Urinary Phosphate Excretion Research Articles

Effects of dietary phosphate and calcium intake on fibroblast growth factor-23.

Little is known about the influence of dietary phosphate intake on fibroblast growth factor-23 (FGF23) and its subsequent effects on vitamin D levels. This study addresses changes in intact FGF23 (iFGF23) and C-terminal FGF23 (cFGF23), phosphaturia, and levels of vitamin D on high and low phosphate and calcium intake. Ten healthy subjects adhered to a diet low or high in phosphate and calcium content for 36 hours each with a 1-week interval during which subjects adhered to their usual diet. Serum phosphate, calcium, vitamin D metabolites, parathyroid hormone (PTH), and FGF23 levels (cFGF23 and iFGF23) were measured several times a day. Phosphate, calcium, and creatinine excretion was measured in 24-hour urine on all study days. Serum phosphate levels and urinary phosphate increased during high dietary phosphate intake (from 1.11 to 1.32 mmol/L, P<0.0001 and 21.6 to 28.8 mmol/d, P=0.0005, respectively). FGF23 serum levels increased during high dietary phosphate/calcium intake (cFGF23 from 60 to 72 RU/ml, P<0.001; iFGF23 from 33 to 37 ng/L, P=0.003), whereas PTH declined. 1,25-dihydroxyvitamin D (1,25D) showed an inverse relation with FGF23. Variation in dietary phosphate and calcium intake induces changes in FGF23 (on top of a circadian rhythm) and 1,25D blood levels as well as in urinary phosphate excretion. These changes are detectable the day after the change in the phosphate content of meals. Higher FGF23 levels are associated with phosphaturia and a decline in 1,25D levels.

FGF-23 as a Predictor of Renal Outcome in Diabetic Nephropathy

Fibroblast growth factor 23 (FGF-23) has emerged as a new factor in mineral metabolism in chronic kidney disease (CKD). An important regulator of phosphorus homeostasis, FGF-23 has been shown to independently predict CKD progression in nondiabetic renal disease. We analyzed the relation between FGF-23 and renal outcome in diabetic nephropathy (DN). DN patients participating in a clinical trial (enalapril+placebo versus enalapril+losartan) had baseline data collected and were followed until June 2009 or until the primary outcome was reached. Four patients were lost to follow-up. The composite primary outcome was defined as death, doubling of serum creatinine, and/or dialysis need. At baseline, serum FGF-23 showed a significant association with serum creatinine, intact parathyroid hormone, proteinuria, urinary fractional excretion of phosphate, male sex, and race. Interestingly, FGF-23 was not related to calcium, phosphorus, 25OH-vitamin D, or 24-hour urinary phosphorus. Mean follow-up time was 30.7±10 months. Cox regression showed that FGF-23 was an independent predictor of the primary outcome, even after adjustment for creatinine clearance and intact parathyroid hormone (10 pg/ml FGF-23 increase = hazard ratio, 1.09; 95% CI, 1.01 to 1.16, P=0.02). Finally, Kaplan-Meier analysis showed a significantly higher risk of the primary outcome in patients with FGF-23 values of >70 pg/ml. FGF-23 is a significant independent predictor of renal outcome in patients with macroalbuminuric DN. Further studies should clarify whether this relation is causal and whether FGF-23 should be a new therapeutic target for CKD prevention.

Hereditary disorders of renal phosphate wasting

Inherited diseases of renal phosphate handling lead to urinary phosphate wasting and depletion of total body phosphorus stores. Clinical sequelae of inherited disorders that are associated with increased urinary phosphate excretion are deleterious and can lead to abnormal skeletal growth and deformities. This Review describes hereditary disorders of renal phosphate wasting taking into account developments in our understanding of renal phosphate handling from the last decade. The cloning of genes involved in these disorders and further studies on their pathophysiological mechanisms have given important insights in to how phosphatonins, such as FGF-23, regulate renal phosphate reabsorption in health and disease. X-linked dominant hypophosphatemic rickets results from mutation of a metalloprotease (PHEX) that has an unidentified role in FGF-23 degradation. Mutation of an RXXR proteolytic cleavage site in FGF-23 prevents degradation and increases circulating levels of FGF-23 in autosomal dominant hypophosphatemic rickets. FGF-23 acts to remove sodium phosphate co-transporters from the luminal membrane of proximal tubular cells with resultant renal phosphate wasting. Loss of function mutations in genes encoding the transporters NaPi-IIc and NaPi-IIa also result in renal phosphate wasting and rickets.

