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Biomedical subjects

X Y Liu

Publications and source records attributed to X Y Liu.

At least 91 records · Page 5Linked to original sources
PubMed1996

Remarkable enhancement of antioxidant activity of vitamin C in an artificial bilayer by making it lipo-soluble.

The reaction kinetics between 4-palmitoyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO-16) and vitamin C (VC) and its lipophilic derivative ascorbyl-6-palmitate (VC-16) was studied by stopped-flow ESR spectroscopy in a synthetic surfactant vesicle sodium 1-pentadecyl hexadecyl sulfate (SPHS). TEMPO-16 reacted with VC very slowly and showed a biphasic first-order kinetics with rate constants of 9.6 x 10(-4) and 2.5 x 10(-4) s-1, corresponding to diffusion of TEMPO-16 from the external monolayer of SPHS to the bulk water and flip-flop of TEMPO-16 from the internal to external monolayer of the vesicle, respectively. On the other hand, the reaction of TEMPO-16 with VC-16 was second-order and over three orders of magnitude faster than that with VC, presumably due to VC-16 induced fusion of the vesicle.

Antioxidants↗
PubMed1996

Ischemic stroke in the elderly. Role of the common factor V mutation causing resistance to activated protein C.

BACKGROUND AND PURPOSE: A common missense mutation in coagulation factor V (Arg 506 Gln) creates phenotypic resistance to the anticoagulant effects of activated protein C and predisposes carriers to venous thrombosis. To assess a correlation between this common hypercoagulable state and ischemic cerebrovascular disease, we have compared the prevalence of this mutation in a group of stroke patients with that in several control patient groups. METHODS: The presence of the factor V Arg 506 Gln mutation was determined by a direct polymerase chain reaction-based assay on peripheral blood leukocytes from 161 elderly patients with acute ischemic stroke, 116 elderly patients with stroke risk factors but without acute stroke, 54 healthy elderly control subjects, and 287 younger control individuals (197 blood donors and 90 neonates). RESULTS: The prevalence of the heterozygous Arg 506 Gln factor V mutation was not significantly different in the elderly stroke patients (2.5%) compared with either of the age-matched control groups (2% to 4%). The prevalence of this mutation was significantly higher in each of two younger control groups (approximately 8%) than in the elderly stroke patients (2.5%). CONCLUSIONS: The common factor V Arg 506 Gln mutation predisposing to venous thrombosis is not a significant genetic risk factor for ischemic stroke in the elderly.

Adult↗
PubMed1996

[Postoperative function exercise for replantation of severed limbs in children].

The speciality of limb replantation in children included thread and thin for blood vessels, growth development for muscles and epiphyses, morable and incooperation in clinical. The function exercises after limb replantation in children must be connected with the clinical speciality of vascular microsurgery, the anthor divided it into four stages; vascular crises stage, limb aliving stage, clinical healing of bone stage, and function recovery stage. The different treatment performed in four stages, and excellent clinical results were achieved.

Amputation, Traumatic↗
PubMed1996

[The practical application on the numbers of control in 1:R matched case-control study].

We applied the data base of a screening program for colorectal cancer in the general population of Jiashan county, Zhejiang province to verify the theory of Pitman Efficiency in 1:R matched case-control study. Forty one detected cases of colorectal cancer were matched with normal controls as 1:R (R from 1 to 50) who were randomly selected from the screened population including 62,667 subjects. Results showed that the number of risk factors with statistical significance and its coincidence rate with results of 1:50 match were increased along with the increasing of R value; meanwhile the trends of standard deviation with 1:R over 1:50 weakened and the stability of results increased accordingly. The change of these values, however, reached their plateau when R > 4. The authors suggest that when taking consideration of sensitivity and stability of matched study, 1:4 of 1:5 ratio might be the most suitable case-control match, particularly when the resources are limited or the study has a exploratory nature.

Case-Control Studies↗
PubMed1996

[Possible mechanism of the analgesic effect of interleukin-2 in central nervous system].

The monoclonal antibody against IL-2R (Tac) could not block the analgesic effect of IL-2, and IL-2 mutant that could not bind to beta subunit of IL-2 receptor still had capability of increasing the pain threshold of rats. All these facts suggest that the analgesic effect of IL-2 in CNS is not mediated through the IL-2 receptor, and that the immune and analgesic effects of IL-2 are mediated through different receptor mechanisms. It is suggested that there are common antigenic determinants and similar structure between IL-2 and endogenous opioid peptides (EOP). This implies that the analgesic effect of IL-2 might be mediated by interaction between IL-2 and opioid receptors in CNS. Using radioimmunoassay the contents of EOP of different nuclei were measured at different times after injecting IL-2 into the lateral ventricle of rats. The results suggested that the analgesic effect of IL-2 may be related to beta-EP and LEK in arcuate hypothalamic nucleus, paraventricular hypothalamic nucleus and locus ceruleus.

