Safety of Inulin and Sinistrin: Combining Several Sources for Pharmacovigilance Purposes.

Introduction: Inulin and its analog sinistrin are fructose polymers used in the food and pharmaceutical industries. In 2018, The French National Agency for the Safety of Medicines and Health Products (ANSM) decided to withdraw products containing sinistrin and inulin due to several reports of serious hypersensitivity reactions, including a fatal outcome. Objective: To assess the safety of inulin and sinistrin use in France. Methods: We searched multiple sources to identify adverse reactions (ARs) to inulin or sinistrin: first, classical pharmacovigilance databases including the French Pharmacovigilance (FPVD) and the WHO Database (VigiBase); second, data from a clinical trial, MultiGFR; third, data regarding current use in an hospital. All potential ARs to inulin or sinistrin were analyzed with a focus on hypersensitivity reactions and relationships to batches of sinistrin. Results: From 1991 to 2018, 134 ARs to inulin or sinistrin were registered in the FPVD or VigiBase. Sixty-three cases (47%) were classified as serious, and 129 cases (96%) were hypersensitivity reactions. We found an association between a batch of sinistrin and the occurrence of hypersensitivity reactions. During the MultiGFR clinical trial, 7 patients (7/163 participants) had an Adverse reaction; of these, 4 were hypersensitivity reactions including one case of grade 4 anaphylactic shock. In the hospital, no ARs were observed. In the literature, ARs to inulin and sinistrin are very rarely reported and mostly benign. Conclusion: Most ARs to inulin and sinistrin are hypersensitivity reactions that appear to be associated with sinistrin batches.

Increased expression of fibroblast growth factor 23 is the signature of a deteriorated Ca/P balance in ageing laying hens.

The present study concerned the effect of ageing in laying hens, from 23 to 90 weeks of age, on the regulation of Ca metabolism related to the requirement for eggshell mineralization. Samples were collected from parathyroid gland (PG), liver, jejunum, medullary bone (MB) and kidney for a quantitative study of candidate gene expression. Although parathyroid hormone (PTH) gene expression in the PG did not vary with age, a stronger challenge to Ca homeostasis was suggested in aged hens. Indeed gene expression of Ca transporters , Vitamin D Receptor (VDR) in the jejunum, and that of transient receptor potential channel subfamily V member 5 (TRPV5) in the kidney decreased. This could exacerbate bone resorption and impair bone accretion, as attested by a higher expression of the Carbonic Anhydrase 2 (CA2) gene and a lower expression of collagen type I alpha 1 chain (COL1A1) in the MB. The increased expression of Fibroblast Growth Factor 23 (FGF23) in the MB likely contributed to the decreased plasma levels of 1.25(OH)2D3 and the altered expression of target genes under its regulation. Our data highlights the molecular mechanisms underlying the osteoporotic syndrome previously documented in aged laying hens, thus providing new perspectives for future interventions.

Possible roles of parathyroid hormone, 1.25(OH)2D3, and fibroblast growth factor 23 on genes controlling calcium metabolism across different tissues of the laying hen.

