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T Z Liu

Publications and source records attributed to T Z Liu.

At least 19 recordsLinked to original sources
PubMed2001

Homocysteine thiolactone induces apoptotic DNA damage mediated by increased intracellular hydrogen peroxide and caspase 3 activation in HL-60 cells.

The cytotoxicity of homocysteine derivatives on chromosomal damage in somatic cells is not well established. The present study used reactive homocysteine derivative of homocysteine thiolactone (Hcy) to investigate its causal effect on apoptotic DNA injury in human promyeloid HL-60 cells. Our results demonstrated that Hcy induced cell death and features of apoptosis including increased phosphotidylserine exposure on the membrane surface, increased apoptotic cells with hypoploid DNA contents, and internucleosomal DNA fragmentation, all of which occurred in a time- and concentration-dependent manner. Hcy treatment also significantly increased intracellular reactive oxygen species H2O2, which coincided with the elimination of caspase 3 proenzyme levels and increased caspase 3 activity at the time of the appearance of apoptotic DNA fragmentation. Preincubation of Hcy-treated HL-60 cells with catalase completely scavenged intracellular H2O2, thus inhibiting caspase 3 activity and protecting cells from apoptotic DNA damage. In contrast, superoxide dismutase failed to inhibit Hcy-induced DNA damage. Taken together, these results demonstrate that Hcy exerted its genotoxic effects on HL-60 cells through an apoptotic pathway, which is mediated by the activation of caspase 3 activity induced by an increase in intracellular hydrogen peroxide.

Apoptosis↗
PubMed2001

Folate deficiency-induced oxidative stress and apoptosis are mediated via homocysteine-dependent overproduction of hydrogen peroxide and enhanced activation of NF-kappaB in human Hep G2 cells.

Folate coenzymes are critical for de novo synthesis of purine and thymidine, and for interconversion of amino acids. Folate deficiency inhibits cellular proliferation, disturbs cell cycling, causes genetic damage and eventually results in cell death. Previously, we demonstrated that the demise of human hepatoma Hep G2 cells mediated by folate deficiency proceeded via a p53-independent apoptosis, and the perturbation of intracellular calcium homeostasis was also shown to be involved. To further delineate the mechanism associated with this observed phenomenon, Hep G2 cells were cultivated in the control or folate-deficient media (control media lacking folate, glycine, thymidine and hypoxanthine) for 4 weeks. At the end of this cultivation period, we found that TBARS (an index of lipid peroxidation) concentrations in the folate-deficient cells were drastically increased as compared to the control cells (0.04 vs 0.01 nmole/10(6) cells), indicating that a severe oxidative stress of the former cells had occurred. This phenomenon was also shown to coincide with the ability of these folate-deficient cells to elaborate increased amounts of H2O2 as compared to its folate-supplemented cells (2.87 vs 0.98 nmole/10(5) cells/h). Furthermore, the accelerated production of H2O2 by the folate-deficient cells was also closely correlated with the elevated homocysteine concentrations released in the culture medium (15.37 +/- 2.4 vs 3.58 +/- 2.4 micromole/L; P< 0.001). Finally, we demonstrated that folate deficiency was indeed capable of activating a redox-sensitive transcription factor, NF-kappaB, which is crucial in the control of a reactive oxygen species-mediated apoptosis. In summary, we show that folate deficiency-induced apoptosis is proceeded via the enhanced activation of NF-kappaB, which is the resulting form of the homocysteine-mediated overproduction of hydrogen peroxide.

Apoptosis↗
PubMed2001

Rapid and specific detection of hydroxyl radical using an ultraweak chemiluminescence analyzer and a low-level chemiluminescence emitter: application to hydroxyl radical-scavenging ability of aqueous extracts of Food constituents.

With the availability of an ultraweak chemiluminescence analyzer, it is possible to monitor the production of a specific oxygen-derived reactive species, such as hydroxyl radical ((*)OH), whenever a suitable chemiluminescent probe is obtainable. Reported herein is the development of a rapid and specific method for detecting (*)OH production using a specific probe, indoxyl-beta-glucuronide (IBG), a low-level chemiluminescence emitter. Using the Fenton reagent as a source of (*)OH, it was shown that IBG could elicit a very strong intensity of chemiluminescence (CL) (16200 +/- 200 photon counts/s). Conversely, IBG was shown to be insensitive to either superoxide radical or hydrogen peroxide with their CL intensities nearly close to the background values (25 +/- 5 and 180 +/- 20 photon counts/s, respectively). Furthermore, it was also shown that this IBG-based CL production could be effectively quenched by the addition of (*)OH scavengers such as sodium salicylate, dimethyl sulfoxide, and penicillamine to the assay system. Taken together, these data indicate that IBG is a specific CL probe suitable for monitoring the production of (*)OH. This system demonstrated inhibitory activities of various aqueous extracts of food constituents on the CL of hydroxyl radicals generated by Fenton's reagents with the order of scavenging efficiencies being Prunus mume > Cordyceps sinensin > Lilium lancifolium > Astragalus membranceus.

