Promotion versus suppression of rat colon carcinogenesis by chlorophyllin and chlorophyll: modulation of apoptosis, cell proliferation, and beta-catenin/Tcf signaling.
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.
Blum
Carmen A
CA
Department of Environmental and Molecular Toxicology, Linus Pauling Institute, Oregon State University, 571 Weniger Hall, Corvallis, OR 97331-6512, USA.
Xu
Meirong
M
Orner
Gayle A
GA
Darío Díaz
G
G
Li
Qingjie
Q
Dashwood
Wan Mohaiza
WM
Bailey
George S
GS
Dashwood
Roderick H
RH
D019813:1,2-Dimethylhydrazine / Q000633:toxicity*; D000818:Animals; D016588:Anticarcinogenic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D002273:Carcinogens / Q000633:toxicity*; D002734:Chlorophyll / Q000494:pharmacology*; D002735:Chlorophyllides / Q000494:pharmacology*; D003110:Colonic Neoplasms / Q000139:chemically induced* / Q000473:pathology / Q000517:prevention & control*; D003598:Cytoskeletal Proteins / Q000502:physiology*; D011804:Quinolines / Q000633:toxicity; D051381:Rats; D015534:Trans-Activators / Q000502:physiology*; D051176:beta Catenin
D016588:Anticarcinogenic Agents; D002273:Carcinogens; D002735:Chlorophyllides; C495268:Ctnnb1 protein, rat; D003598:Cytoskeletal Proteins; D011804:Quinolines; D015534:Trans-Activators; D051176:beta Catenin; D002734:Chlorophyll; C007020:chlorophyllin; D019813:1,2-Dimethylhydrazine