PubMed Health⌕ Search

Biomedical subjects

L Feng

Publications and source records attributed to L Feng.

At least 55 records · Page 3Linked to original sources
PubMed2001

GDNF acutely modulates excitability and A-type K(+) channels in midbrain dopaminergic neurons.

Glial cell line-derived neurotrophic factor (GDNF) prevents lesion-induced death of midbrain dopaminergic neurons, but its function in normal brain remains uncertain. Here we show that GDNF acutely and reversibly potentiated the excitability of cultured midbrain neurons by inhibiting transient A-type K(+) channels. The effects of GDNF were limited to large, tyrosine hydroxylase (TH)-positive dopaminergic neurons, and were mediated by mitogen associated protein (MAP) kinase. Application of GDNF also elicited a MAP kinase-dependent enhancement of the excitability in dopaminergic neurons in midbrain slice. These results demonstrate an acute regulation of GDNF on ion channels and its underlying signaling mechanism, and reveal an unexpected role of GDNF in normal midbrain dopaminergic neurons.

4-Aminopyridine↗
PubMed2001

Direct in vivo transfection of antisense Fas-ligand reduces tumor growth and invasion.

The expression of Fas ligand (FasL) by tumor cells has been reported to have multiple, conflicting effects on tumor growth. The majority of the data support the theory that FasL expressing tumor cells evade immune surveillance by killing T cells expressing Fas. However, the role of the humoral immune-blockade by FasL expressing tumor cells has not been assessed. Using immune-competent mice, we observed that FasL expressing tumor cells reduced the antitumor antibody production together with the T and B cell content of the spleen in these mice. Further, to determine if the expression of FasL in the environment of the tumor suppresses the humoral antitumor immune response and influences tumor growth, a mouse model lacking T cells was used. To assess whether a local reduction of FasL could reduce tumor progression, a plasmid encoding antisense FasL cDNA was delivered directly into a growing tumor (SW620 colon carcinoma). Intratumoral delivery of the plasmid was able to transfect tumor cells, stromal cells, and peritumoral muscle cells. This antisense FasL tumor tissue transfection persisted for at least 25 days, produced a systemic decrease in soluble FasL, and resulted in a 50% reduction in the rate of tumor growth when compared with tumor tissue of the control groups. These results suggest that direct transfection of antisense FasL cDNA impairs FasL translation in tumor and stromal cells, and can inhibit tumor progression by impairing the FasL-mediated, stromal cell-assisted, tumor counter-attack.

Animals↗
PubMed2001

Skeletal muscle pathology in autosomal dominant Emery-Dreifuss muscular dystrophy with lamin A/C mutations.

We present our observations on the skeletal muscle pathology of nine cases from seven families of autosomal dominant Emery-Dreifuss muscular dystrophy (ADEDMD) with identified mutations in the lamin A/C gene, aged 2-35 years at the time of biopsy. The severity of pathological change was moderate and the most common features were variation in fibre size (hypertrophy and atrophy), an increase in internal nuclei and smaller diameter fibres with high oxidative enzyme activity. Only one case showed necrosis, which was present in two separate samples taken from the quadriceps and tibialis anterior, at different ages. Immunocytochemistry detected an age-related reduction of laminin beta1 on the muscle fibres in adolescent and adult cases. Antibodies to lamins A and A/C, and emerin did not reveal any detectable differences from controls. Electron microscopy of two out of three cases showed an abnormal distribution of heterochromatin in many fibre nuclei. Our results show that dystrophic changes in skeletal muscle are not a major feature of ADEDMD, and that nuclear abnormalities may be detected with electron microscopy. Immunodetection of reduced laminin beta1 may be a useful secondary marker in adults with this disorder, as immunocytochemistry of lamins is not yet of diagnostic use.

Adolescent↗
PubMed2001

Etiologic significance of defects in cholesterol, phospholipid, and bile acid metabolism in the liver of patients with intrahepatic calculi.

