Biomedical subjects

Y Huang

Publications and source records attributed to Y Huang.

At least 721 records · Page 40Linked to original sources

PubMed1997

Pulsed brachytherapy as a substitute for continuous low dose rate: an in vitro study with human carcinoma cells.

PURPOSE: Pulsed dose rate (PDR) brachytherapy as a substitute for continuous low dose rate (CLDR) has the potential to be a useful option in brachytherapy. However, the frequency and duration of pulses that will produce results practically equivalent to CLDR is still an open and important question. This study was designed to compare the survival of human tumor cells, cultured in vitro, and exposed to continuous or pulsed irradiation where the pulse frequency was varied. METHODS AND MATERIALS: Three different human carcinoma cells, derived from cervical and breast cancers, were exposed to CLDR gamma rays, or to pulsed irradiations with the same overall dose rate. Pulsed regimens used were 3.8 min every hour, 7.6 min every 2 h, 11.4 min every 3 h, 15.2 min every 4 h, 22.8 min every 6 h, and 45.6 min every 12 h. For each comparison between CLDR and PDR, the overall dose and the overall time were the same. Experimental design was such that significant differences in biological effectiveness, if present, would be detected. RESULTS: For the cell lines investigated, hourly pulses resulted in cell survival indistinguishable from CLDR. However, as the pulse interval was increased, cell survival progressively decreased compared with CLDR, and the pulsed regimes were no longer equivalent to continuous low dose rate. CONCLUSIONS: This study provides some evidence to support the suggestion that a 10-min pulse, repeated every 1 to 2 h, would be functionally equivalent to a continuous low dose rate irradiation, at least in terms of early responding endpoints. Longer intervals between pulses might result in loss of equivalence in some cases.

Brachytherapy↗

PubMed1997

Changes of phosphatidylcholine-specific phospholipase C in hepatocarcinogenesis and in the proliferation and differentiation of rat liver cancer cells.

The biological significance of phosphatidylcholine-specific phospholipase C (PC-PLC) in hepatocarcinogenesis and the proliferation and differentiation of rat liver cancer cells was investigated. The Ca2+-dependent activities of PC-PLC gradually increased during N-nitrosodiethylamine (DEN)-induced hepatocarcinogenesis and peaked at weeks 18-20 when the tumour formed. There was a close relationship between Ca2+-dependent PC-PLC activities and cellular DNA content, membranous gamma-glutamyltranspeptidase (gamma-GT), and tyrosine protein kinase. In contrast, Ca2+-independent PC-PLC activities decreased during hepatocarcinogenesis. Similarly, when CBRH-7919 rat liver cancer cells were treated with phorbol 12-myristate 13-acetate, a proliferation stimulator of the cells, gamma-GT and Ca2+-dependent activities of PC-PLC and the expression of alpha-fetoprotein increased significantly. However, when these cells were induced by retinoic acid to differentiate, Ca2+-dependent PC-PLC and gamma-GT activities decreased significantly, together with alpha-fetoprotein expression. There was a close relationship between Ca2+-dependent PC-PLC and gamma-GT activities during differentiation as there was during proliferation. We suppose that Ca2+-dependent PC-PLC is involved in rat hepatocarcinogenesis induced by DEN and that it plays an important role in the phorbol ester-induced proliferation or retinoic acid-induced differentiation of liver cancer cells.

Animals↗

PubMed1997

Isozymes of nuclear protein tyrosine kinase during chemical induced hepatocarcinogenesis in rats.

The activity changes of isozymes of nuclear protein tyrosine kinase (nPTK) during chemically induced hepatocarcinogenesis in rats was studied. Two isozymes were isolated from rat liver by using ion exchange chromatography. These two isozymes were designated as nPTK-I and nPTK-II, and were found to be minor and major components of total nPTK respectively. These proved to be two different enzymes due to their different characteristics, such as molecular weights, electrical charges and kinetics. The specific activity nPTK-I and its percentages in total nPTK significantly increased in preneoplastic stage (week 10) and slightly elevated further in neoplastic stage (week 18). The specific activity of the nPTK-II moderately increased at week 10, but compared to its value at week 10, it decrease at week 18, resulted in gradual decrease of its percentage in total nPTK. These results indicate that rat hepatic nPTK-I and nTPK-II may be related to neoplastic and preneoplastic stages of rat liver respectively.

