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Biomedical subjects

Thomas J Nelson

Publications and source records attributed to Thomas J Nelson.

12 recordsLinked to original sources
PubMed2007

PKC signaling deficits: a mechanistic hypothesis for the origins of Alzheimer's disease.

There is strong evidence that protein kinase C (PKC) isozyme signaling pathways are causally involved in associative memory storage. Other observations have indicated that PKC signaling pathways regulate important molecular events in the neurodegenerative pathophysiology of Alzheimer's disease (AD), which is a progressive dementia that is characterized by loss of recent memory. This parallel involvement of PKC signaling in both memory and neurodegeneration indicates a common basis for the origins of both the symptoms and the pathology of AD. Here, we discuss this conceptual framework as a basis for an autopsy-validated peripheral biomarker--and for AD drug design targeting drugs (bryostatin and bryologs) that activate PKC isozymes--that has already demonstrated significant promise for treating both AD neurodegeneration and its symptomatic memory loss.

Alzheimer Disease↗
PubMed2006

Predictors of mortality in close proximity blast injuries during Operation Iraqi Freedom.

BACKGROUND: Blast injury is an increasingly common problem faced by military surgeons in the field. Because of urban terrorism worldwide, blast injury is becoming more common in the civilian sector as well. Blast injuries are often devastating and can overwhelm medical resources. We sought to determine whether simple factors easily obtained from the clinical history and primary survey could be used to triage patients more effectively. STUDY DESIGN: A retrospective review of 18 consecutive close-proximity blast injury patients presenting to a forward deployed surgical unit in Iraq was performed. Patients' injuries and outcomes were recorded. We compared the presence of sustained hypotension, penetrating head injury, multiple (three or more) long-bone fractures, and associated fatalities (whether another patient involved in the same explosion died) between nonsurvivors and survivors using Fisher's exact test. RESULTS: All patients who presented alive but exhibited sustained hypotension (n = 5) died, versus 0% who did not exhibit sustained hypotension (n = 9, p < 0.01). There was no marked increase in mortality with presence of multiple long-bone fractures, penetrating head injury, or associated fatalities individually. Having two or more of these factors was associated with a mortality of 86% (6 of 7) versus 20% (2 of 10, p = 0.015) in those who had less than two factors. CONCLUSIONS: Blast injury can overwhelm military and civilian trauma systems alike. Sustained hypotension and presence of two or more easily determined factors, including three or more long-bone fractures, penetrating head injury, and associated fatalities, are associated with increased mortality and can potentially help triage patients and allocate scarce resources more efficiently.

Blast Injuries↗
PubMed2006

A prospective evaluation of opioid weaning in opioid-dependent pediatric critical care patients.

Critically ill children are treated with opioid medication in an attempt to decrease stress and alleviate pain during prolonged pediatric intensive care. This treatment plan places children at risk for opioid dependency. Once dependent, children need to be weaned or risk development of a withdrawal syndrome on abrupt cessation of medication. We enrolled opioid-dependent children into a prospective, randomized trial of 5- versus 10-day opioid weaning using oral methadone. Children exposed to opioids for an average of 3 wk showed no difference in the number of agitation events requiring opioid rescue (3 consecutive neonatal abstinence scores >8 every 2 h) in either wean group. Most of the events requiring rescue occurred on day 5 and 6 of the wean in both treatment groups. Patients may be able to be weaned successfully in 5 days once converted to oral methadone, with a follow-up period after medication wean to observe for a delayed withdrawal syndrome.

Analgesics, Opioid↗
PubMed2005

Protein synthesis required for long-term memory is induced by PKC activation on days before associative learning.

Protein synthesis has long been known to be required for associative learning to consolidate into long-term memory. Here we demonstrate that PKC isozyme activation on days before training can induce the synthesis of proteins necessary and sufficient for subsequent long-term memory consolidation. Bryostatin (Bryo), a macrolide lactone with efficacy in subnanomolar concentrations and a potential therapeutic for Alzheimer's disease, is a potent activator of PKC, some of whose isozymes undergo prolonged activation after associative learning. Under normal conditions, two training events with paired visual and vestibular stimuli cause short-term memory of the mollusc Hermissenda that lasts approximately 7 min. However, after 4-h exposures to Bryo (0.25 ng/ml) on two preceding days, the same two training events produced long-term conditioning that lasted >1 week and that was not blocked by anisomycin (1 mug/ml). Anisomycin, however, eliminated long-term memory lasting at least 1 week after nine training events. Both the nine training events alone and two Bryo exposures plus two training event regimens caused comparably increased levels of the PKC alpha-isozyme substrate calexcitin in identified type B neurons and enhanced PKC activity in the membrane fractions. Furthermore, Bryo increased overall protein synthesis in cultured mammalian neurons by up to 60% for >3 days. The specific PKC antagonist Ro-32-0432 blocked much of this Bryo-induced protein synthesis as well as the Bryo-induced enhancement of the behavioral conditioning. Thus, Bryo-induced PKC activation produces those proteins necessary and sufficient for long-term memory on days in advance of the training events themselves.

Animals↗
PubMed2004

Oxidation of cholesterol by amyloid precursor protein and beta-amyloid peptide.

