Animal model of aluminum-induced osteomalacia: role of chronic renal failure

Urine Aluminum Concentration as a Possible Implant Biomarker of Pseudomonas aeruginosa Infection Using a Fluorine- and Phosphorus-Doped Ti-6Al-4V Alloy with Osseointegration Capacity

Joint prosthesis failure is mainly related to aseptic loosening and prosthetic joint infections, both associated with high morbidity and a substantial cost burden for patients and health systems. The development of a biomaterial capable of stimulating bone growth while minimizing bacterial adhesion would reduce the incidence of prosthetic failure. Using an in vivo rabbit model, this study evaluates the osseointegration effect of the fluorine (F)- and phosphorus (P)-doped bottle-shaped nanostructured (bNT) Ti-6Al-4V alloy and effectiveness of monitoring urine aluminum concentration to determine the presence of Pseudomonas aeruginosa infection in Ti-6Al-4V implants. Unlike chemically polished (CP) Ti-6Al-4V alloy implants, bNT Ti-6Al-4V alloy implants promoted osseointegration and showed effectiveness as a biomaterial marker. The bNT Ti-6Al-4V alloy implants were associated with a twofold increase in bone thickness and up to 15% greater bone density compared to the CP alloy. Additionally, bNT Ti-6Al-4V alloy implants allowed for discrimination between P. aeruginosa-infected and noninfected animals for 15 days postoperatively, as indicated by the decrease of aluminum concentration in urine, while this difference was only appreciable over the first 7 days when CP Ti-6Al-4V alloy implants were used. Therefore, bNT Ti-6Al-4V alloys could have clinical applications by detecting the infection and by avoiding aseptic loosening.

Aluminum as a toxicant

Although aluminum is the most abundant metal in nature, it has no known biological function. However, it is known that there is a causal role for aluminum in dialysis encephalopathy, microcytic anemia, and osteomalacia. Aluminum has also been proposed to play a role in the pathogenesis of Alzheimer’s disease (AD) even though this issue is controversial. The exact mechanism of aluminum toxicity is not known but accumulating evidence suggests that the metal can potentiate oxidative and inflammatory events, eventually leading to tissue damage. This review encompasses the general toxicology of aluminum with emphasis on the potential mechanisms by which it may accelerate the progression of chronic age-related neurodegenerative disorders.

Systematic review of potential health risks posed by pharmaceutical, occupational and consumer exposures to metallic and nanoscale aluminum, aluminum oxides, aluminum hydroxide and its soluble salts

Abstract Aluminum (Al) is a ubiquitous substance encountered both naturally (as the third most abundant element) and intentionally (used in water, foods, pharmaceuticals, and vaccines); it is also present in ambient and occupational airborne particulates. Existing data underscore the importance of Al physical and chemical forms in relation to its uptake, accumulation, and systemic bioavailability. The present review represents a systematic examination of the peer-reviewed literature on the adverse health effects of Al materials published since a previous critical evaluation compiled by Krewski et al. (2007) . Challenges encountered in carrying out the present review reflected the experimental use of different physical and chemical Al forms, different routes of administration, and different target organs in relation to the magnitude, frequency, and duration of exposure. Wide variations in diet can result in Al intakes that are often higher than the World Health Organization provisional tolerable weekly intake (PTWI), which is based on studies with Al citrate. Comparing daily dietary Al exposures on the basis of "total Al"assumes that gastrointestinal bioavailability for all dietary Al forms is equivalent to that for Al citrate, an approach that requires validation. Current occupational exposure limits (OELs) for identical Al substances vary as much as 15-fold. The toxicity of different Al forms depends in large measure on their physical behavior and relative solubility in water. The toxicity of soluble Al forms depends upon the delivered dose of Al(+3) to target tissues. Trivalent Al reacts with water to produce bidentate superoxide coordination spheres [Al(O2)(H2O4)(+2) and Al(H2O)6 (+3)] that after complexation with O2(•-), generate Al superoxides [Al(O2(•))](H2O5)](+2). Semireduced AlO2(•) radicals deplete mitochondrial Fe and promote generation of H2O2, O2 (•-) and OH(•). Thus, it is the Al(+3)-induced formation of oxygen radicals that accounts for the oxidative damage that leads to intrinsic apoptosis. In contrast, the toxicity of the insoluble Al oxides depends primarily on their behavior as particulates. Aluminum has been held responsible for human morbidity and mortality, but there is no consistent and convincing evidence to associate the Al found in food and drinking water at the doses and chemical forms presently consumed by people living in North America and Western Europe with increased risk for Alzheimer's disease (AD). Neither is there clear evidence to show use of Al-containing underarm antiperspirants or cosmetics increases the risk of AD or breast cancer. Metallic Al, its oxides, and common Al salts have not been shown to be either genotoxic or carcinogenic. Aluminum exposures during neonatal and pediatric parenteral nutrition (PN) can impair bone mineralization and delay neurological development. Adverse effects to vaccines with Al adjuvants have occurred; however, recent controlled trials found that the immunologic response to certain vaccines with Al adjuvants was no greater, and in some cases less than, that after identical vaccination without Al adjuvants. The scientific literature on the adverse health effects of Al is extensive. Health risk assessments for Al must take into account individual co-factors (e.g., age, renal function, diet, gastric pH). Conclusions from the current review point to the need for refinement of the PTWI, reduction of Al contamination in PN solutions, justification for routine addition of Al to vaccines, and harmonization of OELs for Al substances.

