Peripheral site ligand-oxime conjugates: A novel concept towards reactivation of nerve agent-inhibited human acetylcholinesterase.

A conceptually novel approach to the design of reactivators of nerve agent-inhibited acetylcholinesterase (AChE) is presented. The concept comprises the linkage of a peripheral site ligand via a spacer to a reactivating moiety with the eventual goal to develop non-ionic reactivators with sufficient affinity for AChE to induce reactivation and potentially improved blood-brain barrier penetration. Herein, the first step towards that goal-the synthesis and biological evaluation of a peripheral site ligand conjugated to a charged pyridinium oxime is discussed. It was found, that the introduction of the peripheral site ligand not only increased affinity of the construct for AChE but also enhanced reactivation of nerve agent-inhibited AChE.

Covalent binding of organophosphorothioates to albumin: a new perspective for OP-pesticide biomonitoring?

We here report on the covalent binding of various organophosphorothioate (OPT) pesticides to albumin at in vitro exposure levels that did not give rise to butyrylcholinesterase inhibition. Adduct formation occurred at the Tyr-411 residue of albumin, as was firmly corroborated by LC-tandem MS analysis of a pepsin digest of OPT-modified albumin. It cannot be excluded that other (tyrosine) residues become modified as well. A convenient method for mass spectrometric determination of the OPT tyrosine adduct has also been developed based on the pronase digestion of albumin and subsequent LC-tandem MS analysis of the digest. The resulting tyrosine phosphorothioate ester displayed favorable chromatographic and mass spectrometric properties for sensitive analysis. In vitro exposure levels of parathion and chlorpyrifos down to 1 microM could readily be assessed. The remarkable affinity of OPTs for albumin opens the way for a more complete assessment of OP pesticide exposure.

Protein adduct formation by glucuronide metabolites of permethrin.

Biomonitoring of exposure to the insecticide permethrin is usually performed by analysis of its urinary metabolites 3-phenoxybenzoic acid (3-PBA) or cis/ trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane-1-carboxylic acid (Cl 2 CA). We are engaged in the development of a methodology to assess the cumulative internal dose of exposure to permethrin, which is based on the assumption that (reactive) glucuronide conjugates of the major permethrin metabolites 3-PBA and Cl 2 CA will form persistent (weeks to months) adducts to proteins, in analogy with the glucuronide conjugates of structurally related drugs. The 3-PBA and Cl 2 CA beta-glucuronide metabolites of permethrin have been successfully chemically and enzymatically synthesized. Their identities have been assessed by means of (1)H NMR spectroscopy and liquid chromatography-tandem mass spectrometry. The reactivity of these metabolites with various amino acids, peptides, and albumin in human plasma has been studied. Several distinct adducts could be identified by liquid chromatography-tandem mass spectrometry. After pronase digestion of albumin isolated from exposed human plasma, various lysine derivatives resulted with favorable mass spectrometric and chromatographic properties. Covalent binding was quantified by using [(14)C]-3-PBA glucuronide; >1.5% of total radioactivity was bound to proteins. It is envisaged that the obtained results can form a firm basis for the development of a protein adduct-based methodology for biomonitoring exposure to permethrin. In view of the widespread use of permethrin, the toxicological relevance of protein binding by its metabolites will be addressed in more detail in future work.

Are thrombocyte membranes altered in Alzheimer's disease? A morphometric and biochemical study.

Morphometric analysis of thrombocytes from patients with Alzheimer's disease, from patients with multi-infarct dementia, and from young and age-matched healthy control donors, did not reveal any Alzheimer-related increase in internal membranes. Biochemical analysis showed a reduced cholesterol content of thrombocyte membrane preparations from Alzheimer patients relative to age-matched controls, but not relative to multi-infarct dementia patients. Overall distribution of protein kinase C activity (PKC) between cytosol and membrane, in resting as well as in activated thrombocytes from Alzheimer patients, was similar to that in the control groups. However, both Alzheimer and multi-infarct dementia patients had lower cytosolic levels of basal kinase and PKC activities than age-matched controls, while only Alzheimer patients had lower cytoskeletal PKC activity than controls.

No evidence for reduced thrombocyte cytochrome oxidase activity in Alzheimer's disease.

We measured cytochrome oxidase activity in thrombocytes from patients with senile dementia of the Alzheimer type. We found no decrease in enzyme activity in Alzheimer's disease patients when compared with patients with multi-infarct dementia, with young control donors, and with age-matched control donors.

[Cutaneous asthenia, a congenital skin disease in a Burmese cat]. / Cutane asthenia, een aangeboren huidafwijking bij een Birmees.

The symptoms and the course run by cutaneous asthenia, a skin disease which is congenital and probably hereditable, are reported in a Birmese tomcat.

[Feline rhinotracheitis in stray cats; to vaccinate or not to vaccinate?]. / Niesziekte bij zwerfkatten; wel of niet enten?

Report on a controlled field trial in an animal home housing both stray cats and animals which were boarders. In this home, a vaccine containing live attenuated feline herpes and calici viruses for intranasal administration was inoculated. The purpose of the trial was to find out why this vaccine which had been very successful in this animal home during the past years, showed disappointing results in stray cats in recent months. The necessary practical measures were taken to ensure that the required procedure should be complied with, i.e., every stray cat was vaccinated on the day of admission and was then held in quarantine for at least 24 hours. In the first group of fifty stray cats, only some local reactions following vaccination were observed. When vaccination was discontinued, feline rhinotracheitis became enzootic in non-vaccinated cats within a month. A second group of forty-five stray cats was then vaccinated with equally satisfactory results. It was found that feline rhinotracheitis can be controlled in stray cats even under enzootic conditions by intranasal vaccination on the day of admission and then holding the cats for at least 24 hours in quarantine.