Reciprocal Control of 1,25-Dihydroxyvitamin D and FGF23 Formation Involving the FGF23/Klotho System

Fibroblast growth factor 23 (FGF23) is a circulating hormone that is synthesized by osteocytes and osteoblasts. This glycosylated peptide controls phosphate balance by modulating urinary phosphate excretion and indirectly intestinal phosphate absorption by reducing expression of the renal and intestinal sodium phosphate transporters. In a feedback loop, 1,25-dihydroxyvitamin D and phosphate intake control FGF23 production. FGF23 is inactivated by cleavage by a still unidentified enzyme. FGF23 cleavage occurs within cells and probably in the circulation. Klotho, a protein expressed at the cell surface of few organs, forms complexes with FGF receptors, which increases their affinity for FGF23. Klotho is also released into the plasma and urine by an enzymatic cleavage. FGF23 plays a central role in vitamin D metabolism: It inhibits calcitriol synthesis in the kidney and stimulates the catabolism of active vitamin D sterols. In turn, calcitriol stimulates FGF23 and Klotho expression. In chronic kidney diseases, FGF23 concentration increases as GFR declines, whereas Klotho tissue expression decreases. The modifications of FGF23 and Klotho expression are probably involved in the genesis of hyperparathyroidism and the resistance to vitamin D receptor (VDR) activation in chronic kidney disease. Low vitamin D, high FGF23 concentrations, and defects in VDR activation are associated with similar risks, which evoke the possibility that potential FGF23 toxicity might be partly mediated by FGF23-induced decrease in calcitriol or 25-hydroxyvitamin D. Conversely, VDR activators could be used to modulate Klotho or FGF23 expression.

Effects of vitamin D replacement therapy on serum FGF23 concentrations in vitamin D-deficient women in short term

Fibroblast growth factor 23 (FGF23), a phosphatonin, inhibits renal phosphate reabsorption and suppresses 1-α hydroxylase activity. Calcitriol stimulates FGF23 synthesis in bone. We aimed to determine the effect of vitamin D replacement therapy on serum FGF23 concentrations in vitamin D-deficient women and to compare the FGF23 concentrations of vitamin D-deficient patients with healthy subjects and patients with genetically determined hypophosphatemic rachitis. The study group was composed of vitamin D-deficient females (n=18, mean age 29.1 ± 9.9 years), vitamin D-sufficient healthy females (control group; n=19, mean age 28.5 ± 5.2 years), and patients with genetically determined hypophosphatemic rachitis (n=13, mean age 26.5 ± 15.1 years). The groups were compared for serum FGF23, 1,25-dihydroxyvitamin D3 (1,25(OH)2D), calcium, phosphate, bone turnover markers, intact parathyroid hormone (PTH), and urinary excretion of calcium and phosphate. The vitamin D-deficient group was re-evaluated after a standard treatment regimen. Serum FGF23 concentrations were significantly lower in vitamin D-deficient patients than in vitamin D-sufficient women and hypophosphatemic rachitis group. Serum FGF23 and phosphate concentrations further decreased significantly during replacement of vitamin D (P<0.05). A significant negative correlation was evident between FGF23 and PTH before vitamin D replacement in the patients (r=-0.469, P<0.05). Decreased FGF23 concentrations, which further decline during vitamin D replacement therapy, may have favorable action on bone mineralization by counterregulatory effect on phosphate homeostasis. Lower 1,25(OH)2D concentrations at baseline and hypophosphatemia during treatment may have dominating effects on FGF23 concentrations in vitamin D deficiency, leading to decreased FGF23 concentrations at baseline and during replacement therapy.

