Biomedical subjects

J Zhao

Publications and source records attributed to J Zhao.

At least 667 records · Page 37Linked to original sources

PubMed1994

[An experimental study of the mechanism of shock-induced enterogenic infection after long-term standard total parenteral nutrition].

In this study, gnotobiotic rats were subjected to total parenteral nutrition (TPN) and subsequent hemorrhagic shock to study the mechanism of enterogenic infection in these circumstances. (1) Long-term (8-12 days) TPN induced impairment of gut barrier function, evidenced by atrophy of intestinal mucosa, significant decrease in diamine oxidase activity of intestinal mucosa and blood, and marked micro-ecologic imbalance of the intestinal mucosa flora with dominant growth of aerobes and relative decrease in anaerobes. The degree of mucosal damage were proportional to the duration of TPN. (2) In TPN+shock groups, further damage was found in the mucosa, with a large number of invading gram-negative organisms and a significant decrease in DAO activity as compared to that with TPN only groups. These changes were significantly correlated with enhanced bacterial translocation, elevation of LPS and MDA levels in the plasma. These findings suggested that long term TPN impairing gut barrier function, precipitated posttraumatic gut barrier failure. The determination of plasma DAO activity may help in the early diagnosis of gut injury during TPN and after trauma.

Actinomycetales Infections↗

PubMed1993

Use of a regenerable immobilized second antibody to determine azidothymidine in a flow system.

A regenerable immobilized second-antibody reactor was used to measure azidothymidine (AZT) by competitive enzyme immunoassay in a flow system. The immobilized antibody was regenerated 4 times with little loss of immunospecificity. A residual enzymatic activity of about 7% of the total response was obtained with horseradish peroxidase as label. AZT was measured below the nanomolar level by allowing competition to proceed for about 2 min. A limit of detection of 6.57 x 10(-11) +/- 1.56 x 10(-11) M AZT was obtained when the concentration of AZT-peroxidase conjugate was 0.125 ng/mL. This system was used to determined azidothymidine in Retrovir capsule with good results. In replicate measurements, RSDs of 5.51% and 2.44%, n = 6, were obtained at 7.48 x 10(-11) and 3.74 x 10(-9) M AZT, respectively.

Animals↗

PubMed1993

An inhibitor of DNA topoisomerase I from Xenopus laevis ovaries.

A novel, heat-resistant and Pronase-sensitive, inhibitor of eukaryotic DNA topoisomerase I has been purified from Xenopus laevis ovaries. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of the most purified fraction revealed three bands with apparent molecular masses of 25, 28.5, and 33.5 kDa. The 25- and 33.5-kDa peptides recovered from an SDS-PAGE gel inhibited X. laevis DNA topoisomerase I. The purified inhibitor was specific to DNA topoisomerase I and did not inhibit other DNA enzymes tested. The inhibitor blocked the catalytic activity of DNA topoisomerase I by interacting with the enzyme, rather than by competing for binding sites on substrate DNA. Binding of DNA topoisomerase I to substrate DNA was blocked by the inhibitor, as was the cleavage reaction catalyzed by DNA topoisomerase I. Inhibition of DNA topoisomerase I was relieved by divalent cations Ca2+, Mg2+, or Mn2+.

Animals↗

PubMed1993

Demonstration that 1 beta,25-dihydroxyvitamin D3 is an antagonist of the nongenomic but not genomic biological responses and biological profile of the three A-ring diastereomers of 1 alpha,25-dihydroxyvitamin D3.

