Search PubMed⌕ Search

Biomedical subjects

Y Xia

Publications and source records attributed to Y Xia.

At least 37 records · Page 2Linked to original sources
PubMed2002

Trehalose-hydrolysing enzymes of Metarhizium anisopliae and their role in pathogenesis of the tobacco hornworm, Manduca sexta.

Trehalose is the main haemolymph sugar in most insects including the tobacco hornworm, Manduca sexta, and is potentially a prime target for an invading pathogenic fungus. There was considerably more trehalose-hydrolysing activity in the haemolymph of caterpillars infected with Metarhizium anisopliae than in controls. This appeared to be due primarily to additional isoforms; one of which could also hydrolyse maltose and was designated an alpha-glucosidase. A comparable isoform was identified in in vitro culture of the fungus, supporting a fungal origin for the in vivo enzyme. The in vitro fungal enzyme, alpha-glucosidase-1 (alpha-gluc-1), was purified to homogeneity and partially characterised. A study with the trehalase inhibitor trehazolin and C14 trehalose suggested that extracellular hydrolysis is important for fungal mobilisation of trehalose. Haemolymph glucose increases significantly during mycosis of tobacco hornworm larvae by M. anisopliae, consistent with the hydrolysis of trehalose by extracellular fungal enzymes. The implications for the host insect are discussed.

Animals↗
PubMed2002

Na(+)/Ca(2+) exchanger expression in the developing rat cortex.

The Na(+)/Ca(2+) exchanger (NCX) participates in the regulation of neuronal Ca(2+) homeostasis and is also believed to be involved in the neuronal responses to hypoxia. However, there are very limited data on how NCX mRNA and protein expression are regulated during brain development. In the present study, we sought to elucidate the developmental expression of NCX1 and NCX2 in the rat cortex from late fetal to adult stages using reverse transcription-polymerase chain reaction and western blot assays. The primers for NCX1 mRNA targeted the alternative splicing domain to allow differentiation between NCX1 splice variants. Our results show that: (1) only two NCX1 mRNA splice variants (NCX1.5 and NCX1.4) are present in the cortex and their expression is age-dependent; (2) total NCX1 mRNA levels are low in fetal tissue, reach maximum density at postnatal day 8 and substantially decline with further maturation; (3) NCX2 mRNA density is significantly greater than total NCX1 mRNA for all ages and increases markedly during maturation from fetus/neonate to adult; and (4) NCX1 protein expression is lowest in late fetal cortex and reaches maximum levels after 2 weeks postnatally, even though expression levels are not significantly different between newborn and adult animals. Also, we found a similar NCX1 protein trend in the subcortical and cerebellar regions during development. From these data we suggest that NCX1 and NCX2 are differentially expressed in the cortex with a predominance of NCX2 levels during postnatal development. We speculate that the developmental increase in NCX2 expression is responsible for the overall increase in Na(+)/Ca(2+) exchange capacity during maturation.

Aging↗
PubMed2002

Immunoreactivity of Hu proteins facilitates identification of myenteric neurones in guinea-pig small intestine.

Hu proteins, together with neurone-specific enolase (NSE), protein gene product 9.5 (PGP-9.5), microtubule-associated protein-2 (MAP-2) and tubulin beta III isoform, were evaluated immunohistochemically as neuronal markers in whole-mount preparations and cultures obtained from the myenteric plexus of guinea-pig small intestine. Anti-Hu immunostaining marked the ganglion cell somas and nuclei without staining of the neuronal processes in the whole-mounts and cultures. The ganglion cell bodies were not obscured by staining of multiple neuronal fibres and this facilitated accurate counting of the neurones. MAP2 immunostaining also provided clear images of individual neurones in both whole mounts and cultures. Immunoreactivity for NSE, PGP-9.5 and tubulin beta III isoform provided sharp images of the ganglion cells in culture, but not in whole-mount preparations. Strong staining of the neuronal processes in the whole-mount preparations obscured the profiles of the ganglion cell bodies to such an extent that accurate counting of the total neuronal population was compromised. Anti-Hu immunostaining was judged to be an acceptable method for obtaining reliable estimates of total numbers of myenteric neurones in relation to other specific histochemical properties such as histamine binding.

