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Biomedical subjects

T Y Liu

Publications and source records attributed to T Y Liu.

At least 73 records · Page 4Linked to original sources
PubMed1995

Mechanistic study of the inhibition of aflatoxin b1-induced hepatotoxicity by dimethyl 4,4'-dimethoxy-5,6,5',6'-dimethylenedioxy biphenyl-2, 2'-dicarboxylate.

The mechanism of DDB (dimethyl 4,4'-dimethoxy-5,6,5',6'-dimethylenedioxy biphenyl-2,2'-dicarboxylate) prevention of aflatoxin B1 (AFB1)-induced hepatotoxicity in rats has been investigated. Pretreatment of DDB (200 mg/kg) daily for 4 days significantly suppressed (P < 0.05) the AFB1-induced hepatic damage as evidenced by the increase of serum marker enzymes. DDB induced rat hepatic cytochrome P450IA1, IIB1 and glutathione S-transferase activities. The hepatic microsomes derived from DDB treated rats increased the mutation frequency of AFB1 and enhanced the binding of AFB1 to DNA. However, the hepatic S9 fraction from DDB treated rats showed a protective effect against AFB1-induced damage. It is concluded that the protective effect of DDB against AFB1-induced damage might be mediated by the induced glutathione S-transferase activity and not from the accelerated hepatic cytochrome P450 detoxification pathway of AFB1 which was previously believed.

Aflatoxin B1↗
PubMed1995

Establishment of in vivo hepatoma models in rat and mouse from rodent hepatoma cell lines.

BACKGROUND: Hepatoma is one of the most common cancers in Southeast Asia and African countries. In Taiwan, it is the leading cause of death in male cancer patients. In order to examine the effect of various factors on the growth of hepatoma, in vivo hepatoma models such as carcinogen-induced hepatoma and subcutaneous implantation of hepatoma in nude mice have been used. However, there are disadvantages in these models. METHODS: Rats and mice were anesthetized by ketamine or ether, respectively. After a midline incision was made, N1S1 rat hepatoma cells were injected intrasplenically to partially hepatectomized or sham-operated rats, while BALB/c mice received intrasplenic injection of ML-2 and ML-3 mouse hepatoma cells. For direct tumor implantation, a 1mm3 N1S1 tumor piece was implanted in liver of Sprague-Dawley (SD) rat using a trocar. Animals were sacrificed at specific times after tumor implantation. Tumor incidence and the number of tumor nodules on the liver surface were recorded. Tumor samples were fixed and embedded for histological examination. RESULTS: After intrasplenic implantation of ML-2 cells, no tumor was observed on the liver in any of the 10 mice 40 days later. In comparison, rapid growth of hepatic ML-3 tumors was observed in all animals. Rat hepatoma cells RH-35, McA-RH7777 and McA-RH8994 cells did not form tumors in SD rats. The tumorigenicity of N1S1 cells in SD rats was dose-dependent on implanted tumor cells. In addition, hepatic N1S1 tumors could be obtained within a few weeks by homograft. CONCLUSIONS: We have successfully established in vivo hepatoma models in both the rat and the mouse. The murine ML-3 cells generated hepatoma in syngeneic BALB/c mice while the tumorigenicity of N1S1 cells in partially hepatectomized SD rats was dose-dependent on implanted tumor cells. These in vivo rodent models will be valuable tools for future studies of hepatoma.

Animals↗
PubMed1995

Carbachol but not bradykinin blocks the enkephalin-induced calcium transient in human neuroblastoma SK-N-SH cells.

Carbachol stimulated significantly higher increase in inositol 1,4,5-trisphosphate (IP3) generation than did leucine-enkephalin (leu-EK) and bradykinin in SK-N-SH cells. When leu-EK was concomitantly added with carbachol, an additive effect was observed in IP3 generation. However, the rise in cytosolic Ca2+ concentration ([Ca2+]i) reached the same level as that induced by carbachol alone. On the other hand, additive effects were observed in both [Ca2+]i rise and IP3 generation when leu-EK was simultaneously added with bradykinin. Furthermore, cells lost their [Ca2+]i response to leu-EK if carbachol was first added to induce a [Ca2+]i increase whereas the response was unchanged if leu-EK was added after addition of bradykinin. Our results suggest that a shared intracellular Ca2+ pool is sensitive to the opioid, bradykinin and muscarinic receptor agonists; however, a specific phospholipase C might be responsible for each receptor activation.