The steroid hormone 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25-(OH)2D3) generates biological responses via both genomic and nongenomic mechanisms. This article reports the biological profile of four A-ring diastereomers of this secosteroid (results are expressed as percentage of the response of 1 alpha,25-(OH)2D3. The activity of the compounds, 1 alpha,25-(OH)2D3, 1 alpha,25-(OH)2-3-epivitamin D3, 1 beta,25-(OH)2D3, 1 beta,25-(OH)2-3-epivitamin D3, for in vivo intestinal Ca2+ absorption and bone Ca2+ mobilization and in vitro binding to the nuclear receptor (genomic responses) was, respectively, 100, 2.8, < 0.1, and < 0.1% (intestinal Ca2+ absorption); 100, 1.5, < 0.1, and < 0.1% (bone Ca2+ mobilization); 100, 24, 0.2, and 0.8% (receptor binding). In the in vivo nongenomic transcaltachia assay the results were 100, 80, 0, and 20-30%, and in ROS 17/2.8 cells (45Ca2+ uptake through voltage-gated Ca2+ channels) 1 alpha,25-(OH)2D3 had 100% activity and 1 beta,25-(OH)2D3 (the only diastereomer evaluated) had no agonist activity. Keratinocyte proliferation was inhibited in the order 1 alpha,25-(OH)2D3 > 1 alpha,25-(OH)2-3-epivitamin D3 > 1 beta,25-(OH)2D3 > 1 beta,25-(OH)2-3-epivitamin D3. 1 beta,25-(OH)2D3 was a potent antagonist of 1 alpha,25-(OH)2D3-mediated transcaltachia and 45Ca2+ uptake in ROS 17/2.8 cells but was unable to block the genomic 1 alpha,25-(OH)2D3 induction of chick calbindin-D28k (in vivo), induction of MG-63 cell osteocalcin, and HL-60 cell differentiation. These results suggest that analogs of 1 alpha,25-(OH)2D3 may be synthesized which are selective agonists or antagonists of genomic or nongenomic responses in the vitamin D endocrine system.

Animals↗

PubMed1993

Characterization of the [3Fe-4S] and [4Fe-4S] clusters in unbound PsaC mutants C14D and C51D. Midpoint potentials of the single [4Fe-4S] clusters are identical to FA and FB in bound PsaC of photosystem I.

In a previous paper we showed that the C51D mutant of PsaC contains a [3Fe-4S] cluster in the FA site and a [4Fe-4S] cluster in the FB site and that the C14D mutant contains an uncharacterized cluster in the FB site and a [4Fe-4S] cluster in the FA site [Zhao, J. D., Li, N., Warren, P. V., Golbeck, J. H., & Bryant, D. A. (1992) Biochemistry 31, 5093-5099]. In this paper we describe the electrochemical and electron spin resonance properties of the recombinant C14D and C51D holoproteins after in vitro reinsertion of the iron-sulfur clusters. Unbound PsaC shows no significant resonances in the oxidized state, but the unbound C14D and C51D mutant proteins show an intense set of resonances at g approximately 2.02 and 1.99 characteristic of an oxidized [3Fe-4S]1+/0 cluster. The Em' values for the [3Fe-4S]1+/0 clusters in C14D (FB*) and C51D (FA*) are -98 mV, and both represent one-electron transfers. After reduction with dithionite at pH 10.0, wild-type PsaC shows a broad set of resonances resulting from the superposition of FA- and FB- characterized by a low-field peak at an apparent g value of 2.051 and a high-field trough at an apparent g value of 1.898. The FB resonances in C51D were slightly narrower, with a low-field peak at an apparent g value of 2.039 and high-field trough at an apparent g value of 1.908.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial Proteins↗

PubMed1993

Contribution of platelet microparticle formation and granule secretion to the transmembrane migration of phosphatidylserine.

