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PubMed1987

[Possible molecular mechanisms of limited or infinite division of cells].

A new approach to the possible molecular mechanisms which determine the ability of cells to the infinite or limited division is presented. The ideas proposed are based on the experimentally demonstrated premise that the realization of DNA reparation and replication depends on the maintenance of a strict balance between the growth rate of replication forks and SSB-protein synthesis within the cells. The limited ability of cells to the division is considered to be a result of the disorganization of DNA reparation and replication processes when the above-mentioned balance is disturbed. The infinite ability of cells to the division is interpreted as a result of the absence of the disorganization of the above-mentioned processes with disturbance of the same balance. The molecular mechanisms which determine either the presence or absence of the cell response to the disturbed balance between the growth rates of replication forks and SSB-protein synthesis are discussed in detail. The conclusion is drawn that the ssb-gene is a protooncogene converted into an oncogene as a result of the dotted mutation manifesting in the functional inactivation of the third domain of the SSB-proteins.

Bacterial Proteins↗
PubMed1988

Production of protein-associated DNA breaks by 10-[diethylaminopropylamino]-6-methyl-5H-pyrido[3',4':4,5]pyrrolo [2,3-g]isoquinoline in cultured L1210 cells and in isolated nuclei: comparison with other topoisomerase II inhibitors.

10-[3-Diethylaminopropylamino]-6-methyl-5H-pyrido[3',4':4,5] pyrrolo[2,3-g]isoquinoline (PZE) is an ellipticine derivative currently in clinical trials. PZE has been postulated to produce cellular DNA lesions by an uncommon mechanism. PZE-induced DNA damage was further investigated in L1210 cells in culture. PZE was highly cytotoxic for these cells (90% inhibitory concentration = 3.1 microM). The effects of PZE on cellular DNA were studied first by alkaline sucrose sedimentation, in comparison with those of 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA). Like m-AMSA, PZE induced DNA strand breaks which were detected without a proteolytic treatment of the cell lysate. This result rules out the existence of covalent protein bridges sealing DNA termini at the break sites. PZE was less active than m-AMSA. DNA fragmentation was maximum at 5 microM and was lower at higher concentrations. The DNA effects of PZE were also studied by alkaline elution, and compared with those of Adriamycin and m-AMSA. Like Adriamycin, PZE induced single-strand breaks (SSBs) in a bell-shaped manner with respect to drug concentration. The maximum SSB frequency [1784 +/- 370 (SEM) rad equivalents)] was obtained at 16 microM. The kinetics of SSB reversion after drug removal was slower than in the case of m-AMSA. Similar bell-shaped curves were obtained for PZE-induced double-strand breaks and DNA-protein cross-links. PZE induced more double-strand breaks per SSB than did m-AMSA. However, as in the case of m-AMSA, PZE induced equal SSB and DNA-protein cross-link frequencies. These results suggest that PZE induces DNA breaks by inhibiting topoisomerase II as do other antitumor intercalators.

Animals↗
PubMed1986

The homologous recombination system of phage lambda. Pairing activities of beta protein.

The red genes of phage lambda specify two proteins, exonuclease and beta protein, which are essential for its general genetic recombination in recA- cells. These proteins seem to occur in vivo as an equimolar complex. In addition, beta protein forms a complex with another polypeptide, probably of phage origin, of Mr 70,000. The 70-kDa protein appears to be neither a precursor nor an aggregated form of either exonuclease or beta protein, since antibodies directed against the latter two proteins failed to react with 70-kDa protein on Ouchterlony double diffusion analysis. beta protein promotes Mg2+-dependent renaturation of complementary strands (Kmiec, E., and Holloman, W. K. (1981) J. Biol. Chem. 256, 12636-12639). To look for other pairing activities of beta protein, we developed methods of purification to free it of associated exonuclease. Exonuclease-free beta protein appeared unable to cause the pairing of a single strand with duplex DNA; however, like Escherichia coli single strand binding protein (SSB), beta protein stimulated formation of joint molecules by recA protein from linear duplex DNA and homologous circular single strands. Like recA protein, but unlike SSB, beta protein promoted the joining of the complementary single-stranded ends of phage lambda DNA. beta protein specifically protected single-stranded DNA from digestion by pancreatic DNase. The half-time for renaturation catalyzed by beta protein was independent of DNA concentration, unlike renaturation promoted by SSB and spontaneous renaturation, which are second order reactions. Thus, beta protein resembles recA protein in its ability to bring single-stranded DNA molecules together and resembles SSB in its ability to reduce secondary structure in single-stranded DNA.

