Biomedical subjects

C F Chen

Publications and source records attributed to C F Chen.

At least 91 records · Page 5Linked to original sources

PubMed2000

A novel agarofuran sesquiterpene, celahin D from Celastrus hindsii Benth.

A novel agarofuran sesquiterpene polyol ester, 1beta,2beta,6alpha,15beta-tetracetoxy-8 beta,9alpha-dibenzoyloxy-beta- dihydroagarofuran (celahin D) (1), two known analogues of 1,1beta-acetoxy-8beta,9alpha-dibenzoyloxy-4al pha6alpha-dihydroxy-2beta(alphamethylbutanoyloxy)-beta-++ +dihydroagarofuran (2) and beta-acetoxy-8beta,9alpha-dibenzoyloxy-6alpha-hy droxy-2beta(alpha -methylbutanoyloxy)-beta-dihydroagarofuran (3), and a known cytotoxic sesquiterpene pyridine alkaloid, emarginatine E (4) were isolated from the stems of Celastrus hindsii Benth. Three known triterpenes, loranthol (5), lupenone (6) and friedelinol (7) were also obtained from the titled plant. Structural elucidation of compound 1 was established by 2D NMR spectra.

Magnetic Resonance Spectroscopy↗

PubMed2000

Effect of the plant-extract osthole on the relaxation of rabbit corpus cavernosum tissue in vitro.

PURPOSE: We investigated the cavernosal relaxant effect of osthole, a coumarin isolated from Cnidium monnier (L.) Cusson which has been long used in China as a herbal medicine to improve male sexual dysfunction. MATERIALS AND METHODS: Strips of rabbit corpus cavernosum were precontracted with phenylephrine. Corporal relaxation evoked by osthole was then determined in the absence and presence of nitric oxide synthase inhibitor (L-NAME), soluble guanylate cyclase inhibitor (ODQ), cyclooxygenase inhibitor (indomethacin), tetradotoxin, and after endothelium deprivation. RESULTS: Corpus cavernosal strips showed relaxation in response to osthole (0.1 approximately 30 microM) in a dose-dependent manner. These effects were reduced partially but significantly by pretreatment with L-NAME, ODQ and by endothelial disruption. However, they were not affected by indomethacin and tetradotoxin treatment. Osthole pretreatment (from 1 to 30 microM) enhanced the sodium nitroprusside (0.3 microM)-induced relaxation of corpus cavernosum in a dose-dependent manner to a maximum of 3 times the pretreatment level at 30 microM osthole. However, this effect was abolished in the presence of zaprinast. Additionally, a higher concentration of osthole (30 microM) also enhanced forskolin-induced relaxation. CONCLUSION: The data suggested that osthole possesses a relaxant effect on rabbit corpus cavernosal tissues which is attributable to the release of NO from sinusoidal endothelium and to the potentiation of the cGMP and/or cAMP signal mediating relaxation of cavernosal smooth muscle by inhibiting phosphodiesterase.

Animals↗

PubMed1999

Determination of unbound cefmetazole in rat blood by on-line microdialysis and microbore liquid chromatography: a pharmacokinetic study.

A specific and sensitive microbore liquid chromatographic method for the determination of unbound cefmetazole in rat blood was developed. A microdialysis probe was inserted into the jugular vein/right atrium of a Sprague-Dawley rat. Cefmetazole (10 mg/kg, i.v.) was then administered via the femoral vein. Dialysates were automatically injected into a liquid chromatographic system via an on-line injector. Isocratic elution of cefmetazole was achieved by LC-UV within 10 min. Intra- and inter-assay accuracy and precision of the assay were < or = 10%. The detection limit of cefmetazole was 20 ng/ml. Pharmacokinetic analysis of results indicated that unbound cefmetazole levels in rats best fit a biexponential decay model.

Animals↗

PubMed1999

Determination of unbound ceftriaxone in rat blood by on-line microdialysis and microbore liquid chromatography.

In vivo microdialysis was used to determine unbound ceftriaxone in rat blood. A microdialysis probe was inserted into the jugular vein/right atrium of Sprague-Dawley rats, and dose of 10 mg/kg ceftriaxone was then administered via the femoral vein. Dialysates were automatically collected and injected into a liquid chromatographic system via an on-line injector. Isocratic elution of ceftriaxone within 10 min was achieved using a microbore liquid chromatographic system. The chromatographic mobile phase consisted of methanol-100 mM monosodium phosphoric acid (15:85, v/v, pH 7.0). The wavelength of the UV detector was set at 280 nm. Intra- and inter-assay accuracy and precision of the assay were less than 15%. The detection limit of ceftriaxone was 20 ng/ml. The results suggest that unbound ceftriaxone in rat blood is best fit to a biexponential decay model.