Animals↗

PubMed1997

Effect of amino acid cardioplegia on myocardial metabolism and function of ischemic canine heart.

To evaluate the effect of amino acid cardioplegia on myocardial metabolism and function of ischemic canine heart, canine cardiopulmonary bypass (CPB) model was established and the dog heart was subjected to a 120 min ischemic arrest. Animals were divided into 3 groups, group 1: warm blood cardioplegia induction and terminal perfusion plus 4 C ST. Thomas hospital solution (STS) during ischemia; group 2: warm blood cardioplegia enriched with amino acid (L-asparte and L-glutamate 13 mmol/L each) and STS without amino acid (A. G.) and group 3: both warm blood cardioplegic solution and STS enriched with A. G. . The result demonstrated that the cardiac function of animals in group 2 and 3 had a significantly better recovery after ischemic-re-perfusion. By the end of ischemia the content of myocardial ATP in group 3 was distinctly higher than that in group 1 (P < 0.05), with the release of cardiac enzyme being the least. Myocardial ultra-structure almost remained intact before and after ischemia. Our experiment suggests that the cardioplegia arrest with warm blood and cold crystalloid solution enriched with amino acids could diminish the ischemia-re-perfusion injuries of the heart and enhance the effect of myocardial protection.

Amino Acids↗

PubMed1997

Introducing dielectrophoresis as a new force field for field-flow fractionation.

We present the principle of cell characterization and separation by dielectrophoretic field-flow fractionation and show preliminary experimental results. The operational device takes the form of a thin chamber in which the bottom wall supports an array of microelectrodes. By applying appropriate AC voltage signals to these electrodes, dielectrophoretic forces are generated to levitate cells suspended in the chamber and to affect their equilibrium heights. A laminar flow profile is established in the chamber so that fluid flows faster with increasing distance from the chamber walls. A cell carried in the flow stream will attain an equilibrium height, and a corresponding velocity, based on the balance of dielectrophoretic, gravitational, and hydrodynamic lift forces it experiences. We describe a theoretical model for this system and show that the cell velocity is a function of the mean fluid velocity, the voltage and frequency of the signals applied to the electrodes, and, most significantly, the cell dielectric properties. The validity of the model is demonstrated with human leukemia (HL-60) cells subjected to a parallel electrode array, and application of the device to separating HL-60 cells from peripheral blood mononuclear cells is shown.

Cell Separation↗

PubMed1997

Dielectrophoretic manipulation of cells with spiral electrodes.

Electrokinetic responses of human breast cancer MDA-MB-231 cells were studied in suspensions of conductivities 18, 56, and 160 mS/m on a microelectrode array consisting of four parallel spiral electrode elements energized with phase-quadrature signals of frequencies between 100 Hz and 100 MHz. At low frequencies cells were levitated and transported toward or away from the center of the spiral array, whereas at high frequencies cells were trapped at electrode edges. The frequencies of transition between these characteristic cell behaviors increased with increasing suspension conductivity. Levitation heights and radial velocities were determined simultaneously for individual cells as a function of the applied field magnitude and frequency. Results were compared with theoretical predictions from generalized dielectrophoresis theory applied in conjunction with cell dielectric parameters and simulated electric field distributions corrected for electrode polarization effects. It was shown that the conventional and traveling-wave dielectrophoretic force components dominated cell levitation and radial motion, respectively. Both theoretical predictions and experimental data showed that the cell radial velocity was very sensitive to the field frequency when the in-phase component of the field-induced polarization was close to zero. Applications of spiral electrode arrays, including the isolation of cells of clinical relevance, are discussed.

Breast Neoplasms↗

PubMed1997

Massive hydronephrosis associated with traumatic rupture.

Twelve cases of traumatic rupture of a massive hydronephrosis are reported. The key points in the diagnosis are: injury around the loin, peritonitis, a fall of pH in the abdominal paracentesis fluid, a rise of blood urea nitrogen (BUN) and structural abnormality of the affected renal pelvis seen on ultrasonography. The treatment differed according to the disease causing the hydronephrosis before the injury. All patients were treated surgically with a satisfactory overall cure rate. Follow-up of 12 years has not revealed any significant sequelae.

