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

Black Tea Source, Production, and Consumption: Assessment of Health Risks of Fluoride Intake in New Zealand

In countries with fluoridation of public water, it is imperative to determine other dietary sources of fluoride intake to reduce the public health risk of chronic exposure. New Zealand has one of the highest per capita consumption rates of black tea internationally and is one of the few countries to artificially fluoridate public water; yet no information is available to consumers on the fluoride levels in tea products. In this study, we determined the contribution of black tea as a source of dietary fluoride intake by measuring the fluoride content in 18 brands of commercially available products in New Zealand. Fluoride concentrations were measured by potentiometric method with a fluoride ion-selective electrode and the contribution of black tea to Adequate Intake (AI) and Tolerable Upper Intake Level (UL) was calculated for a range of consumption scenarios. We examined factors that influence the fluoride content in manufactured tea and tea infusions, as well as temporal changes in fluoride exposure from black tea. We review the international evidence regarding chronic fluoride intake and its association with chronic pain, arthritic disease, and musculoskeletal disorders and provide insights into possible association between fluoride intake and the high prevalence of these disorders in New Zealand.

Multiple Testing to Establish Superiority/Equivalence of a New Treatment Compared with k Standard Treatments for Unbalanced Designs

In clinical studies, multiple superiority/equivalence testing procedures can be applied to classify a new treatment as superior, equivalent (same therapeutic effect), or inferior to each set of standard treatments. Previous stepwise approaches (Dunnett and Tamhane, 1997, Statistics in Medicine16, 2489-2506; Kwong, 2001, Journal of Statistical Planning and Inference 97, 359-366) are only appropriate for balanced designs. Unfortunately, the construction of similar tests for unbalanced designs is far more complex, with two major difficulties: (i) the ordering of test statistics for superiority may not be the same as the ordering of test statistics for equivalence; and (ii) the correlation structure of the test statistics is not equi-correlated but product-correlated. In this article, we seek to develop a two-stage testing procedure for unbalanced designs, which are very popular in clinical experiments. This procedure is a combination of step-up and single-step testing procedures, while the familywise error rate is proved to be controlled at a designated level. Furthermore, a simulation study is conducted to compare the average powers of the proposed procedure to those of the single-step procedure. In addition, a clinical example is provided to illustrate the application of the new procedure.

Effect of iron status on the intestinal absorption of aluminum: a reappraisal

Clinical and experimental studies have shown that serum aluminum (Al) is bound to transferrin and that cellular uptake of Al appears to be mediated by transferrin receptors. Based on these findings it is widely believed that intestinal Al absorption occurs via iron-specific, transferrin-dependent pathways and that iron (Fe) deficiency increases the intestinal absorption of Al. However, since no transferrin receptors are expressed on the absorptive surface of small intestinal epithelial cells this notion is doubtful. To further clarify the issue the present study investigated the effect of marked alterations of body Fe stores on the intestinal absorption of Al using three different rat models. (I) Serum Al concentrations and urinary excretion rates of Al were measured in iron-overloaded (Fe+) or iron-deficient (Fe-) rats with either normal (C) or impaired (5/6 nephrectomy) renal function (Nx) employing oral A1 loads in single dose studies. (II) Tissue A1 accumulation as well as serum and urine A1 were determined in respective experimental groups exposed to a prolonged (41 days) dietary Al load. (III) To assess the effect of Fe status on the intestinal absorption of Al directly at the organ level perfusions of in situ rat gut preparations were performed. In the single dose studies administration of Al resulted in similar urinary excretion rates of Al in intact kidney groups (C+Fe-, 229 +/- 85 nmol/5 days; C+Fe+, 240 +/- 59 nmol/5 days) despite marked differences in liver Fe (C+Fe-, 1.34 +/- 0.16 vs. C+Fe+, 55.69 +/- 13.20 mumol/g) and duodenal mucosal Fe (C+Fe-, 0.68 +/- 0.11 vs. C+Fe+, 3.17 +/- 0.82 mumol/g). In addition, mucosal Al concentration 24 hours after the load was not affected by the Fe status (C+Fe-, 37 +/- 16 nmol/g, C+Fe+, 56 +/- 19 nmol/g). Regardless of the Fe status post-load Al excretion was enhanced in Nx rats (Nx+Fe-, 533 +/- 234 nmol/five days, Nx+Fe+, 536 +/- 201 nmol/five days). Irrespective of Fe status a prolonged dietary Al load resulted in a similar increase in tissue Al concentration (nmol/g) in liver (baseline, 159 +/- 22; C+Fe-, 276 +/- 125; C+Fe+, 251 +/- 71; Nx+Fe-, 330 +/- 119; Nx+Fe+, 437 +/- 67) and in bone (baseline, 219 +/- 119; C+Fe-, 433 +/- 174, C+Fe+, 485 +/- 141; Nx+Fe-, 504 +/- 185; Nx+Fe+, 548 +/- 215). The increase in spleen Al was significantly larger in Fe-overloaded rats (baseline, 194 +/- 20; C+Fe+, 511 +/- 129 vs. C+Fe-, 308 +/- 62, P < 0.05; Nx+Fe+, 514 +/- 67 vs. Nx+Fe-, 389 +/- 119, P < 0.05). Brain Al tended to rise in Nx rats only (baseline, 96 +/- 33; Nx+Fe+, 174 +/- 100, Nx+Fe-, 156 +/- 78, P = NS). Analogous results were obtained in in situ intestinal perfusion studies: Fe deficiency and Fe overload both did not affect the time-dependent increase in serum Al in either systemic or portal vein blood. When paracellular intestinal permeability was assessed mannitol absorption was significantly higher in uremic animals as compared to controls. Pharmacological blockade (2 mM kinetin) of the paracellular permeability substantially reduced the time-dependent increase in serum Al in uremic rats but had little effect in control animals, suggesting that even the excess absorption of Al observed in uremia occurs via a paracellular rather than an iron-specific pathway. In conclusion, the findings of the present study provide several lines of evidence against the commonly accepted view that the intestinal absorption of Al occurs via iron-specific pathways. Most likely, this is related to the fact, that neither the absorption of Fe nor the absorption of Al are mediated via transferrin receptors. In addition, the enhanced intestinal absorption of Al observed in uremic rats does also not occur via iron-specific pathways, but seems to due to increased paracellular permeability of the intestine.

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.