Biomedical subjects

K Vo

Publications and source records attributed to K Vo.

11 recordsLinked to original sources

PubMed1999

Tumor suppression by p27Kip1 and p21Cip1 during chemically induced skin carcinogenesis.

p27Kip1 and p21Cip1 are cyclin dependent kinase inhibitors which can arrest cell proliferation and p27 is a tumor suppressor gene. To address the mechanism of tumor suppression by p27 and to determine if p21 has a tumor suppressor phenotype, we utilized the two stage skin carcinogenesis model on p27 and p21 knockout mice. In this model, initiation, which involves mutation of H-ras induced by DMBA, can be distinguished from promotion induced by TPA, and progression to carcinoma. The mean number of papillomas did not differ between p27-/- and control littermates, but papilloma growth rate was increased and carcinomas developed earlier. Thus, p27 deficiency did not enhance initiation, but resulted in more rapid clonal expansion of initiated cells during promotion. TPA treatment reduced p27 expression in keratinocytes also supporting a role for p27 during promotion. Tumors from p27-/- mice contained mutant H-ras indicating that p27 deficiency did not substitute for mutant ras and further, that during ras driven tumor growth, p27 is partially antagonistic since its removal led to faster growth. The treated p27-/- mice also developed intestinal adenomas. p21-/- mice did not display a significant increase in tumor numbers, growth rate or progression to carcinomas and these tumors also had mutated H-ras. Carcinomas from p21-/- mice were more poorly differentiated with a high frequency of anaplastic spindle cell carcinomas. Thus p21 deficiency mainly resulted in higher grade undifferentiated tumors.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1999

Improving high-resolution MR bold venographic imaging using a T1 reducing contrast agent.

Recently, a new imaging method was proposed by Reichenbach et al (Radiology 1997;204:272-277) to image small cerebral venous vessels specifically. This method, referred to as high-resolution blood oxygen level-dependent venography (HRBV), relies on the susceptibility difference between the veins and the brain parenchyma. The resulting phase difference between the vessels and the brain parenchyma leads to signal losses over and above the usual T2* effect. At 1.5 T, a rather long TE (roughly 40 msec) is required for this cancellation to become significant, leading to enhanced susceptibility artifacts and a long data acquisition time. In this study, we examine the utility of incorporating a clinically available T1 reducing contrast agent, Omniscan (Sanofi Winthrop Pharmaceuticals, NY, NY), with the HRBV imaging approach to reduce susceptibility artifacts and imaging time while maintaining the visibility of cerebral veins. Using a double-dose injection of Omniscan, we were able to reduce TE from 40 to 25 msec. This led to a decrease in TR from 57 to 42 msec, allowing a 26% reduction in data acquisition time while maintaining the visibility of cerebral venous vessels and reducing susceptibility artifacts. J. Magn. Reson. Imaging 1999;10:118-123, 1999.

Artifacts↗

PubMed1999

Resistance to skin tumorigenesis in DNAPK-deficient SCID mice is not due to immunodeficiency but results from hypersensitivity to TPA-induced apoptosis.

Scid/scid mice have a mutation in the gene encoding the catalytic subunit of DNA-dependent protein kinase (DNAPK(cs)) and are defective in end joining of DNA double-strand breaks. As a consequence, they are radiosensitive, lack mature T and B lymphocytes and are predisposed to lymphomagenesis. To determine if this DNA repair defect also increased predisposition to skin tumor formation, we treated the dorsal skin of scid/scid mice with the carcinogen 7,12-dimethylbenz[a]anthracene followed by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). Contrary to expectations, we observed a 5-fold reduction in skin tumor multiplicity in scid/scid mice. We addressed whether this was related to their immunodeficiency by similarly treating Rag1(-/-) and Rag2(-/-) knockout mice which also lack mature T and B lymphocytes. We observed no difference in skin tumor multiplicity for either strain compared with control littermates. This indicates a lack of a significant role for T or B lymphocyte mediated immunity on either papilloma or carcinoma formation. We observed a significant increase in apoptotic and necrotic cell death in follicular and interfollicular epithelial cells of scid/scid mice following TPA treatment. This hypersensitivity of SCID (severe combined immunodeficient) cells to TPA indicates that the resistance to skin tumor formation in scid/scid mice is due to loss of initiated cells through TPA-induced cell killing.

Animals↗

PubMed1998

Exploring structure-activity relationships around the phosphomannose isomerase inhibitor AF14049 via combinatorial synthesis.

Phosphomannose Isomerase (PMI) has been shown by genetic methods to be an essential enzyme in fungal cell wall biosynthesis. The PMI inhibitor AF14049 was discovered as an unanticipated side product from high-throughput library screening against the enzyme from C, albicans. Solid-phase synthetic methods were developed and a series of libraries and discrete analogs synthesized to explore SAR around AF14049.

Amides↗

PubMed1998

DNA double-strand breaks, p53, and apoptosis during lymphomagenesis in scid/scid mice.

