Biomedical subjects
Publications and source records attributed to A W Hsie.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
The frequency of ethyl methanesulfonate (EMS)-induced mutations to 6-thioguanine resistance in a Chinese hamster ovary cells clone K1-BH4 was studied at many EMS doses including the minimally lethal range (0-100 microng/ml) as well as the exponential killing portion (100-800 microng/ml) of the survival curve. The mutation frequency increases approximately in proportion with increasing EMS concentration at a fixed treatment time. The pooled data for the observed mutation frequency, f(X), as a function of EMS dose X, is adequately described by a linear function f(X)=10(-6)(8.73+3.45 X), where 0 less than or equal to X less than or equal to 800 microng/ml. One interpretation of the linear dose-response is that, as a result of EMS treatment, ethylation of cellular constituents occurs, which is directly responsible for the mutation. Biochemical analyses demonstrate that most of the randomly isolated 6-thioguanine-resistant variants possess a highly reduced or undetectable level of HGPRT activity suggesting that the EMS-induced mutations to 6-thioguanine resistance affect primarily, if not exclusively, the HGPRT locus.
Exposure of Chinese hamster ovary (CHO) cells clone K1BH4 to ultraviolet (UV) light at doses up to 86 ergs/mm2 did not significantly reduce cell survival, but UV doses of 86-648 ergs/mm2 produced an exponential cell killing. Observed mutation frequency ro 6-thioguannine resistance induced by UV increases approximately in proportion to increasing doses up to 260 ergs/mm2 in a range of 5-648 ergs/mm2 examined. The pooled data of mutation frequency f(X) as a function of dose X from 0-260 ergs/mm2 is adequately described by f(X)=10(-6) (13.6 + 2.04 X). That the UV-induced mutations to 6-thioguanine resistance affects the hypoxanthine-guanine phosphoribosyl transferase (HGPRT) locus is supported by the observation that all randomly isolated drug-resistant colonies contained highly reduced or undetectable HGPRT activity.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Adenosine, dibutyryl cyclic AMP, monobutyryl cyclic AMP, cyclic AMP, and 5'-AMP have a remarkable morphogenetic effect on cultured iris epithelial cells obtained from adult newt. They alter the broad undulating membrane of the cell into branching strands of cytoplasm, a configuration that has been named "stellate." Theophylline, a phosphodiesterase inhibitor also induces the stellate configuration. This transient morphological alteration is detectable by 30 min and becomes maximal 80 min after treatment. In the continued presence of the effective compounds the altered cells return to their normal shape, although the recovery period is variable. The morphological alteration of iris epithelial cells in vitro observed in the present experiment is reminiscent of that which occurs during the dedifferentiation phase in lens regeneration in vivo. These observations suggest that induction of the stellate configuration is relevant to the mechanism of dedifferentiation of newt iris epithelial cells during Wolffian lens regeneration.
The first manifestation of reverse transformation, in which a permanent epithelial-like cell is reversibly transformed into a fibroblast-like cell by dibutyryl adenosine cyclic 3':5'-monophosphate, is the disappearance of a set of violently extending and retracting knobbed structures on the cell membrane with consequent tranquilization of the membrane. The cell then elongates to assume a fibroblast-like morphology. Permanently fibroblast-like cells, which have smooth membranes, can be changed into knobbed epithelial-like cells by the addition of either colcemid or cytochalasin B, agents that disorganize one or the other component, respectively, of the microtubular-microfibrillar system. Permanently smoothmembraned, epithelial-like cells also become knobbed by such treatment. All of these knobbed epithelial-like cells can be converted into smooth-membraned fibroblast-like cells by dibutyryl cAMP alone or with the aid of supporting molecules like testosterone. It is proposed that these are general phenomena and that the knobbed epithelial-like forms and the more highly differentiated smooth-membraned fibroblast-like cells represent extreme situations with respect to the degree of organization of the microtubular-microfibrillar system inside the cell.
Explore the source record for details and available documents.
Treatment of Chinese hamster ovary cells in vitro with dibutyrl adenosine cyclic 3':5'-monophosphate converts the culture from one of compact, randomly oriented cells that grow in multilayers to a monolayer of elongated, fibroblast-like cells growing parallel to one another. Testosterone propionate, which has a similar though smaller effect at high concentrations and after prolonged incubation, potentiates the action of dibutyryl cyclic AMP even when added at very low concentrations. The transformation is recognizable within one hour, affects cells throughout all or most of the life cycle, and is completely reversible. Both cell forms can reproduce, with approximately the same generation time. Agents like colcemid and vinblastine, which inhibit assembly of microtubules, prevent the transformation to the fibroblast-like form. It is postulated that the dibutyryl cyclic AMP and testosterone act by promoting organization of microtubules from protein monomers.
