Co-exposure to lead increases the renal response to low levels of cadmium in metallurgy workers.

PURPOSE: Research on the effect of co-exposure to Cd and Pb on the kidney is scarce. The objective of the present study was to assess the effect of co-exposure to these metals on biomarkers of early renal effect. METHODS: Cd in blood (Cd-B), Cd in urine (Cd-U), Pb in blood (Pb-B) and urinary renal biomarkers, i.e., microalbumin (µ-Alb), beta-2-microglobulin (ß2-MG), retinol binding protein (RBP), N-acetyl-ß-d-glucosaminidase (NAG), intestinal alkaline phosphatase (IAP) were measured in 122 metallurgic refinery workers examined in a cross-sectional survey. RESULTS AND CONCLUSIONS: The median Cd-B, Cd-U, Pb-B were: 0.8 µg/l (IQR = 0.5, 1.2), 0.5 µg/g creatinine (IQR = 0.3, 0.8) and 158.5 µg/l (IQR = 111.0, 219.3), respectively. The impact of Cd-B on the urinary excretion of NAG and IAP was only evident among workers with Pb-B concentrations ≥ 75th percentile. The association between Cd-U and the renal markers NAG and RBP was also evidenced when Pb-B ≥ 75th percentile. No statistically significant interaction terms were observed for the associations between Cd-B or Cd-U and the other renal markers under study (i.e., µ-Alb and ß2-MG). Our findings indicate that Pb increases the impact of Cd exposure on early renal biomarkers.

Effects of strontium on the physicochemical characteristics of hydroxyapatite.

In a previous experimental study using a chronic renal failure rat model, a dose-related multiphasic effect of strontium (Sr) on bone formation was found that could be reproduced in an in vitro set-up using primary rat osteoblasts. The results from the latter study allowed us to distinguish between a reduced nodule formation in the presence of an intact mineralization at low Sr-doses (1 microg/ml) and an interference of the element with the hydroxyapatite (HA) formation at high doses (20-100 microg/ml). To further investigate the latter effect of Sr on physicochemical bone mineral properties, an in vitro study was set up in which the UMR-106 rat osteosarcoma cell line was exposed to Sr, added to the cell culture medium in a concentration range varying between 0-100 microg/ml. Temporal growth and functionality of the culture was investigated by measurement of the alkaline phosphatase activity and calcium (Ca) concentration in the culture medium (used as an index of Ca-incorporation, i.e., HA formation) at various time points. At the end of the culture period (14 days post-confluence), samples of the mineralized cultures were taken for further analysis using X-ray diffraction (XRD) and Fourier Transform Infra-Red Spectroscopy (FTIR). Synthetic HA doped with various Sr concentrations (based on the cell culture and previous experimental studies and yielding Sr/(Sr + Ca) ratios ranging from 0-60%), was prepared and examined for crystal growth and solubility. Crystal size was assessed using scanning electron microscopy (SEM). Ca incorporation indicated a reduced mineralization in the 20 and 100 microg/ml Sr groups vs. controls. Sr-doped synthetic HA showed a significant dose-dependent reduction in crystal growth, as assessed by SEM, and an increase in solubility, apparent from 12.7% Sr/(Sr + Ca) on. Moreover, in both mineralized cultures and synthetic HA, XRD and FTIR analysis showed a reduced crystallinity and altered crystal lattice at similar concentrations. These new data support our previous in vivo and in vitro findings and point to a potential physicochemical interference of Sr with HA formation and crystal properties in vivo.

Transferrin-mediated uptake of aluminium by human parathyroid cells results in reduced parathyroid hormone secretion.

