Biomedical subjects

J Y Chang

Publications and source records attributed to J Y Chang.

At least 73 records · Page 4Linked to original sources

PubMed1997

A two-stage mechanism for the reductive unfolding of disulfide-containing proteins.

Reductive unfolding of disulfide-containing proteins can be experimentally dissected into two distinct stages. In the presence of denaturant and thiol catalyst, native proteins unfold by reshuffling their native disulfides and convert to a mixture of scrambled structures. Subsequent reduction of the disulfide bonds of scrambled proteins requires only mild concentration of reductant (0.2-0.5 mM reduced dithiothreitol) and undergoes intermediates that consist of highly heterogeneous disulfide isomers. These properties have been characterized with three cystine-containing proteins, namely hirudin, tick anticoagulant peptide (TAP), and bovine ribonuclease A. In the cases of hirudin and TAP, most intermediates observed during the oxidative folding were found to exist along the pathway of reductive unfolding as well.

Animals↗

PubMed1997

Single neuronal responses in medial prefrontal cortex during cocaine self-administration in freely moving rats.

Chronic single neuronal recording techniques were applied to investigate the involvement of the medial prefrontal cortex (mPFC) during cocaine self-administration in the rat. Rats were trained to press a lever for cocaine under continuous reinforcement and fixed ratio schedules. Different patterns of phasic neuronal activity changes were found to be associated with lever-pressing for cocaine. The neuronal responses could be classified into five categories: 1) increases in neuronal firing before the lever press (15 out of 121 neurons, 12.4%); 2) decreases in neuronal firing before the lever press (13 neurons, 10.7%); 3) increases in neuronal firing after cocaine infusion (4 neurons, 3.3%); 4) decreases in neuronal firing after cocaine infusion (32 neurons, 26.4%); and 5) no alteration of neuronal activity throughout the self-administration session (67 neurons, 55.4%). The anticipatory responses, i.e., neuronal activity appearing before the lever press, were observed for both the continuous reinforcement and fixed ratio schedules. In a few cases, alteration of firing rate was not observed for the first lever press but appeared before subsequent lever presses in fixed ratio schedules. Eliminating cocaine abolished the inhibitory neuronal responses observed after lever press, suggesting that these inhibitory responses after cocaine self-administration were attributable to the pharmacologic effect of cocaine. The data provide initial electrophysiological evidence that the mPFC may play a role in mediating the task sequencing which leads to cocaine self-administration.

Animals↗

PubMed1997

Cyclic AMP and sympathetic neuronal programmed cell death.

The survival and proper functioning of sympathetic neurons are dependent on nerve growth factor (NGF). When immature sympathetic neurons are deprived of NGF, they undergo an 'active' dying process usually termed 'programmed cell death' or 'apoptosis'. This trophic factor dependence is age-related such that the cells become less dependent on NGF as they mature. Removal of NGF in immature cultures, which triggered the process of programmed cell death, resulted in a significant decrease of intracellular cAMP levels. In contrast, when these cells matured in culture and became relatively NGF independent, NGF withdrawal did not lead to a drop of cAMP levels. Pituitary adenylate cyclase-activating polypeptide (PACAP), a naturally occurring bioactive peptide structurally similar to VIP, could increase cAMP levels in these sympathetic neurons, and delay neuronal cell death resulting from NGF deprivation. These results suggest that PACAP may serve as a neurotrophic factor in sympathetic neurons.

Animals↗

PubMed1997

25-Hydroxycholesterol causes death but does not prevent nerve growth factor-induced neurite outgrowth in PC12 cells.

The effects of cholesterol oxides on regular and neuronal PC12 cells were examined. Among the cholesterol oxides tested, 7-beta-, 22(R)- and 25-OH-cholesterol were very toxic to regular PC12 cells such that approximately 80% of cells were killed after a 3 day incubation with 20 micrograms/ml (50 microM) of these agents. Cholesterol oxides caused cytotoxicity in neuronal PC12 cells at concentrations higher than those observed for regular PC12 cells. The nerve growth factor (NGF)-induced neurite outgrowth and nitric oxide synthase expression appeared normal in PC12 cells treated with a sublethal dose of 25-OH-cholesterol. Neurite regeneration from established neuronal PC12 cells was not inhibited by the presence of a toxic dose of 25-OH-cholesterol. Given the fact that 25-OH-cholesterol is a potent inhibitor of cholesterol synthesis pathway, these results suggest that the de novo synthesis of cholesterol may not be required for NGF-induced neurite outgrowth in PC12 cells.

