Bone turnover in preterm infants.

Total parenteral nutrition is associated with osteopenia in preterm infants. Insufficient calcium and phosphate are likely causes: aluminum contamination is another possible contributing factor as this adversely affects bone formation and mineralization. The study was designed to evaluate changes in biochemical markers of bone turnover in 22 preterm infants receiving total parenteral nutrition in comparison with 19 term infants. We collected urine and serum samples from 22 preterm infants, mean gestational age 29 wk, within 48 h and again at 3 wk of life. We also collected urine samples from 19 term infants, mean gestational age 39 wk, during the first day of life. Bone resorption was assessed by the measurement of urinary pyridinium cross-links by HPLC and ELISA and the N-telopeptide of type I collagen by ELISA. Bone formation was assessed in premature infants by the measurement of serum osteocalcin. The N-telopeptide of type I collagen was higher in the preterm infants compared with term at baseline (p < 0.01). There was no difference between the pyridinium cross-links in the preterm and term infants. All the biochemical markers of bone turnover increased significantly in the preterm infants during the first 3 wk of life, e.g. N-telopeptide was a 153% change from baseline (p < 0.001). Aluminum in the total parenteral nutrition solutions did not cause a decrease in bone formation at the level administered (3-6 microg, 0.1-0.2 micromol x kg(-1) x d(-1)).

Effect of iron on renal tubular epithelial cells.

Since iron has been implicated as a potential nephrotoxin, we examined the effect of iron on several aspects of cultured renal tubular epithelial cell biology. We found that exposure to 10(-4) M of either the ferrous or ferric form of iron impaired healing of denuded areas made within confluent monolayers of LLC-PK1 cells. This impairment required 30 to 80 hours of exposure to iron to occur and was also seen in another renal tubular epithelial cell line (MDCK cells). To delineate the potential mechanism(s) of this impairment, we examined the expression of a key integrin subunit involved in cell-matrix adhesion. Exposure of LLC-PK1 cells to 10(-4) M ferric citrate for 72 hours significantly decreased expression of the beta 1 integrin subunit as determined by flow cytometry. To determine if iron impairs another process that occurs at the basolateral surface, the effects of 72 hours of exposure to iron on adenylate cyclase activity were examined. Both ferric and ferrous citrate significantly enhanced vasopressin- and forskolin-stimulated adenylate cyclase activity. To examine if iron can regulate proliferation, the effect of iron on 3H-thymidine uptake was measured. We found that ferric citrate diminished proliferation and this decrease required the presence of either serum or transferrin. To ascertain if iron affected ultrastructure, we used transmission electron microscopy and found that iron accumulation within cells was much more apparent with ferric than ferrous citrate. Ferric iron induced mild-to-moderate cytopathic changes. These results indicate that iron is capable of inducing multiple changes in renal tubular epithelial function. The effect of iron to impair wound healing may be related to diminished expression of the beta 1 integrin subunit and perhaps to impaired proliferation.

Status and future concerns of clinical and environmental aluminum toxicology.

A wide range of toxic effects of aluminum (Al) have been demonstrated in plants and aquatic animals in nature, in experimental animals by several routes of exposure, and under different clinical conditions in humans. Aluminum toxicity is a major problem in agriculture, affecting perhaps as much as 40% of arable soils in the world. In fresh waters acidified by acid rain, Al toxicity has led to fish extinction. Aluminum is a very potent neurotoxicant. In humans with chronic renal failure on dialysis, Al causes encephalopathy, osteomalacia, and anemia. There are also reports of such effects in certain patient groups without renal failure. Subtle neurocognitive and psychomotor effects and electroencephalograph (EEG) abnormalities have been reported at plasma Al levels as low as 50 micrograms/L. Infants could be particularly susceptible to Al accumulation and toxicity, reduced renal function being one contributory cause. Recent reports clearly show that Al accumulation occurs in the tissues of workers with long-term occupational exposure to Al dusts or fumes, and also indicate that such exposure may cause subtle neurological effects. Increased efforts should be directed toward defining the full range of potentially harmful effects in humans. To this end, multidisciplinary collaborative research efforts are encouraged, involving scientists from many different specialties. Emphasis should be placed on increasing our understanding of the chemistry of Al in biological systems, and on determining the cellular and molecular mechanisms of Al toxicity.

