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Biomedical subjects

R L Wang

Publications and source records attributed to R L Wang.

At least 19 recordsLinked to original sources
PubMed2001

Hydrodynamic potential-modulated reflectance spectroscopy: theory and experiment.

This article describes the development and application of a new electrochemical methodology based on potential-modulated UV-vis reflectance spectroscopy (PMRS). The device configuration is based upon a thin-layer flow-through channel cell incorporating a platinum working electrode. Reagent solutions are pumped through the cell under well-defined hydrodynamic conditions and electrolyzed at the platinum working electrode. Measurements are presented for linear sweep and fixed dc potentials with a superimposed small amplitude sinusoidal potential perturbation. A UV-vis source is employed to irradiate the electrode region, and the resulting reflected signal is analyzed using a phase sensitive detector. Experimental studies using tris(4-bromophenyl) amine (TBPA) in acetonitrile are presented which quantify the relationship between the absorption spectrum and reflected light intensity as a function of the transport rate, electrolysis reactions, and the modulation frequency of the incident irradiation. The experimental results are analyzed using numerical simulations based on a finite difference strategy. These permit the quantitative prediction of the concentration distribution of reagents within the cell. A fast Fourier transform (FFT) routine was used to analyze the frequency response of the numerically predicted reflectance signal. Excellent agreement was observed between the numerical predictions and experimental observations.

Journal Article↗
PubMed2000

[Application of capillary chromatography in benzene boiling range analysis].

The experimental data were analyzed by regression analytical method and the relation between the quantity of impurities and the boiling range of benzene was demonstrated. It was proved that when the quantity of hydrocarbon impurities was within certain limits, the quality of benzene fractions can be determined by analyzing the hydrocarbon impurities in it. So the distillation method for analyzing benzene boiling range may be replaced by capillary chromatography for analyzing the hydrocarbon impurities. The practical applications support the above suggestion.

English Abstract↗
PubMed1999

The limits of selection during maize domestication.

The domestication of all major crop plants occurred during a brief period in human history about 10,000 years ago. During this time, ancient agriculturalists selected seed of preferred forms and culled out seed of undesirable types to produce each subsequent generation. Consequently, favoured alleles at genes controlling traits of interest increased in frequency, ultimately reaching fixation. When selection is strong, domestication has the potential to drastically reduce genetic diversity in a crop. To understand the impact of selection during maize domestication, we examined nucleotide polymorphism in teosinte branched1, a gene involved in maize evolution. Here we show that the effects of selection were limited to the gene's regulatory region and cannot be detected in the protein-coding region. Although selection was apparently strong, high rates of recombination and a prolonged domestication period probably limited its effects. Our results help to explain why maize is such a variable crop. They also suggest that maize domestication required hundreds of years, and confirm previous evidence that maize was domesticated from Balsas teosinte of southwestern Mexico.

Agriculture↗
PubMed1997

Determination of thiamphenicol in human plasma by micellar electrokinetic capillary chromatography.

A micellar electrokinetic chromatographic method is described for the determination of thiamphenicol in human plasma. The plasma sample was basified by adding K2HPO4 and was then extracted with ethyl acetate. After the solvent was evaporated, the residue was reconstituted in water. Approximately 40 nl of the solution were injected hydrodynamically. The running buffer was 20 mM borate (pH 9.2) containing 40 mM sodium dodecyl sulfate and 10% acetonitrile. The applied voltage was 18 kV and the detector wavelength was set at 195 nm. On-column sample stacking was achieved during the analysis to enhance the sensitivity; the limit of quantitation was 0.1 microg/ml. Linearity was over the range of 0.2 to 10 microg/ml. Recovery was 93.7+/-3.3%, the intra-day precision and accuracy was 99.6+/-2.8%; the inter-day precision and accuracy was 98.4+/-3.4%. The concentration of thiamphenicol in human plasma from eight volunteers was measured after administering thiamphenicol capsules orally.

Acetonitriles↗
PubMed1997

Gene flow and natural selection in the origin of Drosophila pseudoobscura and close relatives.

The divergence of Drosophila pseudoobscura and close relatives D. persimilis and D. pseudoobscura bogotana has been studied using comparative DNA sequence data from multiple nuclear loci. New data from the Hsp82 and Adh regions, in conjunction with existing data from Adh and the Period locus, are examined in the light of various models of speciation. The principal finding is that the three loci present very different histories, with Adh indicating large amounts of recent gene flow among the taxa, while little or no gene flow is apparent in the data from the other loci. The data were compared with predictions from several isolation models of divergence. These models include no gene flow, and they were found to be incompatible with the data. Instead the DNA data, taken together with other evidence, seem consistent with divergence models in which natural selection acts against gene flow at some loci more than at others. This family of models includes some sympatric and parapatric speciation models, as well as models of secondary contact and subsequent reinforcement of sexual isolation.

