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Biomedical subjects

S M Newman

Publications and source records attributed to S M Newman.

At least 19 recordsLinked to original sources
PubMed1999

The effects of light intensity, temperature, and comonomer composition on the polymerization behavior of dimethacrylate dental resins.

One of the most common combinations for the organic phase of dental restorative materials is BisGMA (2,2bis[4-(2-hydroxy-3-methacryloyloxypropoxy) phenyl]propane) and TEGDMA (triethylene glycol dimethacrylate). However, this copolymer has some drawbacks, such as volume shrinkage during cure and lack of complete double-bond conversion. If the properties of this system are to be improved, an attempt must be made to understand the underlying kinetics of the reaction. This work examines the effects of light intensity, temperature, and composition on the polymerization behavior of BisGMA/TEGDMA copolymerizations. Using differential scanning calorimetry, we monitored the rates of photopolymerization for various experimental conditions. The BisGMA/TEGDMA copolymerization behaved similarly to other dimethacrylate systems and exhibited diffusion-controlled kinetics. It was found that the maximum rate of polymerization was significantly affected by the intensity of the light, and the temperature of the polymerization affected the conversion at which the maximum rate occurred. When the composition of the mixture was varied, it was discovered that the viscosity of the system played a significant role in the polymerization rate and the onset of reaction-diffusion-controlled termination. Mixtures which contained from 50 wt% to 75 wt% BisGMA displayed the highest maximum rate. This feature suggests that TEGDMA is an excellent diluent, since it increases the mobility of the reacting medium; however, the high reactivity is due to the presence of BisGMA. Therefore, based on compositional dependence, we conclude that the BisGMA portion of the mixture largely controls the polymerization mechanisms and kinetics.

Algorithms↗
PubMed1999

Extracorporeal circulatory support in near-fatal flecainide overdose.

Flecainide, a class 1c antiarrhythmic, has a high mortality associated with significant overdose. We report the case of a 20-year-old female who took approximately 4 grams of flecainide and a small amount of paracetamol as an impulsive gesture. Circulatory failure unresponsive to pacing, inotropes and sodium bicarbonate was successfully treated with cardiopulmonary bypass (CPB). Resolution of her myocardial failure occurred over 24 hours and she was weaned from CPB 30 hours after its initiation. Coagulopathy and intravascular haemolysis were apparent during bypass and necessitated substantial use of blood products. Ischaemic renal dysfunction manifested early in her admission and required haemodiafiltration. Despite a prolonged period of unresponsiveness and pupillary dilatation during resuscitation and CPB she made a full recovery. We believe this is the first reported case of flecainide overdose, requiring extracorporeal circulatory support, not resulting in neurological deficit.

Adult↗
PubMed1998

Functions of the high mobility group protein, Abf2p, in mitochondrial DNA segregation, recombination and copy number in Saccharomyces cerevisiae.

Previous studies have established that the mitochondrial high mobility group (HMG) protein, Abf2p, of Saccharomyces cerevisiae influences the stability of wild-type (rho+) mitochondrial DNA (mtDNA) and plays an important role in mtDNA organization. Here we report new functions for Abf2p in mtDNA transactions. We find that in homozygous deltaabf2 crosses, the pattern of sorting of mtDNA and mitochondrial matrix protein is altered, and mtDNA recombination is suppressed relative to homozygous ABF2 crosses. Although Abf2p is known to be required for the maintenance of mtDNA in rho+ cells growing on rich dextrose medium, we find that it is not required for the maintenance of mtDNA in p cells grown on the same medium. The content of both rho+ and rho- mtDNAs is increased in cells by 50-150% by moderate (two- to threefold) increases in the ABF2 copy number, suggesting that Abf2p plays a role in mtDNA copy control. Overproduction of Abf2p by > or = 10-fold from an ABF2 gene placed under control of the GAL1 promoter, however, leads to a rapid loss of rho+ mtDNA and a quantitative conversion of rho+ cells to petites within two to four generations after a shift of the culture from glucose to galactose medium. Overexpression of Abf2p in rho- cells also leads to a loss of mtDNA, but at a slower rate than was observed for rho+ cells. The mtDNA instability phenotype is related to the DNA-binding properties of Abf2p because a mutant Abf2p that contains mutations in residues of both HMG box domains known to affect DNA binding in vitro, and that binds poorly to mtDNA in vivo, complements deltaabf2 cells only weakly and greatly lessens the effect of overproduction on mtDNA instability. In vivo binding was assessed by colocalization to mtDNA of fusions between mutant or wild-type Abf2p and green fluorescent protein. These findings are discussed in the context of a model relating mtDNA copy number control and stability to mtDNA recombination.

