Biomedical subjects

M J Li

Publications and source records attributed to M J Li.

At least 19 recordsLinked to original sources

PubMed2001

The genome of the natural genetic engineer Agrobacterium tumefaciens C58.

The 5.67-megabase genome of the plant pathogen Agrobacterium tumefaciens C58 consists of a circular chromosome, a linear chromosome, and two plasmids. Extensive orthology and nucleotide colinearity between the genomes of A. tumefaciens and the plant symbiont Sinorhizobium meliloti suggest a recent evolutionary divergence. Their similarities include metabolic, transport, and regulatory systems that promote survival in the highly competitive rhizosphere; differences are apparent in their genome structure and virulence gene complement. Availability of the A. tumefaciens sequence will facilitate investigations into the molecular basis of pathogenesis and the evolutionary divergence of pathogenic and symbiotic lifestyles.

Agrobacterium tumefaciens↗

PubMed2001

Precision and reproducibility of temperature response of a thermo-responsive membrane embedded by binary liquid crystals for drug delivery.

A thermo-responsive membrane embedding with the binary mixture of 36% cholesteryl oleyl carbonate (COC) and 64% cholesteryl nonanoate (CN) was successfully developed to achieve a rate-controlled and time-controlled drug release in response to the skin temperature (i.e., 32 degrees C) of the human body. The thermophysical properties of this binary mixture were determined by differential scanning calorimetry (DSC) and a microscopic Fourier transform infrared (FT-IR) spectrometer equipped with a thermal analyzer (FT-IR/DSC microscopic system). The phase transition temperatures of this binary mixture at 35.1 and 64.0 degrees C were clearly evidenced by both analytical methods. The temperature response of this binary mixture of COC and CN with 36%:64% ratio were also investigated for eight cycles by the isothermal FT-IR/DSC microscopic system to continuously and repeatedly alter the temperature cycle between 25 and 37 degrees C. The results show that this binary mixture revealed a good temperature response in precision, sensitivity, obedience and reproducibility. The temperature-sensitive on-off pulsatile function of drug penetration through this thermo-responsive membrane was investigated. The switching mechanism of this thermo-responsive membrane was also proposed. The present result strongly indicates that the binary COC-CN mixture-embedded membrane can be used to deliver the drug in a pulsatile fashion with respect to skin temperature.

Cholesterol Esters↗

PubMed2001

Micronized ethylcellulose used for designing a directly compressed time-controlled disintegration tablet.

Ethylcellulose (EC) of varying particle sizes has been used as an outer coating layer to design a novel dry-coated tablet with time-controlled drug release. This dry-coated tablet, containing a core tablet of sodium diclofenac and an outer coating layer of EC, was prepared by direct compression. The drug release from dry-coated tablet exhibited an initial lag period that was dependent on the particle size of the EC powder, followed by a stage of rapid drug release. The smaller the EC particle size used the longer the lag time obtained, suggesting the particle size of EC powder could modulate the timing of drug release from such a dry-coated tablet. The period of the lag time for sodium diclofenac released from dry-coated tablets was correlated with the penetration distance of the solvent into dry-coated tablet by an in vitro dye penetration study. The densest packing of EC powders appeared on the upper and lower surfaces of dry-coated tablet after compression, resulting in a tight structure yielding a slower penetration of the solvent. Whereas loose packing of EC powders occurred in the middle of the lateral surface of dry-coated tablet, this loosely packed surface readily allowed solvent penetration and that finally caused the splitting of tablet shell into two halves in the dissolution medium. The results suggest that these dry-coated tablets prepared with different particle sizes of EC powder as an outer coating layer might offer a desirable release profile for drug delivery at the predetermined times and/or sites.

Cellulose↗

PubMed2001

Compression forces and amount of outer coating layer affecting the time-controlled disintegration of the compression-coated tablets prepared by direct compression with micronized ethylcellulose.

