Biomedical subjects

W K Li

Publications and source records attributed to W K Li.

At least 19 recordsLinked to original sources

PubMed2006

Value at risk estimation using independent component analysis-generalized autoregressive conditional heteroscedasticity (ICA-GARCH) models.

We suggest using independent component analysis (ICA) to decompose multivariate time series into statistically independent time series. Then, we propose to use ICA-GARCH models which are computationally efficient to estimate the multivariate volatilities. The experimental results show that the ICA-GARCH models are more effective than existing methods, including DCC, PCA-GARCH, and EWMA. We also apply the proposed models to compute value at risk (VaR) for risk management applications. The backtesting and the out-of-sample tests validate the performance of ICA-GARCH models for value at risk estimation.

Computer Simulation↗

PubMed2005

Deriving sediment quality guidelines from field-based species sensitivity distributions.

The determination of predicted no-effect concentrations (PNECs) and sediment quality guidelines (SQGs) of toxic chemicals in marine sediment is extremely important in ecological risk assessment. However, current methods of deriving sediment PNECs or threshold effect levels (TELs) are primarily based on laboratory ecotoxicity bioassays that may not be ecologically and environmentally relevant. This study explores the possibility of utilizing field data of benthic communities and contaminant loadings concurrently measured in sediment samples collected from the Norwegian continental shelf to derive SQGs. This unique dataset contains abundance data for ca. 2200 benthic species measured at over 4200 sampling stations, along with co-occurring concentration data for >25 chemical species. Using barium, cadmium, and total polycyclic aromatic hydrocarbons (PAHs) as examples, this paper describes a novel approach that makes use of the above data set for constructing field-based species sensitivity distributions (f-SSDs). Field-based SQGs are then derived based on the f-SSDs and HCx values [hazardous concentration for x% of species or the (100-x)% protection level] by the nonparametric bootstrap method. Our results for Cd and total PAHs indicate that there are some discrepancies between the SQGs currently in use in various countries and our field-data-derived SQGs. The field-data-derived criteria appear to be more environmentally relevant and realistic. Here, we suggest that the f-SSDs can be directly used as benchmarks for probabilistic risk assessment, while the field-data-derived SQGs can be used as site-specific guidelines or integrated into current SQGs.

Animals↗

PubMed2005

Coccidiosis immunization: effects of mushroom and herb polysaccharides on immune responses of chickens infected with Eimeria tenella.

An experiment was conducted to investigate the effects of polysaccharide extracts (E) of two mushrooms, Lentinus edodes (LenE) and Tremella fuciformis (TreE), and an herb, Astragalus membranaceus (AstE), on the immune responses of chickens infected with Eimeria tenella. A total of 180 broiler chickens were assigned to nine groups: three groups were fed with each of the extracts (LenE, TreE, and AstE), three groups were fed with the extracts and immunized with live oocyst vaccine (LenE+V, TreE+V, and AstE+V), a group was immunized with the vaccine only, and there were two controls (E. tenella-infected and noninfected groups). The oocyst vaccine was given at 4 days of age, and the extracts (1 g/kg of the diet) were supplemented from 8 to 14 days of age. At 18 days of age, all birds except those in the noninfected group were infected with 9 x 10(4) sporulated oocysts. The results showed that at 7 days postinfection (p.i.), birds fed the extracts without vaccination had lower body weight (BW) gain than those given the vaccine only. However, the extracts in conjunction with the vaccine significantly enhanced BW gain of the infected chickens compared with the vaccine group. Of the three extracts, LenE and TreE showed a better growth-promoting effect. The extracts largely increased oocyst excretion of droppings during the primary response postvaccination. The cecal peak oocyst output and lesion scores measured at 7 days p.i. were higher in the groups fed the extracts than in the group immunized with the vaccine only, whereas those of the groups fed with the extracts and immunized with the vaccine were not significantly different from the vaccine group. Of the three extracts, both LenE- and AstE-fed groups showed lower cecal oocyst output. Thus, as compared with the extracts, the live, attenuated vaccine showed better results with significantly increased immune response in coccidial infected birds. The polysaccharide extracts may prove useful against avian coccidiosis, and, particularly when they are used in conjunction with vaccine, they have shown preliminary promise against the experimental coccidial infection.

Agaricales↗

PubMed2004

Effects of mushroom and herb polysaccharides, as alternatives for an antibiotic, on growth performance of broilers.

