Biomedical subjects

P Todd

Publications and source records attributed to P Todd.

At least 37 records · Page 2Linked to original sources

PubMed1999

Migration of Polystyrene Latex Particle Bands in Density-Gradient Electrophoresis.

Electrophoretic migration of sulfated polystyrene latex particle bands was investigated in a density-gradient electrophoresis apparatus. The bands spread with time, and their velocity was found to depend on particle concentration and to decrease during the initial stages of electrophoresis. A change in pH during electrophoresis occurred, and this change may have caused variations in band velocity. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

The goodpasture autoantigen. Mapping the major conformational epitope(s) of alpha3(IV) collagen to residues 17-31 and 127-141 of the NC1 domain.

The Goodpasture (GP) autoantigen has been identified as the alpha3(IV) collagen chain, one of six homologous chains designated alpha1-alpha6 that comprise type IV collagen (Hudson, B. G., Reeders, S. T., and Tryggvason, K. (1993) J. Biol. Chem. 268, 26033-26036). In this study, chimeric proteins were used to map the location of the major conformational, disulfide bond-dependent GP autoepitope(s) that has been previously localized to the noncollagenous (NC1) domain of alpha3(IV) chain. Fourteen alpha1/alpha3 NC1 chimeras were constructed by substituting one or more short sequences of alpha3(IV)NC1 at the corresponding positions in the non-immunoreactive alpha1(IV)NC1 domain and expressed in mammalian cells for proper folding. The interaction between the chimeras and eight GP sera was assessed by both direct and inhibition enzyme-linked immunosorbent assay. Two chimeras, C2 containing residues 17-31 of alpha3(IV)NC1 and C6 containing residues 127-141 of alpha3(IV)NC1, bound autoantibodies, as did combination chimeras containing these regions. The epitope(s) that encompasses these sequences is immunodominant, showing strong reactivity with all GP sera and accounting for 50-90% of the autoantibody reactivity toward alpha3(IV)NC1. The conformational nature of the epitope(s) in the C2 and C6 chimeras was established by reduction of the disulfide bonds and by PEPSCAN analysis of overlapping 12-mer peptides derived from alpha1- and alpha3(IV)NC1 sequences. The amino acid sequences 17-31 and 127-141 in alpha3(IV)NC1 have thus been shown to contain the critical residues of one or two disulfide bond-dependent conformational autoepitopes that bind GP autoantibodies.

Amino Acid Sequence↗

PubMed1999

Bacterial growth in space flight: logistic growth curve parameters for Escherichia coli and Bacillus subtilis.

Previous investigations have reported that bacterial suspension cultures grow to higher stationary concentrations in space flight than on Earth; however, none of these investigations included extensive ground controls under varied inertial conditions. This study includes extensive controls and cell-growth data taken at several times during lag phase, log phase, and stationary phase of Escherichia coli and Bacillus subtilis. The Marquardt-Levenberg, least-squares fitting algorithm was used to calculate kinetic growth parameters from the logistic bacterial growth equations for space-flight and control growth curves. Space-flight cultures grew to higher stationary-phase concentrations and had shorter lag-phase durations. Also, evidence was found for increased exponential growth rate in space.

Bacillus subtilis↗

PubMed1999

Autolysis of Escherichia coli and Bacillus subtilis cells in low gravity.

The role of gravity in the autolysis of Bacillus subtilis and Escherichia coli was studied by growing cells on Earth and in microgravity on Space Station Mir. Autolysis analysis was completed by examining the death phase or exponential decay of cells for approximately 4 months following the stationary phase. Consistent with published findings, the stationary-phase cell population was 170% and 90% higher in flight B. subtilis and E. coli cultures, respectively, than in ground cultures. Although both flight autolysis curves began at higher cell densities than control curves, the rate of autolysis in flight cultures was identical to that of their respective ground control rates.

Bacillus subtilis↗

PubMed1999

Early root cap development and graviresponse in white clover (Trifolium repens) grown in space and on a two-axis clinostat.

