Biomedical subjects

T Huang

Publications and source records attributed to T Huang.

At least 73 records · Page 4Linked to original sources

PubMed1999

Messenger RNAs encoding mouse histone macroH2A1 isoforms are expressed at similar levels in male and female cells and result from alternative splicing.

Two protein isoforms of histone macroH2A1 (mH2A1) are found in mammalian cells. One isoform, mH2A1.2 is highly concentrated on the heterochromatinized inactive X chromosome (Xi) of female cells. mH2A1.2 protein is also present in male cells, but fails to form dense concentrations. Another protein isoform, mH2A1.1, differs from mH2A1.2 by a single short segment of amino acids. In this study, we cloned and characterized the genomic locus of the mouse mH2A1 gene and mapped it to chromosome 13. Two alternatively spliced transcripts derived from the mH2A1 locus are responsible for the generation of the two mH2A1 protein isoforms with mH2A1.2 mRNA being the most abundant spliced form in all tissues examined. The absolute amount of mH2A1 mRNA is similar in male and female cells for most tissues with the exception of testes where it is par-ticularly abundant. Both spliced forms are present in all adult tissues analyzed as well as in female embryonic stem cells. In contrast, male embryonic stem cells expressed mH2A1.1 at low levels if at all. The relatively abundant expression of mH2A1 in both sexes suggests that mH2A1 has functions in addition to a possible involvement in X chromosome inactivation.

Aging↗

PubMed1999

The novel Mrf-2 DNA-binding domain recognizes a five-base core sequence through major and minor-groove contacts.

Recent NMR studies of the purified Mrf-2 DNA-binding domain peptide have shown that its structure differs significantly from previously characterized classes of DNA-binding domains. Here we report biochemical studies of the DNA-binding properties of this peptide. Binding interference and binding site selection assays indicated that Mrf-2 requires the core sequence AATA(C/T) for high affinity binding. Kinetic analyses of several selected sequences indicated that the core sequence alone is not sufficient for high affinity binding, however. Kinetic analyses were also performed using a series of synthetic oligonucleotides with single base analogues at each position in the core sequence. Base analogues that altered the major groove structure reduced or eliminated Mrf-2 binding when present in the second, third, and fourth base-pairs of the core sequence, but had little or no effect in the first and fifth positions. These results suggest that Mrf-2 contacts both the major and minor grooves of its target sequences.

Base Sequence↗

PubMed1999

The alpha-helical domain of Galphat determines specific interaction with regulator of G protein signaling 9.

RGS proteins (regulators of G protein signaling) are potent accelerators of the intrinsic GTPase activity of G protein alpha subunits (GAPs), thus controlling the response kinetics of a variety of cell signaling processes. Most RGS domains that have been studied have relatively little GTPase activating specificity especially for G proteins within the Gi subfamily. Retinal RGS9 is unique in its ability to act synergistically with a downstream effector cGMP phosphodiesterase to stimulate the GTPase activity of the alpha subunit of transducin, Galphat. Here we report another unique property of RGS9: high specificity for Galphat. The core (RGS) domain of RGS9 (RGS9) stimulates Galphat GTPase activity by 10-fold and Galphai1 GTPase activity by only 2-fold at a concentration of 10 microM. Using chimeric Galphat/Galphai1 subunits we demonstrated that the alpha-helical domain of Galphat imparts this specificity. The functional effects of RGS9 were well correlated with its affinity for activated Galpha subunits as measured by a change in fluorescence of a mutant Galphat (Chi6b) selectively labeled at Cys-210. Kd values for RGS9 complexes with Galphat and Galphai1 calculated from the direct binding and competition experiments were 185 nM and 2 microM, respectively. The gamma subunit of phosphodiesterase increases the GAP activity of RGS9. We demonstrate that this is because of the ability of Pgamma to increase the affinity of RGS9 for Galphat. A distinct, nonoverlapping pattern of RGS and Pgamma interaction with Galphat suggests a unique mechanism of effector-mediated GAP function of the RGS9.

3',5'-Cyclic-GMP Phosphodiesterases↗

PubMed1999

Different TBX5 interactions in heart and limb defined by Holt-Oram syndrome mutations.