(1) This in vivo trial was conducted to study the effects of polysaccharide extracts of two mushrooms, Lentinus edodes (LenE) and Tremella fuciformis (TreE), and a herb, Astragalus membranaceus (AstE) on growth performance, and the weights of organs and the gastrointestinal tract (GIT) of broiler chickens. (2) Three extracts (LenE, TreE and AstE) were supplemented at inclusion rates of 0.5, 1, 2, 3 and 4 g/kg from 7 to 14 d of age and compared with an antibiotic treatment group (20 mg/kg, virginiamycin (VRG) as well as a group of non-supplemented birds. (3) Body weight (BW) gain, feed intake and feed conversion ratio (FCR) of the extract-supplemented groups were not significantly different from those of the antibiotic group. Significant effects of type of extract and concentration on growth performance were found from 7 to 28 d of age. Generally, birds fed with LenE showed higher BW gain and lower FCR from 7 to 28 d of age than those fed with TreE and AstE and 2 g/kg LenE was considered the optimal inclusion rate for enhanced broiler growth. However, the extracts had no significant effect on the relative weights of organs and GIT compared with the antibiotic group. (4) The birds fed the extracts showed better growth performance than the non-supplemented birds, but were not significantly different from those fed VRG. Of the three extracts, LenE appeared to be a potential growth promoter. Future studies are needed to investigate whether the extracts can be used as alternatives for antibiotic growth promoters in challenged birds, and to elucidate the mechanisms for potentially enhanced growth performance in poultry.

Animal Nutritional Physiological Phenomena↗

PubMed2004

Effects of mushroom and herb polysaccharides, as alternatives for an antibiotic, on the cecal microbial ecosystem in broiler chickens.

An in vivo experiment was conducted to study the potential prebiotic effects of mushroom and herb polysaccharide extracts, Lentinus edodes extract (LenE), Tremella fuciformis extract, and Astragalus membranaceus Radix extract, on chicken growth and the cecal microbial ecosystem, as compared with the antibiotic Apramycin (APR). This investigation was carried out in terms of a dose-response study. The chickens were naturally infected with avian Mycoplasma gallisepticum prior to the experiment. The BW gain, cecal pH, viscosity, and predominant microbial populations were measured 1 wk after the extract and APR treatments. The extracts and APR significantly stimulated growth of the chickens infected with avian Mycoplasma gallisepticum. The average BW gain of the groups fed with the extracts was significantly lower than that of the antibiotic group. The extracts had no significant effect on cecal pH. However, cecal viscosity and microbial populations were significantly affected by feeding extracts and antibiotic. In contrast to APR, the extracts stimulated the number of the potentially beneficial bacteria (bifidobacteria and lactobacilli), while reducing the number of the potentially harmful bacteria (Bacteroides spp. and Escherichia coli). Of the 3 extracts, LenE was associated with the most cecal bifidobacteria and lactobacilli. With each increase in the LenE dose, birds tended to have higher BW gain and total aerobe and anaerobe counts. Numbers of predominant cecal bacteria, in particular, E. coli, bifidobacteria, and lactobacilli, were significantly increased with increases in the LenE dose. It would seem that these specific mushroom and herb polysaccharide extracts hold some promise as potential modifiers of intestinal microbiota in diseased chickens.

Agaricales↗

PubMed2004

Effects of mushroom and herb polysaccharides on cellular and humoral immune responses of Eimeria tenella-infected chickens.