Bacteriophage lambda↗
PubMed1985

Correlations between intercalator-induced DNA strand breaks and sister chromatid exchanges, mutations, and cytotoxicity in Chinese hamster cells.

Intercalator-induced DNA strand breaks in mammalian cells represent topoisomerase II:DNA complexes trapped by intercalators. These complexes are detected as protein-associated DNA single-strand breaks (SSB) and DNA double-strand breaks (DSB) by filter elution. Using Chinese hamster lung fibroblasts (V79 cells) that were treated for 30 min with various concentrations of 4'-(9-acridinylamino)methanesulfon-m-anisidide or 5-iminodaunorubicin, we measured DNA strand breaks (SSB and DSB), sister chromatid exchanges (SCE), mutations at the hypoxanthine:guanine phosphoribosyltransferase locus, and cell killing. Further, we correlated DNA strand breakage with the three other parameters. Both drugs induced SCE, mutations, and cell killing at concentrations which also produced reversible DNA strand breaks. While the quantity of DSB correlated with SCE, mutations, and cytotoxicity for both drugs, we found more SCE, mutations, and cytotoxicity per SSB in cells treated with 5-iminodaunorubicin than in those treated with 4'-(9-acridinylamino)methanesulfon-m-anisidide. These data show that the DSB (but not the SSB) induced by 4'-(9-acridinylamino)methanesulfon-m-anisidide and 5-iminodaunorubicin at DNA topoisomerase II binding sites correlated closely with SCE, mutations, and cell killing and could therefore be responsible for their production.

Aminoacridines↗
PubMed1987

DNA helicase II of Escherichia coli. Characterization of the single-stranded DNA-dependent NTPase and helicase activities.

Escherichia coli helicase II has been purified to near homogeneity from cells harboring a multicopy plasmid containing the structural gene for helicase II, uvrD. In this paper a detailed description of the single-stranded DNA-dependent nucleoside 5'-triphosphatase and helicase reactions catalyzed by helicase II is presented. The results of this study suggest that nucleoside 5'-triphosphate hydrolysis provides the energy required for translocation of the enzyme along single-stranded DNA. Measurements of the rate of ATP hydrolysis using a variety of single-stranded DNAs of known structure and length suggest a processive translocation mechanism for helicase II. Single-stranded DNA coated with either Escherichia coli single-stranded DNA binding protein (SSB) or bacteriophage T4 gene 32 protein fails to support helicase II ATPase activity. Moreover, helicase II is apparently unable to displace a molecule of bound SSB protein from single-stranded DNA when it is encountered in the process of translocation along a single-stranded DNA effector. The helicase reaction has been characterized using an in vitro strand displacement helicase assay. The helicase reaction requires concomitant nucleoside 5'-triphosphatase hydrolysis that is satisfied by the hydrolysis of either rATP or dATP. As the length of duplex DNA present in the partial duplex helicase substrate is increased from 71 base pairs to 343 base pairs, the fraction of duplex DNA molecules that are unwound by helicase II decreases in the absence of any accessory proteins. However, the total number of base pairs of duplex DNA unwound depends primarily on the amount of enzyme added to the helicase reaction and not on the length of the duplex DNA present in the partial duplex DNA substrate. These data suggest the number of base pairs of duplex DNA unwound is directly proportional with the concentration of helicase II in the reaction mixture. In addition, the rate of the unwinding reaction is independent of the length of the duplex DNA available for unwinding. Helicase II has been shown to dissociate from single-stranded DNA molecules infrequently acting as an ATPase. However, the enzyme dissociates from partial duplex helicase substrates more frequently. This suggests a more distributive reaction mechanism on duplex DNA than was observed on single-stranded DNA substrates. The fraction of 343-base pair partial duplex DNA molecules unwound by helicase II can be increased by the addition of appropriate concentrations of E. coli SSB to the reaction. This suggests that helicase II and SSB may act in a concerted reaction to unwind duplex DNA.

