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Biomedical subjects

A J Davison

Publications and source records attributed to A J Davison.

At least 73 records · Page 4Linked to original sources
PubMed1990

Variations in the uptake of beta-carotene in the oral mucosa of individuals after 3 days of supplementation.

Variations in the response of individuals to beta-carotene supplementation were studied by measuring the accumulation of beta-carotene in oral mucosa cells. Beta-carotene was administered orally to 178 individuals for 3 consecutive days, exfoliated oral mucosa cells were collected by brushing the entire oral mucosa on the 7th day following supplementation, and the beta-carotene content was measured by HPLC analysis of the pronase-treated cells. The rise in beta-carotene levels in the oral mucosa following supplementation varied considerably. Significant differences in mean beta-carotene levels in the oral mucosa were observed in 4 population groups. After supplementation, beta-carotene levels increased by factors of 10.3 (100 Mile House), 7.8 (Williams Lake), 6.9 (Lytton) and 3.4 (Vancouver), respectively. This difference in mean beta-carotene values is due to there being different proportions of weak and strong responders in the various population groups. Neither peak levels nor increases in beta-carotene levels were correlated with base-line concentrations of beta-carotene in the pre-supplementation samples. A second supplementation was given to 54 individuals several months after the initial supplementation. Of 17 weak responders in the first supplementation study, 10 (58.8%) individuals again showed only a small increase. A time-course study revealed that low responders showed no significant changes in beta-carotene levels over the 21 days following supplementation. Particular attention should be paid to weak responders when results of intervention trials using beta-carotene are interpreted.

Adult↗
PubMed1990

Multiple actions of superoxide dismutase: why can it both inhibit and stimulate reduction of oxygen by hydroquinones?

Superoxide dismutase can either inhibit or stimulate autoxidation of different hydroquinones, suggesting multiple roles for O2.-. Inhibitory actions of superoxide dismutase include termination of O2.(-)-propagated reaction chains and metal chelation by the apoprotein. Together, chelation of metals and termination of O2.(-)-propagated chains can effectively prevent reduction of oxygen. Chain termination by superoxide dismutase can thus account for negligible accumulation of H2O2 without invoking a superoxide:semiquinone oxidoreductase activity for this enzyme. One stimulatory action of superoxide dismutase is to decrease thermodynamic limitations to reduction of oxygen. Whether superoxide dismutase inhibits or accelerates an autoxidation depends on the reduction potentials of the quinone and the availability of metal coordination for inner sphere electron transfers.

Animals↗
PubMed1990

Mitochondrial mutations may increase oxidative stress: implications for carcinogenesis and aging?

The sensitivity of mitochondrial DNA to damage by mutagens predisposes mitochondria to injury on exposure of cells to genotoxins or oxidative stress. Damage to the mitochondrial genome causing mutations or loss of mitochondrial gene products, or to some nuclear genes encoding mitochondrial membrane proteins, may accelerate release of reactive species of oxygen. Such aberrant mitochondria may contribute to cellular aging and promotion of cancer.

Aging↗
PubMed1990

Identification of the genes encoding two capsid proteins of herpes simplex virus type 1 by direct amino acid sequencing.

Amino-terminal amino acid sequencing was carried out on proteins purified from herpes simplex virus type 1 capsids. The sequences of two capsid proteins (VP19C and VP23) showed them to be encoded by genes UL38 and UL18, respectively. The product of UL38 has been shown to be essential for capsid assembly, but no role has previously been assigned to the product of UL18.

Amino Acid Sequence↗
PubMed1989

Structure of vaccinia virus early promoters.

