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Biomedical subjects

X Zhao

Publications and source records attributed to X Zhao.

At least 163 records · Page 9Linked to original sources
PubMed2001

Nootropic drug modulation of neuronal nicotinic acetylcholine receptors in rat cortical neurons.

Nefiracetam (DM-9384) is a new pyrrolidone nootropic drug being developed for the treatment of Alzheimer's type and poststroke vascular-type dementia. Because the cholinergic system plays an important role in cognitive functions and Alzheimer's disease dementia, the present study was conducted to elucidate the mechanism of action of nefiracetam and aniracetam on neuronal nicotinic acetylcholine receptors (nnAChRs). Currents were recorded from rat cortical neurons in long-term primary culture using the whole-cell, patch-clamp technique. Two types of currents were evoked by acetylcholine (ACh): alpha-bungarotoxin-sensitive, alpha 7-type currents and alpha-bungarotoxin-insensitive, alpha 4 beta 2-type currents. Although nefiracetam and aniracetam inhibited alpha 7-type currents only weakly, these nootropic agents potentiated alpha 4 beta 2-type currents in a very potent and efficacious manner. Nefiracetam at 1 nM and aniracetam at 0.1 nM reversibly potentiated alpha 4 beta 2-type currents to 200 to 300% of control. Nefiracetam at very high concentrations (approximately 10 microM) also potentiated alpha 4 beta 2-type currents but to a lesser extent, indicative of a bell-shaped dose-response relationship. Nefiracetam markedly increased the saturating responses induced by high concentrations of ACh. However, human alpha 4 beta 2 subunits expressed in human embryonic kidney cells were inhibited rather than potentiated by nefiracetam. The specific protein kinase A inhibitors (H-89, KT5720, and peptide 5-24) and protein kinase C inhibitors (chelerythrine, calphostin C, and peptide 19--63) did not prevent nefiracetam from potentiating alpha 4 beta 2-type currents, indicating that these protein kinases are not involved in nefiracetam action. The nefiracetam potentiating action was not affected by 24-h pretreatment of neurons with pertussis toxin, but was abolished by cholera toxin. Therefore, G(s) proteins, but not G(i)/G(o) proteins, are involved in nefiracetam potentiation. These results indicate that nnAChRs are an important site of action of nefiracetam and G(s) proteins may be its crucial target.

Acetylcholine↗
PubMed2001

Modulation of neuronal nicotinic acetylcholine receptors by halothane in rat cortical neurons.

Inhalational general anesthetics have recently been shown to inhibit neuronal nicotinic acetylcholine (ACh) receptors (nnAChRs) expressed in Xenopus laevis oocytes and in molluscan neurons. However, drug actions on these systems are not necessarily the same as those seen on native mammalian neurons. Thus, we analyzed the detailed mechanisms of action of halothane on nnAChRs using rat cortical neurons in long-term primary culture. Currents induced by applications of ACh via a U-tube system were recorded by the whole-cell, patch-clamp technique. ACh evoked two types of currents, alpha-bungarotoxin-sensitive, fast desensitizing (alpha 7-type) currents and alpha-bungarotoxin-insensitive, slowly desensitizing (alpha 4 beta 2-type) currents. Halothane suppressed alpha 4 beta 2-type currents more than alpha 7-type currents with IC(50) values of 105 and 552 microM, respectively. Halothane shifted the ACh dose-response curve for the alpha 4 beta 2-type currents in the direction of lower ACh concentrations and slowed its apparent rate of desensitization. The rate of recovery after washout from halothane block was much faster than the rate of recovery from ACh desensitization. Thus, the halothane block was not caused by receptor desensitization. Chlorisondamine, an irreversible open channel blocker for nnAChRs, caused a time-dependent block that was attenuated by halothane. These results could be accounted for by kinetic simulation based on a model in which halothane causes flickering block of open channels, as seen in muscle nAChRs. Halothane block of nnAChRs is deemed to play an important role in anesthesia via a direct action on the receptor and an indirect action to suppress transmitter release.

Acetylcholine↗
PubMed2001

Enhancement of fluoroquinolone activity by C-8 halogen and methoxy moieties: action against a gyrase resistance mutant of Mycobacterium smegmatis and a gyrase-topoisomerase IV double mutant of Staphylococcus aureus.