The tumor-suppressing phenotype of p53 is thought to be due to its accumulation in response to DNA damage and resultant cell cycle arrest or apoptosis. scid/scid mice are defective in DNA double-strand break repair due to a mutation in DNA-dependent protein kinase (DNAPK). Treatment of scid/scid mice with gamma radiation or N-ethyl-N-nitrosourea resulted in approximately 86% incidence of T-cell lymphomas, compared with <6% in wild-type mice. The incidence of other tumor types was not increased in scid/scid mice, suggesting that the types of DNA double-strand break that are unrepaired in these mice are not strongly carcinogenic. To determine whether mutations in DNAPK and p53 interact, we examined mice deficient in both genes. Both scid/scid p53-/- and scid/scid p53+/- mice spontaneously developed lymphomas at shorter latency than did mice with either defect alone. Loss of the wild-type p53 allele was observed in 100% of tumors from scid/scid p53 +/- mice, indicating strong selection against p53. In contrast, p53 was not inactivated in lymphomas from scid/scid p53+/+ mice. Exposure of these tumor-bearing mice to gamma radiation resulted in p53 protein accumulation and high levels of apoptosis in all tumors that were not observed in tumors from scid/scid p53+/- mice. Thus, there was a bifurcation of molecular pathways to tumorigenesis. When p53 was heterozygous in the germ line, loss of the wild-type allele occurred, and the tumors became apoptosis resistant. When p53 was wild type in the germ line, p53 was not inactivated, and the tumors remained highly apoptosis sensitive.

Animals↗

PubMed1997

Levels of expression of P-selectin, E-selectin, and intercellular adhesion molecule-1 in coronary atherectomy specimens from patients with stable and unstable angina pectoris.

Unstable angina occurs when atherosclerotic plaque ruptures. Recent evidence suggests a role for inflammation in this process. Leukocyte-endothelial cell interactions are important in inflammation and are regulated by cell adhesion molecules. This study was designed to examine the vascular expression of cell adhesion molecules and cytokines in patients with unstable angina. Directional coronary atherectomy was performed in patients with unstable and stable angina. Expression of the cell adhesion molecules P-selectin, E-selectin, and intercellular adhesion molecule-1 in the tissue obtained was examined using immunohistochemistry. In addition, expression of the cytokines tumor necrosis factor-alpha and interleukin-1beta, which participate in the regulation of cell adhesion molecule expression, was also examined. Atherectomy specimens had significantly greater P-selectin expression from patients with unstable angina than from patients with stable angina. P-selectin expression was observed primarily on endothelial cells. There were no differences in any of the other factors between patients with unstable and stable angina. In addition, other clinical and angiographic variables were not associated with differential expression of any of the cell adhesion molecules or cytokines. These results indicate a possible role for P-selectin in the process of unstable angina.

Adult↗

PubMed1996

Conformational studies on analogs of recombinant parathyroid hormone and their interactions with phospholipids.

Through the use of oligonucleotide-directed mutagenesis we have generated variants of a recombinant human parathyroid (PTH) hormone-(1-34)-homoserine (RPTH) in which a positively charged residue (Arg or Lys), a negatively charged residue (Glu), or a neutral residue (Gly) has been substituted at every position throughout the peptide. These 106 PTH analogs have been tested for their ability to stimulate cAMP production in the rat osteosarcoma cell line, UMR106. Analysis of these peptides led to the construction of several analogs containing multiple substitutions at sites of potential structural importance. Several of these analogs were shown to have 3-5-fold enhanced activity and receptor affinity. Circular dichroism (CD) and lipid binding studies were then performed on these analogs. Circular dichroism demonstrates enhanced helical content in the presence of lipid vesicles, particularly anionic lipid. The [Arg15,19,22,Lys29]RPTH (+6RPTH) analog requires higher concentrations of trifluoroethanol to attain enhanced helicity. The intrinsic tryptophan fluorescence of the peptides are blue shifted more in the presence of the anionic lipid dimyristoyl phosphatidylglycerol (DMPG) than with the zwitterionic lipid dimyristoyl phosphatidylcholine (DMPC). Effects of the peptides on the phase transition behavior of DMPC shows that +6RPTH has less effect on the lipid than does RPTH. This difference in lipid interaction is also exhibited with isothermal titration calorimetry, in which RPTH reacts exothermally with DMPG, while +6RPTH shows little or no heat change. The pH dependence of binding of the hydrophobic probe 1,1'-bis(4-anilino)-naphthalene-5,5'-trisulfonic acid, also shows a difference in exposure of hydrophobic sites between RPTH and +6RPTH. The +6RPTH has about a 5-fold greater affinity for receptor binding. We suggest that this enhanced activity is a consequence of the altered lipid interaction of +6RPTH, combined with increased conformational flexibility, particularly in the carboxyl-terminal region of the molecule.

Amino Acid Sequence↗

PubMed1996

Bryostatin 1 acts synergistically with interleukin-1 alpha to induce secretion of G-CSF and other cytokines from marrow stromal cells.

