Effect of ascorbic acid on gastrointestinal aluminium absorption

The interaction of aluminum with catecholamine-based neurotransmitters: can the formation of these species be considered a potential risk factor for neurodegenerative diseases?

The potential neurotoxic role of Al(iii) and its proposed link with the insurgence of Alzheimer's Disease (AD) have attracted increasing interest towards the determination of the nature of bioligands that are propitious to interact with aluminum. Among them, catecholamine-based neurotransmitters have been proposed to be sensitive to the presence of this non-essential metal ion in the brain. In the present work, we characterize several aluminum-catecholamine complexes in various stoichiometries, determining their structure and thermodynamics of formation. For this purpose, we apply a recently validated computational protocol with results that show a remarkably good agreement with the available experimental data. In particular, we employ Density Functional Theory (DFT) in conjunction with continuum solvation models to calculate complexation energies of aluminum for a set of four important catecholamines: l-DOPA, dopamine, noradrenaline and adrenaline. In addition, by means of the Quantum Theory of Atoms in Molecules (QTAIM) and Energy Decomposition Analysis (EDA) we assessed the nature of the Al-ligand interactions, finding mainly ionic bonds with an important degree of covalent character. Our results point at the possibility of the formation of aluminum-catecholamine complexes with favorable formation energies, even when proton/aluminum competition is taken into account. Indeed, we found that these catecholamines are better aluminum binders than catechol at physiological pH, because of the electron withdrawing effect of the positively-charged amine that decreases their deprotonation penalty with respect to catechol. However, overall, our results show that, in an open biological environment, the formation of Al-catecholamine complexes is not thermodynamically competitive when compared with the formation of other aluminum species in solution such as Al-hydroxide, or when considering other endogenous/exogenous Al(iii) ligands such as citrate, deferiprone and EDTA. In summary, we rule out the possibility, suggested by some authors, that the formation of Al-catecholamine complexes in solution might be behind some of the toxic roles attributed to aluminum in the brain. An up-to-date view of the catecholamine biosynthesis pathway with sites of aluminum interference (according to the current literature) is presented. Alternative mechanisms that might explain the deleterious effects of this metal on the catecholamine route are thoroughly discussed, and new hypotheses that should be investigated in future are proposed.

Vitamin use among children attending a Canadian pediatric emergency department

Increasing use of vitamins has been documented worldwide in children and adolescents, and potential for vitamin-drug interactions exists. The aim of this study was to identify vitamin use by children visiting a pediatric emergency department (ED). A survey of parents and/or patients 0-18 years was conducted at a large pediatric ED in Canada. A total of 1804 families were interviewed. The main outcome measure was prevalence of vitamin use by children in the preceding 3 months. A third (32.3%) of the patients in our cohort had used vitamins in the preceding 3 months, and 48% of them were taking vitamins daily. Over 8% of all children used vitamins within the last 24 h. The use of vitamins was higher with older patient and parental age (P<0.001), chronic patient illness (P<0.001), completed immunization (P<0.001), concurrent patient use of prescribed medications (P=0.02), higher parental education (P<0.01), and English as a primary language spoken at home (P=0.002). Prevalence of vitamin use among children in the ED is 32% in the preceding 3 months and 8% within the last 24 h. In light of these findings, pediatricians should ask about vitamin use and discuss with parents potential interactions and possible adverse effects.

Safety considerations and potential interactions of vitamins: should vitamins be considered drugs?

OBJECTIVE

To examine adverse effects, adverse events, and potential interactions of vitamins in light of their current prevalence of use, and to discuss whether vitamins should be considered over-the-counter drugs or natural health products/dietary supplements.

DATA SOURCES

We performed a MEDLINE/PubMed search, explored 4 online databases (Medline Plus, Drug Digest, Natural Medicine Comprehensive Database, and the database of the University of Maryland), and examined reference lists of included studies published from 1966 through October 2009.

STUDY SELECTION AND DATA EXTRACTION

The studies were reviewed, with an emphasis on randomized controlled clinical trials. We included articles with the most clinically important information with regard to adverse events and interactions.

