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Biomedical subjects

M D Watson

Publications and source records attributed to M D Watson.

At least 19 recordsLinked to original sources
PubMed2004

Prototypical single-molecule chemical-field-effect transistor with nanometer-sized gates.

A prototypical single-molecule chemical-field-effect transistor is presented, in which the current through a hybrid-molecular diode is modified by nanometer-sized charge transfer complexes covalently linked to a molecule in an STM junction. The effect is attributed to an interface dipole which shifts the substrate work function by approximately 120 meV. It is induced by the complexes from electron acceptors covalently bound to the molecule in the gap and electron donors coming from the ambient fluid. This proof of principle is regarded as a major step towards monomolecular electronic devices.

Journal Article↗
PubMed2003

Hippocampal nitric oxide upregulation precedes memory loss and A beta 1-40 accumulation after chronic brain hypoperfusion in rats.

Chronic brain hypoperfusion (CBH) using permanent occlusion of both common carotid arteries in an aging rat model, has been shown to mimic human mild cognitive impairment (MCI), an acknowledged high risk condition that often converts to Alzheimer's disease. An aging rat model was used to determine whether hippocampal nitric oxide (NO) is abnormally expressed following CBH for two or eight weeks. At each time point, spatial memory was measured with the Morris water maze and hippocampal A beta 1-40/1-42 concentrations were obtained using sandwich ELISA. Real-time amperometric measures of NO representing the constitutive isoforms of neuronal nitric oxide synthase (nNOS) and endothelial (e)NOS were also taken at each time point to ascertain whether NO levels changed as a result of CBH, and if so, whether such NO changes preceded or followed any memory or amyloid-beta pathology. We found that two weeks after CBH, NO hippocampal levels were upregulated nearly four-fold when compared to nonoccluded rats but no alteration in spatial memory of A beta products were observed at this time point. By contrast, NO concentration had declined to control levels by eight weeks but spatial memory was found significantly impaired and A beta 1-40 (but not A beta 1-42) had increased in the CBH group when compared to control rats. Since changes in shear stress are known to upregulate eNOS but generally not nNOS, these results suggest that shear stress induced by CBH hyperactivated vascular NO derived from eNOS in the first two weeks as a reaction by the capillary endothelium to maintain homeostasis of local cerebral blood flow. The return of vascular NO to basal levels after eight weeks of CBH may have triggered metabolic changes within hippocampal cells resulting in hippocampal dysfunction as reflected by spatial memory impairment and by accumulation of A beta 1-40 peptide. In conclusion, our study shows that CBH initiates spatial memory loss in aging rats thus mimicking human MCI and also increases A beta 1-40 in the hippocampus. The memory and amyloid changes are preceded by NO upregulation in the hippocampus. These preliminary findings may be important in understanding, at least in part, the molecular mechanisms that precede memory impairment during chronic brain ischemia and as such, the pre-clinical stage leading to Alzheimer's disease.

Alzheimer Disease↗
PubMed2001

Disruption and basic phenotypic analysis of six novel genes from the right arm of chromosome XII of Saccharomyces cerevisiae.

Six open reading frames (ORFs) of unknown function from the right arm of Saccharomyces cerevisiae chromosome XII were deleted in two genetic backgrounds by disruption cassettes with regions of short flanking homology. This work was carried out within the framework of the EUROFAN consortium. The SFH disruption cassettes, obtained by PCR, were made by amplification of the kanMX marker module with oligonucleotides containing approximately 40 bp of homology to either the promoter or translation terminator regions of the relevant ORF. Transformants resistant to geneticin (G418) were selected. The SFH disruption cassettes were cloned into a bacterial vector. Each cognate gene was also cloned into a yeast centromeric plasmid. Sporulation and tetrad analysis of the disrupted heterozygous strains revealed that ORF YLR153c (now known as ACS2) is essential. Basic phenotypic analysis was performed on haploid deletants of both mating types of the five non-essential ORFs, YLR082c (now known as SRL2), YLR149c, YLR151c, YLR152c and YLR154c. Plate growth tests on different media at 15 degrees C, 30 degrees C and 37 degrees C did not reveal any significant differences between parental and mutant cells. Mating and sporulation efficiencies were not affected in any of the viable disruptants as compared to wild-type cells.

Chromosomes, Fungal↗
PubMed2001

Current awareness on yeast.

