Effect of aluminum on normal and uremic rats: tissue distribution, vitamin D metabolites, and quantitative bone histology

Aluminum intake in the neonatal phase disrupts endochondral ossification in rodents

OBJECTIVE

This study evaluated the effects of aluminum (Al) intake on endochondral ossification during the neonatal phase.

METHOD

Twelve male newborn Gerbils (Meriones unguiculatus) were randomly divided into control (C) and aluminum (Al) groups (n = 6 animals/group). From the 1st to 15th day of life, gerbils received an AlCl₃ solution (10 mg/kg/day) via gavage. The control group received only the saline solution. On the 16th day, their tibias were processed for paraffin embedding and were submitted to histomorphometric, histochemical, and immunohistochemical analyses.

RESULTS

In the epiphyseal cartilage Al did not affect the proteoglycan content or cell proliferation; however, it increased matrix metalloprotease-2 (MMP-2) immunostaining and the hypertrophic layer thickness. In bone, Al decreased trabeculae number, trabecular width, cortical bone width, and proliferation. Furthermore, the relative frequency of bone matrix and fibrillar collagen decreased 3.9% and 16.2%, respectively. The number of osteoclasts and osteocalcin digital optical density (D.O.D) remained the same.

CONCLUSION

The results suggest that Al intake during the neonatal period impairs endochondral ossification by affecting epiphyseal cartilage and bone architecture.

Silicosis decreases bone mineral density in rats

Silicosis is the most common occupational lung disease in China, and is associated with a variety of complications, many of which are poorly understood. For example, recent data indicate that silicosis associates with the development of osteopenia, and in some cases this bone loss is severe, meeting criteria for osteoporosis. Although many factors are likely to contribute to this relationship, including a sedentary lifestyle in patients with advanced silicotic lung disease, we hypothesized that silica might directly reduce bone mineral density. In the present study, six Wistar rats were exposed to silica for 24 weeks in order to induce pulmonary silicosis and examine the relationship to bone mineral density. As expected, all rats exposed to silica developed severe pulmonary fibrosis, as manifested by the formation of innumerable silicotic nodules and the deposition of large amounts of interstitial collagen. Moreover, micro-CT results showed that bone mineral density (BMD) was also significantly reduced in rats exposed to silica when compared control animals and this associated with a modest reduction in serum calcium and 25-hydroxyvitamin D levels. In addition, we found that decreased BMD was also linked to increased osteoclast activity as well as fibrosis-like changes, and to the deposition of silica within bone marrow. In summary, our findings support the hypothesis that silicosis reduces bone mineral density and provide support for ongoing investigations into the mechanisms causing osteopenia in silicosis patients.

Effects of aluminum chloride on normal and uremic adult male rats. Tissue distribution, brain choline acetyltransferase activity, and some biological variables

Normal and uremic adult male rats were given a daily ip injection of 20 mg Al (Al chloride)/kg for 14 d. The results indicate that Al induces a significant decrease in food ingestion, weight gain, and total protein concentration in the plasma. Compared with control animals, very high increases in Al levels were found in plasma and hepatic homogenates (about 36 and 19 times, respectively). In the brain homogenates, the Al increases were lower (about 23%). The brain cholineacetyltransferase activity was reduced: 10.6 and 14.9% in normal and uremic rats, respectively. The nephrectomy and the food restriction did not affect the total protein concentrations in plasma and the cerebral cholineacetyltransferase activity. Both were only found to be reduced in the rats treated by Al chloride.

Effect of aluminium hydroxide administration on normal mice: tissue distribution and ultrastructural localization of aluminium in liver

In order to assess the risk of parenteral aluminium (Al) exposure, we evaluated the effects of intraperitoneal administration of aluminium hydroxide, a compound widely used in medicine. Mice (strain Pzh:SFIS) received intraperitoneally, every two weeks 1 mg Al or 0.1 mg Al for five days a week. Controls received injections of saline. Al concentrations in liver, bone and brain were evaluated by electrothermal atomic absorption spectrometry after exposure to 2 mg, 4 mg, and 6 mg Al. The concentration was the highest in liver and occurred after exposure to only 2 mg Al (265.1 +/- 27.7 mg/kg, 233.5 +/- 28.0 mg/kg). Generally further accumulation was not dose- and treatment-dependent. The only exception was a significant Al increase in the liver after exposure to 6 mg Al, injected 0.1 mg Al five days/week. Development of resorption granulomas was observed in the liver, Al being revealed by Morin fluorescence in constituent macrophages and giant cells. By electron probe X-ray microanalysis, Al was identified predominantly in lysosomes of macrophages and Kupffer cells. In tibia of mice, a dose-dependent Al accumulation was observed. The highest level of Al concentration after the 6 mg treatment was 23.5 +/- 3.82 mg/kg and 25.06 +/- 2.3 mg/kg. The Al concentration in the brain of mice had not changed significantly during Al treatment.

