Biomedical subjects

X Liu

Publications and source records attributed to X Liu.

At least 811 records · Page 45Linked to original sources

PubMed1999

Expression of growth hormone and insulin-like growth factor in the immune system of children.

Our objective was to study the effect of the growth hormone--insulin-like growth factor axis on the development of the immune system in children. We used radio receptor analysis, dot blot, in situ hybridization, and immunohistochemical techniques to determine the expression and distribution of growth hormone and growth hormone receptors, insulin-like growth factors, receptors and binding proteins in the thymus, lymph nodes and peripheral blood lymphocytes of children and adults. Our results showed that almost all components of the growth hormone-insulin-like growth factor axis were expressed in immune organs and cells, but the levels of expression varied. Growth hormone, insulin-like growth factor I, and insulin-like growth factor-binding proteins 1-6 were produced by immune cells in autocrine or paracrine ways. The expression of growth hormone receptors on peripheral blood lymphocytes was to be age-related. The growth hormone-insulin-like growth factor axis may help regulate the development and function of the immune system in children.

Adolescent↗

PubMed1999

A nonNMDA antagonist, GYKI 52466 improves microscopic O2 balance in the cortex during focal cerebral ischemia.

This study was performed to test whether GYKI 52466, a nonNMDA receptor antagonist, would improve microregional oxygen supply and consumption balance in the focal cerebral ischemic area. Rats were anesthetized with 1.4% isoflurane. For the GYKI Group (n = 8), 10 min before middle cerebral artery (MCA) occlusion, a bolus of 5 mg kg-1 of GYKI 52466 i.v. was administered and was followed by an infusion of 5 mg kg-1 h-1. For the Control Group (n = 8), the same volume of the vehicle was administered. One hour after MCA occlusion, regional cerebral blood flow (rCBF) was measured using the 14C-iodoantipyrine autoradiographic technique. Microscopic arterial and venous oxygen saturations were determined using microspectrophotometry. In the cortex contralateral to MCA occlusion, the average rCBF and the average O2 consumption were lower in the GYKI Group than in the Control Group (rCBF: GYKI 65.5 +/- 24.1 ml 100 g-1 min-1, Control 97.7 +/- 33.4 ml 100 g-1 min-1; O2 consumption: GYKI 3.9 +/- 1.2 ml O2 100 g-1 min-1, Control 6.2 +/- 2.5 ml O2 100 g-1 min-1) without a significant difference in the number of veins with SvO2 < 50%. In the ischemic cortex, the number of veins with SvO2 < 50% was significantly smaller in the GYKI Group (21 veins out of 63) than in the Control Group (45 out of 59) without a significant difference in the average rCBF (GYKI 44.9 +/- 17.7, Control 29.7 +/- 10.4) or regional O2 consumption between these two groups (GYKI 3.3 +/- 1.4, Control 2.7 +/- 1.2). Our data demonstrated that GYKI 52466 was effective in improving microscopic O2 balance in the focal ischemic cortical area of the brain and it decreased O2 consumption in the non-ischemic cortex.

Animals↗

PubMed1999

Longitudinal changes in sexual risk behavior among HIV+ and HIV- male injecting drug users.

UNLABELLED: Injecting drug users (IDUs) play a prominent role in the transmission of human immunodeficiency virus (HIV), particularly in urban areas such as New York City, where they comprise nearly half of all adult acquired immunodeficiency syndrome (AIDS) cases. Intervention studies have demonstrated that IDUs are responsive to safer sex messages, but sexual behavior appears to be more resistant to change than drug use behavior. This multidisciplinary study (without an intervention component) assesses changes in sexual risk behavior as a function of time, HIV status, and disease progression in a cohort of HIV+ and HIV- male IDUs (N = 144) for 4 years. RESULTS: For HIV+ and HIV- men, there were increases in abstinence and monogamy, with decreases in the frequency of unprotected vaginal/anal sex and sexual risk index scores. With the exception of monogamy, HIV+ men reported lower levels of risk. Although there was also a decline in substance use, this accounted for only some of the decline in sexual risk behavior. Among the HIV+ men, a CD4 level below 200 was associated with more abstinence and monogamy. HIV-related medical symptoms were associated with increased abstinence, less unprotected sex, and lower sexual risk index scores. Lower neuropsychological memory test scores were associated with increased abstinence and lower sexual risk index scores. Neurological impairment and depression were not associated with sexual risk behavior. CONCLUSION: IDU men in New York City have modified their sexual behavior toward safer practices. Lower levels of risk are found among HIV+ men, particularly those with more progressed HIV illness. Nevertheless, a substantial amount of sexual risk behavior remained in this cohort, indicating the continued need for education and intervention.