The increasing prevalence of antibiotic resistance among bacterial pathogens prompted a microbiological study of fluoroquinolone structure-activity relationships with resistant mutants. Bacteriostatic and bactericidal activities for 12 fluoroquinolones were examined with a gyrase mutant of Mycobacterium smegmatis and a gyrase-topoisomerase IV double mutant of Staphylococcus aureus. For both organisms C-8 halogen and C-8 methoxy groups enhanced activity. The MIC at which 99% of the isolates tested were inhibited (MIC(99)) was reduced three- to fivefold for the M. smegmatis mutant and seven- to eightfold for the S. aureus mutant by C-8 bromine, chlorine, and methoxy groups. With both organisms a smaller reduction in the MIC(99) (two- to threefold) was associated with a C-8 fluorine moiety. In most comparisons with M. smegmatis the response to a C-8 substituent was similar (within twofold) for wild-type and mutant cells. In contrast, mutant S. aureus was affected more than the wild type by the addition of a C-8 substituent. C-8 halogen and methoxy groups also improved the ability to kill the two mutants and the respective wild-type cells when measured with various fluoroquinolone concentrations during an incubation period equivalent to four to five doubling times. Collectively these data help define a group of fluoroquinolones that can serve (i) as a base for structure refinement and (ii) as test compounds for slowing the development of fluoroquinolone resistance during infection of vertebrate hosts.

Anti-Infective Agents↗
PubMed2001

Mutant prevention concentrations of fluoroquinolones for clinical isolates of Streptococcus pneumoniae.

The mutant prevention concentration (MPC) represents a threshold above which the selective proliferation of resistant mutants is expected to occur only rarely. A provisional MPC (MPC(pr)) was defined and measured for five fluoroquinolones with clinical isolates of Streptococcus pneumoniae. Based on their potential for restricting the selection of resistant mutants, the five fluoroquinolones, in descending order, were found to be moxifloxacin > trovafloxacin > gatifloxacin > grepafloxacin > levofloxacin. For several compounds, 90% of about 90 clinical isolates that lacked a known resistance mutation had a value of MPC(pr) that was close to or below the serum levels that could be attained with a dosing regimen recommended by the manufacturers. Since MPC(pr) overestimates MPC, these data identify moxifloxacin and gatifloxacin as good candidates for determining whether MPC(pr) can be used as a guide for choosing and eventually administering fluoroquinolones to significantly reduce the development of resistance.

Anti-Infective Agents↗
PubMed2001

Development and characterization of a xylose-dependent system for expression of cloned genes in Bacillus subtilis: conditional complementation of a teichoic acid mutant.

We have developed a xylose-dependent expression system for tight and modulated expression of cloned genes in Bacillus subtilis. The expression system is contained on plasmid pSWEET for integration at the amyE locus of B. subtilis and incorporates components of the well-characterized, divergently transcribed xylose utilization operon. The system contains the xylose repressor encoded by xylR, the promoter and 5' portion of xylA containing an optimized catabolite-responsive element, and intergenic xyl operator sequences. We have rigorously compared this expression system to the isopropyl-beta-D-thiogalactopyranoside-induced spac system using a thermostable beta-galactosidase reporter (BgaB) and found the xyl promoter-operator to have a greater capacity for modulated expression, a higher induction/repression ratio (279-fold for the xyl system versus 24-fold with the spac promoter), and lower levels of expression in the absence of an inducer. We have used this system to probe an essential function in wall teichoic acid biosynthesis in B. subtilis. Expression of the teichoic acid biosynthesis gene tagD, encoding glycerol-3-phosphate cytidylyltransferase, from the xylose-based expression system integrated at amyE exhibited xylose-dependent complementation of the temperature-sensitive mutant tag-12 when grown at the nonpermissive temperature. Plasmid pSWEET thus provides a robust new expression system for conditional complementation in B. subtilis.

Bacillus subtilis↗
PubMed2001

The CYP450 hydroxylase pathway contributes to P2X receptor-mediated afferent arteriolar vasoconstriction.

This study was conducted to test the hypothesis that the cytochrome P-450 (CYP450) metabolite 20-hydroxyeicosatetraenoic acid (20-HETE) contributes to the afferent arteriolar response to P2 receptor activation. Afferent arteriolar responses to ATP, the P2X agonist, alpha,beta-methylene ATP and the P2Y agonist UTP were determined before and after treatment with the selective CYP450 hydroxylase inhibitor, N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS) or the 20-HETE antagonist, 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid (20-HEDE). Stimulation with 1.0 and 10 microM ATP elicited an initial preglomerular vasoconstriction of 12 +/- 1% and 45 +/- 4% and a sustained vasoconstriction of 11 +/- 1% and 11 +/- 2%, respectively. DDMS or 20-HEDE significantly attenuated the sustained afferent arteriolar constrictor response to ATP. alpha,beta-Methylene ATP (1 microM) induced a rapid initial afferent vasoconstriction of 64 +/- 3%, which partially recovered to a stable diameter 10 +/- 1% smaller than control. Both DDMS and 20-HEDE significantly attenuated the initial vasoconstriction and abolished the sustained vasoconstrictor response to alpha,beta-methylene ATP. UTP decreased afferent diameter by 50 +/- 5% and 20-HEDE did not change this response. In addition, the ATP-induced increase in the intracellular Ca2+ concentration in preglomerular microvascular smooth muscle cells was significantly attenuated by 20-HEDE. Taken together, these results are consistent with the hypothesis that the CYP450 metabolite 20-HETE participates in the afferent arteriolar response to activation of P2X receptors.

