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Biomedical subjects

F Chen

Publications and source records attributed to F Chen.

At least 415 records · Page 23Linked to original sources
PubMed1997

[The role of NADPH in the development of neonatal jaundice with G6PD deficiency].

OBJECTIVE: To investigate the role of NADPH in the development of neonatal jaundice with G6PD deficiency. METHODS: The enzyme activities of G6PD, catalse (Cat) and glutathione peroxidase (GSH-px) were measured by quantitative determination of enzyme activity. The level of MDA was analyzed with alpha-thiobarbituric acid and the level of NADPH was determined with modified Nisselbaum JS's. Comparisons of these markers between G6PD normal and deficient erythrocytes were made before and during the incubation of the erythrocytes with H2O2. RESULTS: The level of MDA, which was 36 +/- 8n-mol.L-1.gHb-1, was increased and that of NADPH, which was 1792 +/- 106mumol.L-1.gHb-1, was decreased in jaundiced neonates with G6PD deficiency compared with those with normal G6PD activity. When the cells were incubated with H2O2, the level of NADPH and the activities of Cat and GSHpx in erythrocytes with normal G6PD activity increased at first, and then turned to decrease as the incubation lasted longer than 30 minutes. But in G6PD-deficient erythrocytes all these markers decreased continuously as the cells were incubated with H2O2. CONCLUSIONS: The diminished capability of generation of NADPH in G6PD-deficient erythrocytes may contribute directly to the more extensive peroxidation of the cells. The defect capacity of generation of NADPH, which resulted in the weakened capability of antiperoxidation and finally the lysis of erythrocytes, was one of the important mechanisms in the development of jaundice in G6PD-deficient neonates.

Glucosephosphate Dehydrogenase Deficiency↗
PubMed1997

Changes of ultrasonography and two serum biochemical indices for hepatic fibrosis in schistosomiasis japonica patients one year after praziquantel treatment.

OBJECTIVE: To observe the changes of abdominal sonography and 2 biochemical indicators for hepatic fibrosis before and after treatment with praziquantel in schistosomiasis japonica patients. METHODS: Fifty-five persons infected with Schistosoma japonicum and treated with praziquantel were examined with ultrasonography and serum hyaluronic acid (HA) and type III procollagen (PC III) before and 1 year after treatment, and their data were compared with those in 55 normal controls. RESULTS: With comparison of the data before praziquantel treatment, the length of the left liver lobe and the spleen in 55 patients all decreased (P < 0.01) 1 year after treatment. No significant change was seen in interior diameter (d) of the portal vein, while a decrease in the ratio of the exterior diameter (D) and interior diameter of the second branch of the portal vein was very significant (P < 0.01). Compared with the data in normal control, significantly higher levels in the thickness of the left lobe, the maximum oblique diameter of the right lobe, the length of the spleen, spleen index, the interior diameter of the portal vein and D/d ratio were seen in the patients both before and after treatment. The abnormal rate of the 2 serum parameters for hepatic fibrosis decreased significantly after treatment. CONCLUSIONS: Parameters of hepatic fibrosis either by ultrasonography or by the 2 biochemical tests showed a significant improvement in 55 patients 1 year after treatment, although some of the indices did not yet return to normal levels.

Adolescent↗
PubMed1997

[The measurement of cardiac myosin light chain I in diagnosis of postburn cardiac injury].

In order to estimate myocardial damage after severe burn injury, the cardiac myosin light chain I (CMLC1) contents and myocardial enzyme spectrum (CK, AST and LDH) in serum were measured in rats with full thickness burn of 30% TBSA. The results showed that the CMLC1 contents in serum increased markedly at 1 h postburn and about 20 times higher than control value at 12 h postburn, remaining at high level at 24 h or 48 h postburn, and decreasing slightly at 72 h postburn. CK, AST and LDH activities were increased at 3 h postburn and tended to decrease markedly at 24 h or 48 h postburn, recovering to control level at 72 h postburn. These results suggest that high increase in CMLC1 in serum implies that myocardium is damaged after severe burn injury, and it can be used as a reliable index in the diagnosis of postburn cardiac injury with higher sensitivity and specificity than myocardial enzyme spectrum.