Free Radical Scavengers↗
PubMed2001

Diethylenetriaminopentaacetic acid is unsuitable for long-term preservation of RBCs.

BACKGROUND: The addition of an appropriate metal chelator, such as diethylenetriaminopentaacetic acid (DTPA) to stored blood has been shown to be effective in a short-term (0-12 days) prevention of lipid peroxidation of stored RBCS: However, its long-term effectiveness has not been carefully evaluated. STUDY DESIGN AND METHODS: Blood was preserved in simulated blood bank conditions with or without the addition of DTPA for 4 weeks. Aliquots of stored blood were taken weekly from the storage bag and the deformability profile was determined using a custom-built laser viscodiffractometer. Malondialdehyde (MDA), an index of lipid peroxidation, and the extent of vesiculation of the stored blood were quantified concurrently. RESULTS: It was found that MDA values for DTPA-supplemented blood at the end of a 28-day storage period were significantly elevated compared with the DTPA-free counterpart (23.50 +/- 3.2 vs. 16.10 +/- 2.5 microM; p<0.05). In addition, DTPA-supplemented blood was more susceptible to vesiculation than its DTPA-free counterpart (31.26 +/- 4.1 vs. 10.26 +/- 1.5% of acetyl cholinesterase release, p<0.001). These data are also in accordance with the finding of the deformability profile result, indicating that DTPA-supplemented blood exhibits not only a decrease in deformability index, but also a tendency to shift the profile to a lower osmolality compared with that of controls (a dehydration phenomenon). CONCLUSION: Long-term (0-28 days) preservation of human RBCs with DTPA caused a gradual increase in MDA production, a progressive enhancement of the severity of vesiculation, and an alteration in the deformability profile. Free-radical-mediated oxidative damage is likely to be the culprit for this observed phenomenon. In addition, the direct effect of DTPA on RBC structural integrity must be considered.

Blood Preservation↗
PubMed2001

Free radical-triggered hepatic injury of experimental obstructive jaundice of rats involves overproduction of proinflammatory cytokines and enhanced activation of nuclear factor kappaB.

Excessive production of hydroxyl radicals in blood and liver has previously been demonstrated by us in rats with obstructive jaundice induced by common bile duct ligation (CBDL). In this study, we demonstrate overproduction of superoxide radicals in circulating blood of CBDL rats by the lucigenin-amplified chemiluminescence technique. To pinpoint the molecular agents that mediate these processes, we measured circulating proinflammatory cytokines, such as tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta ( IL-1beta), and interleukin-6 (IL-6) in controls and CBDL rats. Concentrations of these cytokines in blood of CBDL rats were markedly elevated when compared to the controls (TNF-alpha: 36.7 +/- 5.0 vs 13.8 +/- 0.5 pg/mL; IL-6: 2,814 +/- 1,740 vs 0 pg/mL; IL-1beta: 11.9 +/- 2.6 vs 0 pg/mL). The overproduction of free radicals triggered by elevated cytokines in CBDL rats was correlated with the activation of NF-kappaB in hepatic tissue. Using the TdT-mediated dUTP nick-end label staining technique, we showed that hepatic tissue sections from CBDL rats had an increase in the apoptotic index (AI). Based on these findings, we propose that the severe hepatic injury in CBDL rats is mediated by a cycle that involves the activation of NF-kappaB by combined action of proinflammatory cytokines and reactive oxygen species (ROS). NF-KB, in turn, initiates the transcription of cytokine genes (eg, IL-6, IL-8, TNF-alpha), which triggers hepatic injury, at least in part, by a free radical-mediated apoptotic mechanism. Elevated ROS may be as a positive-feedback signal that triggers NF-KB reactivation; the severe hepatic injury of CBDL rats may result from perpetuation of this vicious cycle.

Animals↗
PubMed2000

Differentiation status modulates transcription factor NF-kappaB activity in unstimulated human hepatocellular carcinoma cell lines.

