Biomedical subjects

X Shi

Publications and source records attributed to X Shi.

At least 397 records · Page 22Linked to original sources

PubMed1994

Novel delivery of antioxidant enzyme catalase to alveolar macrophages by Fc receptor-mediated endocytosis.

Excessive production of reactive oxygen species by alveolar macrophages (AMs) in response to inhaled toxic substances is a major cause of oxidative lung injury. Therapeutic approaches designed to protect the lungs from oxidative injury by administering native antioxidant enzymes such as catalase and superoxide dismutase have been suggested. However, problems associated with poor penetration of these enzymes to the intracellular target sites have limited their effective use. The present study reports a drug targeting method based on receptor-mediated endocytosis of the antioxidant enzyme catalase to the AMs. This method employs molecular conjugate consisting of a cognate moiety, in this case IgG which recognizes the macrophage Fc receptor, covalently linked to the enzyme catalase via the reversible disulfide linkage. The uptake efficiency of the enzyme conjugate and its protection against oxidative injury were evaluated microfluorometrically using the intracellular oxidative probe dichlorodihydrofluorescein BSA: anti BSA antibody complex (DCHF-IC), and the cell viability indicator propidium iodide. The DCHF-IC-stimulated macrophages exhibited a dose- and time-dependent increase in intracellular fluorescence with a half maximal response dose of approximately 120 micrograms/ml. Free catalase (50-500 U/ml) failed to inhibit the DCHF-IC-induced oxidative burst and had only a marginal protective effect on AM injury. In contrast, the catalase-IgG conjugate (50-500 U/ml) strongly inhibited both the DCHF-IC-induced oxidation and injury in a dose-dependent manner. Effective inhibition was shown to require both the antioxidant catalase moiety ant the cognate moiety for the cell surface receptor. Specific internalization of the conjugate through the Fc receptor was also investigated by competitive inhibition using free IgG.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Reaction of Cr(VI) with ascorbate and hydrogen peroxide generates hydroxyl radicals and causes DNA damage: role of a Cr(IV)-mediated Fenton-like reaction.

Incubation of Cr(VI) with ascorbate generated Cr(V), Cr(IV) and ascorbate-derived carbon-centered alkyl radicals, as well as formyl radicals. H2O2 caused generation of hydroxyl radicals (OH) and much higher levels of Cr(V), showing that .OH can be generated via a Cr(IV)-mediated Fenton-like reaction (Cr(IV) + H2O2-->Cr(V) + .OH + OH-). 1,10-Phenanthroline and deferoxamine inhibited the formation of both .OH and Cr(V) from the reaction of Cr(VI) with ascorbate in the presence of H2O2. Electrophoretic assays showed that ascorbate-derived free radicals caused DNA double-strand breaks. .OH radicals generated by Cr(V)- and Cr(IV)-mediated Fenton-like reactions also caused DNA double-strand breaks. HPLC measurements showed that .OH radicals generated by Cr(IV) and Cr(V) from H2O2 caused 2'-deoxyguanine hydroxylation to form 8-hydroxy-2'-deoxyguanine.

8-Hydroxy-2'-Deoxyguanosine↗

PubMed1994

Hepatitis A and evidence against the community dissemination of Helicobacter pylori via feces.

Seroprevalence data from 1501 subjects was used to test the hypothesis that Helicobacter pylori may be transmitted by the fecal-oral route. Antibody to hepatitis A virus was used as a marker of fecal-oral exposure. Of the 1501 subjects, 35.5% were seropositive for both H. pylori and hepatitis A, 19.1% were seronegative for both, 36.5% were seropositive for hepatitis A only, and 8.8% were seropositive for H. pylori only. Cross-sectional data from rural areas supported an association between hepatitis A and H. pylori. However, in the urban area there was no evidence of hepatitis A infection in persons < 10 years old, yet the seroprevalence of H. pylori was high in this group (approximately 32%). From our data, we suggest that communitywide fecal-oral spread of H. pylori may be of limited importance.

