Biomedical subjects

G Chen

Publications and source records attributed to G Chen.

At least 739 records · Page 41Linked to original sources

PubMed1994

Immunological changes in pregnancy-induced hypertension.

Aspects of T and B cell function were studied in women with pregnancy-induced hypertension (PIH) and normotensive pregnant women by determining the proliferation of peripheral blood mononuclear cells (PBMC) with or without stimulation by mitogens (PHA, ConA and PWM) and by determining IgG and IgM levels in the culture supernatant. The results showed that the proliferation of PBMC without mitogens was significantly increased in PIH women without proteinuria compared with normotensive pregnant women. In the presence of PHA, [3H]thymidine uptake in PBMC was statistically higher in PIH women both with and without proteinuria than that in normotensive pregnant women. ConA and PWM mitogen activities were not significantly different between PIH women and normotensive pregnant women. Compared with normotensive pregnant women, IgG production was significantly increased in PIH women with proteinuria but not in those without proteinuria. IgM production was not changed in PIH women. We concluded that immunologic responses in PIH women were increased rather than decreased. This increased immunologic activity is in accordance with some important changes seen in PIH, such as an increase in intracellular calcium, the presence of blood-borne mitogenic factor and a decrease in prostaglandin E series. These findings also support the hypothesis that PIH might result from the imbalance between fetal antigenic load and maternal production of immunologic blockade.

Adult↗

PubMed1994

Glutathione increases interleukin-2 production in human lymphocytes.

It is known that glutathione (GSH) has an immunological effect on several features of the immune system. The present study investigated the effects of GSH on interleukin-2 (IL-2) production from normal human peripheral blood lymphocytes (PBL). The results showed that both exogenous GSH and 2-mercaptoethanol (2-ME) significantly increased intracellular GSH levels after PBL were incubated with both agents. IL-2 production from PBL was markedly increased at the presence of exogenous GSH (0.5-8 mmol/l) or 2-ME (12.5-50 mumol/l) which corresponded to 1.57-2.82 nmol/10(6) cells and 1.41 - 1.80 nmol/10(6) cells of intracellular concentrations of GSH, respectively. However, IL-2 production seemed to reach a steady level when exogenous GSH concentrations in cell culture were between 2 and 8 mmol/l. The findings also showed that there was a positive correlation between the IL-2 concentrations and intracellular GSH levels. This study indicated that both exogenous GSH and 2-ME were able to elevate intracellular GSH levels and the increased intracellular GSH could increase IL-2 production in vitro. It is suggested that GSH may exert its effects on the immune system via the regulation of IL-2 synthesis.

Cells, Cultured↗

PubMed1994

Identification of 3-MI-derived N-centered radicals obtained from incubation of 3-MI with microsomal-NADPH system by EPR-HPLC spin trapping.

3-Methylindole (3-MI) is a metabolite of tryptophan that causes acute pulmonary edema and emphysema in ruminants when administered orally or intravenously. Electron paramagnetic resonance (EPR) spin-trapping techniques have been used to investigate the in vitro and in vivo formation of free radicals during 3-MI metabolism by goat lung. Utilizing C-phenyl-N-tert-butyl nitrone (PBN), a nitrogen-centered free radical has been detected from 3-MI in goat lung microsomal incubation. The EPR spectrum of the spin adduct is identical to that observed when 3-MI is irradiated with ultraviolet light. The formation of a nitrogen-centered 3-MI free radical is followed by the appearance of a carbon-centered radical in microsomal preparations. The objective of the present study is to prove that the nitrogen-centered radical generated from the 3-MI incubation system is a 3-MI radical utilizing [14C]-3 MI and the EPR-HPLC technique. The HPLC chromatogram includes three peaks that give EPR signals. These peaks are assigned to nitrogen-, oxygen- and carbon-centered radical adducts. The polarity of the three peaks follows the order: carbon-centered radical adduct > oxygen-centered radical adduct > nitrogen-centered radical adduct. The last has a polarity that is weaker than 3-MI. Only the nitrogen-centered peak and the 3-MI peak possessed radioactivity. The retention time of the nitrogen centered radical is the same as the spin adduct generated by 3-MI irradiation with ultraviolet light. These results demonstrate that the nitrogen-centered radical is a 3-MI-PBN spin adduct, and supports the hypothesis that 3-MI-induced lung damage results from activation of 3-MI to a free radical. Also, in this study the stability of the radical spin adducts and the best conditions to produce the radicals in the incubation system was investigated.