Animals↗
PubMed2002

Characteristics of topographical heterogeneity of articular cartilage over the joint surface of a humeral head.

OBJECTIVE: To investigate the topographical variations among the morphological and physical properties of articular cartilage over a canine humeral head. DESIGN: Nine side-by-side specimens from a canine humeral head were used in the combined polarized light microscopy (PLM) and microscopic magnetic resonance imaging (muMRI). Sixteen images were acquired from each specimen in muMRI. Subsequently, ten to fourteen histological slices were prepared at the location of the muMRI slice from each specimen. Four optical images were acquired from each histological slice. Using these images, the images of the T(2) relaxation, the optical retardation, and the collagen-fiber orientation were constructed in two dimensions. RESULTS: Along the medial/lateral direction of the humeral head, we have observed a number of topographical variations. These include the total thickness of the cartilage tissue, the thickness of the individual histological zones, the depth of the minimum optical retardation in the tissue, and the depth of the maximum T(2) relaxation in the tissue. We found that the depth of the minimum retardation from PLM occurs at the geometric middle point of the transitional zone in histology, and that the depth of the maximum T(2) relaxation from muMRI is closely correlated with the minimum retardation depth in PLM. In addition, although the thickness of the total tissue increases approximately by the same amount on both the lateral and medial sides of the joint, a slight asymmetry exists between the measurements from the medial and lateral halves of the humerus. CONCLUSIONS: Cartilage from different sites over a single joint could have different properties, possibly the consequence of the variation in load-bearing status. Because of these topographical variations, one must keep in mind that a different sampling site within a relatively small area of the same joint may significantly influence the results of the study.

Animals↗
PubMed2002

Follistatin concentrations in maternal and fetal fluids during the oestrous cycle, gestation and parturition in Merino sheep.

The aim of this study was to investigate the changes in follistatin, an activin binding protein, during the oestrous cycle, gestation and parturition in ewes using a radioimmunoassay for total follistatin, which uses dissociating reagents to remove the interference of activin. Follistatin concentrations remained unchanged (2.7 +/- 0.2 ng ml(-1)) during the oestrous cycle and decreased as pregnancy progressed. Follistatin concentrations in allantoic fluid also decreased during gestation, whereas in amniotic fluid follistatin concentrations reached a peak at day 75 of gestation (9.8 ng ml(-1)) and had decreased to 4.4 ng ml(-1) at day 140. Follistatin concentrations in fetal blood (7.0 +/- 0.5 ng ml(-1)) did not change from day 50 to day 140 of gestation but were significantly higher than in matched maternal samples (3.1 +/- 0.3 ng ml(-1)). Circulating follistatin in ewes was significantly increased on the day of parturition (5.6 +/- 0.6 ng ml(-1)) compared with the days before parturition (2.7 +/- 0.4 ng ml(-1)), but had decreased by day 2 after birth. Blood samples from newborn lambs showed that plasma follistatin concentration (13.4 +/- 2.3 ng ml(-1)) was significantly higher than that of the mothers and remained high for at least 7 days after birth. These data support previous studies of the human menstrual cycle indicating that follistatin is not an endocrine signal from the ovary; however, in contrast to human pregnancies, follistatin concentrations in sheep decreased and become high only after or during parturition. This difference observed between species may reflect different physiological effects of follistatin or may be the result of measurement of different isoforms.

Activins↗
PubMed2001

Thrombocytopenia caused by the development of antibodies to thrombopoietin.

