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Biomedical subjects

S Tan

Publications and source records attributed to S Tan.

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

Nitrosation of uric acid by peroxynitrite. Formation of a vasoactive nitric oxide donor.

Peroxynitrite (ONOO-), formed by the reaction between nitric oxide (. NO) and superoxide, has been implicated in the etiology of numerous disease processes. Low molecular weight antioxidants, including uric acid, may minimize ONOO---mediated damage to tissues. The tissue-sparing effects of uric acid are typically attributed to oxidant scavenging; however, little attention has been paid to the biology of the reaction products. In this study, a previously unidentified uric acid derivative was detected in ONOO--treated human plasma. The product of the uric acid/ONOO- reaction resulted in endothelium-independent vasorelaxation of rat thoracic aorta, with an EC50 value in the range of 0.03-0.3 microM. Oxyhemoglobin, a .NO scavenger, completely attenuated detectable .NO release and vascular relaxation. Uric acid plus decomposed ONOO- neither released .NO nor altered vascular reactivity. Electrochemical quantification of .NO confirmed that the uric acid/ONOO- reaction resulted in spontaneous (thiol-independent) and protracted (t1/2 approximately 125 min) release of .NO. Mass spectroscopic analysis indicated that the product was a nitrated uric acid derivative. The uric acid nitration/nitrosation product may play a pivotal role in human pathophysiology by releasing .NO, which could decrease vascular tone, increase tissue blood flow, and thereby constitute a role for uric acid not previously described.

Animals↗
PubMed1998

The regulation of reactive oxygen species production during programmed cell death.

Reactive oxygen species (ROS) are thought to be involved in many forms of programmed cell death. The role of ROS in cell death caused by oxidative glutamate toxicity was studied in an immortalized mouse hippocampal cell line (HT22). The causal relationship between ROS production and glutathione (GSH) levels, gene expression, caspase activity, and cytosolic Ca2+ concentration was examined. An initial 5-10-fold increase in ROS after glutamate addition is temporally correlated with GSH depletion. This early increase is followed by an explosive burst of ROS production to 200-400-fold above control values. The source of this burst is the mitochondrial electron transport chain, while only 5-10% of the maximum ROS production is caused by GSH depletion. Macromolecular synthesis inhibitors as well as Ac-YVAD-cmk, an interleukin 1beta-converting enzyme protease inhibitor, block the late burst of ROS production and protect HT22 cells from glutamate toxicity when added early in the death program. Inhibition of intracellular Ca2+ cycling and the influx of extracellular Ca2+ also blocks maximum ROS production and protects the cells. The conclusion is that GSH depletion is not sufficient to cause the maximal mitochondrial ROS production, and that there is an early requirement for protease activation, changes in gene expression, and a late requirement for Ca2+ mobilization.

Animals↗
PubMed1998

The ubiquitin-related protein RUB1 and auxin response in Arabidopsis.

The AXR1 (auxin-resistant) protein, which has features of the ubiquitin-activating enzyme E1, is required for normal response to the plant hormone auxin in Arabidopsis thaliana. ECR1 functions together with AXR1 to activate members of the RUB/NEDD8 family of ubiquitin-related proteins. Extracts from mutant seedlings lacking AXR1 did not promote formation of the RUB-ECR1 thiolester, indicating that AXR1 is the major activity in this tissue. AXR1 was localized primarily to the nucleus of dividing and elongating cells, suggesting that the targets of RUB modification are nuclear. These results indicate that auxin response depends on RUB modification of one or more nuclear proteins.

Amino Acid Sequence↗
PubMed1998

Bactericidal monoclonal antibodies that define unique meningococcal B polysaccharide epitopes that do not cross-react with human polysialic acid.

