Biomedical subjects

X Tan

Publications and source records attributed to X Tan.

At least 91 records · Page 5Linked to original sources

PubMed1999

[Study on measuring method of pulse oxygen saturation in clinical monitor].

In this paper, a measuring system of pulse oxygen saturation is presented, which is based on the Lambert-beer Principle, using the relative intensities at two wavelengths in the red and infrared ranges. In order to meet the special demand of continuous clinical physiological monitoring, two circuits and appropriate algorithms are designed, one circuit, a feedback circuit controlled by micro-controller, automatically regulates the base line of signal, another circuit is a controlled integral circuit which automatically regulates the amplitude of waveforms. As the result, the drift of base line in this system, especially the effects caused by the physiological differences of human bodies, which will deteriorate the system, have been reduced. The system is satisfactory to clinical monitoring.

Algorithms↗

PubMed1998

Structure-based design of peptides that recognize the CD4 binding domain of HIV-1 gp120.

DESIGN: Envelope protein-specific antiviral peptides, called mucibodies, that can specifically recognize and bind to the surface unit protein gp120 of HIV-1 were designed. The initial mucibody binding target was the V3 loop of HIV-1 gp120. Here, the gp120-CD4 binding domain was chosen as the site of mucibody binding. The CD4 binding domain of gp120 is known to be a conformational epitope and is involved in the earliest events of viral entry into many cells. METHODS: The design of the mucibody antivirals was based on previous observations that antibody complementarity determining regions (CDR) are generally similar to the repeating loops or knob structures found in the 20-residue tandem repeat domain of human mucin MUC1. The heavy chain CDR3 from the bacteriophage display antibody b12 was used to construct two mucibodies, b12-CDR1 and b12-26. RESULTS: Peptides corresponding to three tandem repeats were shown to bind directly to the CD4 binding domain of HIV-1 gp120 in a solid-phase enzyme-linked immunosorbent assay. These mucibody peptides also disrupted the gp120-CD4 interaction in a solution-phase inhibition assay. Finally, mucibodies neutralized primary and laboratory macrophage-tropic isolates of HIV-1. CONCLUSIONS: There is a potential for medical use of these peptides as topical vaginal microbicides in preventing HIV-1 transmission during sexual contact. These results also suggest that multivalent, non-immunogenic binding proteins of virtually any specificity could be constructed for use in therapeutic applications involving infectious diseases and immune system dysfunction.

Anti-HIV Agents↗

PubMed1998

Genistein inhibits the growth of human-patient BPH and prostate cancer in histoculture.

BACKGROUND: There is strong epidemiological evidence that prostate disease is significantly less prevalent in the Orient, where the intake of soy products is very high, than in the United States. We therefore undertook a study of the effects of genistein, a major component of soy, on growth of human-patient benign prostatic hypertrophy (BPH) and prostate cancer tissue in three-dimensional collagen gel-supported histoculture. METHODS: Surgical specimens of human BPH and cancer were histocultured for 5 days to study the effects of genistein on growth, as measured by inhibition of 3H-thymidine incorporation per microgram protein on day 5. RESULTS: Genistein in doses of 1.25-10 micrograms/ml decreased the growth of BPH tissue in histoculture in a dose-dependent manner, with little additional effect at higher doses. Prostate cancer tissue in histoculture was similarly inhibited by these doses of genistein. CONCLUSIONS: Genistein decreases the growth of both BPH and prostate cancer tissue in histoculture. The data suggest that genistein has potential as a therapeutic agent for BPH and prostate cancer.

Antineoplastic Agents↗

PubMed1998

Mucosal IL-12 gene delivery inhibits allergic airways disease and restores local antiviral immunity.

