Biomedical subjects

H Xiang

Publications and source records attributed to H Xiang.

At least 73 records · Page 4Linked to original sources

PubMed1997

[Clinical application of expanded radical operation with improved Whipple technique to late pancreas head cancer].

Studies on the expanded eradicative and modified operation for treatment in patients of late pancreas head cancer, so as to enhance the incised rate, survival rate and life quality. Elective laparotomy was done in 20 patients. Expanded eradicative operation was performed in 18 patients (portal vein excision 19, left outer leaf of liver 8, transverse colon 3). We have reconstructed the portal vein 6, modified the Whipple operation, reconstructed the elementary tract using Roux-Y interposed jejunum with orientatied intussusception of artificial papilla. The incised rate of expanded eradication was 90% without postoperative serious complications such as biliary and pancreatic leakage, massive hemorrhage and operative death. The longest survival time was 5 years. The two-year survival rate was 50%. Statistical analysis (t test and x2) showed signithicant differences (P < 0.001).: (1) The exsion of original carcinomous focus may relieve the patient's symptoms and can prevent portal vein from carcinomous cell infiltration. (2) After enbloc incision with metastatic focus, sequential treatment could be given successfully.

Adult↗

PubMed1997

[Study of the antioxidative effect of tea polyphenol and allitridi on cultured rat lens in vitro].

PURPOSE: To investigate the oxidative modification of lens proteins in the presence of H2O2 in vitro and the protective effect of tea polyphenol(TP) and allitridi. METHODS: Rat lenses were cultured in DMEM medium containing H2O2(1mM) at 37 degrees C in CO2 incubator. Iron and copper salts were added to the medium. At 24 or 48 hours, photographs were recorded the changes in transparency of rat lens and lens proteins were analysed by SDS-PAGE and IEF. TP and allitridi were added to the medium with lens in order to test the antioxidant effects. RESULTS: Lens opacities occurred at the equatorial region by 24 hours, progressing to totally opaque by 48 hours. SDS-PAGE revealed new bands higher than 43KD were found. In addition the 30KD band disappeared in medium containing copper salt. With addition of TP or allitridi to the culture system, all lens remained transparent. CONCLUSION: Exposure rat lens to H2O2 with iron or copper salt resulted in opacification of lens with crosslinking of crystallins and degradation of lens polypeptides. Addition of TP or allitridi prevented the lens from oxidative stress.

Allyl Compounds↗

PubMed1996

Evidence for p53-mediated modulation of neuronal viability.

A role for p53-related modulation of neuronal viability has been suggested by the finding that p53 expression is increased in damaged neurons in models of ischemia and epilepsy. These findings were recently extended with the demonstration that mice deficient in p53 ("knock-out" mice) exhibit almost complete protection from seizure-induced brain injury, whereas wild-type mice display significant neuronal cell loss in the hippocampus and other brain regions. Because the p53 knock-out mice used in the latter study expressed a global p53 deficiency in all cell types, it was not possible to conclude that protection was conferred by the exclusive absence of p53 in neurons. Therefore, in the present study, we determined whether p53 expression in isolated neurons is directly coupled to a loss of viability associated with excitotoxic challenge. Primary cultures of hippocampal or cortical neurons were derived from animals containing p53 (+/+, +/-) or those deficient in p53 (-/-). p53-Deficient neurons appeared identical to wild-type neurons with respect to morphology, neurofilament expression, and resting levels of intracellular calcium. Neurons containing at least one copy of p53 were severely damaged by exposure to kainic acid or glutamate. Cell damage was assessed by direct cell counting and by nuclear morphology after propidium iodide staining of DNA. In contrast, neurons deficient in p53 (-/-) exhibited little or no damage in response to excitotoxin treatment. Despite their divergent outcomes, p53 (+/+) and p53 (-/-) neurons demonstrated similar sustained elevations in intracellular calcium levels triggered by glutamate exposure. Restoring p53 expression to p53-deficient neurons, using adenovirus-mediated transduction, was sufficient to promote neuronal cell death even in the absence of excitotoxin. These results demonstrate a direct relationship between p53 expression and loss of viability in CNS neurons.

