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Biomedical subjects

W Wu

Publications and source records attributed to W Wu.

At least 379 records · Page 21Linked to original sources
PubMed1995

Sequence-specific double-strand cleavage of DNA by Fe-bleomycin. 2. Mechanism and dynamics.

The mechanism of iron-bleomycin-mediated ds-cleavage of DNA has been investigated at specific sites within specific sequences using hairpin oligonucleotides (Absalon et al., 1995) and our recently developed technique for determining sequence-specific isotope effects upon oxidative degradation of DNA (Kozarich et al., 1989; Worth et al., 1993). Isotope effects upon ds-cleavage have been observed when the C-4' hydrogen of either nucleotide involved in the ds-break was substituted with deuterium. The values of the isotope effects determined for ss and ds events occurring at the same site were indistinguishable at four sites examined in detail. The results are consistent with a mechanism of ds-cleavage in which the pathways leading to ss- and ds-cleavage partition from a common intermediate subsequent to abstraction of the C-4' hydrogen from the first nucleotide involved in the cleavage. Deuterium substitution at the primary cleavage site of a ds-break failed to result in an equivalent effect on the amount of cleavage at the secondary cleavage site, suggesting that ds-cleavage may be initiated from either of the nucleotides involved in the ds-cleavage event. A kinetic preference for cleavage initiated at the 1 degree site, however, is probable. The requirement in the ds-cleavage process for O2, in addition to that needed to form "activated BLM", has been clearly demonstrated by the absence of ds-cleavage products in reactions performed under anaerobic conditions in which ss-cleavage still occurs. These results support, in part, the basic model for ds-cleavage proposed by Steighner and Povirk [(1990) Proc. Natl. Acad. Sci. U.S.A. 87, 8350-8354], in which a single molecule of BLM effects ds-cleavage and requires reactivation to effect cleavage at the second strand. The essential factor establishing the ratio of ss- to ds-cleavage at a specific site may be related to the efficiency by which Fe-BLM can be reactivated and/or repositioned at a second site for cleavage.

Bacterial Proteins↗
PubMed1995

Strand transfer mediated by human immunodeficiency virus reverse transcriptase in vitro is promoted by pausing and results in misincorporation.

Human immunodeficiency virus (HIV-1) is able to recombine by transfer of the growing DNA strand from internal regions of one genome to another. The strand transfer reaction, catalyzed by HIV-1 reverse transcriptase (RT), was conducted in vitro between donor and acceptor RNA templates that were derived from natural HIV-1 nef genes. The donor and acceptor templates shared a nearly homologous region where strand transfer could occur, differing only in that the acceptor had a 36-nucleotide insertion and 6 widely spaced base substitutions compared with the donor. We sequenced elongated primers that underwent transfer. The position of transfer was revealed by the change of sequence from that of the donor to that of the acceptor. Results showed a positive correlation between positions where the RT paused during synthesis and enhancement of strand transfer. Elimination of a pause site, with a minimal change in sequence, decreased the frequency of strand transfer in the immediate area. Analysis of the sequence of DNA products resulting from transfer at a frequently used site showed that mutations had been introduced into the DNA at about the point of transfer. Remarkably, approximately 30% of the products contained mutations. Base substitutions, short additions and deletions were observed. Mutations did not appear in DNA products extended on the donor template without transfer. The identity of the mutations suggests that they were caused by a combination of slippage and non-template-directed nucleotide addition. These results indicated that the detected mutations were related to the process of strand transfer.

Base Sequence↗
PubMed1995

Comparative cytotoxicity of fumonisin B1 and moniliformin in chicken primary cell cultures.

Two water-soluble Fusarium metabolites, fumonisin B1 (FB1) and moniliformin (MN) were compared for their cytotoxicity in a variety of chicken primary cell cultures. Cardiac and skeletal myocytes and hepatocytes derived from embryos, and splenocytes, macrophages, and chondrocytes derived from 3- to 4-week old chickens were cultured in media containing either FB1 or MN (0 to 1 mM) for 48 hr. The colorimetric tetrazolium cleavage assay was then used for measuring cell survival. FB1 was not toxic to macrophages, hepatocytes, cardiac and skeletal myocytes but toxic to splenocytes and chondrocytes. MN was not toxic to chondrocytes and macrophages, but toxic to splenocytes, cardiac and skeletal myocytes. Median effective concentration (EC50) of MN in skeletal myocytes was 42 mu M (fiducial limits: 33 to 50 mu M) and in cardiac myocytes was 95 mu M (fiducial limits: 84 to 122 mu M). Estimated EC50 of FB1 in chondrocytes and splenocytes and EC50 of MN in splenocytes were all greater than 200 mu M.

Animals↗
PubMed1995

Neural regeneration and neuronal migration following injury. I. The endocrine hypothalamus and neurohypophyseal system.