Activation of human platelets by complement proteins, C5b-9, thrombin plus collagen, or a Ca2+ ionophore results in surface exposure of phosphatidylserine (PS), accompanied by the expression of membrane catalytic activity for the tenase (VIIaIXa) and prothrombinase (VaXa) coagulation enzyme complexes. The mechanism underlying this surface exposure of PS upon platelet activation remains unresolved. Using fluorescent derivatives of PS (NBD-PS), we have investigated how the transmembrane migration of PS is related to microvesiculation of the platelet plasma membrane and to fusion of storage granules with the plasma membrane. Gel-filtered platelets were incubated with NBD-PS, allowing 90 +/- 10% of the incorporated NBD-PS to accumulate into the inner leaflet of the plasma membrane. Migration of NBD-PS from the inner leaflet to the plasma membrane surface was monitored by time-based flow cytometry, and correlated with the appearance of platelet microparticles and alpha-granule secretion. Platelet activation by C5b-9 or the Ca2+ ionophore, A23187, increased surface exposure of NBD-PS, due to acceleration of the apparent rate of migration from inner to outer plasma membrane leaflets. The onset of this accelerated migration of NBD-PS to the surface coincided with the onset of plasma membrane vesiculation, and the NBD-PS that partitioned into the membrane of the shed microparticle was also rapidly exposed to the surface (t1/2 < 2 min). In addition to a temporal correlation, microparticle formation and the surface exposure of inner leaflet NBD-PS showed a similar requirement for Ca2+. These results demonstrate that agonist-induced microvesiculation of the platelet plasma membrane is accompanied by accelerated migration of a PS analogue from the inner leaflet to the surface of the shed microparticle membrane, suggesting the mechanism by which induction of platelet microparticle formation exposes catalytic surface for tenase and prothrombinase assembly.

Alkaloids↗

PubMed1993

Detection of liquid injection using an atmospheric pressure ionization radiofrequency plasma source.

An atmospheric pressure rf plasma source which operates in a variety of different buffer gases has been developed as an ionization method for organic samples introduced by liquid injection into atmospheric pressure ionization mass spectrometry (API/MS). The rf source can operate in He at < 1 W of load power at 165 kHz. It can also be sustained in Ar, N2, air, and CO2 at a load power of < 15 W. In most cases studied, the protonated molecule, MH+, is observed with little or no fragmentation even under the relatively high current conditions of the discharge. However, using increasingly higher acceleration voltages between the skimmers in the differentially pumped region between atmospheric pressure and high vacuum, one can induce fragmentation via collision-induced dissociation. This can be assisted in these experiments via the use of a heavy buffer gas. The detection limits achieved for rf/API plasma detection are typically in the low femtomole region for small organic molecules including neurotransmitters, PTH-amino acids, steroids, drugs, pesticides, and explosives. The detection can be performed with quantitation over at least 4 orders of magnitude.

Air Ionization↗

PubMed1993

Interaction between apolipoproteins A-I and A-II and the membrane attack complex of complement. Affinity of the apoproteins for polymeric C9.

We have previously observed enhanced binding of HDL and apolipoproteins A-I and A-II to human endothelial cells exposed to activated complement. Induction of these binding sites required complement activation through C9, suggesting a specific role for the C9 component of the C5b-9 complex. We now report that specific and saturable binding sites for apoA-I and -A-II are expressed by C9 polymers (polyC9), whereas little binding was observed to native monomeric C9. These data suggested an interaction of the apoproteins with a site(s) which is exposed only upon C9 polymerization, and also suggested that binding of the apoproteins to this new site might interfere with assembly of C9 into the polyC9 tubule and insertion into the cell membrane. ApoA-I was found to inhibit zinc-catalyzed polymerization of C9 in a concentration-dependent fashion. Formation of SDS-resistant C9 polymers was completely inhibited at apoA-I or -A-II concentrations > or = 5 microM. ApoA-I also produced a concentration-dependent inhibition of C9 incorporation into C5b-9 complexes on endothelial cells, which was accompanied by a corresponding decrease in SDS-resistant C9 polymers associated with the cell membrane. In summary, the ability of the HDL apoproteins A-I and A-II to interact with an activation-dependent conformer(s) of the C9 component of the C5b-9 complex appears to explain the expression of HDL binding sites on endothelial cells exposed to complement. These apoproteins are also inhibitors of C9 polymerization, which may underlie the protective effect of HDL for blood cells exposed to activated complement.

Amino Acid Sequence↗

PubMed1993

Biologic activity of dihydroxylated 19-nor-(pre)vitamin D3.

