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Biomedical subjects

R W Hart

Publications and source records attributed to R W Hart.

At least 127 records · Page 7Linked to original sources
PubMed1981

Interrelationships between cellular proliferation, DNA alkylation and age as determinants of ethylnitrosourea-induced neoplasia.

Thirty-day-old Sprague--Dawley rats were used to study the persistence of DNA lesions (e.g., O6-alkylguanine) induced by various doses of ethylnitrosourea (ENU). Cellular proliferation was measured as an increment of DNA content per organ at 7 days post-treatment. We observed that the persistence of O6-EtGua was not affected by the various dose levels. Comparing the 3 organs, the persistence of O6-EtGua ranked in the order of brain greater than kidney greater than liver, while the percent increase in DNA content was measured as liver greater than kidney greater than brain. When the target specificity of ENU carcinogenesis in 30-day-old rats was compared to that following transplacental exposure in terms of its relationship to the persistence of DNA lesions and the rate of target cellular proliferation, it permitted the conclusion that induction of neoplasia in target cells is not only determined by persistent DNA lesions but also by the rate of proliferation of target cells at the time of exposure.

Age Factors↗
PubMed1981

Growth characteristics of human glioma-derived and fetal neural cells in culture.

Growth characteristics of human fetal neural cells (CH) and human glioblastoma multiforme-derived cells (12-18) in culture were compared. Cells were grown to confluent densities of 38,000 to 42,500 cells/cm2 for CH and 85,800 to 87,100 for 12-18. Population doubling times were 40.0 +/- 5.1 hr and 66.5 +/- 9.8 hr for CH and 12-18 cells, respectively. The mean DNA content per cell of the glioma-derived cells was twice that of the fetal brain cells at sparse, log, and confluent cell densities. High concentrations (40%) of serum in growth medium increased DNA contents in confluent CH, but not 12-18, cells. The amount of protein per cell also was consistently higher in glioma cells than CH cells, but, as cell densities increased, protein contents decreased for both: 1200 to 700 pg/cell in glioma cells, and 840 to 560 pg/cell in CH cells. In each cell line, initial rates of [3H]ThdR incorporation into TCA precipitable material decreased as cell density increased, but confluent glioma-derived cells incorporated 10 times more [3H]ThdR than confluent fetal cells. Almost all CH cells had a normal diploid chromosome number of 46. A histogram showing the relative frequencies of chromosome numbers of glioma-derived cells had peaks of 52, 79, and 105 chromosomes per metaphase, indicating a haploid number of 26 for most cells. Lengths of cell cycle phases, determined using autoradiographic techniques, indicate that glioma-derived cells had a longer generation time and S period than fetal neural cells. These data demonstrate several biological differences between glioblastoma-derived cells and non-neoplastic fetal neural cells, indicating that this system is of potential value for comparative studies on growth control and contact inhibition.

Cell Count↗
PubMed1981

Analysis of alkylated sites at N-3 and N-7 positions of purines as an indicator for chemical carcinogens.

This study reports a rapid assay to distinguish depurination from other forms of alkaline-labile lesions induced in DNA by alkylating agents. Covalently closed circular duplex PM2 DNA was treated with various alkylating agents such as N-methyl-N-nitrosourea, dimethyl sulfate, methyl methanesulfonate, N-ethyl-N-nitrosourea, diethyl sulfate, and ethyl methanesulfonate at pH 6.5. Apurinic sites and subsequent strand breaks were introduced by the hydrolysis of the alkylated purines under nondenaturing conditions by heating alkylated DNA at 70 degrees for 1.5 hr with 0.05 M 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid:KOH (pH 7.4), 0.1 M KCl, 0.01 M MgCl2, 0.0005 M ethylenediaminetetraacetate, 0.05 M glycine, and 0.01 M putrescine. The number of strand breaks produced, representing the alkylated sites at N-3 and N-7 positions of purines, were quantitated by electrophoresis in 1% neutral agarose slab gels. These results were compared with previously reported carcinogenic and mutagenic effects of these compounds, and a correlation between the apurinic sites, the total alkylated sites, and the biological effect of the alkylating agent was determined.

Alkylating Agents↗
PubMed1980

Relationship between gangliosides and doubling times in cultured human brain and brain tumor cells.