Central to this investigation are several basic hypotheses that are designed to test the role of nitric oxide (NO) in the complex process of central regeneration and plasticity in a well established model system of the mammalian brain. We have employed histochemical techniques at the light and ultrastructural level coupled with correlative scanning electron microscopy, immunoelectron microscopy, and in situ hybridization in order to determine the functional significance of the increased expression of nitric oxide synthase (NOS) in neurons of the supraoptic (SON) and paraventricular (PVN) nuclei which accompanies regeneration of their axotomized neurites following hypophysectomy. The aim of this investigation was to determine the potential role and temporal up-regulation of NOS in this basic regenerative process and to establish the ultrastructural and neuroanatomical correlates during critical periods of regeneration and regrowth of SON and PVN axons following hypophysectomy in the endocrine hypothalamus of the rat. Our data support the hypothesis that NO may serve as a second messenger molecule that may act in some fashion to govern not only the process of central regeneration and regrowth of magnocellular (SON/PVN) axons into the median eminence, neural stem, and neural lobe (the neurohypophyseal system) but may also influence the regeneration of neurites into new neuroanatomical domains such as the adjacent lumen of the third cerebral ventricle. We have demonstrated a distinct temporal relationship between injury (axotomy) of SON/PVN axons and the establishment of new neurovascular zones following hypophysectomy with the up-regulation of NOS. This up-regulation appears to correlate well with successful regeneration in the mammalian neurohypophyseal system. We have also successfully inhibited axonal regeneration with the use of nitroarginine, a competitive antagonist of NO. NOS up-regulation attendant to regeneration of SON and PVN axons may have inestimable clinical implications, particularly with respect to closed head injury and cerebral contusion that involves the mechanical shearing of the infundibular stalk. In addition, this investigation has reaffirmed that large numbers of bona fide neurons migrate and emerge upon the floor of the adjacent third cerebral ventricle shortly following hypophysectomy (within 2 weeks). The origin and mechanisms of neuronal migration and plasticity following hypophysectomy are the subject of interpretation and discussion in this investigation.

Amino Acid Oxidoreductases↗
PubMed1995

Effect of daily voluntary running on in vivo insulin action in rat skeletal muscle and adipose tissue as determined by the microdialysis technique.

The effect of physical training on in vivo insulin-stimulated glucose utilization in relation to glycolysis (lactate formation) in rat peripheral tissues was investigated in 8 sedentary controls (SC) and 7 voluntary running rats (VR). We used a sequential euglycemic clamp procedure (insulin infusion rate; 6.0, 30.0 mU/kg.min) in combination with a microdialysis technique in M. quadriceps femoris, vastus lateralis, and inguinal adipose tissue. In the clamp study, glucose infusion rate (GIR) averaged over 45-75 min during the 6.0-mU/kg.min insulin infusion was significantly (p < 0.01) higher in VR (15.36 +/- 0.83 mg/kg.min, mean +/- SE) than in SC (10.41 +/- 0.88 mg/kg.min), and the lack of a significant difference in GIR between VR and SC was found during the 30.0-mU/kg.min insulin infusion. In these tissues, there was no significant difference in dialysate lactate levels between VR and SC in the basal state without insulin or glucose infusion, or at an insulin infusion rate of 30.0 mU/kg.min. However, dialysate lactate concentrations in muscle averaged over 45-75 min during the 6.0-mU/kg.min insulin clamp procedure in VR (8.51 +/- 0.71 mg/dl) were significantly (p < 0.05) higher than in SC (6.18 +/- 0.48 mg/dl). These results indicated that insulin action in skeletal muscle and adipose tissue could be evaluated in vivo by using the microdialysis technique, and that an increase in GIR in VR was, in part, explained by an increase in lactate formation in skeletal muscle.

Adipose Tissue↗
PubMed1995

Regulation of the switch from myometrial contractures to contractions in late pregnancy: studies in the pregnant sheep and monkey.

Myometrial contractility occurs throughout pregnancy and characteristic patterns of myometrial activity exist according to the endocrine status and the relationship to parturition. These characteristic patterns differ between species, yet certain common features can be observed. Throughout pregnancy, myometrial activity is of the contractures type, long-lasting, low-amplitude epochs of activity switching to contraction-type activity at term. This switch from contractures to contractions tends to occur at night and is related to alteration in maternal plasma oestrogen concentrations, and maternal oxytocin function. Studies in several animal species support the hypothesis that maternal oestrogen prepares the myometrium for a periodic signal that causes the switch from contractures to contractions. Several lines of evidence implicate oxytocin in the switch. These studies show that the detailed preparation for parturition takes longer than previously considered and is brought about by a carefully regulated sequence of events in which oestrogen production by the placenta plays a central role.

Animals↗
PubMed1995

The effect of fumonisin B1 on isolated chondrocytes and on bone formation.

Toxic effects of fumonisin B1 (FB1) were observed with cultured chondrocytes isolated from epiphyseal growth plates and with growing broiler chicks. Viability of chondrocytes was reduced after 48 h exposure to FB1, and half lethal concentration of FB1 was estimated to be greater than 250 microM. Increase in cell size was inhibited by as low as 25 microM FB1. Dietary inclusion of fumonisins (55 and 110 ppm) caused a reduction in body weight, increase in liver weight, and decrease in feed efficiency (P < .05). However, diarrhea and bone malformation were not observed. It is concluded that fumonisin by itself is not sufficient to cause skeletal problems in poultry.