Thrombocytopenia developed in some individuals treated with a recombinant thrombopoietin (TPO), pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF). Three of the subjects who developed severe thrombocytopenia were analyzed in detail to determine the cause of their thrombocytopenia. Except for easy bruising and heavy menses, none of these subjects had major bleeding episodes; none responded to intravenous immunoglobulin or prednisone. Bone marrow examination revealed a marked reduction in megakaryocytes. All 3 thrombocytopenic subjects had antibody to PEG-rHuMGDF that cross-reacted with endogenous TPO and neutralized its biological activity. All anti-TPO antibodies were immunoglobulin G (IgG), with increased amounts of IgG4; no IgM antibodies to TPO were detected at any time. A quantitative assay for IgG antibody to TPO was developed and showed that the antibody concentration varied inversely with the platelet count. Anti-TPO antibody recognized epitopes located in the first 163 amino acids of TPO and prevented TPO from binding to its receptor. In 2 subjects, endogenous TPO levels were elevated, but the TPO circulated as a biologically inactive immune complex with anti-TPO IgG; the endogenous TPO in these complexes had an apparent molecular weight of 95 000, slightly larger than the full-length recombinant TPO. None of the subjects had atypical HLA or platelet antigens, and the TPO cDNA was normal in both that were sequenced. Treatment of one subject with cyclosporine eliminated the antibody and normalized the platelet count. These data demonstrate a new mechanism for thrombocytopenia in which antibody develops to TPO; because endogenous TPO is produced constitutively, thrombocytopenia ensues.

Adult↗
PubMed2001

Analyses of micronuclei in exfoliated epithelial cells from individuals chronically exposed to arsenic via drinking water in inner Mongolia, China.

The groundwater in Bayingnormen (Ba Men), located in Central West Inner Mongolia, China, is naturally contaminated with arsenic at concentrations ranging from 50 microg/L to 1.8 mg/L. Various adverse health effects in this region, including cancer, have been linked to arsenic exposure via drinking water. A pilot study was undertaken to evaluate frequencies of micronuclei (MN), as measures of chromosomal alterations, in multiple exfoliated epithelial cell types from residents of Ba Men chronically exposed to arsenic via drinking water. Buccal mucosal cells, airway epithelial cells in sputum, and bladder urothelial cells were collected from 19 residents exposed to high levels of arsenic in drinking water (527.5 +/- 24 microg/l), and from 13 control residents exposed to relatively low levels of arsenic in drinking water (4.4 +/- microg/L). Analytical results from these individuals revealed that MN frequencies in the high-exposure group were significantly elevated to 3.4-fold over control levels for buccal and sputum cells, and to 2.7-fold over control for bladder cells (increases in MN frequency significant at p < .001 for buccal cells; p < .01 for sputum cells; p < .05 for bladder cells). When smokers were excluded from high-exposure and control groups the effects of arsenic were observed to be greater, although only in buccal and sputum cells; approximately 6-fold increases in MN frequency occurred in these tissues. The results indicate that residents of Ba Men chronically exposed to high levels of arsenic in drinking water reveal evidence of genotoxicity in multiple epithelial cell types; higher levels of induced MN were observed in buccal and sputum cells than in bladder cells.

Adult↗
PubMed2001

P2X(7) receptors in the enteric nervous system of guinea-pig small intestine.

The P2X(7) purinergic receptor subtype has been cloned and emphasized as a prototypic P2Z receptor involved in neurotransmission in the central nervous system and ATP-mediated lysis of macrophages in the immune system. Less is known about the neurobiology of P2X(7) receptors in the enteric nervous system (ENS). We studied the distribution of the receptor with indirect immunofluorescence and used selective agonists and antagonists to analyze pharmacologic aspects of its electrophysiologic behavior as determined with intracellular "sharp" microelectrodes and patch-clamp recording methods in neurons identified morphologically by biocytin injection in the ENS. Application of ATP or 2'- (or-3'-) O-(4-benzoylbenzoyl) adenosine 5'-triphosphate (BzBzATP) activated an inward current in myenteric neurons. Brilliant blue G, a selective P2X(7) antagonist, suppressed the responses to both agonists. Potency of the antagonist was greatest (smaller IC(50)) for the current evoked by BzBzATP. The P2X(7) antagonists 1-[N,O-bis (1,5-isoquinolinesulfonyl)-N-methyl-l-tyrosyl]-4-piperazine (KN-62) and oxidized ATP also suppressed the BzBzATP-activated current. Micropressure application of BzBzATP evoked rapidly activating depolarizing responses in intracellular studies with "sharp" microelectrodes. Oxidized-ATP suppressed these responses in both myenteric and submucosal neurons. Rapidly activating depolarizing responses evoked by application of nicotinic, serotonergic 5-HT(3), or gamma-aminobutyric acid A (GABA(A)) receptor agonists were unaffected by brilliant blue G. Immunoreactivity for the P2X(7) receptor was widely distributed surrounding ganglion cell bodies and associated with nerve fibers in both myenteric and submucous plexuses. P2X(7) immunoreactivity was colocalized with synapsin and synaptophysin and surrounded ganglion cells that contained either calbindin, calretinin, neuropeptide Y, substance P, or nitric oxide synthase. The mucosa, submucosal blood vessels, and the circular muscle coat also showed P2X(7) receptor immunoreactivity.

