Mineral and bone metabolism markers and mortality in diabetic patients on haemodialysis

BACKGROUND

Diabetic patients on haemodialysis have a higher risk of mortality than non-diabetic patients. The aim of this COSMOS (Current management of secondary hyperparathyroidism: a multicentre observational study) analysis was to assess whether bone and mineral laboratory values [calcium, phosphorus and parathyroid hormone (PTH)] contribute to this risk.

METHODS

COSMOS is a multicentre, open-cohort, 3-year prospective study, which includes 6797 patients from 227 randomly selected dialysis centres in 20 European countries. The association between mortality and calcium, phosphate or PTH was assessed using Cox proportional hazard regression models using both penalized splines smoothing and categorization according to KDIGO guidelines. The effect modification of the association between the relative risk of mortality and serum calcium, phosphate or PTH by diabetes was assessed.

RESULTS

There was a statistically significant effect modification of the association between the relative risk of mortality and serum PTH by diabetes (P = .011). The slope of the curve of the association between increasing values of PTH and relative risk of mortality was steeper for diabetic compared with non-diabetic patients, mainly for high levels of PTH. In addition, high serum PTH (>9 times the normal values) was significantly associated with a higher relative risk of mortality in diabetic patients but not in non-diabetic patients [1.53 (95% confidence interval 1.07-2.19) and 1.17 (95% confidence interval 0.91-1.52)]. No significant effect modification of the association between the relative risk of mortality and serum calcium or phosphate by diabetes was found (P = .2 and P = .059, respectively).

CONCLUSION

The results show a different association of PTH with the relative risk of mortality in diabetic and non-diabetic patients. These findings could have relevant implications for the diagnosis and treatment of chronic kidney disease-mineral and bone disorders.

Phosphorus May Induce Phenotypic Transdifferentiation of Vascular Smooth Muscle Cells through the Reduction of microRNA-145

Phosphorus is a vital element for life found in most foods as a natural component, but it is also one of the most used preservatives added during food processing. High serum phosphorus contributes to develop vascular calcification in chronic kidney disease; however, it is not clear its effect in a population without kidney damage. The objective of this in vivo and in vitro study was to investigate the effect of high phosphorus exposure on the aortic and serum levels of miR-145 and its effect on vascular smooth muscle cell (VSMCs) changes towards less contractile phenotypes. The study was performed in aortas and serum from rats fed standard and high-phosphorus diets, and in VSMCs exposed to different concentrations of phosphorus. In addition, miR-145 silencing and overexpression experiments were carried out. In vivo results showed that in rats with normal renal function fed a high P diet, a significant increase in serum phosphorus was observed which was associated to a significant decrease in the aortic α-actin expression which paralleled the decrease in aortic and serum miR-145 levels, with no changes in the osteogenic markers. In vitro results using VSMCs corroborated the in vivo findings. High phosphorus first reduced miR-145, and afterwards α-actin expression. The miR-145 overexpression significantly increased α-actin expression and partially prevented the increase in calcium content. These results suggest that miR-145 could be an early biomarker of vascular calcification, which could give information about the initiation of the transdifferentiation process in VSMCs.

Experimental Models to Study Diabetes Mellitus and Its Complications: Limitations and New Opportunities

Preclinical biomedical models are a fundamental tool to improve the knowledge and management of diseases, particularly in diabetes mellitus (DM) since, currently, the pathophysiological and molecular mechanisms involved in its development are not fully clarified, and there is no treatment to cure DM. This review will focus on the features, advantages and limitations of some of the most used DM models in rats, such as the spontaneous models: Bio-Breeding Diabetes-Prone (BB-DP) and LEW.1AR1-iddm, as representative models of type 1 DM (DM-1); the Zucker diabetic fatty (ZDF) and Goto-kakizaki (GK) rats, as representative models of type 2 DM (DM-2); and other models induced by surgical, dietary and pharmacological-alloxan and streptozotocin-procedures. Given the variety of DM models in rats, as well as the non-uniformity in the protocols and the absence of all the manifestation of the long-term multifactorial complications of DM in humans, the researchers must choose the one that best suits the final objectives of the study. These circumstances, added to the fact that most of the experimental research in the literature is focused on the study of the early phase of DM, makes it necessary to develop long-term studies closer to DM in humans. In this review, a recently published rat DM model induced by streptozotocin injection with chronic exogenous administration of insulin to reduce hyperglycaemia has also been included in an attempt to mimic the chronic phase of DM in humans.

A single-oral bolus of 100,000 IU of cholecalciferol at hospital admission did not improve outcomes in the COVID-19 disease: the COVID-VIT-D-a randomised multicentre international clinical trial

BACKGROUND

Vitamin D status has been implicated in COVID-19 disease. The objective of the COVID-VIT-D trial was to investigate if an oral bolus of cholecalciferol (100,000 IU) administered at hospital admission influences the outcomes of moderate-severe COVID-19 disease. In the same cohort, the association between baseline serum calcidiol levels with the same outcomes was also analysed.

