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Biomedical subjects

E E Clarke

Publications and source records attributed to E E Clarke.

9 recordsLinked to original sources
PubMed2000

Quantitation of amyloid-beta peptides in biological milieu using a novel homogeneous time-resolved fluorescence (HTRF) assay.

Many of the recent advances in the understanding of the pathological processes underlying Alzheimer's disease have come about as a result of the development of assays that can specifically quantitate in biological milieu amyloid-beta (A beta) peptides ending at amino-acid positions Ala-42 (A beta(42)) and Val-40 (A beta(40)). The existing technologies, however, although proven in their utility are limited in their application with regards to sample manipulation and suitability for high-throughput screening. To overcome these limitations, in this report we describe the development of a novel homogeneous time-resolved fluorescence (HTRF) immunoassay for A beta(42) and A beta(40) peptides. This assay has the sensitivity, selectivity and dynamic range to allow specific, direct quantitation of A beta peptides in cell culture medium, plasma, cerebrospinal fluid and brain tissue extracts, and has the major advantage of minimising sample manipulation and its inherent inaccuracies.

Adult↗
PubMed2000

L-685,458, an aspartyl protease transition state mimic, is a potent inhibitor of amyloid beta-protein precursor gamma-secretase activity.

Progressive cerebral amyloid beta-protein (A beta) deposition is believed to play a central role in the pathogenesis of Alzheimer's disease (AD). Elevated levels of A beta(42) peptide formation have been linked to early-onset familial AD-causing gene mutations in the amyloid beta-protein precursor (A beta PP) and the presenilins. Sequential cleavage of A beta PP by the beta- and gamma-secretases generates the N- and C-termini of the A beta peptide, making both the beta- and gamma-secretase enzymes potential therapeutic targets for AD. The identity of the A beta PP gamma-secretase and the mechanism by which the C-termini of A beta are formed remain uncertain, although it has been suggested that the presenilins themselves are novel intramembrane-cleaving gamma-secretases of the aspartyl protease class [Wolfe, M. S., Xia, W., Ostaszewski, B. L., Diehl, T. S., Kimberly, W. T., and Selkoe, D. J. (1999) Nature 398, 513-517]. In this study we report the identification of L-685,458 as a structurally novel inhibitor of A beta PP gamma-secretase activity, with a similar potency for inhibition of A beta(42) and A beta(40) peptides. This compound contains an hydroxyethylene dipeptide isostere which suggests that it could function as a transition state analogue mimic of an aspartyl protease. The preferred stereochemistry of the hydroxyethylene dipeptide isostere was found to be the opposite to that required for inhibition of the HIV-1 aspartyl protease, a factor which may contribute to the observed specificity of this compound. Specific and potent inhibitors of A beta PP gamma-secretase activity such as L-685,458 will enable important advances toward the identification and elucidation of the mechanism of action of this enigmatic protease.

Amino Acid Sequence↗
PubMed1999

Involvement of caspases in proteolytic cleavage of Alzheimer's amyloid-beta precursor protein and amyloidogenic A beta peptide formation.

The amyloid-beta precursor protein (APP) is directly and efficiently cleaved by caspases during apoptosis, resulting in elevated amyloid-beta (A beta) peptide formation. The predominant site of caspase-mediated proteolysis is within the cytoplasmic tail of APP, and cleavage at this site occurs in hippocampal neurons in vivo following acute excitotoxic or ischemic brain injury. Caspase-3 is the predominant caspase involved in APP cleavage, consistent with its marked elevation in dying neurons of Alzheimer's disease brains and colocalization of its APP cleavage product with A beta in senile plaques. Caspases thus appear to play a dual role in proteolytic processing of APP and the resulting propensity for A beta peptide formation, as well as in the ultimate apoptotic death of neurons in Alzheimer's disease.

Acute Disease↗
PubMed1997

The problems associated with pesticide use by irrigation workers in Ghana.

The use of pesticides in Ghanaian agriculture, though beneficial in reducing crop loss both before and after harvest, has been associated with threats to human health often due to the misapplication of the chemicals. This study was an initial attempt to explore the knowledge, attitudes and practices of 123 farm workers on three irrigation project areas in the Accra Plains, Ghana, regarding the safe handling and use of pesticides, to assess the prevalence of symptoms associated with organophosphorus pesticides (OPs) and carbamates and to determine the prevalence of pesticide-related symptoms, and blood cholinesterase. The study design was cross-sectional in type. Methods used were interviews and observation, and biological monitoring. The results revealed moderate levels of knowledge of the routes of absorption of pesticides and of potential symptoms following exposure. Knowledge of personal protective measures was poor to moderate. High risk practices included frequent handling of the chemicals, home storage of pesticides and short re-entry intervals. Despite knowledge of some health risks associated with pesticides, the use of personal protective equipment (PPE) was minimal due primarily to financial constraints. The prevalence of symptoms was higher and cholinesterase levels lower than in a control group of teachers. It is suggested that there is a need for more epidemiologic studies to investigate the problems associated with pesticide induced ill health as well as research into appropriate and affordable PPE. PPE needs to be subsidized. Training of agriculture and health workers in safety precautions, recognition, and management of pesticide-related ill health is a matter of urgency.

Adult↗
PubMed1996

Characterization of the ecdysteroid UDP-glucosyltransferase gene from Mamestra brassicae nucleopolyhedrovirus.

The ecdysteroid UDP-glucosyltransferase (egt) gene of Mamestra brassicae multinucleocapsid nucleopolyhedrovirus (MbMNPV) has been cloned and characterized. MbMNPV egt potentially encodes a protein of 528 amino acids. Analysis of the substrate specificity of the MbMNPV EGT protein showed that it mirrors that of Autographa californica MNPV (AcMNPV) EGT. MbMNPV EGT also appears to be secreted from infected cells. Confirmation that the cloned gene encodes an active EGT was obtained by transient expression assays. Phylogenetic trees of NPVs were generated based on the alignment of baculovirus EGT sequences. These phylogenies support the classification of MbMNPV as a group II NPV that is most closely related to Spodoptera exigua MNPV. Comparison of the EGT-based phylogenies with polyhedrin/granulin-based phylogenies shows that the position of AcMNPV is different in the two trees, possibly indicating that AcMNPV acquired its polyhedrin gene by recombination with another virus.

Amino Acid Sequence↗
PubMed1991

Altered in vitro adaptive responses of lymphocyte Na+,K(+)-ATPase in patients with manic depressive psychosis.

When lymphocytes from healthy subjects are incubated in lithium (8 mM) or ethacrynate (1 microM) they show a time-dependent adaptive response, which consists of a significant increase in the number of Na+,K(+)-ATPase molecules in the lymphocyte membrane. We have studied the lymphocytes from nine euthymic drug-free patients with a history of manic depressive psychosis, and have found that this normal adaptive response was absent. It was also absent from the lymphocytes of euthymic patients taking lithium. We conclude that this altered in vitro adaptive response of lymphocyte Na+,K(+)-ATPase represents an enduring trait marker in manic depressive psychosis.

Bipolar Disorder↗