Animals↗

PubMed1996

Identification of active site residues essential to 4-chlorobenzoyl-coenzyme A dehalogenase catalysis by chemical modification and site directed mutagenesis.

4-Chlorobenzoyl-coenzyme A (4-CBA-CoA) dehalogenase catalyzes the hydrolysis of 4-CBA-CoA to 4-hydroxybenzoyl-coenzyme A (4-HBA-CoA) via a nucleophilic aromatic substitution pathway involving the participation of an active site carboxylate side chain in covalent catalysis. In this paper we report on the identification of conserved aspartate, histidine, and tryptophan residues essential to 4-CBA-CoA catalysis using chemical modification and site-directed mutagenesis techniques. Treatment of the dehalogenase with diethyl pyrocarbonate resulted in complete loss of catalytic activity (Kinact = 0.17 mM-1 min-1 at pH 6.5, 25 degrees C) that was fully regained by subsequent treatment with hydroxylamine. The protection from inactivation afforded by enzyme bound 4-HBA-CoA indicated that the essential histidine residues are located at the active site. Replacement of conserved histidine residues 81, 90, 94, and 208 with glutamine residues resulted in a significant loss of catalytic activity only in the cases of the histidine 81 and 90 mutants. Substrate and product ligand binding studies showed that binding is not significantly inhibited in these mutants. Site directed mutagenesis of a selection of conserved aspartate and glutamate residues, identified aspartate 145 as being essential to dehalogenase catalysis. Ligand binding studies showed that this residue is not required for tight substrate/product binding. Chemical modification of the dehalogenase with N-bromosuccinimide resulted in full loss of catalytic activity that was prevented by saturation of the active site with product ligand, providing evidence favoring an essential active site tryptophan. Phenylalanine replacement of conserved tryptophan residues 179 and 137 reduced catalytic activity only in the latter (Kcat = 0.03% of wild-type dehalogenase). On the basis of these results and the recently determined X-ray crystal structure of the complex of 4-CBA-CoA dehalogenase and 4-HBA-CoA [Benning, M. M., Taylor, K.L., Liu, R.-Q., Yang, G., Xiang, H., Wesenberg, G., Dunaway-Mariano, D., Holden, H.M. (1996) Biochemistry 35,8103-8109] we propose that aspartate 145 functions as the active site nucleophile, that tryptophan 137 serves as a hydrogen bond donor to the aspartate 145 C = O, and that histidine 90 serves to deprotonate the bound H2O molecule.

Amino Acids↗

PubMed1996

Structure of 4-chlorobenzoyl coenzyme A dehalogenase determined to 1.8 A resolution: an enzyme catalyst generated via adaptive mutation.

Here we describe the three-dimensional structure of 4-chlorobenzoyl-CoA dehalogenase from Pseudomonas sp. strain CBS-3. This enzyme catalyzes the hydrolysis of 4-chlorobenzoyl-CoA to 4-hydroxybenzoyl-CoA. The molecular structure of the enzyme/4-hydroxybenzoyl-CoA complex was solved by the techniques of multiple isomorphous replacement, solvent flattening, and molecular averaging. Least-squares refinement of the protein model reduced the crystallographic R factor to 18.8% for all measured X-ray data from 30 to 1.8 A resolution. The crystallographic investigation of this dehalogenase revealed that the enzyme is a trimer. Each subunit of the trimer folds into two distinct motifs. The larger, N-terminal domain is characterized by 10 strands of beta-pleated sheet that form two distinct layers which lie nearly perpendicular to one another. These layers of beta-sheet are flanked on either side by alpha-helices. The C-terminal domain extends away from the body of the molecule and is composed of three amphiphilic alpha-helices. This smaller domain is primarily involved in trimerization. The two domains of the subunit are linked together by a cation, most likely a calcium ion. The 4-hydroxybenzoyl-CoA molecule adopts a curved conformation within the active site such that the 4-hydroxybenzoyl and the adenosine moieties are buried while the pantothenate and pyrophosphate groups of the coenzyme are more solvent exposed. From the three-dimensional structure it is clear that Asp 145 provides the side-chain carboxylate group that adds to form the Meisenheimer intermediate and His 90 serves as the general base in the subsequent hydrolysis step. Many of the structural principles derived from this investigation may be directly applicable to other related enzymes such as crotonase.