Dynamic analysis of exposure to aluminum and an acidic condition on bone formation in young growing rats

The toxic effects of exposure to aluminum (Al) in an acidic condition on bone formation in young growing rats were studied. Wistar rats were divided randomly into Al-treated group (100mg Al(3+)/L; pH 5.6) and control group (distilled water). Al-treated rats showed lower body weight, lower serum pH, higher accumulation of Al, in addition to disordered metabolism of calcium and phosphorus compared with control rats. The levels of parathyroid hormone, calcitonin, osteocalcin, procollagen carboxy-terminal propeptide and bone alkaline phosphatase were significantly lower in the Al-treated group than in the control group from days 90, 30, 60, 60 and 90, respectively. The bone mineral density of the distal and proximal femoral metaphysis was significantly lower in the Al-treated group than in the control group on days 120 and 150. These findings suggest that long-term Al exposure in an acidic condition inhibits bone formation and induces bone loss in young growing animals.

Trace metals and degenerative diseases of the skeleton

Aluminum related osteodystrophy is the most important manifestation of trace metal toxicity related to degenerative diseases of the skeleton. Aluminum overload occurs in chronic renal failure patients on hemodialysis treatment and results from transfer from dialysis solutions and from oral intake of aluminum containing phosphate binding gels. Laboratory diagnosis involves serum and bone analysis and bone staining for aluminum. A challenge test with desferrioxamine also aids in the diagnosis. Electrothermal atomic absorption spectrometry is widely used for aluminum detection. Guidelines for toxic concentrations of aluminum have been established.

Biodegradable magnesium scaffolds: Part II: peri-implant bone remodeling

In this study, histomorphometrical parameters of the peri-implant bone remodeling around degrading open-porous scaffolds made of magnesium alloy AZ91D were investigated and compared with the peri-implant bone remodeling around an autologous bone transplant in the contralateral side in a rabbit model after 3 and 6 months. Osteoblast activity was displayed by collagen I (alpha 2) mRNA in situ hybridization. Major scaffold degradation was completed within 3 months after implantation showing no osteolysis around the scaffolds, both after 3 and 6 months. Enhanced formation of unmineralized extracellular matrix and an enhanced mineral apposition rate adjacent to the degrading magnesium scaffolds were accompanied by an increased osteoclastic bone surface, which resulted in higher bone mass and a tendency to a more mature trabecular bone structure around the magnesium scaffolds compared to the control. These results show that even fast-degrading magnesium scaffolds induce extended peri-implant bone remodeling with a good biocompatibility. In summary, this study shows that degrading magnesium scaffolds promote both bone formation and resorption in a rabbit model and are therefore very promising candidates for the development of novel implants in musculoskeletal surgery.