Urinary iron speciation in nephrotic syndrome.

In nephrotic syndrome, iron is presented to the tubule fluid in a nonreactive form in association with transferrin as a result of the glomerular protein leak. At an alkaline pH, iron remains bound to transferrin throughout the nephron and is excreted as such in the urine. As urine pH decreases below 6, iron is dissociated from transferrin. In the dissociated form, iron exists in the urine in a soluble, ultrafiltrable, and labile state. It is suggested that iron is maintained in this state by chelation to a relatively small organic compound, such as citrate. This non-transferrin-bound iron is capable of catalyzing bleomycin degradation of DNA, suggesting that this labile form of iron is able to catalyze free radical formation and cause tubule cell injury. Urine from proteinuric states represents one of the few, if not only, biologic fluids containing large amounts of reactive iron species. This may explain the mechanism by which proteinuric states cause tubulointerstitial disease and renal failure.

Aluminum and lead absorption from dietary sources in women ingesting calcium citrate.

Animal models suggest that citrate-containing compounds augment absorption of aluminum from food and tap water, causing aluminum accumulation in bone and brain despite normal renal function. Citrate also enhances lead absorption in animals. We questioned whether use of calcium citrate by women as a calcium supplement causes an increase in aluminum or lead absorption from dietary sources. Changes in 24-hour urine aluminum and lead excretion, plasma aluminum level, and whole blood lead level were assessed in 30 healthy women before and during treatment with calcium citrate (800 mg of elemental calcium per day). During calcium citrate therapy, urinary aluminum excretion and plasma aluminum level increased significantly. In contrast, there were no changes in urine or whole blood lead levels. We conclude that treatment with calcium citrate significantly increases absorption of aluminum from dietary sources. Additional studies are needed to determine whether long-term use of calcium citrate leads to aluminum accumulation and toxicity.

Active lithium transport by rat renal proximal tubule: a micropuncture study.

We tested the hypothesis that proximal tubular Li+ reabsorption is due to passive transport. Clearances of [14C]inulin (CIn) and Li+ (CLi), proximal transepithelial electrical potential difference (PD), and tubular fluid-to-plasma Li+ concentration ratios [(TF/P)Li] were measured in anesthetized rats before and after induction of osmotic mannitol diuresis. Late proximal (TF/P)Li was measured after acute intravenous LiCl administration and after addition of LiCl to the diet for 2 days. Glomerular filtration rate (CIn) decreased, whereas CNa and CLi increased during osmotic diuresis. Control early proximal PD was -0.6 mV (lumen negative); late proximal PD (PDLP) was 1.1 mV (lumen positive). PDLP decreased by 1.5 mV to -0.4 mV (lumen negative) after mannitol infusion. Late proximal (TF/P)Li was 1.01 after oral Li+, 1.16 after intravenous Li+ (P < 0.01), and 1.00 during osmotic diuresis. It is concluded that proximal Li+ transfer is distinct from that of Na+, closely parallels proximal water transfer, and involves an active transport mechanism independent of the PD. The data suggest that acute elevation of plasma Li+ concentration may activate a delayed Li+ transport pathway in the proximal convoluted tubule.

Risk of aluminum accumulation in patients with burns and ways to reduce it.

Severely burned patients experience a bone lesion consisting of markedly reduced bone formation and evidence of decreased resportion. The cause of the lesion may be multifactorial, but aluminum loading, which also occurs in patients with burns, has been documented to produce this type of injury in both humans and animals. To assess the risk of aluminum loading with patients with burns, we analyzed fluids, creams, and medication used in the management of acute burn injury for aluminum content. These substances were classified according to route of administration: cutaneous, enteral, or parenteral, to assess the risk of aluminum loading. Cutaneous exposure to aluminum is greatest from baths, which may provide up to 8 mg aluminum. However, the dynamics of aluminum entry into the blood via a damaged skin barrier are unclear. Enteral exposure to aluminum is no greater than daily dietary exposure. Parenteral sources of aluminum, especially 25% human serum albumin and calcium gluconate, provide the most significant risk of loading because of direct introduction of aluminum into the circulation. Substitution with a different brand of albumin and calcium chloride can reduce the parenteral aluminum load by as much as 95% and minimize any role aluminum may play in the pathogenesis of this bone lesion.

