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Biomedical subjects

J K Lin

Publications and source records attributed to J K Lin.

At least 127 records · Page 7Linked to original sources
PubMed1995

p53 gene mutational spectra in hepatocellular carcinomas induced by 2-acetylaminofluorene and N-nitroso-2-acetylaminofluorene in rats.

In this study, the mutation frequencies of the p53 gene in rat hepatocellular carcinomas (HCCs) induced by N-nitroso-2-acetylaminofluorene (NO-AAF) and 2-acetylaminofluorene (AAF) were 19.23% (20 of 104) and 31.1% (33 of 106), respectively. Four noteworthy features of the mutation spectrums of the p53 gene in HCCs induced by both NO-AAF and AAF were observed: (i) There was preferential clustering of mutations at exons 5-8 in both the NO-AAF or AAF groups. (ii) Nearly all the mutations (98%) induced by NO-AAF and AAF were point mutations. (iii) A high frequency of the p53 mutations were transition mutations, and the ratios of transition to transversion in the NO-AAF and the AAF group were 13:6 and 21:12, respectively. Almost all the mutations were G-->A transitions and guanosine was the major target base. (iv) The frequency and base location of p53 mutations were significantly associated with cancer cell differentiation. In poorly differentiated HCCs (58 individual tumor samples), mutations were detected in 24 of 58 samples (41.1%) and clustered mostly in exons 7 and 8 (19 of 24 samples), whereas in well-differentiated HCCs (105 individual tumor samples), the incidence of mutations was low (one of 10 in the AAF group, 17 of 95 in the NO-AAF group), and the mutations were located in exon 5 (11 of 18). The biological significance of these different mutational spectra among p53 genes deserves further investigation.

2-Acetylaminofluorene↗
PubMed1995

Estimation of selected phenols in drinking water with in situ acetylation and study on the DNA damaging properties of polychlorinated phenols.

Gas chromatography/mass spectrometry with selected-ion monitoring (GC/MS-SIM) method were used to analyze 23 selected phenols in natural and drinking waters by an in situ acetylation technique. This method was suitable for determining phenol concentrations at the ng/L level because of less background interference and better recoveries. The application range for all these phenols was from 0.01 or 0.04 to 10 micrograms/L, using a 800 ml water sample. The levels of trace phenols in four Taiwan water treatment plants were in the range of 12-312 ng/L. The polychlorinated phenols, namely 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol, and pentachlorophenol, were evaluated for their ability to induce deoxyribonucleic acid (DNA) damage using a DNA precipitation assay employing mouse embryonic fibroblast cells (C3H10T1/2) with or without a liver microsomal activation system. These agents exhibited a weak positive response when microsomal activation enzymes were present in this assay. When the tetrachlorohydroquinone, a toxic metabolite of pentachlorophenol, was measured by the same method without the activation system, a significant and dose-dependent DNA damage was found. This result indicates that in the evaluation of the carcinogenic potential of these agents, their corresponding metabolites should be taken into consideration. DNA strand breakage caused by these active metabolites may play an important role in the tumorigenetic process of polychlorinated phenols.

3T3 Cells↗
PubMed1995

Oxidative modification of DNA bases in rat liver and lung during chemical carcinogenesis and aging.

The extent of DNA modification in cancerous rat live and lung tissues was investigated and compared to their respective normal tissues. Liver tumors were induced by 2-fluorenylacetamide (2-FAA) or N-nitroso-N-2-fluorenylacetamide (N-NO-2-FAA), and lung tumors were induced by sodium nitrite plus trimethylamine. In the DNA samples isolated from these tissues, two pyrimidine-derived and four purine-derived modified DNA bases were identified and quantified by gas chromatography/mass spectrometry with selected-ion monitoring. These compounds were characterized as 5-hydroxyuracil (5-OHUra), thymine glycol (TG), 4,6-diamino-5-formamidopyrimidine (FapyAde), 2,6-diamino-4-hydroxy-5- formamidopyrimidine (FapyGua), 8-hydroxyadenine (8-OHAde), and 8-hydroxyguanine (8-OHGua). Elevated amounts of modified DNA bases were found in most cancerous tissues when compared to the controls. Chemicals used for tumor induction were responsible for inducing DNA lesions that could be promutagenic in vivo and could lead to various types of mutations. When endogenous oxidative damage to DNA during aging was examined, a roughly 2-fold increase of thymine glycol, 8-OHAde and 8-OHGua was found in aged (12 months) rat liver tissues compared to young tissues (1 month). The same results were also found in lung tissues, except that the amount of thymine glycol exhibited more than a 10-fold increase in aged tissues when compared to young tissues. The association of the modified bases with the processes of aging and carcinogenesis deserves further investigation.