Functional elements of a vaccinia virus early promoter were characterized by making a complete set of single nucleotide substitutions, as well as more complex mutations, and assaying their effects on gene expression. Synthetic oligonucleotides, based primarily on the sequence of the 7.5-kD early promoter, were inserted into a plasmid vector containing the lacZ gene of Escherichia coli flanked by sequences from the thymidine kinase (TK) gene of vaccinia virus. The lacZ gene, under control of the synthetic promoter, was introduced into the vaccinia virus genome at the TK locus by homologous recombination, and each of the 331 different recombinant viruses thus obtained was assayed for beta-galactosidase expression. The relative amounts and precise 5' ends of lacZ mRNAs specified by a subset of the recombinants were determined by primer extension. Many promoters were tested for their ability to direct specific transcription in vitro. A generally good correlation was noted between measurements of promoter strength estimated by beta-galactosidase expression, primer extension of in vivo mRNA and transcription in vitro. A relatively simple picture emerged from the analysis. The early promoter consists of a 16 base-pair critical region, in which most single nucleotide substitutions have a major effect on expression, separated by 11 base-pairs of a less critical T-rich sequence from a seven base-pair region within which initiation with a purine usually occurs. For the critical region of the 7.5-kD promoter, AAAAgTaGAAAataTA, any substitution of an upper-case nucleotide reduced expression, usually drastically, whereas certain substitutions of lower-case nucleotides maintained or significantly enhanced expression. On the basis of this analysis, the wide range of activities of natural promoters could be attributed to the presence of one or more non-optimal nucleotides in the critical region. Moreover, single nucleotide substitutions in such promoters had the predicted enhancing effects. Most mutations in the critical region of the 7.5-kD promoter behaved independently, but some nucleotide substitutions compensated for potentially detrimental nucleotides at other positions. Promoters substantially stronger than any natural ones examined were constructed by combining several up-mutations within the critical region of the 7.5-kD promoter and by repeating the critical region sequence. Like the TATA box of eukaryotic RNA polymerase II promoters, the critical region specifies the site of transcriptional initiation.

Base Sequence↗
PubMed1989

Structure of vaccinia virus late promoters.

Functional elements of vaccinia virus late promoters were characterized by mutagenesis. Synthetic oligonucleotides were inserted into a plasmid vector containing the lacZ gene of Escherichia coli flanked by sequences from the thymidine kinase (TK) gene of vaccinia virus. The lacZ gene, under control of the synthetic promoter, was introduced into the vaccinia virus genome at the TK locus by homologous recombination, and each of the 122 recombinants thus obtained was assayed for beta-galactosidase expression. The relative amounts and 5' ends of lacZ mRNAs specified by a subset of the recombinants were determined by primer extension. The analysis indicated that late promoters may be considered in terms of three regions; an upstream sequence of about 20 base-pairs, rich in T and A residues, separated by a spacer region of about six base-pairs from a highly conserved (-1)TAAAT(+4) element within which transcription initiates. All single nucleotide substitutions within the three A residues of the TAAAT, as well as the addition of a fourth A residue, caused drastic reductions in promoter strength. All substitutions of the T residues at -1 and +4 were also detrimental to promoter activity, to an extent that depended on the strength of the promoter as determined by the upstream sequence. mRNA synthesis appeared to initiate within the three A residues regardless of promoter strength. The 5'-poly(A) leader, which is a unique feature of poxvirus late mRNAs, was diminished in length when either of the T residues at -1 and +4 was mutated, was absent or limited to a few nucleotides when any of the three A residues was substituted, but was unaffected by changes outside the TAAAT sequence. The data are consistent with a model for the generation of the normal 5'-poly(A) leader by an RNA polymerase slippage mechanism requiring three consecutive A residues. Single nucleotide substitutions within the six base-pairs upstream and three base-pairs downstream from the TAAAT sequence had modest effects on promoter strength. The most and least favourable changes led to a fourfold increase and an eightfold decrease in activity, respectively. Sequences further upstream were essential for late promoter function; tracts of T or A residues enhanced expression up to 20-fold, the former conferring much greater activity. Highest expression was obtained with a tract of 18 or 20 T residues.(ABSTRACT TRUNCATED AT 400 WORDS)

Base Sequence↗
PubMed1989

Effects of active oxygen generated by DTT/Fe2+ on cardiac Na+/Ca2+ exchange and membrane permeability to Ca2+.

Sarcolemmal vesicles isolated from bovine heart were preincubated at 37 degrees C with an oxygen radical generating system consisting of 1 mM dithiothreitol (DTT) and 50 microM FeSO4. Exposure of the vesicles for 1 to 40 mins stimulated Na+/Ca2+ exchange about 2.5-fold. The DTT/Fe2+ treatment decreased the apparent Km for Ca2+ of Nai+-dependent Ca2+ uptake by 80% (from 63 to 13 microM). The effect on Vmax was much smaller however. The resulting stimulation of exchange activity was diminished by the presence of desferrioxamine (95%) or catalase (60%). In contrast, superoxide dismutase and sodium formate did not prevent the effects of DTT/Fe2+ on the exchanger. Neither Zn2+ nor Ga3+ could replace Fe2+ in the stimulation of Na+/Ca2+ exchange. Passive Ca2+ efflux was determined by first allowing Na+/Ca2+ exchange to continue to plateau values and then diluting the loaded vesicles in the presence of EGTA. Ca2+ leakage from the vesicles was slightly but significantly (P less than 0.05) increased by the action of DTT/Fe2+, the rate constants for the passive Ca2+ efflux being 0.22 and 0.26/min in control and treated groups, respectively. The calcium loading observed in myocytes in ischemia/reperfusion injury suggests that the stimulation of Na+/Ca2+ exchange by active oxygen may moderate the myocardial response to oxygen mediated injuries including ischemia/reperfusion injury. However, the clinical relevance of these phenomena is far from clear as the stimulation depends in part on the Km for Ca2+ prior to treatment.