Adenosine Triphosphate↗
PubMed2001

Redox regulation of endothelial barrier integrity.

Intestinal ischemia-reperfusion is associated with the generation of reactive oxygen metabolites as well as remote, oxidant-mediated lung injury. Oxidants elicit endothelial redox imbalance and loss of vascular integrity by disorganizing several junctional proteins that contribute to the maintenance and regulation of the endothelial barrier. To determine the specific effect of redox imbalance on pulmonary vascular barrier integrity, microvascular permeability was determined in lungs of animals subjected to chemically induced redox imbalance. The effect of redox imbalance on microvascular permeability and endothelial junctional integrity in cultured lung microvascular cells was also determined. Whole lung and cultured pulmonary endothelial cell permeability both increased significantly in response to chemical redox imbalance. Thiol depletion also resulted in decreased endothelial cadherin content and disruption of the endothelial barrier. These deleterious effects of intracellular redox imbalance were blocked by pretreatment with exogenous glutathione. The results of this study suggest that redox imbalance contributes to pulmonary microvascular dysfunction by altering the content and/or spatial distribution of endothelial junctional proteins.

Animals↗
PubMed2001

Comparative analysis of pharmacologic and/or genetic disruption of cyclooxygenase-1 and cyclooxygenase-2 function in female reproduction in mice.

Cyclooxygenase (COX)-derived prostaglandins are critical in female reproduction. Gene targeting studies show that ovulation, fertilization, implantation, and decidualization are defective in COX-2 deficient mice. We used genetic and pharmacologic approaches to perturb COX function and examine the differential and synergistic effects of inhibition of COX-1, COX-2, or of both isoforms on reproductive outcomes during early pregnancy in mice. The results demonstrate that simultaneous inhibition of COX-1 and COX-2 produces more severe effects on early pregnancy events than inhibition of either isoform alone. The effects of pharmacological inhibition of COX-2 on female reproductive functions were less severe than the null mutation of the COX-2 gene. A combined approach showed that COX-2 inhibition in COX-1(-/-) mice induced complete reproductive failure, suggesting a lack of alternative sources of prostaglandin synthesis. This investigation raises caution regarding the indiscriminate use of COX inhibitors and shows for the first time the distinct and overlapping pathways of the cyclooxygenase systems in female reproduction.

Animals↗
PubMed2001

Expression of auxilin or AP180 inhibits endocytosis by mislocalizing clathrin: evidence for formation of nascent pits containing AP1 or AP2 but not clathrin.

Although uncoating of clathrin-coated vesicles is a key event in clathrin-mediated endocytosis it is unclear what prevents uncoating of clathrin-coated pits before they pinch off to become clathrin-coated vesicles. We have shown that the J-domain proteins auxilin and GAK are required for uncoating by Hsc70 in vitro. In the present study, we expressed auxilin in cultured cells to determine if this would block endocytosis by causing premature uncoating of clathrin-coated pits. We found that expression of auxilin indeed inhibited endocytosis. However, expression of auxilin with its J-domain mutated so that it no longer interacted with Hsc70 also inhibited endocytosis as did expression of the clathrin-assembly protein, AP180, or its clathrin-binding domain. Accompanying this inhibition, we observed a marked decrease in clathrin associated with the plasma membrane and the trans-Golgi network, which provided us with an opportunity to determine whether the absence of clathrin from clathrin-coated pits affected the distribution of the clathrin assembly proteins AP1 and AP2. Surprisingly we found almost no change in the association of AP2 and AP1 with the plasma membrane and the trans-Golgi network, respectively. This was particularly obvious when auxilin or GAK was expressed with functional J-domains since, in these cases, almost all of the clathrin was sequestered in granules that also contained Hsc70 and auxilin or GAK. We conclude that expression of clathrin-binding proteins inhibits clathrin-mediated endocytosis by sequestering clathrin so that it is no longer available to bind to nascent pits but that assembly proteins bind to these pits independently of clathrin.