2-Acetylaminofluorene↗
PubMed1995

Assessment of p53 expression in nasopharyngeal carcinoma.

We analyzed the expression of the p53 protein by immunohistochemical methods from 101 patients with nasopharyngeal carcinoma (NPC): 24 with NPC and dysplastic lesions adjacent to carcinoma and 14 with primary and metastatic specimens. Ninety-six of 101 lesions (95%) had detectable p53 protein in the nuclei of tumor cells, indicating that overexpression of the p53 protein might be closely associated with NPC. Among 24 patients who had NPC and dysplastic lesions adjacent to carcinoma, 19 of the dysplastic lesions (79.2%) and 22 of the carcinomas (91.7%) showed positive staining for the p53 protein. In dysplastic epithelia p53 antigenicity was generally in a basal location. The significant association of p53 expression in NPC and dysplastic lesions adjacent to carcinoma (P < .0001, Fisher's exact probability test) suggests that p53 overexpression seems to occur at an early stage in the development of NPC. p53 expression in NPC does not correlate with histological grading, degree of lymphocytic infiltration between tumor cells, clinical stage, sex, or age (P > .05, chi-squared test). A comparison of p53 expression between primary and metastatic NPC was performed in 14 lesions. Although the p53 protein was consistently expressed in primary and metastatic tumor cells, there was no significant difference in p53 expression in both distinct but related lesions (P > .05, paired t-test). Our results suggest that the association of overexpression of the p53 protein in NPC may not be indicative of a mutant type p53 protein.

Adult↗
PubMed1995

The inhibition of DMBA-induced carcinogenesis by neoxanthin in hamster buccal pouch.

Neoxanthin, a major carotenoid pigment of spinach, is found in the Chloroplast membrane and has an unknown function in plants. Neoxanthin inhibited the production of superoxide anions in an artificial xanthine and xanthine oxidase system and depressed DNA synthesis in methylcholanthrene (MCA)-initiated C3H10T1/2 fibroblasts. in two-stage carcinogenesis experiments, neoxanthin at 0.2 micrograms/0.2 ml inhibited the formation of tumors that were induced sequentially by 7,12-dimethylbenz[a]anthracene (DMBA) and 12-O-tetradecanoylphorbol-13-acetate (TPA) in the buccal pouch of Syrian Golden hamsters. To assess the ongoing process of carcinogenesis, the activity of ornithine decarboxylase (ODC), required for cell proliferation, was analyzed. Neoxanthin inhibited the activity of ODC when animals were treated with neoxanthin one hour before the application of TPA in two-stage carcinogenesis. However, neoxanthin did not inhibit ODC activity when animals were treated with neoxanthin one hour before the application of DMBA in two-stage carcinogenesis, and there was no subsequent tumor formation. In a short-term anti-initiation experiment, neoxanthin inhibited the covalent binding of isotope-labeled DMBA to DNA by 53%. These results indicate that neoxanthin inhibits the initiation stage and the promotion stage in two-stage carcinogenesis. This suggests that neoxanthin may act as a potential chemopreventive agent.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1995

Inhibition of tumor promotion in benzo[a]pyrene-initiated CD-1 mouse skin by crocetin.

The effects of topical application of crocetin on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced promotion of skin tumors, hyperplasia, hydrogen peroxide, ornithine decarboxylase (ODC) and inflammation were evaluated in female CD-1 mice. Topical application of crocetin (0.2 or 1.0 mumol) with TPA (15 nmol) twice weekly for 20 weeks to mice previously initiated with benzo[a]pyrene (B[a]P) inhibited the number of TPA-induced tumors per mouse by 69 and 81% respectively. Pre-application of the same amount of crocetin also afforded significant protection against TPA-induced hyperplasia in the ear skin. Topical application of crocetin inhibited tumor promoter-caused induction of epidermal ODC activity by TPA (5 nmol). The topical application of crocetin (0.2 or 1.0 mumol) inhibited TPA-induced edema of mouse ears by 76 and 87% respectively. Pretreatment of mouse skin with various amounts of crocetin caused inhibition of hydrogen peroxide and myeloperoxidase production by TPA. These results indicate that crocetin possesses potential as a cancer chemopreventive agent against tumor promotion.

