Parenteral citric acid for aluminium intoxication

Chelating effect of novel pyrimidines in a model of aluminum intoxication

Long time ago aluminum (Al) was considered as a non-toxic element and its use had no restrictions. However, over the last two decades, scientific publications have indicated that Al is a toxic element. In line with this, aluminum accumulation in the organism is associated with a variety of human pathologies. Efficient therapeutics approach to treat Al intoxication are still not available, but there is a consensus that chelation therapy is the procedure to be used. However, the development of new chelating agents are highly desirable to improve the efficacy of the treatment of Al intoxication. The present study evaluates the chelating effect of two novel pyrimidines: 4-tricloromethyl-1-H-pyrimidin-2-one (THP) and (4-methyl-6-trifluoromethyl-6-pyrimidin-2-il)-hydrazine (MTPH) in a mice model of aluminum intoxication and compares their efficacy with those of desferrioxamine (DFO), a classical agent used for treat Al accumulation. The animals were exposed to aluminum by gavage (0.1 mmol aluminum/kg/day) 5 days/week for 4 weeks. At the end of this period, DFO was injected i.p. and the novel pyrimidines were given by gavage at 0.2 mmol/kg/day for five consecutive days. Aluminum concentration in tissues (brain, liver, kidney and blood) was determined by graphite furnace atomic absorption spectroscopy (GFAAS). The results showed that when administered by gavage, aluminum accumulated in the brain, kidney and liver of mice. MTPH was able to decrease aluminum levels in aluminum plus citrate animal groups, whereas THP was inefficient for this purpose. However, the novel pyrimidines used in this study were unable to surpass the aluminum chelating property of DFO. Thus, new studies must be performed utilizing other chelating agents which can decrease aluminum toxicity.

Aluminum speciation studies in biological fluids. Part 7. A quantitative investigation of aluminum(III)-malate complex equilibria and their potential implications for aluminum metabolism and toxicity

As a nonessential element, aluminum may be toxic at both environmental and therapeutic levels, depending on ligand interactions. Dietary acids that normally occur in fruits and vegetables and commonly serve as taste enhancers are good ligands of the Al(3+) ion. Malic acid is one of these and also one of the most predominant in food and beverages. The present paper reports an examination of its potential influence on aluminum bioavailability through speciation calculations based on Al(III)-malate complex formation constants especially determined for physiological conditions. According to the results obtained, malate appears to be extremely effective in maintaining Al(OH)(3) soluble over the whole pH range of the small intestine under normal dietary conditions. In addition, two neutral Al(III)--malate complexes are formed whose percentages are maximum from very low malate levels. When aluminum is administered therapeutically as its trihydroxide, the amount of metal neutralized by malate peaks as its solubility pH range regresses to its original limits in the absence of malate. The enhancing effect of malate towards aluminum absorption is therefore virtually independent of the aluminum level in the gastrointestinal tract. The presence of phosphate in the gastrointestinal juice is expected to limit the potential influence of malate on aluminum absorption. Under normal dietary conditions, phosphate effectively reduces the fraction of aluminum neutralized by malate but without nullifying it. Aluminum phosphate is predicted to precipitate when aluminum levels are raised as with the administration of aluminum hydroxide, but a significant amount of neutral aluminum malate still remains in solution. Even therapeutic aluminum phosphate is not totally safe in the presence of malate, even at low malate concentrations. As plasma simulations predict that no compensatory effect in favor of aluminum excretion may be expected from malate, simultaneous ingestion of malic acid with any therapeutic aluminum salt should preferably be avoided.

Aluminum speciation studies in biological fluids. Part 6. Quantitative investigation of aluminum(III)-tartrate complex equilibria and their potential implications for aluminum metabolism and toxicity