The influence of compression force to inner core tablet or to outer coating layer of the compression-coated tablet on the function of time-controlled disintegration was investigated. The inner core tablet was directly compacted by sodium diclofenac (model drug) and ethylcellulose (EC) with 4.6-microm particle size was used as an outer coating layer. The immersion time of the compression-coated tablet previously soaked in pH 1.2 solution to simulate the residence time of the tablet in the GI tract affecting the dissolution behavior of the compression-coated tablet was also investigated. The effect of the amount of the outer coating layer used on the drug release was examined. The results indicate that sodium diclofenac released from these compression-coated tablets exhibited a longer lag of a period about 16.3 h in both distilled water and pH 6.8 buffer solution, followed by a different drug release behavior. The lag time was independent of the pH of dissolution medium, and the immersion time in pH 1.2 solution. After that lag time, the outer shell of the compression-coated tablets broke into two halves to make a rapid drug release. However, the drug release behavior of the soaked tablet in pH 6.8 buffer solution was dependent on the immersion time. The compression force < 200 kg/cm(2) to the inner core tablet influenced the release behavior of drug less, but > 200 kg/cm(2) might delay the lag time. The lag time of the compression-coated tablets was linearly correlated with the compression force to the outer coating layer (r = 0.9896). We also found that the more the amount of outer coating layer added, the longer the lag time obtained. The study demonstrates that the time-controlled disintegration of the compression-coated tablet was effectively controlled by the compression force applied and the amount of outer coating layer added.

Cellulose↗

PubMed2001

Beam hardening correction for computed tomography images using a postreconstruction method and equivalent tissue concept.

A postreconstruction method for correcting the beam-hardening artifacts in computed tomography (CT) images is proposed. This method does not require x-ray spectrum measurement. The authors assumed that a pixel in a CT image can be decomposed into equivalent tissue percentages, depending on its CT number. A scout view of the step wedges made of these equivalent tissues was performed to obtain a beam-hardening correction curve for each tissue. Projecting through the CT image from various angles generated simulated projection data and the total thickness of each tissue along the ray. The correction term was estimated using the tissue thickness traveled by the ray, and this term was then added to its corresponding projection data. A second reconstruction using the corrected projection data yielded a beam-hardening corrected image. The preliminary results show that this method reduces beam hardening artifacts by 14% for aluminum and increased the object contrast by 18% near the aluminum-water boundary. The variation in CT numbers at different locations were reduced, and the aluminum CT number also was restored.

Artifacts↗

PubMed2001

Use of dexamethasone on the prophylaxis of nausea and vomiting after tympanomastoid surgery.

OBJECTIVE: The aim of this study was to evaluate the prophylactic effect of dexamethasone on postoperative nausea and vomiting (PONV) in patients undergoing tympanomastoid surgery. STUDY DESIGN: Eighty patients (n = 40 in each of two groups) undergoing tympanomastoid surgery under general anesthesia were enrolled in this randomized, double-blind, placebo-controlled study. METHODS: After tracheal intubation, group 1 received 10 mg dexamethasone intravenously, whereas group 2 received saline intravenously. Several parameters concerning with the occurrence of PONV were evaluated. RESULTS: We found that dexamethasone reduced the total incidence of nausea and vomiting by 45%, with a 95% confidence interval of 26% to 64% (P <.001). Furthermore, dexamethasone reduced the incidence of vomiting episodes >4 times and the incidence of patients requiring rescue antiemetics (P <.05). CONCLUSION: Dexamethasone at a dosage of 10 mg administered intravenously is effective in preventing PONV in patients undergoing tympanomastoid surgery.

Adult↗

PubMed2001

Continuous UVB irradiation to modify the biophysical properties and protein conformation of rat skin.

