Bone aluminum and histomorphometric features of renal osteodystrophy

Effects of vitamin D metabolites on healing of low phosphate, vitamin D-deficient induced rickets in rats

A model of low-phosphate, vitamin D-deficient rachitic rats was used to compare the effects of 1 alpha(OH)D3, 1,25(OH)2D3, and 24,25(OH)2D3 on cartilage and bone. The rats were maintained for 3 weeks on a high-calcium, low-phosphate, vitamin D-deficient diet, during which period they developed severe rickets. The rachitic rats were injected for 2 or 3 consecutive days with a physiologic dose of either metabolite. Other littermates were given a single dose of 50,000 IU of cholecalciferol in combination with a normal diet. Samples of cartilage fluid (Cfl) and of blood were removed prior to sacrifice for biochemical studies of some parameters of calcification. These parameters were correlated with the results of light and electron microscopic studies of the growth plate cartilage and bone. Treatment with 1 alpha (OH)D3 or with 1,25(OH)2D3, in spite of increasing Ca and P levels in the Cfl, induced only partial healing of the rickets. In contrast, 24,25(OH)2D3 or vitamin D with a normal diet resulted in complete morphologic and biochemical healing of the rickets. Transmission electron microscopic (TEM) studies have shown partial mineralization of the wide hypertrophic zone of the growth plate following treatment with 1 alpha(OH)D3 or with 1,25(OH)2D3. Mineralization was more complete with 24,25(OH)2D3 treatment. The results of this study emphasize the importance of 24,25(OH)2D3 for normal endochondral bone formation and mineralization.

Evidence of increased parathyroid activity on discontinuation of high-aluminum dialysate in patients undergoing hemodialysis

High-aluminum dialysate exposure has been incriminated in the pathogenesis of vitamin D-resistant osteomalacia in patients undergoing long-term hemodialysis. Parathyroid-mediated osteitis fibrosa is rare in these patients. Thirteen patients undergoing longterm hemodialysis were transferred from a center (Unit A) where water used to prepare dialysate was high in aluminum (100 to 450 micrograms/liter) to a new center (Unit B) where dialysate was highly purified (aluminum concentration less than 10 micrograms/liter), and changes in calcium metabolism were studied over a 12-month period. After transfer of patients to Unit B, serum aluminum levels fell (p less than 0.01), whereas serum immunoreactive parathyroid hormone levels rose (p less than 0.01) over 10 months. Over this time, predialysis serum calcium levels did not alter significantly, whereas postdialysis serum calcium levels declined slightly (p less than 0.05). Serum phosphate levels did not alter. Serum alkaline phosphatase levels rose progressively in Unit B (p less than 0.001). Discontinuation of dialysate high in aluminum in patients undergoing long-term hemodialysis may facilitate a rise in parathyroid activity.

The use of deferoxamine in the management of aluminum accumulation in bone in patients with renal failure

Aluminum frequently accumulates in patients with end-stage renal failure. We investigated the value of long-term, intermittent infusions of deferoxamine for the removal of aluminium from bone in seven patients undergoing long-term maintenance dialysis. Transient rises in serum aluminum levels occurred initially after treatment. Three patients who were studied by bone biopsy had absent or reduced levels of bone aluminum. Histologic studies of bone before and after therapy showed differences similar to those observed between patients with uremia who had an accumulation of aluminum in bone and those who did not. The diagnostic value of rises in the serum aluminum level after a single infusion of deferoxamine was studied in 12 patients with and 10 patients without aluminum accumulation in bone. All patients with bone aluminum had rises in serum aluminum levels, but rises were also observed in some patients without bone aluminum. Thus, the test cannot be used to diagnose aluminum accumulation in bone. Urinary aluminum levels increased significantly after a single infusion of deferoxamine in three patients with kidney transplants and accumulation of aluminum in bone. These findings indicate that deferoxamine is beneficial for the therapy of aluminum accumulation in the bone of patients with renal failure.