Animals↗
PubMed1997

Incorporation of fludarabine and 1-beta-D-arabinofuranosylcytosine 5'-triphosphates by DNA polymerase alpha: affinity, interaction, and consequences.

Fludarabine and 1-beta-D-arabinofuranosylcytosine (ara-C) are effective nucleoside analogues for the treatment of leukemias when used as single agents or together. Recent trials of the fludarabine and ara-C therapy with or without growth factors suggested an improved clinical response by combining fludarabine and ara-C. The activity of these antimetabolites depends on their phosphorylation to the respective triphosphates, F-ara-ATP and ara-CTP. The principal mechanism through which these triphosphates cause cytotoxicity is incorporation into DNA and inhibition of further DNA synthesis. A model system of DNA primer extension on a defined template sequence was used to quantitate the consequences of incorporation of one or two analogues by human DNA polymerase alpha (pol alpha). The template (31-mer) was designed so that DNA pol alpha incorporated six deoxynucleotides (alternately G and T) on the 17-mer primer, followed by insertion of an A and then a C. The primer was then elongated with G and T to the full-length product. The apparent Kms of DNA pol alpha to incorporate these analogues (0. 053 and 0.077 microM, respectively) were similar to the Km for dCTP (0.037 microM) and dATP (0.044 microM), suggesting that the enzyme recognized these analogues and incorporated them efficiently on the growing DNA primer. The velocity of extension (Vmax) of these primers ranged between 0.53 and 0.77%/min when normal nucleotides were present. Once inserted at the 3'-terminus, F-ara-AMP or ara-CMP were poor substrates for extension. However, in reactions lacking dCTP and dATP and with high concentrations of ara-CTP, ara-CMP was inserted by pol alpha after incorporation of the F-ara-AMP residue. This tandem incorporation of the two analogues resulted in almost complete inhibition (99.3%) of further extension of the primer. In the presence of competing deoxynucleotides, each analogue resulted in a dose-dependent inhibition of DNA synthesis. When present together, inhibition of the primer elongation was more than additive at low concentrations of analogue triphosphates. Based on these results and the intracellular pharmacokinetics of ara-CTP and F-ara-ATP in leukemia blasts, we propose a pharmacodynamic model to explain interactions between these analogues during combination chemotherapy.

Antineoplastic Agents↗
PubMed1997

[The application of intracoronary stenting to type B and C lesions of coronary arteries].

Intracoronary stenting was introduced to 4 lesions due to coronary arterial dissections and to 2 lesions owing to elastic recoil of coronary arteries and stent placement was directly performed in 6 complex coronary lesions after 12 target lesions from 7 patients with Types B and C lesions of coronary arteries had been pre-dilated with balloon. Coronary angiography showed that dissections and recoils had disappeared. Target lesions were well dilated and blood flow was well improved in all cases, one patient was complicated with hemorrhage which was cured quickly. During the follow-up period of 1 to 24 months, another case had recurrence of angina after 2 months of stenting which could be controlled with anti-angina agents. These indicate that intracoronary stenting had good therapeutic effect and is considered as a safe, fast and effective method in dealing with acute complications of coronary artery after routine PTCA.

Aged↗
PubMed1997

[Expression level of MDR1, and MRP in patients with malignant blood disease and its clinical significance].

RT-PCR method was used to detect the expression level of multi-drug resistance gene (MDR1) and multi-drug resistance associated protein (MRP) in patients with malignant blood disease, including 19 cases of acute leukemia and 6 cases of multiple myeloma. The results showed: expression level of MDR1 in patients with known clinical drug resistance elevated obviously and was significantly associated with clinical drug resistance (r = 0.612, P < 0.01), which indicated that expression of MDR1 was the main mechanism of clinical drug resistance. There is no obvious relationship between expression level of MDR1 and MRP (r = 0.035, P > 0.05).

