PubMed Health⌕ Search

Biomedical subjects

A J Ryan

Publications and source records attributed to A J Ryan.

At least 19 recordsLinked to original sources
PubMed1992

Characterisation and correction of a mammalian cell mutant defective in late step of base excision repair.

An Indian muntjac cell line, SVM, is unusually sensitive to cell killing induced by a range of alkylating agents. Cells transfected with the Escherichia coli ada gene or human genomic DNA have allowed the response of SVM to alkylating agents to be dissociated into two distinct components. Thus, in SVM, which expresses very low levels of alkyltransferase (AT), O6-alkylguanine appears to be the major cytotoxic, clastogenic, and recombinogenic lesion following exposure to agents such as methylnitrosourea (MNU). However, SVM is also very sensitive to agents such as dimethylsulfate (DMS), which produce only very low levels of O6-methylguanine damage. Sensitivity to DMS resides in an inability to complete base excision repair, with the appearance of persistent single-strand DNA breaks (SSBs), and does not appear to involve defects in glycosylase, apurinic/apyrimidinic endonuclease, or DNA ligase activities. Another, possibly related, phenotypic trait in SVM is its limited ability to ligate transfected linear plasmid DNA. Transfectants of SVM, harboring human DNA sequences, show a significant correction of DMS-induced cytotoxicity and clastogenicity and a reduction in the levels of DMS-induced DNA SSBs. The DMS-resistant transfectants have an increased ability to ligate linear plasmid DNA, and also express AT, making these lines resistant to alkylating agents such as MNU. These results suggest that cells possess a mechanism that regulates AT expression, plasmid break-joining ability, and certain aspects of base excision repair. Transfectants of SVM containing human DNA provide a means to isolate genes involved in a coordinate response to alkylation damage.

Alkylating Agents↗
PubMed1992

Acute heat stress protects rats against endotoxin shock.

The purpose of this study was to determine 1) whether prior (24-h) heat stress could render rats cross-resistant to the lethal activity of bacterial lipopolysaccharide (LPS) and 2) whether this acquired state of resistance is associated with endotoxemia during the heat stress event. Four groups (n = 7/group) of rats were examined: 1) saline treated, 2) LPS treated, 3) heat stressed and saline treated, and 4) heat stressed and LPS treated. Saline or LPS (Escherichia coli, serotype 0111:B4, 20 mg/kg body wt) was given intravenously 24 h after exposure to heat (ambient temperature 47-50 degrees C, relative humidity 30%) for heat-stressed rats and at the same time of day for nonheated rats; survival was monitored for 48 h. Thermal responses were similar (P > 0.05); values for maximum core temperature (Tc) and time above Tc of 40 degrees C were 42.7 +/- 0.1 and 42.6 +/- 0.1 degrees C (SE) and 44.0 +/- 2.1 and 47.9 +/- 3.7 (SE) min for the heat-stressed saline-treated and heat-stressed LPS-treated rats, respectively. Administration of LPS to nonheated rats resulted in 71.4% (5 of 7 rats) lethality. In contrast, all (7 of 7) rats subjected to a single nonlethal heat stress event 24 h before LPS treatment survived (P < 0.05). Endotoxin was not detected in arterial plasma immediately after heat stress in rats (n = 6) exposed to a Tc of 42.9 +/- 0.1 degrees C. These findings demonstrate that acute heat stress can protect rats from the lethal activity of LPS.

Animals↗
PubMed1992

The formation of proximate carcinogens from three polycyclic aromatic compounds by human liver microsomes.

1. The metabolism of 3H-benzo[a]pyrene (BP), 3H-7-methylbenz[c]acridine (7MBAC) and 3H-dibenz[a,j]acridine (DBAJAC) have been studied in human liver microsomes from 13 subjects. 2. When the metabolism of these carcinogens to more polar ethyl acetate-soluble metabolites were compared, the activities towards the nitrogenous carcinogens were twice that determined for BP. 3. The specific rates of formation of the three proximate carcinogens, BP-7,8-dihydrodiol, 7MBAC-3,4-dihydrodiol and DBAJAC-3,4-dihydrodiol per nmol cytochrome P-450 for 12 subjects were positively correlated. 4. These dihydrodiols constituted 5.9 +/- 0.7% (mean +/- SEM), 57.8 +/- 2.6% and 3.0 +/- 0.4% of the total metabolites identified by cochromatography with standards, 7MBAC, DBAJAC and BP respectively.