Binding Sites↗
PubMed1997

The influence of culture time and passage number on the morphological and physiological development of Caco-2 cells.

The Caco-2 cell line is used by many investigators as a model of the intestinal epithelium to study nutrient uptake and transport. Our goal was to create an awareness of inherent variabilities in the Caco-2 cell line which may influence their suitability as a model or their application to specific problems. To study the influence of passage on the model, cultures were monitored from passage 20 to 109. Transepithelial electrical resistance (TEER) and sucrase activity (measured in 21-day-old cultures) increased through about passage 36. TEER values declined after about passage 60; sucrase remained elevated but variable. Cells at passage 22, 33, and 72 were grown simultaneously for 24 days. Older-passaged cells reached plateau phase sooner. Before Day 15, passage 72 cells had higher TEER and lower permeability to 14C-mannitol than passages 22 and 33; however, after Day 15 all passages showed similar permeability. On Day 21, passage 72 cells had significantly lower alkaline phosphatase activity than did the other passages. Electron microscopy did not reveal any major morphological differences between the passages; however, it did show that some areas of cells grown on membranes were not monolayers but were several cells thick with varied morphology. Investigation of the formation of these multilayered areas showed them to be an inherent part of cell growth under the conditions used. These results emphasize the inherent variability in Caco-2 cell models and emphasize the need to monitor closely the culture characteristics during growth and differentiation under specific experimental conditions.

Alkaline Phosphatase↗
PubMed1996

Analysis of mitochondrial DNA nucleoids in wild-type and a mutant strain of Saccharomyces cerevisiae that lacks the mitochondrial HMG box protein Abf2p.

DNA-protein complexes (nucleoids) are believed to be the segregating unit of mitochondrial DNA (mtDNA) in Saccharomyces cerevisiae. A mitochondrial HMG box protein, Abf2p, is needed for maintenance of mtDNA in cells grown on rich dextrose medium, but is dispensible in glycerol grown cells. As visualized by 4',6'-diamino-2-phenylindole staining, mtDNA nucleoids in mutant cells lacking Abf2p ( delta abf2) are diffuse compared with those in wild-type cells. We have isolated mtDNA nucleoids and characterized two mtDNA-protein complexes, termed NCLDp-2 and NCLDs-2, containing distinct but overlapping sets of polypeptides. This protocol yields similar nucleoid complexes from the delta abf2 mutant, although several proteins appear lacking from NCLDs-2. Segments of mtDNA detected with probes to COXII, VAR1 and ori5 sequences are equally sensitive to DNase I digestion in NCLDs-2 and NCLDp-2 from wild-type cells and from the delta abf2 mutant. However, COXII and VAR1 sequences are 4-to 5-fold more sensitive to DNase I digestion of mtDNA in toluene-permeabilized mitochondria from the delta abf2 mutant than from wild-type cells, but no difference in DNase I sensitivity was detected with the ori5 probe. These results provide a first indication that Abf2p influences differential organization of mtDNA sequences.

DNA, Fungal↗
PubMed1996

High zinc concentrations in culture media affect copper uptake and transport in differentiated human colon adenocarcinoma cells.

Previous studies suggest that high dietary zinc reduces the copper status of animals by reducing copper transport across the intestinal mucosa. The present study used an enterocyte mimic, the Caco-2 cell, grown on porus membranes as a model to assess the effects of various concentrations of zinc (6 to 200 micromol/L) in the culture and assay media on 67Cu uptake and transport. Differentiated cells incubated for 7 d in a culture medium containing 50 micromol zinc + 0.7 micromol copper/L transported significantly less 67Cu across the monolayer than similar cells exposed to 6 micromol zinc/L. However, cells exposed to 200 micromol zinc/L for the same period transported significantly more 67Cu than those exposed to 6 micromol zinc/L. Cells exposed for only 1 h to 200 micromol zinc/L in the uptake-transport medium alone did not show lower 67Cu uptake or transport, suggesting that time of exposure of the cells to high zinc was a contributing factor. Caco-2 cells exposed to 50 through 200 micromol zinc/L had higher cellular metallothionein (MT) than those exposed to 6 micromol zinc/L. As the amount of MT in cells increased upon exposure to 50 and 100 micromol zinc/L, the rate of 67Cu transport decreased. At higher zinc concentrations in the medium, there was even more MT in the cells, but a greater rate Of 67Cu transport. These studies demonstrate the use of the Caco-2 cell as a model for copper uptake-transport studies, but the conditions must be rigorously defined and controlled.

