Rectal Aberrant Crypt Foci in Humans Are Not Surrogate Markers for Colorectal Cancer Risk

Methylation study of tumor suppressor genes in human aberrant crypt foci, colorectal carcinomas, and normal colon

BACKGROUND

Aberrant crypt foci (ACF) are the earliest preneoplastic lesions in human colon, identifiable on chromoendoscopic screening. Our objective was to evaluate the %methylation of APC, CDKN2A, MLH1, RASSF1, MGMT, and WIF1 tumor suppressor genes (TSG) in ACF, corresponding colorectal carcinomas (CRC), and normal colonic mucosal controls.

METHODS

In this study, macroscopically normal-appearing mucosal flaps were sampled 5-10 cm away from the tumor mass from 302 fresh colectomy specimens to identify ACF-like lesions. Thirty-five cases with multiple ACFs were selected (n 35) as the main study group, with corresponding sections from CRC (n 35) as disease controls, and mucosal tissue blocks from 20 colectomy specimens (normal controls), operated for non-neoplastic pathologies. Genomic DNA was extracted, and methylation-specific polymerase chain reaction (PCR) was performed on a customized methylation array model. %Methylation data were compared among the groups and with clinicopathological parameters. Selected target mRNA and protein expression studies were performed.

RESULTS

%Methylation of TSGs in ACF was intermediate between normal colon and CRC, although a statistically significant difference was observed only for the WIF1 gene (P < 0.01). Also, there was increased nuclear β-catenin expression and upregulation of CD44-positive cancer-stem cells in ACF and CRCs than in controls. Right-sided ACFs and dysplastic ACFs had a higher %methylation of CDKN2A (P < 0.01), whereas hyperplastic ACFs had a higher %methylation of RASSF1 (P 0.04). The topographic characteristics of ACFs did not correlate with TSG %methylation.

CONCLUSIONS

Early epigenetic methylation of WIF1 gene is one of the mechanisms for ACF development in human colon.

Targeting the Leukotriene Pathway for Colon Cancer Interception

The role of chronic inflammation and arachidonic acid (AA) metabolism in tumor progression has been well characterized for variety of cancers, with compelling data for colon cancer. Several preclinical and clinical studies primarily focused on inhibiting the cyclooxygenase pathways using NSAIDs and aspirin for colon cancer prevention. However, emerging evidence clearly supports the pro-tumorigenic role of 5-lipoxygenase and its downstream leukotriene pathway within AA metabolism. As discussed in the current issue, targeting the leukotriene pathway by cysteinyl leukotriene receptor antagonist (LTRA) montelukast suppressed formation of aberrant crypt foci (ACF) and cell proliferation in colonic epithelium, suggesting the potential of LTRAs for colon cancer prevention. Although this is a short clinical chemoprevention trial to explore the effects of LTRAs against ACF development, it is a significant and timely study opening avenues to further explore the possibilities of using LTRAs in other inflammation-associated precancerous lesions as well. In this spotlight commentary, we highlight the implications of their data and the opportunities for developing LTRAs as potential candidates for colorectal cancer interception. See related article by Higurashi et al., p. 661.