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Increased histone H1 phosphorylation and relaxed chromatin structure in Rb-deficient fibroblasts.

Fibroblasts derived from embryos homozygous for a disruption of the retinoblastoma gene (Rb) exhibit a shorter G1 than their wild-type counterparts, apparently due to highly elevated levels of cyclin E protein and deregulated cyclin-dependent kinase 2 (CDK2) activity. Here we demonstrate that the Rb-/- fibroblasts display higher levels of phosphorylated H1 throughout G1 with the maximum being 10-fold higher than that of the Rb+/+ fibroblasts. This profile of intracellular H1 phosphorylation corresponds with deregulated CDK2 activity observed in in vitro assays, suggesting that CDK2 may be directly responsible for the in vivo phosphorylation of H1. H1 phosphorylation has been proposed to lead to a relaxation of chromatin structure due to a decreased affinity of this protein for chromatin after phosphorylation. In accord with this, chromatin from the Rb-/- cells is more susceptible to micrococcal nuclease digestion than that from Rb+/+ fibroblasts. Increased H1 phosphorylation and relaxed chromatin structure have also been observed in cells expressing several oncogenes, suggesting a common mechanism in oncogene and tumor suppressor gene function.

CDC2-CDC28 Kinases↗
PubMed1996

Excision of 2',2'-difluorodeoxycytidine (gemcitabine) monophosphate residues from DNA.

The activity of gemcitabine (dFdC), an effective agent against solid tumors, depends on the incorporation of its triphosphate into DNA. In vitro investigations demonstrated that, depending on the sequence of template DNA, polymerases may pause after incorporation of gemcitabine nucleotide at either the 3'-terminal or 3'-penultimate position. Proofreading enzymes such as 3'-->5' exonucleases, which are associated with DNA polymerases, can excise mismatched deoxynucleotides from DNA. To model this reaction, we evaluated excision of the gemcitabine nucleotide from oligodeoxynucleotide (19-mer) containing 3'-penultimate dFdC monophosphate (dFdCMP) or dCMP by the 3'-->5' exonuclease of the Klenow fragment. The rate of excision of the 3'-terminal deoxynucleotide was similar, with both primers resulting in formation of primers with terminal dCMP or dFdCMP. The primer containing dCMP was further excised, and by 40 min, more than 75% of total radioactivity was in excision products smaller than 18-mer. In contrast, most of the primers (90%) with terminal dFdCMP were unexcised. When primers terminated with either dFdCMP or dCMP were used as substrates, normal primer was hydrolyzed almost completely by 20 min; however, only 40% of primers containing dFdCMP had excision of dFdCMP molecule. Kinetic studies demonstrated that the enzyme had similar affinity for primers containing penultimate or terminal dFdCMP, but the apparent Vmax for excision was 4-5-fold greater for removal of a 3'-terminal deoxynucleotide than for cleavage of a dFdCMP molecule. Reaction conditions that permitted polymerization of one deoxynucleotide to primers containing either 3'-penultimate dCMP or dFdCMP were used to evaluate excision during DNA synthesis. The excised primers could not be extended because the reaction lacked the requisite deoxynucleotide triphosphate. After 5 min, more than one-half of the dCMP primers were extended, whereas only 15% had been excised. In comparison, 30% of the analogue-containing primers lost the terminal deoxynucleotide, with a proportional lower incidence of extension (30%). Lesser excision of dFdCMP-containing substrate was observed in reactions containing deoxynucleotide triphosphates required to make full-length products. Consistent with this result, in the absence of 3'-->5' exonuclease activity, both primers were extended similarly by the polymerization unit of the Klenow fragment. Taken together, these data demonstrate that dFdCMP residues are difficult to excise from DNA, and DNA polymerase can extend primers with 3'-dFdCMP. This results in the internal incorporation of dFdCMP into DNA, as observed in whole cells.

