Decrease in kidney calbindin-D 28kDa as a possible mechanism mediating cyclosporine A- and FK-506-induced calciuria and tubular mineralization

Increased Endocytosis of Cadmium-Metallothionein through the 24p3 Receptor in an In Vivo Model with Reduced Proximal Tubular Activity

BACKGROUND

The proximal tubule (PT) is the major target of cadmium (Cd2+) nephrotoxicity. Current dogma postulates that Cd2+ complexed to metallothionein (MT) (CdMT) is taken up through receptor-mediated endocytosis (RME) via the PT receptor megalin:cubilin, which is the predominant pathway for reuptake of filtered proteins in the kidney. Nevertheless, there is evidence that the distal parts of the nephron are also sensitive to damage induced by Cd2+. In rodent kidneys, another receptor for protein endocytosis, the 24p3 receptor (24p3R), is exclusively expressed in the apical membranes of distal tubules (DT) and collecting ducts (CD). Cell culture studies have demonstrated that RME and toxicity of CdMT and other (metal ion)-protein complexes in DT and CD cells is mediated by 24p3R. In this study, we evaluated the uptake of labeled CdMT complex through 24p3R after acute kidney injury (AKI) induced by gentamicin (GM) administration that disrupts PT function. Subcutaneous administration of GM at 10 mg/kg/day for seven days did not alter the structural and functional integrity of the kidney's filtration barrier. However, because of PT injury, the concentration of the renal biomarker Kim-1 increased. When CdMT complex coupled to FITC was administered intravenously, both uptake of the CdMT complex and 24p3R expression in DT increased and also colocalized after PT injury induced by GM. Although megalin decreased in PT after GM administration, urinary protein excretion was not changed, which suggests that the increased levels of 24p3R in the distal nephron could be acting as a compensatory mechanism for protein uptake. Altogether, these results suggest that PT damage increases the uptake of the CdMT complex through 24p3R in DT (and possibly CD) and compensate for protein losses associated with AKI.

Hypomagnesemia in the Cancer Patient

Hypomagnesemia is a common medical problem that contributes to the morbidity and mortality of patients with cancer. This review summarizes magnesium physiology and highlights the mechanisms underlying magnesium disturbances due to cancer and cancer treatment. The causes of hypomagnesemia can be categorized according to the pathophysiologic mechanism: decreased intake, transcellular shift, gastrointestinal losses, and kidney losses. Patients with cancer are at risk for opportunistic infections, frequently experience cardiovascular complications, and often receive classes of medications that cause or exacerbate hypomagnesemia. Also, cancer-specific therapies are responsible for hypomagnesemia, including platinum-based chemotherapy, anti-EGF receptor mAbs, human EGF receptor-2 target inhibitors (HER2), and calcineurin inhibitors. Urinary indices, such as the fractional excretion of magnesium, can provide useful information about the etiology. The management of hypomagnesemia depends on the magnitude of hypomagnesemia and the underlying cause. We recommended checking serum magnesium at the beginning of treatment and as part of routine monitoring throughout cancer treatment. Opportunities exist for potential research and practice improvement, including further characterization of hypomagnesemia regarding the clinical effect on cancer outcomes, preventing hypomagnesemia in patients receiving high-risk anticancer agents, and developing effective therapeutic strategies.

Tacrolimus-induced hypomagnesemia and hypercalciuria requires FKBP12 suggesting a role for calcineurin

Calcineurin inhibitors (CNIs) are immunosuppressive drugs used to prevent graft rejection after organ transplant. Common side effects include renal magnesium wasting and hypomagnesemia, which may contribute to new-onset diabetes mellitus, and hypercalciuria, which may contribute to post-transplant osteoporosis. Previous work suggested that CNIs reduce the abundance of key divalent cation transport proteins, expressed along the distal convoluted tubule, causing renal magnesium and calcium wasting. It has not been clear, however, whether these effects are specific for the distal convoluted tubule, and whether these represent off-target toxic drug effects, or result from inhibition of calcineurin. The CNI tacrolimus can inhibit calcineurin only when it binds with the immunophilin, FKBP12; we previously generated mice in which FKBP12 could be deleted along the nephron, to test whether calcineurin inhibition is involved, these mice are normal at baseline. Here, we confirmed that tacrolimus-treated control mice developed hypomagnesemia and urinary calcium wasting, with decreased protein and mRNA abundance of key magnesium and calcium transport proteins (NCX-1 and Calbindin-D28k ). However, qPCR also showed decreased mRNA expression of NCX-1 and Calbindin-D28k , and TRPM6. In contrast, KS-FKBP12-/- mice treated with tacrolimus were completely protected from these effects. These results indicate that tacrolimus affects calcium and magnesium transport along the distal convoluted tubule and strongly suggests that inhibition of the phosphatase, calcineurin, is directly involved.

Long-term renal tubular damage in intrauterine growth-restricted rats

BACKGROUND

Intrauterine growth restriction (IUGR) has been shown to be associated with increased risk of renal disease or hypertension in later life. Glomerular dysfunction, however, has mainly been reported, and limited information is available to link IUGR with renal tubular damage. The aim of this study was therefore to investigate urinary markers of tubular damage in a rat model of IUGR induced by bilateral uterine artery ligation.

METHODS

Pregnant Sprague-Dawley rats underwent bilateral uterine artery ligation, while the control group underwent sham surgery.

RESULTS

Birthweight was reduced, and urinary β2-microglobulin (β2-MG)-, cystatin C (Cys-C)-, and calbindin-to-creatinine ratios were significantly higher at weeks 4 and 8 in the IUGR group compared with the control group. These urinary markers were not significantly different at week 16 between the two groups. Increased excretion of urinary β2-MG, Cys-C, and calbindin was observed in IUGR rats at ≥8 weeks of age.

CONCLUSION

Children born with IUGR are at increased risk for renal tubular damage.

TRPV5: a Ca(2+) channel for the fine-tuning of Ca(2+) reabsorption

TRPV5 is one of the two channels in the TRPV family that exhibit high selectivity to Ca(2+) ions. TRPV5 mediates Ca(2+) influx into cells as the first step to transport Ca(2+) across epithelia. The specialized distribution in the distal tubule of the kidney positions TRPV5 as a key player in Ca(2+) reabsorption. The responsiveness in expression and/or activity of TRPV5 to hormones such as 1,25-dihydroxyvitamin D3, parathyroid hormone, estrogen, and testosterone makes TRPV5 suitable for its role in the fine-tuning of Ca(2+) reabsorption. This role is further optimized by the modulation of TRPV5 trafficking and activity via its binding partners; co-expressed proteins; tubular factors such as calbindin-D28k, calmodulin, klotho, uromodulin, and plasmin; extracellular and intracellular factors such as proton, Mg(2+), Ca(2+), and phosphatidylinositol-4,5-bisphosphate; and fluid flow. These regulations allow TRPV5 to adjust its overall activity in response to the body's demand for Ca(2+) and to prevent kidney stone formation. A point mutation in mouse Trpv5 gene leads to hypercalciuria similar to Trpv5 knockout mice, suggesting a possible role of TRPV5 in hypercalciuric disorders in humans. In addition, the single nucleotide polymorphisms in Trpv5 gene prevalently present in African descents may contribute to the efficient renal Ca(2+) reabsorption among African descendants. TRPV5 represents a potential therapeutic target for disorders with altered Ca(2+) homeostasis.

