Search PubMed⌕ Search

Biomedical subjects

D Liu

Publications and source records attributed to D Liu.

At least 145 records · Page 8Linked to original sources
PubMed2001

Abnormal fetal growth is not associated with altered chorionic villous expression of vascular endothelial growth factor mRNA.

Altered placental and circulating levels of vascular endothelial growth factor (VEGF) and its receptor (flt-1) may be associated with pre-eclampsia and intrauterine growth restriction (IUGR). The aim of this study was to determine whether chorionic villous VEGF or flt-1 mRNA are altered at early gestation in pregnancies subsequently found to be complicated by abnormal fetal growth. Quantitative reverse transcription-polymerase chain reaction was performed on chorionic villous samples for VEGF and flt-1 using an internal RNA standard. Using the individualized birthweight ratio (IBR), the subjects (n = 51) were divided into three groups; IUGR (IBR <10th centile, n = 6), normal (IBR 10th-90th centiles, n = 41) and macrosomic (IBR >90th centile, n = 4). There was no correlation between the mRNA expression of VEGF(121) or VEGF(165) and gestational age of the normal controls. There was also no difference in the expression of either of the VEGF isoforms between the IUGR or macrosomic groups and the normal controls. Expression of flt-1 was below the detection limit of the assay. In conclusion, we have found that altered chorionic villous expression of VEGF is not associated with the initial stages of development of IUGR or macrosomia.

Actins↗
PubMed2001

Engineering variegated floral patterns in tobacco plants using the Arabidopsis transposable element Tag1.

Variegated flower phenotypes were generated using the Arabidopsis transposon Tag1 and the maize R regulatory gene. Tag1 was inserted between the CaMV 35S promoter and the maize R gene and transformed into tobacco plants. In half of the transgenic plants, variegated flower patterns were observed. Each line had a different pattern, with varying intensities with three lines showing only tiny sectors indicative of late excision and one showing large sectors indicative of earlier excision.

Arabidopsis↗
PubMed2001

Design, high-level expression, purification and characterization of soluble fragments of the hepatitis C virus NS3 RNA helicase suitable for NMR-based drug discovery methods and mechanistic studies.

RNA helicases represent a family of enzymes that unwind double-stranded (ds) RNA in a nucleoside triphosphate (NTP)-dependent fashion and which are required in all aspects of cellular RNA metabolism and processing. The hepatitis C virus (HCV) non-structural 3 (NS3) protein possesses a serine protease activity in the N-terminal one-third, whereas RNA-stimulated NTPase and helicase activities reside in the C-terminal portion of the 631 amino acid residue bifunctional enzyme. The HCV NS3 RNA helicase is of key importance in the life cycle of HCV, which makes it a target for the development of therapeutics. However, neither the precise mechanism nor the substrate structure has been defined for this enzyme. For nuclear magnetic resonance (NMR)-based drug discovery methods and for mechanistic studies we engineered, prepared and characterized various truncated constructs of the 451-residue HCV NS3 RNA helicase. Our goal was to produce smaller fragments of the enzyme, which would be amenable to solution NMR techniques while retaining their native NTP and/or nucleic acid binding sites. Solution conditions were optimized to obtain high-quality heteronuclear NMR spectra of nitrogen-15 isotope-labeled constructs, which are typical of well-folded monomeric proteins. Moreover, NMR binding studies and functional data directly support the correct folding of these fragments.

Adenosine Triphosphatases↗
PubMed2001

Maternal dietary lipids modify composition of bone lipids and ex vivo prostaglandin E2 production in early postnatal Japanese quail.

This study examined the effects of maternal dietary lipids on fatty acid composition and ex vivo prostaglandin E2 (PGE2) biosynthesis in bone tissues of progeny of Japanese quail. Laying hens were fed a basal diet containing soybean oil (SBO), hydrogenated soybean oil (HSBO), poultry fat (PF), or menhaden fish oil (FO) at 50 g/kg of diet. Fertilized eggs were incubated, and newly hatched quail were used for tibial fatty acid analysis and PGE2 measurement or were fed an identical diet until 2 wk of age. Yolks and tibiae of newly hatched quail from hens fed the SBO diet contained higher levels of total n-6 fatty acids and arachidonic acid [AA; 20:4(n-6)], whereas those from hens consuming the FO diet had increased concentrations of total n-3 fatty acids, eicosapentaenoic acid [EPA; 20:5(n-3)], docosapentaenoic acid [22:5(n-3)], docosahexaenoic acid [DHA; 22:6(n-3)], and total saturated fatty acids (SAT) but greatly reduced amounts of AA in egg yolks and tibiae. The maternal diet containing HSBO resulted in the accumulation of trans 18:1 egg yolks and tibiae of newly hatched quails. At 1 wk of age, the concentrations of EPA, DHA, and trans 18:1 in tibiae still reflected the maternal dietary fatty acid profile. At 2 wk of age, however, differences in fatty acid composition between treatments had disappeared. Addition of FO or HSBO to the maternal diet significantly lowered the ex vivo PGE2 production of tibiae in newly hatched quail compared to those from hens fed SBO or PF diet. These results suggest that maternal dietary lipids may have the potential to influence bone metabolism of embryos by modifying the fatty acid composition of this tissue.

