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F Xiao

Publications and source records attributed to F Xiao.

84 records · Page 5Linked to original sources
PubMed1992

Identification of a glycine-rich sequence as an NAD(P)H-binding site and tyrosine 128 as a dicumarol-binding site in rat liver NAD(P)H:quinone oxidoreductase by site-directed mutagenesis.

Site-directed mutagenesis was utilized to identify binding sites for NAD(P)H and dicumarol in rat liver NAD(P)H:quinone oxidoreductase (NQOR, EC 1.6.99.2). The mutant cDNA clones were generated by a procedure based on the polymerase chain reaction and were expressed in Escherichia coli. The mutant enzymes were purified to apparent homogeneity as judged by SDS-polyacrylamide gel electrophoresis and were found to contain 2 FADs/enzyme molecule identical with that of the wild-type NQOR. Purified mutant enzymes Y128D, G150F, G150V, S151F, and Y155D showed dramatic decreases in activities in the reduction of dichlorophenolindophenol in comparison with the activities of the wild-type enzyme, whereas the activities of F124L, T127V, T127E, Y128V, Y128F, S151A, and Y155V were similar to those of NQOR. Enzyme kinetic analysis revealed that the Km values of T127E, Y128D, G150F, G150V, S151F, and Y155D were, respectively, 4-, 2-, 13-, 5-, 26-, and 19-fold higher than the Km of NQOR for NADPH, and were, respectively, 2-, 3-, 7-, 3-, 20-, and 11-fold higher than that of NQOR for NADH. The kcat values of Y128D, G150F, and G150V were also much lower than those of NQOR, but the kcat values of other mutants were similar to those of the wild-type enzyme. The Km values of the mutants for dichlorophenolindophenol were the same or slightly higher than that of NQOR. The apparent inhibition constants (Ki) for dicumarol on Y128V and F124L were elevated 12 and 8 times, respectively. Similar, but smaller, changes on Ki for 4-hydroxycoumarin were also observed. This study demonstrated that residues Gly150, Ser151, and Tyr155 in the glycine-rich region of NQOR are essential for NADPH and NADH binding and Tyr128 is important for dicumarol binding. Based on the results of the study, it is proposed that the glycine-rich region of the enzyme, along with other residues around the region, forms a beta sheet-turn-alpha helix structure important for the binding of the pyrophosphate group of NADPH and NADH.

Amino Acid Sequence↗
PubMed1992

The role of ultraviolet B-irradiated leukocyte transfusions and cyclosporine in intestinal transplantation.

To explore the efficacy of ultraviolet B-irradiated donor-specific leukocyte transfusions (UV-DSLT) with short-term cyclosporine to control intestinal allograft rejection, 75 adult Lewis (RT1l) rats underwent total small-intestinal transplantation from Brown-Norway (RT1n) donors. Recipients were randomly divided into ten treatment and control groups utilizing various combinations of donor-specific and third-party (Wistar-Furth, RT1u) leukocyte transfusions (TPLT), with or without transfusion UVB irradiation, and either alone or in combination with short-term cyclosporine administration (5 mg/kg intramuscularly on days -7, 0, 1, and 2 relative to transplantation). Leukocytes (10(8) cells) separated from a spleen cell suspension were infused on day -7. Certain transfused leukocytes were treated with 12,000 joules/m2 of UVB irradiation. Groups were monitored for mean survival time (MST) and cause of death. UV-DSLT alone (MST = 19.8 +/- 4.6) or in combination with cyclosporine (UV-DSLT+CsA, MST = 53.1 +/- 22.5) significantly (P less than 0.003-0.0002, Mantel-Cox) prolonged recipient survival when compared with appropriate controls (i.e., no treatment, MST = 11.2 +/- 3.4; CsA, MST = 17.2 +/- 9.0; UV-TPLT, MST = 12.4 +/- 4.0; and UV-TPLT+CsA, MST = 25.1 +/- 9.7) No significant increase in graft-versus-host disease occurred in any group, with 85% (64/75) of the recipients dying of acute rejection. Conversely, the UV-DSLT+CsA group had a significant increase (9/11; chi-square, P less than 0.0001) in chronic rejection. Because UV-DSLT+CsA improved survival as compared with third-party controls, a limited donor-specific unresponsiveness may have been induced. Furthermore, this treatment produces a consistent, chronic rejection rodent intestinal allograft model.

Animals↗
PubMed1991

Modulation of rat hepatic microsomal monooxygenase enzymes and cytotoxicity by diallyl sulfide.