Animals↗

PubMed1997

A longitudinal study of skeletal side effects induced by rapid maxillary expansion.

Orthopedic expansion of the maxillary arch--rapid maxillary expansion (RME)--is a commonly used treatment technique that has become increasingly popular during the last 25 years. During this time, however, clinicians routinely have imputed a variety of undesirable side effects to RME, particularly bite opening. Whereas there have been many explanations as to the mechanisms underlying such RME-related effects as bite opening, few studies have considered the long-term effects of RME in the vertical and sagittal dimensions of the face. The purpose of this investigation was to examine cephalometrically the long-term effect that the Haas-type rapid maxillary expansion may have on bite opening and on the anteroposterior position of the maxilla. The sample consisted of 25 patients who had undergone RME with the Haas-type expander, followed by standard edgewise therapy. This RME sample was compared with a group of 25 patients who had standard edgewise treatment (SET) only and with a control (CTRL) group of 23 subjects. Mean initial form and mean age at start of treatment for the RME, SET, and CTRL groups were similar. Statistically significant among-group differences were documented for only 2 of 10 cephalometric variables sensitive to anteroposterior and vertical skeletal changes. These differences, however, were not clinically significant. The current investigation implies therefore that RME therapy with the Haas-type expander has little long-term (more than 6 years after treatment) effect on either the vertical dimensions or the anteroposterior dimensions of the face.

Adolescent↗

PubMed1997

Morphological and biochemical changes during programmed cell death of rat cerebellar granule cells.

Cultured cerebellar granule cells deprived of depolarizing concentrations of KCl and serum die by programmed cell death. Recently, it was shown that serum removal by itself can lead to oxidative stress and DNA fragmentation in these cells. We have modified the protocol which initiates cell death in such a way that only the effect of KCl withdrawal-induced cell death was observed. We have performed a series of experiments to correlate the structural and biochemical changes in this process of cell death. Significant morphological alterations occur in cell bodies and neurites during a 48-hour period of KCl removal. Cell viability dropped to 53%, 34% or 10% of control levels, respectively, as a result of 1-, 2-, or 3-day KCl removal. A series of experiments was conducted to determine the change of total protein level, protein synthesis rate, RNA synthesis rate, and mitochondrial activity during the first 48 hours of KCl removal. These studies not only provide a picture correlating the morphological and biochemical changes in the process of programmed cell death, but also serve as a reference for future studies of this complex phenomenon.

Animals↗

PubMed1997

Mechanical forces alter growth factor release by pleural mesothelial cells.

The mesothelial cells that form the visceral pleura of the lung are subjected to physical forces such as stretch due to lung expansion and fluid shear stress due to the sliding motion of the lung against the chest wall. In this study, the effect of mechanical forces on the production of growth factors by mesothelial cells was investigated. Rat visceral pleura mesothelial (RVPM) cells were exposed to fluid shear stress by perfusing a column of cell-covered beads. RVPM cells grown on a silicone elastomer were subjected to cyclic strain by applying an oscillating vacuum to the bottom of the wells using the Flexercell apparatus. Fluid shear stress (5.2-15.7 dyn/cm2) stimulated the release of endothelin-1 (ET-1) by RVPM cells two- to fivefold over static cells. ET-1 secretion by RVPM cells was also stimulated approximately twofold by cyclic stretch (20% maximum strain, 30 cycles/min). RVPM cells released significant levels of platelet-derived growth factor (PDGF), but there was no effect of either shear stress or cyclic strain on PDGF release. These results suggest that the production of growth factors by pleural mesothelial cells is regulated in part by physical forces.

Animals↗

PubMed1997

Neurotoxicity of tunicamycin on cultured cerebellar granule cells.

Tunicamycin (TM) is known to cause severe neurological diseases in the central nervous system of animals. Cultured cerebellar granule cells were used to investigate the direct cytotoxicity of this agent on cerebellar neurons. Results indicate that TM is a potent inhibitor of glycosylation and protein synthesis. This agent killed granule cells in a dose- and time-dependent manner. TM treatment of these neurons lead to atrophic cell bodies and condensed nuclei. This TM-induced cell death could be prevented by cycloheximide and aurintricarboxylic acid. In contrast, TM had no apparent toxicity toward nerve growth factor-differentiated PC12 cells under similar conditions. These results suggest that TM kills cerebellar granule cells in a manner similar to programmed cell death.

Animals↗

PubMed1996

Inhibition of intratracheal lung cancer development by systemic delivery of E1A.