To better understand the role of TBX5, a T-box containing transcription factor in forelimb and heart development, we have studied the clinical features of Holt-Oram syndrome caused by 10 different TBX5 mutations. Defects predicted to create null alleles caused substantial abnormalities both in limb and heart. In contrast, missense mutations produced distinct phenotypes: Gly80Arg caused significant cardiac malformations but only minor skeletal abnormalities; and Arg237Gln and Arg237Trp caused extensive upper limb malformations but less significant cardiac abnormalities. Amino acids altered by missense mutations were located on the three-dimensional structure of a related T-box transcription factor, Xbra, bound to DNA. Residue 80 is highly conserved within T-box sequences that interact with the major groove of target DNA; residue 237 is located in the T-box domain that selectively binds to the minor groove of DNA. These structural data, taken together with the predominant cardiac or skeletal phenotype produced by each missense mutation, suggest that organ-specific gene activation by TBX5 is predicated on biophysical interactions with different target DNA sequences.

Adult↗

PubMed1999

Angiopoietins 3 and 4: diverging gene counterparts in mice and humans.

The angiopoietins have recently joined the members of the vascular endothelial growth factor family as the only known growth factors largely specific for vascular endothelium. The angiopoietins include a naturally occurring agonist, angiopoietin-1, as well as a naturally occurring antagonist, angiopoietin-2, both of which act by means of the Tie2 receptor. We now report our attempts to use homology-based cloning approaches to identify new members of the angiopoietin family. These efforts have led to the identification of two new angiopoietins, angiopoietin-3 in mouse and angiopoietin-4 in human; we have also identified several more distantly related sequences that do not seem to be true angiopoietins, in that they do not bind to the Tie receptors. Although angiopoietin-3 and angiopoietin-4 are strikingly more structurally diverged from each other than are the mouse and human versions of angiopoietin-1 and angiopoietin-2, they appear to represent the mouse and human counterparts of the same gene locus, as revealed in our chromosomal localization studies of all of the angiopoietins in mouse and human. The structural divergence of angiopoietin-3 and angiopoietin-4 appears to underlie diverging functions of these counterparts. Angiopoietin-3 and angiopoietin-4 have very different distributions in their respective species, and angiopoietin-3 appears to act as an antagonist, whereas angiopoietin-4 appears to function as an agonist.

Amino Acid Sequence↗

PubMed1999

Isolation of oncogenes from rat mammary tumors by a highly efficient retrovirus expression cloning system.

A majority of mammary tumors induced with N-methyl-N-nitrosourea in rats contain G to A transitional mutation of c-Ha-ras at the 12th codon. Additional oncogene activation is known to be necessary for further tumor progression. To isolate novel oncogenes, we used an expression cloning system utilizing the pMX retroviral vector in combination with BOSC23 packaging cells. First, we elucidated the sensitivity of this system in the NIH 3T3 focus assay; foci were detectable even after 10(-6) dilution using v-Ha-ras, neuT, and beta-galactosidase constructs in pMX vector. This system is sensitive enough to detect low copy number cDNAs. We used the pMX/BOSC23 expression cloning system to clone novel oncogenes from rat mammary tumors harboring an activated c-Ha-ras and isolated several candidate oncogenes that caused transformation of NIH 3T3 cells and/or generated tumors when transplanted to nude mice.

3T3 Cells↗

PubMed1999

Local inhibition of chlorhexidinum on Lewis pulmonary carcinoma in mice.

C57 inbred mice (n = 100) were employed to develop animal models of Lewis pulmonary carcinoma. The study on the tumor inhibition was performed by infiltrative injection of 3.5% Cy or chlorhexidinum of two different concentrations around the tumor respectively. The survival, survival rate, tumor growth rate, and pulmonary metastasis node number were compared. The results showed that the inhibitory effects of 0.1% and 0.5% chlorhexidinum were the same as that of 3.5% Cy, but the toxic and side effects were obviously reduced as compared with 3.5% Cy. The optimal concentration of chlorhexidinum was 0.5%. This provides a new approach for infiltrative injection of the tumor for clinical use.

Animals↗

PubMed1999

Bioavailability of carotenoids in human subjects.

There is growing need for accurate information regarding the bioavailability of carotenoids, both with respect to carotenoids per se and to the vitamin A value of provitamin A carotenoids in foods or supplement preparations. Little quantitative information is currently available, owing primarily to the lack of adequate methods to assess carotenoid bioavailability. Methods applied to xenobiotic drugs are in most cases not useful for carotenoids, many of which circulate in appreciable quantities in human plasma. Reported ranges of carotenoid bioavailability (% dose absorbed) range from 1-99, and variability is generally high both within and between treatments. With the current methods, relative bioavailability is more readily assessed than absolute bioavailability. The most commonly applied methods include measuring the increase in plasma carotenoid concentration following chronic intervention, and use of postprandial chylomicron (PPC) carotenoid or retinyl ester response following a single dose of carotenoid. The advantages and limitations of these approaches, together with examples of each, are discussed. A new PPC approach utilizing extrinsic-stable-isotope-labelled vitamin A (2H4-labelled retinyl acetate) is under development in our laboratory, and examples of its application are presented. The currently available data suggest that oil solutions of carotenoids are more bioavailable than those from food matrices, and heating can improve the bioavailability of carotenoids from some food products. Increased availability of labelled carotenoids and retinoids should aid the development of reliable methods of carotenoid bioavailability assessment. Such data are needed for dietary recommendations, supplement formulation, and design of intervention strategies involving carotenoids.