Animals↗

PubMed1994

Chronic sodium valproate selectively decreases protein kinase C alpha and epsilon in vitro.

Valproic acid (VPA) is a fatty acid antiepileptic with demonstrated antimanic properties, but the molecular mechanism or mechanisms underlying its therapeutic efficacy remain to be elucidated. In view of the increasing evidence demonstrating effects of the first-line antimanic drug, lithium, on protein kinase C (PKC), we investigated the effects of VPA on various aspects of this enzyme. Chronic exposure (6-7 days) of rat C6 glioma cells to "therapeutic" concentrations (0.6 mM) of VPA resulted in decreased PKC activity in both membrane and cytosolic fractions and increased the cytosol/membrane ratio of PKC activity. Western blot analysis revealed isozyme-selective decreases in the levels of PKC alpha and epsilon (but not delta or zeta) in both the membrane and cytosolic fractions after chronic VPA exposure; VPA added to reaction mixtures did not alter PKC activity or 3H-phorbol ester binding. Together, these data suggest that chronic VPA indirectly lowers the levels of specific isozymes of PKC in C6 cells. Given the pivotal role of PKC in regulating neuronal signal transduction and modulating intracellular cross-talk between neurotransmitter systems, the specific decreases in PKC alpha and epsilon may play a role in the antimanic effects of VPA.

Animals↗

PubMed1994

Studies on the ocular hypotensive effects of prostaglandin F2 alpha ester prodrugs and receptor selective prostaglandin analogs.

The use of natural prostaglandins (PG), such as PGD2, PGE2, PGF2 alpha, and PGI2, for treating glaucoma is limited by their ocular side effects. One approach to achieve the required separation of ocular hypotensive activity from side effects is to employ ester prodrugs. From a novel series of 11- and 15-mono and 11,15-diacyl esters of PGF2 alpha we identified prodrugs where PGF2 alpha formation rates in the iris-ciliary body exceeded those in the conjunctiva, sclera, and corneal endothelium. Compared to PGF2 alpha-1-isopropyl ester the ocular tissue hydrolysis rates of the 11-monopivaloyl, the 11,15-dipivaloyl ester and the 1,11-lactone were up to 1000 fold less. Despite this large disparity in hydrolysis rates, the pivaloyl esters and the 1,11-lactone were potent ocular hypotensives in our animal models. In studying prostaglandin analogs, we found that a diverse variety of prostanoid receptor selective agonists lowered intraocular pressure in dogs and/or monkeys. These included DP-, EP1-, EP2-, EP3-, and FP-receptor selective compounds. These findings were surprising and prompted us to re-examine the receptor selectivity of these agonists by radioligand binding studies. Using radiolabelled PGE2, 17-phenyl PGF2 alpha, and sulprostone we were able to confirm the selectivity of the agonists currently used for receptor characterization directly by radioligand binding competition studies. It appears that multiple prostanoid receptor subtypes may be involved in regulating intraocular pressure.

3T3 Cells↗

PubMed1994

Emendation of the description of Acidaminococcus fermentans, a trans-aconitate- and citrate-oxidizing bacterium.

Ruminal fluid which was enriched with trans-aconitate yielded a gram-negative diplococcus (strain AO) which was identified by 16S ribosomal DNA sequence analysis as Acidaminococcus fermentans. In contrast to the original description, the A. fermentans type strain and strain AO were found to utilize citrate as an energy source and to produce hydrogen and hydrogen sulfide. The descriptions of the genus and species are emended accordingly.