Adult↗

PubMed1999

Evidence for effective suppression of recombination in the chromosome 17q21 segment spanning RNU2-BRCA1.

Characterization of associations between polymorphic sites located throughout the approximately 200-400-kb variable-length region spanning RNU2-BRCA1 reveals nearly complete linkage disequilibrium. This segment spans the RNU2 array, which includes 6-30 tandem copies of the U2 snRNA gene, and an adjacent region containing NBR1, the LBRCA1 pseudogene, NBR2, and BRCA1 in a tandemly duplicated structure. A series of biallelic polymorphisms define two common haplotypes that do not vary significantly, in structure or frequency, between populations of primarily European (n=275) or Asian (n=34) ancestry. Lower-frequency variants occurring at distantly located sites within this region also show very strong associations. The rarer haplotype classes appear to be distinguished by mutational alteration and are not recombination products of the two major classes. The two major haplotypes also exhibit significantly different allele-length distributions for local simple tandem-repeat markers. The conservation of extensive distinct chromosomal haplotypes during a long period of human population expansion and divergence indicates that selective forces or specific chromosomal mechanisms result in effective recombination suppression. The extreme degree of long-range linkage disequilibrium at this locus may be exceeded only by that reported for the human MHC locus, where allele-specific functional interactions are believed to be significant. These findings have implications for the estimation of the time of origin of BRCA1 mutations having a founder effect, the interpretation of the significance of rare allelic variants, and the study of the origins of modern populations.

Alleles↗

PubMed1999

Identification of genes controlling malpighian tubule and other epithelial morphogenesis in Drosophila melanogaster.

The Drosophila Malpighian tubule is a model system for studying genetic mechanisms that control epithelial morphogenesis. From a screen of 1800 second chromosome lethal lines, by observing uric acid deposits in unfixed inviable embryos, we identified five previously described genes (barr, fas, flb, raw, and thr) and one novel gene, walrus (wal), that affect Malpighian tubule morphogenesis. Phenotypic analysis of these mutant embryos allows us to place these genes, along with other previously described genes, into a genetic pathway that controls Malpighian tubule development. Specifically, wal affects evagination of the Malpighian tubule buds, fas and thr affect bud extension, and barr, flb, raw, and thr affect tubule elongation. In addition, these genes were found to have different effects on development of other epithelial structures, such as foregut and hindgut morphogenesis. Finally, from the same screen, we identified a second novel gene, drumstick, that affects only foregut and hindgut morphogenesis.

Animals↗

PubMed1999

Evaluating payment mechanisms: how can we measure unnecessary care?

There has been substantial concern that linking hospital or physician remuneration to the amount of care provided will encourage excessive provision of health care. Studies that seek to explore this relationship require methods to measure unnecessary care. This paper presents and discusses a method used to assess the magnitude of unnecessary care in the context of an evaluation of the impact of paying bonuses to physicians employed in public hospitals in Shandong Province, China.

Adolescent↗

PubMed1999

The effect of a levonorgestrel-releasing intrauterine device on human endometrial oestrogen and progesterone receptors after one year of use.