This study provides an integrative description of candidate gene expression across tissues involved in calcium (Ca) metabolism during the egg laying cycle, using the well-defined model of Ca supply as fine or coarse particles of calcium carbonate (CaCO3). Plasma and tissue samples were collected from hens at the peak of laying at 0 to 1, 9 to 10, and 18 to 19 h postovulation (PO). After mRNA preparation from the parathyroid gland, medullary bone, liver, kidney, duodenum, and jejunum, gene expressions were quantified using RT-qPCR. The highest levels of parathyroid hormone (PTH) mRNA in the parathyroid gland (P < 0.05), and of the active form of vitamin D3 1.25(OH)2D3 in the plasma (P < 0.01) were observed at 18 to 19 h PO. During this active phase of eggshell formation, bone resorption was attested to high levels of plasma inorganic phosphorus (iP) and the receptor activation of nuclear factor-κB expression in the bone (P < 0.001 and P < 0.05, respectively). At this stage, 5 genes of the transcellular and the paracellular Ca absorption pathways in the intestine (P < 0.05) and the Ca channel transient receptor potential cation channel subfamily V member 5 (P < 0.05), involved in its reabsorption in the kidney, were overexpressed. At 0 to 1 h PO during the subsequent daylight period, 2 candidates of the transcellular and the paracellular Ca pathways (P < 0.05) remained at high levels in the intestine, while calbindin D 28K expression was the highest in the kidney (P < 0.05). As PTH mRNA and 1.25(OH)2D3 were low, bone accretion was likely active at this stage. The phosphaturic hormone fibroblast growth factor 23 (FGF23) was overexpressed at 18 to 19 h PO (P < 0.05) in the bone when plasma iP was high, which suggested a role in the subsequent reduction of P reabsorption in the kidney, as attested to the decreased expression of P cotransporters, leading to iP clearance from the plasma at 0 to 1 h PO (P < 0.05). The low levels of 1.25(OH)2D3 at this stage coincided with increased expression of the 24-hydroxylase gene in the kidney (P < 0.05). In hens fed fine particles of CaCO3, higher plasma levels of 1,25(OH)2D3 and higher expression of several genes involved in bone turnover reflected a stronger challenge to Ca homeostasis. Altogether, these data support the hypothesis that FGF23 could drive vitamin D metabolism in the laying hen, as previously documented in other species and explain the tight link between P and Ca metabolisms.

Candidate genes of the transcellular and paracellular calcium absorption pathways in the small intestine of laying hens.

To meet the high calcium (Ca) demand during eggshell biomineralization (2 g of Ca per egg), laying hens develop specific metabolic regulations to maintain Ca homeostasis. The intake of Ca, its solubilization, and absorption capacity are enhanced at sexual maturity (SM). A better knowledge of the intestinal Ca transporters involved in their variations at this stage could indicate new nutritional strategies to enhance Ca digestive utilization. Transcellular Ca absorption pathway and its major player calbindin-D 28 K (CALB1) mediate a saturable transport, which has been extensively described in this model. Conversely, a contribution by the paracellular pathway involving non-saturable Ca transport through intercellular tight junction has also been suggested. The aim of the present study was to identify candidate genes of these two pathways and their patterns of expression, in immature pullets (12, 15, and 17 wk old) and mature laying hens (23 wk old) in the duodenum, jejunum, and ileum. Using RT-qPCR, this study identifies 3 new candidate genes for transcellular, and 9 for paracellular Ca transport. A total of 5 candidates of the transcellular pathway, transient receptor potential cation channels subfamily C member 1 (TRPC1) and M member 7 (TRPM7); CALB1 and ATPase plasma membrane Ca2+ transporting 1 (ATP2B1) and ATPase plasma membrane Ca2+ transporting 2 (ATP2B2) were enhanced with age or after SM in the duodenum, the jejunum or all 3 segments. A total of 4 candidates of the paracellular pathway Claudin 2 (CLDN2) and tight junction proteins 1, 2, and 3 (TJP1, TJP2 and TJP3) increased in the small intestine after SM. Additionally, CALB1, ATP2B2, and CLDN2 were overexpressed in the duodenum or the jejunum or both segments after SM. The enhanced expression of candidate genes of the paracellular Ca pathway after SM, supports that the non-saturable transport could be a mechanism of great importance when high concentrations of soluble Ca are observed in the intestinal content during eggshell formation. Both pathways may work cooperatively in the duodenum and jejunum, the main sites of Ca absorption in laying hens.

Familial renal glycosuria and modifications of glucose renal excretion.