Ciclosporin therapy is associated with minimal changes in calcium metabolism in dogs with atopic dermatitis

BACKGROUND

Ciclosporin is widely used in the management of canine atopic dermatitis. In humans, ciclosporin therapy has been linked to disturbances in calcium metabolism and resultant skeletal disorders.

OBJECTIVES

The objective of this study was to assess calcium homeostasis in dogs before and after a 6 week course of once daily oral ciclosporin at the licensed dose (5 mg/kg).

ANIMALS

Sixteen client-owned dogs with spontaneous atopic dermatitis.

METHODS

Serum concentrations of calcium, phosphate, creatinine, 25-hydroxyvitamin D, 1,25-dihyroxyvitamin D and plasma concentrations of ionized calcium and parathyroid hormone (PTH) were measured, together with the urinary fractional excretion of calcium and phosphate. The extent of skin lesions was scored using the Canine Atopic Dermatitis Extent and Severity Index (CADESI)-03 and the degree of pruritus by the Edinburgh Pruritus Scale prior to and at the end of the study.

RESULTS

The CADESI-03 and the Edinburgh Pruritus Scale scores decreased satisfactorily in all dogs by the end of the study. Plasma PTH concentrations were significantly increased (P = 0.02) following ciclosporin treatment, whereas all other biochemical parameters were not significantly different from their starting values. The increase in PTH was mild in most cases and the proportion of dogs that had a PTH concentration above the reference range was not significantly different following treatment.

CONCLUSIONS AND CLINICAL IMPORTANCE

This study indicates that ciclosporin has minimal impact on calcium metabolism in dogs with atopic dermatitis when used at the licensed and clinically effective dosage for 6 weeks.

Cyclosporine metabolic side effects: association with the WNK4 system

BACKGROUND

Cyclosporine is used for treatment of transplanted patients and for immune-mediated diseases. Cyclosporine is known to cause a combination of metabolic side effects including hypertension, hyperkalemia, hypercalciuria and hypomagnesemia. These side effects except for hypomagnesemia are the cardinal features of familial hyperkalemia and hypertension (FHHt), also called pseudohypoaldosteronism type II (PHA II). FHHt is caused by mutations in the kinases WNK1 and WNK4 resulting in an increase in renal Na-Cl cotransporter (NCC) apical distribution and function. Therefore, we studied whether cyclosporine's metabolic side effects are mediated by WNK4 and NCC.

DESIGN

Sprague-Dawley (SD) rats were treated by cyclosporine 25 mg kg(-1) subcutaneously for 14 days. Blood pressure, blood chemistry values and kidney WNK4 protein were determined. In addition, mDCT cells were exposed to cyclosporine, and their WNK4 mRNA and protein content, and their NCC protein content and phosphorylation were determined.

RESULTS

The rats developed an FHHt-like syndrome including hypertension, hyperkalemia and salt-sensitive hypercalciuria. A significant increase in their kidney WNK4 protein content (0·13 ± 0·01 vs. 0·67 ± 0·16 WNK4/GAPDH in controls, P = 0·0183) was found. In mDCT cells, cyclosporine caused a rise in WNK4 mRNA levels and also a threefold rise in WNK4 protein content. This rise was followed by a rise in NCC protein content and pSer71 phosphorylation.

CONCLUSIONS

These observations may explain in part the mechanism of cyclosporine-induced hypertension, hyperkalemia and hypercalciuria.

Genomic-derived markers for early detection of calcineurin inhibitor immunosuppressant-mediated nephrotoxicity

Calcineurin inhibitor (CI) therapy has been associated with chronic nephrotoxicity, which limits its long-term utility for suppression of allograft rejection. In order to understand the mechanisms of the toxicity, we analyzed gene expression changes that underlie the development of CI immunosuppressant-mediated nephrotoxicity in male Sprague-Dawley rats dosed daily with cyclosporine (CsA; 2.5 or 25 mg/kg/day), FK506 (0.6 or 6 mg/kg/day), or rapamycin (1 or 10 mg/kg/day) for 1, 7, 14, or 28 days. A significant increase in blood urea nitrogen was observed in animals treated with CsA (high) or FK506 (high) for 14 and 28 days. Histopathological examination revealed tubular basophilia and mineralization in animals given CsA (high) or FK506 (low and high). We identified a group of genes whose expression in rat kidney is correlated with CI-induced kidney injury. Among these genes are two genes, Slc12a3 and kidney-specific Wnk1 (KS-Wnk1), that are known to be involved in sodium transport in the distal nephrons and could potentially be involved in the mechanism of CI-induced nephrotoxicity. The downregulation of NCC (the Na-Cl cotransporter coded by Slc12a3) in rat kidney following CI treatment was confirmed by immunohistochemical staining, and the downregulation of KS-Wnk1 was confirmed by quantitative real-time-polymerase chain reaction (qRT-PCR). We hypothesize that decreased expression of Slc12a3 and KS-Wnk1 could alter the sodium chloride reabsorption in the distal tubules and contribute to the prolonged activation of the renin-angiotensin system, a demonstrated contributor to the development of CI-induced nephrotoxicity in both animal models and clinical settings. Therefore, if validated as biomarkers in humans, SLC12A3 and KS-WNK1 could potentially be useful in the early detection and reduction of CI-related nephrotoxicity in immunosuppressed transplant patients when monitoring the health of kidney xenographs in clinical practice.

Biomarkers of immunosuppressant organ toxicity after transplantation: status, concepts and misconceptions

INTRODUCTION

A major challenge in transplantation is improving long-term organ transplant and patient survival. Immunosuppressants protect the transplant organ from alloimmune reactions, but sometimes also exhibit limiting side effects. The key to improving long-term outcome following transplantation is the selection of the correct immunosuppressive regimen for an individual patient for minimizing toxicity while maintaining immunosuppressive efficacy.

AREAS COVERED

Proteomics and metabolomics have the potential to develop sensitive and specific diagnostic tools for monitoring early changes in cell signal transduction, regulation and biochemical pathways. Here, we review the steps required for the development of molecular markers from discovery, mechanistic and clinical qualification to regulatory approval, and present a critical discussion of the current status of molecular marker development as relevant for the management and individualization of immunosuppressive drug regimens.

EXPERT OPINION

Although metabolomics and proteomics-based studies have yielded several candidate molecular markers, most published studies are poorly designed, statistically underpowered and/or often have not gone beyond the discovery stage. Most molecular marker candidates are still at an early stage. Due to the high complexity of and the resources required for diagnostic marker development, initiatives and consortia organized and supported by funding agencies and regulatory agencies will be critical.