Thirty-four women bearing a levonorgestrel-releasing intrauterine device, 20 micrograms/day (LNG-IUD-20), for 12-15 months were recruited. Endometrial biopsies were collected during the late proliferative phase of the cycle (on cycle days 10-12) before (control) and after the use of the IUD for 12 months, and assayed for oestrogen receptors (ER) and progesterone receptors (PR). An immunohistochemical technique with the peroxidase-antiperoxidase detection system (PAP method) was employed. D75 and JZB39 were the primary antibodies for ER and PR respectively. The immunostaining semiquantitative analysis was performed with a computerized microscope image processor, and expressed as 'grey value'. Both endometrial ER and PR populations were significantly lower after insertion of the IUD (P < 0.01) than in control biopsies. The intensity of nuclear staining and the percentage of positively stained cells for ER and PR in women with LNG-IUD were each about 50% of those in control biopsies. The results suggested that LNG released locally from the IUD has a depressive action on the ER and PR, which may contribute to the contraceptive effectiveness of this type of IUD and also to the possible causes of LNG-IUD-induced irregular bleeding and amenorrhoea.

Adult↗

PubMed1999

Developmental regulation of proteoglycan synthesis and decorin expression during turkey embryonic skeletal muscle formation.

To delineate the role of proteoglycans in turkey skeletal muscle development, proteoglycan expression was examined in pectoral muscle from 14-, 20-, and 25-d-old embryos. Proteoglycans were separated by DEAE (diethylaminoethyl cellulose) anion exchange and molecular sieve chromatography. Glycosaminoglycan composition was measured by enzyme digestion and nitrous acid deamination. The proteoglycan decorin was analyzed at each of these stages of development for core protein size by polyacrylamide gel electrophoresis and for spatial distribution by immunohistochemistry. Chondroitin sulfate-containing proteoglycans were the predominant proteoglycans found throughout turkey embryonic skeletal muscle development. However, in 20- and 25-d-old pectoral muscle, higher levels of heparan and dermatan sulfate were observed compared with their values at 14 d. Two decorin core protein bands with molecular weights of 45 and 46 kDa were detected. Immunostaining for decorin showed that, as the connective tissue layers developed, decorin was localized in the perimysium and epimysium. These data indicate that turkey embryonic skeletal muscle proteoglycan expression is dynamic and changes from a matrix that is rich in a large chondroitin sulfate proteoglycan to one containing dermatan sulfate, heparan sulfate, and chondroitin sulfate proteoglycans, and suggests the presence of two forms of decorin.

Animals↗

PubMed1999

The effects of propranolol on heterogeneity of rat cerebral small vein oxygen saturation.

UNLABELLED: beta-Adrenergic receptors are involved in altering cerebral metabolism and blood flow. This study was performed to determine whether propranolol would alter the microregional O2 balance in the brain. Rats were anesthetized with 1.4% isoflurane. Isotonic sodium chloride solution (control group), propranolol 2 mg/kg (low propranolol group) or propranolol 20 mg/kg (high propranolol group) was administered IV to the rats. Twenty minutes later, regional cerebral blood flow (rCBF) was measured using the 14C-iodoantipyrine autoradiographic technique. Small (diameter <70 microm) arterial and venous oxygen saturation (SaO2 and SvO2, respectively) was determined using microspectrophotometry in the alternate slices of the tissue sections used to measure rCBF. In both the low and high propranolol groups, average cortical rCBF was 35% lower than that in the control group. The average O2 consumption of the cortex of the propranolol groups was significantly lower than control (low propranolol: -41%, high propranolol: -49%). In all groups, SaO2 was almost identi-cal. The heterogeneity of the microregional SvO2 expressed as the coefficient of variation (CV = 100 x sD/mean) was significantly lower in the propranolol groups (low propranolol: 8.0+/-2.3, high propranolol: 7.3 +/- 2.9) than in the control group (13.4 +/- 3.5). The proportion of cortical veins with Svo2 <55% was significantly smaller in the low and high propranolol groups (4 of 60 and 3 of 60, respectively) than that in the control group (15 of 60). In the other brain regions, the data followed a similar pattern. Our data demonstrated that propranolol is effective in decreasing O2 consumption, improving microregional O2 balance, and reducing its heterogeneity in the brain. IMPLICATIONS: Our data suggest that the linkage of O2 supply and consumption is not tightly coupled under isoflurane anesthesia. beta-Adrenergic blockers may tighten this linkage and reduce the number of low O2-saturated microregions.

Adrenergic beta-Antagonists↗

PubMed1999

Prevalence and risk factors of behavioral and emotional problems among Chinese children aged 6 through 11 years.