Animals↗

PubMed1999

Simultaneous measurement of cefuroxime in rat blood and brain by microdialysis and microbore liquid chromatography. Application to pharmacokinetics.

To characterize the pharmacokinetics of cefuroxime in rat blood and brain, microdialysis probes were inserted into the jugular vein and brain striatum, respectively. Cefuroxime (20 mg/kg, i.v.) was administered via the femoral vein. Blood microdialysates were automatic injected onto microbore liquid chromatography via an on-line injectors. The mobile phase consisted of methanol-100 mM monosodium phosphoric acid (25:75, v/v, pH 5.0) with a flow-rate of 0.05 ml/min. Ultraviolet detector was set at a wavelength of 280 nm for cefuroxime. The present assay enhanced the detection sensitivity and enabled the determination of cefuroxime down to 5 ng/ml. The pharmacokinetic data demonstrated that the area under the concentration curve (AUC) ratio of unbound cefuroxime in rat brain and blood was about 4.2% after cefuroxime (20 mg/kg, i.v.) administration. These results provided further evidence that cefuroxime could penetrate the blood-brain barrier.

Animals↗

PubMed1999

Measurement of hydroxyl radical in rat blood vessel by microbore liquid chromatography and electrochemical detection: an on-line microdialysis study.

Salicylic acid (0.5 mM) is used as a trapping reagent of hydroxyl radical, and the formed 2,3- and 2,5-dihydroxybenzoic acids were collected via an on-line microdialysis device from the blood vessels. This study revealed the use of a sensitive liquid chromatographic system with electrochemical detection for the determination of 2,3- and 2,5-dihydroxybenzoic acids. Mobile phase consisted of 0.1 M monochloroacetic acid, 10 mM EDTA, 0.5 mM sodium octylsulfate, 20% acetonitrile and 5% tetrahydrofuran in 1 l (pH 3.0 adjusted with 1 M NaOH), and the flow-rate of 0.05 ml/min were found to be optimum. Isocratic separation of these adducts on a microbore column (reversed-phase C18, 150x1 mm I.D., 5 microm) was achieved within 10 min. The optimal applied potential of dihydroxybenzoic acids was set at 750 mV based on a hydrodynamic study. This method has the detection limits of 1.3 pmol/ml (or 0.2 ng/ml) for 2,3- and 2,5-dihydroxybenzoic acids in Ringer solution (at signal-to-noise ratio=3).

Animals↗

PubMed1999

Expression of BRC repeats in breast cancer cells disrupts the BRCA2-Rad51 complex and leads to radiation hypersensitivity and loss of G(2)/M checkpoint control.

BRCA2 is a breast tumor suppressor with a potential function in the cellular response to DNA damage. BRCA2 binds to Rad51 through its BRC repeats. In support of the biological significance of this interaction, we found that the complex of BRCA2 and Rad51 in breast cancer MCF-7 cells was diminished upon conditional expression of a wild-type, but not a mutated, BRC4 repeat using the tetracycline-inducible system. Cells expressing a wild-type BRC4 repeat showed hypersensitivity to gamma-irradiation, an inability to form Rad51 radiation-induced foci, and a failure of radiation-induced G(2)/M, but not G(1)/S, checkpoint control. These results strongly suggest that the interaction between BRCA2 and Rad51 mediated by BRC repeats is critical for the cellular response to DNA damage.

Amino Acid Sequence↗

PubMed1999

Inhibition of cyclin-dependent kinases 2 and 4 activities as well as induction of Cdk inhibitors p21 and p27 during growth arrest of human breast carcinoma cells by (-)-epigallocatechin-3-gallate.

(-)-Epigallocatechin-3-gallate (EGCG) potently inhibits cell proliferation and suppresses tumor growth both in vitro and vivo, but little is known regarding the cell cycle regulatory proteins mediating these effects. This study investigated the effects of EGCG and other catechins on the cell cycle progression. DNA flow cytometric analysis indicated that 30 microM of EGCG blocked cell cycle progression at G1 phase in asynchronous MCF-7 cells. In addition, cells exposed to 30 microM of EGCG remained in the G1 phase after release from aphidicolin block. Over a 24-h exposure to EGCG, the Rb protein changed from hyper- to hypophosphorylated form and G1 arrest developed. The protein expression of cyclin D1, and E reduced slightly under the same conditions. Immunocomplex kinase experiments showed that EGCG inhibited the activities of cyclin-dependent kinase 2 (Cdk2) and 4 (Cdk4) in a dose-dependent manner in the cell-free system. As the cells were exposed to EGCG (30 microM) over 24 h a gradual loss of both Cdk2 and Cdk4 kinase activities occurred. EGCG also induced the expression of the Cdk inhibitor p21 protein and this effect correlated with the increase in p53 levels. The level of p21 mRNA also increased under the same conditions. In addition, EGCG also increased the expression of the Cdk inhibitor p27 protein within 6 h after EGCG treatment. These results suggest that EGCG either exerts its growth-inhibitory effects through modulation of the activities of several key G1 regulatory proteins such as Cdk2 and Cdk4 or mediates the induction of Cdk inhibitor p21 and p27.