Amplification or overexpression of HER-2/neu in human lung cancer has been correlated with poor prognosis and chemoresistance. We have previously reported that the adenovirus type 5 early region 1A (E1A) gene product can suppress HER-2/neu-mediated transformation phenotypes through inhibition of HER-2/neu expression. To find an efficient way to treat HER-2/neu-overexpressing lung cancer with E1A, a replication-deficient adenovirus containing the E1A gene, Ad.E1A(+), was used to transduce E1A into HER-2/neu-overexpressing and low expressing human lung cancer cell lines. Tumour cell growth in vitro and colony formation in soft agarose were greatly inhibited by Ad.E1A(+) transduction in HER-2/neu-overexpressing lung cancer cell lines. In HER-2/neu low expressing cell lines, E1A could not inhibit cell growth in vitro but could reduce the colony formation ability in soft agarose, indicating different effects of E1A in these two types of cancer cells. To test the therapeutic efficacy of E1A to lung cancer by systemic delivery in vivo, tumor-bearing mice were established by intratracheal injection of lung cancer cells and treated by i.v. tail injections of Ad.E1A(+). As a result, Ad.E1A(+) suppressed HER-2/neu overexpression and inhibited intratracheal lung cancer growth. However, no significant tumor suppression effect of Ad.E1A(+) was observed in mice bearing HER-2/neu low expressing cell line when the same therapeutic procedure was followed. Thus, we conclude that systemic delivery of Ad.E1A(+) can efficiently achieve therapeutic effect in HER-2/neu-overexpressing lung cancer in vivo.

Adenovirus E1A Proteins↗

PubMed1996

The disulfide folding pathway of tick anticoagulant peptide (TAP), a Kunitz-type inhibitor structurally homologous to BPTI.

The pathway of oxidative folding of tick anticoagulant peptide (TAP, 60 amino acids and three disulfides) has been analyzed by characterization of the acid and iodoacetate trapped folding intermediates. The results reveal a high degree of heterogeneity of the one- and two-disulfide intermediates and the presence of three-disulfide scrambled species along the folding pathway. The picture of TAP folding differs significantly from the well-documented case of bovine pancreatic trypsin inhibitor (BPTI), despite the fact that both proteins share close structural homology in term of 3-D conformation and disulfide pattern.

Amino Acid Sequence↗

PubMed1996

Expression of Epstein-Barr virus-encoded RNAs as a marker for metastatic undifferentiated nasopharyngeal carcinoma.

BACKGROUND: Epstein-Barr virus (EBV) is associated with undifferentiated nasopharyngeal carcinoma (NPC). EBV-encoded nonpolyadenlyated RNAs (EBERs) are often used as a marker to detect EBV-infected NPC cells. This study was conducted to document the expression and determine the significance of EBERs in NPC cells at various metastatic sites. METHODS: An in situ hybridization (ISH) technique was used to identify the presence of EBERs in paraffin embedded tissues of primary and metastatic sites obtained from 21 patients with NPC. Nineteen of these patients had undifferentiated lesions, and 2 had squamous cell carcinoma. One hundred and fifty specimens of normal tissues and tissues from patients with a variety of benign and malignant diseases other than NPC served as controls. In the NPC specimens, the expression of latent membrane protein (LMP) and a lytic protein, BZLF-1, were also examined by immunohistochemistry. RESULTS: Tissues from all patients with undifferentiated NPC and one patient with squamous cell carcinoma contained EBERs in the malignant cells; the other case of squamous cell carcinoma was negative. In metastatic NPCs, LMP was expressed in 18% (4 of 22) of tissues whereas BZLF-1 was not expressed in any tissues. EBERs were not detected in the 43 patients with normal tissues and benign lesions. In malignant diseases other than NPC, EBERs were detected in only 2 of 12 cases of non-Hodgkin's lymphoma, 1 of 2 cases of Hodgkin's lymphoma, and 1 of 6 cases of gastric cancer. CONCLUSIONS: By virtue of the direct correlation between latent EBV infection and NPC, the authors conclude that EBERs can be used as a sensitive marker to identify NPC cells at various metastatic sites by techniques of in situ hybridization, and that demonstration of EBERs in lesions of undifferentiated histology may be useful as a diagnostic adjunct for NPC presenting as metastatic cancer of unknown origin.

Biomarkers, Tumor↗

PubMed1996

Cyclic AMP and pituitary adenylate cyclase-activating polypeptide (PACAP) prevent programmed cell death of cultured rat cerebellar granule cells.