Acyl Coenzyme A↗

PubMed1996

Ligand-induced conformational change in the ferrichrome-iron receptor of Escherichia coli K-12.

Ferrichrome-iron is actively transported across the outer membrane of Escherichia coli by the TonB-dependent receptor FhuA. To obtain FhuA in a form suitable for secondary-structure analyses, a hexahistidine tag was inserted into a surface-located site and the recombinant protein was purified by metal chelate chromatography. Functional studies indicated that the presence of the hexahistidine tag did not interfere with FhuA localization or with ligand-binding activity. Ferrichrome protected lysine 67 but not lysine 5 of purified recombinant FhuA from trypsinolysis. Results from trypsin digestion were interpreted as a conformational change in FhuA which had occurred upon ferrichrome binding, thereby preventing access of trypsin to lysine 67. Circular dichroism and Fourier transform infrared spectroscopy revealed a predominance of beta-sheet structure for the purified protein. In the presence of ferrichrome, FhuA exhibited a secondary structure and a thermostability which were similar to FhuA without ligand. The addition of ferrichrome to purified FhuA reduced the ability of certain anti-FhuA monoclonal antibodies to bind to the receptor. All antibodies which could in this manner discriminate between FhuA and FhuA bound to ferrichrome had their determinants within a loop which is toward the N-terminus and which is exposed to the periplasm. These data indicate that the binding of ferrichrome induces a structural change that is propogated across the outer membrane and results in an altered conformation of a periplasmically exposed loop of FhuA. It is proposed that by such an alteration of FhuA conformation, TonB is triggered to energize the active transport of the bound ligand across the outer membrane.

Antibodies, Monoclonal↗

PubMed1995

[Gene diagnosis and carrier detection of hemophilia B by using genomic amplification with transcripts sequencing].

Using GAWTS technique (genomic amplification with transcripts sequencing), we studied germline mutation patterns of 36 hemophilia B patients from the mainland of China. Some distinctions between Chinese and USA caucasians were found. The GAWTS was strongly recommanded to be used in the direct genomic sequencing as a good technique. Seventeen carriers were identified.

Asian People↗

PubMed1994

[Differential diagnosis of endometrial abnormality by transvaginal sonography].

Transvaginal sonography examination was performed 450 times in 281 women to diagnose the endometrial abnormality by measuring the thickness of endometrium. There were 37 women with normal ovulatory cycles, 200 postmenopausal women with no vaginal bleeding, and 44 women with irregular vaginal bleeding. For ovulatory cycles, the mean of endometrial thickness was 7.8 +/- 2.1 mm (3-13 mm) in the follicular phase, 10.4 +/- 1.9 mm (8-13 mm) around ovulation and 10.4 +/- 2.3 mm (8-19 mm) in the luteal phase. The average thickness of endometrium for postmenopausal women without bleeding was 1.4 +/- 0.7 mm (1-5 mm). The measurement of the thickness of endometrium in women with irregular vaginal bleeding was also confirmed by histological analysis. Atrophy endometrium was diagnosed in 6 cases, the thickness of endometrium was 2.2 +/- 2.0 mm, hydrohystera was found in 8 women, thickness of endometrium was 14.5 +/- 6.1 mm, endometrial hyperplasia in 10 cases, thickness was 17.4 +/- 6.7 mm, endometrial polyps in 12 cases, thickness was 16.7 +/- 7.7 mm, and endometrial carcinoma in 8 cases, thickness was 24.4 +/- 11.9 mm. Generally, the normal thickness of endometrium for postmenopausal women should be less than 5.0 mm.

Adult↗

PubMed1994

Comparative aspects of the role of neuropeptide Y in the regulation of the vertebrate heart.

