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Biomedical subjects

W H Lewis

Publications and source records attributed to W H Lewis.

At least 91 records · Page 5Linked to original sources
PubMed1979

Isolation of hydroxyurea-resistant CHO cells with altered levels of ribonucleotide reductase.

A Chinese hamster ovary cell line selected for resistance to hydroxyurea was serially cultivated in the absence of a selective agent, and cells with decreased resistance to the cytotoxic effects of hydroxyurea gradually accumulated in the population. Three stable subclones with differing drug sensitivities were isolated from this mixed population and were found to contain intracellular levels of drug-sensitive ribonucleotide reductase which correlated with the degree of cellular resistance to hydroxyurea. This new class of hydroxyurea resistance was expressed in a codominant fashion in cell-cell hybridization studies. Also, the enhanced enzyme activity in the drug-resistant cells was observed only during the cell cycle S phase of synchronized cells. The properties of these drug-resistant lines indicate that they will be useful for genetic and biochemical studies.

Animals↗
PubMed1979

North American pollinosis due to insect-pollinated plants.

In warmer regions of North America many newly introduced plants are cultivated widely and others are becoming aggresive naturalized weeds. A large number are insect-pollinated and shed considerable quantities of airborne pollen. Levels of allergenicity based on skin test data, numbers of patients having immediate hypersensitivity and localities where airborne pollen grains have been identified are presented for each genus of entomophilous plants considered incitants of pollinosis. Among the most relevant are Acacia, Brassica, Citrus, Ligustrum, Olea and Schinus.

Air Pollution↗
PubMed1978

Assay of ribonucleotide reduction in nucleotide-permeable hamster cells.

Ribonucleotide reduction was measured in Chinese hamster ovary cells made permeable to nucleotides by treatment with the detergent Tween-80. When compared to the respective ribonucleotide reductase activity in partially purified cell extracts, CDP and GDP reductase activities in permeabilized cells responded in a similar fashion to dithiothreitol, pH, MgCl2, FeCl3, substrate concentration and the presence of positive or negative allosteric effectors. At low protein concentrations both CDP and GDP reduction with whole cells increased linearly with cell number and was greater than the activity in corresponding cell extracts. Permeabilized cells were used to measure the level of CDP and GDP reductase in a hamster cell line resistant to the cytotoxic effects of hydroxyurea. The hydroxyurea-resistant cell line contained four to ten times more CDP and GDP reductase activity compared to parental or revertant cell lines. The permeabilized cell assay was also used to measure CDP and GDP reductase activities in Chinese hamster ovary cells synchronized by isoleucine starvation. CDP reductase activity was low in G1 arrested cells but increased 10-fold by 16 hours after the readdition of isoleucine to the growth medium. GDP reductase, which is present at much higher levels, is similarly induced after isoleucine addition, but only by 2-fold. The maximum activity of both CDP and GDP reductase occurred from 14 to 16 hours after isoleucine addition, which corresponded to the period of maximum DNA synthesis.

Animals↗
PubMed1978

Genetic characterization of hydroxyurea-resistance in Chinese hamster ovary cells.

Hydroxyurea is an excellent selective agent for obtaining drug-resistant mutants. At a frequency of approximately 1 X 10(-5) it was possible to select, in a single step, colonies that exhibited significant resistance to the cytotoxic effects of the drug. These hydroxyurea-resistant cell lines maintained their resistant phenotype after extensive cultivation in the absence of the drug. Reconstruction experiments indicated that the expression of hydroxyurea-resistance and the frequency of drug-resistant colonies was independent of cell densities up to 5 X 10(5) cells per 100-mm selection plate. Luria-Delbrück fluctuation analyses indicated that the appearance of hydroxyurea-resistant cells in wild type populations occurred spontaneously and at a rate of 4.8 X 10(-6) per cell per generation in the presence of 0.33 mM drug. Studies with the mutagen, ethyl methane sulfonate indicated that it was capable of increasing the frequency of hydroxyurea-resistant cells by a factor of approximately 10. Also, cell-cell hybridization experiments showed that hydroxyurea-resistance behaves as a dominant or codominant trait and that hydroxyurea-resistance was a useful new genetic marker for selection of somatic cell hybrids. Furthermore, similar to many other drug-resistant cell lines hydroxyurea-resistant cells were found to exhibit an altered sensitivity to a number of non-selective agents (guanazole, N-carbamoyloxyurea, formamidoxime, and hydroxyurethane). Except for guanazole these compounds are structurally very similar to hydroxyurea and may be expected to have similar modes of action. The results presented in this paper support the view that hydroxyurea-resistance is expressed as a normal genetic trait and is a useful genetic marker for somatic cell genetic studies.

Animals↗
PubMed1978

Ribonucleotide reductase from wild type and hydroxyurea-resistant chinese hamster ovary cells.

The kinetic properties of partially purified ribonucleotide reductase from Chinese hamster ovary cells have been investigated. Double reciprocal plots of velocity against substrate concentration were found to be linear for three the substrates tested, and yielded apparent Km values of 0.12 mM for CDP, 0.14 mM for ADP and 0.026 mM for GDP. Hydroxyurea, a potent inhibitor of ribonucleotide reduction, was tested against varying concentrations of ribonucleotide substrates and inhibited the enzyme activity in an uncompetitive fashion. Intercept replots were linear and exhibited Ki values for hydroxyurea of 0.08 mM for CDP reduction, 0.13 mM for ADP reduction and 0.07 mM for GDP reduction. Guanazole, another inhibitor of ribonucleotide reductase, interacted with the enzyme in a similar manner to hydroxyurea showing an uncompetitive pattern of inhibition with CDP reduction and yielding a Ki value of 0.57 mM. Partially purified ribonucleotide reductase from hydroxyurea-resistant cells was compared to enzyme activity from wild type cells. Significant differences were observed in the hydroxyurea Ki values with the three ribonucleotide substrates that were tested. Also, CDP reductase activity from the drug-resistant cells yielded a significantly higher Ki value for guanazole inhibition than the wild type activity. The properties of partially purified ribonucleotide reductase from a somatic cell hybrid constructed from wild type and hydroxyurea-resistant cells was also examined. The Ki value for hydroxyurea inhibition of CDP reductase was intermediate between the Ki values of the parental lines and indicated a codominant expression of hydroxyurea-resistance at the enzyme level. The most logical explanation for these results is that the mutant cells contain a structurally altered ribonucleotide reductase whose activity is less sensitive to inhibition by hydroxyurea or guanazole.