Safety assessment of titanium dioxide (E171) as a food additive

The present opinion deals with an updated safety assessment of the food additive titanium dioxide (E 171) based on new relevant scientific evidence considered by the Panel to be reliable, including data obtained with TiO2 nanoparticles (NPs) and data from an extended one-generation reproductive toxicity (EOGRT) study. Less than 50% of constituent particles by number in E 171 have a minimum external dimension < 100 nm. In addition, the Panel noted that constituent particles < 30 nm amounted to less than 1% of particles by number. The Panel therefore considered that studies with TiO2 NPs < 30 nm were of limited relevance to the safety assessment of E 171. The Panel concluded that although gastrointestinal absorption of TiO2 particles is low, they may accumulate in the body. Studies on general and organ toxicity did not indicate adverse effects with either E 171 up to a dose of 1,000 mg/kg body weight (bw) per day or with TiO2 NPs (> 30 nm) up to the highest dose tested of 100 mg/kg bw per day. No effects on reproductive and developmental toxicity were observed up to a dose of 1,000 mg E 171/kg bw per day, the highest dose tested in the EOGRT study. However, observations of potential immunotoxicity and inflammation with E 171 and potential neurotoxicity with TiO2 NPs, together with the potential induction of aberrant crypt foci with E 171, may indicate adverse effects. With respect to genotoxicity, the Panel concluded that TiO2 particles have the potential to induce DNA strand breaks and chromosomal damage, but not gene mutations. No clear correlation was observed between the physico-chemical properties of TiO2 particles and the outcome of either in vitro or in vivo genotoxicity assays. A concern for genotoxicity of TiO2 particles that may be present in E 171 could therefore not be ruled out. Several modes of action for the genotoxicity may operate in parallel and the relative contributions of different molecular mechanisms elicited by TiO2 particles are not known. There was uncertainty as to whether a threshold mode of action could be assumed. In addition, a cut-off value for TiO2 particle size with respect to genotoxicity could not be identified. No appropriately designed study was available to investigate the potential carcinogenic effects of TiO2 NPs. Based on all the evidence available, a concern for genotoxicity could not be ruled out, and given the many uncertainties, the Panel concluded that E 171 can no longer be considered as safe when used as a food additive.

Two intertwined compartments coexisting in sporadic conventional colon adenomas

Sporadic conventional colon adenomas are microscopically built of 2 intertwined compartments: one on top, harboring the dysplastic tissue that defines their histo-biomolecular attributes, and the other below, composed of non-dysplastic crypts with corrupted shapes (CCS). The CCS of 306 colon adenomas revealed asymmetric, haphazardly-distributed proliferating cell-domains (PC). In contrast, the PC-domains in normal controls were symmetric, being limited to the lower thirds of the crypts. In 28% out of 501 sporadic conventional adenomas, foci of p53-upregulated dysplastic tissue were found. The CCS in 30% of 108 sporadic adenomas showed p53-upregulated single cells, suggesting mounting somatic mutations. No p53-upregulated cells were found in the crypts of controls. In polypoid adenomas, the mucosa of the stalk without dysplastic tissue on top disclosed CCS with asymmetrical PC-domains and single p53-upregulated cells. The latter observations suggested that CCS had developed prior to and not after the growth of the dysplastic tissue on top. CCS were also found below colon adenomas in carcinogen-treated rats. It is concluded that the 2 intertwined histo-biological compartments of sporadic conventional colon adenomas are probably interdependent components. These findings may open new directions aimed to uncover the link between the normal colonic mucosa and the histogenesis of, conventional adenomas.

Identification of key candidate genes and pathways associated with colorectal aberrant crypt foci-to-adenoma-to-carcinoma progression

AIM

The present study aimed to detect key candidate genes and pathways involved in colorectal aberrant crypt foci-to-adenoma-to-carcinoma progression.

BACKGROUND

Although colorectal cancer (CRC) is the third most common type of cancer, the involved signaling pathways and driver-genes remain largely unclear. CRC begins with the malignant transformation of precancerous lesions including aberrant crypt foci (ACF) and benign adenomatous polyp or adenoma.

METHODS

A list of formerly reported ACF, adenoma, and CRC-associated proteins was obtained from GeneCards, and then the data in online David Bioinformatics Resources was analyzed. The protein-protein interactions were surveyed utilizing String database and Cytoscape software. After hubs and bottlenecks were recognized, the key genes and pathways were identified through different bioinformatics analysis.

RESULTS

The most important pathways associated with colorectal aberrant crypt foci-to-adenoma progression were attributed to "pathways in cancer" and "chemokine signaling pathway" and those in adenoma-to-carcinoma progression were related to "pathways in cancer," "chemokine signaling pathway," and "Ras signaling pathway." The genes participating in these pathways are key ones. Furthermore, PRKACB, CUL2, and GSK3B were significant as the seed in the clusters related to adenoma and GNB1, RALBP1, ROCK1, and IKBKG in the clusters related to cancer.

CONCLUSION

The key candidate genes and pathways in progress CRC formed precursor lesions were identified by integrated bioinformatics analysis. The results could lead to a better understanding of the cause and underlying molecular events as well as detection of therapeutic targets for CRC.