Vitamin D3 and its hydroxylated metabolites are normally in thermal equilibrium with their previtamin D isomers. To evaluate the biologic activity of 1 alpha, 25-dihydroxyprevitamin D3, we synthesized 19-nor analogs of 1 alpha, 25-dihydroxy(pre)vitamin D3 because the absence of a C19 methylene group prevents the isomerization of these analogs. The affinity of 1 alpha, 25-(OH)2D3-19-nor-D3 for the intestinal vitamin D receptor and plasma vitamin D binding protein was mildly decreased [30 and 20% of the affinity of 1 alpha, 25-(OH)2D3, respectively], but the affinity of 1 alpha, 25-(OH)2-19-nor-previtamin D3 was only 1 and 6% of that of 1 alpha, 25-(OH)2D3 for the receptor and DBP, respectively. The in vitro effects on human promyeloid leukemia (HL-60 cell) differentiation and osteocalcin secretion by human osteosarcoma (MG-63) cells by 1 alpha, 25-(OH)2-19-nor-D3 were nearly identical to those of 1 alpha-25-(OH)2D3, whereas 19-nor-previtamin D3 showed poor activity (2%). The in vivo calcemic effects of both analogs, studied in vitamin D-deficient chicks treated for 10 consecutive days with the analogs, showed no activity of the previtamin D3 analog and reduced calcemic effects (< or = 10%) of 1 alpha, 25-(OH)2-19-nor-D3. We conclude that the previtamin D form of 1 alpha, 25-(OH)2D3 has lost most of its biologic activity in vitro and in vivo.

Animals↗

PubMed1993

Relationship of levels and kinetics of H-ras expression to transformed phenotype and loss of TGF-beta 1-mediated growth regulation in intestinal epithelial cells.

Immortalized, nontumorigenic rat intestinal epithelial cells (IEC-18) can be transformed to tumorigenicity by expression of an activated human H-ras gene. Here we describe the characteristics of an IEC-18 cell line in which the activated human H-ras gene has been introduced under the control of the steroid-sensitive promoter of the mouse mammary tumor virus long-terminal repeat. The clonal cell line (IEC-18 C125) is phenotypically normal in the absence of the transcription inducer, dexamethasone, and transformed when treated with high levels of inducer. Transformed morphology and growth characteristics are dependent on levels of H-ras expression. IEC-18 C125 cells have been used to demonstrate a general relationship (dose and kinetic) between H-ras expression and loss of TGF-beta 1-mediated growth regulation. This effect occurs concomitantly with a ras-dependent change in the profile of TGF-beta 1 binding proteins.

Animals↗

PubMed1993

Developmental studies of dystrophin-positive fibers in mdx, and DRP localization.

Dystrophin positive fibers (DPFs) were observed in about 1% of the total muscle fibers in 1-year-old mice. Some of these fibers were found to have positive staining with all six antibodies, while others showed a negative reaction with specific antibodies. These results suggest that the most likely mechanism giving rise to these DPFs is a second site mutation which prepares in-frame deletion. A study of the frequency of DPF during development showed single and scattered DPFs in younger mice, which gradually increased in number and began to form small groups with age. DRP was observed constantly on the neuromuscular junctions in both control and mdx muscle, and surface membrane of immature muscle fibers such as regenerating fibers in mdx and newborn muscle during 2 weeks of age in control and mdx.

Aging↗

PubMed1993

High-performance liquid chromatography to assess the effect of serum storage conditions on the detection of hepatitis C virus by the polymerase chain reaction.

The effect of various serum storage conditions on the detection of hepatitis C virus (HCV) by the polymerase chain reaction (PCR) was assessed. 50 microliters aliquots of serum from four HCV PCR positive patients were subjected, in triplicate, to: (a) storage at -20 degrees C for 1, 5, 10 days; (b) storage at room temperature (RT) for 1, 2, 7 days; (c) 1, 3, 5, and 10 successive freeze-thaw cycles; (d) incubation at 37 degrees C, and 56 degrees C for 1, 3, 24 h; and (e) storage in guanidium-thiocyanate extraction buffer at RT, and 4 degrees C for 1, 5, 10 days. PCR products were detected by agarose gel electrophoresis (AGE) and quantitatively by high-performance liquid chromatography (HPLC). Only storage in extraction buffer at RT for 5-10 days and incubation at 56 degrees C for 24 h appeared to result in a loss of > or = 50% of detectable HCV PCR product. Up to 10 successive freeze-thaw cycles, storage at -20 degrees C for up to 10 days or at RT for up to 7 days, storage in extraction buffer at RT for 1 day or at 4 degrees C for up to 10 days, and incubation at 37 degrees C for up to 24 h resulted in minimal PCR signal loss. HPLC was a reproducible method of detecting and quantitating HCV PCR products, and was more sensitive than AGE.

