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Biomedical subjects

A Eastman

Publications and source records attributed to A Eastman.

107 records · Page 6Linked to original sources
PubMed1982

The significance of DNA cross-linking to cis-diamminedichloroplatinum(II)-induced cytotoxicity in sensitive and resistant lines of murine leukemia L1210 cells.

The cross-linking of DNA by cis-diamminedichloroplatinum(II) (cis-DDP) has been studied in a murine leukemia L1210 line (L1210/0) and a 30-fold resistant subline (L1210/DDP2) utilizing the technique of alkaline elution. The kinetics of cross-link formation were similar in both cell lines. After 1-h treatment with cis-DDP, cross-linking continued to increase to a maximum at 12 h posttreatment. Although cross-linking decreased by 24 h some lesions were seen to persist. After 72 h interstrand cross-links were completely removed by both cell lines, however 50% of the DNA-protein cross-links still remained in the sensitive cells even though they were undetectable in the resistant subline. To correlate cross-linking with cytotoxicity, a range of drug concentrations were used for concomitant growth inhibition studies and alkaline elution analyses. In addition to the 30-fold resistant subline, two other sublines developed in our laboratory which show 20- and 50-fold resistance to cis-DDP were included in these determinations. All the resistant sublines exhibited the same degree of cross-linking at the same applied drug doses although these doses elicited markedly different cytotoxicities; cross-linking varied only with applied drug concentrations. The degree of cross-linking in L1210/0 was also directly related to the dose of cis-DDP. However, the sensitive cell line displayed equivalent total cross-linking at a 5-fold lower applied dose. This may implicate an uptake phenomenon as a contributor to resistance. However, such a phenomenon can account for only part of the resistance observed as there existed 6-fold more total cross-links and 9-fold more interstrand cross-links in L1210/DDP2 at doses that were equitoxic to L1210. This suggests the existence of a more critical cytotoxic lesion that was not detectable by alkaline elution, probably interstrand cross-links. Resistance could be due to a differential removal of these lesions.

Animals↗
PubMed1982

Modulation of the interaction of benzo[a]pyrene with a hamster tracheal epithelial cell line.

A hamster tracheal cell line rapidly absorbed and subsequently metabolized benzo[a]pyrene (B[a]P). At 10(-7) M B[a]P, less than 5% of the applied hydrocarbon was retained by the cell after 8 h incubation. However, at higher concentrations up to 20% was retained. During a subsequent 24 h incubation in the absence of polycyclic hydrocarbon, the residual B[a]P was metabolized and, for the most part, excreted. Analysis of B[a]P bound to DNA showed that alkylation increased as a consequence of metabolism of the B[a]P retained after replacement of the culture medium. Analysis of DNA repair is therefore markedly affected by the contribution from this continued alkylation. At 10(-7) M B[a]P, DNA alkylation was rapidly completed, and within 24 h a marked reduction in total adducts was observed. During this phase, a specific removal was observed of two adducts that have been tentatively identified as derived from deoxyadenosine. A slower second phase of repair was followed for up to 5 days at which time 25% of the adducts still remained in DNA. During this slow phase, the repair appeared to show preference for two of the four remaining adducts. In cells that were incubated for 8 h with 10(-6) M B[a]P, no rapid early phase of repair was seen during the following 24 h because of the continued alkylation. Thereafter, only a slow repair was observed. The deoxyadenosine adducts were still detectable 5 days after treatment suggesting that their repair was inhibited or saturated at this high concentration of B[a]P.

Alkylation↗
PubMed1981

A system in mouse liver for the repair of O6-methylguanine lesions in methylated DNA.

An activity from mouse liver with catalyzes the disappearance of O6-methylguanine from DNA methylated with methylnitrosourea has been partially purified by ammonium sulfate fractionation and DNA-cellulose chromatography. The activity does not require divalent metal ions and is not affected by EDTA. It is specific for the repair of O6-methylguanine lesions and does not affect the removal of 7-methylguanine, 7-methyladenine or 3-methyladenine. The disappearance of O6-methylguanine is linear with respect to the concentration of protein and is dependent on incubation temperature. The kinetics and substrate dependence experiments suggest that the protein factor is product-inactivated. Amino acid analysis of hydrolysates of protein obtained after incubation of methylated DNA with the protein factor indicates the presence of radiolabeled S-methyl-L-cysteine, suggesting that during the repair of O6-methylguanine from methylated DNA, the methyl group is transferred to a sulfhydryl of a cysteine residue of a protein. This represents the first such demonstration in a mammalian system.

Amino Acids↗
PubMed1981

Formation and removal of benzo(a)pyrene adducts of DNA in hamster tracheal epithelial cells.

