Biomedical subjects

C Yu

Publications and source records attributed to C Yu.

At least 55 records · Page 3Linked to original sources

PubMed2001

An image fusion study of the geometric accuracy of magnetic resonance imaging with the Leksell stereotactic localization system.

A special acrylic phantom designed for both magnetic resonance imaging (MRI) and computed tomography (CT) was used to assess the geometric accuracy of MRI-based stereotactic localization with the Leksell stereotactic head frame and localizer system. The acrylic phantom was constructed in the shape of a cube, 164 mm in each dimension, with three perpendicular arrays of solid acrylic rods, 5 mm in diameter and spaced 30 mm apart within the phantom. Images from two MR scanners and a CT scanner were obtained with the same Leksell head frame placement. Using image fusion provided by the Leksell GammaPlan (LGP) software, the coordinates of the intraphantom rod positions from two MRI scanners were compared to that of CT imaging. The geometric accuracy of MR images from the Siemens scanner was greatly improved after the implementation of a special software patch provided by the manufacturer. In general, much better accuracy was achieved in the transverse plane where images were acquired. Most distortion was found around the periphery while least distortion was present in the middle and most other parts of the phantom. For most intracranial lesions undergoing stereotactic radiosurgery, accuracy of target localization can be achieved within size of a voxel, especially with the Siemens scanner. However, extra caution should be taken for imaging of peripheral lesions where the distortion is the greatest.

Humans↗

PubMed2001

A translational couch technique for total body irradiation.

We have constructed a computer controlled translational couch to administer total body irradiation reproducibly and safely. The system has replaced the previous stationary anterior-posterior technique in our institution and 30 plus patients have been treated with it so far. In this technique, patients comfortably lie on a couch in supine and prone positions and are transported slowly through a narrow beam with the gantry in an upright position. Dose to the patient is determined by the couch velocity that is calculated based on physical parameters such as patient's dimensions, beam geometry, and machine dose rate. In our design, the couch velocity is continuously updated to compensate for machine dose rate fluctuations. The translational couch technique provides better dose uniformity within the patient compared to fixed beam techniques, and allows a more precise shielding block placement for organs at risk. At the same time, it presents a special challenge for dosimetry calculations. A dosimetry parameter is introduced that converts the moving beam output to the fixed beam output factor. Based on this factor, a simple dosimetry calculation method has been developed that takes advantage of conventional dosimetry parameters, eliminating extensive dosimetry measurements. Multiple point dose measurements within a phantom confirmed the validity of the calculation method.

Dose Fractionation, Radiation↗

PubMed2001

Sequence-dependent potentiation of paclitaxel-mediated apoptosis in human leukemia cells by inhibitors of the mitogen-activated protein kinase kinase/mitogen-activated protein kinase pathway.

Effects of inhibitors of the mitogen-activated protein kinase kinase/mitogen-activated protein kinase (MEK/MAPK) cascade have been examined in relation to paclitaxel-induced apoptosis in human monocytic leukemia cells (U937). Cells treated with paclitaxel (250 nm; 6 h) followed by PD98059 [corrected] exhibited a significant increase in mitochondrial dysfunction (e.g., cytochrome c release), caspase activation, poly ADP-ribose polymerase cleavage, and apoptosis, whereas pretreatment of cells with PD98059 reduced lethality. Similar results were obtained with other MEK/MAPK inhibitors (e.g., U0126 and PD184352). Subsequent exposure of paclitaxel-treated cells to PD98059 did not enhance dephosphorylation/activation of p34(cdc2) but diminished expression of the antiapoptotic protein Mcl-1. The caspase inhibitor ZVAD-fmk opposed potentiation of paclitaxel-induced loss of mitochondrial membrane potential (Deltapsi(m)) and apoptosis by PD98059, but not cytochrome c release. Paclitaxel treatment induced sustained phosphorylation/activation of MAPK, an effect prevented by subsequent, but not prior, exposure to PD98059. Paclitaxel treatment also induced c-Jun N-terminal kinase phosphorylation, but this effect was enhanced only slightly by subsequent PD98059 administration. Although paclitaxel alone failed to induce p38 MAPK activation, subsequent (but not prior) exposure to PD98059 induced a dramatic increase in p38 MAPK phosphorylation. Moreover, coadministration of the p38 MAPK inhibitors SB203580 and SB202190 abrogated the increase in paclitaxel-mediated apoptosis induced by PD98059. Finally, subsequent PD98059 exposure increased, whereas prior exposure decreased inhibition of clonogenicity by paclitaxel. Together, these findings suggest that subsequent exposure of paclitaxel-treated U937 cells to MEK/MAPK inhibitors induces perturbations in signaling pathways, particularly the p42/44 MAPK and p38 MAPK cascades, that lower the threshold for mitochondrial injury and induction of cell death.

