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Biomedical subjects

T Xia

Publications and source records attributed to T Xia.

At least 55 records · Page 3Linked to original sources
PubMed1999

[The detection of high risk human papillomaviruses in papillary transitional cell carcinoma of urinary bladder].

OBJECTIVE: To investigate the histological evidence of high risk human papillomavirus infection in bladder cancer. METHODS: 52 cases of papillary transitional cell carcinoma of the urinary bladder were studied for the incorporation of high risk human papillomavirus type 16 and type 18 DNA by non-isotopic in situ hybridization (NISH). RESULTS: 19 of 52 cases (36.5%) were positive for HPV DNA with punctuate and/or diffuse purple-blue staining in the nucleus of cancer cells, including two cases positive both for HPV16/18. HPV DNA were predominantly expressed in superficial tumors. Among these positive tumors, adjacent normal epithelium and Brunn's nests also showed positive staining. Morphologically, HPV positive cells existed in the whole layer of papillary tumor cells, 3 of them presented koilocytoid change. CONCLUSIONS: HPV infection might be a common event in urinary bladder and a potential factor for carcinogenesis of bladder cells.

Adult↗
PubMed1999

[Clinicopathologic study of 11 patients with Paget's disease of scrotum].

OBJECTIVE: To probe the relationship of clinicopathologic presentations and prognosis of Paget's disease primarily involving the scrotum. METHODS: 11 cases of scrotal Paget's disease were studied retrospectively from 1984 to 1997. PAS was stained and EMA, S-100, HMB45, CEA and CA15-3 were immunostained in all cases for the differential diagnosis from Bowen's disease and malignant melanoma. RESULTS: Six of 11 cases involved hair follicle and/or sweat glands, and 3 cases involved dermis (one had metastasis of left superficial and deep inguinal lymph nodes, and left internal iliac lymph nodes). Paget's cells were positive for PAS (11/11), EMA (11/11), CEA (6/11), CA15-3 (11/11), and negative for S-100, HMB45. Wide local excision of the lesions was performed in 10 of 11 patients both for primary disease and recurrent disease. 3 of the 10 patients underwent lymph nodes resection and metastasis was found in 1 case pathologically. One patient accepted chemotherapy and died, from respiratory insufficiency after one month. The other 10 patients were followed up for 6 to 127 months and no patient died of Paget's disease. CONCLUSIONS: Involvement of hair follicles and sweat glands by Paget's cell does not influence the prognosis.However, invasion of dermis by Paget's cells may suggest possible metastasis.

Aged↗
PubMed1998

Thermodynamic parameters for an expanded nearest-neighbor model for formation of RNA duplexes with Watson-Crick base pairs.

Improved thermodynamic parameters for prediction of RNA duplex formation are derived from optical melting studies of 90 oligoribonucleotide duplexes containing only Watson-Crick base pairs. To test end or base composition effects, new sets of duplexes are included that have identical nearest neighbors, but different base compositions and therefore different ends. Duplexes with terminal GC pairs are more stable than duplexes with the same nearest neighbors but terminal AU pairs. Penalizing terminal AU base pairs by 0.45 kcal/mol relative to terminal GC base pairs significantly improves predictions of DeltaG degrees37 from a nearest-neighbor model. A physical model is suggested in which the differential treatment of AU and GC ends accounts for the dependence of the total number of Watson-Crick hydrogen bonds on the base composition of a duplex. On average, the new parameters predict DeltaG degrees37, DeltaH degrees, DeltaS degrees, and TM within 3.2%, 6.0%, 6.8%, and 1.3 degreesC, respectively. These predictions are within the limit of the model, based on experimental results for duplexes predicted to have identical thermodynamic parameters.

Base Pairing↗
PubMed1998

[The detection and isolation of fetal nucleated erythrocytes from maternal blood using flow cytometry].

