CYP27A1 and CYP24 expression as a function of malignant transformation in the colon.

Vitamin D deficiency is strongly associated with the risk of developing colorectal cancer (CRC). Because of the propensity of bioactive 1,25-dihydroxyvitamin D3 to cause toxic hypercalcemia, considerable effort has been directed to identifying safer drugs while retaining the efficacy of the parent compound. However, vitamin D precursors do not present toxicity concerns and may be sufficient for CRC chemoprevention or chemotherapy, providing the appropriate enzymes are present in colonic epithelia. We previously showed that CYP27B1 is present at equally high levels in the colon and CRC irrespective of differentiation but was not present in metastases. In this study we used quantitative immunohistochemistry to show that CYP27A1, converting D3 to 25-hydroxycholecalciferol, is present in increasing concentrations in the nuclei of normal colonic epithelia, aberrant crypt foci (ACF), and adenomatous polyps. Whereas total cellular CYP27A1 remains high in CRC and lymph node metastases, the amount of enzyme present in the nuclei decreases with tumor cell dedifferentiation while rising in the cytoplasm. Similarly, increasing amounts of the deactivating enzyme CYP24 are present in the nuclei of normal colonic epithelia, ACFs, and adenomatous polyps. Although the amount of total CYP24 decreases slightly in CRC as a function of tumor cell dedifferentiation and metastasis, location of this enzyme shifts almost entirely from the nuclear compartment to the cytoplasmic compartment. These data indicate that non-toxic vitamin D precursors should be sufficient for CRC chemoprevention, but that neither vitamin D nor its precursors may be sufficient for CRC chemotherapy.

Evaluation of the potential carcinogenicity and genetic toxicity to humans of the herbicide acetochlor.

Comprehensive toxicological studies of the herbicide acetochlor are presented and discussed. Although it gave a negative profile of responses in the many toxicity tests conducted there were some findings that prompted further investigation. First, although non-mutagenic in the Salmonella assay, acetochlor was clastogenic to mammalian cells treated in vitro. This clastogenic potential was not expressed in vivo in four rodent cytogenetic assays (bone marrow and germ cells). Second, although acetochlor gave a negative response in rat liver UDS assays when tested at the acute MTD, gavage administration of a single, supra-MTD dose (2000 mg/kg) gave a weak positive assay response. This dose-level (2000 mg/kg) was necrotic to the liver, depressed hepatic glutathione levels by up to approximately 80%, altered the metabolism of acetochlor, and was associated with up to 33% lethality. In contrast, reference liver genotoxins such as DMN, DMH and 2AAF were shown to elicit UDS in the absence of such effects, and at approximately 400 x lower dose-levels. Finally, microscopic nasal polypoid adenomas were induced in the rat when acetochlor was administered for two years at the maximum tolerated dose (MTD). The tumours were not life-threatening, they did not metastasize, and no DNA damage was induced in the nasal cells of rats maintained on a diet containing the MTD of acetochlor for either 1 or 18 weeks (comet assay). In order to probe the mechanism of action of these high dose toxicities a series of chemical and genetic toxicity studies was conducted on acetochlor and a range of structural analogues. These revealed the chloroacetyl substructure to be the clastogenic species in vitro. Although relatively inert, this substituent is preferentially reactive to sulphydryl groupings, most evidently, to glutathione (GSH). Similar chemical reactivity and clastogenicity in vitro was observed for two related chemicals bearing a chloroacetyl group, both of which have been defined as non-carcinogens in studies reported by the US.NTP. These collective observations indicate that the source of the clastogenicity of acetochlor in vitro is also the source of its rapid detoxification in the rat in vivo, via reaction with GSH. Metabolic studies of acetochlor are described which reveal the formation of a series of GSH-associated biliary metabolites in the rat that were not produced in the mouse. The metabolism of acetochlor in the rat changes with increasing dose-levels, probably because of depletion of hepatic GSH. It is most likely that a rat-specific metabolite is responsible for the rat nasal tumours observed uniquely at elevated dose-levels. The absence of genetic toxicity to the nasal epithelium of rats exposed acutely or subchronically to acetochlor favours a non-genotoxic mechanism for the induction of these adenomas. The observation of a time- and dose-related increase in S-phase cells in the nasal epithelium is consistent with this conclusion. Despite some confusion caused by the early use of perilethal gavage administrations of acetochlor to rodents, and supra-MTD dietary concentrations in some of the chronic studies, the available MTD data are consistent with acetochlor not posing a genetic or carcinogenic hazard to humans.

