Transmission of mitochondrial DNA disorders: possibilities for the future.
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Amniocentesis↗
Biomedical subjects
D T Brown
Publications and source records attributed to D T Brown.
The elastic properties of morsellised cortico-cancellous bone graft are dependent on its prior loading.
Confined compression experiments were carried out on cortico-cancellous bone taken from bovine femoral condyles to assess the effect of prior loading on the elastic confined modulus, E(c) of morsellised cortico-cancellous bone (MCB). Measurements were taken to find the values of E(c) for MCB subjected to cyclic loading resulting in axial stresses in the range of 0.5-3.0 N mm(2). Two values of E(c) were considered: E(ic), the instantaneous modulus, and E(dc), the delayed modulus allowing for stress relaxation effects. It was found that the values of E(c) increased with increasing maximum axial stress. It was also found that for each stress level the values of E(c) increased as the number of load cycles increased. The dependence of E(c) on the maximum axial stress and the number of load cycles is seen to explain the wide range of values for the apparent modulus of MCB found in previous studies. Tests examining the stress relaxation behaviour of MCB are also discussed. The results indicate that a minimum of 10 compaction episodes are required for MCB to achieve around 90% of its predicted maximum stiffness for a given compaction force.
Animals↗
Effects of coupling methods on galvanic corrosion behavior of commercially pure titanium with dental precious alloys.
BACKGROUND: When a dissimilar couple is exposed to corrosive environment, it will normally exhibit a galvanic corrosion. The galvanic corrosion might be influenced by various factors, including type and concentration of electrolyte, surface area ratio between anode and cathode, type of coupling material, and coupling manner. PURPOSE: The purpose of this study was to investigate and compare the galvanic corrosion behavior of commercially pure titanium when coupled with type IV Au alloy, Au-Ag-Pt alloy, and Ag-Au-Pd alloy by different coupling methods. MATERIALS AND METHODS: Couples were prepared by a laser welding or a mechanical adhering method. Electrochemical corrosion studies were conducted in a Ringer's solution at a scanning rate of 0.1 mV/sec in a range from -250 mV to +250 mV with respect to E(OCP). Corrosion parameters (E(OCP), I(CORR), E(CORR)) were obtained. RESULTS: It was found that (i) there was a significant difference between LWC and AJC for three couples (p<0.05), (ii) the crevice line caused all three couples more corrosive than weld joint line, (iii) for both joint, it was found that type (IV) Au alloy exhibited discoloration to some extent. CONCLUSIONS: It is concluded that among the three couples with two different coupling methods, Ti/Ag-Au-Pd couple exhibited best corrosion resistance in a room temperature Ringer's solution.
Corrosion↗
Mechanical properties of four methylmethacrylate-based resins for provisional fixed restorations.
The use of a provisional restoration is an important phase in the treatment of the dental prosthetic patient. A good provisional restoration should satisfy the following requirements: pulpal protection, positional stability, ease in cleaning, accurate margins, wear resistance, dimensional stability, and serve as a diagnostic aid in treatment assessment and esthetics. There is a tendency for discoloration, occlusal wear, and fracture that eventually leads to unnecessary repair. Heat-processed and reinforced methacrylate-based resins have been used to improve the mechanical and physical properties of provisional restorations. Among various improvements, the interpenetrating network crosslinked PMMA (IPN) has been shown to have superior mechanical properties if manufactured through a dough compression molding process at 130 degrees C. However, there have been no published data that relate with the use of this material for fixed provisional restorations. The objective of this study was to compare four methyl methacrylate-based resins for provisional crowns and bridges with varying processing cycles, including JET [self-cure], ACRALON [heat-cured], titanium dioxide filled PMMA [heat-cured], and IPN [heat-cured denture tooth resin]. Properties studied included transverse strength, toughness, rigidity, and hardness. From the results of this study the following conclusions can be made: the IPN group may have had a lower degree of conversion as demonstrated by decreased strength, toughness, and hardness data as compared with Acralon. Increasing the polymerization cycle of unmodified Acralon resin causes a significant increase in strength.
Biocompatible Materials↗
NDUFA-1 is not a nuclear modifier gene in Leber hereditary optic neuropathy.
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Adult↗
The epidemiology of Leber hereditary optic neuropathy in the North East of England.