Spectrofluorimetric determination of trace aluminum in diluted hemodialysis solutions

In this study, a spectrofluorimetric method has been developed for the determination of aluminum based on the formation of an aluminum complex with N,N'-disalicylidene-1,3-diamino-2-hydroxypropane (DSAHP). The most suitable pH, solvent medium, complex formation time, Schiff base concentration and temperature were determined. The excitation and emission wavelengths were 270 and 437 nm, respectively, in which the DSAHP-Al complex gave the maximum fluorescence intensity at pH 3.0 and 6.0 in 50% dioxan-50% water medium. Under these conditions, calibration curves were obtained in three different linear limits, and was found that aluminum could be detected within the concentration limit of 0-10.0 microM and the lowest detection limit being 0.27 ng ml(-1). The stoichiometry of the DSAHP-Al complex was also determined spectrofluorimetrically under optimal conditions and the molar ratio of DSAHP-Al was calculated as 2:1. Using the developed method, aluminum was detected in hemodialysis solutions, and the results obtained were similar and comparable with those obtained using the method described in the British Pharmacopoeia within 95% confidence limits. This method can be used successfully for the routine determination of aluminum because it is quick, requires less amount of reactives, is sensitive, reliable and reproducible.

Effects of aluminum on phosphate metabolism in rats: a possible interaction with vitamin D3 renal production

The effect of chronic aluminum (Al) administration on the phosphorous (Pi) metabolism of different target tissues was studied. Male Wistar rats received aluminum lactate for 3 months (5.75 mg/kg bodyweight of Al, i.p., three times per week). The animals were studied at the end of the 1st, 2nd and 3rd month of treatment. They were housed individually in metabolic cages for 4 days to study Pi and calcium (Ca) balance. Daily food and water intakes were recorded for all animals and urine and feces were collected for Pi and calcium assays. After 3 months the Pi intestinal absorption and the Pi deposition in bone were studied using 32Pi. Another group of rats was treated daily for 7 days with calcitriol (0.08 microg/kg body weight in sesame oil, i.p.) and the Pi balance was studied for the last 4 days. The results indicated that chronic administration of Al affected simultaneously the Pi and calcium balance, with a significant diminution of calcium and increased Pi accretion in bones, together with a diminution in the intestinal absorption of Pi. The treatment of the rats with calcitriol promoted a normalized Pi balance in Al treated rats. These findings suggest that Al could modify the Pi metabolism acting directly on intestine, kidney and bone, or indirectly through possible changes in the levels of vitamin D3.

Spectrophotometric determination of silicate traces in hemodialysis solutions

Reliable methods for the analysis of silicon are of great importance, because it seems that the silicate anion can reduce aluminum bioavailability in patients undergoing dialysis. Thus, a simple and sensitive spectrophotometric method is described for the determination of silicate traces in dialysis solutions. The method is based on the reaction between silicate ions and excess ammonium molybdate reagent to give a yellow silico-molybdic complex. This complex is then reduced to the heteropoly blue compound by means of ascorbic acid. Absorbance values are measured at 830 nm, and are stable for more than 2 h. A good linearity was obtained up to 300 ng ml(-1) of silicon concentration. The accuracy and the precision of the method were good; relative standard deviation values of 2% intraday and of 3.9% interday for six replicates on 40 ng ml(-1) standard silicate solutions were found. Results of the analysis of some commercial hemodialysis solution samples, obtained by means of the 'standard additions' method, are provided.

Strontium causes osteomalacia in chronic renal failure rats

BACKGROUND

We recently reported an association between increased bone strontium (Sr) levels and osteomalacia in dialysis patients.

METHODS

To delineate whether or not Sr acts as a causal factor in the development of osteomalacia, we devised the following study: four groups of chronic renal failure (CRF) rats were given Sr, aluminum (Al), both of these compounds or none of the elements (controls).

RESULTS

Administration of Sr and/or A1 resulted in increased bone levels of the respective elements. Histological examination revealed impairment of mineralization in the Sr group and to a lesser extent in the Al group as compared to the control group. There was also a significant increase in osteoid area in the Sr group, but not in the Al group. No differences in bone surface or erodic perimeter were noted between the various study groups. Histochemically, Sr could be localized in calcified bone, mainly in new bone close to the osteoid/calcification front, a critical site of bone mineralization. Histochemical findings were confirmed by electron probe X-ray microanalysis.