BACKGROUND: The present study investigates whether aluminium-transferrin (Al-Tf) uptake by Tf receptor-mediated endocytosis induces hypoparathyroidism and thus might contribute to the increasing prevalence of adynamic bone disease (ABD) in the current dialysis population. METHODS AND RESULTS: Human parathyroid glands as well as in vitro cultured human parathyroid cells were shown to express Tf receptors. Five-day-old cultures of parathyroid cells were incubated for 48 h in serum-free DMEM/F12 supplemented with 12 microM apo-Tf: 12 microM Tf to which 150 microg/l Al or 150 microg/l Al-citrate (Al-ci) was bound. The amount of Al taken up by the parathyroid cells either as Al-Tf or Al-ci did not differ. However, incubation of cell cultures with Al-Tf showed a significant proportional decrease (mean+/-SEM, -23.1+/-4.5%) in iPTH secretion as compared to the reference apo-Tf cultures. Al-ci did not suppress PTH secretion (+3.4+/-6.5%). The Al uptake after incubation with Al-Tf was found to be dose-dependent. With regard to iPTH secretion, a tendency toward a dose response relationship was observed. Northern blot analysis of parathyroid cells incubated in 12 microM apo-Tf or 12 microM Al-Tf demonstrated that the PTH mRNA synthesis was unaffected by the Tf-mediated uptake of Al. These observations suggest an effect of Al on PTH release rather than on PTH synthesis. Since the cytoskeleton can play an important role in the release of secretory vesicles, the influence of Al on the structure of actin, beta-tubulin and vimentin was investigated by confocal microscopy. Comparison of cultures incubated with apo-Tf and Al-Tf revealed no difference in the organization of these cytoskeletal proteins in relation to the inhibitory effect of Al-Tf on PTH secretion. CONCLUSION: In summary, data in the present paper demonstrate that the (i) human parathyroid gland/parathyroid cells exhibit Tf receptors; (ii) Al-Tf complex is taken up by the parathyroid gland in a dose-dependent manner; and (iii) uptake of Al by Tf receptor-mediated endocytosis reduces the secretion of PTH but not its synthesis. These in vitro findings allow us to suggest that Tf receptor-mediated uptake of Al might, besides other factors such as vitamin D, high calcium dialysate or CaCO(3) intake, play a role in the development of hypoparathyroidism associated with ABD. The exact mechanism by which Al-Tf suppresses iPTH secretion remains to be elucidated.

Increased bone strontium levels in hemodialysis patients with osteomalacia.

BACKGROUND: In this study, we report on the association between increased bone strontium levels and the presence of osteomalacia in end-stage renal failure patients treated by hemodialysis. METHODS: We performed a histologic examination and determined the strontium content and strontium/calcium ratios in bone biopsies of 100 hemodialysis patients recruited from various centers all over the world. Aside from the bone strontium concentration, the bone aluminum content was assessed. The bone zinc concentration, a nonrelevant element for bone toxicity, was also measured. RESULTS: Bone strontium levels and bone strontium/calcium ratios were increased in subjects with osteomalacia when compared with those with the other types of renal osteodystrophy. Bone strontium and bone calcium levels correlated with each other. The slope of the linear regression curve correlating these parameters was much steeper in the osteomalacic group (Y = 2.22X - 120) as compared with the other types of renal osteodystrophy (Y = 0.52X - 5.7). Within the group of patients with osteomalacia, bone strontium levels also significantly correlated with the bone aluminum content (r = 0.72, P = 0.018). No such correlation was found for the other types of renal osteodystrophy. The bone zinc concentration of subjects with normal renal function did not differ significantly from the values noted for the various types of renal osteodystrophy taken as separate groups, nor could increased bone zinc concentrations be associated with a particular bone lesion. CONCLUSIONS: Our data demonstrate an association between osteomalacia and increased bone strontium concentrations in dialysis patients. Further studies are warranted to establish whether strontium plays either a primary, secondary, or contributive role in the development of the latter type of renal osteodystrophy.

Increased serum strontium levels in dialysis patients: an epidemiological survey.