The poor immunogenicity of the Neisseria meningitidis group B polysaccharide capsule, a homopolymer of alpha(2-->8) sialic acid, has been attributed to immunologic tolerance induced by prenatal exposure to host polysialyated glycoproteins. Substitution of N-propionyl (N-Pr) for N-acetyl groups on the meningococcal B polysaccharide, and conjugation of the resulting polysaccharide to a protein carrier, have been reported to yield a conjugate vaccine that elicits protective Abs with minimal autoantibody activity. To characterize the protective epitopes on the derivatized polysaccharide, we isolated 30 anti-N-Pr meningococcal B polysaccharide mAbs. These Abs were heterogeneous with respect to complement-mediated bactericidal activity, fine antigenic specificity, and autoantibody activity as defined by binding to the neuroblastoma cell line, CHP-134, which expresses long-chain a(2-->8)-linked polysialic acid. Eighteen of the Abs could activate complement-mediated bacteriolysis. Seven of these 18 Abs cross-reacted with N-acetyl meningococcal B polysaccharide by ELISA and had strong autoantibody activity. Thus, N-Pr meningococcal B polysaccharide conjugate vaccine has the potential to elicit autoantibodies. However, 7 of the 18 bactericidal mAbs had no detectable autoantibody activity. These Abs may be useful for the identification of molecular mimetics capable of eliciting protective Abs specific to the bacteria, without the risk of evoking autoimmune disease.

Animals↗
PubMed1998

Crystal structure of the yeast MATalpha2/MCM1/DNA ternary complex.

The structure of a complex containing the homeodomain repressor protein MATalpha2 and the MADS-box transcription factor MCM1 bound to DNA has been determined by X-ray crystallography at 2.25 A resolution. It reveals the protein-protein interactions responsible for cooperative binding of MATalpha2 and MCM1 to DNA. The otherwise flexible amino-terminal extension of the MATalpha2 homeodomain forms a beta-hairpin that grips the MCM1 surface through parallel beta-strand hydrogen bonds and close-packed, predominantly hydrophobic, side chains. DNA bending induced by MCM1 brings the two proteins closer together, facilitating their interaction. An unusual feature of the complex is that an eight-amino-acid sequence adopts an alpha-helical conformation in one of two copies of the MATalpha2 monomer and a beta-strand conformation in the other. This 'chameleon' sequence of MATalpha2 may be important for recognizing natural operator sites.

Binding Sites↗
PubMed1998

Mechanisms of resistance to oxidative stress in Alzheimer's disease.

It is likely that amyloid beta-protein (A beta) mediates nerve cell death in Alzheimer's disease (AD). Some nerve cell populations, however, remain undamaged in AD brain. To understand the biochemical basis for resistance to A beta toxicity, a series of cell lines were isolated which are resistant to A beta toxicity. It is shown that a major component of the resistance mechanism is the transcriptional elevation of two H2O2 degrading enzymes, glutathione peroxidase and catalase. These data support other evidence for the role of oxidative damage in A beta toxicity, and suggest strategies for clinical approaches to the disease.

Alzheimer Disease↗
PubMed1998

Effects of treatment with formoterol on bronchoprotection against methacholine.

PURPOSE: In addition to their bronchodilatory effects, beta(2)-agonists protect against bronchoconstriction, such as that caused by methacholine challenge. However, tachyphylaxis to this beneficial effect develops after chronic use of beta(2)-agonists. We studied whether the frequency or dose of treatment with a long-acting beta(2)-agonist (formoterol) affects the degree of bronchoprotection afforded against methacholine challenge and to compare this with the effects of a short-acting beta(2)-agonist (terbutaline). PATIENTS AND METHODS: In a randomized, parallel group, double-blind study at two centers, patients with stable asthma of mild to moderate severity who were treated with inhaled corticosteroids were treated with formoterol 6 micrograms twice daily, 24 micrograms twice daily, 12 micrograms once daily; terbutaline 500 micrograms four times daily; or placebo. Treatments were given by dry powder inhaler for a period of 2 weeks. Of the 72 patients who were enrolled, 67 completed the study. Methacholine challenge was performed to calculate the provocative dose that caused a 20% fall in forced expiratory volume in 1 second at baseline (unprotected) after an initial 1-week run-in without beta(2)-agonists, 1 hour after the first dose of study treatment, and again 1 hour after 7 and 14 days of study treatment. RESULTS: Each of the four active treatments exhibited significant tachyphylaxis (P < 0.05) to protection against methacholine challenge when comparing first/last dose (as geometric mean protection ratio versus baseline): formoterol 24 micrograms twice daily (9.6-fold/1.6-fold), 12 micrograms once daily (7.1-fold/2.2-fold), 6 micrograms twice daily (6.2-fold/2.3-fold), and terbutaline 500 micrograms four times daily (2.9-fold/2.0-fold). There were no significant differences among treatments after 2 weeks in bronchoprotection against methacholine challenge. For all formoterol regimens, the bronchodilator response 1 hour after inhalation was maintained over the 2-week treatment period. Diurnal control of morning and evening peak flow was significantly better with formoterol 24 micrograms twice daily than with terbutaline. CONCLUSIONS: Tachyphylaxis to bronchoprotection against methacholine challenge develops after 2 weeks of therapy with formoterol, a long-acting beta(2)-agonist, at all three dosage regimens that were tested. In contrast, the bronchodilator effects of formoterol were maintained during the 2 weeks of treatment.