Adenosine Triphosphatases↗
PubMed1988

Interaction of a folded chromosome-associated protein with single-stranded DNA-binding protein of Escherichia coli, identified by affinity chromatography.

A single-stranded DNA-binding protein (SSB) affinity column was prepared by optimizing the coupling of Escherichia coli single-stranded DNA-binding protein to Affi-Gel 10. The bound SSB retained its ability to specifically bind single-stranded DNA. When nuclease-treated cell extracts were incubated with the SSB beads overnight at 4 degrees C, a major protein of Mr = 25,000 was bound. At shorter incubation times, two additional proteins of Mr = 32,000 and 36,000 were also detected. In the absence of nuclease treatment, eight additional proteins ranging from Mr = 14,000 to 160,000 also bound to the affinity column. The major Mr = 25,000 protein has been shown to be a folded chromosome-associated protein. Its binding to SSB is strongly enhanced by the addition of DNA polymerase III or DNA polymerase III holoenzyme.

Bacterial Proteins↗
PubMed1986

Serological profiles in subgroups of patients with Sjögren's syndrome.

The serological profiles of 54 patients with primary Sjögren's syndrome (pSS) and 92 rheumatoid arthritis (RA) patients with or without secondary SS (sSS), were retrospectively evaluated and correlated with: different subgroups of SS, degree of minor salivary gland biopsy lymphocytic infiltrates and the presence of glandular and extraglandular manifestations. Antibodies to nuclear antigens (ANA), anti-Ro(SSA) and anti-La(SSB) as well as rheumatoid factor (RF) correlate with definite pSS, while in RA, ANA and anti-Ro(SSA) are associated with the presence of sSS and anti-La(SSB) is practically absent. In pSS patients, the incidence of anti-Ro(SSA) and anti-La(SSB), as well as the titers of ANA and RF, correlate with the degree of salivary lymphocytic infiltrates in class 1+ to 3+. In class 4+, a substantial decrease of the autoantibodies is noted. In pSS patients, anti-Ro(SSA) and anti-La(SSB) correlate with earlier disease onset and longer disease duration, recurrent parotid gland enlargement (RPGE), as well as with the presence of extraglandular manifestations (extr. manif.) particularly splenomegaly/lymphadenopathy and vasculitis. Anti-Ro(SSA) correlates with positive Schirmer's test, ANA with decreased parotid flow rate and extr. manif., while RF correlates with RPGE and subjective xerostomia. In RA patients, autoantibodies were predominantly found in the presence of features of eye dryness: ANA correlate with positive Schirmer's test, Rose-Bengal stain and subjective xerophthalmia, the latter also correlated with anti-Ro(SSA). This study, re-emphasizes the diagnostic significance of autoantibodies for SS, and possibly contributes in the delineation of biological processes in this disease.

Arthritis, Rheumatoid↗
PubMed1983

Detection of DNA single-strand breaks during the repair of UV damage in xeroderma pigmentosum cells.

In this investigation, xeroderma pigmentosum (XP) fibroblasts, XP12BE, were uv-irradiated and then incubated with cytosine arabinoside and hydroxyurea for 4 hr to inhibit the polymerase step of DNA excision repair. By alkaline elution, DNA single-strand breaks (SSB) were detected in XP cells with this regimen with an efficiency of 0.1-0.2 SSB per 10(9) daltons of DNA per J m-2. There was an approximately linear relation between the SSB frequency and uv dose over a range of 0.2 to 25 J m-2. This effect was approximately two orders of magnitude greater in excision-proficient normal human fibroblasts than in XP cells. These results support the conclusion that a low residual level of DNA excision repair occurs in XP group A cells and that the SSB generated during this repair can be accumulated with this polymerase inhibitor.