DATA SYNTHESIS

Vitamins are used by over one third of the North American population. Vitamins have documented adverse effects and toxicities, and most have documented interactions with drugs. While some vitamins (biotin, pantothenic acid, riboflavin, thiamine, vitamin B(12), vitamin K) have minor and reversible adverse effects, others, such as fat-soluble vitamins (A, E, D), can cause serious adverse events. Two water-soluble vitamins, folic acid and niacin, can also have significant toxicities and adverse events.

CONCLUSIONS

Our recommendation is that vitamins A, E, D, folic acid, and niacin should be categorized as over-the-counter medications. Labeling of vitamins, especially those intended for children and other vulnerable groups, should include information on possible toxicities, dosing, recommended upper intake limits, and concurrent use with other products. Vitamin A should be excluded from multivitamin supplements and food fortificants.

Potential vitamin-drug interactions in children: at a pediatric emergency department

BACKGROUND

A significant increase in vitamin use has been observed in recent years and interactions between vitamins and medications have been reported.

OBJECTIVE

To determine the frequency and types of potential interactions between vitamins and medications in children arriving at a large tertiary, pediatric emergency department. We also compared family characteristics of children with potential interactions with those of children with no potential interactions, in order to determine children at a higher risk.

METHODS

A cross-sectional study in which a survey was conducted of parents/caregivers and/or patients aged 0-18 years registered at a large pediatric emergency department in Canada. A total of 1804 families underwent a face-to-face interview. The main outcome measure was the rate of potential vitamin interactions in the preceding 3 months.

RESULTS

A considerable number of patients (11% of our cohort) had potential vitamin-medication interactions in the preceding 3 months, which could theoretically result in adverse events, and over one-third of these children had more than one potential interaction. Patients with potential interactions and their parents were significantly older (p < 0.001 for the child and mother, p = 0.02 for the father), the children were much more likely to have a chronic illness (p < 0.001) and concurrently receive prescribed or over-the-counter medication (p < 0.001), and more children with potential interactions were completely immunized (p = 0.02). The child's sex, parental education, employment status, family income, and primary language spoken at home were not associated with potential interactions.

CONCLUSIONS

Taking into account the high rate of potential vitamin-drug interactions, especially among older children and patients with chronic illness, parents and healthcare providers need to balance the potential benefit of concurrent vitamin-medication use with its potential harms.

Potential interactions of drug-natural health products and natural health products-natural health products among children

OBJECTIVE

To determine the frequency of concurrent use of conventional medications and natural health products (NHP) and their potential interactions in children arriving at an emergency department.

STUDY DESIGN

A survey of parents and patients 0 to 18 years at a large pediatric ED in Toronto, Ontario, Canada.

RESULTS

A total of 1804 families were interviewed in this study. Concurrent drug-NHP use was documented in 355 (20%) of patients and 269 (15%) of NHP users were receiving more than one NHP simultaneously. Theoretically possible NHP-drug or NHP-NHP interactions in the preceding 3 months were identified in 285 (16%) children. There were 35 different NHP-medication interaction pairs and 41 NHP-NHP interaction pairs. NHP-medication interactions were predominantly pharmacokinetic (modified absorption, 35%); potential NHP-NHP interactions were mostly pharmacodynamic (increased risk of bleeding, 47%).

CONCLUSIONS

Medications are used concurrently with NHP in every fifth pediatric patient in the emergency department and many NHP users are receiving more than 1 NHP simultaneously. One quarter of all paired medication-NHP or NHP-NHP could potentially cause interactions. Although we can not confirm that these were true interactions resulting in clinical symptoms, parents and health care providers need to balance the potential benefit of concurrent NHP-medication use with its potential harms.

Iron therapy for renal anemia: how much needed, how much harmful?

Iron deficiency is the most common cause of hyporesponsiveness to erythropoiesis-stimulating agents (ESAs) in end-stage renal disease (ESRD) patients. Iron deficiency can easily be corrected by intravenous iron administration, which is more effective than oral iron supplementation, at least in adult patients with chronic kidney disease (CKD). Iron status can be monitored by different parameters such as ferritin, transferrin saturation, percentage of hypochromic red blood cells, and/or the reticulocyte hemoglobin content, but an increased erythropoietic response to iron supplementation is the most widely accepted reference standard of iron-deficient erythropoiesis. Parenteral iron therapy is not without acute and chronic adverse events. While provocative animal and in vitro studies suggest induction of inflammation, oxidative stress, and kidney damage by available parenteral iron preparations, several recent clinical studies showed the opposite effects as long as intravenous iron was adequately dosed. Thus, within the recommended international guidelines, parenteral iron administration is safe. Intravenous iron therapy should be withheld during acute infection but not during inflammation. The integration of ESA and intravenous iron therapy into anemia management allowed attainment of target hemoglobin values in the majority of pediatric and adult CKD and ESRD patients.