In order to determine the continuous irradiation effects of UVB on the skin of live Sprague Dawley (SD) rats, the changes in biophysical properties and protein conformation of the skin were studied. The continuous UVB irradiation affecting the water content, skin color and protein structure of the rat skin was investigated by using a skin surface hygrometer, a Chroma meter and an attenuated total reflection (ATR)/Fourier transform infrared (FT-IR) spectroscopy. Test areas on the dorsal skin were continuously irradiated with 600 +/- 10 microW/cm2 UVB for 56 h. Part of the dorsal skin was covered with a bandage as a non-irradiated control. The results indicated that the water content of the irradiated skin decreased with UVB irradiation, but the non-irradiated control skin exhibited a higher level of water content. The decrease in the skin's water-binding capacity from cracks induced by continuous UVB irradiation, and the occlusive dressing of the non-irradiated skin to prevent water loss and form full hydration might be responsible for the results. The decrease of L* value and the increase in a*, b* and delta E values in the skin color parameters with UVB irradiation indicates an incremental darkening of the skin and a marked increase in erythema. However, there was no significant change in skin color for the non-irradiated control skin. A slight modification of the protein secondary structure in the skin after continuous UVB irradiation was also evidenced by transforming the alpha-helix structure into a beta-sheet structure after long-term continuous UVB irradiation. Continuous UVB irradiation of SD rat skin may decrease the skin's water-binding capacity, cause darkening, increase erythema and modify the protein secondary structure of the skin.

Animals↗

PubMed2000

Endoglin expression as a measure of microvessel density in cervical cancer.

OBJECTIVE: To evaluate endoglin, a membrane protein and member of the transforming growth factor beta-1 receptor complex, as an endothelial marker of angiogenesis in cervical cancer tissues. METHODS: Tumor tissue was collected from 31 surgically treated stage IB nonbulky (under 5 cm) cervical cancer subjects, and samples were fixed in formalin and embedded in paraffin. Endoglin was stained on 5-microm slide sections by the DAKO Catalyzed Signal Amplification method (DAKO Corporation, Carpinteria, CA). Factor VIII was stained by standard immunohistochemistry. Positively stained microvessels were counted in "hot spots" at 200x magnification. Clinical data were correlated with vessel counts by Spearman correlation. Mean differences in counts were tested using paired t tests. RESULTS: This staining method for endoglin identified significantly more vessels than the factor VIII method (mean 92 +/- 45 versus 33 +/- 16, P <. 001). Endoglin and factor VIII counts correlated significantly with deep stromal invasion (Spearman rho 0.466 and 0.522, respectively, P <.05); however, only endoglin counts correlated significantly with lymph node metastases (rho =.495, P <.01). CONCLUSION: Endoglin is stimulated in tumor angiogenesis and might be relatively more specific than commonly used endothelial markers. The endoglin system was more sensitive for staining capillaries in neoplastic cervical tissue, better predicted lymph node metastases, and should be widely applicable for the study of other tumors.

Antigens, CD↗

PubMed2000

Differentiation of hair growth cycle from scalp hair roots for the diagnosis of glucose-6-phosphate dehydrogenase deficiency in neonates.

Hair analysis can be used as a screening tool in the diagnosis of genetic diseases. The scalp hair roots of 67 normal neonates and 39 neonates with glucose-6-phosphate dehydrogenase (G6PD) deficiency were analysed using Fourier transform infrared (FT-IR) microspectroscopy to differentiate the stages of the hair growth cycle and to diagnose the genetic disorder on the basis of spectral differences. We have demonstrated that FT-IR microspectroscopy is a rapid and effective noninvasive diagnostic method to differentiate scalp hair roots of normal neonates into the anagen, catagen or telogen phases of the hair growth cycle, using IR spectral differences within the 3000-2800 cm(-1) region and the IR peak area ratio of 2854 cm(-1)/2873 cm(-1) or 1084 cm(-1)/amide II band (p<0.001). Moreover, G6PD-deficient neonates could be accurately diagnosed from telogen phase hair roots owing to significant differences in IR peak area ratios of 2854 cm(-1)/2873(-1) or 1084 cm(-1)/amide II band compared to normal values in healthy neonates. The result suggests that the application of FT-IR microspectroscopy may be capable not only of differentiating the hair growth cycle into anagen, categen or telogen phases but also of detecting G6PD deficiency. Hair root analysis promises to be a useful complement to serum and urine analysis in the diagnosis of genetic diseases.

Female↗

PubMed2000

Effect of skin-penetrating enhancers on the thermophysical properties of cholesteryl oleyl carbonate embedded in a thermo-responsive membrane.