Allergic asthma strongly correlates with airways inflammation driven by interleukin (IL)-4 and IL-5 secreted by allergen-specific CD4+ T cells. It is possible that over-production of these factors in the lungs may render asthmatic individuals less able to resolve virus infection of the respiratory tract by down-regulating type 1 cytokine-driven immune responses. IL-12 is important for the establishment of cell-mediated immunity (CMI) and may also inhibit responses driven by type 2 cytokine production. Sustained expression of IL-12 in the airways may, therefore, represent an effective preventive treatment or therapy for allergic asthma and any adverse consequences of excessive production of type 2 cytokines for the development of local CMI. Here, we show that allergic responses in airways profoundly inhibit the development of antiviral CMI in mice following local immunization with vaccinia virus (VV) leading to persistent lung infection. However, mucosal gene transfer of IL-12 in the lung, via a VV vector, inhibited local type 2 cytokine production, both prevented the development of allergic disease and airways hyperreactivity in a manner largely dependent on endogenous interferon-gamma expression and suppressed established allergic disease, and reversed the suppression of local antiviral CMI responses resulting in rapid resolution of virus infection. Our study provides the first direct demonstration that allergic conditions, particularly in airways, may inhibit immune responses to concomitant virus infection and suggests that transient mucosal IL-12 gene therapy represents an effective approach to both the prevention and treatment of allergic airways disease and associated immunosuppression of CMI.

Animals↗

PubMed1998

Complement C1q inhibits cellular spreading and stimulates adenylyl cyclase activity of fibroblasts.

C1q selectively localizes at injured tissues, where it may function as a regulator of cell-matrix interactions. We show here that purified C1q, added to the culture medium of human gingival fibroblasts (HF) spread onto fibronectin substrates, elicited a round morphology that was accompanied by altered F-actin and correlated with inhibition of cellular spreading. Shape modification required integrity of the molecule and was specific, dose dependent, nontoxic, and reversible. Antispreading activity was mediated, at least in part, by specific cell-surface C1q receptors. We hypothesized that ligand occupancy of C1q receptors could influence shape by affecting intracellular levels of cyclic AMP (cAMP). Within 20 min of exposure of adhering HF to C1q, we detected an increase in adenylyl cyclase activity (six- to ninefold) in cAMP accumulation (by 20%) and in cAMP-dependent protein kinase activity (by 20%). These changes suggested that the rounding effect of C1q may be associated with activation of the adenylyl cyclase pathway.

Adenylyl Cyclases↗

PubMed1998

Polyethylene glycol conjugation of recombinant methioninase for cancer therapy.

Recombinant methioninase (rMETase) is a homotetrameric pyridoxal 5'-phosphate enzyme of 172-kda molecular mass derived from Pseudomonas putida and cloned in Escherichia coli. rMETase has been found previously to be an effective, anti-tumor agent in vitro and in vivo. The enzyme targets the elevated minimal methionine requirement seen in all tumor types. In order to prevent immunological reactions which might be produced by multiple dosing of rMETase and to prolong the serum half-life of rMETase, the N-hydroxysuccinimidyl ester of methoxypolyethylene glycol propionic acid (M-SPA-PEG 5000) has been coupled to rMETase. Molar ratios of M-SPA-PEG-5000 (PEG) to rMETase from 10 to 40 were used for PEGylation of rMETase. PEGylation reactions were run at 20 degrees C for 30 to 60 min in reaction buffer (20 mM sodium phosphate buffer, pH 8.3). The PEGylated molecules (PEG-rMETase) were purified from unreacted PEG with Amicon 30 K centriprep concentrators or by Sephacryl S-300 HR gel-filtration chromatography. Unreacted rMETase was removed by DEAE Sepharose FF anion-exchange chromatography. The resulting PEG-rMETase subunit, from a PEG/rMETase ratio of 30/1 in the synthetic reaction, had a molecular mass of approximately 53 kda determined by matrix-assisted laser desorption/ionization mass spectrometry, indicating the conjugation of two PEG molecules per subunit of rMETase and eight per tetramer. PEG-rMETase molecules obtained from reacting ratios of PEG /rMETase of 30/1 had enzyme activities of 70% of unmodified rMETase. PEGylation of rMETase increased the serum half-life of the enzyme in rats to approximately 160 min compared to 80 min for unmodified rMETase. PEG-rMETase could deplete serum methionine levels to less than 0.1 microM for approximately 8 h compared to 2 h for rMETase in rats. Efficacy studies of PEG-rMETase on human lung cancer and kidney cancer cells in vitro demonstrated a 50% inhibitory concentration (IC50) of 0.04 and 0.06 units/ml, respectively. These IC50 values were almost identical to unmodified rMETase, thus indicating maintenance of antitumor efficacy in the PEGylated enzyme. PEG-rMETase had an IC50 for normal lung and kidney cells of 0.8 and 1.5 units/ml, respectively, similar to rMETase. The efficacy data indicated that PEG-rMETase maintained the high level tumor selectivity of rMETase. PEG-rMETase injected intravenously in mice demonstrated a tumor/blood retention ratio of approximately 1/6 compared to 1/10 of unmodified enzyme, indicating that PEG-rMETase distributes to the tumor at least as effectively as rMETase.