Under physiological conditions, the kidneys contribute to glucose homoeostasis by producing glucose by gluconeogenesis and preventing glucose loss in urine. The glucose filtered by the glomeruli is completely reabsorbed in the renal proximal tubule. Renal gluconeogenesis produces 25% of the circulating glucose in the postabsorptive state, while the amount of glucose reabsorbed by the kidneys largely exceeds the quantity synthesized by kidney gluconeogenesis. Sodium-glucose cotransporter type 2 (SGLT-2) and glucose transporter 2 (GLUT2) carry out more than 90% of renal glucose uptake. In diabetes, both gluconeogenesis and renal glucose reabsorption are increased. The augmentation of glucose uptake in diabetes is due to the overexpression of renal glucose transporters SGLT-2 and GLUT2 in response to the increase in expression of transcription activator hepatic nuclear factor 1-alpha (HNF1α). The rise in glucose uptake contributes to hyperglycaemia and induces glomerular hyperfiltration by increasing sodium and water reabsorption in the proximal tubule that, in turn, modifies urine flux at the macula densa. SGLT-2 inhibitors improve glycaemic control and prevent renal hyperfiltration in diabetes. Loss of SGLT-2 transporter function is a benign state characterized by glycosuria. In contrast, mutations of other glucose transporters expressed in the kidney are responsible for severe disorders.

[Hyperuricemia in sickle cell disease in France]. / Hyperuricémie chez les patients drépanocytaires suivis en France.

PURPOSE: Hyperuricemia has been reported to be a common feature of sickle cell disease occurring between 32 to 41% of the patients, in studies conducted during the 1970's. Since then, this notion has been rarely challenged. The objective of this study was to assess the prevalence of hyperuricemia and gout in adult patients with sickle cell disease in France. METHODS: Between May 2007 and March 2009, serum and urinary urate concentration, creatininemia and hemogram were prospectively assessed in all consecutive sickle cell patients, followed in our sickle cell disease centre. All subjects were in a clinically steady state. Clinical acute gout history was also recorded. RESULTS: Sixty-five patients (mean age 31±10.3 years) were investigated. Mean uric acid serum level was 281.6±74µmol/L. Hyperuricemia was evidenced in six patients only (9.2%) (95% IC: 3.5-19.0). None of the patient had a medical history of acute gout. Patients in the higher serum uric acid tertile concentration had higher serum creatinine level (62.3±17.1µmol/L vs 51.5±12.6µmol/L, P<0.01), lower fractional excretion of urate (4.5% vs 6.8%, P<0.03) and higher reticulocyte count (median 219500/mm(3) vs 144000/mm(3), P=0.08) compared to the other patients. CONCLUSION: Hyperuricemia and gout are not a clinical problem in sickle cell disease in our country. Nevertheless, our findings indicate that kidney function has to be fully explored if serum uric acid level is elevated or significantly deteriorates during follow-up. Serum uric acid level could be an early marker of renal dysfunction in sickle cell disease patients.

[Update on vitamin D and evaluation of vitamin D status]. / Actualité sur les effets de la vitamine D et l'évaluation du statut vitaminique D.

Knowledge about vitamin D has greatly improved during the last few years. Vitamin D cannot any more be considered as exclusively necessary to prevent ricket/osteomalacia. Its role in the prevention of some osteoporotic fractures in the elderly (in association with calcium nutrition) is now well demonstrated and many epidemiologic and laboratory data argue for a role in the prevention of several diseases or anomalies (cancer, auto-immune diseases, cardiovascular events, sarcopenia...). A few intervention studies confirming some of these effects also exist. Vitamin D status can easily be assessed by measuring serum 25 hydroxy vitamin D (25OHD) level. However, many experts have claimed that the population-based reference values for 25OHD are too low and that the cut-off value below which vitamin D insufficiency can be present is somewhere between 20 and 40 ng/mL with a clear tendency to target values above 30 ng/mL (75 nmol/L). The main consequences are that vitamin D insufficiency is highly frequent whereas the currently recommended supplementation doses are not sufficient.

Bone mass does not correlate with the serum fibroblast growth factor 23 in hemodialysis patients.