Diallyl sulfide (DAS) and other organosulfur compounds inhibit chemically induced carcinogenic and toxic responses in rodent model systems. A possible mechanism of action is the inhibition of the hepatic cytochrome P450IIE1-dependent bioactivation of the procarcinogens and protoxicants. Previous work showed competitive inhibition by DAS of N-nitrosodimethylamine (NDMA) demethylase activity in vitro, and a reduction in the microsomal level of P450IIE1 after in vivo treatment with DAS. The present studies demonstrated a time- and dose-dependent decrease of hepatic microsomal P450IIE1 activity, induction of P450IIB1 and pentoxyresorufin dealkylase activity, and moderate induction of ethoxyresorufin dealkylase activity by oral DAS treatment. DAS treatment elevated P450IIB1 mRNA but had no effect on P450IIE1 mRNA. Treatment with putative metabolites of DAS, diallyl sulfoxide and diallyl sulfone, led to similar modulations in monooxygenase activities, but the decrease of P450IIE1 activity by the sulfone occurred more rapidly. In studies in vitro, diallyl sulfone caused a metabolism-dependent inactivation of P450IIE1, but such inactivation was not observed with DAS or diallyl sulfoxide. The profile of microsomal testosterone metabolism after DAS treatment indicated an enhancement of P450IIB1-dependent 16 beta-hydroxylase activity, and a decrease in 6 beta-hydroxytestosterone production possibly related to a lower level of P450IIIA1 or IIIA2. When rats were subjected to a 48-hr fast and DAS treatment, the starvation-induced microsomal P450IIE1 level was decreased by DAS. Inhibition of hepatotoxicity due to exposure to P450IIE1 substrates, CCl4 and NDMA, by DAS was observed under a variety of treatment schedules.

Allyl Compounds↗
PubMed1991

Effects of disulfiram on hepatic P450IIE1, other microsomal enzymes, and hepatotoxicity in rats.

Disulfiram, widely used in avoidance therapy for alcohol abuse, has been shown to have protective effects against chemically induced toxicity and carcinogenesis. The purpose of this work was to elucidate the biochemical mechanisms of this protective action by examining its effects on cytochrome P450IIE1 and other related microsomal enzyme activities. When a dose of disulfiram was given intragastrically to rats, a very rapid decrease of N-nitrosodimethylamine (NDMA) demethylase activity, possibly due to the inactivation of P450IIE1, was seen. The loss of P450IIE1 protein from the microsomal membrane was observed at 18 hr after receiving disulfiram, but not within the first 5 hr after the treatment. P450IIB1, on the other hand, was induced markedly between 15 and 72 hr after the disulfiram treatment. The treatment, however, caused only moderate changes in some other P450 isozymes. Carbon disulfide, a putative metabolite of disulfiram, produced similar effects on P450IIE1, but with shorter duration. Carbon disulfide, however, did not induce P450IIB1. Diethyldithiocarbamate, a reductive product of disulfiram, was an inhibitor of P450IIE1 activity in vitro, and upon preincubation with microsomes, it produced an NADPH-dependent inactivation of NDMA demethylase activity. The results suggest that this or other metabolites of disulfiram are inhibitors of P450IIE1 and are responsible for the inactivation of P450IIE1 in vivo. Hepatotoxicity of NDMA or CCI4 in rats was blocked by pretreatment with disulfiram. The present work demonstrates that P450IIE1 was inhibited and inactivated by disulfiram, and this mechanism can account for many of the reported inhibitory actions of disulfiram against chemically induced toxicity and carcinogenesis.

Animals↗
PubMed1991

[Clinical observation of macular disease in patients with diabetic retinopathy].

The population was 65 cases (122 eyes) of diabetic macular disease. Background diabetic retinopathy was observed in 40 eyes, i.e., 32.80%. For the 82 eyes present proliferative diabetic retinopathy, i.e., 67.20%. According to Sigelmen's classification, 17 eyes were in stage I, i.e., 13.93% of the cases; 41 eyes were in stage II, i.e., 33.60% of the cases; 40 eyes were in stage III, i.e., 32.80% of the cases; 24 eyes were in stage IV, i.e., 19.67% of the cases. There were 122 eyes in this group. The visual acuity of 66 eyes showed > or = 0.3, i.e., 54.00%, while that of 56 eyes showed 40.3 i.e. 46.00%. Nearly half patients showed low visual acuity and loss of vision. This result was responsible for the cases who were at the late stage of diabetic and with a long history of diabetic or the diabetic was poorly controlled. So the writer appeal to ophthalmologists and physicians to prescribe the effective guides to all the diabetic patients. We suggest that it is important that dynamic observation be carried out of hemorhelological manifestation and early treatment diabetic retinopathy for the clinical prevention and treatment of diabetic retinopathy.