Alzheimer's disease (AD) is characterized by accumulation of the neurotoxic peptide beta-amyloid, which is produced by proteolysis of amyloid precursor protein (APP). APP is a large membrane-bound copper-binding protein that is essential in maintaining synaptic function and may play a role in synaptogenesis. beta-Amyloid has been shown to contribute to the oxidative stress that accompanies AD. Later stages of AD are characterized by neuronal apoptosis. However, the biochemical function of APP and the mechanism of the toxicity of beta-amyloid are still unclear. In this study, we show that both beta-amyloid and APP can oxidize cholesterol to form 7beta-hydroxycholesterol, a proapoptotic oxysterol that was neurotoxic at nanomolar concentrations. 7beta-Hydroxycholesterol inhibited secretion of soluble APP from cultured rat hippocampal H19-7/IGF-IR neuronal cells and inhibited tumor necrosis factor-alpha-converting enzyme alpha-secretase activity but had no effect on beta-site APP-cleaving enzyme 1 activity. 7beta-Hydroxycholesterol was also a potent inhibitor of alpha-protein kinase C, with a K(i) of approximately 0.2 nm. The rate of reaction between cholesterol and beta-amyloid was comparable to the rates of cholesterol-metabolizing enzymes (k(cat) = 0.211 min(-)1). The rate of production of 7beta-hydroxycholesterol by APP was approximately 200 times lower than by beta-amyloid. Oxidation of cholesterol was accompanied by stoichiometric production of hydrogen peroxide and required divalent copper. The results suggest that a function of APP may be to produce low levels of 7-hydroxycholesterol. Higher levels produced by beta-amyloid could contribute to the oxidative stress and cell loss observed in Alzheimer's disease.

ADAM Proteins↗
PubMed2004

Therapeutic effects of PKC activators in Alzheimer's disease transgenic mice.

Alzheimer's disease (AD) characteristically presents with early memory loss. Regulation of K(+) channels, calcium homeostasis, and protein kinase C (PKC) activation are molecular events that have been implicated during associative memory which are also altered or defective in AD. PKC is also involved in the processing of the amyloid precursor protein (APP), a central element in AD pathophysiology. In previous studies, we demonstrated that benzolactam (BL), a novel PKC activator, reversed K(+) channels defects and enhanced secretion of APP alpha in AD cells. In this study we present data showing that another PKC activator, bryostatin 1, at subnanomolar concentrations dramatically enhances the secretion of the alpha-secretase product sAPP alpha in fibroblasts from AD patients. We also show that BL significantly increased the amount of sAPP alpha and reduced A beta 40 in the brains of APP[V717I] transgenic mice. In a more recently developed AD double-transgenic mouse, bryostatin was effective in reducing both brain A beta 40 and A beta 42. In addition, bryostatin ameliorated the rate of premature death and improved behavioral outcomes. Collectively, these data corroborate PKC and its activation as a potentially important means of ameliorating AD pathophysiology and perhaps cognitive impairment, thus offering a promising target for drug development. Because bryostatin 1 is devoid of tumor-promoting activity and is undergoing numerous clinical studies for cancer treatment in humans, it might be readily tested in patients as a potential therapeutic agent for Alzheimer's disease.

Alzheimer Disease↗
PubMed2004

Hippocampal protein-protein interactions in spatial memory.

Memory consolidation in mammalian brain is accompanied by widespread reorganization of synaptic contacts and dendritic structure. Understanding of the protein-protein interactions that underlie these structural changes has been hampered by the difficulty of studying protein-protein interactions produced in vivo by signaling, learning, and other physiological responses using current methodologies. Using a novel technique that separates interacting proteins from noninteracting proteins on the basis of their protein-target affinity, we identified 16 proteins for which protein-target binding is altered in vivo by spatial learning, including stathmin, complexin I, 14-3-3, and several structural proteins including F-actin capping protein, tubulin, GFAP, and actin. Interactions between complexin and its targets (p25alpha and Drac1-like protein) and the interaction between CapZ and tubulin were calcium-dependent. The preponderance of structural proteins and proteins involved in synapse formation and reorganization of growth cones among proteins undergoing memory-specific changes in protein-protein interactions suggests that synaptic structural reorganization is a predominant feature of the consolidation phase of memory.

Adaptor Proteins, Vesicular Transport↗
PubMed2003

Calcium-regulated GTPase activity in the calcium-binding protein calexcitin.