Biological Availability↗

PubMed1999

Concurrent improvements in ambulatory cardiac catheterization practices following inpatient interventions.

Questions have been increasingly raised about the value of performing right heart catheterization. A preliminary analysis done in 1992 revealed significant interhospital variation in the frequency of the procedure among Medicare Part A and Medicaid patients in New York State, and it also suggested that the procedure was being performed routinely in some hospitals. In 1993, IPRO initiated a cooperative health care quality improvement program involving the state's 53 catheterization laboratories. As a result of this educational intervention, the rate of bilateral catheterization among Medicare Part A patients fell from 89/100,000 beneficiaries in 1992 to 65/100,000 in 1996, and the overall percentage of catheterized Medicare patients undergoing bilateral catheterization fell from 30.5% in 1992 to 17.4%. A major question was whether a corresponding decrease had occurred among ambulatory patients (Medicare Part B). To determine the answer, the Medicare Part B database was analyzed for the identical period of time. It was found that the percentage of ambulatory Medicare patients who underwent bilateral catheterization at the 53 laboratories fell from 37.6% in 1992 to 17.0% in 1996, paralleling the decline observed among inpatients. The results of this quality improvement study show that an educational intervention directed at inpatient practice patterns can have a similar impact on outpatient patterns.

Ambulatory Surgical Procedures↗

PubMed1999

Experimental studies on topoisomerase inhibitor camptothecin as an antipsoriatic agent.

OBJECTIVES: To elucidate the therapeutic mechanism of topical camptothecin (CPT) in treating psoriasis and to detect the effects of CPT on keratinocyte proliferation, differentiation and apoptosis. METHODS: Mitotic numbers in mouse vaginal epithelium at estrus and numbers of scale with granular layer per 100 scales in mouse tail epidermis were determined in vivo. Experiments on cultured normal human keratinocytes were performed using the methods of crystal violet staining, absorbance-cell number converting, cell counting and quantitation of morphologic changes during differentiation, transglutaminase assay and nucleosomal enrichment assay. RESULTS: Inhibition of cell proliferation and promotion of cell differentiation by camptothecin were showed in animal models and were reconfirmed in cultured keratinocytes. Apoptosis was induced by camptothecin and was showed by activation of "tissue" transglutaminase and increase in nucleosomes. The endonuclease activity was reduced by an endonuclease inhibitor aurintricarboxylic acid. CONCLUSION: The therapeutic effects of camptothecin on psoriasis can at least partly be explained by its multiple effects on DNA as a topoisomerase inhibitor.

Animals↗

PubMed1999

[The role of endogenous nitric oxide in airway hyperresponsiveness of asthmatic rats].

OBJECTIVE: Nitric oxide (NO) precursor L-arginine (L-Arg) and NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME) were used to investigate the role of endogenous NO in airway hyperresponsiveness of asthmatic rats. METHODS: Asthmatic wistar rats were developed by sensitization and challenging with ovalbumin. Airway responsivess to acetylcholine (Ach) was measured in vitro in isolated and perfused rat tracheal rings with or without epithelium after inhibiting or stimulating NO synthesis. RESULTS: After asthmatic rat tracheal rings were incubated in vitro with L-NAME 10(-5) mol/L, the maximal response of tracheal rings to Ach was increased compared with that of the control group. When asthmatic rat tracheal rings were coincubated with L-Arginine 2 x 10(-5) mol/L and L-NAME 10(-5) mol/L, the maximal response was decreased compared with that of the L-NAME group. Incubation with higher concentrations of L-Arginine did not change asthmatic rat tracheal responsiveness to Ach. Epithelium-denuded tracheal rings in the asthmatic rats showed a significant (P < 0.05) upward shift in the Ach concentration response curve; the maximal response was increased compared with the tracheal intact group. In the denuded tracheal rings, L-NAME and L-Arginine did not influence the shape of the Ach concentration-response curve and the maximal response. CONCLUSIONS: Endogenous nitric oxide, a mediator of bronchodilation, is synthesized from L-Arginine by NO synthase in asthmatic rats. The epithelium lining airway smooth muscle probably contributes to nitric oxide synthesis. Our finding suggests that the airway in asthmatic rats could not use exogenous L-Arginine to synthesize nitric oxide.