Association of immunosuppressant-induced protein changes in the rat kidney with changes in urine metabolite patterns: a proteo-metabonomic study

The basic mechanisms underlying calcineurin inhibitor (CI) nephrotoxicity and its enhancement by sirolimus are still largely unknown. We investigated the effects of CIs alone and in combination with sirolimus on the renal proteome and correlated these effects with urine metabolite pattern changes. Thirty-six male Wistar rats were assigned to six treatment groups (n = 4/group for proteome analysis and n = 6/group for urine (1)H NMR metabolite pattern analysis): vehicle controls, sirolimus 1 mg/kg/day, cyclosporine 10 mg/kg/day, cyclosporine 10 mg/kg/day + sirolimus 1 mg/kg/day, tacrolimus 1 mg/kg/day, tacrolimus 1 mg/kg/day + sirolimus 1 mg/kg/day. After 28 days, 24 h-urine was collected for (1)H NMR-based metabolic analysis and kidneys were harvested for 2D-gel electrophoresis and histology. Cyclosporine affected the following groups of proteins: calcium homeostasis (regucalcin, calbindin), cytoskeleton (vimentin, caldesmon), response to hypoxia and mitochondrial function (prolyl 4-hydroxylase, proteasome, NADH dehydrogenase), and cell metabolism (kidney aminoacylase, pyruvate dehydrogenase, fructose-1,6-bis phosphate). Several of the changes in protein expression, confirmed by Western blot, were associated with and explained changes in metabolite concentrations in urine. Representative examples are an increase in kidney aminoacylase expression (decrease of hippurate concentrations in urine), up regulation of pyruvate dehydrogenase and fructose-1,6-bisphosphatase, (increased glucose metabolism), and down regulation of arginine/glycine-amidino transferase (most likely due to an increase in creatinine concentrations). Protein changes explained and qualified immunosuppressant-induced metabolite pattern changes in urine.

Development of a polymeric micellar formulation for valspodar and assessment of its pharmacokinetics in rat

The aim of this study was to assess the potential of polymeric micelles to solubilize valspodar and modify its pharmacokinetics following intravenous and oral administration in rat. Drug-loaded methoxy poly(ethylene oxide)-b-poly(epsilon-caprolactone) (PEO-b-PCL) micellar solutions were prepared and administered either intravenously or orally to healthy Sprague-Dawley rats. Plasma pharmacokinetic parameters of valspodar in its polymeric micellar formulation were compared to its clinical formulation, which uses Cremophor EL and ethanol as solubilizing agents. High loading level was achieved for valspodar in PEO-b-PCL leading to an aqueous solubility of 2.8 mg/mL. Following i.v. administration (5 mg/kg), valspodar in the PEO-b-PCL micelles provided significantly higher (approximately 77%) plasma AUC compared to the Cremophor EL formulation. The PEO-b-PCL micelles also significantly decreased the volume of distribution (Vd(ss)) and clearance (CL) of valspodar by nearly 49% and 34%, respectively. After oral administration (10 mg/kg), the average C(max) were similar for both formulations and were both reached at approximately 2 h. The plasma unbound fraction of valspodar in the polymeric micellar formulation was significantly lower than control (8.27% versus 14.85%). Our results show that PEO-b-PCL micelles can efficiently solubilize valspodar and favorably modify its pharmacokinetic profile in rat after i.v. administration by decreasing the CL and Vd.

Pharmacokinetics of PSC 833 (valspodar) in its Cremophor EL formulation in rat

Valspodar is a P-glycoprotein inhibitor widely used in preclinical and clinical studies for overcoming multidrug resistance. Despite this, the pharmacokinetics of valspodar in rat, a commonly used animal model, have not been reported. Here, we report on the pharmacokinetics of valspodar in Sprague-Dawley rats following intravenous and oral administration of its Cremophor EL formulation, which has been used for humans in clinical trials. After intravenous doses, valspodar displayed properties of slow clearance and a large volume of distribution. Its plasma unbound fraction was around 15% in the Cremophor EL formulation used in the study. After 10 mg kg(-1) orally it was rapidly absorbed with an average maximal plasma concentration of 1.48 mg l(-1) within approximately 2 h. The mean bioavailability of valspodar was 42.8%. In rat, valspodar showed properties of low hepatic extraction and wide distribution, similar to that of its structural analogue cyclosporine A.

Different renal toxicity profiles in the association of cyclosporine and tacrolimus with sirolimus in rats

BACKGROUND

The association of calcineurin inhibitors (CNIs) with mTOR inhibitors (mTORi) is still a problem in clinical practice and there is substantial interest in better understanding the impact of these associations on kidney toxicity. We aimed to analyse the functional and histological profiles of damage and to define the contribution of inflammatory and pro-fibrotic mediators in the association of cyclosporine (CsA) and/or tacrolimus (Tac) with sirolimus (SRL).

METHODS

A well-defined model of nephrotoxicity in salt-depleted male rats was used. Monotherapy groups were distributed as a non-treated control group with saline solution (n = 12), the Tac group (n = 16) (tacrolimus 6 mg/kg/day) and the CsA group (n = 13) (CsA 15 mg/kg/day). The groups with different associations were scattered as the Tac + SRL group (n = 14) (tacrolimus 6 mg/kg/day and rapamycin 3 mg/kg/day) and the CsA + SRL group (n = 7) (CsA 15 mg/kg/day and rapamycin 3 mg/kg/day). Groups were divided into 30 and 70 days of follow-up, but the CsA + SRL group was only studied for 30 days because animals became sick.

RESULTS

Rats with the CsA + SRL association were the only ones which showed a significant reduction in body weight, impairment of renal function and severe and diffuse tubular vacuolization and tubular atrophy following a striped distribution, and scarce areas of the kidney were still preserved. The Tac + SRL association did not produce renal function impairment, and mild histological damage including enhanced periglomerular tubular atrophy was observed. This local damage affected the distal convoluted tubule involving macula densa and juxtaglomerular apparatus. Pro-inflammatory mediators paralleled functional and structural data. ED-1 and TNF-alpha were noticeably higher in the CsA + SRL than in the Tac + SRL association. Only in the CsA + SRL association an important increase in alpha-SMA+ cells was seen, mainly found in the areas with tubular atrophy. TGF-beta1 was also markedly enhanced in the CsA + SRL association whilst monotherapy or Tac + SRL groups at 30 days TGF-beta1 did not show any changes. However, at 70 days of treatment TGF-beta1 was significantly increased in the Tac + SRL group. Animals receiving SRL showed a decrease in renal vascular endothelial growth factor (VEGF) expression. This growth factor was significantly down-regulated in both CNI associations than in SRL monotherapy. P-glycoprotein (Pgp) was overexpressed in CsA and CsA + SRL therapy whilst Tac and TAC + SRL showed a middle increase Pgp expression but higher than the control and SRL group.

CONCLUSION

We conclude that the association of SRL with high doses of CsA or Tac produces a different functional, histological, inflammatory and pro-fibrogenic pattern. Thus, the addition of SRL to high doses of CsA leads to severe renal injury. Combination with high doses of Tac is clearly less deleterious in the short term. However, there is a low grade of pro-fibrotic inflammatory expression when this association is prolonged.

