Maddalena Salvadori

Frequent Mutation of Apc Gene in Rat Colon Tumors and Mucin-Depleted Foci, Preneoplastic Lesions in Experimental Colon Carcinogenesis

Mucin-depleted foci (MDF) are microscopic dysplastic lesions induced in the colon of rodents by specific colon carcinogens. Most MDF show Wnt pathway activation, whereas only a subset shows mutations in the Ctnnb1 gene, coding for beta-catenin. Because Apc is a member of the Wnt pathway and the most frequent mutated gene in human colon cancer, we tested whether MDF harbor Apc mutations. F344 rats were treated twice with 150 mg/kg of 1,2-dimethylhydrazine. After 15 or 28 weeks, MDF, aberrant crypt foci (ACF), and tumors were collected. We screened a segment of the Apc gene comprising the region homologous to the mutation cluster region (MCR) of human APC, which frequently shows mutations in experimental colon tumors. Mutations were identified by PCR amplification and sequencing in 6:24 MDF (25%), 7:23 tumors (30%), 0:24 ACF (0%). Most of the mutations (92%) in MDF and tumors were localized in a region upstream from the MCR. All mutations were single-base substitutions and mainly formed by G:C-->A:T and C:G-->T:A transitions. The pattern of nucleotide changes was similar in MDF and tumors, and, interestingly, the same mutation in codon 1047 was found in two MDF and in three tumors. Four out of the six mutations found in MDF were nonsense mutations, and two were missense. All mutations in tumors determined a protein truncation. These results show that Apc mutations are present in MDF with a frequency similar to that of tumors, strengthening the evidence that they are precancerous lesions in colon carcinogenesis.

Mucin-depleted foci have β-catenin gene mutations, altered expression of its protein, and are dose- and time-dependent in the colon of 1,2-dimethylhydrazine-treated rats

Mucin‐depleted foci (MDF) are purported preneoplastic lesions that can be easily visualized in the unsectioned colon of carcinogen‐treated rats stained with high‐iron diamine alcian blue (HID‐AB). In F344 rats treated twice with 150 mg/kg of 1,2‐dimethylhydrazine (DMH) and sacrificed after 5, 9, 13 and 28 weeks, MDF increased over time from 5 to 13 weeks, whereas they decreased at 28 weeks, when tumors appear. MDF multiplicity (crypts/MDF) linearly increased with time. Increasing doses of DMH (100, 150 and 200 mg/kg × 2 times) caused a dose‐related increase in MDF. Mutations in Ctnnb1 gene codifying for β‐catenin were identified with PCR amplification and direct sequencing in 6/15 tumors (40%), 7/28 MDF (25%) and 2/27 (7%) aberrant crypt foci (ACF) identified in HID‐AB‐stained colon. All mutations in tumors and MDF caused amino acid substitution, while one mutation in ACF was silent. β‐catenin detected at membrane level by immunohistochemistry was markedly reduced in MDF and tumors and, to a lesser extent, in ACF identified with HID‐AB. By contrast, nuclear localization of β‐catenin was significantly increased in MDF and tumors, while no variation was observed in ACF. β‐catenin cytoplasmic expression was also significantly increased in MDF and tumors but to a lesser extent in ACF. In conclusion, MDF are induced dose‐dependently by DMH, increase in size with time, have mutations in the β‐catenin gene and marked alterations in β‐catenin cellular localization. Since all these phenomena are considered specific steps for colon tumorigenesis, these results further support the hypothesis that MDF are cancer precursors and can be proposed as endpoints in short‐term carcinogenesis experiments.

Sister-chromatid exchanges in human lymphocytes induced by dimethoate, omethoate, deltamethrin, benomyl and their mixture.

Dimethoate and omethoate, two common organophosphorus insecticides, induced a dose-related increase in the frequency of sister-chromatid exchanges (SCEs) in human lymphocytes in vitro (P of the regression lines less than 0.01). Two other common pesticides, the pyrethroid insecticide deltamethrin and the systemic fungicide benomyl, induced a modest increase in SCEs which bordered on statistical significance (P = 0.053 and 0.055, respectively). Mixtures of the four pesticides at total concentrations of 41.5 and 83 micrograms/ml (composed of 43% dimethoate, 43% omethoate, 12% deltamethrin and 1.2% benomyl) induced a dose-dependent increase in SCEs (P less than 0.01). The effects of these mixtures of pesticides were variable using lymphocytes from different individuals, although these differences did not attain statistical significance. Moreover, low concentrations of the four pesticides that did not increase SCEs significantly when tested alone, were positive for SCE induction when tested as a mixture. The experiments show that sub-threshold doses of pesticides may increase SCEs when present in a mixture.