The biological behaviour and bioavailability of aluminium in man, with special reference to studies employing aluminium-26 as a tracer: review and study update

Until 1990 biokinetic studies of aluminium metabolism and biokinetics in man and other animals had been substantially inhibited by analytical and practical difficulties. Of these, the most important are the difficulties in differentiating between administered aluminium and endogenous aluminium-especially in body fluids and excreta and the problems associated with the contamination of samples with environmental aluminium. As a consequence of these it was not possible to detect small, residual body burdens of the metal following experimental administrations. Consequently, many believed aluminium to be quantitatively excreted within a short time of uptake in all, but renal-failure patients. Nevertheless, residual aluminium deposits in a number of different organs and tissues had been detected in normal subjects using a variety of techniques, including histochemical staining methods. In order to understand the origins and kinetics of such residual aluminium deposits new approaches were required. One approach taken was to employ the radioisotope (67)Ga as a surrogate, but this approach has been shown to be flawed-a consequence of the different biological behaviours of aluminium and gallium. A second arose from the availability, in about 1990, of both (26)Al-a rare and expensive isotope of aluminium-and accelerator mass spectrometry for the ultra-trace detection of this isotope. Using these techniques the basic features of aluminium biokinetics and bioavailability have been unravelled. It is now clear that some aluminium is retained in the body-most probably within the skeleton, and that some deposits in the brain. However, most aluminium that enters the blood is excreted in urine within a few days or weeks and the gastrointestinal tract provides an effective barrier to aluminium uptake. Aspects of the biokinetics and bioavailability of aluminium are described below.

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.

Evaluation of the protective activity of deferiprone, an aluminum chelator, on aluminum-induced developmental toxicity in mice

BACKGROUND

Since deferiprone can be an effective chelating agent for the treatment of aluminum (Al) overload, in the present study we investigated whether this chelator could protect against Al-induced maternal and developmental toxicity in mice.

METHODS

A single oral dose of Al nitrate nonahydrate (1,327 mg/kg) was given on gestation day 12, the most sensitive time for Al-induced maternal and developmental toxic effects in mice. At 2, 24, 48, and 72 hr thereafter, deferiprone was given by gavage at 0 and 24 mg/kg. Cesarean sections were performed on day 18 of gestation and fetuses were examined for malformations and variations.

RESULTS

Aluminum-induced maternal toxicity was evidenced by significant reductions in body weight gain, corrected body weight change, and food consumption. Developmental toxicity was evidenced by a significant decrease in fetal weight per litter and an increase in the total number of fetuses and litters showing bone retardation. No beneficial effects of deferiprone on these adverse effects could be observed. By contrast, a more pronounced decrease in maternal weight gain and corrected body weight change, as well as a higher number of litters with fetuses showing skeletal variations was noted in the group exposed to Al nitrate and treated with deferiprone at 24 mg/kg.

CONCLUSIONS

According to the current results, deferiprone would not be effective to prevent Al-induced maternal and embryo/fetal toxicity in mice.

Does aluminum exposure of pregnant animals lead to accumulation in mothers or their offspring?

There is concern that environmental and dietary aluminum (Al) might cause developmental toxicity. To better understand this concern, we reviewed published studies which administered Al compounds to pregnant animals and measured accumulation of Al in mother, fetus, or born offspring. A total of 7 studies were identified which administered Al during gestation and evaluated fetal accumulation. Another 7 studies administered Al at least until birth and then evaluated accumulation in mothers and/or pups. These 14 studies included 4 different Al compounds (hydroxide, chloride, lactate, and citrate) administered by 4 different routes (gavage, feed, intraperitoneal injection, and subcutaneous injection) with total doses ranging from 13.5 to 8,400 mg/kg. Fetal Al levels were not increased in 6 of 7 studies and pup Al levels were not increased in 4 of 5 studies in which they were measured. Maternal Al levels were increased in some studies, but there was no consistent pattern of organ-specific accumulation and several positive studies were contradicted by subsequent reports from the same laboratory. Placental levels were increased in 6 of 9 studies and were greater than corresponding fetal levels. The weight of evidence in these studies suggests that environmental and dietary Al exposures are unlikely to pose risks of Al accumulation to pregnant animals or their fetuses.

