Biomedical subjects

Feng Chen

Publications and source records attributed to Feng Chen.

At least 163 records · Page 9Linked to original sources

PubMed2004

Evaluation of antioxidant activity of Australian tea tree (Melaleuca alternifolia) oil and its components.

Antioxidant activity of Australian tea tree (Melaleuca alternifolia) oil (TTO) was determined using two different assays. In the 2,2-diphenyl-1-picrylhydrazyl assay, 10 microL/mL crude TTO in methanol had approximately 80% free radical scavenging activity, and in the hexanal/hexanoic acid assay, 200 microL/mL crude TTO exhibited 60% inhibitory activity against the oxidation of hexanal to hexanoic acid over 30 days. These results were equivalent to the antioxidant activities of 30 mM butylated hydroxytoluene in both tests at the same experimental conditions. This indicated that the TTO could be a good alternative antioxidant. Inherent antioxidants, i.e., alpha-terpinene, alpha-terpinolene, and gamma-terpinene, in the crude TTO were separated and identified chromatographically using silica gel open chromatography, C(18)-high-pressure liquid chromatography, and gas chromatography-mass spectrometry. Their antioxidant activities decreased in the following order in both assays: alpha-terpinene > alpha-terpinolene > gamma-terpinene.

Aldehydes↗

PubMed2004

Separation and determination of astaxanthin from microalgal and yeast samples by molecularly imprinted microspheres.

In this work, molecularly imprinted microspheres (MIMs) were synthesized by aqueous microsuspension polymerization using astaxanthin (3,3'-dihydroxy-beta,beta'-carotene-4,4'-dione) as imprinting molecule. The MIMs obtained were subsequently packed into the stainless steel column and the chromatographic characterization of the column was investigated. The effects of pH and composition of the mobile phase on the retention factor (k') were investigated in detail. The mixture of methanol and dichloromethane (DCM) (8:2, v/v) was used as mobile phase A while the mixture of methanol and water (5:5, v/v) as mobile phase B. The separation of astaxanthin and zeaxanthin (3,3'-dihydroxyl-beta-carotene) was obtained when the concentration of mobile phase B was higher than 30% (v/v) due to their strong lipophilicity. The method developed was successfully applied to separate astaxanthin in the saponified samples of the microalga Haematococcus pluvialis and the yeast Phaffia rhodozyma. The recovery of adding 40 mg astaxanthin to 1.0 g microalgal sample was 95.5% with an R.S.D. (n =5) of 5.3%. The results of determination of astaxanthin in the microalga and the yeast were 3.7% (R.S.D (n = 1.5%, n = 9) and 0.041% (R.S.D n= 7.3%, n = 9), respectively.

Eukaryota↗

PubMed2004

Role for glyoxalase I in Alzheimer's disease.

P301L mutant tau transgenic mice develop neurofibrillary tangles, a histopathologic hallmark of Alzheimer's disease and frontotemporal dementia (FTDP-17). To identify differentially expressed genes and to gain insight into pathogenic mechanisms, we performed a stringent analysis of the microarray dataset obtained with RNA from whole brains of P301L mutant mice and identified a single up-regulated gene, glyoxalase I. This enzyme plays a critical role in the detoxification of dicarbonyl compounds and thereby reduces the formation of advanced glycation end products. In situ hybridization analysis revealed expression of glyoxalase I in all brain areas analyzed, both in transgenic and control mice. However, levels of glyoxalase I protein were significantly elevated in P301L brains, as shown by Western blot analysis and immunohistochemistry. Moreover, a glyoxalase I-specific antiserum revealed many intensely stained flame-shaped neurons in Alzheimer's disease brain compared with brains from nondemented controls. In addition, we examined a single nucleotide polymorphism predicting a nonconservative amino acid substitution at position 111 (E111A) in ethnically independent populations. We identified significant and consistent deviations from Hardy-Weinberg equilibrium, which points to the presence of selection forces. The E111A single nucleotide polymorphism was not associated with the risk for Alzheimer's disease in the overall population. Together, our data demonstrate the potential of transcriptomics applied to animal models of human diseases. They suggest a previously unidentified role for glyoxalase I in neurodegenerative disease.