OBJECTIVE: To isolate fetal nucleated red blood cells (NRBCs) from maternal blood and to confirm its fetal origin. METHODS: Monoclonal antibody against the glycophorin A (GPA) was used to identify nucleated erythrocytes in the peripheral blood of pregnant women. Candidates fetal cells from 3 pregnancies at 16 to 24 weeks of gestation were isolated successfully. Sorted cells were also confirmed using Y-special probe (PY3.4) repeated sequences (SRY) in maternal blood from women carrying male fetuses were detected by polymerase chain reaction (PCR). RESULTS: The PY3.4 position hybridization rates were 31.5%, 0 and 38% respectively in sorted GPA positive cells (GPA+)of 3 samples by FISH, and the results of GPA+ cells of the 3 cases by PCR were positive, negative and positive respectively, which were manifested by the gender after aborticide. CONCLUSION: This study demonstrates that fetal NRBCs are present in the peripheral blood of pregnant women and it is possible to isolate and detect them.

Erythrocytes↗
PubMed1998

Substrate ambiguity of 3-deoxy-D-manno-octulosonate 8-phosphate synthase from Neisseria gonorrhoeae in the context of its membership in a protein family containing a subset of 3-deoxy-D-arabino-heptulosonate 7-phosphate synthases.

3-Deoxy-D-manno-octulosonate 8-phosphate (KDOP) synthase and 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP) synthase catalyze similar phosphoenolpyruvate-utilizing reactions. The genome of Neisseria gonorrhoeae contains one gene encoding KDOP synthase and one gene encoding DAHP synthase. Of the two nonhomologous DAHP synthase families known, the N. gonorrhoeae protein belongs to the family I assemblage. KDOP synthase exhibited an ability to replace arabinose-5-P with either erythrose-4-P or ribose-5-P as alternative substrates. The results of periodate oxidation studies suggested that the product formed by KDOP synthase with erythrose-4-P as the substrate was 3-deoxy-D-ribo-heptulosonate 7-P, an isomer of DAHP. As expected, this product was not utilized as a substrate by dehydroquinate synthase. The significance of the ability of KDOP synthase to substitute erythrose-4-P for arabinose-5-P is (i) recognition of the possibility that the KDOP synthase might otherwise be mistaken for a species of DAHP synthase and (ii) the possibility that the broad-specificity type of KDOP synthase might be a relatively vulnerable target for antimicrobial agents which mimic the normal substrates. An analysis of sequences in the database indicates that the family I group of DAHP synthase has a previously unrecognized membership which includes the KDOP synthases. The KDOP synthases fall into a subfamily grouping which includes a small group of DAHP synthases. Thus, family I DAHP synthases separate into two subfamilies, one of which includes the KDOP synthases. The two subfamilies appear to have diverged prior to the acquisition of allosteric-control mechanisms for DAHP synthases. These allosteric control specificities are highly diverse and correlate with the presence of N-terminal extensions which lack homology with one another.

3-Deoxy-7-Phosphoheptulonate Synthase↗
PubMed1998

Effect of beverage osmolality on intestinal fluid absorption during exercise.

To determine how osmolality of an orally ingested fluid-replacement beverage would alter intestinal fluid absorption from the duodenum and/or jejunum during 85 min of cycle exercise (63.3 +/- 0.9% peak O2 uptake) in a cool environment (22 degreesC), seven subjects (5 men, 2 women, peak O2 uptake = 54.5 +/- 3.8 ml . kg-1 . min-1) participated in four experiments separated by 1 wk in which they ingested a water placebo (WP) or one of three 6% carbohydrate (CHO) beverages formulated to give mean osmolalities of 197, 295, or 414 mosmol/kgH2O. CHO solutions also contained 17-18 meq Na+ and 3.2 meq K+. Nasogastric and multilumen tubes were fluoroscopically positioned in the gastric antrum and duodenojejunum, respectively. Subjects ingested a total of 23 ml/kg body mass of the test solution, 20% (370 +/- 9 ml) of this volume 5 min before exercise and 10% (185 +/- 4 ml) every 10 min thereafter. By using the rate of gastric emptying as the rate of intestinal perfusion (G. P. Lambert, R. T. Chang, D. Joensen, X. Shi, R. W. Summers, H. P. Schedl, and C. V. Gisolfi. Int. J. Sports Med. 17: 48-55, 1996), intestinal absorption was determined by segmental perfusion from the duodenum (0-25 cm) and jejunum (25-50 cm). There were no differences (P > 0.05) in gastric emptying (mean 18.1 +/- 1.3 ml/min) or total fluid absorption (802 +/- 109, 650 +/- 52, 674 +/- 62, and 633 +/- 74 ml . 50 cm-1 . h-1 for WP, hypo-, iso-, and hypertonic solutions, respectively) among beverages; but WP was absorbed faster (P < 0.05) from the duodenum than in the jejunum. Of the total volume of fluid ingested, 82 +/- 14, 74 +/- 6, 76 +/- 5, and 68 +/- 7% were absorbed for WP, hypo-, iso-, and hypertonic beverages, respectively. There were no differences in urine production or percent change in plasma volume among solutions. We conclude that total fluid absorption of 6% CHO-electrolyte beverages from the duodenojejunum during exercise, within the osmotic range studied, is not different from WP.