METHODS

The COVID-VIT-D is a multicentre, international, randomised, open label, clinical trial conducted throughout 1 year. Patients older than 18 years with moderate-severe COVID-19 disease requiring hospitalisation were included. At admission, patients were randomised 1:1 to receive a single oral bolus of cholecalciferol (n=274) or nothing (n=269). Patients were followed from admission to discharge or death. Length of hospitalisation, admission to intensive care unit (ICU) and mortality were assessed.

RESULTS

In the randomised trial, comorbidities, biomarkers, symptoms and drugs used did not differ between groups. Median serum calcidiol in the cholecalciferol and control groups were 17.0 vs. 16.1 ng/mL at admission and 29.0 vs. 16.4 ng/mL at discharge, respectively. The median length of hospitalisation (10.0 [95%CI 9.0-10.5] vs. 9.5 [95%CI 9.0-10.5] days), admission to ICU (17.2% [95%CI 13.0-22.3] vs. 16.4% [95%CI 12.3-21.4]) and death rate (8.0% [95%CI 5.2-12.1] vs. 5.6% [95%CI 3.3-9.2]) did not differ between the cholecalciferol and control group. In the cohort analyses, the highest serum calcidiol category at admission (>25ng/mL) was associated with lower percentage of pulmonary involvement and better outcomes.

CONCLUSIONS

The randomised clinical trial showed the administration of an oral bolus of 100,000 IU of cholecalciferol at hospital admission did not improve the outcomes of the COVID-19 disease. A cohort analysis showed that serum calcidiol at hospital admission was associated with outcomes.

TRIAL REGISTRATION

COVID-VIT-D trial was authorised by the Spanish Agency for Medicines and Health products (AEMPS) and registered in European Union Drug Regulating Authorities Clinical Trials (EudraCT 2020-002274-28) and in ClinicalTrials.gov ( NCT04552951 ).

Fibrosis in Chronic Kidney Disease: Pathogenesis and Consequences

Fibrosis is a process characterized by an excessive accumulation of the extracellular matrix as a response to different types of tissue injuries, which leads to organ dysfunction. The process can be initiated by multiple and different stimuli and pathogenic factors which trigger the cascade of reparation converging in molecular signals responsible of initiating and driving fibrosis. Though fibrosis can play a defensive role, in several circumstances at a certain stage, it can progressively become an uncontrolled irreversible and self-maintained process, named pathological fibrosis. Several systems, molecules and responses involved in the pathogenesis of the pathological fibrosis of chronic kidney disease (CKD) will be discussed in this review, putting special attention on inflammation, renin-angiotensin system (RAS), parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), Klotho, microRNAs (miRs), and the vitamin D hormonal system. All of them are key factors of the core and regulatory pathways which drive fibrosis, having a great negative kidney and cardiac impact in CKD.

Survival with low- and high-flux dialysis

Background

Besides advances in haemodialysis (HD), mortality rates are still high. The effect of the different types of HD membranes on survival is still a controversial issue. The aim of this COSMOS (Current management Of Secondary hyperparathyroidism: a Multicentre Observational Study) analysis was to survey, in HD patients, the relationship between the use of conventional low- or high-flux membranes and all-cause and cardiovascular mortality.

Methods

COSMOS is a multicentre, open-cohort, 3-year prospective study, designed to evaluate mineral and bone disorders in the European HD population. The present analysis included 5138 HD patients from 20 European countries, 3502 randomly selected at baseline (68.2%), plus 1636 new patients with <1 year on HD (31.8%) recruited to replace patients who died, were transplanted, switched to peritoneal dialysis or lost to follow-up by other reasons. Cox-regression analysis with time-dependent variables, propensity score matching and the use of an instrumental variable (facility-level analysis) were used.

Results

After adjustments using three different multivariate models, patients treated with high-flux membranes showed a lower all-cause and cardiovascular mortality risks {hazard ratio (HR) = 0.76 [95% confidence interval (CI) 0.61-0.96] and HR = 0.61 (95% CI 0.42-0.87), respectively}, that remained significant after matching by propensity score for all-cause mortality (HR = 0.69, 95% CI 0.52-0.93). However, a facility-level analysis showed no association between the case-mix-adjusted facility percentage of patients dialysed with high-flux membranes and all-cause and cardiovascular mortality.

Conclusions

High-flux dialysis was associated with a lower relative risk of all-cause and cardiovascular mortality. However, dialysis facilities using these dialysis membranes to a greater extent did not show better survival.

Serum phosphate optimal timing and range associated with patients survival in haemodialysis: the COSMOS study

BACKGROUND

Serum phosphate is a key parameter in the management of chronic kidney disease-mineral and bone disorder (CKD-MBD). The timing of phosphate measurement is not standardized in the current guidelines. Since the optimal range of these biomarkers may vary depending on the duration of the interdialytic interval, in this analysis of the Current management of secondary hyperparathyroidism: a multicentre observational study (COSMOS), we assessed the influence of a 2- (midweek) or 3-day (post-weekend) dialysis interval for blood withdrawal on serum levels of CKD-MBD biomarkers and their association with mortality risk.

METHODS

The COSMOS cohort (6797 patients, CKD Stage 5D) was divided into two groups depending upon midweek or post-weekend blood collection. Univariate and multivariate Cox's models adjusted hazard ratios (HRs) by demographics and comorbidities, treatments and biochemical parameters from a patient/centre database collected at baseline and every 6 months for 3 years.