Recent epidemiological studies have confirmed the existence of a correlation between aluminum level in low-silica drinking water and prevalence of Alzheimer's disease. Also, oral aluminum-based phosphate binders and antacids may induce acute aluminum toxicity. Whatever the source of the metal ingested, its bioavailability is a function of the chemical forms under which it occurs in the gastrointestinal tract, i.e. of the ligands with which the Al3+ ion may associate. Dietary acids in particular can favor the bioavailability of aluminum in different ways: by increasing its solubility, by complexing it into neutral species, and/or by acting indirectly on its absorption process. Among these, tartaric acid is commonly found in fruits and in industrial foods and drinks, and may therefore be ingested together with environmental or/and therapeutic aluminum. The present work examines its potential influence on aluminum bioavailability. Firstly, Al(III)-tartrate complex formation constants have been determined under physiological conditions (37 degrees C, 0.15 M NaCl). Then these constants have been used to simulate the influence of tartrate on aluminum speciation in different gastrointestinal situations in which phosphate was also taken into account. Under normal conditions of aluminum contamination, tartrate is expected to keep the metal soluble throughout the whole pH range of the small intestine, which is likely to enhance its bioavailability. Even at low concentrations, tartrate also gives rise to two neutral complexes that span over the 1.5-7.5 pH interval, a phenomenon that is aggravated by increased aluminum levels as may result from aluminum hydroxide therapy. The co-occurrence of dietary phosphate reduces the fraction of aluminum neutralized by tartrate under normal conditions, but this effect quickly decreases with increasing aluminum doses. Even the therapeutic use of aluminum phosphate is not expected to be totally safe in the presence of tartaric acid. As plasma simulations show that no aluminum mobilization can be expected from tartrate that could enhance aluminum excretion, avoiding ingestion of tartaric acid during any form of aluminum-based therapy appears advisable.

Influence of some dietary constituents on aluminum absorption and retention in rats

Eight groups of female Sprague-Dawley rats were treated with 281 mg Al(OH)3/kg/day by gastric intubation five times a week for five weeks. Concurrently, animals in seven groups received ascorbic acid (56.3 mg/kg/day), citric acid (62 mg/kg/day), gluconic acid (62.7 mg/kg/day), lactic acid (28.8 mg/kg/day), malic acid (42.9 mg/kg/day), oxalic acid (28.8 mg/kg/day), and tartaric acid (48 mg/kg/day) in the drinking water. The eighth group did not receive any dietary constituent in the water and was designated as the control group. Animals were placed in plastic metabolic cages and urine was collected during the treatment period. The liver, spleen, kidney, brain and bone aluminum levels of each rat were measured, as well as the total amount of aluminum excreted into urine. All the dietary constituents significantly increased the aluminum concentrations in most of the tissues, with ascorbic and citric acids showing the highest rate of aluminum accumulation. In contrast, no significant differences between control and treated rats were observed in the concentrations of aluminum excreted into urine. In view of these results, we suggest that the effects of the simultaneous ingestion of aluminum hydroxide and those dietary constituents in uremic animals should be evaluated. Meanwhile, the diet of uremic patients should be carefully monitored.

Aluminum speciation studies in biological fluids. Part 3. Quantitative investigation of aluminum-phosphate complexes and assessment of their potential significance in vivo

Following the discovery that specific health disorders affecting patients with renal disease were due to their excessive body accumulation of aluminum, it was established that aluminum toxicity was mainly due to the ingestion of aluminum-containing phosphate binders. Suspicion of toxicity was thus cast on aluminum-containing antacids, and subsequent tests held on healthy subjects did reveal that aluminum hydroxide gels were also potential oral sources of aluminum, especially in the presence of citric acid. Nevertheless, authors of these tests concluded that there was only marginal absorption of aluminum phosphate. In contrast with these clinical conclusions, it has recently been contended on theoretical grounds that aluminum phosphate represents a serious health hazard. To help elucidate this issue, this paper first deals with a quantitative investigation of aluminum-phosphate equilibria under physiological conditions. Then appropriate computer simulations based on corresponding results are used to assess the actual extent to which phosphate can influence aluminum bioavailability. These simulations confirm that aluminum phosphate is not expected to induce absorption of high amounts of aluminum when administered by itself. Nevertheless, this result may no longer apply in the presence of food, whose various acidic components are likely to modify the involved chemical equilibria. Moreover, it is shown that rising blood plasma phosphate levels should tend to increase aluminum tissue penetration and hence favor its potential toxicity.

The use of chelating agents in the treatment of aluminum overload

Desferrioxamine (DFO), traditionally used as an iron chelator has been shown to increase urinary aluminum output in humans and aluminum-loaded mice, rats and rabbits. However, major side-effects of DFO treatment have been observed and the drug may accumulate in dialysis patients receiving repeated doses. In recent years, it has been reported that some dicarboxylic or tricarboxylic acids such as succinic, malic or citric may be considered as possible alternatives to DFO in the management of aluminum accumulation. Ethylene-di-(o-hydroxyphenylacetic acid)-like compounds may also have potential as alternatives to DFO in the treatment of aluminum accumulation and aluminum-induced toxicity. Investigation of new therapeutic agents with lower toxicity than DFO and clinical advantages in administration and cost is clearly encouraged.