Aluminium-induced bone disease in uremic rats: effect of deferoxamine

We have previously established a rat model of chronic uremia, which is suitable to investigate the effect of various treatment modalities on renal osteodystrophy [1]. After four months subsequent to 5/6 nephrectomy, some animals were treated by gavage for 9 weeks with tap water (controls), or with aluminium (Al-citrate) 3 x 25 mg/week/kg b.wt +/- subsequent deferoxamine (DFO) 3 x 50 mg/week/kg b.wt. for 4 weeks. At termination of the study, serum clinical chemistry, femoral chemical composition and mechanical properties, calvarial parathyroid hormone (PTH)-elicited adenylate cyclase (AC) and phospholipase C (PLC) activities, cross-sectional femoral area, as well as bone histomorphometry, were analyzed. Animals given Al displayed moderately enhanced serum Al and bone Al accumulation, however, DFO-treatment did not fully alleviate bone Al retainment. A small increase in serum PTH was seen in all animals rendered uremic. Furthermore, a marked fall in serum alkaline phosphatase (ALP) below normal controls was observed in Al +/- DFO-treated animals compared with uremic controls. The uremic condition led to reduced femoral ratios of hydroxyproline (HYP) over Ca(2+) and phosphate (P(i)), while Al-intoxication alone enhanced femoral Hyp contents above values seen for normal controls. The protracted ureamia caused a deterioration of long bone resilience and brittleness, however, Al +/- DFO-treatment seemed to normalize the latter. Contrastingly, Al +/- DFO-gavage enhanced time to fracture. Uremic rats intoxicated with Al showed a complete loss of calvarial PTH-sensitive AC and PLC activities. DFO-treatment normalized PTH-elicited PLC, while PTH-susceptible AC remained super-normal. Al apparently exerts a long term down-regulation of both PTH-sensitive signaling systems as evidenced by studies of rat UMR 106 osteosarcoma cells in culture. The uremic condition enhanced endosteal bone resorption as shown by femoral shaft dimension analysis, while Al +/- DFO-treatment insignificantly reversed the condition. Finally, histomorphometrical analyses showed that DFO-administration tended to normalize aberrant trabecular bone volume, while rectifying both bone resorption and degree of mineralization. In conclusion, we assert that Al-intoxication hampers both processes (i.e. formation and resorption) of bone turnover, and that DFO-treatment to a certain extent prevents the uremia- and Al-induced bone disease in rats.

Absorption of silicon and aluminum by hens fed sodium zeolite A with various levels of dietary cholecalciferol

Two experiments were conducted to determine whether 1) serum Si and Al is increased in hens intubated with sodium zeolite A (SZA); and 2) dietary cholecalciferol (vitamin D3) influences the absorption of Si or Al by hens fed SZA. In Experiment 1, hens were intubated at oviposition with 0, 1, or 2 g of SZA. Blood samples were collected from the brachial vein at oviposition, and 4, 8, 12, 16, and 20 h postoviposition. Serum samples were analyzed for Si and Al. Peak serum Si and Al were observed at 4 and 8 h postoviposition, respectively. In Experiment 2, hens consumed commercial layer diets ad libitum containing five levels of dietary cholecalciferol (100 to 500 IU/kg) with or without .75% SZA for 6 wk. Blood samples were collected at the end of the 6-wk period by cardiac puncture at oviposition. When dietary cholecalciferol was increased from 100 to 200 IU/kg of diet there was an increase (P < .05) in serum Si but not Al. Levels of cholecalciferol above 200 IU/kg did not produce an additional increase in serum Si. The results showed increased (P < .01) serum concentrations of Si and Al for hens intubated with or fed SZA. It was concluded that Si and Al from SZA are absorbed by commercial Leghorn hens, and a possible involvement of Si or Al should be considered in the mechanism of action of SZA associated with improved eggshell quality and bone development.

Experimental osteodystrophy of chronic renal failure induced by aluminum- and ferric-nitrilotriacetate in Wistar rats

The aluminum (AI) and iron (Fe) chelate complexes of nitrilotriacetate (NTA) cause renal insufficiency when they are administered intraperitoneally to rats. Their effects on bone metabolism were studied in 4 week old Wistar rats. Daily intraperitoneal administration of AI-NTA (3mg AI/kg for 11 weeks) induced osteomalacia, impaired bone growth, decreased bone mineral density, lower serum PTH levels than normal as well as renal insufficiency. Al staining showed diffuse deposition in the trabecula and a strong linear band of aluminum deposited at the mineralization front and along the cement line. The osteoid seen markedly within the trabecula was probably the decalcified portion of the bone, the calcium apatite of which was defectively fabricated because of diffuse Al deposition in the trabecula. Al deposition along the cement line would make it much more susceptible to external shear stress than normal. Although daily intraperitoneal administration of Fe-NTA (6 mg Fe/kg for 11 weeks) caused impaired bone growth, decreased bone mineral content and renal insufficiency, the osteoid volume did not increase. Fe staining showed that Fe was deposited diffusely in the cytoplasm of osteoblasts. The results of this study demonstrated that during renal insufficiency, different minerals exhibit different modes of action on bone metabolism, and that Al-NTA is useful for experimental animal models of Al-induced osteomalacia in renal insufficiency.