Electrolyte imbalances in pediatric living related small bowel transplantation

BACKGROUND

Pediatric small bowel transplantations are associated with pronounced electrolyte disturbances in the postoperative period. We investigated the pattern of electrolyte disturbances with regard to enteral malabsorption, renal compensation, and the influence of immunosuppression.

METHODS

We reviewed 11 small bowel transplantations between October 2002 and February 2007. The data collected included frequent serum, ostomy, and urine electrolyte profiles, renal function parameters, and FK 506 levels in the postoperative period up until either discharge or graft loss.

RESULTS

Our results show enteral losses most prominent during the first 4 weeks postoperatively that are only partially compensated by the kidneys. Subsequently, enteral losses improved, although renal function remained challenged, particularly glomerular filtration and phosphorus, magnesium losses, which correlated with high FK 506 levels.

CONCLUSION

Our data reveal several electrolyte imbalances different and unique to postoperative small bowel transplants. Although enteral losses improve along with graft villi formation, electrolyte abnormalities continue, to which FK 506-mediated renal toxicity might contribute.

TRP channels in kidney disease

Mammalian TRP channel proteins form six-transmembrane cation-permeable channels that may be grouped into six subfamilies on the basis of amino acid sequence homology (TRPC, TRPV, TRPM, TRPA, TRPP, and TRPML). Recent studies of TRP channels indicate that they are involved in numerous fundamental cell functions and are considered to play an important role in the pathophysiology of many diseases. Many TRPs are expressed in kidney along different parts of the nephron and growing evidence suggest that these channels are involved in hereditary, as well as acquired kidney disorders. TRPC6, TRPM6, and TRPP2 have been implicated in hereditary focal segmental glomerulosclerosis (FSGS), hypomagnesemia with secondary hypocalcemia (HSH), and polycystic kidney disease (PKD), respectively. In addition, the highly Ca(2+)-selective channel, TRPV5, contributes to several acquired mineral (dys)regulation, such as diabetes mellitus (DM), acid-base disorders, diuretics, immunosuppressant agents, and vitamin D analogues-associated Ca(2+) imbalance whereas TRPV4 may function as an osmoreceptor in kidney and participate in the regulation of sodium and water balance. This review presents an overview of the current knowledge concerning the distribution of TRP channels in kidney and their possible roles in renal physiology and kidney diseases.

Bone mineral content and mineral metabolism during cyclosporine treatment of nephrotic Syndrome

OBJECTIVE

Although cyclosporine (Cy) has been associated with bone loss following transplantation, its effects on bone in growing children are largely unknown.

STUDY DESIGN

Thirty-seven patients (2-16 years of age) with remitting nephrotic syndrome (NS), n = 16 receiving Cy for 39 +/- 27 months and n = 21 without Cy, underwent mineral metabolism and bone turnover assessment. In 28 of 37 patients, bone mineral density (BMD) was obtained while off corticosteroid therapy (Rx).

RESULTS

Urinary calcium (Ca), phosphate (PO(4)), and magnesium (Mg) excretion was normal, but serum Mg was lower in patients receiving Cy (1.8 +/- 0.1 v 1.95 +/- 0.2 mg/dL, P < .05). BMD Z scores were similar at the spine (-0.45 +/- 0.74 v 0.04 +/- 0.9) and femur (-0.17 +/- 0.52 v 0.38 +/- 1.28) with no Z score <-2. Serum bone-specific alkaline phosphatase was normal, and N-telopeptide of type I collagen also normal, was higher on Cy (P < .05). Cumulative prednisone exposure was similar and had no significant effect on height and BMD Z scores. Length of Cy-Rx and time elapsed from onset of NS did not correlate with BMD, height Z score, or markers of bone turnover.

CONCLUSIONS

In growing children with NS, during long-term Cy-Rx urinary wasting of Ca and Mg was absent and bone density was preserved.

The immunophilin FKBP52 inhibits the activity of the epithelial Ca2+channel TRPV5

In the kidney, the epithelial Ca2+channel TRPV5 constitutes the apical entry pathway in the process of active Ca2+reabsorption. The regulation of Ca2+influx through TRPV5 is of crucial importance, because it determines the final amount of Ca2+excreted in the urine. The present study identifies FKBP52 as an auxiliary protein of TRPV5, inhibiting channel activity. FKBP52 shows specific interaction with TRPV5, and both proteins colocalize in the distal part of the nephron. On the functional level, FKBP52 decreases Ca2+influx through TRPV5 as demonstrated in radioactive45Ca2+uptake measurements and electrophysiological studies in TRPV5-overexpressing human embryonic kidney 293 cells. On the other hand, gene silencing of FKBP52 or administration of the FKBP52 blocker FK-506 enhances Ca2+influx through TRPV5. The inhibitory action of FKBP52 on TRPV5 activity is blunted by mutation of its peptidyl-propyl cis- trans isomerase domain, showing that the FKBP52 catalytic property is critical for channel activity. In conclusion, these results suggest that FKBP52 plays an important role in the regulation of TRPV5 and thus in the process of Ca2+reabsorption.

The epithelial calcium channels TRPV5 and TRPV6: regulation and implications for disease

The epithelial Ca(2+) channels TRPV5 and TRPV6 represent a new family of Ca(2+) channels that belongs to the superfamily of transient receptor potential channels. TRPV5 and TRPV6 constitute the apical Ca(2+) entry mechanism in active Ca(2+) transport in kidney and intestine. The central role of TRPV5 and TRPV6 in active Ca(2+) (re)absorption makes it a prime target for regulation to maintain Ca(2+) balance. This review covers the hormonal regulation, interaction with accessory proteins and (patho)physiological implications of these epithelial Ca(2+) channels.

TRPV5 and TRPV6 in Ca(2+) (re)absorption: regulating Ca(2+) entry at the gate

Many physiological functions rely on the exact maintenance of body Ca(2+) balance. Therefore, the extracellular Ca(2+) concentration is tightly regulated by the concerted actions of intestinal Ca(2+) absorption, exchange of Ca(2+) to and from bone, and renal Ca(2+) reabsorption. Renal distal convoluted and connecting tubular cells as well as duodenal epithelial cells are unique in their ability to mediate transcellular (re)absorption of Ca(2+) at large and highly variable rates. Two members of the transient receptor potential (TRP) superfamily, TRP vanilloid (TRPV)5 and TRPV6, are specialized epithelial Ca(2+) channels responsible for the critical Ca(2+) entry step in transcellular Ca(2+) (re)absorption in intestine and kidney, respectively. Because transcellular Ca(2+) transport is fine-tuned to the body's specific requirements, regulation of the transmembrane Ca(2+) flux through TRPV5/6 is of particular importance and has, therefore, to be conspicuously controlled. We present an overview of the current knowledge and recent advances concerning the coordinated regulation of Ca(2+) influx through the epithelial Ca(2+) channels TRPV5 and TRPV6 in transcellular Ca(2+) (re)absorption.