Aconitic Acid↗

PubMed1994

Stability and Activities of Antibiotics Produced during Infection of the Insect Galleria mellonella by Two Isolates of Xenorhabdus nematophilus.

Xenorhabdus nematophilus subsp. dutki, an entomopathogenic bacterium, is vectored by steinernematid nematodes into insects, where it produces broad-spectrum antibiotics. The use of the nematode-bacterium complex against soil-dwelling pest insects could introduce antibiotics into the soil via the dead insect fragments during the emergence phase of the nematodes. Studies on the stability and activities of these antibiotics produced in the insect Galleria mellonella may contribute to assessing the possible impact of antibiotics on soil bacteria. Two isolates of X. nematophilus subsp. dutki (isolates GI and SFU) produced xenocoumacins 1 and 2 in cadavers of G. mellonella larvae in a 1:1 ratio. Total xenocoumacin 1 and 2 production was 800 ng/200 mg (wet weight) of insect tissue for the GI isolate. Antibiotic activity of water extracts from insects that had been infected with X. nematophilus was stable at 60 degrees C for 1 h and after repeated freeze-thaw cycles. The antibiotic titer of extracts held at 27 degrees C declined by day 10. The spectrum of bacterial species killed by antibiotics produced in insect cadavers varied with the isolate of X. nematophilus. Levels of antibiotic activity were greater in vivo than in tryptic soy broth, which may represent a nutrient effect. The bacterial isolate, culture condition, and presence of nematodes influenced the total antibiotic production in vivo. However, the levels of activity were not correlated with bacterial levels in the different growth environments. Insect cadavers with antibiotic activity transiently lowered the numbers of the bacteria in the soil, the extent of decline varying with the strain of X. nematophilus and the time of sampling.

Journal Article↗

PubMed1994

Studies on a novel series of acyl ester prodrugs of prostaglandin F2 alpha.

A novel series of prostaglandin F2 alpha (PGF2 alpha) prodrugs, with acyl ester groups at the 9, 11, and 15 positions, was prepared in order to design clinically acceptable prostaglandins for treating glaucoma. Studies involving isolated esterases and ocular tissue homogenates indicated that 9-acyl esters cannot provide a prodrug since PGF2 alpha would not be formed as a product. In contrast, 11-mono, 15-mono, and 11, 15-diesters were converted to PGF2 alpha in ocular tissues and could, therefore, be considered as prodrugs of PGF2 alpha. Carboxylesterase (CE) appeared critically important for the hydrolytic conversion of those PGF2 alpha prodrugs where the 11 or 15-OH group was esterified and such prodrugs were not substrates for acetylcholinesterase (ACHE) or butyrylcholinesterase (BuCHE). The enzymatic hydrolysis of PGF2 alpha-1-isopropyl ester was also investigated for comparative purposes. This PGF2 alpha prodrug was a good substrate for CE, but was also hydrolysed by BuCHE, albeit at a much slower rate. The most striking feature of the enzymatic hydrolysis of PGF2 alpha-1-isopropyl ester in ocular tissue homogenates was that it was much faster than for prodrugs esterified at the 11 and/or 15 positions. In terms of ocular hypotensive activity, all prodrugs which showed detectable conversion to nascent PGF2 alpha were potent ocular hypotensives. Although no separation of ocular hypotensive and ocular surface hyperaemic effects was apparent for PGF2 alpha-1-isopropyl ester, a temporal separation of these effects was apparent for the novel PGF2 alpha ester series. This difference may reflect an unfavourably rapid conversion of PGF2 alpha-1-isopropyl ester in ocular surface tissues compared with anterior segment tissues.

3T3 Cells↗

PubMed1994

Synthesis of carboxylated poly(NIPAAm) oligomers and their application to form thermo-reversible polymer-enzyme conjugates.