Bradykinin↗
PubMed1994

A phospholipase A2 inhibitor from the plasma of the South American rattlesnake (Crotalus durissus terrificus). Protein structure, genomic structure, and mechanism of action.

The lethal toxicity of the South American rattlesnake (Crotalus durissus terrificus) venom can be attributed mainly to the presence of a pre-synaptic neurotoxin, crotoxin, with phospholipase A2 activity. Crotoxin is a heterodimer of an acidic protein (CA) and a basic phospholipase A2 (CB). An anti-toxic protein of subunit molecular mass 23.6 kDa that neutralizes both lethal and PLA2 activity of crotalid venom and crotoxin has been previously purified from the plasma of this snake (Fortes-Dias, C., Fonseca, B. C. B., Kochva, E., and Diniz, C. R. (1991) Toxicon 29, 997-1008). The protein has been named CNF for Crotalus neutralizing factor. In the present study, we have shown that CNF exists as an oligomeric aggregate of (CNF)n, where n = 6-8, and when it interacts with crotoxin, it replaces the acidic protein CA of crotoxin to form a stable near stoichiometric complex of CNF.CB. The CNF.CB complex no longer exhibits PLA2 activity and is inert in vivo. Thus, the exchange reaction between CA.CB of crotoxin and CNF to form CNF.CB and free CA is reminiscent of the interaction of crotoxin with its target receptor at the neuromuscular transmission site in the presynaptic cells. A cDNA encoding CNF has been isolated from a liver cDNA library using an appropriate nucleotide probe. The nucleotide sequence codes for a 19-residue signal peptide, followed by a 181-residue protein of which 16 are half-cystines. Calculated molecular mass is 20.06 kDa, and there is a putative N-linked carbohydrate site at Asn157.

Amino Acid Sequence↗
PubMed1994

C-reactive proteins, limunectin, lipopolysaccharide-binding protein, and coagulin. Molecules with lectin and agglutinin activities from Limulus polyphemus.

In 1964, Levin and Bang discovered that gram-negative bacterial endotoxin could rapidly induce gelation of Limulus amebocyte lysate. This observation has led to the development of the most sensitive and specific method for the detection of bacterial endotoxin in pharmaceuticals and drugs intended for human use. Over 10 years ago, Bang injected endotoxin into young horseshoe crabs and observed a time and dose-dependent coagulation of the whole hemolymph. Limunectin, LEBP-PI, and Limulus CRP are found together with coagulin as part of the hemolymph clot at the time of endotoxin-induced exocytosis of amebocytes. In this manner, these molecules with agglutinin/lectin activities could work in concert to assist in the recognition and eventual removal of invading microorganisms from the circulating system. Although the mechanism of endotoxin-induced clot formation is to a large extent understood, the mechanism of clot dissolution and removal in the Limulus hemolymph remains to be clarified.

Acute-Phase Proteins↗
PubMed1994

Bacterial mutagenicity, metabolism, and DNA adduct formation by binary mixtures of benzo[a]pyrene and 1-nitropyrene.

Air pollutants are a complex mixture containing polycyclic organic compounds. Among these are 1-NP and B[a]P, which are important contributors to the mutagenicity of diesel exhaust and airborne particulate matters. To investigate the interaction of a complex mixture of airborne mutagens, the mutagenicity of 1-NP was examined with S. typhimurium TA98 and TA98NR in the presence and absence of B[aP. B[a]P exhibited a more antagonistic effect on the mutagenicity of 1-NP in strain TA98 than in strain TA98NR. Also studied were (1) the inhibitory effects of B[a]P on the nitroreductive metabolism of 1-NP and (2) DNA adduct formation by 1-NP. Nitroreductase was associated with the metabolism of 1-NP, and was reduced in a dose-dependent manner in a binary mixture of 1-NP and B[a]P. HPLC analysis showed that the amounts of 1-AP and NAAP, the metabolites of 1-NP, were significantly decreased by the addition of B[a]P in mixtures. The results indicate that the antagonistic effect of B[a]P on the mutagenicity of 1-NP is mediated through altering its nitroreductive metabolism.