White clover (Trifolium repens) was germinated and grown in microgravity aboard the Space Shuttle (STS-60, 1994; STS-63, 1995), on Earth in stationary racks and in a slow-rotating two-axis clinostat. The objective of this study was to determine if normal root cap development and early plant gravity responses were dependent on gravitational cues. Seedlings were germinated in space and chemically fixed in orbit after 21, 40, and 72 h. Seedlings 96 h old were returned viable to earth. Germination and total seedling length were not dependent on gravity treatment. In space-flown seedlings, the number of cell stories in the root cap and the geometry of central columella cells did not differ from those of the Earth-grown seedlings. The root cap structure of clinorotated plants appeared similar to that of seedlings from microgravity, with the exception of three-day rotated plants, which displayed significant cellular damage in the columella region. Nuclear polarity did not depend on gravity; however, the positions of amyloplasts in the central columella cells were dependent on both the gravity treatment and the age of the seedlings. Seedlings from space, returned viable to earth, responded to horizontal stimulation as did 1 g controls, but seedlings rotated on the clinostat for the same duration had a reduced curvature response. This study demonstrates that initial root cap development is insensitive to either chronic clinorotation or microgravity. Soon after differentiation, however, clinorotation leads to loss of normal root cap structure and plant graviresponse while microgravity does not.

Fabaceae↗

PubMed1999

Particulates from PTFE degradation in terrestrial and microgravity.

It has recently been discovered that the ultrafine particles generated during polymer thermodegradation are a major health hazard, owing to their unique pathway of processing in the lung. This hazard in manned spacecraft is poorly understood because the particulate products of polymer thermodegradation are generated under low gravity conditions. Particulates generated from the degradation of polytetrafluoroethylene (PTFE), insulation coating for 20 AWG copper wire (representative of spacecraft application) under intense current overload, were studied in terrestrial gravity and microgravity. Microgravity tests were done in a 1.2-s drop tower at the Colorado School of Mines. Thermophoretic sampling was used for particulate collection. Transmission electron microscopy (TEM) was used to examine the smoke particulates. The pigmentation of PTFE insulation seems to have an overwhelming effect on size, shape and morphology of the particulate. Nanometer-sized particles were found in all cases, but their extent of aggregation and size distribution were dependent on both PTFE pigmentation and gravity; higher aggregation occurred in low gravity. Four different color insulations (viz. white, black, red and yellow) were studied.

Air Pollution, Indoor↗

PubMed1999

Effects of space flight and mixing on bacterial growth in low volume cultures.

Previous investigations have shown that liquid suspension bacterial cultures grow to higher cell concentrations in spaceflight than on Earth. None of these studies included ground-control experiments designed to evaluate the fluid effects potentially responsible for the reported increases. Therefore, the emphasis of this research was to both confirm differences in final cell concentration between 1g and microgravity cultures, and to examine the effects of mixing as a partial explanation for this difference. Flight experiments were performed in the Fluid Processing Apparatus (FPA), aboard Space Shuttle Missions STS-63 and STS-69, with simultaneous 1g static and agitated controls. Additional static 1g, agitated, and clino-rotated controls were performed in 9-ml culture tubes. This research revealed that both E. coli and B. subtilis samples cultured in space flight grew to higher final cell densities (120-345% increase) than simultaneous static 1g controls. The final cell concentration of E. coli cells cultured under agitation was 43% higher than in static 1g cultures and was 102% higher with clino-rotation. However, for B. subtilis cultures grown while being agitated on a shaker or clino-rotated, the final cell concentrations were nearly identical to those of the simultaneous static 1g controls. Therefore, these data suggest that the unique fluid quiescence in the microgravity environment (lack of sedimentation, creating unique transfer of nutrients and waste products), was responsible for the enhanced bacterial proliferation reported in this and other studies.

Bacillus subtilis↗

PubMed1999

Gentamicin: effect on E. coli in space.