Blood Preservation↗

PubMed1993

Locomotion of aged rats: relationship to neurochemical but not morphological changes in nigrostriatal dopaminergic neurons.

Spontaneous locomotion and motor coordination was evaluated in young (5-6 month old) and aged (24-25 month old) rats. Animals were tested for spontaneous locomotor activity in Digiscan Animal Activity Monitors during the nocturnal cycle. Aged animals exhibited a significant hypoactivity compared to their young counterparts. Evaluation of the time course of activity revealed that the young animals had a cyclical pattern of activity during the 12-hour testing period with clear peaks at 2-4 hours after the initiation of testing and at 8- to 10-hour intervals thereafter. In contrast, the aged animals exhibited a blunted initial activity peak. During the remainder of the test period the aged animals activity was stable with no further peaks in activity. Compared to the young animals the aged animals also (a) remained suspended from a horizontal wire for less time, (b) were unable to descend a wooden pole covered with wire mesh in a coordinated manner, (c) fell more rapidly from a rotating rod and (d) were unable to maintain their balance on a series of wooden beams with either a square or rounded top of varying widths. Histological analysis demonstrated that there was no reduction in the number, area, or length of tyrosine hydroxylase-immunoreactive neurons within the A8, A9, or A10 region of the aged animals. Neurochemical analysis revealed that while DA and HVA levels were not decreased in the aged rats, DOPAC levels, as well as the ratios of DA/DOPAC and DA/HVA, were decreased. These results indicate that neurochemical but not morphological changes within the nigrostriatal dopaminergic system underlie the deficits in motor behavior observed in aged rats.

Aging↗

PubMed1993

A carrageenan hydrogel stabilized colloidal gold multi-enzyme biosensor electrode utilizing immobilized horseradish peroxidase and cholesterol oxidase/cholesterol esterase to detect cholesterol in serum and whole blood.

The preparation of two immobilized enzyme electrodes is described. One electrode contains horseradish peroxidase absorbed to colloidal gold and deposited on a glassy carbon electrode along with cholesterol oxidase entrapped in a carrageenan hydrogel. The second electrode also includes cholesterol esterase entrapped in the carrageenan. The incorporation of ferrocene or ferrocenecarboxylic acid mediator is brought about by either evaporation on the glassy carbon electrode or, in the latter case, entrapment in the carrageenan hydrogel. Amperometric signal generation results from the HRP catalyzed turnover of H2O2, a secondary product of the cholesterol oxidase catalyzed oxidation of cholesterol. Use of these enzyme electrodes makes cholesterol detection possible in human serum, low density lipoprotein, and whole blood.

Biosensing Techniques↗

PubMed1993

Arteriovenous crossing patterns in branch retinal vein occlusion. The Eye Disease Case-Control Study Group.

PURPOSE: The study was designed to evaluate the relative anatomic position of the crossing vessels at the site of occlusion in eyes with branch retinal vein occlusion (BRVO). METHODS: Fundus photographs of 106 eyes (104 patients) with recent BRVO from the Eye Disease Case-Control Study were used to examine the relative position of artery and vein at occluded crossings. Three separate comparison groups were formed by identifying corresponding arteriovenous crossings for each occluded crossing in: (1) the ipsilateral but opposite vessel arcade within eyes affected by BRVO; (2) the same quadrant in unaffected eyes of BRVO patients; and (3) the same quadrant in eyes of patients without BRVO, matched by age, sex, and race with the BRVO patients. RESULTS: The site of obstruction of the branch vein was an arteriovenous crossing in all affected eyes. In 99% of eyes with BRVO, the artery was located anterior to the vein at the obstructed site. In the three comparison groups, the artery was anterior to the vein in 62%, 61%, and 54% of the crossings, respectively, yielding statistically significant differences for each group of control crossings compared with BRVO crossings (P < 0.001). CONCLUSION: Finding the vein to be consistently between the more rigid artery and the retina at almost all arteriovenous crossings affected by BRVO suggests a possible role for mechanical obstruction in the pathogenesis of BRVO.