Osteomalacia and osteitis fibrosa in a man ingesting aluminum hydroxide antacid

A 53-year-old man with a history of long-term aluminum hydroxide antacid ingestion reported diffuse bone pain and multiple stress fractures over a two-year period. An undecalcified transiliac bone biopsy specimen revealed osteomalacia with osteitis fibrosa; plasma parathyroid hormone and cyclic AMP levels were normal. Following withdrawal of antacids and treatment with calcium and phosphorus, an initially elevated plasma, 1,25-dihydroxyvitamin D level fell to within the normal range, accompanied by decreased bone pain, healed stress fractures, and increased axial bone mineral content as determined by computed tomography of lumbar trabecular bone. Phosphate deprivation and 1,25-dihydroxyvitamin D excess may contribute to the poor mineralization and exaggerated resorption of bone observed in this syndrome. The clinical, biochemical, radiologic, and histologic features of previously reported cases are reviewed. Early recognition of this syndrome is important, since appropriate therapy promotes skeletal remineralization and prevents morbidity.

Aluminium concentrations in the brain and bone of rats fed citric acid, aluminium citrate or aluminium hydroxide

Male Sprague-Dawley rats were treated daily by gastric intubation (6 days/wk) with 100 mg aluminium/kg body weight in the form of aluminium hydroxide (9 wk) or aluminium citrate (4 wk), with citric acid (4 wk) or with tap-water (control, 9 wk). Young adult and aged Wistar rats were treated with 100 mg aluminium/kg body weight as aluminium hydroxide or with carboxymethylcellulose (vehicle controls). The cerebral cortex, hippocampus, cerebellum and samples of bone from each rat were analysed for aluminium, after digestion with nitric acid, using graphite furnace atomic absorption spectroscopy. The mean aluminium concentrations detected in the control Sprague-Dawley rats were 0.013-0.022 microgram/g wet weight in the various brain regions and 0.355 microgram/g in the bone. No significant increase in tissue aluminium concentrations was observed in Sprague-Dawley or Wistar rats after treatment with aluminium hydroxide. However the rats treated with aluminium citrate showed significantly increased concentrations of aluminium in all the brain regions studied (0.057-0.121 microgram A1/g) and in the bone (12.9 micrograms A1/g). Elevated aluminium concentrations in the cerebral cortex and bone were also observed in the animals fed citric acid suggesting possible absorption of the citrate chelate presumably formed with the traces of aluminium present in the diet.

Bone ultrastructure and x-ray microanalysis of aluminum-intoxicated hemodialyzed patients

In hemodialyzed patients aluminum (Al) intoxication may induce osteomalacic lesions which are mainly observed when plasma immunoreactive parathyroid hormone (iPTH) concentrations are low, and osteitis fibrosa absent. In this study, the bone tissue of eight hemodialyzed patients with elevated plasma and bone Al concentrations was examined by histomorphometry, electron microscopy, and x-ray microanalysis. Five patients (group 1) had osteomalacia and minimal osteitis fibrosa, three patients (group 2) had severe osteitis fibrosa. In group 1, Al was concentrated at the mineralizing front, in hexagonal structures measuring 200 to 1,000 A which also contained phosphorus, but not calcium. Hydroxyapatite needles had a normal aspect. Osteoblasts appeared inactive. In group 2, Al was also present at the mineralizing layer of osteoid, but, in these cases, in small clusters next to abnormal calcium deposits. Osteoblasts appeared very active. Their mitochondria contained calcium and phosphorus granules, or amorphous material, measuring 1,500 to 2,000 A, emitting x-rays characteristic for Al and phosphorus. These results suggest that secondary hyperparathyroidism, by stimulating the cellular activity, may increase the uptake and release of Al by the osteoblasts. The presence of Al within the mitochondria of these cells may be one of the factors inducing the mineralization defect.