CDC2-CDC28 Kinases↗

PubMed1999

Determination of unbound 20(S)-camptothecin in rat bile by on-line microdialysis coupled to microbore liquid chromatography with fluorescence detection.

To evaluate the biliary excretion of unbound camptothecin, a flow-through microdialysis probe was constructed for bile sampling. The shunt linear probe was connected from the bile duct, between the liver side to the duodenum to avoid obstruction of the bile duct or bile salt waste. For automatic analysis of microdialysate, an on-line injector was connected to a microbore high-performance liquid chromatographic column with fluorescence detection. Samples were eluted with a mobile phase containing methanol-100 mM monosodium phosphoric acid (35:65, v/v, pH 2.5, adjusted with orthophosphoric acid). The limit of quantification was 1 ng/ml for camptothecin. Following camptothecin administration (5 mg/kg, i.v.), it was found in the bile microdialysate. It was concluded that the in vivo microdialysis technique yields useful data on the biliary excretion of camptothecin. This method is suitable for additional pharmacokinetic studies in rat bile.

Animals↗

PubMed1999

Association of BRCA1 with the hRad50-hMre11-p95 complex and the DNA damage response.

BRCA1 encodes a tumor suppressor that is mutated in familial breast and ovarian cancers. Here, it is shown that BRCA1 interacts in vitro and in vivo with hRad50, which forms a complex with hMre11 and p95/nibrin. Upon irradiation, BRCA1 was detected in discrete foci in the nucleus, which colocalize with hRad50. Formation of irradiation-induced foci positive for BRCA1, hRad50, hMre11, or p95 was dramatically reduced in HCC/1937 breast cancer cells carrying a homozygous mutation in BRCA1 but was restored by transfection of wild-type BRCA1. Ectopic expression of wild-type, but not mutated, BRCA1 in these cells rendered them less sensitive to the DNA damage agent, methyl methanesulfonate. These data suggest that BRCA1 is important for the cellular responses to DNA damage that are mediated by the hRad50-hMre11-p95 complex.

Acid Anhydride Hydrolases↗

PubMed1999

Measurement of unbound caffeic acid in rat blood by on-line microdialysis coupled with liquid chromatography and its application to pharmacokinetic study.

To monitor the levels of caffeic acid in rat blood, an on-line microdialysis system coupled with liquid chromatography was developed. The microdialysis probe was inserted into the jugular vein/right atrium of male Sprague-Dawley rats. Caffeic acid (100 mg/kg, i.v.) was then administered via the femoral vein. Dialysates were automatically injected onto a liquid chromatographic system via an on-line injector. Samples were eluted with a mobile phase containing methanol-100 mM monosodium phosphoric acid (35:65, v/v, pH 2.5). The UV detector wavelength was set at 320 nm. The detection limit of caffeic acid was 20 ng/ml. The in vivo recoveries of the microdialysis probe for caffeic acid at 0.5 and 1 microg/ml were 48.34+/-2.68 and 47.64+/-3.43%, respectively (n=6). Intra- and inter-assay accuracy and precision of the analyses were < or = 10% in the range of 0.05 to 10 microg/ml. Pharmacokinetics analysis of results obtained using such a microdialysis-chromatographic method indicated that unbound caffeic acid in the rat fitted best to a biexponential decay model.

Animals↗

PubMed1999

Measurement and pharmacokinetic study of unbound tropisetron in rat blood by microdialysis with high-performance liquid chromatography.