We investigated the effects of polysaccharide extracts from 2 mushrooms, Lentinus edodes (LenE) and Tremella fuciformis (TreE), and an herb, Astragalus membranaceus (AstE), on cellular and humoral immune responses of Eimeria tenella-infected chickens. A total of 150 broiler chicks were assigned to 5 treatment groups: 3 groups were infected with E. tenella and fed with extracts (LenE, TreE, and AstE), and 2 control groups were infected with or without E. tenella. The 3 extracts were given at the level of 1 g/kg of the diet from 8 to 14 d of age. Specific systemic and cecum mucosal antibody production, proliferation of splenocytes, and peripheral T and B lymphocytes were measured during the 3 wk following Eimeria infection. A significantly higher production of specific IgA, IgM (at d 14 and 21 postinfection), and IgG (at d 21 postinfection) were detected in the Eimeria-infected groups fed with the extracts than in the infected group not fed with the extracts. Of the 3 extracts, TreE stimulated a slightly higher production of specific IgM (P = 0.052), and a significantly higher IgG production at 21 d postinfection. The cecal antibody production showed a similar trend to that of serum antibodies. The overall mean levels of cecal-specific IgA and IgG of the groups fed with extracts were significantly higher at 14 and 21 d postinfection compared with the group not fed with extracts. Of the 3 extracts, the AstE-fed group showed the highest IgG production at d 7 postinfection. Both TreE- and LenE-fed groups had significantly higher IgM and IgG levels compared with the AstE group at d 21 postinfection. The extract-fed groups also showed a significantly higher antigen-specific proliferation of splenocytes at 14 and 21 d postinfection compared with the group not fed with the extracts. The overall mean of erythrocyte rosette-forming cells (ERFC %) (at d 14 and 21) and erythrocyte-antibody-complement cells (EAC %) (at d 14) of the groups fed with the extracts was significantly higher compared with the group not fed the extracts. It is concluded from this study that supplementation with mushroom and herb extracts resulted in enhancement of both cellular and humoral immune responses in E. tenella-infected chickens.

Animals↗

PubMed2001

Monitoring phytoplankton, bacterioplankton, and virioplankton in a coastal inlet (Bedford Basin) by flow cytometry.

BACKGROUND: To establish the prevailing state of the ecosystem for the assessment of long-term change, the abundance of microbial plankton in Bedford Basin (Nova Scotia, Canada) is monitored weekly by flow cytometry. METHODS: Phytoplankton are detected by their chlorophyll autofluorescence. Those that contain phycoerythrin are designated as Synechococcus cyanobacteria or cryptophyte algae according to the intensity of light scatter. Bacteria and viruses are stained with DNA-binding fluorochromes and detected by green fluorescence. Distinction is made between bacterial and viral subpopulations exhibiting high and low fluorescence. RESULTS: Time series data are presented for weekly observations from 1991 to 2000. Weekly averages are computed for the complete annual cycle of temperature, salinity, river discharge, nitrate, phosphate, silicate, chlorophyll, total phytoplankton including Synechococcus and cryptophytes, total bacteria including high and low-fluorescence subpopulations, and total viruses including high and low-fluorescence subpopulations. CONCLUSIONS: The microbial biomass in the surface water of Bedford Basin is dominated by phytoplankton. The spring bloom of phytoplankton represents a maximum in algal biovolume, but not in cell number. Phytoplankton, bacteria, and viruses all attain their annual numerical maxima between the summer solstice and the autumn equinox. A vigorous microbial loop and viral shunt is envisioned to occur in the summer.

Bacteria↗

PubMed2001

Photodissociation of ethylene sulfide at 193 nm: a photofragment translational spectroscopy study with VUV synchrotron radiation and ab initio calculations.

Photodissociation of ethylene sulfide at 193 nm has been studied using photofragment translational spectroscopy and ab initio theoretical calculations. Tunable synchrotron radiation was used as a universal but selective probe of the reaction products to reveal new aspects of the photodissociation dynamics. The channel giving S + C2H4 was found to be dominated by production of ground-state sulfur atoms (S(3P):S(1D) = 1.44:1), mostly through a spin-forbidden process. The results also suggest the presence of a channel giving S(3P) in conjunction with triplet ethylene C2H4 (3B(1u)) and allow insight into the energy of the latter species near its equilibrium geometry, in which the two methylene groups occupy perpendicular planes. In addition, a channel leading to the production of H2S with C2H2 also has been observed. Our experimental results are supported and elaborated by theoretical calculations.

Journal Article↗

PubMed2000

Effects of euxanthone on neuronal differentiation.

The growth inhibitory and differentiation inducing effects of euxanthone (1,7-dihydroxyxanthone) from the medicinal plant Polygala caudata on the neuroblastoma (Neural 2A, subclone BU-1) were investigated. At the concentration range of 0-100 microM, euxanthone inhibits the growth of BU-1 cells in a dose dependent manner. The 50% growth inhibitory concentration (IC50) was 41 microM. Significant induction of morphological differentiation and neurite growth was observed at the concentration of 100 microM. Frequency of proliferative neuroblastoma cells was determined after induction of differentiation. The frequency of proliferating BU-1 cells was markedly reduced from 1/1.1 to <1/99. Confocal microscopy also confirmed that the morphological differentiation of BU-1 was associated with the expression of neurite specific marker MAP-2 protein in neurites. These data suggest that euxanthone may be one of the neuropharmacological active compounds in the medicinal plant Polygala caudata.