Experimental Induction of Calcium Oxalate Nephrolithiasis in Mice

The availability of various transgenic and knockout mice provides an excellent opportunity to better understand the pathophysiology of calcium oxalate stone disease. However, attempts to produce calcium oxalate nephrolithiasis in mice have not been successful. We hypothesized that calcium oxalate nephrolithiasis in mice requires increasing urine calcium and oxalate excretion, and experimentally induced hyperoxaluria alone is not sufficient. To provide evidence we induced hyperoxaluria by administering hyperoxaluria inducing agents in normocalciuric and hypercalciuric mice, and investigating various aspects of nephrolithiasis. We administered ethylene glycol, glyoxylate or hydroxyl proline via diet in male and female normocalciuric B6 mice, and in hypercalciuric sodium phosphate co-transporter type 2 a -/- mice for 4 weeks. We collected 24-hour urine samples on days 0, 3, 7, 14, 21 and 28, and analyzed them for pH, creatinine, lactate dehydrogenase calcium and oxalate. Kidneys were examined using light microscopy. Urine was examined for crystals using light and scanning electron microscopy. Hypercalciuric mice on hydroxyl proline did not tolerate treatment and were sacrificed before 28 days. All mice on ethylene glycol, glyoxylate or hydroxyl proline became hyperoxaluric and showed calcium oxalate crystalluria. No female, normocalciuric or hypercalciuric mice showed renal calcium oxalate crystal deposits. Calcium oxalate nephrolithiasis developed in all mice on glyoxylate and in some on ethylene glycol. In all mice the kidneys showed epithelial injury. Male mice particularly on glyoxylate had more renal injury and inflammatory cell migration into the interstitium around the crystal deposits. Results confirm that hyperoxaluria induction alone is not sufficient to create calcium oxalate nephrolithiasis in mice. Hypercalciuria is also required. Kidneys in male mice are more prone to injury than those in female mice and are susceptible to calcium oxalate crystal deposition. Perhaps epithelial injury promotes crystal retention. Thus, calcium oxalate nephrolithiasis in mice is gender dependent, and requires hypercalciuria and hyperoxaluria.

Pilot study of dietary phosphorus restriction and phosphorus binders to target fibroblast growth factor 23 in patients with chronic kidney disease

High levels of fibroblast growth factor 23 (FGF23) are associated with mortality and progression of chronic kidney disease (CKD). Reducing dietary phosphorus intake lowers FGF23 secretion in healthly individuals, but there is little data on its effects in patients with pre-dialysis CKD. Using a 2×2 factorial design, we randomly assigned 16 normophosphataemic CKD stage 3-4 patients to receive a 2-week treatment with either lanthanum carbonate 1000 mg three times daily or placebo, and to ingest a tightly controlled diet containing 750 or 1500 mg of dietary phosphorus daily. We analysed serial measurements of FGF23, parathyroid hormone, serum phosphate and calcium, and 24-h urinary phosphate and calcium excretion using repeated-measures analyses. Compared with the 1500-mg phosphorus diet, patients assigned to the 750-mg diet had greater reduction in 24-h urinary phosphate excretion (66% vs. 29%; P<0.0001). Lanthanum-treated patients experienced a significant reduction in 24-h urinary phosphate excretion compared with baseline (64%; P<0.0001), but the difference compared with placebo did not reach significance (64% vs. 31%). Despite the significant reductions in 24-h urinary phosphate excretion, no group demonstrated a significant reduction in FGF23 levels; FGF23 levels actually increased significantly in the 1500-mg diet plus placebo group, suggesting dietary phosphorus loading. Although dietary phosphorus restriction and lanthanum lowered urinary phosphate excretion consistent with a rapid decrease in phosphorus absorption, inducing a reduction in FGF23 levels in CKD patients may require interventions with a longer duration than in healthy volunteers.

FGF-23: More than a regulator of renal phosphate handling?