Circulating fibroblast growth factor 23 (FGF23) increases renal phosphate excretion, decreases bone mineralization and is markedly increased in hemodialysis patients. Bone cells express fibroblast growth receptor 1, suggesting that FGF23 could alter bone mineralization by means of a direct effect on the skeleton and/or secondarily due to hypophosphatemia. To distinguish between these possibilities we measured serum concentrations of FGF23, parathyroid hormone, phosphate, calcium, and markers of bone remodeling, and assessed bone mineral density in 99 hemodialysis patients. FGF23 concentrations were increased in all hemodialysis patients, even in those without hyperphosphatemia, and positively correlated with serum phosphate but not with parathyroid hormone. Hemodialysis did not decrease the serum FGF23 concentration. We found no significant correlation between serum FGF23 levels and bone mineral density. Further analysis by gender or T-score did not modify these results. Serum markers of bone remodeling significantly correlated with parathyroid hormone but not with FGF23 levels. The increase in serum FGF23 concentration in hemodialysis patients cannot be solely ascribed to hyperphosphatemia. Our study suggests that the effects of FGF23 on bone mineralization are mainly due to hypophosphatemia and not a direct effect on bone.

Klotho: an antiaging protein involved in mineral and vitamin D metabolism.

Klotho gene mutation leads to a syndrome strangely resembling chronic kidney disease patients undergoing dialysis with multiple accelerated age-related disorders, including hypoactivity, sterility, skin thinning, muscle atrophy, osteoporosis, vascular calcifications, soft-tissue calcifications, defective hearing, thymus atrophy, pulmonary emphysema, ataxia, and abnormalities of the pituitary gland, as well as hypoglycemia, hyperphosphatemia, and paradoxically high-plasma calcitriol levels. Conversely, mice overexpressing klotho show an extended existence and a slow aging process through a mechanism that may involve the induction of a state of insulin and oxidant stress resistance. Two molecules are produced by the klotho gene, a membrane bound form and a circulating form. However, their precise biological roles and molecular functions have been only partly deciphered. Klotho can act as a circulating factor or hormone, which binds to a not yet identified high-affinity receptor and inhibits the intracellular insulin/insulin-like growth factor-1 (IGF-1) signaling cascade; klotho can function as a novel beta-glucuronidase, which deglycosylates steroid beta-glucuronides and the calcium channel transient receptor potential vallinoid-5 (TRPV5); as a cofactor essential for the stimulation of fibroblast growth factor (FGF) receptor by FGF23. The two last functions have propelled klotho to the group of key factors regulating mineral and vitamin D metabolism, and have also stimulated the interest of the nephrology community. The purpose of this review is to provide a nephrology-oriented overview of klotho and its potential implications in normal and altered renal function states.

[Oncogenic osteomalacia: the role of the phosphatonins. Diagnostic usefulness of the Fibroblast Growth Factor 23 measurement in one patient]. / L'ostéomalacie oncogène : rôle des phosphatonines. Intérêt du dosage du fibroblast growth factor 23 démontré chez un malade.

INTRODUCTION: Oncogenic osteomalacia (OO) is a rare paraneoplastic syndrome characterized by severe hypophosphatemia induced by phosphaturic factors which are secreted by some tumors of mesenchymal origin. Fibroblast Growth Factor 23 (FGF-23) belongs to this family. Measurement of FGF-23 might improve the diagnosis of OO. EXEGESIS: We report the case of 71-year-old Caucasian man who had a history of severe osteomalacia with multiples fractures and extreme hypophosphatemia with hyperphosphaturia and normal serum calcium level. Serum FGF-23 was 199 RU/ml (N < 100 RU/ml). The tumor, detected by F-18 FDG PET/CT SCAN was localized in the mandible. Surgical removal of the tumor relieved all symptoms with normalization of serum phosphate levels within 3 days after surgery. CONCLUSION: We conclude that FGF-23 measurement is likely to be of considerable importance for facilitating early diagnosis of OO.

Oncogenic osteomalacia: diagnostic importance of fibroblast growth factor 23 and F-18 fluorodeoxyglucose PET/CT scan for the diagnosis and follow-up in one case.

