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Biomedical subjects

Q Ren

Publications and source records attributed to Q Ren.

At least 37 records · Page 2Linked to original sources
PubMed1999

[Low level of residual renal function in the initial month and high transport characteristic as important causes of peritoneal dialysis failure].

OBJECTIVE: To evaluate what kind of patients was at high risk on peritoneal dialysis (PD) treatment. METHODS: 96 patients on PD for (23.1 +/- 10.0) months were studied. The patients were divided into two groups. Group A: patients (25) who died or switched to hemodialysis because of cardiovascular disease, malnutrition, ultrafiltration inefficiency, hydrothora, relapsing peritonitis, etc. Group B: stable PD patients (71) up to now. Age, body surface area (BSA) and dialysate fill volume (DV) were not different between the two groups. The nutritional status, dialysis adequacy, peritoneal membrane transport characteristics, and residual renal function (RRF) in the initial month of dialysis were compared. Patient survival rate was studied by Kaplan-Meier method. RESULTS: It was demonstrated that Kt/V and Ccr in group A were lower than those in group B (P < 0.05). Meanwhile, RRF was significantly different between the two groups; patients with better RRF (> or = 2 ml/min) had higher survival. The percentage of high transporters in group A was greater than in group B. CONCLUSION: Higher clearance in the initial month of dialysis seems to keep PD successful. PD failure maybe related to high transport characteristic and its treatment modality is DAPD. Hemodialysis will be a better choice when RRF is very low as water balance is poorly controlled by DAPD.

Adolescent↗
PubMed1999

[The development of a hemorrhologity observating and measuring instrument].

A new instrument for observing blood cell state and the process of variation on hemorrheology has been developed. There are three ways of shear rate: setting by hand, automatically setting and simulating pulsative state. It can provide different variable flow fields. The shear rate can be set in the range from 0.1 to 1000 s-1. It needs only a little blood. It can be easyly and rapidely operated. it has clear images. The hemorrheology state of blood cells can be directly perceived through thd instrument by eyes. The display and measurement and record of blood cell's hemorrheology state can be finished in real time dynamically and simultaneously.

Equipment Design↗
PubMed1999

[The visible spectra study of the conformation equilibrium of iron-metal-free porphyrin dimers].

A series of iron(III)-metal-porphyrin dimers linked with flexible alkoxyl chain at para position of two phenyl rings have been synthesized and characterized. An equilibrium of two conformations of porphyrin dimers (open and closed) has been studied by visible spectra. The intensity of absorption band 680 nm relates to equilibrium of two conformations. With the increase of the length of the alkoxyl chain,the closed conformation forms more easily. With the addition of axial ligand, the ferric ion of the dimers tends to bind with imidazole, and the intensity of the band 680 nm gradually decreases and disappears.

Dimerization↗
PubMed1998

Palmitoylation of neurofascin at a site in the membrane-spanning domain highly conserved among the L1 family of cell adhesion molecules.

This report presents the first evidence that a member of the L1 family of nervous system cell-adhesion molecules is covalently modified by thioesterification with palmitate, and identifies a highly conserved cysteine in the predicted membrane-spanning domain as the site of modification. Neurofascin is constitutively palmitoylated at cysteine-1213 at close to a 1:1 molar stoichiometry. Kinetics of palmitate incorporation into neurofascin expressed in resting neuroblastoma cells indicate that the palmitate modification has the same turnover rate as the polypeptide chain and does not affect the protein stability of neurofascin. Palmitoylation of neurofascin expressed in dorsal root ganglion neurons is not required for delivery of neurofascin to the plasma membrane or targeting to axons. Palmitoylation also has no effect on ankyrin-binding activity of neurofascin, on the oligomeric state of neurofascin in solution, or on cell-adhesion activity of neurofascin expressed in neuroblastoma cells. A significant difference between native and C1213L neurofascin is that these proteins were localized in distinct fractions within a low-density membrane population enriched in signaling molecules. These results indicate a palmitate-dependent targeting of neurofascin to a specialized membrane microdomain.

Amino Acid Sequence↗
PubMed1998

p53, but not p16 mutations in oral squamous cell carcinomas are associated with specific CYP1A1 and GSTM1 polymorphic genotypes and patient tobacco use.