Fibroblast growth factor 23 (FGF-23) is likely to be the most important regulator of phosphate homeostasis, which mediates its functions through FGF receptors and the coreceptor Klotho. Besides reducing expression of the sodium-phosphate cotransporters NPT2a and NPT2c in the proximal tubules, FGF-23 inhibits the renal 1α-hydroxylase and stimulates the 24-hydroxylase, and it appears to reduce parathyroid hormone (PTH) secretion in short-term studies. FGF-23 synthesis and secretion by osteocytes and osteoblasts is upregulated through 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] and through an increased dietary phosphate intake. FGF-23 levels are elevated or inappropriately normal in patients with tumor-induced osteomalacia and several inherited hypophosphatemic disorders, but the most significant increases are found in patients with chronic kidney disease (CKD). During the early stages of CKD, increased FGF-23 production enhances urinary phosphate excretion and thus prevents the development of hyperphosphatemia, reduces the circulating levels of 1,25(OH)2D3, and therefore contributes to the development of secondary hyperparathyroidism. In patients with end-stage renal disease (ESRD), FGF-23 levels can be extremely high and were shown to be predictors of bone mineralization, left ventricular hypertrophy, vascular calcification, and mortality. It remains to be determined, however, whether FGF-23 represents simply a sensitive biomarker of an abnormal phosphate homeostasis or has, independent of serum phosphate levels, potentially negative “off-target” effects. Nonetheless, reducing the production and/or the biologic activity of FGF-23 may be an important therapeutic goal for this patient population. © 2010 American Society for Bone and Mineral Research.

Refractory Diffuse Bony Pain 20 Years After Jejunoileal Bypass

Osteomalacia can be a late but unrecognized complication following jejunoileal bypass. We describe a 53-year-old man who underwent jejunoileal bypass for morbid obesity twenty years earlier who suffered from progressive diffuse bony pain refractory to nonsteroidal anti-inflammatory drugs. He was initially diagnosed with a malignancy with bone metastasis. However, pertinent laboratory data were notable for hypocalcemia (7.5 mg/dL, albumin 4.1 mg/dL) with low urinary calcium excretion (14 mg/day), hypophosphatemia (2.0 mg/dL) with low urinary phosphate excretion (53 mg/day), hypomagnesemia (1.5 mg/dL) with low urine magnesium excretion (23 mg/day), low 1, 25 (OH)2 vitamin D3, and elevated serum alkaline phosphatase and intact parathyroid hormone (iPTH). These laboratory findings pointed to a defect in calcium, phosphate, and magnesium handling in the gastrointestinal tract. Bone biopsy of the iliac crest clearly demonstrated typical changes of osteomalacia with excessive osteoid accumulation and reduced mineralization. His clinical symptoms were refractory to oral 1, 25 (OH)2 vitamin D3 and calcium supplementation but significantly improved with the addition of intermittent intravenous active 1, 25 (OH)2 vitamin D3, calcium, phosphate, and magnesium supplementation. Osteomalacia is an easily misdiagnosed late complication of jejunoileal bypass. Early recognition can avoid circuitous diagnosis and inappropriate management.

Fibroblast Growth Factor 23 and Disordered Vitamin D Metabolism in Chronic Kidney Disease

The discovery of fibroblast growth factor 23 (FGF23) has clarified much of our understanding of abnormalities in phosphorus and vitamin D metabolism in chronic kidney disease (CKD). FGF23 is a bone-derived hormone that promotes phosphaturia and decreases the synthesis of 1,25-dihydroxyvitamin D (1,25(OH)(2)D). The primary systemic stimuli of FGF23 secretion are increased 1,25(OH)(2)D levels and increased dietary phosphorus intake. In kidney failure, FGF23 levels increase early and steadily rise with progression of kidney disease, likely as an appropriate physiologic adaptation to maintain normal phosphorus balance by helping to augment urinary phosphate excretion in conjunction with increased parathyroid hormone levels and by decreasing gut phosphorus absorption through decreased 1,25(OH)(2)D. In the long term, this compensation may become maladaptive by causing a progressive decline in 1,25(OH)(2)D levels with attendant consequences such as secondary hyperparathyroidism. Moreover, excess FGF23 levels have been independently linked with cardiovascular disease and mortality, suggesting that chronically elevated FGF23 levels may directly contribute to adverse CKD outcomes. Together, these findings have sparked increased interest in elucidating the potential interconnections between dietary phosphorus intake, FGF23, and clinical outcomes in patients with CKD. In addition, given that treatment with activated vitamin D compounds stimulates FGF23, these data have raised important new questions about the optimal use of activated vitamin D compounds in the management of bone and mineral disorders in CKD.

