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Biomedical subjects

X Pan

Publications and source records attributed to X Pan.

At least 19 recordsLinked to original sources
PubMed2001

Microwave-assisted extraction of tanshinones from Salvia miltiorrhiza bunge with analysis by high-performance liquid chromatography.

A novel microwave-assisted extraction (MAE) method has been developed for the extraction and determination of tanshinones (tanshinone IIA, cryptotanshinone and tanshinone I) from the root of Salvia miltiorrhiza bunge with analysis by HPLC. Various experimental conditions were investigated to optimize the percentage extraction. Under appropriate MAE conditions, such as ethanol concentrations of 95% (v/v), MAE for 2 min, liquid/solid ratio of 10:1 (ml/g), the percentage extraction can reach high in a short time. The percentage extraction (tanshinone IIA: 0.29%; cryptotanshinone: 0.23%; tanshinone I: 0.11%) by MAE was the same or even higher than conventional extraction methods. MAE only needs 2 min, but extraction at room temperature, heat reflux extraction, ultrasonic extraction and Soxhlet extraction need 24 h, 45 min, 75 min and 90 min, respectively. MAE was also available in pilot plant form for larger scale extraction.

Abietanes↗
PubMed2001

Microwave-enhanced dehydration and solvent washing purification of penicillin G sulfoxide.

In the present study, a new microwave-enhanced dehydration and solvent washing purification of penicillin G sulfoxide technique has been developed. The results show that microwave irradiation can dehydrate penicillin G sulfoxide from a water content of 14-26 to below 0.5% in 40-60 min in N2 or air. After washing with ethyl acetate to remove impurities and residual water, the penicillin G sulfoxide can be used to synthesize cephalosporanic acid. The recovery of cephalosporanic acid was equal to and the purity of cephalosporanic acid was higher by 2% than that of the current dehydration technique. FTIR spectroscopy was used to study the process of microwave-enhanced dehydration and solvent washing purification of penicillin G sulfoxide.

Chemistry, Pharmaceutical↗
PubMed2001

Distribution of streptococcal inhibitor of complement variants in pharyngitis and invasive isolates in an epidemic of serotype M1 group A Streptococcus infection.

Streptococcal inhibitor of complement (Sic) is a highly polymorphic extracellular protein made predominantly by serotype M1 group A Streptococcus (GAS). New variants of the Sic protein frequently appear in M1 epidemics as a result of positive natural selection. To gain further understanding of the molecular basis of M1 epidemics, the sic gene was sequenced from 471 pharyngitis and 127 pyogenic and blood isolates recovered from 598 patients living in metropolitan Helsinki, Finland, during a 37-month population-based surveillance study. Most M1 GAS subclones recovered from pyogenic infections and blood were abundantly represented in the pool of subclones causing pharyngitis. Alleles shared among the pharyngitis, pyogenic, and blood samples were identified in throat isolates a mean of 9.8 months before their recovery from pyogenic infections and blood, which indicates that selection of most sic variants occurs on mucosal surfaces. In contrast, no variation was identified in the emm and covR/covS genes.

Alleles↗
PubMed2001

Comments on the filtered backprojection algorithm, range conditions, and the pseudoinverse solution.

The filtered backprojection (FBP) algorithm is widely used in computed tomography for inverting the two-dimensional Radon transform. In this paper, we analyze the processing of an inconsistent data function by the FBP algorithm (in its continuous form). Specifically, we demonstrate that an image reconstructed using the FBP algorithm can be represented as the sum of a pseudoinverse solution and a residual image generated from an inconsistent component of the measured data. This reveals that, when the original data function is in the range of the Radon transform, the image reconstructed using the FBP algorithm corresponds to the pseudoinverse solution. When the data function is inconsistent, we demonstrate that the FBP algorithm makes use of a nonorthogonal projection of the data function to the range of the Radon transform.

Algorithms↗
PubMed2001

Fourier-based approach to interpolation in single-slice helical computed tomography.