Influence of short-term aluminum exposure on demineralized bone matrix induced bone formation

The effects of aluminum exposure on bone formation employing the demineralized bone matrix (DBM) induced bone development model were studied using 4-week-old Sprague-Dawley rats injected with a saline (control) or an aluminum chloride (experimental) solution. After 2 weeks of aluminum treatment, 20-mg portions of rat DBM were implanted subcutaneously on each side in the thoracic region of the control and experimental rats. Animals were killed 7, 12, or 21 days after implantation of the DBM and the developing plaques removed. No morphological, histochemical, or biochemical differences were apparent between plaques from day 7 control and experimental rats. Plaques from day 12 control and experimental rats exhibited cartilage formation and alkaline phosphatase activity localized in osteochondrogenic cells, chondrocytes, osteoblasts, and extracellular matrix. Unlike the plaques from control rats that contained many osteoblastic mineralizing fronts, the plaques from the 12-day experimental group had a preponderance of cartilaginous tissue, no evidence of mineralization, increased levels of alkaline phosphatase activity, and a reduced calcium content. Plaques developing for 21 days in control animals demonstrated extensive new bone formation and bone marrow development, while those in the experimental rats demonstrated unmineralized osteoid-like matrix with poorly developed bone marrow. Alkaline phosphatase activity of the plaques continued to remain high on day 21 for the control and experimental groups. Calcium levels were significantly reduced in the experimental group. These biochemical changes correlated with histochemical reductions in bone calcification.(ABSTRACT TRUNCATED AT 250 WORDS)

Impairment of bone formation with aluminum and ferric nitrilotriacetate complexes

The deleterious effects of aluminum(AL) and iron(Fe) on bone formation were studied in the presence of nitrilotriacetate (NTA) as a chelator. Both Al-NTA (1.0-1.5 mg Al/kg/day, n = 12)- and ferric nitrilotriacetate (Fe-NTA) (2.0 mg/kg/day, n = 4)-treated Wistar rats showed renal insufficiency blood urea nitrogen [BUN] levels of 25 +/- 8.8-20 +/- 0.7 compared to 12 +/- 0.7-11 +/- 0.4 mg/dl), osteomalacia with a relative osteoid volume of 31.5 +/- 5.6-13.2 +/- 2.4 compared to 4.6 +/- 1.8-0.83 +/- 0.12%, and bone growth retardation (3.1 +/- 0-3.0 +/- 0.2 compared to 3.4 +/- 0-3.3 +/- 0.1 cm) in 24 control rats. Dietary vitamin E(VE) supplementation prevented the Fe-NTA-induced impairment, but not the Al-NTA toxicity. Aluminum was deposited at the interface between osteoid and mineralized bone, while Fe was deposited in the osteoblasts and osteoclasts. There seems to be a positive correlation between hypophosphatemia and osteomalacia but carboxy-terminal parathyroid hormone (C-PTH) and calcium (Ca) levels in the serum were not related to the degree of osteomalacia. Administration of Al-NTA results in more bone Al deposition than that of aluminum chloride (AlCl3) (450 +/- 40 compared to 211 +/- 18 mg/kg fat-free dry weight). The Fe-NTA bone change is related to VE-preventable cellular injury, being consistent with the notion that Fe-NTA toxicity is caused by lipid peroxidation. Al-NTA can be used as an animal model of renal osteodystrophy. Osteodystrophy by Al in chronic renal failure may be mediated by the intrinsic chelator or chelating substance(s) retained in the body fluid due to renal insufficiency.

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.

Effect of parathyroidectomy on aluminum toxicity and azotemic bone disease in the rat

In maintenance dialysis patients, low-turnover osteomalacia and aplastic bone disease are generally attributed to aluminum toxicity. Both groups of patients have a relative deficiency of PTH. The reason for the development of osteomalacia versus aplastic bone disease is unclear. The present study was performed to evaluate whether parathyroidectomy (PTX) modifies the effect of aluminum administration on bone histology in renal failure. Seven groups of pair-fed rats were studied: normals (N); renal failure (RF); RF + PTX; PTX; RF + aluminum (AL); RF + PTX + AL; and PTX + AL. Aluminum was administered intraperitoneally 5 days/week for 6 weeks. All groups were sacrificed at 6 weeks. Renal failure increased the serum calcium in both the parathyroid intact (RF versus N, 11 +/- 0.1 versus 10 +/- 0.3 mg/dl, X +/- SEM, P less than 0.05) and calcium-supplemented PTX groups (PTX + RF versus PTX, 9.7 +/- 0.2 versus 9.2 +/- 0.2 mg/dl, P less than 0.05). After PTX, aluminum administration increased the serum calcium (PTX + AL versus PTX, 9.8 +/- 0.3 versus 9.2 +/- 0.2, P less than 0.05, and PTX + RF + AL versus PTX + RF, 10.8 +/- 0.1 versus 9.7 +/- 0.2 mg/dl, P less than 0.05). In rats with renal failure receiving aluminum, PTX decreased osteoid volume and surface but not osteoid thickness. Rats receiving aluminum did not mineralize bone. Additionally, in PTX rats receiving aluminum, renal failure per se increased osteoblast surface, osteoid surface, osteoid volume, and osteoclast number.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum administration in the rat separately affects the osteoblast and bone mineralization