Antineoplastic Agents, Phytogenic↗

PubMed2001

Activation of NF-kappaB by hepatitis B virus X protein through an IkappaB kinase-independent mechanism.

pX, the hepatitis B virus-encoded transcription coactivator, is involved in viral infection in vivo. pX stimulates the activity of several transcription factors including nuclear factor-kappaB (NF-kappaB), but the mechanism of activation is poorly understood. The IkappaB kinase complex (IKK) mediates activation of NF-kappaB in response to various extracellular stimuli, including inflammatory cytokines like tumor necrosis factor and interleukin 1, human T cell lymphoma virus 1 Tax protein, and tumor promoters like phorbol esters. It is not known whether IKK also mediates activation of NF-kappaB by pX. Here we report that IKK was not essential for activation of NF-kappaB by pX. Expression of pX resulted in the degradation of IkappaBalpha in the absence of its phosphorylation at Ser(32) and Ser(36) residues. Although pX stimulated the activity of cotransfected IKK-beta when it was overexpressed, it failed to activate endogenous IKK. Furthermore, expression of pX stimulated NF-kappaB nuclear translocation and transcriptional activity in IKK-gamma-null fibroblast 5R cells. Our data indicate that pX stimulates NF-kappaB activity through a mechanism that is dependent on IkappaBalpha degradation but not on IKK activation.

Cell Line↗

PubMed2001

Carbon monoxide produced by isolated arterioles attenuates pressure-induced vasoconstriction.

Studies were conducted on isolated rat gracilis muscle arterioles to examine the role of vascular heme oxygenase (HO)-derived carbon monoxide (CO) on myogenic constrictor responses to stepwise increments in intraluminal pressure. The arterioles express HO-2 but not HO-1 and manufacture CO. Both HO-2 protein expression and CO production are reduced in arterioles maintained for 18 h before experimentation in media containing HO-2 antisense oligodeoxynucleotides (AS-ODN). Pressurization of arterioles mounted on a myograph over the pressure range of 40--100 mmHg elicits reduction of internal diameter. At pressures >40 mmHg, the internal diameter of vessels treated with either HO-2 AS-ODN, the HO inhibitor chromium mesoporphyrin (CrMP), or the K(+) channel blocker tetraethylammonium (TEA) are smaller than the corresponding control values. The inclusion of exogenous CO, but not of biliverdin, in the superfusion buffer attenuates pressure-induced vasoconstriction in CrMP-treated vessels. However, exogenous CO does not attenuate pressure-induced vasoconstriction in vessels treated with both CrMP and TEA. Collectively, these data suggest that CO of vascular origin attenuates pressure-induced arteriolar constriction via a mechanism involving a TEA-sensitive K(+) channel.

Animals↗

PubMed2001

Prenatal glucocorticoid modifies hypothalamo-pituitary-adrenal regulation in prepubertal guinea pigs.

We hypothesized that exposure to synthetic glucocorticoid during rapid brain growth (d50-52, birth = 68 days) in fetal guinea pigs modifies hypothalamo-pituitary-adrenal (HPA) function after birth, and that this involves changes in central corticosteroid receptor regulation. On the basis of our previous studies, we proposed that this effect is sex-specific. Pregnant guinea pigs were treated with dexamethasone (1 mg/kg) or vehicle on d50-51 of gestation, and juvenile offspring were euthanized at rest or following isolation stress on postnatal day 18. Dexamethasone increased the length of gestation (1.5 days) and altered body and organ (brain, heart, adrenal) growth. Resting plasma cortisol concentrations were significantly elevated in young male, but not female guinea pigs exposed to dexamethasone as fetuses. In female offspring born to dexamethasone-treated mothers, cortisol responses to isolation stress were attenuated. In males, elevated basal cortisol levels were not increased further by isolation. In the brain, hippocampal glucocorticoid receptor (GR) mRNA levels were significantly lower (10-25%) in females exposed to dexamethasone in utero. In contrast, GR mRNA levels were elevated (10-20%) in males from this prenatal treatment group. Mineralocorticoid receptor mRNA in the limbic system and GR mRNA levels in the pars distalis were unaffected. Pro-opiomelanocortin mRNA was significantly lower (30%) in the male pars intermedia following dexamethasone exposure. In conclusion, prenatal glucocorticoid exposure affects growth and HPA function as well as limbic and hypothalamic GR expression in juvenile offspring, and these effects are highly sex-specific.