Calexcitin (CE) is a calcium-binding protein, closely related to sarcoplasmic calcium-binding proteins, that is involved in invertebrate learning and memory. Early reports indicated that both Hermissenda and squid CE also could bind GTP; however, the biochemical significance of GTP-binding and its relationship to calcium binding have remained unclear. Here, we report that the GTPase activity of CE is strongly regulated by calcium. CE possessed a P-loop-like structure near the C-terminal similar to the phosphate-binding regions in other GTP-binding proteins. Site-directed mutagenesis of this region showed that Gly(182), Phe(186) and Gly(187) are required for maximum affinity, suggesting that the GTP-binding motif is G-N-x-x-[FM]-G. CE cloned from Drosophila CNS possessed a similar C-terminal sequence and also bound and hydrolyzed GTP. GTPase activity in Drosophila CE was also strongly regulated by Ca(2+), exhibiting over 23-fold higher activity in the presence of 0.3 microM calcium. Analysis of the conserved protein motifs defines a new family of Ca(2+)-binding proteins representing the first example of proteins endowed with both EF-hand calcium binding domains and a C-terminal, P-loop-like GTP-binding motif. These results establish that, in the absence of calcium, both squid and Drosophila CE bind GTP at near-physiological concentrations and hydrolyze GTP at rates comparable to unactivated ras. Calcium functions to increase GTP-binding and GTPase activity in CE, similar to the effect of GTPase activating proteins in other low-MW GTP-binding proteins. CE may, therefore, act as a molecular interface between Ca(2+) cytosolic oscillations and the G protein-coupled signal transduction.

Amino Acid Sequence↗
PubMed2002

Isolation of protein subpopulations undergoing protein-protein interactions.

A new method is described for isolating and identifying proteins participating in protein-protein interactions in a complex mixture. The method uses a cyanogen bromide-activated Sepharose matrix to isolate proteins that are non-covalently bound to other proteins. Because the proteins are accessible to chemical manipulation, mass spectrometric identification of the proteins can yield information on specific classes of interacting proteins, such as calcium-dependent or substrate-dependent protein interactions. This permits selection of a subpopulation of proteins from a complex mixture on the basis of specified interaction criteria. The new method has the advantage of screening the entire proteome simultaneously, unlike the two-hybrid system or phage display, which can only detect proteins binding to a single bait protein at a time. The method was tested by selecting rat brain extract for proteins exhibiting calcium-dependent protein interactions. Of 12 proteins identified by mass spectrometry, eight were either known calcium-binding proteins or proteins with known calcium-dependent protein interactions, indicating that the method is capable of enriching a subpopulation of proteins from a complex mixture on the basis of a specific class of protein interactions. Because only naturally occurring interactions of proteins in their native state are observed, this method will have wide applicability to studies of protein interactions in tissue samples and autopsy specimens, for screening for perturbations of protein-protein interactions by signaling molecules, pharmacological agents or toxins, and screening for differences between cancerous and untransformed cells.

Animals↗
PubMedDate not supplied

Comparison of three commercially available fit-test methods.

American National Standards Institute (ANSI) standard Z88.10, Respirator Fit Testing Methods, includes criteria to evaluate new fit-tests. The standard allows generated aerosol, particle counting, or controlled negative pressure quantitative fit-tests to be used as the reference method to determine acceptability of a new test. This study examined (1) comparability of three Occupational Safety and Health Administration-accepted fit-test methods, all of which were validated using generated aerosol as the reference method; and (2) the effect of the reference method on the apparent performance of a fit-test method under evaluation. Sequential fit-tests were performed using the controlled negative pressure and particle counting quantitative fit-tests and the bitter aerosol qualitative fit-test. Of 75 fit-tests conducted with each method, the controlled negative pressure method identified 24 failures; bitter aerosol identified 22 failures; and the particle counting method identified 15 failures. The sensitivity of each method, that is, agreement with the reference method in identifying unacceptable fits, was calculated using each of the other two methods as the reference. None of the test methods met the ANSI sensitivity criterion of 0.95 or greater when compared with either of the other two methods. These results demonstrate that (1) the apparent performance of any fit-test depends on the reference method used, and (2) the fit-tests evaluated use different criteria to identify inadequately fitting respirators. Although "acceptable fit" cannot be defined in absolute terms at this time, the ability of existing fit-test methods to reject poor fits can be inferred from workplace protection factor studies.

Aerosols↗
PubMedDate not supplied

Evaluation of a quantitative fit testing method for N95 filtering facepiece respirators.

A method for performing quantitative fit tests (QNFT) with N95 filtering facepiece respirators was developed by earlier investigators. The method employs a simple clamping device to allow the penetration of submicron aerosols through N95 filter media to be measured. The measured value is subtracted from total penetration, with the assumption that the remaining penetration represents faceseal leakage. The developers have used the clamp to assess respirator performance. This study evaluated the clamp's ability to measure filter penetration and determine fit factors. In Phase 1, subjects were quantitatively fit-tested with elastomeric half-facepiece respirators using both generated and ambient aerosols. QNFT were done with each aerosol with both P100 and N95 filters without disturbing the facepiece. In Phase 2 of the study elastomeric half facepieces were sealed to subjects' faces to eliminate faceseal leakage. Ambient aerosol QNFT were performed with P100 and N95 filters without disturbing the facepiece. In both phases the clamp was used to measure N95 filter penetration, which was then subtracted from total penetration for the N95 QNFT. It was hypothesized that N95 fit factors corrected for filter penetration would equal the P100 fit factors. Mean corrected N95 fit factors were significantly different from the P100 fit factors in each phase of the study. In addition, there was essentially no correlation between corrected N95 fit factors and P100 fit factors. It was concluded that the clamp method should not be used to fit-test N95 filtering facepieces or otherwise assess respirator performance.

Adult↗