A cloned cell line derived from normal hamster tracheal epithelium has been characterized with respect to its response to the environmental pollutant and carcinogen benzo(a)pyrene [B(a)P]. These cells metabolize B(a)P to ultimate reactive forms as assayed by alkylation of DNA. Alkylation with radiotracer amounts of B(a)P was maximum at 8 hr, at which time 70% of the applied hydrocarbon had been converted to water-soluble forms. At longer incubation times, the rate of removal of adducts exceeded the rate of formation. When B(a)P-containing medium was replaced with fresh medium at two or four hr, a subsequent biphasic removal of adducts occurred, a rapid removal for the first four hr postincubation and then a slower repair. About 50% of the DNA-bound hydrocarbon remained in DNA after 48 hr. Cells were able to divide in the presence of these lesions, undergoing five doublings (five days), while only 60% of the adducts were removed from the DNA. Integrity of DNA during this period was monitored by the alkaline elution technique. A toxic dose of B(a)P was required to cause any increase in the rate of elution. Minimal single-strand breakage was observed from two to eight hr of B(a)P treatment, but at 15 hr DNA appeared normal. Comparison was made with a nontoxic dose of methyl methanesulfonate which caused very rapid elution of DNA after only one hr treatment. At least 15 deoxyribonucleoside-bound B(a)P adducts were separated by high-pressure liquid chromatography. Four adducts, probably deoxyadenosine-B(a)P, were removed almost completely in 24 hr, while the others appeared to be poorly removed. The possible significance to neoplasia of persistent and repairable lesions is discussed.

Animals↗
PubMed1979

Persistent binding of 3-methylcholanthrene to mouse lung DNA and its correlation with susceptibility to pulmonary neoplasia.

A/J, C3H/HeJ, DBA/2J, and C57BL/6J mice have different susceptibilities to polycyclic aromatic hydrocarbon-induced pulmonary neoplasia, whereas the livers from these animals are uniformly resistant to the carcinogenic actions of these substances. After i.v. injection of [3H]-3-methylcholanthrene, radiolabel was detected in the DNA of both lung and liver of all these strains. The DNA was digested to deoxyribonucleosides and chromatographed on Sephadex LH-20. The amounts of nucleoside-bound adducts detected varied markedly with the different tissues and strains. These adducts were undetectable in liver DNA by 28 days. Although all lung preparations showed some reduction in adducts by 28 days, the amounts in A/J lung were always highest; this correlated with its high susceptibility to neoplastic transformation. In all preparations, radioactivity eluted from Sephadex LH-20 with the column void volume or with underivatized nucleosides. Tissue, but not strain differences were observed in these chromatographic profiles. The predominance of these early-eluting peaks in liver, rather than lung, suggests that they may represent noncarcinogenic lesions. This radiolabeled material remains uncharacterized, but some possibilities are discussed.

Animals↗
PubMed1978

Comparison of in vivo and in vitro binding of polycyclic hydrocarbons to DNA.

The in vivo binding of [3H]benzo(a)pyrene (BP) and 3-[3H]methylcholanthrene (3MC) to liver and lung DNA was studied in A/J mice. Only in liver was there any reduction in total DNA-bound radioactivity between 4 h and 24 h after administration of the hydrocarbon. DNA was fractionated on Sephadex LH-20 after enzymatic digestion. A single deoxyribonucleoside-BP adduct was detected whereas two major 3MC-adducts were observed. Wtih both BP and 3MC, three additional peaks of radioactivity eluted rapidly in the lung DNA experiments while a fourth was noted with liver DNA. The nucleoside-bound adducts from lung represented a much larger proportion of the total radioactivity than with liver. In vitro analysis of 3MC binding to DNA showed the nucleoside-bound adducts to be predominantly deoxyguanosine-dependent but that the early peaks were independent of base suggesting binding to another part of the DNA molecule, perhaps phosphate, i.e, phosphotriesters.

Animals↗
PubMed1978

A technique for the measurement of breakage and repair of DNA alkylated in vivo.

The alkaline elution technique has been adapted for use in the assessment of DNA damage induced in the livers and lungs of mice after administration of an alkylating agent, methylemthanesulfonat (MMS). At 4 h after administration of MMS, damage ot DNA was readily demonstrable; the damage was repaired in liver by 24 h. The lung, particularly of the A/J mouse, exhibited an increased alkaline elution rate when compared to C57BL/6J, and repair was not entirely complete (as judged from the rate of alkaline elution of DNA) by 24 h. The rate of elution was dependent upon temperature. It is believed that this adaptation should have great utility in examining DNA repair in vivo.

Alkylation↗
PubMed1975

Factor XIII deficiency in two Melanesian families from Papua New Guinea.

Three patients from two families in Papua New Guinea with a deficiency of Factor XIII activity are described. Lowered levels of Factor XIII activity were found in the parents of both families. Simple screening tests for Factor XIII deficiency should be included in all coagulation screening tests, even in a developing country.

Black People↗
PubMed1975

Haemophilia A in PNG.

A three year old Highland boy presented with unilateral swelling of the knee. Specific coagulation factor assay confirmed the clinical diagnosis of Haemophilia A. Brief mention is made of other recently detected patients in Papua New Guinea and aspects of management.

Child, Preschool↗
PubMedDate not supplied

Activation of programmed cell death by anticancer agents: cisplatin as a model system.

The anticancer drug cisplatin exerts its action as a consequence of interaction with DNA. Cell cycle progression facilitates sensitivity to the drug, but inhibition of DNA synthesis is not necessarily the critical step. Lethally damaged cells can progress to and arrest for several days in the G2 phase of the cell cycle before dying. Certain features of cisplatin-induced cell death, such as chromatin condensation and the activation of a DNA endonuclease, are reminiscent of apoptosis, or programmed cell death. Many other anticancer drugs produce the same phenotypic effects, suggesting that these agents may all interact with the same signal transduction pathway leading to cell death.

Cell Cycle↗