Reproductive and developmental toxicity of aluminum: a review

It is well known that aluminum is a developmental toxicant when administered parenterally. However, until recently, there was little concern about embryo/fetal consequences of aluminum ingestion because bioavailability was considered low. The importance of the route of exposure and the chemical form of the aluminum compound on the developmental toxicity of this element are now well established. Although no evidence of maternal and embryo/fetal toxicity was observed when high doses of aluminum hydroxide were given orally to pregnant rats and mice during organogenesis, signs of maternal and developmental toxicity were found in mice when aluminum hydroxide was given concurrently with citric or lactic acids. On the other hand, studies in rabbits have shown that aluminum-induced behavioral toxicity is greater in adult and aged animals than in young adults. However, maternal dietary exposure to excess A1 during gestation and lactation which did not produce maternal toxicity would be capable of causing permanent neurobehavioral deficits in weanling mice and rats. Adverse effects of parenteral aluminum administration on the mouse male reproductive system have also been reported. The embryo/fetal toxicity of aluminum administration, the potential reproductive toxicology of aluminum exposure, and the neurodevelopmental effects of aluminum are here reviewed.

Comparative aluminium mobilizing actions of several chelators in aluminium-loaded uraemic rats

The relative effectiveness of deferoxamine (DFO), 1,2-dimethyl-1,3-hydroxypyrid-4-one (L1), and citric and succinic acids in mobilizing and promoting excretion of aluminium (Al) were compared in female uraemic rats which had previously received aluminium nitrate nonahydrate i.p. in a daily dose of 45 mg kg-1 for 3 weeks (5 days/week). Chelators were administered s.c. at doses equal to one-eighth of their respective LD50 for five days. L1 was also given p.o. in doses of 200 mg kg-1 day-1. Total urines were collected 24 h after each chelator administration. Total urinary Al excreted over the 5-day period, expressed as mg kg-1, were: controls, 3.4; DFO-treated, 4.5 (P < 0.05); citric acid-treated, 3.7; and succinic acid-treated, 2.7. Although the daily amounts of Al excreted into urine by L1-treated rats were significantly higher (P < 0.001) than those of the controls, most animals died during the period of treatment. Measurements of Al in selected tissues 24 h after the last administration of each chelator revealed that none of the compounds significantly altered the Al concentration in bone, kidney, and brain, whereas only DFO and succinic acid significantly reduced the levels of Al in spleen. Moreover, L1 (given s.c. or p.o.) and citric acid treatment led to a significant reduction in the liver Al burden. These results indicate the need for further investigations to determine the toxicity and the therapeutical safety margins of L1.

Aluminum chelation: chemistry, clinical, and experimental studies and the search for alternatives to desferrioxamine

This review focuses on aluminum (Al) chelation, its chemistry and biology. The toxicology and biology of Al in mammalian organisms are briefly reviewed to introduce the problems associated with excessive Al exposure and accumulation and the challenges facing an effective Al chelator. The basics of Al chelation chemistry are considered to help the reader understand the Al chelation chemical literature. The chemical properties of Al enable prediction of effective functional groups for Al chelation. A compilation of distribution coefficients between octanol and aqueous phases (Do/a) for chelators and their complexes with Al shows the effect of complexation on lipophilicity. A compilation of stability constants for Al.chelator complexes illustrates the role of oxygen in ligands that form stable complexes. The history of clinical Al chelation therapy is reviewed, with emphasis on desferrioxamine (DFO), which has been extensively used since 1980. The beneficial and adverse effects and limitations of DFO use in end-stage renal-diseased patients, in patients with neurodegenerative disorders, including Alzheimer's disease, and in animal models of Al intoxication are presented. The methods to evaluate potential Al chelators in vitro, in vivo, and using computer modeling are discussed. The Al chelation literature is reviewed by the chemical class of chelators, including fluoride, carboxylic acids, amino acids, catechols, polyamino carboxylic acids, phenyl carboxylic acids, the hydroxypyridinones, and hydroxamic acids.