Search PubMed⌕ Search

Biomedical subjects

K Yu

Publications and source records attributed to K Yu.

At least 91 records · Page 5Linked to original sources
PubMed1998

A simple and sensitive ribonucleotide reductase assay.

Ribonucleotide reductase (RR) is a key regulatory enzyme in the DNA synthesis pathway and is the target of the cancer chemotherapeutic agent hydroxyurea. The study of RR is significantly hindered by the tedious and labor-intensive nature of enzymatic assay. In this report, we present a novel RR assay in which detection of the deoxyribonucleotides produced by RR occurs via coupling to the DNA polymerase reaction, and is enhanced by using RNase to degrade endogenous RNA. Cell extracts from various cell lines were treated with RNase and then reacted with ATP and radioactive ribonucleotide diphosphate as the substrate. Incorporation of the radioactive substrate [14C]CDP into DNA was linear over 30 min and was linear with the amount of extract, which provided RR activity. The reaction was inhibited by hydroxyurea and required Mg2+ and ATP, suggesting that the assay is specific to RR activity. While RR activities determined by our method and by a conventional method were comparable, this novel method proved to be simpler, faster, more sensitive and less expensive. In addition, assay of the RR activity for multiple samples can easily be performed simultaneously. It is superior to other RR assays in all aspects.

Calibration↗
PubMed1998

Quantification of 5-(hydroxymethyl)uracil in DNA by gas chromatography/mass spectrometry: problems and solutions.

Oxidation of the thymine methyl group results in the formation of 5-(hydroxymethyl)uracil (HmU). HmU is a recognized endogenous DNA damage product, and HmU levels in DNA are increased by oxidant stress. Previous studies have reported substantially conflicting values for HmU levels in DNA. In studies utilizing postlabeling methods, HmU levels have been reported to be as high as or higher than the levels of some of the more commonly described DNA oxidation damage products such as 8-oxoguanine. In some studies utilizing GC/MS methods, however, HmU has been undetectable. In acid solution, the hydroxymethyl group of HmU can undergo condensation reactions with carboxylic acids, alcohols, and amines. While HmU can be accurately measured by GC/MS, the first step in the preparation of samples for GC/MS analysis is acid hydrolysis of the DNA. Such hydrolysis would be expected to result in substantial derivatization of HmU. We have utilized chemically synthesized oligonucleotides containing a known amount of HmU as well as an isotopically enriched standard to investigate the chemical modification of HmU during the acid hydrolysis of DNA. We conclude that HmU levels reported by GC/MS following acid hydrolysis may be up to an order of magnitude lower than the actual levels. Further, we propose modifications to the standard hydrolysis protocols which maximize recovery of HmU prior to silylation and analysis by GC/MS.

DNA↗
PubMed1998

Guar gum-based sustained release diltiazem.

PURPOSE: This study was performed to examine the use of guar gum to sustain the release of diltiazem under in vitro and in vivo conditions. METHODS: Guar gum tablet formulations were prepared and evaluated under a variety of in vitro dissolution conditions. The formulations, along with Dilacor XR, were administered to a group eight fasted, healthy volunteers in a four period crossover study. RESULTS: Varying the lot of guar gum as well as using guar from different suppliers had little effect on diltiazem dissolution. Also, dissolution of diltiazem from guar gum tablets was essentially independent of stir speed under normal conditions (USP Apparatus II) The stability of guar-based formulations under stressed conditions (40 degrees C/75% relative humidity for 3 months) was also established. All four formulations gave similar plasma concentrations over time in the healthy volunteers pharmacokinetic study. CONCLUSIONS: Guar gum-based matrix tablets represent a simple and economical alternative to existing diltiazem sustained release dosage forms.

Antihypertensive Agents↗
PubMed1998

Optimization of sustained-release diltiazem formulations in man by use of an in-vitro/in-vivo correlation.

In-vitro/in-vivo correlations (IVIVC) are useful for predicting in-vivo results from in-vitro data. An IVIVC has been used to optimize a hydrocolloidal-based matrix tablet designed to be bioequivalent to an existing once-daily diltiazem HC1 product (Dilacor XR 240mg; Rhone-Poulenc Rorer). Data from a preliminary formulation dosed to fasted and fed subjects were used to establish the IVIVC. The correlation was then used during reformulation of the dosage forms to predict changes in the maximum plasma concentration (Cmax) and the area under the plasma-concentration-time curve (AUC) for fasted and fed subjects using in-vitro dissolution data. The IVIVC adequately predicted plasma profiles of two optimized formulations in studies with fasted and fed subjects.

Cardiovascular Agents↗
PubMed1998

Binocular rivalry and motion perception.