Previous investigations have shown that liquid bacterial cultures grown in space flight were not killed as effectively by antibiotic treatments as were cultures grown on Earth. However, the cause for the decreased antibiotic effectiveness remains unknown. Possible explanations include modified cell proliferation and modified antibiotic transport in the culture medium. Escherichia coli cultures were grown in space flight (STS-69 and STS-73), with and without gentamicin, on a solid agar substrate thus eliminating fluid effects and reducing the unknowns associated with space-flight bacterial cultures in suspension. This research showed that E. coli cultures grown in flight on agar for 24 to 27 hours experienced a heightened growth compared to simultaneous controls. However, addition of gentamicin to the agar killed the bacteria such that both flight and ground control E. coli samples had similar final cell concentrations. Therefore, while the reported existence of a decrease in antibiotic effectiveness in liquid cultures remains unexplained, these data suggest that gentamicin in space flight was at least as effective as, if not more effective than, on Earth, when E. coli cells were grown on agar.

Agar↗

PubMed1998

Hydrophilic membrane-based humidity control.

A dehumidification system for low gravity plant growth experiments requires the generation of no free-liquid condensate and the recovery of water for reuse. In the systems discussed in this paper, the membrane is a barrier between the humid air phase and a liquid-coolant water phase. The coolant water temperature combined with a transmembrane pressure differential establishes a water flux from the humid air into the coolant water. Building on the work of others, we directly compared different hydrophilic membranes for humidity control. In a direct comparison of the hydrophilic membranes, hollow fiber cellulose ester membranes were superior to metal and ceramic membranes in the categories of condensation flux per surface area, ease of start-up, and stability. However, cellulose ester membranes were inferior to metal membranes in one significant category, durability. Dehumidification systems using mixed cellulose ester membranes failed after operational times of only hours to days. We propose that the ratio of fluid surface area to membrane material area (approximately = membrane porosity) controls the relative performances among membranes. In addition, we clarified design equations for operational parameters such as the transmembrane pressure differential. This technology has several potential benefits related to earth environmental issues including the minimization of airborne pathogen release and higher energy efficiency in air conditioning equipment. Utilizing these study results, we designed, constructed, and flew on the space shuttle missions a membrane-based dehumidification system for a plant growth chamber.

Air Conditioning↗

PubMed1998

Cellular responses to gravity: extracellular, intracellular and in-between.

Our understanding of gravitational effects (inertial effects in the vicinity of 1 x g) on cells has matured to a stage at which it is possible to define, on the basis of experimental evidence, extracellular effects on small cells and intracellular effects on eukaryotic gravisensing cells. Yet undetermined is the nature of response, if any, of those classes of cells that are not governed solely by extracellular physical events (as are prokaryotes) and are devoid of obvious mechanical devices for sensing inertial forces (such as those possessed by certain plant cells and sensory cells of animals). This "in-between" class of cells needs to be understood on the basis of the combination of intracellular and extracellular gravity-dependent processes that govern experimentally-measurable variables that are relevant to the cell's responses to modified inertial forces. The forces that certain cell types generate or respond to are therefore compared to those imposed by approximately 1 x g in the context of cytoskeletal action and symmetry-breaking pathways.

Animals↗

PubMed1998

Functional weightlessness during clinorotation of cell suspensions.

A clinostat is a device often used in gravitational biology studies. Selecting an appropriate speed of rotation, however, is a frequently debated topic, particularly for suspended cells. In an attempt to define the necessary criteria for determining an acceptable revolution speed, the primary forces governing particle behavior during clinorotation--gravity, diffusion and centrifugation--were mathematically assessed. In support of the theoretical exercise, bacterial growth experiments indicated that results obtained using a clinostat followed trends resembling previous space flight results. It is suspected that this is due, in part at least, to similarly altered external transport processes in each environment.

