Gastrointestinal absorption of aluminium in chronic renal insufficiency

Risk Factors for Hyperaluminemia in Continuous Ambulatory Peritoneal Dialysis

The authors evaluated risk factors for hyperaluminemia and aluminum toxicity in 51 CAPD patients, who received aluminum-containing phosphate binders. Serum aluminum correlated with total intake of elemental aluminum after starting CAPD (p = 0.001), with aluminum intake in the previous six months (p = 0.001), with duration of CAPD (p = 0.003), and with serum phosphate (p = 0.05). Eight patients had elevated serum aluminum, but only one had clincial evidence of aluminum toxicity (he had been on hemodialysis with untreated water until he was changed to CAPD 30 months before the study). Although the incidence of clinical aluminum toxicity appears to be low, we conclude that the aluminum intake from aluminum-containing phosphate binders is a major factor in the evolution of hyperaluminemia and, potentially, aluminum toxicity in CAPD patients. We believe that alternative effective, phosphate binders are much needed.

It has been shown that tissue accumulation of aluminum in brain, bone and blood in uremic patients causes encephalopathy (I. 2), osteomalacia (3, 4), and anemia (5, 6). Clinically aluminum toxicity has been observed mainly in hemodialysis patients (1–6), although it has been reported in few cases before dialysis (7–9) and in those on continuous ambulatory peritoneal dialysis (10. II). The major cause of aluminum toxicity during hemodialysis has been transfer of aluminum from untreated water in the dialysate (1–5); this mechanism has tended to obscure the contribution of other factors, such as diet and drugs. Peritoneal dialysate contains a low concentration of aluminum (less than 15 μg/L) and there is a net removal of aluminum in the dialysate in those with serum aluminum levels within the reference range for dialysed uremics (11–13). Serial aluminum levels in CAPD patients not receiving aluminum -containing phosphate binders (ACPB) showed no significant change during a two-year follow-up (12, 14); this suggests that aluminum removal in the dialysate compensates for the failure of the kidney to excrete absorbed dietary aluminum in end-stage renal disease. Since the combination of CAPD and diet appears to have minimal influence on serum aluminum, this study was done to identify those factors which determine serum aluminum levels in CAPD patients, receiving aluminum-containing phosphate binders.

Phosphate binding therapy in dialysis patients: focus on lanthanum carbonate

Hyperphosphatemia is an inevitable consequence of end stage chronic kidney disease and is present in the majority of dialysis patients. Recent observational data has associated hyperphosphatemia with increased cardiovascular mortality among dialysis patients. Dietary restriction of phosphate and current dialysis prescription practices are not enough to maintain serum phosphate levels within the recommended range so that the majority of dialysis patients require oral phosphate binders. Unfortunately, conventional phosphate binders are not reliably effective and are associated with a range of limitations and side effects. Aluminium-containing agents are highly efficient but no longer widely used because of well established and proven toxicity. Calcium based salts are inexpensive, effective and most widely used but there is now concern about their association with hypercalcemia and vascular calcification. Sevelamer hydrochloride is associated with fewer adverse effects, but a large pill burden and high cost are limiting factors to its wider use. In addition, the efficacy of sevelamer as a monotherapy in lowering phosphate to target levels in severe hyperphosphatemia remains debatable. Lanthanum carbonate is a promising new non-aluminium, calcium-free phosphate binder. Preclinical and clinical studies have demonstrated a good safety profile, and it appears well tolerated and effective in reducing phosphate levels in dialysis patients. Its identified adverse events are apparently mild to moderate in severity and mostly GI related. It appears to be effective as a monotherapy, with a reduced pill burden, but like sevelamer, it is significantly more expensive than calcium-based binders. Data on its safety profile over 6 years of treatment are now available.

Lanthanum carbonate (Fosrenol): a novel agent for the treatment of hyperphosphataemia in renal failure and dialysis patients

Approximately 70% of patients with end-stage renal disease and dialysis have hyperphosphataemia, which is associated with renal osteodystrophy, metastatic calcification and increased mortality and morbidity. Despite dietary restriction and dialysis, most patients will require a phosphate-binding agent to treat this condition. However, phosphate control has not significantly improved over the last two decades, mainly because of the lack of an ideal phosphate-binding agent. Aluminium-based and calcium-based agents are associated with major side-effects despite their efficacy. Although sevelamer hydrochloride represents a step forward in the management of hyperphosphataemia, it has drawbacks and therefore is not the ideal phosphate binder. Lanthanum carbonate is a non-calcium, non-aluminium phosphate-binding agent. It has shown to be effective, well-tolerated and has a positive effect on bone histology.