Effect of aluminum and parathyroid hormone on osteoblasts and bone mineralization in chronic renal failure

Bone aluminum, quantitative bone histology, and plasma parathyroid hormone (PTH) were compared in 29 patients undergoing chronic hemodialysis. Histologic techniques included double tetracycline labeling and histochemical identification of osteoclasts and osteoblasts. Bone aluminum was measured chemically by flameless atomic absorption spectrophotometry, and histochemically. When measured chemically, the bone aluminum was 67 +/- 46 (SD) mg/kg dry weight (normal 2.4 +/- 1.2 mg/kg); histochemically, aluminum was present at 2.9 +/- 4.4% of trabecular surface. The biochemical and histochemical results agreed well (r = 0.80, P less than 0.001). No double tetracycline labels were seen at the mineralization front where aluminum was deposited, indicating cessation of mineralization at these sites. The osteoblast surface correlated positively with plasma PTH (r = 0.67, P less than 0.001) and negatively with bone aluminum level (r = -0.42, P less than 0.05). Multiple linear regression showed a correlation of aluminum with osteoblasts additional to that of PTH, consistent with a direct effect of aluminum in depressing osteoblast numbers. Though a relationship between PTH and chemically determined bone aluminum level could not be demonstrated, there was a negative correlation between osteoclast count and aluminum, and the nine patients with severe hyperparathyroid bone disease had lower chemically determined aluminum levels than the other patients. These results suggest that aluminum (a) directly inhibits mineralization, (b) is associated with decreased PTH activity and hence osteoblast numbers, and (c) directly reduces osteoblast numbers. In addition to inducing severe, resistant osteomalacia, aluminum appears to contribute to the mild osteomalacia commonly seen in renal failure, characterized by extensive thin osteoid and low tetracycline and osteoblast surfaces.

Parenteral aluminum administration in the dog: II. Induction of osteomalacia and effect on vitamin D metabolism

There is an association between bone aluminum (Al) accumulation and dialysis-associated osteomalacia (OM). To study whether Al is pathogenic in OM, quantitative bone histomorphometry was done in six dogs before (Bx 1) and after (Bx 2) 3 to 5 weeks of intravenous Al administration (1 mg Al /kg/day). Bone Al was determined by histochemical and chemical methods. The percent osteoid rose from 2.8 +/- 0.8 to 7.0 +/- 4.3% (mean +/- SD), P less than 0.05, and osteoid width increased from 5.7 +/- 0.6 to 8.0 +/- 1.2 mu, P less than 0.01, after Al. Bone Al rose from 1.3 +/- 1.6 to 94.0 +/- 19.0 mg/kg after Al, and the severity of OM, expressed as either percent forming surface or percent osteoid, correlated with bone Al measured histochemically and expressed as either percent surface or percent area of trabecular bone staining for Al (r = 0.85 - 0.90, P less than 0.01). Poor tetracycline uptake (six dogs), which indicates impaired mineralization, and little or no separation of tetracycline labels (four dogs) were noted at Bx 2; thus, bone apposition and formation rates were below the limits of detection. Resorptive surface did not change but trabecular volume, expressed as percent of tissue volume, fell from 22.1 +/- 3.0 to 17.1 +/- 1.4%, P less than 0.05. Serum levels of 1,25(OH)2D fell from 26.8 +/- 9.1 to 4.5 +/- 5.5 pg/ml after 17 days of Al; serum 25(OH)D levels were unchanged. These data indicate that Al can cause OM and that its severity correlates with the bone Al content.2 +

Parenteral aluminum administration in the dog: I. Plasma kinetics, tissue levels, calcium metabolism, and parathyroid hormone