A case of oncogenic osteomalacia is reported in a 71-year-old man who presented with bone pain, muscle weakness, and severe hypophosphatemia. The tumor which was localized in the left lower mandible was not detected by tomodensitometry, resonance magnetic imaging, and (111)IN-octreotide scintigraphy, but was easily localized by F-18 fluorodeoxyglucose PET/CT SCAN (F-18 FDG PET/CT SCAN). To our knowledge, the value of this technique for detecting tumors in oncogenic osteomalacia has never been reported. Secondly, this case provided an opportunity for confirming the usefulness of serum fibroblast growth factor 23 (FGF23) measurement for the diagnosis and follow-up. We conclude that FGF23 measurements combined with F-18 FDG PET/CT SCAN were decisive tools in a case of oncogenic osteomalacia and are likely to be of considerable importance for facilitating early diagnosis and follow-up in the future.

P-glycoprotein inhibitors stimulate renal phosphate reabsorption in rats.

BACKGROUND: Dipyridamole (Dip) was previously shown to increase renal phosphate (Pi) reabsorption in humans. However, the mechanism(s) underlying this renal tubular effect is not fully elucidated. It is known that Dip inhibits the activity of the P-glycoprotein (Pgp) multidrug resistance protein 1 (MDR1) expressed on the apical membrane of renal proximal tubular cells where the Na-Pi cotransporter (NPT2) is also expressed. We hypothesized that Dip could increase renal Pi reabsorption by inhibiting Pgp activity. METHODS: To test this hypothesis, the effects of Dip, verapamil (Ver), and cyclosporine A (CsA), three unrelated Pgp inhibitors, were studied on the renal Pi reabsorption in rats. RESULTS: All three drugs decreased the fractional excretion of Pi (FE(Pi)) in a dose-dependent manner within one hour after beginning the drug infusion, without altering the glomerular filtration rate or serum parathyroid hormone concentration. Sodium-dependent Pi uptake but not Na-glucose transport was increased in brush-border membrane vesicles (BBMVs) when comparing treated with untreated rats. Western blot analysis showed that NPT2 protein was increased in BBMVs from treated rats. Dip and Ver had no effect when applied directly to BBMVs prepared from untreated rats. Pretreatment of rats with colchicine prevented the effects of Dip on the FE(Pi) and NPT2 expression in brush-border membranes. CONCLUSIONS: Our results suggest that inhibition of Pgp in the proximal tubule increases Pi uptake and NPT2 translocation to the apical membrane.

Frequency of renal phosphate leak among patients with calcium nephrolithiasis.

BACKGROUND: Nephrolithiasis is a frequent disorder affecting 10 to 15% of the population in Europe and the United States. More than 80% of renal stones are made of calcium oxalate and calcium phosphate. The main identified risks for calcium renal stone formation are hypercalciuria and urinary saturation. A urine phosphate (Pi) loss is often associated with hypercalciuria; furthermore, hyperphosphaturia increases urinary saturation. METHODS: To determine whether urinary phosphate loss is associated with calcium urolithiasis, we measured renal Pi threshold (TmPi) in 207 stone formers with normal parathyroid hormone (PTH) serum concentration and in 105 control subjects. RESULTS: The TmPi followed a normal distribution in both groups. The mean TmPi was significantly lower in stone formers versus controls (0.72 +/- 0.13 vs. 0.87 +/- 0.18 mmol/L, P < 0.0001) because of a shift to the left of the TmPi distribution curve in the stone former population, with no evidence for bimodal distribution. Five percent of the controls had a TmPi <0.63 versus 19% of the stone formers. Daily urinary calcium excretion was significantly higher in stone formers than in controls. Calcium excretion was also significantly higher in stone formers with TmPi <0.63 mmol/L compared with those with TmPi > or =0.63. Serum PTH and ionized calcium concentrations were not different in stone formers and in control subjects, whatever the TmPi value. CONCLUSIONS: : A low TmPi is more frequently encountered in stone formers with a normal PTH concentration than in control subjects and is associated with a high urinary Ca excretion. The hypophosphatemia induced by a renal phosphate leak may predispose the subject to calcium stone formation by increasing the serum calcitriol level, calcium excretion, and urinary saturation.

HNF1alpha controls renal glucose reabsorption in mouse and man.