Intrahepatic calculi, highly prevalent in the Far East, including Japan, are characterized clinically by chronic proliferative cholangitis with frequent stone recurrences. Intrahepatic calculi consist of 2 groups, i.e., brown pigment stones, including a high cholesterol content, and cholesterol stones, with the former predominating. To gain insights into the pathogenesis of intrahepatic calculi, cholesterol and bile acid biosynthesis, as well as alterations in intracellular transport and/or canalicular secretion of phospholipid and bile acid were investigated in liver of patients with intrahepatic calculi. Enzyme activities of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase were increased (12.8 +/- 1.9 pmol/min/mg protein, mean +/- SEM vs. 5.5 +/- 0.4 in controls; P < .01) and cholesterol 7 alpha-hydroxylase activities were decreased (1.3 +/- 0.4 vs. 4.9 +/- 0.6; P < .01) in liver specimens of patients with brown pigment stones. In addition, messenger RNA (mRNA) levels of multidrug resistance P-glycoprotein 3 (MDR3 Pgp) and phosphatidylcholine transfer protein (PCTP) were markedly low in the liver specimens compared with the levels in specimens of control subjects, gallbladder stone patients, and patients with obstructive cholestasis. The protein levels and the immunohistochemical staining were decreased for MDR3 Pgp and PCTP in the liver. Consistently, the concentrations of phospholipid were markedly reduced in the hepatic bile from both affected and unaffected hepatic segments. In patients with intrahepatic calculi, biliary cholesterol supersaturation and the formation of cholesterol-rich brown pigment as well as cholesterol stones may be attributed to decreased hepatic transport and biliary secretion of phospholipids, in the setting of increased cholesterogenesis and decreased bile acid synthesis.

Adult↗
PubMed2001

Expression of AhR and ARNT mRNA in cultured human endometrial explants exposed to TCDD.

Endometriosis is a debilitating disease found in 10-15% of reproductive-age women and is characterized by the presence of endometrial tissue outside of the uterus. The present study characterizes the expression of AhR and ARNT mRNA in a human endometrial explant culture model in the absence and presence of TCDD exposure. In a parallel, companion study using this model, TCDD exposure was shown to induce CYP1A1 mRNA, CYP1B1 mRNA, EROD (7-ethoxyresorufin-O-deethylase) activity, and CYP1B1 protein in human endometrial explants. Explants were prepared from specimens obtained at laparoscopy or laparotomy from women undergoing surgery for tubal ligation, endometriosis, or pelvic pain unrelated to endometriosis. These specimens were a subset of the specimens used in the parallel study. The explants were cultured in medium containing 10 nM estradiol (E(2)) or 1 nM estradiol plus 500 nM progesterone (E(2) + P(4)) with or without TCDD (first 24 h). After culture, AhR and ARNT mRNA expression were quantified by RT-PCR. TCDD treatment significantly increased the expression of AhR mRNA, but not ARNT mRNA. The expression of both genes was similar for all individual explants and the ratio of AhR:ARNT mRNA expression across all samples was 1.7 to 1.8. Constitutive AhR mRNA expression was donor age dependent (increasing with age), while ARNT mRNA expression was donor age and tissue phase dependent (increased in older and proliferative phase specimens). Similar to results in the parallel study on expression of CYP1A1 mRNA, CYP1B1 mRNA, EROD activity, and CYP1B1 protein, the presence of endometriosis did not affect the expression of AhR or ARNT mRNA, either constitutively or following TCDD exposure. However, the detection of disease-specific change was limited by small sample size and variability in tissue cycle phase. The human endometrial explant culture model will be useful for future studies of the effects of dioxin-like compounds on human endometrium in relationship to cycle phase, hormonal exposure, and donor age.

Aryl Hydrocarbon Hydroxylases↗
PubMed2001

Effect of TCDD exposure on CYP1A1 and CYP1B1 expression in explant cultures of human endometrium.