Biological Transport↗
PubMed1996

The influence of comonomer composition on dimethacrylate resin properties for dental composites.

During the polymerization of multifunctional monomers for dental restorations, typical final double-bond conversions range from 55 to 75%. The low conversion results in a large amount of extractable monomer, reduced adhesion to the filler, and the potential for increased swelling. In this work, the ability to increase the maximum conversion by optimizing the copolymer composition is explored. A series of multi-ethylene glycol dimethacrylate monomers of various lengths was used as a model system to determine how the copolymer composition affects the final conversion, the mechanical properties, and the predicted shrinkage. It was found that the ultimate conversion can be significantly increased, shrinkage decreased, and mechanical properties maintained. It was found that up to 30 wt% of poly(ethylene glycol) 600 dimethacrylate could be added to diethylene glycol dimethacrylate without reducing the strength and increasing the conversion. Results for other comonomer combinations were similar.

Acrylates↗
PubMed1995

Effects of curet and ultrasonics on root surfaces.

PURPOSE: To compare the effect on root surfaces of three ultrasonic scalers to each other and to a periodontal curet. MATERIALS AND METHODS: Forty extracted teeth were washed and embedded in acrylic resin leaving one entire coronal-apical tooth aspect exposed. The teeth were divided between four treatments: piezoelectric A - Group A, piezoelectric B - Group B, magnetostrictive - Group C, hand instrumentation with a curet - Group D. A single experienced operator simulated clinical instrumentation over a 9 mm square area on each tooth until the surface was judged smooth by the operator. Three evaluations were used in the study: (1) root tracings with a surface roughness meter to determine the roughness average (Ra) and roughness maximum (Rmax) in microns, (2) use of a new EXD 11/12 explorer to assess planed roots and (3) visual evaluation of the root surfaces through a stereoscopic microscope (X 20). During examinations 2 and 3, root surfaces were assigned to one of four "smoothness categories" by the examiners. Data for evaluation 1 was analyzed by ANOVA. Data from evaluations 2 and 3 were analyzed using the Kruskal-Wallis non-parametric test. RESULTS: The mean Ra and Rmax were not significantly different between the four groups. The results from both clinicians' examinations showed a significant difference in the four groups (P=0.001). The curet produced the smoothest surfaces, the two piezoelectric instruments produced the next smoothest surface and the magnetostrictive instrument the least smooth root surfaces.

Analysis of Variance↗
PubMed1995

Tray-forming technique for dentist-supervised home bleaching.

This article provides a comprehensive and detailed description of the technique for making a custom tray for the delivery of bleaching gel in dentist-supervised home bleaching systems. Specific recommendations about certain steps and materials are made and the advantages offered by these variations are explained. This information should facilitate the preparation of the tray by the dental staff in office or provide some guidelines to the dental laboratory to improve its service. The resulting appliance may offer some advantages for patient comfort during specific treatment regimens.

Carbamide Peroxide↗
PubMed1994

Cell survival measurements in an argon, aluminium and sulphur filtered neutron beam: a comparison with 24 keV neutrons and relevance to boron neutron capture therapy.

Boron neutron capture therapy (BNCT) has been advanced as a suitable alternative therapy for the treatment of glioma. BNCT involves the selective uptake of a tumour with a boron-bearing substance and subsequent irradiation with a beam of neutrons. Previous attempts with BNCT have utilized thermal neutrons, but this involves resection of the scalp prior to treatment and is only possible with superficial tumours. An alternative is to use a beam of intermediate-energy neutrons which will produce a peak in the thermal neutron fluence at depth in tissue and so enable deep-seated tumours to be treated. A neutron beam with a mean energy of approximately 9 keV, obtained by filtering neutrons from a reactor with aluminium, argon and sulphur, has been used to explore the radiobiological advantage over thermal and 24 keV neutrons for BNCT. Irradiation of V79 and HeLa cells at various positions in a polythene phantom suggest that the beam is less cytotoxic for a given neutron fluence than the 24 keV neutron beam previously considered as an alternative to thermal neutrons for BNCT. However, optimization of boron distribution via the development of new compounds still appears to be necessary for BNCT to become a safe alternative option for the treatment of glioma.