Fibroblast Growth Factor-23 in Early Chronic Kidney Disease

The discovery of fibroblast growth factor-23 (FGF-23) and the elucidation of its function as a phosphaturic and 1,25(OH)2VitD counter-regulatory hormone provides a new conceptual framework for the understanding of the pathogenesis of secondary hyperparathyroidism. This study aims to elucidate the complex associations between FGF-23, parathyroid hormone (PTH), 1,25(OH)2D, and phosphate in patients with early-stage chronic kidney disease (CKD) and to provide clinical evidence in favor of the new phosphate-centric paradigm for the pathogenesis of secondary hyperparathyroidism. Serum biointact PTH and FGF-23, 25(OH)D, 1,25(OH)2D, calcium, phosphate, 24-hour urine excretion of phosphate and calcium, and urinary fractional excretion of phosphate were determined in a cross-sectional study including 125 patients with CKD stages 1 to 3. Serum phosphate levels showed an inverse association with estimated GFR (eGFR), but were within the normal range in all but one patient. FGF-23 and PTH were inversely associated with eGFR, even in the subgroup of patients with CKD stages 1 and 2. High FGF-23 levels were significantly more prevalent than high PTH levels. The urinary fractional excretion of phosphate was highest in patients with both a high serum FGF-23 and PTH level. Increased FGF-23 and phosphate and decreased 25(OH)D were independently associated with decreased 1,25(OH)2D. Our data are in favor of the new paradigm for the pathogenesis of secondary hyperparathyroidism according to which a reduced phosphate excretion capacity is the principal abnormality that initiates secondary hyperparathyroidism.

Phosphaturic action of fibroblast growth factor 23 in Npt2 null mice

In the present study, we evaluated the roles of type II and type III sodium-dependent P(i) cotransporters in fibroblast growth factor 23 (FGF23) activity by administering a vector encoding FGF23 with the R179Q mutation (FGF23M) to wild-type (WT) mice, Npt2a knockout (KO) mice, Npt2c KO mice, and Npt2a(-/-)Npt2c(-/-) mice (DKO mice). In Npt2a KO mice, FGF23M induced severe hypophosphatemia and markedly decreased the levels of Npt2c, type III Na-dependent P(i) transporter (PiT2) protein, and renal Na/P(i) transport activity. In contrast, in Npt2c KO mice, FGF23M decreased plasma phosphate levels comparable to those in FGF23M-injected WT mice. In DKO mice with severe hypophosphatemia, FGF23M administration did not induce an additional increase in urinary phosphate excretion. FGF23 administration significantly decreased intestinal Npt2b protein levels in WT mice but had no effect in Npt2a, Npt2c, and DKO mice, despite marked suppression of plasma 1,25(OH)(2)D(3) levels in all the mutant mice. The main findings were as follow: 1) FGF23-dependent phosphaturic activity in Npt2a KO mice is dependent on renal Npt2c and PiT-2 protein; 2) in DKO mice, renal P(i) reabsorption is not further decreased by FGF23M, but renal vitamin D synthesis is suppressed; and 3) downregulation of intestinal Npt2b may be mediated by a factor(s) other than 1,25(OH)(2)D(3). These findings suggest that Npt2a, Npt2c, and PiT-2 are necessary for the phosphaturic activity of FGF23. Thus complementary regulation of Npt2 family proteins may be involved in systemic P(i) homeostasis.

FGF23–parathyroid interaction: implications in chronic kidney disease

Over the past few years there have been considerable advances in our understanding of the physiological regulation of mineral homeostasis. One of the most important breakthroughs is the identification of fibroblastic growth factor 23 (FGF23) and its role as a key regulator of phosphate and 1,25-dihydroxyvitamin D metabolism. FGF23 exerts its biological functions by binding to its cognate receptor in the presence of Klotho as a cofactor. FGF23 principally acts on the kidney to induce urinary phosphate excretion and suppresses 1,25-dihydroxyvitamin D synthesis, thereby indirectly modulating parathyroid hormone secretion. FGF23 also acts directly on the parathyroid to decrease parathyroid hormone synthesis and secretion. In patients with chronic kidney disease, FGF23 levels increase progressively to compensate for phosphate retention, but these elevated FGF23 levels fail to suppress the secretion of parathyroid hormone, particularly in the setting of uremia. Recent data suggest that this parathyroid resistance to FGF23 may be caused by decreased expression of Klotho-FGFR1 complex in hyperplastic parathyroid glands. This review summarizes recent insights into the role of FGF23 in mineral homeostasis and discusses the involvement of its direct and indirect interaction with the parathyroid gland, particularly focusing on the pathophysiology of secondary hyperparathyroidism in chronic kidney disease.

