Search PubMed⌕ Search

Biomedical subjects

C C Chang

Publications and source records attributed to C C Chang.

At least 613 records · Page 34Linked to original sources
PubMed1982

Evaluation of the carcinogenic potential of 2,4-dinitrofluorobenzene and its implications regarding mutagenicity testing.

Tumor promoters are compounds which dramatically enhance the appearance of tumors when chronically applied after an initiating dose of a carcinogen. Initiators are generally considered mutagens while promoters have previously been shown not to induce either DNA damage or mutations. 2,4-Dinitrofluorobenzene (2,4-DNFB), a compound used in the identification of N-terminal amino acids of polypeptides, had been previously reported to be a tumor promoter in mouse skin, while other investigators have found it to be a mutagen in bacteria and yeast. To investigate this apparent discrepancy, we chose to study the carcinogenic potential of 2,4-DNFB utilizing various methods available in V79 Chinese hamster cells. 2,4-DNFB exposure did not result in any unscheduled DNA synthesis a measure of DNA excision repair, nor did it increase the frequency of sister chromatid exchanges in V79 cells either in the presence or absence of rat liver postmitochondrial supernatant (S-15). Forward mutations in V79 cells, either to ouabain or 6-thioguanine resistance, were not induced by 2,4-DNFB, in the presence or absence of S-15. 2,4-DNFB was, however, able to induce reversions in methionine-requiring E. coli auxotrophs in a dose-dependent fashion. Phylogenetic differences between lower organisms and mammals may account for this discordance. 2,4-DNFB was found to inhibit metabolic cooperation, in a dose dependent manner, in V79 cells. This property has previously been shown to be correlated with tumor promoting ability in mouse skin. Therefore, we conclude that the carcinogenic potential of 2,4-DNFB might reside in its ability as a tumor promoter and not as a carcinogenic initiator. Furthermore, these studies serve to illustrate the need for caution when extrapolating bacterial data for risk assessment in humans.

Animals↗
PubMed1982

Inhibition of metabolic cooperation in Chinese hamster V79 cells in culture by various polybrominated biphenyl (PBB) congeners.

Using an in vitro assay system to measure a form of cell-cell communication in Chinese hamster V79 cells, several purified polybrominated biphenyl (PBB) congeners were analyzed for their ability to affect colony-forming ability and "metabolic cooperation" in these cells. Results clearly demonstrate the assay's ability to distinguish differences in the cytotoxic and metabolic cooperation-inhibiting properties of these congeners related to their structure. It appears that if a carbon ortho to the bridge carbon of each phenyl ring is brominated, the molecule has the property by which metabolic cooperation is inhibited. The results suggest that several PBB congeners share at least one property associated with several known tumor promoters, such as the phorbol esters. Although we have not ruled out that the mixture of PBB congeners might contain initiators or that various PBB metabolites would be mutagen/initiators, based on these and other results, it was concluded that the reported carcinogenic potential of PBB seems to be mediated by its action as a tumor promoter, rather than as a complete carcinogen or an initiator.

Animals↗
PubMed1982

Studies on gossypol. I. Toxicity, antifertility, and endocrine analyses in male rats.

Toxicity, antifertility, and endocrine effects of gossypol have been studied in male rats. The animals grew nearly normally when administered a daily dose of 7.5 mg/kg orally for 12 wk. At 15 and 30 mg/kg/d doses growth rates were significantly reduced. Infertility occurred at all dose levels, but mating behavior was maintained throughout the period of treatment. Examination of the cauda epididymis after 6 wk at the 30-mg/kg/d dose and after 12 wk at the lower doses showed reductions in sperm numbers as compared with controls. All of the sperm from the groups receiving the 15- and 30-mg/kg/d doses were immotile; and at the 7.5-mg/kg/d dose level most sperm were immotile. Many of nonmotile sperm showed sharply bent tails or lacked tails. There was no significant change in the serum levels of testosterone, LH, or FSH in animals receiving 7.5 and 15 mg/kg/d of gossypol for 12 wk. However, at a dose of 30 mg/kg/d for 6 wk, the serum testosterone and LH concentrations were significantly reduced. FSH concentrations remained normal in all groups. A group of 5 animals receiving 15 mg/kg/d were allowed a recovery period of 6 wk after 12 wk of therapy and they evidenced complete recovery of fertility.