Alcohol Dehydrogenase↗
PubMed1996

The speciation history of Drosophila pseudoobscura and close relatives: inferences from DNA sequence variation at the period locus.

Thirty-five period locus sequences from Drosophila pseudoobscura and its siblings species, D. p. bogotana, D. persimilis, and D. miranda, were studied. A large amount of variation was found within D. pseudoobscura and D. persimilis, consistent with histories of large effective population sizes. D. p. bogotana, however, has a severe reduction in diversity. Combined analysis of per with two other loci, in both D. p. bogotana and D. pseudoobscura, strongly suggest this reduction is due to recent directional selection at or near per within D. p. bogotana. Since D. p. bogotana is highly variable and shares variation with D. pseudoobscura at other loci, the low level of variation at per within D. p. bogotana can not be explained by a small effective population size or by speciation via founder event. Both D. pseudoobscura and D. persimilis have considerable intraspecific gene flow. A large portion of one D. persimilis sequence appears to have arisen via introgression from D. pseudoobscura. The time of this event appears to be well after the initial separation of these two species. The estimated times since speciation are one mya for D. pseudoobscura and D. persimilis and 2 mya since the formation of D. miranda.

Amino Acid Sequence↗
PubMed1994

Human CYP2A6 activation of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK): mutational specificity in the gpt gene of AS52 cells.

The tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1- butanone (NNK) is a potential human carcinogen that is known to be metabolized to DNA-reactive intermediates by the cytochromes P450. We have examined the nature of NNK's DNA damaging effects in a mammalian cell system expressing a specific human cytochrome P450 (2A6) and containing a target gene for mutagenesis. Human CYP2A6, which is known to activate NNK to a mutagen, was lipofected via a retroviral vector into the Chinese hamster ovary AS52 cell line, which contains the bacterial gpt gene and can be mutated to 6-thioguanine resistance. AS52 cells expressed negligible CYP2A6-specific coumarin 7-hydroxylase activity (0.7 pmol/mg protein/min), while a CYP2A6 transfected clone (AS52-E8) expressed 30 pmol/mg protein/min. Both cell lines were equally sensitive to the cytotoxic and mutagenic effects of the direct-acting mutagen ethylmethanesulfonate; however, only the AS52-E8 cells exhibited a dose-dependent increase in cytotoxicity and mutant frequency upon treatment with NNK. At the highest NNK dose (1200 micrograms/ml), the mutant frequency in AS52-E8 cells was 14-fold (339 x 10(-6)) greater than the spontaneous frequency of 24 x 10(-6). Ninty-eight mutant clones were isolated following NNK treatment. Based on PCR analysis, 21 clones contained deletions/rearrangements and 77 were putative point mutants. Sequencing potential point mutants showed that 81% contained G:C to A:T transitions. Four of six G:C to A:T hotspots were at the second G of the GGT motif, which is the motif and major mutation found in codon 12 of Ki-ras from NNK-induced lung tumors in strain A mice. Since NNK may be metabolized via different pathways to pyridyloxobutylate or methylate DNA, the data suggest that methylation damage causes the major mutagenic events in AS52-E8 cells when NNK is activated by human CYP2A6.

Amino Acid Sequence↗
PubMed1993

Retroviral mediated expression of human cytochrome P450 2A6 in C3H/10T1/2 cells confers transformability by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK).

In order to develop more efficient in vitro systems for the study of pro-mutagenic or pro-carcinogenic chemicals, we have produced transgenic C3H/10T1/2 cell lines expressing human cytochrome P450 (CYP) 2A6. A retroviral vector containing the cDNA was packaged in psi-2 cells, and used to infect C3H/10T1/2 cells. From 100 G418-resistant clones initially isolated, three cell lines were chosen for further study based upon their morphologies, growth rates and CYP2A6-dependent coumarin 7-hydroxylase activities. Infected clone 10T1/2-04, like the 10T1/2 cells, had no detectable CYP2A6 enzyme activity, while clones 10T1/2-10 and 10T1/2-29 had microsomal CYP2A6 enzyme activities within the range found in human liver microsomes. CYP2A6 protein levels were in agreement with the observed enzyme activities. Southern blots revealed that cells from clone 10T1/2-04 contained a vector lacking the CYP2A6 cDNA, while cells from clones 10T1/2-10 and 10T1/2-29 contained multiple full-length inserts. Southern analysis also indicated the presence of an endogenous CYP2A6 ortholog in the four cell lines. All cell lines exhibited about equal sensitivity to induction of cytotoxicity and conversion to ouabain resistance by the direct acting mutagen N-methyl-N'-nitro-N-nitrosoguanidine. The four lines were also about equally sensitive to transformation by benzo[a]pyrene, a chemical requiring metabolic activation. However, only clones 10T1/2-10 and 10T1/2-29, which express CYP2A6 activity, were mutated and morphologically transformed by the tobacco specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone.