Animals↗
PubMed2001

Antitumor Agents. 211. Fluorinated 2-phenyl-4-quinolone derivatives as antimitotic antitumor agents.

Fluorinated 2-phenyl-4-quinolone derivatives were synthesized and evaluated in National Cancer Institute's 60 human tumor cell line in vitro screen. From the results, the ketone moiety plays an essential role in activity. Among the compounds tested, 2'-fluoro-6-pyrrol-2-phenyl-4-quinolone (13) exhibited the most potent cytotoxic activities (log GI(50) < -8.00) against renal and melanoma tumor cell lines. Compound 13 was also a potent inhibitor of tubulin polymerization (IC(50) = 0.46 microM) and of radiolabeled colchicine binding to tubulin, with activities comparable to those of the potent antimitotic natural products colchicine, podophyllotoxin, and combretastatin A-4.

Antineoplastic Agents↗
PubMed2001

Gamma(2)-melanocyte-stimulating hormone suppression of systemic inflammatory responses to endotoxin is associated with modulation of central autonomic and neuroendocrine activities.

Central autonomic and neuroendocrine activities are important components of the host response to bacterial inflammation. We demonstrate that intravenous infusion of gamma(2)-melanocyte-stimulating hormone (gamma(2)-MSH), a potent autonomic regulating peptide, prevents lipopolysaccharide (LPS)-induced hypotension and tachycardia, and modulates the ACTH response to endotoxin. In the hypothalamic paraventricular nucleus, a major neuroendocrine and autonomic center, gamma(2)-MSH inhibits LPS-induced increases in CRF mRNA levels, but does not suppress LPS-augmented arginine vasopressin heteronuclear RNA expression. In the locus coeruleus, a brainstem noradrenergic center, gamma(2)-MSH inhibits LPS-induced increases in tyrosine hydroxylase mRNA levels. Gamma(2)-MSH inhibits LPS-induced IL-1beta gene expression in the brain, pituitary and thymus, and prevents increases in plasma NO levels. These findings reveal that gamma(2)-MSH attenuates systemic inflammatory responses to endotoxin and suggest that modulation of central autonomic and neuroendocrine activities by gamma(2)-MSH contributes to its anti-inflammatory effects.

Adrenocorticotropic Hormone↗
PubMed2001

Acid phosphatases of Metarhizium anisopliae during infection of the tobacco hornworm Manduca sexta.

Three acid phosphatase (AcP) isozymes, pI 8.1, 8.0 and 7.8, were isolated, purified and partially characterised from optimised cultures of the entomopathogenic fungus Metarhizium anisopliae. The enzymes had similar molecular masses (approximately 44.0 kDa), and could degrade sugar phosphates found in the haemolymph of a host insect, the tobacco hornworm Manduca sexta. The AcP activity in haemolymph of mycosed insects increased significantly over controls, and some new isozymes were present. The infection-related isoforms were similar in molecular mass and pI to some of the in vitro AcP isozymes of M. anisopliae. Results of dot blot and Western blot analyses using anti-AcP antibodies suggested that at least one Metarhizium phosphatase isoform was present in haemolymph of infected caterpillars. Antibodies did not cross-react with immune (chemically stimulated) or non-immune haemolymph from Manduca sexta. Consistent with the appearance of highly active fungal phosphatase in caterpillar blood, free phosphate concentration increased dramatically during the late stages of infection to a level two to five times that of controls. Phosphate was limiting to growth of the fungus at the concentration found in control haemolymph and supplementation of phosphate significantly increased fungal growth in vitro in haemolymph. These results suggest that Metarhizium AcP may play a key role in providing phosphorus for fungal growth at the expense of the insect.

