Suppression of tumour-promoting factors in fat-induced colon carcinogenesis by the antioxidants caroverine and ubiquinone.

Fatty acid hydroperoxides are produced from unsaturated fatty acids in the presence of oxygen at elevated temperatures during food processing. Their effects on gene expression in colorectal tumour cells were studied using linoleic acid hydroperoxide (LOOH) as a model compound. Addition of LOOH to the medium of LT97 adenoma and SW480 carcinoma cells enhanced the production of hydrogen peroxide. Both cell lines were observed to increase VEGF factors based on mRNA. High consumption of dietary fat promotes colon carcinogenesis in the long-term. While this effect is well known, the underlying mechanisms are not understood. An approach was made starting from the assumption that LOOH is present in dietary fats as a result of heating. LOOH undergoes homolytic cleavage in the presence of iron. Various radicals are formed on mixing LT97 or SW480 cells with LOOH. The expression of tumour-promoting factors was inhibited by caroverine and ubiquinone, which may be justified as active chemopreventive agents.

Ubiquinol and the papaverine derivative caroverine prevent the expression of tumour- promoting factors in adenoma and carcinoma colon cancer cells induced by dietary fat.

High consumption of dietary fat promotes colon carcinogenesis. While this effect is well known the underlying mechanism is not understood. Fatty acid hydroperoxides (LOOH) arise from unsaturated fatty acids in the presence of oxygen and elevated temperature during food processing. An approach was made starting from the assumption that LOOH are present in dietary fats as a result of boiling. LOOH undergoes homolytic cleavage in the presence of iron. We studied their effects on gene expression in colorectal tumour cells using linoleic acid hydroperoxide (LOOH) as model compound. Addition to the medium of LT97 adenoma and SW480 carcinoma cells enhanced the production of hydrogen peroxide. Both cell lines were observed to increase VEGF and COX-II expression based on mRNA. Expression of VEGF was inhibited by caroverine and ubiquinon.

Bile acid induced gene expression in LT97 colonic adenoma cells.

LT97 human colonic adenoma cells reflecting early premalignant genotype and growth characteristics have been posed to tumor promoting bile acids in order to identify marker genes that permit identification of tumor promoters in vitro. Physiologically relevant concentrations of desoxycholate (DOC) and chenodesoxycholate (CDC) upregulated expression of c-fos and COX-2 in a concentration- and time-dependent manner. Transient induction of c-fos was seen with the non-promoting taurodesoxycholate (TDOC) as well as DOC, however extended induction at 3 h was only achieved by DOC and CDC reaching 3-6-fold as compared to the control. Stimulation of COX-2 expression was completely specific for the tumor promoting analogs DOC and CDC. It was about 4-fold in the 80 microM DOC and CDC groups after 3 h and increased to 12- and 7-fold respectively after 6 h. Expression of VEGF was stimulated 4-5-fold in the tumor promoter (DOC and CDC) groups and about 2-fold in the non-promoting controls TDOC and GCDC. At later times the tumor promoter specific difference was lost. Our results show that all three genes are modulated in a tumor promoter dependent way and that their upregulation in LT97 adenoma cells can be used for in vitro testing of colon tumor promoters and chemopreventive compounds.

Dietary lipid hydroperoxides induce expression of vascular endothelial growth factor (VEGF) in human colorectal tumor cells.

Fatty acid hydroperoxides arise from unsaturated fatty acids in the presence of oxygen and elevated temperature during processing of food. Here we have studied their effects on gene expression in colorectal tumor cells using linoleic acid hydroperoxide (LOOH) as a model compound. Its addition to the medium of LT97 human adenoma cells and SW480 human carcinoma cells enhanced the production of intracellular hydrogen peroxide. Furthermore, in both cell lines, increases in VEGF mRNA and protein were observed. Unoxidized linoleic acid had little or no activity. Concomitantly, COX-2 expression was up-regulated. In the LT97 cells, the COX inhibitors SC58560 and SC58236 completely prevented the VEGF induction, suggesting that the effect was dependent on prostaglandin synthesis. In vivo prostaglandin-mediated induction of VEGF secretion is known to be essential for the growth of adenomatous polyps and their progression to carcinomas. Therefore, our results for the first time implicate dietary lipid hydroperoxide as a key risk factor in colon carcinogenesis.

Induction of lipid peroxidation in biomembranes by dietary oil components.

Prooxidant formation and resulting lipid peroxidation are supposed to be involved in the pathogenesis of various diseases including cancer. Cancer risk is possibly influenced by the composition of diet with high intake of fat and red meat being harmful and high consumption of fruits and vegetables being protective. Since dietary oils may contain potential prooxidants, the aim of the present study was to prove (i) whether oxidative stress in biomembranes may be induced by dietary oils and if, (ii) which impact it has on the viability and proliferation of cultured colon (carcinoma) cells. Lipid hydroperoxide content in dietary oils increased after heating. Linoleic acid hydroperoxide (LOOH) and/or oils with different hydroperoxide contents induced lipid peroxidation in liposomes, erythrocyte ghosts and colon cells. Upon incubation with liposomes, both LOOH and heated oil induced lipid peroxidation only in the presence of iron and ascorbate. LOOH was sufficient to start lipid peroxidation of erythrocyte ghosts. LOOH incorporates into the lipid bilayer decreasing membrane fluidity and initiating lipid peroxidation in the lipid phase. When cultured cells (IEC18 intestinal epithelial cells, SW480 and HT29/HI1 colon carcinoma cells) were exposed to LOOH, they responded by cell death both via apoptosis and necrosis. Cells with higher degree of membrane unsaturation were more susceptible and antioxidants (vitamin E and selenite) were protective indicating the involvement of oxidative stress. Thus, peroxidation of biomembranes can be initiated by lipid hydroperoxides from heated oils. Dietary consumption of heated oils may lead to oxidative damage and to cell death in the colon. This may contribute to the enhanced risk of colon cancer due to regenerative cell proliferation.