Developmental patterns of aluminum in mouse brain and effects of dietary aluminum excess on manganese deficiency

Importance of considering the framework principles in risk assessment for metals

The recent EPA Framework for Metals Risk Assessment provides the opportunity for contextual risk assessment for sites impacted by metals (such as the depicted Dauntless Mine in Colorado).

Lifelong feeding of a high aluminum diet to mice

In three experiments, high aluminum diets (1000 microg Al/g diet) were fed to mice throughout their life span to determine whether neurodegenerative changes were seen with aging. Brain Al concentrations were slightly lower in Al-treated mice than controls. Generally, no increased mortality or gross evidence of neurodegeneration was seen in Al-treated mice. Eighteen and 24 month old Swiss Webster mice fed the high aluminum diet differed from controls on some neurobehavioral tests, but differences were no greater than previously seen with shorter term exposure in younger mice. Both brain Al concentration and susceptibility to oxidative damage, as measured with TBARS, were lower in the Al-treated aged mice than in controls. In addition, Al-treated aged Swiss Webster and C57BL/6J mice showed somewhat enhanced performance in the Morris water maze. Finally, Al treatment did not exacerbate the effect of MPTP treatment on a grip strength measure in either 66 or 235 day old male mice. Swiss Webster and C57BL/6J mice do not appear to provide useful models for studying Al-induced neurodegenerative changes in aging.

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.

Developmental patterns of aluminum and five essential mineral elements in the central nervous system of the fetal and infant guinea pig

Al is found in the developing conceptus, but little information is available concerning its tissue distribution and its changes in concentration with age. Because Al has affinity for many of the same biological ligands as the essential mineral cations Ca, Mg, Zn, Fe, and Mn, we hypothesized that Al might show a pattern of developmental concentrations that was similar to one or more of these elements in the brain, a major target of Al toxicity. Concentrations of Al, Ca, Mg, Zn, Fe, and Mn were measured in spinal cord, brainstem, cerebellum, and forebrain of guinea pig fetuses on gestation day (GD) 30 and 45, at birth, and on postnatal day (PND) 3, 6, and 12. Dams were fed commercial guinea pig chow, which contained 47 micrograms Al/g. Tissue Al and Mn were measured with electrothermal atomic absorption spectrophotometry (ETAAS), and the other elements with inductively coupled axial plasma spectroscopy (ICAP-AES). Al concentrations in the brain regions were highest in spinal cord, brainstem, and cerebellum, and decreased during late gestation and lactation. Al did not show marked increases in regional brain concentrations during the final third of gestation as did Fe, Mg, and Zn. In contrast to Fe and Ca, Al did not accumulate in placenta. Al was the only element to show higher concentrations in spinal cord than in any other tissue at birth. In summary, the tissue distribution of Al did not follow that of essential cations as examined in this study.

Iron and manganese uptake by offspring of lactating mice fed a high aluminum diet

High dietary A1 can result in lowered tissue Mn and Fe concentrations in weanling mice. Possible mechanisms underlying this effect of A1 (altered milk Fe and Mn content, altered absorption or retention of Fe and Mn) were investigated in this experiment. To determine if milk composition was changed, milk was analyzed for Fe and Mn at 0, 3, 7, and 12 days postnatal. To determine if A1 influenced absorption and/or retention of Fe and Mn, a single milk meal containing 54Mn and 59Fe was administered by gavage to 12 day old pups and tissues were obtained 6 and 24 h later. Pup body and tissue weights were not affected by the high A1 diet. Milk from dams fed high A1 diets (1000 micrograms A1/g, n = 11, A11000) had similar Fe and Mn concentrations as milk from dams fed a control diet (7 micrograms A1/g, n = 11), although A1 concentrations were higher. Absorption and tissue distribution of 54Mn and 59Fe, as determined at the 6 h timepoint, were unaffected by maternal diet group (control n = 16, AL1000 n = 10). However, total retention of both 54Mn and 59Fe was 8-10% lower in the AL1000 pups 24 h after gavage (P = 0.030 for Mn and 0.017 for Fe). These data suggest that high dietary A1 during development alters the ability of nursing mouse pups to retain absorbed Fe and Mn.

Aluminum alters iron and manganese uptake and regulation of surface transferrin receptors in primary rat oligodendrocyte cultures

Transferrin (Tf) is a major transport protein for both iron (Fe) and aluminum (Al), as well as manganese (Mn) and it can mediate cellular uptake of these elements via cell surface Tf receptors. To study the effect of Al-Tf on Tf receptor regulation, primary oligodendrocyte cultures were prepared from cortices of newborn rats. The effects of Al-Tf on 54Mn and 59Fe uptake were compared to those of apo-, Fe-, or Mn-Tf (1.25 microM). To examine changes in cell surface Tf binding capacity, preincubation (4 h, 37 degrees C) was performed with apo-, Al- or Fe-Tf and homologous receptor binding studies were subsequently conducted with 125I-Fe-Tf at 4 degrees C. Incubation with Al-Tf, but not with equimolar amounts of Al chloride or Al citrate, led to dose-related increases in cellular Al. Incubation with either Al- or Fe-Tf decreased 59Fe uptake, while incubation with either Al- or Mn-Tf decreased 54Mn uptake. Surface Tf receptor sites/cell were 1.05, 0.60 and 0.46 x 10(5) after incubations with equivalent amounts of apo-, Fe-, and Al-Tf respectively. The data suggest that Al-Tf down-regulates surface Tf receptors on oligodendrocytes and can limit Fe and Mn uptake through this mechanism.

Evaluation of the developmental neuroendocrine and reproductive toxicology of aluminium

Two experiments evaluating functional endpoints pertaining to the developmental neuroendocrine effects of aluminum in the rat are reported. A total of 31 timed mated dams were fed by daily gastric gavage 0, 5, 25, 50, 250, 500 or 1000 mg/kg body weight/day aluminum as a solution of aluminum lactate in distilled water from days 5 to 15 of gestation. The 390 offspring were evaluated for morphological and physiological parameters of reproductive functioning, including birth weight, anogenital distance (AGD), timing of vaginal opening, regularly of oestrous cycles, duration of pseudopregnancy (PSP), number of superovulated oocytes, and gonadal weight. No consistent or reproducible findings suggestive of toxic effect were found in the parameters of birth weight, AGD, timing of vaginal opening, duration of PSP, number of superovulated oocytes, and adult gonadal weight. A temporary increase in the proportion of aberrant oestrous cycles was detected during the first four cycles after vaginal opening, in the 250 mg/body weight/day group, with none by the fifth consecutive oestrous cycle. These results suggest that, apart from a transient disturbance of oestrous cycle regularity, aluminum does not have a developmental reproductive toxic effect.