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A R Morgan

Publications and source records attributed to A R Morgan.

At least 37 records · Page 2Linked to original sources
PubMed1994

DNA fragmentation is an early event in cytokine-induced islet beta-cell destruction.

The cytokines, interleukin 1, tumour necrosis factor, and interferon gamma are cytotoxic to islet beta cells, however, their mechanisms of beta-cell killing are not fully characterized. Since DNA damage is a mechanism of cytokine-induced cell death in some cell types, we sought evidence for cytotoxic effects of cytokines at a nuclear level in islet beta cells by measuring DNA fragmentation in rat islets and islet beta-cell lines. The individual cytokines, interleukin 1 (10 U/ml), tumour recrosis factor (10(3) U/ml) and interferon gamma (10(3) U/ml) inhibited insulin release from rat islets, but did not cause DNA fragmentation or destroy islet cells; by contrast, combination of the three cytokines induced DNA fragmentation and islet-cell death. Cytokine-induced DNA fragmentation preceded cell lysis in islet beta-cell lines (RINm5F, rat insulinoma cells; and NIT-1, NOD/Lt mouse transgenic beta cells), whereas in non-islet cell lines (GH-3, rat pituitary; and PC-12, rat adrenal) the cytokines induced cell lysis and no or late DNA fragmentation. Nicotinamide prevented both DNA fragmentation and destruction of RINm5F islet cells by the cytokines. These findings identify DNA as an early target of cytokine action in islet beta cells, and implicate DNA fragmentation as a mechanism of cytokine-induced beta-cell destruction.

Animals↗
PubMed1994

Three-stranded (triplex) DNAs (RNAs): do they have a role in biology?

The first triplexes were homopolymer mixtures, e.g. dTn.dAn.dTn. More complex triplexes could be made on the basis that the base triads [symbol: see text] and [symbol: see text] containing Watson-Crick and Hoogsteen base pairs are isomorphous and so could be expected to give regular triple helices. It follows that such triplexes can only be formed from asymmetric DNAs with pyrimidines (Yn) in one strand and purines (Rn) in the complementary strand. Such triplexes Yn.Rn.Yn are formed with the above rules for pairing of triads with the Hoogsteen C protonated, [symbol: see text]. There are also triplexes built on the theme Yn.Rn.Rn (with triads T:A:A and [symbol: see text]). Here the triads are nearly isomorphous. Recently other triplexes without isomorphous triads at all have been obtained. Also RecA protein can promote triplex formation between a duplex DNA of any sequence and an homologous single-stranded DNA. The latter triplex is evidently important in recombination. The other possible roles for triplexes include transcriptional control, and roles in origins of replication and DNA condensation.

Base Sequence↗
PubMed1993

Evolution of severe aphasia in the first two years post onset.

In this longitudinal recovery study of severe aphasia, subjects were tested five times at 6-month intervals with the Boston Assessment of Severe Aphasia (BASA), for a period of 2 years post onset. The majority of subjects had global aphasia (n = 17), but five had severe Wernicke's aphasia, and two had other varieties of severe aphasia. Significant improvements in communicative functions were noted for up to 18 months post onset, but the greatest improvement occurred in the first 6 months post onset. Most subjects did not change aphasia classification during the 2-year period. Initial individual BASA cluster (subtest) scores were less accurate than the 6-month scores in the prediction of later BASA Total scores. Cluster scores obtained at 6 months post onset could reliably predict BASA Total scores at 24 months post onset.

Adult↗
PubMed1993

Binding of drugs to human plasma proteins, exemplified by Sn(IV)-etiopurpurin dichloride delivered in cremophor and DMSO.