TRPV5 and TRPV6 in Ca(2+) (re)absorption: regulating Ca(2+) entry at the gate

Many physiological functions rely on the exact maintenance of body Ca(2+) balance. Therefore, the extracellular Ca(2+) concentration is tightly regulated by the concerted actions of intestinal Ca(2+) absorption, exchange of Ca(2+) to and from bone, and renal Ca(2+) reabsorption. Renal distal convoluted and connecting tubular cells as well as duodenal epithelial cells are unique in their ability to mediate transcellular (re)absorption of Ca(2+) at large and highly variable rates. Two members of the transient receptor potential (TRP) superfamily, TRP vanilloid (TRPV)5 and TRPV6, are specialized epithelial Ca(2+) channels responsible for the critical Ca(2+) entry step in transcellular Ca(2+) (re)absorption in intestine and kidney, respectively. Because transcellular Ca(2+) transport is fine-tuned to the body's specific requirements, regulation of the transmembrane Ca(2+) flux through TRPV5/6 is of particular importance and has, therefore, to be conspicuously controlled. We present an overview of the current knowledge and recent advances concerning the coordinated regulation of Ca(2+) influx through the epithelial Ca(2+) channels TRPV5 and TRPV6 in transcellular Ca(2+) (re)absorption.

Cyclosporin A promotes mineralization by human cementoblastoma-derived cells in culture

OBJECTIVE

The immunosuppressive drug cyclosporin A has been shown to induce cementum deposition in vivo in experimental animals. Using cementoblastoma-derived cells, we have studied whether this drug will be useful to study cementum mineralization and differentiation in vitro.

METHODS

Human cementoblastoma cells and gingival fibroblasts (controls) were cultured and treated with 0.5, 1.0 and 5.0 microg/ml of cyclosporin A. Cell proliferation was evaluated by MTT (tetrazolium) assay and cell number, and cell viability was assessed by trypan blue dye exclusion. Induction of mineralization was evaluated by alizarin red S staining to detect mineralized nodules and by reverse transcription-polymerase chain reaction (RT-PCR) to assess the expression of bone differentiation markers alkaline phosphatase, osteocalcin, bone sialoprotein and core-binding factor a1 (Cbfa1).

RESULTS

Cyclosporin A at 5.0 microg/ml concentration reduced significantly the increase in the number of cementoblastoma cells. A dose-dependent increase in the number of mineralized nodules occurred in cultures of cementoblastoma-derived cells treated with cyclosporin A, and RT-PCR analyses showed significantly higher levels of expression of alkaline phosphatase, bone sialoprotein, type I collagen, matrix metalloproteinase-1, osteocalcin, osteopontin, and Cbfa1. Human gingival fibroblast proliferation and cell number were not affected. Mineralized nodules were not detected in gingival fibroblasts and bone specific proteins were not expressed.

CONCLUSIONS

Presence of cyclosporin A during 14-day culture period appears to suppress the proliferation of cementoblastoma cells and induce the formation mineralized-like tissue by these cells.

Proteomic identification and immunolocalization of increased renal calbindin-D28k expression in OVE26 diabetic mice

Diabetic nephropathy is a common diabetic complication that is associated with alterations in the expression of several renal proteins and abnormal calcium homeostasis. We performed proteomic analysis to screen for global changes of renal protein expression in diabetic kidney. Proteins extracted from the whole kidney of 120-day-old OVE26 (a transgenic model of Type 1 diabetes) and FVB (non-diabetic background strain) mice were separated by two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) and visualized by SYPRO Ruby staining (n = 5 in each group). Quantitative intensity analysis revealed 41 differentially expressed proteins, of which 30 were identified by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) followed by peptide mass fingerprinting. One of the altered proteins with the greatest magnitude of change was the calcium-binding protein, calbindin-D28k, whose expression was increased 6.7-fold in diabetic kidney. We confirmed the increase in calbindin-D28k expression in diabetic kidney by Western blot analysis. Immunohistochemical study demonstrated that calbindin-D28k expression was markedly increased in tubular epithelial cells of distal convoluted tubules (DCT), collecting ducts (CD), and proximal convoluted tubules (PCT) in diabetic kidney. Calbindin-D28k plays a critical role in maintaining calcium homeostasis. The elevation in renal calbindin-D28k expression in our model may indicate a compensatory mechanism to overcome hypercalciuria in diabetes.

Calcium absorption across epithelia

Ca(2+) is an essential ion in all organisms, where it plays a crucial role in processes ranging from the formation and maintenance of the skeleton to the temporal and spatial regulation of neuronal function. The Ca(2+) balance is maintained by the concerted action of three organ systems, including the gastrointestinal tract, bone, and kidney. An adult ingests on average 1 g Ca(2+) daily from which 0.35 g is absorbed in the small intestine by a mechanism that is controlled primarily by the calciotropic hormones. To maintain the Ca(2+) balance, the kidney must excrete the same amount of Ca(2+) that the small intestine absorbs. This is accomplished by a combination of filtration of Ca(2+) across the glomeruli and subsequent reabsorption of the filtered Ca(2+) along the renal tubules. Bone turnover is a continuous process involving both resorption of existing bone and deposition of new bone. The above-mentioned Ca(2+) fluxes are stimulated by the synergistic actions of active vitamin D (1,25-dihydroxyvitamin D(3)) and parathyroid hormone. Until recently, the mechanism by which Ca(2+) enter the absorptive epithelia was unknown. A major breakthrough in completing the molecular details of these pathways was the identification of the epithelial Ca(2+) channel family consisting of two members: TRPV5 and TRPV6. Functional analysis indicated that these Ca(2+) channels constitute the rate-limiting step in Ca(2+)-transporting epithelia. They form the prime target for hormonal control of the active Ca(2+) flux from the intestinal lumen or urine space to the blood compartment. This review describes the characteristics of epithelial Ca(2+) transport in general and highlights in particular the distinctive features and the physiological relevance of the new epithelial Ca(2+) channels accumulating in a comprehensive model for epithelial Ca(2+) absorption.

Effect of calbindin-D28K on cyclosporine toxicity in cultured renal proximal tubular cells

Cyclosporine A (CsA) is known to have direct toxicity to renal tubular cells. Its toxicity may be mediated by intracellular calcium because CsA increases intracellular calcium concentration and enhances the activities of calcium-dependent calpains and caspases. Calbindin-D28k, a cytosolic calcium binding protein, has been used as an intracellular Ca2+ buffer to reduce calcium-mediated cytotoxicity in non-renal cells such as neuronal cells. We investigated the effects of gene transfer of calbindin-D28k cDNA on CsA cytotoxicity and intracellular calcium concentration ([Ca2+]i) in cultured murine proximal tubular (MCT) cells. A plasmid containing calbindin-D28k cDNA under the control of CMV promoter was transfected to MCT cells with liposomes. Cytotoxicity was assessed by LDH release and cell viability assay, and [Ca2+]i was measured ratiometrically with fura-2. Compared with MCT cells, cells transfected with calbindin-D28k cDNA showed a reduction in LDH release by 27, 30, 32, 33, and 19% (all P < 0.05), respectively, after 24 h exposure to 1, 2.5, 5, 10, and 25 microM CsA. Cell viability after CsA treatment was also significantly higher in CB cells. A mock transfection using plasmid without calbindin-D28k cDNA insert did not affect the LDH release or cell viability after CsA treatment. CsA treatment did not affect the protein and mRNA abundance of transfected calbindin-D28k cDNA. The expression of calbindin-D28k did not affect the baseline [Ca2+]i, but significantly suppressed CsA-induced elevation in [Ca2+]i. The expression of calbindin-D28k in renal tubular cells provides cytoprotective effects against CsA toxicity, probably through its buffering effects on [Ca2+]i.