In order to keep subscribers up-to-date with the latest developments in their field, this current awareness service is provided by John Wiley & Sons and contains newly-published material on yeasts. Each bibliography is divided into 10 sections. 1 Books, Reviews & Symposia; 2 General; 3 Biochemistry; 4 Biotechnology; 5 Cell Biology; 6 Gene Expression; 7 Genetics; 8 Physiology; 9 Medical Mycology; 10 Recombinant DNA Technology. Within each section, articles are listed in alphabetical order with respect to author. If, in the preceding period, no publications are located relevant to any one of these headings, that section will be omitted. (4 weeks journals - search completed 3rd Jan. 2001)

Yeasts↗
PubMed2000

The role of complement in Alzheimer's disease pathology.

Complement proteins are integral components of amyloid plaques and cerebral vascular amyloid in Alzheimer brains. They can be found at the earliest stages of amyloid deposition and their activation coincides with the clinical expression of Alzheimer's dementia. This review will examine the origins of complement in the brain and the role of beta-amyloid peptide (Abeta) in complement activation in Alzheimer's disease, an event that might serve as a nidus of chronic inflammation. Pharmacology therapies that may serve to inhibit Abeta-mediated complement activation will also be discussed.

Alzheimer Disease↗
PubMed2000

Xenopus NK cells identified by novel monoclonal antibodies.

Early-thymectomized (Tx) Xenopus frogs, which are permanently deficient in T cells, are used as a model sytem for the characterization of novel monoclonal antibodies (mAb) which identify candidate NK cells at the amphibian level of evolution. Hybridomas, generated from mice immunized with splenocytes from Tx Xenopus following B cell and thrombocyte depletion, were screened by flow cytometry. Three mAb (1F8, 4D4 and 1G5) were identified that stained increased proportions of splenocytes from Tx compared with control frogs. These mAb identified lymphoid populations from Xenopus spleen, liver and gut which, after 48 h culture in growth factor-rich medium, exhibited spontanous killing of MHC-deficient allotumor targets. mAb-defined splenocytes also rapidly induced apoptosis of such tumor targets. Dual color analysis confirmed that NK cells are neither T nor B cells. Cytospins of splenocytes isolated with anti-NK mAb revealed large lymphoid cells with distinct pseudopodia. Immunohistology indicated each anti-NK mAb routinely labeled cells within the gut epithelium but NK cells were difficult to visualize in spleen sections. Western blotting of spleen, liver and intestinal lysates subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that 1G5 reacted strongly with protein bands of approximately 70 - 85 kDa, whereas mAb 1F8 and 4D4 stained less intensely, but identified similar protein bands.

Animals↗
PubMed2000

Elevated abeta42 in skeletal muscle of Alzheimer disease patients suggests peripheral alterations of AbetaPP metabolism.

The levels of amyloid-beta40 (Abeta40) and Abeta42 peptides were quantified in temporalis muscles and brain of neuropathologically diagnosed Alzheimer disease (AD) and of nondemented individuals. This was achieved by using a novel analytical approach consisting of a combination of fast-performance liquid chromatographic (FPLC) size exclusion chromatography developed under denaturing conditions and europium immunoassay on the 4.0- to 4.5-kd fractions. In the temporalis muscles of the AD and nondemented control groups, the average values for Abeta42 were 15.7 ng/g and 10.2 ng/g (P = 0.010), and for Abeta40 they were 37.8 ng/g and 29.8 ng/g (P = 0.067), respectively. Multiple regression analyses of the AD and control combined populations indicated that 1) muscle Abeta40 and muscle Abeta42 levels were correlated with each other (P < 0.001), 2) muscle Abeta40 levels were positively correlated with age (P = 0. 036), and 3) muscle Abeta42 levels were positively correlated with Braak stage (P = 0.042). Other forms of the Abeta peptide were discovered by mass spectrometry, revealing the presence of Abeta starting at residues 1, 6, 7, 9, 10, and 11 and ending at residues 40, 42, 44, 45, and 46. It is possible that in AD the skeletal muscle may contribute to the elevated plasma pool of Abeta and thus indirectly to the amyloid deposits of the brain parenchyma and cerebral blood vessels. The increased levels of Abeta in the temporalis muscles of AD patients suggest that alterations in AbetaPP and Abeta metabolism may be manifested in peripheral tissues.

Aged↗
PubMed2000

Traumatic brain injury elevates the Alzheimer's amyloid peptide A beta 42 in human CSF. A possible role for nerve cell injury.

