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Biomedical subjects

J Fu

Publications and source records attributed to J Fu.

249 records · Page 14Linked to original sources
PubMed1986

Effects of fluorides on in vitro acid production by dental plaque.

A method that holds human dental plaque on a glass micro-electrode has been used to measure the pH depressions in plaque samples exposed to different concentrations of fluoride from sodium fluoride or sodium monofluorophosphate. Fluoride from both sources gave some inhibition of sucrose-induced acid formation at levels as low as 10 ppm and parallel results at other test concentrations of up to 200 ppm F. Repeated exposures of plaque to fluoride solutions did not interfere with its subsequent ability to ferment sucrose.

Acids↗
PubMed1985

A deterministic approach for the estimation of mutation rates in cultured mammalian cells.

Unequal growth rates between mutant and wild-type cells in a large population constitute a problem for the estimation of mutation rate. Over a period of cell growth, a selective advantage of one cell type over the other might lead to considerable error in the estimation of mutation rate if equal growth rates are assumed. In this study, we propose a formula and apply it to the estimation of spontaneous mutation rate in a growing population of Chinese hamster V79 cells in which ouabain-resistant mutant cells exhibit a slower growth rate than the wild-type cells. The formula is a generalization of that previously presented by Armitage (1953), and this is the first attempt to apply the deterministic approach for mutation rate estimation to cultured mammalian cells. The value of the estimated rate is compared with that derived from a parallel experiment using the fluctuation test of Luria and Delbrück (1943). The limitations and advantages of taking the deterministic approach to mutation rate estimation in mammalian cell systems are discussed.

Animals↗
PubMed1983

Estimation of mutation rates in cultured mammalian cells.

The factors that affect reliable estimations of mutation rates (mu) in cultured mammalian somatic cell populations by fluctuation analysis are studied experimentally and statistically. We analyze the differential effect of the final cell population size in each culture (Nt) and the number of parallel cultures (C) on the variation in the rate estimates (mu) inferred from the P0 method. The analysis can be made after the derivation of the variance of mu, which is a measure of variation of mu for a given combination of Nt and C in a number of repeat experiments. The variance of mu is inversely proportional to C and to the square of Nt . Nt determines the probability of occurrence of mutations in a cell culture. By influencing the size of P0, Nt also determines whether a rate estimate is obtainable from the experiment. Since Po is estimated from the fraction of cultures containing no mutation in a set of C cultures, C becomes a determining factor for the accuracy of mu. The rate estimated from P0 is biased, but the bias is in general 2 orders of magnitude smaller than mu. By the selection of an appropriate combination of Nt and C for the experiment, this bias can be reduced even further. Based on the notion of comparing two proportions, we propose a test statistic and have applied it to experimental results for a test of equality of mutation rates in different cell lines. This development places the comparison of mutation rates on a statistical basis.

Animals↗
PubMedDate not supplied

Ribosomal S6 kinase 1 (RSK1) activation requires signals dependent on and independent of the MAP kinase ERK.

BACKGROUND: The rsk1 gene encodes the 90 kDa ribosomal S6 kinase 1 (RSK1) protein, which contains two kinase domains. RSK1, which is involved in regulating cell survival and proliferation, lies at the end of the signaling cascade mediated by the extracellular signal-regulated kinase (ERK) subfamily of mitogen-activated protein (MAP) kinases. ERK activation and subsequent phosphorylation of the RSK1 carboxy-terminal catalytic loop stimulates phosphotransferase activity in the RSK1 amino-terminal kinase domain. When activated, RSK1 phosphorylates both nuclear and cytoplasmic substrates through this amino-terminal catalytic domain. It is thought that stimulation of the ERK/MAP kinase pathway is sufficient for RSK1 activation, but how ERK phosphorylation activates the RSK1 amino-terminal kinase domain is not known. RESULTS: The individual isolated RSK1 kinase domains were found to be under regulatory control. In vitro kinase assays established that ERK phosphorylates RSK1 within the carboxy-terminal kinase domain, and the phosphoinositide-dependent kinase 1 (PDK1) phosphorylates RSK1 within the amino-terminal kinase domain. In transiently transfected HEK 293E cells, PDK1 alone stimulated phosphotransferase activity of an isolated RSK1 amino-terminal kinase domain. Nevertheless, activation of full-length RSK1 in the absence of serum required activation by both PDK1 and ERK. CONCLUSIONS: RSK1 is phosphorylated by PDK1 in the amino-terminal kinase-activation loop, and by ERK in the carboxy-terminal kinase-activation loop. Activation of phosphotransferase activity of full-length RSK1 in vivo requires both PDK1 and ERK. RSK1 activation is therefore regulated by both the mitogen-stimulated ERK/MAP kinase pathway and a PDK1-dependent pathway.

3-Phosphoinositide-Dependent Protein Kinases↗
PubMedDate not supplied

Escherichia coli host cell modifications in continuous culture affecting heterologous protein overproduction: a population dynamics study.

There are many published studies of plasmid segregational instability in Escherichia coli in the literature. However, the formation of plasmid-free segregants can be controlled by the addition of selective chemical agents like antibiotics. This solution has become commonplace in both the laboratory and industry. On the other hand, host cell modifications, which result in low production of plasmid-encoded protein and lead to loss of culture productivity, have not been adequately addressed. Continuous culture of an inducible (ptac) Escherichia coli vector containing strain, RB791(pKN), was characterized by strong dynamic changes in the cell population and product (beta-lactamase) expression. Long-term cultivation resulted in the loss of high-level production of beta-lactamase. Loss of productivity was not due to the formation of plasmid-free cells or structural modifications to the plasmid; instead, continuous operation resulted in a culture dominated by irreversibly altered, low-producing cells. Two distinct classes of lac- mutants which inhibited induction were identified (Y- and I(s)).