BACKGROUND: We previously reported on increased bone strontium levels in dialysis patients with osteomalacia versus those presenting other types of renal osteodystrophy. A causal role of strontium in the development of osteomalacia was established in a chronic renal failure rat model. METHODS: To further elucidate the latter issue and to find out whether dialysis patients from particular centers/countries are at an increased risk for strontium accumulation, a worldwide multicenter study was established. In total, 834 patients from 34 dialysis centers in 23 countries were included. In each of the patients, a serum sample was taken for strontium determination, and water and dialysate samples were taken at the various steps of the water purification process. For each patient clinical data and for each center dialysis modalities were recorded. RESULTS: Strontium levels in serum of dialysis patients showed major differences between the various centers, ranging from mean values of 25 +/- 8 microgram/liter in the center with the lowest level up to 466 +/- 90 microgram/liter in the center with the highest concentration. It is of interest that these high levels were mainly found in developing countries. Furthermore, our data point toward a role of the final dialysate in the accumulation of the element, as indicated by the strong correlation (r = 0.74, P < 0.001) between mean serum and dialysate strontium levels. As the high tap water concentration of strontium was adequately reduced during the water purification process, contamination of the final dialysis fluid occurred by the addition of concentrates contaminated with strontium. Besides the dialysate, other factors, such as duration of dialysis, vitamin D supplements, or types of phosphate binders, played a less important role in the accumulation of the element. CONCLUSIONS: Data of this multicenter study indicate patients of particular dialysis centers to be at an increased risk for strontium accumulation, the clinical consequence of which is under current investigation.

Aluminum, iron, lead, cadmium, copper, zinc, chromium, magnesium, strontium, and calcium content in bone of end-stage renal failure patients.

BACKGROUND: Little is known about trace metal alterations in the bones of dialysis patients or whether particular types of renal osteodystrophy are associated with either increased or decreased skeletal concentrations of trace elements. Because these patients are at risk for alterations of trace elements as well as for morbidity from skeletal disorders, we measured trace elements in bone of patients with end-stage renal disease. METHODS: We analyzed bone biopsies of 100 end-stage renal failure patients enrolled in a hemodialysis program. The trace metal contents of bone biopsies with histological features of either osteomalacia, adynamic bone disease, mixed lesion, normal histology, or hyperparathyroidism were compared with each other and with the trace metal contents of bone of subjects with normal renal function. Trace metals were measured by atomic absorption spectrometry. RESULTS: The concentrations of aluminum, chromium, and cadmium were increased in bone of end-stage renal failure patients. Comparing the trace metal/calcium ratio, significantly higher values were found for the bone chromium/calcium, aluminum/calcium, zinc/calcium, magnesium/calcium, and strontium/calcium ratios. Among types of renal osteodystrophy, increased bone aluminum, lead, and strontium concentrations and strontium/calcium and aluminum/calcium ratios were found in dialysis patients with osteomalacia vs the other types of renal osteodystrophy considered as one group. Moreover, the concentrations of several trace elements in bone were significantly correlated with each other. Bone aluminum was correlated with the time on dialysis, whereas bone iron, aluminum, magnesium, and strontium tended to be associated with patient age. Bone trace metal concentrations did not depend on vitamin D intake nor on the patients' gender. CONCLUSIONS: The concentration of several trace elements in bone of end-stage renal failure patients is disturbed, and some of the trace metals under study might share pathways of absorption, distribution, and accumulation. The clinical significance of the increased/decreased concentrations of several trace elements other than aluminum in bone of dialysis patients deserves further investigation.

Low serum aluminum values in dialysis patients with increased bone aluminum levels.