Cultured cerebellar granule cells undergo programmed cell death when they are deprived of depolarizing KCl. Results from this study indicate that the cAMP analog cyclic 8-(4-chlorophenylthio) adenosine-3'5'-monophosphate (CPT-cAMP) can prevent the cell death in a dose-dependent manner, with the maximal effect seen at 500 microM. Approximately 70% of cells can be saved with this concentration of CPT-cAMP for at least 6 days. Pituitary adenylate cyclase-activating polypeptide (PACAP) increased the intracellular cAMP levels of these cells in a time- and dose-dependent manner. This agent can prevent the decrease of cAMP and cell death induced by KCl withdrawal. These results suggest that PACAP could function as a neurotrophic factor for cerebellar granule cells in vivo.

Animals↗

PubMed1996

Cytosine arabinoside differentially alters survival and neurite outgrowth of neuronal PC12 cells.

Cytosine arabinoside, a potent antimitotic agent, is used clinically as an anticancer drug with the side effect of severe neurotoxicity. Earlier reports suggested that this agent blocks the signaling pathway of nerve growth factor in sympathetic neurons, which results in neuronal death. The present study demonstrated that neuronal PC12 cells deprived of nerve growth factor showed a decrease of neurite outgrowth, which was not seen in cytosine arabinoside-treated neuronal PC12 cells, suggesting that this agent may not interfere with the part of the NGF signaling pathway that leads to neurite outgrowth. On the other hand, treatment of neuronal PC12 cells with cytosine arabinoside led to a dose- and time-dependent decrease of viability. These results suggest that there is a distinction between the neurite outgrowth and the survival promoting activities of nerve growth factor.

Animals↗

PubMed1996

Camptothecin resistance involving steps subsequent to the formation of protein-linked DNA breaks in human camptothecin-resistant KB cell lines.

To identify mechanisms of camptothecin (CPT) resistance/toxicity, sublines from a human KB cell line were made resistant to CPT by continuous selection in increasing concentrations of CPT. Two CPT-resistant lines, 100 and 300, were 32- and 54-fold resistant to the growth-inhibitory properties of CPT compared to the KB line. After CPT-free culturing, partial revertant lines were established from each resistant line. These partial revertant lines, 100rev and 300rev, were 2.5- and 3.2-fold resistant to CPT compared to KB. When growth inhibition and toxicity were compared, the resistant lines alone displayed an enhanced cytostatic response to CPT. The resistant and partial revertant lines displayed no cross-resistance to etoposide or cisplatin. Comparisons of topoisomerase I (TOPI) activity, content, and protein-linked DNA break production by CPT revealed that resistant and partial revertant lines had one-half the levels as KB, with TOP1 activity that was equally sensitive to CPT in all cell lines tested. However, double-stranded DNA break induction by CPT was significantly reduced only in the resistant lines. Coincubation with 3-aminobenzamide, an inhibitor of poly(ADP-ribosyl) polymerase, potentiated CPT toxicity in the resistant lines alone, without affecting CPT: TOP1 interactions. Therefore, CPT resistance in the 100 and 300 lines was characterized by factors independent of TOP1, specific for CPT, and attenuated by poly(ADP-ribosyl) polymerase inhibition. This resistant phenotype produced fewer double-stranded DNA breaks and enhanced a cytostatic response to CPT.

Benzamides↗

PubMed1996

Specific toxicity of tunicamycin in induction of programmed cell death of sympathetic neurons.

Tunicamycin belongs to a group of antibiotics which can cause severe a nd often fatal neurological malfunction in animals, commonly known as "annual ryegrass toxicity." At the cellular level, tunicamycin is a potent glycosylation inhibitor which is often used to elucidate the importance of glycosylation in protein functions. Earlier reports suggested that tunicamycin was able to interfere with the binding of nerve growth factor to its receptors. In this report, we showed that tunicamycin was able to kill sympathetic neurons in cultures. The mechanism of cell death was observed to be similar to that of "programmed cell death" in sympathetic neurons induced by nerve growth factor deprivation. Such tunicamycin-induced cell death could be prevented by the protein synthesis inhibitor cycloheximide, which was known to prevent the programmed cell death in sympathetic neurons. These results demonstrated that, in addition to the proven CNS neurotoxicity in animals, tunicamycin causes programmed cell death in peripheral (sympathetic) neurons.

Animals↗

PubMed1996

Intrathecal ketamine reduces morphine requirements in patients with terminal cancer pain.