OBJECTIVE: To examine the prevalence and risk factors of behavioral and emotional problems in Chinese children. METHOD: A sample of 2,940 children aged 6 through 11 years was randomly drawn from household registers in Shandong Province of China. Parents completed the Child Behavior Checklist (CBCL) and a structured self-rating questionnaire. RESULTS: The mean CBCL Total Problems score was 16.1 (SD = 14.0). There was no significant age effect on the Total Problems score; boys scored significantly higher than girls (17.2 versus 15.0; F = 24.94, p < .01). The overall prevalence rates of behavioral problems were 12.5% for boys and 8.3% for girls (chi 2 = 14.23, p < .01). Logistic regression analysis showed that a number of parental, prenatal, perinatal, and postnatal factors were significantly associated with increased risk of children's behavioral problems. CONCLUSIONS: The prevalence of parent-reported behavioral problems in Chinese children is lower than those found in other countries. Of multiple psychosocial and biological factors associated with children's behavioral problems, separation or divorce of parents is the most significant factor.

Behavioral Symptoms↗

PubMed1999

No evidence of linkage disequilibrium between a CAG repeat in the SCA1 gene and schizophrenia in Caucasian and Chinese schizophrenic subjects.

Several recent studies have reported evidence for a schizophrenia locus on chromosome 6p, with a variety of linked markers spanning a approximately 40 cM region between D6S470 and D6S291. However because of the wide region implicated and the difficulty of inferring phenotype from genotype in complex disorders, it is difficult to define its location precisely using linkage data. An alternative approach is to search for linkage disequilibrium. On chromosome 6p, allelic association with a (CAG)29 allele of a triplet repeat marker in the SCA1 gene has been reported, and we have attempted to replicate this finding using a Caucasian case-control sample of 211 affected subjects and 204 controls, and a Han Chinese sample of 100 affected family trios. In the case-control sample, the frequency of the (CAG)29 allele was similar in cases and controls (35%), and no other alleles provided evidence for allelic association. Likewise, there was no evidence for preferential transmission of the (CAG)29 allele to affected offspring in the Chinese sample, although a different allele, (CAG)26, was more often transmitted to the affected offspring. However this data did not reach statistical significance (P = 0.1). We conclude that our data does not support the notion that there is a locus for schizophrenia close to the SCA1 gene. However, since linkage disequilibrium will vary between distinct populations, we cannot exclude this possibility.

Asian People↗

PubMed1999

Characterization of ethylene biosynthesis associated with ripening in banana fruit.

We investigated the characteristics of ethylene biosynthesis associated with ripening in banana (Musa sp. [AAA group, Cavendish subgroup] cv Grand Nain) fruit. MA-ACS1 encoding 1-aminocyclopropane-1-carboxylic acid (ACC) synthase in banana fruit was the gene related to the ripening process and was inducible by exogenous ethylene. At the onset of the climacteric period in naturally ripened fruit, ethylene production increased greatly, with a sharp peak concomitant with an increase in the accumulation of MA-ACS1 mRNA, and then decreased rapidly. At the onset of ripening, the in vivo ACC oxidase activity was enhanced greatly, followed by an immediate and rapid decrease. Expression of the MA-ACO1 gene encoding banana ACC oxidase was detectable at the preclimacteric stage, increased when ripening commenced, and then remained high throughout the later ripening stage despite of a rapid reduction in the ACC oxidase activity. This discrepancy between enzyme activity and gene expression of ACC oxidase could be, at least in part, due to reduced contents of ascorbate and iron, cofactors for the enzyme, during ripening. Addition of these cofactors to the incubation medium greatly stimulated the in vivo ACC oxidase activity during late ripening stages. The results suggest that ethylene production in banana fruit is regulated by transcription of MA-ACS1 until climacteric rise and by reduction of ACC oxidase activity possibly through limited in situ availability of its cofactors once ripening has commenced, which in turn characterizes the sharp peak of ethylene production.

Amino Acid Oxidoreductases↗

PubMed1999

How RhoGDI binds Rho.

