Aluminum-26 metabolism in rats and effect of aluminum on calcium absorption and bone strength

Tasleem Ara Zafar, Purdue University

Abstract

Research on aluminum has focused on its potential adverse health role in renal patients on dialysis and senile dementia. However, little is known about its metabolism in the body due to lack of a suitable tracer. Because of the lack of a suitable isotope and sensitive technique of analysis, aluminum has been studied indirectly using analogues such as $\sp{67}$Ga (t${1\over2}=78$ hr). Recently, with the development of Accelerator Mass Spectrometry (AMS), it has become possible to use the artificially produced radionuclide of aluminum, $\sp{26}$Al, (t${1\over2}=7.16\times10\sp5$ yr). Both $\sp{67}$Ga and $\sp{26}$Al accumulated in rat tissues as: bone $>$ spleen $>$ kidney $>$ liver $>$ pancreas $>$ brain. $\sp{26}$Al cleared from the blood faster than $\sp{67}$Ga. Absorption and retention of $\sp{67}$Ga (2.26%) was significantly greater than $\sp{26}$Al (0.97%). Since $\sp{67}$Ga does not mimic aluminum metabolism, AMS is the only technique available for tracer aluminum study.^ Aluminum (Al) has been implicated in altering calcium metabolism because it suppresses calbindin-D28k in chick intestine and deposits at the calcification front in the bones, thereby interfering with normal bone mineralization. The effect of aluminum on calcium absorption, regulators of calcium absorption, intestinal adequate male Sprague-Dawley weanling rats was tested. Rats were fed a calcium adequate (0.5% calcium) diet or calcium deficient diet (0.1% calcium) with 0% aluminum, 0.05% aluminum, or 0.1% aluminum for 3 weeks. Half of the rats were sacrificed and the rest were all fed calcium adequate diets with the previous aluminum concentration for another 3 weeks. $\sp{45}$Ca absorption and parathyroid hormone increased during calcium deficiency but was only modestly affected by aluminum level. Aluminum suppressed calbindin-D9K upregulation, but not its mRNA at both time points. Less calbindin-D9k was synthesized in the fasting than the nonfasting rats.^ A supplementary study was conducted to investigate the effect of aluminum at a higher level (0.25%) in a severe calcium deficiency (0.02% calcium). Aluminum had an adverse effect on growth (food efficiency ratio) and bone calcium content. Bone strength measurements were not different than from the calcium deficient, 0 aluminum group. Calcium status was more important to bone health than aluminum exposure at the levels tested. ^

Degree

Ph.D.

Advisors

Major Professor: Connie M. Weaver, Purdue University.

Subject Area

Biology, Molecular|Health Sciences, Nutrition

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