We report herein a novel finding that under an unstimulated condition, a group of four human hepatocellular carcinoma (HCC) cell lines with varying degrees of differentiation, can spontaneously activate NF-KB. The propensity of activation coincided inversely with the differentiation status, with order being SK-Hep-1 > J5 > Hep3B > HepG2. Further studies indicate that this pattern of activation correlates excellently with the descending order of intracellular GSH/GSSG ratios as well as with the ascending order in the ability of these cells to generate hydrogen peroxide. Taken together, our data suggest that differentiation status may play a pivotal role in modulating intracellular thiol redox status and the extent of catalase expression, which may be crucial in the control of NF-kappaB activity in these HCC cells.

Carcinoma, Hepatocellular↗
PubMed2000

cDNA cloning of pig testicular lactate dehydrogenase-C, thermal stability of the expressed enzyme, and polymorphism among strains.

Pig testicular lactate dehydrogenase-C (LDHC) cDNA was cloned and sequenced. The deduced sequence of 332 amino acids from pig LDHC shows 73% and 67% identity with that of pig LDHA (muscle) and LDHB (heart) respectively, whereas pig LDHA and LDHB isozymes shows 74% sequence identity. Pig and mouse LDHC cDNAs were subcloned into bacterial expression vector, and the expressed pig LDHC isozyme was shown to be as thermally stable as mouse LDHC isozyme. Pig genomic DNAs from Chinese Meishan, English Yorkshire, Danish Landrace and American Duroc were shown to exhibit polymorphic sites for restriction enzymes EcoRI, BamHI and PstI.

Animals↗
PubMed2000

Antimutagenicity of ethanol extracts of bee glue against environmental mutagens.

The antimutagenicity of ethanol extracts of bee glue (propolis) (EEBG) was evaluated, using Salmonella typhimurium strain TA98 as a test model, against two direct mutagens, 4-nitro-O-phenylenediamine (4-NO) and 1-nitropyrene (1-NP), and two indirect mutagens, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and benzo[a]pyrene (B[a]P) with S9 mix. EEBG was shown to suppress the mutagenicity of these compounds in a dose-dependent fashion. To delineate the mechanism of action of the antimutagenic effects of EEBG on the two indirect mutagens IQ and B[a]P, two possible points of blocking were considered: (1) cytochrome P-450 activity (route 1) and (2) interaction with microsome-generated proximate mutagens to generate an inactive complex (route 2). Our results clearly demonstrated, at a very low dose, remarkable suppression of the mutagenicity of both compounds by inhibiting either route 1 or route 2 pathway. Further studies indicated that EEBG was capable of inhibiting both the activities of hepatic cytochrome P-450 IA1-linked 7-ethoxyresorufin-O-deethylase (EROD) and IA 2-linked 7-ethoxycoumarin-O-deethylase (ECD) in a similar dose-dependent manner. Taken together, we demonstrated that EEBG was a good inhibitor for mutagenicity of direct mutagens, 1-NP and 4-NO, as well as for the indirect mutagens IQ and B[a]P in the presence of S9 mix via inactivation of microsomal enzyme activities (e.g. EROD and ECD) or antagonizing metabolic generation of the proximate mutagens of IQ and B[a]P.

7-Alkoxycoumarin O-Dealkylase↗
PubMed2000

[Enhancement of fermentative glycerol yield with heat shock treatment].

A heat shock treatment was studied in glycerol fermentation of osmotolerant yeast Candida krusei. The experiment results showed that the optimal temperature and duration time for heat shock is 45 degrees C and 30 min respectively, and the optimal start time of the treatment is at the mid term in exponential growth stage. With such treatment, glycerol yield was enhanced greatly, while no significant effects on both cell growth and glucose consumption were observed.

Candida↗
PubMed1999

Folate deficiency induces a cell cycle-specific apoptosis in HepG2 cells.

The human hepatoma HepG2 cell line was chosen as a representative of solid tissue-derived cell systems in which folate metabolism and apoptosis induction have not been thoroughly investigated. HepG2 cells were cultivated in the control or folate-deficient media (control media lacking of folate, glycine, thymidine and hypoxanthine) for 4 wk. This resulted in a decrease in intracellular folate levels to 32% of the control within 1 wk, which was followed by growth arrest and greater cell death rates. These disturbances of folate deficiency coincided with apoptotic induction, as characteristically shown by nucleosomal DNA fragmentation of 180-200 base pair multimers, nuclear chromatin condensation and positive terminal transferase-mediated dUTP nick end labeling assay. Apoptosis coincided with an accumulation of cells in S-phase, a subsequent G2/M phase block and a significant increase in mean protein content as evaluated by flow cytometric analyses employing a double-staining method. The growth and cell cycle arrest under folate-deficient conditions was independent of a change of p53 expression as measured by an enzyme-linked immunosorbent assay. Supplementation of 2 micromol/L folate normalized cell cycles and diminished DNA fragmentation. Taken together, these data indicate that HepG2 cells cultivated in folate-deficient medium have a low folate concentration, decreased growth and viability, and increased apoptotic propensity. This occurrence of apoptosis was associated with a cell cycle-specific mechanism and independent of p53-mediated pathway.

