Evaluation of Blood-Brain Barrier Passage of a Muscarine M1 Agonist and a Series of Analogous Tetrahydropyridines Measured by In Vivo Microdialysis |
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Authors: | Helle Hagen Sveigaard Lars Dalgaard |
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Affiliation: | (1) Department of Drug Metabolism, H.Lundbeck A/S, Ottiliavej 9, 2500 Valby-Copenhagen, Denmark;(2) Department of Drug Metabolism, H.Lundbeck A/S, Ottiliavej 9, 2500 Valby-Copenhagen, Denmark |
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Abstract: | Purpose. To investigate the blood-brain barrier (BBB) passage of theM1 muscarine agonist Lu 25-109(5-(2-Ethyl-2H-tetrazol-5-yl)-1,2,3,6-tetrahydro-methylpyridine) and potential metabolites using in vivomicrodialysis.Methods. Anesthetized rats were administered an intravenous infusionof one of seven analogs with a Log D7.4 ranging from 0.35 to –2.4.Microdialysis probes were implanted in the brain and the jugular vein.The integrity of the BBB was evaluated using2-amino-3-(3-hydroxy-5-phenylisoxazol-4-yl)propionic acid (APPA), a compound notexpected to penetrate the BBB. The data was corrected for in vitrorecovery.Results. Lu 25-109, Lu 24-165 (demethylated Lu 25-109) and Lu25-077 (N-demethylated Lu 25-109) entered the brain in a 1:1 ratio withthe blood. Although Lu 29-081 (hydroxylated Lu 25-109) presented asimilar Log D7.4 to Lu 25-109 and Lu 24-164, it entered the brain witha lower brain:blood ratio of 0.5. Lu 32-181 (Lu 25-109 N-oxide), Lu35-026 (deethylated and oxidized Lu 25-109) and Lu 31-126(deethylated Lu 25-109) were not detected in the brain samples, indicating nopenetration. Infusion of Lu 25-109 resulted in a time perspective ofthe formation and distribution of the two metabolites Lu 25-077 andLu 32-181. Although the hydroxylated compound (Lu 29-081) had aLog D7.4 of –0.6, within the range 0.35 to –0.83 of the compoundspenetrating the BBB, it showed a brain: blood ratio of 0.5. Lu 35-026showed an unusual infusion profile with a tmax of 100–150 min and asubsequent decrease in blood concentration.Conclusions. Compounds with Log D7.4 above –0.83 penetrated theBBB, whereas compounds below –1.5 did not. Knowledge of LogD7.4 values is not sufficient to evaluate BBB passage because the valuedoes not predict the influence of active transport processes. |
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Keywords: | in vivo microdialysis blood-brain barrier rat log D7.4 metabolism Lu 25-109 |
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