Antimetabolites, Antineoplastic↗
PubMed1996

Induction of myelin basic protein-specific experimental autoimmune encephalomyelitis in C57BL/6 mice: mapping of T cell epitopes and T cell receptor V beta gene segment usage.

Early studies of murine experimental autoimmune encephalomyelitis (EAE) induced with myelin basic protein (MBP) divide various mouse strains into either "susceptible" or "resistant" phenotypes. Resistance is defined as lack of encephalitogenic responses after active immunization or adoptive transfer. It is now becoming clear that this unresponsiveness is not due to the inability of T cells to recognize MBP in the context of major histocompatibility complex (MHC) gene products. Using various manipulations, many laboratories are able to induce severe EAE in these strains. We previously reported that a combination of adoptive transfer and subsequent challenge of the recipients with MBP could overcome the resistance in many mouse strains (Shaw et al.: J Neuroimmunol 39:139-150, 1992). This approach now enables us to identify the encephalitogenic epitope and T cell receptor V beta usage in a prototype strain, C57BL/6 (B6). Pepsin-digested MBP fragments first located a major T cell epitope in a polypeptide containing residues 44-88. Overlapping synthetic peptides narrowed this epitope to p60-80. Truncated peptides from the carboxyl- or amino-terminus further mapped a minimal peptide to p67-76. This encephalitogenic epitope appears to be unique to B6 mice. Independent encephalitogenic T cell clones specific for this epitope were also generated. Of six such clones analyzed, five different TCR V beta's were found. Whether unbiased usage of encephalitogenic TCR V beta gene segments in B6 mice is related to its EAE resistant phenotype is not clear at this point.

Amino Acid Sequence↗
PubMed1996

A Cys374Tyr homozygous mutation of platelet glycoprotein IIIa (beta 3) in a Chinese patient with Glanzmann's thrombasthenia.

A 20-year-old woman from a consanguineous family in the Hunan Province of the People's Republic of China was diagnosed as having Glanzmann's thrombasthenia based on (1) nearly a lifelong history of epistaxis, gum bleeding, petechiae, and purpura; (2) severe menorrhagia resulting in anemia and need for whole-blood transfusion; (3) normal coagulation assays; (4) prolonged bleeding time; (5) absent clot retraction; (6) decreased glass bead retention; (7) absent platelet aggregation in response to adenine diphosphate, epinephrine, and collagen; and (8) normal initial slope of platelet aggregation in response to ristocetin, but with a diminished maximal extent. The patient's platelets had a decreased level of platelet fibrinogen, but the deficiency was not as severe as in other Glanzmann's thrombasthenia patients. As judged by monoclonal antibody binding studies, surface glycoprotein (GP) IIb/IIIa (alpha IIb beta 3) expression was less than 15% of normal and alpha v beta 3 vitronectin receptor expression was 15% to 19% of normal, suggesting that the defect was in GPIIIa (beta 3). Immunoblotting of platelet lysates demonstrated decreased levels of GPIIb (approximately 30% to 35% of normal) and GPIIIa (approximately 10% of normal), and the GPIIb had undergone normal maturational processing into GPIIb heavy and light chains. Sequence analysis of the patient's GPIIIa RNA identified a G to A mutation at nucleotide 1219, predicting a Cys to Tyr substitution at residue 374. The patient's parents, who are first cousins, are asymptomatic and have only minor reductions in platelet aggregation. Direct sequencing of polymerase chain reaction-amplified cDNA and GPIIIa exon VIII indicated that the patient is homozygous and her parents are heterozygous for the mutation. Transient transfection studies in Chinese hamster ovary cells indicated that the mutation results in an 85% to 90% reduction in GPIIb/IIIa surface expression, but these cells retain the ability to mediate adhesion to immobilized fibrinogen. The relative preservation of platelet fibrinogen despite the very low level of platelet surface GPIIb/IIIa expression in this patient raises some interesting questions regarding the mechanism of fibrinogen uptake and the pathophysiology of Glanzmann's thrombasthenia.