Aluminum administration in the experimental animal results in osteomalacia as characterized by osteoid accumulation and decreased mineralization. Previous in vivo and in vitro studies have indicated that either aluminum directly inhibits mineralization or is toxic to the osteoblast. In the present study, PTH was continuously infused in rats with aluminum-induced osteomalacia to evaluate whether aluminum administration decreased mineralization without a concomitant decrease in osteoblasts. Four groups of rats were studied: chronic renal failure (CRF); CRF + aluminum (AL); CRF + PTH; and CRF + PTH + AL. Rats were sacrificed 5 and 12 days after aluminum or diluent administration; in the PTH groups, bovine PTH (1-34) was administered at 2 units/h via a subcutaneously implanted Alzet pump. Aluminum administration decreased osteoblast surface, increased osteoid accumulation, and produced a cessation of bone formation. The infusion of PTH alone increased osteoblast surface and bone formation. The simultaneous administration of aluminum and PTH resulted in an osteoblast surface intermediate between aluminum and PTH alone; however, despite a PTH-induced restoration of osteoblast surface, bone formation did not increase. These findings indicate (1) aluminum is toxic to osteoblasts and also directly inhibits mineralization even when osteoblasts are not decreased; (2) PTH is capable of increasing osteoblasts even in the presence of aluminum; and (3) despite a PTH-induced increase in osteoblast surface, mineralization of osteoid was not improved.

[Aluminum toxicity]

In view of the increasing pollution of our environment and forest decline, growing interest has been focused on aluminum toxicity. Aluminum is one of the most abundant metals and commonly present in tap water, beverages, food, cosmetics, and pharmaceutical preparations. Thus everybody is exposed to aluminum to a greater or lesser extent. It is now beyond any doubt that aluminum intoxication may cause encephalopathy, fracturing vitamin D resistant osteomalacia, and microcytic anemia in patients with chronic renal insufficiency as well as in experimental animals. The risk of aluminum intoxication has also to be considered in several other groups. These include elderly individuals with physiologically impaired excretory renal function who are treated with aluminum-containing antacids, patients with chronic liver disease, infants who are fed highly aluminum-contaminated formula at a time when their excretory renal function has not jet fully developed, patients on total parenteral nutrition, and, possibly, patients with Alzheimer's disease.

The evolution of osteomalacia in the rat with acute aluminum toxicity

Aluminum toxicity is the presumed cause of aluminum-associated osteomalacia. In animal models, osteomalacia has been produced after a prolonged course of aluminum. In the present study, rats with renal failure received 20 mg intraperitoneal aluminum during a 2 day period. This model allows sequential observations in the development of osteomalacia. Rats were sacrificed and studied 5, 12, 25, and 40 days after aluminum administration. No differences were observed in serum calcium, phosphorus, or creatinine as a consequence of aluminum administration. Compared with control rats, parathyroid hormone was decreased at 12 and 25 days. A direct correlation was present between plasma and bone aluminum at 12 days (r = 0.92, p less than 0.01), 25 days (r = 0.85, p less than 0.005), and 40 days (r = 0.88, p less than 0.001) but not 5 days after aluminum administration. Plasma aluminum peaked at 5 days (727 +/- 89 micrograms/liter, mean +/- SEM) and bone aluminum at 40 days (273 +/- 40 micrograms/g). Aluminum had profound effect on bone histology. At 5 days there was a decrease in osteoblast surface and osteoid surface; at 12 days osteoblast surface and osteoid surface returned to normal but osteoclast surface decreased. Subsequently there was a progressive increase in osteoid surface and osteoid volume. Bone formation rate measured at 12, 25, and 40 days was decreased at these intervals. In conclusion, (1) high plasma aluminum may be directly toxic to the osteoblast; (2) progressive osteoid accumulation is secondary to matrix (osteoid) deposition, which exceeds the depressed bone formation rate; (3) the progressive decrease in plasma aluminum and increase in bone aluminum suggest that bone has a high affinity for aluminum but may have a relatively slow rate of uptake at any given time; (4) aluminum may directly decrease parathyroid hormone; (5) the correlation between plasma and bone aluminum suggest an exchange is present; and (6) aluminum toxicity may independently affect the osteoblast and bone mineralization.

The influence of early parathyroidectomy on aluminum-induced rickets in growing uremic rats

Rats were subjected to a two-stage 5/6 nephrectomy and treated with aluminum for 2 and 4 weeks with a cumulative dose of 4.2 and 8.4 mg of aluminum, respectively. Other animals were parathyroidectomized and loaded with 8.4 mg of aluminum for 4 weeks. Histomorphometry and electron microscopy (tibiae), aluminum tissue (bone, kidney, liver) determination, serum (Ca, Mg, Zn, P, urea, creatinine, alkaline phosphatase, 1,25(OH)2D3, PTH) and urine (creatinine, A1) revealed that: (a) a dose of 8.4 mg aluminum was sufficient to induce rickets within 4 weeks of treatment and was associated with decreased serum calcitriol values and high aluminum accumulation within organs (electron-dense material was found in osteoblasts only); (b) previous parathyroidectomy prevented the occurrence of any aluminum-induced alteration of bone. It was associated with higher calcitriol and phosphorus values than in corresponding non-parathyroidectomized rats and significantly reduced aluminum accumulation within organs. The results was influenced neither by a drop in serum calcium values nor by different degrees of renal failure. We suggest that aluminum-induced rickets in growing uremic rats is prevented or delayed when previous parathyroidectomy has been performed.