Levels of the adducts of 4-aminobiphenyl to hemoglobin in control subjects and bladder carcinoma patients

We determined the hemoglobin adduct levels of one aromatic amine of cigarette smoke, 4-aminobiphenyl (4-ABP), in smoking controls and in patients with transitional cell bladder carcinoma. Covalently bound 4-ABP was measured by capillary gas-chromatography and negative-ion chemical ionization mass-spectrometry, using deuterated 4-ABP as internal standard. Smoking was quantified measuring the urinary excretion of cotinine. Thirteen cases and controls were paired for urinary cotinine levels. Bladder carcinoma patients had slightly higher levels of 4-ABP hemoglobin adducts than controls (means +/- S.D. were 103 +/- 47 and 65 +/- 44, respectively). This difference was significant using a t-test for paired samples (P = 0.04) and non-parametric Kruskal-Wallis rank analysis (P = 0.033).

Identification of Mucin Depleted Foci in the Human Colon

Aberrant crypt foci (ACF) originally described in rodents treated with colon-specific carcinogens have been identified also in humans at high risk of colon cancer (CRC) and are extensively used as cancer biomarkers. However, studies documenting the heterogeneity of ACF have questioned their precancerous nature. Recently, we described dysplastic foci depleted of mucins (MDF) in the colon of rats treated with colon-specific carcinogens. Like colon tumors, MDFs show activation of Wnt signaling driven by mutations in the β-catenin gene and Apc, a key gene in colorectal carcinogenesis. Because MDFs have been identified thus far only in rodents, we wanted to search for similar lesions in humans. Familial adenomatous polyposis (FAP) subjects, carrying germ-line mutations in the APC gene, are at high risk of CRC. Therefore, we first searched for MDF-like lesions in unsectioned colon samples from FAP patients and then in patients with sporadic CRC. MDFs were present in the colon of FAP patients (average of 0.0577 lesions/cm2) and at a much lower density in CRC patients (average of 0.0006 lesions/cm2). ACFs were also observed in all patients. Histologic preparations of all the MDFs identified in FAP and CRC consisted of microadenomas at variable grades of dysplasia. The occurrence of MDF-like lesions in high-risk patients provides evidence that these lesions have a counterpart in human pathology and, as observed in rodents, may represent the very early stages of CRC.

Reduction of colonic inflammation in HLA-B27 transgenic rats by feeding Marie Ménard apples, rich in polyphenols.

Inflammatory bowel diseases (IBD) are immunomediated ailments affecting millions of individuals. Although diet is regarded as an important factor influencing IBD, there are no accepted dietary recommendations presently available. We administered 7.6 % lyophilised apples obtained from two cultivars (Golden Delicious and Marie Ménard, low and high in polyphenols, respectively) to HLA-B27 transgenic rats which develop spontaneous IBD. After 3 months feeding, rats fed Marie Ménard apples had reduced myeloperoxidase activity (3.6 (sem 0.3) v. 2.2 (sem 0.2) U/g tissue; P < 0.05) and reduced cyclo-oxygenase-2 (P < 0.05) and inducible NO synthase gene expression (P < 0.01) in the colon mucosa and significantly less diarrhoea (P < 0.05), compared with control rats. Cell proliferation in the colon mucosa was reduced significantly by feeding Golden Delicious apples, with a borderline effect of Marie Ménard apples. Gene expression profiling of the colon mucosa, analysed using the Whole Rat Genome 4 x 44 K Agilent Arrays, revealed a down-regulation of the pathways of PG synthesis, mitogen-activated protein kinase (MAPK) signalling and TNFalpha-NF-kappaB in Marie Ménard-fed rats. In the stools of the animals of this group we also measured a significant reduction of bacteria of the Bacteriodes fragilis group. In conclusion, the administration of Marie Ménard apples, rich in polyphenols and used at present only in the manufacturing of cider, ameliorates colon inflammation in transgenic rats developing spontaneous intestinal inflammation, suggesting the possible use of these and other apple varieties to control inflammation in IBD patients.