In a series of experiments psychophysical techniques were used to study the relation between binocular rivalry and motion perception. An initial series of experiments confirmed that motion enhances the predominance of an eye during rivalry, although the direction of motion does not matter. The presence of an annulus of motion immediately surrounding one eye's rival target greatly enhances dominance of that target, but the influence of the annulus progressively decreases as the separation between disk and annulus increased. Opponent directions of motion in disk and annulus yield greater dominance than when dots in the disk and annulus moved in identical directions. In a second experiment that two eyes were adapted to orthogonal directions of motion, generating strong, distinctively different monocular motion aftereffects (MAEs). Even though the two eyes view physically identical random-motion displays following differential adaptation, binocular rivalry of the discrepant MAEs can occur. Finally, using a stimulus replacement technique to measure detectability of translational and rotational motion, it was found that both types of motion were readily detected during periods of dominance but went undetected during periods of suppression. Taken together, these results bear on the process responsible for rivalry and its neural locus relative to the analysis of different types of motion.

Adaptation, Ocular↗
PubMed1998

[PCR in detecting the correlation between infection of HBV and cholelithiasis].

OBJECTIVE: To study the correlation between cholelithiasis and the infection of HBV. METHOD: 32 formalin-fixed and paraffin-embedded gallbladder samples of cholelithiasis patients and 20 gallbladder samples of non-cholelithiasis patients were investigated using the polymerase chain reaction-Ethidium bromide (PCR-EB) assay. The 52 patients were positive to HBV serologic markers. RESULT: The results showed that HBV-DNA was found in 13 gallbladder samples of 32 cholelithiasis patients (40.63%), significantly higher than that in 3 gallbladder samples of 20 non-cholelithiasis patients (15%). CONCLUSION: The infection of HBV and the formation of cholelithiasis are correlated.

Adult↗
PubMed1998

[The effects of graded spinal cord injuries on transcranial electric stimulation motor evoked potentials in the rat].

OBJECTIVE: To study the effects of graded spinal cord injury (SCI) on the motor evoked potentials (MEP) characteristics and the prognostic value of MEP for the motor function. METHOD: Modified Allen's method was used by weight drop force of 30 gcf, 50 gcf, 80 gcf and 100 gcf on the T(8 - 9) spinal cord of 40 SD rats in order to make SCI models. MEP was recorded continuously at L(1 - 2) epidurally and bilateral gastrocnemius muscles before and after the spinal cord lesion was produced (followed up for 1 month). The inclined plane and Tarlov technique were used to assess clinical neurological function. RESULT: The amplitude of rat's MEP changed significantly with graded SCI, the more sever the lesion, the lower the potentials. mMEP was more sensitive than scMEP, though the abolishment of mMEP soon after SCI didn't indicate that the animals could not regain ambulation. Changes in amplitude of scMEP recorded early after SCI were collaborate significantly with inclined plane (gamma = 0.9665, P < 0.01) and Tarlov scale (gamma = 0.8893, P < 0.01) assessed 1 month later, and can be used as a chronic measure parameter of motor function prognosis. scMEP still existed 1 month after SCI in 3 of 11 rats (27.3%) without any voluntary movement in bilateral hindlimbs, suggesting that some parts of conductive function still existed in the spinal cord. So it should be called "discomplete SCI". CONCLUSIONS: scMEP can be used as a reliable parameter for motor function prognosis, because it reflects objectively and sensitively the severity of central motor neurol fiber injury.

Animals↗
PubMed1998

[Clinical significance of early diagnosis of cervical spondylotic myelopathy].

OBJECTIVE: To probe into the possibility of early diagnosis of cervical spondylotic myelopathy (CSM) prospectively and to screen the premorbid signs of CSM clinically, radiologically and electro-physiologically. METHOD: Twenty-nine items related to the occurring of CSM were chosen as common characteristics of CSM and considered as the criteria of prospective study. 81 patients who met the criteria were studied. All patients were followed up and observed for 2 - 6.5 years (mean 3.7 years). RESULT: Twenty-nine patients showed CSM during investigation. Thirteen items of the criteria were related to the occurring of CSM. The significant items include upper limb pain and abnormal sensation limb numbness, positive dynamic Hoffmann's sign, cervical canal stenosis, lower cervical instability, cervical intervertebral disc herniation, and delay of central motor conduct time. CONCLUSION: CSM can be early diagnosed. The patients who meet the established criteria should be followed up and observed closely. Early operation results in good effect.

Adult↗
PubMed1998

[A randomized control clinical trial of glaucoma filtering surgery with homoharringtonine].