Reduced intestinal calcium and dietary calcium intake, increased aluminum absorption, and tissue concentration in the rat

To test the influence of calcium (Ca) on aluminum (Al) absorption, Ca was withheld from or added (1mM) to the perfusate of the in situ rat gut. The rats had been maintained on Purina Rat Chow. Ca addition significantly decreased (to 70%) the rate of Al disappearance from the gut and decreased (to 55%) the area under the curve of Al appearance in portal blood. To test the influence of Ca deficiency on Al absorption, rats were maintained on a low-Ca (0.008%) or a Ca-replete (0.5%) diet for 1-4 wk. The in situ gut was prepared, and a perfusate containing approximately 1 microM Ca was used. The rate of Al disappearance from the gut of low-Ca diet rats was significantly faster than from the gut of rats maintained on the Ca-replete diet, averaging 156% of the latter. Al appearance in portal blood was significantly greater (averaging 38%) in rats maintained on the low-Ca diet than in controls. To determine if Ca deficiency influences Al tissue distribution independent of gastrointestinal Al absorption, rats maintained on a low-Ca or a Ca-replete diet received 20 ip Al injections over 1 mo. Rats eating the low-Ca diet demonstrated enhanced tissue Al accumulation in all tissues studied, except for muscle and cerebral cortex. These results demonstrate enhanced Al absorption and tissue retention in the presence of reduced intestinal Ca concentration and reduced Ca intake.

Distribution of aluminium following intraperitoneal injection of aluminium lactate in the rat

An animal experiment was performed to evaluate the absorption and distribution of aluminium in serum and tissues of normal rats. The animals were intraperitoneally injected with an aluminium lactate solution at a pH adjusted to 7.0. Before starting, a short preliminary study was carried out in order to verify the validity of the treatment with aluminium lactate instead of aluminium chloride at endogenous pH 3.4. Thirty-one rats were used in the main experiment, divided in four groups. In treated animals, the total Al-administered dose was 75.6 mg during 78 days of treatment. Furthermore, to evaluate the influence of the parathyroid hormone on Al absorption and/or distribution, 200 USP/rat of parathyroid hormone extract (PTH) were also administered during the last 5 days of the experiment. Aluminium content in serum, tibia, rib, brain, liver, muscle, kidney and spleen was determined. Calcium analysis in serum and bone was also performed. The highest concentrations of aluminium were found in liver and spleen, whereas the lowest level was found in the brain. The PTH effect on Al absorption was evident in brain and bone.

Aluminum and chronic renal failure: sources, absorption, transport, and toxicity

In normal subjects the gastrointestinal tract is a relatively impermeable barrier to aluminum with a low fractional absorption rate for this metal ion. Aluminum absorbed from the gastrointestinal tract is normally excreted by the kidneys; in the presence of impaired renal function aluminum is retained and accumulates in body tissues. Aluminum-containing medications are given, by mouth, to patients with chronic renal failure as phosphate-binding agents for the therapeutic control of hyperphosphatemia. Patients with chronic renal failure are also exposed to aluminum in domestic tap-water supplies used either for drinking or, in those on dialysis treatment, in the preparation of their dialysate. In patients with end-stage chronic renal failure, particularly in those on treatment by hemodialysis, the accumulation of aluminum in bone, brain, and other tissues is associated with toxic sequelae. An increased brain content of aluminum appears to be the major etiological factor in the development of a neurological syndrome called either "dialysis encephalopathy" or "dialysis dementia"; an increased bone content causes a specific form of osteomalacia. An excess of aluminum also appears to be an etiological factor in a microcytic, hypochromic anemia that occurs in some patients with chronic renal failure on long-term treatment with hemodialysis. The various mechanisms involved in the toxic phenomena associated with the accumulation of aluminum in body tissues have not been clearly defined but are the subject of extensive investigations.

Aluminum intoxication in vitamin D-deficient rats: studies of bone aluminum localization and histomorphometry before and after vitamin D repletion

Aluminum accumulation by both dialysis patients and nonuremic patients, requiring chronic total parenteral nutrition, may be an etiological factor in the development of severe osteomalacia. To study the role of aluminum toxicity in bone, further experiments have been conducted in the nonuremic, vitamin D-deficient rat. Weanling rats were raised on vitamin D-deficient diets, and half received parenteral aluminum (5 mg/wk), for 30 days. In the first experiment low doses of 25-OH cholecalciferol (500 ng/week) were given subcutaneously for a further 30 days. Control rats were maintained on a similar protocol, but were supplemented with cholecalciferol (5 micrograms/week) from the outset until sacrifice at 60 days. In the second experiment a single bolus of cholecalciferol (5 micrograms) was given to study short-term changes in serum biochemistry and bone histology at 96 hr. Quantitative bone histomorphometric analyses of the proximal tibial metaphysis were made in all experimental groups. In the experimental vitamin D-deficient group, with the highest bone aluminum content (as assessed by extraction of whole bone aluminum), X-ray microanalysis was performed to determine the distribution of aluminum in bone tissue and bone cell organelles. The results showed that control rats treated with prolonged aluminum therapy (30 mg over 60 days) had evidence of both reduced osteoid matrix synthesis and mineralization. However, in vitamin D-deficient rats, there was no evidence that aluminum exacerbated the osteomalacic lesion, even though there was histochemical evidence of aluminum deposition at the bone-osteoid interface.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum and bone disorders: with specific reference to aluminum contamination of infant nutrients