Aluminum↗
PubMed1993

Organisation of the tomato polyphenol oxidase gene family.

We report the isolation and characterization of seven nuclear genes encoding polyphenol oxidase (PPO) in tomato (Lycopersicon esculentum cv. VFNT Cherry). The seven genes (PPOs A, A', B, C, D, E and F) fall into three structural classes (I, II, and III) based on Eco RI and Hind III restriction fragment length polymorphisms (RFLP). RFLP mapping and PFGE analysis demonstrated that the genes reside on chromosome 8, and may be clustered within a 165 kb region. Phage insert mapping demonstrated PPO E and PPO F (both class III), and PPOs B, D and A (classes I, II and I respectively) are grouped within separate 12.4 kb clusters. The complete nucleotide sequence was determined for each gene. Comparison to cDNAs revealed that the PPOs lack introns. A transcript of about 2 kb is expected for each PPO. Each PPO possesses a region encoding a transit peptide characteristic of polypeptides targeted to the thylakoid lumen. Predicted precursor polypeptides range in mass from 66 to 71 kDa and predicted mature polypeptides range from 57 to 62 kDa. All the PPOs encode two putative copper-binding sites characteristic of bacterial, fungal and mammalian tyrosinases. Five of the seven PPOs possess divergent DNA sequences in their 5' promoter regions. These flanking sequence differences may regulate the differential expression of PPO genes.

Amino Acid Sequence↗
PubMed1993

cDNA cloning and expression of potato polyphenol oxidase.

Polyphenol oxidases (PPOs) of plants are copper metalloproteins which catalyze the oxidation of mono- and o-diphenols to o-diquinones. Although PPOs are believed to be primarily responsible for the deleterious browning of many fruit and vegetable crops and are thought to be involved in plant-pest interactions, direct evidence for these roles is lacking. We report the cloning of two PPO cDNAs from Solanum tuberosum leaves. These cDNAs exhibit 97% and 98% sequence similarity at the DNA and deduced amino acid levels, respectively. Putative copper-binding regions of both cDNAs are very similar to those of mammalian, bacterial and Neurospora tyrosinases. Both leaf PPO cDNAs appear to encode polypeptides which are processed to a mature molecular weight of 57,000. In potato leaves, petioles, roots, and flowers, PPO is encoded by ca. 2 kb transcripts. Leaf PPO mRNA is developmentally regulated and only detectable in young foliage. In contrast, the protein profile of immunologically detectable PPO remains constant from the apical node through the eleventh leaf node.

Amino Acid Sequence↗
PubMed1992

Nonrandom distribution of chloroplast recombination events in Chlamydomonas reinhardtii: evidence for a hotspot and an adjacent cold region.

Intermolecular recombination of Chlamydomonas chloroplast genes has been analyzed in sexual crosses and following biolistic transformation. The pattern and position of specific exchange events within 15 kb of the 22-kb inverted repeat have been mapped with respect to known restriction fragment length polymorphism markers that distinguish the chloroplast genomes of the interfertile species Chlamydomonas reinhardtii and Chlamydomonas smithii. Recombinant progeny were selected from two- and three-factor crosses involving point mutations conferring herbicide (dr) and antibiotic resistance (er and spr) in the psbA, 23S and 16S ribosomal RNA genes, respectively. Exchange events were not randomly distributed over the 15-kb region, but were found to occur preferentially in a 0.7-kb sequence spanning the 3' end of the psbA gene and were much less common in an adjacent region of ca. 2.0 kb. These findings are corroborated by data showing that the dr mutation is unlinked genetically (3% recombination/kb) to the er and spr rRNA mutations, which are themselves linked and show ca. 1% recombination/kb. This discrepancy is significant since the dr-er and er-spr intervals are about the same length (ca. 7 kb). During chloroplast transformation, the 0.7-kb recombination hotspot also functions as a preferential site for exchange events leading to the integration of donor psbA gene sequences. The 0.7-kb hotspot region contains four classes of 18-37-bp direct repeats also found in other intergenic regions, but no open reading frame. Using deletion constructs in a chloroplast transformation assay, the hotspot was localized to a 500-bp region that lacks most of these repeats, which suggests that the repeats themselves are not responsible for the increased recombination frequency. Within this region, a 400-bp sequence is highly conserved between the chloroplast genomes of C. reinhardtii and C. smithii and includes several structural motifs characteristic of recombination hotspots in other systems.