Adenosine Triphosphatases↗
PubMed1989

Intermediates in the aerobic autoxidation of 6-hydroxydopamine: relative importance under different reaction conditions.

Autoxidation of 6-hydroxydopamine (6-OHDA) proceeds through a balanced network of: transition metal ions, superoxide, hydrogen peroxide, hydroxyl radicals, and other species. The contribution of each to the reaction mechanism varies dramatically depending upon which scavengers are present. The contribution of each propagating intermediate increases when the involvement of others is diminished. Thus, superoxide (which is relatively unimportant when metal ions can participate) dominates the reaction when transition metal ions are bound (especially at higher pH), and it becomes essential in the simultaneous presence of catalase plus chelators. Transition metal ions participate more if superoxide is excluded; hydrogen peroxide becomes more important if both .O2- and metal ions are excluded; and hydroxyl radicals contribute more to the reaction mechanism if both H2O2 and .O2- are excluded. Superoxide dismutase inhibited strongly, by two distinct mechanisms: a high affinity mechanism (less than 13% inhibition) at catalytically effective concentrations, and a low affinity mechanism (almost complete inhibition at the highest concentrations) which depends upon both metal binding and catalytic actions. In the presence of DETAPAC catalytic concentrations of superoxide dismutase inhibited by over 98%. Conversely, metal chelating agents inhibited strongly in the presence of superoxide dismutase. When present alone they stimulated (like EDTA), inhibited (like desferrioxamine), or had little effect (like DETAPAC). Catalase which stimulated slightly but consistently (less than 5%) when added alone, inhibited 100% in the presence of superoxide dismutase + DETAPAC. However, in the absence of DETAPAC, catalase decreased inhibition by superoxide dismutase, yielding a 100% increase in reaction rate. Hydroxyl scavengers (formate, mannitol or glucose) alone produced little or no (less than 10%) inhibition, but inhibited by 30% in the presence of catalase + superoxide dismutase. Paradoxically, they stimulated the reaction in the presence of catalase + superoxide dismutase + DETAPAC.

Aerobiosis↗
PubMed1988

Correlation clusters in the accumulation of metals in human scalp hair: effects of age, community of residence, and abundances of metals in air and water supplies.

Scalp hair samples taken from 122 children and 27 adults from three native Indian villages in northern Alberta, Canada were analyzed for 32 metals, in an attempt to trace industrial pollution into the human population. One of the villages has been exposed since 1967 to increased levels of several metals due to its proximity to the world's first two oil sands petroleum extraction plants (Suncor and Syncrude), which release large amounts of metals into the environment. Metal-enriched particulates are emitted at a rate of 547-780 kg h-1 for Suncor, and 713-1067 kg h-1 for Syncrude. To test the hypothesis that hair content reflected accumulation of environmental metals, water and aerometric samples were collected and analyzed for their metal content. These analyses demonstrated that elevated levels of nine metals in hair from children in one of the control villages (Garden River) are (with the exception of Al) correlated with increased levels of metals in water and air. Moreover, increased levels of Cu, but lowest levels of all other metals were found in hair and environmental samples from one control village (Fort Chipewyan). Correlation matrices for metals in the hair samples revealed three sets of highly intercorrelated metals ('correlation clusters'): (i) Pb/Cd; (ii) Al/V/Fe; (iii) Ca/Mg/Sr/Ba. These groups of metals were significantly intercorrelated (r greater than 0.6, p less than 0.001) in the total population, and in both children and adults, or both males and females, as well as when the population was compared according to community of residence. The robustness of the clusters is particularly noteworthy in view of large differences in the proportions and absolute amounts of the various metals in hair from children in the three villages. Plots of metal levels in hair as a function of age of subject reveal a dramatic decrease in concentrations of Al, V, and Fe during the first years of life. The high levels of Al and V in hair from very young children may reveal a lower selectivity in metal absorption, and a higher risk of toxicity during a period of rapid growth when need for nutritionally essential metals is particularly high.

Adult↗
PubMed1988

The complete DNA sequence of the long unique region in the genome of herpes simplex virus type 1.