Evidence of a Parathyroid Hormone-independent Chronic Effect of Estrogen on Renal Phosphate Handling and Sodium-dependent Phosphate Cotransporter Type IIa Expression

The effects of estrogen on phosphate metabolism are not well understood. To better define the chronic effects of estrogen on phosphate balance and on renal phosphate handling, the following groups were examined: A. young male and female rats, age- and weight-matched (age 8-10 weeks, 1 (st) study), and B. ovariectomized female rats (OVX), 22 weeks old, ovariectomized aged-matched rats receiving estrogen replacement (15 micromol x 3/week) for 14 weeks (OVX+E), control female rats (intact ovaries), and male rats, both age matched to OVX and OVX+E (2 (nd) Study). In younger females (1 (st) study), plasma phosphate was lower, whereas the urinary excretion of phosphate was higher than in males. In adult intact females and in OVX+E urinary excretion of phosphate was higher than in males and OVX (2 (nd) Study). In these rats, a significant correlation between plasma phosphate and estrogen level was found. Sodium-dependent phosphate cotransporter (NaPiIIa) mRNA expression and protein abundance were higher in the renal cortex of younger male rats than in age- and weight-matched females. In adult rats, NaPiIIa mRNA and protein abundance were higher in OVX than in OVX+E, and in mature males as compared with age-matched females. These differences were not related to the parathyroid hormone (PTH) levels. Chronic estrogen administration was also associated with increased plasma calcium level and urinary calcium excretion. These results suggest that chronic estrogen treatment is associated with an inhibitory, PTH-independent effect on the expression of NaPiIIa in the kidney, leading to sex-related differences in phosphate balance.

Protective effect of the hydro-alcoholic extract of Rubia cordifolia roots against ethylene glycol induced urolithiasis in rats

This study investigated the protective effect of the hydro-alcoholic extract of roots of Rubia cordifolia Linn. (HARC) against ethylene glycol induced urolithiasis and its possible underlying mechanisms using male Wistar albino rats. Ethylene glycol feeding resulted in hyperoxaluria, hypocalciuria as well as increased renal excretion of phosphate. Supplementation with HARC significantly prevented change in urinary calcium, oxalate and phosphate excretion dose-dependently. The increased calcium and oxalate levels and number of calcium oxalate crystals deposits in the kidney tissue of calculogenic rats were significantly reverted by HARC treatment. The HARC supplementation also prevents the impairment of renal functions. Results Indicate that the HARC can protect against ethylene glycol induced urolithiasis as it reduced and prevented the growth of urinary stones. Therefore, HARC is helpful to prevent the recurrence of the disease as it showed its effect on early stages of stone development. The mechanism underlying this effect is mediated possibly through an antioxidant, nephroprotection and its effect on the urinary concentration of stone-forming constituents and risk factors.

Mutation analysis and serum FGF23 level in a patient with pulmonary alveolar microlithiasis

Pulmonary alveolar microlithiasis (PAM) is a rare, hereditary disorder characterized by ectopic formation of calcium-phosphate microliths in the alveolar space. PAM has been reported to arise from inactivating mutations in SLC34A2, encoding a sodium-dependent phosphate co-transporter essential for phosphate transport in the lungs and small intestine. Serum levels of the phosphaturic hormone fibroblast growth factor-23 (FGF23) in PAM have not been determined. Our objectives were to investigate the genetic etiology and circulating level of FGF23 in a 50-year-old male with clinical characteristics of PAM and extra-pulmonary calcifications. The SLC34A2 and FGF23 genes were sequenced for mutations and serum FGF23 analyzed by ELISA. We found no disease-causing mutations or single nucleotide polymorphisms in the genes investigated. Importantly, repeated measurements revealed undetectable or markedly low serum FGF23 (<3-11 RU/ml). Surprisingly, in the face of low serum FGF23, 1,25-dihydroxy vitamin D₃ level was low-normal and parathyroid hormone mildly elevated. Total 24-h urinary excretion of phosphate and calcium were low, as was fractional urinary excretion of calcium. In contrast, fractional excretion of phosphate was above normal, likely due to elevated PTH. Collectively, PAM may be a polygenic disorder that arises from mutations other than in SLC34A2. The low FGF23 level in our PAM patient supports an intestinal-bone axis, leading to decreased FGF23 expression when intestinal phosphate absorption is compromised.