1. The mode-delivery-effect upon the binding of Sn(IV)-etiopurpurin dichloride (SnET2) in human plasma has been studied by ultracentrifugation, combined with absorption and fluorescence spectroscopy. SnET2 was delivered to plasma either in Cremophore EL (CRM) or in dimethyl sulfoxide (DMSO). To facilitate interpretation, optical, conductivity and aggregation properties of SnET2 were obtained for various solutions. 2. The second order rate constant for the aggregation of SnET2 monomers seemed to be remarkably small, of the order of 10(3) M-1 min-1. 3. SnET2 was bound as monomeric entities. Such entities had environmental-sensitive fluorescent properties dependent on the type of protein or solvent (DMSO, CRM, H2O) with which they interacted. 4. SnET2 showed saturable binding with high density subfraction(s) of high density lipoproteins and with one or more high density proteins. Complete or substantial saturation was achieved at the SnET2 level of 3.5 micrograms/ml. Such binding might be mediated by apolipoprotein D and alpha 1-acid glycoprotein. 5. There was little effect of SnET2 concentrations (3.5-35 micrograms SnET2/ml) upon the plasma binding of SnET2, irrespective of the mode of delivery. 6. The percentages of SnET2 bound to low density lipoproteins (LDL), high density lipoproteins (HDL), and high density proteins (HDP) were 10, 70 and 20%, respectively, for delivery in DMSO. The value for LDL also includes binding with very low density lipoproteins (VLDL). For delivery in CRM the corresponding values were 20, 50 and 30%. Apparently, CRM interacted with HDL entities and reduced their affinity for SnET2. 7. The distribution pattern of SnET2 among lipoproteins reflects interactions with apoproteins and/or with surface phospholipids rather than with core lipid constituents of lipoproteins. 8. Conductivity measurements showed that SnET2 was partly an ionic entity in water. 9. The plasma binding of SnET2 is compared with the corresponding binding of other drugs, both tetrapyrroles and nontetrapyrroles.

Adsorption↗
PubMed1993

Base mismatches and mutagenesis: how important is tautomerism?

Tautomerism of nucleotides is an attractive model to explain transitional mutations; the structure of the mismatched base pairs in their enol or imino forms do not distort the DNA double helix. However recent structural data suggest that the mismatched nucleotides are in their normal keto and amino forms. 'Wobble' and other base pairings (for transversions) have C1'-C1' distances close to those found in the classical Watson-Crick base pairs. Kinetic studies show substrates are in their major tautomeric forms in their transition states. This suggests tautomerism may not be important for substitution mutations.

Base Composition↗
PubMed1993

Copper benzochlorin, a novel photosensitizer for photodynamic therapy: effects on a transplantable urothelial tumor.

An iminium salt of octaethylbenzochlorin with copper in the aromatic ring, CDS1, was tested for its tumoricidal effects on the AY-27 N-[4-(5-nitro-2-furyl)-2-thiazolyl] formamide tumor line. CDS1 was found to be an effective photosensitizer in vivo when used in combination with either a xenon arc lamp or a pulsed alexandrite laser. Hemodynamically, CDS1 and light caused a rapid decrease in tumor blood flow. Skin photosensitization was found to be minimal when drug-injected mice were illuminated in a solar simulator.

Animals↗
PubMed1993

Cholecystectomy: a study of patient satisfaction.

A prospective study of 77 patients undergoing open cholecystectomy was undertaken to establish the degree of satisfaction experienced by these patients. Specific symptoms were recorded preoperatively and at one year postoperatively. Two patients died from unrelated diseases during the year of follow-up and were excluded from the analysis. All symptoms inquired about reduced in frequency postoperatively, the best cures being achieved for jaundice, upper abdominal colic, fatty food intolerance and back/shoulder pain. A third of patients developed at least one new symptom during the year of follow-up. Seventy-seven per cent graded themselves either completely or well satisfied. It was not possible to predict from preoperative symptoms those who would be dissatisfied or those who would develop a new symptom. This study refutes recent suggestions that up to 50% of patients are dissatisfied with cholecystectomy and provides data which may be used to counsel patients preoperatively.

Cholecystectomy↗
PubMed1992

The distribution of the tumour photosensitizers Zn(II)-phthalocyanine and Sn(IV)-etiopurpurin among rabbit plasma proteins.