Aluminum (Al) impairment of bone matrix formation and mineralization may be mediated by its direct effect on bone cells or indirectly by its effect on parathyroid hormone and calcium metabolism. Its toxic effects are proportional to tissue Al load. Al contamination of nutrients depends on the amount of Al present naturally in chemicals or from the manufacturing process. Intravenous calcium, phosphorus, and albumin solutions have high Al (greater than 500 micrograms/L), whereas crystalline amino acid, sterile water, and dextrose water have low Al (less than 50 micrograms/L) content. Enteral nutrients including human and whole cow milk have low Al, whereas highly processed infant formulas with multiple additives, such as soy formula, preterm infant formula, and formulas for specific disorders are heavily contaminated with Al. Healthy adults are in zero balance for Al. The gastrointestinal tract excludes greater than 95% of dietary Al, and kidney is the dominant organ for Al excretion. However, even with normal renal function, only 30-60% of an Al load from parenteral nutrition is excreted in the urine, resulting in tissue accumulation of Al. The risk for Al toxicity is greatest in infants with chronic renal insufficiency, recipients of long term parenteral nutrition, i.e., no gut barrier to Al loading, and preterm infants with low Al binding capacity. The rapid growth of the infant would theoretically potentiate Al toxicity in all infants, although the critical level of Al loading causing bone disorders is not known. To minimize tissue burden, Al content of infant nutrients should be similar to "background" levels, i.e., similar to whole milk (less than 50 micrograms/L).

Renal osteodystrophy: some new questions on an old disorder

The two major lesions of renal osteodystrophy are osteitis fibrosa cystica (OFC) and osteomalacia (OM). OFC is the characteristic bone lesion of uremic hyperparathyroidism. Although renal failure causes predictable parathyroid hyperplasia, the precise pathogenetic mechanism is still not defined. The "hyperphosphatemia-hypocalcemia-parathyroid hormone (PTH) hypersecretion" sequence of events is no longer an adequate model for the pathogenesis of uremic hyperparathyroidism. Other abnormalities associated with uremia include reduced 1,25-dihydroxyvitamin D (1,25D) synthesis, changes in intracellular phosphorus content or transcellular phosphate fluxes, or alteration in PTH metabolism, eg, change in set-point for PTH secretion. Each abnormality interacts with others and contributes to PTH hypersecretion, but none can completely account for the development and persistence of hyperparathyroidism in renal failure. The possibility that uremia may directly cause parathyroid hyperplasia remains open. It is also possible that factor(s) that initiate hyperparathyroidism may turn out to be quite different from that which sustains the hyperparathyroid state. Although both vitamin D-deficient and vitamin D-resistant OM may develop in patients with renal failure, the majority of uremic OM seen currently is "vitamin D-refractory." Although now there is persuasive evidence implicating aluminum (Al) accumulation as the major pathogenetic cause for the mineralization defect seen in this disorder, additional disturbances may play important contributory roles. Such factors would include extraskeletal effects of Al, differences in host-susceptibility to this element, the localization of Al within bone, uremia per se, and the participation of other metals and toxins. Finally, possible interactions between hyperparathyroidism and OM of uremia are speculated on.

Induction of de novo bone formation in the beagle. A novel effect of aluminum

To define the primary effects of aluminum on bone in the mammalian species, we examined the dose/time-dependent actions of aluminum in normal beagles. Administration of low dose aluminum (0.75 mg/kg) significantly elevated the serum aluminum (151.7 +/- 19.9 micrograms/liter) compared with that in controls (4.2 +/- 1.35 micrograms/liter) but did not alter the calcium, creatinine, or parathyroid hormone. After 8 wk of therapy, bone biopsies displayed reduced bone resorption (2.6 +/- 0.63 vs. 4.5 +/- 0.39%) and osteoblast covered bone surfaces (2.02 +/- 0.51 vs. 7.64 +/- 1.86%), which was indicative of low turnover. In contrast, prolonged treatment resulted in increased bone volume and trabecular number (38.9 +/- 1.35 vs. 25.2 +/- 2.56% and 3.56 +/- 0.23 vs. 2.88 +/- 0.11/mm) which was consistent with uncoupled bone formation. Administration of higher doses of aluminum (1.20 mg/kg) increased the serum aluminum further (1242.3 +/- 259.8 micrograms/liter) but did not affect calcium, creatinine, or parathyroid hormone. However, after 8 wk of treatment, bone biopsies displayed changes similar to those after long-term, low-dose therapy. In this regard, an increased trabecular number (3.41 +/- 0.18/mm) and bone volume (36.5 +/- 2.38%) again provided evidence of uncoupled bone formation. In contrast, in this instance poorly mineralized woven bone contributed to the enhanced bone volume. High-dose treatment for 16 wk further enhanced bone volume (50.4 +/- 4.61%) and trabecular number (3.90 +/- 0.5/mm). These observations illustrate that aluminum may stimulate uncoupled bone formation and induce a positive bone balance. This enhancement of bone histogenesis contrasts with the effects of pharmacologic agents that alter the function of existing bone remodeling units.