Animal Feed↗
PubMed2001

Polymorphism of human Alpha class glutathione transferases.

The recognition of the importance and utility of single nucleotide polymorphisms has generated an interest in the development of new strategies for their identification. Analysis of the Expressed Sequence Tag (EST) database can provide a rapid and efficient means of identifying polymorphisms. Screening of the Alpha class glutathione transferases (GSTs) in the EST database identified 10 putative polymorphisms in the coding region of the GSTA1 and GSTA2 genes, six of which were subsequently verified by sequence analysis. Polymerase chain reaction/restriction fragment length polymorphism analysis revealed the existence of three variants, a silent base substitution, K125K (G365A) in GSTA1, and T112S and E210A in GSTA2, in European Australian, African and Chinese populations. The variant isoforms of GSTA2 were expressed in Escherichia coli, purified, and enzymatically characterized. Modelling of the two GSTA2 polymorphisms into a three-dimensional structure of GSTA2, and characterization of their enzymatic properties, has shown that the structure and function of the wild-type GSTA2-2 isoenzyme is not significantly altered by these polymorphisms. This report demonstrates that analysis of the EST database provides a rapid and efficient means of identifying variant proteins.

Alleles↗
PubMed2001

Intra-hepatic expression of scavenger receptor and CD14 and their relationship with local inflammatory responses in endotoxemia in mice.

Our objective was to investigate the expression of scavenger receptor (SR) and CD14 in the liver and their relationship with local anti-inflammatory and proinflammatory responses in endotoxemia in order to uncover the mechanism for the liver to turn into effector organ from defense one at the level of cell receptors in sepsis. Mouse models of endotoxemia of different severity were reproduced by injection of different doses of lipopolysaccharide (LPS) via tail vein. Expression of SR and CD14 in the liver was assayed by immunohistochemistry and was then analyzed with an image analysis system. The levels of TNFalpha, IL-6, IL-4, and IL-10 in liver tissue were determined with ELISA. Expression of SR in the liver in the high-dose group was markedly decreased 1 h after injection of LPS, and also in low- and medium-dose groups at 3 h. The expression of SR in the liver in the three groups was shown to be progressively decreased with the time prolonged. There was significant difference in average optical density (OD) values of SR among the three groups. The expression of CD14 in the liver in the three groups was shown to be significantly increased 1 h after injection of LPS, and much more with the time prolonged. But there was no significant difference in OD values of CD14 among the three groups. The contents of intrahepatic proinflammatory mediators TNFalpha and IL-6 and anti-inflammatory mediators IL-4 and IL-10 were successively significantly increased after injection of LPS. The release of anti-inflammatory mediators was shown to be later than that of proinflammatory mediators. Correlation analysis indicated that there was negative correlation between expression of SR and CD14, and that changes of TNFalpha, IL-6, IL-4, and IL-10 levels in liver tissues were correlated significantly positively with OD values of CD14 and negatively with OD values of SR. Expression of SR in the liver was shown to be progressively decreased, and that of CD14 increased in endotoxemia, which was closely related to the uncontrolled inflammatory response in liver. This might be an important mechanism for the liver to turn into effector organ from defense one in sepsis.

Animals↗
PubMed2001

Somatic and germinal excision activities of the Arabidopsis transposon Tag1 are controlled by distinct regulatory sequences within Tag1.

Various sequences within Tag1, the endogenous transposon of Arabidopsis, were examined to determine how Tag1 excision and expression are regulated. The 5' intron for the major 2.3-kb Tag1 transcript was found to be critical for the accumulation of Tag1 transcripts and for high rates of somatic excision. This was true for the autonomous element in cauliflower mosaic virus 35S-Tag1-beta-glucuronidase constructs and for a two-component system using the 35S promoter to produce Tag1 transposase and a beta-glucuronidase::dTag1 marker construct to score for excision. The 3' introns of Tag1, although not needed for high transposase expression in primary transgenic plants, were important for maintaining high levels of somatic excision and accumulation of the major but not the minor Tag1 transcripts in subsequent generations. With both 5' and 3' introns present, exchanging the 5' promoter region of Tag1 with the 35S promoter did not affect the timing of Tag1 excision significantly, but it did disrupt germinal excision. Removal of the 5' intron did not abolish germinal excision activity, however. These results indicate that somatic and germinal excision of Tag1 are differentially controlled, with the 5' promoter region being critical for germinal excision activity and the 5' intron playing an important role for somatic excision, possibly via intron-mediated enhancement.