Zn-phthalocyanine (ZnPc) and Sn-etiopurpurin (SnET2) incorporated in unilamellar liposomes or solubilized in a Cremophor-EL emulsion have been incubated in vitro with rabbit plasma or intravenously administered to rabbits. Ultracentrifugation and chromatographic analysis of the plasma showed that ZnPc and SnET2 are mainly released to lipoproteins; within the lipoprotein family, both dyes are preferentially bound by low-density (LDL) and high-density (HDL) lipoproteins. The amount of dye bound with these two lipoprotein classes was related to their relative concentration in the plasma; in most cases a larger amount of photosensitizer was bound to HDL as compared to LDL on a protein concentration basis.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1992

Base alterations in yeast induced by alkylating agents with differing Swain-Scott substrate constants.

The base alterations induced by four alkylating agents, methyl methanesulfonate (MMS), ethyl methanesulfonate (EMS), N-nitroso-N-methylurea (MNU), and N-nitroso-N-ethylurea (ENU), have been determined at the URA3 locus in the yeast Saccharomyces cerevisiae. The mutagen treatment was carried out on yeast cells in the logarithmic phase of growth. The mutants were selected by their resistance to 7.3 mM-5-fluoroorotic acid at pH 3.8. DNA sequence analysis was carried out by the dideoxy chain termination method. The alkylating agents were selected for their widely differing Swain-Scott substrate constants (s values), which are as follows: MMS, s = 0.83; EMS, s = 0.67; MNU, s = 0.42; ENU, s = 0.26. A higher s value is correlated with a higher ratio of 7-alkylguanine to O6-alkylguanine in native DNA in vitro. 125 forward mutations from URA3----ura3 were sequenced with marked differences in the mutational spectra being observed as the s value changed. Five hotspots were recorded for the four alkylating agents. They were all G.C----A.T transition mutations. There was one common hotspot for all of them; there were two additional ones for the two ethylating agents (ENU and EMS) and two different ones for MNU. Four of the five hotspots have the 5'-GG-3' sequence with the 3'-guanine mutated. It was seen that MMS, which has the highest Swain-Scott substrate constant, yielded the widest array of mutational types. As the substrate constants decreased, the types of mutations became more and more restricted to the G.C----A.T transitions and the A.T----T.A transversions. The transitions are consistent with the concept that mutations arise from O6-alkylation of guanine and alkylation of thymine. The transversions are consistent with the notion of N1-alkylation of adenosine or adenylic acid.

Alkylating Agents↗
PubMed1992

Observations on the synthesis and in vivo photodynamic activity of some benzochlorins.

An improved synthesis of benzochlorins is reported. Demetallation of the meso-hydroxymethylvinyl derivative of octaethylporphyrin, followed by treatment with sulfuric acid results in cyclization to generate the corresponding octaethylbenzochlorin in high yield. Prolonged treatment with acid generates the sulfonated derivative. These sensitizers were shown to be efficient photodynamic agents in vivo. Animals bearing a transplanted N-[4-(5-nitro-2-furyl)-2-thiazoly]formamide induced urothelial tumor were treated with either the benzochlorin or its sulfonated derivative. Irradiation of tumors 24 h later resulted in a significant tumoricidal effect in a short term assay. We conclude that benzochlorins warrant further examination as potential agents for use in photodynamic therapy.

Animals↗
PubMed1991

Interaction of recA protein with left-handed Z-DNA.

The ability of recA protein to interact with a Z-DNA polymer, Br-poly(dG-dC), or M13 bacteriophage single-stranded DNA was investigated. RecA protein binds more avidly to Z-DNA than to single-stranded DNA in the absence of a nucleotide cofactor. This binding pattern changes in the presence of adenosine 5'-(gamma-thio)triphosphate (ATP[S]), however, such that the binding to Z-DNA decreases while binding to single-stranded DNA increases roughly 2-fold. When present together, the two forms of DNA compete with each other in the presence of ATP[S]. Experiments involving recA protein binding to recombinant plasmids showed neither a preferential binding of recA protein to the plasmid containing Z-DNA nor a similar effect of ATP[S] to that observed with the Z-DNA polymer. In contrast, maximal binding was obtained with a plasmid (linear or supercoiled) containing a polypurine.polypyrimidine insert, thus suggesting that recA protein displays sequence preferences in its interaction with DNA. The results of the present study provide no evidence that recA protein specifically interacts with or stabilizes the Z-DNA insert of a recombinant plasmid in the left-handed conformation.