Adolescent↗

PubMed1994

An auxin-inducible element in soybean SAUR promoters.

The soybean SAUR (Small Auxin-Up RNA) genes are transcriptionally induced by exogenous auxins within a few minutes after hormone application. This response is specifically induced by auxins primarily in epidermal and cortical cells within elongation zones of hypocotyls and epicotyls. We have previously shown that an 832-bp soybean SAUR promoter/beta-glucuronidase (GUS) reporter gene fusion is responsive to auxin in transgenic tobacco plants (Y. Li, G. Hagen, T.J. Guilfoyle [1991] Plant Cell 3: 1167-1175). Similar results were obtained with an 868-bp SAUR 15A promoter-GUS reporter gene in transgenic tobacco (Y. Li, unpublished results). We have now analyzed a soybean SAUR 15A promoter in transgenic tobacco plants using 5' unidirectional deletions, internal deletions and mutations, and gain-of-function assays with a minimal cauliflower mosaic virus 35S promoter. Our results indicate that the distal upstream element/NdeI restriction endonuclease site element (NDE) (B.A. McClure, G. Hagen, C.S. Brown, M.A. Gee, T.J. Guilfoyle [1989] Plant Cell 1: 229-239) in the SAUR 15A promoter is necessary and sufficient for auxin induction. Our results also show that the 30-bp NDE portion of this element is responsible for most, if not all, of the auxin inducibility of the SAUR 15A promoter. The NDE contains two adjacent sequences, TGTCTC and GGTCCCAT, which have been previously identified as putative auxin-responsive elements. We propose that these elements might function independently or together, possibly with an additional element(s), to confer auxin inducibility to the SAUR promoters.

Base Sequence↗

PubMed1994

Soybean GH3 promoter contains multiple auxin-inducible elements.

The soybean GH3 gene is transcriptionally induced in a wide variety of tissues and organs within minutes after auxin application. To determine the sequence elements that confer auxin inducibility to the GH3 promoter, we used gel mobility shift assays, methylation interference, deletion analysis, linker scanning, site-directed mutagenesis, and gain-of-function analysis with a minimal cauliflower mosaic virus 35S promoter. We identified at least three sequence elements within the GH3 promoter that are auxin inducible and can function independently of one another. Two of these elements are found in a 76-bp fragment, and these consist of two independent 25- and 32-bp auxin-inducible elements. Both of these 25- and 32-bp auxin-inducible elements contain the sequence TGTCTC just upstream of an AATAAG. An additional auxin-inducible element was found upstream of the 76-bp auxin-inducible fragment; this can function independently of the 76-bp fragment. Two TGA-box or Hex-like elements (TGACGTAA and TGACGTGGC) in the promoter, which are strong binding sites for proteins in plant nuclear extracts, may also elevate the level of auxin inducibility of the GH3 promoter. The multiple auxin-inducible elements within the GH3 promoter contribute incrementally to the overall level of auxin induction observed with this promoter.

Agrobacterium tumefaciens↗

PubMed1994

Plasmids bearing hfq and the hns-like gene stpA complement hns mutants in modulating arginine decarboxylase gene expression in Escherichia coli.

Biodegradative arginine decarboxylase is inducible by acid and is derepressed in an hns mutant. Several plasmids from an Escherichia coli library that could complement the hns phenotype were characterized and placed into groups. One group includes plasmids that contain the hns gene and are considered true complements. Another group was found to carry the hfq gene, which encodes the host factor HF-1 for bacteriophage Q beta replication. Plasmids of the third group contain inserts that mapped at 60.2 min on the E. coli chromosome. We identified an open reading frame (stpA) with a deduced amino acid sequence showing more than 60% identity with the sequences of H-NS proteins from several species as being responsible for the hns complementing phenotype of the third group.

