High frequency of K-ras mutations in sporadic colorectal adenomas

The frequency of activating mutations at codons 12 and 13 of the K-ras gene was investigated in 57 sporadic adenomas from 47 patients using the polymerase chain reaction and oligonucleotide hybridisation assay. Sixty eight per cent of the adenomas tested were positive for K-ras mutations. This high frequency, combined with the lack of a correlation between mutations and adenoma size, suggest that K-ras mutations occur earlier in the adenoma-carcinoma sequence than has previously been suggested. The high frequency observed in sporadic adenomas contrasts with the reported low frequency (18%) in adenomas from patients with familial adenomatous polyposis (FAP), suggesting a possible difference in the molecular genesis of FAP and non-FAP adenomas. Finally, it was found that adenomas from patients with a personal history of colorectal cancer were more likely to contain a K-ras mutation than those from patients with no such history. This is a new finding and worthy of further study.

Dose response and proliferative characteristics of aberrant crypt foci: putative preneoplastic lesions in rat colon

Foci of aberrant crypts (ACF) have been identified in the unsectioned methylene blue stained rodent colons and hypothesized to represent precursor lesions of colon cancer. In the present study, induction and growth characteristics of ACF were investigated in response to a single injection of varying dosages of 1,2-dimethylhydrazine-2HCl (DMH), a colon carcinogen. Female Sprague-Dawley rats were given a single injection of DMH (5-150 mg/kg). Two and 19 weeks after the injection, animals were killed and their distal 10 cm of colons were enumerated for the number and crypt multiplicity of ACF. Number of ACF increased with increasing dosages of DMH plateauing at 100 mg/kg. However, percentage of ACF exhibiting different crypt multiplicity (1 to greater than 4) were similar among different dose groups. Aberrant crypts and normal crypts were enumerated for total number of cells and number and distribution of S-phase cells along the crypt height 19 weeks after DMH injection after autoradiography. The labeling index (LI) (percentage of S-phase cells) and LI along the crypt height were determined. Compared to the surrounding normal crypts, aberrant crypts exhibited significantly higher (P less than 0.05) number of cells (1122 +/- 81 versus 411 +/- 28) and higher (P less than 0.05) LI (21 +/- 1 versus 12 +/- 1). For the eight ACF analysed in the present study, the distribution of S-phase cells in the aberrant crypts were similar to that of normal crypts in that S-phase cells were restricted to the lower two-thirds of the crypts rather than distributed throughout the height of the crypts as reported for adenomatous epithelium.

Sequential analyses of the growth and morphological characteristics of aberrant crypt foci: putative preneoplastic lesions

The main objective of the present study was to sequentially analyze growth and morphological characteristics of aberrant crypt foci (ACF) in the rat colon. Sprague-Dawley rats were given a single injection of a carcinogenic dose of 1,2-dimethylhydrazine-HCl and at varying time points ranging from 2 to 57 weeks, groups of 5 rats were terminated. The number and crypt multiplicity of ACF were determined in the distal 8 cm of the colon. In addition, ACF were processed for histology and then graded for the presence of nuclear atypia using a score of 0-4. The findings of the present study demonstrated that ACF exhibit the characteristics expected for precursor lesions. ACF were present at all time intervals in large numbers in the colons of rats treated with 1,2-dimethylhydrazine-HCl and were present when adenocarcinomas were observed. The number of ACF with 4 or more crypts and those exhibiting a higher grade (grade 4) of nuclear atypia increased significantly at or beyond 19 weeks. These features of ACF, particularly the presence of nuclear atypia indicative of dysplasia, provide strong support for the hypothesis that ACF are precursor lesions of chemically induced colon cancer.