Endometriosis is a debilitating disease estimated to affect 10% of reproductive-age women and characterized by the growth of endometrial tissue outside of the uterus. The present study characterizes a human endometrial explant culture model for studying the direct effects of TCDD exposure by assessing the expression of CYP1A1 and CYP1B1 mRNA (Northern blotting), protein (Western blotting), and activity (7-ethoxyresorufin-O-deethylase; EROD) in explants cultured with and without TCDD. Explants were obtained at laparoscopy or laparotomy from women undergoing surgery for tubal ligation, endometriosis, or pelvic pain unrelated to endometriosis. The explants were cultured with 10 nM estradiol (E(2)) or 1 nM E(2) plus 500 nM progesterone (P(4)) with or without TCDD (first 24 h). The expression of CYP1A1 and CYP1B1 mRNA was greatest with 10 nM TCDD and increased up to 72 h after initial exposure. EROD activity increased up to 120 h. Explants from a secretory phase biopsy became reorganized in culture and formed a new epithelial membrane, while maintaining basic endometrial morphology and viability for up to 120 h. At 24 h, TCDD significantly increased CYP1A1 and CYP1B1 mRNA, and at 72 h, TCDD significantly increased EROD activity and CYP1B1 protein compared to explants cultured without TCDD for similar times. CYP1B1 protein also exhibited substantial constitutive expression that was similar in uncultured biopsies, where CYP1B1 protein was immunolocalized in the cytoplasm of epithelial glands, with only occasional patches of protein in the surface epithelial membrane. In explants cultured with and without TCDD exposure, CYP1B1 protein was localized in the cytoplasm of the new surface epithelial membrane and glands closest to the surface. CYP1A1 protein was not detected in uncultured biopsies or explants. Both younger age (age 30 and under) and proliferative phase were associated with higher TCDD-induced EROD activity in specimens treated with E(2):P(4). No significant endometriosis-related differences were observed for any of the biomarkers, but the detection of disease-specific change was limited by small sample size and variability in tissue-cycle phase. The human endometrial explant culture model will be useful for future studies of the effects of dioxin-like compounds on human endometrium in relationship to cycle phase and hormonal exposure.

Aryl Hydrocarbon Hydroxylases↗
PubMed2001

Experimental study of structure-borne sound transmission loss of mechanical joints.

A mechanical joint is one of the most effective ways to reduce the transmission of structure-borne sound. In order to increase the transmission loss, heavily damped joints are often used, which, in many cases, will reduce the structure integrity and hence can only be used in limited cases. In this study attention is focused on a type of resonant joint, i.e., a joint which will increase the transmission loss but will not reduce the structure integrity. The study is based on experiments in a one-dimensional structure. It is found that by adjusting the overlap of the joint, the transmission loss of 30 dB can be obtained at a certain frequency range without adding any dissipative materials. The mechanism of this high transmission loss is the cantilever-type resonance. The resonant frequency can be predicted precisely. The influence of extra dissipative material is investigated. The performance of the same joint in a finite structure is also examined by using the concept of vibrational insertion loss. When there is a certain damping in a finite system, a rather high insertion loss can still be achieved by using the above-mentioned joint, but the resonant frequency is shifted to higher end. It seems that the effective length of the cantilever is shortened by the finiteness.

Journal Article↗
PubMed2001

Cyclooxygenase-2 overexpression is a marker of poor prognosis in stage I non-small cell lung cancer.

Cyclooxygenase-2 (COX-2), the enzyme that converts arachidonic acid to prostaglandins, is overexpressed in a variety of different tumors, including those of the colon, pancreas, lung, and head and neck. We used in situ hybridization with a digoxgenin-labeled COX-2 antisense riboprobe to assess the presence of strong or intermediate versus weak or absent COX-2 expression in specimens from 160 patients with stage I non-small cell lung cancer (NSCLC). Of these, 3 specimens had strong expression, 69 had intermediate expression of COX-2, 24 had weak expression, and 64 had no detectable COX-2. The strength of COX-2 expression was associated with a worse overall survival rate (P = 0.001) and a worse disease-free survival rate (P = 0.022). The median survival times for the strong, intermediate or weak, and null COX-2 expressors were 1.04, 5.50, and 8.54 years, respectively. Interestingly, all three specimens with strong COX-2 expression came from patients who died within 18 months. Retinoic acid receptor beta (RAR-beta) is a nuclear retinoid receptor whose expression is frequently lost in aerodigestive tract carcinogenesis. We previously demonstrated that expression of RAR-beta in stage I NSCLC indicates a poor prognosis. Retinoids have been shown to prevent induction of COX-2 by mitogens and tumor promoters. Expression of COX-2 correlated with RAR-beta expression (P = 0.053), but not with k-ras mutational status, vascular endothelial growth factor, basic fibroblast growth factor, interleukin 8 levels, or other markers of angiogenesis, invasion, and metastases. Thus, like RAR-beta positivity, COX-2 overexpression appears to portend a shorter survival among patients with early stage non-small cell lung cancer. Future studies of RAR-beta and COX-2 regulation in NSCLC should further the development of prevention and therapy interventions with retinoids and/or COX-2 antagonists in this patient population.