CONCLUSIONS

These findings indicate that Sr accumulation in chronic renal failure rats resulted in the development of osteomalacic lesions, in contrast to the Al group where adynamic bone disease was induced in the present set-up. Further studies are required to define the mechanism by which way Sr causes osteomalacia in chronic renal failure rats.

Chronic effect of aluminium ingestion on bone in calcium-deficient rats

In order to elucidate the relationship of osteogenesis with aluminum and iron deposition, we investigated the histopathological findings of bone in calcium and/or aluminium-deficient rats, together with levels of calcium, aluminium and iron in sera and bone tissues, and also the level of serum parathyroid hormone. Four week old male STD-Wistar rats were divided into four groups to examine the effects of four kinds of diets for ten weeks. The rats on normal diet (Group I) and normal diet+aluminum (Group II) did not show any pathological changes of the bones, but in both calcium-deficient diet group (Group III) and calcium deficient diet added aluminium (Group IV), the compact bone converted into spongy bone in varying degrees, particularly in Group IV. Aluminium deposition was demonstrated at the calcification fronts and the cement lines only in Group IV as red or violet-red lines with aluminium stain, together with iron deposition as revealed with Berlin blue stain, showing similar distribution pattern as aluminum. It was clearly indicated that aluminium and iron, instead of calcium, deposited on the calcification front of the bone under the condition of calcium deficiency, inhibiting the normal osteogenesis.

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.

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.

The role of vitamin D in toxic metal absorption: a review

Vitamin D increases intestinal calcium and phosphate absorption. Not so well known, however, is that vitamin D stimulates the co-absorption of other essential minerals like magnesium, iron, and zinc; toxic metals including lead, cadmium, aluminum, and cobalt; and radioactive isotopes such as strontium and cesium. Vitamin D may contribute to the pathologies induced by toxic metals by increasing their absorption and retention. Reciprocally, lead, cadmium, aluminum, and strontium interfere with normal vitamin D metabolism by blocking renal synthesis of 1,25-dihydroxyvitamin D. This is the first review of the role of the vitamin D endocrine system in metal toxicology.

Bone demineralization induced by cementless alumina-coated femoral stems

The biologic compatibility of ceramic materials has been widely demonstrated, and alumina (Al2O3) has been used extensively in clinical applications for nearly 20 years. The authors examined the behavior of bone tissue adjacent to the alumina coating in eight cementless hip prosthetic stems that appeared radiologically stable and were explanted because of pain. Histologic evaluation demonstrated the presence of a consistent layer of decalcified bone tissue in continuity with and parallel to the prosthetic interface. Based on laboratory findings, the authors attribute this demineralization phenomenon to a high local concentration of aluminum ions with metabolic bone disease, which is histologically comparable to the osteomalacic osteodystrophy described in dialysis patients. These findings must be carefully considered given the potential long-term implications for alumina-coated implants.

Aluminum and renal osteodystrophy A diminishing clinical problem

Aluminum-associated osteomalacia is a serious complication of advanced renal disease. Sources o f aluminum include the water used for hemodialysis and the gastrointestinal absorption o f aluminum from the antacids used to bind dietary phosphorus in an effort to prevent hyperparathyroidism. Definitive diagnosis is made by bone biopsy and staining for aluminum. Noninvasive testing using the deferoxamine challenge test together with serum PTH levels is also of value in many instances. The goal for the future is to eliminate aluminum-related osteodystrophy by the avoidance of aluminum, control of phosphorus with non-aluminum-containing binders, and development of novel approaches to facilitate phosphorus removal by dialysis.