Adolescent↗
PubMed1998

Endothelial injury from a circulating mediator following rat liver ischemia.

Ischemia-reperfusion to the liver results in increased microvascular permeability in a nonischemic lung. We hypothesized that a circulatory mediator released from ischemic liver contributed to endothelial cell (EC) damage. Isolated rat livers, made ischemic for 2 h, were reperfused for 10 min. Bovine ECs were incubated for 5 h with pooled liver effluent collected before ischemia (Baseline) or after 10 min of reperfusion (Reperfusion). In the Reperfusion group, there was increased endothelial cell injury, as determined by release of 8-[14C]adenine, (39 +/- 2%) compared to the Baseline group (22 +/- 2%). Permeability of ECs to rhodamine B-labeled dextran (70,000 Mr) was also increased in the Reperfusion group by 54 +/- 9%. There was no significant attenuation in EC injury following incubation with reperfusion effluent stored for 24 h, supplementation with antioxidants (superoxide dismutase + catalase), or inhibition of xanthine oxidase with allopurinol or tungstate. We conclude that the reperfused liver releases a long-lived circulatory mediator of EC injury, which may produce the clinical microvascular injury observed following hepatic ischemia. The mechanism of injury in our model is independent of oxidants or oxidants generated from the circulating xanthine oxidase released from reperfused ischemic liver.

Adenine↗
PubMed1998

Eukaryotic transcription factors.

The structural characterization of eukaryotic transcription factors that interact with DNA has advanced on two fronts in the past two years. New complexes of transcription factors bound to TATA-box DNA include the TFIIA-TBP-DNA complex as well as human and archaeal TBP-DNA and TFIIB-TBP-DNA complexes, respectively. In addition, recent studies of proximal/distal promoter complexes demonstrate that DNA-binding motifs may be modified in nature by adding secondary structure elements to diversify DNA-binding specificities and affinities.

Animals↗
PubMed1998

Oxidative stress induces a form of programmed cell death with characteristics of both apoptosis and necrosis in neuronal cells.

Oxidative stress is implicated in a number of neurological disorders including stroke, Parkinson's disease, and Alzheimer's disease. To study the effects of oxidative stress on neuronal cells, we have used an immortalized mouse hippocampal cell line (HT-22) that is particularly sensitive to glutamate. In these cells, glutamate competes for cystine uptake, leading to a reduction in glutathione and, ultimately, cell death. As it has been reported that protein kinase C activation inhibits glutamate toxicity in these cells and is also associated with the inhibition of apoptosis in other cell types, we asked if glutamate toxicity was via apoptosis. Morphologically, glutamate-treated cells underwent plasma membrane blebbing and cell shrinkage, but no DNA fragmentation was observed. At the ultrastructural level, there was damage to mitochondria and other organelles although the nuclei remained intact. Protein and RNA synthesis inhibitors as well as certain protease inhibitors protected the cells from glutamate toxicity. Both the macromolecular synthesis inhibitors and the protease inhibitors had to be added relatively soon after the addition of glutamate, suggesting that protein synthesis and protease activation are early and distinct steps in the cell death pathway. Thus, the oxidative stress brought about by treatment with glutamate initiates a series of events that lead to a form of cell death distinct from either necrosis or apoptosis.