Cells, Cultured↗
PubMedDate not supplied

Inhibitory effect of hydrocortisone on the release of prostaglandins from dog's brain in hypoxia and cerebral embolism.

Cerebral hypoxia and embolism evoke the release of prostaglandin (PG)-like substances, predominantly of E type, into cerebral venous blood. This has been shown by bioassay used for monitoring the level of PG-like substances in sagittal sinus blood (ssb) in dogs. Hypoxia was induced by inhalation of 8% O2 in N2, embolism by an injection of air into internal carotid artery. This led to an increase in the level of PG-like substances in ssb, with no detectable change in the concentration of PGs in peripheral venous blood, indicating that PGs detected in ssb originate from cerebral venous outflow. The output amounted 6 ng/ml (in PGE2 equivalents). Hydrocortisone (HC) in a dose of 30 mg/kg suppressed the release of PG-like substances induced by either hypoxia or embolism. These results were confirmed by radioimmunoassay of PGs in ssb. Plasma levels of PGs E and F2 alpha were elevated following cerebral embolism as compared to initial values and greatly suppressed by HC administration. Suppression of PG formation by HC in this experimental system seems to be related to the membrane--stabilizing action of this hormone. This is of interest in view of the usefulness of steroid therapy in cerebrovascular pathology.

Animals↗
PubMed1994

Targeted versus non-targeted DNA helicase activity of the RuvA and RuvB proteins of Escherichia coli.

The RuvA and RuvB proteins of Escherichia coli promote the branch migration of Holliday junctions in vitro. To understand the relationship between branch migration and the intrinsic 5'-->3' DNA helicase activity of RuvAB, the requirements and substrate specificity of the helicase reaction have been studied in more detail. We find that RuvAB-mediated DNA unwinding and branch migration reactions show similar requirements for Mg2+ and ATP and are inhibited to a similar extent by ADP and ATP gamma S (adenosine 5'-O-(3-thiotriphosphate)). The helicase activity, measured by the dissociation of a short fragment from circular single-stranded DNA, requires both RuvA and RuvB and is stimulated by subsaturating concentrations of single-strand binding protein (SSB). In contrast, saturating concentrations of SSB are inhibitory. Using substrates that contain a DNA junction, which permits the specific binding of RuvA, we find that the RuvA and RuvB proteins promote two types of helicase reactions: nonspecific reactions, which are sensitive to inhibition by stoichiometric amounts of SSB, and junction-targeted reactions, which are not inhibited by SSB. Using three-armed structures, we observe that junction-targeted reactions display a polarity and result in asymmetric product formation. Junction-specific binding and the subsequent initiation of DNA unwinding are likely to represent early steps in the process of branch migration.

Adenosine Triphosphatases↗
PubMed1993

[The repair of gamma-induced single-stranded breaks in the transcribed and nontranscribed DNA of HeLa cells].

The repair of gamma-ray-induced DNA single-strand breaks (SSB) in transcribed (Alu-enriched DNA, proto-oncogene c-myc) and non-transcribed (human satellite III) DNA of HeLa cells has been investigated. A special methodical approach has been developed. The method involved alkaline sucrose sedimentation followed by Southern hybridization in situ of 32P labelled plasmids (probes) containing sequences analysed with total DNA distributed through sucrose gradient fractions. The degree of the probes hybridization with cellular DNA was the criteria of the damage and that of DNA repair. The induction of DNA SSB after irradiation (100 Gy) in Alu-enriched DNA and c-myc gene was shown to be 1.3-1.4 time more often while than in satellite DNA, and 1.4 time lower compared to that in total DNA. The rate of DNA repair was different: the most part of lesions was eliminated in the first 10-20 minutes in all cases. For this time 60-67, 50-66, 35-50 and 45-50% DNA SSB were eliminated from transcribed DNA (c-myc, Alu), non-transcribed DNA (satellite III) and total DNA, respectively. Thus, the preferable (fast) repair of gamma-ray-induced DNA SSB takes place in transcribed DNA compared to that in non-transcribed DNA of HeLa cells.