Carnitine Deficiency and Oxidative Stress Provoke Cardiotoxicity in an Ifosfamide‐Induced Fanconi Syndrome Rat Model

In addition to hemorrhagic cystitis, Fanconi Syndrome is a serious clinical side effect during ifosfamide (IFO) therapy. Fanconi syndrome is a generalized dysfunction of the proximal tubule which is characterized by excessive urinary excretion of glucose, phosphate, bicarbonate, amino acids and other solutes excreted by this segment of the nephron including L-carnitine. Carnitine is essential cofactor for β-oxidation of long-chain fatty acids in the myocardium. IFO therapy is associated with increased urinary carnitine excretion with subsequent secondary deficiency of the molecule. Cardiac abnormalities in IFO-treated cancer patients were reported as isolated clinical cases. This study examined whether carnitine deficiency and oxidative stress, secondary to Fanconi Syndrome, provoke IFO-induced cardiomyopathy as well as exploring if carnitine supplementation using Propionyl-L-carnitine (PLC) could offer protection against this toxicity. In the current study, an animal model of carnitine deficiency was developed in rats by D-carnitine-mildronate treatment Adult male Wistar albino rats were assigned to one of six treatment groups: the first three groups were injected intraperitoneally with normal saline, D-carnitine (DC, 250 mg/kg/day) combined with mildronate (MD, 200 mg/kg/day) and PLC (250 mg/kg/day), respectively, for 10 successive days. The 4th, 5th and 6th groups were injected with the same doses of normal saline, DC-MD and PLC, respectively for 5 successive days before and 5 days concomitant with IFO (50 mg/kg/day). IFO significantly increased serum creatinine, blood urea nitrogen (BUN), urinary carnitine excretion and clearance, creatine phosphokinase isoenzyme (CK-MB), lactate dehydrogenase (LDH), intramitochondrial acetyl-CoA/CoA-SH and thiobarbituric acid reactive substances (TBARS) in cardiac tissues and significantly decreased adenosine triphosphate (ATP) and total carnitine and reduced glutathione (GSH) content in cardiac tissues. In carnitine-depleted rats, IFO induced dramatic increase in serum creatinine, BUN, CK-MB, LDH, carnitine clearance and intramitochondrial acetyl-CoA/CoA-SH, as well as progressive reduction in total carnitine and ATP in cardiac tissues. Interestingly, PLC supplementation completely reversed the biochemical changes-induced by IFO to the control values. In conclusion, data from the present study suggest that: Carnitine deficiency and oxidative stress, secondary to Fanconi Syndrome, constitute risk factors and should be viewed as mechanisms during development of IFO-induced cardiotoxicity. Carnitine supplementation, using PLC, prevents the development of IFO-induced cardiotoxicity through antioxidant signalling and improving mitochondrial function.

Vitamin D deficiency in two young adults with biochemical findings resembling pseudohypoparathyroidism type I and type II