Alzheimer Disease↗

PubMed2004

Chronic antidepressant treatment causes a selective reduction of mu-opioid receptor binding and functional coupling to G Proteins in the amygdala of fawn-hooded rats.

We have previously documented that chronic alcohol consumption or alcohol withdrawal affects mu-opioid receptor density and receptor-mediated G protein coupling in Fawn-Hooded (FH) rat brain, especially in mesolimbic regions. FH rats demonstrate comorbid depression and high voluntary alcohol consumption; treatment with standard antidepressants improves both facets of this phenotype. Accordingly, we sought to examine whether mu-opioid receptor binding and the receptor-mediated functional coupling to G protein is affected by this drug treatment. Using quantitative autoradiography, binding of mu-opioid receptors labeled by [125I]FK33,824 (D-Ala2,N-Me-Phe4,Met(O)5-ol enkephalin) and the coupling between receptors and G proteins determined by agonist-stimulated guanosine 5'-O -(3-[35S]thio)triphosphate ([35S]GTPgammaS) binding was mapped throughout brain sections of FH rats after 10-day treatment with vehicle, desipramine, or sertraline. Both desipramine and sertraline produced significant decreases of [125I]FK33,824 binding in many brain regions; 13 of 20 measured regions for desipramine and 16 of 20 measured regions for sertraline. The coupling efficiency of mu-opioid receptors to G proteins was determined by an increase of [35S]GTPgammaS binding induced by stimulation with the mu-opioid receptor agonist [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (10 microM). In contrast to the receptor binding profile, functional coupling of receptors to G proteins was only significantly reduced in the amygdala, whereas it remained unchanged in other regions compared with control. The present findings suggest that antidepressants regulate opioid systems; however, this occurs differentially, and region-specific alteration of functional coupling of mu-opioid receptors to G proteins in the amygdala suggests that opioid function within the amygdala may be modulated by antidepressants.

Amygdala↗

PubMed2004

Proteolysis of the mismatch repair protein MLH1 by caspase-3 promotes DNA damage-induced apoptosis.

Caspases are critical proapoptotic proteases that execute cell death signals by selectively cleaving proteins at Asp residues to alter their function. Caspases trigger apoptotic chromatin degradation by activating caspase-activated DNase and by inactivating a number of enzymes that sense or repair DNA damage. We have identified the mismatch repair protein MLH1 as a novel caspase-3 substrate by screening small pools of a human prostate adenocarcinoma cDNA library for cDNAs encoding caspase substrates. In this report, we demonstrate that human MLH1 is specifically cleaved by caspase-3 at Asp(418) in vitro. Furthermore, MLH1 is rapidly proteolyzed by caspase-3 in cancer cells induced to undergo apoptosis by treatment with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) or the topoisomerase II inhibitor etoposide, which damages DNA. Importantly, proteolysis of MLH1 by caspase-3 triggers its partial redistribution from the nucleus to the cytoplasm and generates a proapoptotic carboxyl-terminal product. In addition, we demonstrate that a caspase-3 cleavage-resistant D418E MLH1 mutant inhibits etoposide-induced apoptosis but has little effect on TRAIL-induced apoptosis. These results indicate that the proteolysis of MLH1 by caspase-3 plays a functionally important and previously unrecognized role in the execution of DNA damage-induced apoptosis.

Adaptor Proteins, Signal Transducing↗

PubMed2004

Preparative purification of glycyrrhizin extracted from the root of liquorice using high-speed counter-current chromatography.

Glycyrrhizin is one of the main bioactive components in liquorice (Glycyrrhiza uralensis Fisch) which has recently been found to be highly active in inhibiting replication of the severe acute respiratory syndrome (SARS)-associated virus. The separation and purification of glycyrrhizin from a methanol-water (70:30 (v/v)) extract of liquorice roots was achieved using high-speed counter-current chromatography. The separation was performed at a preparative scale in a one-step separation with a two-phase solvent system composed of ethyl acetate-methanol-water (5:2:5 (v/v)). The lower phase was used as the mobile phase in the head-to-tail elution mode. The present method yielded 42.2 mg glycyrrhizin at 96.8% purity from 130 mg of the crude exact with 95.2% recovery as determined by HPLC analysis.

