title: Effects of dietary folate on DNA strand breaks within mutation-prone exons of the p53 gene in rat colon.
abstract: OBJECTIVE
  Diminished folate status has been observed to increase colorectal cancer risk. Folate plays an important role in DNA synthesis and repair. This study investigated the effects of dietary folate on DNA strand breaks in the p53 and Apc genes, and how these changes are related to steady-state levels of the corresponding transcripts.
  
  
  METHODS
  Three groups of rats were fed diets containing 0, 2 (basal requirement), or 8 mg folate/kg for 5 weeks. At each weekly time point, plasma and colonic mucosal folate concentrations were determined. Site-specific DNA strand breaks were assessed by semiquantitative PCR. Steady-state levels of messenger RNA were measured by semiquantitative RT-PCR.
  
  
  RESULTS
  Dietary folate deficiency produced progressive DNA strand breaks within exons 5-8 of the p53 gene in rat colon (P<0.02). Accumulation of strand breaks was not observed in other exons of the p53 gene, in the Apc and beta-actin genes, or at the genomic level. Folate supplementation at 4 times the basal requirement significantly increased p53 integrity compared with the basal and deficient diets (P<0.05). p53 integrity in exons 5-8 was significantly correlated with folate status (P<0.03). Dietary folate deprivation progressively decreased, whereas supplementation increased, steady-state levels of p53 transcript over 5 weeks (P<0.05). No such changes were observed for the Apc gene. Steady-state levels of p53 transcript were significantly correlated with folate status and p53 integrity in exons 5-8 (P<0.002).
  
  
  CONCLUSIONS
  These data provide a plausible mechanism by which folate deficiency promotes, and folate supplementation suppresses, colorectal carcinogenesis.
authors.affiliation: Division of Gastroenterology, Department of Medicine, St. Michael's Hospital and University of Toronto, Toronto, Ontario, Canada. youngin.kim@utoronto.ca
authors.forename: Y I
authors.initials: YI
authors.lastname: Kim
authors.forename: S
authors.initials: S
authors.lastname: Shirwadkar
authors.forename: S W
authors.initials: SW
authors.lastname: Choi
authors.forename: M
authors.initials: M
authors.lastname: Puchyr
authors.forename: Y
authors.initials: Y
authors.lastname: Wang
authors.forename: J B
authors.initials: JB
authors.lastname: Mason
mesh_terms: D011125:Adenomatous Polyposis Coli / Q000235:genetics; D000818:Animals; D001835:Body Weight; D003106:Colon / Q000378:metabolism / Q000473:pathology / Q000502:physiology*; D004249:DNA Damage / Q000187:drug effects*; D004032:Diet; D005091:Exons / Q000235:genetics*; D005492:Folic Acid / Q000008:administration & dosage* / Q000097:blood / Q000378:metabolism / Q000494:pharmacology; D016158:Genes, p53 / Q000235:genetics*; D016678:Genome; D006454:Hemoglobins / Q000032:analysis; D006706:Homeostasis; D006710:Homocysteine / Q000097:blood; D007413:Intestinal Mucosa / Q000378:metabolism; D008297:Male; D009154:Mutation; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D006454:Hemoglobins; D012333:RNA, Messenger; D006710:Homocysteine; D005492:Folic Acid