Adult↗

PubMed1997

Influence of endothelium in contraction induced by phorbol ester in isolated rat aortic rings.

The present study aimed to investigate the possible role of endothelium in contractile response to phorbol 12,13-diacetate (PDA) by measuring the contractile force in rat isolated aortic rings. PDA at low concentrations induced small and sustained tension in arteries with intact endothelium. N(G)-Nitro-L-arginine (100 microM), a nitric oxide synthase inhibitor and methylene blue (10 microM), an O2-generator induced a large increase in tension in the presence of PDA. The magnitude of contractions in response to N(G)-Nitro-L-arginine was related to concentrations of PDA. Staurosporine (10 nM), an inhibitor of protein kinase C completely inhibited contractile response to PDA as well as potentiating effects of N(G)-Nitro-L-arginine and methylene blue. Removal of the endothelium abolished contractile responses to both N(G)-Nitro-L-arginine and methylene blue in the presence of PDA. Removal of extracellular Ca2+ suppressed contractile responses to both PDA and N(G)-Nitro-L-arginine. On the other hand, N(G)-Nitro-L-arginine (100 microM) did not induce contractions of the rat aorta pre-treated with 4-alpha-phorbol 12-myristate 13-acetate, an inactive form of phorbol ester. Acetylcholine concentration-dependently induced reduction of tension induced by PDA (0.3 microM) in rat aorta. N(G)-Nitro-L-arginine or removal of endothelium prevented the effect of the acetylcholine-induced relaxation. Indomethacin (1 microM), glibenclamide (3 microM) and charybdotoxin (100 nM) did not affect the PDA response in rat aorta. These results indicate that in rat aorta, the basal release of nitric oxide could modulate the PDA-induced contraction, which is likely to accounts for the smaller contractile response induced by PDA in arteries with intact endothelium compared to much larger contractions seen in arteries without endothelium.

Acetylcholine↗

PubMed1997

Studies on vasorelaxation by tetrapentylammonium ions in rat aortic rings.

Tetrapentylammonium ions (TPA+) relaxed the isolated rat aortic rings precontracted with phenylephrine and high extracellular K+ in a concentration-dependent manner with respective IC50 values of 38.9 +/- 3.9 microM and 40.2 +/- 2.9 microM. Other quaternary ammonium ions with a carbon side chain of varying length did not induce relaxation. The relaxant effect of TPA+ was independent of the presence of the endothelium, and was unaffected by various putative blockers of K+ channels such as iberiotoxin (100 nM), glibenclamide (3 microM) and 4-aminopyridine (1 mM). In addition, tetrodotoxin (3 microM), indomethacin (10 microM) and methylene blue (10 microM) had no effect on the TPA+-induced relaxation. TPA+ (50 microM) and procaine (10 mM) completely abolished the phasic contractile response to caffeine in Ca2+-free solution. In the absence of extracellular Ca2+, phorbol 12,13-diacetate (PDA) evoked a sustained tension and TPA+ concentration-dependently reduced the contraction with IC50 of 30.7 +/- 3.1 microM. TPA+ reduced the sustained tension of the similar magnitude induced by phenylephrine, 60 mM K+ and active phorbol ester with similar potencies. These results indicate that TPA+ could act as a non-selective relaxant in arterial smooth muscle. This vasorelaxant effect is unique for TPA+ since other quaternary ammonium ions did not show the similar action in the rat aorta.

Animals↗

PubMed1997

Cardiorespiratory components of defense reaction elicited from paraventricular nucleus.

The present study was conducted to test the hypothesis that the paraventricular nucleus of the hypothalamus (PVN) is involved in the mediation or modulation of the cardiorespiratory components of the defense reaction (DR) in rabbits. Electrical stimulation of the PVN elicited increases in blood pressure and heart rate, hyperventilation, decreased blood flow to the visceral organs, and an increase in blood flow to the hindlimbs that was mediated by an atropine-sensitive vasodilation system. This response pattern is nearly identical to the one that is elicited by electrical stimulation of the hypothalamic defense area. In addition, the cardiomotor component of the baroreceptor reflex was observed to be suppressed during electrical stimulation of the PVN. Previous studies have shown that electrical stimulation of the hypothalamic defense area also leads to inhibition of the cardiomotor component of the baroreceptor reflex. The results of the present study provide evidence that the PVN is involved in the mediation or modulation of the defense reaction.