Arabidopsis↗
PubMed2001

Direct activation of an inwardly rectifying potassium channel by arachidonic acid.

Arachidonic acid (AA) is an important constituent of membrane phospholipids and can be liberated by activation of cellular phospholipases. AA modulates a variety of ion channels via diverse mechanisms, including both direct effects by AA itself and indirect actions through AA metabolites. Here, we report excitatory effects of AA on a cloned human inwardly rectifying K(+) channel, Kir2.3, which is highly expressed in the brain and heart and is critical in regulating cell excitability. AA potently and reversibly increased Kir2.3 current amplitudes in whole-cell and excised macro-patch recordings (maximal whole-cell response to AA was 258 +/- 21% of control, with an EC(50) value of 447 nM at -97 mV). This effect was apparently caused by an action of AA at an extracellular site and was not prevented by inhibitors of protein kinase C, free oxygen radicals, or AA metabolic pathways. Fatty acids that are not substrates for metabolism also potentiated Kir2.3 current. AA had no effect on the currents flowing through Kir2.1, Kir2.2, or Kir2.4 channels. Experiments with Kir2.1/2.3 chimeras suggested that, although AA may bind to both Kir2.1 and Kir2.3, the transmembrane and/or intracellular domains of Kir2.3 were essential for channel potentiation. These results argue for a direct mechanism of AA modulation of Kir2.3.

Animals↗
PubMed2001

Transcriptional induction of hepatic NADPH: cytochrome P450 oxidoreductase by thyroid hormone.

Studies were carried out to elucidate the mechanism whereby thyroid hormone (T3) induces NADPH:cytochrome P450 oxidoreductase (P450R) mRNA in rat liver in vivo. Northern blot analysis revealed that T3 treatment increases unspliced liver nuclear P450R RNA 4-fold within 8 h and that this induction precedes the induction of mature, cytoplasmic P450R RNA. Unspliced nuclear P450R RNA was suppressed below basal levels 24 h after T3 treatment, despite the continued presence of elevated circulating T3 levels. To determine whether the T3-stimulated increase in nuclear P450R RNA reflects an increase in P450R transcription initiation, nuclear run-on transcription assays were carried out. T3 induced a 6- to 8-fold increase in P450R transcription rate within 12 h, sufficient to account for the observed increase in nuclear P450R precursor RNA, followed by a decrease back to basal transcription levels at 24 h, consistent with the nuclear RNA profile. Similar transcriptional increases were observed in nuclear run-on transcription studies using hybridization probes corresponding to nine different fragments of the P450R gene, spanning exon 2 to exon 16. Thus, P450R transcription initiation, not transcription elongation, is the T3-regulated event. Similar results were obtained during short (5 min) compared with long (45 min) nuclear run-on transcription assays, suggesting that changes in nuclear RNA processing or regulated degradation do not contribute to the overall RNA induction. This finding was confirmed by the ability of the RNA polymerase inhibitor actinomycin D, administered in vivo, to block T3 induction of P450R transcriptional activity. We conclude that P450R transcription, rather than nuclear RNA processing or mRNA stabilization, is the primary mechanism whereby T3 induces hepatic P450R mRNA.

Animals↗
PubMed2001

Cloning of a novel EGFR-related peptide: a putative negative regulator of EGFR.

Although epidermal growth factor receptor (EGFR) plays a key role in regulating cell proliferation, differentiation, and transformation in many tissues, little is known about the factor(s) that may modulate its function. We have isolated a cDNA clone from the rat gastroduodenal mucosa whose full length revealed 1,958 bp that contained 227 bp of 5'-untranslated region (UTR) and an open-reading frame encoding 479 amino acids, followed by 290 bp of 3'-UTR. It showed ~85% nucleotide homology to the external domain of the rat EGFR. We refer to the product of the newly isolated cDNA as EGFR-related protein (ERRP). In Northern blot analysis with poly(A)(+) RNA from different rat tissues, ERRP cDNA hybridized to several mRNA transcripts with the strongest reaction noted with a transcript of approximately 2 kb. Maximal expression of the 2-kb mRNA transcript was observed in the small intestine, followed by colon, liver, gastric mucosa, and other tissues. Transfection of ERRP cDNA into a colon cancer cell line, HCT116, resulted in a marked reduction in proliferation in monolayer and colony formation in soft agar compared with the vector-transfected controls. In another colon cancer cell line, Caco-2, with a tetracycline-regulated promoter system, induction of ERRP expression in the absence of doxycycline was associated with a marked reduction in EGFR activation and proliferation. We conclude that the ERRP cDNA may represent a new member of the EGFR gene family and that ERRP plays a role in regulating cell proliferation by modulating the function of EGFR.