Autoradiography↗
PubMed1994

Differential regulation of Hsp70 subfamilies by the eukaryotic DnaJ homologue YDJ1.

In Saccharomyces cerevisiae Ydj1p, a DnaJ homolog, is localized to the cytosol with the Ssa and Ssb Hsp70 proteins. Ydj1p helps facilitate polypeptide translocation across mitochondrial and endoplasmic reticulum membranes (Caplan, A. J., Cyr, D. M., and Douglas, M. G. (1992) Cell 71, 1143-1155) and can directly interact with Ssa1p to regulate chaperone activity (Cyr, D. M., Lu, X., and Douglas, M. G. (1992) J. Biol. Chem. 267, 20927-20931). In this study, the role of Ydj1p in modulating ATP-dependent reactions catalyzed by Ssa and Ssb Hsp70 proteins has been examined using purified components and compared with that of other Hsp70 homologs BiP and DnaK. Ssa1p, Ssa2p, and Ssb1/2p all formed stable complexes with the mitochondrial presequence peptide, F1 beta(1-51). ATP alone had only modest effects on polypeptide complex formation with Ssa1p and Ssa2p, but prevented the majority of polypeptide binding to BiP and DnaK. ATP by itself also reduced polypeptide binding to Ssb1/2p to a level that was intermediate between that observed for the Ssa Hsp70 proteins tested and BiP and DnaK. ATP hydrolysis by Ssa1p, Ssa2p, and Ssb1/2p occurred at similar rates. Ydj1p was a potent modulator of the both the ATPase and polypeptide binding activities of Ssa1p and Ssa2p. In contrast, Ydj1p had little effect on the ATPase and polypeptide binding activity of Ssb1/2p. Therefore the chaperone-related activities of Ssa and Ssb Hsp70 proteins exhibit significant differences in sensitivity to ATP and YDJ1p. These data indicate that regulation of Hsp70 activity by DnaJ homologs can be specific. The specificity of interactions between Ydj1p and the Ssa and Ssb Hsp70 proteins observed could contribute in determining the functional specificity of these chaperones in the cytosol. In related experiments, F1 beta(1-51) was found to reduce the extent to which Ydj1p stimulated Ssa1p ATPase activity. This effect correlated with the formation of F1 beta(1-51).Ssa1p complexes. We propose that intramolecular communication between the polypeptide binding, ATPase and DnaJ regulatory domains on Ssa1p plays a role in the regulation of chaperone activity.

Adenosine Triphosphatases↗
PubMed1994

Yield of single-strand breaks due to attack on DNA by scavenger-derived radicals.

We have measured the yield of single-strand breaks (SSBs) in plasmid DNA after 137Cs gamma irradiation, in the presence of dimethyl sulfoxide (DMSO). In the presence of oxygen, the formation of SSBs is due to hydroxyl radical attack. As the DMSO concentration is increased from 10(-4) mol dm-3 to 1 mol dm-3, the SSB yield in the presence and absence of oxygen decreases by over 100-fold and less than 10-fold, respectively. From the DMSO and DNA concentration dependencies of the SSB yield in the absence of oxygen, the second-order rate constant for the reaction of the methyl radical (derived from DMSO) and DNA can be estimated as k2 = 8.8 x 10(4) dm3 mol-1 s-1. Several other scavengers were compared with DMSO under anoxia. Radicals derived from isopropyl alcohol and glycerol also caused SSB formation in DNA, while those from 2-deoxyribose, thymine, 1,3-dimethylthymine and 1,3-dimethyluracil did not. In the case of the scavenger tert-butyl alcohol, it is unclear whether the hydrogen atom (H.) or an organic radical is responsible for the higher SSB yield under anoxic conditions.