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)

Effect of fluoride on aluminum-induced bone disease in rats with renal failure

Aluminum (Al) accumulation in renal failure is an etiological factor in the pathogenesis of low turnover bone disease. Aluminum-induced impairment of mineralization has been related to a reduced extent of active bone-forming surface. The present study investigated the effect of fluoride, a potent stimulator of osteoblast number, on the toxicity of aluminum in rats with renal failure (Nx). Following a large parenteral aluminum load (3.2 mg/kg x day) over a period of nine weeks, bone histomorphometry of vertebral cancellous bone revealed a severe low-turnover osteodystrophy as evidenced by a fall in osteoblastic osteoid surfaces and mineral apposition rates. Concurrent administration of fluoride [20 mg/liter (F20) or 40 mg/liter (F40) supplied with the drinking water] resulted in a significant increase in the number of osteoblasts (Nx+Al+F40 vs. Nx+Al, 33.75 +/- 2.83 vs. 1.81 +/- 0.43 mm-1, P less than 0.001) together with an overall reduced deposition of aluminum in bone (469.3 +/- 24.6 vs. 592.2 +/- 28.3 micrograms/g, P less than 0.01). However, there was an increase in the fraction of osteoid surface exhibiting stainable aluminum at the bone-osteoid interface (70.7 +/- 7.1 vs. 44.3 +/- 6.0%, P less than 0.005). Fluoride-exposed rats accumulated a significantly larger osteoid volume, suggesting an exacerbation of the osteomalacic lesion, and furthermore, dynamic histomorphometric parameters remained depressed. These results indicate that fluoride has a distinct effect on the pattern of aluminum deposition in bone. In addition, fluoride antagonizes the aluminum-induced reduction in osteoblast number but provides no amelioration of the impaired mineralization in aluminum-intoxicated rats. Thus, in this model a decrease in the extent of osteoblast surface does not account for the development of aluminum-related bone disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Musculoskeletal complications after renal transplantation: pathogenesis and treatment

Renal transplantation is associated with several abnormalities of function and structure of the musculoskeletal system. Some of these skeletal problems result from incomplete resolution of abnormalities of bone and mineral metabolism present at the time of transplantation. In this regard, persistent hyperparathyroidism, diabetes mellitus type 1, and accumulation of beta 2-microglobulin may lead to residual skeletal effects despite excellent function of the allograft. Persistent hyperparathyroidism may accelerate bone loss and increase the risk for osteonecrosis, as well as cause hypercalcemia and hypophosphatemia; some patients with severe hyperparathyroidism require parathyroid surgery. Osteonecrosis is the most debilitating skeletal complication after transplantation and frequently requires surgical therapy. Although osteomalacia associated with aluminum overload generally resolves after transplantation, bone complications due to dialysis amyloidosis and diabetes mellitus type 1 often fail to improve. Alternatively, skeletal abnormalities can be acquired after transplantation. Most of the new derangements of bone and mineral metabolism are due to the immunosuppressive medications. Toxic effects of glucocorticoids on bone contribute to the pathogenesis of osteonecrosis, increase the risk for fractures by decreasing cancellous bone mass and synthesis of bone matrix, and dampen the linear growth response in pediatric recipients. Whether cyclosporine independently causes appreciable toxic effects on bone metabolism is not yet clear, but use of this drug increases the prevalence of gout and dental problems. Osteonecrosis, osteopenia, and short stature remain important skeletal complications in recipients of renal allografts. Therapeutic efforts should be directed toward alleviating pretransplant bone disease and attenuating bone loss after transplantation.

Effects of systemic aluminum on the resolution of a uremic and dietary phosphorus-dependent model of uremic osteomalacia in rats

We have developed a model of osteomalacia that is dependent on both uremia and the feeding of a diet low in phosphorus and that can be reversed by subsequent dietary phosphorus repletion. The objectives for this study were to use this model to investigate the role of aluminum (Al) in both the induction and resolution of osteomalacia. Adult male Sprague-Dawley rats were five-sixths nephrectomized and fed either low or normal dietary phosphorus, both with and without intraperitoneal Al injections. Uremic rats fed low phosphorus developed osteomalacia characterized by increased osteoid surface, volume, and thickness and osteoid maturation time and decreased mineralizing surface. Al-treated uremic rats fed low phosphorus were similarly affected, developing increased osteoid volume and thickness and osteoid maturation time and decreased osteoblastic surface, mineralizing surface, and bone formation rate. In addition, they had a significantly increased Al-positive surface. Al-treated uremic rats fed normal phosphorus had only increased osteoid thickness and aluminum-positive surface and decreased osteoblastic surface. Osteomalacic rats continuously treated with Al during the induction and phosphorus repletion stages had increased growth plate thickness, osteoid volume and thickness, and Al-positive surface and decreased osteoblastic and mineralizing surface. Mineralization in these rats was impaired to such a degree that no detectable double labels were present. Osteomalacic rats treated with Al during the induction phase but not during phosphorus repletion had increased osteoid surface and volume and Al-positive surface and decreased osteoblastic and mineralizing surface. Double labels were not detectable in these rats, either.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum alters calcium influx and efflux from bone in vitro