Acid Phosphatase↗
PubMed2001

Template-assisted self-assembly: a practical route to complex aggregates of monodispersed colloids with well-defined sizes, shapes, and structures.

This paper describes a strategy that combines physical templating and capillary forces to assemble monodispersed spherical colloids into uniform aggregates with well-controlled sizes, shapes, and structures. When an aqueous dispersion of colloidal particles was allowed to dewet from a solid surface that had been patterned with appropriate relief structures, the particles were trapped by the recessed regions and assembled into aggregates whose structures were determined by the geometric confinement provided by the templates. We have demonstrated the capability and feasibility of this approach by assembling polystyrene beads and silica colloids (> or =150 nm in diameter) into complex aggregates that include polygonal or polyhedral clusters, linear or zigzag chains, and circular rings. We have also been able to generate hybrid aggregates in the shape of HF or H2O molecules that are composed of polymer beads having different diameters, polymer beads labeled with different organic dyes, and a combination of polymeric and inorganic beads. These colloidal aggregates can serve as a useful model system to investigate the hydrodynamic and optical scattering properties of colloidal particles having nonspherical morphologies. They should also find use as the building blocks to generate hierarchically self-assembled systems that may exhibit interesting properties highly valuable to areas ranging from photonics to condensed matter physics.

Journal Article↗
PubMed2001

Major difference in the expression of delta- and mu-opioid receptors between turtle and rat brain.

The reptilian turtle brain has a remarkably higher endurance for anoxia than mammalian brains. Since the response to O(2) deprivation is dependent in a major way on the expression and regulation of membrane proteins, differences in such proteins may play a role in the species-related differences in hypoxic responses. Because opioid system is involved in the regulation of hypoxic responses, we asked whether there are differences between rat and turtle brains in terms of opioid receptor expression. In this work, we compared the expression and distribution of delta-and mu-opioid receptors in the turtle and rat brains. Our results show that (1) the dissociation constant (K(d)) for delta-receptor binding was approximately four times lower and B(max) was more than double in the turtle brain homogenates than in rat ones; (2) the delta-receptor binding density was heterogeneously distributed in the turtle brain, with a higher density in the rostral regions than in the brainstem and spinal cord, and was generally much higher than in rat brains from the cortex to spinal cord; (3) the delta-opioid receptors in the rat brains were mostly located in the cortex, caudate putamen, and amygdala with an extremely low density in most subcortical (e.g., hippocampus and thalamus) and almost all brainstem regions; and (4) in sharp contrast to delta-opioid receptors, mu-opioid receptor density was much lower in all turtle brain regions compared with the rat ones. Our results demonstrate that the turtle brain is actually an organ of delta-opioid receptors, whereas the rat brain has predominantly mu-opioid receptors. Because we have recently found that delta-opioid receptors protect neurons against glutamate and hypoxic stress, we speculate that the unique pattern of delta-receptor receptor expression and distribution plays a critical role in the tolerance of turtle brain to stressful situations characterized by glutamate excitotoxicity.

Analgesics, Opioid↗
PubMed2001

Effect of prolonged hypoxia on Na+ channel mRNA subtypes in the developing rat cortex.