Acridines↗
PubMed1991

Camptothecin cytotoxicity in mammalian cells is associated with the induction of persistent double strand breaks in replicating DNA.

Camptothecin is a specific topoisomerase I poison and is highly cytotoxic to eukaryotic cells. In the present study, we show, using a pulse field gel electrophoresis assay, that camptothecin induces DNA double strand breaks (DSBs) specifically in newly replicated DNA. Camptothecin induces these replication associated DNA DSBs in a dose-dependent manner. At levels of the drug which are toxic to the cell, these breaks are long-lived, and still measurable 24 hr after treatment. Both camptothecin induced DSBs and cytotoxicity are prevented by co-exposure with aphidicolin--a result which indicates that ongoing DNA synthesis is required for the production of DNA DSBs and cell killing. It has been proposed that camptothecin toxicity involves an interaction between the replication machinery and a drug-mediated topoisomerase I-DNA cleavable complex. The present work indicates, for the first time in mammalian cellular DNA, that one possible outcome of this interaction is a replication-associated DSB, a lesion which is likely to be highly cytotoxic.

Antiviral Agents↗
PubMed1991

A class of amphipathic proteins associated with lipid storage bodies in plants. Possible similarities with animal serum apolipoproteins.

The lipid-storing tissues of plants contain many small (0.2-1 microns) lipid (normally triacylglycerol) droplets which are surrounded and stabilized by a mixed phospholipid and protein annulus. The proteinaceous components of the lipid storage bodies are termed oleosins and are not associated with any other cellular structures. The major oleosins of rapeseed and radish have been isolated by preparative SDS-PAGE and are respectively classes of 19 kDa and 20 kDa proteins. Both protein classes were N-terminally blocked for direct sequencing, but were partially sequenced following limited proteolytic digestion. The major rapeseed oleosin was made up of at least two 19 kDa polypeptides, termed nap-I and nap-II, which have closely related but different amino acid sequences. A single 20 kDa oleosin, termed rad-I, was found in radish. A near full length cDNA clone for a major rapeseed oleosin was sequenced and found to correspond almost exactly to the sequence of nap-II. The sequences of nap-I and rad-I show very close similarity to one another, as do the sequences of nap-II and the previously determined sequence for the major oleosin from maize. All four oleosins have a large central hydrophobic domain flanked by polar N- and C-terminal domains. Secondary structure predictions for the four oleosins are similar and a novel model is proposed based on a central hydrophobic beta-strand region flanked by an N-terminal polar alpha-helix and a C-terminal amphipathic alpha-helix. The possibility that oleosins exhibit structural and functional similarities with some animal apolipoproteins is discussed.

Amino Acid Sequence↗
PubMed1991

Sex-dependent inhibition by retinoic acid of thyroid-hormone action on rabbit reticulocyte Ca2(+)-ATPase activity.

The interaction was examined in vitro of retinoic acid and thyroid hormone with rabbit reticulocyte Ca2(+)-ATPase. L-Thyroxine (T4) (0.1 nM) stimulated female-source Ca2(+)-ATPase activity (+21%; P less than 0.03) and inhibited male-source enzyme (-20%; P less than 0.05). Addition of retinoic acid (10 nM-1 microM) did not influence T4-inhibitable male-source Ca2(+)-ATPase, but caused a 52% loss of T4 effect on the female-source enzyme. Incubation of female-source membranes with testosterone caused the enzyme response to T4 and retinoic acid to become that of male-source membranes, and the male-source enzyme response was converted into the 'female' pattern by exposure to 17 beta-oestradiol. We postulate that a membrane-associated sex-steroid-dependent factor imparts a gender-specific interaction of thyroid hormone and retinoic acid on Ca2(+)-ATPase, and that ultimately the factor is shed during erythrocyte maturation.

Animals↗
PubMed1991

Anthropometric characteristics as discriminators of body-building success.