Animals↗
PubMed1981

Detection of circulating metallothionein in rats injected with zinc or cadmium.

Circulating metallothionein was measured by radioimmunoassay over a 13-day period in male Sprague-Dawley rats that received a sequence of three intraperitoneal injections (at 3-day intervals) of either 5 milligrams of zinc or 0.8 milligrams of cadmium per kilogram of body weight. These amounts of zinc and cadmium produced metallothionein concentrations in the range of 2 to 5 nanograms per milliliter of serum (zinc) and 2 to 15 nanograms per milliliter of serum (cadmium). In control rats given saline injections over the same period the metallothionein concentration ranged from 1 to 3 nanograms per milliliter of serum.

Animals↗
PubMed1981

Evidence indicating that inactivation of 3-hydroxy-3-methylglutaryl coenzyme A reductase by low density lipoprotein or by 25-hydroxycholesterol requires mediator protein(s) with rapid turnover rate.

The half-life (t 1/2) of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase of Chinese hamster ovary cells grown in fetal calf serum medium is approximately 2 h. When cells are switched to grow in delipidated serum medium (DeL-M) for more than 24 h, the t 1/2 of the enzyme is found to be drastically altered to approximately 13 h. Exposure of low density lipoprotein (LDL) (100 micrograms of protein/ml) or 25-hydroxycholesterol (1 microgram/ml) to cells grown in DeL-M suppresses reductase activity more rapidly than would be expected solely if reductase synthesis were suppressed, showing that inactivation of reductase activity by sterols, previously demonstrated using only analogs of cholesterol, is a normal mechanism for regulation of HMG-CoA reductase activity by the physiologically important sterol source (LDL). This inactivation effect by LDL or by 25-hydroxycholesterol is shown to be at least in part due to acceleration of reductase degradation rate. Furthermore, the inactivation effect by sterols is shown to be largely abolished if cycloheximide (250 micrograms/ml) is added simultaneously to the growth medium, indicating that continuous synthesis of a class of mediator protein(s) is necessary in mediating the effect of LDL or 25-hydroxycholesterol. Two different protein synthesis inhibitors (emetine and puromycin) were used and gave essentially identical results. Preincubation of cell culture with cycloheximide for 2 h essentially completely abolishes the effect of 25-hydroxycholesterol, indicating that the mediator protein(s) turns over rapidly, with t 1/2 less than 3 or 4 h.

Animals↗
PubMed1981

Isolation and partial characterization of mutagen-sensitive and DNA repair mutants of Chinese hamster fibroblasts.

Through a new approach, we have sought to isolate ultraviolet light (UV)-sensitive and DNA repair mutant Chinese hamster fibroblasts. The procedure consisted of 1) mutation induction by 5-bromodeoxyuridine (Brd U)-blacklight and UV treatments; 2) incorporation of 3H-thymidine in repair-proficient cells at high temperature (38.5 degrees C) following UV damage; 3) cold holding (4.0 degrees C) of these cells to induce tritium killing; and 4) recovery and testing of repair-deficient and UV-sensitive cells which have survived and formed colonies at low temperature (34.0 degrees C). In our initial attempt at this protocol, we isolated 72 surviving colonies from 2 x 10(7) cells plated for selection. Of the 72 colonies, 20 demonstrated potential interest and four were selected for extensive study. One, identified as UVs-7, is slightly more sensitive to UV, but not sensitive to X rays or N-acetoxy-2-acetylaminofluorene (NAc-AAF). The mutant exhibits a highly reduced level of unscheduled DNA synthesis (UDS), as compared to the parental line. Two additional lines, UVs-40 UVs-44, are sensitive to UV, X ray, N-methyl-N-nitro-N-nitrosoguanidine (MNNG), and NAc-AAF, but exhibit normal UDS. A fourth line, UVr-23, has enhanced UDS, is resistant to UV, but exhibits no difference in sensitivity to x ray or NAc-AAf. These mutants are all stable, and should be useful for the study of mammalians DNA repair processes and mechanisms of mutagenesis.

Animals↗
PubMed1981

The mutation studies of mutagen-sensitive and DNA repair mutants of Chinese hamster fibroblasts.