RESULTS

There were no differences in serum calcium or parathyroid hormone levels between midweek and post-weekend patients. However, in post-weekend patients, the mean serum phosphate levels were higher compared with midweek patients (5.5 ± 1.4 versus 5.2 ± 1.4 mg/dL, P < 0.001). Also, the range of serum phosphate with the lowest mortality risk [HR ≤ 1.1; midweek: 3.5-4.9 mg/dL (95% confidence interval, CI: 2.9-5.2 mg/dL); post-weekend: 3.8-5.7 mg/dL (95% CI: 3.0-6.4 mg/dL)] showed significant differences in the upper limit (P = 0.021).

CONCLUSION

Midweek and post-weekend serum phosphate levels and their target ranges associated with the lowest mortality risk differ. Thus, clinical guidelines should consider the timing of blood withdrawal when recommending optimal target ranges for serum phosphate and therapeutic strategies for phosphate control.

Bone and mineral metabolism at 55 haemodialysis centres in Lima

BACKGROUND

Mineral and bone metabolism disorders are common complications in haemodialysis patients that present significant geographical variability.

OBJECTIVES

The objective of this study was to assess these disorders for the first time in haemodialysis patients from Peru.

METHODS

The study included 1551 haemodialysis patients from 55 centres affiliated with the Social Health System of Peru in the city of Lima. Demographic data, comorbidities, treatments and biochemical parameters were collected from each patient. Serum calcium, phosphorus and PTH levels were categorised according to the recommended ranges in the KDOQI and KDIGO guidelines.

RESULTS

The mean age of the patients was 59.5±15.6 years, with a mean time on haemodialysis of 58.0±54.2 months. All patients were dialysed with a calcium concentration in the dialysis fluid of 3.5 mEq/l and 68.9% of patients were prescribed phosphate-binding agents (98.4% of them calcium carbonate). A high percentage of patients showed serum calcium above, and serum phosphorus below, the recommended ranges in the KDOQI guidelines (32.8% and 37.3%, respectively). More than half of the patients had serum PTH values below the recommended ranges of both the KDOQI and KDIGO guidelines (56.4% and 51.6%, respectively).

CONCLUSIONS

Patients included in this study were younger than those from other studies and showed both hypophosphataemia and suppressed PTH, probably due to an excessive calcium overload through dialysis fluid and the use of calcium-containing phosphate binding agents.

Risk of hospitalization associated with body mass index and weight changes among prevalent haemodialysis patients

The impact of body mass index (BMI) and body weight on hospitalization rates in haemodialysis patients is unknown. This study hypothesizes that being either underweight or obese is associated with a higher hospitalization rate. Observational study of 6296 European haemodialysis patients with prospective data collection and follow-up every six months for three years (COSMOS study). The risk of being hospitalized was estimated by a time-dependent Cox regression model and the annual risk (incidence rate ratios, IRR) by Poisson regression. We considered weight loss, weight gain and stable weight. Weight change analyses were also performed after patient stratification according to their baseline BMI. A total of 3096 patients were hospitalized at least once with 9731 hospitalizations in total. The hospitalization incidence (fully adjusted IRR 1.28, 95% CI [1.18-1.39]) was higher among underweight patients (BMI <20kg/m²) than patients of normal weight (BMI 20-25kg/m²), while the incidence of overweight (0.88 [0.83-0.93]) and obese patients (≥30kg/m², 0.85 [0.79-0.92]) was lower. Weight gain was associated with a reduced risk of hospitalization. Conversely, weight loss was associated with a higher hospitalization rate, particularly in underweight patients (IRR 2.85 [2.33-3.47]). Underweight haemodialysis patients were at increased risk of hospitalization, while overweight and obese patients were less likely to be hospitalized. Short-term weight loss in underweight individuals was associated with a strikingly high hospitalization rate.

Plasma Cardiotrophin-1 as a Marker of Hypertension and Diabetes-Induced Target Organ Damage and Cardiovascular Risk

The search for biomarkers of hypertension and diabetes-induced damage to multiple target organs is a priority. We analyzed the correlation between plasma cardiotrophin-1 (CT-1), a chemokine that participates in cardiovascular remodeling and organ fibrosis, and a wide range of parameters currently used to diagnose morphological and functional progressive injury in left ventricle, arteries, and kidneys of diabetic and hypertensive patients, in order to validate plasma levels of CT-1 as clinical biomarker.This is an observational study with 93 type 2-diabetic patients, 209 hypertensive patients, and 82 healthy controls in which we assessed the following parameters: plasma CT-1, basal glycaemia, systolic blood pressure (SBP), diastolic blood pressure (DBP), pulse pressure (PP), left ventricular hypertrophy (LVH by electrocardiographic indexes), peripheral vascular disease (by pulse wave velocity-PWV, carotid intima-media thickness-C-IMT, and ankle-brachial index-ABI), and renal impairment (by microalbuminuria, albumin/creatinine urinary ratio, plasma creatinine concentrations, and glomerular filtration rate).Hypertensive or diabetic patients have higher plasma CT-1 than control patients. CT-1 positively correlates with basal glycaemia, SBP, DBP, PP, LVH, arterial damage (increased IMT, decreased ABI), and early renal damage (microalbuminuria, elevated albumin/creatinine ratio). CT-1 also correlates with increased 10-year cardiovascular risk. Multiple linear regression analysis confirmed that CT-1 was associated with arterial injury assessed by PWV, IMT, ABI, and cardiac damage evaluated by Cornell voltage duration product.Increases in plasma CT-1 are strongly related to the intensity of several parameters associated to target organ damage supporting further investigation of its diagnostic capacity as single biomarker of cardiovascular injury and risk and, possibly, of subclinical renal damage.