Animals↗

PubMed1998

High expression, purification, and properties of recombinant homocysteine alpha, gamma-lyase.

Homocysteine alpha,gamma-lyase from the anaerobic protozoan parasite Trichomonas vaginalis has been cloned from genomic DNA using PCR methods and expressed in Escherichia coli with a vector containing the T7 promoter. The recombinant homocysteine alpha,gamma-lyase (rHCYase) is expressed as the major protein in the host E. coli cells. The enzyme was purified to approximately 90% purity using heat treatment at 50 degreesC, precipitation steps with polyethyleneimine, polyethylene glycol 8000, and high sodium chloride, DEAE-Sepharose FF chromatography, and phenyl-Sepharose 6 FF chromatography. The final yield was greater than 50%, which encompassed an approximate 18-fold purification. The enzyme is a homotetramer with a monomer molecular weight of 43K and contains pyridoxal phosphate. The Trichomonas rHCYase is selective for homocysteine with respect to very low cysteinase activity in contrast to the alpha,gamma-lyase from Pseudomonas putida, which has very high cysteinase activity with respect to homocysteine. The T. vaginalis and P. putida alpha,gamma-lyases readily separate on a phenyl-Sepharose 6 FF column with the T. vaginalis enzyme eluting first. rHCYase is stable up to 50 degreesC and active over a pH range of 6-8. These properties of high recombinant expression in E. coli, a simple and effective high-yield purification procedure and high relative specificity for homocysteine with respect to cysteine, make rHCYase a promising candidate to use for the diagnosis of hyperhomocystenemia, which has been demonstrated to be a major risk factor for the onset and mortality of cardiovascular disease of all types.

Animals↗

PubMed1998

Benzodiazepine effects on human sleep EEG spectra: a comparison of triazolam and flunitrazepam.

The effects of 0.5 mg triazolam (TRI) and 4 mg flunitrazepam (FNZ) on the sleep electroencephalogram (EEG) were studied in eleven (six for TRI, and five for FNZ) healthy young male subjects. C3 EEG channel data of one baseline night, three drug nights and two withdrawal nights were recorded and their analyzed using a fast Fourier transformation (FFT) method. Changes in the 0.5 Hz to 40 Hz power spectrum showed that: 1) both TRI and FNZ increased higher frequency activity and reduced lower frequency activity on the drug nights; 2) on drug nights, NREM sigma frequency power was more strongly enhanced by TRI than FNZ, while the beta power of both NREM and REM was more strongly enhanced by FNZ than TRI; 3) NREM alpha power increased on the second night of withdrawal from both TRI and FNZ; 4) the power spectra for both NREM and REM sleep returned to baseline levels by the fourth night of withdrawal from either TRI or FNZ. These findings suggest that 0.5 mg TRI and 4 mg FNZ have both common and differing pharmacological effects on the central nervous system. Such differences could be caused by differences in the dose, half-life or systemic distribution of these two drugs.

Adult↗

PubMed1998

CAT-transfected epithelial cells provide evidence for a CD4 independent pathway of HIV infection.

Several laboratories have presented evidence that HIV can productively infect CD4- cell lines. However, this data could be challenged on the basis that the target cells may express low levels of the CD4 receptor. In addition, it could be argued that assays might be detecting residual virus. In the case of cell-mediated infection, it is possible that virus detected in assays could be secreted from HIV-infected donor cells rather than the target CD4- cells. In this report we describe a CD4- epithelial cell line which has been transfected with a plasmid containing the chloramphenicol acetyltransferase (CAT) gene ligated to the HIV LTR. CAT-ELISA and immunocytochemistry indicate that target cells synthesize CAT after exposure to HIV-infected primary activated peripheral blood mononuclear cells (PBMC). Results correlate very well with p24 ELISA assays. Infection of epithelia by primary NSI strains of HIV can be blocked by patient antisera or by certain sulfated polysaccharides. Since the CAT assay is not dependent on virus production, the data reported here confirm that CD4- epithelial cells derived from the human cervix can be productively infected by HIV. The observations also support the theory that sexual transmission of HIV could be initiated by infection of genital tract epithelia. Furthermore, the findings support the suppositions that sexual transmission of HIV could be prevented by antibodies to HIV or alternately by a topical formulation containing certain sulfated polysaccharides.