Amino Acid Sequence↗

PubMed1994

Effects of rpoA and cysB mutations on acid induction of biodegradative arginine decarboxylase in Escherichia coli.

For Escherichia coli, there have been more and more examples illustrating that the alpha subunit of RNA polymerase is directly involved in the activation of gene transcription by interaction with activator proteins. Because of the vital function of the alpha subunit in cell growth, only a limited number of mutations in its structural gene, rpoA, have been isolated. We obtained a number of these mutants and examined the effects of these mutations on the acid induction of adi and cad gene expression. Several mutations caused a small reduction in adi promoter activity at inducing pH. One mutation, rpoA341, essentially eliminated adi promoter activity, while it had little effect on the cad promoter. During the course of a separate study, we isolated a plasmid that enhanced adi expression. Further characterization of this plasmid showed that it contained cysB, the structural gene for the positive regulator for most cys operon genes. Introduction of a cysB mutation into an adi::lac fusion strain and beta-galactosidase assay studies of the resultant adi::lac cysB mutant established that a wild-type cysB gene was required for efficient acid induction of adi expression. These results suggest that a possible interaction between CysB and the alpha subunit of RNA polymerase is involved in activation of adi transcription.

Acids↗

PubMed1994

Effects of solution osmolality on absorption of select fluid replacement solutions in human duodenojejunum.

These experiments examined relationships between initial osmolality and carbohydrate (CHO) composition of an infused solution and osmolality and water and CHO absorption in a test segment. A triple-lumen tube with a 10-cm mixing segment and a 40-cm test segment was passed into the duodenojejunum. The infusion port was approximately 10 cm beyond the pyloric sphincter. Perfusion solutions were hypotonic (186 mosmol/kg; solution A), isotonic (283 mosmol/kg; solution B), and hypertonic (403 mosmol/kg; solution C). All solutions contained 18 meq Na+ and 3 meq K+. In the mixing segment, osmolality increased 83 mosmol/kg and decreased 90 mosmol/kg for solutions A and C, respectively. Corresponding changes in the test segment were an increase of 60 mosmol/kg and a decrease of 34 mosmol/kg. The osmolality of solution B did not change. In the test segment, mean osmolality and water and total solute fluxes were not significantly different among solutions, but solution C produced 27% greater fluid absorption than did solution A. When net fluid movement from mixing and test segments was determined, solution A produced 17% greater fluid absorption than did solution C. The mean increases in plasma and urine volumes over the 80-min test period were not significantly different. In the test segment, water flux correlated with CHO and Na+ fluxes but not with osmolality. In conclusion, 1) significant differences in solution osmolality were eliminated within the proximal duodenum and 2) perfusing 6% CHO solutions with osmolalities ranging from 186 to 403 mosmol/kg did not produce significant differences in fluid homeostasis (plasma volume) at the end of an 80-min test period.

Body Water↗

PubMed1994

Silica radical-induced DNA damage and lipid peroxidation.

In recent years, more attention has been given to the mechanism of disease induction caused by the surface properties of minerals. In this respect, specific research needs to be focused on the biologic interactions of oxygen radicals generated by mineral particles resulting in cell injury and DNA damage leading to fibrogenesis and carcinogenesis. In this investigation, we used electron spin resonance (ESR) and spin trapping to study oxygen radical generation from aqueous suspensions of freshly fractured crystalline silica. Hydroxyl radical (.OH), superoxide radical (O2.-) and singlet oxygen (1O2) were all detected. Superoxide dismutase (SOD) partially inhibited .OH yield, whereas catalase abolished .OH generation. H2O2 enhanced .OH generation while deferoxamine inhibited it, indicating that .OH is generated via a Haber-Weiss type reaction. These spin trapping measurements provide the first evidence that aqueous suspensions of silica particles generate O2.- and 1O2. Oxygen consumption measurements indicate that freshly fractured silica uses molecular oxygen to generate O2.- and 1O2. Electrophoretic assays of in vitro DNA strand breakages showed that freshly fractured silica induced DNA strand breakage, which was inhibited by catalase and enhanced by H2O2. In an argon atmosphere, DNA damage was suppressed, showing that molecular oxygen is required for the silica-induced DNA damage. Incubation of freshly fractured silica with linoleic acid generated linoleic acid-derived free radicals and caused dose-dependent lipid peroxidation as measured by ESR spin trapping and malondialdehyde formation. SOD, catalase, and sodium benzoate inhibited lipid peroxidation by 49, 52, and 75%, respectively, again showing the role of oxygen radicals in silica-induced lipid peroxidation.(ABSTRACT TRUNCATED AT 250 WORDS)