Aluminum (Al) may cause both osteomalacia and encephalopathy in dialysis patients. Little is known about the biology of Al. This study examined the initial distribution kinetics of Al and its biological effects after injections of 1 mg/kg/day into dogs for 3 to 5 weeks. Following one intravenous dose, the plasma half-life (x +/- SE) was 276 +/- 51.8 min, with an apparent volume of distribution of 1.30 +/- 0.17 liters or 5.90 +/- 0.30% body wt; 10 to 21% of administered Al was excreted in the urine over 150 min, and the renal contribution to plasma clearance of Al correlated with GFR (r = 0.77, P less than 0.05). The total plasma clearance of Al (4.43 +/- 2.83 ml/min) exceeded the renal contribution to plasma clearance (1.94 +/- 0.36 ml/min) in each dog, and in only two instances did the renal contribution reach 50% of total plasma clearance. Serum calcium rose from 9.4 +/- 0.2 to 11.1 +/- 0.3 mg/dl and immunoreactive parathyroid hormone (iPTH) fell by 27 +/- 4% following one Al injection. With repeated Al injections, serum calcium increased from baseline levels of 10.2 +/- 0.07 mg/dl to 11.1 +/- 0.22 and 11.3 +/- 0.46 mg/dl after 1 and 2 weeks, respectively. Renal function declined in all dogs, and serum creatinine exceeded 3.5 mg/dl in four; over the 5 weeks of study, serum calcium correlated with serum creatinine (r = 0.91, P less than 0.001). Liver, kidney, and spleen showed the highest tissue content of Al, and there was substantial uptake by bone; the parathyroid content of Al was modest.(ABSTRACT TRUNCATED AT 250 WORDS)

Short-term aluminum administration in the rat. Effects on bone formation and relationship to renal osteomalacia

Aluminum may be pathogenic in the osteomalacia observed in some patients receiving hemodialysis. To study the early effects of Al on bone growth, bone formation, mineralization, and resorption were measured during short-term Al exposure in the tibial cortex of pair-fed control (C, n = 10), aluminum-treated (AL, n = 9), subtotally nephrectomized control (NX-C, n = 7), and subtotally nephrectomized aluminum-treated (NX-AL, n = 8) rats using double tetracycline labeling of bone. Animals received 2 mg/d of elemental Al intraperitoneally for 5 d/wk over 4 wk. Total bone and matrix (osteoid) formation, periosteal bone and matrix formation, and periosteal bone and matrix apposition fell by 20% in AL from C, P less than 0.05 for all values, and by 40% in NX-AL from NX-C, P less than 0.01 for all values. Moreover, each measurement was significantly less in NX-AL than in AL, P less than 0.05 for all values. Osteoid width did not increase following aluminum administration in either AL or NX-AL. Resorption surface increased from control values in both AL and NX-AL; also, resorptive activity at the endosteum was greater in NX-AL than in NX-C, P less than 0.05. Thus, aluminum impairs new bone and matrix formation but does not cause classic osteomalacia in the cortical bone of rats whether renal function is normal or reduced. These findings may represent either a different response to aluminum administration in cortical bone as contrasted to trabecular bone or an early phase in the development of osteomalacia. Aluminum may increase bone resorption and contribute to osteopenia in clinical states associated with aluminum accumulation in bone.

Parathyroid hormone response to hypocalcemia in hemodialysis patients with osteomalacia

The parathyroid hormone response to hypocalcemia was investigated in hemodialysis patients with osteomalacia and compared to those with osteitis fibrosa. Hypocalcemia was induced during hemodialysis by employing a dialysate devoid of calcium. Patients with osteomalacia had a blunted maximum amino terminal parathyroid hormone response (+/- SD) (0.39 +/- 0.33 vs. 0.87 +/- 0.53 ng/ml, P less than 0.05) and maximum carboxy terminal parathyroid hormone response (+/- SD) (0.36 +/- 0.20 vs. 0.84 +/- 0.47, P less than 0.02) to hypocalcemia. The decline in plasma calcium was greater in patients with osteomalacia at 90 (P less than 0.05), 120 (P less than 0.01), and 150 min (P less than 0.01). In osteomalacia patients the surface density of histologically detectable trabecular bone aluminum correlated directly with the percent relative osteoid volume (P less than 0.005) and inversely with the maximum amino terminal parathyroid hormone response to hypocalcemia (P less than 0.025). These results suggest that hemodialysis patients with osteomalacia have diminished secretion of parathyroid hormone and a decreased ability to restore plasma calcium homeostasis during hypocalcemia.

