali required could be derived by the sum of the urinary excretion of bicarbonate plus 2 mEq/kg/day, which represents mean endogenous acid production. Although calciuria was normal when metabolic acidosis was corrected, patients with higher urinary sodium excretion had higher urinary excretion of calcium and thus were at greater risk of developing nephrocalcinosis if therapy was not carefully controlled.

Control of nephrocalcinosis by manipulating the calcium:phosphorus ratio in commercial rodent diets

Changing the calcium: phosphorus ratio in 2 commercial diets from 0·73 and 0·84 to 1·25 and 1·20 reduced the incidence of nephrocalcinosis (which occurred almost entirely in female rats) virtually to nil.

[The radioprotective effect of iodine and its preventive action on renal calcification (author's transl)]

The protective effect of iodine against injurious damage caused by ionizing radiation was studied in 26 rats irradiated with cobalt-60 gamma rays as a single dose of 1000 rads (10 joule/kg). Twelve rats were pretreated 13 times every second day before irradiation. After irradiation they were treated daily during 21 days with 2.5 to 3.0 mg iodine given subcutaneously along with 9 mg Ca2+ (as gluconolactobionate) intramuscularly. In addition, they received 500 micrograms of iodine in their food daily. 67% of the iodine-treated rats remained alive after 30 days in contrast to 36% of the control rats which received Ca2+ only. 10 further rats which received neither iodine nor Ca2+ died within 3 to 5 days after irradiation. Deposition of calcium in the renal parenchyma was observed in 12 out of the 14 control rats, but only in 2 out of the 12 iodine-treated rats. It can be concluded from the results that iodine has a protective effect on ionizing radiation. It is assumed that iodine promotes the energy-conserving mechanism in mitochondria and also prevents the irradiation-induced decrease in calcium efflux.

The effects of amphotericin B therapy on the intrarenal vasculature and renal tubules in man. A study of biopsies by light, electron and immunofluorescence microscopy

Renal morphology was studied by light and electron microscopy in 10 patients after 25 mg/kg body weight of amphotericin B as part of a controlled study designed to evaluate the possible protective effects of mannitol against the nephrotoxicity of amphotericin B. Five patients received amphotericin B 1 mg/kg body weight every other day and five received amphotericin B and mannitol 1 g/kg body weight in the infusion. Small arterial and arteriolar changes were present in all biopsies and were characterized by focal vacuolization of medial smooth muscle cells. Electron microscopy suggested formation of these vacuoles by fusion of dilated endoplasmic reticulum. A few small vacuoles were also seen in renal biopsies of age matched patients who did not receive amphotericin B. Vacuoles in biopsies of the amphotericin treated patients were considerably larger (P less than 0.001) and much more numerous (P less than 0.001) than in controls. It is hypothesized that the vacuoles in the amphotericin B treated group represent the morphologic effect of intrarenal vasoconstriction caused by amphotericin B therapy. Nephrocalcinosis was observed in all biopsies and appeared to originate by precipitation of calcium salts in tubular casts.

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.

Effect of fluoride on the mobilization of skeletal magnesium and soft-tissue calcinosis during acute magnesium deficiency in the rat

To investigate the effect of fluoride on the mobilization of skeletal magnesium and on kidney calcification during magnesium depletion, male Holtzman rats were fed a magnesium-sufficient diet (400 ppm of magnesium) and drinking water containing either 0, 50 or 100 ppm of fluoride for a 20-day period prior to the initiation of magnesium deficiency. The high fluoride regimen resulted in a 100-fold increase in the fluoride content of the skeleton. On day 20 magnesium depletion was initiated by feeding the animals a diet containing 12 ppm of magnesium. Over a 4-week period of magnesium deprivation, a 26% decrease of the total magnesium in the humeri was observed. Fluoride exerted a significant effect in retarding the mobilization of skeletal magnesium. Four weeks of magnesium deficiency was associated with a decreased rate of skeletal mineral accretion and with an increase in the kidney calcium content. The decreased rate of mineral accretion was accentuated by the administration of fluoride during the deficiency state. While fluoride exerted an initial protective effect on calcinosis of the kidneys, the overall effect of the administration of fluoride during magnesium deficiency was to promote calcification of the kidneys rather than to prevent it.