Inactivation of tumor suppressor genes like p53 and p16 play a key role in tumor progression, with a high incidence of mutations existing for both genes in oral squamous cell carcinomas. Previous studies have demonstrated, (i) a correlation between the prevalence of p53 mutations and tobacco use [Brennan et al. (1995) New Engl. J. Med., 332, 712-717; Lazarus et al. (1996) Carcinogenesis, 17, 733-739], and (ii) a link between genotypes in specific xenobiotic metabolizing enzymes and oral cancer susceptibility [Park et al. (1997) Cancer Epid. Biomarkers Prev., 6, 791-797). In this paper, we present results of our examination of a series of 80 oral squamous cell carcinomas for p53 exons 5-9 and p16 exons 1-2 mutations, and the potential association of these mutations with specific genotyping patterns. p53 mutation prevalence in oral tumors was linked with increased patient tobacco use using several stratification criteria. There was a significantly higher prevalence of p53 mutations in OCSCCs from patients who smoked > 30 pack-years as compared to tumors from patients who smoked < or = 30 pack-years (OR = 2.8; CI = 1.1-7.2). No significant association was observed with patient alcohol consumption. There was a significant association between the prevalence of p53 mutations in oral tumors and CYP1A1 genotyping patterns in these oral cancer patients, with the highest p53 mutation prevalence observed in subjects with the CYP1A1 [val]/GSTM1 [+] genotype (OR = 6.0; CI = 1.2-29.7). A significant association was not observed between the prevalence of p16 mutations in oral tumors and tobacco use, or CYP1A1 [val] or GSTM1 (0/0) genotypes. These data suggest that the induction of mutations in specific tumor suppressor genes or oncogenes in oral tumors may be associated with specific carcinogen exposures, and that this association may be linked to specific polymorphic genotypes in xenobiotic-metabolizing enzyme genes.

Benzo(a)pyrene↗
PubMed1998

Modulation of fluorouracil cytotoxicity by interferon-alpha and -gamma.

Because interferons (IFN)-alpha and -gamma individually have increased fluorouracil (FUra) cytotoxicity in several in vitro models, we studied the effects of FUra combined with IFN-alpha + gamma in HT29 colon cancer cells. A 96-hr exposure to IFN-alpha (500 units/ml) plus IFN-gamma (10 units/ml) and a 72-hr exposure to 0. 25-1 microM FUra (hr 24-96) inhibited cell growth and colony formation in an additive or more-than-additive fashion. When cells were exposed to IFN-alpha + gamma and FUra, free FdUMP levels became detectable, whereas [3H]FUra-RNA incorporation decreased. Exposure to IFN-alpha + gamma, FUra, or the combination decreased dTTP pools to 58%, 43%, and 17% of control, respectively. A marked increase in the dATP to dTTP ratio was seen with FUra with or without IFN-alpha + gamma. Thymidylate synthase catalytic activity was reduced to 28% and 24% of control with FUra with or without IFN-alpha + gamma, suggesting that the enhanced dTTP depletion must be due to another mechanism. FUra-mediated thymidylate synthase inhibition was accompanied by a 124-fold increase in total deoxyuridylate immunoreactivity and a 31-fold increase in dUTP pools, but the addition of IFN-alpha + gamma attenuated the accumulation. Treatment with IFN-alpha + gamma and FUra individually interfered with nascent DNA chain elongation, whereas the three-drug combination produced the most striking effects. IFN-alpha + gamma plus FUra produced the greatest amount of single-strand breaks in nascent DNA and dramatically decreased net DNA synthesis. IFN-alpha + gamma with or without FUra produced double-strand breaks in parental DNA. These results suggest that dTTP depletion, dATP/dTTP imbalance, pronounced inhibition of DNA synthesis, and damage to nascent and parental DNA contribute to the enhanced cytotoxicity with the triple combination.

DNA Fragmentation↗
PubMed1998

Cytotoxicity and DNA fragmentation associated with sequential gemcitabine and 5-fluoro-2'-deoxyuridine in HT-29 colon cancer cells.

