ALUMINUM EXPOSURE AND METABOLISM

Aluminum (Al) is a nonessential, toxic metal to which humans are frequ ently exposed. Oral exposure to aluminum occurs through ingestion of a luminum-containing pharmaceuticals and to a lesser extent foods and wa ter. Parenteral exposure to aluminum can occur via contaminated total parenteral nutrition (TPN), intravenous (iv) solutions, or contaminate d dialysates. Inhalation exposure may be important in some occupationa l settings. The gut is the most effective organ in preventing tissue a luminum accumulation after oral exposure. Typically gastrointestinal a bsorption of aluminum from diets is <1%. Although the mechanisms of al uminum absorption have not been elucidated, both passive and active tr anscellular processes and paracellular transport are believed to occur . Aluminum and calcium may share some absorptive pathways. Aluminum ab sorption is also affected by the speciation of aluminum and a variety of other substances, including citrate, in the gut milieu. Not all abs orbed or parenterally delivered aluminum is excreted in urine. Low glo merular filtration of aluminum reflects that most aluminum in plasma i s nonfilterable because of complexation to proteins, predominantly tra nsferrin. The importance of biliary secretion of aluminum is debatable and the mechanism(s) is poorly understood and appears to be saturable by fairly low oral doses of aluminum.