Adaptor Protein Complex 1↗
PubMed2001

Phylogenetic position of Eimeria antrozoi, a bat coccidium (Apicomplexa: Eimeriidae) and its relationship to morphologically similar Eimeria spp. from bats and rodents based on nuclear 18S and plastid 23S rDNA sequences.

Partial plastid 23S and nuclear 18S rDNA genes were amplified and sequenced from 2 morphologically similar Eimeria species. E. antrozoi from a bat (Antrozous pallidus) and E. arizonensis from deer mice (Peromyscus spp.), as well as some other Eimeria species from bats and rodents. The phylogenetic trees clearly separated E. antrozoi from E. arizonensis. The phylogenies based on plastid 23S rDNA data and combined data of both plastid and nuclear genes grouped 2 bat Eimeria and 3 morphologically similar Eimeria species from rodents into 2 separate clades with high bootstrap support (100%, 3 rodent Eimeria species; 72-97%, 2 bat Eimeria species), which supports E. antrozoi as a valid species. The rodent Eimeria species did not form a monophyletic group. The 2 bat Eimeria species formed a clade with the 3 morphologically similar rodent Eimeria species (E. arizonensis, E. albigulae, E. onychomysis, all from cricetid rodents) with 100% bootstrap support, whereas 2 other rodent Eimeria species (E. nieschulzi, E. falciformis, from murid rodents) formed a separate clade with 100% bootstrap support. This suggests that the 2 Eimeria species from bats might be derived from rodent Eimeria species and may have arisen as a result of lateral host transfer between rodent and bat hosts.

Animals↗
PubMed2001

Cloning of bovine eukaryotic translation initiation factor 4E (eIF-4E) and its expression in the bovine mammary gland at different physiological stages.

Bovine eIF-4E cDNA was cloned and its expression in the bovine mammary gland at distinct physiological stages was investigated. Bovine eIF-4E cDNA and protein sequences are highly homologous to those from other mammals. Using Northern blot analysis, we did not detect eIF-4E expression in the prepubertal bovine mammary gland, whereas a low level of eIF-4E mRNA was observed in the mammary tissues of heifers during the third estrous cycle. The eIF-4E mRNA level was significantly higher in the lactating mammary gland compared to the mammary tissues obtained from heifers during the third estrous cycle. Alteration of eIF-4E expression in bovine mammary tissues during different physiological stages indicates the involvement of eIF-4E in mammary development. Elevated eIF-4E expression during lactation may be related to increased translation of certain mRNA or the acceleration of overall protein synthesis.

Amino Acid Sequence↗
PubMed2001

Induction of nitric oxide production by bovine mammary epithelial cells and blood leukocytes.

A recent study from our laboratory has shown that significant amounts of nitric oxide are released by somatic cells recovered during endotoxin-induced mastitis. The present study was undertaken to investigate which cell type(s) among milk somatic cell population can produce nitric oxide under inflammatory conditions. Nitric oxide release from mammary epithelial cell lines and from bovine neutrophils and monocytes extracted from blood was measured in response to cytokines and Escherichia coli lipopolysaccharides. An epithelial cell line isolated from bovine mammary gland, FbE cells, was found to release nitric oxide after exposure to interleukin-1beta. This nitric oxide production was completely abolished by addition of L-N6-(1-iminoethyl) lysine, a potent inducible nitric oxide synthase inhibitor. Bovine monocytes produced nitric oxide in response to recombinant bovine interferon-gamma alone or in combination with E. coli lipopolysaccharides. In these cells, nitric oxide release was reduced by the addition of inducible nitric oxide synthase inhibitors L-N6-(1-iminoethyl) lysine and aminoguanidine. Lipopolysaccharides and recombinant bovine interferon-gamma increased nitric oxide synthase mRNA in neutrophils, but nitric oxide release could not be detected under any of the experimental conditions used. These results show that bovine epithelial cells and mononuclear phagocytes produce nitric oxide under inflammatory conditions and suggest that these cell populations are responsible for nitric oxide release observed during mastitis.

Animals↗
PubMed2001

Nesidioblastosis coexisting with islet cell tumor and intraductal papillary mucinous hyperplasia.