Bacterial Physiological Phenomena↗

PubMed1998

Electrokinetic demixing of aqueous two-phase systems. 3. Drop electrophoretic mobilities and demixing rates

Scale-up of aqueous two-phase extraction, which is useful in the isolation and purification of certain bioproducts, is limited by the slow demixing rates of the two aqueous phases. Electrokinetic demixing has been shown to increase by more than 5-fold the demixing rates of systems up to 100 mL in volume in a manner that depends on field strength, field polarity, pH, and phase composition. The present study is an attempt to relate demixing rates to droplet electrokinetic mobilities which were measured microscopically and inferred from demixing data. A clear dependence of demixing rate was observed on drop electrophoretic mobility and pH. The electrophoretic mobility of individual phase droplets suspended in the other phase was measured for poly(ethylene glycol)/Dextran systems using a microelectrophoresis unit and compared with mobilities predicted by electrokinetic theory. We confirmed earlier reports that the droplet electrophoretic mobility increased with increasing drop diameter and explained this increase on the basis of an internal electroosmotic flow model. Effective electrophoretic mobilities were estimated from electrokinetic demixing data in a 100-mL column and compared with predicted as well as experimentally measured values of electrophoretic mobility. The mobilties increased with increased phosphate ionization due to change in pH irrespective of the sign (or polarity) of the applied electric field. The electroosmotic flow model could explain satisfactorily the following two paradoxes: (1) the direction of migration of drops is the opposite of that predicted by colloid electrokinetics and (2) the phase demixing rate increased irrespective of the sign of the applied electric field.

Journal Article↗

PubMed1998

A double blind placebo controlled study to determine the effects of intermittent cyclical etidronate on bone mineral density in patients on long-term oral corticosteroid treatment.

BACKGROUND: A double blind, placebo controlled study was undertaken to determine the effects of 104 weeks of intermittent cyclical etidronate therapy on bone mineral density (BMD) in patients undergoing long-term oral corticosteroid therapy. METHODS: Forty nine patients of mean age 59 years on long-term (> 6 months) corticosteroid treatment were randomised to receive either 400 mg/day etidronate or placebo for 14 days followed in both groups by calcium (equivalent to 97 mg elemental Ca/day) with vitamin D (400 IU) for 76 days. The cycle was repeated a total of eight times over a period of two years. Dual energy x ray absorptiometry (DEXA) measurements of the lumbar spine and hip BMD and biochemical bone marker analyses were performed at baseline and every six months. RESULTS: Twenty six patients (10 men) received cyclical etidronate and 23 (nine men) received placebo. The mean (SD) dose of corticosteroid (prednisone or equivalent) at baseline in the etidronate group was 8 (4) mg/day and in the placebo group was 7 (4) mg/day. Most of the patients (43%) suffered from asthma. Forty one patients completed the study (22 in the etidronate group and 19 in the placebo group). All had a low BMD at entry and with treatment a significant difference was observed between groups in the mean (SE) percentage change from baseline in lumbar spine BMD at week 104 of 4.5 (1.65)% (p = 0.007) with a 95% confidence interval (CI) of 1.12 to 7.87%. No clinically or statistically significant treatment differences were observed at the hip or with bone markers. The incidence of adverse events was similar in the two groups. CONCLUSIONS: The results show that intermittent cyclical etidronate therapy with calcium and vitamin D supplementation significantly increases lumbar spine BMD in patients with osteoporosis resulting from long-term treatment with corticosteroids.

Aged↗

PubMed1998

Early intervention in psychosis. The critical period hypothesis.

BACKGROUND: We consider the evidence for the proposition that the early phase of psychosis (including the period of untreated psychosis) is a critical period in which (a) long-term outcome is predictable, and (b) biological, psychological and psychosocial influences are developing and show maximum plasticity. METHOD: First-episode prospective studies, predictors of outcome and the genesis of patients' key appraisals of their psychosis are reviewed. RESULTS: The data support the notion of the 'plateau effect', first coined by Tom McGlashan, which suggested that where deterioration occurs, it does so aggressively in the first 2-3 years; and that critical psychosocial influences, including family and psychological reactions to psychosis and psychiatric services, develop during this period. CONCLUSIONS: The early phase of psychosis presents important opportunities for secondary prevention. We outline a prototype of intervention appropriate to the critical period. The data challenge the widely held assumption that first-episode psychosis is a benign illness posing little risk.