DNA Damage↗

PubMed1994

Mechanisms of carcinogenesis by crystalline silica in relation to oxygen radicals.

The carcinogenic effects of crystalline silica in rat lungs were extensively demonstrated by many experimental long-term studies, showing a marked predominance for adenocarcinomas originating from alveolar type II cells and associated with areas of pulmonary fibrosis (silicosis). In contrast with its effects in rats, silica did not induce alveolar type II hyperplasia and lung tumors in mice and hamsters, pointing to a critical role for host factors. Using these animal models, we are investigating the role of cytokines and other cellular mediators on the proliferation of alveolar type II cells. Immunohistochemical localization of TGF-beta 1 precursor in alveolar type II cells adjacent to silicotic granulomas was shown to occur in rats, but not in mice, and hamsters, suggesting a pathogenetic role for this regulatory growth factor. Recent investigations in our laboratory on the biologic mechanisms of crystalline silica included determination of anionic sites on crystalline silica surfaces by binding of the cationic dye Janus Green B; binding of crystalline silica to DNA, demonstrated by infrared spectrometry; production of oxygen radicals by crystalline silica in aqueous media; induction of DNA strand breakage and base oxidation in vitro and its potentiation by superoxide dismutase and by hydrogen peroxide; and induction by crystalline silica of neoplastic transformation and chromosomal damage in cells in culture. On the basis of these in vitro studies, we propose that DNA binding to crystalline silica surfaces may be important in silica carcinogenesis by anchoring DNA close to sites of oxygen radical production on the silica surface, so that the oxygen radicals are produced within a few A from their target DNA nucleotides.

Animals↗

PubMed1994

Generation of hydroxyl radical by chromate in biologically relevant systems: role of Cr(V) complexes versus tetraperoxochromate(V).

While Cr(V) species and .OH radicals have been suggested to play significant roles in the mechanism of chromate-related carcinogenesis, controversy still exists regarding the identity of the Cr(V) species and their role in the generation of .OH radicals. Some recent studies have suggested that the primary Cr(V) species involved is the tetraperoxochromate(V) (CrO8(3-)) ion, which produces .OH radical either on decomposition or by reaction with H2O2. The present study utilized ESR and spin trapping techniques to probe this mechanism. The results obtained show that (i) CrO8(3-) is not formed in any significant quantity in the reaction of chromate with biologically relevant reductants such as glutathione, glutathione reductase, NAD(P)H, ascorbate, vitamin B2, etc. (ii) Decomposition of CrO8(3-), or its reaction with H2O2 does not generate any significant amount of .OH radicals. (iii) The major Cr(V) species formed are complexes of Cr(V) with reductant moieties as ligands. (iv) These Cr(V) complexes generate .OH radicals from H2O2 via Fenton-like reaction. The present study thus disagrees with the recently proposed "tetraperoxochromate(V) theory of carcinogenesis from chromate." Instead, it suggests an alternative mechanism, which might be labeled as "the Cr(V)-complexation-Fenton reaction model of carcinogenesis from chromate.

Ascorbic Acid↗

PubMed1994

Enhanced generation of hydroxyl radical and sulfur trioxide anion radical from oxidation of sodium sulfite, nickel(II) sulfite, and nickel subsulfide in the presence of nickel(II) complexes.