Biomarkers, Tumor↗
PubMed2001

Microarray-based genetic analyses for studying susceptibility to arterial and venous thrombotic disorders.

We describe the potential of microarray technology for parallel, high-throughput approaches to molecular detection of DNA variations associated with progression to arterial and venous thrombotic diseases. The use of the newly commercialized NanoChip platform and a framework for genetic screening with a list of potential genetic targets useful to the evaluation of cardiovascular risk are presented. Implementation in clinical setting of analytical silicon and glass microarrays will facilitate early diagnosis, help direct specific advice to high-risk individuals and evaluate treatment strategies.

Factor V↗
PubMed2001

Effect of outliers and nonhealthy individuals on reference interval estimation.

BACKGROUND: Improvement in reference interval estimation using a new outlier detection technique, even with a physician-determined healthy sample, is examined. The effect of including physician-determined nonhealthy individuals in the sample is evaluated. METHODS: Traditional data transformation coupled with robust and exploratory outlier detection methodology were used in conjunction with various reference interval determination techniques. A simulation study was used to examine the effects of outliers on known reference intervals. Physician-defined healthy groups with and without nonhealthy individuals were compared on real data. RESULTS: With 5% outliers in simulated samples, the described outlier detection techniques had narrower reference intervals. Application of the technique to real data provided reference intervals that were, on average, 10% narrower than those obtained when outlier detection was not used. Only 1.6% of the samples were identified as outliers and removed from reference interval determination in both the healthy and combined samples. CONCLUSIONS: Even in healthy samples, outliers may exist. Combining traditional and robust statistical techniques provide a good method of identifying outliers in a reference interval setting. Laboratories in general do not have a well-defined healthy group from which to compute reference intervals. The effect of nonhealthy individuals in the computation increases reference interval width by approximately 10%. However, there is a large deviation among analytes.

Disease↗
PubMed2001

Genomics and the evolution of aminoacyl-tRNA synthesis.

Translation is the process by which ribosomes direct protein synthesis using the genetic information contained in messenger RNA (mRNA). Transfer RNAs (tRNAs) are charged with an amino acid and brought to the ribosome, where they are paired with the corresponding trinucleotide codon in mRNA. The amino acid is attached to the nascent polypeptide and the ribosome moves on to the next codon. Thus, the sequential pairing of codons in mRNA with tRNA anticodons determines the order of amino acids in a protein. It is therefore imperative for accurate translation that tRNAs are only coupled to amino acids corresponding to the RNA anticodon. This is mostly, but not exclusively, achieved by the direct attachment of the appropriate amino acid to the 3'-end of the corresponding tRNA by the aminoacyl-tRNA synthetases. To ensure the accurate translation of genetic information, the aminoacyl-tRNA synthetases must display an extremely high level of substrate specificity. Despite this highly conserved function, recent studies arising from the analysis of whole genomes have shown a significant degree of evolutionary diversity in aminoacyl-tRNA synthesis. For example, non-canonical routes have been identified for the synthesis of Asn-tRNA, Cys-tRNA, Gln-tRNA and Lys-tRNA. Characterization of non-canonical aminoacyl-tRNA synthesis has revealed an unexpected level of evolutionary divergence and has also provided new insights into the possible precursors of contemporary aminoacyl-tRNA synthetases.