We have determined the DNA sequence of the long unique region (UL) in the genome of herpes simplex virus type 1 (HSV-1) strain 17. The UL sequence contained 107,943 residues and had a base composition of 66.9% G + C. Together with our previous work, this completes the sequence of HSV-1 DNA, giving a total genome length of 152,260 residues of base composition 68.3% G + C. Genes in the UL region were located by the use of published mapping analyses, transcript structures and sequence data, and by examination of DNA sequence characteristics. Fifty-six genes were identified, accounting for most of the sequence. Some 28 of these are at present of unknown function. The gene layout for UL was found to be very similar to that for the corresponding part of the genome of varicella-zoster virus, the only other completely sequenced alphaherpesvirus, and the amino acid sequences of equivalent proteins showed a range of similarities. In the whole genome of HSV-1 we now recognize 72 genes which encode 70 distinct proteins.

Amino Acid Sequence↗
PubMed1988

Characterization of the genome of equine herpesvirus 1 subtype 2.

The genome structure of equine herpesvirus 1 (EHV-1) subtype 2 was shown by electron microscopic studies and restriction endonuclease site mapping to comprise two covalently linked segments (L, 109 kbp; S, 35 kbp). The S segment contains a unique sequence (US) flanked by a substantial inverted repeat (TRS/IRS). Thus, the genome structure of EHV-1 subtype 2 is similar to that published previously for EHV-1 subtype 1, but the two subtypes differ in the occurrences of EcoRI and BamHI restriction sites. Hybridization studies using cloned EHV-1 DNA showed that the genome of EHV-1 subtype 2 is colinear with the genomes of EHV-1 subtype 1 and herpes simplex virus type 1. DNA sequence data for four EHV-1 subtype 2 genes, including one potentially encoding a glycoprotein, were obtained by sequencing a 4574 bp BamHI fragment containing the junction between US and TRS. The genome structure, hybridization and sequence data confirm that EHV-1 subtype 2 is of the alphaherpesvirus lineage.

Amino Acid Sequence↗
PubMed1988

Mead Johnson Critical Care Symposium for the Practising Surgeon. 5. The diagnosis and management of common soft-tissue infections.

Soft-tissue bacterial infections range from the superficial, relatively benign form, readily treated by oral administration of antibiotics, to the highly lethal variety which requires extensive surgical débridement, administration of broad-spectrum antibiotics and patient monitoring in the intensive care unit. The key to patient survival in the latter group is early diagnosis and treatment. Those at risk of serious infections include diabetic and cirrhotic patients and trauma victims who have been treated either surgically or medically. In addition to awareness of the possibility of serious infection, x-ray films of the soft tissue to show gas, aspiration of fluid collections for Gram's staining and local incision of the tissue to inspect fascia and muscle are all useful aids in diagnosis. This review attempts to classify soft-tissue infections and to recommend an approach to diagnosis and management.

Bacterial Infections↗
PubMed1987

Interactions between metals, ligands, and oxygen in the autoxidation of 6-hydroxydopamine: mechanisms by which metal chelation enhances inhibition by superoxide dismutase.

Transition metal ions and superoxide participate in different autoxidations to a variable extent. In the reaction of 6-hydroxydopamine (6-OHDA) with oxygen at pH 7.0 or 8.0, addition of 5 to 300 U/ml superoxide dismutase inhibited autoxidation by up to 96% at the highest concentrations. Superoxide dismutase at concentrations of 5-20 U/ml inhibited by less than 40% when present alone, but inhibited by over 99% in the presence of desferrioxamine or histidine. EDTA also enhanced the inhibition by 20 U/ml superoxide dismutase to 86%, even though EDTA accelerated the autoxidation of 6-OHDA when present alone or with desferrioxamine. In contrast, other ligands, such as ADP or phytic acid, had little or no effect on inhibition by superoxide dismutase. Proteins such as albumin, cytochrome oxidase, or denatured superoxide dismutase also enhanced inhibition by active superoxide dismutase from less than 40% to over 90%. Evidently, in the presence of redox active metals, autoxidation occurs by inner sphere electron transfer, presumably within a ternary 6-OHDA.metal.oxygen complex. This mechanism does not involve free O2-. and is not inhibited by superoxide dismutase. On the other hand, the presence of certain ligands (including proteins) diminishes the ability of trace metals to exchange electrons with 6-OHDA or oxygen by an inner sphere mechanism. These ligands render autoxidation dependent on propagation by O2-. and therefore inhibitable by superoxide dismutase. Previously conflicting reports that superoxide dismutase alone inhibits 6-OHDA autoxidation are thus explicable on the basis that at sufficient concentration the apoprotein coordinates trace metals in such a way to preclude inner sphere metal catalysis.