Cells cultured in vitro from normal human white matter and 3 individual brain tumors exhibited the following population doubling times: cells from normal human white matter, 64 +/- 22 h, glioblastoma multiforme, 43 +/- 11 h; malignant astrocytoma, 98 +/- 19 h; and anaplastic oligodendroglioma, 81 +/- 24 h. Cells were seeded at subconfluent density, pulse-labelled for 24 h with the ganglioside precursor D-[1-14C]glucosamine and harvested. Radioactive patterns of extracted gangliosides showed that incorporation of label into disialoganglioside was significantly higher in the samples with longer population doubling times than in samples with shorter population doubling times. These findings suggest gangliosides may play a role in regulation of cell growth.

Brain↗
PubMed1980

Retention of promutagenic O6-ethylguanine in the DNA of various rat tissues following transplacental inoculation with ethylnitrosourea.

Pregnant Fischer rats at their 20th day of gestation were inoculated intravenously with [14C]ENU (75 mg/kg). The O6-ethylguanine content of liver, kidney, and brain DNA from both fetuses (offspring) and adults were quantitatively determined 3 h and 7 days after carcinogen treatment. Removal of O6-ethylguanine from the DNA of brain (target) was much slower than from liver (non-target) and kidney (low-target). Retention of O6-ethylguanine was found to be relatively similar in adult and fetal brains, although 100% of the offspring transplacentally exposed to 75 mg/kg ENU were shown to develop tumors of the nervous system, whereas the inoculated pregnant dams did not.

Alkylation↗
PubMed1980

Putative inhibitory effects of chrysotile, crocidolite, and amosite mineral fibers on the more complex surface membrane glycolipids and glycoproteins.

Syrian hamster embryo cells were treated with galactose oxidase, followed by reduction with tritiated sodium borohydride at pH 7.4. The labeling patterns of galactosyl and N-acetyl galactosaminyl residues on the cell surface were altered in comparing scraped vs. unscraped and buffer vs. media-soaked cells treated with galactose oxidase. From these preliminary studies, the procedure to be used in most of the asbestos treatment studies was to treat cells in situ, in buffer with galactose oxidase, and then to label treated scraped cells with NaB(3)H(4). After 20 hr interaction between chrysotile asbestos and Syrian hamster cell cultures, an alteration in surface labeling of glycolipids and glycoproteins was observed. Tritiated disialogangliosides (G(Dla)) and the higher molecular weight labeled glycoproteins were significantly reduced by asbestos treatment. Similar chrysotile asbestos-treated cultures were grown in monolayers in MEM (Eagles) with 10% fetal bovine serum for 2, 24, 48, and 72 hr and then surface-labeled with galactose oxidase-. NaB(3)H(4) in phosphate buffer. Little or no difference was observed between surface-labeled lipid or protein distribution in untreated cells and those treated with asbestos for 2 hr. Asbestos-induced polar and neutral glycolipid pattern changes were observed at 24, 48, and 72 hr. Disialo- and trisialogangliosides (the more complex gangliosides) were decreased 85%, whereas globoside GL-4 was decreased by 60% at 72 hr. An overall decrease of labeled glycoproteins was observed at 24-48 hr. By 72 hr there was a complete loss of labeled protein bands with 80,000 dalton molecular mass. Since the changes in glycoproteins and glycolipids occur only after extended exposure of the cells to asbestos, the present studies support the concept that a metabolic rather than immediate masking effect is involved. Comparisons of treatment of Syrian hamster embryo cells with various asbestos fibers for 48 hr in the order of decreasing reduction in complex gangliosides were crocidolite>chrysotile (intermediate)>amosite. Effects of the above fibers on high molecular weight glycoproteins labeling followed the same order. The labeling pattern is reminiscent of the increased simplification of glycolipids and glycoproteins found in transformed cells. In the case of asbestos which appears to have no independent mutagenic capability, it is more likely that the membrane changes induced by asbestos serve to allow other mutagens to pass into the cell so as to act on the nuclear structure.

Animals↗
PubMed1980

Elemental modifications and polycyclic aromatic hydrocarbon metabolism in human fibroblasts.