OBJECTIVE: To study the antiproliferative effects of homoharringtonine (Hh) on glaucoma filtering surgery. METHODS: In a randomized control clinical trial, 78 patients (88 eyes) with refractory glaucoma underwent trabeculectomy with and without Hh. In the Hh-treated eyes (n = 46), the therapeutic dose of Hh was: intraoperative application of Hh 0.4 mg and postoperative subconjunctival injections of Hh 0.62 +/- 0.20 mg (ranged 0.53 - 0.75 mg). In the control eyes (n = 42), Hh was not used. The follow-up period was 18 to 48 months, and the data were analyzed by using the life-table method of Kaplan-Meier. RESULTS: The cumulative success probability in Hh group was 84.5% and that in control group was 50.9%, the difference being significant (P < 0.05). The cumulative percentage of functioning bleb in Hh group was 84.2% and that in control group was 52.9% (P < 0.05). The rates of corneal erosion were 23.9% and 7.1%, and the rates of conjunctival wound leak were 6.5% and 2.4% in Hh and control group respectively. There was no significant change in corneal endothelial density following the use of Hh (P > 0.05). CONCLUSION: The study indicates that Hh is a safe and effective antiproliferative agent for the use in glaucoma filtering surgery, it not only can increase the success probability considerably, but also maintain at least the postoperative IOP at relatively low normal level for 3 years.

Adult↗
PubMed1998

[Study on EEG signals data compression and spikes recognition with wavelet neural network].

A novel method of EEG signals compression representation and epileptiform spikes recognition based on wavelet neural network and its algorithm is presented in this paper. Wavelet network not only can compress data effectively but also can recover original signal. In addition the characteristics of the spikes and the spike-slow rhythm are detected automatically from the time-frequency isoline of EEG signal. This method can be generalized in the field of the electrophysiological signal processing and time-frequency analyzing.

Electroencephalography↗
PubMed1998

[Study on the method of adsorbing albumin for enwrapping human hard tissue substitute biomaterials].

The aim of this study was to cover up the surface of human hard tissue substitute biomaterials with albumin. The cidex cross-link method was adopted to adsorb albumin so as to form a membrane for wrapping hydroxyapatite(HA), bio-glass ceramics(BGC), and hydroxyl poly-calcium sodium phosphate (HP). The results showed that this membrane of protein could enwrap the biomaterials so firmly that urea solution could not wash it off.

Adsorption↗
PubMed1998

Melanoma during pregnancy: a case report and review of the literature.

Approximately 40,300 patients are diagnosed with cutaneous melanoma annually in the United States with a disease-related mortality rate of approximately 7,300 per year. Although treatment strategies have been defined for cutaneous melanoma, therapeutic approaches for this hormonally sensitive tumor are difficult in the gravid patient. Epidemiologic studies suggest that there continues to be an increasing incidence of melanoma with an associated decrease in age at presentation for patients in the United States. These trends suggest that approximately 35% of women will be diagnosed with melanoma during their childbearing years. Hence, the perplexing challenge of melanoma management during pregnancy will perhaps increase over the next decade. This case report documents the occurrence of cutaneous melanoma in women during pregnancy and highlights key issues in the natural history of this disease. Detailed review of the current literature related to melanoma during pregnancy will provide insight into optimal therapeutic approaches.

Adult↗
PubMed1997

Identification of several human homologs of hamster DNA damage-inducible transcripts. Cloning and characterization of a novel UV-inducible cDNA that codes for a putative RNA-binding protein.

Low ratio hybridization subtraction technique was previously used in this laboratory to enrich and isolate a number of low abundance UV-inducible hamster transcripts (Fornace, A. J., Jr., Alamo, I. J., and Hollander, M. C. (1988) Proc. Natl. Acad. Sci. U. S. A. 85, 8800-8804) that led to the identification and cloning of five important hamster and human GADD genes (Fornace, A. J., Jr., Nebert, D. W., Hollander, M. C., Luethy, J. D., Papathanasiou, M., Fargnoli, J., and Holbrook, N. J. (1989) Mol. Cell. Biol. 9, 4196-4203). In this study we have characterized the remaining DNA damage-inducible (DDI) transcripts. Of the 24 DDI clones, 3 clones (A13, A20, and A113) representing different regions of the same hamster cDNA exhibited near perfect homology to human p21(WAF1/CIP1) cDNA. The DDI clones A26, A88, and A99 displayed very high sequence homologies with the human proliferating nuclear antigen, rat translation initiation factor-5 (eIF-5), and human thrombomodulin, respectively, whereas clones A29 and A121 matched with express sequence tagged sequences of unknown identity. The DDI clones A18, 106, and A107 were different isolates of the same hamster cDNA (hereafter referred to as A18) and displayed high sequence homology with the members in the heterogeneous ribonucleoprotein (hnRNP) family. Using the hamster A18 partial-length cDNA as a probe, we screened human fibroblast cDNA library and isolated the corresponding full-length human cDNA. The deduced amino acid sequence revealed that the putative protein contains all the canonical features of a novel glycine-rich hnRNP. The A18 mRNA levels were specifically increased in response to DNA damage induced by UV irradiation or UV mimetic agents. Thus the putative A18 hnRNP is the first hnRNP whose mRNA is specifically regulated in response to UV-induced DNA damage; accordingly, it may play some role in repair of UV-type DNA damage.