Air Pollutants↗
PubMed1994

Flowcytometric analysis of the effect of berberine on the expression of glucocorticoid receptors in human hepatoma HepG2 cells.

Berberine is an alkaloid found in many plants, including the Coptis chinensis and Arcangelisia flava. Berberine has been reported to have cytostatic effect on tumor growth. Previously, we have found that the level of glucocorticoid receptors (GR) was significantly higher in hepatoma than in adjacent liver tissues. Using human HepG2 hepatoma cells, we have found that GR were expressed not only in G0-G1 phases, but also in S and G2+M phases. The objective of the present study was to examine the effect of berberine on the expression of GR and its relation to cell cycle progression of HepG2 cells. Continuous exposure of HepG2 cells to various concentrations (1-50 microM) of berberine resulted in growth inhibition in a dose dependent manner. The viability of berberine-treated HepG2 cells was greater than 90% in all treatment groups. Flowcytometric analysis of berberine-treated HepG2 cells showed that the S phase fraction was significantly reduced. GR levels were higher in berberine-treated HepG2 cells than in vehicle (DMSO)-treated cells. In addition, the secretion of alpha-fetoprotein by HepG2 cells was inhibited by berberine. Finally, the berberine induced cell growth arrest was partially reversible in HepG2 cells.

Analysis of Variance↗
PubMed1993

Aromatic DNA adducts in brain tumors by 32P-postlabeling analysis.

DNA from human brain tumor samples was analysed by the 32P-postlabeling technique for the presence of aromatic DNA adducts. Thirteen out of 16 samples showed low levels of adducts at 0.14-3.53 adducts per 10(9) nucleotides. Inter-individual variations in the patterns of these aromatic adducts were observed. On the other hand, none of 5 brain samples from epilepsy patients revealed any evidence of such adducts. The data demonstrated the presence of low level, large molecule aromatic DNA adducts in malignant brain tissues and these adducts may either result from environmental exposure to an undetermined genotoxic agent or from the aging process.

Adenoma↗
PubMed1993

Isolation and characterization of C-reactive protein (CRP) cDNA and genomic DNA from Xenopus laevis. A species representing an intermediate stage in CRP evolution.

C-reactive protein (CRP) is a prototypic acute phase protein in human and rabbit. Although it is structurally and functionally conserved from invertebrate to human, there are species-specific differences in patterns of expression and putative function. To further investigate the biological significance, regulation, and evolution of CRP, we isolated Xenopus CRP and subsequently derived and sequenced corresponding cDNA and the genomic clones. The structure and expression of Xenopus CRP were also compared to those of the other CRPs. Analyses of the amino acid sequence and the nucleotide sequence reveal that the mature Xenopus CRP is a 222-amino acid protein preceded by a 16-residue signal peptide. During development, Xenopus CRP is expressed, only when the liver appears, and therefore is not likely to play a role in early embryonic development. Compared to other species, Xenopus CRP is present at an intermediate low level of < 1 microgram/ml in the normal serum. Unlike human and rabbit CRP, Xenopus CRP is not induced by turpentine or heatshock treatment. The heatshock consensus sequence (Woo, P., Korenberg, J. R., and Whitehead, A. S. (1985) J. Biol. Chem. 265, 4136-4142) are not present in the Xenopus CRP gene. It is suggested that Xenopus CRP represents a transitional period in CRP evolution when host defenses switched from primitive innate immunity to a much more complex immune system. The constitutive functions of CRP gradually became less essential as the result of the development of a complex immune system.

Amino Acid Sequence↗
PubMed1993

Differential sensitivity of human hepatoma cell line and primary rat hepatocyte culture to benzo(a)pyrene-induced unscheduled DNA synthesis and adduct formation.

We studied the genotoxic potential of a carcinogen in the human hepatoma cell line, HepG2, and in primary rat hepatocyte culture. HepG2 is a well differentiated human hepatoblastoma cell line with biotransforming capacity. Rat hepatocytes were obtained by the standard two-step in situ perfusion technique. Following benzo(a)pyrene treatment, both HepG2 and primary rat hepatocyte culture showed unscheduled DNA synthesis with different sensitivity. In 32P-postlabelling analysis, the chromatogram revealed quantitative and qualitative differences between HepG2 and primary rat hepatocyte cultures when treated with 10 microM benzo(a)pyrene for 18 hr. The results have demonstrated that the HepG2 cell line may be used in addition to primary rat hepatocytes in risk assessment for detection of environmental carcinogens.