Role of iron and oxygen radicals in the progression of chronic renal failure.

As nephron population is lost from injury or disease the remaining nephrons undergo functional and anatomic hypertrophy. The compensatory or secondary events responsible for these changes may exert a detrimental effect on the remaining nephrons that ultimately leads to their destruction. Most studies have examined how these alterations cause glomerular injury. Although glomerular injury and functional alterations are the initial result of these events, tubulointerstitial disease may be the major determinate of subsequent nephron loss and progressive renal failure. Proteinuria has been used largely as an indicator of the severity of the glomerular involvement. However, an alternative hypothesis is that the proteinuria, resulting from the glomerular injury, actually perpetuates renal injury as a result of its damaging effect on renal tubules and the surrounding interstitium. Because of being the major protein fraction it has been assumed that albumin is largely, if not solely, responsible for the induction of tubulointerstitial injury. However, with glomerular disease all protein classes can be excreted. One protein of interest is transferrin. In association with the glomerular transferrin leak, iron also would be presented to the tubule fluid. Iron is a transition element capable of catalyzing the Haber Weiss reaction with formation of hydroxyl radicals. Normally, iron is maintained in a nonreactive state in virtually all biologic tissues and fluid. However, at the reduced pH of tubule fluid iron can dissociate from transferrin and assume a reactive state capable of catalyzing hydroxyl radical formation. The kidney in patients with the nephrotic syndrome appears to be unduly susceptible to free radical injury, as documented by its increase iron content in association with depletion of copper and selenium.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum toxicity in patients with chronic renal failure.

During the past two decades, in association with the commencement of chronic dialysis therapy and prolongation of the uremic state, aluminum toxicity has represented a major cause of morbidity and mortality in uremic patients. The uremic patient has been found to be at higher risk of aluminum loading and toxicity from various sources of parenteral exposure, enhanced gastrointestinal absorption, and compromised ability to eliminate any systemically administered aluminum due to renal impairment. However, the potential sources of aluminum exposure and loading resulting in toxicity in uremic patients have recently been identified. As a result, this toxicity can largely be prevented by eliminating aluminum from the water used to prepare the dialysate, substituting calcium-containing phosphate-binding agents for those containing aluminum, and strict avoidance of the concomitant use of citrate- and aluminum-containing compounds. Thus, in the future, aluminum toxicity should represent a rare and unusual side effect in dialyzed uremic patients.

[Effect of parathyroidectomy (PTX) on aluminum (Al) induced bone disease].

Al-treated or untreated decalcified sections of bone matrix were implanted subcutaneously into the abdominal wall of parathyroidectomized (PTX) or control rats for 21 or 28 days. The bone remodeling and Al, Ca content in the implants were measured by using histomorphometry and atomic absorption spectrum method. The results showed that bone area, osteoclast number, osteoblast number and bone mineralization rate of Al-treated or untreated bone in PTX rats and of Al-treated bone in control rats were significantly lower than those of untreated bone in control rats (P < 0.05). There was no marked difference between these parameters of Al-treated bone in control rats and untreated bone in PTX rats (P > 0.05), and these of Al-treated bone in PTX rats were the lowest (P > 0.05- < 0.05). Ca contents were consistent with the histological parameters. Bone Al removing rate between PTX and control rats was not markedly different. In conclusion, both PTX and Al impair bone formation and mineralization, bone biopsy and removal of Al from bone is necessary before PTX treatment in uremic patients with secondary hyperparathyroidism.

[Histological classification of uremic bone disease and clinical significance of bone biopsy].

Bone biopsy was performed in 429 cases of uremic bone disease and they were classified histologically into 3 groups--high turnover 129 (30%), low turnover 102 (24%) and mixed type 198 (46%) cases. The histological features of the high turnover type were increased corrected mineralization rate (CMR) and osteoclast member and decreased mineralization lay time (MLT), while those of the low turnover type were on the contrary. In the mixed there were decrease of CMR and increase of MLT and osteoclast number. Bone aluminum positive rate was determined; it was 75% and 80% respectively in the low turnover and mixed type and 29% in high turnover. Biochemical study showed that significantly higher levels of serum PTH and alkaline phosphate in the high turnover type and low levels of serum 1,25(OH)2D3 and 25(OH)D3 in the low turnover. These results suggested that high turnover uremic bone disease is caused by secondary hyperthyroidism and low turnover mainly related to aluminum toxicity or other causes such as vitamin D deficiency.