Animals↗

PubMed2001

Carbon monoxide of vascular origin attenuates the sensitivity of renal arterial vessels to vasoconstrictors.

Rat renal interlobar arteries express heme oxygenase 2 (HO-2) and manufacture carbon monoxide (CO), which is released into the headspace gas. CO release falls to 30% and 54% of control, respectively, after inhibition of HO activity with chromium mesoporphyrin (CrMP) or of HO-2 expression with antisense oligodeoxynucleotides (HO-2 AS-ODN). Patch-clamp studies revealed that CrMP decreases the open probability of a tetraethylammonium-sensitive (TEA-sensitive) 105 pS K channel in interlobar artery smooth muscle cells, and that this effect of CrMP is reversed by CO. Assessment of phenylephrine-induced tension development revealed reduction of the EC(50) in vessels treated with HO-2 AS-ODN, CrMP, or TEA. Exogenous CO greatly minimized the sensitizing effect on agonist-induced contractions of agents that decrease vascular CO production, but not the sensitizing effect of K channel blockade with TEA. Collectively, these data suggest that vascular CO serves as an inhibitory modulator of vascular reactivity to vasoconstrictors via a mechanism that involves a TEA-sensitive K channel.

Animals↗

PubMed2001

Spectroscopic studies and photodynamic actions of hypocrellin B in liposomes.

Hypocrellin B (HB), a lipid-soluble natural pigment of perylenequinone derivative, is considered as potential photosensitizer for photodynamic therapy. Liposomes loaded with HB can constitute a simple model system, appropriate for better understanding the photodynamic action of HB in vivo. The steady-state absorption and emission spectra, quantum yield and lifetime of fluorescence of HB incorporated into egg L-a-phosphatidyl-choline (EPC) liposome were examined. The photochemical properties (Type I and/or Type II) of HB have also been studied in aqueous dispersions of small unilamellar liposomes of EPC using electron paramagnetic resonance and spectrophotometric methods, respectively. The quantum yield of 1O2 generated by HB is ca 0.76 in chloroform solution and it did not change upon the incorporation of HB into liposomes of EPC. The superoxide anion radical was generated by the electron transfer from the anion radical of HB (HB.-) to oxygen. The disproportionation of O2.- can generate H2O2 and ultimately the highly reactive .OH via the Fenton reaction. It could be that the disproportionation proceeded too fast, so we could not detect O2.- directly in aqueous dispersions of liposome EPC. Moreover, the self-sensitized photooxygenation of HB embedded in liposomes was studied, and almost fully (87%) inhibiting this reaction of HB by p-benzoquinone (as the quencher of O2.-) in aqueous dispersion of liposome EPC indicated that the radical mechanism (Type I) might be mainly involved in this oxygenation. All these findings suggested that the photodynamic action of HB proceeded via both Type-I and -II mechanisms, but Type-I mechanism might play a more important role in the aqueous dispersion.

Electron Spin Resonance Spectroscopy↗

PubMed2001

Stimulating effects of low-dose fructose on insulin-stimulated hepatic glycogen synthesis in humans.

