Azoxymethane-induced rat aberrant crypt foci:Relevance in studying chemoprevention of colon cancer

The pathogenesis of colon cancer involves sequential and multistep progression of epithelial cells initiated to a cancerous state with defined precancerous intermediaries. Aberrant crypt foci （ACF） represent the earliest identifiable intermediate precancerous lesions during colon carcinogenesis in both laboratory animals and humans. ACF are easily induced by colon-specific carcinogens in rodents and can be used to learn more about the process of colon carcinogenesis. For over two decades, since its first discovery, azoxymethane （AOM）-induced rodent ACF have served as surrogate biomarkers in the screening of various anticarcinogens and carcinogens. Several dietary constituents and phytochemicals have been tested for their colon cancer chemopreventive efficacy using the ACF system. There has been substantial effort in defining and refining ACF in terms of understanding their molecular make-up, and extensive research in this field is currently in progress. In chemoprevention studies, AOM-induced rat ACF have been very successful as biomarkers, and have provided several standardized analyses of data. There have been several studies that have reported that ACF data do not correlate to actual colon tumor outcome, however, and hence there has been an ambiguity about their role as biomarkers. The scope of this mini-review is to provide valuable insights and limitations of AOM-induced rat ACF as biomarkers in colon cancer chemoprevention studies. The role of the dynamics and biological heterogeneity of ACF is critical in understanding them as biomarkers in chemoprevention studies.

Accumulation of aberrant DNA methylation during colorectal cancer development

Despite the recent advances in the therapeutic modalities,colorectal cancer(CRC)remains to be one of the most common causes of cancer-related death.CRC arises through accumulation of multiple genetic and epigenetic alterations that transform normal colonic epithelium into adenocarcinomas.Among crucial roles of epigenetic alterations,gene silencing by aberrant DNA methylation of promoter regions is one of the most important epigenetic mechanisms.Recent comprehensive methylation analyses on genome-wide scale revealed that sporadic CRC can be classified into distinct epigenotypes.Each epigenotype cooperates with specific genetic alterations,suggesting that they represent different molecular carcinogenic pathways.Precursor lesions of CRC,such as conventional and serrated adenomas,already show similar methylation accumulation to CRC,and can therefore be classified into those epigenotypes of CRC.In addition,specific DNA methylation already occurs in the normal colonic mucosa,which might be utilized for prediction of the personal CRC risk.DNA methylation is suggested to occur at an earlier stage than carcinoma formation,and may predict the molecular basis for future development of CRC.Here,we review DNA methylation and CRC classification,and discuss the possible clinical usefulness of DNA methylation as biomarkers for the diagnosis,prediction of the prognosis and the response to therapy of CRC.

Inflammatory pathways in the early steps of colorectal cancer development

Colorectal cancer is a major cause of cancer-related death in many countries.Colorectal carcinogenesis is a stepwise process which,from normal mucosa leads to malignancy.Many factors have been shown to influence this process,however,at present,several points remain obscure.In recent years some hypotheses have been considered on the mechanisms involved in cancer development,expecially in its early stages.Tissue injury resulting from infectious,mechanical,or chemical agents may elicit a chronic immune response resulting in cellular proliferation and regeneration.Chronic inflammation of the large bowel(as in inflammatory bowel diseases),has been associated with the subsequent development of colorectal cancer.In this review we examine the inflammatory pathways involved in the early steps of carcinogenesis,with particular emphasis on colorectal.Firstly,we describe cells and proteins recently suggested as central in the mechanism leading to tumor development.Macrophages and neutrophils are among the cells mostly involved in these processes and proteins,as cyclooxygenases and resolvins,are crucial in these inflammatory pathways.Indeed,the activation of these pathways establishes an oxidative and anaerobic microenvironment with DNA damage to epithelial cells,and shifting from an aerobic to an anaerobic metabolism.Many cellular mechanisms,such as proliferation,apoptosis,and autophagy are altered causing failure to control normal mucosa repair and renewal.

Feeding Walnuts and Peanuts Reduced Development of Azoxymethane-Induced Precancerous Lesions

Walnuts and peanuts contain phytochemicals that exhibit properties that may prevent colon cancer development. The objective was to determine the potential of walnuts and peanuts on Azoxymethane (AOM) induced Aberrant Crypt Foci (ACF) and the activity of detoxification enzymes: Glutathione S-Transferase (GST), Catalase (CAT), and Superoxide Dismutase (SOD) in Fisher 344 male rats. After 1 week acclimatization period, 20 rats were randomly divided into 5 groups. One was fed AIN93G Control (C) diet, 4 groups were fed walnuts (W) and peanuts (P) at 5% and 10%. At 7 - 8 weeks, rats received AOM injections at 16 mg/kg body weight (subcutaneously). Rats were killed by CO2 asphyxiation at 17 weeks. Enzyme activities GST, CAT and SOD were determined. ACF incidence in rats fed W (5% and 10%) was 131 and 95, and in those fed P (5% and 10%) was 110 and 56. Rats fed W and P had a significant (p < 0.05) percent reduction (17.92% - 65.09%) in total ACF compared to C (159). Liver GST activity (μmol/mg) in rats fed W (5% and 10%) was 3.64 and 3.98, and in those fed P (5% and 10%) was 3.84 and 3.30, compared to rats fed C (0.26). CAT activity (μmol/mg) in rats fed W (5% and 10%) was 0.57 and 0.65 and in those fed P (5% and 10%), was 0.76 and 1.26, compared to rats fed C (0.14). SOD activity (U/mg) in rats fed W (5% and 10%) was 529.38 and 576.57 and in those fed P (5% and 10%), was 293.50 and 466.95, compared to rats fed C (82.42). Feeding walnuts and peanuts, especially at 10%, significantly (p < 0.05) reduced the incidence of AOM induced ACF, likely due to the phytochemicals present in nuts.