Animals↗

PubMed1999

Residence times and half-lives of nicotine metabolites in rat brain after acute peripheral administration of [2'-(14)C]nicotine.

The residence times of nicotine and its metabolites in rat brain after acute peripheral nicotine administration were determined. We hypothesize that nicotine metabolites will reach pharmacologically significant concentrations in brain. Cotinine, nornicotine, and norcotinine were structurally identified by dual label radiochemical and gas chromatography-mass spectrometric analysis as biotransformation products of nicotine present in rat brain after s. c. injection of S(-)-nicotine. Two unidentified minor metabolites were also detected in brain. The half-lives in brain of nicotine metabolites were determined after a single s.c. injection of [2'-(14)C]-(+/-)nicotine (0.8 mg/kg) and analysis of radiolabeled metabolites by high pressure-liquid radiochromatography. The brain half-lives of nicotine, cotinine, and nornicotine were 52, 333, and 166 min, respectively. Peak brain concentrations of nicotine metabolites were 300, 70, and 7 nM for cotinine, nornicotine, and norcotinine, respectively. Even with potential accumulation of cotinine in brain after chronic nicotine administration, it is likely that the brain concentration of cotinine will be insufficient to produce neuropharmacological effects resulting from activation of nicotinic receptors to induce dopamine release. Conversely, the concentration of nornicotine in brain after acute nicotine approaches the range found to be neuropharmacologically active. It is likely that nornicotine will accumulate in brain on chronic nicotine administration based on the brain half-life of this metabolite. Importantly, nornicotine is also a major alkaloidal component of tobacco. Thus, as a consequence of tobacco use, alkaloidal and metabolically formed nornicotine may reach concentrations in brain sufficient to produce pharmacological effects.

Animals↗

PubMed1998

Effect of berbamine on T-cell mediated immunity and the prevention of rejection on skin transplants in mice.

Berbamine, an ingredient of Berberis, which itself is widely utilized in Chinese folk-medicine has been used as a source of leukogenics, anti-arrhythmics and anti-hypertensives. In recent years, the immunosuppressive effects of berbamine has been demonstrated. In order to further investigate the value of berbamine as an immunosuppressive agent, the delayed type hypersensitivity reaction (DTH) response with sheep red blood cells (SRBC), the mixed lymphocyte reaction (MLR) and a skin model of allograft rejection on mice were studied. Berbamine showed suppressive effects on DTH and MLR and significantly prolonged allograft survival compared with untreated transplanted mice. The results indicate that berbamine may be a potential agent in clinical transplantation.

Alkaloids↗

PubMed1996

Anhydroicaritin 3-O-rhamnosyl(1-->2)rhamnoside from epimedium koreanum and a reappraisal of other rhamnosyl(1-->2, 1-->3 and 1-->4)rhamnoside structures.

An anhydroicaritin 3-O-rhamnosylrhamnoside from Epimedium koreanum is defined as the 3-O-alpha-L-[alpha-L-rhamnopyranosyl(1-->2)rhamnopyranoside] on the basis of 2D NMR evidence. Complete assignments of the 1H and 13C NMR spectra of this compound are presented for the first time. The NMR distinction of 1-->2, 1-->3 and 1-->4 linked rhamnopyranosylrhamnopyranosides are discussed and indicate that baohuosides III and V from E. davidii and baohuoside VI from E. davidii and E. pubescens, respectively, are (1-->2) linked.

Carbohydrate Conformation↗

PubMed1996

Flavonoids from Epimedium wanshanense.

A novel flavonol glycoside named wanepimedoside A was isolated from the whole plant of Epimedium wanshanense, along with fifteen known flavonoids, anhydroicaritin, desmethylanhydroicaritin, icarisid I and II, quercetin, ikarisoside A and B, sagittatoside B, 2"-O-rhamnosylicarisid II, icariin, 2"-O-rhamnosylikarisoside A, epimedin B, epimedin C, and diphylloside A and B.

Carbohydrate Conformation↗

PubMed1995

Flavonol glycosides from Epimedium koreanum.