Fructose has been shown to have a catalytic effect on glucokinase activity in vitro; however, its effects on hepatic glycogen metabolism in humans is unknown. To address this question, we used (13)C nuclear magnetic resonance (NMR) spectroscopy to noninvasively assess rates of hepatic glycogen synthesis and glycogenolysis under euglycemic (approximately 5 mmol/l) hyperinsulinemic conditions (approximately 400 pmol/l) with and without a low-dose infusion of fructose (approximately 3.5 micromol. kg(-1). min(-1)). Six healthy overnight-fasted subjects were infused for 4 h with somatostatin (0.1 micromol. kg(-1). min(-1)) and insulin (240 pmol. m(-2). min(-1)). During the initial 120 min, [1-(13)C]glucose was infused to assess glycogen synthase flux followed by an approximately 120-min infusion of unlabeled glucose to assess rates of glycogen phosphorylase flux. Acetaminophen was given to assess the percent contribution of the direct and indirect (gluconeogenic) pathways of glycogen synthesis by the (13)C enrichment of plasma UDP-glucuronide and C-1 of glucose. In the control studies, the flux through glycogen synthase and glycogen phosphorylase was 0.31 +/- 0.06 and 0.17 +/- 0.04 mmol/l per min, respectively, and the rate of net hepatic glycogen synthesis was 0.14 +/- 0.05 mmol/l per min. In the fructose studies, the glycogen synthase flux increased 2.5-fold to 0.79 +/- 0.16 mmol/l per min (P = 0.018 vs. control), whereas glycogen phosphorylase flux remained unchanged (0.24 +/- 0.06; P = 0.16 vs. control). The infusion of fructose resulted in a threefold increase in rates of net hepatic glycogen synthesis (0.54 +/- 0.12 mmol/l per min; P = 0.008 vs. control) without affecting the pathways of hepatic glycogen synthesis (direct pathway approximately 60% in both groups). We conclude that during euglycemic hyperinsulinemia, a low-dose fructose infusion causes a threefold increase in net hepatic glycogen synthesis exclusively through stimulation of glycogen synthase flux. Because net hepatic glycogen synthesis has been shown to be diminished in patients with poorly controlled type 1 and type 2 diabetes, stimulation of hepatic glycogen synthesis by this mechanism may be of potential therapeutic value.

Adult↗

PubMed2001

[Expression of human anti-HBsAg-interferon fusion protein in CHO cells].

OBJECTIVE: To study the possibility of expressing human anti-HBsAg-interferon fusion protein in CHO cells as a putative targeting drug for hepatitis B. METHODS: Both the heavy and light chain genes of human anti-HBsAg antibody derived from a phage display library were fused with alpha-2b interferon (IFN-alpha-2b) gene in vitro by polymerase chain reaction. The IFN alpha-2b gene was placed at the C terminal and a 15 amino acid linker was introduced at the fusion site. The light chain-IFN expression plasmid pLIC was constructed with a mammalian expression vector pcDNA3.1(+) and the heavy chain-IFN expression plasmid pFID was constructed with another mammalian expression vector pCdhfr1. These plasmids and the anti-HBsAg full-length light and heavy chain expression plasmids (pLIC and pHFD, respectively) were transfected into CHO (dhfr-) cells by the following three combinations:I, pLIC + pHFD;II, pLIC + pFID; III, pLFC + pFID. The cultured supernatant of the transfected cells was collected and assayed for IFN activity and HBsAg affinity. RESULTS: The supernatant of combination I and II displayed IFN activity but only combination I supernatant exhibited HBsAg affinity. CONCLUSIONS: The successful expression of a fusion protein with both HBsAg affinity and interferon activity may lead to a new way to make a targeting drug for hepatitis B.

Animals↗

PubMed2001

[Accumulation, chemical fractions and phytoavailability of Cr in tannery sludge-amended soils].

The phytoavailability of various fractions in the tannery sludge amended soils was investigated employing a sequential extraction procedure as well as seedling culture experiment. The results showed that 2 mol/L HCl extractable Cr could be the major fraction of soil Cr available to the plants. When the Cr content in soil was about 220 mg/kg, the Cr concentration of in plant reached maximum of 23.5 mg/kg, which was hardly approachable in field condition.

Chromium↗

PubMed2001

[CT appearance and its diagnosis value in liver cancer after transcatheter oily chemoembolization combining with high intensity focused ultrasound therapy].