Adult↗
PubMed1998

[Culture of murine HPP-CFC in vitro using conditioned medium substitutefor recombinant growth factors].

OBJECTS: To study the clonal growth on single layer, agar of high proliferative potential colony-forming cells (HPP-CFC) of bone marrow obtained from both normal mice (NBM) and mice treated 2 days earlier with 5-fluorouracil (FU,BM) using conditioned media. MATERIAL AND METHODS: Using liquid cell culture to harvert WEHI2-CM and L929-CM as the substitutes for IL-3 and M-CSF respectively; using semi-solid culture to assay HP-CFCin vitro. RESULTS: (1) the combination of WEHI3-CM and L929-CM produced HPP-CFC in vitro, and the addition of rhIL-1 alpha, rhIL-6 and rmGM-CSF further enhanced HPP-CFC was enriched in the FU2 BM. Morphological investigation showed that the HPP-CFC colony was large and compact, great than 0.5mm in diameter and contained more than 50,000 cells, most of which were macrophage like cells. The hydroxyurea suicide rate for HPP-CFC was less than 10%. CONCLUSION: The results suggested that (1) WEHI3-CM and L929-CM can be used as the substitutes of IL-3 and M-CSF to stimulate the formation of HPP-CFC; (2) FU can enrich HPP-CFC of the mice.

Animals↗
PubMed1997

Thermodynamics of nonsymmetric tandem mismatches adjacent to G.C base pairs in RNA.

The thermodynamic stabilities and structures of a series of RNA duplexes containing nonsymmetric tandem mismatches in the context of , where are tandem mismatches, were studied by UV melting and imino proton NMR. The contribution of one mismatch to the free energy increment for tandem mismatch formation depends on the identity of the other mismatch. Imino proton NMR indicates that this is partly because the structure of a mismatch is dependent on the adjacent mismatch. The results suggest that differences in size, shape, and hydrogen bonding of the adjacent mismatches play important roles in determining loop stability. A model for predicting stabilities of all possible tandem mismatches is proposed based on these and previous results.

Base Composition↗
PubMed1997

Fructose transport mechanisms in humans.

BACKGROUND & AIMS: The possible mechanisms of fructose transport are diffusion, a disaccharidase-related transport system, and glucose-facilitated fructose transport. However, these mechanisms in the human small intestine have not been systematically examined. This study was designed to investigate the mechanisms of fructose transport in the human duodenojejunum. METHODS: A triple-lumen tube was fluoroscopically positioned in the duodenojejunum of 7 men. Nine carbohydrate-electrolyte solutions were perfused at the rate of 15 mL/min. Acarbose and lactulose were used to examine the disaccharidase-related transport system and glucose-facilitated fructose transport, respectively. RESULTS: Fructose absorption was greater (P < 0.05) from fructose-glucose (FruGlu) and fructose-glucose-acarbose (FruGluA) solutions than from fructose-mannitol (FruMann) and fructose-mannitol-acarbose (FruMannA) solutions, but there was no difference between FruGlu and FruGluA solutions. A sucrose solution produced greater (P < 0.05) sucrose absorption than a sucrose-acarbose solution. Lactulose absorption (0.016-0.039 mmol.h-1.cm-1) was observed from solutions containing glucose or sucrose. Water absorption was not different among sucrose, FruGlu, and glucose solutions. FruMann solution produced net water secretion. These data suggest that free fructose and glucose transport were not inhibited by acarbose and that the presence of glucose induced lactulose absorption and enhanced fructose absorption. CONCLUSIONS: Fructose is transported transcellularly by facilitated diffusion and paracellularly (based on lactulose transport) via glucose-activated solution drag. In the human small intestine, free fructose and glucose transport does not occur via the disaccharidase system.