Measurement of the proliferative status of colonic epithelium as a risk marker for colon carcinogenesis: effect of bile acid and dietary fiber

The proliferative status of mouse colonic epithelium, as affected by dietary fibers with or without cholic acid (CA), was studied by autoradiography and the metaphase arrest technique. In the first study, groups of mice were fed natural ingredient (laboratory chow) or semisynthetic diets containing 0% (control) or 0.2% (test) CA. After the mice were fed two weeks, the effect of CA was significantly more pronounced in the semisynthetic diet group than in the natural ingredient diet group with respect to labeled cells/crypt section (7.8 +/- 0.8 vs. 2.9 +/- 0.4) and mitotic figure (MF)/crypt section (3.0 +/- 0.5 vs. 1.8 +/- 0.2). In the second study, diets formulated to contain 5 or 10% cellulose (C), pectin (P), or wheat bran (WB) with or without CA (0.2%) were fed to animals for two weeks and colonic proliferative indices were measured. When compared with 5% C group, the 10% WB group exhibited lower labeling index (LI) values (4.2 +/- 0.5 vs. 6.4 +/- 1.0) and the 10% P group exhibited higher LI values (10.0 +/- 1.1 vs. 6.4 +/- 1.0). CA-induced increases in the LI and MF values responded independently in some cases to dietary fiber. Among the CA-treated groups, only the 10% P diet resulted in lower LI when compared with the 5% C group (p less than 0.05) (7.4 +/- 0.8 vs. 12.5 +/- 2.8) but had no effect on MF/crypt section. However, the 5 or 10% WB diet resulted in lower MF values (1.7 +/- 0.2 and 1.8 +/- 0.6 vs. 2.6 +/- 0.3). A long-term feeding study comparing 10% P with 10% C diets also demonstrated that the LI was elevated in the 10% P group without any effect on the mitotic activity of the colonic epithelium. This paradoxical finding suggests that the value of the LI and/or mitotic index as a risk marker of colon carcinogenesis should be further investigated.

Specificity study to evaluate induction of aberrant crypts in murine colons

We have previously reported on our findings of aberrant crypts (AC) in the colons of rodents treated with a colon carcinogen. In this report, the specificity of AC formation was assessed by testing a variety of agents for their ability to induce AC in the colons of CF1 and C57BL/6J mice. In addition, the ability of each of the agents to induce nuclear aberrations (NA) was assessed and compared with the AC data. The test agents included hydrazines, polycyclic aromatic hydrocarbons, aromatic amines, and nitrosocompounds. The colons were assessed for AC 2 or 4 weeks following a single treatment with the test agent. Of the seven agents that induced AC formation, five were colon carcinogens and the other two were agents believed to be carcinogenic to organs other than the colon. None of the five agents believed to be noncarcinogens induced AC whereas three of them did induce NA in at least one of the strains of mice tested. Comparison of AC and NA induction for each test agent showed that all agents that induced AC also induced NA and that the converse was not true. The findings of the present study indicate that AC are induced specifically in response to colon carcinogens and support our contention that AC are preneoplastic lesions.

Aberrant crypts: potential preneoplastic lesions in the murine colon

Murine colons treated with the colon carcinogen azoxymethane (AOM) have been reported to contain aberrant crypts (AC), which are characterized by their larger size and wider pericryptal zones. The methodology used to visualize AC consists of staining the fixed, unsectioned colonic mucosa with methylene blue and transillumination of the luminal surface at a magnification of 40x. The objective of the present studies was to determine if AC demonstrate characteristics to support our hypothesis that they are putative preneoplastic lesions. Studies were designed to determine the time of occurrence of AC (Study I), the induction of AC in response to varying dosages of AOM ranging from 0.0 to 10.0 mg/kg body weight (Study II), and the effect of a high fat diet (20% fat by weight) on the number and size of AC (Study III). In all studies 4-6-week-old female CF1 mice were used. In addition C57BL/6J female mice were used in Study I. The major findings were as follows: (a) the time period required to form AC was approximately 2 weeks following a single AOM injection (5 mg/kg); (b) a dose-dependent increase in the induction of AC was noted in response to AOM from none in the control group to a plateau level of 2.90 +/- 0.38 foci at a dose of 5.0 mg/kg; (c) in comparison to the low fat group, the high fat group had a greater (P less than 0.05) mean number of foci of AC per 5 cm of colon (15.67 +/- 1.32 vs. 11.44 +/- 1.44) and a larger (P less than 0.05) mean size of foci of AC (0.0296 +/- 0.0012 mm vs. 0.0249 +/- 0.0012 mm) after 16 weeks on the respective diets; and (d) preliminary histological appearance of foci of AC revealed mild atypia to unequivocal dysplasia. The findings of the present study are consistent with the hypothesis that AC are putative preneoplastic lesions.