Use of phosphate-binding agents is associated with a lower risk of mortality

Hyperphosphatemia has been associated with higher mortality risk in CKD 5 patients receiving dialysis. Here, we determined the association between the use of single and combined phosphate-binding agents and survival in 6797 patients of the COSMOS study: a 3-year follow-up, multicenter, open-cohort, observational prospective study carried out in 227 dialysis centers from 20 European countries. Patient phosphate-binding agent prescriptions (time-varying) and the case-mix-adjusted facility percentage of phosphate-binding agent prescriptions (instrumental variable) were used as predictors of the relative all-cause and cardiovascular mortality using Cox proportional hazard regression models. Three different multivariate models that included up to 24 variables were used for adjustments. After multivariate analysis, patients prescribed phosphate-binding agents showed a 29 and 22% lower all-cause and cardiovascular mortality risk, respectively. The survival advantage of phosphate-binding agent prescription remained statistically significant after propensity score matching analysis. A decrease of 8% in the relative risk of mortality was found for every 10% increase in the case-mix-adjusted facility prescription of phosphate-binding agents. All single and combined therapies with phosphate-binding agents, except aluminum salts, showed a beneficial association with survival. The findings made in the present association study need to be confirmed by randomized controlled trials to prove the observed beneficial effect of phosphate-binding agents on mortality.

Residue 826 in the calcium-sensing receptor is implicated in the response to calcium and to R-568 calcimimetic compound

Within the extracellular loops of the seven-transmembrane domain of the calcium-sensing receptor (CaR) there is a region (I819-E837) relevant for calcimimetic activity. As the naturally occurring variant Ala826Thr is within this important region, it may be postulated that this change may influence the CaR response to calcium and R-568. Human embryonic kidney (HEK-293) cells transiently transfected with three different human CaRs (wild-type [A826], variant allele [T826], and artificial mutant [W826]) were used to test the ability of calcium alone or in combination with the calcimimetic R-568 to modulate CaR activity. CaR activation was detected by flow cytometry using a fluorescent probe. Intracellular calcium changes were measured in response to changes in extracellular calcium alone or with different R-568 concentrations. The change of the alanine in the 826 position (A826) for threonine (T826) worsened calcium sensitivity, increasing the EC(50) value from 2.34 +/- 0.48 mM (A826, wild-type) to 2.96 +/- 0.75 mM (T826) (P < 0.05). The T826 receptor reached a similar response with 1 muM R-568 compared with the wild-type receptor. On the contrary, the artificial introduction of a tryptophan in the same position (W826) did not affect calcium sensitivity (EC(50) = 2.64 +/- 0.81 mM) but reduced the ability of the receptor to respond to R-568. The results demonstrate the importance of the 826 residue in the CaR response to calcium and calcimimetics. Since the A826T change was described as a natural variant, the differences in the calcium and calcimimetic responses observed between the alleles could have potential clinical impact.

Mineral metabolism: Should cinacalcet be used in patients who are not on dialysis?

Cinacalcet is an effective treatment for secondary hyperparathyroidism in patients on dialysis. Until now, no randomized, placebo-controlled, long-term trial has tested this drug in individuals with chronic kidney disease who are not receiving dialysis.

Effect of VDR gene polymorphisms on osteocalcin secretion in calcitriol-stimulated human osteoblasts

BACKGROUND

The impact of vitamin D receptor (VDR) gene polymorphisms in bone metabolism remains controversial. Some authors have found a beneficial effect of some VDR gene polymorphisms, while others found no differences, or even a lower bone mass in subjects with the same type of polymorphisms. The aim of this study was to assess if the VDR gene polymorphisms could have an effect on the calcitriol-stimulated osteocalcin in human osteoblasts.

METHODS

Osteoblasts were obtained from human femoral necks replaced because of osteoarthritis. Bones were cut into pieces of 1 to 2 mm and placed in a nylon mesh. After the migration of osteoblasts, the pieces were collected and cultured with different concentrations of calcitriol (10(-8), 10(-9), and 10(-1)0 mol/L). After 48 hours of incubation with calcitriol, the osteocalcin secreted into the medium (corrected by either total proteins or total DNA content) was measured. The DNA was extracted from the osteoblasts, amplified by polymerase chain reaction (PCR), and analyzed for target sequences sites of the BsmI, ApaI, TaqI, and FokI restriction enzymes.