Electron spin resonance (ESR) spin trapping was utilized to investigate the generation of free radicals from oxidation of sodium sulfite, nickel(II) sulfite, and nickel subsulfide (Ni3S2) by ambient oxygen or H2O2 at pH 7.4. The spin trap used was 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). Under ambient oxygen, a solution of sodium sulfite alone generated predominantly sulfur trioxide anion radical (.SO3-) due to the autoxidation of sulfite. Addition of nickel(II) chloride [Ni(II)] enhanced the .SO3- yield about 4-fold. Incubation of sulfite with Ni(II) in the presence of chelators such as tetraglycine, histidine, beta-alanyl-3-methyl-L-histidine (anserine), beta--L-histidine (carnosine), gamma-aminobutyryl-L-histidine (homocarnosine), glutathione, and penicillamine did not have any significant effect on that enhancement. In contrast, albumin, and especially glycylglycylhistidine (GlyGlyHis), augmented the enhancing effect of Ni(II) by factors of 1.4 and 4, respectively. Computer simulation analysis of the spin-adduct spectrum and formate scavenging experiment showed that the mixture of sodium sulfite, Ni(II), and GlyGlyHis generated both hydroxyl (.OH) radical and .SO3- radical, in the ratio of approximately 1:2. The free-radical spin adduct intensity reached its saturation level in about 5 min. The yield of the radical adducts could be slightly reduced by deferoxamine and very strongly reduced by diethylenetriaminepentaacetic acid (DTPA). Aqueous suspensions of sparingly soluble nickel(II) sulfite in the presence of air and GlyGlyHis generated surface-located .SO3- and .OH radicals. The same radicals were generated in Ni3S2 suspension in the presence of GlyGlyHis and H2O2, indicating sulfite production by oxidation of the sulfide moiety of this compound.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1994

Operations on aneurysms of the anterior communicating artery not visualized by cerebral angiography--report of four cases.

Four cases of anterior communicating aneurysms are reported with clinical presentations of recurrent intracranial hemorrhage undisclosed in their cerebral angiography. Operative exploration revealed anterior communicating aneurysms in these patients. It is thought possible that these patients harbored aneurysms which failed to exhibit on angiograms due to temporary thrombosis or development of abnormal cerebral vessels. CT scanning was important for diagnosis of these patients.

Adult↗

PubMed1994

[An experimental study of the auditory brainstem implant in guinea pigs].

In order to examine the characteristics of the auditory brainstem implant, an animal model with electrical stimulation of the cochlear nucleus in guinea pigs was created. Middle latency response (MLR) to pulsatile electrical stimulation of the cochlear nucleus was recorded from the auditory cortex with bipolar plantinumiridium electrodes and stereotaxic technique. The electrically and acoustically generated MLRs have a similar morphology though there are little differences in the latencies, wave intervals and dynamic ranges. The results indicated that the central auditory pathways can be activated by means of electrical stimulation. The safety of the brain tissue to the electrical stimulation are also discussed.

Acoustic Stimulation↗

PubMed1994

[The uvulopalatopharyngoplasty operation for obstructive sleep apnea syndrome].

We performed uvulopalatopharyngoplasty operations on 216 patients and conducted 6-month to 2-year follow-ups. 40 patients have had polysomnograms before and after operations. The clinical results showed 50 percent markedly improved, 28 percent somewhat improved, and 22 percent unimproved. The total success rate was 78%. The surgical procedures and polysomnogram methods have been introduced, and the pathogenesis, diagnostic criteria and results were discussed.

Adult↗

PubMed1994

[Comparative study on hemolytic toxicity of trifluoroacetoprimaquine and primaquine in rabbits].