The effect of skin-penetrating enhancers such as propylene glycol (PG), Azone and ethanol on the thermophysical properties of cholesteryl oleyl carbonate (COC) was investigated using differential scanning colorimetry (DSC) and microscopic Fourier-transform infrared (FT-IR) spectroscopy. The results indicate that PG did not influence the DSC thermograms and IR spectra of COC in the different ratios of COC and PG mixture; whereas Azone interacted with COC not only to lower the semectic-cholesteric phase transition temperature of COC but also to induce a new IR spectral peak at 1653 cm(-1) which shifted from the carbonyl stretching band (1636 cm(-1)) of Azone. Ethanol did not interact with COC, but it influenced the IR spectral peak intensity of COC at 1253 cm(-1). The peak intensity at 1253 cm(-1) gradually rose with the time of ethanol evaporation and was similar to that of the temperature effect. The solubility parameter was also used to explain the miscibility and interaction between COC and PG, Azone or ethanol.

Journal Article↗

PubMed1999

Activation and targeting of immunoglobulin switch recombination by activities induced by EBV infection.

EBV is strongly associated with Burkitt's lymphoma, a B cell malignancy. In certain types of Burkitt's lymphoma, the c-myc gene has undergone translocation to the S regions associated with heavy chain switch recombination. It has not been established whether EBV infection induces recombination activities, which in turn promote translocation of c-myc, or whether translocation precedes viral infection and provides a growth advantage that is further enhanced by factors encoded or induced by the virus. To distinguish between these possibilities, we have compared the level of switch recombination activities in the EBV-negative lymphoma, BJAB, and in its EBV-infected derivative, BJAB-B1, in experiments that assayed recombination of an extrachromosomal switch substrate during transient transfection. We have found that BJAB-B1 and other EBV-positive B cell lines supported high levels of recombination of switch substrates, to produce junctions like those found in products of chromosomal switch recombination. In contrast, BJAB did not support comparable levels of switch substrate recombination. In EBV-positive B cell lines, the ability to support switch substrate recombination correlated with levels of LR1, a B cell-specific factor which is a transcriptional regulator of c-myc and which also appears to function in switch recombination. Our observations support the hypothesis that EBV infection can induce activities that affect switch recombination and thus contribute to the translocations of c-myc to the S regions that characterize certain classes of lymphomas.

Adjuvants, Immunologic↗

PubMed1999

Characterization of differentially expressed genes in purified Drosophila follicle cells: toward a general strategy for cell type-specific developmental analysis.

Axis formation in Drosophila depends on correct patterning of the follicular epithelium and on signaling between the germ line and soma during oogenesis. We describe a method for identifying genes expressed in the follicle cells with potential roles in axis formation. Follicle cells are purified from whole ovaries by enzymatic digestion, filtration, and fluorescence-activated cell sorting (FACS). Two strategies are used to obtain complementary cell groups. In the first strategy, spatially restricted subpopulations are marked for FACS selection using a green fluorescent protein (GFP) reporter. In the second, cells are purified from animals mutant for the epidermal growth factor receptor ligand gurken (grk) and from their wild-type siblings. cDNA from these samples of spatially restricted or genetically mutant follicle cells is used in differential expression screens employing PCR-based differential display or hybridization to a cDNA microarray. Positives are confirmed by in situ hybridization to whole mounts. These methods are found to be capable of identifying both spatially restricted and grk-dependent transcripts. Results from our pilot screens include (i) the identification of a homologue of the immunophilin FKBP-12 with dorsal anterior expression in egg chambers, (ii) the discovery that the ecdysone-inducible nuclear hormone receptor gene E78 is regulated by grk during oogenesis and is required for proper dorsal appendage formation, and (iii) the identification of a Drosophila homologue of the human SET-binding factor gene SBF1 with elevated transcription in grk mutant egg chambers.

Animals↗

PubMed1999

pH-dependent secondary conformation of bovine lens alpha-crystallin: ATR infrared spectroscopic study with second-derivative analysis.