It has recently been shown that longitudinal aliasing can be a significant and detrimental presence in reconstructed single-slice helical computed tomography (CT) volumes. This aliasing arises because the directly measured data in helical CT are generally undersampled by a factor of at least 2 in the longitudinal direction and because the exploitation of the redundancy of fanbeam data acquired over 360 degrees to generate additional longitudinal samples does not automatically eliminate the aliasing. In this paper we demonstrate that for pitches near 1 or lower, the redundant fanbeam data, when used properly, can provide sufficient information to satisfy a generalized sampling theorem and thus to eliminate aliasing. We develop and evaluate a Fourier-based algorithm, called 180FT, that accomplishes this. As background we present a second Fourier-based approach, called 360FT, that makes use only of the directly measured data. Both Fourier-based approaches exploit the fast Fourier transform and the Fourier shift theorem to generate from the helical projection data a set of fanbeam sinograms corresponding to equispaced transverse slices. Slice-by-slice reconstruction is then performed by use of two-dimensional fanbeam algorithms. The proposed approaches are compared to their counterparts based on the use of linear interpolation-the 360LI and 180LI approaches. The aliasing suppression property of the 180FT approach is a clear advantage of the approach and represents a step toward the desirable goal of achieving uniform longitudinal resolution properties in reconstructed helical CT volumes.

Algorithms↗
PubMed2001

Transmission dynamics and molecular characterization of Mycobacterium tuberculosis isolates with low copy numbers of IS6110.

Population-based analysis of Mycobacterium tuberculosis transmission in Houston, Tex., over 5 years identified 377 patients infected with an isolate containing one to four copies of IS6110. The isolates were analyzed by spoligotyping and assigned to one of three major genetic groups based on nucleotide polymorphisms in codons katG 463 and gyrA 95. Prospectively obtained patient interviews were reviewed to assess epidemiologic links between apparently clustered patients. A total of 13 groups of isolates with the same IS6110 profile were identified, representing 326 of the 377 patients (86.5%; range 2 to 113 patients). In contrast, 28 groups of isolates containing 334 patients (88.6%) had the same spoligotype (range, 2 to 143 patients). Combination of IS6110 profile and spoligotype data identified 31 clusters with 300 patients (79.6%; range, 2 to 82 patients). All 377 isolates belonged to major genetic group 1 (77 patients) or genetic group 2 (300 patients); no major genetic group 3 isolates were identified. Among the 228 patients interviewed, 33 patients (14.5%) were directly linked to another patient in the same cluster. Possible epidemiologic links were also found among 11 patients. Moreover, many clusters consisted of individuals with the same ethnicity. In conclusion, we confirmed that IS6110 profiling and spoligotyping together provide enhanced molecular discrimination of M. tuberculosis isolates with low copy numbers of IS6110. Identification of epidemiologic links among some of the patients verified that the combination of these two methods reliably indexes tuberculosis transmission.

Bacterial Typing Techniques↗
PubMed2001

Insulin deprivation leads to deficiency of Sp1 transcription factor in H-411E hepatoma cells and in streptozotocin-induced diabetic ketoacidosis in the rat.