Animals↗

PubMed1999

[Effects of humic acid on lipid peroxidation in arsenosis prevalent areas].

OBJECTIVE: To explore the causes of blackfoot disease in Taiwan. METHODS: Experiments to induce lipid peroxidation by arsenic and humic acid were made in vitro. Arsenic was determined for the water sampled from the arsenosis prevalent areas in Inner Mongolia and blackfoot disease prevalent areas in Taiwan and humic acid determined for the extracts of the coal rich in arsenic sampled from Guizhou Province in China by MDA-TBA colorimetry. RESULTS: Experiments found that humic acid could induce lipid peroxidation caused by sodium salt of unsaturated fatty acids in vitro in a weak and unstable manner, which could be promoted by 0.05 mmol/L of Fe(+ +) and not by 1 mmol/L As(2)O(3). The extent of lipid peroxidation caused depended on the sources, constituents and structure of humic acid samples, those from Inner Mongolia ranked the highest, those from Guizhou and Taiwan the medium and the commercial humic acid (Aldrich Co. in the US) the lowest. The experiments also found that lipid peroxidation caused by commercial humic acid presented a dynamic process in the existence of trace amount of iron, and humic acid could decompose the products of lipid peroxidation. CONCLUSION: The experiments suggested the relations of humic acid and arsenic to iron and other transition elements in the blackfoot disease prevalent areas and areas with an environment rich in arsenic and humic acid.

Arsenic Poisoning↗

PubMed1999

Effects of 16O+6 ion irradiation on human sperm spontaneous chemiluminescence, motility, acrosome reaction and viability in vitro.

Effects of 16O+6 ion irradiation with different doses on human sperm spontaneous chemiluminescence (SCL), motility, acrosome reaction (AR) and viability were examined. Spermatozoa were irradiated with 0, 0.25, 0.5, 1, 2, 4, 8, 16, 32, or 64 Gy 16O+6 ion beam at the energy of 3.17 MeV/u. After irradiation, samples were analyzed by SCL measurement at 1, 2 and 3 h of incubation; motility was determined by the transmembrane migration method within 2 h of incubation; the percentage of AR and viability was evaluated by the triple-stain technique at 3.5 h of incubation. The results showed: sperm SCL was significantly increased with irradiation doses and the lowest effective dose was 0.5 Gy; compared with controls, the transmembrane migration ratio of spermatozoa progressively elevated with irradiation doses at 0.5, 1, and 2 Gy; the percentage of sperm AR markedly increased in 0.5-4 Gy irradiation and the optimal dose was 2 Gy, and then significant decreased with further increase of irradiation doses; the viability had no significant change within 0.25-8 Gy, but was progressively decreased at 16, 32 and 64 Gy. These data suggested that heavy ion at low doses increased motility and AR, whereas had deleterious effects at higher doses, which are associated with free radical reactions induced by heavy ion irradiation.

Acrosome Reaction↗

PubMed1999

[Chromatographic properties of tetradecylamine bonded stationary phase for reversed-phase liquid chromatography].

A novel bonded stationary phase, tetradecylamine bonded stationary phase (TABP), for reversed-phase HPLC was prepared by bonding 1-tetradecylamine to YWG-80 silica gel through 3-glycidoxypropyltrimethoxysilane. Hydrophobicity, selectivity and silanophilic activity of TABP were evaluated by using aromatic compounds as analytes and methanol-water as binary mobile phase. The orgainc components including acidic, basic and neutral aromatic analytes could be separated satisfactorily with excellent selectivity and peak shape. The relative retention alpha for ethylbenzene-toluene was found to be 1.66 and the asymmetry factors of basic aniline, p-toluidine and N,N-dimethylaniline were found to be 1.26, 1.21 and 1.10, respectively, with the V(methanol):V(water) = 55:45 mobile phase. Aniline was eluted before phenol due to the suppress of the ion exchange activity of residual silanols by the internal masking interaction.

Amines↗

PubMed1999

[The improvement on related condition of corneal cryopreservation and roles of cryopreserved corneas in emergent keratoplasty].