5' Untranslated Regions↗
PubMed2001

Stereotactic radiosurgery for primary trigeminal neuralgia using the Leksell Gamma unit.

OBJECTIVE: Previous papers have reported Gamma Knife radiosurgery to be a safe, effective method for primary trigeminal neuralgia. Since November 1996, we have treated primary trigeminal neuralgia using the Leksell Gamma Knife at the Tianjin Medical University. The present study reports clinical results of Gamma Knife radiosurgery in the treatment of trigeminal neuralgia in 80 cases. METHODS: The mean patient age was 67 years (range 32-92), the mean duration of facial pain was 7.6 years (range 1.5-29). The male:female ratio was 31:49. The right side of the face was involved in 45 patients (56.25%) and the left side in 30 cases (37.5%), with bilateral involvement in 5 cases (6.25%). Under local anesthesia, all patients underwent stereotactic MRI to identify the trigeminal nerve. A single isocenter, using a 4-mm collimator, was positioned at the sensory root of the trigeminal nerve entry zone of the pons, 4-6 mm from the brainstem surface, so that no more than the 20% isodose was administered to the brainstem. The maximum dose was between 70 and 90 Gy, with a mean of 75.6 Gy. For bilateral trigeminal neuralgia, two separate matrices were employed, and bilateral Gamma Knife radiosurgery was performed on the same day. RESULTS: Follow-up ranged from 12 to 43 months (mean 23.7 months). Neurological evaluation indicated excellent response in 42 cases (52.5%), good response in 25 cases (31.25%), effective response in 8 cases (10%), so the total pain control rate was 93.75%. The latency from Gamma Knife surgery to pain relief ranged from 1 to 120 days (mean 22 days). Among the 75 patients 7 with pain control experienced pain recurrence 5-26 months after being completely free from pain. A second Gamma Knife radiosurgery was performed in 7 recurrent cases and 5 patients with treatment failure. A maximal dose ranging from 70 to 80 Gy was given (mean 74.2 Gy). After a mean follow-up of 18 months (8-33 months), 9 patients achieved excellent results, and 2 had good results. The latency interval to pain relief ranged from 1 to 120 days (mean 15 days). Nine patients developed new facial numbness, while no other complication appeared in the remainder of the patients. CONCLUSIONS: Gamma Knife radiosurgery is a safe and effective method in the treatment of trigeminal neuralgia once diagnosis is established.

Adult↗
PubMed2001

Double-stranded ribonucleic acid (RNA) induces beta-cell Fas messenger RNA expression and increases cytokine-induced beta-cell apoptosis.

Type 1 diabetes mellitus (T1DM) is an autoimmune disease caused by progressive destruction of insulin-producing pancreatic beta-cells. Both viral infections and the cytokines interleukin-1beta (IL-1beta) and interferon-gamma (IFN-gamma) have been suggested as potential mediators of beta-cell death in early T1DM. We presently investigated whether the viral replicative intermediate double stranded RNA [here used as synthetic polyinosinic-polycytidylic acid (PIC)] modifies the effects of IL-1beta and IFN-gamma on gene expression and viability of rat pancreatic beta-cells. For this purpose, fluorescence-activated cell sorting-purified rat beta-cells were exposed for 6-16 h (study of gene expression by RT-PCR) or 6-9 days (study of viability by nuclear dyes) to PIC and/or IL-1beta and IFN-gamma. PIC increased the expression of Fas and Mn superoxide dismutase messenger RNAs by 5- to 10-fold. IL-1beta and a combination of PIC and IFN-gamma (but not PIC or IFN-gamma alone) induced expression of inducible nitric oxide (NO) synthase (iNOS) and consequent NO production. Induction of iNOS expression by PIC and IFN-gamma requires nuclear factor-kappaB activation, as suggested by transfection experiments with iNOS promoter-luciferase reporter constructs into primary beta-cells. Combinations of IL-1beta plus IFN-gamma, PIC plus IFN-gamma, or PIC plus IL-1beta induced a 2- to 3-fold increase in the number of apoptotic beta-cells. Blocking of iNOS activity significantly decreased PIC- plus IL-1beta-induced, but not PIC- plus IFN-gamma-induced, apoptosis. In conclusion, PIC alone or in combination with cytokines modifies the expression of several genes in pancreatic beta-cells. Two of these genes, Fas and iNOS, may contribute to beta-cell death. The transcription factor nuclear factor-kappaB is required for PIC-induced iNOS expression. PIC has an additive effect on cytokine-induced beta-cell death by both NO-dependent (in the case of IL-1beta) and NO-independent (in the case of IFN-gamma) mechanisms. These findings suggest that viral intermediates in synergism with local cytokine production may play an important role in beta-cell apoptosis in early T1DM.