Adult↗

PubMed1993

Cloning and characterization of the psaE gene of the cyanobacterium Synechococcus sp. PCC 7002: characterization of a psaE mutant and overproduction of the protein in Escherichia coli.

The psaE gene, encoding a 7.5 kDa peripheral protein of the photosystem I complex, has been cloned and characterized from the cyanobacterium Synechococcus sp. PCC 7002. The gene is transcribed as an abundant monocistronic transcript of approximately 325 nt. The PsaE protein has been overproduced in Escherichia coli, purified to homogeneity, and used to raise polyclonal antibodies. Mutant strains, in which the psaE gene was insertionally inactivated by interposon mutagenesis, were constructed and characterized. Although the PS I complexes of these strains were similar to those of the wild type, the strains grew more slowly under conditions which favour cyclic electron transport and could not grow at all under photoheterotrophic conditions. The results suggest that PsaE plays a role in cyclic electron transport in cyanobacteria.

Amino Acid Sequence↗

PubMed1993

Isolation and characterization of the ndhF gene of Synechococcus sp. strain PCC 7002 and initial characterization of an interposon mutant.

The ndhF gene of the unicellular marine cyanobacterium Synechococcus sp. strain PCC 7002 was cloned and characterized. NdhF is a subunit of the type 1, multisubunit NADH:plastoquinone oxidoreductase (NADH dehydrogenase). The nucleotide sequence of the gene predicts an extremely hydrophobic protein of 664 amino acids with a calculated mass of 72.9 kDa. The ndhF gene was shown to be single copy and transcribed into a monocistronic mRNA of 2,300 nucleotides. An ndhF null mutation was successfully constructed by interposon mutagenesis, demonstrating that NdhF is not required for cell viability under photoautotrophic growth conditions. The mutant strain exhibited a negligible rate of oxygen uptake in the dark, but its photosynthetic properties (oxygen evolution, chlorophyll/P700 ratio, and chlorophyll/P680 ratio) were generally similar to those of the wild type. Although the ndhF mutant strain grew as rapidly as the wild-type strain at high light intensity, the mutant grew more slowly than the wild type at lower light intensities and did not grow at all under photoheterotrophic conditions. The roles of the NADH:plastoquinone oxidoreductase in photosynthetic and respiratory electron transport are discussed.

Amino Acid Sequence↗

PubMed1993

Smooth muscle myosin regulation by serum and cell density in cultured rat lung connective tissue cells.

RNA and protein analyses were used to detect expression of SM1 and SM2 smooth muscle myosin heavy chain (MHC) in cultured adult rat lung connective tissue cells (RL-90). Smooth muscle MHC mRNA expression in confluent cells grown in 10% serum was approximately 50% of the level in adult stomach. Similar results were obtained in cells cultured at low density (25% confluency) in 1% serum. However, in low-density cultures transferred to 10% serum for 24 h, the level of MHC mRNA decreased to approximately 20% of that in adult stomach. Smooth muscle alpha-actin showed a pattern of expression similar to that for smooth muscle MHC. Expression of nonmuscle MHC-A mRNA was higher in all culture conditions compared to stomach. MHC-A mRNA expression was less in low-density cultures in low serum and increased when low-density cultures were transferred to 10% serum for 24 h. MHC-B mRNA expression was less in low- vs. high-density cultures. In contrast to MHC-A, however, MHC-B mRNA expression in low-density cultures was higher in low serum. Immunofluorescence and immunoblotting with SM1-specific antibody demonstrated the presence of the SM1 protein isoform as well as reactivity to a protein band migrating slightly faster than SM2. These results demonstrate that cultured rat lung connective tissue cells express smooth muscle MHC and that expression is modulated by culture conditions.

Amino Acid Sequence↗