The increased risk for Alzheimer's Disease (AD) associated with traumatic brain injury (TBI) suggests that environmental insults may influence the development of this age-related dementia. Recently, we have shown that the levels of the beta-amyloid peptide (A beta 1-42) increase in the cerebrospinal fluid (CSF) of patients after severe brain injury and remain elevated for some time after the initial event. The relationships of elevated A beta with markers of blood-brain barrier (BBB) disruption, inflammation, and nerve cell or axonal injury were evaluated in CSF samples taken daily from TBI patients. This analysis reveals that the rise in A beta 1-42 is best correlated with possible markers of neuronal or axonal injury, the cytoskeletal protein tau, neuron-specific enolase (NSE), and apolipoprotein E (ApoE). Similar or better correlations were observed between A beta 1-40 and the three aforementioned markers. These results imply that the degree of brain injury may play a decisive role in determining the levels of A beta 1-42 and A beta 1-40 in the CSF of TBI patients. Inflammation and alterations in BBB may play lesser, but nonetheless significant, roles in determining the A beta level in CSF after brain injury.

Acute-Phase Proteins↗
PubMed1999

Inhibitors of V-type ATPases, bafilomycin A1 and concanamycin A, protect against beta-amyloid-mediated effects on 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction.

The functional viability of cells can be evaluated using a number of different assay determinants. One common assay involves exposing cells to 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), which is converted intracellularly to a colored formazan precipitate and often used to assess amyloid peptide-induced cytotoxic effects. The MTT assay was employed to evaluate the role of endosomal uptake and lysosomal acidification in amyloid peptide-treated differentiated PC12 cell cultures using selective vacuolar-type (V-type) ATPase inhibitors. The macrolides bafilomycin A1 (BAF) and concanamycin A (CON) block lysosomal acidification through selective inhibition of the V-type ATPase. Treating nerve growth factor-differentiated PC12 cells with nanomolar concentrations of BAF or CON provides complete protection against the effects of beta-amyloid peptides Abeta(1-42), Abeta(1-40), and Abeta(25-35) and of amylin on MTT dye conversion. These macrolides do not inhibit peptide aggregation, act as antioxidants, or inhibit Abeta uptake by cells. Measurements of lysosomal acidification reveal that the concentrations of BAF and CON effective in reversing Abeta-mediated MTT dye conversion also reverse lysosomal pH. These results suggest that lysosomal acidification is necessary for Abeta effects on MTT dye conversion.

Adenosine Triphosphatases↗
PubMed1998

Traumatic brain injury increases beta-amyloid peptide 1-42 in cerebrospinal fluid.

The beta-amyloid peptides, A beta1-42 and A beta1-40, were quantified in ventricular CSF taken daily for up to 3 weeks from six individuals with severe traumatic brain injury (TBI). There was considerable interindividual variability in the levels of A beta peptides, but in general A beta1-42 levels equalled or exceeded those of A beta1-40. Averaging the daily totals of our trauma cohort revealed that the levels of A beta1-42 and A beta1-40 rose after injury, peaking in the first week and then declining toward control levels over the next 2 weeks. A beta1-42 levels were on average two to three times higher in the trauma cohort than in CSF from nontrauma samples. Compared with nontrauma samples, the A beta1-40/A beta1-42 ratio decreased about fivefold in the trauma patients, further indicative of increased A beta1-42 levels. The ratio remained low at all time points studied. No change was measured in the levels of beta-amyloid precursor protein during the same interval. These results suggest that A beta1-42 becomes elevated in the CSF after severe brain trauma.

Adult↗
PubMed1998

T-cell and natural killer cell development in thymectomized Xenopus.

The Xenopus early-thymectomy model system is used to investigate the extent to which the thymus controls T-cell development and to probe the evolution of natural killer (NK) cells. Loss of T-cell function following thymectomy, together with the paucity of cells expressing monoclonal antibody-defined T-cell surface markers, and greatly reduced expression of T-cell receptor beta transcripts in spleen, liver and intestine, indicate that T-cell development in minimal in the absence of the thymus. Our findings therefore mitigate against the idea that a substantial extrathymic pathway of T-cell development exists in early vertebrate evolution. Rather, they suggest that in this amphibian representative T cells are predominately thymus dependent. In vitro studies with control and thymectomized Xenopus splenocytes reveal that a non-T/non-B population and also two T-cell subsets all display natural cytotoxicity towards allogeneic thymus lymphoid tumour cells (which are deficient in MHC antigen expression). Since Xenopus thymectomized early in larval development are permanently deficient in T cells, they may provide a useful phylogenetic model for the study of NK cells.