Animals↗

PubMed1998

The caspase-RB connection in cell death.

Execution of the cell-death programme requires the activation of a family of cysteine proteases known as caspases. Specific cellular proteins are cleaved by caspases during apoptosis, including the retinoblastoma tumour-suppressor protein (RB1). A caspase-resistant RB1 can attenuate the death response to tumour necrosis factor alpha. The cleavage of RB1 during cell death, together with the increased cell death during embryonic development of Rb-knockout mice, suggests that RB1 degradation contributes to the activation of the cell-death pathway.

Animals↗

PubMed1998

An association study of a functional polymorphism of the serotonin transporter gene with personality and psychiatric symptoms.

A functional polymorphism in the regulatory region of the serotonin transporter gene has been reported to be associated with anxiety-related personality traits. We attempted to replicate this finding in an association study involving 759 Caucasians selected from the general Australian population. We found no associations with personality traits (including neuroticism, negative affect and behavioral inhibition), anxiety and depressive symptoms, or alcohol misuse.

Alcoholism↗

PubMed1998

Fibroblast heterogeneity of signal transduction mechanisms to complement-C1q. Analyses of calcium mobilization, inositol phosphate accumulation, and protein kinases-C redistribution.

Fibroblasts of healthy and granulation gingiva are phenotypically heterogeneous with regard to binding C1q collagen-like (cC1qR) or C1q globular-heads (gC1qR) regions, respectively. Here, isolated fibroblast subsets, expressing either the cC1qR or the gC1qR phenotype, were stimulated with C1q, and assessed for changes in cytosolic free calcium [Ca2+]i, accumulation of inositol trisphosphate (IP3), and redistribution of Ca2+-dependent protein kinases-C (cPKCs) from cytosol to membranes. Changes in [Ca2+]i were determined using Indo-1 fluorescence in combination with adhering cell analysis and sorting (ACAS) cytometry. Accumulation of IP3 was quantified using a competitive radioreceptor binding assay. Redistribution of cPKCs was evaluated by immunoblotting with antibodies to PKCalpha/betaI-betaII/gamma. Subsets manifested different fluctuations in [Ca2+]i levels 20 seconds after C1q-stimulation in the presence of millimolar concentrations of external calcium. Whereas cC1qR fibroblasts responded with a 38% over baseline [Ca2+]i increase which was sustained for 20 to 30 minutes, gC1qR fibroblasts responded with a higher (264% over baseline) and more rapid (2 to 3 minutes) transient. Likewise, subsets exhibited different kinetics of IP3 accumulation. Whereas cC1qR fibroblasts responded with an IP3 increase of 32 +/- 3 pmol/10(4) cells over baseline after 5 seconds stimulation, gC1qR fibroblasts responded after 15 to 20 seconds with a lower increase (13 +/- 0.8 IP3 pmol/10(4) cells over baseline). Subsets differed in cPKCs redistribution which peaked in gC1qR-membranes 30 seconds after stimulation and remained sustained between 10 and 30 minutes. No cPKC redistribution was detectable in stimulated cC1qR-cells. We conclude that fibroblasts are heterogeneous in phosphoinositide-Ca2+ signaling and cPKC redistribution to C1q, and suggest that these differences may affect activities of normal and granulation gingiva.

Analysis of Variance↗

PubMed1998

Cloning and characterization of a family of cDNAs from human histiocyte macrophage cells encoding an arginine-rich basic protein related to the 70 kD U1-snRNP splicing factor.

This paper describes the cloning and characterization of five cDNA members of a novel family of mRNAs, termed hm-1, isolated from human U937 macrophage cells. Two family members (clones 46 and 11) show complete mRNA features [including ribosome binding sites (RBS), polyadenylation signals, and poly(A) tails], and encode the same protein (designated HM-1), but differ substantially in their 5' untranslated regions. The three other cDNAs (clones 20, 60, and 38) appear to represent partial cDNAs. The protein sequences deduced from the five hm-1 cDNAs are identical (some truncated), except for one Trp --> Cys substitution. Full-length HM-1 is 246 amino acids long, has a predicted MW of 29431, is rich in arginine residues, has a pI of 10.25, and a mean hydrophobicity index of -1.23. HM-1 contains no obvious hydrophobic N-terminal cleavable signal sequence, and no potential N-glycosylation sites, but does contain three highly conserved motifs present in U1-70K splicing factors, and contains numerous C-terminal Arg/Asp and Arg/Glu dipeptides characteristic of "RD" family members that function as regulators of mRNA splicing. Northern hybridizations indicate that hm-1 is a family of mRNAs differentially expressed in a variety of human tissues.