BACKGROUND: Using an HPLC/ETAAS hybrid speciation technique we previously demonstrated iron to have a multifold effect on the binding of aluminum to transferrin by limiting the number of available binding sites and decreasing the affinity of transferrin for aluminum. Theoretically, at a 60% iron-transferrin saturation the aluminum-transferrin fraction in serum should not exceed 30 microg/l. In the present study previous experimental data were confronted with recent clinical observations in patients with either normal iron status or iron overload. PATIENTS AND RESULTS: Serum aluminum levels and iron overload: In 38 dialysis patients with a normal iron status and of whom 63% received Al(OH)3 for phosphate binding 26 (68%) had a serum aluminum level >30 microg/l. On the other hand out of 28 transfusional iron overloaded patients; 68% of them taking Al(OH)3, only 1 subject (4%) had a serum aluminum value in excess of 30 microg/l. Taking patients of both groups receiving Al(OH)3 together a significant (p = 0.001) negative correlation (r = -0.5017) was found between the iron-transferrin saturation and the serum aluminum levels. Iron status and parenteral aluminum loading: Also could a significant (p = 0.001) negative correlation (r = -0.6383) between these parameters be found in an independent group of 44 patients which were acutely intoxicated by the use of aluminum-contaminated dialysis fluids. Since in this population aluminum loading occurred parenterally and not via the gastrointestinal tract, a direct effect of iron on the transferrin binding of aluminum rather than on the element's gastrointestinal absorption must have been responsible for the inverse relationship. Bone aluminum and iron overload: Out of 22 patients with a normal iron status (mean + SD serum ferritin: 216 +/- 245 microg/l; iron-transferrin saturation 20.4 +/- 9.6%), all of them having aluminum overload (bone aluminum level >15 microg/g and/or positive Aluminon staining) none of them presented with a serum aluminum <30 microg/l (mean +/- SD: 82.2 +/- 51.6 microg/l). On the other hand out of 13 iron overloaded patients (serum ferritin >800 microg/l; iron-transferrin saturation 61.4 +/- 17.6%) 10 (77%) presented the proposed criteria of aluminum overload in the presence of a serum aluminum level <30 microg/l. CONCLUSIONS: Our data indicate that in dialysis patients with iron overload (iron-transferrin saturation >60%; serum ferritin >800 microg/l) serum aluminum levels are low (<30 microg/l) despite exposure to aluminum by the intake of Al(OH)3 or the use of aluminum-contaminated dialysis fluids. Low serum aluminum nevertheless may be associated with aluminum overload and even aluminum-related bone disease. An effect of iron on the serum aluminum speciation may at least in part explain our observations. Our findings allow a more accurate interpretation of baseline serum aluminum values.

Strontium causes osteomalacia in chronic renal failure rats.

BACKGROUND: We recently reported an association between increased bone strontium (Sr) levels and osteomalacia in dialysis patients. METHODS: To delineate whether or not Sr acts as a causal factor in the development of osteomalacia, we devised the following study: four groups of chronic renal failure (CRF) rats were given Sr, aluminum (Al), both of these compounds or none of the elements (controls). RESULTS: Administration of Sr and/or A1 resulted in increased bone levels of the respective elements. Histological examination revealed impairment of mineralization in the Sr group and to a lesser extent in the Al group as compared to the control group. There was also a significant increase in osteoid area in the Sr group, but not in the Al group. No differences in bone surface or erodic perimeter were noted between the various study groups. Histochemically, Sr could be localized in calcified bone, mainly in new bone close to the osteoid/calcification front, a critical site of bone mineralization. Histochemical findings were confirmed by electron probe X-ray microanalysis. CONCLUSIONS: These findings indicate that Sr accumulation in chronic renal failure rats resulted in the development of osteomalacic lesions, in contrast to the Al group where adynamic bone disease was induced in the present set-up. Further studies are required to define the mechanism by which way Sr causes osteomalacia in chronic renal failure rats.

Aluminium speciation in cerebrospinal fluid of acutely aluminium-intoxicated dialysis patients before and after desferrioxamine treatment; a step in the understanding of the element's neurotoxicity.