Excretion and retention of low or moderate levels of aluminium by human subjects

During a 40-day balance study, eight adult males were fed two levels of aluminium: 5 mg/day for 20 days (control diet) and 125 mg/day for 20 days (test diet). Every subject excreted more than 96% and more than 74% of his aluminium intake in his faeces when fed the test and control diets, respectively. Subjects excreted two- to five-fold more aluminium in their urine and had significantly higher levels of aluminium in their sera when fed the test diet rather than the control diet. No retention of aluminum was detected when faecal and urinary losses of aluminium were compared with intakes.

Suppression of parathyroid hormone secretion by aluminum

The effect of aluminum on parathyroid hormone secretion was examined using collagenase-dispersed bovine parathyroid cells. An increase in the medium aluminum concentration over the range of 0.5 to 2.0 mM, in low calcium medium, progressively inhibited the secretion of radioimmuno-assayable hormone. At 2.0 mM aluminum hormone secretion was inhibited by 68% while high medium calcium, without aluminum, maximally inhibited parathyroid hormone secretion only 39%. Individually, 2.0 mM aluminum or 2.0 mM calcium inhibited isoproterenol-stimulated hormone secretion by 43%. Either metal suppressed basal and isoproterenol-stimulated cyclic AMP levels of the parathyroid cells. That the inhibitory effect of aluminum on parathyroid hormone secretion was not due to an irreversible toxic effect was demonstrated by a restoration of normal secretion when cells were returned to 0.5 mM calcium medium without aluminum. The incorporation of [3H]leucine into total cell protein, parathyroid secretory protein, proparathyroid hormone, or parathyroid hormone was not affected by aluminum. The secretion of radiolabeled protein was, however, inhibited by aluminum. These results suggest that aluminum does not affect protein biosynthesis of the parathyroid cell or the conversion of proparathyroid hormone to parathyroid hormone. Aluminum appears to directly affect the secretion of protein from dispersed parathyroid cells.

Parathyroid gland responsiveness to acute hypocalcemia in dialysis osteomalacia

The majority of chronic hemodialysis patients have elevated serum iPTH levels and bone disease characterized by osteitis fibrosa. However, a small group of patients develop osteomalacic bone disease associated with normal or slightly elevated iPTH values and a tendency to hypercalcemia which occurs either spontaneously or after treatment with small doses of vitamin D sterols. To examine the causes of the relatively low iPTH levels, we evaluated the change in serum iPTH levels that occurred in response to acute hypocalcemia, produced by dialysis using a low calcium dialysate, in 11 patients with osteomalacia and 8 control hemodialysis patients. Dialysis against a dialysate free of calcium for 60 to 90 min led to a fall in serum calcium to 7.5 +/- 0.2 and 7.2 +/- 0.2 mg/dl in the osteomalacic and control patients, respectively. Serum iPTH rose in controls from 1380 +/- 287 to 1960 +/- 287 pg/ml (P less than 0.01), whereas in patients with osteomalacia it rose from 360 +/- 58 to 507 +/- 104 pg/ml (P less than 0.05), a value only slightly above normal for this PTH assay. These data suggest that the relatively low basal levels of serum iPTH do not arise as a consequence of physiologic suppression of parathyroid gland function. This reduction in parathyroid function could contribute to the pathogenesis of low turnover osteomalacia.