A thermo-reversible poly(N-isopropylacrylamide) poly(NIPAAm) oligomer with a carboxyl functional end group has been synthesized by radical polymerization using beta-mercaptopropionic acid as a chain transfer reagent. This polymer has been conjugated to an enzyme, beta-D-glucosidase, to form a thermo-reversible water soluble-insoluble polymer-enzyme conjugate. This conjugate can be used for separation, recovery and recycle of an enzyme simply by applying small temperature changes to the reaction medium. In contrast to the random polymer-enzyme conjugates reported in the literature, in this study the enzyme is coupled to each polymer chain by a single end attachment. These preliminary studies show that the conjugated enzyme exhibits very high retention of activity (> 90%) compared to the native enzyme and shows improved thermal stability.

Acrylic Resins↗

PubMed1994

Attributes of effective managers and implications for health care management education in the Asia-Pacific region.

This paper explores the perceptions of managers and students from 11 countries in the Asia-Pacific region regarding the attributes needed for becoming effective managers and the broad implications of these findings for health care management education. The study forms part of a wider international project aimed at exploring the role of national culture in managerial behavior and effectiveness.

Administrative Personnel↗

PubMed1994

The role of cytokines in the production of prostacyclin and thromboxane in human mononuclear cells.

The aim of the present work was to study the regulatory effects of cytokines (TNF alpha, IL-1 beta and IL-2) on the production of the prostglandins (PGI2 and TXA2) from human mononuclear cells. Our major findings were: (1) TNF alpha, IL-1 beta and IL-2 were all able to induce PGI2 and TXA2 syntheses in mononuclear cells. (2) TNF alpha exerted a biphasic effect on prostaglandin production. The lower concentrations of TNF alpha enhanced prostaglandin synthesis while the higher concentrations did not. (3) TNF alpha had a positive effect after only a 30-minute incubation, whereas IL-1 beta and IL-2 required a 8-hour incubation to produce a significant effect. This suggests that the different mechanisms are involved in their actions. (4) The effects of cytokines on the production of PGI2 were greater than that on the production of TXA2. It is concluded that cytokines can not only regulate the production of prostaglandins but also change the pattern of their formation.

Cells, Cultured↗

PubMed1994

Normal superoxide dismutase (SOD) gene in pregnancy-induced hypertension: is the decreased SOD activity a secondary phenomenon?

Reactive oxygen species (ROS) have been implicated in the pathogenesis of pregnancy-induced hypertension (PIH). A genetic factor is also thought to be associated with the disease. The aim of the present study was to investigate whether decreased superoxide dismutase (SOD) activity in PIH resulted from gene abnormalities. Fourteen patients with PIH were enrolled in the study. Normal pregnant women and normal nonpregnant women served as controls. Genomic DNA and mRNA were isolated from white cells and subjected to Southern and Northern blot analysis with a 600 bp CuZn-SOD probe. SOD activity was also determined in the white blood cells and red blood cells. The results showed that SOD activity was significantly reduced in patients with PIH compared to both control groups. There were no significant differences in the size of the CuZn-SOD gene and its expression between the patients with PIH and the controls. This study confirmed that there was a decreased SOD activity in PIH but revealed neither major structural changes in the genomic DNA nor mRNA size of CuZn-SOD. Our results suggest that the decreased SOD levels in PIH are not due to abnormalities in the CuZn-SOD gene and are an acquired phenomenon which occurs during the development of the disease.

Adult↗

PubMed1994

Pharmacokinetic-pharmacodynamic modeling of electroencephalographic effects of midazolam in eight Chinese men.