Chromosomes, Bacterial↗
PubMedDate not supplied

Higher ploidy in Saccharomyces cerevisiae supports enhanced hepatitis B virus S cloned gene expression at the pilot scale.

The effect of host strain ploidy on the production of hepatitis B surface antigen (HBsAg) in Saccharomyces cerevisiae was evaluated at the pilot scale (75 L). We found that the accumulation of HBsAg normalized to cell protein was 2-fold higher for the diploid strain compared to its isogenic haploid. No detectable differences in many fermentation parameters were observed (e.g., rate of fermentation, growth rate, final cell yield). However, the enhancement of productivity in the diploid strain appeared to be associated with a slower rate of plasmid shedding (2 microns element) and, thus, a higher average copy number (2-fold at stationary phase) compared to those of the haploid strain.

Cloning, Molecular↗
PubMedDate not supplied

Adenine quantitation in yeast extracts and fermentation media and its relationship to protein expression and cell growth in adenine auxotrophs of Saccharomyces cerevisiae.

We have described a method to reliably measure the free adenine content of yeast extract powders or the adenine concentrations found in chemically-defined and complex fermentation samples. This method relies on the selective precolumn derivatization of adenine with chloroacetaldehyde to form the fluorescent adenine adduct 1,N6-ethenoadenine. The derivatized adenine can then be resolved from other components found in samples with reverse phase HPLC and selectively monitored with fluorescence. This method was then used to study the adenine nutritional requirements of adenine auxotrophs of recombinant Saccharomyces cerevisiae. The adenine content of individual yeast extract powders was examined in relation to the cell mass (dry cell weight, DCW) achieved in culture media formulated with these powders. A general increase in DCW was observed with increasing adenine concentration in the yeast extract. Conversely, we observed that as adenine concentration increased in complex media the expression levels of a heterologous protein decreased. This method also allowed us to examine the adenine/DCW ratio in both steady-state continuous culture and batch culture. In both cases, the total in vivo adenine content as measured by the amount of adenine utilized from the culture media was estimated to be ca. 25-40 mg/g DCW. However, data suggest that this value is in excess of what is strictly required for cell growth and represents the quantity of adenine required to saturate intracellular pools of adenine or adenine metabolites. A minimum requirement for cell growth is at least as low as 12.5 mg of adenine/g of cells.

Adenine↗
PubMedDate not supplied

Sensitive biomarker of polycyclic aromatic hydrocarbons (PAHs): urinary 1-hydroxyprene glucuronide in relation to smoking and low ambient levels of exposure.

The study was conducted in a Chinese population with occupational or environmental exposures to polycyclic aromatic hydrocarbons (PAHs). A total of 106 subjects were recruited from coke-oven workers (workers), residents in a metropolitan area (residents) and suburban gardeners (gardeners). All subjects were monitored twice for their personal exposures to PAHs. The biological samples were collected for measurements of 1-hydroxypyrene (1-OHP) and cotinine in urine. The geometric means of personal exposure levels of pyrene, benz(a)anthracene (BaA) and benzo(a)pyrene (BaP) in workers were 1.470, 0.978 and 0.805 microg m-3, respectively. The corresponding levels in residents were 0.050, 0.034 and 0.025 microg m-3; and those in gardeners were 0.011, 0.020 and 0.008 microg m-3, respectively. The conjugate of 1-OHP with glucuronide (1-OHP-G) is the predominant form of pyrene metabolite in urine and it showed strong associations with exposures not only to pyrene, but also to BaA, BaP and total PAHs. Most importantly, a significant difference in 1-OHP-G was even detected between the subgroups with exposures to BaP at < 0.010 and > 0.010 but < 0.020 microg m-3, suggesting that 1-OHP-G is a good marker that can be used for the risk assessment of BaP exposure at levels currently encountered in ambient air. Furthermore, multiple regression analyses of 1-OHP-G on PAHs exposure indicated that cigarette smoke was a major confounding factor and should be considered and adjusted for while using 1-OHP to estimate PAHs exposure.

Air Pollutants↗
PubMedDate not supplied

The effectiveness of sponge-type intraoral applicators for applying topical fluorides in institutionalized older adults.

Many older adults who reside in nursing homes have disabilities which limit their capacity to benefit from the usual protocols for prevention of dental caries. This is a report of a study of the effectiveness of an alternative method of applying topical fluoride in the institutionalized elderly. Fluoride gel (1.1% NaF) was applied to the facial tooth surfaces of 10 elderly nursing home residents using a sponge-type intraoral applicator (IA). Subsequently, the same subjects rinsed with a commercial fluoride solution (0.05% NaF). Salivary fluoride levels were then assessed by the Taves (1968) method. The IA with fluoride produced significantly higher salivary fluoride levels over a period of three hours compared with rinsing.

Aged↗
PubMedDate not supplied

Fluoride concentrations in enamel and dentin of primary teeth after pre- and postnatal fluoride exposure.

The aim of this study was to determine any existing difference in the amount of fluoride incorporated in the surface, body enamel and dentin of two groups of deciduous teeth, either exposed to pre- and postnatal fluoride supplements or to postnatal fluoride only. One hundred and eighty five subjects with intact deciduous incisors were selected from a randomized, double blind study of the caries preventive efficacy of prenatal fluoride (F) supplementation. Surface and body enamel samples were obtained by the acid etch biopsy technique. Dentin microsamples were obtained by drilling to a depth of 100 microm using the microdrill biopsy technique. It was concluded that fluoride exposure during the prenatal period offered no additional measurable fluoride uptake by dental tissues other than that attributable to postnatal fluoride alone.

Cariostatic Agents↗