Apoptosis↗
PubMed1998

Evidence for accelerated generation of hydroxyl radicals in experimental obstructive jaundice of rats.

We present evidence herein of the accelerated generation of hydroxyl radical (.OH) in the plasma and the liver tissue of common bile duct ligated (CBDL) rats, a model for experimental obstructive jaundice. .OH production in the plasma was monitored in vivo by the identification of dihydroxybenzoates in plasma [2,3-dihydroxybenzoate (2,3-DHB) and 2,5-dihydroxybenzoate (2,5-DHB)] using high performance liquid chromatography (HPLC). The average concentrations of 2,3-DHB and 2,5-DHB produced in the plasma of the controls were 33+/-3 microM and 232+/-34 microM (n = 15), respectively, whereas their respective concentrations increased to 149+/-28 microM and 604+/-88 microM in the CBDL rats (n = 19). Furthermore, we also observed a time-dependent decreasing trend of 2,3-DHB and 2,5-DHB production after surgical removal of the ligation of the experimental animals. In addition, the generation of .OH in the liver tissue was studied by using dimethyl sulfoxide (DMSO) as a molecular probe and measuring the amount of methanesulfinic acid (MSA), the product of the trapping reaction. The net production of MSA in the liver tissue of the control rats was 1.22+/-0.05 O.D. unit/g protein (n = 5), whereas its respective concentration of MSA in the liver tissue of CBDL rats increased to 2.05+/-0.15 O.D. unit/g protein (n = 5). In addition, we showed that CBDL rats receiving a pretreatment of mannitol, an .OH scavenger, resulted in the decreased production of MSA. Electron micrographic study indicated that the most prominent change observed in CBDL rats was the alteration of mitochondria, which were swollen with distorted cristae. Meanwhile, the bile canaliculi were moderately more dilated than that of the controls, and an increased neutrophil peripheral blood count was found in CBDL rats when compared to the controls. Taken together, our data suggest that accelerated generation of .OH in the CBDL rats is obvious and may play a key role in the pathogenesis of liver damage associated with obstructive jaundice.

Animals↗
PubMed1997

Indium as internal standard in square wave anodic stripping analysis of lead in blood with microelectrode arrays.

The toxic effects of lead on humans, especially children have been well documented. ASV has been an important technique in the analysis of lead in blood of humans. This research has demonstrated that indium(III) can be used as an internal standard in the analysis of lead in blood samples with mercury film microelectrode arrays. Indium is a good choice because of a low endogenous blood concentration and because baseline separation of anodic stripping peaks among Cd, In, and Pb can be achieved under appropriate conditions. The concentration of sodium bromide strongly influences the resolution of these metals and the sensitivity of ASV to In(III) in solution. Square wave anodic stripping voltammetry together with screen-printed microelectrode arrays showed that the ratio of the anodic stripping peak currents of Pb and In varies linearly with the concentration of Pb in blood samples ranging from 1.2 to 30.0 micrograms/dL. The average intraassay precision (rsd) was 6.7%.

Electrochemistry↗
PubMed1997

Palladium or platinum exacerbates hydroxyl radical mediated DNA damage.

Strand breakage of supercoiled pBR322 DNA by a Fenton system is increased in the presence of palladium or platinum (Pt) ions. Neither Pd nor Pt ions can substitute for iron in the Fenton system. We have obtained several lines of evidence that Pd and Pt ions in the presence of a Fenton system can augment the production of OH., as monitored by a spectrophotometric method quantifying hydroxylated salicylate or by a fluorometric method quantifying catechol production. Furthermore, the promoting effect of both metal ions on OH. production was substantiated by the identification of multiple hydroxylated products of salicylate [2,3-dihydroxybenzoate (A), 2,5-dihydroxybenzoate (B), and catechol (C)] using HPLC. The concentrations of A, B, and C produced in the control were 4.5, 8.0, and 2.0 microM, respectively; whereas, their respective concentrations increased to 23.6, 42.0 and 10.0 microM with the addition of Pd ions. The observed phenomenon was further confirmed by the identification of HO-DMPO spin adducts using ESR spectroscopy. Taken together, our data suggest that the mechanism of Pd or Pt ion-mediated exacerbation of DNA damage by a Fenton system is due to the promotion of OH. production by these metal ions.