Animals↗
PubMed1995

A new mutagenicity assay method for frameshift mutagens based on deleting or inserting a guanosine nucleotide in the beta-lactamase gene.

The conventional method of site-directed mutagenesis was used to develop two Salmonella strains, JK-1 and JK-2, for detecting frameshift mutagens. The JK-1 strain was derived from Salmonella typhimurium TA1537 strain transformed by a mutant construct. A guanosine nucleotide was inserted between nucleotide residues 312 and 313 of the beta-lactamase gene. The JK-2 strain was obtained by the same procedure, but a guanosine nucleotide in position 315 of the beta-lactamase gene was deleted. The strains were tested with ten frameshift mutagens and the revertants were selected by ampicillin resistance. Representative mutagens including 2-nitrofluorene (2-NF), 2-acetylaminofluorene (AAF), 9-aminoacridine (9-AA), 2,7-diaminofluorene (2,7-DAF) and 2-methoxy-6-chloro-9-(3-(ethyl-2-chloro-ethyl)-aminopropylamino)acridine (ICR-170) were more potent in the JK-1 strain than the JK-2 strain, and the number of revertant colonies were dose related. Under the same conditions, the ampicillin test was more sensitive than the Ames test. Other types of compounds such as 2-methoxy-6-chloro-9-(2-chloroethylaminopropylamino)acridine (ICR-191), benzo[a]pyrene (BP), 4-nitroquinoline N-oxide (4-NQNO), hycanthone and aflatoxin B1 (AFB1) were not as mutagenic to these new strains. The method is quite promising for studying certain specific frameshift mutagens, but more chemical mutagens should be tested to validate its applicability and reproducibility in general use.

Amino Acid Sequence↗
PubMed1995

HER-2/neu overexpression in Chinese breast cancers: correlation with other prognostic factors.

HER-2/neu oncogene amplification or overexpression has generated considerable interest in predicting the outcome of breast cancer in Caucasians. In the present study, Northern blot analysis was used to investigate 44 primary breast cancers of different stages in Chinese patients. Nineteen tumors (43.2%) demonstrated more than two-fold expression of HER-2/neu mRNA over adjacent non-tumor breast tissue. The incidence of HER-2/neu overexpression in this series is higher than those reported in Caucasian studies. Ethnic variation is perhaps the only contributing factor. In node-negative patients, the incidence of HER-2/neu overexpression was also higher (33.3%), which could imply a worse prognosis in node-negative Chinese patients than in their Caucasian counterparts. A significant correlation between HER-2/neu overexpression and cancer stage was demonstrated. There were also trend relationships between HER-2/neu overexpression and other prognostic factors, including the number of positive axillary lymph nodes, tumor size, hormone receptor status and age at diagnosis, but none of these correlations were statistically significant. In axillary lymph node-negative patients, HER-2/neu overexpression was associated with estrogen receptor-negative status, a factor predicting worse outcome. These findings imply that HER-2/neu overexpression may identify a subgroup of node-negative patients with a poor prognosis who would otherwise have a favorable prognosis.

Blotting, Northern↗
PubMed1994

Reversion of the transformed phenotypes of v-H-ras NIH3T3 cells by flavonoids through attenuating the content of phosphotyrosine.

Fifteen flavonoids were employed to examine their effects on the morphological changes, foci formation in soft agar and cellular growth in v-H-ras-transformed NIH3T3 cells. The data presented here demonstrated that only three specific flavonoids--apigenin, kaempferol, and genistein--exhibited the reverting effect on the transformed phenotypes of ras-3T3 cells. For example, treatment with 25 microM of these flavonoids could effectively reverse the transformed morphology of ras-3T3 cells into flatter cells with contact inhibition. Colony formation in soft agar was decreased to 0.11%, 0.15%, and 0.35% by 25 microM apigenin, kaempferol, and genistein, respectively, as compared with control (0.92%). It was also found that the proliferation of ras-3T3 cells was significantly inhibited by these compounds in a dose-dependent manner. Finally, two biochemical parameters, the content of phosphotyrosine and cAMP, were examined to see whether affected by these compounds. The results showed the phosphotyrosine content in ras-3T3 cells was dramatically decreased by apigenin and kaempferol, but that was slightly reduced by genistein. By contrast, these three flavonoids all failed to significantly alter the level of cAMP within this transformant. Based on these observations, we suggest that some specific flavonoids are capable of reverting the transforming properties of v-H-ras transformed cells. The possible mechanism of this reversion is not mediated by activating the protein kinase A or its associated pathways, but rather inhibiting tyrosine kinases, subsequently leading to the blockage of p21ras-mediated signal transduction circuitry.