Analgesics, Non-Narcotic↗
PubMed1996

[Experimental treatment of brain tumor cells using CD suicide gene].

A negative selection system for glioma gene therapy was established in vitro. C 6 rat glioma cells were infected with recombined retrovirus which contain Escherichia coli cytosine deaminase (EC-CD) gene. The enzyme CD can transform the non-toxic prodrug 5-Fluorocytosine (5-FC) to the highly cellular toxic compound 5-Fluorouracil (5-FU). The growth inhibition studies proved that CD-positive cells were highly sensitive to 5-FC, the IC50 about 3 mumol/L, compared with an IC50 of approximately 6000 mumol/L in parental C 6 cells. Both CD-positive and negative cells were sensitive to 5-FU at very low concentration (IC50 < 1 mumol/L). Mixed cellular assay showed CD-positive cells had "bystander effect" on CD-negative cells when exposed to 5-FC. Our results demonstrate that EC-CD gene should be an efficient suicide gene for the treatment of glioma.

Animals↗
PubMed1995

Gene therapy of Parkinson disease model rat by direct injection of plasmid DNA-lipofectin complex.

Lipofectin-mediated gene transfer was used to introduce plasmid harboring the tyrosine hydroxylase (TH) gene into the striatum of rats with lesions of the nigrostriatal pathway. The rotational asymmetry of Parkinson disease model rat was reduced quickly and significantly, suggesting that plasmid-DNA-transfected brain cells can generate L-dopa locally in the striatum in quantities sufficient to compensate partially for the loss of intrinsic striatal dopaminergic input. Immunohistochemical staining and reverse transcription polymerase chain reaction (RT-PCR) also confirm that striatal cells can express exogenous TH gene. Such in vivo plasmid DNA transfer strategy may be useful in other neurologic disease therapy, especially acute brain insults.

Animals↗
PubMed1995

Molecular detection of a common mutation in coagulation factor V causing thrombosis via hereditary resistance to activated protein C.

More than half of all patients with familial or recurring venous thrombosis have hereditary resistance to activated protein C (HRAPC) as the result of specific missense mutation in the gene for coagulation factor V. Because the mutant factor Va (with an Arg to Gln substitution at codon 506) cannot be cleaved and inactivated by activated protein C, carriers of this mutation are at significantly increased risk of venous thrombosis. We have recently introduced a direct polymerase chain reaction (PCR)-based clinical diagnostic test for the factor V codon 506 mutation based on the destruction of an Mnl I restriction site by the causative nucleotide substitution. To assess the accuracy of this PCR-based assay, we compared a functional clotting time test for HRAPC with the direct mutation test. Of 47 patients dually tested, only five had discrepant values for the functional test versus the DNA test. Either of these two complementary assays is useful for the accurate diagnosis of HRAPC. The DNA-based test is, however, specifically recommended for evaluation of anticoagulated patients or patients with borderline functional tests and confirmation of genotype in HRAPC families. In an additional analysis of 287 normal individuals, we found an extremely high prevalence of the mutated codon 506 allele-- approximately 4% in each of two different populations. The absence of disease in the majority of heterozygous carriers suggests that symptomatic thrombosis requires the simultaneous presence of both a mutated factor V protein and additional synergistic factors.

Codon↗
PubMed1995

Mechanism of inhibition of duck hepatitis B virus polymerase by (-)-beta-L-2',3'-dideoxy-3'-thiacytidine.