Members of the family of Sp transcription factors include Sp1, Sp3, and Sp4 and are important regulators of eukaryotic gene expression. We previously reported that Sp1 mediated stimulation of rat calmodulin I gene expression in response to insulin. To test whether other members of the Sp family are direct targets of insulin action, we compared the levels of Sp1 and Sp3 proteins from nuclear extracts obtained from both insulin-treated and untreated rat hepatoma (H-411E) cells. We demonstrated by Western blot analysis that levels of Sp1 and Sp3 proteins were increased more than 2-fold in the insulin-treated group. Additionally, the up-regulation of both Sp1 and Sp3 transcription factors by insulin was antagonized by tumor necrosis factor-alpha, a known inhibitor of insulin action. Immunohistochemical analysis demonstrated that H-411E cells treated with insulin (10,000 microU/ml) had a marked increase in demonstrable Sp1 in the nucleus compared with cells incubated in insulin-free medium. We extended these in vitro observations to in vivo studies in the streptozotocin-diabetic rat model. We demonstrated in rat liver tissue by both Western blot and immunohistochemical staining with anti-Sp1 antibody that 1) livers of fully diabetic streptozotocin rats have low levels of Sp1 transcription factor; and 2) insulin treatment of the diabetic rat rapidly reversed this process by markedly stimulating accumulation of Sp1 in rat liver. Studies of the signal transduction mechanisms involved in insulin's effect on Sp1 demonstrate a facilitating role for phosphoinositol 3-kinase and an inhibitory role for cyclic nucleotides. In summary, insulin stimulates Sp1 protein, a transcription factor that is shown to regulate calmodulin gene expression and most likely other, as yet untested, genes.

Animals↗
PubMed2001

[Detection of gangliosides in human milk with a high performance thin layer chromatography (HPTLC)].

OBJECTIVES: To determine the ganglioside composition in human milk during lactation, and to evaluate the biological significance. METHODS: The gangliosides extracted from 68 milk samples were examined with a high performance thin layer chromatography (HPTLC). RESULTS: The concentration of total lipid bound sialic acid was 7.8-10.4 microliters/ml. Four gangliosides were found and designated as GM3, GD3, GX1 and GX2, respectively. GX1 and GX2, which had not been described previously, were tentatively assumed to be gangliosides of the c-pathway because they did not react to the GA1 antibody after sialidase treatment. GD3 and GM3 were the major gangliosides in human milk (accounted for 50%-65%). CM3 decreased sharply at eight days postpartum. Both GM3 and GD3 changed significantly during lactation (GM3, r = 0.65, P < 0.01; GD3, r = -0.58, P < 0.01). CONCLUSIONS: Four gangliosides, GM3, GD3, GX1 and GX2 were found in human milk. Both GM3 and GD3 changed significantly during lactation.

Adult↗
PubMed2001

[The effect of EB virus bhrfl gene expressing on the topoisomerase I expression in nasopharyngeal carcinoma cell line].

OBJECTIVE: To study the effect of bhrfl expressing on the topoisomerase I expression in nasopharyngeal carcinoma cell line CNE2. METHODS: bhrfl recombinant expressing vector was constructed and used to transfect the nasopharyngeal carcinoma cell line CNE2. The CNE2 cells were then tested for changes of the topoisomerase I expression and anti-apoptotic ability under the treatment of camptothecin. RESULTS: bhrfl expressing could enhance the topoisomerase I expression in CNE2 cells, that in end reduced cell sensitivity to camptothecin increased cell survival span and decreased apoptotic rate(P < 0.01). CONCLUSION: By increasing the expression of topoisomerase I, bhrfl expressing can enhance the resistance of CNE2 cells to apoptosis induced by camptothecin.

Antineoplastic Agents, Phytogenic↗
PubMed2001

[UV photolysis mechanism of CCl4 and CHCl3 in water].

The photolysis mechanism of CCl4 and CHCl3 in water was studied by using transient absorption spectra. The results showed that aqueous CCl4 was dissociated into CCl3 and Cl radicals by 248 nm laser, and CHCl3 was dissociated into CHCl2 and Cl radicals after adding C6H6. The radicals CCl3 and CHCl2 were able to react with O2 to form CCl3O2 and CHCl2O2 respectively, or to form C2Cl6 and C2H2Cl4 without O2. The rate coefficients of some reactions were obtained.

Carbon Tetrachloride↗
PubMed2001

[The role of beta3-adrenergic receptor Trp/Arg mutation in childhood obesity].