Effect of acute aluminium overload on calcium and parathyroid-hormone metabolism

Accidental exposure of 25 patients on continuous ambulatory peritoneal dialysis to a high aluminium level in the dialysate for a month provided an opportunity to investigate the interrelation between the metabolism of parathyroid hormone (PTH), calcium, and aluminium. After exposure to the high-aluminium dialysate, the mean serum aluminium had risen from 1.85 to 7.11 mumol/l and serum calcium from 2.27 to 2.44 mmol/l, and serum PTH had fallen from 744 to 580 ng/l. After a further 2 months, during which time the dialysate was aluminium-free, the mean serum aluminium and calcium fell to previous levels. There were no changes in calcium or vitamin-D therapy which could have influenced these results. The rise in serum calcium and fall in PTH during a period of aluminium toxicity strongly support the hypothesis that aluminium suppresses PTH through an elevation of serum calcium.

Preliminary trials with 24,25-dihydroxyvitamin D3 in dialysis osteomalacia

Fifteen patients with dialysis osteomalacia were treated with 24,25-dihydroxyvitamin D3 in dosages up to 10 micrograms per day for two to 24 months. All had previously had no improvement during treatment with calcitriol but had been remarkably susceptible to hypercalcemia. When 24,25-dihydroxyvitamin D3 was given with either calcitriol or dihydrotachysterol, serum calcium levels were significantly lower than during treatment with calcitriol or dihydrotachysterol alone. Eight of nine patients who received combined therapy with 24,25-dihydroxyvitamin D3 and calcitriol for longer than two months had clinical improvement; six patients underwent repeated bone biopsy and showed evidence of improved bone mineralization. Patients who received 24,25-dihydroxyvitamin D3 alone did not improve clinically. Since 24,25-dihydroxyvitamin D3 appears to improve calcium homeostasis and bone mineralization in some patients with severe dialysis osteomalacia when administered with 1-hydroxylated vitamin D metabolites, further controlled studies are warranted.

Hypercalcaemic osteomalacia due to aluminium toxicity

In 16 patients with chronic renal failure and osteomalacia resistant to vitamin-D therapy, aluminium was demonstrated in bone biopsy specimens at the interface between thickened osteoid and calcified bone by means of both X-ray microanalysis and a specific histochemical stain. 14 patients also had hypercalcemia. It is suggested that this is due to the blocking by aluminium of additional calcium uptake into bone coupled with the availability of additional calcium from dialysis fluid and vitamin-D therapy. This study provides more aetiological evidence linking aluminium and the development of osteomalacia in chronic renal failure. Further, if hypercalcaemia develops in such patients it is important that aluminium toxicity be excluded as the cause to prevent unnecessary parathyroidectomy.

The prevalence of bone aluminum deposition in renal osteodystrophy and its relation to the response to calcitriol therapy

A histochemical stain for bone aluminum allowed us to determine the prevalence and staining characteristics of aluminum in renal osteodystrophy. The staining method correlated well with the results of atomic-absorption studies in 96 samples (r = 0.81; P less than 0.001). We examined 315 bone-biopsy samples. No aluminum was seen in controls or patients with nonrenal bone disease. In renal osteodystrophy, the mean level of stainable aluminum was significantly higher in osteomalacic lesions (1.12 +/- 0.09 mm per square millimeter of tissue area) than in mild, mixed, of fibrotic lesions (0.43 +/- 0.06, 0.34 +/- 0.11, and 0.10 +/- 0.03 mm per square millimeter, respectively; P less than 0.001). Seventy per cent of osteomalacic samples had heavy aluminum staining. The bone-apposition rate, measured by double tetracycline labels, was low in 89 per cent of the samples with high levels of aluminum. The mean level of stainable bone aluminum in patients who had a clinical response to calcitriol was significantly lower than in those who did not respond (0.13 +/- 0.4 vs. 1.06 +/- 0.9 mm per square millimeter; P less than 0.01). We conclude that aluminum deposition is associated with impaired bone formation or mineralization and with a poor response to calcitriol therapy.