Adaptation, Psychological↗

PubMed1997

Isoform switching of type IV collagen is developmentally arrested in X-linked Alport syndrome leading to increased susceptibility of renal basement membranes to endoproteolysis.

Normal glomerular capillaries filter plasma through a basement membrane (GBM) rich in alpha3(IV), alpha4(IV), and alpha5(IV) chains of type IV collagen. We now show that these latter isoforms are absent biochemically from the glomeruli in patients with X-linked Alport syndrome (XAS). Their GBM instead retain a fetal distribution of alpha1(IV) and alpha2(IV) isoforms because they fail to developmentally switch their alpha-chain use. The anomalous persistence of these fetal isoforms of type IV collagen in the GBM in XAS also confers an unexpected increase in susceptibility to proteolytic attack by collagenases and cathepsins. The incorporation of cysteine-rich alpha3(IV), alpha4(IV), and alpha5(IV) chains into specialized basement membranes like the GBM may have normally evolved to protectively enhance their resistance to proteolytic degradation at the site of glomerular filtration. The relative absence of these potentially protective collagen IV isoforms in GBM from XAS may explain the progressive basement membrane splitting and increased damage as these kidneys deteriorate.

Basement Membrane↗

PubMed1997

In vitro kinetic studies of formation of antigenic advanced glycation end products (AGEs). Novel inhibition of post-Amadori glycation pathways.

Nonenzymatic protein glycation (Maillard reaction) leads to heterogeneous, toxic, and antigenic advanced glycation end products ("AGEs") and reactive precursors that have been implicated in the pathogenesis of diabetes, Alzheimer's disease, and normal aging. In vitro inhibition studies of AGE formation in the presence of high sugar concentrations are difficult to interpret, since AGE-forming intermediates may oxidatively arise from free sugar or from Schiff base condensation products with protein amino groups, rather than from just their classical Amadori rearrangement products. We recently succeeded in isolating an Amadori intermediate in the reaction of ribonuclease A (RNase) with ribose (Khalifah, R. G., Todd, P., Booth, A. A., Yang, S. X., Mott, J. D., and Hudson, B. G. (1996) Biochemistry 35, 4645-4654) for rapid studies of post-Amadori AGE formation in absence of free sugar or reversibly formed Schiff base precursors to Amadori products. This provides a new strategy for a better understanding of the mechanism of AGE inhibition by established inhibitors, such as aminoguanidine, and for searching for novel inhibitors specifically acting on post-Amadori pathways of AGE formation. Aminoguanidine shows little inhibition of post-Amadori AGE formation in RNase and bovine serum albumin, in contrast to its apparently effective inhibition of initial (although not late) stages of glycation in the presence of high concentrations of sugar. Of several derivatives of vitamins B1 and B6 recently studied for possible AGE inhibition in the presence of glucose (Booth, A. A., Khalifah, R. G., and Hudson, B. G. (1996) Biochem. Biophys. Res. Commun. 220, 113-119), pyridoxamine and, to a lesser extent, thiamine pyrophosphate proved to be novel and effective post-Amadori inhibitors that decrease the final levels of AGEs formed. Our mechanism-based approach to the study of AGE inhibition appears promising for the design and discovery of novel post-Amadori AGE inhibitors of therapeutic potential that may complement others, such as aminoguanidine, known to either prevent initial sugar attachment or to scavenge highly reactive dicarbonyl intermediates.

Animals↗

PubMed1997

Effects of inflammation and treatment on bone turnover and bone mass in polymyalgia rheumatica.