The morphological conversion in vitro of Chinese hamster ovary cells to a fibroblast form by a relatively large amount of dibutyryl adenosine cyclic 3':5'-monophosphate, or by a combination of small amounts of this compound and testosterone, is attended by appearance of the following additional properties: acquisition of strict contact inhibition of growth; reorientation of the random growth pattern into one in which cells grow parallel to their long dimension; disappearance of the randomly distributed, knob-like, pseudopodal structures around the cell periphery; induction of collagen synthesis; and decrease in the ability to be agglutinated and rounded up by plant agglutinins and specific cell antibodies. The changes in these characteristics are consistent with the conversion from a malignant to a normal fibroblastic state. This conversion is under genetic control, as demonstrated by the production of specific mutants with altered characteristics. The response to testosterone is specific since steroids like estradiol and hydrocortisone are inactive, and others have limited activity. Some prostaglandins are equal in activity to testosterone and 5alpha-dihydrotestosterone. This system appears useful in study of the regulation of phenotypic expression in mammalian cells.
Explore the source record for details and available documents.
No correlation was found between the cellular steady-state concentrations of glucose-6-phosphate, 6-phosphogluconate, and reduced nicotinamide dinucleotide phosphate and resistance versus sensitivity to catabolite repression.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Conjugation and detoxification of mixed function oxidase (MFO)-mediated benzo(a)pyrene [B(a)P] metabolites with glucuronic acid and glutathione (GSH) are major pathways of B(a)P elimination and ultimately excretion in vivo. We have studied the effects of uridine diphosphate alpha-D-glucuronic acid (UDPGA) and GSH, a cofactor for the synthesis of glucuronide and GSH conjugates, respectively, on B(a)P-induced cytotoxicity and mutagenicity in mammalian cells. The S9-mix used in the Chinese hamster ovary cell/hypoxanthine-guanine phosphoribosyltransferase (CHO/HPRT) mutational assay was supplemented with either UDPGA, GSH, or GSH plus purified GSH-S-transferases (GSHTs), to study modulation of glucuronide and GSH detoxification mechanisms on B(a)P-induced cytotoxic and mutagenic effects. We found that the addition of UDPGA to S9-mix reduces cytotoxicity induced by either B(a)P or B(a)P 6-OH but not by B(a)P 7,8-diol [B(a)P-diol]. The reduction of B(a)P and B(a)P 6-OH-induced cytotoxicity by glucuronide conjugation is likely due to elimination of cytotoxic phenols and quinones. The addition of GSH to the S9-mix resulted in a reduction of B(a)P- and B(a)P-diol-induced cytotoxicity. GSH plus GSHT reduced B(a)P-induced cytotoxicity and mutagenicity. GSH inhibited the mutagenicity at low concentrations of B(a)P-diol. GSH plus GSHTs inhibited the cytotoxicity and mutagenicity of B(a)P-diol at concentrations not affected by GSH alone. These studies demonstrate that mechanisms of detoxification can affect the biological activity of B(a)P and B(a)P-diol as profoundly as bioactivation by the MFO system. Future research should address studies of mutagenicity modulation by metabolic effectors at both the molecular (DNA sequence) and cellular (quantitative mutagenesis) level.
Previously, we have shown that Chinese hamster ovary (CHO) cells are useful for quantifying chemical-induced gene mutations. We have defined the conditions of a Multiplex CHO System which permits determination of mutagen-induced chromosome aberration, and sister chromatid exchange (SCE) in addition to cytotoxicity and gene mutation in the same treated culture. This allows us to extend the spectrum of quantitative mutagenesis to include clastogenic endpoints. In the present study, we used four carcinogenic/noncarcinogenic pairs to validate the relative utility and sensitivity of each endpoint, and to study the interrelationship of these four distinct biological effects. These compounds include the direct-acting carcinogens N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), ICR 170 and their noncarcinogenic analogue N-methyl-N'-nitroguanidine (MNG) and ICR 170-OH, and the procarcinogens benzo[a]pyrene (B[a]P) and dimethylnitrosamine (DMN) and their noncarcinogenic analogues pyrene and dimethylamine (DMA) respectively. A rat liver homogenate preparation (S9) was used to assay for the biological activities of procarcinogens. Under our experimental conditions, we observed that carcinogens DMN, B[a]P, MNNG and ICR 170, but not their noncarcinogenic counterparts, showed all four biological effects. Our studies with these chemicals showed that cytotoxicity does not necessarily correlate with any of the genetic endpoints. On a molar basis, noncarcinogens, pyrene and ICR 170-OH show similar toxicity to carcinogens B[a]P and ICR 170, respectively. The other two non-carcinogenic analogues, DMA and MNG, exhibit minimal toxicity at concentrations 10-1,000 times higher than cytotoxic concentrations of the corresponding carcinogens, DMN and MNNG. In general, gene mutation and SCE are more sensitive than chromosome aberration assay. The gene mutation assay is more specific than SCE and chromosome aberration assays since none of the noncarcinogens exhibit a detectable response in the gene mutational assay. ICR 170 and MNNG are much more active than B[a]P and DMN as ranked on a molar basis. These results indicate that the Multiplex CHO System is capable of discriminating divergent structural classes of carcinogenic and noncarcinogenic compounds, such as the eight chemicals chosen for our study.