Effects of 1 alpha,25- and 24R,25-dihydroxyvitamin D3 on aluminum-induced rickets in growing uremic rats

Rats were subjected to a two-stage subtotal nephrectomy or sham operation, and treated with aluminum (Al) or both aluminum and vitamin D3 metabolites for 5 weeks with a cumulative dose of 13.6 mg aluminum. Animals were injected with 3H-thymidine and 3H-proline. The following analyses were performed: quantitative histology of tibial metaphyses and cytomorphometric electron microscopy of osteoclasts, quantitative (ICP-spectroscopy) and qualitative determination (histochemical staining) of aluminum within organs, and serum biochemistry (Ca, P, Mg, vitamin D3 metabolites, alkaline phosphatase, urea). The following new facts of the aluminum-related bone disease became evident: (a) Application of aluminum to growing uremic rats induced rickets, whose major epiphyseal growth plate changes were 1 alpha,25(OH)2D3-dependent. Addition of 1 alpha,25(OH)2D3 prevented the formation of rachitic metaphysis, but failed to prevent osteoid accumulation on epiphyseal and metaphyseal trabecular surfaces. Moreover, calcitriol produced hyperosteoidosis and osteosclerosis in the same rats. Aluminum did not alter the function of osteoblasts, while osteoclasts seemed inactivated. (b) The development of rickets was associated with suppressed serum levels of 1,25(OH)2D3, reduced phosphorus level and the high content of aluminum in the bone, kidney, and liver. The addition of 24R,25(OH)2D3 markedly exaggerated the reduction of serum levels of calcitriol. We suggested that aluminum induces rickets in growing uremic rats, which consists of two components: vitamin D refractory osteomalacia and 1 alpha,25(OH)2D3-dependent epiphyseal growth plate changes.

Thyroparathyroidectomy modifies the skeletal response to aluminum loading in the rat

Diminished parathyroid hormone (PTH) secretion may contribute to the accumulation of aluminum (Al) in bone and to impaired bone formation in Al-related bone disease. Therefore, intact (AL, N = 9) and thyroparathyroidectomized (TPTX-AL, N = 9) rats were given intraperitoneal injections of Al, 2 mg/day, for 42 days; intact control (C, N = 11) and TPTX control (TPTX-C, N = 9) animals received i.p. injections of vehicle only. Quantitative bone histology and measurements of mineralized bone formation (Rbf) using double tetracycline labeling were done for cortical and for trabecular bone; trabecular bone aluminum content (BA) was determined by histochemical methods. BA did not differ between AL and TPTX-AL, 33 +/- 13% versus 39 +/- 14%, and Rbf decreased similarly from control values in both Al-treated groups. In contrast, osteoid production was impaired to a greater extent in TPTX-AL than in AL. Thus, osteoid area and osteoid seam width were each lower in TPTX-AL than in TPTX-C; these values did not differ between AL and C. TPTX can aggravate Al induced reductions in osteoid synthesis, and low serum PTH levels may contribute to the pathogenesis of aplastic bone. However, reductions in Rbf during Al loading are not mediated by PTH.

Calcitriol, parathyroid hormone, and accumulation of aluminum in bone in dogs with renal failure

Accumulation of aluminum in bone is a frequent finding in patients requiring chronic dialysis and is associated with considerable morbidity and/or mortality. Until now, evidence seemed to point to relatively low circulating levels of parathyroid hormone as a contributing factor, but because levels of parathyroid hormone and calcitriol are interrelated, calcitriol might be also involved. In this study we employed an animal model to evaluate the single and combined effects of parathyroid hormone and calcitriol on bone aluminum accumulation. The results show significantly less aluminum accumulation in calcitriol-replete dogs independent of the presence or absence of parathyroid hormone. These results indicate that low levels of calcitriol may play a role in the development of aluminum related bone disease. Further studies are needed to demonstrate whether administration of calcitriol in patients with renal insufficiency will prevent development of aluminum-related bone disease.

Tissue and cellular basis for impaired bone formation in aluminum-related osteomalacia in the pig

Bone formation is impaired in aluminum-associated bone disease. Reductions in the number of osteoblasts or in the function of individual osteoblasts could account for this finding. Thus, quantitative bone histology and measurements of bone formation were done at three skeletal sites in piglets given aluminum (Al) parenterally, 1.5 mg/kg per d, for 8 wk (Al, n = 4) and in control animals (C, n = 4). Bone Al was 241 +/- 40 mg/kg per dry weight in Al and 1.6 +/- 0.9 in C, P less than 0.001. All Al-treated animals developed osteomalacia with increases in osteoid seam width, osteoid volume, and mineralization lag time at each skeletal site, P less than 0.05 vs. C for all values. Mineralized bone formation at the tissue level was lower in Al than in C, P less than 0.05 for each skeletal site, due to reductions in active bone forming surface. Bone formation at the cellular level was similar in each group, however, and total osteoid production by osteoblasts did not differ in C and Al. Aluminum impairs the formation of mineralized bone in vivo by decreasing the number of active osteoblasts, and this change can be distinguished from the effect of aluminum to inhibit, either directly or indirectly, the calcification of osteoid.

