The brain H3-receptor as a novel therapeutic target for vigilance and sleep–wake disorders

Brain histaminergic neurons play a prominent role in arousal and maintenance of wakefulness (W). H(3)-receptors control the activity of histaminergic neurons through presynaptic autoinhibition. The role of H(3)-receptor antagonists/inverse agonists (H(3)R-antagonists) in the potential therapy of vigilance deficiency and sleep-wake disorders were studied by assessing their effects on the mouse cortical EEG and sleep-wake cycle in comparison to modafinil and classical psychostimulants. The H(3)R-antagonists, thioperamide and ciproxifan increased W and cortical EEG fast rhythms and, like modafinil, but unlike amphetamine and caffeine, their waking effects were not accompanied by sleep rebound. Conversely, imetit (H(3)R-agonist) enhanced slow wave sleep and dose-dependently attenuated ciproxifan-induced W, indicating that the effects of both ligands involve H(3)-receptor mechanisms. Additional studies using knockout (KO) mice confirmed the essential role of H(3)-receptors and histamine-mediated transmission in the wake properties of H(3)R-antagonists. Thus ciproxifan produced no increase in W in either histidine-decarboxylase (HDC, histamine-synthesizing enzyme) or H(1)- or H(3)-receptor KO-mice whereas its waking effects persisted in H(2)-receptor KO-mice. These data validate the hypothesis that H(3)R-antagonists, through disinhibition of H(3)-autoreceptors, enhancing synaptic histamine that in turn activates postsynaptic H(1)-receptors promoting W. Interestingly amphetamine and modafinil, despite their potent arousal effects, appear unlikely to depend on histaminergic mechanism as their effects still occurred in HDC KO-mice. The present study thus distinguishes two classes of wake-improving agents: the first acting through non-histaminergic mechanisms and the second acting via histamine and supports brain H(3)-receptors as potentially novel therapeutic targets for vigilance and sleep-wake disorders.

Dog EEG for wake-promotion studies

Described in this unit is a protocol for investigating the wake-promoting activity of new chemical entities (NCEs) in dog. The experimental approach is based on scoring of sleep/wake stages in animals implanted with a telemetry device for recording EMG and cortical EEG signals. A major advantage of this procedure is that it is conducted in nontethered animals, limiting possible bias and complications encountered with conventional recording systems. In this procedure, polygraphic recording is conducted using four implanted beagles. Results of studies with modafinil, a wake-promoting agent, are described to demonstrate the utility of this test procedure.

Prevention of carotid artery thrombosis after oral administration of the glycoprotein IIb/IIIa antagonist CRL42796

This study investigates the effect of the glycoprotein IIb/IIIa receptor antagonist CRL42796 in a canine model of carotid artery thrombosis. Both carotid arteries developed occlusive thrombosis in each of the five control animals (time to occlusion: right carotid artery, 92.6 minutes; left carotid artery, 89.0 minutes). A single oral dose of CRL42796 (3 mg/kg) prevented occlusive thrombosis in 4 of 6 vessels and increased time to thrombosis, albeit not significantly (right carotid artery, 134.1 minutes; left carotid artery, 145.0 minutes). When the initial dose of CRL42796 was followed by a second oral dose (3 mg/kg) 2 hours later, 10 of 10 carotid arteries remained patent throughout the period of electrolytic injury. CRL42796 reduced thrombus weight in both treatment protocols. Ex vivo platelet aggregation with arachidonic acid (AA) or adenosine diphosphate (ADP) was reduced at 120, 240, and 360 minutes after two doses of CRL42796. A single oral dose reduced ADP-induced responses at 240 and 360 minutes, but significant effects were not observed with AA. Bleeding time increased 360 minutes after two oral doses of CRL42796, but not at 120 minutes. Bleeding time was unchanged with the single dose of CRL42796. The results demonstrate that oral administration of CRL42796 prevents carotid artery thrombosis in response to deep vessel wall injury and may have potential value to be characterized in extended preclinical and clinical study.

Design and synthesis of a series of indole glycoprotein IIb/IIIa inhibitors

Synthesis of 1,3-disubstituted indoles derivatives as potential glycoprotein (GP) IIb/IIIa antagonists was reported. Substitution of the indolic nitrogen atom by piperidino or benzamidino moieties was used as mimics of an arginine residue. The acid carboxylic group was linked to the indole scaffold in position-3 via a methylene unit (compounds 4, 9, 10). Introduction of a beta-alanine chain was carried out on the acids (17-22) which after deprotection and basic hydrolysis afforded the final compounds 39-46. The distance between the indole scaffold and the amide bond was modulated from no methylene unit (compound 39) to 1 (compounds 40, 41) or 2 methylene units (compounds 42-46). The presence of a tosylamino group on the beta-alanine chain (compound 56) slightly increased the inhibiting action on platelet aggregation initiated by collagen.