A coexisting of intraductal papillary mucinous hyperplasia (IPMH) and islet cell tumor with nesidioblastosis of the pancreas in a 51-year-old man is reported. All of the clinical data indicated an insulinoma. A distal pancreatectomy was performed. A discrete mass measuring 1.9 x 2.0 cm was grossly identified in the tail of the pancreas. There were no other gross lesions. An islet cell tumor with nesidioblastosis was confirmed by immunostains and ultrastructural study. In addition, an IPMH was found that involved mainly branches of the pancreatic duct. The islet cell tumor and IPMH were topographically separated; however, there was a histologically intimate relationship between the nesidioblastosis and the IPMH. These findings indicate that the IPMH may have derived from autocrine and paracrine influences on the existing duct epithelial cells. To the best of our knowledge, this is the first report of nesidioblastosis coexisting with islet cell tumor and IPMH.

Adenoma, Islet Cell↗
PubMed2001

Fipronil modulation of gamma-aminobutyric acid(A) receptors in rat dorsal root ganglion neurons.

The gamma-aminobutyric acid (GABA) receptor is an important site of action of a variety of chemicals, including barbiturates, benzodiazepines, picrotoxin, bicuculline, general anesthetics, alcohols, and certain insecticides. Fipronil is the first phenylpyrazole insecticide introduced for pest control. It is effective against some insects that have become resistant to the existing insecticides. To elucidate the mechanism of fipronil interaction with the mammalian GABA system, whole-cell patch-clamp experiments were performed using rat dorsal root ganglion neurons in primary culture. Fipronil suppressed the GABA-induced whole-cell currents reversibly in both closed and activated states. The IC(50) values and Hill coefficients for fipronil block of the GABA(A) receptor were estimated to be 1.66 +/- 0.18 microM and 1.23 +/- 0.14 for the closed receptor, respectively, and 1.61 +/- 0.14 microM and 0.96 +/- 0.06 for the activated receptor, respectively. The association rate and dissociation rate constants of fipronil effect were estimated to be 673 +/- 220 M(-1) s(-1) and 0.018 +/- 0.0035 s(-1) for the closed GABA(A) receptor, respectively, and 6600 +/- 380 M(-1) s(-1) and 0.11 +/- 0.0054 s(-1) for the activated GABA(A) receptor, respectively. Thus, both the association and dissociation rate constants of fipronil for the activated GABA(A) receptor are approximately 10 times as large as those for the closed receptor. Experiments with coapplication of fipronil and picrotoxinin indicated that they did not compete for the same binding site to block the receptor. It is concluded that although fipronil binds to the GABA(A) receptor without activation, channel opening facilitates fipronil binding to and unbinding from the receptor.

Animals↗
PubMed2001

[Effect of five kinds of vegetable seed oil on serum lipid and lipid peroxidation in rats].

The effects of vegetable seed oil on hyperlipidemia induced by high lipid diet in rats. Male adult Wistar rats were fed on the test diet containing 94% high lipid diet and 6% lard pinon seed oil, perilla seed oil, blackcurrent seed oil, borage seed oil and evening primrose seed oil respectively for 3 weeks. The results showed that the vale of trilyceride(TG), total cholesterol(TC), low density lipoprotein cholesterol (LDL-C), LDL-C/HDL-C(high density lipoprotein cholesterol) ratio increased and the vale of HDL-C/TC ratio and lecithin-cholesterol acyltransferase(LCAT) activity decreased in the groups with vegetable seed oil were less than that of the control group. The results suggested that all the five kinds of vegetable seed oil had the effect of regulating lipid metabolism of hyperlipidemia rats to some extent. Pinon seed oil and borage seed oil may be well suited for the prevention of atherosclerosis.

Animals↗
PubMed2001

[Effect of a complex tea on reducing blood lipid in rabbits].

In order to observe the effect of a complex tea composed of tea, ginkgo leaf, red koji and fructus lycii on reducing blood lipids in experimental rabbits, 40 rabbits weighted from 1.5 to 2.0 kg were divided randomly into 5 group: (I) normal control group, (II) hyperlipidemia model(positive control), (III) green tea control group, (IV) low dose complex tea group, and (V) high dose complex tea group. Blood triglyceride(TG), cholesterol(TC), lower density lipoprotein(LDL) and high density lipoprotein(HDL) were measured before experiment and 6.12 weeks later. Then the pathological changes of heart, aorta and liver were observed. After 12 weeks of experiment, the results showed that, (1) hyperlipidemia characterized by high TC has been induced by high-fat feeds in group II, (2) the complex tea can reduce body weight and eliminate the lipids deposition in aorta and liver. (3) the complex tea can decrease serum TG, TC,LDL and increase serum HDL in the high complex tea group. The results indicate that the complex tea is more effective than green tea on reducing blood lipids in experimental rabbits.

Animals↗