RESULTS

The response observed in osteocalcin secretion in the bb or TT genotypes doubled the response observed in the BB or tt genotypes (calcitriol 10(-8) and 10(-9) mol/L). A slight trend was also observed with the aa genotype. Men showed higher levels of osteocalcin secretion than women. Age did not show any influence in osteocalcin secretion.

CONCLUSION

VDR alleles and gender demonstrated an effect on the osteocalcin secretion. BB or tt genotypes, and also the "A" allele, showed the lowest calcitriol-stimulated osteocalcin secretion.

Effect of aluminium on calcium-sensing receptor expression, proliferation, and apoptosis of parathyroid glands from rats with chronic renal failure

BACKGROUND

To assess the effect of aluminium on the calcium-sensing receptor expression, proliferation, and apoptosis in parathyroid glands from rats with chronic renal failure, 2(1/2)-month-old male Wistar rats were 7/8 nephrectomized.

METHODS

Eight weeks after surgery the rats were divided into two groups, one receiving intraperitoneal AlCl3 for 8 weeks and the other receiving intraperitoneal placebo. Serum Al, Ca, P, creatinine, and PTH were measured. Parathyroid glands were removed, formaldehyde-fixed, and paraffin-embedded. Calcium-sensing receptor and proliferation were detected by immunohistochemistry and apoptosis by TUNEL and propidium iodide uptake.

RESULTS

At the end of the study, despite higher levels of serum P in the aluminium group (6.27 +/- 0.63 vs. 5.56 +/- 0.58 mg/dL; P = 0.045), serum PTH was lower (89.6 +/- 57.7 vs. 183.1 +/- 123.8 pg/mL; P = 0.059). No significant differences were found in the calcium-sensing receptor expression between groups (aluminium: 27.1 +/- 7.6; placebo: 25.4 +/- 3.5 RU). Rats receiving aluminium showed a significantly lower cell proliferation rate than the control rats (0.54 +/- 0.69 vs. 4.43 +/- 3.10 cells/mm2; P = 0.003). No apoptotic events were detected.

CONCLUSION

Aluminium was able to reduce the cell proliferation of the parathyroid glands. Due to the low apoptosis rate, however, it was not possible to find any change. Aluminium had no effect on the calcium-sensing receptor expression.

Effect of aluminium load on parathyroid hormone synthesis

BACKGROUND

Aluminium overload leads to parathyroid hormone (PTH) suppression. However, it is unclear whether a decrease in synthesis or release of the hormone is mainly involved. The aim of this study was to assess the effect of an acute administration of aluminium on PTH synthesis and release in rats with chronic renal failure and secondary hyperparathyroidism.

METHODS

The study was performed using 100 adult male Wistar rats (body weight 443+/-54 g). 7/8 nephrectomy was performed and the rats were maintained on a high dietary phosphorous intake. Five weeks after surgery, the rats were randomly divided into two groups, one loaded with aluminium (AlCl3) and the other given placebo. Aluminium or placebo were administered i.p. for two consecutive days. The placebo group received saline at the same pH as the aluminium solution. After 2 weeks, serum calcium, phosphorous, creatinine, PTH, and aluminium were measured. The parathyroid glands were removed and PTH messenger RNA (mRNA) was measured by northern blot. Intact PTH was measured by IRMA (Rat PTH, Nichols Institute).

RESULTS

No differences in serum PTH levels were found between the two groups after 5 weeks of renal failure. At the end of the study the rats given aluminium had higher aluminium levels than the placebo group and lower PTH levels. No significant differences were found for calcium, phosphorous, renal function, or body weight. PTH mRNA expression was lower in the aluminium group than in the placebo group.

CONCLUSION

The administration of aluminium in rats with chronic renal failure resulted in reductions in serum PTH and PTH mRNA. Thus far, previous studies had demonstrated that aluminium suppressed PTH release. The present findings suggest that PTH synthesis is also reduced.

Bone aluminum uptake in uremic rats receiving intraperitoneal iron

To assess the effect of concomitant iron and aluminum loads on bone aluminum accumulation and on the response to the deferoxamine test in rats with the same aluminum surcharge, Wistar rats with chronic renal failure were divided into three groups: iron-overloaded rats (N = 6) (intraperitoneal iron); iron-depleted rats (N = 6) (blood withdrawal two to three times per week); control rats (N = 4) (no manipulation). All groups received intraperitoneal aluminum simultaneously. After 6 wk, a deferoxamine challenge test was performed. Thereafter, bone aluminum and iron were measured. The iron-overloaded rats showed higher bone iron content (iron overloaded: 147.7+/-55.4 microg/g; iron depleted: 7.9+/-1.0, and controls 13.3+/-9.9 microg/g, p < 0.010) and lower bone aluminum content (iron overloaded: 14.2+/-4.0 microg/g; iron depleted: 70.9+/-35.1 microg/g; controls: 72.7+/-28.3 microg/g p < 0.005). No differences were found between the iron-depleted and control rats. After the deferoxamine infusion, the iron-depleted rats tended to have higher serum aluminum increments (p = NS) and higher urinary aluminum excretion (p < 0.012, p < 0.020) than control rats despite similar amounts of aluminum in bone of the two groups. Aluminum bone accumulation was minor if iron and aluminum loads were given concomitantly. The iron depletion influenced the results of the deferoxamine challenge test in rats with similar bone aluminum burden.

