Chemopreventive effects of dietary canola oil on colon cancer development.

Fatty acid composition of dietary fat plays a vital role in colon tumor development in animal models. Fats containing ω-6 fatty acids (e.g., corn oil) enhanced and ω-3 fatty acids (e.g., flaxseed oil) reduced chemically induced colon tumor development in rats. The objective of the present investigation was to study the effects of dietary canola oil, a source of ω-3 fatty acid on azoxymethane-induced colon cancer development in Fischer rats and compare with dietary corn oil. Dietary canola oil significantly (P<0.05) decreased colonic tumor incidence and tumor multiplicity as compared to dietary corn oil in rats. Fatty acid analysis showed that corn oil group had higher levels of ω-6 fatty acid levels, whereas the canola oil groups exhibited higher levels of ω-3 fatty acids from the colon and serum samples of rats. For the mechanistic study, COX-2 expression in the colon samples from the canola oil group was significantly lower (P<0.05) as compared to the corn oil group. Taken together, dietary canola oil may be chemopreventive for colon tumor development in Fischer rats as compared to possibly by increasing ω-3 fatty acid levels and decreasing COX-2 levels.

Increase in thiol oxidative stress via glutathione reductase inhibition as a novel approach to enhance cancer sensitivity to X-ray irradiation.

Depletion of the reduced form of glutathione (GSH) has been extensively studied for its effect on sensitizing cancer to radiation. However, little is known about the effects of thiol oxidative stress created through an increase in glutathione disulfide (GSSG) on cancer sensitivity to radiation. In this study, an increase in GSSG was effectively created using 2-acetylamino-3-[4-(2-acetylamino-2-carboxyethylsulfanylthiocarbonylamino)phenylthiocarbamoylsulfanyl]propionic acid (2-AAPA), an irreversible glutathione reductase (GR) inhibitor. Our results demonstrate that the GSSG increase significantly enhanced cancer sensitivity to X-ray irradiation in four human cancer cell lines (A431, MCF7, NCI-H226, and OVCAR-3). When cells were pretreated with 2-AAPA followed by X-ray irradiation, the IC(50) values for X-ray irradiation of A431, MCF7, NCI-H226, and OVCAR-3 cells were reduced, from 24.2 +/- 2.8, 42.5 +/- 3.0, 43.0 +/- 3.6, and 27.8+/-3.5 Gy to 6.75 +/- 0.9, 8.1 +/- 1.1, 6.75 +/- 1.0, and 12.1 +/- 1.7 Gy, respectively. The synergistic effects observed from the combination of X-rays plus 2-AAPA were comparable to those from the combination of X-rays plus buthionine sulfoximine, a reference compound known to increase cancer sensitivity to radiation. The synergistic effect was correlated with an increase in cell thiol oxidative stress, which was reflected by a five-to sixfold increase in GSSG and 25% increase in total disulfides. No change in GSH or total thiols was observed as a result of GR inhibition.

Effects of dietary flaxseed on intestinal tumorigenesis in Apc(Min) mouse.

Dietary flaxseed has been shown to prevent azoxymethane (AOM)-induced colorectal cancers in male Fisher rats. The present study was designed to investigate the chemopreventive effects of dietary flaxseed on the development of intestinal tumors in Apc(Min) mice. Apc(Min) mice were divided into five different groups, fed with control (AIN-93M meal), corn meal, flaxseed meal, corn oil, and flaxseed oil supplemented diets. Results showed that dietary flaxseed significantly decreased (P < 0.05) tumor multiplicity and size in the small intestine and colon as compared to control, corn-treated groups. Intestine, colon, and serum samples of corn-treated groups showed higher levels of omega -6 fatty acids, whereas the flaxseed treated groups exhibited higher levels of omega -3 fatty acids. Lignans were detected in the serum, intestine, and colon samples for flaxseed meal group. COX-1 and COX-2 expression in the colon samples from the flaxseed meal group were significantly lower (P < 0.05) as compared to the corn meal group. Dietary flaxseed may be chemopreventive for intestinal tumor development in Apc(Min) mice possibly by increasing omega -3 fatty acid levels, lignans, and decreasing COX-1 and COX-2 levels.

Chemopreventive effects of dietary flaxseed oil on colon tumor development.