Animals↗
PubMed1993

Autumn southward 'return' migration of the mosquito Culex tritaeniorhynchus in China.

Direct evidence for a southward 'return' migration in autumn of the mosquito Culex tritaeniorhynchus in China was obtained by aerial sampling with a net suspended from a balloon. In a preliminary study between 2 and 20 September 1990 at Jiangpu, near Nanjing, in Jiangsu Province, 11 females and 4 males of this species were taken at heights of 150-250 m. During 17-26 October 1991 at Dongxiang in northern Jiangxi Province, 44 mosquitoes (8 males, 36 females) were caught in the aerial net at heights of 80-380 m in northeasterly winds (E-NNW). Most of the specimens were flying within the subsiding air-mass behind a cold front. Cx tritaeniorhynchus was the only species identified (31 females) among the mosquitoes from Dongxiang. Of 24 females dissected, 17 had N stage ovaries--interpreted as diapause, five had stage I ovaries, one had stage II ovaries, and one was gravid (stage V), but none was freshly blood-fed. Cx tritaeniorhynchus is the main vector of Japanese viral encephalitis in China, and it is possible that the virus is reintroduced to northern temperate areas in spring by northward migration of infected Cx tritaeniorhynchus females.

Animals↗
PubMed1993

[A report of 40 cases of esophageal carcinoma surviving for more than 5 years after treatment with drugs].

From August 1974 to January 1987, 650 cases of moderately and advanced esophageal carcinoma were treated with a combination of chemotherapy and Rabdosia rubescens or Rabdosia rubescens and/or tradition chinese medicinal prescription. After treatment, 40 patients survived for over 5 years (5-year survival rate 6.15%): 32 for over 6 years, 23 for more than 10 years, 5 for more than 15 years and 20 die of tumors (16 cases) or other diseases (4 cases). There were 20 patients who are still living and some of them have been living for more than 18 years. Analyzing the data, it is believed that the age, the state of activity, the length of illness, the effectiveness of primary treatment, the multi-course extensive therapy, long-term maintenance treatment, etc, are all important factors affecting the results of drug treatment.

Adult↗
PubMed1992

Possible transplacental transmission of human papillomaviruses.

OBJECTIVE: The objective of this study was to examine the possibility of intrauterine human papillomavirus infection of fetuses by transplacental transmission of human papillomavirus before delivery. STUDY DESIGN: Specimens of cervicovaginal cells and peripheral blood mononuclear cells were obtained from 52 consecutive pregnant women in the third trimester of pregnancy. Cord blood specimens were also obtained from the neonates born to these mothers. Presence of human papillomavirus types 16 and 18 deoxyribonucleic acid was analyzed by an in vitro enzymatic deoxyribonucleic acid amplification method. RESULTS: Human papillomavirus type 16 deoxyribonucleic acid was found in 6 (11.5%) cervicovaginal and in 9 (17.3%) peripheral blood mononuclear cell specimens. Seven cord blood specimens from neonates born to mothers who were positive for peripheral blood mononuclear cell human papillomavirus type 16 deoxyribonucleic acid were found to contain human papillomavirus type 16 deoxyribonucleic acid. One cervicovaginal and two peripheral blood mononuclear cell specimens contained human papillomavirus type 18 deoxyribonucleic acid, but none of the cord blood specimens contained human papillomavirus type 18 deoxyribonucleic acid. CONCLUSION: These results seem to suggest possible transplacental transmission of the virus and the potential association of such transmission with the status of human papillomavirus in peripheral blood mononuclear cells.

Base Sequence↗
PubMed1992

Dietary intake, exercise, obesity and noncommunicable disease in rural and urban populations of three Pacific Island countries.

Dietary intake surveys of rural and urban communities in three Pacific Island countries were conducted using an adjusted 24-hour dietary recall method. Dietary survey samples were drawn from noncommunicable disease surveys of Melanesians and Indians in Fiji, Micronesians in Kiribati and Melanesians in Vanuatu. Comparisons of total energy and macronutrient intakes and of obesity, hypertension, diabetes mellitus, serum cholesterol and physical activity levels revealed similar rural/urban trends. Urban subjects were more obese than rural ones, had higher prevalence rates of diabetes and hypertension, and generally had higher cholesterol levels. Rural subjects were leaner, suffered less from diabetes and hypertension, and had greater total energy intakes than urban dwellers. Rural people ate a greater proportion of carbohydrates, while urban subjects ate proportionally more protein and fat, apart from the outer Kiribati atolls with high coconut intakes. Rural subjects in all three studies had higher levels of physical activity. These studies provide persuasive evidence that exercise as well as diet has a significant effect on rural/urban differentials in obesity and noncommunicable disease, and that energy intake reflects energy expenditure.