Like all Rho (Ras homology) GTPases, RhoA functions as a molecular switch in cell signaling, alternating between GTP- and GDP-bound states, with its biologically inactive GDP-bound form maintained as a cytosolic complex with RhoGDI (guanine nucleotide-exchange inhibitor). The crystal structures of RhoA-GDP and of the C-terminal immunoglobulin-like domain of RhoGDI (residues 67-203) are known, but the mechanism by which the two proteins interact is not known. The functional human RhoA-RhoGDI complex has been expressed in yeast and crystallized (P6(5)22, unit-cell parameters a = b = 139, c = 253 A, two complexes in the asymmetric unit). Although diffraction from these crystals extends to 3.5 A and is highly anisotropic, the experimentally phased (MAD plus MIR) electron-density map was adequate to reveal the mutual disposition of the two molecules. The result was validated by molecular-replacement calculations when data were corrected for anisotropy. Furthermore, the N-terminus of RhoGDI (the region involved in inhibition of nucleotide exchange) can be identified in the electron-density map: it is bound to the switch I and switch II regions of RhoA, occluding an epitope which binds Dbl-like nucleotide-exchange factors. The entrance of the hydrophobic pocket of RhoGDI is 25 A from the last residue in the RhoA model, with its C-terminus oriented to accommodate the geranylgeranyl group without conformational change in RhoA.

Binding Sites↗

PubMed1999

Exact rebinning methods for three-dimensional PET.

The high computational cost of data processing in volume PET imaging is still hindering the routine application of this successful technique, especially in the case of dynamic studies. This paper describes two new algorithms based on an exact rebinning equation, which can be applied to accelerate the processing of three-dimensional (3-D) PET data. The first algorithm, FOREPROJ, is a fast-forward projection algorithm that allows calculation of the 3-D attenuation correction factors (ACF's) directly from a two-dimensional (2-D) transmission scan, without first reconstructing the attenuation map and then performing a 3-D forward projection. The use of FOREPROJ speeds up the estimation of the 3-D ACF's by more than a factor five. The second algorithm, FOREX, is a rebinning algorithm that is also more than five times faster, compared to the standard reprojection algorithm (3DRP) and does not suffer from the image distortions generated by the even faster approximate Fourier rebinning (FORE) method at large axial apertures. However, FOREX is probably not required by most existing scanners, as the axial apertures are not large enough to show improvements over FORE with clinical data. Both algorithms have been implemented and applied to data simulated for a scanner with a large axial aperture (30 degrees), and also to data acquired with the ECAT HR and the ECAT HR+ scanners. Results demonstrate the excellent accuracy achieved by these algorithms and the important speedup when the sinogram sizes are powers of two.

Algorithms↗

PubMed1999

Stability of the interface between neural tissue and chronically implanted intracortical microelectrodes.

The stability of the interface between neural tissue and chronically implanted microelectrodes is very important for obtaining reliable control signals for neuroprosthetic devices. Stability is also crucial for chronic microstimulation of the cerebral cortex. However, changes of the electrode-tissue interface can be caused by a variety of mechanisms. In the present study, intracortical microelectrode arrays were implanted into the pericruciate gyrus of cats and neural activities were recorded on a regular basis for several months. An algorithm based on cluster analysis and interspike interval analysis was developed to sort the extracellular action potentials into single units. We tracked these units based on their waveform and their response to somatic stimulation or stereotypical movements by the cats. Our results indicate that, after implantation, the electrode-tissue interface may change from day-to-day over the first 1-2 weeks, week-to-week for 1-2 months, and become quite stable thereafter. A stability index is proposed to quantify the stability of the electrode-tissue interface. The reasons for the pattern of changes are discussed.

Action Potentials↗

PubMed1999

Lymphotropic virions affect chemokine receptor-mediated neural signaling and apoptosis: implications for human immunodeficiency virus type 1-associated dementia.