Recently it has been shown that dominant mutations in the human hepatocyte nuclear factor 1alpha (HNF1alpha) gene, encoding for a homeoprotein that is expressed in liver, kidney, pancreas and intestine, result in maturity onset diabetes of the young type 3 (MODY3). HNF1alpha-null mice are diabetic, but at the same time suffer from a renal Fanconi syndrome characterized by urinary glucose loss. Here we show that MODY3 patients are also characterized by a reduced tubular reabsorption of glucose. The renal murine defect is due to reduced expression of the low affinity/high capacity glucose cotransporter (SGLT2). Our results show that HNF1alpha directly controls SGLT2 gene expression. Together these data indicate that HNF1alpha plays a key role in glucose homeostasis in mammals.

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors increase fibrinolytic activity in rat aortic endothelial cells. Role of geranylgeranylation and Rho proteins.

3-Hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase inhibitors (HRIs) have been recently shown to prevent atherosclerosis progression. Clinical benefit results from combined actions on various components of the atherosclerotic lesion. This study was designed to identify the effects of HRI on one of these components, the endothelial fibrinolytic system. Aortas isolated from rats treated for 2 days with lovastatin (4 mg/kg body wt per day) showed a 3-fold increase in tissue plasminogen activator (tPA) activity. In a rat aortic endothelial cell line (SVARECs) and in human nontransformed endothelial cells (HUVECs), HRI induced an increase in tPA activity and antigen in a time- and concentration-dependent manner. In SVARECs, the maximal response was observed when cells were incubated for 48 hours with 50 micromol/L HRI. An increase of tPA mRNA was also in evidence. In contrast, HRI inhibited plasminogen activator inhibitor-1 activity and mRNA. The effects of HRI were reversed by mevalonate and geranylgeranyl pyrophosphate, but not by LDL cholesterol and farnesyl pyrophosphate, and were not induced by alpha-hydroxyfarnesyl phosphonic acid, an inhibitor of protein farnesyl transferase. C3 exoenzyme, an inhibitor of the geranylgeranylated-activated Rho protein, reproduced the effect of lovastatin on tPA and plasminogen activator inhibitor-1 activity and blocked its reversal by geranylgeranyl pyrophosphate. The effect of HRI was associated with a disruption of cellular actin filaments without modification of microtubules. A disrupter of actin filaments, cytochalasin D, induced the same effect as lovastatin on tPA, whereas a disrupter of microtubules, nocodazole, did not. In conclusion, HRI can modify the fibrinolytic potential of endothelial cells, likely via inhibition of geranylgeranylated Rho protein and disruption of the actin filaments. The resulting increase of fibrinolytic activity of endothelial cells may contribute to the beneficial effects of HRI in the progression of atherosclerosis.

Dipyridamole decreases renal phosphate leak and augments serum phosphorus in patients with low renal phosphate threshold.

It has been shown that an acute infusion of dipyridamole increased renal phosphate reabsorption in rats and humans. A prospective study was performed to determine whether chronic treatment by dipyridamole given orally could decrease renal phosphate leak and increase serum phosphorus in patients with idiopathic low renal phosphate threshold (TmPO4/GFR < 0.77 mM). Sixty-four patients with low TmPO4/GFR were included and treated with dipyridamole (75 mg, 4 times daily) for more than 12 mo. Serum phosphorus, TmPO4/GFR, parathyroid hormone, serum calcium, and 1,25-dihydroxyvitamin D were measured sequentially before treatment, and after 3, 6 to 9, and 12 mo of treatment. Under chronic treatment with dipyridamole, TmPO4/GFR and serum phosphorus significantly increased in 80% of patients within 3 mo, with maximal values reached within 9 mo. This improvement persisted after 12 mo of treatment. In 28 patients, 1,25-dihydroxyvitamin D concentrations were above the normal range (> 42 pg/ml) and normalized in parallel with the increase of serum phosphorus. The 24-h calcium excretion (which was initially increased in patients with high vitamin D concentrations) and urolithiasis decreased under treatment. Ionized serum calcium and parathyroid hormone remained unchanged. After 2 yr, treatment was discontinued in three patients; serum phosphorus and TmPO4/GFR decreased within 1 mo after discontinuation. Dipyridamole at a dose of 75 mg 4 times daily increases low TmPO4/GFR and improves hypophosphatemia in patients with renal phosphate losses and can be used to treat these patients.

