Cytostatic effect of polyethylene-glycol on human colonic adenocarcinoma cells

Polyethylene glycol (PEG 8000) is a potent cancer chemopreventive agent. This osmotic laxative polymer markedly suppresses colon cancer in rats. To explain the mechanism, we have tested the in vitro effect of PEG on four human cell lines. Two poorly differentiated adenocarcinoma lines (HT29 and COLO205), a fetal mucosa line (FHC) and a differentiated line (post-confluent Caco-2) were incubated with various PEG concentrations for 2-5 days. Results show that PEG markedly and dose-dependently inhibited HT29 and COLO205 cell growth. This cytostatic effect was asso-ciated with a blocking of the cell cycle in G0/G1 phase. In addition, PEG decreased the viability of HT29 and COLO205 adenocarci-noma cells. In contrast, post-confluent intesti-nal-like Caco-2 cells and normal FHC cells were, respectively, not or little affected by PEG. Moreover, the lactate concentration increased twofold in the medium of PEG-treated HT29 cells compared with untreated cells. Microscopic observations showed that PEG induced cell shrinking, membrane blebbing and the condensation of nuclear chromatin. However, because no DNA ladder and no annexin staining were detected, we presume that PEG did not induce apoptosis. PEG increased the osmotic pressure of the culture medium. Hyperosmotic media with added NaCl or sorbitol also inhibited HT29 cell growth, and increased lactate release. These results suggest that PEG may be selectively cytostatic for proliferating cancer cells. This growth inhibition may be due to the high osmotic pressure induced by PEG in vitro. Because the osmotic pressure is high in feces of PEG-fed rats, it may explain the suppression of colon carcinogenesis by PEG

Effect of Meat (Beef, Chicken, Bacon) on Rat Colon Carcinogenesis

High intake of red meat or processed meat is associated with increased risk of colon cancer. In contrast, consumption of white meat (chicken) is not associated with risk and might even reduce the occurrence of colorectal cancer. We speculated that a diet containing beef or bacon would increase and a diet containing chicken would decrease colon carcinogenesis in rats. One hundred female Fischer 344 rats were given a single injection of azoxymethane (20 mg/kg i.p.), then randomized to 10 different AIN-76-based diets. Five diets were adjusted to 14% fat and 23% protein and five other diets to 28% fat and 40% protein. Fat and protein were supplied by 1) lard and casein, 2) olive oil and casein, 3) beef, 4) chicken with skin, and 5) bacon. Meat diets contained 30% or 60% freeze-dried fried meat. The diets were given ad libitum for 100 days, then colon tumor promotion was assessed by the multiplicity of aberrant crypt foci [number of crypts per aberrant crypt focus (ACF)]. The ACF multiplicity was nearly the same in all groups, except bacon-fed rats, with no effect of fat and protein level or source (p = 0.7 between 8 groups by analysis of variance). In contrast, compared with lard- and casein-fed controls, the ACF multiplicity was reduced by 12% in rats fed a diet with 30% bacon and by 20% in rats fed a diet with 60% bacon (p < 0.001). The water intake was higher in bacon-fed rats than in controls (p < 0.0001). The concentrations of iron and bile acids in fecal water and total fatty acids in feces changed with diet, but there was no correlation between these concentrations and the ACF multiplicity. Thus the hypothesis that colonic iron, bile acids, or total fatty acids can promote colon tumors is not supported by this study. The results suggest that, in rats, beef does not promote the growth of ACF and chicken does not protect against colon carcinogenesis. A bacon-based diet appears to protect against carcinogenesis, perhaps because bacon contains 5% NaCl and increased the rats' water intak

Cancer colorectal : le rôle controversé de la consommation de viande

L’alimentation est considérée comme un facteur déterminant du développement du cancer colorectal. Les études internationales d’épidémiologie descriptive montrent une forte corrélation entre la mortalité due au cancer du côlon et la consommation de viande. La grande majorité des études rétrospectives cas-témoin (22 sur 29) montre un risque plus important de développer un cancer du côlon chez ceux qui consomment le plus de viande. Mais seulement quelques études prospectives de cohorte confirment cette association pour la viande rouge (2 sur 5) ou pour les viandes « traitées » (2 sur 4). La consommation de viande blanche (volailles) ou de poisson n’aurait pas d’effet, ou serait plutôt protectrice d’après les études de cohorte. Plusieurs hypothèses ont été proposées sur les mécanismes cellulaires et moléculaires expliquant cet éventuel effet promoteur de certaines viandes. Ces hypothèses impliquent les graisses saturées, les protéines, le fer héminique, les amines hétérocycliques produites lors de la cuisson et les N-nitrosamines. Les graisses agiraient en raison de leur densité énergétique ou via les acides biliaires dont elles favorisent la sécrétion. Les études métaboliques sur des volontaires humains ont permis d’éclairer certaines de ces hypothèses. L’effet de la viande a été peu étudié expérimentalement. Dans quelques études, des rongeurs ont reçu un régime contenant de la viande, ainsi que des injections de cancérigène chimique pour initier des tumeurs intestinales. Les résultats de ces études expérimentales ne confortent pas du tout l’hypothèse d’un effet promoteur spécifique de la viande bovine. Au contraire, à teneur égale en graisses et en protéines, la viande bovine (crue ou cuite) diminue plutôt la cancérogenèse. Cependant, les régimes les plus riches en graisses et/ou en protéines, qu’elles soient animales ou végétales, augmentent souvent la cancérogenèse, mais pas toujours. Au total, ces études ne permettent pas d’affirmer, mais pas non plus d’écarter, l’implication des viandes dans l’étiologie des cancers du côlon

Polyethylene glycol, unique among laxatives, suppresses aberrant crypt foci, by elimination of cells.