Animals↗
PubMed1995

[Induced expression of whiG, a gene crucial for sporulation of Streptomyces coelicolor].

whiG gene has been subcloned into Streptomyces expression vector pAK203 containing inducible promoter tipA. The expression of whiG gene promoted the spore formation of S. coelicolor J1501 and recovered the sporulation ability of whiG-deficient S. coelicolor C71. Increased amount of whiG gene product was detected by Western blot hybridization after induction of thiostrepton. It will be helpful for the future study of in vitro transcription of whiG-dependent promoters.

Gene Expression Regulation, Bacterial↗
PubMed1995

[Relationship between tumour necrosis factor and anemia of malaria].

In this paper, the relation between the level of the reactive oxygen species (ROS) and relevant free radicals in the blood plasma of the BALB/c mice infected with Plasmodium berghei ANKA strain and their erythrocytic deformability (ED), and the relation between the ED and the Hb indices of these mice were studied by chemiluminescence (CL), induced CL (ICL) and laser diffraction method. The results indicated that the ED decreased with the increase of the level of ROS and free radicals in blood plasma when the anemia is developing. The use of antioxidants may restrain the course and raise the Hb index. The authors deem that the excess TNF produced in the later stage of malaria may induce the release of excess ROS and free radicals from phagocytes, which may cause damage on the deformability of erythrocytes and a drop in ED, resulting in the anemia of malaria.

Anemia↗
PubMed1995

Pituitary microadenoma. MR appearance and correlation with CT.

Twenty surgically proven pituitary microadenomas were examined with MR imaging and CT. MR demonstrated 20 of 20 microadenomas: 90% of the tumors were hypointense on T1-weighted images before Gd-DTPA administration and in 45% the tumors were more clearly delineated postcontrast. CT demonstrated 19 of 20 diagnosed microadenomas: showing low attenuation in 85% of the tumors precontrast. Iohexol facilitated delineation of the tumors in 45%. Focal enlargement of the gland and diaphragma sellae convexity were more useful than infundibular tilting and sellar-floor erosion as ancillary findings supporting the diagnosis. In general, CT and MR agreed regarding the microadenomas size and location, measurement of enlarged intrasellar contents, detection of the diaphragma sellae bulge, and demonstration of infundibulum abnormality. CT was more sensitive than MR in identifying sellar-floor erosion. We suggest that CT be the first method for demonstration of microadenomas.

Adenoma↗
PubMed1995

[Anti-lipid peroxidation effects of sini decoction and its components on ischemic myocardium and the dose- and time-effects].

The complete Sini Decoction can significantly reduce the content of MDA in ischemic myocardium. Single ingredients of the decoction, such as Radix Aconoti Praeparata or Radix Glycyrrhizae, except Rhizoma Zingiberis, also have similar effect but inferior to that of the complete decoction. Under the present conditions of experiment, anti-lipid peroxidation of Sini Decoction is significant at doses ranging from 0.05 to 0.2ml/20g administered for 2-7 days at 0.1ml/(20g.d).

Animals↗
PubMed1995

An association study between essential hypertension and HLA-DRB1 alleles.

It is well established that genetic and environmental factors are involved in the etiology of essential hypertension (EH). Previous studies have suggested that at least one of the HLA genes is responsible for the genetic susceptibility to EH. Our aim in the present study was to investigate this issue in China by the PCR-SSP HLA-DRB1 typing method. The results showed an increased frequency of HLA-DR2 and a decreased frequency of HLA-DR7 with EH patients compared with controls. We consider that HLA-DR2 may represent a marker for susceptibility to EH in the North Chinese population.

Alleles↗
PubMed1995

Protective effect of radix Salviae Miltiorrhizae Composita on cerebral ischemia.

The protective effects of Radix Salviae Miltiorrhizae Composita (RSMC) on cerebral ischemia in gerbils produced by unilateral ligation of left common carotid artery and on the development of ischemic cerebral edema were studied. It was found that the administration of RSMC resulted in a very significant decrease in neurological deficits and the time for exhibiting first signs of neurological deficit delayed compared with untreated animals. Although the values of specific gravity of fresh cerebral tissue on the ligated side of common carotid artery in untreated animals (1.0406 +/- 0.0039 SD) and in RSMC-treated animals (1.0453 +/- 0.0009) were decreased significantly compared to that (1.0468 +/- 0.0003) of sham-operated animals, the specific gravity of cerebral tissue in RSMC-treated animals was significantly heavier than that in untreated animals (t = 5.5022, P < 0.001), i.e. the administration of RSMC decreased the severity of cerebral edema. A significant negative correlation was found between stroke index and specific gravity, and it suggests that one of the protective mechanisms of RSMC might be related to its ameliorating cerebral edema.

Animals↗