3T3 Cells↗
PubMed1994

Oxidation of LDL by nitric oxide and its modification by superoxides in macrophage and cell-free systems.

Oxidative modification of low density lipoproteins (LDL) can increase the atherogenicity of LDL. Here we demonstrate the potential role of nitric oxide (NO) in LDL modification. Dose-dependent alterations of LDL including an increase in electrophoretic mobility, generation of peroxides and degradation of apoprotein B occurred during incubation with NO. Sodium nitroprusside was also shown to increase the electromobility of LDL. Superoxide dismutase (SOD) and catalase did not affect this result. NO treatment also increases the negative charges on other lipoproteins. In addition, we have demonstrated that NO plays a protective role in macrophage or superoxide-induced LDL modification through its neutralizing action.

Animals↗
PubMed1994

Sympathetic innervation of the eustachian tube in rats.

The glyoxylic catecholaminergic histofluorescence method was employed on the mucosa of the rat's eustachian tube (ET) in order to study the sympathetic innervation present. One percent neutral red was used as counterstain. Many noradrenergic fibers were demonstrable around blood vessels, glands and submucosa of the ET, but not in the epithelium. In a group of rats following neurectomy, the superior cervical ganglia (SCG) were removed unilaterally or bilaterally. Changes in sympathetic innervation of the ET were examined 14 days after SCG ganglionectomy. In those animals after unilateral SCG ganglionectomy, no noradrenergic histofluorescence was found in the ipsilateral ET, although some scant fluorescence could be detected in the tube's nasopharyngeal (NP) orifice. However, no noradrenergic histofluorescence could be observed in animals bilateral SCG ganglionectomies. Our results indicate that sympathetic innervation of the ET in the rat originates in the SCG, with some cross-innervation of sympathetic fibers occurring in the tube's NP orifice.

Animals↗
PubMed1994

Mutagenicity and cytotoxicity of nitropyrrole compounds derived from the reaction of 2-acetyl pyrrole with nitrite.

2-Acetylpyrrole (AP) is a product of model browning systems, and has been isolated as a major flavour component of many foods. Reaction of AP with nitrite produces two N-nitropyrrole compounds, 1-nitro-2-acetyl-pyrrole (NAP) and 1,3,5-trinitro-2-acetylpyrrole (TNAP), the chemical structures of which have been confirmed by spectral studies, including UV mass, nuclear magnetic resonance, infra-red and elemental analysis (EA). NAP and TNAP are moderately mutagenic to the Salmonella strains TA98 and TA100 in the absence of a mammalian activation system and are markedly cytotoxic to mouse C3H10T1/2 cells. These results suggest that the formation of direct-acting mutagens of nitro-derivatives may take place in nitrite-containing food or in vivo by nitrosation following ingestion of AP.

Animals↗
PubMed1994

Inhibitory effect of curcumin on xanthine dehydrogenase/oxidase induced by phorbol-12-myristate-13-acetate in NIH3T3 cells.

Treatment of NIH3T3 cells with the tumor promoter phorbol-12-myristate-13-acetate (PMA) results within 30 min in a 1.8-fold elevation of xanthine oxidase (XO) activity, an enzyme capable of generating reactive oxygen species such as superoxide and hydrogen peroxide. Simultaneous administration of 2 and 10 microM curcumin with 100 ng/ml PMA inhibits PMA-induced increases in XO activity measured 30 min later by 22.7% and 36.5%, respectively. The PMA-induced conversion of xanthine dehydrogenase (XD) to XO is reduced by curcumin to the basal level noted in untreated cells. Activity of XO is remarkably inhibited by curcumin in vitro, but not by its structurally related compounds caffeic acid, chlorogenic acid and ferulic acid. Based on these findings, induction of XO activity is deemed to be one of the major causative elements in PMA-mediated tumor promotion, and the major inhibitory mechanism of curcumin on PMA-induced increases in XD/XO enzyme activities is through direct inactivation at the protein level.

3T3 Cells↗
PubMed1994

A reverse mutagenicity assay for alkylating agents based on a point mutation in the beta-lactamase gene at the active site serine codon.