We performed the first population-based clinical and molecular genetic study of Leber hereditary optic neuropathy (LHON) in a population of 2,173,800 individuals in the North East of England. We identified 16 genealogically unrelated families who harbor one of the three primary mitochondrial DNA (mtDNA) mutations that cause LHON. Two of these families were found to be linked genetically to a common maternal founder. A de novo mtDNA mutation (G3460A) was identified in one family. The minimum point prevalence of visual failure due to LHON within this population was 3.22 per 100,000 (95% CI 2.47-3.97 per 100,000), and the minimum point prevalence for mtDNA LHON mutations was 11.82 per 100,000 (95% CI 10.38-13.27 per 100,000). These results indicate that LHON is not rare but has a population prevalence similar to autosomally inherited neurological disorders. The majority of individuals harbored only mutant mtDNA (homoplasmy), but heteroplasmy was detected in approximately 12% of individuals. Overall, however, approximately 33% of families with LHON had at least one heteroplasmic individual. The high incidence of heteroplasmy in pedigrees with LHON raises the possibility that a closely related maternal relative of an index case may not harbor the mtDNA mutation, highlighting the importance of molecular genetic testing for each maternal family member seeking advice about their risks of visual failure.
Adult↗
Observations on a consecutive series of patients who have had Trilucent breast implants removed as recommended by the MDA Hazard Notice (May 2000).
A prospective study of 25 female cosmetic-surgery patients who had a total of 50 Trilucent breast implants forms the basis of this paper. All but one patient elected to have new implants, of which all but three patients had silicone implants (the others selected glucose saline implants). The Trilucent implants were more difficult to remove than expected because of a 'Velcro-like' attachment to the internal surface of their capsules. As a result, several implants were ruptured on removal (though none were ruptured on initial exposure). The sites of rupture suggest a structural weakness, possibly related to the microchip panel or folds in the implant shell. Varying degrees of encrustation of the implants and internal capsules were found, which did not appear to be related to the duration of implantation. Histological studies of the capsule changes generally showed lipids and giant cell infiltrations. It would seem that, contrary to expectations, leaking of the filler occurs early and is associated with varying degrees of cellular reactions. The adherence problem appears to be related to the amount and distribution of the leaked material. Only three patients in this series had problems with their Trilucent implants that required additional surgery. One of these remains a significant and unsolved problem.
Adult↗
Spinocerebellar ataxia and the A3243G and A8344G mtDNA mutations.
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DNA, Mitochondrial↗
Reinforcement of acrylic resins for provisional fixed restorations. Part III: effects of addition of titania and zirconia mixtures on some mechanical and physical properties.
Acrylic resins have been used in many different applications in dentistry, especially in the fabrication of provisional fixed partial dentures. Ideally, a provisional crown and bridge material should be easy to handle and should protect teeth against physical, chemical, and thermal injuries. Some of the problems associated with this use are related to the material's poor mechanical properties. It has been demonstrated that acrylic resin can be strengthened through the addition of structural component of different size distributed in the acrylic matrix, thus forming a composite structure. The purpose of this study was to investigate the addition effects of mixtures of titania (titanium dioxide, TiO(2)) powder and zirconia (zirconium dioxide, ZrO(2)) powder being incorporated with pre-polymerized beads mixed in monomer liquid, on some mechanical and physical properties of PMMA resin. The pre-polymerized powder poly(methyl methacrylate) resin was admixed with titania and zirconia powder. A mixing ratio was controlled by volume % of 0, 1.0, 2.0, and 3.0 (samples with 0 v/o served as control groups). For using mixture of titania and zirconia, total amount of the mixture was controlled by volume % of 1.0, 2.0, and 3.0, in which titania and zirconia were mixed at the ratio 1 :1, 1 :2 and 2 :1. Prior to mechanical tests, all rectangular-shaped samples (25 mm x 2 mm x 5 mm) were stored in 37 degrees C distilled water for 7 days after polishing all six sides of samples. Samples were then subjected to the three-point bending flexion test to evaluate the bending strength as well as the modulus of elasticity. Weight gain and exothermic reaction survey were investigated as well. All data were collected and analyzed with one-way analysis of variance (ANOVA) and Sidak method (p=0.05). It was found that the addition of particles generally decreased the water absorbed by the composite system. Only 1 percent by volume concentration of 1 :1 ratio and 2 percent by volume concentration of 1 :2 and 2 :1 ratios had significantly higher strength than control group. There was significantly higher toughness (in terms of energy-to-break) for 1 percent by volume concentration of 1 :1 ratio and 2 percent by volume concentration of 2 :1 ratio than control group. There was no significant difference between control group and all percent by volume combinations in modulus of elasticity. In addition, there was no significant variations of exothermic reaction.
Absorption↗
Histone variants: are they functionally heterogeneous?