The protein kinase C (PKC) activator bryostatin 1 (bryo) has substantial antileukemic and hematopoietic actions. Bryo promotes the in vitro growth of normal hematopoietic progenitors by inducing the release of growth factors from accessory cells. We have examined the effects of bryo on the expression and release of certain myeloid growth factors from fibroblastlike marrow stromal cells (MSC). Substantial release of granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF). or interleukin-6 (IL-6) following bryo treatment was seen only in MSC cultures contaminated with macrophages. Bryo alone was ineffective in inducing release of the cytokines from MSC cultures containing only fibroblastlike stromal cells. When MSC were treated with IL-1alpha, substantial quantities of the cytokines (G-CSF, GM-CSF,IL-6) were released. Bryo acted synergistically with IL-1 alpha to significantly increase cytokine release to- to nine-fold compared to IL-1alpha alone (p < 0.016). Neither Il-1alpha nor bryo, alone or in combination, induced release of stem cell factor (scf) from MSC. The synergistic interaction between IL-1alpha and bryo was dose- and schedule-dependent, requiring simultaneous application of IL-1alpha and bryo for optimum effect. Bryo alone induced no G-CSF mRNA accumulation but increased the level seen with IL-1alpha treatment by 50%. The synergistic interaction of bryo and IL-1alpha required PKC, since it was antagonized by agents which depleted or inhibited PKC but not by a protein kinase A antagonist. The increase in G-CSF mRNA was associated with a marked increase in mRNA stability. Bryostatin may promote the release of cytokines from several accessory cell populations, including MSC, to accomplish its in vivo hematopoietic effects.

Bone Marrow↗

PubMed1995

Effect of intraamniotic dexamethasone administration on intestinal absorption in a rabbit gastroschisis model.

Infants with gastroschisis experience delayed intestinal motility and absorption for several weeks after birth. This intestinal dysfunction is believed to occur primarily in the third trimester and to be largely caused by the prolonged exposure of the intestine to amniotic fluid. Previous studies have shown that prenatal steroid administration will enhance mucosal disaccharidase activity and nutrient uptake. The present study evaluates the effects of dexamethasone on intestinal function in a rabbit fetal gastroschisis model. Thirty-four fetuses from 10 New Zealand white rabbits were divided into three groups: (1) gastroschisis group (GSC, n = 10), gastroschisis was created on gestational day (GD) 24 (term = 31 to 33 days); (2) dexamethasone group (GSD, n = 10), after the creation of gastroschisis, a small osmotic pump was placed into the rabbit doe for dexamethasone infusion into the fetal amniotic cavity for 7 days (0.2 microgram/g/d); (3) normal group (NF, n = 10), unoperated littermates from the GSC group. There were no maternal deaths, and fetal survival rate was 85%. The fetal small intestinal disaccharidase enzyme, lactase (UE/g protein), was markedly decreased in GSC fetuses. It was increased 70% in the GSD group but lower than in normal fetuses (GSC = 10.0 +/- 1.6; GSD = 17.3 +/- 1.6 [GSD versus GSC, P < .05]; NF = 48.0 +/- 6.7). Maltase activity in the GSD group was significantly increased (GSC = 7.2 +/- 1.1; GSD = 13.9 +/- 1.8 [GSD versus GSC, P < .05]; NF = 12.2 +/- 1.3).(ABSTRACT TRUNCATED AT 250 WORDS)

Abdominal Muscles↗

PubMed1992

Laser-triggered repetitive fluorescein angiography.

Liposome-encapsulated fluorescent dye has been altered to allow full fundus angiography after a single laser shot. By exposing the retinal arteries to laser energy where they emerge at the optic disc nerve head, dye release is elicited simultaneously in all four quadrants of the retina, without choroidal fluorescence, allowing visualization of the retinal microcirculation. Because the quantity of dye release is limited, recirculation does not increase background fluorescence. The procedure can be repeated many times without delay with consistent results. Increasing the laser spot size to 1.5 mm allows consistent dye release at energy densities from 0.5 J/cm2 to 3.4 J/cm2. This refinement will allow direct comparison in primates of this technique and conventional fluorescein angiography. The laser energy delivered to the retina is below suggested levels that may be tolerated by the optic nerve.

Animals↗

PubMedDate not supplied

Syntheses of 2-alkylamino- and 2-dialkylamino-4,6-diarylpyridines and 2,4,6-trisubstituted pyrimidines using solid-phase-bound chalcones.

Several substituted 2- and 4-hydroxyacetophenones are linked to Wang resin via a modified Mitsunobu protocol. These resin-bound acetophenones are condensed with aromatic aldehydes, and the resulting chalcones 5 are used for the synthesis of 2-dialkylamino- (9a-d) and 2-alkylamino-4,6-diarylpyridines (11a-f), and 2-alkyl-4,6-diaryl- (14a) and 2,4,6-triarylpyrimidines (14b,c) in a manner suitable for combinatorial applications.

Acetophenones↗