Mineral fibers and particulates represent one of the best documented, economically important, and ubiquitously occurring categories of human carcinogens. Yet, while a wealth of information exists concerning the mechanism of action of physical, chemical, and viral carcinogens, virtually nothing is known relative to the mechanism of action of this economically important class of carcinogenic compounds known as mineral fibers and particulates. While the length and diameter of various forms of asbestos have been associated with both cellular toxicity in vitro and tumor occurrence in vivo, nothing is known about whether or not these same physical properties are responsible for the purported synergistic interaction between cigarette smoking and asbestos exposure relative to the induction of bronchogenic carcinoma. Thus, while the risk of bronchogenic carcinoma for nonsmokers exposed to asbestos appears to be only slightly greater than that for unexposed nonsmoking populations, the risk of occurrence of this same tumor in asbestos workers who also smoke is approximately 100-fold greater than in nonsmoking asbestos workers. The risk of bronchogenic carcinoma is increased approximately 8-fold in asbestos workers who smoke over non-exposed smokers. Since it is clear that cigarette smoke contains over 150 polycyclic aromatic hydrocarbons, some of which are known animal carcinogens, and since other laboratories have reported that metals associated with asbestos redirect the metabolism of these agents, it was of interest to us to investigate the effects of mineral fibers on the metabolism and biochemistry of polycyclic aromatic hydrocarbons.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1980

The effects of asbestos on plasma membrane; surface glycolipids and glycoproteins of Syrian hamster embryo cells.

Syrian hamster embryo cells were treated with galactose oxidase (EC 1.1.3.9) followed by reduction with tritiated sodium borohydride (NaB3H4) at pH 7.4. Labeling patterns of galactose and galactosamine in glycolipids and glycoproteins were determined by thin-layer chromatography and SDS-gel electrophoresis respectively. After 20 hours of interaction between the chrysotile asbestos and Syrian hamster cell cultures, a decrease in surface labeling of both glycolipids and glycoproteins was observed. Tritiated disialoganglioside (GDla) and the higher molecular weight labeled glycoproteins were significantly reduced by asbestos interaction.

Animals↗
PubMed1979

Longevity, stability and DNA repair.

The functional capacity of a cell, tissue, organ, or organism is dependent upon its ability to maintain the stability of its unit components. The higher the differentiated state of the system, the greater the amount of stability required to maintain that state as a function of time. Stability can be achieved via either redundancy or repair. Redundancy while easily achievable in biological systems is both costly and limited by thermodynamic considerations. Repair, in its general sense, has no such limitations. Repair at the cellular and macromolecular level is multiple in its forms and varies as a function of species, tissue, and stage of the cell cycle. The repair of DNA damage is a dynamic process with many components and subcomponents, each interacting with one another in order to achieve a balance between individual stability and evolutionary diversity. Thus, between internal and external factors which damage DNA and the subsequent expression of alterations in the functional stability of DNA lie the multi-functional pathways which attempt to maintain DNA fidelity. A strong correlation between ulta-violet light induced excision or pre-replication repair, as measured by autoradiogrphy and maximum species lifespan has been reported within different strains of the same species, between related species (e.g. Mus musculus and Peromyscus leucopus), between five orders of mammals, and most recently within members of the primate family. As has been demonstrated by the authors and others, differences in excision repair between species and tissues may relate to the turning off of portions of the repair processes during embryogenesis. Regardless of why such correlations exist or the nature of their mechanisms, it is naive to either assert or deny a causal role for DNA repair in longevity assurance systems. For example, while species-related differences in DNA repair may reflect the turning off of such repair processes during fetal development this does not mean that rates of accumulation of DNA damage are not altered by such changes. Indeed, such a phenomena might well explain the rapid evolution of lifespan within the primates without a concurrent input of new genes.

Aging↗
PubMed1979

DNA repair in Syrian hamster embryo cells treated with 7,12-dimethylbenz[a]anthracene and its weakly carcinogenic 5-fluoro analog.

The postreplication repair capacity of Syrian hamster embryo cells in culture was determined after treatment with the potent carcinogen 7,12-dimethylbenz[a]anthracene (DMBA) and its weakly carcinogenic analog 5-F-DMBA. The size and amount of daughter DNA sedimenting as high-molecular-weight DNA were found to be less in the DMBA treated cells than in the 5-F-DMBA-treated cells. This difference probably depends upon the types of adducts entering DNA replication.

9,10-Dimethyl-1,2-benzanthracene↗