Evaluation of blood-brain barrier passage of a muscarine M1 agonist and a series of analogous tetrahydropyridines measured by in vivo microdialysis.
OBJECTIVE
To investigate the blood-brain barrier (BBB) passage of the M1 muscarine agonist Lu 25-109 (5-(2-Ethyl-2H-tetrazol-5-yl)-1,2,3,6-tetrahydro-methylpyridine) and potential metabolites using in vivo microdialysis.


METHODS
Anesthetized rats were administered an intravenous infusion of 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 using 2-amino-3-(3-hydroxy-5-phenylisoxazol-4-yl)propionic acid (APPA), a compound not expected to penetrate the BBB. The data was corrected for in vitro recovery.


RESULTS
Lu 25-109, Lu 24-165 (demethylated Lu 25-109) and Lu 25-077 (N-demethylated Lu 25-109) entered the brain in a 1:1 ratio with the blood. Although Lu 29-081 (hydroxylated Lu 25-109) presented a similar Log D7.4 to Lu 25-109 and Lu 24-164, it entered the brain with a lower brain:blood ratio of 0.5. Lu 32-181 (Lu 25-109 N-oxide), Lu 35-026 (deethylated and oxidized Lu 25-109) and Lu 31-126 (deethylated Lu 25-109) were not detected in the brain samples, indicating no penetration. Infusion of Lu 25-109 resulted in a time perspective of the formation and distribution of the two metabolites Lu 25-077 and Lu 32-181. Although the hydroxylated compound (Lu 29-081) had a Log D74 of -0.6, within the range 0.35 to -0.83 of the compounds penetrating the BBB, it showed a brain: blood ratio of 0.5. Lu 35-026 showed an unusual infusion profile with a tmax of 100-150 min and a subsequent decrease in blood concentration.


CONCLUSIONS
Compounds with Log D7.4 above -0.83 penetrated the BBB, whereas compounds below -1.5 did not. Knowledge of Log D7.4 values is not sufficient to evaluate BBB passage because the value does not predict the influence of active transport processes.
Sveigaard
H H
HH
Department of Drug Metabolism, H.Lundbeck A/S, Valby-Copenhagen, Denmark. hhs@lundbeck.com
Dalgaard
L
L
D000818:Animals; D001812:Blood-Brain Barrier; D008297:Male; D017551:Microdialysis; D018721:Muscarinic Agonists / Q000493:pharmacokinetics*; D011725:Pyridines / Q000493:pharmacokinetics*; D051381:Rats; D017208:Rats, Wistar; D043643:Receptor, Muscarinic M1; D011976:Receptors, Muscarinic / Q000187:drug effects*; D013777:Tetrazoles / Q000493:pharmacokinetics*
C108369:LU 25-109-T; D018721:Muscarinic Agonists; D011725:Pyridines; D043643:Receptor, Muscarinic M1; D011976:Receptors, Muscarinic; D013777:Tetrazoles