DNA Damage↗
PubMed1993

An interaction between replication protein A and SV40 T antigen appears essential for primosome assembly during SV40 DNA replication.

Replication protein A from human cells (hRPA) is a multisubunit single-stranded DNA-binding protein (ssb) and is essential for SV40 DNA replication in vitro. The related RPA from Saccharomyces cerevisiae (scRPA) is unable to substitute for hRPA in SV40 DNA replication. To understand this species specificity, we evaluated human and yeast RPA in enzymatic assays with SV40 T antigen (TAg) and human DNA polymerase alpha/primase, the factors essential for initiation of SV40 DNA replication. Both human and yeast RPA stimulated the polymerase and (at subsaturating levels of RPA) the primase activities of human DNA polymerase alpha/primase on homopolymer DNA templates. In contrast, both human and yeast RPA inhibited synthesis by DNA polymerase alpha/primase on natural single-stranded DNA (ssDNA) templates. T antigen reversed the inhibition of DNA polymerase alpha/primase activity on hRPA-coated natural ssDNA, as previously described, but was unable to reverse the inhibition on scRPA or Escherichia coli ssb-coated templates. Therefore, the ability of an ssb to reconstitute SV40 DNA replication correlated with its ability to allow the TAg stimulation of polymerase alpha/primase in this assay. Enzyme-linked immunoassays demonstrated that hRPA interacts with TAg, as previously described; however, scRPA does not bind to TAg in this assay. These and other recent results suggest that T antigen contains a function analogous to some prokaryotic DNA replication proteins that facilitate primosome assembly on ssb-coated template DNAs.

Animals↗
PubMed1993

Variation of single-strand break yield with scavenger concentration for plasmid DNA irradiated in aqueous solution.

We have measured the yield of single-strand breaks (SSBs), induced by 137Cs gamma radiation as assayed by agarose gel electrophoresis, for three plasmids and SV40 DNA irradiated in aerobic aqueous solution. DNA SSBs are caused mainly by the hydroxyl radical under these conditions. To characterize the reactivity of DNA with the hydroxyl radical, we investigated the variation of the G value for SSBs [G(SSB)] with the concentration of added hydroxyl radical scavengers. We find that simple competition kinetics does not describe our results, but that a nonhomogeneous kinetics model is in good agreement. At a DNA concentration of 50 micrograms cm-3, G(SSB) for the direct effect is about 1 x 10(-5) mumol J-1 for the DNA substrates studied. This is equivalent to 2 x 10(-10) SSB Gy-1 Da-1. Estimates of the efficiency of SSB induction per OH. radical interaction with DNA (0.32-0.44) reveal that all plasmids are essentially equal in reactivity.

Cesium Radioisotopes↗
PubMed1996

[The repair of DNA single-stranded breaks and degradation under the action of novobiocin in gamma-irradiated HeLa cells].

A method of sedimentation in alkaline sucrose gradients was used to study repair of gamma-induced DNA single strand breaks (SSB) and DNA degradation in HeLa cells treated with novobiocin (Nb), an inhibitor of topoisomerase II. After irradiation in a dose of 150 Gr, Nb in a concentration of 1 mM does not affect the effectivity of SSB repair and DNA molecular mass in the irradiated cells treated with Nb for 60-180 min before irradiation. Besides, it does not lead to additional DNA degradation in cells treated with Nb for 60-180 min before gamma-rays, as well as following a postirradiation incubation during 60-180 min. Nb in a concentration of 4 mM, much exceeding the Nb concentration when DNA synthesis and cell transit through the cycle are inhibited, causes the following changes. It does not affect DNA molecular mass in non-irradiated cells, inhibits repair of DNA SSB, causes partial DNA degradation, if cells are treated for 60-180 min before gamma-rays and during the following postirradiation incubation (60-180 min). Taking into account the Nb-mediated DNA degradation, the inhibition of DNA repair by Nb appears not significant. Since in a concentration, which inhibits topoisomerase II, Nb does not affect repair of gamma-induced DNA SSB, one may assume the lack of involvement of topoisomerase II into repair of these DNA lesions. Inhibition of DNA repair by 4 mM Nb may result from its effect on the number of proteins, including reparative DNA polymerase, rather than from a selective effect on topoisomerase II.