Animals↗
PubMed1997

Inhibiting the formation of classical C3-convertase on the Alzheimer's beta-amyloid peptide.

Amyloid plaques are the pathological hallmark of Alzheimer Disease (AD) brains, being found primarily in the hippocampus and neocortex, where AD pathology is most evident. Complement activation is associated with amyloid plaques which are made from fibrils of aggregated amyloid peptides, 39-42 amino acids long. In vitro studies show that aggregated amyloid peptides activate complement via the classical pathway, implying that amyloid plaques themselves cause complement activation in AD brains. In order to test this hypothesis, we sought to determine if a major peptide component of amyloid plaques, A beta 1-42, supports the formation of the classical pathway C3 convertase. Using normal human serum depleted of C3, we are able to detect C3 convertase activity on aggregated A beta 1-42 in vitro. The convertase activity is associated with the binding of C1q and activation of C4 on the aggregated peptide. Inhibitors of C1 esterase and the cation chelator EGTA both block the formation of the convertase activity. Congo red, a histochemical stain for amyloid deposits and an inhibitor of amyloid aggregation, reduces C3 convertase activity on aggregated A beta 1-42, indicated by decreased C3a production. Our results provide further evidence that aggregated A beta 1-42 alone is sufficient to serve as a nidus for complement activation, and thus may be involved directly in initiating the inflammation seen in AD brains.

Alzheimer Disease↗
PubMed1996

The Pisum sativum MAP kinase homologue (PsMAPK) rescues the Saccharomyces cerevisiae hog1 deletion mutant under conditions of high osmotic stress.

Previous analysis of the MAP kinase homologue from Pisum sativum (PsMAPK) revealed a potential MAP kinase motif homologous to that found in eukaryotic cdc2 kinases. Sequence comparison showed a 47% identity on amino acid sequence basis to the Saccharomyces cerevisiae Hog1p MAP kinase involved in the osmoregulatory pathway. Under conditions of salt-stress aberrant morphology of a hog1 deletion mutant was completely restored and growth was partially restored by expression of the PsMAPK. This shows that PsMAPK is functionally active as a MAP kinase in S. cerevisiae. Comparison of PsMAPK with other kinases involved in osmosensitivity, showed a high degree of homology and implicates a possible role for PsMAPK in a P. sativum osmosensing signal transduction pathway.

Base Sequence↗
PubMed1996

NK-like activity against allogeneic tumour cells demonstrated in the spleen of control and thymectomized Xenopus.

This paper addresses the issue of natural killer (NK) cell evolution by searching for NK-like activity in an amphibian representative, the immunologically well-characterized clawed frog, Xenopus laevis. Using in vitro 6 h 51chromium release assays, we have shown that splenocyte effectors from early thymectomized (Tx) year-old frogs, but not from control siblings, are able to spontaneously lyse allogeneic thymus tumour cell lines that lack MHC antigen expression. Such lytic capacity can be readily induced in control Xenopus and elevated in Tx frogs by a single injection of tumour cells, with maximal splenocyte cytotoxicity occurring 3 days postinjection, the amount of 51Cr-release correlating directly with effector: target ratios. Splenocytes, even those from tumour-injected frogs, are unable to lyse allogeneic splenic lymphoblasts or erythrocyte targets, even when the latter are coated with IgY (the Xenopus IgG equivalent); moreover, we were unable to demonstrate any splenocyte-induced lysis of the human NK cell target K562. Lymphokine-activated killing (LAK) in Xenopus is suggested, since Tx splenocytes cultured in cytokine-rich medium (from concanavalin A-stimulated control splenocytes) display significantly elevated killing of allogeneic tumour targets. Flow cytometric analysis highlights the loss of T cell markers from the spleen of Tx frogs and reveals a variable staining pattern of both control and Tx splenocytes when treated with a mAb that binds to both fish non-specific cytotoxic cells and human NK cells. Prospects for identifying the cellular basis of NK-like activity in Xenopus are discussed in the light of these experiments.

Animals↗
PubMed1996

Popliteal vein thrombosis causing compartment syndrome: a case report.

Compartment syndrome as a result of venous thrombosis is an uncommon occurrence. Generally, phlegmasia cerulea dolens or proximal venous thrombosis results in elevated compartment pressures. Distal venous occlusion rarely is reported as a cause of compartment syndrome. This is a case report of an otherwise healthy patient in whom popliteal vein thrombosis developed and resulted in elevation > 40 mm Hg of 3 leg muscle compartments requiring fasciotomies.

Acute Disease↗