Countercurrent Distribution↗

PubMed2004

Defective expression of transforming growth factor beta receptor type II is associated with CpG methylated promoter in primary non-small cell lung cancer.

PURPOSE: Reduced expression of the transforming growth factor beta receptor type II (TGF beta RII), a key inhibitor of epithelial cell growth and tumor suppressor gene, was reported frequently in many types of tumors including non-small cell lung cancer (NSCLC). This study explored the significance of the TGF beta RII gene in NSCLC carcinogenesis. EXPERIMENTAL DESIGN: With 43 independent pairs of tumor and paracarcinoma tissue samples from patients with primary NSCLC, we carried out PCR-denaturing gradient gel electrophoresis screening for DNA variants over the coding sequence of the TGF beta RII gene, immunohistochemical assay of TGF beta RII expression, methylation-specific PCR analysis, and semiquantitative reverse transcription-PCR. RESULTS: The PCR-denaturing gradient gel electrophoresis did not detect variation in the whole coding sequence of the TGF beta RII gene, but the immunohistochemistry experiment revealed reduced or lost expression of the gene in 44% (19 of 43) of the tumor samples. The methylation analysis on the 19 pairs detected the frequent occurrence of methylated TGF beta RII promoter in tumor tissues, whereas most of the paracarcinoma tissues were free of methylation. The reduced TGF beta RII expression was highly significantly associated with the methylation event (P < 10(-4)). The reverse transcription-PCR analysis demonstrated a clear agreement between reduced TGF beta RII expression and decreased mRNA level of the gene in the tumor tissue samples. CONCLUSIONS: TGF beta RII plays an important role as a tumor suppressor in NSCLC carcinogenesis. The defective expression may serve as one of most important molecular mechanisms in explaining progression of the disease. In particular, aberrant 5' CpG methylation of the gene has explained the down-regulation of the gene at a transcriptional level.

Adult↗

PubMed2004

Fatty acid composition and squalene content of the marine microalga Schizochytrium mangrovei.

Certain species of thraustochytrids are being explored as potential producer of polyunsaturated fatty acids for nutritional enrichment of food products and use as feed additives in aquaculture. The fatty acid composition and squalene content were determined in the thraustochytrid, Schizochytrium mangrovei that was newly isolated from decaying Kandelia candel leaves in Hong Kong mangrove habitat. The major fatty acid constituents identified in all three S. mangrovei strains were tetradeanoic acid (C14:0), hexadecanoic acid (C16:0), docosapentaenoic acid (C22:5 n-6, DPA) and docosahexaenoic acid (C22:6 n-3, DHA). DHA was the most predominant polyunsaturated fatty acid, and the percentage of DHA (of total fatty acids) in all these strains varied from 32.29 to 39.14%. Only slight changes were observed in fatty acid composition of the S. mangrovei strains harvested at their early (day 3) and late stationary (day 5) phases. In contrast, the cellular squalene content was affected significantly by the culture time; the largest decrease of squalene content from 0.162 mg/g to 0.035 mg/g was found in S. mangrovei FB1 as the culture aged.

Docosahexaenoic Acids↗

PubMed2004

A complementary transposon tool kit for Drosophila melanogaster using P and piggyBac.

With the availability of complete genome sequence for Drosophila melanogaster, one of the next strategic goals for fly researchers is a complete gene knockout collection. The P-element transposon, the workhorse of D. melanogaster molecular genetics, has a pronounced nonrandom insertion spectrum. It has been estimated that 87% saturation of the approximately 13,500-gene complement of D. melanogaster might require generating and analyzing up to 150,000 insertions. We describe specific improvements to the lepidopteran transposon piggyBac and the P element that enabled us to tag and disrupt genes in D. melanogaster more efficiently. We generated over 29,000 inserts resulting in 53% gene saturation and a more diverse collection of phenotypically stronger insertional alleles. We found that piggyBac has distinct global and local gene-tagging behavior from that of P elements. Notably, piggyBac excisions from the germ line are nearly always precise, piggyBac does not share chromosomal hotspots associated with P and piggyBac is more effective at gene disruption because it lacks the P bias for insertion in 5' regulatory sequences.