Toxicogenomics in drug development

Toxicogenomics represents the merging of toxicology with technologies that have been developed, together with bioinformatics, to identify and quantify global gene expression changes. It represents a new paradigm in drug development and risk assessment, which promises to generate a wealth of information towards an increased understanding of the molecular mechanisms that lead to drug toxicity and efficacy, and of DNA polymorphisms responsible for individual susceptibility to toxicity. Gene expression profiling, through the use of DNA microarray and proteomic technologies will aid in establishing links between expression profiles, mode of action and traditional toxic endpoints. Such patterns of gene expression, or 'molecular fingerprints' could be used as diagnostic or predictive markers of exposure, that is characteristic of a specific mechanism of induction of that toxic or efficacious effect. It is anticipated that toxicogenomics will be increasingly integrated into all phases of the drug development process particularly in mechanistic and predictive toxicology, and biomarker discovery. This review provides an overview of the expression profiling technologies applied in toxicogenomics. and discusses the promises as well as the future challenges of applying this discipline to the drug development process.

Regulation of gene expression by dietary Ca2+ in kidneys of 25-hydroxyvitamin D3-1α-hydroxylase knockout mice

BACKGROUND

Pseudovitamin D deficiency rickets (PDDR) is an autosomal disease, characterized by undetectable levels of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), rickets and secondary hyperparathyroidism. Mice in which the 25-hydroxyvitamin D3-1 alpha-hydroxylase (1 alpha-OHase) gene was inactivated, presented the same clinical phenotype as patients with PDDR.

METHODS

cDNA Microarray technology was used on kidneys of 1 alpha-OHase knockout mice to study the expression profile of renal genes in this Ca2+-related disorder. Genome wide molecular events that occur during the rescue of these mice by high dietary Ca2+ intake were studied by the use of 15K cDNA microarray chips.

RESULTS

1 alpha-OHase knockout mice fed a normal Ca2+ diet developed severe hypocalcemia, rickets and died with an average life span of 12 +/- 2 weeks. Intriguingly, 1 alpha-OHase-/- mice supplemented with an enriched Ca2+ diet were normocalcemic and not significantly different from wild-type mice. Inactivation of the 1 alpha-OHase gene resulted in a significant regulation of +/- 1000 genes, whereas dietary Ca2+ supplementation of the 1 alpha-OHase-/- mice revealed +/- 2000 controlled genes. Interestingly, 557 transcripts were regulated in both situations implicating the involvement in the dietary Ca2+-mediated rescue mechanism of the 1 alpha-OHase-/- mice. Conspicuous regulated genes encoded for signaling molecules like the PDZ-domain containing protein channel interacting protein, FK binding protein type 4, kinases, and importantly Ca2+ transporting proteins including the Na+-Ca2+ exchanger, calbindin-D28K and the Ca2+ sensor calmodulin.

CONCLUSION

Dietary Ca2+ intake normalized disturbances in the Ca2+ homeostasis due to vitamin D deficiency that were accompanied by the regulation of a subset of renal genes, including well-known renal Ca2+ transport protein genes, but also genes not previously identified as playing a role in renal Ca2+ handling.

Cyclosporine A-induced hypercalciuria in calbindin-D28k knockout and wild-type mice

BACKGROUND

It is known that cyclosporine A (CsA) treatment induces high bone-turnover osteopenia and hypercalciuria. It has been proposed that down-regulation of renal calbindin-D28k by CsA results in renal calcium wasting. We investigated the role of the kidney and bone in CsA-induced hypercalciuria in calbindin-D28k knockout (KO) and wild-type (WT) mice.

METHODS

Two sets of experiments were performed. In experiment 1, KO and WT mice were treated with CsA 20 mg/kg/day intraperitoneally (IP) for 7 days. In experiment 2, to eliminate the CsA effect on bone resorption, pamidronate (APD) 2.5 mg/kg IP was given every 4 days with the first dose given 4 days prior to the 7-day course of CsA. Serum levels of creatinine, calcium, and osteocalcin, as well as renal calcium excretion were measured to assess CsA's effects on calcium homeostasis. Effects of CsA on the expression of calbindin-D28k, and two calcium channels in the apical membrane of the distal tubule, epithelial calcium channel (ECaC) and alpha1G-subunit of a voltage-dependent Ca channel (alpha1G), in the kidney were examined by semiquantitative reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

KO mice had a threefold increase in renal calcium excretion when compared with WT mice at the baseline. This difference disappeared when calcium load was reduced by overnight fasting. After the CsA treatment, both WT and KO mice had a significant increase of renal calcium excretion (urine Ca/Cr ratio in WT, 0.11 +/- 0.01 to 1.29 +/- 0.17; in KO, 0.39 +/- 0.04 to 1.18 +/- 0.13; both P < 0.01). CsA treatment decreased renal calbindin-D28k mRNA by 61%, but did not affect the expression of ECaC and alpha1G. Baseline serum osteocalcin level of KO mice was significantly lower than that of WT mice. After CsA treatment, both groups had a 50% increase in the serum osteocalcin level, indicating increased bone turnover. When mice were treated with both CsA and APD, the increase in serum osteocalcin level was prevented, and renal calcium excretion was significantly lower than that in mice treated with CsA alone. However, there was still a significant increase in the urine Ca/Cr ratio in WT and KO mice compared with pretreatment levels (urine Ca/Cr in WT, 0.11 +/- 0.01 to 0.76 +/- 0.05, P < 0.01; in KO, 0.39 +/- 0.05 to 0.79 +/- 0.06; P < 0.01).

CONCLUSION

Calbindin-D28k KO mice have diet-dependent hypercalciuria and a lower bone turnover rate. CsA treatment suppresses the expression of calbindin-D28k in mice, but has no effects on ECaC and alpha1G gene expression at the mRNA level. The pathogenesis of CsA-induced hypercalciuria involves both down-regulation of calbindin-D28k with subsequent impaired renal calcium reabsorption and CsA-induced high turnover bone disease. Additionally, our results suggest that mechanism(s) independent of calbindin-D28k within the kidney also may contribute to the CsA-induced calcium leak.

Intratubular calcification in a post-renal transplanted patient with secondary hyperparathyroidism

In this article, we present a case in which marked intratubular calcification occurred in the transplanted kidney. The patient received living renal transplantation without control of severe secondary hyperparathyroidism, and the tacrolimus hydrate was used as an immunosuppressive agent, the adverse effects of which can induce intratubular calcification. Biopsy of the renal allograft revealed many intratubular calcifications in the cortex region of the specimen, although the histological grade was borderline for the Banff classification. The pathogenic causes of intratubular calcification were difficult to distinguish from the adverse effects of tacrolimus and the uncontrolled hyperparathyroidism.

