In our previous short-term experiment, Citrus auraptene inhibited the development of azoxymethane (AOM)-induced aberrant crypt foci, which are precursor lesions for colorectal carcinoma. In the present study, the possible inhibitory effect of dietary administration of auraptene was investigated using an animal colon carcinogenesis model with a colon carcinogen AOM. Male F344 rats were given s.c. injections of AOM (15 mg/kg body weight) once a week for 3 weeks to induce colon neoplasms. They also received diets containing 100 or 500 ppm auraptene for 4 weeks in groups of "initiation" feeding, starting 1 week before the first dosing of AOM. The diets containing auraptene were also given to rats for 38 weeks in groups of "postinitiation" feeding. At the termination of the study (38 weeks), dietary administration of auraptene caused dose-dependent inhibition in AOM-induced large bowel carcinogenesis. Auraptene feeding during the initiation phase reduced the incidence of colon adenocarcinoma by 49% at 100 ppm (P = 0.099) and 65% at 500 ppm (P = 0.0075). Auraptene administration during the postinitiation phase inhibited the incidence of colon adenocarcinoma by 58% at 100 ppm (P = 0.021) and 65% at 500 ppm (P = 0.0075). Also, the multiplicity of colon carcinoma was significantly reduced by initiation feeding at a dose level of 500 ppm (P < 0.01) and postinitiation feeding at a level of 100 and 500 ppm (P < 0.05 and P < 0.01, respectively). Feeding of auraptene suppressed the expression of cell proliferation biomarkers (ornithine decarboxylase activity and polyamine content) in the colonic mucosa and reduced the production of aldehydic lipid peroxidation [malondialdehyde and 4-hydroxy-2(E)-nonenal]. In addition, auraptene increased the activities of Phase II drug-metabolizing enzymes (glutathione S-transferase and quinone reductase) in the liver and colon. These findings suggest that the inhibitory effects of auraptene on AOM-induced colon tumorigenesis at the initiation level might be associated, in part, with increased activity of Phase II enzymes, and those at the postinitiation stage might be related to suppression of cell proliferation and lipid peroxidation in the colonic mucosa.

Citrus Auraptene Exerts Dose-dependent Chemopreventive Activity in Rat Large Bowel Tumorigenesis : The Inhibition Correlates with Suppression of Cell Proliferation and Lipid Peroxidation and with Induction of Phase II Drug-metabolizing Enzymes.

In our studies to find natural compounds with chemopreventive efficacy in foods, using azoxymethane (AOM)‐induced colonic aberrant crypt foci and colonic mucosal cell proliferation as biomarkers, a x an thine oxidase inhibitor, 1′‐acetoxychavicol acetate (ACA), present in the edible plant Languas galanga from Thailand was found to be effective. This study was conducted to test the ability of ACA to inhibit AOM‐induced colon tumorigenesis when it was fed to rats during the initiation or post‐initiation phase. Male F344 rats were given three weekly s.c. injections of AOM (15mg/kg body weight) to induce colonic neoplasms. They were fed diet containing 100 or 500 ppm ACA for 4 weeks, starting one week before the first dosing of AOM (the initiation feeding). The other groups were fed the ACA diet for 34 weeks, starting one week after the last AOM injection (the post‐initiation feeding). At the termination of the study (week 38), AOM had induced 71% incidence of colonic adenocarcinoma (12/17 rats). The initiation feeding with ACA caused significant reduction in the incidence of colon carcinoma (54% inhibition by 100 ppm ACA feeding and 77% inhibition by 500 ppm ACA feeding, P=0.03 and P=0.001, respectively). The post‐initiation feeding with ACA also suppressed the incidence of colonic carcinoma (45% inhibition by 100 ppm ACA feeding and 93% inhibition by 500 ppm ACA feeding, P=0.06 and P=0.00003, respectively). Such inhibition was dose‐dependent and was associated with suppression of proliferation biomarkers, such as ornithine decarboxylase activity in the colonic mucosa, and blood and colonic mucosal polyamine contents. ACA also elevated the activities of phase II enzymes, glutathione S‐transferase (GST) and quinone reductase (QR), in the liver and colon. These results indicate that ACA could inhibit the development of AOM‐induced colon tumorigenesis through its suppression of cell proliferation in the colonic mucosa and its induction of GST and QR. The results confirm our previous finding that ACA feeding effectively suppressed the development of colonic aberrant crypt foci. These findings suggest possible chemopreventive ability of ACA against colon tumorigenesis.

