title: Temporal variation and identification of factors associated with endogenous retinoic acid isomers in serum from Brazilian women.
abstract: OBJECTIVE
  Retinoids (natural and synthetic derivatives of vitamin A) have cancer chemotherapeutic and chemopreventive activities. Retinoic acid (RA) treatment has been associated with significant regression of preneoplastic lesions. However, serious toxicity associated with some therapies has made long-term chemoprevention in healthy populations unfeasible. Recently, serum RA has been shown to increase in response to oral retinol (vitamin A) supplementation. Here, we assess the variability of circulating RA levels and the lifestyle, demographic, and nutritional factors that explain such variability.
  
  
  METHODS
  Total RA concentration and the concentrations of RA isomers (all-trans-RA, 13-cis-RA, and 9-cis-RA) were measured by high-pressure liquid chromatography in serum samples obtained 4 months apart from 502 women participating in the Ludwig-McGill Cohort (Sao Paulo, Brazil).
  
  
  RESULTS
  The relative abundance of the three RA isomers was similar for each visit (baseline and month 4), with 13-cis-RA having the highest concentrations followed by 9-cis-RA and all-trans-RA. The within-person variability of total RA and individual isomers was low. Using multivariate logistic regression models (upper tertile versus low/middle tertile of serum RA), we found that age, race, oral contraceptive use, total number of pregnancies, and season of initial blood draw were significantly associated with at least one endogenous RA isomer level. All endogenous RA isomers were positively associated with serum retinol, beta-carotene, and beta-cryptoxanthin levels.
  
  
  CONCLUSIONS
  These results have implications for the design of future epidemiologic studies focused on assessing RA-disease association and intervention studies aimed at modulating RA levels.
authors.affiliation: H. Lee, Moffitt Cancer Center and Research Institute, 12902 Magnolia Drive, MRC-2E, Tampa, FL 33612, USA.
authors.forename: Erin M
authors.initials: EM
authors.lastname: Siegel
authors.forename: Neal E
authors.initials: NE
authors.lastname: Craft
authors.forename: Denise J
authors.initials: DJ
authors.lastname: Roe
authors.forename: Eliane
authors.initials: E
authors.lastname: Duarte-Franco
authors.forename: Luisa L
authors.initials: LL
authors.lastname: Villa
authors.forename: Eduardo L
authors.initials: EL
authors.lastname: Franco
authors.forename: Anna R
authors.initials: AR
authors.lastname: Giuliano
mesh_terms: D000328:Adult; D001938:Brazil; D002784:Cholesterol / Q000097:blood; D002851:Chromatography, High Pressure Liquid; D004032:Diet; D005260:Female; D006801:Humans; D007641:Keratolytic Agents / Q000097:blood*; D008019:Life Style; D012621:Seasons; D012923:Social Class; D013237:Stereoisomerism; D014212:Tretinoin / Q000097:blood*
chemical_list: D007641:Keratolytic Agents; D014212:Tretinoin; D002784:Cholesterol