BACKGROUND: In order to simulate the usage of different formulations of ophthalmic solution, the protein conformational changes of lens alpha-crystallin in buffer solutions of different pH were investigated. METHODS: The secondary structure of bovine lens alpha-crystallin in different Mcllvaine buffer solutions (pH 2.2, 4.0, 6.0, 7.2 and 8.0) was determined by attenuated total reflection (ATR)/Fourier transform infrared (FT-IR) spectrometry with second-derivative technique. The turbidity of alpha-crystallin in different buffer solutions was observed. RESULTS AND CONCLUSION: The results indicate that alpha-crystallin exists mainly in beta-sheet structure at 1627-1637 cm-1. The conformational components of alpha-crystallin may be closely similar in pH 7.2 buffer solution and in pH 8.0 buffer solution. Once alpha-crystallin dissolved in pH 6.0 and 4.0 buffer solution, the appearance of a component at 1618 or 1620 cm-1, associated with the presence of intermolecular beta-sheet structure or beta-turn structure or amino acid side chains, implied the denaturation of alpha-crystallin, which was even more marked in pH 4.0 buffer solution. Due to the effect of dissociation and stability of alpha-crystallin in pH 2.2 buffer solution, the secondary structure of the intact alpha-crystallin was difficult to evaluate. This study demonstrates that different pH can vary secondary conformational structure of alpha-crystallin, particularly if the pH is below 6.0. This suggests that the secondary structure of alpha-crystallin in buffer solution exhibits pH-dependent characteristics.

Acids↗

PubMed1999

UV-B-induced secondary conformational changes in lens alpha-crystallin.

The changes in turbidity and protein secondary structure of alpha-crystallin after a 72 h UV-B (302 nm) irradiation in aqueous solution have been determined by UV spectrophotometry and Fourier transform infrared (FT-IR) microspectroscopy with reflection mode. The relative transmission of alpha-crystallin aqueous solution gradually decreases with the exposure time, indicating that the transparent alpha-crystallin aqueous solution becomes opaque with prolonged UV-B irradiation. The turbidity induced by UV-B shows first-order kinetics due to the photo-induced aggregation. The modification of the secondary structure of the alpha-crystallin molecule in aqueous solution caused by this aggregation might enhance the alpha-helix and beta-turn structures from 8.14 to 14.92% and from 24.46 to 35.54%, respectively; reduce the beta-sheet structure from 60.20% to 43.77%; and leave the random coil structure almost unaltered. The secondary conformation of alpha-crystallin changes gradually but evidently with its increase of turbidity during UV-B exposure.

Animals↗

PubMed1999

pH-dependent secondary conformation of the peptide hormone leptin in different buffer solutions.

The secondary structure of leptin in each different pH buffer solution (pH 5.35, 6.75, 7.58 and 8.45) was first determined by attenuated total reflection (ATR)/Fourier transform infrared (FT-IR) spectrometer with second-derivative, Fourier self-deconvolution and band curve-fitting methods to quantitatively estimate the secondary structure of leptin. The results indicate that pH induced more stretching vibration of CH2 and bending vibration of C-H and/or symmetric stretching of carboxylate of leptin structure in higher pH buffer solution than in lower pH buffer solution. Moreover, the band area of amide I for leptin in the higher pH buffer solution markedly enlarged, suggesting the amide I contour of leptin was very sensitive to pH to alter the secondary conformation of leptin structure. The structural component and composition of amide I band for leptin in both pH 6.75 and pH 7.58 buffer solutions were similar and had 50-52% helical structure including alpha-helix at 1654 cm-1 and 3(10)-helical structure at 1659-1667 cm-1 and 1640 cm-1. Although the secondary structure of leptin in pH 5.35 and 8.45 buffer solutions were also similar, a different structural information was obtained.

Animals↗

PubMed1999

Use of novel plasmid constructs to demonstrate fludarabine triphosphate inhibition of nucleotide excision repair of a site-specific 1,2-d(GpG) intrastrand cisplatin adduct.