Animals↗
PubMed1977

Inhibition of mammalian ribonucleotide reductase by a dinucleotide produced in eucaryotic cells.

HS3, a highly phosphorylated dinucleoside originally purified from the fungus Achlya, has been isolated from Chinese hamster ovary cells undergoing glutamine starvation. The HS3 compounds obtained from the fungal and mammalian sources exhibited similar physical and chemical properties. This unusual dinucleotide may be an important regulator of eucaryotic ribonucleoside diphosphate reductase activity; for 50 micrometer HS3, isolated from either mammalian or fungal cells, significantly inhibited CDP reduction in Achlya or hamster cell preparations, but only marginally affected the activity of the enzyme from E. coli. Studies with HS3 isolated from Achlya and partially purified mammalian ribonucleotide reductase indicated that the compound noncompetitively inhibited the reduction of varying concentrations of the substrates CDP, ADP and GDP with Ki values of 23 micrometer, 14 micron and 16 micron respectively. These inhibitor concentrations are well below the estimated intracellular levels of HS3 in glutamine starved cells and suggest that HS3 inhibition of ribonucleotide reduction may be responsible for the rapid inhibition of DNA synthesis seen under these culture conditions.

Adenosine Diphosphate↗
PubMed1977

The blood composition of different breeds of bulls undergoing beef performance tests.

Blood samples taken on three occasions from each of 66 bulls undergoing beef performance tests were analysed for packed cell volume, blood glucose, haemoglobin, serum albumin, urea nitrogen, total protein, inorganic phosphate, Ca, Ca, Mg, K, Na, Cu, Fe and total iron binding capacity. The bulls were individually fed and situated at two centres, one accommodating Lincoln-Red, Devon and Sussex breeds and the other, Hereford. Significant differences between the Lincoln-Red, Devon and Sussex breeds were observed in concentrations of glucose, urea nitrogen, total iron binding capacity (P less than 0.001), Ca (P less than 0.01), Na and Cu (P less than 0.05). There were no significant correlations between the growth rates of individual bulls and their blood composition.

Animals↗
PubMed1975

Allergy epidemiology in the St. Louis, Missouri, area. I. Fungi.

1728 patients prick skin tested for eight fungi in the St. Louis, Missouri metropolitan area exhibited overall a rather low level of allergenicity as well as a general lack of cross-reactivity. Alternaria, however, elicited a high allergic reaction in both reactivity level and reaction frequency in the population. Response of pediatric patients was higher than that of adults, and the extract concentration and source varied the allergenic response only slightly.

Adolescent↗
PubMed1975

Allergy epidemiology in the St. Louis, Missouri, area. III. Trees.

A population skin-tested with pollen from twelve wind pollinated tree species showed a variable level of allergenicity, particularly among adults. Pollen extracts of Box Elder, Willow and Hickory elicited the highest allergic reactions, Oak, Birch, Sycamore, Black Walnut and Poplar more moderate reactions, while allergens from Cottonwood, Maple, Elm and White Ash were less reactive. Since Box Elder is ubiquitous and produces a strongly positive reaction among adults, it should be included among skin tests of those patients known to be allergic to early spring pollen.

Cross Reactions↗
PubMed1975

Allergy epidemiology in the St. Louis, Missouri, area: II grasses.

3219 patients for seven species of grass pollen extracts and mixtures of these grasses in the St. Louis, Missouri, metropolitan area exhibited specific levels of allergenicity to different grasses, as well as a degree of cross-reactivity among all species tested. Adult patient reactions to these extracts generally were similar to those of the pediatric patients tested. Mixed grass pollen preparations proved to be inadequate as a gauge of patient allergenicity to individual species. Intersection of the prick skin testing method and the intracutaneous technique was found at specific concentrations. For the first time phylogenetic and taxonomic conclusions regarding the grass family are supported by immunological data.

Adolescent↗
PubMed1975

Allergy epidemiology in the St. Louis, Missouri, area. IV. weeds.

Weeds elicit two levels of allergenicity, a high level by the Ragweeds and other members of the Asteraceae, and a much lower level by members of the families Amaranthaceae (Pigweed, Western Water Hemp), Chenopodiaceae (Lamb's Quarters, Kochia, and Russian Thistle), and Plantaginaceae (Plantain) in the St. Louis, Missouri area. The frequency of reaction among both adults and children as well as the cross-reactivity values are similarly divided.

Cross Reactions↗
PubMed1975

Allergy epidemiology in the St. Louis, Missouri, area. V. Cereal ingestants.

Among the cereal ingestants, rice, rye, wheat, corn and oats, provocative skin tests of patients differed according to age. Sensitivity to rice and oats was low for children and that to rice in particular was high for adults, suggesting a differential immunological response to rice allergens. Compared to patient grass pollen reactions, response to ingestants was noticeably lower. Cross-reactivity among ingestants was also lower, particularly between oats and the other cereals.

Adult↗