Use of sucralfate in renal failure

OBJECTIVE

To assess the potential for the development of aluminum toxicity in patients with renal insufficiency or chronic renal failure who are taking sucralfate.

DATA SOURCES

Clinical literature accessed through MEDLINE (1966-December 1999) and International Pharmaceutical Abstracts (1970-December 1999). Key search terms included sucralfate, renal failure, renal insufficiency, and end-stage renal disease.

DATA SYNTHESIS

Urinary excretion is an important route of elimination for systemically absorbed aluminum. Accumulation of aluminum in patients with impaired renal function may lead to significant toxicity. A potential source of aluminum is the antiulcer medication sucralfate. Studies and case reports evaluating the use and toxicity of sucralfate in patients with normal renal function, as well as those with renal failure or renal insufficiency, were reviewed.

CONCLUSIONS

Aluminum accumulation and toxicity have been reported with the use of sucralfate in patients with compromised renal function. The risk of toxicity most likely represents a long-term complication of sucralfate use in this patient population. Toxicity may be enhanced by concurrent use of other aluminum-containing medications, such as phosphate binders or antidiarrheal preparations. These medications, in addition to sucralfate, should be avoided if possible in patients with end-stage renal disease. Patients with renal failure or renal insufficiency who are undergoing prolonged sucralfate therapy should be monitored for potential signs of aluminum toxicity.

Aluminum absorption and excretion following sucralfate therapy in chronic renal insufficiency

PURPOSE

To measure serum aluminum levels and urinary aluminum excretion in patients with chronic renal insufficiency (CRF) receiving therapeutic doses of sucralfate.

PATIENTS

Six patients with CRF were enrolled in the study. Creatinine clearances ranged from 0.2 to 0.9 mL/second (mean +/- SD 0.40 +/- 0.25 mL/second). Seven subjects with normal renal function were also studied.

METHODS

Each subject received sucralfate 1 g four times daily for 21 days. Serum and urine samples (serum only) were collected on baseline and on Days 2, (3), 8, 15, 22, (23, 24), 29, and 36. Samples were assayed by graphite furnace atomic absorption spectrophotometry.

RESULTS

In CRF, serum aluminum levels (mumol/L) increased by Day 2 and remained elevated to Day 24. Urinary aluminum excretion (mumol/day) was elevated throughout the study. The elimination half-life of serum aluminum after therapeutic dosing of sucralfate was 13.1 +/- 3.1 days. In subjects with normal renal function, baseline serum aluminum levels were similar to those in CRF (0.12 +/- 0.12 versus 0.11 +/- 0.12 mumol/L), but serum aluminum levels were higher at the end of the study in CRF (Day 22, 0.24 +/- 0.17 versus 0.83 +/- 0.48 mumol/L).

CONCLUSIONS

After therapeutic doses of sucralfate, significant elevations of serum aluminum levels occurred in CRF. Serum aluminum levels were higher in patients with CRF than in normal subjects. Long courses of sucralfate should be used with caution or avoided in CRF.

Developmental toxicity evaluation of oral aluminum in rats: influence of citrate

To evaluate the influence of citrate on the potential developmental toxicity of high doses of aluminum (133 mg/kg/day), three groups of pregnant Sprague-Dawley rats were given by gavage aluminum hydroxide (384 mg/kg/day), aluminum citrate (1064 mg/kg/day), or aluminum hydroxide (384 mg/kg/day) concurrent with citric acid (62 mg/kg/day) on gestational days 6 through 15. Control animals received distilled water. At termination on gestation day 20, live fetuses were examined for external, visceral, and skeletal alterations. There were no significant differences between controls and Al-treated rats on pre- or postimplantation loss, number of live fetuses per litter, or sex ratio. Fetal body weight was significantly reduced in the group treated with Al(OH)3 and citric acid. Although no increases in the incidence of malformations were observed, the incidence of skeletal variations was significantly increased in the group given Al(OH)3 concurrent with citric acid. In summary, although the administration of citric acid did not modify the lack of embryotoxicity and teratogenicity of Al(OH)3 in rats, some signs of maternal toxicity and fetotoxicity could be observed in this group.