Animals↗

PubMed1997

Functional relationship between the hypothalamic vigilance area and PAG vigilance area.

The vigilance reaction is characterized by a large bradycardia, a pressor response, and inspiratory apnea in anesthetized rabbits and the inhibition of movement in conscious rabbits. This affective response pattern can be elicited by electrical stimulation of the dorsolateral hypothalamus (the hypothalamic vigilance area) or the ventrolateral periaqueductal gray (the periaqueductal gray vigilance area). The present study sought to advance our understanding of the functional relationship between the hypothalamic vigilance area (HVA) and the periaqueductal gray vigilance area (PVA) by measuring the effects of transverse transections of the caudal portion of the ventrolateral PAG (vlPAG) upon the cardiovascular responses elicited from the dorsolateral hypothalamus and the rostral vlPAG. Selective transverse transections of the caudal vlPAG significantly reduced the magnitudes of the bradycardia and pressor response elicited by stimulation of the PVA rostral to the transection site, but had minimal impact on the cardiovascular responses evoked by stimulation of the HVA. These findings suggest that the cardiovascular responses elicited by stimulation of the vlPAG are mediated by a neural pathway that is parallel, at least in part, to the one that subserves the response elicited from the HVA. The results also provide support for the view that the PAG is not an essential structure in the mediation of the autonomic components of affective behaviors involving behavioral inhibition.

Animals↗

PubMed1997

Transcriptional inhibition of manganese superoxide dismutase (SOD2) gene expression by DNA methylation of the 5' CpG island.

Manganese superoxide dismutase (MnSOD) enzyme activity and SOD2 gene expression have often been reported to decrease during the development of cancer. SOD2 has also been implicated as a candidate tumor suppressor gene for human malignant melanoma. Genomic DNA methylation patterns are also known to change during carcinogenesis and serve as a mechanism for tumor suppressor gene inactivation. We hypothesized that decreased SOD2 gene expression in some malignant cell populations may be due, at least in part, to methylation of upstream transcriptional regulatory sequences in the SOD2 gene. To test this hypothesis we transfected methylated and unmethylated SOD/2-CAT promoter-reporter constructs in cells known to express the SOD2 gene. Our results indicate that methylation of specific cytokines in the SOD2 5' flanking region is sufficient to repress transcriptional activity of the SOD2 promoter by at least 50%. Moreover, we show that this transcriptional repression was likely mediated by inhibition of AP-2 DNA binding and transactivation from a methylated AP-2 binding site in the SOD2 promoter. DNA methylation may provide a mechanism for transcriptional inactivation of the SOD2 gene during the development of some cancers.

Animals↗

PubMed1997

Estrogen increases intracellular p26Bcl-2 to p21Bax ratios and inhibits taxol-induced apoptosis of human breast cancer MCF-7 cells.

Recent studies have demonstrated that following estrogen ablation, estrogen responsive breast cancer cells undergo apoptosis. In addition, estrogen receptor (ER) expression has been strongly correlated with the expression of the bcl-2 gene product, p26Bcl-2 protein, which is known to inhibit apoptosis. In the present studies, we investigated whether estrogen affects the intracellular levels of p26Bcl-2 and thereby modulates taxol-induced apoptosis of estrogen responsive human breast cancer MCF-7 cells. Transfer of MCF-7 cells to a culture-medium without estrogens reduced their intracellular p26Bcl-2 levels by 50%. Inclusion of 0.1 microM estradiol in the medium produced approximately a four-fold increase in p26Bcl-2, but not p29Bcl-x1, or p21Bax levels; the expression of the c-myc and mdr-1 genes remained unchanged. Estradiol-induced four-fold increase in the ratio of the p26Bcl-2 to p21Bax levels caused a significant decline in the lethal, kilobase size DNA fragments of apoptosis, which had resulted when MCF-7 cells were cultured in a medium without estrogen. In addition, in MCF-7 cells, estradiol-induced increase in the intracellular p26Bcl-2 to p21Bax ratios was associated with a significant reduction in the large-sized DNA fragmentation induced by treatment with taxol. The increased ratios also protected MCF-7 cells against taxol-mediated cytotoxicity as assessed by the MTT assay. These results suggest that by modulating p26Bcl-2 levels, estrogens may affect the antitumor activity of taxol and potentially of other anti-breast cancer drugs against estrogen responsive human breast cancer cells.