The effects of aluminum loading on the renal response to parathyroid hormone in the vitamin D-replete rat

Aluminum (Al) may cause vitamin D-resistant osteomalacia and depress the serum levels of immunoreactive parathyroid hormone (iPTH) in patients treated with maintenance dialysis and those on total parental nutrition (TPN). Both conditions have been associated with low serum levels of 1,25(OH)2-vitamin D (1,25(OH)2D). Al may inhibit PTH secretion in vitro; however, induction of hypocalcemia can enhance endogenous PTH secretion in Al-loaded dogs and TPN patients. Despite hypocalcemia and/or increased endogenous iPTH levels, Al-loaded TPN patients fail to show the expected rise in serum 1,25(OH)2D levels. Such observations suggest that Al may impair the renal response to PTH. We studied vitamin D-replete rats given Al or saline vehicle IP for 5 days. Al and control rats then received a saline infusion with an IV bolus of PTH 1-34. Urinary cyclic AMP and P excretion rose in Al and control rats by 1 hr post-PTH, without differences between the groups. Serum P and ionized Ca levels were not different between Al and control rats. In other Al and control rats, serum 1,25(OH)2D levels were measured after saline without PTH. Serum 1,25(OH)2D levels were higher in controls given PTH than in those without, but 1,25(OH)2D levels were not different between Al rats given PTH and those with none. Thus, aluminum does not affect cyclic AMP or P excretion but may impair 25(OH)D-1 alpha-hydroxylase activity in response to PTH.

Aluminum-associated bone disease in chronic renal failure: high prevalence in a long-term dialysis population

Twenty-seven asymptomatic patients treated with hemodialysis longer than 8 years (mean 12.9 +/- 3.1 years) underwent bone biopsy to determine the prevalence of aluminum-associated bone disease. None had excess aluminum exposure from the dialysate. Ten patients (37%) had aluminum-associated bone disease as defined by a bone formation rate (BFR) below normal in the presence of stainable bone aluminum that covered more than 25% of the trabecular surface. The predominant type of bone histology in this group was the aplastic lesion characterized by low bone turnover, a decreased number of osteoblasts, and lack of excess unmineralized osteoid. Osteoblastic osteoid was highly correlated with stainable surface bone aluminum (r = -.82, p less than .001). Among the dynamic bone parameters, the double-tetracycline labeled surface was a more sensitive indicator of impaired bone function than was the bone apposition rate (BAR), since half of the patients with aluminum-associated bone disease had a normal BAR. In all of the biopsies the extent of double-labeled surfaces was inversely proportional to the amount of stainable aluminum on the bone surface (r = -.71, p less than .001), whereas stainable bone aluminum did not correlate with BAR. In seven of the patients with aluminum-associated bone disease, amino-terminal PTH levels were in the normal range while only one patient had a normal plasma mid-region PTH. PTH correlated directly with osteoblastic osteoid, BFR, and double-labeled surfaces. These results indicate that long-term oral aluminum intake in hemodialysis patients results in a high prevalence of aluminum-associated bone disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Tissue distribution of subcutaneously administered aluminum chloride in weanling rabbits

The purpose of our investigation was to determine blood and tissue levels of aluminum (Al) in normal young rabbits. Furthermore, we wished to determine tissue distribution and accumulation of Al as related to its blood concentration in Al-dosed rabbits. The levels of Al accumulated were determined in different tissues of growing rabbits after continuous subcutaneous administration of Al chloride (3.78 mg/d) for 28 d. No signs of toxicity were apparent from comparisons of hematocrit or weight gain between control and Al-dosed rabbits. The largest concentration of the Al was observed in bone, which was also found to have the highest levels in the control rabbit tissues. Following bone, the experimental animals showed the greatest increase of Al levels in kidney cortex, kidney medulla, liver, testes, skeletal muscle, heart, brain white matter, and brain hippocampus, in that order. No significant difference was found in brain grey matter between control and experimental animals. As the brain tissue of the Al-treated animals had the lowest Al level of the tissues measured, it appears that there is a partial blood-brain barrier to entry of Al.

The effect of desferrioxamine on concentration and distribution of aluminum in bone

Aluminum (Al) loaded rats were injected chronically with either desferrioxamine (DFO) or saline. Six rats of each treatment group were sacrificed before and after one, three, and nine months of treatment for determination of tissue and serum Al, and for histological localization of bone Al. Urinary Al was measured during one week before sacrifice. Al loading caused significant elevations of bone (136.2 +/- 22.0 micrograms/g) and liver (114.4 +/- 41.9 micrograms/g) aluminum. Serum Al in DFO-treated animals was not different from their controls (216.4 +/- 80.5 and 226.9 +/- 42.9 micrograms/liter after one month; 151.0 +/- 20.8 and 138.0 +/- 63.9 micrograms/liter after three months; 72.1 +/- 40.7 and 61.6 +/- 14.2 micrograms/liter after nine months in control and DFO-treated animals respectively). Urinary Al excretion in the DFO-treated group was increased at all times as compared to the control rats. A decrease of muscle Al occurred after one month of DFO treatment, but no significant differences of liver and bone Al could be shown between DFO-treated rats and their controls. Al decreased to a comparable degree in all tissues of both DFO and control rats after nine months of treatment. Histomorphometric examination of the bones showed that after one and three months of treatment, significantly less Al was localized at the calcification front of DFO-treated rats compared to their controls (75.6 +/- 6.9% and 53.4 +/- 20.9% after one month; 52.3 +/- 10.2% and 34.8 +/- 10.6% after three months in control and DFO rats respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum accumulation in individuals with normal renal function

In individuals with normal renal function, oral aluminum may be absorbed, but the kidneys are able to excrete the load, and significant pathology is not seen. If aluminum is given parenterally, however, it can accumulate in tissues and lead to osteomalacia or aplastic bone lesions. Low calcitriol and PTH levels are often seen, and may contribute to the bone disease. These findings in individuals with normal renal function add to the growing body of evidence that aluminum is toxic to bone.