Acarbose↗
PubMed1997

Absorption from different intestinal segments during exercise.

This study evaluated intestinal absorption from the first 75 cm of the proximal small intestine during 85 min of cycle exercise [63.6 +/- 0.7% peak O2 consumption (VO2 peak)] while subjects ingested either an isotonic carbohydrate-electrolyte beverage (CHO-E) or a water placebo (WP). The CHO-E beverage contained 117 mM (4%) sucrose, 111 mM (2%) glucose, 18 meq Na+, and 3 meq K+. The two experiments were performed a week apart by seven subjects (6 men and 1 woman; mean VO2 peak = 53.5 +/- 6.5 ml . kg-1 . min-1). Nasogastric and multilumen tubes were fluoroscopically positioned in the gastric antrum and duodenojejunum, respectively. Subjects ingested 23 ml/kg body weight of the test solution, 20% (383 +/- 11 ml) of this volume 5 min before exercise and 10% (191 +/- 5 ml) every 10 min thereafter. By using the rate of gastric emptying (18.1 +/- 1.1 vs. 19.2 +/- 0. 7 ml/min for WP and CHO-E, respectively) as the rate of intestinal perfusion, intestinal absorption was determined by segmental perfusion from the duodenum (0-25 cm) and jejunum (25-50 and 50-75 cm). Water flux was different (P < 0.05) between solutions in the 0- to 25- and 25- to 50-cm segments for WP vs. CHO-E (30.7 +/- 2.7 vs. 15.0 +/- 2.9 and 3.8 +/- 1.1 vs. 11.9 +/- 3.3 ml . cm-1 . h-1, respectively). Furthermore, water flux differed (P < 0.05) for WP in a comparison of the 0- to 25- to the 25- to 50-cm segment. Total solute flux (TSF) was not significantly different among segments for a given solution or between solutions for a given segment. There was no difference between trials for percent change in plasma volume. These results indicate that 1) fluid absorption in the proximal small intestine depends on the segment studied and 2) solution composition can significantly effect water absorption rate in different intestinal segments.

Adult↗
PubMed1997

[Effects of lithium on the proliferation of murine high proliferative potential colony-forming cells and granulocyte macrophage colony forming unit in vitro].

The effects of LiCl on the proliferation of high proliferative potential colony-forming cells (HPP-CFC) and granulocyte macrophage colony-forming unit (CFU-GM) from bone marrow of BALB/c mice were observed. The colonies of HPP-CFC were supported by IL-1, IL-6, WEHI-3 conditioned medium (WEHI-3 CM, which contained IL-3) and L929 conditioned medium (L929-CM, which contained M-CSF); the colonies of CFU-GM were supported by WEHI-3 CM. It was shown that LiCl at concentrations ranging from 0.4 mmol/L to 2 mmol/L significantly inhibited the proliferation of HPP-CFC (P < 0.01), but concentrations ranging from 0.4 mmol/L to 1 mmol/L significantly increased the production of CFU-GM (P < 0.05), both effects displayed in dose-dependent manners. The different effects of LiCl on the proliferation of HPP-CFC and CFU-GM suggest that LiCl may induce HPP-CFC differentiation into more mature cells.

Animals↗
PubMed1997

[Drug resistance and its mechanism of intrinsic drug-resistant cell line GRC-1].