The combined cytotoxic effects of the antimetabolites gemcitabine (dFdCyd) and 5-fluoro-2'-deoxyuridine (FdUrd) were studied. Cytotoxicity, biochemical perturbations, and DNA damage seen with dFdCyd and FdUrd alone and in combination were evaluated in HT-29 human colon cancer cells. A 4-h exposure to dFdCyd followed by FdUrd for 24 h produced more than additive cytotoxicity and marked S-phase accumulation. Cells progressed through the cell cycle, however, after a 22-h drug-free interval. [3H]dFdCyd was rapidly metabolized to the 5'-triphosphate and incorporated into DNA. [3H]FdUrd was anabolized exclusively to FdUrd monophosphate, and preexposure to dFdCyd did not affect FdUrd monophosphate formation. Thymidylate synthase catalytic activity was inhibited by 48% after a 4-h exposure to 10 nM FdUrd and by 80% after exposure to the combination. Sequential 4-h exposures to 15 nM dFdCyd and 10 nM FdUrd led to greater depletion of dTTP pools (29% of control) than with either drug alone. Greater effects on nascent DNA integrity were seen with sequential dFdCyd followed by FdUrd. Although parental DNA damage was not evident immediately after exposure to 15 nM dFdCyd for 4 h followed by 10 nM FdUrd for 24 h, high molecular mass DNA fragmentation was evident 72-96 h after drug removal. Sequential dFdCyd/FdUrd was associated with prominent disturbance of the cell cycle, dTTP pool depletion, dATP/dTTP imbalance, and nascent DNA damage. Induction of double-strand parental DNA damage and cell death was delayed, consistent with postmitotic apoptosis.

Antimetabolites, Antineoplastic↗
PubMed1997

Tyrosine phosphorylation at a site highly conserved in the L1 family of cell adhesion molecules abolishes ankyrin binding and increases lateral mobility of neurofascin.

This paper presents evidence that a member of the L1 family of ankyrin-binding cell adhesion molecules is a substrate for protein tyrosine kinase(s) and phosphatase(s), identifies the highly conserved FIGQY tyrosine in the cytoplasmic domain as the principal site of phosphorylation, and demonstrates that phosphorylation of the FIGQY tyrosine abolishes ankyrin-binding activity. Neurofascin expressed in neuroblastoma cells is subject to tyrosine phosphorylation after activation of tyrosine kinases by NGF or bFGF or inactivation of tyrosine phosphatases with vanadate or dephostatin. Furthermore, both neurofascin and the related molecule Nr-CAM are tyrosine phosphorylated in a developmentally regulated pattern in rat brain. The FIGQY sequence is present in the cytoplasmic domains of all members of the L1 family of neural cell adhesion molecules. Phosphorylation of the FIGQY tyrosine abolishes ankyrin binding, as determined by coimmunoprecipitation of endogenous ankyrin and in vitro ankyrin-binding assays. Measurements of fluorescence recovery after photobleaching demonstrate that phosphorylation of the FIGQY tyrosine also increases lateral mobility of neurofascin expressed in neuroblastoma cells to the same extent as removal of the cytoplasmic domain. Ankyrin binding, therefore, appears to regulate the dynamic behavior of neurofascin and is the target for regulation by tyrosine phosphorylation in response to external signals. These findings suggest that tyrosine phosphorylation at the FIGQY site represents a highly conserved mechanism, used by the entire class of L1-related cell adhesion molecules, for regulation of ankyrin-dependent connections to the spectrin skeleton.

Amino Acid Sequence↗
PubMed1997

Cytoplasmic protein mRNA interaction mediates cGMP-modulated translational control of the asialoglycoprotein receptor.

Expression of the asialoglycoprotein receptor by the human hepatocellular carcinoma cell line HuH-7 in response to intracellular cGMP concentrations was previously shown to be regulated at the translational level. In a cell-free system, initiation of asialoglycoprotein receptor mRNA translation was dependent on the presence of the 7-methylguanylate cap site and was independent of 8-bromo-cGMP levels in which the cells were grown prior to RNA isolation. Stable transfection of COS-7 cells with deletion constructs of the asialoglycoprotein receptor H2b subunit localized the cGMP-responsive cis-acting element to the mRNA 5'-untranslated region (UTR). Addition of biotin (an activator of guanylate cyclase) induced the expression of beta-galactosidase present as a chimeric plasmid containing the H2b 187-nucleotide 5'-UTR. An RNA gel retardation assay identified a 37-nucleotide cognate sequence within this 187-nucleotide region. Titration of the 5'-UTR with a cytosolic fraction isolated from HuH-7 grown in the presence or absence of 8-bromo-cGMP or biotin provided direct evidence for an RNA-binding protein responsive to intracellular levels of cGMP. Based on these findings, it seems reasonable to propose that reduction of intracellular levels of cGMP by biotin deprivation results in a negative trans-acting factor associating with the 5'-UTR of asialoglycoprotein receptor mRNAs, thereby inhibiting translation.