Increased biliary transferrin excretion following parenteral aluminium administration to rats.

Aluminium accumulates in the livers of patients receiving either parenteral nutrition or haemodialysis. When given parenterally to rats, aluminium causes cholestasis. However, the mechanism of hepatic aluminium uptake and the fate of aluminum in the liver are poorly understood. We examined the effect of parenteral aluminium administration on biliary excretion of transferrin, the major circulating aluminum-binding protein. Male Wistar rats were given parenterally aluminum 5 mg/kg/day for 1-14 days. Bile was collected for 3 hr at the end of the study period. Biliary total protein concentration and IgA/total protein were unaffected by up to 14 days of parenteral aluminium administration. However, biliary transferrin excretion increased with duration of aluminum administration up to five-fold by day 14. Biliary transferrin concentration and transferrin/total protein was higher in aluminum treated rats than controls after 7 and 14 days of study. Hepatic aluminum concentration reached a maximum after 4 days of parenteral aluminum administration, at which time serum bile acid and alanine amino transferase values were not different from controls. Since biliary transferrin is normally derived from the serum, it is likely that aluminum promotes hepatocellular uptake of transferrin and that aluminum enters the hepatocyte bound to transferrin. We postulate that transferrin may direct aluminum to intracellular sites where its toxic effects would be minimized.

Toxicity of tubule fluid iron in the nephrotic syndrome.

This study was carried out in rats with nephrotoxic serum nephritis after autologous phase proteinuria was well established to determine the effect of tubule fluid iron chelation on the course of this disease. Deferoxamine administration caused a reduction in urinary iron potentially capable of catalyzing hydroxyl radical (.OH) formation and kidney iron uptake (224 +/- 60 vs. 398 +/- 152 mg/kg). This was associated with a decrease rate of progression of renal failure over the 21-day study period (creatinine clearance -0. 199 +/- 0.152 vs. -0.509 +/- 0.336 ml/min, P < 0.05) and improved survival (8/8 vs. 4/8, P < 0.05). In addition deferoxamine caused a reduction in urinary transferrin excretion (32 +/- 15 vs. 74 +/- 16 mg/day) and fractional excretion of transferrin (2.01 +/- 1 vs. 5.9 +/- 3.7%) and an increase in serum transferrin levels (229 +/- 36 vs. 139 +/- 45 mg/dl, all P < 0.05). It is suggested that iron presented to the tubule fluid as a result of the glomerular leak for transferrin is dissociated from transferrin. In turn the iron is available in a form capable of catalyzing .OH formation, resulting in lipid peroxidation of tubule cell membranes. Deferoxamine chelation of tubule fluid iron retards the development of both tubulointerstitial injury and superimposed glomerular sclerosis in this model of membranous nephropathy.

Urinary albumin, transferrin and iron excretion in diabetic patients.

The present study was undertaken to determine urinary and serum iron, transferrin and albumin levels in diabetic patients with varying amounts of proteinuria. A highly significant correlation was found between urinary albumin and transferrin excretion over a wide range of urinary albumin excretion (0.005 to 18 g/g creatinine) (r = 0.972). The urine/serum ratio of transferrin and albumin were identical, documenting a similar glomerular leak and tubule handling for these two proteins. In contrast to the above correlation between transferrin and albumin, there was no correlation between iron and either of these proteins until nephrotic range proteinuria had occurred, and even at that time the correlation was much weaker than that found between the proteins (r = 0.680). Urinary iron excretion increased early in the course of diabetic renal disease, being increased in 3 of 11 patients without proteinuria and in 8 of 10 patients with mild proteinuria. All patients with nephrotic range proteinuria had markedly increased urinary iron excretion (150 +/- 166 micrograms/g creatinine vs. 6.4 +/- 0.7 micrograms/g creatinine in controls) and decreased serum iron levels (592 +/- 189 micrograms/liter vs. 979 +/- 394 micrograms/liter in the control group). The iron/transferrin ratio in urine was consistently greater than the iron/transferrin ratio in plasma at all stages of proteinuria. In patients with both subnephrotic and nephrotic range proteinuria, approximately 35 to 40 micrograms Fe/g creatinine was present in the urine with an excess of transferrin. In conclusion, urinary iron excretion is increased early in the course of diabetic renal disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of mineralization of glutaraldehyde-pretreated bovine pericardium by AlCl3. Mechanisms and comparisons with FeCl3, LaCl3, and Ga(NO3)3 in rat subdermal model studies.