Adult↗
PubMed1996

Genomic structure and chromosomal assignment of the mouse Ku70 gene.

DNA-dependent protein kinase (DNA-PK) consists of three polypeptide subunits: Ku70, Ku80, and the DNA-PK catalytic subunit (DNA-PKcs). Mammalian mutants deficient in either Ku80 or DNA-PKcs function have been shown to be lacking in DNA double-strand break repair and V(D)J recombination, respectively. The precise role of the Ku70 gene in this process has not yet been determined, in part because no cell lines, animals, or human diseases involved with deficiencies in this gene have yet been identified. Both the human and the mouse Ku70 cDNAs have been cloned, and the human gene has been mapped to chromosome 22q13. The original mouse cDNA clones, however, lacked a complete 5'-region, and none of the mammalian Ku70 genomic sequences have been characterized. This report contains an analysis of the 5'-region of the mouse cDNA sequence, a characterization of the mouse Ku70 genomic structure, and fluorescence in situ hybridization data that map the mouse gene to chromosome 15. The deduced amino acid sequence of the mouse gene consists of 608 amino acids compared to 609 for the human gene. The genomic sequence is 24 kb and consists of 13 exons, including an untranslated first exon. Sequences from the upstream region of exon 1 revealed four consensus GC box sequences and a strong transcription initiation site at a reasonable location. The assignment of the mouse Ku70 gene to chromosome 15 is consistent with the syntenic relationship of this gene in human (chromosome 22q13) and mouse and adds to the comparative mapping data for the genes involved in the SCID phenotype.

Animals↗
PubMed1996

Evolutionary relationships among large double-stranded DNA viruses that infect microalgae and other organisms as inferred from DNA polymerase genes.

In order to examine genetic relatedness among viruses that infect microalgae, DNA polymerase gene (DNA pol) fragments were amplified and sequenced from 13 virus clones that infect three genera of distantly related microalgae (Chlorella strains NC64A and Pbi, Micromonas pusilla and Chrysochromulina spp.). Phylogenetic trees based on DNA pol sequences and hybridization of total genomic DNA showed similar branching patterns. Genetic relatedness calculated from the hybridization and sequence data showed good concordance (r=0.90), indicating that DNA pol sequences can be used to determine genetic relatedness and infer phylogenetic relationships among these viruses. The phylogenetic tree inferred from the deduced amino acid sequences of DNA pol from 24 dsDNA viruses, including phycodnaviruses, herpesviruses, poxviruses, baculoviruses, and African swine fever virus corresponded well with groupings based on the International Committee on Taxonomy of Viruses. Microalgal viruses are more closely related to each other than to the other dsDNA viruses and form a distinct phyletic group, suggesting that they share a common ancestor and belong to the Phycodnaviridae. Moreover, the Phycodnaviridae are more closely related to the Herpesviridae than to other virus families for which DNA pol sequences are available.

Amino Acid Sequence↗
PubMed1996

Corticotropin-releasing factor modulates basal and stress-induced excitatory amino acid release in the locus coeruleus of conscious rats.

The in vivo interactions between corticotropin-releasing factor (CRF) and excitatory amino acid (EAA) release in the locus coeruleus (LC) were studied. Superfusion of the LC with CRF (0.1 microM) led to a prolonged increase in the release rate of aspartate and, to a lesser extent, of glutamate. The CRF antagonist alpha-helical CRF9-41 (1 microM) had no effect on basal EAA release but abolished the enhanced aspartate and glutamate release induced by noise stress (95 dB). Tail pinch-induced EAA release was not influenced by alpha-helical CRF9-41. Results demonstrate a facilitatory action of CRF on in vivo EAA release in the LC. Furthermore, modulation by CRF of stress-induced EAA release in the LC depends on the nature of stress.

Animals↗