Variable efficacy of calcium carbonate tablets

Orally administered calcium carbonate tablets are commonly prescribed as a calcium supplement and for their phosphate-binding effects in renal failure patients. Two cases are reported in which a commercially available brand of calcium carbonate tablets appeared to be ineffective. Formal investigation of the bioavailability of this product revealed it to have impaired disintegration and dissolution and a lack of clinical efficacy. Recommendations that will enable physicians to avoid prescribing and pharmacists to avoid dispensing ineffective calcium carbonate tablets are proposed.

Neurobehavioral effects in offspring of mice given excess aluminum in diet during gestation and lactation

Aluminum (Al) as Al lactate in a purified diet (25, 500 or 1000 micrograms Al/g diet) was fed to Swiss-Webster mice from conception through weaning. Weights, food intake and toxic signs were recorded at regular intervals and pregnancy outcome evaluated. Pups were assessed for growth, neurobehavioral development and toxic signs prior to weaning. Offspring were also evaluated with a multi-item neurobehavioral test battery immediately after weaning and again after a 2-week period during which they were all fed control (25 micrograms/g Al) diet. No maternal or reproductive toxicity was detected and there were no group differences in pup mortality, growth, toxic signs, or neurobehavioral development prior to weaning, with the exception of poor performance in a climbing test in the 1000 micrograms Al/g diet group. Parameters significantly affected by Al in the postweaning neurobehavioral testing were foot splay, forelimb and hindlimb grip strengths, and thermal sensitivity. Negative geotaxis was inconsistently affected and startle responses were not affected. These results show that maternal dietary exposure to excess Al during gestation and lactation which do not produce maternal toxicity can result in persistent neurobehavioral deficits in weanling mice.

The influence of high dietary aluminum on brain microtubule polymerization in mice

One of the possible mechanisms that has been proposed to underlie the deleterious effects of excess aluminum on brain function is an impairment in the normal formation of the cytoskeletal network. Based on recent reports that aluminum can promote the in-vitro polymerization of purified tubulin, in the present study we characterized the effects of high dietary aluminum on in-vitro microtubule formation in brain supernatants. Mice were fed diets containing aluminum 25-1000 micrograms/g for up to 10 weeks. Tubulin polymerization in high-speed brain supernatants was not found to be affected by dietary aluminum. However, we observed that the addition of aluminum in vitro stimulated microtubule assembly in brain supernatants from mice fed control diets, as had been previously reported. Thus, impaired brain microtubule function is not an early general biochemical lesion in aluminum toxicosis.

Gastrointestinal absorption and urinary excretion of aluminium in patients with predialysis chronic renal failure

In a randomized cross-over study, serum and urinary aluminum (A1) was measured in 8 patients with predialysis chronic renal failure. Samples were taken after ingestion of an A1-containing phosphate binder (ACPB) with either water or 7% citric acid, and A1 was analyzed by electrothermal atomic absorption spectrometry. Both serum levels and urinary excretion of A1 increased markedly after ingestion of ACPB with citric acid. Only urinary A1 excretion increased significantly after ACPB with water. Citric acid alone caused no change in serum concentration or urinary excretion of A1. The serum A1 increase after ACPB with citric acid indicates that absorption of A1 is taking place in both upper and lower intestines. Marked individual variations in gastrointestinal A1 absorption, independent of kidney function, were seen after intake of ACPB with citric acid. These variations could not be predicted from changes in serum concentrations or from urinary excretion of A1 after intake of ACPB with water. Intake of ACPB caused a significant decrease in serum phosphate.

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.

Elimination of absorbed aluminum in patients undergoing continuous ambulatory peritoneal dialysis