PURPOSE: To study the cryopreserved corneal endothelium viability on the condition that a series of related factors on long-term corneal cryopreservation were modified. The frozen corneas were used for emergent penetrating keratoplasty on poor condition patients. To evaluate the role of cryopreserved corneas on clinical application, especially on emergent keratoplasty. METHODS: Residual peripheral corneas were stained with Trypan blue and Alizarin red in order to assess endothelium survival rate after central grafts were punched. Specular microscope was used to measure corneal thickness and count endothelium density. The transparent rate of grafts, infective control rate, retinal restorative rate and the recovery degree of visual acurity were emphasized respectively. RESULTS: Endothelium survival rate of grafts was 82.1% averagely. Postoperative endothelium density was 1,642 cells/mm2 and graft thickness was 0.59 mm averagely. The epithelial defects healed after 2-5 days of the operation and edematous grafts were reclear after 2-4 weeks of the operation in all grafts, except for chemical burn and thermal burn. The transparent rate was 87.5%. Infective controll rate was 90.63%. Retinal restorative rate was 55.56%. Some useful visual acurity can be obtained when the infection was under controlled and the retinal was reattached. CONCLUSION: Modified long-term corneal cryopreservation is effective in maintaining endothelium viability and integrity. Furthermore, it could provide donors anytime because of it's unlimited preservative duration. Our study emphasizes especially the role of cryopreserved corneas in emergent keratoplasty.

Adolescent↗

PubMed1999

Fresh amniotic membrane transplantation for conjunctival surface reconstruction.

PURPOSE: To determine whether fresh human amniotic membrane can be used to reconstruct the conjunctival detect created during symblepharon lysis. METHODS: Forty-two eyes of 39 consecutive patients with eye burns and Stevens-Johnson syndrome were randomized to accept fresh or preserved human amniotic membrane transplantation (AMT) during the period of severe scarring. Impression cytology was performed in 12 eyes with normal tear secretion which received fresh AMT. RESULTS: During a mean follow-up of 11 months (range, 6 to 18 months), thirty-five patients (37 eyes) showed successful ocular surface reconstruction and resolution of motility restriction while four patients (2 eyes with fresh AMT, 3 eye with preserved AMT) with minimal recurrence of symblepharon. There was no significant difference statistically between two groups (Chi-square test). Amniotic epithelial cells can survive about three months after being transplanted onto ocular surfaces with normal tear secretion. CONCLUSION: Both fresh and preserved human amniotic membrane can be considered an ideal alternative substrate for conjunctival surface reconstruction during removal of severe symblepharon.

Adolescent↗

PubMed1999

[UV-Vis spectroscopic characterization of LB films of hydroxyl-substituted porphyrin derivatives].

The LB films forming properties of two hydroxyl-substituted porphyrins with double hexadecyl chains have been characterized. UV-Vis spectra show that the two porphyrins possess various aggregation behaviors in LB films. The porphyrin with symmetrically attached chains tend to form J-aggregate and the other asymmetric porphyrin can form hydrogen-bonded aggregate in LB films. The orientation of porphyrin rings was examined by polarized UV-Vis spectra. The results indicate that the situation of side-chain attached on porphyrin ring has no influence on porphyrin ring orientation, but has great influence on mean molecular areas or the distanses between porphyrin rings, and so as to affect the aggregation behaviors of porphyrin in LB films.

Molecular Structure↗

PubMed1998

Thermodynamic analysis of the binding of the polyglutamate chain of 5-formyltetrahydropteroylpolyglutamates to serine hydroxymethyltransferase.

The thermodynamic parameters for the binding of 5-formyltetrahydrofolate (5-CHO-H4PteGlun) and its polyglutamate forms to rabbit liver cytosolic serine hydroxymethyltransferase (SHMT) were determined by a combination of isothermal titration calorimetry and spectrophotometry. Binding of 5-CHO-H4PteGlun to SHMT exhibits both positive enthalpy and entropy, showing that binding is entropically driven. 5-CHO-H4PteGlu5 has a 300-fold increased affinity for SHMT compared to 5-CHO-H4PteGlu. This increase in affinity is due primarily to a decrease in the positive enthalpy with little change in entropy. A variety of anions inhibit the binding of 5-CHO-H4PteGlu5 with Ki values in the 10-20 mM range. Anions are ineffective inhibitors of 5-CHO-H4PteGlu binding to SHMT, showing that anions compete for the polyglutamate binding site. There was little difference in the Ki values for a series of dicarboxylic acids as inhibitors of 5-CHO-H4PteGlu5, suggesting that spacing of the negative charges may not be important in determining their effectiveness as inhibitors. Both the mono- and pentaglutamate derivatives of 5-CHO-H4PteGlun were cross-linked to SHMT by a carbodiimide reaction to Lys-450 which resides in a stretch of Lys, His, and Arg residues.

Amino Acid Sequence↗