Use of ultrafiltration and chromatography to assess aluminum speciation in serum after deferoxamine administration

Deferoxamine effectively chelates aluminum by forming aluminoxamine, a low-molecular-weight compound removable by dialysis. However, aluminum-bound species other than aluminoxamine might be present in serum after the administration of deferoxamine. To study aluminum speciation after the administration of deferoxamine, high-performance liquid chromatography (HPLC) and ultrafiltration techniques were used. Samples of serum were obtained from six dialysis patients 44 hours after the administration of a single dose of deferoxamine. HPLC and ultrafiltration studies were performed. In the HPLC studies, samples underwent ultrafiltration, the filtrate was injected into the chromatographic system, and detection was performed by UV light and atomic absorption spectrometry. Unknown species of aluminum other than aluminoxamine were found in the early elution fractions. In the ultrafiltration studies, the same samples of serum from the six patients underwent ultrafiltration using membranes with different molecular-weight cutoff values from 1 to 30 kd. The percentages of aluminum found by ultrafiltration using membranes with cutoff values of 5, 10, and 30 kd were greater (64.4% +/- 2.5%, 63.5% +/- 3.7%, and 65.6% +/- 4.3%, respectively) than the percentages obtained with membranes with a 1-kd cutoff value (38.7%), suggesting that the unknown species of aluminum have a molecular weight between 1 and 5 kd. The unknown species of aluminum cannot be aluminoxamine because they behaved in a different way with HPLC.

Aluminum exposure in chronic renal failure in iberoamerica at the end of the 1990s: overview and perspectives

Epidemic aluminum neurotoxicity has virtually disappeared in the dialysis population; however, sporadic toxic effects caused by contamination of water with aluminum are still reported. In this review, the current situation in Iberoamerica is analyzed. Exposure to aluminum through dialysate shows considerable geographical differences even within the same country, including seasonal variability. Sometimes the tap water showed very high aluminum content that does not permit the water treatment system to efficiently remove all the aluminum, forcing the use of water treatment systems with a double reverse-osmosis filter on line. The use of adequate water treatment systems and a correct control policy has improved the quality of the dialysate, minimizing the aluminum exposure. However, an additional problem in Iberoamerica is the difficulty to obtain aluminum-free concentrates for the preparation of the final dialysis solution. Aluminum still seems to be implicated in a great percentage of symptomatic low-bone remodeling lesions in South America compared with Europe, demonstrating that exposure to aluminum through dialysate is still a cause of concern in some areas of the world.

Aluminum-induced osteogenesis in osteopenic rats with normal renal function

Previous studies have shown a different effect of aluminum (Al) on bone metabolism in animals with chronic renal failure and conversely, positive osteogenic effects in animals with normal renal function. The aim of this study was to evaluate the effect of aluminum on bone metabolism in osteopenic rats. We studied male Wistar rats with severe osteopenia induced by adding NH4Cl (2%) to the drinking water over a 6-month period. The rats were divided into two groups and followed for 4 months. The Aluminum group (G1) received AlC13 intraperitoneally (10 mg/kg/5 days/week) (n = 8); the Control group (G2) did not receive any treatment after stopping the administration of NH4Cl (n = 5). In all animals we measured biochemical markers (serum Ca, P, Cr, Al, osteocalcin, hydroxyproline) as well as bone mineral density and bone histomorphometry (BV/TV, CTh, ObS/BS, OTh, and NOc/TV). Bone aluminum content, measured by atomic absorption spectrometry, was 101.6 +/- 13 microg/g in the Al overloaded group and 1.31 +/- 0.14 in controls. Bone mineral density, evaluated by dual X-ray absorptiometry (DXA) at the proximal extremity of the tibia was significantly higher in G1 (0.292 +/- 0.01 g/cm2 versus 0. 267 +/- 0.02 g/cm2). No significant differences were found between the biochemical markers. In the histomorphometric parameters we observed significant differences in G1 compared with G2: an increase in BV/TV (18.59 +/- 5.6 versus 7.69 +/- 3.08%) and in CTh (0.52 +/- 0.06 versus 0.36 +/- 0.07 mm) with a moderate increment of the osteoid thickness (14.05 +/- 4.72 versus 5.25 +/- 0.9 microm) (P < 0. 05). Changes in others parameters and the relationship between biochemical parameters of bone remodeling, Al, and histology were analyzed. These findings indicate that in rats with normal renal function, Al is able to induce bone formation even when osteopenia is present.

Low percentage of aluminoxamine and ferrioxamine in uremic serum after desferrioxamine administration

HPLC was used to study the effectiveness of two different desferrioxamine (DFO) administration strategies (15 mg/kg DFO, 1 h or 44 h before dialysis) on generation of aluminoxamine and ferrioxamine in five hemodialysis patients. The percentage of ultrafilterable aluminum and iron in these patients was also investigated by electrothermal atomic absorption spectrometry. The administration of DFO in both schemes increased the ultrafilterable serum aluminum concentrations from a mean of 17.1 +/- 1.6% to a mean of 75.7 +/- 14.1%. However, 1 h after DFO infusion, only 38.8 +/- 7.7% of the total serum aluminum was bound to DFO; 44 h after DFO infusion, only 15.8 +/- 8.0% was bound. Similar results were obtained for ferrioxamine. These results suggest that the ultrafilterable serum fraction contains aluminum and iron chelated by DFO and by DFO metabolites, which retain similar metal-chelating abilities.