Animals↗
PubMed2001

Multipulse feed strategy for glycerol fed-batch fermentation: a steady-state nonlinear optimization approach.

During glycerol fed-batch fermentation, the process could be divided into multiple equal subintervals, and the feed operation was performed in pulse form at the start of each subinterval. Based on the macrokinetic models, the multipulse feed strategy for both glucose and corn steep slurry was determined by a general nonlinear optimization approach to maximize the final glycerol productivity and still control the residual glucose at a low concentration. The experimental results in a 600-mL Airlift Loop Reactor showed that the tested data with this strategy agreed well with the corresponding model prediction, and that the feed mode with nonlinear optimization could improve the glycerol productivity significantly compared with those determined just by limited experimental optimization in previous studies.

Bioreactors↗
PubMed2001

End-labeling of long DNA fragments with biotin and detection of DNA immobilized on magnetic beads.

To immobilize DNA fragments onto magnetic beads coated with streptavidin for isolation purpose, it is important to label one biotin molecule at one terminus of DNA fragment. After failure to label long DNA with biotin by PCR and filling-in reaction, a 9.2 kb DNA was labeled with biotin by a modified ligation strategy. A simple method is also reported to detect the quantity and integrity of DNA immobilized on the magnetic beads.

Base Sequence↗
PubMed2001

Does nifedipine aggravate cyclosporin--induced gingival overgrowth? An experiment in rats.

BACKGROUND: Nifedipine (NIF) may aggravate cyclosporin A (CsA)-induced gingival overgrowth because the potentiated gingival overgrowth has been observed in the patients treated with CsA and NIF. The purpose of this study was to evaluate whether NIF could aggravate the CsA-induced gingival overgrowth in a rat model. METHODS: Ninety male Sprague-Dawley rats were divided into 6 groups: the first group received 8 mg/kg of CsA daily by gastric feeding for 6 weeks; the second and third groups received NIF daily at a dosage of 10 or 50 mg/kg; the fourth and fifth groups received CsA (8 mg/kg) and NIF (10 or 50 mg/kg); and the sixth group received solvents as a negative control. Gingival dimensions (including bucco-lingual depth, mesio-distal width, and vertical height) were assessed bi-weekly from impressed stone models of the mandibular incisal region. At the end of the experiment, the animals were sacrificed. Following histopathological procedures, serial horizontal sections were obtained at the base of the central incisal papilla. Two tissue levels were selected for histometric analysis. Level 1 was defined as the point where the lingual gingiva embraced the bucco-lingual midpoint of the roots and the level 2 as the point where the lingual gingiva at the enamel-dentinal junction approximated the bucco-proximal angle of the roots. The bucco-lingual depth and the mesio-distal width of the papilla were recorded on 5 consecutive sections at the 2 levels, respectively. RESULTS: At the 6-week observations, the gingival dimensions (including the depth, width, and height) significantly increased after CsA therapy and the increasing treatment duration; however, only the mesio-distal width increased after NIF therapy. For NIF therapy alone, a positive linear relation was noted by increased NIF treatment dosages in all gingival dimensions at week 6. But, this relationship was not found in the combined therapies. By histometry, tissue dimensions increased following single drug therapy, either CsA or NIF, at both levels. In animals with the combined therapies, the tissue dimensions decreased if the animals received 10 mg NIF, while they rebounded to control levels with the 50 mg dosage. A dose-dependent positive pattern by NIF was noted in tissue dimensions, but the pattern did not occur in animals that received combined therapy. CONCLUSIONS: The gingival dimensions increased after CsA or NIF therapy, although they were more prevalent with CsA. But the augmenting pattern in gingival morphology observed with CsA therapy decreased when the animals received additional NIF. Therefore, we question whether NIF is a critical factor in aggravating the CsA-induced gingival overgrowth.

Animals↗