A total of 36 non-elite male body builders were observed at the time of competition. Their mean physical characteristics (+/- S.D.) were: age, 24.6 +/- 4.8 years; height, 174.4 +/- 6.7 cm; bodyweight, 80.3 +/- 11.0 kg. Their body composition values were: percentage body fat, 9.3 +/- 1.6%; fat-free mass, 72.8 +/- 9.8 kg. The mean somatotype for all subjects was: endomorphy, 2.3 +/- 0.6; mesomorphy, 6.2 +/- 0.9; ectomorphy, 1.2 +/- 0.6. The body proportions (cm) included: biacromial diameter/bi-iliac diameter, 1.463 +/- 0.132; torso length/height, 0.468 +/- 0.018; chest circumference/abdominal circumference, 1.345 +/- 0.059. The body builders in the present study were younger, had lower bodyweights, lower fat-free mass, lower mesomorphy ratings, smaller circumferences, and smaller skeletal dimensions than elite body builders reported in the scientific literature. When the body builders in the present study were divided into successful and unsuccessful groups based on actual competition results, a multiple-discriminant analysis found that biacromial diameter/bi-iliac diameter, torso length/height, chest circumference/abdominal circumference, percentage body fat, height, and bodyweight accounted for 80.6% of the explained variance. These data indicate that the success of a body builder can be accounted for in large part by easily obtained physical variables.

Adult↗
PubMed1991

Consumption of carbonated and noncarbonated sports drinks during prolonged treadmill exercise in the heat.

These studies were done to determine the effect of carbonation and carbohydrate content on either gastric emptying or ad libitum drinking during treadmill exercise in the heat. Four test drinks were used: a 6% carbohydrate, noncarbonated; a 6% carbohydrate, carbonated; a 10% carbohydrate, noncarbonated; and a 10% carbohydrate, carbonated drink. For gastric emptying studies, subjects completed four 1-hr treadmill runs in the heat. They were given 400 mL of test drink at 0 min and 200 mL at 15, 30, and 45 min of exercise. For ad libitum drinking studies, subjects completed four 2-hr treadmill runs in the heat. Gastric residual volumes were similar during the four 1-hr runs. During the 2-hr runs, ad libitum drinking of the four beverages was also similar. Mean values for sweat rate, percentage of body weight lost, and percentage of fluid replaced by ad libitum drinking were similar for the four trials. Similar changes in heart rate, rectal temperature, and ratings of perceived exertion were also observed during the four 2-hr treadmill runs. We conclude that the presence of carbonation in a carbohydrate drink did not have a significant effect on either gastric emptying or ad libitum drinking.

Adult↗
PubMed1991

Serotypes and subtypes of Neisseria meningitidis serogroup B strains associated with meningococcal disease in Canada, 1977-1989.

Typing of Neisseria meningitidis serogroup B disease isolates was carried out using a panel of serotype-and subtype-specific monoclonal antibodies (MAbs) in enzyme-linked immunosorbent assays (ELISA). Three hundred and sixty-two strains isolated from 1977 to 1986 were typed using five serotyping and seven subtyping reagents and outer membrane vesicles as antigens. Serotype 2b accounted for 30% of the disease isolates. The most common subtype was P1.2, which occurred on 18.5% of all strains or 48.6% of the serotype 2b strains. Of the 362 strains typed, 135 (37.3%) were serotyped and 122 (33.7%) were subtyped. Overall, 185 (51.1%) of the strains could be assigned a serotype and (or) subtype. Strains (221) isolated during the years 1987-1989 were typed using a panel of 6 serotyping and 12 subtyping reagents by whole-cell ELISA. Strains of serotypes 4 (21.7%) and 15 (20.8%) were the most common and carried a wide variety of subtypes. The most common subtypes were P1.2 (11.8%) and P1.16 (9.5%). Of the 221 strains analyzed, 132 (59.7%) were assigned a serotype and 123 (55.7%) a subtype and with all 18 MAbs, 192 (86.9%) of the strains were serotyped and (or) subtyped. Two different MAbs to the four epitopes 2a, 15, P1.2, and P1.16 gave discordant reactions of 0.3, 6.6, 2.6, and 2.2%, respectively, when used to analyze over 300 strains of N. meningitidis.