Animals↗
PubMed1991

Targeted disruption of chloroplast genes in Chlamydomonas reinhardtii.

We have developed an efficient procedure for the disruption of Chlamydomonas chloroplast genes. Wild-type C. reinhardtii cells were bombarded with microprojectiles coated with a mixture of two plasmids, one encoding selectable, antibiotic-resistance mutations in the 16S ribosomal RNA gene and the other containing either the atpB or rbcL photosynthetic gene inactivated by an insertion of 0.48 kb of yeast DNA in the coding sequence. Antibiotic-resistant transformants were selected under conditions permissive for growth of non-photosynthetic mutants. Approximately half of these transformants were initially heteroplasmic for copies of the disrupted atpB or rbcL genes integrated into the recipient chloroplast genome but still retained photosynthetic competence. A small fraction of the transformants (1.1% for atpB; 4.3% for rbcL) were nonphotosynthetic and homoplasmic for the disrupted gene at the time they were isolated. Single cell cloning of the initially heteroplasmic transformants also yielded nonphotosynthetic segregants that were homoplasmic for the disrupted gene. Polypeptide products of the disrupted atpB and rbcL genes could not be detected using immunoblotting techniques. We believe that any nonessential Chlamydomonas chloroplast gene, such as those involved in photosynthesis, should be amenable to gene disruption by cotransformation. The method should prove useful for the introduction of site-specific mutations into chloroplast genes and flanking regulatory sequences with a view to elucidating their function.

Animals↗
PubMed1991

A nuclear mutant of Chlamydomonas that exhibits increased sensitivity to UV irradiation, reduced recombination of nuclear genes, and altered transmission of chloroplast genes.

Meiotic progeny of Chlamydomonas reinhardtii normally receive chloroplast genomes only from the mt+ parent. However, exceptional zygotes, which transmit the chloroplast genomes of both parents or, more rarely, only those of the mt- parent, arise at a low frequency. Mutations at the mt(+)-linked mat-3 locus were found previously to elevate the transmission of chloroplast genomes from the mt- parent, resulting in a much higher than normal frequency of exceptional zygotes. In this paper we demonstrate that an ultraviolet-sensitive nuclear mutation mapping at the uvsE1 locus, which is unlinked to mating type, also promotes chloroplast genome transmission from the mt- parent. This mutant, which was previously shown to reduce recombination of nuclear genes in meiosis, acts synergistically with the mat-3-3 mutation to produce an extremely high frequency of exceptional zygotes. Through the use of restriction fragment length polymorphisms existing in the chloroplast genomes of C. reinhardtii and the interfertile strain C. smithii, we show that chloroplast DNA fragments from the mt- parent normally begin to disappear shortly after zygote formation. However, this process appears to be blocked totally in the absence of wild-type uvsE1 and mat-3 gene products. Our findings are consistent with the hypothesis that both gene products contribute to the mechanism responsible for uniparental inheritance of the chloroplast genome from the mt+ parent.

Alleles↗
PubMed1991

Chorionic structure of the egg of the screwworm, Cochliomyia hominivorax (Diptera: Calliphoridae).

The chorion of the Cochliomyia hominivorax (Coquerel) egg is described using observations from scanning and transmission electron microscopy and light microscopy. Included are the gross structure and surface characteristics of the chorion, the basic architecture and internal components of the chorion proper, the location and function of the hatch lines, and the functional morphology of the plastron region as a respiratory structure. In the regular hexagonal arrangement and form of individual structural units, the chorion of the screwworm egg exhibits basic architectural features common to other higher Diptera. Within the open spaces of the endochorionic layer, however, are previously undescribed membranous structures of unknown function which appear to line the cavities of the endochorion. The plastron region partially encircles the micropyle (anterior end) of the egg and extends along the dorsal surface to the posterior pole; it is delineated laterally by the hatch lines. The chorion ruptures along the anterior region of the hatch lines as the larva emerges. The plastron region is composed of elaborate stalked aeropyles above a highly dissected inner reticulum. This structure is believed to function as a respiratory organ when the egg is immersed in fluid.

Animals↗