The serine at the active site of beta-lactamase is responsible for the ester link to the acyl group of beta-lactam during hydrolysis of the substrate to its acid derivatives. A construct was made from a plasmid in which the active-site serine of beta-lactamase was substituted by glycine by site-directed mutation. This mutation results in the loss of beta-lactamase activity. This plasmid was used to transform Salmonella typhimurium TA1535. When the new strain JK947 was treated with a mutagen such as N-methyl-N'-nitro-nitrosoguanidine (MNNG), the bacteria could be recovered as they became ampicillin resistant. The sequence of the active-site serine codon in these revertants was mutated from GGC to AGC. Based upon these findings, we developed a model reverse mutagenicity assay. In this procedure, we treated JK947 with a test chemical, such as N-methyl-nitrosourea (MNU), dimethyl sulphate (DMS) or methylmethane sulphonate (MMS), for 30 min, and then scored the revertants on agar plates containing 50 micrograms/ml ampicillin after incubation at 37 degrees C for 16 h. MNU and MNNG were more potent than DMS and MMS in this assay. Treatment with MNU and MNNG resulted in larger colony numbers in our test than in the Ames test. However, our test was less sensitive to DMS and MMS than the Ames test.

Alkylating Agents↗
PubMed1994

N-nitroso-2-acetylaminofluorene: a direct-acting carcinogen inducing hepatocellular carcinoma in Sprague-Dawley rats.

To compare the hepatotoxicity and hepatocarcinogenicity of N-nitroso-2-acetylaminofluorene (NO-AAF) and its parent compound, 2-acetylaminofluorene (AAF), male Sprague-Dawley rats were given intraperitoneal (i.p.) or subcutaneous (s.c.) injections of AAF or NO-AAF (60 mg/kg body weight/week) for ten months. In the AAF group, morphological changes were produced which involved gross distortions of the liver with multiple nodule formations. The rat livers in the NO-AAF group appeared to be smooth with a blunt-thick superior segment of the lateral lobe. The serum gamma-glutamyl transpeptidase activity in both the AAF group and the NO-AAF group was significantly elevated (P < 0.0005). The present study shows that i.p. and s.c. injections of NO-AAF resulted in a high incidence of well-differentiated hepatocellular carcinomas (HCC) (7/9 and 4/6, respectively), while poorly differentiated HCCs were induced by i.p. or s.c. administration of AAF (6/9 or 2/6, respectively). Subcutaneous lesions consisting of an inflammatory reaction and fibroadenoma formation were observed in the NO-AAF-treated rats, whereas no such skin lesions were detected in the AAF-treated animals. These results suggest that NO-AAF is a new direct-acting carcinogen which may be useful for investigating hepatocarcinogenesis.

2-Acetylaminofluorene↗
PubMed1993

Effects of tannic acid on 12-O-tetradecanoylphorbol-13-acetate-induced protein kinase C activation in NIH 3T3 cells.

Tannic acid (TA) is a naturally occurring phenol, which has been found to display an antipromotion effect on mouse skin carcinogenesis. In order to explore the molecular mechanism, we have examined the process of 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced protein kinase C (PKC) activation, including phorbol ester binding, enzyme translocation, autophosphorylation and substrate phosphorylation, and finally the TPA-stimulated DNA synthesis. In an initial study, we found that TA slightly inhibited [3H]phorbol dibutyrate (PDBu) binding to intact cells, and only 30% reduction of phorbol ester binding was observed at the highest dose of TA (100 microM). Further analysis by Scatchard plot showed that TA reduced the Bmax of [3H]PDBu from 1.3 pmol/10(6) cells to 1.1 pmol/10(6) cells, but the Kd was increased from 24 to 30 nM. Analysis by western blot indicated that TA did not interfere with the TPA-induced PKC translocation, whereas TA effectively blocked the TPA-evoked phosphorylation of the membrane-bound PKC moiety and its 80 kDa substrate in a dose-dependent manner. We also found that pre- or post-treatment with TA both lead to a similar reduction of 80 kDa protein phosphorylation and that the TPA-stimulated DNA synthesis was also inhibited by TA in a dose-dependent manner, suggesting that the blockage of protein phosphorylation by TA was of biological significance. In conclusion, the work presented here demonstrated that the antitumor promoting effect of TA was not mediated by competing for the binding site with phorbol ester or interrupting the PKC translocation, but rather by effectively blocking phosphorylation by membrane-bound PKC, possibly through altering the biophysical properties of the membrane environment.

3T3 Cells↗