BACKGROUND: The association between aluminium and dialysis encephalopathy and deterioration of the neurological state during desferrioxamine treatment of dialysis patients is well established. At present little is known about the speciation and the mechanisms underlying the element's neurotoxicity. METHODS: Aluminium speciation was performed in cerebrospinal fluid samples of acutely aluminium-intoxicated dialysis patients using a recently developed high-performance liquid chromatographic/electrothermal atomic absorption spectrometric hybrid method. RESULTS: Baseline cerebrospinal fluid aluminium levels of samples taken shortly after the intoxication were low but elevated (5.0 +/- 2.0 micrograms/l, n = 3) as compared to subjects with normal renal function (< 1 microgram/l). In contrast to the situation noted in serum and to the iron speciation in cerebrospinal fluid, aluminium was not bound to transferrin but appeared as two distinct compounds, the main fraction eluting at the elution volume of aluminium-citrate/silicate. The second compound was not identified. Forty-four hours after desferrioxamine administration the cerebrospinal fluid aluminium levels had increased up to a concentration of 10.3 +/- 2.5 micrograms/l (n = 3). This was accompanied by a change in the speciation profile with aluminium appearing at the elution volume of aluminoxamine. CONCLUSIONS: Our findings may contribute to a better understanding of the neurotoxic effects of aluminium and its desferrioxamine chelate in dialysis patients.

Competition of iron and aluminum for transferrin: the molecular basis for aluminum deposition in iron-overloaded dialysis patients?

In the recent literature an inverse relationship between iron status and serum aluminum levels has repeatedly been reported in dialysis patients. To check whether this observation is, at least in part, due to an interference of iron with the protein binding of aluminum, we studied the effect of the latter element on both the number of free binding sites on transferrin (Tf) and on the affinity of the protein for aluminum. For the purpose of this, a recently developed HPLC-ETAAS hybrid method was used, allowing protein-binding studies at clinical relevant metal concentrations and under contamination-free conditions. After we incubated apo-Tf with iron and aluminum which were added in amounts equivalent to the calculated number of metal-binding sites on the protein (i.e., 2 mol metal/mol Tf), we found that Tf can be saturated for 100% with iron. However, for aluminum only a 23% aluminum-Tf saturation was observed. In Tf solutions with iron saturations ranging between 0 and 60% as well as in the serum of 15 subjects with iron-Tf saturations varying between 12 and 48%, a significant (p < 0.001) negative correlation between the degree of iron-Tf saturation and the percentage of aluminum (added in amounts equivalent to the number of the remaining binding sites on Tf) bound to Tf was noted (y = -0.26x + 24.5, r = -0.87 in serum). It is concluded that the iron-Tf saturation influences the Tf binding of aluminum not only by occupying binding sites otherwise available for aluminum, but also by lowering the affinity of Tf for aluminum. The effects of iron on serum aluminum levels and bone aluminum deposition are discussed.

Measurement of strontium in serum, urine, bone, and soft tissues by Zeeman atomic absorption spectrometry.

To study the possible accumulation of Sr in chronic renal failure patients, methods were developed for the determination of the element in serum, urine, bone, and soft tissues by using Zeeman atomic absorption spectrometry. Serum samples were diluted 1:4 with a Triton X-100-HNO3 mixture, whereas urine samples were diluted 1:20 with HNO3. Bone samples were digested with concentrated HNO3 in stoppered polytetrafluoroethylene (Teflon) tubes, whereas soft tissues were dissolved in a tetramethylammonium hydroxide solution in water. For serum and urine we used matrix-matched calibration curves, whereas bone and tissue samples were measured against aqueous calibrators. Atomization was performed from the wall of pyrolytically coated graphite tubes for all of the matrices under study. Both inter- and intraassay CVs were <6% (n = 12, n = 10, respectively), and the recovery of added analyte was close to 100% for all of the biological matrices under study. Detection limits were 1.2 microg/L (serum), 0.3 microg/L (urine), 0.4 microg/g (bone), and 2.2 ng/g (soft tissues), whereas the sensitivity determined by the slope of the calibration curve, i.e., the amount of Sr producing a 0.0044 integrated absorbance change in signal, was 2.4 pg, 2.4 pg, 3.9 pg, and 2.6 pg for these matrices respectively. We conclude that the present methods are precise and accurate and easily applicable for both routine use and research investigations. They will allow us to study the metabolism of the element in chronic renal failure patients and shed some light on the association that was recently noted between increased bone Sr concentrations and the development of osteomalacia in these individuals.