OBJECTIVE: To understand with greater clearness the role of beta3- adrenergic receptor Trp/Arg mutation in childhood obesity. METHODS: One hundred and seventy-seven children, aged 6-12 years, were selected. The genotype was detected by restricted fragment length polymorphism, the children's dietaries were surveyed by a 3-day recalling and recording method. Their height, weight were measured, and the data on their living habits were collected from their parents. RESULTS: The intake of total amount of food and energy of obese children were higher in children with Trp/Trp genotype, but there was no difference between the obese and non-obese children with Trp/Arg genotype. Among children with the Trp/Arg genotype, obese children were less active and did less exercise, they slept more, but there was no difference among children with Trp/Trp genotype. CONCLUSION: The children with beta3-AR Trp/Arg mutation may become obese because of the low energy metabolism; less active and exercise may increase the risk of obesity.

Child↗
PubMed2000

The roles of mutS, sbcCD and recA in the propagation of TGG repeats in Escherichia coli.

A 24 triplet TGG.CCA repeat array shows length- and orientation-dependent propagation when present in the plasmid pUC18. When TGG(24) is present as template for leading-strand synthesis, plasmid recovery is normal in all strains tested. However, when it acts as template for lagging-strand synthesis, plasmid propagation is seriously compromised. Plasmids carrying deletions in the 5' side of this sequence can be isolated and products carrying 15 TGG triplets do not significantly interfere with plasmid propagation. Mutations in sbcCD, mutS and recA significantly improve the recovery of plasmids with TGG(24) on the lagging-strand template. These findings suggest that TGG(24) can fold into a structure that can interfere with DNA replication in vivo but that TGG(15) cannot. Furthermore, since the presence of the MutS and SbcCD proteins are required for propagation interference, it is likely that stabilisation of mismatched base pairs and secondary structure cleavage are implicated. In contrast, there is no correlation of triplet repeat expansion and deletion instability with predicted DNA folding. These results argue for a dissociation of the factors affecting DNA fragility from those affecting trinucleotide repeat expansion-contraction instability.

Adenosine Triphosphatases↗
PubMed2000

Interaction of H2 with Si(001)-(2 x 1): solution of the barrier puzzle.

The sticking probability of H2 on Si(001) is immeasurably small at room temperature, indicating the presence of a large energy barrier to adsorption. Surprisingly, the final state energy distributions of H2 molecules desorbing from Si(001) show no signs of having traversed such a barrier, in apparent contradiction with microscopic reversibility. Here we report experimental and theoretical evidence resolving this long-standing puzzle. Adsorption and desorption proceeding along two distinct, microscopically reversible pathways can explain all observations.

Journal Article↗
PubMed2000

Microwave-assisted extraction of glycyrrhizic acid from licorice root.

In the present study, a microwave-assisted extraction (MAE) technique has been developed for the extraction of glycyrrhizic acid (GA) from licorice root. Various experimental conditions, such as extraction time, different ethanol and ammonia concentration, liquid/solid ratios, pre-leaching time before MAE and material size for the MAE procedure were investigated to optimize the efficiency of the extraction. Under appropriate MAE conditions, such as extraction times of 4-5min, ethanol concentrations of 50-60% (v/v), ammonia concentrations of 1-2% (v/v) and liquid/solid ratios of 10:1(ml/g), the recovery of GA from licorice root with MAE was equivalent with conventional extraction methods. Those methods include extraction at room temperature (ERT), the traditional Soxhlet extraction, heat reflux extraction and ultrasonic extraction. Due to the considerable savings in time and solvent, MAE was more effective than the conventional methods. This novel method is suitable for fast extraction of GA from licorice root.

Journal Article↗
PubMed2000

Pleiotropic resistance to diverse antimalarials in actinomycin D-resistant Plasmodium falciparum.