Adenosine Diphosphate↗
PubMed1987

Identification and sequence of the gene encoding gpIII, a major glycoprotein of varicella-zoster virus.

The genome of varicella-zoster virus (VZV) encodes three major glycoproteins, two (gpI and gpII) having been mapped and sequenced, which carry epitopes capable of eliciting neutralizing antibodies. The product of the third major glycoprotein gene (gpIII) was purified, and seven consecutive amino acids at its N-terminus were identified. A degenerate pool of oligonucleotides based upon this sequence was used as a probe to localize the gpIII gene to the HindIII B fragment of the VZV genome. An analysis of the DNA sequence from this region revealed an open reading frame (ORF) encoding 841 amino acids. Rabbit antisera against three synthetic peptides derived from the putative gpIII gene recognized a protein which comigrated with gpIII in Western blots and immunoprecipitation analysis. Preclearing with a monoclonal antibody to gpIII specifically abolished immunoprecipitation of this protein. Also a polypeptide translated from mRNA selected by the putative gpIII gene could be immunoprecipitated by the anti-peptide sera. Therefore, we conclude that gpIII is encoded by the identified ORF in HindIII B. In addition, gpIII is implicated as essential for the cell-to-cell spread of VZV.

Animals↗
PubMed1987

Varicella-zoster virus as a live vector for the expression of foreign genes.

The previous demonstration of the efficacy and tolerability of the Oka strain of varicella-zoster virus (VZV) in clinical trials involving vaccination of both normal and immunocompromised individuals has laid the foundation for its use in preventing chickenpox. In this context, VZV could be useful as a vector for vaccinating against other infectious agents as well. As an initial application, a live recombinant VZV expressing Epstein-Barr virus (EBV) membrane glycoproteins (gp350/220) was generated by inserting a gene fusion of the VZV gpI promoter and hydrophobic leader-encoding sequence with the gp350/220 coding sequence into the thymidine kinase (TK) gene of VZV (Oka). Insertion of the foreign DNA into the thymidine kinase gene was demonstrated by Southern blot analysis and the ability of the recombinant virus to replicate in the presence of bromodeoxyuridine. RNA splicing, glycosylation, and plasma membrane presentation of gp350/220 in cells infected with the recombinant virus were similar to those seen in EBV-infected cells. In addition, the expression of VZV-specific glycoproteins was unaltered by the concomitant expression of this large foreign glycoprotein. Thus, VZV can be used as a live viral vector for active immunization against EBV and other pathogens.

Cell Line↗
PubMed1987

Early promoter-binding factor from vaccinia virions.

A factor, present in transcriptionally active extracts prepared from purified vaccinia virus particles, binds to vaccinia early promoter sequences. The specificity of binding was demonstrated by electrophoretic mobility shift assays using the 5'-terminal segments of two early genes and related and unrelated competitor DNA fragments. DNase I "footprint" analysis indicated that the factor formed a complex with promoter regions of both genes and protected sequences of 10-15 nucleotides centered 21-24 nucleotides upstream of the RNA start sites. The lack of protection of a late regulatory sequence and of an early promoter with transcriptionally inactivating single-nucleotide substitutions suggested that the protein is an early transcription factor. When subjected to glycerol gradient centrifugation, the DNA-binding factor was resolved from RNA polymerase and sedimented as a 7.5S species with an estimated molecular weight of 130,000.

Binding Sites↗
PubMed1987

Genetic relations between varicella-zoster virus and Epstein-Barr virus.

Varicella-zoster virus (VZV) and Epstein-Barr virus (EBV) are important human pathogens which belong to different subfamilies of the herpesviruses: the Alpha- and Gammaherpesvirinae, respectively. Computer comparisons of the amino acid sequences of proteins predicted from the published complete VZV and EBV DNA sequences resulted in the detection of EBV counterparts to 29 of the 67 unique VZV genes. Conserved genes were detected only in the UL component of each genome, and are located in three major regions, within which conserved genes are generally colinear. However, the three regions are arranged differently in the two genomes. These results make it possible in principle to propose the functions of EBV genes on the basis of the functions of their VZV counterparts. The data also allow identification of the types of events which may have occurred during divergence of VZV and EBV, as representatives of the Alpha- and Gammaherpesvirinae, from a common ancestor.

Base Sequence↗