A microdialysis system coupled with liquid chromatography was applied for the measurement of unbound tropisetron in rat blood. The microdialysis probe was inserted into a jugular vein/right atrium of male Sprague-Dawley rats. Tropisetron (5 or 10 mg/kg, i.v.) was then administered via a femoral vein of rat. Samples were eluted with a mobile phase containing acetonitrile-100 mM monosodium phosphate (pH 5.0, 26:74, v/v). The UV detector wavelength was set at 284 nm. The detection limit of tropisetron was 20 ng/ml. The in vivo recovery of microdialysis probe in rat jugular vein/atrium for tropisetron at 1, 2, and 5 microg/ml were between 49 and 53% (n=5). Intra- and inter-assay accuracy and precision of the analyses were <10% in the range of 0.1-1 microg/ml. The method has been applied to pharmacokinetic analysis of unbound tropisetron in rat intravenous administration. Rapid distribution followed by a slower elimination phase was observed from the blood concentration-time curve. The disposition of tropisetron at each dose fitted well to a two-compartment model.

Animals↗

PubMed1999

Thyroid hormone, T3-dependent phosphorylation and translocation of Trip230 from the Golgi complex to the nucleus.

Trip230 is a novel coactivator of the thyroid hormone receptor that is negatively regulated by the retinoblastoma tumor-suppressor protein. In an examination of its subcellular distribution, Trip230 localized predominantly to the vicinity of the Golgi instead of the nucleus, as other nuclear hormone receptor coactivators. Using a series of deletion mutants, a critical region identified for Golgi area targeting coincided with a previously defined thyroid hormone receptor-binding domain of Trip230. During cell cycle progression, the expression level of Trip230 is constant and a significant portion is imported into the nucleus at S phase. Within an hour of treating cells with T3, Trip230 immunofluorescence transiently colocalized with TR in prominent subnuclear structures. T3-dependent nuclear import of Trip230 does not require new protein synthesis. Coincident with T3 treatment and nuclear import, newly phosphorylated residue(s) appeared in Trip230, suggesting that phosphorylation may be involved in its nuclear import. These findings provided a novel mechanism for the regulation of nuclear hormone transcription factors by hormone-responsive phosphorylation and nuclear import of cytoplasmically located coactivators.

Animals↗

PubMed1999

Measurement and pharmacokinetic study of tetramethylpyrazine in rat blood and its regional brain tissue by high-performance liquid chromatography.

We used a rapid, sensitive and reliable high-performance liquid chromatographic method for the determination of tetramethylpyrazine in rat brain tissue and plasma. The lower limit of quantification in plasma and brain tissue was 0.1 microgram/ml and 0.1 microgram/g, respectively, and only a small amount of plasma (100 microliters) or brain tissue (100 micrograms) was required for analysis. The decline in the concentration of tetramethylpyrazine in plasma was generally two-exponential at a dose of 2, 5, or 10 mg/kg administered intravenously. Concentrations of tetramethylpyrazine in various regions of the brain (cerebral cortex, brainstem, striatum, hippocampus, cerebellum and midbrain) were not significantly different at 15 min following drug administration (10 mg/kg, i.v.). In additional analysis, mean concentration of the tetramethylpyrazine in rat plasma was approximately five-times greater than the drug in brain tissue.

Animals↗

PubMed1999

Binding of dimemorfan to sigma-1 receptor and its anticonvulsant and locomotor effects in mice, compared with dextromethorphan and dextrorphan.

Dextromethorphan ((+)-3-methoxy-N-methylmorphinan, DM) has been shown to have both anticonvulsant and neuroprotective effects. The mechanisms of these CNS effects of DM have been suggested to be associated with the low-affinity, noncompetitive, N-methyl-d-aspartate (NMDA) antagonism of DM and/or the high-affinity DM/sigma receptors. DM is largely O-demethylated into the phencyclidine (PCP)-like compound dextrorphan (DR), which may limit its therapeutic use by producing PCP-like adverse effects, such as hyperlocomotion. Dimemorfan ((+)-3-methyl-N-methylmorphinan, DF), an analog of DM, which has been safely used as an antitussive for more than 20 years, is also known not to form DR. This study therefore characterized the binding of DF to the sigma receptors and NMDA-linked PCP sites and examined the anticonvulsant as well as locomotor effects of DF in mice in comparison with those of DM and DR. We found that DF, DM, and DR were relative high-affinity ligands at sigma-1 receptors (Ki=151, 205, 144 nM, respectively) while all of them were with low affinity at sigma-2 receptors (Ki=4-11 microM). Only DR exhibited moderate affinity for PCP sites (Ki=0.9 microM), whereas DF (Ki=17 microM) and DM (Ki=7 microM) were much less active. DF, DM and DR produced prominent anticonvulsant effects in mice as measured by the supramaximal electroshock test with comparable potency (ED50 approximately 70 micromol/kg, i.p.). At the tested doses (20-260 micromol/kg, i.p.), DM and DR exhibited biphasic effects on the locomotor activity whereas DF produced a consistent dose-dependent decrease. These results revealed that, unlike DM and DR, DF did not cause a PCP-like hyperlocomotion adverse effect that is parallel with the PCP sites binding data. Furthermore, since they have equipotent anticonvulsant effects and similar binding affinities to sigma-1 receptors, the very low affinity of DF at PCP sites may suggest that acting on the PCP sites may not be the requisite for mediating the anticonvulsant activity of these DM analogs. With the history of safety and relative less adverse effects, DF appears to be worth further studying on its CNS effects other than the antitussive effect.