Animals↗
PubMed1997

Ablation rate of PMMA and human cornea with a frequency-quintupled Nd:YAG laser (213 nm).

BACKGROUND AND OBJECTIVE: As an alternative to the standard excimer laser used for PRK, we investigated the ablation rate at 213 nm of PMMA, and human corneas under controlled hydration. STUDY DESIGN/MATERIALS AND METHODS: The output of a frequency-quintupled Nd:YAG laser (213 nm) was transformed into a quasi-Gaussian beam. PMMA and corneal lenticules maintained under controlled hydration were ablated until perforation was detected. RESULTS: The ablation rate of PMMA and cornea at 213 nm were similar to that at 193 nm when radiant exposure was below 200 mJ/cm2 and increased gradually between one and two times faster than that at 193 nm when radiant exposure was > 200 mJ/ cm2. CONCLUSIONS: PMMA and cornea ablation at 213 nm are similar to that at 193 nm and are different from that at 248 nm. The difference between PMMA and cornea ablation rates should be considered when using PMMA to test ablated diopter and smoothness for photorefractive surgery.

Cornea↗
PubMed1997

[Simultaneous analysis of theophylline, phenobarbital, amobarbital and carbamazepine in serum by high performance liquid chromatography].

Theophylline, phenobarbital, amobarbital and carbamazepine are the chief therapeutic drugs in clinical practice. Because of the differences among inter-individuals in the metabolic clearance of these drugs and their toxicity at certain levels of concentration in serum, the dosage should be regulated to maintain a therapeutic blood drugs level. To achieve this a rapid and accurate assay method for drugs in blood is necessary. This paper reports that a reversed phase high performance liquid chromatographic (HPLC) method had been established for the simultaneous separation and quantitative determination of the four drugs in serum. The separation was performed on RP-C18 column using methanol:water (1:1) as mobile phase and 4-aminoantipyrime as internal standard. The eluted substances were detected at 210nm.

Amobarbital↗
PubMed1997

[Rapid determination of low molecular weight aldehydes in air by gas chromatography].

This paper reports a method for determination of low molecular weight aldehydes in polluted air by GC-FID using a GDX-401 packed column (3 mm x 3 m). The advantages of this method are simple, rapid, accurate and sensitive. The method requires only 8 minutes for the whole analysis. In the concentration range of 1.7-442.4 mg/m3 for formaldehyde and 0.5-680 mg/m3 for acetaldehyde and propionaldehyde the calibration curves are linear. The minimun detectable amounts are 3.5 ng, 1 ng and 1 ng, and the average recoveries (n=5) are 89.4%, 89.6%, 88.1% for formaldehyde, acetaldehyde and propionaldehyde respectively. The quantitative determination is performed by external standard calibration method. The results of sample analysis are satisfactory.

Air Pollutants↗
PubMed1997

Determinants of cytotoxicity with prolonged exposure to fluorouracil in human colon cancer cells.