Antineoplastic Agents, Phytogenic↗

PubMed1997

Nucleotide sequence of a 5423 base pairs fragment of the LsNPV genome and comparison with the AcNPV genome.

A 5423 bp fragment of LsNPV genome was sequenced, in which PDV-E66 gene and another four ORFs were found. The PDV-E66 gene of LsNPV was compared with the PDV-E66 gene of AcNPV, and a 51.9% nucleotide sequence homology and 38.8% amino acid sequence homology were found between the two genes. Two conserved late transcriptional motifs TAAG were found in LsNPV PDV-E66 gene, similar to those in AcNPV PDV-E66. The LsNPV PDV-E66 ORF is 204 base pairs shorter than the AcNPV PDV-E66 ORF at the 5' end. This is agreement with the fact that the N-terminus of the AcNPV PDV-E66 mature protein is 69 amino acids interior to the N-terminus predicted by the AcNPV PDV-E66 ORF. The 5' regulatory region of ORF1 contains early (CGTGC) and late (TAAG) transcriptional initiation motifs and ORF1 is predicted to encode a protein with 114 amino acid residues. The 5' regulatory region of ORF2 which can encode a protein with 115 amino acid residues contains only an early transcriptional initiation motif. Compared with all the genes from AcNPV and other baculoviruses, ORF1 and ORF2 have no homologous genes. It is suggested that ORF1 and ORF2 may be two novel baculovirus genes. ORF3 (PDV-E66 gene), ORF5 and an incomplete ORF, ORF6-part, have homologous regions in the AcNPV genome. ORF3, ORF5, ORF6-part are linked together in LsNPV genome, but their homologous regions are separated by about 58 kb fragment in the AcNPV genome. This fact indicates that the organization of the above genes in LsNPV is different from that of AcNPV. ORF4 is included in ORF6-part and can encode a 48 amino acid residues polypeptide, but ORF4 and ORF6-part are located on different DNA strands.

Amino Acid Sequence↗

PubMed1997

Serum withdrawal and etoposide induce apoptosis in human lung carcinoma cell line A549 via distinct pathways.

The molecular events associated with apoptosis induced by two distinct triggers (1) serum withdrawal and (2) etoposide treatment were investigated in the human lung carcinoma cell line A549. Although both serum withdrawal and etoposide treatment resulted in internucleosomal DNA fragmentation, the morphologic features were distinct. Serum deprived apoptotic cells appeared small, round and refractile, with little evidence of nuclear fragmentation; etoposide-induced apoptotic cells appeared enlarged and flattened and displayed prominent nuclear fragmentation. p53 and p21/waf1 protein levels were elevated in etoposide-treated cells, but not in cells subjected to serum with-drawal. Apoptosis induced by both treatments was accompanied by a significant reduction in Rb protein levels. However, etoposide treatment led to hypo-phosphorylation of Rb, while serum withdrawal did not alter the Rb phosphorylation pattern. Serum withdrawal-induced apoptosis was correlated with activation of JNK and suppression of ERK activities, while both JNK and ERK activities were slightly elevated during etoposid- induced apoptosis. Together, these results support the hypothesis that apoptosis induced by serum withdrawal and etoposide treatment occurs through different pathways and involves distinct mediators.

Journal Article↗

PubMed1997

Effect of alpha-ketoisocaproate and leucine on the in vivo oxidation of glutamate and glutamine in the rat brain.