We have previously reported the isolation and partial characterization of DNA repair and/or mutagen-sensitive mutant Chinese hamster cell strains. Here we present the results of a detailed study of the ultraviolet light (UV)-induced mutability of one of these strains, UVs-7, and provide preliminary mutability data on two additional lines, UVr-23 and UVs-40. UVs-7 in extremely deficient in unscheduled DNA synthesis (UDS) but only slightly more sensitive to UV than the parental line. When examined for the UV-inducibility of mutants resistant to ouabain, 6-thioguanine, or diphtheria toxin, UVs-7 was found to be hypermutable at all three loci as compared to the parental line. The degree of hypermutability was not the same for any two loci. UVs-40, a highly UV-sensitive strain, was also found to be hypermutable at the ouabain-resistant (ouar) locus. UVr-23, which is UV-resistant and more proficient at UDS than the parental line, appeared to exhibit a tendency toward hypomutability at both the ouabain(ouar) and 6-thioguanine--resistant (6TGr) loci. Further characterization of all these lines should aid in delineating mammalian mechanisms of DNA repair and mutagenesis.

Animals↗
PubMed1981

Isolation and characterization of a UV-sensitive hypermutable aphidicolin-resistant Chinese hamster cell line.

Aphidicolin is a specific inhibitor of DNA polymerase alpha and blocks DNA synthesis in vivo. The inhibition of purified alpha-polymerase has been shown to be competitive with dCTP but not with the other three deoxynucleoside triphosphates (dNTPs). In order to study the various roles that the alpha-polymerase might play in DNA replication and/or repair, we have attempted to isolate Chinese hamster V79 cells that are resistant to aphidicolin. Four resistant mutants were isolated from BrdU--black light- and UV-mutagenized cells. None of the mutants isolated contains an alpha-polymerase that is resistant, in crude extract measurements, to aphidicolin. Three mutants isolated, however, were found to be resistant to araC. Two mutants tested were found to be sensitive to cytidine and have elevated levels of dCTP or all 4 dNTPs. These results indicate that they are nucleotide pool mutants instead of alpha-polymerase mutants. One mutant, aphr-4, is characterized by the following: (1) high level of dCTP; (2) thymidine (or CdR, UdR) auxotrophic; (3) sensitive to thymidine (and AdR, GdR); (4) slow-growing; (5) cytidine sensitive; (6) UV sensitive and hypermutable at the ouabain-resistant locus; and (7) a ninefold increase in frequency of chromatid gaps and breaks when cells are exposed to BrdU-containing medium. Revertants of aphr-4 which are partially aphidicolin-resistant and retain the first three characteristics listed above, but not the others, have been isolated. The appearance of this type of revertant indicates that either aphr-4 or its "revertant" is a double mutant.

Animals↗
PubMed1981

Selection of aphidicolin-resistant CHO cells with altered levels of ribonucleotide reductase.

Chinese hamster ovary cells were initially selected for resistance to aphidicolin at 0.3 microgram/ml. Serial cultivation with aphidicolin at concentrations up to 5.0 micrograms/ml yielded a series of mutants with increasing resistance. The most resistant mutant isolated was 44 times more resistant to aphidicolin than the parental CHO. The alpha-polymerases, assayed in the cytoplasmic extracts of the mutants, did not increase in specific activity or differ from the parental CHO in their sensitivity to aphidicolin. When cultured in the presence of deoxythymidine, deoxyadenosine, and 1-beta-D-arabinofuranosyl cytosine (araC) the mutants showed considerably more resistance to these inhibitors than did the parental CHO. The intracellular pools of all four deoxynucleoside triphosphates (dNTPs) in the mutants increased with increasing resistance to aphidicolin. The elevated dNTP pools in the mutant most resistant to aphidicolin appear to be the result of a 4- to 8-fold increase in the level of ribonucleotide reductase (2'-deoxyribonucleoside diphosphate:oxidized thioredoxin 2'-oxidoreductase, EC 1.17.4.1).

Animals↗
PubMed1981

Elevated spontaneous mutation rate in Bloom syndrome fibroblasts.