Aluminum retention can cause osteomalacia and adynamic lesions of bone in patients undergoing long-term dialysis. It is not known, however, whether aluminum inhibits the mineralization of bone directly or whether alterations in osteoblastic function mediate this response. To examine this issue, the uptake of 45Ca by 14-day embryonic chick calvaria was measured in vitro. Comparative studies were done in living and devitalized tissues to evaluate the role of bone cells in aluminum-related changes in 45Ca uptake. Aluminum was added to serum-free media as the citrate complex, and paired hemicalvaria maintained in equimolar sodium citrate served as controls. Aluminum citrate decreased the uptake of 45Ca into bone during 24 hour incubations to 76 +/- 3% and 38 +/- 2% (x +/- SD) of control values at 10 microM and 100 microM aluminum, respectively. No change in 45Ca uptake was observed at the end of four hour incubations with 100 microM aluminum citrate, whereas 45Ca uptake decreased from 356 +/- 48 to 266 +/- 36 cpm/micrograms bone, P less than 0.05, at eight hours and from 327 +/- 22 to 269 +/- 41 cpm/micrograms bone, P less than 0.05, at 24 hours. The inhibitory effects of 10 microM and 100 microM aluminum on 45Ca uptake were eliminated, however, in devitalized tissues, and reductions in 45Ca uptake during incubations with aluminum were markedly attenuated by lowering the media phosphorus level from 4.0 mM to 2.0 mM.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum salts stimulate luminol-enhanced chemiluminescence production by human neutrophils

Aluminum intoxication is currently thought to play a major role in the development of Alzheimer's disease and in certain pathologic manifestations seen during long-term hemodialysis and aging. The hypothesis that aluminum toxicity is mediated via an increased free radical production was tested by studying the effects of two aluminum and five other metallic compounds on the production of luminol-enhanced chemiluminescence (LECL) by human neutrophils. AlCl3, Al2(SO4)3 and FeCl3 were found to stimulate LECL production by human neutrophils whereas FeCl2, CuCl, CuCl2, AuCl3 were inactive. Metal chelators such as Desferal, EDTA and DETAPA suppressed aluminum-induced stimulation and depressed cell-dependent LECL below basal levels. Sodium azide and Cytochalasin B greatly depressed both basal and aluminum-induced stimulation of LECL production, suggesting that, in this system, most of this stimulation was due to myeloperoxidase. These results suggest that high tissue aluminum concentrations may induce cell-tissue lesions by stimulating local production or release of mediators of tissue damage.

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.

Aluminum-induced neo-osteogenesis: a generalized process affecting trabecular networking in the axial skeleton

To determine if aluminum-induced neo-osteogenesis occurs in the axial skeleton, we compared spinal bone density and vertebral histology of beagles treated with aluminum for 8 and 16 weeks to that of untreated normals. Administration of aluminum (1.25 mg/kg) did not alter serum calcium, phosphorus, or creatinine but did result in a significant elevation of vertebral bone density, measured by quantitative computed tomography, after both 8 (286.7 +/- 12.4 mg/ml) and 16 (361.7 +/- 46.5 mg/ml) weeks of treatment compared with controls (212.2 +/- 4.5 mg/ml). In accord with the increased bone density, biopsies from the spine displayed evidence of neo-osteogenesis, including the presence of woven bone, both mineralized and unmineralized, within the marrow space. The genesis of such woven bone units resulted after 16 weeks in a significant increase in trabecular bone volume, woven and lamellar (51.2 +/- 4.4 versus 32.4 +/- 1.2%; p less than 0.05), woven bone volume (9.1 +/- 3.6 versus 0 +/- 0%; p less than 0.05), and trabecular number (4.5 +/- 0.3 versus 3.5 +/- 0.2 per mm; p less than 0.05). In addition, scanning electron microscopic evaluation of the bone biopsies confirmed the existence of new trabecular plates that provided interconnections between existent units. These observations illustrate that aluminum-induced neo-osteogenesis positively influences trabecular networking in the axial skeleton. Such enhancement of bone histogenesis contrasts with the effects of other pharmacologic agents that solely alter the thickness of existing trabecular plates or rods within the vertebral spongiosa.