We report two patients with vitamin D deficiency due to unbalanced diet. The patients initially presented with severe hypocalcemia, normophosphatemia and markedly elevated serum PTH levels. Although nutritional vitamin D deficiency was suspected from their history of gastrointestinal problems and dietary restriction, we conducted Ellsworth- Howard test to exclude the possibility of pseudohypoparathyroidism (PHP). Both patients showed no incremental response of urinary phosphate excretion. However, the urinary cAMP response to exogenous PTH was different between the two. Case 1 showed a blunted response (5-fold and 1.54 micro mol/h increase) and case 2 showed a normal response (39-fold and 3.04 micro mol/h increase). According to the criteria of Ellsworth-Howard test, the data of case 1 was compatible with PHP type I, and of case 2 with PHP type II. The final diagnosis of vitamin D deficiency was established in both patients based on very low serum 25-hydroxyvitamin D levels (less than 5 ng/mL) and the effect of treatment. After calcium supplementation with or without vitamin D, their biochemical abnormalities disappeared. They maintained normocalcemia without medication after correction of their unbalanced diet. The present study indicated that patients with vitamin D deficiency occasionally showed biochemical findings suggestive of PHP and that such patients could exhibit not only PHP type II pattern of response to exogenous PTH but also of type I pattern. Thus our clinical observation suggests the complexity of PTH resistance in vitamin D deficiency and underscores the importance of diet to prevent the disorder.

Phosphaturia as a Promising Predictor of Recurrent Stone Formation in Patients with Urolithiasis

PurposeRecent studies have suggested that renal phosphate leakage and the associated phosphaturia are significant underlying causes of calcium urolithiasis. The aims of this study were to assess whether phosphaturia relates to urinary metabolic abnormalities and recurrent stone formation.Materials and MethodsA database of patient histories and urine chemistries was analyzed for 1,068 consecutive stone formers (SFs) and 106 normal controls. Urine values for phosphaturia that were higher than 95% of the normal control values were defined as indicating hyperphosphaturia, and the effect of phosphaturia on urinary metabolites and stone recurrence was determined. Of these patients, 247 patients (23.1%) who had been followed up for more than 36 months or had a recurrence of stones during follow-up (median, 46.0 months; range, 5-151) were included in the analyses for stone recurrence.ResultsOf the SFs, 19.9% (212/1,068) had increased urinary phosphate excretion. SFs with hyperphosphaturia had a greater urinary volume and higher levels of calcium, uric acid, oxalate, and citrate than did SFs with normophosphaturia. A multivariate Cox regression model, stratified by stone episodes, revealed that hyperphosphaturia was an independent predictor of recurrent stone formation in first-time SFs (hazard ratio [HR]: 2.122; 95% confidence interval [CI]: 1.100-4.097; p=0.025). No association was detected between hyperphosphaturia and recurrent stone formation in recurrent SFs. Kaplan-Meier curves showed identical results.ConclusionsThis study demonstrates that hyperphosphaturia is closely associated with urinary metabolic abnormalities. Furthermore, hyperphosphaturia is a significant risk factor for stone recurrence in first-time SFs.

Bone Disease in Medullary Sponge Kidney and Effect of Potassium Citrate Treatment

In medullary sponge kidney (MSK)-a common malformative renal condition in patients with calcium nephrolithiasis-hypercalciuria, incomplete distal renal tubular acidosis, and hypocitraturia are common. Clinical conditions with concomitant hypercalciuria and/or incomplete distal renal tubular acidosis are almost invariably associated with bone disease, making osteopathy highly likely in MSK, too. Patients with MSK have never been investigated for osteopathy; neither has the potential effect of potassium citrate administration (CA) on their urinary metabolic risk factors and on bone mineralization. These issues were retrospectively analyzed in 75 patients with MSK and primary stone risk factor (PSRF; hypercalciuria, hypocitraturia, hyperuricosuria, and/or hyperoxaluria) on an outpatient basis; 65 received CA (2.9 +/- 0.8 g/d), whereas 10 received only general "stone clinic" suggestions. The 24-h urinary excretion of calcium, phosphate, oxalate, uric acid, and citrate; morning urine pH; serum biochemistry; and bone mineral density were investigated at baseline and at the end of follow-up (78 +/- 13 and 72 +/- 15 mo in groups A and B, respectively). CA led to a significant rise in urinary pH and citrate and decreased urinary calcium and phosphate (all P < 0.001). Patients with MSK and PSRF had reduced bone density. Bone density improved significantly in the group that was treated with oral CA. Bone disease is very frequent in patients with MSK and concomitant PSRF. Long-term CA improves bone density. The concurrent effects of treatment on PSRF suggest that the subtle acidosis plays a pivotal role in bone disease and hypercalciuria in patients with MSK.