PubMed Health⌕ Search

Biomedical subjects

R B Setlow

Publications and source records attributed to R B Setlow.

At least 37 records · Page 2Linked to original sources
PubMed1989

Animal model for ultraviolet radiation-induced melanoma: platyfish-swordtail hybrid.

Sunlight exposure is strongly indicated as one of the important etiologic agents in human cutaneous malignant melanoma. However, because of the absence of good animal models, it has not been possible to estimate the wavelengths or wavelength regions involved. We have developed a useful animal model from crosses and backcrosses of platyfish (Xiphophorus maculatus) and swordtails (Xiphophorus helleri). Two strains of these fish are susceptible to invasive melanoma induction by exposure to filtered radiation from sunlamps in the wavelength ranges lambda greater than 290 nm and lambda greater than 304 nm. Multiple exposures on 5-20 consecutive days beginning on day 5 after birth or a single exposure of approximately 200 J/(m2.day) of lambda greater than 304 nm result in a tumor prevalence of 20% to 40% at 4 months of age compared with a background rate of 12% in one strain and 2% in another. Exposure of the fish to visible light after UV exposure reduces the prevalence to background. The melanomas are similar in many respects to mammalian melanomas, as judged by light and electron microscopy. The genetics of the crosses determined by others and the high sensitivity of the hybrids to melanoma induction indicate that the UV radiation probably inactivates the one tumor repressor gene (or a small number of tumor repressor genes) in the hybrid fish. The small size of the animals and their high susceptibility to melanoma induction make them ideal for action spectroscopy.

Animals↗
PubMed1989

Inactivation of O6-alkylguanine-DNA alkyltransferase in HeLa cells by cisplatin.

Inactivation of O6-alkylguanine-DNA alkyltransferase (O6-AGT) in HeLa CCL2 cells by cisplatin was studied. HeLa CCL2 cells treated with cisplatin showed a dose-dependent decline in O6-AGT activity. After cisplatin was removed and replaced with fresh medium, the transferase level began to rise slowly. By 72 h slightly more than 80% of the activity was recovered. It seems that the activity of the alkyltransferase can be inactivated by platinated DNA adducts. The data suggest that the O6-platinum-guanine formation and the O6-alkyltransferase depletion are not responsible for cytotoxicity but may result in a base substitution mutation in mammalian cells.

Cell Survival↗
PubMed1987

DNA repair by articular chondrocytes. IV. Measurement of Micrococcus luteus endonuclease-sensitive sites by alkaline elution in rabbit articular chondrocytes.

The ability of resting and dividing rabbit articular chondrocytes to repair low doses of ultraviolet (UV) damage was measured through removal of UV endonuclease-sensitive sites (ESS, pyrimidines dimers) as measured by alkaline elution. The repair of damage was significantly (P less than 0.001) greater in dividing than non-dividing cells. An age-related decrease in repair capability was found in resting chondrocytes, but not in their dividing counterpart. These results support earlier findings of unscheduled DNA synthesis by the same cells. (Mech. Ageing Dev., 32: 39-55, 1985).

Animals↗
PubMed1987

DNA repair by articular chondrocytes. V. O6 methylguanine-acceptor protein activity in resting and cultured rabbit and human chondrocytes.

The level of O6-methylguanine acceptor protein activity was examined in rabbit and human articular chondrocytes of different ages. The activity per microgram of DNA in rabbit chondrocytes was 5-fold lower than in humans. There was no age-dependent decrease in the activity of resting or cultured chondrocytes of either species. The values for resting cells were comparable to those of cultured cells. The lack of age-related differences in methyltransferase activity, in contrast to nucleotide excision repair [Mech. Ageing Dev. 32 (1985) 39-55], indicates that separate repair systems behave differently with respect to chronological aging. The methyl transferase activity may be more essential for survival of articular chondrocytes and therefore more highly conserved with age.

Aging↗
PubMed1986

Quantitation of radiation-, chemical-, or enzyme-induced single strand breaks in nonradioactive DNA by alkaline gel electrophoresis: application to pyrimidine dimers.