Quantitative determination of transferrin in cerebrospinal fluid using an enzyme linked immunosorbent assay.

An enzyme linked immunosorbent assay (ELISA) based method for the determination of transferrin in cerebrospinal fluid (CSF) is described. This method allows transferrin determinations in ultra-small (

Low-dose (5 mg/kg) desferrioxamine treatment in acutely aluminium-intoxicated haemodialysis patients using two drug administration schedules.

BACKGROUND: According to the recommendations proposed at The Consensus Conference on Diagnosis and Treatment of Aluminium Overload in End-Stage Renal Failure Patients, Paris, 1992 low-dose desferrioxamine (DFO) treatment was applied for the first time in 41 acutely aluminium-intoxicated patients. METHODS AND RESULTS: DFO-related neurological/ophthalmological side-effects were observed in nine of 11 patients with a post-DFO serum aluminium level > 300 micrograms/litre and in two patients of 30 below this level after a single administration of a 5-mg/kg dose of the chelator in the conventional way (i.e. the last hour of a dialysis session). They were no longer observed after introducing an alternative DFO administration schedule (i.e. administration of the chelator 5 h prior to the start of a haemodialysis session; group I: n = 14). A significant decrease in the serum aluminium levels as well as in the post-DFO serum aluminium increment (delta s A1) was observed during the first 6 months, course of low-dose DFO treatment in group I as well as group II (which consisted of patients receiving DFO in the conventional way; n = 27). Low-dose DFO treatment was accompanied by a significant increase in the mean +/- SD serum iPTH levels (group I: 174 +/- 245 up to 286 +/- 285 ng/litre; group II: 206 +/- 272 up to 409 +/- 424 ng/litre; P < 0.005) and the mean corpuscular volume (group I: 80 +/- 6.4 up to 85 +/- 3.7 fL, P < 0.005; group II: 76 +/- 5.0 up to 87 +/- 4.3 fL, (P < 0.0001). Serum ferritin levels significantly decreased in both groups. No further side-effects were observed during the DFO course. Patients in which DFO treatment could be stopped (i.e. subjects in which both serum aluminium and delta sA1 were below 50 micrograms/litre at two successive occasions) before the end of the 6 months' treatment course had a significantly greater residual diuresis (700 +/- 682 ml/min vs 84 +/- 109 ml/24 h). Also, residual diuresis was found to protect against aluminium intoxication as reflected by the values noted in group I versus those in group II. CONCLUSION: The 5-mg/kg DFO treatment provides a safe and adequate therapy for aluminium overload. In severely aluminium-intoxicated patients presenting post-DFO serum aluminium levels above 300 micrograms/litre DFO should be given once weekly 5 h prior to high-extraction dialysis ensuring (i) maximal chelation of aluminium (ii) limited exposure to circulating aluminium noxamine levels, and (iii) adequate removal of the latter compound. Finally, the necessity for a better communication between the local water distribution companies and the dialysis centres is a major lesson that can be drawn from this dramatic intoxication.

Increased silicon levels in dialysis patients due to high silicon content in the drinking water, inadequate water treatment procedures, and concentrate contamination: a multicentre study.