OBJECTIVE: Polymyalgia rheumatica (PMR) has an abrupt onset of inflammatory symptoms, making it a useful model for studying the effects of inflammation in bone. PMR requires corticosteroid treatment, which may itself have a detrimental effect on bone. This study used serially measured biochemical markers of bone turnover and bone density to address the relative contributions of systemic inflammation and corticosteroid therapy to bone loss. METHODS: Fifty untreated patients with PMR were randomized to receive oral prednisolone or intramuscular methylprednisolone. Biochemical bone markers (pyridinoline [PYR], deoxypyridinoline [DPYR], procollagen type I carboxy-terminal peptide [PICP]) and bone mineral density (BMD) were measured at baseline and at 6, 12, and 24 months. RESULTS: The median disease duration at presentation was 12 weeks (range 5-32 weeks). Levels of urinary crosslinks were increased in patients with untreated PMR compared with controls (PYR 74.9 +/- 30.0 nmoles/mmole creatinine, DPYR 14.6 +/- 6.4 nmoles/mmole creatinine [mean +/- SD]; P = 0.0001); the PICP level was normal (115.0 +/- 39.0 microg/liter). With treatment, the crosslinks levels fell and PICP levels rose within 6 months (P = 0.01). Bone resorption (PYR) correlated with untreated disease activity (erythrocyte sedimentation rate [ESR]) (r = 0.5, P = 0.003) and with interleukin-6 levels (r = 0.48, P = 0.05). There was a significant reduction in BMD of both the hip and the spine after 12 months of treatment (P = 0.0002), with no difference between treatment groups. As the steroid dosage was reduced, bone mass improved. Initial ESR influenced the percent change in BMD at 1 year (r = 0.35, P = 0.05), while cumulative steroid dose, mean ESR, and type of steroid used did not. CONCLUSION: Inflammation in PMR increases bone resorption and appears to have a more detrimental effect on bone than does low-dose corticosteroid. If corticosteroids can be tapered and discontinued, bone loss in PMR can be a transient phenomenon.

Adrenal Cortex Hormones↗

PubMed1997

Modulation of statolith mass and grouping in white clover (Trifolium repens) growth in 1-g, microgravity and on the clinostat.

Current models of gravity perception in higher plants focus on the buoyant weight of starch-filled amyloplasts as the initial gravity signal susceptor (statolith). However, no tests have yet determined if statolith mass is regulated to increase or decrease gravity stimulus to the plant. To this end, the root caps of white clover (Trifolium repens) grown in three gravity environments with three different levels of gravity stimulation have been examined: (i) 1-g control with normal static gravistimulation, (ii) on a slow clinostat with constant gravistimulation, and (iii) in the stimulus-free microgravity aboard the Space Shuttle. Seedlings were germinated and grown in the BioServe Fluid Processing Apparatus and root cap structure was examined at both light and electron microscopic levels, including three-dimensional cell reconstruction from serial sections. Quantitative analysis of the electron micrographs demonstrated that the starch content of amyloplasts varied with seedling age but not gravity condition. It was also discovered that, unlike in starch storage amyloplasts, all of the starch granules of statolith amyloplasts were encompassed by a fine filamentous, ribosome-excluding matrix. From light micrographic 3-D cell reconstructions, the absolute volume, number, and positional relationships between amyloplasts showed (i) that individual amyloplast volume increased in microgravity but remained constant in seedlings grown for up to three days on the clinostat, (ii) the number of amyloplasts per cell remained unchanged in microgravity but decreased on the clinostat, and (iii) the three-dimensional positions of amyloplasts were not random. Instead amyloplasts in microgravity were grouped near the cell centers while those from the clinostat appeared more dispersed. Taken together, these observations suggest that changing gravity stimulation can elicit feedback control over statolith mass by changing the size, number, and grouping of amyloplasts. These results support the starch-statolith theory of graviperception in higher plants and add to current models with a new feedback control loop as a mechanism for modulation of statolith responsiveness to inertial acceleration.

Fabaceae↗