Abnormal sulfate metabolism in vitamin D-deficient rats.

To explore the possibility that vitamin D status regulates sulfate homeostasis, plasma sulfate levels, renal sulfate excretion, and the expression of the renal Na-SO4 cotransporter were evaluated in vitamin D-deficient (D-D-) rats and in D-D- rats rendered normocalcemic by either vitamin D or calcium/lactose supplementation. D-D- rats had significantly lower plasma sulfate levels than control animals (0.93+/-0.01 and 1.15+/-0.05 mM, respectively, P < 0.05), and fractional sulfate renal excretion was approximately threefold higher comparing D-D- and control rats. A decrease in renal cortical brush border membrane Na-SO4 cotransport activity, associated with a parallel decrease in both renal Na-SO4 cotransport protein and mRNA content (78+/-3 and 73+/-3% decreases, respectively, compared with control values), was also observed in D-D- rats. Vitamin D supplementation resulted in a return to normal of plasma sulfate, fractional sulfate excretion, and both renal Na-SO4 cotransport mRNA and protein. In contrast, renal sulfate excretion and renal Na-SO4 cotransport activity, protein abundance, and mRNA remained decreased in vitamin D-depleted rats fed a diet supplemented with lactose and calcium, despite that these rats were normocalcemic, and had significantly lower levels of parathyroid hormone and 25(OH)- and 1,25(OH)2-vitamin D levels than the vitamin D-supplemented groups. These results demonstrate that vitamin D modulates renal Na-SO4 sulfate cotransport and sulfate homeostasis. The ability of vitamin D status to regulate Na-SO4 cotransport appears to be a direct effect, and is not mediated by the effects of vitamin D on plasma calcium or parathyroid hormone levels. Because sulfate is required for synthesis of essential matrix components, abnormal sulfate metabolism in vitamin D-deficient animals may contribute to producing some of the abnormalities observed in rickets and osteomalacia.

Overexpression of ecto-5'-nucleotidase promotes P-glycoprotein expression in renal epithelial cells.

UNLABELLED: P-glycoprotein (P-gp), responsible for multidrug resistance (MDR) of tumoral cells, is also expressed in apical membranes of normal epithelial cells, among which are proximal tubular cells. Ecto-5'-nucleotidase (5'Nu), co-located with P-gp in renal brush border membranes, could be instrumental in the expression of MDR phenotype. P-gp activity [assessed by rhodamine 123 (R123) and [3H]vinblastine (3H-VBL) accumulation] was evaluated in MDCK cell lines in which human 5'Nu was expressed at different levels after retroviral infection: MDCK-5'NU/- cells with a low 5'Nu activity (Vmax < 2 pmol/mg protein/min) and MDCK-5'NU/+ cells, which expressed a high level of 5'Nu (Vmax 150 +/- 18.5 pmol/mg protein/min). MDCK-5'NU/- cells did not display functional expression of MDR. In MDCK-5'NU/+ cells, R123 and 3H-VBL accumulation was significantly lower than in MDCK-5'NU/- cells and was dramatically enhanced by P-gp inhibitors. This high P-gp activity in MDCK-5'NU/+ cells was confirmed by their resistance to colchicine (measured by LDH release and MTT assay) as compared to MDCK-5'NU/- and was accounted for by increased membrane expression of P-gp assessed by Western blot. Neither AMP nor adenosine, the substrate and the product of 5'Nu, respectively, affected P-gp activity. Inhibition of 5'Nu with alpha beta-methylene-adenosine-diphosphate (alpha beta MADP) or with a blocking anti-5'Nu antibody (1E9) did not blunt MDR expression in MDCK-5'NU/+ cells. Conversely, the anti-5'Nu antibody 5F/F9, which did not block the enzymatic site, induced a decrease of P-gp activity. Further, incubation of MDCK-5'NU/- cells with conditioned medium from MDCK-5'NU/+ cells, which contained significant amounts of released 5'Nu, induced MDR phenotype. IN CONCLUSION: (i) expression of ecto-5'Nu promotes multidrug resistance (MDR) activity in renal epithelial cells by enhancement of P-gp expression; (ii) this effect does not involve enzymatic activity of 5'Nu; (iii) supernatants of cells that express 5'Nu conferred P-gp activity to 5'Nu negative cells.