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)

Effects of renal failure

The multiple features of the syndrome of uremia are a result of the retention of a wide variety of metabolic end products. Although a number of metabolites have been incriminated as "the uremic toxin," none of them accounts for all aspects of uremia. It is likely that the uremic syndrome is a result of the pathological effects of many retained substances. Of major current interest is the development of toxicity in brain, bone and other tissues due to accumulation of aluminum. The recognition of aluminum toxicity may have implications not only in patients with impaired renal function but also in other disease states.

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.

Desferrioxamine therapy in hemodialysis patients with aluminum-associated bone disease

Aluminum toxicity in dialysis patients is associated with decreased bone turnover and a relative parathyroid hormone (PTH) deficiency. Desferrioxamine (DFO), a chelating agent, has been reported to improve bone histology in aluminum associated, low turnover bone disease in dialysis patients not subjected to parathyroidectomy. Information on the effect of DFO therapy on parathyroid gland function is lacking. In the present study, in addition to changes in bone histology, parathyroid gland function was evaluated in 18 hemodialysis patients with aluminum associated, low turnover bone disease (osteomalacia and aplastic bone disease) before and after one year of DFO treatment (1 to 6 g/week). Parathyroid gland function was assessed by using a calcium free and high calcium (3.5 to 4 mEq/liter) hemodialysis bath.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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).

Evidence for a toxic effect of aluminum on osteoblasts: a histomorphometric study in hemodialysis patients with aplastic bone disease

To evaluate the potential role of aluminum (Al) in a subset of dialysis patients with aplastic bone disease, we have studied tetracycline-labeled bone biopsies of 32 patients (22 males and 10 females, 45-73 years) on maintenance hemodialysis. Selection criteria included normal resorption surfaces (RS) and osteoid thickness. Eleven patients (Group I) had no stainable bone Al (Al-; 61.7 +/- 7.2 years) and 21 (Group II) had stainable bone Al (Al+; 57.7 +/- 6.8 years). Serum Al was normal to slightly elevated in Group I, but significantly higher in Group II (p less than 0.01). Al surfaces (AlS), undetectable in Group I, were 67.8 +/- 17.9% in Group II. Bone Al content (BAC) was much lower in Group I than in Group II (14.8 +/- 3.7 vs. 113.8 +/- 100.2 micrograms/g, p less than 0.01), but higher in Group I than in controls (p less than 0.05). Extensive thin osteoid seams were present in Group II. AlS was correlated with OS (r = 0.56, p less than 0.001) and OV (r = 0.48, p less than 0.01). Labeled surfaces were decreased in both groups. Labeled osteoid surfaces (TLS/OS) were below 2 SD of the mean control values in 96% of patients and calcification rate (CR) was depressed below 0.20 micros/day in 44% of patients. Bone formation rate (BFR) was strikingly depressed, values being below one SD of the mean control value in 92-100% of patients at both levels and below 2 SD of the mean in 82% of patients at BMU levels. Mineralization lag time (OMP) was markedly prolonged above 2 SD of controls in 89% of patients.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Histochemical demonstration of iron but not aluminum in a case of dialysis-associated osteomalacia

A patient undergoing hemodialysis is described in whom osteomalacia developed despite protracted treatment with calcitriol. Appropriately stained biopsy sections exhibited iron at all marrow-osteoid interfaces and a small fraction of trabecular mineralization fronts. Aluminum, the metal usually associated with osteomalacia in patients undergoing hemodialysis, was not histochemically demonstrable, even though spectrophotometrically measured bone aluminum content was substantial. These observations suggest two interpretations: iron may have caused osteomalacia through effects on bone cells and at mineralization fronts; alternatively, aluminum may have caused osteomalacia while remaining histochemically undetectable. It is possible that both metals exerted toxic effects simultaneously.

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.