To explore the determinants of cytotoxicity during prolonged exposure to pharmacologically relevant concentrations of 5-fluorouracil (FUra), we studied the effects of FUra at concentrations ranging from 0.1 to 1 microM in HCT 116 and HT 29 colon cancer cells grown in the presence of physiologic levels of leucovorin. A 5- and 7-day exposure to 1 microM FUra reduced cell growth to 46% and 20% of control in HT 29 cells and to 74% and 38% of control in HCT 116 cells. Concurrent exposure to thymidine (10 or 20 microM) or uridine (1 mM) provided partial protection against FUra toxicity in HT 29 cells, but did not protect HCT 116 cells. After a 24-h exposure to 1 microM [3H]FUra, free 5-fluoro-2'-deoxyuridine-5' -monophosphate (FdUMP) and FUDP. + FUTP levels were 0.7 and 144 pmol/10(6) cells in HT 29 cells, respectively, and 3.9 and 178 pmol/10(6) cells in HCT 116 cells. FdUMP and FUDP + FUTP pools increased by 5.7- and 2.0-fold in HT 29 cells and by 1.7- and 3.3-fold in HCT 116 cells over the next 48 h, but did not accumulate thereafter. After a 24-h exposure to 1 microM [3H]FUra, FUra-RNA levels were 158 and 280 fmol/microgram in HT 29 and HCT 116 cells, respectively; FUra-RNA levels increased over time, and reached 700 and 1156 fmol/microgram at day 5. Concurrent exposure to 1 mM uridine for 72 h did not diminish [3H]FUra-RNA incorporation. Upon removal of [3H]FUra following a 24-h exposure, FUra-RNA levels remained relatively stable with 57-78% retained at 120 h. A low level of [3H]FUra-DNA incorporation was detected in HT 29 cells. Thymidylate synthase (TS) catalytic activity in control cells was 2-fold higher in HCT 116 cells compared to HT 29 cells (47 vs. 23 pmol/min/mg). Total TS content increased 1.5- to 3-fold over control in both cell lines during FUra exposure, and ternary complex formation was evident for up to 96 h-dTTP pools were not depleted in FUra-treated cells, suggesting that residual TS catalytic activity was sufficient to maintain dTTP pools relative to demand. Surprisingly, the partial inhibition of TS was accompanied by a striking accumulation of immunoreactive "dUMP" pools in both lines; dUTP pools also increased 2-to 3-fold. In summary, the gradual and stable accumulation of FUra in RNA noted in both lines may account for the thymidine-insensitive component of FUra toxicity. Because dTTP pools were not appreciably diminished, the interference with nascent DNA chain elongation and induction of single-strand breaks in newly synthesized DNA in both cell lines may be due to misincorporation of deoxyuridine nucleotides.

Cell Division↗
PubMed1997

CYP1A1 and GSTM1 polymorphisms and oral cancer risk.

The importance of both the CYP1A1 exon 7 (ile:val) and GSTM1 (0/0) polymorphisms in oral cancer susceptibility was assessed by examining polymorphic prevalences in 135 patients with oral cancer and 135 noncancer controls frequency-matched by age at diagnosis (+/- 5 years), race, sex, and institute of patient recruitment. The prevalence of the GSTM1 (0/0) genotype was approximately 51% in both cases and controls. The prevalence of the CYP1A1 (ile:val) polymorphism [including both the (ile/val) and (val/val) genotypes] was significantly higher in cases as compared to controls (17.6% versus 7.6%, respectively; crude odds ratio, 2.6; confidence interval, 1.2-5.7). No association was observed between polymorphic prevalence and levels of smoking or alcohol consumption in cases. These results suggest that the GSTM1 null genotype is not associated with oral cancer risk. These results also suggest that individuals with the CYP1A1 exon 7 ile:val polymorphism are at increased risk for oral cancer, and that this risk may not be influenced by differences in exposure to tobacco smoke.

Adult↗
PubMed1996

Effect of 2,3-dimercaptosuccinic acid on nephrosclerosis in the Dahl rat. I. Role of reactive oxygen species.

2,3-Dimercaptosuccinic acid (DMSA), a sulfhydryl-containing chelator, has previously been shown to reduce mean blood pressure in lead-treated rats. In the present study we have demonstrated that DMSA (0.5% for 5 days every 2 weeks) also reduces mean blood pressure in the Dahl salt-sensitive (SS) rat. Six-week-old Dahl SS and salt resistant (SR) rats were placed on a 0.3% NaCl diet for two weeks, followed by an 8% NaCl diet for four weeks. Eight SS and 8 SR rats remained untreated while 8 SS and 8 SR rats were treated with DMSA. DMSA treatment ameliorated the mean blood pressure rise in the Dahl SS rats (141 +/- 5 vs. 120 +/- 4 mm Hg at 6 weeks, P < 0.001). Nephrosclerosis was severe in untreated SS rats but absent in treated SS rats as well as in both treated and untreated SR rats. Reactive oxygen species formation, as assessed by kidney cortex content of malondialdehyde (MDA) and immunohistochemical demonstration of nitrotyrosine (a byproduct of peroxynitrite) in interlobular arteries, was increased in Dahl SS rats, but abolished by DMSA (MDA 9.65 +/- 0.33 nmol/g wet wt, untreated SS, vs. 6.46 +/- 0.51, treated SS, P < 0.001). The anti-nephrosclerotic action of DMSA was clearly disproportionate to the reduction in blood pressure. We conclude that the effect of DMSA was related instead to the reactive oxygen species scavenging properties of the thiol groups.

Animals↗