Pharmaceutical proteomics

Genomics and proteomics are today well established in drug discovery and, in combination with combinatorial chemistry and high-throughput screening, are helping to bring forward an unprecedented number of potential lead compounds. To avoid the generation of bottlenecks downstream in drug development, increasing pressure is arising to integrate these technologies into the development environment. Proteomics has demonstrated proof-of-concept in toxicology as shown by a number of successful applications in mechanistic toxicology and lead selection. The "technology wave" is now starting to impact the clinical phase of drug development. Expected benefits are optimized clinical trials based on the availability of biologically relevant markers of drug efficacy and safety.

The role of calbindin and 1,25dihydroxyvitamin D3 in the kidney

The identification of a putative apical Ca++ channel in 1,25dihydroxyvitamin D3 responsive epithelia (proximal intestine and the distal nephron) as well as recent studies using calbindin-D28k knock-out mice indicating the first direct in-vivo evidence for a role for this calcium-binding protein in renal calcium absorption suggest mechanisms, which had remained incomplete, related to the control of renal calcium absorption.

Proteomics: applications and opportunities in preclinical drug development

Advances in DNA sequencing and the near-term availability of whole genome sequences for several pharmaceutically relevant organisms promise to dramatically alter the breadth and scale of high-throughput proteomic studies. The substantial amount of literature is available in the public domain, demonstrate the potential of proteomics in the preclinical phases of pharmaceutical development. Over the next few years, it is anticipated that functional genomics and proteomics will have major impacts on the clinical phases of drug development. Expected benefits are earlier proof-of-concept studies in man and increased efficiency of clinical trials through the availability of biologically relevant markers for drug efficacy and safety.

Evidence for the impairment of the vitamin D activation pathway by cyclosporine A

Cyclosporine A (CsA) is a potent immunosuppressant with the drawback of renal side effects. We reported that CsA markedly decreases calcium-binding protein calbindin-D28k mRNA levels in rat kidneys, and showed that this decrease is associated with its adverse renal effects. The transcription of the calbindin-D28k gene is activated via the vitamin D pathway. In this work, the potential CsA-mediated impairment of the vitamin D pathway was investigated. Wistar rats were treated for 12 days with 50 mg/kg/day CsA or for 20 days with 50 mg/kg/day of the non-immunosuppressant and non-nephrotoxic SDZ PSC 833, which had been previously shown not to affect calbindin-D28k mRNA levels. The expression of the three vitamin D-regulated genes calbindin-D28k, 1,25-dihydroxyvitamin D3-24-hydroxylase (24-OHase), and vitamin D receptor (VDR) were quantified in rat kidney homogenates by real-time reverse transcription-polymerase chain reaction. Plasma parathyroid hormone (PTH) as well as plasma and kidney 1,25 dihydroxyvitamin D3 (calcitriol) levels were monitored in all animals. CsA induced a 85% decrease in calbindin-D28k mRNA levels as well as a 40% and 69% decrease in VDR and 24-OHase mRNA levels, respectively. Plasma and kidney 1,25 dihydroxyvitamin D3 as well as plasma PTH levels were increased by CsA, but not by SDZ PSC 833. The treatment with SDZ PSC 833 did not affect calbindin-D28k or VDR expression, but did cause a 73% decrease in 24-OHase mRNA levels. Taken together, these results indicate an association between CsA-mediated down-regulation of rat renal calbindin-D28k mRNA and the decrease in other 1,25 dihydroxyvitamin D3-regulated genes, suggesting an impairment of the vitamin D pathway by CsA which may be related to its adverse renal side effects and its immunosuppressive activity.

FK506 nephrotoxicity

Tacolimus (FK506) is a potent immunosuppressive agent with significant nephrotoxic properties. FK506 is complexed with an intracellular binding protein FKBP-12. Both the immunosuppressive and nephrotoxic effects may be linked to the inhibitory effect of this complex on calcineurin. The initial phase of FK506 nephrotoxicity is associated with a reduction in renal blood flow and glomerular filtration rate. More significant microvascular injury may follow with endothelial damage. Tubular epithelial cell vacuolation, atrophy and micocalcification may be associated with the development of irreversible interstitial fibrosis. At times, mesangial cell proliferation adds to the glomerular abnormalities. These effects may be mediated by the inhibitory effect on calcineurin and its role in regulating cellular calcium channels. FK506 stimulates several inflammatory cytokines, such as transforming growth factor-beta, with potential deleterious effects. Also abnormalities in the reninangiotensin system, endothelin, renal prostaglandins, adrenergic receptors may all play a role in the nephrotoxic effects.

High prevalence of osteoporosis in cardiac transplant recipients and discordance between biochemical turnover markers and bone histomorphometry

OBJECTIVE

All patients attending the cardiac transplantation clinic at the Royal Perth Hospital were investigated to determine the prevalence of osteoporosis and to assess changes in bone metabolism and histomorphometry in a cohort of cardiac transplant recipients.

DESIGN

Retrospective cross-sectional study.

PATIENTS

Thirty-two patients (27 male; 5 female) who had received a cardiac transplant during the past 10 years and who were receiving immunosuppressive therapy with cyclosporin, azathioprine and prednisolone were studied.

MEASUREMENTS

All patients had bone densitometry by DEXA of the lumbar spine and femoral neck and X-rays of the thoracolumbar spine. Fasting serum ionized calcium, intact PTH, creatinine, 25 hydroxy-vitamin D, alkaline phosphatase, osteocalcin, testosterone and free thyroxine and urine calcium, creatinine, hydroxyproline and deoxypyridinoline were measured. Six osteoporotic patients consented to transiliac bone biopsy following double tetracycline labelling.

RESULTS

Osteoporosis was present at the lumbar spine in eight patients, femoral neck in seven patients and was present at one or more sites in 13 patients (41%). Seven patients (22%) had vertebral fractures which were asymptomatic in five patients. Secondary hyperparathyroidism was present in 16 patients (53%) but significant renal failure (creatinine clearance < 70 ml/min) was only found in 8 (50%). Levels of biochemical markers of bone turnover were increased in 23 patients (72%). Serum osteocalcin (P = 0.02) and alkaline phosphatase (P = 0.04) were significantly higher in osteoporotic patients than in nonosteoporotic patients. Histomorphometric findings varied markedly between patients. Microscopic features of hyperparathyroidism were not observed.

CONCLUSIONS

Osteoporosis and asymptomatic vertebral fractures are common following cardiac transplantation. Biochemical markers of bone turnover were increased in the majority of patients. Many had biochemical evidence of secondary hyperparathyroidism but this could be attributable to significant renal failure in only 50% of cases. Osteocalcin and alkaline phosphatase correlated inversely with bone density. Histomorphometric findings did not correlate with these biochemical changes in most cases. These results suggest that multiple factors are responsible for osteoporosis in cardiac transplant recipients. Osteocalcin and alkaline phosphatase may be useful biochemical markers, predicting patients at highest risk of fracture.