Canada↗
PubMed1991

Synthesis of 70K stress protein by human leukocytes: effect of exercise in the heat.

To determine whether reinduction of 70,000-Da (70K) stress protein synthesis could be used as an assay for thermal history and/or cellular levels of 70K stress protein in hyperthermic humans, leukocytes were obtained before and after 2 h of exercise and then incubated at 37 or 41 degrees C. Five healthy males completed 2 h of treadmill exercise consisting of running at 4-6 km/h for 30-45 min followed by 75-90 min of walking up a 2-10% grade. This exercise bout was performed by two subjects in hot (46 degrees C, 15% relative humidity) and by five subjects in cooler (30 degrees C, 40% relative humidity) environmental conditions. Exercise resulting in rectal temperature (Tre) less than 40 degrees C did not alter the amount of 70K stress protein synthesized by leukocytes incubated at 41 degrees C. In contrast, exercise resulting in Tre greater than 40 degrees C reduced the amount of 70K stress protein synthesized by leukocytes incubated at 41 degrees C. A protein immunoblot, probed with an antibody specific for the inducible 72K stress protein, showed that the reduction of 35S-labeled 70K stress protein in these postexercise leukocyte samples occurred without marked elevations of this protein. In vitro incubation of human leukocytes at 40 degrees C for 15-120 min reduced, in a time-dependent manner, the amount of 70K stress protein synthesized during a subsequent 41 degrees C heat stress. This reduction of 70K stress protein synthesis in 41 degrees C-treated leukocytes was abolished when cycloheximide was present during the 40 degrees C preincubation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Deoxyguanosine enhances the cytotoxicity of the topoisomerase I inhibitor camptothecin by reducing the repair of double-strand breaks induced in replicating DNA.

Deoxyguanosine (dG) enhances the S phase cytotoxicity of camptothecin (CPT), a topoisomerase I (topo I) inhibitor, but by contrast does not affect the toxicity of VM26, a topoisomerase II inhibitor. The 80% survival of S phase human fibroblasts after a 60 min exposure to 0.2 microM CPT is reduced by half in the presence of 25 microM dG. G1 cells are resistant to CPT toxicity, though the levels of the single-strand DNA breaks induced by the drug are similar in G1 and S phase cells. Higher concentrations of dG retard the recovery of RNA and DNA synthesis and inhibit recovery from the S-G2 cycle block after CPT removal. At 100 microM dG the number of CPT-induced protein-linked single-strand DNA breaks is almost doubled, suggestive of a direct effect of dG on the cellular activity of topo I. In the presence or absence of dG, single-strand breaks disappear within minutes of the removal of CPT. We found that the inhibition of topo I by CPT induces the formation of double as well as single-strand breaks in the chromosomal DNA. Previously we have shown, using a pulse-field gel electrophoresis technique, that the double-strand breaks (DSBs) are generated predominantly at sites of replication and not in the bulk DNA. A number of these DSBs are long-lived. The present study shows that dG affects the repair of these DSBs in a dose-dependent manner, and that a higher proportion of the initial lesions induced in nascent DNA remain 24 h after removal of CPT. We suggest that the long-lived double-strand breaks, formed in replicating DNA at the time of CPT exposure, are the lethal drug-induced lesions, which explains both the selective cytotoxicity of CPT towards S phase cells and the enhancement of CPT cytotoxicity by dG.

Camptothecin↗
PubMed1990

High-performance liquid chromatographic method for the determination of polycyclic hydrocarbon metabolite distributions.

Analytical separations and quantification of eight metabolites of benzo[a]pyrene, nine metabolites of 7-methylbenz[c]acridine and nine metabolites of dibenz[a,j]acridine have been carried out on two reversed-phase high-performance liquid chromatographic systems using 3- and 10-microns C8 packings. Quantitative results for the distributions of primary metabolites for the two systems closely agreed and showed that up to 70% savings in chromatographic time could be achieved with the 3 micron particle size columns.

Acridines↗
PubMed1979

Listening.

Explore the source record for details and available documents.

Communication↗