Diet↗
PubMed1992

Detection of bcr/c-abl mRNA in chronic myelogenous leukemia by polymerase chain reaction to identify chromosome translocation.

The hallmark of chronic myelogenous leukemia (CML) is the Philadelphia chromosome (Ph1) which is caused by a translocation of the c-abl gene from chromosome 9 to the breakpoint cluster region (bcr) on chromosome 22. Polymerase chain reaction (PCR) can be used to detect the chimeric bcr/c-abl mRNA as evidence of the translocation. We applied a very simple and quick method of isolating cytoplasmic RNA, as well as reverse transcription and PCR in detecting bcr/c-abl mRNA of seven CML patients in various stages. Our results showed that only a small amount of either peripheral blood or bone marrow material was required for the expression of the bcr/c-abl mRNA. This is a very fast and time-saving method since a one-step method of cytoplasmic RNA isolation is used instead of the several steps in total RNA isolation as published in other literature.

Base Sequence↗
PubMed1990

[Immunohistochemical study and lectin distribution of thyroid carcinoma originated from follicular epithelium].

97 cases of thyroid carcinoma originated from follicular epithelium were investigated by using histological and immunohistochemical techniques with special reference to lectin distribution. According to the WHO histological typing of thyroid tumours, these cases were divided into three categories as follows: papillary carcinoma of thyroid (PCT) 56, follicular carcinoma of thyroid (FCT) 31 and undifferentiated carcinoma of thyroid (UCT) 10. Results showed that three different kinds of thyroid carcinoma presented various hormone function and distribution of lectins. The positive rate of Tg immunoreactivity was significantly different between these three kinds of tumour, i.e. PCT greater than FCT greater than UCT. Additionally, the positive rate of T4 and T3 immunoreactivity was lower than that of Tg. Some Gastrin, SS and calcitonin positive cells were also recognized in carcinoma of thyroid. Lectin--binding rate of WGA, PNA, SBA and UEA to 97 cases of thyroid carcinoma and 9 cases of normal thyroid tissue revealed that different lectin had a selective binding activity to various types of thyroid carcinoma and normal thyroid cells. From the data obtained, it seemed that the morphological differentiation of thyroid carcinoma was in correspondence with difference of function, and the extent of cell differentiation may be closely related to the biological behavior of the tumour.

Adenocarcinoma↗
PubMed1989

[Comparative studies on diapause responses between Culex tritaeniorhynchus and Culex pipiens pallens].

By comparing the diapause responses between locally hibernating species, C. pipiens pallens, and C. tritaeniorhynchus the overwintering way of which is yet unknown, we found the relative identities of these 2 species in their ovarian diapause criteria, change of the mid-gut and the behaviour of refusing blood feeding. The increases in body weight and fatty contents in the dispersed tritaeniorhynchus were much less than those in diapause pipiens species. Moreover, their ability to resist low temperature was also found significantly weaker. In Shanghai area, the date of the critical photoperiod for C. tritaeniorhynchus was found around the 25th of September with a daylight exposure length (including twilight) of about 13 hours and 43 minutes, being 20 days earlier than that of the locally hibernating species C. pipiens pallens. The gonotrophic dissociation during critical photoperiod occurred more frequently in tritaeniorhynchus than in pipiens mosquitoes. In contrast to pipiens species, it is extremely difficult to obtain diapause tritaeniorhynchus in nature post critical photoperiod. The possibility of a seasonal migratory behaviour of C. tritaeniorhynchus was discussed.

Animals↗
PubMed1988

Gossypol acetate-induced SCEs in spermatogonia and bone marrow cells of mice: dose-response relationships.

Gossypol acetic acid has been shown to have the effect of increasing the SCE frequencies in the spermatogonial cells of mice. This study further confirmed the genotoxic effects of gossypol acetic acid by investigating the dose-response relationships of gossypol acetic acid-induced SCEs in spermatogonial cells and bone marrow cells of mice. Twelve or over 12 mg/kg body weight of the dosage per day could increase the SCE frequencies of both bone marrow cells and spermatogonial cells. The increase of SCE frequency appeared to be directly correlated with the doses used at significant levels (p less than 0.001). Regression lines indicated that, in spite of cell type variation, the SCE induced was proportional to the dose of gossypol acetic acid.

Animals↗