Animals↗

PubMed2004

Application of preparative high-speed counter-current chromatography for separation of chlorogenic acid from Flos Lonicerae.

Chlorogenic acid, an ester formed between caffeic acid and quinic acid, is a major phenolic compound in the traditional Chinese medicinal herb Flos Lonicerae. The separation and purification of chlorogenic acid from the crude extract of Flos Lonicerae was achieved by high-speed counter-current chromatography (HSCCC). A high acid, highly polar two-phase solvent system containing n-butanol-acetic acid-water (4:1:5) was run on a preparative scale. The upper phase was used as the mobile phase in the head to tail elution mode. A 300-mg quantity of the crude extract containing 5.97% chlorogenic acid was loaded on a 342-ml HSCCC column. Double separations were performed with the same solvent system yielding 16.9 mg chlorogenic acid at 94.8% purity with approximately 90% recovery.

Chlorogenic Acid↗

PubMed2004

Preparative high-speed counter-current chromatography for purification of shikonin from the Chinese medicinal plant Lithospermum erythrorhizon.

The bioactive compound shikonin was successfully isolated and purified from the crude extract of the traditional Chinese medicinal plant Lithospermum erythrorhizon Sieb. et Zucc. by preparative high-speed counter-current chromatography (HSCCC). The preparative HSCCC was performed using a two-phase solvent system composed of n-hexane-ethylacetate-ethanol-water (16:14:14:5 (v/v)). A total amount of 19.6 mg of shikonin at 98.9% purity was obtained from 52 mg of the crude extract (containing 38.9% shikonin) with 96.9% recovery. The preparative isolation and purification of shikonin by HSCCC was completed in 200 min in a one-step separation.

Countercurrent Distribution↗

PubMed2004

Dynamic contrast-enhanced MRI of the pancreas: initial results in healthy volunteers and patients with chronic pancreatitis.

PURPOSE: To characterize pancreatic perfusion in volunteers and patients with chronic pancreatitis (CP) by dynamic contrast-enhanced (DCE) MRI. MATERIALS AND METHODS: Pancreatic enhancement after bolus injection of Gd-DTPA with a three-dimensional ultrafast partial-Fourier radiofrequency (RF) spoiled gradient-echo (GE) acquisition was examined prospectively. An acquisition volume of the pancreatic parenchyma was obtained every 4.2 seconds during a single breath-hold in 31 volunteers and 19 patients with CP. We calculated the wash-in rate and a newly defined parameter, the "time-to-inflow deceleration" (TID). A statistical analysis of the differences between both groups was performed with the use of Student's t-test. RESULTS: Significant differences in the TID and wash-in rate were found for the head and body of the pancreas: the TID was 22.4 sec +/- 4.4 sec and 23.5 sec +/- 6.1 sec in the pancreatic head and body of the healthy volunteers, and 29.8 sec +/- 8.6 sec and 29.4 sec +/- 3.8 sec in patients with CP. The wash-in rate was 96 +/- 37 sec(-1) and 101 +/- 27 sec(-1) in controls, and 62 +/- 17 sec(-1) and 75 +/- 27 sec(-1) in CP. CONCLUSION: CP can be identified by semiquantitative changes on DCE-MRI. Whether DCE-MRI of the pancreas can be used to detect early CP remains to be validated.

Adult↗

PubMed2004

Cell wall proteomics of the green alga Haematococcus pluvialis (Chlorophyceae).