Adenosine Triphosphate↗
PubMed1991

An assay for proteinases and their inhibitors based on DNA/ethidium bromide fluorescence.

Proteinases and their inhibitors have become the subject of intense research interest recently, since they control a multitude of very important biological processes, from the development of lambda phage to hypertension in humans. We have developed a simple and sensitive assay for detecting the activity of proteinases and of their proteinase inhibitors. The assay is based on ethidium bromide fluorescence, according to the following principles: (i) Ethidium bromide increases its fluorescence by 25-fold when it intercalates between base pairs of double-stranded DNA. (ii) Histones prevent this large increase in fluorescence by binding with high affinity to DNA thus blocking ethidium bromide intercalation. (iii) A proteinase that digests histones will make more DNA available for ethidium bromide intercalation, thereby producing an increase of fluorescence. Proteinase activity can easily be determined, in the presence of a DNA/histone complex, from the rate of ethidium fluorescence increase. In contrast, activity of a proteinase inhibitor is quantitated by the inhibition of fluorescence gain in the presence of a known amount of proteinase. This assay is rapid, simple, inexpensive, and, at the same time, accurate and sensitive enough to allow quantitation of nanogram amounts of various broad-specificity proteinases and their inhibitors. We show some possible applications of the assay (i) in testing column fractions during protein purifications, (ii) quantitation of alpha 1-antitrypsin in human serum, and (iii) detection of proteinase activity in cell extracts.

DNA↗
PubMed1991

Photophysics and photochemistry of new verdin compounds.

Five different verdins, including one zinc metal chelate, were examined by laser flash techniques. Triplet molar absorption coefficients, triplet and singlet oxygen quantum yields and triplet lifetimes were determined. Zinc methyl pyroverdin (ZNMPV), copro II verdin trimethyl ester (CVTME) and deuteroverdin methyl ester (DVME) have the highest triplet and singlet oxygen quantum yields. ZNMPV and CVTME have the longest triplet lifetimes. Our data are consistent with singlet oxygen as the primary modality for phototherapy and it is suggested that DVME and CVTME may be useful agents.

Lasers↗
PubMed1991

Synthesis and in vivo photodynamic activity of some bacteriochlorin derivatives against bladder tumors in rodents.

Bacteriochlorins have been suggested as potential photosensitizers for use in photodynamic therapy. We have shown that bacteriochlorin-like macrocycles can be generated through cyclization of either 5,10- or 5,15-bis[(ethoxycarbonyl)vinyl]porphyrins; however, the resulting products are rapidly decomposed on exposure to air. More stable systems can be generated by Diels-Alder reactions between dienophiles such as dimethyl acetylenedicarboxylate or tetracyanoethylene, and vinylporphyrinones. Although spectroscopic properties of these latter products resemble those of porphyrinones rather than bacteriochlorins, in vivo studies using the N-[4-(5-nitro-2-furyl)-2-thiazolyl]-formamide-induced rat bladder tumor (AY-27) transplanted into Fisher CDF (F344)/CrlBr rats demonstrated a powerful photodynamic response.

Animals↗
PubMed1991

Treatment of the transplantable FANFT induced bladder tumors with the purpurin SnET2 and red light emitted by a pulsed frequency doubled Nd:YAG laser.

Photodynamic therapy of transplantable N-[4-(5-nitro-2-furyl)-2-thiazolyl] formamide-induced tumors engrafted onto Fischer CDF (F-344)/CrlBR rats that had been sensitized with the photosensitizer tin (ll) etiopurpurin dichloride was performed in combination with visible light (approximately equal to 660 nm) emitted by either a continuous wave argon-dye laser or a pulsed, frequency-doubled Nd:Yag laser. Tumor control was assessed either by tumor dry-weight 12 days after treatment or by the palpatory absence of tumor at 60 days after treatment. Both laser sources were effective in creating the desired photodynamic effect. This study demonstrates the potential for the use of a solid-state pulsed laser for photodynamic therapy when used in combination with the tumor sensitizer tin (ll) etiopurpurin dichloride.

Animals↗