Lacidipine protects against cyclosporine-induced nephrotoxicity in rats

The effect of lacidipine (LA), a new calcium channel blocker with an antioxidant effect, has been studied on cyclosporine (CsA)-induced nephrotoxicity in male Wistar rats. Lacidipine (1 mg/kg BW) was administered orally 3 days before and 14 days concurrently with CsA (50 mg/kg BW orally). Urine volume, Na+, K+, Li+ and creatinine in urine, and blood urea, serum creatinine, lithium, plasma malondialdehyde (MDA) and CsA levels were estimated in blood after 14 days CsA treatment. Kidneys were examined using histological techniques. Blood urea and serum creatinine were increased by 305 and 211%, respectively, with CsA when compared to the saline-treated animals. Creatinine clearance (Ccr) and lithium clearance (Licr) were decreased and proximal tubule fractional reabsorption 1-(Licr/Ccr) was significantly increased with CsA. Lacidipine protected rats from CsA-induced nephrotoxicity. Changes in blood urea, serum creatinine, Ccr, Licr and proximal tubule fractional reabsorption induced by CsA were significantly prevented by LA. There was a 160% rise in MDA levels with CsA, which was significantly reduced equal to control with LA. Histomorphology showed microcalcification with CsA, while it was normal with LA. In rats treated with LA, CsA did not show any microcalcification. Our data suggest that supplementation of LA may be helpful to reduce CsA nephrotoxicity.

New insights into cyclosporine A nephrotoxicity by proteome analysis

Using two-dimensional gel electrophoresis (2-DE), we recently discovered an association between decreased calcium-binding protein, calbindin-D 28 kDa, urinary calcium wasting and intratubular corticomedullary calcifications in rat kidney. This observation prompted us to investigate kidney tissues of other species, including man. In this paper we show that in dogs and monkeys, which are generally devoid of cyclosporine A (CsA)-mediated nephrotoxicity, renal calbindin levels were not affected by the CsA treatment whereas in CsA-treated human kidney-transplant recipients with renal vascular or tubular toxicity, a marked decrease in renal calbindin-D 28 kDa protein level was found in most of the kidney biopsy sections. The present results strongly suggest that calbindin is a marker for CsA-nephrotoxicity. The discovery of calbindin-D 28 kDa being involved in CsA toxicity has evolved from the application of 2-DE and has not been reported previously, proving that proteomics can provide essential information in mechanistic toxicology. Considering the current improvements in proteome methods it is expected that high throughput proteomics will become an indispensable tool in preclinical safety testing.

Cyclosporine A-induced decrease in calbindin-D 28 kDa in rat kidney but not in cerebral cortex and cerebellum

Recently, we reported that in rat, cyclosporine A (CsA) markedly decreases the levels of calbindin-D (CABP-D) 28 kDa in kidney. CABP-D 28 kDa is a calcium-binding protein which is highly expressed in calcium-transporting tissues such as kidney or brain. In this study, we investigated whether, in addition to the kidney, CsA also has an effect on CABP-D 28 kDa in rat brain. Three groups of male Wistar rats received 15 mg/kg/day or 50 mg/kg/day of CsA orally for 12 days, whereas controls received vehicle solution for the same period. CABP-D 28-kDa protein and CsA were quantified in homogenates of kidney, cerebral cortex and cerebellum, and the localization of CABP-D 28 kDa was assessed in the different tissue sections by immunohistochemistry. In kidney, CABP-D 28 kDa was strongly and dose dependently decreased, and was located in tubular epithelial cells. In brain, CABP-D 28 kDa was not changed and was mainly located in pyramidal cells of the cortex and in cerebellum exclusively in Purkinje cells. High CsA concentrations were measured in kidney, more than 17-fold greater than those found in cortex. In cerebellum, CsA was below the limit of detection. These data suggest that at clinically relevant doses, CsA may not affect CABP-D 28-kDa levels in brain.

Chronic cyclosporine nephrotoxicity

Cyclosporine has improved patient and graft survival rates in solid organ transplantation, and has been increasingly applied with considerable clinical benefit in the treatment of autoimmune diseases. However, the therapeutic benefits of immunosuppressive therapy for transplant and autoimmune indications have frequently been limited by the occurrence of chronic nephrotoxicity. Cyclosporine nephrotoxicity therefore remains an important clinical challenge. The clinical aspects and pathophysiology of chronic cyclosporine nephrotoxicity, which is characterized by a decrease in glomerular filtration rate, afferent arteriolopathy, and striped tubulointerstitial fibrosis, are reviewed. Insights gained from experimental models of chronic nephrotoxicity associated with tubulointerstitial fibrosis are presented to elucidate the pathophysiology.

The cyclosporine A-induced decrease in rat renal calbindin-D28kDa protein as a consequence of a decrease in its mRNA

Cyclosporine A (CsA) is a potent immunosuppressant with the drawback of renal side-effects. We recently reported that relatively high doses of CsA markedly decreased the calcium-binding protein calbindin-D28kDa in kidneys of male Wistar rats, and showed that this decrease could be associated with some of the drug-induced adverse renal effects. To investigate the events leading to this decrease, the calbindin-D28kDa mRNA level in kidneys of rats treated with 15 or 50 mg/kg/day CsA for 12 days was analysed by reverse transcription followed by polymerase chain reaction. At both doses, a marked dose-dependent decrease in the calbindin-D28kDa mRNA level was found, one very similar to the decrease measured in the calbindin-D28kDa protein abundance. Thus, the CsA-mediated down-regulation of the renal calbindin-D28kDa protein is most likely the result of a decrease in the calbindin-D28kDa mRNA level.

A tacrolimus-related immunosuppressant with reduced toxicity

BACKGROUND

Tacrolimus (FK506) has potent immunosuppressive properties reflecting its ability to block the transcription of lymphokine genes in activated T cells through formation of a complex with FK506 binding protein-12, which inhibits the phosphatase activity of calcineurin. The clinical usefulness of tacrolimus is limited, however, by severe adverse effects, including neurotoxicity and nephrotoxicity. Although this toxicity, like immunosuppression, appears mechanistically related to the calcineurin inhibitory action of the drug, a large chemistry effort has been devoted to search for tacrolimus analogs with reduced toxicity but preserved immunosuppressive activity that might have enhanced therapeutic utility.

METHODS

Here, we report on the identification of such an analog, which was synthetically derived from ascomycin (ASC), the C21 ethyl analog of tacrolimus, by introducing an indole group at the C32 position. The profile of biological activity of indolyl-ASC was characterized in rodent models of immunosuppression and toxicity.

RESULTS

Indolyl-ASC was found to exhibit an immunosuppressive potency equivalent to that of tacrolimus in T-cell activation in vitro and in murine transplant models, even though indolyl-ASC bound about 10 times less to intracellular FK506 binding protein-12 than tacrolimus or ASC. Further evaluation of indolyl-ASC revealed that it is threefold less potent than tacrolimus in inducing hypothermia, a response that may reflect neurotoxicity, and in causing gastrointestinal transit alterations in mice. Moreover, indolyl-ASC was at least twofold less nephrotoxic than tacrolimus upon 3-week oral treatment in rats.

CONCLUSIONS

Altogether, these data indicate a modest but definite improvement in the therapeutic index for indolyl-ASC compared with tacrolimus in rodent models.