In order to probe the characteristics of drug resistance and its mechanisms of renal cell carcinoma, drug-resistant spectrum of renal cell carcinoma cell line GRC-1 was detected by in vitro MTT colorimetric assay, the mechanism of drug resistance in GRC-1 was also studied by the methods of both immunocytochemistry assay and flow fluorescence cytometry. The results demonstrated that GRC-1 was cross-resistant to adriamycin, vincrinstine, etoposide and carboplatinium, both mdr1 gene product P-glycoprotein and GST-pi which was an isozyme of glutathione S-transferases were expressed in GRC-1. The accumulation of net intracellular drugs of GRC-1 was less than that of drug sensitive breast cancer cell line MCF7, and the ability of pumping drugs out of cells was higher than that of MCF7. The results suggested that there is an intrinsic multidrug resistance in GRC-1 cell line, and both P-glycoprotein and glutathione systems play a role in the development of drug resistance for GRC-1. GRC-1 is an ideal target cell line for the study of drug resistance.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Comparison of cleavage site specificity of gelatinases A and B using collagenous peptides.

The gelatinases (type IV collagenases) are members of the matrix metalloproteinase family that not only have a high degree of structural homology but are known to be nearly identical in their digestion profile against macromolecular substrates. We have shown previously that the preferred cleavage sites in the hydrolysis of type I gelatin, catalyzed by gelatinase A (72 kDa type IV collagenase), are bracketed by hydroxyproline in the P5 and P5' positions. In this report, a kinetic investigation using a series of collagenous dodecylpeptides in which the P5 and P5' hydroxyprolines were systematically varied and used as substrates for recombinant human gelatinase A, we show that replacement with either proline or alanine always resulted in increased Km. In contrast, substitution of the hydroxylated amino acids tyrosine and serine at P5 and P5' reduced the Km significantly, indicating that the hydroxyl moiety of the hydroxyproline is the functional group responsible for favorable enzyme-substrate affinity. This was shown by the kcat/Km ratio, which was doubled by the substitution of serine in that site. Cleavage of the same series of dodecylpeptides by recombinant human gelatinase B (92 kDa type IV collagenase) showed a very different kinetic profile for which no patterns were discernible. In subsequent comparisons of the two enzymes, it was found that gelatinase B cleaved the thiopeptolide substrate AcProLeuGly-S-LeuGly-OC2H5 at double the velocity of gelatinase A. In contrast, gelatinase A digested type I gelatin about 2.5-times faster than gelatinase B. SDS-PAGE analysis of gelatin cleavage products showed different patterns of product peptides for each enzyme. Further comparisons of the proteinases using synthetic peptide substrates with variations in size and in substituents at the P2' site again showed marked kinetic differences. Although these two matrix metalloproteinases seem similar in that they are both gelatinolytic and can degrade a nearly identical battery of macromolecular matrix components including type IV collagen, it is clear from these results that they are very different enzymatically. Since the regulatory portions of gelatinases A and B differ markedly, it has been assumed that the enzymes serve the same function, but respond to different stimuli. The differences in substrate specificity described herein suggest that their proposed physiological roles may require reevaluation.

Amino Acid Sequence↗
PubMed1996

[Proliferation and apoptosis status in benign prostatic hyperplasia].

The aim of this study was to examine the proliferation and apoptosis status in normal prostate and benign prostatic hyperplasia. The proliferation status was evaluated by using monoclonal antibodies which recognize the proliferating cell nuclear antigen and the proliferating associated nuclear antigen Ki67. The apoptosis status was detected by in situ end-labeling of fragmented DNA using the terminal deoxynucleotidyl transferase reaction. A total of 22 cases benign prostatic hyperplasia and 20 cases of normal protate specimens were studied. The proliferation index of BPH was much higher than that of normal prostates, and the apoptosis index of hyperplasia epithelium was much lower than that of normal prostatic epithelium. The results suggest that both high proliferating rate and low apoptosis rate are associated with the pathogenesis of benign prostatic hyperplasia.

Antibodies, Monoclonal↗
PubMed1995

[Action of Rhodobrum roserm Limpr on changes of red cell aggregation and yield-shear stress in dogs with acute experimental coronary occlusion].