Adult↗
PubMed1990

Metabolism of methyl tertiary-butyl ether by rat hepatic microsomes.

Exposure to methyl tertiary-butyl ether (MTBE), a commonly used octane booster in gasoline, has previously been shown to alter various muscle, kidney, and liver metabolic activities. In the present study, the metabolism of MTBE by liver microsomes from acetone- or phenobarbital-treated Sprague-Dawley rats was studied at concentrations of up to 5 mM MTBE. Equimolar amounts of tertiary-butanol, as measured by head-space gas chromatography, and formaldehyde were formed. The Vmax for the demethylation increased by 4-fold and 5.5-fold after acetone and phenobarbital treatments, respectively. The apparent Km value of 0.70 mM using control microsomes was decreased slightly after acetone treatment, but was increased by 2-fold after phenobarbital treatment. The metabolism of MTBE (1 mM) was inhibited by 35% by monoclonal antibodies against P450IIE1, the acetone/ethanol inducible form of cytochrome P450, suggesting a partial contribution by this isozyme. A single 18-h pretreatment of rats with 1 or 5 ml/kg MTBE (i.p.) resulted in a 50-fold induction of liver microsomal pentoxyresorufin dealkylase activity but no change in N-nitrosodimethylamine demethylase activity. These trends in activity agreed with immunoblot analysis which showed an elevation in P450IIB1 but no change in P450IIE1 levels.

Acetone↗
PubMed1990

Alteration of rat liver microsomal monooxygenase activities by gasoline treatment.

Previous work has shown an increase in rat liver enzyme activities after chronic exposure to gasoline vapor. In the present study, male Sprague-Dawley rats were pretreated with unleaded gasoline at 1 and 5 ml/kg, i.p., and selected hepatic microsomal monooxygenase activities were determined at 18, 48, and 72 h. At 18 h, moderate increases were observed in P450 content (1.3-fold), cytochrome c-reductase activity (1.25-fold), and in N-nitrosodimethylamine demethylation rate (1.25- to 1.6-fold). Pentoxyresorufin dealkylase activity (an activity displayed primarily by P450IIB1) was significantly elevated at 18 and 48 h (30- to 60-fold), and ethoxyresorufin dealkylase activity (an activity displayed by P450 IA1) was elevated (2- to 4-fold). Immunoblot analysis revealed no change in P450IIE1 at these time points, but an elevation in P450IIB1 in agreement with the pentoxyresorufin dealkylase activity measurements.

Animals↗
PubMed1989

Induction of cytochromes P450IIE1 and P450IIB1 by secondary ketones and the role of P450IIE1 in chloroform metabolism.

It has been shown previously that the potentiation of chloroform-induced hepatotoxicity by linear secondary ketones increases with the carbon-chain length. The present work examines the possibility that this potentiation is due to the induction of P450IIE1. The metabolism of chloroform, as measured using headspace gas chromatography, in the presence of microsomes from acetone-treated rats was elevated threefold compared to controls. Inclusion of monoclonal antibody against P450IIE1 inhibited the metabolism by 81%. Alternate substrates of P450IIE1 were also inhibitory. Chloroform metabolism was observed using purified, reconstituted P450IIE1 plus cytochrome b5, but was not detected using P450IIB1. The inductive effect of 18-hr oral pretreatment (15 mmol/kg body wt) with each of three secondary ketones on two isozymes of rat liver microsomal cytochrome P450, P450IIE1, and P450IIB1 was studied. The content of total microsomal P450 and NADPH-dependent cytochrome c reductase, the rates of oxidation of N-nitrosodimethylamine, benzphetamine, and pentoxyresorufin, as well as levels of immunoreactive protein for both of the isozymes were elevated by the pretreatments in the rank order of acetone less than or equal to 2-butanone less than 2-hexanone, in agreement with other trends noted by previous investigators. The results provide further evidence for the role of P450IIE1 induction in the potentiation phenomenon.

Animals↗
PubMedDate not supplied

The effect of head-down tilt on brain potentials related to visual attention.

To study the possible effect of simulated weightlessness on brain function state, the brain event-related potentials (ERPs) in a simple visual selective response task were compared between HDT and HUT in 9 normal subjects. The results were: The Target(T) and non-Target(NT) flash signals both induced significant slow positive potentials which were supposed to related to the attention state; the amplitude of the positive potentials in frontal regions decreased significantly especially for NT-ERPs during HDT compared with that during HUT. The data reported provide new evidence indicating that more attention should be paid on the brain function study during space flight.

Adult↗