BACKGROUND: Although silicon is considered as an essential element, little is known about the basic effects and clinical significance of increased concentrations of the element in dialysis patients. METHODS AND RESULTS: In a multicentre study we found silicon levels in haemodialysis (HD) patients to be markedly increased. In these patients silicon concentrations were significantly higher than those noted in subjects with normal renal function as well as in patients with chronic renal failure not yet in dialysis and patients treated by continuous ambulatory peritoneal dialysis (CAPD). Moreover we noted that in both HD and CAPD patients mean silicon levels differed from one centre to another. Also, was there in the HD population a significant difference in serum silicon levels among patients from different countries. In HD patients differences in serum silicon levels were either due to the use of silicon contaminated dialysis fluids or an increased oral intake of the element mainly originating from the high silicon content of the drinking water. Silicon contamination of the dialysis fluid was found to be due to either the use of reverse osmosis membranes that insufficiently retain the element during water treatment or by the addition of concentrates containing high amounts of silicon. Using a recently developed high-performance liquid chromatographic/atomic absorption spectrophotometric (HPLC/ETAAS) hybrid technique, we found silicon in serum to be present as a low-molecular-weight non-protein-bound component, which in the presence of a low silicon dialysate is adequately removed during treatment. CONCLUSIONS: The clinical relevance of increased serum silicon levels is not yet known and as such deserves further investigation. In view of the controversy that exists on the element's assumed protective as well as toxic role in the development of some (aluminium-related) neurodegenerative diseases and its vital role in bone formation, monitoring of the silicon levels in serum, tap water, and dialysis fluids might become important.

Use of the low-dose desferrioxamine test to diagnose and differentiate between patients with aluminium-related bone disease, increased risk for aluminium toxicity, or aluminium overload.

BACKGROUND: Aiming at a safe method in the diagnosis of aluminium-related bone disease (ARBD)/aluminium overload the low-dose desferrioxamine (DFO) test was developed. In a multicentre study histological and histochemical data and aluminium bulk analysis of bone biopsies of 77 dialysis patients were correlated with the results of both the 5 mg/kg and 10 mg/kg DFO tests. METHODS: ARBD was considered to be present when > 15% of the bone surface was positively stained for aluminium and the bone formation rate was below 220 microns 2/mm2/day. Patients in which the Aluminon staining was positive (> 0%) were considered at an increased risk for aluminium toxicity independent of the type of renal osteodystrophy. Patients were considered aluminium overloaded when the bone aluminium content was > 15 micrograms/g wet weight and/or the Aluminon staining was positive (> 0%). RESULTS: Using the proposed criteria 15 patients were found to have ARBD; 13 of them presenting with a serum iPTH below 150 ng/l. In conjunction with an iPTH measurement the DFO test had a more than acceptable sensitivity and specificity in the diagnosis of ARBD. The test was considered positive when a post-DFO serum aluminium increment (delta sA1) above 50 micrograms/l (5 mg/kg) or 70 micrograms/l (10 mg/kg) together with a serum iPTH below 150 ng/l was found. Using these cut-off levels the 5 and 10 mg/kg tests in the diagnosis of ARBD had a sensitivity of 87% and a specificity of 95% and 92% respectively whereas the predictive value for a positive test for the population under study was 80% (5 mg/kg). Not a single patient with a serum iPTH > 650 ng/l had a positive staining (> 0%) even when the bone aluminium level was elevated (> 15 micrograms/g wet weight). In the detection of patients at risk for aluminium toxicity delta sA1 thresholds of 50 micrograms/l (5 mg/kg) and 70 micrograms/l (10 mg/kg) in combination with a serum iPTH < 650 ng/l had a sensitivity of 92% and specificity of 86% and 84% respectively. In the clinical setting of aluminium overload, threshold delta sA1 levels of 50 micrograms/l (5 mg/kg) and 70 micrograms/l (10 mg/kg) had a sensitivity of 91% and a specificity of 95% and 90% respectively. CONCLUSIONS: The low-dose DFO test is a reliable test for the detection of aluminium overload; however, it is not specific enough to differentiate between ARBD, increased risk of aluminium toxicity, and aluminium overload unless it is used in combination with a serum iPTH measurement. In conjunction with a serum iPTH measurement it is an important tool in the differential diagnosis and may avoid the necessity of a bone biopsy in the majority of patients. Data obtained in the present study have allowed us to update the strategies for monitoring, diagnosis and patient follow-up proposed at the Consensus Conference on Diagnosis and Treatment of Aluminium Overload in End-Stage Renal Failure; Paris, 1992.