The rates of spontaneous mutation to 6-thioguanine resistance were determined in fibroblasts derived from normal and two Bloom syndrome individuals (GM 2548 and GM 1492). Two methods were utilized to determine the rates. Method I obtained the spontaneous mutation rate from the increase in the mutation frequency of a cell population in logarithmic-phase growth over 10 days. The two Bloom syndrome strains had spontaneous mutation rates of 16 X 10(-6) and 17 X 10(-6) mutations per cell per generation, whereas two normal strains had rates of 1.5 X 10(-6) and 1.1 X 10(-6). Method II utilized fluctuation analysis to measure the rate of spontaneous mutation. This method resulted in rates of 19 X 10(-6) and 23 X 10(-6) mutations per cell per generation in Bloom syndrome cells, compared to rates of 4.6 X 10(-6) and 4.9 X 10(-6) in the control strains. These data suggest that Bloom syndrome may be a mutator mutation, a previously unrecognized phenomenon in humans, and that an elevated spontaneous mutation rate in vivo may be responsible for the clinical phenotype of primordial dwarfism and increased cancer incidence.

Abnormalities, Multiple↗
PubMed1981

Metabolism of Glycolate in Isolated Spinach Leaf Peroxisomes : KINETICS OF GLYOXYLATE, OXALATE, CARBON DIOXIDE, AND GLYCINE FORMATION.

The flow of glyoxylate derived from glycolate into various metabolic routes in the peroxisomes during photorespiration was assessed. Isolated spinach leaf peroxisomes were fed [(14)C] glycolate in the absence or presence of exogenous glutamate, and the formation of radioactive glyoxylate, CO(2), glycine, oxalate, and formate was monitored at time intervals. In the absence of glutamate, 80% of the glycolate was consumed within 2 hours and concomitantly glyoxylate accumulated; CO(2), oxalate, and formate each accounted for less than 5% of the consumed glycolate. In the presence of equal concentration of glutamate, glycolate was metabolized at a similar rate, and glycine together with some glyoxylate accumulated; CO(2), oxalate, and formate each accounted for an even lesser percentage of the consumed glycolate. CO(2) and oxalate were not produced in significant amounts even in the absence of glutamate, unless glycolate had been consumed completely and glyoxylate had accumulated for a prolonged period. These in vitro findings are discussed in relation to the extent of CO(2) and oxalate generated in leaf peroxisomes during photorespiration.

Journal Article↗
PubMed1981

A study on the interaction of crotapotin with crotoxin phospholipase A2, notexin and other presynaptic neurotoxins.

1 Crotapotin, the acidic subunit of crotoxin, greatly potentiated the presynaptic effect of isolated basic phospholipase A (PLA) of crotoxin in both mouse diaphragm and chick biventer cervicis muscles whereas the myotoxic effect was not affected significantly.2 In contrast to crotoxin PLA, the presynaptic effects of notexin and notechis-5, self-active single chain toxins, were antagonized by crotapotin while actions of beta-bungarotoxin were not affected.3 By assaying PLA activity, crotoxin PLA was found to be unstable in physiological salt solution, especially when in contact with muscle, due to massive non-specific binding to and destruction by the muscle.4 The decline of crotoxin PLA was greatly reduced by the presence of crotapotin but not by another acidic protein, volvatoxin A(2), or heparin.5 Notechis-5 was found to be stable even when in the presence of muscles.6 [(3)H]-acetylated crotoxin PLA, which retained about 40% of its original enzyme and presynaptic blocking activities, also bound rapidly to the mouse diaphragm on incubation and this binding was greatly hindered by the simultaneous addition of crotapotin.7 The prevention of binding of crotoxin PLA by crotapotin occurred mostly at those sites where the binding was easily dissociable on washing. No antagonism of binding occurred at the firmly binding site.8 The binding of [(3)H]-acetylated crotapotin was much less than that of crotoxin PLA, and interestingly, the binding was increased by the latter, suggesting that crotapotin may be first bound to the diaphragm together with crotoxin PLA.9 No specific binding at the endplate zone was found either for crotoxin PLA or for crotapotin.10 It is concluded that crotapotin potentiates the presynaptic effect of crotoxin PLA by curtailing its non-specific affinity with muscles, minimizing its dispersal and destruction en route to the nerve terminal, but not by acting as an affinity probe for the nerve terminal.

Animals↗