Amino Acid Chloromethyl Ketones↗
PubMed1998

Hypoxia-reoxygenation is as damaging as ischemia-reperfusion in the rat liver.

OBJECTIVE: We hypothesized that the extent of injury and release of xanthine oxidase, an oxidant generator, into the circulation would be less in normal-flow hypoxia-reoxygenation than in equal duration no-flow ischemia-reperfusion. DESIGN: Randomized study. SETTING: University-based animal research facility. SUBJECTS: Male Sprague-Dawley rats. INTERVENTIONS: The livers were isolated, perfused, and then randomly subjected to 2 hrs of hypoxia (normal flow, low oxygen) or ischemia (no flow, no oxygen), and 2 hrs of reperfusion. Hepatocytes were also isolated, and were subjected to either: a) hypoxia (0, 2, 4, and 6 hrs); or b) hypoxia (2 and 4 hrs) with reoxygenation (2 hrs). MEASUREMENTS AND MAIN RESULTS: The extent of liver injury (as assessed by release of hepatocellular enzymes) and the release of xanthine oxidase were measured from isolated-perfused rat livers and cultured hepatocytes. The pattern of release of xanthine oxidase in isolated-perfused liver effluent was different in hypoxia-reoxygenation compared with ischemia-reperfusion. During hypoxia, xanthine oxidase gradually increased in the effluent; then, the xanthine oxidase decreased to low concentrations during reoxygenation. After ischemia, there was a sharp spike in xanthine oxidase at 1 min of reperfusion, with a rapid decrease to low concentrations. The total release of xanthine oxidase during hypoxia-reoxygenation was similar to that during ischemia-reperfusion. Lactate dehydrogenase and other markers of liver injury showed a pattern of release that was similar to that of xanthine oxidase, but the total release of markers was not different between the two groups. In hepatocytes, most of the release of enzymes occurred in hypoxia, and the rate of release was not different between hypoxia and hypoxia-reoxygenation. CONCLUSIONS: Hypoxia-reoxygenation results in as much damage to the liver as ischemia-reperfusion, and results in the release of a similar amount of oxidant-producing xanthine oxidase into the circulation.

Alanine Transaminase↗
PubMed1998

Sustained hypoxia-ischemia results in reactive nitrogen and oxygen species production and injury in the premature fetal rabbit brain.

Free radical-mediated injury is implicated in hypoxic-ischemic encephalopathy observed in neonates. We investigated in utero free radical production and injury following hypoxia-ischemia to premature fetal brain utilizing a rabbit model of acute placental insufficiency. Pregnant rabbits at 29 days gestation were randomized to uterine ischemia for 50 minutes (min) (hypoxia) or nonischemic controls. Fetal brains were obtained immediately after ischemia for oxidative and acute-injury markers or 24 hours (h) post-ischemia for histopathology. Nitrotyrosine formation, a marker of NO-derived species such as peroxynitrite, was observed only in hypoxic brains. Hypoxia resulted in a significant increase in nitrogen oxides, lipid peroxidation, and protein oxidation, with a concomitant decrease in total antioxidant capacity, compared with controls. Peroxynitrite addition to brain homogenate increased nitrogen oxides linearly (1:1), although protein carbonyls were unchanged. Concomitantly, in vitro cortical and hippocampal cell viability and ATP levels decreased, with an increase in brain edema in hypoxic brains. Fetuses delivered 24 h post-ischemia had increased hippocampal nuclear karyorrhexis on histology compared with controls. Antioxidant administration (ascorbic acid and Trolox) intraperitoneally ameliorated changes in cellular viability and brain edema. Acute fetal hypoxia-ischemia without reoxygenation results in increased nitrogen and oxygen free radical production that may cause brain injury. The merits of the described model are discussed.

Animals↗
PubMed1998

Fetal and placental cyclic inositol phosphohydrolase in normoxia and hypoxia.