Utility of Argyrophilic nucleolar organizer regions (AgNOR) in differentiating malignant from benign of colorectal tumors.

BACKGROUND: Argyrophilic nucleolar organizer regions (AgNOR) can reflect the activity of cellular proliferation. The purpose of this study is to evaluate the potential value of AgNOR in differentiating benign from malignant colon epithelial neoplasms, and to determine the correlation between the nucleus AgNOR and the grade of colonic adenocarcinomas. METHODS: In this study, AgNOR technique was applied to 61 paraffin embedded sections of colorectal tissue including normal mucosa (n = 10), adenomatous polyp (n = 16), and adenocarcinoma (n = 35). RESULTS: The mean +/- standard error (SE) numbers of AgNOR dots per nucleus of normal mucosa, adenomatous polyp, and adenocarcinoma were 2.17 +/- 0.07 (n = 10) 3.89 +/- 0.10 (n = 16) and 5.52 +/- 0.10 (n = 35), respectively (p < 0.00001). In addition, the mean numbers of AgNOR dots per nucleus of well differentiated (WD) adenocarcinoma (n = 14), moderately differentiated (MD) adenocarcinoma (n = 11) and poorly differentiated (PD) adenocarcinoma (n = 10) were 5.20 +/- 0.12, 5.81 +/- 0.20, 5.67 +/- 0.15, respectively. MD and PD tumor had significantly higher AgNOR count than that of WD tumor (p < 0.05). However, there was no significant difference between MD and PD colorectal adenocarcinoma. CONCLUSION: AgNOR method is a simple, rapid method in diagnosis of colorectal tumors, and it provides a useful adjunct to histopathology in the diagnosis of colorectal tumors.

Cuerpos de Leuchtenberger (cuerpos apoptóticos) en adenomas de intestino grueso / Leuchtenberger bodies (apoptotic bodies) in adenomas of the large bowel

En 1954 Leuchtenberger describió unos cuerpos de inclusión de 1 a 2 micras de diámetro, que se tiñen con la técnica de Feulgen, en el citoplasma de las células epiteliales de pólipos rectales. Rubio y col mencionaron que el hallazgo de numerosos cuerpos de Leuchtenberger (CL) en adenomas colo-rectales debe hacer sospechar una poliposis múltiple familiar(PMF). El objetivo de este trabajo fue conocer la frecuencia de los CL en los adenomas tubulares de la PMF y compararla con la frecuencia observada en adenomas no familiares y otras lesiones hiperplásicas e inflamatorias del tubo digestivo. Los CL fueron más frecuentes en al PMF (88 por ciento) y los adenomas papilares 75 por ciento) que en los pólipos tubulares no familiares (38 por ciento), los pólipos hiperplásicos del estómago (45 por ciento), los pólipos inflamatorios de colon (45 por ciento) y la colitis ulcerosa inespecífica (12 por ciento). Aunque el hallazgo de numeros CL es más común en la PMF que en pólipos tubulares no familiares (p<0.0001), la ausencia de estas partículas en un adenoma no descarta la posibilidad de una PMF. Por sus caracteres histológicos, histoquímicos y ultraestructurales sugiere que los CL corresponden a cuerpos apoptóticos que se forman probablemente por necrosis de las células epiteliales