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Biomedical subjects

Richard E Olson

Publications and source records attributed to Richard E Olson.

9 recordsLinked to original sources
PubMed2004

Binding sites of gamma-secretase inhibitors in rodent brain: distribution, postnatal development, and effect of deafferentation.

gamma-Secretase is a multimeric complex consisted of presenilins (PSs) and three other proteins. PSs appear to be key contributors for the enzymatic center, the potential target of a number of recently developed gamma-secretase inhibitors. Using radiolabeled and unlabeled inhibitors as ligands, this study was aimed to determine the in situ distribution of gamma-secretase in the brain. Characterization using PS-1 knock-out mouse embryos revealed 50 and 80% reductions of gamma-secretase inhibitor binding density in the heterozygous (PS-1(+/-)) and homozygous (PS-1-/-) embryos, respectively, relative to the wild type (PS-1(+/+)). The pharmacological profile from competition binding assays suggests that the ligands may target at the N- and C-terminal fragments of PS essential for gamma-secretase activity. In the adult rat brain, the binding sites existed mostly in the forebrain, the cerebellum, and discrete brainstem areas and were particularly abundant in areas rich in neuronal terminals, e.g., olfactory glomeruli, CA3-hilus area, cerebellar molecular layer, and pars reticulata of the substantia nigra. In the developing rat brain, diffuse and elevated expression of binding sites occurred at the early postnatal stage relative to the adult. The possible association of binding sites with neuronal terminals in the adult brain was further investigated after olfactory deafferentation. A significant decrease with subsequent recovery of binding sites was noted in the olfactory glomeruli after chemical damage of the olfactory epithelium. The findings in this study support a physiological role of PS or gamma-secretase complex in neuronal and synaptic development and plasticity.

Afferent Pathways↗
PubMed2003

Imidazo[4,5-b]pyridines as corticotropin releasing factor receptor ligands.

A series of high affinity CRF receptor ligands with an imidazo[4,5-b]pyridine core is described. Individual analogues were synthesized and tested in a rat CRF receptor binding assay. The best compounds were further tested in the dog N-in-1 pharmacokinetic model to assess plasma levels at 1mg/kg (po) and in the rat situational anxiety model to assess anxiolytic efficacy at 3mg/kg (po). The structure-activity relationships for good receptor binding affinity are described herein.

Animals↗
PubMed2003

Imidazo[4,5-c]pyridines as corticotropin releasing factor receptor ligands.

A series of high affinity CRF receptor ligands with an imidazo[4,5-c]pyridine core is described. Individual analogues were synthesized and tested in vitro in rat brain receptors to determine binding affinity. The best compound was further tested in the dog N-in-1 pharmacokinetic model to assess oral bioavailability at 1 mg/kg po.

Administration, Oral↗
PubMed2003

A double antibody radioimmunoassay for the determination of XV459, the active hydrolysis metabolite of roxifiban, in human plasma.

A radioimmunoassay (RIA) was developed for the determination of XV459, the active hydrolysis metabolite of the oral prodrug roxifiban (DMP 754), in human plasma. XV459 is a potent antagonist of the glycoprotein IIb/IIIa receptor. The method utilizes a competitive double antibody format employing an 125I-labeled XV459 analogue tracer which competes with XV459 for antibody binding sites and a second antibody precipitation step to separate antibody bound analyte from free analyte. The method has a validated lower quantification limit of 0.35 ng/ml (0.81 nM) using 12.5 microl of plasma and with dilution can accommodate clinical plasma samples ranging up to 48.0 ng/ml (110.7 nM). Cross-validation to an existing quantitative liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) method showed good correlation (r(2)=0.98). The RIA has been successfully used to assay over 10000 clinical samples with sensitivity and specificity comparable to the LC-MS/MS method, but with faster turn around time and at greatly reduced costs.

Amidines↗
PubMed2002

Gamma-secretase activity is not involved in presenilin-mediated regulation of beta-catenin.

Presenilins (PS) are involved in gamma-secretase-mediated processing of beta-amyloid precursor protein (APP) and the Notch family of proteins. In addition, presenilin 1 (PS-1) binds to members of the armadillo family of proteins. In this study the relationship between PS-1-mediated proteolytic activity and PS-1-mediated regulation of beta-catenin function was investigated. Incubation of cells with a potent, small molecule gamma-secretase inhibitor did not affect PS-1/beta-catenin interaction as determined by co-immunoprecipitation, or affect the regulation of beta-catenin turnover, as determined by pulse-chase analysis, even at inhibitor concentrations that completely blocked PS-mediated APP processing. Moreover, inhibition of PS-1-mediated proteolytic activity did not affect beta-catenin trafficking, as determined by immunolocalization and immunoblotting, or beta-catenin-mediated transcription. These results indicate that PS-1-mediated regulation of gamma-secretase activity and PS-1-mediated regulation of beta-catenin function can be pharmacologically separated and support the idea that these are distinct functions.

Active Transport, Cell Nucleus↗
PubMed2002

Mutations at the P1' position of Notch1 decrease intracellular domain stability rather than cleavage by gamma-secretase.

Gamma-secretase is a unique protease which cleaves within the transmembrane domain of several substrate proteins. Among gamma-secretase substrates are members of the Notch family of receptors and the amyloid precursor protein. In this study we used a cell-free Notch-cleavage assay and specific gamma-secretase inhibitors to study the cleavage of Notch by gamma-secretase. Using this assay, we found that, in contrast to previous reports, the presence of valine at the P1(') position of Notch1 is not required for gamma-secretase cleavage. Our results suggest that the presence of valine at the N-terminus of the Notch intracellular domain cleavage product is important for its stability. Thus it appears that Notch cleavage is very similar to APP cleavage with respect to the lack of sequence specificity.

Acetylcysteine↗
PubMed2001

Identification and characterization of presenilin-independent Notch signaling.

Presenilin (PS) proteins control the proteolytic cleavage that precedes nuclear access of the Notch intracellular domain. Here we observe that a partial activation of the HES1 promoter can be detected in PS1/PS2 (PS1/2) double null cells using Notch1 Delta E constructs or following Delta 1 stimulation, despite an apparent abolition of the production and nuclear accumulation of the Notch intracellular domain. PS1/2-independent Notch activation is sensitive to Numblike, a physiological inhibitor of Notch. PS1/2-independent Notch signaling is also inhibited by an active gamma-secretase inhibitor in the low micromolar range and is not inhibited by an inactive analogue, similar to PS-dependent Notch signaling. However, experiments using a Notch1-Gal4-VP16 fusion protein indicate that the PS1/2-independent activity does not release Gal4-VP16 and is therefore unlikely to proceed via an intramembranous cleavage. These data reveal that a novel PS1/2-independent mechanism plays a partial role in Notch signal transduction.

Amyloid Precursor Protein Secretases↗