Leucine and alpha-ketoisocaproate (alpha-KIC) were perfused at increasing concentrations into rat brain hippocampus by microdialysis to mimic the conditions of maple syrup urine disease. The effects of elevated leucine or alpha-KIC on the oxidation of L-[U-14C]glutamate and L-[U-14C]glutamine in the brain were determined in the non-anesthetized rat. 14CO2 generated by the metabolic oxidation of [14C]glutamate and [14C]glutamine in brain was measured following its diffusion into the eluant during the microdialysis. Leucine and alpha-KIC exhibited differential effects on 14CO2 generation from radioactive glutamate on glutamine. Infusion of 0.5 mM alpha-KIC increased [14C]glutamate oxidation approximately 2-fold; higher concentrations of alpha-KIC did not further stimulate [14C]glutamate oxidation. The enhanced oxidation of [14C]glutamate may be attributed to the function of alpha-KIC as a nitrogen acceptor from [14C]glutamate yielding [14C]alpha-ketoglutarate, an intermediate of the tricarboxylic acid cycle. [14C]glutamine oxidation was not stimulated as much as [14C]glutamate oxidation and only increased at 10 mM alpha-KIC reflecting the extra metabolic step required for its oxidative metabolism. In contrast, leucine had no effect on the oxidation of either [14C]glutamate or [14C]glutamine. In maple syrup urine disease elevated alpha-KIC may play a significant role in altered energy metabolism in brain while leucine may contribute to clinical manifestations of this disease in other ways.

Animals↗

PubMed1997

A novel RNA-binding motif in influenza A virus non-structural protein 1.

The solution NMR structure of the RNA-binding domain from influenza virus non-structural protein 1 exhibits a novel dimeric six-helical protein fold. Distributions of basic residues and conserved salt bridges of dimeric NS1(1-73) suggest that the face containing antiparallel helices 2 and 2' forms a novel arginine-rich nucleic acid binding motif.

Binding Sites↗

PubMed1997

Co-expression of several molecular mechanisms of multidrug resistance and their significance for paclitaxel cytotoxicity in human AML HL-60 cells.

Overexpression of P-glycoprotein (PGP), MRP or LRP has been characterized as the 'proximal', while overexpression of the anti-apoptosis Bcl-2 or Bcl-xL relative to the pro-apoptosis Bax protein has been recognized as the 'distal' mechanism of multidrug resistance in human AML cells. In the present studies, we examined whether these mechanisms can co-exist in human AML HL-60 cells. We also determined how these mechanisms would affect the accumulation and cytotoxicity of a PGP substrate, such as Taxol (paclitaxel). For this, immunoblot analyses were performed to determine the expression of PGP, MRP, Myc, Bcl-2, Bcl-xL and Bax on either the multidrug-resistant HL-60 sublines created under the selection pressure of doxorubicin (HL-60/AR), paclitaxel (HL-60/TAX1000) or vincristine (HL-60/VCR), or sublines created by transfection and overexpression of the bcl-2 (HL-60/Bcl-2) or bcl-xL gene (HL-60/Bcl-xL). As compared to the control HL-60, HL-60/AR cells possess high MRP while HL-60/TAX1000 and HL-60/VCR cells express high levels of the mdr-1 encoded PGP. In addition, these multidrug-resistant cells possess 1.5- to 2.5-fold higher Bcl-2, while their Bax and Myc levels are similar to those in the control HL-60 cells. HL-60/TAX1000 and HL-60/VCR cells also express three- and 2.5-fold higher Bcl-xL levels. PGP, but not MRP, overexpression significantly impaired paclitaxel accumulation and paclitaxel-induced apoptosis, as well as reduced its cytotoxic effects as determined by the MTT assay. In contrast, enforced and much higher expression of Bcl-2 in HL-60/Bcl-2 (five-fold) or Bcl-xL in HL-60/Bcl-xL cells (10-fold) significantly reduced paclitaxel-induced apoptosis and the loss of cell viability, without affecting its intracellular accumulation. These results confirm the possibility of co-expression of multiple mechanisms of multidrug resistance in human leukemic cells which had been selected by exposure to a single drug. The results also indicate that MRP overexpression does not confer resistance against paclitaxel. In addition, these findings suggest that, for Bcl-2 and Bcl-xL, enforced overexpression to high levels is necessary to induce paclitaxel resistance in HL-60 cells.

ATP Binding Cassette Transporter, Subfamily B, Mem↗