Amino Acid Sequence↗
PubMed1997

The regulators of G protein signaling (RGS) domains of RGS4, RGS10, and GAIP retain GTPase activating protein activity in vitro.

Regulators of G protein signaling (RGS) proteins accelerate GTP hydrolysis by Gi but not by Gs class alpha-subunits. All RGS proteins share a conserved 120-amino acid sequence termed the RGS domain. We have demonstrated that the RGS domains of RGS4, RGS10, and GAIP retain GTPase accelerating activity with the Gi class substrates Gialpha1, Goalpha, and Gzalpha in vitro. No regulatory activity of the RGS domains was detected for Gsalpha. Short deletions within the RGS domain of RGS4 destroyed GTPase activating protein activity and Gialpha1 substrate binding. Comparable protein-protein interactions between Gialpha1-GDP-AlF4- and the RGS domain or full-length RGS4 were detected using surface plasmon resonance.

GTP Phosphohydrolases↗
PubMed1997

Extracellular ATP activates calcium signaling, ion, and fluid transport in retinal pigment epithelium.

The presence of receptors for ATP has not been established in any native preparation of retinal neurons or glia. In the present study, we used conventional electrophysiological and [Ca2+]in fluorescence imaging techniques to investigate the effects of ATP added to Ringer's solution perfusing the retinal-facing (apical) membrane of freshly isolated monolayers of bovine retinal pigment epithelium (RPE). ATP (or UTP) produced large, biphasic voltage and resistance changes with a Kd of approximately 5 microM for ATP and approximately 1 microM for UTP. Electrical and pharmacological evidence indicates that the first and second phases of the response are attributable to an increase in basolateral membrane Cl conductance and a decrease in apical membrane K conductance, respectively. The ATP-induced responses were not affected by adenosine, but were reduced by the P2-purinoceptor blocker suramin. ATP also produced a large, transient increase in [Ca2+]in that was blocked by cyclopiazonic acid, an inhibitor of endoplasmic reticulum Ca2+-ATPases. The calcium buffer BAPTA attenuated the voltage effects of ATP. We also found that apical DIDS significantly inhibited the ATP-evoked [Ca2+]in and electrical responses, suggesting that DIDS blocked the purinoceptor. Measurements of fluid movement across the RPE using the capacitance probe technique demonstrated a significant increase in fluid absorption by apical UTP. These data indicate the presence of metabotropic P2Y/P2U-purinoceptors at the RPE apical membrane and implicate extracellular ATP in vivo as a retinal signaling molecule that could help regulate the hydration and chemical composition of the subretinal space.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1997

Ras-dependent apoptosis correlates with persistent activation of stress-activated protein kinases and induction of isoform(s) of Bcl-x.

Ras proteins are signal transducers for many cellular responses. However, it is not well established whether Ras-signaling also contributes to apoptosis. We have constructed H-RasR12-transformed Rat1 fibroblasts using tetracycline operator/repressor (TetO/TetR)-based conditional vectors. Rat1/TetO-RasR12 (Rat1-Ras) cells produced high levels of H-RasR12 protein and exhibited oncogenic transformation. Treatment of Rat1-Ras cells with 0.1% serum triggered massive apoptosis. Rat1-Ras cells expressed increased basal activities of extracellular response kinase (ERK) and p46/p54 stress-activated protein kinase/c-Jun NH2-terminal kinase (SAPK/JNK). Interestingly, Ras-dependent apoptosis correlated with further persistent activation of both p46 and p54 SAPK/JNK and concurrent inhibition of ERK. Differential modulation of SAPK/JNK and ERK was not detected in tetracycline-treated cells that did not commit apoptosis. Furthermore, two Bcl-x related proteins of 15 kDa and 18 kDa were highly induced in apoptotic Rat1-Ras cells. Our results establish a direct role for Ras in apoptosis, and suggest a functional relationship between H-Ras, SAPK/JNK, ERK and Bcl-x in regulating apoptosis.

Journal Article↗