Chemoprevention of Azoxymethane‐induced Rat Colon Carcinogenesis by a Xanthine Oxidase Inhibitor, 1′‐Acetoxychavicol Acetate

The modifying effect of three doses of dl-α-difluoromethylornithine (DFMO) given p.o. during the postinitiation phase of tongue carcinogenesis initiated by 4-nitroquinoline 1-oxide (4-NQO) was studied in male ACI/N rats. Animals were given 4-NQO at 20 ppm for 8 weeks in the drinking water to induce tongue neoplasms. One week after the stop of 4-NQO treatment, rats were transferred to the drinking water containing DFMO at concentrations of 100, 1000, and 2000 ppm for 25 weeks. The other groups consisted of rats given 2000 ppm DFMO alone or untreated rats. Thirty-four weeks after the start of the experiment, all animals were necropsied, and the incidences of neoplasms and preneoplastic lesions in the tongue, polyamine levels in the bloods and tongue tissues, and cell proliferation estimated by the number and area of silver-stained nucleolar organizer regions in the tongue epithelium were compared among the groups. Feeding of DFMO at all doses significantly inhibited the incidence of tongue neoplasms compared to the group give 4-NQO alone. DFMO at levels of 1000 and 2000 ppm significantly reduced the incidence of preneoplastic lesions of the tongue. Results analyzed by the linear regression method suggested a dose-dependent inhibition in the incidences of neoplastic and preneoplastic lesions of the tongue with increasing levels of DFMO. Increased levels in polyamines in the blood and tongue tissue were significantly suppressed by the treatment of DFMO. Also, silver-stained nucleolar organizer region indices were significantly reduced by the DFMO exposure. These results indicate that increasing levels of DFMO in the drinking water inhibited 4-NQO-induced tongue carcinogenesis in a dose-dependent manner and such inhibition was related to reduction in the polyamine levels of blood and tissue and decrease in the cell proliferation.

/pdf/chemoprevention-of-oral-carcinogenesis-by-dl-a-43371nlyho.pdf

Chemoprevention of Oral Carcinogenesis by dl-α-Difluoromethylornithine, an Ornithine Decarboxylase Inhibitor: Dose-dependent Reduction in 4-Nitroquinoline 1-Oxide-induced Tongue Neoplasms in Rats

The enzymatic method for isolation and determination of urinary polyamines was modified to measure the polyamines in the blood. High recovery rates of polyamine in blood by enzymatic hydrolyzation were obtained, namely, 101.9 +/- 4.4% for diamine, 96.0 +/- 5.4% for spermidine and 104.1 +/- 3.3% for spermine. Furthermore excellent linearity was demonstrated. Within-run precision of polyamine in blood was excellent, namely, in C.V., 1.15% for Reaction 1, 2.11% for Reaction 2 and 2.79% for Reaction 3. This method was compared with high pressure liquid chromatography (HPLC), and a close correlation was demonstrated for all the fractions: diamine r = 0.8824, y = 1.367x+0.0417 (n = 15); spermidine r = 0.9878, y = 0.806x+5.218 (n = 15); spermine r = 0.9764, y = 1.068x-0.9195 (n = 15).

Detection of Polyamines by a New Enzymatic Differential Assay (4) : Fundamental Study on a New Enzymatic Differential Assay of Blood.

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Detection of Polyamines by a New Enzymatic Differential Assay (4) : Fundamental Study on a New Enzymatic Differential Assay of Blood.