The effects of midazolam (Mid) on the electroencephalogram (EEG) were related to Mid concentrations in serum in 8 Chinese healthy male volunteers for the assessment of concentration-effect relationship. The total number of waves per second within the frequency range of 12-30 Hz (TNW12-30) in the central-occipital (C1-O1) lead EEG obtained by aperiodic analysis was used as EEG effect of the drug. The PK-PD parameters were calculated by PK-PD software using the sigmoid Emax model. They were: T1(2)keo = 1.3 +/- 0.9 min-1, EC50 = 254 +/- 54 micrograms.L-1, N = 2.9 +/- 0.6. E0 and Emax were calculated from the observed values, being 3.4 +/- 1.3 and 11.4 +/- 2.2 TNW12-30, respectively. Our results showed that the concentration-EEG effect relationship of Mid could be characterized in individual Chinese man using TNW12-30 as a measure of pharmacological response.

Adult↗

PubMed1994

[Mechanism of changes in coagulation after electric burns in rabbits].

The changes in local lesion after high-voltage electric burns ares dependent on many factors. One of the important factors is the change in coagulation. In this paper, a high-voltage electrical burn model was reproduced in rabbits for the purpose of investigating the coagulation mechanism. It was found that AT-III and PC showed elevation and declination, respectively, at 6h and 12h postburn. PAI:A and t-PA:A also showed obvious changes, while FDP showed continuous elevation at 6h up to 5d postburn. The findings probable provided the explanation of the occurrence of thrombosis at 6h to 12h postburn, and the second episode of thrombosis on the 5th day.

Animals↗

PubMed1994

[Anatomy of the eyebrow and upper eyelid region and its significance in ptosis surgery].

The article reports the results of the anatomic observations from dissecting 30 upper eyelids and 8 eyebrows of adult cadavers. In the eyebrow region, the anterior and posterior sheaths of the galea enclose the muscle plane where the frontalis, orbicularis and corrugator muscles are interdigitated. The posterior sheath attaches to supraorbital ridge through the brow fat pad. It was found that a few fibers of the frontalis muscle insert to the skin of the brow. In the upper eyelid, the orbital septum fuses with the aponeurosis at or just below the upper margin of the tarsus. The levator aponeurosis, Muller's muscle, particularly their attachments were carefully observed and measured. Finally, the application of the anatomy in the ptosis surgery is discussed.

Blepharoptosis↗

PubMed1994

[Effect of indirect fluorescent antibody test for the diagnosis of amoebiasis].

Indirect fluorescent antibody test (IFAT) was performed by the method of [symbol: see text] (1971) with some slight modifications for the diagnosis of amoebiasis. The antigen used was prepared from 48-hour culture of Entamoeba histolytica (strains G2, G3, and G5) in LAS diphasic medium and only those amoebae clinging the culture were collected. The serum samples or blood drops on filter paper were positive by the improved IFAT in all of the 54 cases of amoebic liver abscess and the positive reactions of most cases were very marked. Of 23 cases of acute amoebic dysentery, 19 were positive, the positive rate being 82.6%. The results also show that 42 cases of other diseases and 40 healthy persons were all negative.

Animals↗

PubMed1994

[Development of a monoclonal antibody (AF9) to human breast carcinoma].

A monoclonal antibody AF9 (IgG1) was raised against human breast carcinoma by fusing murine myeloma SP2/0 cells with spleen cells from BALB/c mice immunized with cell membrane extracts from primary breast carcinoma. Immunohistochemical staining using the antibody showed reactivity in 19 out of 20 breast carcinoma tissues and in some nonbreast carcinomas such as hepatic, ovarian, lung, colon, and gastric carcinoma tissues. But no staining was observed in either normal tissues or other carcinomas. By immunological treatment, the antigen recognized by AF9 was referred to be glycoprotein with lipid component, and Western blotting revealed that its molecular weight is 51, 56, 67 and 73kd.

Animals↗

PubMed1994

[Observations on sensory heterotropia].

The authors analysed the records of 73 cases with sensory heterotropia, and discussed the correlation between the age of sensory obstacles in sensory heterotropia and the type of heterotropia, the restores of binocular vision after surgical correction and the reversion of eye position. The authors suggested that sensory heterotropia should be treated as early as possible so that binocular vision could be restored.

Adolescent↗