Amino Acid Sequence↗

PubMed1998

[Exploration for an early discriminant model of non-skeletal phase in endemic fluorosis exposed to coal-burning].

OBJECTIVE: To detect, diagnose and treat for endemic fluorosis earlier. METHODS: Six kinds of indices, such as environmental fluoride level, were collected from the population in epidemic and non-epidemic areas of endemic fluorosis with a 1:1 paired-match design. A discriminant analysis model was established by multivariate analysis. Levels of fluoride in environment and biological materials were determined by fluoride electrode method. Living condition of the subjects were measured and interviewed. Function of skeletons and joints was measured. Biochemical and enzyme indices were measured with reagent kits and gel electrophoresis. Other indices were measured by interview. All data collected were analyzed by SAS and MDAS computer software. RESULTS: There was significant overall difference between four kinds of discriminant functions, with an overall agreement of 85.78% (83.33% to 98.86%), based on resubstitution with sampled data. Posterior probabilities for new classification of sampled data automatically and randomly produced from a computer were 86.39% to 99.99%. CONCLUSION: The discriminant functions mentioned above, except for the third one with a too small sample size, can be used in early discrimination of endemic fluorosis caused by exposure to coal burning, or in evaluation for the effectiveness of pharmaceutical therapy, with a power of 95%.

Adolescent↗

PubMed1998

[Correction of square face].

OBJECTIVE: This work was to provide an advanced operation method for square face correction. METHODS: The method is characterized by resecting hyperostosis of the mandibular angle, the bulky masseter and the buccal fat pad through intraoral or combined extra-intraoral approach. RESULTS: Good results were obtained in 10 cases after follow-up of 4 to 28 months. CONCLUSION: This operative method proved to be quite ideal and applicable to treat square face.

Adult↗

PubMed1998

[Effects of mild hypothermia on Na(+)-K+ ATPase and lipid peroxidation in canine brain tissue following cardiac arrest and resuscitation].

The effect of mild hypothermia on Na(+)-K+ ATPase and lipid peroxidation in canine brain tissue following a 18-minute cardiac arrest and resuscitation for 8 hours were studied. Mild hypothermia improved the restoration of the activity of Na(+)-K+ ATPase, LDH, protect the activity of SOD, decrease the loss of GSH, but not completely blocked the ischemia reperfusion induced lipid peroxidation.

Animals↗

PubMed1998

[Efficacy of epimedium compound pills in the treatment of the aged patients with kidney deficiency syndrome of ischemic cardio-cerebral vascular diseases].

One hundred-twenty aged patients with kidney deficiency syndrome of ischemic cardio-cerebral vascular diseases were treated with Epimedium compound granules. The results showed that after therapeutic period the total and marked effective rates were 96.7%, 39.5% respectively in treatment group. The rates of improvement were 70% in electrocardiogram of the patients with coronary heart diseases, and 75% in electro-encephalogram of the patients with cerebral arterosclerosis. The therapeutic effectiveness in treatment group was better than that in control group treated with Su-Guan-Bian. According to experimental observation, the therapeutic effectiveness was related to the facts that Epimedium compound granules lower blood lipid have anti-free radicals and adjust balance between prostacyctin I2 and thromboxane A2(TXA2/PGI2).

Aged↗

PubMed1998

[A rapid simple and reliable method for sequencing the targeted gene of shuttle vector pSP189].

The authors established a simple, rapid and effective procedures for sequencing the targeted a-gene SupF TRNA of shuttle vector pSP189, which is very important and useful in molecular mechanism research of mutagens. In this method, double-stranded plasmid DNA as template, prepared single-stranded DNA with alkali denaturation, applied r-32P-ATP for labelling 5'-end of primer, were used. A satisfactory result was achieved.

Escherichia coli↗