The influence of calcium and humic substances on aluminium accumulation and toxicity in the minnow, Phoxinus Phoxinus, at low pH

Protection by natural blackwater against disturbances in ion fluxes caused by low pH exposure in freshwater stingrays endemic to the Rio Negro

Stenohaline freshwater stingrays (Potamotrygon spp.) are endemic to the very dilute (Na(+), Cl(-), Ca2(+) <or=30 micromol L(-1)), often acidic blackwaters of the Rio Negro despite gill Na(+) and Cl(-) transport characteristics that appear unfavorable (high K(m), low J(max)). We evaluated the possible protective role of blackwater itself, which is rich in dissolved organic carbon (DOC), as well as the importance of Ca(2+) in allowing this tolerance of dilute, acidic conditions. Responses of stingrays in natural blackwater (DOC=8.4 mg L(-1)) were compared with those in a natural reference water with similar ion levels but low DOC (0.6 mg L(-1)). Comparing these two water types, we found that differences in Na(+) and Cl(-) unidirectional fluxes (JXin, JXout; measured with radiotracers) and net fluxes (JXnet), influx and outflux kinetic relationships, and net ammonia excretion (J(Amm)) were generally small at pH 6.3, though the balance points where Jin=Jout shifted from >300 micromol L(-1) in reference water (low DOC) to about 100 micromol L(-1) in blackwater (high DOC). In reference water, both JNain and JClin were inhibited >90%, both JNaout and JClout more than doubled, and J(Amm) did not change at pH 4.0. In blackwater, the inhibition of influxes was attenuated, the increases in outflux did not occur, and J(Amm) increased by 60% at pH 4.0. Addition of 100 micromol L(-1) Ca(2+) to reference water prevented the increases in JNaout and JClout and allowed J(Amm) to increase at pH 4.0, which demonstrates that the gills are sensitive to Ca(2+). However, addition of Ca(2+) to blackwater had no effect on the responses to pH 4.0. Addition of commercial humic acid to reference water did not duplicate the effects of natural Rio Negro blackwater at the same DOC level; instead, it greatly exacerbated the increases in JNaout and JClout at low pH and prevented any protective influence of added Ca(2+). Thus, blackwater DOC appears to be very different from commercial humic acid. Biogeochemical modeling indicated that blackwater DOC prevents Ca(2+) binding, but not H(+) binding, to the gills and that the protective effects of blackwater cannot be attributed to its higher buffer capacity or its elevated Al or Fe levels. Natural DOC may act directly at the gills at low pH to exert a protective effect and, when doing so, may override any protective action of Ca(2+) that might otherwise occur.

Speciation of aluminium in forest soil extracts by size exclusion chromatography with UV and ICP-AES detection and cation exchange fast protein liquid chromatography with ETAAS detection

Aluminium speciation was studied in forest soil extracts by size exclusion chromatography (SE) with UV and inductively coupled plasma-atomic emission spectrometric (ICP-AES) detection and cation exchange fast protein liquid chromatography (FPLC) with ETAAS detection. Size exclusion chromatography was performed on a Superdex HR75 10/30 column. Isocratic clution with 0.15 mol dm(-3) NaCl in TRIS-HCl buffer (pH = 5.5) was applied over 100 min at a flow rate of 0.35 cm(3) min(-1). The chromatographic run was followed at 278 nm and separated Al species also determined 'off line' in 0.875 cm3 fractions by ICP-AES. The analytical procedure enabled speciation of high molecular weight Al complexes. Cation exchange FPLC was performed on a Mono S HR 5/5 column. Aqueous 8 mol dm(-3) NH4NO3 linear gradient elution was applied over 10 min at a flow rate of 1 cm3 min(-1). Separated Al species were collected in 0.5 cm3 fractions and Al determined 'off line' by ETAAS. The analytical procedure enabled speciation of some positively charged monomeric Al species. Negatively charged species were eluted with the solvent front. The combination of the two analytical techniques was successfully employed in speciation of Al in forest soil extracts. Water was used as an extracting solution. It was found experimentally that 80-95% of Al in aqueous extracts of forest soils exists in monomeric Al forms. Water soluble Al (30-40%) is bound to high molecular weight complexes with humic substances. The remaining monomeric Al in the low molecular weight fraction exists as AIF2+, Al-oxalate and Al-citrate species.

Inhibitory effects of aluminium on vitellogenin induction by estradiol-17 beta in the primary culture of hepatocytes in the rainbow trout Oncorhynchus mykiss

Effects of Al on estradiol-induced vitellogenin (VTG) induction were electrophoretically examined in primary hepatocyte cultures in rainbow trout. Hepatocytes were precultured for 2 days and then estradiol-17 beta (E2, 6 x 10(-6) M) and Al (10(-6)-10(-4) M) were added to the incubation medium. The hepatocytes were cultured for 5 more days. Spent media were analyzed by SDS-PAGE and the relative rate of VTG synthesis was evaluated by a measurement of the integrated optical density of the main VTG band and was expressed as the percentage of VTG to total proteins including the VTG. The addition of Al to the incubation medium had no effect on the viability of hepatocytes in the culture. However, it specifically reduced VTG synthesis by hepatocytes in a concentration-dependent way and there was a significant reduction at Al concentrations greater than 6 x 10(-5) M. VTG synthesis by E2-primed hepatocytes was also reduced by Al concentrations of more than 6 x 10(-5) M 2-6 days after Al addition. Enriched Ca concentrations (1.8 to 2.5 or 5.0 mM) in the incubation medium had no protective effect on the reduction of VTG synthesis by Al. These results suggest that the synthesis of VTG is more susceptible to Al than are other hepatocyte-derived proteins.

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.