We have developed an alkaline agarose gel method for quantitating single strand breaks in nanogram quantities of nonradioactive DNA. After electrophoresis together with molecular length standards, the DNA is neutralized, stained with ethidium bromide, photographed, and the density profiles recorded with a computer controlled scanner. The median lengths, number average molecular lengths, and length average molecular lengths of the DNAs can be computed by using the mobilities of the molecular length standards. The frequency of single strand breaks can then be determined by comparison of the corresponding average molecular lengths of DNAs treated and not treated with single strand break-inducing agents (radiation, chemicals, or lesion-specific endonuclease). Single strand break yields (induced at pyrimidine dimer sites in uv-irradiated human fibroblasts DNA by the dimer-specific endonuclease from Micrococcus luteus) from our method agree with values obtained for the same DNAs from alkaline sucrose gradient analysis. The method has been used to determine pyrimidine dimer yields in DNA from biopsies of human skin irradiated in situ. It will be especially useful in determining the frequency of single strand breaks (or lesions convertible to single strand breaks by specific cleaving reagents or enzymes) in small quantities of DNA from cells or tissues not amenable to radioactive labeling.

DNA Damage↗
PubMed1984

The Amazon molly, Poecilia formosa, as a test animal in carcinogenicity studies: chronic exposures to physical agents.

The Amazon molly, Poecilia formosa, a small, live-bearing fish native to Texas, has an unusual mode of reproduction that makes it highly suitable for carcinogenicity studies. The species is easy to rear and breed, and withstands handling well. Large broods of young are born, numbering up to 90 when the parent fish are fully grown. The Amazon molly reproduces gynogenetically; eggs are activated after mating with males of closely related species. The male makes no genetic contribution; sperm provides only the stimulus for egg development. The offspring of a female comprise a clone with genotypes identical to that of the mother's so that cell and tissue transplants made between members of the clone are not rejected. We used the Amazon molly as an animal model to show that damage to DNA caused by UV and ionizing radiation and by certain chemicals results in tumor development. Thyroid cells were taken from donor mollies, treated precisely in vitro with the agents, and then injected into homologous recipients. Eight months later, recipient fish had developed large thyroid tumors. The genetic homogeneity of the clone also makes the Amazon molly invaluable in acute or chronic bioassays because variability in the responses of the individual fishes is minimal. Therefore, a limited number will suffice to give statistically significant results. The findings from a study of chronic exposure to asbestos are also described.

Animal Husbandry↗
PubMed1984

Enzymology of repair of DNA adducts produced by N-nitroso compounds.

The biological effects of DNA adducts depend on their nature, and on their half-lives relative to the rates of DNA replication and transcription. Their half-lives are determined by the rates of spontaneous decay, such as depurination, and the rates of enzymatic repair of the adducts or their decay products. The principal modes of repair of methylating and ethylating agents are by glycosylase-catalysed depurination of 7-alkylguanine and 3-alkyladenine and by the dealkylation of O6-alkylguanine. The latter repair is accomplished by the transfer of the alkyl group to cysteine residues of acceptor proteins in a stoichiometric reaction. Repair by dealkylation cannot be detected by the standard methods used to measure DNA repair, but it is easy to estimate the acceptor activity in cell extracts by measuring the transfer of radioactive O6-alkyl groups in an exogenous DNA to protein. In extracts of cells treated with alkylating agents, the activity is depressed because the endogenous DNA is rapidly dealkylated, using up the acceptor activity. In many cell types, the decrease in activity is followed by an increase to the normal constitutive level. In other cells, there is no such adaptive response. We may catalogue the cell strains and lines investigated into three classes: (1) high constitutive activity (30 000-100 000 acceptor sites per cell) and rapid adaptive response (several hours), (2) high constitutive activity and very slow adaptive response, and (3) low constitutive activity. The cytotoxicity of methylating agents is highest for the last and lowest for the first class. Differences in constitutive levels of methyl accepting activity in extracts of human lymphocytes and in the acceptor activity in lung macrophages from smokers (low activity) and nonsmokers (high activity) have been observed.

Alkylation↗
PubMed1983

DNA repair by articular chondrocytes. II. Direct measurements of repair of ultraviolet and X-ray damage in monolayer cultures.

The abilities of human and rabbit articular chondrocytes to repair ultraviolet (UV) and X-ray damage were measured in terms of the removal of UV--endonuclease-sensitive sites (pyrimidine dimers) and single-strand breaks, respectively. The initial 3-h rate of dimer repair in human cells, incubated in medium containing 10% human serum, was about 2.5 times as large as in rabbit cells incubated in medium containing 10% or 20% fetal bovine serum. Similar results have been previously reported for unscheduled DNA synthesis (UDS), indicating that UDS is a valid quantitative measure of repair in this cell system. The repair of single-strand breaks was rapid (approx. 50% completed in less than 10 min). An estimate, from the measured numbers of lesions and patch sizes, indicated that the amount of UDS following 20 krad would be 100 to 300 times less than that in 3 h following 10 J/m2 of 254 nm and hence would not be detectable radioautographically.

Adult↗