In most eukaryotes, histones, which are the major structural components of chromatin, are expressed as a family of sequence variants encoded by multiple genes. Because different histone variants can contribute to a distinct or unique nucleosomal architecture, this heterogeneity can be exploited to regulate a wide range of nuclear functions, and evidence is accumulating that histone variants do indeed have distinct functions.
Animals↗
Electrochemical corrosion of titanium and titanium-based alloys.
STATEMENT OF PROBLEM: Two varieties of unalloyed titanium, Ti-6Al-4V and NiTi, commonly are used in medical and dental fields. Several other types of alloys for potential use in these fields have been developed, including Ti-4.5Al-3V-2Mo-2Fe and vanadium-free alloys (Ti-5Al-2.5Fe and Ti-5Al-3Mo-4Zr). The corrosion of these alloys under simulated physiologic conditions is not known. Purpose. This study compared the corrosion behaviors of 6 titanium materials through electrochemical polarization tests in 37 degrees C Ringer's solution. MATERIAL AND METHODS: The applied voltage was potentiostatically scanned from -0.6 to 1.0 V. From polarization curves, the corrosion rate (averaged over 3 samples) for each alloy was calculated and compared with that of other alloys. Analysis of variance (ANOVA) and the Student-Newman-Keuls multiple range test were performed at a 95% overall confidence level to identify statistically significance differences in corrosion rates. Surface oxide films were identified by electron diffraction, and the electrolyte medium was analyzed by atomic absorption spectrophotometry after each alloy was tested. RESULTS: Commercially pure titanium and Ti-5Al-2.5Fe were the most resistant to corrosion; Ti-5Al-3Mo-4Zr, Ti-6Al-4V, and NiTi were the least resistant to corrosion. NiTi exhibited pitting corrosion along with transpassivation. CONCLUSION: Electron diffraction patterns indicated that all titanium alloys were covered mainly with rutile-type oxide (TiO(2)) after corrosion tests. The oxides that formed on Ti-5Al-2.5Fe were identified as a mixture of TiO(2) and Ti(9)O(17), and those that formed on NiTi were identified as a mixture of TiO(2) and Ni(2)Ti(4)O.
Alloys↗
The mitochondrial ND6 gene is a hot spot for mutations that cause Leber's hereditary optic neuropathy.
Leber's hereditary optic neuropathy (LHON) is a common cause of bilateral optic nerve disease. The majority of LHON patients harbour one of three point mutations of the mitochondrial DNA (mtDNA) complex I, or NADH:ubiquinone oxidoreductase (ND) genes (G11778A in ND4, G3460A in ND1, T14484C in ND6). As a consequence, screening for these mutations has become part of the routine clinical investigation of young adults who present with bilateral optic neuropathy, and the absence of these mutations is interpreted as indicating there is a low likelihood that an optic neuropathy is LHON. However, there are many individuals who develop the clinical features of LHON but who do not harbour one of these primary LHON mutations. We describe two LHON pedigrees that harbour the same novel point mutation within the mtDNA ND6 gene (A14495G). This mutation was heteroplasmic in both families, and sequencing of the mitochondrial genome confirmed that the mutation arose on two independent occasions. This is the seventh mutation in the ND6 gene that causes optic neuropathy, indicating that this gene is a hot spot for LHON mutations. Protein modelling studies indicate that all of these pathogenic mutations lie within close proximity to one another in a hydrophobic cleft or pocket. This is the first evidence for a relationship between a specific disease phenotype and a specific structural domain within a mitochondrial respiratory chain subunit. These findings suggest that the mtDNA ND6 gene should be sequenced in all patients with LHON who do not harbour one of the three common LHON mutations.
Adolescent↗
Exposure to low pH is not required for penetration of mosquito cells by Sindbis virus.
It is widely held that the penetration of cells by alphaviruses is dependent on exposure to the acid environment of an endosome. The alphavirus Sindbis virus replicates in both vertebrate and invertebrate cell cultures. We have found that exposure to an acid environment may not be required for infection of cells of the insect host. In this work, we investigated the effects of two agents (NH(4)Cl and chloroquine), which raise the pH of intracellular compartments (lysosomotropic weak bases) on the infection and replication of Sindbis virus in cells of the insect host Aedes albopictus. The results show that both of these agents increase the pH of endosomes, as indicated by protection against diphtheria toxin intoxication. NH(4)Cl blocked the production of infectious virus and blocked virus RNA synthesis when added prior to infection. Chloroquine, in contrast to its effect on vertebrate cells, had no inhibitory effect on infectious virus production in mosquito cells even when added prior to infection. Treatment with NH(4)Cl did not prevent the penetration of virus RNA into the cell cytoplasm or translation of the RNA to produce a precursor to virus nonstructural proteins. These data suggest that while these two drugs raise the pH of endosomes, they do not block insect cell penetration. These data support previous results published by our laboratory suggesting that exposure to an acid environment within the cell may not be an obligatory step in the process of infection of cells by alphaviruses.