Ultrafiltrable aluminium after very low doses of desferrioxamine

BACKGROUND

The recommended dose of desferrioxamine for the treatment of aluminium intoxication is 5 mg/kg/week. However, there are no data about the efficiency of lower doses. The objective of this study was to investigate the capacity of very low doses of desferrioxamine in the generation of ultrafiltrable aluminium.

METHODS

Five patients undergoing haemodialysis with a similar biochemical profile and serum aluminium levels >40 microg/l were studied. The three different doses of desferrioxamine used (0.5, 2.5 and 5.0 mg/kg) were administered randomly to each patient at 1 week intervals. Total and ultrafiltrable serum aluminium was measured before and 44 h after the administration of desferrioxamine.

RESULTS

All doses of desferrioxamine significantly increased the total serum aluminium; no differences were found between 2.5 and 5.0 mg/kg. The total serum aluminium levels doubled with the 2.5 and 5.0 mg/kg doses, while the increase with 0.5 mg/kg was lower (32.6%, P<0.05). Ultrafiltrable aluminium increased with the three doses; from 7.1+/-2.8, 3.9+/-0.6 and 7.5+/-4.1 to 25.7+/-7.3, 44.3+/-10.1 and 59.1+/-19.8 microg/l, respectively (P<0.05). The efficiency of each dose was calculated using the ratio between the increase in ultrafiltrable aluminium and the dose of desferrioxamine administered. The efficiency ranged from 10.3+/-3.9 for the higher dose (5 mg/kg) to 37.2+/-10.3 for the lower dose (0.5 mg/kg).

CONCLUSIONS

Our results suggest that very low-dose desferrioxamine (>5 mg/kg) increases the ultrafiltrable (potentially dialysable) aluminium.

Aluminium removal with the double chamber technique: paired filtration-dialysis (PFD)

Several dialysis techniques have been used to improve aluminium removal. So far there are no data available using paired filtration-dialysis (PFD). In this study, we evaluated the aluminium removed by PFD in two phases. Bovine plasma with known concentrations of aluminium and desferrioxamine was used in both experiments. In phase I, the aluminium removal was investigated using the PFD system (single pass) in its usual configuration, modifying the order of the convective and diffusive processes, dialysis with high permeability membranes and dialysis with low permeability membranes. During the second phase, the experiment lasted longer using recirculation, and the PFD was compared with conventional dialysis using high permeability membranes. Changes in the PFD configuration did not alter the aluminium removal; the efficiency of PFD for aluminium removal was very close to that of dialysis with high permeability membranes and much greater than with low permeability membranes. The aluminium is removed mainly in the first part of the dialysis. Aluminium mobilization using the double chamber technique (PFD) was efficient and might be of value for those patients with aluminium overload who needs high depurative techniques and are unable to tolerate high-flux techniques.

Prevention of aluminium exposure through dialysis fluids. Analysis of changes in the last 8 years

Despite extensive measures to control aluminium exposure, chronic and acute episodes of aluminium intoxication still occur. The objective of this study was to analyse the changes in the aluminium content of dialysis fluid and the effect on serum aluminium in different dialysis centres in Spain in the last 8 years. For this purpose, the aluminium content in dialysis fluid and serum samples (N=5609) from 17 dialysis centres was analysed for >8 years (from the last quarter of 1988 to 1996). In that period of time, the percentage of dialysis fluid samples with acceptable concentrations of aluminium (<2 microg/l) increased from 0% in 1988 to 80% in 1996. The percentage of dialysis fluid samples with high aluminium levels (>6 microg/l) ranged between 37.5% in 1988 and 2.3% in 1996. The improvement in the quality of the dialysis fluid resulted in lower values of serum aluminium. The percentage of serum samples with low aluminium (<20 microg/l) increased from 16.5% in 1988 to 54.2% in 1966. The mean serum aluminium correlated with the mean dialysis fluid aluminium (r=0.55, P<0.001). A higher correlation was found when the aluminium in dialysis fluid ranged between 4 and 10 microg/l (r=0.802, P<0.001), and no correlation was found when the aluminium in dialysis fluid was <4 microg/l. Even taking into account that the dialysis fluid is not the only source of aluminium for dialysis patients, our study clearly demonstrated a close relationship with the serum aluminium content. Therefore, we must emphasize the necessity for controlling the aluminium content in dialysis fluid more often than is done at present.