The role of neuropeptide Y (NPY) in the regulation of cardiac function was compared in mammalian and fish hearts. In mammalian heart, most studies have shown that neuropeptide Y inhibits coronary flow and exerts a negative inotropic effect in isolated perfused hearts and cardiac muscles. The mechanisms involved in the action of neuropeptide Y in the heart are under active investigation. Our studies have shown that [Leu31,Pro34]NPY. NPY13-36, neuropeptide Y and peptide YY induced a concentration-dependent decrease in inositol 1,4,5-trisphosphate levels in rat cardiomyocytes, which was blocked by neuropeptide Y antagonists NPY18-36 or PYX-2. There is no difference in the inhibitory effect of neuropeptide Y and peptide YY on inositol 1,4,5-trisphosphate formation. Furthermore, the effects of neuropeptide Y and its analogues were insensitive to pertussis toxin pretreatment. These observations indicate that Y1 and Y2 subtypes of neuropeptide Y receptor in rat cardiomyocytes may be associated with inositol 1,4,5-trisphosphate formation through a pertussis toxin-insensitive Gq protein. The decreased formation of inositol 1,4,5-trisphosphate may be implicated in the negative inotropic effect of neuropeptide Y in the mammalian heart. In dogfish hearts, on the other hand, neuropeptide Y increased cardiac output by increasing heart rate, whereas norepinephrine increased cardiac output by increasing stroke volume. Although neuropeptide Y or norepinephrine alone did not have significant effects on pressure development in these hearts, neuropeptide Y plus norepinephrine did increase pressure development. The inositol 1,4-5-triphosphate level was elevated by norepinephrine alone and was further increased by neuropeptide y plus norepinephrine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

K+ channel and alpha 2-adrenergic effects on glucose-induced Ca2+i surges: aberrant behavior in ob/ob mice.

Glucose-induced shifts in intracellular free Ca2+ concentration ([Ca2+]i) were quantitatively and temporally the same in ob/ob and +/+ beta-cells. In both, epinephrine promptly and protractedly inhibited the glucose-induced [Ca2+]i surge via a pertussis toxin-sensitive alpha 2-adrenergic mechanism that was reversible by potassium depolarization. When added before glucose, epinephrine blocked completely in the ob/ob beta-cells, but in the +/+ beta-cells it produced a delayed, reduced, and transient intracellular Ca2+ (Ca2+i) surge. Neither the ATP-sensitive K+ channel blocker tolbutamide nor the large-conductance Ca(2+)-activated K+ channel (Kmaxi) blocker charybdotoxin reversed the effect of epinephrine. Tetraethylammonium (TEA), a blocker of both the Kmaxi and the delayed-rectifier K+ channel, and forskolin attenuated the effect of epinephrine in +/+ but not in the ob/ob beta-cells. The data show that 1) alpha 2-adrenoreceptor activation decreases the glucose-stimulated Ca2+i surge in +/+ beta-cells primarily by activating a tolbutamide- and charybdotoxin-insensitive, TEA- and forskolin-sensitive K+ channel; 2) the hypersecretion of insulin in ob/ob beta-cells is not due to enhanced glucose-induced Ca2+ influx; and 3) the ob/ob beta-cells are aberrant with regard to alpha 2-adrenergic modulation.

Animals↗

PubMed1993

Inhibitory effect of neuropeptide Y and its analogues on inositol 1,4,5-trisphosphate level in rat cardiomyocytes.