Aedes↗
Random genetic drift determines the level of mutant mtDNA in human primary oocytes.
We measured the proportion of mutant mtDNA (mutation load) in 82 primary oocytes from a woman who harbored the A3243G mtDNA mutation. The frequency distribution of mutation load indicates that random drift is the principal mechanism that determines the level of mutant mtDNA within individual oocytes.
DNA, Mitochondrial↗
Point mutations of the mtDNA control region in normal and neurodegenerative human brains.
Recent observations in cultured human fibroblasts suggest that the accumulation of point mutations in the noncoding control region of mtDNA may be important in human aging. We studied the mtDNA control region in brain tissue from 31 normal elderly individuals, from 35 individuals who had Alzheimer disease, and from 47 individuals who had dementia with Lewy bodies. We found no evidence that these somatic mtDNA point mutations accumulate either in the brains of normal elderly individuals or in the brains of individuals with neurodegenerative disease.
Aged↗
Dynamic binding of histone H1 to chromatin in living cells.
The linker histone H1 is believed to be involved in chromatin organization by stabilizing higher-order chromatin structure. Histone H1 is generally viewed as a repressor of transcription as it prevents the access of transcription factors and chromatin remodelling complexes to DNA. Determining the binding properties of histone H1 to chromatin in vivo is central to understanding how it exerts these functions. We have used photobleaching techniques to measure the dynamic binding of histone H1-GFP to unperturbed chromatin in living cells. Here we show that almost the entire population of H1-GFP is bound to chromatin at any one time; however, H1-GFP is exchanged continuously between chromatin regions. The residence time of H1-GFP on chromatin between exchange events is several minutes in both euchromatin and heterochromatin. In addition to the mobile fraction, we detected a kinetically distinct, less mobile fraction. After hyperacetylation of core histones, the residence time of H1-GFP is reduced, suggesting a higher rate of exchange upon chromatin remodelling. These results support a model in which linker histones bind dynamically to chromatin in a stop-and-go mode.
3T3 Cells↗
Core histone acetylation is regulated by linker histone stoichiometry in vivo.
We investigated the relationship between linker histone stoichiometry and the acetylation of core histones in vivo. Exponentially growing cell lines induced to overproduce either of two H1 variants, H1(0) or H1c, displayed significantly reduced rates of incorporation of [(3)H]acetate into all four core histones. Pulse-chase experiments indicated that the rates of histone deacetylation were similar in all cell lines. These effects were also observed in nuclei isolated from these cells upon labeling with [(3)H]acetyl-CoA. Nuclear extracts prepared from control and H1-overexpressing cell lines displayed similar levels of histone acetylation activity on chromatin templates prepared from control cells. In contrast, extracts prepared from control cells were significantly less active on chromatin templates prepared from H1-overexpressing cells than on templates prepared from control cells. Reduced levels of acetylation in H1-overproducing cell lines do not appear to depend on higher order chromatin structure, because it persists even after digestion of the chromatin with micrococcal nuclease. The results suggest that alterations in chromatin structure, resulting from changes in linker histone stoichiometry may modulate the levels or rates of core histone acetylation in vivo.
Acetates↗
Temporomandibular disorder treatment outcomes: first report of a large-scale prospective clinical study.
The diagnosis and treatment of temporomandibular disorders (TMD) has been surrounded by considerable controversy. Clinical research in the field to date has been inconsistent and methodologically limited and has not firmly established the role of treatment interventions. This large scale, multisite study attempts to answer some of the questions regarding TMD diagnosis and treatment. More than 6,500 patients are currently being analyzed and 1,212 have completed TMD therapy, providing the basis for comparison with 198 untreated patients. A wide variety of treatments have been administered from 60 practice sites, whose practitioners were carefully calibrated to maximize inter-rater reliability. A validated symptom measurement system, the TMJ Scale, was employed to assure uniform assessment of treatment outcomes. Treated patients reported statistically and clinically significant symptom improvement, while untreated patients reported unchanged symptom levels. Data presented here do not support the hypothesis that TMD patients improve spontaneously without treatment.
Adult↗