Search PubMed⌕ Search

Biomedical subjects

M W Anderson

Publications and source records attributed to M W Anderson.

At least 181 records · Page 10Linked to original sources
PubMedDate not supplied

Role of DNA methylation in the activation of proto-oncogenes and the induction of pulmonary neoplasia by nitrosamines.

The relationships between DNA methylation and repair induced by the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) to the activation of proto-oncogenes and the induction of pulmonary neoplasia by this carcinogen is described. The formation of the O6-methylguanine (O6MG) adduct following metabolic activation of NNK appears to be a major factor in the induction of lung tumors in both rats and mice and in the activation of the K-ras oncogene in lung tumors from A/J mouse. The potent carcinogenicity of NNK in the rat lung correlated strongly with cell specificity for formation and persistence of the O6MG adduct in the Clara cells. This conclusion was supported by studies with nitrosodimethylamine (NDMA), a weak carcinogen in the rodent lung. Treatment with NDMA was not associated with any pulmonary cell specificity for DNA methylation. The high affinity for activation of NNK compared to NDMA was ascribed to a difference in cytochrome P-450 isozymes involved in the activation of these two nitrosamines. In the A/J mouse, the induction of pulmonary tumorigenesis involved direct genotoxic activation of the K-ras proto-oncogene as a result of the base mispairing produced by formation of the O6MG adduct. In contrast, the induction of pulmonary tumors in the rat by NNK does not appear to involve the ras pathway. It is apparent that different molecular mechanisms are involved in the development of pulmonary tumors by NNK in the mouse and rat. The studies described in this paper illustrate the utility of performing dose-response experiments and the quantitation of DNA methylation and repair in not only target tissues but also target cell types. The fundamental knowledge gained from unraveling the mechanism of carcinogenesis by NNK could lead ultimately to the identification of factors important in the development of human lung cancer.

Animals↗
PubMedDate not supplied

Magnetic resonance imaging of the wrist.

MR imaging of the wrist has the unique capability of simultaneously demonstrating bone and soft tissue structures. Its exquisite sensitivity for detecting bone marrow edema makes it and ideal screening tool for diagnosing radiographically occult osseous injuries and areas of AVN. This, together with its ability to provide a comprehensive, non-invasive assessment of the ligaments, tendons, nerves, and components of the TFC make MRI a very powerful tool for evaluating patients with wrist pain of uncertain etiology. Its exact role in the work-up of these patients has not been entirely established, but with further advances in technology and the radiologist's understanding of wrist anatomy and pathology, MRI is assuming a more central role in this clinical setting.

Humans↗
PubMedDate not supplied

Proliferative lesions of the mouse lung: progression studies in strain A mice.

The progression of pulmonary neoplasia was examined in strain A/J male mice treated with a single dose of vinyl carbamate (60 mg/kg, i.p.) 6 weeks after birth. Interim sacrifices were performed at 7, 8, 10, 12, or 14 months. Proliferative lesions of the lung were divided into four categories: hyperplasias, adenomas, carcinomas arising within adenomas, and carcinomas. Grossly visible surface tumor counts, histologic diagnoses, and morphometric measurements of histologic lesions were used to evaluate progression. Vinyl carbamate-treated mice showed increased mean surface tumor counts at all time points. Diagnostic evaluation suggested that as a function of time, the relative frequency of hyperplasias decreased and the relative frequency of adenomas increased. The relative frequency of adenomas subsequently decreased, whereas the relative frequency of carcinomas increased. At all time points, carcinomas arising within adenomas were present. As time progressed, the number of carcinomas arising within adenomas decreased, whereas the number of "pure" carcinomas increased. Morphometric analysis of lesions indicated hyperplasias to be small, that adenomas were larger than hyperplasias, and carcinomas were larger than adenomas and hyperplasias, suggesting that few adenomas or carcinomas arise de novo. Collectively, these data suggest that the majority of pulmonary tumors in A/J mice treated with vinyl carbamate arise as hyperplasias, progress to adenomas, and ultimately result in carcinomas.

Animals↗
PubMedDate not supplied

Role of Clara cells and type II cells in the development of pulmonary tumors in rats and mice following exposure to a tobacco-specific nitrosamine.