We previously showed that fludarabine triphosphate (F-ara-ATP) acts as a potent inhibitor of nucleotide excision repair (NER). To determine how F-ara-ATP inhibits NER, we designed closed circular DNA duplexes, each containing a site-specific d(GpG) cisplatin adduct, as the substrate for an in vitro repair assay. We used the assay to determine the effects of F-ara-ATP on the incision, repair synthesis, and ligation steps in the NER process. A closed circular DNA duplex, pSSA, was first constructed by inserting an 87-bp oligonucleotide into pGEM-7Zf(+), from which a single-stranded plasmid (pTDS) was derived. The 87-bp insert included two potential repair patches; each contained a d(GpG) site flanked by unique sequences 22 nucleotides upstream and 6 nucleotides downstream so that four dAMP sites were strategically placed in patch 1 but were absent from patch 2. Each duplex substrate was then synthesized by annealing a unique primer containing a platinated and 32P-end-labeled oligonucleotide to the pTDS template, which was then converted to a duplex through polymerization and ligation. At 50 microM, F-ara-ATP inhibited repair synthesis; F-ara-ATP also inhibited incision and ligation, but only at concentrations of 200 microM and above. Chemical DNA sequencing of the repair patch revealed that F-ara-ATP induced the formation of a truncated repair patch in which DNA polymerization stopped one nucleotide before the first installed dAMP site - a potential site for F-ara-ATP's incorporation. In contrast, truncation of a repair patch was not detectable when the repair patch contained no dAMP. Taken together, the results suggest that F-ara-ATP induced patch truncation by self-incorporation and the incorporated F-ara-AMP was subsequently excised, presumably by polymerase-associated exonuclease activity. We conclude that F-ara-ATP blocks the NER process by strongly inhibiting DNA repair synthesis as well as by less strongly inhibiting incision and ligation. Our approach of designing plasmid constructs that contain sequence-specific repair patches with a strategically placed 32P label may provide a powerful tool for dissecting the mechanism of NER inhibition not only for F-ara-ATP but also for other NER inhibitors.

Adenosine Triphosphate↗

PubMed1998

Thermal stability and reversibility of secondary conformation of alpha-crystallin membrane during repeated heating processes.

Reflectance FT-IR/DSC microspectroscopy was first used to study the structural conformation of alpha-crystallin membranes in the heating-cooling-reheating cycle. The thermotropic transition and the changes in secondary structure of alpha-crystallin membrane during heating and reheating processes were investigated. A thermal transition ranging between 50 and 70 degrees C with a midpoint at 60 degrees C for the alpha-crystallin membrane was easily obtained from the three-dimensional plots of the reflectance FT-IR spectra as a function of temperature. The secondary structural components of the alpha-crystallin membrane were modified step-by-step with the increase of temperature from 25 to 120 degrees C, but restored to original values after cooling to 25 degrees C. During the heating process, the compositions of the alpha-helix, random coil and beta-sheet structure decreased with temperature, but the content of the beta-turn structure increased, however, all of them were restored after cooling. The absence of significant alteration in the secondary structures for the alpha-crystallin membrane before and after the first-heating process strongly suggests the high thermal stability and reversibility of alpha-crystallin. Interestingly, the thermal behavior of the first-heated alpha-crystallin membrane during the reheating process exhibited a unique thermal behavior with two transitional temperatures at 35-50 and 55-70 degrees C. The reflectance FT-IR/DSC microscopic data indicated that alpha-crystallin in the membrane state had higher thermal stability and reversibility.

Animals↗

PubMed1998

The human HNRPD locus maps to 4q21 and encodes a highly conserved protein.

The hnRNP D protein interacts with nucleic acids both in vivo and in vitro. Like many other proteins that interact with RNA, it contains RBD (or "RRM") domains and arg-gly-gly (RGG) motifs. We have examined the organization and localization of the human and murine genes that encode the hnRNP D protein. Comparison of the predicted sequences of the hnRNP D proteins in human and mouse shows that they are 96.9% identical (98.9% similar). This very high level of conservation suggests a critical function for hnRNP D. Sequence analysis of the human HNRPD gene shows that the protein is encoded by eight exons and that two additional exons specify sequences in the 3' UTR. Use of two of the coding exons is determined by alternative splicing of the HNRPD mRNA. The human HNRPD gene maps to 4q21. The mouse Hnrpd gene maps to the F region of chromosome 3, which is syntenic with the human 4q21 region.

Amino Acid Sequence↗