Amino Acyl-tRNA Synthetases↗
PubMed2001

The role of sexual related Y gene detection in the diagnosis of patients with gonadal dysgenesis.

OBJECTIVE: To clarify the role of sexual related Y (SRY) gene detection in the diagnosis of gonadal dysgenesis. METHODS: Sixteen cases of gonadal dysgenesis were included in this study: 5 with androgen insensitivity syndrome, 1 with 17-alpha-hydroxylase deficiency, 4 with true hermaphrodite, 2 with 45, X/46, XY gonadal dysgenesis, 1 with 45, X gonadal dysgenesis, 1 with XY pure gonadal dysgenesis, 1 with testicular regression, and 1 XY female who gave birth to a normal baby. SRY gene was detected by using polymerase chain reaction (PCR) in blood and gonad samples and by direct sequencing of the SRY motif. RESULTS: Among the 16 cases, 15 were blood SRY positive, among which 13 (86.7%) showed the presence of testicular tissue, and 2 showed ovaries without testicular tissue. One SRY negative case showed the presence of testicular tissue. In 3 cases, SRY detection in gonadal tissue correlated with pathological findings but not with blood karyotype. The correlation between peripheral blood SRY and the pathology of the gonads was 81.25% and the correlation between the presence of peripheral blood Y chromosome and pathology of the gonads was 68.75%. Sequencing of the SRY motif in an XY female who gave birth to a normal baby showed no mutation. CONCLUSIONS: SRY detection is more sensitive and specific than blood karyotype in the prediction of the presence of testicular tissue. Peripheral blood karyotype does not necessarily reflect gonadal type. There may be testicular related factors other than the SRY gene.

DNA↗
PubMed2001

Incidence of deep venous thrombosis after gynaecological laparoscopy.

OBJECTIVE: To evaluate the incidence of deep venous thrombosis (DVT) after gynaecological laparoscopy. METHODS: The incidence of DVT was studied in 72 consecutive patients who underwent gynaecological laparoscopy in the Liverpool Health Service between May and September 1997. B-mode ultrasound supplemented by Doppler was used to examine venous patency and intraluminal echoes to diagnose DVT. Sixty-one patients who had pneumoperitoneum less than 60 minutes were classified a minor procedure and 11 who had pneumoperitoneum more than 60 minutes were classified as major procedure. Two Doppler ultrasound scans were planned for every patient. The first one was done within 24 hours and the second was performed on day 7 post-surgery. All 72 patients had the first scan and 40 out of 61 in the minor procedure group and 9 out of 11 in the major procedure had the second scan. Twenty-three patients who did not come for the second scan were followed up by phone. RESULTS: No DVT was found in our study. CONCLUSION: This study confirms an impression that gynaecological laparoscopic procedure has a very low incidence of DVT. If it occurs, the diagnosis and treatment must be made as soon as possible so that the fatal complications such as pulmonary embolus can be avoided.

Adult↗
PubMed2001

[Biomaterials used in tissue engineering for cartilage regeneration].

In this paper are reviewed the research reports on biomaterials used in recent years in the field of tissue engineering for cartilage regeneration. The preparation of these biomaterials are also discussed. Finally, ideas are proposed to solve the problems in the field of cartilage tissue engineering.

Biocompatible Materials↗
PubMed2000

High-level expression and mutagenesis of recombinant human phosphatidylcholine transfer protein using a synthetic gene: evidence for a C-terminal membrane binding domain.