Following acute occlusion of the left anterior descending coronary artery in dogs, significant increases were observed in the red cell aggregation index, yield-shear stress and red cell electrophoretic time in blood drained from ischemic area. When transfusion was performed with Rhodobrum roseum solution from the right femoral vein, significant rises of the above-said items were observed.

Animals↗
PubMed1994

Regulation of rat liver phenylalanine hydroxylase. II. Substrate binding and the role of activation in the control of enzymatic activity.

Activation by phenylalanine and reduction by the co-factor (6R)-tetrahydrobiopterin (BH4) are required for formation of active liver phenylalanine hydroxylase. This work describes effects of the activation and redox state on substrate and effector recognition of this enzyme, it establishes relationships among the pterin and phenylalanine binding sites on the different forms of the enzyme, and it provides a quantitative description of the enzyme's presumptive regulatory and catalytic sites. BH4, 7,8-dihydrobiopterin (BH2), 6-methyltetrahydropterin, and 5-deaza-6-methyltetrahydropterin were found to bind to unactivated phenylalanine hydroxylase with a stoichiometry of 1/enzyme subunit and with hyperbolic kinetics; all appear to compete for the same binding site on the enzyme, and all appear to bind in the proximity of, but not to, the enzyme's non-heme iron. In the transition from unactivated to activated enzyme, phenylalanine and pterin binding is modified, a new site for phenylalanine is formed, and the pterin site is replaced by a site of greatly decreased affinity for BH4 and BH2, one which does not appear to recognize the dihydroxypropyl side chain of BH4 and BH2. The pterin- and phenylalanine-binding sites on activated phenylalanine hydroxylase appear to be part of the enzyme's active site. Despite large effects on substrate binding, neither chelator binding ability nor solvent accessibility of the iron are affected by activation; activation appears to affect the nearby environment of the enzyme's iron but not the iron itself. Studies of oxidized and reduced phenylalanine hydroxylase indicate that the redox state is not a major determinant of pterin and phenylalanine association with enzyme.

Animals↗
PubMed1994

Regulation of rat liver phenylalanine hydroxylase. III. Control of catalysis by (6R)-tetrahydrobiopterin and phenylalanine.

Effects of phenylalanine and di- and tetrahydropterins on presteady-state and steady-state catalytic behavior of rat liver phenylalanine hydroxylase are analyzed. From this and previous work (Shiman, R, Xia, T., Hill, M., and Gray, D.(1994) J. Biol. Chem. 269, 24647-24656), which analyzed binding of the same compounds to the enzyme in the absence of catalysis, a model of phenylalanine hydroxylase regulation is proposed. The mechanism appears novel in that 1) one substrate, phenylalanine, is a positive effector (activator), 2) a second substrate, (6R)-tetrahydrobiopterin (BH4), is a negative effector that blocks phenylalanine activation by forming an inactive BH4.enzyme complex, and 3) the BH4.enzyme complex sequesters BH4 and controls its metabolic availability. Reaction progress curves showing regulatory effects of BH4, 7,8-dihydrobiopterin (BH2), and phenylalanine are fit by the model with high precision. Data are presented that the high affinity pterin-binding site on unactivated phenylalanine hydroxylase is the pterin site that regulates catalysis. Occupancy of this site by BH4 or BH2 causes non-cooperative, linear inhibition of phenylalanine activation of the enzyme. All inhibitory effects of BH4 appear due to its binding at the pterin regulatory site on unactivated enzyme. BH2 inhibits by binding at the active site as well as the pterin regulatory site. 6-Methyltetrahydropterin also appears to bind at the pterin regulatory site, but its effect is only seen at high phenylalanine concentrations. Using kinetic constants measured in this and earlier work, quantitative effects of phenylalanine and BH4 regulation on the rate of the phenylalanine hydroxylase reaction in vitro and in vivo are calculated. The effects of formation of the BH4.enzyme complex on free BH4 concentration, on enzyme activity, and on regulation of the rate of phenylalanine hydroxylation in liver are discussed.

Animals↗