DNA Damage↗
PubMed1997

An adaptive training method for optimal interpolative neural nets.

In contrast to conventional multilayered feedforward networks which are typically trained by iterative gradient search methods, an optimal interpolative (OI) net can be trained by a noniterative least squares algorithm called RLS-OI. The basic idea of RLS-OI is to use a subset of the training set, whose inputs are called subprototypes, to constrain the OI net solution. A subset of these subprototypes, called prototypes, is then chosen as the parameter vectors of the activation functions of the OI net to satisfy the subprototype constraints in the least squares (LS) sense. By dynamically increasing the numbers of subprototypes and prototypes, RLS-OI evolves the OI net from scratch to the extent sufficient to solve a given classification problem. To improve the performance of RLS-OI, this paper addresses two important problems in OI net training: the selection of the subprototypes and the selection of the prototypes. By choosing subprototypes from poorly classified regions, this paper proposes a new subprototype selection method which is adaptive to the changing classification performance of the growing OI net. This paper also proposes a new prototype selection criterion to reduce the complexity of the OI net. For the same training accuracy, simulation results demonstrate that the proposed approach produces smaller OI net than the RLS-OI algorithm. Experimental results also show that the proposed approach is less sensitive to the variation of the training set than RLS-OI.

Algorithms↗
PubMed1997

Hemin-induced membrane sulfhydryl oxidation: possible involvement of thiyl radicals.

Sublytic levels (microM) of hemin destabilized RBC membrane as indicated by ghost fragmentation pattern using a laser viscodiffractometer. Furthermore, electron microscopic study shows that 5 microM of hemin induced echinocytic transformation whereas higher hemin concentration (40 microM) induced spherocytic transformation. In addition, hemin oxidized sulfhydryl groups in a dose dependent fashion and Electron Spin Resonance study suggests that such oxidation may involve a thiyl radical. Moreover, sulfhydryl compounds enhanced hemin-induced lipid peroxidation. Desferroxamine could prevent hemin-induced sulfhydryl oxidation as well as hemin-induced decrease in membrane stability. In contrast, vitamin E could effectively prevent hemin-induced lipid peroxidation but could not prevent hemin-mediated membrane destabilization.

Deferoxamine↗
PubMed1997

Fibroblasts derived from tissue explants of dilantin-induced gingival hyperplasia and idiopathic gingival fibromatosis show distinct disparity in proliferative responsiveness to epidermal growth factor.

Human gingival fibroblasts derived from tissue explants of two patients with dilantin-induced gingival hyperplasia (DGH) and one patient with idiopathic gingival fibromatosis (GF) were studied with respect to the effect of epidermal growth factor (EGF) on the proliferative characteristics of these cells. Immunohistochemical staining showed that there were more EGF receptor-positive cells among DGH fibroblasts than among either normal gingival fibroblasts (NG) or GF cells. Furthermore, EGF binding studies showed that, in spite of there being no disparity in binding affinity among all these cells, DGH fibroblasts possessed approximately two-fold more EGF receptors than either NG or GF cells. In addition, the growth-promoting effect of exogenously added EGF was concentration-dependent in DGH fibroblasts but was not in either NG or GF cells. All of the above findings clearly demonstrate that DGH and GF fibroblasts exhibit distinct disparity in proliferative responsiveness to EGF and suggest that different mechanisms may be involved in the pathogenesis of these two forms of gingival hyperplasia. These observations also suggest a possible therapeutic approach for blocking EGF-induced cell proliferation in DGH.

Anticonvulsants↗
PubMed1996

Enhanced vesiculation exacerbates complement-dependent hemolysis in glucose-6-phosphate dehydrogenase deficient red blood cells.

Glucose-6-phosphate dehydrogenase (G6PD) deficient red blood cells (RBCs) are known to be more susceptible to oxidant-induced hemolysis. Erythrocytes from G6PD-deficient individuals are significantly more susceptible to Ca(2+)-induced vesiculation than normal control cells. The enhanced susceptibility of G6PD-deficient RBCs to Ca(2+)-induced vesiculation is not due to ATP depletion. The remnant G6PD-deficient RBCs following vesiculation are more sensitive to complement-mediated hemolysis than control normal RBCs. A strong positive correlation exists between the level of Ca(2+)-induced vesiculation and the extent of complement mediated hemolysis.

Calcium↗