Animals↗

PubMed1999

Pharmacokinetics of granisetron in rat blood and brain by microdialysis.

To characterize the pharmacokinetics of protein-free granisetron in blood and brain we implanted microdialysis probes into the jugular vein and cerebral frontal cortex of the rat. Granisetron (3 or 6 mg/kg, i.v., n=6) was then administered, and microdialysates from blood and brain were collected from both sites and assayed by a validated high-performance liquid chromatographic method. Pharmacokinetics parameters were calculated from the corrected dialysate concentrations of granisetron versus time data. The elimination half-lives of granisetron in blood and brain were 51.3+/-5.5 and 69.7+/-6.3 min for 6 mg/kg, and 50.7+/-4.3 and 74.3+/-12.5 min for 3 mg/kg, respectively. Granisetron rapidly entered the extracellular fluid of cerebral frontal cortex at Tmax of 24 min. The results suggest that simultaneous microdialysis in blood and brain can be usefully applied to study the pharmacokinetics of granisetron in the periphery and the central nervous system.

Animals↗

PubMed1999

Simultaneous blood and biliary sampling of esculetin by microdialysis in the rat.

Biliary excretion and intestinal reabsorption in enterohepatic circulation play major dispositional roles for some drugs. To circumvent multiple blood sampling and interruption of enterohepatic circulation in conventional biliary cannulation, the present study utilized the minimally invasive sampling technique of microdialysis in pharmacokinetics and biliary excretion studies. Microdialysis probes were inserted into the jugular vein and bile duct in the anesthetized rat for simultaneous and continuous sampling following intravenous administration of esculetin, a bioactive coumarin derivative. Placements of the microdialysis probes were designed to minimize obstruction to normal flows of the body fluids. Separation and quantitation of esculetin in the dialysates were achieved using high performance liquid chromatography (HPLC) coupled to UV detection. The results indicated higher drug concentrations in the bile than in the blood, suggesting active biliary excretion. The study also provided an example of successful application of in vivo microdialysis as an interesting and feasible alternative for pharmacokinetics and biliary drug excretion studies.

Animals↗

PubMed1999

In vitro and in vivo effects of naringin on cytochrome P450-dependent monooxygenase in mouse liver.

In vitro and in vivo effects of naringin on microsomal monooxygenase were studied to evaluate the drug interaction of this flavonoid. In vitro addition of naringin up to 500 microM had no effects on benzo(a)pyrene hydroxylase (AHH) activity of mouse liver microsomes. In contrast, the aglycone naringenin at 300 to 500 microM decreased AHH activity by 50% to 60%. Analysis of Lineweaver-Burk and Dixon plots indicated that naringenin competitively inhibited AHH activity with an estimated Ki of 39 microM. Naringenin at 100 microM also reduced metabolic activation of benzo(a)pyrene to genotoxic products as monitored by umuC gene expression response in Salmonella typhimurium TA1535/pSK1002. In the presence of equimolar naringenin and benzo(a)pyrene, umuC gene expression presented as beta-galactosidase activity was reduced to a level similar to the control value. Administration of a liquid diet containing 10 mg/ml naringin for 7 days caused 38% and 49% decreases of AHH and 7-methoxyresorufin O-demethylase activities, respectively. In contrast, the administration had no effects on cytochrome P450 (P450)-catalyzed oxidations of 7-ethoxyresorufin, 7-ethoxycoumarin, N-nitrosodimethylamine, nifedipine, erythromycin and testosterone. Microsomal P450 and cytochrome b5 contents and NADPH-P450 reductase activity were not affected. Immunoblot analysis using MAb 1-7-1, which immunoreacted with both P450 1A1 and 1A2, revealed that the level of P450 1A2 protein was decreased by 38%. These results demonstrate that naringenin is a potent inhibitor of AHH activity in vitro and naringin reduces the P450 1A2 protein level in vivo. These effects may indicate a chemopreventive role of naringin against protoxicants activated by P450 1A2.

Animals↗