Fatty acid composition of dietary fat, primarily the levels of omega-3 and omega-6 polyunsaturated fatty acids, has shown profound effect on colon tumor development in animal studies. Fats containing omega-6 fatty acids (for example, corn oil) enhanced and omega-3 fatty acids (for example, fish oil and mustard oil) reduced chemically induced colon tumors in rats. The purpose of this study was to investigate the effects of dietary flaxseed oil (containing alpha-linolenic acid, an omega-3 polyunsaturated fatty acid) on azoxymethane-induced colon tumor in rats and how it compared with the dietary corn oil-treated group. Male Fischer rats, separated into 2 groups of 30, were assigned to the AIN-93M diet, which was supplemented with either 15% corn oil or 15% flaxseed oil. Carcinogenesis was initiated with subcutaneous injections of azoxymethane (15 mg/kg) once a week for three consecutive weeks. Thirty-five weeks after initiation, the rats were sacrificed under ether anesthesia. Blood was collected by cardiac puncture. The gastrointestinal tract was isolated and flushed with ice-cold normal saline. The site, size, and number of tumors were recorded. The incidence and multiplicity of the tumors in the colon were determined. The fatty acid composition in the serum, colon, and tumors was estimated by using gas chromatography-flame ionization detection. Colon tumor incidence was found to be 100% and 54%, whereas multiplicity was found to be 3.1 and 0.7 tumors per rat in corn oil- and flaxseed oil-treated groups, respectively. Tumor size was significantly larger in the corn oil-treated group than in the flaxseed oil group. Colon and serum samples of the corn oil group showed an increase in the omega-6 fatty acid levels, whereas the flaxseed oil group exhibited an increase in the omega-3 fatty acid levels. The results indicate that dietary flaxseed oil, containing high levels of omega-3 fatty acids, is effective in preventing colon tumor development when compared with dietary corn oil containing omega-6 fatty acids in rats.

A simultaneous liquid chromatography/mass spectrometric assay of glutathione, cysteine, homocysteine and their disulfides in biological samples.

A liquid chromatography/mass spectrometric (LC/MS) method was developed for simultaneous detection and quantitation of glutathione (GSH), glutathione disulfide (GSSG), cysteine (CysSH), homocysteine (HCysSH) and homocystine in biological samples (rat brain, lung, liver, heart, kidneys, erythrocytes and plasma). Thiols were derivatized with a large excess of Ellman's reagent, a thiol-specific reagent, to ensure an instantaneous and complete derivatization. The derivatization blocked the oxidation of the thiols to disulfides, preventing errors caused by thiol oxidation. The samples were then analyzed by LC/MS. The method provides a highly selective and sensitive assay for these endogenous thiols and their corresponding disulfides. The detection limits for GSH, GSSG, CysSH, HCysSH and homocystine were 3.3, 3.3, 16.5, 29.6 and 14.9 pmol, respectively. An attempt for cystine analysis was unsuccessful due to earlier elution of the compound and strong interferences caused by other endogenous compounds. This method will be a useful tool in the investigation of the roles of these important thiol-containing compounds and their corresponding disulfides in physiological and pathological processes.

Chemopreventive effects of alpha-santalol on skin tumor development in CD-1 and SENCAR mice.

Studies from our laboratory have indicated skin cancer chemopreventive effectsof sandalwood oil in CD-1 mice. The purpose of this investigation was to study the skin cancer chemopreventive effects of alpha-santalol, a principal component of sandalwood oil in CD-1 and SENCAR mice. alpha-Santalol was isolated from sandalwood oil by distillation under vacuum and characterized by nuclear magnetic resonance and gas chromatography-mass spectrometry. Chemopreventive effects of alpha-santalol were determined during initiation and promotion phase in female CD-1 and SENCAR mice. Carcinogenesis was initiated with 7,12-dimethylbenz(a)anthracene and promoted with 12-O-tetradecanoylphorbol-13-acetate (TPA). The effects of alpha-santalol treatment on TPA-induced epidermal ornithine decarboxylase (ODC) activity and (3)H-thymidine incorporation in epidermal DNA of CD-1 and SENCAR mice were also investigated. alpha-Santalol treatment during promotion phase delayed the papilloma development by 2 weeks in both CD-1 and SENCAR strains of mice. alpha-Santalol treatment during promotion phase significantly (P < 0.05) decreased the papilloma incidence and multiplicity when compared with control and treatment during initiation phase during 20 weeks of promotion in both CD-1 and SENCAR strains of mice. alpha-Santalol treatment resulted in a significant (P < 0.05) inhibition in TPA-induced ODC activity and incorporation of (3)H-thymidine in DNA in the epidermis of both strains of mice. alpha-Santalol significantly prevents papilloma development during promotion phase of 7,12-dimethylbenz(a)anthracene-TPA carcinogenesis protocol in both CD-1 and SENCAR mice, possibly by inhibiting TPA-induced ODC activity and DNA synthesis. alpha-Santalol could be an effective chemopreventive agent for skin cancer. Additional experimental and clinical studies are needed to investigate the chemopreventive effect of alpha-santalol in skin cancer.