Animals↗
PubMed1993

Effect of an extract from Phyllanthus amarus on hepatitis B surface antigen gene expression in human hepatoma cells.

It has been suggested that Phyllanthus amarus may be helpful in the treatment of hepatitis B virus infection. We studied the effect of an aqueous extract of P. amarus on the cultured hepatoma cell line HepA2. This cell line had been transfected with tandemly arranged HBV DNA and continued to synthesize and secrete both HBsAg and HBeAg. Extract of P. amarus reversibly inhibited cellular proliferation and suppressed HBsAg production but not HBeAg production in HepA2 cells. We also found that P. amarus suppressed HBsAg gene expression at mRNA level in a time-dependent manner, and selectively abolished the HBsAg gene promoter driven CAT activity. Our results demonstrate that P. amarus contains some active components which can suppress the HBsAg gene expression in human hepatoma cells. Such suppression may contribute the antiviral activity of P. amarus in vivo.

Animals↗
PubMed1993

Agglutination activity of Limulus polyphemus coagulogen following limited proteolysis.

1. A 14 kDa protein with cell agglutination properties has been purified from endotoxin-activated L. polyphemus amebocyte lysate. Amino terminal sequence analysis indicates that this protein corresponds to a proteolytically cleaved product (coagulin) of coagulogen. 2. Similar cell agglutination activity can be generated, in vitro, by proteolytic cleavage of the coagulogen with either trypsin, endogenous protease or an alpha 2M/enzyme complex isolated from amebocytes. 3. Studies with [125I]-labeled coagulogen showed that only coagulin, not the intact coagulogen, binds to rabbit erythrocytes and formalin-fixed amebocytes. 4. The cell agglutination activity of coagulin towards erythrocytes was not inhibited by various sugars tested, and was not Ca(2+)-dependent. 5. These findings suggest that coagulogen and coagulin are reminiscent of their mammalian counterparts, fibrinogen and fibrin, in their clotting and relative adhesive properties.

Amino Acid Sequence↗
PubMed1993

Analysis of glucocorticoid receptors in human hepatocellular carcinoma and HepG2 cells.

Hepatocellular carcinoma is the leading cause of male cancer death in Taiwan. We have found that the level of glucocorticoid receptor in hepatocellular carcinoma is significantly higher than that in the peritumoral tissue. In this study, we used a rat liver glucocorticoid receptor complementary DNA probe to examine the expression of glucocorticoid receptor gene in 15 paired samples of hepatocellular carcinoma and their peritumoral tissues. No differences in genomic DNA patterns of the glucocorticoid receptor gene were found between the tumor and peritumoral tissues. The amount of glucocorticoid receptor was found to be significantly higher in hepatoma samples than in peritumoral liver samples. The levels of glucocorticoid receptor messenger RNAs were increased in most tumors compared with their peritumoral samples. To examine the function of glucocorticoid receptors in hepatoma, we examined the expression of glucocorticoid receptor and its relation to cell-cycle progression in human HepG2 cells. Using specific monoclonal antibodies and flow cytometric study, we found glucocorticoid receptor to be expressed constitutively in all cell-cycle phases. In addition, hydrocortisone treatment of HepG2 cells resulted in increased expression of glucocorticoid receptors and increased secretion of alpha-fetoprotein. RU-486, a glucocorticoid antagonist, blocked the hydrocortisone effect, indicating that glucocorticoid receptors are functional in HepG2 cells. Taken together, our data suggest that glucocorticoids and their receptors play an important role in the growth of hepatoma.

Adult↗
PubMed1992

The cis-acting 3'-element of rubella virus RNA has DNA promoter activity.