Anti-Bacterial Agents↗
PubMed1997

Studies on the modulation of DNA damage. 1: A simple kinetic model for radioprotection of DNA in aqueous solution.

A simple kinetic model, based on the assumption that direct and indirect interactions of ionising radiations with DNA lead to formation of DNA-radicals which are precursors of single strand break (ssb) and double strand break (dsb) is presented. Considering accessibility of OH attack on DNA and assuming homogenous kinetics, the model has been validated by using experimental data on radiation-induced strand break formation in presence of methanol (MeOH) and glutathione (GSH). Fitting the D37 values for ssb in aqueous solution of pBR322 DNA in the presence of the predominantly A-T minor groove-ligand Hoechst 33258, the value of the rate constant of OH scavenging by DNA-bound Hoechst was estimated by Martin and his group as 2.7 x 10(11) dm3 mol-1 s-1 (Martin, R.F. and Denison, L. (1992), Int. J. Radiat. Oncol. Biol. Phys., 23, 578-584). Using aqueous solution of calf thymus DNA in the presence of Hoechst this rate constant has been determined by pulse radiolysis as 1.1 x 10(9) dm3 mol-1 s-1. The yield of strand breaks has also been measured by low angle laser light scattering. Using the experimentally measured value of the rate constant of OH scavenging by DNA-bound Hoechst in the model, calculations show that OH scavenging alone could not explain the overall protection provided by Hoechst; there should be quenching of DNA-radicals by Hoechst. Fitting the yield of radiation-induced ssb (G(ssb)) obtained for CT DNA and pBR322 DNA, the rate constant of this DNA-radical quenching has been calculated as 10(6) dm3 mol-1 s-1, which agrees with pulse radiolytic data. Using these rate constant values, calculations show that the protection against radiation-induced dsb formation provided by the combination of Hoechst with GSH is more than that by the combination of MeOH with GSH.

DNA Damage↗
PubMed1998

A prospective randomised trial of four-layer versus short stretch compression bandages for the treatment of venous leg ulcers.

This trial was undertaken to examine the safety and efficacy of four-layer compared with short stretch compression bandages for the treatment of venous leg ulcers within the confines of a prospective, randomised, ethically approved trial. Fifty-three patients were recruited from a dedicated venous ulcer assessment clinic and their individual ulcerated limbs were randomised to receive either a four-layer bandage (FLB)(n = 32) or a short stretch bandage (SSB)(n = 32). The endpoint was a completely healed ulcer. However, if after 12 weeks of compression therapy no healing had been achieved, that limb was withdrawn from the study and deemed to have failed to heal with the prescribed bandage. Leg volume was measured using the multiple disc model at the first bandaging visit, 4 weeks later, and on ulcer healing. Complications arising during the study were recorded. Data from all limbs were analysed on an intention to treat basis; thus the three limbs not completing the protocol were included in the analysis. Of the 53 patients, 50 completed the protocol. At 1 year the healing rate was FLB 55% and SSB 57% (chi 2 = 0.0, df = 1, P = 1.0). Limbs in the FLB arm of the study sustained one minor complication, whereas SSB limbs sustained four significant complications. Leg volumes reduced significantly after 4 weeks of compression, but subsequent volume changes were insignificant. Ulcer healing rates were not influenced by the presence of deep venous reflux, post-thrombotic deep vein changes nor by ulcer duration. Although larger ulcers took longer to heal, the overall healing rates for large (> 10 cm2) and small (10 cm2 or less) ulcers were comparable. Four-layer and short stretch bandages were equally efficacious in healing venous ulcers independent of pattern of venous reflux, ulcer area or duration. FLB limbs sustained fewer complications than SSB.

Adult↗