5-trifluoroacetoprimaquine (M8506) exhibited high effect on tissue schizont of P. cynomolgi and low toxicity in mice, rats and dogs as compared with primaquine (PQ) according to our previous studies. In order to determine their hemolytic toxicity, we dosed rabbits with M8506 and PQ at a dose of 40 mg/kg per day for 4 days, respectively. Blood samples were drawn from the ear vein of the rabbits for determining of the following parameters, ie. methemoglobin (metHb), reticulocyte (ret) and Heinzbody (Hbd) on d0 before treatment and on d3, d5, d7, d10, d14 and d21 after treatment. The results showed that after drug administration the levels of metHb, ret and Hbd in PQ group increased on d3-d5, and reached their peak levels on d7-d10, and then declined gradually from d10-d14. The mean percentage concentration of metHb, mean count of ret and Hbd in PQ group on d7 after medication were 22.1 +/- 21.8%, 92.0 +/- 88.0/1,000 RBC and 203.8 +/- 126.7/1,000 RBC, which were significantly higher than those of the control (8.2 +/- 5.3%, 37.5 +/- 16.2/1,000 RBC and 57.4 +/- 45.1/1,000 RBC). In M8506 group, the mean Hbd count (196.3 +/- 123.1/1,000 RBC, on d7 after treatment was also higher than that of the controls, but its mean metHb percentage concentration (10.8 +/- 8.9%) and mean ret count (42.2 +/- 20.3/1,000 RBC) were similar to those of the controls (P > 0.05). The results suggested that the hemolytic toxicity induced by M8506 in rabbits might be similar to or even lower than that induced by PQ.

Anemia, Hemolytic↗

PubMed1994

Laboratory interproximal access efficacy of two compact manual toothbrushes.

The Colgate Precision Compact, soft texture toothbrush and the Oral-B 35 toothbrush were compared using a laboratory device designed to simulate clinical toothbrushing motions and pressures. The toothbrushing time was sixty seconds for each vertical or horizontal toothbrushing sequence, for each of the three brushing weights tested (250, 500 or 750 g). Interproximal access efficacy (IAE) was determined by measuring the maximum width of the brushing stroke on pressure-sensitive paper placed around simulated anterior or posterior teeth. Twenty-four toothbrushes of each design were evaluated for each toothbrushing motion, tooth shape and toothbrushing weight. Using the vertical toothbrushing motion on anterior teeth, IAE means for the Colgate Precision Compact toothbrush were significantly higher (p < 0.001) than the Oral-B 35 toothbrush at 250 and 750 g of brushing weight. With vertical toothbrushing across posterior-shaped teeth, IAE values for the Colgate Precision Compact toothbrush were significantly higher (p < 0.001) than the Oral-B 35 toothbrush at each of the 250, 500 and 750 g brushing weights tested. With horizontal toothbrushing motions, the Colgate Precision Compact toothbrush had significantly higher (p < 0.001) IAE means, compared to the Oral-B 35 toothbrush, on both anterior and posterior tooth shapes and at each of the brushing weights tested. When all factors tested were combined, the total IAE for the Colgate Precision Compact toothbrush was significantly superior (p < 0.001) to the Oral-B 35 toothbrush.

Analysis of Variance↗

PubMed1993

A human gene that shows identity with the gene encoding the angiotensin receptor is located on chromosome 11.

We report the cloning of a gene, intronless in its coding region, which we have named APJ. This gene was cloned using the polymerase chain reaction (PCR), with a set of primers designed on the basis of the conservation that members of G protein-coupled receptors (GPCR) have in their transmembrane (TM) regions. The putative receptor protein, APJ, shares closest identity to the angiotensin receptor (AT1) ranging from 40 to 50% in the hydrophobic TM regions of these receptors. The transcripts for this gene were detected in many regions of the brain. PCR analysis of somatic cell lines found APJ-related sequences to be only present on chromosome 11, and high-resolution mapping by fluorescence in situ hybridization (FISH) sublocalized APJ on band q12.

Amino Acid Sequence↗