The role of the Clara and type II cell in the development of pulmonary tumors in the A/J mouse and Fischer rat was investigated by determining the relationship of DNA methylation and repair in pulmonary cells to oncogene activation and by characterizing the morphology of pulmonary tumors induced by treatment with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Marked differences in the formation of the promutagenic adduct O6-methylguanine (O6MG) were observed in pulmonary cells following treatment of rats with NNK. Concentrations of this adduct in Clara cells greatly exceeded (3- to 30-fold) those detected in type II cells and whole lung with doses of NNK ranging from 0.1 to 50 mg/kg. In addition, very low rates of repair of this adduct were detected in Clara cells, whereas efficient adduct removal occurred in type II cells. The importance of this adduct and the role of cell specificity was suggested by the fact that a strong correlation was observed between the concentration of O6MG in Clara cells and tumor incidence in the Fischer rat with doses of NNK ranging from 0.03-50 mg/kg. In contrast, no differences in adduct concentration between type II and Clara cells from A/J mice were observed under conditions resulting in pulmonary tumor formation. Activation of the K-ras gene was detected in lung tumors from A/J mice. This gene was activated by a mutation in codon 12 involving a GC to AT transition (GGT to GAT) and is consistent with base mispairing produced by the formation of O6MG. Activation of this gene was not associated with lung tumor formation in the Fischer rat. DNA from rat lung tumors did induce tumors in the nude mouse carcinogenicity assay. In addition, rat repetitive sequences were detected in DNA isolated from these nude mouse tumors. In spite of the cell selectivity for DNA methylation in Clara cells from rat and the relationship between O6MG formation and tumorigenicity, early proliferative lesions observed in both mice and rats involved the alveolar areas. Ultrastructural examination of these lesions and adenomas revealed morphologic features characteristic of the type II cell. Thus the lack of agreement between biochemical and morphological findings makes it difficult to hypothesize a cell of origin for the pulmonary neoplasms induced by NNK. However, these studies indicate that the concentration of O6MG in Clara cells is an excellent indicator of the carcinogenic potency of NNK in the rat.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMedDate not supplied

Activation of protooncogenes in mouse lung tumors.

The detection of activated protooncogenes in mouse lung tumors has led to a major advance in our understanding of carcinogenesis of the lung at the molecular level. A high frequency of activated K-ras protooncogenes has been detected in tetranitromethane (TNM)- and 1,3-butadiene-induced lung tumors in B6C3F1 mice. In the past several years, we have pursued protooncogene activation in spontaneous and chemically induced tumors of strain A mice. The strain A mouse has a high incidence of spontaneous lung tumors and is susceptible to tumor induction by chemical carcinogens. We have detected and characterized the activated protooncogenes in the DNA of both spontaneously occurring and chemically induced lung tumors of strain A mice. Activated K-ras genes were detected using the NIH/3T3 transfection assay, and the activating mutations were identified by utilizing the polymerase chain reaction (PCR) and direct sequence analysis. A strong selectivity of mutations in the K-ras genes were observed in chemically induced lung tumors, as compared to spontaneous tumors, indicating that the carcinogens directly induced point mutations in the K-ras protooncogene. These findings suggest that the strain A mouse lung tumor model appears to be a very sensitive system to identify the mechanism by which chemical carcinogens activate the K-ras gene in lung tissue in vivo.

Animals↗
PubMedDate not supplied

A preliminary pharmacokinetic model for several chlorinated biphenyls in the rat.

A mathematical model is presented to describe the kinetics of distribution, metabolism, and excretion of 4-chloro-, 4,4'-dichloro-, 2,2',4,5,5'-pentachloro-, and 2,2',4,4',5,5'-hexachlorobiphenyl in rats given an intravenols dose of 0.6 mg/kg. A modified flow-limited model simulates the penta- and hexachlorobiphenyl data for periods up to 96 hr but underestimates the mono- and dichlorobiphenyl data beyond 48 hr. The rate constant for metabolism by the liver decreases as degree of chlorination increases such that the rate constant is 200 times smaller for the hexachlorobiphenyl than for the monochlorobiphenyl. The value of the biliary clearance of metabolites is nearly the same for each chlorinated biphenyl, whereas the value of the urinary clearance decreases with increasing degree of chlorination, being 10 times smaller for hexachlorobiphenyl than for monochlorophenyl. The distribution coefficients between most tissues and blood are larger for each parent compound than for its metabolites. Hexachlorobiphenyl has the largest distribution coefficient of all the chlorinated biphenyls in each tissue, whereas the mono-, di-, and pentachlorobiphenyls show no consistent variation. For each compound the distribution coefficient is greater in the fat than in any other tissue. Changes in the fat volume of the growing rats were incorporated into the model in order to simulate the hexachlorobiphenyl concentrations in blood and fat for 42 days.

Animals↗
PubMedDate not supplied

The distribution and excretion of 2,4,5,2',5'-pentachlorobiphenyl in the rat.

Rats received single intravenous doses (0.6 or 6.0 mg/kg) of 2,4,5,2',5'-pentachlorobiphenyl-14C (5-CB). The distribution and ecretion of 5-CB-derived material were investigated at periods ranging from 10 min to 42 days after administration and found to be first-order rate processes in the dose range studied. Blood, liver, muscle, skin, and adipose tissues were found to be the most important tissues to the distribution of this compound. More than 90% of the total dose was removed from the blood within 10 min after administration. Most of the radioactivity was initially deposited in the liver and muscle, and then translocated to the skin and adipose tissue. The decay rate of radioactivity from each of the tissues could be described by the sum of two or more exponentials. Metabolism to more polar compounds appears to be a prerequisite to excretion, and most of the radioactivity was excreted in the bile and ultimately in the feces. Excretion in the urine accounted for less than 7% of the total dose and ceased at approximately 8 or 9 days after 5-CB-administration. Studies of the distribution and excretion of 5-CB-derived material over extended periods of time, 1-42 days, demonstrated the importance of the adipose tissue and skin as long-term storage sites, and demonstrated that the decay rate of 5-CB from the tissues paralleled the decreasing rate of excretion in the feces.

Adipose Tissue↗