Phosphatidylcholine transfer protein (PC-TP) is a 214-amino acid cytosolic protein that promotes intermembrane transfer of phosphatidylcholines, but no other phospholipid class. To probe mechanisms for membrane interactions and phosphatidylcholine binding, we expressed recombinant human PC-TP in Escherichia coli using a synthetic gene. Optimization of codon usage for bacterial protein translation increased expression of PC-TP from trace levels to >10% of the E. coli cytosolic protein mass. On the basis of secondary structure predictions of an amphipathic alpha-helix (residues 198-212) in proximity to a hydrophobic alpha-helix (residues 184-193), we explored whether the C-terminus might interact with membranes and promote binding of phosphatidylcholines. Consistent with this possibility, truncation of five residues from the C-terminus shortened the predicted amphipathic alpha-helix and decreased PC-TP activity by 50%, whereas removal of 10 residues eliminated the alpha-helix, abolished activity, and markedly decreased the level of membrane binding. Circular dichroic spectra of synthetic peptides containing one ((196-214)PC-TP) or both ((183-214)PC-TP) predicted C-terminal alpha-helices in aqueous buffer were most consistent with random coil structures. However, both peptides adopted alpha-helical configurations in the presence of trifluoroethanol or phosphatidylcholine/phosphatidylserine small unilamellar vesicles. The helical content of (196-214)PC-TP increased in proportion to vesicle phosphatidylserine content, consistent with stabilization of the alpha-helix at the membrane surface. In contrast, the helical content of (183-214)PC-TP was not influenced by vesicle composition, implying that the more hydrophobic of the alpha-helices penetrated into the membrane bilayer. These studies suggest that tandem alpha-helices located near the C-terminus of PC-TP facilitate membrane binding and extraction of phosphatidylcholines.

Amino Acid Sequence↗
PubMed2000

Aminotransferase activity and bioinformatic analysis of 1-aminocyclopropane-1-carboxylate synthase.

The mechanistic fate of pyridoxal phosphate (PLP)-dependent enzymes diverges after the quinonoid intermediate. 1-Aminocyclopropane-1-carboxylate (ACC) synthase, a member of the alpha family of PLP-dependent enzymes, is optimized to direct electrons from the quinonoid intermediate to the gamma-carbon of its substrate, S-adenosyl-L-methionine (SAM), to yield ACC and 5'-methylthioadenosine. The data presented show that this quinonoid may also accept a proton at C(4)' of the cofactor to yield alpha-keto acids and the pyridoxamine phosphate (PMP) form of the enzyme when other amino acids are presented as alternative substrates. Addition of excess pyruvate converts the PMP form of the enzyme back to the PLP form. C(alpha)-deprotonation from L-Ala is shown by NMR-monitored solvent exchange to be reversible with a rate that is less than 25-fold slower than that of deprotonation of SAM. The rate-determining step for transamination follows the formation of the quinonoid intermediate. The rate-determining step for alpha, gamma-elimination from enzyme-bound SAM is likewise shown to occur after C(alpha)-deprotonation, and the quinonoid intermediate accumulates during this reaction. BLAST searches, sequence alignments, and structural comparisons indicate that ACC synthases are evolutionarily related to the aminotransferases. In agreement with previously published reports, an absence of homology was found between the alpha and beta families of the PLP-dependent enzyme superfamily.

Amino Acid Sequence↗
PubMed2000

A role for fractalkine and its receptor (CX3CR1) in cardiac allograft rejection.

The hallmark of acute allograft rejection is infiltration of the inflamed graft by circulating leukocytes. We studied the role of fractalkine (FKN) and its receptor, CX(3)CR1, in allograft rejection. FKN expression was negligible in nonrejecting cardiac isografts but was significantly enhanced in rejecting allografts. At early time points, FKN expression was particularly prominent on vascular tissues and endothelium. As rejection progressed, FKN expression was further increased, with prominent anti-FKN staining seen around vessels and on cardiac myocytes. To determine the capacity of FKN on endothelial cells to promote leukocyte adhesion, we performed adhesion assays with PBMC and monolayers of TNF-alpha-activated murine endothelial cells under low-shear conditions. Treatment with either anti-FKN or anti-CX(3)CR1-blocking Ab significantly inhibited PBMC binding, indicating that a large proportion of leukocyte binding to murine endothelium occurs via the FKN and CX(3)CR1 adhesion receptors. To determine the functional significance of FKN in rejection, we treated cardiac allograft recipients with daily injections of anti-CX(3)CR1 Ab. Treatment with the anti-CX(3)CR1 Ab significantly prolonged allograft survival from 7 +/- 1 to 49 +/- 30 days (p < 0.0008). These studies identify a critical role for FKN in the pathogenesis of acute rejection and suggest that FKN may be a useful therapeutic target in rejection.

Animals↗