Voltage-gated Na+ channels are regulated in response to oxygen deprivation in the mammalian cortex. Past investigations have demonstrated that Na+ channel protein expression is up-regulated in the immature brain exposed to prolonged hypoxia. Since it is unknown as to which Na+ channel subtype(s) is involved in this regulation, we used RT-PCR to assess the effect of hypoxia on Na+ channel I, II and III alpha-subunit mRNA expression in the developing rat cortex. Na+ channel II mRNA tended to increase during early development, whereas Na+ channel I and III did not change or slightly decreased with age. Hypoxic exposure for 1-day had no effect on Na+ channel expression, while 5-day hypoxia significantly increased Na+ channel III density, with a slight increase in Na+ channel I and no appreciable change in Na+ channel II. These results suggest that Na+ channel subtype expression in the developing cortex is differentially regulated in response to prolonged hypoxic exposure.

Animals↗
PubMed2001

Crystal structures of 1-aminocyclopropane-1-carboxylate (ACC) synthase in complex with aminoethoxyvinylglycine and pyridoxal-5'-phosphate provide new insight into catalytic mechanisms.

The structures of tomato 1-aminocyclopropane-1-carboxylate synthase (ACS) in complex with either cofactor pyridoxal-5'-phosphate (PLP) or both PLP and inhibitor aminoethoxyvinylglycine have been determined by x-ray crystallography. The structures showed good conservation of the catalytic residues, suggesting a similar catalytic mechanism for ACS and other PLP-dependent enzymes. However, the proximity of Tyr152 to the C-gamma-S bond of model substrate S-adenosylmethionine implies its critical role in the catalysis. The concerted accomplishment of catalysis by cofactor PLP and a protein residue, as proposed on the basis of the ACS structures in this paper, may represent a general scheme for the diversity of PLP-dependent catalyses. PLP-dependent enzymes have been categorized into four types of folds. A structural comparison revealed that a core fragment of ACS in fold type I is superimposable over tryptophan synthase beta subunit in fold type II and mouse ornithine decarboxylase in fold type III, thus suggesting a divergent evolution of PLP-dependent enzymes.

Amino Acid Sequence↗
PubMed2001

Antitumor agents. Part 204: synthesis and biological evaluation of substituted 2-aryl quinazolinones.

A series of 2',3',4',6,7-substituted 2-aryl quinazolinones were synthesized and evaluated for biological activity. Among them, 17 displayed significant growth inhibitory action against a panel of tumor cell lines. Compound 17 was also a potent inhibitor of tubulin polymerization. Compounds 8-10 displayed selective activity against P-gp-expressing epidermoid carcinoma of the asopharynx.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

Cardiovascular responses to subseptic doses of endotoxin contribute to differential neuronal activation in rat brain.

The contribution of cardiovascular activity in the early central responses to systemic inflammation was assessed in rats following intravenous administration of subseptic doses of lipopolysaccharide (LPS). LPS at 12.5 microg/kg increased heart rate (HR) but did not alter mean arterial pressure (MAP), and induced interleukin-1 beta (IL-1 beta) gene expression at 1 h in circumventricular organs (CVOs), choroid plexus, meninges, blood vessels, and pituitary gland. IL-1 beta mRNA levels were attenuated at 2 h in most regions studied. LPS at 50 microg/kg caused a biphasic change in MAP, increased HR, increased levels of arginine vasopressin heteronuclear RNA in the hypothalamic paraventricular nucleus (PVN), and induced IL-1 beta gene expression in the nucleus of the solitary tract (NTS) at 1 h. LPS (both doses) induced Fos-like immunoreactivity (FLI) in the area postrema, organum vasculosum of the lamina terminalis, NTS, preoptic area, supraoptic nucleus, and PVN at 1 h. In the PVN, neurons with FLI were found primarily in the dorsal and dorsal medial parvocellular divisions after 12.5 microg/kg of LPS whereas neurons with FLI were found throughout the PVN after 50 microg/kg of LPS. After 2 h, FLI was widespread throughout the brain. Plasma ACTH levels were elevated at 1 and 2 h in response to both doses of LPS, and levels of CRF mRNA were increased after 2 h in the parvocellular PVN. Our results reveal that central responses to increasing doses of LPS show different patterns which are related to activation of distinct immune and viscerosensory pathways, and that cardiovascular responses contribute to early neuronal activation as LPS concentrations are increased.

Adrenocorticotropic Hormone↗