title: Oligomeric but not monomeric silica prevents aluminum absorption in humans.
abstract: BACKGROUND
  Soluble silica, a ubiquitous component of the diet, may be the natural ligand for dietary aluminum and may prevent its accumulation and toxicity in animals. However, previous studies on the inhibition of aluminum absorption and toxicity by soluble silica have produced conflicting results. We recently identified a soluble silica polymer, oligomeric silica, that has a much higher affinity for aluminum than does monomeric silica and that may be involved in the sequestration of aluminum.
  
  
  OBJECTIVE
  By using (26)Al as a tracer, we investigated the effects of oligomeric and monomeric silica on the bioavailability of aluminum (study 1) and compared the availability of silicon from oligomeric and monomeric silica in the human gastrointestinal tract (study 2).
  
  
  METHODS
  In study 1, three healthy volunteers each ingested aluminum alone (control), aluminum with oligomeric silica (17 mg), and aluminum with monomeric silica (17 mg). In study 2, five healthy volunteers ingested both the oligomeric and monomeric forms of silica (34 mg). Serum and urine samples were analyzed for aluminum and silicon.
  
  
  RESULTS
  Oligomeric silica reduced the availability of aluminum by 67% (P = 0.01) compared with the control, whereas monomeric silica had no effect (P = 0.40). Monomeric silica was readily taken up from the gastrointestinal tract and then excreted in urine (53%), whereas oligomeric silica was not detectably absorbed or excreted.
  
  
  CONCLUSIONS
  The oligomeric, high-aluminum-affinity form of soluble silica reduces aluminum availability from the human gastrointestinal tract. Its potential role in the amelioration of aluminum toxicity in other biological systems requires attention.
authors.affiliation: Gastrointestinal Laboratory, The Rayne Institute, St Thomas' Hospital, London, UK. ravin.jugdaohsingh@kcl.ac.uk
authors.forename: R
authors.initials: R
authors.lastname: Jugdaohsingh
authors.forename: D M
authors.initials: DM
authors.lastname: Reffitt
authors.forename: C
authors.initials: C
authors.lastname: Oldham
authors.forename: J P
authors.initials: JP
authors.lastname: Day
authors.forename: L K
authors.initials: LK
authors.lastname: Fifield
authors.forename: R P
authors.initials: RP
authors.lastname: Thompson
authors.forename: J J
authors.initials: JJ
authors.lastname: Powell
mesh_terms: D000328:Adult; D000535:Aluminum / Q000097:blood / Q000493:pharmacokinetics* / Q000652:urine; D001682:Biological Availability; D005260:Female; D006801:Humans; D007408:Intestinal Absorption / Q000187:drug effects*; D007700:Kinetics; D046911:Macromolecular Substances; D008297:Male; D011868:Radioisotopes; D012825:Silicon / Q000097:blood / Q000652:urine; D012822:Silicon Dioxide / Q000008:administration & dosage / Q000737:chemistry* / Q000494:pharmacology*; D013329:Structure-Activity Relationship
chemical_list: D046911:Macromolecular Substances; D011868:Radioisotopes; D012822:Silicon Dioxide; D000535:Aluminum; D012825:Silicon