Intestinal absorption of aluminum (Al) from the phosphate binder aluminum-hydroxide-chloride (PhosphonormR) and successive renal and peritoneal Al elimination were studied in 11 patients undergoing continuous ambulatory peritoneal dialysis (CAPD). Al was measured by atomic absorption spectrometry in serum, urine, and dialysis fluid. Al levels in serum of all patients increased in average from 28.6 micrograms/l immediately before to a peak level of 41.6 microgramsWl 4 h after intake of 342 mg Al. After 24 h serum Al (34.0 micrograms/l) was still increased. Elimination across the peritoneum increased from 5.6 micrograms Al during the first 4 h to peak levels of 12.9 micrograms between hour 8 and 12 and decreased to 8.1 micrograms during the last 12 h. The Al clearance of the peritoneum was 0.43 ml/min. In the 6 patients with residual diuresis the renal Al excretion was higher than the peritoneal removal (48.1 micrograms/24 h vs. 24.8 micrograms/24 h). The renal Al clearance amounted to 1.6 ml/min. Assuming a gastrointestinal absorption quotient of 0.1% it is concluded that Al removal by CAPD in patients receiving 342 mg Al/day is not sufficient to prevent Al accumulation. In patients with remaining diuresis, the renal Al elimination exceeds the Al removal by the peritoneum.

Results of subtotal parathyroidectomy in hemodialysis patients

In 61 hemodialysis patients undergoing subtotal parathyroidectomy, there was a good correlation between the preoperative serum immunoreactive parathyroid hormone value (iPTH) and the weight of parathyroid tissue removed surgically (p less than or equal to 0.001). Postoperatively, iPTH decreased rapidly from an initial mean (+/- SD) of 2,928 +/- 1,600 muleq/ml and remained at 365 +/- 296 muleq/ml at last follow-up of patients still undergoing hemodialysis (normal, less than 50 muleq/ml). Of six patients who had recurrent hyperparathyroidism (10 percent of total), three required a second subtotal parathyroidectomy. Aluminum-related osteomalacia eventually developed in six patients with bone biopsy-proven hyperparathyroidism before parathyroidectomy. Nine patients with severe fracturing bone disease and hypercalcemia preoperatively but without clear evidence of hyperparathyroidism did not show a favorable response to subtotal parathyroidectomy (high mortality within 28 months, persistence of hypercalcemia, and symptomatic bone disease). Thus, subtotal parathyroidectomy can benefit patients with clearly established severe progressive hyperparathyroidism not responsive to medical therapy but is contraindicated in patients with low iPTH values and no bone biopsy evidence of severe hyperparathyroidism.

Enhanced gastrointestinal absorption of aluminum in uremic rats

To investigate the possibility of enhanced gastrointestinal absorption of aluminum in uremia, we measured the urinary aluminum excretion of rats following an oral load of 11 mg aluminum. Rats, in which uremia had been established by the remnant kidney model, excreted 1.5 to 2.2-fold higher amounts of aluminum in their urine over a collection period of five days compared with their controls. Within this period of time up to 0.17 +/- 0.08% of the oral dose of aluminum was recovered in the urine of the uremic animals. Serum concentrations of aluminum were significantly elevated five hours after ingestion of aluminum, but this increase was similar in rats with normal or reduced renal function. Uremic rats excreted significantly less aluminum during the first 24 hours after i.v. administration of 15 micrograms aluminum if the data were corrected for the higher baseline excretion rates. The excretion rate showed a negative correlation with the serum creatinine. Selective parathyroidectomy had no effect on the pattern or amount of urinary aluminum excretion after an oral load in either uremic rats or in rats with normal renal function. We conclude that the gastrointestinal absorption of aluminum is increased in uremic rats, and that parathyroid hormone has no detectable effect on the magnitude of aluminum absorption, regardless of the renal function in this model.

Aluminum and Alzheimer's disease: perspectives for a cytoskeletal mechanism

A considerable volume of literature has accumulated concerning the association of aluminum with Alzheimer's disease. The pathogenic mechanisms resulting in Alzheimer's disease remain unknown, but recent investigations have focused on cytoskeletal abnormalities as perhaps the key lesion in Alzheimer's disease and related neurological disorders. The diversity of neuronal functions that are dependent on cytoskeletal integrity suggests that subtle effects on polymerization, assembly, transcription, or processing of cytoskeletal elements may have significant and far-reaching neurological effects. That aluminum may participate in the development of neuropathological lesions characteristic of Alzheimer's disease is suggested by evidence that aluminum is a potent cytoskeletal toxin, produces cognitive deficits in laboratory animals, and can be detected within abnormal neurons isolated from brain tissue from Alzheimer's disease patients. In this review, a critical look will be taken at the enigmatic role aluminum has played in Alzheimer's disease research, the possibility of its pathogenicity, and its use as a tool for the investigation of cytoskeletal changes that may result in the biochemical and, ultimately, clinical manifestations of Alzheimer's disease.