The green microalga Haematococcus pluvialis can synthesize and accumulate large amounts of the ketocarotenoid astaxanthin, and undergo profound changes in cell wall composition and architecture during the cell cycle and in response to environmental stresses. In this study, cell wall proteins (CWPs) of H. pluvialis were systematically analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) coupled with peptide mass fingerprinting (PMF) and sequence-database analysis. In total, 163 protein bands were analyzed, which resulted in positive identification of 81 protein orthologues. The highly complex and dynamic composition of CWPs is manifested by the fact that the majority of identified CWPs are differentially expressed at specific stages of the cell cycle along with a number of common wall-associated 'housekeeping' proteins. The detection of cellulose synthase orthologue in the vegetative cells suggested that the biosynthesis of cellulose occurred during primary wall formation, in contrast to earlier observations that cellulose was exclusively present in the secondary wall of the organism. A transient accumulation of a putative cytokinin oxidase at the early stage of encystment pointed to a possible role in cytokinin degradation while facilitating secondary wall formation and/or assisting in cell expansion. This work represents the first attempt to use a proteomic approach to investigate CWPs of microalgae. The reference protein map constructed and the specific protein markers obtained from this study provide a framework for future characterization of the expression and physiological functions of the proteins involved in the biogenesis and modifications in the cell wall of Haematococcus and related organisms.

Cell Cycle↗

PubMed2004

Investigation on apoptosis of neuronal cells induced by Amyloid beta-Protein.

OBJECTIVE: To construct a PC12 cell strain with neuronal differentiation, and observe the apoptosis and proliferation activity effects induced these cells by Amyloid beta-Protein (Abeta-43). METHODS: 1) PC12 cells in logarithmic growth phase were subcultured for 24 h. After the culture fluid was changed, the cells were treated with Rat-beta-NGF and cultured for 9 days. 2) Neuronal differentiation of PC12 cells in logarithmic growth phase were divided into four groups: control group (0), experimental group (1), experimental group (2) and experimental group (3). The concentrations of Abeta in the four groups were 0 micromol/L, 1.25 micromol/L, 2.5 micromol/L and 5 micromol/L, respectively. The cells were harvested at 24, 48 and 72 h later and stained with AnnexinV-FITC/PI after centrifugation and washing. Then flow cytometry was conducted to examine the apoptosis percentage. 3) NGF-induced PC12 cells were selected and Abeta with different concentrations was added. The final concentrations of Abeta were 0 micromol/L, 1.25 micromol/L, 2.5 micromol/L and 5 micromol/L, respectively. After the cells were incubated in an atmosphere of 5% CO2 at 37 degrees C in an incubator for 72 h, the OD values were examined. RESULTS: 1) Neuronal differentiated PC12 cell lines were successfully established. 2) Flow cytometric examination indicated that Abeta (1.25, 2.5, and 5.0 micromol/L) could effectively induce apoptosis of neuronal-differentiated cells at the 24 h, 48 h and 72 h time points. 3) Abeta (0-5.00 micromol/L) had no obvious effect on proliferation or restraining of the neuronal differentiation of the PC12 cells after a 72 h interacting process. CONCLUSION: This investigation revealed successful neuronal differentiation of the PC12 cell strain. The induction of apoptosis of the neurocytes by various concentrations of Abeta was observed and the influence of Abeta on induced proliferation of PC12 cells by Rat-beta-NGF was revealed. This study may provide basis for future research on the molecular cure of AD and interdiction of AD evolution.

Amyloid beta-Peptides↗

PubMed2004

In vitro studies of endophytic fungi from Tripterygium wilfordii with anti-proliferative activity on human peripheral blood mononuclear cells.

