title: Dose dependency of canthaxanthin crystals in monkey retina and spatial distribution of its metabolites.
abstract: OBJECTIVE
  To establish the threshold level of canthaxanthin crystals in the retina of cynomolgus monkeys. To correlate the spatial distribution of all-trans canthaxanthin and its metabolites with the grade of crystals.
  
  
  METHODS
  Monkeys were orally administered 0, 0.2, 0.6, 1.8, 5.4, 16.2, and 48.6 mg/kg body wt canthaxanthin daily for 2.5 to 3 years. A second group of monkeys were administered 200 and 500 mg/kg body wt/d for 5 years. Ophthalmoscopy, electroretinography (ERG), retina and carotenoid analysis were performed as previously reported.
  
  
  RESULTS
  Crystals in the retina periphery were observed by ophthalmoscopy preterminally only in the extreme high doses of 200 to 500 mg/kg body wt/d. There were no adverse effects on visual functions as measured by ERG. Crystals in the peripheral retina, and/or in the macula, were detected microscopically in all canthaxanthin treated groups except at the lowest dose of 0.2 mg/kg body wt/d. The grade of crystals increased up to a dose of 16.2 mg/kg body wt/d. Dose-dependent increases in canthaxanthin content also were noted in the retina, the liver, and in plasma. All-trans canthaxanthin was the major compound in the peripheral and paracentral retina of very highly dosed animals, where its concentration correlated largely with the grade of inclusions. In the macula, 4'-OH-echinenone was the dominant canthaxanthin metabolite.
  
  
  CONCLUSIONS
  The grade of crystals in monkey retinas was dose dependent with a threshold level at 0.6 mg canthaxanthin/kg body wt/d. It correlated in the retinal periphery with the concentrations of all-trans-canthaxanthin and in the macula with its metabolites.
authors.affiliation: Vitamins & Fine Chemicals, Human Nutrition and Health, F.Hoffmann-LaRoche AG, Basel, Switzerland. regina.goralczyk@roche.com
authors.forename: R
authors.initials: R
authors.lastname: Goralczyk
authors.forename: F M
authors.initials: FM
authors.lastname: Barker
authors.forename: S
authors.initials: S
authors.lastname: Buser
authors.forename: H
authors.initials: H
authors.lastname: Liechti
authors.forename: J
authors.initials: J
authors.lastname: Bausch
mesh_terms: D000284:Administration, Oral; D000818:Animals; D016644:Canthaxanthin / Q000008:administration & dosage* / Q000493:pharmacokinetics* / Q000633:toxicity; D003460:Crystallization; D004305:Dose-Response Relationship, Drug; D004596:Electroretinography; D005260:Female; D008099:Liver / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D008252:Macaca fascicularis; D008297:Male; D009887:Ophthalmoscopy; D012160:Retina / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D012164:Retinal Diseases / Q000139:chemically induced* / Q000378:metabolism / Q000473:pathology
chemical_list: D016644:Canthaxanthin