A negative inotropic effect of neuropeptide Y (NPY) in the mammalian heart has been reported. The mechanism(s) involved in the action of NPY in the heart is still unclear. Since D-myo-inositol 1,4,5-trisphosphate[Ins(1,4,5)P3] is known to be an important second messenger in the regulation of cardiac function, we carried out a study to investigate the status of Ins(1,4,5)P3 levels in response to NPY stimulation in rat cardiomyocytes. We also studied the possible involvement of NPY receptor subtypes in Ins(1,4,5)P3 formation. [Leu31, Pro34]NPY,NPY13-36, NPY and peptide YY (PYY) Induced a concentration-dependent decrease in Ins(1,4,5)P3 levels [measured with an Ins(1,4,5)P3 protein binding assay kit] in rat cardiomyocytes, which was blocked by NPY antagonists NPY18-36 or PYX-2. There is no difference in the inhibitory effect of NPY and PYY on Ins(1,4,5)P3 formation. Furthermore, effects of NPY and its analogues were insensitive to pertussis toxin pretreatment. Two new and more specific Y2 receptor agonists, [Ahx5-24]NPY and [Ahx5-24, gamma-Glu2-epsilon-Lys30]NPY, produced similar effects as NPY13-36 on Ins(1,4,5)P3 formation. These observations indicate that Y1 and Y2 subtypes of NPY receptor in rat cardiomyocytes may be associated with Ins(1,4,5)P3 formation through a pertussis-toxin-insensitive Gq protein. The decreased Ins(1,4,5)P3 formation may be implicated in the negative inotropic effect of NPY in the heart.

Animals↗

PubMed1993

[The relationship between increased QT dispersion of acute myocardial infarction and ventricular fibrillation].

We measured 62 patients' QT dispersion (QTd) and JT dispersion (JTd) of acute myocardial infarction (AMT) on first ECG within 48 hour. The results showed that QTd and JTd were greater in 16 patients with ventricular fibrillation (Vf) compared without Vf (QTd mean 107.50 +/- 35.80ms to 48.90 +/- 17.90 ms, P < 0.01; JTd mean 107.50 +/- 31.00ms to 52.60 +/- 19.00 ms, P < 0.01) during the early phase of AMI. That long QTd and/or JTd may possibly relate to Vf of AMI. Thus, we suggest that QTd and/or JTd may be of significant prediction value for prognosis of AMI.

Aged↗

PubMed1992

Protein kinase C activity is altered in diabetic rat hearts.

An elevation in diacylglycerol content in the myocardium from diabetic rats has been reported. Since diacylglycerol is known to be an important second messenger in activating protein kinase C, we carried out a study to investigate the status of protein kinase C activity in the hearts of Wistar diabetic rats. Our results showed that protein kinase C activity was significantly increased in the membrane fraction of diabetic hearts compared with controls, and the increased activity was accompanied by a decrease in cytosolic protein kinase C activity in these diabetic hearts. The increase in the membrane-bound protein kinase C activity thus appears to be due to translocation of the enzyme from the cytosolic to the membrane fraction. These results indicate that the development of diabetic cardiomyopathy is accompanied with a high membrane-bound protein kinase C level.

Animals↗

PubMed1992

Influence of arachidonic acid metabolites on cardiac alpha 1-adrenoceptor responses in diabetic rats.

There is evidence that one or more metabolites of arachidonic acid can produce positive inotropic effects and may also be implicated in the enhanced alpha 1-adrenoceptor responses in hearts from diabetic rats. We therefore carried out a study to investigate the possibility that arachidonic acid metabolites could be involved in the altered cardiac alpha 1-effect of norepinephrine (in the presence of propranolol) in chronic streptozotocin-diabetic rats. Our results have shown that in the presence of the cyclooxygenase inhibitor indomethacin or the thromboxane synthetase inhibitor imidazole, the norepinephrine-stimulated positive inotropic effect and the formation of inositol 1,4,5-trisphosphate were significantly increased in control hearts but were unaltered in hearts from diabetic rats. The addition of the prostacyclin synthetase inhibitor tranylcypromine reduced the norepinephrine-stimulated positive inotropic effect and inositol 1,4,5-trisphosphate formation only in diabetic hearts and had no effect in the controls. The nature and physiological significance of the enhanced positive inotropic effect and inositol 1,4,5-trisphosphate formation in the control heart with the addition of indomethacin and imidazole are still unclear. The effect of tranylcypromine may indicate the participation of prostacyclin in mediating the enhanced alpha 1-inotropic effect of norepinephrine in the chronic diabetic heart.

Animals↗

PubMed1991

Alpha 1-adrenoceptor-mediated phosphoinositide breakdown and inotropic responses in diabetic hearts.