The development and spread of multidrug-resistant Plasmodium falciparum are major health concerns. The molecular mechanisms of multidrug resistance, including resistance to many quinoline-based antimalarials, are largely unknown. In this study, we report on the isolation and partial characterization of actinomycin D (actD)-resistant P. falciparum (3D7(R)/actD2.3) from a chloroquine-susceptible strain, 3D7. The stepwise selection of an actD-resistant clone (3D7(R)/actD2.3) led to the isolation and cloning of P. falciparum that grew in the presence of 2 ng/mL of actD. The parental isolate (3D7) did not grow in the presence of a 10-fold lower drug concentration (0.2 ng/mL). The latter estimate of parasite growth was determined by direct counting of parasites in infected red blood cells. Estimates of drug resistance levels to actD, using a [(3)H]hypoxanthine uptake and incorporation method, showed a 3-fold difference in the IC(50) between 3D7 and 3D7(R)/actD2.3. Interestingly, 3D7(R)/actD2.3 P. falciparum parasites were less sensitive to several antimalarials (chloroquine, mefloquine, quinidine, and artemisinin) and to the mitochondrial specific dye Rhodamine 123. Drug transport studies using [(3)H]actD showed that 3D7(R)/actD2.3 accumulated less drug than 3D7. Moreover, the accumulation of [(3)H]actD was energy dependent. To determine if Pfmdr1 expression, previously implicated in drug resistance to certain antimalarials, mediated the resistance phenotype of 3D7(R)/actD2.3, Pfmdr1 levels in 3D7 and 3D7(R)/actD2.3 were compared by Southern and northern blot analyses. Our results revealed no differences in Pfmdr1 copy number or mRNA levels between 3D7 and 3D7(R)/actD2.3. Furthermore, comparison of Pfmdr1 sequences between 3D7 and 3D7(R)/actD2.3 showed no differences. In addition, verapamil, which reverses P-glycoprotein-mediated drug resistance in mammalian cells, did not reverse the resistance of 3D7(R)/actD2.3 to actD or chloroquine. Taken together, the findings of this study demonstrated that in vitro selection of P. falciparum for resistance to actD leads to decreased sensitivity to diverse drugs and that this pleiotropic drug resistance is associated with reduced drug accumulation not mediated by Pfmdr1.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2000

NMR structure of activated CheY.

The CheY protein is the response regulator in bacterial chemotaxis. Phosphorylation of a conserved aspartyl residue induces structural changes that convert the protein from an inactive to an active state. The short half-life of the aspartyl-phosphate has precluded detailed structural analysis of the active protein. Persistent activation of Escherichia coli CheY was achieved by complexation with beryllofluoride (BeF(3)(-)) and the structure determined by NMR spectroscopy to a backbone r.m.s.d. of 0.58(+/-0.08) A. Formation of a hydrogen bond between the Thr87 OH group and an active site acceptor, presumably Asp57.BeF(3)(-), stabilizes a coupled rearrangement of highly conserved residues, Thr87 and Tyr106, along with displacement of beta4 and H4, to yield the active state. The coupled rearrangement may be a more general mechanism for activation of receiver domains.

Amino Acid Sequence↗
PubMed2000

Inhibition of xanthine oxidase by liquiritigenin and isoliquiritigenin isolated from Sinofranchetia chinensis.

The methanol extract of the stem of Sinofranchetia inhibited the activity of xanthine oxidase in vitro. Bioassay-guided purification led to the isolation ofliquiritigenin and isoliquiritigenin as the main xanthine oxidase inhibitors. This inhibition of enzyme activity was found to be dose dependent, with an IC50 value of approximately 49.3 microM for liquiritigenin and 55.8 microM for isoliquiritigenin. Lineweaver-Burk transformation of the inhibition data indicated that the inhibition was of a mixed type for both liquiritigenin and isoliquiritigenin. For liquiritigenin, the Ki and K(I) were determined to be 14.0 microM and 151.6 microM, respectively. For isoliquiritigenin, the Ki and K(I) were determined to be 17.4 microM and 81.9 microM, respectively. These results suggest that these natural products could be used to treat conditions where the inhibition of xanthine oxidase is warranted.

Animals↗