Quantitative HPLC/ETAAS hybrid method with an on-line metal scavenger for studying the protein binding and speciation of aluminum and iron.

A quantitative metal-free high-performance liquid chromatographic/electrothermal atomic absorption spectrometric (HPLC/ETAAS) technique allowing an adequate separation of the proteins and of the inorganic/organic metal species of interest was developed. A silica-based scavenger was placed proximal to the injection valve retaining any remaining Al and Fe originating from buffer solutions and recipients. ETAAS instrumental conditions and matrix modifiers were carefully selected to eliminate interferences occurring due to the salt gradient elution. The postelution Al recovery (143-1428 micrograms L-1; 100-microL sample volume) was found to be 100.1 +/- 15.3% (N = 50) whereas that of Fe was 97.3 +/- 2.0% (N = 20; 442-2653 micrograms L-1). The protein recovery varied between 95 and 105%. The HPLC/ETAAS intraassay CV (N = 3) was 8.0% for Al (eluted amount of Al bound to transferrin (Tf), 7.3 ng) whereas that of Fe was 1.4% (eluted amount of Fe bound to Tf, 124.8 ng). The intraassay CV of the HPLC Tf determination was 1.6%. The proposed method is sensitive and accurate, allowing for the first time quantitative evaluation of the competition between Al and Fe for protein binding at clinical relevant concentrations. The technique will also be used for studying the protein binding of elements other than Al and Fe.

Urinary and biliary excretion of aluminoxamine and ferrioxamine in dogs with various renal function.

We assessed the pharmacokinetics of aluminoxamine and ferrioxamine in dogs with sustained intermittent bile duct ligation and either normal renal function or stable chronic renal failure. A first group of male beagle dogs were given aluminoxamine and ferrioxamine, while a second group received desferrioxamine after loading them with iron and aluminum. Only minute amounts of ferrioxamine and aluminoxamine were found in the bile after administration of these compounds. The distribution volume of aluminoxamine and ferrioxamine appeared to be confined to the extracellular space and their renal excretion correlated with renal function. Administration of desferrioxamine to iron and aluminum-loaded dogs resulted in an increased biliary ferrioxamine but negligible aluminoxamine excretion. Renal clearance of the in vivo formed ferrioxamine and aluminoxamine in this group strongly correlated with renal function. Our observations indicate that biliary excretion of intravenously administered ferrioxamine and aluminoxamine is negligible even in renal failure. The data presented in this study provide indirect evidence that desferrioxamine administration to iron- and aluminum-loaded dogs results in the intra-hepatic formation of ferrioxamine which is partly excreted in the bile. Biliary excretion of aluminoxamine after desferrioxamine administration remained negligible.

Direct determination of zinc in serum by Zeeman atomic absorption spectrometry with a graphite furnace.

We developed a precise and accurate graphite furnace atomic absorption spectrometric method for the direct determination of zinc in serum. Serum samples are analyzed after 20-fold dilution with water of ultrapure analytical grade. No other reagent is used, from the moment of sampling until measurement. During atomization, the argon flow is kept at 150 mL/min instead of gas stop, to decrease the sensitivity and thus allow lower dilution ratios. Zinc concentrations are determined against a serum-matched calibration curve. Graphite tubes are uncoated and no L'vov platform is used. Between-run CVs were 5.9%, 3.5%, and 1.9% for serum zinc concentrations of 0.93, 1.15, and 1.43 mg/L, respectively. The characteristic mass was 9 pg, and the detection limit (meanblank + 3SDblank) was 0.060 mg/L.