A novel flavonol glycoside named caohuoside-B was isolated from the aerial parts of Epimedium koreanum, along with a known flavonol glycoside, epimedokoreanoside-I. Their structures were established by spectroscopic methods. The new compound was elucidated as anhydroicaritin 3-O-beta-D-(4,6-O- diacetyl)glucopyranosyl-(1-->3)-alpha-L-(4"-O-acetylrhamnopyranoside+ ++)-7-O-beta- D-glucopyranoside.

Carbohydrate Conformation↗

PubMed1995

Seroepidemiological and molecular evidence for the presence of two H3N8 equine influenza viruses in China in 1993-94.

In May 1993, a severe epidemic of respiratory disease began in horses in Inner Mongolia and spread throughout horses in China. The disease affected mules and donkeys as well as horses but did not spread to other species, including humans. The severity of the disease raised the question of whether the outbreak might have been caused by the new avian-like influenza viruses detected in horses in China in 1989 or by current variants ofA/equine/Miami/1/63 (H3N8) (equine-2) or by a reassortant between these viruses. Antigenic and sequence analysis established that all gene segments of the influenza virus causing the epidemic were of recent equine-2 origin and that the virus was not a reassortant. Serological analysis of post-infection horse sera provided evidence for the continued circulation of the A/Equine/Jilin/1/89 (Eq/Jilin) (H3N8) avian-like viruses in horses in Heilongjiang province with original antigenic sin-like responses. It is noteworthy that prior infection with the avian-like Eq/Jilin strain did not afford cross-protection against a current equine-2 strain. Serological evidence for the continued circulation of the avian-like H3N8 influenza virus in horses indicates that this virus has probably established itself in horses in Asia.

Animals↗

PubMed1994

Time series models based on generalized linear models: some further results.

This paper considers the problem of extending the classical moving average models to time series with conditional distributions given by generalized linear models. These models have the advantage of easy construction and estimation. Statistical modelling techniques are also proposed. Some simulation results and an illustrative example are reported to illustrate the methodology. The models will have potential applications in longitudinal data analysis.

Biometry↗

PubMed1993

[Antifertility effects of mifepristone and epostane alone and in combination in rats].

A complete interceptive action on pregnancy was shown after ig mifepristone (RU-486) 16 mg.kg-1 or epostane 96 mg.kg-1 on d 10 of pregnancy in rats. The ig ED50 (95% fiducial limits) of RU-486 when given alone and in combination with epostane 12 mg.kg-1 were found to be 7.8 (5.3-10.0) and 2.6 (2.0-3.3) mg.kg-1, respectively (P < 0.05), while those of epostane when given alone and in combination with RU-486 4 mg.kg-1 were 25.5 (19.4-33.6) and 5.6 (4.7-7.4) mg.kg-1, respectively (P < 0.05). An absorption promotor, sodium dodecyl sulfate 24 mg.kg-1 ig, when given in combination with RU-486 8 mg.kg-1 or epostane 24 mg.kg-1, induced complete interceptive action on pregnancy. Levels of plasma progesterone declined significantly when epostane 12 mg.kg-1 was given in combination with RU-486 4 mg.kg-1 as compared with epostane 12 mg.kg-1 alone (P < 0.05). Results showed that drug combination therapy was of benefit both to RU-486 and epostane in their interceptive actions.

Abortifacient Agents, Steroidal↗

PubMed1992

[Pharmacokinetics of epostane in rabbits by HPLC method].

Epostane (Epo), a 3 beta-hydroxysteroid dehydrogenase inhibitor, interrupted pregnancy in rats, rhesus monkeys, and women. Epo concentrations in serum were determined by high performance liquid chromatography (HPLC) at 0.25, 0.5, 1, 2, 4, 8, 16, 32, and 48 h after intragastric Epo 96 mg.kg-1 in rabbits. The concentration-time curve exhibited a 2-compartment open model. The pharmacokinetic parameters were: T1/2ka 0.79 +/- 0.08 h, T1/2 alpha 0.96 +/- 0.08 h, T1/2 beta 6.6 +/- 1.5 h, Vc 14 +/- 3 ml.kg-1, AUC 12.0 +/- 1.9 micrograms.h.ml-1, Tmax 1.8 +/- 0.5 h, Cmax 3.3 +/- 0.5 microgram.ml-1. After rat copora luteum were incubated with hCG 10 IU.ml-1 and Epo 10 or 100 micrograms.ml-1 for 18 and 48 h, luteal cells showed various degrees of degeneration and progesterone production was significantly inhibited.

Androstenols↗