Staining of bone aluminium: comparison between aluminon and solochrome azurine and their correlation with bone aluminium content

The aim of this study was to compare the sensitivity and specificity of the two histochemical stains most commonly used as indirect markers of the aluminium bone content. The clinical study was made in 28 biopsies from patients undergoing haemodialysis and the experimental study in 17 tibias from Wistar rats aluminium overloaded and with different deposits of iron. All samples were stained with aluminon, solochrome azurine and Perls and aluminium bone content was also measured. When the positive cases with Perls were excluded in the clinical study (without iron interference), the trabecular surface stained with solochrome azurine correlated with the aluminium bone content (r = 0.71, P < 0.001). With aluminon, on the other hand, no correlation was found. Solochrome azurine was always positive with aluminium contents greater than 8 micrograms/g. Aluminon was positive over 17 micrograms/g. In the experimental study, the iron concentration, in addition to other parameters, was also measured. As in the clinical study, the trabecular surface stained with solochrome azurine correlated with the aluminium content. If the positive Perls cases were excluded, the trabecular surface stained with solochrome azurine doubled the trabecular surface stained with aluminon (P < 0.001). No intratrabecular aluminon staining was observed while the intratrabecular solochrome staining correlated with the aluminium content (P < 0.001). Solochrome azurine was more sensitive than the aluminon and its lack of specificity can be easily corrected by employing Perls staining to exclude the iron interference.

Influence of iron status in the response to the deferoxamine test

The study presented here was carried out to evaluate the possible relationship between serum iron and iron transferrin saturation with the response to the deferoxamine test in 86 chronic renal failure patients undergoing hemodialysis. The deferoxamine test was performed as a diagnostic tool for aluminum intoxication. Basal serum aluminum levels correlated with: (1) serum aluminum levels after the infusion of deferoxamine (r = 0.45; P < 0.05); (2) serum iron levels (r = -0.26; P < 0.05), and; (3) iron transferrin saturation (r = -0.33; P < 0.05). The increase in serum aluminum levels after deferoxamine administration (DAI) showed a negative relationship with serum iron levels (r = -0.23; P < 0.05) and iron transferrin saturation (r = -0.26; P < 0.05). The correlations improved when analysis of this study included only those patients with high serum iron levels or high iron transferrin saturation (r = -0.55). Patients with low probability of having aluminum overload (serum iron levels < 40 micrograms/L and DAI < 150 micrograms/L) had significantly higher values of serum iron, iron transferrin saturation, and serum ferritin levels compared with those patients with a high probability of having aluminum overload (serum aluminum levels > 40 micrograms/L and DAI > 150 micrograms/L). The study presented here suggests that patients who have indicators of iron repletion would tend to have lower increases in serum aluminum levels after the challenge with deferoxamine and presumably a higher incidence of false negative results with the deferoxamine test. These findings indicate that iron measurements must be always taken into account when interpreting the deferoxamine test.

Binding of aluminium to plasma proteins: comparative effect of desferrioxamine and deferiprone (L1)

Ultramicrofiltration techniques were used to study both the binding of aluminium to high molecular weight proteins in the presence of different concentrations of desferrioxamine and deferiprone (L1) and the kinetics of aluminium release from human serum proteins. Human serum from healthy volunteers was used in all studies. The serum was spiked with aluminium (100 micrograms/l) and different concentrations of chelators. Ultramicrofiltration was performed with Amicon YMT membranes which had a nominal cut-off of 30,000 Da. Aluminium was measured by graphite furnace atomic absorption spectrometry in total serum and ultrafiltered fluid. Deferiprone shows a higher capability to displace aluminium from serum proteins (80%) than desferrioxamine (60%) at equivalent concentrations of the chelators. The kinetics of the release were also faster for deferiprone, taking 20 min to achieve its maximum effect, whereas, desferrioxamine achieved only 80% of its maximum effect after 2 h. Thus, deferiprone could be an attractive alternative to desferrioxamine, as an aluminium chelator agent.

Role of iron metabolism in absorption and cellular uptake of aluminum

The effect of iron status on aluminum (Al) absorption was investigated in this study in vivo using an animal model and in vitro using an intestinal mucosal cell line. In the in vivo model rats were rendered iron overloaded by intraperitoneal injection of iron dextran (5 mg/48 hr) or iron deficient by phlebotomy (2.5 to 3 ml blood/week). These rats, and normal controls, were then dosed with Al(OH)3 (40 mg/day) for 30 days. Urinary excretion of Al was significantly greater in the iron deficient group than in the other two groups throughout the study period, and brain Al at the end of the experiment was significantly increased in the iron depleted group (1.93 micrograms/g) and decreased in the iron overloaded group (0.73 microgram/g) compared with controls (1.42 micrograms/g). The brain Al levels in iron overloaded rats were no higher than those in normal rats that had not been dosed with Al(OH)3 (0.61 microgram/g). No significant differences were found in serum Al levels. In the in vitro experiments cultures of the rat intestinal cell line RIE1 were iron overloaded by addition of iron nitrilotriacetate (0.1 mM) or iron depleted with desferrioxamine (5 micrograms/ml) for 20 days prior to pulsing with Al transferrin (0.5 mg/ml) for 24 hours. Uptake of Al was significantly greater in the iron depleted cells (2.3 ng/micrograms cell DNA) than in iron overloaded (0.81 ng) or untreated (0.83 microgram) cells. These studies show that iron depletion markedly increases absorption and cellular uptake and suggest that susceptible individuals, such as renal failure patients, run an increased risk of toxicity if they are iron deficient.