TitlePromotion versus suppression of rat colon carcinogenesis by chlorophyllin and chlorophyll: modulation of apoptosis, cell proliferation, and beta-catenin/Tcf signaling.
Publication TypeJournal Article
Year of Publication2003
AuthorsBlum CA, Xu M, Orner GA, G Díaz D, Li Q, Dashwood WMohaiza, Bailey GS, Dashwood RH
JournalMutat Res
Volume523-524
Pagination217-23
Date Published2003 Feb-Mar
ISSN0027-5107
Keywords1,2-Dimethylhydrazine, Animals, Anticarcinogenic Agents, Apoptosis, beta Catenin, Carcinogens, Chlorophyll, Chlorophyllides, Colonic Neoplasms, Cytoskeletal Proteins, Quinolines, Rats, Trans-Activators
Abstract

The carcinogens 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 1,2-dimethylhydrazine (DMH) induce colon tumors in the rat that contain mutations in beta-catenin, but the mutation pattern can be influenced by exposure to dietary phytochemicals, such as the water-soluble derivative of chlorophyll called chlorophyllin. Whereas chlorophyllin is an effective blocking agent during the initiation phase, post-initiation responses depend upon the exposure protocol, and can be influenced by the initiating agent and the concentration of chlorophyllin. Post-initiation treatment with 0.001% chlorophyllin (w/v) in the drinking water promoted colon carcinogenesis in the rat, but much higher concentrations (1.0% chlorophyllin) led to suppression. Bromodeoxyuridine and terminal deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) indices revealed that the promotional concentration of 0.001% chlorophyllin increased the ratio of cell proliferation to apoptosis in the colonic crypts, whereas concentrations in the range 0.0l-1.0% chlorophyllin modestly reduced this ratio. Molecular studies showed that the spectrum of beta-catenin mutations was markedly different in chlorophyllin-promoted colon tumors--many of the mutations led to direct substitutions of critical Ser/Thr residues within the glycogen synthase kinase-3beta (GSK-3beta) region, whereas in all other groups, including DMH and IQ controls, the mutations typically affected amino acids adjacent to Ser(33). Substitution of critical Ser/Thr residues caused beta-catenin and c-Jun proteins to be markedly over-expressed compared with tumors in which the mutations substituted amino acid residues flanking these critical Ser/Thr sites. In a separate study, rats were exposed to IQ or azoxymethane (AOM), a metabolite of DMH, and they were treated post-initiation with chlorophyllin, chlorophyll, copper, or phytol in the diet. Natural chlorophyll (0.08%) suppressed AOM- and IQ-induced aberrant crypt foci (ACF), whereas chlorophyllin had no effect and copper promoted the number of small ACF induced by IQ. The results suggest that further investigation of the dose-response for suppression versus promotion by chlorophyll and chlorophyllin is warranted, including studies of the beta-catenin/Tcf signaling pathway and its influence on cell proliferation and apoptosis in the colonic crypt.

Alternate JournalMutat. Res.
PubMed ID12628520
Grant ListR01 CA080176-03 / CA / NCI NIH HHS / United States
P01 CA090890-01A20003 / CA / NCI NIH HHS / United States
CA34732 / CA / NCI NIH HHS / United States
CA90890 / CA / NCI NIH HHS / United States
P01 CA090890-05S1 / CA / NCI NIH HHS / United States
ES00210 / ES / NIEHS NIH HHS / United States
CA80176 / CA / NCI NIH HHS / United States
ES03850 / ES / NIEHS NIH HHS / United States
P01 CA090890-05 / CA / NCI NIH HHS / United States
R01 CA065525-08 / CA / NCI NIH HHS / United States
R01 CA080176-02 / CA / NCI NIH HHS / United States
R01 CA065525-09 / CA / NCI NIH HHS / United States
T32 ES07060 / ES / NIEHS NIH HHS / United States
R01 CA080176-05 / CA / NCI NIH HHS / United States
CA65525 / CA / NCI NIH HHS / United States
R01 CA065525-07 / CA / NCI NIH HHS / United States
R01 CA080176-04 / CA / NCI NIH HHS / United States
R01 CA065525-06A1 / CA / NCI NIH HHS / United States
P01 CA090890-01A29001 / CA / NCI NIH HHS / United States