The 3'-terminal region of the rubella virus (RV) positive-strand RNA, referred to here as the cis-acting element (CAE), is implicated in the initiation of negative-strand RNA synthesis. Sequence analysis of the 3'-CAE shows that there is a putative TATA box which is surrounded by G + C-rich sequences. To determine whether this element, in a DNA form, has the capability to initiate transcription, a 3'-end 165-bp NarI-EcoRI fragment from the RV cDNA was cloned upstream from a cat reporter gene. The level of CAT activity was dependent on the presence of the 3'-CAE and the SV40 enhancer. Primer extension analysis of the CAT mRNA showed that the transcription start point is in the RV 3'-CAE, 34 bp downstream from the putative TATA box. DNA-gel shift analysis revealed that three nucleoprotein-specific complexes were formed with the 3'-CAE and the binding sites for these proteins were between bp -64 to -108. The possible promoter function of the RV 3'-CAE is discussed in context to RV persistence.

Base Sequence↗
PubMed1992

Debrisoquine metabolism in Chinese patients with Alzheimer's and Parkinson's diseases.

We determined the oxidative phenotype and metabolic ratio of debrisoquine in 96 Chinese patients with Alzheimer's disease (n = 12), Parkinson's disease (n = 55), and using patients with stroke and cervical spondylosis as controls (n = 29). We did not find any difference in debrisoquine metabolic phenotype among Parkinson's disease, Alzheimer's disease, and control patients as judged by chi-square analysis. In addition, the metabolic ratio of all our patients was less than 12.6. The result suggested that Chinese patients with Parkinson's disease and Alzheimer's disease metabolize debrisoquine at a velocity not different from that of their Western counterparts even though the frequency distribution of debrisoquine metabolism phenotyping in these two populations is quite different.

Aged↗
PubMed1992

Effect of sodium butyrate on glucocorticoid-sensitive and -resistant P1798 lymphosarcoma.

This study aims to examine the effect of sodium butyrate on the viability and the level of glucocorticoid receptors and cells cycle progression in glucocorticoid-sensitive and -resistant P1798 cells. Our results indicated that low levels of sodium butyrate had no effect on either the viability or the receptor level. However, high-level (5 mM) sodium butyrate appeared to reduce cell viability as well as the glucocorticoid receptor level. On the other hand, sodium butyrate inhibited cell cycle progression in a dose-dependent manner. This response was similar in both the glucocorticoid-sensitive and -resistant P1798 cells. Results from this study suggested that the sodium butyrate induced effect may be cell cycle related.

Butyrates↗
PubMed1991

Purification and characterization of an endotoxin-binding protein with protease inhibitory activity from Limulus amebocytes.

Using a lipopolysaccharide affinity column and ion exchange chromatography, a 12-kDa protein has been purified from Limulus amebocytes. In solid phase binding assays, the radiolabeled protein binds specifically to lipopolysaccharide (LPS) with a Kd value on the order of 10(-7) M. A cDNA coding for this protein has been isolated and sequenced. The amino acid sequence deduced from the cDNA indicates that this protein shares no sequence homology with LPS-binding proteins isolated from different species of vertebrates (Schumann, R. R., Leong, S. R., Flaggs, G. W., Gray, P. W., Wright, S. D., Mathison, J. C., Tobias, P. S., and Ulevitch, R. J. (1990) Science 249, 1429-1431) and invertebrates (Aketagawa, J., Miyata, T., Ohtsubo, S., Nakamura, T., Morita, T., Hayashida, H., Miyata, T., Iwanaga, S., Takao, T., and Shimonishi, Y. (1986) J. Biol. Chem. 261, 7357-7365). The binding to LPS can be displaced by the unlabeled 12-kDa protein, polymyxin B, lipid A, and to a lesser extent by D-glucosamine. In whole cell binding assays, the 12-kDa protein has also been shown to bind to Escherichia coli. Using both [14C]casein and a synthetic substrate, the protein has been shown to inhibit the proteolytic activity of trypsin, with an IC50 of approximately 10(-7) M. In the presence of LPS, the antitryptic acitivity of the Limulus endotoxin-binding protein-protease inhibitor remains unaffected. The protein is a major component of the cytoplasmic proteins (1%). Immunocytochemical analysis reveals that this protein exists in the secretory granules of the amebocytes where enzymes and substrates for the clotting cascade reside. Based on the unusual dual functional properties, the newly isolated protein was named a "Limulus endotoxin-binding protein-protease inhibitor" (LEBP-PI).

Amino Acid Sequence↗