We have used the endogenous reverse transcriptase reaction of viral core particles from duck liver to elucidate the mechanism of inhibition of duck hepatitis B virus (DHBV) replication by the nucleoside analog (-)-beta-L-2',3'-dideoxy-3'-thiacytidine (3TC). As is the case in human immunodeficiency virus replication, 3TC-5'-triphosphate (3TC-TP) acts as a chain terminator for the DNA polymerase activities. The results of several different experiments support this conclusion, which explains the potent activity of 3TC against the hepadnaviruses. In isolated DHBV core particles, 3TC-TP inhibited the reverse transcriptase in a manner that resembled competitive inhibition with respect to dCTP. However, the kinetics of inhibition was not linear on a double-reciprocal plot for the highest concentrations of 3TC-TP and the lowest concentration of dCTP. This anomaly would be expected if binding to the nucleotide site was followed by DNA chain termination. Calculations that used only the linear part of the curve yielded a Ki of 0.78 +/- 0.10 microM 3TC-TP. The inhibition of core particles incubated in vitro with 3TC-TP was not reversed by removal of the free inhibitor. 3TC-TP inactivated the reverse transcriptase activity in a concentration-dependent manner. The Km of the chain termination reaction was calculated at 0.71 +/- 0.05 microM. Similar competitive kinetics and irreversible inhibition were also obtained on the endogenous DNA polymerase from viral particles from serum, suggesting that 3TC-TP also acts as a chain terminator of the DNA-directed DNA polymerase of DHBV replication.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Therapeutic effect of chai-ling-tang (sairei-to) on the steroid-dependent nephrotic syndrome in children.

37 children with steroid-dependent nephrotic syndrome (SDNS) were administered with Chai-Ling-Tang (Sairei-to) under corticosteroid. After treatment with Chai-Ling-Tang, relapse was markedly improved, time for negative conversion of proteinuria shortened, prednisone dosage significantly reduced, and side effects eased. 32 children with SDNS treated with prednisone and cyclophosphamide served as control. Results showed that short-term and long-term relapse and average prednisone dosage were similar between these two groups. It is considered that Chai-Ling-Tang may be a useful substitute for patients with SDNS who fail to respond to or manifest severe toxic effect from cytotoxic agents.

Child↗
PubMed1995

Population and family studies of three disease-related polymorphic genes in systemic lupus erythematosus.

The contribution to systemic lupus erythematosus (SLE) of three lupus-associated polymorphisms (involving the C4A2 complement component, Humhv3005 and the T cell antigen receptor alpha chain gene) are investigated in 81 individuals from 14 multiplex SLE families, 41 unrelated lupus patients, and 88 unrelated healthy controls. The results show a strong association between C4A deletion and SLE in these families. While the current study confirms the previously reported association between hv3005 deletion and sporadic SLE, the study fails to support this association in familial SLE patients. Moreover, no correlation is detected between the occurrence of hv3005 deletion and C4A null alleles in lupus patients, suggesting that the effects of these genetic polymorphisms on predisposition to lupus are independent. The previously reported lupus-associated T cell receptor (TCR) alpha chain polymorphism is not detected in any of the individuals studied here. The combined data suggest that C4A null alleles predispose strongly to development of lupus, whereas the influence of hv3005 deletion is relatively weak. The results also suggest that contributions of weak susceptibility genes such as hv3005 to disease predisposition may be obscured by the effects of stronger genetic factors and thus need to be examined in patients lacking these factors.

Base Sequence↗
PubMed1994

Geminate recombination of diatomic ligands CO, O2, and NO with myoglobin.

The kinetics of geminate recombination of horse heart myoglobin with the diatomic ligands carbon monoxide, dioxygen, and nitric oxide have been reexamined. The new measurements are distinguished from previous studies by (1) consideration of the complete time range longer than 1 ps, (2) inclusion of the effect of temperature changes near ambient, (3) attention to the relation between recombination kinetics and the yield of dissociated partners on the millisecond time scale, and (4) use of singular value decomposition in the analysis. These picosecond results, together with earlier nanosecond data, for O2 prove that models incorporating one, two, or even three discrete intermediates are not sufficient to account for all features of geminate recombination kinetics. Instead, a continuous evolution of the geminate pair distribution is preferred.

Animals↗
PubMed1994

Adaptive response to mutagenesis and its molecular basis in a human T-cell leukemia line primed with a low dose of gamma-rays.

The effect was studied of a low dose of gamma-ray preexposure on the frequency and molecular spectrum of radiation-induced mutations at the hprt locus in a human T-cell leukemia line. When the cells were preexposed to 0.01 Gy of gamma-rays, the yield of mutations induced by a subsequent 2-Gy challenge dose was reduced by 60%, compared with the 2 Gy of irradiation alone. The data of Southern blot analysis showed that 47% of the mutants induced by 2 Gy in the cells without low-dose preexposure were of the deletion or rearranged mutations type. In contrast, in the low-dose radioadapted cells the proportion of this type of 2-Gy-induced mutations decreased to 28%. This is close to the control level (22%) of spontaneous mutations. Our results confirm that a low dose of gamma-ray preexposure leads to a decreased susceptibility to gene deletions and rearrangements after high-dose irradiation.

Dose-Response Relationship, Drug↗