OBJECTIVE: Polyethylene glycol (PEG), an osmotic laxative, is a potent inhibitor of colon cancer in rats. In a search for the underling mechanisms, the hypothesis that fecal bulking and moisture decrease colon carcinogenesis was tested. We also investigated the PEG effects on crypt cells in vivo. MATERIAL AND METHODS: Fischer 344 rats (n=272) were injected with the colon carcinogen, azoxymethane. They were then randomized to a standard AIN76 diet containing one of 19 laxative agents (5% w/w in most cases): PEG 8000 and other PEG-like compounds, carboxymethylcellulose, polyvinylpyrrolidone, sodium polyacrylate, calcium polycarbophil, karaya gum, psyllium, mannitol, sorbitol, lactulose, propylene glycol, magnesium hydroxide, sodium phosphate, bisacodyl, docusate, and paraffin oil. Aberrant crypt foci (ACF) and fecal values were measured blindly after a 30-day treatment regimen. Proliferation, apoptosis, and the removal of cells from crypts were studied in control and PEG-fed rats using various methods, including TUNEL and fluorescein dextran labeling. RESULTS: PEG 8000 reduced the number of ACF 9-fold in rats (p40-fold) a fecal marker of epitheliolysis in the gut (p<0.001). PEG normalized the percentage of fluorescein dextran labeled cells on the top of ACF (p<0.001). CONCLUSIONS: Among laxatives, only PEG afforded potent chemoprevention. PEG protection was not due to increased fecal bulking, but in all likelihood to the elimination of cells from precancerous lesions

Endogenous N-nitroso compounds, and their precursors, present in bacon, do not initiate or promote aberrant crypt foci in the colon of rats

Processed meat intake is associated with increased risk of colorectal cancer. This association may be explained by the endogenous formation of N-nitroso compounds (NOC). The hypothesis that meat intake can increase fecal NOC levels and colon carcinogenesis was tested in 175 Fischer 344 rats. Initiation was assessed by the number of aberrant crypt foci (ACF) in the colon of rats 45 days after the start of a high-fat bacon-based diet. Promotion was assessed by the multiplicity of ACF (crypts per ACF) in rats given experimental diets for 100 days starting 7 days after an azoxymethane injection. Three promotion studies were done, each in 5 groups of 10 rats, whose diets contained 7%, 14%, or 28% fat. Tested meats were bacon, pork, chicken, and beef. Fecal and dietary NOC were assayed by thermal energy analysis. Results show that feces from rats fed bacon-based diets contained 10-20 times more NOC than feces from control rats fed a casein-based diet (all p < 0.0001 in 4 studies). In bacon-fed rats, the amount of NOC input (diet) and output (feces) was similar. Rats fed a diet based on beef, pork, or chicken meat had less fecal NOC than controls (most p < 0.01). No ACF were detected in the colon of bacon-fed uninitiated rats. After azoxymethane injection, unprocessed but cooked meat-based diets did not change the number of ACF or the ACF multiplicity compared with control rats. In contrast, the bacon-based diet consistently reduced the number of large ACF per rat and the ACF multiplicity in the three promotion studies by 12%, 17%, and 20% (all p < 0.01). Results suggest that NOC from dietary bacon would not enhance colon carcinogenesis in rats

Polyethylene glycol, a potent suppressor of chemically-induced colorectal cancer, discovered while studying the carcinogenicity of meat

Epidemiological studies suggest that a high intake of red meat or processed meat is associated with an increased risk of colorectal cancer. We studied the carcinogenicity of diets with a high beef or bacon content in rats. The study end-point was the size of the aberrant crypt foci (ACF) induced in the colon by a carcinogenic agent, azoxymethane. The ACFs were considered as preneoplastic lesions. Unexpectedly, not only did red meat not promote ACF lesions, but also three independent studies showed that bacon inhibited carcinogenesis. Our recent studies showed that the iron haeme in red meat is a potent promoter of ACFs, but only when the diet contains very little calcium and no antioxidants. While studying the mechanisms of bacon’s paradoxical protective action, which was probably associated with the rats’ increased water intake, we discovered a new chemopreventive agent for gastrointestinal cancers, polyethylene glycol (PEG). PEG 8000 is the most potent ACF suppressor in rats, and is second only to celecoxib in the prevention of chemically induced intestinal cancers. As PEG is not toxic and not absorbed, it should soon be studied in a clinical trial in man.L'épidémiologie suggère que ceux qui consomment beaucoup de viande rouge ou de charcuteries ont un risque élevé de développer un cancer colorectal. Nous avons étudié l'effet promoteur de régimes riches en viande de boeuf ou en bacon chez le rat. La promotion a été estimée par la taille des foyers de cryptes aberrantes (FCA) induits dans le colon par un cancérigène, l'azoxyméthane. Ces FCA seraient des lésions pré-néoplasiques. Contrairement à nos hypothèses, la viande rouge n'a pas eu d'effet promoteur, mais le bacon a inhibé la cancérogenèse dans 3 études indépendantes. Nos études récentes montrent que l'hème de la viande rouge est un puissant promoteur des FCA, mais uniquement quand le régime contient très peu de calcium et pas d'antioxydants. En étudiant le mécanisme de la protection paradoxale par le bacon, probablement due à la consommation d'eau par les rats, nous avons découvert un nouvel agent de chimioprévention des cancers digestifs, le polyéthylène glycol (PEG). Le PEG 8000 est l'agent le plus puissant pour supprimer les FCA chez le rat, et seul le célécoxib est plus efficace que le PEG en prévention des cancers intestinaux. Le PEG n'est ni toxique, ni absorbé. Il devrait donc être étudié dans un essai clinique chez l'Homme