OBJECTIVE: To study the CT appearances of liver cancer after transcatheter oily chemoembolization (TOCE) combining with high intensity focused ultrasound (HIFU) therapy. METHODS: Fifty cases of clinically-proved liver cancer were included into this study. For each case, CT scanning before and after TOCE, HIFU treatment was performed. The volumes of the masses were measured. The appearances of the oily deposition and the density, shape, border of the lesions were observed. RESULTS: The lesions became smaller in 38 cases (38/50, 76%) after the treatment. The differences were detected statistically in the ratio of the tumor shrinkage between the single TOCE therapy and the combined treatment (P<0.05). The ratio of the tumor shrinkage was closely correlative with the quantity of the oily deposition, but not with the diameter of the tumor before treatment. The lowered densities were showed in 30 cases (30/50, 60%) and the borders became regular and clear in 16 cases after HIFU therapy. CONCLUSIONS: TOCE combining with HIFU therapy in the patients with liver cancer can make the tumor smaller. CT is of great value in the evaluation of efficacy and prognosis.

Adult↗

PubMed2000

Impaired preneoplastic changes and liver tumor formation in tumor necrosis factor receptor type 1 knockout mice.

Hepatic stem cells (oval cells) proliferate within the liver after exposure to a variety of hepatic carcinogens and can generate both hepatocytes and bile duct cells. Oval cell proliferation is commonly seen in the preneoplastic stages of liver carcinogenesis, often accompanied by an inflammatory response. Tumor necrosis factor (TNF), an inflammatory cytokine, is also important in liver regeneration and hepatocellular growth. The experiments reported here explore the relationship among the TNF inflammatory pathway, liver stem cell activation, and tumorigenesis. We demonstrate that TNF is upregulated during oval cell proliferation induced by a choline-deficient, ethionine-supplemented diet and that it is expressed by oval cells. In TNF receptor type 1 knockout mice, oval cell proliferation is substantially impaired and tumorigenesis is reduced. Oval cell proliferation is impaired to a lesser extent in interleukin 6 knockout mice and is unchanged in TNF receptor type 2 knockout mice. These findings demonstrate that TNF signaling participates in the proliferation of oval cells during the preneoplastic phase of liver carcinogenesis and that loss of signaling through the TNF receptor type 1 reduces the incidence of tumor formation. The TNF inflammatory pathway may be a target for therapeutic intervention during the early stages of liver carcinogenesis.

Animals↗

PubMed2000

15N NMR relaxation studies of free and ligand-bound human acidic fibroblast growth factor.

15N NMR relaxation data have been used to characterize the backbone dynamics of the human acidic fibroblast growth factor (hFGF-1) in its free and sucrose octasulfate (SOS)-bound states. (15)N longitudinal (R(1)), transverse (R(2)) relaxation rates and (1H)-(15)N steady-state nuclear Overhauser effects were obtained at 500 and 600 MHz (at 25 degrees C) for all resolved backbone amide groups using (1)H- detected two-dimensional NMR experiments. Relaxation data were fit to the extended model free dynamics for each NH group. The overall correlation time (tau(m)) for the free and SOS-bound forms were estimated to be 10.4 +/- 1.07 and 11.1 +/- 1.35 ns, respectively. Titration experiments with SOS reveals that the ligand binds specifically to the C-terminal domain of the protein in a 1:1 ratio. Binding of SOS to hFGF-1 is found to induce a subtle conformational change in the protein. Significant conformational exchange (R(ex)) is observed for several residues in the free form of the protein. However, in the SOS-bound form only three residues exhibit significant R(ex) values, suggesting that the dynamics on the micro- to millisecond time scale in the free form is coupled to the cis-trans-proline isomerization. hFGF-1 is a rigid molecule with an average generalized parameter (S(2)) value of 0.89 +/- 0.03. Upon binding to SOS, there is a marked decrease in the overall flexibility (S(2) = 0.94 +/- 0.02) of the hFGF-1 molecule. However, the segment comprising residues 103-111 shows increased flexibility in the presence of SOS. Significant correlation is found between residues that show high flexibility and the putative receptor binding sites on the protein.

Binding Sites↗

PubMed2000

Functional expression of NAD(P)H oxidase p47 in lung microvascular endothelial cells.

Vascular endothelial cell superoxide (O(*)(2)) has an important role in intracellular signaling, in interaction with other reactive species such as nitric oxide, and in vascular dysfunction. Little is known regarding the source and function of O(*)(2) from microvascular endothelial cells from specific tissues. Mouse lung microvascular endothelial cells stimulated with phorbol ester (PMA) or NADPH generated significant O(*)(2), which was inhibited by diphenyleneiodonium (DPI) but not by allopurinol, rotenone, indomethacin, or quinacrine. Optimal O(*)(2) generation required cytosolic as well as particulate cell fractions of cells. In parallel studies, PMA induced increased expression of the p47 component of the NAD(P)H oxidase in the particulate fraction, which was inhibited by staurosporine and calphostin. These data demonstrate that NAD(P)H oxidase is an important source of O(*)(2) generation in lung microvascular endothelial cells.