The mechanism(s) involved in diabetes-induced changes in the heart is still unclear, but one defect appears to occur in the alpha 1-adrenoceptor system. We evaluated the possibility that the changes in the inotropic responsiveness to alpha 1-adrenoceptor stimulation in streptozotocin-diabetic rat hearts may be linked to altered phosphoinositide turnover. Stimulation of alpha 1-adrenoceptor by norepinephrine (in the presence of propranolol) in right ventricles resulted in the formation of D-myo-inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] [measured with an Ins(1,4,5)P3 protein binding assay kit] in a time- and concentration-dependent manner in both control and diabetic rats. The increase in Ins(1,4,5)P3 preceded the increase in the norepinephrine-mediated positive inotropic effect. Diabetic hearts showed a greater maximum inotropic response to norepinephrine stimulation and also had higher Ins(1,4,5)P3 levels. These observations suggest that the changes in Ins(1,4,5)P3 levels may be implicated in the increased inotropic responsiveness to alpha 1-adrenoceptor stimulation in diabetic hearts. Ca2+ overload, induced by Ins(1,4,5)P3, could further be involved in the development of diabetic cardiomyopathy.

Animals↗

PubMed1991

[Preliminary study of cervicovaginal peroxidase as indicator for ovulation].

The study was designed to determine whether the change in the pattern of cervicovaginal peroxidase activity in the fertile period of women can serve as a basis for the development of a technique to predict ovulation time in natural family planning. Eight healthy women volunteered for this study in Chengdu area. The samples of cervical mucus and vaginal secretion were collected. The specific G-Px activity was measured with reference to the procedure of Tsibris, et al., on days 6, 8, 10, 12 through 16, 18, 20, 22, 24 of each menstrual cycle; at the same time an antecubital venous blood sample was drawn to be analyzed for levels of LH, FSH, E2, and P by RIA. The data showed that in 7 ovulatory cycles the G-Px activity did not vary regularly in vaginal secretion but it did drop rapidly in cervical mucus 2 or 3 days before ovulation time and it rose again one day after ovulation. The results suggest that the measurement of the G-Px activity in cervical mucus can be used to predict ovulation by two to three days before the time.

Cervix Mucus↗

PubMed1990

Omega-3 fatty acid treatment fails to alter alpha 1-adrenergic receptor mediated phosphoinositide turnover in streptozotocin-induced diabetic rats.

1. The effect of omega-3 fatty acid supplementation on alpha 1-adrenergic receptor-mediated phosphoinositide turnover in the hearts of 6-week streptozotocin diabetic rats was studied. 2. The diabetic state was characterized by decreased body weight gain, hypoinsulinemia and hyperglycemia. Omega-3 fatty acid treatment did not have any significant effects on the above parameters. 3. Plasma triglyceride and cholesterol levels were significantly higher in diabetic rats compared with controls. 4. Omega-3 fatty acid treatment reduced the plasma triglyceride levels in the diabetic rats, whereas plasma cholesterol levels remained unaffected. 5. Norepinephrine (10 and 100 microM) stimulated inositol monophosphate (IP1) formation was significantly decreased in the diabetic rat heart compared with controls. Omega-3 fatty acid treatment had no significant effect on the norepinephrine-mediated IP1 formation in these rats. 6. Inositol bisphosphate (IP2) formation in response to 100 microM of norepinephrine was significantly lower in the diabetic rat heart; which was also not affected by omega-3 fatty acid treatment.

Animals↗

PubMed1990

Calcium uptake activity of cardiac sarcoplasmic reticulum in myo-inositol-treated diabetic rats.

1. Cardiac function of STZ-diabetic rats has been shown to be partially improved by myo-inositol treatment. We studied the effect of myo-inositol on Ca2(+)-uptake activity in sarcoplasmic reticulum in diabetic animals. 2. Cardiac sarcoplasmic reticulum Ca2(+)-uptake activity was significantly depressed in 8-week diabetic rats. 3. Myo-inositol treatment could not improve Ca2(+)-uptake activity in diabetic rats. 4. The data suggest that the cardiac dysfunction in diabetic rats is due to factors other than the decreased Ca2(+)-uptake activity in sarcoplasmic reticulum.

Adenosine Triphosphate↗