Lovastatin-induced inhibition of renal epithelial tubular cell proliferation involves a p21ras activated, AP-1-dependent pathway.

Proliferation of tubular epithelial cells underlies the development of cystic lesions and the subsequent impairment of renal function after renal mass reduction. The effect of HMG CoA reductase inhibitors (HRI) on cell proliferation was investigated in rat renal proximal tubular epithelial cells in primary culture. Treatment of renal tubular epithelial cells with three different HRI reduced fetal calf serum (FCS)-induced [3H]-thymidine incorporation (IC50 values were 0.7 microM, 1.7 microM, and 1.6 microM for simvastatin, lovastatin, and compactin, respectively), and lovastatin blocked BrdUrd incorporation, as assessed by immunocytochemical studies. The proliferative effect of epidermal growth factor (EGF) was similarly abolished by lovastatin. The effect of lovastatin (1 microM) was prevented by 100 microM mevalonate, 5 microM farnesyl-pyrophosphate and 5 microM geranylgeranyl-pyrophosphate (in percent of control value, 31% vs. 102%, 60%, and 82%, respectively) while cholesterol and other products of the mevalonate pathway were inactive. Immunoblot analysis showed that lovastatin decreased membrane-bound p21ras and inhibited FCS-induced c-fos and c-jun protein expression. Furthermore, electrophoretic mobility shift assay demonstrated the functional impairement of AP-1 DNA binding activity in lovastatin-treated cells. In conclusion, these results demonstrate that HRI are antiproliferative in epithelial tubule cells and that this effect is exerted, at least in part, via inhibition of the p21ras-activated and AP-1 dependent mitogenic cascade.

Locally formed 5-hydroxytryptamine stimulates phosphate transport in cultured opossum kidney cells and in rat kidney.

UNLABELLED: Renal proximal tubular cells have been shown to express aromatic L-amino acid decarboxylase (L-AAAD), which converts L-dopa into dopamine and 5-hydroxytryptophan [(OH)Trp] into 5-hydroxytryptamine (5-HT; serotonin). Because 5-HT receptors have been demonstrated in proximal cells, we hypothesized that 5-HT may act as an autocrine/paracrine modulator of proximal transport. We evaluated this possibility in opossum kidney (OK) cells, a renal epithelial cell line with a proximal phenotype expressing 5-HT1B receptors, and in intact anaesthetized rats. 5-HT synthesis by OK cells increased with incubation time and (OH)Trp concentration, and was abolished by benserazide, an L-AAAD inhibitor. 5-HT reversed parathyroid hormone (PTH)-induced cAMP accumulation in a pertussis toxin-sensitive manner and reduced the PTH inhibition of P(i) uptake without affecting the NaP(i)-4 mRNA level. The effects of 5-HT on cAMP generation and Na-P(i) co-transport were reproduced by (OH)Trp, except in the presence of benserazide, and by L-propranolol and dihydroergotamine, two 5-HT1B receptor agonists. In rats, (OH)Trp and dihydroergotamine decreased fractional P(i) excretion. Benserazide abolished the effect of (OH)Trp but not that of dihydroergotamine. IN CONCLUSION: (i) locally generated 5-HT blunts the inhibitory effect of PTH on Na-P(i) co-transport in OK cells; (ii) endogenous 5-HT decreases P(i) excretion in rats; and (iii) 5-HT is a paracrine modulator involved in the physiological regulation of renal P(i) transport.