K-ras mutations and mucin profile in preneoplastic lesions and colon tumors induced in rats by 1,2-dimethylhydrazine

K‐ras and mucin profile variations, associated with intestinal carcinogenesis, were studied in the preneoplastic lesions, mucin‐depleted foci (MDF) and aberrant crypt foci (ACF), and in colonic tumors induced in rats by 1,2‐dimethylhydrazine (DMH). The frequency of lesions with K‐ras mutations was 23% (3/13), 5.5% (1/18) and 100% (14/14) in MDF, tumors and ACF, respectively. Two of three MDF mutated in K‐ras also carried a missense mutation in Apc. We also tested the expression of MUC2, a mucin abundantly expressed in normal colon and M1/MUCA5C, up‐regulated in colon carcinogenesis, using immunohistochemistry. MDF and tumors showed a dramatic reduction in the expression of MUC2, whereas ACF showed only a slight reduction. The expression of M1/MUC5AC was almost absent in normal mucosa, but was increased in all the lesions (MDF, tumors and ACF). The expression of the intestinal trefoil factor (ITF), a marker of goblet cell lineage, was reduced in MDF and tumors compared to normal mucosa but not in ACF. In conclusion, although K‐ras mutations are present in all ACF, they are less frequent in MDF and tumors; M1/MUC5AC is a marker associated with all preneoplastic events while the reduction of MUC2 and ITF expression is selectively associated with more advanced lesions such as MDF and tumors.

Mucin-depleted foci show strong activation of inflammatory markers in 1,2-dimethylhydrazine-induced carcinogenesis and are promoted by the inflammatory agent sodium dextran sulfate

Mucin‐depleted foci (MDF), formed by dysplastic crypts devoid of mucins, have been identified in the colon of carcinogen‐treated rodents and in humans at high risk for colon cancer. The lack of the protective layer of mucus may cause inflammation which has been linked to colon carcinogenesis, therefore, the expression of markers such as cyclooxygenase‐2 (COX‐2), inducible nitric oxide synthase (i‐NOS) and macrophage infiltration was studied with immunohistochemistry (IH) in MDF harvested from F344 rats treated with the colon carcinogen 1,2‐dimethylhydrazine (DMH). The same determinations were performed in aberrant crypt foci (ACF) and, at a later time point, in tumours. A dramatic increase in COX‐2, i‐NOS and macrophage infiltration was observed in MDF but ACF showed a moderate increase compared with the paired normal mucosa. Tumours were positive for all the markers. RT‐PCR experiments demonstrated that i‐NOS RNA expression was increased in a set of MDF confirming the results obtained with immunohistochemistry. In an inflammation‐cancer experimental model [mice treated with azoxymethane (AOM) and dextran sodium sulphate (DSS)], we observed that DSS‐induced inflammation promoted MDF in a dose‐dependent manner, whereas ACF were not affected. In conclusion, we report here for the first time a strong activation of the inflammatory process in MDF, which may contribute to the further progression of MDF to tumours.

Urinary mutagens in humans after fried pork and bacon meals

Urinary mutagenic activity on Salmonella typhimurium strain TA1538 with S9 was determined after morning meals of fried pork and bacon. Both in fasting and non-fasting subjects a very marginal elevation of urinary mutagenic activity was observed, accounting for a small fraction only of the total amount of mutagens ingested.

Fecal Levels of Short-Chain Fatty Acids and Bile Acids as Determinants of Colonic Mucosal Cell Proliferation in Humans

We studied the correlation between fecal levels of short-chain fatty acids (SCFA), bile acids (BA), and colonic mucosal proliferation in humans on a free diet. Subjects [n = 43: 27 men and 16 women; 61 ± 7 and 59 ± 6 (SE) yr old, respectively] were outpatients who previously underwent resection of at least two sporadic colon polyps. Mucosal proliferation was determined by [³H]thymidine incorporation in vitro in three colorectal biopsies obtained without cathartics and was expressed as labeling index (LI). BA were analyzed in feces by mass spectrometry and SCFA by gas chromatography. We found that increasing levels of BA in feces did not correlate with higher LI. On the contrary, higher levels of SCFA were significantly associated with lower LI in the colonic mucosa (P for trend = 0.02). In conclusion, in humans on a free diet, intestinal proliferation seems to be regulated by the levels of SCFA in feces and not by BA. Because a lower intestinal proliferation is associated with a decreased colon cancer risk, treatments or diets that increase colonic levels of SCFA might be beneficial for colonic mucosa.