In the present study, the authors investigated the mechanism by which Al3+ preincubations inhibited the pathologic calcification of glutaraldehyde-pretreated bovine pericardium (GPBP) implanted subdermally in rats. The concentration dependency of the Al3+ anticalcification effect was compared with that of other trivalent metal ions (Fe3+, Ga3+, La3+) known to interact with calcium phosphates. In vitro incubations of GPBP were carried out in AlCl3 (10(-3) mol/l [molar] to 10(-1) mol/l) to ascertain both the optimal conditions for uptake of Al3+ and the time course of Al3+ dissociation. Al3+ uptake by GPBP was concentration dependent and occurred rapidly, with tissue levels after 1 hour not differing significantly from those after 72 hours of incubation. Analyses of GPBP samples preincubated in AlCl3 (0.1 mol/l, 24 hours) showed that more than 75% of the Al3+ remained tightly bound after 60 days' in vitro release at 37 degrees C, pH 7.4. Preincubations of GPBP in AlCl3 significantly inhibited calcification after subdermal implantation in rats for 60 days (Ca++ = 5.1 +/- 0.9 microgram/mg, 11.5 +/- 4.6 micrograms/mg, 70.3 +/- 23.0 micrograms/mg, mean +/- standard error [SE], for 10(-1) mol/l, 10(-2) mol/l, 10(-3) mol/l AlCl3, respectively), compared with controls (Ca++ = 110.0 +/- 9.3 micrograms/mg). All animals were free of Al3(+)-mediated adverse effects on bone, as determined by light microscopic evaluation of femoral epiphyseal growth plates. Transmission electron microscopy coupled with electron energy loss spectroscopy (EELS) of GPBP incubated in 10(-1) mol l AlCl3 for 24 hours demonstrated discrete Al3+ localization in the sarcolemma and cytoplasmic and nuclear membranes of devitalized pericardial connective tissue cells at intracellular sites coincident with phosphorus loci. Similar intracellular localization remained prominent in explants removed after 60 days; no calcific deposits were noted in these specimens. Preincubations in Fe3+ but not Ga3+ and La3+ solutions yielded significant inhibition of GPBP calcification, which did not differ significantly from that provided by Al3- and had a comparable concentration dependency. Light microscopic examination (Prussian blue staining) and EELS of FeCl3-preincubated explants demonstrated Fe3+ localization within devitalized GPBP connective tissue cells. The authors conclude that Al3+ and Fe3+ significantly inhibit the pathologic mineralization of glutaraldehyde-pretreated bovine pericardium by mechanisms that are likely related to the high affinity of these cations for membrane associated and other intracellular phosphorus loci.

Effect of aluminum on bone matrix inductive properties.

The effect of aluminum on the bone inductive properties of implanted bone matrix was studied in rats. After decalcification femur sections were placed in either 0.1 or 0.01 M AlCl3 or a solution of similar pH without Al for 24 hours. Following 28 days of implantation in subcutaneous pouches the aluminum content was 3232 +/- 1020 and 51 +/- 6 mg/kg in the matrix pretreated with 0.1 and 0.01 M AlCl3. At the same time period following implantation the matrix calcium content was 794 +/- 539 and 3038 +/- 692 mmol/kg in the 0.1 and 0.01 M AlCl3 pretreated groups versus 4252 +/- 579 mmol/kg in the control group (P less than 0.01). In the control group bone histology showed extensive osteoblastic and osteoclastic remodeling, tetracycline labeling and bone formation. In contrast all of these histological features were virtually absent in aluminum treated matrix. Aluminum-induced resistance of bone matrix to collagenase degradation and restoration of bone inductive properties with chelation suggests that aluminum forms intermolecular cross links between collagen fibrils. Aluminum-induced cross links of collagen fibrils and/or its effects on bone inductive proteins present in bone matrix could explain the mechanism by which aluminum induces osteomalacia.