Allopurinol↗

PubMed2000

Rapid staining of proteins on polyacrylamide gels and nitrocellulose membranes using a mixture of fluorescent dyes.

The present work describes a novel, fluorescence-based method for staining proteins on SDS-PAGE and membrane(s). In this method, proteins are stained using a mixed-dye (sulfo-rhodamine B and 1-anilino-8-naphthalene sulfonic acid (NH(4)(+))) solution. The mixed-dye staining protocol can detect proteins up to a concentration of 15 ng. This method is generally applicable to all proteins and is more sensitive than the conventional Coomassie blue method. The staining method is rapid and efficient. Staining-destaining of proteins using the mixed-dye protocol takes less than half an hour. Another interesting feature of the staining protocol described here is the applicability to the staining of proteins on nitrocellulose membranes.

Anilino Naphthalenesulfonates↗

PubMed2000

Identification and characterization of an equilibrium intermediate in the unfolding pathway of an all beta-barrel protein.

The guanidinium hydrochloride (GdnHCl)-induced unfolding of an all beta-sheet protein, the human acidic fibroblast growth factor (hFGF-1), is studied using a variety of biophysical techniques including multidimensional NMR spectroscopy. The unfolding of hFGF-1 in GdnHCl is shown to involve the formation of a stable equilibrium intermediate. Size exclusion chromotagraphy using fast protein liquid chromatography shows that the intermediate accumulates maximally at 0.96 m GdnHCl. 1-Anilinonapthalene 8-sulfonate binding, one-dimensional (1)H NMR, and limited proteolytic digestion experiments suggest that the intermediate has characteristics resembling a molten globule state. Chemical shift perturbation and hydrogen-deuterium exchange monitored by (1)H-(15)N heteronuclear single quantum coherence spectra reveal that profound structural changes in the intermediate state (in 0.96 m GdnHCl) occur in the C-terminal, heparin binding region of the protein molecule. Additionally, results of the stopped flow fluorescence experiments suggest that the kinetic refolding of hFGF-1 proceeds through the accumulation of an intermediate at low concentrations of the denaturant. To our knowledge, the present study is the first report wherein an equilibrium intermediate is characterized in detail in an all beta-barrel protein.

Anilino Naphthalenesulfonates↗

PubMed2000

The nonsense-mediated decay pathway and mutually exclusive expression of alternatively spliced FGFR2IIIb and -IIIc mRNAs.

Exons IIIb and IIIc of the FGFR2 gene are alternatively spliced in a mutually exclusive manner in different cell types. A switch from expression of FGFR2IIIb to FGFR2IIIc accompanies the transition of nonmalignant rat prostate tumor epithelial cells (DTE) to cells comprising malignant AT3 tumors. Here we used transfection of minigenes with and without alterations in reading frame and with and without introns to examine how translation affects observed FGFR2 splice products. We observed that nonsense mutations in other than the last exon led to a dramatic reduction in mRNA that is abrogated by removal of downstream introns in both DTE and AT3 cells. The mRNA, devoid of both IIIb and IIIc exons (C1-C2), is a major splice product from minigenes lacking an intron downstream of the second common exon C2. From these observations, we suggest that repression of exon IIIc and activation of exon IIIb inclusion in DTE cells lead to the generation of both C1-IIIb-C2 and C1-C2 products. However, the C1-C2 product from the native gene is degraded due to a frameshift and a premature termination codon caused by splicing C1 and C2 together. Derepression of exon IIIc and repression of exon IIIb lead to the generation of both C1-IIIc-C2 and C1-C2 products in AT3 cells, but the C1-C2 product is degraded. The C1-IIIb-IIIc-C2 mRNA containing a premature termination codon in exon IIIc was present, but at apparently trace levels in both cell types. The nonsense-mediated mRNA decay pathway and cell type-dependent rates of inclusion of exons IIIb and IIIc result in the mutually exclusive expression of FGFR2IIIb and IIIc.

Alternative Splicing↗