Cyclic inositol phosphohydrolase (cIPH) converts cyclic inositol monophosphate (cIP), a putative modulator of cell growth, into inositol monophosphate. We hypothesized that hypoxic-ischemic injury alters cIPH activity in the placenta. On the 29th day of gestation pregnant rabbits were randomized to either 50 min of uterine ischemia (hypoxia) or no ischemia (controls). The activity of cIPH was measured by incubating with [3H]cIP and determining the release of [3H]inositol. Although no cIPH has been demonstrated in blood previously, cIPH activity was found in both fetal and maternal blood. cIPH activity was higher on the fetal side of the placenta than on the maternal side and was also higher in fetal blood compared to maternal blood. Hypoxia-ischemia failed to alter the cIPH activity in fetal blood and fetal and maternal placenta. Since cIPH activity is higher in the fetus and is retained even after major ischemia, modulation of cIP may be important in early development.

Animals↗
PubMed1998

[Overexpression of cyclin D1 in laryngeal carcinomas].

Cyclin D1 is a set of periodic protein which governs G1 progression. Cyclin D1 gene is localized on chromosome 11q13 which encodes a 295-aa protein. Overexpression of cyclin D1 leads to abnormal cellular proliferation. Which underlies processes of tumorigenesis. In this paper twenty-five fresh specimens of laryngeal carcinomas were examined by means of immune flurescence technique. Overexpression of cyclin D1 was found in 9 of 16 laryngeal carcinomas (37%). There was no statistical correlation between overexpression of cyclin D1 and TNM staging, differentiation grading (P > 0.05). Normal tissue adjacent to tumors lacked any detectable cyclin D1 expression or rare scattered positive cells. It was likely that cyclin D1 overexpression wasn't an early event in processes of tumorigenesis and tumor progression. Follow-up investigation demonstrated that tumors recurred in 4 of 9 primary tumors overexpressing cyclin D1. But only 1 of 16 that expressed cyclin D1-negative. There was statistical significance between them, so overexpression of cyclin D1 could serve as a new prognostic marker.

Cyclin D1↗
PubMed1998

Methylation of p16 gene in hematological malignancies.

OBJECTIVE: To investigate the incidence of p16 gene methylation in hematological malignancies, and the relations between p16 gene methylation and the prognosis of hematological malignancies. METHODS: Fifty-five patients were studied by restriction enzyme polymerase chain reaction (PCR) to detect p16 gene methylation. RESULTS: p16 gene methylation was detected in 6 of 55 patients (10.9%), who were 1 patient with M2a, 1 patient with M5a, 2 patients with chronic myelogenous leukemia (CML) in blast crisis, 1 patient with progressing multiple myeloma (MM), 1 with non-Hodgkin's lymphoma (NHL) accompanied by B-ALL, respectively. p16 gene methylation correlates with adverse prognostic features. The patients with p16 gene methylation had poor response to therapy, and died shortly after p16 gene methylation was detected. CONCLUSION: The methylation of p16 gene plays an important role in the pathogenesis and the development of some hematological malignancies. The patients with p16 gene methylation have poor prognosis. The detection of p16 gene is a useful tool for evaluating prognosis of hematological malignancies.

DNA Methylation↗
PubMed1998

[Detection of mycobacterium tuberculosis by AmpliSensor-PCR technique and its clinical application].

OBJECTIVE: To explore the value of Amplisensor-PCR method in diagnosis of tuberculosis. METHOD: The samples from 784 patients with tuberculosis, 160 patients with lung cancer were detected by using AmpliSensor-PCR, PCR, smear and culture methods, and the results were compared. RESULT: The sensitivity of AmpliSensor-PCR technique was obviously higher than that of smear and culture (P < 0.01). The specificity of AmpliSensor-PCR method was higher than that of PCR method. CONCLUSION: Amplisensor-PCR method can be determined to detect the lower limit by standard curve, through which the original amount of target-DNA in samples can be calculated. AmpliSensor-PCR method shows higher specificity and sensitivity. It is of clinical value in diagnosis of pulmonary tuberculosis and particularly of extrapulmonary tuberculosis.

DNA, Bacterial↗