An array of endophytic fungi which habitat in a Chinese medicinal plant, Tripterygium wilfordii Hook. f., (TWHf) were isolated and tested for their suppressive activity on phytohemaglutinin (PHA) stimulated proliferation of human peripheral blood mononuclear cells (PBMC). Out of the 343 isolates, representing 60 different morphotypes, were screened. Amongst the screened fungi, only 15 isolates showed anti-proliferative activity. Ethyl acetate extracts of Pestalotiopsis leucothës, Mucor sp. Verticillium sp. or Pestalotiopsis disseminata, in particular, significantly inhibited the proliferation at doses between 0.12 and 500 microg/ml (stimulation index (S.I.) ranges 0.01-0.70) (P < 0.001-0.05). IC50 values of these four fungal extracts were between 0.75-0.80 +/- 0.12 microg/ml. Trypan blue exclusion test and visual examination of cell morphology demonstrate that the anti-proliferative effect of these extracts was not a sequential consequence of their cytotoxicity. Nevertheless, fungal extracts of Acremonium sp. A and C, Pestalotiopsis suffocata, Morphotype sp. 4 and 5 show a much higher cytotoxic effects on PBMC. Our results indicate that some fungal extracts contain significant amount of immunomodulatory principles.

Adult↗

PubMed2004

Klebsiella singaporensis sp. nov., a novel isomaltulose-producing bacterium.

Cells of strain LX3(T), isolated from soil, were Gram-negative, facultatively anaerobic, non-motile, capsulated and non-endospore-forming straight rods, able to grow at 10 degrees C, unable to produce gas from lactose at 45 degrees C and unable to produce indole. The isolate converted sucrose to isomaltulose and did not produce detectable glucose by-products. The G+C content of the DNA was 56.4 mol%. Furthermore, comparison of 16S rRNA and rpoB gene sequences showed that the isolate clearly belongs to the genus Klebsiella. The closest phylogenetic relative was Klebsiella pneumoniae, there being 99.3 and 97.5 % similarity in 16S rRNA and rpoB gene sequences, respectively. DNA-DNA hybridization analysis demonstrated a very low level of relatedness to other members of the genus Klebsiella, indicating that the isolated strain and other species in the genus Klebsiella were not related at the species level. The isolate could be differentiated from other previously described members of the genus Klebsiella on the basis of phenotypic differences and 16S rRNA and rpoB gene sequence divergence, together with DNA-DNA reassociation data. Therefore, it is proposed that strain LX3(T) (=DSM 16265(T)=JCM 12419(T)) should be classified as the type strain of a novel species of genus Klebsiella, Klebsiella singaporensis sp. nov.

Anaerobiosis↗

PubMed2004

Neuropeptides: implications for alcoholism.

The role of neuromodulatory peptides in the aetiology of alcoholism has been relatively under-explored; however, the development of selective ligands for neuropeptide receptors, the characterization and cloning of receptors, and the development of transgenic mouse models have greatly facilitated this analysis. The present review considers the most recent preclinical evidence obtained from animal models for the role of two of the opioid peptides, namely b-endorphin and enkephalin; corticotropin-releasing factor (CRF), urocortin I and neuropeptide Y (NPY) in deleterious and excessive alcohol consumption, focussing on specific brain regions, in particular the central nucleus of the amygdala, that appear to be implicated in the pathophysiology of alcoholism. The review also outlines potential directions for further research to clarify neuropeptide involvement in neuromodulation within discrete brain nuclei pertinent to behavioural patterns.

Alcoholism↗

PubMed2004

Calcineurin is required in urinary tract mesenchyme for the development of the pyeloureteral peristaltic machinery.

Congenital obstructive nephropathy is the principal cause of renal failure in infants and children. The underlying molecular and cellular mechanisms of this disease, however, remain largely undetermined. We generated a mouse model of congenital obstructive nephropathy that resembles ureteropelvic junction obstruction in humans. In these mice, calcineurin function is removed by the selective deletion of Cnb1 in the mesenchyme of the developing urinary tract using the Cre/lox system. This deletion results in reduced proliferation in the smooth muscle cells and other mesenchymal cells in the developing urinary tract. Compromised cell proliferation causes abnormal development of the renal pelvis and ureter, leading to defective pyeloureteral peristalsis, progressive renal obstruction, and, eventually, fatal renal failure. Our study demonstrates that calcineurin is an essential signaling molecule in urinary tract development and is required for normal proliferation of the urinary tract mesenchymal cells in a cell-autonomous manner. These studies also emphasize the importance of functional obstruction, resulting from developmental abnormality, in causing congenital obstructive nephropathy.

Animals↗