PURPOSE: Ketamine has been administered epidurally and intrathecally for operative and post-operative pain control. Animal studies showed potentiation of analgesia induced by ketamine and morphine. We hypothesized that intrathecal ketamine would potentiate the effects of intrathecal morphine in the treatment of cancer pain. METHODS: A double blind, cross over study was designed to evaluate the effect of ketamine on spinal morphine analgesia in terminal cancer pain patients. A two-phase protocol was used; phase M, intrathecal morphine alone twice daily; phase M + K, co-administration of ketamine (1.0 mg) with morphine intrathecally twice daily. The dose of morphine was titrated upwards until acceptable pain relief was achieved, defined by numeric rating scales (0-10) < or = 3, and the rescue dose of morphine was less than 5 mg after each intrathecal administration for two days. The dose of intrathecal morphine was defined as the effective dose. RESULTS: The effective dose of intrathecal morphine in phase M of 0.38 +/- 0.04 mg.day-1 was higher than that in phase M + K (0.17 +/- 0.02 mg.day-1) (P < 0.05). The average pain scales were 7.95 +/- 0.25 before intrathecal drug administration. Pain scales were decreased to 2.2 +/- 0.17 (P < 0.05) in phase M and 1.95 +/- 0.20 (P < 0.05) in phase M + K after the effective dose of morphine had been reached. No serious side effects were observed in this study. CONCLUSION: The present study demonstrates that ketamine enhances the analgesic effect of morphine, thus reducing the dose of intrathecal morphine.

Adult↗

PubMed1996

Neuronal spike activity in rat nucleus accumbens during cocaine self-administration under different fixed-ratio schedules.

Chronic ensemble recording techniques were used to investigate neuronal activity in the nucleus accumbens in freely moving rats during different cocaine self-administration schedules. The issue of concern in this study was the role of nucleus accumbens in initiating and sustaining cocaine self-administration. Specifically, to determine the nature of the neuronal activity, either motor or motivational, which precedes the multiple bar presses required to self-administer cocaine and of the post-lever press neuronal response, we used conventional fixed ratio-5, fixed ratio-10, and modified fixed ratio-3 schedules. In the modified fixed ratio-3 schedule, the first lever press resulted in retraction of the lever for 2 s; the second lever press retracted the lever and turned on a cue light; the third lever press turned off the cue light and delivered cocaine (1.0 mg/kg) intravenously. In the fixed ratio-5 and -10 schedules, rats continuously pressed the lever 5 or 10 times, respectively, to obtain a single infusion of cocaine. Phasic alterations in neural spike activity were observed in 50% of nucleus accumbens neurons before (termed "anticipatory" responses) and after lever pressing for cocaine self-administration. Neurons with anticipatory responses typically exhibited such responses for all lever presses in the modified fixed ratio-3, fixed ratio-5, and fixed ratio-10 schedules, but instances were found when the activity correlate was absent. In addition, some neurons had a prominent alteration in firing rate lasting 1-5 min after cocaine self-administration, and some of these neurons also had anticipatory responses. When cocaine was eliminated during self-administration sessions, the post-lever press inhibitory responses were largely abolished or even reversed, whereas anticipatory responses were not markedly changed when rapid lever presses occurred before behavior ceased. Post-cocaine inhibitory responses compared between self-administered and passively administered cocaine were not significantly different between these two conditions. The results suggest that nucleus accumbens may be involved in initiating general reward-seeking behaviors and action which are not exclusively associated with cocaine self-administration. Moreover, the neuronal responses in the nucleus accumbens to cocaine self-administration may play an essential role in maintaining cocaine reinforcement.

Animals↗

PubMed1996

Down regulation of bcl-2 by p53 in nasopharyngeal carcinoma and lack of detection of its specific t(14;18) chromosomal translocation in fixed tissues.

High levels of bcl-2 protein have been found in a wide variety of human cancers. Since p53 gene inactivation occurs in over half of human cancers, it is possible that loss of p53-mediated repression of bcl-2 gene expression accounts, at least in part, for the frequent abnormalities in bcl-2 protein production seen in tumours. By using immunohistochemical methods, we have analysed thirty-three nasopharyngeal carcinomas for p53 and bcl-2 expression. We found an inverse correlation between the expression of these two proteins (P < 0.001). Moreover, we utilized universal oligonucleotide primers of a region 5' to the bcl-2 MBR and at the 3' end of JH segments to initiate a DNA polymerase chain reaction that amplified these bcl-2-JH junctures. Of the twelve nasopharyngeal carcinomas expressing bcl-2, none showed a t(14;18) chromosome translocation. These findings may indicate potential mechanisms by which bcl-2 regulates apoptosis.

Base Sequence↗