Chemokine receptors pivotal for human immunodeficiency virus type 1 (HIV-1) infection in lymphocytes and macrophages (CCR3, CCR5, and CXCR4) are expressed on neural cells (microglia, astrocytes, and/or neurons). It is these cells which are damaged during progressive HIV-1 infection of the central nervous system. We theorize that viral coreceptors could effect neural cell damage during HIV-1-associated dementia (HAD) without simultaneously affecting viral replication. To these ends, we studied the ability of diverse viral strains to affect intracellular signaling and apoptosis of neurons, astrocytes, and monocyte-derived macrophages. Inhibition of cyclic AMP, activation of inositol 1,4,5-trisphosphate, and apoptosis were induced by diverse HIV-1 strains, principally in neurons. Virions from T-cell-tropic (T-tropic) strains (MN, IIIB, and Lai) produced the most significant alterations in signaling of neurons and astrocytes. The HIV-1 envelope glycoprotein, gp120, induced markedly less neural damage than purified virions. Macrophage-tropic (M-tropic) strains (ADA, JR-FL, Bal, MS-CSF, and DJV) produced the least neural damage, while 89.6, a dual-tropic HIV-1 strain, elicited intermediate neural cell damage. All T-tropic strain-mediated neuronal impairments were blocked by the CXCR4 antibody, 12G5. In contrast, the M-tropic strains were only partially blocked by 12G5. CXCR4-mediated neuronal apoptosis was confirmed in pure populations of rat cerebellar granule neurons and was blocked by HA1004, an inhibitor of calcium/calmodulin-dependent protein kinase II, protein kinase A, and protein kinase C. Taken together, these results suggest that progeny HIV-1 virions can influence neuronal signal transduction and apoptosis. This process occurs, in part, through CXCR4 and is independent of CD4 binding. T-tropic viruses that traffic in and out of the brain during progressive HIV-1 disease may play an important role in HAD neuropathogenesis.

AIDS Dementia Complex↗

PubMed1999

Transcription originating in the long terminal repeats of the endogenous mouse mammary tumor virus MTV-3 is activated in Stat5a-null mice and picks Up hitchhiking exons.

The enhancer within the long terminal repeats (LTRs) of acquired somatic mouse mammary tumor viruses (MMTV) can activate juxtaposed genes and induce mammary tumors. In contrast, germ line proviral MMTV genomes are integrated in the host genome and considered to be genetically confined transcription units. Here we demonstrate that transcription initiated in an MMTV provirus proceeds into flanking host sequences. We discovered multiple polyadenylated transcripts which are induced in Stat5a null mice. These range from 1.5 kb to more than 8 kb and are specifically expressed in mammary tissue from pregnant and lactating mice from the 129 but not C57BL/6 strain. The RNAs emanate from both LTRs of the endogenous MTV-3 provirus on chromosome 11 and proceed at least 10 kb into the juxtaposed genomic territory. Transcripts originating in the 5' LTR splice from the native splice site within the MMTV envelope gene into at least six exons, three of which contain functional internal splice sites. The combination of alternative splicing and the use of several polyadenylation sites ensure the generation of multiple transcripts. To date no significant open reading frame has been discovered. Furthermore, we demonstrate that transcription from the MMTV 5' LTR is highly active in the absence of Stat5a, a transcription factor that had been shown previously to be required for transcription from the MMTV LTR.

Animals↗

PubMed1999

New insights into the mechanism of inhibition of p53 by simian virus 40 large T antigen.

Simian virus 40 (SV40) large tumor antigen (T antigen) has been shown to inhibit p53-dependent transcription by preventing p53 from binding to its cognate cis element. Data presented in this report provide the first direct functional evidence that T antigen, under certain conditions, may also repress p53-dependent transcription by a mechanism in which the transactivation domain of p53 is abrogated while DNA binding is unaffected. Specifically, p53 purified as a complex with T antigen from mouse cells was found to bind DNA as a transcriptionally inactive intact complex, while that purified from human cells was found to bind DNA independently of T antigen and could activate p53-dependent transcription. This difference in activity may be dependent on a different interaction of T antigen with mouse and human p53 and, in addition, on the presence of super T, which is found only in transformed rodent cells. These results suggest that subtle yet important differences exist between the inhibition of p53 by T antigen in mouse and human cells. The implications of this finding with respect to SV40-associated malignancies are discussed.

Animals↗